JPH05104618A - Manufacture for polyester film having favorable tear property and twisting property - Google Patents

Abstract

PURPOSE:To provide a polyester film having favorable hand-tearing properties and twisting properties. CONSTITUTION:This is a manufacture for a polyester film where resin (B) having the melting point which is higher by at least 10 deg.C than the melting point of a polyester resin layer (A) is laminated on at least one side of the polyester resin layer (A) so that a thickness of the resin (B) becomes 5-60% of the whole thickness of a film and after uniaxial orientation, the same is heat-treated at a temperature of at least a temperature lower by 10 deg.C than the melting point of the polyester resin layer (A) and less than the melting point of the resin (B).

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a stretched polyester film. More specifically, a packaging film or tape having good tearability and twistability while maintaining practical properties without losing the excellent properties of stretched polyester film such as heat resistance, aroma retention and water resistance. The present invention relates to a stretched polyester film which is useful as a film.

[0002]

2. Description of the Related Art Cellophane has been known as a film having excellent cuttability. Cellophane is widely used for various packaging materials and pressure-sensitive adhesive tapes because of its excellent transparency, easy-cutting property, and twist-wrinkle fixing property. On the other hand, however, cellophane has hygroscopicity, and its characteristics fluctuate depending on the season, making it difficult to always supply a certain quality. In addition, polyethylene bags containing polyethylene terephthalate as a base film, adhesive tapes, etc. are used by buying the excellent properties of stretched polyethylene terephthalate phthalate film such as toughness, heat resistance, water resistance and transparency. Although it has these excellent characteristics, it is difficult to cut, it is difficult to tear the mouth of the packaging bag, the adhesive tape is difficult to cut, and the twist fixing property is poor, so it can be used for twist packaging. There were drawbacks such as not being able to do it.

As a method for solving the above-mentioned drawbacks, a uniaxially oriented polyester film (Japanese Patent Publication No. 55-85) is used.
51), a copolymer of a diethylene glycol component and the like (Japanese Patent Publication No. 56-50692), and one using a low molecular weight polyester resin (Japanese Patent Publication No. 55-20514).

[0004]

However, in the above-mentioned prior art, the method of uniaxially orienting is capable of easily cutting linearly in the direction of alignment but not in the direction other than the direction of orientation, and in addition, a large amount of diethylene glycol component etc. The method of copolymerization has a drawback that the original characteristics of polyethylene terephthalate are lost by the copolymerization. Furthermore, the method of using a low molecular weight polyester resin is not practical because the problem of film breakage in the stretching step easily occurs.

That is, the present invention pays particular attention to the easy-cutting property and the twist-fixing property among the properties of cellophane, and further has these properties, which are excellent properties of the polyester film, such as heat resistance, moisture resistance, transparency, and This was achieved by conducting research for the purpose of obtaining a film having an aroma retaining property and the like.

[0006]

The present invention has a melting point of 10 ° C. or more higher than the melting point of the polyester resin layer (A) on at least one side of the polyester resin layer (A), and 5% or more of the total thickness, An unstretched laminated film in which a polyester resin layer (B) having a thickness of 60% or less is laminated is at least uniaxially stretched, and then the melting point of the polyester resin layer (A) is 10 or more.
The present invention relates to a method for producing a polyester film having good tearability and twistability, which is characterized in that the heat treatment is performed at a temperature lower than a temperature lower than the temperature by ℃ and lower than a melting point of the polyester resin layer (B).

That is, according to the present invention, after stretching a polyester laminated film having a different melting point, a polyester (B) having a melting point higher than that of the polyester (A) having a lower melting point by 10 ° C. or more is used. By performing the heat treatment at a temperature lower than the melting point, the polyester (A) layer loses its orientation in the stretching step, and tearability and twisting are maintained while maintaining the polyester resin's heat resistance, transparency, water resistance, and aroma retention. A laminated film having two different properties, namely, a layer having fixability, and a polyester (B) layer constituting a layer having excellent properties such as heat resistance, which is a polyester film that maintains orientation. It has the contradictory properties of having excellent tear properties and twist fixing properties while maintaining the excellent properties of polyester film. It found that polyester film is obtained, and have completed the present invention.

The polyester used in the polyester resin layer (B) of the present invention is not particularly limited, and examples thereof include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate and copolymers containing these constituents as main components. Etc. Further, the polyester used in the polyester resin layer (A) is preferably a copolymer having a melting point lower than that of the polyester used in the polyester resin layer (B) by 10 ° C. or higher, preferably 20 ° C. or higher.

Further, the thickness of the polyester resin layer (B) is preferably 5% or more and 60% or less, more preferably 15% or more and 50% or less of the total thickness. When the thickness of the polyester resin layer (B) is less than 5% of the total thickness, the strength of the obtained film becomes low, which is a practical problem. Further, when the thickness of the polyester resin layer (B) exceeds 60% of the total thickness, the target tearability and twistability are deteriorated. Further, the lamination of the polyester resin layer (A) and the polyester resin layer (B) may be either three layers (B / A / B) or two layers (B / A). Further, although the stretched film has a thickness of 12μ to 30μ when used in a packaging bag, an adhesive tape or the like, which is the intended use of the present invention,
It is not particularly limited.

The polyester film of the present invention may contain various known additives such as lubricants, pigments, antioxidants, antistatic agents, etc. within a range that does not impair the effects of the present invention.

The unstretched laminated film as used herein means that unstretched films which are separately melted at a temperature equal to or higher than the melting point in a plurality of extruders and extruded from a die outlet are laminated in a heated state. There is a method. As another method, there is a method in which the surface of one unstretched film is melt-laminated with the other molten film. Yet another method is a method of forming an unstretched film by extruding from a die outlet in a state of being laminated by a coextrusion method.

Next, an example of the method for producing the film of the present invention will be described. The vacuum-dried polyester resin (A) and polyester resin (B) are supplied to two separate extruders, melt-extruded at a temperature equal to or higher than the melting point of each, and passed through a composite adapter to form a two-kind three-layer (B). / A / B) or a two-kind three-layer (B / A / B) extruded from a die and cooled and solidified to form an unstretched laminated film.

The unstretched laminated film thus obtained is uniaxial at a temperature not lower than the higher temperature of the secondary transition points of the polyester resin (A) and the polyester resin (B) and not higher than the melting point of the polyester resin (A). Stretching or biaxial stretching is performed. In the case of uniaxial stretching, it is at least 1.5 times or more, preferably 3 to 5 times, and in the case of biaxial stretching, the stretching area is 2 to 30 times, preferably 9 to 16 times. In the case of biaxial stretching, sequential stretching or simultaneous stretching may be used.

This stretched film is heat-treated at a temperature higher than the melting point of the polyester resin layer (A) and lower than the melting point of the polyester resin layer (B). It goes without saying that in this heat treatment, a relaxation treatment may be performed if necessary.

[0015]

By the heat treatment in the first half, the molecular orientation of the polyester resin layer (A) is almost destroyed by stretching, and the tearing and twisting properties aimed at by the present invention are obtained, while the polyester resin layer (B) maintains the molecular orientation. Therefore, it is considered that a film having the characteristics of the present invention can be obtained.

As described above, the present invention aims at a balance between a layer that imparts tearability and twistability in which the molecular orientation is almost collapsed by the heat treatment in the film-forming line and a layer having the original characteristics of polyester that maintains the molecular orientation. In addition to the advantage that the film characteristics can be freely set, there is an advantage that a breakage trouble or the like in the film formation can be prevented due to the existence of the layer in which the molecular orientation is maintained.

EXAMPLES The present invention will be described below with reference to examples. The evaluation methods in Examples and Comparative Examples were the methods (a) to (c).

(A) Edge tear resistance; JIS C2318-1
The average value measured according to 975 was used for evaluation.

(B) Hand-cutability; sensory test, width 1
When a 5 mm tape-shaped sample was manually cut, those that could be easily cut by hand were marked with ◯, and those that could not be easily cut by hand were marked with x.

(C) Twistability; sensory test was performed and the width was 3
When a 0 mm tape-shaped sample was twisted by hand, the sample that did not return to its original shape when twisted was marked with ◯, and the sample that could not maintain the twisted condition was marked with x.

Example 1 Polyethylene isophthalate (A) having a melting point of 200 ° C. and polyethylene terephthalate (B) having a melting point of 260 ° C. are melted by separate extruders at a temperature of 285 ° C., and the melts are combined by a composite adapter. After that, it was extruded from a T-die and rapidly cooled with a cooling drum to obtain a three-layer unstretched laminated film of (B / A / B) constitution.

The unstretched laminated film is first stretched 90 ° in the machine direction.
The film was stretched at a temperature of 3.5 ° C. at a draw ratio of 3.5 and then at 110 ° C. at a draw ratio of 3.8, and then heat-treated at a temperature of 230 ° C. while being relaxed by 3% to obtain a 25 μ film. B / A / of this film
The thickness ratio of each B layer was 2/21/2.

The thus obtained film could be easily cut in any direction by applying a nail, and when the film was twisted, the twisted state could be maintained as it was. Further, this film was free from troubles such as breakage during film formation and slitting and had good productivity.

Example 2 Using the same raw materials and method as in Example 1, a 25 μ film was obtained in which only the thickness ratio of each B / A / B layer was changed to 4/17/4.
The film thus obtained was also good in twist fixing property, except that a film having a little resistance and hand-cutting property was obtained as compared with Example 1.

Comparative Example 1 Using the same raw materials and method as in Example 1, a 25 μ film was obtained in which only the thickness ratio of each B / A / B layer was changed to 10/5/10. The film thus obtained was not hand-tearable, returned to its original shape when the film was twisted, and was not fixable by twisting.

Comparative Example 2 A 25 μm film was obtained in the same manner, conditions and thickness ratio as in Example 1, except that the melting point of polyethylene isophthalate (A) was changed to 245 ° C. The film thus obtained was not hand-tearable, returned to its original shape when the film was twisted, and was not fixable by twisting.

Examples Table 1 shows the evaluation results of the films obtained in the comparative examples.

[0028]

Industrial Applicability As described above, a polyester film having good hand-cutting properties and twisting properties can be obtained, and it can be seen that it is effective for packaging.

[0029]

[Table 1]

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Claims (1)

[Claims] 1. A polyester resin layer (A) having at least one surface having a temperature of 10 ° C. higher than the melting point of the polyester resin layer (A).
60% or more with a high melting point and 5% or more of the total thickness
% Or less after the unstretched laminated film in which the polyester resin layer (B) having a thickness of 10% or less is laminated is at least 10 ° C. lower than the melting point of the polyester resin layer (A) and less than the melting point of the polyester resin layer (B). A method for producing a polyester film having good tearability and twistability, which comprises heat-treating at 40 ° C.