Nitrile rubber and method of preparing the same

Abstract

Disclosed are nitrile rubber and a method of preparing the same. The nitrile rubber contributing to an excellent polymerization rate and vulcanization rate and having advantageous processability during vulcanization, and a method of preparing the same are disclosed.

Claims

1. A nitrile rubber consisting of 18 to 29 wt % of at least one α,β-unsaturated nitrile monomer, 82 to 71 wt % of at least one conjugated diene monomer, 0.5 to 5 parts by weight of a fatty acid based on 100 parts by weight of the nitrile rubber; 0.01 to 10 parts by weight of alkyl thiol based on 100 parts by weight of the nitrile rubber; and 0.01 to 1 part by weight of oil-soluble peroxide based on 100 parts by weight of the nitrile rubber wherein the α,β-unsaturated nitrile monomer is at least one selected from acrylonitrile, methacrylonitrile, fumaronitrile, α-chloronitrile or α-cyanoethyl acrylonitrile, wherein the conjugated diene monomer is at least one selected from 1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3-pentadiene, or isoprene, wherein ΔACN ranges from 2 to 3, and Mooney stress-relaxation rate (MSR) of the nitrile rubber measured with a shearing-disc viscometer according to ISO 289-4:2003 E at 100° C. is in the range of 0.35 to 0.383.

2. The nitrile rubber according to claim 1, wherein the fatty acid is at least one selected from the group consisting of oleic acid, rosin acid, lauric acid, myristic acid, palmitic acid, stearic acid, naphthalene sulfonic acid, and eicosanoic acid.

3. The nitrile rubber according to claim 1, wherein the alkyl thiol comprises 12 to 16 carbon atoms, and three or more tertiary carbon atoms comprising sulfur bond to one of the tertiary carbon atoms.

4. The nitrile rubber according to claim 3, wherein the alkyl thiol is at least one selected from the group consisting of 2,2,4,6,6-pentamethylheptane-4-thiol and 2,2,4,6,6,8,8-heptamethylnonane-4-thiol.

5. The nitrile rubber according to claim 1, wherein the oil-soluble peroxide is at least one selected from the group consisting of benzoyl peroxide, di-t-butylperoxide, azobisisobutyronitrile, tributyl hydroperoxide, dicumyl peroxide, t-butyl perbenzoate, cumene hydroperoxide, t-butyl peroctoate, methyl ethylketone peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, p-menthane hydroperoxide, and lauryl peroxide.

6. A vulcanizable mixture comprising the nitrile rubber according to claim 1 and at least one crosslinker.

7. A molded product formed from the vulcanizable mixture according to claim 6.

8. The molded product according to claim 7, wherein the molded product has a tensile strength of 225 to 246 kgf/cm2 and an elongation ratio of 377 to 387%, and a 300% modulus of 174 to 185, wherein the tensile strength, elongation ratio, and 300% modulus are measured at a vulcanised state according to DIN 53 504.

9. The molded product according to claim 7, wherein the molded product is seals, caps, hoses or diaphragms, O-ring seals, flat-type seals, corrugated seal rings, seal sleeves, seal caps, dust block caps, plug seals, insulation hoses, oil cooler hoses, inhalation hoses, servo control hoses, or pump diaphragms.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a graph illustrating acrylonitrile content change according to conversion rate in an additional Experimental Example of each of Examples 1 and 3, and Comparative Examples 2 and 3, according to the present invention.

BEST MODE

(2) Hereinafter, preferred examples will be provided for better understanding of the present invention. It will be apparent to those skilled in the art that these examples are only provided to illustrate the present invention and various modifications and alterations are possible within the scope and technical range of the present invention. Such modifications and alterations fall within the scope of claims included herein.

Example 1

(3) <Example of Addition Once within 1.5 to 3.5 Hours and Addition Twice within 4 to 6 Hours after Polymerization Initiation>

(4) 78 parts by weight of 1,4-butadiene, 22 parts by weight of acrylonitrile, 3 parts by weight of oleic acid as a fatty acid, 0.45 part by weight of 2,2,4,6,6-pentamethylheptane-4-thiol as alkyl thiol, 0.05 part by weight of p-menthane hydroperoxide as oil-soluble peroxide, and 200 parts by weight of water were emulsion polymerized to prepare nitrile rubber latex.

(5) In particular, 12 parts by weight of acrylonitrile were added before polymerization initiation and the remainder was added in three equal portions. In particular, 3.33 parts by weight of acrylonitrile were added at 2 hours, 4 hours, and 6 hours after polymerization initiation.

(6) The polymerization was terminated when a conversion rate, in which the amount of a monomer converted into polymer is confirmed by measuring the amount of total solids, was 80% and a total reaction time was total 8 hours. The amount of acrylonitrile per each conversion rate is illustrated in FIG. 1.

(7) Subsequently, a coagulum was obtained through a solidification process of conventional emulsion polymerization and then the coagulum was cleaned and dehydrated. Subsequently, the coagulum was cut into small pieces using a mixer and then was dried in an oven. The dried coagulum was sheeted using a roll, resulting in production of final rubber.

(8) Each of Examples 2 and 3, and Comparative Examples 1 and 7 was carried out in the same manner as in the method of Example 1, except that time and an addition amount of acrylonitrile were divided added, and a type and the amount of a molecular weight controller were modified as disclosed in Table 1 below.

Example 2

(9) <Example of Addition Twice within 1.5 to 3.5 Hours and Addition Twice within 4 to 6 Hours after Polymerization Initiation>

(10) Example 2 was carried out in the same manner as in Example 1, except that 12 parts by weight of acrylonitrile was added at an early stage of polymerization and the other acrylonitrile was equally divided added in 2.5 parts by weight four times, namely, 2 hours, 3.5 hours, 5 hours and 6.5 hours after polymerization. Here, a total time taken to reach a polymerization conversion rate of 80% was total 8 hours.

Example 3

(11) <Example of Addition Once within 1.5 to 3.5 Hours and Addition Once within 4 to 6 Hours after Polymerization Initiation>

(12) Example 3 was carried out in the same manner as in Example 1, except that 12 parts by weight of acrylonitrile was added at an early stage of polymerization and the other acrylonitrile was equally divided added in 5 parts by weight twice, namely, 2.5 hours and 5 hours after polymerization. Here, a total time taken to reach a polymerization conversion rate of 80% was total 7 hours.

Comparative Example 1

(13) <Example of Addition Once within 1.5 to 3.5 Hours and No Addition within 4 to 6 Hours after Polymerization Initiation>

(14) Comparative Example 1 was carried out in the same manner as in Example 1, except that 12 parts by weight of acrylonitrile was added at an early stage of polymerization and the other acrylonitrile was added 2.5 hours after polymerization. Here, a total time taken to reach a polymerization conversion rate of 80% was total 8 hours.

Comparative Example 2

(15) <Example of No Addition within 1.5 to 3.5 Hours and Addition Twice within 4 to 6 Hours after Polymerization Initiation>

(16) Comparative Example 2 was carried out in the same manner as in Example 1, except that 12 parts by weight of acrylonitrile was added at an early stage of polymerization and the other acrylonitrile was added in 5 parts by weight 4 hours and 6 hours after polymerization. Here, a total time taken to reach a polymerization conversion rate of 80% was total 7.5 hours.

Comparative Example 3

(17) <Experimental Example in which Divided Addition was not Performed>

(18) Comparative Example 3 was carried out in the same manner as in Example 1, except that 22 parts by weight of acrylonitrile was added at an early stage of polymerization and divided addition was not performed. Here, a total time taken to reach a polymerization conversion rate of 80% was total 7 hours.

Comparative Example 4

(19) <Experimental Example 1 in which Mercaptan was Alternatively Added and Divided Addition was not Performed>

(20) Comparative Example 4 was carried out in the same manner as in Example 1, except that 22 parts by weight of acrylonitrile was added at an early stage of polymerization, divided addition was not performed, and alkyl thiol was substituted with 0.5 part by weight of t-dodecyl mercaptan. Here, a total time taken to reach a polymerization conversion rate of 80% was total 8.3 hours.

Comparative Example 5

(21) <Experimental Example 2 in which Mercaptan was Alternatively Added and Divided Addition was not Performed>

(22) Comparative Example 5 was carried out in the same manner as in Example 1, except that 22 parts by weight of acrylonitrile was added at an early stage of polymerization, divided addition was not performed, and alkyl thiol was substituted with 0.55 part by weight of n-octyl mercaptan. Here, a total time taken to reach a polymerization conversion rate of 80% was total 7.8 hours.

Comparative Example 6

(23) <Example in which Mercaptan was Alternatively Added and Divided Addition was Performed>

(24) Comparative Example 6 was carried out in the same manner as in Example 1, except that 0.55 part by weight of n-octyl mercaptan as a molecular weight controller was used. Here, a total time taken to reach a polymerization conversion rate of 80% was total 8.5 hours.

Comparative Example 7

(25) <Example in which Fatty Acid Emulsifier was Alternatively Added and Divided Addition was Performed>

(26) Comparative Example 7 was carried out in the same manner as in Example 1, except that oleic acid was substituted with rosin acid. Here, a total time taken to reach a polymerization conversion rate of 80% was total 9 hours.

Experimental Example

(27) Properties of rubber prepared according to Examples 1 to 3 and Comparative Examples 1 to 7 were estimated as follows. Results are summarized in Table 1 below.

(28) (1) Properties of Polymer Mooney viscosity (MV): The Mooney viscosity of a raw polymer was measured according to DIN 53523/3 or ASTM D1646. Mooney stress-relaxation rate (MSR): MSR was measured with a shearing-disc viscometer according to ISO 289-4:2003E at 100° C. For reference, a long chain branch fraction decreases with increasing MSR value. Δ ACN: A glass transition temperature, and an initiation point and an end point thereof were determined using DSC according to ASTM E1356-03 or DIN 11357-2. Based on a measured initiation point and end point, ACN contents of the initiation point and the end point may be calculated by applying Gordon-Taylor relation, and a difference of ACN distribution from the calculated values may be calculated.
Tg=1.4564*[ACN]−77.147, ΔACN=End point of ACN−Initiation point of ACN

(29) (2) Vulcanization Properties (MDR: Moving DieRheometer):

(30) A vulcanization profile and analysis data related therewith were measured with a Monsanto MDF2000 rheometer according to ASTM D5289-95. T5: Time required for 5% vulcanization was measured (160° C., 3 minutes). Vmax (vulcanization rate): Vmax means maximum torque required for 100% vulcanization.

(31) (3) Mechanical Properties:

(32) Mechanical characteristics of rubber at a vulcanised state were measured according to DIN 53 504. Here, the rubber was mixed according to ASTM D3187 using a Banbury mixer.

(33) Tensile strength (TS: tensile strength, kgf/cm2): the mixture was vulcanized for 45 minutes at 145° C. and then tensile strength of a 300% vulcanizate was measured.

(34) Elongation ratio (elongation, %): The mixture was vulcanized for 45 minutes at 145° C. and then an elongation ratio of a vulcanizate was measured.

(35) 300% modulus: The mixture was vulcanized for 45 minutes at 145° C. and then modulus was measured at a 300% elongation state.

(36) TABLE-US-00001 TABLE 1 Example Comparative Example Classification 1 2 3 1 2 3 4 5 7 Properties MV 50 49 51 51 49 53 51 50 49 of polymer MSR 0.350 0.383 0.35 0.281 0.287 0.250 0.301 0.270 0.34 Δ ACN 3 2 3 8 9 12 10 12 6 Vulcanization T5 (min) 2.3 2.1 2.5 2.8 2.9 3.0 3.1 4.0 3.8 characteristics V.sub.max (kgf .Math. cm) 62.5 64.3 65 50 49 55 52 46 55 Mechanical TS (kgf/cm.sup.2) 225 246 235 196 192 205 164 150 190 properties Elongation ratio (%) 387 377 390 301 321 389 340 312 350 300% modulus 174 185 190 157 150 166 143 137 160

(37) As shown in Table 1, the present invention, in which α,β-unsaturated nitrile monomer was added once to twice within 1.5 to 3.5 hours and then once to twice within 4 to 6 hours after polymerization initiation, exhibits high MSR value (See. long chain branch fraction) and improvement regarding a uniform AN composition (See. result of Δ ACN), when compared to Comparative Examples 1, 2, 3, 4, and 5 which were not divided added as described above.

(38) In addition, the present invention using alkyl thiol exhibits fast and high vulcanization properties, and physical properties, when compared to Comparative Example 4, 5, and 6 using conventional mercaptan.

(39) Furthermore, the present invention using the fatty acid exhibits improvement in vulcanization rate and physical properties, when compared to Comparative Example 7 using a rosin acid emulsifier.

Additional Experimental Examples

(40) Example 1 (designated by “three times” in FIG. 1), Example 3 (designated by “twice” in FIG. 1), Comparative Example 2 (designated by “once” in FIG. 1), and Comparative Example 3 (designated by “batch” in FIG. 1) were carried out in the same manner, except that 32 wt % acrylonitrile and 68 wt % 1,3-butadiene were used, in particular, 27 wt % acrylonitrile was used at an initial step of polymerization and 5 wt % acrylonitrile was equally divided added during polymerization. Acrylonitrile content change according to a conversion rate during each of polymerization reactions was measured according to an N-content analysis method using an element analyzer (EA). Results are illustrated in FIG. 1.

(41) Additional Experimental Example of Example 1 is designated by “three times” in FIG. 1, Additional Experimental Example of Example 3 is designated by “twice” in FIG. 1, Additional Experimental Example of Comparative Example 2 is designated by “once” in FIG. 1, and Additional Experimental Example of Comparative Example 3 is designated by “batch” in FIG. 1.

(42) As a results, as illustrated in FIG. 1, it can be confirmed that a curve of “twice” and a curve of “three times” according to the present invention exhibits an acrylonitrile content change (LAN) of 2 or less until polymerization termination at a conversion rate of 80%, but a curve designated by “batch” as Additional Experimental Example of Comparative Example 3 or a curve designated by “once” as Additional Experimental Example of Comparative Example exhibits a content change (LAN) exceeding 2 until polymerization termination at a conversion rate of 80%.