Thermosetting resin composition, embedded molded article, and method for producing thermosetting resin composition

Abstract

A thermosetting resin composition capable of suppressing the occurrence and propagation of cracks is provided. [Solution] A thermosetting resin composition comprising, per 100 parts by weight of thermosetting resin, 1 to 5 parts by weight of a curing agent and 1 to 5 parts by weight of cellulose nanofiber powder, wherein the cellulose nanofiber powder contains, relative to the total weight of the cellulose nanofiber powder, 75 to 99% by weight of cellulose nanofiber, 0.5 to 20% by weight of a phosphate ester, and 0.5 to 5.0% by weight of an alkylammonium salt.

Description

[Technical Field]

[0001] The present invention relates to a thermosetting resin and an implant-molded article. In particular, the present invention relates to a thermosetting resin composition capable of suppressing the generation and propagation of cracks, an implant-molded article obtained by molding such a thermosetting resin composition, and a method for producing such a thermosetting resin composition. [Background technology]

[0002] A conventional technique involves embedding metal parts or the like in a thermosetting resin to produce an embedded molded product. To accelerate the curing of the thermosetting resin, a curing accelerator is generally used. For example, Patent Document 1 (JP 2017-100984 A) discloses an epoxy resin composition characterized by containing a specific imidazole compound. According to this invention, the epoxy resin composition exhibits excellent adhesion to metal and inorganic materials. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-100984 Summary of the Invention [Problem to be solved by the invention]

[0004] When manufacturing potting molded products using thermosetting resin as the potting resin for parts, there is a problem that if the resin hardens too quickly, stress will be generated inside the resin, making it prone to cracks, regardless of the size of the part, such as a hard metal part.

[0005] Conventionally, silica nanoparticles, alumina nanoparticles, titanium oxide nanoparticles, etc. have been used to improve the toughness of epoxy resins and inhibit crack propagation, but problems arise with particle aggregation and delamination at the interface. Furthermore, when silica nanoparticles, alumina nanoparticles, etc. are uniformly dispersed throughout the epoxy resin matrix, a "crack pinning effect" (which physically inhibits crack propagation) and energy absorption due to increased localized plastic deformation are observed during crack propagation. However, even if the occurrence of microcracks can be inhibited, because these particles are spherical, the bridging effect that connects both ends of the crack is weak.

[0006] The present invention has been completed in view of the above problems, and aims to provide, in one embodiment, a thermosetting composition that can suppress the occurrence and propagation of cracks. In another embodiment, the present invention aims to provide an embedded molded article obtained by molding such a thermosetting composition. [Means for solving the problem]

[0007] After extensive research, the inventors came up with the idea of ​​suppressing the occurrence and progression of cracks in thermosetting resins by dispersing nano-sized fibers. Nanofibers include cellulose nanofibers (hereinafter sometimes referred to as "CNF"), carbon nanotubes, and nanofiberglass, but they discovered that using CNF, which is the most flexible, can suppress large cracks.

[0008] Carbon nanotubes and nanofiberglass are harder materials than CNFs, and microcracks increase before the bridging effect is achieved. Nanofiberglass, in particular, has irregular fiber diameters, making it difficult to achieve the fiber bridging effect. On the other hand, incorporating specially treated cellulose nanofibers into epoxy resins has the most effective effect of suppressing the occurrence and progression of cracks in cured thermosetting resins. The present invention was completed based on the above findings and is exemplified below. In yet another embodiment, the present invention aims to provide a method for producing such a thermosetting resin composition.

[0009] [Aspect 1] A thermosetting resin composition, The composition contains 1 to 5 parts by weight of a curing agent and 1 to 5 parts by weight of cellulose nanofiber powder relative to 100 parts by weight of a thermosetting resin, The cellulose nanofiber powder is a thermosetting resin composition containing 75 to 99 wt% of cellulose nanofibers, 0.5 to 20 wt% of a phosphate ester, and 0.5 to 5.0 wt% of an alkylammonium salt, relative to the total weight of the cellulose nanofiber powder. [Aspect 2] 2. The thermosetting resin composition of claim 1, wherein the thermosetting resin comprises an epoxy resin. [Aspect 3] 3. The thermosetting resin composition of claim 1 or 2, wherein the curing agent comprises imidazole. [Aspect 4] Aspect 4. The thermosetting resin composition according to any one of Aspects 1 to 3, wherein the cellulose nanofiber powder has an average fiber length in the range of 0.1 μm to 3.0 μm. [Aspect 5] 5. The thermosetting resin composition according to any one of Aspects 1 to 4, wherein the cellulose nanofiber powder has an average fiber diameter in the range of 0.5 nm to 10 nm. [Aspect 6] A method for producing a thermosetting resin composition, comprising: Step A of preparing a cellulose nanofiber dispersion; Step B: supplying the cellulose nanofiber dispersion to a two-roll mill and rotating the two-roll mill to dry the cellulose nanofiber dispersion and obtain cellulose nanofiber powder; A step C of kneading the thermosetting resin base and the cellulose nanofiber powder to obtain an intermediate mixture; and Step D: Adding a curing agent to the intermediate mixture and kneading the mixture to obtain a thermosetting resin composition. Including, The cellulose nanofiber dispersion is prepared so as to contain, in terms of solid content, 0.5 to 20 wt % of a phosphate ester and 0.5 to 5.0 wt % of an alkylammonium salt; The thermosetting resin composition is prepared to contain 1 to 5 parts by weight of a curing agent and 1 to 5 parts by weight of cellulose nanofiber powder relative to 100 parts by weight of a thermosetting resin. [Effects of the Invention]

[0010] According to one embodiment of the present invention, a thermosetting resin composition capable of suppressing the occurrence and propagation of cracks can be provided. According to another embodiment of the present invention, an embedded molded article obtained by molding such a thermosetting resin composition can be provided. According to yet another embodiment of the present invention, a method for producing such a thermosetting resin composition can be provided. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram illustrating the structure and operating principle of a two-roll mill according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] Next, embodiments of the present invention will be described in detail with reference to the drawings. It should be understood that the present invention is not limited to the following embodiments, and that appropriate design changes and improvements may be made based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention.

[0013] (1. Cellulose nanofiber raw materials) Cellulose nanofibers are made by finely grinding cellulose, the main component of plant fibers, to nano-size particles, and are primarily made from wood pulp (the raw material for paper). They are used primarily to reinforce resin materials and prevent resin shrinkage at low temperatures. In the present invention, there are no particular limitations on the raw materials used for cellulose nanofibers.

[0014] Because cellulose nanofibers are typically plant-derived materials, they are in the form of a slurry dispersed in water when extracted from the plant. The solid content is typically 1 to 10% by weight. For example, when producing a powder dispersant from a cellulose nanofiber dispersion, it is first necessary to remove only the water from the cellulose nanofiber aqueous dispersion dispersed in water to extract the individual cellulose nanofibers. It is also conceivable that the individual cellulose nanofibers may be redispersed in water or a dispersing medium other than water, and then extracted again from the redispersion. Therefore, in the present invention, the dispersing medium in the cellulose nanofiber dispersion is not limited to water. However, the dispersing medium in the cellulose nanofiber dispersion is preferably water.

[0015] As mentioned above, the solids content of a cellulose nanofiber dispersion is usually 1 to 10% by weight, but it may also be further diluted to less than 1% by weight. Therefore, the cellulose nanofiber dispersion can also be pre-dried. There are no particular restrictions on the pre-drying method, and any conventional method can be used. The cellulose nanofiber dispersion can be pre-dried, for example, to a maximum solids content of 12% by weight, and then subjected to the roll drying method described below.

[0016] As described below, cellulose nanofiber powder is obtained by drying a cellulose nanofiber dispersion under specific conditions. The average fiber length of the cellulose nanofiber powder is preferably 0.1 μm or more. This is expected to improve dispersion stability. From this perspective, the average fiber length of the cellulose nanofiber powder is more preferably 0.2 μm or more, even more preferably 0.3 μm or more, and even more preferably 0.5 μm or more. If the average fiber length of the cellulose nanofiber powder is 0.1 μm or more, it will have a high aspect ratio relative to the average fiber diameter.

[0017] Furthermore, it is preferable that the average fiber length of the cellulose nanofiber powder is 3.0 μm or less. This prevents the cellulose nanofiber powder from becoming spherical during processing. From this perspective, it is more preferable that the average fiber length of the cellulose nanofiber powder is 2.5 μm or less, even more preferably 1.5 μm or less, and even more preferably 1.0 μm or less.

[0018] The average fiber length of the cellulose nanofiber powder refers to the D50 (median diameter) of the fibers of the cellulose nanofiber powder measured according to the laser diffraction / scattering method of JIS Z8825:2022.

[0019] The average fiber diameter of the cellulose nanofiber powder is preferably 0.5 nm or more. This is expected to improve dispersion stability. From this perspective, the average fiber diameter of the cellulose nanofiber powder is more preferably 0.7 nm or more, even more preferably 1 nm or more, and even more preferably 3 nm or more.

[0020] Furthermore, it is preferable that the average fiber diameter of the cellulose nanofiber powder is 10 nm or less. If the cellulose nanofiber powder becomes too thick, the aspect ratio decreases, and steric hindrance may occur, making it impossible to maintain interparticle distance. From this perspective, it is more preferable that the average fiber diameter of the cellulose nanofiber powder is 8 nm or less, even more preferably 7 nm or less, and even more preferably 5 nm or less.

[0021] The average fiber diameter of the cellulose nanofiber powder refers to the average particle diameter of the fibers of the cellulose nanofiber powder measured according to the dynamic light scattering method of JIS Z8828:2019.

[0022] (2. Cellulose nanofiber powder) Because cellulose nanofibers have a uniform diameter and a uniform length, they are prone to exhibiting a "fiber bridging effect" when cracks occur. In other words, the fibers bridge the crack surface, effectively preventing the crack from progressing. Cellulose nanofibers are also flexible fibers, making them easy to disperse the stress of fine cracks. However, to take advantage of these advantages of cellulose nanofibers, they must be properly dispersed. Therefore, in this embodiment, a powder made by chemically decorating a cellulose nanofiber slurry is used.

[0023] In one embodiment of the present invention, the cellulose nanofiber powder contains, relative to the total weight of the cellulose nanofiber powder, 75 to 99% by weight of cellulose nanofibers, 0.5 to 20% by weight of phosphate ester (including phosphate ester salts, the same applies below), and 0.5 to 5% by weight of alkylammonium salt.

[0024] If the amount of cellulose nanofibers is less than 75% by weight, the dispersing effect of the dispersant containing cellulose nanofibers as its core will be weakened. From this perspective, the amount of cellulose nanofibers is 75% by weight or more, preferably 78% by weight or more, more preferably 80% by weight or more, even more preferably 82% by weight or more, and even more preferably 85% by weight or more. On the other hand, if the amount of cellulose nanofibers exceeds 90% by weight, the effects of other components will be weakened, resulting in a reduced dispersing effect. From this perspective, the amount of cellulose nanofibers is 99% by weight or less, preferably 98% by weight or less, and more preferably 97% by weight or less.

[0025] In this embodiment, the cellulose nanofiber powder can contain a surfactant. Among the surfactants, it is particularly important to use phosphate esters and alkyl ammonium salts.

[0026] The amount of surfactant added is 1.0 to 25.0 wt% relative to the total weight of the cellulose nanofiber powder. If the amount of surfactant added is less than 1.0 wt%, the effect cannot be fully exerted. From this perspective, the amount of surfactant added is preferably 2.0 wt% or more, more preferably 3.0 wt% or more, and even more preferably 4.0 wt% or more. On the other hand, if the amount of surfactant added exceeds 25.0 wt%, the effect will plateau. From this perspective, the amount of surfactant added is preferably 20.0 wt% or less, more preferably 15.0 wt% or less, even more preferably 10.0 wt% or less, and even more preferably 7.0 wt% or less. The surfactant is usually added in the form of an aqueous solution, but it may also be added as a single substance.

[0027] Phosphate esters are compounds in which the hydroxyl groups of phosphoric acid (H3PO4) form ester bonds with the hydroxyl groups of alcohol or phenol, which changes the surface properties of cellulose. For example, when OH groups on the surface of cellulose are replaced with phosphate ester groups, the hydrophilicity changes and the hydrophobicity increases. This improves dispersibility in composite materials and interfacial adhesion. Surface modification with phosphate esters suppresses aggregation of CNFs and improves dispersibility in organic solvents. This can induce the diffusion of cellulose nanofibers into thermosetting resins.

[0028] There are several types of phosphate esters. For example, monophosphate esters (monoesters), glucose-6-phosphate, AMP (adenosine monophosphate), diphosphate esters (diesters), triphosphate esters (triesters), trimethylphosphate esters, triphenylphosphate esters, tributylphosphate esters, etc. A particularly preferred example is BYK-142 (a phosphate salt of a high molecular weight copolymer, diluted with methylpyrrolidone acetate (MPA)) manufactured by BYK.

[0029] The amount of phosphate ester added is 0.5 to 20.0 wt% relative to the total weight of the cellulose nanofiber powder. If the amount of phosphate ester added is less than 0.5 wt%, its effect will not be fully exerted. From this perspective, the amount of alkylammonium salt added is preferably 1.0 wt% or more, more preferably 2.0 wt% or more, and even more preferably 3.0 wt% or more. On the other hand, if the amount of phosphate ester added exceeds 20.0 wt%, its effect will plateau. From this perspective, the amount of phosphate ester added is preferably 15.0 wt% or less, more preferably 10.0 wt% or less, even more preferably 8.0 wt% or less, and even more preferably 6.0 wt% or less. Note that phosphate ester is usually added in the form of an aqueous solution, but it may also be added as a single substance.

[0030] Examples of alkylammonium salts include, but are not limited to, distearyldimethylammonium chloride, behenyltrimethylammonium chloride, stearyltrimethylammonium chloride, stearyltrimethylammonium chloride, cetyltrimethylammonium chloride, lauryltrimethylammonium chloride, benzalkonium chloride, etc. A particularly preferred example is BYK-9076 (a 50 to 60 mass % solution of alkylammonium salts of high molecular weight copolymers) manufactured by BYK.

[0031] The amount of alkylammonium salt added is 0.5 to 5.0 wt % relative to the total weight of the cellulose nanofiber powder. If the amount of alkylammonium salt added is less than 0.5 wt %, the effect cannot be fully exerted. From this perspective, the amount of alkylammonium salt added is preferably 1.0 wt % or more, more preferably 2.0 wt % or more, and even more preferably 3.0 wt % or more. On the other hand, if the amount of alkylammonium salt added exceeds 5.0 wt %, the effect will plateau. From this perspective, the amount of alkylammonium salt added is preferably 6.0 wt % or less. Note that alkylammonium salts are usually added in the form of an aqueous solution, but they may also be added as a single substance. However, it is preferable to add them in the form of an aqueous solution. Alkylammonium salts have the effect of preventing aggregation of cellulose nanofibers during the water reduction process.

[0032] The method for producing cellulose nanofiber powder of this embodiment includes step A of preparing a cellulose nanofiber dispersion, and step B of supplying the cellulose nanofiber dispersion to a two-roll mill and rotating the two-roll mill to dry the cellulose nanofiber dispersion and obtain cellulose nanofiber powder, where the cellulose nanofiber dispersion is prepared to contain 0.5 to 20% by weight of phosphate ester and 0.5 to 5% by weight of alkylammonium salt on a solids basis.

[0033] In step A of preparing a cellulose nanofiber dispersion, the types and amounts of each component of the cellulose nanofiber dispersion are as described above, and therefore will not be described here.

[0034] After step A, the cellulose nanofiber dispersion is fed into a two-roll mill, and the two-roll mill is rotated to remove the cellulose nanofiber dispersion and obtain a thick, dried cellulose nanofiber powder (step B).

[0035] By supplying the cellulose nanofiber dispersion to the middle of the two-roll mill, the cellulose nanofiber dispersion is absorbed into the roll gap (nip) (Figure 1). A characteristic of the two-roll mill is that before entering the nip, the input raw material rotates in the same direction as the rolls in the roll bank above the roll gap. At this time, the cellulose nanofibers maintain their orientation, and when they enter the nip, the fibers are aligned in the same direction. This causes shear shear in the nip while maintaining the orientation of the cellulose nanofibers. The raw material, whose boiling point is lowered by self-heating due to shear shear and the heating temperature of the two-roll mill, easily vaporizes, shortening the drying time. The distance between the rolls (clearance) is not particularly limited, but in this embodiment, it is preferably 0.3 to 1.5 mm.

[0036] The greater the rotation ratio (i.e., the difference in rotation speed) between the front roll and the rear roll in a two-roll mill, the faster the material will be cut into the nip. On the other hand, if the rotation ratio between the front roll and the rear roll is too high, the shear generated by the rotation ratio will be small and the time it takes for water to evaporate will be short, so it is preferable to set the rotation ratio to 1 to 3. Furthermore, if there is no rotation ratio, the cellulose nanofiber dispersion will not be able to cut into the nip and will tend to stagnate on the roll bank.

[0037] Due to the self-heating in the nip and the heat transfer from the heated two-roll mill, the intermolecular attraction of water molecules and the thermal energy cause the water molecules to attract each other in liquid form and interact with other nearby molecules. Under the sudden high temperature, the water molecules gain enough energy to overcome the intermolecular attraction with the fibers, and the water and alcohol instantly transition from liquid to gas. As mentioned above, the cellulose nanofibers enter the nip while maintaining their orientation, so they undergo vaporization in the same direction due to a steam explosion. This places little random stress on the cellulose nanofibers, allowing them to dry in a state close to their original form (with the double helix structure still largely intact).

[0038] Here, kneading machines other than two-roll mills, such as pressure kneaders, Banbury kneaders, and extruders, are considered. However, because these machines knead randomly, even if the water evaporates instantly, the cellulose nanofibers tend to entangle with each other and form lumps. Furthermore, conventional techniques such as freeze drying, drying ovens, and spray drying do not provide a means for imparting orientation to the cellulose nanofibers, and the drying process takes time, which tends to loosen the double helix structure and cause lumps. Therefore, two-roll processing offers advantages not available with conventional techniques. Note that a two-roll mill can be any device that can knead the raw materials between two rolls, and it may also have a third or subsequent roll.

[0039] Furthermore, if the surface temperature of the two-roll mill is too high, there is a risk that the cellulose nanofibers will be altered, and the surface will harden during powdering, making it difficult to produce fine particles, so the temperature is preferably 130°C or less, and more preferably 120°C or less. Therefore, in one embodiment of the present invention, the surface temperature of the two-roll mill is 95°C to 130°C.

[0040] As a result of the treatment with the two-roll mill, cellulose nanofiber powder is obtained. Note that the method described in Japanese Patent No. 7541411 can be used to dry the cellulose nanofibers, and the description thereof is incorporated herein in its entirety.

[0041] (3. Thermosetting resin composition) The thermosetting resin composition of this embodiment contains 1 to 5 parts by weight of a curing agent and 1 to 5 parts by weight of cellulose nanofiber powder relative to 100 parts by weight of a thermosetting resin (all weights after curing).

[0042] The type of thermosetting resin is not particularly limited and may be any known resin used in embedded moldings. Examples of thermosetting resins include phenolic resins, epoxy resins, melamine resins, urea resins, unsaturated polyester resins, alkyd resins, polyurethane resins, and thermosetting polyimides. One or more selected from these may be used. Among these, epoxy resins are most preferred due to their low shrinkage after curing and high transparency.

[0043] Epoxy resins that can be used in this embodiment include all polyepoxide compounds. Typical examples include aromatic epoxy, alicyclic epoxy, and aliphatic epoxy resins. Examples of epoxy resins include triphenylmethane epoxy resins, cresol novolac epoxy resins, biphenyl epoxy resins, modified bisphenol A epoxy resins, bisphenol A epoxy resins, bisphenol F epoxy resins, modified bisphenol F epoxy resins, dicyclopentadiene epoxy resins, phenol novolac epoxy resins, and phenoxy resins.

[0044] The thermosetting resin composition may contain a curing agent. The type of curing agent is not particularly limited, and any curing agent may be used, such as amines, polyamide resins, imidazoles, and photocuring agents. However, imidazoles are preferred from the viewpoint of exerting the effects of the present invention. In this specification, unless otherwise specified, the term "curing agent" is intended to include a curing accelerator.

[0045] The amount of curing agent added is not particularly limited, but can be 1 to 5% by weight based on 100 parts by weight of epoxy resin. If the amount of curing agent added is less than 0.5% by weight, the effect cannot be fully exerted. From this perspective, the amount of curing agent added is preferably 1 part by weight or more, more preferably 2 parts by weight or more. On the other hand, if the amount of curing agent added exceeds 6 parts by weight, the effect will plateau. From this perspective, the amount of curing agent added is preferably 5 parts by weight or less.

[0046] The epoxy resin composition of this embodiment contains 1 to 5 parts by weight of the above-mentioned cellulose nanofiber powder per 100 parts by weight of epoxy resin. If the amount of cellulose nanofiber powder added is less than 1 part by weight, the effect cannot be fully exerted. From this perspective, the amount of cellulose nanofiber powder added is preferably 2 parts by weight or more, and more preferably 3 parts by weight or more. On the other hand, if the amount of cellulose nanofiber powder added exceeds 5 parts by weight, the effect will plateau. From this perspective, the amount of cellulose nanofiber powder added is preferably 4 parts by weight or less.

[0047] By incorporating the above-described chemically decorated and dried cellulose nanofiber powder into a thermosetting resin composition, the cellulose nanofibers are well dispersed and the fiber bridging effect is more pronounced, thereby suppressing the occurrence and progression of cracks.

[0048] The method for producing a thermosetting resin composition of this embodiment includes, in addition to steps A and B for obtaining the aforementioned cellulose nanofiber powder, step C of kneading a thermosetting resin base with cellulose nanofiber powder to obtain an intermediate mixture, and step D of adding a curing agent to the intermediate mixture and kneading it to obtain a thermosetting resin composition, where the composition is prepared so that it contains 1 to 5 parts by weight of curing agent and 1 to 5 parts by weight of cellulose nanofiber powder per 100 parts by weight of epoxy resin (all weights after curing).

[0049] The kneading machine used in steps C and D is not limited and any known kneading machine can be used, but a three-roll mill is preferred because it can knead even high-viscosity materials. The three-roll mill may be any device capable of kneading raw materials between two rolls, and may have a fourth or subsequent roll.

[0050] (4. Embedded molding products) In another aspect, the present invention discloses an implant-molded article obtained by molding the thermosetting resin composition of the present invention. Since the process for producing the implant-molded article can be a known method, a detailed description thereof will be omitted here. [Example]

[0051] Examples of the present invention will be described below together with comparative examples. These examples are provided for a better understanding of the present invention and its advantages, and are not intended to limit the invention.

[0052] (Cellulose nanofiber powder production process) BYK BYK-142 (phosphate ester) and BYK BYK-9076 (alkylammonium salt) were placed in a container and mixed at room temperature for 10 minutes at 700 rpm using a dissolver mixer. To this mixture, an aqueous solution of cellulose nanofibers with a solid content of 8% by weight was added, and the mixture was mixed at room temperature for 5 minutes at 500 rpm using a dissolver mixer.

[0053] The mixture was placed in a two-roll mill manufactured by Yasuda Seiki Seisakusho Co., Ltd. (roll diameter: 8 inches; surface treatment: gloss plating; nip clearance: 0.5 mm). The amount placed was 300 g. The rolls were heated to a surface temperature of 120°C. Next, the two-roll mill was operated with the front roll rotating at 7 rpm and the rear roll at 6 rpm, and a sample of the dried product was taken after three rotations of the front roll (roll-processed CNF). The drying time was within 30 seconds.

[0054] The amount of each component in the dried cellulose nanofiber powder was confirmed by gas chromatograph mass analysis using a Shimadzu GC-MS series instrument. The entire composition was then heated in a ceramic crucible combustion chamber manufactured by Buhler Co., Ltd., to remove the carbonized material. The residue was then analyzed by FTIR analysis using an IRA1S series instrument manufactured by Shimadzu Corporation to confirm the peak elements. The water-soluble portion was analyzed by mass analysis using a Shimadzu Nexera series high-performance liquid chromatograph. The mass of each component was calculated from the results of these analyses. The cellulose nanofiber powder consisted of 92% CNF by weight, 6% phosphate ester salt, and 2% alkylammonium salt by weight.

[0055] (Process for producing thermosetting resin composition) The thermosetting resin base used was Mitsubishi Chemical Corporation's jER (registered trademark) 828 (epoxy resin) and Nippon Tokushu Toryo Co., Ltd.'s two-component polyester resin for casting (unsaturated polyester resin). Mitsubishi Chemical Corporation's ST14 (alicyclic amine) and Nippon Tokushu Toryo Co., Ltd.'s curing agent (benzoyl peroxide) were used. Mitsubishi Chemical Corporation's P200H50 (imidazole) was used as the epoxy resin curing accelerator. The aforementioned cellulose nanofiber powder was used as the filler, and freeze-dried blank powder (100% CNF) dried in a Sansho Industry Co., Ltd. SF-10 freeze-drying device and kaolin nanopowder (Kawaken Fine Chemicals Co., Ltd.'s Alumina sol10A, main component: alumina silica) were used as fillers for comparison. The amounts of each component added are shown in Tables 1 and 2.

[0056] [Table 1]

[0057] [Table 2]

[0058] (Process for manufacturing embedded molding products) The filler was added to the thermosetting resin base, and the mixture was mixed three times at room temperature using a 6-inch three-roll mill manufactured by Inoue Seisakusho Co., Ltd. The curing agent and curing accelerator were then added to the mixed base and mixed using a drill agitator blade. The mixture was then mixed two times using the three-roll mill at room temperature to obtain a thermosetting resin mixture.

[0059] Next, the thermosetting resin mixture prepared using the above procedure was poured into a SUS container measuring 50 mm in diameter and 20 mm deep, and after degassing using a vacuum vibration device, the epoxy resin was cured for 20 minutes in a thermostatic bath (manufactured by Isuzu Motors Ltd.) at 100°C, and the unsaturated polyester resin was cured for 15 minutes in a thermostatic bath (manufactured by Isuzu Motors Ltd.). These curing conditions of 100°C for 20 minutes or 75°C for 15 minutes are usually conditions that make cracks likely to occur, and are therefore referred to as "accelerated curing tests" in this specification.

[0060] (Performance evaluation) Before curing, the thermosetting resin mixture was checked for the presence of agglomerates in the sol mixture after adding the filler. This is because agglomerates can cause cracks after curing. The particle size of the agglomerates was measured using a grind gauge manufactured by Taiyu Kizai Co., Ltd.

[0061] A grind gauge is an instrument used to easily measure the particle size (particle size and distribution) of dispersed particles, mainly in paints, inks, and pigments. The particle size was confirmed using the following procedure. [Test equipment] Grind gauge body Scraper (specialized one or metal spatula) Sample to be measured (paste, ink, etc.) [Measurement procedure] Clean the surface of the grind gauge and make sure there is no foreign matter or remaining sample from the previous application before applying the sample. At this time, apply an appropriate amount of sample to the deep side of the grind gauge (the higher groove). Next, use a scraper to scrape the sample with a constant force in one go to the shallower side (the shallower groove). At this time, make sure the sample is firmly inserted into the groove. To judge and observe, observe the stretched sample on the grind gauge. The larger the particles, the more "roughness" or "grain lines" will appear before it reaches the shallower part. [How to read the grain size] Read the scale at the point where lines or roughness of the particles begin to appear. This is the maximum particle size (expressed in μm, etc.) in the sample.

[0062] Furthermore, the length and depth of cracks in the hardened embedded molded products obtained above were measured using a crack scale manufactured by Shinwa Measuring Instruments Co., Ltd. and a crank needle gauge manufactured by Togyu ​​Sangyo Co., Ltd. The presence or absence of cracks with a length of 0.5 mm or more and a depth of 0.1 mm or more was confirmed. The results are shown in Tables 1 and 2.

[0063] As can be seen from Tables 1 and 2, the thermosetting resin composition using the cellulose nanofiber powder according to the disclosure of the present invention performed well in the accelerated curing test and was able to suppress the occurrence and progression of cracks. On the other hand, when the cellulose nanofiber powder was not subjected to the specified treatment, the effect of suppressing the occurrence and progression of cracks was limited.

Claims

1. A thermosetting resin composition, The composition contains 1 to 5 parts by weight of a curing agent and 1 to 5 parts by weight of cellulose nanofiber powder relative to 100 parts by weight of a thermosetting resin, The cellulose nanofiber powder contains 75 to 99 wt% of cellulose nanofibers, 0.5 to 20 wt% of a phosphate ester, and 0.5 to 5.0 wt% of an alkylammonium salt, based on the total weight of the cellulose nanofiber powder; A thermosetting resin composition in which OH groups on the surface of the cellulose nanofibers are substituted with phosphate ester groups of the phosphate ester.

2. The thermosetting resin composition of claim 1 , wherein the thermosetting resin comprises an epoxy resin.

3. The thermosetting resin composition of claim 1 , wherein the curing agent comprises an imidazole.

4. The thermosetting resin composition according to claim 1, wherein the cellulose nanofiber powder has an average fiber length in the range of 0.1 μm to 3.0 μm.

5. The thermosetting resin composition according to claim 1, wherein the cellulose nanofiber powder has an average fiber diameter in the range of 0.5 nm to 10 nm.

6. A method for producing a thermosetting resin composition, comprising: Step A of preparing a cellulose nanofiber dispersion; Step B: supplying the cellulose nanofiber dispersion to a two-roll mill, heating the cellulose nanofiber dispersion to 95°C to 130°C, and rotating the two-roll mill to dry the cellulose nanofiber dispersion and obtain cellulose nanofiber powder; A step C of kneading a thermosetting resin base material and the cellulose nanofiber powder to obtain an intermediate mixture; and Step D: Adding a curing agent to the intermediate mixture and kneading the mixture to obtain a thermosetting resin composition. Including, The cellulose nanofiber dispersion is prepared to contain, in terms of solid content, 0.5 to 20 wt % of a phosphoric acid ester and 0.5 to 5.0 wt % of an alkylammonium salt; The thermosetting resin composition is prepared to contain 1 to 5 parts by weight of a curing agent and 1 to 5 parts by weight of cellulose nanofiber powder relative to 100 parts by weight of a thermosetting resin.

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