JP2002096439A - Multi-layer polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multi-layer polyester film having good forming property, heat resistance, solvent resistance, dimensional stability handling property and the like. SOLUTION: The multi-layer polyester film prepared by a co-extrusion process having at least three layers comprises a laminated structure consisting of a polyester layer A having oriented structure to one axis or more and a polyester layer B having substantially non-crystalline structure, wherein both outer layers are composed of the polyester layer A, and a ratio (a/b) of a total thickness (a) of the polyester layer A to a total thickness (b) of the polyester layer B is from 0.01 to 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer polyester film, and more particularly to a multilayer polyester film which is excellent in moldability and workability, stability with time, solvent resistance and dimensional stability, and is used for molding and embossing. The present invention relates to a multilayer polyester film that is particularly useful for applications in which it is used while being held between holding fixtures.

[0002]

2. Description of the Related Art In recent years, in the food packaging field (for example, trays,
Ice cream cup, etc.), medicine packaging field (eg, PTP drug packaging such as capsules, tablets, etc.), and laminate molding field (eg, furniture and indoor / outdoor decorations, electric appliances, automotive parts, etc., film and paper, wood, metal, resin) Films (including lamination molding with rubber), ICs, card materials for magnetic recording (for example, cash cards, ID cards, credit cards, etc.), and agricultural fields (for example, green houses, etc.), including films (including sheets). The same).

[0003] In these applications, not only planar shapes,
Since many products have a non-flat surface morphology such as a curved surface or an uneven surface, a film made of a hard polyvinyl chloride resin is mainly used as a film material from the viewpoint of moldability and workability. However, since the polyvinyl chloride resin has poor heat resistance, the product may be deformed when exposed to high temperatures, for example, when left in a car in the middle of summer. In addition, polyvinyl chloride resin is liable to generate toxic substances due to chlorine when incinerated after use, causing a problem of environmental pollution.

Also, called A-PET (trade name),
An unoriented polyethylene terephthalate film is used. Although it is excellent in moldability, it causes problems such as embrittlement when used for a long time, opacity and reduction in elongation. For the purpose of improving this drawback, Japanese Patent Application Laid-Open
Japanese Patent No. 279150 proposes a method using a non-oriented heat-crystallized polyethylene terephthalate film, but this film has a problem that it is inferior in processing such as embossability and formability.

Further, 1,4-cyclohexane dimethanol derivative copolymerized polyester has been proposed as an alternative resin to polyvinyl chloride. Although this film has an effect of improving moldability and aging, it is difficult to use ink or the like. When used and printed, the polymer on the film surface is poor in durability to organic solvents, such as being easily dissolved by the solvent of ink, etc., and has poor dimensional stability, such as the processed product being easily curled and deformed. It is enough.

[0006]

SUMMARY OF THE INVENTION The present inventors have improved these drawbacks, and have developed, for example, the fields of food packaging, medicine packaging, laminate molding, IC, card material for magnetic recording,
Films useful in the agricultural field, etc., in particular, not only flat, but useful for forming, laminating and transferring non-flat surfaces such as curved surfaces, uneven surfaces, processability, moldability, stability over time,
As a result of intensive studies to develop a film having excellent solvent resistance and dimensional stability, a polyester film having at least three layers of a multilayer film produced by a co-extrusion film forming method and having a uniaxially oriented orientated structure. A and a polyester layer B having a substantially amorphous structure, wherein both outer layers are made of the polyester layer A, and the total thickness (a) of the polyester layer A and the total thickness of the polyester layer B ( b) ratio (a /
The multilayer polyester film having b) of 0.01 to 3 can significantly improve the moldability / workability, stability over time, solvent resistance, dimensional stability, and the like. They have found that they can be manufactured at low cost, and have completed the present invention.

Accordingly, an object of the present invention is to provide a food packaging field,
Providing low cost films with excellent processability, moldability, stability over time, solvent resistance and dimensional stability, useful in the fields of chemical packaging, laminate molding, IC, card materials for magnetic recording, agricultural fields, etc. Is to do.

[0008]

According to the present invention, there is provided, according to the present invention, a multilayer film having at least three layers produced by a coextrusion film forming method, wherein the polyester film has a uniaxially oriented orientated structure. It has a laminated structure of a layer A and a polyester layer B having a substantially amorphous structure, both outer layers are made of the polyester layer A, and the total thickness (a) of the polyester layer A and the total thickness of the polyester layer B This is achieved by the multilayer polyester film, wherein the ratio (a / b) of (b) is from 0.01 to 3.

In a preferred embodiment of the present invention, the multilayer film is composed of three layers of polyester layer A / polyester layer B / polyester layer A, and the polyester having a substantially amorphous structure of layer B is composed of terephthalic acid units and naphthalene. A copolyester comprising a dicarboxylic acid unit mainly composed of a dicarboxylic acid unit and a glycol unit mainly composed of an ethylene glycol unit, wherein the polyester having a substantially amorphous structure in the layer B is a dicarboxylic acid mainly composed of a terephthalic acid unit A copolyester consisting of units and a glycol unit mainly comprising ethylene glycol units and 1,4-cyclohexanedimethanol units, and / or wherein the polyester having a substantially amorphous structure of the layer B mainly contains terephthalic acid units. Dicarboxylic acid units and ethylene glycol units Including pentyl glycol units that copolyesters consisting of glycol units mainly.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The polyester constituting the layer A of the multilayer film in the present invention is a polyester capable of forming an oriented crystallized structure by a uniaxial stretching treatment, a heat fixing treatment or the like after film formation. The polyester is not particularly limited, but is preferably a polyester whose main dicarboxylic acid unit is composed of terephthalic acid and / or 2,6-naphthalenedicarboxylic acid unit, and whose main glycol unit is ethylene glycol unit. If necessary, the polyester may be, for example, isophthalic acid, orthophthalic acid, 2,7-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 4,4′-biphenyldicarboxylic acid, 2,2-biphenyldicarboxylic acid, succinic acid It may contain other carboxylic acid units such as acid, adipic acid, azelaic acid, sebacic acid and the like, and may include, for example, propylene glycol, butanediol, 1,5-pentanediol, 1,6-hexanediol, It may contain other glycol units such as pentyl glycol, 1,4-cyclohexane dimethanol, polyethylene glycol, polytetramethylene glycol, and the like.

Specific examples of the polyester constituting the polyester layer A include polyethylene terephthalate, polyethylene terephthalate in which a small amount of a third component is copolymerized, polyethylene-2,6-naphthalate, and polyethylene in which a small amount of the third component is copolymerized. Preferred is 2,6-naphthalate.

The melting point of the polyester constituting the polyester layer A is 205 ° C. or higher, and more preferably 205 ° C. or higher.
It is preferably 70 ° C. or lower. Here, the melting point is
This is the melting endothermic peak temperature when the quenched and solidified sample is heated at a rate of 10 ° C./min with a differential calorimeter after the polyester is once melted. Further, the glass transition temperature of the polyester is preferably 60 ° C. or more, more preferably 70 ° C. or more. Here, the glass transition temperature refers to a structural change (specific heat change) temperature when a polyester, which is once melted, rapidly cooled and solidified, is heated at a rate of 10 ° C./min by a differential calorimeter.

The polyester constituting the layer B of the multilayer film in the present invention is a substantially amorphous polyester. The amorphous polyester as used herein refers to a polyester having a calorific value of crystallization of 5 cal / g or less when the polyester is cooled from a molten state at a rate of 5 ° C./min by a differential calorimeter. Does not substantially form an oriented crystallized structure by uniaxial stretching or heat-setting. Further, the glass transition temperature of the polyester,
Although not particularly limited, the temperature is preferably 60 ° C. or more, and more preferably 70 ° C. or more, from the viewpoints of dimensional stability, deformation resistance, and curling resistance of films and processed products. In particular, in applications where products and the like are exposed to high temperatures, such as storage in a car in the summer, 80
It preferably has a glass transition temperature of at least ℃.

Examples of the dicarboxylic acid unit of the polyester include terephthalic acid, isophthalic acid, orthophthalic acid, 2,7-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, and 4,4 ′. -Biphenyldicarboxylic acid, 2,2-biphenyldicarboxylic acid, succinic acid, adipic acid, azelaic acid, sebacic acid and the like. Examples of the glycol unit include ethylene glycol, propylene glycol, butanediol, and 1,5-pentane. Diol,
1,6-hexanediol, neopentyl glycol,
1,4-cyclohexanedimethanol, polyethylene glycol, polytetramethylene glycol and the like can be mentioned.

Specific examples of the polyester constituting the polyester layer B include terephthalic acid units and 2,2
Copolyester composed of dicarboxylic acid units mainly composed of 6-naphthalenedicarboxylic acid units and glycol units mainly composed of ethylene glycol units, mainly composed of dicarboxylic acid units mainly composed of terephthalic acid units and isophthalic acid units and ethylene glycol units Copolyester consisting of glycol units, copolyester consisting of dicarboxylic acid units mainly composed of terephthalic acid units and ethylene glycol units and glycol units mainly composed of 1,4-cyclohexanedimethanol units, dicarboxylic acid mainly composed of terephthalic acid units A copolyester comprising a unit and a glycol unit mainly comprising an ethylene glycol unit and a neopentyl glycol unit is preferably exemplified.

More preferably, the terephthalic acid unit in the dicarboxylic acid unit is 80 to 20 mol%,
Copolyesters having a naphthalenedicarboxylic acid unit of 20 to 80 mol% can be mentioned, and particularly preferably, a terephthalic acid unit is 70 to 30 mol% and a 2,6-naphthalenedicarboxylic acid unit is 30 to 7 in a dicarboxylic acid unit.
Copolyesters that are 0 mol% can be mentioned.

Further, as another preferred example, the dicarboxylic acid unit contains a terephthalic acid unit, a 2,6-naphthalenedicarboxylic acid unit and an isophthalic acid unit. The total of the naphthalenedicarboxylic acid units and the isophthalic acid units is 20 to 80 mol%, and the isophthalic acid units /
When the molar ratio of 2,6-naphthalenedicarboxylic acid units is 0.1.
Copolyesters of 1 to 5 can also be mentioned.

In the present invention, it is preferable that the polyester layer A and / or the polyester layer B contains 0.1 to 30 parts by weight of particles and / or a polyolefin resin. Examples of the particles include talc, kaolin, calcium carbonate, amorphous silica, spherical silica,
Titanium oxide, barium sulfate, silicone, cross-linked polystyrene, carbon black and the like can be mentioned. Examples of the polyolefin resin include polyethylene, polypropylene, and poly (4-methylpentene). And, for example, concealing properties, cards required matte surface and the like, in the field of packaging, etc., particles excellent in concealing properties,
For example, it is of course possible to include titanium oxide, barium sulfate, and the like for purposes other than providing the film with easy sliding. The average particle size of these additives is 0.05 to 5 μm, and more preferably 0.1 to 5 μm.
It is preferably in the range of 1 to 3 μm.

The polyester layer A and / or polyester layer A of the present invention
Alternatively, the polyester layer B may further contain various additives as long as the object of the present invention is not impaired.
For example, if necessary, polybutylene terephthalate-
Components such as an elastomer resin such as a polytetramethylene glycol block copolymer, a pigment, a dye, a heat stabilizer, a flame retardant, a foaming agent, and an ultraviolet absorber can be contained.

The polyester constituting the polyester layers A and B in the present invention can be produced by a known method. Specific examples thereof include a method of reacting one or more dicarboxylic acid ester-forming derivatives with one or more glycols in a polyester production reaction step. 2
Examples of the method include a method of performing uniform mixing and transesterification (redistribution) using a screw extruder. In these steps, if necessary, particles, polyolefin,
Other various additives can be contained in the polyester resin.

The layer structure of the multilayer polyester film in the present invention usually comprises a polyester layer A having a uniaxially stretched orientated structure and a polyester layer B having a substantially amorphous structure. For example, A / B / A in which the polyester layer A is the surface layer and the polyester layer B is the inner layer
(Where / indicates the layer configuration) type three-layer configuration, A
A multi-layer configuration such as a five-layer configuration of the / B / A / B / A type, a seven-layer configuration, a nine-layer configuration, and an n + 1 configuration according to the order of these components is exemplified. Also, if necessary, the polyester layer A
In the case of more than one layer, one or more layers can be composed of different polymers. The same applies to the case where there are two or more polyester layers B. For example, the polyester layer A is composed of two polymers (A
1, A2), and the polyester layer B is composed of two kinds of polymers (B
1, B2), A1 / B1 / A2 type 3
Examples thereof include a layer configuration and a five-layer configuration of A1 / B1 / A2 / B2 / A1 type. Of these layer configurations, 3
Layers, 5 layers are preferred, and 3 layers are particularly preferred.

The multilayer polyester film of the present invention comprises a polyester layer A having a uniaxial or more oriented structure.
Need to constitute the outermost layer. When the polyester layer B having a substantially amorphous structure constitutes the outermost layer, when printing characters, images, etc. on the film surface with ink, an organic solvent such that the film is partially dissolved by a solvent or the like and easily set off. In addition, there is a problem that the film is inferior in durability, and the film tends to stick to various rolls and the like in the process during the production of the film. Incidentally, on one or both surfaces of the outermost surface of the film, as long as the effects of the present invention are not impaired, the adhesion is improved,
Surface treatment such as coating treatment, corona discharge treatment, etc. may be performed for surface modification such as antistatic property improvement and mold release property improvement,
In addition, as a surface treatment method such as a coating treatment, a polyester coating agent, a urethane coating agent, an acrylic coating agent or the like is used alone or as a mixture and applied in the process of film production. And then applying in another step.

The multilayer polyester film in the present invention is manufactured by a co-extrusion film forming method. A specific example thereof will be described for the case of the above-mentioned three-layer film (A / B / A). Is dried and melted. At the same time, the polyester chips prepared for the polyester layer B are dried and melted. Subsequently, these molten polymers are laminated into three layers inside the die, for example, three layers are laminated inside the die where the feed block is installed, and then cast on a cooling drum to form an unstretched multilayer film. Is stretched in the vertical and / or horizontal axis direction, and is heat-set to give 1
A multilayer stretched film having a stretch orientation structure of at least the axis is obtained. The same can be applied to the case of five or more layers. The stretching treatment is carried out under the condition that the polyester layer A forms a desired orientation structure. For example, at a temperature (Tc) of −10 ° C. to Tg + 50 ° C. of Tg (glass transition temperature) of the polyester constituting the layer A, 2. 5 times or more, preferably 3 times
The film is preferably stretched by a factor of up to 6 times and then stretched at a temperature of Tc + 5 ° C. to Tc + 50 ° C. by 2.5 times or more, preferably 3 to 6 times in the transverse direction. This stretching is preferably 8 times or more, more preferably 9 times or more in area ratio. The heat setting process
15 ° C. or lower, more preferably 20 ° C., higher than the final stretching temperature and higher than the melting point of the polyester constituting the polyester layer.
It is preferable to carry out at the following temperature. The stretching may be performed by a simultaneous biaxial stretching method. By the stretching treatment, the polyester constituting the polyester layer B is not substantially oriented and crystallized.

In the multilayer polyester film of the present invention, a polyester layer A having a uniaxially stretched orientated structure
The ratio (a / b) of the total thickness (a) of the polyester layer B having a substantially amorphous structure to the total thickness (b) of the polyester layer B is 0.01 to 3, preferably 0.03 to 2, and more preferably 0. .05-1
It is. This thickness ratio is, for example, that the layer configuration is A1 (thickness: a
1) In the case of three layers of / B1 (thickness: b1) / A2 (thickness: a2), the total thickness ratio (a / b) of layer A and layer B, that is, (a1 + a2) / (b1) is 0.01. ~ 3, and the layer configuration is A1 (thickness: a1) / B1
(Thickness: b1) / A2 (thickness: a2) / B2 (thickness: b
2) In the case of five layers of / A3 (thickness: a3), the total thickness ratio (a / b) of layer A and layer B, that is, (a1 + a2 + a)
3) means that (b1 + b2) is 0.01 to 3; When the total thickness ratio is less than 0.01, the outermost layer thickness of the polyester layer A is small, so that it is difficult to control the thickness during film production, and a problem that a part of the polyester layer B is easily exposed to the surface layer occurs. In addition, the dimensional stability of the film is insufficient. On the other hand, when the total thickness ratio exceeds 3, the existence ratio of the polyester layer B having a substantially amorphous structure is small, so that when the film is subjected to deformation processing such as molding processing, embossing processing, etc., the film is sandwiched between holding metal fittings. When fixed and used, the workability and flexibility of the film are insufficient.

The total thickness of the multilayer polyester film is preferably 10 to 3000 μm, more preferably 50 to 2000 μm, and particularly preferably 100 to 1000 μm. In addition,
When this multilayer film is used as a product, it may be used as a single sheet or as a laminate of two or more sheets. In the case of this lamination, the thickness is appropriately determined depending on the number of layers to be laminated, the total thickness, reasons for use, etc., but as a whole, 100 to 5000 μm, further 200 to 200 μm
A thickness of 0 μm is preferred.

Since the multilayer polyester film of the present invention is a film excellent in processability, moldability, stability over time, solvent resistance and dimensional stability, it can be used in the fields of food packaging, chemical packaging, laminate molding, IC, It is suitable for magnetic recording card materials, agricultural fields, and the like. In particular, among these uses, it is suitable for forming, laminating, and transferring not only a flat body but also a non-flat surface such as a curved surface, an uneven surface, and a three-dimensional structure such as a tray and an ice cream cup. In the field of food packaging, capsules, tablets, etc.
In the pharmaceutical packaging field, furniture, electrical appliances, automotive parts, etc., three-dimensionally formed by bending, curved surface processing, irregularity imparting processing, blow molding, etc. at or after lamination of film with wood, metal, resin, rubber. Surface, furniture, appliances, automobile parts, etc.
In the field of transfer foil, such as transfer to a non-flat three-dimensional surface such as an uneven surface, in cash cards, ID cards, credit cards, etc., characters and patterns are embossed, and / or
Or embedded processing of magnetic tape, IC chip, etc.,
In the field of magnetic recording cards, IC recording card materials, and greenhouses, it can be preferably used in the field of agriculture in which frames and clips are used.

[0027]

EXAMPLES The present invention will be further described below with reference to examples, but the present invention is not limited to these examples. In addition, the measuring method and evaluation method of the characteristics used in the examples and comparative examples are as follows.

(1) Evaluating Formability-1 The film is pressed against an embossing roller to prepare an embossed film having an embossment with an Rz of 500 μm on the front surface. Note that Rz mentioned here is the average of the first to fifth peaks and the first to fifth valleys of the straight line parallel to the average line of the portion extracted by the reference length from the cross-sectional curve. It indicates the distance from the average in μm. ：: Even when embossing was applied, no cracking occurred in the embossed film. ：: When embossing is applied, fine cracks occur in the embossed film. X: A large crack occurs in the embossed film during embossing.

(2) Evaluation of formability-2 PTP (Push Through Package) having a heating plug
The film is press-molded at 130 ° C. by a molding machine to prepare a pack film in which pockets having a length of 20 mm, a width of 10 mm, and a depth of 10 mm are provided at intervals of 10 mm. A: The shape of the pocket is the same as that of the mold, and there is no wrinkle in the film between the pockets. ：: The shape of the pocket was the same as the mold, but the film between the pockets had some wrinkles. ×: There are wrinkles in the pockets, and some of the shapes are not the same as the mold. Further, the film between the pockets is often wrinkled.

(3) Evaluation of printability Using an ink in which a pigment is dispersed with methyl ethyl ketone, continuous printing is performed on one side of a film roll using a gravure roll. A: No ink was transferred from the printing surface to the opposite side of the film roll from the printing side (the non-printing side). ：: The transfer of the ink from the printing surface is fine on the opposite side of the printing of the film roll (non-printing surface). X: The transfer of the ink from the printing surface is on the front surface of the film roll opposite to the printing surface (non-printing surface). This printability evaluation is an alternative to the solvent resistance evaluation.

Example 1 A transesterification reaction and a polycondensation reaction were carried out by a conventional method using dimethyl terephthalate and ethylene glycol as main starting materials and manganese acetate, phosphoric acid and antimony trioxide as catalysts. The resulting polymer was discharged from the reactor and cooled to obtain polyethylene terephthalate pellets (hereinafter referred to as PET).

Similarly, except that 75 mol% of dimethyl terephthalate (based on all acid components), 25 mol% of dimethyl 2,6-naphthalenedicarboxylate (based on total acid components) and ethylene glycol are used as starting materials. PET
A transesterification reaction and a polycondensation reaction are carried out in the same manner as described above, and the obtained polymer is discharged from the reactor and cooled, and pellets of copolymerized polyethylene terephthalate (hereinafter CO-P
ET).

The PET and CO-PET obtained above
Are separately dried and melted by a single screw extruder, and then the molten polymer is laminated on three layers of PET / CO-PET / PET inside the die, and then cast on a cooling drum in this state to obtain an unstretched multilayer. A film was obtained. Subsequently, the multilayer film was stretched 3.2 times in the longitudinal direction at 110 ° C., and further stretched 3.4 times in the transverse direction at 120 ° C.
Heat setting was performed at 210 ° C. to obtain a three-layer film. The thickness configuration of this three-layer film was a total of 120 μm in which the surface layers (polyester layer A) on both sides made of PET were 10 μm and the inner layer (polyester layer B) made of CO-PET was 100 μm. The properties and results of the obtained three-layer film are shown in Table 1. Good results were obtained in both the molding process and the printing evaluation.

[Examples 2 to 7, Comparative Examples 1 to 3] Using a polyester resin having the composition shown in Table 1, the same procedure as in Example 1 was carried out to obtain a three-layer film. Table 1 shows the properties of the obtained three-layer film. All the examples satisfying the conditions of the present invention obtained good results.

Example 8 CO-PET Constituting the Inner Layer
The procedure of Example 1 was repeated except that 75 parts by weight of PET of Example 1 and 25 parts by weight of polyethylene-2,6-naphthalate pellets separately prepared were mixed, dried, melted, and subjected to a transesterification reaction (redistribution reaction). As in Example 1,
The molten polymer was laminated on three layers of PET / CO-PET / PET inside the die, cast in this state on a cooling drum, and then stretched and heat-set to obtain a three-layer film. The properties of the obtained three-layer film were the same as those of Example 1, and good results were obtained in both molding and printing.

Example 9 As a polyester constituting Layer B, 2,6-naphthalenedicarboxylic acid was 40 mol%.
50 parts by weight of copolymerized polyethylene terephthalate pellets and copolymerized polyethylene terephthalate pellets 5 obtained by copolymerizing isophthalic acid with 20 mol%
Except that 0 parts by weight were mixed, dried, melted, and transesterified (redistribution reaction) (hereinafter referred to as CO-PET), except that PET / PET was used inside the die in the same manner as in Example 1.
The molten polymer is laminated on three layers of CO-PET / PET,
In this state, the film was cast on a cooling drum, then stretched and heat-set to obtain a three-layer film. The properties of the obtained three-layer film were the same as those of Example 3, and good results were obtained in both the forming process and the printing evaluation.

[Example 10] PET of Example 1 was used as the polyester constituting the layer A, and 2,6-naphthalenedicarboxylic acid was used as the polyester constituting the layer B.
Mol% copolymerized polyethylene terephthalate pellets (hereinafter referred to as CO-PET-1) and 1,4-
Copolymerized polyethylene terephthalate pellets obtained by copolymerizing cyclohexanedimethanol at 30 mol% (hereinafter referred to as CO-
PET-2), dried separately and melted with a single screw extruder, and then PET inside the die.
/ CO-PET-1 / PET / CO-PET-2 / PE
The molten polymer was laminated on five layers of T, and cast on a cooling drum in this state to obtain a five-layer unstretched multilayer film. Subsequently, the five-layer unstretched film is stretched 110 mm in the machine direction.
Stretched 3.2 times at 120 ° C and 3.4 times at 120 ° C in the transverse direction.
After stretching twice, it was heat-set at 210 ° C. to obtain a five-layer film. The thickness configuration of the five-layer film is such that the PET layer is one.
0 μm, and the layers made of CO-PET-1 and CO-PET-1 each had a total of 230 μm of 100 μm. Regarding the characteristics of the obtained film, favorable results were obtained in both the molding process and the printing evaluation.

[0038]

[Table 1]

[0039]

According to the present invention, the processability, moldability, stability over time, and durability are useful in the fields of food packaging, medicine packaging, laminate molding, IC, card materials for magnetic recording, agriculture, and the like. A film having excellent solvent properties and dimensional stability can be provided at low cost.

Continued on the front page F-term (reference) 4F100 AK41A AK41B AK41C AK42B AL01B BA03 BA06 BA10A BA10C BA16 BA25 EH20 EJ37A EJ37C EJ38A EJ38C GB01 GB15 GB23 GB66 JA11A JA11C JA12B JB07 JJ03 Q05 A06A06

Claims (5)

[Claims] 1. A multilayer film having at least three layers produced by a co-extrusion film forming method, comprising a polyester layer A having a uniaxial or more oriented orientation structure and a polyester layer B having a substantially amorphous structure. It has a laminated structure, both outer layers are composed of the polyester layer A, and the total thickness of the polyester layer A (a)
A ratio (a / b) of the total thickness (b) of the polyester layer B to the polyester layer B is 0.01 to 3; 2. The multilayer polyester film according to claim 1, wherein the multilayer film comprises three layers of polyester layer A / polyester layer B / polyester layer A. 3. The polyester having a substantially amorphous structure of the layer B is a copolyester comprising a dicarboxylic acid unit mainly comprising terephthalic acid units and naphthalenedicarboxylic acid units and a glycol unit mainly comprising ethylene glycol units. The multilayer polyester film according to claim 1. 4. The polyester of the layer B having a substantially amorphous structure, comprising a dicarboxylic acid unit mainly composed of terephthalic acid units and a glycol unit mainly composed of ethylene glycol units and 1,4-cyclohexanedimethanol units. 3. The multilayer polyester film according to claim 1, which is a polyester. 5. The polyester having a substantially amorphous structure in the layer B is a copolyester comprising a dicarboxylic acid unit mainly composed of terephthalic acid units and a glycol unit mainly composed of ethylene glycol units and neopentyl glycol units. The multilayer polyester film according to claim 1.