JPS59122554A - Preparation of surface-treating barium sulfate - Google Patents

Abstract

PURPOSE:To prepare a surface-treating BaSO4 having excellent affinity with resins, and giving a coating film having excellent coating film properties such as strength, gloss, etc. when compounded to a paint, etc., by modifying the inert surface of BaSO4 particle by the deposition of hydrous silica. CONSTITUTION:The objective BaSO4 is prepared by adding an aqueous solution of an alkali silicate to an aqueous slurry of BaSO4 having an average particle diameter of 0.1-0.5mu and containing Ba<2+> to precipitate barium silicate to the surface of BaSO4, and adding a mineral acid to the slurry to decompose the barium silicate to hydrous silica and deposit the hydrous silica to the surface of BaSO4. The product may be further treated with a silane coupling agent, or a hydrated oxide of a metal such as Al, Ti, Zn, etc. may be deposited to the surface of the product to improve the affinity of BaSO4 with resin. USE:Compounding to a paint, etc. as an inexpensive pigment in place of expensive TiO2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing surface-treated barium sulfate, and more specifically, it has excellent resin affinity and therefore has pigment properties equivalent to or better than titanium oxide except for hiding power. The present invention relates to a method for producing surface-treated barium sulfate.

Barium sulfate is generally produced by an aqueous reaction in which an aqueous solution of a barium salt such as barium chloride, barium sulfide, or barium nitrate is reacted with an aqueous solution of sulfate or sulfuric acid. 2.0
They are spherical particles of about μ in size, and after filtration and washing with water, the resulting wet cake is dried and pulverized to be used as a product for various purposes.

Conventionally, barium sulfate has generally been used by being blended with resin systems in various fields such as manufacturing resin molded products such as sheets, films, containers, industrial parts, and decorative items, as well as paints and inks. Originally, barium sulfate was used chemically,
It is used as an extender pigment by taking advantage of its physically stable property, and for this reason, various restrictions have hitherto been unavoidable when using it.

For example, as mentioned above, the particle size of barium sulfate is normally 0.3 to 2.0μ, but the primary particles agglomerate during drying and pulverization, and are used as a product. Sometimes, barium sulfate contains tens of percent of particles larger than 2μ, and barium sulfate with such a particle size distribution reduces the gloss of the paint film, so it cannot be used in paints that require clear gloss. Not suitable. In addition, since the barium sulfate particle surface is inert as mentioned above, it has poor affinity with some resins, and when used in paints containing such resins, barium sulfate aggregates and increases paint viscosity. , the required paint performance cannot be obtained.

On the other hand, in the paint industry, titanium oxide has traditionally been widely used as a pigment to give strength to paint films, but titanium oxide is expensive, so there has been a desire to develop pigments to replace it. There is.

As a result of intensive research in order to solve the various problems mentioned above, the present inventors have found that by depositing hydrated silica on the inert surface of barium sulfate particles and modifying the surface, it has been found that the particles have an affinity with resin. Barium sulfate with excellent properties can be obtained, and the barium sulfate thus obtained has pigment properties equivalent to or better than titanium oxide, except for hiding power. The present invention was achieved by discovering that titanium oxide could be used as a substitute for the field in which titanium oxide was used.

Therefore, the present invention provides surface-treated barium sulfate that has resin affinity and can form a coating film having good physical properties such as strength, hardness, sharpness and gloss when used in paints, etc. The purpose is to provide a manufacturing method for.

The method for producing surface-treated barium sulfate according to the present invention involves adding an alkaline silicate aqueous solution to an aqueous slurry of barium sulfate containing barium ions and having an average particle diameter of 0.1 to 0.5μ, thereby coating the surface of barium sulfate with barium silicate. Then, a mineral acid is added to the slurry to decompose the barium silicate into hydrous silica, which is deposited on the surface of barium sulfate.

The barium sulfate λ used in the present invention has an average particle size of 0.
．． It needs to be in the range of 1 to 0.5μ.

If the average particle size is smaller than 0.1μ, even if the surface is treated according to the present invention, the cohesive force between the particles is usually strong, and for example, the dispersibility in the paint is poor, resulting in a coating film with poor gloss. It becomes like this. On the other hand, if it is larger than 0.5μ,
When blended into paint, the coating film does not have sufficient gloss.

Barium sulfate having the average particle size as described above is preferably used at a concentration of 0.3 to 1.2 mol/l and a temperature of 3.
A barium sulfide aqueous solution at 0 to 70°C and a sulfuric acid aqueous solution at a concentration of 0.5 to 5 mol/A and a temperature of 20 to 70°C are continuously introduced into a reaction tank, and the excess amount of barium ions in the reaction solution is reduced to 0.0
It is produced by controlling the amount of the raw material aqueous solution fed into the reaction tank so that the concentration is 1 to 0.1 mol/l.

The factor that has the greatest effect on the particle size of the barium sulfate produced is the excess amount of barium ions in the reaction tank. Excess amount of barium ions in the reaction tank is 0.01
When the amount is less than mol/molar, it is observed that particles close to a plate shape are produced and the particle size tends to become large. on the other hand,
When the excess amount is more than 0.1 mol/l, it is not preferable in industrial practice because it increases production costs. The excess amount of barium ions is usually supplied by barium sulfide as described above, but the excess amount may be supplied by allowing a water-soluble salt such as barium chloride or barium nitrate to coexist with barium sulfide.

The concentration and temperature of the barium sulfide and sulfuric acid aqueous solution used are also
It affects the particle size of the barium sulfate produced; generally, the higher the concentration, the smaller the particle size, and the lower the concentration, the larger the particle size. Furthermore, the higher the reaction temperature, the larger the particle size. Therefore, the reaction temperature is appropriately selected depending on the concentration, temperature, etc. of the barium sulfide or sulfuric acid aqueous solution used, and is usually preferably in the range of 30 to 70°C. Furthermore, as the residence time in the reaction tank becomes longer, the particle size of the barium sulfate produced increases, so it is usually preferably 10 minutes or less. However, depending on the concentration of barium sulfide and sulfuric acid aqueous solution, reaction temperature, etc., the residence time can be made longer.

In the method of the present invention, it is convenient in operation to treat the aqueous slurry in which barium sulfate is produced by the aqueous reaction between barium sulfide and an aqueous sulfuric acid solution with an alkali silicate as described above. Therefore, in this case, the excess amount of barium ions in the water slurry containing barium sulfate is 0.01 to 0.1 mol/l, as described above. However, in the present invention, barium sulfate that has been powdered in advance is made into a water slurry, and water-soluble barium salts such as barium sulfide, barium chloride, barium nitrate, etc. are added to this slurry, and the mixture is melted to contain barium ions. It is also possible to prepare an aqueous slurry of barium sulfate and treat it with an alkali silicate. In this case as well, the amount of barium ions in the water slurry is preferably 0.01 to 0.1 mol/ρ as described above.
is adjusted to the range of

When the amount of barium ions is too small, the generation of barium silicate on the surface of barium sulfate due to the reaction between alkali silicate and barium ions becomes insufficient, and the subsequent hydrolysis of barium silicate by mineral acid produces a sufficient amount. hydrated silica does not deposit on the barium sulfate surface. On the other hand, when the amount of barium ions is too large, it is uneconomical and
A large amount of barium sulfate is newly generated, and the resulting barium sulfate has poor filterability as a whole.
Further, the dispersibility in the resin system becomes poor, which is not preferable.

Further, the concentration of barium sulfate in the aqueous slurry of barium sulfate is preferably 0.2 to 1 mol/β, but is not limited thereto. This concentration is determined by the concentration of the raw material barium sulfide and sulfuric acid aqueous solution when using a slurry resulting from an aqueous reaction between barium sulfide and sulfuric acid, but even when preparing an aqueous slurry separately, if the concentration is too low,
If the amount of treated liquid is too large, it will take time to process, and if it is too large, the thickness of the water slurry will become too high.
This is not preferable because the processability deteriorates.

In the method of the present invention, an alkali silicate is added to an aqueous slurry of barium sulfate as described above, and is reacted with excess barium ions in the aqueous slurry under alkaline conditions to generate barium silicate, which is deposited on the surface of barium sulfate. let In order to stably produce barium silicate, the pH is preferably 9 or higher. As the alkali silicate, specifically, sodium silicate, potassium silicate, etc. are preferably used. The amount of alkali silicate added to the aqueous slurry of barium sulfate is determined by the amount of S
0.1 to 10% by weight in terms of i○2, preferably 0.5 to 10% by weight
It is 5% by weight. If the amount of alkali silicate is too small, it will not be deposited uniformly on the surface of the barium sulfate, and if it is too large, the hydrolyzed hydrated silica will aggregate the barium sulfate, and when the barium sulfate obtained in this way is used in paints, This is not preferable because the coating film formed will have poor dispersibility and gloss.

Next, mineral acid is added to hydrolyze the barium silicate deposited on the barium sulfate surface, resulting in hydrated silica (Sin2
・NH2O) is deposited on the surface of barium sulfate. As the mineral acid, those that do not produce water-insoluble barium salts even if barium ions are still present in the slurry, such as hydrochloric acid and nitric acid, are preferred, but sulfuric acid can also be used if necessary. Since this hydrolysis reaction occurs sufficiently at a pH of 7 or less, the pH of the water slurry is usually adjusted to a range of 2 to 7, but preferably, the pH of the resulting barium sulfate pigment is adjusted to 7±1. In addition, its pH is set to 6±1. The temperature of this hydrolysis reaction of barium silicate is not particularly limited, but is usually 40°C or higher, preferably 60°C to 9°C.
It is 0°C.

The surface-treated barium sulfate obtained in the above manner has excellent resin affinity, so when it is used as a pigment in the production of paints, inks, resin molded products, etc., it improves physical properties such as strength, hardness, and gloss. According to the present invention, such surface-treated barium sulfate is further treated with a silane coupling agent, or aluminum,
By depositing hydrous oxides of metals such as titanium, zirconium, and zinc, the affinity of barium sulfate to resins can be further increased.

That is, another method for producing surface-treated barium sulfate according to the present invention is to produce barium ion-containing particles with an average particle diameter of 0.1 to 0.
．． Add an alkaline silicate aqueous solution to a 5μ aqueous slurry of barium sulfate to generate barium silicate on the surface of the barium sulfate, then add mineral acid to the slurry to decompose the barium silicate into hydrated silica to form a surface of barium sulfate. The barium sulfate thus obtained is treated with a silane coupling agent.

When treating barium sulfate on which hydrated silica has been deposited with a silane coupling agent, the silane coupling agent may be added to and mixed with an aqueous slurry of barium sulfate, or the barium sulfate on which hydrated silica has been deposited may be filtered, washed with water, After drying, it may be mixed with a silane coupling agent, but from the viewpoint of workability, after depositing hydrated silica on barium sulfate in an aqueous slurry as described above, the silane coupling agent is added to this aqueous slurry. It is preferable to add.

In any case, the amount of the silane coupling agent added is 0.01 to 2% by weight, preferably 0.01 to 2% by weight based on barium sulfate.
．． 05 to 1% by weight.

Various types of silane coupling agents are already known, and they usually have the following general formula % () (where X is an alkyl group, vinyl group, acrylic group, methacrylic group, amino group, epoxy group, mercapto group). (R represents an alkyl group), and preferred specific examples include vinyltrimethoxysilane, T-anilinopropyltrimethoxysilane, methyltrimethoxysilane, Examples include γ-methacryloxypropyltrimethoxysilane and γ-glycidoxytrimethoxysilane.

Even if barium sulfate is treated as is with a silane coupling agent, the surface of the barium sulfate particles is inert, so the silane coupling agent will not deposit on the barium sulfate.
According to the present invention, since the hydrated silica is deposited in advance, the silane coupling agent reacts with the hydroxyl group of the hydrated silica and is bonded to the barium sulfate particle surface.
The barium sulfate thus obtained has an excellent affinity for resins.

Furthermore, another method for producing surface-treated barium sulfate according to the present invention is to obtain a surface-treated barium sulfate with an average particle diameter of 0.1
Add an alkaline silicate aqueous solution to an aqueous slurry of ~0.5μ barium sulfate to generate barium silicate on the surface of the barium sulfate, then add mineral acid to the slurry to decompose the barium silicate into hydrated silica. After adding an aqueous solution of a water-soluble metal compound to the thus obtained slurry of barium sulfate, it is neutralized with an alkali or acid depending on the metal compound, and the above metal is deposited on the surface of barium sulfate. It is characterized by depositing hydrous oxides.

In this method, after depositing hydrated silica on barium sulfate in an aqueous slurry of barium sulfate, as described above,
It is preferable to subsequently process this slurry, but it is also possible to process the silica-deposited barium sulfate by filtering, washing, drying, and powdering, and then forming it into a slurry again.

The amount of silica-deposited barium sulfate in the water slurry is not particularly limited, but is usually 0.2 to 1 mol/l, preferably 0.
．． It is in the range of 4 to 0.8 mol/l. In addition, the amount of the water-soluble metal compound added to this water slurry is determined in order to uniformly deposit the hydrated oxide on the barium sulfate as described above.
0.2 to barium sulfate in terms of the metal oxide
10% by weight is preferred, particularly 0.5-5% by weight.

The alkali or acid for decomposing the above-mentioned water-soluble metal compound is not particularly limited, but the alkali is usually sodium hydroxide, potassium hydroxide, ammonia, etc., and the acid is hydrochloric acid, nitric acid, etc., as appropriate. The amount is sufficient for the water-soluble metal compound to form a hydrous oxide,
Usually, it is added so that the pH of the water slurry becomes 7±1. Further, the temperature of this hydrolysis reaction is not particularly limited, but is usually 40°C or higher, preferably 60 to 90°C.

In the present invention, the water-soluble metal compound is not particularly limited as long as it can form a hydrous oxide with an alkali or acid after being added as an aqueous solution to the silica-deposited barium sulfate slurry, and the above-mentioned aluminum, titanium, zirconium It will be clear that in addition to zinc and zinc, various metal compounds can be used.

For example, in order to form hydrated alumina, sodium aluminate is suitably used as the water-soluble aluminum compound. Further, in order to deposit hydrous titanium oxide, for example, titanyl sulfate can be suitably used.

According to the present invention, this reaction can also be carried out at a higher temperature and under pressure, and in this case, a hydrated metal oxide such as hydrated alumina can be more stably deposited on the surface of barium sulfate.

When using an aqueous slurry of barium sulfate that has not been treated with silica, barium sulfate has almost no affinity for these metal oxides, so the hydrated oxides do not precipitate on the barium sulfate and can stand alone. Barium sulfate does not undergo any surface treatment as it precipitates. However, according to the method of the present invention, the hydrated metal oxide is uniformly and strongly deposited on the barium sulfate surface, which is thought to be because the hydrated silica deposited on the barium sulfate surface forms a bond with the hydrated metal oxide. , barium sulfate with extremely good resin affinity is obtained. In addition, barium sulfate treated in this way is
It also has excellent workability such as subsequent filtration.

As mentioned above, barium sulfate on which silica is deposited, barium sulfate on which barium sulfate is further treated with a silane coupling agent, and barium sulfate on which hydrated metal oxides such as hydrated alumina are deposited can be filtered and washed with water using the usual methods. , dried, and then crushed to be used as a product. However, for applications such as water-soluble resin paints, inks, and coated papers, the wet cake after filtration and washing with water can be used as it is.

As described above, the surface-treated barium sulfate obtained by the present invention has a remarkable affinity for resins, so when used in paints, etc., it forms a coating film with excellent mechanical strength and gloss. It has pigment properties equivalent to or better than titanium oxide, which was used to obtain film strength, etc., and thus can be used as a substitute for conventional titanium oxide.

The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples in any way. In the following, parts and % indicate parts by weight and % by weight, respectively.

Example 1 (a) Production of surface treatment barium sulfate A barium sulfide aqueous solution with a concentration of 0.74 mol/β and a temperature of 48°C and a concentration of 1.
28 mol/l, sulfuric acid water/8 liquid at a temperature of 25°C, sulfuric acid aqueous solution 900 A/hour, barium sulfide aqueous solution 1600 ~
It was continuously supplied at a flow rate of 1800β/hour to a reaction tank with a capacity of 250ρ equipped with a stirrer, and the excess barium ion in the reaction solution was 0.03 mol/7! While adjusting the flow rate of the barium sulfide aqueous solution so that
The reaction was carried out in minutes. The average particle size of the barium sulfate thus obtained was about 0.2 μ.

This water slurry of barium sulfate was divided into four equal parts, and the first water slurry was filtered and washed with water using a filter press, dried, and then pulverized using a fluid energy mill. The barium sulfate thus obtained is referred to as comparative barium sulfate.

The second slurry was heated to 70°C, 30% aqueous sodium hydroxide solution was added to adjust the pH to 10, and Si
An aqueous solution of 100 g/6 sodium silicate, 2 rum in terms of O, was added to barium sulfate in an amount of 1.0% in terms of S 102 . After stirring for 10 minutes, the pH was adjusted to 6.0 with approximately 10% aqueous hydrochloric acid solution, and aged for 30 minutes to deposit the hydrated silica on barium sulfate. , dried and pulverized to obtain barium sulfate 1, a product of the present invention.

The third water slurry was treated in the same manner as in the production of the above-mentioned product of the present invention, including ripening, and then a 30% aqueous sodium hydroxide solution was added to adjust p)I to 7, and γ-methacrylate was added to this slurry. Roxypropyltrimethoxysilane was added in an amount of 0.5% based on barium sulfate, and the mixture was further aged for 30 minutes. Thereafter, the product was filtered, washed with water, dried, and pulverized in the same manner as above to obtain barium sulfate 2, a product of the present invention.

The fourth water slurry was prepared by adding 2.0% (calculated as Al2O3) of barium sulfate to a water slurry with a pH of 6.0 in which hydrated silica was deposited in the same manner as the barium sulfate product of the present invention.
of sodium aluminate was added, the po was adjusted to 7.0 with about 10% aqueous hydrochloric acid solution, and hydrated alumina was deposited on the barium sulfate. Thereafter, the product was filtered, washed with water, dried, and pulverized to obtain barium sulfate 3, a product of the present invention.

(bl Preparation of paint and evaluation of physical properties of paint film Polyester resin (M-6003 manufactured by Dainippon Chemical Co., Ltd.)/Melamine resin (J-820 manufactured by Dainippon Chemical Co., Ltd.) (Solid content ratio 85/
15) Solvent #150/n-butanol/butyl cellosolve (weight ratio 70/'20/1)
0) was added to prepare a resin solution having a resin solid content of 50% by weight.

To 100 parts of this solution, as shown in the table, barium sulfate 1.2.3 of the present invention, barium sulfate comparative product, or commercially available titanium oxide treated with silica-alumina and having an average particle size of 0.3μ were added together with carphone black. A paint was prepared by mixing. Adjust this paint to a spray viscosity of 70 mm.
x150xO, 6 pieces of zinc phosphate treated mild steel plate was spray coated to a dry film thickness of 30μ,
The polyester paint film was formed by heating and baking for a minute. The mechanical strength of this coating film was determined according to JIS Z 2247 (
Erichsen test according to method A) and JIS K 5400
-6.13 Examined by impact resistance test (Method B). Further, the pencil strength was examined using the method according to JISK 5400-6.14, and the change in gloss was examined using 20°-20° specular gloss. The results are also shown in the table.

In the table, paints 1, 2 and 3 are paints containing surface-treated barium sulfate obtained by the method of the present invention as a pigment, paint 4 is a comparative paint containing barium sulfate without surface treatment, and paint 5 is a paint containing barium sulfate as a pigment. is a commercially available paint containing titanium oxide.

All of the paints containing barium sulfate according to the present invention have gloss, strength, and hardness that are almost equal to or higher than those of paints containing titanium oxide, whereas the comparative paints containing barium sulfate have the above-mentioned physical properties. It is clear that they are inferior in both respects.

Claims (3)

[Claims] (1) Average particle size containing barium ions: 0.1-0
．． Add an alkaline silicate aqueous solution to a 5μ aqueous slurry of barium sulfate to generate barium silicate on the surface of the barium sulfate, then add mineral acid to the slurry to decompose the barium silicate into hydrated silica to form a surface of barium sulfate. A method for producing surface-treated barium sulfate, characterized by depositing it on a surface. (2) Average particle size containing barium ions: 0.1
Add an alkaline silicate aqueous solution to an aqueous slurry of ~0.5μ barium sulfate to generate barium silicate on the surface of the barium sulfate, then add mineral acid to the slurry to decompose the barium silicate into hydrated silica. A method for producing surface-treated barium sulfate, which comprises depositing it on the surface of barium sulfate and treating the thus obtained barium sulfate with a silane coupling agent. (3) Average particle size containing barium ions: 0.1-0
．． An alkaline silicate aqueous solution is added to a 5μ aqueous slurry of barium sulfate to generate barium silicate on the surface of the barium sulfate.Next, mineral acid is added to the slurry to decompose the silicic acid and rum into hydrated silica, and sulfuric acid is generated. After adding an aqueous solution of a water-soluble metal compound to the slurry of barium sulfate obtained in this way, it is neutralized with an alkali or acid depending on the metal compound, and the hydrated oxidation of the metal is deposited on the surface of barium sulfate. A method for producing surface-treated barium sulfate, which comprises depositing a substance.