JPH08244114A - Polyester type shrinkable film - Google Patents

Abstract

PURPOSE: To provide a polyester type shrinkable film showing unidirectional shrinkability in its longitudinal direction and excellent in mechanical characteristics and heat resistance in a biaxial direction. CONSTITUTION: In a film composed of polyester with an m.p. of 170-250 deg.C, the shrinkage factor (Sm) in the longitudinal direction of the film in hot air of 100 deg.C is 20% or more and the shrinkage factor (St) in the lateral direction thereof is Sm×2/3 or less and both of the refractive indexes in the longitudinal and lateral directions of the film are 1.590 or more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester-based shrinkable film which exhibits a high shrinkage ratio in the longitudinal direction and is excellent in mechanical strength in both the longitudinal and widthwise directions and which is used for shrinkable labels, food packaging and the like. It is a thing.

[0002]

2. Description of the Related Art Conventionally, stretched films made of polyvinyl chloride or polystyrene have been mainly used as shrink labels for glass bottles and polyethylene terephthalate (hereinafter referred to as PET) bottles and shrink films for food packaging. It was However, in recent years, a polyester-based shrink film excellent in safety and hygiene, chemical resistance, and transparency has been demanded, and a stretched film made of polyester has been proposed. In addition, these films are roughly classified into a type exhibiting uniaxial shrinkage and a balance type according to the needs of the market.

The polyester shrink film of the type exhibiting uniaxial shrinkage is stretched at a high ratio in a desired direction, as represented by, for example, JP-A-6-18902, in order to express its characteristics. In many cases, the film is unstretched or slightly stretched in the direction orthogonal to it. Therefore, the mechanical properties in the desired direction are good, but the mechanical properties in the orthogonal direction are inferior.

Most of the uniaxially shrinkable polyester films exhibit uniaxial shrinkage in the film width direction, and almost none exhibit uniaxial shrinkage in the film longitudinal direction.

[0005]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a polyester-based shrinkable film which exhibits uniaxial shrinkage in the longitudinal direction of the film and is excellent in mechanical properties and heat resistance in both axial directions. is there.

[0006]

[Means for Solving the Problems] The above-mentioned object is that the melting point is 1
A film made of polyester having a temperature of 70 ° C. or higher and 250 ° C. or lower, in which 1
The shrinkage rate (Sm) in the longitudinal direction of the film in hot air at 00 ° C. is 20% or more, and the shrinkage rate (St) in the width direction is (shrinkage rate Sm in the longitudinal direction) × 2/3 or less, This is achieved by a polyester-based shrink film having a refractive index of 1.590 or more in both the width direction and the width direction.

The polyester shrink film of the present invention is
A melting point of 170 ° C or higher and 250 ° C or lower, especially 180 ° C
It is preferably not lower than 240 ° C and not higher than 240 ° C. If the melting point is less than 170 ° C, the heat resistance will deteriorate, while if it exceeds 250 ° C, the heat sealability will deteriorate.

The polyester according to the present invention has terephthalic acid, adipic acid, oxalic acid, malonic acid, succinic acid, azelaic acid, sebacic acid as dicarboxylic acid components,
Phthalic acid, isophthalic acid, naphthalene dicarboxylic acid, diphenyl ether dicarboxylic acid, cyclohexane dicarboxylic acid, 5-sulfonate isophthalic acid and long-chain aliphatic dicarboxylic acid dodecanedioic acid, eicoic acid, dimer acid and their derivatives Consists of one or more dicarboxylic acid components, and as diol components, ethylene glycol, propylene glycol, neopentyl glycol, hexamethylene glycol, 1,
4-butanediol, trimethylene glycol, tetramethylene glycol, diethylene glycol, polyethylene glycol, polyalkylene glycol, 1,4-
It is a polyester or copolymerized polyester composed of one or more known diol components such as cyclohexanedimethanol, 2-alkyl 1,3-propanediol, and a diethoxy compound of bisphenol A or bisphenol S.

As the copolyester, those obtained by substituting a part of the dicarboxylic acid component and / or the glycol component with another dicarboxylic acid or glycol component can be used, but other components such as p-oxy can be used. Benzoic acid, oxycarboxylic acids such as p-oxyethoxybenzoic acid, benzoic acid, monofunctional compounds such as methoxypolyalkylene glycol, and polyfunctional compounds such as glycerin, pentaerythritol, trimethylolethane, and trimethylolpropane are also formed. It can be used within a range in which an object can substantially hold a linear polymer.

In the polyester of the present invention, copolymerized polyester having terephthalic acid as the dicarboxylic acid component and ethylene glycol as the main component as the diol component is preferably used, and as the copolymerized component, isophthalic acid or phthalate is used as the dicarboxylic acid component. Copolymerized polyester using acid, adipic acid, sebacic acid, dodecanedioic acid, dimer acid, diethylene glycol, polyethylene glycol, polyalkylene glycol as a diol component, and optionally 1,4-cyclohexanedimethanol is industrially inexpensive. It is preferable because it is available and has good shrinkage characteristics.

In the polyester of the present invention, one kind or two or more kinds of the polyester and / or the copolyester may be blended with the polyester or the copolyester for use. The melting point of the polyester to be blended is not particularly limited as long as the peak temperature of the endothermic peak area of the melting point observed in the differential scanning calorimetry of the polyester mixed after blending is in the range of 170 ° C to 250 ° C.

In the copolyester used in the present invention, preferably 65% by mole or more, more preferably 70% by mole or more of the dicarboxylic acid component is a terephthalic acid unit, and preferably 65% by mole or more of the diol component. Preferably 70% mol or more is an ethylene glycol unit. Copolyesters having less than 65 mol% of terephthalic acid and / or ethylene glycol units are not preferable because the strength and solvent resistance of the formed film are poor.

Further, the above polyester may be one obtained by adding and mixing a polymer other than the polyester, in addition to the polyester, as long as it is 30% by weight or less.

Further, in order to improve the slipperiness of the film, it is preferable to contain fine particles such as an organic lubricant and an inorganic lubricant. Further, it may contain additives such as a stabilizer, a colorant, an antioxidant, an antifoaming agent and an antistatic agent, if necessary. As fine particles imparting slipperiness, known inert external particles such as carion, clay, calcium carbonate, silicon oxide, calcium terephthalate, aluminum oxide, titanium oxide, calcium phosphate, lithium fluoride and carbon black, melting of polyester resin Insoluble high melting point organic compounds during film formation, cross-linked polymers and metal compound catalysts used in polyester synthesis, such as internal particles formed inside the polymer during polyester production by alkali metal compounds, alkaline earth metal compounds, etc. it can. The content of the fine particles contained in the film is usually 0.005 to 0.9% by weight, and the average particle diameter of the fine particles is usually in the range of 0.001 to 3.5 μm.

The intrinsic viscosity of the film of the present invention is preferably 0.50 or more, more preferably 0.55 or more.
When the intrinsic viscosity of the film is less than 0.5, the heat resistance is lowered and the melt film formation becomes unstable, which is not preferable.

In the film of the present invention, the shrinkage ratio (Sm) in the longitudinal direction of the film in hot air of 100 ° C. is 2
It must be 0% or more. In the present invention, when the shrinkage rate of the film in the longitudinal direction is less than 20%, the shrinkage amount becomes insufficient and the film does not sufficiently adhere to the container, which is not preferable.

In the film of the present invention, the shrinkage ratio (St) in hot air at 100 ° C. in the direction orthogonal to the longitudinal direction, that is, in the width direction is (shrinkage ratio Sm in the longitudinal direction) × 2/3.
It must be: A film having a shrinkage ratio in the width direction exceeding (shrinkage ratio Sm in the longitudinal direction) × 2/3 is unfavorable because the uniaxial shrinkage property is lost, and further distortion, wrinkles, curl at the end portion and the like occur during shrinkage.

As described above, the inventors of the present invention exhibit uniaxial shrinkage in the longitudinal direction by setting the melting point, polymer type, shrinkage rate of film, intrinsic viscosity, etc. within a specific range, and also have heat resistance and solvent resistance. The film has excellent properties and has improved distortion and wrinkles during shrinkage. However, the strength in the longitudinal direction and the width direction of the film was not sufficient in the above examination, and further improvement was required.

As a result of further intensive studies, the present inventor has obtained a film exhibiting uniaxial shrinkage in the longitudinal direction and having excellent strength in the lateral direction by setting the refractive index of the film to a certain value or more. Found.

That is, in the film of the present invention,
The refractive index in the longitudinal direction and the refractive index in the width direction must both be 1.590 or more. A film having a refractive index of less than 1.590 is not preferable because the strength is lowered.

Further, in the film of the present invention, the plane orientation coefficient of the film is preferably 0.07 or more. A film having a plane orientation coefficient of less than 0.07 is not preferable because the solvent resistance, thickness unevenness, strength and the like deteriorate.

In the film of the present invention, the Young's modulus is 20 in both the longitudinal and width directions from the viewpoint of mechanical properties during handling.
It is preferably 0 kg / mm ² or more, more preferably 250 kg / mm ² or more. Further, the breaking strength is preferably 8 kg / mm ² or more in both the longitudinal direction and the width direction from the viewpoint of strength.

Further, various coatings may be applied to the film of the present invention. The thickness of the film of the present invention is not particularly limited, but it is 1 to 300 μm, preferably 5 to
It is effectively used at 100 μm.

Next, the method for producing the film of the present invention will be described. After drying the polyester or copolyester having the above-mentioned composition of the present invention by using an ordinary hopper dryer, paddle dryer, vacuum dryer or the like,
Extrusion is carried out at a temperature of 320 ° C. After extrusion, the film is rapidly cooled to obtain an unstretched film. When the T-die method is used, it is preferable to use a so-called electrostatic application adhesion method at the time of rapid cooling because a film with uniform thickness can be obtained.

The unstretched film obtained is 1.5 to 6.0 times, preferably 2.0 to 5, in the longitudinal direction and the transverse direction, respectively, so that the finally obtained film satisfies the constitutional requirements of the present invention. Draw 0 times to obtain a film. The stretching means is not particularly limited, and methods such as roll stretching and tenter stretching are applied, and the shape may be flat, tubular or the like. The stretching method may be uniaxial stretching, sequential biaxial stretching, or simultaneous biaxial stretching.

In the above stretching, further re-stretching in the longitudinal direction is performed at least 1.1 times or more, preferably 1.2 times or more, and further so as to satisfy the range of the refractive index of the film of the present invention. It is possible to obtain a film which has a high shrinkage ratio in the longitudinal direction and which is excellent in mechanical strength and the like in both the longitudinal direction and the width direction, which was not obtained in the above. Also, heat treatment may be performed before re-stretching,
The heat treatment temperature is not particularly limited as long as it is in the range of 250 ° C. or lower, but the glass transition temperature Tg to 250 ° C. of the polymer is preferable from the viewpoint of desired shrinkage rate, thickness unevenness and the like.

It is also a preferable method for obtaining uniform shrinkage of the film that the film thus stretched is subjected to a heat treatment at 50 ° C. to 120 ° C. for 0.01 second to 30 seconds after stretching. The heat treatment is usually carried out under tension, but at the same time, it is possible to perform relaxation or tentering by 20% or less. As the heat treatment method, a known method such as a method of contacting with a heating roll or a method of gripping with a clip in a tenter can be used. It is also possible to perform corona discharge treatment on one side or both sides of the film during the stretching step, before stretching, or after stretching to improve the adhesion of the film to the printing layer and the like. Further, it is also possible to improve the adhesion, antistatic property, slipperiness, light-shielding property, etc. of the film by applying to one side or both sides of the film during the stretching step, before stretching, or after stretching. The film thus obtained is wound into a product.

[0028]

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. First, the measurement and evaluation methods are shown below. (1) Thermal shrinkage The distance between the marked lines of the film sample is set to 200 mm, the film is cut into 10 mm, and the length between the marked lines is measured by heating with hot air of 100 ° C. for 5 minutes. The shrinkage amount of the film is the original size. Is expressed as a percentage.

(2) Melting point (° C.) Differential scanning calorimeter RDC220 manufactured by Seiko Instruments Inc.
Using the mold, collect 5 mg of sample and raise the temperature from room temperature to 20
It was determined from the peak temperature of the endothermic curve when the temperature was raised at ° C / min.

(3) Refractive Index of Film The refractive index of the film was measured using an Abbe refractometer manufactured by Atago Co., Ltd. with a sodium lamp as a light source. The refractive index nγ in the longitudinal direction in the film plane, the refractive index nβ in the lateral direction orthogonal thereto and the refractive index nα in the thickness direction were obtained, and the plane orientation degree ΔP was obtained by the following formula. ΔP = 1/2 (nγ + nβ) -nα

(4) Breaking Strength and Tensile Elastic Modulus (Young's Modulus) According to JIS-Z1702-1976, a sample piece having a width of 10 mm and a length of 100 mm was measured at a pulling speed of 300 mm / min.

(5) Sealing strength Two heat-shrinkable polyester films were heat-sealed with an impulse sealer and a scale 4 in a state of being superposed, and the peeling strength after sealing was measured.

Example 1 800 ppm of silicon oxide particles having a terephthalic acid unit content of 82.5 mol% and an isophthalic acid unit content of 17.5 mol% as a dicarboxylic acid component and ethylene glycol as a diol component, and having an average particle size of 1.4 μm. The copolyester containing the composition was dried by a conventional method, melted at 265 ° C. by an extruder, extruded from a T-die, and rapidly solidified to obtain an unstretched film. The obtained unstretched film was stretched in the machine direction at a temperature of 88 ° C. to 2.7 times, and in the transverse direction at a temperature of 97 ° C. to 3.5 times, and then stretched 125 times.
Heat treated at ℃, then re-stretched in the machine direction at 98 ℃ 1.5 times, heat treated at 85 ℃, cooled to an average thickness of 35
A film of μm was obtained.

Example 2 The polyester used in Example 1 was used in an amount of 90% by weight, the terephthalic acid unit was 100 mol% as a dicarboxylic acid component, the ethylene glycol was 90 mol% as a diol component, and the average molecular weight was 4000. A film having an average thickness of 35 μm was obtained in the same manner as in Example 1 except that 10% by weight of copolymerized polyester consisting of 10 mol% of polyethylene glycol was used.

Example 3 The polyester used in Example 1 was composed of 90% by weight of the copolyester used in Example 1, 90 mol% of a terephthalic acid unit as a dicarboxylic acid component and 10 mol% of sebacic acid, and ethylene glycol as a diol component. A film having an average thickness of 35 μm was obtained in the same manner as in Example 1 except that the content of the copolymerized polyester was 10% by weight.

Example 4 A film having an average thickness of 35 μm was obtained in the same manner as in Example 1 except that the polyester used in Example 1 was changed to 90% by weight of the copolyester used in Example 1 and 10% by weight of polybutylene terephthalate. Got

Example 5 75 mol% of terephthalic acid units as a dicarboxylic acid component,
Isophthalic acid unit 25 mol%, ethylene glycol as diol component, average particle size 1.4 μm
The copolyester containing 800 ppm of silicon oxide particles was dried by a conventional method, melted at 250 ° C. in an extruder, extruded from a T die, and rapidly solidified to obtain an unstretched film. The resulting unstretched film was stretched 2.8 times in the longitudinal direction at 88 ° C. and 3.5 times in the transverse direction at 97 ° C., then heat-treated at 125 ° C. Stretched, 85
It was heat-treated at 0 ° C. and cooled to obtain a film having an average thickness of 35 μm.

Comparative Example 1 A film having an average thickness of 35 μm was obtained in the same manner as in Example 1 except that the stretching conditions in Example 1 were 90 ° C., longitudinal stretching of 1.4 times, and heat treatment at 85 ° C.

Comparative Example 2 The same as Example 1 except that the stretching conditions in Example 1 were 90 ° C., 3.8 times longitudinal stretching, 90 ° C., 1.5 times transverse stretching, and 85 ° C. heat treatment only. As a result, a film having an average thickness of 35 μm was obtained.

Comparative Example 3 An average thickness of 35 μm was obtained in the same manner as in Example 1 except that the polyester used in Example 1 was polyethylene terephthalate.
m film was obtained.

The evaluation results of the obtained film are shown in Tables 1 and 2. The film of Comparative Example 1 had a low transverse refractive index and was inferior in mechanical properties (Young's modulus, breaking strength), which was not preferable. The film of Comparative Example 2 was not preferable because the shrinkage ratio was not satisfied. The film of Comparative Example 3 had a low sealing strength and was not preferable. In contrast to the comparative example, each of the films of the examples has uniaxial shrinkage in the longitudinal direction, good sealing properties, and excellent mechanical properties in the lateral direction.

[0042]

[Table 1]

[0043]

[Table 2]

[0044]

According to the polyester shrink film of the present invention, it is possible to provide a shrink film exhibiting uniaxial shrinkage in the longitudinal direction of the film and having excellent mechanical properties and heat resistance in both axial directions. .

Claims (2)

[Claims] 1. A film made of polyester having a melting point of 170 ° C. or higher and 250 ° C. or lower, wherein the polyester film has a shrinkage ratio (Sm) in the longitudinal direction of the film in hot air of 100 ° C. of 20% or more. , The shrinkage ratio (St) in the width direction is (shrinkage ratio S in the longitudinal direction.
m) × 2/3 or less, and the refractive index in the longitudinal direction and the refractive index in the width direction are both 1.590 or more. 2. The polyester-based shrinkable film according to claim 1, which has a surface orientation coefficient of 0.07 or more.