Method for dispersing alkyd resins with associative polymers in water, formulations thus obtained and aqueous paints containing same

The invention concerns the sector of alkyd resins used to manufacture paints of the same name.

The expression “alkyd paints” refers either to polyesters resulting from the reaction of organic acids with polyols, or to alkyds known as urethane-alkyds resulting from the condensation of polyols with isocynate groups. In the present application, the terms alkyd “resin” and “polymer” will be used interchangeably. Historically, alkyd paints were manufactured from the 1950s in the presence of organic solvents, unlike water-based paints which were developed later.

However, the possibility of manufacturing water-based alkyd paints was envisaged very early, thereby anticipating consumers' demand for products free of organic solvents. This problem appears in the literature from the 1980s, as illustrated by document U.S. Pat. No. 4,497,933, which describes a method for manufacturing a water-based paint which is completely free of solvents, and which uses a very particular alkyd resin with an acid group content of between 15 and 40 mg KOH/g of resin, together with a high number of OH groupings. However, it is understood that such a method is very restrictive, in the sense that, by definition, it cannot be applied to all types of alkyd resin.

The skilled man in the art then developed techniques based on the use of surfactants and/or organic solvents (the latter then being used in lower quantities than for the formulation of solvent-based paints): their function is to solubilise the said alkyd resin in the presence of water, thus enabling the manufacture of a water-based alkyd paint. However, the presence of solvents and of surfactants in paint can impair the efficacy of the rheology modifiers commonly used in “traditional” water-based paints; these thickening agents remain just as essential in water-based alkyd paints, with a view to giving the latter the desired rheological profile.

In addition, international legislation—and more specifically European legislation—in the area of solvents and the disposal of volatile organic compounds (VOCs) is increasingly restrictive, as is emphasised by the recent document “advantages of water-based solvent-free alkyd emulsions for deco paints” (Sbornik Prispevku-Mezinarodni Konference-Naterovich Homtach-37 th -Cz. Rep., 22-24 May 2006, 92-104). With this regard, organic solvent-based paints can no longer be suitable for the skilled man in the art, from the standpoint of environmental regulations. Finally, the presence of solvents does not allow work in satisfactory conditions of safety for the user (risk of inflammation or intoxication, or allergic risks).

It is therefore necessary to develop new methods for preparing alkyd paints in an aqueous medium, free of solvents and surfactants, the general character of which would enable them to be applied to any alkyd resin, and which would be adapted to the use of rheology modifiers traditionally used in water-based paints. The Applicant has committed itself to this research effort, and has succeeded in developing a method for manufacturing such a paint, which is based on an original method of solubilisation of the alkyd resin in question.

Indeed, the dispersion in water of the said alkyd resin is initially accomplished by means of particular acrylic polymers having terminal hydrophobic groupings, with a character known as “associative”. When these polymers are neutralised at sufficiently high pH (higher than 6), associative interactions are created between the hydrophobic groupings: these interactions demarcate fields which are all solvation cages for alkyd resin molecules. These solvation cages enable the alkyd polymer molecules to be dispersed in water through a mechanism known as “encapsulation”. Such polymers are often described in the literature through the English acronym HASE, which stands for “hydrophobically altered soluble alkaline emulsion”. Chemically, they can be defined on the basis of the monomers which constitute them: the first uses a (meth)acrylic acid base, the second is an ester of this acid, and the third is an associative hydrophobic monomer.

One of the Applicant's merits is to have succeeded in identifying and using the phenomenon of structuring of water using such polymers: by this means the dispersion of the alkyd resin by encapsulation is made possible. Such a use of these polymers is, in the state of our current knowledge, a new use of these objects which have been widely described in applications for paint (see documents FR 2 693 203, FR 2 872 815, FR 2 633 930), or again the sector of concretes (see the French patent application with filing number FR 07 00086, and not yet published on the date of filing of the present application).

Moreover, this technique is original in itself, in the sense that it is distinguished from the “traditional” techniques of encapsulation based either on “host” molecules such as the cyclodextrins (see document JP 2001 354515 on encapsulation of a micronised oil), or on interfacial polymerisation (see document U.S. Pat. No. 3,754,062 on the polymerisation of a urethane-epichlorhydrin-amine blend in the presence of a greasy substance), or on the use of carboxylated polymers with a base of one (meth)acrylic acid monomer and one acrylic ester monomer (in this case, the phenomenon of encapsulation is governed solely by the solubility of the polymer as a function of the pH; such polymers are commercially available under the names Eudragit™, Kollicoat™ or Eastacryl 30D™).

Thus, a first object of the invention is a method for the dispersion in water of at least one alkyd resin, characterised in that it comprises the steps of:

a) blending at least one associative polymer consisting: of at least one monomer which is (meth)acrylic acid, of at least one monomer which is a (meth)acrylic ester, and of at least one associative hydrophobic monomer, with at least one alkyd resin and water, b) adjusting the pH of the blend obtained in step a) to a value greater than 6, preferentially 7, very preferentially 8, c) possibly precipitating the blend obtained after step b) through the adjustment of the pH to a value less than 6, preferentially 5, very preferentially 3.

Concretely, the constituent elements (resin, water, associative polymer) are introduced whilst stirring in a reactor; the order of introduction will be chosen by the skilled man in the art, notably according to the solubility in water of the resin to be encapsulated.

The formulation is accomplished by blending of its various constituent elements (water, alkyd resin, associative polymer) and then, according to a first embodiment, by adjusting the pH to a value greater than 6, preferentially 7, very preferentially 8.

According to this first embodiment the method according to the invention does not implement step c) of acidification.

In a second variant, step b) is followed by a reduction of the pH to a value of less than 6; there is then precipitation of the medium, which causes the structure of the associative polymer to collapse in on itself. Formation of a dispersion in the water of particles consisting of alkyd resin molecules occurs, which are trapped within the structure of the associative polymer. Such a dispersion is equally favourable for a complete solubilisation of the alkyd resin in water. The technical link providing the unity of the present invention is based on the presence, in both embodiments, of the 3 fundamental constituents which are the alkyd resin, water and the associative polymer.

Thus, in this second embodiment, the method according to the invention is also characterised in that it uses step c).

The method according to the invention is also characterised in that the pH is adjusted in step b) by means of a mineral or organic base.

The method according to the invention is also characterised in at the pH is adjusted in step c) by means of a moderately strong or strong acid.

The method according to the invention is also characterised in that the blend of step a) consists of 0.1% to 20%, preferentially 0.1% to 10%, and very preferentially 0.1% to 5% by dry weight of the said associative polymer, compared to its total weight.

The method according to the invention is also characterised in that the blend of step a) consists of at least 5%, preferentially of at least 20%, very preferentially of at least 30%, and extremely preferentially of at least 35% by weight of at least one alkyd resin, and at most of 70% by weight of at least one alkyd resin, compared to its total weight.

The method according to the invention is also characterised in that, with regard to the associative polymer, the monomer which is a (meth)acrylic ester is chosen preferentially from among ethyl acrylate, butyl acrylate, methyl methacrylate and their blends.

The method according to the invention is also characterised in that, with regard to the associative polymer, the monomer which is an associative hydrophobic monomer has the general formula (I):

where:

m, n, p and q are integers and m, n and p are less than 150, q is greater than 0 and at least one integer from among m, n and p is non-zero, R has at least one polymerisable vinylic group, R 1 and R 2 are identical or different and represent hydrogen atoms or alkyl groupings, R′ is a hydrophobic grouping having at least 6 and at most 36 carbon atoms, preferentially at least 16 and at most 24 carbon atoms, and very preferentially at least 18 and at most 22 carbon atoms.

The method according to the invention is also characterised in that the alkyd resin is chosen from among the polyester, polyurethane, polyurethane-polyester resins and their blends.

Another object of the invention consists of the water-based formulations obtained by the method according to the invention.

These water-based formulations are characterised in that they include water, at least one alkyd resin, and at least one associative polymer consisting:

of at least one monomer which is (meth)acrylic acid, of at least one monomer which is a (meth)acrylic ester, and of at least one associative hydrophobic monomer.

These water-based formulations, in a first embodiment in which they are obtained by the method of the invention without implementing step c) of precipitation, are also characterised in that their pH is greater than 6, preferentially 7, very preferentially 8.

These water-based formulations, in a second embodiment in which they are obtained by the method of the invention implementing step c) of precipitation, are also characterised in that their pH is less than 6, preferentially 5, very preferentially 3.

These water-based formulations are also characterised in that they also contain a mineral or organic base.

These water-based formulations, in a second embodiment in which they are obtained by the method of the invention implementing step c) of precipitation, are also characterised in that they contain a moderately strong to strong acid.

These water-based formulations are also characterised in that they consist of 0.1% to 20%, preferentially 0.1% to 10%, very preferentially 0.1% to 5%, by dry weight of the said associative polymer, compared to their total weight.

These water-based formulations are also characterised in that they consist of at least 5%, preferentially of at least 20%, very preferentially of at least 30%, and extremely preferentially of at least 35%, by weight of at least one alkyd resin, and at most of 70% by weight of at least one alkyd resin, compared to their total weight.

These water-based formulations are also characterised in that, with regard to the associative polymer, the monomer which is a (meth)acrylic ester is chosen preferentially from among ethyl acrylate, butyl acrylate, methyl methacrylate and their blends.

These water-based formulations are also characterised in that, with regard to the associative polymer, the monomer which is an associative hydrophobic monomer has the general formula (I):

where:

m, n, p and q are integers and m, n and p are less than 150, q is greater than 0 and at least one integer from among m, n and p is non-zero, R has at least one polymerisable vinylic group, R 1 and R 2 are identical or different and represent hydrogen atoms or alkyl groupings, R′ is a hydrophobic grouping having at least 6 and at most 36 carbon atoms, preferentially at least 16 and at most 24 carbon atoms, and very preferentially at least 18 and at most 22 carbon atoms.

These water-based formulations are also characterised in that the alkyd resin is chosen from among the polyester, polyurethane, polyurethane-polyester resins and their blends.

Another object of the invention is the use of the abovementioned water-based formulations, for the manufacture of paints, lacquers, varnishes or wood stained. In concrete terms, the skilled man in the art produces these products by blending the various additives which are traditionally used in the composition of a paint, a lacquer, a varnish or timber preservative, in which the alkyd resin is introduced in the form of the abovementioned water-based formulations.

A final object of the invention lies in the paints, lacquers, varnishes and wood stained, characterised in that they contain a water-based alkyd resin formulation according to the invention.

Examples 1 and 2 illustrate respectively the manufacture of monomers able to be used according to the invention, and the manufacture (from these monomers) of water-soluble associative polymers able to be used according to the invention.

This test illustrates the manufacture of a water-based formulation of an alkyd resin in the presence of an associative hydrophobic polymer.

The first step is to weigh 16.5 grams of a hydrophobic associative polymer in the form of a 30% aqueous dispersion of dry matter; the polymer consists of (expressed as a % by weight of each of the monomers):

a) 37.4% of methacrylic acid, b) 54.3% of ethyl acrylate, c) 8.3% of a monomer of formula (I), in which:

m=p=0, n=25, q=1, R is the methacrylate group, R 1 and R 2 are identical and represent hydrogen, R′ is a branched alkyl group consisting of 16 carbon atoms (hexyldecylic).

150 grams of an alkyd resin sold by the company CRAY VALLEY™ with the brand Synolac™ 6868 WD75 is then introduced into 182 grams of water; this resin contains solvents. 16.5 grams of the associative hydrophobic polymer, as described above, is then introduced into the blend.

Finally, the pH of the blend is adjusted using sodium hydroxide to a value equal to 8.5.

The formation of a creamy blend is observed; the pH is then reduced to 5.8 using a 4% phosphoric acid solution. A fluid resin dispersion in an aqueous medium is then obtained.

The size of these dispersions was determined by dynamic diffusion of light using a Zetasizer™ nano S90 sold by the company MALVERN™; an average value of 1,400 nm is obtained.

This test illustrates the method according to the invention, through the manufacture of a water-based alkyd paint, which manufacturing process uses the water-based formulation obtained for test 1-a.

In concrete terms, the said paint is produced by blending various constituent elements, the proportions of which are given in table 1.

Coadis™ BR85 is a dispersing agent sold by the company COATEX™.

Tego™ 1488 is an antifoaming agent sold by the company TEGO CHEMIE™.

TiO2 Kronos™ 2310 designates titanium dioxide sold by the company KRONOS™.

Octa-soligen™ 144 Aqua designates a siccative agent sold by the company BORCHERS™.

For this paint, a number of rheological measurements were made at 25° C., initially and subsequently after 24 hours, using the techniques well known to the skilled man in the art. The ICI™, Stormer™, and Brookfield™ viscosities were notably determined at 10 and 100 revolutions per minute. The values obtained, reported in table 2, match typical values in rheology for an easily usable and applicable paint, i.e. one with satisfactory stability in the pot, without sedimentation or excessive phase separation, a satisfactory loading of the application tool (roller or brush), and a satisfactory quality of application (brush, roller, spraying). The change of viscosity between t=0 and t=24 is typical for that found for most water-based paints.

To 300 grams of paint produced using test 1-b was added 10 grams of an associative thickening agent sold by the company COATEX™, and intended for water-based paints, which is either Coapur™ XS 22, or Coapur™ 2025. The same rheological measurements as for test 1-b were made at instant t=0 and were reported in table 3.

The values of table 3 shows that thickening agents normally used in standard water-based paints enable the water-based alkyd paint according to the invention to be thickened effectively. This demonstrates after the event that success has indeed been obtained in perfectly dispersing the alkyd resin in water, which has ultimately enabled a water-based alkyd paint to be obtained. The alkyd resin solubilised in this manner in water also has the same potential for developing interactions known as associative interactions with thickening agents which have been hydrophobically modified for water-based products, enabling the main application properties of the paint to be controlled (high build, control of speed of application, resistance to projection, flow). The effectiveness of these interactions is notably quantifiable through the increase of the Stormer and ICI viscosities.

This test illustrates the manufacture of a water-based formulation of a solvent-free alkyd resin in the presence of an associative hydrophobic polymer.

The first step is to weigh in a 1-L reactor fitted with a mechanical stirring mechanism, a heating system and a distillation device 16.5 grams of an associative hydrophobic polymer in the form of an aqueous dispersion with 30% dry matter; the polymer consists (expressed as a % by weight of each of the monomers) of:

a) 37.4% of methacrylic acid, b) 54.3% of ethyl acrylate, c) 8.3% of a monomer of formula (I), in which:

m=p=0, n=25, q=1, R is the methacrylate group, R 1 and R 2 are identical and represent hydrogen, R′ is a branched alkyl group consisting of 16 carbon atoms (hexyldecylic).

150 grams of an alkyd resin sold by the company CRAY VALLEY™ with the brand Synolac™ 6868 WD75 is then introduced into 182 grams of water.

16.5 grams of the associative hydrophobic polymer, as described above, is then introduced into the blend. 48 ml of water and 40 ml of organic solvent is then distilled at atmospheric pressure until the temperature of the blend reaches 100° C.

Finally, the pH of the blend is adjusted using sodium hydroxide to a value equal to 8.5, and it is left for approximately 15 minutes, whilst stirring.

The formation of a creamy blend is observed; the pH is then reduced to 5.8 using a 4% phosphoric acid solution. A fluid resin dispersion in an aqueous medium is then obtained.

The size of these dispersions was determined by dynamic diffusion of light using a Zetasizer™ nano S90 sold by the company MALVERN™; an average value of 1,200 nm is obtained.

This test illustrates the method according to the invention, through the manufacture of a water-based alkyd paint, which manufacturing process uses the water-based formulation obtained for test 2-a.

In concrete terms, the said paint is produced by blending various constituent elements, the proportions of which are given in table 4.

The same rheological measurements as those described above are made on the paint obtained; these are reported in table 5.

Values are obtained characteristic of a paint which is easy to use and apply, with a satisfactory stability in the pot, without sedimentation or excessive phase separation, satisfactory loading of the application tool (roller, brush), and satisfactory application quality (brush, roller, spraying).

To 337 grams of paint produced using test 2-b was added 9 grams of an associative thickening agent sold by the company COATEX™, and intended for water-based paints, namely Coapur™ XS 22. The same rheological measurements as for test 2-b were made at instant t=0 and reported in table 6.

The values of table 6 shows that the thickening agent normally used in standard water-based paints enables the water-based alkyd paint according to the invention to be thickened effectively. This demonstrates after the event that success has indeed been obtained in perfectly dispersing the alkyd resin in water, which has ultimately enabled a water-based alkyd paint to be obtained.