JP2017213875A - Heat-shrinkable laminated film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-shrinkable laminated film excellent in laser color development property by irradiation with laser, heat shrinkage characteristics, transparency, oil resistance and interlayer adhesion.SOLUTION: The heat-shrinkable laminated film is provided which has at least three layers of (I) layer, (II) layer and (III) layer and has a heat shrinkage rate in a main shrinkage direction of 20% or more when immersed in hot water at 80°C for 10 seconds, and in which each of the layers includes the following resins as main components, the (III) layer includes 0.01-5 mass% of a laser color developer with respect to 100 mass% of a resin constituting the (III) layer. The (I) layer is made of a polyester resin. The (II) layer is made of a polyester resin and a polystyrene resin. The (III) layer is made of a polystyrene resin. The laser color developer includes one or more of bismuth oxide, tin oxide, zinc oxide, antimony oxide and lanthanum boride.SELECTED DRAWING: None

Description

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

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

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

  Individual product information such as the date of manufacture, expiry date, lot number, production area display, etc. is printed by the ink-jet 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 be peeled off and the print visibility may be reduced. From the viewpoint of visibility, it is known to select a laser marking method capable of absorbing laser beam irradiation, carbonizing, and coloring to perform laser printing.

For example, Patent Document 1 discloses a laser-markable film characterized by a two-layer / three-layer multilayer resin film having a configuration in which a transparent or translucent resin layer and a laser beam irradiation color-developing film layer are laminated. Patent Document 2 discloses a laminate for laser marking using a laser color former containing bismuth oxide and neodymium oxide.
Conventionally, laser color formers generally generate particles by absorbing the laser beam and generating heat when irradiated with a laser, and carbonizing the surrounding resin. So-called self-coloring color formers that carbonize these resins and color the color formers themselves are also drawing attention. However, this self-coloring type color former has a problem that a molded product such as a film is colored when processed at a high temperature during molding or compounding. For heat-shrinkable films that require clear and high transparency, coloration significantly impairs product value. Further, from the viewpoint of function, there is a problem that when the molded product is colored, the apparent laser colorability is lowered. When the addition amount of the color former is increased to improve the color developability, the transparency is further deteriorated. As described above, the coloring problem of the self-coloring color former has been a big problem when the color former is used for a heat-shrinkable film that requires particularly high transparency.

  Moreover, since many food uses contain oil in the contents of the package, 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 have all the qualities of shrinkage, transparency, interlayer adhesion, etc., while ensuring sufficient visibility of laser printing, are also resistant to oil. It 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 is to provide a heat-shrinkable laminated film excellent in laser color development, heat-shrinkage characteristics, transparency, oil resistance, and interlayer adhesion by laser irradiation. .

As a result of intensive studies, the inventors have succeeded in obtaining a heat-shrinkable laminated film that can solve the above-described 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 of (I) layer, (II) layer and (III) layer, each layer mainly composed of the following resin, and further (III) layer is (III) The thermal contraction rate in the main shrinkage direction is 20% or more when immersed in warm water of 80 ° C. for 10 seconds, containing 0.01 to 5% by weight of the laser color former with respect to 100% by weight of the resin constituting the layer. This is achieved by a heat-shrinkable laminated film.
(I) Layer: Polyester resin (II) Layer: Polyester resin and polystyrene resin (III) Layer: Polystyrene resin

  According to the present invention, it is possible to obtain a heat-shrinkable laminated film that is excellent in laser color development by laser irradiation, heat shrinkage characteristics, transparency, oil resistance, and interlayer adhesion. 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 the present specification, “main component” is intended to allow other components to be included as long as the action and effect of the resin constituting each layer is not hindered. Further, the term does not limit the specific content, but it is 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, and 100% by mass with respect to the total components of each layer. It is a component that occupies the following ranges.

<Heat-shrinkable laminated film>
The film of the present invention comprises a (I) layer containing a polyester resin as a main component, a (II) layer 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. (III) The layer has at least three layers, and the layer (III) contains 0.01 to 5% by mass of a laser color former and is thermally contracted in the main contraction direction when immersed in warm water at 80 ° C. for 10 seconds. Is a heat-shrinkable laminated film characterized by being 20% or more.

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

<Polyester resin>
The film of the present invention can suppress natural shrinkage while imparting rigidity, rupture resistance, and low-temperature shrinkage to the film by using the polyester resin as the main component of the (I) layer. A polyester resin suitable for the present invention is a polyester resin derived from a dicarboxylic acid residue and a diol residue. Examples of dicarboxylic acid residues include terephthalic acid, isophthalic acid, 2-chloroterephthalic acid, 2,5-dichloroterephthalic acid, 2-methylterephthalic acid, 4,4-stilbene dicarboxylic acid, 4,4-biphenyldicarboxylic acid , Orthophthalic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, bisbenzoic acid, bis (p-carboxyphenyl) methane, anthracene dicarboxylic acid, 4,4-diphenyl ether dicarboxylic acid, 4,4-di Aromatic dicarboxylic acids such as phenoxyethanedicarboxylic acid, 5-Na sulfoisophthalic acid, ethylene-bis-p-benzoic acid, adipic acid, sebacic acid, azelaic acid, dodecanedioic acid, 1,3-cyclohexanedicarboxylic acid, 1, Aliphatic dicarboxylic acids such as 4-cyclohexanedicarboxylic acid or Residues derived from their esters derivatives. These dicarboxylic acid residues may be used alone or in combination of two or more. Among 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 residues. In the present specification, among the two or more types of residues, the main residue, that is, the one having the largest mass (mol%) is defined as the first residue, and the smaller amount than the first residue is represented by the mass ( Mol%) residues in the order of the second residue or less (that is, the second residue, the third residue,...). By making the dicarboxylic acid residue and the diol residue into such a mixture system, the crystallinity of the obtained polyester-based resin can be lowered, so that the progress of crystallization can be suppressed, which is preferable.

  Preferred mixtures of diol residues include, for example, the ethylene glycol residue as the first residue, 1,4-butanediol, neopentyl glycol, diethylene glycol, polytetramethylene glycol, and 1,4- Examples thereof include a residue derived from at least one selected from the group consisting of cyclohexanedimethanol, preferably 1,4-cyclohexanedimethanol residue.

  The preferred mixture of dicarboxylic acid residues is, for example, selected from the group consisting of terephthalic acid residues as the first residue and isophthalic acid, 1,4-cyclohexanedicarboxylic acid, succinic acid and adipic acid as the second residue. And a residue derived from at least one kind, preferably an isophthalic acid residue.

  The total content of dicarboxylic acid residues and diol residues below the second residue is the sum of the total amount of dicarboxylic acid residues (100 mol%) and the total amount of diol residues (100 mol%) ( 200 mol%), the lower limit is preferably 10 mol% or more, more preferably 20 mol% or more. As an upper limit, it is preferable that it is 40 mol% or less, and 35 mol% or less is more preferable. If the content rate of the said 2 or less residue is 10 mol% or more, the crystallinity degree of polyester obtained can be restrained low. On the other hand, when the content of the residues of 2 residues or less is 40 mol% or less, the advantages of the first residue can be utilized.

  For example, when 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 residues is the total amount of terephthalic acid residues that are dicarboxylic acid residues (100 mol%), ethylene glycol residues, and 1,4-cyclohexanedimethanol residues. The lower limit is preferably 10 mol% or more, more preferably 15 mol% or more, and even more preferably 25 mol% or more with respect to the total (200 mol%) with the total amount (100 mol%). As an upper limit, it is preferable that it is 40 mol% or less, 38 mol% or less is more preferable, and 35 mol% or less is further more preferable. By using an ethylene glycol residue and a 1,4-cyclohexanedimethanol residue as the diol residue within this range, the crystallinity of the obtained polyester is almost lost, and the fracture resistance can be improved.

  Furthermore, in the above example, when the dicarboxylic acid residue is a terephthalic acid residue as the first residue and an isophthalic acid residue as the second residue, the dicarboxylic acid residue is an isophthalic acid residue and a diol residue. 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, and further preferably 25 mol% or more with respect to the total (200 mol%) of (100 mol%). As an upper limit, it is preferable that it is 40 mol% or less, 38% mol or less is more preferable, and 35 mol% or less is further more preferable.

  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 the possessed monomer. In particular, polylactic acid obtained by condensation polymerization of 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 is preferably 1.5 dl / g or less, more preferably 1.2 dl / g or less, and further preferably 1.0 dl / g or less. If intrinsic viscosity (IV) is 0.5 dl / g or more, it can suppress that a film strength characteristic and heat resistance fall. On the other hand, if the intrinsic viscosity is 1.5 dl / g or less, it is possible to prevent breakage associated with an increase in stretching tension.

  Specific examples of commercially available polyester resins include “Easter Copolyester” (manufactured by Eastman Chemical Co., Ltd.), “SKYGREEN PETG” (manufactured by SK Chemical Co., Ltd.), and the like.

  The content of the polyester resin in the (I) layer is preferably 50% by mass or more, more preferably 75% by mass or more, and more preferably 80% by mass, with the resin composition constituting the (I) layer being 100% by mass. The above is more preferable, and 90% by mass or more is most preferable. If it is in the said range, you may contain other resins other than a polyester-type resin in (I) layer. Examples of such resins include polyolefin resins, polystyrene resins, polycarbonate resins, and acrylic resins, among which polystyrene resins are preferable.

  In the film of the present invention, the (I) layer is preferably located in the outermost layer (front and back layers). Thereby, the rigidity maintenance of a film, suppression of natural shrinkage, oil resistance, and solvent resistance become favorable. In addition, when the front and back layers are composed of a resin composition containing polyester resin as the main component, the film is less likely to curl and remain on the label when printed using a gravure ink containing an ordinary organic solvent as the main component. This is preferable because the amount of the solvent to be increased is increased, and the occurrence of blocking after printing or generation of an organic solvent odor is reduced.

  For the front and back layers of the film of the present invention, it is preferable to add a technique of blending incompatible resins or what is called an antiblocking agent in order to impart slipperiness or prevent blocking of the film.

  Specific examples of the anti-blocking agent include inorganic particles such as silica, talc, and calcium carbonate, inorganic oxides, carbonates, or organic particles such as crosslinked acrylic, crosslinked polyester, crosslinked polystyrene, and silicone. It is done. Further, organic particles having a multilayer structure polymerized in multiple stages can also be used. Of these, silica and organic particles are preferably used.

  Since the anti-blocking agent causes slipping and blocking resistance by roughening the film surface, transparency and gloss of the film are inhibited unless an appropriate addition amount and type are selected. The addition amount of the anti-blocking agent is 100% by mass with respect to the entire resin composition constituting the front and back layers, the lower limit is preferably 0.01% by mass or more, more preferably 0.015% by mass or more, and 0 0.02% by mass or more is more preferable. As an upper limit, it is preferable that it is 2 mass% or less, 1.5 mass% or less is more preferable, and 1 mass% or less is further more preferable. If the lower limit of the anti-blocking agent is within the above range, sufficient slipperiness and blocking resistance can be obtained. If the upper limit of the anti-blocking agent is within the above range, excessive unevenness on the surface of the film will not occur, and the transparency of the film may be hindered, or the roll of the film roll may be wound due to excessive slipperiness. It is preferable.

The shape of the anti-blocking agent is not particularly limited, but it is spherical from the viewpoints of suppressing aggregation in the front and back layers, uniform dispersion, suppressing irregular reflection of transmitted light, and unevenness formed on the film surface. Is preferably used. The lower limit of the average particle size of the antiblocking agent is preferably 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. If the lower limit of the average particle size of the antiblocking agent is within the above range, sufficient slipping property and blocking resistance can be exhibited. Further, if the upper limit of the average particle size of the anti-blocking agent is within the above range, when printing is performed on the film of the present invention to enhance the design, ink loss or the like hardly occurs and the appearance of the printed design is not impaired. .
Further, the particle size distribution of the antiblocking agent is not particularly limited, but those having a narrow particle size distribution are preferred. This is because if the particle size distribution is too wide, there may be a deviation from the above-mentioned range of particle sizes that are preferably used.

<(III) layer>
In the film of the present invention, the (III) layer contains a polystyrene resin as a main component and further contains a laser color former.

<Polystyrene resin>
Examples of the polystyrene resin include styrene homopolymers obtained by polymerizing styrene hydrocarbons, and copolymers of styrene hydrocarbons and other monomers. In the present invention, styrene hydrocarbons are used. Preferably, block copolymerization of conjugated diene hydrocarbons is used.

  Examples of the styrenic hydrocarbon include styrene, p-, m- or o-methylstyrene, 2,4-, 2,5-, 3,4- or 3,5-dimethylstyrene, pt-butylstyrene, and the like. Alkyl styrenes; halogenated styrenes such as o-, m- or p-chlorostyrene, o-, m- or p-bromostyrene, o-, m- or p-fluorostyrene, o-methyl-p-fluorostyrene Halogenated substituted alkylstyrenes such as o-, m- or p-chloromethylstyrene; alkoxystyrenes of 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-vinylbenzylpropyl ether; p Alkylsilyl styrene such as trimethylsilyl styrene; more, and the like vinylbenzyl dimethoxyphosphinyl sulfide. The styrenic hydrocarbon block may contain a copolymerizable monomer other than these homopolymers, copolymers and / or styrenic hydrocarbons.

  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 hydrocarbon block may contain a copolymerizable monomer other than these homopolymer, copolymer and / or conjugated diene hydrocarbon in the block.

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

Other examples of the styrene hydrocarbon and conjugated diene hydrocarbon block copolymer include styrene-isoprene-butadiene block copolymer (SIBS).
In SIBS, the mass% ratio of styrene / isoprene / butadiene is preferably (60-90) / (5-40) / (5-30), (60-85) / (10-30) / ( 5-25) is more preferable, and (60-80) / (10-25) / (5-20) is more preferable. If the content of butadiene is large and the content of isoprene is small, butadiene heated inside the extruder or the like may cause a crosslinking reaction to increase the gel-like material.
The SIBS melt flow rate (MFR) measurement (measurement conditions: temperature 200 ° C., load 49 N) is preferably 2 g / 10 min or more as a lower limit, and more preferably 3 g / 10 min or more. The upper limit is preferably 15 g / 10 min or less, more preferably 10 g / 10 min or less, and even more preferably 8 g / 10 min or less.

  The polystyrene resin is not limited to a simple substance, and may be a mixture of two or more. 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 (80 to 20) / (20 It is more preferable that it is about ~ 80), and it is more preferable that it is about (70-30) / (30-70).

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

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

The polystyrene resin has a vibration frequency of 10 Hz, a strain of 0.1%, and a storage elastic modulus (E ′) at 0 ° C. of preferably 1.00 × 10 ⁹ Pa or more, 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 strength of the film. When the polystyrene-based resin has a storage elastic modulus (E ′) of 1.00 × 10 ⁹ Pa or more, a film having rigidity in addition to transparency can be obtained. This storage elastic modulus (E ′) is within a range that does not impair the transparency of the block copolymer of the styrene-based hydrocarbon and the conjugated diene-based hydrocarbon as described above, or a mixture of the two or more types of the copolymer. It can be obtained by mixing with other resins.

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

Preferred as the styrene-based hydrocarbon-conjugated diene-based hydrocarbon block copolymer capable of imparting fracture resistance are pure block SBS and random block SBS. 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 peak temperature of the loss elastic modulus (E ″) is −20 Those having viscoelastic properties at or below 0 ° C. are particularly preferred.If the storage elastic modulus (E ′) at 0 ° C. is 1.00 × 10 ⁸ Pa or more, it is possible to increase the amount of the resin by increasing the blend amount of the resin responsible for rigidity. On the other hand, at the peak temperature of the loss elastic modulus (E ″), the temperature on the low temperature side mainly shows fracture resistance. Although this characteristic varies depending on the stretching conditions, it is difficult to impart sufficient film breakability to the laminated film when the peak temperature of the loss modulus (E ″) does not exist at −20 ° C. or lower in the state before stretching. There is a case.

Further, as a resin capable of imparting rigidity, a copolymer composed of a styrene hydrocarbon having a storage elastic modulus (E ′) at 0 ° C. of 2.00 × 10 ⁹ Pa or more, for example, a styrene resin having a controlled block structure Examples thereof include block copolymers of hydrocarbons and conjugated diene hydrocarbons, polystyrene, styrene hydrocarbons and aliphatic unsaturated carboxylic acid ester copolymers.

The styrene hydrocarbon-conjugated diene hydrocarbon block copolymer having a controlled block structure has a storage elastic modulus (E ′) at 0 ° C. of 2.00 × 10 ⁹ as a characteristic of the styrene-butadiene block copolymer. SBS that is Pa or higher is exemplified. The composition ratio of styrene-butadiene of SBS satisfying this is preferably adjusted to about styrene / butadiene = (95-80) / (5-20).

  The structure of the block copolymer and the structure of each block part are preferably a random block and a tapered block. More preferably, in order to control the shrinkage characteristics, the peak temperature of the loss modulus (E ″) is 40 ° C. or more, and more preferably, the peak of the clear loss modulus (E ″) is below 40 ° C. There is no temperature. When the peak temperature of the loss elastic modulus (E ″) does not exist up to 40 ° C., the storage elastic modulus characteristic is almost the same as that of polystyrene, so that the rigidity of the film can be imparted. The peak temperature of the loss modulus (E ″) is preferably in the range of 40 ° C. or more and 90 ° C. or less. This peak temperature is a factor that mainly affects the shrinkage rate. If this temperature is in the range of 40 ° C. or more and 90 ° C. or less, the natural shrinkage and the low temperature shrinkage rate are not extremely lowered.

  A polymerization method of a styrene-based hydrocarbon-conjugated diene-based hydrocarbon copolymer that satisfies the above viscoelastic properties is shown below. Usually, after a part of styrene or butadiene is charged to complete the polymerization, a mixture of styrene monomer and butadiene monomer is charged and the polymerization reaction is continued. This preferentially polymerizes butadiene having a higher polymerization activity, and finally a block composed of a single monomer of styrene is generated.

  For example, when styrene is homopolymerized first, and after the polymerization is completed, a mixture of styrene monomer and butadiene monomer is added and polymerization is continued, the styrene / butadiene monomer ratio gradually changes between the styrene block and the butadiene block. A styrene-butadiene block copolymer having a copolymer site is obtained. By providing such a site, a polymer having the above viscoelastic properties can be obtained. In this case, the two peaks due to the butadiene block and the styrene block as described above cannot be clearly confirmed, and it appears that only one peak exists. That is, in a block structure such as SBS of a random block in which a pure block and a butadiene block are clearly present, Tg due to the butadiene block is mainly present at 0 ° C. or less, and therefore, storage modulus at 0 ° C. ( It becomes difficult for E ′) to be not less than a predetermined value.

  Regarding the molecular weight, the melt flow rate (MFR) measurement value (measurement conditions: temperature 200 ° C., load 49 N) is adjusted in the range of 2 g / 10 min to 15 g / 10 min. 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 (III) layer is 100% by mass, It is preferable that it is 20 mass% or more and 80 mass% or less, and it is more preferable to adjust in the range of 40 mass% or more and 70 mass% or less. If the upper limit is within the above range, the rigidity of the film can be greatly improved, and it can be suppressed that the fracture resistance is 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 a 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. If the lower limit of the mass average molecular weight is within the above range, it is preferable without the disadvantage that the film deteriorates. Moreover, if an upper limit is in the said range, it is not necessary to adjust a flow characteristic, and since there is no fault of extrudability falling, it is preferable.

  Examples of commercially available polystyrene resins include “Asaflex” (manufactured by Asahi Kasei Chemicals), “Clearen” (manufactured by Denki Kagaku Kogyo), and the like.

  When using a copolymer of a styrene hydrocarbon and an aliphatic unsaturated carboxylic acid ester as the polystyrene resin, the aliphatic unsaturated carboxylic acid ester copolymerized with the styrene hydrocarbon includes methyl (meth) acrylate, Examples include butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, and stearyl (meth) acrylate. Preferably, it is a copolymer of styrene and butyl (meth) acrylate, more preferably styrene is in the range of 70% by mass to 90% by mass, and Tg (peak temperature of loss elastic modulus E ″). A material having a melt flow rate (MFR) measurement value (measurement conditions: temperature 200 ° C., load 49 N) of 2 g / 10 min or more and 15 g / 10 min or less is suitably used. ) Acrylate refers to acrylate and / or methacrylate.

  Specific examples of commercially available copolymers of styrene hydrocarbons and aliphatic unsaturated carboxylic acid esters include, for example, “TX polymer” (manufactured by Denki Kagaku Kogyo Co., Ltd.) and “Cebian” (manufactured by Daicel Polymer Co., Ltd.). Etc.

  The content of the polystyrene-based resin in the (III) layer is not particularly limited as long as it does not exceed the range specified by the present invention, but the resin composition constituting the (III) layer is defined as 100% by mass. It is preferably at least mass%, more preferably at least 60 mass%, and even more preferably at least 70 mass%. However, when a styrene homopolymer (GPPS), an oxazoline group-containing styrene copolymer described later, a styrene-maleic anhydride copolymer or the like is contained as a polystyrene resin, GPPS or an oxazoline group-containing styrene copolymer, The Tg (peak temperature of loss elastic modulus E ″) of the styrene-maleic anhydride copolymer is as high as about 100 ° C. or higher. Therefore, the mixed GPPS, the oxazoline group-containing styrene copolymer, and the styrene-maleic anhydride copolymer are mixed. The content of the polymer or a mixture thereof is preferably 20% by mass or less, more preferably 15% by mass or less, and more preferably 10% by mass or less, based on 100% by mass of the resin composition constituting the (III) layer. Is more preferable.

<Laser color former>
The laser color former is not particularly limited as long as it has a function of generating heat upon irradiation with a laser beam, and may be a so-called self-coloring color former that develops color itself upon irradiation with laser light, or it does not develop color itself. It may be a thing. When the laser color former generates heat, at least the surrounding forming material is carbonized, and a desired print appears in the (III) layer. Furthermore, if a laser color former that self-colors is used, the color development of the laser color former and the color formation due to the carbonized material produced by carbonization of the film forming material may be synergistic, resulting in a dark color and excellent printability. it can. When the laser color former develops color, the color is not particularly limited. However, from the viewpoint of visibility, it is preferable to use a laser color former capable of developing dark colors including black, amber, and brown.

  Specific examples of laser color formers include, for example, metals such as iron, copper, zinc, tin, gold, silver, cobalt, nickel, bismuth, antimony, and aluminum, and salts thereof such as iron chloride and iron nitrate. And metal salts such as iron phosphate, copper chloride, copper nitrate, copper phosphate, zinc chloride, zinc nitrate, zinc phosphate, nickel chloride, nickel nitrate, bismuth subcarbonate and bismuth nitrate. Examples of metal oxides include metal hydroxides such as magnesium hydroxide, lanthanum hydroxide, nickel hydroxide, bismuth hydroxide, iron oxide, copper oxide, zinc oxide, tin oxide, cobalt oxide, nickel oxide, Examples thereof include metal oxides such as bismuth oxide, indium oxide, antimony oxide, tungsten oxide, neodymium oxide, mica, hydrotalcite, montmorillonite, and smectite. Examples of metal borides include zirconium boride, titanium boride, and lanthanum boride. Examples of the dye series include leuco dyes such as fluorane series, phenothiazine series, spiropyran series, triphenylmethphthalide series, and rhodamine lactam series. A laser color former may be used independently and may use 2 or more types together. In the present invention, as the laser color former, 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 color development effect and cost. Further, a compound containing bismuth is preferable, and among them, a compound containing bismuth oxide is more preferable. As long as it contains bismuth oxide, it develops color and generates heat even in a relatively small amount, so that the effect of the present invention can be sufficiently exhibited without impairing the transparency of the (III) layer in the film of the present invention. . In addition, rare earth element hexaboride has near-infrared absorption ability, and among these, lanthanum hexaboride is preferable because of its excellent laser light absorption efficiency.

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

  Examples of commercially available laser color formers include “Elbima” (manufactured by Toyo Ink), “Iriodin” (manufactured by Merck Japan), “TOMATEC” (manufactured by Toago Material Technology), and “KHDS-06” (Sumitomo). Metal mine).

  The content of the laser color former in the (III) layer 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 former is 0.01% by mass or more, a sufficient color forming effect can be obtained, and if it is 5% by mass or less, there is no possibility that the transparency is greatly lowered.

In the present invention, the (III) layer is preferably located in the intermediate layer. As a result, the film of the present invention is excellent in shrinkage characteristics and further excellent in laser printing visibility, transparency, oil resistance, solvent resistance, and the like.
When the laser color former is added to the resin and stretched, the laser color former present near the surface of the polystyrene resin rises on the surface of the polystyrene resin due to the difference in elastic modulus between the laser color former and the polystyrene resin. Fine irregularities occur and transparency is lowered. In that case, when the (I) layer which does not contain a laser color former is comprised as a front and back layer (outermost layer), since the smoothness of the surface is ensured, it is preferable since the fall of transparency can be suppressed. In addition, since the polystyrene resin has a relatively low oil resistance, it can be provided with a function such as a shrinkage characteristic without losing the oil resistance of the film by being disposed in the intermediate layer.
Furthermore, in the present invention, it is important to include a laser color former in the (III) layer. Thereby, the problem of coloring of a molded product can be solved by processing temperature.
In addition, it is important to dispose 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 print due to abrasion after the label is formed disappears. . When printing on the surface layer, the printed content may become unclear due to rubbing of the printed part due to surface wear. In addition, there is a fastness test as a test method for confirming the phenomenon.

  In addition to the polystyrene resin and the laser color former, other resins can be mixed in the (III) layer 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, and compatibilizers with these resins. Among them, polyester resins are preferably contained.

<Polyester resin contained in layer (III)>
In the film of the present invention, the (III) layer may further contain a polyester resin.
It is preferable that the (III) layer further contains a polyester-based resin from the viewpoint of adhesiveness to the (II) layer mainly composed of a mixed resin composition of a polyester-based resin and a polystyrene-based resin, and the film of the present invention. It is also possible to add a reproduction film such as trimming loss that occurs during production. The content of the polyester-based resin is 100% by mass of the resin composition constituting the (III) layer, and the upper limit is preferably 30% by mass or less, more preferably 25% by mass or less, and more preferably 20% by mass or less. Is more preferable. Although there is no restriction | limiting in particular in a lower limit, Preferably it is 3 mass% or more, More preferably, it is 5 mass% or more, More preferably, it is 10 mass% or more.

  The polyester resin suitably 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 (III) layer may be a polyester resin contained in a recycled material generated by trimming loss or the like.

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

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

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

  The content of the polyester-based resin in the (II) layer is preferably 40% by mass or more, more preferably 45% by mass or more as the lower limit value, with the resin composition constituting the (II) layer being 100% by mass. 50 mass% or more is more preferable. As an upper limit, it is preferable that it is 80 mass% or less, 75 mass% or less is more preferable, and 70 mass% or less is further more preferable. If the lower limit of the content of the polyester-based resin is within the above range, the adhesiveness with the (I) layer is not lowered, and if the upper limit is within the above range, the adhesiveness with the (III) layer is Since it does not fall, it is preferable.

<Polystyrene resin contained in (II) layer>
The (II) layer of the film of the present invention may be the same as the polystyrene resin used in the (III) layer. In addition, the polystyrene resin used in the (II) layer may be the same as the polystyrene resin used in the (III) layer as long as it satisfies the characteristics of the film of the present invention, and a different polystyrene resin is used. Also good.

In the film of the present invention, the polystyrene resin contained in the (II) layer has a vibration frequency of 10 Hz, a strain of 0.1%, and a storage elastic modulus (E ′) at 0 ° C. of 1.00 × 10 ⁷ Pa or more. Preferably, it is 1.50 × 10 ⁷ Pa or more. When the film of the present invention is formed by having a storage elastic modulus (E ′) of 1.00 × 10 ⁷ Pa or more, the adhesiveness with the (I) layer or (III) layer described above can be imparted, When shrinking in a high temperature atmosphere, delamination between the (I) layer and the (III) layer can be suppressed. More importantly, whitening that occurs when the film is bent during processing, that is, so-called folding whitening, can be suppressed, which is preferable. This storage elastic modulus (E ′) is within a range that does not impair the transparency of the block copolymer of the styrene-based hydrocarbon and the conjugated diene-based hydrocarbon as described above, or a mixture of the two or more types of the copolymer. It can be obtained by mixing with other resins.

Preferable examples of the styrene-based hydrocarbon-conjugated diene-based hydrocarbon block copolymer that can impart adhesiveness to the above-described (I) layer or (III) layer 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 preferred: If the storage elastic modulus (E ′) at 0 ° C. is 1.00 × 10 ⁷ Pa or more, the laminate can be formed by increasing the blend amount of the resin responsible for rigidity. When formed into a film, the film can be imparted with stiffness. On the other hand, at the peak temperature of the loss elastic modulus (E ″), the temperature on the low temperature side mainly shows fracture resistance. Although the characteristics vary depending on the stretching conditions, if the peak temperature of the loss modulus (E ″) does not exist below 0 ° C. before stretching, the adhesion to the (I) layer or (III) layer is reduced. When a laminated film is formed, it may be difficult to impart sufficient breakability to the film.

  As a commercial item of the said polystyrene-type resin, "Asaflex" (made by Asahi Kasei Chemicals Co., Ltd.), "clearen" (made by Denki Kagaku Kogyo Co., Ltd.) etc. are mentioned, for example.

  Although the content rate of the said polystyrene-type resin contained in the (II) layer of the film of this invention is not specifically limited as long as the characteristic of the film of this invention is satisfy | filled, The resin composition which comprises a (II) layer The lower limit is preferably 20% by mass or more, more preferably 25% by mass or more, and further preferably 30% by mass or more. As an upper limit, it is preferable that it is 60 mass% or less, 55 mass% or less is more preferable, and 50 mass% or less is further more preferable. If the lower limit of the content of the polystyrene-based resin is within the above range, the adhesiveness with the (III) layer will not decrease, and if the upper limit is within the above range, the adhesiveness with the (I) layer will decrease. It is preferable without doing.

  As long as the (II) layer of the film of the present invention satisfies the characteristics of the film of the present invention, it can contain other resins in addition to the polyester resin and the polystyrene resin. Examples of such a resin include a compatibilizing agent, a polyolefin resin, an acrylic resin, and a polycarbonate resin described later. Among these, it is preferable to contain a compatibilizer described later.

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

  The compatibilizer contained in the layer (II) includes a polar group having 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 styrenic block copolymer or graft copolymer that is compatible with the polystyrene resin contained in the polymer or has a high affinity portion is preferably used. Specific examples of polar groups or reactive functional groups having high affinity with polyester resins include, for example, acid anhydride groups, carboxylic acid groups, carboxylic acid ester groups, carboxylic acid chloride groups, carboxylic acid amide groups, Examples include carboxylic acid groups, sulfonic acid groups, sulfonic acid ester groups, sulfonic acid chloride groups, sulfonic acid amide groups, sulfonic acid groups, epoxy groups, amino groups, imide groups, or oxazoline groups. An anhydride group, carboxylic acid group or carboxylic ester group, and oxazoline group are preferred.

  Moreover, what has a site | part compatible with a polystyrene-type resin means having a chain | strand with affinity with a styrene-type resin, for example. Specific examples include a random copolymer having a styrene chain, a styrene copolymer segment or the like as a main chain, a block chain or a graft chain, or having a styrene monomer unit.

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

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

  The content of the compatibilizing agent in the (II) layer is not particularly limited as long as the characteristics of the film of the present invention are satisfied, but the resin composition constituting the (II) layer is defined as 100% by mass, and the lower limit. Is preferably 1% by mass or more, more preferably 3% by mass or more, and further preferably 5% by mass or more. As an upper limit, it is preferable that it is 20 mass% or less, 15 mass% or less is more preferable, and 10 mass% or less is further more preferable. If the content of the compatibilizing agent is within the above range, it can be expected that the thickness is expected to be uniform and the interlayer adhesion strength is improved, and it is possible to prevent significant deterioration of transparency and inhibition of the shrinkage behavior of the film. Therefore, it is preferable.

<Additives to each layer>
In addition to the components described above, the film of the present invention has a plasticizer and a plasticizer in each layer for the purpose of improving and adjusting the molding processability, productivity, and various properties of the heat-shrinkable film within a range that does not significantly impair the effects of the present invention. / Or tackifying resins can be added. As these addition amounts, the resin composition constituting each layer is 100% by mass, and the lower limit is preferably 1% by mass or more, more preferably 2% by mass or more, and further preferably 3% by mass or more. As an upper limit, it is preferable that it is 10 mass% or less, 8 mass% or less is more preferable, and 5 mass% or less is further more preferable. An addition amount within the above range is preferable because the decrease in melt viscosity and heat fusion resistance are small and natural shrinkage hardly occurs.
In addition to the plasticizer and tackifier resin, the film of the present invention may have various additives depending on the purpose, for example, an ultraviolet absorber, a light stabilizer, an antioxidant, a hydrolysis inhibitor, a stabilizer, and a colorant. In addition, an antistatic agent, a lubricant, an inorganic filler, and the like can be appropriately added according to each application.

<Layer structure of film>
The film of the present invention comprises a (I) layer containing a polyester resin as a main component, a (II) layer containing a mixed resin composition of a polyester resin and a polystyrene resin as a main component, and a polystyrene type containing a laser color former. It has at least three layers of (III) layer mainly composed of resin, and the combination of layer constitutions is appropriately selected according to the purpose and use. In the present invention, (I) layer / (II) It is preferable to have a three-kind five-layer configuration in which layers / (III) layers / (II) layers / (I) layers are stacked in this order.
In the present invention, by adopting the above-mentioned layer structure, the heat shrinkable laminated film excellent in laser colorability, 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 (I) layer to the (III) layer is preferably 2 or more as the lower limit value of the (III) layer when the (I) layer is 1. The above is more preferable, and 4 or more is more preferable. The upper limit is preferably 12 or less, more preferably 10 or less, and even more preferably 8 or less. Further, the lower limit of the thickness of the (II) layer is preferably 7% or more, more preferably 9% or more of the total thickness of the (I) layer. The upper limit is preferably 150% or less of the total thickness of the (I) layer, more preferably 100% or less, and even more preferably 80% or less. If the lower limit of the thickness of the (II) layer is within the above range, a good adhesive effect can be obtained, and the upper limit is within the above range, that is, the thickness of not more than 1.5 times the total thickness of the (I) layer. In this case, the transparency is not significantly lowered, which is preferable. In addition, after shrink wrapping using the film of the present invention, there may be a problem that laser printing becomes unclear due to abrasion due to rubbing, but in order to solve this problem, the thickness of the surface layer of the film is important. Become. Therefore, the surface layer has an average thickness of preferably 3 μm or more, more preferably 4 μm or more. If it is within the above range, no problem due to rubbing will occur.

<Total thickness>
Although the total thickness of the film of the present invention is not particularly limited, it is preferably thinner from the viewpoint of suppressing raw material costs 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.

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

  In this 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 between the longitudinal direction and the lateral direction, and is, for example, a direction corresponding to the outer peripheral direction when being attached to a bottle.

  If the thermal shrinkage rate is greater than 5% when immersed in 50 ° C warm water for 10 seconds, the film's natural shrinkage rate is likely to increase. It is thought that the appearance defect that becomes uneven is caused.

  Further, if the heat shrinkage rate in the main shrinkage direction at 70 ° C. is less than 10%, the heat shrinkage force is small. For example, when a laminated film is used as the container label, it cannot be temporarily fixed to the container. Then, the film may be shifted up in the direction of the top surface. On the other hand, when the thermal shrinkage rate in the main shrinkage direction is greater than 30% at 70 ° C., the thermal shrinkage occurs suddenly in the low temperature region, and thus there is a case where the thermal shrinkage cannot be performed 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%, heat shrinkage may be insufficient at the neck and top surface of the container.

If the thermal contraction rate 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 in a low temperature region near 70 ° C., for example. It has shrinkability, and suddenly shrinks in a high temperature range exceeding 70 ° C. and near 80 ° C. As a result, at a predetermined position, not only the trunk of the container but also the trunk is very thin. No abnormalities such as wrinkles and avatars occur on the neck and top surface, and uniform shrinkage is obtained, resulting in a beautiful shrinkage finish.
Note that the thermal shrinkage in the main shrinkage direction at 99 ° C. represents the distortion of the film. When the thermal shrinkage is greater than 80%, the interface is caused by the difference in elastic modulus between the laser color former and the polystyrene resin in the stretching process that imparts distortion during film formation. There is a risk that voids may be generated and transparency may be impaired. On the other hand, if it is less than 70%, there is a possibility that problems such as insufficient shrinkage occur and the finish does not become tight.

  When the film of the present invention is used as a PET container label, the thermal 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 preferably 10% or less, and more preferably 8% or less. Further, the thermal contraction 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, and further preferably 3% or less. If the upper limit of the shrinkage rate in the orthogonal direction is within the above range, shrinkage in the vertical direction becomes significant after shrinkage in label applications, and troubles such as dimensional deviation and appearance problems do not occur.

<Transparency>
The transparency of the film of the present invention is evaluated by a haze value measured according to JIS K7136, and the haze value is preferably less than 15%, more preferably less than 10%. If 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. 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 laser beams that can be used include YAG (yttrium, aluminum, garnet) laser (wavelength 1064 nm), YVO4 (yttrium vanadate) laser (wavelength 1064 nm), Yb fiber laser (wavelength 1060 nm), carbon dioxide laser (wavelength 10640 nm), and the like. It is done.

  Among them, especially 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 and are not absorbed sufficiently by these resins themselves, so that the laser beam is effective 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 irradiation conditions such as laser power, excitation current, Q-switch frequency, and scanning speed.
If the laser power is increased too much, and if the switch frequency is increased too much, carbonization of the laser irradiated portion may proceed extremely, and a hole may be generated. On the other hand, if the scanning speed is too slow, the printing area is concentrated, so that the carbonization of the laser irradiation portion proceeds extremely and there is a possibility that perforation occurs. Furthermore, since the film of the present invention has imparted heat shrinkage characteristics, in the state where the carbonization of the laser irradiated portion proceeds extremely as described above, heat shrinkage occurs due to the heat generated at that time, and the film There is a risk of deformation.

<Delamination strength>
The film of the present invention was obtained by collecting a test piece with a size of 150 mm in the main shrinkage direction and 15 mm in a direction perpendicular to the main shrinkage direction, and then peeling off a part of the (I) layer from the end surface in the main shrinkage direction of the test piece. (I) The peeled portion is formed on the layer side, and the peeled portion and the peeled portion of the (III) layer are respectively sandwiched by the chuck of a tensile tester, and the 180 ° peel test is performed at a test speed of 100 mm / min in the main shrinkage direction. The delamination strength when performing 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 will not occur.

<The manufacturing method of the film of this invention>
The film of the present invention is produced by laminating at least three layers (I), (II) and (III) simultaneously or sequentially to produce a laminated film, and then heating the laminated film, Obtained by stretching in the axial direction.

  The laminated film can be produced simultaneously with an intermediate layer, front and back layers and an adhesive layer by co-extrusion using an extruder equipped with a multilayer die by an existing method such as a T-die method or a tubular method. In addition, the laminated film can be sequentially produced by separately forming the resin constituting each layer and then laminating them using a press method or a roll nip method.

  The laminated film is cooled with a cooling roll, air, water, etc., and then reheated by an appropriate method such as hot air, hot water, infrared rays, etc., roll stretching method, tenter stretching method, tubular stretching method, long interval stretching method, etc. Uniaxially or biaxially stretched simultaneously or sequentially. In biaxial stretching, stretching in the MD and TD directions may be performed at the same time, but sequential biaxial stretching in which one of them is performed first is effective, and the order of either MD or TD may be first. The stretching temperature needs to be changed depending on the softening temperature of the resin constituting the film and the use required for the heat-shrinkable laminated film, but is generally 60 ° C. or higher, preferably 70 ° C. or higher, and 130 ° C. or lower, preferably It is controlled within a range of 120 ° C. or less. The draw ratio in the main shrink 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, stretching means, stretching temperature, and target product form. Hereinafter, it is suitably determined within a range of preferably 6 times or less. Whether to use uniaxial stretching or biaxial stretching is determined by the application of the target product.

  Even in the case of an application that requires shrinkage characteristics in almost one direction, such as a PET container label, it is effective to stretch the film in a range that does not impair the shrinkage characteristics in the vertical direction. The stretching temperature depends on components other than PET, but typically ranges from 60 ° C. to 90 ° C. Further, as for the draw ratio, the rupture resistance is improved as the draw ratio is increased, but the heat shrinkage rate is increased accordingly, and it becomes difficult to obtain a good shrinkage finish. It is particularly preferable that the ratio is not more than twice.

  Moreover, the film of this invention can provide and hold | maintain shrinkage | contraction property by cooling this film rapidly within the time when the molecular orientation of a stretched film is not relieved after extending | stretching.

<Use of the film of the present invention>
Since the film of the present invention is excellent in laser colorability by laser beam irradiation, it is excellent in visibility of laser printing, and is excellent in heat shrinkage properties, transparency, oil resistance, and interlayer adhesion, and thus various shrink wrapping. It can be used suitably for a use, and can be used suitably for a package, a label, etc. which shrink-wraps to-be-packaged goods, such as a foodstuff, a seasoning, a drink, 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.
In addition, the measured value and evaluation which are shown to an Example were performed as follows. In the examples, the take-up (flow) direction of the laminated film is described as “MD”, and the direction orthogonal thereto is described as “TD”.

<Measurement method>
(1) Thermal shrinkage rate The film obtained in the example was cut into a size of MD 20 mm and TD 100 mm, and the amount of TD shrinkage was immersed in a hot water bath at 80 ° C. for 10 seconds and measured. The thermal shrinkage rate was expressed as a percentage of the shrinkage amount relative to the original size before shrinkage.

(2) Transparency The haze value of the film obtained in the example was measured according to JIS K7136, and the transparency was evaluated.
◎: 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 laser beam irradiation 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 / second. The print density of the obtained printed matter was evaluated.
◎: High print density, no swelling or deformation, good visibility ○: Slightly inferior to the above, but acceptable in practical use ×: No print density, poor visibility

(4) Oil resistance The film obtained in the Example was cut into a 3 cm square, immersed in a glass bottle containing edible oil, stored at a temperature of 23 ° C. for 1 week, and then the film was taken out and visually evaluated for appearance.
○: No change in the film ×: Deterioration in the film (fogging, dissolving, cracking is remarkable)

(5) Interlaminar peel strength After a test piece was sampled from the film obtained in the example with a main shrinkage direction of 150 mm and a direction of 15 mm perpendicular to the main shrinkage direction, from the end surface of the test piece in the main shrinkage direction ( I) A part of the layer is peeled to form a peeled portion on the (I) layer, and this peeled portion and the peeled portion on the (III) layer side are respectively sandwiched by a chuck of a tensile tester, and the test in the main shrinkage direction A 180 ° peel test was performed at a speed of 100 mm / min. The average value at which the load obtained in the peel test became constant to some extent was evaluated as the delamination strength.
○: Delamination strength is 1 N / 15 mm width or more ×: Delamination strength is less than 1 N / 15 mm width

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

Moreover, the raw material used by each Example and the comparative example is as follows.
(Polyester resin)
Copolyester 1 (acid component: terephthalic acid 100 mol%, glycol component: ethylene glycol 65 mol%, diethylene glycol 3 mol%, cyclohexane dimethanol 32 mol%, hereinafter referred to as “Pes (1)”)
Copolyester 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., below (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 of −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, peak temperature of loss elastic modulus E ″ —46 ° C., Hereinafter referred to as “PS (3)”.)

(Laser color former)
Laser color former 1: manufactured by Toago 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 (lanthanum hexaboride dispersion powder, lanthanum hexaboride particle content concentration 21.5%), hereinafter referred to as “LM (2)”.
Laser color former 3: manufactured by Merck & Co., Ltd., 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 & Co., Ltd., trade name: Iriotech 8825 (antimony-doped tin oxide / mica composite), hereinafter referred to as “LM (4)”.
Laser color former 5: manufactured by Hakusui Tech Co., Ltd., trade name: passette CK (aluminum-doped zinc oxide), hereinafter referred to as “LM (5)”.
Laser color former 6: manufactured by Merck & Co., Ltd., 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-type five-layer laminated film including the (I) layer, the (II) layer, and the (III) layer, each raw material was mixed in the formulation shown in Table 1, respectively (the laser color former is (III ) The mass% shown in Table 1 was blended with respect to 100% by mass of the resin constituting the layer.) (I) layer / (II) layer / (III) Layer / (II) layer / (I) In a facility capable of co-extrusion, (I) layer / thickness ratio of each layer after melt-kneading at a preset temperature of each extruder at 200 to 230 ° C. (II) layer / (III) layer / (II) layer / (I) layer = 5/1/28/1/5 co-extruded, taken up with cast roll at 60 ° C., cooled and solidified, unstretched A laminated sheet was obtained. Next, this sheet was stretched 5.0 times in the transverse 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>
(I) In order to produce a monolayer film consisting of layers, as shown in Table 1, after mixing 100% by mass of Pes (1) and 0.3% by mass of LM (1), it was extruded by an extruder and a die. After melt-kneading at a preset temperature of the machine of 200 to 230 ° C., it was taken up with a cast roll at 60 ° C. and cooled and solidified to obtain an unstretched sheet. Next, this film was stretched 5.0 times in the transverse 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. It was. The evaluation results of the obtained film are shown in Table 1.

<Comparative example 2>
In order to produce a monolayer film consisting of (III) layers, as shown in Table 1, after mixing PS (1) 40 mass%, PS (2) 60 mass% and LM (1) 0.3 mass%, Using an extruder and a die, the set temperature of the extruder was melt-kneaded at 200 to 230 ° C., then 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 transverse 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. It was. The evaluation results of the obtained film are shown in Table 1.

<Comparative Example 3>
In order to produce a two-type three-layer laminated film consisting of (I) layer and (III) layer, after mixing each raw material with the composition shown in Table 1, the laser color former is a resin constituting the (III) layer. 100% by mass was blended with the mass% shown in Table 1.) In an equipment capable of co-extrusion of (I) layer / (III) layer / (I) layer by an extruder and a die, extrusion After melt-kneading at a set temperature of 200-230 ° C., co-extrusion 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 by a roll and cooled and solidified to obtain an unstretched sheet. Next, this sheet was stretched 5.0 times in the transverse 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 a laser color former, a prescription except that the amount of LM (2) is 0.005% by mass is the same as in the example, and a heat-shrinkable laminated film having a thickness of 35 μm is obtained by the same manufacturing method as in the example. It was. The evaluation results of the obtained film are shown in Table 1.

<Comparative Example 5>
In order to produce a single layer film consisting of (III) layers, as shown in Table 1, after mixing PS (1) 40 mass%, PS (2) 60 mass% and LM (2) 0.050 mass%, Using an extruder and a die, the set temperature of the extruder was melt-kneaded at 200 to 230 ° C., then 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 transverse 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. It was. The evaluation results of the obtained film are shown in Table 1.

<Comparative Example 6>
As a laser color former, a prescription except that the blending amount of LM (6) is 7.0% by mass is the same as in the example, and a heat-shrinkable laminated film having a thickness of 35 μm is obtained by the same manufacturing method as in the example. It was. 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 express a sufficient heat shrinkage ratio, have a low haze value and excellent transparency, have excellent laser color development by laser beam irradiation and good visibility. In addition, it has good oil resistance and a high value of delamination strength, and a result satisfying the required quality required for a heat shrink film was obtained. Moreover, coloring of the film was not confirmed.
On the other hand, the single-layer film (Comparative Example 1) containing a polyester resin as a main component has excellent color developability and oil resistance, but has a high haze value and insufficient transparency. Film coloring was also confirmed. Moreover, in the single layer film (Comparative Example 2 and Comparative Example 5) having a polystyrene resin as a main component, the film was not colored and excellent in transparency and color developability, but the oil resistance was insufficient. Further, in the film (Comparative Example 3) that does not have the (II) layer that is the adhesive layer of the (I) layer and the (III) layer, the adhesive strength between the (I) layer and the (III) layer was insufficient. It was. Moreover, in the heat-shrinkable laminated film, sufficient color developability could not be obtained with a film (Comparative Example 4) in which the amount of the laser color former was below the range of the present invention. Moreover, although the film (Comparative Example 6) in which the amount of the laser color former exceeded the range of the invention was excellent in color developability, the haze value was high and the transparency was insufficient. The film without the laser color former (Reference Example 1) had no color developability.

  Although the present invention has been described in connection with the most practical and preferred embodiments at the present time, the present invention is not limited to the embodiments disclosed herein, The invention can be appropriately changed without departing from the gist or concept of the invention that can be read from the claims and the entire specification, and a film accompanying such a change should also be understood as being included in the technical scope of the present invention. I must.

  The heat-shrinkable laminated film of the present invention is excellent in laser color development, heat-shrinkage characteristics, transparency, oil resistance and interlayer adhesion by laser beam irradiation, and can be suitably used as various shrink-wrapping films.

Claims (4)

It has at least three layers of (I) layer, (II) layer, and (III) layer, each layer is mainly composed of the following resin, and (III) layer is 100% by mass of resin constituting the (III) layer. On the other hand, the heat shrinkability is characterized by containing a laser color former in an amount of 0.01 to 5% by mass and having a heat shrinkage ratio in the main shrinkage direction of 20% or more when immersed in warm water at 80 ° C. for 10 seconds. Laminated film.
(I) Layer: Polyester resin (II) Layer: Polyester resin and polystyrene resin (III) Layer: Polystyrene resin   The heat-shrinkable laminated film according to claim 1, wherein the laser color former contains at least one of bismuth oxide, tin oxide, zinc oxide, antimony oxide, and lanthanum boride.   The polystyrene resin contained in one or both of the (II) layer and (III) layer is a styrene hydrocarbon-conjugated diene hydrocarbon copolymer. The heat-shrinkable laminated film according to claim 1 or 2.   The polyester resin contained in one or both of the layers (I) and (II) contains a terephthalic acid residue as a dicarboxylic acid residue and ethylene glycol as a diol residue. The heat-shrinkable laminated film according to claim 1, comprising a residue and a 1,4-cyclohexanedimethanol residue.