GB2086916A - Electroconductive Film for Rotary Mimeographic Printing - Google Patents

Abstract

Electroconductive films suitable for electrosensitive blanks to be used for rotary mimeographic printing comprise a carbon black-grafted polymer, a linear saturated polyester resin I having a molecular weight of 16000 to 22000, a glass transition temperature of 46 to 48 DEG C and a softening point of 156 to 160 DEG C, and a linear saturated polyester resin II having a molecular weight of 20000 to 25000, a glass transition temperature of 3 to 5 DEG C and a softening point of 112 to 116 DEG C.

Description

SPECIFICATION Electroconductive Film for Rotary Mimeographic Printing The present invention relates to an electroconductive film. More particularly, the present invention relates to an electroconductive film for an electrosensitive blank to be used in rotary mimeographic printing.

Polyvinyl chloride or a vinyl chloride/vinyl acetate copolymer has heretofore been used for an electroconductive film for an electrosensitive blank to be used for rotary mimeographic printing (hereinafter referred to as "stencil film"). More specifically, a mixture comprising polyvinyl chloride or a vinyl chloride/vinyl acetate copolymer and appropriate amounts of a plasticizer, a stabilizer and a conductive material such as carbon black is shaped into a film having a thickness of 20 to 30 microns and the film is used as a stencil film.

Such stencil film is formed into a recording strip by the known stencilling method using a scanning drum and a recording conductive stylus and is then used for printing by means of a known rotary mimeographic printing machine. This stencil film is widely used as a cheap, convenient and light printing material even at the present.

Since the conventional stencil film comprises vinyl chloride as the main raw material, generation of hydrogen chloride gas due to thermal decomposition of vinyl chloride cannot be avoided at the stencilling operation.

Accordingly, the recording conductive stylus and other parts are corroded by hydrogen chloride gas thus generated, and an unpleasant feeling is given to a worker and the stencilling operation is disliked.

In some stencil cutters, a device for entrapping hydrogen chloride gas is attached as means for eliminating the above disadvantage, but the problem is not radically solved by provision of such entrapping device. Accordingly, development of a stencil film composed of a material other than a vinyl chloride type material has eagerly been desired in the art.

Accordingly, many proposals have heretofornbeen made on selection and processing of materials other than a vinyl chloride type material. For example, polyolefin type resins such as polyethylene, polypropylene, a polyethylene/polypropylene blend, an ethylene/vinyl acetate copolymer, a copolymer of ethylene with acrylic acid or an acrylic acid ester and an ethylene/vinyl alcohol copolymer, a cellulosic resins such as acetyl cellulose and ethyl cellulose, and polyacetal type resins such as polyvinyl butyral have been examined and trial products have been prepared from these resin materials.

Trial products prepared from these resins, however, are inferior to the conventional products prepared from a vinyl chloride type material in the film strength, resolving power and durability on printing, and none of them have been put into practical use.

It is a primary object of the present invention to provide a stencil film which is formed by using a material other than a vinyl chloride type material as the binder and does not generate a harmful gas having a bad smell on the stencilling operation and which is excellent in the film strength, resolving power and durability on printing.

In an electrosensitive stencil blank, in order to enable perforation of a stencil film by electric discharge, the volume resistivity should be about 1 x107 to about 1 x 1 O"Q-cm. It is admitted that in order to realize such volume resistivity, it is necessary to disperse 1 5 to 35 parts by weight of an electroconductive substance, ordinarily carbon black, per 100 parts by weight of a resin component. It is, however, very difficult to homogeneously disperse carbon black in a resin, and a kneading operation requiring a large power should be carried out for a long time, whether the dry blending method or the wet blending method may be adopted. This difficulty is increased as the intended concentration of carbon black is high.Moreover, the larger is the amount of the filler, the more degraded are the properties of the film. Accordingly, a plasticizer or the like should be used in combination so as to moderate reduction of the processability.

It is a secondary object of the present invention to provide a stencil film which is prepared from an electroconductive substance and a resin component, mixing of which can be accomplished very easily, and in which very uniform distribution of the volume resistivity can be obtained because the electroconductive substance can be homogeneously and uniformly dispersed in the resin component.

It is a third object of the present invention to provide a stencil film in which the ink resistance is highly improved.

In a recording strip prepared from a stencil film, the pattern formed on the recording strip is readily deformed by the swelling due to a printing ink and it becomes difficult to obtain a precise and clear image copy. In order to avoid this disadvantage, the stencil film is required to have a high ink resistance.

We zealously made researches and found that when a mixture of two specific linear saturated polyester resins is selected among many resins and this mixture is combined with a carbon blackgrafted polymer, the foregoing objects can be attained. We have now completed the present invention based on this novel finding.

More specifically, in accordance with the present invention, there is provided an electroconductive film for an eiectrosensitive blank to be used for rotary mimeographic printing, which is composed of a resin composition comprising a carbon black-grafted polymer and a mixture of a linear saturated polyester resin I having a molecular weight of 1 6000 to 22000, a glass transition temperature of 46 to 480C and a softening point of 1 56 to 1 600C and a linear saturated polyester resin Il having a molecular weight of 20000 to 25000, a glass transition temperature of 3 to 50C and a softening point of 112 to 11 60C.

In the present invention, the carbon black-grafted polymer (hereinafter referred to as "GC") is used as an electroconductive substance. GC is prepared by grafting a vinyl group-containing monomer such as acrylic acid and/or an acrylic acid ester to carbon black, and GC is ordinarily used in the state dispersed in a medium having a high affinity with the grafted component. For example, "Graft Carbon HO-SOl B" (the trademark for a product supplied by Ryoyu Kogyo Kabushiki Kaisha), which is a suspension having a solid content of 40% by weight and being obtained by dispersing in aqueous ammonia a graft polymer formed by grafting acrylic acid and butyl acrylate to carbon black, is advantageously used in the present invention.

A mixture comprising linear saturated polyester resins I and II having the following different properties is used as the binder: Linear Saturated Linear Saturated Polyester Resin I Polyester Resin 11 Molecular weight 16000 to 22000 20000 to 25000 Glass transition temperature 46 to 480C 3 to 5 C Softening point 156 to 1600C 112 to 1160C Any of linear saturated polyester resins having the above-mentioned properties can be used.For example, there can be mentioned an ethylene terephthalate/ethylene isophthalate copolyester, an ethylene terephthalate/2,2-bis[4-(,B-hydroxyethoxy)phenyl]propane terephthalate copolyester, a bis(P- hydroxyethyl) terephthalate/2,2-bis[4-(,B-hydroxyethoxy)phenyl]propane terephthalate copolyester and a diphenyl terephthalate/diphenyl isophthalate copolyester. As a typical instance of the linear saturated polyester resin I, there can be mentioned Vylon 103 (the trademark for a product supplied by Toyobo Kabushiki Kaisha), and as a typical instance of the linear saturated polyester resin II, there can be mentioned Vylon 530 (the trademark for a product supplied by Tovobo Kabushiki Kaisha).

A polymer having a compatibility with the linear saturated polyester resin, for example, nitrocellulose or a xylene resin, may be used in a minor amount in combination with the linear saturated polyester resin according to need.

The linear saturated polyester resins I and II are used in the state dissolved or emulsified in a solvent. The kind of the solvent is not particularly critical and any of ordinary solvents can be used.

From the practical viewpoint, there are advantageously used hydrocarbons such as benzene, toluene, methylene chloride, 2-nitropropane, trichlene, dichloropropylene and derivatives thereof, and oxygencontaining compounds such as methylethyl ketone, cyclohexanone, ethyl acetate, cellusolve acetate, dioxane and tetrahydrofuran. Furthermore, as the mixed solvent that can practically be used, there can be mentioned toluene/methylethyl ketone, toluene/ethanol, toluene/acetone and toluene/methylethyl ketone/ethyl acetate.

In principle, a plasticizer need not be used for the resin composition of the present invention.

However, a plasticizer may be used in the present invention according to need. Namely, an ordinary plasticizer may be used according to a known recipe. From the practical viewpoint, there are advantageously used phthalate type plasticizers such as dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diisobutyl phthalate and butylbenzyl phthalate and methyl ethyl phthalate, phosphate type plasticizers such as triphenyl phosphate and tricresyl phosphate, glycol type plasticizers such as methylphthalylethyl glycol, ethylphthalylethyl glycol and butylphthalylbutyl glycol, maleate type plasticizers such as diethyl maleate and dibutyl maleate, and fumarate type plasticizers such as dibutyi fumarate. Incidentally, nitrocellulose can also be used as the plasticizer.The amount of the plasticizer used is not particularly critical, but from the practical viewpoint, the plasticizer is preferably used in an amount of 5 to 20% by weight in the resin composition.

The weight ratio of the linear saturated polyester resin I to the linear saturated polyester resin II is controlled within the range of from 6/4 to 7/3 from the practical viewpoint, but if a plasticizer is used, this weight ratio range can be expanded to 5/5 to 8/2. If the weight ratio of the resin I to the resins Il is outside the above range, the pliability and strength of the film are degraded and no good stencil film can be obtained.

From the practical viewpoint, the amount used of GC is adjusted to 10 to 30 parts by weight, preferably 1 2 to 26 parts by weight, per 100 parts by weight of the mixture of the linear saturated polyester resins I and II.

If the amount of GC is smaller than 10 parts by weight per 100 parts by weight of the mixture of the linear saturated polyester resins I and II, perforation by electric discharge becomes difficult, and if the amount of GC is larger than 30 parts by weight per 100 parts by weight of the above mixture, the leak current is increased at the step of perforation by electric discharge and a clear perforation pattern can hardly be obtained.

Ordinary stabilizers, additives and fillers may be added to the resin composition, so far as the properties of the stencil film are not degraded. For example, a lubricant such as calcium stearate, zinc laurate or barium ricinoleate, a thermal stabilizer such as an organic tin compound and an organic metal salt of barium, calcium or zinc and an antioxidant such as di-tert-butylhydroxytoluene may be added to the resin composition of the present invention.

A stencil film is prepared from the above-mentioned resin composition by the solution casting or emulsion casting method, or a stencil film is prepared by extrusion or inflation molding of a solid formed by removing volatile components from the resin composition.

A masking coating layer may be formed on the surface of the stencil film of the present invention as in case of a commercially available stencil film. More specifically, a colored layer for facilitating discrimination of a recording image formed by perforation may be formed by thinly coating a mixture of an inorganic pigment such as titanium oxide or zinc oxide and a resin binder such as an acrylic resin, a cellulose resin or a polyamide resin on the surface portion of the film.

As in case of a conventional stencil film, the so-prepared stencil film of the present invention is bonded to a conductive backing paper to form an electrosensitive blank and this blank is formed into a recording strip by perforation with electric discharge and is used for mimeographic printing.

When the stencil film of the present invention is formed into a recording strip, a harmful gas having a bad smell is not produced at all, and the stencil film of the present invention is excellent in the strength, resolving power and durability on printing and the volume resistivity is uniform throughout the stencil film. Moreover, the stencil film of the present invention has a high ink resistance and is very excellent from the practical viewpoint. Still further, the power necessary for kneading the resin composition to be used for formation of the stencil film of the present invention can remarkably be saved and the operation time can be shortened. Therefore, the stencil film of the present invention is very significant from the energy-saving viewpoint.

The present invention will now be described in detail with reference to the following Examples that by no means limit the scope of the invention.

Examples 1 through 3 and Comparative Examples 1 through 4 A resin composition shown in Table 1 was coated in a thickness of 20 microns after drying on a polyester film, which had been coated a peeling agent previously, according to the solution casting method using a roll coater to obtain a stencil film. The properties of the stencil film were measured according to the methods described below to effect primary evaluation. The volume resistivity, tensile strength and elongation were determined according to the method of JIS C-231 8 (1975). The stencil film was bonded to a commercially available electroconductive backing paper and subjected to the perforation test.Facsimile test chart No.2 of the Institute of Image Electronics Engineers of Japan was used as the original, and a recording strip was prepared by using a commercial stencil cutter (Rex Rotary Press Model 2202S supplied by Rex Co., Denmark). The perforation characteristic was evaluated by observation of an enlarged photographic picture.

In Comparative Examples 1 and 2, only one kind of a linear saturated polyester resin was used but other procedures were the same as in Examples 1 and 2. The perforation characteristic was good but the properties of the resulting film were bad in each of Comparative Examples 1 and 2.

In Comparative Examples 3 and 4, the amount used of GC was changed but other procedures were the same as in Examples 1,2 and 3. The perforation characteristic was bad in each of Comparative Examples 3 and 4.

The ink resistance was tested with respect to each of the films having a good perforation characteristic, which were obtained in Examples 1,2 and 3. More specifically, a mimeograph ink was applied to the entire surface of a recording strip prepared by perforation with electric discharge and the recording strip was allowed to stand still for 24 hours, and the change of the appearance of the strip was checked and the ink resistance was evaluated.

The recipes of the resin compositions, the film-preparing conditions, the properties of the films and the results of the primary evaluation are shown in Table 1.

In each of the foregoing Examples and Comparative Examples, it was confirmed that mixing under agitation could be remarkably facilitated by the use of GC and the mixing and kneading operation could be accomplished in a short time with a small power. Moreover, where the film was formed into a recording strip, no bad smell was produced and the operation could be performed smoothly.

Each of the recording strips prepared from the above-mentioned stencil films of the present invention was subjected to the printing operation by using a commercial rotary press (Duplo Rotary Press Model 750 supplied by Duplo Towa Kabushiki Kaisha) to obtain 500 prints. Clear prints could be obtained stably in each case.

Table 1 Example No. Comparative Example No.

1 2 3 1 2 3 4 Recipe (parts by weight) of Resin Composition Vylon 103" 70 60 60 100 - 70 70 Vylon 530" 30 40 40 - 100 30 30 GC (40% suspension)2) 50.9 50.9 44.1 50.9 50.9 22.5 83.3 Toluene 185 185 185 185 185 185 185 Methylethyl ketone 50 50 50 50 50 50 50 Film-preparing Conditions Coating method roll roll roll roll roll roll roll coater coater coater coater coater coater coater Drying conditions ( C, minutes) 110,2 110,2 cold 110,2 110,2 110,2 110,2 wind Properties of Film Volume resistivity (#-cm) 2.7x107 1.6x107 1.6x109 5.6x107 3.6x108 1.2x1012 5.3x106 Tensile strength (Kg/cm2) 274 253 241 349 189 249 293 Properties of Film Elongation (%) 18 29 32 4 49 39 12 Perforation characteristic good good good good good bad bad Ink resistance good good good not tested not tested not tested not tested Printing resistance good good good not tested not tested not tested not tested Primary Evaluation good good good hard film, soft film, bad perforation bad perforation readily easily characteristic characteristic splittable, elongable, obscure image, obscure image, no practical no practical no practical no practical utility utility utility utility Note 1) The properties of Nylon 103 and Vylon 530 are as follows:: Vylon 103 Vylon 530 Molecular weight 18000-20000 20000-25000 Glass transition temperature (OC) 47 4 Melt viscosity (poise) as measured at 2000C by rotational viscometer 3000 700 Softening point (OC) 158 114 Volume resistivity (Q-cm) 1 x 1 o16 1x1015 2) Graft Carbon HO-SOl B (supplied by Ryoyu Kogyo Kabushiki Kaisha) was used as GC.

Example 4 The stencil film obtained in Example 3 was laminated and bonded onto an electroconductive surface of an electroconductive backing paper prepared separately to obtain an electrosensitive blank for mimeographic printing.

The electroconductive backing paper was prepared according to the following procedures.

A liquid composition shown below was uniformly coated in an amount of about 10 g/m2 after drying on one surface of wood-free paper having a weight of about 80 g/m2 by using a roll coater, and the coating was dried by the continuous drying method using warm air.

Components ofLiquid Composition Amounts (parts by weight) Ethylhydroxyethyl cellulose 500 Carbon black 270 Methylethyl ketone 2150 Toluene 1400 Lanolin 100 Wax 100 The bonding of the stencil film to the so-prepared electroconductive backing paper was performed under a pressure of 5 Kg/cm2 at a temperature of 800C by using a laminator. The peeling strength between the electroconductive backing paper and the laminated film was 2 to 5 Kg/cm as determined at a pulling angle of 900. The volume resistivity of the stencil film was 2.5x 103 Q-cm.

Fifty samples, each having a size of 470 mmx270 mm (the wide size of the Gestetner size standard), were cut from the so-obtained electrosensitive blank for mimeographic printing, and recording strips were prepared from these samples by using a commercial stencil cutter (Rex Rotary Press Model 2202S) while facsimile test chart No. 2 of the Institute of Image Electronics Engineers of Japan, newspaper scraps and Xerox copies of literature references were used as the originals. No bad smell was produced at the step of perforation with electric discharge and the operation could be performed smoothly. Each recording strip was attached to a commercial rotary press (Duplo Rotary Press Model 750 supplied by Duplo Towa Kabushiki Kaisha) and the electroconductive backing paper portion was removed, and the printing operation was conducted to obtain about 2000 prints. Clear copied images were obtained stably in each case.

Claims (16)

Claims

1. An electroconductive film suitable for an electrosensitive blank to be used for rotary mimeographic printing, which film is composed of a resin composition comprising a carbon blackgrafted polymer, a linear saturated polyester resin I having a molecular weight of 1 6000 to 22000, a glass transition temperature of 46 to 480C and a softening point of 1 56 to 1 600 C, and a linear saturated polyester resin II having a molecular weight of 20000 to 25000, a glass transition temperature of 3 to 50C and a softening point of 112 to 1 160C.

2. An electroconductive film according to claim 1, wherein the carbon black-grafted polymer is a polymer obtained by grafting a vinyl group-containing monomer to carbon black.

3. An electroconductive film according to claim 2, wherein the carbon black-grafted polymer is a polymer obtained by grafting at least one monomer selected from acrylic acid and acrylic acid esters to carbon black.

4. An electroconductive film according to claim 3, wherein the carbon black-grafted polymer is a polymer obtained by grafting acrylic acid and butyl acrylate to carbon black.

5. An electroconductive film according to claim 4, wherein the carbon black-grafted polymer had been suspended in aqueous ammonia for use in the preparation of the film.

6. An electroconductive film according to any one of the preceding claims, wherein the carbon black-grafted polymer is present in an amount of 10 to 30 parts by weight per 100 parts of the total weight of the linear saturated polyester resins I and II.

7. An electroconductive film according to any one of the preceding claims, wherein the linear saturated polyester resins are selected from (a) an ethylene terephthalate/ethyiene isophthalate copolyester, (b) an ethylene ternphthalate/2,2-bis[4-(-hydrnxyethoxy)phenyljprnpane terephthalate copolyester, (c) a bis(p-hydroxyethyl)terephthalate/2,2-bis[4-(p-hydroxyethoxy)phenyl]propane terephthalate copolyester, (d) a diphenyl terephthalate/diphenyl isophthalate copolyester and (e) a mixture of two or more of the copolyesters (a) to (d).

8. An electroconductive film according to any one of the preceding claims, wherein the weight ratio of the linear saturated polyester resin I to the linear saturated polyester resin II is from 6/4 to 7/3, no plasticizer being present in the resin composition.

9. An electroconductive film according to any one of claims 1 to 7, wherein a plasticizer is present in the resin composition.

10. An electroconductive film according to claim 9, wherein the weight ratio of the linear saturated polyester resin I to the linear saturated polyester resin II is from 5/5 to 8/2.

11. An electroconductive film according to any one of the preceding claims, wherein the linear saturated polyester resins had been dissolved or emulsified for use in the preparation of the film.

12. An electroconductive film substantially as hereinbefore described in any one of Examples 1 to 4.

13. An electrosensitive blank suitable for use in rotary mimeographic printing, which blank comprises an electroconductive film as claimed in any one of the preceding claims bonded to an electroconductive backing paper.

14. A stencil suitable for use in rotary mimeographic printing, which stencil comprises an electroconductive film as claimed in any one of claims 1 to 1 2 in which an image which it is desired to print has been cut.

1 5. A rotary mimeographic printing process which comprises effecting printing utilising a stencil as claimed in claim 14.

16. Prints obtained by a rotary mimeographic process as claimed in claim 1 5.