CROSS-LINKABLE NITRILE RUBBER COMPOSITION AND CROSS-LINKED RUBBER

Abstract

A cross-linkable nitrile rubber composition including a highly saturated nitrile rubber (a) containing ,-ethylenically unsaturated nitrile monomer units and ,-ethylenically unsaturated dicarboxylic acid monoester monomer units and having an iodine value of 120 or less, organic staple fiber (b) with an average fiber length of 0.1 to 12 mm, and a polyamine cross-linking agent (c) is provided. The cross-linkable nitrile rubber composition able to give cross-linked rubber excellent in tensile stress and low heat buildup can be provided.

Claims

1. A cross-linkable nitrile rubber composition comprising a highly saturated nitrile rubber (a) containg ,-ethylenically unsaturated nitrile monomer units and ,-ethylenically unsaturated dicarboxylic acid monoester monomer units and having an iodine value of 120 or less, organic staple fiber (b) with an average fiber length of 0.1 to 12 mm, and polyamine cross-linking agent (c).

2. The cross-linkable nitrile rubber composition according to claim 1, wherein the organic staple fiber (b) is an aramid staple fiber.

3. The cross-linkable nitrile rubber composition according to claim 1, wherein the organic staple fiber (b) is a copoly-p-phenylene 3,4-oxydiphenylene tetraphthalamide staple fiber.

4. The cross-linkable nitrile rubber composition according to claim 1, wherein a content of the organic staple fiber (b) is 0.5 to 80 parts by weight with respect to 100 parts by weight of the highly saturated nitrile rubber (a).

5. The cross-linkable nitrile rubber composition according to claim 1, wherein in the highly saturated nitrile rubber (a), a ratio of content of the ,-ethylenically unsaturated nitrile monomer units is 10 to 60 wt % and a ratio of content of the ,-ethylenically unsaturated dicarboxylic acid monoester monomer units is 0.1 to 20 wt %.

6. The cross-linkable nitrile rubber composition according to claim 1, further comprising a basic cross-linking accelerator.

7. A cross-linked rubber obtained by cross-linking the cross-linkable nitrile rubber composition according to claim 1.

8. The cross-linked rubber according to claim 7 forming a belt.

Description

EXAMPLES

[0077] Below, the present invention will be explained based on detailed examples, but the present invention is not limited to these examples. Note that, below, unless otherwise indicated, parts are based on weight. Note that the tests and evaluations were based on the following.

[0078] The ratios of contents of the monomer units forming the highly saturated nitrile rubber were measured by the following methods.

[0079] That is, the ratios of contents of the mono-n-butyl maleate units and methacrylic acid units were calculated by taking 0.2 g of 2 mm square highly saturated nitrile rubber, adding 100 ml of 2-butanone, stirring for 16 hours, then 20 ml of adding ethanol and 10 ml of water, and stirring while using a 0.02N hydrous ethanol solution of potassium hydroxide for titration at room temperature with thymol phthalein as an indicator so as to find the number of moles of carboxyl groups with respect to 100 g of highly saturated nitrile rubber, and converting the number of moles found to an amount of mono-n-butyl maleate units or methacrylic acid units.

[0080] The ratios of contents of the 1,3-butadiene units and saturated butadiene units were calculated by measuring the iodine value before the hydrogenation reaction and after the hydrogenation reaction using highly saturated nitrile rubber (according to JIS K 6235).

[0081] The ratio of content of the acrylonitrile units was calculated by measuring the nitrogen content in the highly saturated nitrile rubber by the Kjeldahl method in accordance with JIS K6384.

[0082] Iodine Value

[0083] The iodine value of the highly saturated nitrile rubber was measured based on JIS K 6235.

[0084] Content of Carboxyl Groups

[0085] To 0.2 g of 2 mm square highly saturated nitrile rubber, 100 ml of 2-butanone was added and the mixture stirred for 16 hours, then 20 ml of ethanol and 10 ml of water were added and the mixture stirred. Using a 0.02N hydrous ethanol solution of potassium hydroxide, titration was performed at room temperature with thymol phthalein as an indicator so as to find the number of moles of carboxyl groups with respect to 100 g of highly saturated nitrile rubber (units: ephr).

[0086] Mooney Viscosity (Polymer Mooney)

[0087] The Mooney viscosity of the highly saturated nitrile rubber (polymer Mooney) was measured in accordance with JIS K6300-1 (units: [ML.sub.1+4, 100 C.]).

[0088] 20% Tensile Stress

[0089] The cross-linkable nitrile rubber composition was placed in a vertical 15 cm, horizontal 15 cm, depth 0.2 cm mold and pressed by a press pressure of 10 MPa while heating at 170 C. for 20 minutes to obtain sheet-shaped cross-linked rubber. Next, the obtained cross-linked rubber was transferred to a gear oven and heated at 170 C. for 4 hours for secondary cross-linking. The obtained sheet-shaped cross-linked rubber was punched in the grain direction in a No. 3 type dumbbell shape to obtain a test piece. Further, the obtained test piece was used to measure the 20% tensile stress in accordance with JIS K6251.

[0090] Heat Buildup (Dynamic Viscoelasticity Test)

[0091] The same procedure was followed as with the above evaluation of the 20% tensile stress to obtain sheet-shaped cross-linked rubber, then the obtained sheet-shaped cross-linked rubber was punched to a width 10 mm and length 50 mm in the grain direction to obtain cross-linked rubber for dynamic viscoelasticity test use. Further, the obtained cross-linked rubber for dynamic viscoelasticity test use was measured using a dynamic viscoelasticity measuring device (product name Explexor 500N, made by GABO QUALIMETER Testanlagen GmbH) under conditions of a measurement frequency: 10 Hz, static strain: 1.0%, dynamic strain: 0.2%, temperature: 100 C., chuck distance: 30 mm, and measurement mode: tension mode to obtain the tans.

[0092] Further, the value of the obtained tans was indexed to measured value of Comparative Example 1 as 100. This was used as an indicator of the heat buildup. The smaller this value, the less the dynamic heat buildup and the better the low heat buildup judged.

Synthesis Example 1

Synthesis of Highly Saturated Nitrile Rubber (a-1)

[0093] To a reactor, 180 parts of ion exchanged water, 25 parts of concentration 10 wt % sodium dodecylbenzene sulfonate aqueous solution, 37 parts of acrylonitrile, 6 parts of mono-n-butyl maleate, and 0.5 part of t-dodecyl mercaptan (molecular weight adjuster) were charged in that order. The inside gas was replaced with nitrogen 3 times, then 57 parts of 1,3-butadiene was charged. The reactor was held at 5 C., 0.1 part of cumen hydroperoxide (polymerization initiator) was charged, then the mixture was stirred while continuing the polymerization reaction for 16 hours. Next, 0.1 part of concentration 10 wt % hydroquinone aqueous solution (polymerization terminator) was added to stop the polymerization reaction, then a water temperature 60 C. rotary evaporator was used to remove the residual monomer and obtain a latex of nitrile rubber containing mono-n-butyl maleate units (solid content concentration approximately 30 wt %).

[0094] Next, to the above obtained latex, a palladium catalyst (solution of 1 wt % palladium acetate acetone solution and equal weight of ion exchanged water) was added in an autoclave to give an amount of palladium of 1000 weight ppm with respect to the dry weight of the rubber contained in the latex. The mixture was reacted by a hydrogenation reaction at a hydrogen pressure 3 MPa and temperature 50 C. for 6 hours to obtain a latex of the highly saturated nitrile rubber (a-1).

[0095] Further, to the obtained latex, double the volume of methanol was added to cause it to coagulate, then this was filtered to take out the solid product (crumbs). This was dried at 60 C. for 12 hours in vacuo to thereby obtain the highly saturated nitrile rubber (a-1). The composition of the obtained highly saturated nitrile rubber (a-1) was acrylonitrile units: 35.6 wt %, butadiene units (including saturated part): 59.0 wt %, and mono-n-butyl maleate units: 5.4 wt %, the iodine value was 8, the content of carboxyl groups was 3.110.sup.2 ephr, and the polymer Mooney viscosity [ML.sub.1+4, 100 C.] was 53.

Synthesis Example 2

Synthesis of Highly Saturated Nitrile Rubber (a-2)

[0096] To a reactor, 200 parts of ion exchanged water, 0.2 part of sodium carbonate, and 2.25 parts of fatty acid potassium soap (potassium salt of fatty acid) were added to prepare a soap aqueous solution. Further, to this soap aqueous solution, 37 parts of acrylonitrile and 0.47 part of t-dodecyl mercaptan (molecular weight adjuster) were charged in that order, the inside gas was replaced with nitrogen 3 times, then 63 parts of 1,3-butadiene was charged. The reactor was held at 5 C., 0.1 part of cumen hydroperoxide (polymerization initiator) and suitable quantities of a reducing agent and a chelating agent were charged, then the temperature was held at 5 C. while performing the polymerization reaction for 16 hours. Next, 0.1 part of concentration 10 wt % hydroquinone (polymerization terminator) aqueous solution was added to stop the polymerization reaction, then a water temperature 60 C. rotary evaporator was used to remove the residual monomer and obtain a latex of nitrile rubber (solid content concentration approximately 25 wt %).

[0097] Next, the above obtained latex was added to an aqueous solution of an amount of aluminum sulfate corresponding to 3 wt % of the dry weight of the rubber contained in the latex. This was stirred to coagulate the latex. The coagulated product was separated by filtering while washing them with water, then was dried at 60 C. for 12 hours in vacuo to obtain the nitrile rubber. Further, the obtained nitrile rubber was dissolved in acetone to give a concentration of 12%. This was placed in an autoclave, then a palladium-silica catalyst was added in 450 weight ppm with respect to the nitrile rubber and a hydrogenation reaction was performed at a hydrogen pressure of 3.0 MPa. After the end of the hydrogenation reaction, the product was poured into a large amount of water to cause it to coagulate, then was separated by filtering and dried to obtain highly saturated nitrile rubber (a-2). The composition of the obtained highly saturated nitrile rubber (a-2) was acrylonitrile units: 36.3 wt % and butadiene units (including saturated part): 63.7 wt %, the iodine value was 9, and the polymer Mooney viscosity [ML.sub.1+4, 100 C.] was 63. Further, the highly saturated nitrile rubber (a-2) was measured in accordance with the above method for the content of carboxyl groups, whereupon the content was below the detection limit and carboxyl groups were substantially not contained.

Synthesis Example 3

Synthesis of Highly Saturated Nitrile Rubber (a-3)

[0098] To a reactor, 180 parts of ion exchanged water, 25 parts of concentration 10 wt % sodium dodecylbenzene sulfonate aqueous solution, 37 parts of acrylonitrile, 4 parts of methacrylic acid, and 0.5 part of t-dodecyl mercaptan (molecular weight adjuster) were charged in that order. The inside gas was replaced with nitrogen 3 times, then 59 parts of 1,3-butadiene was charged. The reactor was held at 5 C., 0.1 part of cumen hydroperoxide (polymerization initiator) was charged, then the mixture was stirred while continuing the polymerization reaction for 16 hours. Next, 0.1 part of concentration 10 wt % hydroquinone aqueous solution (polymerization terminator) was added to stop the polymerization reaction, then a water temperature 60 C. rotary evaporator was used to remove the residual monomer and obtain a latex of nitrile rubber containing methacrylic acid units (solid content concentration approximately 30 wt %).

[0099] Next, the obtained latex was processed in the same way as the above Synthesis Example 1 to perform a hydrogenation reaction and obtain a latex of highly saturated nitrile rubber. This was made to coagulate, filtered, and dried in vacuo to obtain the highly saturated nitrile rubber (a-3). The composition of the obtained highly saturated nitrile rubber (a-3) was acrylonitrile units: 36 wt %, butadiene units (including saturated parts): 61 wt %, and methacrylic acid units: 3 wt %, the iodine value was 9, the content of carboxyl groups was 3.510.sup.2 ephr, and the polymer Mooney viscosity [ML.sub.1+4, 100 C.] was 68.

Example 1

[0100] Using a Bambury mixer, 100 parts of the highly saturated nitrile rubber (a-1) obtained in Production Example 1, 40 parts of N550 carbon black (product name Seast SO, made by Tokai Carbon), 1.5 parts of 4,4-di-(,-dimethylbenzyl) diphenylamine (product name Nocrac CD, made by Ouchi Shinko Chemical Industrial, antiaging agent), 5 parts of tri-2-ethylhexyl trimellitate (product name Adeka Cizer C-8, made by Adeka, plasticizer), 1 part of stearic acid, and 10 parts of copoly-p-phenylene 3,4-oxydiphenylene tetraphthalamide staple fiber (product name Technora ZCF T323SB 1 mm, made by Teij in Technoproducts, aramid staple fiber of average fiber length 1 mm, average fiber diameter 12 82 m) were kneaded. Next, the kneaded product was transferred to rolls, then 6.3 parts of 2,2-bis [4-(4-aminophenoxy) phenyl]propane (polyamine cross-linking agent) and 4 parts of 1,8-diazabicyclo [5,4,0]undecene-7 (DBU) (product name RHENOGRAN XLA-60 (GE2014), made by RheinChemie, DBU 60% (including part becoming zinc dialkyldiphosphate salt), basic cross-linking accelerator) were added and kneaded to obtain a cross-linkable nitrile rubber composition.

[0101] Further, the obtained cross-linkable nitrile rubber composition was used in accordance with the above methods to evaluate and test for the 20% tensile stress and heat buildup. The results are shown in Table 1.

Example 2

[0102] Except for using, instead of 10 parts of the average fiber length 1 mm copoly-p-phenylene 3,4-oxydiphenylene tetraphthalamide staple fiber, 3.5 parts of average fiber length 3 mm copoly-p-phenylene 3,4-oxydiphenylene tetraphthalamide staple fiber (product name Technora ZCF T323SB 3 mm, made by Teijin Technoproducts, average fiber length 3 mm, aramid staple fiber of average fiber diameter 12 82 m), the same procedure was followed as in Example 1 to prepare a cross-linkable nitrile rubber composition and the same procedure was followed to evaluate it. The results are shown in Table 1.

Comparative Example 1

[0103] Except for not mixing in the average fiber length 1 mm copoly-p-phenylene 3,4-oxydiphenylene tetraphthalamide staple fiber, the same procedure was followed as in Example 1 to prepare a cross-linkable nitrile rubber composition and the same procedure was followed to evaluate it. The results are shown in Table 1.

Comparative Example 2

[0104] Except for not mixing in 6.3 parts of 2,2-bis[4-(4-aminophenoxy) phenyl]propane and 4 parts of 1,8-diazabicyclo [5,4,0]-undecene-7 (DBU) and, instead of these, mixing in 8 parts of 1,3-bis (t-butylperoxyisopropyl)benzene 40% product (product name Vul Cup 40KE, made by Arkema, organic peroxide cross-linking agent), the same procedure was followed as in Example 1 to prepare a cross-linkable nitrile rubber composition and the same procedure was followed to evaluate it. The results are shown in Table 1.

Comparative Example 3

[0105] Except for using, instead of 100 parts of the highly saturated nitrile rubber (a-1), 100 parts of the highly saturated nitrile rubber (a-2) obtained in Synthesis Example 2, the same procedure was followed as in Comparative Example 2 to prepare a cross-linkable nitrile rubber composition and the same procedure was followed to evaluate it. The results are shown in Table 1.

Comparative Example 4

[0106] Except for using, instead of 10 parts of the average fiber length 1 mm copoly-p-phenylene 3,4-oxydiphenylene tetraphthalamide staple fiber, 3.5 parts of average fiber length 3 mm copoly-p-phenylene 3,4-oxydiphenylene tetraphthalamide staple fiber (product name Technora ZCF T323SB 3 mm, made by Teij in Technoproducts), the same procedure was followed as in Comparative Example 3 to prepare a cross-linkable nitrile rubber composition and the same procedure was followed to evaluate it. The results are shown in Table 1.

Comparative Example 5

[0107] Except for using, instead of 100 parts of the highly saturated nitrile rubber (a-1), 100 parts of the highly saturated nitrile rubber (a-3) obtained in Synthesis Example 3, the same procedure was followed as in Example 1 to prepare a cross-linkable nitrile rubber composition and the same procedure was followed to evaluate it. The results are shown in Table 1.

Comparative Example 6

[0108] Except for not mixing in 6.3 parts of 2,2-bis [4-(4-aminophenoxy) phenyl] propane and 4 parts of 1,8-diazabicyclo [5, 4,0]-undecene-7 (DBU) and, instead of these, mixing in 8 parts of 1,3-bis (t-butylperoxyisopropyl)benzene 40% product (product name: Vul Cup 40KE, made by Arkema), the same procedure was followed as in Comparative Example 5 to prepare a cross-linkable nitrile rubber composition and the same procedure was followed to evaluate it. The results are shown in Table 1.

TABLE-US-00001 TABLE 1 Example Comparative Example 1 2 1 2 3 4 5 6 Highly saturated nitrile rubber Type (a-1) (a-1) (a-1) (a-1) (a-2) (a-2) (a-3) (a-3) Composition Acrylonitrile units (wt %) 35.6 35.6 35.6 35.6 36.3 36.3 36 36 Butadiene units (wt %) 59 59 59 59 63.7 63.7 61 61 Mono-n-butyl maleate units (wt %) 5.4 5.4 5.4 5.4 Methacrylic acid units (wt %) 3 3 Iodine value 8 8 8 8 9 9 9 9 Polymer Mooney viscosity (ML.sub.1+4, 100 C.) 53 53 53 53 63 63 68 68 Composition of cross-linkable nitrile rubber composition Highly saturated nitrile rubber (a-1) (parts) 100 100 100 100 Highly saturated nitrile rubber (a-2) (parts) 100 100 Highly saturated nitrile rubber (a-3) parts 100 100 Aramid staple fiber (average fiber length: 1 mm) (parts) 10 10 10 10 10 Aramid staple fiber (average fiber length: 3 mm) (parts) 3.5 3.5 N550 carbon black (parts) 40 40 40 40 40 40 40 40 Tri-2-ethylhexyl trimellitate (parts) 5 5 5 5 5 5 5 5 4,4-di-(,-dimethylbenzyl) diphenylamine (parts) 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Stearic acid (parts) 1 1 1 1 1 1 1 1 2,2-bis[4-(4-aminophenoxy) phenyl]propane (parts) 6.3 6.3 6.3 6.3 1,8-diazabicyclo[5,4,0]undecene-7 (60%) (parts) 4 4 4 4 1,3-bis(t-butylperoxyisopropyl)benzene 40% product (parts) 8 8 8 8 Evaluation of cross-linked rubber 20% tensile stress (MPa) 15.8 15.2 0.98 11.3 10.8 11.6 unevalu- 10.7 Heat buildup (tan ) (Index) 88 85 100 269 210 217 atable 255

[0109] From Table 1, cross-linked rubber obtained using a cross-linkable nitrile rubber composition containing highly saturated nitrile rubber (a-1) containing ,-ethylenically unsaturated nitrile monomer units and ,-ethylenically unsaturated dicarboxylic acid monoester monomer units and having an iodine value of 120 or less, average fiber length 0.1 to 12 mm organic staple fiber, and a polyamine cross-linking agent was excellent in tensile stress and low heat buildup (Examples 1 and 2).

[0110] On the other hand, when not using organic staple fiber with an average fiber length of 0.1 to 12 mm, the result was that the obtained cross-linked rubber was low in tensile stress and inferior in low heat buildup (Comparative Example 1).

[0111] When using, instead of the polyamine cross-linking agent, an organic peroxide cross-linking agent, the result was that the obtained cross-linked rubber was low in tensile stress and inferior in low heat buildup (Comparative Example 2).

[0112] When using, as the highly saturated nitrile rubber, highly saturated nitrile rubber (a-2) not containing ,-ethylenically unsaturated dicarboxylic acid monoester monomer units and using, as the cross-linking agent, an organic peroxide cross-linking agent, the result was that the obtained cross-linked rubber was low in tensile stress and inferior in low heat buildup (Comparative Examples 3 and 4).

[0113] Further, when using as the highly saturated nitrile rubber, highly saturated nitrile rubber (a-3) containing methacrylic acid units instead of ,-ethylenically unsaturated dicarboxylic acid monoester monomer units, and using, as the cross-linking agent, a polyamine cross-linking agent, the result was that the obtained cross-linked rubber seriously foamed, the various properties could not be evaluated, and, when using an organic peroxide cross-linking agent, the various properties could be evaluated, but the tensile stress was low and the low heat buildup was also inferior (Comparative Examples 5 and 6).