JP2781598B2 - Polyester shrink film - Google Patents

Description

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

<Problems to be solved by conventional technology and invention> Conventionally, as a film for shrink label used for various containers including glass, polyvinyl chloride,
Alternatively, films made of polystyrene have been mainly used. However, in recent years, polyethylene terephthalate (hereinafter abbreviated as PET) bottles have become widespread, mainly for food containers such as juice, sake, tea, soy sauce, and oil. While heat-resistant PET bottles that can withstand the mainstream, in recent years the adoption of aseptic filling has eliminated the need for hot water sterilization and disinfection, and the use of low-cost non-heat-resistant PET bottles has been promoted. I have. However heat-resistant PET
Since the bottle undergoes a volume change when a temperature of about 80 ° C. or higher is applied, the above-mentioned film of polyvinyl chloride or polystyrene showing a high shrinkage at 80 ° C. or higher cannot be used, and at a lower temperature. A film having a high shrinkage is desired. In addition, it is industrially and socially required to collect and reuse PET bottles.Therefore, it is difficult to separate PET bottles and labels with different compositions. Also, polyester shrink films are desired for label applications.

To meet such demands, recently, by using an amorphous copolyester obtained by copolymerizing neopentyl glycol or isophthalic acid, a film having a large shrinkage rate and excellent heat sealability can be obtained. Are disclosed in JP-A-63-156833, JP-A-63-202429, and JP-B-63-7573.

However, the film obtained by copolymerizing neopentyl glycol has a high glass transition temperature of around 75 ° C, and as a result, it exhibits excellent heat shrinkage and uniform shrinkage at 80 ° C or higher. The heat shrinkage behavior at a temperature of less than 80 ° C. has a drawback that tarmi occurs due to insufficient shrinkage or the like.

Further, a film obtained by copolymerizing isophthalic acid can lower the glass transition temperature to around 60 ° C.
A large shrinkage can be obtained even at a temperature lower than ℃. However, when this film is heated in a shrink tunnel device, it shrinks instantly in the initial stage of heating,
Since the film exhibits a unique shrinkage behavior that hardly shrinks even with subsequent heating, the film has uneven shrinkage, wrinkles, ripples, and the like. Attempts to adjust the heat shrinkage, seal strength, heat shrinkage stress, etc. have been proposed to improve these problems, but it is very difficult to control these in the actual operation process, and it is very difficult to control them. Due to the fluctuation, unevenness of contraction is easily generated in the film, and the upper end or lower end of the label after contraction becomes oblique, and the distortion of the design frequently occurs.

An object of the present invention is to provide a shrink film having excellent low-temperature heat shrinkage properties, good adhesion to a PET bottle, no shrinkage spots, whitening and wrinkles, and excellent appearance. is there.

<Means for Solving the Problems> The present inventors have conducted intensive studies in order to achieve these objects, and as a result, by mixing a dicarboxylic acid component and a diol component having a specific composition in a specific ratio, a low-temperature heat shrinkage has been achieved. The inventors have found that a polyester-based shrink film having excellent properties can be obtained, and have reached the present invention.

That is, in the present invention, the composition of the polyester constituting the film, terephthalic acid as a dicarboxylic acid component 95-70.
mol%, isophthalic acid 5 to 30 mol%, ethylene glycol 90 to 40 mol%, diethylene glycol 5 to 30 mol%, neopentyl glycol 5 to 30 mol% as a diol component, and 75 seconds in a glycerin bath at 75 ° C. A polyester shrink film, characterized in that the heat shrinkage of the film is 40% or more in any one of a longitudinal direction and a transverse direction.

 Hereinafter, the present invention will be described in detail.

The composition ratio of each component of the polyester constituting the polyester film of the present invention is one of the important requirements in the present invention, and the composition ratio is 95 to 70 mol%, preferably 90 to 80 mol% of terephthalic acid as a dicarboxylic acid component. 5 to 30 mol%, preferably 10 to 20 mol% of isophthalic acid, 90 to 40 mol%, preferably 84 to 50 mol% of ethylene glycol as a diol component and 5 to 30 m% of diethylene glycol.
ol%, preferably 8 to 25 mol%, and 5 to 30 mol%, preferably 8 to 25 mol% of neopentyl glycol are within the ranges that can be contained.

When the film made of polyester having the composition ratio passes through the shrink tunnel device after being attached to the bottle and shrinks the film, unlike a conventional polyester shrink film made of other components, it has excellent low-temperature heat shrink properties, It is suitable as a shrink film for labels without wrinkles and tarls. The reason is that the composition having the above composition ratio is easier to adopt a more uniform copolymerization form than the other component compositions, so that the original excellent mechanical performance of the polyester is maintained, and the advantages of each of the other components are also obtained. It can be said that the structure is such that it is easy to exert the maximum. That is, depending on the diethylene glycol component, the effect of lowering the glass transition temperature lowers the shrinkage initiation temperature of the film, making it possible to use the film sufficiently even in a low temperature range of less than 80 ° C., and depending on the isophthalic acid component, a shrink device. A large contraction rate is obtained in the early stage of heating when passing through the inside, and for the subsequent heating, it occurs at the initial contraction due to the gradual secondary shrinkage behavior that seems to be due to the neopentyl glycol component. Correction of uniform shrinkage, uniformity, and shrinkage of finish are performed. Also, when the glass transition temperature is usually lowered, the film tends to cause sticking, and the color tends to be yellowish, and the thermal stability tends to be lacking. Also exhibit excellent effects.

Regarding the mixing ratio of each component in the present invention,
When isophthalic acid is more than 30 mol% as a dicarboxylic acid component in the polyester constituting the film, the solvent resistance of the film is lowered, which is not preferable. On the other hand, when it is less than 5 mol%, the shrinkage is lowered, which is not preferable. On the other hand, if the content of diethylene glycol exceeds 30 mol%, the heat resistance is remarkably reduced. On the other hand, if the content is less than 5 mol%, no decrease in the glass transition temperature is observed. As a diol component, neopentyl glycol
If it exceeds 30 mol%, the strength and heat resistance of the film decrease, while if it is less than 5 mol%, secondary shrinkage behavior becomes impossible, shrinkage spots are not eliminated, and wrinkles and the like are undesirably generated.

The polyester constituting the polyester film of the present invention may contain a copolymer component other than the above components as long as the properties of the film are not changed. Components other than the above components include oxalic acid, malonic acid, succinic acid, adipic acid, azelaic acid, and dicarboxylic acid components.
One kind of dicarboxylic acid such as sebacic acid, phthalic acid, naphthalenedicarboxylic acid, diphenyl ether dicarboxylic acid,
Or two or more diol components such as propylene glycol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, polyalkylene glycol, and 1,4-cyclohexane dimethanol. Can be contained.

Still other copolymerization components, e.g., p-oxybenzoic acid, p
An oxycarboxylic acid such as oxyethoxybenzoic acid,
Monofunctional compounds such as benzoic acid, benzoyl benzoic acid, and methoxy polyalkylene glycol; and polyfunctional compounds such as glycerin pentaerythritol, trimethylol, and trimethylenepropane, also have substantially linear polymers in their products. It can be used as far as possible.

Further, other polyesters or polymers or various additives can be added and mixed within a range not changing the gist of the present invention. For example, known inert external particles such as kaolin, clay, calcium carbonate, silicon oxide, calcium terephthalate, aluminum oxide, titanium oxide, calcium phosphate, and lithium fluoride as inorganic lubricants and organic lubricants for improving the lubricity of the film; Formed inside the polymer during the production of polyester, such as a metal compound catalyst used in the production of polyester such as an insoluble high melting point organic compound, a crosslinked polymer, an alkali metal compound or an alkaline earth metal compound to be blended during melt film formation of a polyester resin. There are internal particles. As additives, stabilizers, colorants, antioxidants, defoamers, and the like can be contained as necessary. The fine particles contained in the film are 0.005 to
0.5% by weight.

The intrinsic viscosity of the film of the present invention is 0.50 or more, preferably
It is 0.60 or more, more preferably 0.65 or more. If the intrinsic viscosity of the film is less than 0.50, the mechanical strength becomes weak, and a sufficient shrinkage cannot be obtained, which is not preferable.

The film of the present invention has a shrinkage ratio in a glycerin bath at 75 ° C. for 30 seconds in any one of the vertical and horizontal directions of the film.
At least 40% is required, preferably at least 45%, more preferably at least 50%. A film having a shrinkage ratio of less than 40% is not preferable because a shrink tunnel used for a non-heat-resistant PET bottle has a low setting temperature of a shrinkage zone of less than 80 ° C. and thus cannot sufficiently adhere to a container.

It is important that the polyester constituting the film of the present invention has a glass transition temperature of 70 ° C. or lower, preferably 65 ° C. or lower. If the temperature exceeds 70 ° C., it becomes impossible to lower the shrinkage starting temperature of the film, and
Even if it passes through a shrink tunnel having a temperature of less than 0 ° C., it cannot be sufficiently adhered to the container due to insufficient shrinkage, and undesirably causes tarmi. Therefore, by setting the glass transition temperature to 70 ° C. or lower, the non-heat-resistant PE targeted by the present invention can be obtained for the first time.
It becomes a shrink film that can be used for T bottles. On the other hand, if the glass transition temperature is less than 50 ° C., there is a problem in storage and handling of the shrink film in the non-shrink film, which is not preferable.

Next, the film production method of the present invention will be specifically 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 2.0 times or more in one direction, 5.0 times or less, preferably 2.5 times or more and 4.5 times or more.
It is stretched 1.0 times or less, preferably 1.1 times to 1.8 times in a direction perpendicular to the direction. The first stretching is performed in order to obtain a high shrinkage, and the stretching in the direction perpendicular to the direction is performed in order to solve the poor impact resistance and tear resistance of the film stretched in the direction. It is. There is no particular limitation on the stretching means, and methods such as roll stretching and tenter stretching are applied, and the shape may be flat, tubular, or the like.

The stretching is successive biaxial stretching, simultaneous biaxial stretching, uniaxial stretching,
Alternatively, the film is stretched in a uniaxial direction, a uniaxial direction, a biaxial direction, or the like for the film of the present invention.
Successive biaxial stretching that performs either one first is effective,
Either order may be given first, and when performing the simultaneous biaxial stretching method, the stretching order may be any of vertical and horizontal simultaneous, vertical leading and horizontal leading. The heat setting in these stretchings is performed according to the purpose, but it is recommended to pass through a heating zone at 90 ° C. or lower for 1 second to 30 seconds. The thickness of the film thus obtained is not particularly limited, but is 5 to 25.
A range of 0 μm is practical.

<Examples> Hereinafter, the present invention will be described more specifically 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 The film was thermally shrunk in a glycerin bath at 75 ° C. ± 0.5 ° C. with no load for 30 seconds, and the shrinkage was determined according to the following equation.

(2) Intrinsic viscosity [η] 200 mg of sample was phenol / tetrachloroethaneethane = 5
The solution was added to 20 ml of a 0/50 mixed solvent, dissolved by heating at about 110 ° C. for 1 hour, and then measured at 30 ° C.

(3) Glass transition temperature / Tg (° C) Temperature rise rate 4 ° C / mi using DSC-1B manufactured by PerkinElmer
Measured at n.

(4) Evaluation as Shrink Film After making the film into a cylindrical shape as a shrink label, the film was put on a PET bottle and shrunk by passing through a shrink tunnel at a set temperature of 75 ° C. After passing through the tunnel, it is visually determined whether or not the film is sufficiently adhered.
Was evaluated. Whether the upper end or lower end of the film was oblique or distorted after shrinkage was visually judged, and the shrinkage spots were evaluated with ， and ×.

When the above two items were satisfied as a comprehensive evaluation, the film after shrinkage showed no whitening, wrinkles, sticking between the films, coloring, etc. at all, and the one not at all did not.

Example 1 Using a stainless steel autoclave, terephthalic acid as a dicarboxylic acid component was 85 mol%, and isophthalic acid was 15 m
ol%, 60 mol of ethylene glycol as diol component
%, Diethylene glycol 20 mol%, neopentyl glycol 20 mol%, and antimony trioxide 0.0 as a catalyst.
Polycondensation was carried out by a direct esterification method using 5 mol (based on the acid component). This copolymer has [η] = 0.68, Tg = 61 ° C.
Met.

Using this polyester, it is melted at 270 ° C with an extruder,
It was extruded from a T-die to obtain an unstretched film having a thickness of 180 μm.

The film is stretched 1.2 times in the machine direction and then in the machine direction.
It was stretched 4.0 times to obtain a heat-shrinkable film having a thickness of 40 μm.
When this film was mounted on a PET bottle and tested, it was of high quality without any wrinkles or shrinkage spots.

Examples 2 to 3 In the same manner as in Example 1, a polyester having a composition in which each component described in Table 1 was blended was obtained. Both were excellent in low-temperature heat shrinkage characteristics and were suitable as shrink films.

Comparative Examples 1 to 7 Polyesters having the compositions shown in Table 1 were obtained in the same manner as in the examples. In Comparative Examples 1, 3, 4, and 6, shrinkage was insufficient, and in Comparative Examples 2, 5, and 7, shrinkage was sufficient, but uneven shrinkage or distortion occurred around the heat seal portion.

<Effect of the Invention> A film satisfying the constitutional requirements of the present invention has a heat shrinkage initiation temperature of 80 by mixing a specific ratio of diethylene glycol.
It has a thermal stability such that the temperature can be lowered to less than 0 ° C., and furthermore, sticking between the films is prevented and discoloration is not caused. In addition, by the action of other copolymer components such as isophthalic acid and neopentyl glycol, the shrinkage behavior is good,
A low-temperature heat-shrinkable polyester shrink film having excellent adhesion to PET bottles and excellent appearance without showing shrinkage spots, whitening and wrinkles can be provided, and is extremely useful in industry.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08L 67:02

Claims (2)

(57) [Claims] The composition of the polyester constituting the film is such that the terephthalic acid is 95 to 70 mol as a dicarboxylic acid component.
5 to 30 mol% of isophthalic acid, 90 to 40 mol% of ethylene glycol as a diol component, 5 to 30 mol% of diethylene glycol, and 5 to 5% of neopentyl glycol.
A polyester shrink film containing about 30 mol% and having a heat shrinkage of 40% or more in one of a longitudinal direction and a transverse direction in a glycerin bath at 75 ° C. for 30 seconds. 2. The polyester shrink film according to claim 1, wherein the glass transition temperature of the polyester constituting the film is 50 ° C. or more and 70 ° C. or less.