CA1054421A - Electrographic developing composition and process - Google Patents

Abstract

ELECTROGRAPHIC DEVELOPING COMPOSITION AND PROCESS
Abstract of the Disclosure The present invention relates to an electrographic developing composition containing finely-divided carrier particles and finely-divided toner particles having incorporated therein a fusible, crosslinked binder polymer. An improved electrographic developing process using such toner particles is also disclosed.

Description

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-Ficl~ of tllc Invcntion .
- The present invention relates to electrography and particularly to the dry de~elopment of electrostatic charge patterns.

Description of the Prior Art Electrographic imaging and developing processes, for example electrophotographic imaging process and techniques, have been extensively described in both the patent and other literature, for example, U.S. Patent Nos.

2,221,776 issued November l9, 1940; 2,277,013 issued March 17, 1942; 2,297,691 issued October 6, 1942; 2,357,809 issued September 12, 1944; 2,551~582 issued May 8, 1951;
2,825,814 issued March 4, 1958; 2,833,648 issued May 6, 1958;

3,220,324 issued November 30, 1965; 39220,831 issued November 30, 1965; 3,220,833 issued November 30, 1965 and - many others. Generally these processes have in common the ~ -- steps of forming a latent electrostatic charge image on an insulating electrographic element. The electrostatic latent ~ -image is then rendered visible by treatment with an electro~
20 static developing composition or-developer. -- Conventional developers include a carrier that `
can be either a triboelectrically chargeable, magnetic material such as iron filings,~ powdered lron or iron oxide~
or a triboelectrically chargeable, non-magnetic substance -like glass beads or crystals of inorganlc salts such as sodium or potassium chloride. In a~dition to the carrier, electrostatic developers include a toner which is electrostatically attractable to the carrier. m e toner~is usually a particula~e polymeric material which may,~if desired, be suitably darkene~
or colored for image viewing purposes ~rith a colorant such as - . , ~
dyestuffs or pigments, for example, carbon black.
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~ ~o develop an electr~st~ic ima~e, the dry ~eYe10~r can be applied imagewise to ~he electrostatically charged surface by various techniques. One such technique is known as cascade development and is described in U.S~ Patent No.
2,618,552, issued November 18,-1952.
Another suitable deve10ping technique is known as magnetic brush de~elopment and is described in U.S. Patent No. 3,003,462, issued October 10, 1961.
In conventional electrophotographic app1ications, the developed image is formed on a photoconductive element and is transferred to a receiving sheet. The image thus transferred is then fixed, ie. made permanent typically by heating to fuse the transferred image. Thus, the toner material must be capable of ~ being fused under temperature conditions which will avoid any charring, burning or other physical damage to the receiver shee~
which is typically formed of paper.
A variet- of processes all~ apl-ar;ltlls have heen - dcscriled in the electrogr~phic Drt for .-ccomp1ishillg fixlng of th6 transferre~ iml~e. Typica1ly this is accomp1;s]led by 20 thc comhille(l appl ic~tion of hecat and prcssurc, Eor eYamp1e, by bringill~ the receivillg sheet containill~ the transferrcd dcveloped toner image into contact with a heated fusing roller.
In a~ition to thc use of a hcatcd fusing roller other devices may bc uti1izcd for thc fi~ing oE thc devc10pcd toner imagc such as contacting thc dcvc10l~ccl tOllCl imagc witll a heated p1~tcn or somc otllcr simil~r ]~catc~ mcmber.
In ~ny case, regar~1ess of thc typc oE hcatcd fusing melll~er employc(l, it has bCCII rccogllizc~ in thc clcctrograp]lic art that thcrc exists a su~stallti~l prol)lem 30 associated with tl~c "off-settin~" o~ ind;vid~ 1 toller ~ -particles o~ thc deve10ped im~e during the fi~ing ... , .,..... ... . ~ .
opcration. O~-setting is thc undesir~-ti~æ trans~er of .

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toner particles from the developed toner image carried on a rec-eiving member (e.gO copy sheet) to the surface of ~he heated fusing me~ber. The surface of the fusing member therefore be-comes contaminated with toner particle!3; and, upon further use of such a contaminated fusing member, it is found that these toner particles adhered to the surface of the fusing member are transferred to subse~uent copy sheets or receiving members. As a result, either a ghost image of previously fixed images is formed on subsequent copy sheets, or undesirable deposits of toner material are formed in background areas of subse~uent copy sheets, i.e., scumming or discoloration occurs in background areas of subsequent copies.
Summary of the Invention - Thus, in accordance with the present teachings, an electrographic developing composition is provided which comprises a mixture of finely-divided carrier particles and finely-diviaed crosslinked toner particles electxostatically attractable thereto.
The toner particles have an average particle size within the range of about 0.01 to about lO0 microns and comprise a fusi~le binder polymer, the molecular chai~s o the polymer being covalently crosslinked to an extent sufficient to extend the useful fusing range of the toner particle by at least about 1~C
relative to comparable uncrosslinkea toner particle comprising the same binder polymer except in uncrosslin~ed form.
By ~ fl~rther embodiment of the present concept an improvement is provided in an electrographic imaging process wherein an electrostatic charge pattern is contacted with dry finely-divided toner particles which have an average particle size within the range of about 0.01 to about 100 microns comprising a fusible binder polymer to develop the charge pattern and, sub-sequently, the developed toner particle image corresponding to the charge pattern being fixed to a suitable receiving support by n ~ ~ ~S~4Z~
t~ sing the particles to the support. The improvement comprises that the molecular change of the polymer are crosslinked, and remain crosslinked during fusing, to an exten~ sufficien~ to extend the useful fusing range of the toner particles by at least about 10C relative to comparable uncrosslinked toner particles comprising binder polymer in uncrosslinked form and furthermore the polymer employed has a crosslinked bond energy in excess of about 8 kcal/mole.
The bond strength or bond energy of the individual cross-links characteristically present in the crosslinked binder polymers - used in the invention should be greater than about 8 kcal./mole.
This is because polymers which contain only "weak crosslinks" hav-ing a bond energy of less than about 8 kcal./mole, for example~, ;
polymers in which the only linkage between individual polymer chains is through hydrogen bonding, are insufficiently linked together to result in any substantial increase in the useful fusing range of the resultant polymer.
- In ascordance with ar especially preferred embodiment of the invention, the finely-divided toner particles employed in the invention comprise a colora~t and at least about 50~ by weight of a crosslinked fusible styrene-containing binder poly-mer. These preferred styrene-containing binder polymers are crosslinked to an extent sufficient to provide a useful fusing range of at least about 90C and to extend the useful fusLng range of the toner particles by at least about 20C relative to comparable -4a-~, ' .

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~ S44Zl uncrosslinked toner particles com~rising the same styrene-~ containing polymer, except in uncrosslinke~ form.
Description of Preferred ~mbodiments It has been found unexpectedly that by crosslinking the molecular chains of the binder polymer material used in dry electrographic toner compositions~ one is able to extend the useful fusing range over which such toner particles may be fused-and thereby fixed to a receiving member. By extending the useful fusing range of an electrographic developing composition, the range of permissible variation in surface temperature of a fusing member which is utilized to fix such a developer composition is increased. As a result, it is found that the temperature - range over which little or only minimal toner off-set occurs -- is extended, thereby elimlnating or substantially reducing the amount of toner off-set which is encountered when using a conventional developing composition contain;ng uncrosslinked or merely surface crosslinked polymeric toner particles.
To applicants' knowledge, the electrographic dry developLng art, has generally completely - 20 avoided the use of any type of crosslinked polymeric toner particles, except in a very few specialized situations.
For example, in Wright and Olson, U.S. 3,676,350, issued July 11, 1972, it is noted that certain polymeric toner particles - subjected to a glow discharge treatment ma~ be surface cross- -linked to improve the resistance of these toner particles to - caking. As indicated in the attached exam~les, toner particles -which are only surface crosslinked do not possess the . increase in useful fusing range characteris~ic of the present invention~ -- 3o Similarly, although it -has ~een r~cognized that cross-: , . linking certain s~ecialized kinds of t`hermosetting polymeric . ~. . . .
~- -~--toner particlcs, such as diallyl phthala~e~r isophthalate toncr .. _ _ ... ... . .
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... ... . . _._ _ _ . _ _ . ~.. .. ,, ," _, , __ , 544~1 particles, might enhance the storing characteristics of a permancnt image composed of these particular kindS of thermo-setting materials,crossli~cing of these thermosetting toner particles has previously been carried out only after formulation of the toner particles and after the formation of a developed toner image as described in FrO Patent 2,o83,o64, dated ~ece~ber 10 1971. See also Rr. Paten~ 1,174,571 at page 3, lines 90-9~.
... . ., . . .. . . . .. .. . . . _ .. . . . .
- - Several reasons are apparently responsible for the ~- notion that crosslinked toner materials are generally not suitable for conventional electrostatic developing and fixing operations.
A primary reason is probably the belief that erosslinking ~he toner would increase its melt temFerature and require substantial~y - higher fixing temperatures. This, of course, would be un~esirable7 especially where the receiving member to which the toner is to be -fixed has a low char point, e.g. plain paper.
Another primary reason for this widely held view issimply that crossli~cing the polymeric toner particle wou~d be expected to provide a material that could not easily be rendered molten. By crosslinking the toner polymer, one would expect~ to reduce its thermoplastic character and to obtain a polymer particle -tending to behave as if it were a thermose~ polymeric part-cle.
In such case because of its thermoset character one would expect the crossli~ced polymer to be substantially infusibie, i.e., it could not easily be rendered molten and therefore could not be satisfactorily fixed to a support.
Still another reason for this view is that one , might expect a crosslinked toner particle even if it somehow - could be rendered molten to require an increased amount of heatin~
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time to satisfactorily fuse to a receiving member in COmpaTiSOIl 30 to an unerossli~cèd or merely surf~ce crosslinked pàrticle.
Such increased fixing~times would50 prolong the fixing operation ~ . , , ~ .
`as to make such toner materials unacceptable in high speed copy systems.

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The term "uscful fusing range" employed herein is de-fined in terms of the followin~ roller fuser test: The fusing properties of each sample toner areevaluated by a standard test contact roller fuser apparatus. The test contact roller fuser comprises a cylindrical steel pressure roll coated-with a copolymer of tetrafluoroethylene and fluorinated ethylene propylene (e.g., TEFLON FEP a trademark of the E. T. DuPont de Nemours Co.) and a cylindrical resilient fusing roll.
The two rolls are mounted such that their central axes are par-allel to one another and with their external roller surfaces in contact. The fusing roll has an external silicone rubber su-rface layer composed of a silicone rubber such as that available u~der the trademark of ECCOSIL 4952 from the Emerson-C~ing Co., which has been ground down from an initial thickness to approxi~ately 0.13 cm. Surface speed of the pressure roll and fusing roll is 5 inches per second. The pressure roll is regula~e~ to a~ly a pressure of 15 pounds per lineal inch at the nip formed by the interface of the pressure roll and fusing rollO The outside diameter of the pressure roll is about s.o8 cm. ~nd the outside i 20 diameter of the fusing roll is about 7.94 cm. The fusing roll may be heated by various means, for example, by radiant heating using an infrared lamp. Surface temperature of the fusin~ roll is monitored by a thermocouple contacting the roll.
Before actual testing of toner sa~ples, the test ~using roll is conditloned by (a) passing 100 sheets of bl~nk paper . . .
through the roll while maintaining the surface temperature of the - roll at 177~C. followed by (b) passing 50 sheets of paper com-`~ pletely toned wlth Xero ~ 3600-7000 toner to provide tone~ solid --areas having a reflection optical density of 0~.9 as read by a Macbeth Quantalo ~ ~lodel RD-lOOR Reflection 3ensitometer.

_ ~ Each sheet of paper which is used to condition the . . .
~using roll and which is used to carry out the fusing test de-scribed below is a sheet of white, 20 weight bond Paper such as . . .
- . that available commcrcially as International@ Xerographic ~rhite, 7 - ~
_ 0~421 Subst~nce 20. Toner, if applied to this paper, is applied to that side of the paper which bears a correct reading water mark.
Each toner sample to be tested is ground in a fluid energy mill to a particle size as measured by Coulter Counter of 2 to 40 microns. A toned, solid area~ rectangular test band approximately 1.90 cm. wide and about 10 cm. long of each sample toner is then applied (by conventional electrostatic methods) to a standard 21.6 cm. by 27.9 cm. piece of paper. The test band is placed at the center of the paper with the long dimension of the test band parallel to the long dimension of the paper. The reflective optical density of each toned solid area test band is 0.9 as measured by the above-noted densitometer. The paper bearing the test band is then passed through the above-described contact roller fuser. A blank piece of paper having the same dimensions is fed into the roller fuser immediately following each piece of toned paper to determine whether offset of the toner from the toned paper onto the roller fuser has occurred. Any significant amount of such toner offset can be readily observed simply by visually inspecting each blank sheet of paper to see if any ghost image of the original toner test band is deposited onto the blank paper from the fuslng roll. Offset is defined to have occurred when any area of the following bl~nk - ..,i;i .~
sheet has toner deposited on it in an amount sufficient to produce~
an optical reflection density equal to or greater than 0.02 abo~e - that of the pa?er alone before passlng through the fusing device.
- To determine the useful fusing range of each different -~ toner composition, a series of identical toned paper sampl~s are prepared as described above for each toner composition to be tested. Each toned paper sample followed by a blank sheet of - 30 paper is then passed tprough the standard contact roller fuser in - the manner described above. A temperature profile for each ton~r . . ~ .
;~sampie is then prepared by increasing the surface temperature of -the fusing roll, beginning at room temperature, for each toned paper sample in a given series of identical toner s~nples. As~
_8-`~ 44~1 a result~ ~wv different surface rG ler fusin~ temperatures can be pinpointed for each test toner composition, namely "minim~n adequate fusing" (MAF) temperature and "hot of~set" (HO) tem-perature.
The MAF temperature for each toner composition tested is defined as the lowest fusing roll temperature above room temperature at which no toner offset, as defined above, occurs and at which the toned image is adequately fixed to the paper ~heet. Adequate ~ixing to the paper sheet is evaluated by the adhesive tape test described hereinafter.
The HO temperature for each toner composition tested is the lowest fusing roll temperature above the MAF temperature at which toner offset, as defined above, is again observed.
- As noted above, adequate fixing is evaluated quan~i-tatively in te~ms of an adhesive tape test. To perform the adhesive tape test a 1.27 cm. width adhesive tape of suitable adhesive quality is selected such as Bear~ Brand No. 303 Cello-phanc Tape. Each roll of tape used is checked for "adhesive quality" by applying it to a flat polished stainless steel plate -with four passes at 5.o8 cm/second of a 905 gram brass roller

4.45 cm. in diameter and 6.9 cm. in length. Only the weight of the roller is used in the~application. The stainless steel plate ........................................... , :, has previously been degreased in acetone, washed in an aqueous `
detergent solution, rinsed in distilled water, and dried. The tape is immediately peeled at an angle of 180 and at a rate of 30.48 cm./minute at 50 percent relative humidity (RH) and 25C in an Instron testing machine. The range of the recorded peel force is the release value of the tape in grams/1.27 cm. A single isolated peak or valley on the Instron strip chart recording is not lncluded in the release value, nor are the first or last 1.27 cm. of the peeled tape. Tapes which are acceptable for .. . . ..

use will have-a release value of 300-475 grams/1.27 cm. when t~sted in this manner.
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Each toned image fo~ which adequate fixing is to be ' )' evaluated is equilibrated at 25C and 50 percent RH for at least a day prior to testing. 1-27 cm. width adhesive tape of SUitable adhesive qu~lity is applied to the t;oned image with four passes at 5.o8 cm/second using the weight of the previously described brass rollerO The tape is immediately peeled at an angle o~ ' 180 at a speed of15.24 cm/minute. The test is invalid if paper fibers are remo,ved during the peeling. The optical reflection -density is read in several places where the tape,~,as removed and -, an average is taken.
- Fixing quality is defined as: '' Fixin~ Qualitv = Ima,~e ~CIl~ity Aftcr Ta~e is Rcmo~:ed Im~ge ~nsity l~efore ~'~pe is Applied Thc minimum tcmperature for a~e~luate fixillg is dcined as tl-c low~st fusing roll temperature that will give a fixing quality of greater than 0.~0. ' `~

- Useful fusing range for a given toner compositlon is then expressed as the difference between the H0 temperature and the MAF temperature.` No offset as defined above occurs within 20 this useful fusing range. As indicated, the crosslinked ~
molecular chains of the polymeric binder contained in the cross- -linked toner compositions of the present invention exhibit at ~' least a 10C. increase in useful fusing range and, as a con-sequence, improved resistance to toner offset. (This improve~ent in resistance to offset is sometimes referred to as increasing t~e o~fset latitude ~f the toner.) Those toner compositions which are found especially useful in accord with the present inventIon register an increase in useful fusing range in excess of ~0C.

up to 40~ and above an~ possess a uscful fusing range of 100C.
30 up to 125C. and above.
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~ 2 ~ ~544Zl The 10C. extension in useful fusing range exhibited by the crosslinked toner compositions used in the present inven-tion is measured relative to a comparable uncrosslinked toner.
To provide a meaningful basis for comparison, the crosslinked toner and the uncrosslinded control toner should have an inden-tical amount of polymeric binder and the MAF temperature of the crosslinked toner and the uncrosslinked toner should be similar.
Accordingly, the term-"comparable uncrosslinked toner" is defined herein as a toner which ~a) contains an indentical amount of the same binder polymer used in the crosslinked toner, except that the binder of the uncrosslinked toner is in uncrosslinked form and (b~ has a ~ temperature within tl5C. of the MAF temper-ature of the crosslinked toner.
The crosslinked organic polymeric binders employed in the toner particles of the invention may be selected from a var-iety of crosslinked polymers including natural and synthetic pol-ymers, crosslinked homopolymers and crosslinked copolymerized blends of two or more monomeric components, as well as mixtures of any of the foregoing materials.
The term "crosslinked" is defined herein to include both covalent crosslinking and ionic crosslinking. Both of these types of crosslinking have bond energies greater than about 8 kcal./mole. Covalent crosslinklng is preferred because, among other reasons, useful covalently crosslinked polymers are gener-ally much easier to prepare than useful ionically bonded polymers Covalent crosslinks typically have a bond energy of greater than about 40 kcal./mole and ionic crosslinks typically have a bond energy of greater than about 10 kcal./mole. As mentioned prev-iously, polymers in which the only "cross-links" present between individual polymer chains are linkages due to hydrogen bonding are not useful in the present invention. Hydrogen bonding gener-; ally has a bond energy of about 2-7 kcal./mole~ Further details ;~ `
;; 11 054~21 concerning the use of both covalent crosslinking and ionic crosslinking are presented hereinafter.

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:~0544Zl In accord with especially preferred embodiments of the invention, covalent crosslinking is accomplished by - - chemically reacting a crosslinkin~ organic compound or co~ounds possessing tl~o or more polymerizable ethylenically unsaturated groups such as divinylbenzene, 1,3-butylene dimethacrylate, and the like (hereinafter referred to as type ~a) crosslin~ing compounds) with binder material composed of an organic com-pound or compounds containing one polymerizable ethylenically unsaturated group (hereinafter re~erred to as type (1) binder - 10 material) or by chemically r~acting a crosslinking organic ccm-pound or compounds possessing a polymerizable functionality greater than two such as trimellitic anhydride or 2-hydroxy-~ 2-methyl-1,3-propanediol (hereinafter referred to as type (b) crosslinking compounds) with polyester binder material (hereinafter referred to as type (2) binder material). The crosslinking organic com~ound whether type ~a) or (b) is introduced for reaction with the type (1) or (2) binder ma.erial, respectively, during the actual polymerization.
In accord ~ith the above-described embodiment of the 20 invention wherein a separate type (a) crosslinking compound ~ -is used, one can appreciate that a variety of diffeTent such crosslinking compounds are effective. Typically, these -~
compounds are monomeric. Representative of such materials con- -taining two or more ethylenically~unsaturated groups are vinyl compounds such as di~inylbenzene, allyl-containing compounds such as triallyl cyanurate and N,N-diallylmelamine; mixed . '' : . .,', - .

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allyl-vinyl compounds such as allyl acrylate; vinylidene com-pounds such as ethylene glycol dimethacrylate; mixed allyl-vinylidene compounds such as allyl methacrylate; and mixed vinyl-vinylidene compounds such as the mixed ester prepared from ethylene glycol and acrylic and methacrylic acids. Other useful type ~a) crossli~ing compounds include the following:
polyvinyl aromatic compounds, for example, divinyltoluene, divinylxylene, divlnylethylbenzene, trivinylbenzene, di~inyl-naphthalene, divinylmethylnaphthalenes; the crosslinlcing vinyl esters, allyl esters and vinyl allyl esters of carboxylic and polycarboxylic acids including polymerizable ester monomers such as diallyl maleate, vinyl crotonate, divinyl succinate, divinyl adipate, vinyl acrylate, vinyl methacrylate; the aliphatic acetylenes such as vinylacetylene, and alpha-methyl vinylacetylene.
The amount of type (a) crosslinking compound employed in accord with this embodiment may vary substantially depending on the number of ethylenically unsaturated groups present in the compound, the reactivity of a specific cross~
linking compound with a particular type (1) binder material, and the molecular weight of the par~icular crosslinking compound and type (1) binder material employed. Typically, amoun~s of çrosslinking compound of at least about 0.01 weight percent, 'preferably 0.01 to about 5 weight percent based on the total dry wei~ht of the type (a) crosslinking compounds blended with the type (1) binder materials are employed.

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L0~4~Zl The type (l) binder material which is crosslinked in the preferred embodiment of the invention with the type (a) crosslinking compounds described above may be selected from a wide variety of known materials containing one polymerizable ethylenically unsaturated group. Typically, these materials are monomeric and contain polymerizable ethylenically unsaturated linkages, ,,C=C , such as a vinyl, vinylene, or vinylidene group. A-large number of these monomers are well known in the polymer art. These monom~rs include: monovinyl aro~atic co~-pounds such as styrene; the halogenated sytrenes such as mono-and dichlorostyrene; the alkylstyrenes such as the methyl-styrenes, the ethylstyrenes, the dimethylstyrenes, the diethyl-styrenes, the isopropylstyrenes, the mixed alkylstyre.nes and the halogenated alkylstyrenes, nuclear-substituted vinyl aryl compounds wherein the nuclear substituent is an alkyl, aryl, alkaryl, aralkyl, cycloalkyl, alkoxy, aryloxy, chloro, fluoro, chloromethyl, fluoromethyl or trifluoromethyl group; the vinyl-naphthalenes, methylvinylnaphthalenes.and their halo,,enated ~.
.
derivatives; vinylaryl acids and vinylalkyl acids such as .
acrylic acid,and the alpha-alkyl substituted acryllc acid such as methacrylic acid, and esters of such acids and aliphatic alco- -hols; khe amides of acrylic and methacrylic acids and derivatives ~ thereof such as the methacrylamides, acrylamides, N-methyl- -:.
acrylamides, N,N-diethylacrylamide, N-ethylmethacrylamide, N,N-dimethylmethacrylamide, etc; the nitriles such as acrylonitrile, methacrylonitrile~, ethylacrylonitrile, chloroacrylonitrile a~d other nitriles, the alkyl esters of alpha-ekhylenic aliphatic dicarboxylic acids such as diethyl fumarate and diethyl ikaconate;
the un;saturated ketones, mekhyl vinyl ketone and methyl isopropyl ketone; the vinylpyridines; the vinylquinolines; vinylfurans;
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. vinylcarbazoleS; the esters of vinyl alcohols such as vinyl ' - -14- :
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acetate; acyl~nino substitute~ acrylic and methac~ylic aclds;
the et~lers of olefinic alcohols, especially the ethers of v~lyl and allyl type alcohols such as vinyl ethyl ether, vinyl butyl ether, vinyl tolyl ether, divinyl ether, methyl isopropenyl ether, methallyl ethyl ether; the unsaturated aldehydes such as acrolei~ ;
and methacrolein and the like; copolymerizable alkenyl chlorides including methallyl chloride, allyl chloride~ vinyl chloride, vinylidene chloride, l-chloro-l-fluoroethylene and 4-chloro-butene-l; and the vinylindenes.
Pre~erred type ~1) binder materials which may be used in the invention are styrene, styrene homologs and moro-meric blends comprising such styrene materials. Such binder materials typically are comprised of at least about 4Q up to 100 percent by weight of styrene or styrene homolog.
As used in the present invention the phrase "styrene or styrene homolog" is used interchangeably with the expression "styrene materials". St~rene materials are defined herein to include a monomer or mixture of monomers having the formula ~ `
, R ~C ~ ~ . .

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¦ 20 wherein R represents hydrogen, a halogen such as chlorine-or I bromine, a lower alkyl, including halogenated alkyls, containin~
¦ 1-4 carbon atoms in alkyl moiety such as methyl, ethyl, prop~1, ¦ isopropyl, butyl, and halogenated derivatives thereof. Binder I materials which have been found especially useful in the in~ention ! are blends of from about 40 to about 90 percent by weight of a styrene material, preferably styrene per se, and from about 10 ~o j, about 60 percent by`weight of another~vinyl monomer other~-than s~yrene, for example, an alkyl acrylate or methacrylate, inclu~in ... , , . -~ branched alkyl and cycloalkyl acrylates and methacrylites such as 1 30 cyclohexyl methacrylate, having up to 20 or more carbon atoms in ~ the alkyl group. Typlcal of type (1) binder materials which have~
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~.-been foun~ espeeially useful as deseri~ed hereinabove are blends of 40 to 90 pereent by weight styrene, from about 5 to about 50 pereent by weight of a lower alkyl aerylate or methaerylate having from 1 to about 4 carbon atoms in the alkyl moiety sueh as methyl, ethyl, isopropyl, butyl, etc. and from about 5 to about `-50 percent by weight of a higher alkyl acrylate or methacr~-late having from about 6 to 20 or more carbon atoms in the alkyl group such as ethylhexyl acrylate or methacrylate. A variety o~ other useful styrene material containing toner particles are disclosed in the following U. SO Patents: 2,917,460 issued Deeember 15, 1959; Reissue 25,136 issued March 13, 1962; 2,788,288 issued April 9, 1957; 2,638,416 issued April 12, 1953; 2,618,552 issued November 18, 1952 and 2,659,670 issued November 17, 1953.
m e type (2) polyester binder materials used with the type (b) crossllnking compounds refeTred to above are comprised of one or more dicarboxylic acids and one or more polyhydric alcohols which are capable of reacting with one ;
another to form a polymer having the individual units thereof ~
linked by ester groups. Representative dicarboxylic acids which ` -20 may be used in the preparation of the polyester binder -materials are terephthalic acid and isophthall_ acld including - substituted terephthalic and isophthalic acid; cyclohexane di-carboxylic acid, and the like. Representative polyhydric alc~hols which may be used in the preparation of the polyes~er binder materials are aromatic alcohols such as a bis~hydroxy aIkoxy-phenyl)alkane having from l to about 4 carbon atoms in the alkoxy group and from 1 to about 10 carbon atoms in the ;;
alkane group, cyclohexane dialkanols having from 2 to about 10 carbon atoms in the alkanol groups, and alkylene glycols 30 having from l to about 4 carbon atoms in the alkylene group.
The type (b) crosslinking compouncls used in the ~_.. .. .
present invention to react with the abov~ described polyester bincler materials ~re char~c~eTized by having a po7~merizable .; . ' ' - :- ' 05~2~, function~lity grcatcr th~n 2Ø The polymerizable function~lity of a givcn mat~ri~l is the number of hy~roxy arld caI~boxyl groups chemically bonded to the material which are capable of reacting to form an ester linkage~ -C~0-C-, with the polyester binder materials. These type (b) crosslinking compounds are typically monomeric materials containing from 3 to about 20 carbon atoms.
Representative type (b)crosslinking compounds include trimethylolethane, pentaerythritol, trimellitic acid anhydride, or pyromellitic acid or dianhydride, and the like.
The ~nount of type (b) crosslinking compound which may be used may vary widely depending on a number of factors includin the reactivity of particular type (b) crosslinking compounds and type (2) polyester binder materials, the molecular weight of the respective polyester binder and type (b) crosslinking materials, etc. Typically, an amount of type (b) crosslinking compound greater than about 0.01 percent by weight, preferably from about 0.01 to about 5 percent by weight based on the total dry weight of the type (b) cr.osslinking compounds blended with the type (2) binder materials is employed.
- In accord with another preferred embodiment of the invention a covalent crosslinked pol~neric binder useful in the toner particles of the invention may be obtained simply by curing ~ i a polymer having in its molecular structure crosslinking Sites.
A variety of chemical moieties which may serve as crosslinking sites in the molecular s~ructure of a pol~ner are well kno~rn in the polymer art. Curlng of pol~ners containing these sites may sometimes be accomplished by heat alone but is more ~enerally facilitated by use of heat and a crosslinking compound (co~monly referred to a6 a curing agent). Various catalysts may also be used in accord with conventional polymerization. Included belo~
_ ^ in Table 1 is a partial list of representative crosslinking sites and corresponding curing agents~

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In accord with another embodiment of the invention9 the crosslinked polymeric binders employed in the invention may be prepared without a separate chemical crosslinking compound. For example, many polymeric materials having an appropriate crosslinking site may be covalently crosslinked simply by exposure to an external activating radiation source, such as electron beam or electromagnetic radiation~ for example, ultraviolet radiation.
Representative of thermoplastic, radiation cross-linkable materials useful in the preparation of the crosslinkedtoner materials described herein are the cinnamylidenemalonate-containing polyesters such as those described in U.S. Patent 3,674,7~5 issued July 4, 1972. Such polymers are typically ;~
prepared by reacting a monomeric mixture of approximately 50 mole percent of one or more polyhydric alcohols and 50 mole percent of a composition co~prising dialkyl cinnamylidene-malonate and one or more additional esters of à dicarboxylic acid such as terephthalic acid or isophthalic acid. Typical of useful cinnamylidenemalonate-containing polyers are poly-(ethylene glycol-co-dimethyl terephthalate-co-butanediol-co-dimethyl cinnamylidenemalonate) tetrapolymers composed of about 37.5 mole percent ethylene glycol units~ 6.85 mole percent dimethyl terephthalate units, 12.5 mole percent butanediol units, and 43.15 mole percent dimethyl cinnamylidene-malonate units. ~ ~
The above-described cinnamylidenemalonate-containing polymers are typically crosslinked by exposure to ultraviolet ;
radiation for a period of from about 1 to about 30 hours or more.
The ionic crosslinked binders employed in the present invention are conveniently prepared in a manner similar to that described above wherein covalent crosslinked binders are prepared by curing the polymeric binder in the presence of heat alone or . . .. ~ . . . -- . : . .
.. ..

L0~44Zl in the prescncc of heat and a curin~ a~ent to form covalent ; chemical linkages between the crosslinkin~ sites of adjace.lt polymers~ The difference between ionic crosslinked binders and and the above-described covalently crosslinked binders prepared by curing is that in the former case the linkage between cross---linking sites of adjacent polymer chaîns is believed to be an - ionic linkage rather than an actual covalen~ chemical bond.
The ionic linkage is conveniently formed by subJecting a poly-meric blnder having ionic crosslinking sites in its molecular structure to heat in the presence of an ionic crosslinking ~ompound.
Regardless of the particular chemical composition of the crosslin~ed binders used in the present invention, pre-~erred crosslinked binders have a softening temperature ~-ithin the range of from about 40C. to about 200C. so that the resultant toner particles can readily be fused to conventional recei~ing sheets to form a permanent image. Especially useful crosslinked binders are those having a softening temperature within the range of from about 40C. to about 65C. because toners cor.taining -20 these binders may be used in high speed electrographic copy `
machines employing plain paper as the receiving sheet to which the toned images are fused. Of course, where other types of receiving elements are used, for example, synthetic high melting `
point polymeric sheets, metallic sheets, and the like, cross- ~`
linked polymers having a softening temperature higher than ~he values specified may be used.
- As used herein the term "softening temperature" refers to the softening temperature of a polymer as measured by ;
E.I. duPont de Nemours Model 941 TMA (Thermal Mechanical 30 Analyzer) apparatus using a probe pressure of 48 p.s.i.a. `
and a heating rate o~ 5C/minute. -. . :
.

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.... .. . . ..

() 105~4;~1 The toner particles employed in the presellt invention may comprise varied amounts of the crosslinked binder polymer described hereinabove`depending upon a number of factors, including the amount and types of colorant or other modifying materialsg if any, incorporated in the particle; the amount and - kind of additional binder materials~ if any, such as conventional - linear or straight-chain thermoplastic polymers, incorporated in the toner particle; the desired softening point of the ~oner particles, and the like. Advantageously, the crosslinked lusible binder comprises 25~ by weight or more of the toner particles used in the invention. In accord with preferred embodimen s of the invention where the toner particles of the invention are to be used in relatively high speed office copy devices, it has been found advantageous to use toner particles comprising at le2st 50~ by weight, and preferably 75-95% by weight, of the cross-linked binder polymers described above.
m e toner particles of the present invention can be prepared by various methods, including spra~-drying, melt-blending, etc. Particles having an a~erage diameter between about O.l micron and about 100 microns may be used, although present day office copy devices typically e~ploy particles having an average diameter bétwèren about 1.0 and 30 microns.
However, larger particles or smaller particles can be used where desired for particular methods of development or particular ~ -development conditions. For example, in po~Jder cloud develop~ent such as described in U. S. Patent ~o. 2,691,345, issued Oc~ober 12, 1954, extremely small toner partlcles on the order of about 0~01 microns may be used.

,.

., . , . . , ~ . ,. , ~ . .. . .

' ! 10544Zl The above-noted melt-blending method for preparinO
the toner composition of the present invention involves melting a powdered form o~ binder polymer and mixing it with other necessary or desirable addenda including colorants such as dyes or pigments. The polymer can readi:Ly be melted on heated compounding rolls which are also useful to stir or otherwise blend the polymer and addenda so as to promote the complete intermixing of these various ingredients. After thorough - blending, the mixture is cooled and solidified. m e resultant solid mass is then broken into small particles and finely ~round to form a free-flowing powder of toner particles having the - desired size.
A variety of colorant materials selected from dyestuffs ~ and/or pigments are advantageously employed in the toner nlaterialsof the present invention. Such materials serve to color tile toner and/or render it more visible. Of course, suitable toner ~aterials having the appropriate charging characteristics can be prepa-led without the use of a colora~t material where it is desired to have a developed image of low opticaI opacity. In those instances where it is desired to utiliæe a colorant, the colorants used, can, in principle, be selected from virtually any of the co~-pounds mentioned in the Colour Index,-Volumes 1 and 2, Seccnd -Edition. -Included among the vast number of useful colorantswould be such materials as Hansa Yellow G (C.I. 11680), Nigrosine Spirit soluble ~C.I. 50415) Chromogen Black ET00 (C.I 45170), Solvent 31ack 3 ~C.I. 26150), Fuchsine N (C.I. 42510)$ ~ ;
C.I. Basic Blue 9 (C~Io 52015), etc. Carbon black provldes a particularly useful colorant. The amount of colorant 30 added may vary over a wide range, for exam~le, from about .
. . ~ . , .
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1 to about 20 percent of the weight of the crosslinked binder.
Particularly good results are obtained when the amount is from about 2 to about lO percent. In certain instances, it may be desirable to omit the colorant, in which case the lower limit of concentration would be zero.
Other modifying materials such as various long chain anionic or cationic surfactants, conductive materials, and magnetic materials may also be incorporated, if desired, in the toner particles~of the invention. Still other toner additives which may be incorporated ln the toner particles are materials such as those described in Jacknow et al, U.S. Patent No. 3,577,345 issued May 4~, 1971. Generally, if any of the various modifying materials described above are used in the toner particles of the invention, the total amount thereof (excluding the weight of colorants) s~ould be less than about 30 weight percent of the total weight of the toner particle.
The toners of this invention can be mixed with a carrier vehicle to form developing compositi~ns. The carrier vehicles which can be used with the present toners to form - new developer compositions can be selected from a ~ariety of materials. Suitable carrier vehicles useful in the invention ~ -- include various nonmagnetic particles such as glass beads, -crystals of inorganic salts such as sodium or potassium chloride~
hard resin particles, metal particles, etc. In additiong magnetic carrier particles can be used ~n accordance with the in~ention. Suitable magnetic carrier par~icles are particles of ferromagnetic materials such as iron,-~o~alt, nickel, and alloys and mixtures thereof. Other usefu~ magnctic carriers are ferromagnetic particlcs overcoated w`-lth a thin layer of - ~. .
. ---. .- . -'.-.

- - ~ - , ,~
' ~, . , : ' ~ ' ) 105~4Z~

various film-forming resins, for example, the alkali-soluble carboxylated polymers described in Miller, U.S. Patent No.
3,547,822 issued December 15, 1970; Miller, U.S. Patent No.
3,~32,512 issued January 4, 1972; McCabe, U.S. Patent No.
3,745,617 issued March 5, 1974; Kasper et al, Canadian Serial No. 163,118 filed February 17, 1973, entitled "Electrographic Carrier Vehicle and Developer Composition--Case C"; and Kasper, U.S. Patent No. 3,795,618 issued March 5, 1974. Other useful resin coated magnetic carrier particles include carrier parti-cles coated with various fluorocarbons such as polytetrafluoro-ethylene, polyvinylidene fluoride, and mixtures thereof includ-ing copolymers of vinylidene fluoride and tetrafluoroethylene. -~
A typical developer composition containing the above-described toner and carrier particles generally comprises from ~
about 1 to about 15 percent by weight of particular toner par- -ticles and from about 85 to about 99 percent by weight carrier p~rticles. Typically, the carrler particles are larger than the toner particles. Conventional carrier particles used in cascade or magnetic brush development have an average size 20 particle size on the order of from about 30 to about 1200 microns, preferably 60-300 microns.
The above-described toner and developer compositions can be used to develop electrostatic charge patterns. Such developable charge patterns can be prepared by a number of well~
known means and be carried, for example, on a light sensitive photoconductive element or a non-light sensitive dielectric-surfaced receiving element. Sultable dry development processes ,' .

~.
-~ `~

! ' ~ . : , ~ ' ' ' ' S44;Z~
include casc~ding a cascade dcveloper composition across the electrostatic charge pattern as describ~d in detail in U.S. Patent Nos. 2,618,551; 2,618,552; and 2,638,416. Another process involves applying toner particles from a magnetic brush developer composition as described in U.S. Patent No.
3,003,462. Still another useful development process is - powder-cloud development wherein a gaseous medium such as air is utilizcd as a carrier vehicle to transport the toner particles to the electrostatic charge pattern to be developed.
This development process is more fully described in U. S~ Patent -No. 2,691,345 and U.S. Patent No. 2,725,304. Yet another develop-ment process is fur brush development wherein the bristles of a brush are used to transport the toner particles to the electrostatic charge pattern to be developed. This development process is more fully described in Walkup, U. S. Patent No.
3~251~706.
As will be apparent from the abovc discussion the improved electrographic development process of the present invention using the toner particles described herein ~ `
can employ vàrious types of carrier vehicles ranging from the conventional inorganic particles used in cascade ~
development and magnetic particles used in magnetic brush -development to gaseous media and fur brushes used in powder cloud and fur brush development, respectively.
- After imagewise deposition of the toner particles in accord with the process of the lnvention, the image can be fused as described earlier herèin to ad~ere it to the sub-strate bearing the toner image. If des`ired, the unfused image can be transferred to another suppor~ such as a blank sheet of cop)~ paper and then fused to fo~m a permanent image --- ^ thereon.
. ~_. . . - .
_. . . .. . . .. . , ... , ..... , _ ~

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Example I: Crosslinkin~ a styrene-acrylic polymer with divinylbenzene during polymerization Polymer References: Ia Ib - Ic - Toner Re~erences: I-l Xerox~ 3600-7000 .
-Polymer Description:
Ia - A suspension containing 50 g. styrene, 25 g. 2-ethylhexyl methacrylate, 25 g. methyl methacrylate and 3 g. of ~ azobisisobutyronitrile are suspension polymerized by flushing the monomer suspension with nitrogen and he&ti~.g at 60C. for 24 hours. The polymerization is completed by i~
heating at 95C. for 6 ho~rs. The resultant copolymer is identified as poly(styrene-co-methyl methacryla~e-co-2-ethylhexyl methacrylate).

Ib - This polymer is prepared in a manne~ identical to Ia excep~
that 0.2 g. divinylbenzene (assay 55%) are introduced into the initial reaction mixture. The resultant crosslinked copolymer is identified as poly~styrene-co-methyl methacrylate-co-2~ethylhexyl methacrylate-co-divinylbenzene).
... . . . . . .. _ , _ _ _ _ _ .,, , ., . . . . ~ _ _ ......... . .
- Ic - This polymer is prepared in a manner identical to Ia except that 0.3g. of divinylbenzene (assay 55~) are introduced into the initial reaction mixture.

The resultant crosslinked polymer is identified as poly(styrene-co-methyl methacrylate-co-2-ethylhexyl methacrylate-co-divinyl benzene).
.,_ .. ...

; -27-., .. ' :
.. . . ... ~ . .... . ~

``~ 54~21 Toner Description I-l is an uncrosslinked control toner and is prepared by compounding on a two roll rubber mill 100 parts Ia with 5 parts Regal 300~ carbon black purchased from Cabot Corporation. The composition is ground to toner size particles (2-40 microns) in a fluid energy mill.
I-2 is a control toner prepared in a manner identical to that described in I-l above except that the resultant toner particles are subjected to a glow discharge post ~reat~ent - as described in U.S. 3,676,350 to effect surface cross-linking of the toner particles. The glo~ discharge post .. .
treatment is carried out by placlng a sample of the I-l toner particles described above on a piece of filter paper contained within a polymeric holder capable of vibrating the toner, and the holder is placed between two parallel electrodes. The apparatus is contained in a bell ~ar which is evacuated to a pressure of o.6 mm of mercury. Heli~
is then bled into the bell jar to a total of 2.4 mm oY
mercury. The vibrator is turned on, and a 10 kc A.C. field sufficient to produce a glow at a current of 60 ma is a~p7ied ;;~
across the electrodes. To prevent fusing of tha toner, the current is turned off at regular intervals. Total tLme the ~-toner is subjected to the glow discharge is five minutes.
m e glow discharge treated toner is labelled I-2.
Samples of the I-1 and I-2 control toners are~placed in an oven at 60C for 24 hours and then checked for tendency to cake or agglomerate. I-2 becomes free flowing after several taps on its container, but I-l does not. A spatula is required to break up the lumps formed in the I-l ~-container. This experiment demonstrates that the surface charac~eristics of the toner are indeed altered by a glow ~ . . . .
discharge treatment. Roller fusing tests for I-l and I-2 are carried out in the manner noted below. The results are set forth in Table 2.
-2~-. .
. .... ;~

~05442~
I-3 is a control toner prepared in a manner similar to that deseribed in Example 1 of U.S. ReO 25~136 reissued Mareh 13, 1962. These toner particles consist of 25~
by weight poly(butyl methacrylate) sold by E.I. duPont de Nemours under the trademark ~lvacite 2044, 65~ by wei~h~
of a blend of polymerized styrenes commercially available under the trademark Piccolastic Resin D-125, and 10% by weight of carbon black. This control is noted to have partieularly poor keeping properties~ i.e.~ it tends to elump up and agglomerate, in comparison to the crosslinked toner used in the ir.vention~
- I-4 is a crosslinked toner of the invention prepared by com-pounding on a two roll rubber mill 100 parts Ib with 5 parts Regal 300R earbon blaek. The eomposition is ground to toner size partieles in a fluid energy mill~
I-5 is a erosslinked toner of the invention prepared similarly to I-l exeept that Ic is used as the poiymer binder.
Xero ~ 3600-7000 toner is a eontrol and is eommereially available from the Xerox Corporation. The polymer eomponents of the toner are believed to be composed of an uncrosslinked copolymer of styrene and n-butyl methaerylate plus a small amount of poly(vinyl butyral).
Roller Fuser Performance - Fixing of the toner to the paper is carried out with a roller ; fuser apparatus deseribed previously to yield the following results: ~

' .. ..

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--- `) iL05~42~ -From lable 2, it is noted that the useful fusing range of the crosslin~e~ toner particles used in the present invention has been increased in comparison to the control toner compositions which are composed of various related~ but uncrosslinked, binders. It may be further observed that crosslinking only the surface of polymeric binder containing toner particles does not provide any substantial chan~e in the useful fusing range of the toner particles. (Compare I-l control to I-2 control.) Example II: Crosslinking a styrene-acrylic polymer with 1,3-butylene dimetnacrylate during polymerization Polymer References: Ia of Example I
IIa Toner Refcrences: I-l of Example I

, Polymer Description Ia poly(styrene-co-methyl methacrylate-co-2-ethylhexyl methacrylate) described in Example I

IIa T~lis is a polymer prepared in a manner identical to - polymer Ia of Example I.except that 0.75 g. of 1,3-butylene dimethacrylate crosslinking monomer is added as one of the initial monomeric reactants. The resulting cross-~ linked polymer ls identified as poly(styrene-co-methyl - methacrylate-co-2-ethylhexyl methacrylate-co-1,3- ~
~ butylene dimethacrylate). - "

Toner Description I-l is an uncross1inked control toner and is described in Example I. ~-II-l is a crosslinked toner prepared by compounding on a two roll rubber mill 100 parts IIa with 5 parts Regal 300R carbon black. The composition is ground to toner size particles in _. . ~-.- .a fluid energy mill.

'..
s .... ~

-- ~054~21 .
Rollcr Fuser Performancc The toners are tested on a roller fuser as described previously to yiel~ the following results.

. `:
o ~_ . bC CO C~
. ' ~ , 1 q~ ............. . ..
. eh ~1) OEl~ ~0 0 o~O ,~ ~O

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The data from Table 3 indicate that the useful fusing range has been increased more than 42 C-by crosslinkin~ the toner.
Ex~m~le III: Crosslinking a polyester during polym~rization Polymer References: IIIa IIIb Toner References: III-l Polymer Description .. .. .
IIIa. A mixture of 50 g. of dimethyl isophthalate, 5G g.
dimethyl terephthalate, 67 g. ethylene glycol, 10 mg.
zinc acetate, and 20 mg. antimony trioxide is heated under nitrogen at 200C, and the evolved methanol is .
distilled off. The temperature is raised to 235C., and vacuum is gradually applied to the stirred melt to remove excess glycol. Polymerization proceeds by the removal of glycol until the desired viscosity is reached. The resultant copolymer is identified as poly(ethylene terephthalate-co-isophthalate) and has an inherent viscosity of 0.25. (The inherent viscosity is measured at 25C. by dissolving 0.25 g. of the copolymer in 100 ml.
of chloroform.) --IIIb. This polymer is made in the same manner as IIIa except after the initial ester exchange 2.9 g. of 2-hydroxymethyl-2-methyl-1,3-propanediol is added. The polymerization under vacuum is allowed to proceed~until thé product is ~ ;
no longer soluble in chloroform. The resultant polymer is identified as poly(ethylene terephthalate-co-isophthalate) crosslinked with 2-hydroxymethyl-2-methyl-1,3-propanediol.

, . , . .. .. . -. ~

- `-J 105gL4Z~L

-1 oller Desc r i pt i on III-l is an ullcrosc,lillcd control ~nd is prep;tred l)y compoul~ g on n tl~o roll rubllcr mill 100 p;lrts IIla t~itl~ ~) p~tlts ~Stcrling I r ::
carlon blac~ purch.l~ed rrom Cabot Cor~-oration w;th sul)setlucllt reductioll to toncl~ size particles in a fluid encrgy mill.
III-2 is a cross] i]~kcd tOIlCI prcl)~rcd simllar]y to III-l e~;cer)t IIIb is uscd as the polymer bin~er.
Rollcr T`user rcrrormancc The toncrs are tested on ~ roller fuser ~s dcscril)e(l p reviously 10to yield thc follol~lin~ results:

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~ ::

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o~
' ` . a - ~ ~ ~ r~~

5~
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o ~,.- . ,,~ .~ ' . ' ' P.~ O
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The data in Tabl~ 4 indicate that the useful fusing range has been increased greater tha.n 69~C by crosslinking the toner.
Exam~le IV: Crosslinking a styrene-acrylic polymer while compounding . . Polymer References: Ia IVa Toner References: I-l IY-l Polymer Description : lO Ia poly(styrene-co-methyl methacrylate-co-2-ethylhexyl : methacrylate) described in Example I
-- . ,.
IVa This is a polymer prepared in a manner identical to polymer Ia of Example I except that O.5 g. of - methacrylic acid monomer is added as one of the initial , monomeric reactan~s. The resulting polymer is identi~ied as poly(styrene-co-me~hyl methacrylate-co-2-ethylhexyl.
methacrylate-co-methacrylic acid). The methacrylic ac.d uni~s of the r~sul~ant pol~ner ~erve as crosslinking sites.

Toner Description .-l is an uncrosslinked control toner and is described in - Example I. . - -.
., . . ~ .
. IV-l is a crosslinked toner prepared by compounding on a two roll~
rubber mill 100 parts by weight of polymer -IYa with 0.3 parts ' .
. by weight triethylene diamine, 3 parts by wçight Epon ~ 1001 . ~. ~
.
~an epoxy resin purchased from Shell Chemical Co.), and 5 parts by weight Regal 300R carbon black. Durin~ ~he compounding -~.
operation, the rheological properties of th~ melt chan~ed from ., . ~ , . , .- .
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:. . .. .... . . . .. ~_ 5442~L
that charactcristic of an uncrosslinked polymer to that typical of a crosslinked polymer. The compound is ground to toner .~size particles in a fluid energy mill.
Roller Fuser Performance The toners are tested on a rollcr fuser as described previously to yield the follo~ing results:

o o ~ v~
, 00 . ~.,i o, 0 v~ ~:
u~ ~ ~
~............... :' ' -~R
.
cc o , . . ' ~.
.
. ~.
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:~
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`! The data in Table 5 indicate that crosslinking the toner has increased the useful fusing range 42C.
Example V: Crosslinking a styrene-acrylic polymer after compoundin~

Polymer Reference: Va Toner References: V-l - Polymcr Description -Va . . .
A mixture of 300 g styrene, 210 g methyl methacrylate, 90 g 2-ethylhexyl acrylate, 50 g ethyl acrylylacetate, and 18 g benzoyl -~ ~peroxide is added dropwise with stirring over 2-3 hr. to 800 ml.
o of water at 75 C containing 0.75 g of poly~vinyl alcohol).
The polymerization is conducted under a nitrogen atmosphere and ;~
is allowed to continue for 12 hr. after monomer addition. The product is collected by filtration, washed~with water, and dried, The polymer is identified as poly(styrene-co-methyl methacrylate-co-2-ethylhexyl acrylate-co-ethyl acrylylacetate).
Toner Descri~tion -100 parts by weight of polymer Va is compounded with 5 parts by w~eight Regal 300R carbon black on a two roll rubber mill.
The material is ground to pass thTough a 20 mesh screen and . ~ . ~ ...
divided into two equal parts.~
V-l is an uncrosslinked control toner and is prepared by ~aking ~;
one part of the above-described material and grinding it to toner size particles in a fluid energy mill.
., ~ . . :
, ',' ` ' ' - ' ' ''"
.. ~ .
, , .
~ . ...
~ . . .
.
,. . .:-; . .

. ~ :

: - 10544Zl V-2 is a crosslinked toner prepared by taking the other part of - ~ the above-describcd material and pLacing it in a 35 pcrcent aql~eous flrmaldehyde solution adjusted to pll9 with sodium hydro~ide. The mix-ure is tumbled for 48 hours and dried. The solubility of this : ,material is determined in methylene chloridc before and after - the aqueous formaldehyde treatment. The ma~ter is soluble before treatment and insoluble after treatment indicating that crosslinkillg has taken place. The material is ground to toner size particles in a fluid energy mill~
Roller Fuser Performance The toners are tested on a roller fuser as described previously to yield the following results:
-.,: . - - - . :
. ~
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.
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r'~

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- - :,.

: ,: . - :
`' . ~ ': " ' '; ~ ';' ' ., .

.
~,'', ' ' ' ' ~' : - ~ . . : . :. . ~

:
- lOS442~L
., . ,'~
~ . ` ..
.. o r~ ~G ~ ~
~.,, ~ ~ ;.
.. U), ~ , ..
:, ~ ~ . . ..
, : ' .
OE~V , .~ ~ _ - o ~ oo o ,~ `D ;
,` :, ., td . , .`
~.
Q) ~
~ ~ ~ ,.

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., ,. . ~o ~ ,~,.
.,, ~ .
. . .,, o ~
,~ . ., ~
~ . tn ~: o ; ` 0 . O h . ;:
t~ O , , " , , :.
- ' ` ;
,:' . ' . :' :
~ ., S-~ . , . r . . Q~ . -:~ .
0 ,~

_ ' . ' ~' ' . The data in Table 6 indicate that the useful fusing range has .~ been ;ncreased by greateT than 42C by crosslinking.
~- ~ Example VI: Ionic crosslinking of a styrene-acrylic polymer - while compounding meT References: Ia of Example I

Toner References: I-l of Example I ;~
~ - : - . ~
Polymer Dcscr~
Ia poly~styrene-co-mcthyl methacrylate-co-2-ethylhexyl ~` - ..... ^ methacrylate) as described in Example I : :
~ . ~ . - . . , ;, ~ , ~ . ...
, ~ - 39 - -~ - ~
. . , . ~ !
, ................... . . .

'' . :' ' :' :

~OS~4Z~ -VIa - This is a polymer prepared in a maImer identical to - polymer Ia of Example I except tha~ 5.0 g. of methacrylic acid monomer is added as one of the initial ~onomeric reactants. The resulting po:Lymer is id~ntified as poly(styrene-co-methyl methacrylate-co-2-ethylhe~yl .~ methacrylate-co-methacrylic acid).

Toner Description :
. . .
l is an uncrosslinked control toner and is described in E~a~ple I.
- VI-l lS a crosslinked toner prepared by compounding on a two roll rubber mill 100 parts VIa, 2 parts calciu~ hydroxide, and .- . S parts Regal 300R carbon black. After compoundin~, the blend is heated at 175 C for 90 minutes. The compound is then ground - to toner size particles (2-40 microns) in a fluid energy mill. .
- Roller Fuser P`erformance :
.. , ~
. Fixing of the toner to the paper is carried out with a roller ` fuser apparatus described previously to yield the following ~ .
: results~
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.. .
- . . .

-. .

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:. - ~ - ' - ` - ~
,, `~' '`'` ' ' , ' --~ ~ 4O-.: - . . :

~: . .- . .
..... . ..
;l :

U . .
- o ~ ~.
oo ,,`
.~ ~ ~\ .
. . . ~ V~ ~
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O ~_ ~0 0 V ~1 ~O
o E~_ ~

cB
. ...
. a~ Q, u~ O~ ' ` ' ' C_ ¢ ~

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o a~
.,1 .Y
~ ~:
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rl O
h h v~
~ o O O
~:1 t~
' . :

O
. , E--The- data in Table 7 indicate that the useful fusing range ,:
. ~ - . .
~ may be increased greater than 28C by the use of ionic cross-`. ~ linking.
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.
. ` , :: ' ' "! -"`'; ~

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~xam~le ~ 1054~Zl Approximately 3 to ~ weight percen-t each of crosslinked toners I~ 5, II-l, III-2, IV-l~ V-2, and VI-l are admi~ed with from 96 to 97 weight percent of magnetic carrier particles having an average particle size within the range of about 100 to 250 microns to form a magnetic brush developer composition.
A portion of each of these developers is used in a magnetie ;`
brush development process of the type described in U.S. Paten - 3,003,462 issued October 10, 1961, as follot~s:
m e developer composition is maintained during the = development cycle in a loose, brushlike orientation by a m~gnetic field surrounding a rotatable non-magnetic cylinder having a i magnetic means ~ixedly mounted inside. The magnetic carrier ;~ ~ particles are attracted to the cylinder by the described m~netie ;~
field, and the crosslinked toner particles are held to the ~ -carrier particles by virtue of their opposite electrostatic polarity. Before and during development, the crosslinked toner acquires an electrostatic charge of a sign opposlte to that of the carrier material due to triboelectric charging derived from - 20 their mutual frictional interaction. As this brushlike mass or magnetic brush of carrier and crosslinked toner particles is ~ ~
drawn across a photoconductive surface bearing an electrost3t~c ~ ~`
image, the crossli~ed toner particles are electrostatically attracted to an oppositely charged latent image and form a ~ `~
visible toner image corresponding to the electrostatic image.
The developed crosslinked toner image is then transferred t~
~ plain paper receivl:ng she~t and fused.
Each of the aforementioned crosslinked toner compositions produces ~ood quality ima~es on the resu'tant `~ 30 plain paper receiving sheets. ~ ~`

~ 42- ;
.. . . .

'.'~ ,., - ~ '" ' '~' ~ '~
~L~S~4~3L -The invention has becn described in dctail with particular reference to prcferred embodiments thereof, bu~, it will be understood that variations and ~odifications ca~ b~
effected withln the spirit and scope of the invention.
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.;, . . ~

Claims (17)

We Claim:

1. An electrographic developing composition com-prising a mixture of finely-divided carrier particles and finely-divided crosslinked toner particles electrostatically attractable thereto, said toner particles having an average particle size within the range of about 0.01 to about 100 microns and comprising a fusible binder polymer, the molecular chains of said polymer being covalently crosslinked to an extent sufficient to extend the useful fusing range of said toner particles by at least about 10°C. relative to comparable uncrosslinked toner particles comprising the same binder poly-mer except in uncrosslinked form.

2. An electrographic developing composition compris-ing a mixture of from about 85 to about 99% by weight of finely-divided carrier particles and from about 1 to about 15% by weight of finely-divided crosslinked toner particles electro-statically attractable thereto, said toner particles having an average particle size within the range of from about 0.1 to about 100 microns and comprising at least about 25% by weight of a fusible binder polymer, said polymer being covalently crosslinked to an extent sufficient (a) to provide a useful fusing range for said toner particles of at least about 90°C.
and (b) to extend the useful fusing range of the toner particles by at least about 20°C. relative to comparable uncrosslinked toner particles comprising the same binder polymer except in uncrosslinked form.

3. In an electrographic developing composition com-prising a mixture of from about 85 to about 99% by weight of finely-divided carrier particles and from about 1 to about 15%
by weight of finely-divided toner particles electrostatically attractable thereto, said toner particles having an average particle size of from about 0.1 to about 100 microns and com-prising at least about 50% by weight of a fusible binder polymer, the improvement wherein said binder is a covalently crosslinked polymeric reaction product of (1) one or more crosslinking organic compounds possessing two or more polymerizable ethylenically unsaturated groups and (2) one or more organic compounds possessing one polymerizable ethylenically unsaturated group, said binder being crosslinked to an extent sufficient (a) to provide a useful fusing range for said toner particles of at least about 90°C.
and (b) to extend the useful fusing range of said toner parti-cles by at least about 20°C. relative to comparable uncross-linked toner particles comprising the same binder polymer except in uncrosslinked form.

4. In an electrographic developing composition com-prising a mixture of from about 85 to about 99% by weight of finely-divided carrier particles and from about 1 to about 15%
by weight of finely-divided toner particles electrostatically attractable thereto, said toner particles having an average particle size within the range of from about 0.1 to about 100 microns and comprising at least about 50% by weight of a fusible polymeric binder, the improvement wherein said binder is a covalently crosslinked polymeric reaction product of (1) one or more crosslinking organic compounds possessing a polymeri-zable functionality greater than two or (2) a blend comprising a dicarboxylic acid and a polyhydric alcohol capable of react-ing with one another to form a polymer having individual units thereto linked by ester groups, said binder being crosslinked to an extent sufficient (a) to provide a fusing range for said toner particles of at least about 90°C. and (b) to extend the useful fusing range of said toner particles by at least about 20°C. relative to comparable uncrosslinked toner particles comprising the same binder polymer in uncrosslinked form.

5. In an electrographic developing composition comprising a mixture of from about 85 to about 99% by weight of finely-divided carrier particles and from about 1 to about 15% by weight of finely-divided toner particles electrostatically attractable thereto, said toner particles having an average particle size of from about 0.1 to about 100 microns and com-prising at least about 50% by weight of a fusible polymeric binder, the improvement wherein said binder is a covalently crosslinked polymeric reaction product of a curing agent and a polymer having crosslinking sites along its molecular structure capable of reacting with said curing agent, said binder being crosslinked (a) to provide a useful fusing range for said toner particles of at least about 90°C. and (b) to an extent sufficient to extend the useful fusing range of said toner particles by at least about 20°C. relative to comparable uncrosslinked toner particles comprising the same binder polymer in uncrosslinked form.

6. The developer composition as defined in claim 5 wherein said crosslinking site on said polymer is selected from the group consisting of a carboxylic acid, an epoxide, a halide, an active methylene, an ethylenically unsaturated group, and a hydroxyl group.

7. An electrographic developing composition comprising a mixture of from about 85 to about 99% by weight of finely-divided carrier particles and from about 1 to about 15% by weight of finely-divided crosslinked toner particles electrostatically attractable thereto, said toner particles having an average particle size within the range of from about 0.1 to about 100 microns and comprising a dye and/or pigment as colorant and a fusible styrene-containing binder polymer, said binder polymer being covalently crosslinked (a) to provide a useful fusing range for said toner particles of at least about 90°C.
and (b) to an extent sufficient to extend the useful fusing range of the toner particles by at least about 10°C. relative to comparable uncrosslinked toner particles comprising said styrene-containing polymer in uncrosslinked form.

8. The developer composition as defined in claim 7 wherein said covalently crosslinked styrene-containing polymer has a softening temperature within the range of about 40°C. to 200°C.
and is a crosslinked polymeric reaction product of (1) at least one crosslinking organic compound having two or more polymerizable ethylenically unsaturated groups and (2) a blend of monomers having one polymerizable ethylenically unsaturated group and comprising from about 40 to 100% by weight of styrene or styrene homolog.

9. The developer composition as defined in claim 7 wherein said covalently crosslinked styrene-containing polymer has a softening temperature within the range of about 40°C. to 65°C.
and comprises a polymeric reaction product of (1) at least one crosslinking organic compound possessing two or more polymerizable ethylenically unsaturated groups and (2) a monomeric blend comprising from about 40 to about 90% by weight of styrene or styrene homolog, from about 5 to about 50% by weight of a lower alkyl acrylate or methacrylate having from 1 to about 4 carbon atoms in the alkyl group thereof, and from about 5 to about 50% by weight of a higher alkyl acrylate or methacrylate having from about 6 to about 20 carbon atoms in the alkyl group thereof.

10. An electrographic developing composition comprising a mixture of from about 85 to about 99% by weight of finely-divided magnetically attractable carrier particles and from about 1 to about 15% by weight of finely-divided crosslinked toner particles electrostatically attractable thereto, said toner particles having an average particle size within the range of from about 0.1 to about 100 microns, and comprising at least about 75% by weight of a fusible binder polymer, said polymer having a softening temperature within the range of about 40°C. to 200°C. and being covalently crosslinked to an extent sufficient (a) to provide a useful fusing range for said toner particles of at least about 100°C. and (b) to extend the useful fusing range of the toner particles by at least about 40°C. relative to comparable uncrosslinked toner particles comprising said binder polymer in uncrosslinked form.

11. An electrographic developing composition comprising a mixture of finely-divided carrier particles and finely-divided crosslinked toner particles electrostatically attractable thereto, said toner particles having an average particle size within the range of about 0.01 to about 100 microns and comprising at least about 25 weight percent of a crosslinked fusible binder polymer, said polymer covalently cross-linked with at least about 0.01 weight percent of a crosslinking compound.

12. The developer composition of claim 11 wherein said polymer is a crystalline polymer.

13. An electrographic developing composition comprising a mixture of from about 85 to about 99% by weight of finely-divided carrier particles and from about 1 to about 15% by weight of finely-divided crosslinked toner particles electrostatically attractable thereto, said toner particles having an average particle size within the range of from about 0.01 to about 100 microns and comprising at least about 25 weight percent of a co-valently crosslinked binder polymer, said polymer a polymeric re-action product of a mixture comprising (1) from about 0.01 to about 5 weight percent of one or more crosslinking organic compounds possessing two or more polymerizable ethylenically unsaturated groups and (2) one or more organic compounds possessing one polymerizable ethylenically unsaturated group.

14. An electrographic developing composition comprising a mixture of from about 85 to about 99% by weight of finely-divided carrier particles and from about 1 to about 15% by weight of finely-divided crosslinked toner particles electro-statically attractable thereto, said toner particles having an average particle size within the range of from about 0.1 to about 100 microns and comprising a pigment as colorant and at least about 50% by weight of a fusible covalently crosslinked styrene-containing polymer, said polymer a polymeric reaction product of a mixture comprising (1) from about 0.01 to about 5 weight percent of one or more crosslinking compounds possessing two or more polymerizable ethylenically unsaturated groups and (2) a monomeric blend having one polymerizable ethylenically unsaturated group and comprising from about 40 to 100% by weight of styrene or styrene homolog, said polymer having a softening temperature within the range of 40°C. to 200°C.

15. The developer composition as defined in claim 14 wherein said polymer has a softening temperature within the range of from about 40°C. to about 65°C. and wherein said monomeric blend comprises from about 40 to about 90% by weight of styrene or styrene homolog and from about 10 to about 60% by weight of an alkyl acrylate or methacrylate having from about 1 to about 20 carbon atoms in the alkyl moiety.

16. In an electrographic imaging process wherein an electrostatic charge pattern is contacted with dry finely-divided toner particles having an average particle size within the range of about 0.01 to about 100 microns comprising a fusible binder polymer to develop said charge pattern and, subsequently, the developed toner particle image corresponding to said charge pattern is fixed to a suitable receiving support by fusing said particles to said support, the improvement wherein (a) the molecular chains of said polymer are crosslinked, and remain crosslinked during fusing, to an extent sufficient to extend the useful fusing range of said toner particles by at least about 10°C. relative to comparable uncrosslinked toner particles comprising said binder polymer in uncrosslinked form and (b) said polymer has a crosslink bond energy in excess of about 8 kcal/mole.

17. An electrographic imaging process according to claim 16 wherein said molecular chains are covalently cross-linked.