IL38025A - Process for the preparation of coatings - Google Patents

Description

man*? η^ηη Process for the preparation of coatings UCB S.A.

It has long been known and cusvtomary to produce paints or other coatings for decorative and/or protective purposes on the most diverse types of substrates from aqueous- dispersions of synthetic, res.insi. For this purpose, very finely divided aqueous dispersions of thermoplastic or elastomeric saturated synthetic resins are applied to the object to be coated and the water present in the dispersion is' removed by evaporation, soaking up by the support . or both at the same, time, whereby the synthetic resin particles now coming into close contact can form a continuous film. For this film-forming, a certain plasticity of the synthetic resin is required.

This plasticity can be characterized either by the hardness of the synthetic resin material or * ·.. by the film forming temperature (minimum filming temperature M.F.T.), which means the minimum temperature required for forming a continuous, homogeneous film, of the separate synthetic resin particles. This temperature can be determined, e.g. , according to the method of Th.Protzman and G.Brown, Journal of Applied Polymer Science 4, 81 (1960). A further, characteristic value is the glass tran-sition temperature T , that is the temperature above which the polymer molecules attain a certain free mobility. It approximately corresponds to the. temperature at which the polymer softens (softening point) and can be determined, next to other methods, by means of the. thermomechanical penetration method." According to this method, is derived from the penetration rate of a calibrated probe tip under constant load into the coating film heated at a linear rate of 5°C per minute. The M.F.T. in a first approximation is a linear function of the Tg.

Synthetic resin dispersions which are to form a continuous film (M.F.T. ^ room temperature) necessarily are to consist of very soft, plastic material and therefore also yield soft, not very strong coatings of low glass transition temperature. If the dispersion is composed of a harder synthetic resin (high M.F.T. and high T ,) the dispersion applied to y the substrate must be heated to a higher temperature in order to soften it above the M.F.T. and thus make · possible the forming of a film. The result after ■· cooling off is then a film of adequate continuity . which is still hard enough.

:. But in many cases, the temperatures required for this are too high for practical application, in particular when the synthetic resins are difficult to soften thermically and/or the substrates are sensitive to heat. Due to the great advantages of dispersions as paint and coating media, respecti- ·■'.,' vely,. (high content of solids - about 50 % and . high molecular weight of the synthetic resin - 5 7 from about 10 to about 10 , at still low vis- ·'■ ■:· cosity of the total dispersion, which makes for an easy and well reproducible application to the substrate; good, suitability for storage; low combustion hazard; no escaping of solvent vapors through the freshly applied coating . layer, etc.) it · is desirable, however, to make possible the application of dispersions in these cases also. The film forming temperature M.F.T. can be influenced at constant, hardness (constant T ) of the dispersed syn- ' thetic resin by other parameters also. The diameter of the dispersed particles, nature and amount of ' ' the surfactants employed and the type of substrate exert only a minor influence; but it is possible to substantially .reduce the M.F.T. by the addition of socalled plasticizers (coalescing agents) . These agents have a dissolving or swelling effect on the synthetic resin and at the same time reduce M.F.T. as well as T^. A multitude of organic solvents for · this purpose has been suggested in pertinent literature. But plastification by the addition of solvents cannot be considered a satisfactory solution of this problem, as this can only be done at the expense of several of the essential advantages in employing aqueous dispersions. The solvents previously added must be removed again after film forming in order to obtain a strong film in the -end, this requires either a. very long period of volatilization in air (during- . which the film is still soft and tacky) or furthe thermal treatment. In addition, the weight loss '. during this volatilization brings about flaws in the uniform film structure, financial losses and the 'form ing of undesirable solvent vapors.

A' test was made, e.g., to apply coatings to.-a surface by simultaneous spraying onto it of a, synthetic resin dispersion in an organic carrier liquid (of an organosol) and of a solvent optionally on basis of a monomer and to harden them there..: The disadvantages of this process consist in the fact that on the one hand, technologically complicated devices are required for the simul- '._·. taneous spraying of organosol and solvent and application by means of rollers or brushes is also impossible and, on the other hand, substantial -fluctuations in the quantity ratios of the two components bringing about irregularities in the . properties of the finished coating cannot be . prevented. Moreover, there is only . little time available for the required swelling of the synthetic resin particles by means of the solvent.

Further specified is a process for the production of coatings according to which an unsa- ... turated synthetic resin is mixed with a monomer and a suspension prepared from these two components 13· applied to metal by means of an electric field and there polymerized. The. range of application of this process is limited to specific types of . synthetic resins with a certain number of double . bonds and acid groups in the polymer molecule,-which makes for a correspondingly costly and complicated production process. Moreover, the substrates are limited to electrically conductive media and even in these, technologically elaborate devices are required for the application of the .·:■ coatings.

Object of the present invention is to create a process free of the disadvantages mentioned above and at the same time warranting the. product- . ion of uniform protective coatings of high quality by means of simple application, methods under retention of the advantages arising from the employment of aqueous dispersions.

According to the present invention, the problem is solved by mixing an aqueous dispersion of a sa-. turated synthetic resin with a polymerizable organic- liquid for swelling the synthetic resin particles, then applying this to the substrate and finally ·. hardening it there by means of polymerisation. . Optionally, pigments, fine-ly divided fillers and/ ' or other additives are added to the synthetic resin dispersion.

The addition of the liquid monomers to the./ aqueous synthetic resin dispersion prior to .. .·'' application brings about the 'desired plastification . . polymer izabie JLiq td actted.under stirrir of the synthetic resin. The s irred in liquid first ° forms an individual phase separate from the synthetic resin in the form of small droplets dispersed in wa- ie then converted ter. This state/- more or less fast depending upon the conditions - is then convortod into, more star . brie states in which the liquid is incorporated . ' into the synthetic resin particles and causes these to swell up first only on their surface but then also on their inside. While this swelled state is. characterized from the outset by the fact that at least the surface of the synthetic resin particles is swelled, without bringing about a change in the. properties of the dispersion, and is thereby made, soft and even tacky ,. respectively , the. intimate con tact between the synthetic resin particles and the liquid and the superficial plastification of the . former also occurs in the event when the liquid .,■'· added forms a separate phase at the latest after evaporation or, respectively, soaking up of the water present in the dispersion layer applied.

Once a continuous film has formed from the plastified synthetic resin grains after application, plastification can be reversed by conversion of ·'-the liquid added to the polymeric, solid form and thereby, a well-set film can be produced. This can be effected either by polymerization of the liquid employed. per se or by its graft copolymerization -onto the polymer structure of the synthetic resin employed, or, respectively, by means of both procedures taking place simultaneously.

This type of procedure not only achieves the object of the present invention, that of obtaining flawless films, from aqueous dispersions of harder, saturated synthetic resins on substrates sensitive to heat, but beyond this, it makes possible the production of . decorative and/or protective coatings with new properties not obtainable by any other method. By variation of the production conditions, in particular of the starting materials, coatings . of the most diverse chemical compositions and the . most diverse microscopic structure may be produced; this also makes possible the variation of the properties within a wide range. The advantages inherent in t;he aqueous dispersions are preserved in this to a large extent. The processibility of the disper-sions is generally little or not at all changed by the addition of monomers. The keeping properties of aqueous dispersions to which monomers have been added are divergent. They can, as has surprisingly \ been found, extend over periods of many months and even more: Where storability is short, the liquid is added to the dispersion immediately prior to · processing. The combustion hazard of dispersions to which monomers have been added is only slightly higher than that of conventional synthetic resin dispersions. Since the liquid added is not evaporated like a. solvent after the . dispersion has been added to the substrate, but instead is incorporated into' '■"· the coating, the problem of nuisance arising from potential combustible and or poisonous vapors is negligible. The process according to the present invention for the production of decorative and/or protective coatings therefore represents a new process principle of great practical significance.

A further important advantage of- the invention '■ consists in the fact that the film surfaces obtained .'; become hard and tack-free also in the presence of air. It is known that air oxygen has an inhibiting effect.. in radical polymerization reactions. The surface must /be therefore protected from air oxygen in coating films which are produced by polymerization of polymerizable or/respectively, co-polymerizable solutions. This '· type of protection is offered,# e. g. , by setting under an inert protective gas free of oxygen or by covering the surface with a paraffinic oxygen barrier such as is usual, e.g. in the polymerization of unsaturated polyesters dissolved in styrene. In the-process according to the present invention, the in- . fluence exerted by oxygen on the polymerization rate was surprisingly small and the surfaces obtained are tackfree even when hardened in the presence of air. Obviously, the macroscopic properties of the finished film surface are not affected by the influence of oxygen on the polymerization of the liquid share due to the presence in great excess of the high molecular weight synthetic resin used , as a starting material. Suitable as starting ma--,, terials for the process of■ the invention are aqueous dispersions of any type of saturated synthetic resin. The term "saturated" is intended to mean that the synthetic .resins in question do not contain any polymerizable or, respectively, co-polymerizable double bonds incorporated on pur- '· pose, such as is the case in the unsaturated poly- . ester resins or the unsaturated acrylic resins , ■ suitable' for setting by, means of exposure to. ''. ··. irradiation by electrons. The presence of trace ' amounts of olefinic double bonds formed as the result of impurities, secondary reactions in the production or by the disproportioning reaction in bimolecular chain- stopping in the course of the polymerization reaction employed in the production is not precluded in this. Moreover, the overall chemical structure of the synthetic resin is not to be restricted by this and, vice versa, the presence of a certain chemical or structural arrangement is. not required. Examples for such dispersions of sa-turated synthetic resins are aqueous dispersions .. of polyvinyl chloride resins (vinyl chloride homo- '· polymers, vinyl chloride - vinyl acetate - copoly-mers and other copolymers, of vinyl chloride) , dispersions of acrylic resins (polymers and copolymers of various acrylic or, respectively, methacrylic compounds), dispersions of polystyrene, resins (polymers and co-polymers of styrene, with e.g., butadiene, acrylic acid, etc.) and chlorinated ■rubber ·■· and polyurethane dispersions. But mixtures of two or more different dispersions which are . further processed after addition of a liquid plastifying both resins are also suitable for use.

But of course the additives conventionally used in a fu'lly compounded coating, such as pigments,, finely granulated fillers, etc., can be added to the aqueous synthetic resin dispersion employed, in addit ion to the synthetic resin functioning as a' binder, either before or after the addition of the polymeri- . zable organic liquid. Among those additives are also those which are known to change the properties of the coating film in a characteristic manner,, such as, e.g., silicones which make the film surface imper- ; meable. to water (such as, e.g., those according to Belgian Patent No.542 765.) The effect of such ...■ ·■ additives is preserved in the process according to .the present invention.

Suitable as a polymerizable organic liquid is any liquid suitable for induction of polymerization, or, respectively, graft polymerization onto the ·' synthetic resin of the dispersion used by simple and gentle methods, without using extreme reaction conditions. This particularly includes liquids con- sisting of, next to the additives required for carrying out polymerization, such as, e.g., initiators, accelerators, regulators, UV- sensibilizers, .; etc., mainly a compound or, respectively,, a mixture' of compounds, having at least one activated olefinic double bond in their molecule. These are the vinyl compounds (including the vinylidene and acrylic compounds) characterized by an olefinic double bond . = in the final position such as, e.g., vinyl acetate, vinylidene chloride, vinyl sulfonic acid,: acrylic acid, acrylte- nitrile, acrylic and methacrylic acid esters, styrene, vinyl carbazole, etc., and the allylic compounds, characterized by the group ''.

^CH - CH = CI-L , such as, e.g., the esters and ethers of allyl alcohol, as well as maleic-unsaturated t. · compounds characterized by the group -CO-.CH=CH-CO- ,'·■;. ■ such as, e.g. maleic acid and its derivatives.

From this results' a large number of potential ; combinations .. The. only limitation to the number of ·■' possible combinations of synthetic resin and the polymerizable organic liquid is imposed by the requirement of the synthetic resin being sufficient-, ly swelled by the liquid. This, in general, is the case (but not only then) when the liquid mainly or at least substantially consists of a compound, or, respectively, of a mixture of compounds having a chemical structure (not including the double. ond) ',Γ which is similar or identical to that of the synthetic resin. For this reason, it is of advantage to emplo mixtures of liquids containing a large amount of styrene for polystyrene dispersions and mixtures consisting for the major part of acrylic and methacrylic acid esters for acrylic resins. But even, when the structural similarity between the synthetic :. resin and the liquid added is lacking, there are untold possibilities for combinations also -meeting the requirement mentioned above.

The required amount of polymerizable organic liquid to be added may also be varied within a wide , range. It is subject, on the one hand, to the extent of ■ the desired, or, respectively, required plasti- !fying effect, - the more the film forming tempera- ;:V ture of the aqueous synthetic resin employed is to..' - be lowered, or has^to be lowered, respectively, the more liquid must be added, - on the other hand, it depends upon the solubility of the liquid in the . synthetic resin and the properties of the solid or. semi-solid solution formed. In general, it ranges., between i and 100 parts by- weight for each 100 parts by weight of the synthetic resin present in the. dispersion, preferably between .2 and 30 parts b weight. When adding lower .amounts than that, the effect achieved, generally speaking, is negligible,' if the amounts added are higher than that, the individual; synthetic resin' particles are converted to liquid. droplets and the system loses the properties characteristic for a dispersion of solid particles. ;■' - In rder to accelerate the transition of the system synthetic resin dispersion/liquid added to -: the stable final state previously described, namely, the complete soaking up of the liquid by the' syn-thetic resin particles and the even distribution therein, it is useful to stir thoroughly during the addition of the liquid and, · optionall , to ■ raise the. temperature at this time. If necessary, this may be done up to a temperature where the polymerizable organic liquid employed begins to boil. Reaching of the final state is also pro-moted by adding the liquid not immediately prior ... to use of the dispersion, but at a much earlier time, for practical reasons up to about 6 months prior to use. Storage in the meantime can op- . tionally be at increased temperatures for the entire period or at least parts of it. , , , in order to attain certain properties and to mini-'., mize the amount of liquid' required, not to distribute the polymerizable, organic liquid evenly over the · entire cross section of the synthetic resin particles, but to concentrate it on their surface, this may be achieved by not raising the temperature of the liquid added, but instead lowering it optionally , to the freezing point of the water at the most, and to effect the addition immediately prior to application of the dispersion.

The process according to the present invention thus possesses extreme adaptability to the conditions and the properties of the starting materials as well as to the requirements to be met by the final products. If the step of separating the admixture of the polymerizable organic liquid from the process ' step of application to. the substrate to be coated is omitted, that is to say, if the aqueous dispersion '. and the polymerizable organic liquid are sprayed on simultaneously in one operating procedure, this adap-tability is completely lost. In addition, the simultaneous application of two components in a volume · ratio constant as far as time and place are concerned (over large areas of thin coatings} is difficult to realize in actual technical practice.

After the aqueous dispersion to which the liquid has been added is applied to the respective substrate according to a known method - such as painting, pouring on, spraying on, - the water in the thin .layer applied is removed by letting it be soaked up by. the - substrate and/or by evaporation. There is the possibility, already during this process and of course.' afterwards, up to the time of complete setting, that part of the polymerizable organic liquid '.' added also volatilizes. But contrary to water, the organic compounds are present not in the form of an • individual phase-, but dissolved in 'synthetic resirt ; and therefore have a much lower %¾B¾m ; pressure and . . a lower evaporation rate even when their boiling ' , point is lower than that of water. As a result, if -, the dispersion coating applied to the substrate . .·. is quickly freed of water (e.g., if the substrate." absorbent has good soakAng- properties) and is subsequently . . set by means of a fast and heatless method (e.g. by irradiation with ultraviolet light or with high- energy rays) , the amount of evaporating, organic liquid, even when monomers with a relatively low boiling point (such as, e.g., vinyl acetate, acrylic nitrile, etc.) are employed, is 'small and does not . interfere.

If these preconditions are not met, that is to say, absorbent if the substrate has no coakin^ properties and the hardening is subsequently done slowly and at raised temperatures, the losses due to evaporation are of..: course higher. In order to fully preserve the. advantages of the method in this case, also, it is practical to work with a liquid consisting at least to a .substantial, part of higher boiling compounds dif-'· ..·' ficult to volatilize, such as e.g., hydroxyalkyl . . acrylates, hydroxya Iky1 methacrylates , acrylic or methacrylic acid esters of glycols or other poly- ·'.·'. alcohols, allylic esters, of polybasic acids, etc' According to what has been said about it so far, the process described is particularly practi- abeorbent ,cal for application on soaking' substrates, as in- , this case, the limitations concerning the use of low boiling monomers are less applicable. Suitable for use as such sic materials are a whole series of substrates such as, e.g., wood, plywood, plyboard, fiberboard.;. cardboard, paper, textiles, concrete, asbestos cement, natural stone, etc.

The last step of the process specified, namely, the polymerization or, respectively, the graft co-; .. polymerization of the organic liquid added, can be < effected according to various methods known pe se. So, e.g., it. is possible to use the thermo-catal tic hardening method in which an initiator..; .; (peroxide, an azo compound, a redox system, etc.) is added to the polymerizable organic liquid before it is added. to the synthetic resin dispersion and .. the final hardening is induced by thermal decomposition of this initiator. This method, tested in ■'.·'.:. other processes, is simple and universally applicable. But things to be put up with in this are ' that due to the' addition of the initiator, the stora-bility of the dispersion to which the liquid has been, added is lowered, that addition of liquid and Storage cannot be done at increased temperatures and that sub- strates highly sensitive to temperatures cannot be treated according to this method, as a warming up of the substrate when warming the dispersion coating to the starting temperature of the initiator can hardly be avoided. · In application to substrates sensitive to temperatures, it is practical to effect the hardening without heat, by means of ultraviolet light or high-energy (ionizing) rays. Both methods also have the advantage that the hardening occurs very quickly, ·.· within seconds o even fractions thereof. When hardening by means of UV light, the addition of a UV sensibilizer is necessary. Known sensibilizers ., . which can be used in conjunction with the present invention are: benzoin, bensphenone , anthraquinone and their derivatives, aromatic disulfides; 0-alkylxanthates , bis-xanthogen "disulfides, alpha- . haloketones, haloacetic acids and sulfonyl chlorides.. UV- induced hardening, however, is restricted to . coatings whose absorption in the wavelength range used is not so high that the undermost parts of the" coating applied are not sufficiently irradiated. For. this reason, only UV-transparent additions, such as,' . e.g., CaS04, talc, etc.-, can be used. The possible thickness of the coating is limited for the > same reason.

In ;irradiation with high-energy rays, these li- ' mitations do not apply.. No sensibilizers need be ad- ■■ ' · . * ' ■ ·'. ·. ,-' ded, the- polymerizable liquid can be added even in the inhibited state, which makes the. storability of the system practically unlimited. The same applies to ; all limitations in regard to temperature during the addition of the liquid and subsequent storage. It is also possible to harden strongly filled or, respectively, pigmented coatings even of greater thickness. Particularly advantageous is the use of irradiation by electrons with a penetratimg capacity sufficient for . penetrating- the coating layer, ' but not , or at least very little,- the substrate underneath.

. In . conventional coating thicknesses, this requires average energies of about 50 to 500 keV. If required,' irradiation can be effected- under a protective gas free of oxygen in vacuo instead of in air. \ - Polymerization of the organic liquid present in the synthetic resin particles in dissolved form is greatl facilitated in comparison to polymerization of the pure liquid, due to the gel effect. The high viscosity of the system brings about strong increases of the polymerization rates, independently of the '.· hardening being done either thermo-catalytically or by means of irradiation. Besides the polymerization of the liquid added per se which in the long run. leads to a mixture of the synthetic resin originally present with one newly formed, there occurs a graft-co-polymerization of the liquid onto the polymer structure of the synthetic esin employed, that is to say, a chemical bond between old and new synthetic resin. ■. '. While the graft co-polymerization plays but a secon- dary part in thermo-catalytic hardening and hardening '. by means of UV irradiation, as it can only occur as . the result of occasional chain transfers, it is the major reaction in hardening by means of irradiation by electrons. For in this, the chain- starting radicals are mainly formed in the polymer chain of the synthetic resin used as a starting material and the monomeric / units of the organic liquid added, are grafted onto these radical positions. But in addition to this, a .non-grafting polymerization of the liquid added per . se also occurs in the hardening by means of electrons.; In the following, the nature of the invention is explained in detail by means of examples. The range..1' of application of the present invention, however, is by no means limited by the choice of these examples.

■Fxamnlft 1: An aqueous dispersion of a methyl methacr late/-' ethyl aerylate copolymer (weight ratio of the two co- polymerization components 50 : 50) of a solid content of 40 percent by weight was mixed with 5 percent-.: by weight of ethylene glycol dimethy lac ylate . The. . · mixture obtained is completely stable. Its storability is the same" as that o.f the · dispersion used as a ' ./·. starting material. The mixture thus produced was spray- coated onto an ashwood veneered plywood board . Of- 6 mm thickness (13 x 40 cm) to form a wet coating.. up to 153 g m . This spraycoating can be' done at any . given time after the addition of the ethylene glycol/'/ dimethacrylate. After 1 minute, the water is soaked / up by. the wood support aad a flawlessly continuous, uniform but soft- coating film with a pencil hardness of 2B forms at room temperature. The sample was subsequently irradiated in air with a dose of 4 Mrad of fast electrons (I.C.T. electron accelerator, 500 keV, 20 mA. conveying speed 30 m/min) . The result is a flawless hard film with a pencil hardness of 4H.

Example 2; The dispersion of Example 1 was mixed with 5 .percent by weight of ethylene glycol dimethacry late and 0,1 % methyl ether of benzoine. This mixture is ·. as stable and storable as the one produced according to Example 1. 2 The mixture was applied to a weight of 49 g/m (determined in the wet state) to a further sample of · the substrate used in Example 1. After 1 minute, ·. the sample was irradiated for 5 minutes by a 1000 Watt HTQ-4 UV-lamp (Philips) . at a distance of 10 cm. · The result was a film with- an open- pore · structure which can.be slightly sanded to a decorative finish.. ' Example 3; .. .

The same dispersion as indicated in Example 1..·/■' was mixed with 5 percent by weight of ethylene ■ glycol dimethacry late, cast onto a plate-glass pane and exposed for 10 minutes to anair current' of 25°C. An. even but. soft coating film was formed. ..; This film was subsequently irradiated, as des- ·,. cribed in Example 1, with a dose of 4 Mrad of fast electrons. Small samples of the film were de- ■'. tached from the glass substrate prior to and afte electronic irradiation and the glass transition temperature T was determined on them according to y the thermomechanical penetration method. Wiiile. the coating film showed .a of 1.4°C prior to irradiation a Tg of 52°C. after irradiation by- electrons was found.

In a comparative test without the addition of.V.. ethylene glycol dimethacrylate, the .temperature of the forced air current had to be increased to 50°C in order to obtain a coherent film^ The' glass .' transition temperature was 45°C before as well as after irradiation by electrons.

Example 4: . '. ' '' .' Example 3 was repeated, but under supplementary addition of 0,1 percent by weight of butyl ether of benzoine and replacement of electron-irradiation by' exposure to the UV-lamp described in Example 2 for' various periods. The films produced without the addition of ethylene glycol dimethacrylate yielded a constant T^ of 45°C for all exposure times from ■ 0 to 10 minutes. The samples, produced under addition of ethylene glycol dimethacrylate yielded T values'' y of 14, 15, 19,· 26, 49, 51 und 52°C for irradiation periods of 0, 1, 2, '3, 5, 7 and 10 minutes , ' res-pectively .

Examples 5 - 7 t '.

A commercially available aqueous dispersion of a copolymer consisting of methyl methacry late, ethyl, acrylate, acrylic nitrile and acrylic acid with a solids content of 40 percent by weight, a minimum film forming temperature (M.F.T..) of 64°C and a T y of 70°C was cast onto plateglass panes under a heated forced air stream without further additions (Example 5) , the addition of 6,7 percent by weight of the conventional plastifying agent butyl glycol ·.; acetate (Example 6), or, respectively, after simultaneous addition of 6,7 percent by weight of ethylene glycol dimethacrylate and 0,08 percent by weight of. benzoyl peroxide (Example 7) . The air stream was heated to a temperature which was 5°C above the respective minimum film forming temperature M.F.T. of the mixture. The glass transition temperatures T on the coating films thus formed 9 were determined according to Example 3. The samples were subsequently heated in a hot' air stream to 140°C for 2 minutes and the weight loss ..: of the film occurring in this as well as the glass .transition temperatures T , again, were determined.; The, results are summarized in Table I.

T a b l e I: Example Addition M.F.T. Tg after 2 minutes at 140°C (°C) (°c) loss of weiqht Tq(°C) \ 5 · none .64 7P none 70 . 6 ' 6,7% butylglycol 28 53 15 % '68 acetate ;. 7 6,7% ethylene glycol dimethacrylate +0,08% benzoylper- 20 42 •0 0/ o 75 .. oxyde Example 8: The aqueous dispersion employed in Examples 5 . .to 7 was mixed with 6,7.percent by weight of ethylene glycol dimethacrylate and 0,08 percent by . weight of benzoyl peroxide and sprayed onto a plate of asbestos cement of 5 mm thickness to give a 2 coating of 85 g/m .(determined in the wet state).

By the effect of an air stream of 45°C, a continuous coating film was formed. The sample was subsequent-. ly heated in a hot air stream for 2 minutes to ' 140°C. A flawless hard film was obtained after this time .

■ Example 9; The dispersion . described in Example 1 was mixed under stirring with 6 percent by weight of a mixture of n-butyl methacrylate and ethylene glycol dimethacrylate (in a weight ratio 1 : 2). The .mixture thus obtained is completely stable and storable. After a week, the mixture thus obtained was sprayed onto an asbestos cement plate 5 mm thick (10 x 15 cm) to ^ give a coating of about 75 g/m . After an airing .' period of 2 minutes at room temperature, the sample was irradiated in air with a dose of 3 rad of fast electrons (acceleration voltage 300 kV, beam current 10 mA, conveying speed 25 m/rnin.) The result is a ' ' flawless, well adhering* crack-resistant coating.' The hardness of the coating was determined accords ing to the onig pendulum hardness method (DIN 53 157) and was 103 sec. In a comparative test without the addition of the polymerizable liquid, ■ no continuous film was obtained. In a further comparative test without the addition of the' polymery zable liquid, the film sprayed on was heated with the substrate to 60°C. The result is a flawless. " film whose pendulum hardness, however, amounts to., only 70 sec.

Example ' 10 : Example 9 was repeated, but the polymerizable liquid added consisted of a mixture of methyl acrylate and butylene glycol dimethacrylate in a weight ratio ' of 1 : 2 instead of n-butyl methacrylate and ethylene glycol dimethacrylate. The result is a flawless, ' strongly adhering, crack resistant coating with a pendulum hardness of 95 s.ec.

Example 11: .97,8 parts by weight of the dispersion described' in Example 1 were mixed under stirring with 12,2 ■.'··, ' parts by weight of a mixture of n-but l meth- ·· · acrylate and ethylene glycol dimethacrylate ( in a weight ratio of 1 : 2). The mixture thus obtained is · completely stable and storable. After a week, 60' parts of an aqueous dispersion of a polymethyl ■ ','' ' phenyl siloxane resin with a solids content of ' 15 percent by weight were added and the mixture thus obtained was sprayed on and ■ irradiated as described in Example 9. The result. is a flawless. smooth, strongly adhering and crack resistant coating with a pendulum hardness of 94 sec.

Example 12: • Example 11 was repeated, but the polymerizable liquid used- was a mixture of methyl aery late and butylene glycol dimethacr late in a weight ratio of 1 : 2 instead of the mixture of n-butyl methacrylate and ethylene glycol dimethacrylate. The result -is a. flawless, smooth, strongly adhering, crack resistant .. • coating with a pendulum hardness of 89 sec.

Example 13: '._ · Example 11· was repeated, but to the mixture of n-butyl methacrylate and ethviene glycol methacrylate, 10 percent by weight of carbon tetrachloride were added and the dimensions of the asbestos cement substrate were increased to 120 x 54 cm. The result is a flawless, strongly adhering, smooth and crack resistant coating with a pendulum hardness of 94 sec. The sample was then divided and further tests were carried out on the individual parts. The samples did not show any deteriorations either after the boiling test (24 hours' in boiling water) or after the frost, test according to ONORM B 3422 (25 f ost-thaw-cycles at 3 hours each at -20°C and 1 hour at +20°C in water).

Example 14: An aqueous dispersion of a copolymer consisting of methyl methacrylate ethyl acrylate, acrylic nitrile and acrylic acid (in weight ratio of 73 : 15 : 10 : 2) with a solids content of 36 percent by weight was- ·. ; mixed under stirring with 13 percent by weight of a mixture of methyl acrylate and butylene glycol di-methacrylate in a weight ratio of 1 : 2. The mixture, thus obtained is completely stable and storable.

After a week, .it was applied and irradiated accord-, ing to Example 9. The result is a flawless, strongly adhering and crack resistant coating with a pendulum hardness of 127 sec.

In comparative tests without the addition of the polymerizable liquid, no coherent films which adhered to their substrates were obtained even when heating the film applied, and the substrate to temperatures up to 150°C. ■ Example 15: On the basis of this example, the plastifying ; effect of the polymerizable liquid added is demonstrated:' The dispersion described in Example 1 was mixed under intensive stirring with 7 percent by weight of methyl methacry late , to which 0,2 percent by weight of a green coloring agent (Macrolex Green, GG, Bayer) had been added to enhance the visibility. This mixture was centrifuged. in an ultracentrifuge at 85 000 times ... gravity for 4 1/2 hours. After this, the dispersion-was separated into only two phases, namely, into a . top layer of water without'any color and a rubbery, ,·'·.". soft bottom layer of strongly greenish coloration.

Since methyl methacry late is lighter than water and any methyl methacry late present in a phase of -its.'-own would be separated out as the topmost layer even ... ' above the water, this proves, that all the methyl ■·..· · methacr late -.present is bonded to the acrylic . resin-dispersion .

Example 16 ; The dispersion described in Example 1 was mixed with 4, 8 percent by weight of butylene. glycol dimeth-acrylate and the mixture was sprayed onto a polyethylene film of 20C u. thickness. After drying in. an air stream, a coherent ,. uniform film with a thickness of 5C u was obtained. A piece 5 x 4 cm of the coated polyethylene film was cut out, and put into a frame and inserted in a reproducible manner into an infra red photo spectroscope. After determination of the intensity of the. C=C vibration band at 1635 cm""1", v . which is a standard for the amount of butylene glycol dimethacr late present, the film was taken . from the spectroscope and irradiated with a dose -of. 2 rad of fast electrons in. air as described in Example 1. The result was a coating film which ; strongly adhered to its substrate. Renewed deter- ... minatibn by means of the infrared spectroscope showed that 79 percent of- the unsaturation originally ' present had been used up.- . . ■ . · " ' s ■ ■■ ·■ .. ■' ■'■:■.

Example 17 : An aqueous dispersion (solids content 50 percent by weight) of a styrene resin, obtained by copolymeri- zation of a mixture of 74 percent by weight of. styrene, 25 percent by weight of butyl aery late and 2 percent by weight of acrylic acid has a minimumfilm forming temperature of 69°C. After addition of 5 percent b weight of methyl methacr late or styrene, respectively, the M.F.T. is lowered to 62 and 42°C, respectively,- corresponding to the better swelling properties of ■ the styrene. for this resin.

The styrene-containing dispersion was sprayed . onto an asbestos cement plate of 5 mm thickness. Under the. influence of a heated air current. of about 47°C, a homogeneous coating film is formed. The sample is. subsequently irradiated in air with a dose of 2 Mrad of fast electrons. The result is a hard, strongly adhering and tack-free coating film.

Example 18:' . ■; ' · .' . ■ An aqueous dispersion (solids content 46 percent by weight) of a vinyl chloride resin, obtained by' copolymerization of a mixture of 86 percent by weight' of vinyl chloride, 13 percent by weight of vinyl acetate and 1. percent by weight of maleic acid, has a minimum ■ film forming temperature M.F.T. of 36°C. The glass transition temperature T^ of an anhydrous polymer film produced from this is 52°C. To this dispersion, 6,9 percent by weight of butylene . glycol dimethacrylate were added, the. mixture was sprayed onto an al.uminum substrate and the film formed was dried at 25°C. It was subsequently exposed to irradiation, in air with . a dose of 3 rad of fast electrons. The result is a.' hard, strongly adhering film with an pendulum hardne (persoz) of 190 sec. and an Erichsen · indentation index of 90. . ·: Example 19: An aqueous polyurethane dispersion containing the poly condensation product of 200 parts by weight of polyester diol (molecular weight 400, produced ''··'. from phthalic acid anhydride and ethylene glycol) , .·· 504 parts by weight of hexamethy lene diisocyanate , 104 parts by weight of neopentyl glycol and 135' part by weight of butane diol has a film forming temperature M.F-.T. of 33°C.

To this dispersion, 10. percent by weight of di-ethylene glycol dimethacry late were added, and the mixture was poured, onto a steel sheet at room temperature. After drying at 25°C, irradiation was e -fected as described in Example 1 with a dose of 3 Mrad of fast electrons. The result is a hard, smooth coating.. : 38025/2.

Claims (16)

1. A process for producing a decorative and/or protective coating on a heat-sensitive sub-strate having absorbent properties, characterized in that an aqueous dispersion of a saturated synthetic resin as hereinbefore defined is mixed with a poiy-merizable organic liquid which is a swelling agent for said resin, said liquid consisting of a least one compound having at least one activated olefinic bond in its molecule, the mixture obtained is applied to said substrate to form a film thereon and finally the film is hardened by exposure to irradiation with electrons or to UV radiation.

2. # Δ process according to claim 1, characterised in that the aqueous synthetic resin dispersion employed is the aqueous dispersion of a polyvinyl chloride resin.

3. · A process according to claim 1, characterized in tha the aqueous synthetic resin dispersion employed is the aqueous dispersion of an acrylic resin.

4. · A process according to claim 1, characterized in that the aqueous synthetic resin dispersion employed is the aqueous dispersion of a polystyrene resin. - 3P -

5. A process according to claim 1, characterized in-'', that the aqueous synthetic resin dispersion employed is an aqueous chlorinated rubber dispersion.

6. A process according to claim 1, characterized in. that the aqueous synthetic resin dispersion employed is an aqueous polyurethane dispersion.

7. A process according to claim 1, characterized in. that the aqueous synthetic resin dispersion employed is a mixture of two or more of the aqueous dispersions mentioned above.

8. A process according to any one of the preceding -:. claims, characterized in that the polymerizable organic liquid employed is a liquid consisting mainly of a vinylic-, allylic-, or maleic-unsaturated compound,' or, respectively, a mixture of such compounds, as':', well as of the additives required for . carrying out ■ polymerization such as, e.g., initiators, accelerators, regulators, UV- sensibilizers, etc.

9. A process according to any one of the preceding · claims, characterized in that the amount of the polymerizable organic liquid added to the aqueous syntheti parts by weight for each 100 parts by weight of ' ; synthetic resin contained in the dispersion.

10. A process according to any one of the preceding claims, haracterized in that the polymerizable organic . liquid is added to the aqeuous synthetic resin dispersion' at temperatures between room temperature and the temperature at which the liquid employed begins to boil.

11. A process according to any one of the preceding claims, characterized in that the time of admixture is up to 6 months prior to the use of the mixture and that ■ the mxiture to which, the liquid has been added is kept during the entire storage period or at least during parts thereof at temperatures ranging between room temperature · and the temperature at which the liquid employed begins. -. to boil.

12. A process according to any one of the claims 1 to -9,. characterized in that the polymerizable organic liquid is mixed with the aqueous synthetic resin dispe.ra.on immediately prior to application of the dispersion to the substrate at temperatures ranging between 0°C and room temperature..

13. A process according to any one of the preceding 38025/2 liquid contains at least 30 percent by weight of higher boiling components difficult to volatilize, such as, hydroxyalkyl aerylates, hydrojtyallcyl me hacry-lates, acrylic or methacr lio acid esters of glycols and other polyalcohols,, such as, e.g., the allylic esters of polybasic acids or the like.

14. · A process according to any of the preceding , claims, characterized in that the heat-sensitive substrate having absorbent properties is wood, wooden material, cardboard, paper, textile, concrete* asbestos cement, or natural stone*

15. A process according to any one of the claims 1.to 14, characterized in that polymerization, or respectively, graft copolymerization of the polymerizable organic liquid added is effeoted by means of irradiation with ultraviolet light.

16. A process according to any one of the claims 1 to 14, characterized in that the polymerization, or, respectively, graft copolymerization of the polymerizable organic liquid added is effected by -exposure to electrons with an' average energy of 50 to 500 keV under protective gas, in vaouo, or in particular in air*