JP6077891B2 - Heat-shrinkable multilayer film and heat-shrinkable label - Google Patents

Description

The present invention is a heat-shrinkable multilayer that has excellent adhesion between the front and back layers and the intermediate layer not only at room temperature but also at low temperatures, can effectively prevent delamination, and is less likely to leave white streaks at the folds. Related to film. The present invention also relates to a heat-shrinkable label using the heat-shrinkable multilayer film.

In recent years, many containers such as plastic bottles and metal bottles are equipped with a heat-shrinkable label obtained by printing a base film made of a heat-shrinkable resin.
For heat-shrinkable labels, polystyrene-based resin films are frequently used because of excellent low-temperature shrinkability. However, the polystyrene resin film has a problem that heat resistance and solvent resistance are insufficient. Therefore, attempts have been made to use a polyester resin film excellent in heat resistance and solvent resistance. However, since the polyester resin film has a low temperature shrinkage and shrinks rapidly, wrinkles may occur when it is attached to a container. Likely to happen. In addition, the heat-shrinkable label is often provided with perforations so that the heat-shrinkable label can be easily peeled off from the container after use in order to recycle the container. The cut property at the perforation is poor.

In order to solve such a problem, for example, a multilayer film having front and back layers containing a polyester resin and an intermediate layer containing a polystyrene resin has been studied. Preventing peeling is an important issue.

In order to prevent delamination between the layers, an adhesive layer is provided between the front and back layers and the intermediate layer. Patent Document 1 discloses that a polyester resin and a polystyrene resin are used as the adhesive resin of the adhesive layer. A heat-shrinkable multilayer film using a mixture of However, such a heat-shrinkable multilayer film has a problem that the adhesive strength between the front and back layers and the intermediate layer is low, and the adhesive strength between the layers is not sufficient.

Patent Document 2 discloses that as an adhesive resin for the adhesive layer, a soft polystyrene resin having a styrene content of 10 to 50%, a modified styrene resin containing a large amount of an elastomer component, or a polyester has high affinity and is compatible. A heat-shrinkable laminated film using a resin or a mixture thereof is described.

However, these heat-shrinkable laminated films have a problem that the adhesive strength between the front and back layers and the intermediate layer is lowered after printing for use as a label, and the adhesive strength between the layers is not sufficient.

Patent Document 3 discloses a heat-shrinkable multilayer film using a polyester-based elastomer as a component constituting the adhesive layer.
However, in such a heat-shrinkable multilayer film, for example, when the film is strongly folded in the center sealing step when producing a heat-shrinkable label, the heat-shrinkable label is put on a container and thermally shrunk. However, the appearance of the film may be impaired by white streaks remaining in the folds.

Furthermore, for example, even in the case of heat-shrinkable labels using a multilayer film in which an adhesive layer is provided between front and back layers containing a polyester resin and an intermediate layer containing a polystyrene resin, even in a low temperature environment such as winter In the case where the heat-shrinkable label is attached to a PET bottle after storage or when the installation site is in a low temperature environment, peeling occurs between the layers of the heat-shrinkable label during heat shrinkage, resulting in poor appearance, Problems such as peeling of the heat-shrinkable label from the PET bottle may occur.

JP 2006-315416 A JP 2006-015745 A JP 2008-037093 A

The present invention has excellent adhesion between the front and back layers and the intermediate layer not only at room temperature but also at low temperatures, can effectively prevent delamination, and white stripes remain in the crease after heat shrinking. An object is to provide a heat-shrinkable multilayer film that is difficult to heat. Another object of the present invention is to provide a heat-shrinkable label using the heat-shrinkable multilayer film.

The present invention is a heat-shrinkable multilayer film in which a front and back layer containing a polyester-based resin and an intermediate layer containing a polystyrene-based resin are laminated via an adhesive layer, and the adhesive layer is a polystyrene-based film A heat-shrinkable multilayer film containing 25 to 65% by weight of a resin and 35 to 75 % by weight of a polyester elastomer.
The present invention is described in detail below.

The present inventors laminate the front and back layers containing a polyester resin and the intermediate layer containing a polystyrene resin via an adhesive layer containing a polystyrene resin and a polyester elastomer in a predetermined mixing ratio. As a result, a heat-shrinkable multilayer film that can increase the adhesive strength between the layers (hereinafter also referred to as interlayer strength) not only at room temperature but also in a low-temperature environment and that hardly causes white stripes to remain in the crease portion is obtained. I found out that Such a heat-shrinkable multilayer film excellent in adhesiveness and crease whitening-preventing property is also suitably used when used for heat-shrinkable labels of containers such as PET bottles.
In this specification, “normal temperature” refers to 18 to 28 ° C., and “low temperature” refers to 0 to 10 ° C.

The heat-shrinkable multilayer film of the present invention has front and back layers and an intermediate layer.
In addition, in this specification, a front and back layer means both a surface layer and a back surface layer. Therefore, the heat-shrinkable multilayer film of the present invention has a structure in which the intermediate layer is sandwiched between the front surface layer and the back surface layer.

The front and back layers contain a polyester resin.
Examples of the polyester-based resin include those obtained by polycondensation of a dicarboxylic acid component and a diol component. In particular, the dicarboxylic acid component is preferably an aromatic polyester resin in which terephthalic acid is 55 mol% or more of 100 mol% of the dicarboxylic acid component. In addition to the terephthalic acid, the dicarboxylic acid component is o-phthalic acid, isophthalic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, octyl succinic acid, cyclohexanedicarboxylic acid, naphthalenedicarboxylic acid, fumaric acid, maleic acid. , Itaconic acid, decamethylene carboxylic acid, their anhydrides and lower alkyl esters.

The diol component is not particularly limited. For example, ethylene glycol, 1,3-propanediol, 1,4-butanediol, diethylene glycol, 1,5-pentanediol, 1,6-hexanediol, dipropylene glycol, tripropylene glycol, Ethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-butanediol, 2,3-butanediol, neopentyl glycol (2,2-dimethylpropane-1,3-diol), 1,2- Hexanediol, 2,5-hexanediol, 2-methyl-2,4-pentanediol, 3-methyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, polytetramethylene ether glycol, etc. Aliphatic diols; 2,2-bis (4-hydroxysic Hexyl) propane, 2,2-bis (4-hydroxycyclohexyl) alkylene oxide adducts of propane, 1,4-cyclohexane diol, alicyclic diols such as 1,4-cyclohexanedimethanol.

Among the polyester-based resins, those containing a component derived from terephthalic acid as the dicarboxylic acid component and a component derived from ethylene glycol and / or 1,4-cyclohexanedimethanol as the diol component are among others. preferable. By using such an aromatic polyester random copolymer resin, excellent shrinkage can be imparted to the heat-shrinkable multilayer film.
When it is desired to further improve the shrinkage, the content of the component derived from ethylene glycol is 60 to 80 mol% and the content of the component derived from 1,4-cyclohexanedimethanol is 10% among 100 mol% of the diol component. It is preferable to use one that is -40 mol%.

Such an aromatic polyester random copolymer resin may further contain 0 to 30 mol%, preferably 1 to 25 mol%, more preferably 2 to 20 mol% of a component derived from diethylene glycol. By using diethylene glycol, the tensile elongation at break in the main shrinkage direction of the heat-shrinkable multilayer film is increased, and delamination occurs when the perforation is broken, preventing only the front and back layers on the inner surface from remaining in the container. can do. When the component derived from diethylene glycol exceeds 30 mol%, the low-temperature shrinkability of the heat-shrinkable multilayer film becomes too high, and wrinkles tend to occur when it is attached to a container.

Moreover, what contains the component derived from 1, 4- butanediol as a diol component can also be used for the polyester-type resin containing the component derived from terephthalic acid as said dicarboxylic acid component. Such a polyester resin is generally called a polybutylene terephthalate resin.
The polybutylene terephthalate resin contains a component derived from terephthalic acid as the dicarboxylic acid component, and an aromatic polyester random containing a component derived from ethylene glycol and 1,4-cyclohexanedimethanol as the diol component. It is preferably used in combination with a copolymer resin. By using such a mixed resin, more excellent finish can be imparted.

As the polybutylene terephthalate resin, in addition to a polybutylene terephthalate resin consisting only of a component derived from terephthalic acid and a component derived from 1,4-butanediol, a dicarboxylic acid component other than a component derived from terephthalic acid and / or Alternatively, it may be a polybutylene terephthalate resin containing a diol component other than the component derived from 1,4-butanediol.
In addition, it is preferable that content of dicarboxylic acid components other than the component originating in the said terephthalic acid is 10 mol% or less among 100 mol% of dicarboxylic acid components. When it exceeds 10 mol%, the heat resistance of the polybutylene terephthalate resin is lowered, which may be economically disadvantageous. Moreover, it is preferable that content of diol components other than the component originating in the said 1, 4- butanediol is 10 mol% or less among 100 mol% of diol components. When it exceeds 10 mol%, the heat resistance of the polybutylene terephthalate resin is lowered, which may be economically disadvantageous.

The addition amount of the polybutylene terephthalate resin is not particularly limited, but is preferably 30% by weight or less. If it exceeds 30% by weight, the natural shrinkage rate may increase or the rigidity of the film may decrease.

The preferable lower limit of the Vicat softening temperature of the polyester resin constituting the front and back layers is 55 ° C., and the preferable upper limit is 95 ° C. If the Vicat softening temperature is less than 55 ° C., the shrinkage start temperature of the heat-shrinkable multilayer film may be too low, or the natural shrinkage rate may be increased. When the Vicat softening temperature exceeds 95 ° C., the low-temperature shrinkability and shrink finish of the heat-shrinkable multilayer film may be lowered, or the low-temperature shrinkability may be greatly deteriorated over time. The more preferable lower limit of the Vicat softening temperature is 60 ° C., and the more preferable upper limit is 90 ° C.
The Vicat softening temperature can be measured by a method based on JIS K 7206 (1999).

The preferable lower limit of the tensile elastic modulus of the polyester resin constituting the front and back layers exceeds 1000 MPa, and the preferable upper limit is 4000 MPa. When the tensile elastic modulus is 1000 MPa or less, the shrinkage start temperature of the heat-shrinkable film may be too low, or the natural shrinkage rate may be increased. When the tensile elastic modulus exceeds 4000 MPa, the low-temperature shrinkability and shrink finish of the heat-shrinkable multilayer film may decrease, or the decrease in low-temperature shrinkability over time may increase. A more preferable lower limit of the tensile elastic modulus is 1500 MPa, and a more preferable upper limit is 3700 MPa.
In addition, the said tensile elasticity modulus can be measured by the method based on ASTM-D882 (TestA).

Examples of commercially available polyester resins constituting the front and back layers include “Easter”, “EmbracerLv” (Eastman Chemical), “Belpet” (Bell Polyester Products), “Nova Duran” (Mitsubishi Engineering). Plastics).

As a polyester-type resin contained in the said front and back layer, the polyester-type resin which has the composition mentioned above may be used independently, and 2 or more types of polyester-type resins which have the composition mentioned above may be used together. Further, the polyester resin may be a polyester resin having a composition different between the front surface layer and the back surface layer, but is a polyester resin having the same composition in order to suppress troubles caused by curling of the film. It is preferable.

The above front and back layers are, as necessary, antioxidants, heat stabilizers, ultraviolet absorbers, light stabilizers, lubricants, antistatic agents, antiblocking agents, flame retardants, antibacterial agents, fluorescent whitening agents, colorants, etc. The additive may be contained.

The intermediate layer contains a polystyrene resin.
Examples of the polystyrene resin include aromatic vinyl hydrocarbon-conjugated diene copolymers, aromatic vinyl hydrocarbon-conjugated diene copolymers, and aromatic vinyl hydrocarbon-aliphatic unsaturated carboxylic acid ester copolymers. Mixed resin, rubber-modified impact-resistant polystyrene, and the like. By using the polystyrene resin, the heat-shrinkable multilayer film of the present invention can start shrinking from a low temperature and has high shrinkability.

In this specification, the aromatic vinyl hydrocarbon-conjugated diene copolymer refers to a copolymer containing a component derived from an aromatic vinyl hydrocarbon and a component derived from a conjugated diene.
The aromatic vinyl hydrocarbon is not particularly limited, and examples thereof include styrene, o-methylstyrene, and p-methylstyrene. These may be used independently and 2 or more types may be used together. The conjugated diene is not particularly limited. For example, 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene Etc. These may be used independently and 2 or more types may be used together.

Since the aromatic vinyl hydrocarbon-conjugated diene copolymer is particularly excellent in heat shrinkability, it preferably contains a styrene-butadiene copolymer (SBS resin). The aromatic vinyl hydrocarbon-conjugated diene copolymer is prepared by using 2-methyl-1,3-butadiene (isoprene) as the conjugated diene in order to produce a heat-shrinkable multilayer film with less fish eye. It is preferable to contain the used styrene-isoprene copolymer (SIS resin), styrene-isoprene-butadiene copolymer (SIBS), and the like.
In addition, the said aromatic vinyl hydrocarbon-conjugated diene copolymer may contain any one of SBS resin, SIS resin, and SIBS resin, and may contain it in combination. Moreover, when using two or more of SBS resin, SIS resin, and SIBS resin, each resin may be dry-blended, and each resin is kneaded with a specific composition using an extruder and a compounded resin is used. May be.

When the aromatic vinyl hydrocarbon-conjugated diene copolymer contains SBS resin, SIS resin and SIBS resin alone or in combination, a heat-shrinkable multilayer film excellent in heat shrinkability can be obtained. The styrene content in 100% by weight of the aromatic vinyl hydrocarbon-conjugated diene copolymer is preferably 65 to 90% by weight, and the conjugated diene content is preferably 10 to 35% by weight. When the styrene content exceeds 90% by weight or the conjugated diene content is less than 10% by weight, it becomes easy to break when tension is applied to the heat-shrinkable multilayer film, It may break without depending on it. When the styrene content is less than 65% by weight or the conjugated diene content exceeds 35% by weight, foreign matters such as gels are likely to be generated during molding, and the heat-shrinkable multilayer film becomes weak. The handleability may deteriorate.

In the present specification, the aromatic vinyl hydrocarbon-aliphatic unsaturated carboxylic acid ester copolymer includes a component derived from an aromatic vinyl hydrocarbon and a component derived from an aliphatic unsaturated carboxylic acid ester. It refers to a copolymer.
The aromatic vinyl hydrocarbon is not particularly limited, and an aromatic vinyl hydrocarbon similar to the aromatic vinyl hydrocarbon exemplified in the aromatic vinyl hydrocarbon-conjugated diene copolymer can be used. The aliphatic unsaturated carboxylic acid ester is not particularly limited, and examples thereof include methyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, and the like. It is done. Here, (meth) acrylate refers to both acrylate and methacrylate.

When a styrene-butyl acrylate copolymer is used as the aromatic vinyl hydrocarbon-aliphatic unsaturated carboxylic acid ester copolymer, the styrene content in 100% by weight of the styrene-butyl acrylate copolymer is 60. It is preferable that it is -90 weight% and a butylacrylate content is 10-40 weight%. By using the aromatic vinyl hydrocarbon-aliphatic unsaturated carboxylic acid ester copolymer having such a composition, a heat-shrinkable multilayer film excellent in heat-shrinkability can be obtained.

The mixed resin of the aromatic vinyl hydrocarbon-conjugated diene copolymer and the aromatic vinyl hydrocarbon-aliphatic unsaturated carboxylic acid ester copolymer is not particularly limited, but the aromatic vinyl hydrocarbon-aliphatic It is preferably a mixed resin having a saturated carboxylic acid ester copolymer content of 80% by weight or less.

The rubber-modified impact-resistant polystyrene is composed of a continuous phase composed of a terpolymer of styrene, alkyl methacrylate and alkyl acrylate, and a dispersed phase composed of a rubber component mainly composed of conjugated diene. Basic.

Examples of the alkyl methacrylate forming the continuous phase include methyl methacrylate and ethyl methacrylate, and examples of the alkyl acrylate include methyl acrylate, ethyl acrylate, propyl acrylate and butyl acrylate.
The proportion of styrene in the copolymer forming the continuous phase is preferably 20 to 80% by weight, more preferably 30 to 70% by weight. The proportion of alkyl methacrylate is preferably 10 to 50% by weight, more preferably 15 to 40% by weight. The proportion of alkyl acrylate is preferably 1 to 30% by weight, and more preferably 5 to 20% by weight.

As the rubber component mainly composed of the conjugated diene forming the dispersed phase, polybutadiene or a styrene-butadiene copolymer having a styrene content of 5 to 30% by weight is preferable.
The particle size of the rubber component mainly composed of conjugated diene forming the dispersed phase is preferably 0.1 to 1.2 μm, more preferably 0.3 to 0.8 μm. When the particle diameter is less than 0.1 μm, the impact resistance of the rubber-modified impact-resistant polystyrene may be insufficient, and when it exceeds 1.2 μm, the transparency of the intermediate layer may be lowered.

In the rubber-modified impact-resistant polystyrene, the proportion of the continuous phase composed of a terpolymer of styrene, alkyl methacrylate and alkyl acrylate is 70 to 95% by weight, and the dispersed phase composed of a rubber component mainly composed of conjugated diene. The proportion is preferably 5 to 20% by weight. When the proportion of the dispersed phase is less than 5% by weight, the impact resistance of the rubber-modified impact-resistant polystyrene may be insufficient, and when it exceeds 20% by weight, the transparency of the intermediate layer is lowered. There is.

The preferable lower limit of the Vicat softening temperature of the polystyrene resin is 60 ° C, and the preferable upper limit is 85 ° C. When the Vicat softening temperature is less than 60 ° C., the low-temperature shrinkability of the heat-shrinkable multilayer film becomes too high, and wrinkles are likely to occur when it is attached to a container. When the Vicat softening temperature exceeds 85 ° C., the low-temperature shrinkability of the heat-shrinkable multilayer film is lowered, and an unshrinked portion is likely to be generated when it is attached to a container. A more preferable lower limit of the Vicat softening temperature is 65 ° C., and a more preferable upper limit is 80 ° C. The Vicat softening temperature can be measured by a method based on JIS K 7206 (1999).

The preferable lower limit of MFR (melt flow rate) at 200 ° C. of the polystyrene resin is 2 g / 10 minutes, and the preferable upper limit is 15 g / 10 minutes. When the MFR at 200 ° C. is less than 2 g / 10 minutes, film formation becomes difficult. If the MFR at 200 ° C. exceeds 15 g / 10 min, the mechanical strength of the film will be low and it will not be practical. The more preferable lower limit of MFR at 200 ° C. is 4 g / 10 minutes, and the more preferable upper limit is 12 g / 10 minutes. In addition, MFR can be measured by the method based on ISO1133.

Examples of commercially available polystyrene resins constituting the intermediate layer include “Clearen” (manufactured by Denki Kagaku Kogyo Co., Ltd.), “Asaflex” (manufactured by Asahi Kasei Chemicals), “Styrolux” (manufactured by BASF), “PSJ”. -Polystyrene "(manufactured by PS Japan) and the like.

The intermediate layer may contain an antioxidant, a heat stabilizer, an ultraviolet absorber, a light stabilizer, a lubricant, an antistatic agent, an antiblocking agent, a flame retardant, an antibacterial agent, a fluorescent whitening agent, a colorant, and the like as necessary. The additive may be contained.

In the heat-shrinkable multilayer film of the present invention, the front and back layers and the intermediate layer are laminated via an adhesive layer containing 20 to 65% by weight of a polystyrene resin and 35 to 80% by weight of a polyester elastomer. It will be.
By using such an adhesive layer, the adhesive strength between the layers of the heat-shrinkable multilayer film can be increased not only at room temperature but also at a low temperature, and also occurs at the fold portion when the heat-shrinkable multilayer film is folded. White stripes can be suppressed.

As a polystyrene-type resin used for the said adhesive layer, the thing similar to the polystyrene-type resin used for the intermediate | middle layer mentioned above may be used, and another thing may be used. When using another, a softer one than the polystyrene resin used for the intermediate layer is preferable.

The polystyrene-based resin used for the adhesive layer preferably contains an aromatic vinyl hydrocarbon-conjugated diene copolymer because it is particularly excellent in adhesiveness. In particular, a styrene-butadiene copolymer (SBS resin). It is preferable to contain. Further, in order to produce a heat-shrinkable multilayer film having better adhesion, 2-methyl-1,3-butadiene (isoprene) was used as the conjugated diene of the aromatic vinyl hydrocarbon-conjugated diene copolymer. It preferably contains a styrene-isoprene copolymer (SIS resin), a styrene-isoprene-butadiene copolymer (SIBS), or the like.
In addition, the said aromatic vinyl hydrocarbon-conjugated diene copolymer may contain any one of SBS resin, SIS resin, and SIBS resin, and may contain it in combination. Moreover, when using two or more of SBS resin, SIS resin, and SIBS resin, each resin may be dry-blended, and each resin is kneaded with a specific composition using an extruder and a compounded resin is used. May be.

In the case where the polystyrene resin is an aromatic vinyl hydrocarbon-conjugated diene copolymer and contains SBS resin, SIS resin and SIBS resin alone or in plural, heat shrinkability particularly excellent in adhesive strength between the respective layers. Since a multilayer film can be obtained, the styrene content in 100% by weight of the aromatic vinyl hydrocarbon-conjugated diene copolymer is preferably 50 to 90% by weight, and the conjugated diene content is preferably 10 to 50% by weight. . If the styrene content is less than 50% by weight or the conjugated diene content exceeds 50% by weight, foreign substances such as gel may be easily generated during the molding process. When the styrene content exceeds 90% by weight or the conjugated diene content is less than 10% by weight, the adhesive strength between the layers tends to decrease.

The preferable lower limit of the Vicat softening temperature of the polystyrene resin used in the adhesive layer is 55 ° C., and the preferable upper limit is 85 ° C. When the Vicat softening temperature is less than 55 ° C., the heat-shrinkable multilayer film is likely to delaminate between layers due to heating when it is attached to a container. When the Vicat softening temperature exceeds 85 ° C., the adhesive strength of the heat-shrinkable multilayer film tends to decrease. The more preferable lower limit of the Vicat softening temperature is 60 ° C, the still more preferable lower limit is 65 ° C, the particularly preferable lower limit is 70 ° C, and the more preferable upper limit is 80 ° C. The Vicat softening temperature can be measured by a method based on JIS K 7206 (1999).

The preferable lower limit of MFR (melt flow rate) at 200 ° C. of the polystyrene-based resin used for the adhesive layer is 2 g / 10 minutes, and the preferable upper limit is 15 g / 10 minutes. When the MFR at 200 ° C. is less than 2 g / 10 minutes, the resin stays in the extruder in the continuous production process, and foreign matters such as gels are easily generated. When the MFR at 200 ° C. exceeds 15 g / 10 minutes, the pressure is not sufficiently applied in the film forming process, and the thickness variation tends to increase. The more preferable lower limit of MFR at 200 ° C. is 4 g / 10 minutes, and the more preferable upper limit is 12 g / 10 minutes. In addition, MFR can be measured by the method based on ISO1133.

In the adhesive layer, the content of the polystyrene resin has a lower limit of 20% by weight and an upper limit of 65% by weight.
When the content of the polystyrene-based resin is less than 20% by weight, when the film is strongly folded to produce a heat-shrinkable label, white streaks remain in the fold portion, and the appearance of the film is impaired. If the content of the polystyrene resin exceeds 65% by weight, sufficient interlayer strength cannot be obtained at low temperatures, and delamination tends to occur during actual use. A preferred lower limit for the content of the polystyrene resin is 25% by weight, a more preferred lower limit is 30% by weight, a preferred upper limit is 60% by weight, a more preferred upper limit is 55% by weight, and a particularly preferred upper limit is 49% by weight.

The polyester-based elastomer is composed of polyester as a hard segment and polyether or polyester as a soft segment rich in rubber elasticity. Specifically, for example, an aromatic polyester as a hard segment, Examples include a block copolymer composed of an aliphatic polyether as a soft segment, or a block copolymer composed of an aromatic polyester as a hard segment and an aliphatic polyester as a soft segment. In particular, a saturated polyester elastomer containing a polyalkylene ether glycol segment as a soft segment is preferable.
As the saturated polyester elastomer containing the polyalkylene ether glycol segment, for example, a block copolymer comprising an aromatic polyester as a hard segment and a polyalkylene ether glycol as a soft segment is preferable.

When a block copolymer composed of an aromatic polyester and a polyalkylene ether glycol is used as the polyester elastomer, the proportion of the segment composed of the polyalkylene ether glycol is preferably 5% by weight, and preferably 90% by weight. is there. If it is less than 5% by weight, the adhesion to the intermediate layer is lowered, and if it exceeds 90% by weight, the adhesion to the front and back layers is lowered. A more preferred lower limit is 30% by weight, a more preferred upper limit is 80% by weight, and a still more preferred lower limit is 55% by weight.

Examples of the polyalkylene ether glycol include polyethylene glycol, poly (propylene ether) glycol, poly (tetramethylene ether) glycol, poly (hexamethylene ether) glycol, and the like.

The preferable lower limit of the number average molecular weight of the polyalkylene ether glycol is 400, and the preferable upper limit is 6000. A more preferred lower limit is 600, a more preferred upper limit is 4000, a still more preferred lower limit is 1000, and a more preferred upper limit is 3000. Use of a polyalkylene ether glycol having a number average molecular weight within the above range is preferable because good interlayer strength can be obtained. In the present specification, the number average molecular weight refers to that measured by gel permeation chromatography (GPC).

Although it does not specifically limit as a method of producing the said polyester-type elastomer, For example, (i) C2-C12 aliphatic and / or alicyclic diol, (ii) Aromatic dicarboxylic acid and / or alicyclic A dicarboxylic acid or an ester thereof and (iii) a polyalkylene ether glycol having a number average molecular weight of 400 to 6000 are used as raw materials to obtain an oligomer by an esterification reaction or a transesterification reaction, and then the oligomer is further polycondensed. Can be produced.

As said C2-C12 aliphatic and / or alicyclic diol, what is conventionally used as a raw material of a polyester, especially the raw material of a polyester-type thermoplastic elastomer can be used, for example. Specific examples include ethylene glycol, propylene glycol, trimethylene glycol, 1,4-butanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol and the like. Among these, ethylene glycol and 1,4-butanediol are preferable, and 1,4-butanediol is more preferable. These may be used alone or in combination of two or more.

As said aromatic dicarboxylic acid and / or alicyclic dicarboxylic acid, what is conventionally used as a raw material of polyester, especially as a raw material of a polyester-type thermoplastic elastomer can be used, for example. Specific examples include terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, and cyclohexanedicarboxylic acid. Among these, terephthalic acid and 2,6-naphthalenedicarboxylic acid are preferable, and terephthalic acid is more preferable. These may be used alone or in combination of two or more.

Among the above-mentioned polyester elastomers, for example, the product name “Primalloy” (manufactured by Mitsubishi Chemical Corporation), the product name “Perprene” (manufactured by Toyobo Co., Ltd.), and the product name “Hytrel” (Toray DuPont) Manufactured) and the like.

The melting point of the polyester elastomer is preferably 120 to 200 ° C. When the temperature is lower than 120 ° C., the heat resistance is lowered, and when the container is coated as a heat-shrinkable label, peeling easily occurs from the solvent seal portion. When the temperature exceeds 200 ° C., sufficient adhesive strength may not be obtained. . A more preferred lower limit is 130 ° C, and a more preferred upper limit is 190 ° C.
In addition, the said melting | fusing point can be measured on the conditions of the temperature increase rate of 0 degree-C / min using a differential scanning calorimeter (The Shimadzu Corporation make, DSC-60).

The melting point of the polyester-based elastomer is caused by the copolymerization ratio or structure of the polyester that is the hard segment and the polyether or polyester that is the soft segment. In general, the melting point of a polyester-based elastomer is likely to depend on the copolymerization amount of polyether or polyester, which is a soft segment, and the melting point is low when the copolymerization amount of polyether or polyester is large, and the melting point is high when it is small.
Further, the melting point of the polyester, which is a hard segment constituting the polyester elastomer, can be adjusted by changing the copolymerization component to adjust the melting point of the entire polyester elastomer.
Moreover, since the block property of the polyester-type elastomer obtained when the molecular weight of polyether or polyester which is a soft segment becomes small, melting | fusing point tends to fall.

The preferable lower limit of JIS-D hardness of the polyester elastomer is 10, and the preferable upper limit is 80. By setting the JIS-D hardness to 10 or more, the mechanical strength of the adhesive layer is improved. By setting the JIS-D hardness to 80 or less, the flexibility and impact resistance of the adhesive layer are improved. A more preferred lower limit of JIS-D hardness is 15, a more preferred upper limit is 70, a still more preferred lower limit is 20, and a more preferred upper limit is 60.
In addition, the said JIS-D hardness can be measured by using the durometer type D by the method based on JISK6253.

The preferable lower limit of the specific gravity of the polyester elastomer is 0.95, and the preferable upper limit is 1.20. When the specific gravity is 0.95 or more, heat resistance can be imparted, and peeling from the solvent seal portion can be suppressed when the container is coated as a heat-shrinkable label. Moreover, the adhesive strength of a front-and-back layer and an intermediate | middle layer can be raised by making specific gravity 1.20 or less.
The more preferable lower limit of the specific gravity is 0.98, and the more preferable upper limit is 1.18.
In addition, the said specific gravity can be measured using the underwater substitution method by the method based on JISK7112 (1999).

The preferable lower limit of the tensile elastic modulus of the polyester elastomer constituting the adhesive layer is 1 MPa, and the preferable upper limit is 1000 MPa. When the tensile elastic modulus is less than 1 MPa, the mechanical strength of the adhesive layer tends to decrease. If the tensile modulus exceeds 1000 MPa, the adhesive strength between the front and back layers and the intermediate layer tends to decrease. A more preferable lower limit of the tensile elastic modulus is 5 MPa, and a more preferable upper limit is 900 MPa. In addition, the said tensile elasticity modulus can be measured by the method based on ASTM-882 (TestA).

The polyester elastomer may be a modified product. Examples of the modified product include a polyester elastomer modified by grafting an α, β-ethylenically unsaturated carboxylic acid to the polyester elastomer.
Examples of the α, β-ethylenically unsaturated carboxylic acid include unsaturated carboxylic acids such as acrylic acid, maleic acid, fumaric acid, tetrahydrofumaric acid, itaconic acid, citraconic acid, crotonic acid, and isocrotonic acid; succinic acid 2 -Octen-1-yl anhydride, 2-dodecen-1-yl anhydride, succinic acid 2-octadecen-1-yl anhydride, maleic anhydride, 2,3-dimethylmaleic anhydride, bromomalein Acid anhydride, dichloromaleic acid anhydride, citraconic acid anhydride, itaconic acid anhydride, 1-butene-3,4-dicarboxylic acid anhydride, 1-cyclopentene-1,2-dicarboxylic acid anhydride, 1,2, 3,6-tetrahydrophthalic anhydride, 3,4,5,6-tetrahydrophthalic anhydride, exo-3,6-epoxy-1,2,3,6-tetra Hydrophthalic anhydride, 5-norbornene-2,3-dicarboxylic anhydride, methyl-5-norbornene-2,3-dicarboxylic anhydride, endo-bicyclo [2.2.2] oct-5-ene-2 , 3-dicarboxylic acid anhydride, and unsaturated carboxylic acid anhydrides such as bicyclo [2.2.2] oct-7-ene-2,3,5,6-tetracarboxylic acid anhydride. Of these, acid anhydrides are preferred because of their high reactivity.

In the adhesive layer, the content of the polyester elastomer has a lower limit of 35% by weight and an upper limit of 80% by weight.
When the content of the polyester elastomer is less than 35% by weight, sufficient interlayer strength cannot be obtained at low temperatures, and delamination phenomenon tends to occur during actual use. When the content of the polyester elastomer exceeds 80% by weight, when the film is strongly folded, white streaks remain in the fold portion, and the appearance of the film is impaired. A preferred lower limit for the content of the polyester elastomer is 40% by weight, a more preferred lower limit is 45% by weight, a particularly preferred lower limit is 51% by weight, a preferred upper limit is 75% by weight, and a more preferred upper limit is 70% by weight.

The adhesive layer may contain an antioxidant, a heat stabilizer, an ultraviolet absorber, a light stabilizer, a lubricant, an antistatic agent, an antiblocking agent, a flame retardant, an antibacterial agent, a fluorescent whitening agent, a colorant and the like as necessary. An additive may be contained.

As for the thickness of the entire heat-shrinkable multilayer film of the present invention, a preferred lower limit is 10 μm, a preferred upper limit is 100 μm, a more preferred lower limit is 15 μm, a more preferred upper limit is 80 μm, a further preferred lower limit is 20 μm, and a more preferred upper limit. 70 μm. When the thickness of the entire heat-shrinkable multilayer film is within the above range, excellent heat-shrinkability, excellent converting properties such as printing or center seal, and excellent mounting properties can be obtained.
In the heat-shrinkable multilayer film of the present invention, the thickness of the front and back layers is preferably 5% and preferably 25% with respect to the total thickness of the heat-shrinkable multilayer film, and the thickness of the intermediate layer is The preferable lower limit for the thickness of the entire heat-shrinkable multilayer film is 50%, and the preferable upper limit is 90%. When the thicknesses of the front and back layers and the intermediate layer are within the above ranges, high interlayer strength, high transparency, and the like are obtained.

In the heat-shrinkable multilayer film of the present invention, the adhesive layer has a preferable lower limit of 0.3 μm and a preferable upper limit of 3.0 μm. When the thickness of the adhesive layer is less than 0.3 μm, the adhesive layer may not have sufficient adhesiveness. When the thickness of the adhesive layer exceeds 3.0 μm, the heat shrink property and the optical property of the heat shrinkable multilayer film may be deteriorated. A more preferable lower limit of the thickness of the adhesive layer is 0.5 μm, and a more preferable upper limit is 2.0 μm.
The thickness of the entire heat-shrinkable multilayer film can be adjusted by subtracting the thickness of the adhesive layer to adjust the thicknesses of the front and back layers and the intermediate layer.

For example, the heat-shrinkable multilayer film of the present invention has a five-layer structure of surface layer (A) / adhesive layer (E) / intermediate layer (B) / adhesive layer (E) / back surface layer (C), When the thickness of the entire shrinkable multilayer film is 40 μm, the thicknesses of the surface layer (A) and the back layer (C) are each preferably 2.0 to 10.0 μm, and 3.0 More preferably, it is -8.0 micrometers. Moreover, it is preferable that it is 0.3-3.0 micrometers, and, as for the thickness of the said contact bonding layer (E), it is more preferable that it is 0.5-2.0 micrometers. Moreover, it is preferable that it is 19.0-35.4 micrometers, and, as for the thickness of the said intermediate | middle layer (B), it is more preferable that it is 20.0-33.0 micrometers.

In the heat-shrinkable multilayer film of the present invention, the shrinkage in the main shrinkage direction is preferably 5 to 50%, more preferably 8 to 47%, still more preferably 10 to 45%, and particularly preferably 15 to 10 seconds at 70 ° C. 45% at 80 ° C. for 10 seconds, preferably 35 to 70%, more preferably 38 to 69%, still more preferably 41 to 68%, particularly preferably 43 to 67%, and boiling water for 10 seconds, preferably 65 to 85% More preferably, it is 68-83%, More preferably, it is 70-82%. By setting it as such a shrinkage rate, the outstanding shrinkage finishing property can be provided in a hot wind tunnel and a steam tunnel.

In the heat-shrinkable multilayer film of the present invention, the interlayer strength at normal temperature in the direction (MD direction) orthogonal to the main shrink direction (TD direction) is preferably 0.50 to 2.00 N / 10 mm. If the interlayer strength is less than 0.50 N / 10 mm, delamination may occur when the container is covered with a heat-shrinkable label. A more preferable lower limit of the interlayer strength is 0.60 N / 10 mm, and a more preferable lower limit is 0.70 N / 10 mm.
The heat-shrinkable multilayer film of the present invention preferably has an interlayer strength in the main shrinkage direction (TD direction) of 0.50 to 2.00 N / 10 mm. When the interlayer strength is less than 0.50 N / 10 mm, delamination may occur due to wear when the container is covered with a label and transported by cardboard. A more preferable lower limit of the interlayer strength is 0.60 N / 10 mm, and a more preferable lower limit is 0.70 N / 10 mm.

The heat-shrinkable multilayer film of the present invention preferably has an interlayer strength at a low temperature in the main shrink direction (TD direction) of 0.50 to 2.00 N / 10 mm. When the interlayer strength is less than 0.50 N / 10 mm, delamination occurs when the label is placed on the mounting machine at low temperature, or delamination occurs due to wear when the container is covered with the label and transported by cardboard at low temperature. May occur. A more preferable lower limit of the interlayer strength is 0.60 N / 10 mm, and a more preferable lower limit is 0.70 N / 10 mm.
In addition, the said interlayer strength can measure the interlayer strength when a layer is peeled 180 degree direction in MD direction and TD direction about a measurement sample, for example using a peeling tester or an autograph.

The method for producing the heat-shrinkable multilayer film of the present invention is not particularly limited, but a method of simultaneously forming each layer by a coextrusion method is preferable. When the co-extrusion method is T-die co-extrusion, the lamination method may be any of a feed block method, a multi-manifold method, or a method using these in combination.

As a method for producing the heat-shrinkable multilayer film of the present invention, specifically, for example, the raw materials constituting the front and back layers, the intermediate layer and the adhesive layer are respectively put into an extruder, and are formed into a sheet shape by a multilayer die. And a method of stretching uniaxially or biaxially after extruding, cooling and solidifying with a take-up roll.
As the stretching method, for example, a roll stretching method, a tenter stretching method, or a combination thereof can be used. The stretching temperature is changed according to the softening temperature of the resin constituting the film, the shrinkage characteristics required for the heat-shrinkable multilayer film, etc., but the preferred lower limit is 65 ° C, the preferred upper limit is 120 ° C, and the more preferred lower limit is 70 ° C A more preferred upper limit is 115 ° C. The stretching ratio in the main shrinkage direction is changed according to the resin constituting the film, stretching means, stretching temperature, etc., but is preferably 3 times or more, more preferably 4 times or more, preferably 7 times or less, more Preferably it is 6.5 times or less. By setting such a stretching temperature and stretching ratio, excellent thickness accuracy can be achieved, and when the perforation is split, delamination occurs and only the inner and outer layers remain in the container. This can be prevented.

The use of the heat-shrinkable multilayer film of the present invention is not particularly limited, but the heat-shrinkable multilayer film of the present invention has high interlayer strength, and when the overlapping portion is scratched after the container is mounted and when the perforation is torn. Since it suppresses delamination and is excellent in transparency, it is suitably used as a base film for heat-shrinkable labels that are mounted on containers such as PET bottles and metal bottles. A heat-shrinkable label using the heat-shrinkable multilayer film of the present invention is also one aspect of the present invention.

According to the present invention, it is possible to provide a heat-shrinkable multilayer film that has excellent adhesion between the front and back layers and the intermediate layer, can effectively prevent delamination, and is less likely to leave white stripes at the crease portion. it can.
Moreover, the heat-shrinkable multilayer film of the present invention does not cause zipping because there is no unevenness in interlayer strength even if delamination occurs. Furthermore, the heat-shrinkable multilayer film of the present invention has a feature that the heat-shrinkable label is hardly peeled off because delamination does not occur at the interface between the front and back layers and the adhesive layer.
Furthermore, according to this invention, the heat-shrinkable label which uses this heat-shrinkable multilayer film can be provided. In the heat-shrinkable label of the present invention, delamination hardly occurs at the solvent seal portion, and the heat-shrinkable label can be effectively prevented from peeling off.

It is a schematic diagram which shows the peeling method of the film in interlayer strength evaluation. It is a schematic diagram which shows the peeling method of the film in interlayer strength evaluation. It is a schematic diagram of the heat-shrinkable multilayer film when peeling occurs at the interface between the intermediate layer and the adhesive layer. It is a schematic diagram of the heat-shrinkable multilayer film when peeling occurs at the interface between the surface layer and the adhesive layer. It is a schematic diagram of the heat-shrinkable label used for label bending evaluation. It is a photograph which shows an example in case the crease whitening in fold whitening evaluation cannot be observed. It is a photograph which shows an example in case fold whitening in fold whitening evaluation can be observed.

Examples of the present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.
In the examples and comparative examples, the following raw materials were used.

(Polyester resin)
PET-1: Using 100 mol% of terephthalic acid as the dicarboxylic acid component, 65 mol% of the component derived from ethylene glycol as the diol component, 12 mol% of the component derived from diethylene glycol, derived from 1,4-cyclohexanedimethanol Aromatic polyester random copolymer resin (Vicat softening temperature 69 ° C.) containing 23 mol%
PET-2: 100 mol% of terephthalic acid is used as the dicarboxylic acid component, 68 mol% of the component derived from ethylene glycol is used as the diol component, 2 mol% of the component derived from diethylene glycol is derived from 1,4-cyclohexanedimethanol Aromatic polyester random copolymer resin (Vicat softening temperature 85 ° C.) containing 30 mol% of components and having a tensile modulus of 1950 MPa
(Polystyrene resin)
PS-1: Styrene-butadiene copolymer (styrene 78 wt%, butadiene 22 wt%: Vicat softening temperature 72 ° C., MFR 5.6 g / 10 min)
PS-2: Styrene-butadiene copolymer (styrene 80% by weight, butadiene 20% by weight: Vicat softening temperature 75 ° C., MFR 5.5 g / 10 min)
PS-3: Styrene-butadiene copolymer (styrene 84 wt%, butadiene 16 wt%: Vicat softening temperature 75 ° C, MFR 6.2 g / 10 min)
PS-4: Styrene-butadiene copolymer (styrene 80% by weight, butadiene 20% by weight: Vicat softening temperature 76 ° C., MFR 9.7 g / 10 min)
PS-5: Styrene-butadiene copolymer (Asaflex Chemicals, Asaflex 830, Vicat softening temperature 72 ° C., MFR 6.1 g / 10 min)
PS-6: Styrene-butadiene copolymer (manufactured by Denki Kagaku Kogyo Co., Ltd., Clearen 220M, Vicat softening temperature 78 ° C., MFR 7.2 g / 10 min)
(Polyester elastomer)
TPE-1: A polyester elastomer composed of polyester as a hard segment and polyalkylene ether glycol as a soft segment and having a tensile elastic modulus of 55 MPa (manufactured by Toray DuPont, Hytrel 4057, melting point 163 ° C., specific gravity 1 .15)
TPE-2: Polyester elastomer composed of polyester as a hard segment and polyalkylene ether glycol as a soft segment and having a tensile elastic modulus of 45 MPa (manufactured by Mitsubishi Chemical Corporation, Primalloy A1600N, melting point 160 ° C., specific gravity 1 .00)

The Vicat softening temperature is 120 ° C. while applying a 10 N load to the needle-shaped indenter placed on the test piece after collecting the test piece from each polyester-based resin and polystyrene-based resin by a method according to JIS K 7206 (1999). The temperature was measured at a rate of / h, and the temperature when the needle-like indenter entered 1 mm was confirmed.
The MFR was measured by melting each polystyrene resin at 200 ° C. by a method based on ISO 1133 and measuring the discharge amount of the resin in terms of 10 minutes under a 5 kg load condition.
The melting point was measured by heating each polyester elastomer at a rate of 10 ° C./min using a differential scanning calorimeter (manufactured by Shimadzu Corporation, DCS-60).
The specific gravity was measured by an underwater displacement method using an ethanol as an immersion liquid for each polyester elastomer in accordance with JIS K 7112 (1999) (manufactured by Alpha Mirage, electronic hydrometer MD-300S).
The tensile elastic modulus was measured by a method based on ASTM-D882, using a non-stretched sheet of polyester resin and polyester elastomer using a STRograph VE10 manufactured by Toyo Seiki Seisakusho.

Example 1
A polyester resin (PET-1) was used as the resin constituting the front and back layers.
Polystyrene resin (PS-1) was used as the resin constituting the intermediate layer.
As the resin constituting the adhesive layer, polystyrene resin (PS-5) 60% by weight (60 parts by weight) and polyester elastomer (TPE-1) 40% by weight (40 parts by weight) were used.
These were put into an extruder having a barrel temperature of 160 to 250 ° C., extruded from a multilayer die at 250 ° C. into a sheet having a five-layer structure, and cooled and solidified with a take-up roll at 30 ° C. Next, after stretching at a stretching ratio of 6 in a tenter stretching machine having a preheating zone of 105 ° C., a stretching zone of 90 ° C., and a heat setting zone of 85 ° C., the direction perpendicular to the main shrinkage direction is MD by winding with a winder. A heat-shrinkable multilayer film having a main shrinkage direction of TD was obtained.
The obtained heat-shrinkable multilayer film has a total thickness of 35 μm, and has a front and back layer (4.0 μm) / adhesive layer (0.8 μm) / intermediate layer (25.4 μm) / adhesive layer (0.8 μm) / front and back It was a 5-layer structure of layers (4.0 μm).

(Example 2)
As the resin constituting the adhesive layer, 60% by weight of a polystyrene resin (PS-6) and 40% by weight of a polyester elastomer (TPE-1) were used.
Others are the same as in Example 1, and the total thickness is 35 μm, and the front and back layers (3.7 μm) / adhesive layer (0.7 μm) / intermediate layer (26.2 μm) / adhesive layer (0.7 μm) / front and back A five-layer film having a layer (3.7 μm) was obtained.

(Example 3)
Polystyrene resin (PS-2) was used as the resin constituting the intermediate layer.
As the resin constituting the adhesive layer, 50% by weight of a polystyrene resin (PS-5) and 50% by weight of a polyester elastomer (TPE-2) were used.
Others were the same as in Example 1, and the total thickness was 35 μm. Front and back layers (5.0 μm) / adhesive layer (0.7 μm) / intermediate layer (23.6 μm) / adhesive layer (0.7 μm) / front and back A film having a five-layer structure of layers (5.0 μm) was obtained.

Example 4
Polystyrene resin (PS-2) was used as the resin constituting the intermediate layer.
As the resin constituting the adhesive layer, 40% by weight of polystyrene resin (PS-5) and 60% by weight of polyester elastomer (TPE-1) were used.
Others were the same as in Example 1, and the total thickness was 35 μm, and the front and back layers (4.0 μm) / adhesive layer (0.8 μm) / intermediate layer (25.4 μm) / adhesive layer (0.8 μm) / front and back A five-layer film having a layer (4.0 μm) was obtained.

(Example 5)
Polystyrene resin (PS-3) was used as the resin constituting the intermediate layer.
As the resin constituting the adhesive layer, 40% by weight of a polystyrene resin (PS-5) and 60% by weight of a polyester elastomer (TPE-2) were used.
Others were the same as in Example 1, and the total thickness was 35 μm. Front and back layers (5.0 μm) / adhesive layer (0.8 μm) / intermediate layer (23.4 μm) / adhesive layer (0.8 μm) / front and back A film having a five-layer structure (5.0 μm) was obtained.

( Reference Example 6)
A polyester resin (PET-2) was used as the resin constituting the front and back layers.
Polystyrene resin (PS-4) was used as the resin constituting the intermediate layer.
As the resin constituting the adhesive layer, 20% by weight of a polystyrene resin (PS-5) and 80% by weight of a polyester elastomer (TPE-2) were used.
Others were the same as in Example 1, and the total thickness was 35 μm. Front and back layers (3.5 μm) / adhesive layer (0.8 μm) / intermediate layer (26.4 μm) / adhesive layer (0.8 μm) / front and back A film having a five-layer structure of layers (3.5 μm) was obtained.

(Example 7)
A polyester resin (PET-2) was used as the resin constituting the front and back layers.
Polystyrene resin (PS-3) was used as the resin constituting the intermediate layer.
As the resin constituting the adhesive layer, 50% by weight of a polystyrene resin (PS-6) and 50% by weight of a polyester elastomer (TPE-1) were used.
Others were the same as in Example 1, and the total thickness was 35 μm, and the front and back layers (4.0 μm) / adhesive layer (0.8 μm) / intermediate layer (25.4 μm) / adhesive layer (0.8 μm) / front and back A five-layer film having a layer (4.0 μm) was obtained.

(Comparative Example 1)
As the resin constituting the adhesive layer, 75% by weight of a polystyrene resin (PS-5) and 25% by weight of a polyester elastomer (TPE-1) were used.
Others were the same as in Example 1, and the total thickness was 40 μm, and the front and back layers (5.5 μm) / adhesive layer (0.8 μm) / intermediate layer (27.4 μm) / adhesive layer (0.8 μm) / front and back A film having a five-layer structure of layers (5.5 μm) was obtained.

(Comparative Example 2)
Polystyrene resin (PS-2) was used as the resin constituting the intermediate layer.
As the resin constituting the adhesive layer, 15% by weight of a polystyrene resin (PS-6) and 85% by weight of a polyester elastomer (TPE-2) were used.
Others were the same as in Example 1, and the total thickness was 35 μm. Front and back layers (5.0 μm) / adhesive layer (0.7 μm) / intermediate layer (23.6 μm) / adhesive layer (0.7 μm) / front and back A film having a five-layer structure of layers (5.0 μm) was obtained.

(Comparative Example 3)
A polyester resin (PET-2) was used as the resin constituting the front and back layers.
Polystyrene resin (PS-2) was used as the resin constituting the intermediate layer.
Polyester elastomer (TPE-2) was used as the resin constituting the adhesive layer.
Others were the same as in Example 1, and the total thickness was 35 μm. Front and back layers (5.0 μm) / adhesive layer (0.7 μm) / intermediate layer (23.6 μm) / adhesive layer (0.7 μm) / front and back A film having a five-layer structure of layers (5.0 μm) was obtained.

(Comparative Example 4)
As the resin constituting the adhesive layer, 25% by weight of polystyrene resin (PS-5) and 75% by weight of polyester resin (PET-1) were used.
Others were the same as in Example 1, and the total thickness was 40 μm. Front and back layers (5.0 μm) / adhesive layer (0.8 μm) / intermediate layer (28.4 μm) / adhesive layer (0.8 μm) / front and back A film having a five-layer structure of layers (5.0 μm) was obtained.

(Evaluation)
The following evaluation was performed about the heat-shrinkable multilayer film obtained by the Example , the reference example, and the comparative example. Table 1 shows the constitution and evaluation results of the heat-shrinkable multilayer film.

(1) Heat shrinkage rate After the heat shrinkable multilayer film is cut into a size of 100 mm in the main shrink direction (TD) x 100 mm in the direction perpendicular to the main shrink direction (MD) and immersed in warm water at 70 ° C. for 10 seconds, The heat-shrinkable multilayer film was taken out and immediately immersed in tap water for 10 seconds. The length (L) of one side of TD of this heat-shrinkable multilayer film was measured, and the heat shrinkage rate in the TD direction was determined according to the following formula (1).
Thermal contraction rate (%) = {(100−L) / 100} × 100 (1)

In addition, the average value was used for the shrinkage rate, assuming that the number of samples (n) = 3. The heat shrinkage rate was similarly measured for warm water and boiling water at 80 ° C.

(2) Interlaminar strength at room temperature The heat-shrinkable multilayer film was cut into a size of 100 mm length × 10 mm width, and a part of the film edge was delaminated as shown in FIG. The strength (N / 10 mm) at room temperature (23 ° C.) when peeled in the length direction of the sample at a pulling speed of 500 mm / min and in the direction of 180 degrees as shown in FIG. -17, manufactured by Shinto Kagaku Co.). 1 and 2 are schematic views showing a film peeling method in evaluation of interlayer strength.
The test was performed so that the length direction was the main shrinkage direction (TD) or the direction perpendicular to the main shrinkage direction (MD).
In addition, the test was conducted 10 times in both directions of MD and TD, and the average value of the interlayer strength in each direction of MD and TD was obtained.

Evaluation was made according to the following criteria from the average value of the interlayer strength in each direction of the obtained MD and TD. If these evaluations are “◯”, it is possible to suppress label peeling failure when the heat-shrinkable label is mounted on a container or the like.

(Interlayer strength in MD direction)
An average interlayer strength of 0.50 N / 10 mm or more was evaluated as “◯”, and an average interlayer strength of less than 0.50 N / 10 mm was evaluated as “x”.
(Interlayer strength in TD direction)
An average interlayer strength of 0.50 N / 10 mm or more was evaluated as “◯”, and an average interlayer strength of less than 0.50 N / 10 mm was evaluated as “x”.

(3) Determination of peeled surface at normal temperature In measurement of delamination strength at normal temperature, the delamination interface at the time of TD measurement was observed and evaluated according to the following criteria.

(Peeling surface judgment)
The case where the delamination was at the interface between the intermediate layer and the adhesive layer was “◯”, and the case where the delamination was at the interface between the front and back layers and the adhesive layer was “x”.

When the heat-shrinkable label is attached to the container, the surface layer located outside the heat-shrinkable label may be damaged by a load such as folding of the label by the attaching machine. When the surface layer is scratched, delamination progresses starting from this scratch, and in the worst case, the label may be peeled off after mounting. Whether the label is peeled off depends on which interface of the heat-shrinkable multilayer film has undergone delamination. FIG. 3 is a schematic diagram of a heat-shrinkable multilayer film when peeling occurs at the interface between the intermediate layer and the adhesive layer, and FIG. 4 shows a heat-shrinkable multilayer film when peeling occurs at the interface between the surface layer and the adhesive layer. It is a schematic diagram of a film.
As shown in FIG. 3, when delamination occurs at the interface between the intermediate layer and the adhesive layer, even if there is a scratch by the mounting machine, the scratch must not penetrate the surface layer and the adhesive layer. Further, delamination does not proceed and label peeling hardly occurs. On the other hand, as shown in FIG. 4, when delamination occurs at the interface between the surface layer and the adhesive layer, delamination proceeds only by scratching the surface layer, causing label peeling.

(4) Presence or absence of zipping at room temperature After cutting the heat-shrinkable multilayer film into a size of 100 mm length x 10 mm width and leaving it to stand at room temperature (23 ° C.) for 10 minutes, a part of the end of the film is measured in the same manner as the interlayer strength measurement Was delaminated. The presence or absence of zipping was evaluated according to the following criteria. If these evaluations are “Yes”, it can be seen that the interlayer strength is uneven.
Zippering means that when a heat-shrinkable multilayer film is peeled off, due to unevenness in interlayer strength, the peel resistance is high in areas where the interlayer strength is high and the peel resistance is low in areas where the interlayer strength is low. It is a state in which the part where peeling progress stops and the part where peeling progresses at a stroke appear regularly or irregularly.

(Zip occurrence or not)
Existence: Stepped traces are made on the peeled front and back layers.
None: Stepped traces do not appear on the peeled front and back layers.

(5) Interlaminar strength at low temperature The heat-shrinkable multilayer film was cut into a size of length 100 mm × width 10 mm, and allowed to stand at low temperature (5 ° C.) for 10 minutes, and then the interlayer strength (N / 10 mm) was measured. The measurement was performed in the same manner as the interlayer strength evaluation at room temperature except that the measurement temperature was 5 ° C.
The interlayer strength and minimum value in the TD direction were measured for each measurement, and the test was repeated 10 times. The average of the interlayer strength in the TD direction for each measurement was taken as the TD direction average value. The minimum value in the TD direction was used. In the evaluation at a low temperature, by measuring the interlaminar strength in the TD direction in particular, the resistance to delamination when the load is applied in the TD direction of the heat-shrinkable label with a mounting machine or the like in a low-temperature environment can be understood. Further, by obtaining the average value and the minimum value of the interlayer strength in the TD direction, the magnitude of the variation in the delamination strength in a low temperature environment can be understood.

(Interlayer strength in TD direction)
An average interlayer strength of 0.50 N / 10 mm or more was evaluated as “◯”, and an average interlayer strength of less than 0.50 N / 10 mm was evaluated as “x”.

(6) Determination of peeling surface at low temperature In measurement of delamination strength at low temperature, the delamination interface at the time of measuring in the TD direction was observed and evaluated according to the same criteria as the peeling surface determination at normal temperature.

(7) Presence of zipping at low temperature A heat shrinkable multilayer film was cut into a size of 100 mm length × 10 mm width, left at low temperature (5 ° C.) for 10 minutes, and then a part of the film edge as in the measurement of interlayer strength Was delaminated. The presence or absence of zipping was evaluated according to the same criteria as the presence or absence of zipping at room temperature.

(8) Evaluation of delamination after label bending The obtained heat-shrinkable multilayer film was cut into a width of 227 mm in the TD direction, and a solvent in which 30 parts by weight of cyclohexane was mixed with 100 parts by weight of 1,4-dioxolane was used as MD. It was applied with a width of 3 mm so as to be parallel to the direction, and was flatly folded and bonded so as to have a width in the TD direction of 108 mm to form a cylinder. As shown in FIG. 5, the cylindrical heat-shrinkable multilayer film was cut into a width of 100 mm in the MD direction to obtain a heat-shrinkable label. FIG. 5 is a schematic diagram of a heat-shrinkable label used for label bending evaluation. A portion where both ends of the label are bonded with a solvent is also referred to as a “solvent seal portion”.
Next, both ends of the seal portion of the heat-shrinkable label were held with fingers in a low temperature (5 ° C.) atmosphere, and the label was bent 20 times so that a force was applied in the TD direction. The label was bent at six locations on the heat-shrinkable label to obtain a heat-shrinkable label after bending.
The heat-shrinkable label after bending was immersed in boiling water for 10 seconds in a 275 g bottle can container having a round shape of about 66 mm in diameter, and the appearance of the bonded part when heat-shrinked and coated on the container was evaluated according to the following criteria.

○: No delamination occurred in the solvent seal portion in all 10 labels.
(Triangle | delta): The delamination has generate | occur | produced in the solvent seal | sticker part in 1-2 labels among 10 labels.
X: In three or more labels out of 10 labels, delamination occurs at the solvent seal portion.

(9) Folding whitening evaluation After printing on a heat-shrinkable multilayer film (film width: 500 mm) by a gravure printing method using Fine Star Black (manufactured by Toyo Ink), Fine Star White (Toyo Ink) Ink Co., Ltd.) was used for printing. As a result, a heat-shrinkable multilayer film with black and white two-color backside printing was obtained. As the printing plate, a plate produced by direct laser plate making with a plate depth of 30 μm and a line number of 175 lines was used.
Next, the heat-shrinkable multilayer film was cut from the black printed portion into a rectangle of 100 mm in the MD direction and 200 mm in the TD direction. The cut sample was creased by pressing the rubber roller twice at a speed of 2 seconds / 100 mm with a load of 2 kg in parallel with the MD direction at room temperature (23 ° C.) so that the printing surface was inside. Thereafter, the cut sample was developed, and the crease was restored by pressing the rubber roller once at a speed of 2 seconds / 100 mm with a 2 kg load. After that, using a jig that can regulate the shrinkage rate in the TD direction, the sample was immersed in warm water at 75 ° C. for 7 seconds and shrunk by 5% in the TD direction. The appearance of the folds at that time was evaluated according to the following criteria.
The appearance was evaluated by irradiating fluorescent light from an angle of 45 degrees on the sample, and 10 persons visually observing the position at an angle of 45 degrees opposite to the fluorescent lamp. An example when the whitening of the folds cannot be observed is shown in FIG. 6, and an example when the whitening of the folds can be observed is shown in FIG.

(Fold whitening evaluation)
○: All 10 people cannot observe crease whitening.
(Triangle | delta): Two or less people can observe crease whitening among ten people.
X: 3 or more out of 10 people can observe whitening of folds.

(Comprehensive evaluation)
A: In the evaluations (1) to (9) above, there is no “x”.
X: In evaluation of said (1)-(9), there exists one or more "x".

In the heat-shrinkable multilayer films obtained in Examples 1 to 5 and 7 and Reference Example 6 , good results were obtained in all evaluations. Further, even if delamination occurs in the heat-shrinkable multilayer film, label peeling does not occur because peeling occurs at the interface between the intermediate layer and the adhesive layer.
On the other hand, when the mixing ratio of the resin constituting the adhesive layer does not satisfy the range defined in the present invention as in Comparative Examples 1 to 4, the interlayer strength at low temperatures is reduced, or the film is used in the solvent sealing process. When the film was strongly folded, the folds were whitened, resulting in poor appearance or delamination due to impact when mounted on the container. Further, zipping occurred at a low temperature.

According to the present invention, the adhesiveness between the front and back layers and the intermediate layer is excellent not only at room temperature but also at low temperatures, the delamination can be effectively prevented, and the white stripes are formed on the crease portion after heat shrinkage. Can be provided. Moreover, according to this invention, the heat-shrinkable label which uses this heat-shrinkable multilayer film can be provided.

1 Front and back layers 2 Intermediate layer 3 Adhesive layer

Claims (6)

A heat-shrinkable multilayer film in which front and back layers containing a polyester-based resin and an intermediate layer containing a polystyrene-based resin are laminated via an adhesive layer,
The heat-shrinkable multilayer film is characterized in that the adhesive layer contains 25 to 65% by weight of a polystyrene resin and 35 to 75 % by weight of a polyester elastomer. The heat-shrinkable multilayer film according to claim 1, wherein the polystyrene resin constituting the adhesive layer is an aromatic vinyl hydrocarbon-conjugated diene copolymer. The heat-shrinkable multilayer film according to claim 1 or 2, wherein the polyester elastomer constituting the adhesive layer has a melting point of 120 to 200 ° C. The heat-shrinkable multilayer film according to claim 1, 2 or 3, wherein the polyester-based elastomer constituting the adhesive layer has a specific gravity of 0.95 to 1.20. The heat-shrinkable multilayer film according to claim 1, 2, 3, or 4, wherein the polyester-based elastomer constituting the adhesive layer is modified with α, β-ethylenically unsaturated carboxylic acid. A heat-shrinkable label comprising the heat-shrinkable multilayer film according to claim 1, 2, 3, 4 or 5.