NO761010L - - Google Patents

Description

The present invention relates to a new type of film-forming polymer dispersions at an elevated temperature intended for the surface coating of primarily absorbent substrates of various types which have in common that they at least withstand a certain heating above room temperature.

Thanks to their many good properties and their relatively low price, such polymer dispersions have already found a relatively extensive application for several years, including for coating asbestos cement sheets, cast cement products of various kinds as well as cardboard and paper products. The commonly used method has involved adding the dispersions to the already heated substrate, whereby the continuous phase of the dispersion, which in the vast majority of cases consists of water, leaves or is absorbed by the substrate, while the polymer particles are made to float together into a coherent film. This method is both quick and simple, and in the case of products that are to be heated for other reasons, e.g. when autoclaving asbestos cement sheets, it is easy to carry out the surface coating in connection with this heating.

The fact that the polymer dispersions that give the hardest coatings also require the highest temperatures to form a film has . however, this has led to the fact that up until now, one has always had to choose a compromise between the desire for a permanent coating and a dispersion which forms a film already at a relatively limited temperature rise above room temperature.

A frequently recurring problem with surface coatings produced in this way is also that the obtained polymer film often sticks to other surfaces coated in the same way. The problem usually manifests itself in color damage occurring if the products are stored paint layer against paint layer. The damage occurs when one layer of paint follows the other and wears away from its original substrate when the products are separated from each other. High pressures, high temperatures and a high humidity in the surrounding atmosphere favor the appearance of such stickiness. Above all, the sticking problem has been difficult to deal with when it comes to asbestos-fibre-reinforced cement sheets surface-coated in this way, because with the type of mass production involved, it is practically impossible to avoid storing the products on top of or they against each other. The specific weight of the plates also means that very high pressures can be a problem in such a stack of plates at the same time that very high temperatures can occur inside it in the summer.

In the case of the polymer dispersions used up to now, the adhesion tendency of the film obtained has been directly proportional to the dispersion's film formation temperature (MFT=Minimum Filmformation Temperature), which in turn can be directly derived from the glass transition temperature (Tg) for the homopolymers of the constituent monomers. In order to achieve a continuous film with certainty, the application must take place at a temperature that is several degrees above the MFT of the dispersion.

It is of course possible to choose a dispersion with a high MFT in order to thereby avoid adhesive damage to the finished products, but in that case this entails extra trouble and costs with regard to heating devices and also cooling devices. You are also often forced to use a dispersion with a lower MFT than you would like to avoid damage to the substrate. This applies, among other things, to asbestos cement products that cannot withstand excessively high temperatures.

Various methods have previously been tried to produce dispersions with reduced stickiness despite a relatively low MFT value. It is thus described in the literature that adhesion can be eliminated by cross-linking the polymers. In certain cases, however, very high temperatures are required for a longer period of time for this mechanism, which entails high costs. There is also an obvious risk with a continuous belt process that the polymer film will not cross-link completely, after which residual moisture or a relatively high temperature when stacking the finished products easily causes cross-linking between the paint layers, which of course in such a case increases the degree of paint damage instead of to

lower it.

It is also previously known that conventional anti-adhesive agents such as calcium stearate, lead stearate, aluminum stearate, silicones or certain surfactants can be applied after the surface coating in order to eliminate the problems with adhesion in this way. However, the disadvantages of such a method are, in addition to the costs, that these additional surface coatings in certain cases give rise to white, spotted or flamed discoloration of the products.

When surface coating asbestos-cement sheets with polymer dispersion, there is also a problem with so-called lime scale. These occur when calcium hydroxide penetrates primarily through damage in the polymer layer to its surface, and where the calcium hydroxide on contact with the carbon dioxide of the air turns into poorly soluble calcium carbonate which is precipitated in the form of white, flaming coatings. Another problem that often occurs with asbestos-cement sheets is frost cracking. Apart from damage to the paint layer, the scale deposits must be attributed to a polymer film that is too open to diffusion, depending on the size of the polymer particles as well as the film's salt content and the type of surfactant included. The frost blasts, on the other hand, are a direct consequence of an overly diffusion-tight polymer film.

The present invention relates to an improved type of film-forming polymer dispersions with which one has succeeded in eliminating the problems described above. It has surprisingly been shown that it is possible to produce acrylate-based polymer dispersions which give a film with a significantly lower stickiness than previously had reason to suppose that it would be possible to produce these components with. consideration of Tg for the homopolymers of the constituent monomers.

In addition to the monomers, which are thus predominantly made up of acrylates, the finished dispersion also includes initiators and emulsifiers (surfactants) and, of course, a continuous phase whose main part is made up of water.

In the production of acrylic dispersions, different monomer combinations are usually used, usually consisting of a softness-promoting monomer in combination with a hardness-promoting monomer, e.g. ethyl acrylate/methyl methacrylate, butyl acrylate/methyl methacrylate or 2-ethylhexyl acrylate/styrene. As a rule, the monomer combinations are stabilized with acrylic and/or methacrylic acid or itaconic acid. The terms softness-promoting, medium-hard and hardness-promoting monomers are generally used. However, there is no fully agreed classification of which monomers should be attributed to which group, since the designations mostly indicate the effect the monomer has on the combination in question. To which group a certain monomer. is to be attributed in a certain special case thus partly depends on which and which other monomers it is combined with. It is also well known that one can theoretically calculate Tg (the glass transition temperature) for different copolymers according to the general formula adopted below:

where m^ M2mn= parts by weight of constituent monomer while Tq Ta T =9lass transformation temperature for respective monomers expressed in K.

A commonly used rule of thumb further states that the MFT is 9 - 12PC higher than the calculated Tg value.

Since the Tg values are determined experimentally, slightly different values can be obtained depending on how the experiments are carried out. In the literature, one can therefore find several different Tg values for one and the same compound. In the table above, some are collected that are considered to be the representative Tg value.

It has now surprisingly been found that the formula I does not generally apply to all monomer combinations, and that this has a very great importance when it comes to producing film-forming polymer combinations with a relatively low MFT (e.g. 20 - 60°C) combined with a low stickiness, which was previously considered completely impossible because previously it was always considered necessary to use a composition with a high MFT in order to obtain a really low stickiness.

It has thus been found that, under certain conditions, one combines a soft monomer in the form of one or more ethyl- or methyl-substituted branched esters of acrylic acid whose chemical formula comprises a total of 7-12 (preferably 8-10) carbon atoms in the alcohol part with one or more straight-chain hard monomers, then a larger amount of the soft branched monomer is required for the combination to have a certain MFT than what should generally have been necessary according to formula I. This discovery has made it possible to produce monomer combinations that form films at a rela- , tively low temperature, but despite this has a very small adhesive flexibility.

The above applies e.g. for the combinations 2-ethylhexylacrylate/methylmethacrylate and 2-5 dimethylhexylacrylate/methylmethacrylate. Despite the 2-ethylhexyl acrylate's low Tg value (-55°C), in this case significantly more of this soft monomer is required in relation to the methyl methacrylate than would have been required in a similar case for the significantly harder n-butyl acrylate (-45° C) to give a combination with the same MFT.

It has also been found that there are certain possibilities to further lower the film formation temperature for polymer dispersions of the type currently in question by adding a water-soluble temporary solvent with a suitable boiling point to the prepared dispersion. An addition of such a temporary solvent, which can be included in a content of up to 8% calculated on the dry substance of the polymer part, has been shown to be able to significantly lower the film formation temperature without weakening the film obtained or increasing its tendency to stick. . By exploiting this discovery, it is thus possible to produce polymer dispersions that form films at a lower temperature than what is indicated by their MFT. This is particularly valuable when it comes to producing polymer coatings that can withstand significant heating without exhibiting increased adhesion.

Temporary solvents that have proven to work excellently in this context are primarily hexylene glycol and diacetone alcohol. Butyl glycol, butyl diglycol and butyl glycol acetate also work as MFT reducing agents, but these solvents in many cases exhibit a slightly too great combinability with the polymer.

It has also been found that it is extremely important that the right type of surface-active substances or surfactants are added to the dispersion as an emulsifier, since it has been shown that certain surface-active substances have a negative effect on the polymers formed during the polymerization and thereby also on the produced polymer film. After the polymerization is completed, surface-active substances are found in the water phase and around each polymer particle in the dispersion there is a layer of such surface-active substance, or surfactant. When film formation occurs, the particles are pressed against each other and form a cohesive unit. Surface-active substances are initially present in the boundary surfaces and cavities between the particles. Certain of these, and primarily those with a nonionically active character, such as nonylbenzene polyglycol ether, however, show a noticeable combinability with pure acrylic and acrylic styrene or acrylic vinyl acetate polymers. This combinability immediately gives rise to an increased tendency to stick to the film, as the surfactants will act as plasticizers on it.

There it has been found that this latter problem can be avoided by choosing . surfactant. It has been found that its hydrophobic part should be made up of an alkyl, aryl, alkylaryl or other similar organic group, while its hydrophilic group should be made up of a sulphate, sulphonate, phosphate or other mineral acid derivative. This results in an ion-active emulsifier which does not show any noticeable combinability with the polymer. The surfactant will thereby be adapted to the cavity between and the surface of the particles.

In comparative experiments, it has been established that also

completely conventional polymer compositions such as ethyl acrylate/methyl acrylate and butyl acrylate/methyl acrylate show a noticeable reduction in the tendency to stick if one replaces a conventional type of nonion active surfactant or a combined nonion-anion type surfactant with the surface-active substance of the type described above.

As previously stated in the preamble, there are also certain special problems when it comes to surface coating asbestos-cement sheets with a polymeric surface layer. Of these problems, it is primarily limescale on top and the frost blasts on the panels' top surface layer and attached polymer layer that have been difficult to deal with. There is. now found that in order to avoid limescale and frost blasts, in addition to the choice of monomers and t.ensiders, it is also critical that the dispersion contains a certain amount of surfactant and a certain amount of salt. This results in a polymer film with suitable diffusion density combined with water absorption. Calculated on a solid polymer substance, the previously described surfactants should amount to 1.0 - 4.0% by volume.

In order to provide good lime resistance, the polymer dispersion must also contain a certain amount of salts which, together with calcium, give more or less poorly soluble compounds. Examples of suitable salts include potassium persulphate, ammonium hydrogen phosphate, ammonium phosphate, sodium pyrosulphite, disodium hydrogen phosphate and sodium dihydrogen phosphate. It has been found that the critical salt content corresponds to 0.1 - 2.0 v-% calculated on the dry polymer substance. A certain amount of salt can e.g. included in the initiators used, but as a rule a further addition of salt is required to provide a completely good lime safety. As described above, the salts and tensides of the type characteristic of the invention are transported to boundary surfaces and cavities between the particles. When acrylic dispersions of the type characteristic of the invention are applied to asbestos-cement substrates, a certain part of the salt and surfactant content reacts spontaneously with calcium from the cement, and this gives the polymer an excellent anchoring to the substrate. During continued aging (carbonation), calcium hydroxide penetrates towards the cavities between the particles and along their boundary surfaces. By reaction with the salts and surfactants characteristic of the invention, however, the calcium hydroxide is converted into poorly soluble compounds already before it has reached the surface of the paint layer, thereby preventing its further penetration of the paint layer, whereby the appearance of lime scale is effectively made impossible.

Certain particularly advantageous monomer combinations appear in table II below, while the invention as a whole is defined in the subsequent patent claims and exemplified in a large number of examples which follow immediately after the table.

Corresponding percentage compositions also apply if the dimethylhexyl acrylate is replaced with 2-ethylhexyl acrylate. Of course, the surface coating according to the invention can be colored by adding conventional pigment in the desired amount in a known manner.

Execution example

Examples 1-12 below illustrate the preparation of a number of dispersions according to the invention as well as the preparation of some comparison dispersions. Example 13 initially illustrates the preparation of the paint pigment used in attempts to pigment the surface coating compositions, while examples 13 - 28 illustrate how the surface coatings were tested. Finally, the test results are illustrated in a table.

Step 3

Execution

Distilled water, emulsifier and initiator at a temperature of 45°C were introduced into a 3-liter wooden-necked flask equipped with stainless stirrer, reflux condenser, thermometer, introduction device for nitrogen gas and immersed in a tempered water bath at 50°C, followed by monomer mixture. 1 was added. The temperature rose to approx. 65°C, after which the mixture was cooled. When the temperature reached 55°C, the components of step 2 were added, then the temperature was maintained at 60°C during the one hour post-reaction. Afterwards, stripping with nitrogen gas was carried out for 30 minutes to remove any unreacted monomer. The batch was cooled to room temperature, filtered and pH adjusted with 25% ammonia to pH 9.5.

Analysis values

Example 2.

In a 3-liter wooden-necked flask equipped with a stirrer, reflux condenser, thermometer, dropping funnel, inlet for nitrogen gas and placed in an 80°C water bath, 1200 g of distilled water, 40 g of a mixture of phosphoric acid mono- and diesters of nonylbenzene polyglycol ether in the form of potassium salt present as 40% active content, 4 g of potassium persulphate and 6 g of disodium hydrogen phosphate. When the contents of the flask reached a temperature of 67°C, a mixture of 512 g of methyl methacrylate, 272 g of 2-ethylhexyl acrylate and 16 g of methacrylic acid was added dropwise over the course of 2 hours and under a nitrogen atmosphere. Due to heat of reaction, the temperature rose to 84°C. For

to complete the polymerization, the temperature was kept at 80°C for 2 hours. The batch was cooled to 25°C and adjusted with 25% ammonia to pH 9.5. While stirring, 61.5 g of diacetone-alcohol-water mixture 1:1 was added to half the batch.

Analysis

Example 3

1200 g of water (dist.), 12 g of sodium dodecyl sulphate, 4 g of potassium persulphate and 2 g of sodium pyrosulphite were introduced into a 3 liter three-necked flask equipped with a stainless stirrer, reflux condenser, thermometer, dropping funnel and intake for nitrogen gas. The flask was immersed in a water bath with an immersion element as a heat source and set to a temperature of 60°C. When. the temperature of the flask contents reached 40°C, a monomer mixture of 432 g methyl methacrylate, 352 g butyl acrylate and 16 g methacrylic acid was added dropwise over the course of 1 1/2 hours. The temperature rose in the flask during the dropwise addition with a highest value of approx. 67°C. After finishing the monomer addition, the temperature was kept at 60°C for one hour. Stripping with nitrogen gas for 1/2 hour to remove any unreacted monomer was then carried out. The batch was cooled, filtered and pH-adjusted with 25% ammonia to pH 9.5.

Analysis values

Example 4

1100 g of distilled water, 12 g of sodium were introduced into a 3 liter wooden-necked flask equipped with a stirrer, reflux condenser, thermometer, dropping funnel, inlet for nitrogen gas and placed in a 60°C water bath. umdodecyl sulfate, 4 g of potassium persulfate, 2 g of sodium pyrosulphite and 6 g of ammonium hydrogen phosphate. When the contents of the flask reached a temperature of 42°C, a mixture of 472 g of methyl methacrylate, 304 g of 2,5-dimethylhexyl acrylate and 24 g of methacrylic acid was added over the course of 2 hours and under a nitrogen gas atmosphere. Due to the heat of reaction, the temperature rose to 65°C. To remove residual monomer, the temperature was maintained at 60°C for 2 hours. The batch was cooled to 25°C and adjusted with 25% ammonia to pH 9.5.

Analysis

Example 5

In a 3-liter wooden-necked flask equipped with a stainless stirrer, reflux condenser, thermometer, dropping funnel and inlet for nitrogen gas, 1200 g of water (dist.), 12 g of sodium dodecyl sulfate,

18 g of nonylbenzene polyglycol ether (10 glycol units), 4 g of potassium persulfate, 2 g of sodium pyrosulfite and 6 g of disodium hydrogen phosphate. The flask was immersed in a water bath with immersion element as heat source and set to a temperature of 60°C. When the contents of the flask reached a temperature of 40°C, a mixture of 440 g of styrene, 336 g of 2-ethylhexyl acrylate and 24 g of acrylic acid was added over the course of 1 1/2 hours. The temperature in the flask rose during the addition to ea. 6 5°C. When all the monomer had been added, the temperature was held at 60°C for one hour. After that. stayed there. purged with nitrogen gas for 1/2 hour to remove any unreacted monomer. This was followed by cooling, filtration and pH adjustment to pH 9.5 with 25% ammonia. Analysis values

Example 6

In a 3-liter wooden-necked flask equipped with a stirrer, reflux condenser, thermometer, dropping funnel, intake for nitrogen gas and placed in an 80°C water bath, 1050 g of distilled water, 24 g of Na-octyl sulfate, 6 g of potassium persulfate, 4 g of ammonium phosphate were added. that in the flask reached a temperature of 67°C, a mixture of 496 g of methyl methacrylate, 288 g of dimethylhexyl acrylate and 16 g of methacrylic acid was added over the course of 2 hours and under a nitrogen gas atmosphere. Due to the exothermic reaction, the temperature rose to 84 - 86°C. To complete the polymerization, the temperature was kept at 80°C for 2 hours. The batch was cooled to 25°C and adjusted with 25% ammonia to pH 9.5. While stirring, 37.5 g of hexylene glycol-water mixture 1:1 was added to half the batch.

Analysis

Example 7.

1125 g of distilled water, 96 g of sodium, the salt of nonylbenzene sulphonate (25% water solution), 6 g potassium persulphate and 3 g of sodium pyrosulphite. When the contents of the flask had reached a temperature of 44°C, a mixture of 408 g of methyl methacrylate was added over the course of 2 1/2 hours and under a nitrogen atmosphere.

376 g of 2-ethylhexyl acrylate and 16 g of methacrylic acid. Because of it

exothermic reaction, the temperature rose to 67°C. To complete the reaction, the temperature was maintained at 60°C under increased nitrogen gas flow for 2 hours. The batch was cooled to 25°C and adjusted by 25%

ammonia to pH 9.5.

Analysis

Example 8

In a 3-liter wooden-necked flask equipped with a stainless stirrer, reflux condenser, thermometer, dropping funnel and inlet for nitrogen gas, 900 g of distilled water, 96 g of sodium salt of nonyl-benzene sulfonate (25% water solution), 4 g of ammonium nitrogen phosphate, 4 g of potassium persulfate and 6 g of dinate 4 g of potassium persulfate and 6 g of disodium hydrogen phosphate. The flask was immersed in a water bath with immersion element as heat source set at a temperature of 80°C. When the temperature of the flask contents had reached 60°C, a mixture of 528 g of methyl methacrylate, 256 g of butyl acrylate and 16 g of acrylic acid was added dropwise over the course of 1 1/2 hours. The temperature rose in the flask during the addition to approx. 84°C.. When all the monomer had been added, the temperature was held at 80°C for 1 hour. Then, a purge with nitrogen gas was carried out for 1/2 hour to remove any unreacted monomer. The mixture was then cooled, filtered and pH adjusted to 9.5 with ammonia. While stirring, 36 g of hexylene glycol/diacetone alcohol 50/50 water mixture 1-1 was added to half the batch.

Analysis

Distilled water, emulsifier and initiator were added to a 3-liter wooden-necked flask equipped with a stainless stirrer, reflux condenser, thermometer, intake for nitrogen gas and immersed in a tempered water bath at 50°C. At a temperature of 45°C, monomer mixture 1 was added. The temperature rose to approx. 65°C, after which the mixture was cooled. When the temperature reached 55°C, the contents of step 2 were added. The same procedure was used in steps 2 and 3 as in step 1. The temperature was kept at 60°C for 1 hour. Stripping with nitrogen gas was carried out for 1/2 hour to remove any unreacted monomer. The batch was cooled to room temperature, filtered and pH-adjusted with ammonia to pH 9.5.

Analysis values

Example 10

945 g of distilled water, 40 g of a mixture of phosphoric acid mono- and diesters of nonylbenzene polyglycol ether were added to a 3-liter wooden-necked flask equipped with a stirrer, reflux condenser, thermometer, dropping funnel, intake for nitrogen gas and placed in an 80°C water bath potassium salt present as 40% active

content, 72 g of the sodium salt of nonylbenzene sulfonate (25% water solution.), 2 g of potassium persulfate. When the contents of the flask had reached a temperature of 66°C, a mixture of 552 g of styrene was added dropwise over the course of 2 hours and under a nitrogen gas atmosphere,

216 g 2-ethylhexyl acrylate, 32 g acrylic acid. The exothermic reaction gave a rise in temperature to 83°C. To complete the polymerization, the temperature was kept at 80°C for 2 hours, after which the nitrogen gas flow was increased for 1/2 hour to remove the last monomer residues. The batch was cooled to 25°C and adjusted with 25% ammonia to pH 9.5. While stirring, 37.0 g of butyl-glycol-water mixture 1:1 was added to half the batch.

Analysis

Example 11

In a 3-liter wooden-necked flask equipped with a stirrer, reflux condenser, thermometer, dropping funnel and inlet for nitrogen gas,

introduced 1200 g of water (distilled), 12 g of sodium dodecyl sulfate, 4 g of potassium persulfate and 4 g of sodium hydrogen phosphate. The flask was immersed in a water bath with immersion element as heat source and set to a temperature of 80°C. When the temperature of the flask contents reached 60°C, a monomer mixture of 464 g of methyl methacrylate, 320 g of isodecyl acrylate and 16 g of methacrylic acid was added dropwise over the course of 1 1/2 hours. The temperature rose in the flask during the dropwise addition with a highest value of 85°C. After finishing the monomer addition, the temperature was kept at 80°C for 1 hour. Afterwards, stripping with nitrogen gas was carried out for 1/2 hour to remove any unreacted monomer. The batch was cooled, filtered and pH-adjusted with 25% ammonia to pH 9.5.

Analysis values

Example 12

1200 g of water (distilled), 12 g of sodium dodecyl sulphate, 4 g of potassium persulphate and 6 g of ammonium hydrogen phosphate were introduced into a 3 liter three-necked flask equipped with a stirrer, reflux condenser, thermometer, dropping funnel and intake for nitrogen gas. The flask was immersed in a water bath with an immersion element as a heat source and set to a temperature of 80°C. When the contents of the flask reached 60°C, a monomer mixture of 416 g of methyl methacrylate, 368 g of isodecyl acrylate and 16 g of methacrylic acid was added dropwise over the course of 1 1/2 hours. The temperature rose in the flask during the dropwise addition with a highest value of 84°C. After finishing the monomer addition, the temperature was kept at 80°C for 1 hour. Therefore, stripping with nitrogen gas was carried out for 1/2 hour to remove any unreacted monomer. The batch was cooled, filtered and pH-adjusted with 25% more ammonia

pH 9.5.

Analysis values

Example 13

Preparation of pigment addition

A paint paste consisting of 200 g iron oxide black, 125 ml water, 25 g kaolin B, 25 g Mistron Monomix (TALK), 3.4 g Bentone EW, 1.0 g Dispersol T, 1.0 g Na hexametaphosphate and 1.0 ml Antifoam H 10.

Bentone EW, Dispersol T and Na-hexametaphosphate were dissolved in 52 g of water. The paint paste was scraped for 25 minutes.

Execution

To 100 g of dispersion according to example 1, 25 g of water and 54 g of paint paste prepared as described above were added with good stirring. The paint was conditioned at 23°C, 50% relative humidity for 24 hours.

On two 200 cm<2> plates of corrugated eternite which had been pre-heated to 55°C, a paint prepared as described above was sprayed on the front and back of the plate using an air-driven spray gun to a layer thickness of 40 m. Immediately after spraying, the plate was placed in a ventilated heating cabinet at 50°C for 5 minutes for film formation. The plates were taken out and allowed to cool to 40°C and coated with a layer of paint against a layer of paint between two wooden profile blocks. Immediately the plates were loaded with 8000 kp/m<2>, 40°C and 100% RH. After 18 hours, the plates were inspected..

Example 14

As described in example 13, a paint was produced which was sprayed onto plates with dispersion containing temporary solvent according to example 2.

Example 15

As described in example 13, a paint was prepared which was sprayed onto plates with dispersion according to example 4.

Example 16

As described in example 13, a paint was prepared which was sprayed onto plates with dispersion containing temporary solvent according to example 6.

Example 17

As described in example 13, a paint was prepared which was sprayed onto plates with dispersion containing temporary solvent according to example 8.

Example 18

As described in example 13, a paint was prepared which was sprayed onto plates, with the difference that the storage temperature under pressure was 28°C, with dispersion according to example 3.

Examples 19 and 20

As described in example 18, dispersions as described in examples 5 and 7 were used.

Examples 21, 22, 23, 24, 25, 26 and 27

According to the method described in example 13, paints were prepared which were sprayed onto plates, with the difference that the plates were preheated to 65°C, and the storage temperature under pressure was 53°C. Dispersions according to examples 2, 6, 8, 9, 10, 11 and 12 were used without temporary solvents.

Example 28

Sheets of sprayed paint as described in examples 13 - 27 were placed 10 cm above a 50°C thermostatically controlled water bath. After 48 hours, the boards' lime resistance was assessed according to the following scale:

0 = color layer not affected

1 = tendency white, flamed appearance

2 = intense white, flamed appearance

After the painted boards according to examples 13 - 27 had been tested for adhesion according to the described method, the following rating scale was used:

Result of adhesion and lime resistance:

Claims (7)

1. Polymeric acrylic-based surface coating material consisting of a polymer composition dispersed in a continuous phase with a film-forming temperature of 20 - 60°C, including at least one softening-promoting and one hardness-promoting monomer as well as necessary initiators and surfactants, which when driving off the continuous phase combined with heating of the composition well and also its film formation temperature forms a continuous film with a significantly lower stickiness for the finished film than what one generally has reason to assume with regard to the glass transition temperature (Tg) for the homopolymers of the constituent monomers, characterized by the composition being made up of one or more branched softness-promoting monomers combined with one or more straight-chain hardness-promoting monomers, while the surfactants present are mainly of anion-active nature. 2. Polymeric acrylic-based surface coating material according to claim 1, characterized in that the softness-promoting branched monomer consists of an ethyl- or methyl-substituted branched ester of acrylic acid with a total of 7 - 12, and preferably show 8-10 carbon atoms in the alcohol part. Polymeric acrylic-based surface coating material according to claim 1 or 2, characterized in that the continuous phase of the dispersion, in addition to water, also contains a water-soluble temporary solvent. 4. Polymeric acrylic-based surface coating material according to claim 3, characterized in that the temporary solvent consists of 0 - 8 v-% calculated on the polymer material's solids of hexylene glycol or diacetone alcohol. 5. Polymeric acrylic-based surface coating material according to any one of the preceding claims, characterized in that the dispersion contains 1.0 4.0 v-% calculated as dry matter on the polymer part of an anion actrtr: surfactant whose hydrophobic part consists of alkyl-, aryl-, alkylaryl or similar organic group while its hydrophilic part consists of sulfate, sulfonate phosphate or similar mineral acid derivative. 6. Polymeric acrylic-based surface coating material according to any one of the preceding claims, characterized in that the dispersion, in addition to the previously mentioned components, also contains 0.2-2% by volume calculated as dry matter on the polymer part of a salt that forms poorly soluble compounds with calcium ions. 7. Water-dispersed polymer surface coating composition. including 65 N - 50 v-%, calculated as dry matter on the polymer part of methyl methacrylate, 35 - 47 v-% dimethylhexyl acrylate, 0-3 v-% methacrylic acid, 1.0 - 4 v-% of an anionic surfactant according to claim 5, 0-8 v-% of a water-soluble temporary solvent and 0.5-: 2 v-% of a water-soluble salt that forms sparingly soluble compounds with calcium ions.