JP3047441B2 - Film for heat-sensitive stencil printing base paper - Google Patents

Description

The present invention relates to a polyester film for heat-sensitive stencil printing base paper. More specifically, the present invention relates to a film for heat-sensitive stencil printing base paper having excellent perforation properties and excellent resolution and gradation during printing.

[Problems to be solved by conventional technology and invention]

Conventionally, as a heat-sensitive stencil sheet, a sheet obtained by laminating a porous thin paper on a thermoplastic resin film of polyester or the like is known, and such a film has the following required characteristics.

(1) Good thermal piercing property. That is, the resin must have a sufficient heat shrinkage rate so that it can be melted with a small amount of heat and a perforation of an appropriate size can be obtained so that an image at the time of printing becomes clear.

(2) It must have sufficient strength and elasticity to withstand operations during lamination with porous thin paper and printing.

(3) Good gradation of thermal perforation. When used as a base paper, if a portion that should not be perforated melts due to the effect of surrounding perforations, the gradation of the printed image becomes inferior, which is not preferable. That is, it is necessary to have a thermal perforation characteristic so that a perforated portion and a non-perforated portion can be clearly distinguished.

Further, in addition to these requirements, it is necessary to have excellent productivity during film production. That is, it is necessary that the film has good stretchability and does not cause troubles such as breakage, and that the winding property and the slit property are good and that wrinkles do not occur during winding or that a winding shift does not occur. .

Further, it must be excellent in handling workability when preparing a base paper using such a film. Conventionally, as a film used for such an application, a biaxially stretched film intended for a thermoplastic resin and having improved printing characteristics by defining its thermal characteristics (Japanese Patent Laid-Open No. Sho 62
Japanese Patent Application Laid-Open No. 149496/1989) or a film having a specified heat shrinkage property (Japanese Patent Application Laid-Open No. 62-282983), but none of the above requirements have been satisfied.

[Means for solving the problem]

In view of the above problems, the present inventors have conducted intensive studies,
A biaxially oriented polyester film containing fine particles having a specific thermal conductivity and having a specific heat shrinkage satisfying a specific condition has been found to be suitable as a film for heat-sensitive stencil printing paper. Reached.

That is, the gist of the present invention is that the average particle size is 0.01 to 1.5 μm.
m, a heat-sensitive stencil film consisting of a biaxially oriented polyester film containing 0.05 to 25% by weight of inorganic particles having a thermal conductivity of 0.05 cal / cm · sec · deg or more.

 Hereinafter, the present invention will be described in detail.

The polyester in the present invention refers to a polyester containing an aromatic dicarboxylic acid as a main acid component and an alkylene glycol as a main glycol component. As aromatic dicarboxylic acids, terephthalic acid, isophthalic acid, 2,6-
And naphthalenedicarboxylic acid. Examples of the alkylene glycol include ethylene glycol, trimethylene glycol, tetramethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol, and the like.

Such a polyester may be a polyester starting from one kind of aromatic dicarboxylic acid and one kind of alkylene glycol, but is preferably a copolymer containing two or more kinds of components. Other than the above, examples of the copolymerization component include diethylene glycol, polyalkylene glycol, aliphatic dicarboxylic acids such as adipic acid and sebacic acid, and oxycarboxylic acids such as p-hydroxybenzoic acid.

The thickness of the film of the present invention is generally in the range of 0.5 to 3 μm, preferably in the range of 0.5 to 2.5 μm. When the thickness of the film becomes thinner, the heat transfer distance is shortened, and the heat energy required at the time of perforation is also reduced, so that the perforation property is improved,
Improves printing resolution and print quality, but has a thickness of 0.5μ
If it is less than m, the printing is unclear and shading tends to occur, and the productivity and winding workability deteriorate even in the production of a film. A film having a thickness of more than 3 μm is not preferable because the perforation property is deteriorated and unevenness occurs during printing.

The present inventors have found that the average particle size in the film is 0.01 to 1.5 μm.
It has been found that by containing 0.05 to 25% by weight of fine particles having a thermal conductivity of at least 0.05 cal / cm · sec · deg, the sensitivity of perforation is improved.

The reason why such an effect is exhibited is that the thermal conductivity of polyester is as low as 0.0004 cal / cmsec-deg, so by adding fine particles having high thermal conductivity to this, the thermal conductivity when receiving heat is improved. It is thought to be enhanced. Use of fine particles having an average particle size of more than 1.5 μm is not preferable because the particle size is too large, so that the film forming property at the time of film production deteriorates and troubles such as breakage at the time of stretching frequently occur. If the average particle size is less than 0.01 μm, the effect of improving thermal conductivity cannot be sufficiently obtained, which is not preferable. When the content of the fine particles in the film exceeds 25% by weight, the film-forming properties deteriorate, and when the content is less than 0.05% by weight, the effect of improving the thermal conductivity of the present invention cannot be obtained.

The average particle size of the fine particles is preferably 0.03 to 1.3 μm, and the content is preferably 0.1 to 15% by weight.

Examples of such fine particles include particles of aluminum oxide, magnesium oxide, silicon carbide, boron carbide, boron nitride, and the like.

In the present invention, at least one kind of these particles is contained, but when two or more kinds are used, the effects of the present invention are obtained when the average particle diameter, thermal conductivity and content of the whole are within the above-mentioned ranges. You can enjoy.

In the present invention, in addition to such fine particles, for the purpose of further improving the handleability of the film and the like, the thermal conductivity is 0.
Other particles of less than 05 cal / cm · sec · deg may be blended. However, also in this case, the average particle diameter of the particles is preferably 0.01 to 1.5 μm from the viewpoint of the film forming property described above, and the blending amount is preferably 1% by weight or less.

In the present invention, in order to obtain a high degree of heat perforation when used as a stencil sheet, the film is usually heated at 150 ° C.
The average of the heat shrinkage after processing for 5 minutes in the vertical and horizontal directions is 5
It is in the range of 40%, preferably 10-35%. In addition to the conditions for containing fine particles having high thermal conductivity, when such requirements are satisfied, higher heat porosity can be obtained. When the average of the heat shrinkage is less than 5%, high heat piercing property cannot be obtained, and the resolution at the time of printing becomes poor. If it exceeds 40%, curling due to shrinkage of the film after forming the base paper may occur, or extra perforation may occur due to the effect of perforations in the vicinity when used as the base paper. Is not preferable because it becomes worse.

Since the film of the present invention is manufactured as an extremely thin film, if the strength is low, the handling workability is unfavorably deteriorated. In the present invention, when the tensile modulus in the longitudinal direction and the tensile modulus in the width direction of the film are both 300 kg / mm ² or more, preferably 350 kg / mm ² or more, handling workability and printing durability become more favorable, which is preferable.

If the degree of polymerization of the polyester used in the present invention is too low, the mechanical viscosity decreases, so the intrinsic viscosity is usually 0.40 or more, preferably 045 to 0.90.

Next, a method for producing the polyester film of the present invention will be described. In the present invention, the polymer is supplied to a known melt extruder represented by an extruder, and is heated to a temperature equal to or higher than the melting point of the polymer to be melted. Next, the molten polymer is extruded from a slit-shaped die, and rapidly cooled 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 necessary to increase the adhesion between the sheet and the rotary cooling drum. In the present invention, preferably, the electrostatic application adhesion method and / or the liquid application adhesion method are employed.

The electrostatic application adhesion method is to apply a linear electrode on the upper surface side of the sheet in a direction orthogonal to the flow of the sheet, and apply about 5 to 10 kV to the electrode.
In this method, an electrostatic charge is applied to the sheet by applying the DC voltage of the above (1) to improve the adhesion to the drum. Also,
The liquid application and adhesion method is a method for improving the adhesion between the drum and the sheet by uniformly applying the liquid to the whole or a part of the surface of the rotary cooling drum (for example, only the part in contact with both ends of the sheet). In the present invention, both may be used as needed.

In the present invention, the unoriented sheet thus obtained is biaxially stretched to form a film. That is, the unoriented sheet is stretched in a unidirectional direction at a temperature of preferably 50 to 120 ° C., more preferably 60 to 110 ° C. by 2.5 to 7 times by a roll or tenter type stretching machine.
Next, in the direction perpendicular to the first stage, preferably 55 to 125 ° C,
More preferably, the film is stretched 2.5 to 7 times in a temperature range of 65 to 115 ° C. to obtain a biaxially oriented film. In addition, a method of performing unidirectional stretching in two or more stages can be used, but also in this case, it is preferable that the final stretching ratio is within the above range. It is also possible to simultaneously biaxially stretch the unoriented sheet so that the area magnification becomes 6 to 30 times.

The film thus obtained is preferably subjected to heat treatment, but if necessary, may be stretched in the longitudinal and / or transverse directions again before or after the heat treatment.

In the present invention, it is preferable that the average of the thermal shrinkage of the film in the longitudinal direction and the horizontal direction after the treatment at 150 ° C. for 3 minutes is 5 to 40%. Is preferably in the range of 100 to 200 ° C., preferably 120 to 180 ° C., and the heat treatment time is usually 1 second to 10 minutes. Such heat treatment may be performed under limited shrinkage or elongation of the film within 20%, or under constant length, and may be performed in two or more steps.

In the present invention, about 10% by weight or less of other polymer (for example, polyethylene, polystyrene, polycarbonate, polysulfone, polyphenylene sulfide, polyamide, polyimide, etc.) can be contained based on the total amount of polyester used for film formation. Further, additives such as an antioxidant, a heat stabilizer, a lubricant, a dye, and a pigment may be blended as needed.

Thus, the obtained polyester film of the present invention has excellent thermal perforation by laminating a predetermined porous thin paper using a known adhesive according to a conventional method, and has a resolution and gradation property at the time of printing. The heat-sensitive stencil printing paper having excellent heat resistance can be obtained.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist. 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
Particle size was measured by the sedimentation method based on Stokes' resistance law using -CP3 type. The average particle size (d ₅₀ ) was determined using a value of 50% of the integrated (weight basis) in the equivalent spherical distribution of the particles obtained by the measurement.

(2) Heat Shrinkage The sample was heat-treated for 3 minutes in an oven maintained at 150 ° C. in a non-tension state, and the length of the sample before and after the heat treatment was measured and calculated by the following equation.

The film was measured at five points in the vertical and horizontal directions, and the average value was determined.

(3) Practical characteristics of stencil printing base paper Polyester porous thin paper was bonded to the obtained film to prepare base paper. The obtained base paper was subjected to plate making of a character image and a 16-step gradation image at an applied energy of 0.10 mJ and 0.13 mJ by a thermal head. 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.

(I) Perforation sensitivity…: Predetermined perforation is reliably performed and good.

Δ: A part where a predetermined perforation cannot be obtained is rarely seen, but there is no practical problem.

×: There are many parts where the predetermined perforation cannot be obtained.
There is a problem in practical use.

(Ii) Gradation property…: Predetermined perforation is reliably performed, and good gradation property is exhibited even in a high density portion.

Δ: The gradation is slightly inferior in the high density portion. Alternatively, perforation unevenness is observed in a low concentration portion.

X: In the high density part, the film is almost completely removed by melting, and no gradation is observed in 4 to 7 levels of the high density part. Alternatively, perforation unevenness frequently occurs in a low density portion, resulting in poor gradation.

Further, using the plate making paper, printing was actually performed using a lithographic AP7200 printing machine manufactured by Riso Kagaku Kogyo KK, and the following characteristics of the obtained characters and images were visually judged.

(Iii) Printing quality ○: Clear printing without unevenness of density and blurring, and good.

Δ: Slight unevenness and bleeding were observed, and the image lacked sharpness.

×: Uneven shading, blurring, or blurring is apparent.

Example 1 83 parts of dimethyl terephthalate, 17 parts of dimethyl isophthalate
, 64 parts of ethylene glycol and 0.11 part of calcium acetate-water salt were placed in a reactor, and a transesterification reaction was performed.
That is, the reaction start temperature was set to 180 ° C., and the reaction temperature was gradually increased with the distillation of methanol.
The transesterification reaction was substantially terminated.

Next, after adding 0.07 parts of triethyl phosphate, the average particle diameter is 0.3 μm, and the thermal conductivity is 0.086 cal / cm · sec · deg.
1.55 parts of magnesium oxide particles and antimony trioxide
0.04 part was added and a polycondensation reaction was carried out by a conventional method. In this reaction, the temperature was gradually increased and the pressure was gradually reduced from normal pressure. After 2 hours, the temperature was set to 270 ° C. and the pressure was set to 0.3 mmHg. Five hours after the start of the reaction, the reaction was stopped, and the polymer was discharged under nitrogen pressure. The intrinsic viscosity of the obtained copolymerized polyester (A) was 0.68.

In the same manner, the starting materials were 85 parts of dimethyl terephthalate, 15 parts of dimethyl isophthalate, and 64 parts of ethylene glycol, and the average particle diameter was 1.0 μm and the thermal conductivity was 0.0037 cal.
A copolymerized polyester (B) to which 0.5 parts of silica particles having a density of / cm · sec · deg was added. The intrinsic viscosity of the obtained polyester (B) was 0.67.

Next, 90 parts of the copolymerized polyester (A) and 10 parts of (B) are mixed, extruded at 280 ° C. into a sheet from an extruder, and cooled by electrostatic application on a rotary cooling drum having a surface temperature set at 40 ° C. Using a method, the mixture was quenched and solidified to obtain a substantially amorphous sheet having a thickness of 30 μm.

Next, the obtained sheet was stretched 3.7 times at 80 ° C. in the longitudinal direction and 4.1 times at 95 ° C. in the transverse direction, and heat-treated at 145 ° C. for 6 seconds to produce a biaxially oriented film having a thickness of 2.0 μm.

Example 2 As in Example 1, the content of isophthalic acid was 17 mol%, the average particle size was 0.05 μm, and the thermal conductivity was 0.070 cal / cm.
A copolymerized polyester (C) having an intrinsic viscosity of 0.68 and containing 1.5% by weight of aluminum oxide particles of sec · deg was produced.

90 parts of the obtained copolymerized polyester (C) and Example 1
And 10 parts of the copolymerized polyester (B) produced in
A biaxially oriented film having a thickness of 2.0 μm was produced in the same manner as in Example 1 under the film forming conditions.

Example 3 Copolymerized polyester (PETG6763 manufactured by Eastman) 100 containing 67 mol% of ethylene terephthalate units and 33 mol% of 1,4-cyclohexane dimethylene terephthalate units
Part, average particle size 1.2μm, thermal conductivity 0.15cal / cm ・ sec
Deg. Of boron nitride particles (3 parts) were added and blended using a biaxial kneader.

Using the obtained copolyester, film forming conditions were the same as in Example 1 except that the heat treatment temperature was 140 ° C.
A biaxially oriented film having a thickness of 2.0 μm was produced.

Comparative Example In the same manner as in Example 1, the content of isophthalic acid was 15 mol%, the average particle size was 1.2 μm, and the thermal conductivity was 0.0037 cal / cm.
A copolymerized polyester having an intrinsic viscosity of 0.69 containing 0.1% by weight of silica particles of sec · deg was produced.

Using the obtained copolyester as a raw material, a biaxially oriented film having a thickness of 2.0 μm was produced in the same manner as in Example 1 under the film forming conditions.

The thus obtained film was bonded to a porous thin paper according to a conventional method to prepare a heat-sensitive stencil sheet and evaluated for practical characteristics.

Table 1 below summarizes the physical properties of the film and the results of evaluating the practical properties of the base paper.

[Effect of the Invention] The heat-sensitive stencil printing paper comprising the polyester film of the present invention has excellent perforation sensitivity, and shows good gradation from a low density portion to a high density portion, and a high quality printed image is obtained. And its industrial value is high.

Claims (1)

(57) [Claims] An average particle diameter of 0.01 to 1.5 μm and a thermal conductivity of 0.0
A film for heat-sensitive stencil printing paper comprising a biaxially oriented polyester film containing 0.05 to 25% by weight of inorganic particles of 5 cal / cm · sec · deg or more.