JP7013676B2 - Heat shrinkable laminated film - Google Patents

Description

The present invention relates to a heat-shrinkable laminated film, and more particularly to a heat-shrinkable laminated film having excellent laser color development property, heat shrinkage property, transparency, oil resistance, and interlayer adhesion by laser irradiation.

Currently, soft drinks such as juice, alcoholic drinks such as beer, food seasonings, and toiletry products are sold in containers such as PET bottles and bottles. For these applications, a heat-shrinkable film that can be attached to a container by heat shrinkage is used as one of the packaging forms.

In the food industry that handles the above applications, the importance of labeling is increasing from the viewpoint of prevention of counterfeiting and defects, and traceability. It is required to print on.

Individual product information such as date of manufacture, best-by date, lot number, production area display, etc. is printed by the inkjet method, stamp method, etc., but since it is printed on the surface, the printed part is worn or soiled during the distribution process. For example, the ink may peel off and the print visibility may decrease. From the viewpoint of this visibility, it is known to select a laser marking method capable of absorbing energy by irradiating with a laser beam, carbonizing, and developing color to perform laser printing.

For example, Patent Document 1 knows a film capable of laser marking, which comprises a two-kind three-layer multilayer resin film having a structure in which a transparent or translucent resin layer and a laser beam irradiation color-developing film layer are laminated. Further, Patent Document 2 discloses a laminate for laser marking using a laser coloring agent containing bismuth oxide and neodymium oxide.
Conventionally, laser color formers generally develop color by carbonizing the surrounding resin when particles absorb the laser light and generate heat when irradiated with a laser, but in recent years, when irradiated with a laser, the surroundings are the same as conventional products. A so-called self-coloring type coloring agent, which carbonizes the resin of the above and further develops a black color in the coloring agent itself, is attracting attention. However, this self-coloring type color former has a problem that a molded product such as a film is colored when it is processed at a high temperature during molding or compounding. For heat-shrinkable films that require clear and high transparency, coloring significantly impairs the product value. In terms of functionality, there is a problem that when the molded product is colored, the apparent laser color development property is deteriorated. If the amount of the color former is increased in order to improve the color developability, the transparency is further deteriorated. As described above, the problem of coloring of the self-coloring type color-developing agent has been a big problem when the color-developing agent is used for a heat-shrinkable film that requires particularly high transparency.

Further, in many food applications, the content of the packaged body contains oil, so that the heat-shrinkable film is particularly required to have resistance to oil. Films with such a wide range of required characteristics, that is, films that ensure sufficient visibility for laser printing, are resistant to oil, and have all the qualities such as shrinkage characteristics, transparency, and interlayer adhesiveness. , Has not been put into practical use yet.

Patent No. 4241122 Patent No. 5471404

The present invention has been studied in view of the above problems, and an object of the present invention is to provide a heat-shrinkable laminated film having excellent laser color development property, heat shrinkage property, transparency, oil resistance, and interlayer adhesion by laser irradiation. ..

As a result of diligent studies, the present inventors have succeeded in obtaining a heat-shrinkable laminated film capable of solving the above-mentioned problems of the prior art, and have completed the present invention.
That is, the object of the present invention is to have at least three layers (I), (II) and (III), each layer containing the following resin as a main component, and the (III) layer is further (III). The laser color-developing agent is contained in an amount of 0.01 to 5% by mass with respect to 100% by mass of the resin constituting the layer, and the heat shrinkage rate in the main shrinkage direction when immersed in warm water at 80 ° C. for 10 seconds is 20% or more. This is achieved by a heat shrinkable laminated film characterized by the above.
(I) Layer: Polyester-based resin (II) Layer: Polyester-based resin and polystyrene-based resin (III) Layer: Polystyrene-based resin

According to the present invention, it is possible to obtain a heat-shrinkable laminated film having excellent laser color development property, heat shrinkage property, transparency, oil resistance, and interlayer adhesion by laser irradiation. The film can be suitably used for various shrink wrapping applications.

Hereinafter, the heat-shrinkable laminated film of the present invention (hereinafter referred to as “the film of the present invention”) will be described in detail.
In addition, in this specification, "as a main component" means that it is permissible to contain other components as long as it does not interfere with the action and effect of the resin constituting each layer. Further, although the term does not limit the specific content, it is 50% by mass or more, preferably 60% by mass or more, and more preferably 70% by mass or more and 100% by mass of the total constituents of each layer. It is a component that occupies the following range.

<Heat shrinkable laminated film>
The film of the present invention contains a layer (I) containing a polyester resin as a main component, a layer (II) containing a mixed resin composition of a polyester resin and a polystyrene resin as a main component, and a polystyrene resin as a main component. It has at least three layers (III), and the layer (III) further contains 0.01 to 5% by mass of a laser color-developing agent, and the heat shrinkage rate in the main shrinkage direction when immersed in warm water at 80 ° C. for 10 seconds. Is a heat-shrinkable laminated film, characterized in that the content is 20% or more.

<(I) layer>
In the film of the present invention, the layer (I) is mainly composed of a polyester resin.

<Polyester resin>
By using the polyester resin as the main component of the film (I) in the film of the present invention, it is possible to suppress natural shrinkage while imparting rigidity, fracture resistance and low temperature shrinkage to the film. A polyester-based resin suitable in the present invention is a polyester-based resin derived from a dicarboxylic acid residue and a diol residue. Examples of dicarboxylic acid residues are terephthalic acid, isophthalic acid, 2-chloroterephthalic acid, 2,5-dichloroterephthalic acid, 2-methylterephthalic acid, 4,4-stylbenzicarboxylic acid, and 4,4-biphenyldicarboxylic acid. , Orthophthalic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, bisbenzoic acid, bis (p-carboxyphenyl) methane, anthracendicarboxylic acid, 4,4-diphenylether dicarboxylic acid, 4,4-di Aromatic dicarboxylic acids such as phenoxyetanedicarboxylic acid, 5-Nasulfoisophthalic acid, ethylene-bis-p-benzoic acid, adipic acid, sebacic acid, azelaic acid, dodecanedioic acid, 1,3-cyclohexanedicarboxylic acid, 1, Included are residues derived from aliphatic dicarboxylic acids such as 4-cyclohexanedicarboxylic acid or their ester derivatives. These dicarboxylic acid residues may contain one kind alone or two or more kinds. Of these, a polyester resin containing a terephthalic acid residue and an ethylene glycol residue is preferably used.

The polyester resin is more preferably a mixture in which at least one of a dicarboxylic acid residue and a diol residue is composed of two or more kinds of residues. In the present specification, among the two or more kinds of residues, the main residue, that is, the one having the largest mass (mol%) is the first residue, and the residue smaller than the first residue is the mass ( (Mol%) The residues are the second and lower residues (that is, the second residue, the third residue, and so on) in this order. By using such a mixture system of the dicarboxylic acid residue and the diol residue, the crystallinity of the obtained polyester resin can be lowered, and the progress of crystallization can be suppressed, which is preferable.

Preferred diol residue mixtures include, for example, the ethylene glycol residue as the first residue, 1,4-butanediol, neopentyl glycol, diethylene glycol, polytetramethylene glycol, and 1,4- as the second residue. Residues derived from at least one selected from the group consisting of cyclohexanedimethanol, preferably those using 1,4-cyclohexanedimethanol residues can be mentioned.

The preferred mixture of dicarboxylic acid residues is, for example, selected from the group consisting of terephthalic acid residue as the first residue, isophthalic acid as the second residue, 1,4-cyclohexanedicarboxylic acid, succinic acid and adipic acid. Residues derived from at least one of the above, preferably those using isophthalic acid residues can be mentioned.

The content of the total amount of the dicarboxylic acid residue and the diol residue below the second residue is the sum of the total amount of the dicarboxylic acid residue (100 mol%) and the total amount of the diol residue (100 mol%) ( The lower limit is preferably 10 mol% or more, more preferably 20 mol% or more, with respect to 200 mol%). The upper limit is preferably 40 mol% or less, more preferably 35 mol% or less. When the content of the residues having 2 or less residues is 10 mol% or more, the crystallinity of the obtained polyester can be suppressed to a low level. On the other hand, if the content of the residues having 2 or less residues is 40 mol% or less, the advantages of the first residue can be utilized.

For example, if the dicarboxylic acid residue is a terephthalic acid residue, the first residue of the diol residue is an ethylene glycol residue, and the second residue is a 1,4-cyclohexanedimethanol residue, the second residue. The content of 1,4-cyclohexanedimethanol residue is the total amount of terephthalic acid residue (100 mol%), which is a dicarboxylic acid residue, and ethylene glycol residue and 1,4-cyclohexanedimethanol residue. The lower limit is preferably 10 mol% or more, more preferably 15 mol% or more, still more preferably 25 mol% or more, based on the total amount (200 mol%) with the total amount (100 mol%). The upper limit is preferably 40 mol% or less, more preferably 38 mol% or less, still more preferably 35 mol% or less. By using an ethylene glycol residue and a 1,4-cyclohexanedimethanol residue as the diol residue in this range, the crystallinity of the obtained polyester is almost eliminated and the break resistance can be improved.

Further, in the above example, when the dicarboxylic acid residue consists of a terephthalic acid residue as a first residue and an isophthalic acid residue as a second residue, it is an isophthalic acid residue and a diol residue which are dicarboxylic acid residues. The content of 1,4-cyclohexanedimethanol residue is the total amount of terephthalic acid residue and isophthalic acid residue (100 mol%) and the total amount of ethylene glycol residue and 1,4-cyclohexanedimethanol residue. The lower limit is preferably 10 mol% or more, more preferably 15 mol% or more, still more preferably 25 mol% or more, based on the total (200 mol%) of (100 mol%). The upper limit is preferably 40 mol% or less, more preferably 38% mol or less, still more preferably 35 mol% or less.

In addition to the polyester resin derived from the dicarboxylic acid residue and the diol residue, the polyester resin used in the film of the present invention contains a carboxylic acid residue and an alcohol residue in one molecule. It is also possible to use a polyester resin obtained by polymerizing a monomer having the same. In particular, polylactic acid obtained by polycondensing lactic acid can be suitably used because it imparts rigidity, low temperature shrinkage, and low natural shrinkage.

The refractive index (n1) of the polyester resin is preferably 1.560 or more and 1.580 or less, and more preferably 1.565 or more and 1.574 or less.

The lower limit of the intrinsic viscosity (IV) of the polyester resin is preferably 0.5 dl / g or more, more preferably 0.6 dl / g or more, and further preferably 0.7 dl / g or more. The upper limit value is preferably 1.5 dl / g or less, more preferably 1.2 dl / g or less, still more preferably 1.0 dl / g or less. When the intrinsic viscosity (IV) is 0.5 dl / g or more, deterioration of film strength characteristics and heat resistance can be suppressed. On the other hand, when the intrinsic viscosity is 1.5 dl / g or less, it is possible to prevent breakage or the like due to an increase in stretching tension.

Specific examples of commercially available polyester-based resins include "Easter Copolyester" (manufactured by Eastman Chemical Company) and "SKYGREEN PETG" (manufactured by SK Chemical Company).

The content of the polyester resin in the layer (I) is preferably 50% by mass or more, more preferably 75% by mass or more, and 80% by mass, assuming that the resin composition constituting the (I) layer is 100% by mass. The above is more preferable, and 90% by mass or more is most preferable. As long as it is within the above range, the layer (I) may contain a resin other than the polyester resin. Examples of such resins include polyolefin resins, polystyrene resins, polycarbonate resins, and acrylic resins, with polystyrene resins being preferred.

In the film of the present invention, the layer (I) is preferably located on the outermost layer (front and back layers). As a result, the rigidity of the film is maintained, the natural shrinkage is suppressed, and the oil resistance and the solvent resistance are improved. In addition, when the front and back layers are composed of a resin composition containing a polyester resin as a main component, the film does not easily curl when printed using a gravure ink containing a normal organic solvent as a main component, and remains on the label. This is preferable because the amount of solvent to be used increases, blocking occurs after printing, and the odor of organic solvent is less likely to occur.

In order to impart slipperiness to the film and prevent blocking, it is preferable to add a method of blending an incompatible resin or an antiblocking agent to the front and back layers of the film of the present invention.

Specific examples of the antiblocking agent include inorganic particles such as silica, talc and calcium carbonate, inorganic oxides and carbonates, and organic particles such as crosslinked acrylic, crosslinked polyester, crosslinked polystyrene and silicone. Be done. In addition, organic particles having a multi-layered structure polymerized in multiple stages can also be used. Of these, silica and organic particles are preferably used.

Since the anti-blocking agent develops slipperiness and blocking resistance by roughening the surface of the film, transparency and gloss of the film are impaired unless an appropriate addition amount and type are selected. The amount of the anti-blocking agent added is preferably 0.01% by mass or more, more preferably 0.015% by mass or more, and 0, with the entire resin composition constituting the front and back layers as 100% by mass, and the lower limit is preferably 0.01% by mass or more. .02% by mass or more is more preferable. The upper limit value is preferably 2% by mass or less, more preferably 1.5% by mass or less, still more preferably 1% by mass or less. When the lower limit of the anti-blocking agent is within the above range, sufficient slipperiness and blocking resistance can be obtained. Further, if the upper limit of the anti-blocking agent is within the above range, excessive unevenness on the film surface does not occur, transparency is impaired due to surface roughness, and film roll winding occurs due to excessive slipperiness. Not preferable.

The shape of the anti-blocking agent is not particularly limited, but is spherical from the viewpoint of suppressing aggregation in the front and back layers, suppressing uniform dispersion, suppressing diffused reflection of transmitted light, and unevenness formed on the film surface. Is preferably used. The average particle size of the antiblocking agent preferably has a lower limit of 0.5 μm or more, and more preferably 1 μm or more. The upper limit is preferably 10 μm or less, more preferably 8 μm or less, still more preferably 6 μm or less. When the lower limit of the average particle size of the antiblocking agent is within the above range, sufficient slipperiness and blocking resistance can be exhibited. Further, when the upper limit of the average particle size of the antiblocking agent is within the above range, ink leakage is unlikely to occur and the appearance of the printed pattern is not spoiled when printing is applied to the film of the present invention to improve the design. ..
The particle size distribution of the antiblocking agent is not particularly limited, but it is preferable that the particle size distribution is narrow. This is because if the particle size distribution becomes too wide, some particles may deviate from the above-mentioned preferably used particle size range.

<Layer (III)>
In the film of the present invention, the layer (III) contains a polystyrene-based resin as a main component and further contains a laser coloring agent.

<Polystyrene resin>
Examples of the polystyrene-based resin include a styrene-based homopolymer obtained by polymerizing a styrene-based hydrocarbon or a copolymer of a styrene-based hydrocarbon and another monomer. In the present invention, the styrene-based hydrocarbon is used. Block copolymerization of and conjugated diene hydrocarbons is preferably used.

Examples of the styrene-based hydrocarbon include styrene, p-, m- or o-methylstyrene, 2,4-, 2,5-, 3,4- or 3,5-dimethylstyrene, pt-butylstyrene and the like. Alkylstyrene; o-, m- or p-chlorostyrene, o-, m- or p-bromostyrene, o-, m- or p-fluorostyrene, o-methyl-p-fluorostyrene and the like halogenated styrene. Halogen-substituted alkyl styrenes such as o-, m- or p-chloromethyl styrene; alkoxy styrenes of p-, m- or o-methoxystyrene, o-, m- or p-ethoxystyrene; o-, m- , Carboxyalkyl styrene such as p-carboxymethyl styrene; alkyl ether styrene such as p-vinylbenzyl propyl ether; alkyl silyl styrene such as p-trimethylsilyl styrene; further, vinyl benzyl dimethoxyphosphide and the like. The styrene-based hydrocarbon block may contain a copolymerizable monomer other than these homopolymers, copolymers and / or styrene-based hydrocarbons in the block.

Examples of conjugated diene hydrocarbons include butadiene, isoprene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene and the like. Can be mentioned. The conjugated diene-based hydrocarbon block may contain a copolymerizable monomer other than these homopolymers, copolymers and / or conjugated diene-based hydrocarbons in the block.

As an example of a block copolymer of a styrene-based hydrocarbon and a conjugated diene-based hydrocarbon, a styrene-butadiene-based block copolymer (SBS) in which the styrene-based hydrocarbon is styrene and the conjugated diene-based hydrocarbon is butadiene. ).
In SBS, the mass% ratio of styrene / butadiene is preferably about (95 to 60) / (5 to 40), more preferably (93 to 60) / (7 to 40), and more preferably (90 to). It is more preferably about 60) / (10 to 40).
The measured value of the melt flow rate (MFR) of SBS (measurement conditions: temperature 200 ° C., load 49N) is preferably 2 g / 10 minutes or more as a lower limit value, and more preferably 3 g / 10 minutes or more. The upper limit is preferably 15 g / 10 minutes or less, more preferably 10 g / 10 minutes or less, and even more preferably 8 g / 10 minutes or less.

Further, as another example of the styrene-based hydrocarbon and the conjugated diene-based hydrocarbon block copolymer, a styrene-isoprene-butadiene block copolymer (SIBS) can be mentioned.
In SIBS, the mass% ratio of styrene / isoprene / butadiene is preferably (60 to 90) / (5 to 40) / (5 to 30), and is preferably (60 to 85) / (10 to 30) / (. 5 to 25) is more preferable, and (60 to 80) / (10 to 25) / (5 to 20) is even more preferable. If the content of butadiene is high and the content of isoprene is low, the butadiene heated inside the extruder may cause a cross-linking reaction and the gel-like substance may increase.
The measured value of the melt flow rate (MFR) of SIBS (measurement conditions: temperature 200 ° C., load 49N) is preferably 2 g / 10 minutes or more as a lower limit value, and more preferably 3 g / 10 minutes or more. The upper limit is preferably 15 g / 10 minutes or less, more preferably 10 g / 10 minutes or less, and even more preferably 8 g / 10 minutes or less.

The polystyrene-based resin is not limited to a single substance, and may be a mixture of two or more types. For example, when the polystyrene resin is a mixture of SBS and SIBS, the mass% ratio of SBS / SIBS is preferably about (90 to 10) / (10 to 90), and is preferably (80 to 20) / (20). It is more preferably about 80), and further preferably about (70 to 30) / (30 to 70).

When the polystyrene-based resin is a block copolymer of a styrene-based hydrocarbon and a conjugated diene-based hydrocarbon, the refractive index (n2) measured in accordance with JIS K7142 of the block copolymer is set as the lower limit. It is preferably 1.540 or more, more preferably 1.550 or more, and even more preferably 1.555 or more. The upper limit is preferably 1.600 or less, more preferably 1.590 or less, and even more preferably 1.585 or less.
In relation to the refractive index (n1) of the polyester resin constituting the layer (I), the refractive index (n2) of the block copolymer is ± 0.02 of the refractive index (n1) of the polyester resin. It is desirable that it is within the range of ± 0.015. By adjusting the difference between the refractive index (n2) of the polystyrene-based resin and the refractive index (n1) of the polyester-based resin within a predetermined range, a film having good transparency can be obtained.

The block copolymer of styrene-based hydrocarbon and conjugated diene-based hydrocarbon can adjust its refractive index (n2) to almost a desired value by appropriately adjusting the composition ratio of styrene-based hydrocarbon and conjugated diene-based hydrocarbon. can. When the polyester-based resin is contained in the layer (III), n1 ± 0.02 is adjusted by adjusting the composition ratio of the styrene-based hydrocarbon and the conjugated diene-based hydrocarbon in accordance with the refractive index (n1). The refractive index (n2) within the range of is obtained. This predetermined refractive index may be adjusted by using a styrene-based hydrocarbon and a conjugated diene-based hydrocarbon block copolymer alone, or by mixing two or more kinds of resins.

The storage elastic modulus (E') of the polystyrene resin at a vibration frequency of 10 Hz, a strain of 0.1%, and 0 ° C. is preferably 1.00 × 10 ⁹ Pa or more, and more preferably 1.50 × 10 ⁹ Pa or more. .. The storage elastic modulus (E') at 0 ° C. represents the rigidity of the film, that is, the waist strength of the film. When the polystyrene-based resin has a storage elastic modulus (E') of 1.00 × ¹⁰⁹ Pa or more, a film having rigidity as well as transparency can be obtained. The storage elasticity (E') is a simple substance of the block copolymer of the above-mentioned styrene-based hydrocarbon and the conjugated diene-based hydrocarbon, a mixture of two or more kinds of the copolymer, or a range that does not impair the transparency. Obtained by mixing with other resins.

(III) When a mixture of a block copolymer of a styrene-based hydrocarbon and a conjugated diene-based hydrocarbon or a mixture of this copolymer and another resin is used as the main component of the layer, the copolymer weight that bears break resistance. Good results can be obtained by appropriately selecting a copolymer or resin and a copolymer or resin that bears rigidity. That is, by combining a styrene-based hydrocarbon-conjugated diene-based hydrocarbon block copolymer having high fracture resistance and a styrene-based hydrocarbon-conjugated diene-based hydrocarbon block copolymer having high rigidity, or by combining it with high value. By mixing a styrene-based hydrocarbon-conjugated diene-based hydrocarbon block copolymer having break resistance and another type of resin having high rigidity, those styrene-based hydrocarbons-conjugated diene-based hydrocarbons can be mixed. The total composition, or a mixture of them with other types of resins, can be adjusted to meet the desired refractive index (n2) and storage elasticity (E') at 0 ° C.

Pure block SBS and random block SBS are preferable as the styrene-based hydrocarbon-conjugated diene-based hydrocarbon block copolymer capable of imparting break resistance. Above all, the storage elastic modulus (E') at 0 ° C. is 1.00 × 10 ⁸ Pa or more and 1.00 × 10 ⁹ Pa or less, and at least one of the peak temperatures of the loss elastic modulus (E ”) is −20. Those having viscoelastic properties at ° C. or lower are particularly preferable. When the storage elastic modulus (E') at 0 ° C. is 1.00 × ¹⁰⁸ Pa or more, the amount of the resin that bears the rigidity is increased to increase the blending amount of the waist. Strength can be imparted. On the other hand, at the peak temperature of the loss elastic modulus (E ″), the temperature on the low temperature side mainly exhibits break resistance. Although this characteristic changes depending on the stretching conditions, it is difficult to impart sufficient film breakability to the laminated film when the peak temperature of the loss elastic modulus (E ") does not exist at −20 ° C. or lower in the state before stretching. May be.

Further, as a resin capable of imparting rigidity, a copolymer composed of a styrene-based hydrocarbon having a storage elastic coefficient (E') at ⁰ ° C. of 2.00 × 109 Pa or more, for example, a styrene-based resin having a controlled block structure. Examples thereof include a block copolymer of a hydrocarbon and a conjugated diene hydrocarbon, a polystyrene, a styrene hydrocarbon and an aliphatic unsaturated carboxylic acid ester copolymer.

As a styrene-based hydrocarbon-conjugated diene-based hydrocarbon block copolymer having a controlled block structure, the storage elastic modulus (E') at 0 ° C. is 2.00 × 10 ⁹ as a characteristic of the styrene-butadiene block copolymer. Examples thereof include SBS having Pa or more. The composition ratio of styrene-butadiene of SBS satisfying this is preferably adjusted to about styrene / butadiene = (95 to 80) / (5 to 20).

The structure of the block copolymer and the structure of each block portion are preferably random blocks and tapered blocks. More preferably, in order to control its shrinkage characteristics, the peak temperature of the loss elastic modulus (E ″) is 40 ° C. or higher, and more preferably 40 ° C. or lower, there is a clear peak loss elastic modulus (E ″). There is no temperature. When the peak temperature of the loss modulus (E ″) is apparently absent up to 40 ° C., the storage modulus property is almost the same as that of polystyrene, so that the rigidity of the film can be imparted. The peak temperature of the loss elastic modulus (E ″) is preferably in the range of 40 ° C. or higher and 90 ° C. or lower. This peak temperature is a factor that mainly affects the shrinkage rate, and if this temperature is in the range of 40 ° C. or higher and 90 ° C. or lower, the natural shrinkage and the low temperature shrinkage rate do not decrease extremely.

A method for polymerizing a styrene-based hydrocarbon-conjugated diene-based hydrocarbon copolymer that satisfies the above viscoelastic properties is shown below. Normally, a part of styrene or butadiene is charged to complete the polymerization, and then a mixture of a styrene monomer and a butadiene monomer is charged to continue the polymerization reaction. As a result, butadiene having the higher polymerization activity is preferentially polymerized, and finally a block composed of a single monomer of styrene is generated.

For example, when styrene is first independently polymerized, and after the polymerization is completed, a mixture of styrene monomer and butadiene monomer is charged to continue the polymerization, the styrene-butadiene monomer ratio gradually changes between the styrene block and the butadiene block. A styrene-butadiene block copolymer having a copolymer moiety can be obtained. By having such a portion, a polymer having the above-mentioned viscoelastic property can be obtained. In this case, the two peaks caused by the butadiene block and the styrene block as described above cannot be clearly confirmed, and it seems that only one peak is apparently present. That is, in a block structure such as SBS of a random block in which a pure block or a butadiene block is clearly present, Tg caused by the butadiene block is mainly present at 0 ° C. or lower, so that the storage elastic modulus at 0 ° C. ( It becomes difficult for E') to exceed a predetermined value.

Regarding the molecular weight, the melt flow rate (MFR) measured value (measurement conditions: temperature 200 ° C., load 49N) is adjusted in the range of 2 g / 10 minutes or more and 15 g / 10 minutes or less. The mixing amount of the styrene-butadiene block copolymer imparting this rigidity is appropriately adjusted according to the characteristics of the heat-shrinkable laminated film, and when the resin composition constituting the layer (III) is 100% by mass, It is preferably 20% by mass or more and 80% by mass or less, and more preferably 40% by mass or more and 70% by mass or less. When the upper limit is within the above range, the rigidity of the film can be significantly improved and the fracture resistance can be suppressed from being lowered. On the other hand, if the lower limit is within the above range, sufficient rigidity can be imparted to the film.

As the molecular weight of the polystyrene-based resin, the mass average molecular weight (Mw) is preferably 100,000 or more, and more preferably 150,000 or more as the lower limit. The upper limit is preferably 500,000 or less, more preferably 400,000 or less, still more preferably 300,000 or less. When the lower limit of the mass average molecular weight is within the above range, there is no drawback that the film is deteriorated, which is preferable. Further, when the upper limit is within the above range, it is not necessary to adjust the flow characteristics and there is no drawback such as deterioration of the extrudability, which is preferable.

Examples of commercially available polystyrene-based resins include "Asaflex" (manufactured by Asahi Kasei Chemicals Co., Ltd.) and "Clearlen" (manufactured by Denki Kagaku Kogyo Co., Ltd.).

When a copolymer of a styrene hydrocarbon and an aliphatic unsaturated carboxylic acid ester is used as the polystyrene resin, the aliphatic unsaturated carboxylic acid ester to be copolymerized with the styrene hydrocarbon is methyl (meth) acrylate. Examples thereof include butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, and stearyl (meth) acrylate. It is preferably a copolymer of styrene and butyl (meth) acrylate, and more preferably, styrene is in the range of 70% by mass or more and 90% by mass or less, and Tg (peak temperature of loss elastic modulus E ”) is high. Those having a melt flow rate (MFR) measurement value (measurement conditions: temperature 200 ° C., load 49N) of 2 g / 10 minutes or more and 15 g / 10 minutes or less are preferably used at 50 ° C. or higher and 90 ° C. or lower. ) Styrene means acrylate and / or methacrylate.

Specific examples of commercially available products of copolymers of styrene-based hydrocarbons and aliphatic unsaturated carboxylic acid esters include, for example, "TX Polymer" (manufactured by Denki Kagaku Kogyo Co., Ltd.) and "Sevian" (manufactured by Dycel Polymer Co., Ltd.). And so on.

The content of the polystyrene-based resin in the layer (III) is not particularly limited as long as it does not exceed the range specified in the present invention, but the resin composition constituting the layer (III) is taken as 100% by mass and 50. It is preferably 7% by mass or more, more preferably 60% by mass or more, and further preferably 70% by mass or more. However, when a styrene homopolymer (GPPS), an oxazoline group-containing styrene-based polymer described later, a styrene-maleic anhydride copolymer or the like is contained as a polystyrene-based resin, GPPS or an oxazoline group-containing styrene-based copolymer, Since the Tg (peak temperature of loss elasticity E ") of the styrene-maleic anhydride copolymer is extremely high at about 100 ° C. or higher, GPPS to be mixed, a styrene-based copolymer containing an oxazoline group, and styrene-maleic anhydride are used together. The content of the polymer or a mixture thereof is preferably 20% by mass or less, more preferably 15% by mass or less, and 10% by mass or less, assuming that the resin composition constituting the layer (III) is 100% by mass. Is even more preferable.

<Laser color former>
The laser color-developing agent is not particularly limited as long as it has a function of generating heat by irradiation with a laser beam, and may be a so-called self-coloring type color-developing agent that develops its own color by irradiation with a laser beam, or does not develop its own color. It may be a thing. When the laser color former generates heat, at least the forming material around it is carbonized, and the desired printing appears on the layer (III). Furthermore, when a self-coloring laser color-developing agent is used, the color-developing of the laser color-developing agent and the color-developing by the carbide generated by carbonization of the film-forming material synergize with each other to express printing with deep color and excellent visibility. can. When the laser color-developing agent develops a color, the color thereof is not particularly limited, but from the viewpoint of visibility, it is preferable to use a laser color-developing agent capable of developing a dark color including black, navy blue, and brown.

Specific examples of the laser color former include metals such as iron, copper, zinc, tin, gold, silver, cobalt, nickel, bismuth, antimony, and aluminum, and their salts such as iron chloride and iron nitrate. , Iron phosphate, copper chloride, copper nitrate, copper phosphate, zinc chloride, zinc nitrate, zinc phosphate, nickel chloride, nickel nitrate, bismuth subcarbonate, bismuth nitrate and other metal salts. Examples of the metal oxide system include metal hydroxides such as magnesium hydroxide, lanthanum hydroxide, nickel hydroxide, and bismuth hydroxide, as well as iron oxide, copper oxide, zinc oxide, tin oxide, cobalt oxide, and nickel oxide. Examples thereof include metal oxides such as bismuth oxide, indium oxide, antimony oxide, tungsten oxide, neodium oxide, mica, hydrotalcite, montmorillonite and smectite. Examples of the metal boride system include zirconium borate, titanium boride, and lanthanum boride. Examples of the dye type include leuco dyes such as fluorine type, phenothiazine type, spiropyran type, triphenylmethphthalide type, and rhodamine lactam type. The laser color former may be used alone or in combination of two or more. In the present invention, as the laser coloring agent, a compound containing at least one of bismuth oxide, tin oxide, zinc oxide, antimony oxide and lanthanum boride is preferable from the viewpoint of laser coloring effect and cost. Further, a compound containing bismuth is preferable, and a compound containing bismuth oxide is more preferable. If it contains bismuth oxide, it develops color and generates heat well even in a relatively small amount, so that the effect of the present invention can be fully exerted without impairing the transparency of the layer (III) in the film of the present invention. .. Further, the hexaboride of a rare earth element has a near-infrared absorption ability, and among them, lanthanum hexaboride is preferable because it has an excellent absorption efficiency of laser light.

When the laser color former is granular such as a metal compound, the average particle size is preferably 10 μm or less, more preferably 5 μm or less. If the particle size is 10 μm or less, there is no possibility that the transparency will be significantly reduced.

Commercially available laser color formers include, for example, "Elbima" (manufactured by Toyo Ink), "Iriodin" (manufactured by Merck Japan), "TOMATEC" (manufactured by Tokan Material Technology), and "KHDS-06" (Sumitomo). (Made by metal mine) and so on.

The content of the laser color former in the layer (III) is 0.01% by mass or more, preferably 0.03% by mass or more, and 5% by mass or less, preferably 1.0% by mass or less. If the content of the color-developing agent is 0.01% by mass or more, a sufficient color-developing effect can be obtained, and if it is 5% by mass or less, the transparency is not significantly reduced.

In the present invention, the layer (III) is preferably located in the intermediate layer. As a result, the film of the present invention has excellent shrinkage characteristics, and is further excellent in laser printing visibility, transparency, oil resistance, solvent resistance, and the like.
When a laser color-developing agent is added to the resin and stretched, the laser color-developing agent existing near the surface of the polystyrene-based resin rises on the surface of the polystyrene-based resin due to the difference in elastic coefficient between the laser color-developing agent and the polystyrene-based resin and reaches the surface. Fine irregularities occur and transparency decreases. At that time, when the layer (I) containing no laser coloring agent is formed as the front and back layers (outermost layers), it is preferable because the smoothness of the surface is ensured and the decrease in transparency can be suppressed. Further, since the polystyrene-based resin has a relatively low oil resistance, by arranging it in the intermediate layer, it is possible to impart functions such as shrinkage characteristics without impairing the oil resistance of the film.
Furthermore, in the present invention, it is important to include the laser color former in the layer (III). This makes it possible to solve the problem of coloring of the molded product depending on the processing temperature.
It is also important to arrange the (III) layer containing the laser color former in the intermediate layer, that is, to print on the intermediate layer in order to avoid the problem that the printing disappears due to wear after the label is formed. .. When printing is performed on the surface layer, the written content may be blurred due to rubbing of the printed portion due to surface wear. As a test method for confirming the phenomenon, there is a fastness test.

In addition to the polystyrene-based resin and the laser color former, other resins can be mixed in the layer (III) as long as the characteristics of the film of the present invention are satisfied. Examples of such resins include polyester resins, polyolefin resins, acrylic resins, polycarbonate resins, compatibilizers with these resins, and the like, and among them, polyester resins are preferably contained.

<Polyester resin contained in layer (III)>
In the film of the present invention, the layer (III) can further contain a polyester resin.
It is preferable that the layer (III) further contains a polyester-based resin from the viewpoint of adhesiveness to the layer (II) containing a mixed resin composition of the polyester-based resin and the polystyrene-based resin as a main component, and the film of the present invention. It is also possible to add a recycled film such as trimming loss generated during manufacturing. The content of the polyester resin is preferably 30% by mass or less, more preferably 25% by mass or less, and 20% by mass or less, with the resin composition constituting the layer (III) as 100% by mass and an upper limit of 30% by mass or less. Is more preferable. The lower limit is not particularly limited, but is preferably 3% by mass or more, more preferably 5% by mass or more, and further preferably 10% by mass or more.

The polyester-based resin preferably used in the (III) layer of the film of the present invention is the same as that in the (I) layer. Further, the polyester resin used in the layer (III) may be a polyester resin contained in the recycled raw material caused by trimming loss or the like.

<(II) layer>
The (II) layer of the film of the present invention contains a mixed resin composition of a polyester resin and a polystyrene resin as a main component.
In the present invention, the layer (II) is positioned as an adhesive layer between the layer (I) containing a polyester resin as a main component and the layer (III) containing a polystyrene resin as a main component.

The layer (II) is configured to improve the delamination strength between the layer (I) containing a polyester resin as a main component and the layer (III) containing a polystyrene resin containing a laser color former as a main component. A mixed resin composition of a polyester resin and a polystyrene resin is used as the resin.

<Polyester resin contained in layer (II)>
In the layer (II) of the film of the present invention, the same polyester resin used in the layer (I) can be used. Further, the polyester resin used in the layer (II) may be the same as the polyester resin used in the layer (II) as long as it satisfies the characteristics of the film of the present invention, or a different polyester resin may be used. May be good.

The content of the polyester resin in the layer (II) is preferably 40% by mass or more, more preferably 45% by mass or more, with the resin composition constituting the (II) layer as 100% by mass and a lower limit value of 40% by mass or more. , 50% by mass or more is more preferable. The upper limit value is preferably 80% by mass or less, more preferably 75% by mass or less, still more preferably 70% by mass or less. If the lower limit of the content of the polyester resin is within the above range, the adhesiveness with the layer (I) does not decrease, and if the upper limit is within the above range, the adhesiveness with the layer (III) is good. It is preferable because it does not decrease.

<Polystyrene resin contained in layer (II)>
In the (II) layer of the film of the present invention, the same polystyrene-based resin used in the above (III) layer can be used. Further, the polystyrene-based resin used in the layer (II) may be the same as the polystyrene-based resin used in the layer (III) as long as it satisfies the characteristics of the film of the present invention, or a different polystyrene-based resin may be used. May be good.

In the film of the present invention, the polystyrene-based resin contained in the layer (II) has a vibration modulus of 10 Hz, a strain of 0.1%, and a storage elastic modulus (E') at 0 ° C. of 1.00 × ¹⁰⁷ Pa or more. It is preferably 1.50 × ¹⁰⁷ Pa or more, and more preferably 1.50 × 107 Pa or more. By having a storage elastic modulus (E') of 1.00 × 10 ⁷ Pa or more, when the film of the present invention is molded, the adhesiveness to the above-mentioned (I) layer or (III) layer can be imparted, and the adhesiveness can be imparted. When shrunk in a high temperature atmosphere, delamination between the layer (I) or the layer (III) can be suppressed. More importantly, it is preferable because it can suppress whitening that occurs when the film is bent during processing or the like, that is, so-called bending whitening. The storage elasticity (E') is a simple substance of the block copolymer of the above-mentioned styrene-based hydrocarbon and the conjugated diene-based hydrocarbon, a mixture of two or more kinds of the copolymer, or a range that does not impair the transparency. Obtained by mixing with other resins.

Block SBS and random block SBS are preferable as the styrene-based hydrocarbon-conjugated diene-based hydrocarbon block copolymer capable of imparting adhesiveness to the above-mentioned layer (I) or layer (III). Above all, the storage elastic modulus (E') at 0 ° C. is 1.00 × 10 ⁷ Pa or more and 5.00 × 10 ⁹ Pa or less, and at least one of the peak temperatures of the loss elastic modulus (E ”) is 0 ° C. Those having the following viscoelastic properties are particularly preferable. When the storage elastic modulus (E') at 0 ° C. is 1.00 × ¹⁰⁷ Pa or more, the laminated body is formed by increasing the blending amount of the resin responsible for rigidity. When molded into a film, it is possible to impart waist strength to the film. On the other hand, at the peak temperature of the loss elastic modulus (E ″), the temperature on the low temperature side mainly exhibits break resistance. Although the characteristics change depending on the stretching conditions, when the peak temperature of the loss elastic modulus (E ″) is not present at 0 ° C. or lower in the state before stretching, the adhesiveness with the layer (I) or the layer (III) is lowered. When the laminated film is molded, it may be difficult to impart sufficient breakability to the film.

Examples of commercially available polystyrene-based resins include "Asaflex" (manufactured by Asahi Kasei Chemicals Co., Ltd.) and "Clearlen" (manufactured by Denki Kagaku Kogyo Co., Ltd.).

The content of the polystyrene-based resin contained in the (II) layer of the film of the present invention is not particularly limited as long as it satisfies the characteristics of the film of the present invention, but the resin composition constituting the (II) layer is not particularly limited. Is 100% by mass, and the lower limit is preferably 20% by mass or more, more preferably 25% by mass or more, still more preferably 30% by mass or more. The upper limit value is preferably 60% by mass or less, more preferably 55% by mass or less, still more preferably 50% by mass or less. If the lower limit of the polystyrene resin content is within the above range, the adhesiveness with the layer (III) does not decrease, and if the upper limit is within the above range, the adhesiveness with the layer (I) decreases. It is preferable without doing.

The layer (II) of the film of the present invention may contain other resins in addition to the polyester-based resin and the polystyrene-based resin as long as the characteristics of the film of the present invention are satisfied. Examples of such resins include compatibilizers, polyolefin resins, acrylic resins, polycarbonate resins, etc., which will be described later. Above all, it is preferable to contain a compatibilizer described later.

<Compatible agent contained in layer (II)>
The (II) layer of the film of the present invention can further contain a compatibilizer that promotes compatibilization between the polyester resin and the polystyrene resin. The compatibilizer is not particularly limited as long as it can promote the compatibilization of the polyester resin and the polystyrene resin, but it is preferably at least one of an oxazoline group-containing styrene-based copolymer and a styrene-maleic anhydride copolymer. By further containing a compatibilizer, the dispersibility of the polyester resin or the styrene resin is improved, the transparency of the film is improved, the thickness is made uniform, which is preferable from the viewpoint of manufacturing / productivity improvement, and further, the phase. Adhesive strength can be improved by using a solubilizer.

The compatibilizer contained in the layer (II) has a polar group having a high affinity with the polyester resin contained in the layer (II) or a polar group capable of reacting with the polyester resin, and the layer (II). A styrene-based block copolymer or a graft copolymer having a site that is compatible with or has a high affinity with the polystyrene-based resin contained in the above is preferably used. Specific examples of a polar group or a functional group that can react with a polyester resin include an acid anhydride group, a carboxylic acid group, a carboxylic acid ester group, a carboxylated compound group, and a carboxylic acid amide group. Examples include functional groups such as carboxylic acid bases, sulfonic acid groups, sulfonic acid ester groups, sulfonated compounds, sulfonic acid amide groups, sulfonic acid bases, epoxy groups, amino groups, imide groups, or oxazoline groups, among which acids. An anhydride group, a carboxylic acid group or a carboxylic acid ester group, and an oxazoline group are preferable.

Further, as a substance having a portion capable of being compatible with the polystyrene-based resin, for example, it means having a chain having an affinity with the styrene-based resin. Specific examples thereof include a random copolymer having a styrene chain, a styrene-based copolymer segment or the like as a main chain, a block chain or a graft chain, or a styrene-based monomer unit.

From the above viewpoint, the compatibilizer is preferably at least one of an oxazoline group-containing styrene-based copolymer and a styrene-maleic anhydride copolymer.

Specific examples of commercially available oxazoline group-containing styrene-based copolymers include Epocross (manufactured by Nippon Shokubai Co., Ltd.) and the like. Examples of the styrene-maleic anhydride copolymer include the Xiran series (manufactured by Polycopy).

The content of the compatibilizer in the layer (II) is not particularly limited as long as it satisfies the characteristics of the film of the present invention, but the resin composition constituting the layer (II) is set to 100% by mass as the lower limit. Is preferably 1% by mass or more, more preferably 3% by mass or more, still more preferably 5% by mass or more. The upper limit value is preferably 20% by mass or less, more preferably 15% by mass or less, still more preferably 10% by mass or less. When the content of the compatibilizer is within the above range, the expected thickness uniformity and the improvement of the interlayer adhesive strength can be expected, and it is possible to prevent a significant deterioration in transparency and an inhibition on the shrinkage behavior of the film. Therefore, it is preferable.

<Additives to each layer>
In addition to the above-mentioned components, the film of the present invention has a plasticizer and a plasticizer in each layer for the purpose of improving and adjusting the moldability, productivity and various physical properties of the heat-shrinkable film within a range that does not significantly impair the effects of the present invention. / Or a tackifier resin can be added. The amount of these additions is preferably 1% by mass or more, more preferably 2% by mass or more, still more preferably 3% by mass or more, with the resin composition constituting each layer being 100% by mass and the lower limit value being 1% by mass or more. The upper limit value is preferably 10% by mass or less, more preferably 8% by mass or less, still more preferably 5% by mass or less. When the addition amount is within the above range, the decrease in melt viscosity and the decrease in heat-resistant fusion property are small, and natural shrinkage is unlikely to occur, which is preferable.
Further, the film of the present invention has various additives such as an ultraviolet absorber, a light stabilizer, an antioxidant, an antioxidant, a stabilizer, and a colorant, in addition to the plasticizer and the tackifier resin, depending on the purpose. , Antistatic agents, lubricants, inorganic fillers and the like can be appropriately added according to each application.

<Film layer structure>
The film of the present invention has a layer (I) containing a polyester-based resin as a main component, a layer (II) containing a mixed resin composition of a polyester-based resin and a polystyrene-based resin as a main component, and a polystyrene-based film containing a laser color former. It has at least three layers (III) containing a resin as a main component, and the combination of layer configurations is appropriately selected according to the purpose and application. In the present invention, the layer (I) / (II) It is preferable to have a three-kind five-layer structure in which layers / (III) layers / (II) layers / (I) layers are laminated in this order.
In the present invention, by adopting the above layer structure, a heat-shrinkable laminated film excellent in laser color development, heat shrinkage characteristics, transparency, oil resistance, and interlayer adhesion at room temperature by laser beam irradiation, which is the object of the present invention. Can be obtained with good productivity and economy.

<Thickness of each layer>
In the film of the present invention, the thickness ratio of the layer (I) to the layer (III) is preferably 2 or more as the lower limit of the layer (III) when the layer (I) is 1. The above is more preferable, and 4 or more is further preferable. The upper limit is preferably 12 or less, more preferably 10 or less, and even more preferably 8 or less. The lower limit of the thickness of the layer (II) is preferably 7% or more, more preferably 9% or more of the total thickness of the layer (I). The upper limit is preferably 150% or less of the total thickness of the layer (I), more preferably 100% or less, still more preferably 80% or less. If the lower limit of the thickness of the layer (II) is within the above range, a good adhesive effect can be obtained, and if the upper limit is within the above range, that is, the thickness is 1.5 times or less the total thickness of the layer (I). For example, it is preferable because the transparency is not significantly reduced. After shrink-packing using the film of the present invention, there may be a problem that the laser printing becomes unclear due to wear due to rubbing. In order to solve this problem, the thickness of the surface layer of the film is important. Become. Therefore, the average thickness of the surface layer is preferably 3 μm or more, more preferably 4 μm or more. If it is within the above range, the problem due to rubbing does not occur.

<Total thickness>
The total thickness of the film of the present invention is not particularly limited, but it is preferably thin from the viewpoint of suppressing raw material costs as much as possible, specifically, the thickness after stretching is preferably 60 μm or less, and more preferably 55 μm or less. , 50 μm or less is more preferable.

<Heat shrinkage characteristics>
The film of the present invention has a heat shrinkage rate of 20% or more in the main shrinkage direction when immersed in warm water at 80 ° C. for 10 seconds. The lower limit of the shrinkage rate is preferably 25% or more, more preferably 30% or more. The upper limit is not particularly limited, but is generally preferably 70% or less, more preferably 65% or less, still more preferably 60% or less.
Further, the film of the present invention preferably has a heat shrinkage rate of 5% or less in at least one direction when immersed in warm water at 50 ° C. for 10 seconds, more preferably 3% or less, still more preferably 1% or less.
Further, the film of the present invention preferably has a heat shrinkage rate of 10% or more and less than 30% in at least one direction when immersed in warm water at 70 ° C. for 10 seconds, more preferably 10% or more and 25% or less, and 10%. More preferably 20% or less.
Further, the film of the present invention preferably has a heat shrinkage rate in the main shrinkage direction of 70% or more, more preferably 71% or more, and more preferably 72%, when immersed in warm water at 99 ° C. for 10 seconds. The above is more preferable. The upper limit is preferably 80% or less, more preferably 79% or less, still more preferably 78% or less.

In the present specification, "at least one direction" means either or both of the main contraction direction and the direction orthogonal to the main contraction direction, and usually refers to the main contraction direction. Here, the "main contraction direction" means a direction in which the stretching direction is larger than the vertical direction and the horizontal direction, and is, for example, a direction corresponding to the outer peripheral direction when the bottle is mounted on a bottle.

When the heat shrinkage rate when immersed in warm water at 50 ° C. for 10 seconds is larger than 5%, the natural shrinkage rate of the film is likely to be high, and the film is likely to be rolled up and squeezed when stored in a roll shape, or the end face of the roll. It is conceivable that the appearance may be uneven and the appearance may be poor.

Further, when the heat shrinkage rate in the main shrinkage direction at 70 ° C. is less than 10%, the heat shrinkage force is small, and for example, when the laminated film is used as the label for the container, it cannot be temporarily fixed to the container, so that the temperature becomes high. In that case, the film may shift up in the direction of the top surface. On the other hand, when the heat shrinkage rate in the main shrinkage direction becomes larger than 30% at 70 ° C., heat shrinkage occurs rapidly in a low temperature range, so that heat shrinkage may not be possible at a predetermined position. On the other hand, if the heat shrinkage rate in the main shrinkage direction at 80 ° C. is less than 20%, the heat shrinkage may be insufficient on the neck or top surface of the container.

If the heat shrinkage in at least one direction when immersed in warm water at 70 ° C. and 80 ° C. for 10 seconds is within the above range, the heat is such that the laminated film is temporarily fixed to a container, for example, in a low temperature range near 70 ° C. It has shrinkage and contracts rapidly in the high temperature range of over 70 ° C and around 80 ° C, and as a result, it is very thin compared to the body of the container as well as the body at a predetermined position. Abnormalities such as wrinkles and avatars do not occur even on the neck and top surface, and uniform shrinkage is obtained, resulting in a beautiful shrinkage finish.
The thermal shrinkage rate in the main shrinkage direction at 99 ° C. represents the strain of the film. Voids may occur in the film and impair transparency. On the other hand, if it is less than 70%, there is a possibility that a problem such as insufficient shrinkage and a tight finish may occur.

When the film of the present invention is used as a label for PET containers, the heat shrinkage rate in the orthogonal direction (direction orthogonal to the main shrinkage direction) when immersed in warm water at 80 ° C. for 10 seconds is 20% or less. Is preferable, 10% or less is more preferable, and 8% or less is further preferable. Further, the heat shrinkage rate in the orthogonal direction when immersed in warm water at 70 ° C. for 10 seconds is preferably 10% or less, more preferably 5% or less, still more preferably 3% or less. When the upper limit of the shrinkage rate in the orthogonal direction is within the above range, the shrinkage in the vertical direction becomes remarkable after the shrinkage in the label application, and troubles such as dimensional deviation and appearance defects do not occur, which is preferable.

<Transparency>
The transparency of the film of the present invention is evaluated by the haze value measured according to JIS K7136, and the haze value is preferably less than 15%, more preferably less than 10%. When the haze value is less than 15%, good transparency can be obtained and beautiful printing or the like becomes possible.

<Laser color development>
The film of the present invention contains a laser color former, and when irradiated with a laser beam, the irradiated portion is carbonized and colored, and a printed matter having excellent visibility such as letters and numbers can be obtained. Examples of the laser beam that can be used include a YAG (yttrium aluminum garnet) laser (wavelength 1064 nm), a YVO4 (yttrium vanadate) laser (wavelength 1064 nm), a Yb fiber laser (wavelength 1060 nm), and a carbon dioxide gas laser (wavelength 10640 nm). Will be.

Among them, especially the YAG laser and the Yb fiber laser transmit 90% or more of the polystyrene-based resin and the polyester-based resin film used for the film of the present invention and are not sufficiently absorbed by these resins themselves, so that the laser beam is efficient as a laser color former. Since it is well absorbed, it can be suitably used.

For the laser beam, it is necessary to appropriately adjust the irradiation conditions such as laser power, excitation current, Q-switch frequency and scanning speed.
If the laser power is increased too much or the switch frequency is increased too much, carbonization of the laser irradiation portion progresses extremely, and there is a possibility that holes may occur. Further, if the scanning speed is too slow, the printing area is concentrated, so that carbonization of the laser irradiation portion progresses extremely, and there is a possibility that holes are formed. Further, since the film of the present invention is imparted with heat shrinkage characteristics, in a state where carbonization of the laser irradiation portion progresses extremely as described above, heat shrinkage occurs due to the heat generated at that time, and the film becomes There is a risk of deformation.

<Delamination strength>
In the film of the present invention, after collecting a test piece having a size of 150 mm in the main contraction direction and 15 mm in the direction orthogonal to the main contraction direction, a part of the layer (I) is peeled off from the end face in the main contraction direction of the test piece. A peeling portion is formed on the (I) layer side, and the peeling portion and the peeled portion of the (III) layer are sandwiched by the chucks of a tensile tester, respectively, and a 180 ° peeling test is performed at a test speed of 100 mm / min in the main contraction direction. The delamination strength at the time of performing the above is preferably 1 N / 15 mm width or more, and more preferably 1.5 N / 15 mm width or more. If the delamination strength is within the above range, troubles such as vibration during transportation and delamination due to scratching of nails or the like do not occur.

<Method for manufacturing the film of the present invention>
In the film of the present invention, at least three layers (I), (II) and (III) are laminated simultaneously or sequentially to prepare a laminated film, and then the laminated film is heated to at least one. Obtained by stretching in the axial direction.

The laminated film can be co-extruded by an existing method such as a T-die method or a tubular method using an extruder equipped with a multilayer die to simultaneously produce an intermediate layer, a front and back layer, and an adhesive layer. Further, the laminated film can be sequentially produced by forming the resin constituting each layer into a separate sheet and then laminating them by a press method, a roll nip method or the like.

The laminated film is cooled by a cooling roll, air, water, etc., and then reheated by an appropriate method such as hot air, hot water, infrared rays, etc., and is subjected to a roll stretching method, a tenter stretching method, a tubular stretching method, a long interval stretching method, etc. Simultaneously or sequentially, uniaxially or biaxially stretched. In the biaxial stretching, the MD and the stretching in the TD direction may be performed at the same time, but the sequential biaxial stretching in which either one is performed first is effective, and the order may be either MD or TD first. The stretching temperature needs to be changed depending on the softening temperature of the resin constituting the film and the application required for the heat-shrinkable laminated film, but is generally 60 ° C. or higher, preferably 70 ° C. or higher, preferably 130 ° C. or lower, preferably 130 ° C. or lower. It is controlled in the range of 120 ° C. or lower. The draw ratio in the main shrinkage direction (TD) is 2 times or more, preferably 3 times or more, more preferably 4 times or more, and 7 times, depending on the film constituents, the stretching means, the stretching temperature, and the target product form. Hereinafter, it is appropriately determined in the range of preferably 6 times or less. Further, whether to use uniaxial stretching or biaxial stretching is determined by the intended use of the target product.

Even in the case of applications that require shrinkage characteristics in almost one direction, such as labels for PET containers, it is also effective to stretch the labels in the vertical direction within a range that does not impair the shrinkage characteristics. The stretching temperature depends on components other than PET, but is typically in the range of 60 ° C. or higher and 90 ° C. or lower. Further, regarding the draw ratio, the higher the draw ratio, the better the fracture resistance, but the heat shrinkage rate increases accordingly, and it becomes difficult to obtain a good shrinkage finish. Therefore, 1.03 times or more and 1.5 times or more. It is particularly preferable that it is not more than double.

Further, the film of the present invention can be imparted with shrinkage and held by quickly cooling the film within a time in which the molecular orientation of the stretched film is not relaxed after stretching.

<Use of the film of the present invention>
Since the film of the present invention is excellent in laser color development by irradiation with a laser beam, it is excellent in visibility of laser printing, and also is excellent in heat shrinkage characteristics, transparency, oil resistance, and interlayer adhesion, and therefore, various shrinkage packages. It can be suitably used for various purposes, and can be suitably used for packages and labels for shrink-wrapping objects to be packaged such as foods, seasonings, beverages, miscellaneous goods, cosmetics, and various toiletry products.

Examples of the film of the present invention are shown below, but the present invention is not limited by these examples.
The measured values and evaluations shown in the examples were performed as follows. In the embodiment, the take-up (flow) direction of the laminated film is described as "MD", and the direction orthogonal to it is described as "TD".

<Measurement method>
(1) Heat Shrinkage Rate The film obtained in the example was cut into a size of MD 20 mm and TD 100 mm, and the shrinkage amount of TD was measured by immersing it in a hot water bath at 80 ° C. for 10 seconds. For the heat shrinkage rate, the ratio of the amount of shrinkage to the actual size before shrinkage was expressed as a% value.

(2) Transparency The film obtained in the examples was evaluated for transparency by measuring the haze value in accordance with JIS K7136.
⊚: Haze value is less than 10% ○: Haze value is 10% or more and less than 15% ×: Haze value is 15% or more

(3) Laser Color Development The film obtained in the example was printed by irradiation with a laser beam using a YAG laser for marking (wavelength 1064 nm). Printing was performed under the conditions of an excitation current of 17 A, a Q-switch frequency of 10 kHz, and a scanning speed of 600 mm / sec. The print density of the obtained printed matter was evaluated.
⊚: High print density, no swelling or deformation, good visibility ○: Practically acceptable although there are some parts slightly inferior to the above ×: Poor visibility due to almost no print density

(4) Oil resistance The film obtained in the example was cut into 3 cm squares, immersed in a glass bottle containing cooking oil, stored at a temperature of 23 ° C. for 1 week, and then the film was taken out and the appearance was visually evaluated.
◯: No change in the film ×: Deterioration in the film (clouding, melting, and cracking are remarkable)

(5) Delamination strength A test piece having a size of 150 mm in the main shrinkage direction and 15 mm in the direction orthogonal to the main shrinkage direction is collected from the film obtained in the example, and then from the end face of the test piece in the main shrinkage direction ( I) A part of the layer is peeled off to form a peeled part in the layer (I), and this peeled part and the peeled part on the layer (III) side are sandwiched by the chuck of the tensile tester, respectively, and the test is performed in the main contraction direction. A 180 ° peel test was performed at a speed of 100 mm / min. The average value when the load obtained in the peeling test was constant to some extent was evaluated as the delamination strength.
◯: Delamination strength is 1N / 15 mm width or more ×: Delamination strength is less than 1N / 15 mm width

(6) Storage elastic modulus,
The measurement conditions of the storage elastic modulus and the loss elastic modulus of the raw materials used in each Example and Comparative Example are as follows.
Vibration frequency: 10Hz,
Distortion: 0.1%,

The raw materials used in each Example and Comparative Example are as follows.
(Polyester resin)
Copolymerized polyester 1 (acid component: terephthalic acid 100 mol%, glycol component: ethylene glycol 65 mol%, diethylene glycol 3 mol%, cyclohexanedimethanol 32 mol%, hereinafter referred to as "Pes (1)")
Copolymerized polyester 2 ((acid component: terephthalic acid 100 mol%, glycol component: ethylene glycol 65 mol%, diethylene glycol 12 mol%, cyclohexanedimethanol 23 mol%, hereinafter referred to as “Pes (2)”)
(Polystyrene resin)
Styrene-butadiene copolymer 1 (styrene / butadiene = 90/10 (mass%), storage elastic modulus E'(0 ° C.): 3.15 × 10 ⁹ Pa, loss elastic modulus E ”peak temperature 55 ° C., or less Referred to as "PS (1)")
Styrene-butadiene copolymer 2 (styrene / butadiene = 76/24 (mass%), storage elastic modulus E'(0 ° C.): 0.70 × 10 ⁹ Pa, loss elastic modulus E ”peak temperature −76 ° C., Hereinafter referred to as "PS (2)")
Styrene-butadiene copolymer 3 (styrene / butadiene = 71/29 (mass%), storage elastic modulus E'(0 ° C.): 0.29 × 10 ⁹ Pa, loss elastic modulus E ”peak temperature −46 ° C., Hereinafter referred to as "PS (3)")

(Laser color former)
Laser color former 1: Manufactured by Tokan Material Technology Co., Ltd., trade name: Tomatec 42-920A (bismuth trioxide / neodymium trioxide composite oxide), hereinafter referred to as "LM (1)". )
Laser color former 2: Manufactured by Sumitomo Metal Mining Co., Ltd., trade name: KHDS-06 (hexaholated lanthanum dispersion powder, hexaboride lanthanum particle content concentration 21.5%), hereinafter referred to as "LM (2)".
Laser color former 3: manufactured by Merck, trade name: Iriotech 8820 (antimony-doped tin oxide, mica, titanium oxide, silicon oxide composite), hereinafter referred to as "LM (3)".
Laser color former 4: manufactured by Merck, trade name: Iriotech 8825 (antimony-doped tin oxide-mica composite), hereinafter referred to as "LM (4)".
Laser color former 5: manufactured by HakusuiTech Co., Ltd., trade name: Pazet CK (aluminum-doped zinc oxide), hereinafter referred to as "LM (5)".
Laser color former 6: manufactured by Merck, trade name: Iriotech 8208 (antimony oxide-ethylene-butene copolymer composite), hereinafter referred to as "LM (6)".

<Examples 1 to 19, reference example 1>
In order to produce a three-kind five-layer laminated film containing a layer (I), a layer (II) and a layer (III), each raw material is mixed in the formulation shown in Table 1 (the laser color former is (III). ) The mass% shown in Table 1 was blended with 100 mass% of the resin constituting the layer.) The (I) layer / (II) layer / by three extruders and a three-kind five-layer multi-manifold base. In a facility capable of laminated coextrusion of (III) layer / (II) layer / (I) layer, after melt-kneading at a set temperature of each extruder at 200 to 230 ° C, the thickness ratio of each layer is (I) layer / Coextruded so that (II) layer / (III) layer / (II) layer / (I) layer = 5/1/28/1/5, taken up with a cast roll at 60 ° C., cooled and solidified, and unstretched. A laminated sheet was obtained. Next, this sheet was stretched 5.0 times in the horizontal uniaxial direction at a preheating temperature of 100 ° C. and a stretching temperature of 90 ° C. using a film tenter, and then heat-treated at 75 ° C. to obtain a heat-shrinkable laminated film having a thickness of 35 μm. Obtained. The evaluation results of the obtained film are shown in Table 1.

<Comparative Example 1>
As shown in Table 1, in order to produce a single-layer film composed of (I) layers, 100% by mass of Pes (1) and 0.3% by mass of LM (1) are mixed and then extruded by an extruder and a base. After melt-kneading at a set temperature of 200 to 230 ° C., the machine was taken up with a cast roll at 60 ° C. and cooled and solidified to obtain an unstretched sheet. Next, this sheet was stretched 5.0 times in the horizontal uniaxial direction at a preheating temperature of 90 ° C. and a stretching temperature of 80 ° C. using a film tenter, and then heat-treated at 90 ° C. to obtain a heat-shrinkable film having a thickness of 35 μm. rice field. The evaluation results of the obtained film are shown in Table 1.

<Comparative Example 2>
As shown in Table 1, after mixing PS (1) 40% by mass, PS (2) 60% by mass and LM (1) 0.3% by mass, in order to produce a single-layer film composed of the layer (III). An unstretched sheet was obtained by melting and kneading the set temperature of the extruder at 200 to 230 ° C. with an extruder and a base, taking it up with a cast roll at 60 ° C., and cooling and solidifying it. Next, this sheet was stretched 5.0 times in the horizontal uniaxial direction at a preheating temperature of 100 ° C. and a stretching temperature of 95 ° C. using a film tenter, and then heat-treated at 65 ° C. to obtain a heat-shrinkable film having a thickness of 35 μm. rice field. The evaluation results of the obtained film are shown in Table 1.

<Comparative Example 3>
In order to produce a two-kind three-layer laminated film consisting of a layer (I) and a layer (III), each raw material is mixed in the formulation shown in Table 1 (the laser color former is a resin constituting the layer (III)). The mass% shown in Table 1 was blended with respect to 100% by mass.) Extruded in a facility capable of laminating and coextruding the (I) layer / (III) layer / (I) layer by using an extruder and a base. After melt-kneading at the set temperature of the machine at 200 to 230 ° C, co-extruded so that the thickness ratio of each layer is (I) layer / (III) layer / (I) layer = 6/28/6, and cast at 60 ° C. It was taken up with a roll and cooled and solidified to obtain an unstretched sheet. Next, this sheet was stretched 5.0 times in the horizontal uniaxial direction at a preheating temperature of 100 ° C. and a stretching temperature of 90 ° C. using a film tenter, and then heat-treated at 75 ° C. to obtain a heat-shrinkable laminated film having a thickness of 35 μm. Obtained. The evaluation results of the obtained film are shown in Table 1.

<Comparative Example 4>
As the laser color former, a heat-shrinkable laminated film having a thickness of 35 μm was obtained by the same manufacturing method as in Examples except for the formulation in which the blending amount of LM (2) was 0.005% by mass. rice field. The evaluation results of the obtained film are shown in Table 1.

<Comparative Example 5>
As shown in Table 1, after mixing PS (1) 40% by mass, PS (2) 60% by mass and LM (2) 0.050% by mass, in order to produce a single-layer film composed of the layer (III). An unstretched sheet was obtained by melting and kneading the set temperature of the extruder at 200 to 230 ° C. with an extruder and a base, taking it up with a cast roll at 60 ° C., and cooling and solidifying it. Next, this sheet was stretched 5.0 times in the horizontal uniaxial direction at a preheating temperature of 100 ° C. and a stretching temperature of 95 ° C. using a film tenter, and then heat-treated at 65 ° C. to obtain a heat-shrinkable film having a thickness of 35 μm. rice field. The evaluation results of the obtained film are shown in Table 1.

<Comparative Example 6>
As the laser color former, a heat-shrinkable laminated film having a thickness of 35 μm was obtained by the same manufacturing method as in Examples for the formulation except that the blending amount of LM (6) was 7.0% by mass. rice field. The evaluation results of the obtained film are shown in Table 1.

The heat-shrinkable laminated films (Examples 1 to 19) obtained from the present invention exhibit a sufficient heat-shrinkage rate, have a low haze value, are excellent in transparency, and have excellent laser color development by laser beam irradiation and good visibility. It has good oil resistance and high delamination strength, and the result that meets the required quality for a heat-shrinkable film was obtained. In addition, no coloring of the film was confirmed.
On the other hand, the single-layer film containing a polyester resin as a main component (Comparative Example 1) has excellent color development and oil resistance, but has a high haze value and insufficient transparency. Coloring of the film was also confirmed. Further, in the single-layer film containing a polystyrene resin as a main component (Comparative Example 2 and Comparative Example 5), no coloring was observed in the film, and although the film was excellent in transparency and color development, the oil resistance was insufficient. Further, in the film having no (II) layer, which is an adhesive layer between the (I) layer and the (III) layer (Comparative Example 3), the adhesive strength between the (I) layer and the (III) layer is insufficient. rice field. Further, in the heat-shrinkable laminated film, a film in which the amount of the laser color-developing agent was less than the range of the present invention (Comparative Example 4) could not obtain sufficient color-developing property. Further, in the film in which the amount of the laser color-developing agent exceeded the range of the invention (Comparative Example 6), although the color-developing property was excellent, the haze value was high and the transparency was insufficient. The film having no laser color-developing agent (Reference Example 1) had no color-developing property.

Although the present invention has been described above in relation to embodiments that are considered to be the most practical and preferable at the present time, the present invention is not limited to the embodiments disclosed in the present specification. It can be changed as appropriate within the scope of claims and the gist of the invention that can be read from the entire specification or within the range not contrary to the idea, and the film with such a change must also be understood as being included in the technical scope of the present invention. Must be.

The heat-shrinkable laminated film of the present invention is excellent in laser color development property, heat shrinkage property, transparency, oil resistance, and interlayer adhesiveness by irradiation with a laser beam, and can be suitably used as various shrinkage packaging films.

Claims (4)

It has at least three layers (I), (II) and (III), and each layer contains the following resin in an amount of 50% by mass or more of the total constituents of each layer , and the (III) layer is the above-mentioned (III). III) The laser color former is contained in an amount of 0.01 to 5% by mass with respect to 100% by mass of the resin constituting the layer, and the heat shrinkage rate in the main shrinkage direction when immersed in warm water at 80 ° C. for 10 seconds is 20% or more. The layer composition is (I) layer, (II) layer, (III) layer, (II) layer, (I) layer, and (I) layer, (II) layer, (III) layer. , (II) layer and (I) layer are adjacent to each other, a heat-shrinkable laminated film.
(I) Layer: Polyester-based resin (II) Layer: Polyester-based resin and polystyrene-based resin (III) Layer: Polystyrene-based resin The heat-shrinkable laminated film according to claim 1, wherein the laser coloring agent contains at least one of bismuth oxide, tin oxide, zinc oxide, antimony oxide and lanthanum boride. The polystyrene-based resin contained in either one of the (II) layer and the (III) layer, or both layers, is a styrene-based hydrocarbon-conjugated diene-based hydrocarbon copolymer. The heat-shrinkable laminated film according to claim 1 or 2. The polyester resin contained in either one of the (I) layer and the (II) layer, or both layers, contains a terephthalic acid residue as a dicarboxylic acid residue and ethylene glycol as a diol residue. The heat-shrinkable laminated film according to any one of claims 1 to 3, which comprises a residue and a 1,4-cyclohexanedimethanol residue.