JP7729551B2 - Polyurethane composite material, method for producing molded article made of said polyurethane composite material, and material for dental cutting - Google Patents

Description

The present invention relates to a polyurethane composite material, a method for producing a molded article made from the polyurethane composite material, and a material for dental cutting.

In dental treatment, one method for fabricating dental prostheses such as inlays, onlays, crowns, bridges, and implant superstructures is to use a dental CAD/CAM system for machining. A dental CAD/CAM system uses a computer to design dental prostheses based on three-dimensional coordinate data, and then fabricates the crown restoration using a machining machine. Various materials are used for machining, including glass ceramics, zirconia, titanium, and resin. Resin-based dental machining materials are curable compositions containing inorganic fillers such as silica, polymerizable monomers such as methacrylate, and polymerization initiators, which are cured into block or disk shapes. Machining materials using computer systems are attracting increasing interest due to their improved workability, resulting from the reduced number of steps compared to traditional dental prosthesis fabrication methods, as well as the aesthetic and strength benefits of the cured product.

Such cutting materials are primarily used in the crown area of teeth, and when used for molar crowns or bridges, higher strength is required. However, current cutting materials are based on (meth)acrylic resin, and the limited strength they offer is an issue.

In contrast, polyurethane resins are generally known to have high strength, and their use as dental materials is being considered. For example, Patent Document 1 describes a polyurethane composite material that takes advantage of the "high strength" characteristic of polyurethane resins while improving their drawback of poor water resistance by introducing a crosslinked structure formed by the polymerization of radically polymerizable groups into the polyurethane resin (hereinafter, polyurethane composite materials with crosslinked structures introduced in this manner will also be referred to as "crosslinked structure-introduced polyurethane composite materials"), as well as a method for producing the same.

That is, Patent Document 1 describes a polyurethane composite material produced by using a raw material composition containing as raw materials a diol compound (a1) having one or more radically polymerizable groups; a diisocyanate compound (a2); a polymerizable monomer (B) having one or more radically polymerizable groups in the molecule and not undergoing a polyaddition reaction with either the diol compound (a1) or the diisocyanate compound (a2) (hereinafter also referred to as a "non-polyaddition radically polymerizable monomer"); a radical polymerization initiator (C); and a filler (D), polyadding a1 and a2 to form a polyurethane component (A) of a specific molecular weight, and then reacting the radically polymerizable groups contained in (A) with (B) to introduce a crosslinked structure. The material is uniform throughout, has excellent strength and water resistance, and is suitable as a material for dental cutting.

WO2021/153446

However, in the polyurethane composite material described in Patent Document 1, in order to maintain good uniformity, the proportion of the polyurethane component in the resin component cannot be increased beyond 80% by mass. Specifically, the "polymerizable monomer blending ratio Rr," defined as the proportion (by mass) of B to the total mass of the monomer components in the raw material composition (the total mass of a1, a2, and B), must be 20 to 80% by mass ("100 - Rr," representing the proportion of the polyurethane component, is 80 to 20% by mass).

For this reason, it was unclear what properties crosslinked polyurethane composite materials would have in the region where the polyurethane component content exceeds 80% by mass, or whether they would have the same characteristics as the polyurethane composite material described in Patent Document 1, such as overall uniformity and excellent strength and water resistance. Increasing the polyurethane component content in crosslinked polyurethane composite materials is expected to not only result in increased strength (derived from the polyurethane structure), but also, if crosslinked polyurethane composite materials with polyurethane component contents exceeding 80% by mass can be produced and the existence of a region where uniformity and water resistance are well maintained is confirmed, new crosslinked polyurethane composite materials with properties similar to those of the polyurethane composite material described in Patent Document 1 could be used.

The present invention therefore aims to provide a method for producing a crosslinked polyurethane composite material having a polyurethane component content of more than 80% by mass, and ultimately to provide a crosslinked polyurethane composite material having a polyurethane component content of more than 80% by mass that is uniform, has excellent strength, and is water-resistant.

The present invention solves the above-mentioned problems and provides a polyurethane composite material in which a filler is dispersed in a matrix made of a polyurethane resin, the polyurethane composite material comprising:
The polyurethane resin has a number average molecular weight of 1,500 to 5,000, and has a crosslinked structure formed by radical polymerization of a polyurethane component having a radical polymerizable group (hereinafter also referred to as a "radical polymerizable polyurethane component") with a radical polymerizable monomer;
The proportion of the polyurethane component in the polyurethane-based resin is more than 80% by mass and 95% by mass or less.
The present invention also relates to a method for producing a molded article made of the polyurethane composite material (hereinafter also referred to as "the polyurethane composite material of the present invention") characterized in that:

That is, one aspect of the present invention is a first raw material composition preparation step of preparing a first raw material composition including: a diol compound (a1) having one or more radically polymerizable groups; a polymerizable monomer (B) having one or more radically polymerizable groups in the molecule and not undergoing a polyaddition reaction with either the diol compound (a1) or a diisocyanate compound; a thermal radical polymerization initiator (C) having a 10-hour half-life temperature: _T10 of 60°C or higher; and a filler (D);
a second raw material composition preparation step of mixing the first raw material composition with a diisocyanate compound (a2) to cause a polyaddition reaction between the diol compound (a1) and the diisocyanate compound (a2) to form a polyurethane component (A) having a number average molecular weight of 1,500 to 5,000 and having a radically polymerizable group, thereby preparing a second raw material composition comprising the polyurethane component (A), the polymerizable monomer (B); a thermal radical polymerization initiator (C); and a filler (D), and which may contain unreacted diol compound (a1) and/or unreacted diisocyanate compound (a2);
a molding step of filling the second raw material composition into a mold while maintaining the temperature of the second raw material composition at ₄₀ °C or higher and at a temperature not higher than a temperature 15°C lower than the _T10 of the thermal radical polymerization initiator (C), and then heating the second raw material composition to a temperature 10°C lower than the T10 of the thermal radical polymerization initiator (C) to a temperature 25°C higher than the _T10 to perform radical polymerization, thereby obtaining a molded article of a polyurethane composite material in which the filler (D) is dispersed in a matrix made of a polyurethane resin having a crosslinked structure formed by radical polymerization of the radically polymerizable group of the polyurethane component (A) and the polymerizable monomer (B),
When the contents (parts by mass) of the respective components contained in the second raw material composition are respectively defined as the content of the polyurethane component (A): Ar, the content of the polymerizable monomer (B): Br, the content of the diol compound (a1): a1r, and the content of the diisocyanate compound (a2): a2r,
Formula: Rr=100×Br/[a1r+a2r+Ar+Br]
By setting the polymerizable monomer blending ratio Rr defined by the formula (1) to 5% by mass or more and less than 20% by mass, the proportion of the polyurethane component in the polyurethane-based resin is more than 80% by mass and 95% by mass or less .
The present invention relates to a method for producing a polyurethane composite material molded article.
In this method, the molding step is carried out with the blending ratio of the polymerizable monomer in the second raw material composition within the above range, and therefore the polyurethane composite material constituting the obtained molded body is the polyurethane composite material of the present invention.

In the manufacturing method of the above embodiment (hereinafter also referred to as the "manufacturing method of the present invention"), it is preferable that the content of the filler (D) in the second raw material composition be 60% by mass to 80% by mass.

Furthermore, it is preferable that the non-polyaddition radically polymerizable monomer (B) includes a polymerizable monomer represented by the following structural formula (1):

[In the structural formula (1), R ¹¹ and R ¹² are hydrogen atoms or methyl groups, and n ₁ is an integer of 1 to 10.]
Furthermore, the radically polymerizable diol compound (a1) is preferably a diol compound in which the number of atoms constituting the main chain in the divalent organic residue interposed between two hydroxyl groups contained in the diol compound is 2 to 8.

The present invention provides a polyurethane composite material that, like the polyurethane composite material described in Patent Document 1, has excellent strength, water resistance, and uniformity and can be suitably used as a material for dental cutting. Furthermore, the manufacturing method of the present invention makes it possible to efficiently produce molded articles of the polyurethane composite material of the present invention that have the above-mentioned characteristics.

As mentioned above, in the polyurethane composite material described in Patent Document 1, in order to maintain good homogeneity, the proportion of the polyurethane component in the resin components cannot be increased beyond 80% by mass. However, Patent Document 1 does not specifically disclose the reason for this. Therefore, in order to solve this problem, the present inventors first investigated the reason. As a result, they discovered that crosslinked polyurethane composite materials are typically produced by radically polymerizing and curing a raw material composition (corresponding to the second raw material composition in the manufacturing method of the present invention) containing the radical-polymerizable polyurethane component (A), the polymerizable monomer (non-polyaddition-type radically polymerizable monomer) (B), a radical polymerization initiator (C), and a filler (D) to obtain a molded product of the desired shape, which is then processed as needed for use. However, when the proportion exceeds 80% by mass, the raw material composition becomes very hard and has almost no fluidity, and in some cases, the non-polyaddition-type reactive monomer may become unevenly distributed (rather than uniformly distributed) in the composition.

Based on the above findings, the inventors believed that if the fluidity of the (second) raw material composition could be increased to homogenize the components, a molded article of the uniform raw material composition could be obtained and its physical properties could be evaluated even when the above ratio exceeds 80% by mass. As a result of further investigation, they discovered that (1) a molded article of a uniform crosslinked polyurethane composite material can be obtained by heating the (second) raw material composition to a temperature at which radical polymerization does not substantially occur, and (2) high water resistance can be maintained if the above ratio is 95% by mass or less, which led to the completion of the present invention.

Regarding (1) above, the reason why heating the (second) raw material composition to a relatively low temperature enables the production of a molded article of a uniform crosslinked polyurethane composite material is not entirely clear, and the present invention is not bound by any logic. However, the inventors of the present invention presume that, since many of the radically polymerizable polyurethane components (A) obtained by polyaddition reaction using only the radically polymerizable diol compound (a1) and the diisocyanate compound (a2) had glass transition temperatures of approximately 35 to 50°C, heating the radically polymerizable polyurethane component (A) increases its fluidity, improves its uniformity, and enables it to be molded, even at a relatively low temperature where radical polymerization does not substantially occur.

The polyurethane composite material of the present invention is a polyurethane composite material in which a filler is dispersed in a matrix made of a polyurethane resin. The polyurethane resin has a crosslinked structure formed by radical polymerization of a radically polymerizable group in a polyurethane component having a number-average molecular weight of 1500 to 5000 with a radically polymerizable monomer, and the proportion of the polyurethane component in the polyurethane resin is greater than 80% by mass and not more than 95% by mass. However, its microstructure depends on the manufacturing method, and is difficult to identify by analysis or the like. Because the polyurethane composite material of the present invention is a material that constitutes a molded article manufactured by the manufacturing method of the present invention, the manufacturing method of the present invention will be described in detail below.

In this specification, unless otherwise specified, the expression "x to y" using the numerical values x and y means "greater than or equal to x and less than or equal to y." In such expressions, when a unit is assigned only to the numerical value y, that unit also applies to the numerical value x. Furthermore, in this specification, the term "(meth)acrylic" means both "acrylic" and "methacrylic."

1. Manufacturing Method of the Present Invention The manufacturing method of the present invention is a method for manufacturing a molded article made of the polyurethane composite material of the present invention, comprising the steps of:
a first raw material composition preparation step of preparing a first raw material composition containing a radically polymerizable diol compound (a1); a non-polyaddition-type radically polymerizable monomer (B); a thermal radical polymerization initiator (C); and a filler (D);
a second raw material composition preparation step of mixing the first raw material composition with a diisocyanate compound (a2) to cause a polyaddition reaction between the radically polymerizable diol compound (a1) and the diisocyanate compound (a2) to form a radically polymerizable polyurethane component (A), thereby preparing a second raw material composition comprising the radically polymerizable polyurethane component (A), the non-polyaddition-type radically polymerizable monomer (B); a thermal radical polymerization initiator (C) having a 10-hour half-life temperature: _T10 of 60°C or higher; and a filler (D), and which may contain unreacted radically polymerizable diol compound (a1) and/or unreacted diisocyanate compound (a2);
a molding step of filling the second raw material composition into a mold while maintaining the temperature of the second raw material composition at 40°C or higher and at a temperature not higher than a temperature 15°C lower than the _T10 of the thermal radical polymerization initiator (C), and then heating the second raw material composition to a temperature 10°C lower than the _T10 of the thermal radical polymerization initiator (C) to a temperature 25°C higher than the _T10 to perform radical polymerization, thereby obtaining a polyurethane composite material molded product,
When the contents (parts by mass) of the respective components contained in the second raw material composition are respectively defined as the content of the radical polymerizable polyurethane component (A): Ar, the content of the non-polyaddition polymerizable monomer (B): Br, the content of the radical polymerizable diol compound (a1): a1r, and the content of the diisocyanate compound (a2): a2r,
Formula: Rr=100×Br/[a1r+a2r+Ar+Br]
The polymerizable monomer blending ratio Rr defined as: is 5% by mass or more and less than 20% by mass. Note that, because the effects of the present invention are significant, it is preferable that the Rr is 5 to 15% by mass.

The various raw materials and steps used in the manufacturing method of the present invention are described in detail below.

2. Various raw materials 2-1. Radically polymerizable diol compound (a1)
The radically polymerizable diol compound (a1) is a compound that serves as a raw material for forming the radically polymerizable polyurethane component (A). The two hydroxyl groups of the radically polymerizable diol compound (a1) and the isocyanate groups of the diisocyanate compound (a2), which is the other polyurethane precursor component, undergo a polyaddition reaction in the second raw material composition preparation step, thereby forming the radically polymerizable polyurethane component (A).

As the radically polymerizable diol compound (a1), any compound having at least one radically polymerizable group and two hydroxyl groups in the molecule can be used without particular restrictions. Here, the term "radically polymerizable group" refers to a functional group that reacts with an initiator that generates radicals and polymerizes, and specifically refers to groups having a radically polymerizable carbon-carbon double bond, such as a vinyl group, a (meth)acrylate group, or a styryl group.

Because the diol compound contains radically polymerizable groups, these groups are introduced into the main chain of the polyurethane molecules formed by the polyaddition reaction. Furthermore, during the radical polymerization process in the molding process, radically polymerizable groups within the molecules of the radically polymerizable polyurethane component (A) react with each other, or with radically polymerizable groups within the molecules of the radically polymerizable polyurethane component (A) react with radically polymerizable groups of the non-polyaddition radically polymerizable monomer (B) to form bonds, resulting in crosslinks. This improves the water resistance of the cured polyurethane composite material.

From the viewpoint of the strength and water resistance of the resulting polyurethane composite material, the number of radically polymerizable groups contained in the molecule of the radically polymerizable diol compound (a1) is preferably 1 to 4, and particularly preferably 1 to 2. When the number of radically polymerizable groups is 4 or less, it becomes easier to suppress shrinkage of the cured body formed during the radical polymerization reaction.

Furthermore, the number of atoms constituting the main chain of the divalent organic residue interposed between two hydroxyl groups contained in the molecule of the radically polymerizable diol compound (a1) (hereinafter sometimes referred to as the "OH distance") is preferably 2 to 8, more preferably 2 to 6, and particularly preferably 2 to 4. By ensuring that the OH distance of the radically polymerizable diol compound (a1) is within the above range, it is possible to introduce radically polymerizable groups and urethane bonds at a high density into the molecules of the radically polymerizable polyurethane component (A) obtained by the polyaddition reaction, thereby increasing the strength of the polyurethane composite material.

When two or more types of radical polymerizable diol compounds (a1) are used, the OH distance refers to a value calculated as the average value of the two or more types of radical polymerizable diol compounds (a1). Here, when n types of radical polymerizable diol compounds (a1), where n is an integer of 2 or greater, are used, the average OH distance refers to a value calculated as the sum of the products obtained by multiplying the OH distance (Dx) of each radical polymerizable diol compound by the molar fraction (mol/mol) of each radical polymerizable diol compound (Mx), which is defined as the number of moles of each radical polymerizable diol compound in the total number of moles of radical polymerizable diol compounds.

Examples of compounds suitable for use as the radically polymerizable diol compound (a1) include trimethylolpropane mono(meth)acrylate, glycerol mono(meth)acrylate, erythritol di(meth)acrylate, pentaerythritol di(meth)acrylate, and ring-opened products of ethylene glycol diglycidyl ether with acids ((meth)acrylic acid or vinylbenzoic acid). These can be used alone or in combination with different types.

2-2. Diisocyanate compound (a2)
The diisocyanate compound (a2) is the other polyurethane precursor component for forming the radically polymerizable polyurethane component (A), and any known compound having two isocyanate groups in one molecule can be used without any particular limitation.

Compounds that are suitable for use as diisocyanate compound (a2) include, for example, 1,3-bis(2-isocyanato-2-propyl)benzene, 2,2-bis(4-isocyanatophenyl)hexafluoropropane, 1,3-bis(isocyanatomethyl)cyclohexane, 4,4'-methylenediphenyldiisocyanate, 3,3'-dichloro-4,4'-diisocyanatobiphenyl, 4,4'-diisocyanato-3,3'-dimethylbiphenyl, di ... Examples include cyclohexylmethane 4,4'-diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, norbornane diisocyanate, isophorone diisocyanate, 1,5-diisocyanatonaphthalene, 1,3-phenylene diisocyanate, trimethylhexamethylene diisocyanate, tolylene-2,4-diisocyanate, tolylene-2,6-diisocyanate, and m-xylylene diisocyanate.

Among these, diisocyanate compound (a2) having a phenyl group in the molecule is preferred from the viewpoints of the fluidity of the resulting second raw material composition and the strength of the resulting polyurethane composite material.

The amounts of radically polymerizable diol compound (a1) and diisocyanate compound (a2) used in the second raw material composition preparation step are not particularly limited as long as the molar ratio [amount of diisocyanate compound (a2) used/amount of radically polymerizable diol compound (a1) used] is around 1 mol/mole, but a molar ratio of approximately 0.9 to 1.2 mol/mole is generally preferred. From the perspective of quantitatively reacting the radically polymerizable diol compound (a1) and diisocyanate compound (a2) in the second raw material composition preparation step to form the radically polymerizable polyurethane component (A) while minimizing unreacted materials, a molar ratio of 1.0 to 1.1 mol/mole is preferred.

2-3. Radically polymerizable polyurethane component (A)
The radical polymerizable polyurethane component (A) is a component formed by a polyaddition reaction between a radical polymerizable diol compound (a1) and a diisocyanate compound (a2) in the second raw material composition preparation step. The structure of the radical polymerizable polyurethane component (A) is determined almost uniquely by the radical polymerizable diol compound (a1) used in the first raw material composition preparation step and the diisocyanate compound (a2) used in the second raw material composition preparation step.

Furthermore, the radically polymerizable polyurethane component (A) undergoes radical polymerization with the non-polyaddition-type radically polymerizable monomer (B) under the catalytic action of the thermal radical polymerization initiator (C), thereby forming the polyurethane resin matrix in the final polyurethane composite material. Therefore, the remaining components of the second raw material composition excluding the filler (D)—in other words, the components primarily comprising the radically polymerizable polyurethane component (A), the non-polyaddition-type radically polymerizable monomer (B), and the thermal radical polymerization initiator (C)—can be referred to as the matrix raw material composition. Furthermore, if the second raw material composition further contains a fifth component other than components A through D, and the fifth component dissolves in the radically polymerizable polyurethane component (A) and/or the non-polyaddition-type radically polymerizable monomer (B), the fifth component also constitutes the matrix raw material composition.

The radically polymerizable polyurethane component (A) contained in the second raw material composition must have a number-average molecular weight of 1500 to 5000. A number-average molecular weight of 1500 or greater enables the production of a polyurethane-based composite material with sufficient strength. Furthermore, according to the inventors' studies, it is virtually impossible or extremely difficult to obtain a radically polymerizable polyurethane component (A) with a number-average molecular weight exceeding 5000 in a system in which the five components coexist. Furthermore, within the range of 1500 to 5000, a smaller number-average molecular weight more reliably suppresses the precipitation of the radically polymerizable polyurethane component (A) in the matrix raw material composition, facilitating uniform radical polymerization. From the perspective of achieving a good balance between the fluidity of the second raw material composition and the strength of the polyurethane-based composite material, the number-average molecular weight is preferably 1500 to 3500, and more preferably 2000 to 3000.

The number average molecular weight of the radically polymerizable polyurethane component (A) refers to the polystyrene-equivalent number average molecular weight determined by GPC (gel permeation chromatography). The number average molecular weight of the radically polymerizable polyurethane component (A) in the second raw material composition can be determined by adding a solvent such as THF (tetrahydrofuran) to the second raw material composition as needed, removing insoluble components such as the filler (D) by filtration, centrifugation, or other procedures, and then performing GPC measurement on the resulting solution (i.e., the matrix raw material composition or a solution consisting of a mixture of the matrix raw material composition and an optional solvent). Measurement can be performed using an Advanced Polymer Chromatography (manufactured by Nihon Waters) under the following measurement conditions.

[Measurement conditions]
Column: ACQUITY APCTMXT45 1.7 μm
ACQUITY APCT MXT125 2.5μm
Column temperature: 40°C
Developing solvent: THF
Flow rate: 0.5 ml/min Detector: Photodiode array detector 254 nm (PDA detector)

2-4. Non-polyaddition radically polymerizable monomer (B)
The non-polyaddition radically polymerizable monomer (B) is a compound that has at least one radically polymerizable group in its molecule and does not undergo a polyaddition reaction with either the radically polymerizable diol compound (a1) or the diisocyanate compound (a2). Here, "does not undergo a polyaddition reaction with either the radically polymerizable diol compound (a1) or the diisocyanate compound (a2)" means that the molecule does not contain both a group that undergoes a polyaddition reaction with the radically polymerizable diol compound (a1) and a group that undergoes a polyaddition reaction with the diisocyanate compound (a2). Specifically, this means that the molecule does not contain a hydroxyl group, an amino group, a carboxyl group, an isocyanate group, or a mercapto group. Among these functional groups, the group that can undergo a polyaddition reaction with the radically polymerizable diol compound (a1) is an isocyanate group, and the group that can undergo a polyaddition reaction with the diisocyanate compound (a2) is a hydroxyl group, an amino group, a carboxyl group, or a mercapto group. Therefore, the non-polyaddition radically polymerizable monomer (B) does not contain a hydroxyl group, an amino group, a carboxy group, an isocyanate group, or a mercapto group in its molecule. Furthermore, the radically polymerizable group may be the same as the radically polymerizable group contained in the radically polymerizable diol compound (a1). Suitable radically polymerizable groups include (meth)acrylate groups and/or (meth)acrylamide groups, and groups having the same molecular structure as the radically polymerizable group contained in the radically polymerizable diol compound (a1). From the viewpoint of ease of crosslink formation, the number of radically polymerizable groups contained in the molecule of the non-polyaddition radically polymerizable monomer (B) is preferably 2 to 6, and more preferably 2 to 4. By having two or more radically polymerizable groups, the crosslink density can be increased, making it easier to obtain a cured product with sufficient strength. Furthermore, by having six or fewer radically polymerizable groups, it is easier to suppress shrinkage during curing. The non-polyaddition radically polymerizable monomer (B) is preferably a liquid at room temperature (i.e., 25°C).

Furthermore, it is preferable that the non-polyaddition radically polymerizable monomer (B) does not contain functional groups that strongly interact (particularly hydrogen bonds) with the radically polymerizable polyurethane component (A). Examples of functional groups that strongly interact with the polyurethane component (A) include amide groups, urethane groups, and urea groups. If these functional groups are contained, it may be difficult to achieve sufficient fluidity and uniformity unless the molding process is carried out at a higher temperature.

The viscosity of the non-polyaddition radically polymerizable monomer (B) is not particularly limited, but is preferably in the range of 1 mPa·s to 1,000 mPa·s at room temperature, and more preferably in the range of 1 mPa·s to 100 mPa·s. Using a non-polyaddition radically polymerizable monomer within this range increases the effect of heating during the molding process.

From the viewpoint of facilitating dispersion of the radically polymerizable polyurethane component (A), the non-polyaddition-type radically polymerizable monomer (B) preferably includes a polymerizable monomer represented by the following structural formula (1):

In the structural formula (1), R ¹¹ and R ¹² represent a hydrogen atom or a methyl group, and n ₁ represents an integer of 1 to 10, preferably an integer of 1 to 3.

Examples of compounds that can be suitably used as the non-polyaddition radically polymerizable monomer (B) include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tricyclodecanol (meth)acrylate, trimethylolpropane (meth)acrylate, pentaerythritol (meth)acrylate, ditrimethylolpropane (meth)acrylate, and dipentaerythritol (meth)acrylate. Of these, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, and triethylene glycol di(meth)acrylate are particularly preferred.

The content of the non-polyaddition-type radical polymerizable monomer (B) in the second raw material composition is expressed as follows, when the contents (parts by mass) of the respective components contained in the second raw material composition are defined as Ar, Br, a1r, a2r, and a2r, respectively:
Formula: Rr=100×Br/[a1r+a2r+Ar+Br]
The amount is such that the polymerizable monomer blending ratio Rr defined by: is 5% by mass or more and less than 20% by mass. If it is less than 5% by mass, it becomes very difficult to obtain a polyurethane composite material having a uniform crosslinked structure introduced therein.

2-5. Thermal radical polymerization initiator (C)
The thermal radical polymerization initiator (C) has the function of initiating a radical polymerization reaction in the molding process, and by reacting and bonding radically polymerizable groups together, polymerizes and cures the second raw material composition and forms crosslinking points. In the manufacturing method of the present invention, the thermal radical polymerization initiator (C) is used as a radical polymerization initiator to heat and polymerize the second raw material composition filled into a mold (forming tool). Furthermore, to prevent radical polymerization in the second raw material composition heated to a predetermined temperature before and during filling into the mold, a thermal polymerization initiator having a 10-hour half-life temperature ( _T10) of 60°C or higher is used. The upper limit of _T10 is not particularly limited, but is typically 150°C. From the viewpoint of flowability, etc., it is preferable to use an initiator having a _T10 in the range of 70 to 120°C, particularly 80 to 100°C. Here, the 10-hour half-life temperature ( _T10) refers to the temperature at which the amount of thermal polymerization initiator present decreases to half of the initial amount after 10 hours have passed since the initial time point, and is used as an index of the reactivity of the thermal polymerization initiator. Specific examples of suitable thermal radical polymerization initiators include peroxide initiators such as benzoyl peroxide and tert-butyl peroxylaurate, and azo-based initiators such as azobisbutyronitrile. These thermal polymerization initiators may be used alone or in combination of two or more.

The amount of radical polymerization initiator (C) used may be determined appropriately depending on the type of initiator, but is usually preferably in the range of 0.005% by mass to 2.0% by mass, and more preferably in the range of 0.01% by mass to 1.0% by mass, based on the mass of the matrix raw material composition.
The filler (D) disperses in the polyurethane resin matrix and forms a composite with the polyurethane resin matrix, thereby improving the physical properties such as mechanical strength, abrasion resistance, and water resistance of the polyurethane resin composite material.

As filler (D), it is preferable to use inorganic fillers such as silica, alumina, titania, zirconia, or composite oxides thereof, or glass. Specific examples of such inorganic fillers include spherical or irregularly shaped particles such as amorphous silica, silica-zirconia, silica-titania, silica-titania-zirconia, quartz, and alumina. When using a polyurethane composite material molded product produced by the manufacturing method of the present invention as a dental material, it is preferable to use silica, titania, zirconia, or composite oxides thereof as filler (D), with silica or composite oxides thereof being particularly preferred. These inorganic fillers are unlikely to dissolve in the oral environment, and the refractive index difference with the polyurethane resin matrix can be easily adjusted, making it easy to control transparency and aesthetics.

The shape of the filler (D) is not particularly limited and can be selected appropriately depending on the intended use of the polyurethane composite material. However, a spherical shape is preferable, for example, from the viewpoint of obtaining a polyurethane composite material that is particularly excellent in abrasion resistance, surface smoothness, and gloss retention. Polyurethane composite materials containing dispersed spherical filler (D) are also particularly suitable for dental applications. Here, "spherical" means that the average uniformity obtained by image analysis of images taken with a scanning or transmission electron microscope is 0.6 or greater. An average uniformity of 0.7 or greater is more preferable, and an average uniformity of 0.8 or greater is even more preferable. The average uniformity can be calculated by measuring the long diameter (L), which is the maximum diameter, and the short diameter (B) perpendicular to the long diameter (L) for each of n particles (usually 40 or more, preferably 100 or more) in image analysis of images taken with a scanning or transmission electron microscope, determining the ratio (B/L), and then dividing the sum (ΣB/L) by n.

From the viewpoints of abrasion resistance, surface smoothness, and gloss durability, the average particle size of filler (D) is preferably 0.001 μm to 100 μm, and more preferably 0.01 μm to 10 μm. Furthermore, it is preferable to use filler (D) with multiple particle sizes, as this makes it easier to increase the content of filler (D) in the polyurethane composite material. Specifically, it is preferable to combine particle sizes of 0.001 μm to 0.1 μm with particle sizes of 0.1 μm to 100 μm, and it is more preferable to combine particle sizes of 0.01 μm to 0.1 μm with particle sizes of 0.1 μm to 10 μm.

It is preferable to use a surface-treated filler (D) to improve compatibility with the polyurethane resin matrix and the mechanical strength and water resistance of the polyurethane composite material. Silane coupling agents are generally used as surface treatment agents, and surface treatment with silane coupling agents is particularly effective for silica-based inorganic particle fillers (D). Suitable silane coupling agents include methyltrimethoxysilane, methyltriethoxysilane, vinyltrimethoxysilane, 3-methacryloyloxypropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

The amount of filler (D) used may be determined appropriately depending on the physical properties such as the strength of the desired polyurethane composite material. However, from the perspective of increasing the strength of the polyurethane composite material, the amount is preferably 60% to 80% by mass, and more preferably 65% to 75% by mass, expressed in mass % based on the mass of the second raw material composition (hereinafter sometimes simply referred to as the "filling rate"). Furthermore, when a polyurethane composite material produced by the polyurethane composite material production method of this embodiment is used as a dental cutting material, the filling rate is more preferably 65% to 75% by mass.

2-7. Other Additives In addition to the essential components described above, various other additives may be blended into the first raw material composition or the second raw material composition. Examples of the various additives include polymerization inhibitors, fluorescent agents, ultraviolet absorbers, antioxidants, pigments, antibacterial agents, and X-ray contrast agents. The amounts of these additives added may be determined appropriately depending on the desired purpose.

3. Regarding Each Step The production method of the present invention includes a first raw material composition preparation step, a second raw material composition preparation step, and a molding step. Each step will be described in detail below.

3-1. First Raw Material Composition Preparation Step and Second Raw Material Composition Preparation Step In the first raw material composition preparation step, a first raw material composition is prepared, which contains a radically polymerizable diol compound (a1); a non-polyaddition-type radically polymerizable monomer (B); a thermal radical polymerization initiator (C); and a filler (D). Then, in the second raw material composition preparation step, the first raw material composition and a diisocyanate compound (a2) are mixed to cause a polyaddition reaction between the radically polymerizable diol compound (a1) and the diisocyanate compound (a2), thereby forming a radically polymerizable polyurethane component (A), and a second raw material composition is prepared, which comprises the radically polymerizable polyurethane component (A), the non-polyaddition-type radically polymerizable monomer (B); a thermal radical polymerization initiator (C) having a 10-hour half-life temperature: _T10 of 60°C or higher; and a filler (D), and which may contain unreacted radically polymerizable diol compound (a1) and/or unreacted diisocyanate compound (a2).

The amounts of each component used in these steps are determined as follows: The composition of the first raw material composition is determined based on the composition of the second raw material composition to be obtained. Specifically, assuming that equimolar amounts of radically polymerizable diol compound (a1) and diisocyanate compound (a2) undergo a quantitative polyaddition reaction to produce radically polymerizable polyurethane component (A), the amounts of radically polymerizable diol compound (a1) and diisocyanate compound (a2) used in the second raw material composition preparation step are adjusted so that the molar ratio [amount of diisocyanate compound (a2) used/amount of radically polymerizable diol compound (a1) used] is approximately 1 mol/mole, generally about 0.9 to 1.2 mol/mole, and preferably 1.0 to 1.1 mol/mole, and further so that the polymerizable monomer blending ratio: Rr is a predetermined value (% by mass) in the range of 5% by mass or more but less than 20% by mass. This determines the amounts of (a1) and (B) in the first raw material composition and the amount of (a2) used in the second raw material composition preparation step, and the amounts of (A), (B), remaining (a1), and remaining (a2) in the second raw material composition are automatically determined by these blending amounts. Furthermore, the blending amounts of (C) and (D) may be set to the preferred amounts based on the standards described above.

The first raw material composition may be prepared by mixing all of the components constituting the first raw material composition at once, or by preparing a mixture by mixing some of the components constituting the first raw material composition and then adding and mixing the remaining components constituting the first raw material composition. The mixing method for the individual components in the preparation of the first raw material composition is not particularly limited, and methods using a magnetic stirrer, a mortar and pestle mixer, a planetary mixer, a centrifugal mixer, or the like may be appropriately used. Furthermore, because it is easier to uniformly disperse the filler (D), it is preferable to first mix the radically polymerizable diol compound (a1) and the non-polyaddition-type radically polymerizable monomer (B) to prepare a mixed composition, and then add the filler (D) to this mixed composition and mix it to prepare the first raw material composition. Furthermore, because it is easier to suppress side reactions and facilitate dispersion, it is preferable to add a radical polymerization initiator (C) to the first raw material composition. Similarly, it is preferable to add other additives to the first raw material composition. The first raw material composition prepared in this manner is preferably subjected to a degassing treatment to remove any air bubbles contained therein. Known degassing methods can be used, including pressure degassing, vacuum degassing, and centrifugal degassing.

The first raw material composition may further contain, as other additives, a catalyst that promotes the polyaddition reaction if necessary, but it does not necessarily need to contain a catalyst that promotes the polyaddition reaction. Examples of catalysts that promote the polyaddition reaction include tin octoate and dibutyltin diacetate.

In the second raw material composition preparation step, the radically polymerizable polyurethane component (A) is formed by polyaddition reaction of the radically polymerizable diol compound (a1) and the diisocyanate compound (a2) contained in the first raw material composition. The polyaddition reaction is initiated simultaneously with mixing the first raw material composition with the diisocyanate compound (a2), or by heating the mixture as needed after mixing the first raw material composition with the diisocyanate compound (a2). The polyaddition reaction is carried out until at least one of the radically polymerizable diol compound (a1) and the diisocyanate compound (a2) is substantially consumed by the polyaddition reaction; in other words, until the degree of progress of the polyaddition reaction approaches its maximum value (saturation value). In this case, since the first raw material composition contains a thermal radical polymerization initiator (C) having a 10-hour half-life temperature: _T10 of 60°C or _higher , the polyaddition reaction must be carried out at a reaction temperature lower than the _T10 of the thermal radical polymerization initiator (C) used, and it is preferable to carry out the polyaddition reaction at a temperature maintained at 80°C to 20°C lower than T10, particularly 70°C to 30°C lower. Note that in the production method of the present invention, even when the above-mentioned method is adopted, a small amount of radical polymerization reaction is allowed to inevitably occur.

The reaction time varies depending on the reaction temperature. For example, (1) if the reaction temperature is 30°C or higher but lower than 50°C, it is preferably 60 hours or longer, more preferably 72 hours or longer; (2) if the heating temperature is 50°C or higher but lower than 80°C, it is preferably 24 hours or longer, more preferably 36 hours or longer; and (3) if the heating temperature is 80°C or higher, it is preferably 15 hours or longer, more preferably 24 hours or longer. In the cases shown in (1) to (3) above, there are no particular limitations on the upper limit of the heating time, but from a practical standpoint such as productivity, 120 hours or shorter is preferred.

When preparing the second raw material composition, the mixing means used to mix the components is not particularly limited, and any known mixing means can be used as appropriate. Examples of such mixing means include a magnetic stirrer, a Raikai mixer, a planetary mixer, and a centrifugal mixer. Furthermore, to prevent air bubbles from being mixed into the composition during mixing, mixing may be carried out under pressure and/or under vacuum.

In the molding step, the second raw material composition is filled into a mold while maintaining the temperature at 40°C or higher and at a temperature not higher than a temperature 15°C lower than the 10-hour half-life temperature ( _T10 ) of the thermal radical polymerization initiator (C), and then heated to a temperature 10°C lower than the _T10 of the thermal radical polymerization initiator (C) to a temperature 25°C higher than _T10 to perform radical polymerization, thereby obtaining a polyurethane composite material molded product.

Of the four essential components that make up the second raw material composition, the primary components in terms of content are the radically polymerizable polyurethane component (A), the non-polyaddition radically polymerizable monomer (B), and the filler (D). The non-polyaddition radically polymerizable monomer (B) is a low-molecular-weight substance that is liquid at room temperature. On the other hand, although the radically polymerizable polyurethane component (A) is a polymer, its number-average molecular weight is relatively small, ranging from 1,500 to 5,000 (i.e., its molecular size is quite small). Therefore, when the non-polyaddition radically polymerizable monomer (B) is present in the second raw material composition in an amount such that the polymerizable monomer blending ratio: Rr is 20% by mass or greater, some of the non-polyaddition radically polymerizable monomer (B) dissolves or swells, resulting in the second raw material composition remaining homogeneous and fluid even at room temperature, becoming a paste-like substance. However, if Rr is less than 20% by mass, particularly 15% by mass or less, the second raw material composition loses fluidity and assumes a solid-like state, and in some cases the liquid component, the non-polyaddition-type radically polymerizable monomer (B), separates and becomes unevenly distributed, resulting in a decrease in uniformity.

In the production method of the present invention, before radical polymerization, the second raw material composition is heated to a predetermined temperature, specifically, a temperature that is 40°C or higher and not higher than a temperature that is 15°C lower than the ₁₀ -hour half-life temperature, T10, of the thermal radical polymerization initiator (C) to convert the second raw material composition into a uniform, fluid paste-like state, which is then molded into a predetermined shape, and radical polymerization is carried out while maintaining the uniformity, making it possible to efficiently obtain a molded article made of a uniform crosslinked polyurethane composite material.

From the viewpoint of enabling a more uniform change into a paste state, it is preferred to use a thermal radical polymerization initiator (C) having a 10-hour half-life temperature ( _T10) in the range of 70 to 120°C, particularly 80 to 100°C, and to set the temperature (heating temperature) at which the second raw material composition is maintained before filling into the mold to 45°C to a temperature 15°C lower than _T10 , particularly 50°C to a temperature 20°C lower than _T10 .

Methods of maintaining the second raw material composition at a temperature (heating temperature) before filling the mold include placing the container holding the second raw material composition in an atmosphere maintained at a predetermined temperature to avoid localized high temperatures, or contacting it with a heat transfer medium (a liquid, a solid such as a plate) maintained at a predetermined temperature. The time required to maintain the predetermined temperature is sufficient as long as it does not adversely affect mold filling (due to radical polymerization that occurs during the maintenance period), and is typically 5 minutes to several hours, preferably 10 to 60 minutes, after the predetermined temperature is reached. By maintaining the second raw material composition at the aforementioned temperature, the composition will become homogeneous without any special stirring or other operations; however, stirring may be performed as long as no air bubbles or other impurities remain inside.

The mold (forming tool) used in the molding process can be one with a cavity corresponding to the shape of the desired molded product. There are no particular restrictions on the material, as long as it can withstand the temperatures and pressures encountered during radical polymerization, and metal, ceramic, or resin materials can be used. Specifically, materials made of SUS, polypropylene, polyacetal, polytetrafluoroethylene, etc. are suitable.

The method for filling the mold with the second raw material composition is not particularly limited, as long as it is heated to a temperature within the above-mentioned range, and any known method can be used. This can be suitably done by pressure casting or vacuum casting. Pressure casting is particularly preferred, as it ensures reliable heat transfer to the second raw material composition. There are no particular limitations on the method of pressure application, and mechanical pressure or air pressure can be used.

The second raw material composition filled in the mold is heated to a temperature 10°C lower than the 10-hour half-life temperature ( _T10 ) of the thermal radical polymerization initiator (C) to a temperature 25°C higher than _T10 to undergo radical polymerization, resulting in a polyurethane composite material molded body having the desired shape. In this case, it is preferable to control the heating temperature so that it does not exceed 150°C. By setting the heating temperature at or above the lower limit temperature (10°C lower than _T10 ), the radical polymerization rate can be sufficiently increased and unintended coloration of the cured body can be easily suppressed. Furthermore, by setting the heating temperature at or below the upper limit temperature (25°C higher than _T10 ), rapid radical polymerization can be suppressed. Controlling the heating temperature within the above-mentioned temperature range allows polymerization and curing to proceed at an industrially acceptable reaction rate, suppresses the occurrence of distortion and cracks in the cured body due to rapid reaction progress, and greatly facilitates suppressing deterioration of the non-polyaddition radically polymerizable monomer (B). Furthermore, when radical polymerization is performed by heating, the second raw material composition may be pressurized during radical polymerization in order to prevent voids due to bubbles from being formed in the cured product. There are no limitations on the pressurization method, and the second raw material composition may be pressurized mechanically or with a gas such as nitrogen.

By carrying out the radical polymerization process in this manner, a molded article made of a polyurethane composite material in which filler (D) is dispersed in a polyurethane resin matrix can be obtained.

4. Application example of the manufacturing method of the present invention (manufacturing of materials for dental cutting)
The polyurethane composite material of the present invention maintains high strength and is water resistant even in a hydrophilic environment such as the oral cavity. Because of this high water resistance, the manufacturing method of the present invention can be suitably used as a manufacturing method for a material for dental cutting, particularly when a dental prosthesis is produced by cutting the material for dental cutting using a dental CAD/CAM system. Below, a preferred example of the manufacturing method of the present invention when used to manufacture a material for dental cutting will be described.

First, a second raw material composition is prepared in the same manner as in the manufacturing method of the present invention. Next, the second raw material composition is heated to 40°C to _T10-15 °C and poured into a mold. The composition is then heated to a temperature 10°C lower than _T10 to a temperature 25°C higher than _T10 to carry out radical polymerization (molding process). The mold used for molding is not particularly limited, and rectangular pillars, cylinders, square plates, and disks are appropriately used depending on the shape envisioned for each product form. Furthermore, the dimensions of the mold may be approximately the same as the dimensions of the cured body after radical polymerization, taking into account factors such as shrinkage during radical polymerization. Alternatively, if the cured body obtained by radical polymerization is to be processed in a subsequent process, the dimensions may be larger than the dimensions of the resulting cured body, allowing for processing allowance.

The method for injecting the second raw material composition into the mold is not particularly limited, as long as it is heated to a temperature within the above-mentioned range, and any known method can be used. However, it is preferable to use pressure casting or vacuum casting. By using such an injection method, it is possible to prevent the incorporation of air bubbles and the formation of voids in the resulting cured product (polyurethane composite material), resulting in a dental cutting material with excellent strength and aesthetics. In the case of pressure casting, there are no limitations on the method of pressurization; mechanical pressure can be used, or pressure can be applied using a gas such as nitrogen.

After the resulting hardened body is removed from the mold, it is subjected to post-treatments and processing, such as heat treatment to relieve residual stress, shape correction by cutting, and polishing, as needed. Next, fixing devices such as pins for holding it in a CAD/CAM device are attached to the hardened body that has undergone these post-treatments and processing, thereby obtaining a material for dental cutting.

The present invention will be explained below with reference to examples and comparative examples, but the present invention is not limited to these examples.

1. Raw Materials The components used in each of the Examples and Comparative Examples and their abbreviations are listed below.

(1) Radical polymerizable diol compound (a1)
GLM: glycerol monomethacrylate (OH distance: 2)
EGDGMA: ethylene glycol diglycidyl methacrylate (OH distance: 8)
(2) Diisocyanate compound (a2)
XDI: m-xylylene diisocyanate (3) Non-polyaddition radical polymerizable monomer (B)
TEGDMA: triethylene glycol dimethacrylate UDMA: a mixture of 1,6-bis(methacrylethyloxycarbonylamino)-2,2,4-trimethylhexane and 1,6-bis(methacrylethyloxycarbonylamino)-2,4,4-trimethylhexane (4) Radical polymerization initiator (C)
PBL: t-butyl peroxylaurate (10-hour half-life temperature 98°C)
PBC: t-butylcumyl peroxide (10-hour half-life temperature 120°C)
(5) Filler (D)
F1: Silica-zirconia (average particle size: 0.4 μm, surface treated with 3-(trimethoxysilyl)propyl methacrylate)
F2: Silica-titania (average particle size: 0.08 μm, surface treated with 3-(trimethoxysilyl)propyl methacrylate)
2. Method for Producing Polyurethane Composite Material Examples of the method for producing a polyurethane composite material of the present invention will be described below together with comparative examples.

Example 1
(1) First raw material composition preparation step First, a mixed composition was prepared by mixing GLM (12.5 parts by mass) as the radical polymerizable diol compound (a1), TEGDMA (2.7 parts by mass) as the non-polyaddition radical polymerizable monomer (B), and PBL (0.1 parts by mass) as the radical polymerization initiator (C). Next, F1 (49.0 parts by mass) and F2 (20.9 parts by mass) as the filler (D) were added to this mixed composition and kneaded to prepare a first raw material composition.

(2) Second raw material composition preparation step: A polyaddition-reactive raw material composition was prepared by adding XDI (14.7 parts by mass), which is a diisocyanate compound (a2), to a planetary centrifugal mixer containing the entire amount of the obtained first raw material composition and kneading them. Next, the obtained polyaddition-reactive raw material composition was left to stand in an incubator at 37°C for 72 hours to carry out a polyaddition reaction, forming a radically polymerizable polyurethane component (A) and preparing a second raw material composition.

In this example, the molar ratio of diisocyanate compound (a2) to radically polymerizable diol compound (a1) (hereinafter sometimes referred to as the "a2/a1 molar ratio") was 1.0. The polymerizable monomer blending ratio Rr was 9% by mass. The mass ratio (filling rate) of filler (D) to the mass of the second raw material composition was 70% by mass. Except for the case where the composition was heated to 37°C during the polyaddition reaction, all compositions were prepared at room temperature (25°C).

(3) Evaluation of the second raw material composition (3-1) Measurement of the number average molecular weight of the radically polymerizable polyurethane component (A) (GPC measurement)
1 g of the obtained second raw material composition was weighed into a screw tube bottle, 3.5 ml of THF was added, and the resulting THF solution was stirred. The resulting solution was centrifuged at 10,000 rpm for 10 minutes in a centrifuge (manufactured by AS ONE Corporation). The supernatant obtained by centrifugation was then filtered through a membrane filter (pore size 20 μm, manufactured by ADVANTEC Co., Ltd.) to obtain a filtrate. This filtrate was then subjected to GPC measurement under the GPC measurement conditions shown below to determine the polystyrene-equivalent number average molecular weight of the radically polymerizable polyurethane component (A) obtained by the polyaddition reaction. As a result, the number average molecular weight was 2,500.

[GPC measurement conditions]
Measurement device: Advanced Polymer Chromatography (manufactured by Nihon Waters)
Column: ACQUITY APCTMXT45 1.7 μm
ACQUITY APCT MXT125 2.5μm
Column temperature: 40°C
・Developing solvent: THF (flow rate: 0.5ml/min)
Detector: Photodiode array detector 254 nm (PDA detector)

(3-2) Evaluation of Fluidity The fluidity of the second raw material composition at room temperature (23°C) and at 45°C, the holding temperature (heating temperature) during mold filling, was evaluated by measuring the maximum load when a 5 mm diameter stainless steel (SUS) rod was pressed to a predetermined depth at a predetermined speed, using the following procedure. First, the second raw material composition was loaded into a SUS nut-shaped mold, the surface was smoothed, and the mold was left at the measurement temperature (23°C or the aforementioned holding temperature) for 5 minutes. Next, the SUS nut-shaped mold filled with the second raw material composition and a 5 mm SUS rod as a pressure-sensitive shaft were attached to a Sun Rheometer CR-150 (manufactured by Sun Scientific Co., Ltd.). Subsequently, at 23°C and the aforementioned holding temperature, the pressure-sensitive shaft was compressed into the second raw material composition to a depth of 2 mm at a speed of 120 mm/min. The maximum load [kg] at this time was measured. As a result, the maximum load at 23°C exceeded the upper limit of measurement, 10.0 kg, and the maximum load at 45°C was 9.4 kg.

If the maximum load obtained by the above measurement exceeds 10 kg, the fluidity is significantly low, making it impossible to fill the second raw material composition into the mold (frame) without leaving any gaps.

(3-3) Evaluation of Glass Transition Point of Polyurethane Component (A) For reference, the glass transition point of a polyurethane component obtained by polyaddition reaction of a radical polymerizable diol compound (a1) and a diisocyanate compound (a2) in the same quantitative ratio as in Example 1 was evaluated as follows.

That is, using a DSC8230 (manufactured by Rigaku), the temperature was raised from 20°C to 100°C at a heating rate of 10°C/min in a nitrogen atmosphere, then lowered, and from the point where it reached 20°C, the temperature was raised again to 100°C at a heating rate of 10°C/min. A DSC curve was obtained from this process for the resulting polyurethane component, and the glass transition temperature was determined as 43°C, as the temperature at which the line extending the low-temperature baseline in the curve obtained when it was heated again intersects with the tangent to the stepwise change in temperature.

(4) Molding step The obtained second raw material composition was left to stand for 5 minutes on a heating press (manufactured by Imoto Machinery Co., Ltd.) heated to 45°C (heating temperature: 45°C), poured into a mold (length 12 mm × width 18 mm × thickness 14 mm), pressed under a load of 2 MPa, and held for 5 minutes to fill the mold.

(5) Radical polymerization step (curing step)
The second raw material composition filled in the mold was subjected to radical polymerization at 120°C for 15 hours under nitrogen pressure (0.3 MPa), yielding a polyurethane composite material in which the filler was dispersed in a polyurethane resin matrix. The cured product obtained by radical polymerization had a uniform appearance, with no partially insufficiently cured areas.

(6) Evaluation of Polyurethane Composite Material (Cured Product) The obtained polyurethane composite material was evaluated for flexural strength, underwater flexural strength, water retention rate (water resistance), and uniformity. The evaluation methods and results are shown below.

[Flexural strength BS _d ]
The resulting polyurethane composite material (cured product) was cut using a low-speed diamond cutter (manufactured by Bühler) and then polished with #2000 waterproof abrasive paper to prepare five rectangular columnar test pieces (thickness: approximately 1.2 mm x width: approximately 4.0 mm x length: 14.0 mm). Next, a three-point bending test was performed on each test piece using an autograph (manufactured by Shimadzu Corporation), and the bending load at the maximum point was measured. The bending strength BS was then calculated based on the following formula (1). The bending load at the maximum point was measured with a support distance of 12.0 mm and a crosshead speed of 1.0 mm/min. As a result, the average bending strength BS of the five test pieces (bending strength _BSd ) was 249 MPa.
・Formula (1) BS=3PS/2WB ²
(In formula (1), BS represents the bending strength (MPa), P represents the bending load at the maximum point (N), S represents the distance between supports (12.0 mm), W represents the width of the test piece (actual measurement, mm), and B represents the thickness of the test piece (actual measurement, mm).)

[Underwater bending strength BS _W ]
Five test specimens were prepared in the same manner as described in the [Bending Strength] section, and all test specimens were stored in ion-exchanged water at 37°C for one week. After that, the test specimens were removed from the ion-exchanged water, and moisture adhering to the surface was removed. A three-point bending test was then performed under the same test conditions as described in the [Bending Strength] section, and the bending load at the maximum point of the test specimen after underwater storage was measured. The bending strength BS of each test specimen after underwater storage was then calculated based on Equation (1). As a result, the average bending strength BS of the five test specimens after underwater storage (underwater bending strength BS _w ) was 207 MPa.

[Retention rate (water resistance)]
The retention rate, which is an index showing the water resistance of the cured body, was calculated based on the following formula (2). In this example, the retention rate was 83%, confirming high water resistance.
・Formula (2) Retention rate (%) = 100×BS _W /BS _d
(In formula (2), BS _W represents the average value (MPa) of the bending strengths BS of 10 test specimens after storage in water, and BS _d represents the average value (MPa) of the bending strengths BS of 10 test specimens.)

[Uniformity]
The uniformity of the cured body was evaluated by visually observing the appearance of the cured body and the cross section obtained by cutting the cured body into approximately two equal parts. Here, whether the cured body had uniformity was determined by whether or not there were curing irregularities and cracks on the surface and cross section of the cured body. If neither curing irregularities nor cracks were observed, it was judged to be uniform, and if at least one of curing irregularities and cracks was observed, it was judged to be non-uniform. For the cured body of Example 1, neither curing irregularities nor cracks were observed, and it was found to be uniform.

Examples 2 to 3
The holding temperature (heating temperature) during mold filling in the molding step was changed as shown in Table 2, and the second raw material composition obtained in Example 1 was filled into the mold, followed by a radical polymerization step, to produce a polyurethane composite material. The fluidity of the second raw material composition at the heating temperature in the molding step and the resulting polyurethane composite material were evaluated in the same manner as in Example 1. The results are shown in Table 2.

Comparative Examples 1 and 2
The holding temperature (heating temperature) during mold filling in the molding step was changed as shown in Table 2, and the second raw material composition obtained in Example 1 was filled into the mold, followed by a radical polymerization step, to produce a polyurethane composite material. The fluidity of the second raw material composition at the heating temperature during the molding step and the resulting polyurethane composite material were evaluated in the same manner as in Example 1. The results are shown in Table 2. Note that "uneven" in the uniformity evaluation means that there was uneven curing.

Examples 4 to 8
A second raw material composition was prepared in the same manner as in Example 1, except that the raw materials, a2/a1 molar ratio, polymerizable monomer blending ratio Rr, and filling rate used in Example 1 were changed as shown in Table 1, and the holding temperature (heating temperature) during mold filling in the molding step was changed as shown in Table 2. The resulting second raw material composition was filled into a mold and then radical polymerization was carried out to produce a polyurethane composite material. The fluidity of the second raw material composition at the heating temperature during the molding step and the resulting polyurethane composite material were evaluated in the same manner as in Example 1. The results are shown in Table 2.

Comparative Example 3
The holding temperature (heating temperature) during mold filling in the molding step was changed as shown in Table 2, and the second raw material composition obtained in Example 4 was filled into a mold and then radical polymerization was carried out to produce a polyurethane composite material. The fluidity of the second raw material composition at the heating temperature during the molding step and the resulting polyurethane composite material were evaluated in the same manner as in Example 1. The results are shown in Table 2.

Claims (4)

a first raw material composition preparation step of preparing a first raw material composition comprising: a diol compound (a1) having one or more radically polymerizable groups; a polymerizable monomer (B) having one or more radically polymerizable groups in the molecule and not undergoing a polyaddition reaction with either the diol compound (a1) or a diisocyanate compound; a thermal radical polymerization initiator (C) having a 10-hour half-life temperature: _T10 of 60°C or higher; and a filler (D);
a second raw material composition preparation step of mixing the first raw material composition with a diisocyanate compound (a2) to cause a polyaddition reaction between the diol compound (a1) and the diisocyanate compound (a2) to form a polyurethane component (A) having a number average molecular weight of 1,500 to 5,000 and having a radically polymerizable group, thereby preparing a second raw material composition comprising the polyurethane component (A), the polymerizable monomer (B); a thermal radical polymerization initiator (C); and a filler (D), and which may contain unreacted diol compound (a1) and/or unreacted diisocyanate compound (a2);
a molding step of filling the second raw material composition into a mold while maintaining the temperature of the second raw material composition at ₄₀ °C or higher and at a temperature not higher than a temperature 15°C lower than the _T10 of the thermal radical polymerization initiator (C), and then heating the second raw material composition to a temperature 10°C lower than the T10 of the thermal radical polymerization initiator (C) to a temperature 25°C higher than the _T10 to perform radical polymerization, thereby obtaining a molded article of a polyurethane composite material in which the filler (D) is dispersed in a matrix made of a polyurethane resin having a crosslinked structure formed by radical polymerization of the radically polymerizable group of the polyurethane component (A) and the polymerizable monomer (B);
Including,
When the contents (parts by mass) of the respective components contained in the second raw material composition are respectively defined as the content of the polyurethane component (A): Ar, the content of the polymerizable monomer (B): Br, the content of the diol compound (a1): a1r, and the content of the diisocyanate compound (a2): a2r,
Formula: Rr=100×Br/[a1r+a2r+Ar+Br]
By setting the polymerizable monomer blending ratio Rr defined by the formula (1) to 5% by mass or more and less than 20% by mass, the proportion of the polyurethane component in the polyurethane-based resin is more than 80% by mass and 95% by mass or less .
A method for producing a polyurethane composite material molded article, comprising: 2. The method for producing a polyurethane composite material molded article according to claim 1 , wherein the content of the filler (D) in the second raw material composition is 60% by mass to 80% by mass. 3. The method for producing a polyurethane composite material molded article according to claim 1 , wherein the polymerizable monomer (B) comprises a polymerizable monomer represented by the following structural formula ( 1 ):
[In the structural formula (1), R ¹¹ and R ¹² are hydrogen atoms or methyl groups, and n ₁ is an integer of 1 to 10.] The method for producing a polyurethane composite material molded article according to any one of claims 1 to 3, wherein the diol compound ( a1 ) is a diol compound in which the number of atoms constituting the main chain in the divalent organic residue intervening between the two hydroxyl groups contained in the diol compound is 2 to 8 .