GB2128353A - Electrostatographic toner material - Google Patents

Abstract

An electrostatographic toner material comprising a core material and a shell enclosing the core material, in which the core material comprises a colorant, a non- ferromagnetic inorganic pigment, and a binder which comprises a combination of a polymer and a solvent having a boiling point of higher than 180 DEG C and capable of dissolving or swelling said polymer.

Description

SPECIFICATION Eleetrostatographic toner material BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an electrostatographic toner material, and more particularly relates to a pressure fixable electrostatographic toner material comprising encapsulated toner particles.

2. Description of Prior Arts There is known an electrostatography which comprises developing a tone electrostatic latent image contained on a photoconductor or dielectric surface with a toner material containing a colorant and fixing aid to produce a visible toner image, and transferring and fixing the visible toner image onto a surface of a support medium such as a sheet of paper.

The development of the latent image to produce a visible toner image is carried out by the use of either a developing agent consisting of a combination of a toner material with carrier particles, or a developing agent consisting of a toner material only. The developing process utilizing the combination of a toner material with carrier particles is named "two component developing process," while the developing process utilizing only a toner material is named "one component developing process." The toner image formed on the latent image is then transferred onto a surface of a support medium and fixed thereto. The process for fixing the toner image to the support medium can be done through one of three fixing processes, that is, a heat fixing process (fusion process), a solvent fixing process and a pressure fixing process.

The pressure fixing process which involves fixing the toner material onto the surface of a support medium under application of pressure thereto is described, for instance, in United States Patent No.

3,269,626. The pressure fixing process involving the use of neither a heating procedure nor a solvent produces no such troubles as inherently attached to either the heat fixing process or the solvent fixing process. Moreover, the pressure fixing process can be employed with a high speed automatic copying and duplicating process, and the access time is very short in the pressure and fixing process.

Accordingly, the pressure fixing process is said to be an advantageous fixing process inherently having a variety of preferable features.

However, the pressure fixing process also has a variety of inadvantageous features. For instance, the pressure fixing process generally provides poorer fixability than the heat fixing process does, whereby the toner image fixed onto a paper is apt to rub off easily. Further, the pressure fixing process requires very high pressure for the fixing, and such a high pressure tends to break the cellulose fibers of the support medium such as paper and also produces glossy surface on the support medium. Moreover, the pressing roller requires to have relatively greater size, because the roller necessarily imparts very high pressure to the toner image on the support medium. Accordingly, reduction of the size of a copying and duplicating machine cannot exceed a certain limit defined by the size of a pressing roller.

There has been previously proposed an encapsulated toner material which comprises toner particles enclosed with micro-capsules, so as to overcome the above-described disadvantageous features of the pressure fixing process. The encapsulated toner material is prepared by enclosing a core material (containing a colorant such as carbon black) with a shell which is rupturable by the application of pressure. Thus prepared encapsulated toner material has various advantageous features; for instance, fixing of the encapsulated toner material does not require very high pressure, but the fixability is high. Accordingly, the encapsulated toner material is viewed as suitable for the use in the pressure fixing process.However, the encapsulated toner materials proposed up to now appear unsatisfactory in practical use, because they do not meet some of requirements required for providing smooth copying and duplicating operation and satisfactory toner image fixability and quality.

More in detail, it is required for the toner material for the use as a dry type developing agent in the electrostatography to have excellent powder characteristics (or, powder flowability) to provide high development quality, and to be free from staining the surface of a photosensitive material on which a latent image is formed.

Further, a toner material employed for the two component developing process is also required not to stain the surfaces of the carrier particles employed in combination. The toner material for the use as a developing agent in the pressure fixing process is furthermore required to be satisfactory in the fixability under pressure and not to undergo off-setting on the roller surface, that is, phenomenon that the toner adheres to the roller surface so as to stain it.

In summary, the toner material employed in the pressure fixing process ought to be at a high level in all characteristics such as powder characteristics (powder flowability), fixability onto a support medium (e.g., paper) as well as preservability of the fixed image, resistance to the off-setting, and electron chargeability and/or electroconductivity depending on the system employed. The previously proposed encapsulated toner materials are unsatisfactory in some of these characteristics.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an electrostatographic encapsulated toner material particularly improved in the fixability. The term "fixability" used herein means to include the fixing property of an image made up of the toner material onto a support medium such as a paper, as well as preservability of the toner image fixed onto the support medium. As described hereinbefore, the procedure for fixing the toner material in the pressure fixing process is generally carried out by passing a support medium having the toner material placed thereon through between pressing rollers of hard metal to rupture the encapsulated particles on the support medium.Most of the previously known encapsulated toner materials are unsatisfactory in the fixability, whereby the fixed images easily rub off with fingers or with other papers to stain these materials. The unsatisfactory fixability of the previously known toner materials is one of the factors disturbing practical use of the pressure fixing process involving the use of an encapsulated toner material.

Another object of the invention is to provide an encapsulated toner material improved in the resistance to off-setting as well as improved in the fixability. The term "off-setting" means a phenomenon that a roller is stained with a portion of the core material or the shell of the encapsulated toner material likely occurring when a support medium having a toner image placed thereon is passed through between the metal rollers to rupture the encapsulated particles on the medium. Poor resistance to the off-setting of the previously known toner materials is another factor to disturb practical use of the pressure fixing process involving the use of an encapsulated toner material.

A further object of the invention is to provide an encapsulated toner material showing satisfactory rupturability in the fixing stage but resistant to mechanical shock applied thereto in other stages, as well as the improvements in the pressure fixability and resistance to the off-setting.

There is provided by the present invention an electrostatographic toner material comprising a core material and a shell enclosing the core material, in which the core material comprises a colorant, a non-ferromagnetic inorganic pigment, and a binder comprising a polymer and a solvent having a boiling point of higher than 1 800C and capable of dissolving or swelling said polymer.

DETAILED DESCRIPTION OF THE INVENTION The shell material prepared in the invention is made of a polymer. Examples of the polymer employable as the shell material include a variety of resins such as polyurethane, polyamide, polyester, polysulfonamide, polyurea, epoxy resin, polysulfonate and polycarbonate. Preferred are a polyurethane resin and a polyurea resin.

In the present invention, the terms "polyurethane" and "polyurea" means to include polymers produced by polycondensation reaction between polyisocyanate and one or more of the counterpart compounds such as polyoi, water, polyamine and piperazine. Accordingly, the term "polyurethane" means either a simple polyurethane comprising substantially urethane bondings only or a polymer comprising urethane bondings and a relatively small number of urea bondings. The term "polyurea" means either a simple polyurea comprising substantially urea bondings only or a polymer comprising urea bondings and a relatively small number of urethane bondings.

The shell can be composed substantiaily of a complex layer. For instance, the shell can comprise two or more polymers selected from the group consisting of a polyurethane resin, a polyurea resin and a polyamide resin.

The encapsulation of the core material in the form of droplets with the shell material can be done by a known method for preparing the so-called micro-capsule containing a hydrophobic liquid, for instance, an interfacial polymerization method as described in United States Patents No. 3,577,515 and No. 3,429,827, and British Patents No. 950,443, No. 1,091,007 and No. 1,091.078: an inner polymerization method as described in United States Patents No. 3,660,304, No. 3,726,804, No.

3,796,669 and No. 2,969,330; a phase separation method in an aqueous medium as described in United States Patents No. 2,800,457, No. 2,800,458, No. 3,041,289, and No. 3,205.175: an outer polymerization method as described in United States Patents No. 4,087,376, No. 4,089,802, No.

3,100,103, and No. 4,001,140; and a fusion-dispersion-cooling method as described in United States Patent No. 3,167,602. Other known encapsulating methods and modifications and combinations of these encapsulating methods can be also employed.

Among these encapsulating methods, the interfacial polymerization method comprising the following process is preferably employed for the preparation of the toner material of the invention.

In the first place, the following two substances are selected: Substance (A) which as such is hydrophobic liquid or a substance being soluble, miscible or well dispersable in a hydrophobic liquid; and Substance (B) which as such is a hydrophilic liquid or a substance being soluble, miscible or well dispersable in a hydrophilic liquid, which can react with Substance (A) to produce a polymerization reaction product insoluble in either the hydrophobic liquid or the hydrophilic liquid. Examples of the polymerization reaction product include a polyurethane resin, a polyamide resin, a polyester resin, a polysulfonamine resin, a polyurea resin, an epoxy resin, a polysulfanate resin, and a polycarbonate resin.

In the second place, very small droplets of a hydrophobic liquid including Substance (A) and the core material comprising a colorant, a non-ferromagnetic inorganic pigment, and a binder comprising a polymer and a solvent having a boiling point of higher than 1 800C and capable of dissolving or swelling said polymer, are dispersed into a hydrophilic liquid such as water containing Substance (B).

The Substance (A) is caused to react with Substance (B) to undergo an interfacial polymerization reaction in the dispersion by an appropriate procedure, for instance, by heating the dispersion. Thus, the shell of a polymerization reaction product of Substance (A) with Substance (B) (and/or water) are formed around the hydrophobic droplets to produce micro-capsules comprising the core material and the shell enclosing the core material in which the core material comprises a colorant, a non-ferromagnetic inorganic pigment, and a binder comprising the combination of a polymer and a solvent having a boiling point of higher than 1 800C and capable of dissolving or swelling said polymer.

Examples of Substance ,(A) preferably employed for the preparation of the shell in the invention include compounds having isocyanate groups described below: (1) Diisocyanate m-phenylene diisocyanate, p-phenylene diisocyanate, 2,6-tolylene diisocyanate, 2,4-tolylene diisocyanate, naphthalene 1,4-diisocyanate, diphenylmethane 4,4'-diisocyanate, 3,3'-dimethoxy-4,4'- biphenyl diisocyanate, 3,3Fdimethyldiphenylmethane 4,4'-diisocyanate, xylylene 1,4-diisocyanate, xylylene 1,3-diisocyanate, 4,4'-diphenylpropane diisocyanate, trimethylene diisocyanate, hexamethylene diisocyanate, propylene 1,2-diisocyanate, butylene 1,2-diisocyanate, ethylidyne diisocyanate, cyclohexylene 1 ,2-diisocyanate, cyciohexylene 1,4-diisocyanate, p-phenylene diisocyanate, triphenylmethane diisocyanate; 2J Triisocyanafe 4,4',4"-triphenylmethane triisocyanate, polymethylenepolyphenyl triisocyanate, toluene-2,4,6triisocyanate; (3) Tetraisocyanate 4,4'-dimethyldiphenylmethane 2,2',5,5'-tetraisocyanate; and (4) Polyisocyanate prepolymer an addition product of hexamethylene diisocyanate and hexanetriol, an addition product of 2,4tolylene diisocyanate and catechol, an addition product of 2,4-tolylene diisocyanate and hexanetriol, an addition product of 2,4-tolylene diisocyanate and trimethylolpropane, an addition product of xylylene diisocyanate and trimethylolpropane.

Examples of Substance (B) preferably employed for the preparation of the shell in the invention include compounds described below: (1) Water; (2) Polyol ethylene glycol, propylene glycol, 1 ,4-butanediol, 1 ,5-pentanediol, 1 ,6-heptanediol, I ,7- heptanediol, 1 ,8-octanediol, trimethylolpropane, hexanetriol, catechol, resorcinol, hydroquinone, 1,2 dihydroxy-4-methylbenzene, 1 ;;3-dihydroxy-5-methylbenzene,3,4-dihydroxy-1-methylbenzene,3,5- dihydroxy- 1 -methylbenzene, 2,4-dihydroxy-1 -ethylbenzene, 1 ,3-naphthalenediol, 1 ,5-naphthalenediol, 2,3-naphthalenediol, 2,7-naphthalenediol, o,o'-biphenol, p,p'-biphenol, 1,1 '-bi-2-naphthol, Bisphenol A 2,2'-bis(4-hydroxyphenyl)buta ne, 2 ,2'-bis(4-hy'drnxyphenyl)isopentane, 1,1 '-bis(4 hydroxyphenyl)cyclopenta ne,1,1 '-bis(4-hydroxyphenyl)cyclohexane, 2,2'-bis(4-hydroxy-3- methylphenyl)propane, bis-(2-hydroxyphenyl)-methane, xylylenediol, pentaerythritol, glycerol, sorbitol;; (3) Polyamine ethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, pphenylenediamine, m-phenylenediamine, 2-hydroxytrimethylenediamine, diethylenetriamine, triethylenetetraamine, diethylaminopropylamine, tetraethylenepentaamine, an addition product of an epoxy compound and an amine compound; and (4) Piperazine piperazine, 2-methylpiperazine, 2,5-dimethylpiperazine.

In the above-described combinations, Substance (A) can be replaced with an acid chloride, a sulfonyl chloride, or a bischloroformate to produce a shell of other resinous material such as a polyamide resin.

Examples of these compounds are as follows: (1)Acid chloride oxazoyl chloride, succinoyl chloride, adipoly chloride, sebacoyl chloride, phthaloyl chloride, isophthaloyl chloride, terephthalyol chloride, fumaroyl chloride, 1 ,4-cyclohexanedicarbonyl chloride, polyesters containing acid chloride groups, poiyamides containing acid chloride groups; (2) Sulfonyl chloride 1 ,3-benzenedisulfonyl chloride, 1 ,4-benzenedisulfonyl chloride, 1 ,5-naphthalenedisulfonyl chlo?ide, 2,7-naphthalenedisulfonyl chloride, 4,4'-biphenyldisulfonyl chloride, p,p' .oxybis(benzenesulfonyl chloride), 1,6-hexanedisu Ifonyl chloride:: (3) Bischloroformate ethylene bis(chloroformate), tetramethylene bis(chloroformate), hexamethylene bis(chloroformate), 2,2'-dimethyl-1 ,3-propane bis(chloroformate), p-phenylene bis(chloroformate).

In the preparation of the dispersion of very small hydrophobic droplets containing Substance (A) and the core material, the hydrophobic liquid to be dispersed preferably contains a low-boiling solvent or a polar solvent. These solvents serve for accelerating formation of the shell which is a reaction produced between Substance (A) and Substance (B). Examples of these solvents include methyl alcohol, ethyl alcohol, diethyl ether, tetrahydrofuran, dioxane, methyl acetate, ethyl acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, n-pentane, n-hexane, benzene, petroleum ether, chloroform, carbon tetrachloride, methylene chloride, ethylene chloride, carbon disulfide and dimethylformamide.

There is no limitation on the shell material, so far as the material is rupturable under pressure.

Accordingly, materials other than those described hereinbefore can be likewise employed. Examples of these materials include homopolymers and copolymers of styrene or a substituted styrene such as polystyrene, poly(p-chlorostyrene), styrene-butadiene copolymer, styrene - acrylic acid copolymer, styrene - acrylic ester copolymer, styrene - methacrylic acid copolymer, styrene - methacrylic ester copolymer, styrene -- maleic anhydride copolymer, and styrene -- vinyl acetate copolymer; polyvinyltoluene resin, acrylic ester homopolymer, methacrylic ester homopolymer, xylene resin, methlyvinyl ether -- maleic anhydride resin, vinyl butyral resin, poly(vinyl alcohol) resin, and poly(vinylpyrrolidone).

The encapsulated toner material whose shell is composed substantially of a complex layer comprising two or more polymers selected from the group consisting of a polyurethane resin, a polyurea resin and a polyamide resin can be produced as follows.

In a hydrophobic liquid comprising the aforementioned core material are dissolved an acid chloride and a polyisocyanate. This solution is then dispersed in an aqueous medium comprising a polyamine or piperazine and a dispersing agent to produce fine droplets of the core material having an average diameter in the range from about 0.5 to about 1 ,000 microns in the aqueous medium.

The dispersion produced above is then neutralized or made weak aikaline by addition of an alkaline substance, and subsequently heated to a temperature between 40 and 900 C. Upon completion of these procedures, a complex layer consisting substantially of a polyamide resin and a polyurea resin in which the polyamide resin is a reaction product produced by reaction between the acid chloride and the polyamine, and the polyurea resin is a reaction product produced by reaction between the polyisocyanate and the polyamine, is formed around the droplet of the core material. Thus, the encapsulated particle having the complex layer shell is obtained.

If a polyol is further added to the hydrophobic liquid in the above-described procedure, there is produced around the droplet of the hydrophobic core material a complex layer shell consisting substantially of the polyamide resin and a polyurethane resin, in which the polyurethane resin is a reaction product of the polyisocyanate with the polyol.

In the latter procedure, a complex layer consisting substantially of the polyamide, polyurea and polyurethane resins can be produced, if the polyamine is introduced into the reaction system in an amount exceeding the amount required to react the introduced acid chloride.

The shell of thus produced particle is, as described above, a complex layer shell. The term "complex layer shell" means to include a shell comprising a polymer mixture, as well as to include a double layer shell. The term "double layer shell" is not intended to mean only a shell in which the two layers are completely separated by a simple interface, but include a shell in which the interface is not clearly present in the shell, but the ratio between one polymer and another polymer (or other polymers) varies from the inner phase to the outer phase of the shell.

The acid chloride can be replaced with a dicarboxylic acid or its acid anhydride. Examples of the dicarboxylic acid include adipic acid, sebacic acid, phthalic acid, terephthalic acid, fumaric acid, 1 4- cyclohexane-dicarboxylic acid, and 4,4'-biphenyldicarboxylic acid. Examples of the acid anhydride include phthalic anhydride.

The inner polymerization method can be done in the following manner.

In a hydrophobic liquid to form the core material of the encapsulated toner particle are dissolved Substance (A) and one or more substances polymerizable with Substance (A) in the presence of a lowboiling solvent or a polar solvent. The obtained hydrophobic liquid is dispersed and emulsified in the aforementioned hydrophilic liquid which is not miscible with the hydrophobic liquid. The emulsion is then heated to cause removal of the low-boiling solvent or polar solvent to the outside of the hydrophobic liquid droplet and simultaneously to move the shell-forming substances to the surface of the droplet. The shell-forming substances are polymerized at the surface to prepare the desired shell.

Thus, the desired encapsulated toner particles dispersed in the hydrophilic liquid are obtained.

As for the other aspects of the interfacial polymerization method and the other processes for the preparation of micro-capsules containing a hydrophobic liquid, there are given descriptions in United States Patent No. 3,726,804, which is introduced hereinto as reference.

The core material contains a colorant for producing a visible image from the latent image. The colorant generally is a dye or a pigment, but a certain agent providing no directly visible image such as fluorescent substance can be employed as the colorant, if desired.

The colorant is generally selected from a variety of dyss, pigments and the like employed generally in the conventional electrostatographic copying and duplicating process. Generally the colorant is a black toner or a chromatic toner. Examples of the black toners include carbon black. Examples of the chromatic toners include blue colorants such as copper phthalocyanine and a sulfonamide derivative dye; yellow colorants such as a benzidine derivative dye, that is generally called Diazo Yellow: and red colorants such as Rhoda mine B Lake, that is, a double salt of xanthine dye with phosphorus wolframate and molybdate, Carmine 6B beloning to Azo pigment; and a quinacridone derivative.

The core material contains a binder (adhesive material) for keeping the colorant within the core and assisting the fixing of the colorant onto the surface of a support medium such as a paper.

In one aspect, the present invention-is characterized in that the binder comprises a polymer and a solvent having a boiling point of higher than 1 800C and capable of dissolving or swelling said polymer.

There is known a binder to be contained in the core material, which comprises a mixture of a polymer and a easily volatile low-boiling solvent, as described in-Japanese Patent Provisional Publication No. 56(1981)-144434, etc. This art is based one conception that an encapsulated toner material placed on a support medium such as a paper is ruptured resulting in adhesion of a mixture of the polymer and the volatile low-boiling solvent together with the colorant under pressure, and the polymer assists fixing of both the colorant and remaining shell material upon volatilization of the lowboiling solvent.

As a result of the study of the above-identified prior art, the present inventor has discovered that the binder comprising the polymer and the volatile low-boiling solvent is not able to provide to the colorant satisfactory adhesion to a support medium and that the volatile low-boiling solvent deteriorates the working conditions in the preparation of the encapsulated toner material as well as in the copying procedure, because the low-boiling solvent is apt to emit offensive odor and is inflammable.

Moreover, the encapsulated toner material containing the low-boiling solvent in the core becomes poor in adhesion during storage, presumably because of the volatilization of the low-boiling solvent through the shell.

In contrast, the binder composition of the invention comprising a polymer and the high boiling solvent assists more effectively the adhesion of colorant onto a support medium such as a paper, as compared with the binder composition comprising the polymer and low-boiling solvent. Further, the visible toner image fixed onto the support medium is kept under satisfactory conditions in the storage.

Furthermore, there is brought about no such problems as fire and offensive odor.

Examples of the polymer for the binder include the following polymers: polyolefin, olefin copolymer, polystyrene, -styrene - butadiene copolymer, epoxy resin, polyester, natural and synthetic rubbers, poly(vinylpyrrolidone), polyamide, cumarone-indene copolymer, methyl vinyl ether -- maleic anhydride copolymer, maleic acid-modified phenol resin, phenol-modified terpene resin, silicone resin, epoxy-modified phenol resin, amino resin, polyurethane elastomer, polyurea elastomer, homopolymer and copolymer of acrylic acid ester, homopolymer and copolymer of methacrylic acid ester, acrylic acid-long chain alkyl methacrylate copolymer oligomer, poly(vinyl acetate), and pply(vinyl chloride).

The above-listed polymers and examples of other polymers employable in the invention are described in detail in the following publications: Japanese Patent Publications No. 48(1 973)-30,499, No. 49(1974)-i 588 and No.

54(1 979)--8,1 04: Japanese Patent Provisional Publications No. 48(1 973)--7 5,032, No.

48(1 973)-78,93 1, No. 49(1974)-i 7,739, No. 51(1976)-i 32,838, No. 52(1 977)-98,531, No.

52(1977)-i 08,134, No. 52(1977)-i 19,937, No. 53(i978)-1,028, No. 53(1978)-36,243, No.

53(1 978)-1 18,049, No. 55(1 980)-89,854 and No. 55(1 980)-1 66,655; and United States Patents No. 3,788,994 and No. 3,893,933.

In the present invention, the polymer of the binder is preferably selected from the group consisting of homopolymers and copolymers of acrylic acid esters (acryiates), homopolymers and copolymers of methacrylic acid esters (methacrylates), and styrene -- butadiene copolymers.

Examples of the solvent having a boiling point of higher than 1 800C and capable of dissolving or swelling the polymer include the following liquids: (1) Phthalic acid esters dibutyl phthalate, dihexyl phthalate, diheptyl phthalate, dioctyl phthalate, dinonyl phthalate, dodecyl phthalate, butyl phthalyl butyl glycolate, dibutyl monofluorophthalate:: (2) Phosphoric acid esters tricresyl phosphate, trixylenyl phosphate, tris(isopropylphenyl) phosphate, tributyl phosphate, trihexyl phosphate, trioctyl phosphate, trinonyl phosphate, tridecyl phosphate, trioleyl phosphate, tris(butoxyethyl) phosphate, tris(chloroethyl) phosphate, tris(dichloropropyl) phosphate; (3) Citric acid esters O-acetyl triethyl citrate, O-acetyl tributyl citrate, O-acetyl trihexyl citrate, O-acetyl trioctyl citrate, O-acetyl trinonyl citrate, O-acetyl tridecyl citrate, triethyl citrate, tributyl citrate, trihexyl citrate, trioctvl citrate, trinonyl citrate, tridecyl citrate;; (4) Benzoic acid esters butyl benzoate, hexyl benzoate, heptyl benzoate, octyl benzoate, nonyl benzoate, decyi benzoate, dodecyl benzoate, tridecyl benzoate, tetradecyl benzoate, hexadecyl benzoate, octadecyl benzoate, oleyl benzoate, pentyi o-methylbenzoate, decyl p-methylbenzoate, octyl o-chlorobenzoate, lauryl pchlorobenzoate, propyl 2,4-dichlorobenzoate, octyl 2,4-cichlorobenzoate, stearyl 2,4-dichlorobenzoate, oleyl 2,4-dichlorobenzoate, octyl p-methoxybenzoate; (5) Aliphatic acid esters hexadecyl myristate, dibutoxyethyl succinate, dioctyl adipate, dioctyl azelate, decamethylene 1,10-diol diacetate, triacetin, tributin, benzyl caprate, pentaerythritol tetracaproate, isosorbitol dicaprilate;; (6) Alkylnaphthalenes methylnaphthalene, dimethylnaphthalene, trimethylnaphthalene, tetramethylnaphtharene, ethylnaphthalene, diethylnaphthalene, triethylnaphthalene, monoisopropylnaphthalene, diisopropylnaphthalene, tetraisopropylnaphthalene, monomethylethylnaphthalene, isooctylnaphthalene:: (7) Dialkylphenyl ethers di-o-methylphenyl ether, di-m-methyldiphenyl ether, di-p-methylphenyl ether; (8) Amides of fatty acids and aromatic sulfonic acids N,N,-dimethyllauroamide, N,N-diethylcaprylamide, N-butylbenzenesulfonamide; (9) Trimellitic acid esters trioctyl trimellitate; (10) Diarylalkanes diarylmethanes such as dimethylphenylphenylmethane, diaryiethanes such as 1 -methylphenyl-i - phenylethane, l-dimethylphenyl-l -phenylethane and 1 -ethylphenyl- 1 -phenylethane.

For the purpose of the present invention, the high-boiling solvent is preferably selected from phthalic acid esters, phosphoric acid esters, diarylalkanes and alkyinaphthalenes.

In the invention, each of the polymer and the high-boiling solvent can be employed alone or in combination.

There is no limitation on the ratio between the high-boiling solvent and the polymer, but the ratio is preferably chosen within the range of 0.1 - 4 (high-boiling solvent/polymer), ratio by weight. The mixture of the polymer and high-boiling solvent sometimes shows very high viscosity depending upon the ratio therebetween. Such a viscous mixture is hardly emulsified in satisfactory conditions in the initial stage for the preparation of the small droplets of the core material. In that case, a low-boiling solvent miscible with the high-boiling solvent and polymer but non-miscible with water, such as ethyl acetate or butyl acetate, is preferably added to the mixture to decrease the viscosity and facilitate formation of satisfactory emulsion. The low-boiling solvent is removed upon formation of the emulsion under reduced pressure.

The core material of the present invention is characterized by containing a non-ferromagnetic inorganic pigment. The term "non-ferromagnetic inorganic pigment" means an inorganic pigment showing a magnetic susceptibility of not higher than 10-4 (value shown under saturation of magnetization in an external magnetic field). The non-ferromagnetic inorganic pigment employed in the invention is preferably a non-ferromagnetic metal oxide. Examples of the non-ferromagnetic metal oxide include titanium dioxide, zinc oxide, manganese dioxide, and magnesium oxide. Other nonferromagnetic pigments employable in the invention include carbonates such as calcium carbonate, sulfates such as calcium sulfate, and other metal compounds such as molybdenium disulfide.

The non-ferromagnetic pigment of the invention may be coated with other materials. Examples of the coating materials include organic polymers, silicone polymers, surface active agents, and organic or inorganic solvents. Preferable coating materials are polyhydric alcohols having 2 - 1 8 carbon atoms and 2 - 4 hydroxyl groups in the molecule.

Examples of the polyhydric alcohols having 2 - 4 hydroxyl groups include alcohols having 2 hydroxyl groups such as ethylene glycol, propylene glycol, 1 ,3-diphydroxypropane. 1,4- dihydroxybutane, pentamethylene glycol, 2,5-dihydroxyhexane, 2,4-dihydroxy-2-methylpentane.

heptamethylene glycol, and dodecamethylene glycol; alcohols having 3 hydroxyl groups such as trimethylolethane, trimethylolpropane, glycerol, 2 ,4-dihydroxy-3-hydroxymethylpentane, 1 ,2,6- hexanetriol, and 2,2-bis(hydroxymethyl)-3-butanol; and alcohols having 4 hydroxyl groups such as pentaerythritol. Preferable alcohols are those having 2 - 6 carbon atoms and 3 hydroxyl groups in the molecule. Most preferred is trimethylolethane.

The coating material is generally coated on the non-ferromagnetic inorganic pigment in an amount ranging from approx. 0.01 to 10% by weight, preferably from 0.1 to 1.5% by weight. The coating material is preferably coated over the whole surface of the pigment, but non-uniform coating or portionwise coating may be acceptable. Other examples of the non-ferromagnetic inorganic pigment employable in the invention are described in the following publications: PIGMENT HANDBOOK Vol. 1, edited by Tempe C.Patton (A. Wiley -- Interscience Publication), Collective Edition of New Dyeing Process I: Dye and Pigment (in Japanese), edited by the Japan Society for the promotion of Science, Dyeing Process No. 1 20 Committee (Kyoritsu Shuppan Co., Ltd., Japan), and EXPLANATORY INDUSTRIAL CHEMISTRY (revised edition) written in Japanese by Yozaburo Kohsaka (Maki shoten, Japan).

The non-ferromagnetic inorganic pigment is preferably included in an amount of 5 - 70% by weight based on total amount of the core material. Most preferred range is 10 - 50% by weight.

As described hereinbefore, the core material of the encapsulated toner of the invention necessarily comprises a colorant, a non-ferromagnetic inorganic pigment, a polymer and the high-boiling solvent.

Other additives such as a fluorine-containing resin which is effective in prevention of the off-setting can be also included.

As mentioned hereinbefore, a process for the preparation of the encapsulated toner particles includes a stage for dispersing or emulsifying the hydrophobic liquid containing Substance (A) and the core material in the aqueous medium in the form of very small droplets. For the preparation of the homogeneous dispersion (or emulsion) of the very small droplets of the hydrophobic liquid, it is preferred to incorporate into the reaction liquid a hydrophilic polymer which assists production of the homogeneous dispersion (or emulsion) of the hydrophobic droplets and prevention of agglomeration of the produced hydrophobic droplets.

Examples of the preferred hydrophilic polymer include proteins such as gelatin, graft polymers of gelatin and other polymers, albumin, and casein; cellulose derivatives such as hydroxyethylcellulose, carboxymethylcellulose, and cellulose sulfuric acid ester; saccharine derivatives such as sodium alginate and starch derivatives; and a variety of synthetic hydrophilic homopolymers and copolymers such as poly(vinyl alcohol), partially acetalized poly(vinyl alcohol), poly(N-vinyl pyrrolidone), poly(acrylic acid), poly(acrylic amide), poly(vinylimidazole), and poly(vinylpyrazole).

In the above-listed examples, the gelatin can be a lime-treated gelatin, an acid-treated gelatin, a hydrolyzed gelatin, and an enzymically decomposed gelatin. The graft polymers of gelatin and other polymers can be gelatins carrying graft polymers of gelatin and other polymers or copolymers of vinyl monomers such as acrylic acid, methacrylic acid, their derivatives, e.g., esters and amides, acrylonitrile, and styrene. Examples of the gelatin graft polymers are those miscible with gelatin such as the gelatins carrying the graft chains consisting of polymers of acrylic acid, acrylemide, methacrylamide and hydroxyalkyl methacrylate.

Details of these preferred gelatin graft polymers are described in United States Patents No.

2,763,625, No. 2,831,767, and No.2,956,884.

Representative examples of the synthetic hydrophilic polymers are described, for instance, in West German Offenlegungsschrift No.2,312,718, United States Patents No. 3,620,751 and 3,879,205 and Japanese Patent Publication No. 43(1 968)-7,561.

Dispersing or emulsifying the reaction liquid can be carried out by means of a known homogenizer such as one belonging to the stirring type, the high pressure injecting type, the ultrasonic vibrating type and the kneader type. Particularly preferred homogenizers are a colloid mill, a conventional homogenizer, and an electromagnetic distortion inducing ultrasonic homogenizer.

The encapsulated toner is then produced, for instance, by heating the emulsified reaction liquid in the presence of an appropriate catalyst, as described hereinbefore, so as to form shells around the core material droplets. Subsequently, the encapsulated toner is separated from the aqueous reaction medium and dried to obtain a dry encapsulated toner. The encapsulated toner is preferably washed with water after the separation from the aqueous reaction medium and prior to the drying procedure.

The washing of the encapsulated toner with water is particularly preferred in the case that a hydrophilic polymer has been employed in the preparation of the encapsulated toner. The hydrophilic polymer contained in the reaction mixture is apt to adhere to the surface of the encapsulated toner, and the encapsulated toner having the hydrophilic polymer on the surface is apt to agglomerate easily so as to decrease the powder characteristics of the toner materials. In order to keep the toner material from the disadvantageous agglomeration, the hydrophilic polymer adhering to the surface of the encapsulated toner is preferably removed by washing with water as much as possible.Thus, the hydrophilic polymer on the surface of the encapsulated toner preferably does not exceed 5% by weight based on the total amount of the toner, and more preferably does not exceed 1% by weight.

The drying procedure can be carried out by a known process such as the spray-drying process or the freeze-drying process. The spray-drying process is preferred.

The dried encapsulated toner particles are preferably heated to improve their powder characteristics. The temperature for heating the dried encapsulated toner particles preferably ranges from 50 to 3000 C, and more preferably ranges from 80 to 1 500 C. The period required for the heating procedure varies with the heating temperature, the nature of the binder, etc. Generally, the period ranges from 10 minutes to 48 hours, and preferably ranges from 2 to 24 hours.

There is no limitation on means employed for carrying out the heating procedure. Examples of the heating means include an electric furnace, a muffle furnace, a hot plate, an electric drying oven, a fluid bed drying apparatus, and a infrared drying apparatus.

The dry encapsulated toner can be admixed with an insulating material and/or a charge controller such as a metal-containing dye or Nigrosin dye.

A dry encapsulated toner can be admixed with a flow lubricant such as hydrophobic silica powder so that the flow lubricant can be dispersed over the surface of the encapsulated toner. The encapsulated toner having the flow lubricant such as hydrophobic silica powder over the toner surface shows particularly improved powder quality and property, and accordingly is very advantageous in the practical use.

The encapsulated toner obtained as above can be introduced into an electrostatographic copying and duplicating machine to develop an electrostatographically produced latent image so as to produce a visible toner image in the surface of the photoconductive material. The visible image is then fixed onto a support medium such as a paper by means of an appropriate pressure fixing apparatus. There is no limitation on the pressure fixing apparatus for fixing the encapsulated toner of the invention, and any known apparatus can be applied to the fixing of the encapsulated toner of the invention. Examples of the pressure fixing apparatuses include those illustrated in Japanese Patent Publications No.

44(1 969)-9,880, No.44(1 969)-i 2,797, and No.46(1971)-i 5,876; and Japanese Patent Provisional Publications No. 49(1 974)-62,i 43, No. 49(1 974)-77,641, No. 50(1975)-5 1,333, No.

51 (1 976)-31,235, No. 5i(1976)-40,351, No. 52(1977)-i 5,335, No. 52(1977)-i 02,743, No.

54(1 979)-28,636, No. 54(1 979)-32,326, No. 54(1 979)-41 ,444 and No. 54(1 979)-48,251.

Other features of the electrostatographic copying and duplicating process employing an encapsulated toner material are described in United States Patent No. 3,788,994, which is introduced hereinto as reference.

The present invention will be illustrated by the following examples which are by no means intended to introduce any restriction into the invention. In the examples, the term "part(s)" means "part(s) by weight".

EXAMPLE 1 40 Parts of triisopropylnaphthalene, 5 parts of carbon black and 45 parts of zinc oxide were sufficiently mixed in a mortar two prepare a primary liquid.

Separately, 25 parts of Vernoc D-750, trade name of Dainippon Ink 8 Chemicals Inc., Japan, polyisocyanate having the following formula:

and 2 parts of terephthaloyl chloride were dissolved in 45 parts of ethyl acetate. The resulting solution was mixed with 66 parts of a solution of poly(isobutyl methacrylate) in ethyl acetate (30% by weight solution) to prepare a secondary liquid.

A mixture of the primary liquid and the secondary liquid was dispersed in 200 parts of pre-cooled aqueous gum arabic solution (10% by weight solution) to produce an oil-in-water emulsion containing oily droplets having average diameter of 10 m. To the emulsion was added 1 60 parts of an aqueous solution of hexamethylenediamine (10% by weight solution), and the mixture was stirred for 30 min. To the mixture was added aqueous sodium carbonate solution (10% by weight solution) to adjust the mixture to pH 9.0. The resulting mixture was stirred at 600C for 2 hours to perform the reaction.

Thus obtained aqueous micro-capsule dispersion was washed three times with water through centrifugal separation and spray-dried by means of a spray-drying apparatus (manufactured by Yamato Kagaku Co., Ltd., Japan) to obtain a powdery encapsulated toner material comprising a core (carbon black, zinc oxide, poly(isobutyl methacrylate) and triisopropylnaphthalene) and a shell (a complex layer shell consisting essentially of polyamide resin and polyurea resin) enclosing the core therein.

The encapsulated toner was heated at 1000C for 24 hours in an infrared drying oven, and evaluated on the powder characteristics. The heat-treated encapsulated toner is very flowable.

Microscopic observation of the encapsulated toner indicated that most of the toner particles were present independently of each other. It was confirmed that the encapsulated toner was free from blocking or other disadvantageous phenomena after storage for one day under high temperature high humidity conditions (500 C, RH 90%).

The heat-treated toner was mixed with 0.5% by weight of hydrophobic silica (Aerogil-R-972, produced by Japan Aerogil Co., Ltd.) to obtain an encapsulated toner material more improved in the flowability. This toner was free from blocking or other disadvantageous phenomena even after storage for several days under the high temperature - high humidity conditions (500 C, RH 90%).

Evaluation of the toner containing hydrophobic silica was carried out as follows: Five parts by weight of the toner were admixed with 95 parts by weight of a powdery iron carrier in a shaking apparatus to prepare a developing agent. It was confirmed through microscopic observation that the developing agent contained almost no ruptured toner particles.

A conventional electrostatographic copying and duplicating process was carried out using the above developing agent. The visible toner image produced on a latent image was then transferred onto a paper. The paper carrying the toner image was treated under a pressing roller at a pressure of 350 kg./cm2. There was obtained a toner image with high sharpness and well fixed onto the pauper.

Further, off-setting of the toner was at a very low level.

EXAMPLE 2 A powder encapsulated toner material containing titanium dioxide in place of zinc oxide in the core was prepared through the reaction for the preparation of micro-capsules and the spray-drying of the micro-capsules in the same manner as in Example 1 except that zinc oxide was replaced with titanium dioxide in the preparation of the primary liquid.

The encapsulated toner was heated at 1000C for 24 hours in an infrared drying oven, and evaluated on the powder characteristics. The heat-treated encapsulated toner is very flowable.

Microscopic observation of the encapsulated toner indicated that most of the toner particles were present independently of each other. It was confirmed that the encapsulated toner was free from blocking or other disadvantageous phenomena after storage for one day under the high temperature high humidity conditions (500 C, RH 90%).

The heat-treated toner was mixed with 0.5% by weight of hydrophobic silica (Aerogil-R-972, produced by Japan Aerogil Co., Ltd.) to obtain an encapsulated toner material more improved in the flowability. This toner was free from blocking or other disadvantageous phenomena even after storage for several days under the high temperature - high humidity conditions (500 C, RH 90%).

Evaluation of the toner containing hydrophobic silica was carried out in the same manner as in Example 1 by preparing a developing agent mixed with 'a powdery iron carrier. It was confirmed through microscopic observation that the developing agent contained almost no ruptured toner particles.

A conventional electrostatographic copying and duplicating process was carried out using the above developing agent. The visible toner image produced on a latent image was then transferred onto a paper. The paper carrying the toner image was treated under a pressing roller at a pressure of 350 kg./cm2. There was obtained a toner image with high sharpness and well fixed onto the paper.

Further, off-setting of the toner was at a very low level.

EXAMPLE 3 A powdery encapsulated toner material containing titanium dioxide coated with trimethylolethane (coating amount: 0.5% by weight) in place of zinc oxide in the core was prepared through the reaction for the preparation of micro-capsules and the spray-drying of the micro-capsules in the same manner as in Example 1 except that zinc oxide was replaced with titanium dioxide coated with the trimethylolethane in the preparation of the primary liquid.

The encapsulated toner was heated at 1000C for 24 hours in an infrared drying oven, and evaluated on the powder characteristics. The heat-treated encapsulated toner is very flowable.

Microscopic observation of the encapsulated toner indicated that most of the toner particles were present independently of each other. It was confirmed that the encapsulated toner was free from blocking or other disadvantageous phenomena after storage for one day under the high temperature high humidity conditions (500C, RH 90%).

The heat-treated toner was mixed with 0.5% by weight of hydrophobic silica (Aerogil-R-972, produced by Japan Aerogil Co., Ltd.) to obtain an encapsulated toner material more improved in the flowability. This toner was free from blocking or other disadvantageous phenomena even after storage for several days under the high temperature - high humidity conditions (509C, RH 90%).

Evaluation of the toner containing hydrophobic silica was carried out in the same manner as in Example 1 by preparing a developing agent mixed with a powdery iron carrier. It was confirmed through microscopic observation that the developing agent contained almost no ruptured toner particles.

A conventional electrostatographic copying and duplicating process was carried out using the above developing agent. The visible toner image produced on a latent image was then transferred onto a paper. The paper carrying the toner image was treated under a pressing roller at a pressure of 350 kg./cm2. There was obtained a toner image with high sharpness and well fixed onto the paper.

Further, off-setting of the toner was at a very low level.

Claims (8)

1. An electrostatographic toner material comprising a core material and a shell enclosing the core material, in which the core material comprises a colorant, a non-ferromagnetic inorganic pigment, and a binder comprising a polymer and a solvent having a boiling point of higher than 1 800C and capable of dissolving or swelling said polymer.

2. The toner material as claimed in claim 1, in which the non-ferromagnetic inorganic pigment is coated with an alcohol selected from the polyhydric alcohols having 2 - 4 hydroxyl groups.

3. The toner material as claimed in claim 1 or 2, in which the non-ferromagnetic inorganic pigment is a non-ferromagnetic metal oxide.

4. The toner material as claimed in claim 1, in which the non-ferromagnetic inorganic pigment is included in an amount of 10 - 50% by weight based on the total amount of the core material.

5. The toner material as claimed in claim 1, in which the polymer is selected from the group consisting of homopolymers and copolymers of acrylic acid esters, homopolymers and copolymers of methacrylic acid esters, and styrene-butadiene copolymers.

6. The toner material as claimed in claim 1, in which the solvent having a boiling point of higher than 1 800C and capable of dissolving or swelling said polymer is selected from the group consisting of phthalic acid esters, phosphoric acid esters, alkyinaphthalene, and diarylalkanes.

7. The toner material as claimed in claim 1, in which the shell comprises at least one resin selected from the group consisting of a polyurethane resin and a polyurea resin.

8. The toner material as claimed in claim 7, in which the shell is composed of a complex layer comprising at least two resins selected from the group consisting of a polyurethane resin, a polyurea resin and a polyamide resin.