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Patented Oct. 29, 1946
2,410,078
UNITED STATES. PATENT OFFICE
2,410,078
UNIFIED FIBROUS FABRIC
Waldo Kellgren, St. Paul, Minn., assignor to
Minnesota Mining 8; Manufacturing Company,
,St. Paul, Minn., a corporation of Delaware
No Drawing. Application August 3, 1940,
Serial No. 351,232
. 6 Claims.
1
(Cl. 117-155)
2
.This invention relates to ?exible uni?ed ?brous
cause vulcanization without deteriorating the
fabrics, and method of making, wherein a felted
rubber (and often the resin) to such an extent as
or woven porous fabric (such as a paper or cloth)
to make the fabric “punky” and weaker than it
would be if no vulcanization had been attempted.
More intensive heating caused resiniflcatiton of
the rubber and made the fabric sti? and brittle.
Such prior attempts included the use with sulfur
of an accelerating agent and an activator, in an
attempt to overcome the difficulty, but without
success. It had, therefore, been assumed for some
years that vulcanization of rubber-resin impreg-‘
is uni?ed by saturation or sizing with a non-hy
groscopic water-insoluble rubber-resin composi
tion, vulcanized in situ in a particular manner,
which binds the ?bres together and toughens the
fabric, and at the same time imparts other desir
able characteristics, but without making the back
ing undesirably stiff.
_
,
ll
Uni?ed fabrics made in accordance with this
invention may be used for various purposes, such
as a backing for adhesive tape,,as electrical tape,
nated fabrics was not feasible and offered no com
mercial promise.
I have discovered‘ a technique of vulcanization
as a base for arti?cial leather, as a liner, etc. .
The control of elasticity, so that stretchable 16 which goes contrary to expectations and makes
sheet materials are possible ranging from those
possible successful vulcanization, and in a prac
that are inelastic to those that are highly elastic,
tical manner which is of commercial value be
is an important feature. By variation of the vul
cause the attendant bene?ts more than warrant
canizing technique, a wide variation of constit
the additional expense of such treatment of the
uent proportions can be used to effectuate a wide 20 fabric.
variation in properties to secure products of dif
My discovery is that of producing vulcanization
fering types for various uses.
,
by the use of a self-vulcanizing organic accelera
Other objects, advantages and features'of the . tor, by which is meant that type of organic ac
invention will be apparent from the following fur
celerator which gives a good cure (in the presence
ther description.
'
25 of an activator, such as zinc oxide) to sulfur-free
The unifying composition which I employ is
primarily composed of a ?uxed blend of broken
down rubber, admixed compatible resin which in
rubber stocks. The preferred kind is represented
by the thiuram polysul?de accelerators, illus
trated by “Tetrone-A" (dipentamethylene-thi
creases ‘the cementing action upon the fibres of
uram-tetrasul?de) and “Tuads” (tetramethyl
the fabric to bind them ?rmly, a special type of 30 thiuram-disul?de) . These accelerators liberate
vulcanizing agentv and an‘ activator thereof. A
a nascent form of sulfur during the vulcanization
reinforcing pigment may be included to increase , process, which form of sulfur immediately com-'
cohesiveness and tensile strength, but is not es
bines with the rubber and, for some reason not
sential. Various modifying agents may also be
known to me, produces vulcanization with use of
included, such as ?llers, plasticizers, softeners, 35 temperature-time combinations which do not ad
versely affect the rubber-resin combination. In
anti-oxidants, etc. After impregnation or sizing
stead of such vulcanization producing an impreg
of the fabric with the foregoing composition dis
nated paper or cloth which is weaker and “punky"
persed in a volatile vehicle, the fabric is suitably
or still.’ and brittle, as in past attempts, the uni?ed
heated to drive off the vehicle and vulcanize the
rubber. It may then be coated on one or both 40 fabric has substantially as good ?exibility and
has improved tensile strength, as compared with
sides with such further coatings as are desired. '
fabric impregnated with the same rubber-resin
The successful vulcanization of a ?uxed blend
composition but with no vulcanization thereof.
of broken-down rubber and resin distributed be
By “broken-down" rubber, I mean rubber which
tween paper or cloth ?bres, so as to obtain im
proved results as compared with a uni?ed fabric 45 has been acted upon so that the “nerve” is re
in which the rubber-resin impregnant is not vul
duced and the rubber made less elastic, more
plastic, and more penetrative. This can be ac
canized, has heretofore not been achieved to the
complished by mechanical working in the pres
best of my knowledge. Prior attempts have been
unsuccessful because the resin and the ?bres have
ence of heat and air (oxygen), as by mastication
acted in such a way that vulcanization would not 50 on a rubber mill and in a mixer. Oxidation plays
a necessary part in the process of breaking down
. occur to any appreciable extent under conditions
which could be tolerated by the impregnated fab
ric. That is, vulcanization depends upon tem
perature and time, and no combination of tem
perature and time could be found which would 65
and is accompanied by disaggregation and dis
ruption of the rubber particles, and probably de~
polymerization or degrading of the rubber mole
cules or macro-molecules also occurs. Whatever
2,410,078
3
4
the precise mechanism and nature of the change
sistance. “Dextilose” is a manila hemp ?bre
paper which has substantially the same length
may be, the broken-down rubber permits of se
curing thorough impregnation of the porous fab
wise and crosswise tensile strength and tear re
' ric so as to obtain a uni?ed fabric that is ?exible
or pliant. The degree of breakdown which is nec
essary depends upon the porosity of the fabric.
A cloth or thin open-mesh paper (as in "Troya
sistance.
.
The rubber is preferably latex crepe, but
smoked sheets or reclaimed rubber may be used.
Since reclaimed rubber ordinarily contains zinc
oxide, a reduction may be made in the added
zinc oxide when employed, or the latter may be
tissue”) requires only a small degree in compari
son with paper towelling. The admixed resin fur
ther plasticizes the rubber and decreases the vis 10 omitted. Equivalent vulcanizable synthetic or
cosity of solutions thereof and assists in cement
arti?cial rubbers and rubber-like resins may be
ing the ?bres of the fabric.
substituted for all or part of the natural rubber.
In order to assist in breaking down the rubber
The resin should be compatible with the rubber
with the least effort, peptizing agents may be
(both before and after vulcanization) so as to
employed, as for example R. P. A. No. 1 (zinc
form a homogeneous blend and should improve
chloride double salt of phenyl hydrazine) or
the cementing of the fabric ?bres and make the
naphthyl - beta - mercaptan, which apparently
rubber more plastic and penetrative. The resin
function as oxidation catalysts and aids to de
should also be water-insoluble so that the uni?ed
polymerization. Only a small amount, as less
paper will be resistant to moisture and water
than 1% of the rubber, is needed to produce 20 and be non-hygroscopic. The technique of vul
marked results.
canization permits the use of both solid and
The ?brous fabric may be of an'unwoven na
ture such as cotton wadding, a felt or paper.
?uid resins. _ Without vulcanization, a ?uid resin
Any type of paper or.paper-like sheet may be
used so long as it is sufficiently bibulous or porous
to permit of penetration by the sizing or im
pregnating composition to result in the desired
uni?cation, which uni?cation may be of one side
would make the impregnant too soft and lacking
in cohesive strength, particularly when the rub
ber is highly broken down; but vulcanization of
the rubber can, in accordance with this inven
tion, be used to ?rm up the rubber to the point
of securing the desired cohesive strength of the
of the paper or throughout. The paper may be
impregnant.
made in whole or in part from wood, rope or rag 30
In general, the useful range of resin is 25 to
?bres, or from other ?brous material, natural or
400 parts by weight per 100 parts of rubber. The
synthetic, such as cellulose acetate, glass, etc.
Cellulose paper which has been acetylated may
be used.
'
~
Woven fabrics may be used, such as cloth made
from threads or ?bres of cotton, wool, hemp,
optimum proportion will depend upon the type
of product desired, the degree of rubber break
down, the proportion of reinforcing pigment
which may be used, the degree of vulcanization,
the type of resin, the type of fabric, and the
cellulose derivatives, “nylon,” glass, etc. An ex
presence of modi?ers, etc. The upper limit of
resin proportion is determined by the need of ob
secure a good uni?ed fabric suitable for use as
taining a flexible unified fabric of good strength.
an adhesive tape backing or as an electrical tape, 40 If a solid resin is used, too high a proportion
is a white broadcloth having an 80 by 144 thread
will result in stiffness and brittleness, while too
count per square inch.
1
high a proportion of ?uid resin will result in in
The paper may be creped, crimped, embossed,
adequate cohesiveness which cannot be overcome
ample of a cloth-which may be impregnated to‘
molded, or otherwise formed so as to provide
by increased vulcanization.
rugosities or corrugations, which may be desired 45
Examples of suitable solid resins are rosin
(which may be gum rosin or wood rosin), ester
to provide substantial stretchability and the
ability to conform to curved or irregular outlines
or surfaces. For convenience, all such paper
will be referred to hereafter as creped paper.
gum, hydrogenated rosin, hydrogenated. ester
gum, damar, copal, cumar, "Nevillite resin” (a
cyclopara?in polymer), and an oil-soluble heat
The unifying composition is distortable and 50 hardenable phenol-aldehyde resin that is set up
stretchable and does not impair the aforesaid
during heating of the impregnated fabric. Fluid
characteristics. The creped paper may be im
resins are illustrated by “Hercolyn" (hydrogen
pregnated without causing a loss of the initial
ated methyl abietate), “Abalyn” (methyl abie
stretch of the paper, which'is an important fea
tate) and “Vistac” (isobutylene polymer which is
ture. The paper may be given either a “dead 65 viscid and sticky). Mixtures of two or more of
stretch” or a “live-stretch,” depending upon the
degree of rubber breakdown, proportion and kind
of ‘other impregnant components, and degree of
vulcanization. A creped towelling paper having
the resins may be used.
'
Rosin is a preferred resin, particularly when
employed in conjunction with zinc oxide, in which
case the compounding of the impregnant results
a stretch of 25% may be used, for example. ‘The 60 in the rosin being “hardened” by the zinc oxide
paper may be creped to have a two-way stretch.
whereby zinc abietate .is produced and is the
A ?at, uncreped paper may be employed where
actual resin used in unifying the fabric. While
stretchability is not needed or wanted, and this
it is preferred to harden the rosin in situ during
may be, for example, a. kraft paper.
the compounding, it may be hardened in advance
Desirable types of especially thin uni?ed paper 65 by treatment with zinc oxide, etc. The amount
can be made by using paper stock of a hemp
of zinc oxide consumed by the reaction, when
?bre kind. An illustration is “Flexrope,” a 100%
carried to completion, is not over about 8 parts
rope paper made of reclaimed rope and charac
by weight per 100 parts of rosin. Other basic
terized by long ?bre length, open texture, high
tensile strength and great uniformity. Another 70 oxides may be used in place of or in conjunction
with zinc oxide to form insoluble resinates.
example is “Troya tissue,” made from new manila
Thus a small amount of lime (preferably hy
hemp ?bres and characterized by the fact that
drated lime) may be incorporated in the mix,
the ?bres largely run in one direction, so that
tapes can be made having a high lengthwise
or a small amount of magnesia. The preferred
tensile strength and a high crosswise tear re
proportion of rosin to be used in making masking
2,410,078
tape backings and the like is 75 to 175 parts per
100 parts of rubber.
the accelerator, making it unnecessary to have
free zinc oxide or‘ other activator present when
these hardened rosins are present, although in
The balance or the rosin is added, care being
taken to add slowly to avoid excessive foaming
caused by the water evolved from the reaction
between rosin and the zinc oxide, ‘and mixing is
continued for another hour. The beta-naphthol
is added (if used), and the steam turned 0i‘! and
cooling water introduced intothe heating Jacket
some cases an additional activator may be desir
able or useful.
of the mixer. The oleum spirits is then added
with continued mixing for half an hour, or until
Where zinc oxide is used as an activator, the
minimum proportion needed is about 5 parts per
100 parts of rubber, and this amount will func
tion even though the zinc oxide reacts with rosin
the mixture is homogeneous. The resulting solu
tion may then be drawn off and stored until
to form zinc abietate.
together the "Tetrone-A” and rubber and dis
solving in the oleum spirits. This procedure
facilitates admixture of the vulcanizer with the
Both the zinc abietate and the limed rosin
‘(calcium abietate) will function as activators for
The vuloanizer solution is prepared by milling
‘
The use of a larger proportion of zinc oxide
than may be-required for the foregoing purposes,
is generally desirable in order to provide a rein
15
. rubber-resin solution.
forcing pigment toincrease the cohesive strength
of the impregnant and the tensile strength and
The vulcanizer solution is mixed in with the
rubber-resin solution just prior to use of the
aging properties of the uni?ed fabric, as well as 20 latter for. the fabric treatment, as the composite
to provide opaci?cation. The upper useful limit
solution starts to gel within a few hours, even at
is about 400 parts per 100 parts rubber, and the
room temperature.
‘
optimum proportion depends upon the type of
The ?brous sheet material may be impregnated
tape being made. For a soft, ?exible type of
with the impregnating solution in any suitable
backing, the proportion should be kept low. In 25 manner that will deposit a sui?cient amount of
the case of backings for masking tapes, and like
solids within the ?bre structure to produce ade
uni?ed paper, the preferred proportion is 50 to
quate uni?cation.
125 parts per 100 parts rubber.
A direct saturation method may be used on
Other reinforcing pigments may be used.
ordinary sheets of low density (high porosity).
Dixie clay may be used in about the same way 30 The sheet is passed through theimpregnating
solution until thoroughly permeated, and then
as zinc oxide. In the case of carbon black, the
upper limit of usefulness is generally 50 parts ' ‘between a pair of squeeze rolls to remove unde
per 100 parts rubber and it is ordinarily best
sired excess from the surface. An alternative
not to go above 10 parts. Inert ?llers, such as
procedure, where the sheet is denser, is to pre
whiting, may be used to a limited extent. These 35 saturate with a diluted solution (obtained by
diluting the stock impregnating solution, given
materials do not function as activators and zinc
oxide or other activator .must be present.
in the above examples, some 20-30% by adding
additional solvent), so as to obtain thorough
v
Exmns ‘1'
l I
penetration, dry, and then proceed with impreg
Two batches are compounded, to be united 40 nation with the regular impregnating solution as
shortly before paper treatment, having the fol
lowing formulae, in parts by weight.
described above.
_
x
I
When the sheet is extremely thin and porous,
satisfactory results will be obtained by passing
Rubber-resin solution
-
between two horizontal rollers, the lower of which
100 . 45 dips into the impregnating solution, so as to apply
the solution directly to one side only. The solu
160
tion will be carried through the sheet by capil
100
Parts
Latex crepe
Rosin
Zinc oxide
Beta-naphthol (antioxidant and optional)-..
' 1
Oleum spirits (volatile petroleum hydrocar
larity. The rollers are set so as to remove excess
from the upper side of the sheet, but the ‘lower
bon solvent of 306°-424° F. boiling range) -_ 20o '50 side which directly receives the solution will be
somewhat denser than the other and will bear a
_ Vulcanizer solution
Parts
slight excess.
'
When using relatively heavy paper, a conven
"Tetrone - A" (dipentamethylene - thiuram
ient procedureis to apply a diluted solution to
tetrasul?de) _________________________ ..
3
55 one side and thereafter apply the standard solu
Latex crepe
_
,
3
tion to the reverse side. This order of treat
Oleum spirits
24
ment drives out the air before the more concen
trated solution is used. A somewhat similar ex
The rubber-resin solution is prepared by mill
pedient is to float the paper on the surface of
ing the rubber and zinc oxide for 30 minutes, at
the impregnating solution and then subm‘erge. it
about l50°-160° F., and the resultant sheet is
before it leaves ‘the impregnating bath.
then taken off and placed in an internal mixer
It should be observed that variation in the
(such as a Baker Perkins Mogul mixer), the heat
proportion of solvent will affect the weight of
ing jacket of which carries steam at 40 lbs. pres
solids incorporated into the ?brous sheet. T00
sure, and which has previously been allowed to
warm up. A small proportion of the rosin (say 65 little solvent will make for too high a viscosity
for best penetration, and too much will produce
10-25%) is added to make for lubrication and
undesirable dilution and not enough solids will
a lower power requirement, and the mass. is
be left in the sheet.
,
mixed for about 8-10 hours, or until reduced to
Following impregnation, the fabric sheet is
a semi-fluid consistency. The rosin may be
omitted from this stage of compounding, but with 70 festooned on racks and put through a drying oven
to remove the solvent and vulcanize the rubber.
an increase in the power requirement; and an
even greater proportion, or all, of the rosin may
Various time and temperature combinations may
be used to produce substantially equivalent re
be added, but with a considerable increase in the
time required to produce the same degree of
sults. An oven treatment involving 12 hours at
rubber breakdown.
75 170° F. gives good results.
By increasing the
2,410,078
7
temperature to 250° F., a heating period of 3 hours
has been found suitable. Such temperature
“Hercolyn” (hydrogenated methyl abietate) is
used in place of the rosin. Paper or other fabric
uni?ed with this composition also hasv a live
stretch owing to the proportion of vulcanizer
time combinations do not deteriorate the rubber,
and result in adequate vulcanization to ?rm up
the rubber and make for a de?nite improvement
in properties of the uni?ed ?bre. As previously
pointed out, this is a, distinguishing feature of
used.
.
.
When employing “Tuads’P (tetramethyl-thiu
ram-disul?de) in place of “Tetrone-A," a larger
my invention.
proportion must be used to compensate for the
With respect to the foregoing type of formula,
fact that each molecule contains only one sulfur
little bene?t from vulcanization is obtained with 10 atom available for vulcanization instead of three.
less than 1 part “Tetrone-A” per 100 parts rubber
and at least 11/2 to 2 parts are needed, in general,
Ordinarily an increase of three times the weight
used is sufficient to produce the same results.
to obtain results de?nitely worth the expense of
A wide variety of ?lm-forming materials may
be applied to the unified fabric to provide coat
evidence that vulcanization occurs when less than 15 ings of various types. Likewise various sheet or
1 part “Tetrone-A” is used, andll/z to 2 parts
?lm materials may be laminated to the uni?ed
are generally required to produce a signi?cant
fabric. In some cases bonding may be facili~
increase in tensile strength and aging properties.
tated by treating the fabric with the rubber
In the lower range of vulcanizer proportions,
resin composition so that the side which receives
broken-down rubber does not regain its nerve suf 20 the coating has no excess of the rubber-resin or
?ciently to prevent the uni?ed fabric (such as
is incompletely saturated or does not include the
creped paper) from having the dead-stretch
rubber-resinQ Thus the rubber-resin unifying
characteristic which may be desired.
may be applied to one side of the paper without
With 6 parts “Tetrone-A’f per 100 parts rubber,
penetrating through, and the desired coating is
elasticity begins to be‘ obtained to a de?nitely 25 applied to the other side. Or the fabric may
recognizable degree and when about 10 parts are
have an excess of rubber-resin upon one or both
used the uni?ed fabric (such as creped paper)
sides to provide a smooth surface and the desired
will be quite elastic. By cutting down‘the rosin
coating is applied thereto. An illustrative sizing
proportion, and also by increasing the zinc oxide
which may be applied over the vulcanized rubber
(pigment) proportion, a quicker build-up of elas
resin is shellac, which may be conveniently ap
ticity occurs with increase of vulcanizer propor
plied as a 30-50% solution in denatured ethyl
tion, and vice versa.
alcohol when the web leaves the vulcanizing oven
The incorporation of sulfur, with or without
and is still hot, and drying of the shellac may be
the inclusion of other accelerators than the self
speeded by then subjecting the web to force
vul-canizing accelerator, may yield desirable re 35 drying for 20 minutes at 140° F. Or a varnish or
sults in some cases, as may the inclusion of an
resin coating may be applied prior to vulcaniza
other accelerator without addition of sulfur, but
tionand dried (and set up where a heat-advanc
in general none of these expedients has been
ing resin is present) during the vulcanizing
found to add appreciable value to the basic
operation.
technique.
Uni?ed fabrics may be coated with plasticized
40
Exmns 2
nitrocellulose or methacrylate resin or polyvinyl
acetal resin (such as polyvinyl butyral), and em
Same formula and procedure as in Example 1
bossed if desired, to make arti?cial leathers.
except that 100 parts "Hercolyn" (hydrogenated
The uni?ed fabric may be used as a backing
methyl abietate) is used in place of the rosin
for adhesive tape by coating one or both sides
and the proportion of “Tetrone-A" is increased
with adhesive to provide an adhesive coating of
to 5 parts to compensate for the use of a fluid
a type (as desired) which is activatable by water,
resin, being combined with 5 parts rubber and 40
solvents or heat, or which may be of the normally
parts oleum spirits in making up the vulcanizer
tacky and pressure-sensitive type (as one com
solution. This example also illustrates a com
position for unifying creped paper or other fabric 50 prised of rubber rendered tacky by a resin or
vulcanization treatment. That‘is, there is little
to make a dead-stretch sheet.
_
plasticizer) .
Thus a long-aging, waterproof, tough, pres
sure-sensitive cloth adhesive tape may Ibe made
by impregnating a broadcloth of 80 by 144 thread
Exam?“ 3
Rubber-resin solution
Parts 55 count per square inch with the rubber-resin uni
Latex crepe _
100
fying composition of Example 1, so as to ?ll the
Zinc oxide
Rosin
100
100
cloth and provide a slight excess on the back,
followed by vulcanization and back-sizing with
shellac, after which a pressure-sensitive adhesive
Oleum spirits ___________________________ __ 200 60 is applied to the face-side.
Among the advantageous features of my inven
vulcanizer solution
'
tion, the following points may be noted.
Parts
(a) A wide versatility in properties of treated
“'I'etrone-A" ____________________________ __ 10
fabrics may be secured to meet particular needs,
Latex crepe _____________________________ __ 10
Oleum spirits
80 05 and wider ranges of proportions and types of
components may be used with the rubber, owing
Same technique as in Example 1. The higher
to the control made possible by vulcanization.
vulcanizer proportion makes for an elastic im
Thus ?uid resins may be utilized, and a live
pregnant so that creped paper or other fabric
stretch fabric produced even when the rubber
uni?ed with this compositon has a live-stretch. 70 has been highly broken-down.
Adhesive tape having this type of backing is well
(b) The vulcanization improves the tensile
adapted for use in coil winding, etc.
strength of the uni?ed fabric without rendering
it stiff or brittle. To illustrate this point, a 27
EXAMPLE 4
lb. per ream bibulous creped paper was uni?ed
Beta-naphthol _________________________ __
1
Same as Example 3 except that 50 parts of 75 in accordance with Example 1 (the paper being
2,410,078
9
saturated) and had a tensile strength of 5 lbs.
before uni?cation and 9 lbs. after uni?cation.
When uni?ed in the same-Way but without use of
the vulcanization treatment, the tensile strength
was '7 lbs. Tests were made on a Schopper tensile
tester at a speed of 12 inches per minute, on sam
ples of half-inch width.
10
-
2. An article according to claim 1 in which the
accelerator is dipentamethylene-thiuram-tetra
sul?de.
3. An article according to claim 1 in which the
accelerator is tetramethyl-thiuram-disul?de. '
4. A ?exible sheet comprising an initially por
ous ?brous paper impregnated and uni?ed by a
highly cohesive composition largely composed of
(0) The vulcanization increases the useful life
the in situ vulcanized ?uxed blend of broken
of the uni?ed fabricby decreasing aging effects.
Unified paper retains the desired resistance to 10 down rubber, admixed compatible resin adapted
to increase the cementing action upon the ?bres
splitting and delamination for a longer period
of the paper and present in the proportion of
than uni?ed paper which has not been vulcanized.
about 25 to 400 parts per 100 parts of rubber, a
(d) The vulcanization greatly increases the
reinforcing pigment imparting additional co
resistance of the uni?ed fabric to prolonged heat
ing, which otherwise would lead to embrittle 15 hesiveness, and a self-vulcanizing organic ac
celerator of the thiuram polysul?de type, said
ment, loss of uni?cation and strength, and dis
composition including an activator for the latter,
coloration. Thus a uni?ed paper made in accord
said uni?ed paper having a greater tensile
ance with Example 1, upon exposure to 220° F.
strength than untreated paper per se and at
for 24 hours, did not become brittle or discolored
and there was no destruction of uni?cation 20 least as great as would result without vulcaniza
strength.
(e) Uni?ed paper may be wound in rolls with
tion of the impregnant.
5. A ?exible sheet having a porous ?brous
fabric sized or impregnated by a composition de
out blocking. Without vulcanization, there is a
posited from solution in a volatile organic ve
tendency to block so that turns of the roll may
weld together unless a liner is employed, for al 25 hicle so as to penetrate and bind the ?bres of the
fabric and vulcanized in situ after application,
though the rubber-resin impregnant is relatively
largely composed of a ?uxed blend of broken
non-tacky when absorbed in the paper there is
down rubber, admixed resin of the class consist
apt to be considerable bonding between contact
ing of rosin and derivatives thereof compatible
ing surfaces of the uni?ed paper unless this'is
30 with rubber and present in the proportion of at
overcome by vulcanization.
’
least about 25 parts per 100 parts rubber and
What I claim is as follows, including such range
within the range necessary to produce a ?exible
of equivalents as the nature of the invention and
composition and fabric, a self-vulcanizing or
of the prior art permits:
ganic accelerator of the thiuram polysul?de type
1. A ?exible sheet comprising an initially por
and an activator for the latter.
ous ?brous fabric sized or impregnated by a
6. An article according to the preceding claim
highly cohesive composition essentially comprised
in which the impregnating composition includes
of the in situ vulcanized ?uxed blend of broken
zinc oxide and said accelerator is largely di—
down rubber, admixed compatible resin adapted
pentamethylene-thiuram-tetrasul?de present in
to increase the cementing action upon the ?bres
of the fabric and present in the proportion of 40 the amount of at least 1 part per 100 parts of the
rubber.
about‘25 to 400 parts per 100 parts of rubber, and
WALDO KELLGREN.
a self-vulcanizing organic accelerator of the thi
uram polysul?de type and an activator therefor.
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