JP2579742B2 - Injection molding composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composition for precision injection molding capable of accurately copying the size and shape of a mold.

[0002]

2. Description of the Related Art The point that plastics are inferior to metals in strength has been considerably improved in recent years with the advent of so-called engineering plastics, and metal substitution for plastics is in progress. However, plastics called engineering plastics have a large number of crystalline polymers and have a drawback that molding shrinkage is large. Therefore, it is the present situation that the molding, especially the mold design, is painstaking. A crystalline polymer with a well-ordered molecular arrangement is desirable to achieve strength, but such a polymer will necessarily have a larger change in volume between melting and solidification than non-crystalline polymers. Has the above-mentioned drawbacks based on the nature of the resin. However, in recent years, thermotropic liquid crystal polyesters exhibiting anisotropy upon melting (hereinafter abbreviated as liquid crystalline polyesters)
With the development of, it can be said that the situation has changed completely. Because this liquid crystalline polyester melts while maintaining the crystal structure, the injection molded product has high strength based on the crystal structure, and the volume change between melting and solidification due to the fact that the crystal structure does not change significantly during melting is small, There is an advantage that molding shrinkage is small. However, liquid crystalline polyester also has disadvantages,
Although the absolute value of the molding shrinkage is small, the difference between the molding shrinkage in the flow direction of the resin and the molding shrinkage in the perpendicular direction at the time of molding, that is, the anisotropy of the molding shrinkage is so large that it is difficult to obtain a precision molded product.
As a result of various studies on this problem, the present inventors have reached the present invention.

[0003]

That is, the present invention relates to a thermotropic liquid crystal polyester having a weight average molecular weight of from 2,000 to 200,000 and exhibiting anisotropy when melted, and from 20 to 20% of the total weight of the composition.
A composition for injection molding characterized by comprising, as main components, carbon fibers having a tensile elastic modulus of 60% by weight of 6,000 kg / mm ² or more, a weight average fiber length of 0.15 to 0.60 mm and an aspect ratio of 10 or more.

The individual limiting conditions will be described below. First, the liquid crystalline polyester of the present invention is a melt-processable polyester, and has a property that polymer molecular chains take a regular parallel arrangement in a molten state. The state in which molecules are arranged in this manner is often referred to as a liquid crystal state or a nematic phase of a liquid crystal substance. Such polymers are generally elongate, flat, highly rigid along the long axis of the molecule, and are composed of monomers that have multiple chain-extending bonds, usually in either a coaxial or parallel relationship. Manufactured. The properties of the anisotropic molten phase can be confirmed by a conventional polarization inspection method using an orthogonal polarizer. More specifically, the anisotropic molten phase can be confirmed by using a Leitz polarizing microscope and observing a sample placed on a Leitz hot stage under a nitrogen atmosphere at a magnification of 40 times. The polymer is optically anisotropic. That is, light is transmitted when inspected between orthogonal polarizers. If the sample is optically anisotropic, polarized light will be transmitted, even in the stationary state.

The constituent components of the polymer forming the anisotropic molten phase as described above include one or more of aromatic dicarboxylic acid and alicyclic dicarboxylic acid. Aromatic diol, alicyclic diol, aliphatic One or more of diols one or more of aromatic hydroxycarboxylic acids one or more of aromatic thiolcarboxylic acids one of aromatic dithiols or aromatic thiolphenols
One or more aromatic hydroxyamines and aromatic diamines, and the polymer forming the anisotropic molten phase is only polyester II) and polyester II) Polythiol ester consisting only of polyester III) and polyester IV) V) Polythiol ester consisting of VI) and polythiol ester VII) and polyesteramide consisting of VIII) and combination of polyesteramide and the like Consists of Further, although not included in the category of the combination of the above components, the polymer forming the anisotropic molten phase includes aromatic polyazomethine, and specific examples of such a polymer include poly (nitrilo-2-methyl- 1,4-phenylene nitriloethylidine-1,4-phenyleneethylidine); poly (nitrilo-2-methyl-1,
4-phenylene nitrilomethylidine-1,4-phenylene methylidyne); and poly (nitrilo-2-chloro-1,
4-phenylene nitrilomethylidine-1,4-phenylene methylidyne). Further, although not included in the category of the combination of the above components, polyester carbonate is included as the polymer forming the anisotropic molten phase. It may consist essentially of 4-oxybenzoyl, dioxyphenyl, dioxycarbonyl and terephthaloyl units.

[0006] The compounds constituting the above components I) to VIII) are listed below. As the aromatic dicarboxylic acid, terephthalic acid, 4,4′-diphenyldicarboxylic acid, 4,4′-triphenyldicarboxylic acid, 2,6-naphthalenedicarboxylic acid, diphenylether-4,4′-dicarboxylic acid, Diphenoxyethane-4,4'-dicarboxylic acid, diphenoxybutane-4,4'-dicarboxylic acid, diphenylethane-4,4'-dicarboxylic acid, isophthalic acid, diphenylether-3,3 '
Aromatic dicarboxylic acids such as dicarboxylic acids, diphenoxyethane-3,3'-dicarboxylic acids, diphenylethane-3,3'-dicarboxylic acids, naphthalene-1,6-dicarboxylic acids;
Or chloroterephthalic acid, dichloroterephthalic acid,
Alkyl, alkoxy or halogen-substituted aromatic dicarboxylic acids such as bromoterephthalic acid, methylterephthalic acid, dimethylterephthalic acid, ethylterephthalic acid, methoxyterephthalic acid and ethoxyterephthalic acid. As the alicyclic dicarboxylic acid, trans-1,
Alicyclic dicarboxylic acids such as 4-cyclohexanedicarboxylic acid, cis-1,4-cyclohexanedicarboxylic acid, and 1,3-cyclohexanedicarboxylic acid, or trans-1,4-
(1-methyl) cyclohexanedicarboxylic acid, trans-1,4- (1-chloro) cyclohexanedicarboxylic acid and the like, alkyl, alkoxy,
Or a halogen-substituted product. As the aromatic diol, hydroquinone, resorcinol, 4,4′-dihydroxydiphenyl, 4,4′-dihydroxytriphenyl,
2,6-naphthalenediol, 4,4′-dihydroxydiphenyl ether, bis (4-hydroxyphenoxy) ethane, 3,3′-dihydroxydiphenyl, 3,3′-dihydroxydiphenyl ether, 1,6-naphthalenediol,
2-bis (4-hydroxyphenyl) propane, 2,2-
Aromatic diols such as bis (4-hydroxyphenyl) methane or the above aromatic diols such as chlorohydroquinone, methylhydroquinone, 1-butylhydroquinone, phenylhydroquinone, methoxyhydroquinone, phenoxyhydroquinone: 4-chlororesorcin, 4-methylresorcin; Alkyl, alkoxy or halogen substituents are exemplified. As the alicyclic diol, trans-1,4-cyclohexanediol, cis-1,4-
Cyclohexanediol, trans-1,4-cyclohexanedimethanol, cis-1,4-cyclohexanedimethanol, trans-1,3-cyclohexanediol, cis-1,2-cyclohexanediol, trans-1,3-
Alicyclic diols such as cyclohexanedimethanol, or alkyl, alkoxy or the above alicyclic diols such as trans-1,4- (1-methyl) cyclohexanediol, trans-1,4- (1-chloro) cyclohexanediol And halogen-substituted products. Examples of the aliphatic diol include linear or branched aliphatic diols such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, and neopentyl glycol. Examples of the aromatic hydroxycarboxylic acid include aromatic hydroxycarboxylic acids such as 4-hydroxybenzoic acid, 3-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, and 6-hydroxy-1-naphthoic acid;
4-hydroxybenzoic acid, 3,5-dimethyl-4-hydroxybenzoic acid, 2,6-dimethyl-4-hydroxybenzoic acid, 3-methoxy-4-hydroxybenzoic acid, 3,5-dimethoxy-4-hydroxybenzoic acid Acid, 6-hydroxy-
5-methyl-2-naphthoic acid, 6-hydroxy-5-methoxy-2-naphthoic acid, 3-chloro-4-hydroxybenzoic acid, 2-chloro-4-hydroxybenzoic acid, 2,3
-Dichloro-4-hydroxybenzoic acid, 3,5-dichloro-4-hydroxybenzoic acid, 2,5-dichloro-4-hydroxybenzoic acid, 3-bromo-4-hydroxybenzoic acid, 6-hydroxy-5-chloro -2-naphthoic acid, 6
Alkyl, alkoxy or halogen-substituted aromatic hydroxycarboxylic acids such as -hydroxy-7-chloro-2-naphthoic acid and 6-hydroxy-5,7-dichloro-2-naphthoic acid. Examples of the aromatic mercaptocarboxylic acid include 4-mercaptobenzoic acid, 3-mercaptobenzoic acid, 6-mercapto-2-naphthoic acid, and 7-mercapto-2-naphthoic acid. Benzene-1,4-dithiol, benzene-
1,3 dithiol, 2,6-naphthalene-dithiol, 2,
7-naphthalene-dithiol and the like. Examples of the aromatic mercaptophenol include 4-mercaptophenol, 3-mercaptophenol, 6-mercaptophenol, and 7-mercaptophenol. As aromatic hydroxyamine and aromatic diamine, 4-aminophenol, N-methyl-4-aminophenol,
4-phenylenediamine, N-methyl-1,4-phenylenediamine, N, N'-dimethyl-1,4-phenylenediamine, 3-aminophenol, 3-methyl-4-aminophenol, 2-chloro-4- Aminophenol, 4-amino-1-naphthol, 4-amino-4'-hydroxydiphenyl, 4-amino-4'-hydroxydiphenyl ether, 4-amino-4'-hydroxydiphenylmethane,
4-amino-4'-hydroxydiphenyl sulfide, 4,
4'-diaminophenyl sulfide (thiodianiline),
4,4'-diaminodiphenylsulfone, 2,5-diaminotoluene, 4,4'-ethylenedianiline, 4,4'-diaminodiphenoxyethane, 4,4'-diaminodiphenylmethane (methylenedianiline), 4, 4'-diaminodiphenyl ether (oxydianiline) and the like.

The above polymers I) to VI comprising the above components
II) may or may not form an anisotropic molten phase depending on the constituent components, the composition ratio in the polymer, and the sequence distribution, but the polymer used in the present invention is anisotropic among the above-mentioned polymers. Limited to those that form an acidic molten phase. The polyesters of I), II) and III) and the polyesteramides of VIII), which are polymers forming an anisotropic molten phase suitable for use in the present invention, have a functional group capable of forming a required repeating unit by condensation. It can be produced by various ester forming methods capable of reacting the organic monomer compounds with each other. For example, the functional groups of these organic monomer compounds may be carboxylic acid groups, hydroxy groups, ester groups, acyloxy groups, acid halides, amine groups and the like. The organic monomer compound,
The reaction can be performed without the heat exchange fluid by the melt acidification method. In this method, the monomers are first heated together to form a molten solution of the reactants. As the reaction continues, solid polymer particles become suspended in the liquid. A vacuum may be applied to facilitate removal of by-product volatiles (eg, acetic acid or water) in the final stage of the condensation. Also, a slurry polymerization method can be employed for forming a wholly aromatic polyester suitable for use in the present invention. In this method, the solid product is obtained in suspension in a heat exchange medium. Regardless of which of the above-mentioned melt-acidification and slurry polymerization methods are employed, the organic monomer reactant that derives a fully aromatic polyester is in a modified form in which the hydroxyl group of such a monomer is esterified at room temperature (ie, a lower-grade ester). (As an acyl ester). The lower acyl group preferably has about 2 to 4 carbon atoms. Preferably, the acetate of such an organic monomer reactant is subjected to the reaction. Further, representative examples of catalysts that can be optionally used in either the melt acidilysis method or the slurry method include dialkyltin oxide (eg, dibutyltin oxide), diaryltin oxide, titanium dioxide, antimony trioxide, alkoxytitanium silicate,
Titanium alkoxides, alkali and alkaline earth metal salts of carboxylic acids (eg, zinc acetate), Lewis (eg, B
F ₃ ) and gaseous acid catalysts such as hydrogen halide (eg, HCl). The amount of catalyst used is generally from about 0.001 to 1% by weight, based on the total weight of the monomers, in particular from about 0.01 to 0.
2% by weight. Fully aromatic polymers suitable for use in the present invention tend to be substantially insoluble in common solvents and are therefore unsuitable for solution processing. But,
As already mentioned, these polymers can be easily processed by conventional melt processing methods. Particularly preferred wholly aromatic polymers are somewhat soluble in pentafluorophenol. Fully aromatic polyesters suitable for use in the present invention generally have a weight average molecular weight of about 2,000 to 200,
000, preferably about 10,000 to 50,000, particularly preferably about
It is between 20,000 and 25,000. On the other hand, suitable wholly aromatic polyesteramides generally have a molecular weight of about 5,000 to 50,000, preferably about 10,000 to 30,000, for example 15,000 to 17,000. Such determination of molecular weight can be carried out by gel permeation chromatography and other standard methods without solution formation of polymers, for example by quantifying end groups by infrared spectroscopy on compression molded films. Alternatively, the molecular weight can be measured by using a pentafluorophenol solution and using a light scattering method. The wholly aromatic polyesters and polyesteramides described above also have at least about 2.0 dl / g, such as about 2.0 dl / g, when dissolved in pentafluorophenol at 60% at a concentration of 0.1% by weight.
Logarithmic viscosities (IV) of 2.0 to 10.0 dl / g are generally indicated. The polymer exhibiting an anisotropic melt phase used in the present invention is preferably an aromatic polyester and an aromatic polyesteramide,
Polyesters partially containing an aromatic polyester and an aromatic polyesteramide in the same molecular chain are also preferable examples.

Preferred examples of the compounds constituting them are:
Naphthalene compounds such as 2,6-naphthalenedicarboxylic acid, 2,6-dihydroxynaphthalene, 1,4-dihydroxynaphthalene and 6-hydroxy-2-naphthoic acid, 4,4′-
Biphenyl compounds such as diphenyldicarboxylic acid and 4,4'-dihydroxybiphenyl, and compounds represented by the following general formulas (I), (II) or (III):

[0009]

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(Where X is a group selected from alkylene (C ₁ -C ₄ ), alkylidene, —O—, —SO—, —SO ₂ —, —S— and —CO— Y :—( CH ₂ ) _{n - (n = 1~4),} - O (CH 2) n O- (n = 1~4) from groups selected) p- hydroxybenzoic acid, terephthalic acid, hydroquinone, p- aminophenol and p- phenylene Para-substituted benzene compounds such as diamines and their nuclei-substituted benzene compounds (substituents are selected from chlorine, bromine, methyl, phenyl and 1-phenylethyl), and meta-substituted benzene compounds such as isophthalic acid and resorcinol is there. Further, a preferred example of the polyester partially containing the above-mentioned constituent components in the same molecular chain is polyalkylene terephthalate, wherein the alkyl group has 2 to 4 carbon atoms.
Among the above-mentioned components, those containing one or more compounds selected from a naphthalene compound, a biphenyl compound and a para-substituted benzene compound as essential components are more preferable examples. Among the p-substituted benzene compounds, p-hydroxybenzoic acid, methylhydroquinone and 1-phenylethylhydroquinone are particularly preferred examples. The following are illustrated as specific combinations of the constituent components.

[0011]

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[0012]

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[0013]

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[0014]

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[0015]

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[0016]

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In the formula, Z is a substituent selected from —Cl, —Br, and —CH ₃ , and X is alkylene (C ₁ -C ₄ ), alkylidene, —O—
_{, -SO -, - SO 2 -} , -S-, a substituent selected from -CO-. Particularly preferred anisotropic molten phase-forming polyesters for use in the present invention are naphthalene moiety-containing repeating units such as 6-hydroxy-2-naphthoyl, 2,6-dihydroxynaphthalene and 2,6-dicarboxynaphthalene. It is contained in an amount of about 10 mol% or more. Preferred polyesteramides are those containing repeating units of the naphthalene moiety described above and a moiety consisting of 4-aminophenol or 1,4-phenylenediamine. Specifically, it is as follows.

(1) Polyester consisting essentially of the following repeating units I and II:

[0019]

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The polyester contains about 10 to 90 mol% of unit I and about 10 to 90 mol% of unit II. In one embodiment, unit I is present in an amount of about 65-85 mol%, preferably about 70-80 mol% (eg, about 75 mol%). In another embodiment, unit II is about 15-35 mol%,
It is preferably present in much lower concentrations, such as about 20-30 mole%. Further, at least a part of the hydrogen atoms bonded to the ring is optionally selected from the group consisting of an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, halogen, phenyl, substituted phenyl and a combination thereof. It may be substituted by the selected substituent.

(2) essentially the following repeating units I, II and II
Polyester consisting of I.

[0022]

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The polyester contains about 30 to 70 mol% of unit I. The polyester is preferably
It contains about 40-60 mol% of unit I, about 20-30 mol% of unit II, and about 20-30 mol% of unit III. Further, at least a part of the hydrogen atoms bonded to the ring may be an alkyl group having 1 to 4 carbon atoms,
And 4 may be substituted with a substituent selected from the group consisting of an alkoxy group, halogen, phenyl, substituted phenyl and a combination thereof.

(3) Polyester consisting essentially of the following repeating units I, II, III and IV:

[0025]

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Wherein R represents methyl, chloro, bromo or a combination thereof, and is a substituent for a hydrogen atom on the aromatic ring.
60 mol%, unit II about 5-18 mol%, unit III about 5-35 mol%, and unit IV about 20-40 mol%
In the amount of The polyester preferably has about 35-45 mol% of units I, about 10-15 mol% of units
II, about 15-25 mol% of units III, and about 25-3
Contains 5 mol% of unit IV. However, the total molarity of units II and III is substantially equal to the molarity of unit IV. In addition, at least a part of the hydrogen atoms bonded to the ring may be a group consisting of an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, halogen, phenyl, substituted phenyl, and a combination thereof. May be substituted by a substituent selected from The wholly aromatic polyester has at least 2.0 dl / g, e.g.
A logarithmic viscosity of 10.0 dl / g is generally indicated.

(4) Polyester consisting essentially of the following repeating units I, II, III and IV:

[0028]

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And about 20 to 40 mol% of unit I, more than 10 mol% of unit II, up to about 50 mol%, more than 5 mol% of unit III, up to about 30 mol%, and unit IV In an amount of more than 5 mol% and not more than about 30 mol%. The polyester is preferably about 20-30.
Mole% (e.g., about 25 mole%) of unit I; about 25-40 mole% (e.g., about 35 mole%) of unit II; about 15-25 mole% (e.g., about 20 mole%) of unit III; And about 15-2
Contains 5 mol% (eg about 20 mol%) of unit IV. In addition, at least a part of the hydrogen atoms bonded to the ring may be a group consisting of an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, halogen, phenyl, substituted phenyl, and a combination thereof. May be substituted by a substituent selected from

The units III and IV have one divalent bond connecting these units to other units on both sides in the polymer main chain.
Or symmetrical in the sense that they are symmetrically arranged on two or more aromatic rings (for example, when present on a naphthalene ring, they are arranged para to each other or on a diagonal ring). preferable. However, asymmetric units such as those derived from resorcinol and isophthalic acid can also be used.

Preferred dioxyaryl units III are

[0032]

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And a preferred dicarboxyaryl unit IV is

[0034]

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Is as follows.

(5) The following repeating units I, II and II
Polyester consisting of I:

[0037]

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And contains about 10 to 90 mol% of unit I, 5 to 45 mol% of unit II and 5 to 45 mol% of unit III. The polyester is preferably
It contains about 20-80 mol% of unit I, about 10-40 mol% of unit II, and about 10-40 mol% of unit III. More preferably, the polyester is about 60-8
It contains 0 mole% of unit I, about 10-20 mole% of unit II, and about 10-20 mole% of unit III. In addition, at least a part of the hydrogen atoms bonded to the ring may be a group consisting of an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, halogen, phenyl, substituted phenyl, and a combination thereof. May be substituted by a substituent selected from Preferred dioxyaryl units II
Is

[0039]

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Is as follows.

(6) Polyesteramide consisting essentially of the following repeating units I, II, III and IV:

[0042]

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And about 10 to 90 mol% of the unit I, about 5 to 45 mol% of the unit II, and about 5 to 45 mol% of the unit III.
Mole%, and unit IV in an amount of about 0-40 mole%. Further, at least a part of the hydrogen atoms bonded to the ring may be an alkyl group having 1 to 4 carbon atoms,
And 4 may be substituted with a substituent selected from the group consisting of an alkoxy group, halogen, phenyl, substituted phenyl and a combination thereof. Preferred dicarboxyaryl units II are

[0044]

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Is as follows. Furthermore, in the polymer forming the anisotropic molten phase of the present invention, a part of one polymer chain is composed of the segment of the polymer forming the anisotropic molten phase described above, and the remaining part is Also included are polymers composed of thermoplastic resin segments that do not form an anisotropic molten phase. The above-mentioned liquid crystalline polyester is a high-strength material combined with a self-reinforcing effect, and has a small linear expansion coefficient and a small molding shrinkage, so that there is little dimensional deviation. It has low melt viscosity and good fluidity, but also withstands high temperatures of 180-200 ° C.
Good chemical resistance, weather resistance, hot water resistance, chemical inertness, and has no effect on others.
The above-mentioned chemical composition of the liquid crystalline polyester used in the present invention can be used, but the weight average molecular weight is 2,000.
~ 200,000 is good. If it is less than 2,000, the mechanical strength is not sufficient, and if it is more than 200,000, the molding temperature becomes extremely high, and the dimensions and shape of the mold cannot be accurately captured by injection molding in terms of fluidity. Particularly preferred molecular weight is 10,000 to 80,000. After using a liquid crystalline polyester having a molecular weight in this range, the above-mentioned specific carbon fiber is blended.

Further, the liquid crystalline polyester of the present invention may be a polymer blended with another thermoplastic resin within a range not to impair the intended purpose of the present invention. The thermoplastic resin used in this case is not particularly limited, but examples thereof include polyethylene, polyolefins such as polypropylene, polyethylene terephthalate, aromatic dicarboxylic acids such as polybutylene terephthalate and aromatic polyesters such as diols or oxycarboxylic acids. , Polyacetal (homo or copolymer), polystyrene, polyvinyl chloride, polyamide, polycarbonate, AB
S, polyoxyphenylene oxide, polyoxyphenylene sulfide, fluorine resin and the like can be mentioned.
These thermoplastic resins can be used as a mixture of two or more kinds.

Next, a carbon fiber having a tensile elastic modulus of 6,000 kg / mm ² or more means a relatively rigid fiber, but the effect of the present invention cannot be obtained with a flexible carbon fiber having a tensile elastic modulus less than this. . In general, it is recognized that ordinary plastics containing carbon fibers tend to enhance the directionality due to the flow orientation at the time of molding, and the more rigid the fibers, the stronger the tendency. However, according to the study of the present inventors, an unexpected peculiar phenomenon is seen in the case of the liquid crystalline polyester, which is opposite to the case where the rigid fibrous material decreases the directionality. That is, the liquid crystalline polyester has the effect of reducing the molding shrinkage in all directions as the rigidity of the carbon fiber blended into the polyester increases. Such an effect is small in a flexible carbon fiber, and a strange phenomenon that the molding shrinkage ratio is not much different from that of the liquid crystalline polyester itself is seen. As a result, it is inevitable that rigid carbon fibers have a greater effect of disturbing the molecular orientation of the liquid crystalline polyester to some extent. The next requirement of the carbon fiber used in the present invention is that the weight average fiber length is 0.15 to 0.60 mm. As shown in FIG. 1, the weight-average fiber length in the composition was set at about 0.
It means that it is 15 to 0.60 mm, and it is only necessary to determine the weight average fiber length of the carbon fibers before kneading and the kneading conditions in a preliminary test and knead them. Fig. 1 shows a mixture of 70 parts by weight of various liquid crystalline polyesters and 30 parts by weight of carbon fiber having a tensile modulus of elasticity of 2,400 kg / mm ² and a diameter of 7μ (weight average fiber length before mixing: 6.0 mm), and using an extruder. Then, the mixture was tightly blended to form a pellet, and the weight average fiber length of the carbon fiber when a 120 × 120 × 3 mm square sample piece was injection-molded from a film gate having a thickness of 2 mm provided on one side using the pellet was used. It is a graph which shows the typical relationship with a molding shrinkage. In this case, the injection molding conditions were as follows: cylinder temperature 270-290 ° C, mold temperature 120-130.
° C, injection pressure 600 kg / cm ² , injection speed 0.6 m / min. The mold shrinkage was measured for the injection direction of the square test piece and the direction perpendicular thereto. The present invention satisfies that the maximum molding shrinkage under such molding conditions is 0.5% or less. In the case where no fibrous material is added to the liquid crystalline polyester used in FIG. 1, the molding shrinkage is -0.3 in the flow direction and 0.9 in the right angle direction, both of which have a large difference in directionality. Such a phenomenon is a phenomenon common to liquid crystalline polyesters, and is not seen in other resins. That is, the minimum shrinkage is exhibited at a weight average fiber length of 0.15 to 0.60 mm, preferably 0.2 to 0.4 mm. In this range, not only the shrinkage ratio is small, but also the difference due to the difference in direction is extremely small, which indicates that this is the most effective condition for precision molding aimed at by the present invention. Although such a tendency slightly varies depending on the type, amount, and other conditions of the fibrous material, it is recognized that the tendency is substantially the same within the range specified by the present invention. The carbon fiber used in the present invention is required to have an aspect ratio of 10 or more, and such a carbon fiber should be blended in an amount of 20 to 60% by weight, preferably 25 to 50% by weight based on the total composition. is required. When the amount is less than 20% by weight, the effect of the addition is not exhibited. When the amount is more than 60% by weight, the anisotropy due to the orientation of the carbon fiber becomes strong, and the difference in the molding shrinkage ratio in each direction tends to increase. Is not effective. In order to exhibit the effects of the present invention as a carbon fiber, the aspect ratio needs to be 10 or more, and preferably about 15 to 80. If the aspect ratio is less than 10, the same effect as that of the powdery or granular material is not preferred from the viewpoint of the effects of the present invention. That is, although the anisotropy decreases, the mold shrinkage is as high as that of the non-added product, and the mechanical strength also decreases. The carbon fiber used in the present invention can be used in combination with a commonly used well-known surface treatment agent and sizing agent in order to enhance the adhesiveness to the liquid crystalline polyester, which is desirable. Examples are functional compounds such as epoxy compounds, isocyanate compounds, silane compounds, titanate compounds and the like. These compounds may be used after being subjected to a surface treatment or a convergence treatment in advance, or may be added at the same time when preparing the material.

The composition of the present invention contains a known substance added to general thermoplastic resins and thermosetting resins, that is,
Stabilizers such as plasticizers, antioxidants and ultraviolet absorbers, antistatic agents, flame retardants, coloring agents such as dyes and pigments, and lubricants, lubricants and crystallization accelerators for improving fluidity and mold release. (Nucleating agent) and the like can be appropriately added and used according to the required performance.

[0049]

According to the present invention, as is apparent from the above description,
Only when a specific limited carbon fiber is blended with the liquid crystalline polyester, it is based on the finding that the value itself decreases with the anisotropy of the molding shrinkage rate, and the limited carbon fiber is used. It is possible to obtain a composition having a low shrinkage ratio that cannot be achieved by using a material other than fibers, such as a powder. This means that when the composition of the present invention is injection-molded into a molded article, the dimensional change during molding is small regardless of which part of the molded article and in which direction the molded article is taken. There is an advantage that a good molded product is obtained. In addition, if the viewpoint is changed, it is not necessary to consider molding shrinkage much, so that the mold design becomes simple. Further, the composition of the present invention has the great advantage that the above-mentioned improvement can be achieved without impairing the characteristics of the liquid crystalline polyester, namely, high mechanical strength, high melt fluidity, high melting point and high heat resistance.
Further, a molded article from the composition of the present invention can be obtained as an injection molded article used in combination with an aluminum component because a product having a linear expansion coefficient close to that of aluminum can be obtained. For example, when used in combination with an aluminum component such as a camera, an optical component support incorporated in an aluminum structure such as a laser disk pickup, or a carriage, arm, lead screw of a floppy disk player or a pickup of a compact disk player. Has good performance, combined with the advantage that the mold shrinkage is small, so that it is exactly the same as the mold, and the advantage that the thermal expansion and shrinkage is the same as aluminum due to the temperature change during use, so there is little deviation. It is most suitable for the production of high-performance components with a high degree of precision, such as the production of devices such as floppy disk players or compact disk players.

[0050]

Next, the present invention will be further described with reference to examples, but the present invention is not limited to these examples. Examples 1 to 5 70 parts by weight of various liquid crystalline polyesters A to E to be described later were mixed with 30 parts by weight of carbon fiber having a tensile modulus of elasticity of 2,400 kg / mm ² and a diameter of 7 μm (weight average fiber length before mixing: 6 mm) and extruded. The mixture was tightly blended using a molding machine to form pellets. The pellet was heated to thermally decompose and remove the resin, and the weight average fiber length of the carbon fiber was measured. Further, as described above, the molding shrinkage when a square sample piece of 120 × 120 × 3 mm was injection-molded from a film gate having a thickness of 2 mm provided on one piece was measured. Injection molding conditions are cylinder temperature 270-290 ° C, mold temperature 120-
130 ° C, injection pressure 600 kg / cm ² , injection speed 0.6 m / min. Table 1 shows the molding shrinkage and the coefficient of linear expansion at 40 ° C. for reference.

[0051]

[Table 1]

Comparative Example 1 The procedure of Example 1 was repeated except that the amount of the carbon fiber was changed to 30 parts by weight and the weight average fiber length in the composition was changed to 0.8 mm. The molding shrinkage in the flow direction and the direction perpendicular to the flow direction are respectively
0.08 and 0.58. Example 6 In the same manner as in Example 1 except that the amount of the carbon fiber was changed to 40 parts by weight, molded articles having molding shrinkage ratios of 0.04 and 0.38 in the flow direction and the direction perpendicular thereto were obtained. In this case, the weight average fiber length of the carbon fibers in the composition was 0.20 mm. Example 7 A composition was prepared in the same manner as in Example 1 except that the blending amount of the carbon fiber was changed to 20 parts by weight, and a molded product having a molding shrinkage of 0.03 and 0.32 in the flow direction and the direction perpendicular thereto was respectively obtained. Obtained. The weight average fiber length of the carbon fibers in the composition in this case is 0.57 mm
Met. Comparative Examples 2 to 4 In Example 1, molding was performed in the same manner using various additives shown in Table 2 instead of carbon fibers, and the molding shrinkage was measured.
Table 2 shows the results.

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[Table 2]

Comparative Example 5 In Example 1, polyoxymethylene was used in place of resin A, carbon fibers were blended as shown in Table 3, and the molding shrinkage was measured. However, the weight average fiber length of the carbon fibers in the carbon fiber blend was 0.50 mm. As in Comparative Example 1, in the case of polyoxymethylene, the anisotropy in the molding shrinkage was originally small, but it was found that the anisotropy was increased by the blending of the carbon fibers.

[0055]

[Table 3]

Comparative Example 6 70 parts by weight of liquid crystalline polyester A and a tensile modulus of elasticity of 3000 kg / m
m ² , 12μ diameter carbon fiber (weight average fiber length 6m before mixing)
m) A composition consisting of 30 parts by weight was injection-molded in the same manner as in Example 1, and the evaluation results are shown in Table 4.

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[Table 4]

The polymers A to E used in the examples have the following structural units.

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[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a weight average fiber length of a carbon fiber used in the present invention and a molding shrinkage.

Claims (5)

(57) [Claims] 1. A thermotropic liquid crystal polyester having a weight average molecular weight of 2,000 to 200,000 and exhibiting anisotropy when melted, and a tensile modulus of 6,000 kg of 20 to 60% by weight based on the total weight of the composition.
/ Mm ² or more, the weight average fiber length 0.15～0.60Mm, injection molding composition characterized in that a main component and an aspect ratio of 10 or more carbon fibers. 2. The composition for injection molding according to claim 1, wherein the maximum value of the molding shrinkage is 0.5% or less. 3. The composition according to claim 1, wherein the carbon fiber is a fibrous material having a diameter of 5 to 15 μm and a weight average fiber length of 0.2 to 0.4 mm. 4. The compounding amount of carbon fiber is 25 to the total weight of the composition.
2. The composition for injection molding according to claim 1, wherein the composition is 50% by weight. 5. The composition for injection molding according to claim 1, wherein the thermotropic liquid crystal polyester exhibiting anisotropy upon melting is a liquid crystal polyester having a weight average molecular weight of 10,000 to 80,000.