JP2003183406A - Method for producing resinous powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resinous powder with low discoloration more easily than conventional methods including decoloring step, by lowering discoloration occurring at the production of smaller particle size of a resinous powder through pulverization of a resinous raw material of a larger particle size obtained by crushing or the like of a polymer at the time of producing a resinous powder having a particle size suitable for a filler material of a dental curable composition or the like comprising a spherical silica/zirconia-containing methacrylic resin or the like. <P>SOLUTION: This resinous powder with low discoloration is obtained by wet-pulverization of a resinous raw material by a pulverizer such as a vibrating ball mill using water containing a surfactant such as sodium salt of dodecylbenzenesulfonic acid as a dispersant, filtering and drying. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a resin powder having little coloring, and more specifically,
The present invention relates to a method for producing a resin-based powder having a small particle size and little coloring, which can be suitably used as a raw material of a material such as a dental curable composition that requires aesthetics.

[0002]

2. Description of the Related Art Resin powders made of various organic resins or composite resins of organic resins and inorganic particles and having an average particle diameter of about 5 to 50 μm are powder coating materials, synthetic resin molding materials, liquid crystal light diffusion sheets, It is used in various fields such as paint fillers, cosmetic materials, and dental fillers. Such a resin-based powder is obtained by various polymerization methods from a bulk body to a resin having a size of several hundreds of μm, directly or with an average particle size of 70 μm.
It is produced by roughly pulverizing to about 1 mm and then pulverizing the coarsely pulverized product to a target particle size. The coarse crushing and the crushing are performed using a crusher such as a vibrating ball mill or a jet mill. Further, as the pulverization, both wet pulverization and dry pulverization are adopted as required.

[0003]

However, it is presumed that this is caused by friction during crushing, but when crushed by a known crushing method (apparatus) regardless of whether it is wet or dry, the surface of the crushed product is The phenomenon of coloring in yellow occurs. Such coloring is less noticeable when the particle size of the pulverized product is large, that is, when the specific surface area is small, and is not a problem, but since the specific surface area increases as the particle size of the pulverized product decreases, When a powder made of a pulverized product is used for various product applications, there is a problem in that the product obtained has a strong yellow tint and its value is reduced. In particular, in a dental restorative material that has a high aesthetic demand, the use of a resin powder having a strong coloration poses a serious problem, and a resin powder having a least coloration is required.

With respect to this problem, Japanese Patent Laid-Open No. 10-1146
As described in Japanese Patent Publication No. 16 and the like, there is known a method of decolorizing a resin powder obtained by pulverization with a decolorizing reagent such as peroxide. However, many general decolorizing reagents are dangerous in handling. In addition, there is a problem that the complicated process of decolorization must be increased. In addition, JP-A-8-301884
Japanese Patent Publication reports an example of decolorizing an aromatic phosphate resin using a small amount of a hindered phenol compound and an alkaline aqueous solution, but this also has a problem in that it requires an additional manufacturing process. . Therefore, the present invention is
It is an object of the present invention to provide a method for producing a resin-based powder that is simpler and less colored than conventional methods.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to solve such problems, and as a result, by wet-milling a raw material made of a resin-based substance with water containing a surfactant, The inventors have found that the coloring during pulverization is reduced and have completed the present invention.

That is, the present invention is a method for producing a resin-based powder, which comprises wet-milling a resin-based raw material with water containing a surfactant as a dispersion medium.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing a resin-based powder of the present invention is characterized in that the resin-based raw material is wet-milled using water containing a surfactant as a dispersion medium. When the surfactant is not added to water, the degree of coloring is the same as the conventional method, and it is not possible to obtain a resin powder having little coloring. More specifically showing the production method of the present invention, a resin-based material adjusted to an appropriate size is added to an aqueous solution or dispersion of a surfactant to prepare a slurry, which is then shaken with a ball mill or the like. By crushing by charging it into the crusher of No. 1, and by recovering the resin powder from the slurry after crushing through operations such as filtration and drying,
The desired resin powder can be obtained.

The resin raw material in the present invention may be a resin consisting of only an organic material (hereinafter referred to as an organic resin) or an organic-inorganic composite resin in which an inorganic material such as inorganic particles is mixed and dispersed in the organic resin. Further, various known antioxidants, ultraviolet absorbers, colorants and the like may be added as additives to these resins.

The organic resin to which the production method of the present invention is applied may be a synthetic resin or a natural resin, and can be applied to various known resins without any limitation. Specific examples include chlorinated polyethylene, polyethylene, polypropylene, polybutadiene, styrene resin, high impact polystyrene, polyvinyl chloride, ACS resin, AS resin,
ABS resin, modified polyphenylene oxide, polyamide, polycarbonate, polyphenylene sulfide, polyimide, polyether ether ketone, polyether sulfone, polysulfone, polyarylate, polyether ketones, polyether nitrile, polythioether sulfone, polybenzimidazole, polycarbo Examples thereof include organic resins such as imide, liquid crystal polymer, composite plastic, polyurethane, phenol resin, melamine resin, urea resin, unsaturated polyester, diallyl phthalate resin, polyester resin, epoxy resin and acrylic resin.

Among the above-mentioned organic resins, those having an aromatic hydroxy derivative as a constituent unit are particularly effective in applying the production method of the present invention because they easily produce a coloring substance during pulverization.

These various organic resins may be produced by a known production method such as bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization, interfacial polymerization, vapor phase polymerization of the corresponding monomers.

The production method of the present invention can also be suitably applied to organic-inorganic composite resins in which inorganic particles are mixed and dispersed in the above various organic resins. In general, by blending inorganic particles, various physical properties such as reinforcement of mechanical strength, reduction of thermal expansion coefficient and improvement of abrasion resistance are improved. For such a purpose, the inorganic particles are generally mixed in the range of 5 to 90% by mass, and particularly 20 to 80% by mass.

[0013] Such a composite resin is considered to be influenced by the blended inorganic particles, but it has a greater degree of coloration during crushing than a composite resin consisting of only organic resin, and therefore the production method of the present invention is applied. The effect of doing is particularly remarkable.

The organic-inorganic composite resin can be usually produced by mixing and dispersing inorganic particles in various monomers as a raw material of the organic resin and polymerizing the mixture. When the organic resin is thermoplastic, it can also be produced by adding and dispersing inorganic particles in a state in which the thermoplastic resin is heated and melted, and then allowing it to cool and solidify.

The above-mentioned inorganic particles may be blended with any known inorganic particles depending on the purpose. For example, examples of the material include inorganic compounds such as amorphous silica, mica, talc, zinc oxide, calcium carbonate, silica zirconia, silica titania, barium oxide silica titania, quartz, and inorganic oxides such as alumina. Irregular particles such as crushed particles or spherical particles may be used. Further, the particle size thereof may be any particle size as long as it is equal to or smaller than the particle size of the resin-based powder obtained by the production method of the present invention (preferably 1/5 or less of the particle size), and generally 0.001 to 0.001 It suffices that a material having a thickness of about 10 μm is blended.

The inorganic particles are preferably those whose surface is treated for the purpose of improving dispersibility in a resin or imparting a bondability with the resin. The surface treatment method is not particularly limited and may be any known method. To specifically illustrate a typical surface treatment method, inorganic particles such as silica and a silane coupling agent as a surface treatment agent, for example, γ-methacryloyloxyalkyltrimethoxysilane, an organic silicon compound such as hexamethyldisilazane, Disperse and mix in a suitable solvent using a ball mill, etc., dry with an evaporator or spray dry, and then heat to 50 to 150 ° C., heat the inorganic particles and the surface treatment agent in a solvent such as alcohol for several hours. There are ways to return. There is no particular limitation on the amount of the surface treatment agent used at this time, the optimum value may be determined after confirming the physical properties of the obtained resin-based powder in advance by experiments, but if a suitable range is shown,
The surface treatment agent 1 to 1 with respect to 100 parts by mass of the inorganic particles.
The range is 0 parts by mass.

The above-mentioned organic resin or composite resin is usually obtained as a particle having a particle size of several tens of μm to several mm, or a bulk body, according to the manufacturing method. Particles with a particle size of more than 1 mm, or obtained in bulk form, have a crushing efficiency when crushing to a target particle size, and storage,
For convenience of distribution and measurement, the average particle size is usually 70-
It is roughly crushed to about 1 mm, preferably about 80 to 500 μm. Since the production method of the present invention is wet pulverization using water as a dispersion medium, coarse pulverization to the above range is preferable in order to improve dispersion in the water. Such a coarse pulverizing method is not particularly limited, and a known pulverizing method using a stamp mill, a ball mill, a roller mill or the like may be used.

In the production method of the present invention, the raw material (including coarsely pulverized material) made of the organic resin or composite resin obtained in such a relatively large state is pulverized to a size required according to the purpose. Used for.

The desired particle size after pulverization is appropriately determined according to need, but usually the average particle size is 5 to 5.
It is about 50 μm. Resin powder having such an average particle diameter is generally used for various applications such as dental materials,
Since the specific surface area is large, the effect of the production method of the present invention is remarkably obtained in that various materials obtained by blending the resin-based powder are greatly influenced by the degree of coloring of the resin-based powder.

The pulverization is carried out by using a raw material composed of the above resin powder,
Water containing a surfactant is used as a dispersion medium.

As the surfactant used in the production method of the present invention, known surfactants can be used without any limitation.

Specific examples of the surfactant include anionic surfactants such as sodium decyl sulfate, sodium dodecyl sulfate, potassium dodecyl sulfate, sodium tetradecyl sulfate, sodium octadecyl sulfate, sodium polyoxyethylene dodecyl ether sulfate, Sulfuric acid ester salts such as sodium polyoxyethylene dodecyl ether sulfate, sodium polyoxyethylene dodecyl ether sulfate, sodium polyoxyethylene hexadecyl sulfate, sodium polyoxyethylene octadecyl sulfate, pn-sodium decylbenzenesulfonate pn-
Sodium dodecylbenzenesulfonate, sodium pn-tetradecylbenzenesulfonate, sodium p- (n-decyloxycarbonyl) benzenesulfonate, sodium tetrapropylbenzenesulfonate, sodium dodecylsulfonate, and other sulfonates, potassium dodecylphosphate, Phosphates such as sodium octadecyl phosphate,
Carboxylic acid salts such as potassium myristate, potassium palmitate and the like can be mentioned. As the cationic surfactant,
Quaternary ammonium salts such as decyltrimethylammonium bromide, dodecyltrimethylammonium bromide, dodecyltriethylammonium bromide, tetradecyltrimethylammonium chloride, decyldimethylammonium chloride, dioctyldimethylammonium chloride, decylamine hydrochloride, dodecylamine hydrochloride, dodecylethylenediamineacetic acid Salts, amine salts such as tetradecylethylenediaminepropionate, amphoteric surfactants, N-decylbetaine, decylbetaine, reticine and the like, nonionic surfactants, sorbitan monopalmitate, Sorbitan fatty acid esters such as sorbitan monolaurate, polyoxyethylene sorbitan monooleate, polyoxy Polyoxyethylene sorbitan fatty acid ester such as ethylene sorbitan monolaurate ester, glycerin fatty acid ester such as glyceryl monostearate, decaglyceryl monolinoleate, polyglycerin fatty acid ester such as decaglyceryl tristearate, polyoxyethylene sorbite tetraoleate, etc. Polyoxyethylene sorbit fatty acid ester,
Polyoxyethylene glyceryl monostearate and other polyoxyethylene glycerin fatty acid esters, polyoxyethylene monolaurate, polyethylene glycol dioleate and other polyethylene glycol fatty acid esters, polyoxyethylene cetyl ether and other polyoxyethylene alkyl ethers, polyoxy Examples thereof include polyoxyethylene alkyl phenyl ethers such as ethylene nonyl phenyl ether.

These surfactants may be used alone or in combination of two or more.

Among them, those having an HLB value of 6 to 45 are preferable, and those having an HLB value of 15 to 35 are more preferable, and those having an HLB value of 20 to 30 are more preferable in view of a higher coloring reduction effect.
Most preferably, The HLB value has additivity, and when a plurality of surfactants are used in combination, the average value of the HLB values may be within the above range.

In the production method of the present invention, the concentration of the surfactant is not particularly limited, but is 0.001 to 0.001 relative to water.
It is preferably used in a concentration range of 1% by mass, particularly 0.005 to 0.5% by mass. The higher the concentration of the surfactant is up to about 1% by mass, the higher the effect of reducing coloring is. However, even if the concentration is higher than that, the effect is not improved so much, and the lower the concentration, the higher the pulverization efficiency is. Furthermore, it is easy to remove the surfactant after the pulverization step.

In the production method of the present invention, the above surfactant is dissolved or dispersed in water and used as a dispersion medium for the resin raw material.

Water is used because it has a great manufacturing advantage in terms of environmental hygiene, economy and safety.
As the water used in the present invention, tap water, ion-exchanged water, distilled water and the like can be used without particular limitation. If necessary, a hydrophilic organic solvent such as alcohol may be added to the extent that the effects of the present invention are not impaired.

In the production method of the present invention, the resinous raw material is dispersed in the dispersion medium composed of water and a surfactant and pulverized. At this time, the amount of the resin-based raw material with respect to water is not particularly limited, but the smaller the proportion of the dispersion medium, the higher the pulverization amount per time and the higher the pulverization rate, so the pulverization efficiency is high
On the other hand, the higher the proportion of the dispersion medium is, the higher the coloring reduction effect is. Therefore, it is usually preferable that the content of the resin raw material in the mixture of the resin raw material and the dispersion medium is 5 to 80% by mass. -60 mass% is more preferred.

For the pulverization in the production method of the present invention, a known wet pulverizer can be used without any limitation. As specific examples, various ball mills, medium stirring type crushers, water jet collision type crushers, wet high speed rotary mills, etc. can be used. Further, the time required for crushing may be appropriately determined in consideration of the performance of the crusher used, the target particle size, and the like.

Since the resin-based powder pulverized by the pulverizer is in the form of a slurry containing a dispersion medium, the dispersion medium is usually removed from the slurry, dried, and if necessary, subjected to classification and surface treatment. use.

As a method for removing the dispersion medium from the resin-based powder-containing slurry, known methods can be used without limitation, but since the used surfactant can be easily removed, filtration,
Centrifugal separation and centrifugal filtration can be preferably used. Further, it is also preferable to further wash in order to ensure the reduction of coloration. As the washing solvent, in addition to water, water-soluble organic solvents such as alcohol and acetone are preferably used. The dehydrated and washed resin-based powder is preferably dried. The drying method is also not particularly limited, and known drying methods such as natural drying, heat drying, reduced pressure drying, and blast drying can be used without any limitation. The classification is performed to obtain a particle powder having a desired particle size distribution, and various sieves, air classifiers, water sieving classifiers and the like can be preferably used. As the surface treatment method, the method of surface-treating the above-mentioned inorganic particles can be similarly applied.

The resin powder having the target particle size thus obtained can be used for various known applications according to the purpose without any limitation. Specifically, it can be used for synthetic resin molding materials, liquid crystal light diffusing sheets, paint fillers, cosmetic materials and the like.

Among them, since a resin powder having little coloration is strongly demanded, it can be preferably used as a curable composition for various dentistry, particularly as a filler for a dental filling / restoring material. Specifically, the resin powder, various radically polymerizable monomers known as components of dental materials, radical polymerization initiators, and further inorganic fillers, additives such as polymerization inhibitors and pigments, if necessary. By blending the required amounts of each, a dental restorative material having a good hue can be obtained.

The resin-based powder produced by the production method of the present invention, which is used as a filler of a dental curable composition such as a dental filling / restoring material, is preferably the above-mentioned composite resin. It is preferable that the inorganic particles contained in the resin be a complex oxide containing silica and zirconia as main constituent components, since a cured product having X-ray contrast and more excellent abrasion resistance can be obtained. Is. Further, since a resin surface having good surface lubricity can be obtained, an inorganic filler composed of inorganic particles having an average primary particle diameter of 0.001 to 1 μm and / or an aggregate of the inorganic particles can be preferably used.
Further, it is more preferable that the inorganic particles have a spherical shape or a substantially spherical shape, and that they have excellent monodispersity such that the variation coefficient of the particle diameter is within 0.3.

The radically polymerizable monomer is 2,
2-bis (methacryloyloxyphenyl) propane,
2,2-bis [4- (3-methacryloyloxy) -2
-Hydroxypropoxyphenyl] propane, 2,2-
Bis (4-methacryloyloxyphenyl) propane,
Polyfunctionality of 2,2-bis (4-methacryloyloxypolyethoxyphenyl) propane, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, etc. The (meth) acrylate-based radically polymerizable monomer of is preferably used.

As the radical polymerization initiator, a chemical polymerization initiator composed of organic peroxides and tertiary amines, a photopolymerization initiator composed of α-diketone or acylphosphine oxides and tertiary amines Radical polymerization initiators known as dental polymerization initiators such as a photopolymerization initiator comprising an aryl borate compound, a coumarin-based dye and a photoacid generator can be used without any limitation.

As the inorganic filler, various inorganic particles described above as the component of the composite resin can be used.

The above components and components to be blended as necessary may be mixed and made into paste by a known method to prepare a dental curable composition.

[0039]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. The abbreviations of the surfactants used in the examples and their HLB values are shown below. S-1 Sodium dodecylbenzene sulfonate (HLB
= 10) S-2 Sodium dodecyl sulfate (HLB = 40) S-3 Dodecyl trimethyl ammonium bromide (HL
B = 9) S-4 polyoxyethylene sorbitan monolaurate (repetition number of oxyethylene units is 20: HLB = 1
7) Equal mass mixture of S-5 sodium dodecylbenzenesulfonate and sodium dodecyl sulfate (HLB value = 25) The resin raw material used in each example was produced by the following method.

Production Example 1 Bisphenol A diglycidyl ether type epoxy monomer (Epicote 100 manufactured by Yuka Shell Epoxy Co., Ltd.
4) A mixture of 940 g and adipic acid dihydrazide 60 g was dry-blended, melt-kneaded and dispersed in a Busco kneader, then cooled and coarsely pulverized to obtain a resin material M-1 having an average particle diameter of about 80 μm.

Production Example 2 2,2-bis [4- (3-methacryloyloxy) -2
-Hydroxypropoxyphenyl] propane (D-GMA manufactured by Shin Nakamura Chemical Co., Ltd.) 30 parts by mass, triethylene glycol dimethacrylate (NK ester 3G manufactured by Shin Nakamura Chemical Co., Ltd.) 20 parts by mass, 1,6-bis (methacrylethyloxycarbonylamino) ) 2,2,4-trimethylhexane (ART RESIN SH-500S manufactured by Negami Kogyo Co., Ltd.) To a mixture of 50 parts by mass, 0.5 parts by mass of azobisisobutyronitrile as a polymerization initiator was added and mixed and dissolved. To this, spherical silica zirconia (average particle size 0.2 μm) manufactured according to the method of JP-A-60-11408 was used.
300 parts by mass of the γ-methacryloyloxypropyltrimethoxysilane-treated product of m) was added and kneaded in a mortar to form a paste. This was polymerized and cured by heating at 95 ° C. under nitrogen pressure for 1 hour. This cured product was roughly pulverized to obtain a resin-based raw material M-2 having an average particle diameter of about 80 μm. Example 1 10 g of a resin-based raw material M-1 and a surfactant S- were placed in a pot mill.
15 ml of 0.3 mass% aqueous solution of 1 and alumina ball 50 of φ20 mm
Put 0g, using a new light mill (manufactured by Central Processing Machine)
Grinding was carried out for 15 minutes. The obtained slurry was filtered, washed with ion-exchanged water, and then dried with a vacuum dryer. The average particle size of the obtained resin powder P-1 was 15 μm.

The resin powder thus obtained was evaluated by the following method. That is, 2,2-bis [4- (3
-Methacryloyloxy) -2-hydroxypropoxyphenyl] propane (D-GMA manufactured by Shin Nakamura Chemical Co., Ltd.) 30 parts by mass, triethylene glycol dimethacrylate (NK ester 3G manufactured by Shin Nakamura Chemical Co., Ltd.) 20 parts by mass, 1,6-bis (Methacrylethyloxycarbonylamino) 2,2,4-
Trimethylhexane (ART RESIN SH-500 manufactured by Negami Kogyo Co., Ltd.
S) 50 parts by mass of the mixture, 0.5 parts by mass of camphorquinone as a polymerization initiator and 1.5 parts of N, N-dimethyl-p-toluidine.
Parts by mass were added and mixed to prepare a uniform mixture. 100 parts by mass of the resin powder P-1 in an agate mortar, 100 parts by mass of the mixture of the above monomers are added, and after sufficiently kneading and homogenizing in a dark place, defoaming under reduced pressure to remove bubbles and curable composition Item I was prepared. Next, the curable composition I was put into a mold having a hole of 7 mmφ × 2 mm, and both opening faces were pressed with a polypropylene film. After irradiating both sides with a visible light irradiator (manufactured by Tokuyama) for 30 seconds to cure, remove it from the mold and use a color difference meter (TC-1800MKII, manufactured by Tokyo Denshoku) to measure with a background white color. The yellowness index YI was calculated based on the formula. Yellowness (YI) = 100 × (1.28X-1.06Z) /
Y (however, X, Y, and Z in the formula are tristimulus values defined in JIS Z8701.) Further, the yellowness of the cured sample is visually evaluated,
Those that were almost colorless were evaluated as ⊚, those that were confirmed to have a slight yellow tint were evaluated as ◯, and those that were clearly colored in yellow were evaluated as x.

Examples 2 to 6 Color tone was evaluated in the same manner as in Example 1 except that the resin raw materials and the surfactant shown in Table 1 were used. The results are shown together in Table 1.

[0044]

[Table 1] With all the compositions of Examples 1 to 6, it was possible to obtain a resin cured product having a color tone in which the degree of yellow coloring was sufficiently low.

Comparative Examples 1 and 2 Samples were prepared in the same manner as in Example 1 except that the resin raw materials shown in Table 1 were used and no surfactant was added, and the color tone was evaluated. The results are shown together in Table 1. As is clear from these results, Comparative Examples 1 and 2 have very high yellowness as compared with each Example, and the effect of adding a surfactant is clear.

Comparative Example 3 5 g of the resin-based powder obtained by the method of Comparative Example 2 was washed with 30 ml of acetone, and then a curable composition was prepared and evaluated in the same manner as in Example 1. The coloring degree was 29. And the visual judgment result was x.

[0047]

EFFECTS OF THE INVENTION According to the present invention, it is possible to reduce the coloring that occurs during the production of resin-based powders without performing a decolorizing step. A powder can be provided, and the hue of a product using the resin-based powder can be improved.

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Claims (3)

[Claims] 1. A method for producing a resin-based powder, which comprises wet-milling a resin-based raw material with water containing a surfactant as a dispersion medium. 2. The method for producing resin powder according to claim 1, wherein the resin raw material is a composite resin of inorganic particles and an organic resin. 3. A dental curable composition comprising a resin-based powder produced by the method according to claim 1 or 2.