Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B33—ADDITIVE MANUFACTURING TECHNOLOGY
  • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
  • B33Y70/00—Materials specially adapted for additive manufacturing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C64/00—Additive manufacturing, i.e. manufacturing of three-dimensional [3D] objects by additive deposition, additive agglomeration or additive layering, e.g. by 3D printing, stereolithography or selective laser sintering
  • B29C64/10—Processes of additive manufacturing
  • B29C64/106—Processes of additive manufacturing using only liquids or viscous materials, e.g. depositing a continuous bead of viscous material
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F299/00—Macromolecular compounds obtained by interreacting polymers involving only carbon-to-carbon unsaturated bond reactions, in the absence of non-macromolecular monomers
  • C08F299/02—Macromolecular compounds obtained by interreacting polymers involving only carbon-to-carbon unsaturated bond reactions, in the absence of non-macromolecular monomers from unsaturated polycondensates
  • C08F299/08—Macromolecular compounds obtained by interreacting polymers involving only carbon-to-carbon unsaturated bond reactions, in the absence of non-macromolecular monomers from unsaturated polycondensates from polysiloxanes
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/34—Silicon-containing compounds
  • C08K3/36—Silica
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K9/00—Use of pretreated ingredients
  • C08K9/04—Ingredients treated with organic substances
  • C08K9/06—Ingredients treated with organic substances with silicon-containing compounds
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L83/00—Compositions of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon only; Compositions of derivatives of such polymers
  • C08L83/04—Polysiloxanes
  • C08L83/06—Polysiloxanes containing silicon bound to oxygen-containing groups
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B33—ADDITIVE MANUFACTURING TECHNOLOGY
  • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
  • B33Y10/00—Processes of additive manufacturing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B33—ADDITIVE MANUFACTURING TECHNOLOGY
  • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
  • B33Y80/00—Products made by additive manufacturing

Definitions

• Patent Document 2 a UV-curable, low-viscosity silicone material has been proposed for use in inkjet 3D printers.
• This material has the advantage of being cured by short-term UV irradiation and having excellent modeling accuracy, but it has the drawback of being poor in mechanical strength and heat resistance compared to ordinary silicone materials.
• Patent Documents 3 and 4 new ultraviolet-curable silicone compositions have been developed for use in stereolithography, which has been rapidly increasing in recent years.
• Patent Documents 3 and 4 new ultraviolet-curable silicone compositions have been developed for use in stereolithography, which has been rapidly increasing in recent years.
• Patent Documents 3 and 4 compared to the mechanical strength of thermosetting silicone compositions, they have low elongation and can be brittle. In recent years, however, stereolithography has become possible even with higher viscosities than before.
• the present invention has been made in light of the above circumstances, and aims to provide a UV-curable silicone composition and a cured product thereof that has a viscosity suitable for use in stereolithography methods such as laser and Digital Light Processing (DLP), can be shaped with low UV exposure, and, after post-processing, produces a cured product that exhibits excellent rubber properties.
• stereolithography methods such as laser and Digital Light Processing (DLP)
• the inventors discovered that by adding a photopolymerization initiator to an organopolysiloxane having a specific radically polymerizable group-containing group bonded to a silicon atom via an oxygen atom directly bonded to the silicon atom, and hydrophobic silica particles having an average particle size in the range of 10 nm to 1,000 nm and a hydrophobicity of 60% or more as measured by methanol titration, it is possible to obtain an ultraviolet-curable silicone composition that is also applicable to stereolithography and that, by performing a primary cure by ultraviolet irradiation followed by a secondary cure by condensation, gives a cured product with good rubber properties, thereby completing the present invention.
• the present invention is 1.
• a silicone composition for stereolithography comprising: (B) hydrophobic silica particles having an average particle size of 10 nm to 1,000 nm and a hydrophobicity of 60% or more as determined by a methanol titration method; and (C) a photopolymerization initiator, a UV-curable silicone composition for stereolithography, which is irradiated with UV light having a wavelength of 405 nm at 25°C at a dose of 8,000 mJ/cm2, and then cured for 24 hours at 85°C and 85% RH, resulting in a cured product having a thickness of 2.0 mm and having a tensile strength of 4.5 MPa or more and an
• component (A) is an organopolysiloxane represented by the following formula (1): (In the formula, n is a number satisfying 1 ⁇ n ⁇ 1,000, m is a number satisfying 1 ⁇ m ⁇ 1,000, and the siloxane units to which n and m are attached may be arranged in any order.
• Each Ar is independently an aryl group having 6 to 20 carbon atoms
• each R1 is independently a monovalent hydrocarbon group having 1 to 20 carbon atoms
• A is a group represented by the following formula (2):
• R 1 is the same as above
• R 2 is an oxygen atom or an alkylene group having 1 to 20 carbon atoms
• R 3 is each independently an acryloyloxyalkyloxy group or a methacryloyloxyalkyloxy group
• a is a number satisfying 1 ⁇ a ⁇ 3, and the dashed line represents a bond.
• the ultraviolet-curable silicone composition for stereolithography according to any one of 1 to 3, comprising 10 to 500 parts by mass of component (B) and 0.01 to 20 parts by mass of component (C); 5.
• the ultraviolet-curable silicone composition for stereolithography according to any one of 1 to 4 having a viscosity of 500 Pa ⁇ s or less at 23°C. 6.
• A An organopolysiloxane having, per molecule, two or more radically polymerizable group-containing groups (excluding those containing heteroatoms other than oxygen atoms) bonded to silicon atoms via oxygen atoms directly bonded to the silicon atoms;
• B hydrophobic silica particles having an average particle size of 10 nm to 1,000 nm and a hydrophobicity of 60% or more as determined by a methanol titration method, and
• C a cured product of an ultraviolet-curable silicone composition for stereolithography, the cured product comprising a photopolymerization initiator, the cured product having a tensile strength of 4.5 MPa or more at a thickness of 2.0 mm and an elongation at break of 300% or more; 7.
• the UV-curable silicone composition for stereolithography of the present invention can be used in stereolithography methods such as laser and DLP, and the cured product after UV curing exhibits good rubber properties when moistened.
• UV-curable silicone composition for stereolithography contains the following components (A) to (C): (A) an organopolysiloxane having, per molecule, two or more radically polymerizable group-containing groups bonded to silicon atoms via oxygen atoms directly bonded to the silicon atoms; (B) hydrophobic silica particles having an average particle size in the range of 10 nm to 1,000 nm and a hydrophobicity of 60% or more as determined by methanol titration; and (C) a photopolymerization initiator.
• A an organopolysiloxane having, per molecule, two or more radically polymerizable group-containing groups bonded to silicon atoms via oxygen atoms directly bonded to the silicon atoms
• B hydrophobic silica particles having an average particle size in the range of 10 nm to 1,000 nm and a hydrophobicity of 60% or more as determined by methanol titration
• C a photopolymerization initiator
• Organopolysiloxane Component (A) used in the present invention is the crosslinking component of the composition and is an organopolysiloxane having two or more radically polymerizable group-containing groups per molecule that are bonded to silicon atoms via oxygen atoms directly bonded to those silicon atoms, preferably 2 to 6, and more preferably 2 to 4 such radically polymerizable group-containing groups per molecule, provided that the radically polymerizable group-containing groups do not contain heteroatoms other than oxygen atoms.
• the radically polymerizable group-containing group bonded to the silicon atom via an oxygen atom directly bonded to the silicon atom gives the composition of the present invention both radical curing properties and condensation curing properties.
• a primary cured product obtained by irradiating the composition of the present invention with ultraviolet light (radical curing) can be further post-treated with moisture (condensation curing) to obtain a secondary cured product with even better rubber physical properties.
• radically polymerizable group-containing group examples include an acryloyloxyalkyloxy group or a methacryloyloxyalkyloxy group bonded to a silicon atom.
• (meth)acryloyloxyalkyloxy groups bonded to silicon atoms, which leads to chain extension reactions between the organopolysiloxanes of component (A) and crosslinking reactions between the organopolysiloxanes of component (A) and silanol groups on the surface of the silica particles of component (B), which will be described later.
• (meth)acryloyloxyalkyloxy group refers to an acryloyloxyalkyloxy group or a methacryloyloxyalkyloxy group.
• the radically polymerizable group-containing group may be located at either the molecular chain terminal (one terminal or both terminals), midway along the molecular chain, or both terminals, but is preferably located at the molecular chain terminal (one terminal or both terminals), and more preferably at both terminals.
• groups bonded to silicon atoms other than the radically polymerizable group-containing groups include monovalent hydrocarbon groups having 1 to 20 carbon atoms, preferably monovalent hydrocarbon groups having 1 to 10 carbon atoms, and more preferably monovalent hydrocarbon groups having 1 to 8 carbon atoms, excluding aliphatic unsaturated groups.
• some or all of the hydrogen atoms bonded to carbon atoms of the monovalent hydrocarbon groups may be substituted with other substituents such as halogen atoms.
• the monovalent hydrocarbon group may be linear, branched, or cyclic, and examples thereof include alkyl, aryl, and halogenated alkyl groups, which are easy to synthesize.
• alkyl and aryl groups having 1 to 3 carbon atoms are preferred, with methyl, ethyl, and phenyl groups being more preferred.
• the molecular structure of component (A) is preferably a linear or branched main chain consisting of repeating diorganosiloxane units (including linear main chains with partial branches), and in particular, a linear diorganopolysiloxane in which both molecular chain terminals are blocked with units containing the above-mentioned radically polymerizable group-containing groups is preferred.
• an organopolysiloxane represented by the following formula (1) is more preferred.
• R 1 's are each independently a monovalent hydrocarbon group having 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, and more preferably 1 to 8 carbon atoms.
• the monovalent hydrocarbon group of 1 to 20 carbon atoms for R 1 is preferably a monovalent aliphatic hydrocarbon group of 1 to 20 carbon atoms, which may be linear, branched, or cyclic. Specific examples thereof include linear, branched, or cyclic alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-hexyl, cyclohexyl, n-octyl, 2-ethylhexyl, and n-decyl; and alkenyl groups such as vinyl, allyl (2-propenyl), 1-propenyl, isopropenyl, and butenyl.
• R 1 is preferably an alkyl group having 1 to 3 carbon atoms, more preferably a methyl group or an ethyl group.
• each Ar is independently an aryl group having 6 to 20 carbon atoms, preferably 6 to 10 carbon atoms.
• aromatic hydrocarbon groups such as phenyl, biphenyl, and naphthyl groups, and aromatic groups containing heteroatoms (O, S, N) such as furanyl groups.
• aromatic groups may further contain a substituent such as a halogen atom (e.g., chlorine, bromine, or fluorine atom).
• Ar is preferably an unsubstituted aryl group, and particularly preferably a phenyl group.
• n is a number that satisfies 1 ⁇ n ⁇ 1,000, and in order to further improve the viscosity of the composition and the mechanical properties of the cured product, it is preferably a number that satisfies 1 ⁇ n ⁇ 400, and more preferably 1 ⁇ n ⁇ 200. If n is less than 1, the composition is prone to volatilization, and if n is greater than 1,000, the viscosity of the composition increases, making it difficult to mold.
• m is a number that satisfies 1 ⁇ m ⁇ 1,000, and in order to further improve the viscosity of the composition and the mechanical properties of the cured product, it is preferably a number that satisfies 1 ⁇ m ⁇ 400, and more preferably 10 ⁇ m ⁇ 300. If m is less than 1, the composition is prone to volatilization, and if m is greater than 1,000, the viscosity of the composition increases, making it difficult to mold.
• n+m is preferably a number that satisfies 2 ⁇ n+m ⁇ 2,000, more preferably 2 ⁇ n+m ⁇ 1,000, and even more preferably 2 ⁇ n+m ⁇ 800. If n+m is less than 2, the composition may be prone to volatilization, and if n+m is greater than 2,000, the viscosity of the composition may increase, making it difficult to mold the composition.
• the siloxane units to which n and m are added may be arranged in any order.
• a in formula (1) is a group represented by the following formula (2). (In the formula, the dashed lines represent bonds.)
• R 1 is the same as above.
• R 2 represents an oxygen atom or an alkylene group having 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, and more preferably 1 to 5 carbon atoms.
• the alkylene group having 1 to 20 carbon atoms for R2 may be linear, branched, or cyclic, and specific examples thereof include methylene, ethylene, propylene, trimethylene, tetramethylene, isobutylene, pentamethylene, hexamethylene, heptamethylene, octamethylene, nonamethylene, and decylene groups.
• R 2 is preferably an oxygen atom, methylene, ethylene or trimethylene group, more preferably an oxygen atom or an ethylene group.
• R3 's are each independently an acryloyloxyalkyloxy group or a methacryloyloxyalkyloxy group.
• the number of carbon atoms in the alkyl (alkylene) group in the acryloyloxyalkyloxy group or methacryloyloxyalkyloxy group of R3 is not particularly limited, but is preferably 1 to 10, and more preferably 1 to 5. Specific examples of these alkyl groups include those having 1 to 10 carbon atoms among the groups exemplified for R1 . Specific examples of R3 include, but are not limited to, those represented by the following formulae:
• R4 is an alkylene group having 1 to 10 carbon atoms, preferably an alkylene group having 1 to 5 carbon atoms.
• Specific examples of R4 include those groups exemplified for R2 having 1 to 10 carbon atoms, of which methylene, ethylene, and trimethylene groups are preferred, and an ethylene group is more preferred.
• a is a number that satisfies 1 ⁇ a ⁇ 3, with 1 or 2 being preferred.
• Component (A) may be a single polymer having these molecular structures, a copolymer having these molecular structures, or a mixture of two or more of these polymers.
• organopolysiloxanes for component (A) include, but are not limited to, those represented by the following formulas (3) and (4):
• Me represents a methyl group
• Ph represents a phenyl group
• n and m have the same meanings as above, and the siloxane units to which n and m are attached may be arranged in any order.
• organopolysiloxanes can be obtained, for example, by reacting 2-hydroxyethyl acrylate with the hydrosilylation reaction product of a dimethylsiloxane-diphenylsiloxane copolymer endblocked at both ends with dimethylvinylsiloxy groups and chlorodimethylsilane or dichloromethylsilane.
• Component (B) is hydrophobic silica particles. By including component (B), the mechanical strength of the cured product can be increased while maintaining the fluidity of the composition.
• Component (B) has an average particle size of 10 to 1,000 nm, preferably 20 to 1,000 nm, more preferably 20 to 500 nm, and even more preferably 30 to 200 nm. If the average particle size is smaller than 10 nm, aggregation becomes severe and fluidity is lost. If it is larger than 1,000 nm, the effect of improving mechanical strength is small.
• the above average particle size is a value measured as the volume-based median diameter (D 50 ) in particle size distribution measurement by laser light diffraction method.
• the hydrophobicity of component (B) measured by methanol titration is 60% or higher, preferably 64% or higher. Silica particles with a high hydrophobicity do not aggregate even when highly loaded into the composition, and the mechanical strength of the cured product can be increased without impairing fluidity.
• the degree of hydrophobicity can be determined by the following methanol titration method. (1) The sample is suspended in a predetermined amount of ion-exchanged water, and methanol is added dropwise while stirring. (2) When the entire amount of the sample is suspended in the ion-exchanged water, read the amount of the drop. (3) The value calculated by [ ⁇ amount of methanol added (mL) ⁇ / ⁇ amount of methanol added (mL)+amount of ion-exchanged water (mL) ⁇ ] ⁇ 100 is the hydrophobicity.
• component (B) used in the present invention is not particularly limited, but spherical shape is preferred.
• the amount of component (B) blended is preferably 10 to 500 parts by mass, more preferably 20 to 300 parts by mass, and even more preferably 30 to 200 parts by mass per 100 parts by mass of component (A).
• An amount of 10 parts by mass or more will sufficiently improve the mechanical strength of the cured product, while an amount of 500 parts by mass or less will not result in an excessively high viscosity of the composition, resulting in excellent flowability.
• Component (B) preferably has R 7 SiO 3/2 units (R 7 is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms) and R 9 3 SiO 1/2 units (R 9 is the same or different substituted or unsubstituted monovalent hydrocarbon group having 1 to 6 carbon atoms) on the silica surface.
• Component (B) can be obtained, for example, by hydrolyzing and condensing a tetrafunctional silane compound, an alkyl silicate, or a mixture thereof to obtain hydrophilic silica particles, and then introducing R 7 SiO 3/2 units and then R 9 3 SiO 1/2 units onto the surfaces of the resulting particles through hydrolysis and condensation.
• Step ( ⁇ ) A step of synthesizing hydrophilic silica particles.
• Step ( ⁇ ) A step of subjecting the hydrophilic silica particles to surface hydrophobic treatment to obtain an intermediate of component (B).
• Step ( ⁇ ) A step of further subjecting the intermediate of component (B) to surface hydrophobic treatment to obtain hydrophobic silica particles of component (B).
• Step ( ⁇ ) is a step of obtaining a dispersion of hydrophilic silica particles by hydrolyzing and condensing either or both of a tetrafunctional silane compound represented by the following general formula (I) and an alkyl silicate represented by the following general formula (II) in a mixed solution of a hydrophilic organic solvent and water in the presence of a basic substance.
• Si( OR5 ) 4 (I) (wherein, R5 's are the same or different monovalent hydrocarbon groups having 1 to 6 carbon atoms, and k is a number from 1 to 100.)
• R5 is the same or different monovalent hydrocarbon group having 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms, more preferably 1 or 2 carbon atoms.
• the monovalent hydrocarbon group represented by R5 may be linear, branched, or cyclic. Specific examples thereof include alkyl groups such as methyl, ethyl, n-propyl, isopropyl, and n-butyl; and aryl groups such as phenyl. Of these, R5 is preferably a methyl, ethyl, n-propyl, or n-butyl group, and more preferably a methyl or ethyl group.
• k is a number from 1 to 100, preferably a number from 1 to 50, and more preferably a number from 1 to 25.
• tetrafunctional silane compound represented by the general formula (I) above include tetraalkoxysilanes such as tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane; and tetraaryloxysilanes such as tetraphenoxysilane. Of these, preferred are tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane, and more preferred are tetramethoxysilane and tetraethoxysilane.
• alkyl silicate represented by the general formula (II) include methyl silicate and ethyl silicate, and among these, methyl silicate is preferred. These may be used alone or in combination of two or more.
• hydrophilic organic solvents used in step ( ⁇ ) are not particularly limited, as long as they dissolve the tetrafunctional silane compound represented by general formula (I) or the alkyl silicate represented by general formula (II) and water.
• examples include alcohols; cellosolves such as methyl cellosolve, ethyl cellosolve, butyl cellosolve, and cellosolve acetate; ketones such as acetone and methyl ethyl ketone; and ethers such as dioxane and tetrahydrofuran. Of these, alcohols and cellosolves are preferred, and alcohols are more preferred.
• the alcohols include those represented by the following general formula (VI).
• R 6 OH (VI) (wherein R6 is a monovalent hydrocarbon group having 1 to 6 carbon atoms).
• alcohols represented by general formula (VI) include methanol, ethanol, propanol, isopropanol, and butanol, with methanol and ethanol being preferred.
• methanol is preferred for obtaining the desired small silica particles.
• the amount of water used in the above hydrolysis and condensation is preferably 0.5 to 5 moles, more preferably 0.6 to 2 moles, and even more preferably 0.7 to 1 mole, per mole of the total of hydrocarbyloxy groups in the tetrafunctional silane compound represented by general formula (I) and/or the alkyl silicate represented by general formula (II).
• the ratio of water to hydrophilic organic solvent is preferably 10 to 200 parts by mass of hydrophilic organic solvent per 100 parts by mass of water.
• step ( ⁇ ) Specific examples of the basic substance used in step ( ⁇ ) include ammonia, dimethylamine, diethylamine, etc., of which ammonia and diethylamine are preferred, and ammonia is more preferred.
• the required amount of these basic substances can be dissolved in water, and the resulting aqueous solution (basic) can then be mixed with a hydrophilic organic solvent.
• the amount of the basic substance used is preferably 0.01 to 2 mol, more preferably 0.02 to 0.5 mol, and even more preferably 0.04 to 0.12 mol, per mol of the total of the hydrocarbyloxy groups of the tetrafunctional silane compound represented by general formula (I) and/or the alkyl silicate represented by general formula (II).
• the basic substance may be added to a mixture of a hydrophilic organic solvent and water, and then further added to the resulting mixture together with the tetrafunctional silane compound represented by general formula (I) and/or the alkyl silicate represented by general formula (II).
• the basic substance may be added to a mixture of water and a hydrophilic organic solvent simultaneously with the addition of the tetrafunctional silane compound and/or the alkyl silicate and the hydrophilic organic solvent.
• reaction conditions for step ( ⁇ ) are not particularly limited and can be carried out under conventionally known conditions; for example, temperatures of approximately 10 to 80°C for approximately 1 to 10 hours are preferred.
• the resulting mixed solvent dispersion containing hydrophilic silica particles may be used as is in step ( ⁇ ), but it is preferable to convert it into an aqueous dispersion containing hydrophilic silica particles by adding water to the mixed solvent dispersion containing hydrophilic silica particles, then evaporating off the hydrophilic organic solvent and converting it into an aqueous dispersion, as this will hydrolyze any remaining alkoxy groups.
• Step ( ⁇ ) is a step of adding either or both of a trifunctional silane compound represented by the following general formula (III) and its (partial) hydrolysis condensate to the mixed solvent dispersion of hydrophilic silica particles obtained in step ( ⁇ ) to treat the surfaces of the hydrophilic silica particles, thereby obtaining a dispersion of silica particles (hydrophobic silica particle intermediate), which is an intermediate of component (B).
• a trifunctional silane compound represented by the following general formula (III) and its (partial) hydrolysis condensate to the mixed solvent dispersion of hydrophilic silica particles obtained in step ( ⁇ ) to treat the surfaces of the hydrophilic silica particles, thereby obtaining a dispersion of silica particles (hydrophobic silica particle intermediate), which is an intermediate of component (B).
• R7 is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, more preferably 1 to 3 carbon atoms, and even more preferably 1 or 2 carbon atoms.
• the monovalent hydrocarbon group of R7 may be linear, branched, or cyclic, and specific examples include alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, n-hexyl, and n-decyl.
• R7 is preferably a methyl, ethyl, n-propyl, or isopropyl group, and more preferably a methyl group or an ethyl group.
• some or all of the hydrogen atoms of these monovalent hydrocarbon groups may be substituted with halogen atoms such as fluorine, chlorine, or bromine atoms, and is preferably a fluorine-substituted alkyl group.
• R8 is the same or different monovalent hydrocarbon group having 1 to 6 carbon atoms, preferably 1 to 3 carbon atoms, more preferably 1 or 2 carbon atoms.
• R8 include the same groups as those exemplified for R5 , and among these, R8 is preferably a methyl, ethyl, or n-propyl group, more preferably a methyl group or an ethyl group.
• methyltrimethoxysilane preferred are methyltriethoxysilane, ethyltrimethoxysilane, and ethyltriethoxysilane, and more preferred are methyltrimethoxysilane and methyltriethoxysilane.
• the amount of the trifunctional silane compound represented by general formula (III) added is preferably 0.001 to 1 mol, more preferably 0.01 to 0.4 mol, and even more preferably 0.01 to 0.2 mol per mol of Si atoms in the hydrophilic silica particles obtained in step ( ⁇ ). If the amount added is 0.001 mol or more, the hydrophobicity of the resulting component (B) is increased, resulting in excellent dispersibility, while if the amount added is 1 mol or less, the risk of aggregation of component (B) can be suppressed.
• the treatment conditions in step ( ⁇ ) are not particularly limited, and are preferably, for example, about 10 to 80° C. for about 1 to 10 hours.
• the dispersion medium of the mixed solvent dispersion of silica particles, an intermediate of component (B) obtained in step ( ⁇ ) is converted to, for example, a ketone solvent to obtain a ketone solvent dispersion of hydrophobic silica particle intermediates, and then either one or both of a silazane compound represented by the following general formula (IV) and a monofunctional silane compound represented by the following general formula (V) are added to this ketone solvent dispersion to treat the surfaces of the silica particles, an intermediate of component (B), thereby obtaining hydrophobic silica particles of component (B).
• a silazane compound represented by the following general formula (IV) and a monofunctional silane compound represented by the following general formula (V) are added to this ketone solvent dispersion to treat the surfaces of the silica particles, an intermediate of component (B), thereby obtaining hydrophobic silica particles of component (B).
• R93SiO1 /2 units are introduced onto the surfaces of the hydrophobic silica particle intermediates by triorganosilylating the silanol groups remaining on the surfaces of the hydrophobic silica particle intermediates.
• R93SiNHSiR93 ( IV ) R 9 3 SiX (V) (wherein R 9 is the same or different, substituted or unsubstituted, monovalent hydrocarbon group having 1 to 6 carbon atoms, and X is an OH group or a hydrolyzable group.)
• R9 is the same or different, substituted or unsubstituted, monovalent hydrocarbon group having 1 to 6 carbon atoms, preferably a monovalent hydrocarbon group having 1 to 4 carbon atoms, more preferably 1 or 2 carbon atoms.
• R9 include the same groups as those exemplified for R5 , and among these, R9 is preferably a methyl, ethyl, or n-propyl group, more preferably a methyl group or an ethyl group.
• hydrogen atoms of these monovalent hydrocarbon groups may be substituted with halogen atoms such as fluorine atoms, chlorine atoms, or bromine atoms, and fluorine-substituted alkyl groups are preferred.
• X represents an OH group or a hydrolyzable group.
• hydrolyzable groups include a chlorine atom; alkoxy groups such as methoxy and ethoxy; amino, N-methylamino, N,N'-dimethylamino, N-ethylamino, and N,N'-diethylamino; and acyloxy groups such as acetoxy.
• an alkoxy group or amino group is preferred, an alkoxy group is more preferred, and a methoxy or ethoxy group is even more preferred.
• silazane compound represented by the general formula (IV) examples include hexamethyldisilazane, hexaethyldisilazane, and tetramethyldivinyldisilazane, with hexamethyldisilazane being preferred.
• monofunctional silane compound represented by general formula (V) include monosilanol compounds such as trimethylsilanol and triethylsilanol; monochlorosilanes such as trimethylchlorosilane and triethylchlorosilane; monoalkoxysilanes such as trimethylmethoxysilane and trimethylethoxysilane; monoaminosilanes such as trimethylsilyldimethylamine and trimethylsilyldiethylamine; and monoacyloxysilanes such as trimethylacetoxysilane.
• monosilanol compounds such as trimethylsilanol and triethylsilanol
• monochlorosilanes such as trimethylchlorosilane and triethylchlorosilane
• monoalkoxysilanes such as trimethylmethoxysilane and trimethylethoxysilane
• monoaminosilanes such as trimethylsilyl
• trimethylsilanol trimethylmethoxysilane, and trimethylsilyldiethylamine
• trimethylsilanol and trimethylmethoxysilane preferred are trimethylsilanol and trimethylmethoxysilane. These may be used alone or in combination of two or more.
• the amount of the silazane compound represented by general formula (IV) and/or the monofunctional silane compound represented by general formula (V) used is preferably 0.1 to 0.5 mol, more preferably 0.2 to 0.4 mol, and even more preferably 0.25 to 0.35 mol, per mol of Si atoms in the hydrophobic silica particle intermediate obtained in step ( ⁇ ). If the amount used is 0.1 mol or more, the resulting hydrophobic silica particles will have a high degree of hydrophobicity and excellent dispersibility. Taking cost and other factors into consideration, an amount of 0.5 mol or less is sufficient.
• the dispersion medium of the mixed solvent dispersion of the hydrophobic silica particle intermediate obtained in step ( ⁇ ) can be converted from a mixed solvent of water or a hydrophilic organic solvent and an alcohol generated during hydrolysis to a ketone-based solvent by adding a ketone-based solvent to the mixed solvent dispersion of the hydrophobic silica particle intermediate, and then distilling off the water or the hydrophilic organic solvent and the alcohol mixture (this operation can be repeated as necessary).
• the conditions for this conversion are preferably about 10 to 150°C and about 1 to 20 hours.
• the amount of the ketone solvent added is preferably 50 to 500 parts by mass, more preferably 100 to 300 parts by mass, relative to 100 parts by mass of the obtained hydrophobic silica particle intermediate.
• ketone solvent used here include methyl ethyl ketone, methyl butyl ketone, and acetylacetone, and among these, methyl isobutyl ketone is preferred.
• the surface treatment conditions in step ( ⁇ ) are not particularly limited, and are preferably, for example, at about 10 to 150° C. for about 1 to 20 hours.
• Component (B) obtained as described above can be obtained as a powder by conventional methods such as drying at room temperature or under heat, atmospheric drying, or vacuum drying.
• the component (C) is a photopolymerization initiator.
• photoinitiators that can be used in the present invention include 2,2-diethoxyacetophenone, 2,2-dimethoxy-1,2-diphenylethan-1-one (Omnirad 651), 1-hydroxy-cyclohexyl-phenyl-ketone (Omnirad 184), 2-hydroxy-2-methyl-1-phenyl-propan-1-one (Omnirad 1173), 2-hydroxy-1- ⁇ 4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]-phenyl ⁇ -2-methyl-propan-1-one (Omnirad 127), phenylglyoxylic acid methyl ester (Omnirad MBF), 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one (Omnirad 907), 2-benzyl-2-dimethylamino-1-(4-
• the amount of photopolymerization initiator added is preferably 0.01 to 20 parts by mass, and more preferably 0.1 to 10 parts by mass, per 100 parts by mass of component (A). At least 0.01 parts by mass ensures sufficient surface curing, while at most 20 parts by mass there is no risk of impairing deep curing.
• UV absorber having light absorption in the wavelength range of 360 to 410 nm An ultraviolet absorber having light absorption in the wavelength range of 360 to 410 nm can be added to the composition of the present invention in order to adjust the curing properties during stereolithography using a 3D printer.
• ultraviolet absorbers examples include 2-(2H-benzotriazol-2-yl)-6-dodecyl-4-methylphenol (Tinuvin 571, manufactured by BASF), benzenepropanoic acid 3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy C7-9 side chain and linear alkyl ester (Tinuvin 384-2, manufactured by BASF), 2-(5-chloro-2-benzotriazolyl)-6-tert-butyl-p-cresol (Tinuvin 326, manufactured by BASF), 2-(4,6-bis(2,4-dimethylphenyl)-1,3,5-triazin-2-yl)-5-hydroxyphenyl, and Examples include reaction products with [(C10-C16 mainly C12-C13 alkyloxy)methyl]oxirane (Tinuvin 400, manufactured by BASF), thioxanthone, 2-isopropy
• the amount added is preferably 0.01 to 20 parts by mass, and more preferably 0.1 to 10 parts by mass, per 100 parts by mass of component (A).
• An amount of 0.01 part by mass or more ensures that the ultraviolet absorber is fully effective, while an amount of 20 parts by mass or less prevents deterioration of deep section curing.
• coloring material Various coloring materials may be added to the composition of the present invention for the purpose of adjusting the curability of the composition or for the purpose of coloring the composition.
• coloring material general pigments (iron oxide, titanium oxide, zinc oxide, etc.), dyes, carbon black, etc. can be used. These may be used alone or in combination of two or more.
• the amount added is preferably 0.01 to 20 parts by weight per 100 parts by weight of component (A). At least 0.01 parts by weight ensures the full effect of the colorant, while at most 20 parts by weight there is no risk of deterioration in deep section curing.
• the composition of the present invention may contain additives such as a silane coupling agent, an adhesion promoter, a polymerization inhibitor, an antioxidant, an ultraviolet absorber which is a light resistance stabilizer, and a light stabilizer, as long as the effects of the present invention are not impaired.
• additives such as a silane coupling agent, an adhesion promoter, a polymerization inhibitor, an antioxidant, an ultraviolet absorber which is a light resistance stabilizer, and a light stabilizer, as long as the effects of the present invention are not impaired.
• the composition of the present invention can also be used by appropriately mixing it with other resin compositions.
• the method for producing the silicone composition of the present invention is not particularly limited, and any conventionally known method can be used. That is, the silicone composition of the present invention can be obtained by mixing components (A) to (C) and, if necessary, other components.
• the method for producing the silicone composition of the present invention preferably includes the following steps (1) and (2).
• Step (1) A step of producing component (B) by a method including the following steps ( ⁇ ), ( ⁇ ), and ( ⁇ ):
• Step (1) is a step of producing component (B) by a method including the following steps ( ⁇ ), ( ⁇ ), and ( ⁇ ):
• the UV-curable silicone composition for stereolithography of the present invention can be obtained by mixing the above-mentioned components (A) to (C), and, if necessary, other components, in any order, followed by stirring, etc.
• the equipment used for stirring, etc. is not particularly limited, but includes a crusher, a three-roll mill, a ball mill, a planetary mixer, etc. These equipment may also be used in combination as appropriate.
• the silicone composition of the present invention may be in the form of a one-component or two-component type.
• a one-component composition can be obtained, for example, by adding components (A) to (C) and, if necessary, other components, to a gate mixer (manufactured by Inoue Seisakusho Co., Ltd., product name: Planetary Mixer) and mixing them.
• a gate mixer manufactured by Inoue Seisakusho Co., Ltd., product name: Planetary Mixer
• components (A) and (B) can be placed in a gate mixer and mixed under reduced pressure at room temperature for one hour. After cooling the resulting mixture, component (C) can be added and mixed at room temperature for 30 minutes to obtain the silicone composition.
• the viscosity of the ultraviolet-curable silicone composition for optical shaping of the present invention at 23°C is preferably 500 Pa ⁇ s or less, more preferably 400 Pa ⁇ s or less, and even more preferably 100 Pa ⁇ s or less. If the viscosity exceeds 500 Pa ⁇ s, the shaping properties will deteriorate and it may not be possible to accurately obtain the desired shaped object. There is no particular lower limit, but a viscosity of 1 Pa ⁇ s or more is preferred, and 2 Pa ⁇ s or more is more preferred. In the present invention, the viscosity can be measured using a rotational viscometer (for example, BL type, BH type, BS type, cone-plate type, rheometer, etc.) (the same applies hereinafter).
• a rotational viscometer for example, BL type, BH type, BS type, cone-plate type, rheometer, etc.
• the ultraviolet-curable silicone composition for stereolithography of the present invention can be used to form a cured product with excellent rubber properties by the following process. (i) a step of irradiating the ultraviolet-curable silicone composition for stereolithography of the present invention with ultraviolet light to radically cure the composition and obtain a primary cured product, and (ii) a step of further condensation-curing the obtained primary cured product to obtain a secondary cured product.
• Step (i) is a step of irradiating the ultraviolet-curable silicone composition for stereolithography of the present invention with ultraviolet light to radically cure the composition and obtain a primary cured product.
• examples of the light source for the ultraviolet light to be irradiated include a UV-LED lamp, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a metal halide lamp, a carbon arc lamp, and a xenon lamp.
• the ultraviolet irradiation is preferably carried out, for example, at about room temperature (25° C.) in an inert gas atmosphere such as nitrogen or argon.
• the irradiation dose (cumulative light amount) of ultraviolet light is preferably 1 to 10,000 mJ/ cm2 , and more preferably 10 to 8,000 mJ/ cm2 , for example, for a sheet obtained by molding the composition of the present invention to a thickness of about 2.0 mm.
• irradiation with ultraviolet light for about 0.01 to 100 seconds is sufficient.
• the tensile strength of the primary cured product obtained in step (i) is preferably 2.0 MPa or more, more preferably 3.0 MPa or more. Furthermore, the elongation at break is preferably 150% or more, more preferably 200% or more. These values are measured in accordance with JIS-K6249 (the same applies below).
• Step (ii) Step of Obtaining a Secondary Cured Product
• Step (ii) is a step of further condensation-curing the obtained primary cured product to obtain a secondary cured product.
• the hydrolysis condensation of component (A) and/or component (B) can be accelerated by applying moisture.
• condensation curing is preferably carried out in an environment of 50% RH to 85% RH and 20°C to 85°C for 12 to 36 hours, and particularly 18 to 24 hours.
• the secondary cured product obtained in step (ii) has a tensile strength of 4.5 MPa or more, preferably 5.0 MPa or more, and an elongation at break of 300% or more, preferably 250% or more.
• the tensile strength and elongation at break of a 2.0 mm thick cured product obtained by irradiating the film with ultraviolet light having a wavelength of 405 nm at 25°C at a dose of 8,000 mJ/ cm2 and then curing the film for 24 hours at 85°C and 85% RH can be within the above ranges.
• Component (C) (C-1) Ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate (Omnirad TPO-L, manufactured by IGM Resins B.V.)
• Comparative Synthesis Example 1 A 3-liter glass reactor equipped with a stirrer, a dropping funnel, and a thermometer was charged with 60 g of isopropanol and 100 g of Snowtex OL (a type of colloidal silica, manufactured by Nissan Chemical Industries, Ltd., average particle size 50 nm, dispersed in water, solids concentration 20% by mass) as silica particles, and mixed. 0.48 g of methyltrimethoxysilane was added dropwise to this solution over 0.5 hours, and after the addition, the solution was heated to 50°C and aged for 1 hour. After the reaction was completed, the solution was cooled to 25°C, and the silica particle surfaces were treated.
• Snowtex OL a type of colloidal silica, manufactured by Nissan Chemical Industries, Ltd., average particle size 50 nm, dispersed in water, solids concentration 20% by mass
• Silicone compositions were prepared by mixing the above components (A) to (C) in the ratios shown in Table 2. The viscosity of the compositions shown in Table 2 was measured at 23°C using a rotational viscometer. The prepared silicone composition was cured by irradiating it with ultraviolet light at a wavelength of 405 nm at room temperature (25°C) using a UV curing device manufactured by CCS Inc. in a nitrogen atmosphere at an irradiation dose of 8,000 mJ/ cm2 , yielding a primary cured product. The resulting primary cured product was then treated at 85° C.
• the hardness, elongation at break, and tensile strength of the resulting sheets (2.0 mm thick) of the first cured product and second cured product were measured in accordance with JIS K 6249:2003.
• the UV-curable silicone compositions prepared in Examples 1 to 5 have low viscosities suitable for use in stereolithography, and the cured products obtained after UV irradiation and moisture treatment have good mechanical properties.
• Comparative Example 1 in which the radically polymerizable group-containing group in component (A) was changed to one in which an oxygen atom directly bonded to a silicon atom and a dimethylsilyl group were bonded to the silicon atom, the condensation reactivity with moisture was low and the physical properties of the resulting secondary cured product were poor.
• Comparative Example 2 in which silica particles with an insufficient degree of hydrophobicity were used, the viscosity of the composition increased significantly and the curability was also insufficient.

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