JPS5928233B2 - Coated lead chromate pigment and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a lead chromate pigment having improved heat resistance, chemical resistance, and dispersibility in an organic medium, and a method for producing the same.

Lead chromate pigments, such as yellow lead and chrome vermilion, have great hiding power, excellent solvent resistance, and vivid hues, and are widely used as coloring agents for paints, printing inks, synthetic resins, etc. However, it has the disadvantage that it discolors markedly under conditions where high temperatures are used, such as when coloring road paints and synthetic resins, and it also discolors markedly when exposed to inorganic chemicals such as hydrogen sulfide and alkalis.

As a way to solve these drawbacks, for example,
As typified by Japanese Patent No. 6-9555, a method is known in which the surface of lead chromate pigment particles is coated with amorphous silica. Although the coated pigment produced by this method has excellent heat resistance and chemical resistance, when finely dispersing it in a medium, if a dispersing machine with a large shearing force is used, the pigment coating layer will be destroyed, and its excellent properties will be lost until the end. The drawback is that performance cannot be maintained. Furthermore, since its surface is inorganic, it is more difficult to finely disperse it in an organic medium. As a method to overcome the above-mentioned drawbacks, it has been considered to coat lead chromate pigment particles with organic substances, such as various synthetic resins, but in such a method, the individual particles adhere to each other.
They have a strong tendency to form lumps, and it is almost impossible to coat the particles with a uniform thin film, and even if it were possible, it would not be possible to obtain excellent heat resistance, chemical resistance, or easy dispersibility. Ta.

As a result of intensive research in order to solve the above-mentioned drawbacks of the prior art, the present inventor has found that the above-mentioned drawbacks of the prior art can be solved by coating lead chromate pigment particles with a specific organic material. Based on this knowledge, the present invention was completed.

That is, the present invention is a lead chromate pigment coated with a thin film of a cured resin comprising an amino compound, formaldehyde and sulfamic acid, and a method for producing the same.

To explain the present invention in detail, the lead chromate pigment used in the present invention refers to a pigment containing lead chromate (PbCrO4) as one component, such as Color Index Taki 776001 77603 and 77605. The pigment shown.

Although such lead chromate pigments may be in the form of a dried powder, the most preferable ones are suspensions in water or aqueous pastes immediately after production or after aging. This is what I did. The coating material used in the present invention uses amino compounds, formaldehyde, and sulfamic acid as main raw materials, and alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, and butyl alcohol can also be used. The above-mentioned amino compound is a polyvalent amino compound such as melamine, urea, etc., which can react with formaldehyde to form a polymethylol compound. The coating material used in the present invention, which is made of such raw materials, is formed by reacting the necessary components in water, an organic solvent, or a mixture thereof to form an initial condensate. The method for producing this initial condensate is known per se, but in the present invention, the ratio of each component used is important. That is, based on the amino compound used, formaldehyde is added in an amount of about 3 per mole of amino group of the amino compound.
~6 mol of sulfamic acid, approximately 0.05 mol of sulfamic acid
Preferably, it is used at a concentration of ~0.3 mol. When used in such a ratio, an initial condensate of formaldehyde and an amino compound having a sulfonic acid group at the terminal is formed. At this time, if Surjaamic acid is not used or if the amount is below the above range, precipitation or deposition on the surface of the pigment particles will be insufficient, not only will it not be possible to form a thin resin film, but also the amount of the pigment particles will be insufficient. Baby booming occurs and a satisfactory product cannot be obtained. In addition, if the amount of sulfamic acid used is too large, the precipitation of initial condensates on the surface of the pigment particles will be insufficient, and furthermore, the curing of the film will be unsatisfactory and a strong protective film will not be formed. Pigment Gζ An aqueous paste or suspension in water or a powder pigment is finely dispersed in water and adjusted to an appropriate concentration (for example, a concentration of about 2 to 20% by weight), while an aqueous solution of the above-mentioned initial condensate or Prepare an organic solvent solution or a mixed solvent solution, mix these solutions by an appropriate method, and precipitate or deposit the above-mentioned initial condensate on the surface of the pigment particles by changing the pH, adding heavy metal ions, etc. It is then obtained by curing the formed film by means such as changing the pH or heating.

At this time, the raw material ratio of the initial condensate, the usage ratio to the pigment,
The thickness of the coating on the surface of the pigment particles can be changed appropriately by changing the method of mixing the two, changing the pH, etc. The thickness of such a cured film may be approximately 0.005 to 0.5 microns, and the weight ratio of the pigment to the film may be approximately 1 to 100 parts by weight per 100 parts by weight of the pigment. preferable. If the thickness and weight exceed this range, the vividness, coloring power, etc. of the pigment will tend to decrease slightly, while if the thickness and weight fall below the above range, sufficient heat resistance, chemical resistance, and easy dispersibility will be obtained. I can't get it. In the coated pigment of the present invention obtained as described above, the particles are not adhered to each other, and the particle surfaces are covered with a continuous cured resin film with a thickness of about 0.005 to 0.5 microns. Even when used as a coloring component in road paints, various plastics, or paints, it does not discolor under high temperature conditions, and its heat resistance is equal to or higher than that of conventional silica-coated pigments.

In addition, its dispersibility in various media, especially organic media such as paints and plastics, is far superior to that of conventional pigments. Whereas the coating is destroyed and its performance is lost, the pigments of the present invention fully overcome such drawbacks. Next, the present invention will be specifically explained with reference to Examples.

Note that parts and percentages in the text are based on weight. Example 1 40 parts of melamine, 100 parts of 35% formalin, 20 parts of methanol, and 24 parts of water were mixed and stirred, heated to 80°C, and dissolved in a colorless and transparent mixture.

The solution was then cooled to 45°C and sulfamic acid 2.4
One drop of the reaction solution was dropped into water to allow the reaction to proceed until an initial condensate was precipitated, and then 5.5 parts of 20% sodium hydroxide and 20 parts of methanol were added to terminate the reaction. 30 parts of this resin solution is dissolved in 100 parts of water and used as a dropping liquid. On the other hand, G yellow lead 10
Add water to the aqueous paste containing 0 parts to make 2100 parts,
The pH of the peptized dispersion was sufficiently adjusted to 8.5 to 9, and 130 parts of the above resin solution was added dropwise to the dispersion over a period of 1 hour while stirring the dispersion slowly.

Subsequently, the pH was adjusted to 5 with acetic acid, and stirring was continued at 90° C. for 3 hours to cure the formed film. After that, P passed,
After washing with water and drying, 100 parts of the coated lead chromate pigment of the present invention was obtained. Analysis of this pigment revealed that the weight of the coating material was approximately 10 parts per 100 parts by weight of the pigment. Ivy. Further, when the state of the particles was observed using an electron microscope, the thickness of the coating was about 0.02 microns, and it was a uniform continuous coating, as shown in FIG. Example 2 50 parts of an 80% aqueous solution of methylated methylolmelamine resin was diluted and dissolved in 40 parts of a 50% methanol aqueous solution, 2 parts of sulfamic acid was added to the solution, and the mixture was heated at 45 to 50°C for 20 minutes.
After reacting for a minute, 4.6 parts of a 20% caustic soda aqueous solution was added to neutralize.

After cooling, 10 parts of methanol was added to terminate the reaction to obtain a solution of the initial condensate. This solution had a solids content of approximately 40% and remained clear and dissolved when diluted with water. Thirty parts of the above resin solution was diluted with 100 parts of water to prepare a dropping liquid. On the other hand, an aqueous paste containing 100 parts of chromium vermilion was peptized and dispersed in 2000 parts of water, and the pH was adjusted to 8.5-8.5.
The pH of the solution was adjusted to 9, and the above resin solution for dropping was added dropwise to this solution while stirring slowly. After the dropwise addition was completed, the pH of the solution was adjusted to 5, stirred at 90°C for 4 hours, filtered with f. Washing with water, 90
It was dried at 0.degree. C. to obtain 110 parts of the coated pigment of the present invention.

When this pigment was analyzed, the weight of the coating material was 100% of the pigment.
The amount was about 10 parts per part by weight, and when observed with an electron microscope, the thickness of the film was about 0.02 microns, and the film was a uniform continuous film. Example 3
15 parts of the resin solution obtained in Example 1 and 15 parts of the resin solution obtained in Example 2 were diluted with 100 parts of water to prepare a liquid for dropping.

On the other hand, an aqueous paste containing 100 parts of molypdate orange was peptized and dispersed in 2000 parts of water, and the P of the dispersion was
While adjusting H to 8.5 to 9 and stirring this dispersion,
The above-mentioned dropping liquid was added dropwise to this dispersion.

After the dropwise addition is completed, the pH is adjusted to 5, and 20 parts of a 5% barium chloride aqueous solution is added. Next, after stirring at 90°C for 3 hours,
After washing with water and drying, 110 parts of the coated pigment of the present invention was obtained. Analysis of this pigment revealed that the weight of the coating material was about 10 parts out of 100 parts of the pigment, and the coating was uniform and had a thickness of about 0.02 microns. Example 4 2 parts of sulfamic acid was added to 100 parts of a 50% aqueous methanol solution containing 20 parts of methylolmelamine and 20 parts of methylated methylolmelamine, and after reacting for 10 minutes at 45 to 50°C, 4.6 parts of a 20% aqueous sodium hydroxide solution was added. was added to terminate the reaction.

This reaction solution had a solid content of about 40% and remained a clear solution even when diluted with water. 15 parts of this resin solution to 100 parts
The solution was diluted with 50% of water to prepare a solution for dropping. On the other hand, an aqueous paste containing 100 parts of 10G yellow lead was peptized and dispersed in 2000 parts of water, and the pH of the dispersion was adjusted to 8.5 to 9.
The above-mentioned dropping liquid was added dropwise to the dispersion while stirring the dispersion. After dropping, adjust the pH of the liquid to 5,
After stirring at 0°C for 3 hours, it was filtered with P, aqueous, and dried to 110
100% of the coated pigment of the present invention was obtained. Analysis of this pigment revealed that the weight of the coating material was about 10 parts out of 100 parts by weight of the pigment, and the coating was uniform and had a thickness of about 0.02 microns. Performance Test Example 1 (Heat Resistance Test) A test piece was prepared by coloring polyethylene to a pigment concentration of 5% using the coated pigment of the present invention obtained in the above example, an untreated pigment, and a commercially available silica-coated lead chromate pigment. When we conducted a heat resistance test using this test piece, we found that
The results shown in Table 1 below were obtained.

Comparative Test Example 2 (Dispersibility Test) 50 parts each of the coated pigment of the present invention obtained in the above example, the untreated pigment and the commercially available silica-coated lead chromate pigment,
25 parts of linseed oil-modified alkyd varnish (solid content 60%) and 25 parts of solvent were placed in a mayonnaise-type glass pin containing 80 parts of glass beads, and a dispersibility test was conducted using a Red Devil paint conditioner. (JI
Based on SK54OO Paint General Test Methods 4 and 5 Tube A method)
.

The results were as shown in Table 2 below. Comparative Test Example 3 (Chemical resistance and light resistance test) Using the coated pigment of the present invention obtained in the above example, an untreated pigment, and a commercially available silica-coated lead chromate pigment, the following chemical resistance test and light resistance test were conducted. A weather resistance test was conducted and the results shown in Table 3 below were obtained.

O Alkali resistance・・・・・・3% NaOH solution 1
5 tons of pigment powder was immersed in 00a and treated for 1 hour with occasional stirring, then washed with water, filtered, and dried.

The treated pigment and the pigment that has not been subjected to the immersion treatment are made into a paint using a single coating, applied in two coats with an applicator, and the degree of change is determined. O Sulfide resistance・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・Make it into a paint with Ratsukaichi, apply it to a glass plate with an applicator, immerse the coated plate in saturated hydrogen sulfide water at room temperature for 30 minutes, and compare it with the coated plate before dipping. Determine the degree of change.

O Weather resistance: Make a paint using a lacquer and apply it to an aluminum plate using an applicator.

Claims (1)

[Scope of Claims] 1. A lead chromate pigment coated with a thin film of a cured resin comprising an amino compound, formaldehyde and sulfamic acid. 2. A method for producing a coated lead chromate pigment, which comprises depositing or precipitating an initial condensate consisting of an amino compound, formaldehyde, and sulfamic acid on the surface of each particle of a lead chromate pigment in an aqueous medium, and then curing it. 3. The lead chromate pigment according to claim 1, wherein a portion of the methylol groups of the initial condensate of an amino compound, formaldehyde, and sulfamic acid are lower alkylated. 4. The manufacturing method according to claim 2, wherein a part of the methylol groups of the initial condensate is lower alkylated.