A method for preparing recycled copolyester and heat shrinkable film thereof

Abstract

The present invention discloses a method for preparing a recycled copolyester and a heat-shrinkable film thereof, belonging to the field of waste polyester recycling. The method utilizes technologies such as glycolysis and methanol transesterification of waste polyester to produce recycled dimethyl terephthalate, which is then transesterified with other modifying monomers and ethylene glycol, followed by polycondensation, to produce the recycled copolyester. Finally, the recycled copolyester is directly delivered to the extrusion dies via a melt delivery pipeline and a metering pump to produce the recycled polyester heat-shrinkable film. The recycled polyester heat-shrinkable film exhibits high shrinkage, excellent toughness, and transparency, while also achieving high-value recycling of waste polyester.

Description

Technical Field

[0001] The present invention relates to the field of recycling of waste polyester, more specifically, it relates to a recycled copolyester and a method for preparing a heat shrinkable film of the recycled copolyester. Background Art

[0002] Polyvinyl chloride (PVC) film is often used as shrink sleeve labels on polyethylene terephthalate (PET) beverage and mineral water bottles. Therefore, the sleeves must be removed during the PET bottle recycling process, which increases the pre-processing process and costs of the recycled bottle flakes. Furthermore, if not completely removed, it can affect the purity and quality of the recycled PET flakes. Therefore, ensuring that the label's material, technology, and design are consistent with the PET bottle itself is a crucial issue for achieving efficient and high-quality PET bottle recycling.

[0003] When used as outer labels for PET bottles, polyester heat shrink film can be recycled and regenerated along with the bottle itself. This eliminates the need to peel the label from the PET bottle, which is required with PVC heat shrink film labels, and also reduces the subsequent processing pressure of discarded PVC heat shrink film. Consequently, PVC heat shrink film has been banned in countries and regions such as Japan, Western Europe, and North America. With the growing trend of environmental protection both domestically and internationally, polyester heat shrink film, as an environmentally friendly packaging material, will gradually replace the commonly used PVC heat shrink film.

[0004] However, conventional polyester shrinkage films have a low shrinkage rate, not exceeding 30%, which cannot meet the requirements of practical applications. Therefore, they must be modified. Monomers that can be used for modification include isophthalic acid (IPA), 1,4-cyclohexanedimethanol (CHDM), and neopentyl glycol (NPG). Because IPA contains a rigid benzene ring in its molecular structure, polyester heat shrinkage films modified with it have poor toughness. While polyester films modified with CHDM have a high heat shrinkage rate, their monomer price is high, making the cost of copolyesters high. Neopentyl glycol (NPG) is a typical neopentyl diol with good chemical reactivity and a relatively low monomer price. However, polyester films modified with NPG have a low heat shrinkage rate, and these modified polyesters are currently all virgin polyesters. Therefore, how to comprehensively consider cost and performance to develop recycled copolyester heat shrinkage films with excellent properties such as high shrinkage, high toughness, and high transparency is the only way to achieve high-value recycling of waste polyester.

[0005] Therefore, a new solution needs to be proposed to solve this problem. Summary of the Invention

[0006] The object of the present invention is to solve the above problems and provide a recycled copolyester.

[0007] The above technical objectives of the present invention are achieved through the following technical solutions:

[0008] The present invention utilizes technologies such as glycolysis and methanol transesterification of waste polyester to produce recycled dimethyl terephthalate, which is then transesterified with other modifying monomers and ethylene glycol, followed by polycondensation, to produce recycled copolyester. Finally, the recycled copolyester is delivered directly to the extrusion dies via a melt delivery pipe and metering pump to produce recycled polyester heat-shrinkable film. This recycled polyester heat-shrinkable film exhibits high shrinkage, excellent toughness, and transparency, while also achieving high-value recycling of waste polyester.

[0009] The detailed preparation process of the recycled copolyester heat shrinkable film:

[0010] 1. Pretreatment of waste polyester: crush the waste polyester blocks and send them to the silo; cut the waste polyester textiles, friction-granulate them and send them to the silo; sort, clean, remove impurities, crush the waste polyester bottle flakes and send them to the silo; then mix them in a certain proportion and supply them to the next process.

[0011] 2. Alcoholysis of waste polyester: Add waste polyester to ethylene glycol in a mass ratio of 1:2-3 into an alcoholysis reactor, and add a certain amount of alcoholysis catalyst. Control the reaction temperature at 190-210°C and the reaction time for 2-4 hours to obtain an alcoholysis product whose main component is BHET. After filtering, it is transferred to the transesterification reactor.

[0012] 3. Preparation of Crude DMT: Add methanol at a molar ratio of BHET to methanol of 1:2-3 and a suitable amount of transesterification catalyst. Control the transesterification reaction temperature at 60-70°C for 3-4 hours to obtain crude DMT.

[0013] 4. Purification of DMT: The transesterification product is filtered, centrifuged, distilled and then sent to the transesterification kettle.

[0014] 5. Transesterification: Add 10% to 20% (molar percentage of DMT) of NPG and CHDM, along with an excess of ethylene glycol (EG), to a total alcohol:DMT molar ratio of 2 to 3:1. Add a suitable amount of transesterification catalyst. The transesterification temperature is controlled at 190-210°C for 2 to 4 hours. The resulting transesterification solution is then fed into a pre-polycondensation reactor.

[0015] 6. Polycondensation and Chip Preparation: The esterified product is sequentially fed into Polycondensation-I and Polycondensation-II, with a certain amount of catalyst, antioxidant, and stabilizer added. The reaction temperature is controlled at 220-260°C, the absolute pressure is 1-100 kPa, and the intrinsic viscosity of the prepolymer is 0.2-0.4 dl / g. The product then enters a vertical final polycondensation reactor, where the reaction temperature is controlled at 260-270°C, the absolute pressure is 0.1-1 kPa, and the reaction time is 1-2 hours to produce the recycled copolyester. The recycled copolyester can be processed into recycled copolyester pellets for future use, or it can be delivered to a film-forming device via a melt pump and melt pipeline.

[0016] 7. Preparation of heat shrinkable film: The melt from the polymerization process is directly transported through a melt distribution pipe and then fed to the die by a melt metering pump to extrude a thick sheet. The sheet is then biaxially stretched, shaped, trimmed, and wound to produce the recycled copolyester heat shrinkable film. The die temperature during the film-forming process is 250-255°C, the longitudinal stretching temperature is 110-160°C, the stretch ratio is 2.5-3.5, and the transverse stretching temperature is 110°C, the stretch ratio is 3.0-4.5 times. The resulting shrinkage film has an initial shrinkage temperature of 80-100°C and a shrinkage ratio of 60%-80%.

[0017] The comonomers are: neopentyl glycol, 1,4-cyclohexanedimethanol;

[0018] Alcoholysis catalyst: potassium carbonate, sodium hydroxide and acetate, etc., preferably zinc acetate;

[0019] Transesterification catalyst: acetic acid catalyst, preferably calcium acetate;

[0020] The stabilizer is: triphenyl phosphate, phosphorous acid, trimethyl phosphate, etc., preferably triphenyl phosphate;

[0021] The antioxidant is: a hindered phenol antioxidant, preferably antioxidant 1010;

[0022] The polycondensation catalyst is: an antimony catalyst and a titanium catalyst, preferably ethylene glycol antimony;

[0023] The present invention has the following characteristics:

[0024] 1) Due to the uncertainty of waste polyester raw materials, the alcoholysis product contains many impurities, and the purification of BHET monomer after ethylene glycol alcoholysis is difficult. By converting it into DMT, which is easier to purify, the quality of the recycled product is improved;

[0025] 2) By adding CHDM and NPG as comonomers, the toughness of the copolyester is enhanced, the shrinkage of the polyester film is improved, and the cost is also more competitive;

[0026] 3) The pre-polycondensation intrinsic viscosity is controlled to be relatively low, and a high-efficiency vertical liquid phase viscosity increasing reactor is used as the final polycondensation reactor to reduce the residence time and reaction temperature of the melt in the final polycondensation reactor. This overcomes the shortcomings of the general horizontal final polycondensation reactor, such as long reaction time, high reaction temperature, and melt retention. The product has a better hue and stable quality indicators of the recycled polyester.

[0027] 4) The method of directly sending the melt to the die head for extrusion into film can greatly shorten the production process, reduce operating costs and improve product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1Schematic diagram of the structure of the circulation pipeline of the pre-polycondensation kettle and the final polycondensation kettle in the present invention;

[0029] Figure 2 It is a structural schematic diagram of the booster pump device of the present invention;

[0030] Figure 3 This is a schematic structural diagram of a one-way valve of the present invention;

[0031] Figure 4 It is a structural schematic diagram of the second one-way valve of the present invention;

[0032] Figure 5 It is an enlarged view of the one-way valve 2 of the present invention;

[0033] Figure 6 Schematic diagram of the structure of the pumping cylinder and buffer cylinder of the present invention Figure 1 ;

[0034] Figure 7 Schematic diagram of the structure of the pumping cylinder and buffer cylinder of the present invention Figure 2 ;

[0035] Figure 1: Pump body; 2: Channel; 3: Feed inlet; 4: Discharge outlet; 5: One-way valve (I); 6: One-way valve (II); 7: Pumping cylinder; 8: Pumping chamber; 9: Pumping piston; 10: Telescopic rod; 11: Buffer cylinder; 12: Buffer piston; 13: Stopper; 14: Buffer spring; 15: Guide cylinder; 16: Valve body (I); 17: Valve hole (I); 18: Conical flow-limiting surface (I); 19: Flow-limiting spring (I); 20: Flow-limiting baffle ring (I); 21: Through groove; 22: Flow-limiting ball (I); 23: Adjusting rod; 24: Adjusting sleeve; 25: Through hole; 26: Valve body (II); 27: , valve hole two; 28, annular valve plug; 29, conical flow-limiting surface two; 30, support spring; 31, flow-limiting spring two; 32, flow-limiting ball head two; 33, adjusting baffle ring one; 34, adjusting baffle ring two; 35, adjusting ring groove; 36, flow-limiting baffle ring two; 37, guide rod; 38, connecting rod; 39, pressure end; 40, cable; 41, pre-condensation reactor; 42, final polycondensation reactor; 43, feed pipe one; 44, feed pipe two; 45, feed pipe three; 46, three-way joint; 47, booster pump device; 48, valve; 49, one-way valve device; 50, pressure relief hole. DETAILED DESCRIPTION

[0036] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0037] The physical properties of recycled copolyester chips are tested according to the test method of GBT 14190-2008 fiber-grade polyester chips (PET), and the thermal shrinkage of films is tested according to the test method of GB / T 13519-92.

[0038] Example 1:

[0039] The pretreated waste polyester was added to an alcoholysis reactor at a mass ratio of 1:2 waste polyester to ethylene glycol, with an alcoholysis catalyst dosage of 2‰. The reaction temperature was controlled at 190°C and the reaction time was 4 hours to obtain an alcoholysis product containing BHET, which was filtered and fed to the transesterification reactor.

[0040] The transesterification reaction temperature was controlled at 60°C and the reaction time was 4 hours. Methanol was added at a molar ratio of BHET to methanol of 1:2, and 0.2‰ of a transesterification catalyst was added. The obtained transesterification product was filtered, centrifuged, and distilled to obtain refined DMT with a purity greater than 99%.

[0041] 5% (molar percentage relative to DMT) CHDM, 5% (molar percentage relative to DMT) NPG, and excess ethylene glycol (EG) were added to achieve a total alcohol:DMT molar ratio of 2:1. 0.2‰ of transesterification catalyst was added, and the transesterification reaction temperature was controlled at 190°C for 4 hours. The resulting transesterification solution was fed into a pre-polycondensation reactor.

[0042] The temperatures of polycondensation-I and polycondensation-II were controlled at 220°C and 240°C, respectively, with an absolute pressure of 1-100KPa. 0.4‰ of stabilizer, 0.2‰ of polycondensation catalyst, and 0.5‰ of antioxidant were added, and the intrinsic viscosity of the prepolymer was 0.31dL / g. The prepolymer then entered a vertical final polycondensation reactor, where the reaction temperature was controlled at 260°C, the absolute pressure was 0.1-1KPa, and the reaction time was 2.0h. The prepolymer was then sent to the die through a melt pump and a melt pipe to extrude a thick sheet. The sheet was then biaxially stretched, then shaped, trimmed, and wound to produce a recycled copolyester heat shrinkable film. Film production control conditions were: die temperature 250-255°C, longitudinal stretching temperature 110°C, stretch ratio 2.5 times, transverse stretching temperature 110°C, stretch ratio 3.0 times, and the resulting recycled polyester heat shrinkable film had a shrinkage rate of 62% and an initial shrinkage temperature of 85°C (results shown in Table 1).

[0043] Example 2:

[0044] The pretreated waste polyester was fed into an alcoholysis reactor at a mass ratio of 1:2.5 waste polyester to ethylene glycol, with an alcoholysis catalyst dosage of 2‰. The reaction temperature was controlled at 200°C for 3 hours to obtain an alcoholysis product containing BHET, which was then filtered and fed into an ester exchange reactor.

[0045] The transesterification reaction temperature was controlled at 65°C and the reaction time was 3.5 hours. Methanol was added at a molar ratio of BHET to methanol of 1:2.5, and 0.2‰ of a transesterification catalyst was added. The obtained transesterification product was filtered, centrifuged, and distilled to obtain refined DMT with a purity greater than 99%.

[0046] 7.5% (molar percentage relative to DMT) of CHDM, 7.5% (molar percentage relative to DMT) of NPG, and excess ethylene glycol (EG) were added to a total alcohol:DMT molar ratio of 2.5:1. 0.2‰ of transesterification catalyst was added, and the transesterification reaction temperature was controlled at 200°C for 3 hours. The resulting transesterification solution was fed into a pre-polycondensation reactor.

[0047] The temperatures of polycondensation-I and polycondensation-II were controlled at 230°C and 250°C, respectively, with an absolute pressure of 1-100 kPa. 0.4‰ of stabilizer, 0.2‰ of polycondensation catalyst, and 0.5‰ of antioxidant were added, and the intrinsic viscosity of the prepolymer was 0.38 dL / g. The prepolymer then entered a vertical final polycondensation reactor, where the reaction temperature was controlled at 265°C, the absolute pressure was 0.1-1 kPa, and the reaction time was 1.5 h. The prepolymer was then sent to the die through a melt pump and a melt pipe to extrude a thick sheet. The sheet was then biaxially stretched, then shaped, trimmed, and wound to produce a recycled copolyester heat shrinkable film. The film production control conditions were: die temperature 250-255°C, longitudinal stretching temperature 130°C, stretch ratio 3.0 times, transverse stretching temperature 110°C, stretch ratio 4.0 times, and the resulting recycled polyester heat shrinkable film had a shrinkage rate of 65% and an initial shrinkage temperature of 95°C (results shown in Table 1).

[0048] Example 3:

[0049] The pretreated waste polyester was added to an alcoholysis reactor at a mass ratio of 1:3 waste polyester to ethylene glycol, with an alcoholysis catalyst dosage of 2‰. The reaction temperature was controlled at 210°C and the reaction time was 2 hours to obtain an alcoholysis product containing BHET, which was filtered and fed to the transesterification reactor.

[0050] The transesterification reaction temperature was controlled at 70°C and the reaction time was 3 hours. Methanol was added at a molar ratio of BHET to methanol of 1:3, and 0.2‰ of a transesterification catalyst was added. The obtained transesterification product was filtered, centrifuged, and distilled to obtain refined DMT with a purity greater than 99%.

[0051] 10% (molar percentage relative to DMT) CHDM, 10% (molar percentage relative to DMT) NPG, and excess ethylene glycol (EG) were added to achieve a total alcohol:DMT molar ratio of 3:1. 0.2‰ of transesterification catalyst was added, and the transesterification reaction temperature was controlled at 210°C for 2 hours. The resulting transesterification solution was fed into a pre-polycondensation reactor.

[0052] The temperatures of polycondensation-I and polycondensation-II were controlled at 240°C and 260°C, respectively, with an absolute pressure of 1-100KPa. 0.4‰ of stabilizer, 0.2‰ of polycondensation catalyst, and 0.5‰ of antioxidant were added, and the intrinsic viscosity of the prepolymer was 0.40dL / g. The prepolymer then entered a vertical final polycondensation reactor, where the reaction temperature was controlled at 270°C, the absolute pressure was 0.1-1KPa, and the reaction time was 1.0h. The prepolymer was then sent to the die through a melt pump and a melt pipe to extrude a thick sheet. The sheet was then biaxially stretched, then shaped, trimmed, and wound to produce a recycled copolyester heat shrinkable film. Film production control conditions were: die temperature 250-255°C, longitudinal stretching temperature 160°C, stretch ratio 3.5 times, transverse stretching temperature 110°C, stretch ratio 4.5 times, and the resulting recycled polyester heat shrinkable film had a shrinkage rate of 70% and an initial shrinkage temperature of 98°C (results shown in Table 1).

[0053] Example 4:

[0054] The same method as in Example 2 was used, except that 5% (based on the molar percentage of DMT) of CHDM and 10% (based on the molar percentage of DMT) of NPG were added. The resulting recycled polyester heat-shrinkable film had a shrinkage ratio of 64% and an initial shrinkage temperature of 96°C (see Table 1 for the results).

[0055] Example 5:

[0056] The same method as in Example 2 was used, except that 10% (based on the molar percentage of DMT) of CHDM and 5% (based on the molar percentage of DMT) of NPG were added. The resulting recycled polyester heat-shrinkable film had a shrinkage ratio of 73% and an initial shrinkage temperature of 94°C (see Table 1 for the results).

[0057] Comparative Example 1:

[0058] The same method as in Example 2 was used except that 15% (based on the molar percentage of DMT) of CHDM was added. The resulting recycled polyester heat shrinkable film had a shrinkage rate of 58% and an initial shrinkage temperature of 82° C. (see Table 1 for the results).

[0059] Comparative Example 2:

[0060] The same method as in Example 2 was used except that 15% (in molar percentage with respect to DMT) of NPG was added. The resulting recycled polyester heat shrinkable film had a shrinkage rate of 45% and an initial shrinkage temperature of 87° C. (see Table 1 for the results).

[0061] Table 1 Synthesis conditions and performance indicators of recycled high shrinkage polyester and heat shrinkage film

[0062]

[0063] Example 6

[0064] This embodiment discloses a recycled copolyester production process, in which pumping is achieved between the pre-polycondensation reactor 41 and the final polycondensation reactor 42 by a booster pump device 47. By booster pumping, the smoothness of the pumping process can be maintained. When the material has a certain viscosity, the material can still be pumped smoothly, avoiding the situation where the material has a high viscosity during the pumping process and may cause blockage.

[0065] The pre-polycondensation reactor 41 and the final polycondensation reactor 42 are connected by a booster pump device 47 to pump materials, and are connected by a material conveying pipeline to achieve the pumping of high-viscosity ester materials, maintain smooth material conveying, and maintain the smoothness of the reaction and preparation of the regenerated copolyester.

[0066] like Figure 2 As shown, the booster pump device 47 includes a cylindrical pump body 1, a channel 2 with two ends extending therethrough is opened in the pump body 1, a feed port 3 and a discharge port 4 are respectively provided at both ends of the channel 2, and a conveying pipeline is respectively connected at the feed port 3 and the discharge port 4 to allow the material to pass through, thereby realizing the pumping of the material.

[0067] A one-way valve 1 5 is installed at one end of the feed port 3 of channel 2, and a one-way valve 2 6 is installed at one end of the discharge port 4. The one-way valve 1 5 and the one-way valve 2 6 can maintain a one-way passage of the material and conduct a one-way flow from the feed port 3 to the discharge port 4. The one-way flow structure can ensure that only one-way conveying is achieved during the pumping process. During the pumping process, a certain pressure can be applied, which can exert a pumping force on the material, thereby improving the smoothness of the conveying of the ester material.

[0068] A pumping cylinder 7 is fixedly connected to the middle section of the pump body 1. A pumping chamber 8 is provided in the pumping cylinder 7 and is connected to the channel 2 in the pump body 1. A pumping piston 9 is connected to the piston in the pumping chamber 8. The outward end of the pumping piston 9 is driven back and forth by a telescopic rod 10. During the reciprocating movement of the pumping piston 9, the compression and expansion of the pumping chamber 8 can be achieved.

[0069] When the pumping piston 9 moves outward, the channel 2 of the pump body 1 is lowered, the one-way valve 1 5 is opened, the one-way valve 2 6 is closed, and the pressure in the channel 2 in the pump body 1 is reduced, forming a negative pressure, which can suck the material in the channel 2 of the pump body 1 from the one-way valve 1 5 of the feed port 3; the pre-shrinked material in the pre-condensation reactor 41 will be sucked into the pump body 1; when the pumping piston 9 moves inward, the channel 2 of the pump body 1 is pressurized, the one-way valve 1 5 is closed, and the one-way valve 2 6 is opened, which can squeeze out the material in the channel 2 of the pump body 1 from the one-way valve 2 6 of the discharge port 4, and the material in the pre-condensation reactor 41 is transported to the final condensation reactor 42; the telescopic rod 10 is reciprocated to adjust the pressure in the inner cavity of the pump body 1 to change, thereby realizing continuous transportation of the ester material.

[0070] like Figure 2 、 3As shown, the one-way valve 5 comprises a valve body 16, a flow-limiting ball 22, and a flow-limiting spring 19. The valve body 16 is fixedly mounted within the passage 2 and secured thereto by a stepped surface. A valve hole 17 is formed within the valve body 16, with both ends communicating with the passage 2 within the valve body. A conical flow-limiting surface 18 is formed on the inner circumference of the valve hole 17 at the end facing the feed inlet 3. The conical flow-limiting surface 18 gradually tapers toward the feed inlet 3 and is adapted to mate with the flow-limiting ball 22. When the flow-limiting ball 22 and the conical flow-limiting surface 18 abut against each other, the one-way valve 5 is sealed.

[0071] A flow-limiting baffle ring 20 is formed on the inner circumference of valve hole 17, at the end facing away from discharge port 4. A flow-limiting ball 22 is positioned within valve hole 17. A flow-limiting spring 19 elastically presses between flow-limiting ball 22 and flow-limiting baffle ring 20. The elastic action of the flow-limiting spring pushes flow-limiting ball 22 against the conical flow-limiting surface 18, creating a seal and sealing the one-way valve 5. When material flows through the one-way valve 5, it drives flow-limiting ball 22 inward, compressing flow-limiting spring 19. This creates a clear flow-guiding gap between flow-limiting ball 22 and the conical flow-limiting surface 18, allowing for smooth material flow.

[0072] like Figure 2 、 4 As shown, the one-way valve 26 includes a valve body 26, a flow-limiting ball head 232 and a flow-limiting spring 231. The valve body is a cylindrical structure and is installed in the channel 2 of the pump body 1. A valve hole 27 with two ends passing through is opened in the valve body 26, which can connect the valve body 26 to the channel 2 of the pump body 1.

[0073] An annular valve plug 28 is installed on the inner circumference of the valve hole 27 at the end facing the feed inlet 3, and a fixed flow-limiting baffle ring 26 is formed on the inner circumference of the valve hole 27 at the end facing away from the feed inlet 3. A flow-limiting ball 22 is disposed within the valve hole, and a flow-limiting spring 231 elastically presses between the flow-limiting ball 232 and the flow-limiting baffle ring 236. The elastic action of the flow-limiting spring 231 pushes the flow-limiting ball 232 against the annular valve plug 28, forming a pressure-sealed state. When material flows through the one-way valve 26, it drives the flow-limiting ball 232 to move and compress the flow-limiting spring 231, creating a certain flow-guiding gap between the flow-limiting ball 232 and the conical flow-limiting surface 29, allowing for smooth material flow.

[0074] Furthermore, a buffer cylinder 11 can be fixedly installed in the middle section of the pump body 1. The inner cavity of the buffer cylinder 11 is connected to the channel 2 in the pump body 1. A buffer piston 12 is installed in the buffer cylinder 11. The buffer piston 12 can form a piston connection structure that can be adjusted in a lifting manner in the buffer cylinder 11. A stopper 13 is connected to the end of the buffer piston 12 whose inner cavity faces the pump body 1. The stopper 13 can form a limiting and pressing effect on the buffer piston 12. A buffer spring 14 is installed at the end of the buffer piston 12 away from the pump body 1. The buffer spring 14 can elastically support the buffer piston 12.

[0075] The buffer piston 12 forms an elastic buffer structure within the buffer cylinder 11. During normal pressure fluctuations within the pump body 1, the buffer spring 14 maintains the buffer piston 12 in a fixed position, enabling pumping of the pump body 1 via the pumping piston 9. If a blockage or excessive internal pressure occurs within the pump body 1, the buffer piston 12 within the buffer cylinder 11 provides pressure relief. This pressure pushes the buffer piston 12 to expand the space between the buffer cylinder 11 and the pump body 1, relieving pressure from the pump body 1 and maintaining its operational stability.

[0076] like Figure 7 As shown, further, a pressure relief hole 50 can be opened on the outer wall of the buffer cylinder 11. When the buffer piston 12 moves a certain distance, the buffer piston 12 will pass over the pressure relief hole 50. The pressure relief hole 50 is connected with the channel 2 in the pump body 1 through the buffer cylinder 11. The excess pressure in the pump body 1 will be discharged from the pressure relief hole 50, thereby preventing the pump body 1 from being damaged due to excessive pressure.

[0077] Furthermore, based on the above embodiment, the boost pump device 47 can be further improved. Figure 2 、 3 As shown in Figures 4 and 5, adjustment rods 23 are installed at both ends of channel 2 of pump body 1 corresponding to buffer cylinder 11. Adjustment rods 23 are adjustable axially along channel 2 of pump body 1. Specifically, an adjustment sleeve 24 is fixedly installed in channel 2 within pump body 1. Adjustment rod 23 passes through adjustment sleeve 24, which guides the adjustment rod 23 during sliding to maintain stability during sliding. Adjustment sleeve 24 has through-holes 25 extending through both sides. Adjustment sleeve 24 not only supports and guides adjustment rod 23, but also ensures smooth flow of ester material without affecting the smooth flow of the material.

[0078] The adjusting rod 23 passes through the corresponding adjusting sleeve 24, and the opposite ends of the two adjusting rods 23 are fixedly connected to the flow-limiting ball head 1 22 and the flow-limiting ball head 2 32 respectively. By moving the adjusting rod 23, the corresponding flow-limiting ball head 1 22 and the flow-limiting ball head 2 32 can be adjusted and moved, so that the flow-limiting ball head 1 22 and the flow-limiting ball head 2 32 can seal the one-way valve 1 5 and the one-way valve 2 6 to cooperate in achieving one-way conduction and closure.

[0079] Specifically, the buffer cylinder 11 is perpendicular to the pump body 1. A guide rod 37 is coaxially mounted within the buffer cylinder 11. The guide rod 37 extends through the buffer piston 12 and is adjustable axially along the buffer cylinder 11. A sliding seal is formed between the guide rod 37 and the buffer piston 12, ensuring smooth movement of the guide rod 37. A guide cylinder 15 is fixedly mounted on the outward end of the buffer cylinder 11. The guide rod 37 extends through the guide cylinder 15, providing sliding guidance for the guide rod 37 and maintaining smooth movement.

[0080] Guide rod 37 extends into channel 2 within pump body 1. Movement of guide rod 37 drives axial adjustment of adjustment rod 23, thereby coordinating the movement of the one-way valve and assisting in the opening and closing of the one-way valve. Two connecting rods 38 are hingedly connected to guide rod 37. One end of connecting rod 38 is connected to guide rod 37, and the other end is hinged to adjustment rod 23. As guide rod 37 slides, it drives adjustment rod 23 in a sliding manner.

[0081] like Figure 6 As shown, the connecting rod 38, the adjusting rod 23, and the hinge point are in the same axial position. The two adjusting rods 23 will move in opposite directions. In the left-side one-way valve 5, the adjusting rod 23 will drive the flow-limiting ball head 1 22 to move leftward, maintaining a tight contact between the flow-limiting ball head 1 22 and the conical flow-limiting surface 18 in the one-way valve 5, maintaining the one-way closed state of the one-way valve 5. The right-side adjusting rod 23 will move the flow-limiting ball head 2 32 to the right, separating the flow-limiting ball head 2 32 from the conical flow-limiting surface 29 in the one-way valve 2 6, thus opening the one-way valve 2 6 and allowing the ester material to flow out smoothly.

[0082] One end of the guide rod 37 passes through the channel 2 in the pump body 1 and extends into the pumping chamber 8 of the pumping barrel 7. A cable 40 is connected between the pumping piston 9 and the pressing end 39 of the guide rod 37. When the pumping piston 9 moves outward, the pumping piston 9 can pull the guide rod 37 in the same direction via the cable 40, that is, pull the guide rod 37 upward as shown in the figure.

[0083] As guide rod 37 moves upward, it drives the adjusting rods 23 on either side to retract inward via connecting rod 38, causing flow-limiting ball heads 1 22 and 2 32 on either side to move in opposite directions. The left flow-limiting ball head 1 22 separates from the conical flow-limiting surface 18, actively driving the check valve 1 5 open and allowing material to be smoothly drawn into the valve body. At this time, flow-limiting ball head 2 32 on the right side of connecting rod 38 moves further to the left, further increasing the pressure of the seal formed between flow-limiting ball head 2 32 and the annular valve plug 28 in check valve 2 6, thereby maintaining a stable seal between flow-limiting ball head 2 32 and check valve 2 6.

[0084] When the pumping piston 9 moves inward, the pumping piston 9 can abut against the pressing end 39 of the guide rod 37. The pumping piston 9 can actively drive the guide rod 37 to drive the two adjusting rods 23 to move, so that the one-way valve 1 5 on the left is closed and the one-way valve 2 6 on the right is opened, thereby allowing the material in the pump body 1 to be smoothly discharged from the discharge port 4.

[0085] The reciprocating movement of the pumping piston 9 drives the reciprocating pressure within the pump body 1, thereby driving the corresponding opening and closing of the one-way valve 1 5 and the one-way valve 2 6 to maintain smooth pumping of the ester material. Simultaneously, the movement of the adjusting rod 23 and connecting rod 38 within the pump body 1 drives the flow-limiting ball heads within the one-way valves, thereby actively opening and closing the corresponding one-way valves. This active opening and closing actively drives the one-way valves to open and close, thereby maintaining the open or closed state during the pumping process, maintaining a stable operating state for the pump device.

[0086] Furthermore, a buffer structure can be provided in the one-way valve 2 6 to maintain the annular valve plug 28 in a stable state. The annular valve plug 28 can be elastically adjusted along the length direction of the valve hole 2 27. Through the buffering action, the interference of the action can be avoided.

[0087] like Figure 5 As shown, an annular adjustment ring groove 35 is opened on the inner periphery of the valve hole 27 at one end facing the feed port 3, and the piston of the annular valve plug 28 is connected in the adjustment ring groove 35. The outer periphery of the annular valve plug 28 is sealed with the peripheral wall of the adjustment ring groove 35, and piston adjustment can be realized.

[0088] An adjustment retaining ring 1 33 is fixed to the end of the adjustment ring groove 35 facing the feed port 3, and an adjustment retaining ring 2 34 is fixed to the end facing the discharge port 4. The adjustment retaining ring 1 33 and the adjustment retaining ring 24 are respectively capable of blocking and limiting the positions of the annular valve plug 28 at both ends. A support spring 30 is elastically connected between the adjustment retaining ring 1 33 and the annular valve plug 28. The elastic support of the support spring 30 can elastically push the annular valve plug 28 toward the discharge port 4, maintaining the annular valve plug 28 in a relatively stable state.

[0089] A conical flow-restricting surface 29 is machined on the inner circumference of the annular valve plug 28, on the end facing the discharge port 4. This conical flow-restricting surface 29 gradually widens toward the discharge port 4 and mates with the flow-restricting ball head 32. When the flow-restricting ball head 32 and the conical flow-restricting surface 29 press against each other, they maintain a pressure-sealed state, sealing the one-way valve 6. When the flow-restricting ball head 32 and the conical flow-restricting surface 29 separate, the one-way valve 6 is opened, allowing material to be pumped out.

[0090] By adopting a movable structure, the annular valve plug 28 can be buffered and supported, allowing the adjusting rod 23 and the limiting ball head to adjust smoothly, so as to maintain the appropriate pressure state between the limiting ball head and the conical limiting surface, and ensure that the active adjustment structure can move smoothly, thereby maintaining the normal operation of the booster pump device 47.

[0091] Furthermore, the booster pump device 47 can be used to directly pump between the pre-polycondensation kettle 41 and the final polycondensation kettle 42 to achieve smooth feeding between the pre-polycondensation kettle 41 and the final polycondensation kettle 42. Alternatively, Figure 1 As shown, a circulation pipeline can also be connected between the pre-polycondensation reactor 41 and the final polycondensation reactor 42 to achieve smooth transportation of the ester material.

[0092] like Figure 1 As shown, the circulation pipeline includes two feed pipes 1 43, two feed pipes 2 44, and one feed pipe 3 45. The two feed pipes 1 43 are connected to the bottom of the pre-polycondensation reactor 41 and the final polycondensation reactor 42, respectively, while the two feed pipes 2 44 are connected to the top of the pre-polycondensation reactor 41 and the final polycondensation reactor 42, respectively. The lower end of feed pipe 3 45 is connected to the two feed pipes 1 43 via a tee joint 46, while the upper end of feed pipe 3 45 is connected to the two feed pipes 2 44 via a tee joint 46. A booster pump device 47 is installed on feed pipe 3 45 to pump the material.

[0093] Electronically controlled valves 48 are installed on both feed pipes 1 43 and 2 44 to control the flow of the corresponding feed pipes. Check valves 49 are installed on both feed pipes 1 43 to ensure that material can be fed from the reactor to feed pipe 3 45 . Check valves 49 are installed on both feed pipes 2 44 to ensure that material can be fed from feed pipe 3 45 to the reactor. By regulating the flow of check valves 49 on the circulation pipelines, circulating pumping can be controlled from the pre-condensation reactor 41 to the pre-condensation reactor 41, thereby achieving the conveying of ester material from the pre-condensation reactor 41 to the final condensation reactor 42. This circulating pumping homogenizes the pre-condensed material and mixes the ester material with the added material to maintain material uniformity.

[0094] By closing the valve 48 of the feed pipe 2 44 on the pre-condensation reactor 41 and the valve 48 of the feed pipe 1 43 on the final condensation reactor 42, the material can be pumped from the pre-condensation reactor 41 to the final condensation reactor 42 through the booster pump device 47, and the intermediate to be processed can be sent to the final condensation reactor 42 for reaction.

[0095] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiment. All technical solutions based on the concept of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a heat-shrinkable film of recycled copolyester, comprising using recycled copolyester as a raw material and delivering the recycled copolyester to a film-forming device via a melt pump and a melt pipe; In the preparation of heat shrinkable film, the melt delivered from the polymerization process directly passes through the melt distribution pipe and is pumped to the die head by the melt metering pump to extrude a thick sheet. The thick sheet is then biaxially stretched, and then shaped, trimmed, and wound to produce the recycled copolyester heat shrinkable film. The preparation process of the recycled copolyester is as follows: 1) Pretreatment of waste polyester; 2) Alcoholysis of waste polyester: Add waste polyester to ethylene glycol in a mass ratio of 1:2-3 into the alcoholysis reactor, add an alcoholysis catalyst, control the reaction temperature at 190-210°C and the reaction time for 2-4 hours to obtain the alcoholysis product of BHET, which is then filtered and fed into the transesterification reactor; 3) Preparation of crude DMT: Add methanol at a molar ratio of BHET to methanol of 1:2-3 and add a transesterification catalyst. Control the transesterification reaction temperature at 60-70°C and the reaction time for 3-4 hours to obtain crude DMT as the transesterification product. 4) Purification of DMT: The transesterification product is filtered, centrifuged, distilled and then fed into the transesterification kettle; 5) Transesterification reaction: Add NPG, CHDM and ethylene glycol with a molar percentage of 15% to 20% of DMT, and the molar percentage of NPG to DMT: the molar percentage of CHDM to DMT is 1:1 or 2:1 or 1:

2. The total alcohol:DMT molar ratio is controlled at 2-3:1, and an ester exchange catalyst is added; the ester exchange reaction temperature is controlled at 190-210°C, the reaction time is controlled at 2-4 hours, and the obtained ester exchange liquid is fed into a pre-polycondensation kettle; the ester exchange catalyst is an acetic acid catalyst; 6) Polycondensation: The esterified product enters polycondensation-I and polycondensation-II successively, and a polycondensation catalyst, antioxidant and stabilizer are added. The reaction temperature is controlled at 220-260°C, the absolute pressure is 1-100 kPa, and the intrinsic viscosity of the prepolymer is 0.2-0.4 dl / g. The product then enters a vertical final polycondensation reactor, and the reaction temperature is controlled at 260-270°C, the absolute pressure is 0.1-1 kPa, and the reaction time is 1-2 hours to produce the recycled copolyester. The comonomers in the polycondensation process are: neopentyl glycol and 1,4-cyclohexanedimethanol. During the film forming process, the die head temperature of the heat shrinkable film is 250~255℃, the longitudinal stretching temperature is 110~160℃, the stretch ratio is 2.5~3.5, the transverse stretching temperature is 110℃, the stretch ratio is 3.0~4.5, and the initial shrinkage temperature of the obtained shrinkage film is 80~100℃, and the shrinkage rate is 60%~80%; In step 6) polycondensation, the material is pumped between the pre-polycondensation kettle and the final polycondensation kettle by a booster pump device; the booster pump device (47) comprises a cylindrical pump body (1), a channel (2) with two ends connected is provided in the pump body (1), a feed port (3) and a discharge port (4) are respectively provided at both ends of the channel (2), and the feed port (3) and the discharge port (4) are respectively connected to the conveying pipeline; a one-way valve (5) is installed at one end of the feed port (3) of the channel (2), and a one-way valve (5) is installed at one end of the discharge port (4). A one-way valve (6) is installed. The one-way valve (5) and the one-way valve (6) can maintain the one-way passage of the material and conduct the material in a one-way manner from the feed port (3) to the discharge port (4). The middle section of the pump body (1) is fixedly connected to a pumping barrel (7). The pumping barrel (7) is provided with a pumping chamber (8) in communication with the channel (2) in the pump body (1). A pumping piston (9) is connected to the piston in the pumping chamber (8). The outward end of the pumping piston (9) is reciprocated by a telescopic rod (10). The one-way valve (5) comprises a valve body (16), a flow-limiting ball head (22) and a flow-limiting spring (19). The valve body (16) is fixedly installed in the channel (2) and is fixed by a stepped surface; a valve hole (17) with two ends passing through is provided in the valve body (16), and the two ends of the valve hole (17) are connected to the channel (2) in the valve body; a conical limiting spring is formed on the inner periphery of the valve hole (17) at one end facing the feed port (3). A flow surface (18) is provided, wherein the conical flow-limiting surface (18) gradually narrows toward one end of the feed port (3), and the conical flow-limiting surface (18) can be adapted to the flow-limiting ball head (22); a flow-limiting baffle ring (20) is formed at one end of the inner periphery of the valve hole (17) facing away from the discharge port (4), and the flow-limiting ball head (22) is arranged in the valve hole (17); a flow-limiting spring (19) elastically presses between the flow-limiting ball head (22) and the flow-limiting baffle ring (20); The one-way valve (6) comprises a valve body (26), a flow-limiting ball head (32) and a flow-limiting spring (31). The valve body is cylindrical and is installed in the channel (2) of the pump body (1). A valve hole (27) with two ends passing through is provided in the valve body (26). An annular valve plug (28) is installed on the inner periphery of the valve hole (27) at one end facing the feed port (3). A fixed flow-limiting baffle ring (36) is formed on the inner periphery of the valve hole (27) at one end facing away from the feed port (3). The flow-limiting ball head (22) is provided in the valve hole, and the flow-limiting spring (31) is elastically pressed between the flow-limiting ball head (32) and the flow-limiting baffle ring (36). The flow-limiting spring (31) can push the flow-limiting ball head (32) to press against the annular valve plug (28). A buffer cylinder (11) is fixedly installed at the middle position of the pump body (1), the inner cavity of the buffer cylinder (11) is communicated with the channel (2) in the pump body (1), and a buffer piston (12) is installed in the buffer cylinder (11), and the buffer piston (12) can form a piston connection structure that can be adjusted in the buffer cylinder (11); a stopper (13) is connected to the end of the inner cavity of the buffer piston (12) facing the pump body (1), and the stopper (13) can form a limiting and pressing effect on the buffer piston (12); a buffer spring (14) is installed at the end of the buffer piston (12) away from the pump body (1), and the buffer spring (14) can elastically support the buffer piston (12); The channel (2) of the pump body (1) is provided with adjusting rods (23) at both ends of the buffer cylinder (11), and the adjusting rods (23) can be adjusted axially along the channel (2) of the pump body (1); the adjusting rods (23) pass through the corresponding adjusting sleeves (24), and the opposite ends of the two adjusting rods (23) are fixedly connected to the flow-limiting ball head 1 (22) and the flow-limiting ball head 2 (32) respectively; a guide rod (37) is coaxially installed in the buffer cylinder (11), and the guide rod (37) passes through the buffer piston (12) and can be adjusted axially along the buffer cylinder (11); the outward end of the buffer cylinder (11) is fixedly provided with a guide rod (37). The guide rod (37) passes through the guide cylinder (15) and can guide the guide rod (37) to slide; the guide rod (37) extends into the channel (2) in the pump body (1); the movement of the guide rod (37) can drive the adjusting rod (23) to axially adjust, thereby cooperating with the action of the one-way valve to assist in opening and closing the one-way valve; two connecting rods (38) are hinged on the guide rod (37), one end of the connecting rod (38) is connected to the guide rod (37), and the other end is hinged to the adjusting rod (23); during the sliding process, the guide rod (37) will drive the adjusting rod (23) to slide and adjust; One end of the guide rod (37) passes through the channel (2) in the pump body (1) and extends into the pumping chamber (8) of the pumping cylinder (7). A cable (40) is connected between the pumping piston (9) and the pressing end (39) of the guide rod (37). When the pumping piston (9) moves outward, the pumping piston (9) can pull the guide rod (37) in the same direction through the cable (40); when the guide rod (37) moves upward, the guide rod (37) drives the adjusting rods (23) on both sides to retract inward through the connecting rod (38), so that the flow-limiting ball heads 1 (22) and the flow-limiting ball heads 2 (32) on both sides move in opposite directions, and the flow-limiting ball head 1 (22) on the left side is separated from the conical flow-limiting surface 1 (18), and the one-way valve 1 (5) is opened by active driving, so that the material can be smoothly sucked into the valve body; the flow-limiting ball head 2 (32) on the right side of the connecting rod (38) will further move to the left, and the pressure of the pressure seal between the flow-limiting ball head 2 (32) and the annular valve plug (28) in the one-way valve 2 (6) will be further increased, thereby maintaining the flow-limiting ball head 2 (32) and the one-way valve 2 (6) in a stable sealing state; When the pumping piston (9) moves inward, the pumping piston (9) can abut against the pressing end (39) of the guide rod (37), and the pumping piston (9) can actively drive the guide rod (37), thereby driving the two adjusting rods (23) to move, so that the one-way valve (5) on the left side is closed and the one-way valve (6) on the right side is opened, thereby allowing the material in the pump body (1) to be smoothly discharged from the discharge port (4).

2. The method for preparing a heat shrinkable film of recycled copolyester according to claim 1, characterized in that: The alcoholysis catalyst is potassium carbonate, sodium hydroxide or acetate.

3. The method for preparing a heat shrinkable film of recycled copolyester according to claim 1, characterized in that: The stabilizer is triphenyl phosphate, phosphorous acid or trimethyl phosphate.

4. The method for preparing a heat shrinkable film of recycled copolyester according to claim 1, characterized in that: The antioxidant is a hindered phenol antioxidant.

5. The method for preparing a heat shrinkable film of recycled copolyester according to claim 1, characterized in that: The polycondensation catalyst is an antimony-based catalyst, a titanium-based catalyst, or ethylene glycol antimony.

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