JP2008207487A - Shrink film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a shrink film having an excellent shrink characteristic in which a high shrink stress and a beautiful finishing property are compatible, an interlaminar strength between the films layers of a laminate is high and a strength, transparency are excellent. <P>SOLUTION: The shrink film of this invention is a film composed of two-type three-layer laminate constitution of a front layer/a central layer/a front layer having the front layers at both sides of the central layer wherein the front layer is a resin layer composed of 90-100 wt.% of a polyester resin, the central layer is a resin layer including at least 60-90 wt.% of a styrene unit, 5-30 wt.% of a conjugated diene unit, and 0.5-5 wt.% of an oxazoline unit. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a shrink film. More specifically, the present invention relates to a laminated shrink film having excellent processability, shrinkage characteristics, transparency and interlayer strength.

  Currently, plastic bottles such as PET bottles (polyethylene terephthalate bottles) and metal bottles such as bottle cans are widely used as containers for beverages such as tea and soft drinks. These containers are often equipped with plastic labels for display, decoration, and functionality. In recent years, water vapor and hot air have been used because of their good trackability and increased display area. A heat-shrinkable plastic film (shrink film) that is made to follow and attach to a container by being shrunk by is widely used.

  As the shrink film, a film made of polyester resin or polystyrene resin is generally used. Films made of the above-mentioned polyester resins and polystyrene resins can be highly shrunk, but films made of polyester resins have a high shrinkage rate and stress, and severe shrinkage conditions are required to obtain a beautiful finish. Therefore, the film made of polystyrene resin is easy to obtain a beautiful finish, but has poor dimensional stability during storage, and severe storage management is required, resulting in poor handling. .

  As a method for adjusting these film characteristics (strength, shrinkage, etc.), a film in which resin layers made of different resins of polyester resin and polystyrene resin are laminated is used, and polyester resin is provided on both sides of the polystyrene resin. A heat-shrinkable label (for example, see Patent Documents 1 to 3) made of a laminated film in which layers are laminated is known. However, since these layers have insufficient interlayer strength, a layer made of an adhesive resin is provided between a surface layer made of polyester resin and an intermediate layer made of styrene resin to further improve the interlayer strength. A laminated shrink film having a five-layer structure is known (see, for example, Patent Document 4).

JP-A-7-137212 JP 2002-351332 A JP 2004-170715 A JP 2006-15745 A

  However, when the above-mentioned three-kind five-layer laminated shrink film was studied, when an polystyrene resin containing an oxazoline group was used as the adhesive resin layer, the film layer was poorly formed and produced. It has been found that problems such as deterioration of transparency, transparency, and interlayer strength are caused.

  That is, an object of the present invention is to provide a shrink film that has excellent processability, shrinkage characteristics, transparency, and interlayer strength, and is excellent as a label application.

  As a result of intensive studies to achieve the above-mentioned object, the present inventors have used a film having a specific resin composition and a laminated structure, resulting in good productivity, high shrinkage, moderate shrinkage behavior, and a beautiful finish. It has been found that it is possible to obtain an excellent shrink film having transparency, high interlaminar strength between film layers, strong film stiffness (high compressive strength) Completed the invention.

  That is, the present invention is a film composed of a two-layer / three-layer structure of surface layer / center layer / surface layer having surface layers on both sides of the center layer, and the surface layer is a resin layer composed of 90 to 100% by weight of a polyester resin. A shrink film is characterized in that the central layer is a resin layer comprising at least 60 to 90% by weight of styrene units, 5 to 30% by weight of conjugated diene units, and 0.5 to 5% by weight of oxazoline units.

  Furthermore, the present invention provides the shrink film as described above, wherein the conjugated diene is butadiene and / or isoprene.

  Furthermore, this invention provides the said shrink film whose center layer is a resin layer containing 5 to 20 weight% of ethylene terephthalate units.

  Moreover, this invention is a film which consists of 2 types 3 layer laminated structure of surface layer / center layer / surface layer which has a surface layer on both sides of a center layer, Comprising: Surface layer is a resin layer which consists of 90-100 weight% of polyester-type resin. The center layer is a resin layer comprising at least 50 to 90% by weight of a polystyrene resin (excluding those containing an oxazoline group) and 10 to 50% by weight of an oxazoline group-containing styrene copolymer. Provide shrink film.

  Furthermore, this invention provides the said shrink film whose center layer is a resin layer which further contains 5-20 weight% of polyester-type resins.

  Furthermore, this invention provides the said shrink film whose ratio (center layer thickness / surface layer thickness) of center layer thickness with respect to surface layer thickness (for 1 layer) is 2-6.

  Furthermore, the present invention provides the above shrink film in which the interlayer strength of the shrink film is 1.5 (N / 30 mm) or more, and the compressive strength of the shrink film (conforms to JIS P 8216, converted to a film thickness of 40 μm) is 5 N or more. provide.

  In the shrink film of the present invention, since the layer made of polystyrene resin contains an oxazoline component, the interlayer strength between the layer made of polystyrene resin and the layer made of polyester resin is increased, and the polyester resin is added to the center layer. In this case, the mixing property is improved and the transparency of the film is not lowered. Furthermore, the compressive strength of the shrink film is improved and the suitability for mounting is improved. As described above, the shrink film of the present invention has high transparency, and also has a high shrinkage rate and an appropriate shrinkage speed due to different types of lamination of polystyrene resin and polyester resin, so it is attached to a container having a complicated shape. Beautiful finish when processed. Moreover, since the interlaminar strength and compressive strength are high, troubles due to peeling or buckling in the production process or market are unlikely to occur. Furthermore, the extrusion moldability is good and the productivity is also excellent. Therefore, it is particularly useful as a label used for PET bottles and the like.

  The shrink film of the present invention is a film having a surface layer / center layer / surface layer two-layer three-layer structure having surface layers on both sides of the center layer. The “center layer” and “surface layer” referred to in the present invention both mean a single resin layer (also referred to as a film layer).

  Moreover, each film layer of the shrink film of this invention is laminated | stacked by co-extrusion, without passing through another adhesive bond layer etc. By laminating by coextrusion, the resin in the center layer and the surface layer partially melts and mixes at the interface between the layers, so the effect of improving the interlayer strength is achieved by the interaction between the oxazoline group contained in the center layer and the polyester resin in the surface layer. Demonstrated. Moreover, since the film layer tends to be stretched and oriented effectively, a shrink film having excellent shrinkage characteristics is obtained.

  The central layer in the shrink film of the present invention is a resin layer comprising at least a styrene unit, a conjugated diene unit, and an oxazoline unit. Content of the said styrene unit is 60 to 90 weight% with respect to the total weight of a center layer, Preferably it is 75 to 85 weight%. When the content of styrene units is less than 60% by weight, the film becomes weak (compression strength is low), and when it exceeds 90% by weight, the film becomes brittle. Moreover, content of the said conjugated diene unit is 5-30 weight% with respect to the total weight of a center layer, Preferably it is 15-25 weight%. When the content of the conjugated diene unit is less than 5% by weight, the stretching characteristics are deteriorated, and when it exceeds 30% by weight, the film becomes weak. Furthermore, the content of the oxazoline unit is 0.5 to 5% by weight, more preferably 1 to 2.5% by weight, based on the total weight of the central layer. When the content of the oxazoline unit is less than 0.5% by weight, the adhesion effect is lowered, and when it exceeds 5% by weight, the stretching property is lowered.

  In addition to the above, the center layer of the present invention preferably contains an ethylene terephthalate unit in an amount of 5 to 20% by weight based on the total weight of the center layer, more preferably from the viewpoint of further improving the interlayer strength and the compressive strength. 10 to 20% by weight.

  One configuration aspect of the central layer of the present invention satisfying the above is a resin layer comprising at least a polystyrene resin and an oxazoline group-containing styrene copolymer.

  For example, styrene, α-methyl styrene, m-methyl styrene, p-methyl styrene, p-ethyl styrene, p-isobutyl styrene, pt-butyl styrene, The resin is not particularly limited as long as it is a resin containing one or more styrene monomers such as chloromethylstyrene and exhibiting heat shrinkability when formed into a film. In the case of the polystyrene resin of the present invention, a resin containing an oxazoline group in the molecule is excluded.

  Examples of such polystyrene resins include general polystyrene (GPPS), which is a homopolymer of styrene, a homopolymer or copolymer of styrene monomers; a mixture of polystyrene and synthetic rubber (for example, polybutadiene or polyisoprene), High impact polystyrene (HIPS) with styrene grafted on synthetic rubber; styrene monomer and conjugated dienes such as butadiene and isoprene, such as styrene-butadiene-styrene (SBS) block copolymer Styrene-conjugated diene copolymer that is a polymer (particularly a block copolymer); Styrene-polymerizable unsaturated carboxylic acid that is a copolymer of a styrene monomer and a (meth) acrylate monomer Acid ester copolymer; styrene-conjugated diene-polymerizable unsaturated carboxylic acid ester copolymer; A rubbery elastic material is dispersed in a continuous phase of a copolymer of a monomer and a (meth) acrylic acid ester monomer, and the copolymer is graft-polymerized on the rubbery elastic material. -High impact polystyrene (graft TIPS) etc. are mentioned. Among the polystyrene resins, styrene-conjugated diene copolymers are preferable, and styrene-butadiene-styrene (SBS) block copolymers are particularly preferable.

  Examples of the conjugated diene used in the styrene-conjugated diene copolymer include 1,3-butadiene, isoprene (2-methyl-1,3-butadiene), 2,3-dimethyl-1,3-butadiene, and the like. , 3-pentadiene, 1,3-hexadiene, chloroprene and the like. Among these, a styrene-butadiene copolymer using 1,3-butadiene as a conjugated diene is particularly preferable. The form of copolymerization is not particularly limited, but a block copolymer is preferable, and styrene block (S) -conjugated diene block (D) type, SDS type, DSD type, S type. -DSD type etc. are mentioned. In the styrene-conjugated diene copolymer, the styrene content is preferably about 55 to 95% by weight (conjugated diene content: 5 to 45% by weight).

  As the styrene-butadiene copolymer, a styrene-butadiene-styrene (SBS) block copolymer is preferable. In the styrene-butadiene block copolymer, the styrene content is preferably 65 to 90% by weight (butadiene content: 10 to 35% by weight), more preferably 75 to 88% by weight (butadiene content: 12 to 25% by weight). %). The melt flow rate (MFR) (JIS K 7210: temperature 200 ° C./load 49 N) of the styrene-butadiene-styrene block copolymer is preferably 1 to 20 g / 10 minutes, more preferably 3 to 10 g / 10 minutes. It is. As such a styrene-butadiene-styrene block copolymer, “Asaflex” manufactured by Asahi Kasei Chemicals Co., Ltd., “K-resin” manufactured by Philips Co., Ltd. and the like are available on the market.

Examples of the polymerizable unsaturated carboxylic acid ester used in the styrene-polymerizable unsaturated carboxylic acid ester copolymer include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, ( (Meth) acrylic acid alkyl esters (especially (meth) acrylic acid C _1-10 alkyl esters) such as isobutyl acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate; dimethyl fumarate, Examples thereof include fumaric acid mono- or diesters such as diethyl fumarate; maleic mono- or diesters such as dimethyl maleate and diethyl maleate; itaconic mono- or diesters such as dimethyl itaconate and diethyl itaconate. Among these, methyl acrylate and methyl methacrylate are preferably used because of excellent transparency. Moreover, the (meth) acrylic acid alkyl ester having an alkyl group having 4 or more carbon atoms (for example, about 4 to 10 carbon atoms) such as butyl acrylate or butyl methacrylate has a natural shrinkage (when stored at 30 ° C. for 30 days). This is preferable because it contributes to a reduction in the shrinkage ratio. These polymerizable unsaturated carboxylic acid esters can be used alone or in admixture of two or more. The styrene content in the styrene-polymerizable unsaturated carboxylic acid ester copolymer is preferably 60 to 90% by weight.

  The content of the polystyrene-based resin in the center layer is 50 to 90% by weight, preferably 75 to 85% by weight, based on the total weight of the center layer. If it is less than 50% by weight, good shrinkage cannot be obtained, and if it exceeds 90% by weight, the interlayer strength decreases, which is not preferable.

  The oxazoline group-containing styrene copolymer used in the present invention is a copolymer containing, as constituent components, a styrene monomer and a vinyl monomer containing an oxazoline group as essential components. Examples of the styrene monomer include styrene, α-methyl styrene, m-methyl styrene, p-methyl styrene, p-ethyl styrene, p-isobutyl styrene, pt-butyl styrene, chloromethyl styrene, and the like. Examples of the vinyl monomer containing an oxazoline group include 2-isopropenyl-2-oxazoline, 2-isopropenyl-4,4-dimethyl-2-oxazoline and the like. Among them, a styrene / 2-isopropenyl-2-oxazoline copolymer composed of styrene and 2-isopropenyl-2-oxazoline is preferable.

  In the oxazoline group-containing styrene copolymer, the content of the styrenic monomer is preferably 80 to 98% by weight, more preferably 90 to 98% by weight. The content of the vinyl monomer containing an oxazoline group is preferably 2 to 20% by weight, more preferably 2 to 10% by weight.

  As the oxazoline group-containing styrene copolymer, existing products can be used. For example, “Epocross” manufactured by Nippon Shokubai Co., Ltd. is available on the market.

  The content of the oxazoline group-containing styrenic copolymer in the center layer is 10 to 50% by weight, preferably 12 to 30% by weight, based on the total weight of the center layer. If it is less than 10% by weight, the interlaminar strength is lowered, and if it exceeds 50% by weight, the shrinkability and moldability are deteriorated.

  The center layer of the present invention may contain a recovered raw material. Addition of the recovered raw material is preferable because the adhesiveness with the surface layer is improved and the interlayer strength is increased in addition to cost reduction and industrial waste reduction. Recycled raw materials are non-product polymer scraps such as pre- and post-production parts and film edges, and the remaining parts when product films are collected from intermediate products and non-standard products are flaked and granulated. It is a raw material, and is limited to those produced from the production of the shrink film of the present invention. For this reason, when the collection | recovery raw material is included, a center layer contains the polyester-type resin which forms a surface layer. In this case, the added amount of the recovered raw material is preferably 10 to 30% by weight with respect to the total weight of the center layer, from the viewpoint of improvement of transparency and waist strength. The content of the polyester resin in the center layer is preferably 5 to 20% by weight, more preferably 10 to 20% by weight. When the content of the polyester resin exceeds 20% by weight, the transparency may be lowered or the shrinkage behavior may be too rapid. The polyester resin added to the center layer is not necessarily derived from the recovered raw material.

  The surface layer of the present invention comprises a polyester resin as a main component. Examples of the polyester resin used for the surface layer of the present invention include various polyesters composed of a dicarboxylic acid component and a diol component. Examples of the dicarboxylic acid component include terephthalic acid, isophthalic acid, phthalic acid, 5-t-butylisophthalic acid, 4,4′-biphenyldicarboxylic acid, trans-3,3′-stilbene dicarboxylic acid, and trans-4,4. '-Stilbene dicarboxylic acid, 4,4'-dibenzyldicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,3-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2, 7-naphthalenedicarboxylic acid, 2,2,6,6-tetramethylbiphenyl-4,4′-dicarboxylic acid, 1,1,3-trimethyl-3-phenylindene-4,5-dicarboxylic acid, 1,2- Aromatic dicals such as diphenoxyethane-4,4′-dicarboxylic acid, diphenyl ether dicarboxylic acid, and substituted products thereof Acid; oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid, tetradecanedioic acid, pentadecanedioic acid, Aliphatic dicarboxylic acids such as heptadecanedioic acid, octadecanedioic acid, nonadecanedioic acid, icosanedioic acid, docosanedioic acid, 1,12-dodecanedioic acid, and their substitutions; 1,4-decahydronaphthalenedicarboxylic acid, 1,5-decahydronaphthalenedicarboxylic acid, 2,6-decahydronaphthalenedicarboxylic acid, cis-1,4-cyclohexanedicarboxylic acid, trans-1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, and these And alicyclic dicarboxylic acids such as substitution products thereof. These dicarboxylic acid components can be used alone or in combination of two or more.

  Examples of the diol component include ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 2,2 -Dimethyl-1,3-propanediol, 1,6-hexanediol, 2-ethyl-2-methyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 1,8-octane Aliphatic acids such as diol, 2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2,4-dimethyl-1,3-hexanediol, 1,10-decanediol, polyethylene glycol, polypropylene glycol Diol; 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4 Cycloaliphatic diols such as cyclohexanedimethanol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol; 2,2-bis (4′-β-hydroxyethoxydiphenyl) propane, bis (4′- Examples thereof include ethylene oxide adducts of bisphenol compounds such as β-hydroxyethoxyphenyl) sulfone and aromatic diols such as xylylene glycol. These diol components can be used alone or in combination of two or more.

  In addition to the above, the polyester-based resin includes oxycarboxylic acids such as p-oxybenzoic acid and p-oxyethoxybenzoic acid; monocarboxylic acids such as benzoic acid and benzoylbenzoic acid; and polyvalent carboxylic acids such as trimellitic acid. Structural units such as monohydric alcohols such as polyalkylene glycol monomethyl ether; polyhydric alcohols such as glycerin, pentaerythritol and trimethylolpropane may be included.

  The polyester-based resin used for the surface layer of the present invention is not particularly limited, but polyethylene terephthalate (PET) using terephthalic acid as the dicarboxylic acid component and ethylene glycol (EG) as the diol component, or terephthalic acid as the dicarboxylic acid component. Copolymer polyester (hereinafter referred to as CHDM copolymerized PET) or neopentyl glycol (NPG) using ethylene glycol as the main component and 1,4-cyclohexanedimethanol (CHDM) as the copolymer component. Polyester (hereinafter referred to as NPG copolymerized PET) used as a polymerization component is particularly preferable from the viewpoints of cost, productivity, and the like. Furthermore, diethylene glycol may be copolymerized from the viewpoint of improving low-temperature shrinkage. In the case of CHDM copolymerized PET, the proportion of CHDM copolymerization is preferably 10 to 40 mol%, more preferably 20 to 30 mol%, and the proportion of diethylene glycol is 20 mol% or less with respect to ethylene glycol. By copolymerizing CHDM, the polyester resin becomes amorphous. In the case of NPG copolymerized PET, it is preferable that NPG is 15 to 40 mol% and EG is 60 to 85 mol% in the diol component (that is, relative to 100 mol% of terephthalic acid).

  The IV value (intrinsic viscosity) of the polyester resin of the present invention is preferably 0.5 to 0.9 (dl / g), more preferably 0.7 to 0.8 (dl / g) from the viewpoint of shrinkage suitability. ). The glass transition temperature (Tg) of the polyester resin is preferably 50 to 100 ° C., more preferably 60 to 80 ° C., from the viewpoint of shrinkability.

  As the above polyester-based resin, existing products can be used. For example, PET is “Novapex” manufactured by Mitsubishi Chemical Corporation, and CHDM copolymerized PET is “Easter Copolymer” or “EMBRACE” manufactured by Eastman Chemical Co., Ltd. Are available on the market.

  The content of the polyester resin relative to the total weight of the surface layer of the present invention is 90 to 100% by weight, preferably 95 to 99% by weight, from the viewpoints of transparency, waist strength, heat resistance, and resistance to contents. It is.

  As for the thickness of the shrink film of this invention, 20-80 micrometers is preferable, More preferably, it is 30-60 micrometers.

  1-10 micrometers is preferable and, as for the thickness (1 layer) of the surface layer of the shrink film of this invention, More preferably, it is 2-7 micrometers. When the thickness of the surface layer exceeds 10 μm, the shrinkage behavior becomes abrupt and the workability may be deteriorated. When the thickness is less than 1 μm, the high shrinkage is lowered and the finish is inferior, and it is possible to laminate uniformly. The surface wear resistance and chemical resistance may decrease. The two surface layers on both sides of the center layer may have different thicknesses as long as they are in the above thickness range, but it is preferable that the two layers have the same thickness. When the thicknesses of the two layers are greatly different, problems such as “sledge” and “wrinkle” may occur during shrinkage processing or storage.

  As for the thickness of the center layer of the shrink film of this invention, 18-60 micrometers is preferable, More preferably, it is 26-50 micrometers. When the thickness of the center layer exceeds 60 μm, the economy may be inferior. If it is less than 18 μm, the shrinkage may be reduced.

  When the thickness of the surface layer (one layer) of the shrink film of the present invention is 1, the thickness of the center layer is preferably 2-6, more preferably 3-5. When the thickness of the center layer with respect to the surface layer is less than the above range, the shrinkage behavior becomes abrupt and the workability may be reduced. Moreover, when exceeding the said range, a moldability may be inferior or the shrinkage | contraction rate of a shrink film may fall.

  The shrink film of the present invention is oriented in at least one direction. When all the layers are non-oriented, it becomes difficult to achieve the shrinkage characteristics, rigidity, and interlayer strength of the present invention. A uniaxial or biaxially oriented film oriented in the longitudinal direction (film forming direction) and / or in the width direction (direction orthogonal to the longitudinal direction) is preferred. Among them, the film width direction (when the label is formed into a cylinder, the label A film that is strongly oriented in the circumferential direction (substantially uniaxially stretched in the width direction) is generally used. Moreover, in the shrink film of this invention, it is preferable from the viewpoint of obtaining the outstanding shrinkage | contraction characteristic that all the film layers orientate.

  You may add an additive to each film layer of the shrink film of this invention within the range which does not impair the effect of this invention. Examples of additives include pigments, dyes, lubricants, antiblocking agents (such as inorganic particles), antioxidants, ultraviolet absorbers, deodorants, flame retardants, and stabilizers. The addition amount of these additives is preferably 5% by weight or less with respect to the weight of the film layer to be added.

  As described above, the shrink film of the present invention has a central layer composed mainly of a polystyrene resin such as a styrene-butadiene-styrene block copolymer, and a surface layer composed mainly of a polyester resin. The central layer suppresses the rapid shrinkage of the shrink film and has the effect of slowing the shrinkage behavior and improving the finish. Effect of imparting wear resistance and chemical resistance to the surface. For this reason, the shrink film of the present invention has good shrinkability and excellent shrinkage. Furthermore, since the center layer of the present invention contains an oxazoline group-containing styrene copolymer, the oxazoline group in the center layer interacts with (or reacts with) the hydroxyl group or carboxyl group of the polyester resin in the surface layer. The compatibility between the resins in both layers is increased, and the interlayer strength is dramatically improved. Further, when the center layer contains the same polyester resin (such as a recovered raw material) as the surface layer, the interaction between the center layer and the surface layer polyester resin is also added, so that the interlayer strength is further improved.

  In the shrink film of the present invention, it is important to have a three-layer laminated structure in which the oxazoline group-containing styrene copolymer that exhibits the effect of improving the interlayer strength is contained in the center layer. Oxazoline group-containing styrenic copolymers have relatively poor film moldability, so when used as a thin film layer (for example, an adhesive layer provided between the center layer and the surface layer), the film layer can be formed uniformly. As a result, the effect of improving the interlayer strength cannot be obtained. For this reason, it becomes possible to improve interlayer intensity | strength, maintaining the formation property of a film layer by mixing and using for polystyrene-type resins, such as SBS resin with favorable moldability of a center layer. On the other hand, in the case of a single-layer structure including all of a polyester resin, a polystyrene resin, and an oxazoline group-containing styrene copolymer, shrinkage and transparency are reduced, and wear resistance and chemical resistance are also preferable. Absent.

  In the shrink film of the present invention, when using an oxazoline group-containing styrene copolymer as a central layer, a dispersion resin pellet in which a polystyrene resin and an oxazoline group-containing styrene copolymer are dispersed in advance is prepared and melted. It is preferable to use it for film formation. However, the present invention is not limited to this, and the respective pellets of the polystyrene resin and the oxazoline group-containing styrene copolymer may be dry blended during film formation.

  The interlayer strength of the shrink film of the present invention is preferably 1.5 (N / 30 mm) or more, more preferably 2 (N / 30 mm) or more. When the interlaminar strength is less than 1.5 (N / 30 mm), the film layers are peeled off after processing or commercialization, resulting in reduced productivity or complaints.

  The strength (compressive strength: JIS P 8126) of the shrink film of the present invention is preferably 2N or more, more preferably 5N or more. When the compressive strength is less than 2N, the label may be easily bent in the process of attaching the cylindrical shrink label to the container.

  Thermal shrinkage rate of main shrinkage direction (mainly stretched direction; width direction in the case of shrink film substantially uniaxially stretched in the width direction) at 90 ° C. for 10 seconds (warm water treatment) of the shrink film of the present invention Is preferably 15% or more, more preferably 25 to 70%. If the thermal shrinkage rate is less than 15%, the shrink label is not sufficiently contracted in the process of heat-adhering the shrink label to the container, so that it is difficult to follow the shape of the container, and the finish is particularly poor for a container having a complicated shape. May be. Further, the thermal contraction rate in the direction orthogonal to the main orientation direction is preferably -3 to 15%, more preferably -1 to 10%.

  The storage stability of the shrink film of the present invention (natural shrinkage rate: shrinkage rate after 30 days at 30 ° C.) is preferably 2% or less, more preferably 1.5% or less, and even more preferably 1%. It is as follows. If the film has a natural shrinkage rate of over 2%, it will cause large deformation (shrinkage) while it is stored before processing after manufacturing a shrink label, making subsequent processing difficult and reducing productivity. Or poor mounting on a container or the like, causing a complaint.

  The transparency (haze value: JIS K 7136) (unit:%) of the shrink film of the present invention is preferably less than 10, more preferably less than 5, and still more preferably less than 2. When the haze value is 10 or more, the inside of the shrink film (the side that becomes the container side when the label is attached to the container) is printed, and in the case of a shrink label that shows printing through the film, , Printing may become cloudy and decorative properties may be reduced.

  When the shrink film of the present invention is processed into a shrink label, the surface layer of the shrink film further includes a printed layer, a coating layer, a resin layer, an anchor coat layer, a primer coat layer, an adhesive layer, an adhesive resin layer, and a heat-sensitive adhesive. An agent layer or the like can be provided, and a layer of non-woven fabric, paper, plastic, or the like may be provided as necessary.

  In particular, when a printing layer is provided, the printing layer is a layer displaying a trade name, an illustration, handling precautions, and the like, and can be formed by a conventional printing method such as gravure printing or flexographic printing. The printing ink used for forming the printing layer is composed of, for example, a pigment, a binder resin, and a solvent. Examples of the binder resin include acrylic, urethane, polyamide, vinyl chloride-vinyl acetate copolymer, cellulose, and nitrocellulose. A general resin such as a system can be used. The printed layer is preferably provided on one surface of the shrink film of the present invention. When the printed layer is applied to the surface on the inner side (that is, the container side) when being attached to the container, The print layer is preferred since it does not peel off or become dirty. The thickness of the printing layer is not particularly limited and is, for example, about 0.1 to 10 μm.

  By attaching a shrink label using the shrink film of the present invention to the container, a container with a label can be obtained. Such containers include, for example, soft drink bottles such as PET bottles, milk bottles for home delivery, food containers such as seasonings, alcohol beverage bottles, pharmaceutical containers, chemical containers such as detergents, sprays, cups, etc. This includes noodle containers. The shape of the container includes various shapes such as a cylindrical shape, a square bottle, and a cup type. Further, the material of the container includes plastic such as PET, glass, metal and the like. In addition, the adherend of the shrink label of this invention is not restricted to a container.

  Below, although an example of the manufacturing method of the shrink label using this shrink film and this shrink film and a container with a label is demonstrated, the manufacturing method of this invention is not limited to this. In the following description, in the order of the process, the original film after stretching is “shrink film”, the one subjected to printing treatment is “long shrink label”, and further processed into a cylindrical shape with a long length. It is described as “long cylindrical shrink label”.

[Shrink film]
The polystyrene resin, the oxazoline group-containing styrene copolymer and the polyester resin used for the shrink film of the present invention can be polymerized using a known method. These resins can also be obtained on the market.

  In addition, when producing the mixed resin pellet which consists of a polystyrene-type resin used for the center layer of a shrink film and an oxazoline group containing styrene-type copolymer, it can produce by a cosolvent method or a melt-kneading method. Of these, the melt-kneading method is preferable from the viewpoint of excellent environmental performance without using a solvent and the like and advantageous in terms of production efficiency and economy. When the melt-kneading method is used, the polystyrene resin and the oxazoline group-containing styrene copolymer are put into a uniaxial or biaxial extruder or a biaxial kneader, kneaded, and then extruded to be pelletized. In this case, the kneading temperature is preferably 180 to 230 ° C., and the residence time is preferably about 5 minutes.

  Next, an unstretched laminated film is produced using the obtained raw material. In the present invention, a coextrusion method is used as a lamination method. By using the coextrusion method, the polymers of the respective film layers come into contact with each other in the molten state at the lamination interface, so that the interaction effect between the polymers is increased and high interlayer strength is obtained.

  An example using two extruders (extruders a and b) is shown below. In addition, when providing the surface layer of each different thickness on both sides of a center layer, you may perform coextrusion using three extruders. The extruder a set to a predetermined temperature is charged with dry blending of polystyrene resin and oxazoline group-containing styrene copolymer pellets, and the polyester resin is charged into the extruder b. The polymer melt-extruded from the above two extruders is merged using a merge block such as a manifold or a feed block into a b / a / b laminated structure, and then extruded from a T die, a circular die, or the like. Then, it is rapidly cooled using a cooling drum or the like to produce an unstretched laminated film. At this time, if necessary, the supply amount may be adjusted using a gear pump, and it is preferable to remove foreign substances using a filter because film tearing can be reduced. Further, if necessary, other admixtures such as a lubricant, an antistatic agent, an antifogging agent and an antioxidant may be mixed.

  In the case of the b / a / b lamination, it is preferable that the adapter temperatures of the respective layers at the time of merging are equal from the viewpoint of stability at the time of polymer merging. The adapter temperature is preferably 200 to 240 ° C, more preferably 220 to 230 ° C, from the viewpoint of suppressing the difference in moldability due to the difference in viscosity between the polyester resin and the polystyrene resin. If it is less than 200 ° C., the polyester resin may be insufficiently melted, and if it exceeds 240 ° C., the polystyrene resin may be decomposed.

  The interlayer strength of the unstretched laminated film obtained above is preferably 2 (N / 30 mm) or more, and more preferably 5 (N / 30 mm) or more. When the interlayer strength is less than 2 (N / 30 mm), the interlayer strength of the produced shrink film is low, and after processing and commercialization, peeling occurs at the seal portion, resulting in decreased productivity. Or cause a complaint.

  Next, the obtained unstretched laminated film is stretched to produce a long shrink film. The stretching may be biaxial stretching in the longitudinal direction (longitudinal direction; MD direction) and width direction (transverse direction; TD direction), or may be uniaxial stretching in the longitudinal direction or the width direction. The stretching method may be any of a roll method, a tenter method, and a tube method. The stretching treatment is performed at a temperature of about 70 to 100 ° C., if necessary, for example, 1.01 to 1.5 times, preferably about 1.05 to 1.3 times in the longitudinal direction, and then 3 in the width direction. It is often carried out by stretching about 6 times, preferably about 4 to 5.5 times.

  The surface of the shrink film of the present invention may be subjected to a conventional surface treatment such as corona discharge treatment or in-line coating, if necessary.

[Shrink label]
Next, after forming a printing layer on at least one surface of the long shrink film obtained as described above to produce a long shrink label, the long shrink shrink is formed into a cylindrical shape. Make a label. The method is shown below.

  The obtained elongated shrink film is subjected to a printing process. As a printing method, a conventional method can be used. For example, it can be formed by gravure printing or flexographic printing. After printing, it is slit to a predetermined width and wound into a roll shape to obtain a roll-like product of a long shrink label.

  Next, while rolling out the roll-like material, the shrink film is formed into a cylindrical shape so that the width direction of the shrink film is the circumferential direction of the label and the printing layer is inside. Specifically, after a long shrink label is formed into a cylindrical shape, a solvent or an adhesive (such as tetrahydrofuran (THF)) having a width of about 2 to 4 mm in a longitudinal direction on one side edge of the label ( The solvent is applied to the inner surface, and the coated portion of the solvent is superimposed on the outer surface of the other side edge portion and adhered to the outer surface (center seal), and is a long cylindrical shrink label continuous body. To obtain a long cylindrical shrink label. In addition, it is preferable that the part which coats said solvent etc. is not printed.

  In the case where a perforation for label excision is provided, a perforation having a predetermined length and pitch is formed in the longitudinal direction. The perforation can be applied by a conventional method (for example, a method of pressing a disk-shaped blade having a cut portion and a non-cut portion repeatedly formed around it, a method using a laser, or the like). The process stage for perforating can be appropriately selected after the printing process and before and after the cylindrical processing process.

[Container with label]
Finally, the long cylindrical shrink label obtained above is cut and then attached to a predetermined container, and the label is contracted by heat treatment, and a container with a label is prepared by closely contacting the container.

  The above long cylindrical shrink label is supplied to an automatic label mounting device (shrink labeler), cut to the required length, and then externally fitted into a container filled with contents, and a hot air tunnel or steam tunnel at a predetermined temperature is attached. Passed or heated with radiant heat such as infrared rays to cause heat shrinkage and adhere to the container to obtain a labeled container. Examples of the heat treatment include treatment with 90 ° C. steam.

[Methods for measuring physical properties and methods for evaluating effects]

(1) Interlayer strength between unstretched film and shrink film (T-type peeling)
Evaluation was performed using unstretched films (thickness: 200 to 250 μm) of Examples and Comparative Examples. A strip-shaped sample having a width of 30 mm in the longitudinal direction (film forming direction) of the unstretched film and long in the unstretched film width direction was collected. Hereinafter, the sample width direction refers to the longitudinal direction of the unstretched film.
A T-type peel test (based on JIS K 6854-3) was performed using the long side direction of the sample (width direction of the unstretched film) as the measurement direction. The T-type peel test was performed under the following conditions by peeling between the weakest layers from the edge of the sample and peeling each layer, chucking each edge, and pulling with a tensile tester.
The average value of the peel loads with a peel length (crosshead moving distance) of 50 mm to 150 mm was defined as the interlayer strength (N / 30 mm).
Interlaminar strength (◎) is excellent when the interlaminar strength is so high that the base material breaks without peeling between layers, and when the interlaminar strength is 5 N / 30 mm or more, good interlaminar strength (○ ) When it was 2N / 30 mm or more and less than 5N / 30 mm, it was judged that the usable interlayer strength (Δ) was less than 2N / 30 mm (×).
Measuring device: Shimadzu Corporation autograph (AGS-50G: load cell type 500N)
Temperature and humidity: Temperature 23 ± 2 ° C, humidity 50 ± 5% RH (JIS K 7000 standard temperature state 2nd grade)
Initial chuck interval: 50 mm
Sample width: 30mm
Number of tests: 3 times Crosshead moving speed: 200 mm / min

Subsequently, also about the shrink film (after extending | stretching) of an Example and a comparative example, the sample was produced by the method similar to the above, and the interlayer intensity | strength was measured.
When peeling, it does not peel between layers, or when the interlayer strength is 1.5 N / 30 mm or more, good interlayer strength (◯), and when it is less than 1.5 N / 30 mm, the interlayer strength is inferior (× ).

(2) Shrinkage characteristics (90 ° C thermal shrinkage)
A square sample piece of 100 mm (film longitudinal direction) × 100 mm (film width direction) was prepared from the obtained shrink film.
The sample piece was heat-treated for 10 seconds (under no load) in warm water at 90 ° C., the dimensions of the sample before and after the heat treatment were read, and the thermal shrinkage rate was calculated by the following formula. The average value of the test number of 5 times was defined as the shrinkage rate.
Those with a shrinkage ratio of 30% or more in the main orientation direction are excellent shrinkage characteristics (◎), those with 25% or more and less than 30% are good shrinkage properties (◯), those with 15% or more and less than 25% are used. A possible level of shrinkage characteristics (Δ), less than 15% were judged as poor shrinkage characteristics (x).
In the examples and comparative examples, the main orientation direction was the width direction of the shrink film.
Shrinkage rate (%) = (L ₀ −L ₁ ) / L ₀ × 100
L ₀ : dimension of the sample before heat treatment (longitudinal direction or width direction)
L ₁ : Sample dimensions after heat treatment (same direction as L ₀ )

(3) Haze (transparency)
Evaluation was performed using a shrink film (film thickness 40 μm) obtained by the methods of Examples and Comparative Examples.
Measurement was performed according to JIS K 7105. Excellent transparency (◎) when haze (unit:%) is less than 2.0, good transparency (◯) when 2.0 or more and less than 5.0, 5.0 or more and less than 10.0 In the case of (1), a usable level of transparency (Δ), and in the case of 10.0 or more, it was judged that the transparency was poor (x).
In addition, what is necessary is just to convert and evaluate to 40 micrometers thickness about the sample from which thickness differs.

(4) Compressive strength (ring crush method)
Evaluation was performed using a shrink film (film thickness 40 μm) obtained by the methods of Examples and Comparative Examples.
Based on JIS P 8126, the compressive strength of the shrink film was measured under the following conditions. The measurement direction is the longitudinal direction. As a result of the measurement, those with a compressive strength of 5N or more have excellent compressive strength (）), those with 3.5N or more and less than 5N have good compressive strength (○), those with 2N or more and less than 3.5N can be used. A compressive strength of a certain level (Δ), and a compressive strength of less than 2N were judged to be inferior (x).
Measuring device: Shimadzu Corporation autograph (AGS-50G: load cell type 500N)
Sample size: 15 mm (longitudinal direction) x 152.4 mm (width direction)
Number of tests: 5

(5) Natural contraction (change over time)
Using a sample having the same size as (1), the sample piece was treated for 30 days in a constant temperature and humidity chamber maintained at 30 ° C., and the natural shrinkage was calculated by the following formula. The measurement was performed only in the width direction.
Those with a natural shrinkage rate of less than 1.0% have excellent storage stability (◎), 1.0% or more, and those with less than 1.5% have good storage stability (○), 1.5% or more, Those with less than 2.0% were judged to be usable storage stability (Δ), and those with 2.0% or more were judged to have poor storage stability (x).
Natural shrinkage (%) = (L ₂ −L ₃ ) / L ₂ × 100
L ₂ : Size of sample before processing L ₃ : Size of sample after processing

  Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

Example 1
As a central layer material, 80 parts by weight of a styrene-butadiene-isoprene-styrene block (SBIS) copolymer (Asaflex Chemicals Co., Ltd. “Asaflex 1100”), a styrene-2-isopropenyl-2-oxazoline copolymer (Japan) Catalyst (Epocross RPS1005), styrene content: 2-isopropenyl-2-oxazoline content = 95: 5 (wt%) 20 parts by weight of raw material (styrene component: 80.5 wt%, conjugate) Diene component: 18.5% by weight, oxazoline component: 1% by weight).
As a surface layer material, CHDM copolymerized PET (“EMBRACE (embrace) 21214” manufactured by Eastman Chemical Co .; copolymerization ratio (molar ratio) 70:30) of ethylene glycol and 1,4-cyclohexanedimethanol) was used.
The center layer raw material was charged into the single screw extruder a, and the surface layer raw material was charged into the single screw extruder b, both of which were melted at 250 ° C. and then extruded at 240 ° C. From the T die (slit interval: 1 mm), the resin extruded from the extruder b is merged (adapter temperature: 220 ° C.) using a merge block so that both sides of the resin layer extruded from the extruder a are on both sides. After the extrusion, it was rapidly cooled on a casting drum cooled to 25 ° C. to obtain a two-kind three-layer laminated unstretched film. The lamination thickness ratio of the unstretched film was surface layer / center layer / surface layer = 1/4/1. As shown in Table 1, the obtained unstretched film had good interlayer strength.
Next, the unstretched film was stretched 1.10 times at 85 ° C. in the longitudinal direction using a roll stretching machine, and then stretched 5.0 times at 85 ° C. in the width direction, thereby mainly uniaxially. A biaxially stretched film shrinking in the direction was obtained. The film-forming speed was adjusted to obtain a shrink film having a total film thickness of 40 μm (layer thickness ratio: 1/4/1).
As shown in Table 1, the obtained shrink film had excellent properties in terms of interlayer strength, shrinkage properties, compressive strength, transparency, and natural shrinkage.

Example 2
As shown in Table 1, a shrink film was obtained in the same manner as in Example 1 except that the surface layer material was changed.
As shown in Table 1, the obtained shrink film had excellent properties in terms of interlayer strength, shrinkage properties, compressive strength, transparency, and natural shrinkage.

Example 3
As shown in Table 1, a recovered film was added to the center layer, and a shrink film was obtained in the same manner as in Example 1. In addition, the film after forming into a film was used for evaluation, continuing collection | recovery over 2 hours.
As shown in Table 1, the obtained shrink film had excellent properties in terms of interlayer strength, shrinkage properties, compressive strength, transparency, and natural shrinkage.

Examples 4-6
As shown in Table 1, the raw material composition of the center layer was changed, and a shrink film was obtained in the same manner as in Example 1. In Example 6, the film after film formation was used for the evaluation for 2 hours or longer.
As shown in Table 1, the obtained shrink film had excellent properties in terms of interlayer strength, shrinkage properties, compressive strength, transparency, and natural shrinkage.

Urethane ink (trade name “NT-HIRAMIC”, manufactured by Dainichi Seika Kogyo Co., Ltd.) is applied to one side of the shrink film (thickness 40 μm) obtained in the above example by gravure printing to form a printing layer. A shaku shrink label was obtained. Furthermore, it was rolled into a cylindrical shape so that the printing surface was inside and the width direction of the film was the circumferential direction, and center-sealed with tetrahydrofuran (THF) to obtain a long cylindrical shrink label. Finally, the long cylindrical shrink label is supplied to an automatic label mounting apparatus (LSA-9250 manufactured by Fujistec Corp.) and cut into each label, while a container (500 ml heat-resistant square PET bottle manufactured by Toyo Seikan Co., Ltd.) And heated and shrunk in a steam tunnel with an atmospheric temperature of 90 ° C. to obtain a labeled container.
In the above printing process, label mounting process, etc., troubles such as coating failure and buckling did not occur, the productivity was good, and the obtained labeled container was also excellent.

Comparative Example 1
As shown in Table 1, an unstretched film and a shrink film were obtained in the same manner as in Example 1 without using an oxazoline group-containing polystyrene-based resin as the center layer raw material.
The obtained film was inferior in interlayer strength.

Comparative Example 2
As shown in Table 1, an unstretched film and a shrink film were obtained in the same manner as in Example 1 without using a polystyrene-based resin as the center layer material.
The obtained film was inferior in shrinkage characteristics.

Comparative Example 3
As shown in Table 1, the raw material composition of the center layer raw material was changed, and an unstretched film and a shrink film were obtained in the same manner as in Example 1.
The obtained film was inferior in interlayer strength.

Details of the resins described in Table 1 are shown in Table 2.

Claims (7)

  A film comprising a surface layer / center layer / surface layer two-layer three-layer structure having a surface layer on both sides of the center layer, wherein the surface layer is a resin layer composed of 90 to 100% by weight of a polyester-based resin, and the center layer is a styrene unit A shrink film comprising at least 60 to 90% by weight, a conjugated diene unit of 5 to 30% by weight, and an oxazoline unit of 0.5 to 5% by weight.   The shrink film according to claim 1, wherein the conjugated diene is butadiene and / or isoprene.   The shrink film according to claim 1 or 2, wherein the center layer is a resin layer further containing 5 to 20% by weight of ethylene terephthalate units.   A film composed of two layers and three layers of surface layer / center layer / surface layer having surface layers on both sides of the center layer, wherein the surface layer is a resin layer composed of 90 to 100% by weight of a polyester-based resin, and the center layer is a polystyrene-based film A shrink film characterized by being a resin layer comprising at least 50 to 90% by weight of a resin (excluding those containing an oxazoline group) and 10 to 50% by weight of an oxazoline group-containing styrene copolymer.   The shrink film according to claim 4, wherein the central layer is a resin layer further comprising 5 to 20% by weight of a polyester resin.   The shrink film according to any one of claims 1 to 5, wherein the ratio of the center layer thickness to the surface layer thickness (for one layer) (center layer thickness / surface layer thickness) is 2 to 6.   The interlayer strength of the shrink film is 1.5 (N / 30 mm) or more, and the compressive strength (conforms to JIS P 8216, converted to a film thickness of 40 μm) of the shrink film is 5 N or more. The shrink film as described.