A polyoxymethylene composition, a preparation method thereof and an application

Abstract

The present disclosure provides a polyoxymethylene composition, a preparation method, and applications thereof, relating to the technical field of polyoxymethylene. The present disclosure discloses grafting isocyanate groups onto the surface of glass fibers. The resulting modified glass fibers are used to prepare the polyoxymethylene composition. The isocyanate groups on the modified glass fibers can couple with the end groups of the polyoxymethylene molecular chains, thereby increasing the mechanical properties of the polyoxymethylene composition and reducing the formaldehyde emission of the polyoxymethylene composition.

Description

Technical Field

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

[0002] Polyoxymethylene (POM) is a highly crystalline linear thermoplastic polymer with excellent mechanical properties, wear resistance, self-lubrication, oil resistance, chemical resistance, creep resistance, low water absorption, and the ability to maintain its mechanical, chemical, and electrical properties over a wide temperature range. It is an engineering plastic with excellent comprehensive performance and is widely used in the automotive, electronics, and household appliance industries.

[0003] POM is mainly composed of (-CH2-O-) chain segments, with a small amount of (-CH2CH2O-) or (-CH2CH2CH2CH2O-) chain segments, and a large molecule with a terminal group of methoxy ether or hydroxyethyl ether structure. This results in POM being easily broken by heat and oxygen during melt processing, and this thermal decomposition is autocatalytic, releasing a large amount of formaldehyde. The existing technology mainly enhances the performance of polyoxymethylene by adding glass fiber to polyoxymethylene. Since the terminal groups of POM are hydroxyl groups, their reactivity with the hydroxyl groups of glass fiber is poor, resulting in poor performance and instability of glass fiber reinforced POM. In order to improve the strength of the material, it is necessary to effectively disperse the glass fiber during processing, requiring higher processing temperatures and stronger screw shear strength. This will lead to instability of the POM molecular chain and release more formaldehyde. Formaldehyde will be oxidized to formic acid in the presence of high temperature and oxygen. Formic acid has an auto-accelerating catalytic effect on the degradation reaction of polyoxymethylene. Therefore, heat stabilizers, antioxidants, formaldehyde absorbers, etc. are often added to POM to meet the needs of forming processing. However, the amount of additives added should be appropriate. When sufficient effect is achieved, avoid adding too much to cause problems such as precipitation during the injection molding process.

[0004] Currently proposed methods for improving the strength of glass fiber reinforcement all involve adding coupling agents to enhance the interaction between the glass fiber and POM molecular chains. Patents CN107746540B, DE 2162345, and CN104995254B, for example, enhance the interaction between glass fiber and POM by introducing isocyanates. However, the direct introduction of isocyanates can cause precipitation onto the mold surface during the subsequent injection molding process, thus affecting product quality. Patent CN101343396B optimizes the glass fiber impregnation system and employs a variety of coupling agents to enhance the interaction between glass fiber and POM. However, this impregnation system is aqueous. When isocyanates are used for compatibility, the isocyanate groups undergo hydrolysis during the glass fiber surface treatment to form amines or ureas, thereby losing their ability to couple with the POM terminal hydroxyl groups. Ultimately, the primary effect is not the isocyanate, but rather the other components of the impregnation system. The reaction conditions between isocyanate and the hydroxyl groups on the surface of glass fiber are relatively harsh, and the reaction rate is relatively low. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a polyoxymethylene composition with good mechanical properties and a preparation method thereof.

[0006] To achieve the above-mentioned purpose, the technical solution adopted by the present disclosure is: providing a polyformaldehyde composition, comprising the following components in parts by weight: 100 parts of polyformaldehyde, 25-30 parts of polyisocyanate-modified glass fiber; which contains: 0.04wt%-0.28wt% of polyisocyanate based on 100wt% of the polyformaldehyde composition.

[0007] In one embodiment, the grafting rate of polyisocyanate in the polyisocyanate-modified glass fiber is 0.2-1.2%; preferably, the grafting rate of isocyanate groups in the polyisocyanate-modified glass fiber is 0.2-0.45%;

[0008] And / or, based on 100 wt % of the polyoxymethylene composition, it contains: 0.04 wt % to 0.09 wt % of polyisocyanate;

[0009] And / or, based on 100 wt% of the polyoxymethylene composition, the content of the polyisocyanate-modified glass fiber is 20-23%;

[0010] And / or, the functional group of the polyisocyanate is ≥3.

[0011] In one embodiment, the polyisocyanate is at least one of 4,4'-methylenebisphenylisocyanate trimer, isophorone diisocyanate trimer, 1,6-hexamethylene diisocyanate trimer, 2,4-toluene diisocyanate trimer, and 2,6-toluene diisocyanate trimer.

[0012] In one embodiment, the preparation method of the polyisocyanate-modified glass fiber is as follows: dissolving polyisocyanate in an organic solvent to obtain a polyisocyanate solution; then immersing the glass fiber in the polyisocyanate solution, reacting under inert gas conditions, and after the reaction is completed, removing the solvent and drying to obtain modified glass fiber.

[0013] In one embodiment, the mass percentage concentration of polyisocyanate in the polyisocyanate solution is 0.45-2.3%; preferably, the mass percentage concentration of polyisocyanate in the polyisocyanate solution is 0.5-2%;

[0014] And / or, the mass ratio of the polyisocyanate solution to the glass fiber is (5-10):1; preferably, the mass ratio of the polyisocyanate solution to the glass fiber is (6-8):1.

[0015] In one embodiment, the reaction temperature is 40-55° C. and the reaction time is 5-6 h.

[0016] In one embodiment, the polyoxymethylene composition further comprises 0.1-3 parts by weight of an auxiliary agent.

[0017] In one embodiment, the auxiliary agent is at least one of a lubricant and an antioxidant; the lubricant is a stearamide lubricant; and the antioxidant is a hindered phenol antioxidant.

[0018] The present disclosure provides a preparation method of the polyoxymethylene composition, comprising the following steps: uniformly mixing the components in proportion, adding the components into a screw extruder, and melt-extruding and granulating the components at 180-200° C. to obtain the polyoxymethylene composition.

[0019] The present disclosure also provides applications of the polyoxymethylene composition in automobiles, electronic appliances, and household appliances, such as gears or brackets.

[0020] Compared with the prior art, the beneficial effects of the present disclosure are as follows: the present disclosure grafts isocyanate groups on the surface of glass fibers, and the obtained modified glass is used to prepare a polyoxymethylene composition. The isocyanate groups on the modified glass fibers can couple with the end groups of the POM molecular chains, thereby increasing the mechanical properties of the polyoxymethylene composition and reducing the formaldehyde emission of the polyoxymethylene composition. DETAILED DESCRIPTION

[0021] The advantages and features of the present invention and the methods for achieving the advantages and features will be more readily understood with reference to the detailed description of the following embodiments. However, the present invention may be implemented in various other forms and should not be construed as being limited to the embodiments set forth herein. The embodiments disclosed herein are provided so that the disclosure of the present invention will be thorough and complete and will fully convey the scope of the invention to those skilled in the art.

[0022] The terms used in the specification are intended to describe certain embodiments only and should by no means limit the present invention. Unless clearly used otherwise, expressions in the singular include the meaning of the plural form.

[0023] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Any term defined in a comprehensive dictionary should be interpreted as having the same meaning in the context of the relevant art, and, unless explicitly defined otherwise, should not be interpreted as having an idealistic or overly formalistic meaning.

[0024] Hereinafter, the polyoxymethylene composition disclosed herein and its preparation method and application will be described in detail.

[0025] The present disclosure provides a polyoxymethylene composition, comprising the following components in parts by weight: 100 parts of polyoxymethylene and 25-30 parts of polyisocyanate-modified glass fiber; based on 100 wt % of the polyoxymethylene composition, the composition contains: 0.04 wt % to 0.28 wt % of polyisocyanate.

[0026] During processing, POM resin degrades and releases formaldehyde due to heat, oxygen, and shear. Formaldehyde is further oxidized into formic acid, which accelerates the degradation of POM resin. Therefore, formaldehyde absorbers that react with formaldehyde or alkaline substances that react with formic acid are typically added during POM processing. Formaldehyde absorbers typically contain amino or hydroxyl groups, such as melamine. Furthermore, the terminal hydroxyl groups in POM resin can accelerate its degradation. Polyisocyanates react with these terminal hydroxyl groups, thereby reducing degradation and overall formaldehyde emissions. When polyisocyanate is directly blended with POM for extrusion, due to the small amount of polyisocyanate added and the short extrusion time, the polyisocyanate is not easily dispersed in the POM, resulting in poor reaction between the polyisocyanate and the terminal hydroxyl groups of the POM, which results in the polyisocyanate having a general effect in improving the effect of glass fiber reinforcement of POM and reducing formaldehyde emission. Even by increasing the amount of polyisocyanate added, the mechanical properties of the polyoxymethylene composition cannot be further improved and the formaldehyde emission cannot be reduced.

[0027] Furthermore, when directly extruding isocyanate blends, the dispersion of isocyanate is poor, and the probability of a single isocyanate molecule reacting simultaneously with both the glass fiber and the hydroxyl groups on the POM molecular chain is low. Therefore, the isocyanate content needs to be increased to enhance the coupling between the glass fiber and the POM molecular chain. However, the higher the isocyanate content, the more isocyanate will remain in the composition, leading to precipitation onto the mold surface during the subsequent injection molding process, thus affecting product quality. The reaction conditions between isocyanate and the hydroxyl groups on the glass fiber surface are relatively harsh, and the reaction rate is relatively low. Currently, there is no method for effectively grafting polyisocyanates directly onto the glass fiber surface.

[0028] The present invention grafts polyisocyanate onto the surface of glass fiber so that the surface of the glass fiber has sufficient isocyanate groups. The polyisocyanate-modified glass fiber and polyoxymethylene are added to an extruder. As the glass fiber is dispersed, the isocyanate groups on the surface of the glass fiber can effectively react with the terminal hydroxyl groups of the POM. This reduces the polyisocyanate content in the polyoxymethylene composition, improves the bonding force between the POM molecular chain and the glass fiber, and reduces the amount of formaldehyde released due to the terminal hydroxyl groups of the POM molecular chain. In addition, the addition of the polyisocyanate-modified glass fiber to the polyoxymethylene composition reduces or minimizes the possibility of precipitation.

[0029] In the present disclosure, the grafting rate of isocyanate groups in the polyisocyanate-modified glass fiber can be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.75%, 0.80%, 0.85%, 0.90%, 0.95%, 1.0%, 1.05%, 1.10%, 1.15%, or 1.20%; the present disclosure is not limited thereto; preferably, the grafting rate of isocyanate groups in the polyisocyanate-modified glass fiber is 0.2-0.45% to obtain a polyoxymethylene composition with high mechanical properties, low formaldehyde emission, and low precipitation.

[0030] In the present disclosure, if the grafting rate of the isocyanate group is low, there are not enough isocyanate groups to couple the POM molecular chain and the glass fiber, and the polyisocyanate-modified glass fiber does not sufficiently improve the mechanical properties and formaldehyde emission of the polyoxymethylene composition; if the grafting rate of the isocyanate group is too high, the length of the isocyanate chain segment on the surface of the glass fiber increases, affecting the reaction between the isocyanate group and the POM molecular chain, resulting in a decrease in the coupling effect, and the performance improvement effect may be reduced.

[0031] In the present disclosure, based on the weight of the polyoxymethylene composition as 100wt%, it can contain 0.04wt%, 0.05wt%, 0.06wt%, 0.08wt%, 0.09wt%, 0.10wt%, 0.13wt%, 0.15wt%, 0.17wt%, 0.19wt%, 0.22wt%, 0.25wt%, and 0.28wt% of polyisocyanate, but the present disclosure is not limited thereto; it preferably contains 0.04wt%-0.09wt% of polyisocyanate to obtain a polyoxymethylene composition with high mechanical properties, low formaldehyde emission, and low precipitation.

[0032] In the present disclosure, based on 100 wt % of the polyoxymethylene composition, the content of the polyisocyanate-modified glass fiber is 20-23%;

[0033] In the present disclosure, the functional group of the polyisocyanate is ≥3.

[0034] There are no particular limitations on polyisocyanates with a functional group ≥3, and the number of functional groups can be 3, 4, 5, 6, etc. Based on the degree of improvement the polyisocyanate provides to the polyoxymethylene composition, the polyisocyanate is preferably at least one of 4,4'-methylenebisphenylisocyanate trimer, isophorone diisocyanate trimer, 1,6-hexamethylene diisocyanate trimer, 2,4-toluene diisocyanate trimer, and 2,6-toluene diisocyanate trimer. The present invention has no particular requirements for the brand or source of polyisocyanates with a functionality of 3 or greater; they can be purchased commercially, such as WANNATE HDI-100 (Wanhua Chemical Group Co., Ltd.) and VESTANATE T 1890 / 100 (Evonik Specialty Chemicals Co., Ltd.); they can also be prepared in-house by referring to existing technologies. Common polyisocyanates with a functionality of 3 or greater in the art can be used to achieve the present invention.

[0035] In one embodiment, the preparation method of the polyisocyanate-modified glass fiber is as follows: dissolving polyisocyanate in an organic solvent to obtain a polyisocyanate solution; then adding glass fiber to the polyisocyanate solution, reacting under inert gas conditions, and after the reaction is completed, removing the solvent and drying to obtain modified glass fiber; the functional group of the polyisocyanate is ≥3.

[0036] In the present disclosure, the diameter of the glass fiber is 8-15 μm, and the present invention has no special limitation.

[0037] Preferably, the drying temperature is 70-90° C., and the drying time is 12-48 hours.

[0038] The present invention selects specific parameters to cause the hydroxyl groups on the surface of the glass fiber to react with the isocyanate groups, thereby grafting isocyanate on the surface of the glass fiber. The functional group content of the polyisocyanate affects the performance of the polyoxymethylene composition. The diisocyanate containing three functional groups can react with the end groups of the POM molecular chain, which not only plays a chain extension role, but also reduces the end group content of the polyoxymethylene composition, improves the stability of the polyoxymethylene molecular chain, thereby increasing the mechanical properties of the polyoxymethylene composition and reducing the release of formaldehyde. In addition, the diisocyanate can occupy more sites on the surface of the glass fiber, thereby improving the bonding strength between the glass fiber and the polyisocyanate. In addition, the excess isocyanate in the polyisocyanate reacts with the end groups of the POM molecular chain, thereby improving the bonding strength between the glass fiber and the polyoxymethylene.

[0039] In the present disclosure, the mass percentage concentration of polyisocyanate in the polyisocyanate solution can be 0.45%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, but the present disclosure is not limited thereto; preferably, the mass percentage concentration of polyisocyanate in the polyisocyanate solution is 0.5-2%.

[0040] In the present disclosure, the mass ratio of the polyisocyanate solution to the glass fiber can be 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1, 9.5:1, or 10:1, but the present disclosure is not limited thereto. Preferably, the mass ratio of the polyisocyanate solution to the glass fiber is (6-8):1.

[0041] In the present disclosure, the reaction temperature can be 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, 49°C, 50°C, 51°C, 52°C, 53°C, 54°C, or 55°C, but the present disclosure is not limited thereto; the reaction time can be 5h, 5.5h, or 6h, but the present disclosure is not limited thereto.

[0042] In the present disclosure, the grafting rate of isocyanate groups on the surface of the glass fiber is the key to affecting the performance of glass fiber reinforced POM. An appropriate grafting rate will result in better performance. The grafting rate of isocyanate groups is mainly related to the mass percentage concentration of polyisocyanates in the polyisocyanate solution, the reaction temperature, and the reaction time. The higher the mass percentage concentration of polyisocyanates in the polyisocyanate solution, the higher the reaction temperature, and the longer the reaction time, the higher the isocyanate grafting rate. However, this may also cause some polyisocyanates to self-polymerize, reducing the number of active isocyanate groups remaining on the surface of the glass fiber.

[0043] When other reaction conditions remain unchanged, if the mass concentration of the polyisocyanate solution is less than 0.5%, the number of isocyanate groups grafted onto the glass fiber is small, resulting in an isocyanate group grafting rate of less than 0.2%; when the mass concentration of the polyisocyanate solution exceeds 2%, the degree of self-polymerization of the polyisocyanate increases, and the increase in the isocyanate grafting rate is not obvious.

[0044] In the present disclosure, the inert gas is one of nitrogen and argon.

[0045] In the present disclosure, the organic solvent is not particularly limited as long as it can dissolve the polyisocyanate. From the perspective of availability, the present disclosure preferably uses benzene and / or toluene as the organic solvent.

[0046] In the present disclosure, the type of polyoxymethylene is not particularly limited and may be homopolyoxymethylene (A) and / or copolymer polyoxymethylene (B). Homopolyoxymethylene (A) is generally a homopolymer obtained by polymerizing a monomer represented by formula (1); copolymer polyoxymethylene (B) is generally a copolymer obtained by polymerizing a monomer represented by formula (1) and a monomer represented by formula (2).

[0047] -(-CH2O-)-formula (1); [(CX1X2) a O], formula (2); wherein X1 and X2 are each independently selected from hydrogen, alkyl or aryl, and a is an integer of 2-6.

[0048] The above formula (2) can be a cyclic ether compound and / or a cyclic formal compound, such as ethylene oxide, propylene oxide, butylene oxide, phenylene ether, 1,3-dioxolane, diethylene glycol formal, 1,3-propylene glycol formal, 1,4-butanediol formal, etc.; preferably, at least one of ethylene oxide, 1,3-dioxolane, and 1,4-butanediol formal is copolymerized as formula (2); formula (2) is used as a comonomer, and the addition amount of formula (2) does not exceed 20 weight% (based on 100 weight% of formula (1) and formula (2)), preferably, the addition amount of formula (2) does not exceed 15 weight%, and more preferably, the addition amount of formula (2) is 2 weight%.

[0049] In the present disclosure, polyoxymethylene preferably has terminal hydroxyl groups, for example, hydroxyvinyl groups (-OCH2CH2-OH) and hemiacetal groups (-OCH2-OH); in addition to terminal hydroxyl groups, POM may also have other terminal groups that are typical for these polymers. Examples of these are alkoxy groups, formate groups, acetate groups or acetaldehyde groups.

[0050] The method for preparing the homopolyoxymethylene and copolymer is not particularly limited, and they can be prepared using methods known to those skilled in the art.

[0051] In the present disclosure, the melt index of polyoxymethylene can be measured according to ASTM D1238-2010. The POM melt index test conditions are 190°C and a load of 2.16 kg. From the perspective of moldability, the melt index of polyoxymethylene in the present disclosure is 0.5-300 g / 10 min, preferably 1-100 g / 10 min, and more preferably 2-50 g / 10 min.

[0052] The polyoxymethylene composition of the present disclosure may contain auxiliary agents, and possible auxiliary agents are known to those skilled in the art.

[0053] Suitable auxiliary agents include lubricants, antioxidants, nucleating agents, etc.; the present disclosure preferably uses at least one of lubricants and antioxidants as auxiliary agents.

[0054] The antioxidant is preferably a hindered phenol antioxidant, and specific examples include: 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, 2,5-di-tert-butyl-4-hydroxybenzyldimethylamine, diethyl-3,5-di-tert-butyl-4-hydroxybenzyl phosphate, stearyl-3,5-di-tert-butyl-4-hydroxybenzyl phosphate, 3,5-di-tert-butyl-4-hydroxyphenyl-3,5-distearyl-thiotriazolylamine, 2,6-di-tert-butyl-4-hydroxymethylphenol, 2,4-di-(n-octylthio)-6-(4-hydroxy-3,5-di-tert-butylglycerol allyl ether)-1,3,5-triazine, N,N'-hexamethylenebis(3,5-di-tert-butyl-4-hydroxy-hydrocinnamic acid), N,N'-bis(1,3,5-di-tert-butyl-4-hydroxy-1,3,5-triazine), -(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hexanediamine, octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, pentaerythritol-tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], triethylene glycol-bis[3-(3,5-dimethyl-4-hydroxyphenyl)propionate], triethylene glycol bis[β-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate], 2,2'-thiodiethyl-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; among them, triethylene glycol bis[β-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate] and N,N'-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hexanediamine are preferred. The former is typically BASF's Irganox@245, and the latter is BASF's Irganox@1098. The present disclosure prefers a mixture of Irganox@245 and Irganox@1098 as the antioxidant, with the mass ratio of Irganox@245 to Irganox@1098 being (1-3):1, preferably 2:1.

[0055] The lubricant is a stearamide lubricant, and a specific example is ethylene bisstearamide (EBS).

[0056] The amount of the additive depends on the additive used and the desired effect. Conventional amounts are known to those skilled in the art.

[0057] Based on 100 parts by weight of polyoxymethylene, the amount of lubricant used is 0.05-2 parts by weight, preferably 0.1-1 part by weight.

[0058] Based on 100 parts by weight of polyoxymethylene, the amount of the antioxidant is 0.05-1 part by weight, preferably 0.1-0.5 part by weight.

[0059] The present disclosure provides a preparation method of the polyoxymethylene composition, comprising the following steps: uniformly mixing the components in proportion, adding the components into a screw extruder, and melt-extruding and granulating the components at 180-200° C. to obtain the polyoxymethylene composition.

[0060] The present disclosure also provides applications of the polyoxymethylene composition in automobiles, electronic appliances, and household appliances.

[0061] In order to better illustrate the purpose, technical solutions and advantages of the present disclosure, the present disclosure will be further described below in conjunction with specific embodiments and comparative examples. Its purpose is to understand the content of the present disclosure in detail, rather than to limit the present disclosure. All other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present disclosure. Unless otherwise specified, the experimental reagents and instruments involved in the implementation of the present disclosure are all commonly used ordinary reagents and instruments.

[0062] The raw materials used in the examples and comparative examples are described below, but are not limited to these materials:

[0063] Polyisocyanate 1: isophorone diisocyanate trimer (IPDI trimer), average NCO functionality of 3-4, VESTANAT T 1890 / 100, Evonik Specialty Chemicals GmbH;

[0064] Polyisocyanate 2: 4,4'-diphenylmethane diisocyanate, NCD functionality 2, MDI-100, Wanhua Chemical Group Co., Ltd.

[0065] Glass fiber 1: chopped glass fiber, ECS10-3.0-T445, glass fiber diameter 10 μm, Taishan Glass Fiber Co., Ltd.

[0066] Glass fiber 2: chopped glass fiber, ECS13-4.5-510H, glass fiber diameter 13 μm, China Jushi Co., Ltd.

[0067] Polyisocyanate modified glass fiber 1 is homemade, and its preparation method is as follows:

[0068] Under nitrogen protection, polyisocyanate 1 was added to 50° C. toluene, stirred until polyisocyanate 1 was completely dissolved, and cooled to room temperature to obtain a polyisocyanate solution, wherein the mass percentage concentration of polyisocyanate in the polyisocyanate solution was 1%;

[0069] Under nitrogen protection, glass fiber 1 was added to a polyisocyanate solution in a mass ratio of polyisocyanate solution to glass fiber of 7:1, and stirred at 50°C for 5 hours. The solution was then vacuumed and heated to 60°C to remove toluene. The resulting product was placed in a vacuum oven at 80°C and dried for 24 hours to obtain polyisocyanate-modified glass fiber 1. The grafting rate of isocyanate groups in the polyisocyanate-modified glass fiber 1 was 0.4%.

[0070] Polyisocyanate modified glass fiber 2 is homemade, and its preparation method is as follows:

[0071] Under nitrogen protection, polyisocyanate 1 was added to 50° C. toluene, stirred until polyisocyanate 1 was completely dissolved, and cooled to room temperature to obtain a polyisocyanate solution. The mass percentage concentration of polyisocyanate in the polyisocyanate solution was 1.2%;

[0072] Under nitrogen protection, glass fiber 2 was added to a polyisocyanate solution in a mass ratio of polyisocyanate solution to glass fiber of 6:1, and stirred at 50°C for 6 hours; then, vacuum was applied, the temperature was raised to 60°C, and toluene was removed; the resulting product was placed in a vacuum oven at 80°C and dried for 24 hours to obtain polyisocyanate-modified glass fiber 2; the grafting rate of isocyanate groups in the polyisocyanate-modified glass fiber 2 was 0.4%;

[0073] Polyisocyanate-modified glass fiber 3 was prepared in-house. The only difference between its preparation method and that of polyisocyanate-modified glass fiber 1 was that the mass percentage concentration of polyisocyanate in the polyisocyanate solution was 1.5%, the mass ratio of polyisocyanate solution to glass fiber was 8:1, and the reaction temperature was 40°C. The grafting rate of isocyanate groups in polyisocyanate-modified glass fiber 3 was 0.45%.

[0074] Polyisocyanate-modified glass fiber 4 was prepared in-house. The only difference between its preparation method and that of polyisocyanate-modified glass fiber 1 was that the mass percentage concentration of polyisocyanate in the polyisocyanate solution was 0.5%, the mass ratio of polyisocyanate solution to glass fiber was 6:1, and the reaction temperature was 55°C. The grafting rate of isocyanate groups in polyisocyanate-modified glass fiber 4 was 0.2%.

[0075] Polyisocyanate-modified glass fiber 5 was prepared in-house. The only difference between its preparation method and that of polyisocyanate-modified glass fiber 1 was that the mass percentage concentration of polyisocyanate in the polyisocyanate solution was 2%, the mass ratio of the polyisocyanate solution to the glass fiber was 5:1, and the grafting rate of isocyanate groups in polyisocyanate-modified glass fiber 5 was 0.5%.

[0076] Polyisocyanate-modified glass fiber 6 was prepared in-house. The only difference between its preparation method and that of polyisocyanate-modified glass fiber 1 was that the mass percentage concentration of polyisocyanate in the polyisocyanate solution was 1.5%, the mass ratio of the polyisocyanate solution to the glass fiber was 9:1, and the grafting rate of isocyanate groups in polyisocyanate-modified glass fiber 6 was 0.75%.

[0077] Polyisocyanate-modified glass fiber 7 was prepared in-house. The only difference between its preparation method and that of polyisocyanate-modified glass fiber 1 was that the mass ratio of polyisocyanate solution to glass fiber was 10:1, and the reaction time was 6 h. The grafting rate of isocyanate groups in polyisocyanate-modified glass fiber 7 was 1.2%.

[0078] Polyisocyanate-modified glass fiber 8 was prepared in-house. The only difference between its preparation method and that of polyisocyanate-modified glass fiber 1 was that the mass percentage concentration of polyisocyanate in the polyisocyanate solution was 2.5%, the reaction temperature was 60° C., and the reaction time was 6 h. The grafting rate of isocyanate groups in polyisocyanate-modified glass fiber 8 was 1.4%.

[0079] Polyisocyanate-modified glass fiber 9 was prepared in-house. The only difference between its preparation method and that of polyisocyanate-modified glass fiber 1 was that polyisocyanate 2 was used instead of polyisocyanate 1. The grafting rate of isocyanate groups in polyisocyanate-modified glass fiber 9 was 0.4%.

[0080] Polyoxymethylene 1: copolymerized oxymethylene, POM KP20, melt index 9 g / 10 min, Ticona, Germany;

[0081] Polyoxymethylene 2: Homopolymer, POM 500P, melt index 14g / 10min, DuPont, USA;

[0082] Lubricant: Ethylene bisstearamide, EBS B50, Guangzhou Runfeng Chemical Co., Ltd.

[0083] Antioxidant: triethylene glycol bis[β-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate], trade name Irganox245, BASF, Germany;

[0084] N,N'-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hexanediamine, trade name Irganox 1098, BASF, Germany;

[0085] The antioxidant consists of Irganox 245 and Irganox 1098 in a mass ratio of 2:1.

[0086] Examples 1-9 and Comparative Examples 1-5

[0087] The compositions of the polyoxymethylene compositions of Examples 1-9 and Comparative Examples 1-5 are shown in Tables 1 and 2. The preparation methods of the polyoxymethylene compositions of Examples 1-9 and Comparative Examples 1-2 are as follows:

[0088] (1) Weighing each component in proportion, adding polyoxymethylene, lubricant and antioxidant into a premixer and mixing for 2 minutes to obtain a premix;

[0089] (2) adding the obtained premix into a twin-screw extruder, adding the polyisocyanate modified glass fiber into the middle section of the extruder, and melt-extruding at 180° C.-200° C., with a main engine speed of 300-400 rpm, cooling, and granulating to obtain the polyoxymethylene composition.

[0090] The preparation method of the polyoxymethylene composition of Comparative Examples 3-5 is as follows:

[0091] (1) Weighing each component in proportion, adding polyoxymethylene, lubricant, antioxidant, and polyisocyanate into a premixer and mixing for 2 minutes to obtain a premix;

[0092] (2) adding the obtained premix into a twin-screw extruder, adding glass fiber into the middle section of the extruder, and melt-extruding at 180° C.-200° C., with a main engine speed of 300-400 rpm, cooling, and granulating to obtain the polyoxymethylene composition.

[0093] Performance testing:

[0094] (1) Isocyanate group grafting rate:

[0095] Weigh approximately 2g of polyisocyanate-modified glass fiber, add 50mL of anhydrous toluene, and ultrasonically oscillate for 10 minutes to fully disperse the glass fiber. Use a pipette to add 20mL of a 1mol / L di-n-butylamine-toluene solution, then ultrasonically oscillate for another 10 minutes. Let stand at room temperature for 30 minutes to allow the di-n-butylamine and isocyanate groups to react fully. Add 50mL of isopropanol and titrate with 0.5mol / L standard hydrochloric acid solution using bromocresol green as the indicator. The endpoint is when the solution changes from blue to yellow and does not change color after 15 seconds. Perform a blank test at the same time.

[0096] Isocyanate grafting rate calculation formula:

[0097] Φ NCO =(V0-V S )*C*42 / (1000*m)*100%

[0098] Where V0, V S are the volumes of hydrochloric acid standard solution consumed in blank titration and sample titration, mL;

[0099] C is the concentration of hydrochloric acid solution, mol / L;

[0100] m is the sampling volume, g;

[0101] 42 is the molar mass of the NCO group, g / mol;

[0102] (2) Precipitate evaluation method: A KraussMaffei machine (model CX 160-750) was used, and the injection molding process was as follows: material temperature 190°C, medium-high injection speed, continuous injection of 300 molds, and the amount of precipitates was visually observed.

[0103] Visual inspection of precipitates: Level 0: only some small patches of precipitates; Level 1: fewer precipitates, and the lower surface can be clearly seen through the precipitates at the precipitate collection point; Level 2: general precipitates, and the lower surface can be vaguely seen through the precipitates at the precipitate collection point; Level 3: more precipitates, and the lower surface of the mold can no longer be seen through the precipitates at the precipitate collection point.

[0104] Tensile strength (MPa): The test was carried out in accordance with ISO527-2019 standard, the specimen size was 170 mm × 10 mm × 4 mm, the test speed was 10 mm / min, and the test equipment was an electronic tensile testing machine from Zwick, Germany.

[0105] Formaldehyde emission (ppm): The formaldehyde emission test was conducted in accordance with the VDA 275-1994 test standard. The specific process was as follows: a polyoxymethylene composition was injection molded into a product with dimensions of 100 mm * 100 mm * 2 mm, and then cut into test specimens with dimensions of 100 mm * 40 mm * 2 mm. The test specimen was fixed in a 1-liter polyethylene bottle containing 50 ml of distilled water to prevent the test specimen from contacting the water. The bottle was then sealed and baked in a 60°C oven for 3 hours. Then, 10 mL of the aqueous solution from the polyethylene bottle was taken and placed in a volumetric flask. 10 mL of a standard solution of acetylacetone and 10 mL of ammonium acetate were added. After standing for 1 hour, the absorbance of the water in the volumetric flask was measured using a UV spectrophotometer. The solution after standing for 1 hour with the standard solution of 10 mL of acetylacetone and 10 mL of ammonium acetate was used as a blank sample. The formaldehyde content was calculated using the following formula:

[0106]

[0107] Where: m: sample mass, g;

[0108] H: sample moisture content;

[0109] V: volume of solution, here 50ml;

[0110] f: upward gradient factor of the calibration function, generally 1;

[0111] A B : absorbance of blank sample;

[0112] A S : absorbance of the sample;

[0113] F: coefficient for calculating analysis results, the value is 10; unit is kg [mg / kg].

[0114] Table 1

[0115]

[0116] Table 2

[0117]

[0118]

[0119] It can be seen from the experimental data in Table 1 and Table 2 that the polyoxymethylene composition prepared in the embodiments of the present disclosure has high tensile strength and low formaldehyde emission.

[0120] By comparing Example 1 and Examples 4-7, it can be seen that when the grafting rate of isocyanate groups in the polyisocyanate-modified glass fiber is 0.2-0.45% and the mass of polyisocyanate accounts for 0.04-0.09% of the mass of the polyoxymethylene composition, the tensile strength of the polyoxymethylene composition is ≥132.6 MPa and the formaldehyde emission is ≤33.4 ppm.

[0121] It can be seen from Example 8 and Comparative Example 1 that when the mass percentage of polyisocyanate exceeds 0.28 wt % based on 100 wt % of the polyoxymethylene composition, the mechanical properties of the polyoxymethylene composition are significantly reduced and the formaldehyde emission is increased.

[0122] Comparison of Example 1 and Comparative Example 2 shows that when the functional group of the polyisocyanate is ≥3, the polyoxymethylene composition has high tensile strength and low formaldehyde emission.

[0123] Comparison of Example 1 and Comparative Examples 3-4, and Example 2 and Comparative Example 5 shows that the glass fiber is not modified with polyisocyanate, and the obtained polyoxymethylene composition has low mechanical properties and high formaldehyde emission.

[0124] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of the present disclosure rather than to limit the scope of protection of the present disclosure. Although the present disclosure has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present disclosure may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present disclosure.

Claims

1. A polyoxymethylene composition, characterized in that The invention comprises the following components in parts by weight: 100 parts of polyoxymethylene and 25-30 parts of polyisocyanate-modified glass fiber; based on 100 wt % of the polyoxymethylene composition, the invention contains: 0.04 wt % to 0.28 wt % of polyisocyanate; and the functional group of the polyisocyanate is greater than or equal to 3.

2. The polyoxymethylene composition according to claim 1, wherein The grafting rate of isocyanate groups in the polyisocyanate-modified glass fiber is 0.2-1.2%; And / or, based on 100 wt % of the polyoxymethylene composition, it contains: 0.04 wt % to 0.09 wt % of polyisocyanate; And / or, based on 100 wt % of the polyoxymethylene composition, the content of the polyisocyanate-modified glass fiber is 20-23%.

3. The polyoxymethylene composition according to claim 2, wherein The grafting rate of isocyanate groups in the polyisocyanate-modified glass fiber is 0.2-0.45%.

4. The polyoxymethylene composition according to claim 2, wherein The polyisocyanate is at least one of 4,4'-methylenebisphenyl isocyanate trimer, isophorone diisocyanate trimer, 1,6-hexamethylene diisocyanate trimer, 2,4-toluene diisocyanate trimer, and 2,6-toluene diisocyanate trimer.

5. The polyoxymethylene composition according to claim 1, wherein The preparation method of the polyisocyanate-modified glass fiber is as follows: dissolving polyisocyanate in an organic solvent to obtain a polyisocyanate solution; then immersing glass fiber in the polyisocyanate solution, reacting under inert gas conditions, removing the solvent after the reaction, and drying to obtain the polyisocyanate-modified glass fiber.

6. The polyoxymethylene composition according to claim 5, wherein The mass percentage concentration of polyisocyanate in the polyisocyanate solution is 0.45-2.3%; And / or, the mass ratio of the polyisocyanate solution to the glass fiber is (5-10):

1.

7. The polyoxymethylene composition according to claim 6, wherein The mass percentage concentration of polyisocyanate in the polyisocyanate solution is 0.5-2%; and / or the mass ratio of the polyisocyanate solution to the glass fiber is (6-8):

1.

8. The polyoxymethylene composition according to claim 5, wherein The reaction temperature is 40-55° C. and the reaction time is 5-6 h.

9. The polyoxymethylene composition according to claim 1, wherein The polyoxymethylene composition further comprises 0.1-3 parts by weight of an auxiliary agent.

10. The polyoxymethylene composition according to claim 9, wherein The auxiliary agent is at least one of a lubricant and an antioxidant; the lubricant is a stearamide lubricant; and the antioxidant is a hindered phenol antioxidant.

11. The method for preparing the polyoxymethylene composition according to any one of claims 1 to 10, characterized in that: The method comprises the following steps: mixing the components uniformly in proportion, adding the components into a screw extruder, and melting, extruding and granulating the components at 180-200 DEG C to obtain a polyoxymethylene composition.

12. Use of the polyoxymethylene composition according to any one of claims 1 to 10 in automobiles, electronic and electrical equipment, and household appliances.

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