Stencil printing sheet

Abstract: A stencil printing sheet is disclosed comprising a resin film and optionally a support for the resin film which is sticked to the resin film with an adhesive, wherein the resin film has a layer for preventing thermal fusion comprising a polyethylene wax and arranged on one surface thereof. The stencil printing sheet does not cause breakage of resinous film during a perforating process even at a high printing speed using a thermal head, provides excellent perforation images, and exhibits a long-last, excellent resistance to thermal fusion.

Description: The present invention relates to a stencil printing sheet. More particularly, the invention relates to a stencil printing sheet which has an excellent resistance to thermal fusion with a thermal head (exothermic elements) used in a device for preparing a perforated stencil printing sheet. In the preparation of perforated stencil printing sheet, the following two methods are generally used. In one method, a manuscript paper is affixed to a stencil printing sheet, and then infrared rays are irradiated to them to make perforations on the sheet corresponding to blacked portions of the manuscript. The other method uses a thermal head. In this method, the information contained in a manuscript paper is converted to electric signals, and perforations are made in a stencil printing sheet by predetermined amounts of heat generated in a thermal head according to the signals. In recent years, the former method employing infrared rays has become less popular. On the other hand, the latter method using a thermal head is now adopted in most devices for preparing perforated stencil printing sheets. Therefore, stencil printing sheets which properly fit to thermal heads are desired. The rate at which a stencil printing sheet is perforated by a thermal head used in a device for preparing perforated stencil printing sheets has become increasingly high. For example, the setting or print processing capacity by a thermal head for a word processor has increased to approximately 4- to 5-fold during the past 5 years. This is partly due to improved printing speed. With a high printing speed, a thermal head and a film of a stencil printing sheet are adhered each other by thermal fusion when the sheet is perforated, and as a result, breakage of a resin films of the stencil printing sheet tend to occur. This phenomenon is caused by the fact that the film is adhered by fusion to the exothermic elements where releasability of the exothermic elements of thermal head and the surface of a stencil printing sheet is poor when the thermal head moves relative to the stencil printing sheet while heating the surface thereof. Moreover, if the transfer speed of a thermal head relative to a stencil printing sheet increases, considerable amount of breakage of the film is caused. In addition, under these conditions, perforations will be made in portions of a stencil printing sheet other than the portions corresponding to the manuscript. As a result, quality of images formed on the printed material decreases. Conventionally, a number of methods have been proposed to prevent thermal fusion of a stencil printing sheet. For example, a method of applying a silicone resin and/or silicone oil to the film surface of a stencil printing sheet is disclosed in Japanese Patent Application Laid-open (kokai) Nos. 48-30,570, 58-92,595, 61-295,098, 1-238,992, and 5-64,991. Also, a method of providing a surfactant layer on the film surface of a stencil printing sheet is disclosed in Japanese Patent Application Laid-open (kokai) No. 6-41,234. Further, a method of providing a wax layer on the film surface of a stencil printing sheet is disclosed in Japanese Patent Application Laid-open (kokai) No. 60-19,592. However, in the methods employing a liquid substance such as a silicone oil or a surfactant, these components are transferred as time passes to the support layer which supports a resin film, thereby gradually deteriorating the effect of the liquid substances on the prevention of thermal fusion. On the other hand, although methods of using thermosetting resins such as silicone resins are excellent in preventing thermal fusion and do not have the disadvantage of the transfer of resin components to the support layer, these methods also have the drawback that the thermosetting resin prevents the perforation of a film by exothermic elements. To prevent this, a silicone resin and silicone oil are used in combination, or alternatively, a surfactant and water-soluble polymer are used in combination. But even in such cases, perforating capacities decreases due to the presence of the polymer. Alternatively, the mixed components separate as time passes (causes bleeding phenomenon), thereby reducing the effect of preventing of thermal fusion. If a wax layer is provided, the wax will not be transferred to a support layer which supports a resin film, nor will the film perforating capacity of thermal elements be reduced. However, the effect on preventing thermal fusion is still insufficient when perforations are made at a high printing speed. EP-A-0453579 discloses a laminated polyester film suitable as a base material for a thermal transfer material and for thermal stencil paper. A wax composition is a principal component of a laminate film on at least one of the surfaces of a polyester film. Accordingly, an aim of the present invention is to solve the above problems and to provide a stencil printing sheet which provides excellent perforation images without causing thermal fusion upon contact with a thermal head even under conditions of a high printing speed, and which also provides long-lasting resistance to thermal fusion. The present invention provides a stencil printing sheet comprising a resin film, and optionally a support for the resin film which is adhered to the resin film with an adhesive, characterised in that the resin film has a layer for preventing thermal fusion comprising a polyethylene wax having an average molecular weight of from 500 to 10,000 arranged on one surface thereof. Preferably, the layer for preventing thermal fusion comprises the polyethylene wax on the surface of the resin film in an amount of from 0.01 to 5 g/m 2 on a dry basis. Since the stencil printing sheet of the present invention employs a polyethylene wax having remarkably excellent effects of preventing thermal fusion compared with conventional thermal fusion preventing layers, it is possible to obtain perforated images providing excellent manuscription reproduction without causing breakage of resin films even at a high printing speed. Moreover, the polyethylene wax does not transfer to the support layer as time passes. In addition, since the polyethylene wax is composed of a single component, it causes no bleeding phenomenon, thereby exhibiting a long-last effect of preventing thermal fusion. The polyethylene wax used in the present invention is applied to the resinous film surface of the stencil printing sheet as a thermal fusion inhibiter. The average molecular weight of the polyethylene wax is not more than 10,000 to prevent the resin film from decreasing its perforation quality. More preferably, it is in the range of 500 to 5,000. The polyethylene wax is desirably applied in an amount of 0.01-5 g/m 2 , and preferably 0.1-2 g/m 2 on a dry basis. If the amount is too small, the effect of preventing thermal fusion is insufficient and breakage of a resin film is easily caused. On the other hand, excessive amounts result in poor perforation performance. The polyethylene wax may be used in a solid form such as flake or in an emulsion in which the wax is dispersed in water. Specific form of the polyethylene wax is suitably selected according to the method of applying the wax onto the surface of a resin film. The polyethylene wax may have a carboxyl group or a hydroxyl group in the molecule. Also, it may be substituted by other modification groups such as methyl and phenol group. The layer for preventing thermal fusion comprising a polyethylene wax may optionally contain an antistatic and other additives. Examples of the antistatic includes organic sulfonic metal salts, quaternary ammonium salts, alkyl phosphate, and other common antistatics. The resin film which is used in the present invention may be made of a polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polyesters, polystyrene, polyurethane, polycarbonate, acrylic resin, or silicone resin. Among them, polyvinylidene chloride and polyester are particularly preferred. The thickness of the resin film is generally from 0.5 to 20 µm, and more preferably from 1 to 15 µm. The stencil printing sheet of the present invention may be a compound material obtained by sticking a resin film and a support for supporting the resin film together with an adhesive. Alternatively, it may substantially be constituted by a resin film only. The support for supporting the resin film may be made of a porous material which allows stencil printing ink to pass through, or the support may be a flexible sheet which is non-ink-permeable. When printing is to be performed via a support, a porous supporting material which permits passage of stencil printing ink, including Tengjoh ( a high quality, their Japanese paper comprising paper mulberry ), woven fabrics, nonwoven fabrics, etc. are used. In the case where a perforated stencil printing sheet is produced using a stencil printing sheet having a support, but before printing, the support is peeled off from the sheet, and thus, printing is performed only with a resin film, a flexible sheet such as a resin sheet, woven fabric, nonwoven fabric, printing paper, etc. may be used. In this connection, stencil printing sheets substantially composed of a resin film do not require any support therefor. The adhesive for sticking a resin film and a support together is not particularly limited insofar as it can stick a resin film to a support, and can be molten by heat from exothermic elements to form perforations. Examples: The present invention will hereinafter be described by way of examples, which should not be construed as limiting the present invention thereto. Example 1: A 2.0 µm thick polyester film and a porous Tengjoh paper having a basis weight of 10 g/m 2 were sticked each other using a vinyl acetate resin (in an amount of about 1.0 g/m 2 on a dry basis) and dried. Subsequently, the polyethylene wax indicated in Table 1 was applied on the polyethylene film surface in an amount of 0.5 g/m 2 on a dry basis. Examples 2-4: The procedure of Example 1 was repeated except that the polyethylene wax was replaced by those indicated in Table 1 to obtain stencil printing sheets. Example 5: A polyethylene wax identical to that used in Example 1 was applied onto one surface of a 2.0 µm thick polyester film in an amount of 0.5 g/m 2 on a dry basis to obtain a stencil printing sheet. Comparative Examples 1-4: The procedure of Example 1 was repeated except that the polyethylene wax was replaced by those indicated in Table 1 to obtain stencil printing sheets. Names of the products (manufacturer) Amount (wt%) Average molecular weight Example 1 Highwax 1120H (Mitsui Petrochemical Industries, Ltd.) 100 1,200 Example 2 Highwax 4051E (Mitsui Petrochemical Industries, Ltd.) 100 3,200 Example 3 Sunwax E-300 (Sanyo Chemical Industries Ltd.) 100 2,000 Example 4 PDX 6641 (Johnson Polymer Co.) 100 5,000 Comparative Example 1 LG wax [Montan wax] (BASF) 100 800 Comparative Example 2 KF-96-100,000 cP [Silicone oil] (Shin-etsu Chemical Co., Ltd.) 100 - Comparative Example 3 KS-770A [Thermosetting-type silicone resin] 50 - KF-96-1,000 cP [Silicone oil] (Shin-etsu Chemical Co., Ltd.) 50 - Comparative Example 4 Hostaphat KL 340 [Phosphate surfactant] (Matsumoto Kosho Ltd.) 50 - Polyethylene glycol 1540 [Water-soluble polymer] (Wako Pure Chemical Industries, Ltd.) 50 - Test Examples The stencil printing sheets obtained in Examples 1 to 5 and Comparative Examples 1 to 4 were evaluated for their resistance to thermal fusion (the effect of polyethylene wax on the prevention of thermal fusion), changes in the resistance as time passes, and perforation quality of the stencil ptinting sheets. (1) Resistnce to thermal fusion: Each stencil printing sheet was perforated by using a word processor [Oasis 30 AX301 manufactured by Fujitsu Ltd., printing speed: 190 characters/sec. (printing: 10.5 point character, line space: 3.6 mm)]. The perforated stencil printing sheet thus obtained was subjected to printing with a stencil printing device (model RA-205 manufactured by Riso Kagaku Kogyo K.K.). Breakage of the film was visually confirmed on resulting prints. Symbol "○" indicates that images perfectly identical to those of the original manuscript were obtained, whereas Symbol "X" indicates that images different from those of the original manuscript were obtained and film breakage occurred. (2) Change in the resistance to thermal fusion as time passes: Each stencil printing sheet was allowed to stand for 1 month at 50°C in a rolled state, i.e., in a state where the layer for preventing thermal fusion contacts the support. Thereafter, each stencil printing sheet was evaluated in a manner similar to that described in (1) above. (3) Perforation quality: Each stencil printing sheet was perforated by using a word processor used in (1) above. Perforation qualities were visually observed. Symbol "○" indicates that images exactly reflecting those of the original manuscript were obtained, whereas Symbol "X" indicates that images different from those of the original manuscript were obtained and insufficient perforations were made. Resistance to thermal fusion Changes as time passes Perforation Quality Example 1 ○ ○ ○ Example 2 ○ ○ ○ Example 3 ○ ○ ○ Example 4 ○ ○ ○ Example 5 ○ ○ ○ Comparative Example 1 X ○ ○ Comparative Example 2 ○ X ○ Comparative Example 3 ○ X X Comparative Example 4 ○ X ○ From Table 2 above, it is understood that the stencil printing sheets of the present invention each having a layer for preventing thermal fusion do not cause breakage of film during perforation, provide printed images faithful to the original manuscript, and exhibit long-lasting, excellent resistance to thermal fusion. According to the present invention, a stencil printing sheet can be provided having a long-last, excellent resistance to thermal fusion and causing no breakage of resinous film during perforating process even under conditions of high speed printing using a thermal head. In addition, when a polyethylene wax having an average molecular weight of not more than 10,000 was used in an amount of 0.01 to 5 g/m 2 on a dry basis, images faithful to those of an original manuscript can be obtained without lowering the quality of perforations in the resin film when it is perforated.

Claims: A stencil printing sheet comprising a resin film, and optionally a support for the resin film which is adhered to the resin film with an adhesive, characterised in that the resin film has a layer for preventing thermal fusion comprising a polyethylene wax having an average molecular weight of from 500 to 10,000 arranged on one surface thereof. The stencil printing sheet according to claim 1, wherein the layer for preventing thermal fusion comprises the polyethylene wax on the surface of the resin film in an amount of from 0.01 to 5 g/m 2 on a dry basis.

Inventors: HASHIMOTO HIROHIDE, KOMATA SATORU, OKUDA SADANAO, HASHIMOTO, HIROHIDE, KOMATA, SATORU, OKUDA, SADANAO
Applicants: RISO KAGAKU CORP, RISO KAGAKU CORPORATION
Application year: 1995
Main classification: B41N1
IPC codes: B32B27, B41N1