JPH0234991B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of dispersing colored inorganic pigments or extender pigments in the form of ultrafine particles in an oil-based varnish for lithographic printing by a flushing method. When producing oil-based printing inks, there are two methods commonly used to finely disperse pigments in varnish: a kneading method and a flushing method. The pigment manufacturing process consists of (1) a synthetic reaction step in which the pigment is synthesized in an aqueous medium, and (2) the aqueous pigment dispersion obtained in step (1) is dehydrated to a water content of approximately 30 to 80%. It is divided into four steps: a dehydration step to form a wet pigment cake (hereinafter referred to as wet cake), (3) a drying step to completely dry this wet cake, and (4) a crushing step to crush the dry cake. The kneading method is as described in (1) to (4) above.
A method of finely dispersing the pigment in the varnish by mixing the dry powdered pigment produced through the four steps described above with an oil-based varnish and milling this mixture with a milling device such as a roll mill, ball mill, or sand mill. It is. On the other hand, the flushing method involves mixing the wet cake produced through the two steps (1) and (2) above with an oil-based varnish, and stirring this mixture with a stirring device such as a kneader, agitator mill, or high-speed dispersion stirrer. In this method, the pigment contained in the wet cake is finely dispersed in the oil-based varnish phase, and at the same time, the water contained in the wet cake is separated from the oil-based varnish phase and removed. be. Dry powdery pigment particles re-agglomerate under strong force,
It forms aggregates that have grown to a particle size much larger than the maximum particle size of 10μ allowed for printing ink. The kneading method involves crushing these aggregates in an oil-based varnish to obtain sufficiently small particle sizes.
When a particularly hard pigment such as transparent calcium carbonate is used, it takes a long time to crush it to the required particle size and coarse particles remain. On the other hand, the pigment particles in wet cake either remain as primary particles without agglomerating, or even if they do aggregate, the cohesive force is extremely weak. Therefore, the flushing method simply mixes the wet cake into an oil-based varnish and stirs it to transform the pigment particles into particles with a particle size of about 0.03 to 1 μm, which is much smaller than the maximum particle size allowed for printing inks. This has the advantage that the kneading step can be omitted. For these reasons, in the printing ink manufacturing industry,
Flushing methods are often adopted for purposes such as improving the quality of printing ink, streamlining the manufacturing process, saving energy, and reducing manufacturing costs. However, most of the conventional flushing examples involve flushing of organic pigments, and no practical successful example of flushing of inorganic pigments has yet been reported. Inorganic pigments are highly hydrophilic pigments, so even if their wet cake is mixed into oil-based varnish,
The water and pigment in the cake cannot be separated from each other in an oil-based varnish, so the flushing method cannot be used. In order to flush inorganic pigments, the entire surface of the pigment particles must be sufficiently treated with a specific lipophilic substance. The reason why flushing of inorganic pigments has been difficult in the past is that this sufficient surface treatment cannot be achieved. The present invention makes flushing possible by treating the surface of inorganic pigments in a specific manner. That is, the present invention provides a surface active material having a polyester molecular chain derived from a fatty acid hydroxycarboxylic acid as a lipophilic atomic group in an aqueous dispersion of a pigment obtained in a reaction process for synthesizing colored inorganic pigments or extender pigments using water as a reaction medium. a first step of mixing the agent, and a second step of mixing an alkaline aqueous solution of rosin or modified rosin into the mixed solution so that the pigment content is 96 to 90% by weight and the rosin or modified rosin is 4 to 10% by weight. , a third step of mixing the colored inorganic pigment or extender pigment in the mixed solution in a wet state into an oil-based varnish for plano-letter ink; and stirring the mixture to incorporate the pigment into the oil-based varnish phase. This invention provides a method for finely dispersing colored inorganic pigments or extender pigments into an oil-based varnish for planar letterpress inks, which is characterized by comprising a fourth step of finely dispersing the pigment and separating and removing water from the phase of the oil-based varnish. . Pigment particles in the aqueous pigment dispersion obtained in the synthesis reaction process usually exist as primary particles having a particle size of 0.03 to 0.1 μ. In the method of the present invention, in the first step, a surfactant having a polyester molecular chain as a lipophilic atomic group is adsorbed onto the pigment surface of the primary particles. The lipophilic atomic group of the surfactant used in the method of the present invention includes a polyester molecular chain having a linear structure in which aliphatic hydrocarbon groups are interconnected through ester bonds. As such a molecular chain, a polyester molecular chain derived from an aliphatic hydroxycarboxylic acid is suitable, and in particular, the entire molecule has 12 to 20
Most preferred are polyester molecular chains derived from hydroxycarboxylic acids having 8 to 14 carbon atoms between the carboxyl and hydroxyl groups. In the method of the present invention, any of cationic, anionic, nonionic, and amphoteric surfactants having such a lipophilic atomic group can be used without any restriction on the type of hydrophilic atomic group. However, zwitterionic tamps are particularly preferred. The composition of the aqueous pigment dispersion obtained in the synthesis reaction process varies depending on the chemical structure of the pigment, the synthesis reaction process, etc., but generally speaking, it contains 60 to 95% water and 3 to 25% pigment. minutes and 2-15% unreacted content,
It can be said that it has a composition consisting of water-soluble components such as by-product components. When such an aqueous pigment dispersion is used, 0.01 to 5 parts of the above surfactant is mixed with 100 parts of the aqueous dispersion to uniformly apply the surfactant to the surface of the pigment particles. It can be adsorbed. In the second step, rosin or modified rosin is adsorbed to the liquid mixture obtained in the first step to form a coating made of rosin or modified rosin on the entire surface of the pigment particles. From many experiments, the present inventors have found that a specific surfactant as described above is mixed into the aqueous pigment dispersion obtained in the synthesis reaction process, and then an alkaline aqueous solution of rosin or modified rosin is directly mixed into this mixture. It has been discovered that flushing of inorganic pigments is particularly effective only when the surface of the pigment is treated with. The method of the present invention can be applied to various inorganic pigments synthesized in an aqueous medium, such as colored inorganic pigments such as titanium white, iron oxide (bengara), chromate yellow (yellow lead), and calcium carbonate, sulfuric acid. It can be applied to extender pigments such as barium and barium carbonate. An alkaline aqueous solution of rosin or modified rosin used as a surface treatment liquid for pigment particles can be prepared by dissolving 30 parts of rosin or modified rosin in 100 parts of a 10% aqueous solution of a strong alkaline substance such as sodium hydroxide or potassium hydroxide. An aqueous rosin solution prepared in this way can be used. When using an aqueous pigment dispersion having the composition as described above obtained in the pigment synthesis reaction step, the pigment can be prepared by mixing 1 to 10 parts of the alkali aqueous solution to 100 parts of the aqueous dispersion. The preferred coating described above can be formed on the surface of the particles.
The ratio of rosin to pigment in the mixture of pigment dispersion and rosin aqueous solution affects the amount of coating on the surface of pigment particles, and is important for smooth separation and removal of water in the fourth step. This is important for water, and by setting the ratio to 4% or more, a remarkable water separation effect can be achieved. However, even if the ratio is 10% or more, the effect will not be improved any further and the manufacturing cost will increase, which is disadvantageous. Various types of rosin or modified rosin can be used, such as gum rosin, oil rosin, tall oil rosin and its maleic acid modified product,
Ester modified products etc. can be used. In the third step, the inorganic pigment in the liquid mixture obtained in the second step is mixed into the oil-based varnish in a wet state. The mixing method is to directly mix the mixed liquid as it is into the oil-based varnish, or to first dehydrate the mixed liquid to form a wet cake with a water content of about 50 to 60%, and then mix this wet cake into the oil-based varnish. Any method may be used. As the oil-based varnish, it is advantageous to use a high-viscosity varnish that is used in ordinary printing inks such as lithographic printing ink and letterpress printing ink. The mixing ratio of pigments to oil-based varnish is not particularly limited and can be any ratio within the range of the mixing ratio of pigments contained in ordinary printing inks, for example, 10 to 65% by weight for colored inorganic pigments. , for extender pigments, it can be 10 to 45% by weight. In the fourth step, the mixture obtained in the third step is sufficiently stirred. By stirring, the pigment component moves into the oil-based varnish phase and becomes finely dispersed. At the same time, the water that was the dispersion medium for the pigment or the water contained in the wet cake separates from the oil-based varnish phase and is removed. In order to more fully remove the water remaining in the mixture, it is preferable to use a device such as a kneader and stir it under reduced pressure and heating conditions at a pressure of 100 to 200 mmHg and a temperature of 60 to 105°C. In the pigment-dispersed varnish thus obtained, pigment particles are present with a particle size of 0.03 to 1 μm, and coarse particles with a particle size of 10 μm or more that cause problems in printing are hardly present. As mentioned above, the method of the present invention enables the fine dispersion of inorganic pigments into oil-based varnish by the flushing method, thereby reducing the long working time required in the conventional kneading method. Since it is possible to save a lot of working energy, it is possible to significantly reduce manufacturing costs through rationalization of the manufacturing process and energy conservation. Furthermore, the method of the present invention allows the pigment particles to have a much smaller particle size than the pigment particles obtained by the kneading method, and in particular can be dispersed in the oil-based varnish with almost no remaining coarse particles. Therefore, by using the varnish in which pigments obtained by the method of the present invention are finely dispersed as an ink base, there is no problem of so-called plate residue and blanket residue, in which coarse pigment particles remain attached to the plate and blanket surfaces, and gloss and gloss are improved. Printing ink with high transparency can be produced. Furthermore, in the method of the present invention, the pigment particles can be dispersed in an oil-based varnish with the surface sufficiently coated with rosin or modified rosin, so that the varnish in which the pigment obtained by the method of the present invention is finely dispersed can be used as a base. Accordingly, it is possible to produce a printing ink that does not cause water loss (an emulsification phenomenon of ink caused by mixing of dampening water) on a printing press. Next, the present invention will be specifically explained using examples. Example An aqueous solution with a rosin concentration of 25% was prepared by dissolving maleic acid-modified rosin in an aqueous solution with a potassium hydroxide concentration of 10%. An aqueous dispersion with a calcium carbonate particle concentration of 10% obtained through a synthesis reaction process in which calcium carbonate is synthesized by blowing carbon dioxide into a quicklime aqueous solution.
100 copies of the formula 0.1 part of a surfactant represented by the following formula was mixed, then 2 parts of the above rosin aqueous solution was mixed into this mixed solution, and this mixed solution was dehydrated to form a wet cake with a water content of 40%. Next, 50 parts of this wet cake was mixed with an oil-based varnish for lithographic printing ink (manufactured by Dainippon Ink Chemical Industries, Ltd., trade name: rosin-modified phenolic resin).
12X0132'') and mix this mixture with pressure 190
The mixture was stirred in a kneader under reduced pressure and heating conditions of mmHg and temperature of 90° C. to disperse the pigment in the oil-based varnish phase and simultaneously separate and remove water from the oil-based varnish phase. The obtained pigment-dispersed varnish was mixed with 5 parts of lightweight and 1 part of dryer to prepare medium ink. Comparative Example 30 parts of powdered calcium carbonate produced by drying and pulverizing the wet cake of the example was mixed with 64 parts of the oil-based varnish of the example, and this mixture was sufficiently kneaded using a kneading roll. The obtained pigment-dispersed varnish was mixed with 5 parts of lightweight and 1 part of dryer to prepare medium ink. Evaluation tests were conducted on each of the inks obtained in Examples and Comparative Examples according to the following procedure, and the results are listed in the table below. Transparency - Medium ink is spread with a spatula on black printed paper to form a thin film, and the transparency of this thin film is determined with the naked eye. Pigment dispersion degree - The medium ink is dissolved and dispersed in xylene, and the particle size distribution is measured using a particle size distribution measuring device. Glossiness - Measure the surface gloss of printed paper using a glossmeter (angle of incidence 60 degrees). Water loss resistance - After running the printing press continuously for 5 minutes without feeding paper while supplying dampening water with a pH of 6.5 to the ink on the printing plate, the gloss of the printed paper after paper feeding was measured. The determination is made based on this measured value. Plate Remains - Determine the presence or absence of ink coarse particles adhering to the plate surface on the printing press after printing by touch and with the naked eye. Blanket Remaining - The presence or absence of coarse ink particles adhering to the surface of the blanket on the printing press after printing is determined by touch and with the naked eye. The printing machine used was "Favorit RF-01" made by West German Manroland, and the dampening water was "H liquid" made by Dainippon Ink and Chemicals Co., Ltd. "Product name: DH-78".
A 200 times diluted solution with water was used, the printing paper used was Topcoat B size 90kg paper manufactured by Kanzaki Paper Co., Ltd., and the particle size distribution measuring device was a model PA-720 manufactured by Hyaku Co., Ltd. in the United States. 【table】

[Brief explanation of drawings]

FIG. 1 is a graph showing the results of pigment dispersion measured using a particle size distribution analyzer for medium ink according to the method of the present invention. Number distribution curve 1 in the figure refers to the particle diameter (unit: μ
The ratio (unit: %) of the number of particles corresponding to m) to the total number of measured particles is plotted with the full scale of the vertical axis set as 50%. Volume distribution curve 2 is based on the assumption that all particles are spheres. The ratio (unit: %) of the total volume of particles corresponding to the particle diameter on the horizontal axis to the total particle volume is plotted with the full scale on the vertical axis as 50%. It is a graph showing the results of measurement in the same manner as in the figure. In the figure, 1 indicates a particle number distribution curve, and 2 indicates a particle volume distribution curve.

Claims (1)

[Claims] 1. A surfactant having a polyester molecular chain derived from a fatty acid hydroxycarboxylic acid as a lipophilic atomic group is mixed into an aqueous pigment dispersion obtained in the synthesis reaction process of colored inorganic pigments or extender pigments using water as a reaction medium. The first step is to add an alkaline aqueous solution of rosin or modified rosin to the mixture so that the pigment content is 96 to 96%.
A second step of mixing the rosin or modified rosin to 90% by weight and 4 to 10% by weight of the rosin, and mixing the colored inorganic pigment or extender pigment in the mixture into an oil-based varnish for plano-letter ink in a wet state. A third step of
An oil-based varnish for lithographic ink, comprising a fourth step of finely dispersing the pigment in the oil-based varnish phase by stirring the mixture, and separating and removing water from the oil-based varnish phase. Fine dispersion method of colored inorganic pigments or extender pigments.