JP2008208188A - Method for producing filler for polyamide resin, and particle dispersion reinforced polyamide resin - Google Patents

Abstract

Disclosed is a graphite filler that is finely and uniformly dispersed in a polyamide resin, and a particle dispersion-strengthened polyamide resin having excellent mechanical properties.
In a method for producing a filler for polyamide resin, a raw material mixing step of forming a mixed liquid containing at least graphite particles, a substrate having an affinity for polyamide (preferably ε-caprolactam), a grinding medium, and a solvent; A wet stirring step in which the mixed liquid is stirred (preferably treated with a bead mill) to grind the graphite particles, and the cleavage plane thereof is chemically modified with the substrate; and a medium recovery step in which the grinding medium is recovered. And a desolvation step for removing the solvent.
[Selection] Figure 3

Description

  The present invention belongs to a technical field related to a filler filled to reinforce a polyamide resin, and a particle dispersion strengthened polyamide resin in which the filler is dispersed and reinforced in a matrix.

  Polyamide resin is a thermoplastic polymer that has excellent mechanical properties (toughness, impact resistance) at high temperatures and excellent chemical resistance among thermoplastic polymers. Widely used for members. In addition, the polyamide resin has a high affinity with other substances, so that it is compounded and exhibits further excellent characteristics.

  In the case of a composite polyamide resin used in a high temperature / corrosive atmosphere, naturally, the chemicals to be filled in the polyamide resin are also required to have high chemical resistance. Therefore, a composite polyamide resin obtained by using carbon fine particles having excellent chemical resistance as a filler and dispersing it in a matrix is suitable for use in such an atmosphere.

The carbon fine particles used as a filler for such a composite polyamide resin are desired to have a large aspect ratio from the viewpoint of improving mechanical properties.
As a conventional method for obtaining such carbon fine particles having a large aspect ratio, a method is known in which expanded graphite obtained by the sulfuric acid method is wet-ground to form fine particles (for example, Patent Document 1).
JP-A-8-217434

However, in the technique disclosed in Patent Document 1, the ground graphite fine particles have a high adsorptive power on the cleaved surface, and therefore, the fine particles tend to aggregate. For this reason, even if it is melt kneaded with polyamide, it is difficult to uniformly and finely disperse the graphite fine particles in the matrix, and the sufficient reinforcing effect of the composite polyamide resin cannot be obtained (comparison of FIG. 3B). See example).
An object of the present invention is to solve the above-mentioned problems by providing a graphite fine particle filler that can be finely and uniformly dispersed in a polyamide matrix, and a particle dispersion-strengthened polyamide resin having excellent mechanical properties. The purpose is to provide.

In order to solve the above-described problems, the invention of claim 1 is a method for producing a filler for polyamide resin, comprising: a mixed solution containing at least graphite particles, a substrate having affinity for polyamide, a grinding medium, and a solvent. A raw material mixing step to form, a wet stirring step of grinding the graphite particles by stirring the mixed solution and chemically modifying the cleavage plane with the substrate, a medium recovery step of recovering the grinding medium, and And a desolvation step for removing the solvent.
When the invention is configured in this way, the fine particles produced by grinding the graphite particles are chemically adsorbed by the substrate, so that the adsorptivity is reduced. For this reason, the produced filler for polyamide resin suppresses aggregation of fine particles.

According to a second aspect of the present invention, in the method for producing a filler for polyamide resin according to the first aspect, the substrate is ε-caprolactam.
The invention thus configured improves the dispersibility of the graphite filler in the polyamide resin matrix during kneading.

According to a third aspect of the present invention, in the method for producing a filler for polyamide resin according to the first or second aspect, the wet stirring step is performed by immersing the liquid mixture in a container containing the liquid mixture and the liquid mixture. The grinding medium is a spherical body having a diameter in the range of 0.1 to 2 mm.
When the invention is configured in this way, the fine particles produced by grinding the graphite particles are adjusted to a size and aspect ratio suitable for the particle dispersion strengthened polyamide resin.

According to a fourth aspect of the present invention, in the particle dispersion-strengthened polyamide resin, the polyamide resin filler produced by the method for producing a polyamide resin filler according to any one of claims 1 to 3 is a polyamide. It is characterized by being dispersed in a resin matrix.
With this configuration, the fine particles of graphite filled in the particle dispersion-strengthened polyamide resin are finely formed in the matrix because the surface thereof is chemically modified with a substrate having an affinity for polyamide. It contributes to improving the mechanical properties of the resin.

  ADVANTAGE OF THE INVENTION According to this invention, the filler of the fine particle of graphite which can be disperse | distributed finely and uniformly in the matrix of polyamide, and the particle dispersion strengthening type polyamide resin excellent in a mechanical characteristic can be provided.

  In the present invention, graphite particles used as a raw material for a filler for polyamide resin (hereinafter sometimes simply referred to as “filler”) are bulk graphite (Vein Graphite) obtained by ore refining a natural product, scaly It is derived from graphite (Flake Graphite), earth-like graphite (Amorphous Graphite), artificial graphite (Artificial Graphite) graphitized by heat-treating coke, and scaly graphite is chemically treated and then heated to expand. Or expanded graphite.

Here, the graphite (Graphite) has a structure in which a plurality of turtle shell-like layers are laminated. The plane of one layer constituting the graphite has a strong carbon-carbon bond due to a covalent bond, but the layers are bonded with a weak van der Waals force.
For this reason, graphite is easy to exfoliate (cleave) into layers, and fine particles having a large aspect ratio are easily generated by mechanical grinding. The fine particles of graphite that have been ground have the property that their cleavage faces are attracted by van der Waals forces and are likely to aggregate.

Next, the polyamide resin that can be applied as a matrix of the particle dispersion-strengthened polyamide resin of the present invention (hereinafter sometimes simply referred to as “complexed polyamide resin”) includes an aliphatic skeleton and a large number of monomers by amide bonds. Refers to a polymer formed by bonding.
Polyamide resins include “n-nylon” synthesized by polycondensation reaction of ω amino acids and “n, m-nylon” synthesized by co-condensation polymerization reaction of diamine and dicarboxylic acid.

As “n-nylon”, nylon 6 obtained by polycondensation reaction of ε-caprolactam (carbon number 6), nylon 11 obtained by polycondensation reaction of undecane lactam (carbon number 11), lauryl lactam (carbon number 12) And nylon 12 produced by polycondensation reaction.
Examples of “n, m-nylon” include nylon 66 obtained by co-condensation polymerization of hexamethylenediamine (carbon number 6) and adipic acid (carbon number 6), hexamethylenediamine (carbon number 6) and sebacic acid ( Nylon 610 obtained by co-condensation polymerization with 10 carbon atoms, nylon 6T obtained by co-condensation polymerization of hexamethylene diamine (6 carbon atoms) and terephthalic acid, hexamethylene diamine (6 carbon atoms) and isophthalic acid Nylon 6I obtained by co-condensation polymerization, Nylon 9T obtained by co-condensation polymerization of nonanediamine (carbon number 9) and terephthalic acid, methylpentadiamine (Methyl group + carbon number 5) and terephthalic acid Mention may be made of nylon M5T formed by condensation polymerization.

Next, a substrate that can be applied to the present invention is one that has an affinity for polyamide and chemically modifies the cleaved surfaces of the ground graphite particles. Here, chemical modification refers to the case where the substrate is physically adsorbed on the cleaved surface immediately after being ground in the process of stirring the graphite particles and the substrate together with the grinding medium and solvent described later, and the mechanochemical described later. In some cases, the carbon atom on the cleavage plane and the substrate are chemically bonded by the reaction.
Thus, once the fine particles of graphite whose cleaved surface has been chemically modified, the surface thereof is modified and loses its activity, so that it becomes difficult to aggregate.

The substrate preferably has a property of being dissolved in a solvent, exhibiting a solid phase at room temperature, and exhibiting a liquid phase at the kneading temperature of the polyamide resin described later.
By using a substrate having such a property, after cleavage of the graphite particles, the substrate can be immediately distributed to the surface of the fine particles, and the cleavage surface can be chemically modified at high density.
Furthermore, the storage stability of the manufactured filler for polyamide resin is improved, and even when the filler adheres between the fine particles during storage, the substrate at the adhesion interface melts at the time of kneading. It separates and diffuses into the matrix of the polyamide resin.
Examples of the substance that can be used as the substrate include the above-mentioned raw materials of polyamide resin, and ε-caprolactam (melting point: 70 ° C.) is preferably used.

As referred to JIS K5101-1-4 (or ISO 8780-4), the bead mill includes a container containing a mixed liquid containing at least graphite particles, a substrate, a solvent, and a grinding medium (hereinafter referred to as beads), It comprises at least a rotating body that is dipped in a mixed solution and driven to rotate.
As the graphite particles are stirred together with the beads in the solvent in this way, the grinding energy of the beads is softly propagated to the graphite particles, and the surface is peeled off in layers to generate fine particles having a large aspect ratio.
In addition, during the grinding process of graphite particles, mechanical energy such as impact, shear, shear stress, and friction is applied to the generated fine particles, so that some of them accumulate in the fine particles, improving activity and reactivity. The mechanochemical phenomenon is caused, and the chemical modification of the cleavage plane by the substrate is promoted.

Here, the beads used in the bead mill are a plurality of spherical bodies whose particle diameters are adjusted to be constant.
The applicable range of the bead diameter is 0.1 mm to 2 mm. In general, the smaller the particle size of the beads, the more fine the graphite particles that are ground. Therefore, if the bead particle size is smaller than 0.1 mm, the bead becomes light and difficult to separate from the slurry, and if the bead particle size is larger than 2 mm, the graphite particles are not finely divided. .
Examples of the material of the beads include soda glass, low soda glass, sodaless glass, high specific gravity glass, quartz, titania, silicon nitride, alumina, zirconia, steel, and stainless steel. Becomes larger.

In addition, the centrifugal force applied to the beads increases and the pulverization energy increases as the rotational speed of the rotating body that is driven and rotated by being immersed in the liquid mixture increases.
Thus, the greater the bead grinding energy and the smaller the bead particle size, the greater the tendency of the graphite particles to become finer. However, if this tendency is exceeded, the graphite particle monolayer will be destroyed. This causes a disadvantage that the aspect ratio of the image becomes lower.
Therefore, when the mixed liquid is stirred by the bead mill, conditions such as the rotational speed of the rotating body, the processing time, and the selection of the beads need to be appropriately examined according to the desired properties of the filler.
The bead mill as a means for agitating the mixed liquid and grinding the graphite particles is an example, and the means for grinding graphite particles applied to the method for producing a filler for polyamide resin of the present invention includes It is not limited.

Next, with reference to FIG. 1, the manufacturing process of the filler for polyamide resin is demonstrated.
First, in the raw material mixing step (S10), ethanol (solvent) in which ε-caprolactam (substrate) is dissolved is introduced into a bead mill container, and the average particle size is between several tens μm to several hundreds μm in advance. The adjusted graphite particles are charged together with beads (grinding medium) having a predetermined diameter to prepare a mixed solution. And it sets so that a rotary body may be immersed in a liquid mixture.

  Next, in the wet stirring step (S20), when the rotating body is driven and rotated, a vortex is generated in the mixed liquid, and centrifugal force acts on the beads in a direction substantially perpendicular to the rotation axis of the rotating body, and the inner wall of the container and Repeat collisions between beads. Due to the energy generated by the collision of the beads, the weak binding force acting between the layers constituting the graphite particles is cut, and cleavage from the surface layer proceeds to generate fine particles.

The cleaved surface of the generated fine particles has a high adsorbing power, so it tends to adsorb again with the cleaved surfaces of other fine particles, but the molecules of ε-caprolactam dissolved in the ethanol solvent interposed between the cleaved surfaces. Will be drawn preferentially. In this way, the cleavage plane of the fine particles immediately after generation is chemically modified by the molecules of ε-caprolactam, and the activity to aggregate between the fine particles is lost. It is not known in detail whether ε-caprolactam that chemically modifies the cleavage plane of the fine particles is simply physically adsorbed or has a chemical bond by mechanochemical reaction.
When such a wet stirring step (S20) is completed, the mixed solution becomes a homogeneous slurry.

  The medium recovery step (S30) is a step of recovering only beads (grinding medium) from the mixed liquid in the form of a homogeneous slurry. The beads are collected by a known mechanism attached to a bead mill apparatus. And if the apparatus of a bead mill is a continuous type, the recovered beads are mixed together with the newly added graphite particles and an ethanol solution of ε-caprolactam, and used for the next wet stirring step (S20). The Moreover, if the apparatus of a bead mill is a batch type, the recovered beads are discarded or washed and used for the next wet stirring step (S20).

  The solvent removal step (S40) is a step of removing the solvent from the mixed solution after removing the beads. Specifically, the slurry-like mixed solution is subjected to a centrifugal separator to remove the supernatant and then vacuum-dried. Thereby, the granular filler for polyamide resin is manufactured. The produced filler for polyamide resin can be packed and stored / stored.

In the resin kneading step (S50), the manufactured filler and the polyamide resin constituting the matrix of the composite polyamide resin are kneaded at the melting temperature of the polyamide resin, and the filler is uniformly dispersed in the matrix. It is a process to make.
In this kneading process, even if the stored graphite fine particles adhere to each other and become lumpy, the ε-caprolactam on the adhesion interface melts during the kneading process, and the lumps are scattered. The fine particles are finely dispersed in the matrix.

The molding step (S60) is a step of injecting a polyamide resin melt in which fine particles of graphite are finely dispersed into a predetermined molding die to manufacture a molded product of a composite polyamide resin. This molded article has a feature of excellent mechanical characteristics because fine graphite particles having a large aspect ratio are uniformly dispersed in the matrix without agglomeration.
In this process, not only the final molded product is manufactured, but also a material for injection molding such as a pellet may be manufactured.

  Next, examples in which the effects of the present invention have been confirmed will be described with reference to Table 1.

The apparatus used for the wet stirring process was a bead mill apparatus manufactured by Ashizawa Finetech Co., Ltd., and the beads used were zirconia materials with a diameter of 1 mm.
The graphite particles used were expanded graphite having an average particle size of 35.1 μm, 67.4 μm, 202 μm, and scaly graphite having an average particle size of 71.2 μm.

Then, any one of the above-described graphite particles is put into a container of a bead mill apparatus, and ethanol as a solvent and ε-caprolactam as a substrate so that the weight fraction of the graphite particles in the total composition of the mixed solution becomes 10 wt%. Was formulated.
In addition, this ε-caprolactam was also tested by varying the composition. Specifically, for graphite particles having an average particle diameter of 35.1 μm, ε-caprolactam is blended so that the weight fraction of graphite is 20, 30, 50, 100 wt%, and the average particle diameter is 67 .Epsilon.-caprolactam was blended so that the weight fraction with respect to graphite was 10.30 wt% with respect to 4 .mu.m graphite particles, and the weight fraction with respect to this graphite was with respect to graphite particles having an average particle diameter of 202 .mu.m. Ε caprolactam was blended so that the average particle size was 71.2 μm, and ε caprolactam was blended so that the weight fraction with respect to this graphite was 30,50 wt%.

As described above, nine types of mixed liquids having different blending compositions were prepared (hereinafter referred to as Table 1, corresponding to Table 1, respectively), and each mixed liquid was rotated. The body was immersed and rotated. And the result of having measured the average particle diameter of microparticles | fine-particles (prepared filler) obtained after extracting a suitable amount of the slurry after a process and drying this is described in the 7th line of Table 1.
From this result, it can be concluded that the average particle size of the produced filler does not depend on the particle size of the graphite particles as the starting material.

Next, nylon 66 is used as the matrix resin, and this nylon 66 and the filler are blended so that the weight fraction of the filler relative to the total composition of the molded product is 15 wt%, and the biaxial extrusion kneader is used. Kneaded.
And the molten resin after kneading | mixing was inject | poured into the production die of ASTM_D790 bending test piece, and the test piece was produced. Further, this test piece is mounted on an Instron 5582 universal testing machine, a mechanical property test based on ASTM_D790 is performed, and the test results are shown in the bottom two of Table 1.
This result suggested a correlation between the mechanical properties of the molded product and the blending ratio of ε-caprolactam (substrate) to graphite. In this example, it was found that the mechanical properties of the particle dispersion reinforced polyamide resin had a maximum value when the blending ratio of ε-caprolactam (substrate) to graphite was around 30 wt%.

(Comparative example)
Next, Comparative Examples 1, 2, and 3 to be compared with the present embodiment will be described with reference to Table 2.

Comparative Example 1 has the same conditions as Example 2 except that ε-caprolactam is not blended in the mixed solution.
Comparative Example 2 has the same conditions as Example 2 except that the treatment method is a wet ball mill.
Comparative Example 3 has the same conditions as Example 2 except that the processing method is a dry ball mill.

When Example 1 is compared with Comparative Example 2, there is no significant difference in the average particle size values of the fillers prepared as shown in Tables 1 and 2, but as shown in FIG. -It was found that Example 1 in which caprolactam was blended in the mixture had a smaller particle size distribution.
This is because in Comparative Example 1, the distribution of the large particle size spreads because the finely divided graphite aggregates, and further, the distribution on the small particle size side also breaks down into beads in this aggregated state. It is thought to spread.

Next, FIG. 3A is an image obtained by observing a cross section of an ASTM_D790 test piece of a particle dispersion strengthened polyamide resin prepared by blending the filler prepared in Example 2 with a magnification of 200. FIG. 3 (b) is an optical microscope observation image at a magnification of 200 of the same cross section produced by blending the filler produced in Comparative Example 1. FIG.
From the optical microscope observation image of FIG. 3A, it can be seen that the fine particles of graphite having a large aspect ratio are finely and uniformly dispersed in the matrix of the polyamide resin. On the other hand, from the optical microscope observation image of FIG. 3 (b), it can be seen that the aggregates aggregated after cleavage and the pulverized products pulverized into pieces are unevenly mixed.

  When comparing the mechanical properties described in Tables 1 and 2 for Example 1 and Comparative Example 2, it is clear that the former is superior. This is considered to be derived from the dispersion state of the fine particles in the particle dispersion strengthened polyamide resin as shown in FIGS. 3 (a) and 3 (b).

Next, when the results of Comparative Example 2 and Comparative Example 3 are examined, these mechanical properties are inferior to those of Example 1, and the tendency of the mechanical properties and the average particle diameter of the filler are also shown. The findings were consistent with the trend of size.
As described above, as a factor for determining the average particle size of the graphite fine particles, in the wet ball mill of Comparative Example 2, the ball used is larger than the beads of the bead mill because of the agitation using gravity, and energy for grinding the graphite. Therefore, it is considered that fine particles having a low aspect ratio are easily formed by being finely pulverized.
Further, it is considered that the dry ball mill of Comparative Example 3 has a large energy for grinding graphite and produces fine particles having a low aspect ratio because it has a high energy for grinding graphite because there is no solvent and no viscous resistance.

It is a flowchart explaining embodiment of the manufacturing method of the filler for polyamide resins of this invention. The graph which compares the particle size distribution of the fine particle of the produced filler in the case where the substrate (ε-caprolactam) for chemically modifying the cleavage surface of the graphite particles is blended as an example and the case where it is not blended as a comparative example. is there. (A) is a cross-sectional observation image by an optical microscope of a particle dispersion strengthened polyamide resin in which a filler whose surface is chemically modified with a substrate (ε-caprolactam) is blended as an example, and (b) is a comparative example. It is a cross-sectional observation image by the optical microscope of the particle | grain dispersion-strengthening-type polyamide resin which mix | blended the filler whose surface is not chemically modified.

Claims (4)

A raw material mixing step of forming a mixed liquid containing at least graphite particles, a substrate having an affinity for polyamide, a grinding medium, and a solvent;
A wet agitation step of agitating the mixed liquid to grind the graphite particles and chemically modify the cleavage plane with the substrate;
A medium recovery step for recovering the grinding medium;
And a solvent removal step for removing the solvent. A method for producing a filler for polyamide resin, comprising:   The method for producing a filler for polyamide resin according to claim 1, wherein the substrate is ε-caprolactam. The wet stirring step is performed by a bead mill including a container that contains the mixed solution, and a rotating body that is dipped in the mixed solution and driven to rotate,
The method for producing a filler for polyamide resin according to claim 1 or 2, wherein the grinding medium is a spherical body having a diameter in a range of 0.1 to 2 mm.   A particle dispersion-strengthened polyamide resin, wherein the polyamide resin filler produced by the method for producing a polyamide resin filler according to any one of claims 1 to 3 is dispersed in a polyamide resin matrix. .