Manufacturing method for three-dimensional stereolithography

Abstract

The present invention provides a method for producing high-strength three-dimensional stereolithography by a liquid bath photopolymerization method using a liquid photocurable composition comprising 100 parts by mass of a radical polymerizable monomer, 5.0 to 400 parts by mass of an inorganic filler, 0.05 to 10.0 parts by mass of a photopolymerization initiator, and 0.01 to 5.0 parts by mass of a polymerization inhibitor. This method involves obtaining a molded body made of a primary cured body by a liquid bath photopolymerization method, followed by a postpolymerization step of washing the molded body and performing additional activation light irradiation and heat treatment, thereby preventing the occurrence of fine cracks in the interior and surface of the target object. [Solution] The additional irradiation of activation light is performed by applying a solution containing an oxygen-blocking substance such as polyvinyl alcohol to the surface of the molded body after cleaning, and while the surface and the solution are in contact.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a three-dimensional object by optical shaping.

Background Art

[0002] A technique of irradiating a photocurable composition containing a polymerizable monomer and a photoinitiator (sometimes referred to as "photocurable resin" or "photocurable resin composition") with light (activation light) that activates the photoinitiator to cure it and form a three-dimensional object is known as a stereolithography method. Although several methods are known for the stereolithography method, the liquid bath photopolymerization method, which has a relatively inexpensive apparatus and can manufacture a shaped object with a smooth surface with high precision, is widely used.

[0003] In the liquid bath photopolymerization method, from three-dimensional shape data indicating the shape of a three-dimensional object to be manufactured, the height direction of the three-dimensional object is digitized and serialized, and two-dimensional shape data indicating the cross-sectional shape of the three-dimensional object at each serialized height is generated. Then, for the liquid photocurable composition held in the bath (here, "liquid" means a state of a dispersion in which a liquid or inorganic powder particles are dispersed in the use environment), the activation light is irradiated at a predetermined position determined in advance based on the two-dimensional shape data, and the liquid photocurable composition existing at that position is selectively primary-cured to form a shaped layer having the cross-sectional shape. At the same time, shaped layers having cross-sectional shapes at each height are sequentially formed and laminated in the order of serialization to obtain a laminate having a shape corresponding to the shape of the three-dimensional object. Generally, after washing this with an organic solvent as necessary, secondary curing (also referred to as "post-polymerization") is performed to obtain the desired object. This secondary curing is generally performed by performing additional light irradiation and / or heat treatment on the laminate to improve the polymerization rate and increase its strength.

[0004] In the field of dentistry, there is a growing interest in manufacturing dental restorations such as dentures and crowns, which require high precision to produce unique shapes tailored to the individual oral conditions of each patient. These restorations are being developed using stereolithography (SLA) based on CAD data designed using digital data obtained from intraoral scans, etc. (See, for example, Patent Document 1).

[0005] When manufacturing dental restorations for use in the oral cavity, a photocurable resin composition containing a large amount of inorganic filler in a radical polymerizable monomer is sometimes used to increase strength. However, in this case, if sufficient curing is performed in the second stage to obtain high precision that allows for a proper fit when placed in the oral cavity of each individual patient, it is known that cracks (microscopic cracks that are not visible to the naked eye) are prone to occur inside and / or on the surface of the three-dimensional object due to deformation caused by polymerization shrinkage and the resulting stress generated between the fabricated layers during photopolymerization. Techniques to prevent such problems are also known.

[0006] Specifically, Patent Document 1 describes a photocurable resin composition that hardens upon irradiation with activating light, comprising: 100 parts by mass of a radical polymerizable monomer, 5.0 to 400 parts by mass of an inorganic filler, 0.05 to 10.0 parts by mass of a photopolymerization initiator that absorbs the activating light and generates radicals, 0.01 to 2.7 parts by mass of an activating light absorber that absorbs the activating light, and 0.01 to 5.0 parts by mass of a polymerization inhibitor. The photocurable resin composition is then subjected to a liquid bath photopolymerization method to obtain a molded three-dimensional object (consisting of a laminate of primary cured products of the photocurable resin composition), and after obtaining a molded object containing an effective amount of the photopolymerization initiator, the molded object is subjected to 10 to 10,000 mW / cm². 2 A method for manufacturing a three-dimensional object is disclosed, characterized by performing a post-polymerization step (secondary curing step) by irradiating the molded body with activation light of a certain irradiation intensity and then heating the molded body irradiated with the activation light to a temperature of 50°C or higher and less than 110°C. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] International Publication No. 2023 / 008233 Brochure [Patent Document 2] Japanese Patent Application Publication No. 9-241304 [Patent Document 3] Japanese Patent Publication No. 2000-128723 [Overview of the project] [Problems that the invention aims to solve]

[0008] According to the technology described in Patent Document 1 above, it is possible to manufacture three-dimensionally fabricated objects that have excellent mechanical strength, good shape accuracy, and are substantially free of internal cracks.

[0009] On the other hand, the method described in Patent Document 1 requires the inclusion of an activation light absorber as an essential component. Depending on the specific heating conditions of the post-polymerization process (secondary curing process), crack formation (inside the three-dimensional object) can be prevented, but cracks were sometimes observed on the surface (see Example 11 of Patent Document 1). Furthermore, the inventors' studies have revealed that as the thickness of the molded body (laminated body) formed in the molding process increases, the amount of cracks remaining on the surface tends to increase. Since cracks remaining on the surface exist only in the surface layer, if the amount is small, it has little effect on the overall mechanical strength of the object, and can be removed by surface polishing during post-polymerization, so it is usually not a problem. However, there are concerns that it may become a problem if the amount increases.

[0010] Therefore, the present invention aims to provide a method for manufacturing a three-dimensional object that does not require the addition of an activating light absorber and is not dependent on the specific processing conditions in the post-polymerization step of 50°C to less than 110°C, and that can prevent the occurrence of fine cracks not only inside the three-dimensional object but also on its surface. [Means for solving the problem]

[0011] The present invention solves the aforementioned problems, and the first embodiment of the present invention is a molding step in which, from three-dimensional shape data showing the shape of a three-dimensional object, the height direction of the three-dimensional object is digitized and sequentially arranged, and two-dimensional shape data showing the cross-sectional shape of the three-dimensional object at each of the sequentially arranged heights is generated, and by using a liquid tank photopolymerization method in which the liquid photocurable resin composition held in a tank is selectively cured by irradiating a predetermined position of the liquid photocurable resin composition with an activation light, which is ultraviolet light or visible light, at that position, a molded layer having a shape corresponding to the two-dimensional shape at each height is sequentially formed and laminated according to the sequentially arranged order based on the two-dimensional shape data, thereby obtaining a molded body consisting of a cured body of the liquid photocurable resin composition having a shape corresponding to the shape of the three-dimensional object, and containing an effective amount of the photopolymerization initiator; A cleaning step in which the molded article obtained in the above step is cleaned using an organic solvent; and The molded body cleaned in the above process is subjected to 10 to 10,000 mW / cm². 2 A post-polymerization step in which the unpolymerized components contained in the molded body are polymerized by heating the molded body irradiated with the activation light at a temperature of 50°C or higher and less than 110°C after irradiation with the activation light of the irradiation intensity; A method for manufacturing a three-dimensional object, including The liquid photocurable resin composition comprises: (A) a radical polymerizable monomer: 100 parts by mass; (B) an inorganic filler: 5.0 to 400 parts by mass; (C) a photopolymerization initiator that absorbs the activation light and generates radicals: 0.05 to 10.0 parts by mass; and (D) a polymerization inhibitor: 0.01 to 5.0 parts by mass. Using a composition containing, The irradiation of the activation light in the post-polymerization step is performed in a state in which the surface of the molded article is in contact with an oxygen-blocking substance or a solution in which the oxygen-blocking substance is dissolved. A method for manufacturing a three-dimensional stereolithographic object, characterized by the following features.

[0012] In the manufacturing method of the above form (hereinafter, also referred to as "the manufacturing method of the present invention"), the content of the inorganic filler (B) is 20 to 350 parts by mass, and an activated light absorber (E) {excluding the above (C)}: 0.1 to 3.0 parts by mass is further included, and it is preferable to use the above liquid photocurable resin composition.

[0013] Further, the second form of the present invention is a manufacturing method of a dental restoration, characterized by manufacturing a dental restoration by the manufacturing method of the present invention.

Effects of the Invention

[0014] According to the present invention, when manufacturing a three-dimensional optical molded object that requires high mechanical strength like a dental restoration using a photocurable resin composition in which a large amount of an inorganic filler is blended in a radical polymerization initiator, an activated light absorber does not particularly need to be blended, and it is possible to prevent the generation of fine cracks on the surface of the three-dimensional molded object regardless of the specific treatment conditions in the heat treatment.

Brief Description of the Drawings

[0015] [Figure 1] This figure is an optical microscope photograph (magnification 50 times) of the surface of the three-dimensional optical molded object obtained in Example 1. [Figure 2] This figure is an optical microscope photograph (magnification 50 times) of the surface of the three-dimensional optical molded object obtained in Comparative Example 2.

Modes for Carrying Out the Invention

[0016] The manufacturing method of the present invention solves the above problems. In the manufacturing method described in Patent Document 1, the irradiation of the activating light in the post-polymerization process (secondary curing process) is carried out in a state where the surface of the molded body is in contact with an oxygen-blocking substance or a solution in which the oxygen-blocking substance is dissolved, which is a major feature. And by this, it becomes possible to prevent the generation of fine cracks not only inside the three-dimensional molded object but also on its surface without particularly blending an activation light absorber.

[0017] Regarding the reason why such an effect is obtained, the inventors have speculated as follows. As described above, when forming a three-dimensional shaped molded body by the liquid bath photopolymerization method, a single molding layer is formed by the light source mounted on the three-dimensional optical shaping apparatus, and the molded body is obtained by overlapping a plurality of such single layers. When forming the single molding layer, when the activating light irradiated from the light source passes through the uncured resin, attenuation of the activating light occurs. As a result, there are portions with a relatively high polymerization rate and portions with a relatively low polymerization rate in the molded body (polymerization unevenness). During additional light irradiation during secondary curing, the surface of the molded body is subject to polymerization inhibition by oxygen in the air, so the polymerization unevenness on the surface of the molded body remains even after light irradiation in secondary curing. Here, in the secondary curing process, it is considered that the region with a low polymerization rate is broken by the shrinkage stress during secondary curing and cracks occur. On the other hand, in the manufacturing method of the present invention, since an oxygen-blocking substance is present on the surface of the molded body when performing light irradiation in the post-polymerization process, it is not subject to polymerization inhibition by oxygen, and the polymerization unevenness on the surface of the molded body is eliminated. Therefore, it is considered that cracks do not occur during the subsequent heat treatment.

[0018] The manufacturing method of the present invention has no particular difference from the manufacturing method of the three-dimensional molded object described in Patent Document 1 except for the points that the irradiation of the activating light in the post-polymerization process is carried out in a state where the surface of the molded body is in contact with an oxygen-blocking substance or a solution in which the oxygen-blocking substance is dissolved, and that an activation light absorber is not essential. Hereinafter, including these, the liquid photocurable resin composition used in the manufacturing method of the present invention (hereinafter, also referred to as "this liquid photocurable resin composition") and the manufacturing method of the present invention will be described in detail.

[0019] In this specification, unless otherwise specified, the notation "x~y" using numerical values ​​x and y means "greater than or equal to x and less than or equal to y". If a unit is attached only to the numerical value y in such notation, that unit shall also apply to the numerical value x. Furthermore, in this specification, the term "(meth)acrylic" means both "acrylic" and "methacrylic". Similarly, the term "(meth)acrylate" means both "acrylate" and "methacrylate", and the term "(meth)acryloyl" means both "acryloyl" and "methacryloyl".

[0020] 1. About this liquid photocurable resin composition In the manufacturing method of the present invention, the liquid photocurable resin composition used is a liquid photocurable resin composition comprising: (A) 100 parts by mass of a radical polymerizable monomer, (B) 5.0 to 400 parts by mass of an inorganic filler, (C) a photopolymerization initiator that absorbs the activation light and generates radicals: 0.05 to 10.0 parts by mass of a polymerization inhibitor (D): 0.01 to 5.0 parts by mass.

[0021] In order to ensure that the target object, a stereolithographically printed object, is fabricated with high precision and that air bubbles and other impurities are prevented from being incorporated into the object, the viscosity of the liquid photocurable resin composition described above at 25°C is preferably 5 to 50,000 mPa·s, and particularly preferably 10 to 30,000 mPa·s. The components of this liquid photocurable resin composition are described below.

[0022] (1) Radical polymerizable monomer (A) As the polymerizable monomer (A), it is preferable to use a (meth)acrylate monomer because it has a fast curing rate and excellent strength in the resulting photopolymerized product. From the viewpoint of being able to produce a higher strength photopolymerized product, it is preferable that 50% or more by mass, particularly 80% or more by mass, and even more preferably 95% or more by mass of the total mass of all radical polymerizable monomers be a bifunctional or polyfunctional (meth)acrylate.

[0023] Examples of bifunctional or polyfunctional (meth)acrylates that can be suitably used include BPA skeleton-containing (meth)acrylates such as 2,2'-bis{4-[3-(meth)acryloyloxy-2-hydroxypropoxy]phenyl}propane, 2,2'-bis[4-(meth)acryloyloxyphenyl]propane, and 2,2'-bis[4-(meth)acryloyloxypolyethoxyphenyl]propane, as well as ethylene glycol-based (meth)acrylates such as triethylene glycol dimethacrylate and ethylene glycol dimethacrylate. Examples include aliphatic di(meth)acrylates such as 1,3-propanediol di(meth)acrylate and 1,9-nonanediol dimethacrylate, urethane group-containing (meth)acrylates such as 1,6-bis(methacryloyloxy-2-ethoxycarbonylamino)-2,2,4-trimethylhexane, trifunctional (meth)acrylates such as trimethylolpropanetrimethacrylate, and isocyanate skeleton-containing (meth)acrylates such as tris(2-methacryloyloxyethyl)isocyanurate. Among these, it is preferable to use 2,2'-bis[4-(meth)acryloyloxyphenyl]propane, 2,2'-bis[4-(meth)acryloyloxypolyethoxyphenyl]propane, triethylene glycol dimethacrylate, tris(2-methacryloyloxyethyl) isocyanurate, etc., due to their low viscosity and high strength.

[0024] Furthermore, suitable monofunctional (meth)acrylates for use in combination with polyfunctional (meth)acrylates of two or more functions include hydroxyethyl methacrylate, methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, hydroxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, and glycidyl (meth)acrylate.

[0025] Furthermore, as the polymerizable monomer (A), only one of these (meth)acrylate monomers may be used, or a combination of several may be used.

[0026] (2) Inorganic filler (B) To enhance the mechanical strength, such as rigidity, of the resulting three-dimensional molded object, this liquid photocurable resin composition contains 5.0 to 400 parts by mass of inorganic filler (B) per 100 parts by mass of radical polymerizable monomer (A). The higher the inorganic filler content, the higher the mechanical strength; therefore, it is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 100 parts by mass or more. However, if the amount is too high, the viscosity of the photocurable resin of the present invention will increase, making it difficult to perform three-dimensional photopolymerization. For this reason, the inorganic filler content is preferably 350 parts by mass or less, more preferably 300 parts by mass or less, and even more preferably 250 parts by mass or less.

[0027] As the inorganic filler (B), an inorganic powder or granular material composed of one or more types of inorganic particles is used. The material of the inorganic particles is not particularly limited; for example, materials used as fillings in dental restorations can be used without any particular restrictions. Specifically, examples include elemental metals; metal oxides or metal composite oxides; metal salts such as metal fluorides, carbonates, sulfates, silicates, hydroxides, chlorides, sulfites, and phosphates; and composites of these metal salts. Preferably, materials used include: amorphous silica, quartz, alumina, titania, zirconia, metal oxides such as barium oxide, yttrium oxide, lanthanum oxide, and ytterbium oxide; silica-based composite oxides such as silica-zirconia, silica-titania, silica-titania-barium oxide, and silica-titania-zirconia; glass such as borosilicate glass, aluminosilicate glass, and fluoroaluminosilicate glass; metal fluorides such as barium fluoride, strontium fluoride, yttrium fluoride, lanthanum fluoride, and ytterbium fluoride; inorganic carbonates such as calcium carbonate, magnesium carbonate, strontium carbonate, and barium carbonate; and metal sulfates such as magnesium sulfate and barium sulfate.

[0028] When manufacturing dental restorations, it is preferable to use powders composed of particles such as silica-zirconia, silica-titania, silica-titania-barium oxide, and silica-titania-zirconia, due to their strong radiopaque properties. From the viewpoint of wear resistance of the hardened material, it is most preferable to use powders composed of silica-zirconia particles.

[0029] Inorganic powders and granules used as inorganic fillers are preferably treated with surface treatment agents, such as silane coupling agents, to improve their compatibility with polymerizable monomers and enhance mechanical strength and water resistance. Surface treatment can be carried out by known methods. Suitable silane coupling agents include methyltrimexisilane, methyltriethoxysilane, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, vinyltrichlorosilane, vinyltriethoxysilane, vinyltris(β-methoxyethoxy)silane, γ-methacryloyloxypropyltrimethoxysilane, methacryloxyoctyl-8-trimethoxysilane, γ-chloropropyltrimethoxysilane, γ-glycidoxypropylmethoxysilane, and hexamethyldisilazane.

[0030] The average particle size of the inorganic powders constituting the inorganic filler is not particularly limited. Generally, those with an average particle size of 0.01 to 100 μm (preferably 0.01 to 10 μm), which are commonly used as dental restorative materials, can be used. However, from the viewpoint of suppressing viscosity increase and sedimentation of the photocurable composition, it is preferable to use inorganic fillers in which 80% or more of the particle size distribution, measured by microscopy using a scanning microscope, falls within the range of 0.05 to 5.0 μm, more preferably within the range of 0.08 to 2.0 μm, and most preferably within the range of 0.1 to 1.0 μm. Furthermore, it is preferable that the number of particles within these particle size ranges accounts for 90% or more of the total, and particularly 95% or more. In addition, as long as the overall particle size distribution is such that it is possible to mix and use multiple inorganic powders with different particle size distributions and materials. Furthermore, it is preferable to blend the inorganic powders as they are, but some or all of them may be blended as powders composed of composite particles (organic-inorganic composites) formed by compounding them with resin.

[0031] (3) A photopolymerization initiator (C) that absorbs the activation light and generates radicals. The above-mentioned photopolymerization initiator (C) has the function of generating radicals by irradiating with activation light, specifically ultraviolet or visible light, from a light source mounted on a stereolithography apparatus, and radically polymerizing the radical polymerizable monomer. Therefore, the photopolymerization initiator needs to absorb light and generate radicals according to the type of activation light used (wavelength: hereinafter also referred to as the "polymerization initiation wavelength"). Furthermore, the amount to be blended may be 0.05 to 10.0 parts by mass per 100 parts by mass of the radical polymerizable monomer (A), but in order for an effective amount of photopolymerization initiator to remain in the molded body more efficiently, the above-mentioned content of photopolymerization initiator (C) is preferably 0.3 to 5.0 parts by mass, and particularly preferably 0.5 to 3.0 parts by mass.

[0032] Furthermore, if the activation light irradiated in the post-polymerization step in the manufacturing method of the present invention is of a different wavelength than the activation light irradiated in the molding step, it is preferable that the liquid photocurable resin composition used in the present invention contains, in addition to the photopolymerization initiator that absorbs the activation light irradiated in the molding step, a photopolymerization initiator (C') that absorbs the activation light irradiated in the post-polymerization step. In this case, the amount of the above (C') photopolymerization initiator blended is preferably 0.05 to 5.0 parts by mass, particularly 0.1 to 3.0 parts by mass, and most preferably 0.3 to 1.0 parts by mass, per 100 parts by mass of the radical polymerizable monomer (A).

[0033] The photopolymerization initiators (C) and (C') can be appropriately selected from known photopolymerization initiators that satisfy the above conditions. The photopolymerization initiators to be selected are not particularly limited, and for example, self-cleaving photopolymerization initiators, two-molecule hydrogen abstraction type photopolymerization initiators, photoacid generators, and combinations thereof can be used. Furthermore, these photopolymerization initiators may be used in combination with photosensitizing dyes or electron-donating compounds.

[0034] Examples of photopolymerization initiators, photosensitizing dyes, and electron-donating compounds that can be suitably used are given below.

[0035] In other words, suitable self-cleaving photopolymerization initiators include acylphosphine oxide compounds such as diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide and phenylbis(2,4,6-trimethylbenzoyl)-phosphine oxide, benzoketal compounds, benzyne compounds, α-aminoacetophenone compounds, α-hydroxyacetophenone compounds, titanocene compounds, and acyloxime compounds. In addition, suitable photoacid generators include iodonium salt compounds such as p-isopropylphenyl-p-methylphenyliodonium tetrakispentafluorophenylborate salt, sulfonium salt compounds such as dimethylphenacylsulfonium hexafluoroantimonate salt, and halomethyl group-substituted triazine compounds such as 2,4,6-tris(trichloromethyl)-s-triazine. Suitable photosensitizing dyes include ketone compounds, coumarin dyes, cyanine dyes, merocyanine dyes, thiazine dyes, azine dyes, acridine dyes, xanthene dyes, squalium dyes, pyrylium salt dyes, and condensed polycyclic aromatic compounds such as anthracene and perylene, as well as thioxanthone compounds. Suitable electron donors include 4-dimethylaminobenzoic acid ester, 4-dimethylaminotoluene, p-dimethoxybenzene, 1,2,4-trimethoxybenzene, and thiophene compounds.

[0036] Furthermore, considering that the wavelength of activation light emitted from a light source in a typical stereolithography apparatus is 350 nm to 420 nm, when considering a case where a molding process is performed using a stereolithography apparatus with such a light source, and activation light with a wavelength of 450 to 490 nm is irradiated in the post-polymerization process, it is preferable to use phenylbis(2,4,6-trimethylbenzoyl)-phosphine oxide as the photopolymerization initiator (C), and camphorquinone and an amine as the photopolymerization initiator (C').

[0037] (4) Polymerization inhibitor (D) To improve the storage stability and molding accuracy of this liquid photocurable resin composition, a polymerization inhibitor (D) is added at a rate of 0.01 to 5.0 parts by mass per 100 parts by mass of polymerizable monomer (A). The amount of polymerization inhibitor (D) added is preferably 0.03 to 4.0 parts by mass, and more preferably 0.05 to 2.5 parts by mass. As the polymerization inhibitor (D), a compound that reacts with radicals generated in the photocurable composition to deactivate the radicals can be used, and for example, di-tert-butyl-p-cresol and 4-methoxyphenol are preferably used.

[0038] (5) Other ingredients This liquid photocurable resin composition may further contain, as needed, an activating light absorber (E), a chain transfer agent, a thermal polymerization initiator, a coloring agent, and the like.

[0039] The activating light absorber (E) consists of a compound that absorbs the activating light irradiated from the stereolithography apparatus during the molding process and does not function as a polymerization initiator {therefore, it does not fall under the category of photopolymerization initiator (C)}. To prevent excessive transmission of activating light irradiated from the stereolithography apparatus and a decrease in molding accuracy, it is preferable to blend the activating light absorber (E) in an amount of 0.01 to 2.7 parts by mass per 100 parts by mass of the radical polymerizable monomer (A). A more preferable blending amount of the activating light absorber is 0.08 to 2.0 parts by mass, and the most preferable blending amount is 0.25 to 1.0 parts by mass. The activating light absorber (E) is not particularly limited as long as it is a compound that absorbs the activating light emitted from the light source mounted on the photopolymerization apparatus used. Examples include triazole compounds such as 2-(hydroxy-5-methylphenyl)-2H-benzotriazole and 2-(3-tert-butyl-2-hydroxy-5-methylphenyl)-5-chloro-2H-benzotriazole, and benzophenone compounds such as 2,4-dihydroxybenzophenone and 2-hydroxy-4-methoxybenzophenone.

[0040] Examples of chain transfer agents include thiol compounds such as butanethiol, thiophenol, mercaptoethanol, octylthiol, and lauryl mercaptan; α-alkylstyrene compounds such as 2,4-diphenyl-4-methyl-1-pentene (α-methylstyrene dimer) and 2-phenyl-1-propene (α-methylstyrene); and hydrocarbons substituted with at least one halogen atom, such as halogenated hydrocarbons like carbon tetrachloride and ethylene bromide. α-alkylstyrene compounds, particularly α-methylstyrene dimer, are preferred due to their high crack-inhibiting effect. When a chain transfer agent is included, the amount is typically in the range of 0.00001 to 1.0 parts by mass per 100 parts by mass of the radical polymerizable monomer (A).

[0041] The thermal polymerization initiator functions as a polymerization initiator for secondary curing in a subsequent process, and from the viewpoint of remaining effectively in the laminate without functioning during primary curing in the molding process, it is preferable to use a thermal polymerization initiator with a 10-hour half-life temperature of 50 to 130°C. Examples of thermal polymerization initiators that can be suitably used include organic peroxides such as tert-butylperoxylaurate and benzoyl peroxide, and azo compounds such as azobutyronitrile and azobis(dimethylvaleronitrile). The amount of thermal polymerization initiator to be blended is usually 0.001 to 1.0 parts by mass, more preferably 0.005 to 0.3 parts by mass, and particularly preferably 0.01 to 0.1 parts by mass, per 100 parts by mass of polymerizable monomer (A).

[0042] Coloring substances are added to dental restorations such as inlays, onlays, crowns, and dentures to reproduce tooth color and oral mucosa color. Coloring substances may be pigments or dyes. Examples of pigments include inorganic pigments such as titanium dioxide, zinc oxide, zirconium oxide, zinc sulfide, aluminum silicate, calcium silicate, carbon black, iron oxide, copper chromite black, chromium oxide green, chromium green, violet, chromium yellow, lead chromate, lead molybdate, cadmium titanate, nickel titanium yellow, ultramarine blue, cobalt blue, bismuth vanadate, cadmium yellow, and organic pigments such as monoazo pigments, diazo pigments, diazo condensation pigments, perylene pigments, and anthraquinone pigments.

[0043] 2. Regarding each step of the manufacturing method of the present invention The method for manufacturing a three-dimensional stereolithography object described in Patent Document 1 involves manufacturing a three-dimensional object by a liquid bath photopolymerization method including a molding step, a washing step, and a post-polymerization step. In the molding step, a photopolymerization curable composition containing an activating light absorber as an essential component is primary cured to obtain a molded body containing an effective amount of photopolymerization initiator. The post-polymerization step, performed after the washing step, involves applying 10 to 10,000 mW / cm² to the molded body. 2 The process involves irradiating the molded body with the aforementioned activation light at an irradiation intensity, followed by heating the irradiated body at a temperature of 50°C to less than 110°C, thereby preventing the formation of fine cracks inside the three-dimensional molded object. In this manufacturing method, controlling the heating temperature in the post-polymerization process is considered important for efficiently obtaining high-strength three-dimensional molded objects that do not have internal cracks. It is preferable to sequentially perform the following temperature conditions 1, 2, and 3, and it is preferable that the total heating time be 5 minutes or more. Temperature condition 1: 50°C or higher and less than 75°C Temperature condition 2: 75°C or higher and less than 90°C Temperature condition 3: 90°C or higher and less than 110°C.

[0044] In the manufacturing method of the present invention, compared to the manufacturing method described in Patent Document 1, the irradiation of the activation light in the post-polymerization step is performed while the surface of the molded body is in contact with an oxygen-blocking substance or a solution in which the oxygen-blocking substance is dissolved. As a result, even though an activation light absorber is not an essential component, it is possible to prevent not only the occurrence of cracks inside the three-dimensional stereolithography object but also the occurrence of cracks on the surface, even without strictly controlling the heating temperature during the heating performed after light irradiation in the post-polymerization step.

[0045] Therefore, except for the points mentioned above, each step in the manufacturing method of the present invention is the same as the method described in Patent Document 1, but each step will be briefly explained below.

[0046] (1) Molding process In the molding process, three-dimensional shape data representing the shape of a three-dimensional object is used to digitize and sequentialize the height direction of the three-dimensional object, and two-dimensional shape data representing the cross-sectional shape of the three-dimensional object at each sequential height is generated. Using a tank photopolymerization method in which the liquid photocurable resin composition held in a tank is irradiated with activation light, such as ultraviolet or visible light, at predetermined positions to selectively cure the liquid photocurable resin composition present at those positions, molding layers having shapes corresponding to the two-dimensional shapes at each height are sequentially formed and laminated according to the sequential order based on the two-dimensional shape data, thereby obtaining a molded body made of a cured liquid photocurable resin composition having a shape corresponding to the shape of the three-dimensional object, and containing an effective amount of the photopolymerization initiator.

[0047] The three-dimensional shape data defining the shape of the molded body can be easily obtained as digital data by scanning the outer surface of an article having the desired three-dimensional shape or the inner surface of the mold of the article using a 3D scanner or a three-dimensional digitizer. Alternatively, three-dimensional shape digital data created using CAD or the like can be used, either with or without the digital data obtained in this way. For example, when obtaining three-dimensional shape (digital) data for a dental prosthesis for tooth restoration in a specific patient, three-dimensional shape (digital) data obtained by 3D scanning using an intraoral scanner can be suitably used.

[0048] The three-dimensional shape (digital) data obtained in this way is then divided discontinuously in the height direction of the three-dimensional object at predetermined minute intervals (height widths): typically tens to hundreds of micrometers, using CAD, for example. This division (digitization) and sequence is then performed in the height direction, generating two-dimensional shape data that shows the cross-sectional shape of the three-dimensional object at each of these sequenced heights.

[0049] To explain the above molding process in more detail, first, based on the two-dimensional shape data at the height of the initial ranking, activation light is irradiated onto a predetermined position of the liquid photocurable resin composition held inside the tank to cure it, thereby forming a "formed layer" having a shape corresponding to the two-dimensional shape data, and this "formed layer" becomes the "layer to be bonded" (first step). Next, the "layer to be bonded" is moved up or down, and the liquid photocurable resin composition is supplied directly above or directly below the "layer to be bonded" in the tank (second step). Subsequently, based on the two-dimensional shape data at the height of the next ranking in the ranking in the previous step, activation light is irradiated onto a predetermined position of the liquid photocurable resin composition supplied directly above or directly below the "layer to be bonded" to cure it, thereby forming a "new formed layer" having a shape corresponding to the two-dimensional shape data, and bonding it to the "layer to be bonded," thereby obtaining a "laminated body" having the "new formed layer" as the "new layer to be bonded" (third step). Then, the "laminated body" is moved up or down, and a liquid photocurable resin composition is supplied directly above or directly below the "new layer to be bonded" in the tank (fourth step). The "new layer to be bonded" is used as the "layer to be bonded" in the third step, and the cycle consisting of the third and fourth steps is repeated. In the final third step, a new molded layer is formed based on the two-dimensional shape data at the height of the final ranking, and a laminate is obtained, and the obtained laminate becomes the molded body.

[0050] "Vat photopolymerization" is known to include methods such as Stereolithography (SLA), Digital Light Processing (DLP), and Liquid Column Display (LCD), depending on the light irradiation method. In the manufacturing method of the present invention, such methods can be adopted without particular limitation, and the photopolymerization apparatus is not particularly limited as long as it is a photopolymerization apparatus for vat photopolymerization; any apparatus can be used depending on the method adopted. The activation light to be irradiated may be monochromatic light having a specific single wavelength peak or light having a relatively narrow wavelength distribution, and multiple lights with different peak wavelengths may be irradiated. It is preferable to use an SLA type photopolymerization apparatus in order to produce a higher resolution and higher strength object.

[0051] (2) Washing process In the washing step, the molded article obtained in the molding step is washed using an organic solvent. Examples of organic solvents used in the washing step include alcohol-based solvents such as ethanol, methanol, and isopropyl alcohol; ketone-based solvents such as acetone and methyl ethyl ketone; ether-based solvents such as diethyl ether, diisopropyl ether, tripropylene glycol monomethyl ether, and tetrahydrofuran; amide-based solvents such as N-methylpyrrolidone and dimethylacetamide; and halogen-based solvents such as methylene chloride and chloroform. Among these, alcohol-based solvents and ether-based solvents are preferred due to their high cleaning effect, and alcohol-based solvents are more preferred due to their low environmental impact.

[0052] (3) Post-polymerization step In the post-polymerization step, the molded body cleaned in the previous step is subjected to a polymerization treatment of 10 to 10,000 mW / cm². 2 After irradiating the molded body with the activation light at the specified irradiation intensity, the unpolymerized components contained in the molded body are polymerized by heating the molded body at a temperature of 50°C or higher and less than 110°C. In the manufacturing method of the present invention, the irradiation with the activation light must be performed in a state in which the surface of the molded body is in contact with an oxygen-blocking substance or a solution in which the oxygen-blocking substance is dissolved.

[0053] Generally, polymerization inhibition by oxygen in radical polymerization occurs because oxygen atoms in the air are highly reactive with radicals and suppress the growth reaction of radical polymerization. Therefore, when the molded body is subjected to additional light irradiation, polymerization is particularly difficult to proceed in the surface portion of the molded body that is in direct contact with air, and the areas with high and relatively low polymerization rates (uneven polymerization) that occur during molding as described above are not eliminated. However, if additional light irradiation is performed while the surface of the molded body is in contact with an oxygen-blocking substance or a solution in which the oxygen-blocking substance is dissolved, it is thought that the polymerization rate will improve on the surface of the molded body as well as inside the molded body, eliminating the uneven polymerization and suppressing cracking during heating.

[0054] Here, oxygen-blocking substances refer to substances with low oxygen permeability that are used as so-called air barrier agents. Specifically, examples include gelatin with a number average molecular weight of 15,000 to 250,000, such as the "gelatin" manufactured by Wako Pure Chemical Industries, Ltd. disclosed in Patent Document 2 (JP-A-09-241304) and Patent Document 3 (JP-A-2000-128723), polyvinyl alcohol with a number average molecular weight of 20,000 to 200,000, polyvinyl acetate with a number average molecular weight of 20,000 to 200,000, polyvinylpyrrolidone with a number average molecular weight of 20,000 to 200,000, polyethylene oxide with a number average molecular weight of 10,000 to 100,000, copolymers of alkyl vinyl ether and maleic anhydride with a number average molecular weight of 10,000 to 100,000, and water-soluble polymer substances such as gum arabic, poly(meth)acrylic acid and its metal salt compounds with a number average molecular weight of 5,000 to 250,000, polyacrylamides with a number average molecular weight of 5,000 to 250,000, and polysaccharides such as cellulose and sodium alginate. Among these, it is preferable to use water-soluble polymers, particularly those with a number-average molecular weight of 5,000 to 150,000.

[0055] As a method for bringing the surface of the molded body after the cleaning process into contact with an oxygen-blocking substance or a solution in which the oxygen-blocking substance is dissolved, the following methods can be employed: (1) directly attaching the oxygen-blocking substance to the surface of the molded body; (2) applying a solution in which the oxygen-blocking substance is dissolved to the surface of the molded body after the cleaning process; or (3) immersing the molded body in the solution. However, from the viewpoint of ease of operation and effectiveness, it is preferable to employ method (2) or (3), and method (2) is particularly preferable.

[0056] When preparing a solution containing an oxygen-blocking substance, any solvent that dissolves the oxygen-blocking substance can be used without particular restriction. When using a water-soluble oxygen-blocking substance, it is preferable to use water and / or a water-soluble organic solvent such as alcohols. Furthermore, it is preferable to add a surfactant to improve the solubility of the water-soluble oxygen-blocking substance. As a surfactant, cationic surfactants such as anionic surfactants such as sodium dodecyl sulfate, quaternary ammonium salt surfactants, and amine surfactants, nonionic surfactants such as polyoxyethylene alkyl ethers, and amphoteric surfactants such as alkyl carboxybetaine can be used as appropriate. The concentration of the oxygen-blocking substance in the solution containing the dissolved oxygen-blocking substance is usually 1.0 to 40% by mass, and preferably 3.0 to 10% by mass.

[0057] When additional activation light irradiation is performed in the post-polymerization process, the irradiation wavelength is not particularly limited as long as it is a wavelength that is absorbed by the photopolymerization initiator remaining in the laminate and generates radicals. Furthermore, the irradiation intensity of the additional activation light irradiation should be 10 to 10,000 mW / cm². 2 That would be ideal, but the lower limit is 30 mW / cm². 2 The above is preferable. Furthermore, the irradiation time is not particularly limited, but is preferably 1 minute or more, more preferably 3 minutes or more, and even more preferably 5 minutes or more.

[0058] Furthermore, the temperature at which the molded body irradiated with activation light is heated may be 50°C or higher and less than 110°C, but it is more preferably 50 to 90°C, and even more preferably 55 to 80°C.

[0059] Furthermore, the above heat treatment can also be performed by microwave irradiation using a microwave oven or similar device.

[0060] The method for manufacturing dental restorations described herein is characterized by manufacturing dental restorations such as inlays, onlays, crowns, and dentures using the method for manufacturing three-dimensional stereolithography described herein. When manufacturing such dental restorations, it is preferable to incorporate an activating light absorber into the stereolithography curable composition of the present disclosure. Furthermore, as the three-dimensional shape data indicating the shape of the dental restoration (three-dimensional object) used in the molding process, CAD data designed based on digital data obtained by scanning the oral cavity shape of an individual patient or an oral cavity model created for each individual patient may be used. According to the method for manufacturing dental restorations described herein, it is possible to manufacture dental restorations that have high mechanical strength and are free from cracks on the actual surface. [Examples]

[0061] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The compounds and their abbreviations used in the examples and comparative examples are as follows.

[0062] (1) Radical polymerizable monomer (A) Monomer compositions A1 to A6 were prepared by mixing the monomer compounds shown below. <Monomer Compounds> UDMA: Urethane dimethacrylate • 3G: Triethylene glycol dimethacrylate • D-2.6E: Bisphenol A ethylene glycol (EO) adduct dimethacrylate, average number of EO adducts: 2.6 <Monomer composition> ·A1:UDMA: 25 parts by mass, 3G: 25 parts by mass, D-2.6E: 50 parts by mass ·A2:UDMA: 50 parts by mass, 3G: 20 parts by mass, D-2.6E: 30 parts by mass.

[0063] (2) Inorganic filler (B) The following mixture of inorganic powders was used. • D-1: Average particle size 280 nm, spherical silica-zirconia (γ-methacryloyloxypropyltrimethoxysilane surface treated material) · D-2: A mixture of 70 wt% spherical silica-zirconia (γ-methacryloyloxypropyltrimethoxysilane surface-treated material) with an average particle size of 500 nm and 30 wt% spherical silica-zirconia (γ-methacryloyloxypropyltrimethoxysilane surface-treated material) with an average particle size of 80 nm.

[0064] (4) Photopolymerization initiator (C) BAPO: Phenylbis(2,4,6-trimethylbenzoy)phosphine oxide (generates radicals upon irradiation with 405 nm activation light).

[0065] (5) Polymerization inhibitor (D) BHT: Dibutylhydroxytoluene HQME: Hydroquinone methyl ether.

[0066] (6) Activated light absorber (E) SS3:2-(3-tert-butyl-2-hydroxy-5-methylphenyl)-5-chloro-2H-benzotriazol.

[0067] (7) Solution containing an oxygen-blocking substance ·AB-1: A mixture of 5.0 wt% polyvinyl alcohol (average degree of polymerization approximately 1500), 1.0 wt% sodium dodecyl sulfate, 20 wt% ethanol, and 74 wt% purified water.

[0068] Example 1 To 100 parts by mass of monomer composition A1, BTPO (1.0 part by mass), SS3 (0.7 parts by mass), BHT (0.1 part by mass), and HQME (0.1 part by mass) were added and stirred under red light until homogeneous. Then, the mixture was mixed with inorganic filler D-1 (150 parts by mass), degassed, and a liquid photocurable resin composition was prepared. Subsequently, using the obtained liquid photocurable resin composition, a rectangular parallelepiped shape (made from the cured liquid photocurable resin composition) measuring 2.05 mm × 2.05 mm × 25.05 mm was obtained using a 3D printer (DWS Corporation: DW029D), and this was washed with ethanol. After applying AB-1 to the resulting cleaned molded body, it was irradiated with light for 10 minutes using a dental laboratory polymerization apparatus (Tokuyama Dental Co., Ltd.: Portalight), and then heat-treated in an incubator at 90°C for 30 minutes to produce multiple test specimens (rectangular prisms with a base of 2.05 mm x 2.05 mm square and a height of 25.05 mm). Using the obtained test specimens, bending strength measurements and crack evaluations were performed as shown below.

[0069] (1) Measurement of bending strength The above test specimen was polished with #800 waterproof sandpaper to create a prismatic shape with a 2mm x 2mm square base and a height of 25mm. Microscopic observation confirmed that no cracks remained on the surface of this prismatic sample. This prismatic sample was then mounted on a bending test machine (Shimadzu Corporation, Autograph AG5000D) and the three-point bending fracture strength was measured with a support distance of 20mm and a crosshead speed of 1mm / min. The evaluation results are shown in Table 1.

[0070] (2) Crack assessment The surface (1.0 mm × 2.0 mm) of the sides of the rectangular parallelepiped test specimens, which were not polished on the surface, at heights of approximately 1.0 mm, 1.0 mm, and 12.5 mm was observed with an optical microscope (50x magnification). The number of cracks observed within the surface (1.0 mm × 2.0 mm) was observed. In addition, the same test specimens were polished in the depth direction to a depth of 100 to 500 μm, and the surface was observed under a microscope every 100 μm to evaluate the presence or absence of cracks inside the hardened material according to the evaluation criteria below. The crack evaluation was performed twice during the test specimen preparation process: before light irradiation (after ethanol washing) and after the post-polymerization process (after heat treatment). As a result, the evaluation was "A0" before light irradiation and "A1" after the post-polymerization process.

[0071] <Evaluation Criteria> A0: No cracks were observed on the surface of the hardened material, nor were any cracks observed inside the hardened material. A1: No cracks were observed inside the hardened body, and a few minute cracks (5 or fewer) were observed on the surface of the hardened body, but this is acceptable. A2: No cracks are observed inside the hardened body, but numerous fine cracks (6 or more) are observed on the surface of the hardened body, which is acceptable. B: Obvious cracks were observed on the surface of the hardened material, which is unacceptable. C: Numerous obvious cracks were observed on the surface of the hardened material, which is unacceptable.

[0072] Example 2 Test specimens were prepared and evaluated in the same manner as in Example 1, except that monomer composition A2 was used instead of monomer composition A1. The results are shown in Table 1.

[0073] Comparative Example 1 In Example 1, test specimens were prepared and evaluated in the same manner as in Example 1, except that AB-1 was not applied after the cleaning process, and light irradiation and heat treatment were performed instead. The results are shown in Table 1.

[0074] Comparative Example 2 In Example 2, test specimens were prepared and evaluated in the same manner as in Example 2, except that AB-1 was not applied after the cleaning process, and light irradiation and heat treatment were performed instead. The results are shown in Table 1.

[0075] [Table 1]

[0076] As shown in Table 1, the three-dimensional stereolithography objects produced by the manufacturing methods of Examples 1 and 2 showed almost no cracks on the surface of the cured body even after secondary curing, and had high flexural strength. Comparative Examples 1 and 2 did not have an oxygen-blocking material applied before the secondary curing process, so cracks occurred on the surface of the objects, and the flexural strength was reduced due to the effects of the cracks.

Claims

1. A molding process to obtain a molded body consisting of a cured liquid photocurable resin composition having a shape corresponding to the shape of the three-dimensional object, and comprising a cured liquid photocurable resin composition containing an effective amount of the photopolymerization initiator, by sequentially forming and stacking molded layers having shapes corresponding to the two-dimensional shapes at each height in the order of the sequence, based on the two-dimensional shape data; and using a liquid bath photopolymerization method in which the height direction of the three-dimensional object is digitized and sequenced from three-dimensional shape data showing the shape of the three-dimensional object, and two-dimensional shape data showing the cross-sectional shape of the three-dimensional object at each sequenced height; and sequentially forming and stacking molded layers having shapes corresponding to the two-dimensional shapes at each height in the order of the sequence, based on the two-dimensional shape data; A cleaning step in which the molded article obtained in the above step is cleaned using an organic solvent; and The molded body cleaned in the above process will be subjected to a load of 10 to 10,000 mW / cm². ２ A post-polymerization step in which the unpolymerized components contained in the molded body are polymerized by heating the molded body irradiated with the activation light at a temperature of 50°C or higher and less than 110°C after irradiation with the activation light of the irradiation intensity; A method for manufacturing a three-dimensional object, including The liquid photocurable resin composition comprises: (A) a radical polymerizable monomer: 100 parts by mass; (B) an inorganic filler: 5.0 to 400 parts by mass; (C) a photopolymerization initiator that absorbs the activation light and generates radicals: 0.05 to 10.0 parts by mass; and (D) a polymerization inhibitor: 0.01 to 5.0 parts by mass. Using a composition containing, The irradiation of the activation light in the post-polymerization step is performed in a state in which the surface of the molded article is in contact with an oxygen-blocking substance or a solution in which the oxygen-blocking substance is dissolved. A method for manufacturing a three-dimensional stereolithographic object, characterized by the following features.

2. A method for producing a three-dimensional photopolymer according to claim 1, using the liquid photocurable resin composition which contains 20 to 350 parts by mass of the inorganic filler (B), and further contains 0.1 to 3.0 parts by mass of (E) an activating light absorber {excluding (C)}.

3. A method for manufacturing a dental restoration, characterized by manufacturing a dental restoration by the method for manufacturing a three-dimensional stereolithographic object described in claim 1.

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