Field of the Invention
In general, this invention relates to the field of synthetic polymer latex, more particularly an aqueous emulsion of novel vinyl pyridine latex having a mixture of monomers comprising a 4-9-carbon atoms hydrocarbon, an unsaturated carboxylic acid, a polymerizable emulsifler and a synthetic anionic emulsifler as the base emulsifler with 50 % solid content.
Background of the Invention
Vinyl pyridine latex is generally a composition of Terpolymer of Styrene, Butadiene and 2 Vinyl Pyridine Monomer and effectively used for 'DIPPING' of Rayon, Nylon and Polyester Tyre Cord Fabric.
Generally the Vinyl pyridine latex is comprised of a monomer ratio of 5-20 % 2- Vinyl Pyridine, 5-20 % Styrene and 60-90 % of Butadiene. For producing Vinyl pyridine latex, a rosin acid based emulsifier solution is prepared initially and aspirated to the reactor followed by above said monomers. There after the post incorporation is done with the help of fatty acid (naturally originated mixture of fatty acids of C14 to C18) sodium/potassium soaps. There is a common drawback of the use of post soap stabilizers. The excess soaps used to prevent coagulation may cause excess foaming during dipping operation when high mechanical force is exerted to the latex solution. This foaming causes non-uniformity both in the amount of dip applied to a cord and in the coating on the dipped cord surface and in turn results in non-uniform adhesion. Also presence of carboxylic acid groups in the fatty acid and rosin acid may result in widowing effect (Cationic part of fatty acid soap — -COOK / COONa goes to a reversible reaction and fatty/rosin soaps become free as fatty/rosin acids COOH and corresponding cationic hydroxides like NaOH and KOH) during long term storage which in turn result in poor mechanical stability, chemical stability and also high foaming. Also, there is possibility of migration of soap to the interface of tire at elevated temperature. Deposition of soap at one stage might cause separation of the rubber components at that particular interface causing tire failure. Presence of rosin acid soap and fatty acid soaps make the latex prone to microbial attack and reduces the self-life period of latex.
In view of the drawback associated with the prior known composition there is a need to develop a novel composition to provide better physical properties to the latex and accordingly better use of the same.
Prior Arts Description:
US Patent 3,960,796 discloses about the polyester reinforcing elements which can readily be bonded or adhered to curable rubbery compounds by dipping the elements in a dip consisting essentially of an aqueous alkaline dispersion of a minor amount by weight of a mixture of a major amount by weight of a rubbery vinyl pyridine copolymer and a minor amount by weight of a heat reactable 2,6-bis (2,4-dihydroxy phenylmethyl)-4-chlorophenol composition, drying the same, and combining said dipped and dried element with a vulcanizable rubber compound and vulcanizing the same.
United States Patent 4,040,999 reveals about the discoveries of the phenol formaldehyde resole preparation and use in a cord dip without the necessity of isolation and purification of the resole. The products of the process are not adversely affected by the presence of formaldehyde, salts, phenols and other by-products, which were discarded earlier.
United States Patent 4,134,869 reveals about the use of the resorcinol-formaldehyde novolak, normally used as a compounding ingredient for tire cord dips to stabilize the vinyl pyridine latex. Vinyl pyridine latexes containing resorcinol-formaldehyde novolaks compare quite favorably in shear stability with vinyl pyridine latexes stabilized with soap. The present invention eliminates the necessity for adding soap to post-stabilize the vinyl pyridine latex, eliminates the damage done by the alkaline metal ions of the soap upon cord such as polyester that can cause separation of the tire components at that interface. In addition, the resorcinol-formaldehyde novolak stabilizers of the present invention help to prevent the bacterial attack on the vinyl pyridine latexes and also help to prevent the excessive foaming and the resulting problems caused by the presence of soaps in the latexes.
US Patent 4,248,938 reveals about processes for preparing a polyester fiber composite material having an excellent bonding property to rubber, a proper softness and a high resistance to fatigue, comprises the steps of first impregnating a polyester fiber material
much as fabric, cord or thread, with a first treating liquid containing (A) a polyepoxide compound having two or more epoxy groups per molecule of the compound, (B) a blocked polyisocyanate compound, for example, an addition product of a polyisocyanate compound with a phenol, tertiary alcohol or aromatic secondary amine compound and (C) a rubber latex such as vinyl pyridine-styrene-butadiene terpolymer latex; first drying and heat treating the first impregnated material at a temperature of, preferably,180.degree. C. or higher but lower the melting point of the polyester fiber material; second impregnating the first impregnated and heat-treated material with a second treating liquid containing a resorcinol formaldehyde reaction product.
A cord dip composition comprising styrene-butadiene-vinyl pyridine terpolymer latex and a mixture of an aldehyde condensate and a glyoxal reaction product, are disclosed in US patent 4,263,190.
US Patent 5,171,637 and US Patent 5,034,462 reveal about the preparation of a terpolymer of styrene, butadiene and amino substituted alkyl acrylate, which is used, as an adhesion promoter. The styrene is present 0-30 % butadiene is present in 55 - 97 % and the amine substituted alkyl acrylate is present 1-15 % based on the total wt. of the monomers present in adhesion promoter. The amine substitutions are alkyl / aryl or substituted aromatics.
US Patent 5,922,797 reveals about the preparation of a low cost modified VP latex composition for RFL dip. The latex consists of a polymer made from a conjugated diene monomer, vinyl aromatic monomer, 2- vinyl pyridine and a vinyl aldehyde monomer. This invention also discloses about an adhesive composition consisting of Resorcinol, formaldehyde and modified VP latex. The present invention also relates the process of adhering synthetic textile fibers to rubber in 4 steps i.e., immersing fibers in aq. Dispersion of the above adhesive composition, drying the dipped fabrics, placing the dipped fibers with rubber and curing the rubber fiber composites. It also discloses the composite composition, which consists of modified VP latex.
Objects and Summary of the Invention
It is an object of the present invention to provide novel vinyl pyridine latex having a total solid of 50% with improved freeze thaw stability, microbial resistance and mechanical shear resistance.
Further object of the present invention is to prevent the excessive foaming and the resulting problems caused by the presence of soaps in the lattices. Thus the vinyl pyridine latex of the present invention exhibits better mechanical stability and better utilization in various applications.
Another object of the present invention is to provide a novel vinyl pyridine latex having chemical stability, hard water stability and low foaming during high mechanical shearing with an improved freeze thaw stability than normal vinyl pyridine latex.
The following embodiments of the present invention further describe the objectives of the invention.
In accordance with one preferred embodiment of the present invention, there is provided a novel VP latex comprising five monomers to the polymer backbone having composition of 2-vinyl pyridine, styrene, 1,3 butadiene, unsaturated carboxylic acid and Polymerizable ally/vinyl sulphonates along with a synthetic anionic surfactant as base emulsifiers, wherein the use of conventional fatty acid soaps as post stabilizer is avoided.
In accordance with another preferred embodiment of the present invention, there is provided a novel VP latex wherein said latex is prepared by employing anionic emulsifier as the base emulsifier with a minimal percentage of polymerizable emulsifier along with an unsaturated carboxylic acid, which provides a total solid of 50 to 52 % of said latex.
In accordance with further embodiment of the present invention, there is provided a novel VP latex, wherein said anionic emulsifier is selected from sulphonate, sulphosuccinate, sulphoxylate group having a back bone carbon chain of C3 - C9 (3-9 carbon atoms) and wherein said polymerizable emulsifier is selected from vinyl, allyl sulphonate or sulphosuccinate (2-9 carbon).
In accordance with yet another preferred embodiment of the present invention, there is provided a novel VP Latex, wherein ratio of styrene, 1,3 Butadiene and 2-vinyl pyridine and unsaturated carboxylic acid in said composition is varies from 5:50:30:1 to 30:80:5:5.
In accordance with yet another embodiment of the present invention, the latex has a composition of 5 - 20 % VP, 5 -20 % styrene and 50 - 90 % butadiene, 1-10 % of unsaturated carboxylic acid and 0.2 to 1.0 % of Polymerizable ally/vinyl sulphonates, and a synthetic anionic surfactant is used as the base emulsifier.
In accordance with the further embodiment, the presence of a functional carboxylic group as a pendent group in the polymeric backbone of said VP Latex, helps in improving the adhesion of latex to other polar substrates.
In accordance with yet another embodiment of the present invention, there is provided a process for preparing the novel vinyl pyridine latex by emulsion polymerization process, wherein said process avoids the use of fatty acid soap during post modification step and helps to prevent the excessive foaming and the resulting problems caused by the presence of soaps in the lattices and exhibits better mechanical stability, chemical stability, hard water stability and low foaming during high mechanical shearing with an improved freeze thaw stability and microbial resistance.
Detailed Description of the Invention
While this specification concludes with claims particularly pointing out and distinctly claiming that, which is regarded as the invention, it is anticipated that the invention can be more readily understood through reading the following detailed description of the invention and study of the included examples.
The present invention provides a novel vinyl pyridine latex stabilized aqueous emulsion of styrene, butadiene, vinyl pyridine and carboxylic acid with polymerizable emulsifiers along with a synthetic anionic surfactant as base emulsifiers. It also describes the process for preparation of said polymer latex employing the emulsion polymerization process wherein said process is performed without using conventional fatty acid soaps as post stabilizer.
Generally, Vinyl pyridine latex is produced with three different monomers 2-Vinyl Pyridine, Styrene and Butadiene and a base emulsifier of rosin acid with a thermally decomposable initiator at 48 - 55°C. Then the synthetic latex emulsion is stabilized by post incorporation of partially saturated fatty acid soaps which results in mostly excess foams during dipping operation and hence the non-uniformity on cord surfaces. Also presence of carboxylic acid groups in the fatty acids, rosin acids used as base emulsifier have resulted in widowing effect during long term storage resulting in poor mechanical stability, chemical stability and also high foaming in addition to its strong inclination to bacterial attack due to their natural origin.
In the present invention, novel synthetic polymer latex of styrene, butadiene and vinyl pyridine and unsaturated carboxylic acid is synthesized via emulsion polymerization process with the addition of 0.2 to 1.0 % polymerizable emulsifier with a total solid of 50 % unlike 40 % solid in normal vplatex. Absence of conventional rosin acid in base and partially saturated fatty acids soaps in post stabilization, generally helps to increase the microbial resistance of the latex in addition to its mechanical and chemical resistance and improved adhesion to the substrate.
The aqueous emulsion of VP latex disclosed herein comprises styrene, 1,3- butadiene, 2-vinyl pyridine, unsaturated carboxylic acid and a polymerizable emulsifier as monomers, synthetic anionic emulsifier as base emulsifier during emulsion polymerization reaction and tertiary dodecyl mercaptan as a chain modifier along with other ingredients. It is prepared via emulsion polymerization route and the ratio of monomers e.g., styrene, 1,3-Butadiene and 2- vinyl pyridine, unsaturated carboxylic acid varied from 5:50:30:1 to 30:80:5:5. The reaction is controlled in the temperature range of 47 - 70°C during different stages of polymerization and a time span of 10 - 35 hrs is required for generating a termination solid of 50-52 %. The initiator used for the reaction is a thermally decomposable initiator selected from sodium or potassium or ammonium peroxodisulphate. The base emulsifier used in the reaction is synthetic anionic based emulsifier i.e., alkyl aryl /alkyl /aryl /derivatives of alkyl or aryl sulphonates/sulphosuccinates and is used upto 7.0 parts per hundred parts of monomer herein after referred as phm. The said polymeric emulsifier used in the reaction is sodium
or potassium soap of vinyl / allyl sulphonate / sulphosuccinate upto 1.0 %. The chain modifier is selected from primary, secondary or tertiary dodecyl mercaptan and is used upto 2 phm level.
The present invention also provides an aqueous alkaline dispersion useful as tire cord dip, wherein the solids of the dispersion consisting essentially of a major amount by weight of the novel rubbery vinyl pyridine latex of the present invention and a minor amount by weight of a heat readable resorcinol and formaldehyde (RF) resin in a standard ratio of resorcinol to formaldehyde 1:1.7 with a fixed alkali (like Alkali / alkaline earth metal hydroxides) and final adjustment of pH with a fugitive alkali like NFLtOH.
Further, the solids in the aqueous alkaline dispersion are present in an amount of from about 10 to 30% by weight (as dry solids).
Furthermore, the parts by weight ratio of random carboxylated polymer (dry latex) to said resin composition is from about 50:50 to 90:10.
The latex mechanical stability has been measured using a Klaxon Mechanical Stability Tester with 50 gms sample at 14000 ± 200 rpm for 10 minutes according to ASTM D 1417 Cl. 12. Shear generated coagulums has been measured after filtration in a 180 mesh stainless steel screen and drying at 105 degree C to a constant weight.
Mechanical Stability, % = (A-B)*100 / M
Where,
A = Screen plus coagulum weight
B = Tared screen weight
M = Latex sample weight (« 50.0 gms)
The viscosity has been measured using a Brookfield Viscometer Model LVT at 25 degree C ASTM D 1417 Cl. 8. Viscosity is measured with Spindle 1 at 60 rpm for one minute.
The latex foam has been measured using a Klaxon Mechanical Stability Tester with 50 gms sample at 14000 ± 200 rpm for 10 minutes in a graduated cup of 0.1 cm in a ASTM D
1417 Cl. 8 specified test cup. The foam level has been measured in cms after 6 minutes run. The reading should be taken between 6 to 7 minutes of testing as maximum foam observed during this period.
Latex surface tension measurement has been measured in a Fischer Scientific surface Tensiometer according to ASTM D1417 cl.7. The test is a standard test and involves drawing a platinum-iridium ring through surface of latex. The tension at the time the surface film breaks is measured. The ring should be in the liquid, beneath the surface so that the entire ring is wetted.
Latex chemical stability has been studied with resorcinol and formaldehyde solution Clear solution of 37 grams of resorcinol has been prepared in 79 grams of distilled water. 19.50 ml of Formaldehyde (37 % solution) has been added and mixed properly. The mixture has been matured for one hour at 25 degree. Then the 216 gms of latex Has been added to the dry clan erlenmeyer flask. After six hours coagulums has been measured after filtration in a 180-mesh stainless steel screen and drying at 105 degree C to a constant weight.
Chemical stability, % = (A-B) *100 / M
Where, A= Screen plus coagulum weight
B= Tared screen weight M= Latex sample weight
The test for bactericidal effect was run by adding a bacterial culture derived from spoiled vinyl pyridine latex. One ml. of inoculation (3 million counts) was added to 500 ml. of latex. After one day a second one ml. inoculation was added to the 500 ml. Latex sample and the counts repeated. The samples were aged for 6 days at 25 degree C. with bacterial agar and potato dextrose as the nutrient and then plated to get a counts/ml.
Hard water compatibility has been studied by using hard water of 1000 -1200 micro mho conductivity (10 ml water added to 500 ml of latex) in post incorporation and final solid and pH adjustments. After modification latex has been stabilized for 24 hrs. Then
mechanical stability has been measured using a Klaxon Mechanical Stability Tester with 50 gms sample at 14000 ± 200 rpm for 10 minutes. Shear generated coagulums has been measured after filtration in a 180 mesh stainless steel screen and drying at 105 degree C to a constant weight. During washings of coagulums also hard water of 1000 micro-mho has been used
Stability, % = (A-B)* 100 / M
Where,
A = Screen plus coagulum weight
B = Tared screen weight
M = Latex sample weight ( 50.0 gms)
Freeze thaw stability of latex has been studied for three cycles of freezing and thawing of latex with a interval of 12 hrs at -10 degree and +30 degree respectively. After three cycles, stability of the latex has been measured by the above mentioned mechanical stability method. Shear generated coagulums has been measured after filtration in a 100 mesh stainless steel screen and drying at 105 degree C to a constant weight.
Freeze thaw stability, % = (A-B) * 100 / M
Where, A= Screen plus coagulum weight
B= Tared screen weight
M= Latex sample weight
A series of formulations were prepared with the synthetic anionic emulsifiers as the primary emulsifier in emulsion polymerization process of styrene, butadiene and 2-vinyl pyridine and carboxylic acid and Vinyl/allyl sulphonate and sulphosuccinate as the polymerizable emulsifier added at the beginning of the polymerization process. Set 1 experiments has been done with the standard recipes of vinyl pyridine latex manufacturing with standard quantity of rosin and fatty acid soap as the post incorporation. Set 2 experiments has been done with the new recipe and processing conditions.
Dipping solution was prepared with the standard VPlatex, resorcinol, formaldehyde, caustic soda and NH3 solution. The same procedure was repeated with the modified

Vplatex. and final pH was adjusted with caustic soda solutions. After 24 hrs of maturation of dip solution fabric was dipped in the latex and adhesion testing was performed with the standard grade of rubber compound.
Table 1
Contents of latex parts by weight
(Table 1 Removed)
All the above set of experiments has been done and lattices were prepared. All formulations were adjusted pH up to 10.8 with KOH. After addition of fatty acid soaps in VPLatex and Nonionic emulsifier in XVPlatex post incorporation samples were allowed to stand 24 hours before testing.
Table 2

(Table 2 Removed)
Microbial Study :
Nil = 10*0 , Very Scant - 10*1 , Scant = 10*2, Light = 10*4 , Moderate = 10*5, Heavy =
10*6, Dense >10*6
All the above sets of experiments are studied for various properties. It is very clearly observed from the Table -2 that the total solid of the XVP latex (Set 2) observed are 10 % higher than the standard Vplatex (Set 1) with a workable Brookfield viscosity. Mechanical stability of the product is also improved at this higher solid with a lower foam quantity observed in the mechanical stability cup. Surface tension of the XVP latex is reduced significantly with respect to the standard Vplatex whereas the particle size shows a reverse trend. Chemical stability, hard water stability and freeze thaw stability of the XVP latex is improved with respect to the standard Vplatex.
Microbial study shows that after 2nd inoculation and 6 days study in scant growth is observed in set 1 and set 2 shows very scant growth of microbes in the latex. Minimizing the natural products like fatty acid soaps reduces the chances of microbial growth in the latex and hence the life cycle of the latex increases. Due to incorporation of a synthetic originated sulphonate/ sulphosuccinate type of polymerizable anionic emulsifier, the hard water compatibility increases. Incorporation of the polymerizable emulsifier increases the particle size evidently which suffices that the sulphonate/sulphosuccinate added to the system are polymer bound which in turn exhibits the better properties to the latex in terms of mechanical stability, chemical and freeze thaw stability. Post incorporation of fatty acid soap (carboxylic acid soaps) are very prone to the desaponification of soaps and return back to the original acids which is not in case of sulphonates/sulphosuccinates due to better affinity of these groups to the water molecule. With a minimum quantity of
polymerizable emulsifier generates a latex having very good shear, chemical, freeze thaw stability in addition to its synergistic effect on foam, microbial properties.
While this invention has been described in detail with reference to certain preferred embodiments, it should be appreciated that the present invention is not limited to those precise embodiments. Rather, in view of the present disclosure, which describes the current best mode for practicing the invention, many modifications and variations would present themselves to those skilled in the art without departing from the scope and spirit of this invention.

ORIGINAL
WE CLAIM: ^
1. An aqueous emulsion of vinyl pyridine latex comprising of a mixture of 2-
vinyl pyridine, 1,3-butadiene, styrene, an unsaturated carboxylic acid, a polymerizable
emulsifier in combination with an anionic emulsifier as a base emulsifier with a total solid of
50%, wherein said aqueous emulsion of vinyl pyridine latex is characterized by better freeze
thaw stability, enhanced microbial resistance, mechanical stability, chemical stability, hard
water stability and low foaming during high mechanical shearing, without using fatty acid.
2. The vinyl pyridine latex as claimed in claim 1, further comprising an initiator
and/or a chain modifier.
3. The vinyl pyridine latex as claimed in claim 1, wherein the ratio of styrene,
1,3 Butadiene, 2-vinyl pyridine and unsaturated carboxylic acid varies from 5:50:30:1 to
30:80:5:5.
4. The vinyl pyridine latex as claimed in claim 1, wherein the unsaturated
carboxylic acid is preferably methacrylic acid.
5. The vinyl pyridine latex as claimed in claim 1, wherein the unsaturated
carboxylic acid is in the range of 1 to 10% by weight.
^ 6. The vinyl pyridine latex as claimed in claim 1, wherein the base emulsifier is
selected from the group comprising of sulphonate, sulphosuccinate or sulphoxylate group
having a back bone carbon chain of C3 - C9 (3- 9 carbon atoms).
7. The vinyl pyridine latex as claimed in claim 1, wherein the polymerizable
emulsifier is selected from the group comprising of vinyl, allyl sulphonate or sulphosuccinate
(2-9 carbon) or in combination thereof
8. The vinyl pyridine latex as claimed in claim 7, wherein the polymerizable
emulsifier is preferably allyl sulphosuccinate.
-14-
9. The vinyl pyridine latex as claimed in claim 1, wherein the polymerizable
emulsifier used is in the range of 0.2 to 1 .0 % by weight.
10. The vinyl pyridine latex as claimed in claim 2, wherein the initiator is selected
from the group comprising of sodium, potassium or ammonium peroxodisulphate.
11. The vinyl pyridine latex as claimed in claim 2, wherein the chain modifier is
selected from the group comprising of primary, secondary or tertiary dodecyl mercaptan.
12. A process for preparing a vinyl pyridine latex emulsion by a process of
emulsion polymerization of 2-vinyl pyridine, 1,3-butadiene, styrene, unsaturated carboxylic
^ acid in the presence of polymerizable emulsifier in combination with an anionic emulsifier as
a base emulsifier, wherein said process results in prevention of excessive foaming and the
resulting problems caused by the presence of soaps in the lattices, without using fatty acid
soap during post modification step.
Dated this the 14'" Day of August, 2006
MANISHA SINGH NAIR
Agent for the Applicant [IN/PA-740]
LEX ORBIS
Intellectual Property Practice
709/710, Tolstoy House
A 15-17, Tolstoy Marg
New Delhi-110 001
-15-