Branched polyoxymethylene resin

Abstract

To provide a branched polyoxymethylene resin having small spherulite size and superior mechanical strength.SOLUTION: The branched polyoxymethylene resin of the present invention includes a structure represented by general formula (1), wherein the branched polyoxymethylene resin is characterized in that the weight average molecular weight (Mw) in a molecular weight distribution curve obtained by gel permeation chromatography (GPC) measurement is 100,000 to 500,000. (In the formula, a is an integer of 1 to 4. R independently represents a hydrogen atom, a C1-C20 alkyl group which may be substituted, or an aryl group which may be substituted, and when a plurality of R groups are present, at least some of the R groups may be bonded to each other. Each of n, m, and z independently represents an integer of 1 to 1200).SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] Polyoxymethylene is excellent in the balance of mechanical properties, chemical resistance, slidability, etc., and is widely used as a typical engineering plastic mainly for electrical parts, electronic parts, automotive parts, and various other mechanical parts because its processing is easy. In recent years, with the expansion of its scope of use, there has been a tendency for more advanced properties to be required.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Especially in the case of gear parts for automobiles, from the viewpoint of durability, the demand for higher mechanical properties has been increasing. For example, in Patent Document 1, in polyoxymethylene in which a branching site is introduced by cationic polymerization using 1,3,5-trioxane as a monomer, it is disclosed that the branching site acts as a crystal nucleating agent, and the molded residual strain is suppressed and the mechanical properties are improved by the reduction of the spherulite size.

[0005] However, polyoxymethylene obtained by cationic polymerization generally has low mechanical strength because of the presence of oligomers and a low melting point, and is insufficient to meet the above requirements. Therefore, an object of the present invention is to provide a branched polyoxymethylene resin having a small spherulite size and excellent mechanical strength.

Means for Solving the Problems

[0006] That is, the present invention is as follows. [1] A branched polyoxymethylene resin characterized by containing a structure represented by the following general formula (1) and having a weight average molecular weight (Mw) in the molecular weight distribution curve obtained by gel permeation chromatography (GPC) measurement of 100,000 to 500,000. [Chemical formula] (a is an integer of any one of 1 to 4. Each R is independently a hydrogen atom, an optionally substituted alkyl group having 1 to 20 carbon atoms, or an optionally substituted aryl group. When there are a plurality of Rs, at least some of the Rs may be bonded to each other. n, m, and z are each independently an integer of any one of 1 to 1200) [2] The branched polyoxymethylene resin according to [1], wherein the comonomer introduction amount shown below is 0.0009 to 0.3 mol%. Comonomer introduction amount; 1 The value obtained by dividing the integral value of the peak derived from the main chain unit (-CH2O-) and the integral value of the peak derived from the comonomer unit (-CO-(CHR)a-CO―) calculated by 1H-NMR measurement by the number of protons of each is defined as each unit value, and the percentage of the comonomer unit value (comonomer unit value ÷ (main chain unit value + comonomer unit value) × 100) is defined as the comonomer introduction amount. [3] The branched polyoxymethylene resin according to [1] or [2], having a melting point of 172°C or higher. [4] The branched polyoxymethylene resin according to any one of [1] to [3], having an average spherulite size measured by the method shown below of 70 μm or less. After the powder obtained by polymerization is formed into a film with a hot press at 140°C, it is heated from room temperature to 190°C at 300°C / min with a polarizing microscope and then cooled to 175°C. During the process of cooling from 175°C to 156°C at 10°C / min, the global spherulite size 20 seconds after spherulites can be confirmed is measured. [5] The branched polyoxymethylene resin according to any one of [1] to [4], wherein the area ratio of the component having a molecular weight of 1,000,000 or more in the molecular weight distribution curve obtained by gel permeation chromatography (GPC) measurement is 5.0% or more. [6] A resin molded body containing the branched polyoxymethylene resin according to any one of [1] to [5]. [7] The resin molded body according to [6], which is an electrical component, an electronic component, or an automotive component. [8] The resin molded body according to [6], which is a gear or a through anchor component.

Advantages of the Invention

[0007] Since the branched polyoxymethylene resin of the present invention has the above configuration, it has a small spherulite size and excellent mechanical strength.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0009] Hereinafter, the modes for carrying out the present invention will be described in detail. Note that the present invention is not limited to the following description, and various modifications can be made and implemented within the scope of the gist.

[0010] <Branched Polyoxymethylene Resin> The branched polyoxymethylene resin in the present embodiment is characterized by including a structure represented by the following general formula (1).

Chemical Formula

[0011] The branched polyoxymethylene resin in the present embodiment has a weight average molecular weight (Mw) in the molecular weight distribution curve obtained by gel permeation chromatography (GPC) measurement of 100,000 to 500,000, preferably 120,000 to 400,000, and more preferably 150,000 to 300,000. The weight average molecular weight (Mw) can be measured by the method described in the examples below. The above branched polyoxymethylene resin preferably has the above-mentioned weight-average molecular weight and also has a higher molecular weight component. In the molecular weight distribution curve obtained by GPC measurement, the ratio of the area of the component with 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. The upper limit of the ratio is preferably 20.0%, more preferably 15.0%. By containing more high-molecular-weight components, it is expected to improve physical properties such as creep characteristics while maintaining fluidity.

[0012] The melting point of the branched polyoxymethylene resin of this embodiment is preferably 172°C or higher, more preferably 172 - 180°C, still more preferably 173 - 178°C, and particularly preferably 173 - 175°C. The above melting point can be measured by the method described in the examples below.

[0013] The number of spherulites of the branched polyoxymethylene resin of this embodiment is preferably 150 or more, more preferably 200 or more. Also, 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. The above number of spherulites and the above average spherulite size can be measured by the method described in the examples below.

[0014] The above branched polyoxymethylene resin can be obtained by introducing a comonomer when anionic polymerizing formaldehyde.

[0015] (Formaldehyde) The above-mentioned formaldehyde can be produced, for example, by reacting methanol in the presence of a silver catalyst. Although formaldehyde exists as formalin, if it contains water during polymerization, it acts as a chain transfer agent and a polyacetal with a 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. The amount of water contained in formaldehyde is preferably 100 mass ppm or less, more preferably 50 mass ppm or less, and even more preferably 20 mass ppm or less with respect to 100% by mass of formaldehyde.

[0016] (Comonomer) Branched polyoxymethylene can be obtained by copolymerizing formaldehyde and a comonomer.

[0017] The comonomer is preferably a cyclic compound having a carboxylic anhydride structure represented by the following formula. [Chemical formula] Here, a and R are as described in the above formula (1). Specific examples include 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'-tetraone 1,2,3,4-butanetetracarboxylic acid 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, diphenic anhydride, 1,1-cyclopentanediacetic anhydride, 2-octenyl succinic anhydride, dodecenyl succinic anhydride, and the like.

[0018] The introduction amount of the comonomer in the branched polyoxymethylene resin is determined by the method described in the examples below, and is preferably in the range of 0.0009 to 0.5 mol%, more preferably 0.0009 to 0.3 mol%, and still more preferably 0.0009 to 0.1 mol%.

[0019] (Polymerization catalyst) The polymerization catalyst used in the above anionic polymerization is preferably an anionic polymerization catalyst, and more preferably an onium salt-based polymerization catalyst represented by the following general formula (3). [R4R5R6R7M] + X - ···(3) (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 as or different from each other.) Only one kind of polymerization catalyst may be used alone, or two or more kinds may be mixed and used.

[0020] Among the onium salt-based polymerization catalysts, quaternary phosphonium salt-based compounds such as tetraethylphosphonium iodide and tributylethylphosphonium iodide, and quaternary ammonium salt-based compounds such as tetramethylammonium bromide and dimethyldistearylammonium acetate are preferred. The addition amount of the onium salt-based polymerization catalysts such as these quaternary phosphonium salt-based compounds and quaternary ammonium salt-based compounds is preferably 0.00003 to 0.01 mol, more preferably 0.00008 to 0.005 mol, and still more preferably 0.0001 to 0.003 mol with respect to 1 mol of formaldehyde.

[0021] (Chain transfer agent) The molecular weight of the branched polyoxymethylene can be adjusted, for example, by using a chain transfer agent such as a carboxylic anhydride or a carboxylic acid during polymerization. As the chain transfer agent, propionic anhydride and acetic anhydride are preferred, and acetic anhydride is more preferred. The chain transfer agent may be used alone as only one kind, or two or more kinds may be mixed and used.

[0022] (Polymerization solvent) As the polymerization solvent used in the above anionic polymerization, any solvent that does not react with formaldehyde may be used, and it is not particularly limited. For example, hydrocarbon solvents such as pentane, isopentane, hexane, cyclohexane, heptane, octane, nonane, decane, benzene, etc., and polar solvents such as tetrahydrofuran, butyl acetate, cyclopentyl methyl ether, etc. may be mentioned, and hexane is particularly preferred. The polymerization solvent may be used alone as only one kind, or two or more kinds may be mixed and used.

[0023] (Polymerization apparatus) The polymerization reactor for producing branched polyoxymethylene is not particularly limited as long as it can supply the monomer formaldehyde, comonomer, chain transfer agent, polymerization catalyst, and polymerization solvent. However, from the viewpoint of productivity, a continuous polymerization reactor is preferably used.

[0024] (Polymerization temperature) The polymerization temperature of the branched polyoxymethylene is preferably 50 to 65 °C, more preferably 55 to 62 °C.

[0025] The powder of the branched polyoxymethylene polymer in the polymerization reactor is transferred to the next step as a slurry after passing through a certain residence time in the polymerization machine. The residence time of the powder is preferably 20 to 120 minutes, more preferably 30 to 60 minutes.

[0026] (Terminal stabilization) It is preferable to modify the terminal groups of the branched polyoxymethylene polymer obtained by polymerization with an esterifying agent or the like and perform a stabilization treatment.

[0027] The stabilization treatment of the end groups of a branched polyoxymethylene polymer by esterification can be carried out, for example, by respectively charging a branched polyoxymethylene polymer, an esterifying agent and / or an esterification catalyst into an end stabilization reactor into which a hydrocarbon solvent is introduced, and reacting them. As the reaction temperature and reaction time at this time, the reaction temperature is preferably 130 to 155 °C, and the reaction time is preferably 1 to 100 minutes, more preferably the reaction temperature is 135 to 155 °C, and the reaction time is 5 to 100 minutes, and still more preferably the reaction temperature is 140 to 155 °C, and the reaction time is 10 to 100 minutes.

[0028] Examples of the esterifying agent include benzoic anhydride, succinic anhydride, maleic anhydride, glutaric anhydride, phthalic anhydride, propionic anhydride, and acetic anhydride, and acetic anhydride is preferred. These esterifying agents may be used alone or in combination of two or more.

[0029] As the above esterification catalyst, an alkali metal salt of a carboxylic acid having 1 to 18 carbon atoms is preferred, and its addition amount can be appropriately selected in the range of 1 to 1000 mass ppm with respect to the mass of the branched polyoxymethylene polymer. Examples of the alkali metal salt of a carboxylic acid having 1 to 18 carbon atoms include alkali metal salts of carboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caprylic acid, enanthic acid, caproic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, margaric acid, and stearic acid. Examples of the alkali metal include lithium, sodium, potassium, rubidium, and cesium. Among these alkali metal salts of carboxylic acids, alkali metal salts of lithium acetate, sodium acetate, and potassium acetate are preferred.

[0030] The branched polyoxymethylene polymer with stabilized end groups obtained by the above method is dried by removing moisture using a dryer such as a hot air dryer or a vacuum dryer, enclosing air or nitrogen gas adjusted to 100 to 150 °C, thereby obtaining the target branched polyoxymethylene.

[0031] The stabilized branched polyoxymethylene produced by the above manufacturing method may be blended with antioxidants, formic acid scavengers, weather (light) stabilizers, mold release (lubricating) agents, reinforcing agents, conductive agents, thermoplastic resins, thermoplastic elastomers, pigments, plasticizers, peroxide decomposing agents, basic auxiliary agents, antistatic agents, flame retardants, dyes, fillers, etc., which are known additives commonly used as desired. Furthermore, other polymers can be blended with the branched polyoxymethylene of the present embodiment within a range that does not impair its physical properties. The blending ratios of these blending agents are within an appropriate range.

[0032] <Resin molded article> The resin molded article of the present embodiment contains the branched polyoxymethylene resin of the above-described present embodiment. The resin molded article of the present embodiment is preferably an electrical component, an electronic component, or an automotive component. Further, the resin molded article of the present embodiment is preferably a gear or a through anchor component.

Examples

[0033] Hereinafter, the present invention will be described in detail with specific examples and comparative examples, but the present invention is not limited to the following examples.

[0034] The terms and measurement methods of characteristics in the examples and comparative examples were as follows.

[0035] <Spherulite observation> After the powder obtained by polymerization was formed into a film with a hot press at 140 °C, the spherulite state was observed with a polarized light microscope. Measuring instrument: Nikon ECLIPSE E600 POL Microscope heating stage MT-350 Measurement conditions: Sandwich the film with a cover glass and place it on the heating stage. Heat from room temperature to 190 °C at 300 °C / min and then cool to 175 °C. The spherulites growing during the cooling process from 175 °C to 156 °C at 10 °C / min were observed. The number of spherulites and the average value of the global spherulite size were evaluated 20 seconds after spherulites could be confirmed on the screen viewed at a magnification of ×10.

[0036] <Evaluation of comonomer introduction amount> The comonomer introduction amount was calculated by 1 1H-NMR measurement using a nuclear magnetic resonance apparatus. 1 The measurement conditions of 1H-NMR are shown below. Measuring device: Bruker AVANCE500HD Heavy solvent: HFIP-d Sample concentration: 1 mass% Observation frequency: 500 MHz Number of integrations: 512 times Measurement temperature: room temperature (Calculation method) The integrated value of the peak derived from the main chain unit (-CH2O-) of the oxymethylene polymer and the integrated value of the peak derived from the comonomer unit (-CO-(CHR)a-CO―) were divided by the number of protons of each, and the resulting values were used as the unit values for each unit. The percentage of the comonomer unit value (comonomer unit value ÷ (main chain unit value + comonomer unit value) × 100) was taken as the comonomer introduction amount.

[0037] <Molecular weight evaluation (GPC)> The weight average molecular weight Mw of the branched polyoxymethylene resin and the area ratio of the components with a molecular weight of 1 million or more in the molecular weight distribution curve were obtained by measuring with GPC (gel permeation chromatography). Measuring instrument: HLC-8320GPC manufactured by Tosoh Corporation Column: TSK-GEL SUPER HM-H, TSK-GURDCOLUMN SUPER H-H Detector: RI (differential refractive index detector) Eluent: HFIP (hexafluoroisopropanol) Eluent flow rate: 0.3 ml / min The weight average molecular weight was obtained by the calibration curve method using polymethyl methacrylate as the standard substance.

[0038] <MFR (Melt Flow Rate: g / 10 min)> 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. in accordance with ASTM-D-1238.

[0039] <Melting Point> The melting point of the branched polyoxymethylene resin was obtained by measuring it by the DSC method. Measuring Instrument: DSC8000 manufactured by PerkinElmer Measurement Conditions: The sample was set, heated to 200 °C at 300 °C / min, cooled to 130 °C at 10 °C / min. Then, the temperature at the peak of the heat of fusion during the heating process to 200 °C at 2.5 °C / min was taken as the melting point.

[0040] <Tensile Strength> The tensile strength of the branched polyoxymethylene resin was measured in accordance with ASTM D638 using dumbbell test specimens obtained at a cylinder temperature of 190 °C and a mold temperature of 65 °C using an injection molding machine.

[0041] (Example 1) 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 normal hexane solution at 60 °C, and purified formaldehyde was added and polymerized. The addition amount of dimethyldistearylammonium acetate was 0.009 mol% / mol-monomer with respect 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 to obtain branched polyoxymethylene. 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.

[0042] (Example 2) In the process of Example 1, branched polyoxymethylene was obtained in the same manner except that the addition amount of 4-MHHPA was changed to 0.1 mol% / mol-monomer. The evaluation results are shown in Table 1. Also, a photograph of spherulites is shown in Fig. 1.

[0043] (Example 3) In the process of Example 1, branched polyoxymethylene was obtained in the same manner except that the addition amount of 4-MHHPA was changed to 0.01 mol% / mol-monomer. The evaluation results are shown in Table 1.

[0044] (Example 4) In the process of Example 1, branched polyoxymethylene was obtained in the same manner except that the addition amount of 4-MHHPA was changed to 0.001 mol% / mol-monomer. The evaluation results are shown in Table 1.

[0045] (Example 5) In the process of Example 1, branched polyoxymethylene was obtained in the same manner except that octyl succinic anhydride was added in an amount of 0.1 mol% / mol-monomer instead of 4-MHHPA. The evaluation results are shown in Table 1.

[0046] (Example 6) In the process of Example 5, branched polyoxymethylene was obtained in the same manner except that octyl succinic anhydride was added in an amount of 0.05 mol% / mol-monomer. As shown in Fig. 3, the obtained branched polyoxymethylene showed bimodality in the GPC chart. The weight average molecular weight was 297,000, the area ratio of components 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 it had a higher weight average molecular weight and a higher MFR compared to Example 5 (weight average molecular weight 255,000, area ratio of components with a molecular weight of 1 million or more 0.66%, MFR 2.1 g / 10 min) and Comparative Example 1 described below (weight average molecular weight 180,000, area ratio of components with a molecular weight of 1 million or more 0.19%, MFR 3.0 g / 10 min).

[0047] (Comparative Example 1) In the process of Example 1, polyoxymethylene was obtained in the same manner except that 4-MHHPA was not added. The evaluation results are shown in Table 1. Also, a photograph of spherulites is shown in Figure 2.

[0048] (Comparative Example 2) In the process of Example 1, branched polyoxymethylene was obtained in the same manner except that 1 mol% / mol of ethylhexyl glycidyl ether (EHG) was added instead of 4-MHHPA based on the monomer amount. The evaluation results are shown in Table 1.

[0049] (Comparative Example 3) Copolymer by cationic polymerization As a polymerization reactor, a twin-screw paddle type continuous polymerization reactor with a jacket through which a heat medium can pass (manufactured by Kurimoto Iron Works, diameter 2B, L / D = 14.8) was adjusted to 80°C. A mixture of boron trifluoride-diethyl etherate (a complex compound of boron trifluoride) as a polymerization catalyst and ethyl acetate as an organic solvent was used as a catalyst solution. A mixed solution obtained by continuously mixing trioxane as a monomer component, 1,3-dioxolane (4.2 mol% based on 1 mol of trioxane), ethylhexyl glycidyl ether (EHG) as a comonomer (1.0 mol% based on 1 mol of trioxane), and methylal as a low molecular weight acetal compound in a pipe, and the catalyst solution were continuously supplied to the polymerization reactor through separate pipes to carry out a polymerization reaction to obtain branched polyoxymethylene.

[0050] [Table 1]

[0051] As shown in the results in Table 1, in Comparative Examples 1 and 2 where no comonomer was introduced or a comonomer other than an acid anhydride was used, the spherulite size of the obtained polyoxymethylene tended to be large. [Industrial Applicability]

[0052] The present invention can provide a branched polyoxymethylene resin having a small spherulite size, and since it is expected to have a small molding strain and excellent mechanical properties, it can be applied to electrical parts, electronic parts, automotive parts, and other various mechanical parts. Among them, it can be suitably applied to gears, through anchors, etc.

Claims

1. A branched polyoxymethylene resin comprising a structure represented by the following general formula (1), wherein the weight-average molecular weight (Mw) in the molecular weight distribution curve obtained by gel permeation chromatography (GPC) measurement is 100,000 to 500,000. 【Chemical 1】 (a is an integer of any one of 1 to 4. R is each independently a hydrogen atom, an optionally substituted alkyl group having 1 to 20 carbon atoms, or an optionally substituted aryl group. When there are a plurality of Rs, at least some of the Rs may be bonded to each other. n, m, and z are each independently an integer of any one of 1 to 1200)

2. The branched polyoxymethylene resin according to claim 1, wherein the comonomer introduction amount shown below is 0.0009 to 0.3 mol%. Comonomer introduction amount; １ The integral value of the peak derived from the main chain unit (—CH ２ O—) calculated by 1H-NMR measurement and the integral value of the peak derived from the comonomer unit (—CO—(CHR)a—CO—) are divided by the respective number of protons, and the resulting values are taken as the unit values for each unit. The percentage of the comonomer unit value (comonomer unit value ÷ (main chain unit value + comonomer unit value) × 100) is defined as the comonomer introduction amount.

3. The branched polyoxymethylene resin according to claim 1, having a melting point of 172°C or higher.

4. The branched polyoxymethylene resin according to claim 1, wherein the average spherulite size measured by the method shown below is 70 μm or less. The powder obtained by polymerization is formed into a film with a hot press at 140°C, and then heated from room temperature to 190°C at 300°C / min with a polarizing microscope and cooled to 175°C. During the process of cooling from 175°C to 156°C at 10°C / min, the global spherulite size 20 seconds after spherulites can be confirmed is measured.

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

6. A resin molded article comprising the branched polyoxymethylene resin according to any one of claims 1 to 5.

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

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

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