JP2003311905A - Stretched polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester film which has good hand cutting properties and twisting properties and does not lose flexibility of the film even after it is exposed under a high temperature during processing. <P>SOLUTION: The polyester film is prepared by laminating a polyester resin (B) with a melting point of at least 10°C higher than the melting point of a polyester resin layer (A) on at least one face of the polyester resin layer (A) so as to make the total thickness of the film after drawing to be 1-10 μm, at least monoaxially stretching it, and then, heat-treating it at a temperature of 5°C lower than the melting point of a crystalline polyester resin (C) included in the polyester resin layer (A) or higher and at a temperature lower than the melting point of the polyester resin (B). <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a stretched polyester film. More specifically, when the polyester stretched film has excellent properties such as heat resistance, aroma retaining property, and water resistance, it retains practical properties and is exposed to a high temperature during storage or processing. Also, the present invention relates to a stretched polyester film which retains its elongation without losing its flexibility and has good tearability and twistability, which is useful as a packaging film or a tape 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 adhesive tapes because of its excellent transparency, easy cutting property, and wrinkle-fixing property. On the other hand, however, cellophane has hygroscopicity, and its characteristics fluctuate depending on the season, making it difficult to constantly supply a cellophane of constant quality. In addition, packaging bags and adhesive tapes that use polyethylene terephthalate as a base film are used by buying the stretched polyethylene terephthalate phthalate film because of its excellent properties 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.

As a method for solving the above-mentioned drawbacks, a uniaxially oriented polyester film (Japanese Patent Publication No. 55-85).
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). Further, there is proposed a laminated polyester film (Japanese Patent Laid-Open No. 5-104618) which has polyester resin layers having different melting points and is heat-treated between the melting points to collapse the orientation of at least one layer.

However, in the above-mentioned prior art, the method of uniaxial orientation is easy to cut linearly in the orientation direction but difficult to cut in directions other than the orientation direction, and the method of copolymerizing a large amount of diethylene glycol component etc. is It has a drawback that the original properties of polyethylene terephthalate are lost by the copolymerization. Furthermore, the method of using a low molecular weight polyester resin is not practical because it easily causes film breakage problems in the stretching step. Laminated polyester films that have polyester resin layers with different melting points and are heat-treated between the melting points to collapse the orientation of at least one layer are crystallized when heated by printing or laminating. However, there is a problem in that the film becomes brittle and cannot be processed or used thereafter.

[0005]

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

In particular, the present invention aims to have flexibility even after being exposed to the temperature applied during storage and processing, and achieves this. That is, the film of the present invention generally undergoes a processing step of printing, coating with an adhesive, bonding with another material, etc. (in such a step, heat of 50 to 130 ° C. is usually received). However, it can withstand practical use without being easily cut due to large embrittlement when subjected to such heat, fluctuations in tension during processing, and changes in processing speed.

[0007]

That is, the stretched polyester film of the present invention comprises a crystalline polyester resin (a-1) 98-containing terephthalic acid as an acid component as a main component.
80 wt%, a crystalline segment having a melting point of 170 ° C. or higher and a melting point or softening point of 100 ° C. or lower, and a molecular weight of 400 to 800
Of the block copolymerized polyester resin (a-2) consisting of 0 to 20% by weight of the soft polymer, the crystalline polyester resin (a) contained in the polyester resin layer (A) on at least one side of the polyester resin layer (A). -1)
The polyester resin layer (B) having a melting point higher by 10 ° C. or more than the melting point is laminated and at least uniaxially stretched. As a method for producing a stretched polyester film of the present invention, a crystalline polyester resin (a-
1) 98 to 80 wt%, a crystal segment having a melting point of 170 ° C or higher, a melting point or softening point of 100 ° C or lower, and a molecular weight of 40
Crystalline polyester resin contained in the polyester resin layer (A) on at least one surface of the polyester resin layer (A) consisting of 2 to 20 wt% of the block copolymerized polyester resin (a-2) consisting of 0 to 8000 soft polymer (A
-1) the crystalline polyester ester (a-1) contained in the polyester resin layer (A) after at least uniaxially stretching an unstretched film laminated with a polyester resin layer (B) having a melting point higher by 10 ° C or more. The heat treatment is preferably carried out at a temperature 5 ° C. lower than the melting point of 1) or higher and lower than the 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, the polyester resin on the side having a higher melting point than the melting point of the polyester resin (a-1) having a lower melting point by 5 ° C. or more. By carrying out the heat treatment at a temperature lower than the melting point of the layer (B), the polyester resin layer (A) loses its orientation in the stretching step and maintains the properties such as heat resistance, transparency, water resistance and aroma retention of the polyester resin. Of the block copolymer polyester resin (a-2) containing a soft polymer and having tearability and twist fixing property, and having flexibility, the polyester resin layer (B) is A polyester film that maintains the orientation and is a laminated film that has two different properties, that is, a layer that has excellent properties such as heat resistance that is inherent to the polyester film. Is by the finding that a polyester film having a contradictory properties that with good tear resistance and twisting fixation while having ester film inherent excellent characteristics can be obtained.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The polyester used in the polyester resin layer (B) of the present invention is not particularly limited, and includes, for example, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate and their constituents as main components. There are copolymers and the like.

The polyester resin mixture used for the polyester resin layer (A) is a crystalline polyester resin (a-1) 98 to 80 wt% containing terephthalic acid as a main component.
%, A crystalline segment having a melting point of 170 ° C. or higher, a melting point or a softening point of 100 ° C. or lower, and a block copolymerized polyester resin (a- having a molecular weight of 400 to 8000).
2) It is composed of a mixture of 2 to 20 wt% and the crystalline polyester resin (a-1) has a melting point lower than the melting point of the polyester used in the polyester resin layer (B) by 10 ° C. or more, preferably 20 ° C. or more. Copolymers are preferred.

In the block copolymerized polyester resin (a-2) of the present invention, the crystal segment having a melting point of 170 ° C. or higher has a melting point of 170 ° C. or higher when it is made into a polymer by using only the component. Terephthalic acid,
A residue of an aromatic dicarboxylic acid such as isophthalic acid or 2,6-naphthalenedicarboxylic acid, and an aliphatic or aromatic residue such as ethylene glycol, propylene glycol, butanediol, pentamethylene glycol, P-xylene glycol or cyclohexanedimethanol. Polyester or the like composed of an alicyclic diol residue can be used, but it is particularly desirable that the terephthalic acid residue accounts for 80 mol% or more. Further, the soft polyester having a molecular weight of 400 to 8,000 is one having a melting point or a softening point of 100 ° C. or less when measured only with the segment constituent components. When the one having a molecular weight of 400 or less is used, the block copolymerized polyester resin obtained has a low melting point and a large adhesiveness,
It becomes difficult to compound and process the film. On the other hand, when the molecular weight exceeds 8000, the soft polymer is separated into layers, exhibits extremely high melt viscosity, becomes hard and brittle, and is difficult to remove from the polymerization vessel after the copolymerization reaction. When the polymerized polyester resin is used for film formation, the transparency is poor, which is not preferable.
Particularly preferably, it has a molecular weight of 800 to 4000.

The proportion of the low melting point soft polymer in the block copolymerized polyester resin is in the range of 8 to 20 mol%. If it is less than 8 mol%, the properties as a soft polymer cannot be obtained, and if it exceeds 20 mol%, the block copolymerized polyester resin (a-2) is dispersed when mixed and melted with the crystalline polyester resin (a-1). The transparency becomes worse as the size becomes larger or the number of dispersions increases. It is particularly preferably 10 to 15 mol%. Such low melting point soft polymer, polyethylene oxide glycol, polytetramethylene oxide glycol, polypropylene oxide glycol, copolymer glycol of ethylene oxide and propylene oxide, polyether such as copolymer glycol of ethylene oxide and tetrahydrofuran, Examples thereof include aliphatic polyesters such as polyneopentyl azelate, polyneopentyl adipate and polyneopentyl sepacate, and polylactones such as poly-ε-caprolactone and polypivalolactone. Preference is given to polyethylene oxide glycol, polytetramethylene oxide glycol and the like. These block copolymerized polyesters can be produced by a usual condensation polymerization method.

Specific examples of the block copolymer polyester used in the present invention include polyethylene terephthalate-polyethylene oxide block copolymer, polyethylene terephthalate-polytetramethylene oxide block copolymer, polybutylene terephthalate-polyethylene oxide block copolymer. , Polybutylene terephthalate-polytetramethylene oxide block copolymer, polyethylene terephthalate-polyethylene oxide, polypropylene oxide block copolymer, polytetramethylene terephthalate / isophthalate-polytetramethylene oxide block copolymer, polyethylene terephthalate-poly-ε -Caprolactone block copolymer, polyethylene terephthalate-polyneopentyl Block copolymer, polyester of di (4-carboxyphenoxy) ethane and ethylene glycol, block copolymer of polyethylene glycol, polyester of bis (N-paracarboethoxyphenyl) adipamide and ethylene glycol For example, a block copolymer with polyethylene glycol can be used.

In the present invention, the crystalline polyester resin (a-1) and the block copolymerized polyester resin (a-
The compounding ratio with 2) is crystalline polyester resin (a-1) 9
It is necessary to blend the block copolymerized polyester resin (a-2) in a proportion of 2 to 20 wt% with respect to 8 to 80 wt%, and more preferably the crystalline polyester resin (a-
1) 97 to 90 wt% and 3 to 10 wt% of block copolymerized polyester resin (a-2). When the content of the block copolymerized polyester resin (a-2) is less than 2 wt%, the hand-cutting property is poor and the flexibility after exposure to high temperature cannot be obtained. Also,
20 wt% of block copolymerized polyester resin (a-2)
If it exceeds, the tensile strength of the biaxially stretched polyester film will decrease, the dimensional stability and rigidity will decrease, the transparency will deteriorate, and not only will it not withstand use, but the film formation will become unstable. .

Further, the total thickness of the polyester resin layer (B) is preferably 1 μm or more and 10 μm or less, more preferably 2 μm or more and 6 μm or less. When the thickness of the polyester resin layer (B) is less than 1 μm, the strength of the obtained film becomes low, which is a practical problem. Further, when the thickness of the polyester resin layer (B) exceeds 8 μm, the target tearability and twistability deteriorate. Further, the polyester resin layer (A) and the polyester resin layer (B) are laminated in three layers (B
/ A / B) or a two-layer (B / A) structure, but a three-layer (B / A / B) laminate is preferable in terms of curling during processing and heat resistance. Furthermore, the thickness of the stretched film is 12 μm to 30 μm, which is used in the packaging bag, the pressure-sensitive adhesive tape, etc., which is the intended use of the present invention, but is not particularly limited.

The polyester film of the present invention may be added with 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 referred to here is a method in which a plurality of extruders or the like are separately melted at a temperature equal to or higher than the melting point and extruded from a die outlet to form unstretched films which 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. Still 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-1) and block-copolymerized polyester resin (a-2) are supplied to an extruder at a predetermined ratio, and the polyester resin (B) is supplied to another extruder. From two extruders, melt extruded at a temperature higher than the melting point of each, and pass through a composite adapter to allow two kinds of three layers (B / A / B) or two kinds of two layers (B / A / B).
As A), the unstretched laminated film is formed by extruding from a die and cooling and solidifying.

The crystalline polyester resin (a-1) or the polyester resin (B) used in the polyester resin layer (A) is the unstretched laminated film thus obtained.
The uniaxial stretching or the biaxial stretching is performed at a temperature not lower than the higher temperature of the secondary transition points of the above and not higher than the melting point of the polyester resin (a-1). 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 or more.
-30 times, preferably 9-16 times. In the case of biaxial stretching, sequential stretching or simultaneous stretching may be used.

This stretched film is used as the polyester resin layer (A) in the crystalline polyester resin (a-1)
Of the polyester resin layer (B) 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.

[0021]

By the heat treatment in the previous period, the polyester resin layer (A) almost collapses the molecular orientation due to stretching, and the tearing and twisting properties aimed at by the present invention are obtained, and 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. Further, the block copolymerized polyester resin (a-2) contained in the polyester resin layer (A) is a crystalline polyester resin (a-1).
It is considered that by dispersing it inside, even if it is exposed to a high temperature during processing, its elongation is maintained without losing its flexibility.

As described above, the object of the present invention is to balance the layer having the tearability and the twisting property in which the molecular orientation is almost collapsed by the heat treatment in the film-forming line and the layer having the original characteristics of polyester which maintains the molecular orientation. And a flexible block copolymerized polyester resin (a-
However, since 2) is dispersed in the layer that imparts tearability and twistability, it has an advantage that troubles such as breakage during film formation can be prevented.

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 (a-1).

(A) Flexibility after exposure to high temperature After aging for 1 week in a thermostatic chamber at 40 ° C., JI
According to S-K7127, the tensile breaking elongation in the longitudinal direction of the film was measured, and those which did not change from those before aging were evaluated as ◯, and those whose elongation was less than 5% were evaluated as x.

(B) Hand-cutting sensory test was conducted to find the polyester film
After making mAl foil / 20 μm extruded LDPE and heat-sealing the bag and cutting the sealed part by hand, those that could be easily cut by hand were marked with ◯, and those that could not be cut by hand were marked with x.

(C) Twistability A sensory test was conducted, and when a tape-shaped sample having a width of 30 mm was twisted by hand, one that did not return to its original shape when twisted was rated as ◯, and one that could not maintain the twisted state was rated as x.

Example 1 As a polyester resin layer (A), polyethylene isophthalate (a) having a melting point of 220 ° C.
-1) and 100 terephthalic acid as a dicarboxylic acid component
mol%, butanediol 85 mol% as a diol component,
Polytetramethylene glycol with a molecular weight of 1000 15mo
Block copolymerized polyester resin (a-
A mixture of 2) at a ratio of 95/5 wt%. As the polyester resin layer (B), polyethylene terephthalate (B) having a melting point of 260 ° C. is melted by a separate extruder at a temperature of 285 ° C., and the melts are joined by a composite adapter and then extruded from a T die and cooled. It was rapidly cooled in a drum to obtain a three-layer unstretched laminated film of (B / A / B) constitution.

First, the unstretched laminated film is stretched in the longitudinal direction 9
The film was stretched 3.5 times at 0 ° C. and then 3.8 times at 110 ° C. in the transverse direction and then heat-treated at a temperature of 225 ° C. while being relaxed by 3% to obtain a 20 μ film. B of this film
/ A / B thickness ratio of each layer is 2.5μm / 15μm
The ratio was /2.5 μm.

The film thus obtained 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. Furthermore, even after aging at 40 ° C. for 1 week, it had flexibility and did not become brittle. 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, the thickness of each B / A / B layer was changed to 4/12/4 μm.
A 0 μm film was obtained. The film thus obtained was also good in twist fixing property, flexibility and processability 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 20 μ film was obtained in which only the thickness ratio of B / A / B layers was changed to 6/8/6 μm. The film thus obtained was not hand-tearable, returned to its original shape when the film was twisted, and had no twist fixing property.

Comparative Example 2 Example 1 was repeated except that the melting point of polyethylene isophthalate (A) was changed to 245 ° C.
A film having a thickness of 20 μm was obtained by the same method, conditions and thickness ratio. The film thus obtained was not hand-tearable, returned to its original shape when the film was twisted, and had no twist fixing property.

Comparative Example 3 A film having a thickness of 20 μm was obtained with the same raw material, method and thickness ratio as in Example 1, except that the amount of the block copolymerized polyester resin (a-2) added was 1 wt%. The film thus obtained was not flexible after being aged at 40 ° C., and tensile fracture elongation was not obtained.

Example 3 A film was formed by using the same raw material, method and thickness as in Example 1 except that the addition amount of the block copolymerized polyester resin (a-2) was changed to 10 wt%. Is hand-tearable, twistable, flexible,
The workability was also good.

(Comparative Example 4) A film was formed with the same raw material, method and thickness as in Example 1 except that the addition amount of the block copolymerized polyester resin (a-2) was 25 wt%. It was not stable and film formation was difficult.

(Comparative Example 5) A film was formed using the same raw material, method and thickness as in Example 1 except that the heat treatment temperature was 200 ° C.
A film having a thickness of μm was obtained. This film was neither hand-cutable nor fixed by twisting.

Example 4 Using the same raw materials and method as in Example 1, a 20 μm film was obtained in which only the thickness ratio of each B / A / B layer was changed to 1/18/1 μm. The film thus obtained was good in hand-cutting property, twist fixing property, flexibility and processability.

Table 1 shows the evaluation results of the films obtained in Examples and Comparative Examples.

[0039]

[Table 1]

[0040]

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

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 4F100 AK41A AK41B AK41C AK42                       AL02A BA02 BA03 BA10B                       BA10C BA44A EH232 EJ373                       EJ413 GB15 JA04A JA04B                       JA04C JA07A JA11A YY00A                 4F210 AA24A AA24C AA24F AG01                       AG03 AR06 QC06 QG01 QG15                       QG18 QW05

Claims (5)

[Claims] 1. A crystalline polyester resin (a-1) 98 to 80 wt% containing terephthalic acid as a main component as an acid component.
%, A crystalline segment having a melting point of 170 ° C. or higher, a melting point or a softening point of 100 ° C. or lower, and a block copolymerized polyester resin (a- having a molecular weight of 400 to 8000).
2) Polyester resin layer (A) composed of 2 to 20 wt%
Of at least one surface of the polyester resin layer (B) having a melting point higher than the melting point of the crystalline polyester resin (a-1) contained in the polyester resin layer (A) by 10 ° C. or more.
And a stretched polyester film which is laminated at least and is uniaxially stretched. 2. A stretched polyester film, wherein the content of terephthalic acid in the acid component of the crystalline polyester in the polyester resin layer (A) according to claim 1 is 75 mol% or more. 3. A block copolymerized polyester (a) constituting the polyester resin layer (A) according to claim 1 or 2.
-2) is a crystalline polyester resin (a-1) having a sea-island structure and dispersed therein, and a stretched polyester film. 4. The stretched polyester film according to claim 1, 2 or 3, which is used for twist packaging. 5. The method for producing a stretched polyester film according to claim 1, 2, 3 or 4, wherein the crystalline polyester resin (a-1) contained in the polyester resin layer (A) is at least uniaxially stretched. A method for producing a stretched polyester film, which comprises heat-treating at a temperature 5 ° C lower than the melting point or higher and lower than the melting point of the polyester resin layer (B).