NO770197L - POWDERED BREAD MATERIALS AND PROCEDURES FOR THE MANUFACTURE OF THE SAME. - Google Patents

Description

Powdery carrier materials and method for their production.

With the increasing use of paper copiers, developer powders have become increasingly popular over liquid developers. Together with an increased use of developing powders, magnetic brush units have become more and more used, and even units where cascades of powders are used are very often used. Such devices usually have a carrier powder, such as an iron powder, which serves as the carrier material. Cheap and untreated carrier powders cannot be used in systems where magnetic brushes are used, as such powders have insufficient stability against rusting. lacks color stability or has triboelectric charge properties that are adversely affected by conditions of varying humidity. To solve these problems, chemical coating of the carrier particles with polymers, oils, waxes and the like has been used.

Previously known developers of the type used in automatic copying machines often had film problems due to a mechanical brushing of the support surface with soft toner resins. A gradual accumulation of a permanently attached film weakens the normal triboelectric charges in the toner particles in the toner mixture itself. As a result, the toner was either strongly charged or in some cases oppositely charged, resulting in poor copy quality with strong background staining.

In the literature, several ways are described for treating, coating and electrocoating the carrier particles, thereby avoiding the above-mentioned film problems. Examples of such carrier particle modifications are found in U.S. Pat. patents 3,725,118, 3,736,257, 3,778,262, 3,795,618, and 3,849,127. These previously known methods have resulted in a high price and have other disadvantages such as insufficient triboelectricity. charge properties or provides the carrier. a very high electrical resistance, which reduces the electrode effect during development and results in poor filling on large image surfaces.

In an electrostatic imaging,

an electrostatic latent image is formed on a recording surface of a photoconductor. The electrostatic image can then be developed using finely divided toner particles which are electrostatically bound to the surface of the carrier particles. Preferably, the carrier particles should be iron powder or iron beads.

It has been found that a simple fluorotelomer adsorption treatment of iron powder from a solvent gives a treated carrier particle which has good stability against rusting under conditions where there is relatively high humidity,

a constant triboelectric charge property under all conditions when mixed with standard toners, very little dust formation from the toner in units where magnetic brushes are used, and a lower reverse voltage can be used during development, which improves copy quality and the machine's reproducibility -dusing ability.

By using fluorotelomer-treated carrier particles according to the present invention, an improved electrophotographic process is achieved, where a latent electrostatic image is contacted with a developer mixture that includes the treated carrier particles.

The process for producing fluorotelomer-treated carrier particles involves dispersing a fluorotelomer in an organic solvent such as trichlorotrifluoroethane in a concentration of from 0.01 to 10%. The core material is then placed in the solution, and this core material is chosen so that it is either metal, sand or glass. The solution is poured off, after which the treated carrier particles are dried and then heated to a temperature of between 250 and 350°C. It is obvious that this treatment is considerably simpler than the previously described methods for treating or coating core particles.

The core of carrier particles according to the present invention can be any material which can react chemically with the fluorotelomer compounds according to the present invention. As an example, the core material in carrier particles according to the present invention can be sand, glass beads, metallic beads or metal powders.

By the term metal and metallic, as used herein, is meant elemental metals as well as their oxides, carbides or other forms of metallic compounds and alloys which have a solid form.

The core of carrier particles in the pre-

drawn embodiment of the present invention, is a ferro-magnetic material, either iron or steel. Other suitable ferromagnetic materials can also be used, e.g. magnetic oxides and alloys of copper-nickel-iron. The size of the core can vary from 40 to 1000 microns, the preferred size range being between 50 and 400 microns.

The fluorotelomer used can be selected from a number of short-chain fluorine compounds having a molecular weight from 3,000 to 30,000. Fluorotelomers are white, waxy short chain compounds of tetrafluoroethylene with a particle size of 5 - 30 JU and a sharp melting point.

It should be noted that said fluorotelomers are different from long chain polymers, such as polytetrafluoroethylene available from DuPont under the trademark "TEFLON". Examples of commercially available fluorotelomers are "VYDAX AR, VYDAX 5100, VYDAX 550 and VYDAX 1000 (DuPont Petroleum Chemicals, Wilmington, Delaware 19898) U.S.A." which are telomeres dispersed in a suitable solvent.

The first three have the same telomeres dispersed in trichlorotrifluoroethane, the differences being solely in the content of solids. The percentage by weight of fluorotelomeres in these products is as follows: VYDAX AR - 20%, VYDAX 5100 - 10% and VYDAX 550" - 5%. The special telomere used in these products has a density of 2.16 g/cm"^ at 25°C, a softening point of .265°C, a sharp melting point of 300°C

and a molecular weight of approx. 3700. VYDAX 1000 is a 7.5% dispersion of a fluorotelomer in CC^F- CC1F2 and the fluorotelomer

has a density of 2.11 g/cm^ at 25°C, a softening point

of 322°C, a melting point of 325°C and a molecular weight of

about. 25,000. Other properties of these commercially available products are listed in DuPont Bulletin V-3 and Bulletin Y-1. See also M.L. Miller "The Structure of Polymers", Reinhold Publishing Corp. (1966).

Many organic solvents can

is used for the purpose of dispersing a telomere. Examples of suitable solvents are trichlorotrifluoroethane, (which is the preferred solvent) trichloroethane, methyl chloride, perchlorethylene, trichloroethylene, toluenebenzene or combina-

tions of these.

As core material, ANCOR STEEL 1000 S (-80/+230 mesh) Hoeganaes Inc. Riverton, New Jersey is usually used. Spheroidal iron powders from Nuclear Metals Division Whittaker, Concord, Massachusetts have also been used with success. André core materials that can also be used with good results include cobalt and nickel.

Commonly known toners can be used together with'' fluorotelomer-treated carrier particles. Examples of such

. commercial toners are ISC 100 g-14A toner manufactured by Imaging Systems Corp., (hereinafter referred to as ISC toner)

Toner 67-146 manufactured by Phillip A. Hunt Chemical Corp., and IBM Toner H 1162058. A non-commercial toner used with fluorotelomer-treated carriers was a composition of 45.5 parts styrene-butyl methacrylate copolymer, 45 parts PLIOLITE VTL (Goodyear Chemicals) 6 parts mogul-L

(Cabot Corp.) and 3 parts nigrosine base NB (GAF Corp.) This non-commercial toner is hereinafter referred to as

PB tones. The produced toner concentrate in the developer mixture is between 1 and 3%, with the rest being fluorine-telomer-treated powder.

A fluorotelomer treatment of the carrier particles can be performed by dispersing a fluorotelomer in an organic solvent such as trichlorotrifluoroethane. The core material is added to the dispersion and mixed on rollers for approx.

30 to 45 minutes. The mixture is then filtered and dried. The nuclear material was heated to slightly above the melting point of the telomere. This heating causes the telomere to melt and lay itself over the carrier particles, which then acquire a protective layer upon cooling. The thickness of the coating can be from 102 to 25 microns, preferred thickness range is from 1-5 microns.

In certain cases it may be desirable

to perform this heating step in a protective atmosphere. For example, when using a copying machine where the toning-density control is based on light reflection, then it

important to evenly maintain the color of the carrier material. When the heating step is carried out in air, oxidation of the surfaces can occur, resulting in color variations. To prevent such color variation, a protective atmosphere can be used. Examples of such protective atmospheres are hydrogen, helium, argon, exothermic gases and endothermic gases.

Preferably, fluorotelomer treated carrier particles are mixed with a toner in a ratio of 98:2 respectively. This ratio is based on the weight, and the same applies to all ratios and percentages in it" below. Developer powders were evaluated using the following tests: A. Faraday cup measurement: these were performed as a function of fluorotelbmer treatment and exposure over different humidity conditions. It gives a charge to mass measurement that indicates the effectiveness of the treatment. B. Step field measurement: this gives an indication of developer powder etel toning properties. Electrically isolated spots with a diameter of 1 cm were charged to potentials of increasing voltage in steps of 10 V. The spots were then fully developed with the developer powder from a manual magnetic brush. The stains were then judged for density in the impression and other visually observable properties. C. Machine evaluation of the developer powder in a common paper copier such as PBC Copier, Copier Division, Pitney-Bowes, Inc. Danbury, Conn.

Ideally, one would prefer to have no drop in charge to mass ratio at high relative humidity.

Example I

A control sample without protective coating was first prepared for comparative purposes, and here 100 g of ANCOR STEEL 1000 iron powder (Hoeganaes Corp.) Riverton, N.J. with a mesh size from -100/+2 50 heated to 300°C for 30 minutes in air. After cooling in the atmosphere, it was found that the iron had turned blue due to surface oxidation. A 2.4% toner mixture was produced using ISC toners and the charge to mass (C/M) was measured at 10 JA coul/gm. By way of comparison, unheated Ancor Steel 1000 powder gives a C/M of 10.5/{ coul/gm.

Example II

A quantity of 4 kg of ANCOR STEEL 1000 iron powder was placed in a dispersion of 20.5 g of Vydax AR in 700 cm<3>FREON TF (trichlorotrifluoroethane) and 100 cm<3>FREON-11 (tri'-chlorofluoromethane). The ingredients were mixed for 1/2 hour on rollers and then filtered. The solvent was evaporated until the iron powder was dry. A small portion of 2.4 ISC toner mixture was prepared using 100 g of the dry mixture and the C/M was measured to be 15 Jt coul/gram. The remainder of the treated iron powder was heated to 300°C for 15 minutes to melt the telomere thereby forming a coating. The powder was again cooled and again a 2.4% ISC toner mixture was prepared. C/M was this time measured at 2A^ U coul/gram.

Example III

4 kg of the ANCOR STEEL 1000 powder was added to a dispersion of 8 g of VYDAX 550 in 700 cm 3 of FREON TF solvent and 100 cm 3 of FREON-11 solvent and mixed for 1/2 hour. The mixture was then filtered and dried. Again, a 100 g batch of 2.4% ISC toner mix was prepared and the C/M was measured to be 15 µCoul/gram. The rest of the treated iron powder was heated to 300°C for 15 minutes, cooled and.

again a 2.4% ISC toner blend was prepared. C/M was this time measured at 24y^ coul/gram.

Examples IV - VI

The following varying concentrations of VYDAX AR in the solvent from Examples II and III were prepared and coated on iron powder.

IV) 0.16% VYDAX AR

V) 0.2 8% VYDAX AR.

VI) 1.0% VYDAX AR.

Compositions of 2.4% ISC toner mix were prepared with treated iron powders from Examples IV, V

and VI above and they had C/M ratios of 2 0.3, 21.8 and 22.2 M coul/gram respectively.

Example VII

1/2 gram of VYDAX 1000 was dispersed in 250

cm3 FREON TF and 100 g of iron powder was then added to this.

The treated powder was then heated to 325°C for 10 min.

It was found that a 2.4% ISC toner mix had a C/M on it

16/ U coul/gram.

Example VIII

2 g of VYDAX 1000 in 250 cm3 of FREON TF were used to treat 100 g of iron powder. The treated iron powder was heated to 325°C for 10 min. It was found that a 2.4% ISC Toner Bibreath had a C/M of 25 p.coul/gram.

Example IX

4 kg of ANCOR STEEL 1000 powder and 20.5 g

VYDAX AR was placed in 700 cm<3>FREON TF and 100 cm<3>FREON -.11.

and mixed for 1/2 hour. The mixture was then filtered and dried.

A liter 10 g portion of 2.4% PB toner mix was prepared and the C/M was measured to be 15 coul/gram. The rest of the treated iron powder was heated to 300°C for 15 minutes and cooled.

A 2.4% PB toner mixture was produced. C/M was this time measured at 2AjU coul/gram.

Example X

4 kg ANCOR STEEL 1000 and 20.5 g VYDAX Ar

was added to a mixture of 700 cm<3>FREON TF and 100 cm<3>FREON-11 and mixed for 1/2 hour. The mixture was filtered and dried. One

A 10 g portion of 2.4% ISC toner mix was prepared by

the dry mixture and C/M was measured at 15 JA. coul/gram. The rest of the treated iron powder was heated in an argon atmosphere to 300°C for 15 minutes and then cooled.

Again, a 2.4% ISC toner mixture was produced. C/M was this time measured at 2aJU coul/gram.

Example XI

The same procedure as in example X was used, except that the mixture was heated in a hydrogen atmosphere instead of argon. C/m was again measured

to 24 JU. coul/gram.

Example XII

The same procedure as in examples 10 and 11 was used, except that the mixture was heated in nitrogen instead of argon or hydrogen. Again the C/M was measured to be 24 pi coul/gram.

This coated carrier alloy was used for

to prepare a 2% developer mixture with 67-689. This developer powder was evaluated in a Minolta PPC 1000" copier and good results were obtained.

Example XIII

The same procedure was used as in Examples XI to XII, except that the mixture was heated in helium. C/M was again measured at 2Ap[ ^pil/gram.

Example XIV

100 g cobalt powder - 150/+2 70 mesh was treated with 0.5 g VYDAX AR.in 25 cm<3>FREON 11. After 1/2 hour's mixing, the solvent was poured off the mixture and the powder was dried at 80°C for 100°C for 10 min. The -dried powder was further heated to 300 to 315°C in an oven for 5-10 min. and then cooled. C/M of the treated cobalt powder was determined after mixing with toner at 2.4% concentrate and the value was found to be 2 3.7/^C coul/gram. The unheated cobalt powder under the same conditions gave a C/M of 10.2^ coul/gram.

Example XV

The treatment conditions were the same as in the example. XIV except that nickel powder was used instead of cobalt powder. The C/M of the heated nickel powder was 15.2 Ja coul/gram and the C/M of the unheated nickel powder was 1.1 J/l coul/gram.

The developer powder prepared as indicated in Examples I-XV was used in a PBC copier by conventional techniques. The copies presented in the tests showed good filling, good resolution and low background. In each case, the duplicator was run at 100 V instead of a standard level of 150 V. The lower voltage is possible due to the properties arising from the fluorine-telomer treatment. Furthermore, the extraction of iron powder was reduced to 10% compared to what had previously been obtained without treatment of the carrier particles.

As mentioned earlier, the main advantages of giving the carrier powders a fluorotelomer treatment will be to reduce oxidation, achieve a constant triboelectric charge and achieve low dust formation. During the tests used to determine the effectiveness of the various fluorotelomer coated carrier powders as indicated in Examples I-XV, another advantage was discovered. All of these samples used a copier that uses a photoconductive belt with a zinc oxide coating. It was understood that the duration of this photoconductive belt was significantly longer when it was used together with solid toners, where carrier powders were treated as indicated in the present invention. Although it is not known why the belt had a longer lifespan, it is assumed that the fluorotelomer-coated powder had a lubricating effect.

It should be obvious that the ratio of carrier powder to toner as stated in the above examples is for the developer powder that has just been added to the copying machine, and that the developer powder had to be supplemented with toner and carrier particles as these substances were consumed.

Claims (16)

1. Carrier particle for a developer powder, characterized by -consisting of a core selected from the group consisting of a metal, sand and glass, and wherein said core is coated with fluorotelomer. 2. Carrier particle according to claim 1, characterized in that said core is iron. 3. Carrier particle according to claim 2, characterized in that said core is between 40 and 1000 microns. 4. Carrier particle according to claim 3, characterized in that said core is between 50 and 400 microns. 5. Carrier particle according to claim 1, characterized in that said coating has a thickness of from 1/2 to 25 microns. 6. Method for producing a fluorine-telomer coated carrier particle that can be used in a developer powder, characterized in that: a. dispersing an amount of a fluoro-telomer compound in an organic solvent at a concentration of from 0.01 to 10%, b. places a quantity of the core material in said dispersion, c. mixes the core material and the dispersion, d. separates the solvent, and e. heating the treated carrier platelets to a temperature slightly above the melting point of the telomere. 7. Method according to claim 6, characterized in that said core material is metal, sand or glass. 8. Method according to claim 6, characterized in that said core is a metal selected from the iron group. 9. Method according to claim 8, characterized in that said core is between 40 and 1000 microns. 10. Method according to claim 9, characterized in that said core is between 50 and 400 microns. 11. Method according to claim 6, characterized in that the treated carrier particles are in a protective atmosphere during the heating step. 12. Method according to claim 6, characterized in that said organic solvent is selected from the group consisting of trichlorotrifluoroethane, trichloroethane, trichlorofluoromethane, methyl chloride, toluene, hextane, perchloroethulene and trichloroethylene. 13. Electrostatic imaging process, characterized by forming an electrostatic latent image on a recording surface and contacting said electrostatic latent image with a developer powder consisting of finely divided toner particles, electrostatically bound to the surface of the carrier particles, and where said carrier particles consist of a core material coated with a fluorotelomer. 14. Method according to claim 13, characterized in that said core material is made of metal, sand or glass. 15. Method according to claim 13, characterized in that said core is of a metal selected from the iron group. 16. Method according to claim 14, characterized in that said core is between 40 and 1000 microns.