JP4867985B2 - Heat-shrinkable polyester film - Google Patents

Description

  The present invention relates to a heat-shrinkable polyester film, and more particularly to a heat-shrinkable polyester film suitable for display labels such as beverage bottles. More specifically, the present invention relates to a heat-shrinkable polyester film having a light-cutting property without performing a printing process.

  Recently, an increasing number of cases have used shrink labels for the purpose of protecting the contents of containers from ultraviolet rays. Conventionally, a UV-cut type shrink film made of polyvinyl chloride has been used, but there is an increasing demand for UV-cut type of other materials. Although the specific cut property differs depending on the contents, in the case of food and beverage, the contents are altered or colored at a wavelength of 360 nm to 400 nm, which is ultraviolet light in the long wavelength area, so that the long wavelength area, particularly 380 nm and 400 nm Cutability is important. However, none of the conventional heat-shrinkable polyester films cuts the ultraviolet rays in the long wavelength region described above.

  As such a label, a heat-shrinkable film made of polyvinyl chloride, polystyrene or the like has been mainly used (Japanese Patent Laid-Open No. 11-188817, etc.). However, polyvinyl chloride has recently been incinerated at the time of disposal. Chlorine-based gas generation is a problem, and polystyrene has problems such as difficulty in printing. Recently, the use of heat-shrinkable polyester film has attracted attention.

  Moreover, in a plastic bottle, a colored bottle may be used for the content protection. However, since colored bottles are unsuitable for collection and recycling, alternatives have been investigated. As one of the methods, it has been studied to use a non-colored bottle and attach a colored label to the entire bottle.

  Conventionally, when these heat-shrinkable films are used, white printing is usually performed after pattern printing on the inside of the label. The thickness of the printing ink is usually about 3 μm, which is not sufficient to block light. Furthermore, light blocking is attempted by a method of performing white printing twice, but this is disadvantageous in terms of quality factors (change in shrinkage characteristics due to ink thickness, etc.), delivery time, and cost.

  The object of the present invention is to solve the above-mentioned problems, and the object of the present invention is a heat-shrinkable polyester film for full labeling of PET bottles, and it can cut light rays without printing or processing. An object of the present invention is to provide a heat-shrinkable polyester film having properties.

  As a result of earnest research to solve the problems of the prior art, the present inventors have found that the object can be achieved by setting the total light transmittance of the heat-shrinkable polyester film and the hot water shrinkage to a specific range, Based on this, the present invention has been completed.

That is, the present invention is a film comprising a polyester composition containing a polyester resin mainly comprising a dicarboxylic acid component and a diol component and a polyester elastomer , comprising different raw materials A and B, and layer B Is the intermediate layer, the layer A is provided on both surface layers, the total light transmittance of the film is 40% or less, and the hot water shrinkage is 65 to 95 at a treatment temperature of 85 ° C. and a treatment time of 5 seconds in the main shrinkage direction. %, Which is 0 to 5% in the direction perpendicular to the main shrinkage direction.

  In this case, it is preferable that there is at least one layer to which titanium oxide is added. Furthermore, in this case, the titanium oxide content is preferably in the range of 0.1 to 20.0% by weight in terms of film.

  In this case, it is preferable that there is at least one layer to which a polystyrene resin is added. Furthermore, in this case, it is preferable that the content of the polystyrene-based resin is in the range of 1.0 to 20.0% by weight in terms of film.

  According to the present invention, it is possible to obtain a heat-shrinkable polyester film having a light-cutting property without performing printing or processing, and further having excellent solvent adhesion. Therefore, it is extremely useful as a heat-shrinkable polyester film for labels, particularly for labels with high commercial value.

  The heat-shrinkable polyester film of the present invention has a total light transmittance of 40% or less and a hot water shrinkage of 65% or more at a treatment temperature of 85 ° C. and a treatment time of 5 seconds in the main shrinkage direction. It is characterized by being 5% or less in the direction orthogonal to the main contraction direction, whereby the above-mentioned target is achieved.

  The heat-shrinkable polyester film of the present invention is substantially composed of a polyester resin or a polyester resin and titanium oxide and polystyrene resin described later. As a polyester resin, it can use preferably from the polyester composition containing the polyester which has a dicarboxylic acid component and a diol component as a structural component, and a polyester-type elastomer, for example. In the polyester resin composition, the blending ratio of the polyester and the polyester elastomer is usually about 50 to 99% by weight of the former, particularly 70 to 97% by weight, and 1 to 50% by weight of the latter with respect to the total amount of both. It is preferable that the amount is about 3%, particularly about 3 to 30% by weight.

  Examples of the dicarboxylic acid component constituting the polyester include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid and naphthalenedicarboxylic acid, aliphatic dicarboxylic acids such as adipic acid, sebacic acid and decanedicarboxylic acid, and alicyclic rings such as cyclohexanedicarboxylic acid. What is necessary is just to use 1 type, or 2 or more types of well-known dicarboxylic acid, such as a formula dicarboxylic acid. In addition, as the diol component, one kind of known diols such as ethylene glycol, propylene glycol, triethylene glycol, butylene glycol, diethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol, tetramethylene glycol ethylene oxide adduct or the like Two or more types may be used.

  The polyester elastomer is, for example, a polyester block copolymer comprising a high melting crystalline polyester segment (Tm 200 ° C. or higher) and a low melting point soft polymer segment (Tm 80 ° C. or lower) having a molecular weight of 400 or more, preferably 400 to 800. Polyester elastomers using polylactones such as poly-ε-caprolactone for the low melting point soft polymer segment are particularly preferred.

  In order to achieve the total light transmittance specific to the film of the present invention and impart light-cutting properties to the film, for example, fine particles such as an inorganic lubricant and an organic lubricant are added to the film in an amount of 0.1 to 0.1. It is suitable to contain 20% by weight, preferably 0.5 to 10% by weight. When the content of the fine particles is less than 0.1% by weight, it tends to be difficult to obtain light-cutting properties. On the other hand, when the content exceeds 20% by weight, film strength tends to decrease and film formation tends to be difficult. is there.

  The fine particles may be added before polyester polymerization, but are usually added after polyester polymerization. Examples of the inorganic lubricant added as fine particles include known inert particles such as kaolin, clay, calcium carbonate, silicon oxide, calcium tephrate, aluminum oxide, titanium oxide, calcium phosphate, carbon black, and melt film formation of polyester resin. Insoluble high melting point organic compounds, cross-linked polymers, and metal compound catalysts used in the synthesis of the polyester, such as alkali metal compounds and alkaline earth metal compounds, can be internal particles formed inside the polymer during polyester production.

  The average particle diameter of the fine particles contained in the film is usually in the range of 0.001 to 3.5 μm. Here, the average particle diameter of the fine particles is measured by a Coulter counter method. The intrinsic viscosity of the polyester of the present invention is preferably 0.50 or more, more preferably 0.60 or more, and particularly preferably 0.65 or more. If the intrinsic viscosity of the polyester is less than 0.50, the crystallinity becomes high and a sufficient shrinkage cannot be obtained, which is not preferable.

  In the present invention, in order to obtain an appropriate light transmittance, for example, it is preferable to contain fine cavities inside. For example, a foam material or the like may be mixed and extruded, but a preferable method is to obtain a cavity by mixing an incompatible thermoplastic resin in polyester and stretching it in at least one axial direction. The thermoplastic resin incompatible with the polyester used in the present invention is arbitrary, and is not particularly limited as long as it is incompatible with the polyester. Specific examples include polystyrene resins, polyolefin resins, polyacrylic resins, polycarbonate resins, polysulfone resins, and cellulose resins. In particular, a polystyrene resin or a polyolefin resin such as polymethylpentene or polypropylene is preferable because of the formation of cavities.

  Polystyrene resin refers to a thermoplastic resin containing a polystyrene structure as a basic component. In addition to homopolymers such as atactic polystyrene, syndiotactic polystyrene, and isotactic polystyrene, other components are grafted or block copolymerized. Modified resins such as high-impact polystyrene resins and modified polyphenylene ether resins, and also thermoplastic resins having compatibility with these polystyrene resins, such as polyphenylene ether, are included.

  In preparing the polymer mixture formed by mixing the polyester and the incompatible resin, for example, the chips of each resin may be mixed and melt-kneaded in an extruder and extruded, or both resins may be preliminarily mixed by a kneader. The kneaded product may be further melt extruded from an extruder. Moreover, a polystyrene resin may be added in the polyester polymerization step, and a chip obtained by stirring and dispersing may be melt-extruded.

  In the film of the present invention, it is preferable to provide the layer A having fewer cavities than the B layer on at least one side of the layer B containing a large number of cavities inside. In order to achieve this configuration, different raw materials are charged into different extruders A and B, melted, bonded together in a molten state before the T-die or inside the die, and solidified in close contact with the cooling roll. It is preferable to stretch in the direction. At this time, it is preferable that the incompatible resin of the A layer as a raw material is less than the B layer. By doing so, there are few cavities in the A layer, the surface is less rough, and the film does not impair the aesthetics of printing. Moreover, since there are not many cavities, the film does not become weak and the film has excellent wearability.

  Furthermore, it is particularly preferable that the film in the present invention has a layer B containing a large number of cavities inside as an intermediate layer, and A layers having few cavities are provided on both surface layers. By adding polystyrene resin, smoke is generated at the time of melt extrusion, fouling the process and causing deterioration in operability. By using the B layer as an intermediate layer, the problem of smoke generation is eliminated, and stable production over a long period of time becomes possible.

  Moreover, this invention film may contain additives, such as a stabilizer, a coloring agent, antioxidant, and an antistatic agent, as needed.

  The polyester film of the present invention needs to have a total light transmittance of 40% or less as measured according to JIS K 7136. When the transmittance is 40% or more, it is not preferable since the contents can be seen through or the contents cannot be cut and the contents deteriorate. The transmittance is particularly preferably 30% or less.

  In the main shrinkage direction of the film of the present invention, the shrinkage rate of hot water at 85 ° C. and a treatment time of 5 seconds is 65% or more, preferably 65 to 95%. When the shrinkage rate is less than 65%, the label is insufficiently shrunk in the narrow mouth portion of the PET bottle. On the other hand, if it exceeds 95%, since the shrinkage rate is large, the label may jump up while passing through the shrink tunnel, which is not preferable. Here, the main shrinkage direction means a direction with a large shrinkage rate.

  Further, the shrinkage rate in the direction perpendicular to the main shrinkage direction is 0 to 5%, preferably 0 to 3%. When the shrinkage rate is less than 0%, the horizontal wrinkles of the label generated during shrinkage tend to be difficult to disappear. On the other hand, when the shrinkage rate exceeds 5%, the vertical shrinkage of the label increases, and the amount of film used increases and is economical. In this case, neither of them is preferable.

  The glass transition temperature Tg of the film of the present invention is about 50 to 90 ° C, preferably 55 to 85 ° C, more preferably 55 to 80 ° C. If Tg is within this range, the low temperature shrinkage is sufficient and the natural shrinkage is not too large, and the label finish is good.

  The film of the present invention includes aromatic hydrocarbons such as benzene, toluene, xylene and trimethylbenzene, halogenated hydrocarbons such as methylene chloride and chloroform, phenols such as phenol, furans such as tetrahydrofuran, 1,3-dioxolane and the like. It is preferable to have solvent adhesion with an organic solvent such as oxolanes. In particular, from the viewpoint of safety, it is more preferable to have solvent adhesion by 1,3-dioxolane. The solvent adhesive strength is preferably 4 N / 15 mm or more. If it is less than 4N / 15mm, when a label is shrunk to a container, a junction part peels off and is not preferable.

  In order to satisfy the above characteristics, the film of the present invention may be composed of a single layer, but the preferred layer structure is A / B / A. The thickness ratio of the A layer and the B layer is preferably A / B / A = 25/50/25 to 10/80/10. If the thickness ratio of the B layer is less than 50%, the light-cutting property is insufficient, and the contents can be seen through, or the contents cannot be cut and the contents are deteriorated.

  Hereafter, the manufacturing method of the film of this invention is demonstrated concretely.

  A polyester or copolymer polyester containing an appropriate amount of inorganic particles as a lubricant as required is dried using a normal hopper dryer, paddle dryer, vacuum dryer or the like, and then extruded at a temperature of 200 to 320 ° C. In extruding, an existing method such as a T-die method or a tubular method may be used.

  After extrusion, the film is rapidly cooled to obtain an unstretched film. In the case of the T-die method, a so-called electrostatic application adhesion method is preferably used at the time of rapid cooling because a film with less thickness unevenness can be obtained. The obtained unstretched film is uniaxially stretched or biaxially stretched so that the finally obtained film satisfies the constituent requirements of the present invention.

  As a stretching method, in addition to the method of stretching only in the longitudinal axis of the roll or stretching only in the lateral direction with a tenter, the known biaxial stretching is strongly stretched in either the longitudinal or lateral direction, and the other as much as possible. It is also possible to stretch the film small, and re-stretching may be performed as necessary.

  In the above stretching, the film is stretched at least 2.0 times, preferably 2.5 times or more in the main shrinkage direction, stretched in a direction perpendicular to the main shrinkage direction as necessary, and then heat-treated.

  The heat treatment is usually performed under tension fixation, but it is also possible to perform relaxation or tentering of 20% or less at the same time. As a heat treatment method, an existing method such as a method of contacting a heating roll or a method of gripping a clip in a tenter can be used.

  During the stretching step, corona treatment may be applied to one or both sides of the film before or after stretching to improve the adhesion of the film to the printed layer and / or adhesive layer to the adhesive layer.

  In addition, during the stretching step, it is possible to apply on one or both sides of the film before or after stretching to improve the adhesion, release properties, antistatic properties, slipperiness, light shielding properties, etc. of the film. .

  Although the thickness of the heat-shrinkable polyester film of the present invention is not particularly limited, the heat-shrinkable film for labels is preferably in the range of 10 to 200 μm, more preferably 20 to 100 μm.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples unless it exceeds the gist.

(1) Total light transmittance It measured according to JISK7136 using Nippon Denshoku Industries Co., Ltd. NDH-2000T.

(2) Heat shrinkage rate The film is cut into a 10 cm × 10 cm square and immersed in hot water at 85 ± 0.5 ° C. for 5 seconds under no load condition to cause heat shrinkage. The dimensions were measured, and the thermal shrinkage rate was determined according to the following formula. The direction in which the shrinkage rate was large was taken as the main shrinkage direction.

Thermal shrinkage rate = {(length before shrinkage−length after shrinkage) / length before shrinkage} × 100 (%)

(3) Shrinkage finishing property Using a steam tunnel (model: SH-1500-L) manufactured by Fuji Astec Inc., a 500 ml square PET bottle (height 210 mm, bottom long diameter) at a passage time of 2.5 seconds and a zone temperature of 80 ° C. 60 mm: A bottle manufactured by Yoshino Kogyo Co., Ltd. and used in Suntory Co., Ltd. oolong tea) (number of measurements = 20).

  Evaluation was made visually and the criteria were as follows.

No wrinkles, jumps, or insufficient shrinkage: ○ Wrinkles, jumps, or insufficient shrinkage occurs: ×

(4) Solvent adhesiveness 1,3-Dioxolane was used to join the film into a tube shape, and the tube-shaped body was cut to a width of 15 mm in the direction orthogonal to the flow direction during processing to obtain a sample. Using Tensilon (model: UTL-4L), the chuck was pulled and peeled at 20 mm, and the peel resistance was measured. When the measured value was 4N or more, it was set as “◯”.

(5) Tg (glass transition point)
Using a DSC (model: DSC220) manufactured by Seiko Denshi Kogyo Co., Ltd., 10 mg of an unstretched film was heated from −40 ° C. to 120 ° C. at a heating rate of 20 ° C./min, and obtained from the endothermic curve obtained. It was. A tangent line was drawn before and after the inflection point of the endothermic curve, and the intersection was defined as Tg (glass transition point).

Polyesters used in Examples and Comparative Examples are as follows.
Polyester A: Polyethylene terephthalate (IV 0.75)
Polyester B: Polyester (IV 0.72) composed of 100 mol% terephthalic acid, 70 mol% ethylene glycol, and 30 mol% neopentyl glycol
Polyester C: Polyester elastomer comprising 70% by weight of polybutylene terephthalate and 30% by weight of ε-caprolactone (reduced viscosity (ηsp / c) 1.30)
Polyester D: Polybutylene terephthalate (IV 1.20)

Example 1
As shown in Table 1, a polyester composition prepared by mixing 30% by weight of polyester A, 65% by weight of polyester B, and 5% by weight of polyester C as a raw material for layer A 10% by weight, 67% by weight of polyester B, 3% by weight of polyester C, 10% by weight of crystalline polystyrene resin (G797N made by Nippon Polystyrene Co., Ltd.) and 10% by weight of titanium dioxide (made by TA-300 Fuji Titanium) While being fed into separate extruders, mixed and melted, joined with a feed block, and laminated at 280 ° C. so that the A / B / A thickness ratio after stretching from the T die is 5 μm / 20 μm / 5 μm It was melt extruded and quenched with a chill roll to obtain an unstretched film. The unstretched film was stretched 4.0 times in the transverse direction at a film temperature of 70 ° C. with a tenter to obtain a heat-shrinkable polyester film having a thickness of 30 μm.

(Example 2 and Comparative Examples 1 to 3)
As shown in Table 1, a heat-shrinkable polyester film having a thickness of 30 μm was obtained in the same manner as in Example 1 except that the blending ratio of polyester, polystyrene and titanium dioxide, and the film forming conditions were changed.

  The evaluation results of the films obtained in Examples 1-2 and Comparative Examples 1-3 are also shown in Table 1.

  As is apparent from Table 1, the heat-shrinkable polyester films obtained in Examples 1 and 2 are all heat-shrinkable polyester films suitable for full labeling of PET bottles and have good light rays. It had a cutting property.

  The heat-shrinkable polyester film of the present invention is suitable for packaging shrink labels of contents that are high in quality and practical, and are particularly susceptible to deterioration.

  On the other hand, although the heat-shrinkable polyester film obtained in the comparative examples has light-cutting properties, the solvent adhesive strength is inferior, and the heat-shrinkable polyester films obtained in comparative examples 2 to 3 have light-cutting properties. Was inferior. Thus, the heat-shrinkable polyester film of the comparative example was inferior in quality and low in practicality.

  According to the present invention, it is possible to obtain a heat-shrinkable polyester film having a light-cutting property without performing printing or processing, and further having excellent solvent adhesion. Therefore, it is extremely useful as a heat-shrinkable polyester film for labels, particularly for labels with high commercial value.

Claims (6)

A film comprising a polyester composition containing a polyester resin and a polyester-based elastomer mainly comprising a dicarboxylic acid component and a diol component,
The total amount of the polyester resin and the polyester elastomer is 50 to 99% by weight of the polyester resin, 1 to 50% by weight of the polyester elastomer,
The film is composed of different raw materials A and B, and a layer B having a polystyrene resin of 1.0 to 20.0% by weight in terms of a film is an intermediate layer, and a layer A having no polystyrene resin on both surface layers. Further, 0.1 to 20.0 wt% titanium oxide in terms of film,
The total light transmittance of the film is 40% or less, and the hot water shrinkage is 65 to 95% at a treatment temperature of 85 ° C. and a treatment time of 5 seconds in the main shrinkage direction, and 0 to 0 in the direction perpendicular to the main shrinkage direction. A heat-shrinkable polyester film characterized by being 5%. The heat-shrinkable polyester film according to claim 1, wherein the thickness ratio of layer A and layer B is 25/50/25 to 10/80/10. . A heat-shrinkable polyester fill beam according to claim 1 or 2, the heat-shrinkable polyester film characterized in that the layer A is a layer having no titanium oxide. The heat-shrinkable polyester film according to any one of claims 1 to 3, wherein the polyester resin comprises polyethylene terephthalate, 100 mol% terephthalic acid, 70 mol% ethylene glycol, and 30 mol% neopentyl glycol. A heat-shrinkable polyester film characterized by being a mixture with polyester. The heat-shrinkable polyester film according to any one of claims 1 to 4, wherein the layer A is 30% by weight of polyethylene terephthalate, 100% by mole of terephthalic acid, 70% by mole of ethylene glycol, and 30% of neopentyl glycol. % Heat-shrinkable polyester film, comprising 65% by weight of polyester and 5% by weight of polyester elastomer. The heat-shrinkable polyester film according to any one of claims 1 to 5, wherein the layer B is 10% by weight of polyethylene terephthalate, 100% by mole of terephthalic acid, 70% by mole of ethylene glycol, and 30% of neopentyl glycol. A heat-shrinkable polyester film comprising 65 to 67% by weight of polyester, 3 to 5% by weight of a polyester elastomer, 10% by weight of polystyrene and 10% by weight of titanium oxide.