DE2052169A1 - - Google Patents

Description

'Patent Attorneys * - ~

Xerox Corporation Dipl.Ing.F.Weickmann, " _{z # 482}

Rochester, Hew York 14603 DlpUnQ.H.Welckroann, DIpI Ph ^ rR- _{(xD / l6 /} ; ₅₎

Oiol Ina F. A. Weickmann, Dipl. Cham. B. hudbf 8 Munich 27, Höhlstr. 22nd

Process for the production of spherical glass beads and their use as a carrier for electrostatographic developers

The invention is in the field of electrostatography and relates to an improved process for the production of spherical glass beads which are used as supports for electrostatographic Developers are suitable.

Xerography is an example of an electrostatographic Procedure. The basic xerographic process as described by G. F. Carlson in U.S. Patent No. 2,297,691 consists in applying a uniform electrostatic charge to a photoconductive insulating layer and the Exposing the layer to a light-and-echatteri image, causing the Charge on the exposed steeper. ' the layer is distributed; the resulting electrostatic latent image is then developed, ' by using a finely divided? electroscopic material (den so-called "toner") is reflected on it. The "toner" becomes normalerv / ei.se attracted by belaclonen parts of the layer, creating a an image corresponding to the latent-electrostatic image is created, which can then be transferred to a carrier, ie paper. The transfer * :! Image is usually created by heat on the Wearing ro be rf pool fixed; but this step can go through other fixatives, such as disability with dissolving. ;; c; with teln or Ü, has been replaced.

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There are many methods known to make the electroscopic Particles on the z: i developing, latent electrostatic image to raise. A development method such as that proposed by E.N. '»Vise in U.S. Patent No. 2,618,552, the so-called. "cascade" -Eritwicklurig. Here is the developer material of relatively large carrier particles which contain finely divided "toner" particles adhering to their surface. the This developer is applied to the surface carrying the latent electrostatic image in a cascade manner Roll. The composition of the "toner" particles will be like this chosen so that it is opposite to the carrier particles have triboelectric polarity. So Y / ern you get a negative If you want to develop a loaded% fextfostatic image, you have to have a Select electroscopic powder and carrier combination in which the powder is triboelectrically positive with respect to the carrier. Conversely, in order to develop a positively charged electrostatic latent image, one must develop an electroscopic one Choose powder and carrier where the powder is triboelectrically negative with respect to the carrier. This triboelectric Powder and carrier relationships depend on their relative positions in the triboelectric series; there are those Materials arranged in such a way that each substance is positively charged electrically when it is in line with one below it Substance comes into contact - and vice versa, it has a negative electrical charge when it comes into contact with someone standing in a row above it Substance has contact. Whom the developer about the the picture trager.de surface is rolled, the "toner" particles are electrostatically deposited and held by the loaded parts of the latent images », while they are not on the non-loaded, so-called" background "parts of the image get knocked down. Most of the "tpner" particles, which accidentally located on the "background" are removed by the rolling carrier; this is obviously based on the grüiior \! n electrostatic attraction between dom "toner" and to Trngor (compared to attraction between "toner" and unbelaifmorn "background"). The carrier parts and the non-

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used "toner" particles are then recycled. This technique is particularly suitable for developing line copies. The so-called "cascade" development is the most widely used xerographic development technique in commerce; a multipurpose office copier based on this is described in U.S. Patent No. 3,099,943.

The "cascade" development technique involves leaving the carrier particles Roll over the image-bearing surface so that its gravitational force or inertia is greater than the force of attraction the "toner" in the image-bearing surface parts which retain the "toner"; this prevents that the carrier particles adhere to the retained "toner" particles. So the carrier particles should easily over the Image-bearing surface can flow without having to take special means to remove the carrier material from the image-bearing Remove surface.

Glass beads are commonly used with electrostatographic development carriers; around the rolling of the carrier on To facilitate the image-bearing surface, these Pgrlen should be as spherical as possible.

The subject of the invention is an improved method for the production of spherical glass beads for use in electrostatographic developers.

Another object is an improved method for obtaining an electrostatographic development carrier.

Another object is to achieve a more uniform size in spherical glass beads.

Finally, it is an object of the present invention to develop an electrostatographic latent image to improve.

BADOR ₁ Q ₁ NAl.

These and other subjects of the invention are explained in more detail in the following description.

To carry out the method according to the invention finely divided glass applied to a non-wetting ceramic support in such a way that the individual glass parts are isolated from each other, whereupon the glass is heated to a temperature at which the particles irifo'lge their Surface tension can be pulled up as practically spherical pearls. These spherical glass beads are then used in a electrostatographic development carrier used.

The glass used as a starting material in the present invention can be any of a large number of types of glass; E.g. glasses based on soda-lime-silica, lead or barium glasses etc. can be used, both in solid as well as in molten form. If you start from solid glass, then it has to be sieved to the desired size to be brought. In the case of molten glass, the desired size is obtained by evenly cutting off a controlled one molten glass stream emerging from a continuously operating glass melting furnace. By choice A suitable opening size in the glass melting furnace was also used here to determine the size of the molten glass particles influence.

It depends on the particle size of the solid or molten glass which is used as the starting material Particle size of the spherical glass beads produced therefrom. Usually the support material for xerographic Developers have a particle size of about 30-1000 microns; therefore, the particle size is called the "starting material." The glass used is adjusted so that the end product has a particle size suitable for xerographic developer carriers

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The solid or molten glass used as the starting material, which has the appropriate particle size, is then applied to a non-usable ceramic block, ie to a ceramic support to which the glass does not adhere, namely "in such a way that the individual particles stick together Do not touch; this prevents two or more particles from fusing, which would reduce the yield of individual spherical particles. Graphite, chromium oxide, iron oxide, zirconium oxide, aluminum oxide, and other non-wetting ceramic materials can be used for the production of such a block Use tones. (

According to a preferred embodiment of the present invention

Invention contains the surface of the ceramic block on which the glass particles are to be applied, many small impressions which are so large that they can accommodate a single glass particle; in this way each individual particle is best separated from the neighboring particles. These impressions are preferably conical in shape so that the manufacture of spherical beads is facilitated; they can be arranged on the surface of the block in any shape, provided that they are spaced from one another by a sufficient distance so that the individual glass particles are separated. The production . i of suitable impressions on the block for isolating the individual glass particles should be readily possible for a person skilled in the art on the basis of the explanations given here; For a full understanding of the present invention, therefore, no further details need to be given.

The separate Gla3teilchen on the non-wetting ceramic block are now heated to a Tonperatur, wherein the viscosity of the glass is sufficiently reduced 'so that the surface tension can draw the glass particles in spherical bead form. The temperature required for this

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depends on the type of glass used; Here, too, it should be within the scope of the skilled person to select a suitable temperature that allows the glass to pull up as spherical pearls. Typically, heating the glass particles to temperatures of about 65O ⁰ C - 1200 ⁰ C, preferably about 900 to 1000 ⁰ C, at these temperatures, the glass particles rapidly form spherical beads, usually in about 2-5 minutes.

The heating of the glass particles can take place in one of the many types of ovens, and any heat sources can be used; the selection of a suitable apparatus should be readily possible for the person skilled in the art controlled tunnel furnace; the usual types include a preheating, spherodizing, tempering and cooling zone. The non-wetting ceramic block, which contains the glass particles of the appropriate size, is conveyed through the individual zones of the furnace in sequence, whereby the whole process is controlled.

^{After the glass beads have formed 1} on the ceramic block, the beads are left to cool on the block to a temperature at which they solidify; ie the pearls must not have a temperature at which they stick to one another or to other particles. Usually allowed to the beads initially to a temperature of about 1000 - 300 ⁰ C or lower to cool, after which they transferred into suitable containers for subsequent classification by size.

The spherical glass beads produced as described above can then be used in the usual way as core material for a electrostatographic developer carriers can be used. So the gin pearls can be covered with a suitable coating

109819/176? ^BATH

which is necessary for an electrostatographic developer carrier, imparts necessary triboelectric properties; i.e., the carrier properly charges the "toner" when with it is mixed. Any of a large number of coating agents can be used as the coating material for the glass beads, as used in electrostatographic developer carriers, usually plastics, e.g. polyolefins, such as polyethylene, polypropylene etc., vinyl and vinylidene resins such as styrene, vinyl chloride, vinyl acetate, acrylonitrile, Methyl methacrylate resins, phenolic plastics, such as phenol formaldehyde etc., amine resins such as melamine formaldehyde etc. (

The coating is carried out using one of the known methods, e.g. by spraying, dipping, in a fluidized bed, by centrifuging. Brushes etc./After a process, the glass beads with coated with a binding intermediate layer and the coated core then added to the dry synthetic resin with which the glass beads to be coated; here the resinous coating material adheres to the coated glass bead and thus forms a coating that fused with the carnation material or is somehow stuck together. The manufacture of electrostatographic supports is described in more detail in U.S. Patent Kr. 2 618 551 (Walkup).,

The glass beads produced according to the invention can also be used as uncoated electrostatographic developer carriers be used. For example, the US application Ko. 17 877/68 described glass compositions for the Production of non-coated supports are suitable, converted into spherical glass beads by a process according to the invention '.verden.

Any of the large number of "toner" materials that can be used as the developer "toner" particles commonly used in developer compositions.

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Representative examples of typical "toner" materials are: copal gum, sandarac gum, synthetic resins, coumarone-indene resins, Asphalt, gilsonite, phenol-formaldehyde resins, synthetic resin-coated phenol-formaldehyde resins, methacrylic resins, Polystyrene resins, polypropylene resins, epoxy resins, polyethylene resins p and their mixtures. Reference is made in this connection to U.S. Patents No. 2,659,670 (Copley), 2,753,308 (Landrigan), 3 079 342 (Insalaco), Re issue-Kr. 25,136 (Carlson ") and 2,788 (Rheinfrank et al.).

The ⁿ⁴ ".on3r" contains a pigment or a dye in such an amount that it is sufficient to color the "toner"; Usually about 1 - 10 GeW-fo based on the "toner" are sufficient. Any pigment or dye of the wide variety of useful materials may be used; The only requirement is that it does not adversely affect the properties of the "toner". Carbon, commercially available red, blue or yellow dyes, for example, can be used. Since these dyes and / or pigments are known in the art of xerography, a detailed list of such dyes or pigments is superfluous. The "toner" is produced by thoroughly mixing the various components until a uniform dispersion of the dye or pigment in the "toner" material has arisen. The "toner" material is then finely divided, e.g., to a particle size of less than 30 microns, preferably about 2-10 microns average particle size. The manufacture of "toner '^ compositions is well known to the person skilled in the art, so that within the scope of the

present application, a detailed description is superfluous. \.

φ <

The ^TF toner "~ particles are mixed with the carrier, wherein diecer receives a charge which is opposite to the polarity of the carrier; characterized adhere the" toner "particles on the support and envelop ihn.Das extent of the contrast as well as other

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Photographic properties of the finished image can partly changed v / ground by changing the proportions of carrier material and "toner", the selection being more optimal The skilled person is familiar with conditions. Usually the ratio of carrier to "toner" is about 250: 1 to 25: 1, depending on the material.

The one produced by the method according to the invention Electrostatic developer can be used to develop an electrostatic latent image, also using the usual methods of application. So are these new ones Developer especially in "cascade" development technology the xerographic process as described above is useful.

The invention is described in more detail in the following examples; these examples explain preferred embodiments and are not intended to limit the scope of the invention.

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B is ρ ie 1

Crushed soda-lime glass with a particle size of 20-35 mesh is placed on a non-wetting ceramic block of chromium oxide in such a way that the individual particles do not touch one another. The block will turn into a
controlled muffle furnace of 1010 ⁰ C and left for 5 minutes until the glass particles softened
have that the surface tension forces the glass particles to assume a spherical shape.

The spherical glass beads are removed from the oven, cooled and given a resin coating, the im
Example 1 of U.S. Patent No. 2,613,551 (V / alkup) can be used.

The coated yi carrier is then coated with a "toner"
mixed, which consists of a styrene- (η-butyl) methacrylate copolymer, polyvinyl butyral and carbon (cf. Example 1 of US Pat. No. 3,079,342 (Insalaco)
Composition contains approx. 1 wt .- $ "toner". If you leave this
Rolling developers according to the "cascade" method over a latent electrostatic image, which is located on a xerographic plate, results in good development with minimal precipitation in the "background".

In game 2

Crushed flint glass with a particle size before.
20-25 mesh is applied to a non-wetting ceramic block made of graphite, in such a way that the individual parts do not touch me. The block is in a control

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placed muffle furnace of 732 ⁰ C and left in it for 4 minutes until'die Glasteilcher. are softened to the extent that the surface tension forces the glass particles into a spherical shape. The spherical glass beads are then removed from the oven and allowed to cool.

The glass beads are now mixed with a "torier" made from a styrene (η-butyl) methacrylate copolymer, polyvinyl butyral and carbon (see Example 1 of US patent Kr. 3,079,342 (Insalaco); the composition obtained contains approx -fo "toner" is allowed to these developer according de.m "Cascade" -Verfahron roll over a latent electrostatic image, v / hich is located on a xerographic plate. 0.5 wt.., one obtains a good development with minimal precipitation in the "background".

The glass beads produced according to the invention are clean and are more uniform in size than those made by the conventional process. As a result of this more uniform size and the closer to the spherical shape is obtained when using the coated or uncoated glass beads as an electrostatographic developer carrier, an easier rolling of the developer over the image-bearing surface is achieved, whereby an effective transfer of the "toner" to the image-bearing surface is facilitated.

ORIGINAL BATHROOM 109819/176?

Claims (1)

P ate η t η η s ρ r ii ch e IiJ) Process for the production of spherical glass beads, ~. characterized in that glass particles isolated from each other on a non-wetting ceramic support are heated to a temperature at which the glass particles are pulled up into spherical beads, whereupon the beads are allowed to cool and removed from the furnace. 2.) The method according to claim 1, characterized in cc. That "the glass particles are in solid form. 3.) The method according to claim 1, characterized in that the glass particles are in molten form . A.) Method according to claims 1-3 »characterized in that the ceramic carrier contains many small impressions, one glass particle being placed in each case in an e-print ¹ J.) Process according to claims 1-4, characterized in that the glass particles have a size of JO - 1000 microns, fc 6.) Method according to claims 1 - ί ?, characterized in that that the glass particles are heated to a temperature of approx. 650 C to approx. 1200 C. a fi 7.) Pre-lead for the production of an eüektrostatographischen Developer, characterized in that the glass beads obtained by the process are used. Claims 1-6 with a "toner" kombirilrii ^ y-iwerein the latter the glass- ' enveloped in pearls. ,, .- ■ "" " 8.) Method, giimüß claim 7, characterized konr.zoicTtiWi ^. that mar * · -the glass beads with a resin coating before mixing with the "toner * . * ^". 109819/176? BATH ORIGINAL P 20 5Ζ 169.J.1. ιλ XERO X üOJftOJttMj.'IOIT HGK PA -LJvIJ- AJlJlVIlU Ο II W; / UUd 6 7 ·) Use after the glass beads. AnopLUioh 1 to 6 together with einöw! 'one to Ilenatollung an «electrostatographic-. see sir & wi ekler s, 8.) Verv / enduiiK goicäß Aticyruch 7, characterized in that that before you mix with dom toner with a resin coating provided glass beads are used. ίΖ \ Λ BAD ORIGINAL 109819/1762