CA1131488A

CA1131488A - Toner powder containing an epoxy resin with modified expoxy groups

Info

Publication number: CA1131488A
Application number: CA316,144A
Authority: CA
Inventors: Martinus T. J. Peters
Original assignee: Oce Van der Grinten NV
Current assignee: Canon Production Printing Holding BV
Priority date: 1977-11-18
Filing date: 1978-11-10
Publication date: 1982-09-14
Also published as: AU521736B2; SE7811903L; ES475129A1; NL7811188A; FR2409539A1; FR2409539B3; DE2849986C2; IT7869632A0; SE436807B; CH645197A5; DE2849986A1; BE872085A; IT1109716B; AU4169578A

Abstract

A B S T R A C T
A heat fusible toner powder for the development of latent electrostatic images, the components of which include an insulating thermo-plastic resin material, characterized in that the insulating thermoplastic resin material includes (1) a modified epoxy resin of which at least 50% of the total number of initial epoxy groups have been blocked partly by chemical reaction with a monofunctional carboxylic acid, phenol or diarylsulphonamide and, partly by reaction with the hydroxylic groups of the epoxy resin and optionally by reaction with a bi- or polyfunctional epoxy hardener, and, optionally, (2) a phenoxy resin which components (1) and (2) may be mutually cross-linked; the toner powder having a melt viscosity at 140°C of between 2 and 200,000 s.Pa. and a glass transition temperature of between 45 and 85°C.

Description

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The invention relates to a heat-fusible toner powder for the development of latent electrostatic images which substantiall~ consists of finely divided coloured toner particles comprising an insulating thermoplastic resin and colouring material. The invention in particular relates to such a toner powder of which the insulating thermoplastic resin for the major part consists of epoxy resinO
The invention also relates to a process for the preparation of such a toner powder, to two-component developers containing such a toner powder in admixture with a carrier as well as to one-component developers composed of such a toner powder and to the development of latent electrostatic images using such a toner powderO
nYo-component as well as one-component developers comprising a toner powder having toner particles containing an insulating thermoplastic resin and colouring material find general application in the development of latent electrostatic imagesO Such images are, eOgO, obtained on a suitable support in an electrographic or electrophotographic process. The latent electrostatic images may have a positive polarity, as for instance in the case of electrophotographic elements based on selenium, or a negative polarity, as for instance in the case of electrophotographic elements based on zinc-oxide and a number of organic photoconductors.
Examples of insulating thermoplastic resins which have been pro-posed for application in toner powders are polystyrene, copolymers of styrene with an acrylate and/or methacrylate, polyamides, phenol-~ormaldehyde resins, polyesters and to a lesser extent, epoxy-resinsO
The colouring material used in black toner powders to be applied in a two-component developer is usually carbon black whilst in black toner powders to be used as one component developer the colouring material generally consists mainly of finely divided magnetic material, such as, eOgO, iron ' ,.

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powder, chromium oxide or nickel ferrite. In coloured toner powders, eOg.
for application in multi-colour reproduction processes, organic dyes are usually added to the thermoplastic resinO
During development of a latent electrostatic image toner powder is deposited on the charged image areas resulting in a visible imageO One-component developers can be used for the development of electrostatic images with a positive polari~y as well as those having a negative polarity~ without special provisions being required for that purposeO In the case of two-component developers the carrier to be mixed with the toner powder has to be chosen in such a way that the toner powder acquires the desired triboelectric chargeO
Examples of generally applied carriers are iron, nickel, metaloxide, glass, sand or quartz particles of the desired sizeO The particles may be provided with a polymer coating if desired.
Negatively chargeable developers are mainly used for the development of electrostatic images with a positive polarity and positively chargeable developers mainly for the development of electrostatic images with a negative polarityO During the development the toner powder is deposited on the charged latent image areas resulting in a visable imageO
The powder image formed aither by means of the one-component developer or the two-component developer can be fixed directly on the surface on which it has been deposited, which is eOg., the case in the so-called direct electrophotographyO In the so-called indirect electrophotography the powder image is transferred to a suitable receptor sheet on which it is sub-sequently fixedO The fixation usually is effected by the application of heat, e.g. in a so-called radiation or flash fusing device or in a so-called contact fusing device where the powder image is brought into contact with a heated surface such as, eOg~, a roller and/or belt.

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Apart from the ingredients mentioned above, the toner powders often comprise one or more other well known ingredients, particularly plasticisers and polarity control agents.
The basic requirements, which a toner powder should meet for satis-factory results, are pronounced polarity, good charging characteristics such as sufficient chargeability, uniform charge distribution, charge stability and low sensitivity to moisture and temperature, good and reproducible fusing properties, thermal stability and a good permanence during prolonged use. To save fusing energy it is further most desirable that the temperature at which the toner powder begins to melt lies as close as possible above the minimum glass transition temperature required for its thermal stability, which tem-perature in general should lie between 45 and 80 C. For a toner powder for contact fusing it moreover is desirable that the fusing range should be as wide as possible, preferably several tens of degrees centigrade. This is for reducing as much as possible the chance that part of the powder image will be transferred to the fusing roll and from there back to the paper which causes the so-called ghost images, and the chance that the fusing rolls will be polluted. The lower limit of the fusing range is the lowest temperature at which the image is just sufficiently fixed, the upper limit is the temperature at which ghost images begin to be formedO
The object of the present invention is to provide toner powders which acquire a negative charge upon triboelectric contact with metal carrier particles and which powders are highly stable under normal conditions of stor-age and use and to a high degree meet the desired properties for toner powders summed up aboveO A further object of the invention is to provide toner powders which have a lower glass transition temperature and the lower limit of the fusing range of which is much closer to their glass transition tempera-ture than is the case with the present generally applied toner powders~

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In one aspect, the present invention provides a negatively chargeable toner powder characterized by stability at temperatures up to 50C and a melting point of about 65 to 150C, which comprises finely divided toner particles containing an insulating thermoplastic resin and colouring materials, the thermoplastic resin including at least 50% by weight of a modified epoxy resin having an epoxy molar mass (grams resin/grams equivalent of epoxy) of at least 8,000, at least 5~ of epoxy groups of the modified epoxy resin modified with one or a combination of monofunctional reactants selected from the group consisting of carboxylic acid, phenolic compounds and N-aryl-arylsulphonamide, by reaction with the respective carboxyl, hydroxyl or sulfonamide groups thereof, and from 0 to 95% of epoxy groups of the modified epoxy resin modified by intermolecular reaction and/or by cross-linking with a polyfunctional epoxy hardener.
In another aspect, the present invention provides a process for preparing the toner powder as described above, which comprises the steps of homogeneously mixing the thermoplastic resin in a molten state with the colouring materials, cooling the mass thus obtained, and grinding said cooled mass to the desired degree of fineness, wherein epoxy groups of an epoxy resin of lower epoxy molar mass chosen as starting material are modified with the monofunctional carboxylic acid and/or monofunctional phenolic compound and/or N-aryl-arylsulphonamide during said mixing of the ingredients.
In order to meet the requirement that the toner powder according to the invention is stable under normal conditions of storage and use, at least 50% of the total number of epoxy groups in the starting epoxy resin or epoxy resins should be blocked as indicated above. Which percentage of the total number of epoxy groups in the staring epoxy resins must be blocked in order to achieve the desired stability depends on the reactivity of the starting epoxy resin. The higher the reactivity of the starting epoxy resin or resins, i.e. the lower the so-called epoxy-molar-mass of the starting epoxy resin or resins, the higher the percentage of blocked epoxy groups must be for obtain-ing a stable toner powder. By "epoxy-molar-mass" is meant the mass of resin in grams which contains one gram equivalent of epoxy (see page 4-1~ "Handbook of Epoxy Resins" - Lee and Neville, McGraw Hill Book Company, 1967). For the - 4a -~9L3~

sake of brevity epoxy-molar-mass will hereinafter be referred to as E.M.M.
Preferably, the epoxy groups of the starting epoxy resin or resins are blocked to such a degree, that the E.M.Mo of the total mass of the co~ponents ~1) and

(2) in the toner powder according to the invention is at least 80000 For some of the commercially most readily available epoxy resins the following table gives a survey of their average E.M.M. and of the percentage of their epoxy groups which has to be blocked in order to increase its Eo~ Mo to a predetermined higher valueO

Table ~~ ~
Percentage of Epikote 828 1001 1004 1009 blocking 0 av.E.M.M. 190 500 900 3200 " 380 1000 1800 6400 " 760 2000 3600 12850 87.5 " 1520 4000 7200 25600 93.75 ~ 3040 8000 14400 >50000 96.87 " 6080 16000 28800 98.43 " 12160 32000>50000 ~rom the above table it can be seen that from an Epikote 1009 only ~\
slightly more than 50% of its epoxy groups need to be blocked in order to obtain a resin with an EoMoMo of some 8000, whilst of a lower molecular type resin in general at least some 8705% of its epoxy groups will have to be blocked for that purpose.
It should also be remarked that in the case of the lower molecular epoxy resins an increase of the E.MoMo with a few thousand in fact corresponds with a few percent of increase in blocked epoxy groups onlyO It will, there-fore, be obvious that the requirement that the E.MoMo of the total mass of components ~1) and (2) in the toner powder preferably amounts to at least 8000 ~ e ~k 5 _ . ' ..

can be taken in a less stringent sense, the lower the molecular weight of the starting resin has been.
Although the sensitivity of the EoM~Mo as a measure for the reactiv-ity left in the thermoplastic resin constituent apparently decreases with decreasing molecular weight of the epoxy resin used as starting material, applicants believe that the EoM.M. figure still is the best yard stick present-ly available for that purposeO
The modified epoxy resins used in the toner powders according to the invention can be prepared in a most economic way from epoxy resins which are commercially available. Also a mixture of such resins may be usedO By "epoxy resins" are meant in the context of this specification condensation products of a polyphenol, in particular of 4,4'-isopropylidene-diphenol, with a halo-hydrine, in particular l-chloro-2,3-epoxypropane. As may be known the commercially available epoxy resins generally have an E.M.Mo of lower than 4000.
Examples of epoxy resins that may be used as starting material in the preparation of the modified epoxy resin to be used in the toner powder according to the invention are Epikote 1001 ~melting point 60-70C, E.M.Mo 450-500; both data according to suppliers specifications), Epikote 1004 (melting point 90-100C, E.M.M. 850~940), Epikote 1006 (melting point 115-125C, EoM.M. 1,500-1,900) Epikote 1007 (melting point 140-155C, E.M.M. 2,300-3,400)o Mixtures of 2 or more epoxy resins may also be used. For certain applications it may be advantageous to use a liquid epoxy resin as starting material as will be explained hereinafter.
Which blocking method or combination of me~hods mentioned abo~le is chosen is connected with the way in which the toner powder is to be fixed.
Applicants have found that, if the toner powder according to the invention is to be used for fusing by radiation, the viscosity of the toner powder if measured at 140C advantageously should lie between 2 and 1000 s.Pa and its glass transition temperature ~hereinafter called Tg) between ~5 and 65C. ~or application in a contact fusing device its viscosity at 140C preferably should lie between 200 and 200,000 s.Pa and its Tg between 45 and 80C.
Blocking by means of a monofunctional carboxylic acid, phenol or di-aryl-sulphonamide results in the desired increase of the E.M.M. of the epoxy resin started from without substantial increase of its molecular weight and viscosity. This blocking method, therefore, should be predominant where a modified epoxy resin fraction for a toner powder to be used in a radiation fusing device has to be prepared.
~le parameters mentioned hereinbefore for viscosity and Tg with which a toner powder to be fixed by radiation preferably should comply are generally obtained if at least 50% and preferably at least 70% of the initial epoxy groups of the modified epoxy resin, or mixture of epoxy resins, has been blocked by chemical reaction with a monofunctional carboxylic acid, phenol or diaryl-sulphonamide, and only a minor part, say 5-10%, by intermolecular reaction and preferably, none by reaction with an epoxy hardener.
The monofunctional carboxylic acids, phenols or diaryl-sulphonamides to be used in the framework of this invention should, other than the carboxyl-, resp. hydroxyl-, resp. sulphonamide group, comprise no further substituents which could react with the epoxy groups of the starting resin under the reaction conditions occurring during the blocking step. As regards the car-boxylic acids, aliphatic as well as aromatic carboxylic acids can be used for the blocking step. Useful aliphatic carboxylic acids are e.g. heptanoic acid, nonanoic acid, dodecanoic and isododecanoic acid, hexadecanoic acid and octa-decanoic acid. Also good results were obtained with aromatic carboxylic acids and those which have been substituted with one or more alkyl-, aralkyl-, cycloalkyl-, aryl-, alkylaryl-, alkoxy- or aryloxy groups and which are sub-.

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stantially not volatile under the blocking reaction conditions. Examples of such aromatic carboxylic acids are benzoic acid and substituted benzoic acids such as 2,4-dimethylbenzoic acid, 4~ dimethylbenzyl)-benzoic acid, 4-phenylbenzoic acid and 4-ethoxybenzoic acid. Further the perfluoro-carboxylic acids such as e.g. perfluorobutyric acid, perfluoro-octanoic acid and per-fluoro-decanoic acid.
Of the group of phenols especially useful for the blocking appear to be phenols which are substituted with one or more alkyl-, aralkyl-, cyclo-alkyl-, aryl-, alkylaryl-, alkoxy- or aryloxy-groups, and which are substan-tially not volatile under blocking reaction conditions. Examples of such phenols are 4-n-butylphenol, 4-n-pentylphenol, 2,3,4,6-tetramethylphenol, 2,3,5,6-tetramethylpllenol, 4-(~,-dimethyl)benzylphenol, 4-cyclohexylphenol,

3-methoxyphenol, 4-methoxyphenol and 4-ethoxyphenol.
Examples of useful di-aryl-sulphonic acids are benzene-sulphonanilide and its derivatives, such as e.g. those of which one or both benzene-nuclei carry one or more lower alkyl- or alkoxy groups.
Of the above mentioned compounds benzoic acid, substituted benzoic acid, 4-t~,~-dimethyl)benzylphenol and p-toluene sulphonanilide appeared to be exceptionally useful.
In order to comply with the parameters for viscosity and Tg men-tioned hereinbefore which are preferred for a toner powder to be used for con-tact fusing, the modified epoxy resin must comprise a low molecular fraction with a molecular weight of lower than 4000 and a high molecular fraction, which may or may not be cross linked, with a molecular weight of more than 4000, preferably more than 10,000~
A modified epoxy resin comprising a low and a high molecular fraction can e.g. be obtained by blocking the epoxy groups of a commercial epoxy resin or of a mixture of epoxy resins, for at least 5% and preferably for about 10 ; ' '' ' ~
, ~ , to 25% depending on the epoxy started from, by chemical reaction with a mono-f~mctional carboxylic acid, phenol or di-aryl-sulphonamide, whilst the remain-ing epoxy groups up to an overall total of at least 50% are blocked by intermolecular reaction with the alcoholic hydroxyl groups of the resin itself.
The first mentioned blocking method yields the lower molecular fraction, the last mentioned the higher one. Both mentioned types of blocking methods can be carried out simultaneously or one after another. In the second case a higher viscosity and a greater fusing range is obtained but the Tg remains substantially the same as when both methods are carried out simultaneously.
The desired high molecular fraction can, however, also be obtained by reacting part of the epoxy groups of the resin ~or resins) started from with a bi-or polyfunctional epoxy hardener, whereby linear or cross linked structures may be obtained. In this case too the reaction methods can be carried out simultaneously or one after another. A most suitable epoxy hardener appears to be 4,4'-iso-propylidene diphenol.
A third possibility to obtain the high molecular fraction is to pre-pare it in a separate process or buy it as commercial product. Subsequently it can be mixed with the low molecular fraction prepared in any of the ways described above. When 4,4'-isopropylidene diphenol has been used for the preparation of the high molecular fraction the resulting product usually is indicated as phenoxy resin. They have a molecular structure which is substan-tially linear and a molecular weight between 10,000 and 80,000. An example of a commercially available phenoxy resin is ~utapox 0717 ~mol. wt. 30,000) a product of the firm Bakelite.
The increase in molecular weight of the starting epoxy resin by an epoxy hardener, in general, is much larger and is obtained much faster than the increase obtainable by intermolecular reaction. If an epoxy hardener is used for obtaining the high molecular fraction, preferably at least approxi-~: .

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mately 40-75% of the total number of initial epoxy groups of the modified epoxy resin or resins for a major part should have beenblocked by the chemical reaction with a monofunctional carboxylic acid, phenol or di-aryl-sulphonamide and only for a minor part by intermolecular reaction, and at most 25-60% by reaction with an epoxy hardener.
The toner powder according to the invention can be prepared by using one of the methods known in the art for this purpose, such as e.g. the knead-ing, extrusion or hot melt method. According to the first two methods the resin, coloring material and, if desired, other ingredients, such as e.g. a polarity control agent, are mixed together generally at temperatures between approximately 90-160C. In the hot melt method the mixing is usually carried out at temperatures around 200C. After cooling the mass obtained is ground into particles of the desired sizes, usually lying between 2-50~um. It is also possible to obtain the desired particle sizes by spraying the hot m~lt into a cooler medium Of the three methods of preparation mentioned above the hot melt and the kneading method were found to be the most suitable ones for preparing the toner powder according to the invention. The toner powders so prepared were found to be highly satisfactory and reproducible, especially in respect of their most essential properties, especially charging behaviour, stability and fusability. This may be attributed to the fact that with said methods the temperatures and reaction times can most easily be kept in hand. Moreover it was found that these 2 methods are most suitable to carry out the blocking reactions of the epoxy groups of the starting resin to obtain the desired modified epoxy resin during the preparation of the toner powder itself. This has a number of advantages over separate preparation of the modified resin.
Preferably the toner powder according to the invention therefore is prepared by mixing the epoxy resin, or mixture of epoxy resins, to start from in a molten form at temperatures be~ween approximately 150 and 250C with the colouring material and possibly other ingredients, such as e.g. a polarity control agent, plasticisers, flow improving agents and the like, carrying out the blocking reaction, resp. reactions as specified herein before or during the mixing operation. During these mixing operatio~ the blocking reactions easily and without difficulties proceed to a final stage. When in the block-ing reaction a di-aryl-sulphonamide is used the epoxy groups of the starting resin are preferably blocked by said amide and only moderate blocking by intermolecular reaction with the alcoholic hydroxyl groups of the resin itself will occur. If a monofunctional carboxylic acid or phenol is used in the blocking reaction it may be desirable to use a catalyst to prevent the inter-molecular reaction from becoming predominant, since otherwise rather useless toner powders with a far too high melting point may be obtained. Suitable catalysts for this purpose may be found amongst the quaternary ammonium com-pounds. A most suitable catalyst appeared to be tetramethylammoniumchloride.
The colorant materials required for the preparation of toner powders other than black often appear to be not sufficiently soluble in many of the resins applied for the preparation of toner powders. A good solubility, how-ever, is especially desirable if transparent toner powders have to be prepared, 2~ required for many multi-color copying processes. It may be considered an additional advantage of the toner powders of the invention that many coloring dyestuffs appear to be sufficiently soluble therein.
For obtaining a developer of the two-component type the toner powder according to the invention is mixed, either immediately after its preparation or in a later stage, with the desired carrier particles. If the developer is to be used for magnetic brush development, iron particles, which may be pro-vided with a surface coating, are used as carrier. The desired particle sizes of the carriers are known to those skilled in the art. In general they are .

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!38 lying between 50 and 150 ~m. Dependent on the particle sizes of the two components the two-component developer usually contains from 1 to 8% by weight of toner particles.
The toner powders of the invention in general obtain a sufficient negative charge in admixture with usual carriers such as e.g. iron powder and iron oxide coated powder. If desired one of the negative charge control agents known in the art may be added to obtain a higher negative charge. A
most suitable negative working charge control agent appears to be Atlac* 382E, a commercial product of Atlas Company. The active ingredient is 4,4'-iso-propylidene-diphenol-propyleneoxide fumarate. Acid number 10-20.
If positively chargeable toner powders are required the toner powders of the invention can be mixed with a positive charge control agent as described in applicant's Canadian Patent No. 1,115,582, and in applicant's co-pending Canadian patent application no. 314,063~ filed October 24, 1978. Both these types of positively chargeable modified epoxy resin based powders are not in-tended to be covered by the present application and consequently are disclaimed herewith.
It is, however, possible to prepare two-component developers in which the toner powders of the present invention acquire a charge of positive polar-ity without a polarity control agent having been incorporated in the tonerpowder itself. This can be effected by using the appropriate carrier. Such carriers can be obtained in various ways as described in the prior art, such as e.g. United Kingdom Patent Specifications Nos. 1,251,752, 1,389,744, 1,438,973, 1,342,748 and 1,373,000.
If the toner powder according to the invention should be used as such, i.e. as one-component developer, magnetizable material should preferably be incorporated in the resin as the colouring material in order to allow the toner powder to be applied in the so called magnetic brush development system *Trademark - 12 -X

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since this s~stem appeared to be the most suitable one for the application of one-component developers. Generally some 10 to 50 % by weight of magnetizable material is required for that purpose.
The invention is illustrated by means of the following non-limitative examples.
Example 1 In a hot melt apparatus were mixed at a temperature of 150C 164 g of 4~ -dimethylben~ylphenol, 526 g of Epikote 1001 (Shell), 0.3 g tetra-C methylammoniumchloride and 60 g of carbon black ~Printex*G; Degussa). While homogeni~ing, the temperature was increased till 200C and kept there for 60 minutes. The blocking reaction of the epoxy resin was finished at this stage and the lower molecular weight fraction of the toner was ready. Then was added 250 g of the phenoxy resin Rutapox 07-17 ~Bakelite) as the higher molecular weight fraction and the blend was homogenised for another 150 minutes. After cooling to room-temperature the blend was ground and classi-fied. The particle size distribution of the resulting toner powder was 6 to 30lum, its specific area was 0.42lum~l.
The glass transition temperature ~Tg), as measured vith a Du Pont 990 thermal analyser, was 5~C. The epoxy molecular mass ~E.M.M.) was 9,100.
The residue of the monofunctional phenol was less than 0.1%. The melt vis-cosity at 140 C, measured in a cone and plate mechanical spectrometer of Rheometrics Inc. was 210 s.Pa.
Three parts of this toner were mixed with 97 parts of oxidized iron powder ~er-mag MTM Brunito; Tonioli, Italy). This developer was charged by ,`
agitation in a developing unit. The toner acquired a charge of ~19 pc/g.
The developer was used to develop a positively charged latent image on a selenium type photoconductor. The image was transferred electrically to plain paper and fused by means of heat. A good copy was obtained. Large solid f~fiJ~ U4 - 13 -. . : .
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black areas on an original document could be copied with high and even density on the copy, without the so-called edge-effect.
The toner could be fixed in a heat contact-fuser for testing purposes at temperatures between 68 and 114C (fusing-range width 46 C). The test fuser was operating with a contact time of 1.3 sec. between the heated roller and an A4 copy sheet.
Example 2 A commercially available negatively chargeable toner, based on a ~-methylstyrene-butylacrylate copolymer was tested under exactly the same conditions as described in example 1. The glass transition temperature ~Tg) of this toner was 55C. The toner could be fixed on plain paper at temperatures between 88-131C, a fusing range width of 43C. The distance from Tg to the lower limit of the fusing range of this toner is thus considerably larger compared to the one of the toner from example l.
Example 3 The procedure of example 1 was repeated, now with the ingredients Epikote 1001-350 g, 4-~,~-dimethylbenzylphenol- 88 g and in addition tetra-methylammoniumchloride -0.1 g as a catalyst. After 45 minutes a second por-tion of 0.1 g catalyst was added. After 90 minutes reaction time the lower molecular weight fraction was ready. The residual amount of 4-~,~-dimethyl-benzylphenol was less than 0.1% and the E.M.M. was 4470, indicating that approximately 88% of the epoxy groups had been blocked.
A higher molecular weight fraction was made in a Z-blade mixer by reacting 455 g Epikote 1009 (E.M.M. = 3000) with 34 g of 4,4'-isopropylidene-diphenol. Tetramethylammoniumchloride was used in catalytic amounts (0.2 g).
After a reaction time of 2 hours the lower molecular weight fraction as made above and 73 g of carbon black were added and mixed, thoroughly. Tg was 67C, E.M.M. was 10,900, melt-viscosity at 140C was 1600 s.Pa.

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A toner powder made from this blend showed arl equally good electro-statical behaviour as the one from example 1. The fusing range was from 82-135C ~width 53C).
Example 4 A low viscosity toner was made by mixing and reacting Epikote 1001 -601 g, 4-~J~-dimethylbenzylphenol - 151 g and tetramethylammoniumchloride -Q.3 g during 90 minutes at 150C, carbon black 60 g was added and after this 188 g of a 4,4'-isopropylidenediphenol-propylideneoxidefumarate polyester with an acid number of 15. (Atlac 382E, Atlas Co.) Mixing was continued for 2 hours. Tg was 47C, E.M.M. was 8500, melt-viscosity at 140 C was 7 s.Pa.
The blend was ground and classified. The resulting toner powder could be charged tribo-electrically with a negative polarity against the oxidized iron powder of example 1 up to a charge of - 27JUC/g.
The toner was fixed very easily on plain paper in a radiant heat device.
Example 5 Using the procedure of example 1 a toner was made from 48.9 g of Epikote 1001 (E.M.M. = 495), 12.1 g of benzoic acid as the modifying agent, 6 g of carbon black and 33 g of phenoxy resin (R'utapox 07.17). A thermally 2a stable toner powder was obtained having the following characteristics:
melt viscosity ~140 C) = 600 s.Pa., Tg-61 C, E.M.M. = 35.000. The toner could be charged negatively against a commercially available iron carrier powder and could be fixed well either by radiation or by contact heat.
Example 6 A mixture of 450 g of Epikote 1004 ~E.M.M. = 900), 111~2 g of p-toluene sulphonanilide as modifying agent and 35~8 g of carbon black was blended for 3 hours at 200C. The blend had a Tg = 72C, E.M.M. = 18.000, melt viscosity (140 C) = 85 s.Pa. The resulting toner powder was thermally - ' "' ~, ~

stable and could be fixed easily by heat on paper.

Example 7 _ _ In a vessel provided with a stirrer and oil bath heater, a mixture of 25.3 g Epikote 828 21.7 g 4~ dimethylbenzylphenol 0.5 g tetramethylammoniumchloride 6.0 g carbon black was heated to a temperature of about 180C and this temperature was maintained for 90 minutes. The reaction mixture had an E.M.M. of 3800. 88% of the initial epoxy groups had reacted. To the reaction mixture 46~5 g Epikote 1009 (E.M.M. = 3150) were added and the mixture was stirred for 90 minutes at a temperature of 200C. The melt was drained off and cooled down to room temperature. The solid mass was ground and sieved in a known manner to give a toner powder having a particle size between 8 and 24 microns. The toner had a Tg of 51C and an E.M.M. of 4100. Of the initial epoxy groups ~present in the starting Epikote 828 and 1009) about 82% had reacted.
The use of a liquid epoxy resin having an E.M.M. value of less than 500, and preferably of less than 250, as a starting epoxy resin for manu-facturing the modified resin, as illustrated by this example, has the import-~0 ant advantage that a toner powder having a Tg of about 50C and a fusing range starting slightly above the Tg temperature is obtained, without the necessity of adding an auxiliary agent such as N-cyclohexyl-p-toluenesul-phamide as is disclosed for that purpose in Applicant's Dutch Patent Applica- !l tion No. 7415325. The auxiliary agent has the disadvantage that it shows a tendency to migrate out of the toner powder and to deposit on the carrier particles and/or the fusing rollers of the fixing device. It thus unfavourably influences the charging characteristics of the toner powder and the durability of the fusing rollers.

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When being applied in a electrophotocopier provided with a contact fusing device with rolls covered with silicone rubber, provided with a thin layer of silicone oil, the above toner powder could excellently be fixed in an effective contact time of 0.03 sec at a temperature of 165C of the contact roller. To fix a commercially available toner powder on the basis of a styrene-butyl-acrylate copolymer in the same time interval the temperature of the contact roller had to be 210C, a temperature which is less desirable having regard to external heat dissipation and energy economics.
When a toner powder according to the invention should find application in a high volume electrophotocopier it, therefore, is highly advantageous to use a liquid epoxy resin as starting material in the prepara-tion of such toner powder.

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Claims

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

1. A negatively chargeable toner powder characterized by stability at temperatures up to 50°C and a melting point of about 65 to 150°C, which comprises finely divided toner particles containing an insulating thermoplastic resin and colouring materials, the thermoplastic resin including at least 50% by weight of a modified epoxy resin having an epoxy molar mass (grams resin/grams equivalent of epoxy) of at least 8,000, at least 5% of epoxy groups of the modified epoxy resin modified with one or a combination of monofunctional reactants selected from the group consisting of carboxylic acid, phenolic compounds and N-aryl-arylsulphonamide, by reaction with the respective carboxyl, hydroxyl or sulfonamide groups thereof, and from 0 to 95% of epoxy groups of the modified epoxy resin modified by intermolecular reaction and/or by cross-linking with a polyfunctional epoxy hardener.

2. A toner powder according to claim 1, characterized in that the thermoplastic resin additionally includes up to 50% phenoxy resin.

3. A toner powder according to claim 2, characterized in that the phenoxy resin and the modified epoxy resin are mutually cross-linked.

4. A toner powder according to any of claims 1, 2 or 3, characterized in that the modified epoxy resin for at least 20% by weight is derived from a liquid epoxy resin with a molecular mass of at most 500, about 50-95% of the epoxy groups having been modified with one or a combination of mono-functional reactants, and about 5 to 50% having been modified by intermolecular reaction and/or by cross-linking with an epoxy hardener.

5. A toner powder according to claim 1, characterized in that the toner powder has a melt viscosity at 140°C of between 2 and 200,000 s.Pa. and a glass transition temperature of between 45 and 85°C.

6. A toner powder according to claim 5 which is particularly suitable for being fused by radiation, characterized in that the toner powder has a melt viscosity at 140°C of between 2 and 1000 s.Pa and a glass transition temperature of between 45 and 65°C.

7. A toner powder according to claim 6, characterized in that at least 50% of the epoxy groups of the modified epoxy resin have been modified with one or a combination of monofunctional reactants.

8. A toner powder according to claim 7, characterized in that at least 70% of the epoxy groups of the modified epoxy resin have been modified with one or a combination of monofunctional reactants.

9. A toner powder according to claim 5 which is particularly suitable for being fixed by contact fusing, characterized in that the toner powder has a melt viscosity at 140°C of between 200 and 200,000 s.Pa and a glass transition temprature of between 45 and 80°C.

10. A toner powder according to claim 9, characterized in that at least 10-35% of the epoxy groups of the modified epoxy resin have been modified with one or a combination of monofunctional, reactants and at least 40%
of the epoxy groups of the modified epoxy resin have been modified by intermolecular reaction with the alcoholic hydroxyl groups of the resin itself.

11. A toner powder according to any of claims 1, 2 or 3, characterized in that the toner particles additionally include a negatively acting polarity control agent.

12. A toner powder according to claim 1, characterized in that the monofunctional carboxylic acid is a substituted or non-substituted, saturated aliphatic carboxylic acid.

13. A toner powder according to claim 12 characterized in that the monofunctional carboxylic acid is substituted or unsubstituted benzoic acid.

14. A toner powder according to claim 1 characterized in that the monofunctional phenolic compound is substituted with one or more alkyl-, aralkyl-, cyclo-alkyl-, aryl-, alkylaryl-, alkoxy- or aryloxy-groups, and is substantially not volatile under reaction conditions.

15. A toner powder according to claim 14, characterized in that the monofunctional phenolic compound is 4-(.alpha.,.alpha.-dimethylbenzyl)-phenol.

16. A toner powder according to claim 1, characterized in that the N-aryl-arylsulphonamide is p-toluene-sulphonanilide.

17. A toner powder according to claim 1, characterized in that as epoxy hardener 4,4'-iso-propylidene-diphenol has been used.

18. A toner powder according to claim 1, characterized in that the modified epoxy resin is prepared from an epoxy resin starting material of lower epoxy molar mass by reaction of at least 5% of epoxy groups of the epoxy resin starting material with a monofunctional carboxylic acid and/or a monofunctional phenolic compound and/or an N-aryl-arylsulphonamide at a temperature of about 150-250°C, with the proviso that during the reaction, the carboxylic acid and phenolic compound and N-aryl-arylsulphonamide are substantially non-volatile and have no substituents which are reactive towards the epoxy groups other than the respective carboxylic and hydroxyl and sulphonamide groups, and optionally, by reaction of no more than 95% of the epoxy groups of the epoxy resin starting material by intermolecular reaction and/or by cross linking with a polyfunctional epoxy hardener.

19. A toner powder according to claim 18, characterized in that at least about 40-75% of the epoxy groups of the epoxy resin starting material are modified with a monofunctional carboxylic acid and/or a mono-functional phenolic compound and/or an N-aryl-arylsulphonamide, and about 25-60% of the epoxy groups of the epoxy resin starting material are modified by cross-linking with an epoxy hardener, and a minor portion of the epoxy groups of the epoxy resin starting material are modified by intermolecular reaction.

20. A process for preparing the toner powder of claim l, which comprises the steps of homogeneously mixing the thermoplastic resin in a molten state with the colouring materials, cooling the mass thus obtained, and grinding said cooled mass to the desired degree of fineness, wherein epoxy groups of an epoxy resin of lower epoxy molar mass chosen as starting material are modified with the monofunctional carboxylic acid and/or monofunctional phenolic compound and/or N-aryl-arylsulphonamide during said mixing of the ingredients.

21. A process according to claim 20, characterized in that modification during said mixing of ingredients is also achieved by intermolecular reaction and/or cross-linking with the polyfunctional hardener.

22. A two-component developer which comprises a toner powder according to any one of preceding claims 1, 5 or 18 in admixture with a carrier suitable for obtaining a negative triboelectric charge.

23. A one-component developer including a toner powder according to any one of the preceding claims 1, 5 or 18, characterized in that it additionally includes finely divided magnetizable material.