Branched polyoxymethylene resins

Abstract

The invention relates to branched polyoxymethylene resins. The purpose of the present invention is to provide a branched polyoxymethylene resin having a small spherocrystal size and excellent mechanical strength. The branched polyoxymethylene resin according to the present invention is characterized in that the branched polyoxymethylene resin contains a structure represented by general formula (1), and the weight-average molecular weight (Mw) in the molecular weight distribution curve of the branched polyoxymethylene resin as determined by gel permeation chromatography (GPC) is 100,000-500,000.

Description

Technical Field

[0001] The present invention relates to a branched polyoxymethylene resin. Background Art

[0002] The balance of mechanical properties, chemical resistance, slidability, etc. of polyoxymethylene is excellent, and it is easy to process. Therefore, as a representative engineering plastic, it is widely used mainly for electrical components, electronic components, automotive components, and various other mechanical components. In recent years, with the expansion of its application range, higher properties have been gradually required.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent No. 2517698 Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] In particular, for gear components used in automobiles, from the viewpoint of durability, higher requirements for mechanical properties are increasing. For example, Patent Document 1 discloses that in polyoxymethylene in which a branching site is introduced by cationic polymerization using 1,3,5-trioxane as a monomer, the branching site functions as a crystal nucleating agent, the spherulite size becomes smaller, and thus the molding residual strain is suppressed and the mechanical properties are improved.

[0008] However, polyoxymethylene obtained by cationic polymerization generally has low mechanical strength due to the presence of oligomers and a decrease in melting point, and is not sufficient to meet the above requirements.

[0009] Therefore, an object of the present invention is to provide a branched polyoxymethylene resin having a small spherulite size and excellent mechanical strength.

[0010] Means for Solving the Problems

[0011] That is, the present invention is as follows.

[0012] [1] A branched polyoxymethylene resin, characterized in that the branched polyoxymethylene resin contains a structure represented by the following general formula (1), and the weight average molecular weight (Mw) in the molecular weight distribution curve of the branched polyoxymethylene resin measured by gel permeation chromatography (GPC) is 100,000 to 500,000.

[0013] ···(1)

[0014] (In the general formula (1), a is any integer from 1 to 4, each R is independently a hydrogen atom, an alkyl group with 1 to 20 carbon atoms that may be substituted, or an aryl group that may be substituted. When there are multiple Rs, at least a part of the Rs may be bonded to each other. n, m, and z are each independently any integer from 1 to 1200.)

[0015] [2] The branched polyoxymethylene resin according to [1], wherein the amount of the copolymerized monomer introduced is 0.0009 mol% to 0.3 mol%.

[0016] Amount of copolymerized monomer introduced:

[0017] Using 1 The integral value of the peak attributed to the main chain unit (-CH2O-) and the integral value of the peak attributed to the copolymerized monomer unit (-CO-(CHR)a-CO-) calculated by 1H-NMR measurement are divided by the number of protons to obtain the respective unit values, and the percentage of the copolymerized monomer unit value (copolymerized monomer unit value ÷ (main chain unit value + copolymerized monomer unit value) × 100) is used as the amount of the copolymerized monomer introduced.

[0018] [3] The branched polyoxymethylene resin according to [1] or [2], wherein the melting point of the branched polyoxymethylene resin is 172 °C or higher.

[0019] [4] The branched polyoxymethylene resin according to any one of [1] to [3], wherein the average spherulite size of the branched polyoxymethylene resin measured by the following method is 70 μm or less.

[0020] The polymerized powder is formed into a film using a hot press at 140 °C, and then heated from room temperature to 190 °C at 300 °C / min using a polarizing microscope and naturally cooled to 175 °C; the sizes of all spherulites 20 seconds after the spherulites are confirmed during the process of cooling from 175 °C to 156 °C at 10 °C / min are measured.

[0021] [5] The branched polyoxymethylene resin according to any one of [1] to [4], wherein the area ratio of the component with a molecular weight of 1 million or more in the molecular weight distribution curve of the branched polyoxymethylene resin measured by gel permeation chromatography (GPC) is 5.0% or more.

[0022] [6] A resin molded article, wherein the resin molded article contains the branched polyoxymethylene resin according to any one of [1] to [5].

[0023] [7] The resin molded article according to [6], wherein the resin molded article is an electrical component, an electronic component, or an automotive component.

[0024] [8] The resin molded body according to [6], wherein the resin molded body is a gear or a through-anchor member.

[0025] Advantages of the Invention

[0026] The branched polyoxymethylene resin of the present invention has the above-described constitution, and thus has a small spherulite size and excellent mechanical strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a spherulite photograph of the branched polyoxymethylene resin of Example 2.

[0028] Figure 2 It is a spherulite photograph of the branched polyoxymethylene resin of Comparative Example 1.

[0029] Figure 3 It is a GPC chart of the polyoxymethylene resins of Example 5, Example 6, and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0030] Hereinafter, the mode for carrying out the present invention will be described in detail. It should be noted that the present invention is not limited to the following description, and various modifications can be made within the scope of the gist thereof.

[0031] <Branched Polyoxymethylene Resin>

[0032] The branched polyoxymethylene resin in the present embodiment is characterized by containing a structure represented by the following general formula (1).

[0033] ···(1)

[0034] In the general formula (1), a is any integer from 1 to 4, preferably 2 to 3, and more preferably 2.

[0035] Each R is independently a hydrogen atom, an alkyl group having 1 to 20 carbon atoms which may be substituted, or an aryl group which may be substituted. When there are a plurality of Rs, at least a part of the Rs may be bonded to each other. The above alkyl group may be linear, branched, cyclic, or a combination thereof. The above R may be a combination of the alkyl group having 1 to 20 carbon atoms which may be substituted and the aryl group which may be substituted. The number of carbon atoms of the above aryl group is preferably 6 to 10, more preferably 6 to 8. When the Rs are bonded to each other, a ring structure containing a plurality of Rs may be formed. The above ring structure is preferably an alicyclic hydrocarbon or an aromatic ring having 3 to 10 carbon atoms which may be substituted and having a = 2 and two Rs bonded, more preferably an alicyclic hydrocarbon or an aromatic ring having 3 to 6 carbon atoms which may be substituted, and further preferably an alicyclic hydrocarbon having 3 to 6 carbon atoms which may be substituted. Examples of the substituents in the above alkyl group, the above aryl group, and the above ring structure include: a linear or branched alkyl group having 1 to 15 carbon atoms, an alkenyl group having 1 to 15 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, an aromatic hydrocarbon group having 6 to 10 carbon atoms, and a combination thereof.

[0036] n, m, and z are each independently any integer from 1 to 1200, preferably any integer from 1 to 1000.

[0037] The branched polyoxymethylene resin of the present embodiment preferably contains only a structure represented by the general formula (1) having hydrogen atoms at both ends or terminal groups described later (for example, terminal groups introduced using an esterifying agent and / or an esterification catalyst described later).

[0038] The weight-average molecular weight (Mw) in the molecular weight distribution curve of the branched polyoxymethylene resin in the present embodiment measured by gel permeation chromatography (GPC) is 100,000 to 500,000, preferably 120,000 to 400,000, and further preferably 150,000 to 300,000.

[0039] It should be noted that the weight-average molecular weight (Mw) can be measured by the method described in the examples described later.

[0040] The above branched polyoxymethylene resin preferably has the above weight-average molecular weight and has a component with a higher molecular weight. In the molecular weight distribution curve measured by GPC, the ratio of the area of the component having a molecular weight of 1,000,000 or more to the total area is preferably 2.0% or more, more preferably 5.0% or more. As the upper limit of this ratio, 20.0% is preferred, and 15.0% is more preferred. By containing more components with a high molecular weight, it is possible to expect to improve physical properties such as creep characteristics while maintaining fluidity.

[0041] The melting point of the branched polyoxymethylene resin of the present embodiment is preferably 172 °C or higher, more preferably 172 °C to 180 °C, further preferably 173 °C to 178 °C, and particularly preferably 173 °C to 175 °C.

[0042] The above melting point can be measured by the method described in the following examples.

[0043] The number of spherulites of the branched polyoxymethylene resin of this embodiment is preferably 150 or more, more preferably 200 or more.

[0044] In addition, the average spherulite size of the branched polyoxymethylene resin of this embodiment is preferably 200 μm or less, more preferably 100 μm or less, still more preferably 80 μm or less, and particularly preferably 70 μm or less.

[0045] The above number of spherulites and the above average spherulite size can be measured by the method described in the following examples.

[0046] The above branched polyoxymethylene resin can be obtained by introducing a comonomer during anionic polymerization of formaldehyde.

[0047] (Formaldehyde)

[0048] The above formaldehyde can be produced, for example, by reacting methanol in the presence of a silver catalyst. Formaldehyde exists in the form of an aqueous formaldehyde solution, but when water is present during polymerization, water acts as a chain transfer agent and a polyacetal with the desired weight-average molecular weight cannot be obtained. Therefore, it is preferable to purify and remove water to a certain concentration before the start of polymerization.

[0049] As the amount of water contained in formaldehyde, relative to 100% by mass of formaldehyde, it is preferably 100 mass ppm or less, more preferably 50 mass ppm or less, and still more preferably 20 mass ppm or less.

[0050] (Comonomer)

[0051] Branched polyoxymethylene is obtained by copolymerizing formaldehyde with a comonomer.

[0052] The comonomer is preferably a cyclic compound having a carboxylic anhydride structure represented by the following formula.

[0053]

[0054] Here, a and R are as described in the above formula (1).

[0055] As specific examples, the following can be cited: cis-1,2-cyclohexanedicarboxylic anhydride, 4-methylcyclohexane-1,2-dicarboxylic anhydride, 4-tert-butylphthalic anhydride, butyl succinic anhydride, tetrahydro[3,3'-bifuran]-2,2',5,5'-tetrone, 1,2,3,4-butanetetracarboxylic 1,2:3,4-dianhydride, 1,1-cyclohexanediacetic anhydride, 3-methylglutaric anhydride, n-octyl succinic anhydride, phenyl succinic anhydride, 2-dodecen-1-yl succinic anhydride, dodecyl succinic anhydride, biphenyl anhydride, 1,1-cyclopentanediacetic anhydride, 2-octenyl succinic anhydride, dodecenyl succinic anhydride, etc.

[0056] The introduction amount of the comonomer in the above-mentioned branched polyoxymethylene resin is determined by the method described in the following examples, and is preferably in the range of 0.0009 mol% to 0.5 mol%, more preferably 0.0009 mol% to 0.3 mol%, and still more preferably 0.0009 mol% to 0.1 mol%.

[0057] (Polymerization catalyst)

[0058] The polymerization catalyst used in the above anionic polymerization is preferably an anionic polymerization catalyst, more preferably a salt polymerization catalyst represented by the following general formula (3). Salt polymerization catalyst.

[0059] [R4R5R6R7M] + X - ··· (3)

[0060] (In the general formula (3), R4, R5, R6 and R7 each independently represent an alkyl group, M represents an element having a lone pair of electrons, and X represents a nucleophilic group. R4, R5, R6 and R7 may be the same or different from each other.)

[0061] The polymerization catalyst can be used alone as only one kind, or two or more kinds can be mixed and used.

[0062] In the salt polymerization catalyst, tetraethylammonium iodide , tributylethylammonium iodide and other quaternary salt compounds; quaternary ammonium salt compounds such as tetramethylammonium bromide and dimethyldistearylammonium acetate. Relative to 1 mole of formaldehyde, the addition amount of these quaternary salt compounds and quaternary ammonium salt compounds salt polymerization catalysts is preferably 0.00003 mol to 0.01 mol, more preferably 0.00008 mol to 0.005 mol, and still more preferably 0.0001 mol to 0.003 mol.

[0063] (Chain transfer agent)

[0064] The molecular weight of the branched polyoxymethylene can be adjusted, for example, by using a chain transfer agent such as carboxylic anhydride or carboxylic acid during polymerization. As the chain transfer agent, propionic anhydride and acetic anhydride are preferred, and acetic anhydride is more preferred.

[0065] The chain transfer agent can be used alone as only one kind, or two or more kinds can be mixed and used.

[0066] (Polymerization solvent)

[0067] As the polymerization solvent used in the above anionic polymerization, any solvent that does not react with formaldehyde can be used, and there is no particular limitation. For example, hydrocarbon solvents such as pentane, isopentane, hexane, cyclohexane, heptane, octane, nonane, decane, and benzene can be cited; polar solvents such as tetrahydrofuran, butyl acetate, and cyclopentyl methyl ether, and hexane is particularly preferred.

[0068] The polymerization solvent can be used alone as only one kind, or two or more kinds can be mixed and used.

[0069] (Polymerization device)

[0070] The polymerization reactor for manufacturing the branched polyoxymethylene is not particularly limited as long as it can supply formaldehyde, comonomer, chain transfer agent, polymerization catalyst, and polymerization solvent as monomers. From the viewpoint of productivity, a continuous polymerization reactor is preferred.

[0071] (Polymerization temperature)

[0072] The polymerization temperature of the branched polyoxymethylene is preferably 50 °C to 65 °C, and more preferably 55 °C to 62 °C.

[0073] After the powder of the branched polyoxymethylene polymer in the polymerization reactor has passed through a certain residence time in the polymerizer, it is transferred to the next process in the form of a slurry. The residence time of the powder is preferably 20 minutes to 120 minutes, and more preferably 30 minutes to 60 minutes.

[0074] (Terminal stabilization)

[0075] It is preferred to modify the end groups of the branched polyoxymethylene polymer obtained by polymerization using an esterifying agent or the like for stabilization treatment.

[0076] The stabilization treatment of the end groups of the esterification-based branched polyoxymethylene polymer can be carried out, for example, by separately introducing the branched polyoxymethylene polymer, an esterifying agent, and / or an esterification catalyst into an end stabilization reactor into which a hydrocarbon solvent has been introduced and allowing them to react. As the reaction temperature and reaction time at this time, the reaction temperature is preferably 130°C to 155°C, and the reaction time is preferably 1 minute to 100 minutes. More preferably, the reaction temperature is 135°C to 155°C, and the reaction time is 5 minutes to 100 minutes. Further preferably, the reaction temperature is 140°C to 155°C, and the reaction time is 10 minutes to 100 minutes.

[0077] As such an esterifying agent, for example, benzoic anhydride, succinic anhydride, maleic anhydride, glutaric anhydride, phthalic anhydride, propionic anhydride, and acetic anhydride can be cited, and acetic anhydride is preferred.

[0078] These esterifying agents can be used alone, or two or more of them can be used in combination.

[0079] As the above-mentioned esterification catalyst, an alkali metal salt of a carboxylic acid having 1 to 18 carbon atoms is preferred. The addition amount of the esterification catalyst can be appropriately selected within the range of 1 mass ppm to 1000 mass ppm with respect to the mass of the branched polyoxymethylene polymer. As the alkali metal salt of a carboxylic acid having 1 to 18 carbon atoms, for example, alkali metal salts of formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, heptadecanoic acid, stearic acid, etc. can be cited. As the alkali metal, lithium, sodium, potassium, rubidium, and cesium can be cited. Among these alkali metal salts of carboxylic acids, alkali metal salts such as lithium acetate, sodium acetate, and potassium acetate are preferred.

[0080] For the branched polyoxymethylene polymer whose end groups are stabilized by the above method, a dryer such as a hot air dryer or a vacuum dryer is used, and air or nitrogen adjusted to 100°C to 150°C is sealed in to remove moisture and carry out drying, thereby obtaining the target branched polyoxymethylene.

[0081] In the stabilized branched polyoxymethylene produced by the above manufacturing method, antioxidants, formic acid scavengers, weather (light) stabilizers, release (lubricating) agents, reinforcing agents, conductive agents, thermoplastic resins, thermoplastic elastomers, pigments, plasticizers, peroxide decomposing agents, basic auxiliaries, antistatic agents, flame retardants, dyes, fillers, etc., which are well-known additives commonly used, can also be incorporated as needed. In addition, in the branched polyoxymethylene of the present embodiment, other polymers can also be incorporated within the range that does not impair its physical properties. The compounding ratios of these compounding agents are within an appropriate range.

[0082] <Resin molded body>

[0083] The resin molded body of the present embodiment contains the branched polyoxymethylene resin of the present embodiment. The resin molded body of the present embodiment is preferably an electrical component, an electronic component, or an automotive component. Additionally, the resin molded body of the present embodiment is preferably a gear or a through-anchor component.

[0084] Examples

[0085] Hereinafter, specific examples and comparative examples will be listed to describe the present invention in detail, but the present invention is not limited to the following examples.

[0086] It should be noted that the measurement methods of the terms and properties in the examples and comparative examples are as follows.

[0087] <Spherulite Observation>

[0088] The polymerized powder was formed into a film using a hot press at 140 °C, and then the spherulite state was observed using a polarized light microscope.

[0089] Measurement Equipment: Nikon ECLIPSE E600 POL

[0090] Microscope Heating Stage MT-350

[0091] Measurement Conditions: The film was sandwiched between cover glasses and placed on the heating stage.

[0092] It was heated from room temperature to 190 °C at 300 °C / minute and then naturally cooled to 175 °C. The spherulites grown during the cooling process from 175 °C to 156 °C at 10 °C / minute were observed.

[0093] The number of spherulites and the average value of the sizes of all spherulites 20 seconds after the spherulites were confirmed in the image observed at a magnification of ×10 were evaluated.

[0094] <Evaluation of the Amount of Copolymer Monomer Introduced>

[0095] The amount of copolymer monomer introduced was calculated by 1 1H-NMR measurement using a nuclear magnetic resonance apparatus.

[0096] 1 The measurement conditions of 1H-NMR are as follows.

[0097] Measurement Apparatus: Bruker AVANCE500HD

[0098] Deuterated Solvent: HFIP-d

[0099] Sample Concentration: 1 mass%

[0100] Observation Frequency: 500 MHz

[0101] Number of Accumulations: 512 times

[0102] Measured temperature: room temperature

[0103] (Calculation method)

[0104] The integrated value of the peak attributed to the main chain unit (-CH2O-) of the formaldehyde polymer and the integrated value of the peak attributed to the comonomer unit (-CO-(CHR)a-CO-) are divided by the respective number of protons to obtain the respective unit values, and the percentage of the comonomer unit value (comonomer unit value ÷ (main chain unit value + comonomer unit value) × 100) is taken as the comonomer incorporation amount.

[0105] (Molecular weight evaluation (GPC))

[0106] The weight-average molecular weight Mw of the branched polyoxymethylene resin and the area ratio of the components with a molecular weight of more than 1 million in the molecular weight distribution curve are obtained by measurement using GPC (gel permeation chromatography).

[0107] Measuring equipment: HLC-8320 GPC manufactured by Tosoh Corporation

[0108] Column: TSK-GEL SUPER HM-H, TSK-GURDCOLUMN SUPER H-H

[0109] Detector: RI (differential refractive index detector)

[0110] Eluent: HFIP (hexafluoroisopropanol)

[0111] Eluent flow rate: 0.3 ml / min

[0112] Polymethyl methacrylate is used as a standard substance, and the weight-average molecular weight is obtained by the calibration curve method.

[0113] (MFR (melt flow rate: g / 10 min))

[0114] The MFR (melt flow rate: g / 10 min) of the branched polyoxymethylene resin was measured under the conditions of 190 °C and 2160 g using a MELT INDEXER manufactured by Toyo Seiki Co., Ltd. according to ASTM-D-1238.

[0115] (Melting point)

[0116] The melting point of the branched polyoxymethylene resin is obtained by measurement using the DSC method.

[0117] Measuring equipment: DSC8000 manufactured by PerkinElmer

[0118] Measurement conditions: Place the sample and heat it to 200 °C at a rate of 300 °C / minute, then cool it to 130 °C at a rate of 10 °C / minute. Then, the temperature at the melting heat peak during the heating process to 200 °C at a rate of 2.5 °C / minute was taken as the melting point.

[0119] <Tensile strength>

[0120] Regarding the tensile strength of the branched polyoxymethylene resin, dumbbell test pieces obtained using an injection molding machine under the conditions of a barrel temperature of 190 °C and a mold temperature of 65 °C were used, and the tensile strength was measured according to the ASTM D638 method.

[0121] (Example 1)

[0122] Dimethyldistearylammonium acetate as a polymerization catalyst, acetic anhydride as a chain transfer agent, and 4-methylcyclohexane-1,2-dicarboxylic anhydride (4-MHHPA) as a comonomer were added to a n-hexane solution at 60 °C. Purified formaldehyde was added and polymerization was carried out. The addition amount of dimethyldistearylammonium acetate was 0.009 mol% / mol - monomer relative to 1 mol of formaldehyde. The addition amount of acetic anhydride was 0.02 mol% / mol - monomer. The addition amount of 4-MHHPA was 1.0 mol% / mol - monomer. The granular branched polyoxymethylene slurry of the polymer was filtered and dried at 60 °C for 10 hours under a nitrogen atmosphere, whereby branched polyoxymethylene was obtained. The obtained branched polyoxymethylene was subjected to the above-mentioned molecular weight evaluation and spherulite observation, and the weight average molecular weight (Mw), the number of spherulites, and the spherulite size were evaluated. The evaluation results are shown in Table 1.

[0123] (Example 2)

[0124] In the procedure of Example 1, the addition amount of 4-MHHPA was changed to 0.1 mol% / mol - monomer. Otherwise, branched polyoxymethylene was obtained by the same method. The evaluation results are shown in Table 1. In addition, a photograph of the spherulites is as Figure 1 shown.

[0125] (Example 3)

[0126] In the procedure of Example 1, the addition amount of 4-MHHPA was changed to 0.01 mol% / mol - monomer. Otherwise, branched polyoxymethylene was obtained by the same method. The evaluation results are shown in Table 1.

[0127] (Example 4)

[0128] In the procedure of Example 1, the addition amount of 4-MHHPA was changed to 0.001 mol% / mol - monomer. Otherwise, branched polyoxymethylene was obtained by the same method. The evaluation results are shown in Table 1.

[0129] (Example 5)

[0130] In the process of Example 1, 0.1 mol% / mol of the amount of octyl succinic anhydride was added in place of 4-MHHPA, and otherwise, branched polyoxymethylene was obtained in the same manner. The evaluation results are shown in Table 1.

[0131] (Example 6)

[0132] In the process of Example 5, 0.05 mol% / mol of the amount of octyl succinic anhydride was added, and otherwise, branched polyoxymethylene was obtained in the same manner. As Figure 3 shown, the obtained branched polyoxymethylene showed bimodality in the GPC chart. The weight-average molecular weight was 297,000, the area ratio of the component with a molecular weight of 1 million or more was 5.0%, and the MFR was 2.2 g / 10 min. It was found that compared with Example 5 (weight-average molecular weight of 255,000, area ratio of the component with a molecular weight of 1 million or more of 0.66%, MFR of 2.1 g / 10 min) and Comparative Example 1 described later (weight-average molecular weight of 180,000, area ratio of the component with a molecular weight of 1 million or more of 0.19%, MFR of 3.0 g / 10 min), it had a higher weight-average molecular weight and a higher MFR at the same time.

[0133] (Comparative Example 1)

[0134] In the process of Example 1, 4-MHHPA was not added, and otherwise, polyoxymethylene was obtained in the same manner. The evaluation results are shown in Table 1. In addition, a photograph of spherulites is as Figure 2 shown.

[0135] (Comparative Example 2)

[0136] In the process of Example 1, 1 mol% / mol of the amount of 2-ethylhexyl glycidyl ether (EHG) was added in place of 4-MHHPA, and otherwise, branched polyoxymethylene was obtained in the same manner. The evaluation results are shown in Table 1.

[0137] (Comparative Example 3)

[0138] Copolymer obtained by cationic polymerization

[0139] A jacketed biaxial paddle-type continuous polymerization reactor (manufactured by Kurimoto Iron Works, diameter 2B, L / D = 14.8) that can pass a heat medium as a polymerization reactor was adjusted to 80°C. A solution obtained by mixing boron trifluoride-ether complex (a complex of boron trifluoride) as a polymerization catalyst and ethyl acetate as an organic solvent was used as a catalyst solution.

[0140] A mixed solution obtained by continuously mixing paraformaldehyde as a monomer component, 1,3-dioxolane (4.2 mol% relative to 1 mol of paraformaldehyde), ethylhexyl glycidyl ether (EHG) as a comonomer (1.0 mol% relative to 1 mol of paraformaldehyde), and methylal as a low-molecular-weight acetal compound through pipelines, and the above catalyst solution are continuously supplied to a polymerization reactor through their respective pipelines and subjected to a polymerization reaction, thereby obtaining branched polyoxymethylene.

[0141] [Table 1]

[0142]

[0143] As shown by the results in Table 1, in Comparative Example 1 and Comparative Example 2 where no comonomer was introduced or a comonomer other than an acid anhydride was used, there was a tendency for the spherulite size of the obtained polyoxymethylene to be large.

[0144] Industrial Applicability

[0145] According to the present invention, it is possible to provide a branched polyoxymethylene resin with a small spherulite size, and it is expected to have a small molding strain and excellent mechanical properties. Therefore, it can be applied to electrical components, electronic components, automotive components, and various other mechanical components. Among them, it can be suitably applied to gears, through anchors, etc.

Claims

1. A branched polyoxymethylene resin, characterized in that, The branched polyoxymethylene resin contains a structure represented by the following general formula (1), and the weight-average molecular weight (Mw) in the molecular weight distribution curve of the branched polyoxymethylene resin measured by gel permeation chromatography (GPC) is 100,000 to 500,000. ···（1） In the general formula (1), a is any integer from 1 to 4, each R is independently a hydrogen atom, an alkyl group with 1 to 20 carbon atoms that may be substituted, or an aryl group that may be substituted. When there are multiple Rs, at least a part of the Rs may be bonded to each other, and n, m, and z are each independently any integer from 1 to 1200.

2. The branched polyoxymethylene resin according to claim 1, wherein, The introduced amount of the following copolymer monomer is 0.0009 mol% to 0.3 mol%. Introduced amount of copolymer monomer: will be determined by 1 The integral value of the peak attributed to the main chain unit (-CH2O-) and the integral value of the peak attributed to the comonomer unit (-CO-(CHR)a-CO-) calculated by 1H-NMR measurement are used as the respective unit values, and the percentage of the comonomer unit value (comonomer unit value ÷ (main chain unit value + comonomer unit value) × 100) is used as the comonomer incorporation amount.

3. The branched polyoxymethylene resin according to claim 1, wherein, The melting point of the branched polyoxymethylene resin is 172 °C or higher.

4. The branched polyoxymethylene resin according to claim 1, wherein The average spherulite size of the branched polyoxymethylene resin measured by the following method is 70 μm or less. The polymerized powder is formed into a film using a hot press at 140 °C, and then heated from room temperature to 190 °C at 300 °C / min using a polarized light microscope and naturally cooled to 175 °C; the size of all spherulites 20 seconds after the spherulites are confirmed during the process of cooling from 175 °C to 156 °C at 10 °C / min is measured.

5. The branched polyoxymethylene resin according to claim 1, wherein The area ratio of the component with a molecular weight of 1,000,000 or more in the molecular weight distribution curve of the branched polyoxymethylene resin measured by gel permeation chromatography (GPC) is 5.0% or more.

6. A resin molded body, wherein, The resin molded article contains the branched polyoxymethylene resin according to any one of claims 1 to 5.

7. The resin molded body according to claim 6, wherein, The resin molded article is an electrical component, an electronic component, or an automotive component.

8. The resin molded body according to claim 6, wherein, The resin molded article is a gear or a through-anchor component.

Images