Low temperature cross linkable polychloroprene compositions

Abstract

Essentially ethylene thiourea free cross linkable composition comprising a chloroprene rubber having defined contents of cations from the second or third main group and resinate anions are provided, which possess improved curing characteristics for increased productivity and lower vulcanization temperatures for energy-saving manufacturing methods and vulcanizates obtained by using said chloroprene rubber.

Claims

1. A cross-linkable composition comprising: a chloroprene rubber comprising: calcium cations in an amount of 0.05% by weight to 0.25% by weight, based on the total amount of the chloroprene rubber; and resinate anions in an amount of 0.3% by weight to less than 2.5% by weight, based on the total amount of the chloroprene rubber; and a metal oxide cross linker of zinc oxide, magnesium oxide, or a combination of zinc oxide and magnesium oxide, and a vulcanization accelerator of N-methyl-thiazolidine-2-thione.

2. The cross-linkable composition according to claim 1, wherein the amount of resinate anions is 0.4% by weight to 2.3% by weight.

3. The cross-linkable composition according to claim 1, wherein the amount of calcium cations is 0.09% by weight to 0.23% by weight.

4. A process for the production of a vulcanizate, the process comprising heating the cross-linkable composition according claim 1 to a temperature of 100° C. to less than 180° C.

5. A vulcanizate obtained by the process according to claim 4.

6. A molded article of manufacture comprising the vulcanizate according to claim 5.

7. The molded article of manufacture according to claim 6 wherein the article of manufacture comprises an air spring, a conveyor belt, a belt, a cv boot, a bridge bearing, a wiper blade or a diving suit.

8. The process according to claim 4, wherein the temperature is 120° C. to 170° C.

9. The process according to claim 4, wherein the temperature is 140° C. to 160° C.

10. A cross-linkable composition comprising: a chloroprene rubber comprising: calcium cations in an amount of 0.05% by weight to 0.25% by weight, based on the total amount of the chloroprene rubber; and resinate anions in an amount of 0.3% by weight to less than 2.5% by weight, based on the total amount of the chloroprene rubber; and a metal oxide cross linker of a combination of zinc oxide and magnesium oxide, and a vulcanization accelerator of N-methyl-thiazolidine-2-thione.

Description

EXAMPLES

(1) The chloroprene latices used for the following examples were obtained by the following polymerization recipe (batch experiments, quantities given in parts by weight):

(2) TABLE-US-00001 Chloroprene and 2,3-dichlorobutadiene 100 Desalinated water 125 Resin acid 3 Na-Salt of condensation product consisting of 0.5 naphthalene sulfonic acid and formaldehyde n-Dodecylmercaptan (n-DDM) 0.2 KOH 0.5

(3) The polymers obtained from 100 parts by weight technical grade chloroprene were referred to as “homopolymers”, whereas the polymers obtained from a monomer mixture comprising 93 parts by weight technical grade chloroprene and 7 parts by weight technical grade 2,3-dichlorobutadiene were referred to as “copolymers”.

(4) The technical grade chloroprene may also contain 1-chlorobutadiene, typically in an amount of from 0% to 2% by weight.

(5) The polymerization was carried out in a 4 L flask. The aqueous phase made of desalinated water, resin acid, KOH and a Na-Salt of the condensation product of naphthalene sulfonic acid and formaldehyde was placed in this vessel, flushed with nitrogen and heated to a temperature of 45° C. The monomers were added when the medium temperature reached 40° C. Subsequently, the emulsion temperature was stabilized at 45° C. before starting the polymerization.

(6) The polymerization was started by constantly adding a solution of thiourea dioxide in water (3% by weight) at flow rate between 0.1 ml/min and 5 ml/min, the latter being adjusted to achieve 70% monomer conversion within 180 min. The conversion rate was determined by gravimetric analysis. The polymerization was stopped with a 0.03% parts by weight, based on the latex, of an aqueous 2.5% by weight solution of diethyl hydroxylamine when the monomer conversion reached 70%.

(7) The latex was degassed to a residual chloroprene content below 1000 ppm based on the latex.

(8) For reference examples 1 and 2, the degassed latex pH was adjusted to 7.5 with a 20% by weight aqueous acetic acid solution. The polymer was isolated by freezing coagulation and washed with salt-free water. The sheets obtained were dried to a residual moisture content below 0.6% by weight in a circulating air drying cupboard at 70° C.

(9) For reference examples 3 to 5, the degassed latex was diluted with water to a 15% solid content and its pH adjusted to a value between 13 and 11 by addition of 20% aqueous acetic acid. The latex was then precipitated with 0.25% calcium chloride in water at room temperature. The coagulate was washed with salt-free water and dried to a residual moisture content below 0.6% by weight in a circulating air drying cupboard at 70° C.

(10) For inventive examples 1 to 4, the degassed latex was diluted with water to 15% solid content and its pH adjusted to a value between 10 and 7 with a 20% aqueous acetic acid. The latex was then precipitated with 0.25% calcium chloride in water at room temperature. The coagulate was washed with salt-free water and dried to a residual moisture content below 0.6% by weight in a circulating air drying cupboard at 70° C.

(11) All rubber compounds were based on the following recipe:

(12) TABLE-US-00002 No. Component phr 1 Chloroprene rubber (homo- or copolymer) 100 2 Carbon Black N772 30 3 Stearic acid 0.5 4 Maglite DE 4.1 5 Rhenogran MTT-80 0.5 6 Zinc Oxide read seal 5 .sup.1 phr: parts per hundred rubber

(13) They were processed in a 1.5 l intermeshing internal mixer according to the following sequence:

(14) TABLE-US-00003 Absolute time [min] Rotation speed [RPM] Components added (No.) 0 44 1 4 44 2, 3, 4 6 44 5, 6 7 end

(15) Methods

(16) The latex pH was measured with a Schott H 63 glass electrode (Electrolyte: KCl 3 mol/l, Silamid reference system) at 20° C.

(17) In the absence of disturbing substances (e.g. additives) the resinate anion content could be determined by titration of a 2.2% by weight polymer solution in tetrahydrofuran with a 0.1M Perchloric acid solution. The titration was monitored by potentiometry (Metrohm Solovotrode Nr 6.0229.100), the volume of perchloric acid added to reach the first potential step (V.sub.equivalent) was used to calculate the salt amount in the polymer:

(18) $\mathrm{Resinate}\mathrm{anion}\left[\%\right]=\frac{V_{\mathrm{equivalent}}\times 300.5}{{\mathrm{mass}}_{\mathrm{polymer}\mathrm{solution}}\times 2.2}$

(19) Where:

(20) V.sub.equivalent is expressed in milliliters

(21) Mass.sub.polymer solution is expressed in grams

(22) The resulting value is the salt content expressed as a percentage value

(23) For the ion concentration determination, about 0.2 g rubber sample was digested with mineral acid (5 mL HNO.sub.3 (63%), 3 mL H2O) in a microwave oven (Mikrowelle Ultraclave III) according to the following temperature program:

(24) TABLE-US-00004  8 min 70° C. 100 bar  700 Watt 20 min 140° C. 120 bar  700 Watt 10 min 210° C. 160 bar 1000 Watt 12 min 250° C. 160 bar 1000 Watt 18 min 280° C. 160 bar 1000 Watt

(25) The prepared sample was then analyzed by ICP-OES (Varian Vista Pro, wavelength 216.956 nm, 407.771 nm and 421.552 nm (reported value is the mean value), 1.2 kW plasma power, 15 l/min plasma gas, 10 s measurement time repeated 3 times, calibration with external standards. In ICP-OES analysis, atoms were excited by inductively coupled plasma. The emitted light of specific wavelength was detected and corresponded to their concentration (in % by weight) in the sample.

(26) The Mooney scorch is determined at 120° C. according to DIN 53 523 Part 4 and MS-t5 as defined in paragraph 2.2 (MS-t5 is the time from the beginning of the measurement up to the point at which the Mooney viscosity increased by 5 Mooney units above the viscosity minimum).

(27) The vulcanization behavior of the compositions was determined in a Monsanto rheometer MDR 2000E at 160° C. in accordance with DIN 53 529. The characteristic vulcanization times tS1, t10 and t90, as well as ΔS′ were determined in this way.

(28) In accordance with DIN 53 529, part 3: t10: time at which 10% of the conversion has been achieved t90: time at which 90% of the conversion has been achieved ΔS′: difference between the maximum and the minimum torque

(29) The Shore A hardness (H), tensile strength (TS) and the elongation at break (EB) of the vulcanizates were determined by means of a tensile test in accordance with DIN EN ISO 868 and DIN 53504, respectively.

EXAMPLES

(30) TABLE-US-00005 MDR Mechanical Scorch 45 min@160° C. Properties resinate anion Ca.sup.2+ MS t5 ΔS′ t10 t90 t90 − t10 H TS EB Sample Composition pH Latex % % min dNm min min min Sh A MPa % Ref 1 Copolymer 7.5 1.07 <0.01 32.1 10.1 2.9 40 37.3 62 19 349 Ref 2 Homopolymer 7.5 1.15 <0.01 26.7 12 3.4 39.9 36.5 63 20.0 348 Ref 3 Copolymer 12.8 3.02 0.26 47.9 14.4 8.1 37.3 29.2 60 21.5 374 Ref 4 Homopolymer 13.1 3.51 0.29 >50 14.3 9.4 39.6 30.2 61 21.3 371 Ref 5 Homopolymer 11.0 3.21 0.27 49.1 16.1 8.2 34.9 26.7 62 19.6 343 Example 1 Copolymer 9.0 1.84 0.21 45.0 16.5 7.0 29.2 22.2 62 17.9 323 Example 2 Copolymer 7.0 0.73 0.10 19.8 17.2 5.2 24.5 19.3 62 20.6 349 Example 3 Homopolymer 9.0 1.47 0.19 >50 16.3 7.7 25.8 18.1 61 19.9 362 Example 4 Homopolymer 7.0 0.48 0.08 32.4 16.0 4.7 13.1 8.4 61 21.9 403

(31) The results in the table show that when the content of resinate anions and second or third main group metal cations is in the range according to the invention, the effective vulcanization time (t90-t10) and the vulcanization time (t90) are reduced at a vulcanization temperature of 160° C.