GB2336916A

GB2336916A - Thermosensitive stencil

Info

Publication number: GB2336916A
Application number: GB9909704A
Authority: GB
Inventors: Yuji Natori; Takehiko Iwaoka; Fumiaki Arai; Masanori Rimoto
Original assignee: Tohoku Ricoh Co Ltd; Ricoh Co Ltd
Current assignee: Tohoku Ricoh Co Ltd; Ricoh Co Ltd
Priority date: 1998-04-27
Filing date: 1999-04-27
Publication date: 1999-11-03
Anticipated expiration: 2019-04-27
Also published as: GB2336916B; GB9909704D0

Abstract

A thermosensitive stencil has a thermoplastic resin support and a porous resin layer, containing a resin and a needle-like filler with a Mohs hardness of 4.0 or more. The stencil is produced by dissolving a resin in a mixed solvent of a good solvent and a bad solvent with respect to the resin to prepare a resin-dissolved solvent mixture, dispersing a needle-like filler with a Mohs hardness of 4.0 or more in the resin-dissolved solvent mixture to prepare a coating liquid, applying the coating liquid to the thermoplastic resin film, and drying the coating liquid. Preferred fillers are aluminium borate, titanium oxide and potassium titanate and the resin layer may also contain a polymeric dispersant.

Description

2336916

TITLE OF THE INVEN=

THERMOSENSITIVE STENCIL PAPER, METHOD OF PRODUCING THE SAME, AND STENCIL PRINTING METHOD USING THE STENCIL PAPER BACM7ROUND OF -THE INV=ON Field of the Inventinn

The present invention relates to a thermosensitive stencil paper and a method of producing the same, and particularly to a thermosensitive stencil paper comprising a thermoplastic resin film and a porous resin layer provided thereon, comprising a filler in the form of needles, and also to a method of producing such a thermosensitive stencil paper. In addition, the present invention also relates to a stencil printing method using a printing master prepared from the above-mentioned thermosensitive stencil paper.

There is conventionally known a thermosensitive stencil paper which is prepared by attaching a support with an ink-permeability property, such as a porous tissue paper to one surface of a thermoplastic resin film with an adhesive. Further, a sticking preventing layer is 1 - provided on the other surface of the thermoplastic resin film to prevent the zhermoplastic resin film from sticking to a thermal head when perforations are made in the resin film by the application of heat thereto. In practice, not only a sheet of Japanese paper is used as the porous tissue paper, but also hemp fiber, synthetic fiber and wood fiber are mixed to prepare the porous tissue paper. The thus prepared tissue paper and the thermoplastic resin film are laminated with an adhesive, and when necessary, a sticking preventing layer is prov-,ce-- cn the surface of the resin film. Such a therr,.,csensi,-ive stencil paper is widely used in practice. Fcwever, the above-mentioned conventional thermosens-tive stencil paper has the following drawbacks:

SinCe the fibers are partially superimposed in the paper, the adhesive is unfavorably accumulated at the pcr%,icn where the thermoplastic resin film is brought intc contact with the superimposed fibers of the tissue paper. A perforation cannot be easily formed in such a portion as mentioned above even by the application of thermal energy using the thermal head. Further, the ink cannot permeate through the stencil paper at that portion. As a result, the images printed on an image- 2 - receiving medium using a printing Master prepared from the above- mentioned thermosensitive stencil paper are lackin in evenness.

(2) The fibers themselves contained in the porous tissue paper hinder the printing ink from penetrating through the stencil paper, so that the printed images tend to become uneven.

(3) Because the fibers for use in the tissue paper are expensive and many defective products are produced in the preparation of the stencil paper, the cost of the thermosensitive stencil paper is necessarily increased.

In contrast to the above-mentioned conventional thermosensitive stencil paper, there is proposed a thermosensitive stencil paper prepared by providing a porous resin layer on one surface of a thermoplastic resin film (in Japanese Laid-open Patent Applications 3193445, 8-332785 and 1024667).

However, the thermosensitive stencil paper comprising a thermoplastic resin film and a porous resin layer has the shortcoming that the stencil paper easily causes the curling problem. This is because the shrinkage of the thermoplastic resin film is different from that of the porous resin layer depending on the change in - 3 - temperature and humidity. Consequently, the curling problem hinders the transportation of the stencil paper in the apparatus where a printing master is prepared from the stencil paper and the printing operation is carried cut using the printing master.

sumbag,z OF TBZ--lln:cN Accordingly, a first object of the present invention is to provide a thermosensitive stencil paper, having excellent transportation properties free of the abovementioned curling problem depending upon the change in temperature and humidity, and therefore capable of producing clear images when a printing master prepared from the thermosensitive stencil paper is subjected to the printing operation.

A second object of the present invention is to provide a method of producing the above-mentioned thermosensitive stencil paper.

A third object of the present invention is to provide a stencil printing method capable of producing high quality images.

The first object of the present invention can be achieved by a thermosensitive stencil paper comprising a 4 - J thermoplastic resin film and a porous resin layer provided on one surface of the thermoplastic resin film, comprising a resin and a needle-like filler with a Mohs hardness of 4.0 or more.

In this case, the porous resin layer may further comprise a polymeric dispersant, preferably having carboxyl group therein. Further, it is preferable that the polymeric dispersant be contained in an amount of 10 parts by weight or less to 100 parts by weight of the filler.

It is preferable that the needle-like filler for use in the porous resin layer have a diameter of 0.1 to 1 pm and a length of 1.0 to 100.0 pm.

The aforementioned filler may be contained in an amount of 13 to 200 parts by weight to 100 parts by weigh of the resin for use in the porous resin layer.

The needle-like filler may be selected from the group consisting of aluminum borate, titanium oxide, and potassium oxide, each in the form of needles.

The second object of the present invention can be achieved by a method of producing a thermosensitive stencil paper comprising a thermoplastic resin film and a porous resin layer provided on one surface of the - 5 thermoplastic resin film, comprising the steps of dissolving a resin in a mixed solvent comprising a good solvent and a bad solvent with respect to the resin to prepare a resin-dissolved solvent mixture, dispersing a needle-like filler with a Mohs hardness of 4.0 or more in the resindissolved solvent mixture to prepare a coating liquid, applying the coating liquid to one surface of the thermoplastic resin film, and drying the coating liquid so as to form the porous resin layer on the thermoplastic resin film.

Furthermore, it is preferable that a polymeric dispersant be further added to the resin-dissolved solvent mixture while the filler is dispersed therein.

The third object of the present invention can be achieved by a stencil printing method using a printing master prepared from the above-mentioned thermosensitive stencil paper.

BRIEF-DE-SCEIRTIMN OE THE DBANINU A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when - 6 - considered in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic cross-sectional view of a thermosensitive stencil paper according to the present invention.

FIG. 2 is a schematic cross-sectional view of a thermosensitive stencil paper according to the present invention which is subjected to thermal printing to prepare a printing master.

FIG. 3 is a schematic cross-sectional view of a printing master prepared from a thermosensitive stencil paper according to the present invention.

FIG. 4 is a schematic diagram which shows an apparatus of preparing a printing master from the thermosensitive stencil paper of the present invention and carrying out the printing operation using the printing master.

FIG. 5 is a schematic diagram which shows an apparatus of preparing a printing master from the thermosensitive stencil paper of the present invention and carrying out the multicolor printing operation using the printing master.

DESCRIPTION OF THE PREFEWZD-MMOpIMMS

The inventors of the present invention have intensivelv examined the thermosensitive stencil paper comprising a thermoplastic resin film and a porous resin layer formed thereon from various angles. As a result, it is found that when a filler in the form of needles is contained in the porous resin layer, the stiffness of the obtained thermosensitive stencil paper is strong enough to minimize the curling problem and make the transportation of the stencil paper stable in the printing master manufacturing machine.

The thermosensitive stencil paper according to the present invention comprises a thermoplastic resin film and a porous resin layer formed thereon, comprising a needle-like filler with a Mohs hardness of 4.0 or more, such as aluminum borate, titanium oxide or potassium titanate.

The porous resin layer may have such a structure that numerous voids are formed in the layer and on the surface portion of the layer. In this case, it is desirable that the void be continuous in the thickness direction of the layer, that is, penetrating through such a direction of the layer, when the penetration of ink - 8 - 1 into the porous resin layer is taken into consideration. The boundary between the thermoplastic resin film and the porous resin layer may be covered with a resin component for use in the porous resin layer to such a degree that the perforation of the thermosen5itive stencil paper, for example, by use of a thermal head, is not hindered.

It is preferable that the porous resin layer have numerous pores with an average pore diameter of 1 to 100 pm.

When the average pore diameter of the pores formed in the porous resin layer is 1 lim or more, the penetration of printing ink into the porous resin layer is sufficient, so that it is not necessary to employ a lowviscosity ink. Therefore, it is possible to prevent the printed image from being blurred, and to prevent the printing ink from oozing out from the edge of the printing master prepared from the thermosensitive stencil paper which is wound round the printing drum in the course of image printing operation. Further, the voidage of the porous resQLn layer is sufficient, so that the perforation of the thermosensitive stencil paper can be readily carried out by use of the thermal head in order to prepare a printing master from the thermosensitive - 9 - stencil paper. in addition, when the average pore diameter is 100 pm or less, the permeability of a printing master prepared from the thermosensitive stencil paper to printing ink can be properly controlled, so that the portion between the printing drum and the thermoplastic resin film of the stencil paper can be prevented from excessively being filled with the printing ink. Therefore, the offset phenomenon and image blurring can be prevented. In light of the above-mentioned factors, when the average pore diameter is within the range of 1 to 100 pm, high quality images can be obtained.

It is proper that the density of the porous resin layer be in the range of 0.01 g/crn' to 2 g/cm3. When the density of the porous resin layer is within the abovementioned range, the porous resin layer is not fragile, but strong enough to obtain a desired stiffness, so that the permeability of the porous resin layer to the printing ink can be properly controlled.

It is preferable that the deposition amount of the porous resin layer be in the range of 0.5 g/M2 to 25 g/M2. The increase in deposition amount of the porous resin layer hinders the penetration of the printing ink into the porous resin layer, thereby lowering the image - 10 - quality of the obtained ink images. When the deposition amount of the porous resin layer is less than 0.5 9/m', sufficient stiffness of the stencil paper cannot be obtained.

The porous resin layer comprises a resin, preferably a thermoplastic resin. Preferable examples of the thermoplastic resin for use in the porous resin layer include vinyl resins such as polyvinyl acetate, polyvinyl buty&-al, pc-7yvinvl acetal, vinyl chloride - vinyl acetate copo-7yrr,er, vinyl chloride - vinylidene chloride copolymer, vinyl chIcride acrylonitrile copolymer, and styrene acr.lonitr-.le coplymer; polyamide resins such as pol,,b.j-.v-e.ne and nylon; polyphenylene oxide; acrylate and met',nacrya-.e; polycarbonate; cellulose derivatives such as a--etyce-'lulose, acetylbutylcellulose, and acet.vip.-opylcellulose. Of these resins, butyral resin is most preferable.

As the thermoplastic resin film for use in the thermosensitive stencil paper of the present invention, there can be employed any thermoplastic resin films used in the conventional thermosensitive stencil papers, for example, a vinyl chloride - vinylidene chloride copolymer film, a polypropylene film, and a polyester film. 11 - In particular, a polyester film which can be easily perforated with the application of a low energy thereto is preferable. For example, there can be employed a polyester film of which heat of fusion is 3 to 11 callg (disclosed in Japanese Laid-Open Patent Application 62149496), a polyester film with a crystallinity index of 30% or less (disclosed in Japanese Laid-Open Patent Application 62-282983), and a polyester film comprising a butylene terephthalate unit in an amount of 50 mol% or more (disclosed in Japanese Laid-Open Patent Application 2-158391).

The thickness of the thermoplastic resin film is preferably in the range of 0.5 to 10 pm. When the thickness of the thermoplastic resin film is 0. 5 pm or more, coating of the porous resin layer formation liquid on the thermoplastic resin film can be readily achieved. When the thickness of the thermoplastic resin film is 10 gm or less, there is no difficulty in the perforation by use of the thermal head.

Furthermore, in order to prevent the thermosensitive stencil paper from sticking to the thermal head, the thermosensitive stencil paper may further comprise a sticking preventing layer which is provided on the other - 12 - side of the thermoplastic resin film, opposite to the porous res-in layer with respect to the thermoplastic resin film.

The sticking preventing layer may comprise, for example, a silicone releasant, fluorine-containing releasant, or phosphate surfactant.

In general, the bending rigidity of the porous resin layer comprising the previously mentioned thermoplastic resin is low. When the porous resin layer is made thicker in order to increase the stiffness, the penetration of the printing ink into the porous resin layer becomes poor although the rigidity of the porous resin layer is increased. Thus, a desired image density cannot be obtained.

According to the present invention, the porous resin layer comprises a needle-like filler with a Mohs hardness of 4.0 or more. It is remarkably effective to add such a filler to the porous rhsin layer in order to increase the stiffness of the porous resin layer without decreasing the image density, and to minimize the curling of the obtained stencil paper caused by the change in temperature and humidity. In other words, addition of the filler in the form of needles contributes to the increase - 13 - of the mechanical strength of the porous resin layer, that is, the rigidity of the porous resin layer. The filler for use in the porous resin layer is required to be in the form of needles because the needle- like filler particles are entangled with each other to form a network with a high rigidity or the needle-like filler particles are orientated in a fixed direction so as to increase the rigidity of the obtained porous resin layer in the orientation direction. In addition, the rigidity of the filler itself is required to have a Mohs hardness of 4.0 or more.

For the needle-like filler with a Mohs hardness of 4.0 o.- mc--e, there can be employed aluminum borate, titani.ar cx-ide, and Potassium titanate in the form of needles. -.,,-.se needle-like fillers can be used alone or in combination.

It is preferable that the needle-like filler be contained in the porous resin layer in an amount of 13 to 200 parts by weight, more preferably 20 to 100 parts by weight, to 100 parts by weight of the resin for use in the porous resin layer. When the amount of filler is 13 parts by weight or more, the stiffness of the porous resin layer can be effectively increased. Further, when - 14 - the needle-like filler is contained in the porous resin layer in an amount of 200 parts by weight or less to 100 parts by weigh of the resin, the porous resin layer can be provided on the thermoplastic resin film by coating method with no difficulty. Further, since the adhesion of the porous resin layer to the thermoplastic resin film is not excessively decreased, the porous resin layer can be prevented from peeling from the thermoplastic resin film during the preparation of a printing master from the thermosensitive stencil paper or the handling of the printing master.

In the present invention, aluminum borate, titanium oxide or potassium titanate in the form of needles may be used as the needle-like filler. as mentioned above. In this case, when the Mohs hardness of the employed filler is less than 4.0, the rigidity of the porous resin layer cannot be improved, and consequently, the curling of the obtained stencil paper which is caused by the change in temperature or humidity cannot be efficiently prevented.

With respect to the filler, it is preferable to employ a needle-like filler with a diameter of 0.1 to 1 Pm and a length of 1.0 to 100.0 pm. The needle-like filler having a diameter of 0.1 pm or more and a length - is - of 1.0 im or more can effectively work to prevent the curling of the thermosensitive stencil paper. In addition, when the diameter of the filler is 1.0 gm or less and the length thereof is 100.0 gm or less, the needle-like filler can be uniformly dispersed in the porous resin layer formation liquid, and accordingly, the porous resin layer can be uniformly obtained.

it is considered that filler in the form of needles can strengthen the network structure of the porous resin layer and increase the strength of the porous resin layer. As a result, the curling of the thermosensitive stencil paper which is caused by the change in temperature and humidity can be prevented.

For the formation of the porous resin layer comprising the previously mentioned thermoplastic resin and the needle-like filler, the thermoplastic resin is dissolved in a good solvent with respect to the resin to prepare a resin solution, and the needle-like filler is dispersed in the resin solution, and a bad solvent is further added to the above prepared dispersion, so that porous resin layer formation liquid is prepared. The formation liquid thus prepared is coated on the thermoplastic resin film and dried, so that a porous - 16 - resin layer is provided on the thermoplastic resin film.

According to the present invention, it is preferable to add a polymeric dispersant when the filler is dispersed in the resin solution. When the polymeric dispersant is added to the formation liquid, aggregation and sedimentation of the needle-like filler in the porous resin layer formation liquid, which may otherwise occur by vigorous stirring of the formation liquid for a long time, can be prevented. in the porous resin layer formation liquid comprising a thermoplastic resin, a needle-like filler, a good solvent and a bad solvent with respect to the thermoplastic resin, the dispersion of the filler can be stabilized and the filler is not sedimented for an extended period of time.

It is preferable that the polymeric dispersant for use In the present invention be a carboxyl-groupcontaining polymer.

The reason why the needle-like filler is not sedimented by the addition of such a polymeric dispersant has not yet been clarified. It is supposed that the needle-like filler is attached to an aliphatic group contained in a molecule of the polymeric dispersant at the one end thereof, and the carboxyl group of the - 17 - dispersant is extended from the other end thereof. The compatibility of the carboxyl group with the group contained in the thermoplastic resin, such as a butyral resin, for use in the porous resin layer formation liquid is so good that the needlelike filler can be dispersed in the resin solution in a stable condition because the carboxyl group of the dispersant is extended.

Specific examples of the polymeric dispersant for use in the present invention are styrene - acrylic acid copolymer, ethylene - acrylic acid copolymer, styrene maleic acid copolymer, acrylate - acrylic acid copolymer, methacrylate - methacrylic acid copolymer, styrene maleic acid (including partial methyl esterification) copolymer, and styrene - maleic acid (including partial isobutyl esterification) copolymer.

When the polymeric dispersant is employed for the preparation of the porous resin layer formation liquid, a thermoplastic resin is dissolved in a good solvent to prepare a resin solution, a needle-like filler and a polymeric dispersant are dispersed and dissolved in the above prepared resin solution, and a bad solvent is added to the above mixture, whereby a porous resin layer formation liquid is prepared. The porous resin layer is - formation liquid may be coated on the thermoplastic resin film and dried.

When necessary, the porous resin layer formation liquid may further comprise an antistatic agent, an agent for preventing the sticking, a surfactant, an antiseptic agent and an anti-foaming agent so long as the effects of the present invention are not hindered.

The porous resin layer has numerous voids therein and on the surface portion thereof. The above-mentioned void portions or the resin portions come in contact with the thermoplastic resin film at the boundary therebetween. 50 long as the perforation of the thermosensitive stencil paper by the thermal head is not hindered and the ink penetrating property is not lowered, an adhesive layer may be interposed between the porous resin layer and the thermoplastic resin film in the thermosensitive stencil paper of the present invention.

FIG. 1 is a schematic cross-sectional view which shows the structure of a thermosensitive stencil paper according to the present invention. A thermosensitive stencil paper 1 shown in FIG. 1 comprises a thermoplastic resin film 102 and a porous resin layer 103 provided thereon.

- 19 When a printing master is prepared from the thermosensitive stencil paper 1, the stencil paper 1 is disposed between a platen roller 301 and a thermal head 201 shown in FIG. 2.

With the aoplication of heat to the thermosensitive stencil paper 1 through the thermal head 201, the thermoplastic resin film 102 is fused imagewise so that a perforation 102a may be formed therein, as shown in FIG. 3. Thus, a printing master is prepared from the thermosensitive stencil paper according to the present invention.

The method of producing the thermosensitive stencil paper according to the present invention will now be described in detail.

The thermosensitive stencil paper of the present invention can be produced by the following method: A resin is dissolved in a good solvent with respect to the resin to prepare a resin solution, and a needle-like filler is dispersed in the resin solution. In this case, the previously mentioned polymeric dispersant may be added to the resin solution together with the filler. With stirring the mixture, a predetermined amount of bad solvent with respect to the above-mentioned resin is - 20 added to the mixture, whereby a porous resin layer formation liquid is prepared. The porous resin layer formation liquid is ccated on the thermoplastic resin film, and d&-ied. The porous resin layer formation liquid is dried so as to increase the concentration of the resin, and therefore the resin is precipitated to form a porous resin layer.

When the polymeric dispersant is added to the porous resin layer formation liquid, it is preferable that the amount of polymeric dispersant be 10 parts by weight or less to 100 parts by weight of the needle-like filler in light of the dispersion stability of the filler in the porous resin layer formation liquid.

For the preparation of the porous resin layer formation liquid, there is employed a mixed solvent comprising a good solvent and a bad solvent with respect to the resin to prepare a resin-dissolved solvent mixture. In this case, it is recommendable to choose the Combination of a good solvent and a bad solvent so that the good solvent can be evaporated at relatively low temperature as compared with the bad solvent.

TABLE 1 shows the combination between a representative chermoplastic resin for use in the porous - 21 - resin layer and a mixed solvent therefor comprising a good solvent and a bad solvent with respect to the resin. TABLE 1 also shows the mixing ratio by weight of the good solvent to the bad solvent, provided that the temperatures of both solvents are 2CC, and the concentration of the thermoplastic resin.

TABLE 1

Thermoplastic Mixed Solvent Concent- Resin mixing ration of Good Bad ratio by thermo- solvent solvent weight plastic resin (wt.%) vinyl chloride-vinyl Ethyl acetate Acetone alcohol 1.1:29 11 copolymer Polyvinyl Ethyl -utyral alcohol Water 7.2:2.5 a Polystyrene Tetra- Ethyl 8.8:1.2 8.8 hydrofuran alcohol Alcohol- Ethyl soluble nylon alcohol Water 6.6 3.4 3.4 Polycarbonate Tetra- Ethyl 8.4:1:6 8.4 hydrofuran alcohol Acetylbutyl cellulose Acetone Water 8.8:1.2 9.7 Polymethyl methacrylate Acetone Water 9:1 10 1:1 As mentioned above, the method of providing a porous resin layer comprises the steps of dissolving the thermoplastic resin (or the thermoplastic resin and the polymeric dispersant) in a mixed solvent comprising a good solvent and a bad solvent with respect to the resin to prepare a resin-dissolved solvent mixture, dispersing the needle-like filler in the resin-dissolved solvent mixture to prepare a porous resin layer formation liquid, and coating the thus prepared porous resin la.ver formation liquid on the thermoplastic resin film. To be more specific, the thermoplastic resin (or a mixture of the thermoplastic resin and the polymeric dispersant) is disscive... in a solvent to prepare a resin solution, and the needle-like filler is added to the resin solution, and the rixture thus obtained is uniformly dispersed using a grinding and dispersing means such as a ball mill, sand '-.,eads mill or ultrasonic dispersion apparatus.

With the addition of a predetermined amount of the bad solvent 'Co the uniform dispersion thus prepared, a porous resin layer formation liquid can be obtained, The porous resin layer formation liquid is uniformly applied to the thermoplastic resin film using a coating means such as a blade coater, transfer roll coater, wire bar coater, reverse roll coater, gravure roll coater, or die coater.

Thereafter, the coated porous resin layer formation - 23 - liquid is subjected to hot-air drying or infrared drying. The thermoplastic resin film causes heat shrinkage when exposed to high temperature, and in such a case, the thermal sensitivity of the film will be lowered in the course of the preparation of the printing master. Therefore, it is desirable that the porous resin layer formation liquid be dried so as not to cause the heat shrinkage of the thermoplastic resin film. To be more specific, it is preferable to dry the porous resin layer formation liquid at 600C or less.

For the preparation of the printing master, any semiconductor laser having a wavelength in the range from the ultraviolet region to the infrared region is available as well as the thermal head. The semiconductor laser may be used alone or in combination, and further, together with nonlinear optical materials.

FIG. 4 is a schematic diagram which shows one example of the apparatus that is useful to carry out the stencil printing method, using a printing master prepared from the thermosensitive stencil paper of the present invention.

In FIG. 4, a printing master is prepared from the thermosensitive stencil paper 1 before wound round a - 24 - printing drum 8. Alternatively, the printing master can be prepared after the thermosensitive stencil paper 1 is wound round the printing drum 8.

FIG. 5 is a schematic diagram which shows one example of the apparatus that is useful to carry out the multicolor stencil printing method employing the thermosensitive stencil paper of the present invention as a printing master. In this case, a printing master is prepared from the thermosensitive stencil paper 1 before wound round a printing drum 8.Alternatively, the printing master can be prepared after the thermosensitive stencil paper 1 is wound round the printing drum 8. A plurality of printing drums 8 is independently prepared for multicolor printing in FIG. 5. One printing drum may be separately used for a plurality of ink arrangement sections.

In FIG. 4 and FIG. 5, reference numeral 2 indicates an electromagnetic wave irradiation device; reference numeral 3, a feeding roller; reference numeral 4, a paper cutting means; reference numeral 5, a printing master manufacturing unit; reference numeral 6, a laser controlling unit; reference numeral 7, a clamper; reference numeral 9, an ink roller; reference numeral 10., 25 - a doctor roller; reference numeral 11, an ink fountain; reference numeral 12, a printing master separating roller; reference numeral 13, a printing master receiving box; reference numeral 14, an image receiving sheet; reference numeral 15, a paper feed roller; reference numeral 16, a toothed belt; reference numeral 17, a separating roller; reference numeral 18, a separating roller; reference numeral 19, a guide plate; reference numeral 2C, resist rollers; reference numeral 21, a press roller; reference numeral 22, a paper transporting belt; and reference numeral 23, a paper tray.

When -nk images, in particular, multicolor images are pr--duced by the stencil printing method using the print.Jnc master prepared from the thermosensitive stencil paper of the present inventicn, as shown in FIG. 5, there is the problem that subsequent printing drums are stained with the colcr ink image previously transferred to an image receiving sheet. If the transportation position of the image receiving sheet is not precise, the image quality of the multicolor image formed on the image receiving sheet will be lowered because of the occurrence of a ghost image. To prevent such deterioration of image quality, it is preferable that the stencil printing - 26 - method of the present invention employ a printing ink capable of being cured by ultraviolet-light irradiation, a printing ink of which viscosity properties are changeable depending on temperature, or a printing ink of which viscosity properties are changeable depending upon the shear stress applied thereto.

Other features of this invention will become apparent in the course of the following description of exemplary embodiments, which are given for illustration of the invention and are not intended to be limiting thereof.

Example 1

5.0 parts by weight of a polyvinyl butyral resin were dissolved in 45.0 parts by weight of methyl alcohol to prepare a resin solution. With stirring the resin solution, 3.0 parts by weight of water were added dropwise. Further, 2.5 parts by weight of aluminum borate in the form of needles with a Mohs hardness of 7 (Trademark "ALBOREX W", made by Shikoku Corporation) were added to the above prepared resin-dissolved solvent mixture. The resultant mixture was dispersed in a ball mill for 3 hours, so that a porous resin layer formation - 27 - liquid was prepared.

The above prepared porous resin layer formation liquid was coated on a biaxially oriented polyester film with a thickness of 2.0 im by a wire bar coater (with a wire diameter of 1.4 mm). Immediately after the formation liquid was coated, the coated liquid was dried by hot air of 500C for 3 minutes. Thus, a porous resin layer with a thickness of 23 gm was provided on the polyester film.

On the opposite side of the polyester film, a silicone resin layer with a thickness of 0.01 1m, serving as a sticking preventing layer, was provided.

Thus, a thermosensitive stencil paper No. 1 according to the present invention was obtained.

Example 2

The procedure for preparation of the thermosensitive stencil papeAr No. 1 in Example 1 was repeated except that the needle-like aluminum borate employed as the filler in the porous resin layer formation liquid in Example 1 was replaced by electroconductive titanium oxide in the form of needles with a Mohs hardness of 6.5 (Trademark "FT300C, made by Ishihara Sangyo Kaisha, Ltd.).

Thus, a thermosensitive stencil paper No. 2 - 28 - according to the present invention was obtained.

Example 3

The procedure for preparation of the thermosensitive stencil paper No. 1 in Example 1 was repeated except that the needle-like aluminum borate employed as the filler in the porous resin layer formation liquid in Example 1 was replaced by potassium titanate in the form of needles with a Mohs hardness of 4 (Trad-emark "TOFICA V, made by Otsuka Chemical Co., Ltd.).

Thus, a thermosensitive stencil paper No. 3 according to the present invention was obtained.

Example 4

3.3 parts by weight of a vinyl acetate - vinyl chloride copolymer (Trademark 'WYHW', made by Union Carbide Japan K.K.) were dissolved in a mixed solvent of 20.0 parts by weight of acetone and 8.0 parts by weight of ethyl alcohol. To this resin-dissolved solvent mixture, 0.1 parts by weight of polyvinyl butyral were further added and dissolved therein. Thereafter, 2.5 parts by weight of aluminum borate in the form of needles with a Mohs hardness of 7 (Trademark "ALBOREX W, made by - 29 - Shikoku Corporation) were added to the above prepared mixture. The resultant mixture was dispersed in a ball mill for 3 hours, so that a porous resin layer formation liquid was prepared.

The above prepared porous resin layer formation liquid was coated on a biaxially oriented polyester film with a thickness of 2.0 pm by a wire bar coater (with a wire diameter of 1.4 mm). Immediately after the formation liquid was coated, the coated liquid was dried by hot air of SO'C for 3 minutes. Thus, a porous resin layer with a thickness of 23 pm was provided on the polyester film.

On the opposite side of the polyester film, a silicone resin layer with a thickness of 0-01 pm, serving as a sticking preventing layer, was provided.

Thus, a thermosensitive stencil paper No. 4 according to the present invention was obtained.

Comparative Example 1 5.0 parts by weight of a polyvinyl butyral resin were dissolved in a mixed solvent of 45.0 parts by weight of methyl alcohol and 11.0 parts by weight of water, so that a porous resin layer formation liquid was prepared.

The above prepared porous resin layer formation - 30 - liquid was coated on a biaxially oriented polyester film with a thickness of 2.0 gm by a wire bar coater (with a wire diameter of 1.4 mm). Immediately after the formation liquid was coated, the coated liquid was dried by hot air of 5CC for 3 minutes. Thus, a porous resin layer with a thickness of 21 lim was provided on the polyester film.

On the opposite side of the polyester film, a silicone resin layer with a thickness of 0.01 pm, serving as a sticking preventing layer, was provided.

Thus, a comparative thermosensitive stencil paper No. 1 was obtained.

Comparative Example 2 5.0 parts by weight of a polyvinyl butyral resin were dissolved in 45.0 parts by weight of methyl alcohol to prepare a resin solurion. With stirring the resin solution, 3.0 parts by weight of water were added dropwise. Further, 0.8 parts by weight of magnesium silicate (talc) in the form of plates with a Mohs hardness of 1 (Trademark "MICROACE P4", made by Nippon Talc Co., Ltd.) were added to the above prepared resindissolved solvent mixture. The resultant mixture was dispersed in a ball mill for 3 hours, so that a porous - 31 - resin layer formation liquid was prepared.

The above prepared porous resin layer formation liquid was coated on a biaxially oriented polyester film with a thickness of 2.0 pm by a wire bar coater (with a wire diameter of 1.4 mm) Immediately after the formation liquid was coated, the coated liquid was dried by hot air of SO'C for 3 minutes. Thus, a porous resin layer with a thickness of 23 pm was provided on the polyester film.

Thus, a comparative thermosensitive stencil paper No. 2 was obtained.

Comparative Example 3 5.0 parts by weight of a polyvinyl butyral resin were dissolved in 45.0 parts by weight of methyl alcohol to prepare a resin solution. With stirring the resin solution, 3.0 parts by weight of water were added dropwise. Further, 2.5 parts by weight of magnesium silicate in the form of needles with a Mohs hardness of 2 (Trademark "AIDPLUS SP', made by Mizusawa Industrial Chemicals, Ltd.) were added %to the above prepared resin- 32 - dissolved solvent mixture. The resultant mixture was dispersed in a ball mill for 3 hours, so that a porous resin layer formation liquid was prepared.

The above prepared porous resin layer formation liquid was coated on a biaxially oriented polyester film with a thickness of 2.0 pm by a wire bar coater (with a wire diameter of 1.4 mm). Immediately after the formation liquid was coated, the coated liquid was dried by hot air of 50C for 3 minutes. Thus, a porous resin layer with a thickness of 23 pm was provided on the polyester film.

Thus, a comparative thermosensitive stencil paper No. 3 was obtained.

Using each of the thermosensitive stencil papers No. 1 to No. 4 according to the present invention and the comparative thermosensitive stencil papers No. 1 to No. 3, the degree of curling of the stencil paper depending on the change in temperature and humidity, the stiffness of the stencil paper, the adhesion of the porous resin layer to the polyester film, and the image quality and image - 33 - density of the ink image to be produced were measured and evaluated in the following manners.

The results are shown in TABLE 2. (1) Curling of thermosensitive stencil paper Each thermosensitive stencil paper was cut into a sample sheet of 100 mm x 100 mm. The sample sheet was placed in a temperature-controlled bath of 500C for 2 hours, and thereafter subjected to moisture conditioning under the circumstances of 2CC and 9MH for 10 minutes, Then, the sample sheet was allowed to stand at 2VC and 10%RK for 10 minutes. After that, the curling degree, that is, the outer diameter DI (mm(t) of the curling portion of the sample sheet was measured. After that, each sample sheet was again allowed to stand at 200C and 9MH for 10 minutes and the outer diameter D2 (mmcD) of the curling portion of the sample sheet was measured in the same manner as mentioned above.

The curling degree was evaluated on the following scale.

0: Both D! and D2 were 15 mm or more.

X: At least one of DI or D2 was less than 15 mm. (2) Stiffness of thermosensitive stencil paper The rigidity was measured by use of a commercially - 34 - available stiffness tester made by Lorentzen & Wettre Corporation. (3) Adhesion of porous resin layer to polyester film A folding endurance test was carried out in such a manner that the thermo5ensitive stencil paper was folded with the porous resin layer side being disposed outside. The adhesion of the porous resin layer to the polyester film was evaluated on the following scale.

0: There was no peeling of the porous resin layer from the polyester film.

X: There was observed peeling of the porous resin layer from the polyester film. (4) Image quality of printed ink image A printing master was prepared from each thermosensitive stencil paper using the printing master manufacturing apparatus equipped with a thermal head.

Ink images were printed on an image receiving sheet by setting the above prepared printing master in a commercially available printing machine "PRIPORT VT382V (Trademark), made by Ricoh Company, Ltd. The printing speed was set to the medium mode, and the printing conditions were controlled to 2CC and E5%RH.

The image quality was evaluated by visually - 35 - inspecting the presence of non-printed white spots in a solid image portion.

0: There was no non-printed white spots in a solid image portion.

X: There were some non-printed white spots in a solid image pcrtion. (5) Image density The image density of the above-mentioned solid image portion was measured using a McBeth reflection type densitometer. (6) Deposition amount of porous resin layer Each thermosensitive stencil paper was cut into a sample sheet of 100 mm x 100 mm. The weight (wl) of each sample sheet was measured.

A polyester film used as the thermoplastic resin film was similarly cut into a sheet of 100 mm x 100 mm, and the weight (w2) of the sheet was measured.

The weight of the porous resin layer was obtained by subtracting the weight (A) from the weight (wl). The thus obtained weight of the porous resin layer was converted into the deposition amount (g/m2) of the porous resin layer.

- 36 TABLE 2

Filler Used in Porous Resin Layer Results of Evaluation Kind of Mohs Diameter Length Curling Stiffness Adhesion Image Image Deposition tiller bacdne3s of of (MN) of quality density amount of needle- needle- porous porous like like resin resin tiller filler layer layer (pm) Aluminurn borate in Ex. 1 the form of 7 0.8 is 0 16 0 1.08 7.6 needles Titanium oxide in Ex. 2 the form of 6.s 0.27 5.15 0 22 0 0 1.03 9.1 needles Potassium titanate Ex. 3 in the form 4 0-5 15 0 23 0 0 1-08 8.4 of needles Aluminum borate in Ex. 4 the form of 7 0.8 is 0 22 0 0 0.85 7.5 needles C0111p.

Ex. 1 - - - X 14 0 0 0.98 6.0 Magnesium Comp. silicate Ex- 2 in the form 1 1.5 1.5 X 14 0 0 0.99 7.5 of plates Magnesiu silicateln Comp.

in the form: 2 0.2 7.0 X 13 0 0 0.95 6.0 EX, 3 of needles!:

Example 5

5.0 parts by weight of a polyvinyl butYral resin were dissolved in 45,0 parts by weight of methyl alcohol to prepare a resin solution. 0.05 parts by weight of a polymeric dispersant (Trademark "JONCRYL EMULSION 74X, made by Johnson Polymer Corporation) were added to the above prepared resin solution and dissolved therein. Further, 5.0 parts by weight of potassium titanate in the form of needles with a Mohs hardness of 4 (Trademark "TOFICA Y", made by Otsuka Chemical Co., Ltd.) were added to the abcve prepared solution. The resultant mixture was dispe.rsez in a ball mill fcr 3 hours, so that a dispersz--n of filler was prepared. 3.0 parts by weight of water (bat solvent) were added dropwise to the abovementionen dispersion with stirring, so that a porous resin layer &formation liquid was prepared.

:he above prepared porous resin layer formation liquid was coated on a biaxially oriented polyester film with a thickness of 2.0 im by a wire bar coater (with a wire diameter of 1.4 mm). Immediately after the formation liquid was coated, the coated liquid was dried by hot air of SO'C for 3 minutes. Thus, a porous resin layer with a thickness of 23 pm was provided on the polyester film.

On the opposite side of the polyester film, a silicone resin layer with a thickness of 0.01 gm, serving as a sticking preventing layer, was provided.

Thus, a thermosensitive stencil paper No. 5 according to the present invention was obtained.

Example 6

4.0 parts by weight of a polyvinyl butyral resin were dissolved in 46.0 parts by weight of methyl alcohol to prepare a resin solution. 0.1 parts by weight of a polymeric dispersant (Trademark "SMA20OV, made by.Kawahara Petrochemical Co., Ltd.) were added to the above prepared resin solution and dissolved therein. Further, 4.0 parts by weight of aluminum borate in the form of needles with a Mohs hardness of 7 (Trademark "ALBOREX W' made by Shikoku Corporation) were added to the above prepared solution. The resultant mixture was dispersed in a ball mill for 3 hours, so that a dispersion of filler was prepared. 2.0 parts by weight of water (bad solvent) were added dropwise to the above-mentioned dispersion with stirring, so that a porous resin layer formation liquid was prepared.

The above prepared porous resin layer formation - 39 - f liquid was coated on a biaxially oriented polyester film with a thickness of 2.0 pm by a wire bar coater (with a wire diameter of 1.4 mm). Immediately after the formation liquid was coated, the coated liquid was dried by hot air of 50C for 3 minutes. Thus, a porous resin layer with a thickness of 23 pm was provided on the polyester film.

Thus, a thermosensitive stencil paper No- 6 according to the present invention was obtained.

Example 7 -

4.0 parts by weight of a polyvinyl butyral resin were dissolved in 46.0 parts by weight of methyl alcohol to prepare a resin solution. 0.6 parts by weight of a polymeric dispersant (Trademark "JONCRYL EMULSION 74X', made by Johnson Polymer Corporation) were added to the above prepared resin solution and dissolved therein. Further, 4.0 parts by weight of aluminum borate in the form of needles with a Mohs hardness of 7 (Trademark "ALBOREX W, made by ShIkoku Corporation) were added to the above prepared solution. The resultant mixture was - 40 - dispersed in a ball mill for 3 hours, so that a dispersion of filler was prepared. 2.0 parts by weight of water (bad solvent) were added dropwise to the abovementioned dispersion with stirring, so that a porous resin layer formation liquid was prepared.

The above prepared porous resin layer formation liquid was coated on a biaxially oriented polyester film with a thickness of 2.0 pm by a wire bar coater (with a wire diameter of 1. 4 mm). Immediately after the formation liquid was coated, the coated liquid was dried by hot air of 5CC for 3 minutes. Thus, a porous resin layer with a thickness of 23 pm was provided on the polyester film.

On the opposite side of the polyester film, a silicone resin layer with a thickness of 0.01 Am, serving as a sticking preventing layer, was provided.

Thus, a thermosensitive stencil paper No. 7 according to the present invention was obtained.

Comparative ExamTle 4 5.0 parts by weight of a polyvinyl butyral resin were dissolved in 45.0 parts by weight of methyl alcohol to prepare a resin solution. Further, 5. 0 parts by weight of a needle-like filler with a Mohs hardness of 3.5 - 41 - (Trademark "WHISCAW', made by Maruo Calcium Co., Ltd.) were added to the above prepared solution. The resultant mixture was dispersed in a ball mill for 3 hours, so that a dispersion oil filler was prepared. 3.0 parts by weight of water (bad solvent) were added dropwise to the abovementioned dispersion of filler with stirring, so that a porous resin layer formation liquid was prepared.

The above prepared porous resin layer formation liquid was coated on a biaxially oriented polyester film with a thickness of 2.0 pm by a wire bar coater (with a wire diameter of 1. 4 mm). Immediately after the formation liquid was coated, the coated liquid was dried by hot air of 50'C for 3 minutes. Thus, a porous resin layer with a thickness of 23 im was provided on the polyester film.

Thus, a comparative thermosensitive stencil paper No. 4 was obtained.

Each of the porous resin layer formation liquids prepared in Examples 5 to 7 and Comparative Example 4 was subjected to a sedimentation evaluation test in the - 42 following manner.

Each porous resin layer formation liquid was put into a test tube so that the liquid level reached 80 mm, and allowed to stand. The filler was dispersed in the test liquid and the height of the top surface of the filler particles dispersed in the test liquid was measured at regular time intervals.

The results are shown in TABLE 3.

TABLE 3

Time When Test Liquid was Allowed to Stand Initial After After After After After After After stage 5 10 20 30 40 so 60 min. min. min. Min. min. min. min.

Ex. 5 80.0 mm 80.0 80.0 78.0 77.0 76.5 76.0 75.5 Ex. 6 80.0 mm 80.0 80.0 80.0 79.0 78.0 77.5 77.0 Ex. 7 80.0 mm 80.0 80.0 78.0 7.0 76.5 76.0 75.5 Comp. 1 E. 4 80.0 mm 78.0 76. 63.0 38.0 30.0 27.0 25.0 As is apparent from the results shown in TABLE 3, sedimentation of the filler particles scarcely occurs in the porous resin layer formation liquids prepared in Examples 5 to 7 even after 60 minutes. In contrast to this, separation takes place in the porous resin layer formation liquid prepared in Comparative Example 4 after 20 minutes.

43 - Furthermore, using each of the thermosensitive stencil papers No. 5 to No. 7 according to the present invention and the comparative thermosensitive stencil paper No. 4, the degree of curling of the thermosensitive stencil paper depending on the change in temperature and humidity, the stiffness of the thermosensitive stencil paper, the adhesion of the porous resin layer to the polyester film, and the image quality and image density of the printed ink image were measured and evaluated in the same manner as mentioned above.

For the preparation of the thermosensitive stencil paper in Comparative Example 4, the porous resin layer formation liquid was coated on the polyester film after the formation liquid was allowed to stand for 20 minutes. It was impossible to obtain a thermosensitive stencil paper by coating on the polyester film the porous resin layer formation liquid which had been allowed to stand for 60 minutes.

The results are shown in TABLE 4.

44 - 1 TABLE 4

Curl- Stiff- Adhesion Image Image Deposition i.ng ness 01. Quality Density Amount of (MN) Porous Porous Resin Resin Layer Layer (g/M2) Ex. 5 0 20.5 0 1.16 7.7 Ex. 6 0 20.0 0 1.25 7.3 Ex. 7 20.0 0 0 1.15 7.7 Comp. 24.0 C) 1.10 7.9 Ex- 4 As previously explained, the thermosensitive stencil paper according to the present invention is prepared by overlaying the porous resin layer on the thermoplastic resin film. The needle-like filler is uniformly dispersed in the porous resin layer, so that the parosity of the porous resin layer can be uniformly maintained. Therefore, when the printing operation is carried out using a printing master prepared from the thermosensitive stencil paper of the present invention, high quality images can be obtained, and in addition, the transportation properties of the thermosensitive stencil paper in the stencil printing machine are excellent.

Claims

WHAT IS CLAIMED IS:

1. A thermosensitive stencil paper comprising a thermoplastic resin film and a porous resin layer provided on one surface of said thermoplastic resin film, comprising a resin and a needle-like filler with a Mohs hardness of 4.0 or more.

2. The thermosensitive stencil paper as claimed in Claim 1, wherein said porous resin layer further comprises a polymeric dispersant.

3_ The thermosensitive stencil paper as claimed in Claim 1, wherein said needle-like filler has a diameter of 0.1 to 1 pm and a length of 1.0 to 100.0 gm.

4. The thermosensitive stencil paper as claimed in Claim 1, wherein said filler is contained in an amount of 13 to 200 parts by weight to 100 parts by weight of said resin for use in said porous resin layer.

5. The thermosensitive stencil paper as claimed in Claim 1, wherein said needle-like filler comprises at least one ifiller selected from the group consisting of - 46 - aluminum borate, titanium, oxide, and potassium oxide, each in the form of needles.

6. The thermosensitive stencil paper as claimed in Claim 2, wherein said polymeric dispersant is a carboxyl group-containing polymer.

7. The thermosensitive stencil paper as claimed in Claim 2, wherein said polymeric dispersant is contained in an amount of 10 parts by weight or less to 100 parts by weight of said needle-like filler.

8. A method of producing a thermosensitive stencil paper comprising a thermoplastic resin film and a porous resin layer provided an one surface of said thermoplastic resin film, comprising the steps of: dissolving a resin in a mixed solvent comprising a good solvent and a bad solvent with respect to said resin to prepare a resin-dissolved solvent mixture, dispersing a needle-like filler with a Mohs hardness of 4.0 or more in said resin-dissolved solvent mixture to prepare a coating liquid, applying said coating liquid to one surface of said - 47 - thermoplastic resin film, and drying said coated coating liquid so as to form said porous resin layer on said thermoplastic resin film.

9. The method as claimed in Claim 8, wherein a polymeric dispersant is further added to said resindissolved solvent mixture in the course of said step of dispersing said filler in said resin-dissolved solvent mixture.

10. The method as claimed in Claim 8, wherein said needle-like filler has a diameter of 0.1 to 1 gm and a length of 1.0 to 100.0 im.

11. The method as claimed in Claim 8, wherein said filler is contained in an amount of 13 to 200 parts by. weight to 100 parts by weight of said resin for use in said porous resin layer.

12. The method as claimed in Claim 8, wherein said needle-like filler comprises at least one filler selected from the group consisting of aluminum borate, titanium oxide, and potassium oxide, each in the form of needles. - 48 -

13. The method as claimed in Claim 9, wherein said polymeric dispersant is a carbox.vl-group-containing polymer.

14. The method as claimed in Claim 9, wherein said polymeric dispersant is contained in an amount of 10 parts by weight or less to 100 parts by weight of said needle-like filler.

15. A stencil printing method, using a printing master prepared from a thermosensitive stencil paper which corprises a thermoplastic resin film and a porous resin layer provided on one surface of said thermoplastic resin fiirr,, comprising a resin and a needle-like filler with a Mohs hardness c-10 4.0 or more.

16. The stencil printing method as claimed in Claim 15, wherein said porous resin layer of said thermosensitive stencil paper further comprises a polymeric dispersant.

17. The stencil printing method as claimed in Claim 15, wherein said needle-like filler has a diameter of 0.1 - 49 - to 1 pm and a length of 1.0 to 100.0 pm.

le. The stencil printing method as claimed in Claim 15, wherein said filler is contained in an amount of 13 to 200 parts by weight to 100 parts by weight of said resin for use in said porous resin layer.

19. The stencil printing method as claimed in Claim 15, wherein said needle-like filler comprises at least one filler selected from the group consisting of aluminum borate, titanium oxide, and potassium oxide, each In the form of needles.

20. The stencil printing method as claimed in Claim 16, wherein said polymeric dispersant is a carboxylgroup-containing polymer.

21. The stencil printing method as claimed in Claim 16, wherein said polymeric dispersant is contained in an amount of 10 Parts by weight or less to 100 parts by weight of said needle-like filler.