Method for producing oxymethylene copolymer

Abstract

The present invention is directed to a method for producing an oxymethylene copolymer by subjecting trioxane and 1,3-dioxolane to copolymerization using boron trifluoride or a coordination compound thereof as a catalyst, wherein the copolymerization is conducted in the presence of a steric-hindrance phenol in an amount of 0.006 to 2.0% by weight, based on the weight of the trioxane, using 0.01 to 0.07 mmol of boron trifluoride or a coordination compound thereof as a catalyst, relative to 1 mol of the trioxane, and wherein, at a point in time when the polymerization yield becomes 92% or more, the formed oxymethylene copolymer and a polymerization terminator are contacted to terminate the polymerization.

Claims

1. A method for producing an oxymethylene copolymer by subjecting trioxane and 1,3-dioxolane to copolymerization using boron trifluoride or a coordination compound thereof as a catalyst, comprising: charging a monomer mixture of the trioxane and 1,3-dioxolane with a steric-hindrance phenol in an amount of 0.006 to 2.0% by weight, based on the weight of the trioxane, then conducting the copolymerization using 0.01 to 0.07 mmol of boron trifluoride or a coordination compound thereof as a catalyst, relative to 1 mol of the trioxane to form the oxymethylene copolymer, and then contacting the formed oxymethylene copolymer and a polymerization terminator to terminate the polymerization when the polymerization yield has reached at least 92%; wherein the trioxane monomer contains 0.00001 to 0.003 mmol of triethanolamine, relative to 1 mol of the trioxane.

2. The method for producing an oxymethylene copolymer according to claim 1, wherein a portion of or all of the steric-hindrance phenol is added through an inlet of a polymerizer.

3. The method for producing an oxymethylene copolymer according to claim 1, wherein the polymerization terminator is at least one compound selected from the group consisting of triphenylphosphine, a hindered amine, and an alkylated melamine.

4. The method for producing an oxymethylene copolymer according to claim 1, wherein the formed oxymethylene copolymer is contacted with the polymerization terminator when the polymerization yield has reached at least 97%.

5. The method for producing an oxymethylene copolymer according to claim 1, wherein the oxymethylene copolymer is continuously produced using a continuous polymerization apparatus comprising a continuous polymerizer and a terminator mixing machine which are connected in series.

6. A method for producing an oxymethylene copolymer, comprising: subjecting the oxymethylene copolymer obtained by the method for producing an oxymethylene copolymer according to claim 1 to stabilization treatment by further melt-kneading the oxymethylene copolymer at a temperature in the range of from the melting temperature of the oxymethylene copolymer to a temperature 100 C. higher than the melting temperature under a pressure of 760 to 0.1 mmHg.

7. The method for producing an oxymethylene copolymer according to claim 6, wherein the stabilization treatment is performed by means of an apparatus comprising a combination of a single-screw or twin- or multi-screw vented extruder and a surface renewal-type mixer.

8. The method for producing an oxymethylene copolymer according to claim 6, wherein the oxymethylene copolymer is subjected to the stabilization treatment without being washed after termination of the polymerization.

Description

EXAMPLES

(1) Hereinbelow, the present invention will be described with reference to the following Examples and Comparative Examples, which should not be construed as limiting the scope of the present invention. The terms and measurement methods shown in the Examples and Comparative Examples are described below.

(2) (1) Formate Group Content:

(3) About 12 mg of a crude polymer powder, which is an oxymethylene copolymer before subjected to stabilization treatment, was weighed, and dissolved in 1 g of a hexafluoroisopropanol-d.sub.2 solvent and subjected to measurement by means of a .sup.1H-NMR nuclear magnetic resonance apparatus (JNM LA500; manufactured by JEOL LTD.). A formate group content was determined from a ratio of the area of a .sup.1H peak appearing around 8.0 ppm ascribed to the formate group to the area of a .sup.1H peak appearing around 4.9 ppm ascribed to the methylene backbone of the oxymethylene copolymer in the NMR chart. The content of the formate group in 1 g of the polymer was indicated using a unit: mol.

(4) (2) Polymerization Yield:

(5) 20 g of the oxymethylene copolymer obtained after the termination treatment was immersed in 20 ml of acetone, and then subjected to filtration, and the collected copolymer was washed with acetone three times and then, subjected to vacuum drying at 60 C. until the weight of the dried copolymer became constant. Then, the resultant copolymer was accurately weighed, and a polymerization yield was determined from the following formula.
Polymerization yield=M1/M0100 M0: Weight before washing with acetone M1: Weight after washing with acetone and drying

(6) (3) Intrinsic Viscosity:

(7) The oxymethylene copolymer was dissolved in an amount of 0.1% by weight in a p-chlorophenol solvent having added thereto -pinene in an amount of 2%, and measured with respect to an intrinsic viscosity at 60 C. by means of an Ostwald's viscometer.

(8) (4) Melt Index (MI Value):

(9) A melt index was measured in accordance with ASTM-D1238 (at 190 C. under a load of 2.16 kg).

(10) (5) Amount of Formaldehyde Generated:

(11) The obtained pellets were subjected to molding using a molding machine PS-40E5ASE, manufactured by Nissei Plastic Industrial Co., Ltd., at a cylinder temperature of 200 C., and the resultant flat plate having a size of 100 mm40 mmthickness: 2 mm was used as a test specimen. After one day from the molding, with respect to the resultant specimen, an amount of formaldehyde generated was measured in accordance with the method described in German Automobile Industry Association standards VDA275 (quantitative determination of an amount of formaldehyde emission by the automobile interior partsrevised flask method).

(12) (i) 50 ml of distilled water is placed in a polyethylene container, and a specimen is hung above the water in the container, and the container is closed with a cover and kept in a sealed state at 60 C. for 3 hours.

(13) (ii) Then, the container is allowed to stand at room temperature for 60 minutes, and then the specimen is removed from the container.

(14) (iii) A concentration of formaldehyde absorbed in the distilled water in the polyethylene container is measured by an acetylacetone colorimetric method using a UV spectrometer.

(15) (6) Resident Heat Stability:

(16) The stabilized oxymethylene copolymer was kneaded and extruded to produce pellets, and the resultant pellets were dried at 80 C. for 4 hours, and then 6 shots of the resin were allowed to stay in an injection molding machine (IS75E, manufactured by Toshiba Machine Co., Ltd.) having a cylinder temperature of 240 C., and molded every 7 minutes, and the resident heat stability was evaluated by a period of time (minutes) required until a silver streak was caused due to foaming of the resin. Further, the resultant molded article was visually observed with respect to hue.

(17) (7) Weight Loss on Heating (M Value):

(18) The weight loss on heating indicates a weight loss (%) measured by kneading and extruding the stabilized oxymethylene copolymer to produce pellets, and placing the resultant pellets in a test tube, and purging the test tube with nitrogen and then heating the pellets at 240 C. under a reduced pressure at 10 Torr for 2 hours. The higher the heat stability, the smaller the weight loss on heating (M value).

Examples 1 to 9 and Comparative Examples 1 to 8

(19) Using, as a polymerization apparatus, a bench twin-shaft kneader having an inner capacity of 1 L and having a jacket and two Z-type blades, an oxymethylene copolymer was produced by polymerization in a batch-wise manner. Hot water at 85 C. was circulated through the jacket, and further the inside of the apparatus was heated and dried using high-temperature air, and then a cover was attached to the apparatus and the system was purged with nitrogen. 320 g of trioxane (which contains 0.00025 mmol of triethanolamine as a stabilizer relative to 1 mol of the trioxane), a predetermined amount of a comonomer, and a predetermined amount of a steric-hindrance phenol were charged through a raw material inlet, and, while stirring the resultant mixture by Z-type blades, a predetermined amount of boron trifluoride diethyl etherate in the form of a benzene solution (solution concentration: 0.6 mmol/g) was added to the mixture to initiate a polymerization. After the polymerization was conducted for a predetermined period of time, a solution of triphenylphosphine in benzene (solution concentration: 5 mmol/ml) in a molar amount corresponding to 10 times the molar amount of the catalyst used was added to the polymerization apparatus using a syringe, and mixed for 15 minutes to terminate the polymerization, obtaining an oxymethylene copolymer. With respect to the obtained oxymethylene copolymer, a polymerization yield and a formate group content were measured, and the results as well as the reaction conditions were shown in Tables 1 to 3.

Examples 10 to 15 and Comparative Example 9

(20) As a continuous polymerization apparatus, two polymerizers were connected in series, wherein each polymerizer has a long casing having an inner cross-section seen like two circles which partially overlap, and an inner cross-section major diameter of 100 mm, and having a jacket around it, wherein the long casing has therein a pair of shafts, each shaft having incorporated thereto a number of convex lens-type paddles meshing with one another, and the end of the convex lens-type paddle can clean the inner surface of the casing and the surface of the convex lens-type paddle meshing with that paddle. Subsequently, as a terminator mixing machine, a continuous mixer, which has a structure similar to the above polymerizer on the second stage, and which can charge a solution containing a terminator through a feed inlet portion to continuously mix the terminator with the polymer, was connected in series to the above-mentioned two continuous polymerizers, and production of an oxymethylene copolymer was performed. To the inlet of the first-stage polymerizer was fed trioxane at 200 kg/hr (which contains 0.00025 mmol of triethanolamine as a stabilizer relative to 1 mol of the trioxane), and a steric-hindrance phenol was fed in the form of a 11 wt % 1,3-dioxolane solution so that the steric-hindrance phenol of the type and amount shown in Table 4 was fed. Further, 1,3-dioxolane was continuously fed through another line and controlled so that the total amount of the 1,3-dioxolane fed became 8 kg/hr. Simultaneously, as a catalyst, 0.043 mmol of boron trifluoride diethyl etherate relative to 1 mol of the trioxane was continuously fed. Further, as a molecular weight modifier, methylal in an amount required to adjust the intrinsic viscosity to 1.1 to 1.5 dl/g was continuously fed. Boron trifluoride diethyl etherate and methylal were added individually in the form of a benzene solution. The total amount of the benzene used was 1% by weight or less, based on the weight of the trioxane. Then, the terminator shown in Table 4 in a molar amount 2 times the molar amount of the catalyst used was continuously fed in the form of a benzene solution through the inlet of the terminator mixing machine to terminate the polymerization reaction, and the formed oxymethylene copolymer was obtained from the outlet. The continuous polymerization apparatus was operated for polymerization under conditions such that the number of revolutions of the first-stage shaft was about 35 rpm, the number of revolutions of the second-stage shaft was about 60 rpm, the first-stage jacket temperature was 85 C., the second-stage jacket temperature was 85 C., and the terminator mixing machine jacket temperature was 15 C. The polymerization time was about 10 minutes. With respect to the obtained oxymethylene copolymer, a polymerization yield, an intrinsic viscosity, and a formate group content were measured, and the results were shown in Table 4.

Example 16

(21) To 100 parts by weight of the oxymethylene copolymer obtained in Example 12 were added 0.1 part by weight of melamine, 0.3 part by weight of triethylene glycol bis-3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate, 0.05 part by weight of magnesium hydroxide, and 0.005 part by weight of calcium stearate, and they were mixed with one another, and then the resultant mixture was fed to a twin-screw vented extruder (50 mm, L/D=49), and melt-kneaded under a reduced pressure at 160 mmHg at 200 C., and subsequently fed to a surface renewal-type mixer and further stabilized at 220 C. under a reduced pressure at 160 mmHg. The surface renewal-type mixer has two rotating shafts inside the mixer, each shaft having a plurality of scraper blades fitted thereto, and the blades are fitted so that the blades are not in contact when the shafts are rotated in different directions, and arranged so that the shafts are rotated while maintaining a slight gap between the ends of the blades and the inner surface of the casing or the both shafts. The surface renewal-type mixer has a function such that the rotation of the shafts kneads the polymer and constantly renews the surface of the molten polymer so that the volatile components easily volatilize. The average residence time from the inlet of the twin-screw extruder to the outlet of the surface renewal-type mixer was 25 minutes. The stabilized oxymethylene copolymer was pelletized by extrusion from a dice. An amount of formaldehyde generated from the obtained pellets was measured. As a result, the amount of formaldehyde generated was found to be 3.1 g/g-polymer. With respect to the obtained pellets, the MI value was 9.5, the M value was 0.9%, and the resident heat stability was 42 minutes.

Comparative Example 10

(22) Substantially the same procedure as in Example 16 was repeated except that the oxymethylene copolymer obtained in Comparative Example 9 was used. An amount of formaldehyde generated from the obtained pellets was measured. As a result, the amount of formaldehyde generated was found to be 5.2 g/g-polymer. With respect to the obtained pellets, the MI value was 9.7, the M value was 1.6%, and the resident heat stability was 28 minutes.

(23) TABLE-US-00001 TABLE 1 Boron Steric-hindrance phenol trifluoride Amount diethyl etherate Comonomer based Amount Polymerization Polymerization Formate Amount on TOX relative to TOX time yield group content Type (wt %) Type (wt %) (mmol/mol-TOX) sec. wt % mol/g-polymer Example 1 DOL 4.0 HP-1 0.0150 0.05 250 92.4 3.7 Example 2 DOL 4.0 HP-1 0.0150 0.05 380 97.3 5.6 Example 3 DOL 4.0 HP-1 0.0150 0.05 900 99.2 7.0 Comparative DOL 4.0 Not added 0.05 250 92.3 4.6 example 1 Comparative DOL 4.0 Not added 0.05 380 97.1 8.9 example 2 Comparative DOL 4.0 Not added 0.05 900 99.6 11.1 example 3

(24) TABLE-US-00002 TABLE 2 Steric-hindrance Boron phenol trifluoride Amount diethyl etherate Formate Comonomer based on Amount Polymerization Polymerization group content Amount TOX relative to TOX time yield mol/ Type (wt %) Type (wt %) (mmol/mol-TOX) sec. wt % g-polymer Example 4 DOL 4.0 HP-1 0.0150 0.02 900 92.3 3.5 Comparative DOL 4.0 HP-1 0.0150 0.087 900 99.7 12.9 example 4

(25) TABLE-US-00003 TABLE 3 Steric-hindrance phenol Boron trifluoride Amount diethyl etherate Comonomer based on Amount relative Polymerization Polymerization Formate group Amount TOX to TOX time yield content Type (wt %) Type (wt %) (mmol/mol-TOX) sec. wt % mol/g-polymer Example 5 DOL 4.0 HP-2 0.0213 0.05 900 99.6 7.1 Example 6 DOL 4.0 HP-3 0.0154 0.05 900 99.4 8.6 Example 7 DOL 4.0 HP-4 0.0928 0.05 900 98.4 8.8 Example 8 DOL 4.0 HP-5 0.0145 0.05 900 99.5 7.0 Example 9 DOL 4.0 HP-6 0.0111 0.05 900 99.7 8.3 Comparative EO 2.4 HP-1 0.0150 0.087 900 91.0 19.4 example 5 Comparative EO 2.4 HP-1 0.0150 0.05 900 74.0 14.5 example 6 Comparative DOL 4.0 HP-1 0.0150 0.05 85 80.0 2.1 example 7 Comparative DOL 4.0 Not added 0.05 85 80.1 2.1 example 8

(26) The abbreviations used in the tables above have the following meanings:

(27) TOX: 1,3,5-Trioxane

(28) DOL: 1,3-Dioxolane

(29) EO: Ethylene oxide

(30) HP-1: Triethylene glycol bis-3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate (trade name: Irganox 245; manufactured by BASF AG)

(31) HP-2: Pentaerythrityl tetrakis-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate (trade name: Irganox 1010; manufactured by BASF AG)

(32) HP-3: Hexamethylenebis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] (trade name: Irganox 259; manufactured by BASF AG)

(33) HP-4: Dibutylhydroxytoluene

(34) HP-5: 3,9-Bis {2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5]undecane, N,N-hexane-1,6-diylbis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionamide] (trade name: ADK STAB AO-80; manufactured by ADEKA CORPORATION)

(35) HP-6: 2-[1-(2-Hydroxy-3,5-di-t-pentylphenypethyl]-4,6-di-t-pentylphenyl acrylate (trade name: Sumilizer GS(F); manufactured by Sumitomo Chemical Co., Ltd.)

(36) TABLE-US-00004 TABLE 4 Steric-hindrance phenol Formate Amount Polymerization Intrinsic group content based on TOX Terminator yield viscosity mol/ Type (wt %) Type wt % dl/g g-polymer Example 10 HP-1 0.010 STP-1 98.0 1.44 9.3 Example 11 HP-1 0.020 STP-1 97.7 1.44 8.0 Example 12 HP-1 0.035 STP-1 97.1 1.45 7.3 Example 13 HP-1 0.050 STP-1 95.6 1.49 7.4 Example 14 HP-1 0.035 STP-2 97.2 1.47 7.5 Example 15 HP-1 0.035 STP-3 97.4 1.48 7.5 Comparative Not added STP-1 98.1 1.45 11.2 example 9

(37) The abbreviations used in the table above have the following meanings:

(38) STP-1: Triphenylphosphine

(39) STP-2: Hexamethoxymethylmelamine

(40) STP-3: Bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate

(41) It is found that the formate group content is small in each of Examples 1 to 9 in which the polymerization was conducted in the presence of a steric-hindrance phenol and the polymerization was terminated when the polymerization yield has reached at least 92%. Specifically, from a comparison of Examples 1 to 3 with Comparative Examples 1 to 3, it is found that when the polymerization yield is the same, the use of a steric-hindrance phenol in the polymerization can reduce the formate group content (see Table 1). In Example 4 in which the amount of boron trifluoride diethyl etherate was 0.02 mmol relative to 1 mol of the trioxane, a similar excellent reduction effect for the formate group content to Example 1 was exhibited at the same polymerization yield as in Example 1. On the other hand, in Comparative Example 4 in which the amount of boron trifluoride diethyl etherate was 0.07 mmol or more relative to 1 mol of the trioxane, the formate group content was increased even at the same polymerization yield as in Example 3 (see Table 2). In Comparative Example 6 in which ethylene oxide was used as a comonomer, when the amount of the polymerization catalyst added was the same as the amount of the catalyst added for 1,3-dioxolane, the polymerization yield was markedly lowered, increasing the cost of the monomer recovery, and, when the amount of the catalyst added was increased for increasing the polymerization yield like Comparative Example 5, the formate group content was markedly increased (see Table 3). When the polymerization yield is as low as about 80%, no difference is recognized between the case using a steric-hindrance phenol and the case using no steric-hindrance phenol (Comparative Examples 7 and 8). A comparison of Examples 10 to 15 with Comparative Example 9 shows that, under conditions presumed for the actual production facilities, the addition of a steric-hindrance phenol exhibits a reduction effect for the formate group. A comparison of Example 16 with Comparative Example 10 shows that, by adding a steric-hindrance phenol, excellent results are obtained with respect to the polymer quality of a final product, such as the amount of formalin generated and resident heat stability (see Table 4).