JPH04164929A - 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 an specifying the heat shrinkage ratio of the film. CONSTITUTION:This film is made from a polyester comprising a dicarboxylic acid 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-dibutyl-1, 3-propanediol or 2-ethyl-2-butyl-1, 3-- propanediol an has a heat shrinkage ratio as measured by immersion in a glycerol bath at 75 deg.C for 30sec of 40% or above in one the 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 shells, electric wire coverings, and the like.

<Prior Art> Conventionally, films made of polyvinyl chloride or polystyrene have been mainly used as films for plastic labels used for various containers including glass.

On the other hand, polyethylene terephthalate (hereinafter abbreviated as PET) bottles are becoming widely used mainly for food containers such as juice, alcohol, tea, and soy sauce. While heat-resistant PET bottles were the mainstream, in recent years, by adopting an aseptic filling method and omitting the hot water sterilization process, the use of low-cost non-heat-resistant PET bottles has been promoted. .

However, non-heat-resistant PET bottles undergo volume changes 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. , films that exhibit high shrinkage at lower temperatures are 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 in order to reuse the bottle and label without separating them, Polyester-based Nyulink films are also desired for label applications.

In response to these demands, it has recently been disclosed that by using an amorphous copolyester copolymerized with various diols or isophthalic acid, it is possible to obtain a film with a large shrinkage rate and excellent heat sealability. has been
For example, JP-A-63-156833, JP-A-63
-202429, Japanese Patent Publication No. 63-7573, etc.

However, among these films, films copolymerized with relatively good neopentyl glycol have a high glass transition temperature of around 75 degrees Celsius, and therefore, their thermal shrinkage behavior at temperatures above 80 degrees Celsius is said to be large and uniform. Although it exhibits relatively hard performance, it cannot be said to be sufficient, and thermal acid shrinkage 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 with a specific composition and a diol component in a specific ratio, The inventors have discovered that a polyester shrink film with excellent shrinkage properties can be obtained, and have arrived at the present invention. 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 5-30 moffi%,
Contains 0 to 10 mo 1% adipic acid, and 95 to 70 mo 1%, 2 ethylene glycol as a diol component.
, 2-dibutyl-1,3-propanediol or 2-
Ethyl-2-butyl-1,3-propanediol from 5 to
By a polyester shrink film containing 1% of 30mo and characterized in that the heat shrinkage rate of the film in 30 seconds in a 75°C glycerin bath is 40% or more in either the longitudinal direction or the transverse direction. achieved.

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 to 68 mon%, isophthalic acid
~30mo 1%, preferably 10~'l Q m o
1%, adipic acid from 0 to 10 mol%, preferably 3
Contains ~8 mol% of ethylene glycol as a diol component, preferably 95 to 70 mol%, preferably 92 to 80 mol%.
mo 1%, 2.2-dibutyl 1,3-propanediol or 2-ethyl-2-butyl-1,3-propanediol from 5 to 30 mo 1%, preferably 8 to 20
It is important to contain mol%.

A film with this composition ratio has excellent low-temperature heat shrinkage properties and does not wrinkle or sag, unlike conventional polyester shrink films made of other components, when it is attached to a bottle and passed through a shrink tunnel device to shrink the film. It is suitable as a shrink film for labels without the occurrence of such problems.

The reason for this is that polyesters with the above composition ratios tend to form a more uniform copolymerization form than those with other compositions, and therefore retain the excellent mechanical properties inherent to polyester, while maintaining the same characteristics as each other component. It can be said that it has a structure that makes it easy to maximize its strengths. 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 a low temperature range of less than 80'C.

In addition, by incorporating isophthalic acid, a large shrinkage rate can be obtained at the initial stage of heating when passing through the shrink equipment.
For further heating, 2,2-dipyl-1,3-propanediol or 2-ethyl-2
The gradual secondary shrinkage behavior believed to be caused by -butyl 1,3-propanediol corrects and equalizes 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 significantly decrease, making it difficult to obtain a satisfactory product. was impossible. Therefore, the purpose of the present invention can only be achieved by satisfying a specific range of composition ratios.

Further, all of the above composition components are industrially produced in large quantities and are suitable in terms of chemical properties.

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

On the other hand, as a diol component, 2,2-dibutyl-1,3
-propanediol or 2-ethyl-2-butyl-1
,3~When propanediol exceeds 30 mo1%, the strength and heat resistance of the film decrease;
If it is less than %, secondary shrinkage behavior becomes impossible, shrinkage spots are not eliminated, and wrinkles etc. occur, which is not preferable.

In the film of the present invention, copolymerized components other than the above-mentioned components may be contained within a range that does not change its properties.As components other than the above-mentioned components, examples of the dicarboxylic acid component include oxalic acid, malon tl! , succinic acid, azelaic acid, sebacic acid, phthalic acid, naphthalene dicarboxylic acid, diphenyl ether dicarboxylic acid, etc. Also, as a diol component, propylene glycol, trimethylene glycol, tetramethylene glycol, neopentyl glycol.

Other copolymer components that can contain hexamethylene glycol, diethylene glycol, polyalkylene glycol, 1,4-cyclohexane dimetatool, etc., such as oxocarboxylic acids such as p-okinobenzoic acid and p-okynethoquinobenzoic acid. , benzoic acid, hendylbenzoic acid.

Monofunctional compounds such as methoxypolyalkylene glycols, glycerinated pentaerythritol.

Polyfunctional compounds such as trimethylolethane and trimethylolethane may also be used to the extent that the product retains a substantially linear polymer.

Furthermore, other polyesters, other polymers, or various additives may be added to or mixed with the film of the present invention without changing the gist of the present invention. For example, inorganic lubricants that improve the lubricity of the film, kaolin, clay, calcium carbonate, silicon oxide, calcium terephthalate, organic lubricants, etc.
Known inert external particles such as aluminum oxide, titanium oxide, calcium phosphate, and lithium fluoride, insoluble high-melting point organic compounds, crosslinked polymers, alkali metal compounds, and alkaline earth metal compounds that are blended during melt film formation of polyester resins. Examples include internal particles formed inside the polymer during polyester production, such as metal compound catalysts used during polyester production. Also, if necessary, add stabilizer 9 to the colored side.

Antioxidant, antifoaming agent, etc. may be included. The fine particles contained in the film are usually 0.05 to 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.

If the intrinsic viscosity of the film is less than 0.50, the strength and impact resistance of the film tend to be insufficient.

The film of the present invention is prepared in a 75°C glycerin bath for 300°C in at least one of the longitudinal and transverse directions of the film.
The shrinkage rate in seconds is required to be 40% or more, preferably 40% or more.
It is 5% or more, more preferably 50% or more. Films with a shrinkage rate of less than 40% are not preferable because they cannot adhere sufficiently to the container because the set temperature of the shrinkage zone is low, less than 80°C, in the case of unfavorable films used for non-heat-resistant PET bottles.

Further, the glass transition temperature of the polyester constituting the film of the present invention is preferably 50°C or more and 70°C or less, 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 tunnel at a temperature of less than 80°C, it will not be able to sufficiently adhere to the container due to insufficient shrinkage. <, sagging is likely to occur. Furthermore, if the glass transition temperature is less than 50° C., problems tend to occur 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 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 this direction is performed to solve the problem of poor impact resistance and tear resistance of the film stretched in this direction. It is done. There is no particular restriction on the stretching means, and methods such as coal 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, l-axis stretching, or a combination thereof. Particularly in biaxial stretching, successive biaxial stretching in which one of the longitudinal and lateral directions is carried out first is effective. Note that the heat cent in the stretching may be carried out depending on the purpose, but it is recommended that the film be passed through a heating zone of 90° C. or lower for 1 to 30 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 is heat-shrinkable at a low temperature of less than 80°C, has excellent adhesion to PET bottles, and is free from shrinkage spots, whitening, wrinkles, etc. This is a polyester shrink film that is invisible and has an excellent appearance, making it 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 measurement and evaluation methods are 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) PerkinElmer DS (, -IB, heating rate 4
Measured at °C/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 allowed to shrink by passing through a shrink tunnel at a set temperature of 75°C. After passing through the tunnel, it was visually determined whether the film had sufficient adhesion, and those with good adhesion were marked with ◯, and those with poor adhesion were marked with ×. In addition, shrinkage spots on the film were determined visually by whether the upper end or the lower end was slanted or distorted after shrinkage, and similarly expressed as Q and x.

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 6> Dimethyl terephthalate, dimethyl isophthalate.

Ethylene glycol, 2,2-dibutyl-1,3-propanediol or 2-ethyl-2-butyl-1,3-
Propanediol was blended in the proportions shown in Table 1, and 0.05 mol of calcium acetate hydrate was placed in a stainless steel autoclave as a catalyst, and heated at 150 to 24 mol under a nitrogen stream.
The transesterification reaction was carried out at 0'C. Next, adipic acid, antimony trioxide 400ppm (based on polymer)
, 10,100 pp of trimethyl phosphate to polymer] was added to carry out esterification. After esterification, 2
The temperature was raised to 80°C and polycondensation was performed under reduced pressure to produce polyester. Using this polyester, 270
It was melted at °C and extruded through a T-die to obtain an unstretched film with a thickness of 180 μm.

The film was preheated and stretched 1.2 times in the machine direction, and then stretched 4 times in the cross direction to obtain a stretched film with a thickness of 40 μm.

When this film was tested on a PET bottle, as shown in Table 1, it had excellent low-temperature shrinkability and no wrinkles.

A high-quality shrink film with no whitening, shrinkage spots, etc., good adhesion, and excellent appearance was obtained.

<Comparative Examples 1 to 9> Polyesters were produced by blending dicarboxylic acid components and diol components in the proportions shown in Table 1 in the same manner as in Examples, and film formation and stretching were performed.

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-dibutyl-1,3-
propanediol or 2-ethyl-2-butyl-1,
Contains 5 to 30 mol% of 3-propanediol, and 7
A polyester shrink film characterized in that the heat shrinkage rate of the film after 30 seconds in a 5°C glycerin bath is 40% or more in either the machine direction or the transverse direction.