AU427349B2 - Anew electrophotographic liquid developer - Google Patents

Description

18, 7 78 no This invention relates to a new electrophotographic

liquid-developer which is especially suited for reproduction

of multi-colored images. Further it relates to a developer

which exhibits complete color mixing when used in over-print multi-color development and which has improved spectral

absorption characteristics. Electrophotographic process is widely used to produce

visible image informations, referred to as electrophotography or xerography, in which the most prevailing system in photo- copy use comprises the following operations. A photoconductive

layer coated on an electrically conductive support is

uniformly charged electrostatically under subdued light, and then subjected to imagewise exposure by means of suitable imagewise modulated energy source, whereby the surface charge is discharged in proportion to radiation intensity. Thus an

electrostatic surface pattern results on the photoconductive layer having a charge density distribution inversely propor- tional to the amount of exposure. That is, the strongly

irradiated area of the photoconductive layer holds a low re- sidual charge density, while weakly irradiated area retains a relatively high charge density. The electrostatic charge pattern which is sometimes referred to as electrostatic latent image is rendered visible by developing technique well known in the field of xerography. A most common operation of development comprises applying a finely-divided developing poweder or toner on to the exposed layer. The toner deposits in accordance with the charge den-

sity distribution on the latent image thus forming a visible image. A variety of development techniques are carried out 427,349

18,7 78 no A toner which is according to requirement to final images. made to assume a charge of an opposite polarity to the latent image to be developed accomplishes positive to positive re- production by virtue of coulomb attraction. Alternatively a

toner having the same polarity of charge may be employed whereby the toner deposits on discharged area in the latent The image thus realizing negative to positive reproduction. latter process is sometimes referred to as repulsion or in- reversal development and forms a visible image optically verted to the one obtained by attraction development.. Many types of developing agent are known among

which a liquid developer described in, for example, U.S. patent specification 2,907,674 can provide a high-resolution image. The developers disclosed in the above patent are as well remarkably improved by utilizing charge-control agents as dispersed particles in the carrier liquids. The purpose

or function of charge-control agent is to provide dispersed amount particles with desired polarity as well as suitable of charge. In other words, electrophoretic properties un- of pigment particles dispersed by themselves are quite by stable, and such instability can be controlled or overcome agents. covering the particles with resinous charge-control an Accordingly, the toner of the developers based on such idea re associated with resinous surface coating or hbsorb- tion layer. There has been developed an electrophotographic

color print process in which two or more differently colored

toner images are over-printed on a single electrophotographic

sheet by repeating hharging, exposure and development 427.349 sequentially. 18,778/70 This method, usually not including toner transfer operation, is called over-print technique.

When a multi-colored toner image is formed by over- print technique with the use of liquid developers such as described above, unsatisfactory mixing of color takes place due to incomplete transparency of pigment particles. This defect can be improved to some extent by minimizing toner particle size. Besides, spectral absorption characteristics of ordinary pigments considerably deviate from ideal ones; therefore in order to realize a faithful reproduction of color one need to resort to the techniqueof color masking which makes the process quite complicated.

The inventors have developed a new type of developer overcoming the above mentioned deficiencies as a result of investigation.on the possibility of producing developers with materials quite different from those of conventional developers.

Accoringly, the object of the present invention is to provide a new type of liquid developer having new composi- tion and improved properties. Another object is to provide liquid developers capable of accurate reproduction of color in over-printing electrophotographic process. Still another object is to disclose a new method of preparing a new type of liquid developer.

Liquid developers of the present invention are char- acterized by that they comprise an highly electrically insulating carrier liquid and finely-divided toner dispersed therein

comprising a water soluble or hydrophilic polypeptide containing a hydroxyl and/or an amino group which group is chemically bonded with reactions dyestuffs.

A 427 349

18,778no0 invention is It is to be noticed that the present it new technique which has made based on the development of stability polypeptide particles possible to disperse with high in- albumine. ete in nonpolar such as gelatin, glue, casein, has its primary importance sulating liquids. This invention in conjunction with this new in utilization of reactive dyes technique. in accordance The toner in the developer prepared dye-connected polypeptide, and with the present invention is in the polymer in molecular the dye molecules are dispersed with perfect clarity far order thus providing the toner based toners. Thus when such better than that of pigment electrophotography to pro- developers are used for over-print images of noticeably improved duce multi-colored images, perfect mixing of primary colors. quality result by virtue of i I

method of preparing Now there will be explained the

developers according to the invention. REACTION OF POLYPEPTIDES WITH REACTIVE DYES be used.for the pre- Any types of polypeptide may contain hydroxyl and/or sent purpose provided that they into chemical reaction with amino radicals which can enter are soluble in water or strongly reactive dyes and that they include gelatin, glue. casein. hydrophilic. Typical examples such as phthalated albumen, ete and their derivatives 427, 349 gelatin. 18,7 78no One or more of these is dissolved in a solvent system mainly comprising water; to the resulting solution or colloidal dispersion is added one or more of reactive dyes well known in the field of textile or dyestuff industry. The polypeptide and the dye are then allowed to react under a suitable condition. Various types and properties of chemically reactive dyes are described in detail in the following literatures. "Shin Senryo Kagaku". (Revised Dyestuff Chemistry) by Yutaka Hosoda from P. 290-295. "Atarashii Gosei Kagaku vol. 7" (Advance of Synthetic Chemistry) New types of dyes and pigments P. 9 to 34; Journal of Industrial Chemistry Japan vol. 1, No. 1 (1964) P. 17 to 25; and from P. 485 to 522 of Color Index, 2nd edition, published by The society of Dyers and Colorists, the American Association of Textile Chemists and Colorists. Our experiments have proved that chemically re- active dyes which consist of a chromophore and one or more chemically active groups capable of entering into coupling reaction with OH radical in cellulose fiber or NH2 radical in polyamide resin can also react with polypeptides such as gelatin, casein, albumin, ete. to form colored products. Reactive dyes generally consist of a chromophore exhibiting absorption in the visible region of the spectrum, suitable solubilizing groups and reactive groups; typical ones have as reactive group dichlorotriazine or monochloro- triazine radicals. They are designed so as to react with OH or NH2 groups in textile fibers under alkaline conditions. Reaction with polypeptide also proceeds under mildly alkaline condition. Formation of chemical bond between polypeptide 6 427.349

18.7 78 no by the following and reactive dyes can .clearly be confirmed added a testing method; to a processed gelatin solution is insoluble in hardening agent to convert the polypeptide in cold fresh water, then the hardened gelatin is immersed place between the water; when a bond formation has taken of the dye from the gelatin and the dye, no dissolution hardened mass is observed. reactive Structural formulas of several typical dye r o below

Procion/Yellow RS (ICI)

C I

C N C aO 3 S

N NN NH- C

SO3 Na

Procion Blue 3GS (ICI) 0- N- 2

N so 3 Na

NaO3 S 0 NH -C N =C -7 SO3 Na I C/

7 427. 349

Brilliant18, Procion BilatRd2S(ICI) 7 78s no

C/I

N S 3 HO NHS-C IC N NN N-C

NaO3 Na

One can effect a reaction between a polypeptide such as gelatin and these dyes by dissolving the two components to- gether with a weakly alkaline material such as sodium car- bonate in water and keeping the resulting solution at 60 to

100 0c for about ten to several ten minutes. Normally 0.1 to 20 parts by weight of a reactive dye may be chemically united with 100 parts by weight of gelatin. To obtain a pale color toner a dye less than 2 parts is sufficient, while for a deeply colored toner 2 to 10 parts of dye is preferred. A black or grey colored toner can be prepared by utilizing two or more differently colored dyes, or by mixing two or more kinds of toner each of which in- cludes a differently colored dye. For a rapid completion of reaction it is desirable for a polypeptide to be water soluble, but after the reaction the resulting material should preferably be water-insoluble. Accordingly, the dye connected polypeptide is advantageously hardened by a suitable hardening agent. The solvent systems for reaction may comprise solely of water or contain water- miscible organic solvents such as alcohols, ketones, cellop-

-8a- 427, 349

18.7 78 no preferred as regards solves, etc., among which acetone is preparation. The con- the feasibility of liquid developer falls in the range from tent of organic solvents ordinarily to of reaction is The solution after the completion the gel is suitably dehydrated cooled to undergo gelling and and rinsed for subsequent processing. PREPARATION OF A FINELY-DIVIDED POLYPEPTIDE. united with a re- A gel or sol of a polypeptide as dyed polypeptide for active dye, which will be referred to with water or a mixture of simplicity, is adequately diluted amount of the organic water and an organic solvent. The cause the precipitation of solvent is limited so as not to the diluted sol is thrown into the dyed polypeptide. Then as organic solvent under an excessive amount of a water-miscible by means of ultrasonic vibra- vigorous stirring for example dyed polypeptide. tion to form fine particles of the of a dyed poly-, A practical example of formulation organic solvent is given by peptide solution containing an the following; of a dyed gelatin g of water

100g of methanol 0 when heated at 25 C. This mixture forms a clear solution of a dyed It is possible to obtain a fine powder an aqueous solution of the polypeptide by adding directly solvent which is a nonsolvent polypeptide into an organic process is prone to bring for said polypeptide, but such a Alternatively a about coagulation of the polypeptide. 427, 349

18,7 78/70 solution of resin may be added after a dispersion of polypeptide is added into a polar organic solvent such as acetone. Coagulation can be prevented by simultaneously adding a nonpolar organic solvent

427. 349

18.7 78 no solution of a resinous, material which also becomes insoluble be used in the resulting mixture. The non-polar solvent to in- must be compatible with the polar solvent employed to for solubilize the polypcptide. This requirement can be met polar almost any non-polar solvent in case of acetone as the solvent, while methanol is inmiscible with solvents of iso- extremely low solubility parameter such as kerosene or paraffinic solvents. Generally speaking, suitable non-polar solvents include cyclohexane, decalin, benzene, toluene, xylene, the esters, in which there may be dissolved one or more of such following resins which are insoluble in polar solvents as acetone or methanol; polyisobutylene, polybutene, poly-

styrene, styrene-butadiene copolymer, rosin modified phenol- formaldehyde resinr-ofo. When a non-polar solution of such formulation is added with vigorous stirring into a large excess of a polar solution such as acetone, methanol, and ethanol, simultane- ously with the addition of a dyed-polypeptide solution, insolubilization of the polypeptide and of the resin in the nonpolar solution proceed whereby the latter encapsulates the former preventing coagulation of the former. A prominent feature of this coprecipitation method

lies in that it enables formation of an extremely fine toner. as well as perfect removal of residual water content in the polypeptide. The supernatant liquid may be removed by either decantation or centrifugal separation. The precipit- ate usually includes a polypeptide powder of less than 1 micron, and the size of the powder does not tend to grow during a prolonged storage. S11I 4Z 1. 3 4 9

18,7 78 PREPARATION OF A LIQUID DEVELOPER

The precipitate including a finely-divided dyed polypeptide is repeatedly purified by washing to remove in- organic ingredients and residual water. Then it is added to a non-polar organic solvent which plays a roll of carrier liquid for the liquid developer whereby the resin in the- precipitate dissolves in the solvent, releasing the dyed polypeptide in the solvent in the form of fine particles. In the resulting dispersion, part of the resin seems to be adsorbed on the surface of the polypeptide particles to stabilize colloidal dispersion. Therefore no intense stirring operation is necessary at this process.* The dispersion thus prepared experimentally proved quite stable for a prolonged storage.. Cyclohexane, tetralin, decalin, and kerosene are among suitable carrier liquid; isoparaffinic and fluorinated hydrocarbons which have a far weak solving power are less' suited since they cannot-dissolve many of above-mentioned resins. Organic liquids which have solubility parameters greater than 7.0 and about 8.8 at room temperature or Kauri- bitanol values of from 26 to 85 are suited for carrier liquid. A minor--amount of more powerful solvents such as aromatic hydrocarbons or ketones may be added to those solvents, the upper limit of addition being about 5 parts in 100 parts of the total carrier liquid. Mixed solvent systems may also be used provided that the solubility parameters for the systems fall in the above-mentioned range. The carrier liquid phase of a developer prepared in the described manner therefore comprises a non-polar organic

427.349 o ft 18778 n, liquid and a resinous comp e l dissolved in said liquid, and the liquid phase should desirably have an electrical resist- ance not lower than lo ohms-cm not to cause destruction of an 10 electrostatic latent image. Other ingredients permitted include viscosity con- trolling agents and surface active agents. Polypeptide structure is known favorable to assume an electrostatic charge of positive polarity in many non-polar organic liquids which characteristic still holds in most cases after reactive dye- stuffs are united. To strengthen or improve electrophoretic properties of developers of the present invention, one may resort to a technique in which particles having a strong tendency of acquiring a charge of desired polarity are added to the developer. According to this technique developers of either polarity, positive or negative, are possible depending on the amount and the nature of the particles to be added. Materials used to prepare positively charged,particles include ethyl cellulose, hydroxyethyl cellulose, polymethacrylates,. while resinous materials which acquire negative charges in insulating liquids are copolymers containing vinyl chloride, nitrocellulose, polyvinylidene fluoride,-*. Liquid developers of the present invention offers another advantage that the resulting toner images would not accept a high electrical potential because of the extremely hydrophilic nature of the principal ingredients. This means that in the over-printing electrophotographic process, whereby charging of the developed image at the subsequent charging is not desirable, the present developers are especially suited, not permitting undesirable deposition of toner on the already 13 427,349

18,7 78 no developed area. In such uses as require less hydrophilic toners, one may resort to hardening of polypeptides during the manu-

facturing procedures to convert the toner water-insoluble,

or may harden the image after development.

Example I

g of gelatin was dissolved in 20 ml of water by heating after being allowed to swell. A reactive dye soluti was prepared by dissolving 200 mg of Remazol (Registered Tra Mark) Brilliant Violet (Hoechst) in 2 ml of water.

These two solutions were mixed together and 5 g of sodium carbonate solution was further added. The resulti solution was heated over a boiling water bath for 15 minutes Then the solution was left to cool; the resulting gel assumed magenta color. A part of the gel was thrown in cold water kept at 0°C, but no dissolving of the dye was observed to show the formation of chemical bonding between the dye an

the gelatin.

Three g of this gel was dissolved upon heating into a mixture of water and methanol in the ratio of 7 8. On the other hand, a solution was prepared comprisin, g of toluol, 10 g of linseed oil, and 15 g of resin modif phenolformaldehyde resin, which is soluble in toluol or cyclohexane and not in acetone. This solution and the gelatin solution prepared above were simultaneously added into 320 g of acetone whereby a precepitate resulted.

Alternatively a solution of the phenol formaldehyde resin ma be added after a dispersion of the polypeptide is added conti

the organic solvent acetone. The precipitate was separated

427. 349

18,7 78 no with acetone. by means of centrifuge and further washed in 400 ml The obtained pasty precipitate was dispersed

of cyclohexane. proved The dyed gelatin particles in the dispersion to undergo an attractive to be positively charged and thus latent image of negative deposition on an electrostatic image was deep polarity. The appearance of a developed

magenta.

Example II the same pro- A dyed gelatin gel was prepared in ex ample except that cedure as was described in the foregoing ICI was replaced to Remazol Brilliant Violet purchased from

Procion Brilliant Red H-3BS. dissolved in 8 g Five grams of the resulting gel was added 15 g of methanol. hot water, and to the solution was solution of rosin Separately 90 g of 20% toluol was prepared. These two modified phenolformaldehyde resin in 320 g of acetone with solutions were simultaneously added was vigorous stirring. Immediately a bulky precipitate as in Example I. The dis- formed, which was processed just charged toner which gave persion also contained a positively

a reddish magenta image.

Example III Example II were repeated The.same operations described in phenolformaldehyde resin to except replacing rosin modified good liquid developer was obtained. polybutene resin. A similarly

Example IV in 5 g of 1 g of soya bean casein was dissolved of godium carbonate, then water together with a slight amount was dissolved. The mixture mg of Reactone Navy Blue GRL

427,349

18,7 78 no was heated at 100°C for 15 minutes. After cooling, 5 ml of methanol was added.

Separately, a second solution was prepared by dis- solving 10 g of linseed oil and 15 g of rosin modified

427. 349

18,7 78 no in 80 g of toluol. To 300 g of phenolformaldehyde.resin two solutions to obtain acetone were added dropwise these was taken out by a a colored precipitate. The precipitate liquid was replaced by centrifuge, and the supernatant was dispersed in 400: ml acetone. After washing, the paste for electro- of cyclohexane. A satisfactory liquid developer

photography resulted.

toner of negative A liquid developer containing a to 40 parts of the developer polarity was prepared by adding of a dispersion comprising prepared in Example II 60 parts 0.3 micron) vinyl chloride/ a finely-divided (particle size in cyclohexane. vinyl acetate copolymer dispersed Examnle VI by A black toner containing developer was obtaiped I with the use of Cibacron/ following the procedure of Example Remazol. Black RP of Ciba Ltd. in place of

427, 349

Claims (2)

18,7 78 no The claims defining the invention are as follows: 1. An electrophotographic liquid developer comprising a highly insulating non-polar carrier liquid and a toner

dispersed therein, characterized by that said toner comprises a hydrophilic polypeptide compound containing an NH 2 and/or OH group which is chemically united with a reactive dye containing at least one electron-affinitive functional

group capable of reacting with the NH2 abd/or OH group of the

polypeptide compound and containing at least one chromogenic group exhibiting an optical absorption in the visible region of the spectrum.

2. Method of forming a liquid developer comprising a highly insulating, non-polar carrier liquid and a toner dispersed therein,said toner comprising a hydrophic

polypeptide compound selected from gelatin, casein, albumen and glue, said polypeptide containing an NH2 and/or OH group which group is united with a reactive dye containing at least one electron affinitive functional group capable of reacting with NH2 or OH group in the polypeptide compound and containing at least one chromogenic group exhibiting an optical absorption in the visible region of the spectrum, which is characterized by the steps of dispersing in an organic solvent which is miscible with water but is a non-solvent for the reactive dye united polypeptide, an aqueous solution of said polypeptide or a solution of said polypeptide in a mixed solvent of water and an alcohol prepared by incorporating in the

aqueous solution of said polypeptide an alcohol

18 427,349

18,7 78/70 of said in such an amount that precipitation a dispersion polypeptide does not occur, to provide of said polypeptide grains.

427, 349

18,7 78no .adding to the resultant dispersion of said polypeptide a solution of a resin which

is insoluble in the organic solvent for said

polypeptide dispersion but soluble in a carrier liquid having an electric resistance of higher

than 1010 Lcm. to coprecipitate the said poly-

peptide grains and the resin, and

adding the precipitates of said polypep-

tide grains and the resin to the carrier liquid

mentioned above.

3. The method as claimed in claim 2, wherein said

resin used in step is polyisobutylene resin, polybutene

resin, styrene resin, styrene-butadiene copolymer or resin-

modified phenolformaldehyde resin.

DATED this ELEVENTH day of AUGUST, 1970

FUJI PHOTO FIIM CO., LTD.

Patent Attorneys for the Applicant SPRUSON FERGUSON

427.349