JPH10244573A - Production of polyester film for thermal stencil printing base paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively produce a film for high sensitivity thermal stencil printing base paper excellent in film winding characteristics, perforation sensitivity and resolution and density of an image at the time of printing. SOLUTION: This production method consists of a process (a) extruding a molten polyester resin to the surface of a rotary cooling drum to obtain a non-oriented sheet, a process (b) biaxially stretching the obtained non-oriented sheet to obtain a stretched film and a process (c) removing the end part of the obtained stretched film by trimming to obtain a product film. In the process (a), at least one of the end parts of the non-oriented sheet is provided by co- extrusion by using a polyester resin (B) being within 90 deg.C in the difference with the m.p. of a polyester resin (A) constituting the part adjacent to the end part and the m.p. of the polyester resin (A) is 150-240 deg.C.

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 for heat-sensitive stencil printing paper,
More specifically, the present invention relates to a method for producing a film for heat-sensitive stencil printing paper, which is produced using a co-extrusion molding method and is excellent in various properties.

[0002]

2. Description of the Related Art A heat-sensitive stencil printing base paper in which porous thin paper is laminated on a thermoplastic resin film such as polyester is known. The characteristics required for the above-mentioned film used for the heat-sensitive stencil printing paper are as follows. Examples include winding characteristics, perforation sensitivity, curl resistance, image resolution and density during printing.

Various proposals have been made to satisfy such required characteristics. For example, a biaxially stretched film intended for a thermoplastic resin, the film having improved printing characteristics by defining its thermal characteristics (Japanese Patent Application Laid-Open No. 62-149496), surface roughness and number of protrusions (JP-A-63-227634)
Japanese Patent Application Laid-Open No. Sho 62-62), a film having specified heat shrinkage characteristics
-282983, JP-A-63-160895, JP-A-63-31192, JP-A-3-30
No. 996) has been proposed.

However, these films sacrifice one of the above-mentioned required characteristics in order to satisfy one of the required characteristics, and do not satisfy many required characteristics simultaneously and sufficiently.

[0005]

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 method, to greatly reduce the manufacturing cost, and to further reduce the image quality at the time of printing. An object of the present invention is to provide a heat-sensitive stencil film having excellent resolution and density.

[0006]

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), at least one of the ends of the unoriented sheet has a polyester resin (B) having a difference from the melting point of the polyester resin (A) constituting the portion adjacent to the end within 90 ° C. or less. The polyester resin (A) has a melting point of 150 to 24.
A method for producing a polyester film for heat-sensitive stencil printing paper characterized by being at 0 ° C.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
In the present invention, (a) a step of extruding a molten polyester resin into a sheet on a rotary cooling drum to obtain an unoriented sheet, and (b) stretching the obtained unoriented sheet in at least one axial direction to obtain a stretched film. A method for producing a thermoplastic resin sheet or a film, which comprises a step and (c) a step of obtaining an end product of the obtained stretched film by trimming to obtain a product film, is known per se.

The polyester resin referred to in the present invention is one in which the bifunctional acid component is mainly composed of an aromatic dicarboxylic acid or an ester-forming derivative thereof. Specifically, terephthalic acid, 2,6-naphthalenedicarboxylic acid, Examples of the ester-forming derivative include dimethyl terephthalate and dimethyl 2,6-naphthalenedicarboxylate, which are selected according to the intended use. Of these, terephthalic acid and dimethyl terephthalate are preferably selected.

The glycol component includes ethylene glycol, butylene glycol, propylene glycol,
Examples thereof include polyethylene glycol and 1,4-cyclohexanedimethanol, and ethylene glycol and butylene glycol are preferred.

[0010] Such a polyester resin comprises one kind of aromatic dicarboxylic acid or an ester-forming derivative thereof,
The polyester may be a polyester starting from a different glycol component, or may be a copolymer containing two or more components. In addition to the above as components to be copolymerized, for example, diol components such as diethylene glycol, neopentyl glycol, polyalkylene glycol, adipic acid, sebacic acid, phthalic acid, dicarboxylic acid components such as isophthalic acid, trimellitic acid, pyromellitic acid And the like are selected according to the application.

In the present invention, it is preferable that the polyester resin (B) constituting at least one end has an affinity at the interface with the polyester resin (A) constituting a portion adjacent to the end. Therefore, the polyester resin (B) is preferably similar to the polyester resin (A) in polymer structure. If the polyester resins (A) and (B) are composed of completely different components, peeling at the interface may occur. In addition, suitable stretching conditions for each polymer are different, and as a result, crystallization may occur at the time of stretching, and partial adhesion may occur between the polymer and a stretching roll.

In the present invention, it is usually preferable that the polyester resin (B) constituting at least one end is a polymer containing 50 mol% or more of the component constituting the polyester resin (A). As a method for allowing the polyester resin (B) to contain the above constituent components,
Either a method of using a recycled product for the polyester resin (B) or a method of blending a polymer for the center with a polymer for the end may be used.

According to the present invention, the difference in melting point between the polyester resin (B) constituting at least one end and the polyester resin (A) constituting a portion adjacent to the end is within 90 ° C., preferably within 70 ° C. More preferably, the temperature is within 50 ° C. If the melting point difference exceeds 90 ° C., it is difficult to set the temperature in the polymer melting step, and it is not preferable because a desired film cannot be obtained.

Usually, the temperature of the extruder can be set in accordance with the melting point of the polymer for the end portion and the melting point of the polymer for the center portion. Up to the portion, both ends and the central portion are extruded at substantially the same temperature, so that it is difficult to set the temperature according to the melting points of the polymers at the end and the central portion.
If the above melting point difference exceeds 90 ° C., if the extrusion temperature is adjusted to the high melting point polymer, the low melting point polymer is thermally degraded, and if the extrusion temperature is adjusted to the low melting point polymer, Problems such as solidification of a polymer having a high melting point occur, which is not preferable.

The stretching temperature in the stretching process of the film is set in accordance with the polymer at the center of the product. If the melting point of the end polymer is lower than the center polymer by more than 90 ° C., , The end polymer sticks to the stretching rolls or clips, etc., making it impossible to manufacture, 90 ° C
If the temperature is higher than, the polymer at the end is not stretched and undesirably causes a problem such as separation at the interface between the end and the center.

In the case where a copolymerized polyester or two or more polyesters are blended as the polyester resin (B) and two or more melting points of the polymer are measured, if at least one melting point is within the range of the present invention, it does not matter. Absent.

Further, in the present invention, in order to obtain an excellent polyester film for heat-sensitive stencil printing paper, the melting point of the polyester resin (A) is from 150 to 240 ° C., preferably from 170 to 240 ° C.
To 230 ° C, more preferably 180 to 220 ° C. When the melting point of the polyester resin (A) is higher than 240 ° C., the high perforation sensitivity aimed at by the present invention cannot be obtained, and when the melting point is lower than 150 ° C., the gradation of a printed image becomes inferior. .

In the present invention, since both ends are removed by trimming, a recycled material or a material having a low production cost can be used for both ends.

The blending of the recycled material is effective in reducing the production cost of the polyester film. However, when the recycled material is produced from the film edge removed by trimming or the film that has not become a product, foreign materials are not effectively mixed. Inevitably, the mixing of recycled materials is limited by the film properties, and especially when the film thickness is small, the thermal degradation of the polymer and the effects of foreign matter are large and limited. At present, only a small amount of recycled materials can be blended.

In the present invention, since both ends are removed by trimming, even if the recycled material is used at both ends, the effect of the recycled material is not reflected on the product at the center, so that the amount of the blended material at the ends is reduced. There are few restrictions, and it is possible to mix more recycled materials than conventional production methods. As for the central part,
Even if the recycled material is not blended, it may be blended if necessary. However, within the limited blending amount, blending of the recycled material in the central portion is also effective in reducing the production cost.

As in the case of recycled materials, the characteristics required as a product are insufficient, but the production costs can be reduced by using inexpensive raw materials having low production costs at both ends. In the present invention, it is preferable that at least the polyester resin (A) contains particles in order to improve the slipperiness of the obtained film and impart good blocking resistance to handleability.

In one of the methods, fine particles are produced by reacting 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 with a phosphorus compound or the like. 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, but 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 those described in JP-B-59-5216. Examples of the crosslinked polymer fine particles include, but are not limited to, these.

The shape of the fine particles may be spherical, massive or flat, and the hardness, specific gravity,
There is no particular limitation on the color and the like. 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
If the amount exceeds the weight percentage, the degree of surface roughening of the film surface is too large, and the perforation may be non-uniform. In the present invention, a film whose surface is appropriately roughened by the method as described above is obtained.However, in order to further satisfy workability and printing resolution, print quality, the center line average of the film surface is required. The roughness (Ra) is preferably 0.01 to 0.20 μm, and more preferably 0.02 to 0.15.
It is in the range of 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. On the other hand, when Ra exceeds 0.20 μm, the flatness of the film surface is impaired, the perforations become uneven, and the resolution tends to be poor, and the print quality tends to be impaired.

The thickness of the film of the present invention is 0.5 to 10 μm.
m, preferably 0.5 to 7 μm, more preferably 0.1 μm.
The range is 5 to 5 μm. The thinner the film is, the shorter the heat conduction distance is. As a result, the heat energy required at the time of perforation is reduced, the perforation is improved, and the resolution and print quality at the time of printing are improved. However, when the thickness of the film is less than 0.5 μm, the printing tends to be unclear, uneven shading tends to occur, and the printing durability tends to be significantly reduced. vice versa,
When the thickness of the film exceeds 10 μm, the perforation property is deteriorated, so that the printing tends to be uneven.

The method of melt-extruding the polyester resins (A) and (B) in the width direction as described above is a conventionally known method, for example, Japanese Patent Application Laid-Open Nos. -118428, JP-A-8-20
The matching method disclosed in, for example, Japanese Patent No. 7119 can be applied.

With these methods, the molten polyester melt is preliminarily merged in the order of end polyester / central polyester / (if necessary) end polyester when viewed in the width direction of the molten sheet, and is co-extruded. After that, biaxial stretching is performed according to a conventional method. The molten polymer co-extruded from the slit die is quenched and solidified on a rotary cooling drum to a temperature equal to or lower than the glass transition temperature to obtain 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. In the present invention, the electrostatic application adhesion method and / or the liquid application adhesion method are preferably employed.

In the present invention, the unstretched sheet of the polyester at the end, the polyester at the center, and the polyester at the end (if necessary) obtained in the width direction obtained as described above is biaxially stretched. Film. Specifically, first, the unstretched sheet is stretched in one direction by a roll or tenter type stretching machine. In this first stage,
The stretching temperature is usually from 20 to 100 ° C, preferably from 25 to 8 ° C.
At 0 ° C., the stretching ratio is usually 3.0 to 7 times, preferably 3.
5 to 7 times. Next, the film is stretched in a direction orthogonal to the first stage by a tenter-type stretching machine. In the second stage, the stretching temperature is usually 20 to 100 ° C., preferably 2 to 100 ° C.
The stretching ratio is usually 5 to 90 ° C, preferably 3.0 to 7 times, preferably 3.5 to 7 times, and more preferably 4.0 to 7 times.

A method in which unidirectional stretching is performed in two or more stages can be adopted, but in such a case, it is preferable that the final stretching ratio is in 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, and if necessary, before or after the heat treatment, the film may be stretched again in the vertical and / or horizontal direction.

In the present invention, in order to obtain a film having the above-mentioned heat shrinkage characteristics, the stretching ratio is set to 15 times or more in terms of area, and the heat treatment after the stretching is substantially not carried out. Preferably, the following conditions are employed. That is, the heat treatment temperature is usually 110 ° C. or less, preferably 90 ° C. or less, and the heat treatment time is 1 second to 5 minutes. Then, heat treatment is performed on the film under the constant length or under the elongation within 30%.

After being heat-set and cooled to room temperature, it is wound up by a winder, and further slit into widths suitable for each application. During winding or slitting of the winder, the edge is removed from the product by slitting inside the boundary between the end polymer and the center polymer, that is, at the boundary made of the polyester resin (A) having a melting point of 150 to 240 ° C. .

The film of the present invention has excellent heat-perforation properties and is excellent in thermal sensitivity and excellent in printing resolution and gradation by laminating a predetermined porous thin paper with a known adhesive according to a conventional method. It can be used as a stencil sheet. The biaxially oriented polyester film of the present invention thus obtained is most suitable for heat-sensitive stencil printing paper.

[0034]

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) Film thickness A film specimen having a width W (cm) and a length L (cm) is prepared, and the weight of the specimen is G (g) and the density d (g / cm ³ ). The film thickness t (μm) was calculated by the following equation.

[0036]

T = G / (W × L × d) × 10000 (3) Melting point Perkin Elmer 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, heated at a rate of 10 ° C./min, measured in the range of 0 ° C. to 300 ° C., and the melting point was measured as the top of the melting endothermic peak.

(4) Practical properties of heat-sensitive stencil printing base paper Japanese paper was bonded to a film to prepare a base paper. The obtained base paper is applied with an applied energy of 0.0 by a thermal head.
At 9 mJ and 0.12 mJ, character images and 16-step gradation images were made. The perforated state of the gradation image portion was observed with a microscope from the film side of the perforated base paper, and the following items were evaluated. (A) Sensitivity ：: Predetermined perforation is performed reliably and the size of perforation is sufficient and very good ○: Predetermined perforation is performed almost reliably and the size of perforation is sufficient and good △: Rarely predetermined There is a portion where the perforation cannot be obtained or a portion where the perforation size is insufficient. X: There are many portions where the predetermined perforation cannot be obtained, the perforation size is insufficient, and there is a problem in practical use. The base paper was actually printed using a lithograph AP7200 printing machine manufactured by Riso Kagaku Kogyo KK, and the following characteristics of the obtained characters and images were visually judged.

(B) Printing quality ◎: Clear printing without any unevenness or blur of density
Very good ○: Clear printing without density unevenness and bleeding, good Δ: Slightly uneven shading and bleeding observed, and slightly lacking in clearness ×: Uneven shading, bleeding and blurring clearly appear (C) Printing durability ：: Continuous printing of 2,000 or more sheets possible ×: Continuous printing of only about several hundred sheets due to contamination of the thermal head, etc. Next, the raw material polyester resin used in the examples was The manufacturing method will be described.

(Production of Polyester-1) Starting with 80 parts by weight of dimethyl terephthalate, 20 parts by weight of dimethyl isophthalate and 60 parts by weight of ethylene glycol, 0.09 parts by weight of magnesium acetate tetrahydrate was reacted as a catalyst. The reaction start temperature was set to 150 ° C. in the vessel, and the reaction temperature was gradually increased as methanol was distilled off. After 4 hours, the transesterification reaction was substantially terminated. Next, after adding 0.04 parts of ethyl acid phosphate, 0.5 g of spherical silica particles dispersed in ethylene glycol having an average particle diameter of 1.2 μm were added.
And 0.04 part of antimony trioxide, and a polycondensation reaction was carried out for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from the normal pressure, and finally was 0.3 mmHg. After the reaction starts, 4
After a lapse of time, the reaction was stopped, and the polymer was discharged under nitrogen pressure. The intrinsic viscosity of the obtained polyester is 0.6
5. The melting point was 198 ° C.

(Production of Polyesters 2 to 4) Polyesters 2 to 4 were produced in the same manner as in the production of polyester 1 except that terephthalic acid and isophthalic acid were changed as shown in Table 1 below. -4
Was manufactured.

[0041]

[Table 1] テ レ Terephthalic acid Isophthalic acid Melting point ───────────ポ リ エ ス テ ル Polyester-1 80 mol% 20 mol% 200 ° C Polyester-2 90 mol% 10 mol% 229 ° C Polyester-3 100 mol% 0 mol% 254 ° C Polyester-4 65 mol% 35 mol% 162 ° C

(Production of polyester-5) Starting with 60 parts by weight of dimethyl terephthalate, 40 parts by weight of dimethyl isophthalate and 56 parts by weight of 1,4-butanediol, 0.005 part by weight of tetrabutyl titanate was used as a catalyst. In the reactor, the reaction start temperature was set to 150 ° C., and the reaction temperature was gradually increased with the removal of methanol by distillation. After 4 hours, the transesterification reaction was substantially terminated. Next, 0.5 g of spherical silica particles dispersed in ethylene glycol having an average particle diameter of 1.2 μm were added.
Parts, 0.005 tetrabutyl titanate as polymerization catalyst
The polycondensation reaction was performed for 4 hours by adding the weight part. That is, the temperature was gradually raised from 210 ° C. to 260 ° C.
On the other hand, the pressure gradually decreases from normal pressure, and finally 0.3 m
mHg. After 4 hours from the start of the reaction, the reaction was stopped and the polymer was discharged under nitrogen pressure. The intrinsic viscosity of the obtained polyester was 0.85, and the melting point was 147 ° C.

(Production of Polyester-6) In the production of Polyester-5, 60 parts by weight of dimethyl terephthalate was added to 65 parts by weight, and 40 parts by weight of dimethyl isophthalate was added to 35 parts by weight.
A polyester-6 was produced in the same manner as in the production of the polyester-5 except that the amount was changed to parts by weight. The intrinsic viscosity of the obtained polyester was 0.85, and the melting point was 153 ° C.

(Production of Recycled Raw Material) Polyester-1 was dried, melted at 260 ° C. by an extruder, extruded into a sheet from a T-die, and cooled by electrostatic application with a rotary cooling drum having a surface temperature set at 30 ° C. Quenched and solidified using the
A μm substantially amorphous sheet was produced. Next, the amorphous sheet is longitudinally stretched 3.7 times in the longitudinal direction at 70 ° C., stretched 4.0 times in the transverse direction at 75 ° C., and heat-treated at 90 ° C. for 3 seconds to obtain a biaxially oriented film having a thickness of 2 μm. The scraps generated during the production and the ears removed by trimming are crushed, and the chip-shaped regenerated raw material is extruded with an extruder equipped with a vent.
1 was produced. The intrinsic viscosity of the obtained recycled material-1 is 0.1.
63, melting point was 198 ° C.

Example 1 Polyester-1 and recycled material-1 were dried at a temperature of 260 ° C. by separate extruders and then extruded from a T-die. The molten polymer was previously combined so as to have a configuration of -1. The temperature from when the molten polymer merges to when it is extruded from the T-die is set at 260 ° C, extruded into a sheet from the T-die, and rapidly cooled using a rotating cooling drum with a surface temperature set at 30 ° C using the electrostatic application cooling method. Solidified, thickness 30μ
m of substantially amorphous sheet was produced. In this case, each polyester region has a length ratio of 1: 8: 1 in the width direction.
Met. Next, the amorphous sheet was stretched 3.7 times in the machine direction at 70 ° C. and 4.0 times in the transverse direction at 75 ° C.
Heat treatment was performed at 0 ° C. for 3 seconds, and the ears (ends) were removed by trimming to produce a 2 μm-thick biaxially oriented film.

The amount of the recycled material-1 used in the production was 2
5% by weight, and the difference in melting point between both ends and the center was 2 ° C.

Example 2 A biaxially oriented film having a thickness of 2 μm was produced in the same manner as in Example 1 except that the recycled material-1 was changed to polyester-2. At this time, the film had a structure of polyester-2 / polyester-1 / polyester-1 in the width direction, and the difference in melting point between both ends and the center used in the production was 29 ° C.

Example 3 A biaxially oriented film having a thickness of 2 μm was prepared in the same manner as in Example 1 except that polyester-1 was changed to a mixed raw material of polyester-1 and recycled raw material-1. Manufactured. Polyester-1 and recycled material-1 used in the center
Was 80/20.

At this time, the film is made of recycled material in the width direction.
1 / a mixture of polyester-1 and recycled raw material-1 / regenerated raw material-1. The blending amount of recycled raw material-1 used in the production was 40% by weight, and there was no difference in melting point between both ends and the central part. Was.

Example 4 In Example 1, polyester-1 was replaced with polyester-
6, except that the extruder used for polyester-6 and the temperature from the time when the molten polymer at the center and the end merged to the time when the polymer was extruded with a T-die were changed to 230 ° C., in the same manner as in Example 1. A biaxially oriented film having a thickness of 2 μm was produced.

At this time, the film is made of recycled material in the width direction.
The composition of 1 / polyester-6 / recycled raw material-1 was used. The blending amount of the recycled raw material used in the production was 25% by weight, and the difference in melting point between both ends and the center was 45 ° C.

Comparative Example 1 In Example 4, the recycled material-1 was changed to polyester-3, and the melting temperature of the extruder used for polyester-3 and the temperature from the time when the molten polymer merged to the time when it was extruded with a T-die were set to 290. A biaxially-oriented film having a thickness of 2 µm was produced in the same manner as in Example 4 except that the temperature was changed to ° C. The film frequently broke due to generation of air bubbles in the center of the film, and the obtained film had large thickness deflection.

At this time, the film had a structure of polyester-3 / polyester-6 / polyester-3 in the width direction.
° C.

Comparative Example 2 Comparative Example 1 was carried out in the same manner as in Comparative Example 1 except that the temperature from the time when the molten polymer at the center portion and the edge portion merged to the time when the polymer was extruded by the T-die was changed from 290 ° C. to 260 ° C. Method Extrusion was performed, but no film was obtained due to poor extrusion. The melting point difference between the both ends and the center used in the production was 101
° C.

Comparative Example 3 In Comparative Example 1, polyester-6 was replaced with polyester-
3, and a biaxially oriented film having a thickness of 2 μm was produced in the same manner as in Comparative Example 1 except that the temperature from the time when the molten polymer was merged with the extruder to the time when the molten polymer was extruded was changed to 290 ° C. did. At this time, the film had a composition of polyester-3 / polyester-3 / polyester-3 in the width direction, and there was no difference in melting point between the both ends and the center used in the production.

Comparative Example 4 In Example 1, polyester-1 was replaced with polyester-
5 in the same manner as in Example 1 except that the thickness was 2 μm.
Was produced. At this time, the film was made in the width direction by using recycled material-1 / polyester-5 / recycled material-
In this case, the difference in melting point between both ends and the center used in the production was 51 ° C.

Comparative Example 5 After drying 60 parts by weight of polyester-1 and 40 parts by weight of regenerated raw material-1, the mixture was melted at 260 ° C. by an extruder and extruded into a sheet from a T-die. The solid was rapidly cooled and solidified by using the electrostatic cooling method with a rotating cooling drum set as described above to form a substantially amorphous sheet having a thickness of 30 μm. Next, the amorphous sheet was 3.7 mm long at 70 ° C.
The film was stretched twice in the longitudinal direction, stretched 4.0 times in the horizontal direction at 75 ° C., heat-treated at 90 ° C. for 3 seconds, and the ears (ends) were removed by trimming to produce a biaxially oriented film having a thickness of 2 μm.

The amount of the recycled material used in the production was 40% by weight.

Examples 1 to 4 and Comparative Examples 1 to 5 Table 2 below shows the film structures in the width direction of Examples 1 to 3 and Comparative Examples 1 to 5, the blending ratio of the recycled materials, and the polyester used at both ends. And the melting point difference of the polyester used in the center part.

[0060]

[Table 2]

The films obtained in Examples 1 to 4 and Comparative Examples 1 to 5 were laminated on a porous thin paper according to a conventional method to prepare a heat-sensitive stencil sheet, followed by copy printing. Table 3 shows the properties of the obtained film and the properties of the heat-sensitive stencil sheet.

[0062]

[Table 3]

[0063]

According to the film of the present invention, a high perforation sensitivity can be obtained, and an excellent biaxially oriented polyester film which does not lower the heat perforation sensitivity even during multiple plate making can be produced at a low cost. Is expensive.

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Claims (3)

[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), at least one of the ends of the unoriented sheet is adjacent to the end. The difference between the melting point of the polyester resin (A) and the melting point of the polyester resin (A) is 90 ° C. or less.
A method for producing a polyester film for heat-sensitive stencil printing paper, which is at 50 to 240 ° C. 2. The method for producing a polyester film for heat-sensitive stencil printing paper according to claim 1, wherein the polyester resin (B) contains a recycled material. 3. The stretched film has a thickness of 0.5 to 10 μm.
2. The method for producing a polyester film for heat-sensitive stencil printing paper according to claim 1, wherein