Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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IMPROVED PROCESS TO MANUFACTURE PRE-CURED TREAD
AND VULCANIZABLE RUBB:ER COMPOUND
The present invention relates
to an improved process to manu~acture pre-cured tread
s~ructures to replace worn out tire treads on a pneumatic
carcaæs of a pneumatic tire to be restored in local tire
repairing shops, a~ well as to a vulcanizable rubber
compound to bo applied under said tre~d belt.
It is Xnown by the ~rt such as
di~clo~ed in the Brazilian Patont Application S/N PI
8806122 ~corresponding to US patent application 393,126
~iled on August 14, 1989) to improv~ the bonding o~ a
pr~-cur~d tread body into the smoothed sur~ace of a
pneumatic tire to be restored upon the full removal oP the
worn out tire tread, in which the whole lower side of the
tread body is provided with corrugation~ obtained in the
pr~ curing proce~s o~ the tread body by means of a sheet
o cour~e cloth embodied into the said lower face during
the pre-curing stage in the vulcanizing press, the said
pisce o~ cloth being stripped off before applying the
layer o~ bonding material and then submittiny the tire
body and the adhering new pre-cured tire tread to final
vulcanization, in the tire repair shop.
In ~act, the said operation of
~irstly incorporating he piece of fabric onto tha lower
face o~ t~e tread body through its pre-curing, during the
manufacture o~ the tire tread unit to be supplied to the
tire repair shops may give cause to some drawbacks due to
~he need o~ having the piece of cloth stripped ~rom the
tread body to rev al th~ resulting corrugations embossed
into th~ lower sur~ace thereo~ by the pressed rough cloth,
at the very moment the new tread unt is to be bonded to
th~ car~ass of the tire on which the restoration of the
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02 212~73
tread i~ to be performed.
A layer o~ proper bonding
material is th~n applied on t,he said wrinkled lower
surface of the tread body, fllling in all th~ grooves and
a portion of tim~ is to be spent ~or the bonding fluid to
dry out. Only then a rubber connecting layer is placed
betwe0n the tread and the ti.re body to start the
vulcanization of the tread structure.
In some places, lik~ in the
United States, the manufa~turer does strip the piece o~
cloth th~re~rom soon after its pre-curing and then does
apply the adhesive lay~r on the curru~ated surface and
then shi~ld~ it o~f again~t oxida~ion by ~ean~ of a
plastic sheet.
In all cas~s, though, th~ said
~take of the art by whic~ the e~bo~sement of the bonding
sur~aa~ o~ the tread body i~ carr~ed out by m2an~ o~ a
pi~ce of rough iabric, shows the main disadvantageous
~eature of not allowinq a mas~ produc~ion on accoun~ of
the huge lo~ o~ time resulting ~rom ~he ~anual steps of:
a - aligning a~d superimposing the extruded ~read body on
~he shee~ o~ rough cloth;
b - taking the two supeximposed but still separate parts,
to the pre-curinq pre ~ ~or the molding o~ the tread
uni~;
c - stripping of~ the piece of cloth soon after th~ pre~
curing;
d - applying a layer o~ bonding material on the bonding,
corrugated lower face o~ the tread body; and
e - puttlng a protective plastic sheet to wrap the said
lower ~ace, to prevent oxidation o~ the adhesive layer
during its storage.
The expo~ure to pot~ntial
oxidatlon of the adhe~ive layer is a di advan~ageou6
feature ~hat ha~pers th~ ~ea~ibili~y o~ the said known
proce~ , both under ~echnical and sconomical viewpoin~s,
03 2 :~ ~ 0 ~
even when counking with the re-usability of the stripe of
rough cloth.
It iæ so the main scope of
~his invention to improve the said known process through
the dropping of the use of th~ e~bossing stripe o~ rough
cloth and o~ the filling in of a layer o~ liquid adhesive,
thus enhancing the production of the ~read bodies by the
elimination of ~he time con~uming operations of putting in
place and xemoving the piece of c:Loth and of applying the
oxidizable adhesiv~ layer.
Through intense research
applicant has eventually found out what now is disclosed
as the main object of khis invention, that all the said
di~advantageou~ features l~ay be wiped out by substituting
the adhesive liquid layer, whose application has demanded
the corrugation o~ the tread body bonding face and
preventing the use of a stripe o~ tough ~abric, by a self-
adhesive, vulcanizable rubber layer which may eaæily bond
the tire tr~ad onto the smooth surface o~ a tire carcass
to ~e restored in ~hich the said self-bonding layer is
co~pounded by 65 to 75% o~ natural rubber~ 15 to 30% of
strengthening ~ineral pigments and 10 to 15 % of
vulcanization reactants.
The improved process o~ this invention consists o~ :
~a) preparation o~ a layer of sel~-bonding, vulcanizable
rubber composition made o~ 65 to 75% of natural rubber, 15
to 30% o~ strengthening mineral pi~ments selected among
carbon black and silica , alone or combined~ with the
altérnativ~ adding of pi~ment dyes, and from 10 to 15% of
che~ical reactants o~ vulcanization selected among
sulphur, thiurans, zinc oxides, sulfonamides and stearic
acid;
~) aligning ans superimposing the ~read body on a stripe
oP the said rubbar composition, with the same width
(c) wrapping the said sel~-~o~ding lowQr layer with a
thermopla~tic protetive sheet and
o~
212~7~
(d~ submitting the said tread structure to pre~curing in a
vulcanizer press.
Its is t~us obtained an out o~
the press re~dy to sell and use tread units which are
delivered to the tire r~pair shopE; where by easily tearing
off the protective plastic sheet, the unit being arranged
as usual, on the known connecting layer placed on the
smooth bonding face of the tire carcas~, the whole set
being then vulcanized.
As an alternative way to carry out the improved proces~ o~
this invention the said protective pla~tic sheet may be
wrapped around the said sel~-bonding rubber layer after
the pre-curing o~ the tread structure/ by mechanical means
instead of ~y thermal adherence in the pre-curing stage.
The pla~tic protective sheet is selected among those
neutral materials which do not interact with the self-
bonding rubber layer, being selected among polyester
plastic films, poly~thylene film and polyester textile
sheetsO
Yet another alternativ~ way to carry out the process o~
this invention consists o~:
(a) pre-curing the ~read body alone;
(b) applying on the bonding face thereof by any available
means, like by thermofixin~ in an autoclave, the said self
-bonding rubber layer and
(c) wrapping of the said lower layer on the said plastic
sheet
Through the laboratory test, ASTM/D~413 it was measur~d a
20~ increase o~ the adhesiveness o the tread structure to
the tire carcass when co~pared with the state of the art
process as disclosed in the Patent Application BR/
8805122. By the said test a restored tire having a tire
tread replaced in accordance with this invention, endured
an air pressure between 80 and 100 p.s.i without showing
any disengagement or loosening of any portion o~ the tire
tr~ad section.
05
21'2~3
The same lab test carri~d out on a restored tire having
the tire tread fastened in accordance with the process
disclosed in the said ~R -8806122 patent application,
reveled an endurance between 70 and 80 p.s.i.
Under international standards o~ quality , the said figure
is set at a minimum level of 60 p.s.i what stresses the
high performance and the unex]pected superior results
obtained with the process o~ this invention.
As a further advantageous feature it may be stresséd the
fact that by dropping the use of the chemical adhesive
layer, the storing time is substantially lengthened
provided that the risk of oxidation is no longer to be
taken into account.
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