US3915874A - Liquid developer for use in electrophotographic transfer process - Google Patents

Abstract

A liquid developer for use in the electrophotographic transfer process comprising a liquid carrier with an electric resistance of not less than 109 Omega .cm and a dielectric constant not greater than 3, having dispersed therein a toner comprising particles of a colored substance coated with at least one resinous substance which will penetrate cloth or paper, together with fine particles being harder than the toner particles and having an average particle diameter of from 1 to 15 Mu .

Description

United States Patent Machida Oct. 28, 1975 LIQUID DEVELOPER FOR USE IN 3,512,965 5/1970 M'atkan 252 621 L ELECTRQPHQTQGRAPHIC TRANSFER 3,766,072 10/1973 Metcalfe et aL. 117/37 LE 3,806,339 4/1974 Tamai 117/37 LE PROCESS Inventor: Hazime Machida, Tokyo, Japan Kabushiki Kaisha Ricoh, Tokyo, Japan Filed: July 27, 1973 Appl. No.: 383,259

Assignee:

Foreign Application Priority Data July 27, 1972 Japan 47-74604 References Cited UNITED STATES PATENTS 12/1960 Wright 252/621 L Primary ExaminerMaynard R. Wilbur Assistant Examiner-N. Moskowitz Attorney, Agent, or Firm-Coo'pe'r, Dunham, Clark, Griffin & Moran 57 ABSTRACT A liquid developer for use in the electrophotographic transfer process comprising a liquid carrier with an electric resistance of not less than 10 Q.cm and a dielectric constant not greater than 3, having dispersed therein a toner comprising particles of a colored substance coated with at least one resinous substance which will penetrate cloth or paper, together with fine particles being harder than the toner particles and having an average particle diameter of from 1 to 15 1,.

5 Claims, No Drawings LIQUID DEVELOPER FOR USE IN ELECTROPHOTOGRAPI-IIC TRANSFER PROCESS BACKGROUND OF THE INVENTION This invention is concerned with liquid developers for use in electrophotography. It is more particularly concerned with such developers for use in the transfer process for reproducing an image.

The principal methods for developing electrostatic latent images formed on an electrophotographic copying material are the dry developing method employing a powdery toner and the wet developing method employing a liquid toner.

Based on the differences in obtained the final copy, the methods are also classified as direct and indirect, or transfer. In the direct process, the final image is formed directly on the electrophotograhic material. In the transfer process, the image is formed on the electrophotographic material and transferred to another support, such as plain paper.

Theoretically, both dry and wet developing can be used in both the direct and the transfer methods.

One advantage of wet developing is that the edging effect which increases the resolving power of the finished product is minimized compared with the dry developing procedure. The major advantage of the transfer procedure is that the final product is on plain paper. Because of these advantages, it has long been a desideratum of the art to combine the transfer process with wet developing.

The art has not yet developed a satisfactory procedure which combines the transfer process with wet developing. The reason for this is that an image formed by dry developing can be readily transferred to a paper sheet by the application of bias voltage, but a wet developed image adheres tenaciously to the photoconductive layer of the electrophotographic material and is difficult to transfer.

THE INVENTION A liquid developer has now been discovered in accordance with this invention which makes it possible to combine wet developing with the transfer process, without any loss of image quality. The developer of this invention comprises a carrier liquid having an electrical resistance of at least l Q'cm and a dielectric constant up to 3, having dispersed therein a toner comprising particles of a colored substance coated with at least one resin which is capable of penetrating into paper or cloth together with fine particles being harder than the toner particles and having an average diameter of from 1 to l5;1..

The average particle diameter of the fine particles is obtained by dispersing them in an appropriate liquid, placing a measured amount of the suspension on a thin glass plate, and forming a sandwich by placing another glass plate over the suspension. The thin layer of the suspension is photographed with a photomicroscope and the diameter of 200 to 1,000 particles within a visual field is measured. The average particle diameter represents the mode size, i.e., the particle diameter which has been detected most frequently.

The colored particles employed in the preparation of the toners used in this invention include any of those pigments or dyes normally employed in the preparation of liquid developers. The particles are coated with a soft resin of the type normally employed in the preparation of printing inks. Such inks form images on paper because they readily penetrate the paper, thus forming an image which is strongly bonded thereto. The penetration also contributes to increasing the drying rates of the inks. Attempts to utilize these resins in previous methods of preparing toners for liquid development have not been successful. The reasons for this are (l) at the time of transfer the toner particles, since they are coated with a soft resin, are crushed resulting in a blurred image, and (2) the image is also blurred as a result of the toners diffusing through the capillaries of the paper. More precisely, such toners have poor resolving power.

Any of a wide variety of pigments or dyestuffs may be used as the colored materials for the toners of this invention. The following may be mentioned by way of example of typical materials presently commercially available: Carbon Black MITSUBISHI No. 44, Carbon Black MITSUBISHI No. (both of these are the manufacture of MITSUBISHI KASEI K.K.), Printex G, Special Black 15 (a manufacture of Deggusa Co.), Mogal A, Sutetex, Peerless 155 (all of these are the manufacture of Columbia Co.), Elftex 5 (a manufacture of Cabot Co. Acetylene Black (a manufacture of DENKI KAGAKU K.K.), Cyanine Black, Spirit Black (both of these are the manufacture of ORIENT KASEI K.K.), Aniline Black (a manufacture of I.O.l. Co., England), Brilliant Carmine 68 (a manufacture of SANYO SHIKISO K.K. Rhodamine B (a manufacture of TOYO INK K.K. Benzidine Yellow GNH (a manufacture of SANYO SHIKISO K.K., Ultra Rose E (a manufacture of TOYO INK K.K.), Cyanine SANYO SHIKISO K.K., Phthalocyanine Green E7G (a manufacture of DAINICHI SEIKA K.K.),Cyanine Blue LBG (a manufacture of SUMITOMO KAGAKU K.K. Benzidine Yellow GR (a manufacture of TOYO INK K.K. Oil Blue, Alkali Blue (both of these are the manufacture of ORIENT KASEI K.K.), Ultra Blue B (a manufacture of TOYO INK K.K.), Spilon Yellow, Spilon Red (both of these are the manufacture of HODO- GAYA KAGAKU K.K.), Microlith Black C-T, Microlith Blue 4CT, Microlith Green CT, Microlith Yellow 2CT, Microlith Red R-T (all of these are the manufacture of CHIBA, Ltd.), Reflex Blue AG, etc. As particles having a composition similar to these colored particles, there are Graphofax Toner Powder No. 39-50, a dry toner (a manufacture of Hunt Co.), etc., and these are also applicable to the present invention. 1

A variety of resinous substances may be purchased 0 prepared for use in the invention. They may be coated on the foregoing colored particles through kneading, for instance. They include, for example butyl rubbers such as ESSO Butyl 215 and E880 Butyl by ESSO Oil Co., isobutyl rubbers such as Vistanex LM and Vistanex MN by ESSO Oil Co., chlorinated isobutylene rubbers such as Butyl Rubber HT -l066, Butyl Rubber HT-l067 and Butyl Rubber HT-l068 by ESSO Oil Co., alkyd resins such as Beckozol I343, Beckozol J-l334, Beckozol J-534, Beckozol P-789, Beckorin P-75, Beckozol P-450, Beckozol J-6l l, Beckozol J-7l9 and Beckasite J-8l l by DAINIPPON INK K.K., isobutylene butylene copolymers such as Vistaron 4608 and Vistaron 4504 by ESSO Oil Co., and styrene butadiene copolymers such as Pliolite S-5A, Pliolite 8-63 and Plioflex 1502 by Goodyear Corp., under the trade names of JSR-0060, SBR 1500 and SBR 1502 by NIPPON GOSEI GOMU K.K., under the trade names of Solprene 1205, Solprene 1204, Solprene 235 and Solprene. 303 by Fillips Co., and under the trade name of Nipol 1220 and Hycar 1432 by NIPPON-ZEON Co.

In addition to the above enumerated resinous substances, varnish, linseed oil, rosin, modified rosin, tung oil, soybean oil, fish oil, various waxes, various celluloses, asphalt, aliphatic amine resins, etc. may also be used. Typical examples of this type of resinous substances include KO-Blown Asphalt, TOKUKO-Blown Asphalt, S. P-Blown Asphalt (all of these are the manufacture of NIPPON SEKIYU K.K.), Varnish 30, Varnish 50, Alkyd-modified Varnish (all of these are the manufacture of DAINlPPON INK K.K.), Linseed Oil (a manufacture of WAKO JUNYAKU K.K.), etc.

Mixtures of the above resins may be employed as well as mixtures of these highly penetrative resinous substances with other well known resins conventionally employed in wet developers for electrostatic photography, such as acrylic resins, styrene resins, polyester resins, etc., in the proportion of 0.5 4 parts by weight of the latter resin per 1 part by weight of the former resin. The quantity of penetrative resin coated on the particles of the colored substances is substantially the same as in conventional toners employed in the wetdeveloping method. Typically, the toners will include 1 30 parts by weight of resin to 1 part by weight of the particles of said colored substance.

The term a resinous substance being capable of penetrating into a paper or a cloth as used herein refers to materials responding to the following test:

A resinous substance is dissolved in a mixed solvent, the mixing ratio of toluene and petroleum aliphatic hydrocarbon being 1:1, to prepare a 40 wt.% resinous solution. A 0.5 mm thick metal plate having a hole mm in diameter is placed on an Indian paper and the hole is filled with the solution. Any excess resinous solution on the surface of the metal plate is removed with a spatula so that the quantity of filled resinous solution is just equal to the volume of the hole. The metal plate is removed gently so that the resinous solution alone remains on the paper. It is allowed to stand under atmospheric pressure at C. for 10 minutes and the diameter of a circle of the impregnated resinous solution is measured. If the circle is more than 20 mm in diameter, the resin is of sufficient permeability to be used in the invention. If it is less than 20 mm in diameter, the resin is not suitable for use in the invention.

The above described toners are suspended in the carrier liquid together with additional fine particles which are, generally speaking, harder than the toners so that they are not themselves crushed during transfer, and they help to prevent crushing of the toners. Typical examples of such toners include inorganic materials such as glass beads, zinc oxide, titanium dioxide, silica and the like. Many of the toner particles presently employed in the dry developing method can also be used as the fine particles of this invention.

The weight ratio of toner to fine particles in the liquid developers of this invention is from 0. 1:1 to 1:1. Some variation from this range can be tolerated. It has been observed, however, that appreciably below this range there is not a satisfactory improvement in the formability of the image or its distinctness, while above the range there is an undesirable increase in the number of white spots in the body of the image.

The average particle diameter of the fine particles is from 1 to 1511.. Only a relatively small amount of variation from this range can be tolerated. Below the range, there is a loss of image clarity; above it, there is an increase in the number of white spots.

While there is no intention to be limited by theory, it appears that in the liquid developers of this invention, the toner particles suspended in the carrier liquid are adsorbed to the fine particlesv The fine particles therefore play, so to speak, the role of carriers for the toner particles. Therefore, unless the fine particles have a diameter as described above, they will not remain dispersed in the carrier liquid and a distinct image cannot be formed at the time of development or transfer. The ability to faithfully transfer the toner from the surface of the photoconductive layer of a copying material to the surface of a transfer material is enhanced by the ability of the fine particles to prevent crushing of the toner and its diffusion through capillaries of the paper fibers.

The carrier liquid may be any of the conventional liquids utilized in ordinary liquid developers. They are generally characterized as petroleum aliphatic hydrocarbons with an electric resistance of at least 10 Qcm and a dielectric constant up to 3. Among the presently available commercial carriers which may be employed in the invention, there may be, for example: Shell S.B.P., Shellzol (all of these are the manufacture of Shell Oil Co.), lsopar E, lsopar G, lsopar H, lsopar K, lsopar L} lsopar M, Naphtha No. l, Naphtha No. 2, Naphtha No. 3, Naphtha No. 5, Naphtha No. 6, S01- v'esso 100, Solvesso 150 (all of these are the manufacture of Esso Chemical Co.), Pegazol 1030, Pegazol 2130, Pegazol 2l30-C, Pegazol 3040, Pegazol AS- 100, Pegazol ARO-40 (all of these are the manufacture of Mobil Oil Co.), etc., is applicable.

The following non-limiting examples are given by way of illustration only:

Butyl rubber 20 g 50% toluene solution of styrene butadiene copolymer (molar ratio 30 z lsopar G mixture of the above composition was subjected to 24" hours kneading for dispersion in a ball-mill, whereby a concentrated toner containing a highly penetrative resin was prepared. Subsequently, by dispersing 25 g of this concentrated toner and 15 g of zinc oxide (having average particle diameter of 1.];1.) in 500 ml of lsopar G, a liquid developer having a satisfactory transferability for use in wet-type electrostatic photography was prepared.

An electrostatic latent image was formed on a selemium photoconductive plate through electrification and exposure by the known method, and was then developed with the foregoing liquid developer. Next, by superposing an ordinary paper on the image formed by developing as above, the image was transferred to the paper. The transferred image was distinct and not blurred.

EXAMPLE 2 In the same way as in Example 1 except for replacing the fine particles of zinc oxide with titanium oxide having the same particle diameter as the zinc oxide, a liquid developer for use in wet-type electrostatic'photography was prepared.

When an electrostatic latent image was developed with this liquid developer and transferred to paper, there was obtained a satisfactory transferred .copied image equal in quality to that inExample 1.

EXAMPLE 3 In the same way as in Example 1 except for replacing the fine particles of zinc oxide with silica (having average particle diameter of 2p), a liquid developer for use in wet-type electrostatic photography was prepared.

When an electrostatic latent image was developed with this liquid developer and transferred to paper, there was obtained a satisfactory transferred copied image equal in quality to that in Example 1.

EXAMPLE 4 EXAMPLE 5 Ultra Blue B g Special Black 50 g lsoprene 30 g 50% toluene solution of methyl methacrylate styrene copolymer (molar ratio 50 50) 60 g A mixture having the above composition was subjected to 24 hours kneading for dispersion in a ballmill, whereby a concentrated toner containing a highly penetrative resin was prepared. Subsequently, by dispersing 25 g of this concentrated toner and 0.8 g of glass beads (having average particle diameter of 5p.) in 50 ml of Isopar H, a liquid developer having a satisfactory transferability for use in wet-type electrostatic photography was prepared.

Next, an electrostatic latent image formed in the same way as in Example 1 was developed with the foregoing liquid developer, and this image was transferred to an ordinary paper superposed thereon. As a result, substantially all of the toner on the photoconductive plate was transferred to the paper, and the transferred image was distinct.

EXAMPLE 6 Through the same procedure as in Example 5 except for replacing isoprene with butyl rubber (Butyl Rubber HT-lO-68), a liquid developer for use in electrostatic photography was prepared.

When development and transfer were performed in the same way as in Example 1 utilizing this liquid developer, the transferred image on an ordinary paper was as good as that in Example 5, and the toner transferability was also satisfactory.

v g I Comparative Tests In order to confirm the superiority of the transferability of liquid developers of the present invention, the following comparative tests were conducted in which two types of control developers were prepared and their resolving power at the time of'transferwas compared with that of the liquid developers of the presentinvention.

Preparation of Control Developer Test Procedure A selenium photoconductive plate was first charged with electricity by corona discharge. Then, upon superposing thereon a chart for measuring resolving power with one to several tens of lines drawn within fixed lengths, it was exposed and then developed with control developer-A. Subsequently, an ordinary paper was superposed on the image-carrying surface and was thereafter stripped off, to transfer the image from the selenium photoconductive plate to the paper. Then, the resolving power in lines per mm was determined.

The same tests as above were also conducted with control developer-B and the liquid developers of the present present invention prepared in Example 3 and Example 5. The results were as shown in the following Table 1.

Table l Resolving Power Liquid Developer (lines/mm) Liquid developer of Example 1 12 Liquid developer of Example 5 13 Control developer-A 5 Control developer-8* The copied image on the paper had numerous white'spots, so that calculation of exact number of lines was impossible.

The same tests as above were also conducted with liquid developers prepared in Examples 1, 2, 4 and 6.

What is claimed is:

l. A liquid developer for use in electrophotographic transfer process which comprises: a carrier liquid having an electric resistance of at least lO fl'cm and a dielectric constant up to 3; a toner dispersed in said carrier liquid, said toner comprising particles of a colored substance and at least one resinous substance coated on the surface of said particles, said resinous substance the fine particles selected from the group consisting of glass beads, zinc oxide, titanium oxide and silica.

4. A liquid developer according to claim 1, wherein the ratio of resinous substance to particles of colored substance is from I 30 parts by weight of the former to 1 part by weight of the latter.

5. A liquid developer according to claim 1, wherein the ratio of toner to fine particles dispersed in the carrier liquid with said toner is 0.1:1 to 1:1.

Claims (5)

1. A LIQUID DEVELOPMENT FOR USE IN ELECTROPHOTOGRAPHIC TRANSFER PROCESS WHICH COMPRISES: A CARRIER LIQUID HAVING AN ELECTRIC RESISTANCE OF AT LEAST 109*.CM AND A DIELECTRIC CONSTANT UP TO 3 A TONER DISPERSED IN SAID CARRIER LIQUID SAID TONER COMPRISING PARTICLES OF A COLORED SUBSTANCES AND AT LEAST NE RESINOUS SUBSTANCES COATED ON THE SURFACE OF SAID PARTICLES, SAID RESINOUS SUBSTANCE BEING CAPABLE OF PENETRATIONG INTO A PAPER OR A CLOTH TOGETHER WITH FINE INORGANIC PARTICLES BEING HARDER THAN THE TONER PATRICLES AND HAVING AVERAGE PARTICLE DIAMETER RANGING FROM 1 TO 15Y.

2. A liquid developer according to claim 1, wherein said resinous substance is selected from the following group of butyl rubbers, isobutyl rubbers, chlorinated isobutylene rubbers, modified alkyd resins, isobutylene - butylene copolymers and styrene - butadiene copolymers.

3. A liquid developer according to claim 1, wherein the fine particles selected from the group consisting of glass beads, zinc oxide, titanium oxide and silica.

4. A liquid developer according to claim 1, wherein the ratio of resinous substance to particles of colored substance is from 1 -30 parts by weight of the former to 1 part by weight of the latter.

5. A liquid developer according to claim 1, wherein the ratio of toner to fine particles dispersed in the carrier liquid with said toner is 0.1:1 to 1:1.