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(11) EP 2 449 176 B1

(12) EUROPEAN PATENT SPECIFICATION

(45) Date of publication and mention (51) Int Cl.: of the grant of the patent: D21H 21/22 (2006.01) 28.09.2016 Bulletin 2016/39 (86) International application number: (21) Application number: 10727443.3 PCT/EP2010/059466

(22) Date of filing: 02.07.2010 (87) International publication number: WO 2011/000942 (06.01.2011 Gazette 2011/01)

(54) SACK WITH VAPOUR BARRIER SACKPAPIER MIT DAMPFSPERRE PAPIER À SAC AVEC BARRIÈRE DE VAPEUR

(84) Designated Contracting States: • MAGNUSSON, Anna-Karin AL AT BE BG CH CY CZ DE DK EE ES FI FR GB S-586 62 Linköping (SE) GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO • JAKTLUND ENSTRÖM, Lise-Lotte PL PT RO SE SI SK SM TR S-952 92 Kalix (SE)

(30) Priority: 03.07.2009 SE 0900923 (74) Representative: Boult Wade Tennant Verulam Gardens (43) Date of publication of application: 70 Gray’s Inn Road 09.05.2012 Bulletin 2012/19 London WC1X 8BT (GB)

(73) Proprietor: Dow Global Technologies LLC (56) References cited: Midland, MI 48674 (US) EP-A1- 0 441 233 EP-A1- 0 545 228 WO-A1-03/010055 GB-A- 1 136 622 (72) Inventors: GB-A- 2 332 873 US-A- 3 560 227 • ÅVITSLAND, Grete US-A- 3 652 725 US-A1- 2002 016 402 S-605 80 Svärtinge (SE) US-A1- 2003 170 408 US-A1- 2003 211 348

Note: Within nine months of the publication of the mention of the grant of the European patent in the European Patent Bulletin, any person may give notice to the European Patent Office of opposition to that patent, in accordance with the Implementing Regulations. Notice of opposition shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). EP 2 449 176 B1

Printed by Jouve, 75001 PARIS (FR) 1 EP 2 449 176 B1 2

Description inous barrier layer which is adhered to a paper substrate through an olefin adhesion promoting layer. Technical Field of the Invention [0008] GB-A-1,136,622 discloses a packaging wrap- per of fibrous sheet material coated upon at least a part [0001] The present invention relates to a material suit- 5 of its outer surface with an atactic polymer of propylene, able for a ply of a sack and sacks comprising such a butene-1, or 4-methyl pentene-1. material. [0009] US-A-2003/211348 discloses sandwich wrap- pers, fast food wrappers, and gum wrappers comprising Background Art PLA resin. 10 [0010] US-A-2003/170408 discloses a non-fluorocar- [0002] Conventional paper sack constructions suitable bon oil and grease barrier packaging for storing materi- for holding and storing of powdery material, such as ce- als. ment or other building materials, chemicals, food, animal feed and pet food usually has a sack wall that consists Summary of the Invention of two or three paper plies in order increase the weight 15 which can be held by the sack. Further, since a material [0011] The inventors have noted that there is a need such as cement is sensitive to deterioration caused by in the art for an improved sack material that both has e.g. moisture penetration during storage, conventional good barrier properties against moisture such as water paper sacks are also provided with a moisture barrier vapour, and still facilitates a high deaeration rate during film, e.g. of (PE), between the plies. The 20 filling. intermediate film functions as a moisture or water barrier [0012] As a first aspect of the invention, there is pro- and decreases atmospheric vapour penetration through vided a material suitable for a ply of a sack, comprising the sack plies into the sack interior. a paper sheet provided with a on at least one of [0003] However, during filling of the sack, the deaera- its surfaces, wherein said coating comprises at least one tion rate, i.e. the speed at which air inside the sack is 25 ethylene-propylene copolymer having a melting point transported out from the sack, is often the factor that limits from 50 to 95°C, and wherein the extensibility level of the rate at which the sack can be filled. Air trapped in the said paper is a fully extensible (E) paper with a machine sack may lead to under-weight packs, sack rupture and direction (MD) stretch of 7-9% and a of problems when sacks are stacked for transportation. The 100-120 g/m2; or wherein the water vapour transmission use of a moisture or water barrier film as an intermediate 30 rate (WVTR) through said paper, measured with TAPPI layers tends to severely reduce the deaeration rate of a 448, is below 750 g/m2 and a day; or wherein the air sack during filling, since most intermediate moisture bar- permeability measured as Gurley flow according to ISO rier films used are highly impermeable to air. Therefore, 5636/5 through said material is below 10s. the moisture barrier film may be provided with slits or [0013] A sack comprising a ply, which comprises a ma- perforations to facilitate deaeration of the sack. However, 35 terial according to any embodiment or example of the a slitted moisture barrier film obviously decreases the first aspect can be provided. moisture barrier properties of the film, which may lead to [0014] A methodof forming a coating ona porous sheet moisture penetration. can be provided, comprising the steps of: [0004] US-A-2002/016402 discloses a moisture proof hot melt composition comprising 20% to 90% by weight 40 a) providing a porous sheet and a dispersion com- of polyethylene and/or (A) and 10 to 80% prising at least one polyolefin; by weight of a tackifier resin, with the proviso that (A) & b) applying the dispersion on at least one surface of (B) = 100% by weight. the sheet; and [0005] US-B-3,652,725 discloses c) optionally, heating the sheet to a temperature compositions composed of polyethylene, crystalline pro- 45 above the melting temperature of pylene containing polymer and either a polymerized DAC-B hydrocarbon resin or a vinyl toluene-alpha-me- the at least one polyolefin. thyl styrene copolymer. [0015] A method for manufacturing a single ply sack [0006] EP-A-441233 discloses plastic- or can be provided, comprising the steps: , wherein the propylene has been applied to 50 the paper by the coextrusion technique as a barrier either a) providing a sheet that comprises a material ac- with a terpolymer, based on ethylene/acrylate esters with cording to any embodiment or example of the first 5 to 15% by volume of acrylate ester and 2 to 5% by aspect. volume of maleic anhydride, the remainder being ethyl- b) tubing and cutting the sheet to form a tubular piece ene, as adhesion promoter or with a copolymer as ad- 55 with two open ends, wherein the sheet is oriented hesion promoter. such that the coating is facing the interior of the tu- [0007] US-A-3,560,227 discloses high barrier coated bular piece; and comprising a film of resinous polyolefin and res- c) closing at least one end of the tubular piece to

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form the sack. ing. [0026] As a further example, a is not a [0016] As a further aspect of the invention, there is pro- sheet which is suitable for a ply of a sack. vided a method for manufacturing a two-ply sack com- [0027] As an example, the paper may be a prising the steps: 5 sheet. [0028] A Kraft paper sheet refers to a paper sheet pro- a) providing a first and a second sheet, wherein at duced from wood by the . The Kraft least one of the first and the second sheet comprises process removes almost all lignin from the wood, which a material according to any embodiment or example results in almost pure cellulose fibers. The Kraft process of the first aspect; 10 is known to a person skilled in the art. The Kraft paper b) arranging the first and second sheet so that the sheet may be a sack Kraft paper. coating on the first sheet is facing the second sheet [0029] A Kraft paper sheet is characterized by overall and/or the coating on the second sheet is facing the good strength properties and high porosity, and is thus first sheet; suitable for a variety of applications. c) tubing and cutting the arranged sheets from step 15 [0030] The extensibility level of the paper can be se- b) to form a tubular piece with two open ends, where- lected from the group consisting of natural (N), semi-ex- in the first sheet is forming an outer ply and the sec- tensible (SE) or fully extensible (E) paper. ond sheet is forming an inner ply of the tubular piece; [0031] The term extensibility is used herein to describe and papers which have been given enhanced machine direc- d) closing at least one end of the tubular piece to 20 tionstretch properties, either inthe paper making process form the two-ply sack. or by subsequent operation. In the context of the present disclosure, natural paper (N) has a stretch level of 2 - 4 [0017] The use of at least one polyolefin as a water %, such as 3 %, semi-extensible (SE) paper has a stretch vapour barrier coating on a porous sheet suitable for a level of 4-6 %, such as 5 %, and fully extensible (E) paper ply of a sack can be provided. 25 has a stretch level of above 6 %, such as 7.5 %. [0032] A paper with N, SE or E stretch levels are usually Detailed description of the Invention tougher than other papers, and are thus suitable for cer- tain applications were a tough paper is required. [0018] As a first aspect of the invention, there is pro- [0033] As another example, the paper may be creped vided a material suitable for a ply of a sack, comprising 30 or micro-creped, such as a creped or micro-creped paper a porous sheet provided with a coating on at least one having a machine direction (MD) stretch of 2-10 %, such of its surfaces, wherein the coating comprises at least as 6-8 %. one polyolefin. [0034] In the context of the present disclosure, a [0019] A porous sheet refers to a sheet having pores creped paper refers to a paper that has been subjected through which air may pass. 35 to a wet creping process giving the paper a greater ma- [0020] In the context of the present disclosure, a coat- chine direction stretch. Further, a micro-creped paper re- ing refers to a layer or coverage that is spread out over fers to a paper that has been subjected to a creping proc- a surface. The coating may be adhered to the surface. ess which leads to a paper that is mechanically crimped, [0021] A polyolefin refers to any organic substance orcompacted, with a barelyvisible crepingin themachine prepared by polymerization of any type of alkenes. The 40 direction. A micro-creped paper may be produced by the polyolefin may be thermoplastic. Clupak process, which is known in the art. A creped or [0022] The first aspect of the invention is based on the micro-creped paper may for example be a paper having surprising finding and insight that a porous material pro- alternate ridges or grooves, which may or may not be vided with a coating comprising at least one polyolefin parallel. has an unusual combination of properties, which are a 45 [0035] A creped or micro-creped paper is more flexible combination of a water vapour barrier with high air per- than a paper that has not been subjected to any creping meability. Thus, a material according to the first aspect process. Thus, creped or micro-creped papers are suit- of the invention is suitable for forming a ply in a sack. able in a variety of applications, in which high flexibility [0023] In the first aspect of the invention, the porous is required. As an example, a paper with N, SE or E sheet is a paper sheet. 50 stretch levels may be creped or micro-creped, to further [0024] A paper refers to a material manufactured in increase the extensibility. sheets from the pulp of wood or other fibrous substances, [0036] In the first aspect of the invention, the paper is which material may comprise additives such as synthetic an extensible (E) paper with a machine direction (MD) fibers or biodegradable fibers. stretch of 7-9 %, such as about 8 % and a grammage of [0025] A paper sheet may have high porosity and may 55 100-120 g/m2, such as about 110 g/m2. Such a paper easily be covered with a coating comprising polyolefin. may suitably be coated according to the invention Further, paper is normally a relatively cheap material. [0037] The grammage refers to the in Consequently, a paper is a suitable substrate for a coat- terms of mass per unit of area. A paper having a gram-

3 5 EP 2 449 176 B1 6 mage within the specified range may be suitable for e.g. [0047] An average coverage of the coating of 1-20 a ply of a sack. g/m2 is a comparably thin coating, and is thus advanta- [0038] The water vapour transmission rate (WVTR) geous in that low amounts of polyolefins are needed in through the paper, measured with TAPPI 448, is below order to provide such a coating, which means compara- 750 g/m 2 and day, such as below 720 g/m 2 and day, such 5 bly low costs. The comparably thin polyolefin as below 710 g/m 2 and day, such as below 700 g/m 2 and within 1-20 g/m 2 still provides a barrier that has a reduced day. Such papers may be suitable to use in a sack. WVTR as well as a high air permeability, as seen in Ex- [0039] The air permeability measured as Gurley flow amples 1 and 2 of the present disclosure. according to ISO 5636/5 through the paper is below 10 [0048] As an example, the average coverage of the s, such as below 8 s, such as about 5 s. Such papers 10 coating may be 3-14 g/m2, such as 5-12 g/m2, such as may also be suitable to use in a sack. 6-10 g/m2, such as 6-8 g/m 2 on the at least one surface. [0040] In embodiments of the first aspect of the inven- [0049] In the first aspect of the invention, the at least tion, the water vapour transmission rate (WVTR) through one polyolefin has a melting point of 50-95 °C, such as the material, measured with TAPPI 448, is below 670 about 60-85 °C. g/m2 and day, such as below 400 g/m 2 and day, such as 15 [0050] The melting point of the polyolefin refers to the below 200 g/m2 and day, such as below 160 g/m2 and transition of the polyolefin from a crystalline or semi-crys- day. talline phase to a solid amorphous state, i.e. the crystal-

[0041] In context of the present disclosure, the water line melting temperature. The melting point, T m, of a poly- vapour transmission (WVTR) rate refers to the rate at olefin is a property well known to the skilled person. which water migrate through a material. The WVTR may 20 [0051] A polyolefin having a melting point as low as be measured using the TAPPI 448 method, which is well 50-95 °C, such as about 60-85 °C, may be advantageous known to the person skilled in the art, and may be quoted to use during coating of the surface, since only a small as grams per m2 per day (24 hours). temperature increase is needed to melt the polyolefin, [0042] Ifthe materialhas a WVTR belowthe mentioned i.e. a low temperature is needed in order to facilitate co- values, it serves as a water vapour barrier, thus decreas- 25 alescence of crystalline or semi-crystalline polyolefin to ing the rate at which moisture can penetrate through the a coating. material. [0052] In the first aspect of the invention the at least [0043] In another embodiment of the first aspect of the one polyolefin is a copolymer. invention, the barrier improvement factor of the material, [0053] A copolymer refers to a polymer derived from which is the ratio obtained from the WVTR of the material 30 more than one monomer. The copolymer is an ethylene- provided with no coating divided by the WVTR provided propylene copolymer, i.e. a copolymer derived from more with the coating, is at least 1.05, such as at least 2, such than one monomer, in which at least one is ethylene and as at least 3, such as at least 4, such as at least 5. at least one is propylene. [0044] The Gurley flow is a well-known method for As an example, the copolymer may be derived from eth- measuring the air permeance of paper and board. The 35 ylene and propylene monomers only. Such a polyolefin Gurley flow may thus be measured using the Internation- copolymer has shown to give rise to a coating having al Organization for Standardization standard ISO 5636/5. satisfactory water vapour and air permeability properties, A material having a Gurley flow below 20 s, such as below as shown in the Examples of the present disclosure. 15 s, such as below 12 s, has high air permeability, thus [0054] As a further example, the at least one polyolefin facilitating rapid transport of air through the material, e.g. 40 may comprise 1-propene, polymer with ethene, having during filling of a sack comprising the material. CAS number 9010-79-1. [0045] In an embodiment of the first aspect of the in- [0055] The at least one polyolefin can be a functional vention, the average coverage of the coating is 1-20 g/m 2 polymer, such as a polymer having a chemical group on the at least one surface. introduced into the polymer molecule or a polymer in [0046] The average coverage of the coating refers to 45 which a chemical group has been converted into another the average coverage on the part of the surface that has group, so that the chemical or physical properties have been subjected to coating. As an example, if half of a been altered. Functional polymers may lead to a coating surface of the sheet has been subjected to coating, the that has good adhesion properties to specific surfaces, average coverage refers to the average surface cover- such as polar surfaces. age on half of that surface, and if a whole surface has 50 [0056] The coating can comprise at least one polyole- been subjected to coating, the average surface coverage fin, provided that the at least one polyolefin is not poly- refers to the average surface coverage on the whole sur- ethylene (PE) alone. It may be advantageous to use coat- face etc. The coverage may thus vary on the part of the ing that does not only comprise polyethylene as the poly- surface that is coated, and may be calculated based on olefin, since films or coatings consisting only of polyeth- the amount of polyolefin that is added to the surface dur- 55 ylene may not have a desired resistance to oil and grease ing coating. Further, the coverage may be calculated in several applications. Further, a single polyethylene based on the weight difference of the material before and coating may also be associated with a number of prob- after coating. lems, e.g. single polyethylene coatings having a surface

4 7 EP 2 449 176 B1 8 coverage below 20 g/m2 is generally not a good water such that the coating is facing the inner ply. vapour barrier and single polyethylene coatings having [0066] Sacks comprising an inner and outer ply as de- a surface coverage above 34 g/m2 may cause the un- scribed above may thus be able to hold large weights derlying surface to curl. due to both an inner and an outer ply, and still have prop- [0057] In a second aspect a sack comprising a ply, 5 erties of good resistance to water vapour transmission which comprises a material according to any embodi- and high deaeration rate. Consequently, such sacks ment or example of the first aspect above can be provid- does not have to include a free film between the inner ed. and outer ply in order to have water vapour barrier prop- [0058] The terms and definitions used in the second erties, and therefore does not have to comprise slits in aspect are as defined in connection with the first aspect 10 any ply of the sack construction. Slits severely decreases of the invention above. the barrier properties of a ply, which may lead to water [0059] The second aspect is based on the insight that vapour penetration. Multi-ply sacks of the present disclo- the material according to the first aspect is suitable for sure may thus be provided without a free film. use as a ply of a sack. Consequently, a sack comprising [0067] In other embodiments of the second aspect, the such a material may have a low water vapour transmis- 15 sack comprises more than two plies, such as three plies, sion rate, thus preventing water from penetrating the ply four plies etc. to the interior of the sack, and still have high air perme- [0068] In further embodiments of the second aspect, ability, thus facilitating filling of the sack at high speed. the water vapour transmission rate (WVTR) through the [0060] In an embodiment of the second aspect, the sack wall constituted by the ply or plies, measured with sack consists of a single ply comprising a material ac- 20 TAPPI 448, is below 200 g/m2 and day, such as below cording to any embodiment or example of the first aspect 170 g/m2 and day, such as below 150 g/m2 and day. A above. As an example, the single ply may be oriented sack having a WVTR below the above mentioned values such that the coating is facing the interior of the sack. has thus satisfactory water barrier properties, and may [0061] A single sack having a coating as described therefore suitably serve as a for material that above facing the interior may be advantageous, since 25 is sensitive to moisture. It is to be understood that the conventional single ply sacks having a free film facing WVTR in relation to sacks having more than one ply re- the interior has several problems. An example of such a fers to the transmission rate of water vapour measured problem is that the free film normally has to be glued to from the exterior of the sack, through all plies and into the sack paper of the single ply sack. The introduction of the interior of the sack at a part of a sack wall that has gluing obviously increases the complexibility of the sack 30 no overlapping sections. forming process. Further, the gluing of a free film may [0069] In another embodiment of the first aspect of the cause the free film to fold in overlap regions of the sack invention, the barrier improvement factor of the sack, wall and expose openings between the free film and the which is the ratio obtained from the WVTR of a sack hav- ply, which in turn may cause products that are filled into ing no ply comprising a material according to any em- the sack to end up between the paper and the free film 35 bodiment of the first aspect of the invention divided by during filling. Therefore, parts of the product may not be the WVTR of the same type of sack having at least one protected against water vapour. Further, having the coat- ply comprising a material according to any embodiment ing facing the interior of the sack may prevent the coating of the first aspect of the invention, is at least 1.5, such from being ruptured or damaged during storing and han- as at least 2, such as at least 3, such as at least 3.5, such dling of the sack, and a coating facing the interior does 40 as at least 4. not affect the friction properties of the exterior surface of [0070] In another embodiment of the second aspect the sack, which are important during piling of sacks, or the air permeability measured as Gurley flow according the printablity of the exterior surface of the sack. to ISO5636/5 through both the inner and outer ply is be- [0062] In another embodiment of the second aspect, low 30 s, such as below 25 s, such as below 20 s. the sack is comprising an inner ply and an outer ply, of 45 [0071] A sack having a Gurley flow below 30 s, such which at least one comprises a material according to any as below 25 s, such as below 20 s, provides for a high embodiment or example of the first aspect above. deaeration rate and thus facilitates filling of the sack at [0063] An outer ply of a sack refers to the ply of a sack a high rate. having a surface that faces the exterior and the inner ply [0072] In embodiments of the second aspect, the sack of a sack refers to the ply of a sack having a surface that 50 is suitable for holding a powdery or granularly material, faces the interior of the sack. such as cement. The powdery or granularly material may [0064] As an example, the inner ply may comprise a for example be cement, building materials, powdered material according to any embodiment or example of the goods for the construction industry, ready-mix building first aspect above and the inner ply may be oriented such materials, chemicals or garden fertilizers. that the coating is facing the outer ply. 55 [0073] As a related aspect, there is provided a method [0065] As a further example, the outer ply may com- for filling a sack with a powdery or granularly material, prise amaterial according to anyembodiment or example comprising the steps of of the first aspect above and the outer ply may be oriented

5 9 EP 2 449 176 B1 10

a) providing a sack according to any embodiment or free film is formed in a ply of the sack just after filling. example of the second aspect and a powdery or The third aspect provides a convenient method for coat- granularly material; and ing a sheet with at least one polyolefin, since the poly- b) filling the sack with the powdery or granularly ma- olefin is provided in the form of a dispersion. Thus, the terial, such that an overpressure is present inside 5 method does not require any complicated processes as the sack and wherein air is transported through a extrusion, , injection or blow wall of a sack during the filling. molding for applying the at least one polyolefin on a sur- face. [0074] As a third aspect, there is provided a method of [0079] In embodiments of the third aspect, the sheet forminga coating on a porous sheet, comprising thesteps 10 is a paper sheet as described in relation to the first aspect of: above. [0080] Since the at least one polyolefin is applied in a) providing a porous sheet and a dispersion com- the form of a dispersion, no preheating is required. In prising at least one polyolefin; another embodiment of the third aspect, the dispersion b) applying the dispersion on at least one surface of 15 may thus be applied at a temperature below the melting the sheet; and point of the at least one polyolefin. c) optionally, heating the sheet to a temperature [0081] In other embodiments, the dispersion is heated above the melting temperature of the at least one to a temperature above the melting temperature of the polyolefin. at least one polyolefin before applying it to the sheet in 20 step b). [0075] The terms and definitions used in the third as- [0082] In embodiments of the third aspect, the disper- pect are as defined in connection with the other aspects sion has a solids content of 35-60 %, such as 40-55 %. above. [0083] A solids content refers to the weight percentage [0076] The dispersion may for example be a suspen- of solids, such as the particles of the at least one poly- sion, a colloid, or a solution. The at least one polyolefin 25 olefin. Further, the dispersion may be stable at a solids may be present in the form of particles in the dispersion. content of 35-60 %, such as 40-55 %. The dispersion may also be an emulsion dispersion, in [0084] If the solids content of the dispersion is as high which particles of the at least one polyolefin are suspend- aswithin thespecified ranges, or if the dispersion isstable ed with the help of emulsifiers. at a solids content as high as within the specified ranges, [0077] Applying the dispersion on at least one surface 30 a relatively low dispersion volume may be used during refers to distributing the dispersion on the surface in an the coating process. amount that promotes the formation of a coating on the [0085] Further, in embodiments of the third aspect, the surface. The application of the dispersion may be per- dispersion is an aqueous dispersion. An aqueous disper- formed e.g. by roll coating, gravure or spray-coating. sion is advantageous in that no or little solvents are need- These techniques, as well as other techniques for apply- 35 ed to keep the at least one polyolefin dispersed in the ing a dispersion on a surface, are well-known to the dispersion. skilled person. [0086] In another embodiment, the at least one poly- [0078] Heating the sheet to a temperature above the olefin is a copolymer. As an example, the least one co- melting temperature of the at least one polyolefin refers polymer may be an ethylene-propylene copolymer. to subjecting the sheet to heat such that the at least one 40 [0087] Copolymers, such as an ethylene-propylene polyolefin starts to melt. The heating of step c) may be copolymer, have shown to give excellent coatings on pa- performed by means of drying the sheet after applying per sheets, as seen in the Examples of the present dis- the dispersion to the sheet using heated air. If the dis- . persion comprises particles of the at least one polyolefin, [0088] Further, the dispersion may comprise additives the particles may deform and coalesce into a substan- 45 such as plasticizers, fillers, tackifiers, pigments, stabiliz- tially void-free film above the melting temperature of the ers and other common thermoplastic compound ingredi- at least one polyolefin. Further, the heating of step c) may ents. be performed during a manufacture of a sack using the [0089] As a fourth aspect, there is provided a method material obtained from step b). Also, the heating of step for providing a single ply sack comprising the steps: c) may be performed/achieved during filling of a sack50 comprising the material obtained from step b), wherein a) providing a sheet that comprises a material ac- the filling material added to the sack has a high temper- cording to any example or embodiment of the first ature, such as a temperature between 30-100 °C, such aspect of the invention, as 70-90 °C. An example of such a filling material is ce- b) tubing and cutting the sheet to form a tubular piece ment in a powdery form, which may be filled at a temper- 55 with two open ends, wherein the sheet is oriented ature of 70-90 °C. Consequently, the heating of step c) such that the coating is facing the interior of the tu- may be achieved during or just after the sack has been bular piece; and filled with a filling material, so that a substantially void- c) closing at least one end of the tubular piece to

6 11 EP 2 449 176 B1 12

form the sack. or example of the first aspect; b) arranging the first, second and third sheets so that [0090] The method for manufacturing a sack according the coating on the first sheet is facing the second to the fourth aspect is fast, requires only a few process sheet and/or the coating on the second sheet is fac- steps, and is easy to implement industrially. As an ex- 5 ing any of the first or third sheet, and/or the coating ample, step c) may involve closing both ends of the sack. of the third sheet is facing the second sheet; As another example, step c) may involve closing only c) tubing and cutting the arranged sheets from step one end so as to form an open-mouth sack. b) to form a tubular piece with two open ends, where- [0091] In an embodiment of the fourth aspect above, in the first sheet is forming an outer ply and the third the closing of step c) is performed by means of folding. 10 sheet is forming an inner ply of the tubular piece; and [0092] Folding may be performed manually or by ma- d) closing at least one end of the tubular piece to chinery. As an example, the folding may further involve form the three-ply sack. the step of attaching an extra strip of paper on at least part of the folded area so as to increase the stability of [0098] In a fifth aspect, there is provided the use of at the folded area. As another example, folding may involve 15 least one polyolefin as a water vapour barrier coating on folding and gluing the open end around a vent material, a porous sheet suitable for a ply of a sack. which may be a ply of higher basis weight compared to [0099] The coating, polyolefin and porous sheet may the inner ply or the an outer ply, so that an enforced vent be as in any embodiment of the first aspect above. Con- may be formed that is adapted to fit a filling spout of a sequently, in an embodiment of the fifth aspect, the at filling machine. 20 least one polyolefin is a copolymer, and the copolymer [0093] As a further aspect of the present invention, may be an ethylene-propylene copolymer. there is provided a method for manufacturing a two-ply [0100] The use of at least one polyolefin as a water sack comprising the steps: vapour barrier coating on a material suitable for a sack is a convenient and efficient way to provide a material a) providing a first and a second sheet, wherein at 25 that has both a low water vapour transmission rate as least one of the first and the second sheet comprises well as a high air permeability. Thus, a use of at least a material according to any example or embodiment one polyolefin as an air permeable water vapour barrier of the first aspect of the invention; coating on a material suitable for a ply of a sack is also b) arranging the first and second sheet so that the provided. coating on the first sheet is facing the second sheet 30 [0101] As a sixth aspect, there is provided the use of and/or the coating on the second sheet is facing the the sack according to any embodiment of the second first sheet; aspect for holding a powdery or granularly material, such c) tubing and cutting the arranged sheets from step as a material selected from cement, building materials, b) to form a tubular piece with two open ends, where- powdered goods for the construction industry, ready-mix in the first sheet is forming an outer ply and the sec- 35 building materials, chemicals or garden fertilizers, food, ond sheet is forming an inner ply of the tubular piece; animal feed or pet food. and d) closing at least one end of the tubular piece to Brief description of the drawings form the two-ply sack. 40 [0102] [0094] The method for manufacturing a two-ply sack according to the further aspect of the invention is fast, Figure 1 shows the average water vapour transmis- requires only a few process steps, and is easy to imple- sion rate (WVTR) measured using TAPPI 448 for ment industrially. As an example, step d) may involve uncoated papers (0 g/m2) and papers coated with 5 closing both ends of the sack. As another example, step 45 g/m2 and 8 g/m 2, respectively, of a polyolefin coating. d) may involve closing only one end so as to form an The average WVTR of papers coated with 5 g/m2 open-mouth sack. and 8 g/m 2, which had further been subjected to heat [0095] In an embodiment of the further aspect above treatment is plotted in the same figure. The WVTR the closing of step d) is performed by means of folding. is plotted as the average water vapour amount (g) [0096] Folding may be performed as described in re- 50 per m2 per day (24 hours) of three different papers. lation to the fourth aspect above. The error bars represent the standard deviation. [0097] In a related aspect of the present invention, Figure 2 shows the average water vapour transmis- there is provided a method for manufacturing a three-ply sion rate (WVTR) measured using TAPPI 448 for sack, comprising the steps: different combinations of papers: a combination with 55 an uncoated paper and a paper coated with 6 g/m2 a) providing afirst, a second and a third sheet,where- of a polyolefin coating (=Coated 1 (6 g/m 2)), a com- in at least one of the first, second and third sheet bination with an uncoated paper and a paper coated comprises a material according to any embodiment with 6 g/m 2 of a polyolefin coating, wherein the coat-

7 13 EP 2 449 176 B1 14

ed paper had been subjected to heat treatment mm, wet film 40 mm) were used with a coating speed of (=Coated 2 (6 g/m2 + heat)) and a combination of 4-6 m/min. Some samples were heated to a temperature two papers with an intermediate polyethylene (PE) above 60 °C after coating. film (= Papers with PE-film (slitted)).The WVTR is [0105] The water vapour transmission rate (WVTR) of plotted as the average water vapour amount (g) per 5 samples were measured during 8 hours using TAPPI m2 per day (24 hours) of three different papers. The 448, which is a standard method used to measure water error bars represent the standard deviation. vapour transmission rates for specimens at 23 ºC and Figure 3 shows the air permeability in terms of Gurley 50 %RH. Coated papers were attached to cups with a flow (s) measured for different combinations of pa- well-defined area and filled with desiccant (CaCl2). The pers: two papers with an intermediate, standard slit 10 cups were weighed at repeated time intervals and the polyethylene (PE) film (paper+PE+paper), two un- weight plotted as a function of time. When the constant coated papers (Coat(0)paper+paper), a paper with gain rate period was reached, the water transmission rate a 2 g/m2 polyolefin coating in combination with an (WVTR) was calculated using the following relation: uncoated paper (Coat(2)paper+paper), a paper with a 3 g/m2 polyolefin coating in combination with an 15 uncoated paper (Coat(3)paper+paper), a paper with a 6 g/m2 polyolefin coating in combination with an uncoated paper (Coat(6)paper+paper) and a paper with a 8 g/m2 polyolefin coating in combination with an uncoated paper (Coat(8)paper+paper). 20 where, y/x is the slope from the plotted weight of cup Figure 4 shows the air permeability in terms of Gurley versus the time, k is a constant and A is the sample area. flow (s) measured for different combinations of pa- pers: two papers with an intermediate, Results standard slit polyethylene (PE) film (paper+PE+pa- per), two uncoated papers (Coat(0)paper+paper), a 25 [0106] The WVTR of coated papers are shown in Fig.1. paper with a 2 g/m2 polyolefin coating subjected to Two levels of surface coverage were tested; 5 g/m 2 and heat treatment in combination with an uncoated pa- 8 g/m2, respectively. As a comparison, uncoated paper per (Coat(2h)paper+paper), a paper with a 3 g/m2 was also tested (0 g/m 2). Further, coated papers subject- polyolefin coating subjected to heat treatment in ed to heat treatment were also tested (5 g/m 2 + heat and combination with an uncoated paper (Coat(3h)pa- 30 8 g/m2+heat). The average of three samples is shown in per+paper), a paper with a 6 g/m 2 polyolefin coating Fig. 1. The measurements clearly showed that the WVTR subjected to heat treatment in combination with an dropped when the papers were coated with the polyolefin uncoated paper (Coat(6h)paper+paper) and a paper dispersion, from an average of 696 g/m 2 per day for the with a 8 g/m2 polyolefin coating subjected to heat uncoated paper to 662 g/m2 per day with a surface cov- treatment in combination with an uncoated paper 35 erage of 5 g/m2 and down to 151 g/m2 per day for the (Coat(8h)paper+paper). coating of 8 g/m 2. Further, the heat treatment seemed to give a significant reduction, about 19 %, on the WVTR Examples for the high coating level of 8 g/m2. Thus, these results show that a paper with a polyolefin coating had excellent [0103] The following non-limiting examples will further 40 barrier properties against water vapour. illustrate the present invention. [0107] Further, the WVTR for combinations of papers were also tested so as to represent a two-ply sack wall. Example1. Water vapour transmissionrate ofcoated The results are displayed in Fig. 2. The following combi- papers nations were tested: an untreated paper in combination 45 with a paper coated with 6 g/m 2 of the polyolefin disper- Materials and methods sion, an untreated paper in combination with a paper coated with 6 g/m2 of the polyolefin dispersion, which [0104] Unbleached brown sack paper (Quickfill XRUN, had also been subjected to heat treatment, and a com- Billerud AB, a natural (N) paper with a machine direction bination with two papers with an intermediate polyethyl- stretch of about 2.7 % and a grammage of 70 g/m 2) was 50 ene (PE) film. The PE film had slits according to standard coated with a polyolefin dispersion (DPOD 8501, Dow procedures in the art, and the two papers with the PE Chemicals). The polyolefin dispersion comprised about film in between thus represented a standard sack wall 40 % water and about 40 % 1-Propene, polymer with construction within the art. It was seen from the results ethane (CAS # 9010-79-1). The coating was applied us- that the two combinations with coated papers led to sim- ing a laboratory rod coater (RK Print-Coat Instruments 55 ilar low WVTR, 140 and 139 g/m2 day, respectively, as Ltd., K Control Coater 202) and the bars no. 2 (wire di- when using an intermediate PE-film that led to a WVTR ameter 0,15 mm, wet film 12 mm), no. 3 (wire diameter of 113 g/m 2 day. Consequently, the combinations having 0,31 mm, wet film 24 mm) and no. 4 (wire diameter 0,51 a paper with a polyolefin coating had as low WVTR as

8 15 EP 2 449 176 B1 16 two papers with a plastic PE-film in between, and thus Claims forms a suitable water vapour barrier. 1. A material suitable for a ply of a sack, comprising a Example 2. Air permeability of paper materials paper sheet provided with a coating on at least one 5 of its surfaces, wherein said coating comprises at Materials and methods least one ethylene-propylene copolymer having a melting point from 50 to 95°C, and wherein the ex- [0108] The air permeability of a combination of papers tensibility level of said paper is a fully extensible (E) was measured with the Gurley method, which is a stand- paper with a machine direction (MD) stretch of 7-9% ard procedure that measures the time for a defined vol- 10 and a grammage of 100-120 g/m2; or wherein the ume of air to pass through a defined area of the test watervapour transmission rate (WVTR) throughsaid substrate at a constant pressure. The Gurley method is paper, measured with TAPPI 448, is below 750 g/m 2 specified in ISO5636/5. In these examples an internally and a day; or wherein the air permeability measured developed measurement system named the BigGurley as Gurley flow according to ISO 5636/5 through said equipment was used. The measurement area was 400 15 material is below 10s. cm2 (2003200 mm). The working principle was the same as in a larger MegaGurley equipment supplied by Haver 2. A material according to claim 1, wherein said paper & Boecker (Germany), i.e. the flow of air through the de- sheet is a Kraft paper sheet. fined area (400 cm 2) was measured as the time a specific volume at a given pressure difference passes through 20 3. A material according to claim 1 or 2, wherein the the sample. grammage of said paper is about 100 g/m 2.

Results 4. A material according to any one of claims 1-3, where- in said paper is creped or micro-creped. [0109] The air permeability was tested for different25 combination, or layers, of papers in order to mimic the 5. A material according to any previous claim, wherein air permeability through sack wall materials. The papers the average coverage of said coating is 1-20 g/m2 used were Quickfill XRUN, Billerud AB. The following pa- on said at least one surface, such as 3-14 g/m 2, such per combinations/layered structures were tested: two pa- as 5-12 g/m2, such as 6-10 g/m2, such as 6-8 g/m2 pers with an intermediate, standard slit polyethylene (PE) 30 on said at least one surface. film (paper+PE+paper), two uncoated papers (Coat(0)paper+paper), a paper with a 2 g/m2 polyolefin 6. A material according to any one of claims 1-5, where- coating in combination with an uncoated paper in said inner ply comprises said material and said (Coat(2)paper+paper), a paper with a 3 g/m2 polyolefin inner ply is oriented such that said coating is facing coating in combination with an uncoated 35 paper said outer ply, or wherein said outer ply comprises (Coat(3)paper+paper), a paper with a 6 g/m2 polyolefin said material and said outer ply is oriented such that coating in combination with an uncoated paper said coating is facing said inner ply. (Coat(6)paper+paper) and a paper with a 8 g/m2 poly- olefin coating in combination with an uncoated paper 7. A method for manufacturing a two-ply sack compris- (Coat(8)paper+paper). The results are displayed in Fig. 40 ing the steps: 3. Moreover, the same combinations, but in which the coatings were subjected to heat treatment, were also a) providing a first and a second sheet, wherein tested and are displayed in Fig. 4. It could be seen that at least one of said first and second sheet com- the combinations in which a coated paper was used had prises a material as defined in any one of claims a significantly higher air permeability compared to the 45 1-6; combination with the PE film in between. The Gurley flow b) arranging said first and second sheet so that was between 13 and 18 s for the combinations with coat- said coating on said first sheet is facing said sec- ings or heat treated coatings, compared to 40 s for the ond sheet and/or said coating on said second combination with the PE film. Further, the air permeability sheet is facing said first sheet; for the combinations having a polyolefin coating was al- 50 c) tubing and cutting said arranged sheets from most as high as the combination with two uncoated pa- step b) to form a tubular piece with two open pers. Consequently, a combination having a polyolefin ends, wherein said first sheet is forming an outer coating, which had excellent barrier properties as seen ply and said second sheet is forming an inner in Example 1, also surprisingly had high air permeability. ply of said tubular piece; and Thus, these examples clearly demonstrate that a sack 55 d) closing at least one end of said tubular piece wall having a coating comprising a polyolefin has both to form said two-ply sack. excellent water vapour barrier properties and facilitates high speed during filling of the sack. 8. A method according to claim 7, wherein said closing

9 17 EP 2 449 176 B1 18

of step d) is performed by means of folding. Bögen aus Schritt b) zum Bilden eines rohrför- migen Stücks mit zwei offenen Enden, wobei der erste Bogen eine Außenlage bildet und der Patentansprüche zweite Bogen eine Innenlage des rohrförmigen 5 Stücks bildet; und 1. Ein Material, das für eine Lage eines Sacks geeignet d) Schließen mindestens eines Endes des rohr- ist, beinhaltend einen Papierbogen, der mit einer Be- förmigen Stücks zum Bilden des zweilagigen schichtung auf mindestens einer seiner Oberflächen Sacks. versehen ist, wobei die Beschichtung mindestens ein Ethylen-Propylen-Copolymer mit einem10 8. Verfahren gemäß Anspruch 7, wobei das Schließen Schmelzpunkt von 50 bis 95 °C aufweist, und wobei von Schritt d) mittels Faltenbildung durchgeführt der Dehnbarkeitsgrad des Papiers ein vollständig wird. dehnbares (E) Papier mit einer Maschinenrich- tungs(MD)-Streckung von 7-9 % und einem Flä- chengewicht von 100-120 g/m2 ist; oder wobei die 15 Revendications Wasserdampfübertragungsrate (WVTR) durch das Papier, gemessen mit TAPPI 448, unter 750 g/m2 1. Un matériau qui convient pour une épaisseur d’un und einem Tag liegt; oder wobei die Luftdurchlässig- sac, comprenant une feuille de papier pourvue d’un keit, gemessen als Gurley-Strömung nach ISO revêtement sur au moins l’une de ses surfaces, dans 5636/5, durch das Material unter 10 s liegt. 20 lequel ledit revêtement comprend au moins un co- polymère éthylène-propylène ayant un point de fu- 2. Material gemäß Anspruch 1, wobei der Papierbogen sion allant de 50 à 95 °C, et dans lequel le niveau ein Kraft-Papierbogen ist. d’extensibilité dudit papier est un papier complète- ment extensible (E) avec un allongement dans le 3. Material gemäß Anspruch 1 oder 2, wobei das Flä- 25 sens machine (SM) de 7 à 9 % et un grammage de chengewicht des Papiers etwa 100 g/m2 beträgt. 100 à 120 g/m 2 ; ou dans lequel le taux d’étanchéité à la vapeur d’eau (WVTR) à travers ledit papier, me- 4. Materialgemäß einem der Ansprüche 1-3, wobei das suré avec la norme TAPPI 448, est en deçà de 750 Papier Krepppapier oder Mikrokrepppapier ist. g/m2 et d’une journée ; ou dans lequel la perméabi- 30 lité à l’air mesurée en tant qu’écoulement Gurley se- 5. Material gemäß einem der vorhergehenden Ansprü- lon l’ISO 5636/5 à travers ledit matériau est en deçà che, wobei die mittlere Abdeckung der Beschichtung de 10 s. 1-20 g/m2 auf der mindestens einen Oberfläche be- trägt, wie etwa 3-14 g/m2, wie etwa 5-12 g/m2, wie 2. Un matériau selon la revendication 1, dans lequel etwa 6-10 g/m2, wie etwa 6-8 g/m2 auf der mindes- 35 ladite feuille de papier est une feuille de papier Kraft. tens einen Oberfläche. 3. Un matériau selon la revendication 1 ou la revendi- 6. Material gemäß einem der Ansprüche 1-5, wobei die cation 2, dans lequel le grammage dudit papier est Innenlage das Material beinhaltet und die Innenlage d’environ 100 g/m2. so ausgerichtet ist, dass die Beschichtung der Au- 40 ßenlage zugewandt ist, oder wobei die Außenlage 4. Un matériau selon n’importe laquelle des revendica- das Material beinhaltet und die Außenlage so aus- tions 1 à 3, dans lequel ledit papier est crêpé ou gerichtet ist, dass die Beschichtung der Innenlage micro-crêpé. zugewandt ist. 45 5. Un matériau selon n’importe quelle revendication 7. Ein Verfahren zur Herstellung eines zweilagigen précédente, dans lequel la couverture moyenne du- Sacks, das die folgenden Schritte beinhaltet: dit revêtement est de 1 à 20 g/m 2 sur ladite au moins une surface, telle que de 3 à 14 g/m 2, telle que de 5 a) Bereitstellen eines ersten und eines zweiten à 12 g/m2, telle que de 6 à 10 g/m 2, telle que de 6 à Bogens, wobei mindestens einer des ersten und 50 8 g/m2 sur ladite au moins une surface. des zweiten Bogens ein Material wie in einem der Ansprüche 1-6 definiert, beinhaltet; 6. Un matériau selon n’importe laquelle des revendica- b) Anordnen des ersten und zweiten Bogens, tions 1 à 5, dans lequel ladite épaisseur interne com- sodass die Beschichtung auf dem ersten Bogen prend ledit matériau et ladite épaisseur interne est dem zweiten Bogen zugewandt ist und/oder die 55 orientée de telle sorte que ledit revêtement fasse Beschichtung auf dem zweiten Bogen dem ers- face à ladite épaisseur externe, ou dans lequel ladite ten Bogen zugewandt ist; épaisseur externe comprend ledit matériau et ladite c) Verrohren und Schneiden der angeordneten épaisseur externe est orientée de telle sorte que ledit

10 19 EP 2 449 176 B1 20

revêtement fasse face à ladite épaisseur interne.

7. Une méthode pour fabriquer un sac à deux épais- seurs comprenant les étapes consistant : 5 a) à fournir une première et une deuxième feuille, dans laquelle au moins une desdites pre- mière et deuxième feuilles comprend un maté- riau tel que défini dans n’importe laquelle des revendications 1 à 6 ; 10 b) à arranger lesdites première et deuxième feuilles de sorte que ledit revêtement sur ladite première feuille fasse face à ladite deuxième feuille et/ou que ledit revêtement sur ladite deuxième feuille fasse face à ladite première 15 feuille ; c) à former un et à couper lesdites feuilles arrangées de l’étape b) pour former une pièce tubulaire avec deux extrémités ouvertes, dans laquelle ladite première feuille forme une épais- 20 seurexterne et laditedeuxième feuille forme une épaisseur interne de ladite pièce tubulaire ; et d) à fermer au moins une extrémité de ladite pièce tubulaire pour former ledit sac à deux épaisseurs. 25

8. Une méthode selon la revendication 7, dans laquelle ladite fermeture de l’étape d) est effectuée au moyen d’un pliage. 30

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REFERENCES CITED IN THE DESCRIPTION

This list of references cited by the applicant is for the reader’s convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description

• US 2002016402 A [0004] • GB 1136622 A [0008] • US 3652725 B [0005] • US 2003211348 A [0009] • EP 441233 A [0006] • US 2003170408 A [0010] • US 3560227 A [0007]

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