PREPARATION OF TRANSPARENT AND LITTLE COLORED POLYARYLENETHIOETHER PRIMARY MELT MOLDING AND ITS UTILISATION

Abstract: A polyarylenethioether primary melt formed article having a Hunter whiteness higher than 30% and a parallel light trans­ mittance Tp higher than 60%, as measured for a sheet with a thickness of 0.3 mm, at the process for obtaining the article which comprises producing a polyarylenethioether according to the polymerization reaction comprising dehalogenation/sul­ fidization reaction between an alkali metal sulfide and a dihalo­ aromatic compound in a polar organic solvent by carrying out the reaction with addition of an effective amount of a halo-sub­ stituted organic compound to obtain a stabilized polyarylene­ thioether, and then subjecting the polyarylenethioether to melt extrusion. The melt formed article thus produced can be sub­ jected to further melt processing to produce a secondary melt formed article or structure of polyarylenethioether.

Description: BACKGROUND OF THE INVENTION Field of Utilization in Industry This invention relates to a process for producing polyarylenethioether primary melt formed articles obtained by the technique of melt extrusion and having transparency and little coloration, which means in this specification self-coloration or discoloration and does not mean coloation by adding some colorants. Very important primary melt formed articles are pellets, which may then be used to prepare secondary melt formed articles, such as films, sheets, and fibers. Prior Art Polyarylenethioethers are thermoplastic resins having high crystallinity, which can be formed into products, such as films, sheets, plates and fibers, by different techniques, like injection molding, by extrusion, compression molding, inflation, melt spinning, and stretching. Those resins had been expected to provide melt processed articles having excellent properties. However, most of the commercially available polyarylenethioether have been resins with apparent melt viscosities which had been enhanced by "curing" of a relatively low melt viscosity polymer (namely a low molecular weight polymer), that is by a high temperature treatment of the polymer in the presence of oxygen, for example, crosslinking and branching reactions were effected. The resins having melt viscosities increased by such "curing" were, however, accompanied by a number of problems such as excessive coloration and insufficient mechanical strength due to many crosslinked branched structures. It was known from EP-A-53344 and EP-a-33906 to improve melt flow stability of polyarylenesulfides by using certain stabilizing additives. This measure does, however, not influence the excessive coloration observed when forming articles by the melt extrusion technique. Furthermore all working examples for this prior art are applying hot pressing of the reaction product to thereby form sheets of films. This fact demonstrates that both publications do not contribute to a solution of the specific technical problem discussed above. Another prior art (Patent Abstracts of Japan, vol.8, No.184 (C-320), 1571) describes a 2-step polymerization process wherein p-dichlorobenzene is added in each step to the reaction mixture in order to achieve a slow crystallization rate of the end product which itself is characterized by a minimum value for the peak crystallization temperature. Finally Applicant himself recommended a polymerization process in which specific amounts of water are added to the reaction mixture, the polymerization vessel being made from stainless steel (see EP-A-100536). Conceivable measures for solution Applicant developed a process for economically producing a high molecular weight linear polyarylenethioether according to a polymerization method, in which a large amount of water is added, and the polymerization temperature is elevated at the same time in the course of polymerization reaction (two-step polymerization with water supplementation) (EP-A-166368). The polyarylenethioether obtained by this method has generally a sufficiently high melt viscosity and therefore is applicable as it is without "curing" for melt processing such as extrusion, compression molding, stretching, and thermal fixing. Furthermore, since it has a linear structure without undergoing "curing" and has the characteristic of excellent mechanical strength, it has been expected to produce a formed article which is substantially transparent and has little coloration because no "curing" is required. However, even when such a high molecular weight polyarylenethioether developed by the present inventors is used, coloration is liable to occur according to the melt forming method usually practiced in industry, that is, according to the method in which the polymer is extruded by heating and melting within a cylinder by means of an extruder. This behaviour is surprisingly different from the result of a forming method in which the polymer is melted under pressurization by means of a hot press, for example. An article formed by hot pressing may be practically colorless. Generally speaking, in producing formed articles of polyarylenethioethers by melt extrusion, except in special cases, the polymer is ordinarily first formed into pellets by a melt extruder, and then the pellets are melt processed into other formed articles. However, the pellets thus formed are liable to exhibit marked coloration during melt extrusion as described above, and the films, fibers, etc., obtained by subjecting the colored pellets again to melt processing will become further excessively colored and thus give rise to a problem in practical application. Such a coloration also has a serious effect on transparency or aesthetic appearance not only of films, sheets, fibers, but also in other formed products, which is a problem influencing greatly their commercial values. Thus, it has been strongly desired to have polyarylenethioether pellets which are transparent with little coloration. SUMMARY OF THE INVENTION Surprisingly it has now been found that the coloration of primary melt formed articles, like pellets, obtained by the melt extrusion method can be greatly reduced by reducing the contact between the polyarylenethioether and heavy metals (particularly iron) as far as possible. The process according to the invention for producing a polyarylenethioether primary melt formed article having the following properties: (a) Hunter whiteness > 30% (b) parallel light transmittance Tp > 60% as measured for a sheet with a thickness of 0.3 mm, therefore comprises the following features: producing a polyarylenethioether according to the polymerization reaction comprising dehalogenation/sulfidization reaction between an alkali metal sulfide and a dihaloaromatic compound in a polar organic solvent by carrying out the reaction by means of a reactor which is constructed of titanium at least at the portion contacting the reaction mixture to obtain a polyarylenethioether, and then melt extruding the polyarylenethioether through a melt extruder which is constructed of a nonferrous alloy at the surface contacting the molten polymer. Polyarylenethioether secondary melt formed articles may then be obtained by subjecting the polyarylenethioether primary melt formed article having the above properties to a further melt processing. The polyarylenethioether primary melt formed article produced according to the present invention, particularly a pellet, is by far superior to the pellets of the prior art in Hunter whiteness and parallel light transmittance Tp. As described above, the polyarylenethioether formed by a hot press is different in coloration characteristic from that melt extruded by an extruder, and therefore it does not necessarily follow that formed articles with little coloration obtained by the hot press technique as described in examples of the prior art patent literatures can produce products with little coloration when formed articles such as films, fibers, or others are industrially manufactured by melt extrusion. According to the production process of the present invention a pellet can be produced commercially with ease which exhibits excellent Hunter whiteness and parallel light transmittance. Accordingly, formed articles such as films, fibers or others obtained from such pellets are also transparent and have very little coloration. The term "primary melt formed article" as used in the present invention is meant to represent the melt formed article obtained for the first time by melt processing of a polymer base material. This is generally a pellet-shaped material and it is usually subjected further to melt processing for formation of a final or secondary formed article. However, the primary melt formed article may sometimes be provided directly as the final formed product. DETAILED DESCRIPTION OF THE INVENTION Primary Melt Formed Article Polyarylenethioether The polyarylenethioether prepared according to the present invention has a (-Ar-S-) n structure (Ar: arylene group). As the polyarylenethioether polymer, those having arylene groups comprising p-phenylene group as the main component are preferred for their heat resistance and moldability. Examples of arylene groups other than p-phenylene group are m-phenylene group o-phenylene group an alkyl-substituted phenylene group [R: alkyl group (preferably lower alkyl group), n is an integer of 1 to 4], p,p'-diphenylenesulfone group p,p' - diphenylene group p,p'-diphenyleneether group naphthalene group 1,2,4-triphenylene group and 1,3,5-triphenylene group With respect to heat resistance of formed articles, polyphenylenethioethers comprising substantially only recurring units are preferred. On the other hand, with respect to ease in melt processing, which will result in lowering of processing temperature to obtain easily pellets with little coloration, copolymers of polyphenylenethioether are preferred. As the copolymer, those containing 5 to 40 mol%, particularly 10 to 25 mol% of the units or the units are preferred. If these m- or o-phenylenethioether units are contained in an amount of 5 mol% or more, the improved effect of melt processing can be exhibited, while heat resistance and mechanical properties will not be remarkably lowered unless their contents exceed 40 mol%. Further, among the copolymers containing 60 to 95 mol% of the same units, rather than random copolymers, block copolymers containing the recurring units of and the recurring units of in continuous block bondings are preferred. This is because block copolymers can produce final formed articles having the same processability and superior heat resistance and mechanical characteristics than random copolymers. Such block copolymers and their preparation methods are described in EP-A-166451. The polyarylenethioether should desirably have an appropriate molecular weight or melt viscosity in physical properties and processability. That is, those having a melt viscosity (η*) within the range of from 100 to 3000 Pa.s determined at a temperature of 310°C and a shearing rate of 200 sec⁻¹, particularly preferably from 150 Pa.s to 2000 Pa.s, are preferred. With a polymer having a melt viscosity less than 100 Pa.s, the formed article obtained from the pellet is inferior in mechanical properties. On the other hand, with a polymer having a melt viscosity in excess of 3000 Pa.s, it becomes difficult to prepare formed articles in the form of pellets by melt extrusion, and also the processing temperature becomes higher, whereby coloration will more readily occur. The polyarylenethioether to be used for producing the primary melt formed article which is transparent and has little coloration of the present invention should be a high molecular weight polymer which requires no increase in molecular weight by the so-called "curing". It should also be a substantially linear polymer in order to be easily processed by the melt extrusion technique into films, sheets, fibers, etx. Such a substantially linear, high molecular weight polyarylenethioether can be produced particularly economically according to "the two-step polymerization with water supplementation" which is a new polymerization method we have developed (EP-A-166368). This is a process for producing a polyarylenesulfide having a melt viscosity of 100 Pa.s or higher (melt viscosity is measured at 310°C and at a shearing rate of 200 sec⁻¹), which comprises carrying out the reaction between an alkali metal sulfide and a dihaloaromatic compound in a polar organic solvent to obtain a polyarylenesulfide, wherein the reaction is carried out in at least the two steps as described below. (1) The step of carrying out the reaction at a temperature of 180°C to 235°C under conditions such that 0.5 to 2.4 moles of water are present per one mole of the alkali metal sulfide charged to form a polyarylenesulfide having a melt viscosity of 0.5 to 30 Pa.s at a conversion of the dihaloaromatic compound of 50 to 98 mole%. (2) The step of continuing the above reaction by adding water so that 2.5 to 7.0 moles of water will be present per 1 mole of the alkali metal sulfide charged and also elevating the temperature to 245 - 290°C. Transparency and coloration degree The polyarylenethioether produced according to the present invention is in the form of a primary melt formed article thereof, typically pellets, and the pellets are excellent with respect to transparency and coloration characteristic. In the present invention, as evaluation indices of transparency and coloration characteristics, the Hunter whiteness and the parallel light transmittance are used. Although it may be possible to distinguish, according to the Hunter whiteness, a colorless sample from a colored sample provided that both are almost the same in transparency, it is impossible to distinguish a sample which is transparent and colorless from a sample which is not transparent but white. For this reason, other than the Hunter whiteness, which indicates the coloration degree, parallel light transmittance Tp is used as the index for evaluation of transparency. For evaluation of both characteristics, if the samples of melt extruded articles are in the form of pellets, measurements are difficult. Therefore the pellets made according to the present invention are formed into a sheet by melting under pressurization in a non-oxidative atmosphere so as to avoid oxidation of the polymer before the measurements in respect of coloration characteristics and transparency are carried out. Also, since the parallel light transmittance Tp will vary depending particularly on the thickness, a sheet with a thickness of 0.3 mm was used as the sample. Therefore the sample for evaluation of both characteristics is an amorphous sheet with a thickness of 0.3 mm which has been obtained by preheating the pellets in a nitrogen gas stream at 320°C by means of a hot press for 2 minutes, then forming the pellets into a sheet by heating at 320°C for 1 minute and finally quenching the sheet. The Hunter whiteness was measured by means of a color differential meter (Color Ace, produced by Tokyo Denshoku K.K.), and parallel light transmittance Tp by means of a haze meter (TC-H3, produced by Tokyo Denshoku K.K.), based on Japanese Industrial Standards (JIS) K 6714. The pellet produced according to the present invention has a Hunter whiteness higher than 30%, preferably 35% or higher, and also a parallel light transmittance Tp higher than 60%, preferably 65% or higher. It has a higher transparency and less self coloration as compared with the pellets of the prior art, as can be clearly seen from the Comparative Examples set forth hereinfater. The pellet produced according to the present invention has undergone the heating-melting step in the cylinder of an extruder and the mixing step with a screw, and therefore the evaluation of the pellet characteristics as described above can reflect much better the real situation as a practical evaluation method of formed articles such as films and fiber. According to conventional practice samples were prepared on a laboratory scale directly from the polymer base material by means of a hot press. Preparation of Primary Melt Formed Article For the present invention any preparation method of pellets can be adopted provided that the pellets obtained thereby have a Hunter whiteness >30% and parallel light transmittance T p >60%. Applicant investigated the causes for the coloration which occurs during melt extrusion of a polyarylenethioether, and consequently arrived at the following theory for the steps in which coloration occurs: i) By heating in the extruder, decomposition occurs at the chemically active portion of the polymer (particularly terminal ends of the polymer); ii) the decomposed product formed by the decomposition reaction reacts itself with heavy metal components on the metal surface of the extruder (particularly the metal surface containing much iron) or the polymer in the extruder forms oxides of heavy metal or heavy metal compounds such as sulfate, etc., which further react with or are mixed with the polymer in molten state thereby causing coloration. The pellet according to the present invention, therefore, can be prepared according to the two methods broadly classified as follows. (1) Preparation of pellets from polyarylenethioether with little heavy metal content As speculated above, polyarylenethioethers containing heavy metal components (particularly iron) are susceptible to decomposition and coloration. According to the invention it is possible to obtain a pellet having the above mentioned properties by carrying out the polymerization reaction and the melt extrusion of a polyarylenethioether while avoiding contact with iron components as much as possible. More specifically, in preparation of a polyarylenethioether according to the polymerization reaction comprising dehalogenation/sulfidization reaction of an alkali metal sulfide and a dihalogen aromatic compound in a polar organic solvent, when using a conventional corrosive reactor comprising iron as the main component at the portion which contacts the reaction mixture, iron compounds, etc., may be formed by chemical corrosion and physical corrosion until such compounds are contained up to about 30 to 100 ppm in the polymer. Accordingly, in the present invention, by the use of a reactor which is constructed of titanium at least at the portion contacting the reaction mixture (Japanese Patent Application No. 143828/1984), a polyarylenethioether reduced in iron component to about several ppm or less can be obtained. Further, the polyarylenethioether is melt extruded through an extruder constructed of an anticorrosive alloy of a non-iron metal or an anti-corrosive alloy with very little iron content at the surface contacted by the molten polymer (i.e., cylinder, screw, die, etc.). As the non-ferrous alloy, metals or alloys of tungsten, cobalt, chromium, or nickel are particularly preferred. Of course, the surface may be coated with these metals or alloys. By combination of these methods, transparent and little colored pellets can be obtained. (2) Preparation of pellets from stabilized polyarylenethioether The terminal ends of ordinary polyarylenethioethers are thermally or chemically unstable as described above and susceptible to decomposition during a melt extrusion process. Stable polyarylenethioethers can be produced by stabilizing the terminal ends of the main chain by capping with a halo-substituted organic compound during polymerization. More specifically, this preferred embodiment of the process according to the present invention comprises a feature of carrying out the polymerization reaction with post-addition of an effective amount, preferably 0.1 to 20 moles per 100 moles of the dihaloaromatic compound, of a halo-substituted organic compound(preferably when η* has reached at least 50 Pa.s (measured at a temperature of 310°C and a shear rate of 200 sec.⁻¹ )), preferably under the conditions of a temperature of 100°C or higher, more preferably 150°C or higher for 0.5 hours or longer. In this embodiment, the halo-substituted organic compound may include halo-substituted alkanes such as chlorocyclohexane and bromocyclohexane; ether compounds such as chloromethylether; thioether compounds such as chlorodiphenylthioether; halo-substituted alkylbenzenes such as m-chloroethylbenzene; halo-substituted aromatic ethers such as m-chloroanisol and p-chloroanisol; or otherwise halo-substituted aromatic hydrocarbons such as bromobenzene and bromonaphthalene. These have typically C-X (X: halogen) bonds. Among them, preferable are mono-halo-substituted organic compounds, particularly mono-halo-substituted aromatic compounds. Specific examples of mono-halo-substituted aromatic compounds correspond to the mono-halo-derivatives of the di-halo-substituted aromatic compounds as the starting material for polyarylenethioethers. By the reaction with these halo-substituted organic compounds of Ar-SM and ArX (M: alkali metal, X: halogen) which are considered to exist at the terminal ends of the main chain, particularly unstable is considered to be changed to the stable structure (R: organic residue of halo-organic compound), whereby decomposition or liberation of harmful decomposed products at high temperature can be prevented. Generally speaking, melt extrusion is preferably performed at a temperature within the range from the melting point to 390°C. At a temperature over 390°C, coloration may occur . Utilization of primary melt formed article for the preparation of secondary melt formed article The pellet-shaped melt formed article with a Hunter whiteness >30% and parallel light transmittance Tp >60% obtained as described above can be melt processed into transparent and little colored films, sheets, fibers, etc. according to conventional melt processing methods, namely, injection molding, extrusion, melt spinning, compression molding, inflation molding, blow molding, etc. However, when using pellets obtained from polyarylenethioethers other than stabilized polyarylenethioethers, it is desirable to use a melt processing machine in which the portion contacting the molten polymer is constructed of a non-iron type alloy. This is because decomposition of terminal ends, etc. may occur again, and the decomposed products may react with the metal surface to bring about coloration. Typical examples of the secondary melt formed articles are as described below. (1) Biaxially stretched oriented film The pellet of the present invention can be first melt extruded into a sheet, which is subsequently biaxally stretched to form a transparent and substantially colorless biaxially stretched film. More specifically, the pellet of the present invention is fed into a melt extruder provided with a T-die to be extruded into a sheet with a thickness of 10 to 1,000 µm, then immediately, or after being once wound onto a roll, fed to a biaxially stretching device, where it is stretched successively or at one time within the range of 2 to 8-fold in the longitudinal direction and 1.5 to 7-fold in the lateral direction at a temperature range from 80 to 150°C, subsequently optionally heated within a temperature range from 200 to 290°C under a tension not less than null for 0.5 to 1.000 seconds to enhance crystallinity. Then, if necessary, thermal relaxation is carried out practically free of tension with a temperature in the range of from 200 to 290°C, whereby a beautiful biaxially stretched oriented film having high colorless transparency is obtained. To the best of our knowledge, no such substantially colorless and transparent biaxially stretched film has been obtained in the prior art. However, for carrying out a comparison with the prior art product, since the film is thin, and also it is difficult to compare samples with the same thickness, such a thin film is usually unsuitable as regards evaluation of its colorlessness and transparency in terms of Hunter whiteness and Tp. Accordingly, as an evaluation index for colorless transparency which is suitable for measurement of a thin sample with a thickness of 1 to 100 µm and is not influenced by the thickness within that range, the value of εc derived from the law of Lambert-Beer was used. Besides, the value of εc was determined from the absorbance of light with a wavelength of 450 nm which can detect sharply coloration characteristic or opaqueness of a thin film. Absorbance was measured by means of a spectrophotometer (Two Wavelength Spectrophotometer Model 557, produced by Hitachi Seisakusho K.K.). The law of Lambert-Beer is represented by the following formula. log₁₀ (I/Io) = -εcd I/Io: absorbance of light with wave length of 450 nm ε: inherent constant of completely non-colored transparent film d: thickness of measured material (mm) εc: absorption index (mm)⁻¹. Most of the biaxially stretched films of the present invention were found to be substantially colorless and transparent films with εc values of 10 or less. Since the appearance of a biaxially stretched oriented film is a very important property in its uses, it should have a εc value of 15 or less, particularly preferably 10 or less. Other applications of the pellet of the invention The pellet-shaped melt formed article of polyarylenethioether which is transparent and has little coloration of the present invention can be produced in a large amount industrially and economically and therefore can be utilized for various kinds of application fields. When the pellet is melt processed directly as it is into a desired formed secondary article without addition of a colorant or a filler, transparent and little colored films, sheets, fibers, bottles, etc., can be obtained. These can be utilized in various fields such as magnetic recording materials, optical magnetic recording materials, optical materials, and food packaging materials. Into the pellet of the present invention can be blended colorants, fibrous fillers (glass fibers, etc.) and inorganic fillers (SiO₂ powder, TiO₂ powder, Al₂O₃ powder, CaCO₃ powder, kaolin, mica, etc.) before it is melt processed into a formed article. In such a case, the transparency may be reduced due to the presence of fillers, but formed articles with excellent color tone and luster can be obtained. From the pellet-shaped article of the present invention, a thick formed article can also be obtained by injection molding, extrusion, compression molding, etc. In the case of a thick formed article, the product becomes generally devitrified due to formation of coarse spherulites. However, even so, products with excellent tone and luster can be obtained. These polyarylenethioether melt formed articles having beautiful appearance can be utilized in the fields of electronic parts, domestic electrical parts, precision mechanical parts (cameras, watches, etc.). EXPERIMENTAL EXAMPLES Polymerization Example P01 Into a polymerization vessel with a titanium-lined inside were charged 3.75 kg of hydrous sodium sulfide (solid content: 46.0%) and 7 kg of N-methylpyrrolidone, and water was distilled out by elevating the temperature to about 200°C. Then, a mixture of 3.25 kg of p-dichlorobenzene and 3 kg of N-methylpyrrolidone was added, and polymerization was carried out at 220°C for 5.5 hours. Then, 1.1 kg of water was added, and polymerization was carried out at a reactor temperature of 265°C for 5 hours. The polymer was separated by filtration from the reaction mixture, washed with acetone and with water, and then dried overnight in a vacuum dryer at 80°C to obtain a polymer P01 Example P1 In the polymerization of Polymerization Example P01, after elapse of 3.5 hours in the later stage polymerization at 260°C (polymer η* = 440 Pa.s (measured at a temperature of 310°C and a shear rate of 200⁻¹)), 0.5 mol of 1-chloro-n-butane was added per 100 mols of p-dichlorobenzene charged, and the reaction was further continued at 140°C for 1 hour. After completion of the reaction, the same operations as in Polymerization Example P01 were carried out to obtain a polymer P1. Example P2 Into a Ti-lined autoclave were charged 560 g of Na₂S·xH₂O (solid consent: 46.0%) and 1.1 kg of N-methylpyrrolidone, and water was distilled out by heating to about 200°C. Then 460 g of m-dichlorobenzene dissolved in 450 g of N-methylpyrrolidone were added, and polymerization was carried out at 220°C for 8 hours to prepare a reaction mixture Ml containing (m-phenylenethioether) prepolymer. Separately, 3.15 kg of Na₂S·xH₂O (solid content: 46.0%) and 6 kg of N-methylpyrrolidone were charged into a Ti-lined autoclave, and water was distilled out by heating to about 200°C. Then, the reaction mixture Ml and 2.53 kg of p-dichlorobenzene dissolved in 2.72 kg of N-methylpyrrolidone were added to carry out polymerization at 215°C for 10 hours, and further polymerization was carried out with addition of 1.1 kg of water at 260°C for 5 hours. The melt viscosity η* was 320 Pa.s. As the next step, bromobenzene was added in an amount of 4.0 mols per 100 mols of the p-dichlorobenzene charged, and polymerization was further carried out at 260°C for 3 hours. The same post-treatment as in Polymerization Example P01 was effected to obtain a (p-phenylenethioether/m-phenylenethioether) block copolymer P2. Examples P3 and P4 Example P2 was repeated except that 4 mols of m-chloroanisol and m-chloroethylbenzene were respectively added per 100 mols of p-dichlorobenzene charged in place of bromobenzene to obtain block copolymers P3 and P4, respectively. Examples P5 and P6 Example P1 was repeated except that 6.0 mols each of m,m'-dichlorodiphenylthioether and p,p' - dichlorophenylthioether were added respectively per 100 mols of p-dichlorobenzene charged in place of chloro-n-butane, and the reaction was continued at 265°C for 5 hours to obtain polymers P5 and P6, respectively. Polymerization Example P02 Into a titanium-lined autoclave were charged 25 mols of sodium sulfide (solid content: 59.7%), 10 g of sodium hydroxide, 25 mols of lithium acetate (dihydrate) and 7.92 g of N-methyl-pyrrolidone, and water was distilled out by elevating the temperature to 202°C. Then, a mixture of 25.5 mols of p-dichlorobenzene and 2 kg of N-methylpyrrolidone was added, and polymerization was carried out at 245°C for 3 hours. After post-treatment conducted similarly as in Polymerization Example P01, a polymer P02 was obtained. Polymerization Example P03 Into a titanium-interlined autoclave were charged 25 mols of sodium sulfide (solid content: 59.7%), 10 g of sodium hydroxide, 25 mols of sodium benzoate and 7.92 g of N-methylpyrrolidone, and water was distilled out by elevating the temperature to 202°C. Then, a mixture of 25.5 mols of p-dichlorobenzene and 2 kg of N-methylpyrrolidone was added, and polymerization was carried out at 250°C for 5 hours. After a post-treatment realized similarly as in Polymerization Example P01, a polymer P03 was obtained. Polymerization Examples P04, P05 and P06 Polymerization was carried out similarly as in Polymerization Example P01,P02 and P03 except for using an autoclave made of stainless steel to obtain polymers P04, P05 and P06, respectively. Each of these polymer powders was found to be slightly colored. Processing Examples PP1 through PP4, PP01, PP02 and PP03 Each of the polymers P1 through P4 and P01, P02 and P03 was melted by heating to 350°C by means of a single-screw kneading extruder (cylinder: nitrided steel, screw barrel: nitrided steel) and extruded through a die into a cord-like shape, which was immediately cooled with water and cut to prepare respective pellets PP1 through PP4 and PP01, PP02, and PP03. Processing Examples PP5, PP6, PP04, PP05, and PP06 Each of the polymers P5, P6, P04, P05, and P06 was melted by heating to 350°C by means of a single-screw extruder (cylinder: nitrided steel, screw barrel: stainless steel), immediately cooled with water and cut to prepare respective pellets PP5, PP6 and PP04, PP05, and PP06. Processing Examples PP7, PP07, PP08 Each of the polymers P01, P04 and P05 was melted by heating to 350°C by means of a co-direction rotating twin-screw extruder (cylinder: tungsten alloy, screw barrel: hard chromium plated), extruded through a die into a cord-like shape, which was immediately cooled with water, and cut to prepare respective pellets PP7, PP07 and PP08. Processing Examples PP8, PP09 Each of the polymers P02 and P06 was melted by heating to 350°C by means of a single-screw extruder (cylinder: cobalt alloy, screw barrel: hard chromimum plated), extruded through a die into a cord-like shape, which was immediately cooled with water and cut to prepare respective pellets PP8 and PP09. Evaluation The respective pellets of PP1 through PP8 and PP01 through PP09 were molded into a sheet with a thickness of 0.3 mm by means of a hot press and then the Hunter whiteness and the parallel light transmittance Tp of each sheet were measured. The results are summarized in Table 1. Also, by using several kinds of base polymer materials, sheets with a thickness of 0.3 mm were formed directly from that material according to the same method as in case of the pellets, and the values for the Hunter whiteness and the parallel light transmittance were determined. The results are summarized in Table 1. (*1) values in parentheses: values measured for sheets directly formed into sheet from base material (*2) R ○ XALOY (produced by XALLOY CO.) (*3) R ○ H-ALOY (produced by Hitachi Kinzoku K.K.) As can be seen from the results in Table 1, the polyarylenethioethers of the prior art, namely, the polymers polymerized without stabilization of the terminal ends produced the result that the pellets obtained by means of a melt extruder made of an iron rich alloy are having low values for both the Hunter whiteness and the Tp. They are excessively colored and inferior in transparency especially in the case where an autoclave made of stainless steel is used. Also, when an autoclave made of stainless steel was employed, the pellets obtained had low values for both the Hunter whiteness and the Tp even when obtained by means of an extruder made of a non-iron alloy. Also, the sheets melt formed directly from base materials which have been used in the prior art for the evaluation of physical properties were found to produce data which are by far different with respect to coloration characteristic as compared with the pellets melt extruded through an extruder. Thus, it has been found that this evaluation method of the prior art is not appropriate for the evaluation of the coloration characteristic of a film or sheet in practical application. Processing Examples BF-1 through BF-5 and BF01 through BF06 Each of the pellets PP1, PP2, PP3, PP6, PP8, PP01, PP02, PP03, PP04, PP06 and PP08 was melt extruded into a sheet by means of the extruder employed in the Processing Example PP7 provided with a T-die, which sheet was quenched by a cooling drum to prepare a T-die sheet with an average thickness of 0.2 mm. By means of a small-scale film stretcher (produced by T.M. Long Co.), the sheet was stretched 3.0 ∼ 3.5-fold at a temperature of 80 ∼ 90°C each in longitudinal direction and lateral direction to prepare a biaxially stretched oriented film, which was further fixed on a metal frame for heat treatment at 250°C for 15 minutes. Subsequently, the film was taken off from the metal frame and subjected to heat treatment under free tension at 240°C for 5 minutes to prepare biaxially stretched oriented films BF1 through BF5 and BF01 through BF06 having thicknesses of 20 to 30 µm, respectively. For these films, the absorbance at 450 nm was measured by a spectrophotometer to obtain the value of εc (mm⁻¹) from the Lambert-Beer formula. The results are summarized in Table 2. As can be seen from the results in Table 2, from the pellets of the present invention having values of the Hunter whiteness higher than 30% and Tp-values higher than 60%, highly colorless transparent biaxially stretched films can be obtained, showing also low values of εc of 7 or less. On the other hand, the biaxially stretched films (BF01 through BF04) prepared from the pellets outside the scope of the present invention as reported in the prior art literature are considerably colored showing εc values of 20 or higher. The known pellets thereby are distinguishable from the pellet of the present invention. Spinning Example When spinning was performed under the conditions shown below on the pellets PP3 by means of a melt spinning tester (produced by Fuji Filter K.K.), beautiful multi-filaments (monofilament diameter about 50 µm) which were approximately colorless and transparent were obtained. Nozzle: 0.5 mm∮ x 18 holes Nozzle temperature: 315°C Extruded amount: 5.3 g Taking-up speed: 100 m/min. Cooling method: air cooling

Claims: A process for producing a polyarylenethioether primary melt formed article having the following properties: (a) Hunter whiteness > 30% (b) parallel light transmittance Tp >60%, as measured for a sheet with a thickness of 0.3 mm, which comprises producing a polyarylenethioether according to the polymerization reaction comprising dehalogenation/ sulfidization reaction between an alkali metal sulfide and a dihaloaromatic compound in a polar organic solvent by carrying out the reaction by means of a reactor which is constructed of titanium at least at the portion contacting the reaction mixture to obtain a polyarylenethioether, and then melt extruding the polyarylenethioether through a melt extruder which is constructed of a nonferrous alloy at the surface contacting the molten polymer. A process according to claim 1, wherein the reaction is carried out with addition of 0.1 to 20 moles of a halo-substituted organic compound per 100 moles of the dihalo-aromatic compound. A process according to claim 2, wherein the halo-substituted organic compound is a mono-halo-substituted organic compound. A process according to claim 3, wherein the mono-halo-substituted organic compound is a mono-halo-substituted aromatic compound. A process according to any one of claims 2 to 4, wherein the halo-substituted organic compound is added when the melt viscosity determined at a temperature of 310°C at a shearing rate of 200 sec⁻¹ of thr polyarylenethioether formed by the polymerization reaction comprising said dehalogenation/sulfidization reaction becomes at least 50 Pa.s.

Inventors: IIZUKA, YO, KATTO, TAKAYUKI, KOBAYASHI, AKIO, KOUYAMA, TOSHITAKA, SHIIKI, ZENYA
Applicants: KUREHA KAGAKU KOGYO KABUSHIKI KAISHA
Application year: 1986
Main classification: C08G75
IPC codes: B29B9, C08G75, B29K81, B29C47