JP2023149104A - Cellulose fiber resin composite material - Google Patents

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

The present invention relates to cellulose fiber resin composite materials.

Thermoplastic resins are used as parts of various products because they can be easily molded by heating. BACKGROUND ART In recent years, as electronic devices and the like have become smaller and thinner, the parts used in them have also become smaller and thinner, and thermoplastic resins are also required to be moldable into fine and complex shapes. Furthermore, when thermoplastic resins are used in smaller and thinner parts, mechanical properties such as higher tensile strength are required, so thermoplastic resins are used in combination with fibers.

When inorganic fibers are used as the fibers to be composited with the thermoplastic resin, residues derived from the inorganic fibers are generated during incineration during disposal, and this residue must be disposed of in a landfill or the like. For this reason, there is a demand for resin molded products that do not use inorganic fibers, and vegetable fibers such as cellulose fibers are used as composite fibers.

Since such resin molded products made of composite plant fibers do not have high flame retardancy, flame retardant treatment is required. For example, Patent Document 1 discloses a method for manufacturing a resin molded article containing plant fibers made flame retardant by including (impregnating) at least one of boric acid and a boric acid compound.

Japanese Patent Application Publication No. 2007-130868

The production method of Patent Document 1 can produce a flame-retardant resin molded product containing plant fibers as a filler, and in the flame-retardant evaluation based on the UL (Underwriters Laboratory) standard (94V), it has a V- A flame retardant rating of 2 has been achieved. However, depending on the application, the flame retardance of V-2 may be insufficient, and higher flame retardance is required.

Therefore, an object of the present invention is to provide a cellulose fiber resin composite material that has excellent mechanical properties such as tensile strength and even better flame retardancy. Another object of the present invention is to provide a composite molded product that has excellent mechanical properties such as tensile strength and flame retardancy when the cellulose fiber resin composite material is melted and molded as pellets by an injection molding method or the like.

The present inventors have conducted intensive research and found that a cellulose fiber-resin composite material containing cellulose fibers and a thermoplastic resin in which the surface of cellulose fibers is coated with a flame retardant and has a specific average coverage rate has a high mechanical strength such as tensile strength. The present disclosure technology has been completed based on the discovery that the flame retardant properties are excellent. That is, the disclosed technology is as follows.

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. The cellulose fiber has an average fiber length of 10 to 400 μm and an average fiber diameter of 1 to 50 μm, and the content of the cellulose fiber is 100% by mass of the total mass of the cellulose fiber resin composite material. The content of the flame retardant is 5 to 30 mass% when the total mass of the cellulose fiber resin composite material is 100 mass%, and the content of the flame retardant is 10 to 60 mass%. At least a portion thereof covers the cellulose fibers, and the average coverage of the cellulose fibers with the flame retardant is 15% or more and 60% or less, as calculated by the following evaluation method.
(Coverage evaluation method)
An area of 82 μm x 126 μm in a cross section perpendicular to the extrusion direction obtained by extrusion molding the cellulose fiber resin composite material was imaged at a magnification of 1000 times using a scanning electron microscope (SEM), and a cross-sectional SEM image was obtained. get. The obtained cross-sectional SEM image was analyzed, 20 cellulose fibers in the cross section with a fiber cross-sectional circumference of 10 to 50 μm were randomly selected, and each cellulose fiber was The length covered by the flame retardant (covering length) is 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 cellulose fibers are number-averaged to obtain the average coverage rate.
In the cellulose fiber resin composite material of the present disclosure, the coverage is 15 to 60% based on the number of all cellulose fibers whose fiber cross section has a circumferential length of 10 to 50 μm included in the cross-sectional SEM image. It is preferable that the number ratio of cellulose fibers is 80% or more.
In the cellulose fiber resin composite material of the present disclosure, it is preferable that the flame retardant includes either a phosphorus-based flame retardant or a halogen-based flame retardant.
In the cellulose fiber resin composite material of the present disclosure, the thermoplastic resin is 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.

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 even more excellent flame retardancy. Furthermore, when a cellulose fiber resin composite material is melted and molded by injection molding or the like as a raw material, a molded composite material with excellent mechanical properties such as tensile strength and even higher flame retardance can be obtained.

Hereinafter, embodiments of the disclosed technology will be described in detail. In addition, in this specification, the notation "a to b" in the description of numerical ranges represents a range from a to b, unless otherwise specified.

<<<Cellulose fiber resin composite material>>>
The cellulose fiber resin composite material of the present disclosure is a cellulose fiber resin 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. It is a composite material. A composite molded article can be formed by using a cellulose fiber resin composite material as a raw material and melting and molding (for example, injection molding) as described below.

The shape of the cellulose fiber resin composite material is not particularly limited as long as it can be molded by extrusion molding. Further, when the cellulose fiber resin composite material is made into pellets, the shape of the cellulose fiber composite material is a columnar body such as a cylinder, an elliptical cylinder, or a polygonal cylinder. For cellulose fiber resin composite materials, the cross-sectional shape of the extrusion part (resin mixture discharge port) of the mold used when the resin mixture is melted and the cellulose fiber resin composite material is extruded is circular, oval, or polygonal. By doing so, it is possible to obtain columnar pellets such as a cylinder, an elliptical cylinder, and a polygonal cylinder.

When the cellulose fiber resin composite material is made into pellets, the cross-sectional diameter 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 when the cross-sectional shape is circular, it is the diameter, and when the cross-sectional shape is oval, it is the diameter. The length of the major axis is shown, and if the cross-sectional shape is a polygon, the length of the longest side is shown.

The length in the axial direction when the cellulose fiber resin composite material is made into pellets is not particularly limited, but can be 6 to 15 mm. When the cellulose fiber resin composite material is made into pellets, the length in the axial direction is the extrusion part (resin mixture discharge port) of the mold used when the resin mixture is melted and the cellulose fiber resin composite material is extruded. This is the length in the axial direction of a molded product (cellulose fiber resin composite material pellet) of the discharged resin mixture when the discharged resin mixture is cut.

The surface of the cellulose fiber resin composite material may have grooves (or scratches) that are formed parallel to the direction in which the resin mixture is extruded from the mold when the cellulose fiber resin composite material is extruded. 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, it may be abbreviated as the extrusion direction of the cellulose fiber resin composite material). ). When the cellulose fiber resin composite material is made into pellets, the extrusion direction generally corresponds to the axial direction of the columnar pellets. 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 with an optical microscope.

The cellulose fibers within the cellulose fiber resin composite are oriented in the extrusion direction of the cellulose fiber resin composite. The cellulose fibers in the cellulose fiber resin composite are oriented in the direction in which the resin mixture is extruded from the mold when the cellulose fiber resin composite is extruded. That is, the orientation direction of the cellulose fibers corresponds to the extrusion direction of the cellulose fiber resin composite material.
Here, "orientated" or "corresponding to the extrusion direction" means to correspond to the orientation or extrusion direction to the extent that it is understood to correspond to the orientation or extrusion direction based on technical common sense. This does not necessarily mean that all the cellulose fibers are parallel to each other or oriented in accordance with the extrusion direction.

<<Structure of cellulose fiber resin composite material Cellulose fiber resin composite material>>
<Cellulose fiber>
When the cellulose fiber is combined with a thermoplastic resin, the cellulose fiber resin composite material has excellent mechanical properties such as tensile strength. Therefore, by melting and molding (for example, injection molding) a cellulose fiber resin composite material as a raw material, a composite molded product with excellent mechanical properties such as tensile strength can be obtained.
Cellulose fibers are not particularly limited, and include cellulose fibers derived from plants, cellulose fibers derived from animals such as acetic acid bacteria, and regenerated fibers that are artificially manufactured into thin, long continuous fibers by dissolving natural cellulose from trees and wood pulp with a solvent. Any of these can be used. In the method for producing a cellulose fiber-resin composite material described below, pulp is used to improve the dispersibility of cellulose fibers in the cellulose fiber-resin composite material and to facilitate adjustment of the average coverage rate of cellulose fibers with a flame retardant, which will be described later. Cellulose fibers obtained by pulverizing (defibrating) are preferably used. These cellulose fibers can be used alone or in combination in any ratio.

The pulp may be either wood pulp or non-wood pulp from the viewpoint of the raw material, and may be either mechanical pulp or chemical pulp from the viewpoint of the manufacturing method.

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 hardwoods such as eucalyptus and poplar, and these may also be unbleached pulps. Bleached pulp may also be used.

Examples of non-wood pulp include natural fibers other than wood such as cotton, straw, bamboo, esparto, bagasse, linters, kenaf, Manila hemp, flax, hemp, jute, and gampi; others include waste paper and scraps. One example is waste paper pulp made from.

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 dispersibility of the cellulose fibers within the cellulose fiber resin composite material will be excellent. For this reason, cellulose fiber resin composite materials have excellent flowability when melted and have excellent moldability. , a composite molded product with excellent mechanical properties such as tensile strength can be obtained.
In addition, when the average fiber length of cellulose fibers is within this range, the resin mixture has excellent fluidity during extrusion molding, so it is easy to orient the cellulose fibers along the extrusion direction in the cellulose fiber resin composite material. becomes.
When the average fiber length of the cellulose fibers is within this range, the specific surface area of the cellulose fibers is suitable for controlling the coverage rate and average coverage rate of the cellulose fibers with the flame retardant described later, and the cellulose fiber resin The flame retardance of the composite material can be improved. As a result, by melting and molding (for example, injection molding) a cellulose fiber resin composite material as a raw material, a composite molded product with even better flame retardancy can be obtained.

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

The average fiber length of the cellulose fibers is determined by observing an arbitrary cross section of the cellulose fiber resin composite material parallel to the extrusion direction using a scanning electron microscope, and randomly selecting 50 cellulose fibers included in the cross section. , the number average of the measured fiber lengths of these cellulose fibers is obtained.

The average fiber diameter of cellulose fibers is 1 to 50 μm. When the average fiber diameter of the cellulose fibers is within this range, the dispersibility of the cellulose fibers within the cellulose fiber resin composite material will be excellent. Therefore, the cellulose fiber resin composite material has excellent fluidity when melted, excellent moldability, and can have excellent mechanical properties such as tensile strength. Further, by using a cellulose fiber resin composite material as a raw material and melting and molding (for example, injection molding), a composite molded product having excellent mechanical properties such as tensile strength can be obtained.
When the average fiber diameter of the cellulose fibers is within this range, the specific surface area of the cellulose fibers is suitable for controlling the coverage rate and average coverage rate of the cellulose fibers with the flame retardant described later, and the cellulose fiber resin By using a composite material as a raw material, melting and molding (for example, injection molding), a composite molded product with even better flame retardancy can be obtained.
Furthermore, when the average fiber diameter of the cellulose fibers is within this range, the resin mixture has excellent fluidity during extrusion molding, so that the cellulose fibers are not oriented along the extrusion direction in the cellulose fiber resin composite material. It becomes easier.

The average fiber diameter of the cellulose fibers can be adjusted by the amount of cellulose fibers (pulp in the production method described below) and the rotation speed and number of repetitions during kneading in the production method described below.

The average fiber diameter of the cellulose fibers is determined by observing a cross section perpendicular to the extrusion direction of the cellulose fiber resin composite material using a scanning electron microscope, randomly selecting 50 cellulose fibers included in the cross section, and determining the average fiber diameter of the cellulose fibers. It is obtained by calculating the number average of the measured diameters of cellulose fibers (in the case of an ellipse, the length of the major axis, and in the case of a polygon, the length of the longest side).

The cellulose fibers are partially coated with a flame retardant described below, and the average coverage is 15% or more and 60% or less, preferably 20% or more and 50% or less. When the average coverage is within this range, the flame retardant present on the surface of the cellulose fibers is sufficient, so the flame retardancy of the cellulose fibers can be improved, and as a result, the cellulose fiber resin composite The flame retardance of a composite molded product obtained by melting and molding (for example, injection molding) a cellulose fiber resin composite material as a raw material can be improved. In addition, a part of the surface of the cellulose fiber is not coated with the flame retardant, and the adhesion between the cellulose fiber and the thermoplastic resin is appropriately ensured. For this reason, composite molded products obtained by melting and molding (e.g., injection molding) cellulose fiber resin composite materials and cellulose fiber resin composite materials as raw materials have better mechanical properties such as tensile strength. . Cellulose fiber coated with a flame retardant refers to cases in which the cellulose fiber is directly coated with a flame retardant, as well as cases in which a part or all of the surface of the cellulose fiber is coated with a thermoplastic resin, and the outside thereof is further coated with a flame retardant. This shall also include cases where

The coverage and average coverage of flame retardant in cellulose fibers are determined by the amount of cellulose fiber (pulp described later), the average fiber length and diameter of cellulose, the amount of flame retardant, and the amount after adding the flame retardant. It can be adjusted by the stirring time.

The coverage and average coverage of the flame retardant in cellulose fibers are calculated by the following evaluation method. An area of 82 μm×126 μm in a cross section perpendicular to the extrusion direction of the cellulose fiber resin composite material is imaged using a scanning electron microscope (SEM) at a magnification of 1000 times to obtain a cross-sectional SEM image. The obtained cross-sectional SEM image was analyzed, 20 cellulose fibers with a cross-sectional circumference of 10 to 50 μm were randomly selected from among the cellulose fibers in the cross section, and each cellulose fiber was coated with the circumference and flame retardant. Obtain the covered length (covering length) and calculate the coverage rate 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.

In addition, when the number of all cellulose fibers with a fiber cross-section circumference of 10 to 50 μm included in the above-mentioned cross-sectional SEM image is used as a reference, the percentage of cellulose fibers with a coverage rate of 15 to 60% (hereinafter referred to as , occupancy) 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 flame retardant coverage is 15 to 60% and the cellulose fiber occupancy is 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 melting and molding (for example, injection molding) a cellulose fiber resin composite material as a raw material also has excellent mechanical properties such as tensile strength and flame retardancy.

The occupancy of cellulose fibers with a flame retardant coverage of 15 to 60% is determined by the amount of cellulose fibers (pulp described later), the amount of flame retardant, and the mixture of pulp pieces and thermoplastic resin described later. It can be adjusted by adjusting the time from when the flame retardant is added to the device until the flame retardant is added (flame retardant injection timing).

The content of cellulose fiber in the cellulose fiber resin composite material is 10 to 60 mass%, preferably 10 to 50 mass%, and 10 to 40 mass%, when the total mass of the cellulose fiber resin composite material is 100 mass%. % is more preferable. When the content of cellulose fibers in the cellulose fiber resin composite material is within this range, the dispersibility of the cellulose fibers in the cellulose fiber resin composite material will be excellent. Therefore, the cellulose fiber resin composite material has excellent fluidity and moldability when melted, and also has excellent mechanical properties such as strength and elastic modulus. As a result, a composite molded product obtained by melting and molding (for example, injection molding) using a cellulose fiber resin composite material as a raw material also has excellent mechanical properties such as strength and elastic modulus.
In addition, by adjusting the content of the flame retardant described below, the coverage of the flame retardant in the cellulose fibers, the average coverage of the flame retardant in the cellulose fibers, and the coverage of the flame retardant contained in the cellulose fiber resin composite material can be increased from 15 to 15. It is easy to adjust the occupancy rate of cellulose fibers, which is 60%, and the composite material is obtained by melting and molding (for example, injection molding) using a cellulose fiber resin composite material and a cellulose fiber resin composite material as raw materials. The molded article has better flame retardancy.

<Thermoplastic resin>
The thermoplastic resin is not particularly limited, and includes, for example, 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. can be used. These can be used alone or in combination in any ratio.

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

<Flame retardant>
Flame retardants are not particularly limited, and include, for example, 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. can be used. These can be used alone or in combination in any ratio. Among these, halogen-based flame retardants and phosphorus-based flame retardants are preferred in that they make the cellulose fiber resin composite material more excellent in flame retardancy. In addition, since halogen flame retardants and phosphorus flame retardants have excellent compatibility with thermoplastic resins, they can improve the moldability of cellulose fiber resin composite materials and increase their strength (e.g., tensile strength). Composite molded products can be obtained by melting and molding (for example, injection molding) a cellulose fiber resin composite material and a cellulose fiber resin composite material having excellent properties (e.g.) as raw materials. Further, halogen-based flame retardants and phosphorus-based flame retardants are superior in terms of cost and environmental impact.

Examples of the chlorinated flame retardant include chlorinated paraffin, chlorinated polyethylene, dodecachloropentacyclooctadeca-7,15-diene, and het's acid anhydride.

Examples of brominated flame retardants include pentabromodiphenyl ether; octabromodiphenyl ether;
Decabromodiphenyl ether; TBBA compounds such as tetrabromobisphenol A (TBBA), TBBA-epoxy oligomer, TBBA-polycarbonate oligomer, TBBA-bis(dibromopropyl ether), TBBA-bis(aryl ether);
bisphenylpentamethane, 1,2-bis(2,4,6-tribromophenoxy)ethane, 2,4,6-tris(2,4,6-tribromophenoxy)-1,3,5-triazine, Multi-benzene ring compounds such as 2,6-dibromophenol and 2,4-dibromophenol;
Brominated styrene compounds such as brominated polystyrene and polybrominated styrene;
Phthalic acid compounds such as ethylene bistetrabromophthalimide;
Cycloaliphatic compounds such as hexabromocyclododecane; etc. can be mentioned.

Examples of phosphorus flame retardants include red phosphorus flame retardants such as red phosphorus;
Triphenyl phosphate (TPP), tricresyl phosphate (TCP), trixylenyl phosphate (TXP), triethyl phosphate, tributyl phosphate (TBP), trioctyl phosphate (TOP), tris(butoxyethyl) phosphate, cresyl diphenyl phosphate Phosphate ester flame retardants such as (CDP), xylenyl diphenyl phosphate, bis(nonylphenyl) phenyl phosphate (DNP), cresyl bis(di2,6-xylenyl) phosphate;
Melamine polyphosphate flame retardant;
Phosphate-based flame retardants such as triphenylphosphoramide; phosphate-based flame retardants such as ammonium polyphosphate (APP), melamine phosphate, guanidine phosphate, and melamine pyrophosphate;
Phosphine flame retardants such as triphenylphosphine, triphenylphosphine oxide, tetrakis(hydroxymethyl)phosphonium chloride, tetrakis(hydroxymethyl)sulfate;
Examples include phosphazene flame retardants such as phosphorus compounds such as propoxyphosphazene, phenoxyphosphazene, aminophosphazene, poly(fluoroalkylphosphazene), and dipropoxyphosphazene; phosphinic acid flame retardants such as aluminum diethylphosphinate;

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

Examples of silicone flame retardants include silicone oils and silicone compounds such as polyorganosiloxanes.

Examples of the nitrogen-containing compound include nitrogen-containing compounds such as ammonium carbonate and melamine compounds other than those mentioned above.

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. etc. can be mentioned.

The content of the flame retardant in the cellulose fiber resin composite material is 5 to 30 mass%, preferably 7 to 30 mass%, and 9 to 30 mass%, when the total mass of the cellulose fiber resin composite material is 100 mass%. % is more preferable. By adjusting the content of cellulose fiber, the coverage of flame retardant in cellulose fiber, the average coverage of flame retardant in cellulose fiber, and the coverage of flame retardant contained in cellulose fiber resin composite material are 15 to 60%. It becomes easy to adjust the occupancy of fibers, and a cellulose fiber resin composite material with excellent mechanical properties such as tensile strength and flame retardancy can be obtained.

<Other ingredients>
The cellulose fiber resin composite material can contain known additives as other components. Examples of additives include mold release agents, flow modifiers, antistatic agents, compatibilizers, ultraviolet absorbers, fillers, surfactants, coupling agents, colorants, antioxidants, antifoaming agents, Examples include leveling agents and plasticizers.

<<Production method of cellulose fiber resin composite material>>
As a preferred example of a method for producing a cellulose fiber resin composite material, a method for producing a cellulose fiber resin composite material using pulp as a raw material will be described. The method for producing cellulose fiber resin composite materials includes a pulverization process in which pulp, which is the raw material for cellulose fibers, is pulverized into small pulp pieces, a kneading process in which each raw material is mixed and kneaded, and the resin mixture obtained in the kneading process is extruded. and an extrusion step to form a cellulose fiber resin composite.

<Crushing process>
In the crushing process, pulp, which is the raw material for cellulose fibers, is crushed into small pulp pieces. The size of the pulp pieces is not particularly limited, but the diameter of the pulp pieces (the length of the longest part of the pulp pieces) may be 10 to 50 mm in order to facilitate mixing and shorten the time of the kneading process, which will be described later. preferable. By setting the pulp pieces to such a size, they exhibit excellent dispersibility within the resin mixture during the kneading process.

The pulverization can be performed using a known method, such as a pulverization method using a pulverizer such as a hammer mill, cutter mill, or jet mill.

<Kneading process>
In the kneading step, the pulp pieces obtained in the pulverizing step, the thermoplastic resin, and the 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 pieces and the thermoplastic resin are added to the mixing device described later, or the pulp pieces and the thermoplastic resin may be added first and then after a desired period of time has elapsed. good. By adjusting the time from when the pulp pieces and the thermoplastic resin are added until when the flame retardant is added, it is possible to adjust the occupancy of the cellulose fibers, which has a flame retardant coverage of 15 to 60%.

The mixing method and kneading method are not particularly limited, and known methods can be used. In addition, when stirring in the mixing method, adjust the amount of flame retardant added and the rotation speed of the stirring machine (for example, 20 to 40 m/s), etc., so that the pulp becomes fibrous (hereinafter referred to as pulp fiber). Stir until. At this time, the pulp fibers are temporarily coated with the flame retardant. Then, in the kneading process, the pulp fibers are pulverized (defibrated) into fine cellulose fibers, and the cellulose fibers are kneaded with a thermoplastic resin and a flame retardant, and the flame retardant coated on the cellulose fibers is mixed with the molten thermoplastic resin. Adheres to resin. At this time, there are cases where the thermoplastic resin adheres to part or all of the surface of the cellulose fibers, and the flame retardant coats the outside of the resin, and the flame retardant coats the cellulose fibers. , there are cases where the flame retardant is directly coated on the cellulose fibers by being crimped onto the thermoplastic resin.

Examples of the mixing method (mixing device) include a method using a stirrer such as a Henschel mixer, a super mixer, and a ribbon mixer.

Examples of the kneading method include a method using a Banbury mixer, a method using a pressure roller, and the like. Further, for example, kneading can also be carried out using an extrusion molding machine such as a twin-screw extruder. In this case, the kneading process and the extrusion process described below are performed by an extrusion molding machine.

The kneading conditions are not particularly limited, but it is preferable that the heating temperature is equal to or higher than the softening point of the thermoplastic resin. By setting this temperature, the dispersion of cellulose fibers within the cellulose fiber resin composite material is promoted, and the cellulose fibers have excellent moldability due to their excellent fluidity when melted, and have excellent mechanical properties such as strength and elastic modulus. It becomes possible to obtain a resin composite material. Further, the kneading of the thermoplastic resin and the cellulose fibers progresses, and a uniformly dispersed cellulose fiber resin composite material without fiber lumps can be obtained. Furthermore, as the kneading of the cellulose fibers and flame retardant progresses, the coverage of the flame retardant in the cellulose fibers, the average coverage of the flame retardant in the cellulose fibers, and the coverage of the flame retardant contained in the cellulose fiber resin composite material will increase from 15 to 60%. It is now possible to adjust the occupancy of cellulose fibers within a preferable range, and to improve the mechanical properties such as tensile strength and flame retardance of composite molded products obtained from cellulose fiber resin composite materials. Can be done.

The kneading time or the number of times of kneading is not particularly limited, but for example, if the kneading time for one kneading is 5 to 60 seconds, kneading can be performed multiple times under the same conditions. The specific number of kneading times can be, for example, 2 to 5 times.

The rotation speed during kneading is not particularly limited, but can be, for example, 50 to 300 rpm.

<Extrusion process>
In the extrusion step, the resin mixture obtained in the kneading step is molded into a desired shape using a mold to form a cellulose fiber resin composite material.
The resin mixture obtained in the kneading step is heated and melted by an extruder and poured into a mold. The cast resin mixture is molded into a desired cross-sectional shape (a cross-sectional shape perpendicular to the axial direction of the columnar pellet) using a mold, and is discharged from the discharge port of the mold. The discharged molded resin mixture is cut into desired lengths to obtain a cellulose fiber resin composite material.

The heating conditions in the extrusion step are not particularly limited, but it is preferable that the heating temperature be equal to or higher than the softening point of the thermoplastic resin. By setting such a temperature, the cellulose fibers in the cellulose fiber resin composite material are oriented in the extrusion direction during extrusion molding.

A known extrusion molding machine can be used as the extrusion molding machine. Examples of the extrusion molding method include a method using a twin-screw extruder. A twin-screw extruder can be preferably used since it can be used for both kneading and extrusion molding.

When a twin-screw extruder is used, the number of rotations of the screws of the twin-screw extruder is not particularly limited, but can be, for example, 50 to 300 rpm. When the rotational speed of the screw is within this range, the flow of the resin mixture becomes smooth, so that the cellulose fibers of the cellulose fiber resin composite material can be easily oriented along the extrusion direction.

<<Applications of cellulose fiber resin composite materials>>
The cellulose fiber resin composite material of the present disclosure is preferably used as a raw material (for example, pellets) for a composite molded material by a molding method using a mold such as injection molding, a molding method using a 3D printer, or the like. Composite molded products are particularly suitable for use in molded parts for vehicles, equipment, equipment, etc. that have minute or complex structures, industrial materials such as containers, pallets, plastic cores, and building materials, daily necessities, and miscellaneous goods. be.

<<Preparation of cellulose fiber resin composite material>>
<Raw materials>
・Thermoplastic resin polypropylene (MG03BD manufactured by Novatec)
・Pulp (raw material for cellulose fiber)
Softwood pulp (NBKP manufactured by Canfor)
・Flame retardant Phosphorous flame retardant (Phosphorus flame retardant, Fireguard FCX-210 manufactured by Teijin Ltd.)
Halogen flame retardant (brominated flame retardant, SAYTEX8010 manufactured by ALBEMARLE JAPAN CORPORATION)
Boron-based flame retardant (manufactured by Wako Pure Chemical Industries, boric acid)

<Production of cellulose fiber resin composite materials of each example and each comparative example>
The amounts of pulp shown in Tables 1 and 2 were weighed and coarsely ground using a grinder until the pulp became pulp pieces with a length of 40 mm or less and a width of 10 mm or less.
The pulp pieces, the thermoplastic resin, and the flame retardant were dry blended to give the mass ratios shown in Tables 1 and 2 to obtain mixtures of each Example and each 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, respectively. The obtained kneaded materials of each Example and each Comparative Example were extruded through a mold and hot-cut to obtain cellulose fiber resin composite materials of each Example and each Comparative Example. The cellulose fiber resin composite material was made into a cylindrical pellet 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 extrusion molding machine.

<Measurement values of cellulose fiber resin composite materials of each example and each comparative example>
(Average fiber length of cellulose fiber)
The cellulose fiber resin composite materials of each example and each comparative example were cut in a plane parallel to the extrusion direction of the cellulose fiber resin composite material to form a cross section, and the cross section was observed with a scanning electron microscope. Fifty cellulose fibers were randomly selected, and the fiber lengths of the cellulose fibers were measured and calculated by taking a number average.

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

(Average coverage of cellulose fibers, occupancy of cellulose fibers with a coverage of 15 to 60%)
The average coverage of the cellulose fibers with the flame retardant in each Example and each Comparative Example was measured using the following procedure. The cellulose fiber resin composite materials of each example and each comparative example were cut in a plane perpendicular to the extrusion direction of the cellulose fiber resin composite material to form a cross section, and an area of 82 μm x 126 μm in the cross section was examined using a scanning electron microscope. SEM) at a magnification of 1000 times to obtain cross-sectional SEM images of each Example and each Comparative Example. Image analysis was performed on each cross-sectional SEM image obtained, and 20 cellulose fibers with a fiber cross-sectional circumference of 10 to 50 μm were randomly selected from among the cellulose fibers in the cross section. The covered length (covered length) was obtained, and the coverage rate was calculated according to the following formula.
Coverage rate = (Covering length) / (Perimeter) x 100 (%)
The coverage rates obtained for the 20 cellulose fibers selected for each Example and each Comparative Example were number-averaged, and this was taken as the average coverage rate for each Example and each Comparative Example. The results are shown in Tables 1 and 2.

The occupancy rate of cellulose fibers with a coverage rate of 15 to 60% in each Example and each Comparative Example is determined by Based on the number of cellulose fibers, the number of cellulose fibers with a coverage of 15 to 60% was counted, and the ratio with respect to the reference was defined as the occupancy. The results are shown in Tables 1 and 2.

＜＜Evaluation＞＞
<Flame retardant evaluation of composite molded products: Vertical flammability test (UL94V test)>
The flame retardancy of composite molded products obtained from the cellulose fiber resin composite materials of each Example and each Comparative Example by the following method was evaluated by a UL94V test. Evaluation was performed in accordance with ASTM D3801.
The test pieces of the composite molded products were injection molded cellulose fiber resin composite materials of each Example and each Comparative Example, and had a length of 125 ± 5 mm x width of 13 ± 0.5 mm x thickness of 5 mm. . Injection molding was carried out by drying the cellulose fiber resin composite materials of each example and each comparative example in a dryer at 80°C for 30 minutes, using an injection molding machine (manufactured by Nissei Jushi Kogyo Co., Ltd.: TD100-25ASE), and adjusting the cylinder temperature, The resin was melted at a nozzle temperature of 180° C. or 200° C., fed into a mold shaped like a test piece, and cooled to obtain a composite molded product (test piece).
Evaluation was performed on the vertical flammability test results according to the following judgment method. The results are shown in Tables 1 and 2.
(Judgment method)
In the vertical flammability test, those that met the following combustion behavior were classified as V0, V1, and V2, and those that did not meet any of the criteria were determined as nonconforming. In addition, the results in the table shown as "-" indicate that the test piece could not be molded and could not be evaluated.
・V0
The first afterflame time is 10 seconds or less, the total afterflame time of the five test pieces is 50 seconds or less, the second afterflame time + afterglow time is 30 seconds or less, and the clamp part is not burned. No, the drippings will not burn the cotton underneath.
・V1
The first afterflame time is 30 seconds or less, the total afterflame time of the five test pieces is 250 seconds or less, the second afterflame time + afterglow time is 60 seconds or less, and the clamp part is not burned. No, the drippings will not burn the cotton underneath.
・V2
The first afterflame time is 30 seconds or less, the total afterflame time of the five test pieces is 250 seconds or less, the second afterflame time + afterglow time is 60 seconds or less, and the clamp part is not burned. First, the drippings will burn the cotton underneath.

<Moldability evaluation of cellulose fiber resin composite material>
The cellulose fiber resin composite materials of each example and each comparative example were dried at 80°C for 30 minutes in a dryer, and using an injection molding machine (TD100-25ASE, manufactured by Nissei Jushi Kogyo Co., Ltd.), the cylinder temperature and nozzle temperature were both 180°C. ℃ or 200℃, feed it into a mold in the shape of a dumbbell-shaped test piece (the temperature of the mold was 60℃), cool it, and make composites of each example and each comparative example. A molded material was obtained. The dumbbell-shaped test piece had the dimensions of a plate-like test piece 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 determined by visual observation according to the following criteria. The results are shown in Tables 1 and 2.
(Judgment criteria)
A: The test piece can be successfully molded when the cylinder temperature and nozzle temperature are both 180°C and the injection pressure is 800 MPa or more and 1000 MPa or less. B: The test piece can be successfully molded when the cylinder temperature and nozzle temperature are both 180°C and the injection pressure is 800 MPa or more and 1000 MPa or less. The test piece cannot be molded properly if the injection pressure is over 1000 MPa and 1500 MPa or less. C: The test piece cannot be molded normally when the cylinder temperature and nozzle temperature are both 180°C and the injection pressure is over 1000 MPa and 15000 MPa or less. , the test piece can be successfully molded when the cylinder temperature and nozzle temperature are both 200°C and the injection pressure is 800 MPa or more and 1500 MPa or less. D: The test piece can be successfully molded when the cylinder temperature and nozzle temperature are both 180°C and the injection pressure is over 1000 MPa and 15000 MPa or less. cannot be molded, and the test piece cannot be properly molded when the cylinder temperature and nozzle temperature are both 200°C and the injection pressure is 800 MPa or more and 1500 MPa or less.

<Tensile strength test of composite molded product>
Dumbbell-shaped test pieces of composite material moldings of each Example and each Comparative Example prepared for moldability evaluation were tested using an Instron type material testing machine (manufactured by Shimadzu Corporation: Autograph AG25 TA) at a crosshead speed of 50 mm/ The tensile strength was measured from the load at breakage as min. The measurement results are shown in Tables 1 and 2. In addition, the results in the table shown as "-" indicate that the test piece could not be molded and could not be evaluated.

Claims (4)

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 content of the cellulose fiber 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,
At least a portion of the flame retardant coats the cellulose fibers,
A cellulose fiber resin composite material having an average coverage of the cellulose fibers with the flame retardant of 15% or more and 60% or less, as calculated by the following evaluation method.
(Coverage evaluation method)
An area of 82 μm x 126 μm in a cross section perpendicular to the extrusion direction obtained by extrusion molding the cellulose fiber resin composite material was imaged at a magnification of 1000 times using a scanning electron microscope (SEM), and a cross-sectional SEM image was obtained. get. The obtained cross-sectional SEM image was analyzed, 20 cellulose fibers in the cross section with a fiber cross-sectional circumference of 10 to 50 μm were randomly selected, and each cellulose fiber was The length covered by the flame retardant (covering length) is 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 cellulose fibers are number-averaged to obtain the average coverage rate. Based on the number of all cellulose fibers whose fiber cross section has a circumferential length of 10 to 50 μm included in the cross-sectional SEM image, the proportion of the number of cellulose fibers whose coverage is 15 to 60% is 80%. The cellulose fiber resin composite material according to claim 1, which is above. The cellulose fiber resin composite material according to claim 1 or 2, wherein the flame retardant includes either a phosphorus-based flame retardant or a halogen-based flame retardant. The thermoplastic resin includes any one 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, and polyester resin. The cellulose fiber resin composite material according to any one of claims 1 to 3, characterized by: