Method for producing polyester composition

Abstract

To provide a method for producing a polyester composition which has few coarse particles by suppressing aggregation of titanium dioxide in the production step of a polyester containing a high concentration of titanium dioxide and hardly causes clogging of a filtration filter or a molten polymer flow path used in melt molding the polyester or durability deterioration of a molded product or the like.SOLUTION: There is provided a method for producing a polyester composition in which when producing a polyester composition using a dicarboxylic acid or its ester-forming derivative and a diol as main raw materials, in a liquid-phase polycondensation process in which, after obtaining bis-2-hydroxyethyl terephthalate as an intermediate by the ester reaction of the main raw materials and before starting the polycondensation reaction, 1 to 40 mass% of titanium dioxide is added to the resulting polyester composition, a compound containing a calcium element is added at 15 to 60 ppm in terms of element before the addition of titanium dioxide.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a polyester composition. More specifically, the present invention relates to a method for producing a polyester composition containing titanium dioxide at a high concentration, which suppresses the generation of coarse particles in the production process and has excellent passability in a molding process. [Background technology]

[0002] Polyester is widely used in a variety of fields, including fibers and films, due to its excellent properties such as durability and processability. It is generally known that titanium dioxide is added to polyester, particularly in fiber applications, to impart functions such as mold releasability and transparency prevention, and titanium dioxide is a key component in expanding the applications of polyester.

[0003] Titanium dioxide has an electric charge on the particle surface, which makes it easy for titanium dioxide particles to aggregate together, so care must be taken to prevent this from happening, especially when a large amount is added, as titanium dioxide aggregates can clog the filtration filters or molten polymer flow paths used when melt-molding polyester, and can reduce the durability of molded products. Countermeasures against the aggregation of titanium dioxide have been studied in the past, and for example, Patent Document 1 proposes a technique of adding compounds consisting of cobalt, calcium, manganese, and magnesium with the aim of suppressing the aggregation of titanium dioxide. It is certainly believed that these compounds have the effect of suppressing the aggregation of titanium dioxide, but on the other hand, the timing of adding titanium dioxide and these compounds is equally important, and this method does not consider the timing of addition, making it insufficient as a countermeasure against aggregation of polyester containing a high concentration of titanium dioxide.

[0004] Furthermore, Patent Documents 2 and 3 propose a technique for incorporating a high concentration of inert particles containing titanium dioxide, but even in this method, the selection of additives or the timing of addition for the purpose of suppressing particle aggregation are not considered, and therefore this method is insufficient as a measure for suppressing particle aggregation.

[0005] As described above, methods for improving the dispersibility of titanium dioxide and suppressing particle aggregation have been investigated for some time. However, there have been no studies that have taken into consideration the timing of addition of titanium dioxide and additives and optimized this timing. In particular, no production method that is sufficiently effective for polyesters containing high concentrations of titanium dioxide has yet been obtained. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 60-17291 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-045026 [Patent Document 3] Special Publication No. 2019-094374 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in view of the above background, and it is an object of the present invention to provide a method for producing a polyester composition which suppresses aggregation of titanium dioxide during the production process of a polyester containing a high concentration of titanium dioxide, thereby reducing the amount of coarse particles and reducing the risk of clogging of filters or molten polymer flow paths used in melt-molding the polyester, as well as reducing the durability of the molded product. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to solve the above-mentioned problems that could not be solved by conventional techniques, and have arrived at the present invention.

[0009] That is, the present invention can be achieved by a method for producing a polyester composition using dicarboxylic acid or an ester-forming derivative thereof and a diol as main raw materials, by adding 1 to 40 mass% of titanium dioxide, and in a liquid phase polycondensation process in which titanium dioxide is added at a stage after the intermediate bis-2-hydroxyethyl terephthalate is obtained by an esterification reaction of the main raw materials and before the start of the polycondensation reaction, by adding 15 to 60 ppm, in elemental terms, of a compound containing calcium element at a stage prior to the addition of titanium dioxide. [Effects of the Invention]

[0010] According to the present invention, in the process for producing polyester containing a high concentration of titanium dioxide, which has not been possible in the past, it is possible to suppress aggregation of titanium dioxide by adding an appropriate amount of calcium element (ion) to the reaction system, thereby providing a method for producing a polyester composition with fewer coarse particles and less clogging of the filtration filter or molten polymer flow path used in melt-molding the polyester, and less reduction in the durability of the molded product. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention relates to a liquid phase polycondensation process in which titanium dioxide is added when a polyester composition is produced from a dicarboxylic acid or an ester-forming derivative thereof and a diol as main raw materials.

[0012] As the polyester, polyethylene terephthalate is preferred, which can be widely used in the textile field for clothing applications and industrial applications.

[0013] In the present invention, the amount of titanium dioxide added in the liquid phase polycondensation process is 40% by mass or less, and the polycondensation reaction rate is hardly affected, allowing the polycondensation reaction to proceed smoothly. When the amount of titanium dioxide added is 1% by mass or more and 40% by mass or less, the polyester composition can also function as a master material when diluted with other polyesters. From the viewpoint of obtaining a high-quality polyester composition, the amount of titanium dioxide added is more preferably 3 to 35% by mass, and even more preferably 6 to 30% by mass.

[0014] Furthermore, when the amount of the calcium-containing compound added is 15 ppm or more in terms of elements, it is possible to obtain the effect of suppressing the aggregation of titanium dioxide. This is thought to be because calcium ions adsorb to the surface of titanium dioxide particles, increasing the charge on the particle surface, known as the zeta potential, of titanium dioxide, thereby increasing the repulsive force between particles and suppressing aggregation. On the other hand, when the amount of the calcium-containing compound added is 60 ppm or less in terms of elements, it is possible to prevent the formation of foreign substances due to aggregation between calcium-containing compounds. A more preferred amount of the calcium-containing compound added is 30 to 60 ppm, and even more preferably 40 to 60 ppm.

[0015] Furthermore, when the compound containing calcium element is added before the addition of titanium dioxide, the effect of suppressing the aggregation of titanium dioxide can be obtained.

[0016] As the compound containing calcium element, calcium acetate monohydrate is preferably used.

[0017] Furthermore, the liquid phase polycondensation process of the present invention is preferably a three-tank batch polycondensation process comprising two ester reaction tanks and one polycondensation reaction tank, and using the first ester reaction tank, the second ester reaction tank, and the polycondensation reaction tank in that order, and it is preferable to add a compound containing calcium element to the first ester reaction tank, and then add titanium dioxide in divided portions to the first ester reaction tank and the second ester reaction tank.

[0018] Furthermore, in the examples of the present invention, it has been found that titanium dioxide gradually discolors due to heat, affecting the color tone of the resulting polyester composition. Therefore, it is preferable to add a fluorescent brightening agent to adjust the color tone of the polyester composition. An example of a fluorescent brightening agent is 4,4'-bis(2-benzoxazolyl)stilbene. However, it has been found that adding a large amount of fluorescent brightening agent can deteriorate the filterability of the polyester composition, so the amount of fluorescent brightening agent added is preferably 300 ppm or less.

[0019] In view of the recent growing awareness of environmental impacts, it is preferable to use raw materials obtained by recycling polyester waste or unused polyester compositions generated in the polyester product manufacturing process as the main raw material. Specific examples include recycled waste from PET bottles or other polyethylene terephthalate products, or bis-2-hydroxyethyl terephthalate or dimethyl terephthalate obtained by depolymerizing the waste from these polyethylene terephthalate products.

[0020] In addition to the above compounds, compounds that are generally used in esterification reactions and polycondensation reactions of polyesters, such as antimony compounds and phosphorus compounds, can be used in the method for producing the polyester composition of the present invention without any particular restrictions, as long as the object of the present invention is not impaired. [Example]

[0021] The present invention will be described in more detail below with reference to examples. Physical properties were measured using pellets of the polyester composition obtained by the method described below.

[0022] (1) Filterability The titanium dioxide-containing polyester composition obtained according to the present invention and a particle-free polyester composition containing no titanium dioxide were homogeneously mixed in a ratio of 15:85, and the mixture was dried to a moisture content of 150 ppm or less. The pellets were melted at 295°C using an extruder and passed through a nonwoven fabric filter with a mesh size of 5 μm at a rate of 5 g / min, and the difference in pressure between when the feed started and when 1 kg of the polyester composition had passed was measured. The evaluation was based on the following criteria, with ◎ and ○ representing pass and × representing fail. ◎:10.0MPa / kg or less ○: More than 10.0MPa / kg to less than 16.0MPa / kg ×: Over 16.0MPa / kg.

[0023] (2) Color tone (b value) of polyester composition pellets The color tone (b value) of the polyester composition pellets was measured as the Hunter value (b value) using a color difference meter (SM Color Computer, model SM-T45, manufactured by Suga Test Instruments Co., Ltd.). The evaluation was based on the following criteria, with ◎ and ○ representing pass and × representing fail. ◎: 1.5 or less ○: More than 1.5 to less than 2.5 ×: Over 2.5.

[0024] (3) Polycondensation reaction time In the polycondensation reaction step, the time when pressure reduction in the reaction vessel began was defined as zero, and the time until pressure reduction was stopped when a predetermined viscosity (predetermined agitator power value) was reached was defined as the polycondensation reaction time. The time required for each step, including the polycondensation reaction time, is managed to keep one batch within a predetermined cycle time for efficient production, and the evaluation in the present invention is made according to the following criteria, with ◎ and ○ representing pass and × representing fail. ◎: 160 minutes or less ○: More than 160 minutes to less than 210 minutes ×: Over 210 minutes.

[0025] Example 1 Into the first esterification reactor equipped with a rectification column (referred to as an ester exchange reactor), 11 parts by mass of dimethyl terephthalate (non-recycled) and 8 parts by mass of ethylene glycol are charged as main raw materials. Then, 400 ppm of diantimony trioxide, 300 ppm of cobalt acetate tetrahydrate, and 225 ppm of calcium acetate monohydrate are added.

[0026] Thereafter, the temperature of the transesterification reaction vessel is gradually raised to 240°C, and the reaction is allowed to proceed while distilling off the methanol generated during the transesterification reaction outside the vessel, to obtain a low polymer bis-2-hydroxyethyl terephthalate (hereinafter referred to as BHET).

[0027] Trimethyl phosphate is added to the low polymer BHET at 430 ppm. Five minutes later, 11.5 parts by mass of an ethylene glycol slurry of titanium dioxide (a product of Fuji Titanium Industrial Co., Ltd.) diluted to 13% by mass is added over 20 to 30 minutes. Thereafter, 10 parts by mass of ethylene glycol was distilled out of the reaction vessel. The reaction product in the ester exchange reactor is then transferred to the second ester reactor.

[0028] Five minutes after the end of the liquid transfer, 23.1 parts by mass of an ethylene glycol slurry of titanium dioxide diluted to 13% by mass is added over 30 to 40 minutes, and then 17.5 parts by mass of ethylene glycol is distilled out of the reaction vessel. Then, an ethylene glycol slurry of 4,4'-bis(2-benzoxazolyl)stilbene (a product sold by Guangzhou Yinuo Chemical Technology Co., Ltd.) diluted to 1.7% by mass is added as a fluorescent whitening agent, and the reaction product in the second tank of the ester reaction tank is then passed through a nonwoven fabric filter with a filtration accuracy of 10 μm before being transferred to the polycondensation reaction tank.

[0029] After the liquid transfer was completed, the temperature was gradually raised to 275°C, and the pressure was reduced to 50 Pa while distilling off ethylene glycol. When the predetermined agitator power value was reached, the polycondensation reaction tank was purged with nitrogen to return to normal pressure, the polycondensation reaction was stopped, and the reaction product was discharged in the form of strands, cooled, and immediately cut to obtain pellets of the polyester composition.

[0030] The polycondensation reaction time from the start of pressure reduction until the predetermined stirrer power value was reached was 151 minutes, the filterability of the resulting polyester composition was 13.2 MPa / kg, and the color tone b value of the pellets was 1.0.

[0031] [Table 1]

[0032] Examples 2 to 5 Except for changing the amount of titanium dioxide added, the same procedure as in Example 1 was carried out. The results are shown in Table 1.

[0033] Examples 6 to 8 Except for changing the amount of the compound containing calcium element added, the same procedure as in Example 1 was carried out. The results are shown in Table 1.

[0034] Example 9 A two-vessel batch polycondensation process (one ester reaction vessel and one polycondensation reaction vessel) was used and the procedure was the same as in Example 1. The results are shown in Table 1.

[0035] Examples 10 and 11 Except for changing the amount of fluorescent whitening agent added, the same procedure as in Example 1 was carried out. The results are shown in Table 1.

[0036] Example 12 The same procedure as in Example 1 was carried out using bis-2-hydroxyethyl terephthalate oligomer obtained by depolymerization of 10 parts by mass of pre-consumer PET, which is composed of scrap film generated during PET film production, and 6.7 parts by mass of ethylene glycol as main raw materials, charged into the first esterification reactor equipped with a rectification column, and heating the mixture to 240°C. The results are shown in Table 1.

[0037] Comparative Example 1 Except for changing the amount of titanium dioxide added, the same procedure as in Example 1 was carried out. The results are shown in Table 2.

[0038] [Table 2]

[0039] Comparative Examples 2 and 3 Except for changing the amount of the compound containing calcium element added, the same procedure as in Example 1 was carried out. The results are shown in Table 2.

[0040] Comparative Example 4 The same procedure as in Example 1 was repeated, except that the addition of the compound containing calcium to the transesterification reaction vessel was discontinued and the compound containing calcium was added to the second esterification reaction vessel 5 minutes after the addition of the titanium dioxide ethylene glycol slurry. The results are shown in Table 2.

Claims

1. In producing a polyester composition using a dicarboxylic acid or an ester-forming derivative thereof and a diol as main raw materials, In a liquid phase polycondensation process, titanium dioxide is added in an amount of 1 to 40% by mass based on the polyester composition to be obtained after the intermediate bis-2-hydroxyethyl terephthalate is obtained by the esterification reaction of the main raw material and before the polycondensation reaction is started, A method for producing a polyester composition, comprising adding a compound containing calcium element in an amount of 15 to 60 ppm in elemental terms before adding titanium dioxide.

2. 2. The method for producing a polyester composition according to claim 1, wherein the compound containing calcium element is calcium acetate monohydrate.

3. The liquid phase polycondensation process A three-vessel batch polycondensation process comprising two ester reaction vessels and one polycondensation reaction vessel, in which the first ester reaction vessel, the second ester reaction vessel, and the polycondensation reaction vessel are used in this order, A compound containing calcium element is added to the first ester reaction tank, 3. The method for producing a polyester composition according to claim 1 or 2, wherein titanium dioxide is then added in separate portions to the first ester reaction tank and the second ester reaction tank.

4. 4. The method for producing a polyester composition according to claim 3, wherein a fluorescent whitening agent is added.

5. 4. The method for producing a polyester composition according to claim 3, wherein recycled raw materials are used as the main raw materials.

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