JP2011079229A - Heat-shrinkable polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-shrinkable film which has excellent characteristics and is made of a polyester film that produces no crack when used at high temperature for a long time, has excellent alkali resistance and hardly has problems of producing toxic gas and damaging a combustion furnace when burned for waste treatment. <P>SOLUTION: The heat-shrinkable polyester film is obtained by stretching, at least in one direction, a film which consists of 50 to 75 wt.% of crystalline polyethylene terephthalate resin having a glass transition point of 78 to 82°C and 50 to 25 wt.% of amorphous or low crystalline spiro glycol-modified polyethylene terephthalate resin having a glass transition point of 90 to 105°C. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a heat-shrinkable polyester film, and is a longitudinal shrinkable label particularly excellent in durability at high temperatures, and is used for dry batteries and hot beverages.

  Currently used heat shrinkable films include polyvinyl chloride films, polystyrene films, polyolefin films, and polyester films. Polyvinyl chloride films are often used for labels and the like because they have good printability and can be packaged neatly, but they have low heat resistance and have environmental problems such as generation of hydrogen chloride when incinerated. Polystyrene-based films have disadvantages such as a large amount of natural shrinkage during storage and poor solvent resistance. Polyolefin films have relatively high heat resistance, but have poor printability and a narrow range of heat shrinkage temperatures.

  For the purpose of insulating and protecting a dry battery, a dry battery label in which a heat-shrinkable film is printed is used. This film is required to have strict performance according to the environment in which it is used. First, heat resistance that does not cause cracking under high temperature and long time. Secondly, there is an alkali resistance that does not cause cracks or cracks when immersed in an alkaline electrolyte.

  In recent years, polyester-based uniaxially stretched heat-shrinkable films have been used as labels for dry batteries. As the resin component, an amorphous copolyester resin modified with 1,4-cyclohexanedimethanol having a glass transition point (Tg) of about 80 ° C. is used to improve workability and stretchability.

  However, since heat shrinkage becomes large at around 60 ° C. or higher, there is a drawback that the battery is displaced or cracked when stored at a high temperature for a long time. In order to overcome this drawback, production can be performed by changing the stretching conditions. However, since the conditions are special, the production has a big problem.

  Therefore, a heat-shrinkable film using an amorphous to low-crystalline spiroglycol-modified copolymer polyester resin having a high Tg has been developed (see Patent Documents 1 and 2).

JP 2003-183421 A JP 2003-183422 A

  However, it has been found that a heat-shrinkable film using a spiroglycol-modified copolyester resin cracks when used at a high temperature for a long time, for example, when used as an exterior label of a dry battery.

  Therefore, the object of the present invention is excellent in the above-mentioned heat resistance problem and alkali resistance, and in a polyester-based film with less problems such as generation of toxic gas at the time of waste treatment and damage to the combustion furnace. It is in providing a heat shrinkable film having the characteristics.

  The heat-shrinkable polyester film of the present invention comprises 50 to 75% by weight of a crystalline polyethylene terephthalate resin having a glass transition point (Tg) of 78 to 82 ° C. and an amorphous material having a glass transition point (Tg) of 90 to 105 ° C. A film comprising 25 to 50% by weight of a crystalline or weakly crystalline spiroglycol-modified polyethylene terephthalate resin is stretched in at least one direction.

  The heat-shrinkable polyester film has a heat shrinkage rate in the stretching direction of 1% or less at 80 ° C, preferably 0.5% or less, 10% or more at 130 ° C, preferably 15% or more. preferable.

  Moreover, the manufacturing method of the heat-shrinkable polyester film of the present invention comprises 50 to 75% by weight of a crystalline polyethylene terephthalate resin having a glass transition point of 78 to 82 ° C and an amorphous property having a glass transition point of 90 to 105 ° C. Alternatively, a film composed of 25 to 50% by weight of a weakly crystalline spiroglycol-modified polyethylene terephthalate resin is preheated to 90 to 115 ° C. and then stretched 2 to 6 times by an inter-roll stretching method. .

  When the heat-shrinkable polyester film of the present invention is used after being heat-shrinked as an exterior label for a dry battery, it is free from deviation or cracking during storage or use at a high temperature for a long time, and also has alkali resistance and abrasion resistance. Is good.

  Hereinafter, the present invention will be described in detail. The crystalline polyethylene terephthalate resin, which is one component constituting the heat-shrinkable polyester film of the present invention, needs to have a glass transition point of around 80 ° C. If this is too low, the shrinkage start temperature of the film will be too low and partial shrinkage will occur during storage of the film, and if the glass transition point is much higher than 80 ° C., shrinkage will be required. Since it does not appear in the temperature range, it is not preferable.

  The other component in the heat-shrinkable polyester film of the present invention is an amorphous or weakly crystalline spiroglycol-modified polyethylene terephthalate resin having a glass transition point of 90 to 105 ° C. If the glass transition point is lower than 90 ° C., the copolymerization ratio of spiroglycol is decreased, and therefore, it is not preferable because it becomes crystalline and the heat shrinkage rate is hardly exhibited. Further, if the glass transition point is higher than 105 ° C., the shrinkage rate in the practical temperature range does not appear, which is not preferable.

  As the spiroglycol-modified polyethylene terephthalate resin, for example, “Altesta 20” (Tg; 95 ° C.) and “Altester 30” (Tg; 100 ° C.) manufactured by Mitsubishi Gas Chemical Co., Ltd. are commercially available.

  Crystalline polyethylene terephthalate resin having a glass transition point of 78 to 82 ° C. and amorphous or weakly crystalline spiroglycol having a glass transition point of 90 to 105 ° C. used in the heat-shrinkable polyester film of the present invention The blending ratio of the modified polyethylene terephthalate resin is required to be 50 to 75% by weight / 25 to 50% by weight.

  When the ratio of the crystalline polyethylene terephthalate resin is less than 50% by weight, the shrinkage rate is increased in the temperature range of 80 to 90 ° C., and cracking occurs when it is attached to a dry battery, which is not preferable. On the other hand, if it exceeds 75% by weight, the shrinkage rate is insufficient and a problem occurs during mounting.

  In order to obtain the heat shrinkability of the heat shrinkable polyester film having a heat shrinkage rate in the drawing direction of 1% or less at 80 ° C. and 10% or more at 130 ° C., preheating is performed at a temperature of 100 to 110 ° C. as drawing conditions. After that, it is preferable that the draw ratio is 2 to 6 times, preferably 3 to 5 times in the uniaxial direction.

  When producing a heat-shrinkable polyester film having the above-described heat-shrink characteristics by roll-to-roll stretching, there is a problem that if the preheating temperature is increased, the film becomes sticky and the productivity is lowered, and the glass transition point (Tg ) Polyester resin having a high degree of heat shrinkability is required.

  The present invention includes a crystalline polyethylene terephthalate resin having a glass transition point of 78 to 82 ° C. and an amorphous or weakly crystalline spiroglycol-modified polyethylene terephthalate resin having a glass transition point of 90 to 105 ° C. When used in combination, production by roll-to-roll stretching was good, and a heat shrinkage rate of 1% or less at 80 ° C. and 10% or more at 130 ° C. was obtained.

When the heat-shrinkable polyester film according to the present invention is coated as a label on a dry battery and is shrunk, there is no cracking at a high temperature for a long time, and it is immersed in an alkaline electrolyte so as to crack or crack. Improvements such as lack of were recognized.
In addition to the above polymer component, the heat-shrinkable polyester-based film of the present invention improves stabilizers, lubricants, colorants, antioxidants, antistatic agents, and film-to-film lubricity as necessary. Organic and / or inorganic lubricants may be added.

Hereinafter, specific embodiments of the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not limited thereto.
The evaluation of Examples and Comparative Examples was performed as follows.

[Evaluation of cracking]: A heat-shrinkable polyester film is attached to a dry battery as a label, and is kept in an oven at 80 ° C. for 5 days.
○: No cracking ×: Cracking occurred

[Alkali resistance]: After being immersed in a 30% by weight potassium hydroxide solution at room temperature for 24 hours, washed with water and dried to confirm the appearance.
○: No problem.
×: Abnormal (wrinkles, cracks, loose labels, peeling of seals, etc.)

[Heat Shrinkage]: Samples obtained by cutting the heat-shrinkable polyester film produced in each Example / Comparative Example into 10 cm squares were immersed in a glycerin bath at each temperature for 30 seconds, and 30 seconds passed. Immediately after that, the sample was immersed in a water bath at 25 ° C. for 10 seconds, and then the dimensions of the sample were measured to obtain the shrinkage at the measurement temperature.

Resins used in Examples and Comparative Examples are as follows.
PET-1: manufactured by Eastman Chemical Co., Ltd., amorphous cyclohexanedimethanol-modified polyethylene terephthalate resin “PETG Copolyester 6763” (Tg; 80 ° C.)
PET-2: manufactured by Bell Polyester Products, crystalline polyethylene terephthalate resin “FMS20” (Tg; 80 ° C.)
PET-3: weak polyester isophthalic acid modified polyethylene terephthalate resin “IFG8L” (Tg; 76 ° C.), manufactured by Bell Polyester Products
PET-4: Mitsubishi Gas Chemical Co., Ltd., weak crystalline spiroglycol-modified polyethylene terephthalate resin “Artester 20” (Tg; 95 ° C.)
PET-5: manufactured by Mitsubishi Gas Chemical Co., Inc., amorphous spiroglycol-modified polyethylene terephthalate resin “Artester 30” (Tg; 100 ° C.)

Examples 1-2 and Comparative Examples 1-4
After drying the mixed pellets of each resin shown in Table 1 at 120 ° C. for 6 hours using a hot-air shelf dryer, from the T-die while flowing dry nitrogen gas at 100 to 110 ° C. into the hopper of the extruder. The film was extruded and quenched with a cooling roll to form a 200 μm thick film. In addition, the temperature conditions of the extruder were 160-250 degreeC, and T-die temperature was 280 degreeC. Next, a plurality of preheating rolls are used, the preheating roll temperature is preheated from 80 ° C. to the final roll 110 ° C., and the drawing roll using the inter-roll drawing method is used. The roll was set at 30 ° C., and the film was stretched 4 times in the longitudinal direction to obtain a film having a thickness of about 50 μm. Table 1 shows the shrinkage rate in the longitudinal direction at each temperature and each evaluation.

As can be seen from Table 1, each heat-shrinkable polyester film of the Examples has a heat shrinkage rate of approximately 0% at 80 ° C. and a heat shrinkage rate of 130 ° C. of 15% or more. It has excellent alkali resistance and is excellent as a battery exterior label.
On the other hand, Comparative Examples 2 to 4 were inferior in productivity because of stickiness to the roll in high-temperature roll stretching, and all of the Comparative Examples were also inferior in crack evaluation.

  The heat-shrinkable polyester film of the present invention is resistant to slippage and cracking even when stored for a long time in a high-temperature environment of about 40 to 60 ° C. after being subjected to heat-shrinkage on an encapsulated article. Good alkalinity and wear resistance. Therefore, it can be suitably used as an external label for storage and / or use in a high temperature environment, for example, a dry battery exterior label.

Claims (4)

  Crystalline polyethylene terephthalate resin having a glass transition point of 78 to 82 ° C., 50 to 75% by weight, and amorphous or weakly crystalline spiroglycol-modified polyethylene terephthalate resin 25 to 50 having a glass transition point of 90 to 105 ° C. A heat-shrinkable polyester-based film obtained by stretching a film composed of% by weight in at least one direction.   The heat-shrinkable polyester film according to claim 1, wherein the heat-shrinkable polyester film is a uniaxially stretched film, and the heat shrinkage rate in the stretching direction is 1% or less at 80 ° C and 10% or more at 130 ° C. the film.   The heat-shrinkable polyester film according to claim 1 or 2, wherein the heat-shrinkable polyester film is a longitudinally uniaxially stretched film and is used for a label for a dry battery exterior.   Crystalline polyethylene terephthalate resin having a glass transition point of 78 to 82 ° C., 50 to 75% by weight, and amorphous or weakly crystalline spiroglycol-modified polyethylene terephthalate resin 25 to 50 having a glass transition point of 90 to 105 ° C. A method for producing a heat-shrinkable polyester film, comprising preheating a film consisting of% by weight to 90 to 115 ° C. and then stretching it 2 to 6 times by an inter-roll stretching method.