U.S. patent application number 10/720319 was filed with the patent office on 2004-06-03 for rubber composition which is free of carcinogenic nitrosamine precursor and serves as connecting rubber.
Invention is credited to Chauvin, Brigitte, Mangeret, Jean-Luc.
Application Number | 20040106743 10/720319 |
Document ID | / |
Family ID | 9466115 |
Filed Date | 2004-06-03 |
United States Patent
Application |
20040106743 |
Kind Code |
A1 |
Chauvin, Brigitte ; et
al. |
June 3, 2004 |
Rubber composition which is free of carcinogenic nitrosamine
precursor and serves as connecting rubber
Abstract
A rubber composition which is free of precursor of at least one
carcinogenic nitrosamine, is capable of vulcanization at a
temperature of between 95.degree. C. and 140.degree. C., and has a
vulcanization system which includes: a) sulfur; b) an accelerator
compound; c) an ultra-accelerator compound; d) a vulcanization
amine activator. A process for vulcanizing this composition in the
manufacture of a new tire or in the repair and/or recapping of a
worn tire.
Inventors: |
Chauvin, Brigitte;
(Chamalieres, FR) ; Mangeret, Jean-Luc; (Riom,
FR) |
Correspondence
Address: |
BAKER & BOTTS
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
|
Family ID: |
9466115 |
Appl. No.: |
10/720319 |
Filed: |
November 24, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10720319 |
Nov 24, 2003 |
|
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|
08505131 |
Jul 21, 1995 |
|
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Current U.S.
Class: |
525/331.9 ;
525/333.3; 525/333.9; 525/379 |
Current CPC
Class: |
C08K 5/39 20130101; C08K
5/40 20130101; C08K 5/39 20130101; C08L 21/00 20130101; C08K 5/40
20130101; C08L 21/00 20130101 |
Class at
Publication: |
525/331.9 ;
525/333.3; 525/333.9; 525/379 |
International
Class: |
C08F 036/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 3, 1994 |
FR |
94/09740 |
Claims
We claim:
1. A composition which is free of precursor of at least one
carcinogenic nitrosamine containing at least one rubber selected
from the group consisting of natural rubber, polyisoprene,
polybutadiene, styrene-butadiene, styrene-isopreneland
butadiene-isoprene copolymers, and styrene-butadiene-isoprene
terpolymers, and capable of vulcanizing at a temperature between
95.degree. C. and 140.degree. C., characterized by the fact that it
comprises, as vulcanization system: a) sulfur; b) at least one
accelerator compound selected from the group consisting of
benzothiazyl disulfide and mercaptobenzothiazole; c) at least one
ultra-accelerator compound selected from the group consisting of
tetrabenzylthiuram disulfide and zinc dibenzyldithiocarbamate; d)
at least one vulcanization amine activator selected from the group
consisting of amines, guanidines, aldehyde and amine condensates,
and quaternary ammonium salts.
2. A composition according to claim 1, characterized by the fact
that it contains natural rubber or a mixture of natural rubber and
at least one other rubber selected from the group consisting of
polyisoprene polybutadiene, styrene-butadiene, styrene-isoprene,
and butadiene-isoprene copolymers, and styrene-butadiene-isoprene
terpolymers.
3. A composition according to claim 1, characterized by the fact
that it contains at least one additive selected from the group
consisting of carbon blacks, extender oils, and tackiness
agents.
4. A composition according to claim 1, characterized by the fact
that, for 100 parts by weight of the rubber or all the rubbers, the
amount of sulfur is between 0.5 and 5 parts by weight.
5. A composition according to claim 4, characterized by the fact
that, for 100 parts by weight of the rubber or of all the rubbers,
the amount of sulfur is between 1 and 3 parts by weight.
6. A composition according to claim 1, characterized by the fact
that, for 100 parts by weight of the rubber or all the rubbers, the
amount of compound b) or all the compounds b) is between 0.1 and 3
parts by weight.
7. A composition according to claim 6, characterized by the fact
that, for 100 parts by weight of the rubber or of all the rubbers,
the amount of compound b) or all compounds b) is between 0.2 and 2
parts by weight.
8. A composition according to claim 1, characterized by the fact
that, for 100 parts by weight of the rubber or all the rubbers, the
amount of compound c) or all the compounds c) is between 0.2 and 3
parts by weight.
9. A composition according to claim 8, characterized by the fact
that, for 100 parts by weight of the rubber or all the rubbers, the
amount of compound c) or all compounds c) is between 0.4 and 2
parts by weight.
10. A composition according to claim 1, characterized by the fact
that, for 100 parts by weight of the rubber or all the rubbers, the
amount of compound d) or of all compounds d) is between 0.05 and 1
part by weight.
11. A composition according to claim 10, characterized by the fact
that for 100 parts by weight of the rubber or all the rubbers, the
amount of compound d) or of all compounds d) is between 0.1 and 0.5
parts by weight.
12. A composition according to claim 1, characterized by the fact
that it comprises diphenylguanidine as compound d).
13. A composition according to claim 1, characterized by the fact
that it is capable of vulcanizing at a temperature of between
95.degree. C. and 115.degree. C.
14. A composition according to claim 1, characterized by the fact
that it is intended to be used in order to connect two
prevulcanized parts of rubber, the composition serving as
connecting rubber between said parts.
15. A composition according to claim 14, characterized by the fact
that it is intended to be used in order to manufacture a new
tire.
16. A composition according to claim 14, characterized by the fact
that it is intended to be used in order to repair and/or recap a
worn tire.
17. A process consisting of vulcanizing a composition according to
claim 1 at a temperature of between 95.degree. C. and 140.degree.
C.
18. A process according to claim 17, characterized by the fact that
the vulcanization is carried out at a temperature between
95.degree. C. and 115.degree. C.
19. A process according to claim 17, characterized by the fact that
it includes vulcanizing the composition to connect two
prevulcanized parts of rubber, the composition serving as
connecting rubber between said parts.
20. A process according to claim 19, characterized by the fact that
it includes vulcanizing the composition in the manufacture of a new
tire.
21. A process according to claim 19, characterized by the fact that
it includes vulcanizing the composition in the repair and/or
recapping of a worn tire.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a composition comprising at
least one rubber, said composition being intended, in particular,
to serve as connecting rubber for the manufacture of a new tire, or
as connecting rubber or repair rubber for the recapping or repair
of a worn tire.
[0002] The invention also concerns a process which consists in
vulcanizing said composition, for instance in order to assure the
connection between two rubber parts, in particular upon the
manufacture, recapping or repair of a tire.
[0003] Two main recapping processes are known, namely:
[0004] the first process, known as "mold recapping" or "hot
recapping", consists in placing a new raw tread, free of tread
pattern, on the used carcass after it has been decapped and
brushed, and curing the tire assembly thus formed in a mold, under
pressure, at temperatures of about 150.degree. C.; the tread
pattern is imparted upon this operation by the action of the hot
mold under pressure;
[0005] the second process is based on the concept of "cold
vulcanization", that is to say vulcanization at a relatively low
temperature of between 95 and 140.degree. C. and, in particular,
between 95 and 115.degree. C.
[0006] This second cold vulcanization process is described, for
instance, in U.S. Pat. Nos. 3,951,720, 2,976,910, 3,136,673, and
3,236,709, and in "Tire Technology International 1993" (The Annual
Review of Tire Materials and Tire Manufacturing Technology, UK
& International Press, 1993, p. 194).
[0007] In this process, a raw layer of a rubber preparation is
interposed between the decapped tire and the precured replacement
tread, this layer being intended to assure the connection of the
materials after curing at low temperature. Such rubber preparations
are thus commonly referred to in the art as "connecting rubbers".
As the carcass and the replacement tread are already vulcanized,
the precuring temperature upon the recapping should be as low as
possible in order not to impair the performance of the tire, as
mentioned in the reference "La chaleur raccourcit la vie du
pneumatique" [Heat shortens the life of tires] (Bandag,
Communication Pneu, 1992, p. 32).
[0008] In this cold vulcanization process, good adherence of the
connecting rubber to the precured adjacent mixes requires a high
degree of vulcanization. The high coherence necessary for the
connecting rubber is acquired by the cross-linking upon the low
temperature curing. For these connecting rubbers it is therefore
necessary to use vulcanization systems which are very reactive at
low temperature so as to assure fast curing speeds and high degrees
of crosslinking. These two performances of the vulcanization system
are indispensable in order to improve the productivity and quality
of this type of recapping.
[0009] However, it is also indispensable that these vulcanization
systems do not result in early vulcanization of the connecting
rubbers at the temperatures at which they are normally stored or
transported. Vulcanization systems which are very reactive on
curing are frequently unstable in raw state. A solution known in
the art for reconciling the requirements of reactivity and of
stability of these vulcanization systems consists in keeping the
vulcanization agent, on the one hand, and the vulcanization
accelerators, on the other hand, separate during storage and in
permitting them to come into contact with each other only during
the recapping operation. Thus, for example, U.S. Pat. No. 2,976,910
discloses the joint use of a solution containing either the
cross-linking agent or the vulcanization accelerators and of a film
which contains the missing ingredients of the vulcanization system.
It is also possible, as disclosed in U.S. Pat. No. 3,136,673, to
use two films, one containing the cross-linking agent and the other
the vulcanization accelerators.
[0010] On the other hand, new constraints of a toxicological nature
have appeared in recent years based on the strict European
regulations which limit the amount of certain nitrosamines in the
storage areas and curing shops to very low values.
[0011] In Germany, for instance, there exists the "Technical Rule
for Dangerous Substances", TRGS No. 552, which is devoted
specifically to nitrosamines and establishes maximum concentrations
for the latter in the air.
[0012] TRGS No. 552 is cited in several technical articles which
point out the carcinogenic effect of nitrosamines and propose
possible substitutes for the products which are precursors of
carcinogenic nitrosamines:
[0013] "A new safe thiuram, TBZTD" (D. B. Seeberger, 136th Meeting
of the Rubber Division, ACS Paper No. 70, 1989).
[0014] "Les nitrosamines: un defi bien reel" [Nitrosamines: A real
challenge) (H. W. Engels, Caoutchoucs & Plastiques, No. 715,
pages 52 to 57, 1992).
[0015] "Les nitrosamines dans l'industrie du caoutchouc: le point
sur la question en Republique Federale d'Allemagne" [Nitrosamines
in the rubber industry: The focus on the matter in the Federal
Republic of Germany] (P. Lupfert, Kautschuk Gummi, Kunststoffe, Vol
42, No. 1, pages 16 to 21, 1989).
[0016] "N-nitrosamines volatiles et atmospheres industrielles"
[Volatile N-nitrosamines and industrial atmospheres] (N. Daubourg,
A. Coupard and A. Pepe, Caoutchoucs et Plastiques, No. 717, pages
103 to 113, October, 1992).
[0017] In the tire industry, vulcanization accelerators are very
frequently precursors of nitrosamines; now, there are primarily
twelve nitrosamines which are classified as carcinogenic and are
cited in TRGS No. 552, such as N-nitrosomorpholine,
N,N-dimethyInitrosamine, N,N-diethyInitrosamine, and these
nitrosamines are for the most part capable of being produced by
nitrosation of the decomposition products of the vulcanization
accelerators.
[0018] In this context of industrial hygiene, it is therefore
important that the systems for the vulcanization of rubber
compositions in general and the connecting rubbers in particular be
without carcinogenic nitrosamine precursors which are covered by
the regulations.
[0019] The rubber compositions which are intended in particular for
use as connecting rubbers and which contain complete vulcanization
systems, that is to say both vulcanization agents and vulcanization
accelerators, must therefore at the same time present rapid curings
at low temperature with high yields, excellent raw stability under
the ordinary conditions of preservation, storage and
transportation, and be free of any compound or ingredient which is
a precursor of carcinogenic nitrosamines covered by the
regulations.
[0020] In the literature, complete sulfur vulcanization systems for
low-temperature curing are widely cited.
[0021] It is thus known that combinations formed of
ultra-accelerators of the thiuram or dithiocarbamate family and
derivatives of benzothiazole confer a high reactivity at low
temperature on the mixes, as cited in:
[0022] "Room Temperature Curative Systems for Natural Rubber" (S.W.
SIN, Proceedings of Technology Seminar, Dec. 4-5, 1978, pages 178
to 186).
[0023] "Vulcanization and Vulcanizing agents" (W. Hoffmann,
Palmerton Publishing, New York, 1967, page 139).
[0024] Encyclopedia of Chemical Technology, 3rd edition (Vol. 20,
published by John Wiley & Sons, Inc., 1982, pages 350 to
352).
[0025] Moreover, it is also known that such combinations may make
it possible to obtain high vulcanization yields as cited by T. D.
Skinner and A. A. Watson (Rubber Age 99 (11), p. 76, 1967).
[0026] Nevertheless, the high reactivity of these products upon the
curing of the compositions which contain them generally produces a
marked tendency to prevulcanization and scorching at moderate
temperatures which may correspond to the temperatures of
preservation or storage of these compositions, as cited in
"Prevulcanization inhibitor of sulfur-free thiuram vulcanization"
(V. Duchacek, Rubber Chem. & Technol., 46, pages 504 to 510,
1973).
[0027] Furthermore, many thiurams and dithiocarbamates which make
it possible to effect low-temperature curing are precursors of
carcinogenic nitrosamines in accordance with European law such as,
for instance, methyl zimate (zinc dimethyldithiocarbamate) cited in
U.S. Pat. No. 3,951,720, this product being a precursor of
dimethyInitrosamine which is classified as carcinogenic in
Regulation TRGS 552.
[0028] Moreover, complete vulcanization systems conferring good
resistance to scorching and excellent raw stability on raw rubber
compositions are also known. Examples of such systems are cited
in:
[0029] Encyclopedia of Chemical Technology (3rd edition, Vol. 20,
published by John Wiley & Sons, Inc., 1982, pages 390 to
392).
[0030] OTOS/MBT Derivative Vulcanization Systems" (K. C. Moore,
Elastomerics, 110 (6), 1978, pages 36 to 42).
[0031] However, the modest reactivity of these known systems
results in slow curing at low temperature.
[0032] Thus, in the present state of the art, there is no complete
vulcanization system which is a non-precursor of nitrosamines which
are carcinogenic and therefore regulated, which is capable of
conferring in rubber preparations, and in particular in rubber
compositions for connecting rubbers, at the same time:
[0033] rapid curing at low temperature,
[0034] a high cross-linking yield after curing at low
temperature,
[0035] good stability to storage at moderate temperature
(20-40.degree. C.).
SUMMARY OF THE INVENTION
[0036] The object of the present invention is to propose a
composition and a process which make it possible simultaneously to
obtain the combination of the aforementioned advantages with the
use of non-toxic compounds.
[0037] Therefore, the composition in accordance with the invention,
which is without precursor of at least one carcinogenic nitrosamine
and which comprises at least one rubber selected from the group
consisting of natural rubber, polyisoprene, polybutadiene,
styrene-butadiene, styrene-isoprene/butadiene-isoprene copolymers
and styrene-butadiene-isoprene terpolymers, and capable of
vulcanization at a temperature of between 95.degree. C. and
140.degree. C., is characterized by the fact that it comprises as
the vulcanization system:
[0038] a) sulfur;
[0039] b) at least one accelerator compound selected from the group
consisting of benzothiazyl disulfide and mercaptobenzothiazole;
[0040] c) at least one ultra-accelerator compound selected from the
group consisting of tetrabenzylthiuram disulfide and zinc
dibenzyldithiocarbamate;
[0041] d) at least one vulcanization amine activator selected from
the group formed of amines, guanidines, aldehyde and amine
condensates, and quaternary ammonium salts.
[0042] The process in accordance with the invention consists in
vulcanizing the said composition at a temperature of between
95.degree. C. and 140.degree. C., this process being used, for
instance, in order to bond two pieces of rubber, particularly upon
the manufacture, recapping, or repair of tires.
[0043] The composition in accordance with the invention may
furthermore comprise the customary fillers and additives such as,
for instance, carbon black, silica, silicic acid, zinc oxide,
stearic oxide, cobalt salts, resins, protective agents, in
particular antioxidants, extender oils, tackiness agents and
various processing agents.
[0044] The invention will be easily understood on basis of the
non-limitative examples given below.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0045] I. Formulas and Abbreviations
[0046] The meaning of the abbreviations used in the following
specification is indicated below, together with the corresponding
chemical formulas.
[0047] MBT: mercaptobenzothiazole 1
[0048] MBTS: benzothiazyl disulfide 2
[0049] ZBEC: zinc dibenzyldithiocarbamate 3
[0050] TBZTD: tetrabenzylthiuram disulfide 4
[0051] TMTD: tetramethylthiuram disulfide 5
[0052] DPG: diphenylguanidine 6
[0053] BA Condensate: butyraldehyde-aniline condensate 7
[0054] CHA: cyclohexylamine 8
[0055] Aliquat 336.RTM.: methyl trioctyl-ammonium chloride (HENKEL
Corp.)
[0056] CH.sub.3N[(CH.sub.2).sub.7CH.sub.3].sub.3Cl
[0057] II. Definitions and Tests
[0058] The definitions and tests used in the examples are indicated
below.
[0059] 1. Rheometry
[0060] A conventional oscillating rotor rheometer is used such as
described in AFNOR Standard NF-T43-015 (August 1975). The
measurements are made at 110.degree. C.
[0061] The change of the rheometric torque as a function of time
describes the development of the stiffening of the rubber
composition as a result of the cross-linking of the latter by the
sulfur under the action of the heat. The maximum rheometric torque
permits a description of the yield of this cross-linking
reaction.
[0062] The kinetic characteristics of the curing of the
compositions are evaluated in accordance with said Standard by the
following parameters:
[0063] ts(0.2): induction time of the reaction
[0064] t99: curing time for reaching a degree of advance of the
cross-linking of 0.99, with the following relationship: 1 (
rheometric torque at t 99 ) ( maximum rheometric torque ) =
0.99
[0065] CRI: cross-linking rate index, with the following
relationship:
CRI=100/[t99-ts(0.2)]
[0066] 2. Mooney Plasticity
[0067] The measurement of the Mooney plasticity is effected in an
oscillating consistometer in accordance with the principle
described in AFNOR Standard NF-T 43-005 (November 1980), indicated
below.
[0068] The raw composition is molded in a cylindrical enclosure
heated to 100.degree. C. After preheating for one minute, the rotor
turns within the test specimen at 2 rpm and the torque useful for
maintaining this movement after 4 minutes of rotation is
measured.
[0069] The Mooney plasticity is noted as ML(1+4). It is expressed
in "Mooney units" (M.U.):
[0070] 1 M.U. =0.083 newton.meter (N.m).
[0071] The Mooney plasticity makes it possible to note the change
in time of the stability of a raw rubber composition. For this
purpose, for a given composition, the Mooney plasticity ML(1+4) is
determined on the initial composition and on the composition which
has undergone aging by storage at 40.degree. C. for 21 days.
[0072] This change is then given by the Mooney delta which is
defined by the relationship:
[0073] Mooney delta=ML(1+4) after storage--initial ML(1+4)
III. EXAMPLES
[0074] In the examples which follow, the compositions are either
compositions in accordance with the invention or compositions not
in accordance with the invention. In the compositions of these
examples the values which correspond to components are parts by
weight, unless otherwise indicated.
Example 1
[0075] The purpose of this example is to show the good compromise
between reactivity and stability of the compositions in accordance
with the invention.
[0076] A basic mixture is prepared having the following
composition:
1 Natural rubber: 100 Carbon black: 47 Oil: 15 Zinc oxide: 5
Stearic acid: 1 Antioxidant:* 2
*N-1,3-dimethyl-N-phenyl-paraphenylenedi- amine
[0077] sulfur, accelerators, and activators in accordance with
Table 1. The insoluble sulfur used is CRYSTEX.RTM. OY20 sulfur of
Kali-Chemie, Stauffer GmbH, which contains 20% by weight of
naphthenic oil.
[0078] One thus obtains five compositions indicated as 1.1 to
1.5.
2 TABLE 1 Composition 1.1 1.2 1.3 1.4 1.5 MBTS 1.1 0.32 1.1 MBT 0.6
0.6 ZDEC 0.5 TMTD 0.22 TBZTD 0.5 ZBEC 1.35 1.44 DPG 0.44 0.11 0.33
BA condensate 0.3 Insol. sulfur 2.75 3 3 3 2.75
[0079] Composition 1.1 contains TMTD, precursor of
dimethyInitrosamine, which is carcinogenic and therefore regulated;
it is not in accordance with the invention.
[0080] Composition 1.2 contains ZDEC, a precursor of
diethyInitrosamine, which is carcinogenic and therefore regulated;
it is not in accordance with the invention.
[0081] Composition 1.3 contains no amine vulcanization activator;
it is not in accordance with the invention.
[0082] Compositions 1.4 and 1.5 are formulated with combinations of
accelerators and an amine vulcanization activator (MBTS/ZBEC/DPG or
MBTS/TBZTD/BA condensate); they are in accordance with the
invention.
[0083] The rheometric compositions of 1.1 to 1.5 at 110.degree. C.
are given in Table 2.
3 TABLE 2 Composition 1.1 1.2 1.3 1.4 1.5 ts(0.2) (min) 8.7 3.5 1.2
6.2 2.9 t99 (min) 35 31 78 28 24 CRI (min.sup.-1) 3.8 3.64 1.3 4.59
4.74 Maximum 16.2 13.9 12.7 14.7 14.9 rheometric torque (dN
.multidot. m)
[0084] Compositions 1.1, 1.2, 1.4 and 1.5 make it possible to
obtain rapid curings at 110.degree. C. with a high vulcanization
yield.
[0085] Composition 1.3 cures very slowly and reaches a much lower
vulcanization yield.
[0086] It is noted that, as compared with system 1.1 or 1.2, the
use of the combinations MBTS/ZBEC/DPG or MBTS/TBZTD/BA condensate
leads to a decrease in the curing time (t99) and to an increase in
the rate (CRI).
[0087] The compositions 1.4 and 1.5 in accordance with the
invention therefore permit faster curings than the known
compositions (compositions 1.1, 1.2, and 1.3).
[0088] As indicated previously in section 2 of Chapter II, the
stability of the raw rubber compositions is determined by the
development of the Mooney plasticity (Mooney delta) after aging
effected by storage at 40.degree. C. for a period of 21 days.
[0089] The results are regrouped in Table 3.
4 TABLE 3 Composition 1.1 1.2 1.3 1.4 1.5 ML(1 + 4) init. 40.3 48.5
48 45 42.5 ML(1 + 4) after 53.5 80 52.8 49.3 49 storage Mooney
delta 13.2 32 4.8 4.3 6.5
[0090] The development of the plasticity (Mooney delta) of
compositions 1.1 and 1.2 which are not in accordance with the
invention is very substantial, particularly in the case of
composition 1.2.
[0091] The raw stability is very definitely improved with
compositions 1.4 and 1.5 in accordance with the invention.
[0092] The stability of composition 1.3 which is not accordance
with the invention is also very good. Nevertheless, as stated
previously in connection with Table 2, the vulcanization system of
this composition is not sufficiently reactive to confer rapid
curing kinetics at 110.degree. C. on the composition.
Example 2
[0093] This example makes it possible to show the influence of the
relative contents of compounds b) and c) of the invention, compound
b) being MBTS and compound c) being TBZTD or ZBEC.
[0094] To the base mixture of Example 1 insoluble sulfur,
accelerators and activators are added in accordance with Table 4.
The insoluble sulfur used is that described in Example 1.
[0095] In this way six compositions are obtained, 2.1 to 2.6.
5 TABLE 4 Composition 2.1 2.2 2.3 2.4 2.5 2.6 MBTS 0.32 1.1 0.6 1.1
0.32 MBT 0.6 ZDEC 0.5 TBZTD 0.5 1.28 ZBEC 1.44 0.56 0.5 DPG 0.11
0.33 0.33 0.33 BA condensate 0.3 0.3 Insol. sulfur 3 3 3 3 2.75
2.75
[0096] Composition 2.1 contains ZDEC, precursor of
diethyInitrosamine, which is carcinogenic and therefore regulated;
it is not in accordance with the invention.
[0097] Compositions 2.-2 to 2.6 in accordance with the invention
are formulated with combinations MBTS/ZBEC/DPG or MBTS/TBZTD/BA
condensate; modifying for each of these combinations the quantities
of MBTS and of ZBEC or TBZTD.
[0098] The rheometric characteristics at 110.degree. C. of these
compositions are given in Table 5.
6 TABLE 5 Composition 2.1 2.2 2.3 2.4 2.5 2.6 ts(0.2) (min) 3.5 6.2
11.6 15 2.9 8.5 t99 (min) 31 28 39.2 44.8 24 25.5 CRI (min.sup.-1)
3.64 4.59 3.62 3.35 4.74 5.88 Maximum 13.9 14.7 16.6 15.1 14.5 14.2
rheometric torque (dN .multidot. m)
[0099] Compositions 2.1 to 2.6 make it possible to obtain rapid
curings at 110.degree. C. with a high yield.
[0100] The combinations MBTS/ZBEC/DPG or MBTS/TBZTD/BA condensate,
whatever the amounts of accelerators employed, make it possible to
have curing rates (CRI) similar to that of the normal composition
(composition 2.1), or even faster.
[0101] The change in the Mooney plasticity at 100.degree. C. of
compositions 2.1 to 2.6 is given in Table 6.
7 TABLE 6 Composition 2.1 2.2 2.3 2.4 2.5 2.6 ML(1 + 4) init. 48 45
42 42 42.5 38 ML(1 + 4) after 80 49.3 46 45.1 49 47 storage Mooney
delta 32 4.3 4 3.1 6.5 9
[0102] The development of the plasticity of composition 2.1 which
is not in accordance with the invention is very substantial.
[0103] The raw stability of compositions 2.2 to 2.6 in accordance
with the invention is definitely better than that of composition
2.1.
Example 3
[0104] This example makes it possible to show the influence of the
selection of the compound b) (MBT or MBTS) when the compound c) is
fixed (ZBEC).
[0105] To the base mixture of Example 1 there are added insoluble
sulfur, accelerators, and activators in accordance with Table 7.
The insoluble sulfur used is that described in Example 1.
[0106] There are thus obtained four compositions in accordance with
the invention, marked 3.1 to 3.4, which are formulated from a
combination employing a sulfur derivative of benzothiazole (MBT or
MBTS) as compound b), ZBEC as compound c), and DPG as compound
d).
8 TABLE 7 Composition 3.1 3.2 3.3 3.4 MBT 0.32 0.6 MBTS 0.32 0.6
ZBEC 1.44 1.44 0.5 0.5 DPG 0.22 0.33 0.15 0.33 Insoluble sulfur 3 3
3 3
[0107] The rheometric characteristics of these four compositions
measured at 110.degree. C. are given in Table 8.
9 TABLE 8 Composition 3.1 3.2 3.3 3.4 ts(0.2) (min) 4.5 6.2 5.8 15
t99 (min) 26 28 34 44.8 CRI (min.sup.-1) 4.65 4.59 3.54 3.35
Maximum 14.3 14.7 14.3 15.0 rheometric torque (dN .multidot. m)
[0108] Compositions 3.1 to 3.4, which are in accordance with the
invention, make it possible to obtain/curing kinetics at
110.degree. C. with, in parallel to this, a high vulcanization
yield.
[0109] Table 9 shows the development of the Mooney plasticity at
100.degree. C.
10 TABLE 9 Composition 3.1 3.2 3.3 3.4 ML(1 + 4) init. 42 45 42 42
ML(1 + 4) after 45.1 49.3 46 45.1 storage Mooney delta 3.1 4.3 4
3.1
[0110] In all cases, the raw stability of the compositions is
excellent.
Example 4
[0111] The purpose of this example is to show the influence of the
selection of the compound d), amine vulcanization activator.
[0112] To the base mixture of Example 1 there are added an
insoluble sulfur, accelerators, and activators in accordance with
Table 10. The insoluble sulfur used is that described in Example
1.
[0113] In this way there are obtained four compositions in
accordance with the invention, marked 4.1 to 4.4, which are
formulated on the basis of a MBTS/ZBEC combination with an amine
activator of different chemical nature--amine, guanidine,
aldehyde-amine condensate, quaternary ammonium salt.
11 TABLE 10 Composition 4.1 4.2 4.3 4.4 MBTS 0.32 0.32 0.32 0.32
ZBEC 1.44 1.44 1.44 1.44 DPG 0.33 BA condensate 0.15 Aliquat .RTM.
336 0.15 Cyclohexylamine 0.3 Insoluble sulfur 3 3 3 3
[0114] The rheometric characteristics of these compositions
measured at 110.degree. C. are given in Table 11.
12 TABLE 11 Composition 4.1 4.2 4.3 4.4 ts(0.2) (min) 6.2 2.6 4.7
2.7 t99 (min) 28 24.6 32.7 18.6 CRI (min.sup.-1) 4.59 4.54 3.57
6.29 Maximum 14.7 14.1 14.9 13.8 rheometric torque (dN .multidot.
m)
[0115] Whatever the amine vulcanization activator used, the
MBTS/ZBEC systems confer upon the compositions rapid curing
kinetics at 110.degree. C. with a high vulcanization yield.
[0116] Table 12 shows the development of the Mooney plasticity at
100.degree. C.
13 TABLE 12 Composition 4.1 4.2 4.3 4.4 ML(1 + 4) init. 45 43.5 38
36.5 ML(1 + 4) after 49.3 48.5 44 40.2 storage Mooney delta 4.3 5 6
3.7
[0117] Regardless of the nature of the compound d) selected,
compositions 4.1 to 4.4 in accordance with the invention show very
good raw stability.
Example 5
[0118] In this example, compositions having different amounts of
carbon black and oil as compared with the previous examples are
studied.
[0119] A base mixture is prepared having the following
composition:
14 TABLE 13 Natural rubber: 100 Carbon black: 30 Oil: 23 Zinc
oxide: 5 Stearic acid: 1 Antioxidant:* 2
(*)N-1,3-dimethyl-N-phenyl-paraphe- nylenediamine
[0120] To this base mixture there are added insoluble sulfur,
accelerators and activators in accordance with Table 13. The
insoluble sulfur used is that described in Example 1.
[0121] There are thus obtained four compositions, 5.1 to 5.4.
15 TABLE 13 Composition 5.1 5.2 5.3 5.4 MBT 0.6 0.6 0.6 MBTS 0.32
ZDEC 0.5 ZBEC 1.35 0.5 1.44 DPG 0.22 0.22 0.33 Insoluble sulfur 3.5
3.5 3.5 3.5
[0122] Composition 5.1 contains ZDEC, diethyInitrosamine precursor,
which is carcinogenic and therefore regulated; it is not in
accordance with the invention.
[0123] Composition 5.2 contains no amine vulcanization accelerator
d); it is not in accordance with the invention.
[0124] Compositions 5.3 and 5.4 are formulated with combination of
accelerators and a vulcanization activator (MBT/ZBEC/DPG or
MBTS/ZBEC/DPG); they are net in accordance with the invention.
[0125] Table 14 shows the rheometric characteristics at 110.degree.
C. of these compositions.
16 TABLE 14 Composition 5.1 5.2 5.3 5.4 ts(0.2) (min) 2.3 2.5 0.7
4.8 t99 (min) 24.6 46 27.5 21 CRI (min.sup.-1) 4.48 2.3 3.73 6.17
Maximum 9.3 8.6 8.5 8.5 rheometric torque (dN .multidot. m)
[0126] Composition 5.2 cures very slowly.
[0127] Compositions 5.1, 5.3 and 5.4 make it possible to obtain
rapid curings at 110.degree. C. and a high vulcanization rate.
[0128] Table 15 shows the development of the Mooney plasticity at
100.degree. C.
17 TABLE 15 Composition 5.1 5.2 5.3 5.4 ML (1 + 4) init. 27 24.3
25.2 25 ML (1 + 4) after 64 25.5 28 27 storage Mooney delta 37 1.2
2.8 2
[0129] The development of the plasticity of the composition 5.1 is
very substantial. The raw stability, on the other hand, is very
definitely improved with compositions 5.3 and 5.4 in accordance
with the invention.
[0130] The stability of composition 5.2, which is not in accordance
with the invention, is also very good. However, as previously
indicated in connection with Table 14, its vulcanization system is
not sufficiently reactive to confer upon the composition a rapid
curing kinetics at 110.degree. C.
Example 6
[0131] The purpose of this example is to show that the invention
applies to compositions which have an elastomer other than natural
rubber.
[0132] A base mixture is prepared having the following
composition:
18 TABLE 16 SBR (*): 100 Carbon black: 47 Oil: 15 Zinc oxide: 5
Stearic acid: 1 Antioxidant (**): 2 (*) SBR: styrene/butadiene
copolymer comprising 25% of styrene units (**)
N-1,3-dimethyl-N-phenyl-par- aphenylenediamine
[0133] To this base mixture there are added insoluble sulfur,
accelerators, and activators in accordance with Table 16. The
insoluble sulfur used is the same as in Example 1. Three
compositions are thus obtained, marked 6.1 to 6.3.
19 TABLE 16 Composition 6.1 6.2 6.3 MBT 0.6 MBTS 1.1 0.32 ZDEC
TBZTD 0.5 ZBEC 1.35 1.44 DPG 0.33 BA-condensate 0.3 Insoluble
sulfur 3 2.75 3
[0134] Composition 6.1 contains no amine vulcanization activator;
it is not in accordance with the invention. Compositions 6.2 and
6.3 are formulated with MBTS/TBZTD/BA condensate or MBTS/ZBEC/DPG
combinations; they are in accordance with the invention.
[0135] Table 17 sets forth the rheometric characteristics at
110.degree. C. of these compositions.
20 TABLE 17 Composition 6.1 6.2 6.3 ts(0.2) (min) 19.9 2.5 6.5 t99
(min) 82 30.3 30 CRI (min.sup.-1) 1.61 3.6 4.2 Maximum 9.4 14.9
13.3 rheometric torque (dN.m)
[0136] Composition 6.1 cures very slowly and reaches a low
vulcanization rate.
[0137] Compositions 6.2 and 6.3 give rapid curing kinetics at
110.degree. C. with a high vulcanization rate.
[0138] Table 18 shows the development of the Mooney plasticity at
100.degree. C.
21 TABLE 18 Composition 6.1 6.2 6.3 ML (1 + 4) init. 58.5 60 57.3
ML (1 + 4) after 60.9 64 60 storage Mooney delta 2.4 4 2.7
[0139] The raw stability of the three compositions is
excellent.
Example 7
[0140] The purpose of this example is to show the application of
the invention to the recapping of a tire. The following composition
is formulated:
22 Natural rubber: 100 Carbon black: 47 Oil: 15 Zinc oxide: 5
Stearic acid: 1 Tackiness resin (*) 3 Antioxidant (**) 2 Insoluble
sulfur (***) 3 MET 0.6 ZBEC 0.5 DPG 0.15 (*) Koresine
(alkyl-phenol-acetylene resin) (**)
N-1,3-dimethyl-N-phenyl-paraphenylenediamine (***) The insoluble
sulfur used is that described in Example 1.
[0141] This composition in accordance with the invention is used as
connecting rubber in the process of recapping by cold
vulcanization, this process being known also as premolded tread
recapping.
[0142] In this process, a heavy vehicle tire of size 315/80 R 22.5,
at the end of its first life, is decapped. The carcass is cleaned
and brushed. A strip of a thickness of 1 mm of raw connecting
rubber, produced with the preceding composition, is then applied to
the carcass. Finally, the replacement tread, which has been
precured and premolded, is placed onto the carcass which has been
prepared in this manner.
[0143] The recapped tire is introduced into an oven at 110.degree.
C., pressurized at 5 bars for 2 hours.
[0144] At the end of this curing, the tread adheres as perfectly to
the carcass as in the case of a new tire.
[0145] The preceding examples show that the invention makes it
possible to obtain the following advantages simultaneously:
[0146] non-carcinogenic compounds or compounds which are not
precursors of carcinogenic products are used; they are therefore
not regulated;
[0147] a rapid curing at low temperatures of less than 140.degree.
C. with excellent vulcanization yield is obtained;
[0148] the raw stability of the compositions during storage is
excellent;
[0149] this good raw stability makes it possible to store the
components of the vulcanization system together; it furthermore
makes it possible to have less constraining conditions of
transportation and storage than in the case of the known
compositions;
[0150] due to the good raw stability, the compositions retain a
substantial curing rate even after lengthy periods of storage;
[0151] the compositions in accordance with the invention have
multiple uses, and the user can employ them for various purposes
and even, if desired, for the conventional vulcanizations at
temperatures above 140.degree. C., replacing other known
compositions; the user is therefore not compelled to have different
compositions, which simplifies his work.
[0152] The composition in accordance with the invention preferably
has at least one of the following properties:
[0153] it contains natural rubber or a mixture of natural rubber
and at least one other rubber selected from the group consisting of
polyisoprene, polybutadiene, styrene-butadiene, styrene-isoprene,
butadiene-isoprene copolymers, and styrene-butadiene-isoprene
terpolymers;
[0154] it contains at least one additive selected from the group
consisting of carbon blacks, extender oils, and tackiness
agents;
[0155] for 100 parts by weight of the rubber or all the rubbers,
the amount of sulfur is between 0.5 and S parts by weight and
advantageously between 1 and 3 parts by weight; the amount of
compound b) or of all compounds b) is between 0.1 and 3 parts by
weight and advantageously between 0.2 and 2 parts by weight, the
amount of compound c) or of all compounds c) is between 0.2 and 3
parts by weight and advantageously between 0.4 and 2 parts by
weight, the amount of compound d) or of all compounds d) is between
0.05 and 1 part by weight and advantageously between 0.1 and 0.5
parts by weight.
[0156] The process in accordance with the invention preferably
consists of vulcanizing the composition in accordance with the
invention at a temperature of between 95.degree. C. and 115.degree.
C.
[0157] In Example 7 above, the process in accordance with the
invention was employed to recap a worn tire, but the process of the
invention can also be used to manufacture new tires, for instance
to bond a precured tread onto a precured carcass, or to repair
tires, for instance in order to plug holes, in particular in the
sidewalls or in the tread or other parts of these tires.
Furthermore, the invention can be used both to repair and to recap
the same worn tire.
[0158] In these embodiments, the composition of the invention
vulcanizes upon contact with rubbers which may be either completely
prevulcanized or partially pre-vulcanized, the total vulcanization
of these rubbers taking place then either upon the vulcanization of
the composition in accordance with the invention or
subsequently.
[0159] The nature of the rubbers in contact with which the
composition in accordance with the invention vulcanizes in the
aforesaid applications may be any whatsoever, and these rubbers,
which vulcanize with sulfur or with other vulcanization systems may
for instance, but not necessarily, be one or more rubbers selected
from the group formed of natural rubber, polyisoprene,
polybutadiene, the styrene-butadiene, styrene-isoprene, and
butadiene-isoprene copolymers, and styrene-butadiene-isoprene
terpolymers.
[0160] Of course, the invention is not limited to the embodiments
indicated.
* * * * *