CA1090042A - Vulcanisation process - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A process for the vulcanisation of polychloroprene rubbers which comprises heating the uncured rubber in the presence of a mixture of zinc oxide, magnesium oxide and a compound of the formula (1) in which each R independently represents methyl or ethyl.
The compounds exhibit a superior balance of the following technical properties:
good accelerator activity at curing temperatures good scorch safety process temperatures high level of specific desirable qualities in the vulcanised elastomer.

Description

. Dr~281~0 10~.)0~ ' This invention relates to ~ n~w vulcanisation procefis and more particularly to a new process for the wlcanisati.on of polychloroprene syn-thetic rubbers.
' Polychloroprene synthetic ~ubbers are different from natural and mo6t synthetic rubbers in that vulcanisation is ef~ected by heating witll a mixture of zinc and magnesium oxides instead of with sulphur. With some polychloroprene elastomers, a vulcanisation accelerator is not essential, though frequently added,~ut with non-sulphur modified types, an accelerakor is essential for the development o~ desired technieal properties in the finj,hed article~ However, accelerators used in the curing of natur~l or ~ynth~tic rubbers with sulphur usually have an inadequate per~ormance as accelerators ~or polychloroprene rubbers.
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me present invention provides a process for the VU].C~niGation of polychloroprene rubbers which comprises heatin~
the uncured rubber in the presence o~ a mixture of zinc oxide, m~nesium oxide and a compound of the formula ~ .
S = P-~ - NHR (1) \ NHR
in which eAch R independently represents methyl or ethyl~
As compounds of formula (1~ ~rhich may be used, there may be mentioned:
N,N',N"~trimethyl phosphorothioic triamide N,N'-dimethyl-N"-ethyl phosphorothioic tri~mide N-methyl-N',N"-diethyl phosphorothioic triamide N,N',N"-triethyl phosphorothioic triamide ~nd mixtures of one or more of these compo~lds. They may be obtailled by reacting thiophosphoryl chloride with methylamirle, ethylamine or both methylamine and ethylamine, in whlch case the reaction may be carried out sequentially or by using a mixture of the amines.
The rubber can also be mixed with Gther conventional additives for polychloroprene rubber69 e~g. stearic acid, carbon black, china clay, pigmentfi, processing oils, retarderfi, other elastomers, antioxidants and antiozonants, e.g. alkylated diphenylamine, acetone~diphenylamine condensation products, alkylaminodiphenylamines and xylenol-for~,aldehyde condensation products~ Cellular and microcellular products can be obtain~d by incorporating blowir~
agentfi e.g. dinitrosopentamethylene tetramine, aæodicarbonamide und benene svlphonyl hydrazide into the mixture.

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If desired, other accelerators for polychloroprene rubbers can also be added~ -The compound o~ formula (1) will normally be used in a amount from 0~1% to 5~ and preferably 0.25% to 105~ by weight of the uncured polychloroprene rubber, but more o.r less than these amountæ
may be used if desiredO
The æinc and magnesium oxides rnay bc used in conventional amount, which may conveniently be from 1% to 10% by weight of the uncured polychloropren~ rubber.
The oxides, accelerator and any other additives may be incorporated into th~ uncured polychloroprene rubber by e~y conventional method, e.g~ by use of a two-roll rubber mill, an internal mixer e.gO a "~anbury",or in a dough-mi~er the mixture may ba shaped by ~Ly conventional process, e.g~ extrusion, calendering, preæs-mouldirJg or spreadir~ Vulcanisation may b~ carried out at - any suitable temperature e~g~ from 50C to 300C and preferably from 100C to 200C,but temperatures outside this rarge may b~ used if desiredO
It has been proposed in UK Specification No~858136 to use amido derivatives of pho.phoric and thiophosphoric acids which contain at least one p_~T bo~d as vulcanisation a~celerators ~or natural and synthetic vulcanisable elastomers, irLoluding9 e.g. N,N ~N"-triphenyl~ and tricyclohexyl thiophosphoric triamide; howe~er the majority of compounds disclosed are of the N,N-dialkyl phosphoric or thiophosphoric triamide series. As compared with the compounds of closest structure di~.ciosed in Specification No.858136, the compounds of formula (1) exhibit a superior bal.~nce of the following technical ~' ' . ' :
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good accel~ratol ~otivity at curing temparatures good scorch safety at process temperatur~s high leYel of specific desira~le qualities in the ~lcanised elastomer~
and in thè case of` the trimethyl compound, which ie prefe~red, excellent storage stability of compounded stockO
The invention i6 illustrated but not limited by the following Exampleæ in which parts are by weight:
Exam~les 1 and 2 __.
Using (1) N,N',N"-trimethyl and (2) N~N~9N~I-triethyl phosphorothioic triamide Base Mix Parts Non-sulphur modified polychloroprene 100 Zinc oxide 5 Stearic acid 0.5 -Light magnes;um oxide 2 Medium thermal blac~ 50 Accelerator 0.5 Test mixes were made on R labolatory two-roll mixing mill at a roll temperature of 50-55C and sheeted out. Scorch-safety and cure behaviour were determined by Mooney scorch-test at 120C and by ar oscillating-disc rheometer at 150~C. Compression set wae de'cermi~ed by a method similar to B.S.903 Part -A6 on 12.5 mm thick disc samples cured at 150C for 30 minutes in a laboratory platen pr~se. These were compressed to 9.375 mm, and kept for 24 hours in an air oven at 100C.
The results are summarised in the following table, in which the first column gives the results from the methyl compound of formula ~1), and th~ second from the ethyl compound of ~ormula (1).

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: Dr~8180 1(~9~ 09~ , Also include~l in the table are comparative result~ from tri-n~butyl pho.sphoric tri~mide, (t.hird column~ ~xample 5 o.~ UK 858136) and N9N-diethyl pho~phorothioic triamid~ (fourth column, of Fxample 12 or 16 o~ UK Specifi.cation NoO858136).
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Mooney Scorcl1 tmins to min +10)10.5 12.5 50 6 Oscillating ~isc Vlscometer at 150C T2 (mins) 3.7 300 11 3~3 10Torque in ft/lbs.
after 15 minsO 76 59 21 54 30 mins. 91 80 28 74 45 mins~ 98 87 33 8L~

~ Compression set at 100C
15for 24 hours 31 33 92 35 The following ta~le comp~res the storaga ~tability of compounded stock by measurement of the MoGney Scorch time at minimurn ~ lO~
and the Mooney viscosity (at minimum~ at peri.ods of 19 2 and 3 weeks at room temperature and after 1 week at 38C; the accelerators used &re 20column 1 - ethylen~ thiourea

2 ~.,N,,N'tN"-trimethylphosphorothioic triamide

3 - N91~1~,N"-triethylphosphorothioio triamidc

4 ~ N,N diethylphosphorothioic triami.de ~ Dr~28180 1~119(~0~2 TABLE
im~ Moone,y Sco~ch time M n~L___ co~it~
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1 week at room temp.7.~/4 10~6 3/4 4 60~ 58 66 72 2 weeks at roonl temp~ 7~9.3/4 5 ~ 62~59 76 93 3 week~ at room temp.7~ 10z~ 3.3/4 1~ 65 60 85 113~ :
1 week at 38C 8 7~ cured 68 67 126curod ,.. ..... .

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Claims (2)

The embodiments of the invention in which an exclusive privilege and property are defined as follows:

1. A process for the vulcanisation of polychloro-prene rubbers which comprises heating the uncured rubber in the presence of a mixture of zinc oxide, magnesium oxide and a compound of the formula (1) in which each R independently represents methyl or ethyl.

2, A process as claimed in Claim 1 wherein the compound of formula 1 is N,N',N''-trimethylphosphorothioic triamide.