JPH0160045B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing polyester, and more particularly to a method for producing polyester suitable for high-speed spinning. Polyester, particularly polyalkylene terephthalate, has many excellent properties and is therefore used in a wide range of fields such as fibers, films, and resins. Among them, polyesters represented by polyethylene terephthalate are most widely used in large quantities in the textile field. Conventionally, in order to produce processed yarns of polyester fibers, such as polyester filaments, the mainstream method has been to perform spinning, drawing, and false twisting in separate steps. However, in recent years, by increasing the spinning speed, intermediately oriented undrawn yarns have appeared, and the so-called POY-DTY method, in which drawing and false twisting are performed in one continuous stage, has come to be practiced. This method makes it possible to improve the productivity and shorten the process of manufacturing processed polyester filament yarn, and is also excellent from the viewpoint of reducing manufacturing costs, and will become the mainstream of future yarn spinning technology. However, as the speed of spinning technology increases, various problems have arisen. For example, the spinning speed
At high speeds of 2,500 m/min or higher, especially 3,000 m/min or higher, the quality of the spinning process often deteriorates, such as yarn breakage during spinning or yarn breakage during stretching and false twisting, and the resulting processed yarn becomes fluffy and its strength decreases. Problems such as quality deterioration such as the occurrence of dyeing spots occurred, and it was extremely difficult to sufficiently improve productivity by increasing the spinning speed. Various studies have been made to address these problems. For example, attempts have been made to optimize spinning conditions such as spinning temperature, cooling air flow rate and temperature, and to improve spinning tubes, spinnerets, etc., but sufficient improvements have not been achieved. Modification of polyester is also being studied, including copolymerization with polyalkylene glycols such as diethylene glycol and polyoxyethylene glycol, compounds with sulfonate groups, and chain branching agents such as pentaerythritol, trimellitic acid, and trimethylolpropane. Furthermore, many attempts have been made to add metal species such as kaolinite, calcium, and lithium. However, the improvement method by copolymerization is accompanied by a decrease in the excellent properties of polyester, and the addition of metals such as calcium and lithium causes foreign matter in the polymer, resulting in increased spin pack pressure and foreign matter accumulation around the spinneret. It is difficult to say that this is a desirable countermeasure, as it also induces other undesirable phenomena. The present inventors investigated various conditions for preventing such drawbacks and achieving high productivity and no quality deterioration even in the high-speed prevention range, and found that the degree of orientation and crystallinity of spun yarn obtained by high-speed spinning Factors based on the fine structure of the yarn greatly affect the quality and quality of the spinning process, and in particular, the most advantageous conditions for productivity and quality are that the resulting spun yarn has a high degree of orientation and a low degree of crystallinity. Knowledge was obtained. Based on this knowledge, we conducted intensive research to provide a polyester that can yield spun yarn with a high degree of orientation and low crystallinity in the high-speed spinning range. Therefore, the inventors have found that the above object can be achieved, and have arrived at the present invention. That is, the present invention involves reacting a difunctional carboxylic acid mainly consisting of terephthalic acid or its dimethyl ester with at least one type of glycol, and then polycondensing the reaction product to produce a polyester. This method of producing polyester is characterized in that at least one compound selected from the group consisting of acidic alkali metal sulfites and alkaline earth metal acidic sulfites is added at any stage until the completion of the process. The polyester referred to in the present invention mainly refers to polyalkylene terephthalate obtained from terephthalic acid or its dimethyl ester and alkylene glycol, and the alkylene glycol used here is preferably an alkylene glycol having 2 to 6 carbon atoms. Particularly preferred are ethylene glycol, trimethylene glycol, and tetramethylene glycol. Further, the third component may be a polyester copolymerized with a bifunctional carboxylic acid component other than terephthalic acid and/or a diol compound other than the alkylene glycol as the main component. In order to produce such polyester, a so-called esterification method or transesterification method is employed. For example, to explain polyethylene terephthalate, terephthalic acid or dimethyl terephthalate and ethylene glycol are heated to cause an esterification or transesterification reaction while distilling off the generated water or methanol, and the resulting reaction product is heated under reduced pressure. It is produced by a method of carrying out a polycondensation reaction until a desired degree of polymerization is achieved. Note that a catalyst can be used in this production reaction if necessary, and in particular, when an antimony compound is used as a polycondensation catalyst, the present invention can achieve greater effects. In the present invention, the compound added in the production of the polyester is an acidic alkali metal sulfite salt and/or an acidic alkaline earth metal sulfite salt,
Preferred specific examples of the metal salts include salts of alkali metals such as acidic lithium sulfite, acidic potassium sulfite, acidic sodium sulfite, and acidic rubidium sulfite; alkaline earth metal salts such as acidic calcium sulfite, acidic magnesium sulfite, and acidic barium sulfite. can be given. These additives may be used alone or in combination of two or more. The amount of such additives used is such that a spun yarn with the desired high degree of orientation and low degree of crystallinity can be obtained with a very small amount; It is preferable to use Further, there is no need to particularly limit the upper limit, but if the amount is too large, the polyester will be colored or foreign matter will be generated, so it is preferably 20 mol% or less. A particularly preferable usage amount is in the range of 1 mmol% or more and 5 mol% or less. The addition time may be any time before the polycondensation reaction is completed, but it is preferably added before the initial stage of polycondensation, specifically before the number average degree of polymerization of the polymer reaches 30. The addition means may be arbitrary, for example, adding the additive as it is,
It may be added as a glycol solution or slurry, or as an aqueous solution. When the polyester thus obtained is spun at a spinning speed of 2,500 m/min or higher, especially 3,000 m/min or higher, problems such as breakage of the spun yarn with a high degree of orientation and low crystallinity may occur. Since it can be easily manufactured without any process, the spinning speed can be further increased, and productivity can be further improved. In addition, there is little variation in the degree of fiber orientation and crystallinity of the obtained spun yarn, there is no trouble during processing, and the quality fluctuations such as dyeing spots in the final processed yarn are reduced, resulting in stable quality. This is what I did. Furthermore, since this polyester exhibits easy crystallinity in a bulk state, it is extremely useful for general molding applications other than fibers and resin applications. In addition, various additives such as antistatic agents, dye-facilitating agents, coloring agents, etc. may be mixed and added to the polyester obtained by the method of the present invention, as necessary, and ether formation inhibitors and crystallizing agents may also be used in combination. It can be adopted without any problem. Next, the present invention will be explained in detail with reference to Examples.
Parts in the examples indicate parts by weight, and symbols and measurement methods used in the examples are explained below. [η]: Intrinsic viscosity determined from the viscosity of the polymer measured in orthochlorophenol solvent at 30°C. col-L, col-b: represents the hue of the polymer, and was measured using a Hunter type color difference meter. The higher the value of col-L, the higher the whiteness of the polymer.
The larger the value of col-b, the stronger the yellowness of the polymer. Δn: Indicates the degree of orientation of the spun yarn and was measured by the Berek method. Boiling water shrinkage (BWS): The degree of crystallinity of the fiber was expressed as boiling water shrinkage (BWS) determined by the following formula. The larger the value of boiling water shrinkage (BWS), the lower the degree of crystallinity. BWS=Lo−Lf/Lo×100 Lo: Fiber length Lf of spun yarn obtained by high-speed spinning: Fiber length after holding the obtained spun yarn in boiling water for 30 minutes Spun joint: 2.5Kg winding 100 It is indicated by the number of books in the book. Example 1 After stirring 970 parts of dimethyl terephthalate, 640 parts of ethylene glycol, 0.31 part of manganese acetate as a transesterification catalyst, and 0.1 part of acidic sodium sulfite, the mixture was charged into a reactor equipped with a rectification column and a condenser, and heated from 140°C to 230°C. The transesterification reaction was carried out while heating and producing methanol was distilled out of the system. Trimethyl phosphate was added as a stabilizer when the internal temperature reached 230℃ 3 hours after the start of the reaction.
After 10 minutes, add 0.18 parts of antimony trioxide as a polycondensation catalyst and titanium dioxide as a matting agent.
After adding a slurry consisting of 2.91 parts of ethylene glycol and 11.6 parts of ethylene glycol, the mixture was transferred to a polymerization vessel equipped with a stirrer and a glycol distillation condenser, and a polycondensation reaction was carried out. The quality of the obtained polymer is shown in Table-1. Next, this polymer was spun at a spinning speed of 3600 m/min.
The physical properties of the resulting spun yarn and spun yarn are also shown in Table 1. As is clear from Table 1, the obtained spun yarn had a high degree of orientation and a low degree of crystallinity, and there was no spun splicing yarn, giving good results. Example 2 The same procedure as in Example 1 was carried out except that 0.06 part of acidic calcium sulfite was used in place of the acidic sodium sulfite used in Example 1. The results are in the table-
As shown in Fig. 1, a spun yarn with a high degree of orientation and a low degree of crystallinity was obtained, and the number of spun spliced yarns was also zero, which was good. Examples 3 to 5 The same procedure as in Example 1 was conducted except that the amount of sodium acid sulfite used in Example 1 and the timing of addition were changed as shown in Table-1. The results are in the table-
As shown in Fig. 1, spun yarn with a high degree of orientation and low crystallinity was obtained, and the number of yarn breakages was also good, with no yarn breakage. Comparative Example The same procedure as in Example 1 was carried out except that sodium acid sulfite was not used. As shown in Table 1, the results were that the degree of orientation was low and the degree of crystallinity was high, and the number of broken yarns was 10, which was poor.

[Table] Example 6 A polymer was produced in the same manner as in Example 1 except that the amount of sodium acid sulfite used in Example 1 was changed to 2 parts. [η] of the obtained polyester is 0.639, the softening point is 263.1℃, and the col-L is
69.3, col-b was 8.5. Additionally, as a result of DSC (differential thermal analyzer) at a heating rate of 20°C/min for this polyester, the crystallization temperature Tci during heating was found to be
The crystallization temperature Tcd when cooling down after melting at 135℃ is
At 213°C, ΔT=Tcd−Tci=78°C, indicating extremely easy crystallinity. On the other hand, the DSC results for the polyester obtained in the comparative example above under the same conditions show that Tci is 136°C and Tcd is
At 202°C, ΔT was 66°C.

Claims (1)

[Claims] 1. In producing a polyester by reacting a difunctional carboxylic acid mainly consisting of terephthalic acid or its dimethyl ester with at least one type of glycol, and then polycondensing the reaction product,
A method for producing polyester, which comprises adding at least one compound selected from the group consisting of acidic alkali metal sulfites and alkaline earth metal acidic sulfites at any stage until the production reaction is completed.