Polybutylene terephthalate (PBT) polyester chip with adjustable transparency and processing method thereof

Abstract

The invention relates to the technical field of PBT polyester, in particular to a transparency-adjustable PBT polyester chip and a processing method thereof. The processing method comprises the following steps: mixing terephthalic acid, isophthalic acid, butanediol, 1, 4-cyclohexanedimethanol, a hybrid titanium catalyst and a dispersant, and sequentially carrying out an esterification reaction, a pre-polycondensation reaction and a final polymerization reaction to prepare the PBT polyester chip. The processing method is a PTA direct esterification method, PTA, PIA, BDO and CHDM are used as raw materials, an environment-friendly titanium catalyst is used as a reaction medium, polyester chips are prepared through esterification melt polycondensation, and the reaction process is simple and rapid. The transparency of the slice is adjusted by adjusting the mass ratio of PTA, PIA, BDO and CHDM, and yarn with excellent gloss and transparency can be obtained after conventional spinning and stretching.

Description

Technical Field

[0001] The present invention relates to the technical field of PBT polyesters, and particularly to a PBT polyester chip with adjustable transparency and a processing method thereof. Background Art

[0002] PBT (polybutylene terephthalate) is a thermoplastic polyester material with excellent comprehensive properties, having outstanding mechanical properties and relatively high tensile strength and flexural strength, and can meet various application scenarios with requirements for material strength. For PBT polyester fibers, transparency is also a crucial appearance index, and scientific methods are usually adopted to treat the polyester fibers to achieve the purpose of improving transparency. For example, the Japanese patent No. JP1986239017A discloses a multi-skin-core composite fiber with a special structure and excellent transparency prepared by alternately arranging dark components and light components in the cross-section; another example is the Japanese patent No. JP2021509936A, which discloses a polyester-ether block yarn prepared by copolymerizing polybutylene glycol, 1,4-butanediol, and terephthalic acid. After the yarn is treated with a water-soluble silicon-based spinning oil and the spinning oil is removed with caustic soda, and then the yarn is woven and then subjected to heat shrinkage treatment to obtain a fabric with high transparency. Thus, it can be seen that the method of using blending and copolymerization modification to achieve the purpose of improving transparency has broad value.

[0003] At present, most polycondensation reactions use antimony-based catalysts as reaction media, but antimony catalysts have the following problems: ① It is easily reduced to metallic antimony during the reaction process, resulting in the polyester turning gray; ② Antimony is easily leached out during subsequent dyeing treatment, causing water pollution; ③ The presence of antimony in the polyester will cause an increase in the spinning filtration pressure, affecting the continuous spinning process. Therefore, studying how to select new raw materials and use a non-antimony environmentally friendly catalyst as the reaction medium to prepare PBT with high transparency is one of the development directions of PBT. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: to provide a PBT polyester chip with adjustable transparency prepared by using a non-antimony environmentally friendly catalyst and a processing method thereof.

[0005] To solve the above technical problem, the technical solution adopted by the present invention is: a processing method of a PBT polyester chip with adjustable transparency, comprising the following steps: mixing terephthalic acid (PTA), isophthalic acid (PIA), butanediol (BDO), 1,4-cyclohexanedimethanol (CHDM), a hybrid titanium-based catalyst, and a dispersant, and successively performing an esterification reaction, a pre-polycondensation reaction, and a final polycondensation reaction to prepare a PBT polyester chip.

[0006] Another technical solution adopted by the present invention is: the PBT polyester chips prepared by using the processing method of the above-mentioned PBT polyester chips with adjustable transparency.

[0007] The beneficial effects of the present invention are as follows: The processing method of the PBT polyester chips with adjustable transparency in the present invention is the PTA direct esterification method. Using PTA, PIA, BDO and CHDM as raw materials and an environmentally friendly titanium-based catalyst as the reaction medium, polyester chips are prepared by esterification and melt polycondensation. The reaction process is simple and fast. The transparency of the chips can be adjusted by adjusting the mass ratio of PTA, PIA, BDO and CHDM, and yarns with excellent gloss and transparency can be obtained after conventional spinning and stretching. Description of the Drawings

[0008] Figure 1 It is a finished product diagram of fabrics with different transparencies in the embodiment of the present invention. From left to right, they are the opaque state, the semi-transparent state and the transparent state. Detailed Embodiments

[0009] To describe the technical content, the achieved objectives and the effects of the present invention in detail, the following is described in conjunction with the embodiments and accompanied by the drawings.

[0010] A processing method of PBT polyester chips with adjustable transparency includes the following steps: Mix terephthalic acid, isophthalic acid, butanediol, 1,4-cyclohexanedimethanol, a hybrid titanium-based catalyst and a dispersant, and carry out esterification reaction, pre-polycondensation reaction and final polycondensation reaction in sequence to prepare PBT polyester chips.

[0011] As can be seen from the above description, the beneficial effects of the present invention are as follows: The present invention uses PTA, PIA, BDO and CHDM as raw materials and an environmentally friendly titanium-based catalyst as the reaction medium to prepare polyester chips through esterification, pre-polycondensation and final polycondensation reactions in sequence; avoiding the toxicity and environmental pollution problems caused by antimony catalysts, adding a dispersant to promote the dispersion of PTA in the polymer to improve the reaction efficiency and make the esterification more complete. During the reaction process, PIA and PTA are added. When the meta structure of PIA participates in the polymerization reaction, it destroys the regularity of the polymer molecular chain. During the formation of BHBT (bis(4-hydroxybutyl) terephthalate), the addition of PIA makes the arrangement of benzene rings in the molecular chain no longer as regular and orderly as when only PTA participates in the reaction; this irregular molecular arrangement reduces the close packing between molecular chains and lowers the crystallinity of the polymer; and the reduction of crystallinity enhances the light transmittance and has a positive impact on the product transparency. The transparency of the chips can be adjusted by adjusting the mass ratio of PTA, PIA, BDO and CHDM, and yarns with high permeability and high brightness can be prepared.

[0012] Moreover, in the molecular structure of PIA, the two carboxyl groups are in the meta-position of the benzene ring. This meta-position structure causes a difference in the carboxyl activity between PIA and PTA. Compared with PTA, PIA has a larger steric hindrance of the carboxyl group and relatively lower reactivity. However, when reacting with BDO and CHDM, it can complement PTA. Under slightly positive pressure conditions, PTA and PIA participate in the reaction simultaneously. The high reactivity of PTA ensures the initiation and progress of the reaction, while the relatively low reactivity of PIA makes the reaction process more controllable, avoiding a large number of side reactions caused by overly intense reactions, resulting in high-quality products and improved safety of the process route.

[0013] Furthermore, the mass ratio of terephthalic acid to isophthalic acid ≥ 7 / 3.

[0014] Furthermore, the mass ratio of butanediol to 1,4-cyclohexanedimethanol ≥ 7 / 3.

[0015] Furthermore, the ratio of the total moles of terephthalic acid and isophthalic acid to the total moles of butanediol and 1,4-cyclohexanedimethanol is 1:1.1 - 2. That is, n(PTA + PIA):n(BDO + CHDM) = 1:1.1 - 2.

[0016] As can be seen from the above description, the addition amounts of PIA and CHDM should not be too much, otherwise it will cause a significant decrease in the melting point of the polyester, resulting in a decrease in spinnability and practicality.

[0017] The transparency and brightness of the yarn change with the addition amount of the modifying monomer. By adjusting the ratios of PTA to PIA and BDO to CHDM, different products from semi-transparent to transparent can be prepared.

[0018] Preferably, the mass ratio of terephthalic acid to isophthalic acid is 3 / 1 - 7 / 3.

[0019] Preferably, the mass ratio of butanediol to 1,4-cyclohexanedimethanol is 3 / 1 - 7 / 3.

[0020] As can be seen from the above description, the smaller the values of the mass ratio of terephthalic acid to isophthalic acid and the mass ratio of butanediol to 1,4-cyclohexanedimethanol, the higher the transparency. Within the range of 3 / 1 - 7 / 3, high transparency can be achieved while ensuring the spinnability of the yarn.

[0021] Furthermore, the addition amount of the dispersant is 250 - 300 PPM.

[0022] As can be seen from the above description, adding a dispersant can better promote the dispersion of the solution and improve the reaction rate. If too much dispersant is added, it will lead to a high content of polyester impurities, affecting the chip hue and spinnability.

[0023] Further, the addition amount of the hybrid titanium-based catalyst is 900 - 1100 PPM.

[0024] As can be seen from the above description, if the addition amount of the hybrid titanium-based catalyst is too low, it cannot play a catalytic role. If the addition amount is too high, side reactions will be intense and the polyester color will turn yellow.

[0025] Further, the temperature of the esterification reaction is 180 - 235 °C.

[0026] As can be seen from the above description, the esterification temperature should not be too high, as too high a temperature will result in an increase in by-products.

[0027] Further, when the water output ≥ 95% of the theoretical value, the esterification reaction reaches the end point.

[0028] Further, before the pre-polycondensation reaction, the excess ethylene glycol liquid is drained, and the temperature of the pre-polycondensation reaction is 230 - 240 °C.

[0029] As can be seen from the above description, removing the excess BDO before the pre-polycondensation reaction can avoid its influence on the final polymerization reaction. The temperature of the pre-polycondensation reaction is 230 - 240 °C, which can evaporate the water generated in the reaction.

[0030] Further, the hybrid titanium-based catalyst is a DH-HyTi hybrid catalyst.

[0031] As can be seen from the above description, conventional tetrabutyl titanate will become ineffective when it encounters water and titanium dioxide will be generated, affecting the product transparency. The present invention uses a modified hybrid titanium-based catalyst, which has good stability even in the presence of water, can improve the reaction efficiency and product transparency, and reduce the production cost.

[0032] Compared with the antimony-based catalyst and other titanium-based catalysts, the DH-HyTi hybrid catalyst of the present invention has better catalytic performance, the polymerization process is easy to achieve, the reaction process is highly efficient and controllable, and it has good dispersibility, compatibility and stability in the polyester system, can effectively inhibit side reactions, and the yarn prepared with this catalyst also has good spinnability; at the same time, the hybrid titanium composition is green and safe, does not contain heavy metal ions such as antimony, cobalt, and manganese, does not generate impurities that affect polyester synthesis, and also belongs to non-dangerous goods, and has good thermal properties and will not lose catalytic activity below 310 °C.

[0033] Further, the temperature of the final polymerization reaction is 240 - 260 °C, and the vacuum degree is 190 - 210 Pa.

[0034] As described above, the final polymerization temperature is controlled at 240-260°C. If the temperature is too high, the thermal degradation will be aggravated. The vacuum degree is preferably controlled within 190-210 Pa. If the vacuum degree is too high, it may cause the small molecular by-products of polycondensation to be unable to be discharged from the reaction system, resulting in low degree of polymerization, wide molecular weight distribution, and decreased spinnability of the polyester.

[0035] Furthermore, the esterification reaction, pre-polycondensation reaction, and final polymerization reaction are carried out in the same reaction kettle. The top of the reaction kettle is sequentially connected to a condenser and a collection tank.

[0036] As described above, when the temperature of the kettle rises to 70°C, the methanol generated by the reaction is cooled by the condenser and collected in the collection tank. By controlling the conditions, the present invention completes both esterification and polycondensation in the same kettle, simplifies the production process route, and saves production costs.

[0037] Another technical solution adopted by the present invention is: PBT polyester chips prepared by using the processing method of the above-mentioned PBT polyester chips with adjustable transparency.

[0038] As described above, the yarn prepared from the PBT polyester chips of the present invention can have high transparency, opacity, or semi-transparency.

[0039] Example 1 of the present invention is: a processing method of PBT polyester chips with adjustable transparency. The reaction kettle used is internally provided with a stirrer. The top of the reaction kettle is sequentially connected to a condenser and a collection tank. The processing steps are as follows: S1: Put PTA and PIA into the reaction kettle, then add BDO and CHDM, and finally add 300 PPM DH-HyTi hybrid catalyst (manufacturer: Shanghai Huiyi) and 1000 PPM. The mass ratio of PTA to PIA is 19 / 1, the mass ratio of BDO to CHDM is 19 / 1, and n(PTA + PIA):n(BDO + CHDM)=1:1.3.

[0040] S2. Turn on the stirrer (frequency: 30 HZ), raise the temperature and turn on the condenser, raise the temperature to 235°C, and control the pressure at 0.4 Mpa. When the reaction temperature rises to 180-230°C, slowly remove the water. Since the boiling points of BDO and CHDM are relatively high, the top temperature is controlled at 120°C. When the water output reaches 95% of the theoretical value, the esterification reaction ends.

[0041] S3. Release the pressure to normal pressure state, increase the stirrer frequency from 30 HZ to 50 HZ and raise the temperature, pump out the liquid in the kettle under low vacuum, and keep it warm at 235°C for 30 min.

[0042] S4. Raise the temperature and adjust the opening of the vacuum valve. When the kettle power rises to 2.3 KW, reduce the stirrer speed to 30 HZ until the power slowly rises to 2.2 KW to obtain PBT polyester melt; during this process, the reaction kettle temperature is 250 °C and the vacuum degree is 200 Pa.

[0043] S5. Close the vacuum pumping valve and the polycondensation outlet valve of the reaction kettle, and fill the reaction kettle with nitrogen to break the vacuum to normal pressure; then open the outlet valve. When the melt flows out, cool the melt ester strips through chilled water and then introduce them into the cutting chamber for pelletizing. Slowly fill with nitrogen at 0.2 Mpa, and at the same time slowly adjust the cutting knife speed to reach a balance. The obtained pellets are observed to be opaque to the naked eye.

[0044] S6. The PBT polyester pellets are made into translucent yarns through spinning and hot stretching. After the yarns are woven into cloth, they are heat-set at 180 °C, and the cloth is opaque, as shown in Figure 1 the leftmost view.

[0045] Example two of the present invention is as follows: The difference between example two and example one is only that: the mass ratio of PTA to PIA is 9 / 1, and the mass ratio of BDO to CHDM is 9 / 1; the obtained pellets are observed to be semi-translucent to the naked eye, and the prepared cloth is semi-translucent, as shown in Figure 1 the middle view.

[0046] Example three of the present invention is as follows: The difference between example three and example one is only that: the mass ratio of PTA to PIA is 17 / 3, and the mass ratio of BDO to CHDM is 17 / 3; the obtained pellets are observed to be semi-translucent to the naked eye, and the prepared cloth is semi-translucent.

[0047] Example four of the present invention is as follows: The difference between example four and example one is only that: the mass ratio of PTA to PIA is 4 / 1, and the mass ratio of BDO to CHDM is 4 / 1; the obtained pellets are observed to be semi-translucent to the naked eye, and the prepared cloth is semi-translucent.

[0048] Example five of the present invention is as follows: The difference between example five and example one is only that: the mass ratio of PTA to PIA is 3 / 1, and the mass ratio of BDO to CHDM is 3 / 1; the obtained pellets are observed to be transparent to the naked eye, and the prepared cloth is transparent, as shown in Figure 1 the rightmost view.

[0049] Example six of the present invention is as follows: Example VI is different from Example I only in that: the mass ratio of PTA to PIA is 7 / 3, and the mass ratio of BDO to CHDM is 7 / 3; the obtained chips are transparent to the naked eye, and the produced fabric is in a transparent state.

[0050] Comparative Example I of the present invention is as follows: Comparative Example I is different from Example I only in that: PIA and CHDM are not added; PTA and BDO are separately charged into the polymerization kettle; the obtained chips are opaque to the naked eye.

[0051] Comparative Example II of the present invention is as follows: Comparative Example II is different from Example I only in that: PIA is not added; PTA, CHDM and BDO are separately charged into the polymerization kettle; the obtained chips are opaque to the naked eye.

[0052] Comparative Example III of the present invention is as follows: Comparative Example III is different from Example I only in that: CHDM is not added; PTA, PIA and BDO are separately charged into the polymerization kettle; the obtained chips are opaque to the naked eye.

[0053] The products of Examples I - VI and Comparative Examples I - III were tested, and the test results are shown in Table 1.

[0054] Table 1

[0055] Among them, the measurement method of viscosity was tested according to the regulations of GB / T14190 - 2017 capillary viscometer, and the solvent used was a phenol / tetrachloroethane solution with a mass ratio of 1:1.

[0056] The melting point was measured according to the method specified in GB / T14190 - 2017. Differential scanning calorimetry was used, and a DSC differential scanning calorimeter was used to analyze the melting and crystallization behavior of the polymer at a nitrogen flow rate of 50 mL / min and a mass of 3.5 mg. The sample was quickly heated to 280°C and held at this temperature for 3 min to eliminate the thermal history; then, the sample was cooled from 280°C to 25°C at a rate of 10°C / min to obtain a cooling curve; finally, the sample was heated from 25°C to 280°C at the same temperature change rate to obtain a second heating curve, and the melting point value was read on the DSC curve.

[0057] Example VII of the present invention is as follows: The difference between Example 7 and Example 1 is only that: 250 PPM of DH-HyTi hybrid catalyst and 900 PPM of dispersant 7902 are added, n(PTA + PIA):n(BDO + CHDM)=1:1.1; the temperature of the esterification reaction is 230 °C, and the pressure is 0.2 Mpa; the temperature of the pre-polycondensation is 240; the temperature of the final polycondensation reaction is 260 °C, and the vacuum degree is 210 Pa.

[0058] Example 8 of the present invention is as follows: The difference between Example 8 and Example 1 is only that: 270 PPM of DH-HyTi hybrid catalyst and 1100 PPM of dispersant 7902 are added, n(PTA + PIA):n(BDO + CHDM)=1:2; the temperature of the esterification reaction is 200 °C, and the pressure is 0.5 Mpa; the temperature of the pre-polycondensation is 230; the temperature of the final polycondensation reaction is 240 °C, and the vacuum degree is 190 Pa.

[0059] Example 9 of the present invention is: PBT polyester chips prepared by the processing method of Example 1.

[0060] In summary, the PBT polyester chips with adjustable transparency and the processing method provided by the present invention use PTA, PIA, BDO and CHDM as raw materials, and prepare PBT polyester chips with adjustable transparency by an esterification melt polycondensation process route, saving costs and improving production efficiency; by limiting the ratio of PTA, PIA, BDO and CHDM, the finished fabric can achieve the characteristics of high transparency and brightness. The present invention uses an antimony-free environmentally friendly titanium-based catalyst as the reaction medium, avoiding the toxicity of the antimony catalyst and the environmental pollution problems caused.

[0061] The above are only the embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. All equivalent transformations made by using the content of the specification and drawings of the present invention, or directly or indirectly applied in the relevant technical fields, are equally included in the patent protection scope of the present invention.

Claims

1. A processing method of PBT polyester chips with adjustable transparency, characterized in that, It includes the following steps: Mix terephthalic acid, isophthalic acid, butanediol, 1,4-cyclohexanedimethanol, a hybrid titanium-based catalyst and a dispersant, and conduct esterification reaction, prepolycondensation reaction and final polycondensation reaction in sequence to prepare PBT polyester chips.

2. The processing method of the PBT polyester chip with adjustable transparency according to claim 1, characterized in that, The mass ratio of terephthalic acid to isophthalic acid ≥ 7 / 3.

3. The processing method of the PBT polyester chip with adjustable transparency according to claim 1, characterized in that, The mass ratio of butanediol to 1,4-cyclohexanedimethanol ≥ 7 / 3.

4. The processing method of the PBT polyester chip with adjustable transparency according to claim 1, characterized in that, The ratio of the total molar amount of terephthalic acid and isophthalic acid to the total molar amount of butanediol and 1,4-cyclohexanedimethanol is 1:1.1 - 2.

5. The processing method of the PBT polyester chip with adjustable transparency according to claim 1, characterized in that, The temperature of the esterification reaction is 180 - 235 °C.

6. The processing method of the PBT polyester chip with adjustable transparency according to claim 1, characterized in that When the water output ≥ 95% of the theoretical value, the esterification reaction reaches the end point.

7. The processing method of the PBT polyester chip with adjustable transparency according to claim 1, characterized in that, Before the prepolycondensation reaction, the liquid is evacuated, and the temperature of the prepolycondensation reaction is 230 - 240 °C.

8. The processing method of the PBT polyester chip with adjustable transparency according to claim 1, characterized in that, The temperature of the final polycondensation reaction is 240 - 260 °C, and the vacuum degree is 190 - 210 Pa.

9. The processing method of the PBT polyester chip with adjustable transparency according to claim 1, characterized in that, The esterification reaction, prepolycondensation reaction and final polycondensation reaction are carried out in the same reaction kettle, and the top of the reaction kettle is connected to a condenser and a collection tank in sequence.

10. PBT polyester chips prepared by using the processing method of the PBT polyester chips with adjustable transparency according to any one of claims 1 - 9.

Images