Method for producing a treated silica dispersion monomer composition

Abstract

To obtain a better dispersion state of silica particles in a method for producing a composition comprising silane-treated silica particles dispersed in a polymeric monomer.SOLUTION: A method for producing a treated-silica dispersed monomer composition includes: mixing a basic silica dispersion liquid, in which silica is dispersed in a solvent containing 10 mass% or more of water, with a silane coupling agent to prepare a silane-treated silica dispersion liquid; mixing the silane-treated silica dispersion liquid with a polymerizable monomer to obtain a mixture; and removing a water phase from the mixture and obtaining a composition in which silica treated with the silane coupling agent is dispersed in the polymerizable monomer.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing a treated silica-dispersed monomer composition.

Background Art

[0002] In the dental field, a composition in which silane-treated silica particles are dispersed in a polymerizable monomer is known (see, for example, Patent Documents 1 and 2). Since the composition has good mechanical properties and appropriate fluidity (such as consistency), it is suitably applied to dental materials.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a composition in which silane-treated silica particles are dispersed in a polymerizable monomer as described above, the better the dispersion state of the silica particles in the polymerizable monomer, that is, the more uniformly the silica particles are dispersed by the polymerizable monomer, the better the dispersion state of the silica particles in the material when applied to the material, and the better the properties of the material. However, there was room for improvement in the dispersion state of the silica particles in the composition obtained by the conventional production method.

[0005] In view of the above, one aspect of the present invention is a method for producing a composition in which silane-treated silica particles are dispersed in a polymerizable monomer, and an object thereof is to provide a method capable of obtaining a better dispersion state of the silica particles.

Means for Solving the Problems

[0006] A method for producing a treated silica dispersion monomer composition according to one aspect of the present invention involves mixing a basic silica dispersion in which silica is dispersed in a solvent containing 10% by mass or more of water with a silane coupling agent to prepare a silane-treated silica dispersion containing 10% by mass or more of water, and adding a polymerizable monomer separately from the silane coupling agent used for surface treatment of the silica. (Excluding the silane coupling agent mentioned above) The method includes mixing the oil phase and the aqueous phase to obtain a mixture containing an oil phase and an aqueous phase, separating the oil phase and the aqueous phase in the mixture and removing the aqueous phase to obtain a composition in which silica treated with a silane coupling agent is dispersed in polymerizable monomers. [Effects of the Invention]

[0007] According to one aspect of the present invention, in a method for producing a composition in which silane-treated silica particles are dispersed in a polymer monomer, a better dispersion state of the silica particles can be obtained. [Modes for carrying out the invention]

[0008] One embodiment of the present invention is a method for producing a composition (hereinafter also referred to as a treated silica dispersed monomer composition) in which silane-treated silica particles are dispersed in a polymerizable monomer. The production method according to this embodiment includes at least a first step of preparing a silane-treated silica dispersion (sometimes simply referred to as a treated silica dispersion) by treating silica by mixing a silica dispersion (in which silica is dispersed in a solvent containing water) with a silane coupling agent; a second step of adding a polymerizable monomer to the silane-treated silica dispersion to obtain a mixture; and a third step of removing the aqueous phase from the mixture to obtain a composition (silane-treated silica dispersed monomer composition, or treated silica dispersed monomer composition) in which silica treated with a silane coupling agent is dispersed in a polymerizable monomer.

[0009] <Step 1: Preparation of silane-treated silica dispersion> The first step is to treat the surface of the silica with a silane coupling agent, that is, to react the silane with the silane coupling agent. In this step, a basic silica dispersion is used, in which silica is dispersed in a solvent containing water. That is, instead of directly contacting the silica with the silane coupling agent, the silane coupling agent is applied to the silica that is already dispersed in the dispersion. As a result, the silica and the silane coupling agent can react in the dispersion, so even with silica particles that are small in size, the aggregation of silica can be suppressed, and the dispersion state of silica in the treated silica dispersion monomer composition obtained by this manufacturing method can be improved. In other words, the aggregation of silica can be suppressed, and a state in which silica is uniformly dispersed in the composition can be obtained.

[0010] Furthermore, the solvent in the silica dispersion contains water, and the amount of water is 10% by mass or more of the total amount of solvent in the silica dispersion. By using the above amount of water in the silica dispersion, the dispersion state of silica in the treated silica dispersion obtained in the first step can be improved, and consequently, the dispersion state of silica in the treated silica dispersion monomer composition can be improved.

[0011] The amount of water in the solvent used in the silica dispersion may be preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 50% by mass or more, even more preferably 70% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more, relative to the total amount of solvent. Furthermore, it is preferable that the solvent consists substantially of water or is water.

[0012] Furthermore, the silica dispersion (the liquid before the addition of the silane coupling agent and / or monomers) may contain a solvent other than water. The solvent other than water may be an amphiphilic solvent (a solvent having both hydrophilic and hydrophobic properties) that is miscible with water and has a lower boiling point than water. Specific examples include alcohols such as ethanol, methanol, propanol, isopropyl alcohol, and butanol, as well as acetones and ethers. When the treated silica dispersion monomer composition obtained by this embodiment is used in dental materials, etc., it is preferable to use ethanol from the viewpoint of safety in case of residual solvent.

[0013] Silica is added as an inorganic filler in the treated silica monomer composition obtained by the manufacturing method according to this embodiment. The silica used in this embodiment is nanoscale silica particles, i.e., silica particles with an average primary particle size of less than 1 μm. The average particle size of the silica is preferably 1 to 500 nm, more preferably 1 to 200 nm. Silica particles having the above average particle size are preferable, for example, when the manufactured treated silica dispersed monomer composition is applied to dental materials, from the viewpoint of improving the aesthetics of the dental material. Furthermore, when the particle size distribution of silica is measured, it may have one particle size peak or two or more. Note that the particle size in this specification may be measured by laser diffraction scattering or electron microscopy observation, and the average particle size may be the volume average diameter.

[0014] The silica used in this embodiment may be non-aggregated silica. In this specification, non-aggregated silica is spherical or substantially spherical. The BET specific surface area of ​​the silica is 20 to 500 m². 2 It can be around / g.

[0015] The silica dispersion is basic, which allows the silica and silane coupling agent to react under basic conditions. Reaction under basic conditions is preferable because it suppresses the aggregation of silica particles while promoting the silica surface coupling reaction, resulting in a good dispersion state of silica in the resulting treated silica dispersion monomer composition. The pH of the silica dispersion is preferably 8 to 12, more preferably 9 to 11.

[0016] The silica dispersion may be a silica sol, colloidal silica, or the like, in which silica is dispersed in a water-containing solvent. Examples of silica dispersions include Ludox® PW-50 (pH 9.8~10.6), CL-X, PX-30 from WRGRACE, and Snowtex® ST-ZL (pH 9.0~11.0), ST-YL, ST-30L from Nissan Chemical Corporation. Alternatively, dry silica particles such as fumed silica can be dispersed in a water-containing solvent to prepare the dispersion. In this case, examples of dry silica particles include AEROSIL® OX-50, AEROSIL® 200, AEROSIL® 380 from EVONIK.

[0017] A basic salt may be added to the solvent used to prepare the silica dispersion to prepare a basic aqueous solution. The basic salt may be an inorganic or organic salt, such as sodium hydroxide, sodium tripolyphosphate, or sodium carbonate. By making the silica dispersion basic by adding a basic salt, the possibility of changes in the basicity of the silica dispersion due to volatilization caused by temperature changes can be reduced, and the pH can be stably maintained in the basic range during the processing step. Furthermore, the presence of sodium ions in the silica dispersion, and consequently in the mixture of the silica dispersion and the silane coupling agent, further suppresses the aggregation of silica particles in the liquid.

[0018] The silica concentration in the silica dispersion is preferably 20 to 70% by mass, more preferably 30 to 60% by mass. By setting the concentration within this range, silica aggregation can be suppressed, and the efficiency of the reaction between silica and the silane coupling agent can be increased.

[0019] In the first step, the silica dispersion and the silane coupling agent are mixed. The silane coupling agent may be added directly to the silica dispersion in its untreated state, or it may be added after hydrolyzing at least some of its hydrolyzable groups. Using a pre-hydrolyzed silane coupling agent is preferable because it allows for faster surface treatment of the silica and reduces the amount of flammable solvent used.

[0020] When hydrolyzing the silane coupling agent beforehand, the silane coupling agent is dispersed in an aqueous solvent such as water or alcohol. In this case, the pH of the solvent in which the silane coupling agent is dispersed can be acidic or basic, but as mentioned above, it is preferable to proceed with the reaction between silica and the silane coupling agent under basic conditions, so it is preferable to use a neutral or basic solvent for dispersing the silane coupling agent. In addition, to promote the hydrolysis reaction, an acidic or basic component other than the aqueous solvent mentioned above can be added to the liquid in which the silane coupling agent is dispersed, but it is preferable that the mixture obtained after mixing the liquid in which the silane coupling agent is dispersed with the silica dispersion is basic. Furthermore, when mixing the silane coupling agent with the silica dispersion after hydrolysis, the silane coupling agent can be added as a dispersion with a concentration of about 20 to 50% by mass.

[0021] Silane coupling agents are not particularly limited, but those having polymerizable double bonds, more specifically, unsaturated double bonds that can be radically polymerized, are preferred. Of the silane coupling agents having unsaturated double bonds that can be radically polymerized, those having a (meth)acryloyloxy group are preferred from the viewpoint of transparency, making them suitable for the dental field. Specific examples of silane coupling agents having a (meth)acryloyloxy group include methacryloyloxymethyltrimethoxysilane, 2-methacryloyloxyethyltrimethoxysilane, 3-methacryloyloxypropyltrimethoxysilane (γ-methacryloxypropyltrimethoxysilane), 4-methacryloyloxybutyltrimethoxysilane, 5-methacryloyloxypentyltrimethoxysilane, 6-methacryloyloxyhexyltrimethoxysilane, 7-methacryloyloxyheptyltrimethoxysilane, 8-methacryloyloxyoctyltrimethoxysilane (θ-methacryloxyoctyltrimethoxysilane), 9-methacryloyloxynonyltrimethoxysilane, and 10-methacryloyloxydecyltrimethoxysilane. Examples include silane, 11-methacryloyloxyundecyltrimethoxysilane, 12-methacryloyloxidedodecyltrimethoxysilane, 13-methacryloyloxytridecyltrimethoxysilane, 11-methacryloyloxyundecyldichloromethylsilane, 11-methacryloyloxyundecyltrichlorosilane, 12-methacryloyloxidedodecyldimethoxymethylsilane, 3-(meth)acryloyloxypropylmethyldimethoxysilane, 3-(meth)acryloyloxypropyltriethoxysilane, 3-(meth)acryloyloxypropylethyldiethoxysilane, 3-(meth)acryloyloxypropylmethyldiethoxysilane, and 2-(meth)acryloyloxyethoxypropyltrimethoxysilane. Of these, one or more of 3-methacryloyloxypropyltrimethoxysilane (γ-methacryloxypropyltrimethoxysilane) and 8-methacryloyloxyoctyltrimethoxysilane (θ-methacryloxyoctyltrimethoxysilane) are preferred because they are generally readily available and in circulation. Furthermore, the above silane coupling agents can be used individually or in combination of two or more types.

[0022] When mixing a silane coupling agent into a silica dispersion, the required amount of the silane coupling agent or the dispersion of the silane coupling agent may be charged at once, or the silane coupling agent or the dispersion of the silane coupling agent may be dropped little by little while stirring the silica dispersion. Further, when stirring the silica dispersion and the silane coupling agent, it can be carried out using a stirring device such as a magnetic stirrer, and ultrasonic irradiation or the like may also be carried out.

[0023] <Second Step: Addition of Polymerizable Monomer> The second step is a step of further mixing a polymerizable monomer into the dispersion of the silane-treated silica (treated silica dispersion) obtained in the first step to obtain a mixture. In this embodiment, since the treated silica is dispersed in the liquid, stirring is easy even when the monomer is added. Compared with the integral blend method or the like in which silica and the monomer are previously mixed, a state in which silica is uniformly dispersed in the mixture is maintained.

[0024] The polymerizable monomer is a polymerizable double bond-containing monomer, more specifically, a monomer having a radically polymerizable unsaturated double bond. The polymerizable double bond-containing monomer is not particularly limited, but a polymerizable monomer having a (meth)acryloyloxy group, which is suitable in the dental field from the viewpoint of high transparency, is preferable. In the present specification, "having a (meth)acryloyloxy group" means having an acryloyloxy group or a methacryloyl group, or both of them. Further, "(meth)acrylate" means a monomer, oligomer, or prepolymer of acrylate and / or methacrylate.

[0025] Specific examples of polymerizable monomers having a (meth)acryloyloxy group include methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, hydroxypropyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, glycidyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, benzyl (meth)acrylate, 2-hydroxy-1,3-di(meth)acryloxypropane, ethylene glycol di(meth)acrylate, diethylene glycol di( Examples include meth)acrylate, triethylene glycol di(meth)acrylate, butylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,3-butanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, trimethylolmethane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, polybutylene glycol di(meth)acrylate, bisphenol A diglycidyl(meth)acrylate, and bismethacrylic acid [(dimethylmethylene)bis(4,1-phenyleneoxyethylene)] (Bis-MEPP).Furthermore, specific examples of polymerizable monomers having a (meth)acryloyloxy group include (meth)acrylates having a urethane bond, such as di-2-(meth)acryloxyethyl-2,2,4-trimethylhexamethylenedicarbamate, 1,3,5-tris[1,3-bis{(meth)acryloyloxy}-2-propoxycarbonylaminohexane]-1,3,5-(1H,3H,5H)triazine-2,4,6-trione, 2,2-bis[4-{3-(meth)acryloyloxy-2-hydroxypropyl}phenyl]propane, and 2,2-bis[4-{(meth)acryloxyethoxy}phenyl]propane. Other examples include (meth)acrylates of urethane oligomers consisting of 2,2'-di(4-hydroxycyclohexyl)propane, 2-oxypanone, hexamethylene diisocyanate, and 2-hydroxyethyl (meth)acrylate, and (meth)acrylates of urethane oligomers consisting of 1,3-butanediol, hexamethylene diisocyanate, and 2-hydroxyethyl (meth)acrylate, as well as urethane dimethacrylate (UDMA). Among these, polyfunctional (meth)acrylates, particularly di(meth)acrylates, are preferred, with bismethacrylic acid [(dimethylmethylene)bis(4,1-phenyleneoxyethylene)] (Bis-MEPP) and urethane dimethacrylate (UDMA) being preferred. Polyfunctional (meth)acrylates are preferred because they have a higher boiling point than monofunctional (meth)acrylates, making them less likely to volatilize and boil in the subsequent heating step of 80°C to 150°C (described later in step 4). The polymerizable monomers described above can be used individually or in combination of two or more.

[0026] The amounts of polymerizable monomer and silica can be adjusted according to the properties of the treated silica-dispersed monomer composition or its cured product to be obtained, but the amount of silica per 100 parts by mass of polymerizable monomer can preferably be 50 to 300 parts by mass, more preferably 100 to 250 parts by mass.

[0027] In this second step, when mixing the treated silica dispersion obtained in the first step with the polymerizable monomer, a mixer such as a rotary-orbit mixer can be used.

[0028] <Step 3: Removal of the aqueous phase> This step involves removing unwanted components from the mixture of the treated silica dispersion and polymerizable monomer obtained in the second step described above, and obtaining the treated silica dispersion monomer composition. The mixture at the end of the second step contains an oil phase and an aqueous phase. The oil phase mainly contains polymerizable monomers, silane-treated silica, and residual silane coupling agent. On the other hand, the aqueous phase mainly contains water, an aqueous solvent, ions such as sodium ions, and silica that has not been treated with silane.

[0029] If the mixture at the end of the second step is clearly separated into an oil phase and an aqueous phase by visual inspection, the supernatant oil phase can be removed by a known method such as the inclination method, and the aqueous phase can be removed. Furthermore, whether the mixture at the end of the second step is clearly separated into an oil phase and an aqueous phase or not, the oil phase and aqueous phase can be separated and / or the aqueous phase removed by applying some kind of energy, such as mechanical energy or thermal energy, to the mixture as needed. The above treatment may be, for example, centrifugation, filtration, heating, freeze-drying, or solvent removal. When centrifugation is performed to separate the oil phase and aqueous phase as described above, it is preferable that the specific gravity of the polymerizable monomer is 1 or higher. In particular, if the separation of the oil phase and aqueous phase cannot be visually confirmed, the mixture can be irradiated with ultrasound to separate the oil phase and aqueous phase.

[0030] Furthermore, in the removal of the aqueous phase in the third step, water or acidic water can be added to the oil phase that has been removed as described above to disperse unwanted components in the oil phase (for example, residual unreacted silane coupling agent, residual untreated silica, residual sodium ions, etc.) into the aqueous phase, and then remove the aqueous phase. Such addition of water or acidic water can also be performed on the mixture obtained at the end of the second step.

[0031] In the third step, the aqueous phase is removed, and the remaining oil phase becomes the treated silica dispersed monomer composition. The aqueous phase does not need to be completely removed in the third step, and some aqueous phase may remain in the obtained treated silica dispersed monomer composition (oil phase). However, it is preferable that no phase separation is observed in the treated silica dispersed monomer composition. The properties of the treated silica dispersed monomer composition (oil phase) may be slurry, paste, or clay-like, as long as it has some degree of fluidity.

[0032] Thus, a manufacturing method including at least the first to third steps described above can be used to obtain a composition (treated silica-dispersed monomer composition) in which silica treated with a silane coupling agent is dispersed in polymerizable monomers. The dispersion state of silica (filler) in such a treated silica-dispersed monomer composition may be evaluated by directly observing the composition, or, since a good dispersion state in the treated silica-dispersed monomer composition is reflected in a good dispersion state in its cured product, the cured product obtained by curing the treated silica-dispersed monomer composition may be observed. In that case, for example, the dispersion state can be evaluated by observing aggregates within the cured product on a flat surface or cross-section of the cured product using an electron microscope or the like.

[0033] <4th step: Heating> The fourth step involves heating the oil phase obtained in the third step, if necessary. Heating promotes the dehydration condensation of the silane coupling agent. As the silane coupling agent undergoes dehydration condensation, it becomes immobilized on the silica surface, improving the dispersibility of silica in the composition. Furthermore, heating in the fourth step allows any residual solvent to be removed by evaporation.

[0034] The heating temperature is preferably 80°C to 150°C, more preferably 100°C to 130°C. The heating time is preferably about 30 to 360 minutes.

[0035] [Applications of treated silica-dispersed monomer compositions] The obtained silica-treated dispersion monomer composition can be used for dental curable materials, such as photopolymerizable dental curable materials. In particular, it is suitably used for dental composite resins and one-component dental composite resins. When used as a dental composite resin, additional components, such as photopolymerization initiators, fillers such as barium glass, polymerization inhibitors, ultraviolet absorbers, fluorescent agents, pigments, etc., can be added to the above-described silica-treated dispersion monomer composition. Therefore, one embodiment of the present invention may be a method for producing a dental curable material by adding additional components to the above-described silica-treated dispersion monomer composition. [Examples]

[0036] In each of the following examples, a composition in which treated silica was dispersed in monomers (treated silica monomer composition) was obtained by different methods. Furthermore, cured products were prepared from the obtained compositions, and the dispersion state of silica in the cured products was evaluated.

[0037] <Method for evaluating silica dispersibility> To the compositions obtained in each of the above examples, a photopolymerization initiator (triethylene glycol dimethacrylate (TEGDMA) in which camphorquinone / dimethylaminoethyl methacrylate was dissolved) was mixed in a ratio of [amount of monomer in the composition]:[amount of TEGDMA] = 80:20 to obtain a photopolymerizable composition. This photopolymerizable composition was polymerized by visible light irradiation to produce a cured product. The surface of the cured product was mirror-polished with waterproof abrasive paper to form a smooth surface, which was then observed using a scanning electron microscope (SEM). Specifically, images were obtained at three arbitrary locations on the smooth surface at a magnification that allowed for the confirmation of a 50 μm × 40 μm area. The number of aggregates larger than 3 μm was counted in each of the three obtained images, and the average number of aggregates per image was calculated. The evaluation criteria were as follows: Excellent: Average value is less than 1 Good: Average value is between 1 and 3. Unacceptable: Average value is 3 or higher

[0038] (Example 1) A treated silica dispersion was obtained by mixing 20 g of colloidal silica aqueous dispersion (WRGRACE "Ludox(registered trademark) PW-50", silica concentration: 50% by mass, sodium ion stabilized, pH 9.8-10.6, silica particle size peaks around 20-30 nm and 50 nm) with 3.5 g of γ-methacryloxypropyltrimethoxysilane (Shin-Etsu Chemical "KBM-503") using a magnetic stirrer for 10 minutes at 23°C, and then irradiating with ultrasound at an oscillation frequency of 38 kHz and 120 W for 30 minutes.

[0039] Next, 5.5 g of bismethacrylate [(dimethylmethylene)bis(4,1-phenyleneoxyethylene)] (Bis-MEPP, dimethacrylate monomer) was added, and the mixture was further stirred for 10 minutes at a rotational speed of 1000 rpm using a rotary-rotating mixer to obtain the mixture.

[0040] Furthermore, the aqueous phase was removed from the mixture, which had separated into an oil phase and an aqueous phase, to obtain the oil phase. 25 mL of acidic water (an aqueous acetic acid solution with a pH of 3.5) was added to the obtained oil phase and stirred, and the separated aqueous phase was removed. The mixture was heated in a steam dryer at 120°C for 120 minutes to obtain a treated silica dispersion monomer composition (a composition in which silica treated with γ-methacryloxypropyltrimethoxysilane is dispersed in Bis-MEPP). A cured product was prepared using the obtained treated silica dispersion monomer composition, and the dispersion state of the silica was evaluated as described above, resulting in a "superior" rating.

[0041] (Example 2) A treated silica dispersion monomer composition (a composition in which silica treated with γ-methacryloxypropyltrimethoxysilane is dispersed in Bis-MEPP) was obtained in the same manner as in Example 1, except that 20 g of a different colloidal silica dispersion (Nissan Chemical Corporation's "Snowtex® ST-ZL", silica concentration: 40% by mass, sodium ion stabilized, pH: 9.0~11.0, average silica particle size: 70~100 nm) was used instead of the colloidal silica dispersion in Example 1, the amount of γ-methacryloxypropyltrimethoxysilane (Shin-Etsu Chemical Co., Ltd.'s "KBM-503") was set to 2.4 g, and the amount of Bis-MEPP was set to 5.0 g. A cured product was prepared using the obtained treated silica dispersion monomer composition, and the dispersion state of the silica was evaluated as described above, and the result was "good".

[0042] (Example 3) 20 g of an aqueous sodium hydroxide solution adjusted to pH 10 was mixed with 10 g of fumed silica (EVONIK's "AEROSIL® OX-50," with an average silica particle size of approximately 40 nm and a particle size distribution of 10-100 nm) and stirred with a magnetic stirrer for 10 minutes at 23°C. Furthermore, the silica was dispersed to almost primary particles by irradiating it with ultrasound at an oscillation frequency of 38 kHz and 120 W for 30 minutes to obtain a silica aqueous dispersion (silica slurry). 30 g of the obtained silica aqueous dispersion was mixed with 4.0 g of γ-methacryloxypropyltrimethoxysilane (Shin-Etsu Chemical's "KBM-503"), stirred with a magnetic stirrer for 10 minutes at 23°C, and then irradiated with ultrasound at an oscillation frequency of 38 kHz and 120 W for 30 minutes to obtain a treated silica dispersion.

[0043] Next, a mixture was obtained in the same manner as in Example 1, except that the amount of Bis-MEPP added was 6.0 g, and a treated silica-dispersed monomer composition (a composition in which silica treated with γ-methacryloxypropyltrimethoxysilane is dispersed in Bis-MEPP) was obtained. A cured product was prepared using the obtained treated silica-dispersed monomer composition, and the dispersion state of the silica was evaluated as described above, and the result was "good".

[0044] (Example 4) 20 g of colloidal silica aqueous dispersion (WRGRACE "Ludox PW-50") was prepared. Meanwhile, 3.0 g of θ-methacryloxyoctyltrimethoxysilane (Shin-Etsu Chemical "KBM-5803") was dissolved in a mixed solvent of 40 g of ethanol and 10 g of distilled water, and the mixture was stirred at room temperature for 24 hours to hydrolyze the θ-methacryloxyoctyltrimethoxysilane. Furthermore, the above colloidal silica aqueous dispersion and the solution of the hydrolyzed θ-methacryloxyoctyltrimethoxysilane were mixed by stirring to obtain a treated silica dispersion.

[0045] Next, 6.0 g of Bis-MEPP was added to the silica dispersion and stirred to obtain a mixture.

[0046] The resulting mixture was evaporated to remove ethanol, separating it into an oil phase and an aqueous phase. The oil phase was removed from the mixture, and acidic water was added to the oil phase and stirred. The aqueous phase was then removed. The mixture was heated in a steam dryer at 120°C for 120 minutes to obtain a treated silica dispersion monomer composition (a composition in which silica treated with γ-methacryloxypropyltrimethoxysilane is dispersed in Bis-MEPP). A cured product was prepared using the obtained treated silica dispersion monomer composition, and the dispersion state of the silica was evaluated as described above. The result was "excellent".

[0047] (Example 5) 20 g of colloidal silica aqueous dispersion (WRGRACE "Ludox PW-50") was prepared. Meanwhile, 3.5 g of γ-methacryloxypropyltrimethoxysilane (Shin-Etsu Chemical "KBM-503") was dissolved in a mixed solvent of 40 g of ethanol and 10 g of distilled water, and the mixture was stirred at room temperature for 24 hours to hydrolyze the γ-methacryloxypropyltrimethoxysilane. The above colloidal silica aqueous dispersion and the hydrolyzed γ-methacryloxypropyltrimethoxysilane solution were then mixed by stirring to obtain a treated silica dispersion.

[0048] Next, 5.5 g of urethane dimethacrylate (UDMA, dimethacrylate monomer) is added to the silica dispersion. do The mixture was stirred to obtain a mixture.

[0049] The obtained mixture was evaporated in the same manner as in Example 4, and the oil phase was removed to obtain a treated silica-dispersed monomer composition (a composition in which silica treated with γ-methacryloxypropyltrimethoxysilane is dispersed in UDMA). A cured product was prepared using the obtained treated silica-dispersed monomer composition, and the dispersion state of the silica was evaluated as described above, resulting in a "Superior" rating.

[0050] (Comparative Example 1) 10 g of fumed silica (EVONIK "AEROSIL OX-50") was placed in a mortar, and 3.5 g of γ-methacryloxypropyltrimethoxysilane (Shin-Etsu Chemical "KBM-503") was added dropwise in small amounts while stirring in the mortar. After stirring until the silica (filler) clumps were almost invisible to the naked eye, the mixture was heated in a steam dryer at 120°C for 120 minutes to condense the γ-methacryloxypropyltrimethoxysilane (silane coupling agent) onto the silica surface, obtaining silica treated with the silane coupling agent (silane-treated silica). Subsequently, 5.5 g of Bis-MEPP was added to the silica treated with the silane coupling agent (silane-treated silica) and mixed to obtain a treated silica dispersion monomer composition (a composition in which silica treated with γ-methacryloxypropyltrimethoxysilane is dispersed in Bis-MEPP). When a cured product was prepared using the obtained treated silica-dispersed monomer composition, and the silica dispersion state was evaluated as described above, the result was "unacceptable".

[0051] (Comparative Example 2) A treated silica-dispersed monomer composition (a composition in which silica treated with θ-methacryloxyoctyltrimethoxysilane is dispersed in UDMA) was obtained in the same manner as in Comparative Example 1, except that 3.0 g of θ-methacryloxyoctyltrimethoxysilane (Shin-Etsu Chemical Co., Ltd. "KBM-5803") was used instead of 3.5 g of γ-methacryloxypropyltrimethoxysilane (Shin-Etsu Chemical Co., Ltd. "KBM-503"), and the amount of Bis-MEPP was set to 6.0 g. A cured product was prepared using the obtained treated silica-dispersed monomer composition, and the dispersion state of silica was evaluated as described above, resulting in a "failure" result.

[0052] (Comparative Example 3) In Example 1, replace 20g of colloidal silica aqueous dispersion with colloidal silica aqueous dispersion (Nissan Chemical). Company-made A treated silica-dispersed monomer composition (a composition in which silica treated with γ-methacryloxypropyltrimethoxysilane is dispersed in Bis-MEPP) was obtained in the same manner as in Example 1, except that 40 g of "Snowtex (registered trademark) ST-OL" (silica concentration: 20% by mass, pH: 2.0~4.0, average particle size: 40~50 nm) was used and the amount of γ-methacryloxypropyltrimethoxysilane (Shin-Etsu Chemical Co., Ltd. "KBM-503") was 2.4 g. A cured product was prepared using the obtained treated silica-dispersed monomer composition, and the dispersion state of the silica was evaluated as described above, resulting in a "failure" result.

[0053] (Comparative Example 4) A treated silica dispersion was obtained in the same manner as in Example 3, except that 20 g of ethanol was used instead of 20 g of an aqueous sodium hydroxide solution adjusted to pH 10.

[0054] Next, 6.0 g of Bis-MEPP was added and stirred to obtain a mixture.

[0055] The mixture was evaporated to remove the ethanol, and then heated in a steam dryer at 120°C for 120 minutes to obtain a treated silica-dispersed monomer composition (a composition in which silica treated with γ-methacryloxypropyltrimethoxysilane is dispersed in Bis-MEPP). A cured product was prepared using the obtained treated silica-dispersed monomer composition, and the dispersion state of the silica was evaluated as described above, resulting in a "failure" result.

[0056] Thus, in Examples 1 to 4, which included a step of treating silica under basic conditions by mixing a silica dispersion (silica dispersed in a water-containing solvent) with a silane coupling agent, the dispersion state in the cured products prepared using the obtained treated silica dispersion monomer compositions was found to be good in all cases. In particular, the results for Example 1, which used colloidal silica and had relatively small silica particle sizes, were excellent. In Comparative Examples 1 and 2, where silica and a silane coupling agent were mixed without a solvent, the dispersion state of silica in the cured products prepared using the obtained treated silica dispersion monomer compositions was inferior to the results for Examples 1 to 4. Furthermore, in Comparative Example 3, where the reaction was carried out under acidic solvent conditions, and Comparative Example 4, where ethanol was used as the medium, the dispersion state of silica in the resulting photopolymerizable compositions was inferior to the results for Examples 1 to 4.

[0057] Although embodiments of the present invention have been described above, the present invention is not limited to any particular embodiment, and various modifications and changes are possible within the scope of the invention as described in the claims.

Claims

1. A silane-treated silica dispersion is prepared by mixing a basic silica dispersion in which silica is dispersed in a solvent containing 10% by mass or more of water with a silane coupling agent, thereby maintaining a water content of 10% by mass or more. The silane-treated silica dispersion is mixed with a polymerizable monomer (excluding the silane coupling agent) added separately from the silane coupling agent used for the surface treatment of the silica to obtain a mixture containing an oil phase and an aqueous phase. A method for producing a treated silica-dispersed monomer composition, comprising separating the oil phase and the aqueous phase in the mixture and removing the aqueous phase to obtain a composition in which silica treated with a silane coupling agent is dispersed in polymerizable monomers.

2. The method for producing the treated silica-dispersed monomer composition according to claim 1, wherein the polymerizable monomer is a polymerizable monomer having a (meth)acryloyloxy group.

3. The method for producing the treated silica-dispersed monomer composition according to claim 2, wherein the polymerizable monomer having a (meth)acryloyloxy group is a di(meth)acrylate.

4. A method for producing a treated silica-dispersed monomer composition according to any one of claims 1 to 3, wherein the silane coupling agent is a silane coupling agent having a (meth)acryloyloxy group.

5. A method for producing a treated silica dispersion monomer composition according to any one of claims 1 to 4, wherein the pH of the silica dispersion is 9 to 11.

6. A method for producing a treated silica-dispersed monomer composition according to any one of claims 1 to 5, wherein the silica is colloidal silica.

7. A method for producing the treated silica dispersion monomer composition according to any one of claims 1 to 6, wherein the solvent contains sodium ions.

8. A method for producing a treated silica-dispersed monomer composition according to any one of claims 1 to 7, wherein removing the aqueous phase from the mixture includes removing the separated aqueous phase by adding water or acidic water and stirring.

9. A method for producing a treated silica-dispersed monomer composition according to any one of claims 1 to 8, comprising removing the aqueous phase and then heating at 80°C to 150°C.