JPH0555179B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to an aqueous dispersion stabilizer for fine-particle silica powder. More specifically, it has good dispersibility and does not produce sediment or hard cake even when stored for a long time.
This invention relates to an aqueous dispersion stabilizer for fine silica powder with good redispersibility. [Prior art and problems] Particulate silica is an industrial byproduct obtained by collecting dust from gases generated during the production of ferrosilicon and silicon metal, and its uses include concrete admixtures, plastic fillers, and pesticide binders. etc. However, fine particle silica generally has an average particle size of about 0.1 μm, and handling thereof is not necessarily easy. In particular, environmental pollution and silicosis due to the scattering of dust are serious problems and are hindering the development of applications. In order to solve this problem, a method is known in which fine-particle silica powder is made into a slurry (Japanese Patent Laid-Open No. 111963/1983). However, this method has the disadvantage that long-term stability and redispersibility are poor, and furthermore, the sediment forms a hard cake. [Means for Solving the Problems] The present invention has been made to improve the above-mentioned drawbacks of the conventional technology, and it has good dispersibility of fine silica particles and does not produce sediment or hard cake even after long storage. The present invention provides an aqueous dispersion stabilizer for fine-particle silica powder that does not form and has good redispersibility. The fine particle silica referred to in the present invention is a by-product during the production of silicon metal, ferrosilicon, etc.
It contains 70% or more and has a specific surface area of 100,000 to 300,000 cm ² /g. Generally, a surfactant called a dispersant is used to produce a suspension (slurry) of fine powder.
Due to its dispersion action, the fine powder becomes a dispersion system in which it is stably suspended in water. However, this dispersion system is inherently thermodynamically unstable, and if left for a long time, the fine powder particles will settle. In general, the better the dispersibility, the more closely packed the sedimented particles are, resulting in a hard cake that is harder to redisperse. Therefore, if the dispersion system is used immediately after making it, the dispersant has a very good effect, but if it is stored for a long time and used, a hard cake will be generated and it should not be reused. A problem arises in that the dispersibility is poor. Conventional dispersants for fine-particle silica have a strong effect of loosening the secondary particles of fine powder into primary particles and preventing the loosened particles from agglomerating again.
It tends to form a hard cake after sedimentation and is not fully satisfactory when stored for a long time, so improvements have been desired. The present inventors conducted extensive research to find a dispersion stabilizer that has a dispersion effect on fine-particle silica and prevents the precipitation from forming a hard cake. As a result, the present inventors discovered a dispersion stabilizer that has both of the above-mentioned effects, and the present invention has been made. completed. That is, the present invention consists of a copolymer of (meth)acrylic acid and (meth)acrylic acid ester or a salt thereof, or a combination thereof with one or more selected from β-naphthalene sulfonic acid formalin condensate and polyvinyl alcohol. The present invention provides an aqueous dispersion stabilizer for fine-particle silica powder. The copolymer of (meth)acrylic acid and (meth)acrylic acid ester used in the present invention or a salt thereof is generally synthesized by copolymerizing the monomer components using a polymerization initiator. Polymerization is carried out in a solvent. The solvent used at this time includes water, lower alcohols such as isopropyl alcohol, and hydrocarbons such as toluene. Typical polymerization initiators used in water-based polymerizations are water-soluble polymerization initiators such as ammonium or alkali metal persulfates or hydrogen peroxide. For polymerization using a solvent other than water, peroxides such as benzoyl peroxide and azo compounds such as azobisisobutyronitrile are used as polymerization initiators. Molecular weight distribution can be controlled by controlling the amount of polymerization initiator,
This is carried out by combining the polymerization temperature, solvent concentration, amount of chain transfer agent, etc. The polymerization temperature is determined appropriately depending on the type of solvent, amount of polymerization initiator, etc., but is generally 0 to 150°C.
℃ range. The copolymer thus obtained can be used as it is as a dispersion stabilizer for fine particle silica, but if necessary, it can be further neutralized with an alkaline substance before use. Examples of alkaline substances include hydroxides, chlorides, and carbonates of monovalent metals and divalent metals, ammonia, organic amines, and the like. According to the present invention, it has been found that the above copolymer (salt) having a specific molecular weight distribution provides excellent effects. In the present invention, the molecular weight distribution of a compound is determined by gel permeation chromatography using polyacrylic acid as a reference material. It is necessary that the molecular weight is 10 to 90% by weight, the molecular weight of 10,000 to less than 25,000 is 10 to 90% by weight, and the molecular weight of 25,000 or more is 30% by weight or less. If the molecular weight is lower than the above molecular weight distribution, the dispersion effect of fine silica powder will be excellent, but the effect of preventing hard cake formation will be weakened.If the molecular weight is higher than the molecular weight distribution above, the agglomeration effect on the powder will be noticeable and the dispersion effect will be reduced. It is difficult to obtain the desired effect. The amount of the dispersion stabilizer used according to the present invention is preferably 0.01 to 2 percent by weight based on the particulate silica powder. The dispersion stabilizer of the present invention may be used alone as the above-mentioned copolymer (salt), but one type selected from β-naphthalene sulfonic acid formalin condensate as another dispersant, or polyvinyl alcohol as a stabilizer Or, a combination of two or more types exhibits more excellent effects. When using the dispersion stabilizer of the present invention, any dispersion equipment such as an attritor, sand mill, roll mill, ball mill, homogenizer, mixer, etc. may be used. [Effects of the Invention] According to the present invention, there is provided an aqueous dispersion stabilizer in which fine particle silica has good dispersibility, does not produce sediment or hard cake even when stored for a long time, and has good redispersibility. By using an aqueous dispersion stabilizer,
It becomes possible to form fine-particle silica powder into a slurry, and its handling becomes extremely easy. The resulting slurry of particulate silica is used as a concrete admixture.
It can be used for applications such as fertilizer coating materials, cement additives, gypsum additives, firebrick additives, etc., and exhibits excellent effects. [Examples] The present invention will be explained in detail below with reference to Examples, but the present invention is not limited thereto. Example 1 Micropoz (silica hume manufactured by Norsem Cement, Norway, specific gravity 2.10, specific surface area 20000 m ² /Kg, silica content 91%) was used as fine silica powder.
was used. 1000 g of fine silica particles were added to 500 ml of an aqueous solution containing a dispersion stabilizer, stirred with a spatula, and then mixed for 10 minutes with a homogenizer (manufactured by Tokushu Kiki Kogyo Co., Ltd.) to obtain a dispersion. The viscosity of this dispersion is B
After measuring with a type viscometer, put it into a 50ml emulsification test tube,
The dispersion stability was evaluated after 30 days and 90 days after being left in a constant temperature room at 20°C. The dispersion stability was evaluated after 30 and 90 days by qualitatively determining the presence or absence of sediment, the hardness of the sediment, and the ease of redispersibility. Presence or absence of sediment ○: No sediment △: Slight sedimentation ×: Hardness and redispersibility of sediment that has settled by 50% or more ○: Disperses when the supernatant is stirred △: Soft and easy to use with a spatula The copolymer () of acrylic acid and methyl acrylate used in the experiment was synthesized by the following method. In a glass reaction vessel equipped with a thermometer, stirrer, dropping funnel, gas inlet tube and reflux condenser, add 200 ml of water.
The inside of the reaction vessel was purged with nitrogen while stirring, and heated to the boiling point under a nitrogen atmosphere. Next, a mixture consisting of 160 parts of acrylic acid and 40 parts of methyl acrylate, an aqueous solution of 4 parts of ammonium persulfate and 32 parts of water, and an aqueous solution of 8 parts of 2-mercaptoethanol and 40 parts of water were added over 90 minutes (at 75°C), and then A solution of 1 part ammonium persulfate in 8 parts water was added over 90 minutes. After the addition was complete, 50 parts of hydrogen peroxide was added and the temperature was maintained at the boiling point for 120 minutes to complete the polymerization. After that, neutralize with aqueous caustic soda solution (neutralization degree
0.85 to acrylic acid) copolymer aqueous solution was obtained. The molecular weight distribution of the obtained copolymer salt (2) was as shown in the following table.

[Table] The amount of dispersion stabilizer added is 0.25 per particulate silica.
Weight percent (as solids) was added. The pH of the dispersion liquid during the standing period was controlled with acid to be in the range of 6.0 to 7.0. The evaluation results are shown in Table-1.

【table】

[Table] From the results in Table 1, the additive-free dispersion of Experiment No. 1 had an extremely high viscosity of 7340 poise, and also produced sediment and poor dispersion stability. In Experiment No. 2 in which the dispersant β-naphthalene sulfonic acid formalin condensate was added, an effect of reducing the viscosity of the dispersion liquid was observed, but sediment was formed and stability was poor. In Experiment No. 3, in which polyvinyl alcohol as a stabilizer was added, precipitation was less likely to occur and stability was improved, but the viscosity of the dispersion increased and was impractical. Compared to these comparative examples, in experiments No. 4 to No. 7 in which the dispersion stabilizer according to the present invention was added, the effect of reducing the viscosity of the dispersion and stabilizing the dispersion was remarkable, and the viscosity was low and the dispersion stabilized for 90 days. The dispersion showed excellent dispersion stability with no precipitation. Example 2 A dispersion of fine silica powder was produced in the same manner as in Example 1, and its dispersion stability was evaluated. The following samples with different molecular weight distributions were synthesized as dispersion stabilizers. ●Sample L Water was poured into a glass reaction vessel equipped with a thermometer, stirrer, dropping funnel, gas inlet tube, and reflux condenser.
After charging 200 parts, the inside of the reaction vessel was purged with nitrogen while stirring and heated to 75°C under a nitrogen atmosphere. Next, 200 parts of acrylic acid and 4 parts of ammonium persulfate,
Aqueous solution of 50 parts water and 8 parts mercaptoethanol
50 parts of water was added over 90 minutes (75°C),
Additionally, 1 part of ammonium persulfate dissolved in 10 parts of water was added over 90 minutes. After the addition was completed, 50 parts of hydrogen peroxide was added and the temperature was maintained at the boiling point for 120 minutes to complete the polymerization. After that, neutralize with aqueous caustic soda solution (α
=0.7) An aqueous polymer solution was obtained. The molecular weight distribution of this sample was determined by gel permeation chromatography. Molecular weight less than 500; 3 weight percent; 500 to less than 10,000; 64 weight percent; 10,000 to less than 25,000; 31 weight percent; 25,000 or more; 2 weight percent. However, the amount of 2-mercaptoethanol was 20 parts. The molecular weight distribution of this sample is as follows,
This sample has a small amount of molecular weight 10,000 to 25,000. Molecular weight less than 500; 9 weight percent; 500 to less than 10,000; 84 weight percent; 10,000 to less than 25,000; 6 weight percent; 25,000 or more; 1 weight percent ●Sample N A polymer was obtained in the same manner as Sample L. However, the amount of 2-mercaptoethanol was 3 parts. The molecular weight distribution of this sample is as follows,
This is a sample with many molecules having a molecular weight of 25,000 or more. Molecular weight less than 500; 1 weight percent 〃 500 to less than 10,000; 17 weight percent 〃 10,000 to less than 25,000; 47 weight percent 〃 25,000 or more; 35 weight percent ●Sample O A copolymer was obtained in the same manner as Sample L. However, the monomers were 140 parts of acrylic acid and 60 parts of methyl acrylate. The molecular weight distribution of this sample was as follows. Molecular weight less than 500; 5 weight percent 〃 500 to less than 10,000; 62 weight percent 〃 10,000 to less than 25,000; 32 weight percent Molecular weight 25,000 or more; 1 weight percent ● The same procedure as Sample L was carried out to obtain a copolymer.
However, the monomers were 140 parts of acrylic acid and 60 parts of methyl acrylate. Also, 2-mercaptoethanol was made into 20 parts. The molecular weight distribution of this sample is as shown below, and the sample has a small portion with a molecular weight of 10,000 to 25,000. Molecular weight less than 500; 10 weight percent; 500 to less than 10,000; 85 weight percent; 10,000 to less than 25,000; 4 weight percent; 25,000 or more; 1 weight percent ●Sample Q A copolymer was obtained in the same manner as Sample L.
However, the monomers were 140 parts of acrylic acid and 60 parts of methyl acrylate. In addition, 2-mercaptoethanol was added to 3 parts. The molecular weight distribution of this sample is as shown below, and most of the samples have a molecular weight of 25,000 or more. Molecular weight less than 500; 1 weight percent 〃 500 to less than 10,000; 15 weight percent 〃 10,000 to less than 25,000; 46 weight percent 〃 25,000 or more; 38 weight percent The amount of dispersion stabilizer added is based on the fine particle silica powder.
0.25 weight percent (solid content). The evaluation results are shown in Table-2.

[Table] From the results in Table 2, the dispersions of Experiments No. 1 and No. 4 using Samples L and O had low viscosity and did not produce sediment even after standing for 90 days, and were extremely excellent. It showed dispersion stability. On the other hand, the dispersions of Experiments No. 2 and No. 5 using Samples M and P with a small amount of molecular weights from 10,000 to 25,000 showed a reduction in viscosity, but produced sediment and had poor stability. Samples N and Q with more molecular weights of 25,000 or more
The dispersion liquids of Experiments No. 3 and No. 6, which were used, were stable but had extremely high viscosity.

Claims (1)

[Claims] 1. An aqueous dispersion stabilizer for fine-particle silica powder consisting of a copolymer of (meth)acrylic acid and (meth)acrylic acid ester or a salt thereof, wherein the copolymer or salt thereof has the following molecular weight distribution: . Molecular weight less than 500; 30 weight percent or less Molecular weight 500 to less than 10,000; 10 to 90 weight percent Molecular weight 10,000 to less than 25,000; 10 to 90 weight percent Molecular weight 25,000 or more; 30 weight percent or less2 (meth)acrylic acid and (meth)acrylic acid Fine particle silica powder consisting of an ester copolymer or a salt thereof, and one or more selected from β-naphthalene sulfonic acid formalin condensate and polyvinyl alcohol, and the copolymer or salt thereof has the following molecular weight distribution: Aqueous dispersion stabilizer. Molecular weight less than 500; 30 weight percent or less Molecular weight 500 to less than 10,000; 10 to 90 weight percent Molecular weight 10,000 to less than 25,000; 10 to 90 weight percent Molecular weight 25,000 or more; 30 weight percent or less