JP2011251455A - Fiber-reinforced resin pellet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fiber-reinforced resin pellet enhanced in strength and performance by solving a problem wherein the reinforcing effect of fibers is not sufficiently developed because the fibers are cut and the length of the fibers is reduced when fiber-reinforced resin is passed through the screw in a molding machine to injection-mold the fiber-reinforced resin pellet.SOLUTION: In the fiber-reinforced resin pellet containing vegetable fibers and resin, the length of the vegetable fibers is not less than critical fiber length (Lcr) represented by the formula (1) Lcr=σf×φf/(2×τ) (wherein σf is the tensile strength of the vegetable fibers, φf is the diameter of the vegetable fibers and τ is the interfacial adhesive strength between the vegetable fibers and the resin).

Description

The present invention relates to a fiber-reinforced resin pellet and a method for producing a fiber-reinforced resin pellet.

Conventionally, glass fibers having excellent strength have been used as reinforcing materials contained in fiber-reinforced plastics.
And thermal recycling which collects thermal energy by burning this fiber reinforced plastic was performed.

  However, the glass fiber contained in this fiber reinforced plastic is an incombustible material, causing damage to the combustion furnace and lowering the combustion efficiency. was there. For this reason, the fiber reinforced plastic which used glass fiber as a reinforcing material cannot be recycled appropriately.

  In order to deal with such problems, fiber reinforced plastics using natural fibers such as plant fibers as reinforcing materials have been proposed.

  For example, Patent Document 1 discloses a manufacturing method in which a natural fiber is used as a reinforcing fiber, and a fiber-reinforced resin pellet is manufactured by using a twisted yarn or impregnating a long natural fiber with a molten thermoplastic resin while twisting it. And fiber reinforced resin pellets are disclosed.

JP 2007-1225739 A

  However, in the fiber reinforced resin pellet of Patent Document 1, the resin does not spread sufficiently between individual natural fibers, resulting in poor fiber dispersion.

  As a result, when the produced fiber reinforced resin pellet is molded by injection molding, the fiber is cut when passing through the screw in the molding machine and the fiber length is shortened, so that the fiber reinforcing effect cannot be sufficiently achieved.

  Therefore, an object of the present invention is to solve the above-described problems and provide a fiber-reinforced resin pellet having high strength performance.

In order to achieve the above object, the fiber reinforced resin pellet is a fiber reinforced resin pellet containing a plant fiber and a resin, and the fiber length of the plant fiber is represented by the critical fiber length (Lcr) represented by the formula (1). It is the above length.
Lcr = σf × Φf / (2 × τ) (1)
(Where σf is the tensile strength of the plant fiber, Φf is the diameter of the plant fiber, and τ is the interfacial bond strength between the plant fiber and the resin)
Furthermore, in order to achieve the said objective, the manufacturing method of a fiber reinforced resin pellet is a manufacturing method which makes a plant fiber impregnate the melted resin and manufactures a fiber reinforced resin pellet, Comprising: 100 Mpa or more and 800 MPa or less are made to a plant fiber. This is a method for producing fiber-reinforced resin pellets characterized in that plant fibers are mixed into a molten resin by applying a tensile force.

  As mentioned above, according to the manufacturing method of the fiber reinforced resin pellet and fiber reinforced resin pellet of this invention, a fiber reinforced resin pellet with high intensity | strength performance can be provided.

The figure which shows the manufacturing equipment of the fiber reinforced resin pellet The figure which shows the experimental result of each fiber reinforced resin pellet

The fiber reinforced resin pellet of the present invention is a fiber reinforced resin pellet containing plant fibers and a resin, and the fiber length of the plant fibers is equal to or longer than the critical fiber length (Lcr) represented by the formula (1). It is characterized by being.
Lcr = σf × Φf / (2 × τ) (1)
(Where σf is the tensile strength of the plant fiber, Φf is the diameter of the plant fiber, and τ is the interfacial bond strength between the plant fiber and the resin)
1. 1st Embodiment 1-1, fiber reinforced resin pellet 1-1-1, plant fiber The plant fiber used for this invention is a leaf fiber obtained from wood fiber derived from wood, New Zealand hemp, Manila hemp, sisal hemp, cannabis, Bast fiber and coconut fiber obtained from hemp such as flax, jute, kenaf, ramie. These plant fibers are composed of cellulose, hemicellulose, lignin, pectin and the like.
In particular, bast fibers are generally used as processed twisted yarns or processed products of twisted yarns.
More specifically, it is used for ropes used as materials, hemp bags used for transportation and storage of grains, and clothing characterized by a refreshing feeling.
The bast fiber is present in the plant body as a bundling of bast fibers in which a plurality of bast fibers are bundled in the bast portion on the outer periphery of the stem.

The plant fiber used in the present embodiment has a fiber length that satisfies the critical fiber length or more.
Here, when the tensile force is applied to the fiber reinforced resin pellet with the critical fiber length, the axial force applied to the reinforcing material in the fiber reinforced resin pellet reaches the yield stress of the plant fiber, and the reinforcing material breaks. It is defined as length.

A plant fiber having a fiber length equal to or greater than the critical fiber length is in a form to bear an external force corresponding to the tensile strength of the plant fiber. Therefore, the function as a reinforcing material is drawn out to the maximum. Therefore, it becomes the fiber form which can draw out the strength characteristic of fiber reinforced plastic most.
More specifically, the critical fiber length of plant fibers will be described using [Formula 1].
From the balance of the forces in the longitudinal direction of the plant fibers, the critical fiber length of the plant fibers can be expressed as [Equation 1].
Lcr = σf × Φf / (2 × τ) (1)
However, (sigma) f shows the tensile strength of a vegetable fiber, (PHI) f shows the diameter of a vegetable fiber, (tau) shows the interface adhesive strength between a vegetable fiber and resin.
In addition, the diameter of a vegetable fiber is the value which averaged the diameter of the cross section when cross-sectional cut | disconnecting three places perpendicular | vertical with respect to the fiber longitudinal direction of a vegetable fiber.
The tensile strength σf of the plant fiber was determined by preparing a tensile test piece from the plant fiber by the method described in JIS L 1069, and performing a tensile test with a universal testing machine (universal testing machine Autograph AGS-500NX, manufactured by Shimadzu Corporation). It is calculated by doing.
The diameter Φf of the plant fiber is measured with a microscope (microscope VHX-1000, manufactured by Keyence Corporation).
The interfacial adhesive strength τ between the plant fiber and the resin is obtained by applying a load to a test piece embedded in a resin in which one plant fiber is combined, and a universal testing machine (universal testing machine Autograph AGS-500NX, Inc. Calculated by measuring the force of pulling out the plant fiber by Shimadzu Corporation).

In this embodiment, as an example of a plant fiber having a fiber length equal to or longer than the critical fiber length, a raw grass in which a plurality of bast fibers obtained from hemp are combined is used.
This raw grass is obtained through the following steps [1] to [3].
[1] The harvested raw stem is immersed in water for about 1 to 2 weeks for fermentation (immersion fermentation), and the bast portion on the outer periphery of the stem is peeled off.
[2] The peeled bast portion is washed with water to remove impurities.
[3] Dry and carefully select the bast portion from which impurities have been removed.

The volume content of the plant fiber with respect to the fiber reinforced resin pellet is preferably 5 vol% or more and 60 vol% or less when the volume of the fiber reinforced resin pellet is 100.
If the volume content of the plant fiber in the fiber reinforced resin pellet exceeds 60 vol%, when molding the fiber reinforced resin pellet, the fluidity of the resin melted in the plant fiber cannot be secured, and molding failure may occur. Is expensive.
On the other hand, when the volume content of the plant fiber is less than 5 vol%, the resin is not sufficiently reinforced.
In addition, the plant fiber used by this embodiment may be individual, or 2 or more types may be sufficient as it.

1-1-2, Resin As the resin used in the present embodiment, the following resins can be used.
For example, polystyrene, acrylonitrile-styrene copolymer resin, polystyrene resin such as acrylonitrile-butadiene-styrene copolymer resin, polyolefin resin such as polyethylene and polypropylene, thermoplastic polyester resin such as polyethylene terephthalate and polybutylene terephthalate, vinyl chloride, Halogen-containing polyolefin resins such as chlorinated polypropylene, polyamide resins such as 6-nylon, 6,6-nylon, 4,6-nylon, 11-nylon, 12-nylon, and aromatic nylon, polyethyl acrylate, polymethyl methacrylate, etc. Acrylic resin, sulfonic acid resin, amorphous polyarylate resin, polyetherimide resin, polyamideimide resin, polyimide resin, polyanil ether elnitrile resin, polyether Sulfone resin, polyphenyl ether resin, polyacetal resin, liquid crystalline aromatic polyester resin, polyphenyl ether resin, polyphenylene sulfide resin, polyether ketone resin, polyether ether ketone resin, polybenzimidazole resin, biodegradable thermoplastic resin Etc.

Furthermore, examples of biodegradable thermoplastic resins include polylactic acid, polybutylene succinate adipate, polybutylene succinate carbonate, polyethylene succinate, captolactone, polyesteramide, modified polyester, polyester carbonate, polybutylene succinate carbonate. And chemical synthetic resins such as polyvinyl alcohol, microorganism-producing resins such as polyhydroxybutyrate valerate, polyhydroxybutyrate, and pullulan, and natural product resins such as cellulose acetate and starch / aliphatic polyester.
These resins may be used alone or in combination of two or more.

  In the resin shown above, for example, a thermoplastic resin that is sufficiently melted at a heating temperature of 220 ° C. or more and hardly undergoes modification due to heat, such as polypropylene, is more preferable. For example, polypropylene is the lightest thermoplastic resin among general-purpose resins. Therefore, a lightweight and high-strength fiber-reinforced resin pellet can be obtained by combining polypropylene and plant fibers.

  When general-purpose extrusion molding or injection molding is used, the volume content of the resin relative to the fiber-reinforced resin pellet is preferably 40 vol% or more and 95 vol% or less. If the volume content of the resin exceeds 95 vol%, the reinforcing effect of the resin in the fiber reinforced resin pellet is not sufficient. On the other hand, when the resin content is less than 40 vol%, when molding fiber reinforced resin pellets, the fluidity of the resin melted in the plant fibers cannot be secured, and there is a high possibility that molding defects will occur.

1-2. Manufacturing method of fiber reinforced resin pellet Next, the manufacturing method of the fiber reinforced resin pellet in this Embodiment is demonstrated using FIG. FIG. 1 shows a production apparatus for producing fiber-reinforced resin pellets. In the method for producing fiber-reinforced resin pellets in the present embodiment, a bundle 2 of plant fibers is drawn through a crosshead die 4 to which a thermoplastic resin 6 melted by a kneading extruder 5 is supplied.
More specifically, fiber reinforced resin pellets are produced by the following method. First, a bundle 2 of vegetable fibers fed out from the creel 1 is guided to a crosshead die 4 through a guide roll 3. Therefore, the creel 1 is required to have a function capable of controlling the tension of the bundle 2 of plant fibers to be delivered.

  The temperature in the crosshead die 4 is set in consideration of the melting temperature of the thermoplastic resin to be used. A temperature equal to or higher than the melting temperature of the thermoplastic resin is required, and the higher the temperature in the crosshead die 4, the higher the impregnation rate can be expected as the resin viscosity decreases. However, it is necessary to pay attention to the thermal decomposition temperature of plant fibers and thermoplastic resins. For example, there is cellulose which is a main component of plant fiber and has an excellent reinforcing effect. Accordingly, the temperature is preferably set to about 220 ° C. or less in order to suppress the thermal decomposition of cellulose.

  In the bundle 2 of plant fibers, individual plant fibers are bound with a weak binding force by lignin, pectin or the like. Therefore, when the vegetable fiber bundle 2 is passed through the molten resin bath in the crosshead die 4, it is preferable to apply a tension of 100 to 800 MPa to the vegetable fiber bundle 2. By applying tension, the weak bond is broken and the individual plant fibers are cleaved by shearing force. When the bundle 2 of plant fibers passes through the molten resin bath in the crosshead die 4 or between the rollers 7 by the cleavage, the molten resin is efficiently impregnated between the plant fibers. This is because more space is secured for the molten resin to easily penetrate between the plant fibers. However, care must be taken so that the bundle 2 of plant fibers does not break due to an overload of tension.

  Furthermore, there is a method of utilizing a mesh as a method of replacing tension. For example, a mesh is placed immediately before the bundle 2 of plant fibers passes through the crosshead die 4. As a result, it is possible to mechanically dissociate the partial weak bond due to lignin and pectin remaining between the plant fibers. By passing the plant fiber bundle 2 through the crosshead die 4 in a state where the individual plant fibers are separated, it is possible to more efficiently impregnate the thermoplastic resin up to the center of the plant fiber bundle 2. It becomes. The mesh opening to be arranged is determined according to the diameter of the plant fiber, but it is preferable to use a mesh having an opening of 500 μm or less.

  Thereafter, the bundle 2 of the plant fibers impregnated with the resin is passed through at least two or more rollers 7 that freely rotate in a columnar shape placed perpendicular to the longitudinal direction of the fibers. The roller 7 has a role of impregnating the inside of the bundle 2 of plant fibers with the resin adhering to the surface of the bundle 2 of plant fibers.

  Therefore, in order to allow the bundle 2 of plant fibers to reach the roller 7 in a molten state where the thermoplastic resin does not solidify, it is preferable that the distance between the crosshead die 4 and the roller 7 is short.

  A short distance between the crosshead die 4 and the roller 7 contributes to an improvement in production speed. After passing through the roller 7, it is cut into a predetermined length by a pelletizer 9 to produce a fiber reinforced resin pellet.

2. Second Embodiment Next, a second embodiment of the present invention will be described. In the fiber reinforced resin pellet and the method for producing the fiber reinforced resin pellet in the second embodiment, only differences from the fiber reinforced resin pellet in the first embodiment will be described, and the other description will be omitted.

2-1, Fiber Reinforced Resin Pellet 2-1-1, Silane Coupling Agent The fiber reinforced resin pellet of the second embodiment uses a silane coupling agent in addition to the plant fiber and the resin.
Below, a silane coupling agent is demonstrated in detail.
Examples of silane coupling agents include vinyl-based compounds such as vinyltrimethoxysilane, styryltrimethoxysilane, and metalryloxyalkyltrimethoxysilane, and methacryloxy compounds such as 3-methacryloxypropylmethyldimethoxysilane and 3-methacryloxypropyltrimethoxysilane. An epoxy system such as glycidoxypropyltrimethoxysilane, an amino system such as aminoalkyltrimethoxysilane, and an isocyanate system such as isocyanate alkyltrimethoxysilane can be used.

  By using the silane coupling agent, when injection molding is performed, the strength by controlling the interface between the plant fiber and the resin is improved, and it becomes possible to provide a fiber-reinforced resin pellet having an excellent reinforcing effect. The alkoxy group contained in the silane coupling agent reacts with moisture in the air or in the plant fiber to generate a silanol group, and this silanol group undergoes dehydration condensation with the hydroxyl group of cellulose contained in the plant fiber 2. Moreover, a siloxane bond is formed by condensation of silanol groups that do not react with cellulose.

  On the other hand, functional groups other than alkoxy groups in the silane coupling agent react with the functional groups of the resin. For example, an epoxy group reacts with a polyester resin or an acrylic resin. Vinyl groups and methacryloxy groups react with polypropylene resins. Furthermore, amino groups react with acrylic resins and polystyrene resins, and isocyanurate groups react with urethane resins.

Therefore, by using the silane coupling agent, the plant fiber and the resin are bonded via the silane coupling agent, and the interfacial adhesive force between the resin and the plant fiber is greatly improved.
The amount of the silane coupling agent added is not particularly limited, but is preferably 0.5 wt% or more and 2.0 wt% or less with respect to the plant fiber, for example.
It is also conceivable to refer to the treatment amount calculated by the general formula such as the following formula (2) as the addition amount of the silane coupling agent necessary for covering the plant fiber with the monomolecular film.
(Treatment amount of silane coupling agent (g)) = (weight of plant fiber (g)) × (specific surface area of plant fiber (m ² / g)) / (minimum coverage area of silane coupling agent (m ² / g))
... Formula (2)
2-1-2, Plant Fiber As the plant fiber, the same raw grass as in the first embodiment is used, no twisted yarn is used, and the plant fiber bundle 2 does not contain impurities such as mineral oil. .

  Normally, when using raw grass such as jute fiber, during processing from raw grass to twisted yarn, mineral oil is added to the raw grass and subjected to fermentation by controlling temperature and time, carding and It goes through a process called. In this process, the fibers are loosened and wound up in the manner of scratching with a needle. And after passing through this process, the fiber is twisted and processed into a twisted yarn. In any case, a fermentation process using mineral oil is entered at the stage of processing twisted yarn from raw grass. Mineral oil has glycerin and fatty acid esters as main components. Mineral oil is deposited on the vegetable fiber and is on the fiber surface of the twisted yarn. This prevents the silane coupling agent from approaching and acting on the plant fiber 2 due to the presence of the ester when twisted yarn is used as a raw material for the plant fiber.

  However, in the present invention, raw grass is used as the plant fiber 2. Accordingly, the silane coupling agent imparts stronger affinity between the plant fiber 2 and the resin, and the uniform dispersion of the plant fiber in the resin is promoted.

  As a result, it becomes possible to use the plant fiber in a form with a higher aspect ratio, and it is possible to improve the reinforcing effect of the plant fiber.

  Furthermore, the effect which prevents the fiber cutting | disconnection by the screw of a cylinder part in the injection molding used as a general purpose molding method for shape | molding a molding material from a fiber reinforced resin pellet is shown. This is because the molten resin is in a form covering the periphery of the plant fiber, so that the shearing force applied to the plant fiber itself can be relaxed.

2-1-3 Resin When a silane coupling agent is used, it is preferable to use a resin that is reactive or compatible with a functional group other than the alkoxy group of the coupling agent.
For example, when polypropylene is used, it is preferable to use a vinyl or methacryloxy silane coupling agent.

2-2, Method for Producing Fiber Reinforced Resin Pellets There are two possible methods for producing fiber reinforced resin pellets using a silane coupling agent.

  That is, it is divided into the case where a plant fiber is pretreated with a silane coupling agent and the case where a resin is pretreated with a silane coupling agent.

  The treatment effect is higher when the plant fiber is treated first, but the method with fewer steps and excellent workability is the method of treating the resin first.

  The melting temperature of the resin set in any case is selected in consideration of the reaction temperature of the silane coupling agent used as the treatment agent for the plant fiber 2.

2-2-1. When a plant fiber is previously treated with a silane coupling agent First, a silane coupling agent solution is prepared. First, an acetic acid aqueous solution having a concentration of 0.1 to 2.0% is prepared. Some aminosilane coupling agents do not require the use of water to prepare an aqueous acetic acid solution. A silane coupling agent is added dropwise while stirring an aqueous acetic acid solution or water. The concentration of the silane coupling agent is preferably from 0.1 to 2.0%. After completion of dropping the silane coupling agent, stirring is further continued for 30 to 60 minutes to complete hydrolysis of the silane coupling agent. The reason why the silane coupling agent is dropped into the weakly acidic solution using acetic acid is to suppress the condensation reaction of silanol groups generated from the alkoxy groups in the silane coupling agent. However, in some aminosilane coupling agents, the condensation reaction of the silanol group is suppressed by the interaction between the amino group and the silanol group, so that it is not necessary to add acetic acid.

Next, the plant fiber bundle 2 is treated with a silane coupling agent solution. Stir the aqueous solution of the silane coupling agent prepared above again, add the bundle 2 of plant fibers, and stir at room temperature for another 30 to 60 minutes. After stirring, the solution is filtered to remove excess aqueous solution of the silane coupling agent.
The obtained bundle 2 of plant fibers with the silane coupling agent attached to the surface is dried at 105 ° C.
Further, the bundle of plant fibers 2 treated with the silane coupling agent and the resin are combined. The mixture of the silane coupling agent obtained above and the bundle 2 of plant fibers is sent out from the creel 1 and combined with the resin.

2-2-2. When the resin is previously treated with a silane coupling agent A predetermined amount of the silane coupling agent is mixed with the total amount of the resin to be used, and the mixture is introduced into the kneading extruder 5 to pass through the bundle 2 of plant fibers. Is supplied to the crosshead die 4 to be combined with the plant fiber.
A predetermined amount of the silane coupling agent may be mixed with a part of the resin to be used, and the resulting mixture may be fed into the kneading extruder 5 as a master batch.

3. Other Embodiments The first embodiment and the second embodiment have been described above. However, the present invention is not limited to these embodiments. Therefore, other embodiments of the present invention will be described collectively in this section. Plant fibers may be used alone or in combination of two or more. In addition to the silane coupling agent, a flame retardant, a pigment, and a conductive filler may be used. When these additives are used, as in the case of the silane coupling agent, together with the resin, they are put into the kneading extruder 5 to be combined with plant fibers.
Hereinafter, specific types of flame retardants, pigments, and conductive fillers and effects to be used will be described.

3-1. Flame retardant Specific examples include aluminum hydroxide, magnesium hydroxide, and phosphorus compounds.
The flame retardant is used for flame retardant resin. One of the flame retardant mechanisms of aluminum hydroxide and magnesium hydroxide causes dehydration reaction at high temperatures, and the polyphosphoric acid and phosphoric acid ester in phosphorus compounds, which is an air barrier effect by the generated water vapor, has long been a cellulosic fiber Has been used as a flame retardant.

3-2, Pigments Specific examples include titanium oxide, zinc oxide, and carbon black. The pigment performs the coloring function of the resin. In particular, titanium oxide and zinc oxide are typical white pigments, and carbon black is a typical black pigment.

3-3, conductive filler Specific examples include stainless steel fiber, graphite fiber, and carbon black. The conductive filler imparts conductivity to the resin material. Since imparting conductivity requires formation of a conductive path, a high aspect ratio filler is used.

4. Experiments Fiber reinforced resin pellets in each embodiment were manufactured, the critical fiber length of the fiber reinforced resin pellets made, the fiber length of the fiber reinforced resin molded material formed by injection molding of the fiber reinforced resin pellets, and the bending strength The measurement results are shown in FIG. In addition, the critical fiber length of the vegetable fiber in the fiber reinforced resin molding material shape | molded with the injection molding machine shows the same value as the critical fiber length in a fiber reinforced resin pellet. For example, when the critical fiber length in the fiber reinforced resin pellet is 10.9 mm, the critical fiber length of the plant fiber in the fiber reinforced resin molded material is also 10.9 mm.

4-1, Experiment 1
In this experiment, jute fiber was used as the plant fiber, and polypropylene (Novatech MA1B (Nippon Polypro Co., Ltd.)) was used as the resin.The ratio of the jute fiber and the resin combined was plant fiber / resin = 20/80. When the plant fiber and the resin were combined, the temperature in the crosshead die 4 was 200 ° C. Further, the pellet length was cut with a pelletizer 9 so as to be 20 mm. In the pellet, the critical fiber length of the plant fiber was measured based on the formula (1), σf (plant fiber tensile strength) was 600 MPa, Φf (plant fiber diameter) was 100 μm, τ (between plant fiber and resin) The interfacial adhesive strength of the plant fiber was 2.75 MPa, and thus the critical fiber length of the plant fiber in the produced fiber-reinforced resin pellet was 10.9 mm.

Furthermore, the fiber reinforced resin molding material was manufactured from the fiber reinforced resin pellet with the injection molding machine (not shown). In the injection molding machine, for example, fiber reinforced resin pellets are put into a hopper, and after the injection, the fiber reinforced resin pellets in the cylinder are injected into a mold by the rotation of a screw and molded as a fiber reinforced resin molding material. In this experiment, an injection molding machine shown below was used.
Screw diameter (D) is 50 mm, screw length (L) / screw diameter (D) is 17, compression ratio is 1.7, screw groove depth (supply part) is 9.0 mm, screw nozzle diameter is It was 6.0 mm. The molding conditions for injection molding were as shown below.

  The fiber reinforced resin pellets before being put into the hopper were pre-dried at 105 ° C. for 4 hours. The cylinder temperature was set to a temperature gradient, the front part being 190 ° C., the middle part being 170 ° C., and the rear part being 150 ° C. The mold temperature was 50 ° C. Furthermore, the screw rotation speed was set to 80 rpm, and the mold was pressed from the mold to the cylinder side with a back pressure of 5 MPa. Note that the gate shape of the mold is a direct gate.

  Furthermore, the fiber strength and bending strength (MPa) were measured in order to evaluate the fiber length and strength performance of the fiber reinforced resin molded material molded by an injection molding machine. The fiber length of the vegetable fiber in the fiber reinforced resin molded material was 12 mm. The bending strength was measured by a method based on the ASTM standard. The bending strength was 53 MPa.

4-2, Experiment 2
Only differences from Experimental Example 1 will be described. In Experimental Example 1, a silane coupling agent was further used.
As the silane coupling agent, a methacryloxy silane coupling agent (KBM-503, Shin-Etsu Chemical Co., Ltd.) was used. The addition amount of the silane coupling agent was 1.5 wt% with respect to the plant fiber. More specifically, the silane coupling agent was dropped into a 1.0% acetic acid aqueous solution, and stirring was continued for 60 minutes after the dropping. The prepared aqueous solution of the silane coupling agent was stirred again, the plant fiber was added, and the mixture was further stirred at room temperature for 60 minutes.

In the fiber reinforced resin pellet of Experiment 2, the critical fiber length of the plant fiber was measured based on the formula (1). σf (tensile strength of plant fiber) was 600 MPa, Φf (plant fiber diameter) was 100 μm, and τ (interfacial bond strength between plant fiber and resin) was 3.37 MPa. Therefore, the critical fiber length of the plant fiber in the manufactured fiber reinforced resin pellet was 8.9 mm.
Furthermore, in the fiber reinforced resin molding material molded with the injection molding machine, the bending strength was measured in order to evaluate the fiber length and strength performance of the plant fiber. The fiber length of the vegetable fiber in the fiber reinforced resin molded material was 15 mm. The bending strength was 58 MPa.

4-3, Comparative experiment 1
Only differences from Experimental Example 1 will be described. In this comparative experiment, injection molding was performed using only polypropylene resin without using plant fibers.
Then, the bending strength of the fiber reinforced resin molded material was 43 MPa.

4-4, comparative experiment 2
Only differences from Experimental Example 1 will be described. In this comparative experiment, plant fibers were simultaneously added together with polypropylene resin using a twin-screw kneading extruder and kneaded.
The critical fiber length of the plant fiber in the produced fiber reinforced resin pellet was 10.9 mm. Furthermore, the fiber reinforced resin molding material was shape | molded with the injection molding machine. The fiber length of the vegetable fiber in the fiber reinforced resin molded material was 0.8 mm. The bending strength was 45 MPa.

4-5, comparative experiment 3
Only differences from Experimental Example 1 will be described. In this comparative experiment, a twisted yarn having a diameter of 1.5 mm was used as a raw material for plant fibers. The compounding method with the resin was carried out in the same manner as in Experimental Example 1 except that the raw material of the plant fiber was different.
The critical fiber length of the plant fiber in the produced fiber reinforced resin pellet was 10.9 mm. Furthermore, the fiber reinforced resin molding material was shape | molded with the injection molding machine. The fiber length of the vegetable fiber in the fiber reinforced resin molded material was 0.8 mm. The bending strength was 46 MPa.

5. Summary of Experimental Results From the above experimental examples and comparative examples, the following were found.
(1)
The critical fiber length of the fiber reinforced resin pellet in Example 1 was 10.9 mm. Moreover, the fiber length of the vegetable fiber in a fiber reinforced resin molding material was 12 mm.
Therefore, in the fiber reinforced resin pellet containing the vegetable fiber and the resin, the fiber length of the vegetable fiber is not less than the critical fiber length (Lcr) represented by the formula (1). It was found that the pellets had a higher bending strength than the comparative examples 1, 2, and 3 in the fiber reinforced resin molded material.
Lcr = σf × Φf / (2 × τ) (1)
(However, σf represents the tensile strength of the plant fiber, Φf represents the diameter of the plant fiber, and τ represents the interfacial adhesive strength between the plant fiber and the resin.)
(2)
The critical fiber length of the fiber reinforced resin pellet in Example 2 was 10.9 mm. Moreover, the fiber length of the vegetable fiber in a fiber reinforced resin molding material was 15 mm.

  Therefore, the fiber-reinforced resin pellet according to (1) is characterized by using a vinyl-based or methacryloxy-based silane coupling agent, so that the bending strength of the fiber-reinforced resin molded material is a comparative example. It was found to be larger than 1, 2, and 3. Further, it was found that the bending strength was greater than that of Experimental Example 1.

  The fiber-reinforced resin pellet and the method for producing the fiber-reinforced resin pellet according to the present invention can provide a fiber-reinforced resin pellet having higher strength.

DESCRIPTION OF SYMBOLS 1 Creel 2 Bundle of vegetable fiber 3 Guide roll 4 Crosshead die 5 Kneading extruder 6 Thermoplastic resin 7 Roller 8 Take-out device 9 Pelletizer

Claims (9)

In fiber reinforced resin pellets containing plant fiber and resin,
A fiber-reinforced resin pellet, wherein the vegetable fiber has a length equal to or longer than the critical fiber length (Lcr) represented by the formula (1).
Lcr = σf × Φf / (2 × τ) (1)
(However, σf represents the tensile strength of the plant fiber, Φf represents the diameter of the plant fiber, and τ represents the interfacial adhesive strength between the plant fiber and the resin.)   The fiber reinforced resin pellet according to claim 1, wherein the plant fiber is oriented in a longitudinal direction of the pellet. In the plant fiber,
The fiber reinforced resin pellet according to claim 1, wherein the fiber length is the same length as the fiber reinforced resin pellet.   The fiber-reinforced resin pellet according to claim 1, wherein the plant fiber is a raw grass obtained from a bast portion of hemp.   The fiber-reinforced resin pellet according to claim 1, wherein a vinyl-based or methacryloxy-based silane coupling agent is used. A manufacturing method for producing fiber-reinforced resin pellets by impregnating a molten resin into a plant fiber,
A method for producing fiber-reinforced resin pellets, wherein a tensile force of 100 MPa to 800 MPa is applied to the plant fiber to mix the plant fiber into a molten resin. In a method for producing a resin composition for producing a resin composition comprising a plant fiber and a resin,
Passing the plant fibers through a mesh having an opening of 500 μm or less; mixing the plant fibers that have passed through the mesh into the molten resin; and
The manufacturing method of the fiber reinforced resin pellet of Claim 6 characterized by the above-mentioned.   The method for producing fiber-reinforced resin pellets according to claim 6, further comprising a step of adding a silane coupling agent to the plant fiber and the resin. In the fiber reinforced resin molding material in which the fiber reinforced resin pellet according to any one of claims 1 to 5 is injection-molded,
The fiber reinforced resin molding material characterized by the fiber length of the said vegetable fiber being the length more than the critical fiber length (Lcr) represented by Formula (1).
Lcr = σf × Φf / (2 × τ) (1)
(However, σf represents the tensile strength of the plant fiber, Φf represents the diameter of the plant fiber, and τ represents the interfacial adhesive strength between the plant fiber and the resin.)

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