Production method of colored polyethylene glycol terephthalate
By synthesizing non-ferrous PET in situ during PET synthesis, the problems of high dyeing process cost and environmental pollution in the existing technology are solved, and the production process simplification and environmental protection effects are achieved.
Patent Information
- Application Number
- CN202510575035.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-06
- Publication Date
- 2025-08-08
AI Technical Summary
In the prior art, when preparing colored PET, the dyeing process is expensive and pollutes the environment, and requires two steps of reaction generation and coloring.
Using an inorganic dye that can react with polyethylene terephthalate terminal hydroxyl groups, colored polyethylene terephthalate is synthesized in situ during the reaction process, simplifying the production process, and combining synthesis and dyeing into one step.
Reduced production steps, saved time and cost, reduced emissions of harmful substances, met customized needs, and achieved green manufacturing.
Smart Images
Figure CN120441823A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the technical field of polymer materials, and in particular to a method for producing colored polyethylene terephthalate. Background Art
[0002] Polyethylene terephthalate (PET) is a common plastic material used extensively in industry and daily life. PET is commonly used to make beverage bottles, food packaging, fibers, engineering plastics, carpet fibers, and more. PET is also commonly used as a 3D printing material and medical sutures.
[0003] Currently, the majority of colored PET produced domestically and internationally uses direct esterification and melt polycondensation of 1,4-dicarboxybenzene (PTA) and ethylene glycol (EG), or transesterification and melt polycondensation. The PET is then colored through molding, blending, or dyeing and impregnation. However, this method requires two steps: the reaction to form the PET and then coloring. The dyeing process also requires the use of large amounts of water and other chemicals, resulting in high costs and environmental pollution. Summary of the Invention
[0004] The purpose of the present application is to provide a method for producing colored polyethylene terephthalate, which uses an inorganic dye that can react with the terminal hydroxyl groups of polyethylene terephthalate to synthesize colored polyethylene terephthalate in situ during the reaction process, thereby solving the problems of high cost and environmental pollution caused by the dyeing process in the prior art and simplifying the production process.
[0005] In order to achieve one of the above-mentioned objectives of the invention, one embodiment of the present application provides a method for producing colored polyethylene terephthalate, comprising the following steps:
[0006] Pretreatment: constructing a reaction system using bis(hydroxyethyl) terephthalate, a first catalyst, and a stabilizer, and heating and stirring until the bis(hydroxyethyl) terephthalate is melted;
[0007] Pre-polycondensation: After the bis(hydroxyethyl) terephthalate is melted, continue stirring and heat to 240-270°C, and start vacuuming until the pressure of the reaction system is less than 400 Pa;
[0008] Final polycondensation: The reaction system is restored to normal pressure, the first inorganic dye is added to the reaction system, and then vacuum is applied to reduce the pressure of the reaction system to less than 400 Pa. The reaction is stirred and heated to 270-300° C. for 2-8 hours to terminate the reaction; wherein the first inorganic dye reacts with the terminal hydroxyl groups of the polyethylene terephthalate.
[0009] As a further improvement of one embodiment of the present application, the first inorganic dye is a mixed metal oxide inorganic dye.
[0010] As a further improvement of one embodiment of the present application, the mass ratio of the first inorganic dye to bis(hydroxyethyl) terephthalate is (0-0.08):1.
[0011] As a further improvement to one embodiment of the present application, a pre-reaction step is further included before the pretreatment step: terephthalic acid, a second catalyst, and ethylene glycol dissolved with a first organic dye are added to a reaction vessel, heated to 240-260° C. and stirred to obtain bis(hydroxyethyl)terephthalate having a chromophoric group, and the bis(hydroxyethyl)terephthalate having a chromophoric group is added to the reaction system in the pretreatment step; wherein the first organic dye has a group capable of reacting with the terminal hydroxyl groups of the bis(hydroxyethyl)terephthalate.
[0012] As a further improvement of one embodiment of the present application, the first organic dye contains at least one group selected from -COOH, -OH, -NH2, -Cl, -Br, -I, -POCl3, -PCl3, and -SH.
[0013] As a further improvement of one embodiment of the present application, the second catalyst is one or more of antimony ethylene glycol, tetrabutyl titanate, p-toluenesulfonic acid, N,N'-dicyclohexylcarbodiimide, cuprous halide, and cuprous iodide.
[0014] As a further improvement of one embodiment of the present application, the mass ratio of the first organic dye to terephthalic acid is (0-0.25):1, and the molar ratio of terephthalic acid to the second catalyst is 1:(0.01-0.0001).
[0015] As a further improvement of one embodiment of the present application, in the pretreatment step, a second organic dye and / or a second inorganic dye is also dispersed in the reaction system, and the second organic dye and the second inorganic dye are dispersed by ultrasound, wherein the second organic dye and the second inorganic dye do not participate in the chemical reaction.
[0016] As a further improvement of one embodiment of the present application, in the pretreatment step, the gas pressure in the reaction system is controlled to be 1 to 5 bar; in the pre-polycondensation step, the reaction time is controlled to be 0.5 to 4 hours.
[0017] As a further improvement of one embodiment of the present application, the molar ratio of the first catalyst to bis(hydroxyethyl) terephthalate is (0.01-0.00001):1, and the molar ratio of the stabilizer to bis(hydroxyethyl) terephthalate is also (0.01-0.00001):1.
[0018] As a further improvement of one embodiment of the present application, the first catalyst includes an acidic catalyst, an alkaline catalyst, a metal catalyst, an enzyme catalyst, and an organic peroxide catalyst; the stabilizer includes an antioxidant, a light stabilizer, a heat stabilizer, an antioxidant, and a chelating agent.
[0019] One or more technical solutions provided in this application have at least the following technical effects or advantages:
[0020] 1. Reduce production steps: In situ synthesis combines the synthesis and dyeing steps into one process, which simplifies the production process, saves time and cost, and improves production efficiency.
[0021] 2. Flexibility and customization: Using the in-situ synthesis method, the amount and proportion of color powder can be adjusted according to specific needs to obtain a specific color and meet the customized needs of different customers.
[0022] 3. Reduce costs and resource consumption: In situ synthesis reduces the demand for water and other chemicals, which is conducive to resource conservation.
[0023] 4. Prevent the release of volatile organic compounds (VOCs): Traditional dyeing processes may release harmful volatile organic compounds. Through in-situ synthesis, the emission of these harmful substances can be greatly reduced and green manufacturing can be promoted. BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Figure 1 This is a physical picture of the colored polyethylene terephthalate prepared in Example 1 of the present application.
[0025] Figure 2 This is the DSC chart of the colored polyethylene terephthalate prepared in Example 1 of the present application.
[0026] Figure 3 This is a physical picture of the colored polyethylene terephthalate prepared in Example 2 of the present application.
[0027] Figure 4 This is the DSC chart of the colored polyethylene terephthalate prepared in Example 2 of the present application.
[0028] Figure 5 This is a physical picture of the colored polyethylene terephthalate prepared in Example 3 of the present application.
[0029] Figure 6 This is the DSC chart of the colored polyethylene terephthalate prepared in Example 3 of the present application.
[0030] Figure 7 This is a physical picture of the colored polyethylene terephthalate prepared in Example 4 of the present application.
[0031] Figure 8 This is the DSC chart of the colored polyethylene terephthalate prepared in Example 4 of the present application. DETAILED DESCRIPTION
[0032] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.
[0033] The present invention provides a method for producing colored polyethylene terephthalate, comprising the following steps:
[0034] Pretreatment: constructing a reaction system using bis(hydroxyethyl) terephthalate, a first catalyst, and a stabilizer, and heating and stirring until the bis(hydroxyethyl) terephthalate is melted;
[0035] Pre-polycondensation: After the bis(hydroxyethyl) terephthalate is melted, continue stirring and heat to 240-270°C, and start vacuuming until the pressure of the reaction system is less than 400 Pa;
[0036] Final polycondensation: The reaction system is restored to normal pressure, the first inorganic dye is added to the reaction system, and then vacuum is applied to reduce the pressure of the reaction system to less than 400 Pa. The reaction is stirred and heated to 270-300° C. for 2-8 hours to terminate the reaction; wherein the first inorganic dye reacts with the terminal hydroxyl groups of the polyethylene terephthalate.
[0037] In the pretreatment step, reaction raw materials are added, and bis(hydroxyethyl) terephthalate) is heated to melt. After the bis(hydroxyethyl) terephthalate is melted, it is heated to 240-270° C. for polycondensation to obtain a polymer and generate ethylene glycol as a byproduct. The byproduct ethylene glycol is extracted by vacuuming, and the reaction progress of the pre-polycondensation step is judged by the amount of ethylene glycol extracted. When the pre-polycondensation step reaches the end, the pressure in the reaction vessel is stabilized at less than 400 Pa. The progress of the pre-polycondensation reaction is judged specifically by calculating the molar mass of the ethylene glycol as a byproduct and comparing it with the molar mass of the bis(hydroxyethyl) terephthalate added in the pretreatment step. The closer the molar mass of the ethylene glycol as a byproduct is to the molar mass of the bis(hydroxyethyl) terephthalate, the more complete the pre-polycondensation reaction.
[0038] In the final polycondensation step, before the final polycondensation begins, a first inorganic dye capable of reacting with the terminal hydroxyl groups of polyethylene terephthalate is added to the reaction system. The first inorganic dye can be first dispersed in ethylene glycol and then added to the reaction system. The system is then evacuated to below 400 Pa and heated to a higher temperature to allow the polymers to continue reacting to form polyethylene terephthalate. The first inorganic dye then chemically reacts with the terminal hydroxyl groups of the polyethylene terephthalate to ultimately form colored polyethylene terephthalate. The chemical reaction tightly replaces the original groups at both ends of the polyethylene terephthalate molecular chain, resulting in more stable coloration.
[0039] Preferably, the first inorganic dye may be a mixed metal oxide inorganic dye, such as titanium bismuth yellow, titanium nickel yellow, cobalt green, titanium chrome brown, and the like.
[0040] During the final polycondensation step, as the molecular chains grow, the product viscosity increases. The degree of the final polycondensation reaction can be determined by the resistance of the stirring motor / the current drawn by the motor. When the resistance / current remains constant, the reaction is complete, and polyethylene terephthalate is formed. The stirring speed during the production process is controlled between 100 and 1000 rpm.
[0041] In some embodiments, the mass ratio of the first inorganic dye to bis(hydroxyethyl) terephthalate is (0-0.08):1.
[0042] In some embodiments, a pre-reaction step is further included before the pretreatment step: terephthalic acid, a second catalyst, and ethylene glycol dissolved with a first organic dye are added to a reaction vessel, heated to 240-260° C. and stirred to obtain bis(hydroxyethyl) terephthalate having a chromophoric group, and the bis(hydroxyethyl) terephthalate having a chromophoric group is added to the reaction system in the pretreatment step; wherein the first organic dye has a group capable of reacting with the terminal hydroxyl group of bis(hydroxyethyl) terephthalate.
[0043] In addition to the first inorganic dye, a first organic dye can also be used to produce colored polyethylene terephthalate. At a temperature of 240-260°C, terephthalic acid and ethylene glycol react in the presence of a second catalyst to form bis(hydroxyethyl)terephthalate. The first organic dye then chemically reacts with the hydroxyl groups of the bis(hydroxyethyl)terephthalate, imparting chromophoric groups to the bis(hydroxyethyl)terephthalate.
[0044] The bis(hydroxyethyl) terephthalate reacted with the first organic dye is added to the system of the pretreatment step and undergoes a polycondensation reaction with the bis(hydroxyethyl) terephthalate in the pretreatment step to obtain colored polyethylene terephthalate.
[0045] Preferably, the first organic dye has at least one group selected from -COOH, -OH, -NH2, -Cl, -Br, -I, -POCl3, -PCl3, and -SH, and these groups can react with the hydroxyl group of bis(hydroxyethyl) terephthalate.
[0046] In some embodiments, the second catalyst in the pre-reaction step is one or more of a metal salt catalyst, a protonic acid catalyst, a condensation agent catalyst, a metal organic catalyst, a nucleophilic substitution reaction catalyst, and a transition metal complex catalyst.
[0047] Preferably, the second catalyst in the pre-reaction step is one or more of antimony ethylene glycol, tetrabutyl titanate, p-toluenesulfonic acid, N,N'-dicyclohexylcarbodiimide, cuprous halide, and cuprous iodide.
[0048] In some embodiments, the mass ratio of the first organic dye to terephthalic acid is (0-0.25):1, and the molar ratio of terephthalic acid to the second catalyst is 1:(0.01-0.0001).
[0049] The amount of the first organic dye added depends on the target color, but there is an upper limit. Otherwise, it may affect the degree of polymerization of the polyethylene terephthalate or the first organic dye may only adhere to the surface of the polymer, causing it to easily fade. If no toner is added, the resulting polyethylene terephthalate will retain its original color.
[0050] The amount of catalyst added is usually small, and the specific molar ratio varies depending on the relative molecular weight of the selected catalyst. The smaller the relative molecular weight of the second catalyst, the larger the molar ratio is, and the larger the relative molecular weight of the second catalyst, the smaller the molar ratio is.
[0051] In some embodiments, in the pretreatment step, a second organic dye and / or a second inorganic dye is further dispersed in the reaction system, and the second organic dye and the second inorganic dye are dispersed by ultrasound, wherein the second organic dye and the second inorganic dye do not participate in the chemical reaction.
[0052] In addition to the dye that participates in the chemical reaction, a dye that does not participate in the reaction can also be added in the pretreatment step. This can be the aforementioned second organic dye, the aforementioned second inorganic dye, or both. Ultrasonic dispersion is used to enhance the dispersion uniformity of the second organic dye and the second inorganic dye. The second organic dye and / or the second inorganic dye are added to the reaction system in the pretreatment step. Under stirring during the reaction process, the second organic dye and / or the second inorganic dye can be uniformly dispersed in the polymer product, polyethylene terephthalate. Compared to the current process of polymerizing first and then dyeing, this process does not require the use of large amounts of water or other organic solvents, and simplifies the production process.
[0053] Preferably, the second organic dye and the second inorganic dye are first dispersed and stirred using a high-speed dispersant, a planetary mixer or a homogenizer.
[0054] Preferably, the second organic dye may be an azo disperse dye, an anthraquinone dye, or a heterocyclic dye; and the second inorganic dye may be a metal oxide or a metal sulfide.
[0055] More preferably, the second organic dye may be disperse orange, disperse yellow 23, or fluorescent yellow 8GFF; and the second inorganic dye may be titanium dioxide, zinc oxide, cadmium sulfide, or lithopone.
[0056] In some embodiments, in the pretreatment step, the pressure in the reaction system is controlled to be 1 to 5 bar; in the pre-polycondensation step, the reaction time is controlled to be 0.5 to 4 hours. The reaction system is controlled to have a relatively high pressure and heated to above the melting point of bis(hydroxyethyl) terephthalate to ensure that the bis(hydroxyethyl) terephthalate is completely melted and the substances in the reaction system are evenly mixed. Vacuuming is started based on the pressure of 1 to 5 bar in the pretreatment step, and the pressure in the reaction vessel is reduced to below 400 Pa during the 0.5 to 4 hour reaction time of the pre-polycondensation step. That is, the vacuuming rate needs to be controlled in the pre-polycondensation step to ensure that the by-product ethylene glycol in the reaction vessel can be completely extracted.
[0057] In some embodiments, the molar ratio of the first catalyst to bis(hydroxyethyl) terephthalate is (0.01-0.00001):1, and the molar ratio of the stabilizer to bis(hydroxyethyl) terephthalate is also (0.01-0.00001):1. The amount of catalyst and stabilizer added is typically small, and the specific molar ratio varies depending on the relative molecular weight of the selected catalyst / stabilizer. A larger molar ratio is selected for a smaller relative molecular weight catalyst / stabilizer, while a smaller molar ratio is selected for a larger relative molecular weight catalyst / stabilizer.
[0058] Preferably, the first catalyst is one or a combination of acidic catalyst, alkaline catalyst, metal catalyst, enzyme catalyst, and organic peroxide catalyst.
[0059] More preferably, the first catalyst is selected from one or more of antimony trioxide, antimony glycol, titanium dioxide, tetrabutyl titanate, sodium hydroxide, and potassium hydroxide.
[0060] Preferably, the stabilizer is one or a combination of antioxidants, light stabilizers, heat stabilizers, and chelating agents.
[0061] More preferably, the stabilizer is selected from one or more of phenol, catechol, triethyl phosphate, ethylenediaminetetraacetic acid, benzoic acid compounds, organophosphorus heat stabilizers, and metal salt heat stabilizers.
[0062] In some embodiments, during the pretreatment step, a protective gas is used to replace the air in the reaction system. Preferably, the protective gas can be nitrogen, an inert gas, or other gas that does not react with the substances in the reaction vessel.
[0063] In order to prevent oxygen in the air from affecting the substances in the reaction system, the air in the reaction vessel is replaced with a protective gas before heating.
[0064] The technical solution of the present application is further described below with reference to some specific embodiments.
[0065] Example 1
[0066] Pretreatment: Add 3000g of bis(hydroxyethyl) terephthalate, 0.72g of catalyst antimony glycol, and 0.116g of stabilizer triethyl phosphate to the reactor, then replace the air in the reactor with nitrogen three times while maintaining the pressure in the reactor at 2 bar. Heat to 240°C and stir to melt the bis(hydroxyethyl) terephthalate.
[0067] Pre-polycondensation: The temperature was then raised from 240°C to 270°C within 1.5 hours, and the pressure in the reactor was gradually adjusted to a vacuum state, and finally stabilized at a high vacuum state of less than 200 Pa, completing the pre-polycondensation reaction.
[0068] Final polycondensation: The reactor was restored to normal pressure, and an ethylene glycol dispersion containing 5.5 g of titanium bismuth yellow was quickly added. The vacuum degree in the reactor was then increased and heated to a higher temperature. The reaction temperature was stabilized at 278°C and controlled at a high vacuum degree of less than 200 Pa. The final polycondensation reaction lasted for 4 hours to obtain colored recycled polyethylene terephthalate (rPET).
[0069] The obtained polymer had an intrinsic viscosity of 0.688 dL / g, a terminal carboxyl group content of 3.7 mol / t, a diethylene glycol content of 1.22%, a melting point of 251.50° C., and color values L: 66.1, a: 16.4, and b: 44.2.
[0070] Example 2
[0071] Pre-reaction: Dissolve 6.30g of Acid Yellow 36 and 5.50g of Acid Red 3B in 75g of ethylene glycol. Then add 250g of terephthalic acid, 0.25g of catalyst antimony glycol, and ethylene glycol dissolved with the above-mentioned organic dye to a 5L reactor. Then replace the air in the reactor with nitrogen three times while maintaining the pressure in the reactor at 2 bar and raising the temperature to 240°C.
[0072] Pretreatment: Return the reactor to normal pressure, add 2700g of bis(hydroxyethyl) terephthalate, 0.72g of catalyst antimony ethylene glycol, and 0.116g of stabilizer triethyl phosphate into the reactor, and heat and stir to melt the bis(hydroxyethyl) terephthalate.
[0073] Pre-polycondensation: The temperature is raised from 240°C to 270°C within 1.5 hours, and the pressure in the reactor is gradually adjusted to a vacuum state, and finally stabilized at a high vacuum state of less than 200 Pa, and the pre-polycondensation reaction is completed.
[0074] Final polycondensation: restore the reactor to normal pressure, quickly add ethylene glycol dispersion containing 6g of titanium nickel yellow, then increase the vacuum degree in the reactor and heat to a higher temperature, stabilize the reaction temperature at 278°C, and control it under a high vacuum degree of less than 200Pa. The final polycondensation reaction lasts for 4 hours to obtain colored recycled polyethylene terephthalate (rPET).
[0075] The obtained polymer had an intrinsic viscosity of 0.69 dL / g, a terminal carboxyl group content of 3.6 mol / t, a diethylene glycol content of 1.32%, a melting point of 251.50° C., and color values L: 48.3, a: 37.6, and b: 17.5.
[0076] Example 3
[0077] Pretreatment: Add 2700g of bis(hydroxyethyl) terephthalate, 0.65g of catalyst antimony ethylene glycol, 0.104g of stabilizer triethyl phosphate, and 15g of zinc oxide dispersed in 50g of ethylene glycol using a planetary mixer and ultrasonic waves into the reactor. Then, replace the air in the reactor with nitrogen three times while maintaining the pressure in the reactor at 2 bar and heating to 240°C.
[0078] Pre-polycondensation: The temperature is raised from 240°C to 270°C within 1.5 hours, and the pressure in the reactor is gradually adjusted to a vacuum state, and finally stabilized at a high vacuum state of less than 200 Pa, and the pre-polycondensation reaction is completed.
[0079] Final polycondensation: The reactor was restored to normal pressure, and an ethylene glycol dispersion containing 6 g of cobalt green was quickly added. The vacuum degree in the reactor was then increased and heated to a higher temperature. The reaction temperature was stabilized at 278°C and controlled at a high vacuum degree of less than 200 Pa. The final polycondensation reaction lasted for 4 hours to obtain colored recycled polyethylene terephthalate (rPET).
[0080] The obtained polymer had an intrinsic viscosity of 0.675 dL / g, a terminal carboxyl group of 3.8 mol / t, a diethylene glycol content of 1.29%, a melting point of 253.00° C., and color values L: 25.6, a: -6.6, and b: -17.9.
[0081] Example 4
[0082] Pre-reaction: 7.20g of Chrome Blue Black R and 5.50g of Disperse Blue 3GR were dissolved in 75g of ethylene glycol, and then 250g of terephthalic acid, 0.27g of catalyst ethylene glycol antimony and ethylene glycol dissolved with the above-mentioned organic dye were added to a 5L reactor. The air in the reactor was then replaced with nitrogen three times, and the pressure in the reactor was maintained at 2 bar. The temperature was raised to 240°C, and then 16g of zinc white dispersed in 50g of ethylene glycol was added to the reactor using a planetary mixer and ultrasonic waves.
[0083] Pretreatment: 2700 g of bis(hydroxyethyl) terephthalate, 0.65 g of catalyst antimony ethylene glycol, and 0.104 g of stabilizer triethyl phosphate were added to the reactor, and the mixture was heated and stirred to melt the bis(hydroxyethyl) terephthalate.
[0084] Pre-polycondensation: The temperature is raised from 240°C to 270°C within 1.5 hours, and the pressure in the reactor is gradually adjusted to a vacuum state, and finally stabilized at a high vacuum state of less than 200 Pa, and the pre-polycondensation reaction is completed.
[0085] Final polycondensation: The reactor was restored to normal pressure, and an ethylene glycol dispersion containing 6 g of titanium chrome brown was quickly added. The vacuum degree in the reactor was then increased and heated to a higher temperature. The reaction temperature was stabilized at 278°C and controlled at a high vacuum degree of less than 200 Pa. The final polycondensation reaction lasted for 4 hours to obtain colored recycled polyethylene terephthalate (rPET).
[0086] The obtained polymer had an intrinsic viscosity of 0.668 dL / g, a terminal carboxyl group of 4.2 mol / t, a diethylene glycol content of 1.35%, a melting point of 252.50° C., and color values L: 16.2, a: 1.6, and b: -3.9.
[0087] It should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each implementation method can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.
[0088] The series of detailed descriptions listed above are only specific descriptions of feasible implementation methods of this application. They are not intended to limit the scope of protection of this application. Any equivalent implementation methods or changes that do not deviate from the technical spirit of this application should be included in the scope of protection of this application.
Claims
1. A method for producing colored polyethylene terephthalate, characterized in that: The steps include: Pretreatment: constructing a reaction system using bis(hydroxyethyl) terephthalate, a first catalyst, and a stabilizer, and heating and stirring until the bis(hydroxyethyl) terephthalate is melted; Pre-polycondensation: After the bis(hydroxyethyl) terephthalate is melted, continue stirring and heat to 240-270°C, and start vacuuming until the pressure of the reaction system is less than 400 Pa; Final polycondensation: The reaction system is restored to normal pressure, the first inorganic dye is added to the reaction system, and then vacuum is applied to reduce the pressure of the reaction system to less than 400 Pa. The reaction is stirred and heated to 270-300° C. for 2-8 hours to terminate the reaction; wherein the first inorganic dye reacts with the terminal hydroxyl groups of the polyethylene terephthalate.
2. The method for producing colored polyethylene terephthalate according to claim 1, characterized in that: The first inorganic dye is a mixed metal oxide inorganic dye.
3. The method for producing colored polyethylene terephthalate according to claim 2, characterized in that: The mass ratio of the first inorganic dye to bis(hydroxyethyl) terephthalate is (0-0.08):
1.
4. The method for producing colored polyethylene terephthalate according to claim 1, wherein: Before the pretreatment step, a prereaction step is also included: terephthalic acid, a second catalyst, and ethylene glycol dissolved with a first organic dye are added to a reaction vessel, heated to 240-260° C. and stirred to obtain bis(hydroxyethyl)terephthalate having a chromophoric group, and the bis(hydroxyethyl)terephthalate having a chromophoric group is added to the reaction system in the pretreatment step; wherein the first organic dye has a group capable of reacting with the terminal hydroxyl group of the bis(hydroxyethyl)terephthalate.
5. The method for producing colored polyethylene terephthalate according to claim 4, characterized in that: The first organic dye has at least one group selected from -COOH, -OH, -NH2, -Cl, -Br, -I, -POCl3, -PCl3, and -SH.
6. The method for producing colored polyethylene terephthalate according to claim 4, characterized in that: The second catalyst is one or more of antimony ethylene glycol, tetrabutyl titanate, p-toluenesulfonic acid, N,N'-dicyclohexylcarbodiimide, cuprous halide, and cuprous iodide.
7. The method for producing colored polyethylene terephthalate according to claim 6, characterized in that: The mass ratio of the first organic dye to terephthalic acid is (0-0.25):1, and the molar ratio of terephthalic acid to the second catalyst is 1:(0.01-0.0001).
8. The method for producing colored polyethylene terephthalate according to claim 1 or 4, characterized in that: A second organic dye and / or a second inorganic dye is also dispersed in the reaction system. The second organic dye and the second inorganic dye are dispersed by ultrasound, wherein the second organic dye and the second inorganic dye do not participate in the chemical reaction.
9. The method for producing colored polyethylene terephthalate according to claim 1, characterized in that: In the pretreatment step, the gas pressure in the reaction system is controlled to be 1 to 5 bar; in the pre-polycondensation step, the reaction time is controlled to be 0.5 to 4 hours.
10. The method for producing colored polyethylene terephthalate according to claim 1, characterized in that: The molar ratio of the first catalyst to bis(hydroxyethyl) terephthalate is (0.01-0.00001):1, and the molar ratio of the stabilizer to bis(hydroxyethyl) terephthalate is also (0.01-0.00001):
1.
11. The method for producing colored polyethylene terephthalate according to claim 10, characterized in that: The first catalyst includes an acidic catalyst, an alkaline catalyst, a metal catalyst, an enzyme catalyst, and an organic peroxide catalyst; the stabilizer includes an antioxidant, a light stabilizer, a heat stabilizer, an antioxidant, and a chelating agent.