JPH0753737A - Shrinkable polyester film - Google Patents

Abstract

PURPOSE:To prepare a polyester film which has a good stretchability, an excellent uniformity in thickness, and a good bondability with a solvent, can provide wide heat-shrinking characteristics by the selection of stretching conditions, and exhibits tear resistance when stretched monoaxially. CONSTITUTION:This polyester film is produced by compounding 100 pts.wt. copolyester produced from a carboxylic acid component contg. terephthalic acid and/or isophthalic acid and a diol component comprising 50-95mol% ethylene glycol and 5-50mol% at least one glycol selected from the group consisting of diethylene glycol, tetramethylene glycol, 1,4-cyclohexanedimethanol, and a propanediol deriv. of the formula (wherein R1 and R2 are each a 1-6C linear or branched satd. hydrocarbon group) with 0.01-5 pts.wt. polycarboxylic anhydride, forming the resulting compsn. into a film, and stretching it.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester shrink film used for shrink labels, packaging and the like.

[0002]

2. Description of the Related Art Conventionally, as shrink labels used for glass bottles and polyethylene terephthalate (hereinafter referred to as PET) bottles, and shrink films for food packaging, stretched films made of polyvinyl chloride or polystyrene are mainly used. Came. But in recent years
The demand for polyester shrink films with excellent safety and hygiene, chemical resistance, and heat shrinkage characteristics has led to demand for terephthalic acid and ethylene glycol, neopentyl glycol, isophthalic acid, 1,4-cyclohexanedimethanol, etc. A stretched film made of a polyester obtained by copolymerizing the above has been proposed (for example, JP-A-57-42).
726, JP-A-63-156833).

[0003]

However, these copolymerized polyesters are inherently inferior in stretch processability to PET, and certain uniform stretching conditions (stretching temperature, stretch ratio, etc.) are required for uniform stretching. You have to choose. Therefore, the shrink film obtained, for example, the thickness and shrinkage at the central portion and the end portion of the transversely stretched film may differ depending on the location, and it is also difficult to obtain a shrinkable film according to various applications by appropriately changing the stretching conditions. is there. With respect to applications, for example, shrinkage of 30% or more in two directions for packaging and 60% or more in one direction is required for shrink labels.

[0004]

Means for Solving the Problems As a result of intensive studies to achieve these objects, the present inventors have found that a polycarboxylic acid anhydride is added to a copolyester obtained from a dicarboxylic acid component and a diol component having a specific composition. It was found that a polyester-based shrink film having uniform thickness and shrinkability, a wide range of shrinkage characteristics, solvent adhesion, tear resistance, etc. can be obtained by blending the materials and stretching the film. The invention has been reached.

That is, the present invention provides, as the dicarboxylic acid component,
Includes terephthalic acid and / or isophthalic acid, 50 to 95 mol% of ethylene glycol as a diol component, diethylene glycol, tetramethylene glycol, 1,
4-cyclohexanedimethanol, and

[Chemical 2] 100% by weight of a copolyester containing 5 to 50 mol% of one or more kinds selected from propanediol derivatives represented by (R ₁ and R ₂ are linear or branched saturated hydrocarbon groups having 1 to 6 carbon atoms) Part, 0.01 to 5 polycarboxylic acid anhydride
A polyester shrink film formed by blending parts by weight, formed into a film, and stretched, and a polycarboxylic acid anhydride are pyromellitic dianhydride, mellitic acid dianhydride, tetrahydrofuran tetracarboxylic acid dianhydride, or phthalic anhydride. The polyester shrink film is an acid anhydride having two or more groups.

The present invention will be described in detail below. Each component constituting the copolyester of the present invention is terephthalic acid and / or isophthalic acid as a dicarboxylic acid component,
The terephthalic acid content is preferably 70 to 95 mol%. On the other hand, ethylene glycol is 50 to 50 as the diol component.
95 mol%, preferably 70 to 85 mol%, and 5 to 50 of one or more selected from diethylene glycol, tetramethylene glycol, 1,4-cyclohexanedimethanol, and the propanediol derivative represented by the above chemical formula 2.
It is mol%, preferably 15 to 30 mol%. Examples of the propanediol derivative include neopentyl glycol, 2,2-diethyl-1,3-propanediol, and 2
Examples include -n-butyl-2-ethyl-1,3-propanediol.

The dicarboxylic acid component is preferably terephthalic acid and / or isophthalic acid from the viewpoint of ease of polymerization and physical properties, and the diol component cannot obtain solvent adhesiveness as a shrink film when ethylene glycol exceeds 95 mol%. If it is less than 50 mol%, the mechanical strength and stretchability of the film will be reduced, and heat shrinkage will reach saturation in a short time, causing shrinkage unevenness.

As a method for synthesizing the copolyester from the above-mentioned dicarboxylic acid component and diol component, a known method for obtaining polyester such as direct polymerization method or transesterification method can be used. The intrinsic viscosity, which is a measure of molecular weight, is
From the viewpoint of mechanical strength of the film, it is preferably 0.5 or more, more preferably 0.6 or more.

The polycarboxylic acid anhydride of the present invention can be selected from those having two or more carboxylic acid anhydride structures and reacting with the copolyester in the molten state to form a crosslinked structure,
Among them, pyromellitic dianhydride, mellitic trianhydride, tetrahydrofuran tetracarboxylic dianhydride, or acid anhydride having two or more phthalic anhydride groups is preferable. The acid anhydride having two or more phthalic anhydride groups is 3,
3 ', 4,4'-biphenyltetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride and the like. To be The blending amount of these polycarboxylic acid anhydrides is 0.0 with respect to 100 parts by weight of the copolyester.
If the amount is 1 to 5 parts by weight and less than 0.01 parts by weight, there is no effect of improving the drawability, and if it exceeds 5 parts by weight, gel (undissolved material) is generated and melt viscosity remarkably increases, and film formation is difficult. become.

The timing of compounding the polycarboxylic acid anhydride is not particularly limited as long as it is before the film-forming step, and the compounding method is a method of adding the compound to an autoclave in which polymerization of the copolymerized polyester is completed and mixing it, Any method can be selected, such as a method of preliminarily mixing and forming a film, a method of supplying a polycarboxylic acid anhydride to an extruder at the time of film formation, and mixing with a melted copolyester. The form of the polycarboxylic acid anhydride is not particularly limited, such as powder, granules, or masterbatch.

Copolymer components other than those described above can be added to the copolyester of the present invention within a range that does not significantly change the properties thereof. For example, dicarboxylic acids include adipic acid, oxalic acid, malonic acid, succinic acid, azelaic acid, sebacic acid, phthalic acid, 5-t-butylisophthalic acid, naphthalenedicarboxylic acid, diphenyletherdicarboxylic acid, cyclohexanedicarboxylic acid, 5-sulfone. Examples of the acid salt include isophthalic acid and dimer acid. Examples of the diol component include propylene glycol, hexamethylene glycol, polyalkylene glycol, and a diethoxy compound of bisphenol A or bisphenol S.

Further, oxycarboxylic acids such as p-oxybenzoic acid and p-oxyethoxybenzoic acid, benzoic acid,
Bezoylbenzoic acid, monofunctional compounds such as methoxypolyalkylene glycol, polyfunctional compounds such as glycerin, pentaerythritol, trimethylolethane, and trimethylolpropane, as long as the product can retain substantially linear polymer Can be used inside.

Further, other polyesters, other polymers or various additives may be added within the scope of the present invention. For example, known inorganic external particles such as kaolin, clay, calcium carbonate, silicon oxide, calcium terephthalate, aluminum oxide, titanium oxide, calcium phosphate, lithium fluoride as an inorganic lubricant and an organic lubricant for improving the slipperiness of a film. Insoluble high melting point organic compounds to be blended during melt film formation of polyester resin, and cross-linked polymers, and further formed inside polymers such as alkali metal compounds or alkaline earth metal compounds, such as metal compound catalysts used in polyester production. There are internal particles. Further, as additives, if necessary, stabilizers, colorants, antioxidants, ultraviolet absorbers and the like can be contained. The amount of the fine particles and additives added to the film is 0.
005 to 0.5 parts by weight is suitable.

Next, the film manufacturing method of the present invention will be specifically described. Using a copolyester blended with a polycarboxylic acid anhydride, an unstretched sheet is made by a known method such as a melt extrusion method or a calender method, and then a known roll stretching method, a tenter stretching method, a tubular stretching method, or the like, Depending on the application, uniaxial stretching, sequential biaxial stretching, simultaneous biaxial stretching and the like are performed. The film may have any shape such as a flat shape or a tube shape, and the thickness of the film is usually 2
0 to 200 μm is used. The draw ratio is 2.0 to 5.0 times in one direction or two directions, and more preferably 2.5 to 5.0 times.
The stretching temperature is 4.5 times, and the stretching temperature is appropriately selected depending on the stretching stress and the stretched film, but is usually 10 to 60 ° C. higher than the glass transition temperature. For high shrinkage,
In order to increase the draw ratio or draw at a relatively low temperature and suppress the shrinkage, on the contrary, select a low draw ratio and a high draw temperature.

By blending the polycarboxylic acid anhydride with the copolyester of the present invention, in stretching after film formation, there is no unevenness in thickness and heat shrinkability depending on the location of the film, and the range of stretching conditions is wide. Since it is wide, it is possible to make a shrink film suitable for various applications by appropriately selecting the stretching conditions. It is also excellent in low-temperature heat shrinkage properties, solvent adhesion, tear resistance, etc. required for shrink films.

[0016]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. The measurement and evaluation methods are shown below.

(1) Intrinsic viscosity ([η]) A sample concentration of 1 g / dl was used for the copolyester using a mixed solvent of phenol / tetrachloroethane = 50/50.
It was measured at 30 ° C.

(2) Glass transition temperature (Tg) Using an unstretched sheet, it was measured by DSC at a temperature rising rate of 10 ° C./min.

(3) Uniformity of Film Thickness After preheating an unstretched sheet to a temperature of Tg + 30 ° C., one end is fixed and the other is stretched (constant length in the direction perpendicular to stretching) Magnification 2
A ~ 5 times uniaxially stretched film was prepared. With respect to this film, the difference in thickness between the fixed end and the other end (moving end) was measured and evaluated as follows from the ratio to the average thickness. ○
Less than 10%, Δ 10 to 25%, and more than x 25%.

(4) Heat Shrinkage A test piece was taken from the center of the film prepared in the same manner as in (3) Evaluation of uniformity of film thickness, and immersed in a 100 ° C. glycerin bath for 30 seconds to measure the shrinkage.

(5) Solvent Adhesion Property (3) was prepared in the same manner as the film thickness uniformity evaluation,
Using the central part of the film with a draw ratio of 3 times, the two films were bonded together using tetrahydrofuran. Then, the adhesive strength and the appearance of the adhered portion were evaluated as follows. ○ Good, △ Adhesive but practically problematic, × Bad.

(6) Tear resistance A film having a draw ratio of 3 times produced in the same manner as the above evaluation was subjected to a tensile test in the direction perpendicular to the drawing and evaluated as follows. ○ Good, × Bad.

Examples 1 to 4 and Comparative Examples 1 to 4 First, using a stainless steel autoclave, each dimethyl ester of terephthalic acid and isophthalic acid and the diol component shown in Table 1 were transesterified at 230 ° C., and then 250 Polycondensation reaction was performed under reduced pressure at 280 ° C. to obtain a copolyester. Next, the copolyester and pyromellitic dianhydride were supplied to a T-die single-screw extruder, mixed and melt-extruded to form an unstretched sheet having a thickness of about 200 μ, and further uniaxially stretched to form a film. .
The composition of the copolyester, the intrinsic viscosity, the glass transition temperature, and the blending amount of pyromellitic dianhydride are shown in Table 1, and the gel generation state and the above-mentioned evaluation results are shown in Table 2.

Examples 5 to 7 The same copolymerized polyester as in Example 2 was added with 1 part by weight of mellitic dianhydride as a polycarboxylic acid anhydride (Example 5).
1 part by weight of tetrahydrofuran tetracarboxylic acid dianhydride (Example 6) or 1 part by weight of 3,3 ′, 4,4′-biphenyltetracarboxylic acid dianhydride (Example 7) was mixed and evaluated. . As a result, a gel was not generated in the obtained film, and it was possible to obtain a shrink film having a stretching ratio of 2 to 5 and excellent thickness uniformity, solvent adhesion, and tear resistance.

[0025]

[Table 1]

[0026]

[Table 2]

As shown in Table 2, in Examples, there is no problem of gel, solvent adhesion and tear resistance when uniaxially stretched are good, and a heat shrinkage ratio of uniform thickness at a draw ratio of 2 to 5 times. It was possible to obtain different shrink films. On the other hand, in the comparative example, a well-balanced shrink film was not obtained.

[0028]

EFFECT OF THE INVENTION The polyester shrink film of the present invention has excellent thickness uniformity, and can be used in a wide range of properties depending on the application by selecting the stretching conditions. It also has good tear resistance.

Claims (2)

[Claims] 1. A dicarboxylic acid component containing terephthalic acid and / or isophthalic acid, and a diol component containing 50 to 95 mol% of ethylene glycol, diethylene glycol, tetramethylene glycol, 1,4-cyclohexanedimethanol, and ] 100% by weight of a copolyester containing 5 to 50 mol% of one or more kinds selected from propanediol derivatives represented by (R ₁ and R ₂ are linear or branched saturated hydrocarbon groups having 1 to 6 carbon atoms) Part, 0.01 to 5 polycarboxylic acid anhydride
A polyester shrink film formed by blending parts by weight, forming a film, and stretching. 2. The polycarboxylic acid anhydride is pyromellitic dianhydride, mellitic acid dianhydride, tetrahydrofuran tetracarboxylic acid dianhydride, or an acid anhydride having two or more phthalic anhydride groups. 1. The polyester shrink film according to 1.