JP5393143B2 - Polyester film for screen printing - Google Patents

Description

  The present invention relates to a biaxially oriented polyester film for screen printing. More specifically, the present invention is a screen printing excellent in thermal perforation and printing durability such as a thermal head, a xenon plate making method, and a flashback method, which is used by being bonded to a screen woven with fibers of silk, nylon, polyester, etc. The present invention relates to a biaxially oriented polyester film.

Conventionally, screen plate making using a heat-sensitive stencil film is a simple method with less number of plate making steps because it does not use photosensitive oil and fat, and is an advantageous method in terms of cost. Has the disadvantage of being inferior. Properties required for the heat-sensitive stencil film used for screen plate making include printing durability, film winding properties, perforation sensitivity, image resolution during printing, etc., but conventionally used as a heat-sensitive stencil film for screen printing. However, vinylene chloride, which has weak mechanical strength and poor printing durability, and poor perforation sensitivity, did not satisfy all of the above required characteristics such as high thermal energy when perforating the film. . In order to solve this problem, a biaxially oriented polyester film having a specific melting point, shrinkage rate, tensile elastic modulus, and thickness has been proposed (Patent Document 1). In this method, a high quality used in digital stencil printing or the like is proposed. Printing on thin materials with a uniform surface, such as paper or plastic, will not interfere, but it is sufficient for printing on fabrics such as T-shirts, cardboard, and other materials with relatively large surface irregularities. The problem remains that sufficient printing durability is not obtained.
JP 9-220867 A

  An object of the present invention is to provide a heat-sensitive stencil film for screen printing that is excellent in printing durability, perforation sensitivity, and resolution at the time of printing regardless of the surface shape of the printed matter.

  As a result of intensive studies in view of the above problems, the present inventors have found that a specific biaxially oriented polyester film is suitable for a screen printing film, and have completed the present invention.

That is, the gist of the present invention is that isophthalic acid copolymerized polyethylene terephthalate and polybutylene terephthalate are mixed with polyethylene terephthalate or polyethylene naphthalate, and 50 to 97 mol % of the acidic component is composed of terephthalic acid component and glycol component. Of these, 5-70 mol% is made of polyester composed of a 1,4-butanediol component, the film has a melting point of 245 ° C. or lower, an intrinsic viscosity of 0.55 dl / g or higher, and a heat shrinkage rate at 150 ° C. 30 to 70%, and the thickness is 2.5 to 7 μm.

Hereinafter, the present invention will be described in detail.
Screen printing as used in the present invention means that a screen woven with fibers of silk, nylon, polyester, etc. is fixed to a frame, and an opening and a non-opening are formed in an arbitrary shape by various methods on the screen. Ink is put into the shaped screen frame, and the ink is pushed through the screen with a rubber spatula called a squeegee to push the ink through the screen area to the back of the plate. It is a method of printing. In general, the screen plate making method includes a screen by a manual method, a photoresist screen, and a special screen to which the present invention belongs using a heat sensitive stencil film instead of a photosensitive resin.

  Special screen plate making also converts the reflected light from the original into an electrical signal, amplifies it, disperses the carbon in a thermoplastic resin film such as vinyl chloride or vinyl chloride copolymer by discharge from the recording needle, and makes it conductive The discharge type to perforate the sheet with stencil to make the screen plate, and various screen meshes and the thermoplastic film such as vinylidene chloride which is perforated by heat are adhered to the original, and the thermal head, xenon plate making There is a heat-sensitive method, such as a method, a heat-sensitive method such as making a plate with heat energy such as a flash bulb, and the biaxially oriented polyester film of the present invention is used in a heat-sensitive stencil method for special screen plate making, among screen printing.

  The polyester film of the present invention, as a heat-sensitive stencil sheet for screen printing, after being bonded to a screen woven with silk, nylon, polyester or other fibers, and then perforated by thermal energy such as a thermal head, a xenon plate making system, a flash valve, It becomes the plate making for screen printing.

  The polyester referred to in the present invention is 50 to 97% of the acid content, preferably 70 to 97% is the terephthalic acid component and the glycol component is 5 to 70 mol%, preferably 10 to 60 mol%, more preferably. Polyester comprising 10 to 50 mol% of 1,4-butanediol component refers to a polyester composed of the dicarboxylic acid component described above and a glycol component, but includes other components in order to bring the melting point to 245 ° C or lower. A copolymer may also be used. Such copolymerizable components include 2,6-naphthalenedicarboxylic acid, isophthalic acid, sebacic acid, adipic acid and other dicarboxylic acids, ethylene glycol, diethylene glycol, triethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol, etc. It is preferable that 3-30 mol% of the acidic component is composed of an isophthalic acid component.

  As a method of obtaining such a polyester, a predetermined amount of a dicarboxylic acid component and a glycol component are charged at the time of polymerization, and a target polyester is obtained by copolymerization, or two or more kinds of copolymer polyesters having different component ratios are blended. The method of adjusting so that it may become a predetermined component amount by melt-kneading is mentioned.

  As described above, the polyester constituting the film of the present invention has a specific range of acidic components and glycol components. However, when the 1,4-butanediol component is less than 5 mol%, a highly sensitive film cannot be obtained. If it exceeds 70 mol%, the heat-resistant dimensional stability of the film deteriorates, curling and local tarmi occur during storage of the master film and when the master film is transported, and the gradation of the printed image becomes inferior. Absent.

  Furthermore, as glycol components other than 1,4-butanediol, ethylene glycol is preferably constituted in an amount of 30 to 95 mol%, preferably 40 to 90 mol%, more preferably 50 to 90 mol%.

  The film of the present invention has a thickness of 2.5 to 7 μm, preferably 3 to 5 μm. The thinner the film is, the shorter the heat conduction distance is. As a result, the thermal energy required for perforation is reduced, the perforation is improved, and the resolution and quality of printing are improved. However, if the thickness of the film is less than 2.5 μm, the stiffness of the film is lowered. Therefore, when printing on thick paper such as fibers and corrugated cardboard and materials with relatively large surface irregularities, uneven shading is likely to occur, and printing durability There is also a tendency for the properties to decrease significantly. On the contrary, when the thickness of the film exceeds 7 μm, sufficient perforation diameter and perforation probability cannot be ensured and unperforation occurs.

  In the present invention, other polymers (for example, polyethylene, polystyrene, polycarbonate, polysulfone, polyphenylene sulfide, polyamide, polyimide, etc.) of about 10% by weight or less can be contained with respect to the total amount of polyester used for film formation. Moreover, you may mix | blend additives, such as antioxidant, a heat stabilizer, a lubricant, an antistatic agent, dye, and a pigment, as needed.

  The method of blending the above additive is not particularly limited. For example, a method of directly blending the additive and the polyester chip, a master batch chip in which the additive is blended in a high concentration in the polyester in advance, and obtaining the polyester again A so-called master batch method for blending with the above can be employed.

  The melting point of the film in the present invention is 245 ° C. or lower, preferably 170 to 245 ° C., more preferably 170 to 230 ° C. Even more preferably, it is 170 ° C to 230 ° C. When the melting point of the film is higher than 245 ° C., it is difficult to obtain the high perforation sensitivity intended by the present invention, and when the melting point of the film is too low, a master film is produced due to deterioration of the heat-resistant dimensional stability of the film. Curling occurs during the process and storage of the master film, and the gradation of the printed image is inferior.

  In the present invention, the difference between the highest melting point (Tm2) and the lowest melting point (Tm1) is preferably less than 50 ° C., more preferably less than 30 ° C., but Tm1 and Tm2 may be the same. When the temperature difference is 50 ° C. or more, uniform perforation does not occur in a short time, and the gradation of the printed image tends to be inferior.

  The glass transition temperature of the film of the present invention is preferably 40 to 85 ° C, more preferably 50 to 74 ° C. When the glass transition temperature is less than 40 ° C., the heat-resistant dimensional stability is deteriorated, curling and local tarmi are likely to occur during storage of the master film or during conveyance of the master film, and the gradation of the printed image may be inferior. When the glass transition temperature is higher than 85 ° C., the perforation sensitivity is deteriorated.

  The intrinsic viscosity [η] of the film of the present invention is 0.55 dl / g or more, preferably 0.60 dl / g or more. When the intrinsic viscosity [η] is lower than 0.55 dl / g, curling may occur during storage of the master film or during conveyance of the master film, or sufficient printing durability may not be obtained. Further, the perforation sensitivity is deteriorated, which is not preferable.

  The film of the present invention is suitable for a film in order to improve the winding process during film production, the coating during film master creation, and the workability during printing, or to prevent the thermal head and the film from being fused. Gives slipperiness.

  Specifically, in order to moderately roughen the surface, for example, 0.01 to 3.0% by weight, preferably 0.1 to 1.% by weight of fine particles having an average particle diameter of 0.05 to 5.0 μm are added to the film. 5% by weight is contained.

  Examples of such fine particles include calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, lithium phosphate, magnesium phosphate, lithium fluoride, aluminum oxide, silicon oxide, titanium oxide, kaolin, talc, carbon black, silicon nitride. , Boron nitride, and crosslinked polymer fine powders as described in JP-B-59-5216, but are not limited thereto.

  At this time, the fine particles to be blended may be a single component, or two or more components may be used simultaneously. When two or more components are used, it is preferable that the average particle diameter and content thereof are in the above-described range.

  When the average particle size is less than 0.05 μm or the content of fine particles is less than 0.01% by weight, the film surface is insufficiently roughened and the effect may not be obtained sufficiently. When the average particle size exceeds 5.0 μm or the content exceeds 3.0% by weight, the degree of roughening of the film surface is too large, resulting in uneven heat transfer and uneven perforation. , The resolution may be inferior or the print quality may be impaired.

  The method for blending the respective particles with the raw material polyester is not particularly limited. For example, a method of adding each particle to the polyester polymerization step or a method of melt-kneading the raw material polyester and each particle is suitable.

  The film of the present invention preferably has a center line average roughness (Ra) in the range of 0.01 to 0.20 μm in order to highly satisfy properties such as workability, printing resolution, and print quality. The range of 0.02 to 0.15 μm is more preferable. When Ra is less than 0.01 μm, the film tends to be wrinkled at the time of winding the film, and when Ra exceeds 0.20 μm, the flatness of the film surface is impaired and the heat transfer. Unevenness occurs, the perforations become uneven, the resolution is poor, and the print quality tends to be impaired.

  The film heat shrinkage rate of the present invention is 30 to 70%, preferably 35 to 65% at 150 ° C. for 3 minutes. If the heat shrinkage rate at 150 ° C. is less than 30%, sufficient drilling diameter and punching probability cannot be secured from the viewpoint of low energy drilling, and unperforation occurs. Curling that occurs during storage and the level of gradation of the printed image are poor, which is not preferable for practical use.

Next, the manufacturing method of the polyester film of this invention is demonstrated.
In the present invention, the polymer is supplied to a well-known extruder represented by an extruder, heated to a temperature equal to or higher than the melting point of the polymer, and melted. Next, the molten polymer is extruded from a slit-shaped die and rapidly cooled and solidified on the rotary cooling drum so that the temperature is 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 improve the adhesion between the sheet and the rotary cooling drum, and usually an electrostatic application adhesion method is employed.

In the present invention, the unstretched sheet obtained as described above is stretched biaxially to form a 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 40 to 120 ° C., preferably 50 to 100 ° C., and 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 this second stage, the stretching temperature is usually 20 to 100 ° C., preferably 25 to 90 ° C., and the stretching ratio is usually 3.0 to 7 times, preferably 3.5 to 7 times, more preferably 4.0. ~ 7 times.
A method of performing unidirectional stretching in two or more stages can also be employed, but in this case as well, it is preferable that the final stretching ratio falls within the above-described range. Further, the unstretched sheet can be simultaneously biaxially stretched so that the area magnification is 10 to 40 times. The obtained film can be optionally heat-treated, and if necessary, it may be stretched again in the longitudinal and / or transverse directions before or after the heat treatment.

  In the present invention, in order to obtain a film having the above-described heat shrinkage characteristics, it is preferable that the draw ratio is 15 times or more as the area ratio and the heat treatment temperature is as follows. That is, the heat treatment temperature is usually 130 ° C. or lower, preferably 110 ° C. or lower, and the heat treatment time is 1 second to 5 minutes. And heat processing is performed about the film under fixed length or the expansion | extension within 30%.

  The screen-sensitive heat-sensitive stencil film of the present invention thus obtained is bonded to a screen woven with fibers of silk, nylon, polyester, etc., and then perforated with high sensitivity by thermal energy, and has excellent printing durability. It becomes plate making.

  According to the present invention, a thermal stencil film for screen printing excellent in printing durability, perforation sensitivity, and resolution at the time of printing can be provided regardless of the surface shape of the printed matter, and the industrial value of the present invention is high.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is exceeded. In addition, the physical-property measuring method used by this invention is as showing below.

(1) Measurement of sample component content A solution in which a polymer sample was dissolved in a deuterium trifluoroacetic acid solvent to a concentration of 3% by weight was prepared. Using a nuclear magnetic resonance apparatus (DRX-500 manufactured by Bruker Biospin), a ¹ H-NMR spectrum of this solution was obtained, each peak was assigned, and the content of each component was calculated from the integrated value of the peak.

(2) Melting point and glass transition temperature The melting point and glass transition temperature were measured by using a differential scanning calorimeter (DSC), specifically, DSC-2920 manufactured by TAA Instruments. That is, the sample was heated from a temperature of 0 ° C. to 300 ° C. at a heating rate of 10 ° C./min, and the crystal melting endothermic peak temperature was defined as the melting point [Tm]. The glass transition temperature [Tg] was set to the center value of the temperature range in which the DSC curve bends due to the change in specific heat when the sample heated to 300 ° C. was rapidly cooled and then heated at a rate of temperature increase of 10 ° C./min.

(3) Thickness The thickness was measured by the following formula from the weight, length, width and density of the sample.
Thickness = (sample weight) ÷ (sample length x sample width x sample density)

(4) Measurement of intrinsic viscosity 1 g of a sample was dissolved in 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio) and measured at 30 ° C.

(5) Thermal shrinkage (%)
In an oven maintained at a predetermined temperature (150 ° C.), the sample was heat-treated for 3 minutes in a non-tensioned state, the sample length before and after that was measured, and the thermal shrinkage rate was calculated by the following formula. Five points were measured in the longitudinal and lateral directions of the film, and the average value was determined.
Thermal shrinkage = ((sample length before heat treatment) − (sample length after heat treatment)) ÷ (sample length before heat treatment) × 100

(6) Practical characteristics of heat-sensitive stencil printing base paper A base paper was prepared by laminating a polyester screen to the film. A letter image and a 16-step gradation image were made on the obtained base paper with a thermal head at a printing energy of 0.12 mJ and 0.18 mJ. The perforated state of the gradation image portion was observed with a microscope from the film side of the plate-making base paper, and the following items were evaluated.
(A) Perforation sensitivity ◎ ... The predetermined perforation is surely performed and the size of the perforation is sufficient. ○ ... The predetermined perforation is almost certainly performed, and the size of the perforation is sufficient. × ... The predetermined perforation is obtained. There are many parts that do not exist, the size of the perforations is uneven, and there is a problem in practical use.

(B) Printing durability The T-shirt was evaluated by the number of sheets that could be printed before the film was damaged by a printing machine.
◎ ... Can print 2000 sheets or more ○ ... Can print 1000 sheets or more △ ... Can print 500 sheets or more

-Manufacture of polyester-A 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol are used as starting materials. As a catalyst, 0.09 part by weight of magnesium acetate tetrahydrate is placed in a reactor, and the reaction start temperature is 150 ° C. The reaction temperature was gradually increased as methanol was distilled off, and after 3 hours, the temperature was increased to 230 ° C. After 4 hours, the transesterification reaction was substantially terminated. After adding 0.04 part of ethyl acid phosphate to the reaction mixture, 1.0 part by weight of spherical organic crosslinked particles having an average particle size of 1.1 μm and 0.03 part of antimony trioxide were added, and polycondensation for 4 hours. Reaction was performed. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.70 dl / g due to a change in stirring power of the reaction vessel, and the polymer was discharged under nitrogen pressure. The obtained polyester had an intrinsic viscosity of 0.75 dl / g.

・ Production of polyester-B In the production of polyester-A, polyester-B was prepared in the same manner as polyester-A, except that 100 parts by weight of dimethyl isophthalate was changed to 80 parts by weight of dimethyl terephthalate and 20 parts by weight of dimethyl isophthalate. Obtained. The obtained polyester had an intrinsic viscosity of 0.75 dl / g.

-Production of Polyester-C 100 parts by weight of dimethyl terephthalate, 56 parts by weight of 1,4 butanediol, and 0.005 parts by weight of tetrabutyl titanate are placed in a reactor, the reaction start temperature is 150 ° C., and methanol is distilled off. The reaction temperature was gradually raised to 210 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially terminated. To this reaction mixture, 1.0 part by weight of spherical organic crosslinked particles having an average particle size of 1.1 μm was added, 0.005 part of tetrabutyl titanate was added as a polymerization catalyst, and a polycondensation reaction was performed for 4 hours. That is, the temperature was gradually raised from 210 ° C. to 260 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 1.10 dl / g due to a change in stirring power of the reaction vessel, and the polymer was discharged under nitrogen pressure. The intrinsic viscosity of the obtained polyester was 1.10 dl / g.

・ Production of polyester-D 100 parts by weight of dimethyl naphthalene-2,6-dicarboxylate, 65 parts by weight of ethylene glycol, and 0.09 part of magnesium acetate as a polymerization catalyst were added, and a polycondensation reaction was performed according to a conventional method to perform intrinsic viscosity. 0.55 dl / g of polymer was obtained, followed by solid state polymerization in a nitrogen stream. The intrinsic viscosity of the obtained polyester was 0.63 dl / g.

Example 1:
17 parts by weight of the polyester-A raw material, 50 parts by weight of the polyester-B raw material, and 33 parts by weight of the polyester-C raw material were blended and kneaded at 285 ° C. using a bend twin screw extruder, and the intrinsic viscosity was 0.70 dl. A polyester chip of / g was prepared. This polyester chip is extruded into a sheet by an extruder at 270 ° C., and rapidly cooled and solidified using an electrostatic application cooling method with a rotary cooling drum set at a surface temperature of 40 ° C., and a substantially amorphous sheet having a thickness of 50 μm. Got. The obtained sheet was stretched 4.0 times at 70 ° C in the longitudinal direction and 4.0 times at 97 ° C in the transverse direction, and heat-treated in a 95 ° C tenter to produce a biaxially oriented film having a thickness of 3.0 µm. did. The physical properties of the obtained film are shown in Table 1 below. Next, the obtained film was bonded to a polyester screen according to a conventional method to prepare a heat-sensitive stencil printing base paper, and screen printing was performed on a commercially available plain T-shirt made of 100% cotton.

Example 2:
In Example 1, instead of blending 17 parts by weight of the polyester-A raw material, 50 parts by weight of the polyester-B raw material, and 33 parts by weight of the polyester-C raw material, 90 parts by weight of the polyester-B raw material and 10 parts by weight of the polyester-C raw material Except for blending, a heat-sensitive stencil sheet was prepared in the same manner as in Example 1, and screen printing was performed.

Example 3:
In Example 1, instead of blending 17 parts by weight of polyester-A raw material, 50 parts by weight of polyester-B raw material, and 33 parts by weight of polyester-C raw material, 10 parts by weight of polyester-A raw material, 25 parts by weight of polyester-B raw material, A base sheet for heat-sensitive stencil printing was prepared in the same manner as in Example 1 except that 65 parts by weight of the polyester-C raw material was blended and screen-printed.

Example 4:
In Example 1, instead of blending 17 parts by weight of polyester-A raw material, 50 parts by weight of polyester-B raw material, and 33 parts by weight of polyester-C raw material, 50 parts by weight of polyester-B raw material, 33 parts by weight of polyester-C raw material, A base paper for heat-sensitive stencil printing was prepared by the same method as in Example 1 except that 17 parts by weight of polyester-D raw material was blended, and screen printing was performed.

Example 5:
50 parts by weight of the polyester-B raw material and 50 parts by weight of the polyester-C raw material are blended and kneaded at 285 ° C. using a bend-equipped twin screw extruder to prepare a polyester E raw material. Part by weight and 50 parts by weight of polyester E raw material are uniformly blended, extruded into a sheet by an extruder at 280 ° C., and rapidly cooled and solidified using a static cooling method with a rotating cooling drum set at a surface temperature of 40 ° C. A substantially amorphous sheet having a thickness of 50 μm was obtained. The obtained sheet was stretched 4.0 times at 90 ° C in the longitudinal direction and 4.0 times at 100 ° C in the transverse direction, and heat treated in a 95 ° C tenter to produce a biaxially oriented film with a thickness of 3.0 µm. did. Table 1 shows the physical properties of the obtained film. Next, the obtained film was bonded to a polyester screen according to a conventional method to prepare a heat-sensitive stencil printing base paper, and screen printing was performed on a commercially available plain T-shirt made of 100% cotton.

Example 6:
In Example 1, a heat-sensitive stencil sheet was prepared by the same method as in Example 1 except that the film thickness was 6.0 μm, and screen printing was performed.

Example 7:
In Example 1, a heat-sensitive stencil sheet was prepared by the same method as Example 1 except that the heat treatment temperature in the tenter was 105 ° C., and screen printing was performed.

Comparative Example 1:
100 parts by weight of the polyester-B raw material was extruded into a sheet by an extruder at 280 ° C. and rapidly cooled and solidified using an electrostatic cooling method with a rotary cooling drum set at a surface temperature of 40 ° C. A crystalline sheet was obtained. The obtained sheet was stretched 4.0 times at 90 ° C in the longitudinal direction and 4.0 times at 100 ° C in the transverse direction, and heat treated in a 95 ° C tenter to produce a biaxially oriented film with a thickness of 3.0 µm. did. Table 1 shows the physical properties of the obtained film. Next, the obtained film was bonded to a polyester screen according to a conventional method to prepare a heat-sensitive stencil printing base paper, and screen printing was performed on a commercially available plain T-shirt made of 100% cotton.

Comparative Example 2:
In Example 1, instead of blending 17 parts by weight of the polyester-A raw material, 50 parts by weight of the polyester-B raw material, and 33 parts by weight of the polyester-C raw material, 20 parts by weight of the polyester-B raw material and 80 parts by weight of the polyester-C raw material Except for blending, a heat-sensitive stencil sheet was prepared in the same manner as in Example 1, and screen printing was performed.

Comparative Example 3:
In Example 1, a heat-sensitive stencil sheet was prepared by the same method as in Example 1 except that the film thickness was 2.0 μm, and screen printing was performed.

Comparative Example 4:
In Example 1, a heat-sensitive stencil sheet was prepared by the same method as in Example 1 except that the thickness of the film was 8.0 μm, and screen printing was performed.

Comparative Example 5:
In Example 1, 17 parts by weight of the polyester-A raw material, 50 parts by weight of the polyester-B raw material, and 33 parts by weight of the polyester-C raw material were blended and kneaded at 285 ° C. using a twin screw extruder with a bend. A heat-sensitive stencil sheet was prepared in the same manner as in Example 1 except that a polyester chip having an intrinsic viscosity of 0.60 dl / g was prepared, and screen printing was performed.

Comparative Example 6:
In Example 1, a heat-sensitive stencil sheet was prepared by the same method as in Example 1 except that the heat treatment temperature in the tenter was 135 ° C., and screen printing was performed.
The physical properties of the film thus obtained and the stencil paper practical properties are shown in the following table.

  The film of the present invention can be suitably used for screen printing.

Claims (1)

Isophthalic acid copolymerized polyethylene terephthalate and polybutylene terephthalate are mixed with polyethylene terephthalate or polyethylene naphthalate, 50 to 97 mol % of the acidic component is terephthalic acid component, and 5 to 70 mol% of glycol component is 1 , 4-butanediol component, the film has a melting point of 245 ° C. or less, an intrinsic viscosity of 0.55 dl / g or more, a heat shrinkage at 150 ° C. of 30 to 70%, a thickness Is a polyester film for screen printing, characterized by being 2.5 to 7 μm.