JPH1110723A - Manufacture of biaxially oriented polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method for a biaxially oriented film of various superior characteristics. SOLUTION: A central section of a non-oriented film is formed of at least three layers in the thickness direction when viewing from the width direction, and both ends are so coextrusion laminated as to form a single-layer structure in the thickness direction, and as polyester constituting both ends, a polyester B other than a polyester A constituting an outermost layer of the central section is used, and the glass transition point of the polyester B is 50 deg.C or above, while the thickness ratio of the polyester B constituting an inner layer of the central section is set less than 0.3 to the total thickness of a film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polyester film, and more particularly to a method for easily producing a biaxially oriented polyester film which is produced by a co-extrusion molding method and which is excellent in various properties. It is about.

[0002]

2. Description of the Related Art Polyester multilayer films have been used for various applications with diversification of film quality and performance. However, although the multilayer film has more excellent characteristics due to the combination of polymers having different properties, it has the following problems.

That is, in the production of a normal polyester film, both ends of the film, a broken film,
Films of inferior quality are again chipped and can be reused, whereas in the case of multi-layer films, reproduction and use are limited because layers having different properties are mixed during reproduction.
Also, when a polyester film is used for a packaging material, there are many cases where the polyester film is used by being bonded to another material.
Copolyesters are often used. However, the film using the copolymerized polyester has excellent adhesiveness at the time of lamination, but causes a problem of handling property such that the film easily adheres to a metal processing jig or the like in an atmosphere above the glass transition point in the manufacturing process. . In particular, in the biaxial stretching method, when heat-fixed in a tenter which is a transverse stretching apparatus, there are problems such as frequent breakage due to sticking to a tenter clip and a reduction in processing yield.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to solve the above-mentioned drawbacks of the conventional production method and to produce a biaxially oriented polyester film excellent in various properties. About.

[0005]

That is, the gist of the present invention is that (a) a step of extruding a molten polyester resin into a sheet on a rotary cooling drum to obtain an unoriented sheet;
Biaxially stretching the obtained unoriented sheet to obtain a stretched film, and (c) removing the end of the obtained stretched film by trimming to obtain a product film,
In the step (a), the non-oriented sheet is co-extruded and laminated so that the central portion thereof when viewed in the width direction is formed of at least three layers in the thickness direction, and both ends have a structure of one layer in the thickness direction. As the polyester constituting both ends, a polyester (B) other than the polyester (A) constituting the outermost layer at the center is used, the glass transition point of the polyester (B) is 50 ° C. or more, and the inner layer at the center is The thickness ratio of the constituting polyester (B) is 0.1 to the total thickness of the film.
3 is a method for producing a polyester film.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The present invention is characterized by comprising at least two kinds of polyesters, wherein the polyester (A) forms the outermost layer of the laminated structure in the thickness direction at the center in the film width direction, and the polyester (B) is formed by the transverse stretching. Both ends in the width direction, which are sometimes clipped and removed by trimming, and the inner layer of the laminated structure at the center in the film width direction are formed.

In the present invention, the polyester means an aromatic dicarboxylic acid such as terephthalic acid or 2,6-naphthalenedicarboxylic acid or an ester thereof, and a polyester obtained by using ethylene glycol as a main starting material. Components may be contained. In this case, as the dicarboxylic acid component, for example, isophthalic acid,
One or more of phthalic acid, 2,6-naphthalenedicarboxylic acid, terephthalic acid, adipic acid, sebacic acid, and oxycarboxylic acid components such as p-oxyethoxybenzoic acid can be used. As the glycol component, one or more of diethylene glycol, propylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol and the like can be used.

When used as a packaging material that requires heat sealing properties, the outermost layer of the polyester (A) has a copolymer component of 10 to 35 mol%, and more preferably 1 to 35 mol%.
Those having a range of 5 to 30 mol% are preferably used. In the present invention, the polyester (B) forming the end portion of the film and the inner layer at the central portion has a glass transition point of 50 ° C. or more.
When the glass transition point of the polyester (B) is less than 50 ° C,
During transverse stretching or heat fixing, the polymer frequently adheres to the clip, causing frequent breakage, which lowers the processing yield, which is not preferable.

Polyester (A) and polyester (B)
Is preferably within 40 ° C., more preferably within 35 ° C., particularly preferably within 30 ° C. The glass transition point difference is 40 ° C
If it exceeds, the range of the optimal stretching temperature is different, so that the entire film may not be stretched uniformly. As a result,
Breakage may occur frequently or a film having good characteristics may not be obtained.

[0010] Polyester (A) and polyester (B)
The melting point difference is within 60 ° C, more preferably within 50 ° C, especially 4 ° C.
0 ° C or less is good. If the difference in melting point exceeds 60 ° C., the difference in melt viscosity is too large, and it may be difficult to control the flow of the polymer in the die, and the film cross-sectional shape intended in the present invention cannot be obtained. There are cases. Mixing of recycled materials is effective in reducing the production cost of polyester film.However, when manufacturing recycled materials from the film edge removed by trimming or the film that did not become a product, contamination of foreign materials and Thermal degradation of the raw material cannot be avoided, and therefore, the amount of the recycled raw material is limited by film characteristics. In particular, when the film thickness is small, the effect of thermal degradation of the polymer and foreign matters is great, and at present, only a limited amount of recycled material can be blended.

In the present invention, the polyester (B) may be blended with a recycled material in an amount of usually at least 20% by weight, preferably at least 30% by weight, more preferably at least 40% by weight.
Since the polyester (B) is used for the end portion removed by trimming and the inner layer at the central portion which does not appear on the surface of the product, the polyester (B) does not affect the product properties within the scope of the present invention.
Recycled blended raw materials can be used as inexpensive polymers.

[0012] The polyester (A) may be blended as needed, without blending a recycled material.
As in the case of the recycled material, the properties required as a product are insufficient, but the production cost can be reduced by using an inexpensive raw material having a low production cost for the polyester (B).

The center part of the product is polyester (A)
Has a laminated structure of at least three layers as the outermost layer, and the thickness ratio of the polyester (B) constituting the inner layer is less than 0.3 with respect to the total film thickness. When the thickness ratio of the polyester (B) constituting the inner layer is 0.3 or more, the influence of the polyester (B) of the inner layer appears on the outermost layer, which is not preferable.
When the recycled material is used for the polyester (B) to reduce the production cost, foreign substances that cannot be removed when the recycled material is produced appear as projections on the product surface, and impair the film characteristics. If the thickness ratio is less than 0.3, the recycled material can be blended not only at both ends where trimming is removed but also at the inner layer of the film, and more recycled material can be used.

In the present invention, another polymer may be laminated between the outermost polyester (A) and the inner polyester (B) to form a three or more layer structure. In the present invention, the slipperiness of the obtained film is improved,
In order to impart anti-blocking properties and improve handleability, it is preferable that at least the resin for the central part contains particles.

One of the methods is to use a phosphorus compound or the like to act on a metal compound dissolved in the reaction system during the production of polyester, for example, a metal compound dissolved in the system after the transesterification reaction, to form fine particles. There is a so-called precipitated particle method. This method is simple and can be industrially easily adopted. As another method, there is a method of adding fine particles to polyester in any of the steps from the polyester production step to the extrusion step before film formation, that is, a so-called additive particle method. Either method may be employed.

Examples of the fine particles used in the additive particle method of the present invention include silicon oxide, titanium oxide, zeolite, silicon nitride, boron nitride, celite, alumina, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, and barium sulfate. , Calcium phosphate, lithium phosphate, magnesium phosphate, lithium fluoride, aluminum oxide, silicon oxide, titanium oxide, kaolin, talc, carbon black, silicon nitride, boron nitride and as described in JP-B-59-5216. Examples of the crosslinked polymer fine particles include, but are not limited to, these.

The shape of these fine particles may be spherical, massive or flat, and the hardness, specific gravity, color and the like are not particularly limited. The average particle size of the fine particles is not particularly limited, but is usually selected from a range of 0.01 to 10 μm, preferably 0.05 to 8 μm in equivalent sphere diameter. The fine particles to be blended may be a single component, or two or more components may be used simultaneously.

The addition amount of the fine particles is 0.05 to 3% by weight,
Further, the content is preferably 0.1 to 2% by weight. If the amount of the fine particles is less than 0.05% by weight, the film tends to have poor slipperiness and poor winding characteristics. When the amount of the fine particles added is 3
Exceeding the percentage by weight may result in an excessive degree of surface roughening of the film, for example, causing poor electrical insulation when used for capacitors or dropout when used for magnetic recording. There is.

In the present invention, a film whose surface is appropriately roughened by the above-described method is obtained, but the center line average roughness (Ra) of the film surface is 0.01 to 0.20 μm.
m, more preferably 0.02 to
The range is 0.15 μm. If Ra is less than 0.01 μm, winding tends to be difficult, and the film may be wrinkled and may not be a product. Ra is 0.20
If it exceeds μm, the flatness of the film surface will be impaired,
When used for capacitors, it may cause electrical insulation failure, and when used for magnetic recording, it may cause dropout.

Polyester (A) and polyester (B)
As described above, melt extrusion is performed in the width direction and the thickness direction according to a known method, for example,
A matching method disclosed in, for example, JP-A-118832, JP-A-1-118428, and JP-A-8-207119 can be applied. By these methods, when viewed in the width direction, (the end composed of the polyester (B)) /
The molten polyester melt was previously merged so as to be in the order of (central portion which is a laminated structure of polyester (A) and polyester (B)) / (end portion composed of polyester (B)) and coextruded. Thereafter, biaxial stretching is performed according to a conventional method.

The molten polymer coextruded from the slit-shaped die is rapidly cooled and solidified on a rotary cooling drum so as to have a temperature equal to or lower than the glass transition temperature, thereby obtaining a substantially amorphous unoriented sheet. In this case, in order to improve the flatness of the sheet, it is preferable to increase the adhesion between the sheet and the rotary cooling drum.
Alternatively, a liquid application adhesion method is preferably employed.

The electrostatic application adhesion method is generally such that a linear electrode is provided on the upper surface of a sheet in a direction perpendicular to the flow of the sheet, and a DC voltage of about 5 to 10 kV is applied to the electrode to statically apply the sheet. This is a method of improving the adhesion to the drum by giving a charge. In addition, the liquid application adhesion method is a method of improving the adhesion between the drum and the sheet by uniformly applying the liquid to the entire or a part of the surface of the rotary cooling drum (for example, only the part in contact with both ends of the sheet). It is. In the present invention, both may be used as needed.

In the present invention, (polyester (B)) / (laminated structure of polyester (A) and polyester (B)) / (polyester (B)) obtained in the width direction obtained as described above. The unstretched sheet having the structure described above is biaxially stretched to form a film. Specifically, first, the unstretched sheet is stretched in one direction by a roll or tenter type stretching machine. The stretching temperature in the first stage is a temperature of 30 to 170 ° C. and is stretched 3.0 to 7 times.
Next, the film is stretched in a direction orthogonal to the first stage by a tenter-type stretching machine. In this second stage, the stretching temperature is 40 ° C.
Stretching is usually performed at a temperature of up to 240 ° C. and a stretching ratio of 3.0 to 7 times.

A method in which unidirectional stretching is performed in two or more stages can be adopted, but also in this case, it is preferable that the final stretching ratio falls within the above range. It is also possible to simultaneously biaxially stretch the unstretched sheet so that the area magnification becomes 10 to 40 times. The heat treatment of the obtained film can be carried out arbitrarily according to the purpose of use of the film, and if necessary, before or after the heat treatment, the film may be stretched again in the longitudinal and / or transverse directions.

The heat treatment of the obtained biaxially oriented film includes the following steps:
The heat setting is performed in a temperature range of 0 to 250 ° C, preferably 60 to 220 ° C for 1 second to 1 hour. Heat setting temperature is 25
When the temperature is higher than 0 ° C., the breaking strength of the film tends to decrease, and when the temperature is lower than 50 ° C., the breaking elongation of the film tends to increase. Further, the obtained film is rolled at 30 to 140 ° C., preferably 40 to 1 ° C., depending on the use.
The heat treatment can be performed in a temperature range of 20 ° C. for 1 hour to 1500 hours.

Further, in order to control the film characteristics such as the shrinkage of the film, the film may be subjected to longitudinal relaxation or lateral relaxation as required. When heat treatment is performed, the film is cooled to room temperature and slit to a width suitable for each application.

[0027]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the scope of the invention. The methods for measuring physical properties used in the present invention are shown below. (1) Average particle size of fine particles Centrifugal sedimentation type particle size distribution analyzer SA- manufactured by Shimadzu Corporation
The particle size was measured using a CP3 type by the sedimentation method based on Stokes' resistance law. The average particle size was determined using a value of 50% of the integrated (volume basis) in the equivalent spherical distribution of the particles obtained by the measurement. (2) Melting point and glass transition temperature PerkinElmer differential scanning calorimeter DSC7
It was measured using a mold. The DSC measurement conditions are as follows. That is, 6 mg of a sample film was set in a DSC device, melted and held at a temperature of 300 ° C. for 5 minutes, and then rapidly cooled with liquid nitrogen. The quenched sample was heated from 0 ° C. at a rate of 10 ° C./min to obtain a glass transition temperature (Tg) and a melting point (Tg).
m) was detected. (3) Amount of copolymerization A polyester sample was dissolved in deuterated trifluoroacetic acid, and the amount of copolymerization was determined from the composition of the polymer analyzed by ¹ H-NMR. (4) Thickness ratio The thickness ratio was determined from the following equation.

The thickness of the entire film (μm) / the thickness of the inner layer (μm) (4) Continuous film formability The continuous film formability was evaluated according to the following ranks.

[0029]

[Table 1] ○: The film does not adhere to rolls and clips, etc., and is 500
Films of 0 m or more can be continuously formed. Δ: The film does not adhere to rolls and clips, etc., but breakage due to stretching unevenness occurs about once every 5000 m. ×: Adhesion of the film to rolls, clips, etc. occurs. ,
(5) Film surface properties A sample obtained by depositing aluminum on the film surface was observed under a microscope and evaluated according to the following ranks.

[0030]

○: Uniform projections formed, no coarse projections observed ×: Uniform projections formed, coarse projections also observed (Production of polyester-1) dimethyl terephthalate 10
Using 0 parts by weight, 60 parts by weight of ethylene glycol and 0.09 parts by weight of magnesium acetate as a transesterification catalyst, a transesterification reaction was carried out according to a conventional method, and then a spherical particle dispersed in ethylene glycol having an average particle diameter of 0.7 μm. 0.5 parts by weight of silica particles were added. Next, after adding 0.04 parts by weight of antimony trioxide as a polymerization catalyst, a polycondensation reaction was allowed to proceed according to a conventional method to obtain polyester-1 having an intrinsic viscosity of 0.70. The Tg of the obtained polymer is 73
° C and the melting point was 256 ° C. (Production of polyester-2) In the production of polyester-1, instead of dimethyl terephthalate 100 parts by weight,
Polyester-2 was obtained in the same manner as in the production of Polyester-1, except that 85 parts by weight of dimethyl terephthalate and 15 parts by weight of dimethyl isophthalate were used. The copolymerization amount of the obtained polymer was 15 mol%, Tg was 63 ° C., and melting point was 221 ° C. (Production of Polyester-3) Dimethyl terephthalate 78
A transesterification reaction was carried out according to a conventional method, using a mixture of 2 parts by weight, 22 parts by weight of dimethyl isophthalate, 56 parts by weight of 1,4-butanediol, and 0.005 part by weight of tetrabutyl titanate as a transesterification catalyst. 0.
0.5 parts by weight of spherical silica particles dispersed in 7 μm ethylene glycol were added. Next, after adding 0.005 parts by weight of tetrabutyl titanate as a polymerization catalyst, a polycondensation reaction was allowed to proceed according to a conventional method to obtain polyester-3 having an intrinsic viscosity of 0.80. The Tg of the obtained polymer is 28
° C and the melting point was 190 ° C. (Production of Polyester-4) 100 parts by weight of dimethyl naphthalene-2,6-dicarboxylate, ethylene glycol 6
A transesterification reaction was performed according to a conventional method using 5 parts by weight and 0.09 parts by weight of magnesium acetate as a transesterification catalyst, and then 0.5 g of spherical silica particles dispersed in ethylene glycol having an average particle diameter of 0.7 μm were used. Parts by weight were added. Next, after adding 0.04 part by weight of antimony trioxide as a polymerization catalyst, a polycondensation reaction was allowed to proceed according to a conventional method to obtain a polymer having an intrinsic viscosity of 0.53. Next, solid-phase polymerization was performed to finally obtain polyester-4 having an intrinsic viscosity of 0.60. The obtained polymer has a Tg of 113 ° C. and a melting point of 270.
° C. (Production of Recycled Raw Material-1) Polyester-1 was dried, melted at 280 ° C with an extruder, extruded from a T-die into a sheet, and cooled by a rotating cooling drum with a surface temperature set at 30 ° C. The mixture was quenched and solidified by using the above method to prepare a substantially amorphous sheet having a thickness of 220 μm. Next, the amorphous sheet is stretched 3.7 times in the machine direction, stretched 4.0 times in the transverse direction, heat-treated, and removed by scraping and trimming generated when a biaxially oriented film having a thickness of 15 μm is manufactured. The cut ear portion was crushed, and a chip-shaped regenerated raw material-1 was produced with an extruder equipped with a vent. Obtained recycled material-1
Had an intrinsic viscosity of 0.65. (Production of Recycled Raw Material-2)
Polyester-1 to Polyester-4, melt temperature 3
Except that the temperature was changed to 00 ° C., recycled material-2 was obtained in the same manner as in the production of recycled material-1. The intrinsic viscosity of the obtained recycled material-2 was 0.56.

Example 1 Polyester (A) was used as polyester-1 and polyester (B) was used as a recycled material. Each was dried, melted at 280 ° C. in separate extruders, and extruded from a T-die in the width direction. And a layer structure of (end portion composed of polyester (B)) / (center portion of laminated structure composed of both outer layers of polyester (A) and inner layer of polyester (B)) / (edge portion composed of polyester (B)). The molten polymer was previously joined so that The temperature from when the molten polymer merges to when it is extruded from the T-die is 280 ° C,
The sheet was extruded into a sheet shape from a T-die and rapidly cooled and solidified by a rotating cooling drum having a surface temperature set at 60 ° C. by using an electrostatic application cooling method to prepare a substantially amorphous sheet having a thickness of 240 μm.

The area in the width direction at this time was 1: 8: 1 in length ratio in the width direction. Next, this amorphous sheet is stretched 4.0 times in the longitudinal direction at 85 ° C., and is stretched in the transverse direction at 95 ° C.
, And heat-treated at 230 ° C. for 3 seconds, and the ears (ends) were removed by trimming to produce a 15-μm-thick biaxially oriented film composed of three layers. The obtained film had a three-layer structure of polyester (A) / polyester (B) / polyester (A) in the thickness direction, and the thickness ratio of polyester (B) was 0.25.

There was no sticking to the stretching rolls and clips in the stretching step, and the continuity of the film formation was good. Comparative Example 1 In Example 1, the thickness ratio of the polyester (B) was changed to 0.5.
A film was produced in the same manner as in Example 1 except that the above-mentioned conditions were satisfied, and a biaxially oriented film having a thickness of 15 μm was obtained.

There was no sticking to the stretching rolls and clips in the stretching step, and no whitening of the ears was observed. In addition, no break in the winding step of the ear portion removed by trimming was observed, and the continuity of the film formation was good. Examples 2 to 6, Comparative Example 2 A film was produced in the same manner as in Example 1 except that the film was changed as shown in Table 1 below.

The results obtained are summarized in Table 2 below.

[0036]

[Table 3]

[0037]

[Table 4]

[0038]

According to the production method of the present invention, an excellent biaxially oriented polyester film can be produced continuously and stably, and its industrial value is high.

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Claims (2)

[Claims] 1. A step of (a) extruding a molten polyester resin into a sheet on a rotary cooling drum to obtain an unoriented sheet, and (b) a step of biaxially stretching the obtained unoriented sheet to obtain a stretched film. And (c) removing the end of the obtained stretched film by trimming to obtain a product film. In the step (a), the central portion of the unoriented sheet when viewed in the width direction is the thickness direction. A polyester other than the polyester (A) constituting the outermost layer at the center as the polyester constituting the both ends by co-extruding and laminating at least three layers and having both ends having a one-layer structure in the thickness direction. Using (B), the glass transition point of the polyester (B) is 50 ° C. or more, and the thickness ratio of the polyester (B) constituting the inner layer at the center is less than 0.3 with respect to the total thickness of the film. A method for producing a polyester film, comprising: 2. The polyester (A) and the polyester (B) have a glass transition point difference of 40 ° C. or less and a melting point difference of 60 ° C.
The method for producing a polyester film according to claim 1, wherein