Polyacetal copolymer and method for producing the same

Abstract

A method for producing a polyacetal copolymer, which includes a step of copolymerizing 100 parts by mass of trioxane (A), 0.05 to 5 parts by mass of a cyclic acetal compound having an oxoalkylene group having 2 or more carbon numbers in a ring (B), and 0.001 to 0.5 parts by mass of a prescribed fatty glycidyl ether compound (C) having a sodium content of 0.1 to 100 parts by mass ppm in the presence of a linear acetal compound (D) as a molecular weight regulator, wherein in the step, the total mass (g) of (A) to (C) is defined as a, the number of moles of (D) is defined as b, and the total number of moles of moisture and methanol contained in (A) to (C) is defined as c and d, respectively, and is set to satisfy (b + c + d) / a = 4.5 to 9 μmol / g.

Description

Technical Field

[0001] This invention relates to a polyacetal copolymer and a method for manufacturing the same. Background Technology

[0002] Polyacetal resins are widely used as engineering plastics, primarily in electrical / electronic components, automotive parts, and various other mechanical parts, due to their excellent balance of mechanical properties, chemical resistance, and lubricity, as well as their ease of processing. However, in recent years, with the expansion of their applications, there has been a growing demand for higher performance characteristics. For example, when using polyacetal resins in thin-walled parts, it is often necessary to maintain the original flowability, moldability, thermal stability, and lubricity of the polyacetal resin, while ensuring rigidity and creep resistance.

[0003] However, achieving a good balance of the above-mentioned characteristics is extremely difficult. For example, in methods that blend fibrous fillers into polyacetal resin to improve rigidity, poor appearance of the molded product, reduced sliding properties, and reduced flowability can occur. Furthermore, the thermal stability can sometimes be reduced by further blending of fillers. In addition, it is known to improve rigidity by reducing the amount of comonomers in polyacetal copolymers. However, this method does not sufficiently improve rigidity, and on the other hand, the reduced amount of comonomers leads to a decrease in the polymer's thermal stability, which in turn negatively affects flowability and moldability.

[0004] In view of the above facts, this improvement method is proposed by focusing on the improvement of rigidity and other properties achieved by modifying the polymer backbone of the polyacetal resin itself (see Patent Document 1). According to this method, many properties originally possessed by the polyacetal resin can be maintained and rigidity can be improved.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2001-163942 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] The polyacetal copolymers obtained by the above methods generally exhibit good thermal stability. However, further investigation revealed instances where manufacturing processes, polymerization steps, end-stabilization processes, or melt-blending processes with stabilizers or other additives became unstable, leading to a deterioration in the thermal stability of the resulting copolymers. Such copolymers, due to poor thermal stability, exhibit problems such as discoloration when molten and held in the molding machine. Furthermore, it is difficult to obtain satisfactory values ​​for some mechanical and physical properties, particularly impact resistance. Elucidating the causes and improving these properties is an important task for the practical application of polyacetal copolymers obtained by these methods.

[0010] The present invention was made in view of the above-mentioned problems, and its objective is to provide a polyacetal copolymer with excellent rigidity and impact resistance, as well as thermal stability, especially low discoloration during melt retention in the molding machine, and a stable manufacturing method thereof.

[0011] Solution for solving the problem

[0012] In order to solve the aforementioned problems, the inventors conducted in-depth research and found that the sodium content in the specific aliphatic glycidyl ether compound used to form a branched / crosslinked structure on the polymer backbone of the polyacetal copolymer is the key factor in solving the problem and the optimal range and control method of the degree of polymerization of the polyacetal copolymer, thereby achieving the completion of the present invention.

[0013] One aspect of the present invention that solves the aforementioned problems is as follows.

[0014] (1) A method for manufacturing a polyacetal copolymer, comprising a step of copolymerizing 100 parts by weight of trioxane (A), 0.05 to 5 parts by weight of a cyclic acetal compound (B) having two or more carbon atoms in the ring and an oxane group, and 0.001 to 0.5 parts by weight of an aliphatic glycidyl ether compound (C) selected from the group consisting of trimethylolpropane triglycidyl ether, glycerol triglycidyl ether, and pentaerythritol tetraglycidyl ether, with a sodium content of 0.1 to 100 ppm by weight, in the presence of a linear acetal compound (D) as a molecular weight regulator.

[0015] In the process described above, when the total mass (g) of (A), (B) and (C) is defined as a, the number of moles of (D) is defined as b, and the total number of moles of water and methanol contained in (A), (B) and (C) is defined as c and d respectively, it is set to satisfy (b+c+d) / a=4.5~9μmol / g.

[0016] (2) In the method for manufacturing the polyacetal copolymer described in (1) above, the linear acetal compound (D) is selected from one or more of the group consisting of methyl acetal, acetaldehyde and dibutoxymethane.

[0017] (3) A polyacetal copolymer obtained by the manufacturing method of the polyacetal copolymer described in (1) or (2) above.

[0018] Invention Effects

[0019] According to the present invention, a polyacetal copolymer with excellent rigidity, impact resistance, thermal stability, and especially low discoloration during melt retention in the molding machine, and a stable manufacturing method thereof can be provided. Detailed Implementation

[0020] <Method for manufacturing polyacetal copolymers>

[0021] The method for manufacturing the polyacetal copolymer of this embodiment includes a step of copolymerizing 100 parts by mass of trioxymethylene (A), 0.05 to 5 parts by mass of a cyclic acetal compound (B) having two or more carbon atoms in its ring, and 0.001 to 0.5 parts by mass of an aliphatic glycidyl ether compound (C) selected from the group consisting of trimethylolpropane triglycidyl ether, glycerol triglycidyl ether, and pentaerythritol tetraglycidyl ether, with a sodium content of 0.1 to 100 ppm by mass, in the presence of a linear formal compound (D) as a molecular weight regulator. Furthermore, in the aforementioned step, when the total mass (g) of (A), (B), and (C) is defined as a, the molar number of (D) is defined as b, and the total molar numbers of water and methanol contained in (A), (B), and (C) are defined as c and d respectively, the mass is set to satisfy (b+c+d) / a = 4.5 to 9 μmol / g.

[0022] Hereinafter, the components used in the manufacturing method of this embodiment will be described.

[0023] [Trioxymethylene (A)]

[0024] Trioxymethylene (A) is a cyclic trimer of formaldehyde, generally obtained by reacting an aqueous formaldehyde solution in the presence of an acidic catalyst, and then purified by methods such as distillation before use. The trioxymethylene (A) used for polymerization is preferably formulated with minimal impurities such as water and methanol.

[0025] [Cyclic acetals with two or more carbon atoms in the ring (B)]

[0026] Cyclic acetal compounds (B) having two or more carbon atoms in the ring and containing oxyalkylene groups (hereinafter also referred to as "cyclic acetal compounds (B)") are cyclic acetal compounds (B) that can copolymerize with trioxymethylene (A). Examples include 1,3-dioxolane, propylene glycol acetal, diethylene glycol acetal, triethylene glycol acetal, 1,4-butanediol acetal, 1,5-pentanediol acetal, and 1,6-hexanediol acetal, with 1,3-dioxolane being the preferred choice.

[0027] The copolymerization amount of the cyclic acetal compound (B) relative to 100 parts by mass of trioxymethylene (A) is 0.05 to 5 parts by mass, preferably 0.1 to 3 parts by mass, and more preferably 0.3 to 2.5 parts by mass. When the copolymerization ratio of the cyclic acetal compound (B) is less than 0.05 parts by mass, the difficulty in controlling the polymerization reaction increases and the thermal stability of the resulting polyacetal copolymer deteriorates. Conversely, when the copolymerization ratio of the cyclic acetal compound (B) exceeds 5 parts by mass, the mechanical and physical properties such as strength and rigidity decrease.

[0028] [Aliphatic glycidyl ether compound (C)]

[0029] The aliphatic glycidyl ether compound (C) is one or more selected from the group consisting of trimethylolpropane triglycidyl ether, glycerol triglycidyl ether, and pentaerythritol tetraglycidyl ether, and has 3 to 4 glycidyloxy groups in one molecule. Furthermore, the aliphatic glycidyl ether compound (C) has a structure that allows for the formation of branched or cross-linked structures on the polymer backbone through copolymerization with paraformaldehyde. In this respect, it differs from the aforementioned cyclic acetal compound (B). In this embodiment, the aliphatic glycidyl ether compound (C) has a sodium content of 0.1 to 100 ppm by mass.

[0030] The copolymerization amount of the aliphatic glycidyl ether compound (C) is 0.001 to 0.5 parts by mass relative to 100 parts by mass of paraformaldehyde in component (A), preferably 0.01 to 0.5 parts by mass, and particularly preferably 0.1 to 0.5 parts by mass. When the copolymerization amount of component (C) is less than 0.001 parts by mass, the improvement in rigidity may not be achieved. Conversely, when it exceeds 0.5 parts by mass, problems such as poor moldability due to decreased flowability may occur, and the mechanical and physical properties of the resulting copolymer may decrease.

[0031] In this embodiment, the aliphatic glycidyl ether compound (C) is characterized by using a substance with a sodium content of 0.1 to 100 ppm by mass. This allows for the stable production of polyacetal copolymers, particularly those with excellent thermal stability. When the sodium content of the aliphatic glycidyl ether compound (C) exceeds 100 ppm by mass, operations such as the polymerization process, end-stabilization process, and the mixing of stabilizers become unstable, and the thermal stability of the resulting polyacetal copolymer deteriorates. Furthermore, from the viewpoint of economic efficiency in manufacturing the aliphatic glycidyl ether compound (C), the lower limit of the sodium content is 0.1 ppm by mass. Moreover, the sodium content is preferably 0.1 to 30 ppm by mass, and more preferably 0.2 to 5 ppm by mass.

[0032] Aliphatic glycidyl ether compounds are generally produced by the reaction of alcohols with epichlorohydrin. It is known that a method for obtaining glycidyl ether compounds involves ring-opening addition of an alcohol to epichlorohydrin in the presence of an acidic catalyst, followed by intramolecular ring closure in an alkaline aqueous solution (e.g., Japanese Patent Application Publication No. 61-178974). On the other hand, a method for producing glycidyl ether compounds by reacting an alcohol with epichlorohydrin in the presence of a solid alkali metal compound, wherein the reaction is carried out in the reaction mixture in the presence of pulverized solid alkali metal hydroxide (e.g., Japanese Patent Application Publication No. 1-151567). Due to variations in these synthetic methods and purification processes, aliphatic glycidyl ether compounds with different sodium contents can be produced.

[0033] In this embodiment, the polyacetal copolymer is basically obtained by adding appropriate molecular weight regulators to trioxymethylene (A), cyclic acetal compound (B) and aliphatic glycidyl ether compound (C), and performing bulk polymerization using a cationic polymerization catalyst.

[0034] [Linear acetal compound (D)]

[0035] As the molecular weight regulator used in this embodiment, a linear acetal compound can be used. Examples of linear acetal compounds include methyl acetal, acetaldehyde, dibutoxymethane, bis(methoxymethyl) ether, bis(ethoxymethyl) ether, and bis(butoxymethyl) ether. These can be used alone or in combination of two or more. Preferably, one or more are selected from the group consisting of methyl acetal, acetaldehyde, and dibutoxymethane.

[0036] In this embodiment, to obtain a polyacetal copolymer with superior thermal stability, rigidity, and impact resistance, it is preferable that the constituent units of the cyclic acetal compound (B) and the aliphatic glycidyl ether compound (C) in the molecular chain of the polyacetal copolymer are uniformly dispersed. For this purpose, in the manufacture of the polyacetal copolymer achieved by polymerization, a method is effective that involves uniformly mixing the cyclic acetal compound (B) and the catalyst, adding it to a previously uniformly mixed solution of the aliphatic glycidyl ether compound (C) and trioxymethylene (A), and then feeding it to a polymerizer for polymerization. By pre-mixing to form a uniform solution, not only is the dispersion of the branched structure derived from the aliphatic glycidyl ether compound improved, resulting in enhanced mechanical properties, but also superior thermal stability.

[0037] When manufacturing the polyacetal copolymer of this embodiment, which consists of the components described above, the polymerization apparatus is not particularly limited, and any known apparatus, batch or continuous method, can be used. Furthermore, the polymerization temperature is preferably maintained between 65 and 115°C.

[0038] Deactivation after polymerization can be achieved by adding an alkaline compound or its aqueous solution to the reaction products discharged from or in the polymerizer after the polymerization reaction.

[0039] Examples of cationic polymerization catalysts used in this embodiment include lead tetrachloride, tin tetrachloride, titanium tetrachloride, aluminum trichloride, zinc chloride, vanadium trichloride, antimony trichloride, phosphorus pentafluoride, antimony pentafluoride, boron trifluoride, diethyl ether of boron trifluoride, dibutyl ether of boron trifluoride, dioxane ester of boron trifluoride, acetic anhydride of boron trifluoride, triethylamine complex of boron trifluoride, perchloric acid, acetyl perchlorate, tert-butyl perchlorate, glycolic acid, trichloroacetic acid, trifluoroacetic acid, p-toluenesulfonic acid, and other inorganic and organic acids; triethyloxonium tetrafluoroboric acid, triphenylmethyl hexafluoroantimonylate, allyl diazo hexafluorophosphate, allyl diazo tetrafluoroboric acid, and other complex chlorine compounds; alkyl metal salts such as diethylzinc, triethylaluminum, and diethylaluminum chloride; heteropoly acids; and heteropolymers.

[0040] Among these, boron trifluoride coordination compounds such as boron trifluoride, boron trifluoride diethyl ether, boron trifluoride dibutyl ether, boron trifluoride dioxane, boron trifluoride acetic anhydride, and boron trifluoride triethylamine complex are particularly preferred. These catalysts can also be used after pre-diluting with organic solvents, etc.

[0041] Furthermore, the alkaline compounds used to neutralize and deactivate the polymerization catalyst can be ammonia or amines such as triethylamine, tributylamine, triethanolamine, and tributanolamine, or hydroxide salts of alkali metals or alkaline earth metals, or other known catalyst deactivators. Preferably, these aqueous solutions are rapidly added to the product after the polymerization reaction to deactivate it. Following the polymerization and deactivation methods, further cleaning, separation and recovery of unreacted monomers, and drying are performed as needed using existing known methods.

[0042] Furthermore, the unstable ends are decomposed and removed, or the unstable ends of the stable substance are sealed, and stabilization treatment is performed using known methods as needed, and various necessary stabilizers are mixed in. Examples of stabilizers used herein include any one or two or more of hindered phenolic compounds, nitrogen-containing compounds, hydroxides of alkalis or alkaline earth metals, inorganic salts, and carboxylates. Moreover, as long as it does not impair the effect of the polyacetal copolymer of this embodiment, one or more general additives for polyacetal resins, such as dyes, pigments, colorants, lubricants, nucleating agents, release agents, antistatic agents, surfactants, or organic polymers, and inorganic or organic fibrous, powdered, or plate-shaped fillers, can be added as needed.

[0043] In this embodiment, during the copolymerization process, the total mass (g) of trioxymethylene (A), cyclic acetal compound (B), and aliphatic glycidyl ether compound (C) is defined as a, the molar number of linear acetal compound (D) is defined as b, and the total molar numbers of water and methanol contained in components (A), (B), and (C) are defined as c and d, respectively. This is set to satisfy (b+c+d) / a = 4.5–9 μmol / g. When (b+c+d) / a = 4.5–9 μmol / g is satisfied, moldability can be maintained while rigidity and impact resistance are improved.

[0044] Furthermore, the water and methanol contained in (A), (B) and (C) originate from their respective impurities.

[0045] <Polyacetal copolymer>

[0046] The polyacetal copolymer of this embodiment can be obtained by the manufacturing method of the polyacetal copolymer of this embodiment described above. Therefore, the polyacetal copolymer of this embodiment has excellent rigidity and impact resistance, as well as thermal stability, and especially low discoloration when the melt is held in the molding machine.

[0047] Example

[0048] The following examples will be used to illustrate this embodiment in more detail, but this embodiment is not limited to the following examples.

[0049] [Examples 1-10]

[0050] A continuous mixing reactor, consisting of a barrel with a cross-sectional shape having two overlapping circular sections and a paddle-equipped rotating shaft, is used. The two rotating shafts with paddles rotate at 150 rpm, while trioxymethylene (A), a cyclic acetal compound (B), and an aliphatic glycidyl ether compound (C) are added according to the proportions / amounts shown in Table 1. Furthermore, as a molecular weight regulator, a linear acetal compound (D) as shown in Table 1 is continuously supplied according to the proportions / amounts shown in Table 1. This continuous supply ensures that the boron trifluoride gas relative to the trioxymethylene is 0.005% by mass, resulting in a homogeneous mixture, thereby carrying out bulk polymerization. The reaction products discharged from the polymerizer are rapidly passed through a crusher and simultaneously added to an aqueous solution containing 0.1% by mass of triethylamine at 80°C to deactivate the catalyst. After separation, washing, and drying, a crude polyacetal copolymer is obtained.

[0051] Next, relative to 100 parts by weight of the crude polyacetal copolymer, 4 parts by weight of a 5% aqueous solution of triethylamine and 0.03 parts by weight of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] were added, and the mixture was melt-blended at 210°C using a biaxial extruder to remove the unstable components.

[0052] To 100 parts by weight of the branched or crosslinked polyacetal copolymer obtained by the above method, 0.3 parts by weight of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as a stabilizer and 0.15 parts by weight of melamine were further added, and the mixture was melt-blended at 210°C using a biaxial extruder to obtain granular branched polyacetal copolymer. The results of the evaluation by the method described later are shown in Table 1.

[0053] [Comparative Examples 1-4]

[0054] The sodium content of the aliphatic glycidyl ether compound (C) is not specified in this embodiment. The values ​​of formula (b+c+d) / a are not specified in this embodiment. The results of obtaining particulate polyacetal copolymers and evaluating them in the same manner as in the examples are shown in Table 2.

[0055] In addition, the abbreviations for the components listed in Tables 1 and 2 have the following meanings.

[0056] [Cyclic acetal compounds having two or more carbon atoms in the ring]

[0057] DO; 1,3-dioxolane

[0058] [Aliphatic glycidyl ether compounds]

[0059] TPTGE; Trimethylolpropane triglycidyl ether

[0060] GTGE; Glycerol triglycidyl ether

[0061] PETGE; Pentaerythritol Tetraglycidyl Ether

[0062] Furthermore, various aliphatic glycidyl ether compounds are manufactured using different synthetic methods, resulting in a variety of compounds with different sodium contents.

[0063] [Sodium content]

[0064] The sodium content of aliphatic glycidyl ether compounds was determined using the following method: 1 g of the sample was weighed in a platinum crucible and heated using an electric stove to decompose and volatilize the organic components. The crucible was then heated at 600°C for 1 hour using an electric furnace. After cooling, the crucible was cleaned with 3.5% hydrochloric acid, and the cleaning solution was diluted to 25 ml with 3.5% hydrochloric acid to prepare the sample. Inductively coupled plasma optical emission spectrometry (ICP-OES) was performed using a SPECTRO CIROSCCD-120 to quantify the sodium content and determine the sodium content of the sample.

[0065] [The total moisture content of component (A), component (B), and component (C)]

[0066] The water content of a mixture of components (A), (B), and (C) was determined by the Karl Fischer method.

[0067] [The total amount of methanol in component (A), component (B), and component (C)]

[0068] The amount of methanol in the mixture of components (A), (B), and (C) was determined by gas chromatography.

[0069] <Evaluation>

[0070] The flexural modulus, impact resistance, and thermal stability of the particulate polyacetal copolymers involved in the examples and comparative examples were evaluated using the following methods.

[0071] [Stiffness (flexural modulus)]

[0072] Test pieces (4mm × 10mm × 80mm) were formed from the granules in the examples and comparative examples using an injection molding machine (Sumitomo Heavy Industries, Ltd. "SE100DU") at a cylinder temperature of 205°C and a mold temperature of 90°C. The flexural modulus of the test pieces was then measured according to ISO 178.

[0073] [Impact resistance (Charpy impact strength)]

[0074] Using the injection molding machine described above, notched Charpy test pieces were formed from the particles in the examples and comparative examples according to ISO 179 / IeA. Then, the Charpy impact test values ​​at 23°C were determined according to ISO 179 / IeA.

[0075] [Thermal stability (color change during molten retention in the molding machine)]

[0076] Using the injection molding machine described above, the particles from the examples and comparative examples were held in a cylinder set to 220°C for 2 hours to form a flat plate with dimensions of 50×70×3 (mm), and the appearance of the molded product was evaluated. Specifically, the hue (L, a, b) of the molded product was measured using a Z-300A color sensor manufactured by Nippon Denshoku Kogyo Co., Ltd., and the deviation (ΔE) from the initial hue was calculated using the following formula.

[0077] ΔE = [(L1-L0)] 2 +(a1-a0) 2 +(b1-b0) 2 ] 1 / 2

[0078] L, a, and b are the color values ​​measured by a colorimeter. The subscript 1 of L, a, and b means the hue after 2 hours of aging, and 0 means the hue in a normal cycle.

[0079] [Table 1]

[0080]

[0081] [Table 2]

[0082]

[0083] According to Tables 1 and 2, Examples 1-10 show that it is possible to manufacture a product with sufficient rigidity (flexural modulus of elasticity of 2800 MPa or more) and excellent impact resistance (Charpy impact strength of 9 kJ / m). 2 The above-mentioned polyacetal copolymers exhibit good thermal stability (low melt retention discoloration (below 2.5)). In contrast, although the rigidity of Comparative Examples 1-4 is comparable to that of the Examples, at least one of the impact strength and thermal stability is inferior. In particular, Examples 1, 3, 5, and 10, as well as Comparative Examples 1, 8, and 3, differ only in the sodium content of the aliphatic glycidyl ether compound; however, these comparisons show that the thermal stability is poor when the sodium content is outside the specified range.

[0084] Furthermore, Example 2, Comparative Example 2, Example 9, and Comparative Example 4 differ only in the content of the linear acetal compound, i.e. whether the formula (b+c+d) / a = 4.5~9 μmol / g is satisfied. However, based on these comparisons, it can be seen that when the above formula is not satisfied, both rigidity and impact resistance cannot be satisfied.

Claims

1. A method for manufacturing a polyacetal copolymer, comprising: The process involves copolymerizing 100 parts by weight of trioxymethylene (A), 0.05 to 5 parts by weight of a cyclic acetal compound (B) having two or more carbon atoms in the ring, and 0.001 to 0.5 parts by weight of an aliphatic glycidyl ether compound (C) selected from the group consisting of trimethylolpropane triglycidyl ether, glycerol triglycidyl ether, and pentaerythritol tetraglycidyl ether, with a sodium content of 0.1 to 80 ppm by weight, in the presence of a linear acetal compound (D) as a molecular weight regulator or acetaldehyde. In the process described above, when the total mass (g) of (A), (B) and (C) is defined as a, the number of moles of (D) or acetaldehyde is defined as b, and the total number of moles of water and methanol contained in (A), (B) and (C) is defined as c and d respectively, it is set to satisfy (b+c+d) / a=4.5~9μmol / g.

2. The method for manufacturing the polyacetal copolymer according to claim 1, wherein, The linear acetal compound (D) is selected from one or more of the group consisting of methyl acetal and dibutoxymethane.

3. A polyacetal copolymer, characterized in that, It is obtained by the method for manufacturing the polyacetal copolymer according to claim 1 or 2.

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