NO761228L - - Google Patents

Description

Surface coating method

The present invention relates to a new surface coating or measurement method which provides a coherent paint and/or protective coating which can be given a very good resistance to both chemical and mechanical influences. Although the method according to the invention is primarily intended to be used in a painting context, it can also be used for a number of other purposes such as e.g. when it.applies permanently to bind grains or powdery materials to a carrier of one kind or another.

In its general form, the method according to the invention can almost be considered to constitute a new and completely superior variation of the so-called powder painting method according to whose original idea

fine particles of a polymer that does not form a film at room temperature are added to the surface to be coated, after which the paint particles are heated to a temperature well above the polymer's lowest film-forming temperature (MFT), through which the particles are brought to melt together into a continuous layer. The heating can therefore either take place after the particles have been supplied to the relevant surface, or by their being supplied to an already heated surface. Combinations of both of these variants are also conceivable. Besides by adding the polymer particles in a dry state to the relevant surface by e.g. so-called electrostatic coating, harman too

previously proposed to supply them in the form of a sludge whose liquid component must in the event be evaporated before the melting of the particles begins. These so-called mud paints offer the advantage compared to the other powder paint variants that they are easier and cheaper to produce. A polymer slurry with a suitable particle size can be produced in a relatively simple way by passing a concentrated polymer paint

into water under intense stirring, whereby the size of the particles is determined by the recipe, the design of the equipment, the way of introducing the paint into the water and the stirring speed. It is also easy afterwards to modify the water content in such a mud paint.

An advantage of the conventional powder paints that were previously highly valued is that these, at least in their original variants, are completely solvent-free. According to a later proposed variant, however, a smaller amount of solvent is added to lower the film-forming temperature of the polymer.

In US patent 3,565,665 one is proposed. further variant according to which one first coats the surface to be protected with a porous layer containing particles of a suitable polymer material, and then subjects this layer to a solvent treatment which causes the particles to fuse together. The original porous layer is proposed to be produced by electrostatic coating or by providing the surface to be coated with a sticky adhesive layer in advance.

Each one of the methods described above has advantages and disadvantages, and the present invention now has the task of combining the good properties of all these methods and at the same time eliminating as many previous disadvantages as possible.

The heat film-forming powder paints can thus be completely solvent-free, but special methods are required, e.g. electrostatic coating, to apply them at the same time that the substrate's heat resistance limits the range of conceivable polymers, since a perfect film formation requires a heating well above the MFT of the polymer. In practice, the choice is thus limited to polymers with a low MFT value, which in turn implies relatively soft polymers with usually insufficient chemical and mechanical properties and sometimes with a tendency to co-exist on painted surfaces if these are placed in contact with each other. In the method according to the invention, however, there is no restriction for polymers with a specific MFT. There is no need to apply the polymer material in question by expensive methods of the electrostatic coating type or by special separately applied binders in this case either.

The present invention thus relates to a new type of surface coating method according to which the surface to be coated is added to a dispersion consisting of

1) a continuous phase which in most cases at least mainly consists of water, as well as in this continuous phase dispersing and/or dissolved components consisting of 2) a powdery polymer material, hereafter referred to as "main binder" since it will constitute the binder in the final coating 3) a temporary binder that occurs in a significantly smaller amount than the main binder, and which has the task of initially fixing the particles of the main binder to the substrate,

as well as non-mandatory components

4) of the type of pigment, pigment dispersant, filler, thickener, consistency regulating agent, possibly rust protection agent, etc.

After the dispersion has been applied to the relevant surface, it is allowed to dry, i.e. the continuous phase is allowed to evaporate or be driven off, e.g. by an increase in temperature.. If. drying takes place at an elevated temperature, this should be well below the MFT of the main binder. During drying, an even layer of non-film-forming polymer particles and pigment, if present, is formed. This powdery porous coating is held together and bonded to the substrate by the temporary binder. With the appropriate type and quantity of the temporary binder, the coating exhibits sufficient resistance to withstand the handling in the form of transport, stacking of the coated products on top of each other, shaking, etc. to which the coated products may be exposed before the next phase which means that the coating is exposed to a solvent. This means that a suitable solvent is added in sufficient quantity to swell, melt or sinter the particles of the main binder into a continuous layer in which the temporary binder, any pigment and any other originally added components are embedded. The exposure can take place with solvent vapor which is allowed to condense on the binder particles or by liquid solvent being added by immersion in the solvent or by brushing on, spraying or in another way. The exposure can also take place at different temperatures, whereby the particle sintering is of course favored by an elevated temperature, while the temperature must not be so high that it makes it difficult for the solvent to condense on the polymer particles.

After the sintering is complete, residual solvent is suitably driven off in such a way that it can be condensed and recovered. The method also enables a hardening of the thus produced coating.

It is also conceivable to use monomeric solvents which to some extent remain in the sintered material. polymer layer, after which the solvent in turn is polymerised, e.g. by UV irradiation.

By adding solid particles of a different nature instead of pigment, a large number of other products can be produced, which will be described later.

Among the advantages of the method according to the invention can be mentioned: 1) some dry, possibly pigmented powder does not need to be produced as this is formed by drying the dispersion.

2) The dispersion can be applied in any conventional manner.

3) The layer dries quickly due to the porosity of the surface.

4) Substrates that cannot withstand significant heating can be coated. 5) Small amounts of solvent, possibly in combination with a small amount of heating, are used to bring about the particle sintering. 6) The solvent exposure can usually be carried out under such conditions that a large part, often the main part, of the solvent can be recovered. 7) Use of a solvent gives the opportunity to provide sintering of polymers with very high melt viscosity caused e.g. of high molecular weight. Such polymers can sometimes not be sintered with. just heat. Many of these polymers are characterized by good physical and chemical properties, which gives good outdoor resistance. 8) In the method according to the invention, the viscosity of the polymer solvent layer during the sintering of the polymer particles is very high (and must be high to avoid flow). Coatings which, according to known techniques, are applied as solutions in a solvent, on the other hand, have a low viscosity as they cannot otherwise be applied. In order to obtain a reasonably low viscosity, it is therefore required that the polymers used have a low molecular weight. The polymers used according to the invention usually have a high molecular weight. If these were to be used and applied as solutions, one would have to use unrealistic amounts of solvents and still face serious application problems. In order to achieve truly durable coatings, it is essential that polymers with a high molecular weight can be used. 9) The major disadvantage of the previously described heat film-forming dispersions is that the film formation must be carried out at a temperature well above the MFT. It often encounters practical difficulties in practice to use polymers with such a high MFT as would actually be needed with regard to the properties that Mari wants from the finished coating.

In practice, one is thus limited to polymers with a low MFT value, which implies relatively soft polymers with often insufficient physical, chemical and mechanical properties, and sometimes with a tendency to stick together painted surfaces. In coating according to the invention, on the other hand, there is no limitation to MFT since the film formation takes place with the help of a solvent.

In the following, the requirements for the components included in the dispersion according to the invention will be discussed in more detail.

I. The continuous phase of the dispersion

The continuous phase is usually made up of water, but other volatile inert liquids or liquid mixtures can also be used.

II.. The main binder

As previously mentioned, the main binder must consist of a polymer which can be dispersed in the continuous phase, and which, when this is removed, later forms solid particles with a suitable grain size.

The particles thus obtained must, at room temperature, pleating be relatively hard, and the polymer should have an MFT greater than 45°C. When desired, particles with a significantly higher MFT value can be used.

a) Particle size

The particles can generally have a size of from approx. 0.2

/an up to 20 - 30 / um. Particles with a diameter of 0.2 2 µm are most applicable and also possible to produce with rational methods. By size. 0.2 - 2 / ujn it is possible to produce thin coatings, which implies good economy. Sintering is also facilitated by small particles, as the exposed surface becomes large, and the polymer does not have to travel as far to form a continuous coating. In the case of pigmented systems, particles and pigment should be of the same order of magnitude in order to achieve an even distribution of pigment in the finished coating. Many pigments lie exactly in the x range of 0.2 - 2 yum. The maximum covering power" for pigment lies at approx. 0.2 - 0.4 µm.

The upper limit for the particle diameter is therefore determined according to the above stated primarily by the reduced possibilities to produce thin layers, reduced exposure to sintering with solvent, increased difficulty in providing uniform pigment distribution. Most factors are favorably influenced by small polymer particles. There is, however, a practical lower limit of approx. 0.2^m. If the polymer particles are smaller, the temporary binder fails to fix the particles, and the polymer layer acquires insufficient holding strength before solvent exposure. The reduced effect of the temporary binder with a reduced diameter on the polymer particles can probably be explained by the fact that the reduced particle diameter gives a larger specific surface, which in turn implies a reduced amount of temporary binder per surface unit of polymer particles. With reduced particle size, there is also a tendency for cracks to form in the layer of polymer particles. In general, a uniform particle size gives a uniform particle coating according to the dispersion. drying and a uniform final coating. It is not always practical and economically possible to produce particles with a narrow particle size distribution. This particularly applies to products based on certain functional monomers. It has also proven possible to mix in a certain amount of polymer particles with a diameter well below 0.2 µm, provided that the bulk of the polymer material lies within the above stated limits.

The particle size in emulsion polymerization is primarily determined by the type and amount of emulsifier. Emulsifiers which can be used according to the invention can be of non-ionic, anionic, cationic or mixed ionic type. The emulsifiers must be adjusted so that they do not create problems when combined with the other components in the paint composition. Certain emulsifiers can also cause poor adhesion when applying paint on non-absorbent surfaces, such as metal and previously painted surfaces. The finished paint layer's water resistance, water permeability and adhesion in the presence of water are also affected by the type and amount of emulsifier. Certain emulsifiers such as special phosphate esters can also act as corrosion inhibitors. According to the foregoing, the particle size depends on the emulsifier type and amount. However, the particle size cannot be treated as an independent variable, as the choice of emulsifier takes place with regard to many different factors.

b) Particle shape

In principle, the particles can have any geometric shape. The majority of. the polymers in question are, however, produced by emulsion or bead polymerization, and then the particles obtain a spherical shape, which is generally favorable. However, it is possible to use particles obtained in other ways, e.g. during precipitation polymerization, as the particle shape can become irregular, or when grinding granular and block polymers where the particles become angular and of irregular size. It is thus possible to utilize plastic waste as a starting material.

c) The solubility of the particles

The particles must be soluble preferably in certain

commonly occurring solvents. Solvents, as well as the means of obtaining solubility, are dealt with in separate sections. d) The molecular weight of the main binder must be over 10,000 and, for most polymers that are relevant for this purpose, should be between 500,0000 and 1 million or more. A polymer with a lower molecular weight can often be used if pigment is present in the system, and this can have certain advantages since a polymer with a low molecular weight flows better with the pigment and thus allows a higher pigment content.

e) The chemical structure of the particles

According to the foregoing, the particles must have a certain hardness, e.g. indirectly expressed as MFT, solubility in solvents, and possibly also form. Particles with these properties can in principle have widely varying chemical structures. They can e.g.

be produced by polymerisation of unsaturated monomers such as methyl methacrylate or styrene, they can consist of non-crosslinked polyurethane, polyesters, polyamides, cellulose derivatives such as cellulose nitrate, cellulose acetate and other cellulose esters or esters.

According to the foregoing, it is advantageous if the particles have a spherical shape and, if possible, not too much dispersion in terms of particle size and a particle size preferably within the range of 0.2 - 2 yum. Such particles are most advantageously produced by emulsion polymerization. This technique is usually based on polymerisable unsaturated monomers, in the current raw material situation this is also the most interesting raw material group in the present context. These monomers can give homopolymers of highly variable hardness, from very soft polymers with Tg (Glass formation temperature) down to -70°C, up to hard ones with Tg > 100°C. In general, these monomers are usually named according to their properties such as softness-promoting, medium-hardness and hardness-promoting. There is no completely accepted classification except that the designations must be regarded as a linguistic aid. If several different monomers are included in one system, the classification of each individual monomer type is compared with the other monomer types depending on its properties. In addition, so-called functional monomers can be included.

Since, according to the foregoing, the polymer particles must be relatively hard, the polymer can be made up of a homopolymer of hardness-promoting monomer such as polymethyl methacrylate or polystyrene. Sometimes it may be motivated to modify the properties by co-polymerisation with a medium-hard or softness-promoting monomer, e.g. to modify to appropriate polymer hardness. When testing certain copolymers, it has surprisingly been shown that these require a very short exposure time to the solvent. Thus, a polymer based on 90% methyl methacrylate and 10% butyl acrylate requires a much shorter exposure time than 100% polymethyl methacrylate.

The so-called functional monomers, e.g. methacrylic acid and other monomers with functional groups can have different functions. They can e.g. improve the polymer dispersion's mechanical stability, which is important for applicability. They can improve adhesion to substrates, e.g. metal. They can also be used to give reactive, i.e. curable (cross-linked) polymers. The functional monomers are most often included in a few percent, sometimes up to the order of 10%. As previously mentioned, the corrosion protection ability can also be affected by the choice of monomers.

As examples of usable monomers, the following commercially usable monomers can be mentioned. The majority of caries are not used as homopolymers, but only as comonomers in various copolymers: Vinyl aromatics such as styrene, vinyltoluene and chlorostyrene. These are hardness-promoting..

Vinyl halides such as vinyl chloride and vinylidene chloride.

These are hardness-promoting.

Vinyl cyanides such as acrylonitrile and methacrylonitrile.

These are hardness-promoting.-

Vinyl esters such as vinyl acetate (medium hard), vinyl propionate, vinyl laurate and vinyl esters of "Versatic acids", which are trade names for products from Shell I Mykhetsfremmende.

Non-cyclic hydrocarbon monomers of the alkene type such as ethene, propene, butadiene, isoprene, isobutene etc. Softening agent.

Monomers based on esters of unsaturated acids such as

Acrylic acid esters, e.g. Methacrylate

Ethyl acrylate

Butyl acrylate

Hexyl acrylate

2-ethylhexyl acrylate Octyl acrylate and higher esters, all in various isomeric forms. These are softness-promoting. The softening effect increases with the increased length of the alcohol part of the ester.

Methacrylate e.g. Methyl methacrylate Ethyl methacrylate

. Propyl methacrylate

Tert-butyl methacrylate Isobuiyl methacrylate Sec-butyl methacrylate

Cyclic esters such as Benzyl methacrylate Phenyl methacrylate

Cyclohexyl methacrylate Tetrahydrofurfuryl methacrylate

Everyone in this group is hardness-promoting..

Butyl methacrylate which is medium hard Hexyl methacrylate

2-ethylhexyl methacrylate Octyl methacrylate and stretchers esters,

all in different isomeric forms.

Esters of glycol esters such as 2-methoxyethyl methacrylate

.2-ethoxyethyl methacrylate 2-methoxybutyl methacrylate

All of these are softening.

Correspondingly, esters of other polymerizable acids such as . , . ,

α-chloroacrylic acid

Itaconic acid Fumaric acid

The above-mentioned monomers can be included in suitable combinations as main monomers in polymers according to the invention. According to the foregoing, it may also be motivated to introduce small amounts of so-called functional monomers. These monomers often comprise up to 0.3-3% by weight calculated on the total amount of monomers, but in certain cases they can amount to 10 - 30% by weight . As examples of such monomers can be mentioned: Polymerizable acids such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid or monoesters of dibasic acids such as monobutyl itaconate as well as vinyl sulfonic acid, 2-sulfoethyl methacrylate and other polymerizable mineral acid derivatives.

Polymerizable amides, imides or substituted amides and imides of the above or other acids such as acrylamide, methacrylamide, dimethyloxobutylacrylamide, N-vinyl succinimide, methylolamides such as N-methylolacrylamide.

Hydroxymonomers such as hydroxyethyl methacrylate resp. -acrylate, hydroxypropyl methacrylate resp. -acrylate, hydroxybutyl methacrylate or acrylate as well as other hydroxyderivatives' of the above-mentioned polymerizable acids.

During ring opening, reactive monomers such as glycidyl methacrylate resp.

acrylate, 2-aziridinyl ethyl methacrylate resp. acrylate.

■Aminomonomers such as N-dimethylaminoethyl methacrylate resp. -acrylate, N-diethylaminoethyl methacrylate resp. acrylate, tart. butyl aminoethyl methacrylate or acrylate, quaternary monomers e.g. obtained by quaternization of the amino esters according to the above.

Polymerizable pyridine derivatives such as vinylpyridine.

Acrylonitrile and other nitriles which, according to the foregoing, are classified as hardness-promoting monomers, can also function as functional monomers.

By adding UV-absorbing monomers, a UV-absorbing effect can be achieved with the polymer.

According to the foregoing, the functional monomers can be used to induce cross-linking of the surface coating. Such cross-linking is often desirable in order to create resistance to solvent, increase heat resistance and, in general, improve the physical and mechanical properties of the final products. Such cross-linking. can be induced by a reactive group reacting with another group of the same type, for example an epoxy group from e.g. glycidyl methacrylate. This reaction is favored by catalysts. However, it is most common that cross-linking is induced by a reactive group reacting with a reactive group of a different kind, for example a carboxyl group from methacrylic acid reacts with an epoxy group from glycidyl methacrylate:

According to the foregoing, a cross-link provides improved resistance to solvent. The invention, however, assumes that the polymer must dissolve in order for film formation to be obtained. The cross-linking must therefore not take place until after the treatment with solvent. If, for example, methacrylic acid and glycidyl methacrylate are part of the same polymer particle, there is a risk of partial cross-linking. It has been found that premature cross-linking can be avoided by preparing two dispersions, for example one containing methacrylic acid and the other glycidyl methacrylate as functional monomers. The polymers individually are not cross-linked. Cross-linking also does not occur if the dispersions are mixed, since the reactive groups do not. come into contact with each other. A mixture of these particle dispersion ions can thus be applied to a surface and dried as well as exposed before solvent to form a continuous coating when the reactive groups come into contact with each other. By heat activation, cross-linking can be obtained, whereby resistance to , solvent and other effects according to the preceding is achieved. Other types of functional groups can also be utilized in this way.

It is also possible to have a functional group included in the hard polymer particles, and another type of functional group included in the temporary binder or added as a separate component.

It is also possible to cross-link.é e.g. ring-opening reactive groups by allowing a catalyst to participate in the exposure with solvent.

III. Temporary binder

a) Quantity

The temporary binder can be included in varying contents depending on the requirement for binding ability. In general terms, the temporary binder can comprise 0.5 - 25 vol.%, preferably 2 - 12%, calculated on the total amount of dry substance. The lower limit is determined by the requirement for binding capacity. The upper limit is determined by several factors. It is usually necessary for the dried layer to be porous in order for the solvent to be able to penetrate the entire layer and enable complete exposure. A very high content of temporary binder reduces the porosity and thus reduces the possibility of complete exposure with solvent, especially with thick layers.

The temporary binder can also be used as an impact strength-improving additive. Then the quantity should be greater than when it only works as a temporary binder.

b) Hardness expressed as MFT

The temporary binder is suitably, but not necessarily,

digvis, of a polymer dispersion. Certain water-soluble polymers can also be used. These can also be used to some extent as con-

consistency regulator or thickener. The best binder effect is achieved if the binder is relatively soft and sticky. The MFT of the temporary binder should also be clearly below the temperature that will prevail in the powder dirt itself during drying. This temperature can vary according to the invention. In general, the MFT should be at least 20° below the MFT of the main binder.

c) Particle size

If the temporary binder occurs in particulate form, is

the particle size is not essential for the function.. For practical reasons, among other things, from from a manufacturing point of view, it should however lie between 0.1 and 1/m, preferably between 0.05 and 0.5/un. The particle size is determined for a significant part by the type and quantity of the emulsifier included in the emulsion polymerization. This emulsifier can affect the paint composition and the final result. The particle size cannot therefore be treated as a completely independent variable.

d) Ionic activity

The particles can be non-ionic, anionic, cationic

or amphoteric character or practically applicable mixtures thereof. The particle charge must also be chosen with regard to the charge of the main binder and with regard to the charge etc. of the other components in the composition, such as pigment, thickener etc. As regards the emulsifiers that can be included in the temporary binder, the same requirements and assumptions apply as for that of the main binder

e) The chemical structure of the temporary binder

The polymer types acc. monomers, which were previously described in connection with the main binder, are generally usable for the production of temporary binders. However, the monomers must be chosen so that the MFT is lower, i.e. the polymer must be softer. This means that so-called softness-promoting monomers will dominate. So-called functional monomers, which have been described earlier, can also be included with the same functions as for the main binder particles. Functional groups from the temporary binder can also be selected in this way. that they can react with functional groups in the main binder. Thereby, as previously described, cross-linking can be provided, so that the final coating obtains solvent resistance etc.

The chemical composition of the temporary binder determines its combinability with the particles of the main binder. According to the above, the combinability can be created with the help of functional groups. An incompatibility can also be used in a positive way. The impact resistance of hard and brittle polymers, e.g. polystyrene, according to known technology, can be improved by mixing in soft polymers, usually of the elastomer type. This principle can also be utilized here, as the temporary binder has a dual function, i.e. temporary binder and improves impact strength. In this case, a larger amount is suitably used than when only the temporary binder effect is sought.

As previously mentioned, the temporary binder can be soluble in the continuous phase and is precipitated on the particles of the main binder only in connection with the continuous phase evaporating or drifting off. As examples of such water-soluble temporary binders which, by the way, can also serve as a thickener and consistency-regulating agent for the dispersion, cellulose derivatives, water-soluble acrylic polymers etc. can be mentioned.

IV. Pigment etc.

These components are not mandatory, but in most cases surface coatings are pigmented. Generally, conventional pigments etc. can be used, such as iron oxide, titanium dioxide, zinc oxide, zinc chromate, calcium carbonate, asbestos powder, talc, etc. In the same way as in conventional paints, it is important to choose pigments etc. so as to avoid unwanted side effects in combination with the other components. Positive side effects are also possible, such as ion cross-linking of the polymer using zinc. If abrasive grains are used, sanding paper, sanding discs, protection against slipping and the like can be produced. Grains of e.g. potassium chlorate, calcium perchlorate, certain powdery nitro compounds can give initial explosives, igniters for e.g. matches as well as other products that can be used pyrotechnics etc.

The pigment content should not be too high, and as a rule it should apply that the total amount of binder in the layer itself should not fall below 40 vol.%. On the other hand, there is nothing that prevents you from also mixing in slightly larger grains that will only partially lie in the finished binder layer. Only the part of these "larger grains" that lie in the binder layer should then be considered to be included in the actual ballast. Such coarse grains can be used for decorative purposes, as abrasives and in e.g. lighter sets for matches.

In conventional indoor paint, the pigment volume concentration (PVK) is approx. 50%, with conventional paint intended for outdoor painting of approx. 30 - 35%, and in the case of clear lacquer painting of approx. 20%.

With the method according to the invention, it has been established that the main binder plus the temporary binder should constitute at least 40% of the total dry substance, and of this 40%, the temporary binder should not constitute more than 25%. The total pigment content, etc. must therefore not exceed 60% of the dry matter.

V. Other additions

Additives for pigment dispersion and for regulating viscosity, thixotropy, surface flow etc. can be of the ty- . pe which is normally used in emulsion paints. These additives must be chosen in such a way as to avoid unwanted side effects in combination with other components. It is also possible to provide positive effects in combination with other components. Functional groups in the thickener' can e.g. react with functional groups in the powdery material and/or temporary binder. Thereby, cross-linking and improvement of the final product can be obtained. Likewise, the deterioration of water resistance and increase in water absorption which can be caused by thickeners, pigment dispersants etc. are eliminated or reduced. As examples of other additives, foam suppressors and UV absorbers as well as adhesion-improving (promoting) agents can be mentioned.

Placement on the relevant surface

The composition can be applied to the surface to be treated using conventional methods such as brush application, roller painting, spray painting, high pressure spraying (airless), curtain painting, rinse painting and dipping. Different substrates may require different equipment. The substrates can have flat, curved or irregular surfaces. Indentations, such as the inner walls of pipes, can also be treated. Mineral grains, gunpowder and other granulate-like material can also be processed. It is also possible to apply the method in the production of macroporous coatings or bodies such as • casting cores, grinding wheels, etc. Wire and tape coating are particularly well suited for continuous processes. The procedure can also be used for marking roads. The substrate can e.g. consists of paper, cardboard, plastic, rubber, textile, wood, metal, cement and concrete products, including asbestos cement, glass, lime, marble and other natural stone. Sometimes it may be appropriate for the substrate to be treated in advance with a suitable primer, e.g. to provide rust protection or improved adhesion.

The temperature of the substrate can vary according to type and circumstances. The method according to the invention is not strictly dependent. of the substrate temperature. At a low temperature, however, the drying time can be long and the drying possibly incomplete. These factors limit the practical lower temperature limit. Too high a temperature on the substrate can cause blisters in the coating. Drying can also be accelerated using air circulation, suitable hot air. Fast drying is particularly important for continuous coatings during factory production. The temperature in the paint layer itself must is adapted to the paint composition and vice versa. The main binder's MFT value should be 20° above and the temporary binder's MFT value should be below the temperature that prevails in the layer itself during drying.

Solvent-assisted film formation

The final film formation of the polymer particles is provided according to the invention by means of solvent or the combination of solvent and heat. The condition for film formation is, of course, that the solvent or solvent mixture manages to dissolve or swell the particles so much at the current exposure temperature that the particles can flow together and form a continuous surface coating. The dissolving ability increases with increasing temperature. A solvent can thus have insufficient dissolving ability at room temperature, but sufficient effect a few tens of degrees higher. The exposure can be carried out with solvent in gaseous or liquid form according to several methods such as dipping, spraying, blanket coating, coating, gas treatment in the vapor phase over a boiling solvent, gas treatment using air or another gas as a carrier gas. It is also possible to dissolve a polymer or other polyfunctional additives in the solvent partly to regulate the viscosity and partly so that these can have a positive effect on the final surface coating. The polymer can e.g. contain reactive groups that can react with other reactive groups in the coating and thereby cause cross-linking etc.

The solvent treatment can. is carried out using a number of different technical arrangements, among other things with the aim of optimizing the economy of the process, such as heat economy and solvent recovery. The process can be arranged for both stationary and portable use. The treatment is easily carried out at atmospheric pressure, but can be carried out at higher or lower pressure. Evaporated solvent can e.g. is supplied in a device reminiscent of the existing tri-degreasing devices by which the coated surface is held up in the solvent vapor in the upper part of the device. It is also possible to blow solvent vapor towards the surface via an inner tube, and via an outer concentric tube to suck up the excess solvent and then condense it. and/ , or reuse this.

A large number of different solvents can be used according to the invention. The boiling point can vary within wide limits depending on the technique used, type of polymer, etc. Too low-boiling solvent is more difficult to condense and places great demands on the recycling part to keep losses down. A high boiling point causes, among other things, a high exposure temperature and delays drying. A high boiling point can usually only be motivated where the polymer requires special solvents. There are thus practical limits for both the lowest and the highest boiling point of solvents. the hinge remedy. Generally speaking, the boiling point can vary between 0 and 300°C, but in most practical cases the limit is 20 - 140°C, preferably 35 - 120°C.

There must also be taken. consideration of the solvent's toxicity, flammability, explosion limits, corrosivity, stability, possible reactivity with functional groups in the polymer, etc.

List of solvents (with boiling point) usable according to the invention:

Of the above, ethanol and isopropanol are the most interesting due to their solubility properties, boiling point, price and relatively low toxicity. 2-ethoxyethanol is most applicable due to solubility properties, boiling point, price and relatively low toxicity.

Acetone and methyl ethyl ketone are particularly useful because of their solubility properties, boiling point and price.

Examples of ether

The majority of ethers can form peroxides and have a low self-ignition temperature and occasionally a narcosis effect, which to a high degree. limits the application.

Esters, especially the relatively low-boiling ones, are generally good solvents. Ethyl acetate and isopropyl acetate are the most interesting because of solubility properties, boiling point and price. The unsaturated types, i.e. vinyl esters and the methacrylates are polymerizable, which means that they can be made to polymerize in the surface coating itself. '

Examples of hydrocarbons

Pure alkanes such as n-hexane - 68.7 and n-heptane - 98.4 are usually insufficient as sole solvents.

Due to solubility characteristics, price and toxicity, cyclohexane and toluene are most applicable. Styrene and vinyltoluene are also polymerizable and can thus be brought to polymerize in the surface coating itself.

Examples of halogenated solvents

These are usually non-flammable or difficult to burn, which is often a big advantage. Decomposition of hydrogen halide can occur under certain conditions, which must be taken into account.

Methylene chloride, trichlorethylene, methylchloroform and perchlorethylene are generally the most used and most suitable solvents.

Mixtures of different solvents are also useful. Particularly useful are azidetropes of various solvents. Examples of suitable solvent combinations include:

Drying of the coating

The drying is suitably carried out in direct connection, to treatment with solvent. On the one hand, any previous heating can be utilized, and on the other hand, recovery of the solvent is facilitated. The drying temperature is highly dependent on the solvent's boiling point and also on the coating's ability to retain solvent. The use of volatile solvents facilitates the drying, which is suitably carried out by means of the circulator. the hot air. The recovery of solvent can, for example

happen by condensation in a cooler or by adsorption in a regenerable mass such as active carbon or polymeric adsorbents.

Any cross-linking or hardening of the coating

This hardening is suitably carried out directly following the drying. Curing usually requires a temperature of 100 - 175°C, sometimes lower with reactive systems, but higher temperatures can also occur. In this particular case, a heating of an already film-formed material thus applies.

The invention will now be further described in connection with the example below and explained in the subsequent patent claims.

Example 1

Two dispersions were mixed, one . containing 40% hard particles in water (main binder) and the other containing 45% soft particles in water (temporary binder).. The temporary binder part amounted. 5% of the dry volume in the mixture. The main binder was produced by a 5-stage emulsion polymerization with the following ingredients:

The particles were monodisperse with 0.40 µm diameter. Mol-<y>ectene = 1,000,000 weight mean value determined by gel permeation chromatography.

The temporary binder was produced by a 4-stage emulsion polymerization as follows:

The particle size was 0.2 µm diameter.

The mixture was applied with a brush to an eternite plate, whereby the amount was chosen so that the dried and exposed solvent for the layer would be 40 µm thick.

The coating was allowed to dry for 5 hours at room temperature, after which a white, continuous, crack-free and smooth powder coating remained. This was firmly fixed in the substrate (see example 2).

x Twéen 20 from Atlas

xx Berol 733 from Berol Kemi AB

Acetone was heated in an apparatus consisting of a long, upright net plate vessel with a cooling jacket at the top and a wide bottom and placed on a heating plate (see fig.). In this way, the vessel was filled with saturated acetone vapor above the acetone's boiling point (= 56°C) for approx. 1 cm thick layer of boiling liquid at the bottom and under the cooling jacket. The ether rivet plate with the powder layer was then dipped into this solvent vapor (but not into the boiling liquid layer) for 10 seconds. Immediately after this treatment, the surface coating<*>consisted of a non-adhesive transparent polymer film. Almost all the retained amount of acetone was evaporated within 10 minutes at room temperature, so that 10% acetone calculated on the weight of the polymer was dissolved in the layer. This remaining amount of acetone was removed by drying in an oven at 50°C for 30 minutes. The coating obtained was hard, transparent and well anchored in the substrate and had a smooth surface with a high gloss and free of cracks.

Example 2

Mixtures were prepared between two dispersions with dispersion with main binder according to example 1. Dispersion with temporary binder is shown in the table. Thus, 100 parts of dispersion mixture with dry matter content = 40%, and with a ratio between soft and hard particles of 5/95, were mixed with 67 parts of thickening solution resulting in a paint composition with 25% dry matter.

The thickening solution consisted of:

.0.85% high molecular weight hydroxyethyl cellulose x

0.5% silicone emulsion antifoam agent

99.1% distilled water.

The paint was sprayed with a membrane sprayer on eternite sheets to an amount corresponding to a 40 µm thick, dried, exposed layer. The plates were then allowed to dry at room temperature for 5 hours.

In order to judge how resistant the powder-coated, but not solvent-treated plates were to damage in the powder layer, the wear resistance was measured. The measurements were carried out in accordance with SIS 184165 as closely as possible at two points:

x - Natrosol HH 250

xx - H:10 from Dow

1) eternite plates and not iron plates,

2) 200 g of sand and not 4 kg in each batch.

The results appear in the table. The table gives the calculated glass transition temperature for the polymers. This is calculated according to the formula:

where Tg^etc. is the glass transition temperature for each of the homopolymers, and so on. is the constituent content of each monomer, the calculated minimum film formation temperature at which this could be determined experimentally is also given. For one and the same polymer, the minimum film formation temperature (MFT) is 7 - 10°C above its glass transition temperature.

As can be seen from table 1, the temporary binding agents with MFT under the drying temperature (25°C) clearly had a greater ability to hold the powder particles together. Furthermore, the temporary binder based on ethyl acrylate is clearly better than the others. All coatings were exposed with acetone according to example 1. However, the coatings with MFT 20 and 3 2°C were much more sensitive to damage in the layer before the solvent treatment. The exposed and according to example 1 post-dried coatings were transparent, hard, smooth, strongly anchored in the substrate and had a high gloss.

Example 3.

Mixtures between dispersions according to example 1 were prepared with different contents of temporary binder., 100 parts of each and every one of these mixtures was thickened by adding a thickener of the type alkali-soluble acrylic dispersion with copolymer between ethyl acrylate and methacrylic acid x, 1 part per 100 parts dispersion and was pH-adjusted with concentrated ammonia solution to a final pH of 9.

These formulations were placed with a brush on eternite plates with an amount corresponding to 40 µm thick dried, exposed layer. The drying took place for 5 hours at room temperature. To judge how much temporary binder is required to anchor the powder dispersion to the substrate before the solvent treatment was carried out

dry wear test according to example 2, see table:

It should be observed that the amount of thickener for all contents of temporary binder is 1 volume% on a dry matter basis. It has been established that the thickener also works, as temporary binder, and its amount should be added to the amount of temporary binder in order to obtain a correct value of the total amount of film-forming polymer that is active as a binder for the hard polymer particles

Attempts to apply unthickened main binder dispersion sjdn were carried out with consistently negative results.

As can be seen, the temporary binder has an effect even in very small quantities. Furthermore, the wear resistance increases continuously with an increasing amount of temporary binder, at least up to 30 of this.

When comparing the 5% temporary binder with example 2, it appears that the application with a brush gave a higher value than spraying.

The exposure took place, with acetone vapor according to example 1. The results were transparent, hard, smooth and high gloss coatings with the exception of the sample with 30% temporary binder. In this case, a coating was obtained which was film-formed and smooth on the surface, but further inside the layer consisted of unexposed particles. The mechanism with solvent vapor that diffuses into the substrate through the layer, and condenses on the substrate and exposes the film from there to the air surface, does not work in this case as it was not a matter of a porous coating, but of particles in a homogeneous phase of film-formed polymer.

Example 4

Mixtures of dispersions and formulation of unpigmented paint according to example 2 were carried out.

Placement of 55°C eternite sheets was carried out in an amount corresponding to 40^<m dried and exposed layer. The drying took place in an oven at 55°C for 2 hours. Tests were then carried out on the wear resistance according to the method described in example 2. Result:

monomers calculated Tg MFT kg sand/y^m layer thickness

As can be seen from the table, the difference in wear resistance is significantly smaller than in example 2. Furthermore, it can be read that the hardest temporary binders, which do not work at 25°C drying temperature, were now usable at elevated drying temperatures.

Exposure of the plates took place with apparatus according to example 1. Methylene chloride vapor at the boiling point of methylene chloride (54°C) was used as solvent. Exposure time = 10 seconds. The obtained coatings were strongly anchored in the substrate, high gloss, transparent as well as hard and smooth.

Example 5.

Paint formulations were made with four components:

1) Dispersion with main binder according to example .1

2) Dispersion with temporary binder with composition: 3) Pigment paste with iron oxide black according to:

4) Thickener according to example 2.

The included amounts of the four components appear from

the table. The paint was sprayed on eternite sheets in a quantity corresponding to 40ytC m dried and exposed layer. The drying took place at room temperature. The abrasion resistance was measured according to example 2, see table. The table shows the expression PVK, which indicates the volume concentration of pigment in the dried and exposed paint (pigment volume concentration). Furthermore, the expression TbVK is indicated, with which the volume concentration of temporary binder in the dried and exposed paint (temporary binder volume concentration) is indicated.

With the increased content of temporary binder, as high a pigment content as 50 PVK could provide a well-anchored powder coating. Exposure to solvent took place in the apparatus according to example 1 with acetone vapor. Due to the increasing content of non-flowing material with increasing PVK, longer exposure times are required:

Post-drying took place in an oven at 50°C for 3Q minutes.

The coatings obtained were even, hard and strongly anchored to the substrate. The gloss decreased with increasing PVK.

By removing the outermost and not completely incorporated pigment layer in the polymer with a sanding cloth, a higher gloss was obtained also on the plates with 40 and 50 PVK. These highly pigmented plates proved to be absolutely excellent for use as " blackboards", i.e. to write on with chalk and erase with an emery cloth repeatedly. They were also guaranteed to be safe from icy scraping noise.

Example 6

An acrylic dispersion was produced by 4-stage emulsion polymerization with composition:

The pH of the dispersion was adjusted to pH 9 while simultaneously adding water so that a water solution with a high viscosity and 18% solids was obtained. This solution was then used for two functions: partly as a temporary binder and partly as a thickening agent.

This occurred by adding to the main binder dispersion according to example 1 in an amount corresponding to 10% on a dry volume basis. The resulting mixture was placed with a brush on a wooden board in a thickness corresponding to 25 µm dried and exposed layer.

The plate was dried at room temperature. The resulting powder coating was strongly attached to the substrate. The solvent treatment took place by blowing through a nozzle 1-3 cm from the powder surface, and perpendicular to this, a gas mixture consisting of an azeotrope between ethyl acetate and ethanol (in the ratio 69/31) and nitrogen gas. This gas mixture was obtained by bubbling nitrogen gas through boiling liquid of ethyl acetate/ethanol in the ratio 69/31. The temperature of the gas mixture in this example was equal to the boiling point of the azeotrope = 72°C. Furthermore, the ratio nitrogen gas/solvent vapor was in this case = 1/1.

After the exposure, a hard, transpa- pure film coating on the wooden board.

Example 7

A mixture was prepared between a temporary binder according to example 1 (45% water dispersion) and a dispersion of hard, small particles - so that the temporary binder constituted 10% on a dry volume basis. The powder dispersion was produced by emulsion polymerization in 5 steps of:

The particle size was 0.18y(/Lm according to determination with extinction measurement. This method of determining the particle size takes very great account of the large particles in the system according to. where ni = number of particles with diameter Dl. The molecular weight was approx. 800,000. The mixture was thickened with a thickening agent of the polyurethane type X which was added with 2 parts of a 10% solution, per 100 parts of dispersion mixture with 40% dry matter f".'

The paint was placed with a brush on iron plates to a thickness corresponding to 30 m dried and exposed layer. The drying took place at room temperature for 5 hours. The solvent treatment took place by spraying acetone thickened with 1% high molecular weight polymethyl methacrylate with a membrane syringe to a very thin layer. After 5 minutes at room temperature, the remaining solvent was dried away in a heating cabinet at 60°C for .30 minutes. A transparent, uniform, hard and strongly anchored coating was obtained. No hint whatsoever of rust formation could be observed on the iron plate under the coating. This was probably due to the fact that the dispersion with the main binder contained a phosphate emulsifier with a corrosion-inhibiting effect.

Example 8

A mixture between the dispersion containing temporary binder according to example 1 to 8% of the dry volume in the mixture and a dispersion containing main binder was prepared. The latter dispersion was produced by a 5-stage emulsion polymerization process with the following components:

The particle size was 0.30/nm of monodisperse particles. The thickening took place with an acrylic thickener according to example 3. The paint was placed with a brush on a glass plate in a thickness corresponding to the 50 µm dried and exposed layer. The disc was dried at 50°C in a heating cabinet for 4 hours. Solvent treatment took place with the apparatus according to example 1 with methylene ketone at its boiling point (79.6°C) within 20 seconds. A hard, transparent, high-gloss coating was obtained.

Example 9

5% on a dry volume basis of the temporary binder dispersion according to Example 1 was mixed with a main binder dispersion with 40% dry matter and 0.6 x 111-sized particles. This dispersion was produced by a 2-stage emulsion polymerization with the following components: The mixture was thickened and placed on a glass plate according to Example 8. The thickness corresponded to 90 µm dried, exposed layer. The drying took place according to example 8. The solvent treatment took place for 30 seconds according to example 8. Post-drying according to example 8. A thick, uniform, glossy and transparent layer was obtained.

Example 10

A mixture between 5% on a dry volume basis of a temporary binder in dispersion with a solids content of 40% and a water-slurried powder with a particle size of 15 µm. m was produced. The temporary binder was produced by emulsion polymerization with the following components:

The powder was produced by bead polymerization of styrene. The temporary binder was also made to function as a thickener by raising the pH to 9 with a concentrated ammonia solution. The mixture was placed with a brush on a substrate of eternite to a thickness corresponding to 60 µm dried, exposed layer. The drying took place at 60°C in a heating cabinet for 2 hours. Solvent treatment took place with methylene chloride in liquid form thickened with 1% high molecular weight polymethyl methacrylate. This solution was brushed on at room temperature to a thin layer. After 20 minutes at room temperature, a transparent layer was obtained which was subsequently dried. at room temperature for 2 hours. The final layer was hard, even and well anchored to the substrate.

Example 11

A mixture between 2% calculated on a dry volume basis of temporary binder according to example 1 and a 50% water slurry of polymethyl methacrylate particles with a number-average value of approx. 20/ W diameter, but with a significant amount of particles up to 50 pm, and single cells up to 80 yU.. The thickening took place according to example. 3. The mixture was placed with a brush on eternite to a thickness corresponding to 100 dried, exposed layers. The drying was carried out at 60°C in a heating cabinet. After cooling to room temperature, brushing was carried out with 1rl,1-trichloroethane thickened with 2% high molecular weight copolymer between 70% MMA and 30% BA. After 10 minutes at room temperature, the plate was placed in a 70°C heating cabinet for 2 hours. A thick, even, transparent coating was obtained.

Example 12.

Mixtures between dispersion with temporary binder according to example 1 to 5% on a dry volume basis and dispersions containing main binder were prepared. The main binder was partly according to example 1 (1) and partly a copolymer with 70% methyl methacrylate and 30% butyl acrylate (2). The latter main binder had the same particle size and was manufactured identically to (1) •

The thickening took place according to example 3. The paints were placed with a brush on eternite plates to a thickness corresponding to 40 } xm. Drying took place at room temperature for 5 hours. The solvent partial treatment took place in an apparatus according to example 1.

Solvents, exposure times and results are listed in the table.. As. it appears from the table that the solvent must be selected according to the monomer composition of the polymer. The exposure time must be chosen with regard to both the solvent and the monomer composition of the polymer. -A "too fast" solvent dissolves the polymer far too quickly at its boiling point, which is why you get a seal on the surface whereby further necessary solvent vapor can only very slowly penetrate in the form of condensed water. liquid. A "too slow" solvent dissolves the polymer from the surface of the substrate outwards, but the particle sintering is so slow that the surface tends to become matte.

Example 13

In order to determine, among other things, how much MFT for the main binder should be above the relevant drying temperature in order for porous powder, well anchored in the substrate and with a smooth surface to be obtained, 3 mixtures with temporary binder according to example 1 to 5% of the dry volume were added. The dispersions with main binder were: A) - According to example 1 (only ethyl methacrylate as monomer) TG approx. 100°C B) Copolymer between 60% methyl methacrylate and. 40% butyl acrylate produced exactly as the main binder in example 1 and with the same particle size as this. MFT = 41°C C) Copolymer between 55% methyl methacrylate and 45% butyl acrylate according to B).• MFT =. 26°C.

The mixtures were thickened with the type and amount as in example 3. Application with a brush on glass to thicknesses corresponding to 25 and 100 µm dried and exposed layer was made of each mixture.

During the drying, which took place at 25°C and relative humidity = 50%, the following powder coating was obtained:

A) 25 m smooth, white, crack-free coating

A) 100 " " cracked

B) 25 " " " crack free

B) 100 " " " "

C) 25" partially transparent, cracked coating

C) 100" transparent, cracked coating with 2-3 mm wide, re continuous cracks from the substrate up to the air surface

The plates were exposed with solvent in the apparatus

according to example 1.

A) was exposed with acetone for 10 seconds and B) and C) with. toluene vapor for 10 seconds. A) with .25/un as well as B) with 25 p and 100 jam gave smooth, crack-free, transparent coatings. A) with 100 µm it was not possible to expose, as flakes of the paint coating bent and loosened at the first contact with the solvent vapor. C) with 25 and 100 jum gave cracked but firmly anchored coatings.

The example shows»

1) The MFT for the main binder should be 15 above. the relevant drying temperature, 2) Harder particles are less well anchored to a substrate than softer particles with the same tempo binder content.

The main binder and temporary binder and the ratio between these must therefore be chosen with regard to the relevant substrate, the relevant drying temperature and the relevant layer thickness.

Example 14

A mixture was prepared between three dispersions A,

B and C in dry volume ratio 5/60/35..

A [Dispersion A was temporary binder according to example 1.

B [Dispersion B was a copolymer between 70% methyl methacrylate and [30% butyl acrylate with particle size = 0.40 /A-m according to example 12.

C [Dispersion was prepared with 5-stage emulsion polymerization of the constituent components:

The mixture was thickened with the amount and type as described in example 7. Application with a brush was carried out on masonite boards to a thickness corresponding to 10 µm dried, exposed layer. Drying took place at room temperature. Solvent treatment took place with an azeotropic steam mixture between ethyl acetate and water (92/8) in an apparatus as described in example 1 for 12 seconds. After drying at room temperature for 5 minutes, a transparent, high-gloss, hard, even and strongly anchored coating was obtained.

x - Berol 09 from Berol Kemi AB

Example 15

Mixtures were prepared between 5% on a dry volume basis of temporary binder according to example 1 and particle dispersions containing different amounts of acrylonitrile according to the following table.

Thickening took place as described in example 2. The paint was sprayed onto iron plate to a thickness corresponding to 25µm dried, exposed layer. Drying took place at room temperature. Exposure was carried out with acetone for A and B with an exposure time of 10 and 20 seconds respectively in the apparatus according to example 1. For C, the apparatus according to example 6 was used, in which dimethylformamide vapor + nitrogen gas in a ratio of 1:1 and at a temperature of 152°C was blown onto the coating . Post-drying in an oven at 80°C for 1 hour and cooling to room temperature followed.

The layers obtained were transparent, smooth and glossy. The adhesion to the plate and the toughness of the film were so great that very sharp angles could be bent on the plate without the layer being damaged.

Example 16

A mixture between a dispersion was prepared

.containing

95% methyl methacrylate

5% glycidyl methacrylate

and with the other components and the method for the main binder in example 1 as well as a temporary binder according to examples 5 to 3-

dry volume percentage of the latter. The thickening took place as described in example 2. The mixture was sprayed onto aluminum plates to a thickness corresponding to a 35 µm dried, exposed layer. After drying at room temperature, the plates were treated with acetone vapor for 10 seconds as described in example 1. Post-treatment took place in a drying cabinet at 120°C for 30 minutes. A test of the coating's cross-linking was carried out with liquid acetone at room temperature for 1 hour. The coating was completely unswollen, which shows that the cross-linking. occurred between the oxirane groups during the heat treatment after the solvent treatment.

Example 17

Mixtures were prepared between temporary binder according to example 1 in an amount corresponding to 5% on a dry volume basis and dispersions containing copolymers in which methacrylic acid is included, see. table:

The thickening was carried out as described in example 2. The mixtures were sprayed onto glass to a thickness corresponding to 20 µm dried, exposed layer. After drying at room temperature, the plates were exposed to acetone vapor for 10 seconds, as described in example 1. After 10 minutes of drying at room temperature, a transparent, hard layer, strongly anchored to the substrate, was obtained.

Example 18

A mixture between

a) 5% on a dry volume basis of the temporary binder according to example 1 b) 75% on a dry volume basis of a dispersion with a monomer composition

90% methyl methacrylate

10% 2-ethylhexyl acrylate With the other components and the production method for the main binder according to example 1 c) A pigment paste with titanium dioxide pigment for 20 PVK with composition:

The paint, which did not need additional thickening, was applied with a brush, on eternite plate to a thickness corresponding to 35 fjiva dried, exposed layer. The drying took place at room temperature. Exposure took place for 20 seconds in acetone vapor in the apparatus according to example 1. Post-drying took place at room temperature for 2 hours. A high-gloss, even, completely covering and well-anchored paint layer was obtained.

x - Rohm and Haas Example 19

A mixture between

A) 5% on a dry volume basis of temporary binder in dispersion according to example 1. B) 80% on a dry volume basis of a dispersion with a monomer composition of 70% methyl methacrylate, 30% ethyl acrylate with the other components as well as the production method for the main binder according to example 1. C) A pigment paste containing iron oxide red pigment to 15 PVK.

The pasta's other components were as in the pasta according to example 5.

The mixture was thickened as described in example 2 and placed on chipboard to a thickness corresponding to 30 µm. Drying at room temperature. The exposure was carried out in an apparatus according to example 1 with acetone vapour. After drying for 1 hour at room temperature, a hard,<y>el anchored, shiny, uniform coating was obtained.

Example 20

A mixture was prepared with 5% on a dry volume basis of temporary binder dispersion according to example 1, as well as dispersion with the monomer composition 95% methyl methacrylate and 5% hydroxyethyl acrylate. The latter dispersion was prepared as the main binder in example 1. A thickener according to example 2 was added to the mixture. The mixture was applied with a syringe to glass plates in a thickness corresponding to 5 Gy/m dried, exposed layer. Drying took place at room temperature. Exposure occurred

by brushing methyl ethyl ketone containing

A) 13% Desmodur N 75x and 0.5% dibutyl tin dilaurate

B) 13% Desmodur N 75X

C) Only methyl ethyl ketone

The drying took place at room temperature.

In all cases, transparent coatings were obtained. One day after the solvent application, the layers were tested with liquid acetone. It turned out that A) was unswellable in acetone, B) was somewhat swellable, and C) completely soluble. In both cases A) and B), a cross-link had thus taken place between the isocyanate groups in Desmodur. 75 and the hydroxyl groups in the polymer. The cross-linking had occurred at room temperature.

x - from Bayer

Example 21

A mixture of 10% on a dry volume basis of the temporary binder according to example 1 and a dispersion containing 90% methyl methacrylate and 10% diacetonacrylamide with the other components and by the production method described in example 1 for the main binder was produced. The mixture was thickened as described in example 3. The application took place on steel wire by dipping it into the mixture. This was done by passing the thread in a slow continuous motion in an arc through the bath of the mixture. The drying took place at room temperature for 2 hours. The exposure was made by passing the thread in a slow continuous motion through vapor of azebtropene 92% ethyl acetate and 8% water at its boiling point (70.4°C). The residence time in the steam was approx. 15 seconds. The drying took place at room temperature for 1 hour. A transparent, smooth, high gloss coating was obtained. The wire could be bent at sharp angles without the coating loosening or being damaged.

Example 22

A mixture was prepared between 5% on a dry volume basis of a dispersion containing a temporary binder according to example 1 and polystyrene-containing main binder dispersions according to the following table.

The mixtures were thickened as described in example 3 and placed on masonite sheets in a thick layer corresponding to 40 µm dried, exposed layer. The drying was carried out at room temperature. Exposures were carried out with solvent as indicated in the following table in the apparatus as described in example 6 with solvent vapor at its boiling point and with the ratio pond/nitrogen gas = 1/1.

The plates exposed to Freon 11, Freon 112 and tetrahydrofuran produced completely transparent, hard, glossy, well-anchored coatings after 2 hours of drying at 70°C.

Example 23

A mixture was prepared between 5% of the dry volume of temporary binder according to example 1 and a dispersion containing 70% methyl methacrylate, 30% butyl acrylate and 0.1% of the monomer of tertiary dodecyl mercaptan. Other components and production technique were the same as for the main binder in example 1. The mixture was thickened as described in example 2 and placed on a glass plate with a brush to a thickness corresponding to 15 mm of the dried, exposed layer. The drying took place at room temperature. The exposure was with methyl isobutyl ketone vapor at its boiling point (7-6.7°C) for 15 seconds. After drying for 60 minutes at room temperature. The lower molecular weight of the main binder due to the addition of mercaptan meant that a good flow took place even in such a thin layer and with such a large particle size of the main binder (0.4 µm). A smooth, high-gloss, transparent coating was obtained.

Example 24

A mixture was prepared between 5% on a dry volume basis of a temporary binder according to example 1 and a dispersion with monomer composition = 98% methyl methacrylate and .2% of a UV-absorbing monomer

2,4-dihydroxybenzophenone methacrylate.

The other components and the manufacturing method were as described for the main binder in example 1.

The mixture was poured into a Petri dish to a thickness corresponding to 50 fjm dry exposed layer. As a reference, a sample was prepared with the mixture in example 1. Both dried powder coatings were exposed to ethyl acetate at room temperature. After drying, the UV absorption was measured in a spectrophotometer at different wavelengths. The measurements were made directly on the films after they had been removed from the glass without dissolving in the solvent. The values of the transmission converted to an exact 50^cm film thickness with Lambert-Beer's law appear in the table.

As can be seen from the table, a strong lowering of the UV transmission is obtained with this polymer for wavelengths below 370 nm.

Example 25

A mixture between 5% on a dry volume basis of a temporary binder according to Example 1 and a main binder according to Example 1 was prepared. The mixture was placed unthickened on a tightly impregnated cloth with a brush. Immediately afterwards, carborun dummy grains were sprinkled on the dispersion layer to form an almost covering monolayer. In this way, the dispersion orientated itself around the grains so that the binder was used optimally with regard to retaining the grains. The drying took place at 40°C in a heating cabinet for 2 hours. The solvent treatment took place in an apparatus according to example 1 in which acetone vapor at its boiling point was allowed to act for 10 seconds. Post-drying took place for 2 hours at room temperature. Under a microscope, it could be seen that the grains were embedded in the polymer layer to approx. 65% of the height of the grain. The grains were very strongly anchored, and the material was very suitable for grinding.

Example 26

. A mixture was prepared between 5% on a dry volume basis of a temporary binder according to example 1 and a main binder containing 100% ethyl metaxrylate with other components, dry toffee and the production method used for the main binder according to example 1. The mixture was thickened with 0.5 parts/ 100 parts 40% dispersion of acrylic thickener and pH-adjusted to pH 9 with concentrated ammonia. The mixture was placed on plasterboard on the cardboard in a thickness corresponding to 60 µm dry, exposed layer.

Immediately afterwards, decorative mineral corri were sprinkled with approx. 1 mm in diameter, so that they covered approx. 5% of the surface.

After drying at room temperature, the plate was exposed to liquid methylene chloride, thickened with 1% high molecular weight polymethyl methacrylate, which was brushed on. at room temperature. After drying for 30 minutes at room temperature, a decorative surface with well-anchored mineral grains in a glossy, transparent coating was obtained.

x - Rohagit SD-15 from Røhm

Example 27

A mixture was prepared between 5% of the temporary binder according to example 1 and 95% of the main binder with monomer composition = 85% methyl methacrylate and 15 butyl acrylate and with the other components as well as the production method used for the main binder according to example 1.

To the mixture was added 40 parts/100 parts dispersion mixture of an emulsion consisting of

10% benzyl peroxide

10% non-ionic emulsifier Berol 09 from Berol Kemi AB

80% water

The mixture was thickened according to example 3 and placed on glass plates to a thickness corresponding to 60 µm dried, exposed layer. Drying took place at room temperature. Exposure to solvent took place in an apparatus according to example 1. In this apparatus, methyl methacrylate was boiled with the addition of 0.1% hydroquinone.

The glass plates were exposed to the monomer vapor for 3 and 15 minutes respectively. The glass plates were then immediately placed in tight glass shards with a small air volume, which in turn were immediately placed in a heating cabinet at 75°C for 1 hour. After cooling to room temperature, high gloss, well anchored, transparent, hard coatings were obtained. The thicknesses were measured at 150 µm for a 3 minute exposure, and 500 µm for a 15 minute exposure. This shows that methyl methacrylate vapor at the boiling point functioned both as a solvent for the powder coating and that it reacted solidly.

Example 28

Mixtures between 5% of dry volu-. met of the temporary binder according to example 1 as well as 1) Main binder according to example 1. .2) . " " " 1+15 PVK iron oxide black pigment .

3) with copolymer between 15% butyl acrylate and

85% methyl methacrylate and with other components and preparation according to the main binder in example 1.

4) As 3), but with 15 PVK iron oxide black pigment.

The mixtures were thickened as described in example 3

and placed with a brush on eternite sheets to a thickness corresponding to 40 m dried, exposed layer. Drying took place at room temperature.

Exposure took place in the apparatus according to example 1 with methylethyl ketone vapor for 20 seconds. Post-drying took place at room temperature. As a blind test, an Eternite plate with a conventional acrylate dispersion coating was also produced. This paint consisted of a dispersion with copolymer between methyl methacrylate and butyl methacrylate with an MFT value of 28°. Furthermore, 15 PVK iron oxide black was included. This paint was applied with a sprayer to the plate which was kept at 40°C. Furthermore, the plates were dried in a 40 degree oven. All plates were conditioned for 3 days in room-temperature water^ ..Then they were subjected to a freeze-thaw test, which consisted of the plates being completely frozen into a block of ice, after which they were thawed again with room-temperature water flowing over the plates. Each cycle consisted of 20 hours of freezing in a freezer box, followed by 4 hours of thawing in water and assessment of the appearance of the plates.

The result of the experiment was that the blank remained unaffected, during 5 cycles, after which cracking and blistering occurred in the film.

In test plate 3, cracks appeared after 25 cycles. Plates 1, 3 and 4 were completely unaffected after 30 cycles.

Example 29

One mixture was prepared between three dispersions, one of which was a temporary binder of the type and quantity according to example 16.

Dispersions containing the main binder were of two types:

A) Main binder containing oxirane groups according to ex. 16.

B) Main binder containing carboxylic acid groups according to dispersion A in ex. 17.

The mixing ratio between dispersions A and B was partly such that the molar ratio between oxirane groups and carboxylic acid groups was 1/1. The mixture was thickened according to example 2 and placed on aluminum plates to a thickness corresponding to a 35 hour dried, exposed layer. The drying took place at room temperature for 3 hours. The plates were exposed to acetone vapor in the apparatus described in example 1 for 10 seconds. The plates were then dried and hardened in a heating cabinet

at 120°C. for 3 hours. The crosslinking of the coating was tested with liquid acetone at room temperature for 1 hour. The coating was slightly swollen, which shows that cross-linking had taken place between the oxirane and carboxylic acid groups during the heat treatment after the solvent treatment.

Example 30

A mixture was prepared between 95% of the dry volume of the main binder containing carboxylic acid groups according to dispersion A in example 17 and temporary binder containing 30% glycidyl methacrylate and 70% ethyl acrylate with one production method similar to that for the temporary binder in example 1. The mixture was thickened as described in example 2 and placed on aluminum sheet in a thickness corresponding to 3 5 m dried, exposed layer. After drying at room temperature, the layer was exposed to acetone vapor as described in example 1 for 10 seconds. Post-drying took place at 120°C for 3 hours. Test with liquid acetone at room temperature for 1 hour gave negligible swelling, which shows that cross-linking had taken place in the layer between the oxirane groups and the carboxylic acid groups.

Claims (20)

1. Method for surface coating products of various kinds with a continuous layer containing a polymer material that does not form a film at room temperature, which in the finished layer forms its continuous phase, and which is supplied to the relevant surface dispersed in a liquid inert to the dispersed polymer continuous phase, characterized in that said polymer, which will hereafter be referred to as the main binder, is added to the surface in question in a conventional manner for ordinary paint, together with another material of a binder nature included in the dispersion, hereinafter cold temporary binder, as well as any non-mandatory components of the type dispersant, thickener, consistency regulator end agent etc., after which the continuous phase of the dispersion is allowed to evaporate or drive off and whereby the main binder is brought to to fall out in the form of polymer particles with a diameter of 0.1-30 // m, the main part of which preferably has a diameter between 0.2 and 2 / iron, while the polymer MFT is chosen so that it is at least 20°C above that tem - pressure that prevails in the layer while the continuous phase is driven off and whereby the temporary binder precipitated together with the main binder particles whose total amount corresponds to 0.5 - 25 vol.%, preferably 1-12 vol.%, of the total amount of dry matter in the composition and whose film formation temperature is chosen so that it lies below the drying temperature, the particles of the main binder are brought to bind to the substrate with sufficiently strong adhesion forces to allow a certain handling of the thus obtained porous powder layer, and then said powder layer is exposed to a solvent which has the ability to dissolve the main binder and bring the various binder particles to flow together into a continuous layer, after which any excess solvent is washed off es and the layer obtained is dried. 2. Method according to claim 1, characterized in that the solvent chosen is one which has a boiling point of 0 - 300°C. as a rule 20 - 140°C, preferably 35 - 120°C. 3. Method according to claim or 2, characterized in that a substance is selected as temporary binder whose particle size after the removal of the continuous phase is 0.01-1 µm and preferably lies between 0.05 and 0.5 µm. 4. Method according to any one of the preceding claims, characterized in that reactive groups are added to the main binder which, after treatment with the solvent, cause cross-links. 5. Method according to claim 4, characterized in that the main binder is divided into two or more different parts which occur as separate particles in the dispersion and which each contain a different type of reactive group which are selected so that they react with each other after the different particles are sintered together by the action of the solvent. 6. Method according to any one of the preceding claims, characterized in that UV-absorbing groups are incorporated into the main binder. 7. Method according to any one of the preceding claims, characterized in that corrosion-inhibiting groups are incorporated into the main binder. 8. Method according to any of the preceding claims, characterized in that reactive groups are incorporated into the temporary binder, which after the solvent treatment can react with other reactive groups in the main binder. 9. Method according to any of the preceding claims, characterized in that a soft and elastic material, not combined with the binder, is added as a temporary binder whereby the final coating becomes a composite material with good impact strength. 10. A method according to any of the preceding claims, character! se r t by. that the continuous phase of the dispersion consists of water. 11. Method according to any one of the preceding claims, characterized in that a material which is soluble in water is added as a temporary binder. 12. Method according to claim 11, characterized in that the water-soluble temporary binder is also used as a consistency-regulating agent for the dispersion. 13; Method according to any one of the preceding claims, characterized in that added to the dispersion. consistency-regulating agent also contains functional groups which, after the solvent treatment, can react with functional groups in the main binder and/or temporary binder. 14. Method according to any of the preceding claims, characterized in that pigment, corresponding to a maximum of 50% PVK, preferably corresponding to 5 - 25% PVK, is added to the dispersion and whereby the main part of the main binder's particle size after the removal of the continuous phase .does not significantly exceed the grain size of the pigment material. 15. Method according to claims 1 - 13, characterized in that the dispersion is added to coarse grains of a decorative or other nature of up to 5 mm grain size and whereby the part of these grains that will be in the finished coating does not significantly exceed 50% of this total volume. 16. Method according to claim 15, characterized in that the large grains are of an abrasive nature, and that the final product is usable as sanding paper, sanding discs, slip protection and the like. 17. Method according to claims 1-13, characterized in that oxygen-releasing agents such as potassium chlorate or potassium perchlorate or explosive substances such as certain nitro compounds are added to the dispersion whereby the end product can constitute detonators, initial explosives, pyrotechnically applicable products, etc. 18. Method according to any one of the preceding claims, characterized in that catalysts which support the reaction between reactive groups present are added dissolved in the solvent. 19. Method according to any one of the preceding claims, characterized in that polymers possibly containing reactive groups are added dissolved in the solvent. 20. Method according to any one of the preceding claims, characterized in that the solvent is wholly or partly made up of polymerizable monomers which are caused to polymerize by a special treatment, e.g. by UV light, heat or by added initiators.