A WATERBORNE BINDER COMPOSITION AND USE THEREOF

The present invention relates to a waterborne binder composition comprising a water dispersible polymer binder and a coalescing agent, and the use of the composition.

Formation of a strong and uniform film is a desirable coating and adhesive quality. In order to enable film formation at moderate or low temperatures, film forming aids usually called "coalescing agents" are added to aqueous formulations. The functions of a coalescing agent are both to reduce the minimum film forming temperature (MFFT) of the coating and to act as a temporary plasticizer and thereby subsequently promote hardening of the film. MFFT is the lowest temperature at which the particles in waterborne polymer dispersion form a continuous film after the water has been evaporated. Traditional film forming agents are often organic solvents which evaporate when the coating dries and thus give rise to a smell and pollution problem. To minimise the environmental impact of the binder composition it is desirable to develop coalescing agents which do not belong to the group of volatile organic compounds (VOC). Non- volatile or slowly evaporating compounds however have a disadvantage in their plasticizing property, which substantially retards the hardness development process of the film and thereby results in formation of an undesirably soft film.

Reactive coalescing agents, e.g. isocyanates, epoxides and siloxanes, which react with the polymer and thereby permanently become a part of the film, can be used to minimize emissions. Reactive coalescing agents may also improve the hardness development of the film as well as reduce the film formation temperature. Their capability of reducing the film formation temperature is however small and to be able the reach the required film formation temperature, conventional coalescing agents have to be used in addition to the reactive compounds.

The disadvantages of the prior art may be eliminated through the use of glycidyl derivates containing a large-sized hydrocarbyl residue, in particular glycidyl ethers and glycidyl esters, as coalescing agents in waterborne binder compositions. The reason why these compounds reduce the film forming temperature more effectively than conventional coalescing agents is explained by the rather large hydrocarbon group present in the ether or ester.

According to the present invention it has quite unexpectedly been possible to produce a waterborne binder composition comprising a water dispersible polymer binder and a coalescing agent comprising glyceryl triesters. The triesters of the coalescing agent are selected from the group consisting of tripropionin (triester of glycerol and propionic acid), tributyrin (triester of glycerol and butyric acid), tri-isobutyrin (triester of glycerol and isobutyric acid) or trivalerin (triester of glycerol and valeric acid) or combinations of two or more of these. In addition to good compatibility with mixtures containing typical waterborne polymer dispersions, the triesters of the present invention improve film formation properties which make them excellent as coalescing agents in waterborne paint, adhesive and sealant. As mentioned the coalescing agent of the present invention is a triester unlike other ester based coalescing agents used in waterborne binder formulations that usually are monoesters or diesters, e.g. dicarboxylic acids esterified with alcohols or diols esterified with acids.

Experiments show that the triesters of the invention are compatible with a broad range of different polymer dispersions and that they efficiently lower the MFFT of aqueous polymer dispersions. The concept of dispersions of the invention includes emulsions, since the definition of an emulsion is a dispersion of small droplets of one liquid in another liquid. Besides the before mentioned high MFFT reduction efficiency, good storage stability and good compatibility with polymer dispersions, the triesters of the present invention also involve minimal EHS charges. Despite their storage stability the triesters are readily biodegradable, i.e. they cause minimal concerns to the environment or the health. The triesters of the present invention are not classified as VOC substances in Europe because of their high boiling point. The combination of high boiling point and high efficiency is extraordinary for a coalescing agent. When applied as coalescing agent in a waterborne binder composition, the low plasticizing property of the triesters of the present invention enables the formation of a hard film to an acceptable hardness development rate. The triesters of the present invention are well-known compounds that are commercially available, but never have been considered as coalescing agents before.

The coalescing agent of this invention consists of 50-100%, preferably 75-100% and most preferably 90-100% by weight of one or more triesters of glycerol and an acid selected from the group consisting of propionic acid, butyric acid, isobutyric acid or valeric acid. The remaining part of the coalescing agent consists of the corresponding monoesters and diesters of glycerol and the above acids. The coalescing agent of the present invention may comprise

one or more coalescing agents known in the art in addition to the triester or triesters. The known coalescing agent or agents may constitute 1-50% by weight of the total coalescing agent, preferably 1-25%. The content of the coalescing agent constitutes 1-30% by weight of the polymer solids, preferably 2-20% or 2-10%.

The binder in the paint, adhesive or sealant composition of the present invention is a homo- or copolymer comprising monomer units of acrylate, methacrylate, vinyl acetate and/or units of urethane or urethane/urea. Typical binder polymers are styrene acrylate copolymers, acrylate methacrylate copolymers, acrylate or methacrylate copolymers with vinyl acetate, vinyl acetate homopolymers, vinyl versatate homopolymers and copolymers of ethylene and vinyl acetate or vinyl versatate. Thus the same principal types of aqueous polymers can be used in aqueous paint formulations, adhesives and sealants.

In addition to the water dispersible polymer binder and the coalescing agent a paint composition may contain pigments, fillers and relevant additives, such as defoamers, pigment wetting additives and levelling aids.

The invention is further illustrated in the embodiment examples below. The examples are to be construed as illustrative and not limited in any way.

Example 1, 2 and 3 illustrate the effect of tripropionin as coalescing agent in an acrylate homopolymer dispersion. Example 4 illustrates the effect of tributyrin as coalescing agent in the same kind of dispersion. Example 5 illustrates a comparison test that shows the effect of a commercial coalescing agent in the corresponding dispersion.

Example 6 and 7 illustrate the effect of tripropionin as coalescing agent in a styrene acrylate copolymer dispersion. Example 8 illustrates a comparison test that shows the effect of a commercial coalescing agent in the corresponding dispersion.

Example 9, 10 and 11 illustrate the effect of tripropionin as coalescing agent in a styrene acrylate copolymer dispersion. Example 12 illustrates the effect of tributyrin as coalescing agent in the same kind of dispersion. Example 13 illustrates a comparison test that shows the effect of a commercial coalescing agent in the corresponding dispersion.

Example 14 and 15 illustrate the effect of tripropionin as coalescing agent in a vinyl acetate/ vinyl -versatate copolymer dispersion. Example 16 illustrates a comparison test that shows the effect of a commercial coalescing agent in the corresponding dispersion.

Example 17 and 18 illustrate the effect of tripropionin as coalescing agent in a styrene acrylate copolymer dispersion. Example 19 illustrates the effect of tributyrin as coalescing agent in the same kind of dispersion. Example 20 illustrates a comparison test that shows the effect of a commercial coalescing agent in the corresponding dispersion.

Example 21, 22 and 23 illustrate the coalescing ability of tripropionin in a paint formulation containing a styrene acrylate copolymer dispersion as binder. Example 24 illustrates a comparison test that shows the effect of a commercial coalescing agent in the corresponding paint formulation. Results are shown in figure 1.

Example 1 lOOg of an acrylate homopolymer dispersion, Finndisp A2002 (Forcit), having a polymer solids content of 45% by weight and a MFFT of 54 ⁰ C was mixed with 4,5g tripropionin to obtain a mixture containing 10% coalescing agent (the coalescent addition is related to polymer solids). The mixture was blended by means of propeller agitator for 15 minutes and allowed to rest overnight prior to testing. MFFT was measured to be 19 ⁰ C.

Example 2

The procedure according to example 1 was repeated with the exception that the amount of tripropionin added was 6,75g (15%). MFFT was measured to be 15 ⁰ C.

Example 3

The procedure according to example 1 was repeated with the exception that the amount of tripropionin added was 9,Og (20%). MFFT was measured to be 4 ⁰ C.

Example 4

The procedures according to example 1, 2 and 3 were repeated with the exception that tributyrin was added to the acrylate homopolymer dispersion in stead of tripropionin. MFFT was measured to be 24°C, 15 ⁰ C and O ⁰ C respectively.

Example 5

The procedures according to example 1 , 2 and 3 were repeated with the exception that a commercial coalescing agent, 2,2,4-trimethylpentanediol monoisobutyrate (NX795), was added in stead of tripropionin. MFFT was measured to be 25 ⁰ C, 14°C and 0 ⁰ C respectively.

Example 6 lOOg of a styrene acrylate copolymer dispersion, Finndisp AlO (Forcit), having a polymer solid content of 50% by weight and a MFFT of 18°C was mixed with 1 ,0Og tripropionin to obtain a mixture containing 2% coalescing agent. The mixture was blended by means of propeller agitator for 15 minutes and allowed to rest overnight prior to testing. MFFT was measured to be 9 ⁰ C.

Example 7

The procedure according to example 6 was repeated with the exception that the amount of tripropionin added was 2,5Og (5%). MFFT was measured to be I ⁰ C.

Example 8

The procedures according to example 6 and 7 were repeated with the exception that the commercial coalescing agent NX795 was added in stead of tripropionin. MFFT was measured to be 8°C and O ⁰ C respectively.

Example 9 lOOg of a styrene acrylate copolymer dispersion, Pliotec 7104E (Eliokem), having a polymer solid content of 45% by weight and a MFFT of 6O ⁰ C was mixed with 4,5Og tripropionin to obtain a mixture containing 10% coalescing agent. The mixture was blended by means of propeller agitator for 15 minutes and allowed to rest overnight prior to testing. MFFT was measured to be 31°C.

Example 10

The procedure according to example 9 was repeated with the exception that the amount of tripropionin added was 6,75g (15%). MFFT was measured to be 12 ⁰ C.

Example 11

The procedure according to example 9 was repeated with the exception that the amount of tripropionin added was 9,Og (20%). MFFT was measured to be O ⁰ C.

Example 12

The procedures according to example 9, 10 and 11 were repeated with the exception that tributyrin was added to the styrene acrylate copolymer dispersion in stead of tripropionin. MFFT was measured to be 24 ⁰ C, 12 ⁰ C and 0 ⁰ C respectively.

Example 13

The procedures according to example 9, 10 and 11 were repeated with the exception that the commercial coalescing agent NX795 was added in stead of tripropionin. MFFT was measured to be 31 ⁰ C, 17 ⁰ C and 7 ⁰ C respectively.

Example 14 lOOg of a vinyl acetate-/vinyl- versatate copolymer dispersion, Rhodopas AV-439 (Rhodia Iberlatex), having a polymer solid content of 55% by weight and a MFFT of 14°C was mixed with l,10g tripropionin to obtain a mixture containing 2% coalescing agent. The mixture was blended by means of propeller agitator for 15 minutes and allowed to rest overnight prior to testing. MFFT was measured to be 9 ⁰ C.

Example 15

The procedure according to example 14 was repeated with the exception that the amount of tripropionin added was 2,75g (5%). MFFT was measured to be 3 ⁰ C.

Example 16

The procedures according to example 14 and 15 were repeated with the exception that the commercial coalescing agent NX795 was added in stead of tripropionin. MFFT was measured to be 7 ⁰ C and 4 ⁰ C respectively.

Example 17 lOOg of a styrene acrylate copolymer dispersion, Acronal 290 D (BASF), having a polymer solid content of 50% by weight and a MFFT of 2O ⁰ C was mixed with l,00g tripropionin to obtain a mixture containing 2% coalescing agent. The mixture was blended by means of

propeller agitator for 15 minutes and allowed to rest overnight prior to testing. MFFT was measured to be 13 ⁰ C.

Example 18

The procedure according to example 17 was repeated with the exception that the amount of tripropionin added was 2,5Og (5%). MFFT was measured to be 3 ⁰ C.

Example 19

The procedures according to example 17 and 18 were repeated with the exception that tributyrin was added to the styrene acrylate copolymer dispersion in stead of tripropionin. MFFT was measured to be 1O ⁰ C and 4 ⁰ C respectively.

Example 20

The procedures according to example 17 and 18 were repeated with the exception that the commercial coalescing agent NX795 was added in stead of tripropionin. MFFT was measured to be 13°C and 5°C respectively.

Example 21

A glossy white paint was prepared in conventional manner to test the function of tripropionin as a coalescing agent in paint formulation. First 37.23 ppw water, 36.74 ppw propylene glycol, 5.11 ppw of a pigment wetting agent, Orotan 1124 (Rohm & Haas) and 3.77 ppw of a defoamer, Byk 024 (Byk Chemie) were combined in a cylindrical grinding vessel, equipped with a dissolver (powerful mechanical agitator equipped with a typical serrated mixing blade). The dissolver was started and 253.65 ppw of the pigment, Ti-Pure R900 (DuPont) was gradually added at a rate that successive additions become continuously incorporated. When all pigment was added, the dissolver was allowed to run at high speed for about 15 minutes. The mixing rate was then reduced and 620.44 ppw of a styrene acrylate copolymer dispersion, Pliotec 7104E (Eliokem) was gradually added, followed first by addition of 39.78 ppw of a thickener, Acrysol R-2020 (Rohm & Haas) and thereafter by addition of 3.28 ppw ammonia. The paint was finally mixed at moderate stirring rate for 30 minutes for assuring complete homogenisation.

The coalescing agent to be tested was then incorporated in the paint formulation, whereafter the amount of water was adjusted to attain a solid content of 46 % by weight. To achieve 10%

coalescing agent of the polymer solids 2,58g tripropionin and 6,12g water were added to the paint mixture.

100 g aliquot of the paint mixture was then used to test the impact of coalescing aid. MFFT was measured to be 24 ⁰ C.

Example 22

The procedure according to example 21 was repeated with the exception that the amount of tripropionin and water added to the paint mixture was 3,87g respectively 4,83g to achieve 15% coalescing agent of the polymer solids. The hardness of the film was measured by the Koenig hardness test, a test based on an oscillation of a pendulum where the energy is absorbed by the elasticity of the film. The Koenig hardness is determined by the time in seconds it takes to decrease the oscillation of the pendulum. Higher Koenig hardness values indicate a harder surface. The hardness results are shown in figure 1. MFFT was measured to be 12 ⁰ C.

Example 23

The procedure according to example 21 was repeated with the exception that the amount of tripropionin and water added to the paint mixture was 5,16g respectively 3,54g to achieve 20% coalescing agent of the polymer solids. MFFT was measured to be I ⁰ C.

Example 24

The procedures according to example 21, 22, 23 were repeated with the exception that the commercial coalescing agent NX795 was added instead of tripropionin. The Koenig hardness of the film was measured for the paint mixture with 15% coalescing agent, the hardness results are shown in figure 1. MFFT was measured to be 30 ⁰ C, 16 ⁰ C and 8°C respectively.

According to the results of the Koenig hardness test, figure 1, the hardness of the paint films in example 22 and 24 are about the same. The test was performed at 23(+-l) ⁰ C and 50(+-5) % RH.