JP2005263938A - Heat-shrinkable polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-shrinkable polyester film suitable for mounting on an outer periphery of a container in a complicated form such as especially a cosmetic, an aromatic substance container, etc., and shrinking and having light cutting properties without carrying out printing or processing. <P>SOLUTION: The heat-shrinkable polyester film which is a film mainly composed of a polyester resin characterized as follows. The total light transmittance of the film is ≤40% and the fusion sealing strength is ≥10 N/15 mm width. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a heat-shrinkable polyester film, and more particularly to a heat-shrinkable polyester film suitable for being attached to the outer periphery of a container having a complicated shape such as a cosmetic or a fragrance container. 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. The specific cut properties vary depending on the contents. However, in the case of cosmetics and foods, the contents are altered or colored at a wavelength of 360 nm to 400 nm, which is ultraviolet light in the long wavelength region, so that the long wavelength region, 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 (see, for example, Patent Document 1).
JP-A-11-188817

  However, with regard to polyvinyl chloride, in recent years there has been a problem of chlorine gas generation when incinerated at the time of disposal, and polystyrene has problems such as difficulty in printing. Recently, the use of heat-shrinkable polyester films has been problematic. It attracts 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.

Conventionally, a heat-shrinkable film that is shrinkable in only one direction is likely to cause wrinkles, shrinkage spots, and insufficient shrinkage when mounted on a container having a complicated shape and is satisfactory as a heat-shrinkable film. It was not what was done.
For such problems, heat shrinkable polyester film that shrinks even in a direction orthogonal to the main shrinkage direction (see, for example, Patent Document 2) and stretching ratios in the longitudinal and transverse directions are limited to control the shrinkage rate. A method (see, for example, Patent Document 3) is disclosed.
Japanese Patent No. 2692270 JP-A-5-185510

  However, the films obtained by these methods have extremely low fusing seal strength and are not practical. When a heat-shrinkable film is coated on a container having a complicated shape such as cosmetics, melting the film with a heated cutting blade is called a fusing seal (generally an R seal).

In order to solve such a problem, a method (for example, see Patent Document 4) in which the difference (ΔT) between the melting point (Tm) of the polyester used for the heat-shrinkable polyester film and the crystallization temperature (Tc2) is disclosed. Has been.
JP 11-277625 A

  However, although the film obtained by these methods has a high fusing seal strength, there is a problem that the light-cutting property is poor.

  The object of the present invention is to solve the above-mentioned problems, and the object of the present invention is to provide a heat suitable for being attached to the outer periphery of a container having a complicated shape, such as a cosmetic or a fragrance container, and shrinking. An object of the present invention is to provide a heat-shrinkable polyester film that is a shrinkable polyester film and that has a light-cutting property without performing printing or processing, and further has an excellent fusing and sealing property.

  As a result of earnest research to solve the problems of the prior art, the present inventor achieved the object by setting the total light transmittance, fusing seal strength, hot water shrinkage rate of the heat shrinkable polyester film within a specific range. The present inventors have found out what can be done, and based on this, the present invention has been completed.

That is, the present invention is a film mainly made of a polyester resin, and the hot water shrinkage rate is 30% or more at a treatment temperature of 95 ° C. and a treatment time of 10 seconds in the main shrinkage direction, and in a direction orthogonal to the main shrinkage direction. The heat-shrinkable polyester film is characterized by being 10% or more, the total light transmittance of the film being 40% or less, and the fusing seal strength being 10 N / 15 mm width or more.
The fusing seal strength referred to in the present invention is an automatic bag making machine (model: RP500) manufactured by Kyoei Printing Machinery Materials Co., Ltd., and a fusing blade with a blade angle of 70 degrees is heated to 240 ° C. at a bag making speed of 100 bags / min. Made a bag. The melt-sealed seal portion of the bag-made product was cut out with a width of 15 mm, and using a Tensilon (model: UTL-4L) manufactured by Toyo Seiki Co., Ltd., the gap between chucks was 50 mm, and the tensile speed was 200 mm / min. It shall mean the average value of the measured peel strength (n = 10).
The heat shrinkage referred to in the present invention means that a film is cut into a 10 cm × 10 cm square, immersed in warm water of 95 ± 0.5 ° C. for 10 seconds under no load condition, and immediately heat-shrinked, then 25 ± It means a value calculated by immersing the film in water at 0.5 ° C. for 10 seconds, measuring the longitudinal and lateral dimensions of the film, and then following the equation below. At this time, the direction in which the shrinkage rate was large was taken as 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.

  Furthermore, 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.

  The heat-shrinkable polyester film of the present invention is extremely small in wrinkles, shrinkage spots, and under-shrinkage when it is shrunk by being attached to the outer periphery of a container having a complicated shape, such as cosmetics and fragrance containers. Even without processing, it has a light-cutting property, and further has an excellent fusing sealing property. Therefore, the film of the present invention is suitable for various types of coated labels such as cosmetics, fragrance containers and the like having complicated shapes.

  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.

  The polyester film of the present invention is required to have a fusing seal strength of 10 N / 15 mm width or more, and preferably 12 N / 15 mm width or more. When the fusing seal strength is less than 10N / 15mm width, not only is the seal part easily broken when shrink-wrapping after sealing, but also the occurrence of whiskers and adhesion of the film to the fusing blade during sealing. It becomes a heat-shrinkable polyester film that is easy and extremely low in commercial value.

The heat-shrinkable polyester film of the present invention substantially comprises a polyester resin, fine particles, and a thermoplastic resin incompatible with the polyester.
As the polyester resin, for example, a polyester composition comprising a polyester having a dicarboxylic acid component and a diol component as described below as constituent components and a polyester elastomer can be preferably used. In the polyester resin composition, the blending ratio of the polyester and the polyester-based 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.

  Although details will be described later, in the heat-shrinkable polyester film of the present invention, it is desirable to use an ethylene terephthalate unit as a main constituent unit in order to exhibit tear resistance, strength, heat resistance, and the like.

  As other polyhydric alcohols for forming the polyhydric alcohol component, ethylene glycol is used to form an ethylene terephthalate unit, as will be described later. In addition, propylene glycol, triethylene glycol, 1,4-butanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, 2-methyl-1,5-pentanediol, 2 , 2-diethyl-1,3-propanediol, 1,9-nonanediol, alkylene glycol such as 1,10-decanediol, trimethylolpropane, glycerin, pentaerythritol, diethylene glycol, dimer diol, polyoxytetramethylene glycol, Polyethylene glycol, an alkylene oxide adduct of a bisphenol compound or a derivative thereof can be used in combination.

  As the polyvalent carboxylic acids for forming the polyvalent carboxylic acid component, aromatic dicarboxylic acids, ester-forming derivatives thereof, aliphatic dicarboxylic acids and the like can be used in addition to the above-mentioned terephthalic acid (and its esters). . Examples of the aromatic dicarboxylic acid include isophthalic acid, naphthalene-1,4- or -2,6-dicarboxylic acid, and 5-sodium sulfoisophthalic acid. Examples of the ester derivatives of these aromatic dicarboxylic acids, isophthalic acid, and terephthalic acid include derivatives such as dialkyl esters and diaryl esters. Examples of the aliphatic dicarboxylic acid include glutaric acid, adipic acid, sebacic acid, azelaic acid, oxalic acid, succinic acid and the like, and an aliphatic dicarboxylic acid usually called dimer acid. Further, an oxycarboxylic acid such as p-oxybenzoic acid, and a polyvalent carboxylic acid such as trimellitic anhydride or pyromellitic anhydride may be used in combination as necessary.

  In order to improve the solvent adhesion of the film of the present invention, it is effective to use, for example, a low Tg copolymer polyester unit. In addition, as a unit which reduces said Tg, as a polyhydric alcohol component, the ester unit which has a 1, 3- propanediol component, a 1, 4- butanediol component, a dimer diol component, or a polyoxytetramethylene glycol component, As the polycarboxylic acid component, preferred are an ester unit having an aliphatic dicarboxylic acid component such as dimer acid, adipic acid, sebacic acid, azelaic acid, and a unit derived from ε-caprolactone. What is necessary is just to introduce 2 or more types. In addition, the ester unit which reduces Tg may be formed from either of the above-mentioned polyhydric alcohol components and any of the polyvalent carboxylic acid components.

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 in the low melting point soft polymer segment are particularly preferred.
Lactones are those that ring-open to become units having ester bonds at both ends, and a unit derived from one lactone can be considered to be a carboxylic acid component and an alcohol component.

  The polyester constituting the heat-shrinkable polyester film can be produced by melt polymerization according to a conventional method, but a so-called direct polymerization method in which an oligomer obtained by directly reacting a dicarboxylic acid and a glycol is polycondensed is used. Examples include a so-called transesterification method in which a dimethyl ester and a glycol are subjected to a transesterification reaction and then polycondensed, and any production method can be applied. Moreover, the polyester obtained by another polymerization method may be sufficient. The introduction of the lactone-derived unit is, for example, a method of performing polycondensation by adding a lactone before the polycondensation, a method of copolymerizing a polymer obtained by the polycondensation with a lactone, or the like. Can be achieved.

  If necessary, fine particles such as silica, titanium dioxide, kaolin and calcium carbonate may be added to the film raw material, and antioxidants, UV absorbers, antistatic agents, coloring agents, antibacterial agents, etc. are added. You can also

  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 inorganic lubricants 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 during polyester synthesis, such as alkali metal compounds and alkaline earth metal compounds, can be internal particles formed inside the polymer during polyester production. Titanium oxide is preferred.

  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 the purpose of improving the light-cutting property. 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.

  Specific examples of the thermoplastic resin incompatible with the polyester used in the present invention include polystyrene resins, polyolefin resins, polyacrylic resins, polycarbonate resins, polysulfone resins, and cellulose resins. In particular, considering the formability of the cavity, specifically, a polystyrene resin or a polyolefin resin such as polymethylpentene or polypropylene having a large difference in surface tension from polyester is preferable.

  Polystyrene resin refers to a thermoplastic resin that contains a polystyrene structure as a basic constituent element. In addition to homopolymers such as atactic polystyrene, syndiotactic polystyrene, and isotactic polystyrene, other components are grafted or block copolymerized. Modified resins, such as impact-resistant polystyrene resins and modified polyphenylene ether resins, and mixtures of 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.

  The film in the present invention may be a single layer, but it is preferable for providing the fusing seal strength by providing 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. The intermediate layer B is mixed with titanium oxide and an incompatible resin to develop light shielding properties, and both outer layers A are layers not containing titanium oxide and an incompatible resin. Can be secured. If the layer A is melted when titanium oxide or an incompatible resin is present, the titanium oxide particles and the incompatible resin inhibit adhesion and weaken the strength.

  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, the amount of incompatible resin of the A layer as a raw material is less than that of the B layer, and the number of cavities in the A layer is reduced, so that the surface is less rough and the aesthetic appearance of printing is not impaired. It is suitable for making a strong and excellent film.

  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.

  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.

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

  In the main shrinkage direction of the film of the present invention, the shrinkage rate of 95 ° C. hot water and a treatment time of 10 seconds is 30% or more, preferably 35 to 95%. If the shrinkage rate is less than 35%, the container does not adhere to the container and shrinkage is insufficient. On the other hand, if it exceeds 95%, the shrinkage rate is large, and jumping and pattern distortion may occur while passing through the shrinking tunnel. Here, the main shrinkage direction means a direction with a large shrinkage rate.

  The shrinkage rate in the direction perpendicular to the main shrinkage direction is 10% or more, preferably 12% or more. If the shrinkage rate is less than 10%, the horizontal wrinkles of the label generated during shrinkage tend to be difficult to disappear. On the other hand, if it exceeds 50%, the vertical shrinkage of the label increases and the distortion of the pattern increases, and the amount of film used This is not preferable because it causes a problem in terms of economy.

  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 width or more. When the width is less than 4 N / 15 mm, the joint is peeled off when the label is contracted into the container, which is not preferable.

Hereafter, the manufacturing method of the film of this invention is demonstrated concretely.
The raw material polyester chips are dried using a dryer such as a hopper dryer or paddle dryer, or a vacuum dryer, and extruded into a film at a temperature of 200 to 300 ° C. using an extruder. Alternatively, undried polyester raw material chips are similarly extruded into a film while removing moisture in a vented extruder. When extruding, any existing method such as T-die method or tubular method may be adopted. After the extrusion, the film is cooled (rapidly cooled) with a casting roll to obtain an unstretched film. The “unstretched film” includes a film on which a tension necessary for feeding the film is applied.

  Next, the unstretched film is stretched. As described above, since it is practical in terms of production efficiency that the maximum shrinkage direction is the film transverse (width) direction, an example of a stretching method in the case where the maximum shrinkage direction is the transverse direction is also shown here. Even when the maximum shrinkage direction is the longitudinal (longitudinal) direction of the film, the film can be stretched according to ordinary operations such as changing the stretching direction by 90 ° in the following method.

  As a stretching method, it is preferable to perform not only horizontal uniaxial stretching with a tenter but also stretching in the longitudinal direction by 1.0 to 4.0 times, preferably 1.1 to 2.0 times. When such biaxial stretching is performed, either sequential biaxial stretching or simultaneous biaxial stretching may be performed, and restretching may be performed as necessary. Further, in the sequential biaxial stretching, any method such as vertical and horizontal, horizontal and vertical, vertical and horizontal and horizontal and vertical and horizontal may be used as the order of stretching. Even when these longitudinal stretching steps or biaxial stretching steps are adopted, it is preferable to minimize the fluctuation of the film surface temperature as much as possible in the preheating step, the stretching step and the like, similarly to the transverse stretching.

If attention is focused on making the thickness distribution of the heat-shrinkable polyester film uniform, it is preferable to perform a preheating step prior to the stretching step when stretching in the transverse direction using a tenter or the like. In this preheating step, the film surface temperature is Tg + 0 ° C. to low wind speed so that the thermal conductivity coefficient is 0.00544 J / cm ² · sec · ° C. or less (0.0013 calories / cm ² · sec · ° C.). Heating is preferably performed until a certain temperature within the range of Tg + 60 ° C. is reached.

Focusing on the point of suppressing the internal heat generation of the film due to stretching and reducing the film temperature unevenness in the width direction, the heat transfer coefficient of the stretching process is 0.00377 J / cm ² · sec · ° C. (0.0009 calorie / cm ² · sec · ° C.) or higher. 0.00544 to 0.00837 J / cm ² · sec · ° C. (0.0013 to 0.0020 calories / cm ² · sec · ° C.) is more preferable.

  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.

  The heat-shrinkable polyester film roll in the present invention is preferably a roll obtained by winding a heat-shrinkable film having a width of 0.2 m or more around a winding core (core) with a length of 300 m or more. A roll of a film having a width of less than 0.2 m has a low industrial utility value, and a film roll having a width of less than 300 m has a small film winding length, and thus covers the entire length of the film. Since the thermal contraction rate fluctuation is small, the effect of the present invention is hardly exhibited. The width of the film roll is more preferably 0.3 m or more, and further preferably 0.4 m or more. The length of the film wound around the roll is more preferably 400 m or more, and further preferably 500 m or more.

  The upper limit of the width and the winding length of the film roll is not particularly limited, but from the viewpoint of ease of handling, the width is generally 1.5 m or less, and the winding length is preferably 6000 m or less when the film thickness is 45 μm. In addition, as the winding core, a plastic core such as 3 inch, 6 inch, or 8 inch, a metal core, or a paper tube can be usually 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 film which comprises the heat-shrinkable polyester film roll of this invention is not specifically limited, For example, as a heat-shrinkable polyester film for labels, 5-200 micrometers is preferable and 10-100 micrometers is more preferable.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples are not intended to limit the present invention, and modifications and implementations that do not depart from the spirit of the present invention are included in the present invention. The measuring method of the physical property of the film obtained by the Example and the comparative example is as follows.

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

(2) Fusing Seal Strength Using an automatic bag making machine (model: RP500) manufactured by Kyoei Printing Machinery Materials Co., Ltd., a fusing blade with a blade angle of 70 degrees was heated to 240 ° C. to produce a bag at a bag making speed of 100 bags / min. The melt-sealed seal portion of the bag-made product was cut out with a width of 15 mm, and using a Tensilon (model: UTL-4L) manufactured by Toyo Seiki Co., Ltd., the gap between chucks was 50 mm, and the tensile speed was 200 mm / min. The average value of the measured peel strength (n = 10) was taken as the fusing seal strength.

(3) Heat shrinkage rate The film was cut into a 10 cm × 10 cm square, immersed in warm water of 95 ± 0.5 ° C. for 10 seconds under heat-free condition, and immediately heat-shrinked, then immediately 25 ± 0.5 ° C. The film was immersed in water for 10 seconds, and then the vertical and horizontal dimensions of the film were measured, and the thermal shrinkage was determined according to the following equation. The direction in which the shrinkage rate is large was taken as the main shrinkage direction.

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

(4) Shrinkage finish property Using a universal shrinker (model: K2000) manufactured by Kyowa Denki Co., Ltd., mounted on a commercially available laminate tube (revital rinse manufactured by Shiseido Co., Ltd.), passing time 15 seconds, 1, 2 zone temperature 160, 180 The finish was tested at 0 ° C. (number of measurements = 10).
Evaluation was made visually and the criteria were as follows.
No wrinkles, jumps, or insufficient shrinkage: ○
Wrinkles, jumping up, or insufficient shrinkage occurs: ×

(5) Solvent adhesion The film was joined into a tube using 1,3-dioxolane, and the tube was cut to a width of 15 mm in a direction perpendicular to the flow direction during processing. Tensillon (model: UTL-4L) was used to pull and peel between the chucks at 20 mm, and the peel resistance was measured. When the measured value was 4N or more, it was set as “◯”.

(6) 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 obtained endothermic curve. 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) comprising 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, as a raw material for the A layer, a polyester composition in which 30% by weight of polyester A, 65% by weight of polyester B and 5% by weight of polyester C are mixed, and 10% of polyester A is used as the raw material of the B layer. % By weight, 65% by weight of polyester B, 5% 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) After being fed into an extruder, mixed and melted, they are 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 4.5 μm / 16 μm / 4.5 μm. While being melt extruded, it was quenched with a chill roll to obtain an unstretched film.
The unstretched film was stretched by 1.4 times with a roll-type longitudinal stretching machine (roll temperature: 95 ° C.), then stretched 4.0 times in the transverse direction at a film temperature of 70 ° C. with a tenter, and heat shrinkage of 25 μm thickness. A conductive polyester film was obtained.

(Example 2 and Comparative Examples 1 to 3)
As shown in Table 1, a heat-shrinkable polyester film having a thickness of 25 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 shown in Table 2.

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

  As is clear from Table 2, the heat-shrinkable polyester film obtained in Examples 1 and 2 is a heat-shrinkable polyester film suitable for covering a container having a complicated shape, and It had good light-cutting properties.

  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, the heat-shrinkable polyester film obtained in Comparative Example 1 has light-cutting properties but is inferior in shrinking finish when covering a container having a complicated shape, and was obtained in Comparative Examples 2-3. The heat-shrinkable polyester film was inferior in light-cutting property. 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-based film that has a light-cutting property without being printed or processed, and that is suitable for coating a container having a complicated shape. Therefore, it is extremely useful as a heat-shrinkable polyester film for overlapping, particularly for coating with high commercial value. It can be suitably used for applications such as shrink wrapping and contributes greatly to the industry.

Claims (3)

  A film mainly made of a polyester resin, having a hot water shrinkage ratio of 30% or more at a treatment temperature of 95 ° C. and a treatment time of 10 seconds in the main shrinkage direction, and at least 10% in a direction perpendicular to the main shrinkage direction; A heat-shrinkable polyester film characterized in that the total light transmittance of the film is 40% or less and the fusing seal strength is 10 N / 15 mm width or more.   2. The heat-shrinkable polyester film according to claim 1, wherein the heat-shrinkable polyester film has at least one layer to which titanium oxide is added.   The heat-shrinkable polyester film according to any one of claims 1 and 2, wherein there is at least one layer to which a polystyrene resin is added.