WO2016169814A1

WO2016169814A1 - Method for the preparation of water-based paints

Info

Publication number: WO2016169814A1
Application number: PCT/EP2016/058022
Authority: WO
Inventors: Giampietro Margheritis; Barbara GATTI; Giuseppe PIRRONE; Giovanni Floridi; Giuseppe Li Bassi
Original assignee: Lamberti Spa
Priority date: 2015-04-20
Filing date: 2016-04-12
Publication date: 2016-10-27
Also published as: BR112017022408A2; ITUB20150427A1; EP3286267A1

Abstract

Method for the preparation of water-based paints which comprises the use of extruded pellets containing a rheological modifier of natural origin, a dispersant and a defoamer.

Description

METHOD FOR THE PREPARATION OF WATER-BASED PAINTS TECH NICAL FIELD

The present invention relates to a method for the preparation of water- based paints which comprises the use of extruded pellets containing a Theological modifier of natural origin, a dispersant and a defoamer.

PRIOR ART

Paints are surface coatings that are applied to substrates and dried so as to form continuous films for decorative purposes as well as to protect the substrate. Consumer paints are air-drying and primarily decorative architectural coatings applied to interior or exterior surfaces, where the coatings are sufficiently fluid to flow and form a continuous paint film and subsequently dry at ambient temperatures. Industrial maintenance paints are similar coatings applied to substrates in industrial environments to primarily protect the substrate.

Latex paints, also known as emulsion paints and coatings, have captured a significant portion of the indoor and outdoor paint market as a result of the many advantages that such paints have over solvent-based products. They ordinarily comprise organic polymeric binders, pigments, and various paint additives. In dried paint films, the polymeric binder functions as a binder for the pigments and provides adhesion of the dried paint film to the substrate. The pigments may be organic or inorganic and functionally contribute to opacity and color, in addition to durability and hardness, of the dried paint film.

Latex paints require effectiveness in a number of properties to permit proper utilization thereof. For instance, the paint should exhibit a suitable flow out of the storage receptacle as well as adhesion to a brush. Upon application to a surface, the paint should flow and level within the brush stroke or paint roller tracks left on the surface so as to create a uniform coating without streaks therein. Furthermore, a latex paint should exhibit quick drying times to prevent, if applied to a vertical surface, any gravitational pull to cause to run down the target substrate or sag after application. Additionally, paints should show a uniform coloration over the

l target surface, both in terms of the pigments applied, as well as overall coating. Lastly, it is also preferable that latex paints exhibit a propensity for stability when stored after initial preparation on-site or at a place of purchase/production. In fact phase separation of the paint is highly undesirable as non-uniformity in final applied colorations would most likely result if a phase separation has occurred.

Moreover the paint viscosity during storage must be adequately high to prevent settling, but readily reduced by applied shear to spread and flow evenly. Latex paint should exhibits pseudoplastic behaviour to enable the paint to be applied readily by brush or roller or spray application.

To overcome all these problems, additives are used in the formulation of latex paints acting as rheology modifiers (thickeners). Thickeners are used in numerous products for rheological control purposes and particularly for increasing viscosity and imparting the required rheological properties to the products.

The thickeners for latex paints can be natural polymers, such as guar or xanthan, synthetic polymers, such as polyacryiate or polyurethane based thickener, or semi-synthetic polymers, or chemically modified natural polymers, exhibiting the specific characteristic of bonding and coordinating a large amount of water once they are dissolved in water.

Among the chemically modified natural polymers, the thickeners of choice for latex paints have been for a long time the derivatives of celiulose, including carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), ethyl hydroxyethyl cellulose (EHEC), methyl cellulose (MC), methyl hydroxylethyl cellulose (MHEC), hydroxypropyl methyl cellulose (HPMC) ethers alone and blends of them. These polymers thicken the water-phase of the paint and increase the viscosity of the paint overall.

Derivatives of guar and other polygalactomannans, in particular hydroxypropyl guar, are also well known thickeners for latex paints. Like the celiulose derivatives they modify the viscosity and rheology of the paints by imparting pseudoplastic behaviour to the emulsion coating . In addition to rheological modifiers, the formulation of water paints requires the use of other additives, such as dispersants, defoamers, surfactants, thixotropic agents, softeners, pH regulators, further film- forming and leveling agents, drying agents, anti-stripping agents, antifouling agents, protective and stabilizing agents against UV light, biocides, and the like.

Many of these additives are added to the water in the formulation in the form of powders. Powders by their nature have very large surface areas susceptible to humidity and/or to bacterial growth.

The handling of such powders and dust generation during processing create environmental and health problems that must be dealt with by the manufacturer and the final user.

Moreover, some powder additives are difficult to dissolve in the water- based paint, if this is not stirred for a sufficient time and/or with a mixer at high shear stress, they can create lumps or aggregates. If not completely dissolved, lumps or aggregates arising from additives can create defects during fiim formation of the painting. In addition, a partial dissolution of the rheology modifier may make necessary a correction of the viscosity of the paint with wasting of time or, if not corrected, can cause serious drawbacks during the application, for example, leveling problems, pouring or detachment, well known to those skilled in the art. Also the exact dosage and in-toading of powder additives, which have usuaily different densities and different particle sizes, can be the source of further difficulties.

A typical solution to these problems commonly used in many fields is to granulate the powdery compounds or compositions. Unfortunately the granules obtained during the granulation process are different in their forms and dimensions, thus making it necessary to sieve the granulated material, for the purpose of selecting the granules presenting dimensions above a minimum value. Moreover granulation does not eliminate dust. In fact, a percentage of this dust, even if small, remains embedded in between the granules and tends to spread around.

It has now been discovered that the use of extruded pellets which contain at least some of the main additives used for the formulation of water paints is able to solve all the problems mentioned above. The composition and dimensions of the shaped solid printing additive can be easily controlled in order to avoid hazards and to optimize processing, handling/shipping, in-line dosing, etc. At the same time these shaped solids are really compact, do not produce dust when handled and have a better dispersibility than powders, reducing significantly the formation of lumps in the printing paste.

As known to the Applicant, the use of extruded pellets obtained by extruding a mixture of two or more additives for water paints for the preparation of the same has not been described in the literature.

By "pellets", it is meant any shaped solid composition, including but not limited to, tablets, beads, flakes, blocks, bars or blocks.

DESCRIPTION OF TH E INVENTION

It is therefore a fundamental object of the present invention a method for the preparation of water-based paints comprising mixing in water:

a) a pigment and/or a filler;

b) an organic binder;

c) extruded pellets containing : i) from 35 to 75 % by weight (dry weight) of a rheology modifier consisting of one or more polysaccharides or polysaccharide derivatives; ii) from 15 to 35 % by weight (dry weight) of a dispersant; iii) from 8 to 30% by weight (dry weight) of a defoamer;

the pellets being used in an amount ranging from 0.3 to 5.0 % by weight based on the final weight of the water-based paint.

Further object of the present invention are extruded pellets that contain : i) from 35 to 75% by weight (dry weight) of a rheology modifier consisting of one or more polysaccharides or derivatives of polysaccharides; ii) from 15 to 35% by weight (dry weight) of a dispersant; iii) from 8 to 30% by weight (dry weight) of a defoamer.

DETAILED DESCRIPTION OF THE INVENTION

The method for the preparation of water paints according to the invention contemplates the addition in water of pigments and/or filler, binder and pellets that contain rheological modifier, dispersant and defoamer.

The addition to water of the ingredients listed above is carried out by mixing the pigments for paints and/or the filler, the binder, pellets and any other additives under constant stirring at high shear stress to obtain a mixture having high viscosity and high solid content. The manufacturing process of the paint may include a further dilution and rest period.

Paints are commonly characterized in terms of their pigment volume concentration (PVC), which is the volume relationship of pigment/filler to total solids in the dry paint film. The percent PVC is (the total pigment/filler volume divided by the total volume of pigment/filler and binder in the dry film)_*100. The minimum value of the percent PVC for the paint formulations of this invention is preferably about 15%. The maximum value is preferably about 95%. Typical levels of pigment and binder depend on the type of paint, i.e. gloss, semi-gloss or matte finish. Typically, according to the method of the invention, from 1 to 95% by weight, in particular from 5 to 70% by weight, of at least one pigment and/or one filler and from 0.1 to 60% by weight, in particular from 1 to 30% by weight, of binder are mixed in water; the percentages being calculated on the final water-based paint, which usually includes from 10 to 80% by weight of water.

In accordance with the invention, there is no need to impose any restriction regarding the selection of suitable compounds to be used as pigments/fillers, binders or any other additives of the paint formulations of the invention. Pigments and fillers suitable for the present invention include those known from the prior art.

Examples of suitable pigments are inorganic white pigments, inorganic chromatic pigments, organic pigments, carbon blacks and inorganic black pigments.

As inorganic white pigments, mention should be made in particular of oxides, such as titanium dioxide, zinc oxide ( nO, zinc white), zirconium oxide, carbonates such as lead white, sulfates, such as lead sulfate; titanium dioxide is particularly preferred.

As inorganic chromatic pigments, mention should be made of those from the group of oxides and hydroxides in the form of their individual inorganic compounds or mixed phases, especially iron oxide pigments, chromium oxide pigments and oxidic mixed-phase pigments with rutile or spinel structure. Examples of iron oxide pigments are Colour Index Pigment Yellow 42 and Pigment Red 101. Examples of chromium oxide pigments are Colour Index Pigment Green 17 and Pigment Green 18. Examples of oxidic mixed-phase pigments are nickel-titanium yellow and chromium-titanium yellow, cobalt green and cobalt blue.

Examples of inorganic black pigments that should be mentioned include those as already described above together with the inorganic chromatic pigments, in particular black iron oxide and black oxidic mixed-phase pigments.

Examples of preferred organic pigments are those of the monoazo, disazo, azo-lake, beta-naphthol, azo metal complex series, and also polycyclic pigments such as those from the phthalocyanine, quinacridone, and thioindigo series. Also suitable as organic pigments are lake-dyes such as Ca, g and Al lake-dyes containing sulphonic acid or carboxylic acid groups. Mention should be made in particular of carbon blacks obtained by the furnace black process, and also chemically surface- modified carbon blacks, such as suipho- or carboxyl-containing carbon blacks.

Fillers, also called extender pigments, comprise substances other than the pigments mentioned, these substances being primarily light in color and being inert towards the binder component. With particular preference, the fillers have a lower optical refractive index than the aforementioned white pigments. Examples of inorganic fillers that may be mentioned include carbonates, such as chalk, ca!cite or dolomite, silicon dioxide (ground quartz), natural or synthetic silicas, silicates, such as talc, kaolin or mica, and sulfates such as barium sulfate. Examples of organic fillers include polymeric powders and those known as hollow spheres.

The binder may be any standard type and may include different binder materials. Suitable binders include both organic and inorganic compounds. Preferred organic binders are water-soluble, water- dispersible or water-emulsifiable, natural, natural-modified or synthetic, film-forming compounds. Examples of natural binders include natural resins, such as rosin or schellac, natural oils, especially oils containing fatty acids which are saturated or contain various degrees of unsaturation, said oils being oxidatively drying if desired, such as linseed oil, ricinene oil, soya oil, castor oil, and the like. Modified natural binders are, in particular, chemically modified natural resins, e.g. rosin-ma!eate resin, and also modified oils, e.g. isomerized oils, styrenated and acry!ated oils, and also cellulose derivatives such as cellulose nitrates, cellulose esters of organic acids.

Examples of synthetic binders are saturated polyesters obtained by polyesterifying bifunctional or higher polyfunctional alcohols with polyfunctional saturated-aliphatic, cyclo-atiphatic or aromatic carboxylic acids and/or their anhydrides. Further synthetic organic binders are alkyd resins (polyesters modified with unsaturated fatty acids, fatty oils or higher synthetic carboxylic acids) and also chemically modified alkyd resins, examples being styrenated, acrylated or urethanized. Further suitable organic binders include acrylic resins (polyacrylates) in the form of their homopolymers and copolymers, e.g. styrene acrylate, and also polyacrylic polyo!s. Water-dilutable acrylic resins are particularly preferred.

The method of the invention is characterized by the use of extruded pellets that contain : i) from 35 to 75% by weight (dry weight) of a rheology modifier consisting of one or more polysaccharides or polysaccharide derivatives; ii) from 15 to 35% by weight (dry weight) of a dispersant; iii) from 8 to 30% by weight (dry weight) of a defoamer.

Preferably, the extruded pellets of the invention contain : i) from 45 to 70% by weight (dry weight) of a rheology modifier consisting of one or more polysaccharides or polysaccharide derivatives; ii) from 18 to 30% by weight (dry weight) of a dispersant; iii) from 10 to 25% by weight (dry weight) of a defoamer.

The preparation method of the extruded pellets comprises the following steps:

1) preparing a hydrated mixture of i) -iii);

2) extruding the hydrated mixture to form an extruded material; 3) comminuting the resulting extruded material to form a shaped product (pellets).

The hydrated mixture is prepared by mixing rheology modifier, water, dispersant and anti-foaming by conventional means (step 1). This can be done in a suitable mixing device and/or inside the extruder.

The water content of the hydrated mixture is only important in that it should be high enough to allow the intimate and uniform mixing of the different components and should allow the extrusion of the mixture. Conversely, the water content of the mixture should not be so high that it does not maintain its shape after it is extruded. Generally, the water content of the hydrated mixture is from 5.0 to 50 % by weight.

Usually the mixture in the extruder is heated to or maintained at a temperature in the range from about 20 to about 100 °C. The optimum temperature for extrusion will vary somewhat dependent upon the components of the mixture, but the optimum temperature can readily be determined empirically. The temperature of the mixture may vary depending upon where it is in the extruder, but generally a uniform temperature profile is preferred. The temperature referred to herein is the mixture temperature in the extruder just before it passes through the extruder die. High temperatures which can cause decomposition of some ingredient should be avoided.

The hydrated mixture is extruded through a die, preferably a multi-hole die. In general, the shape and size of the orifices fix the cross-sectional shape and size of the extrudate. Although any shape of orifice may be used, i.e. circle, triangle, square, rectangle and star, it is preferred that the extrusion of the mixture is through equiaxial orifices. Equiaxial orifices are orifices that have approximately equal dimensions in all directions. The cross-sectional area of the orifices should be small enough so that the extruded mixture fibers line up parallel to each other in a tightly formed fiiaments (strands). On the other hand, the cross- sectional area of the orifice should not be so small that an excessive amount of energy must be exerted to press the mixture through the orifices. Generally, the orifices are of dimensions ranging from 1.0 to 6.0

s mm, preferably from 2.0 to 3.5 mm.

The extrusion can be done with any device that applies sufficient pressure to push the mixture through the extrusion orifices at a temperature which maintain the hydration of the mixture. For example, a pump-type extruder, such as a positive displacement piston or a gear pump, can be used. Another example of suitable extrusion equipment is a screw-type extruder which advances the mixture by means of a screw rotating inside a cylinder. A twin screw extruder in co-rotating or counter-rotating mode, intermeshing or non-intermeshing may be utilized in the processes of the invention, but equally a single screw extruder or a multi screw extruder may also be suitable providing always that mixing can be achieved. The screw extruders are not as efficient as the pump extruders and convert most of the energy into heat. This causes an increasing of the mixture temperature and to dehydrate the materia! in the extruder. This means that, when using a screw extruder, is normally necessary to use a cooling device to keep the hydrated mixture to a temperature below 100 °C.

Usually the extrusion process is carried out at pressures well above atmospheric pressure, preferably the extrusion is carried out at pressures of from about 2 to about 16 Pa.

The extruded materia! is a firm material appearing uniform in texture and coior. Generally, the material is extruded in the form of long, narrow filaments. The filaments have a uniform cross-sectional area that is approximately the same as the extrusion orifices described above.

Typically, the extruded inhibitor has a residua! moisture content ranging from 5.0 to 50 % by weight, preferably from 15 to 30 % by weight.

In order to transform the filaments into pellets, it is necessary to comminute the extruded material (step 3).

The comminuting can be accomplished by using standard equipment known in the art. Typical comminuting devices are air-swept impact mills, bail mills, hammer mills, and disk mills. This is preferably done in an air- swept impact mill because the other mills, i.e. ball mills, have a tendency to overmill the product into fine particles that are dusty. In addition, an air-swept impact mill will dry the extruded material, if necessary, by blowing hot air across the mill.

Another method for comminuting the shaped bodies is to cut it with a die- faced cutter. A die-face cutter operates by moving a blade across a stationary die or by moving a die across the stationary blade. Thus, the shale inhibitor is cut as it come out through the plurality of orifices in the die.

The size of the orifice fix two of the dimensions of the product. Therefore, it is only necessary to cut the filaments to shorten the length. Typically, the extruded inhibitor is cut to a length/diameter ratio of from 0.5 to 3, preferably to a length/diameter ratio of from 1 to 2,

It may be advantageous to dry the extruded pellets. The drying of the extruded materials can be accomplished with standard drying equipment and methods known in the art. Typical driers include those commonly used in the art, for example belt driers and fluid bed driers.

Typicaily the dried extruded pellets have a residual moisture content generally ranging from 2.0 to 15 % by weight.

The rheology modifier in the pellets preferably consists of a polygalactomanan ether, a cellulose ether, or mixtures thereof.

The polygalactomannan ethers, in particular of guar, cassia, locust bean, fenugreek, sesbania and tara, which can be used in the formulations of the invention, are preferably hydroxyalkyl ethers of polyga!actomannans, for example hydroxyethyl ethers and hydroxypropyl ethers, carboxyalky! ethers of polygalactomannans, for example carboxymethyl ethers and carboxyethyl ethers, mixed ethers, hydroxyalkyl and carboxyalkyi, of polygalactomanans, cationic ethers of polygalactomanans, polygalactomannans or polygalactomannans ethers modified with hydrophobic groups (hydrophobically modified polygalactomannan ethers), for example hydrophobically modified hydroxyalkyl polygalactomannans.

The methods of preparation of polysaccharides ethers are well known in the art and include the reaction of the hydroxyl groups of polygalactomannans with an etherifying agent.

The polygalactomannan ethers may have hydroxyalkyl molar substitution (MS) between 0.1 and 3.0, preferably between 0.3 and 2.0, more preferably between 0.3 and 1.7; the degree of carboxyalkyl substitution (DS) can vary from 0.1 to 1.5, preferably from 0.1 to 1.0.

In the present disclosure, with the expression "molar substitution", we mean the average number of hydroxyalkyl substituents on each anhydrogiycosidic unit of the polysaccharide measured by means of ¹H- NMR.

The expression "degree of substitution" means the average number of hydroxyl groups substituted with a carboxyalkyl group for each anhydrogiycosidic unit of a polysaccharide and can be determined, for example, according to the standard method ASTM D1439 or by ¹H-NMR. The mixed ethers, hydroxyalkyl and carboxymethyl, may have a MS and a DS in the same range of the mono-ethers.

The poiygalactomannan cationic ethers may have a degree of cationic substitution comprised between 0,05 and 1.5.

In the present text, with the expression "degree of cationic substitution", we mean the average number of hydroxyl groups substituted with a cationic group on each anhydrogiycosidic unit of the polysaccharide determined by means of ^- R.

The hydrophobicaSly modified poiygalactomannan ethers may have a degree of hydrophobic substitution (DS_H) of 1_*10^"5 to 5_*10 , preferably from 1_*10^~4 to 1_*10 ^_1.

With the expression "degree of hydrophobic substitution", we mean the average number of hydrophobic substituents on each anhydrogiycosidic unit of the poiygalactomannan measured by means of gas- chromatography or ^- MR.

Preferably, the hydrophobically modified poiygalactomannan and poiygalactomannan ethers of the invention contain C₃-C₂4 alkyl chains as hydrophobic group. More preferably the hydrophobic group is a 2- ethylhexyl group or a Ci₆ chain.

The preferred poiygalactomannan ethers for the preparation of the pellets of the invention are hydroxypropyl ethers of polygalactomannans and hydroxypropyl ethers of polygalactomannans modified with hydrophobic groups.

The suitable cellulose ethers can be chosen, for example, among carboxymethyl cellulose (CMC), hydroxyethyt cellulose (HEC), ethyl hydroxyethyl cellulose (EHEC), methyl cellulose (MC), methyl hydroxyethyl celiulose (MHEC), hydroxypropyl methyl celiulose (HPMC ). Preferably the rheology modifier of the pellets consists of cellulose ethers selected among carboxymethyl celiulose (CMC), hydroxyethyl cellulose (HEC), ethyl hydroxyethyl cellulose (EHEC), methyl cellulose (MC), methyl hydroxyethyl cellulose (MHEC), hydroxypropyl methyl cellulose (HPMC); polyga!actomannan ethers chosen among polygalactomannan hydroxypropyl ethers of and hydrophobically modified polygalactomannan hydroxypropyl ethers polygalactomannans; mixtures thereof.

More preferably, the rheology modifier consists of carboxymethyl cellulose, hydroxypropyl guar, hydroxypropyl cassia, 2-hydroxypropyl-2- hydroxy-3-(2-ethyihexyloxy)propyl guar, Ci₆-hydrophobically modified hydroxypropyl guar, 2-hydroxypropyl-2-hydroxy-3-(2-ethylhexyloxy) propyl cassia, or mixtures thereof.

The carboxymethyl celiulose suitable for the realization of the present invention can be chosen among those commonly used in the industry and known to experts in the art. The carboxymethyl cellulose preferred for the realization of the present invention has a degree of substitution between 0.2 and 1.5, more preferably between 0.5 and 1.2, even more preferably between 0.6 and 1.1. Its Brookfield RVT® viscosity, measured on a 1% by weight water solution, at 20 rpm and 20 °C, is between 5 and 10,000 mPa_*s, preferably between 10 and 5,000 mPa_*s.

The carboxymethyl cellulose useful for the realization of the present invention may be a technical or purified carboxymethyl cellulose, which has a content of active substance comprised between 55 and 99.5 % by weight as dry matter, preferably from 70 to 98.5% by weight , and an about 2 -12% by weight of moisture.

The hydroxypropyl guar, hydroxypropyl cassia, 2-hydroxypropyl-2- hydroxy-3-(2-ethylhexyloxy)propyl guar, hydroxypropyl guar hydrophobically modified with a C₁₆ chain, 2-hydroxypropyl-2-hydroxy-3- (2-ethy!hexyloxy)propyl cassia, have preferably a hydroxypropy! molar substitution comprised between 0.2 and 2.0 and a degree of hydrophobic substitution comprised between 1_*10^"4 and 1_*10

According to a preferred embodiment, the rheoiogy modifier of the pel!ets consists of carboxymethyl cellulose, hydroxypropyl guar, hydroxypropyl cassia, or mixtures thereof.

According to another preferred embodiment, the rheoiogy modifier of the pellets consist of hydroxypropyl guar.

According to an additional preferred embodiment, the rheoiogy modifier of pellets consists of hydroxypropyl cassia .

According to yet another preferred embodiment, the rheoiogy modifier of the pellets consists of carboxymethyl cellulose.

Any of the dispersants that are normally used for the preparation of water-based paints are useful for the preparation of pellets of the present invention. Examples of these dispersants are water-soluble salts of medium/low molecular weight acrylic (co)polymers, such as homopolymers of (meth)acrylic acid; polyphosphates, for example tripolyphosphate and hexametaphosphate; humic acids; lignin sulfonate; sodium silicates, sodium carbonate and mixtures thereof. Preferred dispersants are the water soluble salts of medium/low molecular weight acrylic (co)polymers and polyphosphates.

According to a preferred aspect, the dispersant present in the pellets is a linear water-soluble sodium polyacrylate having a weight average molecular weight comprised between 1,000 and 10,000 daltons, an inorganic polyphosphate, or mixtures thereof.

According to a particularly preferred aspect, the dispersant present in the pellets is a mixture of the said sodium polyacrylate with sodium hexametaphosphate.

The defoamer present in the pellets is usually selected among those commonly used in the field, for example, aluminum stearate, ethylene oxide/propylene oxide copolymers, polydimethylsiloxanes, colloidal silica, mineral oils, or mixtures thereof.

Advantageously the pellets also include other additives for water-based paints, such as surfactants, thixotropic agents, softeners, pH regulators, further film-forming and leveling agents, drying agents, anti-stripping agents, antifouling agents, protective and stabilizating agents against UV light, biocides.

Suitable biocides are, for example, p-chloro-m-cresol, o-phenyl phenol, 2- bromo-2-nitropropane-l,3-dio! (Bronopol) or compounds of the class of derivatives of isothiazolin-3-one, such as benzoisothiazolinone (BIT), 5- chloro-2-methyl-4-isothiazoline-3-one (CIT or CMIT) and methyl-2-4- isothiazoline-3-one (MIT). Other examples are sodium and zinc pyrithione, parabens, sodium benzoate, formaldehyde releasers, etc. They are used both in the form of powders and liquids, and also as synergistic mixtures.

The suitable surfactants are preferably humectants and emulsifiers widely used in paints and in commercial coating materials. In particular, they may be of the anionic, cationic, non-ionic or amphoteric, and both monomeric and polymeric.

Also thixotropic agents can be included the formulations for paints. They include, without limitation, phyllosilicates, pyrogenic silica, and organic compounds, such as high molecular weight polyolefins, hydrogenated castor oil, polyamides or polyacrylates with high molecular weight.

If not introduced into the pellets, the conventional additives for water- based paints indicated above may be separately added to the water during the preparation of painting.

The extruded pellets of the invention can be added to the water during the preparation of the water-based paints, either as such or as a dispersion in water at a concentration of 1 to 30 % by weight; preferably they are added in dry form.

Any kind of water-based paints can be prepared using the extruded pellets of the invention.

The formulations for paints of the invention obtained by the above described method can be used for the preparation of different kinds of paints, such as dispersion paints, wall paints, interior paint, washable paints, emulsion paints, bright paints, super-bright paints, satin paints, exterior paints, paints based only on fillers, silicate paints, mono-layer and double-layer paints, solvent-based paints, structural coatings, spray paints, primers, sand paints, etc.

EXAMPLES

In the Examples, the following materials were used :

• Carboxymethyl cellulose sodium salt (CMC), DS 0.7 and Brookfieid

RVT® viscosity, 1% in water, at 20 °C and 20 rpm, of 2800 mPa_*s. » Hydroxypropyl Cassia (HPCa), MS 1.3 and a Brookfieid RVT® viscosity, 2% by weight in water, at 20° C and 20 rpm of 3000 mPa_*s.

· Polyacrylic Dispersant, 44% by weight solution of a polyacryllc acid, sodium salt, with a weight average molecular weight of about 6000 daltons.

Examples 1-2

The ingredients of Table 1 were homogenized in a mixer, using a "K" shaped stirrer. During the homogenization, deionized water was slowly added (in about 10 minutes) trying to avoid agglomeration of the ingredients.

Table 1

The mixtures of Examples 1-2 were fed into a laboratory Bausano TR80® extruder equipped with 2 counter rotating screws, a multi-hole die with holes with a diameter of 2.5 mm and a die-faced cutter.

The speed of the screws and the cutter was adjusted to produce about 50-80 g/min of pellets about 2.5 mm large and 2.6 mm long. The interna! temperature and pressure during extrusion were around 60-70 °C and 13 Pa respectively.

The extruded pellets were dried on fluid bed at 80 °C to obtain a residual moisture of about 7 % by weight.

Paint Formulations

The extruded pellets of Examples 1 and 2 were used to formulate a water- based paint with PVC of 92 and another with a PVC of 80. The ingredients are reported in Table 2 and 3 respectively.

Table 2

For each kind of pellets 1200 grams of water-based paint were prepared according to the following procedure:

Phase A All the ingredients were weighed in a plastic beaker and mixed stirring gently using a rod stirrer.

Phase B After 5 minutes, the pellets were gradually poured into the mixture.

Phase C After 10 minutes, the pigments/fillers were added in the order as reported in Table 2 and dispersed at high speed for 15 minutes. Phase D At the end of the dispersion, the stirrer speed was reduced and the latest ingredients of the formulations were added to the mixture; after 5 minutes of homogenization each water- based paint was cooled at room temperature.

The quaiity of the water-based paints, that is their homogeneity, i.e. the absence of lumps of additives in the mass, were evaluated by coating a 120 micron film on a suitable substrate, The preparation was carried out on Penopac Chart IB substrate with a 120 micron blade, evaluating visually the presence of gels which would adversely affect the homogeneity of the surface. Table 5 shows the appearance of the obtained films and the Brookfield RVT® viscosity measured at 20 rpm and 20 °C in mPa_*s (Vx) of the water-based paints 24 hours after their preparation.

Table 4

The results demonstrate that the extruded pellets of Examples 1 and 2 are able to give more than adequate characteristics of viscosity and homogeneity to the water-based paints.

ANY REFERENCE TO TABLE 5 SHALL BE CONSIDERED AS NON-EXISTENT

Claims

1) A method for the preparation of water-based paints comprising mixing in water:

a) a pigment and/or a filler;

b) an organic binder;

c) extruded pellets containing : i) from 35 to 75 % by weight (on dry matter) of a rheological modifier consisting of one or more polysaccharides or polysaccharide derivatives; ii) from 15 to 35% by weight (on dry matter) of a dispersant; Mi) from 8 to 30% by weight (on dry matter) of a defoamer,

the pellets being used in an amount ranging from 0.3 to 5 % by weight based on the final weight of the water-based paint.

2) The method according to claim 1) in which the rheologica! modifier of the pellets consists of cellulose ethers, polygalactomannan ethers, or mixtures thereof.

3) The method according to claim 2) in which the rheological modifier of the peliets consists of cellulose ethers selected in group consisting of carboxymethyi cellulose (CMC), hydroxyethyl cellulose (HEC), ethyl hydroxyethyl cellulose (EHEC), methyl cellulose (MC) , methyl hydroxyethyl cellulose (MHEC), hydroxypropyl methyl cellulose (HPMC); polygalactomannan ethers selected in the group consisting of polygalactomannan hydroxypropyl ethers and hydrophobically modified polygalactomannan hydroxypropyl ethers; mixture thereof.

4) The method according to claim 3) in which the rheological modifier of the pellets consists of carboxymethyi cellulose, hydroxypropyl guar, hydroxypropyl cassia, 2-hydroxypropyl-2-hydroxy-3-(2- ethylhexy!oxy)propyl guar, Ci₆-hydrophobical!y modified hydroxypropyl guar, 2-hydroxypropyl-2-hydroxy-3-(2-ethylhexyloxy) propyl cassia, or mixtures thereof.

5) The method according to claim 4) in which the carboxymethyi cellulose has substitution degree comprised between 0.2 and 1.5 and the hydroxypropyl guar, hydroxypropyl cassia, 2-hydroxypropyl-2- hydroxy-3-(2-ethyihexyloxy) propyl guar, C16-hydrophobicaliy

18 modified hydroxypropyl guar and 2-hydroxypropyl-2-hydroxy-3-(2- ethylhexyloxy) propyl have molar substitution comprised between 0.2 and 2 and hydrophobic substitution degree comprised between 1_*10^"4 and 1_*10^~\

6) The method according to c!aim 5) in which the rheology modifier consists of hydroxypropyl cassia hydroxypropyl guar, carboxymethyi cellulose or mixture thereof.

7) The method according to claim 6) in which the rheology modifier consists of carboxymethyi cellulose.

8) The method according to claim 6) in which the rheology modifier consists of hydroxypropyl guar.

9) The method according to claim 6) in which the rheology modifier consists of hydroxypropyl cassia.

10) The method according to any of the preceding claims in which the dispersant of the pellets is a water soluble salt of a linear acrylic polymer having weight average molecular weight between 1,000 and 10,000 dalton, an inorganic polyphosphate, or mixtures thereof.

11) The method according to any of the preceding claims in which the defoamer is aluminium stearate, an ethylene oxide/propyiene oxide copolymer, a poiydimethylsiloxane, colloidal silica, a mineral oil, or mixtures thereof.

19