Field of the invention
The present invention deals with a composition comprising at least one organic
peroxide and at least one sulfur-containing compound chosen among the group
consisting of dialkyl phosphorodithioic acid and salts thereof
The invention also relates to a method for manufacturing an article comprising
curing a composition comprising at least one elastomer, at least one organic peroxide,
at least one sulfur-containing compound chosen among the group consisting of dialkyl
phosphorodithioic acid and salts thereof, in the full or partial presence of oxygen.
The invention also pertains to an article, preferably an article chosen among
15 the group consisting of a seal, hose or gasket, obtained from the aforementioned method.
Background of the invention
Polymers and copolymers crosslinked with organic peroxides are known to
have superior properties, particularly compared to polymers crosslinked by sulfur cure.
20 These properties include high heat ageing resistance, low percent compression set,
decreased staining of metal, and easy production of colored products with enhanced
color stability. In view ofthese beneficial properties, peroxide cure has a great deal of
practical importance. A possible drawback of peroxide cure is that air must be excluded
from the surface of a material during cure; if air is not excluded, a tacky surface may
25 result, due to cure inhibition by oxygen. In other words, peroxide cure of elastomers in
the presence of atmospheric oxygen alters the surface of the produced material by
rendering its surface substantially tacky.
In particular, when oxygen comes into contact with an elastomer being
crosslinked by an organic peroxide, the crosslinking reaction at the elastomer surface
30 may be inhibited, or may not take place at all. Thus, the elastomer surface remains
uncured. Therefore, curing rubber articles with peroxides is typically conducted in steam
tubes, molten salt baths, steam autoclaves, and air-evacuated closed molds, all of which
are designed to apply heat to the elastomer while excluding atmospheric oxygen during
the crosslinking process.
35 Unfortunately, excluding air from these commercial processes involves a
considerable amount of time and surges their costs, especially to ensure the complete
exhaustion of air and oxygen from the medium where the crosslinking reaction takes
place.
wo 2022/074237 2 PCT/EP2021/077944
In contrast, sulfur vulcanization of elastomers can be conducted using lower
cost hot air ovens or tubes in which hot atmospheric oxygen poses no issue. While the
sulfur curatives are generally lower in cost than organic peroxides, the types of
elastomers suitable for sulfur cure are limited to unsaturated elastomers, e.g.,
5 poly( ethylene propylene diene ), poly(butadiene ), natural rubber, synthetic
poly(isoprene ), poly( styrene-butadiene) rubber, poly(butadiene-acrylonitrile) rubber
and the like.
In many cases, manufacturers would like to switch from sulfur to peroxide cure
using existing hot air ovens; however, curing with conventional peroxide systems under
10 these circumstances would not be viable due to the surface cure inhibition by oxygen.
Various methods have been then suggested for preventing surface cure inhibition by
oxygen during free radical crosslinking. These methods have, for various reasons,
generally met with little or no success.
As a result, organic peroxide formulations comprising at least one sulfur-
IS containing compound have been recently implemented in order to alleviate these
shortcomings, especially to significantly reduce the surface tackiness of elastomeric
articles that are peroxide cured in the full or partial presence of oxygen. The sulfurcontaining
compound used in such formulations can be organic sulfide compounds,
which may be monosulfides, disulfides, trisulfides or higher polysulfides. Especially,
20 the sulfur-containing compound can be selected from the group consisting of poly(tamylphenol
disulfide); poly(t-butylphenol disulfide); 4,4-dithiodimorpholine;
benzothiazyl disulfide; N,N'-caprolactam disulfide; and a combination thereof, and
preferably corresponds to poly(t-amylphenol disulfide) sold under the name Vultac® 5.
However, even if such peroxide formulations can provide a tack-free surface,
25 or substantially tack-free surface, when curing an elastomer composition in the full or
partial presence of oxygen, especially in the presence of hot air, it has been observed
that the mechanical properties of the produced elastomeric articles faltered at the same
time.
Indeed, the implementation of such peroxide formulations may namely hinder
30 their high heat ageing resistance, including their tensile properties such as the tensile
strength at break, and their percentage compression set. In particular, it has been noted
that the tensile strength at break of the produced elastomeric articles can in some cases
severally dwindle while the percent compression set may soar. Hence the obtained cured
elastomers are not high temperature resistant as they can display permanent deformation
3 5 under heat and pressure.
It bespeaks that peroxide formulations mixed with the aforementioned sulfurcontaining
compounds cannot provide a tack-free surface while providing at the same
time the desirable mechanical properties obtained with peroxide cure as some of them
can even significantly dwindle.
5
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Accordingly, it remains a real need to provide compositions which are able to
cure commercially available elastomers and/or elastomer compositions in the full or
partial presence of atmospheric oxygen without hampering their mechanical properties,
preferably their mechanical properties after heat aging.
In particular, one of the goals of the present invention is to provide
compositions which are able to lead to articles having at the same time a tack-free
surface, or substantially tack-free surface, and enhanced mechanical properties,
especially after heat aging.
More specifically, another goal of the present invention is to obtain an article
10 having a tack-free surface, or substantially tack-free surface, and an improved tensile
strength at break and a better compression set.
Description of the invention
The present invention namely results from the unexpected findings, by the
15 inventor, that the implementation of a composition comprising at least one organic
peroxide and at least one sulfur-containing compound chosen among the group
consisting of dialkyl phosphorodithioic acid and salts thereof, at a concentration as
defined hereafter, is able to cure at least one elastomer in order to obtain articles having
at the same time a tack-free surface, or substantially tack-free surface and enhanced
20 mechanical properties, especially after heat aging.
25
Therefore, the present invention relates to a composition comprising:
a) at least one organic peroxide,
b) at least one sulfur-containing compound chosen among the group
consisting of dialkyl phosphorodithioic acid and salts thereof, in particular
zinc dialkyl dithiophosphates,
c) optionally sulfur under its free form,
d) at least one filler,
wherein the weight ratio between said at least one organic peroxide and said at
least one sulfur-containing compound is higher than 0.3, preferably higher than 0.5,
30 even more preferably higher than 0.8,
wherein the weight ratio between sulfur under its free form and said at least
one organic peroxide is lower than 0.15, preferably lower than 0.1,
wherein the weight ratio between said at least one filler and said at least one
organic peroxide is higher than 10.
3 5 The composition of the present invention allows the curing of elastomers,
unsaturated or saturated, in the full or partial presence of atmospheric oxygen (e.g.,
using a hot air oven or tunnel, or steam autoclave) which allows to save time and extra
costs compared to organic peroxide cure without altering at the same time the
mechanical properties of the cured elastomers.
wo 2022/074237 4 PCT/EP2021/077944
Furthermore, the composition of the present invention namely leads to the
production of articles having a tack-free surface, or substantially tack-free surface, and
exhibiting better mechanical properties after heat aging than articles cured with organic
peroxide formulations containing at least one sulfur-containing compound chosen
5 among the group consisting of poly(t-amylphenol disulfide); poly(t-butylphenol
disulfide); 4,4-dithiodimorpholine; benzothiazyl disulfide; N,N'-caprolactam disulfide;
and mixtures thereof
In particular, the composition of the present invention allows to obtain articles
displaying enhanced tensile properties and compression set, and specifically a high
10 tensile strength at break and a low percentage compression set at the same time.
According to the present invention, when heat and pressure are applied to a
sulfur-cured elastomer, the sulfur bonds typically break and re-form, causing the
deformation of the elastomer. One test to monitor this deformation is called percentage
(%) compression set test. The greater the crosslinked elastomer specimen exhibits
15 permanent deformation under heat and pressure, the higher the percentage compression
set value. Thus, lower percentage compression set values, equating to less or no
permanent elastomer deformation, are desirable for many elastomers, particularly for
hose, gasket and sealing applications.
As a result, the aforementioned composition advantageously yields products,
20 in particular elastomeric products, having enhanced mechanical properties suitable for
hose, gasket and sealing applications.
25
It bespeaks that the composition of the present invention produces tack-free
surface, or substantially tack-free surface, and high temperature resistant elastomeric
products suitable for various applications, such as hose, gasket and sealing applications.
In addition, the composition of the present invention allows the curing of
elastomers in a shorter range of time than formulations based solely on organic peroxide
or formulations containing a mixture of organic peroxide and at least one sulfurcontaining
compound chosen among the group consisting of poly(t-amylphenol
disulfide); poly(t-butylphenol disulfide); 4,4-dithiodimorpholine; benzothiazyl
30 disulfide; N,N'-caprolactam disulfide; and mixtures thereof
In other words, the composition of the present invention can significantly
reduce the surface tackiness of an article, preferably an elastomeric article, that is
peroxide cured in the full or partial presence of oxygen, that is to say in an open system,
and can provide short curing times, high tensile strength at break and low percentage
3 5 compression set.
Another subject-matter of the present invention pertains to a method for
manufacturing an article comprising curing a composition comprising a) at least one
elastomer, b) at least one organic peroxide, c) at least one sulfur -containing compound
chosen among the group consisting of dialkyl phosphorodithioic acid and salts thereof,
40 in particular zinc dialkyl dithiophosphates, d) optionally sulfur under its free form, in
5
wo 2022/074237 5 PCT/EP2021/077944
the full or partial presence of oxygen; wherein in said composition the weight ratio
between said at least one organic peroxide and said at least one sulfur-containing
compound is higher than 0.3 and the weight ratio between sulfur under its free form and
said at least one organic peroxide is lower than 0.15, preferably lower than 0.1.
In other words, the aforementioned method comprises, consists essentially of,
or consists of curing a composition in the partial or full presence of oxygen, wherein
said composition comprises at least one elastomer, at least one organic peroxide, at least
one sulfur-containing compound chosen among the group consisting of dialkyl
phosphorodithioic acid and salts thereof, in particular zinc dialkyl dithiophosphates,
10 optionally sulfur under its free form, wherein the weight ratio between said at least one
organic peroxide and said at least one sulfur-containing compound is higher than 0.3
and the weight ratio between sulfur under its free form and said at least one organic
peroxide is lower than 0.15.
The method of the invention is less expensive to implement than commercial
15 processes wherein air is excluded and can be achieved in a relatively short period of
time.
Another aspect of the present invention pertains to an article, preferably an
elastomeric article, comprising at least the aforementioned composition in cured form
and which is preferably completely or substantially tack-free.
20 Preferably, such an article can be chosen among the group consisting of a seal,
hose or gasket. The articles can be extruded or molded using methods known in the art.
These articles can be cured in hot air, microwave/UHF, infra-red heat and/or steam
autoclave where steam purging time of atmospheric oxygen can be shortened or
eliminated, while providing a fully cured surface with improved heat aging properties.
25 The invention also deals with an article, preferably an elastomeric article, obtained from
the aforementioned method.
Moreover, the invention relates to the use of the composition according to the
present invention in order to improve the mechanical properties, especially the tensile
properties and the compression set, of a composition comprising at least one elastomer.
30 The enhanced tensile properties are preferably the tensile strength and/or the
percentage of elongation at break.
Other subjects and characteristics, aspects and advantages of the invention will
emerge even more clearly on reading the description and the example that follows.
In the text herein below, and unless otherwise indicated, the limits of a range
35 of values are included in that range, in particular in the expressions "between" and
"ranging from ... to ... ".
40
Moreover, the expression "at least one" used in the present description is
equivalent to the expression "one or more".
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Composition
As intended herein, the term "comprising" has the meaning of "including" or
"containing", which means that when an object "comprises" one or several elements,
other elements than those mentioned may also be included in the object. In contrast,
5 when an object is said to "consist of' one or several elements, the object is limited to the
listed elements and cannot include other elements than those mentioned.
According to the present invention, the term "polymer" encompasses
homopolymers and copolymers, where the term "copolymers" refers to a polymer
comprised of at least two different monomers in polymerized form. For example, a
10 copolymer in accordance with the present disclosure may be a polymer comprising two
different monomers, a terpolymer is a polymer comprising three different monomers or
more.
As previously detailed, the composition according to the present invention
compnses:
15 a) at least one organic peroxide,
20
b) at least one sulfur-containing compound chosen among the group consisting
of dialkyl phosphorodithioic acid and salts thereof, in particular zinc dialkyl
dithiophosphates,
c) optionally sulfur under its free form,
d) at least one filler
wherein the weight ratio between said at least one organic peroxide and said at
least one sulfur-containing compound is higher than 0.3, preferably higher than 0.5,
more preferably higher than 0.8,
wherein the weight ratio between sulfur under its free form and said at least
25 one organic peroxide is lower than 0.15, preferably lower than 0.1,
wherein the weight ratio between said at least one filler and said at least one
organic peroxide is higher than 10.
The organic peroxide used in the aforementioned composition is preferably
solid at room temperature.
30 According to the present invention, the expression "room temperature" stands
for a range of temperatures of from 15°C to 30°C, preferably from 20°C to 30°C.
The organic peroxide can be chosen among the group consisting of dialkyl
peroxides, hemi-perketal peroxides (e.g., Luperox® V10), diperoxyketals, mono-peroxy
carbonates, cyclic ketone peroxides, diacyl peroxides, organosulfonyl peroxides,
35 peroxyesters and solid, room temperature stable peroxydicarbonates.
Preferably, the organic peroxide is selected from the group consisting of dialkyl
peroxides, peroxyketals, cyclic ketone peroxides, monoperoxycarbonates, peroxyesters,
diacyl peroxides and mixtures thereof, preferably dialkyl peroxides.

Claims
1. Composition comprising:
a) at least one organic peroxide,
5 b) at least one sulfur-containing compound chosen among the group consisting of
dialkyl phosphorodithioic acid and salts thereof, in particular zinc dialkyl
dithiophosphates,
c) optionally sulfur under its free form,
d) at least one filler,
10 wherein the weight ratio between said at least one organic peroxide and said at least one
sulfur-containing compound is higher than 0.3, preferably higher than 0.5, more preferably
higher than 0.8,
wherein the weight ratio between sulfur under its free form and said at least one organic
peroxide is lower than 0.15, preferably lower than 0.1,
15 wherein the weight ratio between said at least one filler and said at least one organic
peroxide is higher than 10.
2. Composition according to Claim 1, characterized in that the organic peroxide is selected
among the group consisting of 1,3(4)-bis[1-(tert-butylperoxy)-1-methylethyl]benzene, 1,1-
di(t-butylperoxy)-3,3,5-trimethylcyclohexane, t-butylperoxybenzoate, t-butyl-2-
20 ethylhexylmonoperoxycarbonate, 2, 5-dimethyl-2, 5-di( t-butylperoxy )hexane, dicumyl
peroxide, and t-butylcumylperoxide, and mixtures thereof, preferably 1,3(4)-bis[1-(tertbutylperoxy
)-1-methylethyl ]benzene.
25
3. Composition according to Claim 1 or 2, characterized in that dialkyl dithiophosphates
salts have the following formula (VI):
(VI)
wherein RA, RB, Rc and Rn, identical or different, represent:
- a linear or branched C1-C3o alkyl radical, especially a linear or branched C1-C14 alkyl
radical,
- a cyclic alkyl group comprising from 4 to 30 carbon atoms, especially from 4 to 10 carbon
30 atoms,
wo 2022/074237 33 PCT/EP2021/077944
- M2+ is a divalent metal, preferably chosen in the group consisting of zinc, calcium and
copper, more preferably M2+ is zinc,
preferably RA, RB, Rc and Rn are identical and represent a linear C1-C4 alkyl radical.
4. Composition according to any of the preceding claims, characterized in that said filler is
5 chosen from consisting of water washed clay, e.g., Burgess Clay, black carbon, calcium
carbonate, silica, precipitated silica, calcium silicate, kaolin, liquid saturated hydrocarbon,
and combination thereof, more preferably is chosen in the group consisting ofblack carbon,
calcium carbonate, silica, kaolin and combination thereof
5. Composition according to any of the preceding claims, characterized in that said
10 composition further comprises at least one elastomer.
6. Composition according to Claim 5, characterized in that said elastomer is saturated and
selected among the group consisting of silicon rubber without unsaturation (Q), methylpolysiloxane
(MQ), phenyl-methyl-polysiloxane (PMQ), poly( ethylene-vinyl acetate)
(EVA), high-density polyethylene (HDPE), low-density polyethylene (LDPE), chlorinated
15 poly(ethylene) (CM or CPE), poly(ethylene-propylene) (EPM), fluoroelastomers (FKM,
FFKM) and combinations thereof
7. Composition according to Claim 5, characterized in that said elastomer is unsaturated
and selected among the group consisting of ethylene-propylene-diene terpolymer (EPDM),
vinyl silicone rubber (VMQ), fluorosilicone (FVMQ), nitrile rubber (NBR), acrylonitrile-
20 butadiene-styrene (ABS), styrene butadiene rubber (SBR), styrene-butadiene-styrene block
copolymers (SBS), polybutadiene rubber (BR), styrene-isoprene-styrene block copolymers
(SIS), partially hydrogenated acrylonitrile butadiene (HNBR), natural rubber (NR),
synthetic polyisoprene rubber (IR), neoprene rubber (CR), polychloropropene, bromobutyl
rubber (BIIR), chlorobutyl rubber, and mixtures thereof
25 8. Composition according to any of Claim 5 to 7, characterized in that said at least one
sulfur-containing compound is present in an amount lower than 3.3 phr.
9. Composition according to any of Claims 5 to 8, characterized in that said sulfur under
its free form is present in an amount ranging from 0 to 0.5 phr, preferably from 0 to 0.4 phr,
more preferably from 0 to 0.3 phr, or from 0 to 0.2 phr, even more preferably from 0 to 0.1
30 phr.
10. Composition according to any of the preceding claims, characterized in that said
composition further comprises at least one HALS compound, preferably selected from the
group consisting of poly[[ 6-[ (1, 1 ,3,3-tetramethylbutyl)amino ]-s-triazine-2,4-diyl ][(
2,2,6,6-tetramethyl-4-piperidyl)imino]-hexamethylene-[(2,2,6,6-tetramethyl-4-
35 piperidyl)imino]], [bis(2,2,6,6-tetramethyl-4-piperidinyl)sebacate], and mixtures thereof
wo 2022/074237 34 PCT/EP2021/077944
11. Composition according to any of the preceding claims, characterized in that said
composition further comprises at least one antioxidant, preferably phenolic antioxidant.
12. Method for manufacturing an article, preferably an elastomeric article, comprising a step
of curing a composition in the full or partial presence of oxygen, said composition
5 compnsmg:
10
a) at least one elastomer,
b) at least one organic peroxide,
c) at least one sulfur-containing compound chosen among the group consisting of
dialkyl phosphorodithioic acid and salts thereof, preferably zinc dialkyl
dithiophosphates,
d) optionally sulfur under its free form,
wherein the weight ratio between said at least one organic peroxide and said at least one
sulfur-containing compound is higher than 0.3, preferably higher than 0.5, more preferably
higher than 0.8,
15 wherein the weight ratio between sulfur under its free form and said at least one organic
peroxide is lower than 0.15, preferably lower than 0.1.
13. Article comprising a composition as defined according to any of Claims 5 to 11 in a
cured form, preferably said article being completely or substantially tack-free.
14. Article manufactured according to the method defined in Claim 12.
20 15. Article according to Claim 13 or 14, characterized in that it is selected among the group
consisting of a seal, hose and gasket.
25
30
16. Use of a composition according to any of Claims 1 to 4, in order to improve the
mechanical properties, especially the tensile properties and compression set, of a
composition comprising at least one elastomer as defined in any of the Claims 5 to 7.