Rubber compounds are readily bonded to tire cords using a dip process in which the dip contains an alkaline aqueous dispersion of a mixture of a major amount by weight of a rubbery carboxylated conjugated diene copolymer and a minor amount of a lignin amine formaldehyde reaction product.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to compositions and methods of bonding cord 
tire reinforcement to the conjugated diene based rubber of tire carcasses 
and the improved structure obtained thereby. 
2. Description of the Prior Art 
Tire cord is received from the manufacturer in the form of a fabric. The 
general practice is to prepare the cord by applying a dip coating of a 
latex. The dip coating of the cord generally used contains a vinyl 
pyridine/styrene/butadiene copolymer and a resorcinol-formaldehyde (RF) 
resin. While these dips are quite effective in performing their desired 
function, the resorcinol and vinyl pyridine components are expensive and 
often unobtainable in the quantities needed. In addition, better adhesion 
would be preferred. 
Materials, in addition to RF resins, have been used in the prior art to 
improve adhesion in special circumstances. For instance, proprietary 
formulations of unknown composition are marketed for this purpose. In 
addition, lignin sulfonates are known as replacements for resorcinol in 
cord dips, see U.S. Pat. Nos. 4,016,119 and 4,026,744 of Elmer, 1977. 
Also, acrylic acid type copolymers have been used in cord dips, see U.S. 
Pat. Nos. 2,773,703; 3,364,100 Danielson (1968), 3,367,793 Atwell (1968), 
3,408,249 Brown (1968), 3,843,484; and 3,855,168. Also see British Pat. 
No. 1,256,705 for terpolymers of butadiene and unsaturated dicarboxylic 
acids. 
SUMMARY OF THE INVENTION 
According to the present invention, it has been discovered that reinforcing 
cords, particularly glass, but also other cords such as rayon, nylon, 
polyester, and aramid (also known as Kevlar)*, can be directly bonded or 
adhered to cured rubber by first dipping the cords in a dip containing an 
aqueous alkaline dispersion of a mixture of a rubbery carboxylated 
conjugated diene copolymer and a formaldehyde-lignin amine reaction 
product, drying the same, and combining said dipped and dried element with 
a vulcanizable conjugated diene rubber compound such as a 
butadiene-styrene rubber compound and vulcanizing the same. Reinforcing 
cords treated in this fashion exhibit high rubber to cord adhesion values. 
FNT *available from duPont 
The lignin amines are used to emulsify asphalt and are available or can be 
made available when resorcinol is in short supply. The advantages of the 
present invention over the prior art is that the lignin amines 
carboxylated conjugated diene dips provide better cord adhesion to rubber 
than commercial dips, have further improved adhesion upon aging, and are 
cheaper. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the present application the term "cords" is intended to include 
reinforcing elements used in rubber products including fibers, continuous 
filaments, staple, tow, yarns, fabric and the like, particularly cords for 
use in building the carcasses of tires such as car and truck tires. 
The reinforcing element or cord comprises a plurality of substantially 
continuous fibers or monofilaments. 
In the case of glass, the reinforcing element or fibers contain little or 
no twist. In other words, twist is not intentionally applied to the 
element or fibers; the only twist, if any, in the element or fibers is 
that occasioned on passing through the glass fiber processing apparatus 
and on packaging or winding up the cord to form a bobbin or spool. 
However, in a continuous process, the elements can proceed directly from 
the glass processing apparatus, can be dipped in the aqueous adhesive cord 
dip, dried, and given a twist of about 1.5 turns per inch thereafter. The 
elements then are woven into tire fabric having about one quite small pick 
thread or element, nylon or polyester, which may be a monofilament, per 
inch and calendered with a rubber ply or skim stock. The glass fiber 
reinforced ply stock is then ready to be used in the manufacture of a tire 
or for other purposes. 
Glass compositions, polyesters, polyamides and a number of other materials, 
useful in making the fibers for the reinforcing element or glass tire cord 
are well known to the art. One of the preferred glasses to use is a glass 
known as `E` glass and described in "Mechanics of Pneumatic Tires," Clark, 
National Bureau of Standards Monograph 122, U.S. Dept. of Commerce, issued 
Nov. 1971, pages 241-243, 290 and 291. The number of filaments or fibers 
employed in the fiber reinforcing element or cord can vary considerably 
depending on the ultimate use or service requirements. Likewise, the 
number of strands of fibers used to make a fiber reinforcing element or 
cord can vary widely. In general, the number of filaments in the fiber 
reinforcing element or cord for a passenger car tire can vary from about 
500 to 3,000 and the number of strands in the reinforcing element can vary 
from 1 to 10, preferably the number of strands is from 1 to 7 and the 
total number of filaments about 2,000. A representative commercial glass 
tire cord known as G-75 (or G-72, 5/0) has 5 strands each with 408 glass 
filaments. Another representative cord known as G-15 has a single strand 
containing 2,040 glass filaments. In this connection reference is made to 
Wolf, "Rubber Journal," February, 1971, pages 26 and 27 and U.S. Pat. No. 
3,433,689. 
Shortly after the glass fibers are formed they are usually sized (by 
spraying or dipping and so forth and air drying) with a very small amount 
of fractional amount by weight of a material which acts as a protective 
coating during processing and handling of the glass fibers in forming the 
strands or reinforcing elements and during packaging. During the 
subsequent dipping in the aqueous adhesive tire cord dip, it is believed 
that the size is not removed. Materials for use as sizes for glass fibers 
are well known to the art. It is preferred to use a silane as a size, 
especially a silane which has groups which can bond or coordinate 
chemically or physically with at least parts of the surface of the glass 
of the glass fiber and with at least one or more of the components of the 
glass fiber aqueous adhesive cord dip. A very useful size to employ on the 
glass fibers is gamma-aminopropyl triethoxy silane, or similar amino-alkyl 
alkoxy silanes, which, when applied to the glass fibers, hydrolyzes and 
polymerizes to form a poly (aminosiloxane) in which a portion of the 
polymer is attached to the glass and another portion contains amine groups 
(having active hydrogen atoms) for reaction with components of the cord 
dip such as the lignin amine resin or the carboxylated butadiene copolymer 
compound. Various glass fiber sizing compounds and compositions are shown 
in U.S. Pat. Nos. 3,252,278; 3,287,204 and 3,538,974. 
The type of rubber latex used in the tire cord dip bath of this invention 
is a latex of a copolymer of a conjugated diolefin having 4 to 6 carbon 
atoms and an acrylic acid, lower alkyl substituted acrylic acid. The alkyl 
groups has from 1 to 6 carbon atoms and is preferably methyl. The rubber 
latex is of the type described in U.S. Pat. No. 2,774,703 and comprises an 
aqueous dispersion of a copolymer of 50 to 95% by weight of a conjugated 
diolefin having 4 to 6 carbon atoms, 5 to 40% of an acrylic acid or lower 
alkyl acrylic acid and 0 to 45% of a styrene. 
Examples of suitable non-conjugated dienes are acrylic acid/butadiene, 
methacrylic acid/butadiene and itaconic acid/isoprene. 
In practicing this invention, a latex of a copolymer of from about 60 to 
99% by weight, of 1,3-butadiene and 1 to 40% by weight of acrylic acid or 
lower alkyl acid is used. The preferred range is 80 to 95% conjugated 
diene and 5 to 20% of acrylic or lower alkyl acrylic acid, the percentage 
based on the weight of the two recited components. The Mooney viscosity 
range of the dry solids is 40 to 120, preferably 40 to 90 ML-4. Other 
components may be present but are not used in the calculation. Excellent 
results are obtained using a latex of a copolymer of about 80% of 
1,3-butadiene, and 20% of methacrylic acid, by weight, having a total 
solids content of around 30 to 50%. The copolymer has a 4 minute Mooney 
viscosity ML-4 of 80 at 212.degree. F. Further disclosures relating to 
carboxylated butadiene copolymer latices may be found in U.S. Pat. Nos. 
2,364,100; 3,367,793; 3,408,249 3,774,703; 3,843,484 and 3,855,168. The 
copolymer can be replaced in a minor part with other elastomeric materials 
such as styrene-butadiene, carboxylated styrene-butadiene and other latex 
forming materials well known in the cord dip art. 
The lignin amines usable in the dip of the present invention are selected 
from materials that are known in the art. They are made, for example, by 
the reaction of ammonia, a primary or secondary amine with formaldehyde 
and lignin. The reaction of the amine results in the introduction of amine 
groups into the lignin molecule. The process is described in U.S. Pat. No. 
2,709,696, Wiest, 1955. The preferred amine as a starting material is the 
secondary amine, most preferably dimethyl amine. 
A second procedure for making lignin amines is set forth in U.S. Pat. No. 
3,718,639 Falkehey, 1973. This involves reacting a lignin with the 
reaction product of an epichlorohydrin and a tertiary amine. 
A third class of lignin amines useful in the practice of the present 
invention are the quaternary ammonium salts of lignin as set forth in U.S. 
Pat. No. 3,407,188 Cavagna, 1968. 
The lignin amines used in the practice of the present invention are water 
soluble. The preferred pH range is from 7 to 12. The nitrogen content of 
the lignin amine can vary from 0.1 to 6% and preferably to 3%. 
Primary, secondary and tertiary amines suitable as starting material in 
this invention are presented by the general formula: 
##STR1## 
wherein at least two of R.sub.1, R.sub.2 and R.sub.3 are methyl and/or 
hydrogen groups and the other R.sub.3 contains up to 18 carbon atoms. 
Those tertiary amines possessing at least two methyl and/or hydrogen 
groups attached directly to the nitrogen are used because of their 
superior reactivity with formaldehyde or epichlorohydrin to form the 
desired intermediate. This reactivity with epichlorohydrin is retained 
even when the third group of tertiary amine contains as many as 18 carbon 
atoms, such as is found in dimethyl-stearyl amine. This high reactivity is 
believed to result from the low order of stearic hindrance imparted by the 
two methyl groups, allowing for intimate contact of epihalohydrin with the 
free electron pair of the tertiary amino nitrogen. By way of example, the 
following amines are mentioned as particularly suitable for carrying out 
this invention: methyl, dimethyl, trimethyl, dimethyl-benzyl, 
methyldodecyl, dimethyloctyl and dimethylstearyl amines. The preferred 
secondary amine is the dimethyl amine. 
The lignin amine reaction product of the present invention is prepared by 
dissolving a sufficient amount of NaOH into water to render the final 
solution basic; slow addition of weighed amounts of lignin amine to the 
agitated solution to achieve uniform wetting of the amine; agitation until 
the amine dissolves and addition with stirring of measured amounts of 
formaldehyde solution with agitation. 
The reaction product (including unreacted components, if present) contains 
from 60 to 100% preferably from 70 to 90% lignin amine and from 0 to 40% 
preferably 10 to 30% formaldehyde. All percentages are based on dry solids 
of the above recited components. 
The heat reactable formaldehyde-lignin amine reaction product is preferably 
made by reacting formaldehyde (or formaldehyde donor) with lignin amine in 
aqueous media using sodium hydroxide and the like as a catalyst to form 
water soluble resins containing amine hydroxyl and methylol groups. 
The final dip is prepared by slow addition of the reaction product of the 
copolymer latex. After addition the mixture is aged, preferably at least 
16 hours, before use as a cord dip. The pH of the final dip ranges from 
about 8 to 11 preferably about 9 to 10. 
The ratio of the conjugated diene copolymer (on a dry basis) to the 
reaction product of formaldehyde and lignin amine is from about 100:5 to 
100:30 parts by weight, preferably from about 100:8 to 100:20 parts by 
weight. 
Water is used in the dip in an amount sufficient to provide for the desired 
dispersion of the conjugated diene latex particles and the solution or 
dispersion of the lignin amine reaction product and for the proper solids 
content to get the necessary pick-up of solids on and penetration between 
the fibers of the tire cord. 
The dip thus consists essentially of an aqueous dispersion of the 
conjugated diene copolymer latex, and the lignin amine reaction product; 
the reaction product being present in a total amount (as dry solids, 
dispersed or dissolved in the water per hundred parts of latex solids) of 
from about 1 to 30 parts by weight, preferably 8 to 20 parts and the 
copolymer is present at a level of 100 parts on a dry weight basis 
(assuming complete reaction). Sufficient alkaline material is usually 
present from the lignin amine reaction product solution to render the dip 
alkaline or additional alkaline material such as NaOH can be added to 
achieve this purpose. The function of the alkaline material is to prevent 
premature coagulation of the conjugated diene copolymer and also to 
catalyze the formaldehyde-lignin amine reaction. 
The concentration of lignin amine reaction product on a dry basis in the 
aqueous dispersion is about 0.5% to about 10% and preferably about 2 to 
about 7%. The concentration of conjugated diene copolymer on a dry basis 
is from about 7 to 40% and preferably about 20 to 35%. The concentration 
of solids in the aqueous dispersion (or dip) on a dry basis is 15% to 45%, 
preferably 20% to 40%. A too high solids content results in coagulation of 
the latex and a too low solids content results in a low D.P.U. and poor 
performance of the cord. 
In order to apply the adhesive dip to the cords in a reliable manner, the 
cords are fed through an adhesive dip bath containing the conjugated diene 
copolymer and the lignin amine reaction product, into a drying oven where 
they are dried. Also, as the cords leave the oven they enter a cooling 
zone where they are air cooled. In each case, the adhesive-coated cords 
leaving the dip are dried in the oven at from about 150.degree. to 
360.degree. C. for from about 2 to 150 seconds. The time the cord remains 
in the dip is about a second or so or at least for a period of time 
sufficient to allow wetting of the cord by the adhesive mixture. 
The adhesive containing reinforcing elements of this invention is 
preferably adhered to a vulcanized blend of natural rubber, polybutadiene 
rubber, and rubbery butadiene-styrene copolymer by curing the same in 
combination together. The adhesive containing reinforcing element can also 
be adhered to other vulcanized conjugated diene rubber, by curing or 
vulcanizing the same in combination with the rubber. Examples of other 
conjugated diene rubbers include: nitrile rubbers, chloroprene rubbers, 
polyisoprenes, carboxylated butadiene rubbers, vinyl pyridine rubbers, 
acrylic rubbers, isoprene-acrylonitrile rubbers and the like and mixtures 
of the same. These rubbers, prior to curing, can be mixed with the usual 
compounding ingredients including sulfur, stearic acid, zinc oxide, 
magnesium oxide, accelerators, antioxidants, antizonants and other 
curatives and the like well known to those skilled in the art for the 
particular rubbers being employed. Rubbers, when proportions are referred 
to as referred to here and in the claims, refers to the elastomer 
component and excludes the above compounding ingredients, e.g., a 
reference to a major component of the rubber being a conjugated diene 
polymer would refer to a major component of the elastomeric content of the 
composition. The rubbers referred to above are old and well known in the 
art and will not be described in detail here. 
The major diene component of the rubber used in the practice of the present 
invention is a conjugated diene as opposed to a non-conjugated diene. 
Preferably, the entire elastomeric component is conjugated diene polymer, 
free of ethylene/propylene/non-conjugated diene. 
Fibers, yarns, filaments, cords or fabric and the like coated with the 
adhesive of the present invention can have from about 3 to 50% by weight 
(dry) total solids from the adhesive dip on the cord based on the weight 
of the undipped cord (D.P.U.) and can be used in the manufacture of 
radial, bias, or belted-bias passenger tires, truck tires, motorcycle and 
bicycle tires, off-the-road tires, airplane tires, transmission belts, 
V-belts, conveyor belts, hose gaskets, rubbers, tarpaulins and the like. 
The D.P.U. varies as to substrate as is known in the art. Glass cord for 
example, requires a D.P.U. of 15 to 30% and an organic cord requires 2 to 
10% preferably 3 to 8%.

The following examples will serve to illustrate the invention with more 
particularity to those skilled in the art. In these examples the parts and 
percentages are parts and percentages by weight unless otherwise 
indicated. 
The H-adhesion test referred to above measures the static adhesion of the 
dried adhesive coated cord to cured rubber. 
In each case the rubber test specimens are made from a standard type rubber 
compositions using the following recipe: 
______________________________________ 
Stock Parts by Weight 
______________________________________ 
Natural Rubber (No. 3 smoked sheet) 
36.50 
Butadiene-styrene rubber copolymer 
43.50 
averge 23.5% bound styrene, emul- 
sion polymerized 
Polybutadiene (solution polymerized 
20.0 
BD, about 93% cis-1,4, Raw Mooney 
ML-4@212.degree. F. about 40-50) 
Carbon black, fast extrusion furnace 
35.0 
Carbon black, high abrasion furnace 
35.0 
(high structure) 
Alkyl aromatic polyindene resin 
4.5 
reinforcing and processing aid, 
Picco 100, Pennsylvania Industrial 
Chemical Corp. 
Naphthenic oil, Circosol type 
32.80 
2XH, Sun Oil Co. 
Zinc oxide 3.8 
Stearic acid 1.5 
Mixture of mono, di and tristyrenated 
1.2 
phenols, AgeRite Spar, R.T. Vander- 
bilt Co., Inc., antioxidant 
Benzothiazyl disulfide, Altax, 
1.2 
R.T. Vanderbilt Co., Inc., accel- 
erator 
Tetramethyl thiuram monosulfide, 
0.1 
active ingredient, Thionex, ac- 
celerator, E.I. duPont de Nemours 
& Co., Inc. 
Crystex, about 80% insoluble sulfur 
3.0 
and 20% petroleum oil, Stauffer 
Chemical Co. 
______________________________________ 
Dips were prepared that contained a varying molar ratio of lignin amine to 
formaldehyde varying amounts of lignin amine per 100 parts of butadiene 
latex solids. The ratio of butadiene to methacrylic acid was also varied. 
The dips were prepared by dissolving weighed amounts of lignin amine in 
water by agitation; addition of measured amount of NaOH solution if the 
solution is not sufficiently basic due to lignin amine, agitation until 
powder dissolved; addition with stirring of measured amount of 
formaldehyde solution; agitation and slow addition of this resin to a 
stirred butadiene-methacrylic acid copolymer. The dips are aged at least 
16 hours after formulation before being used to coat cords. The 
butadiene-methacrylic acid copolymer latexes are 41% solids in water 
solution. The copolymer latexes are made by conventional emulsion 
polymerization on acid stable surfactants. 
In each of the following examples each cord tested was passed through a 
cord dip, dried and tested. The H-adhesion test was run using the 
following procedure. 
In every case the cords to be treated are placed in parallel positions in a 
multiple-strand mold of the type described in the single-cord H-pull 
adhesion test designated ASTM D 2138-67, the mold is filled with 
unvulcanized rubber of the above-described compositions, the cords being 
maintained under a tension of 50 grams each, and the rubber is cured 20 
minutes to the elastic state. Each rubber test specimen is 6 mm thick and 
has a 9 mm cord embedment. 
After the rubber has been cured, the hot reticulate cured rubber piece is 
removed from the mold, cooled, and H-test specimens are cut from said 
piece, each specimen consisting of a single cord encased in rubber and 
having a length of around one inch or so. The specimens are then aged at 
least 16 hours at room temperature. The force required to separate the 
cord from the rubber is then determined using an Instron tester provided 
with specimen grips. The maximum force in pounds required to separate the 
cord from the rubber is the H-adhesion value. The hot pad test referred to 
in the H-adhesion testing refers to heating the embedded cord sample for 
four hours (unless otherwise specified), cooling the sample to 25.degree. 
C., then running the H-adhesion test. 
D.P.U. refers to dip pickup in percent by dry weight and represents the 
weight of the coating divided by the bare glass or other cord weight. 
The wet dipped cords of the following examples were all predried at 
98.degree. C. prior to the high temperature drying step recited in the 
examples. In the following examples all of the dips had a 20% solids 
level. The solvent was water. All parts and percentages are on a dry 
solids basis unless otherwise specified. 
The lignin L-3 (lignin amine) used in the examples was a 
lignin-formaldehyde-dimethyl amine reaction product believed to be 
produced by the procedure set forth in the first example of U.S. Pat. No. 
2,709,696. The glass cord used was sized K filament PPG glass normally 
used in tires. After dipping, the cord was dried at 236.degree. C. for 20 
seconds. The cord was then embedded in the rubber stock described earlier 
and the H-adhesion values obtained are listed below under the respective 
aging times and conditions. 
The B/MAA was a butadiene-methacrylic acid copolymer. The ratios 95/5, 
90/10 and 80/20 refer to the ratios of butadiene to methacrylic acid in 
the copolymer. 
TABLE I 
__________________________________________________________________________ 
ROOM TEMPERATURE H ADHESION ON 
PPG GLASS CORD 
Newtons 
Newtons 
Newtons 
Dip Aged After 
After 
After 10 
at R.T.(room temp.) 
24 hrs. 
144 hrs. 
days at 50.degree. C. 
__________________________________________________________________________ 
Vinyl Pyridine 
Dip Dip 
latex** (55) 
Aged* 
Aged 
at 50.degree. C. 
at 50.degree. C. 
95/5-B/MAA (45) 
128.1 
175.2 
181.5 
Lignin L-3 (11) 
Formaldehyde (2.4) 
145.5 
141 
95/5-B/MAA (100) 
Lignin L-3 (14) 
149 140.1 
Formaldehyde (3.2) 
90/10-B/MAA (100) 
Lignin L-3(14) 
160.1 
Formaldehyde (3.2) 
80/20-B/MAA (100) 
Lignin L-3 (14) 
199.3 
Formaldehyde (3.2) 
__________________________________________________________________________ 
*All values increase 27 to 36 Newtons by aging the cured sheets at least 
72 hours before pulling the Hadhesion. 
**Conventional butadiene styrene vinyl pyridine latex 
The above dips were all run at 20% total solids. The numbers in parenthesis 
refer to amounts in parts by dry weight. 
NON-SPECIFIC EXAMPLES 
A number of amine substituted lignins including quaternary ammonium salts 
were evaluated in cord dip compositions similar to those set forth in the 
previous examples. The amines were, (1) produced by reacting a primary 
amine with formaldehyde and a lignin, (2) produced by reacting trimethyl 
amine with epichlorohydrin then reacting the reaction product with a 
lignin, (3) quaternary amine substituted lignins, (4) other amine 
substituted lignins supplied by Westvaco Corporation, N.Y., N.Y. Most of 
the amine substituted lignins performed satisfactorily in cord dips. 
The cord dips of the present invention work best on glass, rayon, nylon; 
fair on Kevlar and poor on polyester.