JP7007962B2 - Heat shrinkable multilayer film - Google Patents

Description

INDUSTRIAL APPLICABILITY The present invention can exhibit excellent light-shielding properties, has excellent aesthetics when a design or the like is printed, has appropriate mechanical strength, and has excellent heat shrinkage. Regarding multilayer films. It also relates to a heat shrinkable label containing the heat shrinkable multilayer film.

Liquid products such as beverages are generally sold by being filled in paper boxes, metal cans, plastic bottles such as PET bottles, and containers such as glass bottles. Of these, since paper boxes and metal cans do not have a resealing means, plastic bottles and glass bottles having a resealing means such as caps are widely used for containers such as beverages having a large content.

However, since such plastic bottles and glass bottles lack light-shielding properties as compared with paper boxes and metal cans, they are used as containers for beverages that are easily altered or discolored by light, such as sake, beer, and green tea. Colored plastic bottles and glass bottles are used to impart light-shielding properties. On the other hand, although such a colored container has excellent light-shielding properties, it contains a coloring agent, so that it is often difficult to recycle the used container when it is recycled.

On the other hand, a colorless and transparent plastic bottle or a glass bottle is attached with a heat-shrinkable label having a light-shielding property to impart light-shielding property to the container.
For example, Patent Document 1 discloses a heat-shrinkable film having an achromatic or chromatic intermediate layer and a white front and back layers.
However, when a white colorant such as titanium dioxide is contained in the film for the purpose of improving the light-shielding property, the heat shrinkage of the film is lowered, the wearability is deteriorated, and problems such as wrinkles after mounting are deteriorated. There was a problem that it occurred. Further, when molding a film by extrusion molding or the like, a white colorant such as titanium dioxide may cause contamination of dies or the like or molding defects.

Further, Patent Document 2 discloses a heat-shrinkable multilayer film having a front and back layer containing a polyester resin and an intermediate layer containing a predetermined amount of titanium dioxide.
However, although such a film is excellent in stainability of dies and sharpness of printing, it has a problem that it has low light-shielding property and cannot sufficiently suppress deterioration of the contents. In addition, there is a problem that the mechanical strength is also inferior.

International Publication No. 2004/094139 Japanese Unexamined Patent Publication No. 2010-284941

In view of the above problems, the present invention can exhibit excellent light-shielding properties, is also excellent in aesthetics when printing a design, etc., has appropriate mechanical strength, and is heat-shrinkable. It is an object of the present invention to provide a heat-shrinkable multilayer film having excellent heat shrinkage. It is also an object of the present invention to provide a heat shrinkable label containing the heat shrinkable multilayer film.

The present invention comprises a surface layer containing a polyester-based resin, a first intermediate layer containing a polystyrene-based resin and a white colorant, a second intermediate layer containing a polystyrene-based resin and a black colorant, and a polyester-based material. A heat-shrinkable multilayer film having a back surface layer containing a resin in this order, wherein the content of the white colorant in the first intermediate layer is 5 to 10 % by weight, and the second intermediate layer has a content of 5 to 10% by weight. A heat-shrinkable multilayer film having a black colorant content of 10 to 15% by weight.
Hereinafter, the present invention will be described in detail.

The present inventors can exhibit excellent light-shielding properties by having a first intermediate layer containing a predetermined amount of a white colorant and a second intermediate layer containing a predetermined amount of a black colorant. The present invention has been completed by finding that it is possible to obtain a heat-shrinkable multilayer film having excellent shrinkage characteristics and high rigidity, which is also excellent in aesthetics when printing a design or the like.

The heat-shrinkable multilayer film of the present invention has a surface layer containing a polyester resin, a first intermediate layer containing a polystyrene resin and a white colorant, and a second layer containing a polystyrene resin and a black colorant. It has an intermediate layer and a back surface layer containing a polyester resin in this order. In the present specification, the front surface layer means a layer on the outer surface side when a heat-shrinkable label is used, and the back surface layer means a layer on the inner surface side when a heat-shrinkable label is used. To say. Hereinafter, the front surface layer and the back surface layer are also collectively referred to as front and back layers.

(Front and back layers)
The heat-shrinkable multilayer film of the present invention has the front and back layers. By having the front and back layers, it is possible to prevent contamination of dies and the like by white colorants and black colorants during film molding, molding defects, and productivity deterioration. In addition, it becomes possible to improve printability. Further, it is possible to prevent the light-shielding property from being lowered due to the lack of the white colorant or the black colorant.

The front and back layers contain a polyester resin.
Examples of the polyester-based resin include those obtained by polycondensing a dicarboxylic acid component and a diol component.

The dicarboxylic acid component is not particularly limited, and for example, o-phthalic acid, terephthalic acid, isophthalic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, octylsuccinic acid, cyclohexanedicarboxylic acid, naphthalenedicarboxylic acid, and fumaric acid. , Maleic acid, itaconic acid, decamethylenecarboxylic acid, anhydrides thereof, lower alkyl esters and the like.

The diol component is not particularly limited, and for example, ethylene glycol, 1,3-propanediol, 1,4-butanediol, diethylene glycol, 1,5-pentanediol, 1,6-hexanediol, dipropylene glycol, and tri. Ethylene glycol, tetraethyleneglycol, 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. Aliper diols; alkylene oxide adducts of 2,2-bis (4-hydroxycyclohexyl) propane, 2,2-bis (4-hydroxycyclohexyl) propane, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol Such as alicyclic diols and the like can be mentioned.

Among the polyester-based resins, those containing a component derived from terephthalic acid as a dicarboxylic acid component and a component derived from ethylene glycol and / or 1,4-cyclohexanedimethanol as a diol component are used. preferable. By using such a polyester-based resin, excellent shrinkage can be imparted to the heat-shrinkable multilayer film.
When it is desired to further increase 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 out of 100 mol% of the diol component. It is preferable to use one having an amount of about 40 mol%.

Such a polyester resin may further contain a component derived from diethylene glycol in an amount of 0 to 30 mol%, preferably 1 to 25 mol%, and more preferably 2 to 20 mol%. 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 perforations are torn, preventing only the front and back layers on the inner surface side from remaining in the container. can do. If the content derived from diethylene glycol exceeds 30 mol%, the low temperature shrinkage of the heat-shrinkable multilayer film becomes too high, and wrinkles are likely to occur when the film is mounted on a container.

Further, as the polyester resin containing a component derived from terephthalic acid as the dicarboxylic acid component, a polyester resin containing a component derived from 1,4-butanediol as a diol component can also be used. Such polyester-based resins are generally called polybutylene terephthalate-based resins.
The polybutylene terephthalate-based resin contains a polyester-based resin containing a component derived from terephthalic acid as the dicarboxylic acid component and a component derived from ethylene glycol and 1,4-cyclohexanedimethanol as a diol component. It is preferable to use them together. By using such a mixed resin, more excellent finishability can be imparted.

The polybutylene terephthalate resin includes 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 the component derived from terephthalic acid, and /. Alternatively, it may be a polybutylene terephthalate resin containing a diol component other than the component derived from 1,4-butanediol.
The content of the dicarboxylic acid component other than the component derived from the terephthalic acid is preferably 10 mol% or less of the 100 mol% of the dicarboxylic acid component. If it exceeds 10 mol%, the heat resistance of the polybutylene terephthalate resin is lowered, which may be economically disadvantageous. The content of the diol component other than the component derived from 1,4-butanediol is preferably 10 mol% or less of the 100 mol% of the diol component. If it exceeds 10 mol%, the heat resistance of the polybutylene terephthalate resin is lowered, which may be economically disadvantageous.

The amount of the polybutylene terephthalate resin added 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 become too low or the natural shrinkage rate may increase. If the Vicat softening temperature exceeds 95 ° C., the low-temperature shrinkage and shrinkage finish of the heat-shrinkable multilayer film may decrease, or the low-temperature shrinkage over time may increase. 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 according to JIS K 7206 (1999).

Commercially available polyester resins constituting the front and back layers include, for example, "Easter", "EmbraceLv" (manufactured by Eastman Chemical Company), "Bellpet" (manufactured by Bell Polyester Products), and "Novaduran" (Mitsubishi Engineering Plastics). (Manufactured by Su), etc.

As the polyester-based resin contained in the front and back layers, the polyester-based resin having the above-mentioned composition may be used alone, or two or more kinds of polyester-based resins having the above-mentioned composition may be used in combination. Further, the polyester-based resin may be a polyester-based resin having different compositions in the front surface layer and the back surface layer, but is a polyester-based resin having the same composition in order to suppress troubles due to curling of the film or the like. Is preferable.

The front and back layers are, if necessary, antioxidants, heat stabilizers, ultraviolet absorbers, light stabilizers, lubricants, antistatic agents, antiblocking agents, flame retardants, antibacterial agents, fluorescent whitening agents, colorants, etc. May contain the additive of.

The ratio of the thickness of each of the front surface layer and the back surface layer is such that the preferable lower limit is 3%, the more preferable lower limit is 5%, the preferable upper limit is 25%, and the more preferable upper limit is 20% with respect to the thickness of the entire heat-shrinkable multilayer film. be.
When the thickness of the front surface layer and the back surface layer is within the above preferable range, the heat resistance of the heat-shrinkable multilayer film can be improved.

(First middle layer)
The heat-shrinkable multilayer film of the present invention contains the first intermediate layer.
By having the first intermediate layer, it is possible to improve the sharpness of printing such as a design on the obtained heat-shrinkable multilayer film.

The first intermediate layer contains a polystyrene-based resin.
Examples of the polystyrene-based resin include aromatic vinyl hydrocarbon-conjugated diene copolymer, aromatic vinyl hydrocarbon-conjugated diene copolymer and aromatic vinyl hydrocarbon-lipid unsaturated carboxylic acid ester copolymer. Examples thereof include mixed resins of the above, rubber-modified impact-resistant polystyrene, and the like. By using the above-mentioned polystyrene-based resin, the heat-shrinkable multilayer film of the present invention can start shrinking from a low temperature and has high shrinkage.

In the present specification, the aromatic vinyl hydrocarbon-conjugated diene copolymer means 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 alone or in combination of two or more. The conjugated diene is not particularly limited, and is, for example, 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and 1,3-hexadiene. And so on. These may be used alone or in combination of two or more.

Since the aromatic vinyl hydrocarbon-conjugated diene copolymer is particularly excellent in heat shrinkage, it is preferable to contain a styrene-butadiene copolymer (SBS resin). Further, in the aromatic vinyl hydrocarbon-conjugated diene copolymer, 2-methyl-1,3-butadiene (isoprene) is used as the conjugated diene in order to produce a heat-shrinkable multilayer film having less fish eyes. It is preferable to contain the styrene-isoprene copolymer (SIS resin), styrene-isoprene-butadiene copolymer (SIBS) and the like used.
The aromatic vinyl hydrocarbon-conjugated diene copolymer may contain any one of the SBS resin, the SIS resin and the SIBS resin alone, or may contain a plurality of them in combination. When a plurality of SBS resin, SIS resin and SIBS resin are used, each resin may be dry-blended, and a compound resin obtained by kneading each resin with a specific composition using an extruder and pelletizing the resin is used. You may.

When the aromatic vinyl hydrocarbon-conjugated diene copolymer contains SBS resin, SIS resin and SIBS resin alone or in a plurality, a heat-shrinkable multilayer film having particularly excellent 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. If the styrene content exceeds 90% by weight or the conjugated diene content is less than 10% by weight, the heat-shrinkable multilayer film is easily cut when tension is applied, or it may be unexpected during processing such as printing. It may break regardless. If the styrene content is less than 65% by weight or the conjugated diene content exceeds 35% by weight, foreign substances such as gels are likely to be generated during the molding process, and the heat-shrinkable multilayer film becomes weak. In some cases, the handleability may deteriorate.

In the present specification, the aromatic vinyl hydrocarbon-polyunsaturated carboxylic acid ester copolymer contains a component derived from an aromatic vinyl hydrocarbon and a component derived from an aliphatic unsaturated carboxylic acid ester. Refers to a copolymer.
The aromatic vinyl hydrocarbon is not particularly limited, and the same aromatic vinyl hydrocarbon as 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, and stearyl (meth) acrylate. Be done. Here, the (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 preferably ~ 90% by weight and the butyl acrylate content is preferably 10 to 40% by weight. By using an aromatic vinyl hydrocarbon-aliphatic unsaturated carboxylic acid ester copolymer having such a composition, a heat-shrinkable multilayer film having excellent heat-shrinkability can be obtained.

The mixed resin of the aromatic vinyl hydrocarbon-conjugated diene copolymer and the aromatic vinyl hydrocarbon-lipid unsaturated carboxylic acid ester copolymer is not particularly limited, but the aromatic vinyl hydrocarbon-lipophilic non-polypolymer is not particularly limited. A mixed resin having a saturated carboxylic acid ester copolymer content of 80% by weight or less is preferable.

The rubber-modified impact-resistant polystyrene is composed of a continuous phase composed of a ternary copolymer of styrene, alkyl methacrylate and alkyl acrylate, and a dispersed phase composed of a rubber component mainly composed of a conjugated diene. It is the basis.

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, 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 the conjugated diene forming the dispersed phase is preferably 0.1 to 1.2 μm, more preferably 0.3 to 0.8 μm. If the particle size is less than 0.1 μm, the impact resistance of the rubber-modified impact-resistant polystyrene may be insufficient, and if it exceeds 1.2 μm, the transparency of the intermediate layer may be lowered.

In the rubber-modified impact-resistant polystyrene, the ratio of the continuous phase composed of a ternary copolymer 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 ratio is preferably 5 to 20% by weight. If 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 if it exceeds 20% by weight, the transparency of the intermediate layer may be lowered. There is.

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

The preferable lower limit of MFR (melt flow rate) of the polystyrene resin at 200 ° C. is 2 g / 10 minutes, and the preferable upper limit is 15 g / 10 minutes. If the MFR at 200 ° C. is less than 2 g / 10 minutes, it becomes difficult to form a film. If the MFR at 200 ° C. exceeds 15 g / 10 minutes, the mechanical strength of the film becomes low and it becomes unusable for practical use. 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. The MFR can be measured by a method compliant with ISO1133.

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

The content of the polystyrene-based resin in the first intermediate layer is preferably 50% by weight at the lower limit and 95% by weight at the upper limit.
When the content of the polystyrene-based resin is 50% by weight or more, the tensile elongation of the obtained heat-shrinkable multilayer film can be improved and the mechanical strength can be made excellent. When the content of the polystyrene-based resin is 95% by weight or less, the content of the white colorant is sufficient and excellent light-shielding property can be exhibited.
The content of the polystyrene-based resin has a more preferable lower limit of 53% by weight, a further preferable lower limit of 55% by weight, a more preferable upper limit of 93% by weight, and a further preferable upper limit of 90% by weight.

The first intermediate layer contains a white colorant.
By containing the white colorant, the light-shielding property can be improved and the deterioration of the contents can be suppressed. In addition, it is possible to improve the sharpness of printing such as a design on the obtained heat-shrinkable film.

Examples of the white colorant include titanium dioxide, calcium carbonate, barium sulfate, zinc oxide and the like. Of these, titanium dioxide is preferable because it can reflect light in a wide wavelength range.

The titanium dioxide has anatase-type, rutile-type, and brookite-type crystal forms, but rutile-type titanium dioxide is preferable from the viewpoint of light-shielding property, weather resistance, heat resistance, and sharpness.

The volume average particle size of the white colorant has a preferable lower limit of 150 nm, a more preferable lower limit of 200 nm, a preferable upper limit of 400 nm, and a more preferable upper limit of 380 nm.
The volume average particle size can be measured by using, for example, a laser diffraction / scattering type particle size distribution measuring device.

The content of the white colorant in the first intermediate layer has a lower limit of 5% by weight and an upper limit of 50% by weight.
When the content of the white colorant is 5% by weight or more, the whiteness can be sufficiently improved to obtain a heat-shrinkable multilayer film having an excellent aesthetic appearance. When the content of the white colorant is 50% by weight or less, the mechanical strength can be sufficiently improved.
The content of the white colorant has a preferable lower limit of 10% by weight, a more preferable lower limit of 15% by weight, a preferable upper limit of 45% by weight, and a further preferable upper limit of 40% by weight.

The first intermediate layer may contain additives such as an antioxidant, a heat stabilizer, an ultraviolet absorber, a light stabilizer, a lubricant, an antistatic agent, a flame retardant, and an antibacterial agent, if necessary. ..

The thickness of the first intermediate layer has a preferable lower limit of 50%, a more preferable lower limit of 60%, a preferable upper limit of 80%, and a more preferable upper limit of 75% with respect to the thickness of the entire heat-shrinkable multilayer film.
When the thickness of the first intermediate layer is in the above-mentioned preferable range, sufficient light-shielding property can be imparted to the heat-shrinkable multilayer film, and mechanical strength can be sufficiently improved.

(Second middle layer)
The heat-shrinkable multilayer film of the present invention has the second intermediate layer.
By having the second intermediate layer, sufficient light-shielding property can be imparted to the heat-shrinkable multilayer film, and deterioration of the contents can be suppressed.

The second intermediate layer contains a polystyrene-based resin.
Examples of the polystyrene-based resin constituting the second intermediate layer include those similar to the polyester-based resin constituting the first intermediate layer.
Further, as the polystyrene-based resin constituting the second intermediate layer, the same polystyrene-based resin as the polystyrene-based resin constituting the first intermediate layer may be used, or a different polystyrene resin may be used.

The content of the polystyrene-based resin in the second intermediate layer is preferably 85% by weight at the lower limit and 97% by weight at the upper limit.
When the content of the polystyrene-based resin is 85% by weight or more, the mechanical strength of the obtained heat-shrinkable multilayer film can be sufficiently improved. When the content of the polystyrene-based resin is 97% by weight or less, the content of the black colorant is sufficient, and a heat-shrinkable multilayer film having excellent light-shielding properties can be obtained.
The content of the polystyrene-based resin has a more preferable lower limit of 87% by weight, a further preferable lower limit of 90% by weight, a more preferable upper limit of 95% by weight, and a further preferable upper limit of 93% by weight.

The second intermediate layer contains a black colorant.
By containing the above-mentioned black colorant, sufficient light-shielding property can be imparted to the obtained heat-shrinkable multilayer film, and deterioration of the contents can be suppressed.

Examples of the black colorant include carbon black, titanium black, graphite, iron oxide, cobalt oxide, copper oxide, nickel oxide, molybdenum sulfide, bismuth sulfide and the like. Of these, carbon black is preferable.

The volume average particle size of the black colorant has a preferable lower limit of 3 nm, a more preferable lower limit of 5 nm, a preferable upper limit of 500 nm, and a more preferable upper limit of 400 nm.

The content of the black colorant in the second intermediate layer is 3% by weight at the lower limit and 15% by weight at the upper limit.
When the content of the black colorant is 3% by weight or more, the light-shielding property of the obtained heat-shrinkable multilayer film can be sufficiently improved. When the content of the black colorant is 15% by weight or less, the heat-shrinkable label can be aesthetically pleasing when the design or the like is printed.
The content of the black colorant is preferably 5% by weight, a preferred lower limit of 7% by weight, a more preferable upper limit of 13% by weight, and a more preferable upper limit of 10% by weight.

The second intermediate layer may contain additives such as an antioxidant, a heat stabilizer, an ultraviolet absorber, a light stabilizer, a lubricant, an antistatic agent, a flame retardant, and an antibacterial agent, if necessary. ..

Regarding the thickness of the second intermediate layer, the preferable lower limit is 1%, the more preferable lower limit is 2%, the preferable upper limit is 15%, and the more preferable upper limit is 10% with respect to the thickness of the entire heat-shrinkable multilayer film.
When the thickness of the second intermediate layer is in the above-mentioned preferable range, sufficient light-shielding property can be imparted to the heat-shrinkable multilayer film, and mechanical strength can be sufficiently improved.

The ratio of the thickness of the first intermediate layer to the thickness of the second intermediate layer is preferably 99: 1 to 85:15, more preferably 95: 5 to 90:10.
When the thickness ratio is in the above preferable range, it is possible to obtain a heat-shrinkable label having an excellent balance between light-shielding property and mechanical strength, preventing deterioration of the contents, and having an excellent aesthetic appearance.

In the heat-shrinkable multilayer film of the present invention, the content of the black colorant with respect to 100 parts by weight of the white colorant has a preferable lower limit of 0.2 parts by weight, a more preferable lower limit of 0.5 parts by weight, and a preferable upper limit of 15. By weight, a more preferred upper limit is 12 parts by weight.
When the content of the black colorant with respect to the white colorant is in the preferable range, the balance between the light-shielding property and the mechanical strength is excellent, the deterioration of the contents can be prevented, and the heat shrinkage is also excellent in aesthetics. A sex label can be obtained.

(Adhesive layer)
The heat-shrinkable multilayer film of the present invention preferably has an adhesive layer between the front surface layer and the first intermediate layer and / or between the second intermediate layer and the back surface layer.
Examples of the adhesive resin contained in the adhesive layer include commercially available adhesive resins, mixed resins of polyester-based resins and polystyrene-based resins, and the like. As the adhesive resin generally on the market, a styrene-based elastomer, a modified styrene-based elastomer, and a polyester-based elastomer are preferable.

The styrene-based elastomer means a product composed of polystyrene, which is a hard segment, and polybutadiene, polyisoprene, a copolymer of polybutadiene and polyisoprene, which are soft segments, and hydrogenated additives thereof. The hydrogenated agent may be a part of polybutadiene, polyisoprene or the like hydrogenated, or may be entirely hydrogenated.
Commercially available products of the above styrene elastomer include, for example, Tough Tech, Tough Plen (above, manufactured by Asahi Kasei Chemicals), Clayton (manufactured by Kraton Polymer Japan), Dynaron, JSR TR, JSR SIS (above, manufactured by JSR), Septon (above, manufactured by JSR). (Made by Kuraray) and the like.

Examples of the modified styrene-based elastomer include those obtained by modifying the styrene-based elastomer with a functional group such as a carboxylic acid group, an acid anhydride group, an amino group, an epoxy group, and a hydroxyl group.

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

When a block copolymer composed of aromatic polyester and polyalkylene ether glycol is used as the polyester-based elastomer, the ratio of the segment composed of polyalkylene ether glycol is preferably 5% by weight in the lower limit and 90% by weight in the upper limit. be. If it is less than 5% by weight, the adhesiveness to the intermediate layer is lowered, and if it exceeds 90% by weight, the adhesiveness to the front and back layers is lowered. A more preferable lower limit is 30% by weight, a more preferable upper limit is 80% by weight, and a further preferable 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 preferred lower limit of the number average molecular weight of the polyalkylene ether glycol is 400, and the preferred upper limit is 6000. A more preferable lower limit is 600, a more preferable upper limit is 4000, a further preferable lower limit is 1000, and a further preferable upper limit is 3000. By using a polyalkylene ether glycol having a number average molecular weight within the above range, good interlayer strength can be obtained, which is preferable. In this specification, the number average molecular weight is measured by gel permeation chromatography (GPC).

The method for producing the polyester-based elastomer is not particularly limited, and for example, (i) an aliphatic and / or alicyclic diol having 2 to 12 carbon atoms and (ii) an aromatic dicarboxylic acid and / or an alicyclic diol are produced. Using a dicarboxylic acid or an ester thereof and (iii) a polyalkylene ether glycol having a number average molecular weight of 400 to 6000 as a raw material, an oligomer is obtained by an esterification reaction or an ester exchange reaction, and then the oligomer is further polycondensed. Can be produced.

As the aliphatic and / or alicyclic diol having 2 to 12 carbon atoms, for example, those commonly used as raw materials for polyesters, particularly polyester-based thermoplastic elastomers can be used. Specific examples thereof include ethylene glycol, propylene glycol, trimethylene glycol, 1,4-butanediol, 1,4-cyclohexanediol, and 1,4-cyclohexanedimethanol. Of 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 the aromatic dicarboxylic acid and / or the alicyclic dicarboxylic acid, for example, those commonly used as raw materials for polyesters, particularly polyester-based thermoplastic elastomers can be used. Specific examples thereof include terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, cyclohexanedicarboxylic acid and the like. Of 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 polyester elastomers, those commercially available include, for example, the product name "Primaloy" (manufactured by Mitsubishi Chemical Corporation), the product name "Perprene" (manufactured by Toyobo Co., Ltd.), and the product name "Hitrel" (Toray DuPont). Made) and the like.

The melting point of the polystel-based elastomer is preferably 120 to 200 ° C. If 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-sealed portion, and if the temperature exceeds 200 ° C, sufficient adhesive strength may not be obtained. .. A more preferable lower limit is 130 ° C., and a more preferable upper limit is 190 ° C.
The melting point can be measured using a differential scanning calorimeter (DSC-60, manufactured by Shimadzu Corporation) under the condition of a heating rate of 10 ° C./min.

The melting point of the polyester-based elastomer is due to the copolymerization ratio and structure of the polyester which is a hard segment and the polyether or polyester which is a soft segment. Generally, the melting point of a polyester-based elastomer tends to depend on the amount of copolymerization of a polyether or polyester which is a soft segment. When the amount of copolymerization of a polyether or polyester is large, the melting point is low, and when the amount is small, the melting point is high.
Further, the melting point of polyester, which is a hard segment constituting the polyester-based elastomer, can be adjusted by changing the copolymerization component, and the melting point of the entire polyester-based elastomer can be adjusted.
Further, when the molecular weight of the soft segment of the polyether or polyester is reduced, the blocking property of the obtained polyester-based elastomer is lowered, so that the melting point is likely to be lowered.

The preferred lower limit of the JIS-D hardness of the polyester-based elastomer is 10, and the preferred 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 preferable lower limit of JIS-D hardness is 15, a more preferable upper limit is 70, a further preferable lower limit is 20, and a further preferable upper limit is 60.
The JIS-D hardness can be measured by using a durometer type D by a method conforming to JIS K6253.

The preferable lower limit of the specific gravity of the polyester-based elastomer is 0.95, and the preferable upper limit is 1.20. By setting the specific gravity to 0.95 or more, heat resistance can be imparted, and peeling from the solvent-sealed portion can be suppressed when the container is coated as a heat-shrinkable label. Further, by setting the specific gravity to 1.20 or less, the adhesive strength between the front and back layers and the intermediate layer can be increased.
The more preferable lower limit of the specific gravity is 0.98, and the more preferable upper limit is 1.18.
The specific gravity can be measured by an underwater substitution method according to JIS K 7112 (1999).

In the mixed resin of the polyester-based resin and the polystyrene-based resin, the polyester-based resin may be the same as the polyester-based resin used for the front surface layer and the back surface layer described above, or another one may be used. You may.
The polyester resin contained in the adhesive layer contains, in particular, a component derived from terephthalic acid as a dicarboxylic acid component and a component derived from ethylene glycol and / or 1,4-cyclohexanedimethanol as a diol component. Those containing are preferable. Such a polyester resin may further contain 0 to 30 mol% of a component derived from diethylene glycol.

The preferable lower limit of the glass transition temperature of the polyester resin contained in the adhesive layer is 50 ° C., and the preferable upper limit is 95 ° C. When the glass transition temperature is in this range, delamination when the heat-shrinkable multilayer film is heat-shrinked can be effectively suppressed, which is preferable. A more preferable lower limit of the glass transition temperature is 55 ° C., a further preferable lower limit is 60 ° C., and a more preferable upper limit is 90 ° C.

In the mixed resin of the polyester resin and the polystyrene resin, the polystyrene resin may be the same as the polystyrene resin used for the first intermediate layer and the second intermediate layer described above. You may use another one.
When the polystyrene-based resin contained in the adhesive layer is a styrene-conjugated diene copolymer, the styrene content in 100% by weight of the styrene-conjugated diene copolymer is 55 to 90% by weight, and the conjugated diene content is 10 to It is preferably 45% by weight. If the styrene content and the conjugated diene content are out of this range, the perforation cut property when the heat-shrinkable multilayer film is perforated may be lowered, or the interlayer strength may be lowered.

The preferable lower limit of the Vicat softening temperature of the polystyrene resin contained in the adhesive layer is 60 ° C., and the preferable upper limit is 85 ° C. If the Vicat softening temperature falls outside this range, the interlayer strength of the heat-shrinkable multilayer film may decrease. The more preferable lower limit of the Vicat softening temperature is 65 ° C., and the more preferable upper limit is 80 ° C.

In the mixed resin of the polyester resin and the polystyrene resin, the weight ratio of the polyester resin and the polystyrene resin is not particularly limited, but is preferably 60:40 to 85:15. If the weight ratio of the polyester resin to the polystyrene resin is out of this range, the perforation cut property when the heat-shrinkable multilayer film is perforated may be lowered, or the interlayer strength may be lowered. .. The weight ratio of the polyester resin to the polystyrene resin is more preferably 65:35 to 80:20.

The thickness of the adhesive layer is not particularly limited, but the preferable lower limit for the thickness of the heat-shrinkable multilayer film residue is 1%, the more preferable lower limit is 2%, the preferable upper limit is 5%, and the more preferable upper limit is 4%.
When the thickness of the adhesive layer is in the above preferable range, delamination of the heat-shrinkable multilayer film can be effectively suppressed, which is preferable.

Antioxidants, heat stabilizers, lubricants, antistatic agents and the like may be added to the adhesive layer, if necessary.

The thickness of the entire heat-shrinkable multilayer film of the present invention has a preferable lower limit of 20 μm, a preferable upper limit of 80 μm, a more preferable lower limit of 25 μm, and a more preferable upper limit of 70 μm. When the thickness of the entire heat-shrinkable multilayer film is within the above range, excellent heat-shrinkability, excellent converting property such as printing or center sealing, and excellent wearability can be obtained.
Further, in the heat-shrinkable multilayer film of the present invention, the thickness of the intermediate layer has a preferable lower limit of 50% and a preferable upper limit of 90% with respect to the thickness of the entire heat-shrinkable multilayer film. When the thickness of the intermediate layer is within the above range, high interlayer strength, high transparency and the like can be obtained.

The haze of the heat-shrinkable multilayer film of the present invention is not particularly limited, but the preferred upper limit is 10%.
The haze can be measured according to JIS-K6782.

The preferred lower limit of the heat shrinkage rate in the main shrinkage direction (TD direction) when the heat-shrinkable multilayer film of the present invention is immersed in warm water at 90 ° C. for 10 seconds is 60%. When the heat shrinkage rate is 60% or more, the problem of shrinkage failure such as wrinkles and strain does not occur, and the film can be suitably used as a heat shrinkable multilayer film.
The lower limit of the heat shrinkage is more preferably 70%. The upper limit of the heat shrinkage is not particularly limited, and the higher the heat shrinkage, the better the finish when mounted on a bottle or the like.

The preferred lower limit of the tensile elongation at break of the heat-shrinkable multilayer film of the present invention in the direction orthogonal to the main shrinkage direction (MD direction) in an atmosphere of 5 ° C. is 200%.
When the tensile elongation at break is 200% or more, the film is less likely to break in steps such as printing and sealing, and productivity is improved.
The more preferable lower limit of the tensile elongation at break is 250%. The upper limit of the tensile elongation at break is not particularly limited, and the higher the elongation at break, the less likely it is that the film will break.

When the heat-shrinkable multilayer film of the present invention is allowed to stand in an atmosphere of 40 ° C. for 7 days, the natural shrinkage rate in the main shrinkage direction (TD direction) is preferably less than 3.0%.
When the natural shrinkage rate is less than 3.0%, the shrinkage during storage is small, and problems such as poor shrinkage do not occur, and the film can be suitably used as a heat-shrinkable multilayer film.
The natural shrinkage rate is more preferably less than 2.5%.

The delamination strength of the heat-shrinkable multilayer film of the present invention has a preferable lower limit of 0.4 N / 10 mm.
When the delamination strength is 0.4 N / 10 mm or more, peeling between the front and back layers and the intermediate layer is unlikely to occur during printing / sealing processing or label attachment, and the label can be suitably used as a heat-shrinkable label.

The method for producing the heat-shrinkable multilayer film of the present invention is not particularly limited, but a method in which each layer is simultaneously molded by a coextrusion method is preferable. When the coextrusion method is coextrusion with a T-die, the laminating method may be a feed block method, a multi-manifold method, or a method in which these are used 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 and, if necessary, the raw materials constituting the intermediate layer are charged into an extruder and die. A method of extruding into a sheet shape, cooling and solidifying with a take-up roll, and then stretching to one or two shafts can be mentioned.
As the stretching method, for example, a roll stretching method, a tenter stretching method, or a combination thereof can be used. The stretching temperature varies depending on the softening temperature of the resin constituting the film, the shrinkage characteristics required for the heat-shrinkable multilayer film, etc., but the preferable lower limit is 65 ° C, the preferable upper limit is 120 ° C, and the more preferable lower limit is 70 ° C. A more preferable upper limit is 115 ° C. The stretching ratio in the main shrinkage direction varies depending on the resin constituting the film, the stretching means, the stretching temperature, etc., but is preferably 3 times or more, more preferably 4 times or more, preferably 7 times or less, and more. It is preferably 6 times or less. By setting the stretching temperature and the stretching ratio as such, excellent thickness accuracy can be achieved.

By using the heat-shrinkable multilayer film of the present invention as a base film, a heat-shrinkable label can be obtained. Such a heat shrinkable label is also one of the present inventions.
In the heat-shrinkable label of the present invention, the heat-shrinkable multilayer film may be used as a base film, and other layers such as a printing layer may be laminated, if necessary.

As a method of attaching a heat-shrinkable label to a container, usually, a heat-shrinkable multilayer film is bonded between the ends of the heat-shrinkable multilayer film to form a tube (center seal processing), and then the heat-shrinkable label is obtained. A method of heating and shrinking while covering the container is adopted.

According to the present invention, it is possible to exhibit excellent light-shielding properties, it is also excellent in aesthetics when printing a design or the like, and it also has appropriate mechanical strength and excellent heat shrinkage. A shrinkable multilayer film can be provided. It is also possible to provide a heat shrinkable label containing the heat shrinkable multilayer film.

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

(Polyester resin)
PET-1: Dicarboxylic acid component (100 mol% of component derived from terephthalic acid), diol component (70 mol% of component derived from ethylene glycol, 20 mol% of component derived from 1,4-cyclohexanedimethanol, derived from diethylene glycol 10 mol% of components), glass transition temperature 74 ° C
(Polystyrene resin)
SBS-1: Styrene-butadiene copolymer (styrene component 85% by weight, butadiene component 15% by weight)
(Adhesive resin)
AD-1: Polyester-based elastomer (aromatic polyester component 70% by weight, polyalkylene ether glycol component 30% by weight)
(White colorant)
TiO ₂ : Rutile type titanium dioxide manufactured by Sumika Color Co., Ltd., volume average particle diameter 0.25 μm
(Black colorant)
CB: Sumika Color Co., Ltd., carbon black, volume average particle diameter 24 nm

(Example 1 , Reference Examples 2 to 7 and Comparative Examples 1 to 3)
The resin, white colorant and black colorant shown in Table 1 are blended as components constituting the front surface layer, the back surface layer, the first intermediate layer, the second intermediate layer and the adhesive layer in the proportions shown in Table 1 to form a surface layer. , A mixture constituting the back surface layer, the first intermediate layer, the second intermediate layer and the adhesive layer was obtained.
The mixture constituting the surface layer, the adhesive layer, the first intermediate layer, the second intermediate layer, the adhesive layer and the back surface layer is charged into an extruder at a barrel temperature of 160 to 190 ° C., and is charged from a multilayer die at 190 ° C. 6 An unstretched sheet was prepared by extruding into a layered sheet and cooling and solidifying with a roll cooled to 30 ° C. This was stretched 5 times in the TD direction with a tenter type stretching machine having a temperature of 90 ° C. to obtain a heat-shrinkable multilayer film.
The obtained heat-shrinkable multilayer film has a layer thickness of 40 μm, and has a surface layer (5 μm) / adhesive layer (1 μm) / first intermediate layer (27 μm) / second intermediate layer (1 μm) / adhesive layer ( It had a 6-layer structure of 1 μm) / back layer (5 μm).

(Example 8)
The resin, white colorant and black colorant shown in Table 1 are blended as components constituting the front surface layer, the back surface layer, the first intermediate layer and the second intermediate layer in the proportions shown in Table 1, and the front surface layer and the back surface layer are mixed. , A mixture constituting the first intermediate layer and the second intermediate layer was obtained.
The mixture constituting the front surface layer, the first intermediate layer, the second intermediate layer and the back surface layer is charged into an extruder at a barrel temperature of 160 to 190 ° C., and at 190 ° C., a multi-layer die is formed into a sheet having a four-layer structure. An unstretched sheet was prepared by extruding and cooling and solidifying with a roll cooled to 30 ° C. This was stretched 5 times in the TD direction with a tenter type stretching machine having a temperature of 90 ° C. to obtain a heat-shrinkable multilayer film.
The obtained heat-shrinkable multilayer film has a layer thickness of 40 μm and has a four-layer structure of a surface layer (5 μm) / first intermediate layer (29 μm) / second intermediate layer (1 μm) / back surface layer (5 μm). Met.

(evaluation)
The heat-shrinkable multilayer films obtained in Examples , Reference Examples and Comparative Examples were evaluated as follows. The results are shown in Table 1.

(1) Total light transmittance (800 nm)
For the films obtained in Examples , Reference Examples and Comparative Examples, the total light transmittance (800 nm) was measured using a haze meter NDH5000 (manufactured by Nippon Denshoku Kogyo Co., Ltd.) by a measurement method based on JIS-K7361-1. However, it was evaluated according to the following criteria.
〇: 20% or less ×: Over 20%

(2) Whiteness With respect to the films obtained in Examples , Reference Examples and Comparative Examples, the brightness index L value was measured using a color difference meter CR-321 (manufactured by Konica Minolta), and the whiteness was determined according to the following criteria. evaluated.
〇: L value is 80 or more ×: L value is less than 80 or cannot be measured

(3) Fracture Test The films obtained in Examples , Reference Examples and Comparative Examples were cut into a size having a marked line spacing of 40 mm and a width of 10 mm to obtain test pieces. The obtained test piece was subjected to a tensile strength-elongation test using a Strograph VE-1D (manufactured by Toyo Seiki Seisakusho Co., Ltd.) by a method according to JIS-K6732. The measurement atmosphere temperature was 5 ° C. and the test speed was 100 mm / min. The tensile strength elongation test was carried out using four test pieces for each Example , Reference Example and Comparative Example, and the number of fractured pieces having an elongation of less than 5% was measured.

(4) Heat shrinkage rate The films obtained in Examples , Reference Examples and Comparative Examples were cut into samples having a size of MD100 mm × TD100 mm to obtain test pieces. The obtained test piece was immersed in boiling water for 10 seconds, then the heat-shrinkable multilayer film was taken out and immersed in water at 15 ° C. for 5 seconds, and the heat shrinkage in the TD direction was determined according to the following formula. The heat collection shrinkage was measured using three test pieces for each Example , Reference Example and Comparative Example, and the average value thereof was used.
Heat shrinkage rate (%) = {(100-L) / 100} x 100
The obtained heat shrinkage was evaluated according to the following criteria.
◯: 60% or more ×: less than 60%

According to the present invention, it is possible to exhibit excellent light-shielding properties, it is also excellent in aesthetics when printing a design or the like, and it also has appropriate mechanical strength and excellent heat shrinkage. A shrinkable multilayer film can be provided. It is also possible to provide a heat shrinkable label containing the heat shrinkable multilayer film.

Claims (8)

It contains a surface layer containing a polyester resin, a first intermediate layer containing a polystyrene resin and a white colorant, a second intermediate layer containing a polystyrene resin and a black colorant, and a polyester resin. A heat-shrinkable multilayer film having a back surface layer in this order.
The content of the white colorant in the first intermediate layer is 5 to 10 % by weight.
A heat-shrinkable multilayer film characterized in that the content of the black colorant in the second intermediate layer is 10 to 15% by weight. The heat-shrinkable multilayer film according to claim 1, wherein the white colorant is titanium dioxide. The heat-shrinkable multilayer film according to claim 1 or 2, wherein the black colorant is carbon black. The heat-shrinkable multilayer film according to claim 1, 2 or 3, wherein the content of the polystyrene-based resin in the first intermediate layer is 50 to 95% by weight. The heat-shrinkable multilayer film according to claim 1, 2, 3 or 4, wherein the content of the polystyrene-based resin in the second intermediate layer is 85 to 90 % by weight. The heat-shrinkable multilayer film according to claim 1, 2, 3, 4 or 5, wherein the polystyrene-based resin is an aromatic vinyl hydrocarbon-conjugated diene copolymer. Claim 1, 2, 3, 4, 5 or 6 comprising an adhesive layer between the front surface layer and the first intermediate layer and / or between the second intermediate layer and the back surface layer. The heat shrinkable multilayer film described. A heat-shrinkable label comprising the heat-shrinkable multilayer film according to claim 1, 2, 3, 4, 5, 6 or 7.