WO1996014360A1

WO1996014360A1 - Epoxy ester vesicles and paints

Info

Publication number: WO1996014360A1
Application number: PCT/US1995/013877
Authority: WO
Inventors: Donald F. H. Wallach; Rajiv Mathur
Original assignee: Micro-Pak, Inc.
Priority date: 1994-11-03
Filing date: 1995-10-26
Publication date: 1996-05-17
Also published as: AU3969595A; CA2204398A1

Abstract

A new type of paucilamellar lipid vesicle having an epoxy ester as the primary wall material has been developed. This lipid vesicle can be used to encapsulate epoxides without leakage. These epoxide-containing vesicles are particularly useful in forming epoxy-latex polymer paints which are shelf stable and polymerize upon drying.

Description

EPOXY ESTER VESICLES AND PAINTS

Background of the Invention

The present invention concerns a new type of vesicles having an epoxy ester as the major wall component. These vesicles can be used in a variety of products but have particular usefulness in paints, coatings and adhesives. Using the vesicles of the invention, it is possible to have a water-based latex paint which hardens into a polymer when drying rather than merely an aggregated film. This latex paint is shelf stable in a single container and only polymerizes upon application and drying.

Epoxies have been used for many years in the adhesive and paint fields. Epoxies are all based on the epoxide ring, which has the following structure:

This epoxide ring has bond angles which average sixty degrees (60°), considerably less than normal tetrahedral carbon angle of 109.5°, or the divalent oxygen angle of 110°. This three membered ring is highly strained so the bonds open easily, causing the epoxide to have high reactivity. Epoxides can under go acid catalyzed reactions, base catalyzed cleavage, and a variety of other reactions. When an epoxide such as a bw-phenol epoxide is reacted with an acid bearing material such as carboxylic acid, it can polymerize and crosslink to form polymers. A familiar form of epoxides is the two-part epoxy resin often used as an adhesive. In this two-part resin, the epoxide and hardener are both stable when kept separate but upon mixing, the polymerization reaction takes place and the epoxy readily hardens into a solid. Those who have worked with epoxies know the rapid speed and hard bond that can be formed with this process.

Latex paints have some advantageous properties as compared with the alkyd or oil based paints, particularly in terms of their water solubility and ease of clean up. However, this same water solubility can be a problem. For many industrial applications, the fact that the latex is water soluble is detrimental since weathering or water under high force under water can cause the latex to deteriorate. This is particularly important in covering metallic, as compared to wooden, structures since the latex can not form as strong a bond with the metal surface as it can with wood. In practice, the latex is painted or coated on to the surface and then allowed to dry, forming a film on the surface.

In order to ameliorate some of these latex problems, attempts have been made to create both water-based alkyd paints and epoxy-latex paints. The basic rationale of an epoxy- latex paint is to have the epoxy (or epoxide) act as a polymerization agent, cross-linking the acid functional groups in the latex, so that it forms a polymer coating as compared with a mere film. However, the mixture of the epoxide polymerization agent and the latex starts reacting almost immediately, so both phases cannot be stored in the same container. For certain applications, high-pressure spray mixers having mixing chambers are used to mix the epoxide and latex and spray the combination product on the surface. The problem with these mixers is that there is always some reaction in the spray head so they clog over time. While the advantages of having a polymerized latex are known, this product has not been easy to achieve.

Accordingly, an object of the invention is to provide a unitary product having both a latex paint and a harder or polymerization agent which will form a latex polymer.

Another object of the invention is to provide vesicles having an epoxide delivery system.

A further object of the invention is to provide a method of forming a unitary product containing both latex and a polymerization agent.

These and other objects and features of the invention will be apparent from the following description and the claims.

Summary of the Invention

The present invention features lipid vesicles having an epoxy as the primary wall material, preferably encapsulating an epoxide which can act as an hardener or polymerization agent. These vesicles have primary use in the paint field but also are advantageous in the manufacture and use of other polymers such as polyurethane, polyacrylics, and different types of coatings.

In its simplest form, the lipid vesicles of the invention have an epoxy ester as the primary lipid of the bilayer. For paint and other similar applications, the vesicles have an epoxide encapsulated therein. The epoxy ester wall is not reactive with the epoxide and acts as a barrier against the release of the epoxide. The preferred vesicles are paucilamellar vesicles which have an amorphous central cavity surrounding 2-10 lipid bilayers, so that substantially all of the epoxide (which is water immicible) is segregated in that amorphous central cavity. The preferred epoxy esters are esters of C12-C20 f^attv acids, and mixtures thereof. Preferred epoxides include those with a phenol derivative, preferably bw-phenol epoxide compounds. A secondary surfactant such as sodium lauryl sulfate or ammonium lauryl sulfate helps to provide stability to the vesicles. In another embodiment, the epoxide containing lipid vesicles are used as a "hardener" in a paint having a hardener and a paint base. Preferably, a latex, most preferably a latex being substantially free of ammonium ions, is used as the paint. The use ofmonium ions to neutralize the acid in the latex appears counterproductive because ammonia (in equilibrium with ammonium ions) can penetrate the vesicle membrane, allowing ammonium ions to react with the epoxide and inactivating the system during storage. Similarly, although in some circumstances an ammonium lauryl sulfate could be used as the secondary surfactant in the vesicle, its use is contraindicated with a latex paint in the present system. The paint is shelf stable, and can be spread on a wall or other area, whereby the latex and the hardener will combine, and react only upon drying. It is believed that the vesicles desiccate and fracture upon drying, thereby releasing the epoxide, which then reacts with the latex to form the latex polymer.

The same type of vesicle could be used in an adhesive system whereby the fracture of the vesicle allows one part of a two-part epoxide adhesive to mix with the other while segregating the components before mechanical stress or drying frees the reactants. This technique can also be with other polymerizable materials such as urethane monomers.

Detailed Description of the Invention

The present invention provides both epoxy ester lipid vesicles as well as a paint or coating made therefrom. These epoxy ester lipid vesicles allow the formation of a unitary latex-epoxy paint, a paint which can be kept in a single container until use. It is only upon drying of the preparation and fracture of the vesicles that the polymerization reaction occur.

In the preferred embodiment of the invention, the vesicles are made of an epoxy ester resin solution, an epoxide, a secondary surfactant, a neutralizing agent (if necessary), an anti- foaming agent (if necessary), and deionized water. These vesicles are made using procedures similar to those described in United States Patent No. 4,911,928 and United States Patent No. 5,160,669, the disclosures of which are incorporated herein by reference. Briefly, the epoxy ester and the epoxide are heated together to flowability, e.g., a temperature of approximately 75°C. The aqueous phase, which contains water soluble materials such as the secondary surfactant, e.g., sodium lauryl sulfate, a neutralizing agent if needed such as ammonium hydroxide or sodium hydroxide, and any anti-foaming agent, all dissolved in deionized water, is then heated to the temperature slightly below that of the epoxy ester/epoxide phase. The phases are blended using a shear mixing device such as the NovaMiχTM lipi vesicle maker from IGI, Inc. or a homogenizer until a vesicular product with a thin, lotion-like consistency is achieved. The vesicular product can then be stored as is or mixed with a paint or other material.

The following reaction sequence is believed to generate the polymer. Specifically, the b/s-phenol epoxide, formed by the reaction of a bw-phenol with epoxides: (1) reacts with the carboxylic acid of the latex, (2) releasing a phenol epoxide, and (3) forming the polymer. This polymer hardens rapidly, forming an exceptionally hard coating on the surface.

CH₃

^H°— ©— " ©~^{0H +} 2 (CH ^CH ₂-CI)

CH₃

H₂C S^> HC— O — -C— --^^-O-CH-CHz (2)

CH,

O

II

R — C — OH

The following examples will more clearly illustrate the efficacy and advantageous properties of the invention and its various embodiments.

Example 1

In this example, epoxy ester vesicles were made and then mixed with an off-the-shelf latex paint to see whether it is possible to make the paint combination of the present invention. The latex has carboxylic acid functional groups and is neutralized with ammonium hydroxide. Ammonium lauryl sulfate was used as the secondary surfactant in making the vesicles. Table 1 shows the formulation used in manufacture of the vesicles. TABLE 1

% W/W

Epoxy Ester Resin Solution 10.0

(057-1250 Cargill, Inc.)

Epoxide 52.0 ( Araldite G Y6010, Ciba-Geigy Corp.)

Ammonium Lauryl Sulfate, 30% 3.3

(ALS Carsonol, Lonza)

Ammonium Hydroxide 0.3

Deionized Water 34.4

The epoxy ester and epoxide were blended together and heated to approximately 75°C, forming the lipophilic phase. The epoxide used has the following general formulation:

H₂

(A)

The ammonium lauryl sulfate, ammonium hydroxide and water were heated to 70°C, forming the aqueous phase. A laboratory size homogenizer was lowered into the aqueous phase and while homogenizing, the lipid phase was added to the aqueous phase. The combination was mixed for ten minutes, yielding a product with a temperature of about 69°C, having a thin, lotion-like consistency and a pH of 8.0-8.5. Microscopic examination showed heterogeneous size vesicles with no free epoxy. No separation of phases occurred upon centrifugation at 3500 RPM for ten minutes.

The epoxy vesicles were then blended with Maincote AE-58 (Rohm and Hass), a commercial latex paint. The proportions were one part vesicles to two, three or four parts latex paint. The mixtures were placed in closed containers and kept at 50°C for observation. On the tenth day, all three mixtures began to solidify. The mixtures were heated in a water bath to 90°C, which caused the latex and epoxide to react, yielding a solid within five minutes. The 90°C bath reliquifies the epoxy ester of the vesicle walls, releasing all the epoxide.

It was hypothesized that the ammonium ion reacted with the epoxide (a classic epoxide base reaction), causing the solidification process. Since the Maincote AE-58 is an ammonium hydroxide neutralized latex and ammonium lauryl sulfate was used in the vesicles, additional experiments using a ammonium-free preparation were conducted.

Example 2

This example illustrates an early experiment using an ammonium-free preparation. Table 2 shows the formulation used in making the vesicles.

TABLE 2

% w/w

Epoxy Ester Resin Solution 10.0

(057-1250 Cargill, Inc.)

Epoxide 52.0

(Araldite GY6010, Ciba-Geigy Corp.)

Sodium Lauryl Sulfate 1.0

Deionized Water 37.0

This same procedure was used as in Example 1 to make the vesicles except that, because after five minutes of homogenization a great deal of foam resulted, 2 ml of Silicone Medical Anti-Foam (Dow Corning) was added. The solution was then homogenized an additional five minutes.

The temperature after homogenization was approximately 60°C and microscopic examination again showed heterogeneous vesicles. Centrifugation showed no separation of free epoxy. The vesicles were then blended with one-four parts of an acid functional latex, not neutralized, with a pH of 6.2 (obtained from the Sherwin-Williams Company). The combined product was stored in closed containers and kept at 50°C. Solidification did not commence occurring until 16 days after formation, showing that the ammonium ion was a contributory factor in solidification.

Example 3

In this example, the vesicles described in Example 2 were used except they were checked for pH and neutralized prior to addition to the latex. When the vesicular pH was found to be 7.1, IN NaOH was added until a pH of 7.8 was achieved.

The same latex was used as in Example 2, except it also was neutralized with IN NaOH to reach a pH of 7.0. Table 3 shows the proportions of epoxy vesicles and sodium neutralized latex used in this experiment, as well as the resulting pH of each preparation.

TABLE 3

Epoxv Vesicles Latex _t__

1 part 0.5 part 7.4

1 part 1 part 7.2

1 1 p paarrtt 2 2 p paarrtt 7.2

1 part 3 part 7.2

1 part 4 part 7.2

The mixtures were placed in closed containers and kept at 50°C as described in the previous two examples. At the end of four weeks (28 days), none of the samples had solidified in the containers. When painted onto a test wall, the combination dried properly, yielding a hard paint coating which contrasted favorably with not just the standard latex but also latex epoxy blends.

Similar uses of the epoxy vesicles could be made with other materials such adhesives, polyurethanes, and other coating materials. For example, urethane monomers or styrene monomers can react with the epoxide to form a hard epoxide co-polymer. Those skilled in the arts may determine other uses for the vesicles. Such other uses are deemed to be encompassed in the following claims.

What is claimed is:

Claims

CLAIMhS

1. A paucilamellar lipid vesicle having 2-10 bilayers surrounding an amorphous central cavity comprising an epoxy ester as the primary wall material.

2. The lipid vesicle of claim 1 with an epoxide encapsulated therein.

3. The lipid vesicle of claim 2 wherein said epoxy ester is selected from the group consisting of C12-C20 fa ty acid esters, and mixtures thereof, containing an epoxide group.

4. The lipid vesicle of claim 2 wherein said epoxide comprises a phenol derivative.

5. The lipid vesicle of claim 1 wherein said lipid vesicle further comprises a secondary surfactant.

6. The lipid vesicle of claim 5 wherein said secondary surfactant is selected from the group consisting of sodium lauryl sulfate and ammonium lauryl sulfate.

7. The lipid vesicle of claim 2 wherein substantially all of said epoxide is segregated in said amorphous central cavity.

8. A paint containing a hardener and a paint base, said hardener including a lipid vesicle comprising an epoxy ester as the primary wall material encapsulating an epoxide.

9. The paint of claim 8 wherein said epoxy ester is selected from the group consisting of C12-C20 fatty acid esters, and mixtures thereof, containing an epoxide group.

10. The paint of claim 8 wherein said epoxide comprises a phenol derivative.

11. The paint of claim 8 wherein said lipid vesicle further comprises a secondary surfactant.

12. The paint of claim 11 wherein said secondary surfactant is selected from the group consisting of sodium lauryl sulfate, other non-ammonium lauryl sulfates, and mixtures thereof.

13. The paint of claim 8 wherein said lipid vesicle comprises a paucilamellar lipid vesicle having 2-10 bilayers surrounding an amorphous central cavity.

14. The lipid vesicle of claim 13 wherein substantially all of said epoxide is segregated in said amorphous central cavity.

15. The paint of claim 8 wherein said paint base comprises a latex paint.

16. The paint of claim 15 wherein said paint is substantially free of ammonium ions.

17. The paint of claim 15 wherein said latex and said hardener are shelf-stable when combined and only react upon drying.

18. The paint of claim 15 wherein said latex and said hardener polymerize upon reaction.