JPH0234992B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for dispersing inorganic pigments in the form of ultrafine particles in an oil-based varnish for plano-plate inks 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 it has the disadvantage that grouped 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 ink. 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, in the present invention, an alkaline aqueous solution of rosin or modified rosin is added to an aqueous pigment dispersion obtained in a reaction process for synthesizing colored inorganic pigments or extender pigments using water as a reaction medium, and the pigment content is 96 to 90% by weight. The first step is to mix the rosin at a concentration of 4 to 10% by weight.
a second step of mixing the colored inorganic pigment or extender pigment in the mixed solution in a wet state into a varnish for plano-letter ink, and stirring the mixture to transfer the pigment to 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 planographic printing inks, which comprises a third step of separating and removing water from the phase of the oil-based varnish. be. 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, rosin or modified rosin is adsorbed onto the face surface of the primary particles to form a coating of rosin or modified rosin on the entire surface of the pigment particles. Through many experiments, the present inventors have found that flushing of inorganic pigments occurs only when the pigment surface is treated by directly mixing rosin or an alkaline aqueous solution of modified rosin into the aqueous pigment dispersion obtained in the synthesis reaction process. We have discovered the fact that this is possible. 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), calcium carbonate, sulfuric acid, etc. 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 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. 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-products. When such an aqueous pigment dispersion is used, 1 to 10 parts of the above alkaline aqueous solution is mixed with 100 parts of the aqueous dispersion to form the above-mentioned preferred coating on the surface of the pigment particles. can do. 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 third 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 second step, the inorganic pigment in the liquid mixture obtained in the first 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. Typical examples include rosin-modified phenolic resins and linseed oil dissolved in high-boiling petroleum solvents. The mixing ratio of the pigment to the 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, for colored inorganic pigments, it is 10 to 65.
% by weight, and for extender pigments it can be 10 to 45% by weight. In the third step, the mixture obtained in the second 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 makes it possible to finely disperse colored inorganic pigments or extender pigments into a varnish for planar letterpress inks by a flushing method,
As a result, the long working time and large amount of working energy required in the conventional kneading method can be saved, so it is possible to significantly reduce the manufacturing cost by streamlining the manufacturing process and saving energy. Furthermore, the method of the present invention allows the pigment particles to be made to have a particle size much smaller than that of the pigment particles obtained by the kneading method, and in particular, to disperse them in an oil-based varnish with almost no remaining coarse particles. Therefore, by using the varnish in which the pigment obtained by the method of the present invention is finely dispersed as the 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 bracket surfaces. Printing ink with high photosensitivity and 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 A maleic acid-modified rosin was dissolved in an aqueous solution with a potassium hydroxide concentration of 10% to prepare an aqueous solution with a rosin concentration of 25%. Aqueous dispersion 100 with calcium carbonate particle concentration of 10% obtained in a synthesis reaction process in which calcium carbonate is synthesized by blowing carbon dioxide into a quicklime aqueous solution.
2 parts of the above rosin aqueous solution was mixed with 2 parts of the above rosin aqueous 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 resulting pigment-dispersed varnish was mixed with 5 parts of light oil and 1 part of a dryer to prepare a 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 the mixture was sufficiently kneaded using a kneading roll. Light oil 5 is added to the resulting pigment-dispersed varnish.
1 part and 1 part dryer were mixed to prepare a 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 machine 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 as printing paper, Top Coat B size 90 kg paper manufactured by Kanzaki Paper Co., Ltd., and a PA-720 model manufactured by Hyaku Co., Ltd. in the United States was used as a particle size distribution measuring device.

【table】

【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, and the number distribution curve 1 in the figure is:
Particle diameter (unit: μm) scaled with common logarithm on the horizontal axis
The ratio (unit: %) of the number of particles corresponding to the total number of measured particles is plotted with the full scale of the vertical axis set as 50%.The volume distribution curve 2 is a plot of the ratio of the number of particles corresponding to The ratio (unit: %) of the total volume of particles corresponding to the particle diameter on the axis to the total particle volume is plotted with the full scale of the vertical axis as 50%. Figure 2 is a comparison example of medium ink compared to Figure 1. It is a graph showing the results measured in the same manner. In the figure, 1 indicates a particle number distribution curve, and 2 indicates a particle volume distribution curve.

Claims (1)

[Claims] 1 Add an alkaline aqueous solution of rosin or modified rosin to an aqueous pigment dispersion obtained in the synthesis reaction process of colored inorganic pigments or extender pigments using water as a reaction medium.
96 to 90% by weight, 4 to 90% rosin or modified rosin
A first step of mixing the mixture to a concentration of 10% by weight, a second step of mixing the colored inorganic pigment or extender pigment in the liquid mixture in a wet state into an oil-based varnish for plano-letter ink, and stirring the mixture. A colored inorganic pigment in an oil-based varnish for planar letterpress ink, characterized by comprising a third step of finely dispersing the pigment in the oil-based varnish phase and separating and removing water from the oil-based varnish phase. Or fine dispersion method of extender pigment.