FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION (See Section 10 and rule 13)
1. TITLE OF THE INVENTION "Improved Natural Rubber based Pressure Sensitive Adhesive "
2. APPLICANTS
(a) Name : PRS Solutions Private Limited
(b) Nationality : Indian
(c) Address : 63, Bombay Samachar Marg, Mumbai - 400 001,
Maharashtra State, India
The following specification particularly describes the invention and the manner in which it is to be performed

FIELD OF THE INVENTION:
"Improved Natural Rubber based Pressure Sensitive Adhesive" comprising of a blend of solvent based natural rubber pressure sensitive adhesive and solution form of hot melt pressure sensitive adhesive enhances the adhesive performance of natural rubber adhesive with respect to peel adhesion and tack thereby improving its adherence to low energy surfaces like Polythene / Polypropylene without primer coat and the process of manufacturing the same.
DESCRIPTION OF THE PRIOR ART:
Thermoplastic rubber polymers like Kraton rubber are a unique class of rubbers designed for use without vulcanization. They are tri-block copolymers with an elastomeric block in the center & a thermoplastic block on each end. These tri-block copolymers can be divided into three basic types of polymers: S-B-S ( Styrene-Butadiene- Styrene), S-I-S ( Styrene- Isoprene- Styrene ) or S-EB-S (Styrene- Ethylene Butylene- Styrene ) types, depending on the rubber, which is used in the midblock in the polymer. There are basic differences in the behavior of the different types of these rubbers, which make one particular rubber preferred over the others for a particular application. The percentage of hard, polystyrene phase is the lowest in the S-I-S polymers. Therefore the S-l-S polymers are softer and have a lower modulus than the S-B-S or S-EB-S types. This is of benefit in formulating soft, tacky adhesives such as pressure sensitive adhesives (PSA). The S-B-S and S-EB-S polymers have about twice the percentage of hard polystyrene phase as in the S-I-S types and are suitable in formulating high modulus, high load bearing capacity adhesives like contact adhesives or construction adhesives.

Pressure sensitive adhesive can be formulated using S-I-S thermoplastic rubber with midblock associating resins like hydrocarbon resin ( Wingtack-95 ) & polyterpene resin & stabilized using antioxidant like Butyl Zimate. This adhesive can be processed by melt processing or Solution processing. However adhesive processed by melt processing has shown higher Tack & adhesion properties than that obtained by solution processing. These melt processed PSA are coated on substrates by Hot melt applicator. Hot Melt PSA are known to give high Peel Adhesion & high Tack but are expensive. Moreover they cannot be used for high temperature applications beyond 80°C.
Natural rubber based Pressure Sensitive Adhesives ( NR PSA ) made using Natural Rubber, Tackifiers like hydrocarbon resins, polyterpene resins, filler like zinc oxide & antioxidant when dispersed in solvent like Toluene & coated on low energy film substrate like BOPP shows moderate tack & Peel adhesion properties. This coated substrate can be used for sticking on smooth surfaces. However in applications where the surface involved is rough like Automobile tyres the adhesive required is rubber based but with high Adhesion & high tack.
Natural rubber based Pressure Sensitive Adhesives (NR PSA) are widely used in tapes and labels, as they are less expensive than other adhesives. However as these adhesives are having moderate Peel Adhesion & moderate Tack they cannot be used in applications where high Peel Adhesion & high Tack are required such as for applications on automotive tyres. The rubber-based adhesives also cannot be coated on low energy substrates such as PE/PP without primer coat. This additional coat of primer adds to the total cost of the final product.

To overcome these drawbacks of moderate tack & moderate Peel adhesion properties of Natural rubber based Pressure Sensitive Adhesives they were modified by addition of melt processed hot melt pressure sensitive adhesive ( HM PSA ) dispersed in solvent like toluene to get Improved Natural Rubber based Pressure Sensitive Adhesive.
The objective of the present invention was to develop an adhesive which -
- Can be coated on low energy substrates like Polythene / Polypropylene without primer coat
- Is less expensive than Hot Melt PSA
- Gives adhesion and tack higher than NR based PSA
- Allows formulator to decide cost Vs desired properties.
SUMMARY OF THE INVENTION:
"Improved Natural Rubber based Pressure Sensitive Adhesive is a blend of hot melt pressure sensitive adhesive and Natural Rubber based Pressure Sensitive Adhesive. To meet the present objective Natural rubber based Pressure Sensitive Adhesives {NR PSA) consisting of Natural Rubber, tackifiers, fillers & anti-Oxidant was manufactured on a 2-roll mill by mastication of Natural Rubber & subsequent addition of tackifiers, fillers & anti-Oxidant to get homogeneous solid adhesive which was then discharged from the 2 roll mill by spading. This solid adhesive discharged from the 2 roll mill was then dispersed in solvent like Toluene in Z- blade mixer to get a homogeneous dispersion of solvent based Natural Rubber Pressure Sensitive Adhesive.

Hot Melt Pressure Sensitive Adhesive (HM PSA) was also
manufactured by first melting the Ingredients consisting of thermoplastic rubber like Kraton 1107, tackifiers like Polyterpene resin, hydrocarbon resin & anti-Oxidant like Zinc Diethyl Dithio Carbamate in a stainless steel kettle at 170°Cand stirring for 4 hrs followed by dispersing in solvent like Toluene in Z- blade mixer to get solvent based Hot Melt Pressure Sensitive Adhesive.
The solvent based Natural rubber based Pressure Sensitive Adhesives was then mixed with solvent based Hot Melt Pressure Sensitive Adhesive in varying proportions to get Improved Natural Rubber based Pressure Sensitive having high Peel adhesion & highTack closer to Hot Melt Pressure Sensitive Adhesive & cost lower than Hot Melt Pressure Sensitive Adhesive.
Improved Natural Rubber based Pressure Sensitive can be used to make different types of single sided and/or double sided adhesive tapes by applying the said adhesive on one side or both sides of any supporting material like tissue paper, cloth, non woven & film. Improved Natural Rubber based Pressure Sensitive will have a wide ranging applications for making varieties of printed labels, where high adhesion and high tack is a desired feature.
INVENTION;
"Improved Natural Rubber based Pressure Sensitive Adhesive is a blend of hot melt pressure sensitive adhesive and Natural Rubber based Pressure Sensitive Adhesive.
Natural rubber based Pressure Sensitive Adhesives comprising of Natural Rubber like PLC, RMA - 48 to 52 parts, tackifiers like

polyterpene resin, Hydrocarbon resin, phenolic resin, Zinc resinate -38-50 parts fillers like zinc oxide 2-5 parts & anti-Oxidant like Zinc Diethyl Dithio Carbamate , 2,5 di tert. Pentylhydroquinone ( 1 to 2 parts) was manufactured on a 2-roll mill .
The rubber was added to 2 roll mill & masticated to form a band. Polyterpene resin was powdered & added to the rubber on the 2 roll mill. This was followed by alternate addition of zinc oxide & phenolic resin & Zinc resinate. Regular spading of rubber with the ingredients added was done on the 2 roll mill to ensure proper mixing. The rubber mix thus formed on the 2 roll mill was then discharged by spading & collected in trays. This PSA was then mixed with solvent like Toluene in Z blade mixer for 6 hrs to get Natural Rubber Pressure Sensitive Adhesive.
The Natural Rubber component comprises of natural rubbers like RMA-1, RMA-II, RMA-III, RMA-IV, PLC of various grades and blends thereof.
The Natural Rubber adhesive of the present invention contains one or more of tackifiers which can be formed of hydrocarbon resins, rosin and rosin derivatives, polyterpenes, coumarone-indene resins, any compatible conventional tackifier or mixtures thereof. The resins can be modified with alpha methyl styrene. It has been found that a mixture of resins can provide a better balance of properties than any one resin alone.
The Natural Rubber adhesive of this invention contains fillers which can be formed of calcium carbonate, barytes, aluminum hydroxide, zinc oxide, clay, and mixtures thereof in order to extend the adhesive and alter its appearance.

The Natural Rubber adhesive of this invention contains small amounts of other additives such as antioxidants, heat stabilizers, pigments and the like. Antioxidants and heat stabilizers are to be used for improved heat stability of the adhesive. Typical antioxidants are 2,5 ditertiary amyl hydroquinone, di-tertiary butyl cresol and amines. At least one of the -conventional heat stabilizers such as Zinc salts of alkyl di-thiocarbomates are used in the present invention. Colored pigment are added to obtain a coloured adhesive.
Hot Melt Pressure Sensitive Adhesive was also prepared in a stainless steel Kettle equipped with thermometer, stirrer and nitrogen inlet . The ingredients consisted of thermoplastic rubber like Kraton 1107 (35 - 45 parts) , tackifiers like Polyterpene resin, hydrocarbon resin (55-65 parts ) & anti-Oxidant like Zinc Diethyl Dithio Carbamate ( 2-3 parts) . The kettle was heated to 170° charged with 50% hydrocarbon resin & 50% of anti oxidant given in formulation & mixed for 45 mins. Kraton D1107 was added & mixed for further 75 mins. Finally Polyterpene & remaining quantity of hydrocarbon resin and anti oxidant was added & mixing continued for 2hrs & then the Hot Melt Pressure Sensitive Adhesive formed was drained through the outlet at the bottom of the kettel. This Hot Melt Pressure Sensitive Adhesive was then mixed with solvent like Toluene in Z blade mixer for 6 hrs to get solution of Hot Melt Pressure Sensitive Adhesive.
Hot Melt Pressure Sensitive Adhesive of the present invention includes thermoplastic rubber like Kraton 1107 which S-I-S ( Styrene-Isoprene- Styrene ) however other grades of S-I-S can also be used.
Hot Melt Pressure Sensitive Adhesive of the present invention includes a tackifier which can be formed of hydrocarbon resins, rosin and rosin derivatives, polyterpenes, coumarone-indene resins, any

compatible conventional tackifier or mixtures thereof along with mineral oils which are used as plastisizers can be used.
Hot Melt Pressure Sensitive Adhesive of this invention contains small amounts of other additives such as antioxidants, heat stabilizers, pigments and the like. Antioxidants and heat stabilizers are to be used for improved heat stability of the adhesive. Typical antioxidants are 2,5 ditertiary amyl hydroquinone, di-tertiary butyl cresol and amines. At least one of the -conventional heat stabilizers such as Zinc salts of alkyl di-thiocarbomates are used in the present invention. Coloured pigment are added to obtain a coloured adhesive
The following example describes one typical experiment carried out and is not limited to the ratios used to describe the invention in detail.
Example 1
[a] Preparation of adhesives
(i) Typical Natural rubber based Pressure Sensitive adhesive:
Ingredient Quantity
PLC Rubber 50 parts
Polyterpene resin 30 parts
Zinc resinate 8 parts
Anti oxidant 2 parts
Phenolic resin 10 parts
The rubber was added to 2 roll mill & masticated to form a band. Polyterpene resin was powdered & added to the rubber on the 2 roll mill. This was followed by alternate addition of zinc oxide & phenolic resin & Zinc resinate. Regular spading of rubber with the ingredients added was done on the 2 roll mill to ensure proper mixing. The

rubber mix thus formed on the 2 roll mill was then discharged by spading & collected in trays. This PSA was then mixed with solvent like Toluene in Z blade mixer for 6 hrs to get Natural Rubber Pressure Sensitive Adhesive
(ii) Typical Hot melt Pressure Sensitive adhesive:
Ingredient Quantity
Kraton Rubber 1107 40 parts
Polyterpene resin 20 parts
Hydrocarbon resin 38 parts
Anti oxidant 2 parts
The kettle was heated to 170°C, charged with 50% hydrocarbon resin & 50% of anti oxidant given in above formulation & mixed for 45 mins. Kraton D1107 was added & mixed for further 75 mins. Finally Polyterpene & remaining quantity of hydrocarbon resin and anti oxidant was added & mixing continued for 2hrs & then the Hot Melt Pressure Sensitive Adhesive formed was drained through the outlet at the bottom of the kettel. This Hot Melt Pressure Sensitive Adhesive was then mixed with solvent like Toluene in Z blade mixer for 6 hrs to get solution of Hot Melt Pressure Sensitive Adhesive.
Blending of Natural rubber PSA & Hot Melt PSA :
Natural rubber based PSA in solution form was mixed with different ratios of Hot Melt PSA also in solution form like 90:10 to 10:90 in Z-blade mixer to form homogeneous Adhesive blends.
[b] Preparation of sample
Samples were prepared by coating the different blends of NR PSA and HM PSA on 60 micron thick white BOPP film with dry adhesive coating

weight of 35-40 gsm followed by drying in air circulating oven at 90°C for 3 mins. Samples were laminated with single side release coated paper on the adhesive and conditioned for 24 hrs at 25°C and 65% RH before testing.
[c] Testing of samples
Adhesive Properties like peel Adhesion & Tack of Natural Rubber PSA & Hot Melt PSA blends were tested as follows:
Adhesion to steel :Test sample was prepared by applying 2.5 cm x 25cm strips on stainless steel plate by using a 2kg roller (as per IS 7809 part II) . 180° peel adhesion was measured after 20 minute dwell time at 25°C using Tensile Strength Testing machine at a jaw separation rate of 300 mm/minute.
Tack : Tack was determined using Tack tester.
[d] Results and analysis
As the % of HM PSA was increased in the blend of NR PSA the peel adhesion to steel values also increased as can be seen from Table 1 and figures 1 and 2.
As the % of HM PSA was increased in the blend of NR PSA the tack also increased as can be seen from Table 2 and figures 3 and 4
The data illustrates that HM PSA has high Peel adhesion to Steel, very good Tack properties & this offers the key advantage of utilizing HM PSA for post modification of Natural rubber based PSA for increasing the Peel adhesion to steel property of the adhesive.

The data also shows that HM PSA when dispersed in solvent & added to Natural rubber based PSA results in increasing the Tack of the adhesive.
The data also exhibits that on accelerated aging the enhancement of all the adhesive properties like Peel adhesion to steel & tack of Natural rubber based PSA is achieved which s a distinct advantage for long term utility of the adhesive.

WE CLAIM:
1. "Improved Natural Rubber based Pressure Sensitive Adhesive "
comprising of a blend of solvent based natural rubber pressure
sensitive adhesive and solution form of hot melt pressure sensitive
adhesive enhances the adhesive performance of natural rubber
adhesive with respect to peel adhesion and tack thereby improving its
adherence to low energy surfaces and the process of manufacturing
the same involves the following steps:-
(a) manufacturing Natural rubber based Pressure Sensitive Adhesives made of Natural Rubber, tackifiers & anti-Oxidant by mixing on a 2-roll mill and then dispersing in the solvent like toluene;
(b) Manufacturing Hot Melt Pressure Sensitive Adhesive made of thermoplastic rubber like Kraton 1107, tackifiers & anti-Oxidant by heating in a stainless steel kettle then dispersing pin the solvent like toluene;
(c) Blending Natural rubber based Pressure Sensitive Adhesives obtained in 1(a) with Hot Melt Pressure Sensitive Adhesive obtained in 1 (b) to get improved Natural Rubber based Pressure Sensitive Adhesive.
2. "Improved Natural Rubber based Pressure Sensitive Adhesive" as
claimed in Claim 1, wherein the Natural rubber based Pressure
Sensitive Adhesives consist of Natural Rubber like PLC, RMA - 38-50
parts, tackifiers like polyterpene resin, Hydrocarbon resin, phenolic
resin, Zinc resinate - 38-50 parts fillers like zinc oxide 2-5 parts

& anti-Oxidant like Zinc Diethyl Dithio Carbamate , 2,5 di tert. Pentylhydroquinone ( 1 to 2 parts) on a 2-roll mill;
3. "Improved Natural Rubber based Pressure Sensitive Adhesive" as claimed in Claim 2 wherein the said Natural rubber based Pressure Sensitive Adhesive has Natural Rubber comprises of various grades of natural rubbers like RMA-1, RMA-II, RMA-III, RMA-IV, PLC and blends thereof;
4. "Improved Natural Rubber based Pressure Sensitive Adhesive" as claimed in Claim 2 wherein the tackifiers of the said natural rubber based Pressure Sensitive Adhesives can be formed of hydrocarbon resins, rosin and rosin derivatives, polyterpenes, coumarone-indene resins, any compatible conventional tackifier or mixtures thereof.
5. "Improved Natural Rubber based Pressure Sensitive Adhesive" as
claimed in Claim 2 wherein the said Natural Rubber adhesive of this
invention contains fillers which can be formed of calcium carbonate,
barytes, aluminum hydroxide, zinc oxide, clay, and mixtures thereof
in order to extend the adhesive and alter its appearance.;
6. "Improved Natural Rubber based Pressure Sensitive Adhesive" as claimed in Claim 2 wherein the said Natural Rubber adhesive contains small amounts of other additives such as antioxidants, heat stabilizers, pigments and the like.
7. "Improved Natural Rubber based Pressure Sensitive Adhesive" as claimed in Claim 2 wherein the said Natural Rubber adhesive of this invention required quantity of organic solvents such as hydrocarbon/ aromatic solvents, more specifically any one or mixture of Toluene, Hexane, Heptane etc. is used to form a compound of

coatable consistency and texture commensurate to the coating equipment;
8. "Improved Natural Rubber based Pressure Sensitive Adhesive" as claimed in Claim 1 wherein the said Hot Melt Pressure Sensitive Adhesive is prepared in a stainless steel Kettle equipped with thermometer, stirrer and nitrogen inlet using materials of thermoplastic rubber like Kraton 1107 (35 - 45 parts) , tackifiers like Polyterpene resin, hydrocarbon resin (55-65 parts ) & antioxidant like Zinc Diethyl Dithio Carbamate ( 2-3 parts) ;
9. "Improved Natural Rubber based Pressure Sensitive Adhesive" as claimed in Claim 8 wherein Hot Melt Pressure Sensitive Adhesive of the present invention includes thermoplastic rubber like Kraton 1107 which S-I-S ( Styrene- Isoprene- Styrene ) however other grades of S-I-S can be used.;

10. "Improved Natural Rubber based Pressure Sensitive Adhesive" as claimed in Claim 8 wherein the said Hot Melt Pressure Sensitive Adhesive of the present invention includes a tackifier which can be formed of hydrocarbon resins, rosin and rosin derivatives, polyterpenes,;
11. "Improved Natural Rubber based Pressure Sensitive Adhesive" as claimed in Claim 8 wherein the said Hot Melt Pressure Sensitive Adhesive of this invention contains small amounts of other additives such as antioxidants, heat stabilizers, pigments and the like.
12. "Improved Natural Rubber based Pressure Sensitive Adhesive" as claimed in Claim 8 wherein the said Hot Melt Pressure Sensitive Adhesive of the present invention includes required quantity of organic solvents such as hydrocarbon/ aromatic solvents, more

specifically any one or mixture of Toluene, Hexane, Heptane etc. is used to form a compound of coatable consistency and texture commensurate to the coating equipment;
13. "Improved Natural Rubber based Pressure Sensitive Adhesive" as claimed in Claim 1 wherein Blending Natural rubber based Pressure Sensitive Adhesives obtained in 1(a) with Hot Melt Pressure Sensitive Adhesive obtained in 1 (b) is done in varying proportions of Natural rubber based PSA to Hot Melt PSA like 90:10 to 10:90 to get improved Natural Rubber based Pressure Sensitive Adhesive;
14. Improved Natural Rubber based Pressure Sensitive Adhesive" as claimed in Claims 1 to 13 above whereby an "Improved Natural Rubber based Pressure Sensitive Adhesive" is obtained.