Polyurethane resin composition for electrical insulation

Abstract

The invention provides a polyurethane resin composition for electrical insulation that has excellent compatibility between an isocyanate component and a polyol component, and that exhibits excellent heat resistance, moisture resistance, and insulation properties. The polyurethane resin composition for electrical insulation comprises (1) Part A comprising a polyisocyanate component obtained from at least one member selected from the group consisting of aliphatic diisocyanates and alicyclic diisocyanates, and containing one or more isocyanurate groups and one or more allophanate groups; and (2) Part B comprising a polyol component, wherein the polyisocyanate component has a molar ratio, (a)/(b), of isocyanurate groups (a) to allophanate groups (b) of 85/15 to 15/85.

Claims

1. A polyurethane resin composition for electrical insulation comprising: (1) Part A comprising a polyisocyanate component obtained from at least one member selected from the group consisting of aliphatic diisocyanates and alicyclic diisocyanates, and from a C.sub.6-9 monoalcohol consisting of a saturated hydrocarbon group; and the polyisocyanate component containing one or more isocyanurate groups and one or more allophanate groups; and (2) Part B comprising a polyol component which comprises a polybutadiene polyol and a castor oil-based polyol, wherein the polyisocyanate component has a molar ratio, (a)/(b), of isocyanurate groups (a) to allophanate groups (b) in the range of 85/15 to 15/85.

2. The polyurethane resin composition for electrical insulation according to claim 1, wherein the polyisocyanate component has a molar ratio, (a)/(b), of isocyanurate groups (a) to allophanate groups (b) in the range of 75/25 to 25/75.

3. The polyurethane resin composition for electrical insulation according to claim 1, wherein Part B comprises a plasticizer that does not have a hydroxyl group.

4. The polyurethane resin composition for electrical insulation according to claim 3, wherein the plasticizer is at least one selected from the group consisting of phthalate esters, trimelitate-based plasticizers, and phosphoric esters.

5. The polyurethane resin composition for electrical insulation according to claim 1, wherein the proportion of the polybutadiene polyol and the castor oil-based polyol in part B is in the range of 90:10% by weight to 50:50% by weight.

6. A sealing member comprising the polyurethane resin composition for electrical insulation of claim 1.

7. An electrical component comprising the sealing member of claim 6.

8. A sealing member comprising the polyurethane resin composition for electrical insulation of claim 2.

9. An electrical component comprising the sealing member of claim 8.

Description

DESCRIPTION OF EMBODIMENTS

Examples

(1) The following Examples and Comparative Examples describe the present invention in more detail. However, the scope of the invention is not limited thereto.

Synthesis Examples

(2) The following are synthesis examples of the polyisocyanate component.

(3) Herein, the molar ratio (a)/(b) of the isocyanurate groups (a) to the allophanate groups (b) contained in a polyisocyanate component was measured by determining, using .sup.1H-NMR (FT-NMRDPX-400, manufactured by Bruker), the ratio of the isocyanurate groups to the allophanate groups based on the ratio of the peak area of the signal near 8.5 ppm assigned to the hydrogen bonded to the nitrogen atom of the allophanate group to the peak area of the signal near 3.8 ppm assigned to the hydrogen of the methylene group adjacent to the nitrogen atom of the isocyanurate ring of the isocyanurate group.

(4) The NCO content was calculated by neutralizing the isocyanate groups with an excessive amount of 2N amine, followed by back titration with 1N hydrochloric acid.

(5) The viscosity was measured at 25 C. with an E-type viscometer (manufactured by Tokimec. Inc.). A standard rotor (134R24) was used for measurement. The rotation speed was as follows.

(6) 100 r.p.m. (when less than 128 mPa.Math.s)

(7) 50 r.p.m. (when 128 mPa.Math.s to 256 mPa.Math.s)

(8) 20 r.p.m. (when 256 mPa.Math.s to 640 mPa.Math.s)

(9) 10 r.p.m. (when 640 mPa.Math.s to 1,280 mPa.Math.s)

(10) 5 r.p.m. (when 1,280 mPa.Math.s to 2,560 mPa.Math.s)

Synthesis Example 1

Synthesis of Polyisocyanate Component A-1

(11) The air in a four-necked flask equipped with a stirrer, a thermometer, and a condenser tube was replaced with nitrogen. 1,200 g of HDI and 0.6 part of isobutanol were fed thereinto, and the temperature inside the reaction apparatus was maintained at 80 C. for 2 hours with stirring. Subsequently, 0.1 g of tetramethylammonium caprate as a catalyst for an isocyanuration reaction was added to the mixture, and the isocyanuration reaction was carried out. When the conversion reached 12%, 0.2 g of phosphoric acid was added thereto to terminate the reaction. The reaction mixture was filtered, and then unreacted HDI was removed at 160 C. (27 Pa) the first time, and at 150 C. (13 Pa) the second time, by the use of a falling film evaporator, thereby giving polyisocyanate component A-1. The resulting polyisocyanate component A-1 was a transparent, pale-yellow liquid. The yield was 230 g, the viscosity at 25 C. was 400 mPa.Math.s, and the NCO content was 22.6%. The molar ratio of the isocyanurate groups to the allophanate groups determined through .sup.1H-NMR measurement was 78/22.

Synthesis Example 2

Synthesis of Polyisocyanate Component A-2

(12) 1,000 g of HDI and 30 g of 2-ethylhexanol were fed into the same apparatus used in Synthesis Example 1, and the mixture was stirred at 80 C. for 1 hour to carry out an urethanation reaction. 0.36 g of a solution of tetramethylamnonium caprate in n-butanol (solids content: 10%) was added thereto as a catalyst for an allophanation and isocyanuration reaction. After additional stirring for 3 hours, 0.58 g of an aqueous solution of phosphoric acid (solids content: 85%) was added thereto to terminate the reaction. The reaction mixture was filtered, and then unreacted HDI was removed at 160 C. (27 Pa) the first time, and at 150 C. (13 Pa) the second time, by the use of a falling film evaporator, thereby giving polyisocyanate component A-2. The resulting polyisocyanate component A-2 was a transparent, pale-yellow liquid. The yield was 300 g, the viscosity at 25 C. was 450 mPa.Math.s, and the NCO content was 20.6%. The molar ratio of the isocyanurate groups to the allophanate groups determined through .sup.1H-NMR measurement was 65/35.

Synthesis Example 3

Synthesis of Polyisocyanate Component A-3

(13) 1,000 g of HDI and 30 g of 2-ethylhexanol were fed into the same apparatus used in Synthesis Example 1, and the mixture was stirred at 90 C. for 1 hour to carry out an urethanation reaction. At a temperature of 90 C., 0.6 g of a solution of tetramethylanmonium caprate in isobutanol (solids content: 5%) was added thereto as a catalyst for an allophanation and isocyanuration reaction. After additional stirring for 2 hours, 0.06 g of an 85% phosphoric acid aqueous solution was added to terminate the reaction. The reaction mixture was filtered, and then unreacted HDI was removed in the same manner as in Synthesis Example 1, thereby giving polyisocyanate component A-3. The resulting polyisocyanate component A-3 was a transparent liquid. The yield was 210 g, the viscosity at 25 C. was 340 mPa.Math.s, and the NCO content was 20.3%. The molar ratio of the isocyanurate groups to the allophanate groups determined through .sup.1H-NMR measurement was 50/50.

Synthesis Example 4

Synthesis of Polyisocyanate Component A-4

(14) 1,000 g of HDI and 50 g of isobutanol were fed into the same apparatus used in Synthesis Example 1, and the mixture was stirred at 90 C. for 1 hour to carry out an urethanation reaction. 0.53 g of a solution of tetramethylammonium caprate in n-butanol (solids content: 10%) was added thereto as a catalyst for an allophanation and isocyanuration reaction. After additional stirring for 3 hours, 0.10 g of an aqueous solution of phosphoric acid (solids content: 85%) was added to terminate the reaction. The reaction mixture was filtered, and then unreacted HDI was removed in the same manner as in Synthesis Example 1, thereby giving polyisocyanate component A-4. The resulting polyisocyanate component A-4 was a transparent, pale-yellow liquid. The yield was 440 g, the viscosity at 25 C. was 450 mPa.Math.s, and the NCO content was 19.6%. The molar ratio of the isocyanurate groups to the allophanate groups determined through .sup.1H-NMR measurement was 40/60.

Synthesis Example 5

Synthesis of Polyisocyanate Component A-5

(15) 1,000 g of HDI and 100 g of 2-ethylhexanol were fed into the same apparatus used in Synthesis Example 1, and the mixture was stirred at 90 C. for 1 hour to carry out an urethanation reaction. 10 g of a solution of bismuth 2-ethylhexanoate in mineral spirits (solids content: 20%) was added thereto as a catalyst for an allophanation and isocyanuration reaction. After additional stirring for 3 hours, 4.5 g of 2-ethylhexyl phosphate ester was added to terminate the reaction. The reaction mixture was filtered, and then unreacted HDI was removed in the same manner as in Synthesis Example 1, thereby giving polyisocyanate component A-5. The resulting polyisocyanate component A-5 was a transparent, pale-yellow liquid. The yield was 420 g, the viscosity at 25 C. was 160 mPa's, and the NCO content was 17.4%. The molar ratio of the isocyanurate groups to the allophanate groups determined through .sup.1H-NMR measurement was 16/84.

Synthesis Example 6

Synthesis of Polyisocyanate Component A-6

(16) 500 g of HDI was fed into the same apparatus used in Synthesis Example 1. 0.08 g of tetramethylammonium caprate was added thereto with stirring at 60 C. The reaction proceeded at 60 C. Four hours later, when the conversion to polyisocyanate reached 20% as determined by measuring the isocyanate-group content and refractive index, 0.2 g of phosphoric acid was added thereto to terminate the reaction. The reaction mixture was filtered, and then unreacted HDI was removed in the same manner as in Synthesis Example 1, thereby giving polyisocyanate component A-6. The resulting polyisocyanate component A-6 was a transparent, pale-yellow liquid. The yield was 102 g, the viscosity at 25 C. was 1,400 mPa.Math.s, and the NCO content was 23.4%. The molar ratio of the isocyanurate groups to the allophanate groups determined through .sup.1H-NMR measurement was 100/0.

Synthesis Example 7

Synthesis of Polyisocyanate Component A-7

(17) 561.9 g of HDI and 38.1 g of isobutanol were fed into the same apparatus used in Synthesis Example 1, and the mixture was stirred at 90 C. for 60 minutes to carry out an urethanation reaction. After the temperature was raised to 120 C., 0.28 g of a solution of zirconyl 2-ethylhexanoate in mineral spirits (solids content: 20%) was added thereto as a catalyst for an allophanation reaction. After additional stirring for 60 minutes, 0.097 g of an aqueous solution of phosphoric acid (solids content: 85%) was added to terminate the reaction. The reaction mixture was filtered, and then unreacted HDI was removed in the same manner as in Synthesis Example 1, thereby giving polyisocyanate component A-7. The resulting polyisocyanate component A-7 was a transparent, pale-yellow liquid. The yield was 203 g, the viscosity at 25 C. was 130 mPa.Math.s, and the NCO content was 18.8%. The molar ratio of the isocyanurate groups to the allophanate groups determined through .sup.1H-NMR measurement was 3/97.

Synthesis Example 8

Synthesis of Polyisocyanate Component A-8

(18) 1,000 parts by weight of diphenylmethane diisocyanate having a 4,4-diphenylmethane diisocyanate content of 99.8 weight percent was fed into a reaction apparatus equipped with a stirrer, a thermometer, an Allihn condenser, and a nitrogen gas inlet tube, and then 12 parts by weight of triethyl phosphate was added thereto with stirring. The temperature was then raised to 190 C. to carry out a carbodiimidation reaction. When the NCO content reached 7.09 mmol/g, the entire reaction apparatus was rapidly cooled to room temperature with ice water to terminate the carbodiimidation reaction. Thereafter, the reaction mixture was aged for 2 days, thereby giving polyisocyanate component A-8. The resulting polyisocyanate component A-8 was a pale-brown liquid. The NCO content was 29.4%.

Synthesis Example 9

Synthesis of Polyisocyanate Component A-9

(19) The polyisocyanate components A-6 and A-7 that were respectively synthesized in Synthesis Examples 6 and 7 were mixed to give a weight ratio of 54/46 (A-6/A-7), thereby giving polyisocyanate component A-9. The resulting polyisocyanate component A-9 was a transparent, pale-yellow liquid. The viscosity at 25 C. was 770 mPa.Math.s, and the NCO content was 21.3%. The molar ratio of the isocyanurate groups to the allophanate groups determined through .sup.1H-NMR measurement was 50/50.

Synthesis Example 10

Synthesis of Polyisocyanate Component A-10

(20) The polyisocyanate components A-2 and A-7 that were respectively synthesized in Synthesis Examples 2 and 7 were mixed to give a weight ratio of 85/15 (A-2/A-7), thereby giving polyisocyanate component A-10. The resulting polyisocyanate component A-10 was a transparent, pale-yellow liquid. The viscosity at 25 C. was 400 mPa.Math.s, and the NCO content was 20.3%. The molar ratio of the isocyanurate groups to the allophanate groups determined through .sup.1H-NMR measurement was 50/50.

Example 1

(21) As a polyol having terminal hydroxyl groups, a product available under the trade name Poly bd (registered trademark) R-45HT, manufactured by Idemitsu Kosan Co., Ltd., was provided. As a hydrogenated castor oil, SR-309 (trade name) manufactured by Itoh Oil Chemicals Co., Ltd., was provided. Further, as a plasticizer, diisononyl phthalate (DINP, trade name, manufactured by J-Plus Co., Ltd.) was provided.

(22) These materials were placed into a reaction vessel equipped with a heater, a cooler, and a decompressor according to the formulations shown in Table 1, and dehydrated at 100 C. under a pressure of 10 mmHg or less over a period of 2 hours, thereby giving a polyol component (Part B).

(23) For a polyisocyanate component, polyisocyanate component A-1 synthesized in the above Synthesis Example 1 was provided as Part A.

(24) In accordance with the formulations shown in Table 1, Part A was added to Part B, and the mixture was stirred and defoamed, thereby giving a polyurethane resin composition for electrical insulation. Part A and Part B were mixed in a ratio to provide one equivalent of the active hydrogen contained in the polyol component for each equivalent of the isocyanate groups contained in the polyisocyanate component.

(25) Preparation of Test Pieces

(26) The polyurethane resin composition for electrical insulation prepared according to the procedure described above was poured into a molding die of 1301303 mm, and a molding die having an inside diameter of 30 mm and a height of 10 mm. In the case of curing, after being poured into the molding dies, the polyurethane resin composition for electrical insulation was heated at 60 C. for 16 hours, and allowed to stand at room temperature for one day, whereby it was cured.

Example 2

(27) The procedure described in Example 1 was repeated, except that the polyisocyanate component A-2 synthesized in the above Synthesis Example 2 was used as a polyisocyanate component (Part A), thereby giving a polyurethane resin composition for electrical insulation.

Example 3

(28) The procedure described in Example 1 was repeated, except that the polyisocyanate component A-3 synthesized in the above Synthesis Example 3 was used as a polyisocyanate component (Part A), thereby giving a polyurethane resin composition for electrical insulation.

Example 4

(29) The procedure described in Example 1 was repeated, except that the polyisocyanate component A-4 synthesized in the above Synthesis Example 4 was used as a polyisocyanate component (Part A), thereby giving a polyurethane resin composition for electrical insulation.

Example 5

(30) The procedure described in Example 1 was repeated, except that the polyisocyanate component A-5 synthesized in the above Synthesis Example 5 was used as a polyisocyanate component (Part A), thereby giving a polyurethane resin composition for electrical insulation.

Example 6

(31) The procedure described in Example 1 was repeated, except that the polyisocyanate component A-9 synthesized in the above Synthesis Example 9 was used as a polyisocyanate component (Part A), thereby giving a polyurethane resin composition for electrical insulation.

Example 7

(32) The procedure described in Example 1 was repeated, except that the polyisocyanate component A-10 synthesized in the above Synthesis Example 10 was used as a polyisocyanate component (Part A), thereby giving a polyurethane resin composition for electrical insulation.

Comparative Example 1

(33) The procedure described in Example 1 was repeated, except that the polyisocyanate component A-6 synthesized in the above Synthesis Example 6 was used as a polyisocyanate component (Part A), thereby giving a polyurethane resin composition for electrical insulation.

Comparative Example 2

(34) The procedure described in Example 1 was repeated, except that the polyisocyanate component A-7 synthesized in the above Synthesis Example 7 was used as a polyisocyanate component (Part A), thereby giving a polyurethane resin composition for electrical insulation.

Comparative Example 3

(35) The procedure described in Example 1 was repeated, except that the polyisocyanate component A-8 synthesized in the above Synthesis Example 8 was used as a polyisocyanate component (Part A), thereby giving a polyurethane resin composition for electrical insulation.

Evaluation

Test Example 1

Evaluation of Hardness (Initial Hardness)

(36) Following JIS 16253, the JISA hardness of each of the test pieces prepared by curing the polyurethane resin compositions for electrical insulation prepared in Examples 1 to 7 and Comparative Examples 1 to 3 was measured.

(37) A hardness of less than A70 was indicated by O, a hardness in the range of A70 to A80 was indicated by , and a hardness of more than A80 was indicated by x.

Test Example 2

Evaluation of Heat Resistance (Hardness after Heat Resistance Test)

(38) The test pieces prepared by curing the polyurethane resin compositions for electrical insulation prepared in Examples 1 to 7 and Comparative Examples 1 to 3 were further heated at 120 C. for 1,000 hours, and allowed to stand at 23 C. for one hour. Subsequently, the JISA hardness was measured following JIS K6253.

(39) A hardness of less than A70 was indicated by O, a hardness in the range of A70 to A85 was indicated by , and a hardness of more than A85 was indicated by x.

Test Example 3

Evaluation of Insulation Properties (Initial Insulation Properties)

(40) The volume resistivity at 23 C. of each of the test pieces prepared by curing the polyurethane resin compositions for electrical insulation prepared in Examples 1 to 7 and Comparative Examples 1 to 3 was measured.

(41) A resistivity of 10.sup.11 .Math.m or more was indicated by O, and a resistivity of less than 10.sup.11 .Math.m was indicated by x.

Test Example 4

Evaluation of Moisture Resistance (Insulation Properties after Moisture Resistance Test)

(42) The test pieces prepared by curing the polyurethane resin compositions for electrical insulation prepared in Examples 1 to 7 and Comparative Examples 1 to 3 were further treated at 121 C. and at 100% RH in a pressure cooker for 200 hours. The volume resistivity at 23 C. was measured.

(43) A volume resistivity of 10.sup.9 .Math.m or more was indicated by O, a volume resistivity in the range of 10.sup.8 .Math.m to less than 10.sup.9 .Math.m was indicated by , and a volume resistivity of 10.sup.7 .Math.m or less was indicated by x.

Test Example 5

Evaluation of Compatibility

(44) The test pieces prepared by curing the polyurethane resin compositions for electrical insulation prepared in Examples 1 to 7 and Comparative Examples 1 to 3 were further heated at 120 C. for 1,000 hours. The compatibility was visually examined based on the evaluation criteria shown below.

(45) O: Droplets are not generated.

(46) X: Droplets are generated on the surface of a test piece.

(47) Table 1 shows the results of evaluations conducted in the above Test Examples 1 to 5.

(48) TABLE-US-00001 TABLE 1 Compar- Compar- Compar- Exam- Exam- Exam- Exam- Exam- Exam- Exam- ative ative ative ple 1 ple 2 ple 3 ple 4 ple 5 ple 6 ple 7 Example 1 Example 2 Example 3 Part B Polyol Having Terminal 37.0 36.0 36.0 35.0 34.0 37.0 36.0 37.0 35.0 38.0 Hydroxyl Groups (wt %) Hydrogenated Castor Oil 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 (wt %) Plasticizer (wt %) 38.0 38.0 38.0 37.0 38.0 38.0 38.0 39.0 37.0 40.0 Part A A-1 (wt %) 16.0 A-2 (wt %) 17.0 A-3 (wt %) 17.0 A-4 (wt %) 19.0 A-5 (wt %) 19.0 A-6 (wt %) 15.0 A-7 (wt %) 19.0 A-8 (wt %) 13.0 A-9 (wt %) 16.0 A-10 (wt %) 17.0 Characteristics Molar Ratio of 78/22 65/35 50/50 40/60 16/84 50/50 50/50 100/0 3/97 of Cured Isocyanurate Groups to Products Allophanate Groups; (a)/(b) NCO/OH 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Evaluation of Hardness Initial Hardness (JISA) 36 34 30 28 26 34 28 40 23 23 Evaluation of Heat Resistance x x Hardness After Heat 70 60 60 60 60 80 65 85 60 90 Resistance Test (JISA) Evaluation of Insulation x Properties Initial Insulation Properties 10.sup.11 10.sup.11 10.sup.11 10.sup.11 10.sup.11 10.sup.11 10.sup.11 10.sup.11 10.sup.10 10.sup.11 (Resistance Value) or more or more or more or more or more or more or more or more or more ( .Math. m) Evaluation of Moisture x Resistance Insulation Properties After 10.sup.9 10.sup.8 10.sup.9 10.sup.9 10.sup.8 10.sup.8 10.sup.9 10.sup.8 10.sup.7 10.sup.8 Moisture Resistance Test (Resistance Value) ( .Math. m) Compatibility x