JPH0460012B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to improvements in a method and apparatus for injection molding liquid crystalline polymers. The method of the invention produces molded articles with improved mechanical properties. PRIOR ART Injection molding of molten thermotropic polymers is well known in the art. The conventional injection molding process consists of first injecting the polymer melt into a closed mold and then filling the cavity with additional melt to compensate for the compression of the melt that occurs during the cooling process. Traditionally, molded parts of liquid crystalline polymers, or other thermoplastic materials whose mechanical properties are directly correlated to the degree of molecular orientation in the molten state, are made from a remote or "end" zone of the mold cavity, from where the melt The problem is that the layers begin to become clogged) and the tensile strength decreases. It is in this end zone of the mold cavity that the laminar flow of polymer flowing into the mold cavity impinges on the walls of the cavity and reverses its direction of flow after filling. This substantial obstruction of laminar flow creates a molecular-scale ripple pattern in the melt, with associated structural weaknesses. In contrast, the molded article produced by the apparatus and method of the present invention has improved mechanical properties because the polymer molecules are oriented in a laminar flow over substantially the entire molded article. The method of the present invention reduces bouncing molecular wave motion (i.e., pattern) within the mold cavity by directing a laminar flow of molten polymer out of the traditionally terminated portion of the injection mold. Therefore, molded products with excellent mechanical properties can be formed. OBJECTS OF THE INVENTION It is, therefore, an object of the present invention to provide an improved method for injection molding thermotropic liquid crystalline polymers, which allows molded articles with excellent mechanical properties to be formed. Another object of the present invention is to provide improved injection molding of thermotropic liquid crystalline polymers capable of forming molded articles in which the constituent polymer molecules of the molded article are oriented in layers substantially throughout the article. The purpose is to provide a method. Another object of the present invention is to provide an injection molding apparatus for thermotropic liquid crystalline polymers capable of forming molded articles with excellent mechanical properties. Yet another object of the present invention is to provide a thermotropic liquid crystalline polymer injection molding apparatus capable of forming molded articles in which the constituent polymer molecules of the molded article are oriented substantially in layers throughout the article. It is to provide. Another object of the present invention is to provide improved molded articles having excellent mechanical properties, molded from thermotropic liquid crystalline polymers. Another object of the present invention is to provide a molded article made of a thermotropic liquid crystalline polymer in which the constituent polymer molecules of the molded article are oriented in layers over substantially the entire article. SUMMARY OF THE INVENTION The present invention provides an improved method for molding thermotropic liquid crystalline polymers and an apparatus for the method. This method involves forming a melt stream of the polymer to be molded; injecting this melt stream into a mold cavity; and allowing a portion of the melt to flow out of the cavity to suppress rebound molecular wave motion within the cavity. substantially maintaining a laminar flow pattern of the melt within the cavity; and solidifying the molten polymer to obtain a molded article. Hereinafter, a method and apparatus for injection molding a liquid crystalline polymer according to the present invention will be described in detail with reference to the accompanying drawings. Representative types of thermotropic liquid crystalline polymers suitable for use in the present invention include fully aromatic polyesters, aromatic-aliphatic polyesters, fully aromatic poly(ester-amides), aromatic-aliphatic These include poly(ester-amide), aromatic polyazomethine, aromatic polyester-carbonate and mixtures thereof. In preferred embodiments, the thermotropic liquid crystalline polymer is a fully aromatic polyester, a fully aromatic poly(ester-amide) or an aromatic-aliphatic poly(ester-amide). In such fully aromatic polyesters and fully aromatic poly(ester-amides), all components present in the polymer chain contain at least 1
gives aromatic rings. In addition, the thermotropic liquid crystalline polymer may contain at least 10 mol% of naphthalene components such as 6-oxy-2-naphthoyl component, 2,6-dioxynaphthalene component, or 2,6-dicarboxynaphthalene component. Preferably, it is present in an amount. A particularly preferred naphthalene component for presence in the thermotropic liquid crystalline polymer is a 6-oxy-2-naphthoyl component in an amount of about 10 mole percent or more. As a typical fully aromatic polyester exhibiting thermotropic liquid crystal properties, U.S. Patent No.
3991013; 3991014; 4066620; 4067952;
4075262; 4083829; 4093595; 4118372;
4130545; 4146702; 4153779; 4156070;
4159365; 4161470; 4169933; 4181792;
4183895; 4184996; 4188476; 4201856;
4219461; 4224433; 4226870; 4230816;
4232143; 4232144; 4238598; 4238599;
4238600; 4242496; 4245082; 4245084;
4247514; 4256624; 4265802; 4267304;
4269965; 4279803; 4299756; 4294955;
4318841; 4337190; 4337191; and commonly assigned U.S. Patent Application No. 270440 (June 4, 1981).
Examples include those disclosed in the application). As discussed below, the fully aromatic polyesters described in US Pat. No. 4,161,470 are particularly suitable for use in the present invention. Representative aromatic-aliphatic polyesters exhibiting thermotropic liquid crystallinity are described by W.J. Jackson, Jr.
HFKuhfuss and TFGray, Jr., Self-Reinforced Thermoplastic Polyester X7G-A, American Plastics Industry Association, Reinforced Plastics/Composites Subcommittee, Vol.
30th Annual Technical Conference (1975), Section 17-D,
Copolymers of polyethylene terephthalate and hydroxybenzoic acid disclosed on pages 1-4. This copolymer is further disclosed in WJJackson.Jr., and HF
Kuhfuss, “Liquid crystal polymers: Preparation and properties of p-hydroxybenzoic acid copolymers,” Journal of
Polymer Science, Polymer Chemistry
Edition, Vol. 14, pp. 2043-58 (1976). Reference may also be made to U.S. Pat. Representative fully aromatic and aromatic-aliphatic poly(ester-amides) exhibiting thermotropic liquid crystallinity are disclosed in U.S. Pat.
No. 4339375 and US Patent Application Nos. 251625 (filed April 6, 1981) and US Patent Application Nos. 251629 and 251629, assigned to the present applicant.
No. 251818 (filed on April 7, 1981) and No. 251819 (filed on April 7, 1981). As discussed below, U.S. Patent No. 4,330,457
Particularly preferred for use in the present invention are the poly(ester-amides) disclosed in the US Pat. A typical aromatic polyazomethine exhibiting thermotropic liquid crystallinity is disclosed in US Pat. No. 3,493,522;
3493524; 3503739; 3516970; 3516971;
3526611; 4048148; and 4122070. Specific examples of such polymers include:
Poly(nitrilo-2-methyl-1,4-phenylenenitriloethyridine-1,4-phenyleneethyridine), poly(nitrilo-2-methyl-1,4
-phenylene nitrilomethylidine-1,4-phenylene methylidine), and poly(nitrilo-2
-chloro-1,4-phenylenenitrilomethylidine-1,4-phenylenemethylidine). A typical aromatic polyester-carbonate exhibiting thermotropic liquid crystal properties is disclosed in U.S. Patent No.
4107143 and commonly assigned U.S. Patent Application No. 319024 (filed Nov. 6, 1981). Examples of such polymers include those consisting essentially of p-oxybenzoyl, p-dioxyphenyl, dioxycarbonyl and terephthoyl units. Thermotropic liquid crystalline polymers for use in producing molded articles according to the invention are generally selected from those exhibiting melting points within a range compatible with injection molding using commercially available equipment. For example, a thermotropic liquid crystalline polymer having a melting temperature within the range of about 200 DEG to 400 DEG C. is generally selected. The thermotropic liquid crystalline polymer used is
at least about 2.0 dl/g when dissolved in pentafluorophenol at 60°C at a concentration of 0.1% by weight;
For example, the logarithmic viscosity (I.
V.) is preferred. Particularly preferred fully aromatic polyesters for use in the present invention are U.S. Pat.
The polyester disclosed in No. The polyester consists essentially of the following repeating components and: It contains about 10 to 90 mol% of the component and about 10 to 90 mol% of the component. In one embodiment, the component is about 65-85 mol%, preferably about 70-80 mol%
(e.g., about 73 mole %). In another embodiment, the components are present in small amounts of about 15-35 mole%, preferably about 20-30 mole%.
In addition, at least a part of the hydrogen atoms bonded to the ring is an alkyl group having 1 to 4 carbon atoms, or an alkyl group having 1 to 4 carbon atoms.
may be optionally substituted with a substituent selected from the group consisting of an alkoxy group, halogen, phenyl, substituted phenyl, and combinations thereof. This polymer has approximately 3.5 to 7.5
Preference is given to the logarithmic viscosity number in dl/g. Particularly preferred fully aromatic poly(ester-amides) or aromatic-aliphatic poly(ester-amides) for use in the present invention are capable of forming an anisotropic melt phase at temperatures below about 400°C. It is disclosed in US Pat. No. 4,330,457. This poly(ester-amide) consists essentially of the following repeating components, and optionally: : [Formula] (wherein A is a divalent group containing at least one aromatic ring or a divalent trans-1,
4-cyclohexylene group): [-Y-Ar-Z]- (wherein, Ar is a divalent group containing at least one aromatic ring, Y is O, NH or NR, Z is NH or NR respectively, and R means an alkyl group or aryl group having 1 to 6 carbon atoms): [-O-Ar'-O]- (wherein, Ar' is a divalent group containing at least one aromatic ring) (In the above formula, at least some of the hydrogen atoms bonded to the ring may optionally be an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, halogen, phenyl, substituted (optionally substituted with a substituent selected from the group consisting of phenyl and combinations thereof), consisting of about 10 to 90 mol% of the component, about 5 to 45 mol% of the component, and about 5 to 45 mol% of the component %, and components in amounts of about 0 to 40 mole %. Preferred dicarboxyaryl components are: and a preferred component is [Formula] or [Formula], and a preferred dioxyaryl component is and a preferred dioxyaryl component is [Formula]. When forming the molded article of the present invention, the molding device of the present invention can be used in combination with a conventional injection device. A suitable injection device is a Stubbe automatic injection molding machine model SKM50/45. The temperature and pressure conditions utilized to mold a molten thermotropic liquid crystalline polymer will depend on the melting temperature of the polymer and its viscosity, as will be apparent to those skilled in the art. Generally, an injection molding temperature of about 5 to 50 degrees Celsius above the melting temperature of the polymer and about
A pressure of 2000-20000psi (140-1400Kg/ ^cm2 ) is adopted. In conventional molding of liquid crystalline polymers, the melt flows into a cavity in laminar flow conditions, with each layer within the melt flowing at a uniform velocity without substantial interlayer mixing. When this flow hits the downstream end of the cavity and bounces back from it, the laminar flow ends at this end due to interference from the rebounding molecular wave pattern. Since the mechanical properties of a molded liquid crystalline polymer are directly related to the degree of regular arrangement of molecules within each layer, this reverse flow creates structural weaknesses in the molded product and reduces its mechanical properties. . In the present invention, as shown in FIGS. 1 and 2, for example, a discharge port 5 is provided at the downstream end of the cavity 4.
The provision of the molten material allows the molten material to flow out of the cavity, thereby preventing undesirable rebound molecular wave motion (patterns) within the cavity. In a preferred embodiment, a channel 6 is provided leading to the downstream outlet 5 to receive the molten material. In addition, in the figure, 1 is a valve, 2 is a runner, and 3
is the upstream inlet or gate. The present invention also encompasses the case where the molten material is introduced into the mold cavity through two upstream inlets provided at both ends of the mold, and the downstream outlet is provided midway between these inlets. Conversely, it is also within the scope of the present invention to allow the molten material to flow into the mold cavity through an upstream inlet located between the two downstream outlets. If desired, there is also at least one additional flow point downstream of the upstream inlet (e.g., intermediate the outlet at the downstream end and the upstream inlet) to further modify the flow characteristics of the molten material. It is also within the scope of the invention to provide an outlet. Furthermore, it is also possible to arrange two or more inlets at one end of the mold. After the molded part is removed from the mold, the flash of material that has solidified within the channel can be trimmed from the molded part.
The molded articles obtained according to the invention exhibit superior mechanical properties compared to products molded by conventional methods. The mechanical properties of the molded article produced by the method of the present invention can be further improved by subjecting it to heat treatment after injection molding. Heat treatment of molded parts should be carried out in an inert atmosphere (e.g. nitrogen, argon,
Helium) or in a flowing oxygen-containing atmosphere (eg, air). For example, the molded product should be heated approximately 5 to 30 degrees Celsius above the melting temperature of the liquid crystalline polymer.
The heat treatment may be carried out by heating to a low temperature (at which temperature the molded article remains a solid article). The heat treatment time generally ranges from a few minutes to several days or tens of days, such as 0.5 to 200 hours or more, preferably the heat treatment time is 1 to 48 hours (eg, about 24 to 30 hours).
This heat treatment increases the molecular weight and crystallinity of the liquid crystalline polymer, thereby improving the mechanical properties of the product. The following examples are given as specific examples of the present invention. However, it goes without saying that the present invention is not limited to the contents of these Examples. EXAMPLE 1 ASTM 8.5 inch (21.6 cm) test bars were molded from a particularly preferred thermotropic liquid crystalline fully aromatic polyester disclosed in U.S. Pat. No. 4,161,470. The polyester used consisted of 70 mol% 4-oxybenzoyl component and 30 mol% 6-oxy-2-naphthoyl component. Molding of the polymer was carried out using a conventional injection apparatus incorporating the mold apparatus shown in FIG. The molten polymer was injected into the valve 1 and flowed in a substantially laminar flow through the runner 2 and into the mold cavity 4 through the upstream inlet 3. The melt exited the mold cavity 4 through the downstream outlet 5 and entered the flow path 6 in order to maintain laminar flow substantially throughout the test article. The results of measuring the mechanical properties of a plurality of tensile test bars manufactured according to this example are shown in Table 1 below. For comparison, a plurality of tensile test bars were separately molded in the same manner as above, except that the discharge port 5 was closed and the mold cavity 4 was filled in the conventional manner. The results of measuring the mechanical properties of this test bar are also shown in Table 1. [Table] The mechanical property values shown in Table 1 above are:
Measured according to ASTM standard test methods D256 and D638. The data in Table 1 shows that the mechanical properties of molded articles molded with open-ended molds of the present invention are significantly improved. Thus, this example demonstrates the highly beneficial effects achieved by substantially maintaining laminar flow during molding of liquid crystalline polymers. Example 2 A plurality of test bars prepared according to Example 1 were heat treated at 270° C. for 42 hours in a nitrogen atmosphere.
The results of measuring the mechanical properties of the test bar after this heat treatment are shown in Table 2 below. [Table] Measurements were performed using the same test method as in Example 1. This data demonstrates the significant improvement in mechanical properties obtained by maintaining laminar flow substantially throughout the liquid crystalline polymer molded article. Example 3 The method of Example 1 was repeated, except that a thermotropic fully aromatic polyester consisting of 75 mol% of 4-oxybenzoyl component and 25 mol% of 6-oxy-2-naphthoyl component was used as the liquid crystalline polymer. did. The mechanical properties of the resulting tensile test bars were measured using the test methods listed in Table 1.
The results are shown in Table 3 below. [Table] [Table] The data in Table 3 again shows that the mechanical properties of molded articles molded by the method of the present invention are significantly improved compared to molded articles molded by conventional methods. Example 4 A tensile test bar manufactured by the method of Example 3 was heat treated at 300° C. for 62 hours in a nitrogen atmosphere. After this heat treatment, the mechanical properties of each test bar made with the open end mold and the conventional mold were measured using the test method listed in Example 1. The results are shown in Table 4 below. TABLE This data again demonstrates the improvement in mechanical properties that can be obtained by flowing the polymer in laminar flow through substantially the entire mold cavity when making molded articles from liquid crystalline polymers. Example 5 The procedure of Example 1 was repeated, except that the liquid crystalline polymer was a fully aromatic poly(ester-amide) or an aromatic-aliphatic poly( ester-amide) was used. The mechanical properties of the resulting tensile test bar were measured by the test method listed in Example 1. An example of the results is shown in Table 5 below. TABLE This data demonstrates that liquid crystalline polymers molded by the method of the present invention exhibit significantly superior tensile properties compared to liquid crystalline polymers molded by conventional methods. Although the present invention has been described above with reference to preferred embodiments, it is of course possible to make various changes and modifications within the scope of the present invention, as will be apparent to those skilled in the art.

[Brief explanation of the drawing]

1 and 2 show a portion of one embodiment of an injection molding apparatus equipped with a two-piece mold according to the present invention;
The figure is an enlarged schematic diagram of one embodiment of injection molding equipment suitable for use in the method of the invention. 1... Valve, 2... Runner, 3... Inlet, 4... Cavity, 5... Outlet, 6... Channel.

Claims (1)

[Claims] 1. (a) forming a molten stream of a thermotropic liquid crystalline polymer; (b) introducing the molten stream into the cavity from an inlet communicating with the upstream end of the cavity in the mold; (c) at the downstream end of the cavity so as to cause the molten material to flow out of the cavity while filling the cavity to suppress rebound molecular wave motion of the molten material within the cavity; A process for producing a thermotropic liquid crystalline polymer comprising the steps of: (d) causing a part of the melt flow to flow out from an outlet communicating with the cavity; and (d) solidifying the molten material remaining in the cavity to obtain a molded article. Improved injection molding method. 2. The thermotropic liquid crystalline polymer is fully aromatic polyester, aromatic-aliphatic polyester, fully aromatic poly(ester-amide), aromatic-aliphatic poly(ester-amide), aromatic polyazomethine, aromatic 2. An improved method of injection molding of thermotropic liquid crystalline polymers according to claim 1, wherein the thermotropic liquid crystalline polymer is selected from the group consisting of polyester-carbonates, and mixtures thereof. 3. An improved injection molding method for a thermotropic liquid crystalline polymer according to claim 1, wherein said thermotropic liquid crystalline polymer is a fully aromatic polyester. 4. Improved injection of a thermotropic liquid crystalline polymer according to claim 1, wherein the thermotropic liquid crystalline polymer is a fully aromatic poly(ester-amide) or an aromatic-aliphatic poly(ester-amide). Molding method. 5. The improved injection molding method for a thermotropic liquid crystalline polymer according to claim 1, wherein the thermotropic liquid crystalline polymer contains 10 mol% or more of repeating units containing a naphthalene moiety. 6 The thermotropic liquid crystalline polymer is 6-
Claim 1, which contains about 10 mole percent or more of repeating units containing a naphthalene moiety selected from the group consisting of an oxy-2-naphthoyl moiety, a 2,6-dioxynaphthalene moiety, and a 2,6-dicarboxynaphthalene moiety. An improved method for injection molding a thermotropic liquid crystalline polymer according to item 1. 7. The improved injection molding method for a thermotropic liquid crystalline polymer according to claim 1, wherein the thermotropic liquid crystalline polymer contains 10 mol% or more of a 6-oxy-2-naphthoyl repeating component. 8. The thermotropic liquid crystalline polymer essentially comprises the following recurring components and: (In the above formula, at least a part of the hydrogen atoms bonded to the aromatic ring may optionally be an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, halogen, phenyl, substituted phenyl, or (optionally substituted with a substituent selected from the group consisting of a combination of An improved injection molding method for thermotropic liquid crystalline polymers according to claim 1. 9. An improved injection molding method for thermotropic liquid crystalline polymers according to claim 8, wherein component 9 is present in an amount of about 65 to 85 mole percent. 9. The method of claim 8, wherein the 10 component is present in an amount of about 70 to 80 mole percent. 9. An improved injection molding method for thermotropic liquid crystalline polymers according to claim 8, wherein component 11 is present in an amount of about 15 to 35 mole percent. 9. The improved injection molding method of thermotropic liquid crystalline polymers according to claim 8, wherein component 12 is present in an amount of about 20 to 30 mole percent. 13 The thermotropic liquid crystalline polymer consists essentially of the following recurring components, and optionally: : [Formula] (wherein A is a divalent group containing at least one aromatic ring or a divalent trans-1,
4-cyclohexylene group): [-Y-Ar-Z]- (wherein, Ar is a divalent group containing at least one aromatic ring, Y is O, NH or NR, Z is NH or NR respectively, and R means an alkyl group or aryl group having 1 to 6 carbon atoms): [-O-Ar'-O]- (wherein, Ar' is a divalent group containing at least one aromatic ring) (However, at least a portion of the hydrogen atoms bonded to the ring may optionally be an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, halogen, phenyl, substituted phenyl, (optionally substituted with a substituent selected from the group consisting of a combination of these), consisting of about 10 to 90 mol% of the component, about 5 to 45 mol% of the component, and about 5 to 45 mol% of the component, and a poly(ester-amide) containing the components in an amount of about 0 to 40 mole percent.
Improved injection molding method for thermotropic liquid crystalline polymers as described in . 14 The ingredients are An improved injection molding method for a thermotropic liquid crystalline polymer according to claim 13. 15. The improved injection molding method for a thermotropic liquid crystalline polymer according to claim 13, wherein the component is [Formula] or [Formula]. 16. The improved injection molding method for a thermotropic liquid crystalline polymer according to claim 13, wherein the component is [Formula]. 17 The thermotropic liquid crystalline polymer is 4
2. An improved method for injection molding a thermotropic liquid crystalline polymer according to claim 1, which comprises about 75 mol% of a -oxybenzoyl component and about 25 mol% of a 6-oxy-2-naphthoyl component. 18 Consists of a mold having a cavity therein, an inlet communicating with the upstream end of the cavity, and an injection device for injecting molten material from the inlet into the cavity to form a molded article. An injection molding apparatus of the type in which the mold is configured to allow molten material to flow out of the cavity while filling the cavity to suppress rebound molecular wave motion of the molten material within the cavity. said injection molding apparatus, characterized in that said injection molding apparatus is provided with an outlet opening into said cavity at the downstream end of said cavity. 19. The apparatus of claim 18, further comprising a channel communicating with the outlet for receiving molten material from the outlet. 20. At least a portion of the melt stream is also caused to flow out through at least one additional outlet communicating with the cavity, which is located downstream of the inlet used for injection of the melt stream. Improved injection molding method for thermotropic liquid crystalline polymers. 21. The injection molding apparatus of claim 18, further comprising at least one additional outlet downstream of the inlet.