JPH04170436A - Heat-shrinkable polyester film - Google Patents

Abstract

PURPOSE:To obtain the title film excellent in transparency, resistance to heat and chemicals, and mechanical strengths and free from uneven shrinkage and pockmark-like wrinkles in thermal shrinkage by compounding a polyethylene terephthalate polymer with a specified amt. of a polybutylene terephthalate polymer and molding the resulting compsn. into a film. CONSTITUTION:A polyethylene terephthalate polymer (pref. having a glass transition point of 50-80 deg.C) is compounded with 40-70wt.% polybutylene terephthalate polymer (pref. having a glass transition point of 20-40 deg.C which is different from that of the polyethylene terephthalate polymer by at least 10 deg.C) and molded to give the title film.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is applicable to food and beverages such as cola, juice, beer, and cup noodles, pharmaceuticals, miscellaneous goods, industrial materials, stationery, toys, tools, and various other products. As labels and cap stickers for packaging and displaying contents and vendor,
Heat-shrinkable polyester used as a safety shield to prevent foreign matter from entering, to prevent battery discharge, to prevent products from deteriorating due to oxidation and moisture absorption, to prevent dirt from being soiled during product display, or as packaging material for bundling multiple products. This is related to series films.

<Prior art> Heat-shrinkable films currently in use include polyvinyl chloride (hereinafter referred to as PvC)-based films, polystyrene (
Polyolefin (hereinafter referred to as PS) based film, polyolefin (hereinafter referred to as P
These include (O-) type films, polyester type films, etc.

PVC films have good printability and can be packaged neatly, so they are often used for labels and the like, but they have low heat resistance and cannot be used in high-temperature retort sterilization. Furthermore, it is difficult to rot when disposed of, and when incinerated, there are problems such as generation of hydrogen chloride, resulting in damage to the furnace, and generation of dioxins.

Since PS film has a large amount of natural shrinkage during storage,
When used as a heat-shrinkable label, the shrinkage progresses and it may become difficult to cover the container. It also has disadvantages such as poor weather resistance and solvent resistance.

PO-based films have relatively high heat resistance and can withstand high-temperature retort sterilization, but their printability is lower than that of PvC-based films, and their heat-shrinkage temperature range is narrow, making them susceptible to shrinkage spots and wrinkles.

On the other hand, polyester film is transparent and has high tensile strength.
It has excellent heat resistance and weather resistance, and is chemically resistant to various chemicals, as well as generating little harmful gas when burned, so it is used for a variety of purposes.

Especially since these characteristics are better these days,
Polyethylene terephthalate (hereinafter referred to as PET) based films are beginning to be used. However, this film has poor shrinkage characteristics at low temperatures and is prone to shrinkage spots and wrinkles during heat shrinkage.

For this reason, there is a method of incorporating 2 to 35% by weight of polybutylene terephthalate (hereinafter referred to as PBT) into PET to improve its shrinkage characteristics at low temperatures (Japanese Patent Laid-Open No. 88550/1983).
was also proposed, but even this method could not prevent the occurrence of shrinkage spots and wrinkles during heat shrinkage.

<Problems to be Solved by the Invention> Therefore, the purpose of the present invention is to provide high transparency, excellent heat resistance, high mechanical strength, and excellent chemical resistance, and to reduce the amount of toxic gas during combustion during waste treatment. It is an object of the present invention to provide a heat-shrinkable polyester film which is less likely to cause problems such as the occurrence of drying and damage to combustion furnaces, and which further prevents the occurrence of shrinkage spots and pock-like wrinkles during heat shrinkage.

<Means for Solving the Problems> In order to solve the above problems, the present inventors first observed the heat shrinkage process and endeavored to elucidate the cause of the occurrence of shrinkage spots and wrinkles. In other words, when a conventional PET film label is placed on a product and heated to a temperature higher than the shrinkage start temperature, rapid shrinkage occurs, but at that time, the shrinkage stops where it contacts the surface of the product earlier, and where it contacts the product surface later. However, it was found that the shrinkage progressed further, causing distortion, shrinkage spots, wrinkles, etc. From this, in order to prevent shrinkage spots, pock-like wrinkles, and distortions during heat shrinkage, it is sufficient to widen the range of heat shrinkage temperatures so that shrinkage proceeds slowly when the film temperature reaches the shrinkage start temperature or higher. It turns out.

Therefore, the inventors of the present invention conducted extensive research into ways to expand the heat shrinkage temperature range of polyester films.
This is achieved by blending 40 to 70% by weight of a PBT-based polymer into a PBT-based polymer and molding it.Also, when this film is placed on a product and heat-shrinked, distortion, shrinkage spots, wrinkles, etc. will almost never occur. The present invention has been developed based on the discovery that this phenomenon no longer occurs.

The present invention will be explained in detail below.

Generally, the glass transition point and the compatibility with the resin to be blended of polyester resins vary greatly depending on their component composition. Depending on the ratio of the polymer blend, they may appear to be evenly compatible, or the compatibility may be so low that the two-phase morphology of the matrix (sea) and the islands dispersed therein may be affected. When common polymers are uniformly miscible, the elastic modulus changes sharply with temperature around the glass transition point like a single polymer, but there are two (or more) phases that appear to have undergone fine phase separation.
, the elastic modulus changes with temperature in multiple steps or gently around the glass transition point.

The PET polymer, which is one of the components constituting the polyester film of the present invention, has a glass transition point of 50 to 80.
℃ is preferred. When this temperature is lower than 50° C., the shrinkage start temperature of the film becomes too low, and the film begins to partially shrink during storage. Further, if the temperature is higher than 80°C, the shrinkage start temperature of the film becomes too high, which is not preferable.

The composition of this polymer is preferably 70 mol% or more, especially 90 mol% or more of terephthalic acid as a dicarboxylic acid component, and when it is desired to raise the glass transition point, 10 to 30 mol% or less of naphthalene dicarboxylic acid is combined. ,
When you want to lower the glass transition point, use compatible dicarboxylic acids such as isophthalic acid, orthophthalic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, azelaic acid, superic acid, oxalic acid, malonic acid, etc. One type or two or more types may be selected and used while considering the following.

In addition, as a diol component, ethylene glycol is 70%
More than 90 mol% is preferable, and propylene glycol, bentanediol, hexanediol, neopentyl glycol, diethylene glycol, triethylene glycol, One of the known diol components such as polyethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimetatool, etc.
One species or two or more species may be selectively used.

The above-mentioned PET-based polymer can be obtained by combining the above two components and subjecting them to a condensation reaction.

The PBT polymer, which is the other component in the polyester film of the present invention, has a glass transition point of 20 to 40°C.
It is preferable that P
When blended with an ET polymer, the glass transition point of the system becomes too low, causing partial spontaneous shrinkage of the film during storage, and when the temperature exceeds 40°C, the glass transition point of the PET polymer becomes too low. If they are too close together, the effect of reducing the shrinkage speed will be almost gone, which is not preferable.

Therefore, the composition of this polymer preferably contains 70 mol% or more, particularly 90 mol% or more of terephthalic acid as the dicarboxylic acid component, and is used to adjust the glass transition point and adjust the compatibility with the PET polymer. In order to
Isophthalic acid, orthonaphthalic acid, 52,6-naphthalene dicarboxylic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, azelaic acid, speric acid, oxalic acid,
One or more types of known dicarboxylic acids such as malonic acid may be selected and combined.

As a diol component, 1,4-butanediol is 70%
It is preferably mol% or more, especially 90 mol% or more, and ethylene glycol, propylene glycol, triethylene glycol, hexanediol, bentanediol, neopentyl glycol, diethylene glycol, polyethylene glycol, while considering the glass transition point and compatibility. , 1°4-cyclohexane dimetatool, and the like may be selected from one or more known diol components.

By combining the above two components and carrying out a condensation reaction, the P
It can be a BT-based polymer.

In order to widen the shrinkage temperature range of a heat-shrinkable polyester film, the difference in glass transition point between PET polymer and PBT polymer must be 10°C or more, especially 20°C or more, and even 40°C or more. preferable. This is 10
If it is below ℃, the shrinkage start temperatures of both polymers will be too close, so the effect of expanding the shrinkage temperature range will be small.If the glass transition point of the PBT-based polymer is too low, the shrinkage start temperature will be low, and the film or packaging material will remain in storage. It naturally shrinks, becoming distorted and making it impossible to cover the product.

If the blending ratio of PBT-based polymer to PET-based polymer is less than 40% by weight, the shrinkage start temperature will be lower depending on the blended ratio, but the shrinkage temperature curve will be as steep as that of PET-based polymer alone. Become. Also PBT
If the proportion of the blended polymer is greater than 70% by weight, the temperature at which the blend begins to shrink becomes too low, and the film or packaging material naturally shrinks during storage and becomes distorted, making it impossible to cover the product. Moreover, the shrinkage temperature curve is PB
The slope is similar to that of the T-based polymer alone, making it impossible to reduce the slope of the shrinkage temperature curve.

In the present invention, when the blending ratio of PBT-based polymer to PET-based polymer is 40 to 70% by weight, the shrinkage start temperature is lower than that of PET-based polymer, and the slope of the shrinkage temperature curve is smaller than that of each polymer. When labels using this film were shrunk, there were very few distortions, shrinkage spots, and wrinkles, which was a significant improvement over conventional polyester films.

In addition to the above polymer components, the polymer composition of the present invention may optionally contain stabilizers, lubricants, colorants, antioxidants, antistatic agents, and organic or inorganic agents for improving the slipperiness between films. A lubricant or the like may be added.

EXAMPLES The present invention will be explained below with reference to Examples, but the present invention is not limited thereto.

<Example> PET-based polymer (indicated as PET-I in the table), PBT-based polymer, PET-based polymer in which a portion of terephthalic acid was replaced with 20 mol% isophthalic acid (indicated as PET-I in the table)
- II) are mixed in the proportions shown in the table,
Mix and dry at 150℃ using a paddle dryer,
With an extruder set at 20 to 300°C, about 10
A sheet with a thickness of 0 μm was pressed and rapidly cooled to below the glass transition point. This was longitudinally stretched to 1.1 times with a heated roll at 80°C, and then 3 times in the transverse direction using a tenter at 70 to 110°C to obtain a film with a thickness of about 30 μl (this condition was ).

This was further heat-treated in a tenter at 80° C. by relaxing it in the transverse direction by 5% to obtain a film with a thickness of about 30 μm (this condition is referred to as B).

The shrinkage state of all the obtained films was observed and the storage stability was tested using the method described below, and the shrinkage temperature curves of the films other than those of Example 4 and Comparative Example 5 were determined using the method described below and are shown in Figure 1. From this, the shrinkage start temperature and shrinkage temperature gradient were determined using the method described below, and the results are also listed in the table.

Observation of shrinkage state: A 1 liter PET bottle filled with water at 25°C was covered with a label prepared from each film, and the bottle was heated and shrunk through a steam shrink tunnel maintained at 90-95°C. The state of contraction of the shoulders and torso was observed wt and evaluated using the following criteria.

O: Beautiful appearance with no shrinkage spots 0: Appearance with no shrinkage spots △: Appearance with minute shrinkage spots After holding a roll-shaped product wound 1000 m around a paper tube in an oven at 40° C. for 72 hours, changes in appearance were observed and evaluated according to the following criteria.

0: No changes such as shrinkage are observed.△: Some changes such as shrinkage are observed. After immersing it in a hot water bath at each temperature in °C intervals for 30 seconds, it was cooled to room temperature, measured in both the vertical and horizontal directions, the average value of the shrinkage rate was determined, and the shrinkage rate (vertical axis) and temperature (horizontal axis) were calculated. Shown in relation.

Shrinkage start temperature: In the shrinkage temperature curve, the linear portion in which the shrinkage rate is in the range of about 20 to 40% is extended downward, and expressed as the temperature at the intersection with the 0% line.

Shrinkage temperature gradient: Expressed as the slope of the straight line portion of the shrinkage temperature curve where the shrinkage rate is in the range of about 20 to 40%.

In Comparative Examples 3 and 4, the films were able to be heat-shrinked at a lower temperature than films made of PET resin alone, but shrinkage spots occurred like PET.

According to the shrinkage temperature curve in Figure 1, the difference between the temperature at which the shrinkage rate is 10% and the temperature at which the shrinkage rate is 50% is approximately 10°C in each comparative example.
However, at about 15° C., the shrinkage rate slowed by more than 50% for each film according to the invention.

<Effects of the Invention> The heat-shrinkable polyester film of the present invention is capable of slowing down the shrinkage speed during shrinkage, and becomes an excellent heat-shrinkable packaging material with extremely few film distortions, shrinkage spots, wrinkles, etc.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between temperature (horizontal axis) and shrinkage rate (vertical axis) for each film obtained in Examples of the present invention. Written amendment dated January 22, 1992 1. Indication of the case 1990 Patent Application No. 298042 2. Name of the invention Heat-shrinkable polyester film 3. Person making the amendment Relationship to the case Name of the patent applicant (206 ) Shin-Etsu Chemical Co., Ltd. 4, Agent Address: 4-4-11 Nihonbashi Honmachi, Chuo-ku, Tokyo 103
No. Nagai Building [Telephone 03-3270-0858] "Voluntary" 6. "Detailed description of the invention column" of the specification to be amended 7. Contents of the amendment

Claims (1)

[Claims] A heat-shrinkable polyester film made by blending and molding 40 to 70% by weight of a polybutylene terephthalate polymer with a polyethylene terephthalate polymer.