MXPA99000762A - Ink composition - Google Patents

Abstract

Novel, improved ink compositions are aqueous-based, shock-resistant, shear-thinning inks for writing instruments having a shear index greater than 0.6. The inks are a substantially uniform dispersion including colorant(s), a water dispersible, polymeric shear-thinning material selected from the group consisting of welan gumrhamsan gum and combinations thereof, and a substantially water-soluble polymeric viscosity modifier in a polar solvent system. While the ink compositions have a high viscosity at low shear rates, they undergo shear-thinning and are readily flowable in response to shear rates produced in writing to provide a writing ink having an especially desirable combination of performance characteristics.

Description

INK COMPOSITION BACKGROUND 1. Technical Field This description relates to novel, improved ink compositions and writing instruments that include such ink compositions. More precisely, aqueous ink compositions comprising polymeric materials that provide water-dispersible shear or shear thinning and writing instruments that include the ink compositions are described herein. 2. Description of the Related Art Ink compositions that include polymeric materials, which provide thinning with shear, dispersible in water, are thickened liquids at rest. In the case of non-Newtonian liquids, these belts exhibit a thinning-shear flow behavior or slimming-shear flow characteristics in use. In other words, they become thin, easily flowable liquids, at the shear rates that occur when writing such as with a ballpoint pen. The ink compositions include a material that provides thinning with water-dispersible polymeric shearing, dispersed in a polar solvent system. Other materials, such as coloring materials, surfactants, preservatives, corrosion inhibitors, humectants and the like, may also be included in the inks. These inks have been described, for example, in U.S. Pat. Nos. 4,671,691 and 5,048,992, the descriptions of which are incorporated herein by reference. A common material used to provide shear thinning characteristics to inks is xanthan gum. However, xanthan gum is not stable at high temperatures such as those that may be encountered during processing, storage or transportation of the inks or pens containing the inks. It would be convenient to provide aqueous ink compositions which exhibit shear thinning flow characteristics and which are stable at relatively high temperatures at which the ink may be exposed; for example during processing, storage, transport or by the user. COMPENDIUM The novel, improved ink compositions described herein are water-based, impact-resistant, shear thinning inks for writing instruments. The ink compositions exhibit non-Newtonian flow characteristics and have a shear rate greater than 0.6. The inks comprise a substantially uniform dispersion of dye (s), a water-dispersible polymeric shear thinning material selected from the group consisting of welan gum, rhamsan gum and combinations thereof and a polymeric viscosity modifier substantially soluble in water in a polar solvent system. While the ink compositions have high viscosity at low shear rates, they are subjected to shear thinning and are easily flowable in response to shear rates produced upon writing, in order to provide a writing ink having an especially convenient combination of performance characteristics. In the writing instruments of the invention, the ink compositions are contained in hollow tubes or reservoirs, which are not subjected to pressure and the ink is fed directly to the pen of a pen. The ink can be used in combination with a follower composition to help ensure a uniform, continuous flow of ink to the ball as the ink supply is consumed. DETAILED DESCRIPTION OF PREFERRED MODALITIES The present ink compositions include particular gums which are stable at higher temperatures (for example greater than 100 ° C), a water soluble polymeric viscosity modifier, a polar solvent system and a dye. Other conventional ingredients (eg, biocides, anticorrosives, sequestrants, surfactants, etc.) may also be included in the present ink compositions.

The ink compositions have a shear rate of 0.6 or greater. The shear thinning index (n) is calculated by adjusting values of shear stress (t) and shear rate (y) obtained from rheological measurements in a viscometer to the equation of the law of empirical powers t = K ? n (where K and n are calculated constants). Additionally, the shear thinning index is obtained by measurements of an aqueous solution of the shear thinning material at shear rates between about 0 to about 500 sec "1. The present ink compositions preferably have the following rheological profile: Speed Shear Rate. (1) Viscosity (cps) 0.01 Less than about 10,000 0.1 Less than about 6,000 1.0 Less than about 2,000 30 Less than about 200 2,000 Less than about 50 Other useful ink compositions have the following rheological profile: Shear Rate (be. "1) Viscosity (cps) 0.01 Less than about 5,000 0.1 Less than about 3,000 Shear Speed (be.'1) Viscosity (cps) 1.0 Less than about 2,000 30 Less than about 200 2,000 Less than about 100 All Viscosities reported here were measured using a Haake RS 100 apparatus with mod or controlled effort using uniform effort programs. The aqueous ink compositions described herein contain welan gum or rhamsan gum or a combination thereof to provide shear thinning to ink flow characteristics. Welan gum is the generic name of the polysaccharide S-130, a microbial polysaccharide. Welan gum is commercially available for example under the designations Welan K1A96 and Welan Ex 7389 from Kelco Co., San Diego, California. Rhamsan gum is a heteropolysaccharide resin composed of glucuronic acid, glucose and rhamnose and is a fermented microorganism alkalis. Rhamsan gum is commercially available for example under the designation K1A112 from Kelco Co., San Diego, California. The welan and rhamsan gums will maintain the viscosity of the ink compositions at temperatures above 100 ° C. This temperature stability is unattainable in conventional shear thinning inks made using xanthan gum. The amount of welan and / or rhamsan gums in the ink compositions will vary depending on a number of factors including the colorant employed and the nature of the polymeric viscosity modifier employed. Normally however, the welan and / or rhamsan gums will be present in an amount from about 0.1 to about 1.0 weight percent of the entire composition, preferably about 0.1 to 0.3 weight percent. The present ink compositions also include a viscosity modifier. The viscosity modifier is a polymeric material substantially soluble in water that increases the high shear viscosity of the ink. Suitable viscosity modifiers include alginates (for example Kelgin MV from Kelco Co.), polymers and copolymers of alkylene oxide (for example Poliox N-10 from Union Carbide) and polyvinylpyrrolidone (for example PVP K-90 from GAF Corp.). Combinations of the above can also be used. The viscosity modifier is present in the ink composition in an amount of about 0.1 to about 10 weight percent based on the weight of the entire composition. Preferably, from about 0.1 to about 1.0 weight percent of the viscosity modifier is employed.

The present ink compositions are based on the use of a solvent system containing aqueous non-polar liquids and water. Water can be used at levels below 50% of the solvent system. Suitable non-aqueous liquids include: (1) mono-, di-, tri- and higher alcohols, (2) glycol ethers, (3) glycol ether acetates and (4) glycol acetates. For a dye-based ink, the solvent system constitutes from about 40 to about 90 weight percent of the ink, preferably about 50 to about 75 weight percent of the ink. Non-limiting examples of alcohols suitable for use in the solvent system are hexylene glycol, octylene glycol, 1,4-butanediol, thiodiglycol, 2,3-butylene glycol, triethylene glycol, diethylene glycol, ethylene glycol, propylene glycol, glycerin, trimethylolethane, trimethylolpropane, diglycerin, isopropyl alcohol and sorbitol. Non-limiting examples of the glycol ethers suitable for use in the solvent system are ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoisopropyl ether, propylene glycol monomethyl ether, diethylene glycol monomethyl ether, propylene glycol phenyl ether, ethylene glycol diethyl ether and propylene glycol phenyl ether. Non-limiting examples of glycol ether acetates suitable for use in the solvent system are propylene glycol monoethyl ether acetate; ethylene glycol monoethyl ether; monophenylether ethylene glycol acetate, diethylene glycol monoethyl ether, ethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monophenyl ether, diethylene glycol monoisopropyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether and monomethyl ether propylene glycol acetate. Non-limiting examples of glycol acetates suitable for use in the solvent system are ethylene glycol monoacetate, ethylene glycol diacetate and diethylene glycol diacetate. The dyes to be used in the present ink compositions can be any of the water soluble or dispersible dyes or pigments or their known mixtures useful in writing inks. From about 2 to 10% and preferably from about 1 to 6% of a dye and / or from about 12 to 35%, preferably about 18 to 22% of a pigment dispersion, is added to the ink formulation to obtain the desired color. Suitable colorants are available under the designation Bayer Special Black HF from Bayer, Pittsburgh, PA. , Violet 204-2 from Miliken Chemicals and Blue 204-3 from Miliken Chemicals. Sequestrants can be added for the stabilizing components of the ink, for example the rubber component.

A sequestrant binds multivalent cations in the solution, improving solubility and stability of the gum. Suitable agents for this purpose are sodium salts of EDTA, such as tetrasodium EDTA or Versene 220 from Dow Chemical, trisodium phosphate, sodium hexametaphosphate or sodium glucoheptanate. These sequestrants are usually added in the amount of 1 to 5 parts by weight of the gum. Many ink components are subject to degradation by microorganisms such as bacteria, yeast and fungi. This degradation is prevented by the addition of a biocide. Suitable biocides are known to those skilled in the art and include Methyl Parasept and Ethyl Parasept available from Bayer and Kathon PFM available from Rohm & Haas. Combinations of these materials can also be used. In general from 0.10 to 0.20%, preferably approximately 0.10% to approximately 0.5% of bactericide (which may contain some water) is added to the ink formulation to control the growth of microorganisms. These inks contain water and non-aqueous polar liquids such as glycol, they can be corrosive to metals used in plugs and pen pens. This corrosivity can be controlled or eliminated by the addition of a corrosion inhibitor, for example benzotriazole, tolitriazole, dicyclohexyl ammonium nitrate and organic phosphate esters, Cobratec 99 available from PMC Specialties. In general, from about 0.10 to 1.0%, preferably from 0.13 to 0.20% by weight of a corrosion inhibitor, is added to the ink formulation to avoid corrosion of the tip by the ink. To ensure that the ink is capable of wetting the metal used at the tip of the pen to provide an acceptable ink supply speed to the writing surface, wetting or lubricating agents may be added to the inks described herein. Suitable humectant agents include but are not limited to surfactants such as sodium lauryl sulfate and fluorinated alkyl esters. Suitable surfactants are available for example under the designation Ethomeen C-15 from Akzo, Dobbs Ferry, NY; Lubriphos LB 400 from Rhone Poulenc, Inc .; and Atlas G-711 of ICI Ame. Inc. A person skilled in the art will appreciate that the selection of the appropriate wetting agent should be based on current writing tests on the type of pen having the type of writing tip where the ink is to be used. In general, however, in an ink based on pigment or dye, the amount of wetting agent is about 0.10 to 1.0% and preferably 0.14 to 0.16% by weight. The present inks may also contain a water-soluble additive to improve the water's firmness of the ink. For example, an acrylic resin that is soluble in alkali when dried, will bind the dye in the written text and therefore will provide a firm text to the water. The acrylic resin binder can also improve the rewettability of the residue at the tip of the pen and therefore greatly prolong the time of uncovering and ease of starting the ink in the pen. A suitable amine-modified acrylic copolymer is available under the designation G-Cryl 5006 from Henkel Corp. The pH of the finished ink is preferably greater than 5.0 and in general ammonia or an amine such as triethanolamine, morpholine, diethanolamine, ethylamine or monoethylamine, is added to the formulation to obtain the desired pH value. In general, an ink based on dye or pigment, the amount of pH control agent added is from about 0.05 to 0.50%, preferably from about 0.09 to 0.11% by weight. The ink compositions of this disclosure are readily prepared by combining the desired ingredients in a blender or mixing with a propeller agitator, until homogeneity is achieved. Preferably, the material that is thinned by polymeric shear is first added to the distilled water and this combination is mixed for about two hours. The other ingredients, if present, they are added in the following order: other polar solvents, sequestering agents, preservatives, surfactants, corrosion inhibitors and dyes and / or pigments. In some cases, it is advisable to pre-moisten the shear thinning material with a material such as ethylene glycol, propylene glycol or glycerol. Table 1 below shows the percentage ranges of the ink components based on the total weight of the ink. TABLE 1 EXAMPLES The following examples are presented to illustrate specific embodiments of the present compositions. These examples are not to be construed as limitations on the scope of the invention. EXAMPLE 1 It is prepared as a specific ink composition with the formulation given below. Ranges for each ingredient are also listed. EXAMPLE 1 EXAMPLES 2-5 The following Table II provides ink formulations according to this description: TABLE II EXAMPLES 6-10 The ink formulations in Table III are prepared in accordance with the present disclosure. TABLE III @ TABLE 4 TABLE 4 (CONTINUED) It will be understood that various modifications can be practiced to the modalities described herein. Therefore, the above description should not be considered as limiting, but simply as exemplifications of preferred embodiments. Those with skill in the specialty will envision other modifications within the scope and spirit of the appended claims.

Claims (20)

1. An ink composition characterized in that it comprises: a) at least one thinning polysaccharide with cillaza selected from the group consisting of welan gum, rhamsan gum and mixtures thereof; b) at least one water-soluble polymeric viscosity modifier, slimming essentially without shear; c) dye, - and d) a solvent system containing one or more polar non-aqueous liquids and the ink has a shear rate greater than about 0.6.

2. The ink composition according to claim 1, characterized in that it has the following rheological profile: Shear rate (sec, "1) Viscosity (cps) 0.01 Less than about 10,000 0.1 Less than about 6,000 1.0 Less than about 2,000 30 Less than about 200 2,000 Less than about 50.

The ink composition according to claim 1, characterized in that the viscosity modifier is selected from the group consisting of alginates, polymers and copolymers of polyalkylene oxide, polyvinyl pyrrolidone and its mixtures

4. The ink composition according to claim 1, characterized in that the dye is a polymeric dye.

The ink composition according to claim 1, characterized in that the shear thinning polysaccharide is present in the composition in an amount in the range of about 0.05 to about 0.3 weight percent.

The ink composition according to claim 1, characterized in that the viscosity modifier is present in the composition in an amount that is in the range of about 0.05 to about 0.5 weight percent.

The ink composition according to claim 1, characterized in that it also comprises a polymeric water-soluble binder that becomes insoluble in water when the composition is dry.

8. The ink composition according to claim 7, characterized in that the polymeric binder is an amine-modified acrylic copolymer.

The ink composition according to claim 7, characterized in that the polymeric binder is present in the composition in an amount of up to about 8 weight percent.

10. The ink composition according to claim 1, characterized in that it also comprises at least one component selected from the group consisting of a buffer, surfactant, biocide, anticorrosive agent, sequestering agent and mixtures thereof.

The ink composition according to claim 10, characterized in that the solvent system includes one or more solvents selected from the group consisting of ethylene glycol, glycerin, benzyl alcohol and mixtures thereof.

12. The ink composition according to claim 1, characterized in that it has a shear thinning index of from about 0.6 to about 0.8.

The ink composition according to claim 1, characterized in that it has the following rheological profile: Shear rate (se .'1) Viscosity (cps) 0.01 Less than about 5,000 0.1 Less than about 3,000 1.0 Less than about 2,000 30 Less than about 200 2,000 Less than about 100

14. The ink composition according to claim 1, characterized in that the shear thinning polysaccharide is welan gum and the viscosity modifier is sodium alginate.

15. The ink composition according to claim 1, characterized in that the shear thinning polysaccharide is rhamsan gum.

16. An ink composition, characterized in that it comprises: a solvent system containing water and at least one polar co-solvent; Welan gum; alginate; and a dye.

17. An ink composition, characterized in that it comprises: a solvent system containing water and at least one polar co-solvent; rhamsan gum; alginate; and a dye.

18. A pen containing an ink composition according to claim 1.

19. A pen containing an ink composition according to claim 16.

20. A pen containing an ink composition according to claim 17. .