This invention relates to polymers and polymer latices for use in anti-corrosive paints, to such use and to a process for preparing the polymers and polymer latices. More particularly, the invention relates to polymers and polymer latices obtainable by aqueous emulsion polymerization of a monomer mixture comprising vinylesters of tertiary, saturated carboxylic acids and derivatives of alpha,beta-unsaturated carboxylic acids.

As is generally known, iron corrodes quickly under the influ¬ ence of oxygen and water. This leads to damage and poor appearance. The most obvious way to prohibit corrosion is to apply a suitable coating system onto the metal surface. Most coating systems consist of at least two layers. Firstly a so-called primer is applied directly to the metal, which renders control over the corrosion process and provides good adhesion to the metal. Secondly a top coat paint is applied to the layer of primer, primarily for decoration, though contributing to some extent to corrosion protection.

The polymeric constituent or binder of anti-corrosive primers hereinafter referred to as "AC paints" should: (a) be easy to manufacture, have storage stability, and be physiologically safe; (b) be compatible with the other constituents of the primer formula and bind them thereby forming a continuous film which adheres to the substrate, and that provides a coating which quickly attains its final properties such as good resistance to mechanical stresses, high impermeability or barrier effect, good wet adhesion, low water absorption, and good UV/weathering stability to prevent quick degradation of the primer coating in case a long time elapses between the application of the primer coating and the topcoat.

US-A-4,968,741 describes AC paints comprising polymer latices from vinyl aromatic monomers, alkyl acrylate monomers and a further unsaturated carbonyl compound. These latices are prepared in the presence of a stabiliser system comprising a phosphate ester 5 surfactant and a water-insoluble non-ionic surface active agent. Such paints, as can be learned from the I.C.I, articles in Polymers Paint Colour Journal, volumes 176, No. 4181 (1986), and 178, No. 4219 (1988) and in J.Oil Col. Chem. Assoc, 64, 175-185 (1981), have a high permeability to both water vapour and oxygen,

10 making them therefore less suitable as primers for iron. Moreover, according to US-A-4,968,741 good integrated films can only be obtained by using a comparatively high amount of coalescing solvent (column 6, last paragraph). The use of (large amounts of) coalescing solvents can, however, for environmental reasons no l-> longer be accepted. Besides, although of lesser relevance for primer coatings, coatings based on vinyl aromatic monomers have a tendency to turn yellow upon exposure and are to some extent deficient in UV and weathering resistance.

From the aforementioned ICI articles, coatings based on vinyl

20 chloride and vinylidene dichloride (VC-VDC based coatings) are known for their very low water absorption, which according to the authors makes them outstanding AC paints.

These VC-VDC based products have a number of serious drawbacks. To prevent degradation of the polymer under release of

25 HC1 they should be formulated at a low pH. This is not always possible as a result of the buffering action of certain pigments and extenders such as the commonly used pigments titanium dioxide or zinc phosphate. Factors contributing to this degradation are exposure to UV-light and heat. As a result of this, not only the

30 paints based on these binders, but also coating compositions derived therefrom show a certain degree of instability. A further problem is the presence of chlorine in the coating, which is these days increasingly considered a problem for environmental reasons. From EP-A-O, 32,811 (inter)polymers are known that show

^■ " interesting properties, enabling them to be used in concretes, or

to be formulated as lacquers, paints, wood coatings, AC paints and textured coatings. These polymers are stabilised by at least one anionic surface active agent to ensure stability of the latex and the reaction mixture during the polymerization, and to facilitate the formation of micelles in which the polymers are formed, and optionally by a non-ionic surface active agent to contribute to the latex stability, or by at least one surface active agent of the mixed anionic/non-ionic type. The preferred and exemplified stabi¬ liser is a combination of a sulphonate-type anionic surfactant and a nonylphenol ethoxylate as non-ionic surfactant. Despite the aforementioned polymers being useful for general purposes, there remains a need for top-quality AC paints.

Surprisingly, a process has now been found enabling the preparation of polymers and polymer latices suitably applied as AC paints, which, as compared to the above VC-VDC type AC paints, have a comparable level of water absorption, whilst not showing the above disadvantages associated therewith.

Accordingly, the invention provides a process for preparing polymers and polymer latices for anti-corrosive paints by aqueous emulsion polymerization of a monomer mixture in the presence of a phosphate ester surfactant, characterised in that the monomer mixture is composed of:

(a) one or more vinylesters of tertiary, saturated carboxylic acids containing 5 to 20, preferably 9, 10 or 11 carbon atoms in the acid moiety;

(b) one or more alkyl esters of alpha,beta-unsaturated carboxylic acids containing up to 12 carbon atoms in the alkyl moiety;

(c) one or more stabilising monomers selected from the group comprising (meth)acrylic acid, (meth)acrylamide, a C--C, hydroxyalkyl (meth) crylate and sodium vinyl sulphonate; and provided that the polymerization is carried out essentially in the absence of a non-ionic surfactant.

Component (a) preferably is the vinylester of a Versatic acid ("Versatic" is a Shell trademark for tertiary, saturated carboxylic acids), sold as VeoVa 9, respectively VeoVa 10 ("VeoVa 9" and

"VeoVa 10" are Shell trademarks for the vinylester of a tertiary, saturated carboxylic acid containing 9, respectively 10 carbon atoms in the acid moiety). However, also vinyl pivalate and blends of the aforementioned vinylesters may be used. The principal difference between VeoVa 9 (tm) and VeoVa 10 (tm) is in the glass transition temperature T of their homopolymers (respectively 60 °C σ and -3 °C) which is an indicator for the hardness it provides to the coatings. Use of VeoVa 9 (tm) is preferred when it is desired to obtain a high surface hardness of the coating. Alternatively, use of VeoVa 10 (tm) is preferred when a flexible coating is desired. A mix of VeoVa 9 (tm) and VeoVa 10 (tm) is used, when a proper balance of hardness and flexibility in the final coating is desired. It is appreciated, that flexibility and hardness may also be influenced by the other components of the monomer mixture. Component (b) suitably is an alkyl ester selected from methyl (meth)acrylate, (iso)butyl (meth)acrylate, 2-ethylhexyl (meth)- acrylate, lauryl (meth)acrylate or mixtures thereof. Component (b) preferably comprises methyl methacrylate for reasons of UV/weather- ing resistance, and/or 2-ethylhexyl acrylate, being more hydropho- bic. Most preferably, component (b) comprises a mixture of methyl methacrylate and 2-ethylhexyl acrylate.

Component (c) preferably is acrylic acid as it copolymerizes (slightly) better than methacrylic acid and results in lesser grid-formation. Preferably, the monomer mixture comprises components (a) to (c) in a ratio based on 100 percent by weight (%wt) of monomers, of: from 40 to 70 %wt of component (a); 0.5 to 5 %wt of component (c) and the remainder making up to 100 %wt being component (b) .

More preferably, the monomer mixture comprises components (a) to (c) in a ratio of: from 45 to 65 %wt of component (a); from 2 to 4 %wt of component (c) ; and the remainder being component (b) . The phosphate ester surfactant is suitably applied in an amount of 0.5 to 3.0 % m/m, preferably of 0.5 to 1.5 % m/m based on the monomer mixture. Using the preferred amount of phosphate ester

surfactant yields the best balance of stability, water-resistance, and adhesion onto metal.

Preferably, the surfactant is an alkylphenol polyoxyethylene phosphate. More preferably, it is the phosphate ester of the condensation product of an alkylphenol such as nonylphenol and up to 12, preferably 6 ethylene oxide molecules. Such stabilisers are for instance available from SERVO under the trademark SERMUL EA-211, and from GAF under the trademark GAFAC PE-510. Other suitable examples of phosphate ester surfactants are given in US-A-4,968,741.

It is remarked that very minute amounts of non-ionic surfac¬ tant may be used without too much sacrifice of the AC properties of the paint. However, preferably no non-ionic surfactant is used at all. As is shown in the examples and comparative examples it was surprisingly found that the best results for anti-corrosive paints were obtained when the common alkaryl sulphonate surfactant was replaced by the present alkaryl phosphate, whilst refraining from the use of the non-ionic surfactant (generally of the nonylphenol/- ethoxylate type) as advocated in both the VeoVa Technical Manual, VM 2.1, page 17 and US-A-4,968,741.

The polymers and polymer latices according to the invention are easily obtained by adopting the instructions given in EP-A-O,432,811. A suitable process would for instance comprise the _US e of initiators such as (hydro)peroxides, and persulphates; and optionally buffering agents like borax.

In a particularly suitable embodiment of the process, the polymer latex is produced by: preparing a premix of: water; a part of one or more alkaryl phosphates; a part of one or more initiators; and comonomers (a) to (c), charging water, and the remaining parts of the alkaryl phos¬ phates and initiators to a reactor, and heating the reactor to about 80 ^β C,

adding over a period of about 2 to 5 hrs the premix to a reactor and subjecting it to emulsion polymerization condi¬ tions.

The polymer latices of the invention find application as anti-corrosive paints. Such paints will in addition generally contain (anti-corrosion) pigments, (flash rust) corrosion inhibit- ers and optional further additives such as fillers, co-solvents, thickeners, dispersants, preservatives, and anti-foaming agents. The invention will now be described with reference to the following examples, however without restricting its scope to these specific embodiments. EXAMPLES 1-3

A three litre reaction flask fitted with a reflux condenser, stirrer, thermowell, nitrogen inlet tube and monomer pre-emulsion inlet tube was used in all examples. A piston pump was used to allow the introduction of the monomer pre-emulsion into the reaction flask. The reaction flask was heated in a water bath containing a heating element. Initial reactor charge water, demineralized 550 grammes aqueous solution containing 10 %wt alkaryl phosphate (pH - 9) 37 grammes potassium persulphate 1 gramme

Pre-emulsion mixture water, demineralized 550 grammes aqueous solution containing 10 %wt alkaryl phosphate (pH - 9) 38 grammes potassium persulphate 4 grammes monomers (cf. Table) 1000 grammes

Whilst the initial reactor charge was heated up to 80 °C, the reaction flask was purged with nitrogen. When the temperature reached 80 °C, and the nitrogen stream was stopped, 2.5% of the monomer pre-emulsion was added at once into the reactor. The temperature rose to about 84 °C, indicating polymerization. The

remaining monomer pre-emulsion was gradually added over a period of three hours, during which a temperature of about 84 °C was main¬ tained. After a two hour digestion period at the same time, the latex was cooled and when necessary, filtered. Latices starting from several different monomer weight ratios and surfactants as specified in the table were prepared. Latices were tested on monomer conversion, solids content and minimum film temperature, and the latex polymer films were tested on water ab¬ sorption, water spot resistance, glass transition temperature, salt spray resistance and adhesion on metal, as specified in the table. COMPARATIVE EXAMPLES A - E

The above procedure was followed, however (A) using an alkaryl sulphonate ("Humifen SF 90", a trademark) instead of the alkaryl phosphate; (B) using a different monomer composition (cf. US-A-4,968,741); (C) using both the phosphate ester surfactant and a non-ionic surfactant ("Arkopal N230", a trademark); or (D) and (E) using the commercially available latices known under trademark "Haloflex 202", respectively "Neocryl Xk62" (both ex I.C.I.). CONCLUSIONS

The examples in accordance with the invention outperformed the commercially available latices in respect of adhesion (cf. Example D) or water absorption (cf. Example E) . Both properties are highly relevant for achieving high AC performance. Both the properties regarding salt spray test and the adhesion of Example B were less than those of Examples 1-3.

Comparing Examples 2 and 3 with Example A, it is noted that use of the sulphonate-type surfactant detrimentally effects all four AC properties.

Finally, it is observed that also the additional use of a non-ionic stabiliser results in inferior AC properties (cf. Examples 3 and C) . Moreover, this latex suffered from grit-formation.

TABLE

Examples

Monomer composition (weight %)

VeoVa 9 (tm) 50 34 60 60 60 * *

VeoVa 10 (tm) 26 * *

Methyl methacrylate 20 18 17 17 17 * *

2-ethylhexyl acrylate 27 19 20 20 20 * *

Butyl acrylate 42 * *

Styrene 55 * *

Acrylic acid 3 3 * *

Surfactant (in % m/m) alkaryl phosphate .75 1.0 .5 .75 .75 alkaryl sulphonate 1.0 nonylphenol ethoxylate 2.0

Latex properties I

Conversion (% on monomer intake) 99.6 99.6 99.7 99.7 99.5 99.7 * * 0

Solid content in % 46.9 46.6 46.7 46.7 45.0 47.4 47.0 41.0 .

Minimum film forming temperature (°C) 16 11 21 22 30 23 10 30

Polymer film properties

T (°C) measured by D.S.C. 7 18 21 19 32 23 7 30 Adhesion on metal (4 days) 10 10 10 9 0 7 1 10 Salt spray (300 hours) 8 7 9 6 0 9 9 10 Water spot resistance (3 days) 10 10 10 9 9 9 + 10 Water absorption in % 11.9 13.1 8.3 14.1 10.9 10.3 9.8 14.4

* no information regarding composition is available. + film cracked.

Test methods

The glass transition temperature (T ) is measured by means of σ

Differential Scanning Calorimetry (DSC), by subjecting the polymer to a temperature range of -30 to 70 °C at a warming-up speed of 20 °C/min. The reported values are so-called second scan figures. The water absorption of latex polymer films is measured as de¬ scribed hereinafter. A wet film of 2 mm thickness is applied on a PTFE foil (the latex is kept on the foil by applying an automotive sealer on the edges of the foil) . To avoid a too fast evaporation of water and as a result severe mud-cracking the panels are covered with some water vapour transmitting material and then stored at

20 °C above the T for a week. The cover is removed after clear g films are formed. Three pieces of 2 x 2 cm are cut from the film after removal from the PTFE foil and weighed to the nearest 0.1 mg. These are stored in demineralized water at 23 °C and reweighed after 14 days (after removal of the excess of water by filter paper) . The water absorption is calculated from the observed weight increase. The results of the triplicate measurements are averaged. The water spot resistance of latex polymer films is measured as follows. A wet latex film of 200 micron is applied on a glass panel and allowed to dry for a week at 20 °C above the T . When cooled to 23 °C a drop of water is brought on the film and the panel is placed on a dark underground. After 3 days the whitening effect is visually judged. A rating between 10 (film is unaffected) and 0 (film is completely white) is given. In order to avoid evaporation of the water, the droplet is covered by a watch glass.

The conversion degree is determined by residual monomer measurement by GLC procedure (cf. VeoVa Technical Manual VM 2.1, pages 24 and 25) which measures residual monomers separately by using standard calibration of the analysis equipment for each monomer to be included in the comonomer starting mixture. The analysis should be carried out shortly after preparation of the latex.

The minimum film-forming temperature (MFT) was measured on an heatable panel having a non-porous surf ce, which panel showed a

temperature gradient over the length of the surface varying approx¬ imately 20 °C. A latex was applied to the panel to give a 60 micron wet film, and the film was allowed to dry with air flowing over the wet film. The MFT was assessed visually as the temperature below which the film begins to crack, indicating incomplete coalescence of the film.

Adhesion is determined as follows. A wet latex film of 200 micron is applied on a glass panel and allowed to dry for a week at

20 °C above the T . The panel is immersed in water at 23 °C for a g period of 4 days. After this period, the panel is roughly dried and a network of crosses is made with a metallic point. An adhesive tape is applied on these crosses. The film adhesion on metal is evaluated by pulling away the adhesive tape. A rating between 10

(film undamaged) to 0 (film totally removed from the substrate) is given.

Salt spray is determined in accordance with ASTM B117-74 for a period of 300 hours.