JP4815214B2 - Heat-shrinkable film, molded article using the heat-shrinkable film, heat-shrinkable label, and container using or fitted with the molded article - Google Patents

Description

  The present invention relates to a heat-shrinkable film, a molded article using the heat-shrinkable film, a heat-shrinkable label, and a container equipped with the molded article or the label, and more particularly, excellent shrinkage characteristics and heat resistance. Further, heat shrinkable films suitable for applications such as shrink wrapping, shrink-bound wrapping, and shrink labels, as well as molded articles using the heat shrinkable films, heat shrinkable labels, and molded articles using or the labels Relates to a container equipped with.

  Currently, soft drinks such as juice and alcoholic drinks such as beer are sold in a state of being filled in a container such as a bottle or a plastic bottle. At that time, in order to differentiate from other products and improve the visibility of the products, a heat-shrinkable label printed on the outside of the container is attached. As a material for the heat-shrinkable label, polyvinyl chloride (PVC), polystyrene, aromatic polyester or the like is generally used.

  On the other hand, the effective use of exhaustible resources has recently been emphasized, and the use of renewable resources has become an important issue. At present, the use of plastics made from plant materials is attracting the most attention as a solution. This plant-derived plastic not only uses non-depleted resources, but can save exhaustible resources during plastic production, and also has excellent recyclability.

  Among these plant-derived plastics, polylactic acid resins are made from lactic acid obtained by fermentation of starch, can be mass-produced by chemical engineering, and have excellent transparency and rigidity. As an alternative material for polyester (polyethylene terephthalate), it has attracted attention in the field of film packaging materials and injection molding.

  However, when polylactic acid is used as a material for heat-shrinkable labels, it is rigid at room temperature, has low-temperature shrinkability, and has good natural shrinkage, but it is a very brittle material. There is a problem that sometimes contraction spots and wrinkles are likely to occur. In addition, the polylactic acid-based heat-shrinkable film also has a problem that when heated, crystallization proceeds and sufficient heat-shrinkage characteristics cannot be obtained.

  As means for solving the above problem, a film in which the copolymerization ratio of L-lactic acid and D-lactic acid in a polylactic acid resin is adjusted is known (see Patent Document 1). However, although this film can suppress crystallization during heating, the problem of causing spots, wrinkles, and avatars due to rapid shrinkage cannot be sufficiently solved.

  In addition, attempts have been made to improve shrink finish by adjusting the crystallinity of the polylactic acid resin and further blending an aliphatic polyester resin (see Patent Document 2). However, compared to PVC heat-shrinkable films, it is still difficult to say that the shrink finish is sufficient.

  Furthermore, since the polylactic acid-based resin is brittle, the material itself has a problem that when it is molded into a single sheet or film, sufficient strength cannot be obtained and it is difficult to put it into practical use.

  Containing an aliphatic polyester other than polylactic acid (see Patent Document 3), polycaprolactone (see Patent Document 4), a copolymer polyolefin such as an ethylene-vinyl acetate copolymer (see Patent Document 5), etc. The method of making it known is known. These mainly have the purpose of improving brittleness while maintaining the transparency of the polylactic acid-based resin film, and there still remains an insufficient point with respect to shrink finish.

  Furthermore, as a technique for improving the brittleness of the polylactic acid-based resin, a composition comprising polylactic acid and a modified olefin compound (see Patent Document 6), a polymer containing lactic acid as a main component, an aliphatic carboxylic acid, and a chain molecular diol A plasticized polylactic acid composition (see Patent Document 7) comprising a plasticizer of an aliphatic polyester containing as a main component, a biodegradable resin composition comprising polylactic acid and an epoxidized diene block copolymer ( Patent Document 8), lactic acid-based polymer composition (Patent Document 9) comprising polylactic acid, aliphatic polyester, and polycaprolactone, crystalline polylactic acid, and at least one rubber selected from natural rubber and polyisoprene A method using a polylactic acid-based resin composition (Patent Document 10) or the like comprising components is disclosed.

  However, when the above polycaprolactone, modified olefin compound, epoxidized diene block copolymer, natural rubber, polyisoprene, etc. are mixed with lactic acid resin, the impact resistance is improved, but as a result, transparency For example, it is difficult to say that the technique is sufficient for use in applications where it is necessary to check contents such as packaging materials.

  In addition, a polyacetal resin and diene rubber, natural rubber, silicone rubber, polyurethane rubber, or a multilayer structure having at least one selected from styrene units and butadiene units in a shell layer in a shell layer and methyl (meth) acrylate in a core layer, etc. Although a method for improving impact resistance by blending an impact modifier with a polylactic acid resin is known (see Patent Document 11), it is not sufficient as a heat shrink film.

Further, a technique of blending a polylactic acid resin to the rubber polymer and graphs preparative copolymer of a vinyl alone obtained by graft polymerization has been proposed (see Patent Document 12), as a heat shrinkable film Is not enough.

JP 2003-119367 A JP 2001-11214 A JP-A-9-169896 JP-A-8-300481 JP-A-9-151310 JP 09-316310 A JP 2000-191895 A JP 2000-219803 A JP 2001-031853 A JP 2003-183488 A JP 2003-286400 A JP 2004-285258 A

  The present invention has been made in view of the above-mentioned problems, and an object of the present invention is excellent in mechanical properties such as heat shrinkage properties, impact resistance, transparency, and shrink finish, shrink shrink packaging, shrink bundled packaging. Another object is to obtain a heat-shrinkable film suitable for applications such as shrinkage labels.

  Another object of the present invention is to provide a molded article using the heat-shrinkable film, heat-shrinkable label and the molded article or heat-shrinkable label suitable for applications such as shrink wrapping, shrink-bound wrapping and shrinkage label. Is to obtain a container.

  The present invention comprises a mixed resin containing a polylactic acid resin and a silicone acrylic composite rubber as main components, and a mass ratio of the polylactic acid resin and the silicone acrylic composite rubber of 95/5 to 50/50, or This mixed resin layer has at least one layer, and the polylactic acid resin is composed of a copolymer of D-lactic acid and L-lactic acid, or a mixed resin of this copolymer, and is composed of D-lactic acid and L-lactic acid. The D / L ratio is 3/97 to 15/85, or 85/15 to 97/3, stretched in at least one direction, and immersed in 80 ° C. warm water for 10 seconds in the direction of main shrinkage of the film. The above problems have been solved by using a heat-shrinkable stretched film having a heat shrinkage rate of 20% or more.

  According to the present invention, since a stretched film having a predetermined heat shrinkage ratio is used using a mixed resin containing a silicone acrylic composite rubber in a predetermined ratio, mechanical properties such as heat shrinkage characteristics, impact resistance and transparency, In addition, the shrinkage finish is excellent.

  Furthermore, according to the present invention, a molded product using the heat-shrinkable film suitable for applications such as shrink-wrapping, shrink-bound packaging, and shrink-label, a heat-shrinkable label, and a container equipped with the molded product or the heat-shrinkable label Can be provided.

  Hereinafter, the heat-shrinkable film, molded product, heat-shrinkable label, and container equipped with the molded product or heat-shrinkable label according to the present invention (hereinafter referred to as “the film of the present invention” and “the molded product of the present invention”, respectively) , “The label of the present invention” and “the container of the present invention”).

  In the present specification, “main component” is intended to allow other components to be included as long as the action and effect of the resin constituting each layer is not hindered. Furthermore, although this term does not restrict | limit a specific content rate, it is a component which occupies 70 mass% or more of the whole component of each layer, Preferably it is 80 mass% or more, More preferably, it is 90 mass% or more.

[Heat shrinkable film]
The film of the present invention is a film made of a mixed resin containing polylactic acid resin and silicone acrylic composite rubber as main components.

<Polylactic acid resin>
The polylactic acid-based resin refers to a homopolymer of D-lactic acid or L-lactic acid, or a copolymer thereof. Specifically, poly (D-lactic acid) having a structural unit of D-lactic acid, a structural unit (L-lactic acid), which is L-lactic acid, and poly (DL-lactic acid), which is a copolymer of L-lactic acid and D-lactic acid, and copolymerization of D-lactic acid and L-lactic acid. A mixed resin of a plurality of the above copolymers having different ratios is also included.

  The copolymer of L-lactic acid and D-lactic acid has a copolymerization ratio of D-lactic acid and L-lactic acid (hereinafter abbreviated as “D / L ratio”) of 3/97 to 15/85, or It is preferably 85/15 to 97/3, more preferably 5/95 to 15/85, or 85/15 to 95/5, and 8/92 to 15/85, or 85/15 to 92. / 8 is more preferable, and 10/90 to 15/85, or 85/15 to 90/10 is most preferable. When the copolymerization ratio of D-lactic acid is higher than 97 or less than 3, it exhibits very high crystallinity, has a high melting point, and tends to be excellent in heat resistance and mechanical properties. However, when used as a heat-shrinkable film, it usually involves printing and a bag-making process using a solvent, so that the crystallinity of the constituent material itself can be lowered appropriately in order to improve printability and solvent sealability. Necessary. Moreover, when crystallinity is too high, orientation crystallization advances at the time of extending | stretching, and there exists a tendency for the film shrinkage | contraction characteristic at the time of heating to fall. Furthermore, even if the film has crystallization suppressed by adjusting the stretching conditions, crystallization proceeds prior to shrinkage due to heating during heat shrinkage, and as a result, there is a tendency to cause shrinkage unevenness or insufficient shrinkage. On the other hand, when the copolymerization ratio of D-lactic acid is less than 85 or higher than 15, the crystallinity is almost completely lost. As a result, when the labels collide with each other after heat shrinkage, they are fused by heat. Troubles such as end up occur easily. Therefore, by adjusting the composition ratio of D-lactic acid and L-lactic acid in the polylactic acid resin within the above range, it is possible to obtain a heat-shrinkable film having excellent shrinkage characteristics that does not cause the problems described above. Become.

  In the film of the present invention, it is possible to blend polylactic acid resins having different D / L ratios, and blending can adjust the D / L ratio of the polylactic acid resins more easily. preferable. In this case, the average value of the D / L ratios of a plurality of lactic acid polymers may be set within the above range. By blending two or more polylactic acid resins having different D / L ratios and adjusting the crystallinity according to the intended use, it is possible to balance heat resistance and heat shrinkage characteristics.

  The polylactic acid resin may be a copolymer of lactic acid and α-hydroxycarboxylic acid, aliphatic diol, or aliphatic dicarboxylic acid as long as the effects of the present invention are not impaired.

  Examples of the α-hydroxycarboxylic acid unit include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 2-hydroxy-n-butyric acid, 2-hydroxy-3,3-dimethylbutyric acid, and 2-hydroxy-3-methylbutyric acid. , Bifunctional aliphatic hydroxycarboxylic acids such as 2-methyllactic acid and 2-hydroxycaproic acid, and lactones such as caprolactone, butyrolactone and valerolactone.

  Examples of the diol unit include ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol and the like. Examples of the dicarboxylic acid unit include succinic acid, adipic acid, suberic acid, sebacic acid, and dodecanedioic acid.

  The copolymerization ratio in the copolymer of lactic acid and α-hydroxycarboxylic acid is not particularly limited, but the higher the occupancy ratio of lactic acid, the less the consumption of petroleum resources, which is preferable. It is preferable to copolymerize at a ratio not exceeding. Specifically, the copolymerization ratio of lactic acid and a copolymer of α-hydroxycarboxylic acid, aliphatic diol, or aliphatic dicarboxylic acid is lactic acid: α-hydroxycarboxylic acid, aliphatic diol, or aliphatic dicarboxylic acid = 95: 5 to 10:90, preferably 90:10 to 20:80, and more preferably 80:20 to 30:70. If the copolymerization ratio is within the above range, a film having a good balance of physical properties such as rigidity, transparency and impact resistance can be obtained.

  The weight (mass) average molecular weight of the polylactic acid-based resin is 20,000 or more, preferably 40,000 or more, more preferably 60,000 or more, and the upper limit is 400,000 or less, preferably 350,000 or less. More preferably, it is 300,000 or less. When the weight (mass) average molecular weight is 20,000 or more, an appropriate resin cohesive force can be obtained, and the film can be prevented from being insufficiently stretched or embrittled. On the other hand, if the weight (mass) average molecular weight is 400,000 or less, the melt viscosity can be lowered, which is preferable from the viewpoint of production and productivity improvement.

  As the polymerization method of the polylactic acid-based resin, a known method such as a condensation polymerization method or a ring-opening polymerization method can be employed. For example, in the case of a condensation polymerization method, a polylactic acid resin having an arbitrary composition can be obtained by directly dehydrating condensation polymerization of D-lactic acid, L-lactic acid, or a mixture thereof. Further, in the ring-opening polymerization method, a lactide which is a cyclic dimer of lactic acid is subjected to ring-opening polymerization in the presence of a predetermined catalyst while using a polymerization regulator or the like, if necessary. A lactic acid resin can be obtained. The lactide includes DL-lactide, which is a dimer of L-lactic acid. By mixing and polymerizing these as necessary, a polylactic acid resin having an arbitrary composition and crystallinity can be obtained. it can. Furthermore, a small amount of chain extender such as a diisocyanate compound, diepoxy compound, acid anhydride, acid chloride, etc. may be used for the purpose of increasing the molecular weight.

  As a commercial item of the said polylactic acid-type resin, "NatureWorks" (made by Nature Works LLC), "LACEA" (made by Mitsui Chemicals, Inc.) etc. are mentioned, for example.

<Silicone acrylic composite rubber>
Next, the silicone acrylic composite rubber will be described.
This silicone acrylic composite rubber is blended in order to improve the impact resistance of the polylactic acid resin. This silicone-acrylic composite rubber is excellent in low-temperature properties and has a high impact resistance improving effect, and because it is finely dispersed in the lactic acid resin by compounding with the acrylic, it hardly resists the transparency of the lactic acid resin. Impact properties can be greatly improved.

  This silicone acrylic composite rubber has a core-shell structure. As a specific example, the core portion is made of a copolymer of a siloxane compound and a (meth) acrylic monomer, and the shell portion is made of a homopolymer or copolymer of a (meth) acrylic monomer. Is mentioned.

  Examples of the siloxane compound include dimethylsiloxane. Moreover, as a (meth) acrylic-type monomer used for a core part, butyl (meth) acrylate, 2-ethylhexyl acrylate, etc. are mentioned. Furthermore, examples of the (meth) acrylic monomer used for the shell part include methyl (meth) acrylate.

  In the present specification, “(meth) acryl” means “acryl or methacryl”.

  When the silicone acrylic composite rubber having the above core-shell structure is used, since the shell portion has a polymer composed of a (meth) acrylic monomer, the affinity to the (meth) acrylic monomer in the core portion is high. And the affinity with the polylactic acid-type resin distribute | arranged to the outer side of a silicone acrylic composite rubber is high. For this reason, the silicone-acrylic composite rubber can have a stable core-shell structure, and can stably maintain a dispersed state in the mixed resin.

  A specific example of the silicone acrylic composite rubber is METABRENE S-2001 manufactured by Mitsubishi Rayon Co., Ltd.

  The blending amount of the silicone acrylic composite rubber is preferably 95/5 to 50/50 in terms of mass ratio of polylactic acid resin to silicone acrylic composite rubber (polylactic acid resin / silicone acrylic composite rubber), and 90/10. -60/40 is more preferable, and 85 / 15-70 / 30 is more preferable. By blending the silicone acrylic composite rubber within such a range, the impact resistance can be improved with almost no loss of the transparency of the polylactic acid resin.

<Additives to mixed resin>
Furthermore, according to the present invention, (meth) acrylic resin, polyethylene resin, polypropylene resin, polystyrene resin (GPPS (general-purpose polystyrene), HIPS (anti-resistant)) are used in the mixed resin as long as the effects of the present invention are not significantly impaired. Impact polystyrene), SBS (styrene-butadiene copolymer), SIS (styrene-isoprene copolymer), SEBS (styrene-ethylene-butylene-styrene copolymer), SEPS (styrene-ethylene-propylene-styrene copolymer) ), A styrene-carboxylic acid copolymer, etc. ) , at least one thermoplastic resin such as a polyamide-based resin and a polyoxymethylene-based resin can be further contained.

  In particular, since (meth) acrylic resins are compatible with polylactic acid resins, blending with polylactic acid resins enables adjustment of the glass transition temperature that affects shrinkage characteristics, and results in shrink finish. It becomes a resin effective for improvement.

  Among the (meth) acrylic resins, methacrylic resins are preferable. The methacrylic resin refers to a methyl methacrylate homopolymer or a copolymer of 50% by weight or more of methyl methacrylate and another vinyl monomer. Examples of the vinyl monomer include methacrylic acid esters, acrylic acid esters, unsaturated acids, styrene, α-methylstyrene, acrylonitrile, methacrylonitrile, maleic anhydride, phenylmaleimide, cyclohexylmaleimide, and the like.

  Specific examples of the methacrylic acid esters include ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl methacrylate, and the like.

  Specific examples of the acrylate esters include methyl acrylate, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, and the like. Is mentioned. Furthermore, examples of the unsaturated acids include methacrylic acid and acrylic acid.

  The copolymer constituting the methacrylic resin further includes elastomer components such as polybutadiene, butadiene-butyl acrylate copolymer, polybutyl acrylate copolymer, glutaric anhydride units, and glutarimide units. It may be included.

  Among these, from the viewpoint of rigidity and moldability, polymethyl methacrylate (PMMA), which is a homopolymer of methyl methacrylate, and methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, acrylic A copolymer composed of two or more selected from acid butyl, acrylic acid, and methacrylic acid is preferably used.

  In the present invention, polymethyl methacrylate (PMMA) is most preferably used. By blending the present resin, it is possible to increase the glass transition temperature of the methacrylic resin, and as a result, the rapid onset of shrinkage at the time of shrinkage can be relieved, and good shrinkage finish can be obtained.

  The content of the (meth) acrylic resin is 5% by mass or more, preferably 10% by mass or more, more preferably 15% by mass or more, and 30% by mass or less, preferably 25% by mass or less, more preferably. It is 20 mass% or less. If the content of the (meth) acrylic resin is 5% by mass or more, the glass transition temperature is shifted to the high temperature side, and the shrinkage start temperature can be brought close to the shrinkage temperature range, so that a gentle shrinkage curve is obtained, As a result, the shrinkage finish can be improved. On the other hand, if the content is 30% by mass or less, it is preferable because a significant decrease in impact resistance of the film can be suppressed.

  Examples of commercially available (meth) acrylic resins include “Sumipex” (manufactured by Sumitomo Chemical Co., Ltd.), “Acrypet” (manufactured by Mitsubishi Rayon Co., Ltd.), and “Parapet” (manufactured by Kuraray Co., Ltd.). , “Artugrass” (manufactured by Atofina Japan), “Delpet” (manufactured by Asahi Kasei Corporation), and the like.

  Furthermore, in the present invention, silicone acrylic composite rubber is used in the above mixed resin for the purpose of improving impact resistance, transparency, molding processability and various properties of heat shrinkable film within a range that does not significantly impair the effects of the present invention. Other soft resins may be added.

  Examples of the soft resin include aliphatic polyester resins excluding polylactic acid resins, aromatic aliphatic polyester resins, copolymers of diol, dicarboxylic acid, and lactic acid resin, core-shell structure type rubber, and ethylene-acetic acid. Vinyl copolymer (EVA), ethylene-acrylic acid copolymer (EAA), ethylene-ethyl acrylate copolymer (EEA), ethylene- (meth) acrylic acid copolymer (EMA), ethylene-methyl (meta) ) Acrylic acid copolymer (EMMA) and the like.

  Among the above soft resins, aliphatic polyester resins excluding polylactic acid resins are particularly preferable. The aliphatic polyester resin excluding the polylactic acid resin is an aliphatic polyester mainly composed of an aliphatic dicarboxylic acid or a derivative thereof and an aliphatic polyhydric alcohol. Examples of the aliphatic dicarboxylic acid residue constituting the aliphatic polyester resin include residues derived from succinic acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid and the like. Examples of the aliphatic polyhydric alcohol residue include aliphatic diol residues derived from ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol and the like.

  The aliphatic dicarboxylic acid residue preferably used in the present invention is a succinic acid residue or an adipic acid residue, and the aliphatic polyhydric alcohol residue is a 1,4-butanediol residue.

  Furthermore, the aliphatic dicarboxylic acid suitably used in the present invention preferably has a melting point of 100 ° C. or higher and 170 ° C. or lower. By adjusting the melting point to the range, the aliphatic polyester can maintain a crystalline state even in the range of 60 ° C. to 100 ° C. in which the normal shrinkage is performed. As a result, it plays a role like a column at the time of shrinkage. As a result, it is possible to obtain even better shrinkage finish.

The content of the aliphatic polyester resin excluding the polylactic acid resin is 5% by mass or more, preferably 10% by mass or more, more preferably 15% by mass or more, and 30% by mass or less, preferably 25% by mass. Hereinafter, it is more preferably 20% by mass or less. If the content of the aliphatic polyester resin excluding the polylactic acid resin is 5% by mass or more, the effect of suppressing the shrinkage in the direction perpendicular to the stretching direction can be exhibited, the shrinkage finish can be improved, and 30% by mass or less. If it is, the fall of transparency can be suppressed.

  In the present invention, a plasticizer may be further added as long as the effects of the present invention are not significantly impaired in order to improve various properties of impact resistance, transparency, moldability and heat shrinkable film. Examples of the plasticizer include fatty acid ester plasticizers, phthalate ester plasticizers, trimellitic ester plasticizers, and the like.

  Specific examples of the fatty acid ester plasticizer include dibutyl adipate, diisobutyl adipate, diisononyl adipate, diisodecyl adipate, di (2-ethylhexyl) adipate, di (n-octyl) adipate, di (n-decyl) adipate, dibutyldi Examples include glycol adipate, dibutyl sebacate, di (2-ethylhexyl) sebacate, di (n-hexyl) azelate, di (2-ethylhexyl) azelate, di (2-ethylhexyl) dodecanedionate, and the like.

  Specific examples of the phthalate ester plasticizer include diisononyl phthalate, diisodecyl phthalate, and di (2-ethylhexyl) phthalate. Further, specific examples of the trimellitic acid ester plasticizer include tri (2-ethylhexyl) trimellitate.

  Furthermore, in the present invention, in the mixed resin of the polylactic acid-based resin and the silicone acrylic composite rubber, in addition to the components described above, the molding processability, productivity, and heat shrinkage are within the range not significantly impairing the effects of the present invention. Recycled resin generated from trimming loss such as film ears, inorganic particles such as silica, talc, kaolin and calcium carbonate, pigments such as titanium oxide and carbon black, difficult Additives such as a flame retardant, a weather resistance stabilizer, a heat resistance stabilizer, an antistatic agent, a melt viscosity improver, a crosslinking agent, a lubricant, a nucleating agent, and an anti-aging agent can be appropriately added.

<Film production method>
The film of this invention can be manufactured by a well-known method using the said mixed resin. The form of the film may be either flat or tube-like, but the flat form is preferable in terms of productivity (a few products can be taken in the width direction of the original film) and printing on the inner surface. .

  As a method for producing a flat film, for example, a resin is melted by using a plurality of extruders, co-extruded from a T die, solidified by cooling with a chilled roll, roll-stretched in the vertical direction, and tenter-stretched in the horizontal direction. In the case of printing, annealing, cooling, and printing, a corona discharge treatment is performed on the surface, and the film is obtained by winding with a winder. Moreover, the method of cutting open the film manufactured by the tubular method and making it planar is also mentioned.

  The stretching ratio in the stretching is such that the longitudinal direction is 2 to 10 times, the transverse direction is 2 to 10 times, and preferably 3 to 6 times in the longitudinal direction, for applications such as overlapping and shrinking in two directions. Hereinafter, the horizontal direction is about 3 to 6 times. On the other hand, in applications such as heat-shrinkable labels that shrink mainly in one direction, the direction corresponding to the main shrinkage direction is 2 to 10 times, preferably 3 to 7 times, more preferably 3 to 5 times. The direction perpendicular thereto is 1 to 2 times (where 1 times refers to the case where the film is not stretched), preferably 1.01 to 1.5 times, and is substantially uniaxially stretched. It is desirable to select a magnification ratio in the category. A biaxially stretched film stretched at a stretch ratio within the above range does not have an excessively large thermal shrinkage rate in the direction orthogonal to the main shrinkage direction.For example, when used as a shrinkage label, It is preferable because the so-called vertical shrinkage phenomenon, in which the film is thermally contracted in the vertical direction, can be suppressed.

  The stretching temperature needs to be changed depending on the glass transition temperature of the resin to be used and the properties required for the heat-shrinkable film, but is generally 60 ° C. or higher, preferably 70 ° C. or higher, and the upper limit is 100 ° C. or lower, preferably 90 ° C. It is controlled within the following range.

  Next, the stretched film is subjected to a heat treatment or relaxation treatment at a temperature of about 50 ° C. or more and 100 ° C. or less for the purpose of reducing the natural shrinkage rate or improving the heat shrink property, if necessary. It cools rapidly within the time not to relax, and becomes a heat-shrinkable film.

  Further, the film of the present invention can be subjected to surface treatment and surface treatment such as corona treatment, printing, coating, and vapor deposition, as well as bag making processing and perforation processing using various solvents and heat sealing, if necessary. .

<Film structure>
The layer structure of the film of the present invention may be a single layer, or as a laminated structure for the purpose of imparting surface functional properties such as slipperiness, heat resistance, solvent resistance, and easy adhesion to the film surface. Also good. That is, it may be a laminate having at least one mixed resin layer. For example, when layers (II) and (III) having different resin compositions or additives are laminated on the layer (I) made of the mixed resin of the present invention, (I) / (II), (II) / (I ) / (II), (II) / (I) / (III), (II) / (I) / (III) / (II) and the like. Moreover, the lamination ratio of each layer can be adjusted timely according to a use and the objective.

In the film of the present invention, the preferred layer structure is when the layer (II) is a layer mainly composed of a polylactic acid resin. In particular, the D / L ratio of the polylactic acid resin constituting the layer (II) is preferably different from the D / L ratio of the polylactic acid resin constituting the layer (I). By adjusting the D / L ratio and changing the crystallinity in the (I) layer and the (II) layer, better shrink finish can be realized.

  Examples of the method for forming the laminate include a co-extrusion method, a method of forming a film of each layer, and then superposing and heat-sealing, a method of bonding with an adhesive, and the like.

  The total thickness of the film of the present invention is not particularly limited, whether it is a single layer or a laminate, but it is preferably thinner from the viewpoint of transparency, shrinkage workability, raw material cost, and the like. Specifically, the total thickness of the stretched film is preferably 80 μm or less, preferably 70 μm or less, and more preferably 50 μm or less. Further, the lower limit of the total thickness of the film is not particularly limited, but is preferably 20 μm or more in consideration of the handleability of the film.

<Physical and mechanical properties>
(Shrinkage factor)
In the film of the present invention, it is important that the thermal shrinkage rate in the main shrinkage direction when immersed in warm water at 80 ° C. for 10 seconds is 20% or more, and more preferably 30% or more.
This is an index for determining the adaptability to the shrinking process in a relatively short time (several seconds to about several tens of seconds) such as the use of shrinkage labels for PET bottles. At present, the shrinkage processing machine most commonly used industrially for labeling of PET bottles is generally called a steam shrinker that uses steam as a heating medium for shrinking. Furthermore, the heat-shrinkable film needs to be sufficiently heat-shrinked at a temperature as low as possible from the viewpoint of the influence of heat on the object to be coated. However, in the case of a film with high temperature dependence and extremely different shrinkage ratios depending on the temperature, parts with different shrinkage behavior tend to occur with respect to the temperature spots in the steam shrinker, so shrinkage spots, wrinkles, avatars, etc. occur. However, the shrink-finished appearance tends to deteriorate. From the viewpoint of including these industrial productivity, if the thermal shrinkage rate in the main shrinkage direction of the film when immersed in warm water at 80 ° C. for 10 seconds is 20% or more, the film is sufficiently adhered to the coated object within the shrinkage processing time. It is preferable because it can produce a good shrink-finished appearance without spots, wrinkles and avatars. From this, it is more preferable that the heat shrinkage rate at 80 ° C. of the film of the present invention is 20% to 70%.
The “main shrinkage direction” means the larger one of the longitudinal direction and the transverse direction in the stretching direction. For example, when attached to a bottle, it is a direction corresponding to the outer circumferential direction.

  When the film of the present invention is used as a heat-shrinkable label, the heat shrinkage rate in the direction perpendicular to the main shrinkage direction is preferably 10% or less when immersed in warm water at 80 ° C. for 10 seconds, It is more preferably 5% or less, and further preferably 3% or less. If the film has a thermal shrinkage rate of 10% or less in the direction perpendicular to the main shrinkage direction, the dimension itself in the direction perpendicular to the main shrinkage direction after shrinkage may be shortened, or the printed pattern or character distortion after shrinkage may occur. In the case of a square bottle, it is preferable because troubles such as vertical sink are unlikely to occur.

  In addition, although the upper limit of said heat shrinkage is not described, since heat shrinkage does not become shorter than the length of the film before extending | stretching, the upper limit of heat shrinkage is a shrinkage rate used as the film length before extending | stretching. .

[transparency]
Regarding the transparency of the film of the present invention, when a film having a thickness of 50 μm is measured according to JIS K7105, the haze value is preferably 10% or less, more preferably 7% or less, and 5% or less. Is more preferable. If the haze value is 10% or less, the transparency of the film can be obtained and a display effect can be obtained.

[Tensile breaking elongation]
The impact resistance of the film of this invention can be evaluated by the tensile elongation at break. This tensile breaking elongation is measured in a tensile test at an atmospheric temperature of 0 ° C. and a tensile speed of 100 mm / min. In particular, in the label application, the elongation is in the film take-off (flow) direction (MD), that is, the direction perpendicular to the main shrinkage direction. 100% or more, preferably 150% or more, more preferably 200% or more. A tensile breaking elongation of 100% or more at an atmospheric temperature of 0 ° C. and a pulling speed of 100 mm / min is preferable because it is difficult to cause problems such as film breakage during printing and bag making processes. Also, when the tension applied to the film increases as the speed of processes such as printing and bag making increases, it is preferable that the tensile breaking elongation is 150% or more, so that it is difficult to break. The upper limit is not particularly limited, but considering the current process speed, it is considered that about 500% is sufficient, and if too much elongation is applied, the rigidity of the film tends to decrease.

[Molded products, heat-shrinkable labels, containers]
The film of the present invention can be processed from a flat shape to a cylindrical shape or the like according to an object to be packaged and used for packaging. When printing is required in a cylindrical container such as a plastic bottle, first print the required image on one side of a wide flat film wound up on a roll, and then cut it to the required width while the print side is inside. The center seal (the shape of the seal portion is a so-called envelope) may be folded into a cylindrical shape. As the center sealing method, an organic solvent bonding method, a heat sealing method, an adhesive method, and an impulse sealer method can be considered. Among these, from the viewpoint of productivity and appearance, an adhesion method using an organic solvent is preferably used.

  In addition, the film of the present invention is excellent in heat shrink characteristics, shrink finish, transparency and the like of the film, so its use is not particularly limited. By laminating and forming functional layers, it can be used as a base material for various molded products such as bottles (blow bottles), trays, lunch boxes, prepared food containers, dairy products containers and the like. The obtained molded product can be used as a container or the like.

  Furthermore, in particular, the film of the present invention can be used as a base material for heat-shrinkable labels for food containers (for example, PET bottles, glass bottles, preferably PET bottles for soft drinks or foods). In this case, even if the shape is complicated (for example, a cylinder with a narrow center, a square column with a corner, a pentagonal column, a hexagonal column, etc.), it can be adhered to the shape, and a beautiful label without wrinkles or avatars can be obtained. A mounted container is obtained. The molded article and container of this invention can be produced by using a normal molding method.

  In addition, since the film of the present invention has excellent low temperature shrinkage and shrink finish, in addition to the heat shrinkable label material of a plastic molded product that deforms when heated to a high temperature, it has a coefficient of thermal expansion, water absorption, etc. A material very different from the heat-shrinkable film of the present invention, for example, polyolefin resin such as metal, porcelain, glass, paper, polyethylene, polypropylene, polybutene, polymethacrylate resin, polycarbonate resin, polyethylene terephthalate, polybutylene terephthalate It can be suitably used as a heat-shrinkable label material for a plastic package (container) using at least one selected from polyester-based resins and polyamide-based resins as a constituent material.

  As the material constituting the plastic package, in addition to the above resins, polystyrene, rubber-modified impact-resistant polystyrene (HIPS), styrene-butyl acrylate copolymer, styrene-acrylonitrile copolymer, styrene-maleic anhydride copolymer Polymer, acrylonitrile-butadiene-styrene copolymer (ABS), (meth) acrylic acid-butadiene-styrene copolymer (MBS), polyvinyl chloride resin, phenol resin, urea resin, melamine resin, epoxy resin, A saturated polyester resin, a silicone resin, etc. can be mentioned. These plastic packages may be a mixture of two or more resins or a laminate.

The present invention will be described below with reference to examples.
In addition, the measured value and evaluation which are shown to an Example were performed as follows. In the examples, the take-up (flow) direction of the laminated film is described as the “longitudinal” direction (or MD), and the perpendicular direction thereof is described as the “transverse” direction (or TD).

<Measurement method>
(1) Thermal contraction rate The film was cut into a size of 100 mm in length and 100 mm in width, and immersed in a hot water bath at 80 ° C. for 10 seconds, and the shrinkage was measured. For the thermal shrinkage, the ratio of shrinkage with respect to the original size before shrinkage was expressed as a% value in the longitudinal direction or the transverse direction.

(2) Haze The haze value of the film was measured according to JIS K7105.

(3) Tensile elongation at break The obtained film was cut into a size of 110 mm in the direction (longitudinal direction) perpendicular to the main shrinkage direction and 15 mm in the main shrinkage direction, and in accordance with JISK6732, at a pulling rate of 100 mm / min. The tensile elongation in the direction (longitudinal direction) perpendicular to the main shrinkage direction of the film at a temperature of 0 ° C. was measured, and the average value of ten measurements was shown in the table.

(4) Shrinkage Finishing A film printed with a grid of 10 mm intervals was cut into a size of MD 170 mm × TD 114 mm, and both ends of TD were overlapped by 10 mm and adhered with a Tetrohydrofuran (THF) solvent to produce a cylindrical film. The cylindrical film is attached to a cylindrical plastic bottle with a capacity of 500 mL and is passed through the shrinking tunnel having a length of 3.2 m (3 zones) of the steam heating method for about 4 seconds without rotating. Coated. The atmospheric temperature in the tunnel in each zone was set to a range of 70 to 90 ° C. by adjusting the amount of steam with a steam valve.

After film coating, the following criteria were evaluated.
◎: Shrinkage is sufficient and no wrinkles, avatars, whitening, or lattice distortions occur. ○: Shrinkage is sufficient, but wrinkles, avatars, whitening, and lattice distortions occur only slightly, but there is no practical problem. : Shrinkage is sufficient, but wrinkles, avatars, whitening, and lattice distortions are slightly caused, which may be a problem depending on the application. ×: Shrinkage is insufficient, or wrinkles, avatars, and lattice distortions are noticeably generated.

Moreover, the raw material used by each Example and the comparative example is as follows.
(Polylactic acid resin)
-Polylactic acid resin: manufactured by Nature Works LLC Product name: Nature Works 4050, L-form / D-form weight = 95/5, hereinafter abbreviated as “A-1”.
-Polylactic acid-based resin: manufactured by Nature Works LLC, trade name: Nature Works 4060, L-form / D-form weight = 88/12, hereinafter abbreviated as “A-2”.
-Polylactic acid-based resin: manufactured by Nature Works LLC, trade name: Nature Works 4032D, L-form / D-form weight = 98.5 / 1. 5. Hereinafter, abbreviated as “A-3”.

(Silicone acrylic composite rubber)
Silicone acrylic composite rubber: manufactured by Mitsubishi Rayon Co., Ltd. Trade name: Methbrene S2001, core-shell structure acrylic-silicone copolymer, hereinafter abbreviated as “S2001”.

(Acrylic resin)
Acrylic resin: manufactured by Mitsubishi Rayon Co., Ltd. Trade name: Acrypet VH01, methyl methacrylate resin), hereinafter abbreviated as “VH01”.
(Aliphatic polyester)
Aliphatic polyester: manufactured by Mitsubishi Chemical Co., Ltd. Product name: GS-Pla AZ91T (polybutylene succinate) Hereinafter, abbreviated as “GSPla”.

(Examples 1-7, Comparative Examples 1-3)
A mixed resin obtained by mixing a polylactic acid resin, a silicone acrylic composite rubber, and other resins and additives shown in Table 1 is put into a twin screw extruder (manufactured by Mitsubishi Heavy Industries, Ltd.), and a set temperature of 200 ° C. After being melt-mixed and extruded from a die having a set temperature of 200 ° C., it was taken up with a cast roll at 50 ° C. and cooled and solidified to obtain an unstretched sheet.
Next, the film was stretched in the machine direction under the conditions shown in Table 1 using a roll longitudinal stretching machine, and then stretched in the transverse direction under the conditions shown in Table 1 using a film tenter (manufactured by Kyoto Machine Co., Ltd.). A heat-shrinkable film was obtained. The evaluation results of the obtained film are shown in Table 1.

From Table 1, the film defined by the present invention had both mechanical properties such as heat shrinkage properties, tensile elongation at break, transparency, and shrink finish. On the other hand, when the D / L ratio is outside the range of the present invention (Comparative Example 1), the shrinkage finish property is inferior. Moreover, when the silicone acrylic composite rubber was not included (Comparative Examples 2 and 3), the impact resistance was poor.
From this, it can be seen that the film of the present invention is a heat-shrinkable film excellent in mechanical properties such as heat-shrinkage properties, impact resistance, transparency, and shrinkage finish.

Claims (7)

  A mixed resin containing a polylactic acid resin and a silicone acrylic composite rubber as main components and having a mass ratio of 95/5 to 50/50 of the polylactic acid resin and the silicone acrylic composite rubber, or the mixed resin The polylactic acid resin has at least one layer, and the polylactic acid-based resin is composed of a copolymer of D-lactic acid and L-lactic acid, or a mixed resin of this copolymer, and D / L of D-lactic acid and L-lactic acid. The ratio is 3/97 to 15/85, or 85/15 to 97/3, the thermal shrinkage rate in the main shrinkage direction when stretched in at least one direction and immersed in 80 ° C. warm water for 10 seconds is 20 % Heat shrinkable film.   The heat-shrinkable film according to claim 1, wherein the mixed resin layer contains 5% by mass or more and 30% by mass or less (meth) acrylic resin with respect to the total amount of the mixed resin. The heat-shrinkable film according to claim 1 or 2, wherein the mixed resin layer contains an aliphatic polyester resin excluding a polylactic acid resin of 5% by mass to 30% by mass with respect to the total amount of the mixed resin.   The heat-shrinkable film according to any one of claims 1 to 3, wherein a tensile breaking elongation in a direction perpendicular to the main shrinkage direction when measured at an atmospheric temperature of 0 ° C and a tensile speed of 100 mm / min is 100% or more. .   A molded article using the heat-shrinkable film according to claim 1 as a base material.   A heat-shrinkable label using the heat-shrinkable film according to claim 1 as a substrate.   A container equipped with the molded product according to claim 5 or the heat-shrinkable label according to claim 6.