DE69209253T2 - TONER AND DEVELOPER WHICH CONTAIN ESTER-CONTAINING QUATERNARY PYRIDINIUM SALTS AS A CHARGE CONTROL - Google Patents

Description

Field of the invention

This invention relates to certain electrostatographic toners and developers containing ester group-containing quaternary pyridinium salts useful as charge control agents and which also serve as adhesion promoters between toner and receiver sheets and as toner fusion temperature reducing compounds.

Description of the state of the art

In the field of manufacturing and using toner powders, charge control agents are commonly used to adjust and control the triboelectric charge capacity and/or electrical conductivity characteristics thereof. Many different charge control agents are known which have been incorporated into various binder polymers and are known for use in toner powders. The need for new and improved toner powders which can be used in improved copying devices has led to ongoing research and development efforts towards the discovery of improved charge control agents.

Of potential interest are substances that not only serve as toner powder charge control agents, but also act as agents that produce additional results or effects, such as increased adhesion between toner and receiver sheets and as agents for reducing the toner fusion temperature. Such multiple functionality provides the potential for cost savings in the manufacture and use of toner powders, developers and the copying device.

Consequently, it would be desirable to provide dry electrostatographic toners and developers containing ester group-containing quaternary pyridinium salts that perform well the charge control function in dry electrostatographic toners and developers and also promote adhesion between toner and receiver sheets in addition to serving as agents that reduce the toner fusion temperature.

Summary of the invention

This invention provides dry, particulate electrostatographic toners and developers containing charge control agents comprising ester group-containing quaternary pyridium salts having the structure:

wherein R is alkyl or aryl, X is (CH₂)n, Y is hydrogen, alkyl, alkoxy or halogen, Z is an anion and n is an integer from 1 to 6.

The toner powders according to the invention comprise a polymeric matrix phase or a polymeric binder in which at least one quaternary pyridinium salt is dispersed, which comprises at least one radical containing an ester group which is bonded to the pyridinium nitrogen atom by a linking alkylene group.

When incorporated into toner powder, such quaternary pyridinium salts not only act as good charge control agents, but they also serve as substances that depress the fusion temperature of the toner powder and promote paper adhesion. These salts are preferably present in the polymeric binder matrix phase dispersed which comprises the core or body portion of a toner particle.

Toner powders containing these salts can also be mixed with a carrier to produce electrostatographic developers.

Toner powders containing these salts incorporated into the polymeric binder thereof can be used to produce developed toned images on a photoconductor element having a latent image, to transfer the toned image from the photoconductor element to a receiver sheet, and to heat fuse the toned image to the receiver using methods and process conditions generally known in the art of electrophotography.

Various other advantages, objects, features, purposes, embodiments and the like related to the present invention will become apparent to those skilled in the art from the present description and the appended claims.

Description of the preferred embodiments (A) Definitions

The term "particle size" as used herein, or the term "size" or "of a size" as used herein in connection with the term "particle" refers to the volume weighted diameter as measured by conventional diameter measuring devices such as a Coulter Multisizer type device sold by Coulter, Inc. The average diameter of the volume weighted diameter is the sum of the mass of each particle times the diameter of a spherical particle of the same mass and density divided by the total particle mass.

The term "glass transition temperature" or "Tg" used here refers to the temperature at which a polymer changes from a glassy state to a rubbery state. This temperature (Tg) can be determined by a differential thermal analysis as described in "Techniques and Methods of Polymer Evaluation," Volume 1, Marcel Dekker Publishing, Inc., N.Y., 1966.

The term "melting temperature" or "Tm" used here refers to the temperature at which a polymer changes from a crystalline state to an amorphous state. This temperature (Tm) can be determined by a thermal differential analysis as described in "Techniques and Methods of Polymer Evaluation".

The term "adhesion index" used here is a measure of toner adhesion to paper after the toner has been fused. The adhesion index test involves the adhesion of a metal block to a toner patch and the measurement of the energy required to cause interface disruption between the toner layer and its contacting substrate by collision of a pendulum with the metal block. The degree of adhesion index ranges from 0 units (no adhesion of the toner to the substrate) to 100 units (excellent adhesion of the toner to the substrate).

(B) Quaternary pyridinium salts containing ester groups

This invention is directed to dry, particulate electrostatographic toners and developers containing ester group-containing quaternary pyridinium salts of the following formula:

wherein R₁ is alkyl or aryl, X is (CH₂)n, Y is hydrogen, alkyl, alkoxy or halogen, Z is an anion and n is an integer from 1 to 6.

The term "alkyl" as used herein includes straight-chain and branched-chain alkyl groups and cycloalkyl groups.

The term "anion" as used herein refers to negative ions, such as m-nitrobenzenesulfonate, tosylate, tetraphenylborate, dicyanamide, chloride and the like.

The term "aryl" as used herein includes phenyl, naphthyl, anthryl and the like.

The term "alkoxy" as used herein includes methoxy, ethoxy, propoxy, butoxy and the like.

The term "halogen" used here includes fluorine, chlorine, bromine and iodine.

Alkyl and aryl groups may be unsubstituted or substituted by a variety of substituents, such as alkoxy, halo or other groups.

Illustrative examples of ester group-containing quaternary pyridinium salts suitable for the present invention include, for example,

N-(ethoxycarbonylmethyl)pyridinium m-nitrobenzenesulfonate;

N-(ethoxycarbonylmethyl)pyridinium tetraphenylborate;

N-(methoxycarbonylethyl)pyridinium m-nitrobenzenesulfonate;

N-(phenoxycarbonylmethyl)pyridinium m-nitrobenzenesulfonate;

N-(ethoxycarbonylmethyl)-4-methylpyridinium m-nitrobenzenesulfonate;

N-(2-naphthoxycarbonylmethyl)pyridinium tetraphenylborate;

N-(phenoxycarbonylmethyl)-3-chloropyridinium tetraphenylborate; and

N-(ethoxycarbonylmethyl)pyridinium bromide.

A presently preferred salt is an ester group-containing quaternary pyridinium salt of the invention, wherein in the formula given above, R₁ is ethyl, n is 1, Z is tetraphenylborate and Y is hydrogen.

(C) Synthesis

The ester group-containing pyridinium salts used in the toners and developers of the present invention can be prepared by any conventional route. One general route is to quaternize a pyridine compound with a haloalkanoate ester. The quaternary pyridinium halide can then be reacted with an alkali arylsulfonate or other acid salt by ion exchange to yield the desired N-(alkyloxycarbonyl or aryloxycarbonylalkyl)pyridinium salt.

A suitable and presently preferred method for preparing the quaternary pyridinium compound is to prepare the haloalkanoate ester and the pyridine compound as solutes in the same highly polar solvent, with acetonitrile being a particularly preferred example at present. The molar ratio of pyridine compound to haloquaternizing agent is preferably about 1:1. Such a solution is then stirred at ambient temperature or heated to reflux for a period ranging from about 10 to about 25 hours. The reaction mixture is then cooled or concentrated by evaporation of the solvent to yield an oil or crystalline solid. The product can be used for the next step of the synthesis without further purification or the product can be purified by recrystallization. , for example from a ketone such as 2-butanone, or the like, followed by washing and drying.

A suitable and presently preferred method for preparing the quaternary organic pyridinium salt from the intermediate halide is to dissolve the ion exchange agent in water and add this solution to a second aqueous solution containing the intermediate quaternary pyridinium salt. The molar ratio of such salt to such ion exchange agent should be about 1:1. Typically, a precipitate is formed immediately. The resulting product can be recrystallized from a suitable solvent, such as acetonitrile or ethyl acetate, after drying.

(D) Toner and toner production

To be useful as charge control agents in the electrostatographic toners of the invention, the quaternary pyridinium salts are incorporated into toner particles. For present purposes, the toner particles can be considered to comprise preferably on a 100 weight percent basis:

(a) about 0.5 to about 10 weight percent of at least one quaternary pyridinium salt;

(b) about 75 to 97.5 weight percent of a thermoplastic polymer; and

(c) about 2 to about 15 weight percent of a coloring component.

It is believed that the size of the toner particles is relatively unimportant from the standpoint of the present invention; rather, the exact size and size distribution is determined by the intended End use is affected. As far as is known to date, the toner particles can be used in all known electrostatographic copying processes. Typically and illustratively, the toner particle size ranges are from about 0.5 to about 100 microns, preferably from about 4 to about 35 microns.

The properties of the thermoplastic polymers used as toner matrix phase materials in the present invention can vary widely. Typically and preferably, amorphous toner polymers having a glass transition temperature in the range of about 50 to about 120°C or a blend of substantially or essentially amorphous polymers with substantially crystalline polymers having a melting temperature in the range of about 65 to about 200°C are used in the present invention. Preferably, such polymers have a number average molecular weight in the range of about 1,000 to about 500,000. The weight average molecular weight can vary, but is preferably in the range of about 2 x 10³ to about 10⁶. Typical examples of such polymers include polystyrene, polyacrylates, polyesters, polyamides, polyolefins, polycarbonates, phenol-formaldehyde condensates, alkyd resins, polyvinylidene chlorides, epoxy resins, various copolymers of the monomers used to make these polymers, such as polyesteramides, acrylonitrile copolymers with monomers such as styrene, acrylics and the like.

Preferably, the thermoplastic polymers used in the practice of this invention are substantially amorphous. However, as indicated above, blends of polymers may also be used if desired, such as blends of substantially or substantially amorphous polymers with substantially or substantially crystalline polymers.

Preferred polymers for use in toner powders at the present time are styrene/n-butyl acrylate copolymers. In general, preferred styrene/n-butyl acrylate copolymers have a glass transition temperature (Tg) in the range of about 50 to about 100°C.

An optional but preferred starting material for incorporation into such a mixture is a colorant (pigment or dye). Suitable dyes and pigments are described, for example, in U.S. Reissue Patent 31,072 and U.S. Patents 4,140,644; 4,416,965; 4,414,152 and 2,229,513. A particularly suitable colorant for toners used in black and white electrophotographic copying devices is carbon black. When used, colorants are generally used in amounts ranging from about 1 to about 30 weight percent on a total toner powder weight basis, and preferably in the range of about 2 to about 15 weight percent.

Toner compositions may, if desired, further comprise other additives of the types heretofore employed in toner powders, including leveling agents, surfactants, stabilizers, and the like. The total amount of such additives may vary. At present, it has been found advantageous to employ no more than about 10% by weight of such additives on a weight basis of the total toner powder composition.

Various methods are known in the art for incorporating additives such as the quaternary pyridinium salts used in the present invention, colorants or the like into a desired polymer or mixture of polymers. For example, a preformed mechanical mixture of particulate polymer particles, quaternary pyridinium salts, colorants, etc. by roll milling or extruding at a temperature sufficient to cause melt mixing of the polymer or to melt a mixture of polymers to yield a uniformly mixed composition. The cooled composition can then be milled and classified, if desired, to achieve a desired toner powder size and size distribution.

Preferably, the toner components, which are preferably previously converted into a particulate form, are mechanically mixed together prior to melt mixing. In the case of a polymer having a Tg in the range of about 50 to about 120°C or a Tm in the range of about 65 to about 200°C, a melt mixing temperature in the range of about 90 to about 240°C using a roll mill or an extruder is suitable. Melt mixing times (i.e., the exposure time for melt mixing at elevated temperatures) are in the range of about 1 to about 60 minutes. After melt mixing and cooling, the composition can be stored prior to milling. Milling can be done by any suitable method. For example, the solid composition may be crushed and then ground, for example using a jet mill or jet mill as described in U.S. Patent 4,089,472. Classification, if used, may be carried out in one or two stages in a conventional manner.

Instead of melt mixing the polymer, it can be dissolved in a solvent and the additives can be dissolved and/or dispersed therein. The resulting solution or dispersion can then be dried by spraying to obtain toner powder particles.

Limited coalescing polymer suspension processes are particularly suitable for producing small-particle, uniform toner powders, such as toner particles of a size of less than about 10 microns.

The toner powders used in the present invention preferably have a fusion temperature latitude in the range of about 275 to about 400°F, although toner powders having higher or lower fusion temperatures may be prepared and used. The toner powders typically exhibit excellent paper adhesion properties. Typically, the toner powders have a paper adhesion index value in the range of about 30 to about 100, although toner powders having lower such values may be prepared and used. Paper adhesion index values of such toner powders are characteristically higher than those of toner powders made with the same polymer and additives but containing a quaternary ammonium salt not according to the invention and are comparable to a toner powder made from the same polymer and additives but containing no charge control agent.

To be used as toners in electrostatographic developers of the invention, toners containing the salts described above can be mixed with a carrier. The carrier used to prepare such developer compositions can be selected from a variety of materials. Such materials include carrier core particles and core particles coated with a thin layer of a film-forming resin. The carrier core materials can comprise conductive, non-conductive, magnetic or non-magnetic materials. For example, carrier cores can comprise or include glass beads; crystals of inorganic salts such as aluminum potassium chloride; other Salts such as ammonium chloride or sodium nitrate; granulated zirconium; granulated silicon; silicon dioxide; particles of hard resins such as poly(methyl methacrylate); metallic materials such as iron, steel, nickel, carborundum, cobalt, oxidized iron or mixtures or alloys of the aforementioned materials. Reference is made, for example, to US Patent Specifications 3,850,663 and 3,970,571. Particularly suitable for magnetic brush development processes are iron particles such as particles of porous iron with oxidized surfaces, steel particles and other "hard" or "soft" ferromagnetic materials such as gamma ferrioxides or ferrites such as ferrites of barium, strontium, lead, magnesium or aluminum. Reference is made, for example, to US Patent Specifications 4,042,518; 4 478 925 and 4 546 060.

As mentioned above, the carrier particles may be coated with a thin layer of a film-forming resin for the purpose of establishing the correct triboelectric relationship and charge level for the toner used. Examples of suitable resins are the polymers described in U.S. Patent Nos. 3,547,822; 3,632,512; 3,795,618 and 3,898,170 and Belgian Patent No. 797,132. Other suitable resins are fluorocarbons such as polytetrafluoroethylene, poly(vinylidene fluoride), mixtures thereof, and copolymers of vinylidene fluoride and tetrafluoroethylene. Reference is made, for example, to U.S. Patent Nos. 4,545,060; 4,478,925; 4,076,857 and 3,970,571. Such polymeric fluorocarbon carrier coatings may serve a number of known purposes. One such purpose may be to assist the developer in meeting the electrostatic force requirements mentioned above by placing the carrier particles in a position in the triboelectric series other than the position of the uncoated carrier core material to adjust the degree of triboelectric charge of both the carrier and toner particles. Another purpose may be to reduce the frictional characteristics of the carrier particles to improve developer flow properties. Another purpose may be to reduce the surface hardness of the carrier particles so that they are less likely to break up during use and less likely to abrade surfaces (e.g., surfaces of photoconductive elements) with which they come into contact during use. Another purpose may be to reduce the tendency of the toner material or other developer additives to undesirably adhere permanently to carrier surfaces when the developer is used (often referred to as scumming). Another purpose may be to change the electrical resistance of the carrier particles.

A typical developer composition comprising the toner described above and a carrier generally comprises from about 1 to about 20 weight percent particulate toner particles and from about 80 to about 99 weight percent carrier particles. Usually, the carrier particles are larger than the toner particles. Typical carrier particles have a particle size on the order of about 20 to about 1200 microns, preferably 30 to 300 microns.

Alternatively, the toners of the present invention can be used in a single-component developer, i.e. without carrier particles.

The toner and developer compositions of this invention can be used in a variety of ways to develop electrostatic charge patterns or latent images. Such developable charge patterns can be produced by a number of means and can be, for example, disposed on a photosensitive, photoconductive element or an element having a non-photosensitive dielectric surface, such as a conductive sheet coated with an insulator. One suitable development technique relies on cascading the developer composition across the electrostatic charge pattern, while another technique relies on applying toner particles from a magnetic brush. This latter technique involves the use of a magnetically attractable carrier in the preparation of the developer composition. After imagewise deposition of the toner particles, the image can be fixed, for example by heating the toner to fuse it to the substrate carrying the toner. If desired, the unfused image can be transferred to a receiver, such as a sheet of copy paper, to which the image can be fused to produce a permanent image.

The invention is further illustrated by the following examples. In these examples, all melting points and boiling points are uncorrected. NMR (nuclear magnetic resonance) spectra were obtained using a Varian Gemini-200 NMR spectrometer. All elemental analyses were performed by combustion. Unless otherwise stated, all starting chemicals were obtained commercially.

Examples Example 1: Preparation of N-(ethoxycarbonylmethyl)pyridinium bromide

To a solution of 47.37 g (0.599 mol) of pyridine in 300 ml of acetonitrile was added 100.0 g (0.599 mol) of ethyl bromoacetate over a period of about 5 minutes. The mixture was then stirred for about 19.3 hours. A solid mass crystallized, which was separated, washed with ether and dried. The yield of product was 113.3 g (76.86% of theory); mp = 133-134°C.

Anal. calcd. for C�9H₁₂BrNO₂: C: 43.92; H: 4.91; N: 5.69;

found: C: 43.87; H: 4.76; N: 5.68.

The NMR spectrum was consistent with the assumed structure.

Example 2: Preparation of N-(ethoxycarbonylmethyl)pyridinium tetraphenylborate

To a solution of 24.61 g (0.10 mol) of N-(ethoxycarbonylmethyl)pyridinium bromide in 100 mL of water was added a solution of 34.22 g (0.10 mol) of sodium tetraphenylborate in 150 mL of water. The mixture was diluted with 1 liter of water and then filtered. The solid mass which separated was dissolved in methylene chloride, the aqueous layer was separated and the organic layer was dried over MgSO4 and concentrated. Recrystallization from ethyl acetate gave 21.9 g of product (45.11% of theory); mp = 150-152°C.

Anal. calcd. for C₃₃H₃₂BNO₂: C: 81.65; H: 6.64; B: 2.23; N: 2.89;

found: C: 81.33; H: 6.62; W: 2.22; N: 2.83.

The NMR spectrum was consistent with the proposed structure.

Example 3: Toner powder production (dry weight basis)

A styrene/n-butyl acrylate copolymer was obtained by limited coalescence polymerization, after which it was mixed with the additive components shown in the following Table 1 in the amounts indicated. TABLE I Component Mixture Styrene butyl acrylate Carbon black Charge control agent: none N-(ethoxycarbonylmethyl)pyridinium tetraphenylborate (composition of Example 2) N-octadecyl-N,N-dimethylbenzylammonium m-nitrobenzenesulfonate ¹Parts by weight

The carbon black consisted of "Regal 300". Each blend was roller milled at 150ºC for 20 minutes, cooled, crushed and classified to produce a toner powder product having a size of about 12 microns and a size distribution of about 2-30 microns. The charge control agent identified in Table I above as N-octadecyl-N,N-dimethylbenzylammonium m-nitrobenzenesulfonate was used for comparison purposes.

Example 4: Fusion and adhesion behavior

Each of the styrene/n-butyl acrylate toner powder blends A, B and C was tested on a fusion breadboard consisting of a fusion roll coated with 100 mils of red rubber engaged at constant speed and pressure with a backup roll coated with polytetrafluoroethylene (commercially available as Silverstone from EI duPont de Nemours and Co.). Both roll surfaces were hand coated with a release oil (60,000 centistoke polydimethylsiloxane oil available from Dow Corning Co.). The gap width between the two rolls was 0.215-0.240 inch and the fusing roll was operated at a speed of 12 inches/sec. The fusing temperature was 350ºF.

Six longitudinal stripes of toner were applied to the wire side of a Kodak Alkaline DP Paper and the toned papers were passed through the fusing breadboard. The transfer density of the toned, fused stripes was between 1.2 and 1.5.

The adhesion index was determined for each strip and the results for each of the different toners are summarized in Table II below. TABLE II Blend Charge Control Agent Average Adhesion Index (AI) of Toner Without N-(Ethoxycarbonylmethyl)pyridinium tetraphenylborate (Composition of Example 2) N-Octadecyl-N,N-dimethylbenzylammonium m-nitrobenzenesulfonate

The adhesion index values are the averages of 8 measurements and the standard deviations were less than 7 units in the case of the measurements. The toner containing a quaternary pyridinium salt having an ester group according to the invention (Blend B) had a considerably higher adhesion index than the toner containing the N-octadecyl-N,N-dimethylbenzylammonium-m-nitrobenzenesulfonate charge control agent, the charge control agent used for comparative purposes outside the scope of the invention, and had a comparable adhesion index to the toner without the charge control agent.

This invention has been described in detail with particular reference to preferred embodiments, it being understood that variations and modifications may be made within the spirit of the invention.

Claims (11)

1. A dry, particulate electrostatographic toner composition comprising a binder and a charge control agent comprising an ester-containing quaternary pyridinium salt of the structure: wherein R₁ is alkyl or aryl, X is (CH₂)n, Y is hydrogen, alkyl, alkoxy or halogen, Z is an anion and n is an integer from 1 to 6. 2. The toner composition of claim 1, wherein the salt is N-(ethoxycarbonylmethyl)pyridinium tetraphenylborate. 3. The toner composition of claim 1, wherein the salt is N-(methoxycarbonylethyl)pyridinium m-nitrobenzenesulfonate . 4. The toner composition of claim 1, wherein the salt is N-(phenoxycarbonylmethyl)pyridinium m-nitrobenzenesulfonate . 5. The toner composition of claim 1, wherein the salt is N-(ethoxycarbonylmethyl)-4-methylpyridinium m-nitrobenzenesulfonate. 6. The toner composition of claim 1, wherein the salt is N-(2-naphthoxycarbonylmethyl)pyridinium tetraphenylborate . 7. The toner composition of claim 1, wherein the salt is N-(phenoxycarbonylmethyl)-3-chloropyridinium tetraphenylborate. 8. The toner composition of claim 1, wherein the salt is N-(ethoxycarbonylmethyl)pyridinium m-nitrobenzenesulfate . 9. The toner composition of claim 1, wherein the salt is N-(ethoxycarbonylmethyl)pyridinium bromide. 10. Electrostatographic developer with: a. the particulate toner composition according to claim 1, and b. carrier particles. 11. A developer according to claim 10, wherein the carrier particles comprise a core material coated with a fluorocarbon.