JP2007182505A - Production method for wholly aromatic thermotropic liquid crystal polyester and its use - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve hue degradation of a wholly aromatic thermotropic liquid crystal polyester without deteriorating good moldability and heat resistance. <P>SOLUTION: The production method for the wholly aromatic thermotropic liquid crystal polyester is carried out by using raw materials including an aromatic hydroxycarboxylic acid, and involves an acetylation process, a melt polycondensation process, a cooling solidification process where the product by the melt polycondensation process is cooled and solidified, a process of pulverizing the solidified product and a solid-phase polycondensation process, in this order. The solidification process comprises the means of cooling with nitrogen stream, where the product is cooled to ≤50°C within 20 hours after being taken out from the melt polyconsensation process. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a wholly aromatic thermotropic liquid crystal polyester excellent in hue, a wholly aromatic thermotropic liquid crystal polyester obtained by the method, and an LED reflector using the polyester.

  As a light-emitting diode (hereinafter referred to as “LED”) device, an LED element is mounted on a circuit pattern on a substrate with a conductive adhesive, solder, etc., and necessary connection is made by wire bonding, and the light utilization rate of the LED is increased. In order to raise, a reflector (reflective frame) is provided around the LED element, and the LED element positioned in the reflector is sealed with a translucent resin. As the reflector, a resin filled with a white pigment or the like is used. Various types of white LEDs are known. For example, generally, a white LED is obtained by combining a plurality of LEDs such as green (G), blue (B), and red (R). There is also one that uses a wavelength conversion effect by blending a fluorescent material in a stop resin. In the case of wavelength conversion, an ultraviolet light emitting LED can also be used as a light source.

  Various heating processes such as soldering when mounting the LED element on the substrate, heat generation during thermosetting of the sealing resin, heating when the LED device is bonded to other members, heating in the environment where the LED device is used, etc. Heating history is inevitable, so heat resistance is required. Furthermore, in white LED, it is requested | required that the reflectance of a reflective surface and whiteness should be maintained at the time of manufacture and use. From this point, it is considered that the wholly aromatic thermotropic liquid crystal polyester having a melting point exceeding 320 ° C. is suitable as a resin for an LED reflector. However, the wholly aromatic thermotropic liquid crystal polyester is excellent in heat resistance and fluidity at the time of molding. However, in order to use it as an LED reflector, it is required to improve hue deterioration and a decrease in reflectance due thereto.

  Fully aromatic thermotropic liquid crystalline polyesters with a melting point of over 320 ° C use monomers containing aromatic hydroxycarboxylic acids as raw materials, but obtaining a polyester with the desired molecular weight only through the melt polycondensation step is the production of a polymerization reaction in the molten state. Since the product is kept in a high temperature environment of 300 ° C. or higher for a long time, it is difficult to avoid thermal degradation of the polymerization reaction product, which is not preferable. The thermal history in the manufacturing process causes the hue of the product to deteriorate. Therefore, the reaction is allowed to proceed to a certain degree of polymerization by a melt polycondensation process at a relatively high temperature and in a relatively short time, and the product is discharged from the reaction vessel, cooled, solidified and pulverized, and then desired in the solid phase polycondensation process. Increasing the degree of polymerization to the molecular weight has been adopted as an industrially preferred method. In this case, low molecular weight compounds such as by-product decomposition products, low molecular weight products and unreacted monomers generated in the melt polycondensation process are considered to cause hue deterioration of the molded product, and these are included in the product. Must be avoided.

  A method in which the monomer is acetylated and used is preferable because the melt polycondensation rate is high, so that the influence of the heat history during melt polycondensation can be reduced. However, the acetic acid compound produced in the acetylation process may remain as a low molecular weight compound. is there. In addition, in order to improve the productivity of the melt polycondensation process, unacetylated monomers are charged into the melt polycondensation tank, acetic anhydride, etc. coexist, and an acetylated product is generated by an esterification reaction under heating, followed by melting. When a polycondensation reaction is carried out, the production of low molecular weight compounds increases.

  Methods for removing low molecular weight compounds out of the system have been conventionally studied during the melt polycondensation step and the solid phase polycondensation step. However, that alone is not sufficient to eliminate the hue deterioration of precision parts such as LED reflectors. On the other hand, with regard to the cooling / solidification / pulverization process between the melt polycondensation process and the solid-phase polycondensation process, studies have been made mainly on improving the efficiency of the cooling / solidification process itself. The removal of molecular weight compounds has not been sufficiently studied from the viewpoint of hue deterioration.

  Until now, as a cooling and solidification method, after the aromatic polyester extracted from the melt polycondensation tank is passed through a quantitative supply device having a flow path narrowing feeder, a double belt cooler is used. A method of cooling and solidifying has been proposed (for example, Patent Document 1). However, in this method, the cooling and solidification is carried out substantially in a closed system, so that the removal of the low molecular weight compound outside the system under the cooling and solidification step is not sufficient. Moreover, although the method (for example, patent document 2) which cools and solidifies with the roll which has a some groove | channel on the surface is proposed, there exists a similar problem.

  Further, the melt is supplied to a cooling device having a pair of cooling rolls having rotation axes parallel to each other and a pair of weirs provided on the pair of cooling rolls, and the pair of weirs on the pair of cooling rolls A method of cooling and solidifying by passing between a pair of cooling rolls rotating a part of the cooling roll while temporarily holding the recess formed in the above is proposed (for example, Patent Document 3). In this method, since cooling solidification is performed in an open system, the release of low molecular weight compounds to the outside of the system is achieved to some extent under the cooling solidification process, but the effect is limited, and is required for resin for LED reflectors. It is difficult to achieve the desired performance. As described above, there has not yet been proposed a specific means that has a sufficient effect for removing low molecular weight compounds in the cooling and solidifying step.

JP-A-6-256485 Japanese Patent Laid-Open No. 2-86412 JP 2002-179779 A

  The heat resistance and moldability of wholly aromatic thermotropic liquid-crystalline polyesters obtained from monomers containing aromatic hydroxycarboxylic acids by the acetylation process, melt polycondensation process, cooling solidification process, grinding process and solid phase polycondensation process It is an object to prevent hue deterioration of a molded product without damaging it. The present inventors have found that the main cause of hue deterioration is a low molecular weight compound contained in a wholly aromatic thermotropic liquid crystal polyester molded product. Therefore, it is required to remove the low molecular weight compound. However, removal of low molecular weight compounds in the conventional melt polycondensation process and solid phase polycondensation process alone cannot sufficiently meet the demand for preventing hue deterioration. The present invention provides a method for efficiently removing a low molecular weight compound in a cooling / solidification step in addition to a melt polycondensation step and a solid phase polycondensation step, and a polyester excellent in hue deterioration and suitable for an LED reflector It is a problem to provide.

  The first of the present invention uses a raw material containing an aromatic hydroxycarboxylic acid, an acetylation step, a melt polycondensation step, a cooling solidification step of cooling and solidifying the product of the melt polymerization step, a step of pulverizing the solidified product, and A method for producing a wholly aromatic thermotropic liquid crystalline polyester comprising solid phase polycondensation steps in this order, comprising means for cooling with a nitrogen stream in the cooling and solidifying step, and the product is removed from the melt polycondensation step. It is a method for producing a wholly aromatic thermotropic liquid crystal polyester, characterized in that the temperature is set to 50 ° C. or less within 20 hours after being released.

  A second aspect of the present invention is a method for producing a wholly aromatic thermotropic liquid crystal polyester according to the first aspect of the present invention, wherein the acetylation step and the melt polycondensation step are performed in the same reaction vessel. is there.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the cooling and solidifying step uses a pair of cooling rolls having parallel rotation axes and a device having a pair of weirs on the cooling roll. And a step of allowing the reactant in the melt polycondensation step in a molten state to pass between the cooling rolls while forming a reservoir on the cooling roll. It is a manufacturing method.

  A fourth aspect of the present invention is a wholly aromatic thermotropic liquid crystal polyester obtained by the method according to any one of the first to third aspects of the present invention.

  A fifth aspect of the present invention is an LED reflector including the wholly aromatic thermotropic liquid crystal polyester according to the fourth aspect of the present invention.

   According to the method of the present invention, by controlling the cooling means by the nitrogen stream in the cooling and solidifying process and the time to reach a predetermined temperature, the total fragrance improved in hue deterioration without major modification or change to the conventional manufacturing process. A group of thermotropic liquid crystal polyesters can be produced. The obtained wholly aromatic thermotropic liquid crystalline polyester is particularly suitable for LED reflectors having severe conditions regarding heat resistance and hue deterioration.

(Totally aromatic thermotropic liquid crystal polyester)
In order to use as an LED reflector, the wholly aromatic thermotropic liquid crystal polyester in the present invention preferably has a melting point of 320 ° C. or higher. In order to obtain a wholly aromatic thermotropic liquid crystalline polyester having a melting point of 320 ° C. or higher, p-hydroxybenzoic acid is preferably used in an amount of 40 mol% or more as a raw material monomer. Other than these, known aromatic hydroxycarboxylic acids, aromatic dicarboxylic acids, and aromatic diols can be used in any combination. For example, polyesters obtained only from aromatic hydroxycarboxylic acids such as p-hydroxybenzoic acid and 2-hydroxy-6-naphthoic acid, and aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid and 2,6-naphthalenedicarboxylic acid. Preferable examples include acid and / or liquid crystalline polyester obtained from an aromatic dihydroxy compound such as hydroquinone, resorcin, 4,4′-dihydroxydiphenyl, and 2,6-dihydroxynaphthalene.

  Particularly preferably, p-hydroxybenzoic acid (I), terephthalic acid (II), 4,4′-dihydroxybiphenyl (III) (including these derivatives) is contained in an amount of 80 to 100 mol% (provided that (I) and (II) is added to 60 mol% or more), and (I), (II), or (III) is condensed with any other aromatic compound capable of decondensation reaction in an amount of 0 to 20 mol%. A wholly aromatic thermotropic liquid crystal polyester.

(Acetylation process)
Melt polycondensation is performed after previously acetylating the hydroxyl groups of the above monomers. The acetylation is preferably carried out in a conventional manner by supplying acetic anhydride to the monomer in the reaction vessel. This acetylation step is preferably performed using the same reaction vessel as the melt polycondensation step. That is, it is preferable to carry out an acetylation reaction with a raw material monomer and acetic anhydride in a reaction vessel, and then proceed to a polycondensation reaction by raising the temperature after completion of the reaction.

(Melt polycondensation process)
In the present invention, a melt polycondensation reaction is carried out with a deacetic acid reaction of the acetylated monomer. The reaction vessel is preferably used using a reaction vessel equipped with monomer supply means, acetic acid discharge means, molten polyester take-out means and stirring means. Such a reaction vessel (polycondensation apparatus) can be appropriately selected from known ones. The polymerization temperature is preferably 150 ° C to 350 ° C. After completion of the acetylation reaction, the temperature is raised to the polymerization start temperature to start polycondensation, the temperature is raised in the range of 0.1 ° C./min to 2 ° C./min, and the final temperature is raised to 280 to 350 ° C. Is preferred. As the catalyst for the polycondensation reaction, compounds such as Ge, Sn, Ti, Sb, Co, Mn, and Mg can be used. The polycondensation temperature rises as the melting temperature of the produced polymer rises as the polycondensation proceeds. The melt polycondensation reaction product subjected to the solid phase polycondensation step is a wholly aromatic thermotropic liquid crystal polyester having a low polymerization degree, and its pour point is preferably 200 ° C or higher, more preferably 220 ° C to 330 ° C.

(Cooling solidification process)
When the degree of polymerization corresponding to the pour point is reached, the fully aromatic thermotropic liquid crystalline polyester having a low degree of polymerization is withdrawn from the polymerization tank in a molten state, supplied to a cooler such as a steel belt or drum cooler, and cooled to solidify. Let Details of the cooling and solidifying step will be described later.

  Before shifting to the pulverization step, it is preferable to crush the solidified product during cooling to an appropriate size in order to improve the cooling efficiency. In this invention, this crushing process is also included as a part of cooling and solidification process.

(Crushing process)
Next, the solidified wholly aromatic thermotropic liquid crystal polyester having a low polymerization degree is pulverized to a size suitable for the subsequent solid phase polycondensation. The crushing method is not particularly limited. For example, impact mills such as feather mill, Victor mill, Coroplex, Pulverizer, Contraplex, scroll mill, ACM pulverizer, etc. manufactured by Hosokawa Micron Co., Ltd. A roll granulator or the like. Particularly preferred is a feather mill manufactured by Hosokawa Micron. In the present invention, the particle size of the pulverized material is not particularly limited, but it is preferably in the range of 4 mesh to 2000 mesh not passing through an industrial sieve (Tyler mesh), preferably 5 mesh to 2000 mesh (0.01 to 4 mm). More preferably, it is most preferably 9 mesh to 1450 mesh (0.02 to 2 mm).

(Solid phase polycondensation process)
Next, the pulverized product obtained in the pulverization step is subjected to a solid phase polycondensation step to perform solid phase polycondensation. There is no restriction | limiting in particular in the apparatus used for a solid-phase polycondensation process, and operating conditions, A well-known apparatus and method can be used. For use as an LED reflector, a solid phase polycondensation reaction is performed until a melting point of 320 ° C. or higher is obtained.

(Details of cooling solidification process)
The present inventors consider the thermal history in the manufacturing process and / or the residual low molecular weight compound in the product polymer or their interaction as the cause of the hue deterioration of the wholly aromatic thermotropic liquid crystal polyester. In particular, since the initial temperature of the polycondensation reaction product in the molten state extracted from the melt polycondensation reaction tank is as high as 280 ° C. to 350 ° C., and there are a relatively large amount of residual low molecular weight compounds, etc. The environment is prone to degradation and oxidative degradation reactions. Appropriate responses at this stage are evident from the facts shown in the examples and comparative examples described below, and the final fully aromatic thermotropic liquid crystal polyester It suppresses hue deterioration.

  In the present invention, in the step of cooling and solidifying the wholly aromatic thermotropic liquid crystal polyester having a low polymerization degree extracted from the melt polycondensation reaction tank after the melt polycondensation step, a means for cooling using a nitrogen stream as a refrigerant is included. It is characterized by that. This cooling means includes a low molecular weight compound released from the wholly aromatic liquid crystal polyester having a low degree of polymerization (in particular, in addition to forced cooling with a nitrogen stream so that the temperature drops more than that of natural cooling (standing). It is necessary that the acetic acid compound) be transferred by a nitrogen stream. Furthermore, suppression of the oxidation reaction is also achieved by the inertness of nitrogen. However, it does not necessarily mean that all the stages of the cooling and solidification process are performed in a closed system that is completely replaced by nitrogen. As the nitrogen source, for example, nitrogen from a nitrogen source permanently installed in a chemical factory can be used.

  In the present invention, the temperature of the cooled solidified product is set to 50 ° C. or less within 20 hours after the product is extracted from the melt polycondensation step. If the temperature of 50 ° C. or more continues for 20 hours or more, a hue deterioration problem may occur when used in a reflector or the like. The temperature and flow rate of the nitrogen stream can be appropriately selected depending on the amount and shape of the object to be cooled, the shape of the apparatus, and the like. When using a nitrogen source in a factory, there is no problem in using one at an outside temperature or room temperature. The upper limit of the temperature of the nitrogen stream only needs to have a cooling effect. That is, it should be lower than the melt polycondensate or melt polycondensate that is to be cooled, and may be cooled by gradually decreasing the temperature. It is preferable to use those. However, a nitrogen stream below the temperature at which moisture in the nitrogen stream and / or the environment solidifies, particularly nitrogen at 0 ° C. or below which freezes the moisture in the system is not preferred.

  In the cooling and solidifying step of the present invention, a reaction product (low polymerization degree) having a molten polycondensation step in a molten state is used by using a pair of cooling rolls having parallel rotation axes and a device having a pair of weirs on the cooling roll. It is preferable to include a step of allowing the wholly aromatic thermotropic liquid crystal polyester) to pass between the cooling rolls while forming a pool portion on the cooling roll. As such a process, what is indicated by JP, 2002-179779, A concerning the present inventors' invention can be used preferably. When this step is performed, since the interface between the melt polycondensation reaction product in a molten state held on the roll and the outside air is continuously updated, the effect of using the nitrogen stream according to the present invention in the part is large. . Moreover, it is also a preferable method that the crushed solidified product is cooled with a nitrogen stream to reach a predetermined temperature within a predetermined time.

  The wholly aromatic thermotropic liquid crystalline polyester obtained by the production method of the present invention has a melting point of 320 ° C. or higher and is excellent not only in heat resistance but also in improved hue deterioration.

  The reflector for LED containing the wholly aromatic thermotropic liquid crystal polyester of the present invention is obtained by a well-known method, for example, by blending rutile type titanium oxide to obtain a composition, which is molded by molding means such as injection molding. It is done.

(Melt polycondensation process)
In a reaction vessel made of SUS316L (stainless steel) having a double helical stirring blade and an internal volume of 1.7 m ³ , 298.3 kg (2.16 kgol) of p-hydroxybenzoic acid (manufactured by Ueno Pharmaceutical Co., Ltd.) 4,4'-dihydroxydiphenyl (Honshu Chemical Co., Ltd.) 134.1 kg (0.72 kgmol), terephthalic acid (Mitsui Chemicals) 89.7 kg (0.54 kgmol), isophthalic acid (AG International) 29.9 kg (0.18 kgole), 0.11 kg of magnesium acetate (manufactured by Kishida Chemical Co., Ltd.), and 0.04 kg of potassium acetate (manufactured by Kishida Chemical Co., Ltd.) were charged as catalysts. Then, after depressurizing and injecting nitrogen into the polymerization tank twice to replace with nitrogen, 385.9 kg (3.78 kgol) of acetic anhydride was added, and the temperature was increased to 150 ° C. at a rotation speed of a stirring blade at 45 rpm in 1.5 hours. The acetylation reaction was carried out for 2 hours at warm and reflux. After the acetylation was completed, the reaction was carried out in acetic acid distillation, the temperature was raised at 0.5 ° C./min and the temperature was raised to 310 ° C., and the polymerization reaction was carried out for 5 hours and 20 minutes while removing the generated acetic acid.

Next, the reaction vessel system was sealed, and the inside of the reaction vessel was pressurized to 14.7 N / cm ² (1.5 kgf / cm ² ) with nitrogen, and a low polycondensation reaction product having a mass of about 480 kg in the reaction vessel. A fully aromatic thermotropic liquid crystalline polyester having a degree of polymerization was extracted from the outlet at the bottom of the reaction vessel and supplied to a cooling and solidifying apparatus described later. The temperature of the melt polycondensation reaction product at this time was 310 ° C.

(Cooling solidification process)
As a cooling and solidifying apparatus, an apparatus having a pair of cooling rolls having a diameter of 630 mm, a distance between rolls of 2 mm, and a pair of weirs having a distance of 1800 mm was used in accordance with Japanese Patent Application Laid-Open No. 2002-179979. The pair of cooling rolls are rotated opposite to each other at a rotation speed of 18 rpm, and a melt polycondensation reaction in a fluid state extracted from a polycondensation reaction tank is formed in a recess formed by the pair of cooling rolls and the pair of weirs. The low polymerization degree thermostat which is gradually solidified immediately after passing between the rolls by adjusting the flow rate of the cooling water in the pair of cooling rolls and adjusting the surface temperature of the rolls while gradually supplying the product and holding it in the recess. The surface temperature of the tropic liquid crystal polyester was 220 ° C. The obtained sheet-like solidified product having a thickness of 2 mm was crushed to approximately 50 mm square by a crusher (manufactured by Nisso Kogyo Co., Ltd.).

  Two containers were filled up to about 80% by volume with the solidified material processed by the above-mentioned crusher. The container is a 1100mm x 1100mm x 1100mm cuboid, with a 700mm portion cut from the bottom in a 45 ° pyramid shape, with a nitrogen inlet at the bottom, a nitrogen outlet at the top, and a conduit connected. The thing connected to the acetic acid type compound trap was used. Nitrogen was allowed to flow from the bottom of the container, passed through the gap between the crushed materials, and discharged from the upper nitrogen outlet. In Examples 1 to 3 and Comparative Example 1, the flow rates shown in Table 1 were used. In Comparative Example 2, air was used instead of the nitrogen stream. In Comparative Example 3, the nitrogen stream was also allowed to cool without flowing air.

  Each temperature of the upper part, the middle part, and the lower part of the crushed material packed bed installed in the container was measured every hour. The time when all the temperatures were 50 ° C. or lower was defined as 50 ° C. arrival time, and the cooling and solidifying step was completed. Table 1 shows the arrival times at 50 ° C. in Examples and Comparative Examples.

(Crushing process and solid phase polycondensation process)
This pulverized product was pulverized with a 1 mm mesh using a feather mill manufactured by Hosokawa Micron Corporation to obtain a raw material for solid phase polycondensation. The pulverized material passed through a mesh having an opening of 1 mm. The pulverized product is stored in a rotary kiln, heated in a nitrogen atmosphere from room temperature to 170 ° C. over 3 hours in a nitrogen stream, then heated up to 280 ° C. over 5 hours, and further up to 300 ° C. for 3 hours. The mixture was heated up and subjected to solid phase polycondensation to obtain a wholly aromatic thermotropic liquid crystal polyester.

(Measurement of hue deterioration)
Biaxially blended 70 parts by mass of the wholly aromatic thermotropic liquid crystal polyester thus obtained and 30 parts by mass of glass fiber PX-1 (average length 3 mm, average system 10 μm) manufactured by Asahi Fiber Glass Co., Ltd. with a ribbon blender. It was melt-kneaded at a maximum barrel temperature of 370 ° C. with an extruder (Ikegai Iron Works Co., Ltd., PCM-30) and pelletized. Using this as a molding material, a sample for ΔE evaluation of 60 mm × 60 mm × 1 mm under molding conditions of a barrel temperature of 350 ° C. and a mold temperature of 80 ° C. using an injection molding machine (manufactured by Nissei Plastic Industry Co., Ltd., UH-1000). Got. ΔE was evaluated according to JISZ8729. The results are shown in Table 1.

  As shown in Table 1, in Examples 1 to 3, which satisfy both requirements of cooling by a nitrogen stream in the cooling and solidifying step and 50 ° C. arrival time, the hue deterioration is improved as compared with the comparative example not satisfying these requirements. Has been.

The wholly aromatic thermotropic liquid crystal polyester of the present invention has improved hue deterioration without impairing the conventional good moldability and heat resistance, so that it has been limited to use due to hue problems so far. It was possible to expand the use possibility as a material of

Claims (5)

  Using raw materials containing an aromatic hydroxycarboxylic acid, this process includes an acetylation step, a melt polycondensation step, a cooling and solidification step for cooling and solidifying the product of the melt polymerization step, a step for pulverizing the solidified product, and a solid phase polycondensation step. A method for producing a wholly aromatic thermotropic liquid crystalline polyester comprising in order, comprising means for cooling with a nitrogen stream in the cooling and solidifying step, and within 20 hours after the product is withdrawn from the melt polycondensation step And a method for producing a wholly aromatic thermotropic liquid crystal polyester, wherein the temperature is 50 ° C. or lower.   The method for producing a wholly aromatic thermotropic liquid crystal polyester according to claim 1, wherein the acetylation step and the melt polycondensation step are performed in the same reaction vessel.   The cooling and solidifying step uses a pair of cooling rolls having parallel rotation axes and a device having a pair of weirs on the cooling roll, and the reaction product in the melt polycondensation step in a molten state is placed on the cooling roll. The method for producing a wholly aromatic thermotropic liquid crystal polyester according to claim 1, further comprising a step of passing between the cooling rolls while forming a pool portion.   A wholly aromatic thermotropic liquid crystal polyester obtained by the method according to any one of claims 1 to 3.   An LED reflector comprising the wholly aromatic thermotropic liquid crystal polyester according to claim 4.