JP5660135B2 - Drying shrinkage reducing agent for ceramic molding and method for reducing drying shrinkage of ceramic molded body - Google Patents

Description

  The present invention relates to a drying shrinkage reducing agent for ceramic molding which is effective for reducing shrinkage in a drying process particularly in water-based ceramic molding and obtaining a highly accurate molded body with good reproducibility, and a method for drying a ceramic molded body using the same. About.

As a general molding method of ceramic, there are various methods such as extrusion molding, injection molding, and casting molding. For example, with regard to extrusion molding, it is a method of molding by applying pressure to a kneaded composition (hereinafter also referred to as a kneaded material) kneaded with ceramic powder, a binder, water, etc., and having a constant cross section. It is suitable for efficiently producing a product having a shape such as a rod or pipe. Filters, catalyst carriers, etc. are also manufactured by this extrusion molding method, but in recent years, highly accurate extrusion molding has been strongly demanded to improve these performances, and the dimensional stability and pores of the molded body have been strongly demanded. High reproducibility is also required for the compact properties such as rate.
As a general method for producing a ceramic, a molding process for obtaining a molded body by extrusion or the like, a drying process for irradiating the molded product with hot air or microwaves, and a firing process for firing organic substances such as a binder are performed. The method of obtaining a ceramic product is mentioned. As a means for improving the molding accuracy described above, there is a method of improving the fluidity of the clay by increasing the moisture content of the binder phase. In this case, the molding is performed because a large amount of water evaporates in the drying process. The degree of shrinkage of the body increases, causing problems such as deviating from the size of the molded body suitable for the production line.

  A method for effectively reducing the shrinkage at the time of drying the ceramic compact has not been proposed. In order to reduce the shrinkage, it is effective to reduce the amount of water used for kneading as much as possible. However, in this case, the viscosity of the kneaded material becomes high, causing a problem in operability. On the other hand, Patent Document 1 discloses a method of adding a dispersant composed of a specific fatty acid salt to reduce the viscosity of the clay, but the moldability is insufficient and it is difficult to obtain a smooth molded body. There was a problem. In addition, Patent Document 2 discloses a polyoxyalkylene unit-containing dispersant having excellent lubricity of a molded product, but a large amount of dispersant is necessary to sufficiently reduce the viscosity of the clay, and this is a binder. In order to inhibit the interaction between molecules, the shape retention and the strength of the molded body may be greatly reduced.

JP 2002-293645 A JP 2009-46385 A

  The object of the present invention is effective in suppressing shrinkage due to drying of a molded product obtained by extrusion molding, etc., in order to obtain a highly accurate molded product with good reproducibility, and also affects characteristics such as porosity. It is to provide a drying shrinkage reducing agent that does not affect the temperature, and a method for reducing dry shrinkage of a ceramic molded body using the same.

  As a result of intensive studies in view of the above-mentioned problems, the present inventors have an average particle diameter of 0.01 to 10 μm in a saturated and swollen state with ion-exchanged water, and a water absorption of ion-exchanged water at normal pressure is 0.1 to The inventors have found that it is effective to use polymer fine particles of 60 mL / g at the time of ceramic molding, and completed the present invention.

The present invention is as follows.
1. The average particle diameter in the saturated swollen state with deionized water is 0.01 to 10 [mu] m, water absorption of ion-exchanged water at normal pressure is I 0.1~60mL / g der, neutralized with an alkali acidic A drying shrinkage reducing agent for forming a ceramic, comprising polymer fine particles having a functional group of 2.0 mmol / g or less .
2. Drying shrinkage-reducing agent according to the above 1, characterized in that one obtained by polymerizing the polymer microparticles consists only Roh anion unsaturated monomer monomer mixture.
3. 3. The drying shrinkage reducing agent according to 2 above, wherein the nonionic unsaturated monomer mixture contains a monomer having one or more functional groups selected from a hydroxyl group, an amide group, and an oxyethylene group.
4). A method for reducing drying shrinkage of a ceramic molded body using the drying shrinkage reducing agent according to any one of 1 to 3 above.
5. 5. The method for reducing drying shrinkage of a ceramic molded article according to 4 above, further comprising using a ceramic pore forming agent.

  By using the drying shrinkage reducing agent for ceramic molding containing the polymer fine particles of the present invention at the time of ceramic molding, the fluidity of the kneaded material is increased, so that extrusion molding or the like is possible even with a small amount of water. Further, it does not affect the porosity and the like of the obtained molded body. For this reason, drying shrinkage in the drying step after molding is suppressed, and a highly accurate molded body can be obtained with good reproducibility.

It is a figure which shows the apparatus used for the measurement of the water absorption amount of a polymer microparticle.

The present invention relates to a drying shrinkage reducing agent for ceramic molding, and specifically has an average particle diameter of 0.01 to 10 μm in a state of saturated swelling with ion-exchanged water, and the water absorption amount of ion-exchanged water at normal pressure ceramic There where I 0.1~60mL / g der, acidic functional groups neutralized with alkali using drying shrinkage-reducing agent and this ceramic formed body containing polymer microparticles or less 2.0 mmol / g The present invention relates to a method for reducing drying shrinkage of a molded body.
The drying shrinkage reducing agent of the present invention is kneaded with ceramic powder, a binder, water and the like and used in ceramic molding such as extrusion molding.
Hereinafter, the drying shrinkage reducing agent for a ceramic molded body of the present invention and the method for reducing the drying shrinkage of a ceramic molded body using the dry shrinkage reducing agent of the present invention will be described in detail. In the present specification, acrylic acid or methacrylic acid is represented as (meth) acrylic acid.

  The polymer fine particles used in the present invention are required to have an average particle size in the range of 0.01 to 10 μm, preferably 0.1 to 10 μm, in a state of saturated swelling with ion exchange water. Range. When the average particle size exceeds 10 μm, the pore characteristics of the obtained ceramic molded body may be affected. On the other hand, the average particle size of the polymer fine particles is generally not less than 0.01 μm.

  Further, the water absorption amount of the polymer fine particles at normal pressure needs to be in the range of 0.1 to 60 mL / g, preferably in the range of 0.1 to 20 mL / g. When the water absorption is less than 0.1 mL / g, the moisture content of the binder phase cannot be sufficiently reduced, and thus the drying shrinkage reduction effect is insufficient. On the other hand, when the amount of water absorption exceeds 60 mL / g, the amount of water absorption of the polymer fine particles becomes too large, so that the water cannot be mixed without increasing the amount of water used for kneading the ceramic, and as a result, drying shrinkage may not be reduced.

The effect when the drying shrinkage reducing agent according to the present invention is used is presumed to be due to the following mechanism.
First, since it has a fine particle shape, it has a function of improving the fluidity of the clay. For this reason, extrusion or the like is possible even with a small amount of water, and shrinkage during drying is reduced.
Furthermore, since the polymer fine particles of the present invention have a water absorption property, the polymer fine particles arranged in the binder phase absorb water from the nearby binder phase, and as a result, water is unevenly distributed in the binder phase. In the drying process, since the binder as the matrix has relatively little moisture, the shrinkage thereof is suppressed. On the other hand, although the polymer particles that have absorbed water are reduced in volume by drying, voids corresponding to the volume reduction of the polymer particles are formed in the binder phase, so the shrinkage of the entire binder phase is reduced. Is done.

  The polymer fine particles used in the present invention preferably have an acidic functional group neutralized with an alkali of 3.0 mmol / g or less, and more preferably 2.0 mmol / g or less. Here, the acidic functional group is introduced by using a vinyl monomer having an acidic group such as carboxylic acid (salt) or sulfonic acid (salt). Alternatively, the polymer can be obtained by using an alkyl ester (meth) acrylate or the like and then saponified with an alkali. If it exceeds 3.0 mmol / g, the water absorption capacity of the polymer fine particles becomes too strong, so that the kneading cannot be performed unless the amount of water used for kneading the ceramic is increased, and as a result, the drying shrinkage may not be reduced.

  Specific examples of the vinyl monomer having an acidic group include carboxyl groups such as (meth) acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, monobutyl itaconic acid, monobutyl maleate, and cyclohexanedicarboxylic acid. A vinyl monomer having a phosphate group such as acid phosphooxyethyl methacrylate, acid phosphooxypropyl methacrylate, and 3-chloro-2-acid phosphooxypropyl methacrylate; 2- (meth) acrylamido-2-methylpropanesulfonic acid, 2-sulfoethyl (meth) acrylate, 2- (meth) acryloylethanesulfonic acid, allylsulfonic acid, styrene Sulfonic acid, vinyl Examples thereof include vinyl monomers having a sulfonic acid group or a phosphonic acid group such as sulfonic acid, allylphosphonic acid and vinylphosphonic acid, or (partial) alkali neutralized products thereof, and one or more of these. Can be used.

  The polymer fine particles used in the present invention are preferably obtained by polymerizing a monomer mixture consisting essentially of only a nonionic unsaturated monomer. When the polymer fine particles are composed of only the nonionic unsaturated monomer, unevenness in drying in the drying process is unlikely to occur, and appearance defects (warping, cracks, etc.) of the final product can be suppressed. Further, “substantially” means that a monomer having an ionic group such as an acidic group or a cationic group is not intentionally used.

Specific examples of the nonionic unsaturated monomer include hydroxyl group-containing monomers such as 2-hydroxyethyl (meth) acrylate and 2-hydroxypropyl (meth) acrylate; (meth) acrylamide, N, N-dimethyl ( Amide group-containing monomers such as (meth) acrylamide, N-isopropylacrylamide, N-methylol (meth) acrylamide, N-alkoxymethyl (meth) acrylamide; polyethylene glycol mono (meth) acrylate, methoxypolyethylene glycol mono (meth) acrylate Oxyethylene group-containing monomers such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate and other (meth) acrylic acid esters having 1 to 3 carbon atoms; methoxyethyl (meth) acrylate, glycidyl (Meta Acrylate, N, N-dimethylaminoethyl (meth) acrylate can be exemplified, and can be used alone or in combination of two or more thereof.
Among these, a hydroxyl group-containing monomer, an amide group-containing monomer and an oxyethylene group-containing monomer are excellent in polymerizability and solubility in water, and are capable of efficiently obtaining polymer fine particles rich in hydrophilicity. preferable.

  In the present invention, it is preferable to use a crosslinking agent in addition to the unsaturated monomer described above.

The crosslinking agent may be any vinyl monomer having at least two radically polymerizable groups with the nonionic unsaturated monomer. Specific examples include polyethylene glycol di (meth) acrylate, polypropylene glycol. Di- or tri- (meth) acrylates of polyols such as di (meth) acrylate, glycerin tri (meth) acrylate, trimethylolpropane tri (meth) acrylate, tri (meth) acrylate modified trimethylolpropane ethylene oxide, methylene bis ( Bisamides such as (meth) acrylamide, divinylbenzene, and allyl (meth) acrylate can be used, and one or more of these can be used.
In addition, glycidyl (meth) acrylate, ethylene glycol diglycidyl ether, N-methylol acrylamide, and the like may be a crosslinking agent of a type that is reacted with a functional group such as a carboxyl group or a hydroxyl group after polymerization.

  Among these, as the polyfunctional vinyl monomer, polyethylene glycol di (meth) acrylate and methylenebis (meth) acrylamide are excellent in solubility in a mixed solution of the hydrophilic hydrophilic vinyl monomer and water, and have a high crosslinking density. It is advantageous and preferably used when increasing the amount used to obtain polyethylene glycol, and particularly preferred is polyethylene glycol di (meth) acrylate.

  The proportion of the crosslinking agent used may vary depending on the type of vinyl monomer used, but if the polymer fine particles require crosslinking properties, they are contained in an amount of 0.01 to 90 mol% in all monomers. It is preferable that it is 0.05 to 50 mol%. If it is 0.01 mol% or more, the strength of the fine particles is secured, and if it is 90 mol% or less, sufficient water absorption performance can be obtained.

As a method for producing the polymer fine particles of the present invention, a known polymerization method such as reverse phase emulsion polymerization, dispersion polymerization, reverse phase suspension polymerization, precipitation polymerization or bulk polymerization can be used.
When the polymer is obtained as an agglomerate or a lump such as a precipitation polymerization or a lump polymerization, it may be pulverized with an electric mill, pin mill, jet mill or the like to form fine particles.
Dispersion polymerization and reverse phase suspension polymerization are preferred in that the particle size distribution is narrow and powdery polymer fine particles can be obtained. Dispersion polymerization is particularly preferable in that pore formation can be more strictly suppressed by using monodispersed fine particles.

Here, the “dispersion polymerization method” in this specification means “a vinyl monomer is dissolved in the presence of a dispersion stabilizer, the vinyl monomer and the dispersion stabilizer are dissolved, but a polymer produced by polymerization is "Method of polymerizing in a solvent that does not substantially dissolve".
In the present invention, a hydrophilic solvent is used as “a solvent that dissolves the vinyl monomer and the dispersion stabilizer but does not dissolve the polymer to be produced”. The polymer produced by dispersion polymerization is in the form of fine particles and dispersed in a hydrophilic solvent.

In the present invention, a hydrophilic organic solvent (a hydrophilic organic solvent not containing water) may be used as the hydrophilic solvent, or a mixed solvent of a hydrophilic organic solvent and water may be used. . At that time, as the hydrophilic organic solvent, those having a solubility in water at 20 ° C. of 5 g / 100 ml or more are preferably used.
Specific examples of the hydrophilic organic solvent described above include monoalcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, sec-butyl alcohol, and tetrahydrofurfuryl alcohol; Polyhydric alcohols such as ethylene glycol, glycerin, diethylene glycol; ether alcohols such as methyl cellosolve, cellosolve, isopropylpyro cellosolve, butyl cellosolve, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether; Ketones such as acetone and methyl ethyl ketone; S such as methyl acetate and ethyl acetate Ethers such as tetrahydrofuran; le such dimethylformamide, dimethyl sulfoxide and the like. Only one type of hydrophilic organic solvent may be used, or two or more types may be used in combination.
An appropriate hydrophilic organic solvent is selected from the hydrophilic organic solvents described above according to the type of vinyl monomer used for polymerization, the type of polymer to be produced, and the like.

In the present invention, as the hydrophilic solvent, a mixed solvent of water and alcohol, and among them, a mixed solvent of water and one or more of lower alcohols such as methanol, ethanol, and isopropyl alcohol is more preferably used. When a mixed solvent of water and the alcohol is used as the hydrophilic solvent, particles of polymer fine particles to be generated are prepared by adjusting the mixing ratio of water and alcohol according to the type and composition of the vinyl monomer. The diameter, particle size distribution, molecular weight, etc. can be easily controlled, and the risk of ignition, explosion, etc. can be reduced, and the burden on the environment is small.
In particular, as a hydrophilic solvent, when using a mixed solvent of water and methanol, among them, a mixed solvent having a water: methanol mass ratio of 10:90 to 50:50, more preferably 20:80 to 40:60, This is more preferable because polymer fine particles having a smaller particle size and a narrow particle size distribution can be produced smoothly.

  The amount of the hydrophilic solvent used in the dispersion polymerization of the vinyl monomer is preferably 1 to 50 times by mass and more preferably 2 to 10 times by mass with respect to the total amount of the vinyl monomer. If the amount of the hydrophilic solvent used is too small, the polymerization stability at the time of dispersion polymerization may be poor, and the particle size distribution tends to be widened. On the other hand, if the amount of the hydrophilic solvent used is too large, the polymer fine particles may not be collected. The rate tends to decrease and productivity tends to deteriorate.

As the polymerization initiator for the dispersion polymerization of the vinyl monomer, a polymerization initiator usually used in radical polymerization can be used and is not particularly limited. Among them, a radical polymerization initiator that is soluble in a hydrophilic solvent is preferably used. Examples of the radical polymerization initiator that can be used in the present invention include t-butyl peroxypivalate, t-butyl peroxy-2-ethylhexanoate, di-t-butyl peroxide, benzoyl peroxide, and lauroyl peroxide. , Organic peroxides such as orthochlorobenzoyl peroxide, orthomethoxybenzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide; azobisisobutyronitrile, azobiscyclohexacarbonitrile, azobis (2,4- Azo compounds such as dimethylvaleronitrile), 2,2′-azobis (2-amidinopropane) dihydrochloride (V-50), 4,4′-azobis (4-cyanovaleric acid) (V-501); Persulfide compounds such as potassium persulfate, and one of these It can be used two or more kinds.
Among these, as the polymerization initiator, t-butyl peroxypivalate and azobis (2,4-dimethylvaleronitrile) are preferably used from the viewpoint that polymer fine particles having a narrow particle size distribution can be produced with high productivity.

  The amount of the polymerization initiator used is not particularly limited and can be appropriately determined in consideration of the molecular weight of the polymer fine particles to be produced, the decomposition temperature of the polymerization initiator to be used, and the like. In general, the polymerization initiator is preferably used in an amount of 0.1 to 40 parts by weight, and preferably in an amount of 1 to 10 parts by weight with respect to 100 parts by weight of the total amount of vinyl monomers. More preferred. If the amount of the polymerization initiator used is too small, the yield of the polymer fine particles tends to be low. On the other hand, if the amount of the polymerization initiator used is too large, the polymerization rate becomes too high, making it difficult to perform dispersion polymerization stably.

  The polymerization temperature during the dispersion polymerization is preferably 40 to 80 ° C, and more preferably 45 to 70 ° C. If the polymerization temperature is too low, the polymerization rate of the vinyl monomer will be low and it will be difficult to produce polymer fine particles with good productivity. On the other hand, if the polymerization temperature is too high, aggregation between the produced polymer fine particles will easily occur. In addition, the particle size distribution of the polymer fine particles becomes wide.

  The amount of the dispersion stabilizer used in producing the polymer fine particles by dispersion polymerization of the vinyl monomer is 0.2 to 10% by mass with respect to the total amount of the vinyl monomer used for the dispersion polymerization. Preferably, it is 0.5-5.0 mass%. If the amount of the dispersion stabilizer used is too small, the stability at the time of polymerization is lowered and the produced polymer tends to aggregate. On the other hand, if the amount of the dispersion stabilizer used is too large, the polymer fine particles to be produced are produced. The particle size distribution becomes wider and the size tends to be uneven.

Specific examples of the dispersion stabilizer include a macromonomer type dispersion stabilizer, polyvinyl pyrrolidone, polyvinyl alcohol, and polyacrylic acid.
Among these, it is preferable to use a macromonomer type dispersion stabilizer. The macromonomer type dispersion stabilizer has a radically polymerizable unsaturated group at the end of a polymer derived from a vinyl monomer.

A preferred macromonomer as the macromonomer-type dispersion stabilizer is a compound derived from the formula (1); H _{2 at} the end of a polymer derived from a vinyl monomer obtained by radical polymerization of a vinyl monomer at 150 to 350 ° C. At the end of a polymer derived from a macromonomer and / or vinyl monomer having an α-substituted vinyl group represented by C = C (X)-(where X is a monovalent polar group) A macromonomer having an acryloyl group is suitable because of its excellent function as a dispersion stabilizer, and the weight average molecular weight of the macromonomer is preferably 1000 to 30000. The macromonomer is derived from a hydrophilic vinyl monomer. It is preferable to have both a structural unit and a structural unit derived from a hydrophobic vinyl monomer, and the structural unit derived from the hydrophobic vinyl monomer at that time is (meth) acrylic acid. Preferably the structural units derived from prime 8 or more alkyl esters, structural unit derived from a vinyl monomer having a carboxyl group is preferred as the structural unit derived from a hydrophilic vinyl-based monomer.

The polymer fine particles produced by the dispersion polymerization may be used in the form of a dispersion of polymer fine particles while being dispersed in a hydrophilic solvent, or may be used after being separated and recovered from the hydrophilic solvent.
As a method for separating and recovering the polymer fine particles from the hydrophilic solvent, for example, a sedimentation separation method, a centrifugal separation method, a decantation method or the like can be adopted, and further, washing and drying are performed as necessary.

  In addition, when the polymer fine particles of the present invention are obtained by reverse phase suspension polymerization, examples of the hydrophobic organic solvent forming the oil phase (dispersion medium) include aliphatic hydrocarbon solvents having 6 or more carbon atoms, benzene, toluene, Aromatic hydrocarbon solvents such as xylene and ethylbenzene, and silicone solvents such as octamethylcyclotetrasiloxane can be used. In particular, hexane, cyclohexane, and n-heptane have low solubility of vinyl monomers and water. And is preferably used because it can be easily removed after polymerization.

As the initiator used for the reverse phase suspension polymerization, a known initiator such as a thermal decomposition type initiator or a redox type initiator can be used, but a redox type initiator is preferably used. The redox reaction can start polymerization at a low temperature, and the vinyl monomer concentration in the polymerization reaction solution can be increased and the polymerization rate can be increased. It becomes possible to increase the molecular weight.
In addition, the use of a redox initiator that uses an oil-soluble oxidant and a water-soluble reducing agent is particularly preferable because polymer fine particles having a narrow particle size distribution can be obtained without producing aggregated particles.

  As described above, since the hydrophobic organic solvent is used as the continuous phase (oil phase) in the reverse phase suspension polymerization, the oil-soluble oxidant means an oxidant that dissolves in these continuous phases. Further, a dispersion stabilizer may be dissolved or dispersed in the oil phase.

  As the oil-soluble oxidant in the present invention, those having an octanol / water partition coefficient (logPow) of -1.4 or more as defined in Japanese Industrial Standard Z7260-107 and OECDTEST Guideline 107 are preferred, and those having 0.0 or more are more preferred. 1.0 or more is particularly preferable.

  Specific examples include t-butyl hydroperoxide (log Pow = 1.3), di-t-butyl hydroperoxide, t-hexyl hydroperoxide, di-t-amyl peroxide, cumene hydroperoxide (log Pow = 2. 2) Organic peroxides such as dicumyl peroxide (logPow = 5.5), t-butylcumyl peroxide, t-butylperoxypivalate, benzoyl peroxide (logPow = 3.5), lauroyl peroxide Is mentioned. Among these, t-butyl hydroperoxide and cumene hydroperoxide are preferable, and cumene hydroperoxide is particularly preferable.

  As the water-soluble reducing agent, known reducing agents can be used as the reducing agent used in the redox polymerization initiator. Among these, sodium sulfite, sodium bisulfite, and sodium hydrosulfite are preferable, and hydrosulfite is particularly preferable. Sodium. In addition, since these water-soluble reducing agents are gradually deactivated by contact with air, it is preferable to dissolve and add to water several minutes before the desired polymerization start timing.

  When using an oil-soluble oxidant and a water-soluble reducing agent, the uniformity of the particle size of the produced particles becomes higher when the water-soluble reducing agent is supplied to the reactor first and then the oil-soluble oxidant is supplied to the reactor. Therefore, it is preferable. It is more preferable to polymerize by supplying an oil-soluble oxidant within 0.5 to 15 minutes after water-soluble reducing agent is made water-soluble and supply it to the reactor, and supply an oil-soluble oxidant within 1 to 5 minutes. More preferably.

The total amount of the oil-soluble oxidant is preferably supplied to the reactor over a period of 20 seconds to 120 seconds, particularly preferably 20 seconds to 60 seconds.
When the supply time of the oil-soluble oxidant is shorter than 20 seconds, the diffusion does not catch up with the supply of the oxidant, and there is a case where a problem such as occurrence of agglomerates occurs due to local generation of radicals. Yes, not preferred. If it is longer than 120 seconds, the reducing agent is decomposed and consumed by another mechanism, so that a part of the oxidizing agent may remain unreacted in the system. If the oxidizing agent remains unreacted, it is not preferable because it may cause problems such as generation of aggregates in a subsequent azeotropic dehydration step or drying step.
The supply time of the water-soluble reducing agent is not particularly limited, but in general, since the reducing agent is easily decomposed by contact with air or the like, it is preferably supplied within 15 minutes.

The oil-soluble oxidant is preferably supplied to the reactor from a supply port located below the liquid level of the reaction solution. In general, the polymerization catalyst inlet is attached to the upper part of the reactor, and the polymerization catalyst is supplied to the liquid level of the reaction liquid from this inlet in a batch or continuously. A method of supplying the reaction solution through a pipe connected to the catalyst is preferable from the viewpoint of uniform diffusion of the catalyst.
The position of the supply port is not limited as long as it is always immersed in the reaction solution, but it is preferably within ± 1 m from the top or bottom of the stirring blade in the vertical direction, and within ± 50 cm. More preferably.
Examples of the method for supplying the oil-soluble oxidant include a method for supplying the oil-soluble oxidant at a gas pressure of an inert gas such as a pump through a pipe leading to a supply port located below the surface of the reaction solution.

The amount of the polymerization initiator used can be adjusted according to the type of vinyl monomer used, the particle size and molecular weight of the resulting polymer fine particles, etc., but the total amount of vinyl monomers is 100 mol. On the other hand, the amount of the oil-soluble oxidant is preferably 0.001 to 0.15 mol, particularly preferably 0.003 to 0.07 mol.
The ratio of the oil-soluble oxidizing agent and the water-soluble reducing agent is not particularly limited, but the oil-soluble oxidizing agent: water-soluble reducing agent is preferably 1.0: 0.25 to 15.0 in terms of molar ratio, Preferably it is 1.0: 1.0-10.0.
If it is out of the above range, the reaction rate of the monomer is reduced, the chain length of the polymer constituting the particle is shortened, or the catalyst remains even after the completion of the polymerization. May occur.

In the reverse phase suspension polymerization of the present invention, a dispersion stabilizer can be used.
Specific examples of the dispersion stabilizer include macromonomer type dispersion stabilizers, sorbitan fatty acid esters, polyglycerin fatty acid esters, sucrose fatty acid esters, sorbitol fatty acid esters, polyoxyethylene alkyl ethers and other nonionic surfactants.
Among these, it is preferable to use a macromonomer type dispersion stabilizer. The macromonomer type dispersion stabilizer has a radically polymerizable unsaturated group at the end of a polymer derived from a vinyl monomer.

  Further, it is preferable to use a macromonomer type dispersion stabilizer in combination with a relatively hydrophobic nonionic surfactant having an HLB of 3 to 8, such as sorbitan monooleate and sorbitan monopalmitate. Two or more species may be used in combination.

  As the macromonomer type dispersion stabilizer, a macromonomer preferably used in the dispersion polymerization is similarly preferably used.

  In particular, when a hydrophilic polymer fine particle is produced by reverse-phase suspension polymerization of a hydrophilic vinyl monomer using a macromonomer type dispersion stabilizer, a polyfunctional vinyl monomer is used together with a monofunctional compound. It is preferable to use a monomer, whereby hydrophilic cross-linked polymer fine particles having improved strength and shape retention are obtained.

The dispersion stabilizer is preferably added to the polymerization system after being dissolved or uniformly dispersed in a hydrophobic organic solvent which is a dispersion medium (oil phase).
In order to obtain hydrophilic polymer fine particles having a uniform particle size while maintaining good dispersion stability, the amount of the dispersion stabilizer used is 0.1 with respect to a total of 100 parts by mass of the vinyl monomer. It is preferable that it is -50 mass parts, It is more preferable that it is 0.2-20 mass parts, It is still more preferable that it is 0.5-10 mass parts. If the amount of the dispersion stabilizer used is too small, the dispersion stability of the vinyl monomer in the polymerization system and the generated polymer particles will be poor, and the generated polymer particles will aggregate, settle, and the particle size will vary. Is likely to occur. On the other hand, if the amount of the dispersion stabilizer used is too large, the amount of by-product fine particles (1 μm or less) produced may increase.

  The drying shrinkage reducing agent of the present invention is kneaded in a clay together with ceramic powder, a binder, water and the like. A preferred use amount is 0.1 to 10% by mass, more preferably 0.1 to 5% by mass as a proportion of polymer fine particles in the clay. If it is 0.1% by mass or more, the effect of reducing drying shrinkage can be shown, and if it is 10% by mass or less, the interaction between binder molecules is hindered and the shape-retaining property and the strength of the molded product are not greatly reduced. .

  In general, in ceramic molding, a molded body is obtained by various molding methods, and then dehydration is performed by irradiating with hot air or microwaves in a drying process. When the drying reducing shrinkage agent of the present invention is used, shrinkage of the molded product due to the evaporation of moisture in the drying step is reduced.

The drying shrinkage reducing agent of the present invention can be used in combination with a pore forming agent in ceramic molding.
As the pore forming agent, those having the property of disappearing by combustion or thermal decomposition in the decalcification and firing processes are used. Specific examples include fine particles such as coke, wheat flour, starch, foamed resin, polymethyl methacrylate, acrylic copolymer (salt), and polyethylene.
It is possible to obtain a porous ceramic by using a pore-forming agent in combination, and the porous ceramic is used for various filtering materials, catalyst carriers, heat storage bodies, battery sintered substrates, heat insulating materials, and wastewater treatment. Used for microorganisms alone.

  The ceramic in the present invention is not particularly limited as long as it can be molded in an aqueous system. Specific examples include oxide ceramics such as alumina, cordierite, mullite, silica, zirconia, and titania, and non-oxides such as silicon carbide, silicon nitride, aluminum nitride, boron nitride, titanium nitride, and titanium carbide. Mention may be made of ceramics.

  In addition, the binder contained in the ceramic kneaded composition is not particularly limited as long as it is applicable in an aqueous system. Examples include cellulose derivatives such as methylcellulose, hydroxypropylmethylcellulose, and hydroxypropylethylcellulose; synthetic polymer compounds such as polyacrylic acid, polyacrylamide, and polyvinyl alcohol. Among the above, cellulose derivatives are widely used for extrusion molding.

  In addition, the average particle diameter in the saturation swelling state by the ion-exchange water of the polymer fine particle in this specification, and the amount of water absorption say the value measured or calculated | required by the method as described in the term of an Example below.

Hereinafter, the present invention will be specifically described based on examples. In the following description, “part” means part by mass, and “%” means mass%.

Production Example 0: Production of Macromonomer Composition UM-1 The temperature of the oil jacket of a 1000 ml capacity pressurized stirred tank reactor equipped with an oil jacket was kept at 240 ° C.
75.0 parts of lauryl methacrylate (hereinafter referred to as “LMA”) as a monomer, 25.0 parts of acrylic acid (hereinafter referred to as “AA”), 10.0 parts of methyl ethyl ketone (hereinafter referred to as “MEK”) as a polymerization solvent As a polymerization initiator, a monomer mixed liquid adjusted at a ratio of 0.45 part of ditertiary butyl peroxide was charged into a raw material tank.
Start supplying the monomer mixture from the raw material tank to the reactor, and supply the monomer mixture and remove the reaction mixture so that the weight in the reactor is 580 g and the average residence time is 12 minutes. went. The reactor internal temperature was adjusted to 235 ° C., and the reactor internal pressure was adjusted to 1.1 MPa. The reaction mixture extracted from the reactor is decompressed to 20 kPa, continuously supplied to a thin film evaporator maintained at 250 ° C., and discharged as a macromonomer composition from which monomers and solvents are distilled off. . Distilled out monomers and solvents were cooled with a condenser and recovered as a distillate. After the start of the monomer mixture supply, 60 minutes after the reactor internal temperature was stabilized at 235 ° C., the recovery start point was set, and the reaction was continued for 48 minutes to recover the macromonomer composition UM-1. During this time, 2.34 kg of the monomer mixture was supplied to the reactor, and 1.92 kg of the macromonomer composition was recovered from the thin film evaporator. In addition, 0.39 kg of distillate was recovered in the distillate tank.
When the distillate was analyzed by gas chromatography, LMA 31.1 parts, AA 16.4 parts, other solvents, etc. were 52.5 parts with respect to 100 parts of distillate.
From the amount and composition of the monomer mixture, the recovered amount of the macromonomer composition, the recovered amount and composition of the distillate, the monomer reaction rate is 90.2%, and the composition of the macromonomer composition UM-1 The monomer composition ratio was calculated as LMA: AA = 76.0 / 24.0 (mass ratio).

Further, when the molecular weight of the macromonomer composition UM-1 was measured by gel permeation chromatograph (hereinafter referred to as “GPC”) using tetrahydrofuran as an eluent, the weight average molecular weight (hereinafter referred to as “Mw”) in terms of polystyrene was measured. And number average molecular weight (hereinafter referred to as “Mn”) were 3800 and 1800, respectively. Moreover, the density | concentration of the terminal ethylenically unsaturated bond in a macromonomer composition was measured from 1H-NMR measurement of a macromonomer composition. As a result of calculating the terminal ethylenically unsaturated bond introduction rate of the macromonomer composition UM-1 from the concentration of terminal ethylenically unsaturated bonds by 1H-NMR measurement, Mn by GPC, and the constituent monomer composition ratio, 97% Met. The solid content of the heating residue after heating at 150 ° C. for 60 minutes was 98.3%.
In addition, about each raw material, such as a monomer, a polymerization solvent, and a polymerization initiator, the commercially available industrial product was used as it was, without performing processes, such as refinement | purification.

(Production Example 1: Production of polymer fine particles A-1)
For the polymerization, a reactor having a capacity of 2 L, having a stirring mechanism comprising a turbine type stirring blade and two vertical baffles, and further equipped with a thermometer, a reflux condenser with a distillate separator, and a nitrogen introduction tube was used. . The nitrogen introduction pipe is branched into two outside the reactor, and nitrogen can be supplied from one side and a polymerization catalyst can be supplied from the other side using a pump. Further, the nitrogen introduction tube is connected to the reactor wall surface which is almost the same height as the upper end of the stirring blade.
1.4 parts of UM-1 as a dispersion stabilizer in the reactor, 10.0 parts of sorbitan monooleate (trade name “Leodol AO-10” manufactured by Kao Corporation), and n-heptane 400. 3 parts were charged and the oil phase was adjusted by stirring and mixing while maintaining the temperature of the solution at 40 ° C. The oil phase was stirred at 40 ° C. for 30 minutes and then cooled to 20 ° C.
On the other hand, in a separate container, AA 50.0 parts, 40% acrylamide aqueous solution (hereinafter referred to as “40% AMD”) 125.0 parts, polyethylene glycol diacrylate (manufactured by Toagosei Co., Ltd., trade name “Aronix M-243”) ”, 4.3 parts of average molecular weight 425) and 30.0 parts of ion-exchanged water were charged, stirred and uniformly dissolved. Further, while cooling so that the temperature of the mixed solution was kept at 40 ° C. or lower, 35.4 parts of 25% aqueous ammonia was slowly added to neutralize to obtain a monomer mixed solution.

  After setting the rotation speed of the stirrer to 1600 rpm, the prepared monomer mixture was charged into the reactor, and a dispersion in which the monomer mixture was dispersed in the oil phase was prepared. At this time, the internal temperature of the reactor was kept at 20 ° C. Further, oxygen in the reactor was removed by blowing nitrogen into the dispersion. When 1 hour and 30 minutes passed from the preparation of the monomer mixture, an aqueous solution of 0.18 part of hydrosulfite Na and 2.9 parts of ion-exchanged water was added from the inlet provided in the upper part of the reactor. Three minutes later, a solution obtained by diluting 0.039 parts of an 80% solution of cumene hydroperoxide (trade name “Park Mill H80” manufactured by NOF Corporation) with 3.1 parts of n-heptane was pumped through a nitrogen introduction tube. Supplied. The supply was performed for 30 seconds. It was confirmed that the temperature inside the reactor immediately rose from the start of the supply, and the polymerization started. The rise in internal temperature reached a peak in about 30 seconds, and the temperature was 66.0 ° C.

After cooling the reaction liquid to a temperature of 20 ° C., an aqueous solution of 0.05 part of hydrosulfite Na and 1.8 parts of ion-exchanged water was added from the inlet provided at the top of the reactor while stirring. Three minutes later, a solution obtained by diluting 0.016 part of a 69% aqueous solution of t-butyl hydroperoxide (trade name “Perbutyl H”, manufactured by NOF Corporation) with 1.6 parts of ion-exchanged water was added from the same inlet. Added. It was confirmed that the internal temperature rose to 23.6 ° C. and the remaining monomer was polymerized.
Next, the temperature of the oil bath was raised to 130 ° C. to heat the reaction liquid, and water contained in the particles and n-heptane were azeotroped to dehydrate to a dehydration rate of 98%. The obtained dewatered slurry was suction filtered, and the fine particles separated by filtration were washed repeatedly with n-heptane to remove the dispersion stabilizer, and then the solvent was completely volatilized with a dryer to dry the polymer fine particles A-1. A powder was obtained.

(Production Example 2: Production of polymer fine particles A-2)
Polymer fine particles A were prepared in the same manner as in Example 1 except that the monomer aqueous solution composition was 30 parts AA, 175.0 parts 40% AMD, 8.7 parts Aronics M-243, and 21.3 parts 25% aqueous ammonia. -2 dry powder was obtained.

(Production Example 3: Production of polymer fine particles A-3)
For the polymerization, a reactor having a stirring mechanism comprising three receding blades and a vertical baffle, and further equipped with a thermometer, a reflux condenser with a distillate separator, and a nitrogen introduction tube was used. A water bath equipped with a heater and a circulator was used for heating the reactor.
In the reactor, 10 parts of UM-1 as a dispersion stabilizer, 820 parts of MEK as a solvent, azobis (2,4-dimethylvaleronitrile) as a polymerization initiator (trade name “V-65” manufactured by Wako Pure Chemical Industries, Ltd.) 0.50 part was added and dissolved uniformly. Further, 50 parts of AA as a monomer, 125 parts of 40% AMD and 2.0 parts of glycidyl methacrylate (hereinafter referred to as “GMA”) as a cross-linking agent were added, and nitrogen was blown at 100 mL / h for 30 minutes at a stirring rotational speed of 120 rpm. Stir. When the temperature of the reaction solution was raised to 65 ° C. as it was, the reaction solution started to become cloudy and the progress of the polymerization reaction was confirmed. After 2 hours of heating and stirring, 0.20 parts of V-65 was added and heating and stirring was further continued for 3 hours. The water bath was set at 95 ° C to boil the reaction solution, and 450 parts of water / MEK solution was distilled. Left.
The reaction solution was cooled and taken out, and fine particles were collected with a centrifuge and the dispersion stabilizer was removed. The obtained fine particles were heated for 1 hour in an air dryer set at 90 ° C. to obtain a dry powder of polymer fine particles A-3.

(Production Example 4: Production of polymer fine particles A-4)
In a reactor equipped with the same equipment as in Production Example 3, 5.0 parts of polyvinylpyrrolidone (manufactured by Wako Pure Chemical Industries, trade name “K-30”, Mw30000) as a dispersion stabilizer, and 50 parts of ion-exchanged water as a solvent Further, 150 parts of ethanol and 0.50 part of 2,2′-azobisisobutyronitrile (trade name “AIBN” manufactured by Otsuka Chemical Co., Ltd.) as a polymerization initiator were added and dissolved uniformly. Furthermore, 100 parts of acrylamide powder as a monomer and 0.2 part of methylenebisacrylamide (hereinafter referred to as “MBAAm”) as a crosslinking agent were added, and the mixture was stirred for 30 minutes at 120 rpm with stirring at 100 mL / h. When the temperature of the reaction solution was raised to 70 ° C. as it was, the reaction solution began to become cloudy and the progress of the polymerization reaction was confirmed. After continuing heating and stirring for 2 hours, 0.20 part of AIBN was added, and when the mixture was further heated and stirred for 3 hours, the polymerization process was terminated and the mixture was cooled to room temperature.
Fine particles are separated from the reaction solution by centrifugal separation, washed repeatedly with methanol and then with cyclohexane, heated for 1 hour in a ventilator set at 90 ° C. to volatilize the solvent, and polymer fine particles A-4 A dry powder was obtained.

(Production Example 5: Production of polymer fine particles A-5)
Add 250.0 parts of 40% AMD as a monomer, 5.0 parts of MBAAm as a crosslinking agent, 0.01 part of 2,2-dimethoxy-2-phenylacetophenone and 0.10 parts of ammonium persulfate as a polymerization initiator, A 146 mm cylindrical glass container was charged, and nitrogen bubbling was performed for 30 minutes while maintaining the temperature of the aqueous solution at 20 ° C. Thereafter, ultraviolet rays were irradiated from above the reactor using a 100 W black light at an irradiation intensity of 5.0 mW / cm ² for 3 minutes to prepare a sheet-like water-containing crosslinked polymer gel. This gel was dried, crushed, and further finely pulverized with a roll mill and an electric stone mill. The pulverized resin was put into cyclohexane, stirred and allowed to stand, and only the upper layer which became cloudy was collected. The precipitation part removed cyclohexane, was further pulverized with a pin mill, and polymer fine particles A-5 were obtained by repeating the same operation.

(Production Example 6: Production of polymer fine particles A-6)
The monomer aqueous solution composition was 70.0 parts of 2-hydroxyethyl acrylate (hereinafter referred to as “HEA”), 30.0 parts of methoxypolyethylene glycol monoacrylate (manufactured by NOF Corporation, trade name “Blemmer AME-400”), Aronix M- Production was conducted in the same manner as in Production Example 1 except that 243 6.5 parts and pure water 95.0 parts were used, and the stirring speed was lowered to 830 rpm, to obtain polymer fine particles A-6.

(Production Example 7: Production of polymer fine particles B-1)
Manufactured in the same manner as in Production Example 2 except that the stirring rotation speed was lowered to 870 rpm, to obtain polymer fine particles B-1.

(Production Example 8: Production of polymer fine particles B-2)
Manufactured in the same manner as in Production Example 1 except that 2.2 parts of Aronix M-243 was used and the stirring rotation speed was 1660 rpm, polymer fine particles B-2 were obtained.

(Production Example 9: Production of polymer fine particles B-3)
In a 2 L glass reaction vessel equipped with a stirrer, reflux condenser, thermometer, and nitrogen introduction tube, 700.0 parts of methanol, 300.0 parts of water, 100.0 parts of methyl methacrylate (hereinafter referred to as “MMA”) , And 12.0 parts of K-30. Using a meniscus stirring blade having a blade diameter of 11 cm, stirring was performed at a stirring speed of 120 rpm. The temperature inside the reactor was adjusted to 65 ° C. while bubbling nitrogen gas. After confirming that K-30 was completely dissolved and the mixed solution in the reactor was completely transparent and that the inside of the reactor was stable at 65 ° C., the nitrogen gas pipe was pulled up from the reaction solution, The tip was fixed so that it was above the liquid level. Next, 2.0 parts of AIBN was charged to initiate polymerization. Turbidity was generated in the reaction solution within a few minutes after the introduction of AIBN, and the progress of polymerization was confirmed. Six hours after the introduction of AIBN, the reaction solution was rapidly cooled to room temperature to obtain a dispersion of polymer fine particles.
The total amount of the dispersion was filtered through a 300-mesh polynet and allowed to stand until the supernatant became transparent, and the sedimented portion was collected and dried at room temperature to obtain polymer fine particles B-3.

( Comparative Example 1)
A dry shrinkage test of the ceramic extrusion was carried out according to the standard formulation shown in Table 1.
The amounts of talc, kaolin, alumina, aluminum hydroxide, and silica shown in Table 1 were weighed as ceramic raw material powders. To this, 4.6 parts of methylcellulose as a binder was added and dry blended. Furthermore, 0.4 parts of polymer fine particles A-1 were added and further dry blended.
While the above powder mixture was kneaded with a kneader, ion-exchanged water was added little by little. However, even when 33.4 parts of the total amount of water was added, a portion of the kneaded product was still crushed. The kneading was continued by adding 2 parts of water. As the kneading, methylcellulose was dissolved and the current value of the kneader increased, and when it became constant, the kneading was judged to be completed and the kneaded product was taken out. The kneaded product was pushed into a piston and extruded into a columnar shape to obtain a cordierite-type ceramic extruded product having a general dimension of φ15 mm × 50 mm.

<< Evaluation of degree of drying shrinkage >>
The length and diameter of the obtained ceramic extrudate were measured with a vernier caliper and dried by heating in a draft dryer at 110 ° C. for 120 minutes. The size of the molded body after drying was measured in the same manner, and the volume of the molded body before and after drying was calculated. From these values, the dimensional ratio was calculated according to the equation (1) (the closer the dimensional ratio is to 1, the smaller the degree of drying shrinkage of the molded body). The test results are shown in Table 2.

<Evaluation of effect on porosity>
Moreover, after heating up the obtained molded object dried material to 1000 degreeC, it heated up to 1400 degreeC with the temperature increase rate of 50 degreeC / hour. Further, when the temperature reached 1420 ° C., the temperature was maintained, and firing was performed for 4 hours. The porosity of the fired body was measured with a mercury porosimeter. The results are shown in Table 2.

<< Evaluation of dryness >>
Furthermore, the drying property when the ceramic extrudate before drying was dried by combining microwaves and hot air was evaluated.
The dehydration rate was adjusted to 50 to 60% by irradiating an electromagnetic wave of 2.45 GHz and 0.5 kW for 5 minutes, and then heated and dried in a hot air dryer at 110 ° C. for 2 hours to set the dehydration rate to almost 100%. The appearance of the molded body after drying was visually confirmed and evaluated according to the following criteria. The results are shown in Table 2.
○: No noticeable defects on appearance △: Warping is observed ×: Warping and cracks are observed on the surface

( Comparative Example 2 and Examples 1 to 4 )
Except for using A-2 to A-6 for the polymer fine particles, the degree of drying shrinkage, the porosity, and the drying property were evaluated in the same manner as in Comparative Example 1. A-2 to A-6 differed from Comparative Example 1 in that a kneaded product could be obtained satisfactorily with 33.4 parts of water. The test results are shown in Table 2.

(Comparative Examples 3 to 5 )
Except for using B-1 to B-3 for the polymer fine particles, the degree of drying shrinkage, the porosity, and the drying property were evaluated in the same manner as in Comparative Example 1. B-1 and B-3 were able to obtain a kneaded product well with 33.4 parts of water, but B-2 required an additional 14.0 parts of water. The test results are shown in Table 3.

(Comparative Example 6 )
Except that the polymer fine particles were not used, the degree of drying shrinkage, the porosity, and the drying property were evaluated in the same manner as in Comparative Example 1. However, it was necessary to add 8.0 parts of water during kneading.
The test results are shown in Table 3.

The analysis conditions (1) to (3) of the polymer fine particles in the above examples are as described below.
(1) About 1 g of a solid content measurement sample was weighed (a), then the residue after drying for 60 minutes at 150 ° C. in an airless dryer was measured (b), and calculated from the following formula. A weighing bottle was used for the measurement. Other operations were in accordance with JIS K 0067-1992 (chemical product weight loss and residue test method).
Solid content (%) = (b / a) × 100

(2) Water-swelling particle diameter 20 ml of ion-exchanged water was added to 0.02 g of the measurement sample, and the sample was uniformly dispersed by shaking well. In order to make the particles into a water-saturated swelling state, the particle size distribution is measured after 1 minute of ultrasonic irradiation using a laser diffraction / scattering particle size distribution meter (manufactured by Nikkiso, MT-3000) for a dispersion dispersed for 30 minutes or more. Went. Ion exchange water was used as the circulating dispersion medium at the time of measurement, and the refractive index of the dispersion was 1.53. The median diameter (μm) was calculated from the particle size distribution on the basis of the volume obtained by the measurement, and was defined as the water-swelled particle diameter.

(3) Water absorption The water absorption was measured by the following method. The measuring device is shown in FIG.
The measuring device is composed of <1> to <3> in FIG.
<1> Consists of a burette 1 with a branch pipe for venting air, a pinch cock 2, a silicon tube 3, and a polytetrafluoroethylene tube 4.
<2> A support cylinder 8 having a large number of holes in the bottom surface on the funnel 5, and a filter paper 10 for the apparatus is installed on the support cylinder 8.
<3> A sample 6 of polymer fine particles is sandwiched between two sample fixing filter papers 7 and a membrane filter 13, and the sample fixing filter paper and the membrane filter are fixed by an adhesive tape 9. All filter papers used are ADVANTEC No. 2 The inner diameter is 55 mm, and the membrane filter is MF-Millipore membrane filter HAWP04700 (pore diameter 0.45 μm).
<1> and <2> are connected by the silicon tube 3.
Further, the funnel 5 and the column cylinder 8 are fixed to the burette 1 at a fixed height, and the lower end of the polytetrafluoroethylene tube 4 installed inside the buret branch pipe and the bottom surface of the column cylinder 8 have the same height. (Dotted line in FIG. 1).

The measurement method will be described below.
The pinch cock 2 in <1> is removed, and ion exchange water is introduced from the upper part of the burette 1 through the silicon tube 3 so that the burette 1 to the apparatus filter paper 10 are filled with the ion exchange water 12. Next, the pinch cock 2 is closed, and air is removed from the polytetrafluoroethylene tube 4 connected to the buret branch pipe with a rubber stopper. In this way, the ion exchange water 12 is continuously supplied from the burette 1 to the filter paper 10 for the apparatus.
Next, after removing the excess ion-exchanged water 12 that oozes from the filter paper for apparatus 10, the reading (a) of the scale of the burette 1 is recorded.
Weigh 0.1 to 0.2 g of the dry powder of the measurement sample and place it uniformly on the center of the sample fixing filter paper 7 as shown in <3>. The sample is sandwiched with another filter paper, and the two filter papers are fastened with the adhesive tape 9 to fix the sample. The filter paper on which the sample is fixed is placed on the apparatus filter paper 10 shown in <2>.
Next, the reading (b) of the scale of the bullet 1 after 30 minutes from the time when the lid 11 is placed on the filter paper 10 for apparatus is recorded.
The sum (c) of the amount of water absorption of the measurement sample and the amount of water absorption of the two sample fixing filter papers 7 is obtained by (ab). By the same operation, the water absorption of only two filter papers 7 not including the polymer fine particle sample is measured (d).
The above operation was performed, and the water absorption was calculated from the following formula. In addition, the value measured by the method of (1) was used for solid content used for calculation.
Water absorption (mL / g) = (cd) / {measurement sample weight (g) × (solid content% ÷ 100)}

In comparison with Comparative Example 6 in which the polymer fine particles of the present invention are not used, each of Examples 1 to 4 can be molded with a small amount of water, the dimensional ratio before and after drying is small, and the degree of shrinkage due to drying is reduced. Can be confirmed. Among these, in Examples 2 to 4 in which the polymer fine particles are composed only of the nonionic unsaturated monomer, a dry molded article having a good appearance can be obtained even when dried by combining microwaves and hot air. It was.
In general, ionic groups have the property of absorbing microwaves more easily than nonionic groups, so when polymer particles containing a large amount of ionic groups are used as shrinkage reducing agents, microwaves can reach the inside of the molded body sufficiently. May not. For this reason, unevenness in drying occurs in the molded body, and it is assumed that problems such as warping and cracking occur in the molded body due to the difference in the degree of shrinkage during subsequent thermal drying.

Further, in Comparative Example 3 having a large average particle size in the state of saturated swelling with ion-exchanged water, the degree of reduction in drying shrinkage is good, but the porosity is greatly changed compared to Comparative Example 6 in which no shrinkage reducing agent is used. The results that affect the porosity of ceramic products were revealed. In Comparative Examples 4 and 5 in which the amount of ion-exchanged water absorbed at normal pressure deviated from the scope of the present invention, a sufficient shrinkage reduction effect was not recognized.

  When the polymer fine particles of the present invention are used for ceramic molding, shrinkage of the molded body in the drying step after molding is reduced, and properties such as porosity are not affected. For this reason, it becomes possible to obtain a highly accurate ceramic compact with good reproducibility.

1 Burette 2 Pinch cock 3 Silicone tube 4 Polytetrafluoroethylene tube 5 Funnel 6 Sample (polymer fine particles)
7 Sample (polymer fine particle) fixing filter paper 8 Strut cylinder 9 Adhesive tape 10 Device filter paper 11 Lid 12 Ion exchange water 13 Membrane filter

Claims (5)

The average particle diameter in the saturated swollen state with deionized water is 0.01 to 10 [mu] m, water absorption of ion-exchanged water at normal pressure is I 0.1~60mL / g der, neutralized with an alkali acidic A drying shrinkage reducing agent for forming a ceramic, comprising polymer fine particles having a functional group of 2.0 mmol / g or less . Drying shrinkage-reducing agent according to claim 1, characterized in that is obtained by polymerizing the polymer microparticles consists only Roh anion unsaturated monomer monomer mixture. 3. The drying shrinkage reducing agent according to claim 2 , wherein the nonionic unsaturated monomer mixture contains a monomer having one or more functional groups selected from a hydroxyl group, an amide group, and an oxyethylene group. . Drying shrinkage-reducing method of a ceramic molded body using the drying shrinkage-reducing agent according to claim 1-3. Furthermore, a ceramic pore formation agent is used together, The drying shrinkage reduction method of the ceramic molded body of Claim 4 characterized by the above-mentioned.

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