JP2945145B2 - Liquid crystal polymer injection molding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molded article made of a thermotropic liquid crystal polymer, and more particularly to a molded article having a small decrease in so-called weld strength which is observed in an injection molded article.

[0002]

2. Description of the Related Art A thermotropic liquid crystal polymer exhibits optical anisotropy when melted, and the molded article obtained by injection molding has an extremely low weld strength, which is a major problem in the injection molding technique of the polymer. I have. For example, the low weld strength is also observed due to a phenomenon such as breakage from a weld portion of a molded article due to mechanical or thermal shock.

Here, in general, a weld line in injection molding is inevitably generated in the case of a multipoint gate, and even in the case of a single point gate, an injection molded product having a large thickness deviation ratio or an injection molded product provided with a push-off pin is used. As in the case of injection molding, the flow of the molten resin injected from the gate into the mold cavity is branched, and this is generated on the surface of the molded body corresponding to the junction where the molten resin flows further. In other words, the weld line indicates a frequently linear joining portion where the joining interface formed by the joining of the molten resin flows is exposed on the surface of the molded product. The weld strength indicates the strength of the compact at the weld line.

Here, the present inventors consider the reason why the weld strength of a molded article obtained by injection-molding a thermotropic liquid crystal polymer is low. It was thought that this was because the resin itself was extremely easily oriented, and the fountain flow effect at the time of filling the inside of the cavity caused molecular orientation of the flowing tip resin in parallel with the weld interface.

In the case of a thermotropic liquid crystal polymer, a simple change in molding conditions such as raising the resin temperature, mold temperature, or increasing the injection pressure or holding pressure, which is conventionally performed to improve the weld strength, is particularly required. However, almost no injection molded article having improved weld strength can be obtained. This is based on the inherent properties of liquid crystal polymers, in which liquid crystal molecules tend to be strongly aligned themselves as described above, and once aligned, the molecules remain in the original alignment state unless some stress is applied again. It is. Therefore, it is considered that the mere change of the injection molding conditions does not fundamentally change the orientation state in which the flowing tip resin is molecularly oriented parallel to the weld interface, but is still in the original orientation state.

The present inventors have also found that the weld strength cannot be substantially improved by simply deforming the shape of the weld interface once formed after a plurality of molten resins have joined.

On the other hand, in an injection mold having at least two plasticizers and a sprue connected to an injection device as disclosed in Japanese Patent Application Laid-Open No. 1-299015, plasticization is performed by two plasticizers and injection devices after filling a cavity. The method by reciprocating the converted resin is a method aiming at obtaining a molded body in which a confluent interface cannot essentially exist.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal polymer injection molded article having a high weld strength.

[0009]

[Means for Solving the Problems]

[0010] The present invention has a weld line that appears on the surface of an injection-molded article by combining a plurality of resin streams,
When the thickness of the molded body in the weld line is X (mm), the reflow length Y (mm), in which the one resin flow that has merged and then reflowed, satisfies the following expression: The present invention relates to a liquid crystal polymer injection molded article. Y ≧ (2.69) ^X · 0.26 Formula (I) (where X is 0.5 mm or more)

The thermotropic liquid crystal polymer of the present invention is a resin that exhibits optical anisotropy when melted by heat.

As described above, a polymer that exhibits optical anisotropy when melted has a property that polymer molecular chains take a regular parallel arrangement in a melted state. The properties of the optically anisotropic molten phase can be confirmed by a normal polarization inspection method using an orthogonal polarizer.

A thermotropic liquid crystal polymer is generally elongated and has a flat molecular structure, has high rigidity along the long chain of the molecule, and has a plurality of chain-extended bonds in either a coaxial or parallel relationship. Manufactured from such monomers.

The thermotropic liquid crystal polymer used in the present invention can be produced from the above compound by various ester forming methods such as a melt acidilysis method and a slurry polymerization method. In the thermotropic liquid crystal polymer used in the present invention, a thermoplastic resin in which a part of one polymer chain is composed of a polymer segment forming an anisotropic molten phase and the remaining part does not form an anisotropic molten phase And a polymer composed of the following segments. Further, a composite of a plurality of thermotropic liquid crystal polymers is also included.

Examples of the polymer forming the optically anisotropic molten phase as described above include, for example, wholly aromatic polyesters and polyester ethers, and the constituent components thereof include (A) an aromatic dicarboxylic acid compound. At least one
Species, (B) at least one aromatic hydroxycarboxylic acid compound, (C) at least one aromatic diol compound, (D) (D1) aromatic dithiol, (D2) aromatic thiophenol, (D3 At least one kind of aromatic thiol carboxylic acid-based compound, and at least one kind of (E) aromatic hydroxyamine and aromatic diamine-based compound. These may be constituted by themselves, but in many cases (A) and (C); (A) and (D); (A),
(B) and (C); (A), (B) and (E); or (A), (B), (C) and (E), and the like.

The aromatic dicarboxylic acid compound (A) includes terephthalic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-triphenyldicarboxylic acid, 2,6-
Naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, diphenylether-4,4'-dicarboxylic acid, diphenoxyethane-4,4'-dicarboxylic acid, diphenoxybutane-4,
4'-dicarboxylic acid, diphenylethane-4,4'-dicarboxylic acid, isophthalic acid, diphenyl ether-3,
3'-dicarboxylic acid, diphenoxyethane-3,3'-
Aromatic dicarboxylic acids such as dicarboxylic acid, diphenylethane-3,3'-dicarboxylic acid and 1,6-naphthalenedicarboxylic acid, or chloroterephthalic acid, dichloroterephthalic acid, bromoterephthalic acid, methylterephthalic acid, dimethylterephthalic acid, and ethyl Alkyl, alkoxy or halogen-substituted aromatic dicarboxylic acids represented by terephthalic acid, methoxyterephthalic acid, ethoxyterephthalic acid and the like can be mentioned.

(B) The aromatic hydroxycarboxylic acid compounds include aromatic hydroxycarboxylic acids such as 4-hydroxybenzoic acid, 3-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid and 6-hydroxy-1-naphthoic acid. Carboxylic acid, or 3-methyl-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, 6-hydroxy-5 Methyl-2-naphthoic acid, 6-hydroxy-5-methoxy-2-naphthoic acid, 2-chloro-4-hydroxybenzoic acid, 3-chloro-4-hydroxybenzoic acid, 2,3-dichloro-4-hydroxybenzoic acid 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 -Hydroxy-
7-chloro-2-naphthoic acid, 6-hydroxy-5,7
Alkyl-, alkoxy-, or halogen-substituted aromatic hydroxycarboxylic acids represented by -dichloro-2-naphthoic acid and the like.

(C) As the aromatic diol, 4,4 '
-Dihydroxydiphenyl, 3,3'-dihydroxydiphenyl, 4,4'-dihydroxytriphenyl, hydroquinone, resorcinol, 2,6-naphthalenediol, 4,4'-dihydroxydiphenyl ether, bis (4-hydroxyphenoxy) ethane, Aromatic diols such as 3,3'-dihydroxydiphenyl ether, 1,6-naphthalenediol, 2,2-bis (4-hydroxyphenyl) propane, bis (4-hydroxyphenyl) methane, chlorohydroquinone, methylhydroquinone, t- Alkyl, alkoxy, aryl and aryl of aromatic diols represented by butylhydroquinone, phenylhydroquinone, methoxyhydroquinone, phenoxyhydroquinone, 4-chlororesorcin, 4-methylresorcin and the like Aryloxy or halogen-substituted derivatives thereof.

(D1) Examples of the aromatic dithiol include benzene-1,4-dithiol, benzene-1,3-dithiol, and 2,6-naphthalene-dithiol.

(D2) As the aromatic thiophenol,
4-mercaptophenol, 3-mercaptophenol, 6-mercaptophenol and the like.

(D3) Examples of the aromatic thiol carboxylic acid include 4-mercaptobenzoic acid, 3-mercaptobenzoic acid, 6-mercapto-2-naphthoic acid, and 7-mercapto-2-naphthoic acid.

(E) As aromatic hydroxyamine and aromatic diamine compounds, 4-aminophenol, N-
Methyl-4-aminophenol, 1,4-phenylenediamine, N, 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'-hydroxydiphenylsulfide, 4,4'-diaminophenylsulfide (thiodianiline), 4,4'-diaminodiphenylsulfone,
2,5-diaminotoluene, 4,4'-ethylenedianiline, 4,4'-diaminodiphenoxyethane, 4,
4'-diaminodiphenylmethane (methylenedianiline), 4,4'-diaminodiphenylether (oxydianiline) and the like.

Among these wholly aromatic polyesters, at least a compound represented by the general formula:

[0024]

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A (co) polymer containing a repeating unit represented by the formula:

[0026]

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[0027]

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And the like.

That is, a particularly preferred wholly aromatic copolyester of the present invention is a copolyester having a repeating unit derived from each of three compounds of p-hydroxybenzoic acid, phthalic acid and biphenol, or p-hydroxybenzoic acid And a copolyester having a repeating unit each derived from two compounds of hydroxynaphthoic acid.

The thermotropic liquid crystal polymer in the present invention is as described above, but within the scope of the present invention, inorganic or organic fibers such as glass fiber and carbon fiber, and conventionally known inorganic or organic fibers such as talc and titanium dioxide. One or more fillers can be included in any amount. However, when an excessively large amount of filler is filled, the compounding operation itself becomes difficult, and the mechanical strength itself of the obtained molded article also decreases. Therefore, the thermotropic liquid crystal polymer in the present invention preferably contains 70% by weight or less of a filler.

Next, the injection molded article of the present invention will be described in more detail by giving one example of the method for producing the injection molded article of the present invention.

FIG. 1 is an illustration of one example of a mold for producing an injection molded article of the present invention having a plate-like shape shown by a plan view. This mold is a split mold for injection-molding a plate-like body provided with two cavities 2 and 3 in one runner 1. In the mold shown in the figure, the cavity 2 has a plurality of gates a and b, and the cavity 2 is a so-called multi-point gate mold. The runner 1 to which the cavity 2 is connected has a gate a
, A cavity 3 separate from the cavity 3 is provided, which is provided with one gate c connected to the runner 1. The mold can be used in two or more dies. Here, the dies in two halves will be described as an example.

The thermotropic liquid crystal polymer melted by the extruder (not shown) is injected into the cavity 2 from the two-point gates a and b via the sprue (arrow) and the runner 1. The molten resin is injected into the separate cavity 3 from the gate c via the runner 1.

The injection molding machine for obtaining a molded body of the thermotropic liquid crystal polymer and its injection molding conditions are not particularly limited. Injection can be performed according to normal injection molding conditions using a normal injection molding machine corresponding to the thermotropic liquid crystal polymer to be injected. For example, the extruder cylinder temperature is 200 to 420 ° C, the mold temperature is 30 to 200 ° C, and the injection pressure is 100 to 100 ° C. It is appropriately selected from a range of 2000 kg / cm ² , an injection speed (cylinder moving speed) of 5 to 500 mm / sec, and an injection molding cycle of 5 to 120 seconds.

Although the mold can be used in two or more halves, here, the halves will be described as an example.
That is, injection is performed under the above-mentioned conditions while applying an appropriate mold clamping pressure, for example, 300 to 800 kg / cm ² to the combined molds. The injected molten resin first fills the runner 1 via a sprue and proceeds. The molten resin flowing into the cavity 2 from the gates a and b merges to form a weld line (indicated by a dotted line) on the surface of the molded body. On the other hand, the resin flowing from the gate c fills the cavity 3.

When a plurality of resin flows from the gates a and b merge in the cavity 2, one of the cavities 3
Are not completely filled by the resin flow from the gate c at the time of merging. Therefore, one cavity 3 is filled after the cavity 2 is filled. As a result, when the pressures of the two resin flows from the gates a and b in the cavity 2 are compared with each other, the resin flow from the gate a relatively decreases, whereby the resin flow from the gate a reverses and reflows. Is generated. It is not necessary to apply a holding pressure for refluidization, but if necessary, 100 to 1000
It is also possible to hold the pressure at a holding pressure of kg / cm ² and a holding time of 2 to 120 seconds. The holding pressure indicates the pressure applied to the mold after substantially all of the molten resin has filled the inside of the mold cavity and the time required for the pressure.

After the injection molding, an appropriate cooling time, for example, 2
Cooling is performed for a cooling time of up to 120 seconds and the mold is released to obtain a desired molded product.

Here, a multi-layer structure of a skin layer and a core layer is usually observed in an injection molded article of a liquid crystal polymer. It is said that the liquid crystal polymer exhibits strong mechanical strength and other excellent physical properties due to such a multilayer structure. This skin layer is a layer obtained by cooling and solidifying a molten resin layer strongly oriented along the inner wall of the mold. The reflow of the molten resin mainly occurs in the resin flow portion corresponding to the core layer.

The present inventors used "reflow length Y" defined by a measurement method described later as an index indicating the degree of reflow, and examined the relationship between this and the weld strength. It has been found that a relationship is established between Y and the minimum thickness X of the molded body at the weld line, when these values satisfy the above formula (I), a practically satisfactory weld strength is achieved. Hereinafter, the method of measuring the reflow length Y and the definition of the molded product thickness X will be described in detail.

(Method of measuring the length Y of the reflow length) The obtained injection molded body is cut perpendicular to the weld line and parallel to the injection flow. It is preferable to cut notch appropriately and mechanically than to cut with a saw, a rotary blade, or the like, because the following flow pattern is easily exposed on the cut surface.

A large number of so-called flow patterns forming a mountain shape in the flow direction are continuously observed in the cross section of the molded body cut as described above, as schematically shown in FIG. In FIG. 3, reference numerals 4 and 5 indicate the positions of the weld lines.

As shown in the figure, the flow pattern has a mountain shape at the position of the weld line, but the flow pattern gradually changes after passing the position of the weld line along the direction of reflow, At position 7, it is observed that it is also substantially parallel to the flow pattern from the opposite side, which is also gradually deformed. In the present invention, the length from the weld lines 4 and 5 to a point where the flow pattern becomes substantially parallel to the flow pattern from the opposite direction is measured, and this is defined as the reflow length Y (mm). .

When the lengths of the weld lines 4 and 5 are different from each other, the longest length is Y.

Since the molten resin flow usually flows in a three-dimensionally similar flow pattern, the above-mentioned cutting is performed at a substantially central point in the width direction of the molded body, and the reflow at this cut surface is performed. The length may be measured.

However, there is often a case where the flow pattern does not have a three-dimensionally similar flow pattern. In such a case, the injection molded body is cut at a plurality of points of the molded body perpendicularly to the weld line and parallel to the injection flow, and all cut surfaces are observed to determine a reflow length,
The longest one is the reflow length Y (m
m).

(Measurement of Molded Body Thickness X) Molded body thickness X (m
m) refers to the minimum thickness among the thicknesses of the compact at the weld line. That is, when the weld line is exposed over portions having different thicknesses of the compact, the smallest value among the different thicknesses is adopted as the thickness X of the compact of the present invention, and the calculation is performed according to the above formula.

In the case of a flat cross-sectional shape such as a rectangular cross-section of a molded body, the thickness means the length of the thinner side, while the circular or polygonal shape indicates the diameter. The thickness needs to be 0.5 mm or more. It is not preferable to use a thin molded body having a thickness of less than 0.5 mm because the effect of the present invention is not exhibited. The upper limit of the thickness X is not particularly limited as long as the thickness can be injection-molded.

In the present invention, the measured reflow length is
It is important to take a value equal to or greater than the value calculated from the thickness X (mm) of the molded body based on the formula (I). If the value is lower than the calculated value, the weld strength is remarkably reduced, and it cannot be a practical injection molded product. The value cannot be so large as long as it follows the usual injection molding machine and injection conditions, and usually it is at most about 100 mm at most.

[0049]

According to the present invention, the injection molded article of the thermotropic liquid crystal polymer of the present invention has a sufficient weld strength due to the existence of a sufficient reflow, not merely a simple deformation of the junction interface once formed. Have.

[0050]

【Example】

Hereinafter, the present invention will be further described with reference to examples and the like.

The mold used first will be described.

FIG. 1 shows a gate a for obtaining a rectangular product.
FIG. 3 is a plan view showing a multipoint gate type injection mold having respective b. In the mold shown in the figure, a cavity 3 separate from the cavity 2 is provided in a runner portion 1 near the gate a of the mold cavity 2. In this embodiment,
The length and length of the separate cavity 3 are not changed.
A mold was used in which only a predetermined length was changed.

The mold of FIG. 2 is a mold corresponding to the mold of FIG. 1 from which the separate cavity 3 and the runner attached thereto are omitted.

The measurement of the molded article thickness X and the reflow length is as follows.
The thickness at the weld line of the molded product obtained as described above was measured, and the calculated value was obtained by calculating according to the above formula. The molded product was cut, and the reflow length was measured from observation of the cut surface.

The molded body of this embodiment has a cross section of width 13
Since it is a rectangular molded body of mm, the length of the thinner side was defined as the molded body thickness X (mm). The thickness of the molded body at any part of the weld line was the same. Further, the molded body was cut at substantially the center of the molded body, and the length Y (mm) of the reflow length was obtained from observation of the cut surface. As a precautionary measure, the reflow lengths at a plurality of locations were measured in parallel with the flow in the width direction of the molded body, but it was confirmed that all of them were almost the same value.

Example 1 An injection mold having the shape and dimensions shown in the plan view of FIG. 1 was used. In addition, the length L of the separate cavity 3 in FIG. 1 is variable, and the length is separately described in Table 1. Using this mold, a thermotropic liquid crystal polymer composed of a quaternary copolyester of p-hydroxybenzoic acid / terephthalic acid / biphenol / isophthalic acid (filled with 30 wt% of glass fiber, DSC measurement melting point of unfilled product)
10 ° C, unfilled products show optical anisotropy when melted)
The cylinder temperature shown in Table 1 was measured using an injection molding machine IS-80 (trade name, mold clamping pressure 80 tons) manufactured by Toshiba Machine Co., Ltd.
Molding was performed under molding conditions such as mold temperature, injection pressure, holding pressure, and injection cycle time. Injection speed is 100mm / sec
Met.

Table 1 shows the measurement results of the bending strength and the tensile strength of the plate-like molded product obtained from the cavity 2.

Example 2 Thermotropic liquid crystal polymer composed of a quaternary copolyester of p-hydroxybenzoic acid / terephthalic acid / biphenol / isophthalic acid (unfilled product, DSC melting point: 410 ° C., optical anisotropy upon melting) (Shown), and molded under the molding conditions shown in Table 1 in the same manner as in Example 1.

Table 1 shows the measurement results of the bending strength and the tensile strength of the plate-like molded product obtained from the cavity 2.

Comparative Example Using the mold shown in FIG. 2, the thermotropic liquid crystal polymer of Example 1 was injection molded.

Table 1 shows the measurement results of the bending strength and the tensile strength of the plate-like molded product obtained from the cavity 2. In this comparative example, from the observation of the cut surface, the flow pattern was almost linear at the weld line, and the reflow length was zero according to the measurement method described above.

[Brief description of the drawings]

FIG. 1 is a plan view showing an injection molding die for obtaining a rectangular product of the same shape used in the present invention.

FIG. 2 is a plan view showing an injection mold used in a comparative example.

FIG. 3 is a schematic view of a cut surface at a weld line of the injection molded article of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Runner 2 Cavity 3 Separate cavity L Length of cavity 2 4,5 Weld line 6 Dotted line where flow pattern became linear Dotted line Weld line exposed on the surface of molded product Arrow Sprue

[Table 1]

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-168429 (JP, A) JP-A-63-221023 (JP, A) JP-A-2-150324 (JP, A) JP-A-3-3 2014 (JP, A) JP-A-3-140221 (JP, A) JP-A-3-215548 (JP, A) JP-A-3-266632 (JP, A) JP-A-1-299015 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) B29C 45/00-45/84

Claims (3)

(57) [Claims] 1. A method according to claim 1, wherein a weld line is formed on the surface of the injection molded body by combining a plurality of resin streams, and when a thickness of the molded body at the weld line is X (mm),
An injection-molded article made of a thermotropic liquid crystal polymer, characterized in that a reflow length Y (mm) in which one of the converging resin streams is reflowed after being merged satisfies the following expression. Y ≧ (2.69) ^X · 0.26 Formula (I) (where X is 0.5 mm or more) 2. The injection molded article according to claim 1, wherein the liquid crystal polymer is a wholly aromatic copolyester. 3. The injection molded article according to claim 1, wherein the liquid crystal polymer contains 70% by weight or less of a filler.