CA1080534A - Carrier particle with core of metal, sand or glass and coating of telomer of tetrafluoroethylene - Google Patents

Abstract

Abstract of the Disclosure Disclosed is a treatment of carrier powders with fluorotelomers. A fluorotelomer is dispersed in a solvent, then the carrier powder is added to and agitated with the solution. The solvent is then decanted and evaporated and the carrier powder is heated to a temperature slightly above the melting point of the flourotelomer to coat the carrier surface. Carrier powders treated in this manner have particular utility as carrier particles for development powders in magnetic brush and cascading units of electrophotography copier equipment.

Description

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Background of the_Invention With the increased use of bond paper copiers, development powders have enjoyed an increased popularity over liquid toners. Along with the increased use of development powders, magnetic brush units are ~ecoming increasingly popular and units using cascading methods are still frequently employed.
Such units usually have a carrier powder, such as iron powder, which serves as the carrier material. Inexpensive, untreated carrier powders cannot be used in magnetic brush systems since such carrier powders may have insufficient stability toward rusting, lack color stability, or triboelectric charge properties which are adversely effected by variable humidity conditions. In order to solve these problems, those in the art have resorted to chemical plating and coating of the carrier particles with polymers, oils, waxes and the like.
Prior art developer materials, which are employed in automatic copy machines, have carrier filming problems due to the mechanical rubbing of the carrier surface with the soft toner resins. The gradual accumulation of permanently attached film impairs the normal triboelectric charging of the toner particles in the toner mix. As I result, the toner is either less highly charged or sometimes oppositèly charged giving rise to poor copy quality with a high degree of background.
}n the literature, several ways of treating, coating and electroplating the carrier partizle ha-e been suggested to overcome the filming problems. Examples of such carrier particle modifications are found in U.S. Patents 3,725,118;
3,736,257; 3,778,262; 3,795,618 and 3,849,127. Most of :

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the prior art coating methods result in high cost and have other dis~dvantages such as yielding improper triboelectric charge properties and imparting a very high eleetrieal resistanee to the carrier that reduces its development electrode effect and results in poorly filled-in large image areas.
Summarv of the Invention In the art of electrostatographic imaging pcoeessing, an electrostatic latent image is formed on a recording surface of a photoconductor. The electrostatic image may then be developed by finely-divided toner particles electrostatically attached to the surface of carrier particles. Preferab the earrier particles are iron powder or beads.
It has been found that a simple fluorotelomer adsorption treatment of iron powder from a solvent produces a treated carrier particle which has good stability to rusting under high relative humidity, a constant triboeleetric eharge property under all conditions when mixed w1th standard toners, very low dusting of the toner in a magnetic brush unit and allows the use of lower reverse biased voltage during development whieh improves copy guality and the reliability of maehine performance.
~y using the fluorotelomer treated earrier partieles of this invention, an improved eleetrophotoqraphic proeess is obtained, wherein a latent electrostatic image is contacted with a developer mixture which includes the treated carrier '' particles.
- The method of producing fluorotelomer treated carrier partieles involves dispersing a fluorotelomer in an organie solvent such as trichlorotrifluoroethane in a concentration of 0.01 to 10~. The eore material is plaeed into the solution, - T
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the core material being selected from either metal, sand, or glass.
The solution is decanted and allowed to dry a~ter which the treated carrier particles is heated to a temperature of 250 to 350 degrees centigrade. It will be appreciated that this treatment is appre-ciably simpler than previously disclosed methods of treating or coating core particles.
In one particular aspect the present invention provides a carrier particle for a development powder comprising a core selected from the group consisting of metal, sand and glass, said core being coated with fluorotelomer having a molecular weight of 3,000 to 30,000.
In another particular aspect the present invention provides in a method of producing a fluorotelomer coated carrier particle for use in a development powder, the steps comprising: a) dispersing a quantity of fluorotelomer compound in an organic solvent in a weight - - concentration of 0.01 to 10%; b) placing a quantity of core material into said dispersion; c) mixing the core material and dispersion;
d) decanting the solvent, and e) heating the treated carrier partlcles to a temperature slightly above the melting point of the telomer.
In a further particular aspect the present invention provides an electrostatographic imaging process comprising the steps of forming an electrostatic latent image on a recording surface and contacting said electrostatic latent image with a development powder ; comprising finely-divided toner particles electrostatically attached to the surface of carrier particles, said carrier particles com-prising a core material being coated with a fluorotelomer having a molecular weight of 3,000 to 30,000.
Description of the Preferred Embodiment The core of the carrier particle formed by the present .~
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invention may be a~y material which can react chemically with the fluorotelomer compounds of this inventlon. Thus, by way of example, the material of the core of the carrier particle may be sand, glass beads, metallic beads or metallic powders. As used in this specif-ication, including the appended claims, the term metal and metallic is intended to $nclude elemental metals as well as their oxides, carbides and other forms of metallic compounds and alloys which have a solid form.
The core of carrier particles of the preferred embodiment is a ferromagnetic material such as iron or steel. Other suitable ferromagnetic materials such as magnetic oxides and alloys of copper-nickel-iron, for example, also may be employed. The size of the core may be between 40 and 1000 microns with the preferred size range being between 50 and 400 microns.
The fluorotelomer may be selected from a number of short chain fluoro compounds having a molecular weight of 3,000 to 30,000.

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Fluorotelomers are white, waxy short-chain compounds of tetrafluoro-ethylene having a particle size of 5 - 30~ and a sharp melting point.

It should be noted that fluorotelomers are different from long chain polymers .

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such as polytetrafluoroethylene available from DuPont under the trademark TEFLON. Examples of commercially available fluorotelomers are VYDAX AR, VYDAX 5100, VYDAX~550 and VYDAX
looo lDuPont Petroleum Chemicals, Wilmington, Delaware 198983 which are telomers dispersed in an appropriate solvent.
The first three have the same telomers dispersed in trichloro-trifluoroethane, the difference being in solid content.
The weight percent of flourotelomers in these formulations are as follows: VYDAX AR - 20~, VYDAX 5100 - 10~ and VYDA
550 - 5~. The particular telomer used in these formulations has density of 2.16 gm/cc at 25 aegrees centigrade, a softening point of 265 degrees centigrade, a sharp melting point of 300 degrees centigrade and a molecular weight of approximately 3,700. The VYDAX~ 000 is a 7.5~ dispersion of a fluorotelomer in CCl2F - CClF2 which fluorotelomer has a density of 2.il gm/cc at 25 degrees centigrade, a softening point of 322 degrees centigrade, a melting point of 325 degrees centigrade and a molecular weight of approximately 25,000. Other properties of these commercially available materials are given in DuPont Bulletin V-3 and Bulletin Y-i. Also see M.L. Miller nThe Structure of Polymers" - Reinhold Publishing Corp. (1966).
~ lany organic solvents may be employed for the purpose of dispersing a telomer. Examples of such solvents are trichlorotrifluoroethane, (which is the preferred solvent), trichloroethane, methyl chloride, perchloroethylene, trichloro-ethylene, toluene benzene, or combinations thereof.
As a core material, ANCOR STEEL 1000S (-80/+230 mesh) Hoegenaes, Inc., Riverton, New Jersey was used. Spherical iron powder from Nuclear Metals Division Whittaker, Concord, ., .
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Commercial toners may be used in conjunction with fluorotelomer treated carrier particles. Examples of such commerical toners are ISC lOOg-14A toner made by Imaging Systems Corp., (hereinafter referred to as ISC toner) Toner ~67-146 made by Phillip A. Hunt Chemical Corp., and IBM
Toner ~ 1162058. A non-commercial toner used in combiantion with fluorotelomer treated carrier particle was a composition or 45.5 parts styrene-butylmethacrylate copolymer, 45.5 parts PLIOLITE VTL (Goodyear Chemicals) 6 parts mogul-L
(Cabot Corp.) and 3 parts nigrosine base ~B ~GAF Corp.).
This non-commercial toner is hereinafter referred to as ; PB toner. The prepared toner concentrate in the developer mix is between 1 and 3%, the balance being fluorotelomer treated powder.
One of the fluorotelomer treatment of the carrier particle is accomplished by dispersing a fluorotelomer in an organic solvent such as trichlorotrifluoroethane. The core material is added to the dispersion and mixed on rollers for about 30 to 45 minutes. Subsequently t:e mixture is filtered and dried. The treated core material is heated to slightly above the melting point of the telomer. The heatlng step melts the telomer and causes it to coat the carrier particles so that upon cooling, a protective layer is provided. The coating thickness may be 1/2 to 25 microns with the preferred coating thickness being 1-5 microns. -In some instances it may be desirable to carry outthis heating step in a protective atmosphere. For example, , . .

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where a copier uses toner density control based on light reflectance, it is important to uniformly maintain the color of the carrier. When the heating step is conducted in air, oxidation of the surfaces occurs which results in color variations. Thus to prevent such color changes, a protective atmosphere may be used. Examples of such protective atmospheres are hydrogen, helium, argon, exothermic gas and endothermic gas.
Preferably the fluorotelomer treated carrier particle is mixed with a toner at a ratio of 98:2 respectively.
These ratios are based on weight as are all ratio and percentage figures in this specification. The developer powder is evaluated using the foilowing tests:
A. Faraday Cup measurement: these are carried out as a function of fluorotelomer treatment and exposure to various humidity conditions. It yields a charge ; to mass measurement that indicates the effectiveness of the treatment.
B. Step tablet measurements: this gives an indication as to toning characteristics of the developer powder.
Electrically insulated spots of 1 cm in diameter are back charged in potentials of increasing voltage in increments of 10 V. These spots are developed to completion with the development powders from a manual magnetic brush. The spots are evaluated for print density fill in and other visually observable characteristics.
C. Machine evaluation of the developer powdee in a plain paper copier such as the PBC Copier, Copier Division, Pitney-Bowes, Inc., Danbury, Conn.

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Ideally one would like to have no drop in charge to mass ratio at high relative hùmidity.

Example I
A control sample having no protective coating was first prepared for purposes of comparison wherein 100 grams of A~CO~ STEEL 1000 iron powder (Hoeganaes Corp.), Riverton, N.J., having a mesh size of -l00/+250 is heated to 300 degrees centigrade for 30 minutes in air. After cooling in the atmosphere it was found that the iron turns blue due to sùrface oxidation. A 2.4~ toner mixture using ISC toner was made and the charge to mass (C/M) was measured at 10 coul/gm. By 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 gram~ of Vydax AR in 700 CC FREO F (trichlorotrifluoroethane) and 100 CC FREON-ll ~trichlorofluoromethane). The ingredients were mixed for 1/2 hour on rollers and filtered. The solvent was evaporated until the iron powder was dry. A small batch of 2.4~ ISC
toner mixture was made using 100 gm. of the dried mixture and the C/M was mèasured in at 15 ~coul/gram. The rest of the treated iron powder was heated to 3D0 degrees centigrade for 15 minutes to melt the telomer in order to form a coating.
It was cooled and aqain a 2.4% ISC toner nixture was made.
The C/M was measured as 24~ c ul/gram.

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Example III

A 4 ~g quantity of ANCOR sTEeL 1000 powder was added (~) (~) .
~i to a dispersion of 8 grams VYDAX 550 in 700 CC FREON TF
solvent and 100 CC FREON-ll solvent and mixed for 1/2 hour on rollers. This mixture was then filtered and dried. Again, a 100 gm batch of 2.4% ISC toner ~ixture was made and the C/M was measured at 15~coul/gram. The rest of the treated iron powder was heated to 300 degrees centigrade for 15 minutes, cooled and again a 2 . 4% ISC toner mixture was made.
The C/M was mea~ured as 24 ~ coul/~ram.

Examples IV - VI ~
The following various concentrates of VYDAX AR
in the solvent of Examples II and III were produced and coated on iron powder.
IV) 0.16% of VYDAX AR.
V) 0.28% of VYDAX AR.
VI) 1.0% of VYDA ~AR.
Groups of 2.4~ ISC toner mixture were made with treated iron powders from IV, V, VI above and they had C/~ ratios of 20.3, 21.8 and 22.2 ~ coul/gram respectively.

Example VII
O~e half gram of VYDA ~l000 was dispersed in 250 CC FREON TF and to that was added 100 gms. of iron powder.
The treated iron was heated to 325 degrees centigrade for ten minutes. A 2. 4% ISC toner mixture was found to have a C/M of 16 ~ coul/gram.

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Example VIII
Two grams of VYDAX 1000 in 250 CC of FREON TF was used in treating 100 grams of iron powder. The treated iron powder was heated to 325 degrees centigrade for ten minutes. A 2.4~ ISC toner mixture was found to have a C/M
of 25 ~coul/gram.
' Example IX
Four kg of ANCOR STEEL 1000 powder and 20.5 grams_ VYDAX Ar were placed in 700 CC FREON TF and 100 CC FREON-ll and mixed for 1/2 hour on rollers. The mixture was then filtered and dried. A small 10 gm. batch of 2.4% PB toner mixture was made and the C/i~ measured at 15 coul/gram.
The balance of the treated iron powder was heated to 300 degrees centigrade for 15 minutes and cooled. A 2.4% PB
toner mixture was made. The C/N was measured as 24 ~ coul/gram.

Example X
Four kg of ANCOR STEEL 1000 and 20.5 grams of VYDAX
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Ar were added to a blend of 700 CC FREON TF and 100 CC FREON-ll and mixed for 1/2 hour on rollers. The mixture was filtered and dried. A ten gram batch with 2.4~ ISC toner mixture was made with the dried mixture and the C/M was measured at 15~ coul/gram. The rest of the treated iron powder was heated in argon atmosphere to 300 degrPes centigrade for 15 minutes and coolad. Again, a 2.4% ISC toner mixture was made. The C/M was measured as 24 ~ coul/gram.

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Example XI
The same procedure as Example X was followed except that the mixture was heated in a hydrogen atmosphere instead o argon. The C/M was again measured as 24 ~ coul/gram.

Example XII
The same procedure as in Example X and XI were followed except that the mixture was heated in nitrogen instead of argon or hydrogen. Once more the C/M was measured as 24 coul/gram.
; This coated carrier material was used to make a 2%
developer mixture with Hunt toner 67-689. This development powder was evaluated in a Minolta PPC 1000 copier and good results were achieved.

Example XIII
The same procedures as in Examples XI-XII were followed except that the mixture was heated in helium. The C/M was again measured as 24 ~ coul/gram.

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Example XIV
One hundred grams of Cobalt powder -150/1270 mesh was treated with 0.5 gram VYDAX AR in 25 CC of FREON 11.
After 30 minutes of mixing, the mixture was decanted and the cobalt powder dried at 80 degrees centigrade -100 degrees -~j centigrade for ten minutes. The dried powder was further heated to 575 degrees fahrenheit -600 degrees fahrenheit ~ in a furnace for 5-10 minutes and cooled. The C/M of treated I cobalt powder was determined when mixed with toner at 2.4%

concentrate and was found to be 23.7 ~ coul/gram. The unheated cobalt powder under the same conditions gave a C/M of 10.2 cou~/gram.

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Treatment conditions similar to that or Example XIV
were repeated except that nickel powder was used instead of cobalt. The C/M of heated nickel powder was 15.2 ~ coul/gram and the C/M of unheated nickel powder was 7.1~ coul/gram.
Development powders produced in accordance with the above Examples I-XV were utilized in a PBC Copier in accordance with standard techniques. Copies produced in those runs showed good fill-in, good resolution and low background.
The copier in each instance was operated at -100 volts bias instead of the standard level of 150 volts. The lower bias is possible because of the characteristics resulting from the fluorotelomer treatment. Additionally, iron pull-out was reduced to 10~ of what was previously experienced without any treatment of the carrier particles.
As stated previously, the primary advantages to giving carrier powders a fluorotelomer teeatment are to reduce oxidation, obtain a constant triboelectric charge and to achieve low dusting. During the tests to determine the effectiveness of the various fluoroterlomer coated carrier materials disclosed in Examples I-XV, another advantage was found. All the tests utilized a copier which uses a photoconductive belt having a zinc oxide coating. It was found that the life of the photoconductive belt was e~tended considerably when used in cooperation with solid toners having carrier powders treated in accordance with the instant invention. Although the reason for the extended life of the belt is not known, it is believed that the fluoro-telomer coating~ have a lubricating e~fect.
It will be appreciated that the ratios of carrier .~ " ' 1 ': . . ; . ;. : : . ' . ' . ' ~' ' ~
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~08~534 po~der to toner ~isclosed in the above examples are for devclopmcllt l-owdcrs ncwly char~cd to a copier and that the development powder llad to be replenished with toner and carrier particles in proper proportion as the same were consumed.

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Claims (14)

E EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
ROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A carrier particle for a development powder comprising a core selected from the group consisting of metal, sand and glass, said core being coated with a telomer of tetrafluoroethylene having a molecular weight of 3,000 to 30,000.

2. The carrier particle of Claim 1 wherein said core is iron.

3. The carrier particle of Claim 2 wherein said core is between 40 and 1000 microns.

4. The carrier particle of Claim 3 wherein said core is between 50 and 400 microns.

5. The carrier particle of Claim 1 wherein said coating thickness is 1/2 to 25 microns.

6. In a method of producing a carrier particle of metal, sand or glass coated with a telomer of tetrafluoroethylene having a molecular weight of 3,000 to 30,000 for use in a development powder, the steps comprising:
a) dispersing a quantity of fluorotelomer compound in an organic solvent in a weight concentration of 0.01 to 10%;
b) placing a quantity of core material formed of metal, sand or glass into said dispersion;
c) mixing the core material and dispersion;
d) decanting the solvent; and e) heating the treated carrier particles to a temperature slightly above the melting point of the telomer.

7. The method of Claim 6 wherein said core is ferromagnetic material.

8. The method of Claim 7 wherein said core is between 40 and 1000 microns.

9. The method of Claim 8 wherein said core is between 50 and 400 microns.

10. The method of Claim 6 wherein the treated carrier particles are in a protective atmosphere during the heating step.

11. The method of Claim 6 wherein said organic solvent is selected from the group consisting of trichlorotrifluoro ethane, trichloroethane, trichlorofluoromethane, methyl chloride, toluene, hexane, perchloroethylene and trichloroethylene.

12. An electrostatographic imaging process comprising the steps of forming an electrostatic latent image on a recording surface and contacting said electrostatic latent image with a development powder comprising finely-divided toner particles electrostatically attached to the surface of carrier particles, said carrier particles comprising a metal, sand or glass core material being coated with a telomer of tetrafluoroethylene having a molecular weight of 3,000 to 30,000.

13. The process of Claim 12 wherein said core is a ferromagnetic material.

14. The process of Claim 13 wherein said core is between 40 and 1000 microns.