Polyformaldehyde composition and preparation method thereof

Abstract

The invention provides a polyformaldehyde composition and a preparation method thereof, and the polyformaldehyde composition comprises the following components by weight: 100 parts of polyformaldehyde powder; 0.15 to 1.0 part of an antioxidant; 0.01 to 1.0 part of a formaldehyde absorbent; 0.5 to 3.5 parts of a flow promoter; 0.02 to 1.0 part of a lubricant; the polyformaldehyde powder comprises binary polyformaldehyde and a ternary polyformaldehyde nucleating agent; the weight ratio of the binary copolyformaldehyde to the ternary copolyformaldehyde nucleating agent is (10-1000): 1, and the melt index of the binary copolyformaldehyde is 8.5 g / 10 min to 11.5 g / 10 min; the melt index of the ternary polyformaldehyde nucleating agent is 0.5 g / 10 min to 3.5 g / 10 min, and a comonomer of the ternary polyformaldehyde nucleating agent comprises a monomeric compound with glycidyl ether. The polyformaldehyde composition based on the invention has high crystallinity and high fluidity.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, and in particular to a polyoxymethylene composition and a preparation method thereof. Background Art

[0002] The molecular chain of polyoxymethylene resin is linear in structure, with the advantages of creep resistance, chemical corrosion resistance, high strength and good rigidity, etc. It is widely used in the processing and manufacturing of structural products, lubricating products, household appliances, daily necessities, etc. Polyoxymethylene resin can be divided into homopolyoxymethylene and copolymer polyoxymethylene according to the polymerization method. In the field of polyoxymethylene production, except for a small number of companies producing homopolyoxymethylene, such as DuPont and Asahi Kasei, other production enterprises all adopt copolymer polyoxymethylene production technology.

[0003] Normally, when copolymer formaldehyde enterprises produce products, they often determine the product type and brand according to different melt indexes. The melt index or average molecular weight of polyformaldehyde resin is controlled by adding molecular weight regulators during the polymerization process. Usually, the amount of molecular weight regulator added is the lowest when producing low melt index polyformaldehyde brands, and the amount of molecular weight regulator added is the highest when producing high melt index. Commonly used molecular weight regulators are acetals, such as methylal, butyral, etc. The molecular weight regulator is controlled during the polymerization process to prepare high-flow polyformaldehyde. This method, on the one hand, has a high production cost and requires the addition of more high-purity molecular weight regulators, such as methylal with a purity of 99.99%; on the other hand, adding a large amount of methylal to prepare high-flow polyformaldehyde, another problem brought about in the production process is that when switching from polyformaldehyde resin with a lower melt index to polyformaldehyde resin with high flow, more transition materials are produced in the middle, which increases production costs and operational difficulties.

[0004] The crystallinity of polyoxymethylene resin is generally 65%-75%, and its crystal form is mostly spherulites with a size greater than 150μm. The significant feature of this type of polyoxymethylene resin in the process of processing and application is that it takes a long time for the nucleus to form and grow. In the injection molding process, since the product is generally small in size and the mold has a cooling system, there will be no obvious defects. However, in the extrusion processing applications such as plates, rods and pipes, for plates, rods and pipes with larger thickness and diameter, the use of polyoxymethylene resin with this type of crystal form is prone to the "white core" phenomenon. This "white core" is formed due to the different cooling and crystallization rates of the outer surface and the center of the center during the extrusion process of plates, rods and pipes, which causes the center of the product to shrink, resulting in different densities between the center and the outside. The "white core" phenomenon often causes cracking and brittle fracture of plates, rods and pipes during the secondary precision machining process to prepare precision instrument components, resulting in product damage and waste. In addition, when the polyformaldehyde resin with oversized spherulites is used for injection molding to prepare complex parts or special-shaped parts or thin-walled parts, the amorphous defects or voids in the vicinity of the large spherulites may cause warping and cracking of the products. In order to improve the crystallinity of polyformaldehyde and solve the problems of warping and cracking of its products, domestic and foreign research institutes and production enterprises have carried out a lot of research work. Inorganic nucleating agents such as talcum powder, calcium carbonate, nano-silicon dioxide, etc. can be added, but the compatibility of inorganic nucleating agents with polyformaldehyde resin is poor, the prepared polyformaldehyde crystal morphology is uneven, and the mechanical properties are affected by the type of inorganic nucleating agents, impurity content and particle size, and the performance fluctuations are relatively large; in addition, organic small molecule nucleating agents such as sorbitol compounds, benzoates, organic phosphates, such as sodium benzoate, aluminum benzoate, etc. can also be added, but organic small molecule nucleating agents are easy to migrate and precipitate in polyformaldehyde resin, affecting the processing efficiency and performance of polyformaldehyde products. Therefore, it is of great significance to develop other polyoxymethylene compositions with high melt index and high crystallinity. Summary of the invention

[0005] The main purpose of the present invention is to provide a polyoxymethylene composition and a preparation method thereof, so as to solve the problems of high production cost and high operation difficulty of high-flow polyoxymethylene resin and low crystallinity of polyoxymethylene in the prior art.

[0006] In order to achieve the above object, according to one aspect of the present invention, a polyoxymethylene composition is provided, comprising the following components in parts by weight:

[0007] 100 parts of polyoxymethylene powder;

[0008] Antioxidant 0.15-1.0 part;

[0009] Formaldehyde absorbent 0.01-1.0 part;

[0010] Flow promoter 0.5-3.5 parts;

[0011] Lubricant 0.02-1.0 part;

[0012] The polyoxymethylene powder includes a binary copolymerized polyoxymethylene and a ternary copolymerized polyoxymethylene crystal nucleating agent; the weight ratio of the binary copolymerized polyoxymethylene to the ternary copolymerized polyoxymethylene crystal nucleating agent is (10-1000):1, the melting index of the binary copolymerized polyoxymethylene is 8.5g / 10min-11.5g / 10min; the melting index of the ternary polyoxymethylene crystal nucleating agent is 0.5g / 10min-3.5g / 10min, and the copolymerized monomer of the ternary polyoxymethylene crystal nucleating agent includes a monomer compound having glycidyl ether;

[0013] The flow promoter is shown in Formula I:

[0014]

[0015] Furthermore, the binary copolymer formaldehyde is obtained by copolymerizing a first monomer and a second monomer; the first monomer is selected from one or two of trioxymethylene and tetraoxymethylene, and the second monomer is selected from one or more of ethylene oxide, propylene oxide, dioxolane and dioxetane.

[0016] Furthermore, the ternary copolymer formaldehyde nucleating agent is obtained by copolymerizing a third monomer, a fourth monomer and a monomer compound having a glycidyl ether, the third monomer is selected from one or two of tripolyformaldehyde and tetrapolyformaldehyde, the fourth monomer is selected from one or more of ethylene oxide, propylene oxide, 1,2-pentacyclo ...

[0017] Preferably, the weight ratio of the first monomer to the second monomer is (87.5-97.5):(2.5-7.5), more preferably (94.8-96.8):(3.2-5.8).

[0018] Preferably, the weight ratio of the third monomer, the fourth monomer and the fifth monomer is (92.5-99.5):(0.5-2.5):(0.05-1.5), more preferably (97.5-98):(1.25-1.8):(0.2-0.75).

[0019] Furthermore, the polyoxymethylene powder is prepared by the following steps:

[0020] Step S1, preparing a slurry containing a binary copolymer formaldehyde and a slurry containing a ternary copolymer formaldehyde crystal nucleating agent respectively;

[0021] Step S2, adding the slurry containing binary copolymer formaldehyde and the slurry containing ternary copolymer formaldehyde crystal nucleating agent into alkaline solution and mixing them to obtain a mixed slurry, performing solid-liquid separation on the mixed slurry to obtain a solid mixture, and drying the solid mixture to obtain polyformaldehyde powder.

[0022] Furthermore, the first monomer, the second monomer and the first catalyst are mixed to obtain a first mixture, the first mixture and the first molecular weight regulator are added to a first screw-type polyoxymethylene reactor, and a first polymerization reaction is carried out at 60-100° C., a screw speed of 10-100 r / min, and a pressure of 0.8-1.2 MPa to obtain a slurry containing binary copolymer formaldehyde.

[0023] Furthermore, the third monomer, the fourth monomer, the fifth monomer and the second catalyst are mixed to obtain a second mixture, the second mixture and the second molecular weight regulator are added to a second screw-type polyoxymethylene reactor, and a second polymerization reaction is carried out at 60-100° C., a screw speed of 10-100 r / min, and a pressure of MPa0.8-1.2 MPa to obtain a slurry containing a ternary copolymer formaldehyde nucleating agent.

[0024] Preferably, the first catalyst is selected from one or more of boron trifluoride, boron trifluoride ethyl ether complex, boron trifluoride butyl ether complex, and boron trifluoride tetrahydrofuran complex.

[0025] Preferably, the first molecular weight regulator is selected from one or more of methylal, acetal and butyral.

[0026] More preferably, based on the sum of the weight of the first mixed material and the first molecular weight regulator being 100%, the weight of the first catalyst is 10 ppm to 100 ppm, and the weight of the first molecular weight regulator is 50 ppm to 100 ppm.

[0027] Preferably, the second molecular weight regulator is selected from one or more of methylal, acetal and butyral.

[0028] Preferably, the first catalyst is selected from one or more of boron trifluoride, boron trifluoride ethyl ether complex, boron trifluoride butyl ether complex, and boron trifluoride tetrahydrofuran complex.

[0029] More preferably, based on the sum of the weight of the second mixed material and the second molecular weight regulator being 100%, the weight of the second catalyst is 10 ppm to 100 ppm, and the weight of the second molecular weight regulator is 100 ppm to 500 ppm.

[0030] Furthermore, the alkali solution is an aqueous solution of an alkaline substance, and the alkaline substance is selected from at least one of ethanolamine, diethanolamine, triethanolamine, and methyldiethanolamine.

[0031] Preferably, the content of alkaline substances in the alkali solution is 5% to 15% by weight.

[0032] Furthermore, step S2 also includes sending the mixed slurry into a grinding machine for grinding, and then performing solid-liquid separation on the ground mixed slurry to obtain a solid mixture.

[0033] Furthermore, the drying temperature in step S2 is 90° C. to 150° C. Preferably, the solid content of the mixed slurry is 25% to 75% by weight.

[0034] Furthermore, the particle size of the polyoxymethylene powder is 0.25 mm to 1.25 mm.

[0035] Further, the melt index of the binary copolymer oxymethylene is 10.2 g / 10 min to 11.0 g / 10 min.

[0036] Furthermore, the melt index of the ternary polyoxymethylene crystal nucleating agent is 1.1 g / 10 min to 2.0 g / 10 min.

[0037] Furthermore, the polyoxymethylene composition has a melt index of 15.0 g / 10 min to 25.0 g / 10 min, and an average spherulite diameter of ≦75 μm.

[0038] Furthermore, the antioxidant is selected from one or both of phenolic antioxidants and phosphite antioxidants.

[0039] Preferably, the antioxidant is a combination of triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, N,N-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionyl) hexanediamine and tris(2,4-di-tert-butylphenyl) phosphite in a weight ratio of (1-2):(1-2):(0.2-1); or, the antioxidant is glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, tris(2,4-di-tert-butylphenyl) phosphite in a weight ratio of (1-2):(1-2):(0.2-1). 2~1); or, the antioxidant is a combination of triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, N,N-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionyl) hexanediamine and dioctadecyl pentaerythritol diphosphite in a weight ratio of (1~2):(1~2):(0.2~1); or, the antioxidant is a combination of triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, N,N-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionyl) hexanediamine and bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite in a weight ratio of (1~ 2): (1-2): (0.2-1); or, the antioxidant is a combination of triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate and tris(2,4-di-tert-butylphenyl) phosphite in a weight ratio of (1-2): (1-2): (0.2-1); or, the antioxidant is a combination of triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate and dioctadecyl pentaerythritol diphosphite in a weight ratio of (1-2): (1 ~2):(0.2~1); or, the antioxidant is a combination of triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate and bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite; or, the antioxidant is a combination of triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate and bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite in a weight ratio of (1~2):(1~2):(0.2~1).

[0040] Furthermore, the formaldehyde absorbent is selected from one or more of melamine, melamine derivatives and inorganic porous nanopowder.

[0041] Preferably, the melamine derivative is selected from one or more of hydroxymethyl melamine, melamine aminodiglycol, and melamine aminolauryl alcohol.

[0042] Preferably, the inorganic porous nano powder is selected from one or both of nano molecular sieve and nano diatomaceous earth.

[0043] More preferably, the formaldehyde absorbent is a combination of melamine and methylol melamine in a weight ratio of (1-2): (1-2), or a combination of melamine and melamine aminodiglycol, or a combination of melamine and melamine aminolauryl alcohol, or a combination of melamine and cyclohexyl melamine in a weight ratio of (1-2): (1-2), or a combination of melamine and nanomolecular sieve in a weight ratio of (1-2): (1-2), or a combination of melamine and nanodiatomaceous earth in a weight ratio of (1-2): (1-2), or a combination of melamine, methylol melamine and nanomolecular sieve in a weight ratio of (1-2): (1-2): (1-2), or a combination of melamine, melamine aminodiglycol and nanomolecular sieve in a weight ratio of (1-2): (1-2): (1-2). ~2), or, melamine, melamine aminolauryl alcohol and nanomolecular sieve according to the weight ratio of (1~2):(1~2):(1~2), or, melamine, cyclohexylmelamine and nanomolecular sieve according to the weight ratio of (1~2):(1~2):(1~2), or, melamine, hydroxymethylmelamine and nanodiatomaceous earth according to the weight ratio of (1~2):(1~2):(1~2), or, melamine, melamine aminodiglycol and nanodiatomaceous earth according to the weight ratio of (1~2):(1~2):(1~2), or, melamine, melamine aminolauryl alcohol and nanodiatomaceous earth according to the weight ratio of (1~2):(1~2):(1~2), or, melamine, cyclohexylmelamine and nanodiatomaceous earth according to the weight ratio of (1~2):(1~2):(1~2).

[0044] Furthermore, the lubricant is selected from one or more of N-ethylene bisstearamide, glyceryl monostearate, silicone oil, Fischer-Tropsch wax and PE wax.

[0045] According to another aspect of the present invention, a method for preparing the above polyoxymethylene composition is provided, comprising the following steps: melt-blending and granulating polyoxymethylene powder, an antioxidant, a formaldehyde absorber, a flow promoter and a lubricant at 165° C. to 235° C. to obtain a polyoxymethylene composition.

[0046] By applying the technical scheme of the present invention, a ternary copolymer formaldehyde crystal nucleating agent of a monomer compound having glycidyl ether is used as a nucleating agent and a flow promoter having a special functional group shown in Formula I is used to obtain a polyoxymethylene composition with high crystallinity and high fluidity; the ternary copolymer formaldehyde is used as a nucleating agent, and it has excellent compatibility with the binary copolymer formaldehyde, and the glycidyl ether of the special monomer structure introduced into the ternary copolymer formaldehyde can further enhance its effect with the binary copolymer formaldehyde, improve the compatibility and affinity of the two, and facilitate crystallization to obtain a polyoxymethylene composition with high crystallinity and regular morphology; in addition, the flow promoter having a special functional group can reduce the polyoxymethylene The distance between molecules and the surface tension of polyformaldehyde molecules increase the fluidity of polyformaldehyde, and the special monomer structure glycidyl ether introduced in the ternary copolymer formaldehyde can react with the functional group of the flow promoter, which is beneficial to form a uniform lubricating film on the polyformaldehyde resin, thereby improving the fluidity and uniformity of polyformaldehyde and improving its processing performance; furthermore, a high-flow polyformaldehyde composition can be obtained without the need to additionally introduce a large amount of molecular weight regulator, and the production cost is low. The formaldehyde composition has a high degree of crystallinity, which is beneficial to enhancing the mechanical properties of the material, such as impact strength, bending strength, thermal stability and chemical stability, and reducing the risk of warping and cracking during the processing of the product.

[0047] The polyoxymethylene composition of the present invention has high crystallinity and high fluidity, and has better processing performance and mechanical properties, can improve the mechanical properties of processed products, reduce the risk of warping and cracking during product processing, and improve processing efficiency and product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0049] Figure 1 shows a polarized photograph of the polyoxymethylene composition prepared in Example 3;

[0050] Figure 2 A polarized photograph of the polyoxymethylene composition prepared in Comparative Example 3 is shown. DETAILED DESCRIPTION

[0051] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0052] As described in the background art, the prior art has the problems of high production cost and high operation difficulty of high flow polyoxymethylene resin and low crystallinity of polyoxymethylene.

[0053] In order to solve the above problems, according to one aspect of the present invention, a polyoxymethylene composition is provided, which comprises the following components in parts by weight:

[0054] 100 parts of polyoxymethylene powder;

[0055] Antioxidant 0.15-1.0 part;

[0056] Formaldehyde absorbent 0.01-1.0 part;

[0057] Flow promoter 0.5-3.5 parts;

[0058] Lubricant 0.02-1.0 part;

[0059] The polyoxymethylene powder includes a binary copolymerized polyoxymethylene and a ternary copolymerized polyoxymethylene crystal nucleating agent; the weight ratio of the binary copolymerized polyoxymethylene to the ternary copolymerized polyoxymethylene crystal nucleating agent is (10-1000):1, the melting index of the binary copolymerized polyoxymethylene is 8.5g / 10min-11.5g / 10min; the melting index of the ternary polyoxymethylene crystal nucleating agent is 0.5g / 10min-3.5g / 10min, and the copolymerized monomer of the ternary polyoxymethylene crystal nucleating agent includes a monomer compound having glycidyl ether;

[0060] The flow promoter is shown in Formula I:

[0061]

[0062] Based on the polyoxymethylene composition of the present invention, a ternary copolymer formaldehyde crystal nucleating agent of a monomer compound having glycidyl ether is used as a nucleating agent and a flow promoter having a special functional group as shown in Formula I is used to obtain a polyoxymethylene composition with high crystallinity and high fluidity; the ternary copolymer formaldehyde is used as a nucleating agent, and it has excellent compatibility with the binary copolymer formaldehyde, and the glycidyl ether of the special monomer structure introduced into the ternary copolymer formaldehyde can further enhance its effect with the binary copolymer formaldehyde, improve the compatibility and affinity of the two, and facilitate crystallization to obtain a polyoxymethylene composition with high crystallinity and regular morphology; in addition, the flow promoter having a special functional group can reduce the polyoxymethylene The distance between aldehyde molecules and the surface tension of polyformaldehyde molecules increase the fluidity of polyformaldehyde, and the special monomer structure glycidyl ether introduced in the ternary copolymer formaldehyde can react with the functional group of the flow promoter, which is beneficial to form a uniform lubricating film on the polyformaldehyde resin, thereby improving the fluidity and uniformity of polyformaldehyde and improving its processing performance; furthermore, a high-flow polyformaldehyde composition can be obtained without the need to additionally introduce a large amount of molecular weight regulator, and the production cost is low. The formaldehyde composition has a high degree of crystallinity, which is beneficial to enhancing the mechanical properties of the material, such as impact strength, bending strength, thermal stability and chemical stability, and reducing the risk of warping and cracking during the processing of the product.

[0063] The polyoxymethylene composition of the present invention has high crystallinity and high fluidity, and has better processing performance and mechanical properties, can improve the mechanical properties of processed products, reduce the risk of warping and cracking during product processing, and improve processing efficiency and product quality.

[0064] In some embodiments, the binary copolymer formaldehyde is obtained by copolymerizing a first monomer and a second monomer; the first monomer is selected from one or two of trioxymethylene and tetraoxymethylene, and the second monomer is selected from one or more of ethylene oxide, propylene oxide, dioxolane, and dioxetanes; preferably, the weight ratio of the third monomer, the fourth monomer, and the fifth monomer is (92.5-99.5): (0.5-2.5): (0.05-1.5), and more preferably (97.5-98): (1.25-1.8): (0.2-0.75).

[0065] In some embodiments, the ternary copolymer formaldehyde nucleating agent is obtained by copolymerizing a third monomer, a fourth monomer and a monomer compound having a glycidyl ether, the third monomer is selected from one or two of trioxymethylene and tetraoxymethylene, the fourth monomer is selected from one or more of ethylene oxide, propylene oxide, dioxolane, and dioxolane, the monomer compound having a glycidyl ether is selected from one or more of phenyl glycidyl ether, ethylene glycol diglycidyl ether, glycerol diglycidyl ether, glycerol propoxy triglycidyl ether, and glycerol triglycidyl ether. The ternary copolymer formaldehyde nucleating agent introduces the above-mentioned third monomer, and the presence of this nucleating agent can To promote the crystallization process of binary copolymer formaldehyde, form a smaller and more uniform spherulite structure, with small amorphous defects or voids, reduce stress concentration during processing and molding, improve the mechanical strength of the product, and reduce the tendency of warping, cracking and the like to occur during product processing; preferably, the weight ratio of the third monomer, the fourth monomer and the fifth monomer is (92.5-99.5): (0.5-2.5): (0.05-1.5), and more preferably (97.5-98): (1.5-1.8): (0.5-0.7), so as to obtain a polyoxymethylene resin with a higher crystallinity, uniform and small-sized spherulite structure.

[0066] In some embodiments, polyoxymethylene powder is prepared by the following steps:

[0067] Step S1, preparing a slurry containing a binary copolymer formaldehyde and a slurry containing a ternary copolymer formaldehyde crystal nucleating agent respectively;

[0068] Step S2, adding the slurry containing binary copolymer formaldehyde and the slurry containing ternary copolymer formaldehyde crystal nucleating agent into alkaline solution and mixing them to obtain a mixed slurry, performing solid-liquid separation on the mixed slurry to obtain a solid mixture, and drying the solid mixture to obtain polyformaldehyde powder.

[0069] In the technical scheme of the embodiment of the present application, polyoxymethylene powder containing binary copolymer formaldehyde and ternary copolymer formaldehyde nucleus agent is prepared by mixing a slurry containing binary copolymer formaldehyde and a slurry containing ternary copolymer formaldehyde nucleus agent and performing solid-liquid separation, thereby improving the uniformity of dispersion between the binary copolymer formaldehyde and the ternary copolymer formaldehyde nucleus agent, so that the role of the nucleus agent can be more effectively exerted during crystallization to form a spherulite structure with high crystallinity, smaller size and more uniformity; in addition, by passivating the residual catalytic activation center with alkali solution and removing the residual monomer by reaction, it is beneficial to form binary copolymer formaldehyde and ternary copolymer formaldehyde nucleus agent with uniform molecular weight distribution and controllable performance, respectively, which is more conducive to controlling the formaldehyde composition with high crystallinity and high fluidity.

[0070] In some embodiments, a first monomer, a second monomer and a first catalyst are mixed to obtain a first mixture, the first mixture and a first molecular weight regulator are added to a first screw-type polyoxymethylene reactor, and a first polymerization reaction is carried out at 60-100°C, a screw speed of 10-100r / min, and a pressure of 0.8-1.2MPa to obtain a slurry containing binary copolymer formaldehyde. In the technical scheme of the embodiment of the present application, the binary copolymer formaldehyde is prepared by the above process, which is conducive to the full reaction of the raw materials; preferably, the first molecular weight regulator is selected from one or more of methylal, acetal, and butyral; preferably, the first catalyst is selected from one or more of boron trifluoride, boron trifluoride ether complex, boron trifluoride butyl ether complex, and boron trifluoride tetrahydrofuran complex; more preferably, the weight of the first catalyst is 10ppm-100ppm, and the weight of the first molecular weight regulator is 50ppm-100ppm, based on the sum of the weight of the first mixture and the first molecular weight regulator as 100%.

[0071] In some embodiments, a third monomer, a fourth monomer, a fifth monomer and a second catalyst are mixed to obtain a second mixture, the second mixture and a second molecular weight regulator are added to a second screw-type polyoxymethylene reactor, and a second polymerization reaction is carried out at 60-100°C, a screw speed of 10-100 r / min, and a pressure of MPa0.8-1.2 MPa to obtain a slurry containing a ternary copolymer formaldehyde nucleating agent. The preparation of the ternary copolymer formaldehyde nucleating agent by the above process is conducive to the full reaction of the raw materials; preferably, the second molecular weight regulator is selected from one or more of methylal, acetal, and butyral; preferably, the first catalyst is selected from one or more of boron trifluoride, boron trifluoride ether complex, boron trifluoride butyl ether complex, and boron trifluoride tetrahydrofuran complex; more preferably, the weight of the second catalyst is 10ppm-100ppm, and the weight of the second molecular weight regulator is 100ppm-500ppm, based on the sum of the weight of the second mixture and the second molecular weight regulator as 100%.

[0072] In some embodiments, the alkali solution is an aqueous solution of an alkaline substance, and the alkaline substance is selected from at least one of ethanolamine, diethanolamine, triethanolamine, and methyldiethanolamine, so as to quickly passivate the residual catalytic activation centers and react to remove the residual monomers; preferably, the content of the alkaline substance in the alkali solution is 5% to 15% by weight.

[0073] In some embodiments, step S2 also includes sending the mixed slurry into a grinder for grinding, and then performing solid-liquid separation on the ground mixed slurry to obtain a solid mixture. In the technical scheme of the embodiment of the present application, by sending the mixed slurry into a grinder for grinding, the polymer particles can be further refined and the particle size can be reduced, so that the particle size distribution of the polyformaldehyde powder is more uniform and the microstructure is more delicate. In the grinding process, the action of mechanical force helps to destroy the polymer aggregates, improve the dispersibility of the polymer, and help to form spherulites with more uniform particle size distribution and smaller particles, thereby optimizing the microstructure of the polyformaldehyde powder and improving the mechanical properties of the product, such as improving impact strength, flexural strength and modulus. At the same time, polyformaldehyde powder with smaller particle size and more uniform distribution exhibits better fluidity in molding processes such as injection molding and extrusion, and can reduce the risk of stress cracking during the molding process and improve its processing performance. Preferably, the solid content in the mixed slurry is 25% to 75% by weight, so as to obtain higher dispersibility and dispersion efficiency.

[0074] In some embodiments, the drying temperature in step S2 is 90° C. to 150° C. to quickly remove moisture to obtain dried polyoxymethylene powder.

[0075] In some embodiments, the particle size of the polyformaldehyde powder is 0.25 mm to 1.25 mm. Using polyformaldehyde powder of this size as raw material is conducive to obtaining more uniform particle size distribution and smaller spherulites, thereby improving the impact strength, bending strength and modulus of the material. The above-mentioned small-particle polyformaldehyde powder has good fluidity under processing conditions, reduces the pressure and shear stress during the processing and molding process, and can improve processing efficiency and product quality.

[0076] In some embodiments, in order to obtain a polyoxymethylene composition with higher crystallinity and better processability, the melt index of the binary copolymerized oxymethylene is 10.2 g / 10 min to 11.0 g / 10 min.

[0077] In some embodiments, in order to obtain a polyoxymethylene composition with higher crystallinity and fluidity, the melt index of the ternary polyoxymethylene crystal nucleating agent is 1.1 g / 10 min to 2.0 g / 10 min.

[0078] In some embodiments, the melt index of the polyoxymethylene composition is 15.0 g / 10 min to 25.0 g / 10 min, and the average diameter of the spherulites is ≦75 μm. The above-mentioned polyoxymethylene composition has high mechanical strength and processing performance, exhibits high fluidity in injection molding, extrusion and other processes, and is beneficial to reducing the risks of warping and cracking during product processing.

[0079] In some embodiments, the antioxidant is selected from one or two of phenolic antioxidants and phosphite antioxidants; preferably, the antioxidant is a combination of triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, N,N-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionyl) hexanediamine and tris(2,4-di-tert-butylphenyl) phosphite in a weight ratio of (1 to 2): (1 to 2): (0.2 to 1); or, the antioxidant is glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, tris(2,4-di-tert-butylphenyl) phosphite in a weight ratio of (1 to 2): (1 to 2): (0.2 to 1). ~2):(1~2):(0.2~1); or, the antioxidant is a combination of triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, N,N-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionyl) hexanediamine and dioctadecyl pentaerythritol diphosphite in a weight ratio of (1~2):(1~2):(0.2~1); or, the antioxidant is a combination of triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, N,N-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionyl) hexanediamine and bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite in a weight ratio of (1~2):(1 ~2):(0.2~1) combination; or, the antioxidant is a combination of triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate and tris(2,4-di-tert-butylphenyl) phosphite in a weight ratio of (1~2):(1~2):(0.2~1); or, the antioxidant is a combination of triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate and dioctadecyl pentaerythritol diphosphite in a weight ratio of (1~2):(1~2):(0.2~1); or, the antioxidant is triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate and dioctadecyl pentaerythritol diphosphite in a weight ratio of (1~2):(1~2):(0.2~1). A combination of glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate and bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite; or, the antioxidant is a combination of triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate and bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite in a weight ratio of (1-2):(1-2):(0.2-1). By compounding the phenolic antioxidant and the phosphite antioxidant in the above weight ratio, a better antioxidant effect can be achieved.

[0080] In the present application, formaldehyde absorbent refers to a compound having a formaldehyde reaction or absorption function. In some embodiments, the formaldehyde absorbent is selected from one or more of melamine, melamine derivatives and inorganic porous nanopowders; preferably, the melamine derivatives are selected from one or more of hydroxymethyl melamine, melamine aminodiglycol, melamine aminolauryl alcohol and cyclohexyl melamine; preferably, the inorganic porous nanopowder is selected from one or two of nano molecular sieves and nano diatomaceous earth; more preferably, the formaldehyde absorbent is melamine and hydroxymethyl melamine in a weight ratio of 1:1. A combination of melamine and melamine aminodiglycol in a weight ratio of (1-2): (1-2), or a combination of melamine and melamine aminolauryl alcohol in a weight ratio of (1-2): (1-2), or a combination of melamine and cyclohexylmelamine in a weight ratio of (1-2): (1-2), or a combination of melamine and nanomolecular sieve in a weight ratio of (1-2): (1-2), or a combination of melamine and nanodiatomaceous earth in a weight ratio of (1-2): (1-2), or a combination of melamine, hydroxymethylmelamine and nanomolecular sieve in a weight ratio of (1-2) :(1~2):(1~2) combination, or, melamine, melamine aminodiglycol and nanomolecular sieve according to the weight ratio of (1~2):(1~2):(1~2), or, melamine, melamine aminolauryl alcohol and nanomolecular sieve according to the weight ratio of (1~2):(1~2):(1~2), or, melamine, cyclohexylmelamine and nanomolecular sieve according to the weight ratio of (1~2):(1~2):(1~2), or, melamine, hydroxymethylmelamine and nanodiatomaceous earth according to the weight ratio of (1~2):(1~2 ):(1-2), or, melamine, melamine aminodiglycol and nano-diatomaceous earth in a weight ratio of (1-2):(1-2):(1-2), or, melamine, melamine aminolauryl alcohol and nano-diatomaceous earth in a weight ratio of (1-2):(1-2):(1-2), or, melamine, cyclohexylmelamine and nano-diatomaceous earth in a weight ratio of (1-2):(1-2):(1-2). By compounding the formaldehyde absorbent with formaldehyde reaction and absorption function under the above weight ratio, a better formaldehyde absorption effect can be achieved.

[0081] In some embodiments, the lubricant is selected from one or more of N-ethylene bisstearamide, glyceryl monostearate, silicone oil, Fischer-Tropsch wax, and PE wax.

[0082] According to another aspect of the present invention, a method for preparing the above polyoxymethylene composition is provided, comprising the following steps: melt-blending and granulating polyoxymethylene powder, an antioxidant, a formaldehyde absorbent, a flow promoter and a lubricant at 165° C. to 235° C. to obtain a polyoxymethylene composition. The polyoxymethylene composition prepared by the polyoxymethylene composition of the present invention can be used to prepare plates, rods and special-shaped products with complex structures by injection molding through an extrusion process. The preparation of raw materials and products is relatively simple, easy to industrialize, low in cost, and has broad application prospects.

[0083] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0084] Example 1

[0085] Step 1: preparing a slurry containing binary copolymer formaldehyde and a slurry containing a ternary copolymer formaldehyde crystal nucleating agent:

[0086] Step 1.1, 95.5 parts of the first monomer trioxymethylene, 4.5 parts of the second monomer dioxolane, and the first catalyst boron trifluoride ether complex premixer are mixed to obtain a first mixed material, and then the first mixed material and the first molecular weight regulator methylal are added into a first screw type polyoxymethylene reactor, and a first polymerization reaction is carried out at 85° C., a screw speed of 35 r / min, and a pressure of 1.0 MPa to obtain a slurry containing binary copolymer formaldehyde; wherein the slurry containing binary copolymer formaldehyde is solid-liquid separated and dried to obtain binary copolymer formaldehyde, and the melt index thereof is 10.2 g / 10 min; wherein, based on the sum of the weight of the first mixed material and the first molecular weight regulator being 100%, the weight of the first catalyst is 45 ppm, and the weight of the first molecular weight regulator is 350 ppm;

[0087] Step 1.2, adding 98.0 parts of the third monomer trimolecular weight, 1.5 parts of the fourth monomer dioxolane, 0.5 parts of the fifth monomer ethylene glycol diglycidyl ether and the second catalyst boron trifluoride ether complex into a premixer and mixing to obtain a second mixed material, then adding the second mixed material and the second molecular weight regulator methylal into a second screw type polyoxymethylene reactor, and performing a second polymerization reaction at 85°C, a screw speed of 35r / min, and a pressure of 1.0MPa to obtain a slurry containing a ternary copolymer formaldehyde nucleating agent; wherein, the slurry containing the ternary copolymer formaldehyde nucleating agent is solid-liquid separated and dried to obtain a ternary copolymer formaldehyde nucleating agent, and the melt index thereof is 2.0g / 10mim; wherein, based on the sum of the weight of the second mixed material and the second molecular weight regulator as 100%, the weight of the second catalyst is 40ppm, and the weight of the second molecular weight regulator is 150ppm.

[0088] Step 2: preparing polyoxymethylene powder:

[0089] The slurry containing binary copolymer formaldehyde prepared in step 1.1 and the slurry containing ternary copolymer formaldehyde nucleating agent prepared in step 1.2 are placed in a homogenizing tank containing an ethanolamine aqueous solution (the content of ethanolamine in the ethanolamine aqueous solution is 10% by weight) at a weight ratio of binary copolymer formaldehyde to ternary copolymer formaldehyde nucleating agent of 98.5:1.5, and mixed evenly to obtain a mixed slurry, and the mixed slurry is sent to a grinding mill for grinding to obtain a mixed slurry with an average particle size of 0.6 mm (the solid content in the mixed slurry is 50%), and then the ground mixed slurry is centrifugally dehydrated and dried to obtain polyformaldehyde powder; wherein the drying temperature is 125°C.

[0090] Step 3, preparing a polyoxymethylene composition:

[0091] 100 parts of polyoxymethylene powder, 0.52 parts of antioxidant, 0.5 parts of formaldehyde absorbent, 1.5 parts of flow promoter and 0.25 parts of lubricant N, N-ethylene bisstearamide are placed in a kneading and granulating unit, melt-blended and granulated at 200°C and a screw speed of 450 r / min to obtain a polyoxymethylene composition; wherein the antioxidant is composed of triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, N, N-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionyl) hexanediamine and tris(2,4-di-tert-butylphenyl) phosphite in a weight ratio of 1.5:1.5:0.5, the formaldehyde absorbent is composed of melamine and hydroxymethyl melamine in a weight ratio of 1:1, the melt index of the polyoxymethylene composition is 17.3 g / 10 min, and the average diameter of the spherulites is 60 μm.

[0092] Example 2

[0093] Step 1: preparing a slurry containing binary copolymer formaldehyde and a slurry containing a ternary copolymer formaldehyde crystal nucleating agent:

[0094] Step 1.1, 94.8 parts of the first monomer trioxymethylene, 5.2 parts of the second monomer dioxolane, and the first catalyst boron trifluoride premixer are mixed to obtain a first mixed material, and then the first mixed material and the first molecular weight regulator methylal are added into a first screw type polyoxymethylene reactor, and a first polymerization reaction is carried out at 85° C., a screw speed of 35 r / min, and a pressure of 1.0 MPa to obtain a slurry containing binary copolymer formaldehyde; wherein the slurry containing binary copolymer formaldehyde is solid-liquid separated and dried to obtain binary copolymer formaldehyde, and the melt index thereof is 10.8 g / 10 min; wherein, based on the sum of the weight of the first mixed material and the first molecular weight regulator being 100%, the weight of the first catalyst is 40 ppm, and the weight of the first molecular weight regulator is 380 ppm;

[0095] Step 1.2, adding 98.0 parts of the third monomer trimolecular weight, 1.25 parts of the fourth monomer ethylene oxide, 0.75 parts of the fifth monomer ethylene glycol diglycidyl ether and the second catalyst boron trifluoride into a premixer and mixing to obtain a second mixture, then adding the second mixture and the second molecular weight regulator methylal into a second screw type polyoxymethylene reactor, and performing a second polymerization reaction at 85°C, a screw speed of 40r / min, and a pressure of 1.0MPa to obtain a slurry containing a ternary copolymer formaldehyde nucleating agent; wherein, the slurry containing the ternary copolymer formaldehyde nucleating agent is solid-liquid separated and dried to obtain a ternary copolymer formaldehyde nucleating agent, and its melt index is 1.8g / 10mim; wherein, based on the sum of the weight of the second mixture and the second molecular weight regulator as 100%, the weight of the second catalyst is 38ppm, and the weight of the second molecular weight regulator is 160ppm.

[0096] Step 2: preparing polyoxymethylene powder:

[0097] The slurry containing binary copolymer formaldehyde prepared in step 1.1 and the slurry containing ternary copolymer formaldehyde nucleating agent prepared in step 1.2 are placed in a homogenizing tank containing an ethanolamine aqueous solution (the content of ethanolamine in the ethanolamine aqueous solution is 10% by weight) at a weight ratio of binary copolymer formaldehyde to ternary copolymer formaldehyde nucleating agent of 99:1, and mixed evenly to obtain a mixed slurry, and the mixed slurry is sent to a grinding mill for grinding to obtain a mixed slurry with an average particle size of 0.6 mm (the solid content in the mixed slurry is 50%), and then the ground mixed slurry is centrifugally dehydrated and dried to obtain polyformaldehyde powder; wherein the drying temperature is 120°C.

[0098] Step 3, preparing a polyoxymethylene composition:

[0099] 100 parts of polyoxymethylene powder, 0.48 parts of antioxidant, 0.45 parts of formaldehyde absorbent, 2.0 parts of flow promoter and 0.35 parts of lubricant glyceryl monostearate are placed in a kneading and granulating unit, melt-blended and granulated at 200°C and a screw speed of 450 r / min to obtain a polyoxymethylene composition; wherein the antioxidant is composed of triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, and tris(2,4-di-tert-butylphenyl) phosphite in a weight ratio of 1:2:0.5, the formaldehyde absorbent is composed of melamine / nano diatomaceous earth in a weight ratio of 1:2, the melt index of the polyoxymethylene composition is 18.6 g / 10 min, and the average diameter of the spherulites is 52 μm.

[0100] Example 3

[0101] Step 1: preparing a slurry containing binary copolymer formaldehyde and a slurry containing a ternary copolymer formaldehyde crystal nucleating agent:

[0102] Step 1.1, 96.2 parts of the first monomer trioxymethylene, 3.8 parts of the second monomer dioxolane, and the first catalyst boron trifluoride tetrahydrofuran complex premixer are mixed to obtain a first mixed material, and then the first mixed material and the first molecular weight regulator methylal are added to a first screw type polyoxymethylene reactor, and a first polymerization reaction is carried out at 85° C., a screw speed of 35 r / min, and a pressure of 1.0 MPa to obtain a slurry containing binary copolymer formaldehyde; wherein the slurry containing binary copolymer formaldehyde is separated from the solid and liquid and dried to obtain a binary copolymer formaldehyde, and the melt index thereof is 11.0 g / 10 min; wherein, based on the sum of the weight of the first mixed material and the first molecular weight regulator being 100%, the weight of the first catalyst is 50 ppm, and the weight of the first molecular weight regulator is 390 ppm;

[0103] Step 1.2, adding 97.5 parts of the third monomer trioxymethylene, 1.8 parts of the fourth monomer dioxane, 0.7 parts of the fifth monomer glycerol propoxy triglycidyl ether and the second catalyst boron trifluoride tetrahydrofuran complex into a premixer and mixing to obtain a second mixed material, then adding the second mixed material and the second molecular weight regulator methylal into a second screw type polyoxymethylene reactor, and performing a second polymerization reaction at 85°C, a screw speed of 40r / min, and a pressure of 1.0MPa to obtain a slurry containing a ternary copolymer formaldehyde nucleating agent; wherein, the slurry containing the ternary copolymer formaldehyde nucleating agent is solid-liquid separated and dried to obtain a ternary copolymer formaldehyde nucleating agent, and the melt index is 1.6g / 10mim; wherein, based on the sum of the weight of the second mixed material and the second molecular weight regulator as 100%, the weight of the second catalyst is 35ppm, and the weight of the second molecular weight regulator is 170ppm.

[0104] Step 2: preparing polyoxymethylene powder:

[0105] The slurry containing binary copolymer formaldehyde prepared in step 1.1 and the slurry containing ternary copolymer formaldehyde nucleating agent prepared in step 1.2 are placed in a homogenizing tank containing an ethanolamine aqueous solution (the content of ethanolamine in the ethanolamine aqueous solution is 10% by weight) at a weight ratio of binary copolymer formaldehyde to ternary copolymer formaldehyde nucleating agent of 99.5:0.5, and mixed evenly to obtain a mixed slurry, and the mixed slurry is sent to a grinding mill for grinding to obtain a mixed slurry with an average particle size of 0.6 mm (the solid content in the mixed slurry is 50%), and then the ground mixed slurry is centrifugally dehydrated and dried to obtain polyformaldehyde powder; wherein the drying temperature is 123°C.

[0106] Step 3, preparing a polyoxymethylene composition:

[0107] 100 parts of polyoxymethylene powder, 0.40 parts of antioxidant, 0.45 parts of formaldehyde absorbent, 1.0 parts of flow promoter and 0.45 parts of lubricant Fischer-Tropsch wax are placed in a kneading and granulating unit, melt-blended and granulated at 200° C. and a screw speed of 450 r / min to obtain a polyoxymethylene composition; wherein the antioxidant is composed of triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, N,N-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionyl) hexanediamine and dioctadecyl pentaerythritol diphosphite in a weight ratio of 2:1:0.5, the formaldehyde absorbent is composed of melamine, hydroxymethyl melamine and nano-diatomaceous earth in a weight ratio of 1:1:2, the melt index of the polyoxymethylene composition is 16.3 g / 10 min, and the average diameter of the spherulites is 48 μm.

[0108] Example 4

[0109] Step 1: preparing a slurry containing binary copolymer formaldehyde and a slurry containing a ternary copolymer formaldehyde crystal nucleating agent:

[0110] Step 1.1, 96.8 parts of the first monomer trioxymethylene, 3.2 parts of the second monomer dioxolane, and the first catalyst boron trifluoride ether complex premixer are mixed to obtain a first mixed material, and then the first mixed material and the first molecular weight regulator methylal are added into a first screw type polyoxymethylene reactor, and a first polymerization reaction is carried out at 85° C., a screw speed of 35 r / min, and a pressure of 1.0 MPa to obtain a slurry containing binary copolymer formaldehyde; wherein the slurry containing binary copolymer formaldehyde is separated from the solid and liquid and dried to obtain a binary copolymer formaldehyde, and the melt index thereof is 10.4 g / 10 min; wherein, based on the sum of the weight of the first mixed material and the first molecular weight regulator being 100%, the weight of the first catalyst is 42 ppm, and the weight of the first molecular weight regulator is 370 ppm;

[0111] Step 1.2, adding 97.8 parts of the third monomer tripolyformaldehyde, 1.8 parts of the fourth monomer dioxane, 0.4 parts of the fifth monomer glycerol propoxy triglycidyl ether and the second catalyst boron trifluoride ether complex into a premixer and mixing to obtain a second mixture, then adding the second mixture and the second molecular weight regulator methylal into a second screw type polyformaldehyde reactor, at 85°C, a screw speed of 35r / min, and a pressure of 1.0MPa, a second polymerization reaction is carried out to obtain a slurry containing a ternary copolymer formaldehyde nucleating agent; wherein, the slurry containing the ternary copolymer formaldehyde nucleating agent is solid-liquid separated and dried to obtain a ternary copolymer formaldehyde nucleating agent, and its melt index is 1.3g / 10min; wherein, based on the sum of the weight of the second mixture and the second molecular weight regulator as 100%, the weight of the second catalyst is 36ppmppm, and the weight of the second molecular weight regulator is 165ppm.

[0112] Step 2: preparing polyoxymethylene powder:

[0113] The slurry containing binary copolymer formaldehyde prepared in step 1.1 and the slurry containing ternary copolymer formaldehyde nucleating agent prepared in step 1.2 are placed in a homogenizing tank containing an ethanolamine aqueous solution (the content of ethanolamine in the ethanolamine aqueous solution is 10% by weight) at a weight ratio of binary copolymer formaldehyde to ternary copolymer formaldehyde nucleating agent of 99.75:0.25, and mixed evenly to obtain a mixed slurry, and the mixed slurry is sent to a grinding mill for grinding to obtain a mixed slurry with an average particle size of 0.6 mm (the solid content in the mixed slurry is 50%), and then the ground mixed slurry is centrifugally dehydrated and dried to obtain polyformaldehyde powder; wherein the drying temperature is 124°C.

[0114] Step 3, preparing a polyoxymethylene composition:

[0115] 100 parts of polyoxymethylene powder, 0.45 parts of antioxidant, 0.36 parts of formaldehyde absorbent, 0.75 parts of flow promoter shown in formula I and 0.40 parts and 0.25 parts of lubricant PE wax are placed in a kneading and granulating unit, melt-blended and granulated at 200° C. and a screw speed of 450 r / min to obtain a polyoxymethylene composition; wherein the antioxidant is composed of triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, and tris(2,4-di-tert-butylphenyl) phosphite in a weight ratio of 1:2:0.5, the formaldehyde absorbent is composed of melamine and hydroxymethyl melamine in a weight ratio of 1:1, the melt index of the polyoxymethylene composition is 15.8 g / 10 min, and the average diameter of the spherulites is 63 μm.

[0116]

[0117] Example 5

[0118] Step 1: preparing a slurry containing binary copolymer formaldehyde and a slurry containing a ternary copolymer formaldehyde crystal nucleating agent:

[0119] Step 1.1, 96.5 parts of the first monomer trioxymethylene, 3.5 parts of the second monomer dioxolane, and the first catalyst boron trifluoride butyl ether complex premixer are mixed to obtain a first mixed material, and then the first mixed material and the first molecular weight regulator methylal are added to a first screw type polyoxymethylene reactor, and a first polymerization reaction is carried out at 85° C., a screw speed of 35 r / min, and a pressure of 1.0 MPa to obtain a slurry containing binary copolymer formaldehyde; wherein the slurry containing binary copolymer formaldehyde is solid-liquid separated and dried to obtain a binary copolymer formaldehyde, and the melt index thereof is 10.6 g / 10 min; wherein, based on the sum of the weight of the first mixed material and the first molecular weight regulator being 100%, the weight of the first catalyst is 40 ppm, and the weight of the first molecular weight regulator is 380 ppm;

[0120] Step 1.2, adding 98.0 parts of the third monomer trimolecular weight, 1.8 parts of the fourth monomer dioxolane, 0.2 parts of the fifth monomer glycerol propoxy triglycidyl ether and the second catalyst boron trifluoride butyl ether complex into a premixer and mixing to obtain a second mixed material, then adding the second mixed material and the second molecular weight regulator methylal into a second screw type polyoxymethylene reactor, and performing a second polymerization reaction at 85° C., a screw speed of 35 r / min, and a pressure of 1.0 MPa to obtain a slurry containing a ternary copolymer formaldehyde nucleating agent; wherein, the slurry containing the ternary copolymer formaldehyde nucleating agent is solid-liquid separated and dried to obtain a ternary copolymer formaldehyde nucleating agent, and the melt index thereof is 1.1 g / 10 min; wherein, based on the sum of the weight of the second mixed material and the second molecular weight regulator as 100%, the weight of the second catalyst is 32 ppm, and the weight of the second molecular weight regulator is 155 ppm.

[0121] Step 2: preparing polyoxymethylene powder:

[0122] The slurry containing binary copolymer formaldehyde prepared in step 1.1 and the slurry containing ternary copolymer formaldehyde nucleating agent prepared in step 1.2 are discharged into a homogenizing tank containing an ethanolamine aqueous solution (the content of ethanolamine in the ethanolamine aqueous solution is 10% by weight) at a weight ratio of binary copolymer formaldehyde to ternary copolymer formaldehyde nucleating agent of 99.5:0.5, and mixed evenly to obtain a mixed slurry, and the mixed slurry is sent to a grinding mill for grinding to obtain a mixed slurry with an average particle size of 0.6 mm (the solid content in the mixed slurry is 50%), and then the ground mixed slurry is centrifugally dehydrated and dried to obtain polyformaldehyde powder; wherein the drying temperature is 125°C.

[0123] Step 3, preparing a polyoxymethylene composition:

[0124] 100 parts of polyoxymethylene powder, 0.54 parts of antioxidant, 0.42 parts of formaldehyde absorbent, 3.0 parts of flow promoter and 0.5 parts of ethylene bisstearamide are placed in a kneading and granulating unit, melt-blended and granulated at 200° C. and a screw speed of 450 r / min to obtain a polyoxymethylene composition; wherein the antioxidant is composed of triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, and bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite in a weight ratio of 1:1:1, the formaldehyde absorbent is composed of melamine, hydroxymethyl melamine, and nano-diatomaceous earth in a weight ratio of 1:2:1, the melt index of the polyoxymethylene composition is 23.2 g / 10 min, and the average diameter of the spherulites is 56 μm.

[0125] Comparative Example 1

[0126] The only difference between it and Example 5 is that the rheology promoter represented by Formula I is not added.

[0127] Comparative Example 2

[0128] The only difference between this embodiment and Example 5 is that the slurry containing the ternary copolymer formaldehyde crystal nucleating agent is not prepared in step 1. The specific steps are as follows:

[0129] Step 1: preparing a slurry containing binary copolymer formaldehyde:

[0130] Step 1.1, 96.5 parts of the first monomer trioxymethylene, 3.5 parts of the second monomer dioxolane, and the first catalyst boron trifluoride butyl ether complex premixer are mixed to obtain a first mixture, and then the first mixture and the first molecular weight regulator methylal are added into a first screw type polyoxymethylene reactor, and a first polymerization reaction is carried out at 85° C., a screw speed of 35 r / min, and a pressure of 1.0 MPa to obtain a slurry containing binary copolymer formaldehyde; wherein the slurry containing binary copolymer formaldehyde is separated from the solid and liquid and dried to obtain a binary copolymer formaldehyde, and its melt index is 10.6 g / 10 min; wherein, based on the sum of the weight of the first mixture and the first molecular weight regulator as 100%, the weight of the first catalyst is 40 ppm, and the weight of the first molecular weight regulator is 380 ppm.

[0131] Step 2: preparing polyoxymethylene powder:

[0132] The binary copolymer formaldehyde slurry prepared in step 1.1 is discharged into a homogenizing tank containing an ethanolamine aqueous solution (the ethanolamine content in the ethanolamine aqueous solution is 10% by weight) and mixed evenly to obtain a mixed slurry, and the mixed slurry is sent to a grinder for grinding to obtain a mixed slurry with an average particle size of 0.6 mm (the solid content in the mixed slurry is 50%), and then the ground mixed slurry is centrifugally dehydrated and dried to obtain polyformaldehyde powder; wherein the drying temperature is 125°C.

[0133] Step 3, preparing a polyoxymethylene composition:

[0134] 100 parts of polyformaldehyde powder, 0.54 parts of antioxidant, 0.42 parts of formaldehyde absorbent, 3.0 parts of flow promoter and 0.5 parts of lubricant ethylene bisstearamide are placed in a kneading and granulating unit, melt-blended and granulated at 200° C. and a screw speed of 450 r / min to obtain a polyformaldehyde composition; wherein the antioxidant is composed of triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, and bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite in a weight ratio of 1:1:1, and the formaldehyde absorbent is composed of melamine, hydroxymethyl melamine, and nano-diatomaceous earth in a weight ratio of 1:2:1.

[0135] Comparative Example 3

[0136] The only difference between this embodiment and Example 5 is that the rheology promoter shown in Formula I is not added, and the slurry containing the ternary copolymer formaldehyde crystal nucleating agent is not prepared in step 1. The specific steps are as follows:

[0137] Step 1: preparing a slurry containing binary copolymer formaldehyde:

[0138] Step 1.1, 96.5 parts of the first monomer trioxymethylene, 3.5 parts of the second monomer dioxolane, and the first catalyst boron trifluoride butyl ether complex premixer are mixed to obtain a first mixture, and then the first mixture and the first molecular weight regulator methylal are added into a first screw type polyoxymethylene reactor, and a first polymerization reaction is carried out at 85° C., a screw speed of 35 r / min, and a pressure of 1.0 MPa to obtain a slurry containing binary copolymer formaldehyde; wherein the slurry containing binary copolymer formaldehyde is separated from the solid and liquid and dried to obtain a binary copolymer formaldehyde, and its melt index is 10.6 g / 10 min; wherein, based on the sum of the weight of the first mixture and the first molecular weight regulator as 100%, the weight of the first catalyst is 40 ppm, and the weight of the first molecular weight regulator is 380 ppm.

[0139] Step 2: preparing polyoxymethylene powder:

[0140] The binary copolymer formaldehyde slurry prepared in step 1.1 is discharged into a homogenizing tank containing an ethanolamine aqueous solution (the ethanolamine content in the ethanolamine aqueous solution is 10% by weight) and mixed evenly to obtain a mixed slurry, and the mixed slurry is sent to a grinder for grinding to obtain a mixed slurry with an average particle size of 0.6 mm (the solid content in the mixed slurry is 50%), and then the ground mixed slurry is centrifugally dehydrated and dried to obtain polyformaldehyde powder; wherein the drying temperature is 125°C.

[0141] Step 3, preparing a polyoxymethylene composition:

[0142] 100 parts of polyformaldehyde powder, 0.54 parts of antioxidant, 0.42 parts of formaldehyde absorbent, 3.0 parts of flow promoter and 0.5 parts of lubricant ethylene bisstearamide are placed in a kneading and granulating unit, melt-blended and granulated at 200° C. and a screw speed of 450 r / min to obtain a polyformaldehyde composition; wherein the antioxidant is composed of triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, and bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite in a weight ratio of 1:1:1, and the formaldehyde absorbent is composed of melamine, hydroxymethyl melamine, and nano-diatomaceous earth in a weight ratio of 1:2:1.

[0143] Comparative Example 4

[0144] The only difference between it and Example 5 is that the fifth monomer, glycerol propoxy triglycidyl ether, is replaced by dioxane.

[0145] Performance test of polyoxymethylene composition:

[0146] (1) Melt index test: GB / T3682-2018 is used for melt index test; the test temperature is 190°C and the load is 2.16 kg;

[0147] (2) Tensile strength test: GB / T1040.2-2006 was used for the tensile strength test; the tensile rate was 50 mm / min;

[0148] (3) Flexural modulus test: GB / T9341-2008 was used for flexural modulus test; the bending speed was 5 mm / min;

[0149] (4) Simple supported beam notched impact strength test: GB / T 1043.1-2008 is used to conduct the simple supported beam notched impact strength test; wherein, a 1 joule pendulum is used;

[0150] (5) A polarizing microscope is used to test the microscopic imaging of the spherulite structure and orientation in the polyoxymethylene combination, and the diameters of the spherulites in the polyoxymethylene combination are counted and averaged to obtain the average diameter of the spherulites. The diameter of the spherulites is determined by the straight-line distance between the two farthest points on the edge of the spherulites in the polarized photo. The polarized photo of the polyoxymethylene composition prepared in Example 3 is shown in FIG. Figure 1 As shown, the polarized photo of the polyoxymethylene composition prepared in Comparative Example 3 is as follows Figure 2 As shown by Figure 1 and Figure 2 By comparison, it can be seen that the spherulite size in the polyoxymethylene composition prepared in Example 3 is significantly smaller than that in Comparative Example 3, and the spherulite size is uniform and the crystal orientation is orderly.

[0151] The crystallinity, melt index, average spherulite diameter, tensile strength and impact strength of the polyoxymethylene compositions prepared in Examples 1-5 and Comparative Examples 1-4 are shown in Table 1.

[0152] Table 1

[0153]

[0154] As shown in Table 1, the polyoxymethylene resins prepared in Examples 1-5 of the present invention have high melt index (melt index is 15.8 g / 10min to 23.2 g / 10min), small spherulite size (average diameter of spherulites is 48 μm to 63 μm) and high crystallinity (more than 90%), and have high tensile strength, bending modulus and impact strength. Compared with Example 5, in Comparative Example 1, no rheology promoter was added, and the melt index and fluidity of the formaldehyde composition prepared therefrom were significantly reduced; in Comparative Example 2, no ternary copolymer formaldehyde crystal nucleating agent was added, and the spherulite size of the formaldehyde composition prepared therefrom was significantly increased; in Comparative Example 3, no rheology promoter and ternary copolymer formaldehyde crystal nucleating agent were added, and the spherulite size of the formaldehyde composition prepared therefrom was significantly increased, and the melt index was significantly reduced; in Comparative Example 4, no special monomer structure glycidyl ether was introduced into the ternary copolymer formaldehyde, and the crystallinity and melt index of the formaldehyde composition prepared therefrom were significantly reduced, and the spherulite size was also significantly increased.

[0155] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A polyoxymethylene composition, characterized in that: By weight, it includes the following components: 100 parts of polyoxymethylene powder; Antioxidant 0.15-1.0 part; Formaldehyde absorbent 0.01-1.0 part; Flow promoter 0.5-3.5 parts; Lubricant 0.02-1.0 part; The polyoxymethylene powder includes a binary copolymerized polyoxymethylene and a ternary copolymerized polyoxymethylene crystal nucleating agent; the weight ratio of the binary copolymerized polyoxymethylene to the ternary copolymerized polyoxymethylene crystal nucleating agent is (10-1000):1, the melting index of the binary copolymerized polyoxymethylene is 8.5g / 10min-11.5g / 10min; the melting index of the ternary polyoxymethylene crystal nucleating agent is 0.5g / 10min-3.5g / 10min, and the copolymerized monomer of the ternary polyoxymethylene crystal nucleating agent includes a monomer compound having glycidyl ether; The flow promoter is shown in Formula I:

2. The polyoxymethylene composition according to claim 1, characterized in that The binary copolymer formaldehyde is obtained by copolymerizing a first monomer and a second monomer; the first monomer is selected from one or both of trioxymethylene and tetraoxymethylene, and the second monomer is selected from one or more of ethylene oxide, propylene oxide, dioxolane and dioxetane; and / or, The ternary copolymer formaldehyde nucleating agent is obtained by copolymerizing a third monomer, a fourth monomer and the monomer compound having glycidyl ether, wherein the third monomer is selected from one or two of trioxymethylene and tetraoxymethylene, the fourth monomer is selected from one or more of ethylene oxide, propylene oxide, dioxolane and dioxolane, and the monomer compound having glycidyl ether is selected from one or more of phenyl glycidyl ether, ethylene glycol diglycidyl ether, glycerol diglycidyl ether, glycerol propoxy triglycidyl ether and glycerol triglycidyl ether; Preferably, the weight ratio of the first monomer to the second monomer is (87.5-97.5):(2.5-7.5), more preferably (94.8-96.8):(3.2-5.8); Preferably, the weight ratio of the third monomer, the fourth monomer and the fifth monomer is (92.5-99.5): (0.5~2.5):(0.05~1.5), more preferably (97.5~98):(1.25~1.8):(0.2~0.75).

3. The polyoxymethylene composition according to claim 2, characterized in that The polyoxymethylene powder is prepared by the following steps: Step S1, preparing a slurry containing a binary copolymer formaldehyde and a slurry containing a ternary copolymer formaldehyde crystal nucleating agent respectively; Step S2, adding the slurry containing binary copolymer formaldehyde and the slurry containing ternary copolymer formaldehyde nucleating agent into alkaline solution and mixing them to obtain a mixed slurry, performing solid-liquid separation on the mixed slurry to obtain a solid mixture, and drying the solid mixture to obtain the polyformaldehyde powder.

4. The polyoxymethylene composition according to claim 3, characterized in that The first monomer, the second monomer and the first catalyst are mixed to obtain a first mixture, the first mixture and the first molecular weight regulator are added into a first screw-type polyoxymethylene reactor, and a first polymerization reaction is carried out at 60-100° C., a screw speed of 10-100 r / min, and a pressure of 0.8-1.2 MPa to obtain the slurry containing the binary copolymer polyoxymethylene; and / or, The third monomer, the fourth monomer, the fifth monomer and the second catalyst are mixed to obtain a second mixture, the second mixture and the second molecular weight regulator are added to a second screw-type polyoxymethylene reactor, and a second polymerization reaction is carried out at 60-100° C., a screw speed of 10-100 r / min, and a pressure of 0.8-1.2 MPa to obtain the slurry containing the ternary copolymer formaldehyde crystal nucleating agent; Preferably, the first catalyst is selected from one or more of boron trifluoride, boron trifluoride ethyl ether complex, boron trifluoride butyl ether complex, and boron trifluoride tetrahydrofuran complex; Preferably, the first molecular weight regulator is selected from one or more of methylal, acetal, and butyral; More preferably, based on the sum of the weight of the first mixture and the first molecular weight regulator being 100%, the weight of the first catalyst is 10 ppm to 100 ppm, and the weight of the first molecular weight regulator is 50 ppm to 100 ppm; Preferably, the second molecular weight regulator is selected from one or more of methylal, acetal, and butyral; Preferably, the first catalyst is selected from one or more of boron trifluoride, boron trifluoride ethyl ether complex, boron trifluoride butyl ether complex, and boron trifluoride tetrahydrofuran complex; More preferably, based on the sum of the weight of the second mixture and the second molecular weight regulator being 100%, the weight of the second catalyst is 10 ppm to 100 ppm, and the weight of the second molecular weight regulator is 100 ppm to 500 ppm.

5. The polyoxymethylene composition according to claim 3, characterized in that: The alkali solution is an aqueous solution of an alkaline substance, and the alkaline substance is selected from at least one of ethanolamine, diethanolamine, triethanolamine, and methyldiethanolamine; and / or, The step S2 further comprises feeding the mixed slurry into a grinding machine for grinding, and then performing solid-liquid separation on the ground mixed slurry to obtain the solid mixture; and / or, The drying temperature in step S2 is 90°C to 150°C; Preferably, the content of alkaline substances in the alkali solution is 5% to 15% by weight; Preferably, in terms of weight percentage, the solid content of the mixed slurry is 25% to 75%.

6. The polyoxymethylene composition according to any one of claims 1 to 5, characterized in that The particle size of the polyoxymethylene powder is 0.25 mm to 1.25 mm; and / or, The melt index of the binary copolymer oxymethylene is 10.2 g / 10 min to 11.0 g / 10 min; and / or, The melt index of the ternary polyoxymethylene crystal nucleating agent is 1.1 g / 10 min to 2.0 g / 10 min; and / or, The polyoxymethylene composition has a melt index of 15.0 g / 10 min to 25.0 g / 10 min, and an average spherulite diameter of ≦75 μm.

7. The polyoxymethylene composition according to any one of claims 1 to 5, characterized in that The antioxidant is selected from one or two of phenolic antioxidants and phosphite antioxidants; preferably, The antioxidant is triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, N,N-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionyl) hexanediamine and tris(2,4-di-tert-butylphenyl) phosphite in a weight ratio (1-2): (1~2):(0.2~1) combination; or, The antioxidant is a combination of glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, and tris(2,4-di-tert-butylphenyl) phosphite in a weight ratio of (1-2):(1-2):(0.2-1); or, The antioxidant is triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, N,N-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionyl) hexanediamine and dioctadecyl pentaerythritol diphosphite in a weight ratio (1-2): (1~2):(0.2~1) combination; or, The antioxidant is a combination of triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, N,N-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionyl) hexanediamine and bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite in a weight ratio of (1-2):(1-2):(0.2-1); or, The antioxidant is triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate and tris(2,4-di-tert-butylphenyl) phosphite in a weight ratio of (1-2): (1-2): (0.2~1) combination; or, The antioxidant is a combination of triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate and dioctadecyl pentaerythritol diphosphite in a weight ratio of (1-2): (1-2): (0.2-1); or, The antioxidant is a combination of triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate and bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite; or, the antioxidant is a combination of triethylene glycol bis-β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate and bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite in a weight ratio of (1-2):(1-2):(0.2-1).

8. The polyoxymethylene composition according to any one of claims 1 to 5, characterized in that The formaldehyde absorbent is selected from one or more of melamine, melamine derivatives and inorganic porous nanopowder; Preferably, the melamine derivative is selected from one or more of hydroxymethyl melamine, melamine aminodiglycol, melamine aminolauryl alcohol, and cyclohexyl melamine; Preferably, the inorganic porous nano powder is selected from one or both of nano molecular sieve and nano diatomaceous earth; More preferably, the formaldehyde absorbent is a combination of melamine and hydroxymethyl melamine in a weight ratio of (1-2): (1-2), or a combination of melamine and melamine aminodiglycol, or a combination of melamine and melamine aminolauryl alcohol, or a combination of melamine and cyclohexyl melamine in a weight ratio of (1-2): (1-2), or a combination of melamine and nanomolecular sieve in a weight ratio of (1-2): (1-2), or a combination of melamine and nanodiatomaceous earth in a weight ratio of (1-2): (1-2), or a combination of melamine, hydroxymethyl melamine and nanomolecular sieve in a weight ratio of (1-2): (1-2): (1-2), or a combination of melamine, melamine aminodiglycol and nanomolecular sieve in a weight ratio of (1-2): (1-2): (1-2). 1-2), or, melamine, melamine aminolauryl alcohol and nanomolecular sieve according to the weight ratio of (1-2): (1-2): (1-2), or, melamine, cyclohexylmelamine and nanomolecular sieve according to the weight ratio of (1-2): (1-2): (1-2), or, melamine, hydroxymethylmelamine and nanodiatomaceous earth according to the weight ratio of (1-2): (1-2): (1-2), or, melamine, melamine aminodiglycol and nanodiatomaceous earth according to the weight ratio of (1-2): (1-2): (1-2), or, melamine, melamine aminolauryl alcohol and nanodiatomaceous earth according to the weight ratio of (1-2): (1-2): (1-2), or, melamine, cyclohexylmelamine and nanodiatomaceous earth according to the weight ratio of (1-2): (1-2): (1-2).

9. The polyoxymethylene composition according to any one of claims 1 to 5, characterized in that The lubricant is selected from one or more of N-ethylene bisstearamide, glyceryl monostearate, silicone oil, Fischer-Tropsch wax and PE wax.

10. The method for preparing the polyoxymethylene composition according to any one of claims 1 to 9, characterized in that: The method comprises the following steps: melting, blending and granulating polyoxymethylene powder, an antioxidant, a formaldehyde absorbent, a flow promoter and a lubricant at 165-235° C. to obtain a polyoxymethylene composition.

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