GB2075703A - Electrophotographic toner - Google Patents

Abstract

This invention is directed generally to dry electrophotographic toner compositions comprising a colourant and a styrene butadiene copolymer resin having a weight average molecular weight between 60,000 and 180,000 and a molecular weight distribution between 5 and 15, the percentage of styrene present ranging from 80 percent to 95 percent, with the percentage of butadiene present ranging from 5 percent to 20 percent, such toner having a minimum fixing temperature of from 120-150 DEG C, a fusing temperature latitude of from 40-120 DEG C, and a blocking temperature of from 40-60 DEG C.

Description

SPECIFICATION Styrene butadiene'toner resins This invention is generally directed to new developer compositions and the use of such developers for causing the development of images in an electrophotographic system. More specifically, the present invention is directed to positively charged toners comprised of styrenebutadiene copolymer type resins, which toners have broad temperature fusing latitudes, low minimum fix temperatures, and are particularly useful with hot roll fusing systems contained in electrophotographic imaging devices.

The electrophotographic process, and in particular the xerographic process, is well-known. In one sequence of the xerographic process the latent electrostatic image formed on the photoconductive surface is developed with a variety of pigmented resin materials specifically made for this purpose, such as toner. Many processes are used for applying the electroscopic particles or toners to the electrostatic latent image to be developed such as for example, the development method described in U.S. Patent 3,618,552, cascade development, U.S. Patent 2,874,063, and 3,357,402, magnetic brush development, U.S. Patent 2,221,776, powder cloud development, and U.S. Patent 3,166,432, touchdown development.

There are instances where it is desirable in electrophotographic systems to produce a reverse copy of the original, thus, for example, it may be desirable to produce a negative copy from a positive original, or a positive copy from negative original. This is referred to in the art as image reversal, and in electrostatic printing such image reversal can be accomplished by applying to the image a developer powder which is repelled by the charged areas of the image and adheres to the discharged areas. Specifically, toners possessing positive charges are found to be more useful and effective in electrophotographic reversal systems, and in particular, in electrophotographic systems employing organic photoreceptors, which in many instances are initially charged negatively rather than positively, thus necessitating the need for a positively charged toner.Reversal developers are, for example, described in U.S. Patent 2,986,521.

In U.S. Patent 3,893,935 there is described the use of certain quaternary ammonium salts as useful charge control agents for electrostatic toner compositions. According to the disclosure of this patent, certain quaternary ammonium salts when incorporated into toner materials were found to provide a particulate toner composition, which exhibited relatively high uniform and stable net toner charge when mixed with a suitable carrier vehicle, and which toner also exhibited a minimum amount of toner throw-off. U.S. Patent 4,079,041 contains a similar teaching with the exception that a different charge control agent is used, namely a diazo type compound.

Several patents are in existence which disclose the use of styrene butadiene resins for use as toners in development systems, however, such patents do not teach the use of such resins of a particular composition and molecular weight for positively charged toners, and in particular for positive toners which have broad fusing latitudes for example. The patents involved include U.S.

Patent 3,326,848 which discloses a toner of styrene butadiene copolymer, U.S. Patent 3,960,737 which discloses a liquid developer of a mixture of styrene butadiene with an acrylate, U.S. Patent 3,766,072 which discloses a developer containing at least two types of particles, one of which can be a styrene butadiene type resin, (Pliolite S5D), Japanese Patent Publication 109483 and U.S. Patent 3,090,755 and 3,965,022.

Many of the above-described toners and developers do not have a broad fusing temperature latitude, described in detail hereinafter, nor a combination of low minimum fix temperatures and broad fusing temperature latitudes, without causing a decrease in the blocking temperature.

Further some of the above-described developers have a tendency to lose their positive charge over a period of time, are difficult to prepare and in view of this the quality of the image that is to be developed is adversely affected. Also the use of a charge control agents and developers as described in U.S. Patent 3,893,935 are soluble in water causing them to be leached to the toner surface by moisture thereby adversely affecting the machine environment and the copy quality.

Accordingly, there is a need for developers which have broad fusing latitude temperature ranges, which toners can be used in hot roll fusing systems, these toners containing positive charges thereon and having low minimum fixing temperatures, that is, from about 250"F to about 300"F, and high blocking temperatures of from about 105"F to about 135"F.

The present invention provides an improved styrene-butadiene copolymer toner which is as claimed in the appended claims.

Many of the styrene/butadiene resins useful in the present invention include those commercially available from Goodyear Chemical Company, and known as Pliolite (Registered Trade Mark), such as Pliolite S5A-E. Also embraced within the scope of the present invention are copolymers of vinyl toluene, with butadiene, the percentage of butadiene being present ranging from about 80 percent to about 95 percent, with the percentage of other monomer, (vinyl toluene) being from about 5 percent to about 20 percent.

The amount of styrene butadiene copolymer resin present in the toner formulation ranges from about 80 percent to about 95 percent, and preferably from about 88 percent to about 94 percent based on the weight of toner, while the amount of colorant present ranges from between about 5 percent to about 20 percent and preferably from about 6 percent to about 1 2 percent. Thus, for example, when 85 percent of the styrene butadiene copolymer resin in present, 1 5 percent of the colorant is present.

By minimum fuse temperature is meant the temperature at which the toner is sufficiently melted, coalesced, and attached to a substrate, such as paper, so as to withstand conventional handling, filing, smearing, smudging, and/or loss of information, while the hot offset temperature is the temperature at which the toner image splits internally, with some of the toner remaining on the fuser roll. The fusing temperature latitude is the difference between the hot offset temperature, and the minimum fuse temperature, as reported in Example I.

Numerous suitable dyes or colorants may be employed together with the styrene butadiene resins for formulating the toner particles, such materials being well-known and including various types of carbon blacks, Nigrosine dye, aniline blue, chrome yellow, ultramarine blue, duPont oil red, phthalocyanine blue, and mixtures thereof, with the preferred material being carbon black.

The colorant should be present in the toner in sufficient quantity to render it highly colored so that it will form a visible image on the recording member. For example, where conventional xerographic copies of documents are desired the toner may comprise a black pigment such as carbon black. Also a black dye such as commercially available from National Aniline Products Inc. can be employed. Preferably the colorant is employed in amounts of from about 5 percent to about 20 percent by weight based on the total weight of toner.

As an additional ingredient there can be included in the toner composition of the present invention various additives especially materials such as nigrosine and charge control additives, such as alkyl pyridinium compounds of the following formula:

wherein- R is a aliphatic radical such a methyl, ethyl, propyl, butyl, hexyl, octyl, nonyl and the like, and A is an anion such as chloride, bromide, fluoride, sulfate, sulfonate, phosphate, borate and the like. The preferred additive is cetyl pyridinium chloride. The purpose of the charge control additive is to impart a positive charge to the toner resin.

The additive is present in amounts of from about 0.25 percent to about 4 percent, and preferably from about 0.5 percent to about 3 percent, Several methods may be employed for producing the toner of the present invention, one such method involving melt blending the resin and the pigment followed by mechanical attrition.

Other methods including those well-known in the art, such as spray drying, melt dispersion and dispersion polymerization. For example a solvent dispersion of resin and colorant is spray dryed under controlled conditions to result in the desired toner. Such a toner produced in this manner results in a positive charged toner in relation to the carrier materials which are present when a developer is formulated, and these toners exhibit the improved properties as mentioned hereinbefore.

Any suitable carrier material can be employed with the toner of the present invention as long as such particles are capable of triboelectrically obtaining a charge of opposite polarity to that of the toner particles. Toner plus carrier is referred to in the art as developer. In one embodiment in the present invention that would be a negative polarity to that of the toner particles which are positively charged so that the toner particles will adhere and surround the carrier particles.

Accordingly, the carriers can be selected to that the toner particles require a charge of positive polarity and include inorganic materials, organic materials, as well as coated carriers, including for example, sodium chloride, ammonium chloride, ammonium potassium chloride, aluminum nitrate, granular zinc, granular silicone, methyl methacrylate, glass, steel, nickel, iron ferrite, silicone dioxide, and the like. Coated carriers that may be used include the above-mentioned carriers coated for example with organic materials such as fluorinated polymers including polyvinylidene fluoride. Many of the carriers that can be used are described in U.S. Patents 2,618,441; 2,638,416; 3,591,503; 3,533,835 and 3,526,533. Also nickel berry carriers as described in U.S. Patents 3,847,604 and 3,767,598 can be employed. These carriers being nodular beads of nickel characterized by surfaces of recurring recesses and protrusions, provide particles with a relatively large external area. The diameter of the coated carrier particle is from about 50 to about 1,000 microns thus allowing the carrier to possess sufficient density and inertia to avoid adherence to the electrostatic images during the development process.

The carrier may be employed with the toner composition in any suitable combination, however, best results are obtained when about 1 part per toner is used and about 10 to about 200 parts per weight of carrier.

Toners of the present invention may be used to develop electrostatic latent images on any suitable electrostatic surface capable of retaining charge including conventional photoconductors, however, the toners of the present invention are best utilized in systems wherein a negative charge resides in the photoreceptor and this usually occurs with organic photoreceptors.

Illustrative examples of such photoreceptors include polyvinyl carbazole, 4-dimethylamino benzylidene, benzhydrazide, 2-benzylideneamino-carbazole, 4-dimethylamino-benzylidene, benzhydrazide, 2-benzylidene-amino-carbazole, polyvinylcarbazole substituted materials, (2-nitrobenzylidene)-p-amino aniline, 2,4-diphenyl-quinazoline, 1,2,4-triazine, 1 ,5diphenyl-3-methyl pyrazoline, 2-(4'-dimethyl amino phenyl)-benzoxazole, 3-amino carbazole, polyvinyl carbazole-trinitrofluorenone charge transfer complexes, phthaldcyanines and mixtures thereof.

The following examples are being supplied to further define the species of the present invention, it being noted that these examples are intended to illustrate and not limit the scope of the present invention. Parts and percentages are by weight unless otherwise indicated.

Minimum fix was evaluated by subjecting the image to be tested which has a focused solid area optical density of 1.2 : O.1, as measured by a Macbeth Model RD517 optical densitometer, to ten cycles of abrasive action on a Teledyne Tabor Abrader Model 503, using #10 wheels and a load of 1,000 grams of weight. The abraded images were then compared to standard images representing various degrees of fix to assess fix on a letter scale from A (best) to D (worst), based on the visual comparison of the image relative to the standard. The standard images were derived from a survey taken with Xerox 9200 images intentionally fused to a range of levels. Fix for the PlioliteR resins was excellent (A) while the fix for the polyester resins, reference Example I, were not of high quality, (C).

Also, in the following examples, hot offset temperature was measured by attaching a trailing piece of white paper to the image so that any toner offset to the fuser roll would print back on the trailing sheet on the subsequent roll revolution. Offset was defined as the appearance of toner any where on the trailing sheet.

Temperatures on the fuser roll were measured using an iron constantan thermocouple in contact with the fusing surface and confirmed using a Barnes infared radiometer.

Images using the toner resins of the following examples were made using Xerox Model D flat plate apparatus and a steel carrier. These images were then evaluated for minimum fix and hot offset on a test fixture comprises of a 75mm diameter internally heated silicone rubber coated fuser roll and a 75mm diameter Teflon (trademark) coated back up roll. The rolls were loaded to form a nip of 5.3mm and operated at a surface speed of 250mm /sec. The silicone rubber coating the fuser roll was a high temperature vulcanized silicone rubber 1.75mm thick.

Toner mechanical requirements for minimum fix and hot offset are incompatible in one respect; a good toner from a fix standpoint is one that softens rapidly with increasing temperature, and flows readily under relatively low pressures (275-1380kNm-2) encountered in the fusing nip, while a good toner for hot offset is one that is relatively temperature insensitive with respect to softening, and one that can support the stresses during release from the fuser roll (48-480kNm-2), without failing internally and creating hot offset.Thus, the ideal toner exhibits a high modulus at room temperature ( > 2750kNm-2), which decreases rapidly with increasing temperature to the range of 96-960kNm 2 (where minimum fix occurs), and which abruptly levels off to form a plateau region where the modulus becomes relatively temperature insensitive. Such plateau. is known in the art as the "rubbery plateau" region and it should extend over as broad a temperature range as possible for maximum latitude.

Another toner mechanical requirement concerns the rate of softening of the toner from room temperature to 55"C. While rapid softening of the toner is desirable for low minimum fix temperatures it is also desirable that the toner remain rigid at temperatures below 55"C to prevent caking during transport and storage. The temperature where caking appears within a twenty four hour period is called the blocking temperature and is correlated to the glass transition temperature, a well known rheological property. It has been experimentally observed (see "The Viscosity of Polymers and Their Concentrated Solutions", by G.C. Berry and T.G.Fox in Advances in Polymer Science, Volume 5, Pages 261-357, (1968)), that for a given glass transition temperature, polymer families exhibiting the lowest polarity exhibit the lowest viscosity at elevated temperatures and thus might be expected to have the lowest minimum fix temperatures. By this criterion, styrene butadienes are excellent resins for toners because of their low polarity relative to other toner resins, such as the styrene methacrylate family.

One object of the present invention is to obtain a broad molecular weight distribution to extend the fusing latitude through an extension of the rubbery plateau. A broad molecular weight distribution can be obtained either during polymerization or by blending two or more resins after polymerization. Typically, a polymer will have a molecular weight distribution (Mw) (Mn) in the range of 2-4, where Mw weight average molecular weight Mn number average molecular weight.

The styrene butadiene copolymers of the present application have molecular weight distributions in the range of 5 to 15, thereby resulting in the improved toners of the present invention. Better fusing behavior would be achieved using still broader molecular weight distributions but the preparation of such materials becomes increasingly difficult for molecular weight distributions above about 10.

EXAMPLE I A toner was prepared comprising 10 percent of a carbon black, commercially available as Raven 5250, and 90 percent of a styrene butadiene copolymer comprised of 90 percent styrene and 10 percent butadiene, having a weight average molecular weight of 163,000

Mw 89 8.9 Mn ,and commercially available from Goodyear Corporation as Pliolite S5A, by melt blending followed by mechanical attrition. Other toners were prepared in a similar manner, and these toners were subjected to fusing experiments using a conformable fuser roll with the following results.

Fusing Minimum Fuse Hot Offset Temp. Blocking Toner Temp.( C) Temp.( C) Latitude( C) Temp.( C) Pliolite* 145 > 285 > 120 50 S5A 10% Raven 5250 Pliolite 1 50 235 70 50 S5E 10% Raven 5250 Pliolite 1 50 220 50 45-50 Vinyl Toluene Copolymer 10% Raven 5250 Commercially available from Goodyear Chemical Company.

Comparative experiments were also accomplished with a conformable fuser roll using toners from different resins that is, resins other than styrene butadiene with the following results: Fusing Minimum Fuse Hot Offset Temp. Blocking Toner Temp.( C) Temp.( C) Latitude( C) Temp.( C) Linear 140 150 7 43 Polyester Resin + 10% BPL* Branched 1 30 180 27 43-45 Polyester Resin + 10% BPL* Branched 145 1 30 25 40-43 Polyester Resin + 10% BPL* Styrene/ 180 230 38 50 n-butyl Methacrylate Copolymer resin 65/35, 82% carbon Black, 9% Polyvinylbutyral, 9% *BPL = Black Pearls (carbon black) commercially available EXAMPLE II There was prepared by melt blending followed by mechanical attrition a toner comprised of 89.5 percent of Pliolite S5E, commercially available from Goodyear Chemical, and containing 90 percent styrene, 10 percent butadiene; 0.5 percent nigrosine, and 10 percent of carbon black, Raven 420, commercially available for Citgo. This toner after being subjected to the minimum fix and hot offset tests in accordance with Example I resulted in the following: Minimum fix temperature 135"C Hot offset temperature 220"C Fusing latitude temperature 60"C Blocking temperature 45"C The quality of fix was excellent, and on a scale of from A (best) to D (worst), the level of fix was A.

EXAMPLE 111 The procedure of Example II was repeated with the exception that the Pliolite resin use was comprised of 89 percent styrene, 11 percent butadiene. The toner of this example has a minimum fix temperature of 150"C a hot offset temperature of 195"C, a fusing latitude temperature of 40"C, and a blocking temperature of 50"C.

EXAMPLE IV The procedure of Example II was repeated with the exception that 88 percent of the Pliolite resin of Example Ill, was mixed with 10 percent of the carbon black and two percent Nigrosine.

The toner of this example had a minimum fix temperature of 125"C, a hot offset temperature of 190"C, and a fusing latitude temperature of 45"C.

EXAMPLE V Each of the toner resins of Examples l-IV, 1 part by weight, were mixed with 50 parts by weight of a steel carrier, resulting in developing compositions.

These developer compositions when used in a xerographic imaging fixture, the Xerox Model D flat plate apparatus, produced acceptable images, as defined herein.

Claims (10)

1. A dry electrophotographic toner composition, including a colorant and a styrenebutadiene copolymer having a weight average molecular weight between 60 000 and 1 80 000, and a molecular weight distribution of from 5 to 15, the percentage of styrene in the copolymer ranging from 80 to 95, wih the remainder butadiene, the composition having a minimum fixing temperature of from 120-150 C, a fusing temperature latitude of from 40-120"C, and a blocking temperature of from 40-60"C.

2. A composition as claimed in claim 1, wherein the molecular weight distribution of the styrene-butadiene resin is 9, and the average molecular weight is 160,000.

3. A composition as claimed in claim 1 or 2, wherein the styrene-butadiene resin employed has a minimum fix temperature of 135"C, a blocking temperature of 66"C, and a fusing temperature latitude of 60"C.

4. A composition as claimed in claim 1 or 2, wherein the styrene-butadiene resin employed has a minimum fix temperature of 150"C, a blocking temperature of 49"C, and a fusing temperature latitude of 40"C.

5. A toner composition as claimed in any preceding claim, wherein the amount of colorant present ranges from 5 percent to 20 percent by weight.

6. A toner composition as claimed in any preceding claim, wherein the colorant is carbon black, and the styrene-butadiene resin contains 90 percent styrene, and 10 butadiene.

7. A toner composition as claimed in any preceding claim, including an additive material for imparting a positive charge to the toner resin

8. A composition as claimed in claim 7, wherein the additive material is cetyl pyridinium chloride.

9. A toner composition as claimed in any preceding claim, combined with a carrier.

10. A developer as claimed in claim 9 wherein the carrier is particles of steel coated with a fluorinated polymer.