FIELD OF THE INVENTION:
The present invention relates to a water-base adhesive composition.
BACKGROUND OF THE INVENTION:
US4948822 discloses one-part laminating adhesive compositions which incorporate acrylic polymer prepared by a "core-shell" emulsion polymerization process. We have found that the resultant adhesive compositions employing polymers which have polymer particles having a core portion surrounded by a shell portion have excellent bond strength, and water and humidity resistance equal to prior art two-part adhesives employing epoxy resin.
US6020435 discloses a process for preparing emulsion polymer particles comprising an aqueous emulsion of a multi-stage emulsion polymer, comprising a core stage polymer and a shell stage polymer, a monomer at a level of at least 0.5 percent by weight based on the weight of the multi-stage emulsion polymer and a swelling agent, wherein the core stage polymer comprises, as polymerized units, from 5 to 100 percent by weight, based on the weight of the core stage polymer, of hydrophilic monoethylenically unsaturated monomer, and from 0 to 95 percent by weight, based on the weight of the core stage polymer, of at least one nonionic monoethylenically unsaturated monomer; and the shell stage polymer comprises, as polymerized units, at least 50 percent by weight of nonionic monoethylenically unsaturated monomer;
CN102690610A discloses a water-based adhesive and a preparation method thereof. The water-based adhesive comprises the following raw materials in part by weight: styrene, butyl acrylate, methyl methacrylate, acrylic acid, methacrylic acid, N-hydroxymethyl acrylamide, an adhesion promoter, an emulsifier, a pH value buffering agent, an initiator, water, other functional aids and a proper amount of ammonia water.
Existing water-base adhesives have poor heat resistance property when checked at 180 °C/0.3Sec/3bar or more. In order to improve heat resistance, addition of 2K (two-component) hardener containing adhesives were proposed, however even these 2K (two-component) hardener containing adhesives failed to achieve an optimum heat resistance.
Currently, different water-base adhesives are used for different laminate structures like paper to CPP (Cast Polypropylene), paper to metallized PET, Paper to BOPP

and paper to aluminium foil. There is no single water-base adhesive currently available that can be used for all of the above said laminates.
Water based adhesives have an unpleasant odour, which persists even after its use in a printed structure.
Existing water-base adhesives impart moderate bond strength that is inadequate for bonding.
OBJECTS OF THE INVENTION:
The principal objective of the present invention is to provide a water-base adhesive that exhibits excellent heat resistance property without any hardener.
Another objective of the present invention is to provide a water-base adhesive that is suitable for different laminate structures like paper to CPP (Cast Polypropylene), paper to metallized PET, Paper to BOPP and paper to aluminium foil.
A further objective of the present invention is to provide a water-base adhesive that is low in odour.
Yet another objective of the present invention is to provide a water-base adhesive that exhibits high bond strength.
SUMMARY OF THE INVENTION:
The present invention relates to a water-base adhesive composition and method of preparation thereof. The water-base adhesive composition comprises 20 to 30 parts by weight of butyl acrylate, 10 to 20 parts by weight of methyl methacrylate (MMA), 0.5 to 1.5 parts by weight of Hydroxy Propyl Acrylate (HPA), 0.5 to 1.5 parts by weight of 2-(Acetoacetoxy)ethyl methacrylate (AAEMA), 0.5 to 1.5 parts by weight of acrylic acid, 0.5 to 1.5 parts by weight of Methacrylamide, 0.1 to 1.0 parts by weight of pH buffer, 0.2 to 1.0 parts by weight of emulsifier, 0.5 to 1.0 parts by weight of water soluble initiator, 50 to 60 parts by weight of water, appropriate amount of radical polymerisation initiator-catalyst, and appropriate amount of liquid ammonia.
The method of preparation involves forming:
a. a first monomer pre-emulsion was formed, and

b. a second monomer pre-emulsion was formed, wherein the two monomer pre-emulsions were sequentially charged with radical polymerisation initiator-catalyst, and liquid ammonia solution.
DETAILED DESCRIPTION OF THE INVENTION:
The preferred embodiments of the present invention will be described in detail with the following disclosure and examples. The foregoing general description and the following detailed description are provided to illustrate only some embodiments of the present invention and not to limit the scope of the present invention. The invention is capable of other embodiments and can be carried out or practiced in various other ways.
Unless otherwise specified, all the technical and scientific terms used herein have the same meaning as is generally understood by a person skilled in the art pertaining to the present invention. All the patents published patent applications referred to throughout the entire disclosure herein, unless specified otherwise, are incorporated by reference in their entirety.
Adhesive Formulation:
The water based adhesive of the invention is formulated using core-shell polymerization process, advantageously in a three-step process, sequential seeding emulsion polymerization occurs in such a manner that a polymer produced in a preceding step is covered with a polymer produced in a succeeding step.
PROCESS OF FORMULATING THE ADHESIVE: Preparation of pre-emulsion or monomer mixture (part I):
Calculated amount of water is taken in a reaction kettle and added are Sodium Sulphate, Noigen Dinol 25P (an anionic surfactant containing Sulfonic acids, C13-17-sec-alkane, sodium salts, CAS # 85711-69-9) from Sigma Aldrich and Rhodoline WA40 (a Non-ionic surfactant of a neutralized low molecular weight sodium polyacrylate polymer solution) solution from Solvay and kept agitating the reaction mixture. Then, added Butyl Acrylate, Methyl Methacrylate (MMA), Acrylic Acid, Hydroxy Propyl Acrylate (HPA) and 2-(Acetoacetoxy)ethyl methacrylate (AAEMA) into the reaction kettle under continuous stirring, and then agitated until a smooth monomer pre-emulsion is formed.
Preparation of pre-emulsion or monomer mixture (part II):

Calculated amount of Butyl Acrylate, Methyl Methacrylate (MMA), Acrylic Acid, Hydroxy Propyl Acrylate (HPA) and 2-(Acetoacetoxy)ethyl methacrylate (AAEMA) is taken in reaction kettle and kept agitating the reaction mixture. Then added calculated amount of Methacrylamide solution prepared using water in the reaction mixture, and then agitated until a smooth monomer pre-emulsion is formed.
Note: Do not over agitate the pre-emulsions as this may cause foaming. This foam when transferred into the reactor during processing can create gel. Also check that there should not any layer separation in pre-emulsion.
REACTION PROCESS:
Step 1: Calculated amount of water is taken in a clean reactor encompassed with condenser, stirrer, thermometer, and heating plate. At 85°C, added is Potassium Persulphate (PPS) solution (radical polymerisation initiator-catalyst Part 1). Then, added is 5% of pre-emulsion or monomer mixture (part I) with the help of transfer pump into reactor within 2-5 minutes. After a wait for about 10 minutes the temperature goes down and exotherm starts. Due to initial exotherm of seed monomer, the temperature will increase in about 10-20 minutes to the maximum temperature. When the temperature starts decreasing, started adding the remaining amount of pre-emulsion or monomer mixture (part I). Adjusted the flow rate of pump in a manner so that the transfer monomer mixture would be completed within next 4 hours along with Potassium Persulphate (PPS) solution (radical polymerisation initiator-catalyst Part 2). Temperatures of reactor during the reaction is maintained between 82-85°C. After addition of monomer and radical polymerisation initiator-catalyst, held the reaction for at least 60 minutes, so that complete reaction will take place between the constituents of the reaction mixture.
Step 2: Now, started adding pre-emulsion or monomer mixture (part II) to the reaction mixture (formed in step 1) along with Potassium Persulphate (PPS) solution (radical polymerisation initiator-catalyst Part-3) within 1 hour. After addition of monomer and radical polymerisation initiator-catalyst, again held the reaction for 1 hour, so that complete reaction will take place between the constituents of the reaction mixture.
Step 3: Again, calculated amount of Potassium Persulphate (PPS) solution (radical polymerisation initiator-catalyst Part-4) is added to the reaction mixture (formed in step 2) within 1 hour. Post addition of radical polymerisation initiator-catalyst, held the

reaction for duration of 1 hour. Cooled down the reactor up to 45°C. Now added liquid ammonia 25% solution with water slowly in reactor.
Calculated amount of additives like defoamer & preservatives are added to the formed product (also known as intermediate) as required.
Suitable defoamers are selected from the wide range of defoamer used such as silicone based defoamers, emulsion defoamers, star polymer based defoamers, powder defoamers, oil based defoamers.
The water-based adhesive composition of the present invention further contains 1 to 5 parts by weight of an adhesion promoter.
Examples:
Formulation of adhesive:
The adhesive composition of the present invention is explained with the help of the following examples given in Table 1.
Table 1

Product Evaluation:
Physical properties Heat resistance and Bond strength of the water-base adhesive of the present invention were measured, and given in Table 2.
Table 2
Extent of Fibre Tear was considered as an indication of Bond strength.
While various aspects and embodiments have been disclosed herein, other aspects, embodiments and uses of the invention will be apparent to those skilled in the art. It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the invention being indicated by the following claims.

We claim:
1. A water-base adhesive composition comprising:
20 to 30 parts by weight of butyl acrylate, 10 to 20 parts by weight of methyl methacrylate (MMA), 0.5 to 1.5 parts by weight of Hydroxy Propyl Acrylate (HPA), 0.5 to 1.5 parts by weight of 2-(Acetoacetoxy)ethyl methacrylate (AAEMA), 0.5 to 1.5 parts by weight of acrylic acid, 0.5 to 1.5 parts by weight of Methacrylamide, 0.1 to 1.0 parts by weight of pH buffer, 0.2 to 1.0 parts by weight of emulsifier, 0.5 to 1.0 parts by weight of water soluble initiator, 50 to 60 parts by weight of water, appropriate amount of catalyst, and appropriate amount of liquid ammonia.
2. The water-base adhesive composition according to claim 1, wherein the emulsifier is composed of 0.1 to 0.6 parts by weight of an anionic surfactant, and 0.1 to 0.6 parts by weight of a nonionic surfactant.
3. The water-base adhesive composition according to claim 2, wherein the anionic surfactant is a sodium salt of C13-17-sec-alkane Sulfonic acids.
4. The water-base adhesive composition according to claim 2, wherein the nonionic surfactant is a neutralized low molecular weight sodium polyacrylate polymer solution.
5. The water-base adhesive composition according to claim 1, wherein the pH buffering agent is sodium sulphate.
6. The water-base adhesive composition according to claim 1, wherein the water soluble initiator is Potassium Persulphate (PPS), wherein Potassium Persulphate (PPS) is also used as the catalyst.
7. The water-based adhesive composition according to claim 1 further contains 1 to 5 parts by weight of functional additives, wherein the functional additives are selected from at least one of a defoamer, a preservative, and a levelling agent.
8. The water-based adhesive composition according to claim 1 further contains 1 to 5 parts by weight of an adhesion promoter.

9. A method of preparation of a water-base adhesive composition including 20 to 30 parts by weight of butyl acrylate, 10 to 20 parts by weight of methyl methacrylate (MMA), 0.5 to 1.5 parts by weight of Hydroxy Propyl Acrylate (HPA), 0.5 to 1.5 parts by weight of 2-(Acetoacetoxy)ethyl methacrylate (AAEMA), 0.5 to 1.5 parts by weight of acrylic acid, 0.5 to 1.5 parts by weight of Methacrylamide, 0.1 to 1.0 parts by weight of pH buffer, 0.2 to 1.0 parts by weight of emulsifier, 0.5 to 1.0 parts by weight of water soluble initiator, 50 to 60 parts by weight of water, appropriate amount of radical polymerisation initiator-catalyst, and appropriate amount of liquid ammonia, comprising the following steps:
c. pH buffer Sodium Sulphate, an anionic surfactant containing sodium salt of
Sulfonic acids of C13-17-sec-alkane and a Non-ionic surfactant of a
neutralized low molecular weight sodium polyacrylate polymer solution were
added to 50-60 parts by weight of the total amount of water, and further
adding Butyl Acrylate, Methyl Methacrylate (MMA), Acrylic Acid, Hydroxy
Propyl Acrylate (HPA) and 2-(Acetoacetoxy)ethyl methacrylate (AAEMA)
under continuous stirring, and agitated until a smooth first monomer pre-
emulsion was formed,
d. Butyl Acrylate, Methyl Methacrylate (MMA), Acrylic Acid, Hydroxy Propyl
Acrylate (HPA), 2-(Acetoacetoxy)ethyl methacrylate (AAEMA) were mixed to
form a monomer mixture and agitated; and Methacrylamide solution in water
was added to the in the monomer mixture, and agitated until a smooth
second monomer pre-emulsion was formed,
e. The remaining water was taken in a clean reactor encompassed with
condenser, stirrer, thermometer, and heating plate, a solution of 25 parts by
weight of the total Potassium Persulphate (PPS) was added when the
temperature of the water reaches 85°C, 5 parts by weight of the first
monomer pre-emulsion was added into the reactor slowly in 2-5 minutes,
when the temperature starts decreasing, remaining amount of the first
monomer pre-emulsion was added to the reactor by adjusting the flow rate in
order to transfer the first monomer pre-emulsion in a time span of 4 hours,
f. further a solution of 25 parts by weight of the total Potassium Persulphate
(PPS) was added in doses, each dose was added in an interval of 5 minutes,
by adjusting the flow rate to complete the addition of Potassium Persulphate
(PPS) solution in a time span of 4 hours at a maintained temperature of 82°C
-85°C; then the reaction was held for at least 90 minutes in order to allow
complete reaction between the constituents of the reaction mixture,
g. the first monomer pre-emulsion was added to the reaction mixture formed in
the previous step (d) by adjusting the flow rate to complete the addition of the

first monomer pre-emulsion in a time span of 1 hour, further a solution of 25 parts by weight of the total Potassium Persulphate (PPS) was added in doses, each dose was added in an interval of 5 minutes, by adjusting the flow rate of Potassium Persulphate (PPS) solution to complete the addition of Potassium Persulphate (PPS) solution in a time span of 1 hour; and the reaction was held for at least 60 minutes in order to allow complete reaction between the constituents of the reaction mixture, h. a solution of the remaining amount of Potassium Persulphate (PPS) was added to the reaction mixture formed in the previous step (e) by adjusting the flow rate of Potassium Persulphate (PPS) dosage to complete the process of addition in 1 hour, the reaction was held for a duration of 1 hour, the reactor was cooled down up to 45°C; and liquid ammonia solution was added with water slowly into the reactor, and filter to obtain the water-based adhesive.