PROCEDE DE VULCANISATION

VULCANISATION PROCESS

Abrégé anglais

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
<IMG> (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.

Revendications

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
<IMG>
(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.

Description

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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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Dr.28180
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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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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).
T e I
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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

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TABLE
im~ Moone,y Sco~ch time M n~L___ co~it~
m~n~
2 3 4 1 2 3 4
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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