Electroscopic powder with sharp melting point containing sucrose benzoate and a thermoplastic resin

Abstract

An electroscopic powder having a sharp melting point which is particularly adaptable for use in high speed electrostatic copying machines is formulated with sucrose benzoate in the range of 40 to 80% by weight and a thermoplastic resin such as a polyamide, polyacrylate or polyurethane in the range of 10 to 40% by weight and optionally a metal soap in the range of 0.01 to 3.0% by weight with the remainder consisting of coloring agents such as pigments or dyes.

Description

BACKGROUND OF THE INVENTION

This invention relates to electroscopic powders which are useful for developing latent electrostatic images produced by electrophotographic copying techniques. More particularly, it relates to electroscopic powders which have been formulated from materials which serve to improve the fixability of the powder onto the copy sheet.

Photoelectrostatic copying processes in which a photoconductive medium is imaged to produce a differential electrostatic charge which is then developed with an electroscopic powder or toner are well known. A wide variety of photoconductive media may be employed such as elemental photoconductors, photoconductive crystalline metal compounds and organic photoconductors, both monomeric and polymeric.

Techniques are well known for developing the differentially charged photoconductive medium including magnetic brush development, powder cloud development, liquid development and cascade development.

The formulation of electroscopic powders for use in a particular electrophotographic copying environment has been widely explored. The powders are applied by the various techniques mentioned above and ultimately fixed so that they will adhere to the copy material being used. The copy material may be the photoconductor itself such as in the case of zinc oxide coated paper. In other systems the powder image is first produced on a photoconductive drum and then transferred to a sheet of plain paper where the powder image is fixed. In either case the electroscopic powder must be permanently fixed to the material which is to become the permanent copy.

In the copying systems previously known the techniques of fixing the image onto the copy generally depended upon the use of heat in order to fuse a thermoplastic resin powder contained in the electroscopic powder onto the copy material. The use of heat energy is generally acceptable but prolonged heating at high temperatures causes some problems. For example, the hazard of igniting papers or at least charring them in the circumstance that there is a paper jam in the paper delivery system is an ever present danger. In addition the introduction of excessive amounts of heat into the working environment causes some discomfort.

Pressure fusing obviates some of the disadvantages inherent in lengthy heat fusing cycles, but pressure fusing requires specially formulated toners.

One important consideration is the time which is required to impart sufficient heat to the thermoplastic powder so that it will properly soften and coalesce. The rate of output of reproductions in any electrophotographic copying system is only as fast as the slowest processing step which heretofore was the heat fusing operation.

Electrostatic powders or toners have been suggested which are formulated especially for rapid fusing. It has been found, however, that because of their broad range of melting points they tend to produce reproductions whose images are feathered and generally of poor resolution when heat fused because of the presence of very low melting point constituents which when combined together with higher melting point materials cause the images to spread out.

OBJECTS OF THE INVENTION

It is accordingly a general object of this invention to provide an improved electroscopic powder having utility in high speed electrophotographic copying machines.

It is another object of the instant invention to provide an improved electroscopic powder for use in high output electrophotographic copying machines capable of producing high quality images.

It is another object of this invention to provide a rapid fusing electroscopic powder having a sharp melting point.

Other objects and advantages of this invention will become apparent from the following detailed disclosure and description.

SUMMARY OF THE INVENTION

It has been found that the use of sucrose benzoate in a major proportion results in electroscopic powder formulations which have a sharp melting point, are rapidly fusible and produce sharp images upon development. Toners formulated using sucrose benzoate have been found to adhere well to the copy sheet. They have low fusing temperatures and yet do not soften or melt so as to cause agglomeration during storage of toner. Greater copying speeds are therefore attainable using these toners.

Another advantage of using the toners of this invention is that copies prepared using these toners do not display high background when printing in very low humidity atmospheres as is the case with other toners. Developer mixes utilizing these toners can, for example, be allowed to stand in a dry atmosphere, that is, one in which the relative humidity is as low as about 10%, for a number of days without affecting the triboelectric properties of the toner.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Electroscopic powders of the instant invention comprise sucrose benzoate in the range of 40 to 80% by weight, a resin component which may be a polyamide resin, a polyacrylate resin, a polyurethane resin or other thermoplastic resin having similar properties in the range of 10 to 40%, a coloring agent in the range of 1 to 10% and various other optional ingredients as hereinafter described.

Sucrose benzoate, C.sub.12 H.sub.14 O.sub.3 (C.sub.6 H.sub.5 --COO).sub.7 is a non-crystalline, non-polymeric frangible solid having a softening point of around 98.degree.C. When used with a suitable thermoplastic resin and coloring agent in a concentration of about 40 to 80% by weight a toner having a sharp melting range which is particularly adaptable to rapid electrophotographic copying results. Such toners also have a relatively high point of tackification, that is, they will stay in their physical state without significantly changing as their melting point is approached. At that point their physical state changes abruptly so that powder images produced using these toners can be fused at higher speeds for a given amount of energy input than toners previously available.

Coloring agents useful in this invention include carbon black, Nubian Resin Black and other pigments or dyes.

Suitable thermoplastic resins include polyamide resins produced by reaction of dicarboxylic acids or their esters with polyamino compounds such as diamines. Preferred esters are the methyl, ethyl, and propyl esters. Suitable polyamino compounds include ethylenediamine, tetramethylenediamine, pentamethylenediamine, piperazine and diethylenetriamine. One group of particularly suitable polyamides sold under the trademark "VERSAMID" by General Mills Company are prepared from dimer acids and polyamines, for example the condensation product of 9,11-linoleic acid and 9,12-linoleic acid with ethylene diamine. Other suitable polyamide resins are available from the Krumbhaar Resin Division of Lawter Chemicals, Inc. under the trademark "POLYMID."

Another group of thermoplastic resins which can be used in the toners of this invention are the acrylic resins or polyacrylates. Examples of suitable polyacrylates include polymethylmethacrylate and polyethylmethacrylate sold under the trademark "ACRYLOID" by Rohm and Haas Company. Acrylic copolymers can also be used, such as the copolymers of vinyl monomers and alkyl acrylates, for example, those sold under the trademark "IONAC" by Ionac Chemical Company. One such copolymer is a copolymer of styrene and butylmethacrylate which is sold under the trademark "IONAC RP 60."

An optional ingredient in the toners of this invention is a metal soap, for example, a lithium, calcium, barium, zinc or aluminum salt of a C.sub.12 to C.sub.18 carboxylic acid such as lauric acid or stearic acid. Such soap is desirable where the toner and the developer mix incorporating the toner are exposed to the excessive stresses present in high speed machines. It has been found that the presence of these metal soaps in a concentration of from 0.01 to 3.0% by weight prolongs the life of the developer mix where it is tumbled and compacted rapidly such as when producing 50 to 60 copies per minute or more. The metal soaps have also been found to prolong the life of the mix where the equipment is used for long periods at high speeds. It is not necessary to include the metal soaps where the machine is operated at slower copymaking speeds or at high speeds only intermittently.

In preparing the electroscopic powders of this invention the resinous materials are first reduced to their molten state and the sucrose benzoate, various coloring agents and the metal soap, if it is to be added, are then mixed into the molten resin.

The following examples are given to illustrate the preferred embodiments of this invention. It will be understood that these examples are merely for the purpose of illustration and are not intended as limitations upon the scope of the invention, which is defined in the claims appended hereto.

In all the examples, the amounts shown are percent by weight of the electroscopic powder formulations.

EXAMPLE I

Ingredient Per Cent ______________________________________ Sucrose benzoate 55.3 Styrene-butylmethacrylate copolymer IONAC RP 60 Ionac Chemical Company 32.5 Zinc laurate 2.1 Carbon black 4PCO5 Richardson Ink Co. 2.8 Nubian Resin Black 7.3 ______________________________________

The sucrose benzoate and styrene-butylmethacrylate copolymer were added to a 1/2 gallon can, melted and agitated well. Zinc laurate was added and agitated at 3,000 rpm. for 8 minutes at a temperature of 171.degree.C. The carbon black was added in the form of a 50% dispersion of carbon black in VERSAMID 930 polyamide resin, and agitated for 15 minutes at 4,500 rpm. at 182.degree.C. The Nubian Resin Black was added and the mixture agitated for 15 minutes at 4,800 rpm. at a temperature of 182.degree.C maximum. The molten mass was removed and immediately poured into shallow pans so as to form a large thin wafer which was rapidly cooled by forced air in order to prevent individual constituents from separating out of the mixture or otherwise stratifying. The large wafer formation was jet milled at 10 lb. per hour and 100 psi. to an average particle size ranging from under 1 micron to about 50 microns in size.

The powder was classified according to particles which pass through a 100 mesh screen so that the largest particle size was under 149 microns.

A developer mix using 40 parts of RZ 150 iron particles to 1 part of the toner prepared according to the foregoing description was placed in a 1-gallon can and rolled on a roll mill for one-half hour.

The resulting developer mix was used in a commercial electrophotographic copying machine, the AM 5000 manufactured by Addressograph-Multigraph Corporation, which utilizes pressure fixing. The copies prepared on zinc oxide coated paper using this developer were sharp and dark.

EXAMPLE II

Ingredient Per Cent ______________________________________ Sucrose benzoate 78.4 Polyurethane resin P250-2 Hooker Chemical Co. 10.1 Zinc laurate 2.1 Carbon black ELF-5 Cabot Carbon Co. 3.8 Nubian Resin Black 5.6 ______________________________________

The sucrose benzoate was carefully melted to prevent burning since it was necessary to provide a high temperature in order to melt the polyurethane. The other ingredients were added in order, first dissolving the polyurethane with the carbon black and Nubian Resin Black being dispersed at 4,500 rpm. The toner was then prepared in the same manner as in Example I.

A developer mix was prepared using 35 parts of the toner to 1,225 parts of RZ 150 iron particles.

The resulting developer was used to make satisfactory copies in a commercial electrophotographic copying machine, the AM 2000 manufactured by Addressograph-Multigraph Corporation which was equipped with a continuous oven fuser and a magnetic brush developer. Zinc oxide coated paper was utilized for making copies.

EXAMPLE III

Ingredient Per Cent ______________________________________ Sucrose benzoate 69.0 Acrylic resin Acryloid B 82 Rohm and Haas Co. 20.7 Zinc laurate 2.1 Carbon black ELF-5 Cabot Carbon Co. 1.4 Nubian Resin Black American Cyanamid Co. 6.8 ______________________________________

The sucrose benzoate and acrylic resin were placed into a half-gallon can, melted and agitated at 2,000 rpm. The zinc laurate was added, melted and agitated at 3,000 rpm.

The carbon black was then added, dispersed in the mixture resulting from the previous additions and agitated at 4,500 rpm. The Nubian Resin Black was then added, dispersed and agitated at 4,500 rpm. until it was completely dispersed. The temperature held at 177.degree.C. and reached a maximum of 179.degree.C.

The resulting mixture as jet-milled at 15 lb. per hour feed at a pressure of 90 psi. resulting in a satisfactory particle size distribution which peaked at 8.1 microns on the volume differential curve for this formulation.

At a feed of 10.4 lb. per hour the toner was a finer particle size and volume differential curve was broader.

Jet-milling at 18.8 lb. per hour feed at 85 psi. resulted in a more desirable particle size distribution.

Seventy-four grams of this toner formulation were mixed with 2,950 grams of RZ 150 iron carrier particles placed in a 1-gallon can and tumbled on a roll mill for one-half hour. Satisfactory copies were made on the commercial electrophotographic copying machine of EXAMPLE I.

EXAMPLE IV

Ingredient Per Cent ______________________________________ Sucrose benzoate 55.2 Acrylic resin Acryloid B 82 Rohm and Hass Co. 34.5 Zinc laurate 2.1 Carbon black ELF-5 Cabot Carbon Co. 1.4 Nubian Resin Black Z-1630 American Cyanamid Co. 6.8 ______________________________________

The ingredients shown above were processed according to the procedure of Example III except that the mixture was jet-milled at a feed of 12.1 lb. per hour at 90 psi.

Mixture softened at 105.degree.C. and melted at 110.degree.C.

Copies were made using a ratio of 30 parts iron carrier particles to 1 part toner.

The electrostatic copier used was equipped with a pressure fixing device so that the powder could be permanently adhered to the photoconductive member by passing between a pair of pressure rollers. The powder readily adhered to the coated paper under a pressure of 300 lb. per lineal inch, assuming a line contact between the pressure rollers.

In order to measure the effectiveness of the pressure fixing step of the powder image, a procedure is used whereby the surface of the image is mechanically rubbed with a piece of white cloth attached to a mechanical wiper under controlled conditions of pressure and rubbing action.

A standard piece of test equipment is utilized to make this rub-off test measurement and is identified as an AATCC Crock Meter (American Association of Textile Colorists and Chemists). This device is equipped with a mechanically operated finger that applies a constant rubbing action to the surface of a copy sheet bearing a pressure fixed image. The finger applies a force of 319 grams to the surface over which it rubs. The rubbing surface of the finger is 1.5 centimeters in diameter covered with a special white cloth and the rubbing action is back and forth in a straight line along a 10.2 centimeter distance along the surface of the test specimen.

In order to determine the permanence of the pressure fixed image, the image density of the electrostatic copies is adjusted so that the solid areas measure 1.0 to 1.10 density units on the copies. The image density measurements are obtained by using a reflective densitometer. This image density represents a standard value so that the test results are comparable between different toners, different copying machines, different paper and varying light conditions. The surface of the rubbing finger covered with a piece of the special test cloth is allowed to move across the surface of the sample through 5 rubbing cycles each rubbing cycle representing a 20.4 centimeter movement or a total rubbing distance of 102 centimeters.

The test cloth is removed from the finger and the optical density of the toner picked up on the surface of the cloth as a result of the rubbing action is read using the same densitometer. The results are shown in Table 1.

TABLE 1 ______________________________________ Rub-Off Original Copy Density Front Center Back ______________________________________ 0.80 - 1.0 0.636 0.800 0.765 ______________________________________

The Fisher-Johns melting point of the toner was 105.degree. to 110.degree.C.

EXAMPLE V

Ingredient Per Cent ______________________________________ Sucrose benzoate 54.6 Polyamide resin "POLYMID 1060" Lawter Chemical Company 32.9 Carbon black 4PCO5 Richardson Ink Co. 2.9 Zinc laurate 2.2 Nubian Resin Black Keystone Aniline and Chemical Co. 7.5 ______________________________________

The polyamide resin is melted and the carbon black, zinc laurate, sucrose benzoate, and Nubian Resin Black added in order and the entire mixture jet-milled at 10 lb. per hour feed at a pressure of 95 psi. which was found to give a satisfactory particle size distribution.

A mixture of 85 grams of the resulting toner and 3,400 grams of RZ 200 iron powder (+ 325) was placed in a one-gallon can and rolled on a roll mill for one-half hour. Toner was then prepared according to the procedure of EXAMPLE I.

Copies were prepared on the commercial electrostatic copier described in EXAMPLE I. It was found that copies prepared were clean with no iron print-out and the density of the copies produced was maintained throughout a run of over 2,000 copies. Over 8,000 copies were made by retoning.

The toner produced using this formulation has a melting point range of 101.degree. to 104.degree.C. as determined on the Fisher-Johns melting point apparatus.

In general in order to prepare a suitable developer mix the electroscopic powder of this invention is combined with a suitable carrier as described above. The ratio of toner to carrier in parts by weight is in the range of 1:15 to 1:60 where the developer mix is to be used with a magnetic brush system and iron particles are used as the carrier. Where glass beads or other carrier of the type used in cascade systems are used the ratio of toner to carrier can be as low as about 1:80.

The unique feature of the instant invention resides in the combination of sucrose benzoate with a thermoplastic resin selected from the group consisting of polyamides, polyacrylates and polyurethanes, which produces a toner formulation which is fixable by heat or pressure and is adaptable to use in high speed machines. Such toners have a melting point within the range of 75.degree. to 150.degree.C. and melt completely within a range of about 5.degree.. An especially preferred toner has a melting range of 105.degree. to 110.degree.C. Because of the sharp melting point displayed by such toner formulations, they demonstrate surprising longevity when combined with carrier particles in the environment of high speed electrostatic copiers, giving acceptable performance in terms of density of image, clean background of copy, and the ability to be pressure fixed to the copy sheet by using pressures in the range of 175 to 350 lb. per lineal inch and preferably 275 to 350 lb. per lineal contact inch as well as the ability to be fused by heat in a relatively short period of time.

Claims

I claim:

1. An electroscopic powder for developing electrostatic images having a sharp melting point range comprising a blend of sucrose benzoate in the range of from 40 to 80% and a thermoplastic resin selected from the group consisting of polyamides, polyacrylates and polyurethanes in the range of from 10 to 40% by weight.

2. An electroscopic powder according to claim 1 which includes a metal soap selected from the group consisting of lithium, calcium, barium, zinc and aluminum salts of C.sub.12 to C.sub.18 carboxylic acids present in an amount in the range of from 0.01 to 3.0% by weight.

3. An electroscopic powder according to claim 1 which has a melting point in the range of 75.degree. to 150.degree.C.

4. An electroscopic powder according to claim 1 which melts completely within a 5.degree. melting range.

5. An electroscopic powder according to claim 1 which melts completely within the range of from 105.degree. to 110.degree.C.