Ink jet ink compositions and printing processes

Abstract: A multicolor ink jet printing process employs an ink jet ink composition comprising water, a colorant of pigment, dye, or mixtures thereof, and a low boiling point additive to produce high quality multicolor ink jet images with minimal intercolor bleed and lines with sharp edges as characterized by a relatively low mid frequency line edge noise (MFLEN) number. The additive is an alcohol or thiol having a boiling point less than or equal to about 115°C. The aforementioned ink jet ink composition can further include an optional additive of alcohol or thiol with a boiling point less than or equal to about 135°C if necessary. The desired additive increases the ink's drying rate with fast evaporation and an accelerated penetration into a print substrate (e.g. paper) upon printing. As a result, little or minimum residual ink (e.g. carbon black ink) comprising the aforementioned additive is available on the surface of the print substrate to intermix with a previously or subsequently printed ink (e.g. a color ink). As a result, the ink composition and multicolor ink jet printing process of the present invention can produce high quality images with minimal intercolor bleed and low MFLEN.

Description: BACKGROUND OF THE INVENTION 1. Field of Invention The present invention is directed to an aqueous ink composition. More specifically, the present invention is directed to aqueous ink compositions comprising a low boiling point thiol as a substrate penetrant additive for use in ink jet printing processes. In addition, the present invention is also directed to an ink jet printing process wherein an aqueous ink composition comprising a low boiling point thiol is used in the production of single or multicolor images. 2. Description of Related Art Ink jet printing is a non-impact printing method that produces droplets that are deposited on a print substrate (recording medium) such as plain paper, coated paper, transparent film (transparency), or textile in response to electronic digital signals. Thermal or bubble jet drop-on-demand ink jet printers have found broad applications as output for personal computers in the office and at home. In existing thermal ink jet printing processes, the printhead typically comprises one or more ink jet ejectors, each ejector includes a channel communicating with an ink supply chamber, or manifold, at one end and having an opening at an opposite end, referred to as a nozzle. A thermal energy generator, usually a resistor, is located in each of the channels at a predetermined distance from the nozzles. The resistors are individually addressed with a current pulse to momentarily vaporize the ink within each respective channel to form a bubble that expels an ink droplet. As the bubble grows, the ink rapidly bulges from the nozzle and is momentarily contained by the surface tension of the ink as a meniscus. This is a very temporary phenomenon, and the ink is quickly propelled toward a print sheet. As the bubble begins to collapse, the ink remaining in the channel between the nozzle and the bubble starts to move toward the collapsing bubble, causing volumetric contraction of the ink at the nozzle resulting in the separation of the bulging ink from the nozzle as a droplet. The acceleration of the ink out of the nozzle while the bubble is growing provides sufficient momentum and velocity to propel the ink droplet in a substantially straight-line direction towards a print substrate, such as a piece of paper. Subsequently, the ink channel refills by capillary action and is ready for the next repeating thermal ink jet process. Thermal ink jet processes are well known and described in, for example, U.S. Patent Nos. 4,251,824, 4,410,889, 4,412,224, 4,463,359, 4,532,530, 4,601,777, 5,139,574, 5,145,518, and 5,281,261. Because the droplet of ink is emitted only when the resistor is actuated, this type of thermal ink jet printing is known as "drop-on-demand" printing. Other types of drop-on-demand printing such as piezoelectric ink jet printing and acoustic ink jet printing are also known. Continuous ink jet printing is also known. In continuous ink jet printing systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. Multiple orifices or nozzles can be used to increase imaging speed and throughput. The ink is perturbed while being ejected from an orifice, causing the ink to break up into droplets at a fixed distance from the orifice. At the point of break-up, the electrically charged ink droplets pass through an applied electrode that switches on and off in accordance with digital data signals. Charged ink droplets pass through a controllable electric field that adjusts the trajectory of each ink droplet in order to direct it to either a gutter for ink deletion and recirculation or to a specific location on a recording substrate (print substrate) to create images. In an ink jet printing apparatus, the printhead typically comprises a linear array of ejectors, and the printhead moves relative to the surface of the print substrate, either by moving the print substrate relative to a stationary printhead, or vice-versa, or both. In some types of apparatuses, at least a relatively small print head supplied with an ink moves across a print sheet numerous times in swaths in order to complete an image. For multi-color ink jet printing, a set of printheads and ink (e.g. cyan, magenta, yellow and black) can move across the print substrate numerous times in swathes and disperse selected inks in any desired patterns (e.g., 1/8, 1/4, 1/2, fulltone (1/1)) according to digital signals. The speed of this type of single or multiple color ink jet printing on a substrate is determined by the moving speed of the printheads across the print substrate, ink jetting frequency (or frequency response), and the desired number of swathes needed for printing. The printing speed of this type of ink jet apparatus can be increased if two or more print heads are budded together to form a partial-width array printhead for printing each ink in a monochrome or multi-color ink jet printing system. The partial-width ink jet printhead has more ink jet nozzles per printhead, and can deliver a large number of ink droplets across the substrate in a swath in a short period of time. Monochrome or multi-color ink jet printing apparatuses using one or several partial-width printheads may have a faster printing speed than current commercial ink jet printers. Alternatively, a printhead that consists of an array of ejectors (e.g., several butted printheads to give a full-width array printhead) and extends the full width of the print substrate may pass an ink down once onto the print substrate to give full line images, in what is known as a "full-width array printer" When the printhead and the print substrate are moved relative to each other, image-wise digital data is used to selectively activate the thermal energy generators in the ink jet printhead over time so that the desired image will be created on the print substrate at a fast speed. For multi-color ink jet printing, several full-width array printheads and inks (e.g., cyan, magenta, yellow, and black) can be used to deliver multiple color inks onto a print substrate. This type of multi-color ink jet printing process is capable of printing multiple color images and monochrome color images on a print substrate at a much faster speed (e.g., more than five pages of full color images per minute) than current commercial color ink jet printers. In multicolor ink jet printing processes, several inks can be printed on a print substrate. In some instances, two different inks can be printed next to each other. Intercolor bleed can occur if the inks are not dried properly or if the printing process is too fast for the inks to set. Undesired ink mixing on a print substrate, especially on the surface of a plain paper, can cause distorted images near the border of two inks. After the inks dry, the border of the two inks can appear irregular with poor edge sharpness (or raggedness) due to the invasion of one ink into the other. Such bleed images are visibly unattractive. This phenomenon is generally called intercolor bleed. Intercolor bleed occurs particularly when a darker colored ink (such as a black ink) and a lighter colored ink (such as a yellow ink, a cyan ink, a magenta ink, or the like) are printed next to each other, because of the high contrast between the two colors. Intercolor bleed can also occur when two color inks are printed next to each other (for example yellow ink next to magenta ink, yellow ink next to cyan ink, magenta ink next to cyan ink or the like). The severity of the intercolor bleed generally is affected by the type and composition of the ink, absorption rate of the ink on a print substrate, printhead design, ink drop mass, ink dot size and method and speed of printing. As a result, there is a need to reduce intercolor bleed and to produce high quality multicolor ink jet images on print substrates, including plain and coated papers, transparencies, textiles and other desired substrates. Ink compositions for ink jet recording which contain water, a colorant and a lower alcohol having a low boiling point are known from EP-A-714960, EP-A-704504, EP-A-719846, EP-A-909798, EP-A-911374, EP-A-985714 and EP-A-1035177. Although known compositions and processes are suitable for their intended purposes, there remains a need for improved multicolor thermal ink jet printing processes. In addition, a need remains for multicolor thermal ink jet printing processes wherein high quality images on a print substrate (e.g. plain papers, etc.) can be obtained. Furthermore, there is a need for improving multicolor thermal ink jet printing processes wherein the printed images exhibit reduced intercolor bleed (high quality color images) when an ink comprising a low boiling thiol is printed adjacent to another ink on a print substrate. Further, a need remains for multicolor thermal ink jet printing processes wherein the prints generated by an ink exhibit excellent image quality. In particular, there is an urgent need for an ink (especially a carbon black ink) that provides good MFLEN ( M id Frequency L ine E dge N oise using a Fourier Transform method) and intercolor bleed performance. In addition, there is a need to decrease drying time of a pigment ink (such as a carbon black ink) without causing image degradation. SUMMARY OF THE INVENTION The present invention provides an ink jet ink composition according to claim 1, an ink jet printing process according to claim 7, and a multicolor ink jet printing process according to claim 8. Preferred embodiments of the invention are set forth in the sub-claims. The present invention is directed to an ink jet ink composition that comprises water, a colorant of dye, pigment, or a mixture of dye and pigment, and an ink additive with a low boiling point being a thiol, as well as printing processes using such a composition. In particular, the present invention is directed to an ink jet ink composition comprising a colorant of pigment (particularly a pigment (e.g. carbon black)), dye, or mixture thereof, and a low boiling point penetrant additive. The low boiling point penetrant additive allows the ink to dry fast on a substrate (print substrate) to produce high quality images and sharp edges by enabling the ink to rapidly penetrate into the print substrate upon printing. Because the ink additive evaporates quickly upon printing, the ink in some cases may assume a higher surface tension and may prevent undesired feathering. In addition, the present invention also directed to the improvement of a multicolor ink jet printing process that can minimize intercolor bleed between two neighboring inks on a print substrate and maintain excellent print quality of text images including lines and graphics. The multicolor ink jet printing process of the present invention may comprise at least a pigment ink containing an ink additive of low boiling point being a thiol. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The present invention provides an ink jet ink composition comprising water, a colorant, and a low boiling point penetrant additive having a boiling point less than or equal to 115°C, said low boiling point penetrant additive being a thiol. Preferably, the colorant is selected from the group consisting of carbon black either with or without chemical modification, a pigment other than carbon black, a dye and a mixture of dye and pigment. Preferably, the low boiling point penetrant additive is selected from the group consisting of 1-butanethiol, t-butylthiol, 1-methyl-1-propanethiol, 2-methyl-1-propanethiol, 2-methyl-2-propanethiol, thiocyclopropanol, and mixtures thereof. Preferably, the low boiling point penetrant additive is present in an amount ranging from 0.1% to 8% by weight of the total weight of the ink composition. The composition may further contain at least one member selected from the group consisting of a humectant, a surfactant, a pigment dispersing agent, a pH buffer, a biocide, an anti-curl agent, an anti-bleed agent, a jetting aid, a drying accelerating agent, a polymeric binder, an anti-clogging agent, and a latency enhancer. The composition may additionally contain a second low boiling penetrant additive having a boiling point of less than or equal to 135°C. The present invention further provides an ink jet printing process comprising printing a first ink and at least a second ink with an ink jet ink composition as defined above and a different colorant from the first ink onto a print substrate according to digital data signals in any desired printing order. The first ink may be printed onto a print substrate first before the second ink is printed adjacent to the first ink and allows the second ink to dry quickly by evaporation and fast penetration into a surface of the print substrate with low intercolor bleed, or the second ink may be printed first onto a print substrate before the first ink is printed adjacent to the second ink onto the print substrate. Preferably, the second ink is a carbon black ink comprising carbon black particles which are selected from a group consisting of chemically modified carbon black particles and/or carbon black particles stabilized by a pigment dispersing agent. The first ink may be a dye-based color ink. Moreover, the present invention provides a multicolor ink jet printing process comprising: (1) incorporating into an ink jet printer a first ink; (2) incorporating into the ink jet printer at least one second ink comprising a thiol additive having a boiling point less than or equal to 115°C; (3) causing droplets of said first ink to be ejected in an imagewise pattern onto a surface of a print substrate; and (4) causing droplets of said at least one second ink to be ejected in an imagewise pattern onto the surface of the print substrate so that a multicolor ink image is formed on the print substrate that exhibits at least one of sharp line edges and minimal intercolor bleed. The ink jet printer may employ any desired printing order for printing the first and second inks. The first ink may be ejected onto the surface of the print substrate prior to ejecting said at least one second ink onto the surface of the print substrate. The print substrate may be optionally heated at any stage of ink jet printing process including at least one of before, during and after printing. Preferably, the printing process further comprises jetting at least one of the inks through a printhead capable of printing at least 300 spots per inch. The printer may employ a printing process selected from continuous stream ink jet printing and drop-on-demand ink jet printing which is selected from a group consisting of thermal ink jet printing, acoustic ink jet printing, and piezoelectric ink jet printing. At least some of said first ink may be printed at least one of on top, below, or adjacent to said at least one second ink. Preferably, the ink jet printer uses a printhead that is a partial width printhead, a partitioned printhead, or a full width array printhead. Preferably, the first ink is selected from the group consisting of a yellow ink, a cyan ink and a magenta ink. The thiol additive may be selected from the group consisting of 1-butanethiol; t-butylthiol; 1-methyl-1-propanethiol; 2-methyl-1-propanethiol; 2-methyl-2-propanethiol; thiocyclopropanol; and mixtures thereof Preferably, the second ink further comprises an alcohol or thiol with a boiling point ≤ 135°C. The alcohols or thiols with a boiling point ≤ 135°C may be selected from 3-methyl-1-butanol; 2,3-dimethyl, 1-butanol; 3,3-dimethyl, 1-butanol; 1-butanol; 2-methyl-1-butanol (d and 1); 2,3,3-trimethyl-1-butanol; 2-pentanol, 3-pentanol; 2-pentanol; 2,4-dimethyl, 2-pentanol; 2-methyl, 2-pentanol; 3-methyl, 2-pentanol; 4-methyl, 3-pentanol; 2-methyl, 3-pentanol; 3-methyl, 1-propanol; 2-chloro, 1-propanol; 1-chloro, 1-propanol; 1-chloro, 2-methyl; 2,2-dimethyl-1-propanol (neopentyl alcohol); 3-fluoro-1-propanol; 1-methoxy-2-propanol; 1-ethoxy-2-propanol; 1-butanethiol, 2-methyl; 1-butanethiol, 3-methyl; and mixtures thereof. According to the present invention, at least one ink in an ink jet printing process comprises a low boiling point thiol (an ink additive) to accelerate the penetration of the ink into a print substrate with a faster drying rate (short dry time). The aforementioned ink (or ink composition) comprising the low boiling point thiol is preferably a pigment ink, such as a carbon black ink, although it can also be a dye-based ink. In another embodiment of this invention the ink jet printing process comprises printing at least one ink having a low boiling point thiol additive in its composition that reduces intercolor bleed when the ink is printed adjacent to another ink (e.g. a fast dry dye-based color ink). The penetrant or low boiling point additive of the ink jet ink composition of the present invention is provided in order to minimize the amount of residual ink on the surface of the print substrate that is available to participate in undesirable intercolor bleed between two neighboring inks (e.g. a black ink and a yellow ink, a black ink and a cyan ink, black ink and a magenta ink, etc.). The penetrant (low boiling point thiol additive) for use in the present invention minimizes the amount of and/or time a residual ink remains on the surface of the print substrate by allowing the ink to rapidly penetrate into the print substrate immediately after being printed onto the substrate surface. The low boiling point thiol additive also can quickly evaporate. As a result, the residual ink remaining on the surface of the substrate is substantially reduced, thereby reducing the likelihood of intermixing between residual ink and other color inks printed in bordering areas. In addition, the low boiling point ink additive can evaporate quickly and allows the printed ink to produce excellent line edge acuity and sharpness (Low Mid Frequency Line Edge Noise (MFLEN)) without causing significant image deterioration (e.g. due to feathering, etc.). In addition, the appropriate use of low boiling point thiols as ink additives can maintain good stability of a pigment ink including a carbon black ink comprising either chemically modified carbon black particles or carbon black particles that are stabilized by a pigment dispersant. According to the present invention, the low boiling point penetrant additive can be included in one or more inks of an ink set in a multicolor ink jet printing process. In addition, the low boiling point penetrant additive can be incorporated into an ink jet ink that is used in a mono-color printing apparatus (e.g. black ink jet printing apparatus). Thus, for example, the present invention applies equally to a printing apparatus that prints multi-color images, as well as to a printing apparatus that prints only a single-color image (e.g. black). However, it will be appreciated that the benefits provided by the present invention are particularly applicable to a multi-color printing process, wherein good black text on plain papers is required and the intercolor bleed reduction is a great concern for the production of multicolor images. Also according to the present invention, the low boiling point penetrant additive can be included in any one or more of the various colored inks in an ink set. Thus, for example, the low boiling point penetrant additive can be included in one or more of the colored inks, such as the black, magenta, yellow, or cyan inks. However, particular benefits are provided by the present invention when the low boiling point penetrant additive is included in the black inks, particularly in carbon black-based inks, since these inks typically are formulated to achieve good print quality but have a longer drying time as compared to inks of other colors. At least one of a set of multi-color ink jet inks comprises a thiol additive having a boiling point less than or equal to 115°C (at atmospheric pressure, 760mm Hg). In an alternative preferred embodiment of the present invention, proposed thiols can be used together (jointly) with a second alcohol or thiol having a boiling point that is less than or equal to 135°C (at atmospheric pressure, 760mm Hg; e.g. B.P. of the ink additive is between 115°C and 135°C). Suitable additives, low boiling point thiols with a boiling point less than or equal to 115°C include 1-butanethiol; t-butylthiol; 1-methyl-1-propanethiol; 2-methyl-1-propanethiol; 2-methyl-2-propanethiol; thiocyclopropanol; and mixtures thereof. In addition, alcohols or thiols with a boiling point ≤ 135°C can be used jointly in ink jet inks with the aforementioned materials (those with a boiling point less than or equal to 115°C) as mixed additives and they include 1-butanol; 3-methyl-1-butanol; 2,3-dimethyl, 1-butanol; 3,3-dimethyl, 1-butanol; 2-methyl-1-butanol (d and 1); 2,3,3-trimethyl-1-butanol; 2-pentanol, 3-pentanol; 2-pentanol; 2,4-dimethyl, 2-pentanol; 2-methyl, 2-pentanol; 3-methyl, 2-pentanol; 4-methyl, 3-pentanol; 2-methyl, 3-pentanol; 3-methyl, 1-propanol; 2-chloro, 1-propanol; 1-chloro, 1-propanol; 1-chloro, 2-methyl; 2,2-dimethyl-1-propanol (tert-butylcarbinol, neopentyl alcohol); 3-fluoro-1-propanol; 1-methoxy-2-propanol; 1-ethoxy-2-propanol; 1-butanethiol, 2-methyl; 1-butanethiol, 3-methyl; and mixtures thereof. These alcohols and thiols have a boiling point in the range of 115-135°C at atmospheric pressure. In embodiments of the present invention, the low boiling point thiol is present in an effective amount to provide the desired effect of increased penetration into the print substrate, without significantly sacrificing print quality, printing characteristics, or stability of the ink composition. Thus, for example, the low boiling point thiol can be present in any desired amount of from 0.01 percent to 8 percent by weight of the ink composition. Preferably, the low boiling point thiol is present in an amount of from 0.1 percent to 6 percent, more preferably from 0.2 percent to 5 percent, by weight of the ink composition. However, amounts outside of these ranges can also be used, as desired. Any ratio of the thiol with a B.P ≤ 115°C to the alcohol or thiol with a B.P. ≤ 135°C can be used in this invention as along as the object(s) of the present invention can be achieved. The higher boiling point alcohols and thiols have lower vapor pressure and are less prone to catch fire. However, they evaporate at a relatively slower rate. An optimum ratio should be used to accommodate all the needs and requirements. In addition to the above additives, the ink composition of the present invention can also include one or more of the following: a humectant, a surfactant, a pigment dispersing agent, a pH buffer, a biocide, an anti-curl agent, an anti-bleed agent, a drying accelerating agent, a polymeric binder, an anti-clogging agent, and a latency enhancer. Various humectants can be used in the ink composition of the present invention. Suitable humectants and co-solvents include glycol derivatives, including ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, poly(ethylene-co-propylene) glycol, as well as their reaction products with alkylene oxides, including ethylene oxides, including ethylene oxide and propylene oxide; triol derivatives containing from 3 to 40 carbon atoms, including glycerine, trimethylpropane, 1,3,5-pentanetriol, 1,2,6-hexanetriol, as well as their reaction products with alkylene oxides, including ethylene oxide, propylene oxide, and mixtures thereof; diols containing from 2 to 40 carbon atoms, such as 1,3-pentanediol, 1,4-butanediol, 1,5-pentanediol, 1,4-pentanediol, 1,6-hexanediol, 1,5-hexanediol, 2,6-hexanediol, neopentylglycol (2,2-dimethyl-1,3-propanediol, neopentylglycol, (2,2-dimethyl-1,3-propaediol), as well as their reaction products with alkylene oxides, including ethylene oxide and propylene oxide in any desirable molar ratio to form materials with a wide range of molecular weights; sulfoxide derivatives containing from 2 to 40 carbon atoms, including dialkylsulfides (symmetric and asymmetric sulfoxides) such as dimethylsulfoxide, methylethylsulfoxide, alkylphenyl sulfoxides; sulfone derivatives (symmetric and asymmetric sulfones) containing from 2 to 40 carbon atoms, such as dimethylsulfone, methylethylsulfone, sulfolane (tetramethylenesulfone, a cyclic sulfone), dialkyl sulfones, alkyl phenyl sulfones, dimethylsulfone, methylethylsulfone, diethylsulfone, ethylpropylsulfone, methylphenylsulfone, methylsulfolane, dimethylsulfolane; amides with from 2 to 40 carbon atoms, such as N-alkylamides, N,N-dialkyl amides, N,N-alkyl phenyl amides, 2-pyrrolidone (a cyclic amide), n-methylpyrrolidone (a cyclic amide), N-cyclohexylpyrrolidone, N,N-dimethyl-p-toluamide (aromatic), N,N-dimethyl-o-toluamide, N,N-diethyl-m-toluamide; ethers, such as alkyl ether derivatives of various alcohols, ether derivatives of triols and diols, including butylcarbitol, hexylcarbitol, triolethers, alkyl ethers of polyethyleneglycols, alkyl ethers of polypropyleneglycols, alkyl ethers of phenylpolyethyleneglycols; urea and urea derivatives; inner salts such as betaine; thio (sulfur) derivatives of the aforementioned materials (humectants), including thioethyleneglycol, thiodiethyleneglycol, trithio- or dithiodiethyleneglycol; hydroxyamide derivatives, including acetylethanolamine, acetylpropanolamine, propylcarboxyethanolamine, propylcarboxy-propanolamine; reaction products of the aforementioned materials (humectants) with alkylene oxides; and mixtures thereof. Further examples of suitable humectants and other additives are disclosed, for example, in U.S. Patent Nos. 5,281,261, 5,531,818, 5,693,129, 4,840,674, 5,365,464, copending application U.S. Ser. No. 08/782,237, and copending application U.S. Ser. No. 08/876,410. Various nonionic stabilizing agents or surfactants can also be used in conjunction with the ink composition of the present invention. Suitable nonionic stabilizing agents or surfactants include ethoxylated monoalkyl or dialkyl phenols, including Igepal® CA and Co series materials (Rhone-Poulenc Co., such as Igepal® CA-630, CO-630); Surfymol® series materials from Air Products and Chemicals Co.; and Triton® series materials (from Union Carbide Company). These anionic surfactants or dispersants can be used alone or in combination with anionic or cationic dispersants. Various anionic, cationic and nonionic pigment dispersing agents can also be used in conjunction with the ink composition of the present invention. Suitable pigment dispersing agents include anionic dispersants such as polymers and copolymers of styrene sulfonate salts (such as Na+, Li+, K+, Cs+, Rb+, substituted and unsubstituted ammonium cations), unsubstituted and substituted (e.g. alkyl, alkoxy, substituted naphthalene derivatives), naphthalene sulfonate salts (such as Na+, Li+, K+, Cs+, Rb+, substituted and unsubstituted ammonium cations) and an aldehyde derivative (such as unsubstituted alkyl aldehyde derivatives including formaldehyde, acetaldehyde, propylaldehyde), maleic acid salts, and mixtures thereof. They can either be in solid form or water solutions. Examples of such dispersants include commercial products such as Versa® 4, Versa® 7, Versa® 77 (National Starch and Chemical Co.); Lomar® D (Diamond Shamrock Chemicals Co.); Daxad® 19, Daxad® K (W.R. Grace Co.); Tamol® SN (Rohn & Haas). Some preferred dispersants comprise naphthalene sulfonate salts, especially a condensation product of naphthalenesulfonic acid or its salts (such as Na+, Li+, K+, Cs+, Rb+, substituted and unsubstituted cations) and formaldehyde as well as copolymers of various acrylic acids salts, or methacrylic acid salts. Also, nonionic dispersants or surfactants can be used in ink jet inks of the present invention, such as ethoxylated monoalkyl or dialkyl phenols including Igepal® CA and CO series materials (Rhone-Poulenc Co.) Briji® Series materials (ICI Americas, Inc.), and Triton® series materials (Union carbide Company). These nonionic surfactants or dispersants can be used alone or in combination with the aforementioned anionic and cationic dispersants. The ratio of pigment to aforementioned pigment dispersants ranges from 1/0.1 to 1/3, preferably from 1/0.1 to ½, and most preferably from 1/0.15 to 1/1.8, although it can be outside of this range. The ratio of naphthalene substituent to aldehyde (e.g. formaldehyde, acetaldehyde) in the aforementioned anionic dispersant condensation product is generally about 1:1, although this ratio can be different depending on the stoichiometry of the feed stock and reaction condition, and can be readily adjusted to obtain a dispersant having a desired molecular weight and the desired ratio of naphthalene substituent to aldehyde. The remainder of the dispersant can comprise active ingredients such as water, solvent or humectant. The weight average molecular weight of the dispersant is generally less than 20,000, preferably less than 13,000, and more preferably less than 10,000. The pigment dispersion should contain enough dispersant to stabilize the pigment particle dispersion such as viscosity, stability and optical density. Various pH buffers can also be included in the ink composition of the present invention. Suitable pH buffers include acids, bases, phosphate salts, carboxylate salts, sulfite salts, sulfate salts, amine salts, imidazole, and its salts. Such pH controlling agents are generally present in an amount from 0 to 10% by weight of the ink, preferably from 0.001 to 5% by weight of the ink and more preferably from 0.01 to 5% by weight of the ink, although the amount can be outside of these ranges. The ink composition of the present invention can also include various biocides. Suitable biocides include biocides such as Dowicil® 150, 200, and 75, benzoate salts, sorbate salts, Proxcel® (available from ICI). When used, such biocides are generally present in an amount from 0 to 10% by weight of the ink, preferably from 0.001 to 8% by weight of the ink, and more preferably from 0.01 to 4% by weight of the ink, although the amount can be outside of these ranges. The ink jet ink composition of the present invention can also comprise various anti-curl and/or anti-cockle agents. Suitable agents include those disclosed in U.S. Patent Nos. 5,356,464 to Hickman et al. and 5,207,824 to Moffatt et al. The ink composition of the present invention can also comprise various anti-bleed agents and/or drying accelerating agents to reduce intercolor bleed. Suitable agents include penetrants including hydroxyethers, including alkyl cellusolves® and alkyl carbitols® such as hexyl carbitol® and butyl carbitol; polyethylene glycol ether derivatives (such as alkyl ethers including methyl, ethyl, propyl, butyl, pentyl, hexyl, dodecyl, lauryl, stearyl, ether derivatives, phenyl and alkylphenyl ether derivatives of polyethyleneglycols); and polypropyleneglycol ether derivatives (such as alkyl ethers including methyl, ethyl, propyl, butyl, pentyl, hexyl, dodecyl, lauryl, stearyl ether derivatives, phenyl and alkylphenyl, ether derivatives of polypropylene glycols); and mixtures thereof Various polymeric binders can also be used in conjunction with the ink composition of the present invention to adjust the viscosity of the composition. Suitable polymeric binders include water soluble polymers and copolymers such as gum arabic, polyacrylate salts, polymethacrylate salts, polyvinyl alcohols, hydroxypropylenecellulose, hydroxyethylcellulose, polyvinylpyrrolidinone, polyvinylether, starch, polysaccharides, polyethyleneimines with or without being derivatized with ethylene oxide and propylene oxide including the Discole® series (DKS International); and the Jeffamine® series (Texaco). Polymeric additives may be present in the ink jet inks of the present invention in amounts from 0 to 10% by weight of the total ink weight, preferably from 0.001 to 8% by weight of the total weight of the ink, and more preferably from 0.01 to 5% by weight of the total ink weight, although the amount can be outside these ranges. The ink composition of the present invention can also include various anti-clogging agents to prevent clogging. Suitable anti-clogging agents include polyethyleneglycol, polypropyleneglycol, poly(ethylene-co-propylene)glycol, polyhydric materials (materials containing more than one hydroxyl group), condensation products of diols or triols (glycerine, trimethylopropane, triethanolamine) with ethyleneoxide and/or propyleneoxide. Various anti-clogging agents can also serve as latency enhancers to increase the latency of the ink of this invention. Long latency is preferred so that the ink does not clog the nozzle of the printhead and reduce the need for frequent printhead maintenance. The ink compositions of the present invention can be suitably used in various printing processes and apparatus. For example, the ink compositions of the present invention can be used in a variety of ink jet printing processes and apparatus including continuous ink jet printing and drop-on-demand printing including piezoelectric ink jet printing, acoustic ink jet printing, and thermal ink jet printing. The ink compositions can be used by themselves, as in a single-color (monochrome) printing process or apparatus, or in combination with other ink compositions, such as in a multi-color ink jet printing process. The ink composition of present invention comprising at least one of the low boiling point thiols is especially useful for formulation of a pigment ink such as a carbon black ink. The carbon black ink tends to be unstable when relatively more nonpolar or hydrophobic materials or penetrants are used to facilitate the ink drying. The low boiling point thiol additives (B.P.≤ 115°C) have a relatively smaller number of carbon atoms and higher surface tension than similar materials with a high boiling point and a larger number of carbon atoms. Unlike other potent ink penetrants, the additives used in the present invention in general do not cause significant degradation in image quality if they are used properly. In addition, the low boiling point thiols used in the present invention do not seriously destabilize a pigment ink when they are used properly. Due to low boiling point nature of the additives used in the present invention, it is preferred to have their boiling point above 80°C to avoid any possible safety issue such as flammability during transportation. If necessary, the aforementioned thiol additives (B.P.≤ 115°C) may also be used in conjunction with alcohols and thiols with a boiling point of ≤ 135°C (e.g. boiling point ranges from 135°C to 135°C) in ink jet ink compositions and processes of the present invention. The ink jet printing process (e.g. multicolor ink jet printing process) of the present invention can include the printing of ink in any chosen orders (e.g. cyan, yellow, magenta, black; black, cyan, magenta, yellow; black, cyan, yellow, magenta). For example, a color ink (e.g. cyan, magenta, yellow) can be printed first followed by a carbon black ink (or a black ink) comprising a low boiling point thiol additive or vice versa. Moreover the multicolor ink jet printing process of the present invention can be performed either with or without heating of the substrate. The print substrate can be optionally heated at any stage of ink jet printing process of the present invention including before, during, after, and combinations thereof. Suitable heating methods include radiant heating, lamp heating, platen or belt heating. The ink jet printing process of the present invention can also include pixel management, underprinting, overprinting and partial toning (e.g. 1/16, 1/8, ¼, ½), as are known in the art. The multicolor ink jet printing process of the present invention can include either pigment- or dye-based inks with at least one ink comprising a low boiling point thiol additive with B.P.≤ 115°C. In addition, the ink additive used in the present invention can be mixed with water, ink vehicles, or other ink additives (e.g. humectants, surfactants, pigment dispersants, jetting aids, biocides, anti-curl agents, anti-bleed agents, pH buffering agents, polymeric additives) including alcohols and thiols with B.P.≤ 135°C. The multicolor ink jet printing process of the present can be conducted using many different printers employing various printing methods including thermal ink jet printing, acoustic ink jet printing, continuous stream ink jet printing, and piezoelectric ink jet printing. In addition, the present invention can also comprise jetting at least one ink through a printhead capable of printing at least 360 spots per inch, preferably at least 400 spots per inch, more preferably at least 420 spots per inch, and most preferably at least 600 spots per inch or more. In an exemplary embodiment, the printing process of the present invention includes several steps. First, a black ink, such as a carbon black ink (containing either chemically modified carbon black particles or carbon black particles stabilized with a pigment dispersant), comprising a low boiling point thiol can be printed onto a print substrate. Once the black ink has been printed, color inks can then be printed. By printing in this order, the black ink comprising the thiol penetrant can quickly penetrate the surface of the print substrate. Rapid print substrate penetration reduces the amount of residual black ink remaining on the surface of the substrate that can mix with later printed color inks, and thereby minimizes intercolor bleed. A long delay between printing of the black ink and a subsequent color ink (especially a yellow ink) can be used to further minimize intercolor bleed. In an alternative embodiment of the multicolor ink jet printing process of the present invention, a color ink can be printed before printing the black ink (e.g. carbon black ink) comprising the low boiling point thiol additive. In this case, because color inks are generally fast drying, the color ink rapidly penetrates the print substrate surface and dries. The carbon black ink can then be selectively printed (e.g. adjacent to, on top of, or below a color ink) on the print substrate surface afterward. Selective printing of the black ink can be done, for example, using a partial toning technique if necessary. In such cases, black ink images can be completed using multiple printing processes (e.g. partial printing in multiple swaths) to further reduce the incidence of intercolor bleed. In this case, because the black ink composition of the present invention comprises a low boiling point penetrant additive, the black ink composition dries more rapidly than conventional carbon black inks with high surface tension (e.g. those without the thiol additive), thereby minimizing feathering and undesirable intermixing that may otherwise occur between the carbon black ink and the previously printed color ink. Regardless of the specific order of printing, the ink jet ink composition and process of the present invention substantially reduce the likelihood of intercolor bleed while maintaining high quality image formation.

Claims: An ink jet ink composition comprising water, a colorant, and a low boiling point penetrant additive having a boiling point less than or equal to 115°C, wherein said low boiling point penetrant additive is a thiol. The ink jet ink composition of claim 1, wherein the colorant is selected from the group consisting of carbon black either with or without chemical modification, a pigment other than carbon black, a dye and a mixture of dye and pigment. The ink jet ink composition of claim 1 or 2, wherein the low boiling point penetrant additive is selected from the group consisting of 1-butanethiol, t-butylthiol, 1-methyl-1-propanethiol, 2-methyl-1-propanethiol, 2-methyl-2-propanethiol, thiocyclopropanol, and mixtures thereof. The ink jet ink composition of any of claims 1 to 3, wherein said low boiling point penetrant additive is present in an amount ranging from 0.1% to 8% by weight of the total weight of the ink composition. The ink jet ink composition of any of claims 1 to 4, further comprising a second low boiling penetrant additive having a boiling point of less than or equal to 135°C. The ink jet ink composition of claim 5, wherein said second low boiling penetrant additive is selected from the group consisting of 3-methyl-1-butanol; 2,3-dimethyl, 1-butanol; 3,3-dimethyl, 1-butanol; 1-butanol; 2-methyl-1-butanol (d and 1); 2,3,3-trimethyl-1-butanol; 2-pentanol, 3-pentanol; 2-pentanol; 2,4-dimethyl, 2-pentanol; 2-methyl, 2-pentanol; 3-methyl, 2-pentanol; 4-methyl, 3-pentanol; 2-methyl, 3-pentanol; 3-methyl, 1-propanol; 2-chloro, 1-propanol; 1-chloro, 1-propanol; 1-chloro, 2-methyl; 2,2-dimethyl-1-propanol (neopentyl alcohol); 3-fluoro-1-propanol; 1-methoxy-2-propanol; 1-ethoxy-2-propanol; 1-butanethiol, 2-methyl; 1-butanethiol, 3-methyl; and mixtures thereof. An ink jet printing process comprising printing a first ink and at least a second ink with an ink jet ink composition according to any of claims 1 to 6 and a different colorant from the first ink onto a print substrate according to digital data signals in any desired printing order. A multicolor ink jet printing process comprising: 1) incorporating into an ink jet printer a first ink; 2) incorporating into the ink jet printer at least one second ink comprising a thiol additive having a boiling point less than or equal to 115°C; 3) causing droplets of said first ink to be ejected in an imagewise pattern onto a surface of a print substrate; and 4) causing droplets of said at least one second ink to be ejected in an imagewise pattern onto the surface of the print substrate so that a multicolor ink image is formed on the print substrate that exhibits at least one of sharp line edges and minimal intercolor bleed. The multicolor ink jet printing process according to claim 8, wherein said first ink is selected from the group consisting of a yellow ink, a cyan ink and a magenta ink.

Inventors: LIN JOHN WEI-PING, LIN, JOHN WEI-PING
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 2001
Main classification: C09D11
IPC codes: C09D11