USOO.5908917A United States Patent (19) 11 Patent Number: 5,908,917 Kawakami et al. (45) Date of Patent: Jun. 1, 1999

54). POLYGLYCOLIC ACID SHEET AND 6-256481 9/1994 Japan. PRODUCTION PROCESS THEREOF OTHER PUBLICATIONS 75 Inventors: Yukichika Kawakami; Nobuo Sato; D.K. Gilding et al (1979) Polymer, vol. 20, pp. 1459–1463. Mitsuru Hoshino; Toshitaka European Search Report for Application No. 97302906.9 Kouyama, all of Fukushima; Zenya dated Sep. 4, 1997. Shiiki, Chiba, all of Japan Primary Examiner Duc Truong 73 Assignee: Kureha Kagaku Kogyo K.K., Tokyo, Attorney, Agent, or Firm-Dinsmore & Shohl LLP Japan 57 ABSTRACT 21 Appl. No.: 08/844,409 The invention provides a polyglycolic acid sheet obtainable by melt-extruding a thermoplastic resin material into a sheet 22 Filed: Apr. 18, 1997 in a temperature range of from the melting point, Tm of the 30 Foreign Application Priority Data polymer to 255 C., wherein the thermoplastic resin material comprises polyglycolic acid having a repeating unit repre Apr. 30, 1996 JP Japan ...... 8-134218 Apr. 8, 1997 JP Japan ... 9-105161 sented by the following formula (1):

(51) Int. Cl." ...... C08G 63/08 (1) 52 U.S. Cl...... 528/354; 528/425; 528/503; O-CH-C 525/419, 525/420; 521/79; 264/46.1; 264/46.2; 264/75; 264/77; 264/160; 264/239 O 58 Field of Search ...... 528/354, 425, 528/503; 264/46.1, 46.2, 75, 77, 160, 239; and the following physical properties: 521/79; 525/419, 420 (a) the melt viscosity, m as measured at a temperature of (the melting point, Tm of the polymer+20° C.) and a 56) References Cited shear rate of 100/sec being 500-100,000 Pa.s; U.S. PATENT DOCUMENTS (b) the melting point, Tm being at least 150° C.; 2,668,162 2/1954 Lowe. (c) the melt enthalpy, AHm being at least 20 J/g, and 2,676,945 4/1954 Higgins. (d) the density being at least 1.50 g/cm as measured in an 5,502,158 3/1996 Sinclair et al. . unoriented, crystallized form, and the sheet has tensile Strength of at least 60 MPa, and a production process FOREIGN PATENT DOCUMENTS thereof. 0677561 10/1995 European Pat. Off.. 6-256480 9/1994 Japan. 19 Claims, No Drawings 5,908.917 1 2 POLYGLYCOLIC ACID SHEET AND With respect to films based on polyglycolic acid, which PRODUCTION PROCESS THEREOF are synthetic polyester films, Higgins et al. (U.S. Pat. No. 2,676.945, issued in 1954) disclose amorphous films having FIELD OF THE INVENTION a thickness of 3 mils and biaxially stretched films obtained by Stretching them. These films are those obtained by using The present invention relates to a sheet formed from a 5 a polymer obtainable by directly polycondensing glycolic thermoplastic resin material comprising polyglycolic acid, acid, not a polymer obtainable by ring-opening polymeriza and more particularly to a polyglycolic acid sheet which has tion of glycolide. However, the polycondensation process of excellent toughness, degradability in Soil and barrier glycolic acid includes heating and polycondensing glycolic properties, and to a production process thereof. By Second acid for a long period of time as about 40 hours at a high temperature of at least 200 C. and hence tends to involve arily processing the polyglycolic acid sheet according to the Side reactions Such as decomposition reaction. Accordingly, present invention, it can be used in a wide variety of fields this proceSS is difficult to provide a practicable polymer as, for example, containers for electronic ranges, retort food having a high molecular weight. U.S. Pat. No. 2,676,945 packaging materials, medical instrument packaging materi describes, in its example, the melt Viscosity of the polymer als capable of Subjecting to high-temperature Sterilization, as about 2,000 poises (at 245 C.). This melt viscosity value containers for boiling water pouring type instant food, egg 15 corresponds to a value measured at a shear rate of about cartons and cushioning materials. 0/sec. This melt viscosity value corresponds to a value extremely as low as about 20 poises (at 245 C.) when BACKGROUND OF THE INVENTION converted into a value measured at a shear rate of 100/sec. In addition, there is a high possibility that this polymer may In recent years, increase in plastic waste has become a have an unstable Structure due to Side reactions. great Social problem. Since many of polymeric materials Accordingly, an extrusion film formed from the polymer have hitherto been developed and produced in Search of high obtained by Such a direct polycondensation process has performance and long-term Stability, they are not easily extremely low mechanical Strength as demonstrated by its decomposed in a natural environment. Therefore, how to tensile strength extremely as low as 5,470 psi (about 39 dispose and manage a large quantity of plastic waste which MPa) and hence has involved a problem that it is unsatis has become useleSS becomes a Social problem on a world 25 factory from the view point of practical use. wide Scale. The plastic waste includes sheets formed from a Gilding et al. POLYMER, 20, 1459 (1979) provide films having a thickness of 250 um from 20% solutions of glycolic variety of Synthetic resins, Such as polyolefin resins Such as acid copolymers (glycolide/lactide=90/10, 70/30, 50/50, polyethylene and polypropylene, polyester resins Such as etc.) by a casting process. However, this process tends to polyethylene terephthalate, polyamide resins Such as nylon, form coarse spherulites upon evaporation of a Solvent, and and chlorine-containing resins Such as polyvinylidene the resultant films are hence extremely brittle and unsatis chloride, and trays and containers obtained by Secondarily factory in mechanical Strength from the viewpoint of prac processing these sheets. tical use. Under the circumstances, biodegradable polymers, which Japanese Patent Application Laid-Open Nos. 256480/ are degraded by natural microorganisms, attract attention as 35 1994 and 256481/1994 disclose that polyglycolic acid hav polymeric materials which impose no burden on the envi ing a Viscosity-average molecular weight of 280,000 or ronment. The biodegradability can be evaluated by, for 250,000 was used as a raw material, this polymer was example, a degradability test in Soil (Soil degradability test). melt-extruded and cast at 280 C. into an unoriented sheet, Since plastic sheets are required to have good mechanical and the unoriented Sheet was then Stretched 3 times in a properties, thermal properties, barrier properties, melt machine direction and 4 or 3 times in a transverse direction processability, profitability and the like, however, any plastic 40 at 160° C. to obtain a biaxially oriented film (in each sheet, which fully Satisfies these requirements and exhibits document, Example 3). However, polyglycolic acid tends to biodegradability, has not been yet obtained. undergo thermal decomposition at a temperature exceeding about 255 C. and actually substantially undergoes thermal Among the conventional biodegradable plastic sheets, for decomposition at the temperature as high as 280 C., so that example, sheets based on Starch are unsatisfactory in 45 any Satisfactory unoriented sheet cannot be obtained. It is a toughness, barrier properties and heat resistance and involve matter of course that if Such an unoriented sheet is biaxially a problem that they are difficult to melt-process, So that its Stretched, it is Scarcely possible to obtain a biaxially oriented processing cost becomes high. Sheets based on cellulose are film having Sufficient Strength. An amorphous sheet of unsatisfactory in toughness and involve a problem that they polyglycolic acid is crystallized at a temperature exceeding are difficult to melt-process, So that its processing cost 50 its crystallization temperature Tcl (about 80° C.) and highly becomes high. Sheets based on a microorganism-produced crystallized at a temperature as high as 160 C., so that the polyester are unsatisfactory in toughness and involve a great biaxial Stretching of the amorphous sheet, for example, 3 problem that their production cost becomes particularly times in a machine direction and 3 or 4 times in a transverse high. Sheets based on a Synthetic type polyester Such as a direction, is extremely difficult or actually impossible under poly Succinate are unsatisfactory in toughneSS and barrier 55 Such stretching conditions. Accordingly, any sheet or ori properties and involve a problem that Succinic acid and ented film having Sufficient Strength cannot be obtained butanediol, which are raw materials for the polyester, are under the conditions disclosed in these publications. considerably expensive. Besides, the meaning of the Viscosity-average molecular Sheets based on polylactic acid, which is a Semi-Synthetic weight of 250,000 or 280,000 and its measuring method are type polyester, are unsatisfactory in toughness. Since 60 also unclear. Accordingly, it can be hardly Said that these L-lactic acid, which is an optically active Substance used as publications actually disclose high-molecular weight polyg a raw material, is required to have a high purity, the sheets lycolic acid in the light of the state of the art. must be produced through fermentation of a biological OBJECTS AND SUMMARY OF THE process, and there is hence a limit to their production at low INVENTION cost. Further, Since polylactic acid has a high glass transition 65 It is an object of the present invention to cheaply provide temperature, Tg, it also involves a problem that it is difficult a polyglycolic acid sheet, which has excellent toughness and to compost under ordinary composting conditions. barrier properties and exhibits high degradability in Soil. 5,908.917 3 4 The present inventors have carried out an extensive which comprises polyglycolic acid having a repeating unit investigation with a view toward overcoming the above represented by the following formula (1): problems involved in the prior art. As a result, it has been found that a sheet formed from a thermoplastic resin mate (1) rial comprising polyglycolic acid having Specific physical O-CH-C properties has high tensile Strength, Satisfactory elongation, exhibits good degradability in Soil and excellent barrier O properties, and can be produced at a relatively low price. In order to obtain the polyglycolic acid sheet of the and the following physical properties: present invention having excellent Strength, it is necessary to (a) the melt viscosity, m as measured at a temperature of use polyglycolic acid having a Sufficiently high molecular (the melting point, Tm of the polymer+20° C.) and a shear weight. Such a polyglycolic acid can be obtained, for rate of 100/sec being 500-100,000 Pa.s; example, by heating glycolide (i.e., a dimeric cyclic ester of (b) the melting point, Tm being at least 150° C.; glycolic acid) in the presence of a catalyst (for example, a (c) the melt enthalpy, AHm being at least 20 J/g, and cationic catalyst Such as a tin organic carboxylate, tin halide 15 (d) the density being at least 1.50 g/cm as measured in an or antimony halide), thereby Subjecting it to bulk ring unoriented, crystallized form, through a T-die into a sheet in opening polymerization or Solution ring-opening polymer a temperature range of from Tm to 255 C.; quenching the ization. In order to obtain polyglycolic acid having excellent sheet to the crystallization temperature, Tc of the polymer physical properties, it is essential to use high-purity gly or lower, and optionally heat-setting the quenched sheet for collide as a monomer. The high-purity glycolide can be 1 Second to 3 hours in a temperature range of from the obtained with good productivity by a proceSS in which an crystallization temperature, Tc to (Tm+10° C) under ten oligomer of glycolic acid is mixed with a high-boiling polar Sion or under no tension. organic Solvent, the mixture is heated under ordinary pres Sure or reduced pressure to a temperature at which depoly DETAILED DESCRIPTION OF PREFERRED merization of the oligomer occurs, thereby depolymerizing 25 EMBODIMENTS the oligomer in a State that the oligomer forms a Solution phase, glycolide formed is distilled out together with the The present invention will hereinafter be described in high-boiling polar organic Solvent, and the glycolide is detail. recovered from the distillate. Structure of polymer An example of a process for forming a sheet from the The polyglycolic acid useful in the practice of the present polyglycolic acid includes a process in which the polygly invention is a polymer having a repeating unit represented colic acid alone or a composition containing the polygly by the following formula (1): colic acid is melt-extruded through a T-die into a sheet. (1) The polyglycolic acid can be industrially mass-produced 35 by using extremely cheep raw materials of CO, H2O and O-CH-C CHO or ethylene glycol. Since the polyglycolic acid sheet O has degradability in Soil, it Scarcely imposes burden on the environment. The proportion of the repeating unit represented by the The present invention has been led to completion on the 40 formula (1) in the polymer is generally at least 70 wt.%, basis of these findings. preferably at least 80 wt.%, more preferably 90 wt.%. If the According to the present invention, there is thus provided proportion of the repeating unit represented by the formula a polyglycolic acid sheet obtainable by melt-extruding a (1) is lower than 70 wt.%, there is a possibility that the thermoplastic resin material into a sheet in a temperature toughness and barrier properties of the resulting polymer range of from the melting point, Tm of the polymer to 255 45 may be deteriorated, and its degradability in Soil may be C., wherein the thermoplastic resin material comprises impaired. polyglycolic acid having a repeating unit represented by the AS examples of other repeating units than the repeating following formula (1): unit represented by the formula (1), may be mentioned a repeating unit represented by the following formula (2): (1) 50 O- CH-C (2) O free-toO O and the following physical properties: 55 (a) the melt viscosity, m as measured at a temperature of wherein n is 1-10, and m is 0–10, a repeating unit repre (the melting point, Tm of the polymer+20° C.) and a shear sented by the following formula (3): rate of 100/sec being 500-100,000 Pa.s; (b) the melting point, Tm being at least 150° C.; 60 (c) the melt enthalpy, AHm being at least 20 J/g, and (3) (d) the density being at least 1.50 g/cm as measured In O - CH- C an unoriented, crystallized form, and the Sheet has tensile (CH2); H O strength of at least 60 MPa. According to the present invention, there is also provided 65 a process for producing a polyglycolic acid sheet, compris wherein j is 1-10, a repeating unit represented by the ing the Steps of melt-extruding a thermoplastic resin material following formula (4): 5,908.917 S 6 preferably 1.52 g/cm as measured in an unoriented, crys tallized form. Low-density polyglycolic acid having a den (4) sity lower than 1.50 g/cm is considered to be such that its degree of crystallinity is lowered due to the disorder of its intramolecular chemical Structure, and consequently the ot" density may be lowered. Accordingly, a sheet formed from R2 O Such a polyglycolic acid has a possibility that the degree of crystallinity may be low, and the toughness and heat resis tance may be insufficient. wherein R and R2 are independently a hydrogen atom or an General properties of sheet alkyl group having 1-10 carbon atoms, and k is 2-10, and a repeating unit represented by the following formula (5): Since the sheet according to the present invention is formed by using the above-described specific polyglycolic (5) acid, it has tensile strength of at least 60 MPa, preferably at - - O - CH-O-CH-CH2-H least 80 MPa, more preferably at least 100 MPa, and often 15 at least 130 MPa. Such a sheet is a sheet having sufficient Strength from the Viewpoint of practical use. When these repeating units are introduced in a proportion Since the sheet according to the present invention is of at least 1 wt.%, the melting point, Tm of the glycolic acid formed by using the above-described specific polyglycolic homopolymer can be lowered to lower the processing tem acid, it has tensile elongation of generally at least 5%, perature of the polymer, whereby thermal decomposition preferably at least 7%, more preferably at least 9%. Such a upon melt processing can be reduced. Besides, the crystal sheet is a sheet having Sufficient elongation from the View lization rate of the polyglycolic acid can be controlled by the copolymerization to improve its extrudability and Stretch point of practical use. ability. However, if the proportion of these repeating units With the cooperation of high tensile Strength and high (2) to (5) exceeds 30 wt.%, the crystallizability inherent in elongation, the polyglycolic acid sheet according to the the polyglycolic acid is impaired, So that there is a possi 25 present invention is a Sufficiently Stiff and tough sheet even bility that the toughness and heat resistance of the resulting when it is thin. The formation of the thin sheet permits a sheet may be deteriorated to a marked extent. considerable reduction in weight per unit area of the film and Physical properties of polymer the provision of a Soil-degradable sheet at low cost. The sheet according to the present invention can be easily The polyglycolic acid used as a raw material for the sheet Subjected to Secondary processing Such as vacuum forming according to the present invention is a high-molecular or pressure forming making good use of the properties of weight polymer. The melt viscosity of the polymer can be being high in tensile Strength and tensile elongation. If the used as an index to its molecular weight. The polyglycolic resulting sheet has tensile strength lower than 60 MPa and/or acid used in the present invention has a melt Viscosity, m of tensile elongation lower than 5%, there is a possibility that 500-100,000 Pas, preferably 1,000–50,000 Pas, more pref 35 it may be easy to be broken upon its Secondary processing, erably 1,500-20,000 Pa.s as measured at a temperature of or the resulting formed product from the sheet may become (Tm+20 C.) (i.e., a temperature corresponding to a usual limp and easy to be broken. melt-processing temperature) and a shear rate of 100/sec. If the melt viscosity, m* of the polyglycolic acid is lower The thickness of the sheet according to the present than 500 Pa.s, there is a possibility that a melt of the polymer 40 invention is generally 0.01-5 mm, preferably 0.05-4 mm, may undergo drawdown upon its melt-forming into a sheet, more preferably 0.1-3 mm. Any sheet having a thickness a sheet melt-extruded through a T-die may undergo defor smaller than 0.01 mm is not preferable because drawdown mation during its quenching, resulting in difficulty in melt or breaking is easy to occur when the polyglycolic acid is processing, or the toughness of the resulting sheet may melt-extruded through a T-die to form the sheet, and So Such become insufficient. If the melt viscosity, m* of the polyg 45 a sheet is difficult to produce, and moreover the resulting lycolic acid is higher than 100,000 Pa.s, its melt processing sheet also involves Such problems that it is limp and easy to requires a higher temperature, and there is a possibility that be broken. On the other hand, any sheet having a thickness the polyglycolic acid may undergo heat deterioration upon exceeding 5 mm tends to cause an uneven crystalline the processing. Structure due to the time lag in crystallization between the 50 Surface portion and the central portion of the sheet in the The melting point, Tm of the polyglycolic acid useful in course of its production. Accordingly, there is a possibility the practice of the present invention is at least 150° C., that the toughness of the resulting sheet may be deteriorated. preferably at least 190° C., more preferably at least 210 C. 65 formed from the polyglycolic acid the Tg of which is not The polyglycolic acid used in the present invention has a very high, So that it is possible to compost it under ordinary density of at least 1.50 g/cm, preferably 1.51 g/cm, more conditions. 5,908.917 7 8 High barrier sheet The Solution-phase depolymerization process is per It is possible to provide a sheet having a low oxygen formed by (1) heating a mixture containing a glycolic acid permeability by using the Specific polyglycolic acid oligomer and at least one high-boiling polar organic Solvent described above. More specifically, the sheet according to having a boiling point within a range of 230-450° C. to a the present invention exhibits high barrier properties as temperature, at which the depolymerization of the oligomer demonstrated by its oxygen permeability (as measured at a takes place, under ordinary preSSure or under reduced pres temperature of 23 C. and 80% relative humidity; in terms Sure; (2) dissolving the oligomer in the Solvent until a of the thickness of 25 um) of generally 100 cc/m.day.atm or residual rate (volume ratio) of a melt phase of the oligomer Smaller, preferably 50 cc/m.day.atm or Smaller, more pref reaches 0.5 or lower; (3) further continuing the heating at the erably 30 cc/m.day.atm or smaller. same temperature to depolymerize the oligomer; (4) distill The sheet according to the present invention is also ing out a dimeric cyclic ester (i.e., glycolide) formed excellent in carbon dioxide barrier property and has a carbon together with the high-boiling polar organic Solvent; and (5) dioxide permeability (as measured at a temperature of 23 C. recovering glycolide from the distillate. and 80% relative humidity in accordance with JIS K 7126; Examples of the high-boiling polar organic Solvent in terms of the thickness of 25 um) of generally 300 15 include aromatic carboxylic acid esters, Such as bis cc/m°.day.atm or smaller, preferably 200 cc/m'..day.atm or (alkoxyalkyl) phthalates Such as di(2-methoxyethyl) smaller, more preferably 50 cc/m.day.atm or smaller. phthalate, alkylene glycol dibenzoates Such as diethylene Production process of sheet glycol dibenzoate, benzylbutyl phthalate, and dibutyl phtha plasticizers and the like into the polyglycolic acid within example, a cyclic monomer Such as ethylene oxalate (i.e., limits not impeding the object of the present invention may 1,4-dioxane-2,3-dione), lactide, a lactone (for example, 40 also be used as the thermoplastic resin material. More B-propiolactone, B-butyrolactone, pivalolactone, Specifically, there may be used a composition (compound) Y-butyrolactone, Ö-Valerolactone, B-methyl-6-Valerolactone obtained by incorporating the inorganic fillers, other ther or e-caprolactone), trimethylene carbonate or 1,3-dioxane, a moplastic resins and plasticizers in proportions of 0-100 hydroxy carboxylic acid Such as lactic acid, parts by weight, 0-100 parts by weight and 0-200 parts by 3-hydroxypropanoic acid, 3-hydroxybutanoic acid, 45 weight, respectively, per 100 parts by weight of the polyg 4-hydroxybutanoic acid or 6-hydroxycaproic acid or an lycolic acid. If the inorganic fillers or other thermoplastic alkyl ester thereof; a Substantially equimolar mixture of an resins are used in a proportion exceeding 100 parts by aliphatic diol Such as ethylene glycol or 1,4-butanediol and weight, or the plasticizers are used in a proportion exceeding an aliphatic dicarboxylic acid Such as Succinic acid or adipic 200 parts by weight, there is a possible problem that the acid or an alkyl ester thereof, or two or more compounds 50 tensile Strength and resistance to heat shrinkage of the thereof. The glycolic acid copolymer may be that obtained resulting sheet may become insufficient, or the melt pro by Subjecting the polyglycolic acid and another polymer ceSSability of the composition may be deteriorated. having repeating units selected from among the formulae (2) Examples of the inorganic fillers include powders, whis to (4) to transesterification under heat. Of the above prepa kers and fibers of inorganic materials. Such as alumina, Silica, ration processes, the process (1) in which glycolide is 55 Silica-alumina, Zirconia, titanium oxide, iron oxide, boron Subjected to ring-opening polymerization is preferred oxide, calcium carbonate, calcium Silicate, calcium because a high-molecular weight polyglycolic acid is easy to phosphate, calcium Sulfate, magnesium carbonate, magne be obtained. sium Silicate, magnesium phosphate, magnesium Sulfate, As the glycolide used as a monomer in the process (1), kaolin, talc, mica, ferrite, carbon, Silicon, Silicon nitride, glycolide obtained by “a Solution-phase depolymerization 60 molybdenum disulfide, glass and potassium titanate. These process” (Japanese Patent Application No. 48000/1996) inorganic fillers may be used either Singly or in any com developed by the present inventors is preferred to that bination thereof. Although the inorganic fillers are generally obtained by the conventional Sublimation depolymerization used in a proportion of 0-100 parts by weight per 100 parts process of a glycolic acid oligomer because a high-purity by weight of the polyglycolic acid, it is desirable to use them product can be mass-produced at a higher yield. The use of 65 in a range of 0.01-10 parts by weight, preferably 0.05-5 high-purity glycolide as a monomer permits the easy pro parts by weight taking film-forming property and toughneSS Vision of high-molecular weight polyglycolic acid. into consideration. 5,908.917 9 10 Examples of the other thermoplastic resins include a sheet. The sheet is optionally heat set for 1 second to 3 hours homopolymer and copolymers of lactic acid, a homopoly in a temperature range of from the crystallization mer and copolymers of ethylene oxalate, a homopolymer temperature, Tc to (Tm+10 C.) (generally 70-240° C.) and copolymers of e-caprolactone, poly Succinates, polyhy under tension or under no tension, whereby a heat Set sheet droxybutanoic acid, hydroxybutanoic acid-hydroxyvaleric can be obtained. When Stretching rolls are arranged in place acid copolymers, cellulose acetate, polyvinyl alcohol, of the cooling roll or prior to the cooling roll to Stretch the Starch, polyglutamates, natural rubber, polyethylene, sheet in a machine direction (M direction), a uniaxially polypropylene, Styrene-butadiene copolymer rubber, oriented sheet can be produced. If the melt-extrusion tem acrylonitrile-butadiene copolymer rubber, polymethyl perature exceeds 255 C., there is a possibility that the methacrylate, polystyrene, Styrene-butadiene-styrene block thermal decomposition of the polymer may be easy to take copolymers, Styrene-ethylene-butylene-styrene block place, and rapid decrease in molecular weight and bubbling copolymers, ABS resins, MBS resins and ethylene-vinyl attendant upon the decomposition may occur, resulting in a alcohol copolymers. These thermoplastic resins may be used sheet having too poor properties to Subject it to Secondary either Singly or in any combination thereof. Although these processing. thermoplastic resins are generally used in a proportion of 15 0-100 parts by weight per 100 parts by weight of the The polyglycolic acid sheet according to the present polyglycolic acid, it is desirable to use them in a proportion invention can be Subjected to sheet forming at a temperature of at most 50 parts by weight, preferably at most 30 parts by of from Tg to (Tm+10°C.) (generally 30–240° C) by means weight taking toughneSS and degradability in Soil into con of, for example, a vacuum forming machine, pressure form sideration. ing machine or match mold forming machine to impart Examples of the plasticizers include phthalates Such as Stereoscopic shapes. Such as irregularities and deep drawing di(methoxyethyl) phthalate, dioctyl phthalate, diethyl phtha to the sheet. The Sheet can be further punched out as needed, late and benzylbutyl phthalate; benzoates Such as diethylene thereby producing various kinds of sheet-forming products. glycol dibenzoate and ethylene glycol dibenzoate, aliphatic Application fields dibasic acid esterS Such as octyl adipate and octyl Sebacate; 25 The polyglycolic acid sheet according to the present aliphatic tribasic acid esterS Such as tributyl acetylcitrate; invention can be used in a wide variety of fields making phosphates Such as dioctyl phosphate and tricresyl phoS good use of its features of high toughness, heat resistance phate, epoxy plasticizerS Such as epoxidized Soybean oil; and transparency. The sheet of the present invention can be and polyalkylene glycol esterS Such as polyethylene glycol Subjected to Secondary processing into various formed prod Sebacate and polypropylene glycol laurate. These plasticiz ucts. Application fields of the Sheet according to the present erS may be used either Singly or in any combination thereof. invention making good use of its high heat resistance Although the plasticizers are generally used in a proportion include, for example, containers (Such as trays and cups) for of 0-200 parts by weight per 100 parts by weight of the electronic ranges, retort food packaging materials, medical polyglycolic acid, it is desirable to use them in a proportion instrument packaging materials capable of Subjecting to of at most 100 parts by weight, preferably at most 50 parts 35 high-temperature Sterilization, containers (Such as cups) for by weight taking film-forming property, toughness and resis boiling water pouring type instant food and various kinds of tance to heat shrinkage into consideration. disposable ware (for example, Soup plates). Application In the present invention, various additives Such as heat fields of the sheet according to the present invention making Stabilizers, light Stabilizers, moistureproofing agents, water good use of its high toughness include, for example, egg proofing agents, water repellents, lubricants, releasing 40 cartons, cushioning materials, Stationery and doll cases. agents, coupling agents, pigments and dyes may be con tained in the thermoplastic resin material as needed. These ADVANTAGES OF THE INVENTION various additives are used in an effective amount as neces According to the present invention, there can be cheaply Sary for the end application intended. provided sheets having excellent toughness and barrier The composition is prepared by a method known perse in 45 properties and exhibiting good degradability in Soil. Since the art by feeding the polyglycolic acid and at least one of the sheets according to the present invention have the the other components Such as the inorganic fillers, thermo features of high toughness, barrier properties and plastic resins, plasticizers and various additives into a transparency, they can be Suitably used in application fields kneading extruder to melt and knead them at a cylinder making good use of their features by Subjecting them to temperature of from Tm to 255° C. (generally, 150–255° C), 50 Secondary processing, for example, containers for electronic extruding them into a Strand, and cooling and chopping the ranges, retort food packaging materials, medical instrument Strand into pellets. packaging materials, instant food containers, various kinds

EXAMPLE 1. 1. 2 3 1. 2 3 Polymer (P-1) was charged into a small twin-screw Polymer code P-1 P-2 P-3 CP-1 CP-2 P-1 extruder equipped with a nozzle having a diameter of 3 mm 55 Composition under a nitrogen gas Stream, and extruded into a Strand at a Kind of additive Al-O Talc - melt temperature of about 230 C-235 C. The strand was Amount added O1 0.1 - quenched and chopped to obtain Pellet (No. 1). (parts by weight) Pellet code 1. 2 3 C1 C2 1. This Pellet (No. 1) was charged into a small extruder Physical properties equipped with a coathanger type T-die under a nitrogen gas 60 of sheet stream to extrude it at a resin melt temperature of about 230 C. into a sheet. The sheet-like extrudate was cut into a Sheet code S1-1 S2-1 S3-1 SC1-1 SC2-1 - Thickness (mm) O.25 O.26 0.25 O.25 O.30 desired length to obtain Sheet (S1-1). Density (g/cm) 1.58 157 1.56 1.26 1.57 EXAMPLE 2 Tensile strength 140 130 130 60 35 65 (MPa) Pellet (No. 2) was prepared in the same manner as in Elongation (%) 15 16 13 2 8 Example 1 except that a mixture of 100 parts by weight of 5,908.917 15 16 9. The sheet according to claim 8, wherein the thermo TABLE 2-continued plastic resin material is a composition composed of the polyglycolic acid and at least one component Selected from Example Comp. Example the group consisting of inorganic fillers, other thermoplastic resins and plasticizers and comprising 100 parts by weight 1. 2 3 1. 2 3 of the polyglycolic acid, 0-100 parts by weight of the O. permeability (at 3 4 4 1SOO 4 inorganic fillers, 0-100 parts by weight of the other ther 80% RH, 23° C.; moplastic resins and 0-200 parts by weight of the plasticiz ccfm? day atm) CS. CO, permeability 15 2O 18 8OOO 2O (at 80% RH, 23° C.: 10. The sheet according to claim 8, wherein the thermo ccfm? day atm) plastic resin material is a composition comprising 100 parts Degradability in High High High High High by weight of the polyglycolic acid and 0.01-10 parts by soil weight of the inorganic fillers. Remarks * 1. * 2 11. The sheet according to claim 1, wherein the polygly colic acid is a homopolymer of glycolide obtained by * 1: Polylactic acid. 15 ring-opening polymerization. *2: Forming was stopped. 12. The sheet according to claim 1, wherein the polygly We claim: colic acid is a copolymer obtained by ring-opening poly 1. A polyglycolic acid sheet obtained by melt-extruding a merization of glycolide in a proportion not lower than 70 wt. thermoplastic resin material into a sheet in a temperature %, but lower than 100 wt. % and at least one cyclic range of from the melting point, Tm, of the polymer to 255 comonomer Selected from the group consisting of ethylene C., wherein the thermoplastic resin material comprises oxalate, lactide, lactones, trimethylene carbonate and 1,3- polyglycolic acid having a repeating unit represented by the dioxane in a proportion higher than 0 wt.%, but not higher following formula (1): than 30 wt.%. 13. The sheet according to claim 12, wherein the polyg (1) 25 lycolic acid is a copolymer of glycolide in a proportion not lower than 70 wt.%, but lower than 100 wt.% and ethylene O- CH-C oxalate. O 14. The sheet according to claim 12, wherein the polyg lycolic acid is a copolymer of glycolide in a proportion not lower than 70 wt.%, but lower than 100 wt.% and lactide. and the following physical properties: 15. A process for producing a polyglycolic acid sheet, (a) the melt viscosity, m, as measured at a temperature of comprising the Steps of melt-extruding a thermoplastic resin the melting point, Tm, of the polymer-20 C. and a material which comprises polyglycolic acid having a repeat shear rate of 100/sec, being 500-100,000 Pa.s; ing unit represented by the following formula (1): (b) the melting point, Tm, being at least 150° C.; (c) the melt enthalpy, AHm, being at least 20 J/g, and 35 (1) (d) the density being at least 1.50 g/cm as measured in an O-CH-C unoriented, crystallized form, and wherein the sheet has tensile strength of at least 60 MPa. O 2. The sheet according to claim 1, wherein the sheet is a polyglycolic acid sheet obtained by melt-extruding the ther 40 moplastic resin material into a sheet in a temperature range and the following physical properties: of from the melting point, Tm, to 255 C., quenching the (a) the melt Viscosity, m*, as measured at a temperature of sheet to the crystallization temperature, Tc, of the polymer the melting point, Tm, of the polymer-20 C. and a or lower and optionally heat-setting the quenched sheet for shear rate of 100/sec, being 500-100,000 Pas; 1 Second to 3 hours in a temperature range of from the 45 (b) the melting point, Tm, being at least 150° C.; crystallization temperature, Tc, to Tm+10 C., under ten (c) the melt enthalpy, AHm, being at least 20 J/g, and Sion or under no tension. (d) the density being at least 1.50 g/cm as measured in an 3. The sheet according to claim 1, wherein the sheet is unoriented, crystallized form, the melt extruding being degradable in Soil. performed through a T-die and in a temperature range 4. The sheet according to claim 1, wherein the sheet has 50 of from the melting point, Tm, to 255 C. to form the an oxygen permeability, as measured at a temperature of 23 thermoplastic resin material into a sheet, quenching the C. and 80% relative humidity and a film thickness of 25 um, sheet to the crystallization temperature, Tc, of the of 100 cc/m.day.atm or smaller. polymer or lower; and optionally heat-Setting the 5. The sheet according to claim 1, wherein the sheet has quenched sheet for 1 Second to 3 hours in a temperature a carbon dioxide permeability, as measured at a temperature 55 range of from the crystallization temperature, Tc, to of 23 C. and 80% relative humidity and a film thickness of Tm+10 C. under tension or under no tension. 25 um, of 300 cc/m.day.atm or smaller. 16. The production proceSS according to claim 15, 6. The sheet according to claim 1, wherein the sheet has wherein the thermoplastic resin material is composed of the an elongation of at least 5%. polyglycolic acid alone. 7. The sheet according to claim 1, wherein the thermo 60 17. The production proceSS according to claim 15, plastic resin material is composed of the polyglycolic acid wherein the thermoplastic resin material is a composition alone. composed of the polyglycolic acid and at least one compo 8. The sheet according to claim 1, wherein the thermo nent Selected from the group consisting of inorganic fillers, plastic resin material is a composition composed of the other thermoplastic resins and plasticizers. polyglycolic acid and at least one component Selected from 65 18. The production process according to claim 15, the group consisting of inorganic fillers, other thermoplastic wherein the polyglycolic acid is a homopolymer of glycolide resins and plasticizers. obtained by ring-opening polymerization. 5,908.917 17 18 19. The production process according to claim 15, ethylene oxalate, lactide, lactones, trimethylene carbonate wherein the polyglycolic acid is a copolymer obtained by and 1,3-dioxane in a proportion higher than 0 wt.%, but not ring-opening polymerization of glycolide in a proportion not than 30 wt.%. lower than 70 wt.%, but lower than 100 wt.% and at least one cyclic comonomer Selected from the group consisting of

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. : 5,908,917 DATE) : June 1, 1999 INVENTOR(S) : Yukichika Kawakami et al It is certified that error appears in the above-indentified patent and that said Letters Patent is hereby corrected as shown below:

Claim 19, column 18, line 3, before “than 30 wt. percent.” insert -higher--.

Signed and Sealed this Ninth Day of November, 1999

O. TOI)) DICKINSON Attestingg OfficerI Act fig Jilinission rif f' i' is a list ridiks