Photo-Curable Liquid Silicone Rubber Compositions for Templating Mother

Europäisches Patentamt *EP000832936B1* (19) European Patent Office

Office européen des brevets (11) EP 0 832 936 B1

(12) EUROPEAN PATENT SPECIFICATION

(45) Date of publication and mention (51) Int Cl.7: C08L 83/07, C08L 83/04 of the grant of the patent: 18.12.2002 Bulletin 2002/51

(21) Application number: 97307441.2

(22) Date of filing: 24.09.1997

(54) Photo-curable liquid silicone rubber compositions for templating mother molds Photohärtbare flüssige Silikonkautschukzusammensetzungen zur Herstellung einer Masterform Composition liquide de caoutchouc de silicone photodurcissable pour la préparation d’une matrice de moulage

(84) Designated Contracting States: (56) References cited: DE FR GB EP-A- 0 152 179 EP-A- 0 237 757 EP-A- 0 336 633 US-A- 4 530 879 (30) Priority: 25.09.1996 JP 27406796 US-A- 4 591 608 US-A- 4 640 939 US-A- 4 640 940 US-A- 4 935 455 (43) Date of publication of application: 01.04.1998 Bulletin 1998/14 • PATENT ABSTRACTS OF JAPAN vol. 096, no. 011, 29 November 1996 & JP 08 183055 A (SHIN (73) Proprietor: SHIN-ETSU CHEMICAL CO., LTD. ETSU CHEM CO LTD), 16 July 1996, Chiyoda-ku Tokyo (JP) • PATENT ABSTRACTS OF JAPAN vol. 095, no. 011, 26 December 1995 & JP 07 216232 A (SHIN (72) Inventors: ETSU CHEM CO LTD), 15 August 1995, • Fujiki, Hironao, c/o Shin-Etsu Chemical Co., Ltd. • PATENT ABSTRACTS OF JAPAN vol. 015, no. Usui-gun, Gunma-ken (JP) 310 (M-1144), 8 August 1991 & JP 03 114711 A • Sakamoto, Takafumi, (JANOME SEWING MACH CO LTD), 15 May 1991, Shin-Etsu Chemical Co., Ltd. • PATENT ABSTRACTS OF JAPAN vol. 016, no. Usui-gun, Gunma-ken (JP) 376 (M-1294), 12 August 1992 & JP 04 122615 A (JANOME SEWING MACH CO LTD), 23 April (74) Representative: Stoner, Gerard Patrick et al 1992, MEWBURN ELLIS York House Remarks: 23 Kingsway The file contains technical information submitted London WC2B 6HP (GB) after the application was filed and not included in this specification

Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). EP 0 832 936 B1

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Description

[0001] This invention relates to a photo-curable liquid silicone rubber composition for forming a templating mother mold adapted to mold a photo-curable liquid resin therein, and also its use, by photocuring, to make such a mother mold. 5 [0002] In a process for developing a new model of automobile part or household appliance, a certain number of products must be produced for the purpose of testing the outer appearance, shape and performance. To this end, various procedures were developed in the prior art. Among others, a procedure of producing a precision part replica using a mold of silicone rubber, known as a vacuum casting procedure, is widely used in the art. In this procedure, a molding pattern serving as a master model is prepared from a suitable material such as wood, plastics or metal by 10 manual modeling or by means of a machine tool (which can be controlled on the basis of three-dimensional CAD data). It was recently developed to produce a master model by an optical shaping system of irradiating photo-curable resin using a UV laser beam in accordance with three-dimensional CAD data inputs. In general, a replica is produced by embedding the master model in an addition/heat curable liquid silicone rubber composition, curing the silicone rubber composition, removing the master model, casting a thermosetting resin into the resulting cavity and heating the ther- 15 mosetting resin to cure it. [0003] What is desired in the art is to produce such replicas within a short time, and attempts have been made. For example, JP-A 114711/1991 discloses a method for producing a molded part by introducing a UV-curable liquid resin (epoxy or acrylic reactive resin) into a mold made of a transparent addition room temperature vulcanizable (RTV) silicone rubber composition, and irradiating UV to the liquid resin for curing. To cause the addition RTV liquid silicone 20 rubber composition to cure, however, sufficient control of metering, agitating and curing steps is necessary. In particular, the curing conditions must be strictly controlled in order to increase the dimensional precision of molded parts. The curing usually takes 6 to 24 hours, suggesting that the process is unsatisfactory with respect to the manufacturing time. [0004] An attempt to form a mother mold by photo-curing is disclosed in JP-A 205157/1995. The mold prepared from a photo-curable organic resin is a hard mold, and the resin to be cured in the mold is a conventional thermosetting 25 resin rather than a photo-curable resin. [0005] The present invention provides a photo-curable liquid silicone rubber composition for forming a templating mother mold adapted to form a moulded article e.g. a repl by casting a photo-curable liquid resin therein, the composition allowing the templating mother mold to be formed through simple operation within a short time while the resultant mother mold allows the photo-curable liquid resin cast therein to be cured with light transmitted by the mother mold. 30 [0006] We find that by exposing a photo-curable liquid silicone rubber composition, as typified by first to third preferred embodiments to be described later, to light, especially UV light having a wavelength of 200 to 500 nm, one can obtain a cured product having a Shore A hardness of 20 to 60 and a light (or actinic radiation) transmittance of at least 10% as measured at a wall gage of 10 mm. The cured product serving as a templating mother mold can be molded through simple operation within a short time. When a photo-curable liquid resin is cast into the mother mold, light or actinic 35 radiation, especially UV light having a wavelength of 200 to 500 nm can be irradiated to the photo-curable liquid resin through the mother mold whereby the liquid resin is photo-cured within the mother mold obtained by curing of the photo-curable liquid silicone rubber composition. [0007] According to the present invention, there is provided a photo-curable liquid silicone rubber composition for a templating mother mold adapted to mold a photo-curable liquid resin therein, which is curable upon exposure to light 40 into a cured product having a Shore A hardness of 20 to 60 and a light transmittance of at least 10% as measured at a wall gage of 10 mm. [0008] Preferably the composition cures with light having a wavelength of 200 to 500 nm. [0009] A first preferred embodiment provides a photo-curable liquid silicone rubber composition comprising 100 parts by weight of an organopolysiloxane and 0.01 to 5 parts by weight of a photo-initiator, the organopolysiloxane consisting 45 of

(A) 30 to 100% by weight of an organopolysiloxane of the following average compositional formula (1):

1 50 RaR bSiO(4-a-b)/2 (1)

wherein groups R, which may be identical or different, are substituted or unsubstituted monovalent hydrocarbon groups free of an aliphatic unsaturated bond or an alkoxy group; groups R, which may be identical or different, are photo-reactive groups selected from a (meth)acryloyl-containing group, vinyloxyalkyl group, and epoxy-containing 55 group; and letters a and b are positive numbers satisfying 1.90 ≤ a < 2.40, 0.0003 ≤ b ≤ 0.10, and 1.90

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1 (B) 10 to 70% by weight of a silicone resin soluble in component (A) and comprising RpR qSiO1/2 units (M), SiO2 1 units (Q), and/or XSiO3/2 units (T) wherein R and R are as defined above, letters p and q each are equal to 0, 1, 2 or 3 and satisfy p + q = 3, X is selected from R and R1, molar ratio M/(Q + T) = 0.6 to 1.2, and molar ratio R1/Si = 0.01 to 0.10; the composition being curable, by exposure to light of a wavelength in the range 200 to 500 nm, 5 to a cured product having Shore A hardness from 20 to 60 and a light transmission of such light measured at a thickness of 10 mm, of at least 10%.

[0010] A second preferred embodiment provides a photo-curable liquid silicone rubber composition comprising 100 parts by weight of an organopolysiloxane and 0.01 to 5 parts by weight of a photo-initiator, the organopolysiloxane 10 consisting of

2 15 RcR dSiO(4-c-d)/2 (2)

wherein groups R, which may be identical or different, are substituted or unsubstituted monovalent hydrocarbon groups free of an aliphatic unsaturated bond or an alkoxy group; groups R2, which may be identical or different, are aliphatic unsaturated groups selected from an alkenyl group and an oxygen atom-containing aliphatic unsatu- 20 rated group and letters c and d are numbers satisfying 1.90 ≤ c < 2,40, 0.0003 ≤ d ≤ 0.10, and 1.90 < c + d ≤ 2.40 the organopolysiloxane containing at least two aliphatic unsaturated groups in a molecule and having a viscosity of 0.1 to 1000 Pa.s (100 to 1,000,000 centipoise) at 25°C, and 2 (D) 10 to 70% by weight of a silicone resin soluble in component (C) and comprising RpR qSiO1/2 units (M), SiO2 2 units (Q), and/or YSiO3/2 units (T) wherein R and R are as defined above, letters p and q each are equal to 0, 1, 25 2 or 3 and satisfy p + q = 3, Y is selected from R and R2, molar ratio M/(Q + T) = 0.6 to 1.2, and molar ratio R2/Si = 0.01 to 0.10, the silicone resin being soluble in component (C), the composition further comprising (E) an organosilane or organosiloxane containing at least two mercapto groups in a molecule in such an amount providing 0.1 to 20 equivalents of mercapto group relative to the aliphatic unsaturated group of components (C) and (D); the composition being curable, by exposure to light of a wavelength 30 in the range 200 to 500 nm, to a cured product having Shore A hardness from 20 to 60 and a light transmission of such light measured at a thickness of 10 mm, of at least 10%.

[0011] A third preferred embodiment provides a photo-curable liquid silicone rubber composition comprising an organopolysiloxane consisting of 35 (C) 30 to 100% by weight of an organopolysiloxane of the following average compositional formula (2):

2 RcR dSiO(4-c-d)/2 (2) 40 wherein groups R, which may be identical or different, are substituted or unsubstituted monovalent hydrocarbon groups free of an aliphatic unsaturated bond or an alkoxy group; groups R2, which may be identical or different, are aliphatic unsaturated groups selected from an alkenyl group and an oxygen atom-containing aliphatic unsaturated group; and letters c and d are numbers satisfying 1.90 ≤ c < 2.40, 0.0003 ≤ d ≤ 0.10, and 1.90 < c + d ≤ 2.40, 45 the organopolysiloxane containing at least two aliphatic unsaturated groups in a molecule and having a viscosity of 0.1 to 1000 Pa.s (100 to 1,000,000 centipoise) at 25°C, and 2 (D) 0 to 70% by weight of a silicone resin soluble in component (C) and comprising RpR qSiO1/2 units (M), SiO2 2 units (Q), and/or YSiO3/2 units (T) wherein R and R are as defined above, p and q are 0, 1, 2 or 3 and satisfy p + q = 3, Y is selected from R and R2, molar ratio M/(Q + T) = 0.6 to 1.2, and molar ratio R2/Si = 0.01 to 0.10, 50 the composition further comprising (F) an organohydrogenpolysiloxane of the following average compositional formula (3):

ReHfSiO(4-e-f)/2 (3) 55 wherein groups R, which may be identical or different, are substituted or unsubstituted monovalent hydrocarbon groups free of an aliphatic unsaturated bond or an alkoxy group, letters e and f are numbers satisfying 0.70 ≤ e ≤

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2.69, 0.01 ≤ f ≤ 1.20, and 1.5 ≤ e=f≤2.7, the organohydrogenpolysiloxane containing at least two SiH groups per molecule, in an amount providing 0.4 to 10 SiH groups per aliphatic unsaturated group supplied from components (C) and (D), and (G) a catalytic amount of a platinum catalyst for effecting hydrosilylation between the aliphatic unsaturated groups 5 in components (C) and (D) and the SiH group in component (F) upon light exposure, the composition being curable, by exposure to light of a wavelength in the range 200 to 500 nm, to a cured product having Shore A hardness from 20 to 60 and a light transmission of such light measured at a thickness of 10 mm, of at least 10%.

[0012] The formed mold is an independent aspect of the invention, as is a method of making it. 10 DETAILED DESCRIPTION

[0013] A photo-curable liquid silicone rubber composition for forming a templating mother mold according to the present invention is a photo-curable composition comprising an organopolysiloxane as a main component. The photo- 15 curable liquid silicone rubber composition cures upon exposure to light into a cured product having a Shore A hardness of 20 to 60 and a light transmittance of at least 10% as measured at a wall gage of 10 mm. Note that the cured product serves as a mother mold for molding a photo-curable liquid resin therein to form a replica. [0014] The cured product resulting from the photo-curable liquid silicone rubber composition has a Shore A hardness of 20 to 60, more preferably 30 to 50. With a mold hardness of less than 20 in Shore A, there would be formed replicas 20 of insufficient precision. With a mold hardness of more than 60 in Shore A, it would become difficult to remove a replica of complex shape such as having inverted taper. The cured mold must be transmissive to actinic radiation in order that the photo-curable liquid resin cast in the mold cavity be cured with the actinic radiation. The cured mold has an actinic radiation transmittance of at least 10%T as measured at a mold gage of 10 mm. With a transmittance of less than 10%T, insufficient light is transmitted by a silicone rubber mold having a wall gage of several tens of millimeter so that 25 the photo-curable liquid resin in the mold cavity might be insufficiently cured, restraining removal of the cured product from the mother mold. It is understood that the silicone rubber mother mold prepared as above may also be used in molding replicas from thermosetting resins by conventional vacuum casting methods. [0015] Broadly stated, the inventive composition may be any of the photo-curable liquid silicone rubber compositions which are defined above. 30 First photo-curable liquid silicone rubber composition

[0016] In the organopolysiloxane of formula (1) constituting component (A), the monovalent hydrocarbon groups represented by R are preferably those having 1 to 10 carbon atoms, especially 1 to 8 carbon atoms, for example, alkyl 35 groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, hexyl, octyl, and decyl, cycloalkyl groups such as cyclopentyl and cyclohexyl, aryl groups such as phenyl and tolyl, and aralkyl groups such as benzyl and phenylethyl. The alkoxy groups represented by R are preferably those having 1 to 8 carbon atoms, especially 1 to 4 carbon atoms, for example, methoxy, ethoxy, propoxy, and butoxy. R is not limited to these unsubstituted monovalent hydrocarbon groups and alkoxy groups, but includes substituted ones of these groups wherein some or all of 40 the hydrogen atoms each attached to a carbon atom are replaced by halogen atoms, cyano groups, alkoxy groups or the like, for example, substituted hydrocarbon groups such as chloromethyl, 3,3,3-trifluoropropyl, and cyanoethyl and substituted alkoxy groups. [0017] R1 is a photo-reactive group selected from a (meth)acryloyl-containing group, vinyloxyalkyl group, and epoxy- containing group. The (meth)acryloyl-containing groups include (meth)acryloxyalkyl groups wherein the alkyl moiety 45 has 1 to 8 carbon atoms such as γ-acryloxypropyl and γ-methacryloxypropyl. The vinyloxyalkyl groups include those groups wherein the alkyl moiety has 3 to 8 carbon atoms such as vinyloxypropyl. The epoxy-containing groups include glycidoxyalkyl groups wherein the alkyl moiety has 3 to 8 carbon atoms such as γ-glycidoxypropyl and (3,4-epoxycyclohexyl)alkyl groups wherein the alkyl moiety has 2 to 8 carbon atoms such as β-(3,4-epoxycyclohexyl)ethyl. [0018] At least two, preferably 2 to about 10, photo-reactive groups represented by R1 should be contained in a 50 molecule. With less than two photo-reactive groups represented by R1, organopolysiloxanes are not curable. It is noted that R1 may be attached to a silicon atom at an end of or intermediate a molecular chain. [0019] The photo-reactive groups are classified in terms of their reaction mode into two types, radical reactive groups and cation reactive groups. Among the above-mentioned photo-reactive groups, the (meth)acryloyl-containing groups belong to the radical reactive groups while the vinyloxyalkyl and epoxy-containing groups belong to the cation reactive 55 groups. Among these, products cured through cationic reaction leave in the cured silicone rubber cationic residues, which can largely affect the heat resistance of silicone rubber and hence, the effective life of a mold. A choice of the radical reactive groups is recommended from this aspect. [0020] Letters a and b are positive numbers satisfying 1.90 ≤ a < 2.40, preferably 1.95 ≤ a ≤ 2.05, 0.0003 ≤ b ≤ 0.10,

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preferably 0.0005 ≤ b ≤ 0.05, and 1.90 < a + b ≤ 2.40, preferably 1.96 ≤ a+b≤2.1. The organopolysiloxane of formula (1) may be linear or branched. Its molecular chain is end-blocked with a triorganosiloxy group which may or may not 1 1 1 1 contain one to three photo-reactive groups R such as R3SiO-, R R2SiO-, R 2RSiO-, and R 3SiO- groups. [0021] The organopolysiloxane has a viscosity of 0.1 to 1000 Pa.s (100 to 1,000,000 centipoise) at 25°C, preferably 5 0.5 to 100 Pa.s (500 to 100,000 centipoise) at 25°C. Organopolysiloxanes having a viscosity of less than 0.1 Pa.s (100 centipoise) fail to provide rubbery nature and are brittle whereas organopolysiloxanes having a viscosity of more than 1000 Pa.s (1,000,000 centipoise) are too viscous to handle as a liquid composition. [0022] The organopolysiloxanes of formula (1) can be synthesized by well-known methods. Organopolysiloxanes having an acryloyl group, for example, can be prepared by a method of attaching γ-acryloxypropyltrimethoxysilane to 10 a diorganopolysiloxane terminated with a hydroxydimethylsilyl group at each end through dealcoholysis condensation, a method of attaching γ-acryloxymethyldimethylsilanol to a diorganopolysiloxane terminated with a trimethoxysilyl group at each end through dealcoholysis condensation, and a method of effecting equilibration between a hydrolyzate of γ- acryloxypropylmethyldimethoxysilane and octamethylcyclotetrasiloxane in the presence of a catalyst. By any of these methods, a diorganopolysiloxane having an acryl group introduced in a side chain is available and useful as component 15 (A). [0023] The silicone resin (B) is a component for imparting strength to the composition and concurrently increasing the hardness thereof. More particularly, since the silicone rubber composition as used herein cures into a product which must subsequently transmit light, high loading of reinforcing fillers used in conventional silicone rubbers is impossible. For this reason, the silicone resin becomes essential when it is desired to provide strength as typified by tensile strength 20 and tear strength. The silicone resin has tri- and tetra-functional siloxane bonds and is soluble in component (A). 1 [0024] More illustratively, the silicone resin contains RpR qSiO1/2 units (M), SiO2 units (Q), and/or XSiO3/2 units (T). 1 1 The silicone resin may further contain RsR tO2/2 units (D) in a molecule. R and R are as defined above, and X is R or R1. Letters p and q each are equal to 0, 1, 2 or 3 and satisfy p+q=3.Letters s and t each are equal to 0, 1 or 2 and satisfy s + t = 2. 25 [0025] The molar ratio of M unit to T and Q units combined, that is, M/(Q + T) is from 0.6 to 1.2, preferably from 0.7 to 1.1. Silicone resins with a molar ratio M/(Q + T) of less than 0.6 are insoluble in component (A) and not reinforcing, or become white turbid and less transmissive to light. A molar ratio M/(Q + T) of more than 1.2 suggests a reduction of silica structure, failing to provide the reinforcing effect. [0026] In order that silicone resin (B) exert the reinforcing effect, it must be integrated with component (A) after 30 crosslinking. For this reason, silicone resin (B) must partially contain a photo-reactive group represented by R1 as does component (A). The content of photo-reactive group R1 is in the range of 0.01 to 0.1 mol, preferably 0.02 to 0.08 mol per mol of silicon atom contained in the silicone resin. A silicone resin with a R1 content of less than 0.01 mol is not incorporated in crosslinkages, resulting in a cured product retaining surface tack. A silicone resin with a R1 content of more than 0.1 mol is too hard and results in a cured product losing elasticity and becoming brittle. 35 [0027] The silicone resin is synthesized, for example, by hydrolyzing γ-acryloxypropyltrimethoxysilane and tetramethoxysilane in such a ratio as to meet the above-mentioned composition. Alternatively, the silicone resin can be obtained by reacting residual silanol of a conventionally prepared silicone resin with γ-acryloxypropyltrimethoxysilane or chlorosilane. [0028] The amount of component (A) is 30 to 90% by weight, especially 50 to 90% by weight and 10 to 70% by 40 weight, especially 10 to 50% by weight of component (B) provided that the total of components (A) and (B) is 100% by weight. Compositions containing more than 70% by weight of component (B) have an increased viscosity, cease to be liquid, and cure into brittle parts which are practically unacceptable. [0029] The first composition is based on (i) an organopolysiloxane consisting of the above-mentioned components (A) and (B) and (ii) a photo-initiator. The photo-initiator is to trigger reaction of component (i) upon light exposure to 45 create a three-dimensional linkage, forming a rubber molding. Among the above-mentioned photo-reactive groups, an organopolysiloxane bearing (meth) acryloyl-containing groups undergoes curing through radical reaction whereas an organopolysiloxane bearing epoxy or vinylether groups undergoes curing through cationic reaction. In this sense, the photo-initiators include radical initiators and cationic initiators. Examples of the radical initiator include acetophenone, propiophenone, benzophenone, xanthol, fluorene, benzaldehyde, anthraquinone, triphenylamine, carbazole, 3-meth- 50 ylacetophenone, 4-methylacetophenone, 3-pentylacetophenone, 4-methoxyacetophenone, 3-bromoacetophenone, 4-allylacetophenone, p-diacetylbenzene, 3-methoxybenzophenone, 4-methylbenzophenone, 4-chlorobenzophenone, 4,4-dimethoxybenzophenone, 4-chloro-4-benzylbenzophenone, 3-chloroxanthone, 3,9-dichloroxanthone, 3-chloro- 8-nonylxanthone, benzoin, benzoin methyl ether, benzoin butyl ether, bis(4-dimethylaminophenol) ketone, benzyl methoxyketal, and 2-chlorothioxanthone. Useful known examples of the cationic photo-polymerization initiator include dia- 55 zonium salts such as 4-morpholino-2,5-dimethoxyphenyl diazonium fluoroborate, and iodonium salts such as a diphenyl iodonium salt of arsenic hexafluoride and an octoxyphenylphenyl iodonium salt of antimony hexafluoride. [0030] The photo-initiator (ii) is added in an amount of 0.01 to 5 parts by weight per 100 parts by weight of component (i), that is, components (A) and (B) combined. Since the silicone rubber composition must play the role of transmitting

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light at the end of curing, the addition of photo-initiator (ii) which essentially absorbs light becomes a negative factor with respect to light transmission. Therefore, the photo-initiator (ii) should preferably be added in a minimum amount enough for the composition to cure, more preferably in an amount of 0.01 to 0.5 part by weight per 100 parts by weight of component (i). Less than 0.01 part of photo-initiator (ii) is insufficient to cause the silicone rubber composition to 5 cure or to form a mold. With more than 5 parts of photo-initiator (ii), the silicone rubber composition would cure into a mold which is less transmissive to light so that a long time is taken in subsequent curing of the photo-curable resin within the mold, that is, the resulting mold is an inadequately light transmissive mold.

second photo-curable liquid silicone rubber composition 10 [0031] In the organopolysiloxane of formula (2), R is as defined in the first composition. R2 is at least one aliphatic unsaturated group selected from an alkenyl group and an oxygen atom-containing aliphatic unsaturated group, preferably having 2 to 10 carbon atoms, especially 2 to 6 carbon atoms. Examples of the group represented by R2 include alkenyl groups such as vinyl, allyl, propenyl, and hexenyl, alkenyloxyalkyl groups (preferably excluding vinyloxyalkyl 15 groups) such as allyloxypropyl, and alkenyloxy groups such as propenoxy. [0032] At least two, preferably 2 to about 10, aliphatic unsaturated groups represented by R2 should be contained in a molecule. With less than two aliphatic unsaturated groups represented by R2, organopolysiloxanes are not curable. It is noted that R2 may be attached to a silicon atom at an end of or intermediate a molecular chain. [0033] Letters c and d are positive numbers satisfying 1.90 ≤ c < 2.40, preferably 1.95 ≤ c ≤ 2.05, 0.0003 ≤ d ≤ 0.10, 20 preferably 0.0005 ≤ d ≤ 0.05, and 1.90 < c + d ≤ 2.40, preferably 1.96 ≤ c+d≤2.1. The organopolysiloxane of formula (2) may be linear or branched. Its molecular chain is end-blocked with a triorganosiloxy group which may or may not 2 2 2 2 contain one to three aliphatic unsaturated groups R such as R3SiO-, R R2SiO-, R 2RSiO-, and R 3SiO- groups. [0034] The organopolysiloxane of formula (2) has a viscosity of 0.1 to 1000 Pa.s (100 to 1,000,000) centipoise at 25°C, preferably 0.5 to 100 Pa.s (500 to 100,000 centipoise) at 25°C. Organopolysiloxanes having a viscosity of less 25 than 0.1 Pa.s (100 centipoise) fail to provide rubbery nature and are brittle whereas organopolysiloxanes having a viscosity of more than 1000 Pa.s (1,000,000 centipoise) are too viscous to handle as a liquid composition. [0035] Like the silicone resin (B), the silicone resin (D) is a component for imparting strength to the composition and concurrently increasing the hardness thereof. More particularly, since the silicone rubber composition as used herein cures into a product which must subsequently transmit light, high loading of reinforcing fillers used in conventional 30 silicone rubbers is impossible. For this reason, the silicone resin becomes essential when it is desired to provide strength as typified by tensile strength and tear strength. The silicone resin has tri- and tetra-functional siloxane bonds and is soluble in component (C). 2 [0036] More illustratively, the silicone resin contains RpR qSiO1/2 units (M), SiO2 units (Q), and/or YSiO3/2 units (T). 2 2 The silicone resin may further contain RsR tO2/2 units (D) in a molecule. R and R are as defined above, and Y is R 35 or R2. Letters p and q each are equal to 0, 1, 2 or 3 and satisfy p+q=3.Letters s and t each are equal to 0, 1 or 2 and satisfy s + t = 2. [0037] The molar ratio of M unit to T and Q units combined, that is, M/(Q + T) is from 0.6 to 1.2, preferably from 0.7 to 1.1. Silicone resins with a molar ratio M/(Q + T) of less than 0.6 are insoluble in component (C) and not reinforcing, or become white turbid and less transmissive to light. A molar ratio M/(Q + T) of more than 1.2 suggests a reduction 40 of silica structure, failing to provide the reinforcing effect. [0038] In order that silicone resin (D) exert the reinforcing effect, it must be integrated with component (C) upon crosslinking. For this reason, silicone resin (D) must partially contain an aliphatic unsaturated group represented by R2 as does component (C). The content of aliphatic unsaturated group R2 is in the range of 0.01 to 0.1 mol per mol of silicon atom contained in the silicone resin. A silicone resin with a R2 content of less than 0.01 mol is not incorporated 45 in crosslinkages, resulting in a cured product retaining surface tack. A silicone resin with a R2 content of more than 0.1 mol is too hard and results in a cured product losing elasticity and becoming brittle. [0039] The silicone resin is synthesized, for example, by hydrolyzing vinyltrimethoxysilane and tetramethoxysilane in such a ratio as to meet the above-mentioned composition. Alternatively, the silicone resin can be obtained by reacting residual silanol of a conventionally prepared silicone resin with vinyltrimethoxysilane or chlorosilane. Furthermore, the 50 silicone resin can also be obtained by hydrolyzing water glass or tetraethoxysilane and reacting the hydrolyzate with 1,3-divinyl-1,1,3,3-tetramethyldisiloxane. [0040] Components (C) and (D) are blended such that there is 30 to 90% by weight, especially 50 to 90% by weight of component (C) and 10 to 70% by weight, especially 10 to 50% by weight of component (D), provided that the total of components (C) and (D) is 100% by weight. Component (D) need not be added in some applications where no 55 strength is necessary. Compositions containing more than 70% by weight of component (D) have an increased viscosity, cease to be liquid, and cure into brittle parts which are practically unacceptable. [0041] Contained as component (E) in the second composition is an organosilane or organosiloxane containing at least two, preferably 2 to about 50, mercapto groups in a molecule. This organosilane or organosiloxane (E) is a

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crosslinking component which reacts with aliphatic unsaturated groups in components (C) and (D) to form a rubbery elastomer. Any desired compound may be used insofar as it contains in a molecule at least two mercapto groups, for example, mercaptoalkyl groups represented by -(CH2)r-SH wherein r is 1 to 6, such as γ-mercaptopropyl. To maintain light transparency, the compound should have a silane or siloxane bond well compatible with the organopolysiloxane. 5 [0042] Illustrative examples of the organosilane or organosiloxane (E) are linear, cyclic or branched organopolysiloxanes of the following formulae.

55 [0043] In the formulae, letter u is an integer of at least 3, x, y and v are integers inclusive of 0, and z and w are integers of at least 2. [0044] These organosiloxanes may be used alone or in admixture of two or more.

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[0045] As component (E), linear compounds are often used because of ease of synthesis as mentioned above although compounds of the structure containing Q units, for example, a hydrolyzate of γ-mercaptopropyltrimethoxysilane and tetramethoxysilane may also be used. [0046] Component (E) is blended in such an amount that the equivalent of mercapto group may be 0.1 to 20, pref- 5 erably 0.5 to 4.0, relative to the aliphatic unsaturated group supplied from components (C) and (D). Insufficient curing occurs with less than 0.1 equivalent whereas beyond 20 equivalents, the crosslinking agent becomes excessive, also leading to insufficient curing. [0047] The second composition is based on (iii) an organopolysiloxane consisting of the above-mentioned components (C) and (D), component (E), and (iv) a photo-initiator. The photo-initiator is to trigger reaction of component (iii) 10 upon light exposure to create a three-dimensional linkage, forming a rubber molding. Examples of the photo-initiator include acetophenone, propiophenone, benzophenone, xanthol, fluorene, benzaldehyde, anthraquinone, triphenylamine, carbazole, 3-methylacetophenone, 4-methylacetophenone, 3-pentylacetophenone, 4-methoxyacetophenone, 3-bromoacetophenone, 4-allylacetophenone, p-diacetylbenzene, 3-methoxybenzophenone, 4-methylbenzophenone, 4-chlorobenzophenone, 4,4-dimethoxybenzophenone, 4-chloro-4-benzylbenzophenone, 3-chloroxanthone, 15 3,9-dichloroxanthone, 3-chloro-8-nonylxanthone, benzoin, benzoin methyl ether, benzoin butyl ether, bis(4-dimethylaminophenol) ketone, benzyl methoxyketal, and 2-chlorothioxanthone. [0048] The photo-initiator (iv) is added in an amount of 0.01 to 5 parts by weight per 100 parts by weight of component (iii). Since the silicone rubber composition must play the role of transmitting light at the end of curing, the addition of photo-initiator (iv) which essentially absorbs light becomes a negative factor with respect to light transmission. There- 20 fore, the photo-initiator (iv) should preferably be added in a minimum amount enough for the composition to cure, more preferably in an amount of 0.01 to 0.5 part by weight per 100 parts by weight of component (iii). Less than 0.01 part of photo-initiator (iv) is insufficient to cause the silicone rubber composition to cure or to form a mold. With more than 5 parts of photoinitiator (iv), the silicone rubber composition would cure into a mold which is less transmissive to light so that a long time is taken in subsequent curing of the photo-curable resin within the mold, that is, the resulting mold 25 is an inadequately light transmissive mold.

Third photo-curable liquid silicone rubber composition

[0049] In the third photo-curable liquid silicone rubber composition 30 [0050] The identity and blending proportion of components (C) and (D) are as described in conjunction with the second composition. [0051] In addition to components (C) and (D), the third composition contains an organohydrogenpolysiloxane of formula (3) as component (F). This organohydrogenpolysiloxane serves as a crosslinking agent for undergoing hydrosilylation with the organopolysiloxane, more specifically aliphatic unsaturated groups in components (C) and (D) in 35 the presence of the platinum catalyst for thereby promoting crosslinking to form a rubbery elastomer. [0052] In formula (3), R is as defined for R in formula (1). Letters e and f are positive numbers satisfying 0.70 ≤ e ≤ 2.69, preferably 1.0 ≤ e ≤ 2.0, 0.01 ≤ f ≤ 1.20, preferably 0.02 ≤ f ≤ 1.1, and 1.5 ≤ e+f≤2.7, preferably 1.9 ≤ e+f≤ 2.4. This organohydrogenpolysiloxane may be linear, branched, cyclic or three-dimensional network insofar as it has at least 2 SiH groups, preferably at least 3 SiH groups, more preferably 3 to about 100 SiH groups (hydrogen atoms 40 each attached to a silicon atom). It is understood that SiH groups may be present at an end of or intermediate a molecular chain. [0053] The organohydrogenpolysiloxane usually has a viscosity of about 0.02 to 1 Pa.s (2 to 1,000 centipoise) at 25°C. [0054] The organohydrogenpolysiloxane is blended in such an amount that 0.4 to 10 SiH groups, preferably 0.8 to 45 4 SiH groups are available per aliphatic unsaturated group supplied from components (C) and (D). Insufficient curing occurs with less than 0.4 equivalent whereas beyond 10 equivalents, the crosslinking agent becomes excessive, also leading to insufficient curing. [0055] Further blended as component (G) in the third composition is a platinum catalyst. The platinum catalyst is preferably a photo-functional platinum catalyst which can give a sufficient pot-life in that after all the above-mentioned 50 components are combined, no curing is induced until preparatory steps necessary to fabricate a silicone rubber mold such as mixing and casting steps are completed. Examples of the photo-functional platinum catalyst include (η-diolefin) (σ-aryl)platinum complexes as disclosed in JP-A 168061/1984 corresponding to US-A-4530879 and platinum compounds controlled with azodicarboxylic acid esters as disclosed in JP-B 50375/1988 corresponding to US-A-4640939. Also useful are platinum compounds controlled with optical active diketones such as benzoylacetone and acetylene 55 dicarboxylic acid esters and platinum catalysts included in photo-degradable organic resins. The platinum catalyst is not limited to these examples. [0056] Component (G) is blended in a catalytic amount, often about 1 to 2,000 ppm, especially about 10 to 200 ppm of platinum metal.

8 EP 0 832 936 B1

[0057] It is understood that the first to third compositions mentioned above may further contain fumed silica, transparent glass beads, and quartz glass powder insofar as the light transmission effect remains adequate. Also a hydrosilylation controlling agent may be blended in the third composition. [0058] The liquid silicone rubber composition preferably has a viscosity of about 100 to 1,000,000 centipoise at 25°C, 5 more preferably about 1,000 to 100,000 centipoise at 25°C. [0059] All the liquid silicone rubber compositions mentioned above cure upon exposure to light. The term "light" used herein designates actinic radiation capable of curing photo-curable liquid silicone rubber compositions and photo- curable liquid resins. The term "photo" is used in the same sense. Ultraviolet light having a wavelength of 200 to 500 nm, especially ultraviolet light having a wavelength of 300 to 400 nm is typically used although the wavelength is not 10 critical provided that the light has a radiative curing ability. Light sources capable of emitting such light include UV fluorescent lamps,. high pressure mercury vapor lamps, metal halide lamps, and xenon lamps although the light source is not critical insofar as it can emit actinic radiation capable of curing photo-curable liquid silicone rubber compositions and photo-curable liquid resins, as appropriate. UV fluorescent lamps are preferred light sources because of the cost and ease of handling. 15 [0060] The liquid silicone rubber composition of the invention is used to form a templating mother mold which is used for the molding of photo-curable liquid resins and rubber, for example, (meth)acrylic resins, epoxy resins, urethane (meth)acrylate resins, fluorinated acrylate resins, and silicone-acrylate copolymers. The overall process involves the step of making a master model, the step of forming a mother mold from the photo-curable liquid silicone rubber composition of the invention on the basis of the master model, and the step of casting a photo-curable liquid resin in the 20 mother mold to form a replica. [0061] The overall replica molding process using the photo-curable liquid silicone rubber composition of the invention is described. A pattern or master model is first produced. Any conventional technique among prior art replica molding methods is applicable. The master model may be made of wood, plastics, metals or composite materials thereof. Useful master model configuring techniques include carving of a wood block and machining of a material by a machine tool. 25 The material can also be machined into the desired shape by computer-aided manufacturing using three-dimensional CAD data. Further, the master model may be produced by machining a plastic material or assembling plastic material pieces. Alternatively, the master model may be produced using an optical shaping system wherein information relating to the position and shape of contour surfaces of the master model is acquired by a three-dimensional CAD system, light is selectively irradiated to a photo-curable liquid organic resin composition at positions corresponding to the de- 30 signed shape, on the basis of that information, curing the resin composition to form a three-dimensional shape. The optical shaping system used herein may be a commercially available one, for example, Solid Creation System by D-MEC Co., SOUP by C-MET Co., SLA by Nippon 3D Systems K.K., and SOLIFORM by Teijin Seiki K.K. [0062] The master model thus prepared is immersed in a photo-curable liquid silicone rubber composition which is held in a container having at least one light transmissive side surface. Light is irradiated to the silicone rubber compo- 35 sition.through the light transmissive side surface of the container to cure the silicone rubber composition into a transparent silicone rubber part in which the master model is embedded and which is to serve as a mother mold. The master model is then removed. The mother mold is formed of the photo-curable liquid silicone rubber composition as mentioned above, which is advantageous in that the time required to form the mother mold and hence, the replica is significantly reduced, as compared with conventional addition heat vulcanizable or room temperature vulcanizable silicone rubber 40 compositions. [0063] A photo-curable liquid resin is then filled into the mother mold of cured silicone rubber through a runner. Light is irradiated to the liquid resin through the transparent silicone rubber mother mold, which has a wall gage of several millimeters to several hundred millimeters, using an irradiating apparatus as used in the curing of a silicone rubber composition, thereby curing the liquid resin within the mother mold. The cured resin or replica is then taken out of the 45 mother mold. The replica is produced in this way. A more precise replica can be obtained by de-aerating the photo- curable liquid resin in vacuum before the curing step.

EXAMPLE

50 [0064] Examples of the invention are given below by way of illustration and not by way of limitation. All parts are by weight.

Example 1

55 [0065] A composition 1 was prepared by blending 75 parts of a dimethylpolysiloxane blocked with a vinyldimethyl- siloxy group at each end and having a viscosity of 100,000 centipoise at 25°C, 25 parts of a silicone resin consisting of CH2=CH(CH3)2SiO1/2, (CH3)3SiO1/2, and SiO2 units in a molar ratio of the total of CH2=CH(CH3)2SiO1/2 and (CH3)3SiO1/2 units to the SiO2 units of 0.8, having a vinyl group equivalent of 0.9 mol/100 g, and soluble in the dimeth-

9 EP 0 832 936 B1

ylpolysiloxane, 7 parts of a mercapto-containing organopolysiloxane of the following formula (1) having a viscosity of 30 centipoise at 25°C, and 0.1 part of 2,2-diethoxyacetophenone.

Example 2

[0066] A composition 2 was prepared by blending 75 parts of a polydimethylsiloxane end-blocked with an acryl- 15 containing siloxy group of the following formula (2), to be abbreviated as Acryl-, hereinafter, and having a viscosity of 100 centipoise at 25°C, 25 parts of a silicone resin consisting of Acryl-(CH3)2SiO1/2, (CH3)3SiO1/2, and SiO2 units in a molar ratio of the total of Acryl-(CH3)2SiO1/2 and (CH3)3SiO1/2 units to the SiO2 units of 0.8, having an acryl group equivalent of 0.9 mol/100 g, and soluble in the dimethylpolysiloxane, and 1.0 part of 2,2-diethoxyacetophenone.

Example 3

[0067] A composition 3 was prepared by blending 75 parts of a dimethylpolysiloxane blocked with a vinyldimethyl- 30 siloxy group at each end and having a viscosity of 100,000 centipoise at 25°C, 25 parts of a silicone resin consisting of CH2=CH(CH3)2SiO1/2, (CH3)3SiO1/2, and SiO2 units in a molar ratio of the total of CH2=CH(CH3)2SiO1/2 and (CH3)3SiO1/2 units to the SiO2 units of 0.8, having a vinyl group equivalent of 0.9 mol/100 g, and soluble in the dimethylpolysiloxane, 7 parts of an organopolysiloxane consisting of H(CH3)2SiO1/2, H(CH3)SiO1/2, (CH3)3SiO1/2, and SiO2 units and having a SiH group equivalent of 0.005 mol/g, and a sufficient amount of (1,5-cyclooctadiene)dimethyl plat- 35 inum(II) to give 30 ppm of platinum based on the siloxane.

Comparative Example 1

[0068] A composition 4 was prepared by the same procedure as in Example 1 except that 7.0 parts of 2,2-diethoxy- 40 acetophenone was blended. [0069] Using Compositions 1 to 4, the following experiment was carried out.

Preparation of a master model

45 [0070] Three-dimensional CAD data of a master model having a shrinkage factor of a photosensitive resin taken into account were produced. At the same time, data regarding a support portion for maintaining strength upon preparation of the master model by means of an optical shaping machine were produced. The master model was prepared by inputting the three-dimensional CAD data into an optical shaping system "SOLIFORM" manufactured by Teijin Seiki K.K., supplying a photo-curable resin TSR800, and irradiating UV laser beams at a pitch of 5 µm. To complete curing 50 of the master model, the master model was exposed to UV from a UV fluorescent lamp for carrying out secondary curing.

Silicone rubber composition and molding of a mother mold

[0071] Silicone rubber mother molds were prepared using the foregoing Compositions 1 to 4. 55 [0072] The support portion was removed by cutting from the master model obtained in the "Preparation" above, obtaining the master model from which a replica was to be duplicated. A piece of tape was attached to a region of the master model where an opening or window was located. [0073] A frame into which a photo-curable liquid silicone rubber composition was to be cast was prepared using a

10 EP 0 832 936 B1

UV-transmissive acrylic resin. The master model was placed in the acrylic frame and secured thereto such that the master model was spaced a gap of 20 to 30 mm from the acrylic frame. [0074] After each of the photo-curable liquid silicone rubber compositions 1 to 4 was previously deaerated in a vacuum tank for removing the air dissolved in the silicone rubber composition, the deaerated silicone rubber composition 5 was cast into the acrylic frame in such a manner that there were entrained as few bubbles as possible until the frame was fully filled with the silicone rubber composition. The acrylic frame filled with the silicone rubber composition was placed in the vacuum tank again and deaeration performed. [0075] The frame filled with the silicone rubber composition was placed in a rectangular exposure chamber where 40-W fluorescent lamps emitting UV at a center wavelength of 370 nm were disposed at six side walls. In this condition, 10 the silicone rubber composition was exposed to UV for 10 minutes. The cured silicone rubber mold having the master model embedded therein was taken out of the acrylic frame. Using a surgical knife, the silicone rubber mold was cut into two sections and the master model removed. The cavity and core sections of the silicone rubber mold were again exposed to UV for 5 minutes under the UV fluorescent lamps for promoting curing. At this point, the silicone rubber mold faithfully reproduced the negative pattern of the master model. It was measured for surface hardness by a JIS A 15 scale hardness meter.

Photo-curable resin and molding of a replica

[0076] Replicas were produced using the following photo-curable resin compositions 1 and 2. 20 Photo-curable resin composition 1

[0077] An unsaturated polyurethane having a methacrylate group at each end and a number average molecular weight of 8,000 was obtained by reacting 1,000 g of polycaprolactone diol having a molecular weight of 500 with 410 25 g of tolylene diisocyanate to form an oligomer blocked with an isocyanate group at each end, and further reacting the oligomer with 410 g of 2-hydroxypropyl methacrylate. [0078] A liquid photo-curable resin composition 1 having a viscosity of 80 poise at 25°C was obtained by mixing 120 g of the unsaturated polyurethane, 40 g of 2-hydroxypropyl methacrylate, 20 g of N-methylol acrylamide, 20 g of meth- acrylamide, 5 g of α-methoxybenzoin methyl ether, and 0.2 g of 2,6-di-t-butyl-p-cresol. 30 Photo-curable resin composition 2

[0079] An unsaturated polyester having an acid value of 35 mg KOH/g was obtained by mixing 430 g of diethylene glycol, 124 g of fumaric acid, 310 g of isophthalic acid, and 140 g of itaconic acid and effecting dehydrating condensation 35 reaction. [0080] A liquid photo-curable resin composition 2 having a viscosity of 120 poise at 25°C was obtained by mixing 100 g of the unsaturated polyester, 20 g of hydroxypropyl methacrylate, 10 g of diacetone acrylamide, 10 g of diethylene glycol dimethacrylate, 3 g of α-methoxybenzoin methyl ether, and 0.2 g of 2,6-di-t-butyl-p-cresol. [0081] The liquid photo-curable resin composition was preheated at 40°C and deaerated under vacuum with stirring. 40 The two sections of the photo-cured silicone rubber mold (obtained from the photo-curable liquid silicone rubber compositions 1 to 4) were mated to define a cavity into which the liquid photo-curable resin composition was cast. The mold filled with the liquid photo-curable resin composition was placed in a rectangular exposure chamber where 40-W fluorescent lamps emitting UV at a center wavelength of 370 nm were disposed at six side walls. In this condition, the liquid photo-curable resin composition was exposed to UV for 10 minutes. 45 [0082] Thereafter, the mold was opened and a cured product of the liquid photo-curable resin composition was taken out as a replica. To complete the curing, the replica was placed in a rectangular exposure chamber where 40-W fluorescent lamps emitting UV at a center wavelength of 370 nm were disposed at six side walls. In this condition, the replica was exposed to UV for 5 minutes. [0083] Replicas associated with the molds of photo-curable silicone rubber compositions 1 to 3 had a Shore D hard- 50 ness of 82 degrees at 20°C and faithfully reproduced the original shape. [0084] In contrast, the mold of photo-curable silicone rubber composition 4 caused short curing of the liquid resin. [0085] Sheets of 2 mm thick were prepared from photo-curable silicone rubber compositions 1 to 4 with a UV energy dose of 2,000 mJ/cm2 and measured for rubber properties according to JIS K6301. The results are shown in Table 1.

55 Comparative Example 2

[0086] A mold and sheet were prepared from an addition curing type silicone rubber composition KE1606 by Shin- Etsu Chemical Co., Ltd. by effecting the same pretreatment as above and heat molding in a heating furnace. The

11 EP 0 832 936 B1

hardness of the mold and the rubber properties of the sheet were measured. [0087] Furthermore, using this silicone rubber composition, a similar process of master model making → mother mold forming → molding of photo-curable resin into a replica was carried out (working time 12 hours). This replica had a Shore D hardness of 82 degrees at 20°C and faithfully reproduced the original shape. 5 [0088] Using this silicone rubber composition, a replica was produced as in Examples 1-3 and Comparative Example 1. This replica had a Shore D hardness of 65 degrees at 20°C and faithfully reproduced the original shape. [0089] The results are shown in Table 1.

Table 1 10 E1 E2 E3 CE1 CE2 Mold hardness (JIS A) 34 55 33 34 31 Hardness (JIS A) 35 57 34 35 30 Elongation (%) 350 120 400 350 300 15 Tensile strength (kgf/cm2) 33 45 35 33 40 Tear strength (kgf/cm) 6.8 9.5 7.5 6.8 6.7 Light transmittance (%T) @370 nm 37 40 36 2 90 20 Curing time to form mold 10 min. 10 min. 10 min. 10 min. 12 hr. State of molded part Good Good Good Short curing Good Light transmittance: sample gage 10 mm

25 Reference Example

[0090] An epoxy acrylate resin was prepared by blending 30 parts of bisphenol-A bis(2-hydroxypropyl) diacrylate, 20 parts of trimethylolpropane triacrylate, 1 part of octylphenol polyether alcohol, 10 parts of PMMA polymer particles (RCP1674 by E. I. duPont), 30 parts of boron nitride powder, and 2 parts of 2,2-dimethoxy-2-phenylacetophenone. 30 The epoxy acrylate resin was cast into the silicone rubber molds prepared in Examples 1-3 and Comparative Examples 1-2, and then cured by irradiating UV light for 5 minutes through the silicone rubber mold from 40-W UV fluorescent lamps. [0091] Satisfactory parts were molded in the molds of Examples 1-3 and Comparative Example 2 whereas the resin cast in the mold of Comparative Example 1 remained short cured. The parts molded in the molds of Examples 1-3 and 35 Comparative Example 2 were easily released from the molds and had luster and high dimensional precision. [0092] According to the invention, a photo-curable liquid silicone rubber composition can be cured with light to form a templating mother mold which is sufficiently transparent to allow a photo-curable liquid resin cast therein to be cured with light transmitted. by the mold wall through simple operation within a short time. [0093] Although some preferred embodiments have been described, many modifications and variations may be made 40 thereto in the light of the above teachings.

Claims

45 1. A photo-curable liquid silicone rubber composition for making a templating mother mold which in turn is for use in molding a photo-curable liquid resin, the composition comprising 100 parts by weight of organopolysiloxane and 0.01 to 5 parts by weight of photo-initiator, said organopolysiloxane consisting of

(A) 30 to 90 % by weight of organopolysiloxane of the following average compositional formula (1): 50

1 RaR bSiO(4-a-b)/2 (1)

wherein groups R, which may be identical or different, are substituted or unsubstituted monovalent hydrocar- 55 bon groups free of aliphatic unsaturated bonds and alkoxy groups; groups R1, which may be identical or different, are photo-reactive groups selected from (meth)acryloyl-containing groups, vinyloxyalkyl groups and epoxy-containing groups; and a and b are numbers satisfying 1.90 ≤ a < 2.40, 0.0003 ≤ b ≤ 0.10, and 1.90 <

12 EP 0 832 936 B1

a+b≤2.40, the organopolysiloxane containing at least two photo-reactive groups in a molecule and having a viscosity of 0.1 to 1000 Pa.s (100 to 1,000,000 centipoise) at 25°C, and 1 (B) 10 to 70 % by weight of silicone resin soluble in component (A) and comprising RpR qSiO1/2 units (M), 1 SiO2 units (Q), and/or XSiO3/2 units (T) wherein R and R are as defined above, p and q are 0, 1, 2 or 3 and 5 satisfy p + q =3, X has the same options as R and R1, the molar ratio M/(Q + T) = 0.6 to 1.2, and the molar ratio R1/Si = 0.01 to 0.10; the composition being curable, by exposure to light having a wavelength in the range 200 to 500 nm, to a cured product having Shore A hardness from 20 to 60 and a light transmittance for such light, measured at a thickness of 10 mm, of at least 10 %. 10 2. A composition according to claim 1 in which in the organopolysiloxane (A) the photo-reactive groups are (meth) acryloyl-containing groups.

3. A photo-curable liquid silicone rubber composition for making a templating mother mold which in turn is suitable 15 for use in molding a photo-curable liquid resin, the composition comprising 100 parts by weight of organopolysiloxane and 0.01 to 5 parts by weight of photoinitiator, said organopolysiloxane consisting of

20 2 RcR dSiO(4-c-d)/2 (2)

wherein groups R, which may be identical or different, are substituted or unsubstituted monovalent hydrocarbon groups free of aliphatic unsaturated bonds and alkoxy groups; groups R2, which may be identical or dif- 25 ferent, are aliphatic unsaturated groups selected from alkenyl groups and oxygen atom-containing aliphatic unsaturated groups, and c and d are numbers satisfying 1.90 ≤ c < 2.40, 0.0003 ≤ d ≤ 0.10, and 1.90 < c + d ≤ 2.40, the organopolysiloxane containing at least two aliphatic unsaturated groups per molecule and having a viscosity of 0.1 to 1000 Pa.s (100 to 1,000,000 centipoise) at 25°C, and 2 (D) 10 to 70 % by weight of silicone resin soluble in component (C) and comprising RpR qSiO1/2 units (M), 30 2 SiO2 units (Q), and/or YSiO3/2 units (T) wherein R and R are as defined above, p and q are 0, 1, 2 or 3 and satisfy p + q = 3, Y has the same options as R and R2, the molar ratio M/(Q + T) = 0.6 to 1.2, and the molar ratio R2/Si = 0.01 to 0.10; the composition further comprising (E) organosilane or organosiloxane containing at least two mercapto groups per molecule in an amount pro- 35 viding from 0.1 to 20 equivalents of mercapto group relative to the aliphatic unsaturated groups of components (C) and (D); and the composition being curable, by exposure to light having a wavelength in the range 200 to 500 nm, to a cured product having Shore A hardness from 20 to 60 and a light transmittance for such light, measured at a thickness of 10 mm, of at least 10 %. 40

4. A composition according to claim 3 in which in the organopolysiloxane (C) the groups R2 are selected from C2-10 alkenyl, alkenyloxyalkyl and alkenyloxy groups.

5. A composition according to any one of claims 1 to 4 which contains from 0.01 to 0.5 parts by weight of the pho- 45 toinitiator.

6. A photo-curable liquid silicone rubber composition for making a templating mother mold which in turn is suitable for use in molding a photo-curable liquid resin, the composition comprising organopolysiloxane consisting of

50 (C) 30 to 100 % by weight of organopolysiloxane of the following average compositional formula (2):

2 RcR dSiO(4-c-d)/2 (2)

55 wherein groups R, which may be identical or different, are substituted or unsubstituted monovalent hydrocarbon groups free of aliphatic unsaturated bonds and alkoxy groups; groups R2, which may be identical or different, are aliphatic unsaturated groups selected from alkenyl groups and oxygen atom-containing aliphatic

13 EP 0 832 936 B1

unsaturated groups, and c and d are numbers satisfying 1.90 ≤ c < 2.40, 0.0003 ≤ d ≤ 0.10, and 1.90 < c + d ≤ 2.40, the organopolysiloxane containing at least two aliphatic unsaturated groups per molecule and having a viscosity of 0.1 to 1000 Pa.s (100 to 1,000,000 centipoise) at 25°C, and 2 (D) 0 to 70% by weight of silicone resin soluble in component (C) and comprising RpR qSiO1/2 units (M) , SiO2 5 2 units (Q) , and/or YSiO3/2 units (T) wherein R and R are as defined above, p and q are 0, 1, 2 or 3 and satisfy p+q=3,Yisselected from the same options as R and R2, the molar ratio M/(Q + T) = 0.6 to 1.2, and the molar ratio R2/Si = 0.01 to 0.10; the composition further comprising (F) organohydrogenpolysiloxane of the following average compositional formula (3): 10

ReHfSiO(4-e-f)/2 3)

wherein groups R, which may be identical or different, are substituted or unsubstituted monovalent hydrocar- 15 bon groups free of aliphatic unsaturated bonds and alkoxy groups, e and f are numbers satisfying 0.70 ≤ e ≤ 2.69, 0.01 ≤ f ≤ 1.20, and 1.5 ≤ e+f≤2.7, the organohydrogenpolysiloxane containing at least two SiH groups per molecule, in an amount providing from 0.4 to 10 SiH groups per aliphatic unsaturated group supplied from components (C) and (D), and (G) a catalytic amount of platinum catalyst adapted to effect hydrosilylation between the aliphatic unsaturated 20 groups in components (C) and (D) and the SiH groups in component (F) in response to exposure to light; the composition being curable, by exposure to light having a wavelength in the range 200 to 500 mm, to a cured product having Shore A hardness from 20 to 60 and a light transmittance for such light, measured at a thickness of 10 mm, of at least 10 %.

25 7. A composition according to claim 6 in which the organopolysiloxane consists of 30 to 90 % by weight of the organopolysiloxane (C) and 10 to 70 % by weight of the silicone resin (D).

2 8. A composition according to claim 6 in which in the organopolysiloxane (C) the groups R are selected from C2-10 alkenyl, alkenyloxyalkyl and alkenyloxy groups. 30 9. A composition according to any one of the preceding claims whereof said cured product has a Shore A hardness from 30 to 50.

10. The use of a composition according to any one of claims 1 to 9 to make, by photocuring said composition, a mother 35 mold which is suitable for use in molding photo-curable liquid resins by irradiation through the walls of the mother mold.

Patentansprüche 40 1. Lichthärtbare, flüssige Silikonkautschuk-Zusammensetzung zur Herstellung einer Masterform, die ihrerseits zum Formen eines lichthärtbaren flüssigen Harzes dient, wobei die Zusammensetzung 100 Gewichtsteile Organopo- lysiloxan und 0,01 bis 5 Gewichtsteile Photoinitiator umfasst, wobei das Organopolysiloxan aus Folgendem besteht: 45 (A) 30 bis 90 Gew.-% Organopolysiloxan der folgenden mittleren Zusammensetzungsformel (1):

1 RaR bSiO(4-a-b)/2 (1) 50 worin die Gruppen R, die identisch oder voneinander verschieden sein können, substituierte oder unsubsti- tuierte einwertige Kohlenwasserstroffgruppen sind, die frei von aliphatischen ungesättigten Bindungen und Alkoxygruppen sind; die Gruppen R1, die identisch oder voneinander verschieden sein können, photoreaktive Gruppen sind, die aus (Meth)acryloyl-hältigen Gruppen, Vinyloxyalkylgruppen und Epoxy-hältigen Gruppen 55 ausgewählt sind; und a und b Zahlen sind, für die gilt: 1,90 ≤ a < 2,40; 0,0003 ≤ b ≤ 0,10; und 1,90 < a+b ≤ 2,40; wobei das Organopolysiloxan pro Molekül zumindest zwei photoreaktive Gruppen enthält und eine Vis- kosität von 0,1 bis 1.000 Pa.s (100 bis 1.000.000 Centipoise) bei 25 °C aufweist; und

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1 (B) 10 bis 70 Gew.-% Silikonharz, das in Komponente (A) löslich ist und RpR qSiO1/2-Einheiten (M), SiO2- 1 Einheiten (Q) und/oder XSiO3/2-Einheiten (T) umfasst, worin R und R wie oben definiert sind, p und q = 0, 1, 2 oder 3 sind, wobei gilt: p+q = 3, X die gleichen Optionen hat wie R und R1, das Molverhältnis M/(Q+T) = 0,6 bis 1,2 ist und das Molverhältnis R1/Si = 0,01 bis 0,10 ist; 5 wobei die Zusammensetzung durch Bestrahlung mit Licht einer Wellenlänge im Bereich von 200 bis 500 nm zu einem gehärteten Produkt gehärtet werden kann, das eine Shore A-Härte von 20 bis 60 und eine Lichtdurchlässigkeit für solches Licht, gemessen bei einer Dicke von 10 mm, von zumindest 10 % aufweist.

2. Zusammensetzung nach Anspruch 1, worin im Organopolysiloxan (A) die photoreaktiven Gruppen (Meth)acryloyl- 10 hältige Gruppen sind.

3. Lichthärtbare, flüssige Silikonkautschuk-Zusammensetzung zur Herstellung einer Masterform, die ihrerseits zum Formen eines lichthärtbaren flüssigen Harzes dient, wobei die Zusammensetzung 100 Gewichtsteile Organopo- lysilxoan und 0,01 bis 5 Gewichtsteile Photoinitiator umfasst, wobei das Organopolysiloxan aus Folgendem be- 15 steht:

2 20 RcR dSiO(4-c-d)/2 (2)

worin die Gruppen R, die identisch oder voneinander verschieden sein können, substituierte oder unsubsti- tuierte einwertige Kohlenwasserstroffgruppen, die frei von aliphatischen ungesättigten Bindungen sind, oder Alkoxygruppen sind; die Gruppen R2, die identisch oder voneinander verschieden sein können, aliphatische 25 ungesättige Gruppen sind, die aus Alkenylgruppen und Sauerstoffatom-hältigen, aliphatischen, ungesättigten Gruppen ausgewählt sind; und c und d Zahlen sind, für die gilt: 1,90 ≤ c < 2,40; 0,0003 ≤ d ≤ 0,10; und 1,90 < c+d ≤ 2,40; wobei das Organopolysiloxan pro Molekül zumindest zwei aliphatische ungesättigte Gruppen enthält und eine Viskosität von 0,1 bis 1.000 Pa.s (100 bis 1.000.000 Centipoise) bei 25 °C aufweist; und 2 (D) 10 bis 70 Gew.-% Silikonharz, das in Komponente (C) löslich ist und RpR qSiO1/2-Einheiten (M), SiO2- 30 2 Einheiten (Q) und/oder YSiO3/2-Einheiten (T) umfasst, worin R und R wie oben definiert sind, p und q = 0, 1, 2 oder 3 sind, wobei gilt p+q = 3, Y die gleichen Optionen hat wie R und R2, das Molverhältnis M/(Q+T) = 0,6 bis 1,2 ist und das Molverhältnis R2/Si = 0,01 bis 0,10 ist; wobei die Zusammensetzung weiters umfasst: (E) Organosilan oder Organosiloxan, das zumindest zwei Mercaptogruppen pro Molekül enthält, in einer Men- 35 ge, die 0,1 bis 20 Mercaptogruppen-Äquivalente in Bezug auf die aliphatischen ungesättigten Gruppen der Komponenten (C) und (D) bereitstellt; und wobei die Zusammensetzung durch Bestrahlung mit Licht einer Wellenlänge im Bereich von 200 bis 500 nm zu einem gehärteten Produkt gehärtet werden kann, das eine Shore A-Härte von 20 bis 60 und eine Lichtdurchlässigkeit für solches Licht, gemessen bei einer Dicke von 10 mm, von zumindest 10 % aufweist. 40 2 4. Zusammensetzung nach Anspruch 3, worin im Organopolysiloxan (C) die Gruppen R aus C2-10-Alkenyl-, -Alke- nyloxyalkyl- und -Alkenyloxygruppen ausgewählt sind.

5. Zusammensetzung nach einem der Ansprüche 1 bis 4, die 0,01 bis 0,5 Gewichtsteile des Photoinitiators enthält. 45 6. Lichthärtbare, flüssige Silikonkautschuk-Zusammensetzung zur Herstellung einer Masterform, die ihrerseits zum Formen eines lichthärtbaren flüssigen Harzes dient, wobei die Zusammensetzung Organopolysilxoan umfasst, das aus Folgendem besteht:

50 (C) 30 bis 100 Gew.-% Organopolysiloxan der folgenden mittleren Zusammensetzungsformel (2):

2 RcR dSiO(4-c-d)/2 (2)

55 worin die Gruppen R, die identisch oder voneinander verschieden sein können, substituierte oder unsubsti- tuierte einwertige Kohlenwasserstroffgruppen, die frei von aliphatischen ungesättigten Bindungen sind, oder Alkoxygruppen sind; die Gruppen R2, die identisch oder voneinander verschieden sein können, aliphatische

15 EP 0 832 936 B1

ungesättige Gruppen sind, die aus Alkenylgruppen und Sauerstoffatom-hältigen, aliphatischen, ungesättigten Gruppen ausgewählt sind; und c und d Zahlen sind, für die gilt: 1,90 ≤ c < 2,40; 0,0003 ≤ d ≤0,10; und 1,90 < c+d ≤ 2,40, wobei das Organopolysiloxan pro Molekül zumindest zwei aliphatische ungesättigte Gruppen ent- hält und eine Viskosität von 0,1 bis 1.000 Pa.s (100 bis 1.000.000 Centipoise) bei 25 °C aufweist; und 5 2 (D) 10 bis 70 Gew.-% Silikonharz, das in Komponente (C) löslich ist und RpR qSiO1/2-Einheiten (M), SiO2- 2 Einheiten (Q) und/oder YSiO3/2-Einheiten (T) umfasst, worin R und R wie oben definiert sind, p und q = 0, 1, 2 oder 3 sind, wobei gilt: p+q = 3, Y aus den gleichen Optionen ausgewählt ist wie R und R2, das Molverhältnis M/(Q+T) = 0,6 bis 1,2 ist, und das Molverhältnis R2/Si = 0,01 bis 0,10 ist; wobei die Zusammensetzung weiters umfasst: 10 (F) Organohydrogenpolysiloxan der folgenden mittleren Zusammensetzungsformel (3):

ReHfSiO(4-e-f)/2 (3)

15 worin die Gruppen R, die identisch oder voneinander verschieden sein können, substituierte oder unsubsti- tuierte einwertige Kohlenwasserstoffgruppen, die frei von aliphatischen ungesättigten Bindungen sind, oder Alkoxygruppen sind, e und f Zahlen sind, für die gilt: 0,70 ≤ e ≤ 2, 0,01 ≤ f ≤ 1,20; und 1,5 ≤ e+f ≤ 2,7, wobei das Organohydrogenpolysiloxan zumindest zwei SiH-Gruppen pro Molekül enthält, in einer Menge, die 0,4 bis 10 SiH-Gruppen pro aliphatischer ungesättigter Gruppe bereitstellt, die von den Komponenten (C) und (D) 20 bereitgestellt wird, und (G) eine katalytische Menge Platinkatalysator, der dazu bestimmt ist, als Reaktion auf Bestrahlung mit Licht Hydrosilylierung zwischen den aliphatischen ungesättigten Gruppen in den Komponenten (C) und (D) und den SiH-Gruppen in Komponente (F) zu bewirken; wobei die Zusammensetzung durch Bestrahlung mit Licht einer Wellenlänge im Bereich von 200 bis 500 25 nm zu einem gehärteten Produkt gehärtet werden kann, das eine Shore A-Härte von 20 bis 60 und eine Lichtdurchlässigkeit für solches Licht, gemessen bei einer Dicke von 10 mm, von zumindest 10 % aufweist.

7. Zusammensetzung nach Anspruch 6, worin das Organopolysiloxan aus 30 bis 90 Gew.-% Organopolysiloxan (C) und 10 bis 70 Gew.-% Silikonharz (D) besteht. 30 2 8. Zusammensetzung nach Anspruch 6, worin im Organopolysiloxan (D) die Gruppen R aus C2-10-Alkenyl-, -Alke- nyloxyalkyl- und -Alkenyloxygruppen ausgewählt sind.

9. Zusammensetzung nach einem der vorangegangenen Ansprüche, wobei das gehärtete Produkt daraus eine Shore 35 A-Härte von 30 bis 50 aufweist.

10. Verwendung einer Zusammensetzung nach einem der Ansprüche 1 bis 9 zur Herstellung einer Masterform, die zum Formen von lichthärtbaren flüssigen Harzen durch Bestrahlung durch die Wände der Masterform hindurch geeignet ist, durch Härten der Zusammensetzung mit Licht. 40

Revendications

1. Composition liquide de caoutchouc de silicone photo-durcissable pour produire un moule original de gabarit qui, 45 à son tour, est pour une utilisation dans le moulage d'une résine liquide photo-durcissable, la composition comprenant 100 parties en poids d'organopolysiloxane et 0,01 à 5 parties en poids de photo-initiateur, ledit organopolysiloxane consistant en

(A) 30 à 90% en poids d'organopolysiloxane de la formule de composition moyenne (1) : 50

1 RaR bSiO(4-a-b)/2 (1)

où les groupes R, qui peuvent être identiques ou différents, sont des groupes hydrocarbures monovalents 55 substitués ou non substitués sans liaison aliphatique insaturées ni groupe alcoxy ; les groupes R1, qui peuvent être identiques ou différents, sont des groupes photo-réactifs sélectionnés parmi des groupes contenant du (meth)acryloyle, des groupes vinyloxyalkyles et des groupes contenant un époxy ; et a et b sont des nombres

16 EP 0 832 936 B1

satisfaisant 1,90 ≤ a < 2,40, 0,0003 ≤ b ≤ 0,10, et 1,90 < a + b ≤ 2,40, l'organopolysiloxane contenant au moins deux groupes photo-réactifs dans une molécule et ayant une viscosité de 0,1 à 1000 Pa.s (100 à 1 000 000 centipoises) à 250°C, et

5 (B) 10 à 70% en poids d'une résine de silicone soluble dans le composant (A) et comprenant des unités 1 1 RpR qSiO1/2 (M) , des unités SiO2 (Q) et/ou des unités XsiO3/2 (T) où R et R sont tels que définis ci-dessus, p et q sont 0, 1, 2 ou 3 et satisfont p+q=3,Xalesmêmes options que R et R1, le rapport molaire M/(Q + T) = 0,6 à 1,2 et le rapport molaire R1/Si = 0,01 à 0,10 ; la composition étant durcissable, par exposition à de la lumière ayant une longueur d'onde dans la gamme de 200 à 500 nm, en un produit durci ayant une dureté 10 Shore A de 20 à 60 et une transmittance de la lumière pour une telle lumière, mesurée à une épaisseur de 10 mm, d'au moins 10%.

2. Composition selon la revendication 1 dans laquelle, dans l'organopolysiloxane (A), les groupes photo-réactifs sont des groupes contenant un (meth)acryloyle. 15 3. Composition liquide de caoutchouc de silicone photo-durcissable pour produire un moule original formant gabarit qui, à son tour, est approprié à une utilisation dans le moulage d'une résine liquide photo-durcissable, la composition comprenant 100 parties en poids d'organopolysiloxane et 0,01 à 5 parties en poids d'un photo-initiateur, ledit organopolysiloxane consistant en 20 (C) 30 à 90% en poids d'un organopolysiloxane de la formule de composition moyenne suivante (2) :

2 RcR dSiO(4-c-d)/2 (2) 25 où les groupes R, qui peuvent être identiques ou différents, sont des groupes hydrocarbures monovalents substitués ou non substitués sans liaison aliphatique insaturée ni groupe alcoxy ; les groupes R2, qui peuvent être identiques ou différents, sont des groupes aliphatiques insaturés sélectionnés parmi des groupes alcényle et des groupes aliphatiques insaturés contenant un atome d'oxygène et cetd sont des nombres satisfaisant 30 1,90 ≤ c < 2,40, 0,0003 ≤ d ≤ 0,10 et 1,90 < c + d ≤ 2,40, l'organopolysiloxane contenant au moins deux groupes à insaturation aliphatique par molécule et ayant une viscosité de 0,1 à 1000 Pa.s (100 à 1 000 000 centipoises) à 25°C, et

(D) 10 à 70% en poids d'une résine de silicone soluble dans le composant (C) et comprenant des unités 35 2 2 RpR qSiO1/2 (M), des unités SiO2 (Q) et/ou des unités YSiO3/2 (T)oùRetR sont tels que définis ci-dessus, p et q sont 0, 1, 2 ou 3 et satisfont p+q=3,Yalesmêmes options que R et R2, le rapport molaire M/(Q + T) = 0,6 à 1,2 et le rapport molaire R2/Si = 0,01 à 0,10 ; la composition comprenant de plus

40 (E) de l'organosilane ou organosiloxane contenant au moins deux groupes mercapto par molécule en une quantité produisant 0,1 à 20 équivalents du groupe mercapto relativement aux groupes à insuration aliphatique des composants (C) et (D) ; et la composition étant durcissable, par exposition à de la lumière ayant une longueur d'onde dans la gamme de 200 à 500 nm, en un produit durci ayant une dureté Shore A de 20 à 60 et une transmittance de la lumière 45 pour une telle lumière, mesurée à une épaisseur de 10 mm, d'au moins 10%.

4. Composition selon la revendication 3 dans laquelle, dans l'organopolysiloxane (C), les groupes R2 sont sélection- nés parmi des groupes alcényle, alcényloxyalkyle et alcényloxy C2-10.

50 5. Composition selon l'une quelconque des revendications 1 à 4 qui contient de 0,01 à 0,5 partie en poids du photo- initiateur.

6. Composition liquide de caoutchouc de silicone photo-durcissable pour produire un moule original formant gabarit qui, à son tour, est approprié pour une utilisation dans le moulage d'une résine liquide photo-durcissable, la com- 55 position comprenant un organopolysiloxane consistant en

17 EP 0 832 936 B1

2 RcR dSiO(4-c-d)/2 (2)

où les groupes R, qui peuvent être identiques ou différents, sont des groupes hydrocarbures monovalents 5 substitués ou non substitués sans liaison aliphatique insaturée ni groupe alcoxy ; les groupes R2, qui peuvent être identiques ou différents, sont des groupes à insaturation aliphatique sélectionnés parmi des groupes alcényles et des groupes à insaturation aliphatique contenant un atome d'oxygène et cetd sont des nombres satisfaisant 1,90 ≤ c < 2,40, 0,0003 ≤ d < 0,10 et 1,90

(D) 0 à 70% en poids d'une résine de silicone soluble dans le composant (C) et comprenant des unités 2 2 RpR pSiO1/2 (M), des unités SiO2 (Q) et/ou des unités YSiO3/2 (T)oùRetR sont tels que définis ci-dessus, p et q sont 0, 1, 2 ou 3 et satisfont p+q=3,Yestsélectionné parmi les mêmes options que R et R2, le rapport 15 molaire M/(Q + T) = 0,6 à 1,2 et le rapport molaire R2/Si = 0,01 à 0,10 ; la composition comprenant de plus

(F) un organohydrogénopolysiloxane de la formule de composition moyenne suivante (3) :

20 ReHfSiO(4-e-f)/2 (3)

où les groupes R, qui peuvent être identiques ou différents, sont des groupes hydrocarbures monovalents substitués ou non substitués sans liaison aliphatique insaturée ni groupe alcoxy, e et f sont des nombres satisfaisant 0,70 ≤ e ≤ 2,69, 0,01 ≤ f ≤ 1,20, et 1,5 ≤ e+f≤2,7, l'organohydrogénopolysiloxane contenant au 25 moins deux groupes SiH par molécule, en une quantité produisant de 0,4 à 10 groupes SiH par groupe à insaturation aliphatique fourni des composants (C) et (D), et

(G) une quantité catalytique d'un catalyseur de platine adapté à effectuer l'hydrosilylation entre les groupes à insaturation aliphatique dans les composants (C) et (D) et les groupes SiH dans le composant (F) en réponse 30 à une exposition à la lumière ; la composition étant durcissable, par exposition à de la lumière ayant une longueur d'onde dans la gamme de 200 à 500 mm, en un produit durci ayant une dureté Shore A de 20 à 60 et une transmittance de la lumière pour une telle lumière, mesurée à une épaisseur de 10 mm, d'au moins 10%.

35 7. Composition selon la revendication 6 dans laquelle l'organopolysiloxane consiste en 30 à 90% en poids de l'organopolysiloxane (C) et 10 à 70% en poids de la résine de silicone (D).

8. Composition selon la revendication 6 dans laquelle, dans l'organopolysiloxane (C), les groupes R2 sont sélection- nés parmi des groupes alcényles C2-10, alcényloxyalkyles et alcényloxy. 40 9. Composition selon l'une quelconques des revendications précédentes où ledit produit durci a une dureté Shore A de 30 à 50.

10. Utilisation d'une composition selon l'une quelconque des revendications 1 à 9 pour produire, par photodurcisse- 45 ment de ladite composition, un moule original qui est approprié pour une utilisation dans le moulage de résines liquides photo-durcissables par irradiation à travers les parois du moule original.