NO763986L - - Google Patents

Description

The present invention relates to water-based air

drying paints containing common additives as well as a latex polymer.

Aqueous dispersions of polymeric substances (or emulsions in which there is a dispersed phase of polymeric particles) which are produced by ordinary emulsion polymerization. ngtechnique. will usually contain fairly large amounts of protective colloids and surfactants. Conventional surfactants or emulsifiers and protective colloids are usually very hydrophilic and will give rise to water sensitivity in products made from the emulsion, which will be described in more detail below, and this is usually an undesirable property.

For certain applications of latex polymers, the uniformity of the particle size and the average particle size will be of some importance. To produce emulsions with uniform particle transfer when using conventional emulsion polymerization techniques. it is usually necessary to use relatively expensive and unusual initiator compounds.

In order to produce pigmented paints with htéy!7lsns, it is usually very desirable that the particle size in the emulsions is very small. In the case of ordinary emulsion polymerization, the particle formation will generally be regulated by the concentration of the solvent. surfactant. The less particle travel we want, the higher the concentration of the surfactant. However, it is the case that high concentrations of the surfactant in the emulsion tend to make the produced films very hydrophilic. It has thus been very difficult to produce an emulsion with a very fine particle size that could be used in water-based applications

rcaling systems where the final film will have a high gloss.

When it was desired to purify such emulsions v. with very small particles, it was usually not only necessary../, to use large amounts of surfactants, but it is also • necessary to add certain water-soluble colloids to stabilize the particles and to prevent that these run together into larger particles. When such manufactured latex polymers have been used

in clear or pigmented air-drying paint types, they have;-. resulting coating tended to be very water sensitive. some The reason for this water sensitivity is due to the surface-.

active molecules have a very high water solubility and because the protective colloids have a great water absorption ability.

Common emulsion polymers are produced by

free radical polymerization<g>. When free radical polymerization is carried out with ordinary water-soluble initiator compounds, so

the pH in the reaction medium will tend to shift towards acidic pH conditions. Acidic pH conditions are not favorable for emulsion polymerization as they lead to inefficiency, instability and coagulorinfr. It is thus common practice to use a series of buffers,3 such as phosphates and borates, to keep the pH in the reaction medium close to the neutral point or at slightly basic values. The usual buffers used are all water-soluble, and their addition thus increases the water sensitivity of the film produced from the emulsions.

Fn other disadvantage of ordinary latex polymers is

a constant shift in pH in the emulsion, and this requires the addition of a buffering agent to achieve storage stability.

A free radical emulsion polymerization will usually give high molecular weight polymeric products. The molecular weight of such polymers is usually in the range from 500,000 to a few million, while the molecular weight of free radical-produced solution-type polymers is in the range from 100,000 to 300,000. The tensile strength. the impact strength, hardness, load-bearing capacity and the film-forming and other mechanical properties are affected by the polymer-glass transition temperature and molecular weight. The mechanical properties of solution3polyeners are affected by the molecular weight. In particular, the polymer molecular weight will affect the rheological properties of the solution polymers. Solution polymers produced in the molecular weight range from 100,000 to 300,000 are good film formers and show sufficient strength properties. In addition to this will. solution polymers have excellent rheological properties, which is due to their relatively low molecular weight.

Due to the free radical polymerization, latex polymers will give polymers with a high molecular weight and consequently have excellent mechanical strength properties. In contrast to solution polymers, the rheological properties of polymers in the form of a latex are usually independent of molecular weight. They are, on the other hand, influenced by the particle size

3 the drying distribution - as well as the number of particles and 3 the type and concentration of emulsifier and protective colloids used during the preparation of the emulsion. As a result, ordinary latex polymers will have poorer rheological properties than the corresponding solution polymers.

Despite the fact that an emulsion polymerization is usually easy, in certain cases it will be difficult to regulate the polymerization itself and consequently the stability of the product, which is due to the fact that the high-molecular polymer particles grow very quickly. In order to regulate the molecular weight of the latex polymers and consequently the stability of the resulting latex, certain chain-terminating agents and/or modifying agents, such as merceptans and alcohols, are usually used. However, it is highly undesirable to use such ingredients as mercaptans and alcohols, as these increase the water solubility of the resulting polymer and, moreover, both alcohols and chlorinated solvents will be a source of pollution and a health risk.

One of the main applications for latex polymers is air-drying, clear and pigmented paints with medium (70% at a -"0° Plansmeter) to low (J0'% at a -60° gloss meter) gloss. However, most latex polymers are unsuitable for the production of high-gloss pigmented paints even with a relatively low content of pigments. Moreover, coatings or films made from these latex polymers will have very poor leveling properties. Organic solvent-based paints (enamel coatings) such as alkyds, urethanes, ural alkyds and epoxies are capable of is ntsr 90$ at a 60° gloss meter, and also has excellent leveling properties However, due to the fact that these organic solvents are highly flammable and toxic, there is a very strong need for suitable water-based coatings or malin <g>'s which : gives a high lance paint after air drying with acceptable spread properties It should be noted that with some latex polymers there is possible to achieve high gloss values. but only with a very low content of - pigments. Coatings with such a low pigment content will usually have too low a cover eye.

In addition to a very low gloss value, usually a maximum of TQt at a 60° gloss meter, paints that are

based on latex polymers tend to have poor ability

to maintain said shine, especially when used outdoors. This is due to the combination of large amounts of emulsifiers, surfactants, water-sensitive thickeners, colloids, pigment dispersants and other water-sensitive ingredients used in such compositions.

As mentioned earlier, latex polymers have poor flowability. and this results in poor equalization of. the on-ironed compositions. The flow resistance in the coating on Virke3 is not only caused by the polymer particles themselves, but also by other components in the composition such as water-soluble thickeners. Latex polymer based pigmented or clear paints must be thickened to provide sufficient film thickness and to provide thixotropy to prevent seepage. To achieve this thickening, it is normal practice to use cellulosic thickeners, as these are readily available. Most rellulosic thickeners have acceptable flow characteristics only for limited purposes. The use of cellulose-containing thickeners results in a reduction of the durability, especially outdoors, of the paint itself, which is very water-sensitive, and the paint tends to break down under the influence of moisture and under ultraviolet radiation. Some of the paints will also turn yellow when exposed outdoors.

Accordingly, a number of synthetic polymeric thickeners suitable for outdoor applications have been developed. These polymeric thickeners3as well as polyacrylates, though

they have a relatively high resistance to moisture and ultraviolet radiation/do not have better scattering properties than the aforementioned cellu-

lye-containing thickeners. In addition to this, it will

thickening effect of such synthetic polymeric thickeners be less than that found in cellulose-containing products.

thickeners, which requires the use of relatively large ones

amounts. When you use paints containing such synthetic polymeric thickeners for outdoor purposes, you will consequently avoid the durability problems that occur in connection with cellulose-containing thickeners, but the flow properties will usually be unsatisfactory.

In addition to the above-mentioned disadvantages, ordinary latex-based paints will have poor resistance to blackening by dirt and dust, poor resistance to solvents and will be softer than paints based on organic solvents. Furthermore, water-based paints will have very poor resistance to attack by fungi and microorganisms.

It is common practice to produce paints in a number of varying colors with variable intensity, e.g. right from pastel colors via medium colors to very strong and deep colors. With organic solvent-based paints, it is possible to produce a number of variable colors without this affecting the gloss and durability of the paint itself. In connection with latex polymers, however, one will run into very great difficulties. When e.g. If tinting agents are added to a latex-based paint, the o-ion value will drop drastically. This drop in gloss value is due to the addition of large amounts of pigment dispersants and auxiliaries to maintain the tinting. Such agents will, in addition to affecting the paint's gloss, reduce the paint's mechanical strength and water resistance.

With the stricter regulations regarding the use of solvent-based paints, the industry has wanted to be able to produce affordable water-based paints for industrial purposes. However, such water-based paints have until now

had significant disadvantages and has not found wide application. One problem has been the production efficiency itself. Water-sensitive ingredients in the latex polymers and the high-molecular nature of the polymer itself have resulted in large amounts of water being retained in the paint for relatively long periods of time. Consequently, when such latex polymers are used for industrial purposes, and one does not provide

sufficient drying or evaporation3 time before curing, then such paint coats will have a tendency to blister due to a very rapid evaporation of the water or other volatile ingredients ;'! when using high drying temperatures. Blistering can, for example, only be avoided by having very long drying times, and this results in poor production efficiency. To avoid this latter problem, the industry has used other water-based systems such as water-reducible or water-dilutable alkyds, polyesters. and such. With such polymers, however, one has the problem that, in addition to water, they contain relatively large amounts of polar solvents such as alcohols and amines, and this significantly increases the production process itself, while it is desirable to recycle the solvents. In addition to these problems, latex-based paints for industrial purposes have had other disadvantages, such as lack of gloss, lack of or poor flow properties and poor hardness.

When water-based systems have been used during electrodeposition. have had major problems with the migration of surface-active agents and jrigment particles. and this results in uneven colors and low quality products. This requires that one constantly controls and replaces and supplements the electrodeposition bath.

On the basis of the above-mentioned disadvantages, considerable research has been conducted in recent years into producing synthetic aqueous dispersions of polymeric compounds as well as methods that only include small amounts of protective colloids and/or surface-active agents. However, Kan has not succeeded in producing an emulsion with uniformly good properties in all fields.

Attempts have been made to add certain specific compounds to the polymer to give it certain surface-active properties. Stable aqueous dispersions of copolymers of ethylene with vinyl and acrylic monomers have thus been prepared in the absence of usual protective colloids and emulsifiers and in the presence of a copolymerizable half-ester of maleic acid or maleic anhydride, the latter half-ester providing the surface-active properties.

He must, however, use very high pressures in the latter method, and this requires expensive equipment, besides the fact that the use of ethylene in the sarapolymer gives it a number of different properties* Furthermore, the method will require the presence of fairly large amounts of toxic solvents -such as.:.-*. , tertiary, butanol. in order to achieve a solution of the water-insoluble reactants. The presence of such solvents, however, very drastically affects the polymerization itself, and results in high-molecular products with very large'; particle size.

In addition to what is mentioned above, the presence of buffers in the aqueous medium has also previously been required to regulate the pH during the polymerization itself so that the pH is kept close to the neutral point or only at a slightly alkaline , value.

This previously known method has only been able to give dispersions with a solids content of 15 to ?5#, and it is necessary to concentrate' dispersions. if a higher content of solids is desired,

which is usually the case.

An alternative for the production of water-based dispersions with a low content of protective colloids and surfactants involves forming aqueous amraonia-calcic and/or alkaline dispersions of high molecular weight acrylic and/or vinyl polymers. The method of manufacture of

these products are very demanding and include several steps. Accordingly, such polymers will be very expensive. Furthermore, such dispersions will contain large amounts of toxic alcohols

and amines and has a relatively low content of polymer, i.e. from 30 to 35$»Such dispersions have been on the market for some time. However, it has been shown; that the high price combined with the relatively limited area of application has resulted in relatively small sales.

It has now surprisingly been found that it is possible to provide stable aqueous emulsions of certain polymers which do not have the disadvantages mentioned above. The present invention thus provides a reactive stable aqueous emulsion with a dispersed phase of a copolymer of an acrylate monomer and a monoester of an alcohol as well as an ethylenically unsaturated dicarboxylic acid, and where the copolymer essentially has uniform particle dryness from 10 to 3000 Å< g>stream, as well as an aqueous phase with a pH from 5.5 to 9 and which is essentially free of protective colloids and common emulsifiers.

The stable aqueous emulsion according to the present invention can be produced by copolymerizing said monomers at atmospheric pressure and at a temperature below 100°C in . an aqueous medium in which protective colloids, common emulsifiers, common buffers and certain chain-terminating compounds are not used, and where organic solvents are preferably not used, while at the same time emulsions with a content of up to *>0% fatty substances are formed.

With regard to the emulsion according to the present invention, the term "stable" means that the polymeric particles remain dispersed in the continuous aqueous phase for an unlimited period of time without the presence of coagulated or sedimented solid particles being detectable.

The term "ordinary emulsifiers" refers to all low molecular weight compounds which are not capable of further polymerisation, but which, due to their structure, are capable of forming "micelles" in aqueous solutions and which would otherwise facilitate other water-insoluble materials to form either stable solutions or dispersions. Such molecules are usually characterized by a hydrophobic chain such as a long-chain hydrocarbon part with up to 3^ carbonate bridges and a very strong hydrophilic group such as sulfates, the sulfonate or the sulfosuccinate group, as well as certain carboxylates and ammonium salts. With the term "protective colloid" is understood a polymer or simple molecules that help to keep otherwise insoluble or unstable molecules in discrete particle form by forming a protective coating around the molecules in a dispersion. 'in addition. , for this, the protective colloids, which are usually easily soluble in the continuous medium, will form a viscous solution. Typical protective colloids are starch, modified celluloses such as hydroxyethyl cellulose and carboxymethyl cellulose, as well as polyvinyl alcohol.

The acrylate monomer used in the production of the emulsion according to the present invention has the following general formula:

where R-^ is -H or -CH^ and Rg is a straight or branched, saturated aliphatic or cycloaliphatic group which may contain up to 8 carbon atoms. ?-;an can use a mixture of 3like acrylates.

A mixture of acrylate monomers and one or more vinyl monomers can be used, and where the acrylate monomer makes up at least 7=5% by weight of the mixture, and where the vinyl monomer has the formula:

where R^ is an aryl group or R^COO-, where R^ is a straight or branched, saturated aliphatic or cycloaliphatic group of up to 8 carbon atoms.

The preferred acrylate monomers with the above-mentioned general formula are methyl acrylate, ethyl acrylate, butyl acrylate, β-ethyl hexacrylate. methyl methacrylate, ethyl methacrylate and butyl methacrylate,

A. The acrylate monomers are usually used as a mixture. of esters of acrylic acid and esters of methacrylic acid, e.g. a mixture of ethyl acrylate, butyl acrylate and methyl methacrylate.

The ratio between the esters of acrylic acid and the esters

of methacrylic acid used to form the emulsion can be varied depending on the product's application. Thus, one will de-

gig of the glass transition temperature (Tg) which is necessary, as well as depending on the hardness or softness of the film being produced, if one wishes to produce film-forming compositions, or depending on the properties of the co-polymer if one is producing non-film-forming compositions, the relative amount ratio could vary between the different esters of acrylic acid and esters of methacrylic acid.

Examples of vinyl esters that can be copolymerized with acrylate monomers include styrene, substituted styrenes and vinyl alkyl esters♦ such as vinyl formate, vinyl acetate, vinyl propionate and vinyl butyrate.

The monoester of an unsaturated dicarboxylic acid which.

is copolymerized with the acrylate monomer or monomers to give the dispersed phase in the stable emulsion according to the present invention, is an acid with the following general formula:

where Rcer is a straight or branched aliphatic or cycloaliphatic group with at least 3 carbon atoms, n and m are each 0 or 1, and where n + m is 0 or 1. Typical examples for said dicarboxylic acid group of the rr.onoester are maleic acid, fumaric acid, itaconic acid and citraconic acid. preferably maleic acid. When raon esters are formed, these can be prepared from the anhydride of the dicarboxylic acid, if this is desired.

The alcohol group in the mono- or half-ester of the dicarboxylic acid can at least be a straight or branched, saturated aliphatic or cycloaliphatic monoalcohol or amino alcohol with at least 3 carbon atoms.

Examples of suitable aliphatic, cycloaliphatic and amino alcohols include n-propanol and isopropanol, n-, iso- or tert.-butanol, pentanol, hexanol, heptanol, octanol, decanol, dodecanol, ?-ethylhexanol, dimethyldecanol, tetradecanol, cetyl alcohol, decalol and myristyl alcohol and cyclohexanol, cyclohexylmethanol. triethylcyclohexanol, borneol, isoborneol, menthol, aminomethylpropanol, t-butylaminoethanol, dibutylaminoethanol and octylaminoethanol. Of these alcohols, those with from 6 to 16 carbon atoms are preferred.

A particularly preferred monoester is raonodecyl maleate.

In addition to the acrylate monomer, small copolymerizable amounts of at least one monomer containing at least one functional group or reactive position can be used to improve various properties of the emulsion, all depending on its application. Typical functional groups of this type are carbox<y>l, hydroxyl, amino and epoxy groups, and typical reactive

positions is an ethylenic unsaturation.

Examples of such reactive and functional monomers include hydroxypropyl acrylic acid, hydroxybutyl acrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, acrylic acid, methacrylic acid, acrylamide, acrylonitrile, . aminoacrylates, aminomethacrylates, cyanoacrylates, glycidyl methacrylate, diacetoneacrylamide, hydroxymethyldiacetoneacrylamide and dimethacrylates.

The amount of such reactive or functional raonomers can be as low as 1 percent by weight of the acrylate monomer and can go up to approx. 10 percent by weight.

The total amount of monomers included in the acrylate monomer, the vinyl monomer, if present, and

reactive and functional monomers, if such are present, should be at least approx. 7.5% by weight of the polymer particles, where the rest of the polymer particles are copolymerized monoester.

It is preferred that the acrylic and/or methacrylic ether monomer constitutes from 90 to 97 percent by weight of the polymer, where the amount of monoester varies from 3 to 10%. preferably approx. 5% by weight of the polymer.

The polymeric particles which make up the dispersed phase of the emulsion according to the present invention have a substantially uniform particle size in the range from 10 to 3000 Angstroms. This stands in contrast to previously known; emulsions which have had a very variable range with regard to particle size. The average size of the particles in such previously known emulsions has also been relatively large, usually in the range from 0.1 to 5 µm.

In contrast to the prior art, so

the particle size in the present emulsions will essentially be regulated by a suitable choice of comonomers as well as the type and concentration of reactive or functional comonomers.

In connection with the prior art, the particle size has usually been controlled by the concentration of the surfactant and has varied inversely proportional to the concentration of the surfactant for most practical purposes. In the present method, this is not the case. The particle size of emulsions produced according to the present invention is essentially unaffected in the practical concentration range of such surface-active monomers, i.e. up to 5% by weight, based on the total amount of added monomers. Contrary to what one might expect, one will at concentrations above. about. 10$ get an Increase on par!-<1>'';^;;' the particle size, this despite the fact that the particle sizea^;, ;.;

the distribution essentially becomes even.

Another unexpected property of emulsions according to the present invention is the relatively low molecular weight

achieved without using chain-terminating compounds. One achieves

rcolecyl weights varying from 300,000 to 400,000, compared with 500,000 to approx. ?. millions that one obtains in emulsions v;

prepared in the usual manner using chain terminating compounds.

The aqueous continuous phase in emulsions according to the present invention has a pH from 5"5 to 9", preferably 6 to 7" and is essentially free of common emulsifiers and protective colloids. The monoester component ' . which is copolymerized in the dispersed particles provides the only emulsifier necessary to keep the polymeric

particles dispersed in a stable manner in the water.

As the only emulsifier that is necessary is incorporated in the solid dispersed phase in the invention according to the present invention, the water sensitivity problems that arise in connection with ordinary emulsifiers and protective colloids will be avoided.

Emulsions according to the present invention have no tendency for the pH to shift during storage, and although the emulsions show a slight increase in particle size during storage, the original configuration of the particles in the aged emulsion will reappear under shear stresses.

Emulsions according to the present invention have excellent flow properties and in this respect have rheological properties similar to those found in acrylic and vinyl polymers, this in contrast to the poor flow properties found in previously known latex polymers.

Emulsions according to the present invention are produced by copolymerizing in an aqueous medium the acrylate monomer or monomers, possibly together with the vinyl monomer or

-the monomers and/or reactive or functional monomers, as well as

the monoester. The reaction is carried out at atmospheric pressure and at a temperature below approx. 100°C.

The aqueous medium is water to which usual emulsifiers, protective colloids or chain-terminating compounds have not been added. During the polymerization, the pH is self-regulating and there is no need to add

buffers.

The reaction is also self-regulating with regard to the molecular weight and particle size of the finished polymer particles in the emulsion formed, and this stands in strong con-. tra3t to previously known technique, whereby the disadvantages previously experienced by adding a chain-terminating compound and emulsifiers are avoided.

The polymerization of the monoester in the polymer particles results in the polymer itself acquiring surface-active properties, so that a stable emulsion can be produced without the addition of usual surface-active agents or protective colloids, thereby avoiding the problems that often arise in connection with such compounds.

As the addition of the functionally reactive monoester provides the necessary surfactant properties necessary to stabilize the emulsion particles, it is necessary that this monomer is evenly distributed in the polymer structure. The konoesters are preferably used in the form of their salts to improve their solubility in the aqueous medium, then especially in the form of their alkali metal or amraonium salts, e.g. with sodium, potassium and ammonium.

In a typical method for producing the emulsion according to the present invention, some or all of the monoester, as a neutralized salt, is initially dissolved in water after which the rest of the monoester is gradually added either as such or in a mixture with the acrylate monomers during the polymerization itself.

When the monomers are easily soluble in the water used, it is necessary to regulate the concentration of the water-soluble monomers, especially the reactive monoester, during the polymerization itself. This prevents a copolymerization between the water-soluble monomers themselves, and gives a uniform polymer structure" In practice, this is achieved by regulating the solubility of the monoester in the first addition, and this is done by pH adjustment. Organic solvents, and these often cause harmful effects, are unnecessary in the present method. It is e.g. it is not necessary to use such solvents to achieve the desired solubility of the reactants. which was necessary in the previously mentioned ethylene-3am polymerization process. Furthermore, according to the present method, the high pressures which are

reversed in said method,.

The emulsion polymerization used to

forming emulsions according to the present invention is carried out in the presence of water-soluble substances or compounds capable of forming free radicals. Examples of such compounds are potassium, sodium, ammonium and sodium-ammonium persulphates as well as hydrogen peroxide in addition to various percarbonates. The aforementioned water-soluble peroxy compounds can be used as redox systems, i.e. in combination with reducing agents. Examples of suitable compounds for such reducing agent combinations include sodium pyrosulfite or bisulfite, sodium formaldehyde sulfoxylate, triethanolamine, ferrous sulfate, cerium ammonium sulfate, cerium ammonium nitrate, and hydrogen peroxide.

The polymerization is preferably carried out during approx. 80°C because the catalyst effect is lost and more homopolymers are produced at higher temperatures. When using a redox system for catalysis, it is also common for the reaction temperature to be significantly lower, usually from approx. 40 to approx. $ Q°C, and such temperatures are preferably used.

Emulsions according to the present invention can be produced with a varying content of solids, e.g. up to 50% by weight. Typical contents of solids are in the range from 15 to 50%, preferably 25 to 30%, preferably so that a solids content varying from 35

to S0#, as solids in this range are the most effective.

The rheological properties of emulsions according to the present invention cover a wide spectrum of such properties depending on a number of factors, and these can be changed by varying the ratio between the surfactant comonomer and/or the amount of the reactive or functional raonomers in the monomer mixture. When e.g. The pH of the emulsion is adjusted with an alkaline compound, ammonia and/or an amino compound, then an :< emulsion which is formed from a monomer mixture that includes a : f^..; hydroxy group-containing monomer as the functional monomer, tend to give a thixotropic effect, while an emulsion formed from a monomer mixture containing a carboxy group-containing monomer as the functional monomer gives an expanding mass. Under the same pH conditions, an emulsion that forms-; from a monomer mixture containing methyl methacrylate and ethyl acrylate, have little effect and will act as a Newtonian liquid.

Formulations according to the present invention can be used for a number of purposes where latex polymers are usually used, but without the disadvantages usually experienced with such polymers. Thus, emulsions according to the present invention can be used for the treatment of textiles, paper surface treatment, the production of industrial varnishes and paints, especially the coating of clear films or the production of air-drying paints.

Latex polymers are widely used for the production of water-based paints, but the resulting products suffer from a number of disadvantages as mentioned above.

It has been found that emulsions according to the present invention prepared from certain monomer mixtures can be used to provide paints capable of giving pigmented coatings with a high gloss, i.e. o^cr 80$. when this is measured using a 60° gloss meter. oet the product has good durability of the aforementioned gloss, has good duration, and resistance to the wear and tear effects of both water and ultraviolet light and has good lime resistance.

Formulations used for such paints can be prepared from ironomers containing up to 10% by weight of a monomer containing a hydroxyl functional group based on the weight of the acrylate monomers or a mixture of acrylate and vinyl monomers.

A particularly preferred monomer mixture contains methyl methacrylate, ethyl acrylate, butyl acrylate and hydroxyethyl acetate acrylate.

Emulsions according to the present invention can be worked up with common pigments, pigment dispersion agents, solvents that inhibit freezing and thawing, such as glycols, thickeners and antifoaming agents to give a satisfactory paint composition. Solvents ..■■ . j, which promotes a confluence may be present, although they typically ;; used in lower concentrations than usual.

The paint can be worked up so that you can get

any desired viscosity, but it is preferred that the values range from 75 to 100 Krebb units.

The high gloss value achieved with paints according to the present invention and the good ability of the paint to maintain this gloss as well as the good durability properties that characterize pigmented coatings according to the present invention stand in contrast to the properties that have in common latex paints which are described in more detail above.

The fine particle size of the present polymer particles means that a given coating has a very good coverage compared to what can be achieved with ordinary latex paints, so that less pigment is needed to achieve a similar coverage. The small particle size and the relatively low molecular weight of the polymer particles also lead to excellent leveling ability and flow properties, which is in contrast to previously known paints, and there is no sign of brush strokes or dry marks on pigmented coatings produced according to the present invention. Pigmented coatings produced from paints according to the present invention have good hardness, flexibility and blocking ability. Pigmented coatings have very little ability to absorb dust and dirt, have good resistance to soil impact, excellent resistance to solvents and have excellent resistance to washing. You will not find these properties in pigmented coatings made from ordinary latex paints. as detailed earlier.

The pigmented coatings according to the present invention also have good resistance to attack by fungi and other microorganisms, and it is not necessary to add agents to prevent fungal attack and microbial attack, which is in contrast to previously known paints where such agents are very common.

It is necessary with significantly less amount of thickening agents with the latex emulsion according to the present

invention to give it the same paint viscosity compared to previously known latex polymers, so that one significantly: reduces the water sensitivity problems that often arose in connection

share with such thickeners.

Paints prepared from emulsions according to the present invention have excellent stability as demonstrated by five cycles of freezing and thawing, and the paints have very little odor.

Emulsions according to the present invention can

is also used to obtain hardened steel paints without the need for extended processing time as was previously known, as paints and coatings according to the present invention dry very quickly and produce coatings with a high gloss, and this occurs in the absence of both cross-linking resins such as methoxymelamines and urea-type resins in addition to acid catalysts.

By using emulsions according to the present invention, one avoids the problems previously experienced with the migration of both pigments and surface-active agents, which easily arose when electrodeposition was used and enamel paints were produced.

Froulsions according to the present invention can also be used to provide clear varnishes or paints that can be used for seizing textiles and paper, or for other applications where ordinary latex polymers have been used up to now.

EXAMPLES

The invention is illustrated by means of the following examples:

Example 1 I

This example illustrates the production of an emulsion according to the present invention.

An aqueous solution of 635 parts water and 21 parts monodecyl maleate neutralized with 5.2 parts potassium hydroxide solution was added to a suitable reaction vessel equipped with devices for temperature regulation, stirring devices and a steam cooler

to a pH of 7.0 + 0.1.

Fn initiator or starting solution consisting of 1.2 parts of ammonium persulfate and 20 parts of water was divided into two parts, and the first part was added to the aqueous solution ■ Ogj. :.- ;'^ consisted of 10.6 parts of said solution, as well as a delayed supply consisting of the other 10.6 parts of the initiator solution.

The aqueous solution was heated to approx. 72° + 2°C, and a delayed monomer feed of 234 parts methyl methacrylate and 366 parts ethyl acrylate (MMA:F,A: :39*.6l) to the aqueous solution was started at a rate of 5 ml per minute.

The delayed initiator solution addition was started and added over the same time period as said monomer supply. Furthermore, a neutralized, , was added very slowly.

(pH 7) solution of 100 parts water and 9 parts monodecyl maleate.' and 2.5 parts K0H when starting approx. 15 minutes after starting to add the delayed monomer supply and

the delayed initiation and this addition was complete within 15 minutes before the addition of the acrylate monomers was completed.

During the addition of the delayed reactants, the temperature in the reaction medium rose to approximately 80°C. and the mixture was held at this temperature for a further 60 minutes before being cooled to <~a. ~5°C and filtered..

The total maleate concentration was 5% based on the acrylates and the ratio between the aqueous and the delayed feed was 7:3.

The resulting emulsion had a solids content of 45.4.5%. had a bluish tone, and had a dispersed phase of uniform particles, showed very little coagulum, and was essentially free of dissolved granular particles.

Film cast from the emulsion on a glass surface had excellent water resistance and showed no signs of blistering when exposed to water in a water spot test.

Example II

This example illustrates the formation of further emulsions according to the present invention using an alternative acrylate monomer.

The procedure from Example I was repeated except that the soft raonomer ethyl acrylate was replaced by ?-ethylhexyl acrylate. The concentration of monodecyl maleate was 12% based on the acrylic monomers and was used in a 38^2 Aqueous/Delayed Feed Weight Ratio The weight ratio of methyl methacrylate to ?-ethylhexyl acrylate was varied in individual experiments and the properties of the resulting emulsions are indicated [ in the following Table I.

Example III

This example illustrates the preparation of other emulsions according to the present invention where one had . hydroxy functionality in the polymer particles.

I'an again repeated the procedure from Example I except that the acrylic monomer combination included a functional reaction monomer containing hydroxy functionality in addition to methyl methacrylate and ethyl acrylate. The monodecyl maleate concentration in this example was 4 percent by weight based on the total weight of the acrylic monomers and exclusive of the self-contained maleate. a pH of 7.0-0.1 by neutralization with potassium hydroxide solution. Different monomers containing hydroxy functionality were used, and the results obtained are set out in Table II:

Example IV

This example illustrates the production of new emulsions according to the present invention containing hydroxy functionality.

Four additives were produced, namely an aqueous reaction medium. a delayed monomer supply, a delayed surfactant supply and a supply of initiator solution. The monomer mixture used was a mixture of methyl methacrylate. ethyl acrylate, butyl acrylate or hydroxyethyl methacrylate in a weight ratio of 13:50:2:5. The surfactant monomer was monoievel maleate, and the initiator compound was ammonium persulfate.

An aqueous reaction medium consisted of 7 parts monodecyl maleate and 24-6 parts water neutralized with ? .54 ml

50/rt COOK. and this Me added to the reaction vessel and heated to approx. 70°P.. To the heated medium was added 6.5 parts of a solution consisting of 0.5 parts of (NH^)pSpOg in 12.5 ml of water,

and this resulted in a slight rise in temperature.

Delayed monomer supply consisting of 107.5

parts methyl methacrylate, 125 parts ethyl acrylate, 5 parts butyl acrylate. and 12.5 parts of hydroxyethyl methacrylate were gradually added to the reaction mixture together with the remaining 6.5 parts of the initiator solution. The delayed monomer supply and initial

the tor supply was added at a uniform addition rate over the course of ?, hours, and the pH of the reaction medium was essentially constant, while the temperature rose to approx. 80°C.

About. 50 minutes after starting to add the delayed monomer addition and the initiator solution,

a delayed surfactant monomer feed containing 3 parts monodeyl maleate, 3$ parts water and 1.05 ml of a 50$ KOH solution was added, and this was added during approx. 1 hour. When this addition was complete, the reaction mixture was held at 80°C for an additional hour to ensure complete conversion of the monomer to latex, after which the mixture was cooled.

The slightly bluish emulsion was filtered to free it of coagulated particles, and less than 0.1% such particles could be observed.

The viscosity of the emulsion was 1580 eps using a (^3 spindle at 60 rpm (Brookfield Viscometer). The emulsion had a solids content of 45%, and the particles had an average size below 0.1 µm and an average molecular weight below 500,000.

The emulsion produced an air-dried film with a gloss value of '83 as measured by a 60° Oardner Gloss Meter, and had good ability to retain this gloss. The emulsion showed excellent flow properties when forming the air-dried film.

Samples of the produced emulsion were stored in

6 months and then examined. No sedimentation could be observed, although there had been some coalescence of particles. However, he could not demonstrate that the storage had any detrimental effect on the emulsion's properties.

Example 7

This example illustrates the formation of emulsions containing acid functionality.

The method from example IV was used except that the functional monomers of the acid type replaced hydroxyethyl methacrylate. The effect of pH on the copolymerization of the acid-type functional monomers was observed, and the results are given in Table III.

Example VI

This example illustrates the effect of the initial pH on the emulsion polymerization process of the present invention.

The procedure of Example IV was repeated except that the pH values of the aqueous addition and the delayed monoester addition were carried out at three different levels, namely 6.0, 9.3 and 12.0. A pH of 9.3 corresponds to a total neutralization of the monoester, that of 12..0 is well above the neutralization point, while that of 6.0 is considerably below. The effect of the pH conditions on the properties of the copolymer is indicated in Table IV.

Oak sample VII

This example shows that the emulsion has a self-buffering effect.

The reaction vessel was equipped with suitable devices for stirring and temperature regulation, and 2.86 parts of water, 56 parts of monoderyl maleate and 18.7 ml of 50% potassium hydroxide solution were added, and it was found that the pH of the mixture was 7.0%. The contents of the vessel were heated to 72<+>2°C, and the system was started with 2 parts ammonium persulfate dissolved in 50 parts water. After the temperature had been maintained at 80<+>2°C,3 the supply of monomer and initiator was titrated as described in example IV. The delayed monoester consisted of 24 parts of monodecyl maleate and 240 parts of water neutralized with 8.0 ml of 50* potassium hydroxide to a pH of 7.0. The delayed monomer feed consisted of 740 parts methyl methacrylate,

1160 parts ethyl acrylate and 100 parts hydroxypropyl acrylate. Under

During the polymerization, samples were taken at 15-minute intervals and the pH was measured. The pH values are shown in Table V below.

The experiment was repeated except that the monomer composition was changed and the pH was measured as

written previously. 7<i0 parts methyl methacrylate, 1160 parts ethyl acrylate and 100 parts methacrylic acid were used as monomer feed. In this experiment, the aqueous feed was neutralized with 15.0 mL of 50% potassium hydroxide solution to a pH of 6.0, and the delayed monoester was added to the delayed monomer feed without neutralization. The results are shown in Table V.

It appears from the above results that

the emulsion polymerization is self-buffering. One can observe the same self-buffering effect when using acid-functional monomers. "

Example VIII

In this example, the concentration and method of addition of the dicarboxylic acid monoester was varied, after which the effect on the properties of the copolymer was observed.

In each case, the reaction was carried out as described in Example IV, and the results are shown in Table VI.

Example IX

In this example, the concentration of hydroxyethyl methacrylate was changed, and the effect on the properties of the copolymer was observed. f.:-The polymerization was carried out as described in Example IV, and the results are given in Table VII.

It appears from the results in Table VII that hydroxy-functional monomers in concentrations of more than oa* 3$ have a beneficial effect on the properties of the emulsions.

Example X

This example illustrates the formation of emulsions using additional functional monomers.

The same procedure as in example IV was used, except that dimethylaminoethyl methacrylate, t-butylaminoethyl methacrylate and glycidyl methacrylate were used instead of said hydroxyethyl methacrylate. • V '•••\ ':'

In addition to this, the example illustrates the formation of emulsions containing more than one functional monomer.

Typically, one of the functional monomers will be a hydroxy acrylate. while the other consists of either amino acrylate or a glycidyl acrylate.

Reaction conditions and properties of the finished emulsions were observed, and the results are given in Table VIII.

<f>MMA is methyl methacrylate, EA is ethyl acrylate, BA is butyl acrylate dg F represents the functional monomer. All paints were prepared as indicated in Example XII, below, 1 DMAEMA and HEMA refer to dimethylaminoethyl methacrylate and hydroxyethyl methacrylate, respectively. 2 t-BAEMA and HEMA refer to t-butylaminoethyl methacrylate and hydroxyethyl methacrylate respectively. 3 OMA and HEMA refer to glycidyl ethacrylate and hydroxyethyl methacrylate respectively. 4 The values were obtained by visual comparison with emulsions, i of corresponding particle size.

Example XI

This example illustrates the addition of acrylamide, N-methylolacrylamide, diacetonacrylamide or hydroxymethyldiacetonacrylamide in the copolymer dispersed phase according to the present invention.

A suitable reaction vessel equipped with stirring devices. and temperature control devices were added 14 parts monodecyl maleate, 38O parts water and 3»! parts potassium hydroxide, whereby an aqueous mixture with a pH of 7.0 + 0.1 was obtained.

The delayed maleate feed consisted of 6 parts monodecyl maleate, 6l parts water and 1.4 parts potassium hydroxide, giving a pH of 7.0 + 0.1, and a total maleate concentration of 6.0 based on the other monomers excluding the maleate .

The monomer feed consisted of 133 parts of methyl methacrylate, ?00 parts of ethyl acrylate and 18 parts of amide-functional monomer, whereby a monomer composition was obtained with a weight ratio of 37:58:5 respectively.

The polymerization was carried out as indicated in Example IV, and the properties of the resulting copolymers are indicated in Table IX:

Example XII

This example illustrates a paint composition based on the emulsion prepared as described in example IV. All parts are per weight.

10 parts water, 7.25 parts Nuosperse HOH, 70 parts ethylene glycol, 4 parts Balab Defoamer 3036-29A, 4 parts Tween 80 and 1 part 28$ NH^OH were premixed and dispersed at high

speed in 300 parts RHD6x Ti02.

With slow stirring, 56 parts of water were added: 730 parts of an emulsion prepared as described in Example IV adjusted to pH 9 to 9.5, and a premix of 23 parts of thickener LN (15$), 40 parts of ethylene glycol and 40 "divides water.

The resulting paint composition flowed easily onto a substrate with good adhesion and dried quickly to give a glossy white surface.

Paint surfaces were also prepared from a variety of commercially available water-based latex paints, a water-based acrylic latex prepared from a commercial emulsion and ingredients recommended by the manufacturer of the commercial emulsion, a water-based acrylic latex prepared from said commercial emulsion and additional ingredients as mentioned above,5 whereby a paint according to the present invention was produced, as well as an organic solvent-based uralkyd and epoxy paints.

The properties of the latter painted surfaces were compared with the painted surface obtained from a paint prepared as described here, and the results are given in the following table X:

the results in the above-mentioned table X clearly indicate that paints produced according to the present invention are far ... better than a number of commercial water-based paints and paints prepared from water-based emulsions.'v ,,

The results in table X also show that water-based latex paints produced from emulsions according to the present invention have an initial gloss of the same type as is found in solvent-based uralkyd and epoxy paints, and that they have very good properties with regard to maintaining said gloss. ', compared to uralkyd and epoxy paints.

Example. XIII

This example illustrates the preparation of paints with a pastel tone, a medium tone and a deep tone, using emulsions prepared as described in Example IV.

The paints were prepared as described in Example .. XII with the ingredients listed in Table XI:

The paints produced were tested for properties and compared with paints based on a commercially available, all-acrylic emulsion and solvent-based uralkyd enamels. The results are given in Table XII.

It appears from Table XI that emulsions according to

present invention is far better when used for the production of colored paints than ordinary commercial latex paints, and compares favorably with solvent-based paints.

Example XIV

This example illustrates an industrial paint of the hardened enamel nailing type based on emulsions prepared as indicated in Examples IV, VIII, IX and X. All parts are per \ weight. •/•'.;,;:100 parts water, 9.25 parts Tamol 73I (25%), 4.00 parts Tween 80 and 1.00 parts Defoamer 6l8 were mixed and dispersed at high speed in 250 parts rutile titanium dioxide (RHD6X) and 3.0 part Defoamer 6l8.

With slow stirring, 730 parts of a suitable emulsion (45% non-volatile solids) adjusted "to pH 9 to 9.5 with 5.0 parts ammonia (28% concentration), 8.0 parts thickener LT-I ( 15$ non-volatile solids) and 122 parts water.

The resulting paints had a low viscosity of approx. 58 Krebb units and was well suited for ironing by means of dipping.

Three types of substrates were chosen for the application of the paint. The following substrates were chosen: 1. Tin plates that were sandblasted and primed with a coat of a metal preparation paint. 2. Anodized aluminum sheet sandblasted and treated once with a primer and another coat of a metalworking primer. 3. Anodized aluminum sheet sandblasted and treated with a coat of a metal finishing paint.

The different emulsions were tested for possible suitability in hardened enamel paints as indicated in Table XIII. In addition to this, a commercial all-acrylic latex polymer and a water-based acrylic colloidal dispersion were tried.

The tin plates were coated with the various paints based on emulsions listed in Table XIII, and the plates were then air dried for ;?0 minutes. The plates were then transferred to a convection oven whose temperature was 177 + 2.5°C. The plates were cured at this temperature for 20 minutes, removed from the oven and cooled.

The anodized aluminum sheets were also coated with the various paints and cured in a similar manner, except that both the air drying and oven curing were reduced to 10 minutes.

All the cured plates were tested after cooling for adhesion, appearance, blistering, etc. The results are given in Table XIV:

Foot otters

A. Tin plate with a coat of raetal processing primer and a coat

era oil paint. B. Anodized aluminum sheet with a coat of metal treatment,

primer and a coat of enamel paint or varnish. 0 C. Anodized aluminum sheet with a coat of factory primer, a coat of metal treatment primer and a coat of enamel-j •■■paint.

1 For details regarding composition, see Table XIII

? The painted surfaces were very sticky after removal

the oven.

3 Presence of small blisters.

4 The films became soft and very sticky.

G is good

VG is very good

FG is relatively good.

F is not good

P is bad

E is excellent

It appears from the results from Table XIV that emulsions according to the present invention are capable of forming durable and hard hardened enamels and paints in the absence of both external cross-linking resins such as me t ole yme lamins and urea type resins as well as acid catalyst.

The present invention thus provides stable aqueous emulsions with superior properties, methods for their production as well as paints produced from said emulsions, codifications can be easily carried out without thereby abandoning the intention of the invention as it appears from the following paragraphs.

Claims (1)

1. Water-based, air-drying paint composition containing common pigments, pigment dispersants, antifreeze solvents, thickeners, antifoam agents and a latex polymer, characterized in that the latex polymer is a conventional emulsion with a dispersed phase of a copolymer of at least 75 wt. % of (A) (i) (a) at least one acrylate monomer with the formula: where R-^ is -H or -CH^ and R 2 is a straight or branched, saturated or aliphatic or cycloaliphatic group of up to 8 carbon atoms, or (b) a mixture consisting of at least about 75% by weight of at least one acrylate monomer and up to approx. 25% by weight of at least one vinyl monomer of the formula: where R3 is aryl or R4 COO-, where R4 is a straight or branched, saturated aliphatic or cycloaliphatic group of up to 8 carbon atoms and (ii) up to approx. 10% by weight of said acrylate monomers (a) or a mixture (b) of a copolymerizable monomer having at least one hydroxy functional group and (B) up to 25% by weight of at least one monoester of an unsaturated dicarboxylic acid of the formula: where Rj. is a straight or branched, saturated aliphatic or cycloaliphatic group with at least 3 carbon atoms, n and m are each 0 or 1, and n + m is 0 or 1, and where said copolymer has substantially uniform particle size in the range from 10-1000 Angstrom.