JP2015208944A - Film for heat-sensitive stencil printing base paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially stretched polyester film which is excellent as a high-quality heat-sensitive stencil printing base paper in punching sensitivity, resolution in printing, printing quality, density and curling properties and usable as high-quality heat-sensitive stencil printing base paper.SOLUTION: A film for heat-sensitive stencil printing base paper is a biaxially stretched polyester film which has a melting point of 250°C or lower, a thickness of 1.0-3.5 μm, a shrinkage percentage, by TMA, in the film longitudinal direction at 50-150°C of 2% or lower and a shrinkage percentage in the film lateral direction of 2% or lower.

Description

  The present invention relates to a polyester film for a thermal stencil printing base paper used for thermal stencil printing base paper that is perforated and made by a thermal head, a halogen lamp, a xenon lamp, a flash lamp, a laser beam, or the like. Relates to a film for heat-sensitive stencil printing paper excellent in perforation sensitivity, printing resolution (gradation), print quality, density, and curling properties.

  Conventionally, as a heat-sensitive stencil printing base paper, a laminate of porous thin paper on a thermoplastic resin film such as polyester is known.

  The thermoplastic resin film used in such applications is perforated by flash irradiation or infrared irradiation using a thermal head, a halogen lamp, a xenon lamp, a flash lamp or the like, and further by pulsed irradiation such as a laser beam, and the porous thin paper is retained by ink. Used as a plate with passability.

  The plate making method using a thermal head is a method of making a plate by reading an original with a sensor and punching an image corresponding to the original with a thermal head in the form of dots in a film portion of the base paper. In such a plate making system with a thermal head, it is necessary to reduce the energy supplied to the head in order to suppress the damage of the thermal head and extend the life, and the film is perforated with low energy and high sensitivity, and is porous. There has been a demand for a film for heat-sensitive stencil printing paper having good resolution, printing quality, and density at the time of printing by allowing the ink retained on the thin paper to pass through the perforated hole.

  For the purpose of improving the sensitivity, a film defining the thermal characteristics of the biaxially stretched polyester film (for example, see Patent Document 1), a film defining the heat shrink characteristics (for example, see Patent Document 2), and a rough surface. A film that defines the degree and the number of protrusions (for example, see Patent Document 3), a film that defines constituent components and thickness unevenness (for example, see Patent Document 4), and the like have been proposed. It is sufficient and further improvement is desired.

JP-A-62-149496 JP-A-3-30996 JP-A 63-227634 JP-A-8-156440

  The present invention has been made in view of the above circumstances, and the problem to be solved is thermal stencil printing excellent in perforation sensitivity, printing resolution, print quality, density, and curling properties when used as a base paper for thermal stencil printing. It is to provide a film for base paper.

  As a result of intensive studies in view of the above problems, the present inventors have found that the above problems can be easily solved by a polyester film having a specific configuration, and have completed the present invention.

  That is, the gist of the present invention is a biaxially stretched polyester film having a melting point of 250 ° C. or less and a thickness of 1.0 to 3.5 μm, and a film shrinkage in the longitudinal direction by TMA at 50 to 150 ° C. is 2% or less. It exists in the film for heat sensitive stencil printing base paper characterized by the shrinkage | contraction rate of a horizontal direction being 2% or less.

  The polyester film of the present invention has a very good curling property, excellent perforation sensitivity, printing resolution, print quality and density, and has excellent perforation characteristics even under low energy by a thermal head. A film for printing base paper and a heat-sensitive stencil printing base paper can be obtained, and its industrial value is high.

  The bifunctional acid component constituting the polyester used in the present invention is mainly an aromatic dicarboxylic acid or an ester-forming derivative thereof, specifically, terephthalic acid, 2,6-naphthalenedicarboxylic acid, or an ester thereof. Examples of the forming derivative include dimethyl terephthalate and dimethyl 2,6-naphthalenedicarboxylate. Among these, terephthalic acid and dimethyl terephthalate are preferable. Examples of the glycol component constituting the polyester include ethylene glycol, butylene glycol, propylene glycol, polyethylene glycol, and 1,4-cyclohexanedimethanol. Among these, ethylene glycol and butylene glycol are preferable.

  Such a polyester is a polyester starting from an aromatic dicarboxylic acid or an ester-forming derivative thereof and an alkylene glycol, and is preferably a copolymer containing two or more components. In addition to the above, the components to be copolymerized include, for example, diol components such as diethylene glycol, neopentyl glycol, and polyalkylene glycol, dicarboxylic acid components such as adipic acid, sebacic acid, phthalic acid, and isophthalic acid, trimellitic acid, and pyromellitic An acid etc. are mentioned. Further, homopolymers each composed of a single component, a copolymer containing a homopolymer and two or more components, and a blended polyester of the copolymers are preferred. Among them, polybutylene terephthalate and isophthalic acid are co-polymerized. A blend polyester with a polyethylene terephthalate copolymer as a polymerization component and a blend polyester with polybutylene terephthalate, polyethylene naphthalate and isophthalic acid as a copolymerization component are more preferable.

  The melting point of the polyester film that is the subject of the present invention is 250 ° C. or lower. Even when it has a plurality of melting points, it is 250 ° C. or lower. When the melting point is higher than 250 ° C., it is not preferable because the perforating property at low energy is lowered when a heat sensitive stencil printing base paper is used, and the high perforation sensitivity intended by the present invention cannot be obtained. In the present invention, when two or more melting points are used, the difference between the highest melting point (Tm2) and the lowest melting point (Tm1) is usually less than 50 ° C., preferably less than 30 ° C., but Tm1 and Tm2 are It may be the same. When the temperature difference is 50 ° C. or more, reliable perforation does not occur in a short time and low energy, and the resolution may be deteriorated.

  The thickness of the film of the present invention is 1.0 to 3.5 μm, preferably 1.0 to 2.5 μm, more preferably 1.5 to 2.5 μm. If the thickness of the film is reduced, the heat conduction distance is shortened, the thermal energy required for perforation is also reduced and the perforation is improved, and the resolution, print quality, and density at the time of printing are improved, but when the thickness is less than 1 μm, The rigidity of the film is lowered, the transportability is deteriorated, wrinkles are generated during printing, the film is broken, and the printing durability is lowered. Furthermore, since the heat conduction distance is too short and adjacent holes are connected at the time of drilling, a predetermined drilling cannot be obtained, and the resolution and print quality are deteriorated. In addition, a thick region having a thickness exceeding 3.5 μm is not preferable because punchability due to low energy deteriorates and unevenness occurs during printing.

  The glass transition temperature (Tg) of the film of the present invention is usually in the range of 40 to 85 ° C, preferably 45 to 80 ° C, more preferably 50 to 75 ° C. When the glass transition temperature is less than 40 ° C., the heat-resistant dimensional stability is deteriorated, the film transportability is deteriorated, and curling during storage of the master film may occur.

  In addition to these characteristics, the shrinkage after the film is treated at 100 ° C. for 3 minutes in the present invention is preferably 5% or more, more preferably 10 to 40%. If it is less than 3%, the perforation sensitivity is insufficient and the image density of printing may be lowered. On the other hand, if it exceeds 40%, uneven shading tends to occur.

  In the present invention, the shrinkage ratio in the longitudinal direction of the film by TMA at 50 to 150 ° C. is 2% or less, and the shrinkage ratio in the transverse direction of the film is 2% or less. When the shrinkage ratio in the machine direction exceeds 2%, the film laminated with the Japanese paper shrinks in the machine direction, and the heat-sensitive stencil sheet curls in the machine direction in the machine direction. Similarly, when the shrinkage rate in the horizontal direction exceeds 2%, the film shrinks in the horizontal direction, so that the heat-sensitive stencil sheet curls in the horizontal direction and the film side. When the heat-sensitive stencil sheet is curled, it may be wound around a guide roll in the stencil printing machine, or may be adversely affected by conveyance, generating clogging of the sheet and causing the printer to malfunction.

  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 additives 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 film of the present invention improves the workability during winding process during film production, coating during film master creation, and printing, or prevents fusion between the thermal head and the film. Gives moderate slipperiness. Specifically, in order to appropriately roughen the surface, for example, fine particles having an average particle size of 0.05 to 2.0 μm are 0.01 to 2.0% by weight, preferably 0.1 to 1.5%. Weight% is contained in the film.

  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 of the fine particles used is less than 0.05 μm or the content of the fine particles is less than 0.01% by weight, the film surface is insufficiently roughened, and the effect may not be obtained sufficiently. In addition, when the average particle size exceeds 2.0 μm or the content exceeds 2.0% by weight, the degree of roughening of the film surface is too large, resulting in uneven heat transfer and uneven perforation. Thus, 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 obtained in the present invention has a centerline average roughness (Ra) in the range of 0.01 to 0.20 μm in order to satisfy the characteristics such as workability, printing resolution, print quality, and density at a high level. It is preferable that it is in the range of 0.02 to 0.15 μm. 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 perforation becomes uneven, the resolution is poor, and the print quality and density tend to be impaired.

  Next, the manufacturing method of the film of this invention is demonstrated.

  The polyester film for heat-sensitive stencil printing of the present invention is first melted by supplying a raw material polymer to a known melt extruder represented by an extruder and heating to a temperature equal to or higher than the melting point of the polymer. Next, the molten polymer is extruded from a slit-shaped die and rapidly cooled and solidified on a rotary cooling drum to obtain a substantially amorphous unstretched sheet. In this case, in order to improve the flatness of the sheet, it is necessary to improve 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 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 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 20-100 ° C., preferably 25-90 ° C., and the stretching ratio is usually 3-7 times, preferably 3.5-7 times, more preferably 3.8-7. Double.

  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 arbitrarily heat-treated, and if necessary, it may be stretched again in the machine direction and / or the transverse direction before or after the heat treatment. In the present invention, it is preferable not to substantially perform the heat treatment after stretching, or to employ the following conditions when performing the heat treatment. That is, the heat treatment temperature is usually 120 ° C. or less, the heat treatment time is 1 second to 5 minutes, the film is heat treated on the film under a constant length or under 30% elongation, and wound on a roll. When winding on a roll, a slit is made to a predetermined width as necessary.

The polyester film of the present invention thus obtained is bonded to a porous support to obtain a base paper. The porous support is a porous material made from natural fibers, synthetic fibers, etc. that can hold and permeate printing ink and does not substantially undergo thermal deformation under heating conditions where the film is perforated. Nonwoven fabrics, woven fabrics or other porous materials are used. The polyester film of the present invention has a silicone oil, a silicone resin, a fluorine resin, a surfactant, an antistatic agent, a release agent, organic particles, inorganic particles, etc. on one side in order to prevent fusion with a thermal head or the like. It can also be applied. The application method is not particularly limited, but it is preferable to apply using a roll coater, gravure coater, reverse coater, bar coater or the like. Moreover, you may perform activation processes, such as a corona discharge process, in the air and various other atmospheres as needed before providing a coating agent.

  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 follows.

(1) Melting point (Tm), glass transition temperature (Tg)
It measured using the Perkin-Elmer differential scanning calorimeter DSC7 type. The DSC measurement conditions are as follows. That is, 6 mg of the sample film was set in a DSC apparatus, melted and held at 300 ° C. for 5 minutes, and then rapidly cooled with liquid nitrogen. The rapidly cooled sample was heated from 0 ° C. at a rate of 10 ° C./min, the temperature corresponding to the glass transition was read, and the top of the melting endothermic peak was detected as the melting point (Tm).

(2) Heat shrinkage (S)
The sample was treated for 3 minutes in an oven kept at 100 ° C. in a tensionless state, the length of the sample before and after that was measured, and the heat shrinkage rate was calculated by the following formula.

S (%) = {(L0−L1) / L0} × 100
(In the above formula, L0 is the sample length before the heat treatment, L1 is the sample length after the heat treatment) Five points were measured in the film longitudinal direction and the transverse direction, and the average value was obtained.

(3) Shrinkage rate by TMA (St)
It measured using TMA / SS6100 made from SII. That is, the shrinkage rate at each temperature was calculated by the following equation with the chuck spacing of 20 mm, the sample width of 4 mm, and the sample under a constant tension of 24.5 mN and a temperature increase rate of 10 ° C./min.
St (%) = {(Lt0−Ltn) / Lt0} × 100
(In the above formula, Lt0 is the sample length before heat treatment, Ltn is the sample length at each temperature)

(4) Practical characteristics of heat-sensitive stencil printing paper (sensitivity)
A film was bonded to Japanese paper using a vinyl acetate adhesive on one side of the film, and a silicone lubricant was applied to the other side of the film using a bar coater to prepare a heat-sensitive stencil printing base paper. A letter image and a 16-tone image were made on the obtained base paper with a thermal head at an applied energy of 0.09 mJ and 0.12 mJ. The perforation state of the gradation image portion was observed with a microscope from the film side of the plate-making base paper, and the evaluation was divided into the following three stages.
○: Predetermined perforation is reliably performed and the size of the perforation is sufficient and good. Δ: In rare cases, there are some portions where the predetermined perforation cannot be obtained, and there are portions where the size of the perforations is insufficient, but practical use is possible. There are many parts where the predetermined perforations cannot be obtained, the size of the perforations is insufficient, and there is a problem in practical use.

(5) Practical characteristics of thermal stencil printing base paper (print quality)
Using the stencil paper obtained by sensitivity measurement, printing was actually performed using a lithographic AP7200 printer manufactured by Riso Kagaku Kogyo Co., Ltd., and the obtained characters and images were evaluated in the following three stages. ○: Clear and clear printing without density spots and blurring △: Slight shading unevenness and blurring are observed, slightly lacking in sharpness ×: Shading shading, blurring, blurring, and blurring are clearly visible

(6) Thermal stencil printing base paper practicality (curling)
The base paper for thermal printing obtained in (4) was cut into a length of 300 mm and a width of 300 mm and left still with the film surface facing upward, and evaluated in the following three stages.
○: The four sides do not curl.
Δ: The curl of the four sides is less than 30 mm ×: The curl of the four sides is 30 mm or more

The polyester used in the following examples and comparative examples was prepared in the following manner.
・ Production of polyester-A Starting from 78 parts by weight of dimethyl terephthalate, 22 parts by weight of dimethyl isophthalate and 60 parts of ethylene glycol, 0.09 parts by weight of magnesium acetate tetrahydrate as a catalyst was started in the reactor. The temperature was 150 ° C., and the reaction temperature was gradually increased as methanol was distilled off. After 4 hours, 10 parts by weight of an ethylene glycol slurry containing 1.0 part by weight of spherical crosslinked polymer particles having an average particle size of 1.1 μm was added to the reaction mixture after the transesterification reaction was substantially completed. 0.04 part of phosphate and 0.04 part of antimony trioxide were added and a polycondensation reaction was performed 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 normal pressure, and finally 0.3 mmHg. 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 0.74 dl / g.

・ Production of polyester-B 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 set in a reactor, the reaction start temperature is set to 150 ° C., and the reaction is performed together with distillation of methanol. The temperature was gradually raised to 210 ° C. after 3 hours. After 4 hours, 0.005 parts by weight of tetrabutyl titanate was added to the reaction mixture after the transesterification reaction was substantially completed, 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 the normal pressure, and finally 0.3 mmHg. 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 B was 0.90 dl / g.

-Production of polyester-C 100 parts by weight of dimethyl terephthalate, 60 parts by weight of ethylene glycol and 0.1 part by weight of calcium acetate monohydrate were placed in a reaction vessel, and the polyester was exchanged. That is, the polyester exchange reaction start temperature was set to 170 ° C., the reaction solution was heated with methanol outflow to start the ester exchange reaction, and heated to 230 ° C. after 4 hours to conduct the ester exchange reaction. . 5 parts by weight of an ethylene glycol slurry containing 0.5% by weight of spherical silica particles having an average particle diameter of 0.70 μm was added to the reaction product after the transesterification reaction, and then 0.04 parts by weight of phosphoric acid was added. Thereafter, 0.005 parts by weight of tetrabutyl titanate was added to carry out a polycondensation reaction. That is, the reaction solution was heated and the pressure in the system was decreased, and after 2 hours from the start of polycondensation, the reaction solution was heated to 280 ° C. and depressurized to 0.3 mmHg. Furthermore, when several hours passed, the polycondensation reaction was stopped to obtain polyester C. This polyester C had an intrinsic viscosity of 0.70 dl / g.

Example 1:
Polyester-A 30%, Polyester-B 30%, 40% recycled products from the ears and film edges generated during film production, and blended uniformly into a sheet from an extruder at 260 ° C Extrusion and rapid cooling and solidification using an electrostatic application cooling method with a rotary cooling drum set at a surface temperature of 40 ° C. gave a substantially amorphous sheet having a thickness of 25 μm. The obtained sheet was stretched 4.0 times at 75 ° C. in the machine direction and 4.0 times at 80 ° C. in the transverse direction, further heat treated at 105 ° C. for 6 seconds, relaxed by 3% at 80 ° C., and thickness 1. A 6 μm biaxially stretched polyester film was obtained. The obtained film was bonded to Japanese paper using vinyl acetate as an adhesive, and a silicone lubricant was applied to the other surface of the film using a bar coater to prepare a thermal stencil printing base paper, which was evaluated.

Example 2:
In Example 1, a heat-sensitive stencil sheet was prepared and evaluated in the same manner as in Example 1 except that the relaxation rate was 5%.

Example 3:
In Example 1, a heat-sensitive stencil sheet was prepared and evaluated in the same manner as in Example 1 except that the relaxation rate was 9%.

Comparative Example 1:
In Example 1, a heat-sensitive stencil sheet was prepared and evaluated in the same manner as in Example 1 except that the relaxation rate was 0%.

Comparative Example 2:
In Example 1, an attempt was made to form a film with a relaxation rate of 15%. However, the amount of relaxation was large, the film became unstable, and breakage occurred frequently, resulting in failure to form a film.

Comparative Example 3:
In Example 1, 15% polyester-A, 15% polyester-B, 30% polyester-C, and an ear generated during film production comprising the composition of polyester-A, polyester-B, and polyester-C. A base sheet for heat-sensitive stencil printing was prepared and evaluated in the same manner as in Example 1 except that 40% of the recycled product from the film and the film edge was uniformly blended.

Comparative Example 4:
Polyester-A 30%, Polyester-B 30%, 40% recycled products from the ears and film edges generated during film production, and blended uniformly into a sheet from an extruder at 260 ° C Extrusion and rapid cooling and solidification using an electrostatic application cooling method with a rotary cooling drum set at a surface temperature of 40 ° C. gave a substantially amorphous sheet having a thickness of 25 μm. The obtained sheet was stretched 4.0 times at 75 ° C. in the longitudinal direction and 4.0 times at 80 ° C. in the transverse direction, further heat treated at 105 ° C. for 6 seconds, relaxed by 5% at 80 ° C., and thickness 0. A 9 μm biaxially stretched polyester film was obtained. The obtained film was bonded to Japanese paper using vinyl acetate as an adhesive, and a silicone lubricant was applied to the other surface of the film using a bar coater to prepare a thermal stencil printing base paper, which was evaluated.

Comparative Example 5:
Polyester-A 30%, Polyester-B 30%, 40% recycled products from the ears and film edges generated during film production, and blended uniformly into a sheet from an extruder at 260 ° C Extrusion and rapid cooling and solidification using an electrostatic application cooling method with a rotary cooling drum set at a surface temperature of 40 ° C. gave a substantially amorphous sheet having a thickness of 65 μm. The obtained sheet was stretched 4.0 times at 75 ° C. in the machine direction and 4.0 times at 80 ° C. in the transverse direction, further heat treated at 105 ° C. for 6 seconds, relaxed 5% at 80 ° C., and thickness 4. A 0 μm biaxially stretched polyester film was obtained. The obtained film was bonded to Japanese paper using vinyl acetate as an adhesive, and a silicone lubricant was applied to the other surface of the film using a bar coater to prepare a thermal stencil printing base paper, which was evaluated.

  The obtained results are summarized in Table 1 below.

  Tm in Table 1 indicates the melting point of the film.

  The film of the present invention can be suitably used, for example, as a film for heat-sensitive stencil printing paper having high quality.

Claims (1)

It is a biaxially stretched polyester film having a melting point of 250 ° C. or less and a thickness of 1.0 to 3.5 μm. The shrinkage in the film longitudinal direction by TMA at 50 to 150 ° C. is 2% or less, and the shrinkage in the film transverse direction is 2. % Or less for heat-sensitive stencil sheet.