WO2020118986A1 - Thermoplastic polyester extrusion foam molding method - Google Patents

Abstract

Disclosed is a thermoplastic polyester extrusion foam molding method, comprising melting a thermoplastic polyester, a lubricant and a foaming aid in a twin-screw extruder, the exit pressure of the twin-screw extruder being 3 MPa to 10 MPa; supplying and mixing a physical foaming agent into the thermoplastic polyester melt, and feeding the mixture via a melt pump to a single screw extruder, the inlet pressure of the single screw extruder being 15 MPa to 25 MPa; and lowering the temperature of the thermoplastic polyester melt comprising the physical foaming agent by means of the single screw extruder, subjecting the thermoplastic polyester melt to extrusion foaming through a die, and cooling and forming the extrudate to obtain a thermoplastic ester foamed product. By adding a high-temperature-resistant lubricant and using a melt pump for regulation, the method achieves thermoplastic polyester foam molding with high efficiency, stability and quality.

Description

Thermoplastic polyester extrusion foaming molding method Technical field

The invention relates to a polymer extrusion molding method, in particular to a thermoplastic polyester extrusion foam molding method.

Background technique

Foam plastic is a composite material with plastic as a matrix and filled with a large number of bubbles, so it has excellent properties such as light weight, material saving, high specific strength, low thermal conductivity, thermal insulation and sound absorption, and ability to absorb impact loads. Therefore, it is widely used Packaging, heat insulation, anti-freezing and thermal insulation, buffer and vibration-proof, and sound-absorbing materials have been widely used in construction, transportation, daily necessities, packaging, and aerospace, navigation, national defense and other fields. Traditional polymer foams such as polyurethane foam (PU), polyethylene foam (PE) and polystyrene foam (PS), etc., have certain deficiencies in the performance and processing methods of the material itself. For example, polyurethane foam releases isocyanate and other harmful residues during the preparation process, and the foamed polyurethane has a problem that it is difficult to recycle. Polystyrene foam has limited use due to its poor high temperature resistance. Polyethylene foam has the disadvantages of poor mechanical properties and low heat resistance. Therefore, people have been devoted to the development of high-performance foamed plastics to broaden the application fields of foamed materials to meet the ever-increasing demands on material performance in the development of society and technology.

Thermoplastic polyester has excellent heat resistance and mechanical properties. Compared with traditional foam plastics, thermoplastic polyester foam has good dimensional stability at high temperatures, excellent mechanical properties and fatigue resistance, low smoke, flame retardant, no Poisonous, low water absorption, good gas barrier and recyclable advantages have wide application prospects in the fields of electronics industry, buffer packaging, building materials, transportation, wind power generation and other fields.

In order to overcome the shortcomings of low melt strength of thermoplastic polyester, it is difficult to maintain the cell structure, and it is easy to cause cell collapse and merging. The prior art mainly increases the viscosity of polyester by adding chain extender or crosslinking agent. For example, US Patent No. US4981631 discloses polyethylene terephthalate (PET) foam tray, using branching agent pyromellitic dianhydride (PMDA) to improve PET melt viscoelasticity, and adding 1-6% Polyolefin (PP, PE) as a nucleating agent, the maximum expansion ratio is 2 times. US3553157 discloses a method of mixing 0.5-1 wt% PMDA with PET and adding it to an extruder to increase the viscosity of PET melt, but it does not involve foaming production. Japanese Patent 59-210955 (1984) discloses a PET foaming method. PET is mixed with 0.01-2 mol% PMDA and 0.03-2.5 mol% multifunctional epoxy compound to improve the melt strength of PET. US5000991 and US5134028 disclose a process for preparing PET foam, which is characterized by a compound containing two or more acid anhydride groups, such as PMDA, added to PET. Among them, the US5000991 patent discloses that the amount of PMDA is in the range of 0.05-5.0wt%, pointing out that when the PMDA content exceeds 5%, gel will be formed. The mixing method of PMDA and PET includes: directly mixing and adding to the extruder, or pre-creating the masterbatch (using PET or other polymers as the matrix) and then adding, or adding PET first, melting and then adding PMDA, but there is no comparison. The advantages and disadvantages of several processes and their impact on PET foaming. In addition, the US5000991 patent also discloses the addition of 0.05-5% sodium carbonate, and shows that the addition of sodium carbonate can make the foamed material have higher tensile elongation and finer cells. US5958164 discloses a thermoplastic polyester extrusion foaming method, using recycled and virgin PET as raw materials, direct extrusion foaming without drying, using PMDA and sodium carbonate as a chain extender, butane as a foaming agent to prepare PET Foamed sheet with a sheet density of 0.23-0.26g/cm ³ . EP2163577A1 discloses the preparation process of the chain extender masterbatch for foamed polyester. The chain extender masterbatch includes anhydride compounds, antioxidants and oxazoline compounds, etc., which can balance the pressure and torque fluctuations during the reaction extrusion process to make the reaction The extrusion foaming process is more stable.

The above patents disclose the use of multifunctional chain extenders to increase the viscosity of PET resin to improve its foaming performance. Usually the number of functional groups of the chain extender is greater than 2, preferably greater than 4 or more. This causes the viscosity of the system to suddenly increase during the extrusion chain extension reaction, which makes the pressure in the extrusion system increase and the torque increases, it is difficult to transport the melt to the downstream of the head, and the excessive melt viscosity and Melt elasticity makes the melt prone to severe melt rupture when passing through the small die gap of the foaming head, resulting in rough surface of the product and gas escape, such as shark skin phenomenon, it is difficult to obtain qualified foam products.

Summary of the invention

In order to achieve efficient, stable and high-quality production of thermoplastic polyester foam molding, the present invention provides a thermoplastic polyester extrusion foam molding method.

The thermoplastic polyester extrusion foaming method provided by the present invention includes: adding thermoplastic polyester, lubricant and foaming aid to a twin-screw extruder for melting, and the outlet pressure of the twin-screw extruder is 3MPa～ 10MPa; physical foaming agent is introduced into the thermoplastic polyester melt in the twin-screw extruder. After mixing, it is pumped into the single-screw extruder through the melt. The inlet pressure of the single-screw extruder is 15MPa-25MPa The temperature of the thermoplastic polyester melt containing the physical blowing agent is reduced by a single screw extruder, extruded and foamed through a die, and cooled and shaped to obtain a thermoplastic polyester foamed product.

In the above method, preferably, the amount of lubricant added is 0.5% to 5% of the total weight of the thermoplastic polyester.

In the above method, preferably, the thermal decomposition temperature of the lubricant is higher than 350° C., and the lubricant is selected from organic fatty acid esters, amide compounds, low molecular weight polyethylene wax, low molecular weight oxidized polyethylene wax, polydimethyl One or more combinations of siloxanes.

In the above method, preferably, the lubricant is added in the form of a master batch, and the master batch includes 10% to 50% of the lubricant by weight.

In the above method, preferably, the twin-screw extruder and the single-screw extruder are connected by a melt pump, the inlet pressure of the melt pump is 3MPa-10MPa, and the outlet pressure is 15MPa-20MPa.

In the above method, preferably, the foaming aid includes a chain extender, a nucleating agent, an antioxidant, and a heat stabilizer.

In the above method, preferably, the chain extender is an acid anhydride compound, and the amount added is 0.2% to 1% of the total weight of the thermoplastic polyester.

In the above method, preferably, the chain extender is a multifunctional epoxy-based compound, and the added amount is 0.5% to 3% of the total weight of the thermoplastic polyester.

In the above method, preferably, the chain extender is added in the form of a masterbatch, and the masterbatch includes 8% to 30% of the chain extender by weight.

In the above method, preferably, the physical blowing agent is carbon dioxide, nitrogen, isobutane, isopentane, cyclopentane, hexane, heptane, one or more combinations of fluorine-containing compounds, the total addition amount It is 1% to 10% of the total weight of the thermoplastic polyester.

The thermoplastic polyester extrusion foam molding method provided by the present invention, on the one hand, effectively controls the melt temperature during the processing process and improves the surface quality of the product by adding a high temperature resistant lubricant; on the other hand, the melt pump is used to regulate and control The outlet pressure of the twin-screw extruder and the inlet pressure of the single-screw extruder are used to avoid the thermal decomposition of the thermoplastic polyester in the twin-screw extruder and to ensure that the head pressure reaches the foaming requirements. Thus, efficient, stable and high-quality production of thermoplastic polyester foam molding is realized.

BRIEF DESCRIPTION

In order to more clearly explain the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the specific embodiments or the description of the prior art.

FIG. 1 is a flowchart of a thermoplastic polyester extrusion foam molding method according to an embodiment of the present invention.

Fig. 2 is a schematic diagram of an apparatus for thermoplastic polyester extrusion foam molding according to an embodiment of the present invention.

3 is a thermal weight loss curve of lubricant pentaerythritol stearate according to an embodiment of the present invention.

detailed description

As shown in FIG. 1, the present invention discloses a thermoplastic polyester extrusion foam molding method, including the following steps:

In S1, the thermoplastic polyester, lubricant and foaming aid are added to the twin-screw extruder for melting, and the outlet pressure of the twin-screw extruder is 3MPa-10Mpa. Among them, foaming aids include chain extenders, nucleating agents, antioxidants and heat stabilizers

S2 is fed with a physical blowing agent in the thermoplastic polyester melt in the twin-screw extruder, and after mixing, it is pumped into the single-screw extruder through the melt. The inlet pressure of the single-screw extruder is 15 MPa to 25 MPa. In this step, after the physical blowing agent is introduced into the thermoplastic polyester melt of the twin-screw extruder, a homogeneous solution is formed after the screws of the twin-screw extruder are mixed.

S3 uses a single screw extruder to reduce the temperature of the thermoplastic polyester melt containing the physical blowing agent to T, T _m -10°C≦T≦T _m +30° C, where T _m is the melting point of the thermoplastic polyester. Extruded and foamed through the die, cooled and shaped to obtain thermoplastic polyester foamed products. In this step, when the thermoplastic polyester is PET, the temperature of the melt is reduced to 240°C to 260°C by a single screw extruder. The foam is extruded through a die, and the foamed product is cooled and shaped on a cooling and setting device to obtain a thermoplastic polyester foamed product. The density of the final thermoplastic polyester foamed product is 60 kg/m ³ to 300 kg/m ³ .

Among them, thermoplastic polyester mainly refers to aromatic polyester, specifically a polymer obtained by polycondensation reaction of aromatic dicarboxylic acid and diol, such as polyethylene terephthalate, polypropylene terephthalate The ester, polybutylene terephthalate, and copolymers thereof are preferably polyethylene terephthalate (PET). In addition, the thermoplastic polyester resin may contain a third component copolymer, such as resorcinol, in addition to the aromatic dicarboxylic acid and the diol. The intrinsic viscosity of the aromatic polyester is between 0.6 and 0.85dl/g, and the intrinsic viscosity is tested according to the method of GB/T14190-2008 (the solvent is phenol/tetrachloroethane (mass ratio 50/50)). You can also use recycled thermoplastic polyester as a raw material, such as recycled PET, whose intrinsic viscosity is greater than or equal to 0.6dl/g.

ADR-4368，四缩水甘油基二氨基二苯基甲烷(TGDDM)等。噁唑啉类化合物是指分子结构中含有氮氧五元杂环的化合物，可以是单噁唑啉或双噁唑啉，优选为双噁唑啉，如1,3-苯基双噁唑啉或1,4-苯基双噁唑啉。酸酐类扩链剂的添加量通常为热塑性聚酯总重量的0.2％～1％，优选地0.3％～0.5％；ADR类环氧类化合物扩链剂的添加量为热塑性聚酯总重量的0.5％～3％，优选为0.6％～1.5％，更优选为0.8％～1.2％；噁唑啉的添加量为热塑性聚酯总重量的0.5％～2％，优选为0.8％～1.2％。在本发明中，酸酐类扩链剂可以与环氧类扩链剂一起使用或者与噁唑啉类扩链剂一起使用。扩链剂以母粒的方式加入，具体地可以加工成以热塑性聚酯为基体的母粒，按重量计，母粒中包括8％～30％的扩链剂，优选为10％～20％。 The chain extender refers to a compound containing two or more compounds that can react with the terminal hydroxyl group or terminal carboxyl group of the thermoplastic polyester, including one of acid anhydride compounds, epoxy compounds and oxazoline compounds or Various combinations. Anhydride compounds such as pyromellitic dianhydride (PMDA), naphthalene tetracarboxylic anhydride, pyromellitic tetracarboxylic anhydride, and cyclopentane tetracarboxylic anhydride, preferably pyromellitic dianhydride (PMDA). Epoxy compounds include multifunctional epoxy compounds or epoxy oligomers, such as BASF’s

ADR-4368, tetraglycidyl diaminodiphenylmethane (TGDDM), etc. Oxazoline compounds refer to compounds containing a nitrogen-oxygen five-membered heterocyclic ring in the molecular structure, which can be monooxazoline or bisoxazoline, preferably bisoxazoline, such as 1,3-phenylbisoxazoline Or 1,4-phenylbisoxazoline. The addition amount of the acid anhydride chain extender is usually 0.2% to 1% of the total weight of the thermoplastic polyester, preferably 0.3% to 0.5%; the addition amount of the ADR epoxy chain extender is 0.5 of the total weight of the thermoplastic polyester % To 3%, preferably 0.6% to 1.5%, more preferably 0.8% to 1.2%; the added amount of oxazoline is 0.5% to 2% of the total weight of the thermoplastic polyester, preferably 0.8% to 1.2%. In the present invention, the acid anhydride-based chain extender may be used together with the epoxy-based chain extender or the oxazoline-based chain extender. The chain extender is added in the form of a masterbatch, specifically it can be processed into a masterbatch based on a thermoplastic polyester. The masterbatch contains 8%-30% of the chain extender by weight, preferably 10%-20% .

Physical blowing agents are carbon dioxide, nitrogen, low molecular weight alkanes, such as isobutane, isopentane, cyclopentane, hexane, heptane, fluorine-containing compounds, such as HCFC-142a, HCFC-22, HFC-134a, HFC -152a, one or more combinations of HFO-1234ze, HFO-1233zd, 1, HCFO-1233zd, etc., the total addition amount is 1% to 10% of the total weight of the thermoplastic polyester.

The nucleating agent, that is, the cell nucleating agent, can be an inorganic nucleating agent or an organic nucleating agent. The inorganic nucleating agent includes talc, calcium carbonate, nano silica, nano montmorillonite, etc. The organic nucleating agent is For azodicarbonamide (AC) and the like, the amount of nucleating agent added is 0% to 5% of the total weight of the thermoplastic polyester, preferably 1% to 3%.

Among them, the antioxidant is a hindered phenol antioxidant, such as (tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionic acid] pentaerythritol ester) (antioxidant 1010), (3- (1,1-dimethylethyl)-β-[3-(1,1-dimethylethyl)-4-hydroxyphenyl]-4-hydroxy-β-methylbenzoic acid-1,2 -Ethylene ester) (antioxidant O ₃ ), β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate octadecyl carbonate (antioxidant 1076), hexanediol bis[ 3,5-di-tert-butyl-4-hydroxyphenyl) acrylate (antioxidant 259), (1,3,5 tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1, 3,5-triazine-2,4,6(1H,3H,5H)-trione) (antioxidant 3114), the amount of antioxidant added is 0.1% to 0.2% of the total weight of the thermoplastic polyester.

Among them, the heat stabilizer is a phosphate ester compound, such as triphenyl phosphate, triethyl phosphoryl acetate, (bis(2,4-di-tert-butylphenyl) pentaerythritol phosphite), tetrakis(2,4- The amount of di-tert-butylphenyl-4,4'biphenyl)bisphosphite, tri(2,4-di-tert-butylphenyl)phosphite, and heat stabilizer added is the total weight of the thermoplastic polyester 0.2%～0.5%. Antioxidant and heat stabilizer are used alone or in combination. Antioxidants and/or heat stabilizers can be processed into masterbatch based on thermoplastic polyester and added to the thermoplastic polyester in the form of masterbatch.

In order to improve the foaming performance of the thermoplastic polyester, a chain extender or branching agent is added to the twin-screw extruder, and a chain extension reaction occurs during the extrusion process, which significantly improves the viscoelasticity of the thermoplastic polyester melt. However, the significant increase in the viscoelasticity of the thermoplastic polyester melt will cause severe shear heat generation during the extrusion process, which is likely to cause thermal degradation of the polyester and affect product quality. On the other hand, it is easy to occur in the high shear area of the foam head The phenomenon of melt fracture makes the surface of the product rough, and even the surface of the foamed product cracks.

In order to overcome these shortcomings in the process of polyester extrusion foaming, the present invention adds lubricants during the extrusion process, on the one hand to reduce the interaction between polyester macromolecular chains, reduce the shear heat, on the other hand, reduce the melting The friction between the body and the barrel and the metal inner wall of the machine head significantly improves the surface quality of the product. The thermal decomposition temperature of the lubricant is higher than 350 ℃, one or more combinations selected from organic fatty acid esters, amide compounds, low molecular weight polyethylene wax, low molecular weight oxidized polyethylene wax and polydimethylsiloxane . For example, pentaerythritol stearate, modified ethylene bis stearamide EBS, etc. The amount of lubricant added is 0.5% to 5% of the total weight of the thermoplastic polyester, preferably 1% to 5%, and more preferably 1% to 3%. Lubricant can be added to the thermoplastic polyester extrusion foaming process in the form of masterbatch. It is preferred to use thermoplastic polyester as the carrier of the masterbatch, such as polyethylene terephthalate and polybutylene terephthalate. Among them, the masterbatch includes 10% to 50% lubricant by weight.

The device for thermoplastic polyester foam molding of the present invention adopts a two-stage extruder series system, the first stage is a co-rotating twin-screw extruder, the second stage is a single-screw extruder, and two extruders Melt pumps are connected in series between them. Figure 2 is a preferred embodiment of a device for thermoplastic polyester foam molding. The reference numbers in Figure 2 are as follows: 1- twin screw feeder 2- twin screw extruder 3-back Pressure valve 4-gas metering pump 5-shut-off valve 6-gas source 7-test point 8-melt pump 9-test point 10-single screw extruder 11-foaming head.

As shown in Figure 2, the device includes: co-rotating twin screw extruder 2 (screw diameter 65mm, L/D = 32; Nanjing Chuangbo Machinery Equipment Co., Ltd.), melt pump 8 (ZB-C300, Zhengzhou Bart Melt Pump Co., Ltd.), a vacuum system, single-screw extruder 10 (diameter 150mm, length-to-diameter ratio 23), static mixer, foaming head 11 (fish-tailed plate head) and installed on the foam Cooling setting device downstream of the head 11 outlet. Among them, the vacuum system is connected to the exhaust port of the twin screw extruder 2. The melt pump 8 is installed in series at the connection between the outlet of the twin screw extruder and the inlet of the single screw extruder, that is, the outlet of the twin screw extruder is connected to the inlet of the melt pump, and the outlet of the melt pump is connected to the inlet of the single screw extruder Connected. The outlet of the single screw extruder is connected to the foaming head 11. The cooling setting device is installed downstream of the foaming head 11. During the foam molding process, the pressure sensors installed at test point 7 and test point 9 can be used to monitor the outlet pressure P1 of the twin-screw extruder and the inlet pressure P2 of the single-screw extruder, respectively. The device also includes a gas injection system, which includes a gas source 6, a shut-off valve 5, a back pressure valve 3, and a gas metering pump 4. During the foam molding process, the melt is fed to the twin-screw extruder 2 through the gas injection system Inject physical blowing agent.

In the foaming process of thermoplastic polyester, on the one hand, the pressure of the twin screw extruder head is too high, which easily causes the resistance of the material in the twin screw to increase, the injection of the foaming agent is difficult, and the material in the twin screw Increased shearing heat generation is prone to thermal degradation; too low pressure will cause the foaming agent to be difficult to dissolve in the polyester melt. On the other hand, in order to increase the nucleation density of foamed products, it is usually required to have a sufficiently high head pressure And, the second-stage single screw is mainly to reduce the melt temperature, so the conveying capacity of the melt is weak, especially for the low-temperature high-viscosity melt conveying capacity. In order to solve the above problems, in the present invention, by controlling the speed of the melt pump and the single screw, the melt pressure of the twin screw outlet P1 is lower than 10 MPa, even lower than 5 MPa, and the inlet pressure of the single screw extruder P2 is higher than 12 MPa, preferably higher than 15MPa. For example, according to a preferred embodiment of the present invention, the pressure P1 is maintained at any set value between 3 MPa and 10 MPa, preferably between 3 MPa and 8 MPa, and more preferably between 5 MPa and 8 MPa. By controlling the melt pump, the inlet pressure P2 of the single screw is greater than or equal to 15 MPa, more preferably greater than or equal to 18 MPa.

The inlet pressure of the melt pump is controlled to be 3MPa to 10MPa, preferably 3MPa to 8MPa, more preferably 5MPa to 8MPa; the outlet pressure of the melt pump is controlled to be greater than or equal to 15MPa, preferably greater than or equal to 18MPa, and more preferably 15MPa to 20MPa.

The outlet pressure of the twin screw and the outlet pressure of the single screw can be achieved by manually adjusting the speed of the melt pump and the speed of the single screw, or by an automatic feedback control system. For example, a pressure sensor is installed at the melt connection at the melt inlet and outlet of the melt pump to monitor the twin-screw extruder outlet pressure P1 and the single-screw extruder inlet pressure P2. A double closed-loop control system is adopted to take the twin-screw inlet pressure P1 and the single-screw The outlet pressure P2 is the control target. The PLC program adjusts and controls the melt pump speed and single screw speed to achieve double closed-loop automatic feedback control, so that P1 is maintained at any set value between 3MPa and 10MPa, preferably any value between 3MPa and 8MPa The set value is more preferably any set value between 5 MPa and 8 MPa; P2 is maintained at any set value between 15 MPa and 20 MPa. Specific implementation examples are as follows:

Example 1:

Raw material: Polyethylene terephthalate (PET), BG80, Sinopec Yizheng Chemical Fiber Co., Ltd., intrinsic viscosity 0.8dl/g;

Chain extender, pyromellitic anhydride (PMDA), Sinopharm Group Chemical Reagent Co., Ltd.;

Nucleating agent: talc powder, 1000 mesh;

Antioxidant: tetrakis(β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid) pentaerythritol ester (antioxidant 1010), Nanjing Hualiming Chemical Co., Ltd.;

Lubricant: pentaerythritol stearate PETs, Jiangsu Xingtai Photochemical Auxiliary Co., Ltd., thermal decomposition temperature 400℃. The decomposition temperature is measured by a thermal weight loss analyzer. The heating rate is 10℃/min, the atmosphere is nitrogen, and the temperature at the maximum thermal weight loss rate on the TG temperature curve is defined as the thermal decomposition temperature. Figure 3 is the thermal weight loss curve of pentaerythritol stearate.

Foaming process: preheat the entire extrusion system and dry PET; after the extrusion system reaches the set temperature, turn on the single screw extruder, then turn on the melt pump, twin screw extruder, and feeding system in sequence to dry Processed PET 100kg, chain extender PMDA 0.3kg, antioxidant 1010, 0.1kg, talc powder 1kg, lubricant pentaerythritol stearate PETs 0.5kg mixed evenly from twin screw feeder 1 (as shown in Figure 2 ) Is added into the feed port, and then the physical blowing agent cyclopentane is injected into the PET melt in the twin screw through the gas injection system, the amount of agent added is 2wt% of the total amount of PET, etc. After that, reduce the temperature of each section of the single screw extruder, control the speed of the melt pump and the single screw, so that the pressure P1 at the outlet of the twin screw extruder and the pressure P2 at the inlet of the single screw extruder are controlled at the set values The specific process parameters are shown in Table 1. The head pressure is 10MPa to obtain PET foam sheet. According to GB/T6343-2009, the density of PET foam sheet was tested. The results are shown in Table 1.

Example 2

The raw materials and process are the same as in Example 1, except that the lubricant pentaerythritol stearate is added in the form of masterbatch, the concentration of the masterbatch is 50% by weight, the base of the masterbatch is PET, and the addition amount is 6% of the total weight of PET, totaling pentaerythritol The amount of stearate added is 3 wt% of the total weight of PET.

Example 3

The raw materials and process are the same as in Example 1, except that the chain extender uses epoxy-based chain extender, BADR's ADR 4368, the addition amount is 1wt%; the lubricant uses modified ethylene bisstearic acid amide EBS, heat Decomposition temperature 300℃, added in the form of 50% masterbatch concentration, the addition amount of masterbatch is 10wt% of the total weight of PET, the blowing agent is CO ₂ and cyclopentane, injected from two pumping systems and two gas injection ports, respectively The injection amount of CO ₂ is 1wt% of the total weight of PET, and the injection amount of cyclopentane is 2wt% of the total weight of PET.

Example 4

The raw materials and process are the same as in Example 1, except that the lubricant is oxidized polyethylene wax, which is added in the form of masterbatch, the masterbatch concentration is 20wt%, the matrix is PET, and the addition amount of masterbatch is 10wt% of the total weight of PET. The content of dimethyl siloxane is 2wt% of the total weight of PET, and the heat stabilizer tetra(2,4-di-tert-butylphenyl-4,4'biphenyl) bisphosphite is added, and the added amount is the total amount of PET 0.2wt% of the weight.

Example 5

The raw materials and processes are the same as in Example 1, except that carbon dioxide is used as a blowing agent, and the injection amount of the blowing agent is 1 wt% of the total weight of PET.

Comparative Example 1

The raw materials are the same as in Example 3, except that no lubricant is added, and the extrusion system is a twin-screw extruder in series with a single-screw extruder. The screw diameter and length-diameter ratio are the same as in Example 1, but the twin-screw and single-screw There is no melt pump during the extrusion process. During PET extrusion and foaming, the pressure between the twin-screw extruder and the single-screw extruder is unstable and shows periodic fluctuations, up to 20MPa. By adjusting the speed of the single screw, the pressure will be reduced to 3MPa, resulting in large fluctuations in the head pressure and discharge, which can not be produced normally, and the surface of the obtained PET foamed product is rough.

Comparative Example 2

The raw materials are the same as those in Example 2, except that no lubricant is added. During the extrusion and foaming process, the temperature of each curve section of the extruder is the same as that in Example 2. As a result, the temperature of the PET melt at the outlet is high, and the surface of the extrudate Rough, there is obvious melt fracture phenomenon, the gas escapes, and the apparent density of the PET foamed sheet is 350kg/m ³ .

The thermoplastic polyester extrusion foaming molding method provided by the present invention adds a high temperature resistant lubricant during the foaming process to reduce the polyester macromolecules after the chain extension, as well as the polyester melt and the inner wall of the extruder and the inner wall of the die Friction between them can, on the one hand, reduce the shear heat generation during the extrusion process and effectively control the melt temperature; on the other hand, it can increase the critical shear rate at which melt fracture occurs, avoid melt fracture, and improve the surface quality of the product. The melt pump is also used to regulate the outlet pressure of the twin-screw extruder and the inlet pressure of the single-screw extruder. On the one hand, the relatively low melt pressure at the outlet of the twin-screw extruder is kept below 5 MPa, which is conducive to the smoothness of the foaming agent Injection, while reducing the shear heat of the twin-screw extruder and avoiding the thermal decomposition of the thermoplastic polyester in the twin-screw extruder, laying the foundation for stable extrusion; on the other hand, the high inlet pressure of the single-screw extruder It provides power for the transmission of high-viscosity polyester melt after chain extension, which can ensure that the head pressure reaches the foaming requirements. The thermoplastic polyester extrusion foaming molding method provided by the invention realizes efficient, stable and high-quality production of thermoplastic polyester extrusion foaming molding.

The above embodiments are only specific implementations of the present invention to illustrate the technical solutions of the present invention, rather than limit them, and the scope of protection of the present invention is not limited thereto, although the present invention has been described in detail with reference to the foregoing embodiments It should be noted that those of ordinary skill in the art should understand that any person skilled in the art within the technical scope disclosed by the present invention can still modify the technical solutions described in the foregoing embodiments or can easily think of changes, or Some of the technical features are equivalently replaced; and these modifications, changes, or replacements do not deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims (10)

A thermoplastic polyester extrusion foaming molding method, characterized in that it includes: Adding thermoplastic polyester, lubricant and foaming aid to the twin-screw extruder for melting, the outlet pressure of the twin-screw extruder is 3MPa-10MPa; A physical blowing agent is introduced into the thermoplastic polyester melt in the twin-screw extruder, and after mixing, it is pumped into the single-screw extruder through the melt. The inlet pressure of the single-screw extruder is 15 MPa. ~25MPa; The temperature of the thermoplastic polyester melt containing the physical foaming agent is reduced by the single screw extruder, extruded and foamed through a die, and cooled and shaped to obtain a thermoplastic polyester foamed product. The method according to claim 1, wherein the amount of the lubricant added is 0.5% to 5% of the total weight of the thermoplastic polyester. The method according to claim 1, characterized in that the thermal decomposition temperature of the lubricant is higher than 350 ℃, and the lubricant is selected from organic fatty acid esters, amide compounds, low molecular weight polyethylene wax, low molecular weight oxidation One or more combinations of polyethylene wax and polydimethylsiloxane. The method according to any one of claims 1 to 3, wherein the lubricant is added in the form of a mother particle, and the mother particle includes 10% to 50% of the lubricant by weight. The method according to claim 1, wherein the twin-screw extruder and the single-screw extruder are connected by the melt pump, and the inlet pressure of the melt pump is 3MPa-10MPa , Outlet pressure is 15MPa ~ 20MPa. The method according to claim 1, wherein the foaming aid includes a chain extender, a nucleating agent, an antioxidant, and a heat stabilizer. The method according to claim 6, wherein the chain extender is an acid anhydride compound, and the added amount is 0.2% to 1% of the total weight of the thermoplastic polyester. According to the method of claim 6, the chain extender is a multifunctional epoxy compound, and the amount added is 0.5% to 3% of the total weight of the thermoplastic polyester. The method according to any one of claims 6 to 8, wherein the chain extender is added in the form of a master particle, and the master particle includes 8% to 30% of the chain extender by weight. The method according to claim 6, wherein the physical blowing agent is one or more of carbon dioxide, nitrogen, isobutane, isopentane, cyclopentane, hexane, heptane, and fluorine-containing compounds In this combination, the total addition amount is 1% to 10% of the total weight of the thermoplastic polyester.

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