Claims:CLAIMS
1. A colloid stabilized latex, the latex comprising:
a non-ionic stabilizer having a saponification value of at least 80%;
a monomer mixture essentially comprising vinyl acetate, methyl methacrylate and butyl acrylate; and
an initiator, wherein the latex is free of polymeric opacifiers, inorganic particles and surfactants, wherein the latex is configured to produce a white/opaque film upon drying with a contrast ratio of greater than 90 and having solids of at least 35 wt%.

2. The colloid stabilized latex of claim 1, wherein the latex is configured to provide required opacity in absence of Titanium Dioxide (TiO2) pigment and a polymeric opacifier, when used in waterborne paints.

3. The colloid stabilized latex of claim 1, wherein the latex is used as an alternate to the polymeric opacifier in the waterborne paints.

4. The colloid stabilized latex of claim 1, wherein the latex is used as a binder for preparing high to mid pigment volume concentration (PVC) paints.

5. The colloid stabilized latex of claim 1, wherein an opacity of the latex is controlled by the saponification value of the non-ionic stabilizer.

6. The colloid stabilized latex of claim 1, wherein the non-ionic stabilizer is poly vinyl alcohol.

7. The colloid stabilized latex of claim 1, wherein the monomer mixture comprises 40 parts of vinyl acetate monomer, 40 parts of methyl methacrylate and 20 parts of butyl acrylate by weight.

8. The colloid stabilized latex of claim 1, wherein the formation of the latex occurs using a semi-batch emulsion polymerization.

9. The colloid stabilized latex of claim 1, wherein the latex has a solid content of about 35 wt% to about 50 wt% and a glass transition temperature (Tg) of about 35 oC to about 45oC.

10. The colloid stabilized latex of claim 1, wherein the latex comprises particles having a size ranging from about 1µm to about 3µm, also a few particles below 1µm , and wherein the particles enable light scattering.

11. The colloid stabilized latex of claim 1, wherein the inorganic particles comprise titanium dioxide and silicon dioxide.

12. A method of forming a colloid stabilized latex, the method comprising:
charging a first portion of a non-ionic stabilizer solution into a reaction vessel, wherein the non-ionic stabilizer solution has a saponification value of at least 80%;
heating the first portion of the non-ionic stabilizer solution to about 75?C- 80?C;
adding a seed monomer, an initiator solution and a buffer solution;
adding a monomer mixture continuously for about 3-5 hours;
charging a remaining portion of the non-ionic stabilizer solution during polymerization;
adding a chaser catalyst to form the colloid stabilized latex; and
cooling the colloid stabilized latex and filtering to remove coagulum.

13. The method of claim 12, wherein the first portion of the non-ionic stabilizer solution comprises 10-20 weight % of aqueous poly vinyl alcohol solution.

14. The method of claim 12, wherein the monomer mixture comprises 40 parts of methyl methacrylate, 40 parts of vinyl acetate monomer and 20 parts of butyl acrylate

, Description:FORM 2

THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003

COMPLETE SPECIFICATION
(Section 10, rule 13)

“OPAQUE FILM FORMING COLLOID STABILIZED LATEX”

Asian Paints Limited
Asian Paint Research and Technology Centre, Plot No. C -3B/1. TTC Industrial Area, MIDC Pawane, Thane Belapur Road, Navi Mumbai – 400703

The following specification particularly describes the invention and the manner in which it is to be performed

OPAQUE FILM FORMING COLLOID STABILIZED LATEX

FIELD
[001] Embodiments of the present invention are generally directed to a latex and in particular directed to a colloid stabilized latex that forms an opaque film.

BACKGROUND

[002] Opacity (whiteness) in paints is brought by incorporating inorganic particles (mainly titanium dioxide, TiO2) in the paint formulation. This contributes to relatively higher cost of the paints. To reduce the cost, alternate organic polymer-based technologies are developed. Organic polymer-based products for such applications are known as polymeric opacifiers, opaque polymers, or hollow polymers. These are hollow spheres with core (void) -shell (polymer) morphology. The core is prepared with high acid content and a polymer. The prepared core is further treated to develop a shell on top of the core. The acidic core is then neutralized with base for the swelling to occur (generally referred to osmotic swelling). Once the polymer is allowed to dry, the water evaporates there by creating voids. Due to the refractive index difference between the air – polymer interface, light is scattered efficiently and opacity is imparted to the paints. However, the synthesis of these opacifiers involve multi step processes. Further, control of void size is essential for achieving opacity of the paints.
[003] The shell polymer usually has a high glass transition temperature (Tg). The polymeric opacifiers are used as an additive to certain paint formulations and (TiO2) is partially replaced from the formulation. However, 100% replacement of TiO2 is not feasible as only with polymeric opacifiers, the required opacity may not be achieved.
[004] Film forming hollow polymers are similar to the polymeric opacifiers except that they contain an outer shell having a low Tg polymer which forms a film upon drying. Due to this ability, these polymers may be used as a binder as well as an opacifier to reduce the TiO2 content in the formulation. However, the synthesis of the film forming hollow polymers also involves multi step processes and complete replacement of TiO2 may not be possible.
[005] Thus, there is a need to develop a method that may produce polymeric opacifiers in a single step process and may completely eliminate the usage of TiO2, thereby reducing the carbon footprint.
SUMMARY
[006] The following summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, example embodiments, and features described, further aspects, example embodiments, and features will become apparent by reference to the drawings and the following detailed description.
[007] Briefly, according to an example embodiment, a colloid stabilized latex comprises a non-ionic stabilizer having a saponification value of at least 80%, a monomer mixture comprising vinyl acetate, methyl methacrylate and butyl acrylate and an initiator. The latex is free of inorganic particles and surfactants. The latex is configured to produce a white/opaque film upon drying. The latex provides required opacity in absence of Titanium Dioxide (TiO2) pigment and a polymeric opacifier, when used in waterborne paints. The latex is used as an alternate to the polymeric opacifier in the waterborne paints.
[008] According to another example embodiment, a method of forming a colloid stabilized latex comprises charging a first portion of a non-ionic stabilizer solution into a reaction vessel. The non-ionic stabilizer solution had a saponification value of at least 80%. The first portion of the non-ionic stabilizer solution was heated to about 75?C- 80?C. A seed monomer, an initiator solution and a buffer solution were added. Further, a monomer mixture is added continuously for about 3-5 hours. A remaining portion of the non-ionic stabilizer solution is added during polymerization. Once the monomer addition is completed, chaser catalyst is added to form the colloid stabilized latex. The colloid stabilized latex is cooled and filtered to remove coagulum.
BRIEF DESCRIPTION OF THE FIGURES
[009] These and other features, aspects, and advantages of the example embodiments will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
[0010] FIG. 1 depicts a flow diagram for an illustrative method of forming an opaque film;
[0011] FIGS. 2A and 2B are AFM images of 3D topography of the latex; and
[0012] FIG. 3 is an SEM image of the latex.
DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS
[0013] This disclosure is not limited to the particular systems, devices and methods described, as these may vary. The terminology used in the description is for the purpose of describing the particular versions or embodiments only, and is not intended to limit the scope.
[0014] The present disclosure provides an opaque film forming latex that imparts opacity to the paints. The latex can be used as an opacifier and a binder in the paints, and especially in any of the high to medium pigment volume concentration products. The latex is composed of particles of different size that help in light scattering and thus provides the opacity of the paints. The conventional emulsion polymerization uses surfactants or colloids as stabilizers to assist the particle formation and stabilization. In the present embodiments, poly vinyl alcohol was used as a stabilizer. The latex preparation was done by semi-batch emulsion polymerization method. The synthesis of the latex was carried out in one-pot and by a single step, unlike the conventional method of preparing polymeric opacifiers wherein the core particles were made first and afterwards the shell was made. There was no osmotic swelling in the present disclosure. Further the latex composition contains no TiO2 and thus reduces the carbon footprint.
[0015] FIG. 1 depicts a flow diagram for an illustrative method 100 to form an opaque film. At block 102, a reaction vessel is charged with a first portion of a non-ionic stabilizer solution. The non-ionic stabilizer is poly vinyl alcohol (PVA). PVA is added to de-mineralized water under stirring and heated till 80oC until the PVA is completely dissolved to form a solution. The non-ionic stabilizer solution has a saponification value of at least 80%. PVA has a saponification value in a range of about 80 % to about 98%. In this embodiment, the saponification value of PVA determines the opacity of the latex formed. The viscosity of PVA solution at a temperature of about 25o C is about 5cP to about 30 cP. The first portion of the non-ionic stabilizer solution comprises about 10 weight % to about 20 weight % of PVA solution.
[0016] At block 104, a seed monomer (a small quantity of monomer mixture comprising methyl methacrylate (MMA), vinyl acetate monomer (VAM) and butyl acrylate (BA)) is added. At block 106, a buffer solution is added followed by addition of an initiator. The initiator is about 0.2 parts by weight of potassium persulphate (PPS).
[0017] The buffer solution and the monomer mixture in a seed quantity are added to the reaction vessel before adding the monomer mixture to the reaction vessel. The seed quantity is about 0.1 wt% to about 3 wt% of the monomer mixture. The addition of the monomer mixture in seed quantity along with the initiator enables particle nucleation/generation. The buffer solution is 0.1 weight% sodium bicarbonate to maintain the pH.
[0018] At block 108, a monomer mixture is added continuously over a period of 3-5 hours. Remaining second portion of the PVA solution is added in small doses to the reaction vessel in between the polymerization process along with the initiator to form a latex. In this embodiment, the latex is formed in absence of inorganic particles and surfactants. The monomer mixture comprises methyl methacrylate (MMA), vinyl acetate monomer (VAM) and butyl acrylate (BA). The monomer mixture has 40 parts of MMA, 40 parts of VAM and 20 parts of BA by weight. Specific monomer combination and ratio are required to achieve the opacity of the latex formed. The same monomer composition when developed using surfactant system did not yield an opaque film. The monomer mixture was slowly added over a time period of about 3 hours to about 5 hours.
[0019] At block 110, the contents of the reaction vessel were cooled to 40o C. At block 112, the latex formed was filtered and collected. The latex had particle size ranging from about 1 micron to about 5 microns. The latex had a Tg of about 35 oC to about 45oC and a solid content of around 35-50%. The latex having a solid content less than 35% did not yield an opaque film. At block 114, the latex was casted to form the opaque film which upon drying forms a white opaque film.
[0020] FIGs. 2A and 2B are AFM images that show 3D topography of the latex. The 3D topography of the emulsion polymer in the AFM images shows particles ranging from 0.6µm to 2.5 µm.
[0021] FIG. 3 is an SEM image of the latex. SEM image shows that there are particles of varied size in the latex.
[0022] EXAMPLES
[0023] The present invention will be described below in further detail with examples and comparative examples thereof, but it is noted that the present invention is by no means intended to be limited to these examples.
Example 1
Synthesis of latex
[0024] 10wt% - 20wt% of poly vinyl alcohol (PVA) solution needed for the reaction was initially charged into a reaction vessel. The solution was heated up to 80 - 82?C. Sodium bicarbonate (0.05 parts by weight) was added into the reaction vessel. A monomer mixture was prepared by adding 17.6 parts by weight (PBW) of methyl methacrylate (MMA), 17.6 PBW of vinyl acetate monomer (VAM) and 8.6 PBW of butyl acrylate (BA). About 0.1 to 3 weight% of the monomer mixture was added as a seed monomer along with an initiator solution to the reaction vessel. A temperature fall of 3-5oC was observed in the reaction vessel for a short while. Then the temperature of the contents of the reaction vessel increased and an exotherm was observed. Once the exotherm settled down by at least 1?C, the monomer mixture was added to the reactor over a period of 3-5 hours. Initiator shots along with PVA solution were added in between the reaction. Once the addition was completed, a redox catalyst was added to polymerize any free monomer left in the reaction vessel. The reaction was continued for an hour. The batch was cooled and filtered to collect the latex. The latex formed may be casted into a film or the latex may be added to a paint formulation. The latex film thus formed or the paint film thus produced is opaque. It is to be noted that the latex provides required opacity in absence of Titanium Dioxide (TiO2) pigment and a polymeric opacifier.
[0025] Tab1e 1 presented below lists the ingredients used for preparing the latex as given in Example 1.
TABLE 1
Ingredients PBW( Parts By Weight)
De-Mineralized water 52.95
Vinyl Acetate Monomer 17.6
Methyl Methacrylate 17.6
Butyl acrylate 8.6
Potassium Persulphate 0.2
Sodium Bicarbonate 0.05
Poly Vinyl Alcohol 3

Example 2
Preparation of opaque film
[0026] The latex prepared in Example 1 was casted into a film. It was air dried to form an opaque film. The film was opaque in absence of Titanium Dioxide (TiO2) pigment and a polymeric opacifier.
Example 3
[0027] The latex prepared in Example 1 was used in a paint formulation, by replacing TiO2 and polymeric opacifier partially and wholly from paint formulation 1. The parameters such as yellowness, whiteness and contrast ratio were compared with the parameters of paint formulation 1 and the comparative results are presented in Table 2. The yellowness of the paint formulation 1 is 2.68, the whiteness is 90.18 and the contrast ratio is 97.85. The paint formulation 1 contains opacifier + binder( emulsion latex) and TiO2 pigment. Opacifiers may be OP – 66® from Visen, Ultra E® from Dow Chemicals.
Experiment 1
[0028] The paint formulation 1 has a binder, a polymer opacifier, and 4 wt.% of TiO2. The opacifier used in paint formulation 1 was replaced with the latex as prepared in Example 1. The yellowness was found to be 2.58, the whiteness was found to be 89.44 and the contrast ratio was 92.53.

Experiment 2
[0029] In this experiment, the binder and the opacifier were completely replaced with the latex as prepared in Example 1. Further, no TiO2 was used in the paint. The yellowness was found to be 1.74, the whiteness was found to be 92.20 and the contrast ratio was 96.47.
[0030] The opacity values are better than the paint formulation 1 wherein the binder and opacifier were replaced by the latex prepared in Example1. The opacity values suggest the latex contributes to the opacity of the final paint without the aid of TiO2
Experiment 3
[0031] In this experiment, binder and opacifier were completely replaced by the latex prepared in Example 1. 2 wt% TiO2 was added in the formulation. The yellowness was found to be 2.673, the whiteness was found to be 90.59 and the contrast ratio was 98.43.
[0032] When the TiO2 was reduced by 50% from the paint formulation 1, the whiteness and the contrast ratio were comparable with the paint formulation 1. So even with reduction in the TiO2, there was no degradation in the opacity values. In the Experiment 2 although whiteness index is better, the contrast ratio is slightly lower than Experiment 3, which is acceptable.
[0033] The entire reduction or the substantial reduction of the TiO2 in the paint formulation is possible by replacing it with the white latex as prepared in Example 1.

TABLE 2

Experiment Yellowness Whiteness Contrast Ratio
Paint formulation 1 [Binder (polymer) + Opacifier + 4 wt% TiO2 + other additives (small quantities)] 2.68 90.18 97.85
Experiment 1 (Opacifier in paint formulation 1 was replaced with the developed latex) 2.58 89.44 92.53
Experiment 2 (Binder and opacifier were replaced in paint formulation 1 by the developed latex. Moreover, no TiO2 is used in this formulation) 1.74 92.20 96.47
Experiment 3 (Binder and opacifier were replaced by the developed latex + 2% TiO2 is used in the formulation) 2.673 90.59 98.43

[0034] The present disclosure is not to be limited in terms of the particular embodiments described in this application, which are intended as illustrations of various aspects. Many modifications and variations can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. Functionally equivalent methods and apparatuses within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is to be understood that this disclosure is not limited to particular methods, reagents, compounds, compositions or biological systems, which can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.
[0035] While various compositions, methods, and devices are described in terms of “comprising” various components or steps (interpreted as meaning “including, but not limited to”), the compositions, methods, and devices can also “consist essentially of” or “consist of” the various components and steps, and such terminology should be interpreted as defining essentially closed-member groups.
[0036] With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.
[0037] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases at least one and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to embodiments containing only one such recitation, even when the same claim includes the introductory phrases one or more or at least one and indefinite articles such as “a” or an (e.g., “a” and/or “an” should be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.”
[0038] In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group.
[0039] As will be understood by one skilled in the art, for any and all purposes, such as in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as “up to,” “at least,” and the like include the number recited and refer to ranges which can be subsequently broken down into subranges as discussed above. Finally, as will be understood by one skilled in the art, a range includes each individual member. Thus, for example, a group having 1-3 cells refers to groups having 1, 2, or 3 cells. Similarly, a group having 1-5 cells refers to groups having 1, 2, 3, 4, or 5 cells, and so forth.
[0040] Various of the above-disclosed and other features and functions, or alternatives thereof, may be combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art, each of which is also intended to be encompassed by the disclosed embodiments.
[0041] While only certain features of several embodiments have been illustrated, and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of inventive concepts.
[0042] The afore mentioned description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure may be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. It should be understood that one or more steps within a method may be executed in different order (or concurrently) without altering the principles of the present disclosure. Further, although each of the example embodiments is described above as having certain features, any one or more of those features described with respect to any example embodiment of the disclosure may be implemented in and/or combined with features of any of the other embodiments, even if that combination is not explicitly described. In other words, the described example embodiments are not mutually exclusive, and permutations of one or more example embodiments with one another remain within the scope of this disclosure.