Modified polyesters and methods of melt processing polyesters

Abstract

The application relates to the field of polyesters, and discloses a modified polyester and a method for melt processing the polyester. The method comprises: sequentially performing first-stage melt processing and second-stage melt processing on a polyester raw material; wherein the temperature T1 of the first-stage melt processing is greater than Tw, and the temperature T2 of the second-stage melt processing is less than Tk, wherein Tw is the temperature at which the polyester raw material completely melts under standard atmospheric pressure, and Tk is the temperature at which the polyester raw material starts to melt under standard atmospheric pressure. The method can be adapted to traditional polyolefin processing equipment, and is particularly suitable for processing of degradable polyester materials. Degradable polyester products obtained by using the method have better pelletizing performance and anti-processing blocking performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of polyester, in particular to a modified polyester and a method for melt processing polyester. BACKGROUND

[0002] At present, the melt processing process of degradable polyester, especially for film bags, has a greater gap compared with traditional polyethylene plastic. The melt processing method of traditional plastic (especially in the field of shopping bags which have strong market demand at present, the raw material is usually polyethylene) has the characteristics that the temperature of the melting section is usually increased step by step and then stabilized, such as the degradable polyester material described in CN108641318A. However, the processing performance of the prepared degradable polyester material is poor, it is easy to stick and not easy to cut, and other shortcomings, which usually further leads to the continuous production process of degradable bags cannot be sustained, often forced to be interrupted, which is a great impact on production efficiency, and needs to be improved.

[0003] In addition, the traditional polyethylene processing equipment cannot be directly used for processing of degradable polyester, and usually needs to make great changes to the processing equipment and process. The processing difficulty of degradable polyester mainly manifests in two points, one is that the degradable polyester usually presents a "too thin" state in appearance, which is difficult to form, and the other is that the degradable polyester usually presents a "slow solidification" characteristic, which needs a long cooling section after the melt is cooled. In view of the above-mentioned material characteristics of degradable polyester, it is not suitable for the processing method of traditional plastic.

[0004] Therefore, it is urgent to develop a processing method which can adapt to the traditional polyolefin processing equipment, is suitable for processing of degradable polyester material, and can make the degradable polyester product obtained by processing have better pelletizing or processing into film and continuous production performance. SUMMARY

[0005] The purpose of the present application is to overcome the above-mentioned problems existing in the prior art, and provide a modified polyester and a method for melt processing polyester, which can adapt to the traditional polyolefin processing equipment, and is particularly suitable for processing of degradable polyester material. The method can make the degradable polyester product obtained by processing have better pelletizing performance and anti-processing sticking performance.

[0006] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a method for melt processing polyester, which comprises: sequentially performing first-stage melt processing and second-stage melt processing on polyester raw material.

[0007] Wherein, the temperature T1 of the first-stage melt processing is greater than Tw, and the temperature T2 of the second-stage melt processing is less than or equal to Tk, wherein Tw is the temperature at which the polyester raw material completely melts under standard atmospheric pressure, and Tk is the temperature at which the polyester raw material begins to melt under standard atmospheric pressure.

[0008] In a second aspect, the present application provides a modified polyester prepared by the method as described above.

[0009] By the technical solution described above, the present application can achieve the following beneficial effects:

[0010] 1. The method provided by the present application can be adapted to traditional polyolefin processing equipment, so that when the polyester is processed by the method of the present application, no great modification of the traditional equipment and process is needed, thereby reducing the equipment cost.

[0011] 2. The method provided by the present application can overcome the difficulties in the traditional degradable polyester processing process, such as forming difficulty, slow solidification, and long cooling section, and can make the processed degradable polyester product have better pelletizing performance and anti-processing blocking performance. DETAILED DESCRIPTION

[0012] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The endpoints of the ranges and the values are approximate values and should be understood to include values approximately the same as the endpoints. For ranges, the endpoints are included in the ranges, and the ranges are inclusive of the single values therein. For values, the value includes approximately the same value.

[0013] In the present application, the "degradable polyester" refers to a polyester that meets the biodegradable requirements defined in GB / T 35795-2017. The "temperature Tw at which the material completely melts at standard atmospheric pressure" and the "temperature Tk at which the material begins to melt at standard atmospheric pressure" refer to the high-temperature peak bottom and the low-temperature peak bottom of the main melting peak of the material measured on a differential scanning calorimeter (DSC) when the temperature is raised at a rate of 10℃ / min at standard atmospheric pressure. The peak bottom refers to the temperature value at the intersection of the peak median line tangent and the baseline. The anti-processing blocking performance refers to the performance of not easily blocking and being easy to process, including not easily blocking during pelletizing and not easily blocking between films during film blowing or casting film processing. The melting range refers to the temperature range in which the polymer melting process occurs, which is also called the melting range.

[0014] In a first aspect, the present application provides a method for melt processing a polyester, which comprises: sequentially performing first-stage melt processing and second-stage melt processing on a polyester raw material.

[0015] In the present application, the "degradable polyester" refers to a polyester that meets the biodegradable requirements defined in GB / T 35795-2017. The "temperature Tw at which the material completely melts at standard atmospheric pressure" and the "temperature Tk at which the material begins to melt at standard atmospheric pressure" refer to the high-temperature peak bottom and the low-temperature peak bottom of the main melting peak of the material measured on a differential scanning calorimeter (DSC) when the temperature is raised at a rate of 10℃ / min at standard atmospheric pressure. The peak bottom refers to the temperature value at the intersection of the peak median line tangent and the baseline. The anti-processing blocking performance refers to the performance of not easily blocking and being easy to process, including not easily blocking during pelletizing and not easily blocking between films during film blowing or casting film processing. The melting range refers to the temperature range in which the polymer melting process occurs, which is also called the melting range.

[0016] Wherein, the first-stage melt processing and the second-stage melt processing are sequentially performed according to the above method, and an intermediate stage of natural cooling of the material can be further included between the first-stage melt processing and the second-stage melt processing, and the temperature of the intermediate stage can not be specially controlled. It can be understood that the residence time of the material in the intermediate stage will not be too long, and generally the material will not be cooled to the temperature of the second-stage melt processing during the process in the intermediate stage.

[0017] It can be understood that the material obtained after the second-stage melt processing can be subjected to subsequent cooling, pelletizing and other treatments according to the conventional operation in the art. If the material still presents a relatively sticky state after cooling, on the one hand, it is difficult to avoid sticking in the process of pelletizing, and on the other hand, it is also difficult to separate the multiple layers of the film roll in the film production. Therefore, in order to enable the material to obtain good processing performance in the subsequent pelletizing process, including pelletizing performance (to enable the particles to present a good cylindrical shape) and anti-processing sticking performance, it is required that the material after melt processing has good processing performance as described above.

[0018] The inventors of the present application found in the research that, compared with the conventional method of gradually increasing the temperature and then tending to be stable, the method of sequentially performing the first-stage melt processing and the second-stage melt processing as described above is suitable for polyester, especially degradable polyester, and can further ensure that the degradable polyester product obtained by processing has better pelletizing performance and anti-processing sticking performance.

[0019] According to the present application, in order to further ensure that the material after melt processing has better pelletizing performance and anti-processing sticking performance, preferably, T1-Tw=10-100℃ (for example, it can be 10℃, 20℃, 30℃, 35℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, 100℃). It can be understood that when the range as described above is met, the temperature of the first-stage melt processing can be further ensured to be higher than the maximum value of the melting limit, so that the polyester raw material is melted as much as possible to enable smooth flow in the screw to avoid excessively high torque.

[0020] According to the present application, preferably, Tk-T2=0-30℃ (for example, it can be 0℃, 5℃, 10℃, 20℃, 30℃). It can be understood that a cooling facility can be provided at the rear end of the processing equipment to achieve the temperature of T2.

[0021] The inventors of the present application found in the research that when the temperatures of the first-stage melt processing and the second-stage melt processing meet the preferred range as described above, the material can be further prevented from sticking in the subsequent processing process.

[0022] According to the present application, preferably, T1 = 150-260°C (for example, it can be 150°C, 180°C, 200°C, 220°C, 240°C, 260°C).

[0023] According to the present application, preferably, T2 = 35-130°C (for example, it can be 35°C, 50°C, 70°C, 90°C, 100°C, 120°C, 130°C).

[0024] According to the present application, preferably, the time for the first-stage melt processing is 0.5-5 min (for example, it can be 0.5 min, 0.6 min, 1 min, 2 min, 3 min, 4 min, 5 min).

[0025] According to the present application, preferably, the time for the second-stage melt processing is 0.5-5 min (for example, it can be 0.5 min, 0.6 min, 1 min, 2 min, 3 min, 4 min, 5 min).

[0026] When the first-stage melt processing and the second-stage melt processing satisfy the time as described above, the material can be further prevented from sticking in the subsequent processing.

[0027] According to the present application, the method is particularly suitable for a polyester raw material (particularly a degradable polyester raw material) having a specific melting point or melting range, and preferably, the polyester raw material is selected from at least one of the following polyester raw materials a)-d):

[0028] a) a copolyester, and the monomers of the copolyester comprise acid A, acid B and alcohol C, the total weight content of the structural units from the acid A, acid B, alcohol C is more than 80% (for example, it can be 81%, 82%, 83%, 84%, 85%, 86%) of the total weight of the copolyester, wherein acid A is a C8-C10 (for example, it can be C8, C9, C10) aromatic dicarboxylic acid; acid B is succinic acid or adipic acid; alcohol C is selected from at least one of C3-C6 (for example, it can be C3, C4, C5, C6) aliphatic diols.

[0029] In which, alcohol C can be a mixture of several C3-C6 aliphatic diols.

[0030] b) a polyester composition comprising the copolyester shown in a), and the total weight of the copolyester shown in a) is more than 80% (for example, it can be 81%, 82%, 83%, 84%, 85%, 86%) of the total weight of the polyester composition.

[0031] c) a polyester composition comprising the copolyester of a) and an α-hydroxypropionic acid homopolymer or copolymer, and the total weight of the copolyester of a) and the α-hydroxypropionic acid homopolymer or copolymer is more than 50% of the total weight of the polyester composition (for example, the polyester composition can be a composition obtained by combining the copolyester of a), the α-hydroxypropionic acid homopolymer and starch, wherein the total weight of the copolyester of a) and the α-hydroxypropionic acid homopolymer is more than 50% of the total weight of the polyester composition).

[0032] The weight average molecular weight of the α-hydroxypropionic acid homopolymer or copolymer can be 50,000-200,000 g / mol.

[0033] It can be understood that the α-hydroxypropionic acid is lactic acid, and the α-hydroxypropionic acid homopolymer is polylactic acid. The α-hydroxypropionic acid copolymer is a product copolymerized from lactic acid and other monomers (such as glycolic acid, or ω-hydroxyhexanoic acid).

[0034] d) a polyester composition comprising the copolyester of a) and an α-hydroxyacetic acid homopolymer or copolymer, and the total weight of the copolyester of a) and the α-hydroxyacetic acid homopolymer or copolymer is more than 50% of the total weight of the polyester composition (for example, the polyester composition can be a composition obtained by combining the copolyester of a), the α-hydroxyacetic acid homopolymer and starch, wherein the total weight of the copolyester of a) and the α-hydroxyacetic acid homopolymer is more than 50% of the total weight of the polyester composition).

[0035] The weight average molecular weight of the α-hydroxyacetic acid homopolymer or copolymer can be 50,000-200,000 g / mol.

[0036] It can be understood that the α-hydroxyacetic acid is glycolic acid, and the α-hydroxyacetic acid homopolymer is polyglycolic acid. The α-hydroxyacetic acid copolymer is a product copolymerized from polyglycolic acid and other monomers (such as lactic acid).

[0037] In the copolyester of a), preferably, the ratio between the total molar content of the structural units from the acid A and the acid B and the molar content of the structural units from the acid A is 100:25-65, more preferably 100:30-55.

[0038] In the copolyester of a), preferably, the ratio between the total molar content of the structural units from the acid A and the acid B and the molar content of the structural units from the alcohol C is 90-110:100, more preferably 95-105:100.

[0039] In the copolyester of a), preferably, the acid A is terephthalic acid.

[0040] a) In the copolyester shown, preferably, the alcohol C is selected from at least one of 1,2-propanediol, 1,4-butanediol and 1,4-cyclohexanedimethanol. The alcohol C can be a mixture of two or three of 1,2-propanediol, 1,4-butanediol and 1,4-cyclohexanedimethanol.

[0041] According to the present application, preferably, the weight average molecular weight of the copolyester shown in a) is 10000-200000 g / mol.

[0042] According to the present application, preferably, the copolyester shown in a) is a butylene terephthalate-succinate butylene copolymer or a butylene terephthalate-adipate butylene copolymer.

[0043] It can be understood that the preparation method of the copolyester shown in a) as described above can comprise:

[0044] (1) Under vacuum conditions, at least one of the acid A, the ester corresponding to the acid A or the acid anhydride corresponding to the acid A, and at least one of the acid B, the ester corresponding to the acid B or the acid anhydride corresponding to the acid B, and the alcohol C, are contacted with a first catalyst to carry out a prepolymerization reaction to obtain a prepolymer.

[0045] The conditions of the prepolymerization reaction can include: the reaction temperature is 190-250°C; the vacuum degree is 200-600 Pa. The reaction time is not particularly limited, so that the small molecules in the reaction container are almost dried, and the distillation temperature remains unchanged. Generally, it can be completed in 1-3 hours.

[0046] (2) The prepolymer is contacted with a second catalyst to carry out a polycondensation reaction to obtain the copolyester.

[0047] The conditions of the polycondensation reaction include: the reaction temperature is 200-300°C, the vacuum degree is <300 Pa, and the reaction time is 3-12 hours.

[0048] The specific composition and amount of the first catalyst and the second catalyst are not particularly limited, can be a conventional selection in the art, and the first catalyst and the second catalyst can be the same or different. For example, the first catalyst and the second catalyst can each independently be an antimony catalyst and a titanium catalyst, such as antimony trioxide and / or tetrabutyl titanate. The molar ratio of the first catalyst to alcohol C can be 1:2000-20000, and the molar ratio of the second catalyst to alcohol C can be 1:5000-50000.

[0049] The container for the prepolymerization and polycondensation reactions is not particularly limited and can be a reaction vessel. The prepolymerization and polycondensation reactions can be performed in the same reaction vessel or in different reaction vessels. For example, the prepolymer can be removed from the container for the prepolymerization reaction and then introduced into the reaction vessel for the polycondensation reaction to perform the polycondensation reaction.

[0050] According to the present application, preferably, the polyester raw material further comprises at least one of nucleating agent, plasticizer, slip agent, reinforcing agent, ultraviolet light resistant agent and crosslinking agent. The specific components and amounts of the nucleating agent, plasticizer, slip agent, reinforcing agent, ultraviolet light resistant agent and crosslinking agent are not particularly limited and can be selected according to the conventional practice in the art, which will not be described herein.

[0051] According to the present application, the equipment for melt processing is not particularly limited and can be selected according to the conventional practice in the art, but preferably, the first-stage melt processing and the second-stage melt processing are performed in a single-screw extruder, a twin-screw extruder or a casting machine. The inventors of the present application have found in the research that when the first-stage melt processing and the second-stage melt processing are performed in the equipment as described above, the material can be further prevented from sticking in the subsequent processing.

[0052] According to a preferred embodiment of the present application, the method comprises: extruding the polyester raw material through a single-screw extruder or a twin-screw extruder, the screw comprising six operation sections in sequence, namely a mixing section (1st operation section), a first-stage melt processing section (2nd-3rd operation sections), an intermediate section (4th operation section) and a second-stage melt processing section (5th-6th operation sections), wherein the temperature in the first-stage melt processing section is T1, the temperature in the second-stage melt processing section is T2, the material is naturally cooled in the intermediate section, the screw rotation speed is 30-80 r / min, the time for the first-stage melt processing is 0.5-5 min, and the time for the second-stage melt processing is 0.5-5 min; after the melt is discharged through the extrusion outlet, the melt travels a distance of 1-4 meters in the air at room temperature and then enters a pelletizer to be pelletized.

[0053] According to another preferred embodiment of the present application, the method comprises: extruding the polyester raw material through a casting machine, the casting machine comprising six operation sections in sequence, namely a mixing section (1st operation section), a first-stage melt processing section (2nd-3rd operation sections), an intermediate section (4th operation section) and a second-stage melt processing section (5th-6th operation sections), wherein the temperature in the first-stage melt processing section is T1, the temperature in the second-stage melt processing section is T2, the material is naturally cooled in the intermediate section, the time for the first-stage melt processing is 0.5-5 min, and the time for the second-stage melt processing is 0.5-5 min; after the melt is discharged through the casting extrusion outlet, the melt travels a distance of 1-4 meters in the air at room temperature and then the thickness of the film is controlled to be wound up.

[0054] In a second aspect, the present application provides a modified polyester prepared by the method as described above.

[0055] According to the present application, preferably, the separation force of the modified polyester is less than 1.8 N. It can be understood that, for the particles prepared by extrusion and pelletization, the separation force refers to the force value required to break the two particles still connected after pelletization, and for the film prepared by extrusion, the separation force refers to the force value required to separate two films with adjacent layers having a width of 1.5 cm. The inventors of the present application have further found in the research that, by using the method as described above to process the polyester, the particles prepared after pelletization or the film prepared after extrusion has a separation force less than 1.8 N, and has good pelletization performance and anti-processing blocking performance.

[0056] The present application will be described in detail below by way of examples. In the following examples,

[0057] Polylactic acid, purchased from Haizheng Biology, with a trade name of REVODE201;

[0058] Polyglycolic acid, purchased from Japan Wuhe, with a trade name of Kuredux;

[0059] Starch, purchased from Wuhan Hualai, with a trade name of HL102;

[0060] 1,4-cyclohexane dimethanol, purchased from Merck Chemistry;

[0061] The mechanical property test was completed on an Instron 5965 universal testing machine;

[0062] The extruder was HAAKE PolyLab OS, equipped with a Rheomex CTW100 OS double screw unit with a diameter of 20 mm, which was a conical counter-rotating double screw unit; and a Rheomex 252 OS single screw unit with a diameter of 19.05 mm; which could be used as a double screw extruder and a single screw extruder;

[0063] The casting machine was a multi-layer extrusion casting machine of LCR400 type from Labtech Company in Sweden, and a water-cooled jacket was additionally installed at the end of the flow channel;

[0064] Other reagents or instruments without specified manufacturers were all conventional products purchased on the market;

[0065] In a twin-screw extruder, a single-screw extruder, and a casting machine, melt processing can include a mixing section (relatively low temperature), a melting section, and an extruding section. When a twin-screw extruder, a single-screw extruder, and a casting machine are used, the first section of melt processing corresponds to the melting section; the second section of melt processing corresponds to the extruding section. Six sections of operation are included in the screw, in order, a mixing section (1st section of operation), a first section of melt processing section (2nd-3rd sections of operation), an intermediate section (4th section of operation, temperature is not controlled), and a second section of melt processing section (5th-6th sections of operation).

[0066] The preparation method of each copolyester is as follows:

[0067] (1) Under vacuum, acid A, acid B, and alcohol C are contacted with a first catalyst, antimony trioxide, to perform a prepolymerization reaction to obtain a prepolymer; the molar ratio of the first catalyst, antimony trioxide, and alcohol C is 1:5000;

[0068] The prepolymerization reaction conditions are as follows: the reaction temperature is 210°C; the vacuum degree is 400 Pa. The reaction is continued until the small molecules in the container are almost exhausted, and the distillation temperature is kept unchanged.

[0069] (2) The prepolymer is contacted with a second catalyst, tetrabutyl titanate, to perform a polycondensation reaction to obtain the copolyester; the molar ratio of the second catalyst, tetrabutyl titanate, and alcohol C is 1:10000;

[0070] The polycondensation reaction conditions include: the reaction temperature is 250°C, the vacuum degree is 250 Pa, and the reaction time is 7 hours.

[0071] In the following examples and comparative examples:

[0072] X1 is prepared from 0.578 mol of terephthalic acid, 0.472 mol of succinic acid, and 1 mol of 1,4-butanediol according to the above method. The weight average molecular weight of X1 is 50000 g / mol. The Tw of X1 is measured to be 157°C, and the Tk is 117°C.

[0073] X2 is prepared from 0.4 mol of terephthalic acid, 0.6 mol of succinic acid, and 1 mol of 1,4-butanediol according to the above method. The weight average molecular weight of X2 is 50000 g / mol. The Tw of X2 is measured to be 136°C, and the Tk is 91°C.

[0074] X3 is prepared from 0.285 mol of terephthalic acid, 0.665 mol of succinic acid, and 1 mol of 1,4-butanediol according to the above method. The weight average molecular weight of X3 is 40000 g / mol. The Tw of X3 is measured to be 96°C, and the Tk is 51°C.

[0075] X4 was obtained by mixing 80 wt% of X1 and 20 wt% of starch, based on the total weight of X4. The Tw and Tk of X4 were measured to be approximately the same as those of X1.

[0076] X5 was obtained by mixing 40 wt% of X1, 20 wt% of polylactic acid (weight average molecular weight of 150000 g / mol), and 40 wt% of starch, based on the total weight of X5. The Tw and Tk of X5 were measured to be approximately the same as those of X1, and at the same time, there was a secondary second melting peak at a higher temperature range.

[0077] X6 was obtained by mixing 80 wt% of X1 and 20 wt% of polylactic acid (weight average molecular weight of 120000 g / mol), based on the total weight of X6. The Tw and Tk of X6 were measured to be approximately the same as those of X1, and at the same time, there was a secondary second melting peak at a higher temperature range.

[0078] X7 was obtained by mixing 30 wt% of X1, 20 wt% of X2, 20 wt% of polyglycolic acid (weight average molecular weight of 60000 g / mol), and 30 wt% of starch, based on the total weight of X7. The Tw of X7 was measured to be 152°C, the Tk was 97°C, and at the same time, there was a secondary second melting peak at a higher temperature range.

[0079] X8 was obtained by mixing 40 wt% of X1, 30 wt% of X2, and 30 wt% of polyglycolic acid (weight average molecular weight of 80000 g / mol), based on the total weight of X8. The Tw of X8 was measured to be 150°C, the Tk was 95°C, and at the same time, there was a secondary second melting peak at a higher temperature range.

[0080] X9 was obtained by using 0.578 mol of terephthalic acid, 0.472 mol of succinic acid, 0.9 mol of 1,4-butanediol, and 0.1 mol of 1,4-cyclohexanedimethanol, according to the above preparation method. The weight average molecular weight of X9 was 40000 g / mol. The Tw of X9 was measured to be 131 °C, and the Tk was 85°C.

[0081] X10 was obtained by using 0.225 mol of terephthalic acid, 0.675 mol of succinic acid, and 1 mol of 1,4-butanediol, according to the above preparation method. The weight average molecular weight of X10 was 50000 g / mol. The Tw of X10 was measured to be 91 °C, and the Tk was 61 °C.

[0082] X11 was obtained by using 0.715 mol of terephthalic acid, 0.385 mol of succinic acid, and 1 mol of 1,4-butanediol, according to the above preparation method. The weight average molecular weight of X11 was 50000 g / mol. The Tw of X10 was measured to be 177°C, and the Tk was 142°C.

[0083] The Tw and Tk were measured by a differential scanning calorimeter (DSC).

[0084] In the following examples and comparative examples:

[0085] For the particles extruded by twin-screw extruder, the separation force refers to the force value needed to pull apart the particles that are still connected after being cut. The method for calculating the separation force is to randomly test 5 groups and take the average value. If the cutting condition is very good and there are no particles connected to each other, the separation force is recorded as 0.

[0086] For the film extruded by the casting machine, the separation force refers to the force value needed to pull apart two films with a width of 1.5 cm on adjacent layers to a separated state. The method for calculating the separation force is to randomly test 5 groups and take the average value. If all the films can be naturally separated under their own weight, the force value is recorded as 0.

[0087] Example 1

[0088] X1 was extruded by a twin-screw extruder, and the temperature of each section of the screw was set as follows: the temperature of the mixing section (the first operating section) was 120°C, the temperature of the first melt processing section (the second and third operating sections) was 167°C, and the temperature of the second melt processing section (the fifth and sixth operating sections) was 87°C. The screw rotation speed was 80 r / min, the first melt processing time was about 0.6 min, and the second melt processing time was about 0.6 min. After the melt was discharged from the twin-screw extruder outlet, it was cut into particles by a cutting machine after traveling a distance of about 2 meters in the air at room temperature. The cutting condition, particle shape after cutting, and separation force were recorded. The results are shown in Table 1.

[0089] Example 2

[0090] X2 was extruded by a single-screw extruder, and the temperature of each section of the screw was set as follows: the temperature of the mixing section (the first operating section) was 120°C, the temperature of the first melt processing section (the second and third operating sections) was 160°C, and the temperature of the second melt processing section (the fifth and sixth operating sections) was 80°C. The screw rotation speed was 50 r / min, the first melt processing time was about 1 min, and the second melt processing time was about 1 min. After the melt was discharged from the single-screw extruder outlet, it was cut into particles by a cutting machine after traveling a distance of about 2 meters in the air at room temperature. The cutting condition, particle shape after cutting, and separation force were recorded. The results are shown in Table 1.

[0091] Example 3

[0092] X3 was extruded through a cast film machine with the temperature settings of 120°C for the mixing section (1st operation section), 196°C for the first melt processing section (2nd-3rd operation sections), and 51°C for the second melt processing section (5th-6th operation sections). The melt was discharged from the cast film extruder and traveled about 2 meters in air at room temperature before being wound up at a thickness of about 50 microns. The roll of film was recorded and the release force was measured. The results are shown in Table 1.

[0093] Example 4

[0094] X4 was extruded through a twin-screw extruder with the temperature settings of 120°C for the mixing section (1st operation section), 190°C for the first melt processing section (2nd-3rd operation sections), and 110°C for the second melt processing section (5th-6th operation sections). The screw speed was 80 r / min, the first melt processing section was about 0.6 min, and the second melt processing section was about 0.6 min. The melt was discharged from the twin-screw extruder and traveled about 2 meters in air at room temperature before being cut into pellets in a pelletizer. The pelletization state, pellet shape, and release force were recorded. The results are shown in Table 1.

[0095] Example 5

[0096] X5 was extruded through a twin-screw extruder with the temperature settings of 120°C for the mixing section (1st operation section), 220°C for the first melt processing section (2nd-3rd operation sections), and 115°C for the second melt processing section (5th-6th operation sections). The screw speed was 30 r / min, the first melt processing section was about 1.2 min, and the second melt processing section was about 1.2 min. The melt was discharged from the twin-screw extruder and traveled about 2 meters in air at room temperature before being cut into pellets in a pelletizer. The pelletization state, pellet shape, and release force were recorded. The results are shown in Table 1.

[0097] Example 6

[0098] X6 was extruded through a cast film machine with the temperature settings of 120°C for the mixing section (1st operation section), 220°C for the first melt processing section (2nd-3rd operation sections), and 115°C for the second melt processing section (5th-6th operation sections). The melt was discharged from the cast film extruder and traveled about 2 meters in air at room temperature before being wound up at a thickness of about 50 microns. The roll of film was recorded and the release force was measured. The results are shown in Table 1.

[0099] Example 7

[0100] X7 was extruded through a twin-screw extruder, with the temperature of each section of the screw set as follows: the temperature of the mixing section (1st operation section) was 150°C, the temperature of the first melt processing section (2nd-3rd operation sections) was 250°C, and the temperature of the second melt processing section (5th-6th operation sections) was 95°C. The screw rotation speed was 80 r / min, the time of the first melt processing section was about 0.6 min, and the time of the second melt processing section was about 0.6 min. After the melt was discharged from the twin-screw extruder, it was conveyed in the air at room temperature for a distance of about 2 meters, and then was cut into particles in a pelletizer. The pelletizing state, the particle shape after pelletizing, and the separation force were recorded. The results are shown in Table 1.

[0101] Example 8

[0102] X8 was extruded through a twin-screw extruder, with the temperature of each section of the screw set as follows: the temperature of the mixing section (1st operation section) was 150°C, the temperature of the first melt processing section (2nd-3rd operation sections) was 250°C, and the temperature of the second melt processing section (5th-6th operation sections) was 95°C. The screw rotation speed was 80 r / min, the time of the first melt processing section was about 0.6 min, and the time of the second melt processing section was about 0.6 min. After the melt was discharged from the twin-screw extruder, it was conveyed in the air at room temperature for a distance of about 2 meters, and then was cut into particles in a pelletizer. The pelletizing state, the particle shape after pelletizing, and the separation force were recorded. The results are shown in Table 1.

[0103] Example 9

[0104] X9 was extruded through a casting machine, with the temperature of each section set as follows: the temperature of the mixing section (1st operation section) was 110°C, the temperature of the first melt processing section (2nd-3rd operation sections) was 150°C, and the temperature of the second melt processing section (5th-6th operation sections) was 80°C. The time of the first melt processing section was about 3 min, and the time of the second melt processing section was about 3 min. After the melt was discharged from the casting extruder, it was conveyed in the air at room temperature for a distance of about 2 meters, and then was wound into a roll with a thickness of about 50 microns. The roll condition and the separation force were recorded. The results are shown in Table 1.

[0105] Example 10

[0106] X10 was extruded through a twin-screw extruder, with the temperature of each section of the screw set as follows: the temperature of the mixing section (1st operation section) was 110°C, the temperature of the first melt processing section (2nd-3rd operation sections) was 150°C, and the temperature of the second melt processing section (5th-6th operation sections) was 60°C. The time of the first melt processing section was about 0.6 min, and the time of the second melt processing section was about 0.6 min. The screw rotation speed was 80 r / min. After the melt was discharged from the twin-screw extruder, it was conveyed in the air at room temperature for a distance of about 2 meters, and then was cut into particles in a pelletizer. The pelletizing state, the particle shape after pelletizing, and the separation force were recorded. The results are shown in Table 1.

[0107] Example 11

[0108] X11 was extruded through a twin-screw extruder, with the temperature of each section of the screw set as follows: the temperature of the mixing section (1st operation section) was 150°C, the temperature of the first melt processing section (2nd-3rd operation sections) was 210°C, and the temperature of the second melt processing section (5th-6th operation sections) was 140°C. The screw rotation speed was 80 r / min, the time of the first melt processing was about 0.6 min, and the time of the second melt processing was about 0.6 min. After the melt was discharged from the twin-screw extruder, it was sent to a pelletizer after traveling about 2 meters in the air at room temperature. The pelletizing state, the pellet shape after pelletizing, and the separation force were recorded. The results are shown in Table 1.

[0109] Example 12

[0110] X1 was extruded through a twin-screw extruder, with the temperature of each section of the screw set as follows: the temperature of the mixing section (1st operation section) was 120°C, the temperature of the first melt processing section (2nd-3rd operation sections) was 160°C, and the temperature of the second melt processing section (5th-6th operation sections) was 85°C. The screw rotation speed was 80 r / min, the time of the first melt processing was about 0.6 min, and the time of the second melt processing was about 0.6 min. After the melt was discharged from the twin-screw extruder, it was sent to a pelletizer after traveling about 2 meters in the air at room temperature. The pelletizing state, the pellet shape after pelletizing, and the separation force were recorded. The results are shown in Table 1.

[0111] Comparative Example 1

[0112] X1 was extruded through a twin-screw extruder, with the temperature of each section of the screw set as follows: the temperature of the mixing section (1st operation section) was 120°C, the temperature of the first melt processing section (2nd-3rd operation sections) was 180°C, and the temperature of the second melt processing section (5th-6th operation sections) was 180°C. The screw rotation speed was 80 r / min, the time of the first melt processing was about 0.6 min, and the time of the second melt processing was about 0.6 min. After the melt was discharged from the twin-screw extruder, it was sent to a pelletizer after traveling about 2 meters in the air at room temperature. The pelletizing state, the pellet shape after pelletizing, and the separation force were recorded. The results are shown in Table 1.

[0113] Comparative Example 2

[0114] X1 was extruded through a twin-screw extruder, with the temperature of each section of the screw set as follows: the temperature of the mixing section (1st operation section) was 120°C, the temperature of the first melt processing section (2nd-3rd operation sections) was 150°C, and the temperature of the second melt processing section (5th-6th operation sections) was 110°C. The time of the first melt processing was about 3 min, and the time of the second melt processing was about 3 min. After the melt was discharged from the twin-screw extruder, it was sent to a pelletizer after traveling about 2 meters in the air at room temperature. The film roll was controlled to have a thickness of about 50 microns, and was wound up. The film roll and the separation force were recorded. The results are shown in Table 1.

[0115] Table 1

[0116]

[0117]

[0118] From the results of Table 1, it can be seen that, in the pelletizing process or the cast film processing, the examples 1-12 of the present application are not prone to sticking, have small separation force, and can make the particles present good cylindrical shape in the pelletizing process, which is beneficial to continuous production. Among them, examples 1-9 have better effects. The comparative examples 1-2 have poor processing performance in the pelletizing process or the cast film processing.

[0119] In addition, in the process of processing the modified polyester, nucleating agents, plasticizers, slip agents, reinforcing agents, ultraviolet resistance agents and crosslinking agents and other processing aids can also be added according to the needs of the product. When the polyester is processed by the method of the present application, the traditional equipment and process do not need to be greatly changed, and the equipment cost can be reduced.

[0120] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as disclosed by the present application, and all belong to the protection scope of the present application.

Claims

1. A method for melt processing polyester, characterized in that, The method includes: sequentially subjecting polyester raw materials to a first-stage melt processing and a second-stage melt processing; Wherein, the temperature of the first stage of melting processing T1 > Tw, and the temperature of the second stage of melting processing T2 ≤ Tk, where Tw is the temperature at which the polyester raw material completely melts under standard atmospheric pressure, and Tk is the temperature at which the polyester raw material begins to melt under standard atmospheric pressure; T1=150-260℃, T2=35-130℃; And / or, the first stage of melting processing takes 0.5-5 minutes; And / or, the second stage of melting processing takes 0.5-5 minutes; The polyester raw material is selected from at least one of the following polyester raw materials: a) A copolyester, wherein the monomers of the copolyester comprise acid A, acid B and alcohol C, and the total weight of the structural units derived from acid A, acid B and alcohol C accounts for more than 80% of the total weight of the copolyester, wherein acid A is at least one of C8-C10 aromatic dicarboxylic acids; acid B is succinic acid or adipic acid; and alcohol C is selected from at least one of C3-C6 aliphatic diols. b) A polyester composition comprising the copolyester shown in a), wherein the total weight of the copolyester shown in a) accounts for more than 80% of the total weight of the polyester composition; c) A polyester composition comprising the copolyester shown in a) and an α-hydroxypropionic acid homopolymer or copolymer, wherein the total weight of the copolyester shown in a) and the α-hydroxypropionic acid homopolymer or copolymer accounts for more than 50% of the total weight of the polyester composition. d) A polyester composition comprising the copolyester shown in a) and an α-hydroxyacetic acid homopolymer or copolymer, wherein the total weight of the copolyester shown in a) and the α-hydroxyacetic acid homopolymer or copolymer accounts for more than 50% of the total weight of the polyester composition.

2. The method according to claim 1, wherein, T1-Tw=10-100℃; And / or, Tk-T2=0-30℃.

3. The method according to claim 1, wherein, The ratio between the total molar content of structural units from acid A and acid B and the molar content of structural units from acid A is 100:25-65; And / or, the ratio between the total molar content of structural units from acids A and B and the molar content of structural units from alcohol C is 90-110:

100.

4. The method according to claim 3, wherein, The ratio between the total molar content of structural units from acid A and acid B and the molar content of structural units from acid A is 100:30-55; And / or, the ratio between the total molar content of structural units from acids A and B and the molar content of structural units from alcohol C is 95-105:

100.

5. The method according to any one of claims 1-4, wherein, Acid A is terephthalic acid; And / or, alcohol C is selected from at least one of 1,2-propanediol, 1,4-butanediol and 1,4-cyclohexanediethanol.

6. The method according to claim 3 or 4, wherein, a) The weight-average molecular weight of the copolyester shown is 10,000-200,000 g / mol; And / or, the copolyester shown in a) is a butylene terephthalate-butylene succinate copolymer or a butylene terephthalate-butylene adipate copolymer.

7. The method according to claim 1, wherein, The polyester raw material also includes at least one of the following: nucleating agent, plasticizer, slip agent, reinforcing agent, UV stabilizer, and crosslinking agent.

8. The method according to claim 1 or 2, wherein, The first and second stages of melt processing are carried out in a single-screw extruder, a twin-screw extruder, or a casting machine.

9. The modified polyester obtained by the method according to any one of claims 1-8.

10. The modified polyester according to claim 9, wherein, The modified polyester has a separation force of less than 1.8 N.

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