GB2027616A - An Electrostatic Record Material - Google Patents

Abstract

An electrostatic record material comprising an electroconductive base sheet and a record layer formed on the base sheet, said electroconductive base sheet having an electroconductive layer containing (i) a zinc oxide powder having a specific resistivity of 0.01 to 500 ohm-cm at pressure of 150 kg/cm<2> and (ii) a water-soluble or water-dispersible adhesive resin.

Description

SPECIFICATION An Electrostatic Record Material This invention relates to an electrostatic record material, and more particularly to an electrostatic record material comprising an electroconductive base sheet and a record layer formed on the base sheet and consisting essentially of insulating resin.

Electrostatic recording processes use a record material comprising an electroconductive base sheet and a record layer formed on the base sheet and composed mainly of insulating resin. With these processes, voltage pulses are applied directly to the record layer of the material or electrostatic latent images formed on a plate are transferred onto the record layer to form electrostatic latent images on the record layer, and the latent images are converted to visible images with a toner. Electrostatic recording processes are widely used for facsimile systems, copying machines and other printers.

While facsimile systems were operated at a low speed of 5 to 6 min/A-4-size sheet, such lowspeed machines have been replaced by medium-speed machines (2-3 min/A-4-size sheet) or highspeed machines (1 min/A-4-size sheet or higher) with an increase in the amount of information to be handled. Accordingly the voltage pulse width used has changed from 500 y sec or longer to 50-1 00 sec or to 20 y sec or shorter. To obtain satisfactory records with stability in accordance with the various changes attendant on the speed-up of the facsimile systems, the electrostatic record material must have reduced impedance.Most suitably the electroconductive base sheet of the electrostatic record material usually has a surface electrical resistivity of 106 to 1 010 ohms. Especially for use in high-speed facsimile systems, the record material must meet a very strict resistivity requirement. For example, a reduced image density will result at a surface electrical resistivity of 1011 ohms, and little or not record will be reproduced at 1012 ohms.Accordingly the electroconductive base sheet of record material for use in usual facsimile processes is adapted to have a resistivity of 106 to 1010 ohms at usual humidity, but the conductive base sheet has a higher resistivity in an atmosphere of lower humidity because the treating agent usually used for rendering the base sheet electroconductive is an electroconductive resin the degree of ionization of which reduces with a decrease in the moisture content of the base sheet to give a lower conductivity, namely a higher resistivity.

An electrostatic record material has been developed which is free of the drawback resulting from the use of such an electroconductive resin (Published Unexamined Japanese Patent Application No.

25140/1976). In place of the conventional electroconductive resin, a zinc oxide powder having a specific resistivity of 1 x 103 to 9 x105 ohm-cm is used for this material. The material, however, still has the following drawbacks. When the zinc oxide powder having such a specific resistivity is used with a water-soluble or water-dispersible adhesive such as polyvinyl alcohol, methyl cellulose, styrenebutadiene copolymer or the like, the resulting material will have reduced conductivity, consequently giving a record of low density.For this reason, the adhesives usable with the powder are limited to those of the organic solvent type incorporating methyl methacrylate, ethyl methacrylate, styrene, melamine, cellulose acetate, vinyl acetate or like polymer, acrylic monomer-styrene copolymer, vinyl chloride-vinyl acetate copolymer, or like resin which is soluble in organic solvents. The use of the organic solvent nevertheless entails various drawbacks such as inconvenience of handling, hazard of fire an expensiveness.

An object of this invention is to provide an electrostatic record material including an electroconductive base sheet which retains a specific resistivity of up to 10'0 ohm-cm even at low humidities despite the use of a water-soluble or water-dispersible resin adhesive.

Another object of the invention is to provide an electrostatic record material which is usable with high stability even for high-speed facsimile processes.

These objects and other features of this invention will become apparent from the following description.

The foregoing objects can be fulfilled by the use of a zinc oxide powder serving as the main electroconductive agent and having a specific resistivity of 0.01 to 500 ohm-cm at pressure of 150 kg/cm2 in place of the conventional electroconductive resin or known zinc oxide powder having a specific resistivity of 1 x103 to 9 x 105 ohm-cm.Stated more specifically the present invention provides an electrostatic record material comprising an electroconductive base sheet and a record layer formed on the base sheet and consisting essentially of an insulating resin, the record material being characterized in that the electroconductive base sheet has an electroconductive layer containing (a) a zinc oxide powder having a specific resistivity of 0.01 to 500 ohm-cm at pressure of 1 50 kg/cm2, and (b) a water-soluble or water-dispersible adhesive resin.

The invention has been accomplished based on the surprising novel finding that when the electroconductive base sheet of electrostatic record material incorporates as its electroconductive component a zinc oxide powder having a specified specific resistivity of 0.01 to 500 ohm-cm at pressure of 1 50 kg/cm2, the base sheet retains a specific resistivity of up to 1 010 ohm-cm even at low humidities although containing a water-soluble or water-dispersible resin adhesive.

The zinc oxide powder to be used in this invention has a specified specific resistivity of 0.01 to 500 ohm-cm at pressure of 150 kg/cm2. The specific zinc oxide powder is prepared by admixing with zinc oxide a small amount of at least one of Awl203, Cr203, Ga203, In203 and a compound which produces such an oxide when heated at a high temperature, and heating the mixture at a high temperature preferably in a reducing atmosphere. Examples of useful compounds which produce Al203 are aluminum chloride, aluminum sulfate, aluminum nitrate, etc., compounds producing Cr203 include chromium chloride, chromium sulfate, etc., those producing Ga203 include gallium chloride, gallium sulfate, gallium nitrate, etc., and those producing In203 include indium chloride, indium sulfate, indium nitrate, etc.The specific resistivity of the zinc oxide powder obtained is adjustable by suitably determining the kind and amount of the additive used, heating temperature, heating time, cooling conditions, etc. The amount of the additive to be used, although not particularly limited, is usually about 0.1 to about 5 mole %, preferably about 0.5 to about 2 mole %. The mixture is heated usually at 800 to 11 000C for 2 to 5 hours. After heating, the product is cooled slowly preferably at a rate of 5 to 1 00C/min. The cooled product is pulverized as desired. The zinc oxide powder thus prepared for use in this invention is usually 0.5 to 3 , preferably about 0.8 to about 2,u, in particle size as determined by the Blain permeability method.

The zinc oxide powder useful in this invention must have a specific resistivity of 0.01 to 500 ohm-cm, preferably 1 to 400 ohm-cm, at pressure of 150 kg/cm2. Zinc oxide powders lower than 0.01 ohm-cm in specific resistivity are very difficult to prepare. Production of such powder, if attempted, requires use of an increased amount of an additive which produces Al203 or like oxide and necessitates a higher heating temperature. Consequently the zinc oxide powder obtained has a slightly blackish color and includes a greatly increased amount of agglomerates of particles due fo sintering. Such powder is extremely difficult to formulate into a coating composition and seriously impairs the quality of the record material produced.Conversely zinc oxide powders higher than 500 ohm-cm in specific resistivity, when used conjointly with a water-soluble or water-dispersible adhesive, exhibit an increased surface resistivity, substantially failing to give the desired record density even at the ambient humidity.

The specific resistivity of the zinc oxide powder in this invention is measured by the following method. The zinc oxide powder (240 to 260 mg) is allowed to stand in an atmosphere at 200C and 60% RH for 2 hours and is thereafter placed into a container of poiytetrafluoroethylene having a specimen packing tube 4.1 mm in diameter. The powder is pressed with brass cylinder, 4 mm in diameter, from opposite ends of the tube at four different pressure values in the range of 100 to 200 kg/cm2. The specific resistivity of the powder is measured at each of the pressure values. The resistivity values obtained are plotted to determine the specific resistivity at 1 50 kg/cm2 from the curve.

Examples of water-soluble or water-dispersible adhesive resins useful in this invention are various adhesive resins which are usually used for coating paper and which include celluloses such as methyl cellulose, hydroxyethyl cellulose and carboxymethyl cellulose, starch, modified starches such as oxidized starch, etherified starch and esterified starch, polyvinyl alcohol, polyvinyl pyrrolidone, sodium alginate, polyacrylamide, alkali salts of isobutene-maleic anhydride copolymer, alkali salts of styrenemaleic anhydride copolymer, alkali salts of styrene-methacrylic acid copolymer, styrene-butadiene copolymer latex, methyl methacrylate-butadiene copolymer latex, polyvinyl acetate latex, polyacrylic acid latex, etc. Also useful are electroconductive resins which are usually used as electroconductive agents for electrostatic record materials of the type described.

With the electroconductive base sheet of the electrostatic record material of the type described incorporating particles of electroconductive substance, the adhesive bonding the conductive substance to the base sheet swells to reduce the contact between the conductive particles by moving the particles away from one another, with the result that the base sheet tends to have a lower conductivity especially at high humidities. Although particulate, the zinc oxide of this invention does not involve a noticeable reduction in electroconductivity at high humidities and is therefore usable free of any troubles.

However, to enable the base sheet to retain the desired conductivity more reliably, it is preferable to use, as a water-soluble or water-dispersible adhesive, a cationic electroconductive resin. Such preferable resins are those having an ammonium salt, sulfonium salt or phosphonium salt as a functional group.Exemplary of these resins are polyethyleneimine hydrochloride, poly(N-methyl-4vinylpyridiniumchloride), poly(2-methacryloyloxyethyltrimethylammoniu mchloride), poly(2-hydroxy-3methacryloyloxypropyltrimethylammoniumchloride), poly(N-acrylamidopropyl-3trimethylammoniumchloride), poly(N,N-dimethyl-3,5-methylenepiperidiniumchloride), polyvinyltrimethylammoniumchloride, polyallyltrimethylammoniumchloride, polydiallyldimethyl ammoniumchloride, polyvinylbenzyltrimethyl ammoniumchloride and like ammonium salts, poly(2 acryloxyethyldimethylsulfoniumchloride) and like sulfonium salts, poly(glycidyltributylphosphoniumchloride) and like phosphonium salts. Among these cationic resins, ammonium salts, especially quaternary ammonium salts are most preferable to use.

In this invention, such water-soluble or water-dispersibie resins are used in an amount suitably determined in accordance with the kind of the resin. Usually about 3 to about 100 parts by weight of the resin is used per 100 parts by weight of the zinc oxide powder. While the use of the zinc oxide powder having the specified specific resistivity according to this invention prevents the reduction of the conductivity of the base sheet at low humidities irrespective of the kind of the adhesive resin used, the above-mentioned cationic electroconductive resin, when used as adhesive resins, effectively permits the base sheet to retain the desired conductivity at high humidities as well as at low humidities.In fact, the objection attendant on low and high humidities can be overcome when the cationic electroconductive resin is used in an amount of 5 to 100 parts by weight per 100 parts by weight of the zinc oxide powder if the electroconductive resins are used singly. Further when 3 to 5 parts by weight of such electroconductive resin is used, it is preferable that the electroconductive resin is used conjointly with an adhesive resin. When the amount is less than 3 parts by weight, conjoint use of the electroconductive resin with another resin eliminates the objection that would result from low and high humidities. In this invention when used singly, the adhesive resin is employed in an amount of up to 50 parts by weight per 100 parts by weight of the zinc oxide.

According to this invention, the zinc oxide powder and the water-soluble or water-dispersible adhesive resin are dissolved or dispersed in water to obtain a coating composition, which may further contain other additives. Useful additives are a wide variety of those heretofore used for the electrostatic record materials of the type described, such for example as clay, kaolin, calcium carbonate, titanium oxide, aluminum hydroxide and like pigments, sodium silicate, sodium phosphate, sodium polyacrylate and like dispersants; octyl alcohol, cyclohexanol, tributyl phosphate, silicone, ethylene glycol and like defoaming agents; phenylsalicyclic acid, hydroxy-benzophenone, 2-(hydroxyphenyl)-benzotriazole and like ultraviolet absorbers; and dyes.The amount of the additive to be used, which varies with the kind of the additive, is usually 0.001 to 50 parts by weight, preferably about 0.01 to about 20 parts by weight, per 100 parts by weight of the zinc oxide powder.

The coating composition prepared is applied to a usual base sheet such as paper, synthetic paper or the like by any means such as bar coater, air knife coater or blade coater, or by impregnation with use of a size press. The composition is applied to the base sheet in such an amount that the sheet will have a surface resistivity of 106 to 1010 ohms at the ambient humidity. The amount is usually 2 to 20 g/m2, preferably about 5 to about 1 5 g/m2 by dry weight.

According to this invention, the record layer can be formed from any of various coating compositions usually used and including those of the organic solvent type and aqueous solution or dispersion type. The resins useful for preparing such coating compositions are those having insulating properties and including polymers or copolymers of vinyl monomers such as vinyl chloride, vinyl acetate, vinyl acetal, vinylidene chloride, ethylene, styrene, butadiene, acrylate, methacrylate, acrylonitrile, acrylic acid, methacrylic acid, etc., silicone resin, polyester resin, polyurethane resin, alkyd resin, epoxy resin and the like. These resins are used singly or in admixture as dissolved in an organic solvent or dispersed in water. The resins useful for the electrostatic record material of this invention are not limited to these resins, but other suitable known insulating resins are also usable.The coating composition may further incorporate additives usually used in the art, such as inorganic pigments, finely divided polymer particles, starch powder and dyes. The composition is applicable by usual means in an amount which,-although not particularly limited, is usually 2 to 10 g/m2, preferably 4 to 7 g/m2 by dry weight.

While another electroconductive layer is conventionally formed on the other surface of the base sheet opposite to the record layer bearing surface thereof when so required, such a conductive layer can be similarly formed in this invention if so desired. The additional conductive layer need not always be the same as the specific conductive layer of this invention underlying the record layer but can be a conductive layer composed of a usual electroconductive resin.

The electrostatic record material thus prepared according to this invention provides record images at a high density with high stability even at extremely low humidities.

Given below for a better understanding of the present invention are reference examples in which the zinc oxide powder to be used in this invention is prepared, and examples of the invention.

Reference Example 1 (Preparation of an Electroconductive Zinc Oxde Powder) To zinc oxide is added the specified mole % of an aqueous solution of the specified compound shown in Table 1 serving as a metal oxide component, and these ingredients are fully mixed together.

The mixture is dried at 1 000C and then pulverized to particles of 0.2 y in size. The particles are heated in a muffle furnace at the temperature for the specified minutes shown in Table 1 to prepare an electroconductive zinc oxide powder. The resulting zinc oxide powders thus obtained are checked for the specific resistivities and the result shown in Table 1 below.

Table 1 Specific Additive Heating resistivity Ref. Ex. Amount Temp. Time of zinc oxide No. Kind (mol %) (0C) (min) lohm-cmJ Property Note Ref. 1-1 Al(NO3)3 9H2O 0.5 900 90 11 0 This invention Ref. 1-2 Al(NO3)3 9H2O 1.0 000 90 0.2 0 This invention Ref. 1-3 Al(NO3)3-9H20 0.5 950 90 5.0 0 This invention Ref. 1-4 Al(NO3)3-9H20 0.5 900 60 52 0 This invention Ref. 1-5 Ai(NO3)3 - 9H2O 0.4 900 60 90 0 This invention Ref. 1-6 Al(NO3)3 9H2O 0.2 900 60 200 0 This invention Ref. 1-7 Al(NO3)3- 9H2O 0.2 900 50 220 0 This invention Ref. 1-8 CrCI3 - 6H2O 1.0 1000 90 150 0 This invention Ref. 1-9 Ga2(SO4)3 18H2O 0.2 1000 90 450 0 This invention Ref.1-10 InCI3 . 6H2O 0.5 900 90 150 0 This invention Ref. 1-11 Al(NO3)3 9H20 1.5 1050 90 0.008 X Comp. Example Ref. 1-12 Al(NO3)3-9H20 0.1 900 60 850 0 Comp. Examplf The mark "0" indicates that the composition can be prepared without any trouble.

The mark "X" indicates that the ingredients can not be formulated into a composition.

Reference Example 2 (Preparation of a Coating Composition) The zinc oxide powder (100 parts by weight) obtained in Reference Example 1 and 100 parts by weight of water are mixed together in a ball mill for 1 hour to obtain a uniform dispersion. With the dispersion is admixed the specified amount of an aqueous solution of the resin shown in Table 2 to prepare a coating composition. The numbers of the zinc oxide powders shown in Table 2 are those shown in Table 1. When the zinc oxide powder Ref. 1-11 is used, no coating composition is obtained.

Table 2 Aqueous solution ofresin Ref. Example Zinc oxide Concentration Amount No. powder Resin { /OJ (part by weiqht) Note Ref. 2-1 Ref. 1-1 A 7 90 This invention Ref. 2-2 Ref. 1-2 A 7 90 This invention Ref. 2-3 Ref. 1-3 A 7 90 This invention Ref. 2-4 Ref. 1-4 C 36 60 This invention Ref. 2-5 Ret 1-5 A 7 90 This invention Ref. 2-6 Ref. 1-6 A 7 90 This invention Ref. 2-7 Ref. 1-7 C 36 60 This invention Ref. 2-8 Ref. 1-11 A 7 90 Comp. Example Ref. 2-9 Ref. 1-12 A 7 90 Comp. Example Ref. 2-10 Ref. 1-1 B 10 100 This invention Ref. 2-11 Ref. 1-1 C 36 60 This invention Ref. 2-12 Ref. 1-2 C 36 60 This invention Ref. 2-13 Ref. 1-11 C 36 60 Comp. Example Ref. 2-14 Ref. 1-12 C 36 60 Comp. Example Ref. 2-15 Ref. 1-1 D 40 54 This invention Ref. 2-16 Ref. 1-1 E 30 72 Comp. Example Ref. 2-17 Ref. 1-1 C 36 185 This invention Ref. 2-18 Ref. 1-1 C 36 93 This invention Ref. 2-19 Ref. 1-1 C 36 15 This invention Ref. 2-20 Ref. 1-1 C 36 515 Comp. Example Ref. 2-21 Ref. 1-1 C 36 3 Comp. Example Ref. 2-22 Ref. 1-1 A 7 310 Comp. Example A, B, C, D and E indicate the following: A: Methyl cellulose (trade mark: "MCSM-15", product of Shinetsu Kagaku Co., Ltd., Japan) B: Polyvinyialcohol (trade mark: "PVA 105", Kuraray Co., Ltd., Japan) C: Poly(vinylbenzyltrimethylammonium chloride) (trade mark: "ECR-34", the Dow Chemical Co., Ltd., U.S.A.) D: Poly(diallyldimethylammonium chloride) (trade mark: "Conductive polymer-261", product of Calgon Co., Ltd.) E: Polystyrenesulfonic acid ammonium Reference Example 3 (Preparation of a Coating Composition) The zinc oxide powder No.Ref. 1-8 obtained in Reference Example 1(100 parts by weight) is mixed with 100 parts by weight of water and 90 parts by weight of 5% aqueous solution of carboxymethylcellulose in a ball mill for 1 hour to prepare a coating composition (hereinafter referred to as Ref. 3).

Reference Example 4 (Preparation of a Coating Composition) To 100 parts by weight of the zinc oxide powder Ref. 1-9 obtained in Reference Example 1, is added 25 parts by weight of 10% aqueous solution of oxidized starch, 50 parts by weight of 5% aqueous solution of sodium salt of isobutenemaleic anhydride copolymer, 20 parts by weight of calcium carbonate and 75 parts by weight of water and then the resulting mixture is dispersed in a ball mill for 1 hour to prepare a coating composition (hereinafter referred to as Ref. 4).

Reference Example 5 (Preparation of a Coating Composition) To 100 parts by weight of the zinc oxide powder Ref. 1-10 obtained in Reference Example 1 is added 50 parts by weight of 10% aqueous solution of polyvinylalcohoi, 5 parts by weight of 50% aqueous emulsion of styrenebutadiene copolymer and 100 parts by weight of water and then the resulting composition is dispersed in a ball mill for a hour to prepare a coating composition (hereinafter reterrea to as Ref. 5).

Reference Example 6 (Preparation of a Coating Composition) The zinc oxide powder Ref. 1-1 obtained in Reference Example 1 (100 parts by weight) is mixed with 100 parts by weight of water in a ball mill for a hour to prepare a uniform dispersion. With the dispersion is admixed 60 parts by weight of 36% aqueous solution of poly(2 methacryloyloxyethyltrimethylammoniumchloride) to prepare a coating composition (hereinafter referred to as Ref. 6).

Example 1 (Preparation of an Electroconductive Base Sheet) The coating composition Ret 2-1 is applied by a coating rod to one side web of wood-free paper weighing 49 g/m2 in an amount of 5 g/m2 by dry weight, and the coated web is dried by an air drier at 1 000C for 1 minutes to prepare an electroconductive base sheet.

Two electroconductive base sheets are prepared in the same manner as in the above procedure except that 10 g/m2 and 15 g/m2 of the coating compositions are employed in place of 5 g/m2 of the coating composition.

Three sheets thus obtained are allowed to stand at 200C and 50% RH for 24 hours and checked for specific resistivities by Teraohm meter (trade mark: "VE-30 type", product of Kawaguchi Denki Co., Ltd., Japan). The results obtained are shown as curve 1 in Fig. 1.

Example 2 (Preparation of Electroconductive Base Sheets) Six electroconductive base sheets are prepared in the same manner as in Example 1 except that coating compositions Ref. 2-2, Ref. 2-3, Ret 2-5, Ret 2-6, Ret 2-9 and Ret 2-10 are used in place of the above coating composition Ret 2-1 and checked for specific resistivities by the above manner. The results are also shown as curves 2 to 7 in Fig. 1.

Example 3 One of the seven kinds of electroconductive coating compositions used in the above examples 1 and 2 is applied by an air knife coater to a web of wood-free paper weighing 49 g/m2 in amounts of 10 g/m2 on one side and 5 g/m2 on the other side by dry weight. The paper web is dried to obtain an electroconductive base sheet. The same procedure as above is repeated with use of the other six kinds of compositions.

A record layer forming composition prepared by adding 20 parts of calcium carbonate to 400 parts of 20% methyl ethyl ketone solution of vinyl chloride-vinyl acetate (50:50) copolymer and stirring the mixture in a mixer to fully disperse the carbonate in the solution is applied by a bar coater to each of the base sheets over the first-mentioned side thereof in an amount of 5 g/m2 by dry weight. The coated sheets are dried to obtain sheets of electrostatic record material. For comparison, a sheet (comparison sheet I) of electrostatic record material is prepared in the same manner as above except that the electroconductive base sheet used is produced by coating a web of wood-free paper weighing 49 g/m2 with a 15% aqueous solution of polyvinylbenzyltrimethyl ammoniumchloride (trade mark: "ECR-34".

product of the Dow Chemical Co., U.S.A.) in an amount of 3 g/m2 by dry weight on each side of the web, and drying the web.

The eight sheets of electrostatic record material thus obtained are tested for recording characteristics by the following method. Each of the sheets is allowed to stand in a hot air drier at 550C for 30 minutes and dried to an extremely low water content of not higher than 2%. The sheet is then recorded by a high-speed facsimile placed in an atmosphere having a temperature of 200C and 20% RH, under the conditions of a line density of 8 lines/mm, pulse width of 12 u sec, pin voltage of -300 V and sub-voltage of +300 V. The density of the images is measured by Macbeth densitimeters Model No. RD-100R (product of Macbeth Co., Ltd.) in terms of reflection density.The result is given in Table 3, which reveals that whereas no images are reproduced on the record sheets of the comparison examples, images are formed with a high density and stability on the record sheets of the examples of this invention.

Table3 Coating composition No. used in Examples 1 and 2 Density of image 1 Ref. 2-1 1.1-1.2 2 Ret 2-2 1.1-1.2 3 Ret 2-3 0.9-1.2 4 Ref. 2-5 1.1-1.2 5 Ret 2-6 0.7-0.8 6 Ret 2-9 No image is formed 7 Ref. 2-10 1.1-1.2 8 Comparison Sheet I No image is formed Example 4 (Preparation of an Electroconductive Base Sheet) The coating composition Ref.2-11 is applied by a coating rod to one side of a web of wood-free paper weighing 49 g/m2 in an amount of 6.5 g/m2 by dry weight, and the coated web is dried by an air drier at 1 000C for 1 minute to prepare an electroconductive base sheet.

The base sheet is allowed to stand at 250C and 1 5% RH for 24 hours and checked for a specific resistivity. The result is shown as curve 1 in Fig. 2.

Three base sheets are produced in the same manner as in the above procedure and are checked for specific resistivities in the same manner as in the above procedure except that the conditions of 45% RH, 609/0 RH and 75% RH are employed in place of 15% RH which are also shown as curve 1 in Fig. 2.

Example 5 Six electroconductive base sheets are produced in the same manner as in Example 4 except that each of coating compositions Ret 2-12, Ret 2-4, Ret 2-7, Ref. 2-14, Ret 2-1 5 and Ret 2-1 6 are used in place of the coating composition Ref. 2-11 and checked for a specific resistivity which is also shown as curves 2 to 7 in Fig. 2 respectively.

Example 6 Each of six electroconductive base sheets is produced in the same manner as in Example 4 except that each of the coating compositions Ret 2-17, Ref. 2-18, Ref. 2-19, Ref. 2-20, Ref. 2-21 and Ref. 2- 22 is used in place of the coating composition Ref.2-11 and checked for a specific resistivity. The results are shown as curves 1 to 6 in Fig. 3.

Example 7 14 sheets of electrostatic record material are prepared in the same manner as in Example 3 except that the specified coating compositions shown in Table 4 are used in place of the coating compositions used in Example 3 and 6.5 g/m2 of coating compositions are applied on both sides in place of the application of 5.0 g/m2 on one side and 10.0 g/m2 on the other side of coating composition. Also Comparison sheet II is produced in the same manner as in preparation of Comparison sheet I. Each of the sheets is allowed to stand under the specified atmosphere shown in Table 4 for 48 hours respectively. The sheet is then recorded by a high-speed facsimile in the same atmosphere as above under the condition of a line density of 8 lines/mm, pulse width of 12 y sec, pin voltage of -300 V and sub-voltage of +300 V. The density of the images is measured by the same manner as in Example 3 and the results obtained are shown in Table 4.

Table 4 Density of Ima.ve Coating Composition Low humidities Ambient humidities High humidities used in Example 7 (25 C, 15% RH) (250C, 55% RH) (250C, 80% RH) Ref. 2-11 1.1-1.2 1.1-1.2 0.8-0.9 Ref. 2-12 1.1-1.2 1.1-1.2 0.8-0.9 Ref. 2-4 1.1-1.2 1.1-1.2 0.8-0.9 Ref. 2-7 0.9-1.0 0.9-1.0 0.7-0.8 Ref. 2-14 No image is formed 0.6-0.7 0.5-0.6 Ref. 2-15 1.1-1.2 1.1-1.2 0.8-0.9 Ref. 2-1 6 No image is formed 0.2-0.3 0.8-0.9 Ref. 2-20 No image is formed 0.9-1.0 0.6-0.7 Ref. 2-1 7 0.9-1.0 0.9-1.0 0.6-0.7 Ref. 2-18 1.1-1.2 1.1-1.2 0.8-0.9 Ref. 2-19 1.1-1.2 1.1-1.2 0.8-0.9 Ref. 2-22 1.1-1.2 0.70.8 0.2--0.3 Comparison sheet Il No image is formed 1.1-1.2 0.7-0.8 Ref.6 1.1-1.2 1.1-1.2 0.7-0.8 Example 8 Three sheets of electrostatic record material are produced in the same manner as in Example 3 except that three kinds of electroconductive coating compositions obtained in Reference Examples 3 to 5 are employed in place of those used in Example 3. Each of the sheets thus obtained is checked for a density of image. The results are shown in Table 5 below.

Table 5 Coating Composition No. used in Example 8 Density of image 1 Ref.3 3 2 Ref. 4 0.6-0.7 3 Ref.5 0.9-1.0

Claims (11)

Claims

1. An electrostatic record material comprising an electroconductive base sheet and a record layer formed on the base sheet and consisting essentially of an insulating resin, the record material being characterized in that the electroconductive base sheet has an electroconductive layer containing (i) a zinc oxide powder having a specific resistivity of 0.01 to 500 ohm-cm at pressure of 150 kg/cm2, and (ii) a water-soluble or water-dispersible adhesive resin.

2. An electrostatic record material as defined in claim 1 wherein the zinc oxide powder has a specific resistivity of 1 to 400 ohm-cm.

3. An electrostatic record material as defined in claim 1 wherein the zinc oxide powder is prepared by admixing with zinc oxide a small amount of at least one of Al2O3, Cr2O3, Ga2O3, In203 and a compound which produces such an oxide when heated at a high temperature and heating the mixture at a high temperature.

4. An electrostatic record material as defined in claim 3 wherein said small amount is about 0.1 to about 5 mole % per 1 mole of zinc oxide.

5. An electrostatic record material as defined in claim 1 wherein the electroconductive layer contains 100 weight parts by weight of said zinc oxide powder and 3 to 100 parts by weight of said resin.

6. An electrostatic record material as defined in claim 1 wherein the water-soluble or waterdispersible adhesive resin is an adhesive resin.

7. An electrostatic record material as defined in claim 6 wherein the adhesive resin is at least one species selected from the group consisting of celluloses, starch, modified starches, polyvinyl alcohol, polyvinyl pyrrolidone, sodium alginate, polyacrylamide, alkali salts of copolymers such as isobutenemaleic anhydride copolymer, styrene-maleic anhydride copolymer, styrene-methacrylic acid copolymer, styrene-butadiene copolymer latex, polyvinyl acetate latex and polyacrylic acid latex.

8. An electrostatic record material as defined in claim 1 wherein the water-soluble or waterdispersible resin is an electroconductive resin.

9. An electrostatic record material as defined in claim 8 wherein the electroconductive resins are those having an ammonium salt, sulfonium salt or phosphonium salt as a functional group.

10. An electrostatic record material as defined in claim 8 wherein the electroconductive resin is used in an amount of 5 to 100 parts by weight per 100 parts by weight of the zinc oxide.

11. An electrostatic record material substantially as herein described with reference to any of the Examples.