JP2021138098A - Heat-shrinkable laminate film - Google Patents

Abstract

To provide a heat-shrinkable laminate film which is excellent in laser color development property by irradiation with a laser beam, heat-shrinkable characteristics and transparency.SOLUTION: A heat-shrinkable laminate film is composed of at least two layers of a layer (I) and a layer (II), in which each of the layers contains the following component as a main component, and the layer (II) contains at least one filler selected from the group consisting of a molybdenum oxide, a copper oxide, mica and carbon black, a content of the filler is 0.002 mass% or more and 0.5 mass% or less when the whole layer (II) is 100 mass%, a haze value measured according to JIS K 7136 is 10% or less, and a heat shrinkage rate in a main shrinkage direction when being immersed in hot water at 80°C for 10 seconds is 20% or more. Layer (I): polyester-based resin. Layer (II): polystyrene-based resin.SELECTED DRAWING: None

Description

The present invention relates to a heat-shrinkable laminated film, and more particularly to a film mainly used for food packaging, specifically, a heat-shrinkable laminated film having excellent laser color development property, heat shrinkage characteristics, and transparency by laser irradiation.

Currently, soft drinks such as juice, alcoholic drinks such as beer, food seasonings, and toiletry products are sold in a container such as a PET bottle or a bottle. 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.

The importance of labeling is increasing from the viewpoint of prevention of counterfeiting and defects and traceability, mainly in the food industry that handles the above applications, and detailed product information such as date of manufacture, expiration date, lot number, and indication of production area. It is required to print on.

Individual product information such as manufacturing date, expiration 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. Therefore, from the viewpoint of 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, a laser-markable film characterized by 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 is known in Patent Document 1. 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 have particles that absorb laser light and generate heat when irradiated with a laser, and carbonize the surrounding resin to develop color. The so-called self-coloring type coloring agent, which carbonizes the resin of the above and further develops the color of the coloring agent itself in black, is attracting attention. However, this self-coloring type color-developing agent 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, or it is colored depending on the usage environment or changes with time. Coloring of the molded product significantly impairs the product value for a heat-shrinkable film that requires clear and high transparency. Further, from the functional aspect, there is a problem that the apparent laser color development property is deteriorated when the molded product is colored. 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, a film used for food applications is required to have a design property, and a printing layer is provided on the film, and the film is used as a packaging material after various printings. Therefore, the film is stable even after printing. There is a demand for a heat-shrinkable film having a laser color-developing property.
That is, a heat-shrinkable film having all the qualities such as shrinkage characteristics and transparency while ensuring sufficient visibility of laser printing regardless of the presence or absence of a print layer and a print pattern has not yet been put into practical use.

Japanese Unexamined Patent Publication No. 2004-268554 JP 2011-126142

The present invention has been studied in view of the above problems, and the heat-shrinkable laminated film is excellent in laser color development, heat-shrinkability, and transparency due to laser irradiation in the film and the film provided with the printing layer. It is an object of the present invention to provide a heat-shrinkable laminated film.

As a result of diligent studies on the above problems, the present inventors mainly use the polystyrene-based resin in a heat-shrinkable laminated film including a layer containing a polyester-based resin as a main component and a layer containing a polystyrene-based resin as a main component. By containing a specific amount of a specific filler in the layer as a component and setting the haze value and the heat shrinkage rate of the heat-shrinkable laminated film within a specific range, laser color development, heat-shrinkability, and transparency can be obtained. We have found that an excellent heat-shrinkable laminated film can be obtained, and completed the present invention.

That is, the present invention comprises at least two layers (I) and (II), each of which contains the following components as main components, and the (II) layer is molybdenum oxide, copper oxide, and mica. Contains at least one filler selected from the group consisting of carbon black, and the content of the filler is 0.002% by mass or more and 0.5% by mass or less when the entire layer (II) is taken as 100% by mass. The heat-shrinkable laminated film has a haze value of 10% or less measured in accordance with JIS K7136, and has a heat-shrinkage rate of 20% in the main shrinkage direction when immersed in warm water at 80 ° C. for 10 seconds. The above-mentioned heat-shrinkable laminated film is the first gist.
Layer (I): Polyester-based resin (II) Layer: Polystyrene-based resin

According to the present invention, it is possible to obtain a heat-shrinkable laminated film having excellent laser color development, heat-shrinkability, and transparency by laser irradiation in the film and the film provided with a printing layer, which is suitable for food packaging applications. Can be used for.

Hereinafter, the heat-shrinkable laminated film of the present invention (hereinafter, may be referred to as “the film of the present invention”) will be described in detail.
In the present specification, "as a main component" means that other components are allowed to be contained within a range that does not interfere with the action and effect of the resin contained as the main component. The term "main component" does not limit the specific content, but preferably is a component having a content of 50% by mass or more with respect to the entire constituent components, and occupies 70% by mass or more. It is more preferably a component, further preferably a component occupying 80% by mass or more, and a component occupying a range of 100% by mass or less.

<Heat shrinkable laminated film>
The film of the present invention has at least two layers, a layer (I) containing a polyester resin as a main component and a layer (II) containing a polystyrene resin as a main component, and the layer (II) is a molybdenum oxide. It contains a specific amount of at least one filler selected from the group consisting of copper oxide, mica, and carbon black. Hereinafter, each component contained in the film of the present invention will be described.

<Layer (I)>
In the film of the present invention, the layer (I) contains a polyester resin as a main component, and by using the polyester resin as a main component, the film is naturally provided with rigidity, fracture resistance and low temperature shrinkage. Shrinkage can be suppressed.

[Polyester resin]
The polyester-based resin is a thermoplastic resin obtained by polymerizing a polymerization component containing a polyvalent carboxylic acid residue and a polyol residue as a constituent raw material.
As the polyester resin which is the main component of the layer (I), a polyester resin obtained by polymerizing a dicarboxylic acid residue and a diol residue is preferable.

Examples of the dicarboxylic acid residue include terephthalic acid, isophthalic acid, 2-chloroterephthalic acid, 2,5-dichloroterephthalic acid, 2-methylterephthalic acid, 4,4-stylbenzicarboxylic acid, and 4,4-biphenyldicarboxylic acid. Acid, orthophthalic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, bisbenzoic acid, bis (p-carboxyphenyl) methane, anthracendicarboxylic acid, 4,4-diphenyl ether dicarboxylic acid, 4,4- Aromatic dicarboxylic acids such as diphenoxyetanedicarboxylic acid, 5-Nasulfoisophthalic acid, ethylene-bis-p-benzoic acid, adipic acid, sebacic acid, azelaic acid, dodecanedioic acid, 1,3-cyclohexanedicarboxylic acid, 1 , 4-cyclohexanedicarboxylic acid and other aliphatic dicarboxylic acids, or residues derived from their ester derivatives and the like. One of these dicarboxylic acid components may be used alone, or two or more thereof may be used in combination. Of these, aromatic dicarboxylic acids are preferable, and terephthalic acid and isophthalic acid are particularly preferable. Further, it is more preferable that terephthalic acid is the main component of the dicarboxylic acid residue.

When terephthalic acid is the main component of the dicarboxylic acid residue, the total amount of the dicarboxylic acid residue is 100 mol% from the viewpoint of mechanical properties such as rigidity, heat shrinkage and breakage resistance of the heat-shrinkable film. On the other hand, 75 mol% or more is preferable, 80 mol% or more is more preferable, 85 mol% or more is further preferable, and 100 mol% or less is preferable.

Examples of the diol residue include aliphatic diols such as ethylene glycol, 1,4-butanediol, neopentyl glycol, diethylene glycol, polytetramethylene glycol, and 1,3-propanediol, and 1,4-cyclohexanedimethanol. The alicyclic diol and the like can be mentioned. One of these diol residues may be used alone, or two or more thereof may be used in combination. Among these, as the diol residue, ethylene glycol, 1,4-butanediol, neopentyl glycol, diethylene glycol and 1,4-cyclohexanedimethanol are preferable, and ethylene glycol, 1,4-butanediol, diethylene glycol, 1 , 4-Cyclohexanedimethanol is particularly preferred. Further, it is more preferable to use ethylene glycol as a main component of the diol residue.

When ethylene glycol is used as the main component of the diol residue, the blending amount is based on 100 mol% of the total amount of the diol residue from the viewpoint of mechanical properties such as rigidity, heat shrinkage and breakage resistance of the heat-shrinkable film. 40 mol% or more is preferable, 45 mol% or more is more preferable, 50 mol% or more is further preferable, 85 mol% or less is preferable, 75 mol% or less is more preferable, and 70 mol% or less is further preferable.

The polyester-based resin is preferably a copolymerized polyester-based resin. That is, it is preferable that at least one of the dicarboxylic acid residue and the diol residue, which are the polymerization components of the polyester resin, is a mixture consisting of two or more kinds of residues. By using such a mixture system for at least one 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. In the present specification, in the mixture consisting of the above two or more kinds of residues, the one having the largest main residue, that is, the mass (mol%) is the first residue, and the one having a smaller amount than the first residue is used. , The residues below the second residue in the order of mass (mol%) (that is, the second residue, the third residue, and so on).

The above-mentioned copolymerized polyester resin contains terephthalic acid as the first residue of the dicarboxylic acid residue and ethylene glycol as the first residue of the diol residue, and further has a low crystalline component as a residue of the second residue or less. For example, containing at least one selected from the group consisting of 1,4-butanediol, neopentyl glycol, diethylene glycol, polytetramethylene glycol, 1,4-cyclohexanedimethanol, 1,3-propanediol, and isophthalic acid. Is preferable. Of these, 1,4-butanediol, diethylene glycol, 1,4-cyclohexanedimethanol, and isophthalic acid are particularly preferably contained.

The total content of the dicarboxylic acid residues below the second residue and the diol residues below the second residue is the total amount of dicarboxylic acid residues (100 mol%) and the total amount of diol residues (100 mol%). ), The lower limit is preferably 10 mol% or more, and more preferably 20 mol% or more. The upper limit is preferably 40 mol% or less, more preferably 35 mol% or less. When the content of the residue below the second residue 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 residue below the second residue 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, 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 fracture resistance can be improved.

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

In the polyester resin used in the present invention, the dicarboxylic acid residue and the diol residue are adjusted as polymerization components so as to have a predetermined component amount, and the polymerization component is first subjected to an esterification reaction according to a known method. After that, it can be obtained by subjecting it to a polycondensation reaction.

Further, as the polyester-based resin, in addition to the polyester-based resin obtained by polymerizing the dicarboxylic acid residue and the diol residue, a monomer having a carboxylic acid residue and an alcohol residue in one molecule is polymerized. It is also possible to use a polyester-based resin. In particular, polylactic acid obtained by polycondensation of lactic acid can be preferably used because it imparts rigidity, low temperature shrinkage, and low natural shrinkage.

The polyester-based resin used in the present invention may contain, for example, a copolymerized polyester-based resin and polyethylene terephthalate (homopolyester) composed of only terephthalic acid and ethylene glycol, and is one type of copolymerized polyester-based resin. It may consist of only two or more types of copolymerized polyester resins having different compositions.

The polyester-based resin preferably has a refractive index (n1) measured in accordance with JIS K7142 of 1.560 or more and 1.580 or less, and more preferably 1.565 or more and 1.574 or less. ..

The intrinsic viscosity 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, and even more preferably 1.0 dl / g or less. When the intrinsic viscosity is equal to or higher than the above value, deterioration of film strength characteristics and heat resistance can be suppressed. On the other hand, when the intrinsic viscosity is equal to or less than the above value, 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 Copperister" (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 more preferably 80% by mass, when the resin composition constituting the layer (I) is 100% by mass. More preferably, it is 90% by mass or more, and most preferably 90% by mass or more. As long as it is within the above range, the layer (I) may contain a resin other than the polyester resin. Examples of the above-mentioned other resins include polyolefin-based resins, polystyrene-based resins, polycarbonate resins, and acrylic-based resins, and polystyrene-based resins are particularly preferable.

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 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 with a gravure ink containing a normal organic solvent as a main component, and remains on the label. This is preferable because the amount of the solvent used is increased, blocking occurs after printing, and the odor of an organic solvent is less likely to occur.

<Layer (II)>
In the film of the present invention, the layer (II) contains a polystyrene resin as a main component and further contains a specific filler in a specific amount.

[Polystyrene resin]
Examples of the polystyrene-based resin include a styrene-based homopolymer obtained by polymerizing a styrene-based hydrocarbon, a copolymer of a styrene-based hydrocarbon and another monomer, and the like. Among them, in the present invention, it is preferable to contain a copolymer, and more preferably to contain a styrene-based hydrocarbon-conjugated diene-based hydrocarbon copolymer. The styrene-based hydrocarbon-conjugated diene-based hydrocarbon copolymer is a block copolymer of a styrene-based hydrocarbon block and a conjugated diene-based hydrocarbon block, and is a styrene-based hydrocarbon-conjugated diene-based hydrocarbon block. It is preferably a polymer.

Examples of the styrene-based hydrocarbon include styrene, p-, m- or o-methylstyrene, 2,4-, 2,5-, 3,4- or 3,5-dimethylstyrene, and pt-butyl. Alkyl styrene such as styrene; halogens such as o-, m- or p-chlorostyrene, o-, m- or p-bromostyrene, o-, m- or p-fluorostyrene, o-methyl-p-fluorostyrene and the like. Styrene chemicals; halogenated substituted alkyl styrenes such as o-, m- or p-chloromethyl styrene; alkoxy styrenes such as p-, m- or o-methoxystyrene, o-, m- or p-ethoxystyrene; o- , M-, or carboxyalkyl styrene such as p-carboxymethyl styrene; alkyl ether styrene such as p-vinylbenzyl propyl ether; alkyl silyl styrene such as p-trimethyl silyl styrene; further, vinyl benzyl dimethoxy phosphide and the like. These may be used alone or in combination of two or more. Of these, styrene is preferable.

The styrene-based hydrocarbon block is obtained by polymerizing or copolymerizing the styrene-based hydrocarbon. For example, a homopolymer obtained by polymerizing the styrene-based hydrocarbon using one kind, and the styrene-based hydrocarbon in 2 Examples thereof include a copolymer polymerized by using more than one species, and a copolymer obtained by polymerizing the above-mentioned styrene-based hydrocarbon and a copolymerizable monomer other than the above-mentioned styrene-based hydrocarbon.

Examples of the conjugated diene hydrocarbon include butadiene, isoprene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and 1,3-hexadiene. Can be mentioned. These may be used alone or in combination of two or more. Of these, butadiene and isoprene are preferable.

The conjugated diene-based hydrocarbon block is obtained by polymerizing or copolymerizing the above-mentioned conjugated diene-based hydrocarbon. For example, a homopolymer obtained by polymerizing the above-mentioned conjugated diene-based hydrocarbon using one kind, the above-mentioned conjugated diene-based Examples thereof include a copolymer obtained by polymerizing two or more kinds of hydrocarbons, and a copolymer obtained by polymerizing the above-mentioned conjugated diene-based hydrocarbon and a copolymerizable monomer other than the above-mentioned conjugated diene-based hydrocarbon.

As the block copolymer of the styrene-based hydrocarbon block and the conjugated diene-based hydrocarbon block, for example, a styrene block in which the styrene-based hydrocarbon is styrene and a butadiene block in which the conjugated diene-based hydrocarbon is butadiene are used together. Examples thereof include polymerized styrene-butadiene block copolymers (SBS).

The mass% ratio of styrene / butadiene is preferably (95 to 60) / (5 to 40), more preferably (93 to 60) / (7 to 40), and (90 to 90 to 40). It is more preferably 60) / (10 to 40).

The melt flow rate (MFR) measured value (measurement conditions: temperature 200 ° C., load 49N) of the SBS 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.

Examples of commercially available SBS products include "Asaflex" (manufactured by Asahi Kasei Chemicals Co., Ltd.) and "Clearlen" (manufactured by Denki Kasei Kogyo Co., Ltd.).

Further, as another example of the block copolymer of the styrene-based hydrocarbon block and the conjugated diene-based hydrocarbon block, there is a styrene-isoprene-butadiene block copolymer (SIBS).

The mass% ratio of styrene / isoprene / butadiene of the SIBS 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 further preferable. If the content of butadiene is high and the content of isoprene is low, the butadiene heated inside the extruder may undergo a cross-linking reaction and the gel-like substance may increase.

The measured value of melt flow rate (MFR) of SIBS (measurement conditions: temperature 200 ° C., load 49N) is preferably 2 g / 10 minutes or more, and more preferably 3 g / 10 minutes or more as a lower limit value. 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 used in the present invention 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 (70-30) / (30-70).

The polystyrene-based resin used in the present invention preferably has a refractive index (n2) measured in accordance with JIS K7142 as a lower limit of 1.540 or more, more preferably 1.550 or more, and 1.555 or more. Is even more preferable. The upper limit is preferably 1.600 or less, more preferably 1.590 or less, and even more preferably 1.585 or less.

Regarding the relationship with the refractive index (n1) of the polyester resin which is the main component of the layer (I), the difference between the refractive index (n2) of the polystyrene resin and the refractive index (n1) of the polyester resin is determined. It is preferably within the range of ± 0.02, preferably 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.

In order to adjust 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, for example, the polystyrene-based resin is a styrene-based hydrocarbon-conjugated diene-based hydrocarbon block. In the case of a block polymer, it can be carried out by appropriately adjusting the composition ratio of the styrene-based hydrocarbon and the conjugated diene-based hydrocarbon. When the polyester resin is contained in the layer (II) as described later, the composition ratio of the styrene hydrocarbon and the conjugated diene hydrocarbon is adjusted according to the refractive index (n1) of the polyester resin. By doing so, the refractive index (n2) of the polystyrene-based resin within the range of n1 ± 0.02 can be obtained. This predetermined refractive index may be adjusted by using the styrene-based hydrocarbon-conjugated diene-based hydrocarbon block copolymer alone, or by mixing two or more kinds of resins.

As for 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, and even 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 are no drawbacks such as a decrease in extrudability, which is preferable.

Also, polystyrene resin used in the present invention, the vibration frequency 10 Hz, distortion 0.1%, is preferably 0 storage modulus at ° C. (E ') is 1.00 × 10 ⁹ Pa or more, 1.50 × 10 ⁹ Pa or more is more preferable. The storage elastic modulus (E') at 0 ° C. represents the rigidity of the film, that is, the waist strength of the film. By polystyrene resin has 1.00 × 10 ⁹ Pa or more storage elastic modulus (E '), in addition to transparency, the film is obtained having a rigidity.

The polystyrene-based resin satisfying the storage elasticity (E') is, for example, a single substance of the above-mentioned styrene-based hydrocarbon-conjugated diene-based hydrocarbon block copolymer, a mixture of two or more kinds of the above-mentioned block copolymers, or a transparent resin. It can be obtained by mixing with other resins as long as the properties are not impaired.

When a mixture of a styrene-based hydrocarbon-conjugated diene-based hydrocarbon block copolymer or a mixture of this block copolymer and another resin is used as the main component of the layer (II), the block that exhibits breakage resistance is used. Good results can be obtained by appropriately selecting the polymer or resin and the block 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 hydrocarbon-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 a predetermined refractive index (n2) and storage elasticity at 0 ° C. (E').

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. Among them, 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. if ° C. is particularly preferred .0 storage modulus at ° C. (E ') is 1.00 × 10 ⁸ Pa or more having a viscoelastic property in the following, the hip by increasing the blending amount of resin carrying a rigid 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 fracture 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 become.

As the applied resin capable stiffness, copolymers storage elastic modulus at 0 ℃ (E ') consists of 2.00 × 10 ⁹ Pa or more styrene-based hydrocarbons, for example, to control the block structure styrene Examples thereof include a block copolymer of a based hydrocarbon block and a conjugated diene hydrocarbon block, a polystyrene, a styrene hydrocarbon, and an aliphatic unsaturated carboxylic acid ester copolymer.

Styrene series hydrocarbon with controlled block structure - Examples of the conjugated diene hydrocarbon block copolymers, the storage modulus at 0 ℃ (E ') is SBS and the like is 2.00 × 10 ⁹ Pa or more. The composition ratio of styrene and butadiene of SBS satisfying the above storage elastic modulus 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 the peak loss elastic modulus (E") is preferably in the range of 40 ° C. or higher and 90 ° C. or lower. There is a temperature. This peak temperature is a factor that mainly affects the shrinkage rate, and if this temperature is within the above range, the natural shrinkage and the low temperature shrinkage rate do not decrease extremely.
Further, more preferably, there is no clear peak temperature of elastic modulus (E ") below 40 ° C. When the peak temperature of elastic modulus (E") is apparently absent below 40 ° C. Since it exhibits a storage modulus property similar to that of polystyrene, it is possible to impart rigidity to the film.

A styrene-based hydrocarbon-conjugated diene-based hydrocarbon block copolymer that satisfies the above-mentioned viscoelastic properties is usually prepared by charging a part of styrene or butadiene to complete the polymerization, and then adding a mixture of a styrene monomer and a butadiene monomer. It is obtained by a method of charging and continuing the polymerization reaction.

By the above method, butadiene having the higher polymerization activity is preferentially polymerized, and finally a block composed of a single monomer of styrene is formed. 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 viscoelastic properties 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 (peak temperature of loss elastic modulus E ”due to the butadiene block is mainly present at 0 ° C. or lower. Therefore, it becomes difficult to set the storage elastic modulus (E') at 0 ° C. to a predetermined value or more.

Regarding the molecular weight, it is preferable that 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.

When a copolymer of the styrene-based hydrocarbon and the aliphatic unsaturated carboxylic acid ester is used as the resin capable of imparting rigidity, the aliphatic unsaturated carboxylic acid ester to be copolymerized with the styrene-based hydrocarbon may be used. For example, methyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate and the like can be mentioned. These may be used alone or in combination of two or more. Of these, butyl (meth) acrylate is preferable. The (meth) acrylate refers to acrylate or methacrylate.

The copolymer of the styrene-based hydrocarbon and the aliphatic unsaturated carboxylic acid ester is preferably a copolymer of styrene and butyl (meth) acrylate, and more preferably 70% by mass or more and 90% by mass or less of the styrene. The Tg (peak temperature of loss elasticity E ") of the copolymer is 50 ° C. or higher and 90 ° C. or lower, and the melt flow rate (MFR) measured value (measurement conditions: temperature 200 ° C., load 49N) is 2 g. It is 10 minutes or more and 15 g / 10 minutes or less.

Examples of commercially available products of the copolymer of the styrene-based hydrocarbon and the aliphatic unsaturated carboxylic acid ester include "TX polymer" (manufactured by Denki Kagaku Kogyo Co., Ltd.) and "Sebian" (manufactured by Daicel Polymer Co., Ltd.). ..

In addition to the polystyrene-based resin, other resins, compatibilizers, and the like can be mixed in the layer (II) as long as the characteristics of the film of the present invention are satisfied. Examples of the other resins include polyester resins, polyolefin resins, acrylic resins, and polycarbonate resins. These may be used alone or in combination of two or more.

Among the above other resins, polyester-based resins are preferable. In particular, when a mixed resin of a polyester resin and a polystyrene resin is used as the main component of the adhesive resin layer described later, it is possible that the (II) layer contains the polyester resin to form the (II) layer and the adhesive resin layer. It is preferable from the viewpoint of adhesiveness with.

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 (II) as 100% by mass and an upper limit value 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 (II) layer of the film of the present invention is the same as that in the (I) layer. Further, the polyester-based resin used in the layer (II) may be a polyester-based resin contained in the recycled raw material generated by trimming loss or the like generated during the production of the film of the present invention.

The content of the polystyrene-based resin in the layer (II) is not particularly limited, but is preferably 50% by mass or more when the resin composition constituting the layer (II) is 100% by mass. 60% by mass or more is more preferable, and 70% by mass or more is further preferable. However, when a compatibilizer such as a styrene homopolymer (GPPS), an oxazoline group-containing styrene-based polymer described later, or a styrene-maleic anhydride copolymer is contained as a polystyrene-based resin, GPPS or an oxazoline group-containing styrene-based polymer is used. Since the Tg (peak temperature of loss elasticity E ") of the copolymer and the styrene-maleic anhydride copolymer is very high, about 100 ° C. or higher, GPPS, an oxazoline group-containing styrene-based copolymer, and styrene-are mixed. The content of the maleic anhydride copolymer or a mixture thereof is preferably 20% by mass or less, more preferably 15% by mass or less, when the resin composition constituting the layer (II) is 100% by mass. It is preferable, and 10% by mass or less is more preferable.

[Filler]
The layer (II) used in the present invention contains a specific amount of a specific filler, and the specific filler has a function as a laser color former that generates heat when irradiated with a laser beam. Further, the specific filler may be a so-called self-coloring agent that develops its own color by irradiation with laser light, or may not develop its own color. When the laser color former generates heat, at least the forming material around it is carbonized, and the desired print appears on the layer (II). 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 carbides 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, its color is not particularly limited, but from the viewpoint of visibility, a laser color-developing agent capable of developing a dark color including black, navy blue, and brown is preferable.

Examples of the specific filler include at least one selected from the group consisting of molybdenum oxide, copper oxide, mica, and carbon black.

Examples of the molybdenum oxide and copper oxide include molybdenum oxide, copper oxide, copper molybdenum composite oxide, and copper molybdenum antimonthine composite oxide. Of these, copper molybdenum composite oxide and copper molybdenum antimony tin composite oxide are preferable.

Examples of the mica include muscovite, phlogopite, phlogopite, sodium tetrasilicon mica, mica antimony-doped tin complex and the like. Of these, the mica antimony-doped tin complex is preferable.

Examples of the carbon black include furnace black, lamp black, acetylene black, channel black, thermal black, and Ketjen black.

Among the above-mentioned specific fillers, carbon black is preferable from the viewpoint of excellent visibility when laser printing is performed.

When the specific filler is granular, the average particle size is preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 1 μm or less. If the average particle size of the filler is less than or equal to the above value, the transparency of the film may not be significantly reduced.

The content of the specific filler in the layer (II) is 0.002% by mass or more, preferably 0.0023% by mass or more, and 0.5% by mass or less when the whole layer (II) is 100% by mass. , Preferably 0.47% by mass or less. If the content of the specific filler is more than the above value, a sufficient color-developing effect can be obtained, and if it is less than the above value, the transparency may not be significantly lowered.

When carbon black is used as the specific filler, the content of carbon black is 0.002% by mass or more, preferably 0.0023% by mass or more, when the entire (II) layer is 100% by mass. It is 0.5% by mass or less, preferably 0.2% by mass or less, and more preferably 0.05% by mass or less. If the content of carbon black is more than the above value, a sufficient color-developing effect can be obtained, and if it is less than the above value, there is no possibility that the transparency is significantly lowered.

When molybdenum oxide, copper oxide, and mica are used as specific fillers, the content of molybdenum oxide, copper oxide, and mica is 0.002% by mass when the entire film of the present invention is taken as 100% by mass. % Or more, preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and 0.5% by mass or less, preferably 0.47% by mass or less. If the contents of molybdenum oxide, copper oxide, and mica are equal to or higher than the above values, a sufficient color-developing effect can be obtained, and if the contents are below the above values, the transparency is not significantly reduced.

In the present invention, the layer (II) 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 the above-mentioned specific filler is added to the resin and stretched, the specific filler existing near the surface of the polystyrene-based resin rises on the surface of the polystyrene-based resin due to the difference in elastic modulus between the specific filler and the polystyrene-based resin. Fine irregularities are formed on the resin, and the transparency is reduced. At that time, when the layer (I) containing no specific filler 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 a specific filler in the layer (II). 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 (II) layer containing a specific filler in the intermediate layer, that is, to print on the intermediate layer in order to avoid the problem that the printing disappears due to abrasion 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.

[Adhesive resin layer]
The film of the present invention is one in which at least the (I) layer and the (II) layer are laminated, and the above-mentioned (I) layer and (II) layer are laminated via an adhesive resin layer. Is preferable.

Examples of the adhesive resin forming the adhesive resin layer include polyester resin, polystyrene resin, polyethylene resin, polypropylene resin, cyclic polyolefin resin, and copolymer resin containing these resins as main components. Examples thereof include a modified resin or a mixture thereof. Of these, a mixed resin in which a polyester resin and a polystyrene resin are mixed is preferable.

By using the mixed resin of the polyester resin and the polystyrene resin (hereinafter, simply referred to as “mixed resin”) as the main component of the adhesive resin layer, the layer (I) containing the polyester resin as the main component and the layer (I) containing the polyester resin as the main component can be obtained. It is possible to improve the delamination strength with the layer (II) containing a polystyrene resin containing a specific filler in a specific amount as a main component.

As the polyester-based resin used in the mixed resin, the same polyester-based resin as that used in the layer (I) can be used as long as it satisfies the characteristics of the film of the present invention. For example, (I) It may be the same as the polyester resin used in the layer, or a different polyester resin may be used, but it is preferably the same as the polyester resin used in the layer (I).

The content of the polyester resin in the mixed resin is preferably 40% by mass or more, more preferably 45% by mass or more, and 50% by mass or more as the lower limit value when the whole mixed resin is 100% by mass. More preferred. The upper limit value is preferably 80% by mass or less, more preferably 75% by mass or less, and further 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 (II) is good. It is preferable because it does not decrease.

Further, as the polystyrene-based resin used in the mixed resin, the same polystyrene-based resin as that used in the layer (II) can be used as long as it satisfies the characteristics of the film of the present invention. It may be the same as the polystyrene-based resin used in the layer (II), or a different polystyrene-based resin may be used, but it is preferable that it is the same as the polystyrene-based resin used in the layer (II).

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

Also, polystyrene resin contained in the resin mixture, the vibration frequency 10 Hz, distortion 0.1%, is preferably 0 storage modulus at ° C. (E ') is 1.00 × 10 ⁷ Pa or more, 1.50 It is more preferable that it is × 10 ^{7 Pa or more.} Since the polystyrene-based resin contained in the mixed resin has the above-mentioned storage elastic modulus (E'), when the film of the present invention is molded, the adhesiveness to the above-mentioned layer (I) or (II) can be imparted. At the same time, when it is shrunk in a high temperature atmosphere, it is possible to suppress delamination between the layer (I) or the layer (II). 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 polystyrene-based resin satisfying the storage elasticity (E') is, for example, a single substance of the above-mentioned styrene-based hydrocarbon-conjugated diene-based hydrocarbon block copolymer, or a mixture of two or more kinds of the above-mentioned copolymers, or transparency. It can be obtained by mixing with other resins as long as the above is not impaired.

Preferred as the styrene-based hydrocarbon-conjugated diene-based hydrocarbon block copolymer are block SBS and random block SBS. Among them, 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 × 10 ⁷ Pa or more, the laminated body is formed by increasing the blending amount of the resin which bears the rigidity. When molded into a film, it is possible to impart stiffness 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 fracture resistance. Although the characteristics change depending on the stretching conditions, if the peak temperature of the loss elastic modulus (E ") does not exist at 0 ° C. or lower in the state before stretching, the adhesiveness with the layer (I) or the layer (II) decreases. 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 adhesive resin layer used in the present invention may contain other compounds as long as it satisfies the characteristics of the film of the present invention, and examples thereof include a compatibilizer, an acrylic resin, and a polycarbonate resin. Among them, when the above mixed resin is used, it is preferable to contain a compatibilizer.

[Compatible agent]
The compatibilizer is not particularly limited as long as it can promote the compatibilization of the polyester resin and the polystyrene resin contained in the mixed resin, but at least one of the oxazoline group-containing styrene copolymer and the styrene-maleic anhydride copolymer. It is preferably a seed. When the mixed resin further contains a compatibilizer, the dispersibility of the polyester resin or the styrene resin is improved, the transparency of the film is improved, and the thickness is made uniform, which is preferable from the viewpoint of improving production and productivity. Furthermore, the interlayer adhesion strength can be improved by using a compatibilizer.

The compatibilizer contained in the mixed resin has a polar group having a high affinity with the polyester resin contained in the mixed resin or a polar group capable of reacting with the polyester resin, and a polystyrene resin contained in the mixed resin. A styrene-based block copolymer or graft copolymer having a site compatible with or having a high affinity with the resin is preferably used. Specific examples of the polar group or reactive functional group having a high affinity with the 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. Functional groups such as a carboxylic acid base, a sulfonic acid group, a sulfonic acid ester group, a sulfonated group, a sulfonic acid amide group, a sulfonic acid base, an epoxy group, an amino group, an imide group, or an oxazoline group can be mentioned. An acid anhydride group, a carboxylic acid group or a carboxylic acid ester group, and an oxazoline group are preferable.

Further, the above-mentioned "having a site capable of being compatible with a polystyrene-based resin" means, for example, having a chain having an affinity with a 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 Polyscape).

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

[Additives to each layer]
In addition to the above-mentioned components, the film of the present invention contains at least one of a plasticizer and a tackifier resin in each layer for the purpose of improving and adjusting the moldability, productivity and various physical properties of the heat-shrinkable film. It can be added within a range that does not significantly impair the effect. When the resin composition constituting each layer is 100% by mass, the lower limit of these addition amounts is preferably 1% by mass or more, more preferably 2% by mass or more, and further preferably 3% by mass or more. preferable. The upper limit value is preferably 10% by mass or less, more preferably 8% by mass or less, and further 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-bonding property are small, and natural shrinkage is unlikely to occur, which is preferable.

Further, in order to impart slipperiness to the film and prevent blocking, it is preferable to blend an incompatible resin or add a so-called anti-blocking 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. Can be mentioned. In addition, organic particles having a multilayer structure polymerized in multiple stages can also be used. Of these, silica and organic particles are preferable.

Since the anti-blocking agent develops slipperiness and blocking resistance by roughening the film surface, transparency and film gloss 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, as the lower limit value when the entire resin composition constituting the front and back layers is 100% by mass. , 0.02% 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, and further 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, when the upper limit of the anti-blocking agent is within the above range, excessive unevenness on the film surface does not occur, transparency is hindered due to surface roughness, and film rolls are wound due to excessive slipperiness. Is preferable.

The shape of the antiblocking 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, and even 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, when printing is performed on the film of the present invention to improve the design, ink loss is unlikely to occur and the appearance of the printed pattern is not spoiled. ..
The particle size distribution of the antiblocking agent is not particularly limited, but a narrow particle size distribution is preferable. This is because if the particle size distribution becomes too wide, some particles may deviate from the above-mentioned preferably used particle size range.

Further, the film of the present invention includes various additives such as an ultraviolet absorber, a light stabilizer, an antioxidant, an antioxidant, a stabilizer, a colorant, an antistatic agent, a lubricant, and the above-mentioned specific additives, depending on the intended purpose. Inorganic fillers other than fillers can be appropriately added according to each application.

[Film layer structure]
The film of the present invention has at least two layers, a layer (I) containing a polyester resin as a main component and a layer (II) containing a polystyrene resin containing a specific filler as a main component, and is preferable. The layer (I) and the layer (II) are laminated films laminated via the adhesive resin layer. The combination of the above layer configurations is appropriately selected according to the purpose and application, but in the present invention, the order is (I) layer / adhesive resin layer / (II) layer / adhesive resin layer / (I) layer. It is preferable to have a laminated three-kind five-layer structure.

In the present invention, by adopting the above layer structure, a heat-shrinkable laminated film excellent in laser color development, heat-shrinkability, 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 (II) is preferably 2 or more as the lower limit of the layer (II) 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 adhesive resin layer is preferably 7% or more, more preferably 9% or more of the total thickness of the layer (I). The upper limit value 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 adhesive resin layer 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 abrasion 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 the cost of raw materials as much as possible. Specifically, the thickness after stretching is preferably 60 μm or less, more preferably 55 μm or less. , 50 μm or less is more preferable.

[Method for producing a film of the present invention]
In the film of the present invention, at least two layers (I) and (II), preferably at least three layers (I), (II), and an adhesive resin layer are laminated simultaneously or sequentially. Then, the laminated film is produced, and then the laminated film is heated and stretched in at least one axial direction.

The laminated film is 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 resin layer. Can be done. Further, the laminated film can be sequentially produced, for example, by separately forming a sheet of the resin constituting each layer and then laminating the resin by using 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.

When the above biaxial stretching is performed, the film may be stretched in the direction (vertical direction) [MD: Machine Direction] and the direction orthogonal to the vertical direction (horizontal direction) [TD: Transverse Direction] at the same time. Sequential biaxial stretching in which either one is performed first is effective, and the order may be either MD or TD.

The stretching temperature at the time of performing the stretching 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 usually 60 ° C. or higher, preferably 70 ° C. or higher. It is controlled in the range of 130 ° C. or lower, preferably 120 ° C. or lower. The stretching ratio in the main shrinkage direction is 2 times or more, preferably 3 times or more, more preferably 4 times or more, preferably 7 times or less, depending on the film constituents, stretching means, stretching temperature, and target product form. Is appropriately determined in the range of 6 times or less. Further, whether to use uniaxial stretching or biaxial stretching is determined by the intended use of the target product. The "main contraction direction" is a direction in which the heat shrinkage rate when contracted by applying heat is high, that is, a direction in which the stretching direction is larger in the vertical direction and the horizontal direction, and is usually the TD direction. Further, when it is attached to a bottle, it is, for example, a direction corresponding to the outer peripheral direction thereof.

Even in the case of applications that require shrinkage characteristics in almost one direction, such as PET container labels, it is also effective to biaxially stretch in the direction perpendicular to the main shrinkage direction as long as the shrinkage characteristics are not impaired.

As for the stretching ratio in the vertical direction, the fracture resistance improves as the stretching ratio increases, but the heat shrinkage rate increases accordingly, and it becomes difficult to obtain a good shrinkage finish. Therefore, 1.03 times or more 1. It is particularly preferable that it is 5 times or less. The stretching temperature is typically in the range of 60 ° C. or higher and 90 ° C. or lower, although it depends on components other than PET.

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

Further, it is preferable to arrange a printing layer containing titanium oxide on one surface of the film of the present invention obtained as described above from the viewpoint of visibility at the time of laser printing. The print layer can be formed by an existing method such as gravure printing.

The thickness of the print layer is usually 1 to 30 μm, preferably 2 to 20 μm, and particularly preferably 2 to 10 μm. When the thickness of the print layer is within the above range, the visibility at the time of laser printing tends to be higher.

<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 10% or less. It is preferably 9% or less, particularly preferably 6% or less. When the haze value is equal to or less than the above value, good transparency can be obtained and beautiful printing or the like can be performed.

<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 value is not particularly limited, but is generally preferably 70% or less, more preferably 65% or less, still more preferably 60% or less. If the heat shrinkage rate in the main shrinkage direction at 80 ° C. is less than 20%, the heat shrinkage may be insufficient at the neck and top surface of the container.

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. % Or more and 20% or less are more preferable. 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. 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.

In addition, in this specification, "at least one direction" means either one or both directions which are orthogonal to the main contraction direction and the main contraction direction, and usually refers to the main contraction direction.

If the heat shrinkage rate in the main shrinkage direction when immersed in warm water at 80 ° C. for 10 seconds and the heat shrinkage rate in at least one direction when immersed in warm water at 70 ° C. for 10 seconds are within the above range, 70 ° C. In the low temperature range in the vicinity, the laminated film has heat shrinkage to the extent that it is temporarily fixed to a container, for example, and shrinks rapidly in the high temperature range exceeding 70 ° C. and around 80 ° C., and as a result, At the specified position, not only the body of the container but also the neck and top surface, which are very thin compared to the body, do not cause abnormalities such as wrinkles and avatars, and uniform shrinkage is obtained, resulting in a beautiful shrinkage finish. It becomes.

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. If the heat shrinkage rate when immersed in warm water at 50 ° C. for 10 seconds is greater than 5%, the natural shrinkage rate of the film is likely to increase, and it is likely that the film will be rolled up and squeezed or rolled when stored. It is possible to cause an appearance defect that the end faces are uneven.

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, and even more preferably 78% or less.
The heat shrinkage rate in the main shrinkage direction at 99 ° C. represents the strain of the film. It may occur and impair transparency. On the other hand, if it is less than 70%, there is a possibility that insufficient shrinkage may occur and problems such as the finish not being tight 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.

<Laser color development>
The film of the present invention contains a specific filler, and by irradiating the specific filler with a laser beam, the specific filler functions as a laser color former. Therefore, the resin component around the filler of the irradiated portion is carbonized and colored, and a printed matter having excellent visibility such as characters and numbers can be obtained.

When the film of the present invention is irradiated with a laser under the following laser irradiation conditions, the reflection density of the laser irradiation portion of the film irradiated with a pulsed laser average output of 5 W, 10 W, or 15 W under at least one laser irradiation condition is 0.10. It is preferably 0.20 or more, more preferably 0.23 or more, and particularly preferably 0.23 or more. If the reflection density is less than the above value, the visibility at the time of laser printing tends to be inferior. Further, it is more preferable that the reflection density of the laser irradiation portion of the film is equal to or higher than the above value when irradiated with a pulsed laser average output of 10 W.
(Laser irradiation conditions)
Pulsed laser average output: 5W, 10W, 15W
Scanning speed: 2000 mm / sec
Distance between scanning lines: 0.14 mm
Beam diameter: 0.14 mm

Further, when the above-mentioned printing layer containing titanium oxide is arranged on one surface of the film of the present invention, when laser irradiation is performed under the above laser irradiation conditions, the pulsed laser average output of 5W and 10W under at least one laser irradiation condition. , Or, the reflection density of the laser-irradiated portion of the film irradiated with 15 W is preferably 0.30 or more, more preferably 0.38 or more, and particularly preferably 0.43 or more. If the reflection density is less than the above value, the visibility at the time of laser printing tends to be inferior. Further, it is more preferable that the reflection density of the laser irradiation portion of the film is equal to or higher than the above value when irradiated with a pulsed laser average output of 10 W.
If the reflection density above a certain level can be obtained with a relatively low average output of the palace laser as in the above laser irradiation conditions, visibility can be achieved by increasing the average output of the palace laser even when the scanning speed is to be increased. High laser printability can be obtained.

Examples of the laser beam that can be used for laser printing 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) and the like. In particular, the YAG laser and Yb fiber laser transmit 90% or more of the polystyrene resin and polyester resin film used in the film of the present invention, are difficult to be absorbed by these resins themselves, and the laser beam is efficient for a specific filler. Since it is well absorbed, it can be preferably used.

For the laser beam, it is necessary to appropriately adjust the irradiation conditions such as the average output of the pulsed laser, the pulse period, and the scanning speed.
If the average output of the pulsed laser is made too large, 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 may be formed. Further, since the film of the present invention imparts heat shrinkage characteristics, in the 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 removed from the end face of the test piece in the main contraction direction. A peeling portion is formed on the (I) layer side by peeling, and the peeling portion and the peeled portion of the (II) layer are sandwiched by chucks of a tensile tester, respectively, and 180 ° at a test speed of 100 mm / min in the main contraction direction. The delamination strength when the peeling test is performed is preferably 1N / 15 mm width or more, and more preferably 1.5N / 15 mm width or more. If the delamination strength is equal to or higher than the above value, troubles such as vibration during transportation and delamination due to scratching of nails or the like do not occur.

<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 packaging. 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 the take-back (flow) direction is described as "TD".
In addition, the transparency, heat shrinkage, laser color development, and comprehensive evaluation of the obtained film were evaluated as follows.

(1) Transparency The obtained film was measured for haze value in accordance with JIS K7136, and the transparency was evaluated according to the following evaluation criteria.
(Evaluation criteria)
⊚: Haze value is 6% or less ○: Haze value is more than 6% and 10% or less ×: Haze value is more than 10%

(2) Heat Shrinkage The obtained film was cut into a size of MD 20 mm and TD 100 mm to prepare a sample. This sample was immersed in a hot water bath at 80 ° C. for 10 seconds, and the amount of shrinkage in the main shrinkage direction was measured. For the heat shrinkage rate, the ratio of the amount of shrinkage to the actual size before shrinkage was expressed as a% value. The main contraction direction in this example and the comparative example was TD.

(3) Laser color development (without printing layer)
The obtained film was printed by laser irradiation using a marking FAYb laser (wavelength 1060 nm). The laser irradiation conditions were pulsed laser average output 5W, 10W, 15W, scanning speed 2000 mm / sec, scanning line distance 0.14 mm, beam diameter 0.14 mm, and printing was performed at the position of just focus. After that, the laser beam irradiation unit was measured with a reflection densitometer (R700 monochrome reflection densitometer) manufactured by Ihara Denshi Kogyo Co., Ltd., and the color development property was evaluated according to the following evaluation criteria. Further, the evaluation result of the laser color development property at a laser average output of 10 W was used as a comprehensive evaluation of the laser color development property of the film (without a printing layer). In actual laser printing, it is sufficient that the optimum conditions can be obtained in the range of the laser average output of 5 to 15 W. Therefore, if the evaluation is “◯” in the range of 5 to 15 W, it can withstand practical use.
(Evaluation criteria)
⊚: Reflection density 0.30 or more 〇: Reflection density 0.10 or more and less than 0.30 ×: Reflection density less than 0.10, or holes and deformation (shrinkage) were observed.

(4) Laser color development (with print layer)
A gravure calibrator (manufactured by Nissho Gravure Co., Ltd., model: CM type) and a solid pattern plate (manufactured by Nabe Process Co., Ltd.) were used to apply white ink containing titanium oxide to one side of the obtained film, and then air-dried. , A printing film having a total thickness of 40 μm was obtained. At this time, the thickness of the white ink was 5 μm. The white ink is a mixture of 60% by volume of "High Conch White RD-2 for Fine Wrap NTV PET" manufactured by DIC and 40% by volume of "Univia NT Reducer No. 2" manufactured by DIC. It was used. The film on which the printing layer was arranged was irradiated with a laser under the same conditions from the opposite side of the printing surface, and the color development property was evaluated according to the following evaluation criteria. Further, the evaluation result of the laser color development property at a laser average output of 10 W was used as a comprehensive evaluation of the laser color development property of the film (with a printing layer).
(Evaluation criteria)
⊚: Reflection density 0.50 or more 〇: Reflection density 0.30 or more and less than 0.50 ×: Reflection density less than 0.30, or holes and deformation (shrinkage) were observed.

(5) Comprehensive evaluation All evaluations of the above haze value, laser color development of laser color development (without printing layer), and laser color development of laser color development (with print layer) are "○" or higher. The case where the heat shrinkage rate was 20% or more was set as “◯”, and the case where the heat shrinkage rate was 20% or more was set as “x”.

The raw materials used in each of the examples and comparative examples are as follows.
[Polyester resin]
Copolymerized polyester 1 (acid component: terephthalic acid 100 mol%, glycol component: ethylene glycol 65 mol%, diethylene glycol 3 mol%, 1,4-cyclohexanedimethanol 32 mol%, hereinafter referred to as "Pes (1)")
Copolymerized polyester 2 (acid component: terephthalic acid 90 mol%, isophthalic acid 10 mol%, glycol component: 1,4-butanediol 100 mol%, hereinafter referred to as "Pes (2)")
Copolymerized polyester 3 (acid component: terephthalic acid 100 mol%, glycol component: ethylene glycol 65 mol%, diethylene glycol 12 mol%, 1,4-cyclohexanedimethanol 23 mol%, hereinafter referred to as "Pes (3)")

[Polystyrene resin]
-Styrene-butadiene copolymer 1 (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 (1)")
Styrene-butadiene copolymer 2 (styrene / butadiene = 81/19 (mass%), storage elastic modulus E'(0 ° C.): 2.13 × 10 ⁹ Pa, loss elastic modulus E ”peak temperature 74 ° C., Hereinafter referred to as "PS (2)")

[Filler]
-Filler 1: Manufactured by Toyo Ink Co., Ltd., trade name: TSM5KF963GRN (polystyrene 95% by mass / copper molybdenum antimony tin composite oxide 5% by mass), hereinafter referred to as "LM (1)".
-Filler 2: Manufactured by Dainichiseika Kogyo, trade name: RS-PMZZ18K8690N-L (containing 90% by mass of polystyrene-based copolymer / 10% of titanium oxide antimony mineral oil compound), hereinafter referred to as "LM (2)".
-Filler 3: manufactured by Toyo Ink Co., Ltd., trade name: TSM1KP980Z-NAT (containing 85% by mass of polystyrene / 15% of mica antimony-doped tin composite), hereinafter referred to as "LM (3)".
-Filler 4: Manufactured by Tokan Material Technology Co., Ltd., trade name: Tomatec 42-920A (bismuth neodymium oxidation complex), hereinafter referred to as "LM (4)".
-Filler 5: manufactured by Tokan Material Technology Co., Ltd., trade name: Tomatec 42-907A (copper molybdenum antimony tin composite oxide), hereinafter referred to as "LM (5)".
-Filler 6: Manufactured by Tokan Material Technology Co., Ltd., trade name: Tomatec 42-903A (copper molybdenum composite oxide), hereinafter referred to as "LM (6)".
-Filler 7: manufactured by Toyo Ink Co., Ltd., trade name: TSM9KE440GRY (containing 99.9% by mass of polystyrene-based copolymer / 0.1% of carbon black), hereinafter referred to as "LM (7)".

<Examples 1 to 6, Comparative Examples 1 to 6>
In order to produce a three-kind five-layer laminated film containing a layer (I), a layer (II), and an adhesive resin layer, each raw material is mixed in the formulation shown in Table 1 (fillers 1 to 7 are: (II) The whole layer was set to 100% by mass and blended so as to have the amount of the filler active ingredient (mass%) shown in Table 1. Described as the amount of the active ingredient equivalent addition), 3 extruders and 3 types of 5 layer mulch. In equipment capable of laminating and co-extruding the (I) layer / adhesive resin layer / (II) layer / adhesive resin layer / (I) layer by the manifold base, the set temperature of each extruder is set to 200 to 230 ° C. After melt-kneading, co-extrusion is performed so that the thickness ratio of each layer is (I) layer / adhesive resin layer / (II) layer / adhesive resin layer / (I) layer = 5/1/28/1/5. It was taken up with a cast roll at 60 ° C. and cooled and solidified to obtain an unstretched laminated 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. rice field. The evaluation results of the obtained film are shown in Table 1.

The heat-shrinkable laminated film (Examples 1 to 6) obtained from the present invention exhibits a sufficient heat-shrinkage rate, has a low haze value, is particularly excellent in transparency, and has excellent laser color development by laser beam irradiation and visibility. It was good, and in particular, the laser color development property when the white print layer was arranged was particularly excellent, and the result satisfying the required quality required for the heat-shrinkable film was obtained.
On the other hand, the heat-shrinkable laminated film of Comparative Example 1 could not obtain sufficient color-developing property when laser-colored. Further, in the heat-shrinkable laminated films of Comparative Examples 2 to 6, although the color-developing property was generally excellent, the haze value was high and the transparency was insufficient.

Although the present invention has been described above in relation to the most practical and preferred embodiments 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 scope of the invention that can be read from the entire specification or within a range that does not contradict 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, heat-shrinkability, and transparency by laser irradiation, and can be suitably used as various shrink-packaging films.

Claims (8)

A group consisting of at least two layers (I) and (II), each of which is mainly composed of the following components, and the (II) layer is composed of molybdenum oxide, copper oxide, mica, and carbon black. A heat-shrinkable laminate containing at least one filler selected from the above, and the content of the filler is 0.002% by mass or more and 0.5% by mass or less when the entire layer (II) is taken as 100% by mass. It ’s a film,
A heat-shrinkable laminated film having a haze value of 10% or less measured in accordance with JIS K7136 and a heat-shrinkage rate of 20% or more in the main shrinkage direction when immersed in warm water at 80 ° C. for 10 seconds.
Layer (I): Polyester-based resin (II) Layer: Polystyrene-based resin The heat shrinkage according to claim 1, wherein when the heat-shrinkable laminated film is laser-irradiated under the following laser irradiation conditions, the reflection density of the laser-irradiated portion of the film is 0.10 or more under at least one laser irradiation condition. Sex laminated film.
(Laser irradiation conditions)
Pulsed laser average output: 5W, 10W, 15W
Scanning speed: 2000 mm / sec
Distance between scanning lines: 0.14 mm
Beam diameter: 0.14 mm The heat-shrinkable laminated film according to claim 1 or 2, wherein the polystyrene-based resin that is the main component of the layer (II) contains a styrene-based hydrocarbon-conjugated diene-based hydrocarbon copolymer. The polyester-based resin that is the main component of the layer (I) is a copolymerized polyester-based resin, and 1,4-butanediol, neopentyl glycol, diethylene glycol, polytetramethylene glycol, and 1,4-cyclohexane are used as copolymerization components. The heat-shrinkable laminated film according to any one of claims 1 to 3, which comprises at least one selected from the group consisting of dimethanol, 1,3-propanediol, and isophthalic acid. The heat-shrinkable laminated film according to any one of claims 1 to 4, wherein the layer (I) and the layer (II) are laminated via an adhesive resin layer. The heat-shrinkable laminated film according to claim 5, wherein the adhesive resin layer contains a mixed resin of a polyester resin and a polystyrene resin as a main component. A heat-shrinkable laminated film in which a printing layer containing titanium oxide is arranged on one surface of the heat-shrinkable laminated film according to any one of claims 1 to 6. When the heat-shrinkable laminated film according to claim 7 is irradiated with a laser from the opposite side of the printing layer under the following laser irradiation conditions, the reflection density of the laser-irradiated portion of the film is 0.30 or more under at least one irradiation condition. Is a heat-shrinkable laminated film.
(Laser irradiation conditions)
Pulsed laser average output: 5W, 10W, 15W
Scanning speed: 2000 mm / sec
Distance between scanning lines: 0.14 mm
Beam diameter: 0.14 mm