Cellulose fiber composite material

Abstract

The purpose of the present invention is to provide a cellulose fiber composite material with which it is possible to produce a molded body that has excellent flame retardancy. One embodiment of the present invention is a cellulose fiber composite material containing cellulose fibers, a thermoplastic resin, a water-soluble flame retardant, and a water-insoluble flame retardant. The water-soluble flame retardant penetrates into the interior of each cellulose fiber in a cross section orthogonal to the axial direction thereof, the cellulose fiber content is 10.0-60.0 mass% with respect to the cellulose fiber composite material, and the thermoplastic resin content is 30.0-80.0 mass% with respect to the cellulose fiber composite material.

Description

Cellulose fiber composite

[0001] The present invention relates to a cellulose fiber composite.

[0002] Cellulose-containing thermoplastic resin compositions have been known in which the strength of resin materials has been improved by using cellulose, a material with low environmental impact. Furthermore, because cellulose itself is a flammable material, methods for improving the flame retardancy of cellulose-containing thermoplastic resin compositions, such as by adding a flame retardant, have been investigated.

[0003] Patent Document 1 discloses a cellulose-containing thermoplastic resin composition that can be incinerated as combustible waste and has excellent flame retardancy without using a halogen-based flame retardant that generates harmful gases when burned.

[0004] Japanese Patent Application Laid-Open No. 2013-170206

[0005] In conventional technologies, high flame retardancy could not be achieved in some cases, such as when a high content of cellulose fiber was added to maintain strength. Furthermore, conventional cellulose-containing thermoplastic resin compositions sometimes had problems with moldability because the content of the resin composition was relatively low when the content of the flame retardant was increased.

[0006] Therefore, an object of the present invention is to provide a cellulose fiber composite material that can be used to produce a molded article with excellent flame retardancy.

[0007] The present inventors have conducted extensive research and found that the above-mentioned problems can be solved by using a cellulose fiber composite material containing a predetermined component, and have thus completed the present invention.

[0008] One aspect of the present invention is a cellulose fiber composite material comprising cellulose fibers, a thermoplastic resin, a water-soluble flame retardant, and a water-insoluble flame retardant, wherein the water-soluble flame retardant permeates the interior of a cross section perpendicular to the axial direction of the cellulose fibers, the cellulose fiber content of the cellulose fiber composite material is 10.0 to 60.0 mass %, and the thermoplastic resin content of the cellulose fiber composite material is 30.0 to 80.0 mass %.

[0009] The impregnation amount of the water-soluble flame retardant is preferably 0.5 to 10.0 parts by mass per 100.0 parts by mass of the cellulose fibers. The water-soluble flame retardant is preferably sodium polyborate. The water-insoluble flame retardant is preferably one or more selected from the group consisting of bromine-based flame retardants, antimony-based flame retardants, phosphorus-based flame retardants, melamine-based flame retardants, and silicone-based flame retardants. The thermoplastic resin is preferably one or more selected from the group consisting of polyethylene resin, polypropylene resin, vinyl chloride resin, (meth)acrylic resin, polystyrene resin, ABS resin, polycarbonate resin, polyacetal resin, polyamide resin, polysulfone resin, PPO resin, polyester resin, and modified resins thereof.

[0010] According to the present invention, there is provided a cellulose fiber composite material from which molded articles having excellent flame retardancy can be produced.

[0011] Fig. 1 shows an SEM photograph of a cross section perpendicular to the fiber orientation direction (long axis direction) of a cellulose fiber composite particle according to Example 3. Fig. 2 is an SEM photograph showing EDS elemental analysis of a cross section perpendicular to the fiber orientation direction (long axis direction) of a cellulose fiber composite particle according to Example 3.

[0012] Hereinafter, when an upper limit value and a lower limit value are separately described, it is considered that a numerical range combining any upper limit value and any lower limit value is substantially disclosed.

[0013] In the following, unless otherwise specified, various measurements are carried out at room temperature (23° C.).

[0014] The components, structure / shape, production method, uses, etc. of the cellulose fiber composite material according to the present disclosure will be described below, but the present invention is not limited to the following in any way.

[0015] <<<Components>>> The cellulose fiber composite preferably contains cellulose fibers, a thermoplastic resin, and a flame retardant. The cellulose fiber composite may also contain other components. Each component will be described below.

[0016] <<Cellulose Fibers>> Examples of cellulose fibers include plant-derived cellulose fibers, animal-derived cellulose fibers such as those derived from acetic acid bacteria, regenerated fibers (fibers artificially produced by dissolving natural cellulose from trees or wood pulp in a solvent to form thin, long, continuous fibers), etc. The type of cellulose fiber is not particularly limited, and multiple types may be used in combination.

[0017] Pulp that can be used as a raw material for cellulose fibers may be either wood pulp or non-wood pulp, and may be either mechanical pulp or chemical pulp.

[0018] Examples of wood pulp include MP, CP, GP, RGP, CGP, SP, AP, KP, and SCP obtained from softwoods such as fir and pine, and hardwoods such as eucalyptus and poplar. The wood pulp may be unbleached or bleached.

[0019] Non-wood pulp includes natural fibers other than wood, such as cotton, straw, bamboo, esparto, bagasse, linter, kenaf, Manila hemp, flax, hemp, jute, gampi, etc. Other pulps include recycled paper pulp made from recycled paper and scraps.

[0020] The average fiber length of the cellulose fibers is preferably 10 μm or more, 50 μm or more, or 100 μm or more, and is preferably 500 μm or less, 400 μm or less, or 300 μm or less. By setting the average fiber length of the cellulose fibers within this range, the dispersibility of the cellulose fibers is improved, aggregation of the cellulose fibers is suppressed, and a composite material with excellent MFR is easily obtained. As a result, various mechanical properties of the obtained molded article can be improved.

[0021] The average fiber diameter of the cellulose fibers is preferably 1 to 50 μm. By setting the average fiber diameter of the cellulose fibers in this range, aggregation of the cellulose fibers is suppressed, and it is easy to obtain a composite material with an excellent MFR. As a result, various mechanical properties of the obtained molded article can be improved.

[0022] The average fiber length and average fiber diameter of the cellulose fibers are number average values ​​calculated by observing the cross section of a cellulose composite material using a scanning electron microscope, randomly selecting 50 cellulose fibers contained in the cross section, and observing them.

[0023] The cellulose fiber content in the cellulose fiber composite is preferably 10.0% by mass or more, 15.0% by mass or more, or 20.0% by mass or more, and preferably 60.0% by mass or less, 55.0% by mass or less, or 50.0% by mass or less. By setting the cellulose fiber content within this range, the reinforcing effect derived from the cellulose fiber is fully exhibited, and it is easy to obtain a composite material with excellent MFR. As a result, various mechanical properties of the obtained molded article can be improved. In addition, the environmental load is easily reduced.

[0024] <<Thermoplastic Resin>> Conventionally known thermoplastic resins can be used, and an appropriate one can be selected depending on the application, etc. The thermoplastic resin is preferably at least one selected from the group consisting of polyethylene resin, polypropylene resin, vinyl chloride resin, (meth)acrylic resin, polystyrene resin, ABS resin, polycarbonate resin, polyacetal resin, polyamide resin, polysulfone resin, PPO resin, polyester resin, and modified resins thereof.

[0025] The content of the thermoplastic resin in the cellulose fiber composite is preferably 30.0% by mass or more, or 35.0% by mass or more, and is preferably 80.0% by mass or less, or 70.0% by mass or less. By setting the content of the thermoplastic resin in this range, various mechanical properties of the obtained molded article can be improved.

[0026] Furthermore, the content of thermoplastic resin per 100.0 parts by mass of cellulose fiber is preferably 50.0 parts by mass or more, or 80.0 parts by mass or more, and is preferably 500.0 parts by mass or less, or 400.0 parts by mass or less.

[0027] <<Flame Retardant>> The flame retardant preferably contains a water-soluble flame retardant and a water-insoluble flame retardant. Combining a water-soluble flame retardant with a water-insoluble flame retardant further enhances the flame retardant effect. As will be described later, the water-soluble flame retardant may be present so as to penetrate into the interior of a cross section perpendicular to the axial direction of the cellulose fiber.

[0028] The water-soluble flame retardant is a flame retardant having a solubility in water (20°C) of, for example, 5.0 g / L or more (preferably, 10.0 g / L or more, 20.0 g / L or more, or 50.0 g / L or more). The non-soluble flame retardant is a flame retardant having a solubility in water of, for example, less than 5.0 g / L (preferably, less than 2.0 g / L or less than 1.0 g / L).

[0029] Examples of water-soluble flame retardants include boric acid, lithium polyborate, sodium polyborate, potassium polyborate, aluminum polyborate, guanidine-based flame retardants (guanidine salts such as guanidine sulfamate, guanidine phosphate, guanidine hydrochloride, and guanidine sulfate, and ammonium sulfamate), ammonium phosphate, ammonium sulfate, phosphate-based flame retardants (ammonium phosphate, ammonium polyphosphate, and the like), and vinyl acetate.

[0030] The water-soluble flame retardant is preferably sodium polyborate. By using sodium polyborate as the water-soluble flame retardant, it is easy to impregnate cellulose fibers and the flame retardant effect of the resulting cellulose fiber composite can be easily enhanced.

[0031] The non-soluble flame retardant is preferably one or more selected from the group consisting of bromine-based flame retardants, antimony-based flame retardants, phosphorus-based flame retardants, melamine-based flame retardants, and silicone-based flame retardants. The use of such a soluble flame retardant facilitates further enhancement of the flame retardant effect. From the viewpoint of reducing environmental impact, phosphorus-based flame retardants are more preferred.

[0032] Examples of brominated flame retardants include polybromobiphenyl, tetrabromobisphenol A (TBBA) and its derivatives [TBBA epoxy oligomer, TBBA carbonate oligomer, TBBA-bis(dibromopropyl ether), TBBA-bis(aryl ether)], pentabromodiphenyl ether, octabromodiphenyl ether, decabromodiphenyl ether, bistribromophenoxyethane, ethylenebistetrabromophthalimide, ethylenebispentabromophenyl, dibromophenol, tribromophenol, hexabromobenzene, hexabromocyclododecane, brominated polystyrene, polybrominated styrene, tris(dibromopropyl)isocyanurate, and tris(tribromophenyl)cyanurate.

[0033] Examples of antimony-based flame retardants include antimony oxides such as antimony trioxide and antimony pentoxide; antimonates such as sodium antimonate and potassium antimonate; and pyroantimonates such as sodium pyroantimonate and potassium pyroantimonate.

[0034] Examples of the melamine-based flame retardant include melamine polyphosphate, melamine sulfate, and melamine isocyanurate.

[0035] Examples of silicone-based flame retardants include silicone compounds such as silicone oil and polyorganosiloxanes.

[0036] Examples of phosphorus-based flame retardants include red phosphorus and phosphoric acid esters. Examples of phosphoric acid esters include aromatic phosphoric acid esters such as triphenyl phosphate, cresyl diphenyl phosphate, tricresyl phosphate, trixylenyl phosphate, tris(t-butylated phenyl)phosphate, tris(i-propylated phenyl)phosphate, and 2-ethylhexyl diphenyl phosphate; 1,3-phenylene bis(diphenyl phosphate), 1,3-phenylene bis(dixylenyl)phosphate, resorcinol bis(diphenyl)phosphate, and bisphenol A bis(diphenyl phosphate). aromatic condensed phosphate esters such as tris(dichloropropyl)phosphate, tris(β-chloropropyl)phosphate, tris(chloroethyl)phosphate, and the like; halogen-containing phosphate esters such as 2,2-bis(chloromethyl)trimethylenebis(bis(2-chloroethyl)phosphate) and polyoxyalkylenebisdichloroalkylphosphate, and the like; 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) and derivatives thereof, and the like.

[0037] The water-insoluble flame retardant may be other flame retardants such as nitrogen-containing compounds, metal oxides, metal hydroxides (aluminum hydroxide, magnesium hydroxide, etc.).

[0038] The impregnation amount of the water-soluble flame retardant per 100.0 parts by mass of cellulose fiber is preferably 0.1 parts by mass or more, 0.2 parts by mass or more, or 0.5 parts by mass or more, and is preferably 15.0 parts by mass or less, 12.0 parts by mass or less, or 10.0 parts by mass or less.

[0039] From another perspective, the content of the water-soluble flame retardant in the cellulose composite is preferably 1.0 mass% or more, 3.0 mass% or more, or 5.0 mass% or more, and is preferably 30.0 mass% or less, 20.0 mass% or less, or 15.0 mass% or less.

[0040] The content of the water-insoluble flame retardant in the cellulose composite is preferably 1.0 mass% or more, 3.0 mass% or more, or 5.0 mass% or more, and is preferably 40.0 mass% or less, 30.0 mass% or less, or 20.0 mass% or less.

[0041] In the cellulose composite material, the ratio of the water-soluble flame retardant content to the water-insoluble flame retardant content is preferably 1.00 or less, 0.80 or less, 0.50 or less, or 0.40 or less. The lower limit is not particularly limited, but is, for example, 0.01 or 0.02.

[0042] <<Other Components>> Examples of other components include known additives, such as a mold release agent, a flow modifier, an antistatic agent, a compatibilizer, an ultraviolet absorber, a filler, a surfactant, a coupling agent, a colorant, an antioxidant, an antifoaming agent, a leveling agent, and a plasticizer.

[0043] The content of other components in the cellulose fiber composite material is, for example, 30.0% by mass or less, 20.0% by mass or less, 10.0% by mass or less, or 5.0% by mass or less.

[0044] <<<Structure / Shape>>> In the cellulose fiber composite, the cellulose fibers may be present dispersed in the thermoplastic resin.

[0045] The water-soluble flame retardant may be present in the cellulose fiber composite in a state in which the water-soluble flame retardant penetrates into the interior of a cross section perpendicular to the axial direction of the cellulose fiber. When the cellulose fiber composite contains a water-insoluble flame retardant, the water-insoluble flame retardant may be present mainly dispersed in the thermoplastic resin.

[0046] The penetration of the water-soluble flame retardant into the cellulose fibers in this way can enhance the flame retardancy of the resulting cellulose fiber composite compared to when the flame retardant is present near the cellulose surface or separately from the cellulose. Furthermore, since sufficient flame retardancy can be achieved even with a reduced flame retardant content, various mechanical properties can be easily improved (i.e., a cellulose fiber composite with an excellent balance between flame retardancy and various mechanical properties can be easily obtained).

[0047] The state in which the water-soluble flame retardant has penetrated into the interior of the cross section perpendicular to the axial direction of the cellulose fibers can be confirmed using a scanning electron microscope (SEM) and an energy dispersive X-ray analyzer (EDS).

[0048] The shape of the cellulose fiber composite is not particularly limited. The cellulose fiber composite may constitute a molded body having a predetermined shape, or may be a raw material for producing a predetermined molded body. The cellulose fiber composite is preferably in the form of particles such as resin pellets used to produce a molded body.

[0049] <<<Production Method>>> A cellulose fiber composite is produced by mixing and kneading the raw materials (cellulose fibers impregnated with a water-soluble flame retardant, a thermoplastic resin, a water-insoluble flame retardant, etc.) at a predetermined temperature (above the softening point of the resin components). When the cellulose fiber composite is to be formed into granules (pellets, etc.), a method such as extrusion molding of the kneaded resin composition and cutting the resulting rod-shaped material can be carried out. After molding the cellulose fiber composite, a step of stretching the material or a step of immersing the material in water or the like to rapidly cool it can be carried out.

[0050] The method for producing a cellulose fiber composite may be a method for producing a cellulose fiber composite containing cellulose fibers by kneading pulp pieces with a thermoplastic resin or the like and simultaneously defibrating the pulp pieces into cellulose fibers. For methods of simultaneously defibrating pulp pieces into cellulose fibers with a resin, reference may be made to methods disclosed in WO 2021 / 256471, JP 2023-149104, and the like. In this case, the amount of cellulose fiber in the cellulose fiber composite can be adjusted based on the amount of pulp pieces. Furthermore, the average fiber length, average fiber diameter, and the like of the cellulose fibers obtained using the pulp pieces can be adjusted based on the kneading conditions (e.g., kneading speed and time).

[0051] An example of a preferred method for producing a cellulose fiber composite material will be described below.

[0052] A preferred method for producing a cellulose fiber composite includes a grinding step of grinding pulp to obtain pulp pieces, a mixing step of mixing the pulp pieces with a water-soluble flame retardant to obtain pulp pieces impregnated with the water-soluble flame retardant, a kneading step of kneading the pulp pieces impregnated with the water-soluble flame retardant with a thermoplastic resin to defibrate the pulp pieces into cellulose fibers, and an extrusion step of extruding the resin mixture obtained in the kneading step to form a cellulose fiber composite.

[0053] In the crushing process, pulp, which is the raw material for cellulose fibers, is crushed into pulp pieces. The size of the pulp pieces is not particularly limited, but for ease of mixing (described later) and to shorten the time required for the kneading process, it is preferable that the diameter of the pulp pieces (the length of the longest part of the pulp pieces) be 10 to 50 mm. By making the pulp pieces into such a size, they exhibit excellent dispersibility in the resin mixture during the kneading process.

[0054] The pulverization can be carried out by a known method, for example, a pulverization method using a pulverizer such as a hammer mill, a cutter mill, or a jet mill.

[0055] The pulp pieces obtained in the grinding process and the flame retardant are placed in a high-speed mixer or the like and stirred. During the stirring process, the water-soluble flame retardant dissolved in water is sprayed onto the mixture. This allows the water-soluble flame retardant to penetrate the pulp pieces. By drying using the heat and reduced pressure from the stirring, pulp pieces impregnated with the water-soluble flame retardant can be obtained. In this case, the amount of water-soluble flame retardant to be added and the concentration of the water-soluble flame retardant aqueous solution can be appropriately adjusted taking into account the amount of pulp pieces, etc. The water-soluble flame retardant aqueous solution may contain an aqueous solvent such as alcohol. In this way, the pulp pieces impregnated with the water-soluble flame retardant can be defibrated in a separate process (e.g., a kneading process) to obtain cellulose fibers impregnated with the water-soluble flame retardant.

[0056] In the kneading step, the pulp pieces obtained in the crushing step, the thermoplastic resin, the water-insoluble flame retardant, etc. are mixed and kneaded to defibrate the pulp pieces into cellulose fibers and produce a resin mixture. The other components may be added at the same time as the pulp pieces and thermoplastic resin are added to the kneading device, or they may be added first and then added after a desired time has elapsed.

[0057] Examples of the kneading method include a method using a Banbury mixer, a method using a pressure roller, etc. Kneading can also be performed using an extrusion molding machine such as a twin-screw extruder. In this case, the kneading step and the extrusion step described below are performed simultaneously by the extrusion molding machine.

[0058] Examples of the kneading device include a method using an agitator such as a Henschel mixer, a super mixer, or a ribbon mixer.

[0059] Although the kneading conditions are not particularly limited, it is preferable to set the heating temperature to the softening point of the thermoplastic resin or higher. By setting the temperature at such a temperature, the dispersion of the cellulose fibers in the cellulose fiber composite material is improved, and the cellulose fiber composite material has excellent flowability when melted, which makes it easy to obtain a cellulose fiber composite material with excellent moldability and mechanical properties such as strength and elastic modulus. In addition, the kneading of the thermoplastic resin and the cellulose fibers is improved, making it easy to obtain a cellulose fiber composite material with few aggregates.

[0060] The average fiber diameter and average fiber length of the cellulose fibers can be appropriately adjusted by adjusting the stirring speed and time.

[0061] In the above-described method, a cellulose fiber composite is obtained by performing the step of obtaining pulp pieces impregnated with a water-soluble flame retardant, and then kneading the pulp pieces impregnated with the water-soluble flame retardant with a thermoplastic resin, thereby simultaneously defibrating the pulp pieces into cellulose fibers and kneading the thermoplastic resin with the cellulose fibers. On the other hand, a cellulose fiber composite can also be obtained by performing the step of obtaining cellulose fibers impregnated with a water-soluble flame retardant in advance, and then kneading the cellulose fibers with a thermoplastic resin.

[0062] In addition to the above-mentioned methods, cellulose fibers impregnated with the water-soluble flame retardant to the inside of the fiber cross section can also be obtained by a process such as mixing pre-defibrated cellulose fibers with an aqueous solution of the water-soluble flame retardant and drying the mixture.

[0063] <<<<Applications>>> The cellulose fiber composite material is preferably used as a raw material for resin molded products. The cellulose fiber composite material is used, for example, as a raw material (pellets, etc.) for resin molded products made using a mold such as injection molding or for resin molded products made using a 3D printer.

[0064] Furthermore, the cellulose fiber composite material (or a molded product obtained using the cellulose fiber composite material) is preferably used as a component for molded parts for vehicles, machines, devices, etc., industrial materials such as containers, pallets, plastic cores, and building materials, daily necessities, miscellaneous goods, etc.

[0065] The cellulose fiber composite material of the present invention will be specifically described below with reference to examples, but the present invention is not limited to these.

[0066] <<Raw Materials>> <Thermoplastic Resin> Polypropylene Polyethylene Resin <Water-Soluble Flame Retardant> Sodium Polyborate Vinyl Acetate Monomer <Water-Insoluble Flame Retardant> Phosphate Ester Polybrominated Biphenyl Aluminum Hydroxide

[0067] <<Manufacturing Cellulose Fiber Composite Material>> <Example 1> A grinding process was performed in which pulp was pulverized into pulp pieces with a longest side of 10 to 50 mm. Sodium polyborate was used as the water-soluble flame retardant, and an aqueous solution of the water-soluble flame retardant (20% concentration) was prepared. A mixing process was performed in which the pulp pieces were impregnated with the water-soluble flame retardant using a high-speed mixer (vacuum drying specification) manufactured by Earth Technica Corporation. The water-soluble flame retardant was sprayed onto the pulp pieces while stirring, and the water-soluble flame retardant was impregnated into the pulp pieces. The amount of water-soluble flame retardant adsorbed per 100.0 parts by mass of pulp pieces corresponded to the impregnation ratio of the water-soluble flame retardant per 100.0 parts by mass of cellulose fiber. Next, the raw materials (cellulose fiber, polypropylene, sodium polyborate, and phosphate ester) were dry-blended in the raw materials and amounts (mass%) shown in Table 1 to obtain mixtures. The resulting mixtures were kneaded using a twin-screw kneader (PCM30 manufactured by Ikegai Corporation). The obtained kneaded material was discharged from the extruder, stretched for about 1 m in the air, then immersed in water to cool and cut to obtain cellulose fiber composite particles (pellets) of Example 1, which were cylindrical in shape and 6 mm long and 3 mm wide.

[0068] <Examples 2 to 13, Comparative Examples 1 to 4, 6> Cellulose fiber composite particles (pellets) according to Examples 2 to 13 and Comparative Examples 1 to 4, 6 were obtained in the same manner as in Example 1, except that the raw materials used and their blending amounts were changed to those shown in Tables 1 and 2.

[0069] As an example, Fig. 1 shows an SEM photograph of a cross section perpendicular to the fiber orientation direction (long axis direction) of a cellulose fiber composite particle according to Example 3. As shown in Fig. 1, cellulose fiber (CF), a thermoplastic resin (TR) as a matrix, and a brominated flame retardant (BR) were observed in the cross section of the cellulose fiber composite particle.

[0070] <Comparative Example 5> Cellulose fiber composite particles (pellets) were obtained in the same manner as in Example 1, except that the mixing step was not performed, and instead, the water-soluble flame retardant was not made into an aqueous solution, and a step of stirring the pulp pieces and the water-soluble flame retardant in a mixer was performed.

[0071] <<Evaluation / Measurement>> <Cellulose Fiber Diameter> In the cellulose fiber composite materials of each Example and Comparative Example, the average fiber length of the cellulose fibers was about 100 to 300 μm.

[0072] <Impregnation of Cellulose Fibers with Water-Soluble Flame Retardant> Using the method described above, we confirmed whether the water-soluble flame retardant had penetrated into the interior of the cross section perpendicular to the axial direction of the cellulose fibers. When the water-soluble flame retardant had penetrated into the interior of the cellulose fibers, it was deemed "permeated," and when the water-soluble flame retardant had not penetrated, it was deemed "non-permeated." The results are shown in Tables 1 and 2. For reference, Figure 2 shows an SEM photograph of the cellulose fiber composite particle of Example 3, showing the state of EDS elemental analysis performed on a cross section perpendicular to the fiber orientation direction (longitudinal direction). In the EDS elemental analysis, elemental analysis was performed on three locations: Region A (the outer periphery of the cellulose [OC], corresponding to Chart (A)), Region B (the brominated flame retardant [BR] present outside the cellulose, corresponding to Chart (B)), and Region C (the interior of the fiber [IF], corresponding to Chart (C)). As shown in Chart (C), a component derived from the water-soluble flame retardant (sodium derived from sodium polyborate) was observed inside the fiber, confirming that the water-soluble flame retardant had penetrated into the fiber.

[0073] <Moldability> Using an injection molding machine (J80ADS, manufactured by The Japan Steel Works, Ltd.), dumbbell test pieces (Type A1 in accordance with ISO 527) were prepared under the following conditions: raw material temperature 200°C or less, mold temperature 60°C, injection speed 40 to 60 mm / s, and holding pressure 35 MPa. If a molded product was easily obtained under the above molding conditions, it was rated as "A." If a molded product could be obtained by increasing the injection speed, it was rated as "B." If the injection pressure exceeded the limit and molding was not possible, it was rated as "D."

[0074] For those samples with moldability rated A or B (those that were moldable), evaluation of flame retardancy and bending test (bending strength and bending modulus) was carried out.

[0075] <Flame retardancy> Based on the UL94V-0 test (vertical flammability test), flame from a gas burner was applied to the bottom end of a vertically held sample to evaluate flame retardancy. The UL94V-0 test grades (V0, V1, V2, no flame retardancy (not corresponding to UL94)) are shown in Tables 1 and 2.

[0076] <Bending test (bending strength, bending modulus)> Using an Instron-type material testing machine (RTC-2410, manufactured by A&D Co., Ltd., load cell 5 kN), a load was applied by contacting an indenter with a radius of 5 mm with the center of the plane of each dumbbell test piece with a support distance of 60 mm. The bending strength was measured from the load at break, and the bending modulus was also measured. The test pieces were placed so that the load applied by the indenter was parallel to the thickness direction of each dumbbell test piece, and the crosshead speed was 2 mm / min. The bending strength and bending modulus were evaluated based on the following criteria. The evaluation results are shown in Tables 1 and 2. (Bending strength) A: 3 GPa or more B: 2 GPa or more but less than 3 GPa C: less than 2 GPa (Bending modulus) A: 4 GPa or more B: 2 GPa or more but less than 4 GPa C: less than 2 GPa

[0077] <Overall evaluation> Those with flame retardancy of "V0" and bending test evaluation of "A" were evaluated as "A", those with moldability of "D", those with flame retardancy of "no flame retardancy", and those with a bending test evaluation including "C" were evaluated as "C", and the rest were evaluated as "B". The evaluation results are shown in Table 1.

[0078]

[0079]

[0080] Since the cellulose fiber composite material according to the present invention can be used to produce molded articles with various excellent mechanical properties, it is preferably used as a raw material (e.g., pellets) for resin molded articles using a mold such as injection molding or resin molded articles using a 3D printer. CROSS-REFERENCE TO RELATED APPLICATIONS

[0081] This application claims priority based on Japanese Patent Application No. 2024-50387, filed with the Japan Patent Office on March 26, 2024, the entire disclosure of which is incorporated herein by reference in its entirety.

Claims

1. A cellulose fiber composite comprising cellulose fibers, a thermoplastic resin, a water-soluble flame retardant, and a water-insoluble flame retardant, wherein the water-soluble flame retardant permeates the interior of a cross section perpendicular to the axial direction of the cellulose fibers, the content of the cellulose fibers in the cellulose fiber composite is 10.0 to 60.0 mass%, and the content of the thermoplastic resin in the cellulose fiber composite is 30.0 to 80.0 mass%.

2. The cellulose fiber composite material according to claim 1, wherein the impregnation amount of the water-soluble flame retardant is 0.5 to 10.0 parts by mass per 100.0 parts by mass of the cellulose fiber.

3. The cellulose fiber composite material according to claim 1 or 2, wherein the water-soluble flame retardant is sodium polyborate.

4. The cellulose fiber composite material according to claim 1 or 2, wherein the water-insoluble flame retardant is one or more selected from the group consisting of bromine-based flame retardants, antimony-based flame retardants, phosphorus-based flame retardants, melamine-based flame retardants, and silicone-based flame retardants.

5. A cellulose fiber composite material according to claim 1 or 2, wherein the thermoplastic resin is one or more selected from the group consisting of polyethylene resin, polypropylene resin, vinyl chloride resin, (meth)acrylic resin, polystyrene resin, ABS resin, polycarbonate resin, polyacetal resin, polyamide resin, polysulfone resin, PPO resin, polyester resin, and modified resins thereof.

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