JPH04288288A - Base paper for thermal screen printing - Google Patents

Abstract

PURPOSE:To enhance printing image quality in thermal screen printing. CONSTITUTION:Base apaper for thermal screen printing is obtained by bonding a thermal film to a support wherein fine particles with a particle side of 50mum or less are fixed to tissue paper mainly through said fine particles. Therefore, the perforation of the film is prevented in this base paper. Since the bonded parts of the support and the film are dispersed in a spotted state, the missing dots of a black solid part are markedly improved as compared with conventional base paper.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a stretched thermoplastic resin film (hereinafter referred to as a film) and an ink permeable porous support (hereinafter referred to as a support) used in the field of thermal stencil printing. It is a base paper for heat-sensitive stencil printing (hereinafter referred to as base paper) that is laminated together, and its purpose is to improve printing image quality by significantly reducing white spots originating from the support fibers that are unique to stencil printing. This relates to the original paper.

0002

[Prior Art] In general, in thermal stencil printing, a heat source such as a thermal head is used to thermally melt and perforate a base paper film in accordance with the characters and figures on the original, and after forming holes in the film, the base paper is Printing is performed by supplying ink from the support side and allowing the ink to seep out from the holes.

Conventionally, heat-sensitive stencil printing uses stretched thermoplastic resin films such as polyester-based, vinylidene chloride-based, vinyl chloride-based, and polypropylene-based films, and nonwoven fabrics (thin paper) and woven fabrics made of natural fibers, synthetic fibers, etc. Base paper is used, which is made by bonding a support such as cloth (gauze) with an adhesive. (For example, Japanese Patent Application Laid-Open No. 51-2513,
Japanese Unexamined Patent Publication No. 57-182495, Japanese Patent Publication No. 49-593
(No. 3 Publication) In recent years, as a means of improving the resolution in the stencil printing field, increasing the density of thermal elements in plate-making thermal heads has been studied, and The pitch between the elements is 6.
3.5 μm) is now being installed in fully automatic stencil printing machines.

0004

[Problem to be solved by the invention] Therefore, the inventors of the present invention
With the aim of directly reflecting the increase in element density in improving image quality, we have been studying how to independently form holes on the film that correspond to the element density of the thermal head (Patent Application No. 149924). As we proceeded with these studies, we found that simply reducing the element size of the thermal head did not lead to significant improvements in image quality, and we considered the structure of the base paper used, that is, the influence of the adhesive part between the film and the support. I discovered that I had to develop a base paper.

In other words, in conventional base paper, since the film and the fibers on the surface of the support are bonded, the shape of the bonded portion has to be linear with a width approximately close to the diameter of the fibers.
Moreover, the thin paper that is generally used as a support,
Since binding of fibers (areas where several fibers are aggregated) is unavoidable, the adhesive shape at that area is a band-like shape in which several fibers are lined up. For base paper with such adhesive shape,
Even if the plate is made, the adhesive part will only be partially opened and the film will remain intact, and even if it is printed, the ink will not get around to that part and it will remain as a white part. This is a phenomenon called white spots in stencil printing, and fibrous white spots are unavoidable in conventional base paper.

In addition, as the element size of the thermal head becomes smaller, the influence of the bond between the support fiber and the film on plate making becomes stronger, and the number of dots that do not open where they should originally open increases. It turns out.

[0007]

[Means for Solving the Problems] As a result of extensive research into the adhesive shape between the base paper film and the support, the present inventor has discovered that by dispersing the adhesive shape in dots, the image is significantly improved compared to conventional base paper. This led to the development of a base paper with improved properties. That is, the present invention is a base paper for heat-sensitive stencil printing made by laminating a thermoplastic film and an ink-permeable porous support, characterized in that fine particles of 50 μm or less are present in the adhesive layer. .

The most important aspect of the present invention is that in contrast to the conventional base paper in which the film and the support were bonded at the contact area between the film and the support fibers, the base paper of the present invention has a bond between the film and the support fiber. The main reason for this is that it is attached to the body mainly through fine particles. In other words, in the base paper of the present invention, since the area where the film is adhesively fixed is smaller, the influence of the adhesive part on the perforation of the film when the film is thermally plated is significantly less than that of conventional base paper. To become
The opening state of the film becomes uniform. Moreover, the white spots in the black solid areas of printed materials, which were unavoidable with conventional base paper due to the inhibition of film perforation and ink permeation at the binding part of the support fibers, are mainly caused by fine particles in the base paper of the present invention. This will be significantly reduced due to the adhesion through.

[0009] Specifically, the method of making fine particles of 50 μm or less exist in the adhesive layer is to make the fine particles exist in the adhesive, to fix the fine particles to a support or film in advance, or by a combination of these methods. fine particles can be present in the In order to efficiently make the fine particles exist at the adhesive portion between the support and the film, it is necessary to make them adhere to the film or the support in advance, and it is more efficient to make the fine particles adhere to the support.

[0010] The fine particles used in the present invention do not need to be completely spherical, but may have a spherical shape on average while having a certain degree of shape distribution. The fine particles here need to have a particle size, that is, a diameter of 50 μm or less at maximum. Particles with a particle size exceeding 50 μm are not suitable for the present invention because the thickness as a base paper becomes too thick and the area of the adhesive portion with the film becomes too large. The lower limit of the particle size may be determined as long as it does not significantly fill the space between the fibers of the support used and inhibit ink permeability, and this lower limit may be determined as appropriate depending on the dispersion state of the support fibers. The preferred range of maximum particle size is 40 μm or less, more preferably 3 μm or less.
It is 0 μm or less, more preferably 20 μm or less. Further, as for the particle size distribution, the smaller the distribution width is, the more preferable it is, but it can be used without any particular limitation. Moreover, the average particle size is 5 to 40 μm, preferably 10 to 30 μm, and particularly preferably 15 to 20 μm as a number average particle size. The particle size and average particle size here are determined by enlarging the particles and using an image analysis device (for example, Nippon Avionics Co., Ltd., SP
The value measured by ICCA-II) is used.

[0011] The fine particles herein may be either organic particles such as thermoplastic resins or thermosetting resins, or inorganic particles, and may have a uniform solid structure, or may be so-called microcapsules. Any hollow shape may be used. For example, organic particles include polystyrene, polydivinylbenzene, polymethyl methacrylate, polyamide, polyester, polyethylene, polypropylene,
Polyvinyl acetate, polyacnylotrile, polyvinyl chloride, polyvinylidene chloride, ethyl cellulose, nitrocellulose, polytetrafluoroethylene, polyvinylidene fluoride, organic silicone, etc., and their copolymer resins, as well as inorganic particles. , silicon oxide, aluminum oxide, titanium oxide, carbon black, and the like are preferably used. Among these, in consideration of abrasion deterioration and corrosion deterioration of the thermal head, fine particles of hydrocarbon-based organic synthetic resin are particularly preferably used. Furthermore, it is believed that hollow particles containing gas in the form of microcapsules can be made into plates with good thermal efficiency due to their heat insulating properties.

Several methods can be considered for bonding the film and the support using the fine particles fixed to the film and/or the support as the main bonding points, and any method can be selected as appropriate. For example, a solid solution with particles dispersed in it,
A method of coating the surface of a support with a coating device, then scattering a solvent to produce a support with particles fixed to the surface, and then laminating it with a film, or coating a fixing agent solution with particles dispersed There is a method in which the film is coated on the surface of the film using a device, and then a solvent is scattered to produce a film with particles fixed to the surface, which is then laminated with a support. There are methods such as laminating with the surface as an adhesive surface. It is also possible to adopt a method in which a fixing agent for fixing the particles is also used as an adhesive, and lamination is performed at the same time as fixing the particles. Furthermore, it is acceptable if the particles can be fixed to the surface of the support during production of the thin paper that is the support. Furthermore, a film with protrusions of a particle size formed by molding fine particles having a particle size larger than the final film thickness in a state where they are dispersed in a raw film can be used as a film to which particles are fixed. is also possible.

[0013] As the fixing agent here, various types of adhesives such as commonly known solvent type, hot melt type, emulsion latex type, reaction curing type, ultraviolet ray and electron beam curing type etc. It is used under conditions that do not impede permeability, and its amount is 0.5 to 5 g/m2, preferably 0.5 to 3 g/m2, more preferably 0.5 to 2 g.
/m2. In either method, to prevent particle agglomeration, various dispersants are added to an extent that does not reduce adhesive strength, and air nozzles or suctions are used during processing to effectively make particles exist on the surface of the support. etc. may be used effectively.

[0014] Here, it is ideal that the film and the support be completely bonded only through the fine particles, but even if the adhesion between the film and the support fibers does not significantly deteriorate the image quality. It is sufficient if the bonding is mainly through fine particles. The optimal range of the fixed distribution density of fine particles varies depending on the particle size of the fine particles used and the density and basis weight of the support, but it is usually 2 to 60 particles/mm2, preferably 3 to 40 particles/mm2, and more preferably is 4 to 30 pieces/mm2.

[0015] As the adhesive for bonding the film and the support through fine particles, there are various types of adhesives known in the art, such as solvent type, hot melt type, emulsion latex type, reaction curing type, ultraviolet ray and electron beam curing type, etc. The agent can be used under conditions that do not interfere with the perforability of the film and the permeability of the ink. Further, the application of the adhesive is usually carried out by a known method, and the adhesive may be applied to the film side, the support side, or both, and then the films are bonded together. The amount of adhesive is 0.1
-5 g/m2, preferably 0.5-3 g/m2, more preferably 0.5-2 g/m2.

The film used for the base paper of the present invention is as follows:
Thickness of 0.5 to 100 mm, with a heat shrinkage rate of at least 30% and a heat shrinkage stress value of at least 75 g/mm2.
A 4 μm thermoplastic resin film is used. First, the heat shrinkage rate of the film needs to be 30% or more, preferably 30 to 90%, more preferably 40 to 8%.
The range is 0%. In addition, this heat shrinkage rate is 50mm
A corner film was sampled, placed in a constant temperature bath set to the measurement temperature, and allowed to shrink freely for 10 minutes.The amount of shrinkage of the film was determined and expressed as a percentage of the original size. This heat shrinkage rate is preferably measured at a temperature of 60
It is desirable that the temperature is expressed in the range of 170°C to 170°C, more preferably 65 to 140°C. This heating shrinkage rate is 30%
If it is less than 90, the opening during drilling will be insufficient, and
If it exceeds %, the pores tend to enlarge and the dimensional stability tends to decrease, which is not preferable. In addition, this heat shrinkage rate is 60
If it occurs at temperatures below ℃, the dimensional stability of the film tends to decrease and the resolution tends to decrease due to enlarged pores.
When the temperature exceeds 170°C, the perforation sensitivity tends to decrease, which is not preferable.

Furthermore, this film has at least 75
g/mm2 or more, preferably 100 to 1200 g/m
m2, more preferably 150 to 1000 g/mm2
It is necessary to have a heat shrinkage stress value of . This heat shrinkage stress value is obtained by sampling the layered film into a strip shape with a width of 10 mm, and placing it in a chuck with a strain gauge.
The chucks were set with a gap of 50 mm and immersed in silicone oil heated to each set temperature, and the stress generated was measured. When the set temperature was 100°C or less, the value was determined 10 seconds after immersion, and when it exceeded 100°C, the value was determined after 5 seconds, and the average value in the vertical and horizontal directions was adopted. Furthermore, this heat shrinkage stress value is 60 to 150°C, preferably 60 to 1
It is desirable that the temperature is expressed at 40°C, more preferably in the range of 70 to 130°C. 75g of this heat shrinkage stress value
If the diameter is less than 1200 g/mm2, the openings during drilling will be insufficient, and if it exceeds 1200 g/mm2, the pores will become too wide and the film will become distorted, leading to a decrease in resolution. In addition, if this heat shrinkage stress value occurs below 60°C, there is a tendency for the dimensional stability of the film to decrease and the resolution to decrease due to the enlargement of the pores, while if it occurs above 150°C, the perforation sensitivity decreases. This is not desirable as it tends to decrease.

Furthermore, the thickness of the film is 0.5 to 6 μm.
, preferably 1 to 4 μm, more preferably 1.5 to 2.
It is 5 μm. If this thickness is less than 0.5 μm, the strength is insufficient and tends to be easily damaged during perforation when peeling off the release layer, and if it exceeds 6 μm, sensitivity tends to decrease and perforation tends to be insufficient. . Furthermore, various resins such as polycondensation resins, vinyl resins, and olefin resins are used as thermoplastic resins for films, but in order to stably stretch and manufacture with high productivity, polyester resins are used. , polyamide resin, vinyl chloride resin, vinylidene chloride resin, polyethylene resin, polypropylene resin, etc. are preferable. Further, in order to form well-shaped pores due to film melting and shrinkage characteristics during plate making, polyester resins are preferred. The polyester resin is, for example, a copolymerized polyester resin, and one or both of the dicarboxylic acid component and the diol component constituting the polyester are composed of two or more different components. Specifically, when using different dicarboxylic acids, terephthalic acid and other dicarboxylic acids, such as aromatic dicarboxylic acids such as isophthalic acid and phthalic acid, or substituents that do not contribute to the esterification reaction on the aromatic ring are used. or a combination of aliphatic dicarboxylic acids such as succinic acid and adipic acid, and when using different diol components, ethylene glycol and other diols, such as propylene glycol, The diethylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, polyethylene glycol, polytetramethylene glycol, cyclohexanedimethanol, etc. are used as appropriate.

[0019] A preferred copolyester resin is, for example, mainly composed of ethylene glycol as the diol component and 40% of 1,4-cyclohexanedimethanol.
It is polycondensed with terephthalic acid using a compound containing mol % or less, preferably 20 to 40 mol %, more preferably 25 to 35 mol %. Among these, the crystallinity of the raw material resin that has been sufficiently annealed to reach an equilibrium state (by wide-angle X-ray method: Rotaflex RU-200B manufactured by Rigaku Denki Co., Ltd. using a graphite monochromator, applied voltage 50 kV) , applied current 160 mA, target Cu, measurement angle 2θ = 5 ~
38°) of 30% or less is suitably used, preferably 20% or less, more preferably 10% or less, particularly preferably 5% or less and is substantially amorphous. This particularly preferred resin was copolymerized using a resin mainly composed of terephthalic acid as the dicarboxylic acid component and a mixture of about 70 mol% ethylene glycol and about 30 mol% 1,4-cyclohexanedimethanol as the diol component. There is something.

[0020] Furthermore, other polymers and oligomers can be blended in the layer within a range that does not impair the necessary properties, and various additives such as antioxidants, heat stabilizers, plasticizers, etc. Agents, lubricants, etc. can be added depending on the purpose. Furthermore, the support used in the base paper of the present invention is made of natural fibers, recycled fibers, synthetic fibers, etc. alone or a mixture of these fibers, which are permeable to printing ink and do not substantially undergo thermal deformation during plate making. A porous material such as tissue paper or nonwoven fabric is used as a raw material, and a basis weight of 4 to 20 g/m2 is suitably used, preferably 6 to 15 g/m2, more preferably 8 to 12 g/m2.

[0021]

EXAMPLES The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to these Examples.

[0022]

[Example 1] First, a thin paper serving as a support was prepared by the following method. Freeness 18°SR (JIS P-812
1) 40% by weight of beaten Manila hemp, freeness 25°S
20% by weight of beaten sisal hemp, 20% by weight of PET fibers of 0.1 denier and 3 mm in length, and 20% by weight of vinylon fibers of 0.3 denier and 3 mm in length are uniformly mixed, and then An aqueous solution of epoxidized polyamide polyamino resin was added to the fiber at a concentration of 2% and mixed uniformly. This was used as paper stock to obtain thin paper using a wet paper making method using a cylinder paper machine. Furthermore, this thin paper was coated with a water-based emulsion type urethane resin (Superflex 1 manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) using a gravure coating machine.
00) was coated at a coating weight of 0.8 g/m2 to obtain thin paper having a basis weight of 10.9 g/m2 and a thickness of 31.1 μm, which was used as a base paper support.

Next, the copolymer particles containing methyl methacrylate as a main component obtained by suspension polymerization were classified using a particle size classification sieve to obtain fine particles having a particle size of 15 to 25 μm. The fine particles were dispersed in a vinyl acetate adhesive methanol solution (Konishi Co., Ltd. KE-60), and the resin-coated surface of the thin paper was coated with a gravure coater so that the vinyl acetate solid content was set at 0.6 g/m2. After that, the solvent was dispersed to obtain a support on which fine particles were fixed (particles were fixed at a density of about 15 to 30 pieces/mm 2 ).

On the other hand, a film was prepared by the following method. Amorphous polyester resin (manufactured by Eastman Chemical Co., PETG6763 resin, crystallinity of resin determined by wide-angle X-ray method is 0%): A and polyoxyethylene as a release agent.
A mixture of ethylene/vinyl acetate copolymer, polypropylene, and ethylene/α-olefin elastomer to which 3% by weight of oleate has been added: B and a multilayered state (A/B/A
) is extruded through a circular die, biaxially stretched in a bubble shape, and then heat treated in a flat shape to achieve the desired 2μm.
A multilayer film was obtained in which polyester was formed on both sides. The heat shrinkage rate of the polyester film is 73%,
The heat shrinkage stress was 360 g/mm2.

On the other hand, an adhesive was formulated as follows. Ethylene glycol diglycidyl ether (Nagase Kasei Kogyo Co., Ltd., Denacol EX-810) and polyamide amine (Sanwa Kagaku Kogyo Co., Ltd., Sanmide 300), 17:
The mixture was prepared at a weight ratio of 83% and dissolved in isopropyl alcohol. First, the above-mentioned particulate fixed support was unrolled from the unwinding machine, and the adhesive was coated in an amount of 1.5 g/m2.
After applying the adhesive solution to this support using a gravure coater, it was superimposed on the aforementioned multilayer film fed out from the second unwinding machine, and dried at a setting of 50°C while stacked. After passing through an oven and evaporating the solvent to dryness, the laminate was wound up with a winder. moreover,
This base paper intermediate was aged at 35° C. for 48 hours to complete adhesion. The base paper intermediate to which the film and fine particle adhesion support were adhered was peeled off from the elastomer laminate, and 0.05 g/m2 of silicone oil was applied to the surface of the film.
This was applied to form an overcoat layer with anti-thermal adhesion properties, and the final base paper was obtained.

Next, a thermal head with an element density of 400 dots/inch (interelement pitch: 63.5 μm) and an element size (main scanning direction width x sub scanning direction length) of 50 μm x 45 μm was heated. The above-mentioned base paper was made into a plate so that it could be installed in a head test printing device (manufactured by Okura Electric Co., Ltd., PH-TMD) and print patterns such as solid black and letters. When the base paper after plate making was observed under a microscope, it was found that holes in pattern areas such as solid black characters were formed independently corresponding to the elements of the thermal head. Furthermore, this base paper was mounted on the drum of a fully automatic digital stencil printing machine (Risograph RC115, manufactured by Riso Kagaku Kogyo Co., Ltd.), and
The printed matter printed at a printing speed of one sheet per minute was very clear with few white spots.

[0027]

[Comparative Example 1] A base paper was prepared using the same film and method as in Example 1, using the thin paper obtained in Example 1 as a support without undergoing fine particle fixation treatment. Furthermore, when the base paper made by the same method as in Example 1 was observed under a microscope, it was found that the holes in the black solid areas and pattern areas such as letters were not perforated in the nonwoven fabric film corresponding to the fiber bonded areas of the tissue paper, and were thermally damaged. They were not formed independently to correspond to the elements of the head. Further, in the printed matter obtained by the same method as in Example 1, white spots originating from the fibers of the thin paper were more noticeable than in the printed matter of Example 1.

[0028]

Effects of the Invention In the base paper of the present invention, since the film and the support are bonded mainly through fine particles, the area where the film is bonded and fixed becomes smaller.
When the film is thermally engraved, the effect of the support on the perforation of the film is significantly reduced compared to conventional base paper, so that the perforation state of the film becomes uniform. Moreover, this is due to the inhibition of film perforation and inhibition of ink permeation at the binding part of the support fibers, which was unavoidable with conventional base paper.
White spots in solid black areas of printed matter are significantly reduced.

Claims (1)

[Claims] 1. A base paper for heat-sensitive stencil printing comprising a thermoplastic film and an ink-permeable porous support bonded together, characterized in that fine particles of 50 μm or less are present in the adhesive layer.