(19) ~a)
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`(12)
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`Européisches Patentamt
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`European Patent Office
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`Office européen des brevets
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`(11)
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`EP1 403 342 A1
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`EUROPEAN PATENT APPLICATION
`
`(43) Date of publication:
`31.03.2004 Bulletin 2004/14
`
`(21) Application number: 030778943
`
`(51)
`
`Int CI.7: 609D 11/00, C08L 27/04,
`CO8L 27/10, C08L 27/12
`
`(22) Date of filing: 15.09.2003
`
`
`(84) Designated Contracting States:
`AT BE BG CH CY CZ DE DK EE ES FI FR GB GR
`HU IE IT LI LU MC NL PT RO SE SI SK TR
`
`Designated Extension States:
`AL LT LV MK
`
`(30) Priority: 27.09.2002 US 256989
`
`(71) Applicant: EASTMAN KODAK COMPANY
`Rochester, New York 14650 (US)
`
`0
`
`0
`
`'
`
`Chen, Huijuan D.
`Rochester, New York 14650-2201 (US)
`Frazier, Ricky G.
`Rochester, New York 14650-2201 (US)
`Wang, Jin-Shan
`Rochester, New York 14650-2201 (US)
`
`Representative: Weber, Etienne Nicolas et al
`Kodak Industrie,
`Département Brevets,
`CRT,
`Zone Industrielle
`
`(72) Inventors:
`0 Wang, Xiaoru
`Rochester, New York 14650-2201 (US)
`
`
`71102 Chalon sur Saone Cedex (FR)
`
`(54)
`
`Ink jet ink composition and ink/receiver combination
`
`An aqueous inkjet ink composition including a pigment, a polymer latex containing at least one halogenated
`(57)
`vinyl monomer, at least one surfactant, and a humectant. An ink and receiver combination for a non-absorbing substrate
`is also disclosed.
`
`EP1403342A1
`
`Printed by Jouve, 75001 PARlS (FR)
`
`

`

`EP 1 403 342 A1
`
`Description
`
`FIELD OF THE INVENTION
`
`[0001] The present invention relates to an aqueous inkjet ink composition comprising pigment and a polymer latex.
`The polymer latex is prepared from at least one halogenated vinyl monomer.
`
`BACKGROUND OF THE INVENTION
`
`lnkjet printing is a non-impact method for producing images by the deposition of ink droplets on a substrate
`[0002]
`(paper, transparent film, fabric, etc.) in response to digital signals. lnkjet printers have found broad applications across
`markets ranging from industrial labeling to short run printing to desktop document and pictorial imaging and largeformat
`printing for outdoor applications such as banners, signages, displays, posters, billboard and buswraps.
`[0003] This technique of printing is well suited for printing on a variety of surfaces (receivers) including porous and
`non-porous surfaces. Porous inkjet receivers have the advantage of large fluid intake and this provides fast printing
`speed. However, in some applications, such as banners, signages, displays, posters, billboard and buswraps; these
`porous receivers suffer from durability issues such as lightfastness, waterfastness, abrasion resistance and weather
`resistance. In order to overcome these problems, the prints are usually post treated by methods such as lamination,
`which adds to the cost considerably. Historically, in orderto overcomethese problems, solvent based inks or UV curable
`inks were developed for printing on non—absorbing substrates such as vinyl to achieve the desired durability. US patent
`4,106,027 describes such a solvent-based ink that is suitable for printing images on non-absorbing receivers with
`improved adhesion and durability. EP 0 882 104 B describes a UV curable inkjet ink composition for better durability
`of the print on non—absorbing substrate. A significant environmental, health and safety concern with both of these types
`of ink is the evaporation of solvent or UV monomer during printing.
`[0004] US Patent 6,087,416 describes the use of an aqueous based pigment ink for printing on non-absorbing vinyl
`substrate. That ink contains a grafted copolymer binder that is soluble in the aqueous vehicle but insoluble in water.
`However, the problem with the ink is that, due to the soluble nature of the binder in the ink vehicle, the ink viscosity is
`high and the printing reliability is poor. In addition, the printed images are not durable to solvents.
`[0005] US Patent 4,762,875 described a printing ink containing pigment and polymer additives for plastics and metal
`surfaces. However, there is a problem with this invention that the solid content forthis ink is high, therefore the viscosity
`of the ink is too high for inkjet ink applications; in addition, the additives used in this invention is hydrophilic in nature
`therefore the resulted coatings has poor water resistance.
`[0006] Therefore, there is a need for an aqueous based inkjet ink that provides good waterfastness, lightfastness,
`abrasion resistance, good adhesion to non—absorbing substrates including untreated vinyl, and that can be printed
`reliablythrough a piezo or thermal printhead.
`
`SUMMARY OF THE INVENTION
`
`[0007] The present invention provides an aqueous based inkjet ink that provides good waterfastness, lightfastness,
`abrasion resistance, good adhesion to non-absorbing substrates including untreated vinyl, and can be printed reliably
`through a piezo or thermal printhead. These and other objects are achieved in accordance with the present invention
`which comprises an inkjet ink composition comprising:
`
`--
`--
`--
`--
`
`a pigment;
`a polymer latex containing at least one halogenated vinyl monomer;
`at least one surfactant; and
`a humectant.
`
`[0008] Another embodiment of the invention discloses:
`An aqueous inkjet ink and receiver combination wherein the aqueous inkjet ink comprises:
`
`--
`--
`--
`--
`
`a pigment;
`a polymer latex containing at least one halogenated vinyl monomer;
`at least one surfactant;
`a humectant; and
`
`the receiver comprises a non-absorbing substrate.
`[0009]
`It was found that the colloid stability, stain resistance and abrasion resistance of an in kjet image was improved
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`EP 1 403 342 A1
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`using the composition described herein.
`
`DETAILED DESCRIPTION OF THE INVENTION
`
`[0010] The ink composition of the present invention is suited for printing on a variety of substrates, including non—
`absorbing substrates. The non-absorbing substrates that may be used in the present invention include any substrate
`that is essentially non-porous. They are usually not specially treated for additional liquid absorption. Therefore, these
`materials have very low or no liquid absorbing capacity. Examples of such non-absorbing substrates are metals such
`as aluminum, copper, stainless steel and alloy etc; plastics such as vinyl, polycarbonate, polytetrafluoroethylene (PT-
`FE), polyethylene, polypropylene, polystyrene, cellulose; and other substrates such as ceramics, glass.
`[0011]
`In orderto achieve good image durability when printing aqueous based inks onto a non-absorbing substrate,
`the polymeric binder in the ink composition needs to be essentially hydrophobic, capable of providing good adhesion
`strength to the non-absorbing substrate, and also must not be easily re-dispersible in water after drying. In addition,
`in order to provide good ink storage stability and prevent potential nozzle clogging, the hydrophobic polymer binder
`also needs to be sufficiently stable as a dispersion and compatible with other ink components, such as surfactant,
`colorants and humectants. Therefore, the polymer binders need to be dispersible in aqueous ink environment but not
`soluble therein to achieve low ink viscosity and print durability to both water and solvents. Furthermore, the ink should
`have sufficiently low surface tension to have good wettability to the non-absorbing substrate.
`[0012] The pigment used in the present invention can be eitherself-dispersible such as those described in US patent
`5,630,868, encapsulated as those described in the pending US patent application Serial No. 09/822,723, filed March
`30, 2001, or can be stabilized by a dispersant. The process of preparing inks from pigments commonly involves two
`steps: (a) a dispersing or milling step to break up the pigment to the primary particle, and (b) dilution step in which the
`dispersed pigment concentrate is diluted with a carrier and other addenda to a working strength ink. In the milling step,
`the pigment is usually suspended in a carrier (typically the same carrier as that in the finished ink) along with rigid,
`inert milling media. Mechanical energy is supplied to this pigment dispersion, and the collisions between the milling
`media and the pigment cause the pigment to deaggregate into its primary particles. A dispersant or stabilizer, or both,
`is commonly added to the pigment dispersion to facilitate the deaggregation of the raw pigment, to maintain colloidal
`particle stability, and to retard particle reagglomeration and settling.
`[0013] There are many different types of materials which may be used as milling media, such as glasses, ceramics,
`metals, and plastics. In a preferred embodiment, the grinding media can comprise particles, preferably substantially
`spherical in shape, e.g., beads, consisting essentially of a polymeric resin. In general, polymeric resins suitablefor use
`as milling media are chemically and physically inert, substantially free of metals, solvent and monomers, and ofsufficient
`hardness and firability to enable them to avoid being chipped or crushed during milling. Suitable polymeric resins
`include crosslinked polystyrenes, such as polystyrene crosslinked with divinylbenzene, styrene copolymers, polyacr—
`ylates such as poly(methyl methylacrylate), olycarbonates, polyacetals, such as DerlinTM, vinyl chloride polymers and
`copolymers, polyurethanes, polyamides, poly(tetrafluoroethylenes), e.g., TeflonTM, and otherfluoropolymers, high den-
`sity polyethylenes, polypropylenes, cellulose ethers and esters such as cellulose acetate, poly(hydroxyethy|methacr-
`ylate), poly(hydroxyethylacrylate), silicone containing polymers such as polysiloxanes and the like. The polymer can
`be biodegradable. Exemplary biodegradable polymers include poly(lactides), poly(glycolids) copolymers of lactides
`and glycolide, polyanhydrides, poly(imino carbonates), poly(N-acylhydroxyproline) esters, poly(N-palmitoyl hydroxy-
`prolino) esters, ethylene—vinyl acetate copolymers, poly(orthoesters), poly(caprolactones), and poly(phosphazenes).
`The polymeric resin can have a density from 0.9 to 3.0 g/cm3. Higher density resins are preferred inasmuch as it is
`believed that these provide more efficient particle size reduction. Most preferred are crosslinked or uncrosslinked pol-
`ymeric media based on styrene.
`[0014] Milling can take place in any suitable grinding mill. Suitable mills include an airjet mill, a roller mill, a ball mill,
`an attritor mill and a bead mill. A high speed mill is preferred. By high speed mill we mean milling devices capable of
`accelerating milling media to velocities greater than about 5 meters per second. Sufficient milling media velocity is
`achieved, for example, in Cowles-type saw tooth impeller having a diameter of 40 mm when operated at 9,000 rpm.
`The preferred proportions of the milling media, the pigment, the liquid dispersion medium and dispersant can vary
`within wide limits and depends, for example, up on the particular material selected and the size and density of the
`milling media etc. After milling is complete, the dispersion of active material is separated from the grinding media by
`simple sieving or filtration. With either of the above modes the preferred amounts and ratios of the ingredients of the
`mill grind will vary widely depending upon the specific materials and the intended applications. The contents of the
`milling mixture comprisethe mill grind and the milling media. The mill grind comprises pigment, dispersant and a liquid
`carrier such as water. For aqueous ink jet inks, the pigment is usually present in the mill grind at 1 to 50 weight %,
`excluding the milling media. The weight ratio of pigment to dispersant is 20: 1 to 1:2. The high speed mill is a high
`agitation device, such as those manufactured by Morehouse-Cowles, Hockmeyer et al.
`[0015] The dispersant is another ingredient in the mill grind. It can be either a small molecule or a polymer. Preferred
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`dispersants used in the present invention include sodium dodecyl sulfate, acrylic and styrene-acrylic copolymers, such
`as those disclosed in U. 8. Pat. Nos. 5,085,698 and 5,172,133, and sulfonated polyesters and styrenics, such as those
`disclosed in U.S. Pat. No. 4,597,794. Other patents referred to above in connection with pigment availability also
`disclose a wide variety of dispersants. The dispersant used in the examples is potassium N-methyl-N-oleoyl taurate
`(K—OMT).
`[0016] The milling time can vary widely and depends upon the pigment, mechanical means and residence conditions
`selected, the initial and desiredfinal particle size, etc. For aqueous mill grinds usingthe preferred pigments, dispersants,
`and milling media described above, milling times will typically rangefrom 1 to 100 hours. The milled pigment concentrate
`is preferably separated from the milling media by filtration.
`[0017] The pigment particles useful in the invention may have any particle sizes which can be jetted through a print
`head. Preferably, the pigment particles have a mean particle size of less than about 0.5 micron, more preferably less
`than about 0.2 micron.
`
`A wide variety of organic and inorganic pigments, alone or in combination, may be selected for use in the
`[0018]
`present invention. Colorant particles which may be used in the invention include pigments as disclosed, for example
`in U.S. Patents 5,026,427; 5,086,698; 5,141,556; 5,160,370; and 5,169,436. The exactchoice of pigments will depend
`upon the specific application and performance requirements such as color reproduction and image stability. Pigments
`suitable for use in the present invention include, for example, azo pigments, monoazo pigments, disazo pigments, azo
`pigment lakes, B-Naphthol pigments, Naphthol AS pigments, benzimidazolone pigments, disazo condensation pig-
`ments, metal complex pigments, isoindolinone and isoindoline pigments, polycyclic pigments, phthalocyanine pig-
`ments, quinacridone pigments, perylene and perinone pigments, thioindigo pigments, anthrapyrimidone pigments, fl—
`avanthrone pigments, anthanthrone pigments, dioxazine pigments, triarylcarbonium pigments, quinophthalone pig-
`ments, diketopyrrolo pyrrole pigments, titanium oxide,
`iron oxide, and carbon black. Typical examples of pigments
`which may be used include Color Index (C. I.) Pigment Yellow 1, 2, 3, 5, 6, 10, 12, 13, 14, 16, 17, 62, 65, 73, 74, 75,
`81, 83, 87, 90, 93, 94, 95, 97, 98, 99, 100, 101, 104, 106, 108, 109, 110, 111, 113, 114, 116, 117, 120, 121, 123, 124,
`126,
`127,
`128,
`129,
`130,
`133,
`136,
`138,
`139,
`147,
`148,
`150,
`151,
`152,
`153,
`154,155,165,166,167,168,169,170,171,172,173,174,175,176,177,179,180,181,182,183,184,185,187,188,190,
`191, 192, 193, 194; C. I. Pigment Orange 1, 2, 5, 6, 13, 15, 16, 17, 17:1, 19, 22, 24, 31, 34, 36, 38, 40, 43, 44, 46, 48,
`49, 51, 59, 60, 61, 62, 64, 65, 66, 67, 68, 69; C.
`l. Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9; 10, 11, 12, 13, 14, 15, 16, 17,
`18, 21, 22, 23,31, 32, 38, 48:1; 48:2, 48:3, 48:4, 49:1, 49:2, 49:3, 50:1, 51, 52:1, 52:2, 53:1, 57:1, 50:1, 63:1, 66, 57,
`68,81,95,112,114,119,122,136,144,146,147,148,149,150,151,164,166,168,169,170,171,172,175,176,
`177, 178, 179, 181, 184, 185, 187, 188, 190, 192, 194, 200, 202, 204, 206, 207, 210, 211, 212, 213, 214, 216, 220,
`222, 237, 238, 239, 240, 242, 243, 245, 247, 248, 251 , 252, 253, 254, 255, 256, 258, 261 , 264; C.l. Pigment Violet 1,
`2, 3, 5:1, 13, 19, 23, 25, 27, 29, 31, 32, 37, 39, 42, 44, 50; C.|. Pigment Blue 1, 2, 9, 10, 14, 15: 1, 15:2, 15:3, 15:4,
`15:6, 15, 16, 18, 19, 24:1 , 25, 56, 60, 61, 62, 63, 64, 66; C.l. PigmentGreen 1,2, 4, 7, 8, 10, 36, 45; C.l. Pigment Black
`1, 7, 20, 31,32, and CI. Pigment Brown 1,5, 22, 23, 25, 38, 41, 42. In a preferred embodiment of the invention, the
`pigment is C.l. Pigment Blue 15:3, C.l. Pigment Red 122, C.l. Pigment Yellow 155, C.l. Pigment Yellow 74, C.l. Pigment
`Black 7 0r bis(phthalocyanylalumino)tetraphenyldisiloxane as described in US. Pat. No. 4,311,775.
`[0019]
`In the case of organic pigments, the ink may contain up to approximately 20% pigment by weight, but will
`generally be in the range of approximately 0.1 to 10%, preferably approximately 0.1 to 5%, by weight of the total ink
`composition for most inkjet printing applications. If an inorganic pigment is selected, the ink will tend to contain higher
`weight percentages of pigment than with comparable inks employing organic pigments.
`[0020]
`Instead of pigment, a dye can also be used in the current invention. Preferably, the dye is a water insoluble
`dye. To make the ink, the water insoluble dye can be dispersed or encapsulated into water dispersible particles as
`disclosed in U. 8. Serial No. 10/020,694, filed December 14, 2001 . A broad range of water-insoluble dyes may be used
`in the invention such as an oil dye, a disperse dye, or a solvent dye, such as Ciba-Geigy Orasol Red G, Ciba-Geigy
`Orasol Blue GN, Ciba-Geigy Orasol Pink, and Ciba-Geigy Orasol Yellow. Preferred water-insoluble dyes can be xan-
`thene dyes, methine dyes, polymethine dyes, anthroquinone dyes, merocyanine dyes, azamethine dyes, azine dyes,
`quinophthalone dyes, thiazine dyes, oxazine dyes, phthalocyanine dyes, mono or poly azo dyes, and metal complex
`dyes. More preferably, the water insoluble dyes can be an azo dye such as a water insoluble analog of the pyrazolea—
`zoindole dye disclosed in US. Serial No. 09/689,184 filed October 12, 2000 and the arylazoisothiazole dye disclosed
`in U. 8. Patent 4,698,651, or a metal-complex dye, such as the water-insoluble analogues of the dyes described in U.
`8. Patents 5,997,622 and 6,001,161, i.e., a transition metal complex of an 8-heterocyclylazo-5-hydroxyquinoline. The
`solubility ofthe water insoluble dye used in the present invention should be less than 1 g/L in water, and more preferably
`less than 0.5 g/L in water.
`[0021] The water insoluble dye can be present in any effective amount in the ink of the present invention, usually up
`to about 20% by weight of an ink jet ink composition, and preferably from about 0.05 to 15 wt. %.
`[0022] The polymer latex used in this invention can be homopolymer or copolymer or cross-linked polymer prepared
`with at least one halogenated vinyl monomer, and optionally other ethylenically-unsaturated monomers such that the
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`EP 1 403 342 A1
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`latex can be stabilized in a water-based medium. The polymer latex contains an ethylenically-unsaturated monomer
`capable of addition polymerization. The ethylenically-unsaturated monomers which can be used in the invention in-
`clude, for example, the following monomers and their mixtures: acrylic acid, methacrylic acid, ethacrylic acid, methyl
`acrylate, ethyl acrylate, ethyl methacrylate, benzyl acrylate, benzyl methacrylate, propyl acrylate, propyl methacrylate,
`iso—propyl acrylate, iso—propyl methacrylate, butyl acrylate, butyl methacrylate, hexyl acrylate, hexyl methacrylate, oc—
`tadecyl methacrylate, octadecyl acrylate, lauryl methacrylate, lauryl acrylate, hydroxyethyl acrylate, hydroxyethyl meth-
`acrylate, hydroxyhexyl acrylate, hydroxyhexyl methacrylate, hydroxyoctadecyl acrylate, hydrowoctadecyl methacr-
`ylate, hydroxylauryl methacrylate, hydroxylauryl acrylate, phenethylacrylate, phenethyl methacrylate, 6-phenylhexyl
`acrylate, B-phenylhexyl methacrylate, phenyllauryl acrylate, phenyllaurylmethacrylate, 3-nitrophenyl-6-hexyl methacr-
`ylate, 3-nitrophenyl-18-octadecyl acrylate, ethyleneglycol dicyclopentyl ether acrylate, vinyl ethyl ketone, vinyl propyl
`ketone, vinyl hexyl ketone, vinyl octyl ketone, vinyl butyl ketone, cyclohexyl acrylate,3-methacryloxypropyl-dimethyl-
`methoxysilane, 3—methacryloxypropyl—methyldimethoxysilane, 3—methacryloxypropylpentamethyldisiloxane, 3—meth—
`acryloxypropyltris-(trimethylsiloxy)silane, 3 -acryloxypropyl-dimethylmethoxysilane, acryloxypropylmethyldimethoxysi-
`lane, trifluoromethyl styrene, trifluoromethyl acrylate, trifluoromethyl methacrylate, tetrafluoropropyl acrylate, tetrafluor-
`opropyl methacrylate, heptafluorobutyl methacrylate, isobutyl acrylate, isobutyl methacrylate, 2-ethylhexyl acrylate,
`2-ethylhexyl methacrylate, isooctyl acrylate, isooctyl methacrylate, N,N-dihexyl acrylamide, N,N-dioctyl acrylamide, N,
`N-dimethylaminoethyl acrylate, N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethyl acrylate, N,N-diethyl-
`aminoethyl methacrylate, piperidino-N-ethyl acrylate, vinyl propionate, vinyl acetate, vinyl butyrate, vinyl butyl ether,
`and vinyl propyl ether ethylene, styrene, vinyl carbazole, vinyl naphthalene, vinyl anthracene, vinyl pyrene, methyl
`methacrylate, methyl acrylate, alpha—methylstyrene, dimethylstyrene, methylstyrene, vinylbiphenyl, glycidyl acrylate,
`glycidyl methacrylate, glycidyl propylene, 2-methyl-2-vinyl oxirane, vinyl pyridine, aminoethyl methacrylate, aminoethyl-
`phenyl acrylate, maleimide, N-phenyl maleimide, N-hexyl maleimide, N-vinyl-phthalimide, and N-vinyl maleimide poly
`(ethylene glycol) methyl ether acrylate, polyvinyl alcohol, vinyl pyrrolidone, vinyl 4—methylpyrrolidone, vinyl 4—phenylpyr—
`rolidone, vinyl imidazole, vinyl 4-methylimidazole, vinyl 4-phenylimidazole, acrylamide, methacrylamide, N,N-dimethyl
`acrylamide, N-methyl acrylamide, N-methyl methacrylamide, aryloxy dimethyl acrylamide, N-methyl acrylamide, N-
`methyl methacrylamide, aryloxy piperidine, and N,N-dimethyl acrylamide acrylic acid, methacrylic acid, chlorometh-
`acrylic acid, maleic acid, allylamine, N,N—diethylallylamine, vinyl sulfonamide, sodium acrylate, sodium methacrylate,
`ammonium acrylate, ammonium methacrylate, acrylamidopropanetriethylammonium chloride, methacrylamidopro-
`pane-triethylammonium chloride, vinyl-pyridine hydrochloride, sodium vinyl phosphonate and sodium 1-methylvinyl-
`phosphonate, sodium vinyl sulfonate, sodium 1-methylvinyl-sulfonate, sodium styrenesulfonate, sodium acrylamido-
`propanesulfonate, sodium methacrylamidopropanesulfonate, and sodium vinyl morpholine sulfonate, allyl methacr—
`ylate, allyl acrylate, butenyl acrylate, undecenyl acrylate, undecenyl methacrylate, vinyl acrylate, and vinyl methacr-
`ylate; dienes such as butadiene and isoprene; esters of saturated glycols or diols with unsaturated monocarboxylic
`acids such as, ethylene glycol diacrylate, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, 1,4—butane—
`diol dimethacrylate, 1,3-butanediol dimethacrylate, pentaerythritol tetraacrylate, trimethylol propane trimethacrylate
`and polyfunctuional aromatic compounds such as divinylbenzene.
`[0023] The halogenated vinyl monomer used in the present invention can be vinyl chloride, vinylidene chloride, vinyl
`fluoride, vinylidene fluoride, vinyl bromide and vinylidene bromide, chloromethacrylic acid and the like.
`[0024]
`Surfactants that can be used in the present invention to synthesize the polymers include, for example, a
`sulfate, a sulfonate, a cationic compound, a reactive surfactant, an amphoteric compound, and a polymeric protective
`colloid.
`
`Specific examples are described in "McCutcheon's Emulsifiers and Detergents: 1995, North American Editor"
`[0025]
`and will be known to those skilled in the art.
`
`[0026] Depending on the types of initiators used, the reaction temperature can vary from about 30°C to about 90°C.
`Preferably the reaction temperature is at least 40°C, and most preferably at least 50°C. To ensure that no free monomer
`is present, usuallythe reaction is continued for a time after the monomer addition. Also, more initiator may need to be
`added as a scavenger during the final stage of the reaction to increase the reaction conversion.
`[0027] Addition polymerization initiators useful in the practice of the invention include, for example, azo and diazo
`compounds, such as 2,2'—azobisisobutyronitrile, 2,2'—azobis(2,4—dimethyl valeronitrile), 2,2'—azobis(2,3—dimethyl buty—
`ronitrile), 2,2'-azobis(2-methyl butyronitrile), 2,2'-azobis(2,3,3-trimethyl butyronitrile), 2,2'-azobis(2-isopropyl butyroni-
`trile), 1,1'-azobis(cyclohexane-1-carbonitrile), 2, 2'-azobis(4-methoxyl-2,4-dimethyl valeronitrile), 2-(carbamoylazo)
`isobutyronitrile, 4,4'-azobis(4-cyanovaleric acid), and dimethyl -2,2'azobis isobutyrate, or peroxide compounds, such
`as butyl peroxide, propyl peroxide, butyryl peroxide, benzoyl isobutyryl peroxide, and benzoyl peroxide, or water soluble
`initiators, for example, sodium persulfate, and potassium persulfate, or any redox initiators. Preferred initiators are the
`oil soluble initiators. Examples of particularly suitable initiators are azo, peroxide, persulfate, and redox initiators. The
`initiators may be used in an amount varying from about 0.2 to 4weight percent or higher by weight ofthetotal monomers.
`A chain transfer agent such as butyl mercaptan, may also be used to control the properties of the polymer formed.
`[0028] The polymers can be made via emulsion polymerization, dispersion polymerization, suspension polymeriza-
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`tion, grand milling, or solution/bulk polymerization and then post-emulsification. Detailed information about the process
`and the stabilizers can be found in "Emulsion Polymerization and Emulsion Polymers" (P. A. Lovell, M. S. El-Aasser,
`John Wiley & Sons Ltd., England, 1997).
`[0029] The polymer latex employed in the invention in general has a Tg of - 50 to 150 °C, preferably 5 to 100 °C,
`most preferably 10 to 80 °C.
`[0030] The polymer latex employed in the invention in general have an average particle size of less than 2 pm,
`preferably less than 0.5 um, more preferably less than 0.25 pm.
`[0031] The polymer latex used in the invention is present in the inkjet ink generally from 0.1% to 20% by weight,
`preferably from 0.5% to 10% by weight.
`[0032]
`All monomer units in the polymer latex used in the invention may be hydrophobic. Alternatively, the polymer
`latex may contain at least one hydrophilic monomer unit. The content of hydrophilic monomer unit is less than 50 mole
`% of the total monomer units in the polymer latex, preferably less than 20 mole % of the total monomer units in the
`polymer latex, most preferably less than 5 mole % of the total monomer units in the polymer latex.
`[0033] The hydrophilic monomer unit in the polymer latex may be selected from the group consisting of acrylic acid,
`methacrylic acid, chloromethacrylic acid, maleic acid, allylamine, N,N-diethylallylamine, vinyl sulfonamide, sodium acr-
`ylate, sodium methacrylate, ammonium acrylate, ammonium methacrylate, acrylamidopropane-triethylammonium
`chloride, methacrylamidopropane-triethylammonium chloride, vinyl-pyridine hydrochloride, sodium vinyl phosphonate
`and sodium 1 -methylvinylphosphonate, sodium vinyl sulfonate, sodium 1-methylvinyl-sulfonate and sodium styrenesul-
`fonate. The hydrophilic monomers can also be non-ionic, such as ethyoxytriethylene glycol methacrylate, methoxypol-
`yethylene oxide methacrylate, methoxypropylene oxide acrylate, polyethyleneoxide methacrylate, polyethylenoxide
`acrylate, N-vinyl pyrrolidone and the like.
`[0034] The aqueous carrier medium for the ink composition is water or a mixture of water and at least one water
`miscible co—solvent. Selection of a suitable mixture depends on requirements of the specific application, such as desired
`surface tension and viscosity, the selected pigment, drying time ofthe pigmented inkjet ink, and the type of paper onto
`which the ink will be printed. Representative examples of water-miscible co-solvents that may be selected include (1)
`alcohols, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol,
`t—butyl alcohol, iso—butyl alcohol, furfuryl alcohol, and tetrahydrofurfuryl alcohol; (2) ketones or ketoalcohols such as
`acetone, methyl ethyl ketone and diacetone alcohol; (3) ethers, such as tetrahydrofuran and dioxane; (4) esters, such
`as ethyl acetate, ethyl lactate, ethylene carbonate and propylene carbonate; (5) polyhydric alcohols, such as ethylene
`glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, polyethylene glycol, glycerol, 2-me-
`thyl—2,4—pentanedio| 1,2,6—hexanetriol and thioglycol; (6) lower alkyl mono— or di—ethers derived from alkylene glycols,
`such as ethylene glycol mono-methyl (or -ethyl) ether, diethylene glycol mono-methyl (or -ethyl) ether, diethylene glycol
`mono-butyl (or - ethyl) ether, propylene glycol mono-methyl (or -ethyl) ether, poly(ethylene glycol) butyl ether, triethylene
`glycol mono—methyl (or —ethyl) ether and diethylene glycol di—methyl (or —ethyl) ether; (7) nitrogen containing cyclic
`compounds, such as pyrrolidone, N-methyl-2—pyrrolidone, and 1,3-dimethyl-2-imidazolidinone; and (8) sulfur-contain-
`ing compounds such as dimethyl sulfoxide, 2,2'-thiodiethanol, and tetramethylene sulfone.
`[0035] The amount of aqueous carrier medium is in the range of approximately 70 to 99 weight %, preferably ap-
`proximately 90 to 98 weight %, based on the total weight of the ink. A mixture of water and a polyhydric alcohol, such
`as diethylene glycol, is useful as the aqueous carrier medium. In a preferred embodiment, the inks contain from about
`5 to about 60 weight "/0 of water miscible organic solvent based on the total weight of the aqueous carrier medium.
`[0036]
`Jet velocity, separation length ofthe droplets, drop size and stream stability are greatly affected by the surface
`tension and the viscosity of the ink. Pigmented inkjet inks suitable for use with ink jet printing systems should have a
`surface tension in the range of about 20 dynes/cm to about 60 dynes/cm and, more preferably, in the range 30 dynes/
`cm to about 50 dynes/cm. Control of surface tensions in aqueous inks is accomplished by additions of small amounts
`of surfactants. The level of surfactants to be used can be determined through simple trial and error experiments, usually
`about 0.1% to about 6%, preferably, 0.5% to about 4% by weight of the total ink composition. Anionic, cationic and
`nonionic surfactants may be selected from those disclosed in U. S. Patents 5,324,349; 4,156,616 and 5,279,654 as
`well as many other surfactants known in the ink jet ink art. Commercial surfactants include the Surfynols® from Air
`Products; the Zonyls® from DuPont and the Fluorads® from 3M. Preferred surfactants can be silicon surfactants or
`fluorinated surfactants. Preferred silicon surfactants are available from BYK-Chemie as BYK surfactants, and from
`Crompton Corp, as Silwet® surfactants. Commercially available fluorinated surfactants can be the Zonyls® from Du-
`Pont and the Fluorads® from 3M, they can be used alone or in combination with other surfactants.
`[0037]
`A humectant is added to the composition employed in the process of the invention to help prevent the ink
`from drying out or crusting in the orifices of the ink jet printhead. Polyhydric alcohols useful in the composition employed
`in the invention for this purpose include, for example, ethylene glycol, diethylene glycol, triethylene glycol, propylene
`glycol, tetraethylene glycol, polyethylene glycol, glycerol, 2—methyl—2,4—pentanediol, 1,2,6—hexanetriol and thioglycol.
`The humectant may be employed in a concentration of from about 10 to about 50 % by weight of the entire ink com-
`position.
`In a preferred embodiment, diethylene glycol or a mixture of glycerol and diethylene glycol is employed a
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`4o
`
`45
`
`50
`
`55
`
`

`

`EP 1 403 342 A1
`
`concentration of between 10 and 20 % by weight of the entire ink composition.
`[0038] The ink has physical properties compatible with a wide range of ejecting conditions, i.e., driving voltages and
`pulse widths for thermal inkjet printing devices, driving frequencies of the piezo element for either a drop-on-demand
`device or a continuous device, and the shape and size of the nozzle.
`[0039]
`A penetrant (0—10% by weight) may also be added to the ink composition employed in the process of the
`invention to help the ink penetrate the receiving substrate, especially when the substrate is a highly sized paper. A
`preferred penetrant for the inks employed in the present invention is n-propanol at a final concentration of 1-6 % by
`weight.
`A biocide (0.01 -1 0% by weight) may also be added to prevent unwanted microbial growth which may occur
`[0040]
`in the ink overtime. A preferred biocide forthe inks employed in the present invention is Proxel® GXL (Zeneca Colours
`Co.) at a concentration of 005-05 °/o by weight. Additional additives which may optionally be present in ink jet inks
`include thickeners, conductivity enhancing agents, anti—kogation agents, pH buffering agents, drying agents, and de—
`foamers.
`
`Inkjet inks made using water-dispersible polymers employed in this invention are employed in ink] et printing
`[0041]
`wherein liquid ink drops are applied in a controlled fashion to an ink receiving substrate, by ejecting ink droplets from
`plurality of nozzles, or orifices, in a pr