EASY-TO-BREAK-THROUGH FILM

Abstract: The invention provides an easily tearable film comprising a composition consisting of about 97-60 % by weight of polyester and about 3-40 % by weight of polyolefin as an essential component.

Description: Field of the Invention The invention relates to an easily tearable film which may be suitably used as a cover material of press through packs (hereinafter referred to as "PTP"s) and blister packs in the field of pharmaceuticals and foods. Background Art Aluminum foil (hereinafter referred to as "Al. foil") which is excellent in easy-tear properties, gas barrier properties and resistance to vapor permeability is conventionally used as a cover material of PTPs and blister packs in the field of pharmaceuticals and foods. Blister sheets prepared by vacuum forming of a monolayer sheet or a multilayer laminated sheet made of plastics, such as polyvinyl chloride (PVC), polypropylene (PP), polyvinylidene chloride (PVDC), polyester (PET), cyclic olefin copolymer (COC) and polyethylene (PE) are used as base materials However, Al foil as a cover material tends to remain without incineration thereof when thermal disposal of a used PTP on which Al foil is adhered as waste product is conducted. Incineration of Al foil until ashing requires a considerably high temperature. Incineration at such a high temperature damages an incinerator leading to a short lifetime thereof. Fractional recovery of Al foil separated from base material requires a great amount of manpower and is thereby substantially impossible. In addition, wastes comprising packaging containers for drugs such as PTPs from medical institutions (hospital, etc) have a problem of environmental pollution so that hospitals are requested to dispose of the wastes,by themselves or to entrust the wastes to waste-disposal companies. Thus, cover material of PTPs and blister packs is requested to be made of materials capable of incineration under the same condition of temperature as the base materials of PTPS and blister packs, under which conditions an incinerator is not damaged. Under such circumstances, a variety of plastics and papers are how used as cover materials of PTPs and blister packs for pharmaceuticals and foods in place of Al foil. For example, a cover material consisting of a plastic film whose easy-tear property is imparted by adding a great amount of mineral filler to a plastic resin so as to reduce film strength thereof, or a cover material consisting of a plastic film whose easy-tear property is imparted by utilizing orientation of the film caused by stretching the film in at least one direction with high stretch ratio is used. Alternatively, a cover material made of papers such as glassine paper is partially used. A Cover material blended with a great amount of the filler has, however, a problem that mineral filler is scattered when torn for unsealing, leading to the contamination of drugs or the adhesion of the filler to foods. The cover material consisting of the above-mentioned film whose easy-tear property is imparted by utilizing orientation of the stretched film has a drawback in that the directional property of the film makes it difficult to take out some packaged products. Furthermore, the cover material made of glassine paper is remarkably poor in resistance to water vapor permeability. The invention is conducted under such circumstances. It is an object of the invention to provide an easily tearable film which is comparable to Al foil in an easy-tear property and excellent in gas barrier property and resistance to water vapor permeability with no possibility of damaging an incinerator during thermal disposal. It is another object of the invention to provide an easily tearable film which is a suitable cover material of a PTPs and a blister pack. The following documents disclose compositions which form part of the background prior art for the present invention: EP-A-0 291 065 discloses a two layered film comprising (i) as a first layer a blend of 3% LLDPE with 97% polyester ; and (ii) as a second layer an olefin layer. US-A-4 046 837 discloses films made from 20% olefin and 80% poly(tetramethylene terephthalate). EP-A-0 104 130 discloses sheets made of a blend comprising 2-5% polyolefin, the balance being polyethylene terephthalate. EP-A-0 644 226 discloses an easily tearable film comprising 20% polypropylene and 80% polybutylene terephthalate JP-A-62 222 831 discloses a film comprising 13 (15-115)-31 (45/145)% of a polyolefin and 87-69% of a polyester. Brief Description of the Drawings Fig. 1 demonstrates a schematic sectional view of a GUNZE-type tear strength measuring apparatus. Disclosure of the Invention The present invention provides a tearable film having a five-layer structure of (A) layer/(B) layer/(C) layer/(B) layer/(A) layer and a thickness of about 25-100µm, wherein each (A) layer comprises 97-60% by weight of polyethylene-2,6-naphthalate having an intrinsic viscosity-(η) of 0.35-0.45 dl/g and 3-40% by weight of at least one polyolefin selected from polypropylene and poly-4-methyl-1-pentene wherein each (B) layer comprises an adhesive and wherein the (C) layer comprises a polyalefin and/or polystyrene. In a preferred aspect of the invention the tearable film is as defined above wherein the polyolefin of the (C) layer is at least one selected from low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene (LLDPE), very low density polyethylene (VLDPE), polypropylene, poly-1-butene, poly-1-hexene, poly-1-pentene, poly-1-heptene, poly-1-octene, poly-4-methyl-1-pentene, ethylene-propylene copolymer, ethylene-1-butene copolymer, propylene-1-butene copolymer, ethylene-ethylacrylate copolymer (EEA), ethylene-vinylacetate copolymer (EVA), ethylene-acrylic acid copolymer (EAA), at least one copolymer of at least one of ethylene, propylene, and butene, and at least one monomer selected from a bicyclo [2,2,1] heptodiene, a tetracyclo-3-dodecene, a hexacyclo-4-heptadecene, an octacyclo-5-docosene, a pentacyclo-4-hexadecene, a pentacyclo-3-pentadecene, a heptacyclo-4-icosene, a nonacyclo-5-pentadocosene and a narbomene. In another preferred aspect the present invention provides a tearable film having a five-layer structure of (A) layer/(B) layer/(C) layer/(B) layer/(A) layer and a thickness of 25-100µm, wherein each (A) layer comprises 97-60% by weight of polyethylene-2,6-naphthalate having an intrinsic viscosity (η) of 0.35-0.45 dl/g and about 3-40% by weight of poly-4-methyl-1-pentene wherein each (B) layer comprises an adhesive resin and wherein the (C) layer comprises a polyolefin and/or polystyrene. A feature of the invention is to provide a tearable multi-layer film comprising an (A) layer of a composition consisting of 97-60% by weight of polyethylene-2,6-naphthalate and 3-40% by weight of at least one polyolefin selected from polypropylene and poly-4-methyl-1-pentene. The (A) layer of the tearable film can consist of a composition consisting of 97-60% by weight of polyethylene-2,6-naphthalate and 3-40% by weight of at least one polyolefin selected from polypropylene and poly-4-methyl-1-pentene, or other components can be further blended therewith as long as the other components do not adversely affect an easy-tear property thereof. A mixing ratio of said composition in said film is generally at least about 10% by weight, preferably at least about 50% by weight, more preferably at least about 70% by weight, in particular preferably at least about 90% by weight. The intrinsic viscosity (η) of polyethylene-2,6-naphtalate of the invention ranges 0.35-0.45 dl/g. When the intrinsic viscosity (η) is about 0.20 dl/g or less, film formation is difficult due to fragility thereof. When the intrinsic viscosity (η) is more than about 1.0 dl/g, the easy-tear property thereof is reduced causing a tendency that taking out of packaged products becomes difficult. Polyolefins used in (C) layer of the invention are not specifically limited, but include a homopolymer or copolymer of α-olefin selected from ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene and 4-methyl-1-pentene or a copolymer of said α-olefin and a monomer capable of copolymerization with α-olefin, for example, at least one polymer selected from a copolymer of α-olefin and other vinyl-group containing monomer or monomers and a copolymer of α-olefin and cyclic olefin or olefins or a mixture thereof. Specifically low density polyethylene medium density polyethylene, high density polyethylene, linear low density polyethylene (LLDPE), very low density polyethylene (VLDPE), polypropylene, poly-1-butene, poly-1-hexene, poly-1-pentene, poly-1-heptene, poly-1-octene, poly-4-methyl-1-pentene, ethylene-propylene copolymer, ethylene-1-butene copolymer, propylene-1-butene copolymer, ethylene-ethylacrylate copolymer (EEA), ethylene-vinylacetate copolymer (EVA), ethylene-acrylic acid copolymer (EAA), at least one copolymer of at least one of ethylene, propylene and butene, and at least one monomer selected from a bicyclo [2,2,1] heptodiene, a tetracyclo-3-dodecene, a hexacyclo-4-heptadecene, a octacyclo-5-docosene, a pentacyclo-4-hexadecene, a pentacyclo-3-pentadecene, a heptacyclo-4-icosene, a nonacyclo-5-pentadocosene, and a norbornene, and a mixture of two or more of said polyolefins are exemplified. Polystyrenes used in (C) layer of the invention are not specifically limited, but include homopolymers of monomers having a styrene structure, or two-component or three-component copolymers having styrene as a main component, polymers of styrene derivatives and mixtures thereof. Specifically, homopolystyrene and like homopolymers of monomers having a styrene structure, styrene-butadiene copolymer, styrene-acrylonitrile copolymer, styrene-acrylonitrile-butadiene three-component copolymer, polymethylstyrene, poly-α-methylstyrene, polydichlorostyren and a mixture of two or more are exemplified. When polyolefin is used in (C) layer, polyolefins used in (A) layer and (C) layer are the same or different. With respect to polyolefins, polyolefins blended with polyethylene-2,6-naphthalate in (A) layer are preferably poly-4-methyl-1-pentene and like polymers with a tendency that no void caused by interfacial peeling is generated during biaxial orientation. When poly-4-methyl-1-pentene and like polymers are used as polyolefin, poly-4-methyl-1-pentene and like polymers include a homopolymer of 4-methyl-1-pentene, and copolymers of 4-methyl-1-pentene and other α-olefins having 2-20 carbon atoms such as ethylene, propylene, 1-butene, 1-hexene, 1-decene, 1-tetradecene, 1-octadecene, preferably copolymers containing 85 mole % or more of 4-methyl-1-pentene. The poly-4-methyl-1-pentene and like polymers are not specifically limited, but include polymers having a melt flow rate (MFR, loading : 5kg, temperature : 260 °C) of 0.5-200 g/10min. When MFR is less than about 0.5 g/10min, the melting viscosity thereof increases leading to a tendency that a mixture with polyethylene-2,6-naphthalate is very heterogeneous. When MFR is more than about 200 g/10min, the melting viscosity thereof decreases leading to a tendency of deterioration of processability and the mechanical strength thereof. A composition of (A) layer of the invention comprises 97-60 % by weight of polyethylene-2,6-naphthalate and 3-40 % by weight of at least one polyolefin selected from polypropylene and poly-4-methyl-1-pentene. In the case that polyethylene-2,6-naphthalate is more than about 97% by weight, and that at least one polyolefin selected from polypropylene and poly-4-methyl-1-pentene is less than about 3% by weight, the interface between the polyethylene-2,6-naphthalate region and the polyolefin region is reduced, leading to improved strength and a decreased easy-tear property of the film. In the case that polyethylene-2,6-naphthalate is less than about 60% by weight, and that at least one polyolefin selected from the group consisting of polypropylene and poly-4-methyl-1-pentene is more than about 40% by weight, the interface between the polyethylene-2,6-naphthalate region and the polyolefin region is increased, leading to easy breakage of the film due to excessive improvement of the easy-tear property thereof; said case is thereby unsuitable. Polyethylene-2,6-naphthalate (PEN) consists of naphthalene-2,6-dicarboxylic acid and ethyleneglycol and is a polymer with a tendency of an excellent easy-tear property because of the hardness and fragility thereof. Polyethylene-2,6-naphthalate may have an intrinsic viscosity (η) of 0.35-0.45dl/g. A preferable mixing ratio is 90-80% by weight of polyethylene-2,6-naphthalate and 10-20% by weight of at least one polyolefin selected from polypropylene and poly-4-methyl-1-pentene, but is not specifically limited. The thickness of the tearable film having a five-layer structure of (A)layer/(B)layer/(C)layer/(B)layer/(A)layer, is preferably 25-100 µm. Adhesive resins of (B) layer typically include modified polymers prepared by graft copolymerization and like copolymerization of polyolefins used in (A) layer and (C) layer using maleic acid, acrylic acid, methacrylic acid, fumaric acid, itaconic acid and like unsaturated carboxylic acid and/or esters acid anhydrides, metal salts and derivatives thereof. Other adhesive resins are not specifically limited, but include a mixture of the modified polymer and other component such as polyolefin resin, ionomer resin, ethylene-ethylacrylate resin (EEA), ethylene-vinylalcohol copolymer and saponified ethylene-vinylacetate copolymer. A method for preparing the composition of (A) layer of the invention, comprising polyethylene-2,6-naphthalate and at least one polyolefin selected fron polypropylene and poly-4-methyl-1-pentene is not specifically limited, and can be carried put according to a conventional method for preparing a polypropylene-containing composition. Specifically, a blend method using for example a ribbon blender, Henschel mixer, tambling mixer, a kneading method using for example a kneader, Banbary mixer, roll, a method comprising strand-like extrusion with uniaxial or biaxial extruder and T-die, cutting in a suitable length to form a pellet, and cooling the pellet are exemplified, but are not specifically limited. A variety of additives, fillers and thermoplastic resins may be added to (A) layer, (B) layer and (C) layer of the invention. The additives include heat stabilizers, antioxidants, light stabilizer, antistatic agents, lubricants and nucleating agents. The fillers include calcium carbonate, barium sulfate, magnesium hydroxide, talc and mica. The thermoplastic resins include ionomers and thermoplastic elastmers. The additives, fillers and thermoplastic resins are not specifically limited to those described above. It is safe not to blend additives, fillers and thermoplastic resins. A preferable embodiment of the tearable film of the invention is an (A)layer/(B)layer/(C)layer/(B)layer/(A)layer laminate film of five layers comprising (A) layers as a skin layer and (C) layer as a core layer, which is symmetrically laminated taking (C) layer as a center. With respect to the tearable film of the invention, (A) layer contributes to impartment of an easy-tear property to the film, but tends to be easily torn during fabrication so that caution is needed. In contrast, with respect to (C) layer, (C) layer is inferior in an easily tearable property, but superior in form stability and resistance to water vapor transmission, and (B) layer improves laminate strength between layers leading to expansion of the applications thereof. With respect to the tearable (A) layer/(B) layer/(C) layer/(B) layer/(A) layer laminate film, in which (A) layer is a skin layer, (C) layer is a core layer, and symmetrical lamination is carried out using (C) layer as a center in a thickness direction, the film is excellent in easy-tear property, form stability, resistance to vapor transmission and curling resistance, and is thereby preferable. The tearable film of the invention is preferably used as a cover material of PTPs and blister packs in the field of pharmaceuticals and foods but is not specifically limited. The tearable film can also be applied to any application other than a cover material. Furthermore, with respect to the tearable film of the invention, a suitable layer comprising one or more resins can be laminated on the surface of (A) layer and/or (B) layer and/or (C) layer or between (A) layer and (B) layer and/or between (B) layer and (C) layer, when necessary as long as the layer does not inhibit the easy-tear property of the film. The resin in the suitable layer is not specificaly limited and is the same as or different from any resin or polymer of (A) layer, (B) layer and (C) layer. Furthermore, the resin can be a composition having a different mixing ratio of polymers to (A) layer, a mixture of at least two polymers used in said layers or a mixture of any one polymer used in said layers and a foreign polymer (resin) not used in said layers. The resin is not specifically limited. In this case, said foreign polymer (resin) preferably includes ethylene-vinylalcohol copolymer, polyvinylidenechloride resin and ethylene-vinylacetate copolymer, but is not specifically limited as long as the resin does not inhibit the easy-tear property and other characteristic properties thereof. Furthermore, with respect to the tearable film of the invention, a printing layer can be formed on the surface of (A) layer, (B) layer, and/or (C) layer, when necessary. A deposit layer comprising SiO x , Al 2 O 3 , MgO, Al and like inorganic compounds can be formed on the surface of at least one of (A) layer, (B) layer and (C) layer, when resistance to vapor transmission and an oxygen barrier property is especially needed. Furthermore, when necessary for use as a cover material, a heat-sealing material comprising at least one selected from vinylacetate resin, vinylchloride-vinylacetate copolymer, vinylchloride resin, acrylic resin, polyester resin, ethylene-vinylacetate copolymer(EVA), polyvinylalcohol resin (PVA), polyolefin resin, modified polyolefin resin, urethane resin, urethane-modified polyester resin, partially urethane-modified polyester resin, polyether resin and modified ether-type polyester resin, and a pressure-sensitive adhesive comprising at least one selected from the group consisting of chloroprene, polyisobutylene, polyisoprene, polyacrylate ester, polyvinylether, styrene-butadiene rubber and butyl rubber can be laminated on the surface of at least one of (A) layer, (B) layer and (C) layer. Said heat-sealing material and pressure-sensitive adhesive may be used together with isocyanates and like curing agents. Said heat-sealing material and pressure-sensitive adhesive are not specifically limited and materials other than the above-exemplified materials can be used and can be selected according to the base material. Types of heat-sealing material and pressure-sensitive adhesive are not specifically limited. Aqueous-type, organic solvent-type, hot-melt type, emulsion-type heat-sealing material and pressure-sensitive adhesive may be used. Lamination may be carried out according to suitable processes such as co-extrusion, extrusion laminating, dry laminating, gravure coating and roll coating, and is not specifically limited. Methods for laminating the layers are not specifically limited and include a co-extrusion method performed by co-extruding layers for lamination to obtain, for example, (A)layer/(B)layer/(C)layer; an extrusion laminating method performed by extrusion and film-formation of (B) layer on (A) layer or (C) layer, or by extrusion and film-formation of (C) layer or (A) layer on (B) layer to obtain, for example, (A)layer/(B)layer/(C)layer; a dry laminating method performed by laminating (A) layer, (B) layer and (C) layer using adhesives therebetween to obtain (A)layer/(B)layer/(C)layer; a thermo compression bonding method performed by laminating (A) layer, (B) layer and (C) layer, followed by thermo-compression of the layers to obtain (A)layer/(B)layer/(C)layer. Methods for laminating the layers are not specifically limited and include co-extrusion, extrusion laminating, dry laminating and thermo compression bonding performed as shown above. The tearable film of the invention can be surface-treated to improve printability and ease of lamination. The film can be surface treated by corona discharge treatment, plasma treatment, flame treatment and acid treatment. According to the invention, any method can be used and the method is not specifically limited. However, a corona discharge treatment is most preferable because of the ease of performance before a rolling step for producing the easily tearable film and handleability. A method for producing the tearable film of the invention is Preferably performed by co-extrusion with T-die because of the capability of melt-lamination, but is not specifically limited. Stated more specifically, a pellet comprising a composition forming (A) layer consisting of polyetylene-2,6-naphthalate and at least one polyolefin selected from polypropylene and poly-4-methyl-1-pentene is dried with a known dryer under suitable drying conditions until the water content thereof is up to about 100 ppm, preferably up to about 50 ppm. The dried pellet comprising a composition consisting of polyethylene-2,6-naphthalate and at least one polyolefin, selected from polypropylene and poly-4-methyl-1-pentene, the polyolefin and/or polystyrene forming (C) layer, and the adhesive resin forming (B) layer are introduced into hoppers of at least three independent extruders linked with T-die for co-extrusion, respectively. The introduced resins (preferably pellet) are melt-extruded by an extruder heated at 270-310 °C, and then cooled and solidified in water or air, or with a cooling roll to form the easily tearable laminate film, for example, (A)layer/(B)layer/(C)layer structure, but are not specifically limited. With respect to the present invention, the tearable laminate film having five layers of (A)layer/(B)layer/(C)layer/(B)layer/(A)layer can be prepared in the same manner as above using five independent extruders. The tearable laminate film of the invention may be unstretched or optionally stretched. A method of stretching the film is not specifically limited and includes a sequential biaxial orientation after melt-extrusion for film-formation, a uniaxial orientation and a simultaneous biaxial orientation. Stretching can be carried out in separate process. Stretching conditions are not specifically limited. With respect to stretching in a longitudinal direction, stretching conditions include 80-140 °C of a surface temperature of a heat roll and a stretch ratio of 1.5-3.5 determined by a rotation speed ratio of a heated slow-driving roll (front) and heated quick-driving roll (back). With respect to stretching in a lateral direction, stretching can be carried out at 90-160 °C at an atmospheric pressure in tenter and a stretch ratio of 3.0-5.0 using a tenter wherein both ends of film are fixed with clips. Stretching may also be carried out by forming a tube-like film with a ring die, followed by uniaxial or biaxial stretching of the film by a tube stretching method. Furthermore, the tearable film of the invention may be optionally heat-set after stretching. A method for heat-setting the film is not specifically limited, but comprises heat-setting a laterally-stretched film for 1.0-20 seconds in a rear room of a tenter at a temperature higher than the stretching temperature and relaxing the film as much as about a few % (0.5-2.0 %) in a width direction. In the case of the films of the five layers of (A) layer/(B)layer/(C)layer/(B)layer/(A)layer of the present invention, about 5-25 µm of a thickness of (A) layer is exemplified, but is not specifically limited. Less than 5 µm of the thickness of (A) layer tends to cause tearlag during film formation. More than 25 µm of a thickness of (A) layer tends to decrease the easy-tear property. The thickness of (B) layer is not specifically limited as long as (B) layer is capable of bonding (A) layer to (C) layer, but ranges about 5 µm or less. The thickness of (C) layer is not specifically limited, but ranges 5-40 µm. Less than about 5 µm of the thickness thereof tends to cause tearing during rolling of the stretched film. More than 40 µm of the thickness thereof tends to decrease the easy-tear property. The thikness of the film is not specifically limited, but ranges about 25-115 µm. Best Mode For Carrying Out The Invention The invention will be described below in detail using examples, but the invention is in no way limited to the examples. Examination items with respect to the examples are determined according to the following methods. {Intrinsic viscosity (η)}: Polyethylene-2,6-naphtalate is dissolved in a mixed solvent of phenol and 1,1,2,2-tetrachloroethane (weight ratio = 6:4) at 100 ° C for 1 hour in a concentration of 0.2-1.0 g/dl. The viscosity of the solvent is determined using an Ubbellohde viscometer at 35 °C. The intrinsic viscosity is determined by extrapolation of the viscosity of the solution toward 0 g/dl. {Tensile strength at break}: Determination is carried out according to JIS K-7127. {Tensile elongation at break}: Determination is carried out according to JIS K-7127. {Easy-tear property}: : Shown as the tear propagation strength. The tear propagation strength is determined with a Gunze-type measuring device. As shown in Fig.1, the Gunze-type measuring device comprises fixing members (4), (4), (4), (4) comprising a metal plate (2) and a rubber plate (3) to fix a laminate film (1), a probe provided with a hemisphere (5) having a diameter of 8 mm which descends until the laminate film is torn and a detector (7) to determine a tear propagation strength of the laminate film (1). {Water vapor transmission}: Determination is carried out according to JIS K-9129. The tensile strength at break is preferably up to 10 kg/mm 2 , more preferably 1.0-6.0 kg/mm 2 ; The tensile elongation at break is preferably up to 50 %, more preferably 1.0-40 %; The tear propagation strength is preferably up to 3.0 kg, more preferably 0.5-2.5 kg; and The water vapor transmission is preferably up to 20g/m 2 /day. Example 1 A pellet was produced by melt-kneading at 300 °C. for 10 minutes a composition comprising 90 % by weight of polyethylene-2, 6-naphthalate (PEN; intrinsic viscosity = 0.4 dl/g) consisting of naphthalene-2,6-dicarboxylic acid and ethylene glycol and 10 % by weight of poly-4-methyl-1-pentene (MFR = 180g/10min, load : 5 kg, temperature : 260 °C) as the composition of a skin layer (A). The resulting pellet (water content 50 ppm) was used in a skin layer (A), an adhesive resin which is a polyethylene resin modified by maleic acid was used in (B) layer, and a very low density polyethylene (VLDPE) having a density of 0.89 g/cm 3 and a MFR (190 °C) of 1.0g/10min was used in a core layer (C). With respect to five extruders independently linked with T-die for five-layer co-extrusion, the composition comprising the polyethylene-2,6-naphthalate (PEN) and the poly-4-methyl-1-pentene to be included in (A) layer was supplied to two extruders, the adhesive resin to be included in (B) layer (adhesive layer) was supplied to two other extruders, and the very low density polyethylene to be included in (C) layer (core layer) was supplied to the remaining one extruder, respectively. A laminate film, (A)/(13)/(C)/(B)/(A), was obtained by melt coextrusion thereof for lamination, followed by quenching of the laminate film with a cooling roll. Subsequently, using a stretching machine for sequential biaxial orientation, the laminate film was stretched with a preheated roll having a surface temperature of 135-145 °C at a stretch ratio of 1.8 in a longitudinal direction as a first step and then stretched with a tenter at an atomospheric pressure in tenter of 150-160 °C at a stretch ratio of 4.2 in a lateral direction as a second step. The resulting film was then heat-set at 210 °C for 3-20 seconds with relaxation of the film by as much as about 2 % in a width direction to obtain an easily tearable laminate film {(A)/(B)/(C)/(B)/(A) = 8/2/10/2/8 µm} having a thickness of 30 µm. The tearable laminate film was gravure-coated in whole area with a heat-sealing material consisting of a polyester resin at a rate of 8g/m 2 to form cover material. Base material was formed by vacuum-forming a sheet comprising a vinyl chloride resin having a thickness of 200 µm to a disc tablet (diameter about 10 mm, height 5 mm). The base material was heat-sealed with said cover material at a seal temperature of 140 °C, a seal pressure of 4 kgf/cm 2 and a seal time of 1 second to obtain a PTP. The PTP using the tearable laminate film had an easy-tear property comparable to Al foil. The tensile strength at break, tensile elongation at break, tear propagation strength and water vapor transmission of the easily tearable laminate film are shown in table 1. Example 2 A PTP was obtained in the same manner as example 1 except that polypropylene-type copolymer (MFR = 10g/10min, ASTM D-1238) was used in place of the poly-4-methyl-1-pentene of skin layer (A) and the very low density polyethylene of core layer (C) of example 1 and that polyethylene modified by maleic anhydride was used in an adhesive layer (B). The resulting PTP had a good easy-tear property. The tensile strength at break, tensile elongation at break, tear propagation strength and water vapor transmission of the tearable laminate film are shown in table 1. Example 3 A PTP was obtained in the same manner as example 1 except that the stretch ratio in the longitudinal direction and the stretch ratio in the lateral direction were 2, respectively. The resulting PTP had a good easy-tear property. The tensile strength at break, tensile elongation at break, tear propagation strength and water vapor transmission of the tearable laminate film are shown in table 1. Example 4 A PTP was obtained in the same manner as example 1 except that polystyrene (MFR determined according to ASTM D-1238 = 7g/10min) was used in place of the very low density polyethylene (VLDPE) of core layer (C) in example 1. The resulting PTP had a good easy-tear property. The tensile strength at break, tensile elongation at break, tear propagation strength and water vapor transmission of the tearable laminate film are shown in table 1. Example 5 A PTP was obtained in the same manner as example 1 except that a composition comprising 50 % by weight of polystyrene (MFR determined according to ASTM D-1238 = 7g/10min ) and 50 % by weight of polypropylene (MFR determined according to ASTM D-1238 = 10g/10min) was used in place of the very low density polyethylene (VLDPE) of core layer (C) in example 1. The resulting PTP had a good easy-tear property. The tensile strength at break, tensile elongation at break, tear propagation strength and water vapor transmission of the easily tearable laminate film are shown in table 1. Comparative example 1 A tearable laminate film, (A)/(B)/(C)/(B)/(A), was obtained in the same manner as example 1 except that the skin layer (A) comprised polyethylene-2,6-naphthalate (PEN; intrinsic viscosity = 0.4 dl/g) consisting of naphthalene-2,6-dicarboxylic acid and ethylene glycol, that (B) layer comprised an adhesive resin which is a polyethylene resin modified by maleic acid, that a core layer (C) comprised polypropylene having a density of 0.90 g/cm 3 and MFR (230 °C) of 1.0g/10min, that a stretch ratio in a longitudinal direction was 3.0, and that a stretch ratio in a lateral direction was 8.0 The tensile strength at break, tensile elongation at break, tear propagation strength and water vapor transmission of the tearable laminate film are shown in table 1. Comparative example 2 A tearable laminate film, (A)/(B)/(C)/(B)/(A), was obtained wherein the skin layer (A) comprised polyethylene-2,6-naphthalate (PEN; intrinsic viscosity = 0.4 dl/g) consisting of naphthalene-2,6-dicarboxylic acid and ethylene glycol, (B) layer comprised an adhesive resin which is a polyethylene resin modified by maleic acid, a core layer (C) comprised a polypropylene having a density of 0.89 g/cm 3 and MFR (230 °C) of 3.0g/10min. The tensile strength at break, tensile elongation at break, tear propagation strength and water vapor transmission of the easily tearable laminate film are shown in table 1. Tensile strength at break (kg/mm 2 ) Tensile elongation at break (%) Tear propagation strength (kg) Water vapor transmission (g/m 2 /day) MD TD MD TD Ex.1 1.0 5.0 1.1 2.5 0.5 10.3 Ex.2 3.0 5.5 1.5 3.5 1.0 11.4 Ex.3 1.2 5.2 1.2 2.9 0.8 8.2 Ex.4 1.8 5.6 1.0 2.3 0.8 5.0 Ex.5 1.0 4.2 1.8 3.9 1.2 15.6 Ex.6 1.1 1.3 1.5 1.5 0.4 11.2 Ex.7 1.1 1.2 1.1 1.3 0.6 10.9 Ex.8 1.1 1.2 1.0 1.2 0.5 18.9 Ex.9 2.2 3.0 1.5 2.2 1.0 14.3 Comp.Ex.1 35.0 110.0 29.0 27.0 21.4 11.5 Comp.Ex.2 30.4 98.0 33.2 25.8 18.9 12.1 It is obvious from table 1 that the tearable films obtained in examples 1-5 have a lower tensile strength at break and tensile elongation at break. than those obtained in comparative examples 1 and 2, showing a lower and suitable tear propagation strength. The films of the invention obtained in examples 1-5 have, therefore, an excellent easy-tear property. The tearable film of the invention is very easily torn. When the film is used as a cover material of a PTP for pharmaceuticals, the films exert an outstanding effect that tablets and the like are easily taken out and that deterioration of packaged products is inhibited due to low water vapor transmission. The film, having a low a heat of combustion, does not damage an incinerator during thermal disposal. Furthermore, the tearable film of the invention has excellent hygienic qualities, unlike conventional films, to which an easy-tear property is imparted by adding to the films great amounts of mineral filler which may be scattered when torn, and the scattered filler is mixed with or attached to packaged products such as pharmaceuticals.

Claims: A tearable film having a five layer structure of (A) layer/(B) layer/(C) layer/(B) layer/(A) layer and a thickness of 25-100 µm, wherein each (A) layer comprises 97-60% by weight of polyethylene-2,6-naphthalate having an intrinsic viscosity (η) of 0.35-0.45 dl/g and 3-40% by weight of at least one polyolefin selected from polypropylene and poly-4-methyl-1-pentene wherein each (B) layer comprises an adhesive resin and wherein the (C) layer comprises a polyolefin and/or polystyrene. A tearable film as defined in claim 1 wherein the polyolefin of the (C) layer is at least one selected from the group consisting of low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene (LLDPE), very low density polyethylene (VLDPE), polypropylene, poly-1-butene, poly-1-hexene, poly-1-pentene, poly-1-heptene, poly-1-octene, poly-4-methyl-1-pentene, ethylene-propylene copolymer, ethylene-1-butene copolymer, propylene-1-butene copolymer, ethylene-ethylacrylate copolymer (EEA), ethylene-vinylacetate copolymer (EVA), ethylene-acrylic acid copolymer (EAA), at least one copolymer of at least one of ethylene, propylene, and butene, and at least one monomer selected from a bicyclo [2,2,1] heptodiene, a tetracyclo-3-dodecene, a hexacyclo-4-heptadecene, an octacyclo-5-docosene, a pentacyclo-4-hexadecene, a pentacyclo-3-pentadecene, a heptacyclo-4-icosene, a nonacyclo-5-pentadocosene, and a norbornene. A tearable film having a five layer structure of (A) layer/(B) layer/(C) layer/(B) layer/(A) layer and a thickness of 25-100 µm, wherein each (A) layer comprises 97-60% by weight of polyethylene-2,6-naphthalate having an intrinsic viscosity (η) of 0.35-0.45 dl/g and 3-40% by weight of poly-4-methyl-1-pentene wherein each (B) layer comprises an adhesive resin and wherein the (C) layer comprises a polyolefin and/or polystyrene.

Inventors: FURUKAWA HIROYUKI, INOUE ISAO, OGUCHI KIYOSHI, WAKAI MUTSUMI, FURUKAWA, HIROYUKI, INOUE, ISAO, OGUCHI, KIYOSHI, WAKAI, MUTSUMI, FURUKAWA, Hiroyuki Shiga Laboratory of Gunze Ltd., INOUE, ISAO DAI NIPPON PRINTING CO., LTD., OGUCHI, Kiyoshi Dai Nippon Printing Co., Ltd., WAKAI, Mutsumi Shiga Laboratory of Gunze Limited
Applicants: DAINIPPON PRINTING CO LTD, GUNZE KK, DAI NIPPON PRINTING CO., LTD., GUNZE LIMITED
Application year: 1996
Main classification: C08J5
IPC codes: C08L67, C08J5, B32B27