Cellulose fiber resin composite material

Abstract

To provide a cellulose fiber resin composite material which is excellent in mechanical characteristics such as tensile strength and is more excellent in flame retardancy, and a composite material molding using the composite material.SOLUTION: A cellulose fiber resin composite material is obtained by extrusion molding a resin mixture containing a cellulose fiber, a thermoplastic resin and a flame retardant, wherein the cellulose fiber has an average fiber length of 10-400 μm and an average fiber diameter of 1-50 μm, the content of the cellulose fiber is 10-60 mass% when the total mass of the cellulose fiber resin composite material is 100 mass%, the content of the flame retardant is 5-30 mass% when the total mass of the cellulose fiber resin composite material is 100 mass%, at least a part of the flame retardant covers the cellulose fiber, and an average coverage ratio of the cellulose fiber by the flame retardant is 15% or more and 60% or less.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] Thermoplastic resins are used as parts of various products because they can be easily molded by heating. In recent years, with the miniaturization and thinning of electronic devices and the like, the parts used therein have also become smaller and thinner, and there is a demand for the moldability of thermoplastic resins into fine and complex shapes. In addition, when thermoplastic resins are used in miniaturized and thinned parts, higher mechanical properties such as higher tensile strength are required, so thermoplastic resins are used in a composite with fibers.

[0003] When inorganic fibers are used as the fibers to be compounded with thermoplastic resins, residues derived from the inorganic fibers are generated during incineration at the time of disposal, and it is necessary to landfill this residue. Therefore, resin molded products that do not use inorganic fibers are required, and plant fibers such as cellulose fibers are used as composite fibers.

[0004] Since resin molded products in which such plant fibers are compounded do not have high flame retardancy, flame retardant treatment is required. For example, Patent Document 1 discloses a method for producing a resin molded product containing plant fibers flame-retarded by including at least one of boric acid and boric acid compounds (by impregnation).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The manufacturing method described in Patent Document 1 can produce flame-retardant resin molded articles containing plant fibers as fillers, and achieves a flame retardancy of V-2 in flame retardancy evaluations compliant with the UL (Underwriters Laboratory) standard (94V). However, V-2 flame retardancy may be insufficient depending on the application, and higher flame retardancy is required.

[0007] Therefore, the object of the present invention is to provide a cellulose fiber resin composite material that has excellent mechanical properties such as tensile strength and is more flame-retardant. Furthermore, when the cellulose fiber resin composite material is melted and molded as pellets by injection molding or the like, the object of the present invention is to provide a composite molded product that has excellent mechanical properties such as tensile strength and is more flame-retardant. [Means for solving the problem]

[0008] The inventors have conducted diligent research and discovered that a cellulose fiber resin composite material, in which the surface of cellulose fibers is coated with a flame retardant and which includes cellulose fibers having a specific average coating rate and a thermoplastic resin, exhibits superior mechanical properties such as tensile strength and superior flame retardancy, thereby completing the disclosed technology. Specifically, the disclosed technology is as follows.

[0009] One aspect of the disclosed technology is a cellulose fiber resin composite material. The cellulose fiber resin composite material is obtained by extruding a resin mixture containing cellulose fibers, a thermoplastic resin, and a flame retardant such that the cellulose fibers are oriented along the extrusion direction, wherein the cellulose fibers have an average fiber length of 10 to 400 μm and an average fiber diameter of 1 to 50 μm, the content of the cellulose fibers is 10 to 60% by mass when the total mass of the cellulose fiber resin composite material is 100% by mass, the content of the flame retardant is 5 to 30% by mass when the total mass of the cellulose fiber resin composite material is 100% by mass, and at least a portion of the flame retardant coats the cellulose fibers, and the average coating rate of the cellulose fibers by the flame retardant, calculated by the evaluation method described below, is 15% or more and 60% or less. (Method for evaluating coverage) When the cellulose fiber resin composite material is extruded, a cross-sectional area of ​​82 μm × 126 μm perpendicular to the extrusion direction is imaged at 1000x magnification using a scanning electron microscope (SEM) to obtain a cross-sectional SEM image. The obtained cross-sectional SEM image is analyzed, and 20 cellulose fibers with a cross-sectional circumference of 10 to 50 μm are randomly selected from the cross-section. For each of these cellulose fibers, the circumference and the length covered by the flame retardant (covering length) are obtained, and the coverage rate is calculated according to the following formula. Coverage rate = (Covering length) / (Perimeter) x 100(%) The coverage rates obtained for the aforementioned 20 cellulose fibers are number-averaged to obtain the average coverage rate. In the cellulose fiber resin composite material of the present disclosure, it is preferable that the proportion of cellulose fibers with a coverage rate of 15-60% is 80% or more, based on the total number of cellulose fibers with a cross-sectional circumference of 10-50 μm included in the cross-sectional SEM image. The cellulose fiber resin composite material of this disclosure preferably contains either a phosphorus-based flame retardant or a halogen-based flame retardant as the flame retardant. The cellulose fiber resin composite material of this disclosure preferably contains any of the following thermoplastic resins: polyethylene resin, polypropylene resin, vinyl chloride resin, methacrylic resin, polystyrene resin, ABS resin, polycarbonate resin, polyacetal resin, polyamide resin, polysulfone resin, modified PPO resin, or polyester resin. [Effects of the Invention]

[0010] According to the disclosed technology, it is possible to provide a cellulose fiber resin composite material that has excellent mechanical properties such as tensile strength and superior flame retardancy. Furthermore, when the cellulose fiber resin composite material is melted and molded using injection molding or the like as a raw material, a composite molded product with excellent mechanical properties such as tensile strength and superior flame retardancy can be obtained. [Modes for carrying out the invention]

[0011] Embodiments of the disclosed technology will be described in detail below. In this specification, unless otherwise specified, the notation "a to b" in descriptions of numerical ranges means a or greater and b or less.

[0012] <<<Cellulose fiber resin composite material>>> The cellulose fiber resin composite material of this disclosure is a cellulose fiber resin composite material obtained by extruding a resin mixture containing cellulose fibers, a thermoplastic resin, and a flame retardant such that the cellulose fibers are oriented along the extrusion direction. Using the cellulose fiber resin composite material as a raw material, a composite molded product can be formed by melting and molding (for example, injection molding) as described later.

[0013] The shape of the cellulose fiber resin composite material is not particularly limited as long as it can be molded by extrusion molding. Furthermore, when the cellulose fiber resin composite material is made into pellets, the shape of the cellulose fiber resin composite material can be a columnar body such as a cylinder, elliptical cylinder, or polygonal cylinder. The cellulose fiber resin composite material can be made into cylindrical, elliptical, or polygonal cylinder pellets by making the cross-sectional shape of the extrusion section (resin mixture discharge port) of the mold used when the resin mixture is melted and the cellulose fiber resin composite material is extruded circular, elliptical, or polygonal, respectively.

[0014] The cross-sectional diameter of cellulose fiber resin composite material when it is formed into pellets is not particularly limited, but can be 1 to 5 mm. Here, the cross-sectional diameter of the cellulose fiber resin composite material refers to the cross-sectional diameter of the cross section perpendicular to the axial direction of the columnar body, and in the case of a circular cross-section, it refers to the diameter, in the case of an elliptical cross-section, it refers to the length of the major axis, and in the case of a polygonal cross-section, it refers to the length of the longest side.

[0015] The axial length of cellulose fiber resin composite material when it is formed into pellets is not particularly limited, but can be 6 to 15 mm. The axial length of cellulose fiber resin composite material when it is formed into pellets is the axial length of the molded product (cellulose fiber resin composite material pellet) of the extruded resin mixture when the resin mixture is cut after it has been melted and the cellulose fiber resin composite material has been extruded from the extrusion section (resin mixture discharge port) of the mold used to form the cellulose fiber resin composite material.

[0016] The surface of a cellulose fiber resin composite material may have grooves (or scratches) formed parallel to the direction in which the resin mixture was extruded from the mold during the extrusion molding process. In this specification, the longitudinal direction of these grooves (or scratches) is defined as the extrusion direction when the resin mixture is extruded to obtain the cellulose fiber resin composite material (hereinafter sometimes abbreviated as the extrusion direction of the cellulose fiber resin composite material). When the cellulose fiber resin composite material is formed into pellets, the extrusion direction generally coincides with the axial direction of the columnar pellet. When the pellet is cubic, the extrusion direction of the pellet can be determined by the direction of the grooves (or scratches) on the surface of the cellulose fiber resin composite material. The direction of the grooves (or scratches) on the surface of the cellulose fiber resin composite material can be confirmed with the naked eye or by an optical microscope.

[0017] The cellulose fibers within a cellulose fiber resin composite are oriented in the direction of extrusion of the cellulose fiber resin composite. Specifically, the cellulose fibers within the cellulose fiber resin composite are oriented in the direction from which the resin mixture is extruded from the mold during the extrusion molding process. That is, the orientation of the cellulose fibers coincides with the extrusion direction of the cellulose fiber resin composite. Here, "oriented" or "aligned with the extrusion direction" means that the cellulose fibers are aligned with the extrusion direction to the extent that it is understood to be aligned with the direction or extrusion direction based on common technical knowledge, and does not necessarily mean that all cellulose fibers are parallel to each other or oriented in line with the extrusion direction.

[0018] <<Composition of Cellulose Fiber Resin Composite Material Cellulose Fiber Resin Composite Material>> <Cellulose Fiber> The cellulose fiber is compounded with a thermoplastic resin to make the mechanical properties such as the tensile strength of the cellulose fiber resin composite material excellent. Therefore, by using the cellulose fiber resin composite material as a raw material and melting and molding (for example, injection molding), a composite material molded product with excellent mechanical properties such as tensile strength can be obtained. The cellulose fiber is not particularly limited, and any of plant-derived cellulose fibers, animal-derived cellulose fibers such as acetic acid bacteria, and regenerated fibers obtained by dissolving natural cellulose of trees and wood pulp in a solvent and artificially manufacturing thin and long continuous fibers can be used. In the manufacturing method of the cellulose fiber resin composite material described later, in order to make the dispersibility of the cellulose fiber in the cellulose fiber resin composite material excellent and to facilitate the adjustment of the average coating rate of the cellulose fiber with a flame retardant described later, the cellulose fiber obtained by pulverizing (defibrating) pulp is preferably used. These cellulose fibers can be used alone or in combination of a plurality at an arbitrary ratio.

[0019] As the pulp, either wood pulp or non-wood pulp may be used from the perspective of raw materials, and either mechanical pulp or chemical pulp may be used from the perspective of manufacturing methods.

[0020] Examples of wood pulp include MP, CP, GP, RGP, CGP, SP, AP, KP, SCP, etc. made from coniferous trees such as fir and pine, and broad-leaved trees such as eucalyptus and poplar. These may be unbleached pulp or bleached pulp.

[0021] Examples of non-wood pulp include natural fibers other than wood, such as cotton, straw, bamboo, esparto, bagasse, linter, kenaf, manila hemp, flax, hemp, jute, and ganpi. Other examples include waste paper pulp made from waste paper and cuttings as raw materials.

[0022] The average fiber length of the cellulose fibers is 10 to 400 μm, preferably 10 to 350 μm. When the average fiber length of the cellulose fibers is within this range, the dispersion of cellulose fibers within the cellulose fiber resin composite material is excellent. As a result, the cellulose fiber resin composite material has excellent fluidity when melted and therefore excellent moldability. Consequently, by using the cellulose fiber resin composite material as a raw material and melting and molding (for example, injection molding), a composite molded product with excellent mechanical properties such as tensile strength can be obtained. Furthermore, when the average fiber length of the cellulose fibers falls within this range, the resin mixture exhibits excellent fluidity during extrusion molding, making it easier for the cellulose fibers in the cellulose fiber resin composite material to be oriented along the extrusion direction. When the average fiber length of the cellulose fibers falls within the specified range, the specific surface area of ​​the cellulose fibers is suitable for achieving an appropriate coating rate and average coating rate of the cellulose fibers with the flame retardant described later, thereby improving the flame retardancy of the cellulose fiber resin composite material. As a result, by using cellulose fiber resin composite material as a raw material and melting and molding it (for example, by injection molding), a composite molded product with superior flame retardancy can be obtained.

[0023] The average fiber length of cellulose fibers can be adjusted by the amount of cellulose fibers (pulp in the manufacturing method described later) used and the rotation speed and stirring time during mixing in the manufacturing method described later.

[0024] The average fiber length of cellulose fibers is obtained by observing an arbitrary cross-section of a cellulose fiber resin composite material parallel to the extrusion direction using a scanning electron microscope, randomly selecting 50 cellulose fibers from the cross-section, measuring the fiber lengths of these fibers, and calculating the number average.

[0025] The average fiber diameter of cellulose fibers is 1 to 50 μm. When the average fiber diameter of cellulose fibers falls within this range, the dispersibility of cellulose fibers within the cellulose fiber resin composite material is excellent. Therefore, the cellulose fiber resin composite material exhibits excellent fluidity during melting, excellent moldability, and superior mechanical properties such as tensile strength. Furthermore, by using the cellulose fiber resin composite material as a raw material and melting and molding it (for example, by injection molding), a composite molded product with excellent mechanical properties such as tensile strength can be obtained. When the average fiber diameter of the cellulose fibers falls within the specified range, the specific surface area of ​​the cellulose fibers is suitable for achieving an appropriate coating rate and average coating rate of the cellulose fibers with the flame retardant described later. By using cellulose fiber resin composite material as a raw material and melting and molding it (for example, by injection molding), a composite molded product with superior flame retardancy can be obtained. Furthermore, when the average fiber diameter of the cellulose fibers falls within this range, the resin mixture exhibits excellent fluidity during extrusion molding, making it easier for the cellulose fibers to orient themselves along the extrusion direction within the cellulose fiber resin composite material.

[0026] The average fiber diameter of cellulose fibers can be adjusted by the amount of cellulose fibers (pulp in the manufacturing method described later) used and the rotation speed and number of repetitions during kneading in the manufacturing method described later.

[0027] The average fiber diameter of cellulose fibers is obtained by observing a cross-section of the cellulose fiber resin composite material perpendicular to the extrusion direction using a scanning electron microscope, randomly selecting 50 cellulose fibers from the cross-section, and calculating the number average of the diameters (major axis length in the case of an elliptical shape, or the longest side length in the case of a polygon) of these cellulose fibers.

[0028] The cellulose fibers are partially coated with a flame retardant, as described later, with an average coating rate of 15% to 60%, preferably 20% to 50%. When the average coating rate falls within this range, there is sufficient flame retardant on the surface of the cellulose fibers, thus improving the flame retardancy of the cellulose fibers. As a result, the flame retardancy of the cellulose fiber resin composite material and the composite molded product obtained by melting and molding (e.g., injection molding) the cellulose fiber resin composite material as a raw material is improved. Furthermore, a portion of the cellulose fiber surface is not coated with the flame retardant, ensuring adequate adhesion between the cellulose fibers and the thermoplastic resin. Therefore, the cellulose fiber resin composite material and the composite molded product obtained by melting and molding (e.g., injection molding) the cellulose fiber resin composite material have superior mechanical properties such as tensile strength. Note that cellulose fibers coated with a flame retardant include not only cases where the cellulose fibers are directly coated with a flame retardant, but also cases where a thermoplastic resin coats part or all of the surface of the cellulose fibers, and a flame retardant coats the outside of that.

[0029] The coating rate and average coating rate of the flame retardant in cellulose fibers can be adjusted by the amount of cellulose fibers (pulp, described later), the average fiber length and average fiber diameter of the cellulose, the amount of flame retardant, and the stirring time after adding the flame retardant.

[0030] The coverage rate and average coverage rate of flame retardants in cellulose fibers are calculated using the following evaluation method. A scanning electron microscope (SEM) is used to image an 82 μm × 126 μm area in a cross-section perpendicular to the extrusion direction of the cellulose fiber resin composite material at a magnification of 1000x to obtain a cross-sectional SEM image. The obtained cross-sectional SEM image is analyzed, and 20 cellulose fibers with a cross-sectional circumference of 10 to 50 μm are randomly selected from the cross-section. For each cellulose fiber, the circumference and the length covered by the flame retardant (covering length) are obtained, and the coverage rate is calculated according to the following formula. Coverage rate = (Covering length) / (Perimeter) x 100(%) The coverage rates obtained for the 20 selected cellulose fibers are number-averaged to obtain the average coverage rate.

[0031] Furthermore, when using the total number of cellulose fibers with a fiber cross-sectional circumference of 10 to 50 μm included in the cross-sectional SEM image described above as a reference, the proportion of cellulose fibers with a coverage rate of 15 to 60% (hereinafter sometimes referred to as occupancy rate) is not particularly limited, and can be, for example, 50 to 100%, more preferably 80% or more, and more preferably 80 to 95%. When the occupancy rate of cellulose fibers with a flame retardant coverage rate of 15 to 60% falls within this range, a cellulose fiber resin composite material with superior mechanical properties such as tensile strength and flame retardancy can be obtained. Therefore, a composite molded product obtained by using a cellulose fiber resin composite material as a raw material and melting and molding (e.g., injection molding) will also have superior mechanical properties such as tensile strength and flame retardancy.

[0032] The percentage of cellulose fibers coated with flame retardant, ranging from 15% to 60%, can be adjusted by the amount of cellulose fibers (pulp, described later) blended, the amount of flame retardant blended, and the time elapsed between the time the pulp fragments and thermoplastic resin are introduced into the mixing apparatus (described later) and the addition of the flame retardant (timing of flame retardant addition).

[0033] The cellulose fiber content in a cellulose fiber resin composite material is 10 to 60% by mass, preferably 10 to 50% by mass, and more preferably 10 to 40% by mass, when the total mass of the cellulose fiber resin composite material is considered to be 100% by mass. When the cellulose fiber content in a cellulose fiber resin composite material is within this range, the dispersibility of the cellulose fibers within the cellulose fiber resin composite material is excellent. As a result, the cellulose fiber resin composite material exhibits superior fluidity and moldability during melting, as well as excellent mechanical properties such as strength and elastic modulus. Consequently, the composite molded product obtained by using the cellulose fiber resin composite material as a raw material and melting and molding (e.g., injection molding) also exhibits excellent mechanical properties such as strength and elastic modulus. Furthermore, by adjusting the content of the flame retardant described later, it becomes easy to adjust the coating rate of the flame retardant in the cellulose fibers, the average coating rate of the flame retardant in the cellulose fibers, and the proportion of cellulose fibers in the cellulose fiber resin composite material where the flame retardant coating rate is 15-60%. In addition, the cellulose fiber resin composite material and the composite molded product obtained by melting and molding (for example, injection molding) the cellulose fiber resin composite material as a raw material have superior flame retardancy.

[0034] <Thermoplastic resin> The thermoplastic resin is not particularly limited, and examples include polyethylene resin, polypropylene resin, vinyl chloride resin, methacrylic resin, polystyrene resin, ABS resin, polycarbonate resin, polyacetal resin, polyamide resin, polysulfone resin, modified PPO resin, polyester resin, etc. These can be used individually or in combination in any ratio.

[0035] The thermoplastic resin content in cellulose fiber resin composite materials is preferably 10 to 85% by mass, more preferably 20 to 80% by mass, and even more preferably 30 to 75% by mass, when the total mass of the cellulose fiber resin composite material is considered to be 100% by mass. When the thermoplastic resin content in the cellulose fiber resin composite material is within this range, the dispersibility of cellulose fibers within the cellulose fiber resin composite material is excellent. As a result, the cellulose fiber resin composite material has superior fluidity and moldability when melted, and also superior mechanical properties such as strength and elastic modulus. Consequently, the composite molded product obtained by melting and molding (e.g., injection molding) using cellulose fiber resin composite material as a raw material has superior mechanical properties such as strength and elastic modulus.

[0036] <Flame retardant> The flame retardant is not particularly limited, and examples include halogen-based flame retardants such as brominated flame retardants and chlorine-based flame retardants; phosphorus-based flame retardants; boron-based flame retardants; silicone-based flame retardants; nitrogen-containing compounds; metal oxides; etc. These can be used individually or in combination in any ratio. Of these, halogen-based flame retardants and phosphorus-based flame retardants are preferred in that they provide superior flame retardancy to the cellulose fiber resin composite material. Furthermore, since halogen-based and phosphorus-based flame retardants have excellent compatibility with thermoplastic resins, they can improve the moldability of the cellulose fiber resin composite material, resulting in a cellulose fiber resin composite material with superior strength (e.g., tensile strength) and a composite molded product obtained by melting and molding (e.g., injection molding) using a cellulose fiber resin composite material as a raw material. In addition, halogen-based and phosphorus-based flame retardants are also superior in terms of cost and environmental impact.

[0037] Examples of chlorine-based flame retardants include chlorinated paraffin, chlorinated polyethylene, dodecachloropentacyclooctadeca-7,15-diene, and hetic anhydride.

[0038] Examples of brominated flame retardants include pentabromodiphenyl ether and octabromodiphenyl ether. Decabromodiphenyl ether; TBBA compounds such as tetrabromobisphenol A (TBBA), TBBA-epoxy oligomer, TBBA-polycarbonate oligomer, TBBA-bis(dibromopropyl ether), and TBBA-bis(aryl ether); Polybenzene ring compounds such as bisphenylpentamethane, 1,2-bis(2,4,6-tribromophenoxy)ethane, 2,4,6-tris(2,4,6-tribromophenoxy)-1,3,5-triazine, 2,6-dibromophenol, and 2,4-dibromophenol; Brominated styrene compounds such as brominated polystyrene and polybrominated styrene; Phthalate compounds such as ethylenebistetrabromophthalimide; Examples include cyclic aliphatic compounds such as hexabromocyclododecane.

[0039] Examples of phosphorus-based flame retardants include red phosphorus and other red phosphorus-based flame retardants; Phosphate ester flame retardants such as triphenyl phosphate (TPP), tricresyl phosphate (TCP), trixylenyl phosphate (TXP), triethyl phosphate, tributyl phosphate (TBP), trioctyl phosphate (TOP), tris(butoxyethyl) phosphate, cresyldiphenyl phosphate (CDP), xylenyldiphenyl phosphate, bis(nonylphenyl)phenyl phosphate (DNP), and cresylbis(di-2,6-xylenyl) phosphate; Polyphosphate melamine-based flame retardant; Phosphate amide flame retardants such as triphenylphosphoamide; phosphate flame retardants such as ammonium polyphosphate (APP), melamine phosphate, guanidine phosphate, and melamine pyrophosphate; Phosphine-based flame retardants such as triphenylphosphine, triphenylphosphine oxide, tetrakis(hydroxymethyl)phosphonium chloride, and tetrakis(hydroxymethyl)sulfate; Examples of phosphazene-based flame retardants include phosphorus compounds such as propoxyphosphazene, phenoxyphosphazene, aminophosphazene, poly(fluoroalkylphosphazene), and dipropoxyphosphazene; and phosphinic acid-based flame retardants such as aluminum diethylphosphinate.

[0040] Examples of boron-based flame retardants include borax; Boron oxides such as diboron trioxide, boron trioxide, diboron dioxide, tetraboron trioxide, and tetraboron pentoxide; Examples include boric acid compounds such as boric acid, lithium borate, sodium borate, potassium borate, cesium borate, magnesium borate, calcium borate, barium borate, zirconium borate, zinc borate, aluminum borate, and ammonium borate.

[0041] Examples of silicone-based flame retardants include silicone compounds such as silicone oils and polyorganosiloxanes.

[0042] Examples of nitrogen-containing compounds include ammonium carbonate and other melamine compounds not mentioned above.

[0043] Examples of metal oxides include magnesium oxide, aluminum oxide, calcium oxide, zinc oxide, potassium oxide, silicon oxide, titanium oxide, iron oxide, copper oxide, sodium oxide, nickel oxide, boron oxide, manganese oxide, lithium oxide, and antimony oxide.

[0044] The flame retardant content in cellulose fiber resin composite materials is 5 to 30% by mass, preferably 7 to 30% by mass, and more preferably 9 to 30% by mass, when the total mass of the cellulose fiber resin composite material is considered as 100% by mass. By adjusting the cellulose fiber content, it becomes easy to adjust the flame retardant coverage rate on the cellulose fibers, the average flame retardant coverage rate on the cellulose fibers, and the percentage of cellulose fibers in the cellulose fiber resin composite material where the flame retardant coverage rate is 15 to 60%, and a cellulose fiber resin composite material with superior mechanical properties such as tensile strength and flame retardancy can be obtained.

[0045] <Other ingredients> Cellulose fiber resin composite materials may contain known additives as other components. Examples of additives include mold release agents, flow modifiers, antistatic agents, compatibilizers, UV absorbers, fillers, surfactants, coupling agents, colorants, antioxidants, defoamers, leveling agents, and plasticizers.

[0046] <<Method for manufacturing cellulose fiber resin composite materials>> As a suitable example of a method for producing cellulose fiber resin composite materials, a method using pulp as a raw material will be described. The method for producing cellulose fiber resin composite materials includes a grinding step of grinding pulp, which is the raw material for cellulose fibers, into pulp fragments; a kneading step of mixing and kneading each raw material; and an extrusion step of forming a cellulose fiber resin composite material by extruding the resin mixture obtained in the kneading step.

[0047] <Grinding process> In the grinding process, the pulp, which will be the raw material for cellulose fibers, is ground into pulp fragments. The size of the pulp fragments is not particularly limited, but in order to facilitate mixing and shorten the time of the kneading process, as described later, it is preferable that the diameter of the pulp fragments (the length of the longest part of the pulp fragment) be 10 to 50 mm. By making the pulp fragments of this size, they exhibit excellent dispersibility in the resin mixture during the kneading process.

[0048] Grinding can be carried out using known methods, such as grinding methods using grinders like hammer mills, cutter mills, or jet mills.

[0049] <Mixing process> In the kneading process, the pulp fragments obtained in the crushing process, thermoplastic resin, and flame retardant are mixed and then kneaded to produce a resin mixture. The flame retardant may be added at the same time as the pulp fragments and thermoplastic resin are put into the mixing apparatus described later, or it may be added after the pulp fragments and thermoplastic resin have been added first and a desired amount of time has elapsed. By adjusting the time between the addition of the pulp fragments and thermoplastic resin and the addition of the flame retardant, the percentage of cellulose fibers covered by the flame retardant, which is 15-60%, can be adjusted.

[0050] The mixing and kneading methods are not particularly limited and can be carried out by known methods. When stirring in the mixing method, the amount of flame retardant to be added and the rotation speed of the stirring machine (for example, 20 to 40 m / s) are adjusted and the mixture is stirred until the pulp becomes fibrous (hereinafter referred to as pulp fibers). At this time, the flame retardant temporarily coats the pulp fibers. Subsequently, in the kneading process, the pulp fibers are crushed (defibrated) into fine cellulose fibers, and the cellulose fibers are kneaded with thermoplastic resin and flame retardant, and the flame retardant that has coated the cellulose fibers adheres to them by the molten thermoplastic resin. At this time, there are cases in which the flame retardant coats the cellulose fibers by having the thermoplastic resin adhere to part or all of the surface of the cellulose fibers and then having the flame retardant coat the outside of that, and cases in which the flame retardant attached to the cellulose fibers is pressed against the thermoplastic resin and the flame retardant directly coats the cellulose fibers.

[0051] Mixing methods (mixing equipment) include using agitators such as Henschel mixers, super mixers, and ribbon mixers.

[0052] Methods of mixing include using a Banbury mixer or a pressure roller. Mixing can also be done using an extrusion molding machine, such as a twin-screw extruder. In this case, both the mixing process and the extrusion process (described later) are performed by the extrusion molding machine.

[0053] The mixing conditions are not particularly limited, but it is preferable to set the heating temperature above the softening point of the thermoplastic resin. By setting such a temperature, the dispersion of cellulose fibers in the cellulose fiber resin composite material is promoted, resulting in excellent fluidity during melting, which leads to excellent moldability and makes it possible to obtain a cellulose fiber resin composite material with excellent mechanical properties such as strength and elastic modulus. Furthermore, as the mixing of the thermoplastic resin and cellulose fibers progresses, a uniformly dispersed cellulose fiber resin composite material without fiber clumps can be obtained. In addition, as the mixing of cellulose fibers and flame retardants progresses, it becomes possible to adjust the coverage rate of the flame retardant on the cellulose fibers, the average coverage rate of the flame retardant on the cellulose fibers, and the occupancy rate of cellulose fibers with a flame retardant coverage rate of 15-60% in the cellulose fiber resin composite material to a preferred range, thereby improving the mechanical properties such as tensile strength and flame retardancy of the composite molded product obtained from the cellulose fiber resin composite material.

[0054] The mixing time or the number of mixing cycles are not particularly limited, but for example, if the mixing time for one cycle is 5 to 60 seconds, multiple cycles of mixing can be performed under the same conditions. Specifically, the number of mixing cycles can be, for example, 2 to 5 times.

[0055] The rotation speed during mixing is not particularly limited, but can be, for example, 50 to 300 rpm.

[0056] <Extrusion Process> In the extrusion process, the resin mixture obtained in the kneading process is molded into a desired shape through a mold, thereby forming a cellulose fiber resin composite material. The resin mixture obtained in the kneading process is heated and melted by an extrusion molding machine and poured into a mold. The poured resin mixture is molded by the mold into the desired cross-sectional shape (a cross-sectional shape perpendicular to the axial direction of the columnar pellet) and discharged from the discharge port of the mold. The discharged molded resin mixture is cut to the desired length to obtain a cellulose fiber resin composite material.

[0057] The heating conditions in the extrusion process are not particularly limited, but it is preferable to set the heating temperature above the softening point of the thermoplastic resin. By setting the temperature to such a level, the cellulose fibers in the cellulose fiber resin composite material will be oriented in the extrusion direction during extrusion molding.

[0058] A known extrusion molding machine can be used. Examples of extrusion molding methods include using a twin-screw extruder. A twin-screw extruder is preferable because it can be used for both mixing and extrusion molding.

[0059] When using a twin-screw extruder, the rotation speed of the twin-screw extruder screws is not particularly limited, but can be, for example, 50 to 300 rpm. When the screw rotation speed is within this range, the flow of the resin mixture becomes smoother, making it easier for the cellulose fibers of the cellulose fiber resin composite material to be oriented along the extrusion direction.

[0060] <<Applications of Cellulose Fiber Resin Composite Materials>> The cellulose fiber resin composite material of this disclosure is preferably used as a raw material (e.g., pellets) for composite molded products produced by methods such as injection molding using molds or 3D printing. The composite molded products are particularly suitable for use in molded parts for vehicles, equipment, and devices having fine or complex structures, as well as industrial materials such as containers, pallets, plastic cores, and building materials, daily necessities, and general merchandise. [Examples]

[0061] <<Fabrication of Cellulose Fiber Resin Composite Materials>> <Raw materials> ·Thermoplastic resin Polypropylene (Novatec MG03BD) • Pulp (raw material for cellulose fibers) Coniferous pulp (manufactured by Canfor, NBKP) Flame retardant Phosphorus-based flame retardant (Teijin Limited, FireGuard FCX-210) Halogen-based flame retardant (bromine-based flame retardant, SAYTEX8010 manufactured by ALBEMARLE JAPAN CORPORATION) Boron-based flame retardant (manufactured by Wako Pure Chemical Industries, Ltd., boric acid)

[0062] <Preparation of Cellulose Fiber Resin Composite Materials for Each Example and Comparative Example> The pulp was weighed in the amounts shown in Tables 1 and 2, and then coarsely ground using a pulverizer until it was reduced to pulp fragments 40 mm or less in length and 10 mm or less in width. The pulp fragments, thermoplastic resin, and flame retardant were dry-blended to the mass ratios shown in Tables 1 and 2 to obtain the mixtures for each example and comparative example. Each of the obtained mixtures was melt-kneaded using a twin-screw extruder (PCM30, manufactured by Ikegai Co., Ltd.) according to the manufacturing methods shown in Tables 3 and 4. The resulting kneaded materials for each example and comparative example were extruded through a mold and then hot-cut to obtain the cellulose fiber resin composite materials for each example and comparative example. The cellulose fiber resin composite materials were formed into cylindrical pellets with a diameter of 3 mm and a length of 6 mm. It was confirmed that the cellulose fibers in the cellulose fiber resin composite material were oriented in the extrusion direction when hot-cut from the discharge port of the extruder.

[0063] <Measured values ​​of cellulose fiber resin composite materials for each example and comparative example> (Average fiber length of cellulose fibers) For each example and comparative example, the cellulose fiber resin composite material was cut in a plane parallel to the extrusion direction of the cellulose fiber resin composite material to form a cross-section. The cross-section was observed using a scanning electron microscope, and 50 cellulose fibers were randomly selected from the cross-section. The fiber lengths of these cellulose fibers were measured and the number average was used to calculate the value.

[0064] (Average fiber diameter of cellulose fibers) The cellulose fiber resin composite materials of each example and comparative example were cut in a plane perpendicular to the extrusion direction of the cellulose fiber resin composite material to form a cross-section. The cross-section was observed using a scanning electron microscope, and 50 cellulose fibers were randomly selected from the cross-section. The fiber diameters of these cellulose fibers were measured and the number average was calculated. The measurement results are shown in Tables 1 and 2.

[0065] (Average coverage rate of cellulose fibers; occupancy rate of cellulose fibers with a coverage rate of 15-60%) The average coating rate of cellulose fibers with flame retardant in each example and comparative example was measured using the following procedure. A cross-section was formed by cutting the cellulose fiber resin composite material of each example and comparative example in a plane perpendicular to the extrusion direction of the cellulose fiber resin composite material. A scanning electron microscope (SEM) was used to image an 82 μm × 126 μm area of ​​the cross-section at a magnification of 1000x to obtain cross-sectional SEM images of each example and comparative example. Image analysis was performed on each obtained cross-sectional SEM image, and 20 cellulose fibers with a cross-sectional circumference of 10 to 50 μm were randomly selected from the cellulose fibers in the cross-section. For each cellulose fiber, the circumference and the length covered by the flame retardant (coating length) were obtained, and the coating rate was calculated according to the following formula. Coverage rate = (Covering length) / (Perimeter) x 100(%) The coverage rates obtained for 20 cellulose fibers selected for each example and comparative example were number-averaged to obtain the average coverage rate for each example and comparative example. The results are shown in Tables 1 and 2.

[0066] For each example and comparative example, the occupancy rate of cellulose fibers with a coverage rate of 15-60% was determined by counting the number of cellulose fibers with a coverage rate of 15-60% relative to the total number of cellulose fibers with a cross-sectional circumference of 10-50 μm included in the cross-sectional SEM image of each example and comparative example, and then calculating the percentage of the total number of cellulose fibers with a coverage rate of 15-60% relative to that total. The results are shown in Tables 1 and 2.

[0067] <<Rating>> <Evaluation of flame retardancy of composite molded materials: Vertical flammability test (UL94V test)> The flame retardancy of composite molded materials obtained from the cellulose fiber resin composite materials of each example and comparative example was evaluated by UL94V testing using the following method. The evaluation was performed in accordance with ASTM D3801. Test specimens of the composite material molded products were prepared by injection molding the cellulose fiber resin composite material of each example and comparative example to a length of 125 ± 5 mm, a width of 13 ± 0.5 mm, and a thickness of 5 mm. For injection molding, the cellulose fiber resin composite material of each example and comparative example was dried in a dryer at 80°C for 30 minutes. Using an injection molding machine (Nissei Plastic Industrial Co., Ltd.: TD100-25ASE), the resin was melted under conditions where both the cylinder temperature and nozzle temperature were 180°C or 200°C, and the resulting material was injected into a mold shaped like the test specimen. The molded composite material (test specimen) was then cooled to obtain the final product. The evaluation was performed on the vertical flammability test results according to the following criteria. The results are shown in Tables 1 and 2. (Judgment method) The judgment was based on the vertical flammability test. Those exhibiting the following combustion behaviors were classified as V0, V1, or V2, while those that did not meet any of the criteria were deemed non-compliant. A "-" in the table indicates that the test specimen could not be molded and therefore could not be evaluated. ·V0 The afterglow time for the first test is 10 seconds or less, the total afterglow time for the five test specimens is 50 seconds or less, the afterglow time for the second test plus the afterglow time is 30 seconds or less, the clamp does not burn, and the dripping material does not ignite the cotton placed underneath. ·V1 The afterglow time for the first test is 30 seconds or less, the total afterglow time for the five test specimens is 250 seconds or less, the afterglow time for the second test plus the afterglow time is 60 seconds or less, the clamp does not burn, and the dripping material does not ignite the cotton placed underneath. ·V2 The afterglow time for the first test is 30 seconds or less, the total afterglow time for the five test specimens is 250 seconds or less, the afterglow time for the second test plus the afterglow time is 60 seconds or less, the clamp does not burn, and the cotton placed underneath burns due to the dripping material.

[0068] <Evaluation of moldability of cellulose fiber composite materials> The cellulose fiber resin composite materials of each example and comparative example were dried in a dryer at 80°C for 30 minutes. Using an injection molding machine (Nissei Plastic Industrial Co., Ltd.: TD100-25ASE), the resin was melted under conditions where both the cylinder temperature and nozzle temperature were 180°C or 200°C. The melted resin was then fed into a mold shaped like a dumbbell test specimen (mold temperature set at 60°C), cooled, and the composite molded products of each example and comparative example were obtained. The dumbbell-shaped test specimens were prepared to the dimensions of a plate-shaped test specimen as specified in JIS Z2201:1968. Injection molding was performed at an injection pressure of 800 to 1500 MPa. The moldability of each composite molded product was observed visually according to the following criteria. The results are shown in Tables 1 and 2. (Judgment criteria) A: The test specimen can be molded normally when both the cylinder temperature and nozzle temperature are 180°C and the injection pressure is between 800 MPa and 1000 MPa. B: With both cylinder and nozzle temperatures at 180°C, the test specimen could not be molded properly when the injection pressure was between 800 MPa and 1000 MPa, but it could be molded properly when the injection pressure was between 1000 MPa and 1500 MPa. C: With both cylinder and nozzle temperatures at 180°C, the test specimen could not be molded properly when the injection pressure was between 1000 MPa and 15000 MPa. With both cylinder and nozzle temperatures at 200°C, the test specimen could be molded properly when the injection pressure was between 800 MPa and 1500 MPa. D: With both cylinder and nozzle temperatures at 180°C, the test specimen could not be molded properly when the injection pressure was between 1000 MPa and 15000 MPa. Furthermore, with both cylinder and nozzle temperatures at 200°C, the test specimen could not be molded properly when the injection pressure was between 800 MPa and 1500 MPa.

[0069] <Tensile strength test of composite molded materials> For the moldability evaluation, dumbbell-shaped test specimens of the composite material molded products of each example and comparative example were prepared, and their tensile strength was measured from the load at which they fractured using an Instron-type material testing machine (Shimadzu Corporation: Autograph AG25 TA) with a crosshead speed of 50 mm / min. The measurement results are shown in Tables 1 and 2. Results marked with "-" in the tables indicate that the test specimen could not be molded and therefore could not be evaluated.

[0070] [Table 1]

[0071] [Table 2]

[0072] [Table 3]

[0073] [Table 4]

Claims

1. A cellulose fiber resin composite material obtained by extruding a resin mixture containing cellulose fibers, a thermoplastic resin, and a flame retardant such that the cellulose fibers are oriented along the extrusion direction, The cellulose fibers have an average fiber length of 10 to 400 μm and an average fiber diameter of 1 to 50 μm. The cellulose fiber content is 10 to 60% by mass when the total mass of the cellulose fiber resin composite material is 100% by mass. The content of the flame retardant is 5 to 30% by mass when the total mass of the cellulose fiber resin composite material is considered to be 100% by mass. At least a portion of the flame retardant coats the cellulose fibers, The average coverage rate of the cellulose fibers by the flame retardant, calculated by the evaluation method described below, is 15% or more and 60% or less. A cellulose fiber resin composite material in which, in the evaluation method described below, the proportion of cellulose fibers with a coverage rate of 15-60% is 80% or more, based on the total number of cellulose fibers with a cross-sectional circumference of 10-50 μm included in the cross-sectional SEM image. (Method for evaluating coverage rate) When the cellulose fiber resin composite material is extruded, a cross-sectional area of ​​82 μm × 126 μm perpendicular to the extrusion direction is imaged at 1000x magnification using a scanning electron microscope (SEM) to obtain a cross-sectional SEM image. The obtained cross-sectional SEM image is analyzed, and 20 cellulose fibers with a cross-sectional circumference of 10 to 50 μm are randomly selected from the cross-section. For each of these cellulose fibers, the circumference and the length covered by the flame retardant (covering length) are obtained, and the coverage rate is calculated according to the following formula. Coverage rate (%) = (Covering length) / (Perimeter) x 100 The coverage rates obtained for the aforementioned 20 cellulose fibers are number-averaged to obtain the average coverage rate.

2. The cellulose fiber resin composite material according to claim 1, characterized in that the flame retardant comprises either a phosphorus-based flame retardant or a halogen-based flame retardant.

3. The cellulose fiber resin composite material according to claim 1 or 2, characterized in that the thermoplastic resin includes any of polyethylene resin, polypropylene resin, vinyl chloride resin, methacrylic resin, polystyrene resin, ABS resin, polycarbonate resin, polyacetal resin, polyamide resin, polysulfone resin, modified PPO resin, or polyester resin.

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