AU6845787A

AU6845787A - Coating compositions containing polyvinyl fluoride

Info

Publication number: AU6845787A
Application number: AU68457/87A
Authority: AU
Inventors: William Gerard Anthony O'Donnell
Original assignee: Plascoat UK Ltd
Current assignee: Plascoat Systems Ltd
Priority date: 1986-01-08
Filing date: 1987-01-07
Publication date: 1987-07-28
Also published as: EP0252134A1; WO1987004176A1

Description

COATING COMPOSITIONS CONTAINING POLYVINYL FLUORIDE

This invention relates to coating compositions having a basis of a fluorinated polymer comprising polyvinyl fluoride as a major component.

On account of their outstanding resistance to sunlight exposure and their excellent mechanical properties fluorine- containing polymers are of considerable interest as protective materials. Hitherto polyvinyl fluoride (PVF) has been used in film form and has been laminated to metals when these have been used in environments in which protection against weather is required. It has however proved difficult to prepare liquid solutions or dispersions of PVF and/or liquid coating compositions, polyvinylidene fluoride has generally been used rather than polyvinyl fluoride, the polyvinylidene fluoride being used in conjunction with 20 to 50% of an acrylic resin.

The present invention consists in a liquid coating composition comprising:

(a) a fluorinated polymer resin in particulate form comprising at least 50 wt. % of polyvinyl fluoride; (b) an organic liquid having a latent solvation action upon said particulate resin and present in an amount sufficient to form a heat fusible dispersion with said resin; (c) a fluorinated surfactant and (d) an organometallic stabilizer containing at least one metal selected from tin, antimony, barium, cadmium, zinc and calcium. the polyvinyl fluoride resin used in the present compositi can be used in conjunction with up to 50 wt.% of another fluorinated resin such as polytetrafluoroethylene or polyvinyli¬ dene fluoride. The fluorinated resins can be of any convenient molecular weight but should be capable of undergoing at least some solvation at elevated temperature by an organic liquid such as a lower alkylene carbonate. The latter may conveniently be a carbonate in which the alkylene group has not more than six carbon atoms. Other organic liquids are however suitable including n-methyl pyrrolidone, tri-ethyl phosphate and dimethyl acrylamide.

The fluorinated polymer resin and the organic liquid which has an elevated temperature solvating action are the main ingredients of the coating compositions of the present invention but other ingredients are also essential to achieve specific performance requirements. A characteristic of polyvinyl fluoride resin dispersions is an extremely high degree of pseudo-plasticity which derives from the electro- chemical activity of the particles. It has been found however that the incorporation of a fluorinated surfactant, typically a nonionic surfactant, is effective in reducing pseudo- plasticity. This effect is sufficiently marked as to eliminate the rheological problems otherwise encountered in applying the liquid paint to a steel substrate using conventional reverse-role coating techniques. Such an additive does not cause any undue deterioration in coating properties and has also been found to enhance the gloss of the finished coated sheet. One fluorinated surfactant which has been found particularly suitable is a nonionic surfactant comprising a mixture of fluorinated alkyl esters which can be obtained from 3M's Manufacturing Co., under the trade mark Fluorad FC 431.

A further difficulty in formulating a polyvinyl fluoride based coating material lies in the interactions which can occur between traces of fluorine or hydrogen fluoride evolved from the resin and the pigments involved. In particular, brown or pink discolourations can arise from the use of the titanium dioxide pigments present in white or light coloured materials. Various organometallic stabilizers based on Sn, Sb, Cd, Ba Zn and/or Ca have been tested and found to be effective in overcoming this difficulty to a greater or lesser degree.

Organotin and organoanti ony stabilizers have been found to be suitable, particularly organotin mercaptides, and carboxylates . Systems based on barium/cadmium, barium/zinc or calcium/zinc can also be used, as can barium and cadmium salts of carboxylic acids or phenols or mixtures of any of the above.

The organic liquid used as a plasticiser may be diluted with another organic liquid miscible therewith but inert towards the other ingredients of the composition. Suitable liquids include the mono esters of dialkylene glycol alkyl ethers such as diethylene glycol mono-n-butyl ether acetate. The compositions are conveniently prepared by blending the ingredients in a high shear mixer. In order further to control the rheological properties of the material it has been found effective to subject either the whole or some part of the production quantity to a heat treatment step. This involves heating to a pre-determined temperature for a pre-determined time whilst ensuring that the liquid is continuously and uniformly agitated. This process can conveniently be carried out in a vessel with an effective means of stirring, jacketed for heating purposes and equipped with a refluxing system. The heating step is best carried out in the presence of all or part of the fluorinated surfac¬ tant additive previously referred to and the conditions applied depend on the solvent system used and the required viscosity/shear dependence. Pigments dispersions, residual fluorinated additive and any untreated portion of the liquid are best added in a low shear mixing step subsequent to cooling after the heat treatment stage.

With respect to the proportions with which the ingre^¬ dients are incorporated, these are usually as follows:

ingredients % by Weight Preferred %s

Fluorinated polymer resin 10 - 40 20 - 35

Plasticising organic liquid 20 - 80 45 - 65

Organic diluent 0 - 50 0 - 20

Fluorinated surfactant 0.05 - 1 0.1 - 0.3

Organometallic

Stabilizer 0.5 - 2 0.5 - 1.0

Pigment as required

The compositions of the present invention can be applied to a primed substrate by conventional methods. The preferred primer is either one based on a polyvinyl fluoride organosol or is of the acrylic/epoxy or phenolic/epoxy type. It is preferable for the primer system to incorporate a corrosion preventing additive such as zinc chromate- and additionally some metallic oxide such as magnesium oxide. . When compositions formulated as described above are applied to a primed substrate and the solvents caused to evaporate a polyvinyl fluoride-containing layer having an excellent gloss finish and outstanding weathering properties is obtained. These films also possess very good flexibility which is in marked contrast with those having a basis of polyvinylidene fluoride and an acrylic resin. The following example illustrates a preferred embodiment of this invention.

EXAMPLE A PVF resin dispersion was made up as follows:

Polyvinyl fluoride resin (PVF116) 35 87 wt

Propylene carbonate 58 30

Tin ercaptide stabiliser 1 08

Hindered phenol antioxidant 0 09

Organic pigment 4 48

Surfactant Fluorad FC 431 0 18

100 00

A galvanized steel sheet substrate having a thickness of 0.7 mm was chemically passivated and coated to a thickness of 5Λ*--τ. with an epoxyphenol acrylic primer including a corrosion-inhibiting pigment.

The PVF resin dispersion was then applied to the primed substrate and cured under conditions giving a peak metal temperature of 215°C to give a smooth, well adhered and tough coating having a thickness of 25lun. the coating had good abrasion resistance and there was no evidence of discolouration. The coating was capable of withstanding a Zero T bend.

The coated substrate was subjected to a salt spray test according to ASTM B117 (1973). After 3000 hours the coating showed 5mm creep from a scribe mark.

On accelerated testing the coating was found to have a resistance to sunlight exposure equivalent to 15 years outside in a temperate zone.

Claims

1. A liquid coating composition comprising:

(a) a fluorinated polymer resin in particulate form comprising at least 50 wt. % of polyvinyl fluoride;

(b) an organic liquid having a latent solvation action upon said particulate resin and present in an amount sufficient to form a heat-fusible dispersion with said resin;

(c) a fluorinated surfactant and

(d) ^"an organometallic stablizer containing at least one metal selected from tin, antimony, barium, cadmium, zinc and calcium.

2. A composition according to claim 1, wherein the fluo¬ rinated polymer resin (a) comprises at least 75 wt. % of polyvinyl fluoride.

3. A composition according to claim 2, wherein the fluorinated polymer resin (a) comprises at least 90 wt. % of polyvinyl fluoride.

4. A composition according to any preceding claim, wherein the organic liquid (b) comprises an alkylene carbonate having up to six carbon atoms in its alkylene group.

5. A composition according to any one of claims 1 to

3, wherein the organic liquid (b) comprises n-methyl pyrolidone, tri-ethyl phosphate or dimethyl acrylamide.

6. A composition according to any preceding claim, wherein the fluorinated surfactant is a nonionic surfactant.

7. A composition according to claim 6, wherein the nonionic surfactant comprises one or more fluorinated alkyl esters .

8. A composition according to claim 6, wherein the nonionic surfactant comprises an amine perfluoroalkyl sulphonate.

. A composition according to any preceding claim, wherein the organometallic stabilizer (d) is selected from organotin mercaptides and carboxylates .

10. A composition according to any one of claims 1 to 8, wherein the organometallic stabilizer (d) is selected from systems based on barium/cadmium, barium/zinc or calcium, zinc, barium or cadmium salts of carboxylic acids or phenols and mixtures thereof.

11. A composition according to any preceding claim, wherein organic liquid (b) is diluted with another organic liquid miscible therewith but inert towards the other ingredients of the composition.

12. A composition according to claim 11, wherein the diluent comprises a monoester of a dialkylene glycol alkyl ether.

13. A composition according to any preceding claim, which comprises 10 to 40 wt.% of the fluorinated polymer resin (a), 20 to 80 wt.% of the organic liquid (b), 0 to 50 wt% of an organic diluent miscible with the organic liquid (b) but inert to the other ingredients, 0.05 to 1 wt.% of the fluorinated surfactants (c) and 0.5 to 2 wt.% of the organometallic stabilizer (d).

14. A composition according to claim 13, which comprises 20 to 35 wt.% of polyvinyl fluoride resin, 45 to 65 wt.% of the organic liquid (b), 0 to 20 wt.% of organic diluent, 0.1 to 0.3 wt.% of fluorinated surfactant (c) and 0.5 to 2 wt.% of organometallic stabilizer (d).

15. A method of making a composition as claimed in any preceding claim, wherein the ingredients are blended in a high-shear mixer and wherein at least a part of the mixture, is subjected to a heat treatment. -8-

16. A method of forming on a primed substrate a coating of a fluorinated polymer resin, which comprises the steps of applying to the substrate a layer of a composition as claimed in any one of claims 1 to 14 and evaporating the solvent.

17. A method according to claim 16, wherein the substrate is a metallic substrate primed with a polyvinyl fluoride organosol-based primer or an acrylic/epoxy or phenolic/epoxy type primer.