JPH08325491A - Ink composition - Google Patents

Abstract

PURPOSE: To obtain an ink compsn. which can be long stored and does not cause the clogging of an ink jet head nor the uneven density of written lines by incorporating a specific substance into an ink compsn. prepd. by dispersing a coloring powder in a solvent. CONSTITUTION: Into an ink compsn. comprising a solvent (e.g. water or an org. solvent) and a coloring powder (e.g. carbon black) dispersed therein is incorporated a thixotropic agent which keeps the viscosity of the compsn. high enough to prevent the precipitation of the powder during the storage of the compsn. and allows the viscosity to be decreased by stirring or shaking. The thixotropic agent comprises at least one substance selected from among smectite, fluorotetrasilicomica, bentonite, silica, montmorillonite, and polysodium acrylate.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to an ink composition used in an ink discharge type image forming apparatus.

2. Description of the Related Art Conventionally, as an ink composition used in an ink discharge type image forming apparatus, an aqueous ink composition in which dyes and pigments are dispersed in an aqueous medium such as water or a water-soluble organic solvent, an organic solvent or a wax. Oily ink compositions in which dyes and pigments are dispersed in oily media such as Further, as an ink composition capable of drawing a line or a character on an object to be drawn such as cloth, leather or paper by an air jet type marking device and erasing by washing with water, JP-A-4-23906 is known.
No. 9 discloses an ink composition in which a water-soluble white powder is finely dispersed in a hydrophilic organic solvent having a small dissolving power for the powder and a white pigment is added to enhance the whiteness hiding power. ing.

However, in the ink composition as described above, the specific gravity of the pigment is large, and further,
Since the viscosity of the ink composition is low, there is a problem that the pigment in the ink settles and agglomerates during stationary storage and sticks to the bottom of the container. It is very difficult to re-disperse the pigment once fixed and it cannot be stored for a long time. Further, if such an ink composition remains in the inkjet head for a long period of time, there is a problem that the inkjet head is clogged or the density of drawn characters or drawing lines becomes uneven. The present invention has been made in order to solve the above-mentioned problems, and can prevent the powder such as pigment from settling, so that the pigment can be stored well for a long period of time, and the ink jet head can be clogged or drawn. It is an object of the present invention to provide an ink composition that does not cause unevenness in the density of characters and lines.

In order to achieve this object, the ink composition of the present invention is an ink composition in which a coloring powder is dispersed in a solvent, and the powder is stored when it is stored in a stationary state. It contains a thixotropic agent that imparts a viscosity to the extent that sedimentation can be prevented and reduces the viscosity by stirring or shaking. Further, it is desirable that the thixotropic agent is one of smectite, tetrafluorosilicon mica, bentonite, silica, montmorillonite and sodium polyacrylate, or a mixture of two or more thereof. In addition, it is desirable that water, which is the solvent, contains smectite, which is the thixotropic agent, at a dispersion concentration of 0.1 to 5% by weight. Furthermore, it is desirable that the organic solvent, which is the solvent, contains smectite, which is the thixotropic agent, at a dispersion concentration of 0.3 to 15% by weight.

The ink composition of the present invention having the above constitution is
Since it contains a material that imparts a viscosity to the extent that it can prevent the powder from settling during static storage and reduces the viscosity by stirring or shaking, the viscosity increases during static storage, and The pigment dispersed therein can be prevented from settling, whereby the ink composition can be stored in good condition for a long period of time. Further, the viscosity is lowered by stirring or shaking before use, and characters and lines can be drawn by the ink discharge type image forming apparatus. Further, by using a thixotropic agent as the material, it is possible to surely realize the above-mentioned action.
Further, as the thixotropic agent, smectite,
Since one type of tetrafluorosilicon mica, bentonite, silica, montmorillonite and sodium polyacrylate, or a mixture of a plurality of types can be used,
A suitable thixotropic agent can be selected depending on the solvent used. Further, 0.3 to 5% by weight of smectite which is the thixotropic agent is added to water which is the solvent.
The above-mentioned effect can be reliably realized by containing the above-mentioned dispersed concentration of. Furthermore, 1 to 1 of smectite which is the thixotropic agent is added to the organic solvent which is the solvent.
By containing a dispersion concentration of 15% by weight, the above-mentioned action can be reliably realized.

EXAMPLES Examples in which the ink composition of the present invention is embodied will be described below with reference to the drawings. The ink composition of this example is constituted by dispersing a thixotropic agent in a solvent and further dispersing a powder. The thixotropic agent is a material having a thixotropic property, and this thixotropic property is expressed by dispersing fine particles called colloidal particles having a particle size of 1 μm to 1 nm in a liquid, and the viscosity increases when left standing, When the viscosity-increased product is stirred or shaken, the viscosity is decreased. Further, when the shape of the colloidal particles has anisotropy, the property becomes more prominent. Specific thixotropic agents include smectite, tetrafluorosilicon mica, bentonite, silicon dioxide, montmorillonite, sodium polyacrylate, and the like. Further, as a dispersion concentration of the thixotropic agent in the ink composition, a viscosity sufficient to prevent settling of the powder can be obtained during stationary storage, and by stirring or shaking, an ink discharge type image forming apparatus It is necessary to set the concentration so that the viscosity can be reduced to the extent that characters and lines can be drawn. Further, there is a difference in viscosity change depending on the type of thixotropic agent and the type of solvent. For example, with smectite, when water is used as the solvent,
A dispersion concentration of 0.1 to 5% by weight is suitable, and 0.3 to 5% by weight is preferable in order to obtain a sufficient viscosity. When an organic solvent is used as a solvent, a dispersion concentration of 0.3 to 15% by weight is suitable, and in order to obtain a sufficient viscosity, it is preferably 1 to
15% by weight is suitable. Further, in the case of tetrafluorosilicon mica, when water is used as a solvent, a dispersion concentration of 1 to 15% by weight is suitable. Further, in the case where the powder is settled quickly, it is necessary to increase the viscosity until it becomes a jelly-like substance when it is stored by standing by adjusting the types and concentrations of the thixotropic agent and solvent. Further, as the composition of the ink composition of this example, the composition of the conventionally used ink can be applied as it is, and a thixotropic agent dispersible in the solvent can be selected and added according to the solvent of the ink composition. Good. For example, if the solvent is water, use hydrophilic smectite, synthetic mica (fluorine tetrasilicon mica), etc. If the solvent is an organic solvent,
Lipophilic smectite, sodium polyacrylate, bentonite, etc. are used. As the organic solvent, methyl alcohol, ethyl alcohol, isopropyl alcohol,
n-propyl alcohol, n-butyl alcohol, se
Alkyl alcohols such as c-butyl alcohol and t-butyl alcohol, amides such as dimethylformamide and dimethylacetamide, ketones or ketone alcohols such as acetone and diacetone alcohol, ethers such as tetrahydrofuran and dioxane, Polyalkylene glycols such as polyethylene glycol and polypropylene glycol, ethylene glycol, propylene glycol, butylene glycol,
Examples include alkylene glycols such as triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol, and diethylene glycol. Also, cellosolves such as methyl cellosolve and ethyl cellosolve, polyhydric alcohols such as glycerin, ethylene glycol and diethylene glycol, lower alkyl ethers of polyhydric alcohols such as diethylene glycol dimethyl (or ethyl) ether, carbitol and triethylene glycol monomethyl ether. And carbitol acetate. The powder dispersed in the solvent may be appropriately selected as necessary from the viewpoints of erasability by washing with water, not disappearing or melting with a steam iron or the like, and hiding power for an object to be drawn. That is, saccharides such as sucrose and glucose, and alkali metal salts of organic acids and inorganic acids are suitable for maximizing erasability. The organic acids and weak inorganic acids / basic salts can be used. Since these dissolve in water, they can be easily erased by washing with water. Also, if you want higher whiteness hiding power, titanium oxide, calcium carbonate,
Zinc oxide, zinc sulfide, lead white, antimony white, zirconium oxide, molybdenum white, lithopone, barium sulfide, white carbon, silica, alumina white, aluminum hydroxide, kaolin clay, talc, bentonite, nepheline sinite, mica and air bubbles By adding a white pigment such as a pigment in an amount of 5% by weight or less, it can be achieved without impairing the erasability. Further, as a powder that simultaneously satisfies the above three conditions, the volume average particle diameter is 1 nm to 10 nm.
Colored particles of 00 μm can be mentioned. In this case, fine particles have a slightly inferior erasability, and coarse particles may clog the inkjet head of the air jet type marking device. Therefore, it is preferable to use colored particles of 1 μm to 500 μm, more preferably 5 μm to 200 μm. Is desirable. For example, colored resin particles obtained by a polymerization method or a pulverization method correspond to this. These show erasability by being washed away when washed with water. Further, as the solvent used for this, various cellosolves, carbitol,
It is necessary to adjust from an organic solvent such as carbitol acetate, ketone alcohol, monohydric alcohol and polyhydric alcohol or water in consideration of a drawing method, a drawing drying speed and the like, alone or in combination. The results of experiments conducted using the ink composition of this example are described below.
However, the amounts (parts) of each component are all parts by weight. (Experiment 1) In Experiment 1, an experiment was conducted on the ink composition used in the ink jet printer, to which this example was applied. Its composition is shown below. Carbon black (Mitsubishi Chemical Co. # 960) 5 parts by weight Dispersant Disperbyk (BYK-Chemie) 5 parts by weight Polyvinyl alcohol (Denki Kagaku B03) 1 part by weight Glycerin 10 parts by weight Smectite (corp chemical hydrophilic) Smectite SWN) 1 part by weight Pure water 79 parts by weight First, a predetermined amount of smectite is dispersed in pure water, glycerin, a dispersant Disperbyk and polyvinyl alcohol are dissolved, and then carbon black is added, and a bead mill is used. And dispersed. The residence time in the bead mill in the vessel was 2230 seconds. When this dispersion was left to stand for 6 hours, an increase in viscosity was visually confirmed, and it was left for another 3 weeks, but there was no change as it was.
No settling of pigment carbon black was observed. When this dispersion was used as an ink for a commercially available inkjet printer, the viscosity was lowered to about 3 cps which can be used in the inkjet recording system when the printer was operating, and characters and lines could be drawn without any problems.
As a comparative example, when the dispersion obtained by removing smectite from the above composition was allowed to stand for 3 weeks in the same manner as the dispersion of this example, precipitation of carbon black was observed in about 1/4 of the total volume of the dispersion, Furthermore, the carbon black layer was stuck to the bottom of the container, and could not be completely redispersed even with vigorous shaking. (Experiment 2) In Experiment 2, an experiment was carried out on an ink composition used in an air jet type marking device to which the present embodiment was applied. Its composition is shown below. L-glutamic acid 230 parts by weight Titanium oxide (anatase type) 13 parts by weight Polyethylene glycol 280 parts by weight Ethylene glycol 300 parts by weight Smectite (lipophilic smectite SPN manufactured by Corp Chemical) 35 parts by weight First, a predetermined amount of smectite is dispersed in ethylene glycol. Then, a predetermined amount of polyethylene glycol, L-glutamic acid and titanium oxide were sequentially added to the dispersion, and the mixture was sufficiently stirred to form a uniform dispersion. When this dispersion was left to stand for 6 hours, the viscosity increased to a jelly. As a comparative example, a dispersion liquid obtained by removing smectite from the above composition was allowed to stand for 3 weeks in the same manner as the dispersion liquid of this example. FIG. 1 (a) shows the dispersion according to the present example left for 3 weeks, and FIG. 1 (b) shows the dispersion according to the comparative example left for 3 weeks. As shown in FIG. 1 (a), the dispersion according to this example did not show any change in the dispersion state.
When it is shaken, it returns to a liquid state and when a character or figure is drawn on a dark-colored cloth with an air jet marking device, a white image line is obtained, and after about 10 minutes, the solvent penetrates into the object to be drawn. , And a part of it transpired and became a clear image. When a steam iron was applied one hour after drawing, the image lines did not disappear at all, and when washed with water, the image lines disappeared completely. In addition, as shown in FIG. 1 (b), in the dispersion liquid of the comparative example, the titanium oxide sedimented in about 1/4 of the total volume of the dispersion liquid, and further, the titanium oxide layer adhered to the bottom of the container. However, even if it was shaken violently, it could not be completely redispersed. (Experiment 3) In Experiment 3 as well, an experiment was carried out on the ink composition used in the air jet type marking device to which the present embodiment was applied. Its composition is shown below. White polymerized resin particles (MBX-20 White manufactured by Sekisui Kasei Co., Ltd.) 150 parts by weight Polyethylene glycol 85 parts by weight Smectite (hydrophilic smectite SWN manufactured by Corp Chemical) 15 parts by weight Pure water 755 parts by weight First, a predetermined amount of smectite is added to pure water Was dispersed, and then a predetermined amount of polyethylene glycol was added and dissolved, and further white polymerized resin particles were added and sufficiently stirred to obtain a uniform dispersion liquid. When this dispersion was left to stand for 6 hours, the viscosity increased to a jelly, and it was left for another 3 weeks, but no change was observed. When it was shaken, it returned to a liquid state, and when it was drawn on the dark-colored cloth with the ink jet type marking device as in Example 1, a clear white line could be drawn and steam iron was applied 1 hour after drawing. The streak never disappears. The streaks disappeared completely after washing with water. As a comparative example, when a dispersion liquid obtained by removing smectite from the above composition was allowed to stand for 6 days, sedimentation of white polymerized resin particles was observed in about 1/3 of the total volume of the dispersion liquid, and some of them were fixed to the bottom of the container. However, even if it was shaken violently, it could not be completely redispersed. Thus, according to the ink composition of the present example, since it contains a thixotropic agent, it is possible to prevent the pigment or resin particles in the ink composition from settling, and the pigment or resin particles at the bottom of the container. Can be prevented from sticking. As a result, the ink composition can be satisfactorily stored for a long period of time, and clogging of the inkjet head can be prevented. Furthermore, when an ink composition containing a thixotropic agent is used in an ink jet printer or an air jet type marking device, there is no problem with the characters and lines drawn, there is no effect of a steam iron, and there is no possibility of washing with water. There is no loss of erasability.

As is clear from the above description,
Since the ink composition of the present invention contains a material that imparts a viscosity to the extent that the powder can be prevented from settling when stored still, and lowers the viscosity by stirring or shaking, Can increase the viscosity and prevent the pigment dispersed in the ink from settling, whereby the ink composition can be stored in a good state for a long time. In addition, the viscosity is lowered by applying by stirring or shaking before use, and characters and lines can be drawn by the ink discharge type image forming apparatus. Also,
By using a thixotropic agent as the material, it is possible to surely realize the above-mentioned action. Further, as the thixotropic agent, one of smectite, tetrafluorosilicon mica, bentonite, silica, montmorillonite and sodium polyacrylate, or a mixture of two or more thereof can be used, and therefore, depending on the solvent used. , A suitable thixotropic agent can be selected.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a result of Experiment 2.

Claims (4)

[Claims] 1. An ink composition in which a coloring powder is dispersed in a solvent, which is given a viscosity at which the powder can be prevented from settling when the powder is stored in a stationary state, and the viscosity is obtained by stirring or shaking. An ink composition containing a thixotropic agent for reducing the above-mentioned problem. 2. The thixotropic agent is one of a smectite, tetrasilicon tetrafluoride mica, bentonite, silica, montmorillonite, and sodium polyacrylate, or a mixture of a plurality of the thixotropic agents. The ink composition according to item 1. 3. The ink composition according to claim 2, wherein the water, which is the solvent, contains smectite, which is the thixotropic agent, in a dispersed concentration of 0.1 to 5% by weight. 4. The ink composition according to claim 2, wherein the organic solvent, which is the solvent, contains smectite, which is the thixotropic agent, in a dispersed concentration of 0.3 to 15% by weight.