GB2036353A

GB2036353A - Toner Power For Use in Developing Latent Electrostatic Images

Info

Publication number: GB2036353A
Application number: GB7936353A
Authority: GB
Original assignee: Oce Van der Grinten NV
Current assignee: Canon Production Printing Holding BV
Priority date: 1978-10-20
Filing date: 1979-10-19
Publication date: 1980-06-25
Also published as: SE7908527L; DE2942114A1; GB2036353B; ES478862A1; IT7969048A0; DE2942114C2; CH651678A5; AU525369B2; CA1131489A; JPS5555346A; NL7810502A; FR2439419A1; IT1121489B; AU5127979A; JPS649629B2; FR2439419B1; SE435766B

Abstract

A positively chargeable heat- fixable toner powder suitable for use in a high volume copying apparatus with a contact fixing device comprises finely divided toner particles comprising a thermoplastic resin, colouring material and a charge regulator (which is other than an epoxy amine), the thermoplastic resin constituent being mainly composed of resin having an epoxy molar mass of approximately 2000 to 7500, the resin being either (i) a derivative of an epoxy resin having a molecular weight of at most approximately 1000 and an epoxy molar mass of at most approximately 700 in which approximately 25 to 95% of the epoxy groups have been blocked by reaction with a monofunctional carboxylic acid, phenol or diarylsulphonamide and approximately 5 to 75% have been blocked by intermolecular reaction with hydroxyl groups on the epoxy resin and/or by reaction with a bi- or poly-functional reagent; or (ii) a mixture comprising at least 20 parts by weight of a resin as defined under (i) and at most 80 parts by weight of a phenoxy resin or of a resin which is a derivative of an epoxy resin having a molecular weight of at least approximately 1500 and an epoxy molar mass of at least approximately 900 in which at least 5% of the epoxy groups have been blocked by intermolecular reaction and/or reaction with a bi- or polyfunctional reagent. p

Description

SPECIFICATION Toner Powder for use in Developing Latent Electrostatic Images This invention relates to heat-fixable toner powder suitable for use in the development of latent electrostatic images, a process for the preparation of such a toner powder, and its use in the development of latent electrostatic images.

Toner powders are widely used in the form of so-called one-and two-component developers to render visible latent electrostatic images of the type formed on a suitable surface in electrography or electrophotography. Such known toner powders generally consist essentially of finely divided coloured toner particles comprising an insulating thermoplastic resin, colouring material and if required a charge regulator.

Two-component developers comprise the toner powder mixed with relatively large carrier particles. By contact with or friction against the carrier particles the toner particles triboelectrically receive an electrostatic charge and consequently adhere to the carrier particles. In general the toner and carrier particles are chosen such that the toner particles assume a charge having an opposite polarity to the latent electrostatic image to be developed. When the developer is brought into contact with the latent electrostatic image the toner particles are removed from the carrier particles by the electrostatic charge of the image and are deposited on the latent image so that it is rendered visible.

Examples of suitable carrier particles are, inter alia, pulverulent metal, e.g. iron or nickel, metal oxide, e.g. chromium oxide or aluminium oxide, glass, sand or quartz. In practice, metal carrier particles, particularly iron particles, are widely used. Iron particles are in fact greatly used in powder developers used in so-called magnetic brush development in which the developer is transferred to the electrostatic image to be developed by magnetic transfer means in the form of a rotary powder brush.

One-component developers generally comprise a toner powder which is substantially insulating i.e. it generally has a specific resistance of > 1 012Q cm or is made conductive by applying finely divided electrically conductive material to the surface of the powder grains or homogeneously distributing finely divided electrically conductive material in the grains, so that its resistance is generally well below 1 012Q, cm. Such developers are generally applied to the latent image to be developed with the aid of a magnetic brush developer system. In this case the toner powder suitably contains a magnetisable iron pigment which can also serve as a colouring material.

Carbon black is generally added to the thermoplastic material as the colouring constituent in the case of black toner powders, whereas organic dyes are added in the case of other coloured toner powders, e.g. for use in electrographic multicolour reproduction processes.

Known natural or synthetic polymers or resins are used as the thermoplastic material. Examples of suitable thermoplastic materials are polystyrene, copolymers of styrene with an acrylate and/or methacrylate, polyamides, modified phenol-formaldehyde resins, polyester resins and epoxy resins.

The powder image deposited during development is subsequently fixed. The fixing can take place directly on the surface on which the powder image has been deposited (direct copying) or after transfer of the image to another receiving surface (indirect copying). Fixing is generally by heating with the aid of radiant heat or by a combination of heating and pressure in a so-called contact fixing apparatus, the powder image being brought into contact with a heated surface such as a roller and/or belt.

U.K. Patent Specification No. 1 550555 describes toner powders capable of acquiring a positive charge upon triboelectric contact with metal carrier particles which mainly comprise resin derived from an epoxy resin in which original epoxy groups have been blocked. The toner powders described comprise toner particles containing an insulating thermoplastic resin having homogeneously distributed therethrough colouring material and a charge regulator, at least 50% by weight of the insulating thermoplastic resin being resin having an epoxy molar mass (as herein defined) of at least 10,000 prepared from an epoxy resin of lower epoxy molar mass by reaction of its epoxy groups with a monocarboxylic acid and/or mono-hydric phenol and, optionally, by intermolecular reaction or by reaction with a polyfunctional epoxy hardener.

Such toner powders satisfy the main requirements made on toner powders in particular they have clearly defined polarity, good charge characteristics, adequate chargeability, uniform charge distribution, charging stability and low light and temperature sensitivity, good fixing properties, easily reproducible fixing characteristics, thermal stability and good permanence during prolonged use. Further the glass transition temperature (Tg) and the start of the melting range of the toner powders can be significantly reduced by use of compounds as described in U.K. Patent Specification No.

1496558. The compounds act as agents to aid the dissolution of given dyes in epoxy resins and are indicated as co-solvents for use during the preparation of the toner powders described in U.K. Patent Specification No. 1 550555. In this way it is possible to obtain toner powders whose Tg is only just above the minimum limit required for satisfactory use, generally between 45 and 550C, whilst the lower limit of the melting range starts just above the Tg. Such toner powders can be rapidly satisfactorily fixed by a minimum of heat which leads to important practical advantages.

However, the Applicant has found that the use of such co-solvents may lead to a number of less desired secondary phenomena. During the preparation of the toner powder to which the cosolvent is added a not inconsiderable proportion thereof evaporates off. Furthermore, while the toner powder is in copying apparatus, part of the co-solvent in the toner powder tends to evaporate off, leading to a danger of migration by the charge regulator and contamination of the copying apparatus and carrier particles.

According to the present invention there is provided a heat-fixable toner powder capable of acquiring a positive charge upon triboelectric contact with metal carrier particles, which toner powder comprises finely divided toner particles comprising a thermoplastic resin, colouring material and a charge regulator which is other than an epoxy amine, the thermoplastic resin constituent being mainly composed of resin having an epoxy molar mass (as herein defined) of approximately 2000 to 7500, the resin being either (i) a derivative of an epoxy resin having a molecular weight of at most approximately 1000 and an epoxy molar mass of at most approximately 700 in which approximately 25 to 95% of the epoxy groups have been blocked by reaction with a monofunctional carboxylic acid, phenol or diarylsulphonamide and approximately 5 to 75% have been blocked by intermolecular reaction with hydroxyl groups on the epoxy resin and/or by reaction with a bi- or poly-functional reagent; or (ii) a mixture comprising at least 20 parts by weight of a resin as defined under (i) and at most 80 parts by weight of a phenoxy resin or of a resin which is a derivative of an epoxy resin having a molecular weight of at least approximately 1 500 and an epoxy molar mass of at least approximately 900 in which at least 5% of the epoxy groups have been blocked by intermolecular reaction and/or reaction with a bior poly-functional reagent.

It has been found that using this material there may be obtained a toner powder of low Tg and having a melting range starting just above the Tg without it being necessary to use a co-solvent and thereby avoiding the disadvantages associated therewith.

By "epoxy resins" are meant in the context of this specification condensation products of a polyphenol, particularly a bisphenol, with a halohydrin and in particular epichlorohydrin.

By "phenoxy resins" are meant products of the epoxy resin type in the preparation of which 4,4' isopropylidenediphenol is used as the bifunctional epoxy hardener. In general they have a linear structure and a molecular weight between 10,000 and 80,000. One commercially available suitable phenoxy resin is Rütapox 0717 (molecular weight 30,000) of Messrs. Bakeiite.

By "epoxy molar mass" of a resin is meant the weight of the resin in grams which contains one gram equivalent of epoxy group (see page 4-14 "Handbook of Epoxy Resins", Lee and Neville, McGraw-Hill Book Company, 1 967). For the sake of brevity "epoxy molar mass" will hereinafter be referred to as E.M.M. In the same way "molecular weight" (molar mass) will be referred to as M.W.

Also for the sake of brevity resins obtained by the blocking of epoxy groups of epoxy resins will be referred to as "modified epoxy resins".

Preferably the thermoplastic resin constituent consists substantially of modified epoxy resin and, if present, phenoxy resin.

Examples of starting epoxy resins for use in the preparation of the toner powder according to the invention with an M.W. of at most 1,000 and an E.M.M. of at most 700 include Epikote (Registered Trade Mark) 1002 (average M.W.

1050, E.M.M. 575-700), Epikote 1001 (average M.W. 900, E.M.M. 450-500), Epikote 828 (average M.W. 370, E.M.M. 184--194) and Epikote 827 (average M.W. 360, E.M.M. 180- 190).

Examples of starting epoxy resins with an M.W.

of at least approximately 1,500 and an E.M.M. of at least approximately 900 for use in the preparation of resin (ii) in the toner powder according to the invention include Epikote 1004 (average M.W. 1400, E.M.M. 850-940), Epikote 1006 (average MW. 2,800, E.M.M. 15501900) and Epikote 1009 (average M.W. 3750, E.M.M. 2300-3400). [Epikote is a Shell trade name and the M.W. and E.M.M. values are as supplied by the manufacturer].

In the preparation of a toner powder according to the invention preference is given to the use of a modified epoxy resin obtained from a liquid epoxy resin with a M.W. of at most approximately 500 and an E.M.M. of at most approximately 300 by blocking approximately 5095% of the epoxy groups by reaction with a monofunctional carboxylic acid, phenol or diarylsulphonamide and approximately 550% by intermolecular reaction and/or by reaction with a bi- or poly-functional agent (epoxy hardener). In this way it is possible to obtain toner powders of low Tg which have a wide melting range commencing just up above the Tg.Preferably the so-obtained modified epoxy resin is mixed with phenoxy resin and/or with a modified epoxy resin obtained from an epoxy resin with an M.W. of at least approximately 2,500 and an E.M.M. of at least approximately 2,000 by blocking at least 5% of the epoxy groups by intermolecular reaction and/or by reaction with a bi- or poly-functional agent (epoxy hardener).

Such toner powders are particularly suitable for use in a high volume copying apparatus with a contact fixing device. Compared with conventional toners such as e.g. toners based on styrene-acrylate polymers, they can be excellently fixed at low temperature and high speed e.g. in a couple of hundredths of a second.

The monofunctional carboxylic acids, phenols or diarylsulphonamides used for blocking the epoxy resin or epoxy resin mixture chosen as the starting material should, apart from the carboxyl, hydroxy or amide group, contain no further substituent which under the conditions of the blocking process can react with the reactive groups of the epoxy resin.

Carboxylic acids which can be used with particular advantage are aromatic carboxylic acids, such as benzoic acid and those substituted by one or more alkyl, aralkyl, cycloalkyl, aryl, alkylaryl, alkoxy or aryloxy groups, which under the conditions of the blocking reaction are substantially involatile. Examples of such substituted aromatic carboxylic acids are 2,4dimethylbenzoic acid, 4-(a,-dimethylbenzyl)- benzoic acid, 4- phenylbenzoic acid and 4-ethoxybenzoic acid. However, it is also possible to use aliphatic carboxylic acids such as e.g. heptanoic, nonanoic, dodecanoic, isododecanoic, hexadecanoic and octadecanoic acids.

Examples of phenols suitable for use in the blocking reaction are 4-n-butylphenol, 4-n pentylphenol, 2,3,4,6-tetramethylphenol, 2,3,5,6- tetramethylphenol, 4-(a,a-dimethylbenzyl)- phenol, 4-cyclohexylphenol, 3-methoxyphenol, 4- methoxyphenol and 4-ethoxyphenol.

Of the above compounds, particular preference is given to substituted or unsubstituted benzoic acids and 4-(a,-dimethylbenzyl)-phenol.

Examples of suitable diarylsulphonamides are benzene-sulphonanilide and derivatives thereof, such as e.g. those in which one or both benzene nuclei carry one or more lower alkyl or alkoxy groups.

In the preparation of the toner powder according to the invention, it is possible first to carry out the blocking of the epoxy resin or resins chosen as starting material and then to prepare the toner powder with the aid of so-obtained modified epoxy resin or mixture of modified epoxy resins. However the blocking can also take place during the preparation of the toner powder, which leads to considerable savings in time and effort.

Accordingly the invention also provides a process for preparing toner powder according to the invention which process comprises carrying out the blocking of epoxy groups of the starting epoxy resin or epoxy resin mixture while homogeneously mixing in the other ingredients in a liquid state. It has been found that the blocking process can readily be kept under control and can be reguiated as required. In this way it is possible to obtain a tailor-made toner powder of particularly good quality.

The toner powder according to the invention can be prepared by methods generally known for the purpose of preparing toner powders, e.g.

kneading, extrusion or hot melting methods. In the first two methods the resin, the colouring material, charge regulator, and if desired other ingredients are generally mixed together at about 90-1 300 C, whereas in the last method temperatures generally of about 1 50 to 2500C are used. After cooling the material obtained is ground into particles with the desired size, in general 2-50 Mm.

Of the three methods of preparation, the hot melting method has been found most suitable for the preparation of the toner powder according to the invention, particularly if the blocking reactions are to take place during the preparation of the toner powder. The toner powder prepared by this preferred method appears to have even better properties than when the other two methods are used and this particularly applies to the quality and reproducibility of the charging, stability and fixing behaviour. A contributing factor in this is that with the preferred method the temperatures and residence time can readily be controlled and regulated.

If it is desired to prepare a toner powder containing modified epoxy resin obtained partly from a liquid epoxy resin and partly from a solid epoxy resin, the two starting resins can be mixed together before carrying out the blocking reaction.

However, it is also possible in a first stage to block in a certain proportion of the final desired percentage (but preferably at least 7080%) of the epoxy groups of the starting liquid epoxy resin by reaction with one of the above-mentioned monofunctional blocking agents, preferably in combination with the intermolecular reaction.

After this the starting solid epoxy resin or mixture of epoxy resins is or are added and blocking is permitted to take place to the final desired percentage in a second stage. The other ingredients of the toner powder are preferably added to the reaction system in the first stage in order to obtain maximum homogeneity of mixing.

The toner powder according to the invention contains a charge regulator in order to ensure that it has a sufficiently positive chargeability. For this purpose there may be used a conventional positive charge regulator, the best known of which are Nigrosine base and Nigrosine hydrochloride. The charge regulator according to the present invention is not however an epoxy amine. In particular the charge regulator is not the reaction product of an epoxy resin with a primary or secondary amine having a pKa greater than 3.

The toner powder according to the present invention may be used as such, i.e. as a onecomponent developer, or together with carrier particles, which may be of metal but are not necessarily so, as a two-component developer.

To prepare a developer of the two-component type the toner powder according to the invention may be mixed by conventional carrier particles such as iron, nickel, metal oxide, glass, sand or quartz.

The invention provides a two-component developer comprising carrier particles and particles of a toner powder according to the invention.

If the toner powder according to the invention is to be used as a one-component developer (i.e.

without carrier for the purpose of so-called unary developing) preference is given to the use of magnetic brush development in which the toner powder is applied to the surface to be developed in the form of a powder brush formed on the rotary outer surface of a developing roller having a magnetic core. For this purpose finely divided magnetisable material, such as e.g. iron particles, is homogeneously dispersed in the toner particles.

The magnetisable material is generally intimately mixed with the toner resin in the liquid phase during preparation of the toner powder. The necessary quantities of iron powder generally represent 30 to 80% by weight based on the resin.

The invention provides a method of developing a negative latent electrostatic image which method comprises depositing on the image toner particles according to the invention.

The invention is further illustrated in the following Example.

Example A toner powder was prepared by mixing during 90 minutes at a temperature between 97 and 1000C: 1 6.6 g Epikote 828 (E.M.M.=185) 14.4 g 4-(a,a-dimethylbenzyl)-phenol 8.0 g carbon 6.0 g of Nigrosine (as charge regulator) subsequently there were added to the mixture so obtained 50.8 g Epikote 1004 (E.M.M.=887) 4.2 g Epikote crosslinking agent (supplied by the firm Anchor Chemicals under the trademark E.D.A.-870).

Thereafter the mixing continued for another 120 minutes at a temperature of about 9oat. The mixture was cooled, ground and sieved, giving particles in the range 10-25 ftm. The Tg was 590C and the E.M.M. 3440.

4 Parts of the toner particles obtained were mixed with 96 parts oxidised iron powder. The (positive) charge was approximately 1 7 MC/g and the permanence exceeded 150,000 copies. The toner showed a highly favourable fixing behaviour when used in contact roller-band fixing device and had a fixing range of 95-1 600C (650C).

Claims

1. A heat-fixable toner powder capable of acquiring a positive charge upon triboelectric contact with metal carrier particles, which toner powder comprises finely divided toner particles comprising a thermoplastic resin, colouring material and a charge regulator which is other than an epoxy amine, the thermoplastic resin constituent being mainly composed of resin having an epoxy molar mass (as herein defined) of approximately 2000 to 75000, the resin being either (i) a derivative of an epoxy resin having a molecular weight of at most approximately 1000 and an epoxy molar mass of at most approximately 700 in which approximately 25 to 95% of the epoxy groups have been blocked by reaction with a monofunctional carboxylic acid, phenol or diarylsulphonamide and approximately 5 to 75% have been blocked by intermolecular reaction with hydroxyl groups on the epoxy resin and/or by reaction with a bi- or poly-functional reagent; or (ii) a mixture comprising at least 20 parts by weight of a resin as defined under (i) and at most 80 parts by weight of a phenoxy resin or of a resin which is a derivative of an epoxy resin having a molecular weight of at least approximately 1 500 and an epoxy molar mass of at least approximately 900 in which at least 5% of the epoxy groups have been blocked by intermolecular reaction and/or reaction with a bior polyfunctional reagent.

2. Toner powder according to claim 1 wherein at least 20% by weight of the said resin is derived from a liquid epoxy resin with a molecular weight of at most approximately 500 and an epoxy molar mass of at most approximately 300 in which approximately 50 to 95% of the epoxy groups have been blocked by reaction with a monofunctional carboxylic acid, phenol or diarylsulphonamide and approximately 5 to 50% of the epoxy groups have been blocked by intermolecular reaction and/or by reaction with a bi- or poly-functional agent.

3. Toner powder according to claim 2 wherein at most 80% by weight of the resin comprises a phenoxy resin or a resin obtained from an epoxy resin with a molecular weight of at least approximately 2500 and an epoxy molar mass of at least approximately 2000 in which at least 5% of the epoxy groups have been blocked by reaction by intermolecular reaction and/or by reaction with a bi- or poly-functional agent.

4. Toner powder according to any one of the preceding claims wherein the phenol used in the blocking reaction is 4-(a:,-dimethylbenzyl)- phenol.

5. Toner powder according to any one of claims 1 to 3 wherein the diarylsulphonamide used in the blocking reaction is a substituted or unsubstituted benzene-sulphonanilide.

6. Toner powder according to any one of the preceding claims which contains finely divided magnetisable material as colouring material.

7. Toner powder substantially as described in the foregoing Example.

8. A process for preparing a toner powder according to any one of the preceding claims which process comprises carrying out the blocking of epoxy groups of the starting epoxy resin or epoxy resin mixture while homogeneously mixing in the other ingredients in a liquid state.

9. A process according to claim 8 for preparing a toner powder as claimed in claim 2 or 3 which process comprises in a first stage carrying out the blocking of a proportion of the final desired percentage of the epoxy groups of the starting liquid epoxy resin and in a second stage adding the starting solid epoxy resin or epoxy resin mixture and continuing the blocking reaction to the final desired percentage.

10. A process according to claim 9 wherein at least 7080% of the epoxy groups of the starting liquid epoxy resin are blocked in the first stage.

11. Toner powder prepared by the process claimed in any one of claims 8 to 10.

12. A two-component developer comprising carrier particles and particles of a toner powder as claimed in any one of claims 1 to 7 and 11.

1 3. A method of developing a negative latent electrostatic image which method comprises depositing on the image toner particles as defined in any one of claims 1 to 7.