JPH04164928A - Shrink polyester film - Google Patents

Abstract

PURPOSE:To obtain the title film excellent in low-temperature shrinkability and adhesion to a bottle and free from uneven shrinkage, whitening, wrinkling, etc., by using a polyester comprising specified components and specifying the heat shrinkage ratio of the film. CONSTITUTION:This film is made from a polyester comprising a dicarboxylic acid component composed of 95-60mol% terephthalic acid, 5-30mol% isophthalic acid and 0-10mol% adipic acid and a diol component composed of 95-70mol% ethylene glycol and 5-30mol% 2, 2-diethyl-1, 3-propanediol and has a heat shrinkage ratio as measure by immersion in a glycerol bath at 75 deg.C for 30sec of 40% or above in lengthwise and/or crosswise directions.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a polyester shrink film that has excellent low-temperature heat shrink properties and is used for shrink labels, electric wire coverings, and the like.

<Prior Art> Conventionally, films made of polyvinyl chloride or polyethylene have been mainly used as shrink label films used for various containers including glass.

On the other hand, polyethylene terephthalate (hereinafter abbreviated as PET) bottles are becoming widely used mainly as food containers for juice, alcohol, tea, soy sauce, oil, etc.
Traditionally, heat-resistant PET bottles that can withstand hot water sterilization have been the mainstream type of bottle, but in recent years, aseptic filling methods have been adopted to omit the hot water sterilization process and reduce costs. The use of PET bottles with low heat resistance is being promoted.

However, non-heat-resistant PET bottles undergo a volume change when heated to temperatures above 80°C, so films such as polyvinyl chloride or polystyrene, which have a high shrinkage rate at temperatures above 80°C, cannot be used. First, a film that exhibits high shrinkage at lower temperatures is desired. Also,
It is industrially and socially required that PET bottles be collected and reused. Therefore, if the bottle and label have different compositions, a separation process is required, so it is recommended that the bottle and label be reused without being separated. Polyester-based TSUYLINK films are also desired for label applications.

In response to these demands, it has recently been disclosed that a film with a large shrinkage rate and excellent heat sealability can be obtained by using an amorphous copolyester copolymerized with various diols or isophthalic acid, etc. and
Examples include JP-A-63-156833, JP-A-63-202429, and JP-B-63-7573.

However, among these films, films copolymerized with relatively good neopentyl glycol have a high glass transition temperature of around 75°C, and therefore have a high shrinkage rate and uniform shrinkage behavior at temperatures above 80°C. Although it exhibits relatively strong performance, it cannot be said to be sufficient. Furthermore, thermal shrinkage behavior at temperatures below 80° C. has the disadvantage that walnuts occur due to insufficient shrinkage.

On the other hand, films copolymerized with isophthalic acid can lower the glass transition temperature to around 65°C,
A large shrinkage rate can be obtained even at temperatures below 80°C. However, when this film is heated in a shrink tunnel device, it shrinks instantly at the initial stage of heating, and exhibits a unique shrinkage behavior in which it hardly shrinks any further when heated. Shrinkage spots occur, causing wrinkles, waves, etc.

In order to improve these problems, attempts have been made to adjust the heat shrinkage rate, seal strength, heat shrinkage stress, etc., but it is very difficult to control these well in the actual operating process, and it is difficult to control these properly in the actual operating process. This also tends to cause shrinkage spots on the film, resulting in frequent problems such as the upper or lower end of the label being slanted after shrinkage and the design becoming distorted.

<Problems to be Solved by the Invention> In order to achieve these problems, the present inventors have made extensive studies and found that by blending a dicarboxylic acid component and a diol component with a specific composition in a specific ratio, the present inventors have achieved low-temperature heat shrinkage. The present invention was achieved by discovering that a polyester shrink film with excellent properties can be obtained. That is, an object of the present invention is to provide a shrink film that has excellent low-temperature heat shrinkability, good adhesion to PET bottles, and is free from shrinkage spots, whitening, and wrinkles, and has an excellent appearance. There is a particular thing.

Means for Solving the Problems> The above object is such that the polyester constituting the film contains 95 to 60 m of terephthalic acid as a dicarboxylic acid component.
o 1%, isophthalic acid 5-30m01%, adipic acid 0-10m01%, as a diol component, ethylene glycol 95-70m01%, 2,2
- 5 to 3 Qmo of diethyl-1,3-propanediol
j! %, and the heat shrinkage rate of the film after 30 seconds in a 75° C. glycerin bath is 40% or more in either the machine direction or the transverse direction.

The present invention will be explained in detail below.

The composition ratio of each component constituting the polyester film of the present invention is one of the important requirements in the present invention.
%, preferably 85-68 mo/%, isophthalic acid
~30mO7! '%, preferably 10-20mo 1%
, 0 to 10 mon% adipic acid, preferably 3 to 8 m
Contains Oβ%, and as a diol component, ethylene glycol is 95 to 70 m o 12%, preferably 92 to 8
0 m o 1%, 2.2-diethyl-1,3-propanediol 5-30 mo A%, preferably 8-20
It is essential to contain m o 44%.

When the film having the above composition ratio is passed through a shrink tunnel device after being attached to a bottle to shrink the film,
Unlike conventional polyester-based shrink films made of other compositions, this film has excellent low-temperature heat shrink properties and is free from wrinkles, sagging, etc., making it suitable as a tsuyu-link film. The reason is that those with the above composition ratio tend to form a more uniform copolymerization form than those with other compositions,
Therefore, it can be said that it has a structure that maintains the excellent mechanical performance inherent to polyester, and also allows the advantages of each of the other components to be maximized. By blending isophthalic acid or adipic acid, the glass transition temperature can be lowered and the shrinkage start temperature can be lowered, so that sufficient heat shrinkage can be achieved even in the low temperature range of less than 80°C. In addition, due to the isophthalic acid formulation, a large shrinkage rate can be obtained at the initial stage of heating when passing through the shrink equipment, and the shrinkage rate is 2°2 for subsequent heating.
The gradual secondary shrinkage behavior, which is believed to be caused by -diethyl-1,3-propanediol, corrects and evens out the shrinkage spots that tend to occur during initial shrinkage, and further allows for finishing shrinkage. In order to obtain excellent heat shrinkage behavior at temperatures below 80°C, it is necessary to contain a suitable amount of isophthalic acid or adipic acid, but if too much is added, the strength of the film will be significantly reduced, making it difficult to obtain a satisfactory product. It was impossible to obtain. Therefore, the purpose of the present invention can only be achieved by satisfying a specific range of composition ratios. Moreover, all of the components of the above composition are industrially produced in large quantities and are suitable in terms of productivity.

Regarding the combination of each component in the present invention, as the dicarboxylic acid component in the film, isophthalic acid is
If 0mo exceeds 1%, the solvent resistance of the film will decrease, which is undesirable.On the other hand, if 5mo! If it is less than %, the shrinkage rate decreases, which is not preferable. In addition, adipic acid is 10moR%
If the temperature exceeds 100%, the glass transition temperature of the film decreases, and cracking, discoloration, and deterioration become significant.

In addition, as a diol component, 2,2-diethyl-1,3
- If propanediol exceeds 30mo 1%, the strength and heat resistance of the film will decrease, while if it is less than 5mo 1%, secondary shrinkage behavior will not be possible, shrinkage spots will not be eliminated, and wrinkles etc. Occurs and is undesirable.

The film of the present invention may contain copolymer components other than the above-mentioned components within a range that does not change its properties. Ingredients other than those listed above include dicarboxylic acid components such as sulfuric acid, malonic acid, succinic acid, azelaic acid, sebacic acid, phthalic acid, naphthalene dicarboxylic acid, diphenyl ether dicarboxylic acid, etc., and diol components such as propylene glycol and tricarboxylic acid. Methylene glycol, tetramethylene glycol, neopentyl glycol.

Hexamethylene glycol, diethylene glycol, polyalkylene glycol, 1,4-cyclohexane dimetatool, etc. can be contained.

In addition, other copolymerizable components, such as oxycarboxylic acids such as p-oxybenzoic acid and p-oxyethoxybenzoic acid, monofunctional compounds such as trihenzoylbenzoic acid, methoxypolyalkylene glycol, glycerin, and pentaerythritol. Polyfunctional compounds such as , trimethylolethane, and trimethylolpropane may also be used to the extent that the composition can maintain a substantially linear polymer.

Furthermore, other polyesters, other polymers, or various additives may be added or mixed with the film of the present invention without changing the gist of the present invention. For example, inorganic lubricants that improve the slipperiness of the film, such as kaolin, clay, and calcium carbonate, are used as lubricants.

Known inert external particles such as silicon oxide, calcium terephthalate, aluminum oxide, titanium oxide, calcium phosphate, lithium fluoride, insoluble high-melting point organic compounds, crosslinked polymers, alkali metal compounds, etc. that are blended during melt film formation of polyester resins. Examples include internal particles formed inside the polymer during the production of polyesters such as metal compound catalysts used in the production of polyesters such as alkaline earth metal compounds. Further, if necessary, the stabilizer 1 may contain a colorant, an antioxidant, an antifoaming agent, and the like.

The fine particles contained in the film usually have a particle size of 0,005 to
It is 0.5% by weight.

Further, the intrinsic viscosity of the film of the present invention is preferably 0.
It is 5 or more, more preferably 0.60 or more, still more preferably 065 or more. If the intrinsic viscosity of the film is less than 0.50, the crystallinity will be high and a sufficient shrinkage rate will tend not to be obtained.

The film of the present invention must have a shrinkage rate of 40% or more in at least one of the vertical and horizontal directions in a 75°C glycerin bath for 30 seconds, preferably 45% or more.
% or more, more preferably 50% or more. Shrinkage rate is 4
A film with a content of less than 0% is not preferable because in a shrink tunnel used for non-heat-resistant PET bottles, the set temperature of the shrink zone is as low as less than 80° C., so that it cannot adhere sufficiently to the container.

Further, the glass transition temperature of the polyester constituting the film of the present invention is preferably 50 to 70°C, more preferably 65°C or less.

If the temperature exceeds 70°C, it will be difficult to lower the shrinkage start temperature of the film, and therefore, even if the film is passed through a shrink tube at a temperature of less than 80°C, it will not shrink sufficiently and will not adhere to the container sufficiently. Niri <, sagging occurs and becomes thick. Furthermore, if the glass transition temperature is less than 50° C., problems arise in storage and handling of the shrink film as an unshrinkable film.

Next, the film manufacturing method of the present invention will be described.

Using a polyester having the composition of the present invention, a film obtained by any method such as an extrusion method or a calendar method is produced, for example, by 2.0 times or more and 5.0 times or less in one direction, preferably 2.0 times or more and 5.0 times or less in one direction.
Stretched 5 times or more and 4.5 times or less, and 1
．． 0 times or more and 2.0 times or less, preferably 1.1 times or more and 1.
Stretch to 8 times or less. The initial stretching is performed to obtain a high shrinkage rate, and the stretching in the direction perpendicular to the above direction is performed to solve the problem of poor impact resistance and tear resistance of the film stretched in this direction. It can be done. There is no particular restriction on the stretching means, and methods such as roll stretching and tenter stretching may be applied, and the shape may be flat, tubular, etc.

Further, the stretching may be carried out by sequential biaxial stretching, simultaneous biaxial stretching, uniaxial stretching, or a combination thereof. In particular, in biaxial stretching, the stretching in the longitudinal and lateral directions is
Sequential biaxial stretching in which one is performed first is effective.

The heat setting in these stretching processes is carried out depending on the purpose, and the heating zone is set at 90°C or less for 1 second to 30°C.
It is recommended to pass for 2 seconds. The thickness of the film thus obtained is not particularly limited, but a range of 5 to 250 μm is practical.

(Effects of the Invention) As described above, the polyester shrink film that satisfies the constituent requirements of the present invention has a temperature lower than 80°C due to the action of copolymer components such as isophthalic acid and 2,2-diethyl-1,3-propanediol. It is a low-temperature heat-shrinkable polyester-based TSUYLINK film that has good shrinkage behavior, excellent adhesion to PET bottles, and an excellent appearance with no shrinkage spots, whitening, or wrinkles. , is extremely useful industrially.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited to these Examples.

The method for measuring and evaluating the film is shown below.

(1) Shrinkage rate The film was heat-shrinked in a 75°C±0.5°C glycerin bath for 30 seconds under no load and was determined according to the following formula.

(2) Intrinsic viscosity [η] 200 mg of sample is phenol/tetrachloroethane = 5
Add to 20 ml of mixed solvent of 0150 and add 1 at about 110°C
After heating and dissolving for a period of time, measurements were taken at 30°C.

(3) Glass transition temperature/Tg (''C) Heating rate: 4℃ by PerkinElmer DSC-IB
/min.

(4) Evaluation as a Shrink Film The film was made into a cylindrical shape as a shrink label, placed on a PET bottle, and passed through a shrink tunnel at a set temperature of 75°C to shrink. After passing through the tunnel, it was visually determined whether the film had sufficient adhesion, and those with good adhesion and those with poor O9 were marked with an x. In addition, shrinkage spots on the film were determined visually to see if the upper end or lower end was slanted or distorted after shrinkage, and similarly marked with ○ and ×.

As a comprehensive evaluation, a film that satisfies the above two items and shows no whitening, wrinkles, etc. in the film after shrinkage is rated ○, and a film that does not is rated x.

<Examples 1 to 3> Dimethyl terephthalate, dimethyl isophthalate.

Ethylene glycol and 2I 2-diethyl-1,3propanediol were blended in the proportions shown in Table 1, and calcium acetate hydrate was used as a catalyst at 0.05 moj! was placed in a stainless steel autoclave and heated for 150 to 240 minutes under a nitrogen stream.
The transesterification reaction was carried out at °C.

Then further adipic acid, antimony trioxide 400ppm
(for polymer), trimethyl phosphate 1o.

ppm (based on polymer) was added to carry out esterification.

After the esterification was completed, the temperature was raised to 280°C, and polycondensation was performed under reduced pressure to produce polyester.

([η] = 0.68) Using this polyester, melt it at 270°C with an extruder and extrude it through a T-die to a thickness of 180 μm.
An unstretched film of m was obtained.

The film was stretched 1.2 times in the machine direction and then 4.0 times in the cross direction to obtain a heat-shrinkable film with a thickness of 40 Im.

When this film was mounted on a PET bottle and tested, as shown in Table 1, a high-quality film with excellent low-temperature heat shrinkage properties, no wrinkles, whitening, shrinkage spots, etc., good adhesion, and an excellent appearance was obtained. .

Comparative Examples 1 to 3> By the same method as in the example, a dicarboxylic acid component and a diol component were blended in the proportions shown in Table 1, polyester was manufactured, and film formation and stretching were performed.

Comparative example 1. Both Comparative Example 3 had insufficient shrinkage, and Comparative Example 2
The shrinkage was sufficient, but distortion occurred around the heat-sealed part, resulting in slightly poor adhesion.

<Comparative Examples 4 to 6> Dicarboxylic acid components and diol components were blended in the proportions shown in Table 1, polycondensation was performed by a direct esterification method using antimony dioxide as a catalyst, polyester was produced, and film formation and stretching were performed. went.

Comparative Example 4 had sufficient shrinkage characteristics, but the glass transition temperature was too low, causing problems in handling.

Claims (1)

[Claims] (1) The polyester constituting the film contains 95 to 60 mol% of terephthalic acid, 5 to 30 mol% of isophthalic acid, and 0 to 10 mol% of adipic acid as dicarboxylic acid components.
Contains 95 to 70 mol% of ethylene glycol as a diol component, 2,2-diethyl-1,3-
Contains 5-30 mol% of propanediol and 75°C
A polyester shrink film characterized in that the heat shrinkage rate of the film after 30 seconds in a glycerin bath is 40% or more in either the machine direction or the transverse direction.