JP3117499B2 - Barium sulfate pigment and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a barium sulfate pigment which has a unique flat particle property having a smooth and round surface and is particularly excellent in a milky effect, and a method for producing the same.

[0002]

2. Description of the Related Art Barium sulfate is chemically and physically stable and is used as an extender pigment in resins, paints, inks, and the like. 2. Description of the Related Art Uses as extenders for milky white synthetic resin molding materials, particularly for materials such as lighting equipment and optical equipment, are known. It is considered that this milky effect is good in that, for example, when it is used in a lighting fixture or the like, light generally passes well and the light source is hard to see. That is, it is required that the total light transmittance of the milky plate is high, the parallel light transmittance is low, and the transmitted light is not discolored.

Conventionally, as a means for industrial production of barium sulfate, a technique of reacting a barium sulfide solution and a borate solution has been a typical method. In addition to this, there is a method using sulfuric acid instead of a solution of bowel nitrate, and a method of reacting a water-soluble barium salt aqueous solution such as barium nitrate, barium chloride or barium hydroxide with sulfuric acid or bowel nitrate. The barium sulfate produced by the method according to the technology has fine particles and a particle diameter of about 1 μm or less.

[0004] In general, the shape of barium sulfate obtained by the above-mentioned manufacturing technique is spherical, scale-like or the like. However, when barium sulfate of this shape is kneaded and mixed with a resin for an opal plate, a spherical one has good parallel light transmittance at an optimum particle diameter and is good, but the total light transmittance is also lowered at the same time. There is. On the other hand, the scale-like one has an advantage that the total light transmittance is higher than that of the spherical product, but there is a problem that a sufficient value of the parallel light transmittance cannot be obtained.

[0005] For these reasons, for a resin addition, especially for an opalescent board, a spherical sulfuric acid having both the advantages of a smooth and rounded spherical barium sulfate and a scale-like barium sulfate having a high total light transmittance. There is a demand for the development of barium.

Techniques for producing barium sulfate corresponding to such a problem include a method of adding an aqueous solution of sulfuric acid to an aqueous solution of barium nitrate or barium chloride and heating and ripening it at 70 ° C. or higher (Japanese Patent Publication No. 50-33986), or a fine-grained method. Barium sulfate particles are heated and aged in a hydrochloric acid solution to form large particles,
In addition, a technique (Japanese Patent Publication No. 56-39787) has been proposed in which a smooth roundness is imparted to the particle surface to enhance the milky white effect.

[0007]

However, among the above-mentioned prior arts, barium sulfate obtained by the former method has an average particle diameter (average in length and width) of 4 μm or more, but has a spherical shape. The total light transmittance does not show a sufficient value. In addition, it requires expensive special raw materials such as barium chloride or barium nitrate as a raw material barium source,
On the other hand, there is a restriction that a sulfate cannot be used as the SO ₄ ^{2 -} source, which is not preferable. Further, in the latter method in which barium sulfate is heated and aged in a hydrochloric acid solution, it is difficult to grow particles to 3 to 4 μm or more, although it has a surface smoothing effect. In particular, when using fine barium sulfate of 1 μm or less obtained by ordinary industrial means as a raw material,
There is a problem that it cannot be matured and grown as barium sulfate having an arbitrary large particle diameter.

The present invention has been made in view of the above technical background, and has been made of a special particle-like barium sulfate pigment exhibiting a high milky effect and an industrial production method for efficiently producing the barium sulfate pigment from inexpensive raw materials. It is intended to be provided.

[0009]

The barium sulfate pigment according to the present invention for attaining the above object has a total light transmittance of at least 20%.
90% or more of barium sulfate crystal particles having an average particle diameter of 2.0 μm or more, X-ray intensity ratio (I) = I _[200] / I
_{[021] wherein} I _[200] and I _[021] represent the diffraction line intensities of the [200] and [021] planes of barium sulfate in the range of 0.15 to 0.50, and the particle surface is smooth. It is a physical feature to have a flat shape having a roundness.

[0010] Among the properties of the present invention, the total light transmittance is
The characteristic of 90% or more is a prerequisite element for imparting the opalescent effect, and the total light transmittance here is obtained by the measuring method shown in Examples described later, similarly to the parallel light transmittance. It is defined as a value. Average particle size is 2.0
The particle size of μm or more is also a characteristic element that functions to give a milky effect, and is indicated as a particle size by the Coulter counter method.

The barium sulfate according to the present invention further comprises Ba
The [200] crystal plane of the crystal grain identified as SO ₄
[021] X-ray intensity ratio of crystal plane (I) = I _[200] / I
_[021] has physical properties in the range of 0.15 to 0.50. This crystal property is the basis for showing a flat particle shape with a smooth and rounded particle surface, and is an element contributing to the improvement of dispersibility in addition to the effect of imparting a milky white color. When the X-ray intensity ratio (I) is less than 0.15, the scale-like tendency becomes strong and the parallel light transmittance does not become sufficiently low.
In the case of exceeding 0.7, in particular, when it is 0.7 or more, a spherical particle shape is exhibited, the total light transmittance does not increase, and in any case, a sufficient milky effect cannot be achieved.

The barium sulfate pigment of the present invention having the above-mentioned properties is obtained by subjecting barium sulfate to thermal aging with a mineral acid to grow grains, wherein the pigment is initially aged using a suspension of barium sulfate particles as a base material. The production method of the present invention in which barium sulfate finer than the base material is added at least once and ripened can be industrially advantageously produced.

Barium sulfate as a base material is applied irrespective of its manufacturing history. Therefore, since the starting material is not specified, any so-called precipitated barium sulfate obtained by an industrial production method can be used. Therefore, for example, the average particle size by the Coulter counter method is 1.0μ
m or more, an inexpensive scale-like general-purpose sedimentable barium sulfate having an X-ray intensity ratio (I) of 0.15 or less can be used as a preferable raw material. However, when the average particle diameter is 1.0 μm or less, X
When barium sulfate having a linear intensity ratio (I) of 0.15 or more is used as a base material, and then barium sulfate finer than the base material is added and aged, crystal growth proceeds but it is difficult to obtain sufficient crystal growth. Become.

The barium sulfate added later may be finer than the base material, but preferably has an average particle size of 1.0 μm.
The following particles should be selected and used. The reason is that, in the production method of the present invention, fine barium sulfate added later on the surface of the base material as a nucleus repeatedly dissolves and precipitates to grow the particle size, so that barium sulfate is larger than the hardly soluble large particles. This is because fine particles having a dissolution rate as fast as possible are more effective for promoting particle size growth. However, when barium sulfate as a particle growth material is mixed and ripened before initial ripening of the base material, the effect is small even with fine particles.

In the process of the present invention, the addition interval, the amount of addition and the number of additions of the fine barium sulfate serving as the grain growth material are important factors for controlling the particle diameter of the aged barium sulfate. . First, the addition interval should be at least 30 minutes, preferably at least 2 hours. The longer the length, the larger the aged particle size and the sharper the particle size distribution. As for the amount added at one time, the larger the amount, the larger the aged particle size.
The particle size distribution is broad. For this reason, there is no particular limitation in relation to the number of additions, but in many cases, 5 to 100% by weight based on the initial amount of barium sulfate serving as a base material.
Preferably, 10 to 50 wt% is a suitable range. The number of additions may be at least one or more, and the aged particle size increases almost linearly in proportion to the number of additions.

The mineral acid used in the present invention is hydrochloric acid, nitric acid or the like, and it is preferable that the solution be heated and aged at a solution concentration of 0.03 N, preferably 0.1 N or more. In this case, the slurry concentration has no essential effect, and any suspension may be adjusted. However, the upper limit is about 35% by weight for operational reasons.
It is desirable to carry out within that range.

Although some salts may be dissolved in the aging suspension, the presence of common ions with barium sulfate greatly affects the aging effect. That is, when the SO ₄ ^{2 -} ion in the suspension is 200 ppm or less, the aging effect is reduced. Therefore, in preparing the suspension, SO
₄ ^{2 -} concentration of ions 200ppm or more, preferably a is preferably condition setting be prepared so that the above 500 ppm.

Such a suspension is stirred for 70 minutes.
The heat aging treatment is performed at a temperature of at least 80 ° C, preferably at least 80 ° C. Since the aging effect becomes better as both the aging temperature and the concentration of the mineral acid are higher, the production may be carried out by appropriately setting practical operating conditions within the above range.

After sequentially performing the above-described treatment operations, the suspension is neutralized with a desired alkaline agent such as caustic soda, separated from the mother liquor, and processed into a product through a conventional operation.

[0020]

The milky effect of barium sulfate is based on the total light transmittance (T
t) and the parallel light transmittance (Tp), and is generally a relationship where Tt is large and Tp is small, in other words, Tt / T
The higher the p-ratio, the greater the opalescent effect. The barium sulfate according to the present invention has a large particle size of 2 μm or more according to the Coulter counter method, and is characterized by exhibiting a total light transmittance of 90% or more, a high value not found in conventional barium sulfate. Can be

For example, barium sulfate whose average particle diameter has been adjusted to 3 to 4 μm by the production method of the present invention, when used for a milky plate, has a total light transmittance as high as or higher than that of a flake-like product, and The parallel light transmittance shows a low value equal to or less than that of a spherical product. Further, when added to the resin, favorable functions such as an increase in mechanical strength of the resin molded product and a decrease in the sedimentation speed in the process of producing a milky plate by the casting method can be imparted as compared with spherical barium sulfate.

The barium sulfate according to the present invention has an X-ray intensity ratio (I) = I of crystal plane [200] plane and [021] plane.
_[200] / I _[021] is in the range of 0.15 to 0.50, and the particle surface has a smooth and rounded flat particle shape. This property functions to impart good dispersibility in addition to the milky effect.

Barium sulfate having the above-mentioned characteristic properties is obtained by adding barium sulfate finer than the base material at least once to a suspension which has been initially aged using an inexpensive barium sulfate particle material as a base material. The simple and short processing steps of the present invention of adding and aging allow industrial production.

[0024]

EXAMPLES Examples of the present invention will be specifically described below in comparison with comparative examples.

Example 1 A commercially available barium sulfate manufactured using barium sulfide and sulfuric acid as raw materials [average particle diameter 1.5 μm, X-ray intensity ratio (I) = 0.12, hereinafter referred to as "barium sulfate A"] and 15.6 kg of a 0.5 N nitric acid aqueous solution, and the ripening treatment was started while stirring at a temperature of 90 ° C while stirring. Four hours after the start of ripening, 600 g of commercially available barium sulphate (average particle diameter: 0.6 μm, hereinafter referred to as “barium sulphate B”) produced from barium sulfide and sulfuric acid were added to the ripening solution, and Aging was continued under the following conditions. Thereafter, the addition interval was set to 4 hours,
At the hour, the 12th hour and the 16th hour, the aging treatment was performed by adding 2.4 kg of the above-mentioned barium sulfate B 600 g each four times in total. At this time, the concentration of SO ₄ ^{2 -} ions in the matured mother liquor was 1000 ppm. Further, 20 hours after the start of the aging treatment, heating was stopped and the slurry was neutralized with an aqueous solution of sodium hydroxide. Then, filtration, washing with water, drying, and pulverization were performed by a conventional method to obtain coarse barium sulfate.

The average particle diameter and X-ray intensity ratio of the finally obtained barium sulfate are as shown in Table 1. FIG. 1 is a graph showing the change of the average particle diameter at each addition. 2 to 5 are electron micrographs of the raw material and barium sulfate particles after the aging treatment. FIG. 2 shows barium sulfate A, FIG. 3 shows barium sulfate B, FIG. 4 shows aged barium sulfate with one addition, and FIG. This shows aged barium sulfate with four additions. From FIG. 1 and FIGS. 2 to 5, it is recognized that the barium sulfate particles grow smoothly by the process of the present invention and are converted into a flat shape with a smooth and round surface.

Example 2 Barium sulfate was obtained by aging under the same conditions as in Example 1 except that the addition interval was changed to 2 hours and the number of additions was changed to 8. Table 1 shows the average particle diameter and the X-ray intensity ratio of the obtained barium sulfate, and FIG. 1 also shows the change of the average particle diameter at each addition.

Example 3 Barium sulfate was obtained by aging under the same conditions as in Example 1 except that the addition interval was changed to 7 hours and the number of additions was changed to 8. The average particle diameter of the obtained barium sulfate and the X-ray intensity ratio are shown in Table 1, FIG. 6 shows an electron micrograph of the aged barium sulfate having been added eight times, and FIG. It was also attached to.

COMPARATIVE EXAMPLE 1 Using barium sulfate A as a raw material, 4.4 kg of this was added to 15.6 kg of a 0.5 N nitric acid aqueous solution, and heated and aged at 90 ° C. for 20 hours. Then, filtration, washing with water, drying, and pulverization were performed in a conventional manner. The average particle diameter of the obtained barium sulfate and the X-ray intensity ratio are also shown in Table 1.

Comparative Example 2 Using barium sulfate B as a raw material, 4.4 kg of this was added to 15.6 kg of a 0.5 N aqueous nitric acid solution, and the mixture was heated and aged at 90 ° C. for 20 hours. Then, filtration, washing with water, drying, and pulverization were performed in a conventional manner. The average particle diameter of the obtained barium sulfate and the X-ray intensity ratio are also shown in Table 1.

Comparative Example 3 A mixed raw material of 2 kg of barium sulfate A and 2.4 kg of barium sulfate B was added to 15.6 kg of a 0.5 N aqueous nitric acid solution at 90 ° C.
Heat aging for hours. Then, filtration, washing with water, drying, and pulverization were performed in a conventional manner. The average particle diameter of the obtained barium sulfate and the X-ray intensity ratio are also shown in Table 1.

[0032]

[Table 1]

Example 4 The concentration of SO ₄ ^{2 -} ion in the aging mother liquor in Example 1 was 100 ppm, 200 ppm, 500 ppm, 1000 ppm and 1500 ppm, respectively.
, Adjusted to 2000 ppm, aged for 4 hours as in Example 1,
The aging treatment was performed four times. Table 2 shows the obtained barium sulfate sizes as average particle sizes.

[0034]

[Table 2]

COMPARATIVE EXAMPLE 4 0.81 l of an aqueous barium nitrate solution having a concentration of 0.4 mol / l was maintained at 80 ° C., and 0.037 l of a 8.73 mol / l sulfuric acid solution was added dropwise over 30 minutes while stirring to react. Thereafter, the reaction slurry was divided into two minutes, and one was heated and aged at 90 ° C. for 2 hours and the other was heated and aged at 90 ° C. for 20 hours to obtain barium sulfate. The obtained barium sulfate particles had a spherical shape as shown in an electron micrograph of FIG.

Comparative Example 5 A general commercial product, barium sulfate, was used for comparison.

[Measurement and evaluation of physical properties] The barium sulfates of Examples 1 and 3 and Comparative Examples 4 and 5 were evaluated for the average particle size, appearance,
The physical properties such as the average particle size, the X-ray intensity ratio, the milky effect and the like were measured, and the results are summarized in Table 3.

The properties were measured by the following methods. (1) Average particle diameter Coulter counter device [Coulter Electronics Inc., T-II type, aperture size 30μm] was used to measure the particle size distribution was expressed with a its median D _50. (2) Appearance and Average Particle Size The shape, surface condition and size of the primary particles of the barium sulfate sample were observed and measured with a scanning electron microscope. (3) X-ray intensity ratio The crystal plane of the barium sulfate sample was identified by X-ray diffraction,
The linear intensity ratio (I) = I _{[200 ]} / I _[021] was determined. (4) Milky White Effect 100 parts by weight of vinyl chloride beads, 50 parts by weight of DOP, 1 part by weight of barium stearate, and 1 part by weight of zinc stearate, 100 parts by weight of a barium sulfate sample were added.
Parts by weight and kneaded with a hot roll at 160 ° C.
It was molded to a thickness of 1 mm by a hot press at 70 ° C. to prepare a milky plate. This milky board is used in accordance with JIS K7105,
The total light transmittance and the parallel light transmittance were measured using a meter [HGM2DD, manufactured by Suga Test Instruments Co., Ltd.].

[0039]

[Table 3]

From the results shown in Table 3, all of the aged barium sulfates according to the present invention have a flat shape with an average particle diameter of 2.0 μm or more, and have an X-ray intensity ratio (I) of 0.2 or more and a total light transmittance of 0.2% or more. It was confirmed that it exhibited an excellent opalescent effect of more than 95% and a parallel transmittance equal to or lower than that of the spherical particles of the comparative example.

[0041]

As described above, according to the present invention, there is provided a barium sulfate pigment having unique particle properties different from conventional barium sulfate pigments and excellent in milky effect, and a method for industrially and inexpensively producing the same. can do. Therefore, it is expected to be useful as an extender for milky white resin moldings especially for lighting equipment and optical equipment.

[Brief description of the drawings]

FIG. 1 is a graph showing a change in average particle diameter with respect to the number of additions of aged barium sulfate in Examples.

FIG. 2 is an electron micrograph (5,000-fold magnification) showing the particle structure of barium sulfate A used in Example 1.

FIG. 3 is an electron micrograph (5,000-fold magnification) showing the particle structure of barium sulfate B used in Example 1.

FIG. 4 is an electron micrograph (5,000-fold magnification) showing the particle structure of barium sulfate aged under the condition of one addition in Example 1.

FIG. 5 is an electron micrograph (5,000-fold magnification) showing the particle structure of barium sulfate aged under the conditions of four additions in Example 1.

FIG. 6 is an electron micrograph (5,000-fold magnification) showing the particle structure of barium sulfate aged under the condition of eight additions in Example 3.

FIG. 7 is an electron micrograph (5,000-fold magnification) showing the particle structure of barium sulfate aged for 20 hours in Comparative Example 4.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-48-14598 (JP, A) JP-A-53-49025 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C01F 11/46 C08K 3/30

Claims (3)

(57) [Claims] 1. Barium sulfate crystal particles having a total light transmittance of 90% or more, an average particle size of 2.0 μm or more, and an X-ray intensity ratio (I) = I _[200] / I _[021] , I _[200] and I _[021] are the [200] face of barium sulfate and [02]
1] The barium sulfate pigment is characterized in that the particle surface has a flattened shape with a smooth and rounded particle surface, which represents the diffraction line intensity of the surface] in the range of 0.15 to 0.50. 2. A method for growing grains by heating and aging barium sulfate with a mineral acid, wherein the barium sulfate particles are initially aged using a suspension of barium sulfate particles as a base material, and thereafter barium sulfate finer than the base material is obtained at least once. A method for producing a barium sulfate pigment, characterized by additional aging as described above. 3. A suspension of barium sulfate particles, SO ₄ ^{2 -}
The method for producing a barium sulfate pigment according to claim 2, wherein the ion concentration is 200 ppm or more.