NO772204L - PROCEDURES FOR PREPARING A STABLE SUSPENSION OF SOLID PARTICLES IN THE OIL PHASE OF AN OIL-IN-WATER EMULSION - Google Patents

Description

•"'""Procedure for producing a stable suspension of solid particles in the oil phase of an oil-in-water emulsion.

The present invention relates to a method for producing a stable suspension of finely divided solid particles in an oil-in-water emulsion. With this method, a stable suspension of solid particles can thus be provided in an easily flowing liquid. In the following, the invention will be explained in more detail with reference to penetrating pigmented stains for the protection of wood and wood products, and which do not, or only to a negligible extent, exhibit a tendency to layering or sedimentation of pigments or other suspended solid particles, but can e.g. also find application in the production of pigmented paints, abrasives, polishing agents, cleaning agents, etc.

When applying stain on a single-pore surface, e.g. a wooden surface, one of the conditions for achieving good penetration is a relatively low viscosity of the liquid in relation to the rate of evaporation. As a short drying time is desired in practice, the absolute viscosity must therefore be low. If the stain is fully or partially colored with the help of pigment particles, these will sediment on standing according to Stoke's law, which applies approximately in the area of practical interest, i.e. that the sedimentation rate is a function of particle size and viscosity. This means that the stain for use must be subjected to vigorous stirring, so that these agents are most often sold in pails or the like. with good agitation. If the stirring is not carried out thoroughly enough, color errors occur with regard to shade and color strength when using the product.

It is known to counter this problem in several ways. The simplest method is to reduce the particle size to colloid dimensions, so that sedimentation, even over long periods of time, becomes negligible. This method can only be used for particularly expensive products, as the production of such a pigment dispersion is very expensive.

Another widely used method is to flocculate the pigment by adding so-called "anti-settling additives", e.g. different polar compounds. This does not prevent settling, but the sediment is of such a nature that it can very easily be stirred up again. - In extreme cases, the pigment flocculates so strongly that the product can even be sold in barrels that only require a brief shake before use. With this flocculation of the pigment, however, the treated surface acquires a gritty, unappealing appearance, and the penetration possibilities of the pigment itself are greatly reduced.

A third possibility that also finds application is to make the viscosity dependent on shear force and time dependent by adding agents that provide the rheological property known as thixotropy, such as e.g. polyamide derivatives, colloidal silicic acid, etc. for stain types based on organic solvents. In this way, the viscosity can be kept high during storage, while it acquires the favorable low value for penetration at the moment of application itself and for a fairly short period of time thereafter. However, this method is limited to cases where very high levels occur

shear forces at. the imposition, e.g. by brush application', and due to the fact that the reduction in viscosity in practice is very short-lived, does not provide opportunities to achieve a sufficiently deep penetration.

The purpose of the present invention is to specify a method which is not affected by the above-mentioned disadvantages and where, in the case of stains, a ± product can be obtained with a good penetration ability and a good protective effect, and which does not have a particular tendency for layering or sedimentation of the pigment even when long delay. More generally, it is the purpose of the invention to provide stable suspensions of finely divided solid particles in an oil phase in an oil-in-water emulsion without a particular tendency to settle.

This is achieved by the method according to the invention by

that the finely divided solid particles are triturated in an oil phase in the presence of one or more dispersing aids, which can make the particles' surface oleophilic, as well as one or more sterically and/or electrostatically stabilizing dispersing agents to form a stabilized suspension, after which this is emulsified in an aqueous medium in the presence of one or more emulsifiers known per se, which are compatible with the dispersing agent or auxiliaries mentioned. The particles are mixed into and thus retained in the inner phase of a stable oil-in-water emulsion, where the outer continuous phase is thus made up of a free-flowing liquid.

It has surprisingly been shown that by thus partly imparting suitable oleophilic surface properties to the particles and partly by providing suitable steric and/or electrostatic forces between the particles and between the particles and. the interface layer to the aqueous phase of the emulsion,

can achieve stable suspensions without or with an extremely small tendency for the particles to settle on standing.

Methods which, on an immediate consideration, have certain points of similarity with the present one, but which on closer analysis turn out to involve decisive differences and which do not intend or lead to products with the long-term stability achievable by the method according to the invention, are described in a number of publications, thus:

DT-OS 22 12 521 describes a method for the production of

an electrophoresis bath in emulsion form, where, among other things, a pigment suspension in a water-dissolved fully neutralized carboxylic acid is added to the bath. The specified precautions take

however, the aim is to maintain the pigment in the water phase, and the method does not aim at the production of long-term stable products.

Swedish patent no. 1^ 9. 292 deals with a method for producing plastic emulsions, which e.g. are usable as glue or for fixing pigments on textiles. In Example 5, copper phthalocyanine blue is dispersed in a concentrated emulsifier solution, to which further emulsifier, water and an aminoplast emulsion are added. This emulsion, which thus does not contain the pigment in the emulsion's internal phase, then the aminoplast emulsion ion. is prepared and added separately, further thickened with an oil-in-water emulsion of gasoline in an emulsifier solution of the aforementioned type. Here too, the pigment must not be expected to bind to the inner phase of the emulsion in any way. The characteristic features of the invention are thus not present here at all.

Swedish patent document no. 1^5.667 describes a method for producing an emulsion concentrate which must be diluted immediately before use, so that the long-term stability becomes immaterial. More specifically, the purpose is to produce emulsions where water-insoluble protective agents are dissolved in the inner phase by a method where these possible negative effects on the emulsion stability due to interaction with the outer phase are eliminated by a cumbersome step-by-step correction for these interactions.

The possibility of dispersed active substances is not described

in more detail in these publications, and nothing is mentioned about the conditions for possibly stabilizing a substance dispersed in the internal phase against precipitation. Thus, there are no points of similarity with the features that are characteristic of the present invention.

DT-OS 22 56 757 describes an emulsion particularly applicable as a spray liquid, which can be both of the water-in-oil type and of the oil-in-water type, and where in one phase there are dispersed particles of a substance with antibacterial, isecticide, herbicide, or plate growth modifying effect.

These liquids are allegedly more stable than known products of the same type, but stability has only been documented for <*>+8 hours, and it is particularly emphasized that the products are well re-dispersible in contrast to the known products.

The special feature of the exchange liquid is partly that you set the density ratio and volume ratio between the phases within specified limits and partly that you choose a suitable non-ionic or anionic surfactant, as here c hydrophobic or hydrophilic, depending on whether you wanted the particles to be itself in the oil or water phase.

It cannot be ruled out that particles of substances of the aforementioned type can be provided with sufficient stability or at least redispersibility for the purpose of application in this way, but it has been demonstrated by forsbk that the aforementioned measures are completely insufficient for a long-term stabilization of pigment.pea oil je-in-water-emulsion ions.

None of the above-mentioned documents thus mention the distinctive combination of a dispersing aid, which can make the particle surface oleophilic, a dispersing agent which can stabilize the internal phase of the emulsion and a compatible emulsifier system, which can stabilize the emulsion itself, which is distinctive for the method according to the invention.

In an oil-in-water emulsion of the type referred to here, the retention of the particles in the inner phase and thus the stability of the suspension in the present invention can be more precisely provided in the following way: To achieve that the particles, e.g. the pigment particles are made oleophilic, i.e. better moistened by oil than by water, they are rubbed out in the presence of suitable surface-active agents, so that they are brought into the condition that is a prerequisite for the actual mixing in the oil phase. These agents are here and in the following referred to as dispersing aids and, in the case of pigments, can also be referred to as "pigment humectants-1".

In the method according to the invention, this can be done by treatment with one or more surface-active agents selected from among non-ionic agents, such as e.g. alkyl polyethoxylates and alkyl aryl polyglycol ethers, further ampholytic agents such as e.g. electroneutral salts of cation-active and anion-active groups, e.g. salts of fatty amines' with fatty acids or polycarboxylic acids, further anionic agents such as e.g. fatty alcohol sulfonates, sulfimides, alkylaryl sulfonates, especially alkylbenzene and -naphthalene sulfonates, phosphate esters, metal naphthenates and metal salts of fatty acids, as well as cationic agents such as e.g. quaternary ammonium compounds, alkylimidazole salts and lecithin. These agents can also give the individual particles an electric surface charge as if the particles' original potential

(zeta potential) Is not sufficiently large, contributes to an anti-flocculating effect as a result of electrostatic repulsion (repulsion). Thus, e.g. the pigment particles from the manufacturing process or storage are often surrounded by a film of water, which, in order to achieve a good dispersion, must be displaced by the rubbing in the presence of the surface-active agent(s). In addition to this change in the surface properties of the particles themselves, the resulting suspension of the particles in the oil phase can be further stabilized by the invention by adding agents to the oil phase during the rubbing which provide electrostatically acting forces between the particles. These can be selected from the same types as the above-mentioned oleophilizing dispersing aids, except for the non-ionic ones.

However, it has been shown that the best stability of the suspension is achieved if oil-dissolving agents are added to the oil phase during the extraction, which can also provide steric stabilization. Such funds are e.g. surface-active soluble polymers with a polar character, such as polymers of oxidized unsaturated fatty acids and esters or ethers thereof, partially polymerized esters of polycarboxylic acids, such as e.g. alkyds, and styrene-, isocyanate- and silicone-modified variants thereof, acrylic-modified and/or epoxidized oils~ and resins, aldehyde condensation products with amines and/or phenols, as well as polyethers and polyvinyl derivatives. It has been shown that an effective stabilization is usually first observed with polymers with a molecular weight of approx. 1,500 and rises with increasing molecular weight up to approx. 10,000, after which the effect may diminish.

It should be noted that a number of the aforementioned types of surface-active agents beyond both an electrostatic and a steric stabilization, as well as they can affect the particle surface itself, after which, depending on the circumstances, one can use the same or several different surface-active agents in addition to the dispersing aid.

The specific choice of surface-active agents depends, among other things, on the nature of the particles and the desired end product and can be determined by the expert by trial. A preferred combination when producing pigmented stains is a dispersing aid containing a hydrophobic group of a cationically active character, such as e.g. an amine, optionally in the form of an amine salt, especially with a hydrophobic anion (electroneutral salt), or in the form of an amine ester, such as e.g. a lecithin, in combination with a sterically stabilizing surfactant polymer as discussed above.

It is of decisive importance for a successful implementation of the method that the particles are incorporated into a stable emulsion. This stability is provided by the addition of one or more emulsifiers, which induce steric and/or electrostatic forces between the individual particles of the inner phase (oil phase) of the emulsion. In this connection, it is of decisive importance that this stabilization of the emulsion does not occur at the expense of the stability of the suspension in the inner phase, and for this reason such emulsifiers are chosen that do not affect the stability of the oil phase induced by the dispersants and auxiliaries.

These emulsifiers, which can be ionic or non-ionic

type can be added to one or both phases of the emulsion.

For ionic species (cationic or anionic), electrostatic repulsion between the droplets in the internal phase plays a significant role in the stabilization, while the effect of non-ionic species is primarily based on steric repulsion and is largely independent of pH. The stability is further influenced by the distribution of the surfactant between the two phases, and especially for non-ionic types, a so-called HLb value is often calculated

(hydrophilic-lipophilic balance) for the selection of the emulsifier best suited for a given type of oil.

To achieve electrostatically acting forces during the stabilization of the emulsion, one or more surface-active substances can be added, which act in the outer phase and in the boundary layer against the inner phase, selected from among ionic emulsifiers and protective colloids, such as alkylaryl and alkyl sulfonates,

amine and metal salts thereof, such as e.g. calcium alkylaryl sulfonates, carboxylic acids and polycarboxylic acids and their salts (soaps), such as e.g. polyacrylic acid salts with ammonia, amines and alkali metals, polyvinyl carboxylic acids and partial esters and/or salts thereof, cellulose derivatives as well as polycondensed inorganic acids and salts thereof, such as e.g. sodium hexameta-phosphate and lithium polysilicate.

To achieve sterically acting forces during the stabilization of the emulsion, one or more ionic surfactants of the type mentioned above under electrostatic stabilization and/or non-ionic agents, such as e.g. fatty acid

and fatty alcohol polyglycol ethers, polyethoxylated alkylphenols, polycarboxylic acid esters and ethers, such as e.g. fatty alcohol succinates, sorbitol esters and their ethers, sorbitan ether polyethoxylates, polyvinyl alcohols, polyethylene oxide and ethers and esters thereof as well as cellulose derivatives such as e.g. hydroxyethyl-r

cellulose.

It has been shown that a combination of a non-ionic

emulsifier with the correct HLb value (e.g. of the alkylphenol-polyethylene oxide adduct type)' added to the inner phase and a small amount of anionic surfactant of the protective colloid type, e.g. a polyacrylate or a polyvinyl maleinate, added to the outer phase is particularly suitable for stabilizing the emulsion itself, as it e.g. works satisfactorily in suspending pigments in the inner phase of emulsions of vegetable oils and their synthetic analogues or derivatives thereof, and,_ does not adversely affect the particle stability in the inner phase. The anionic component mentioned can also function to set a suitable viscosity and to complex-form heavy metal ions, which otherwise as contamination can .- ...j..j. -enhance the electrostatic stabilization, but these functions can also be ensured by separate components of a cationic, anionic or non-ionic nature, e.g. using sodium tripolyphosphate.

The oil phase can also be used to improve stability, especially when the suspension is used in a highly diluted state, where there may be a risk of stratification due to large density differences, one or more specific weight equalizing agents, including light liquids, such as aliphatic and aromatic hydrocarbons, and heavy liquids such as e.g. halogenated hydrocarbons, e.g. ethylene dichloride, tris-2,3-dibromopropyl phosphate and chlorinated paraffins. You can also add solids, e.g. light substances such as wax and microscopic hollow glass balls (microballoons) and heavy substances such as solid chlorinated paraffin and antimony trioxide. These can also serve as flame retardants.

As usable pigments, e.g. mention is made of oxides and sparingly soluble salts of alkaline earth metals and metals in the transition series, e.g. iron oxides, chromium oxide, zinc oxide, barium sulphate, titanium dioxide, calcium carbonate, aluminum and magnesium silicate, other oxides and elements such as e.g. silicon oxide, "carbon-black", aluminum powder and zinc dust, as well as organic compounds such as helium green, phthalocyanine blue, benzidine yellow and perylenercfc. However, the nature of the pigment is not critical to the invention.

Finally, other protective substances of various kinds can be added to the oil or water phase, which may also be possible

have the form of finely divided solid particles, e.g. biocides, such as -. fungicides, e.g. tetrachloroisophthalonitrile, copper-8-hydroxyquinoline, tributyltin oxide and derivatives thereof, preservatives such as e.g. sodium pyridone-thione-1 and 2,2-dibromoglutaro-dinitrile, insecticides such as lindane or endosulfan, IR-reflecting agents and special UV-absorbing agents, as well as oil-soluble pigment binders can be added to the oil phase, e.g. possibly modified oils that dry by oxidation. It has surprisingly turned out, however, that the need for UV-absorbing agents in the pigmented stains in question is very low, as they result in particularly good penetration and distribution of the pigment in treated wooden surfaces.

Water-soluble or water-dispersible binders can be added to the water phase, e.g. polyacrylate dispersions, styrene-butadiene-polymer dispersions or polyvinyl acetate dispersions If desired, an oxidation catalyst (siccative) can also be added, which is complexed in such a way that the equilibrium concentration of the free catalyst in the outer phase is so small that the emulsion's stabilization system is not significantly affected thereof, and optionally a stabilizer and/or an antioxidant to stabilize the siccative.

The stable pigment suspensions produced by the invention have the further advantage that they are suitable for obtaining reproducible color shades. When different pigments are mixed together in the oil phase, co-flocculation has previously been observed, which makes accurate and reproducible tinting difficult. It has been shown that both by mixing ready-made pigment suspensions of the type in question and by crushing the pigments in the oil phase in the method according to the invention, this co-flocculation is avoided, and thus a desired color shade can be achieved in a simple way.

The mixing ratio between the constituents can vary within wide limits depending on the desired end product and not least on the type of solid particles.

The water-in-water emulsion can thus contain from 1-70% oil by weight, but will usually contain approx. 20-30% by weight.

For the production of e.g. A pigmented stain is usually first extracted with a paste with the following composition:

as the sum of the components amounts to 100 parts by weight.

50 parts by weight of this paste are then used

This oil phase is emulsified in a water phase which may contain:

as well as demineralized water to 1,000 parts by weight.

The invention is illustrated in more detail using the following examples:

EXAMPLE 1

Preparation of a pigmented stain.

By dispersing on a ball mold, an orange-red paste was prepared by trituring 50 parts by weight of transparent iron oxide red (e.g. "VN 188", which is an orange-red hydrophilic pigment sold by Siegle & Co.), 5 parts by weight of dispersing aid

(pigment moisturizer) e.g. "Disperbyk", which is an electroneutral salt prepared by reacting an alkylolamine salt with a polycarboxylic acid, sold by Byk-Mallinckrodt, and 55 parts by weight of soybean oil alkyd with an oil length of 65% (sterically stabilizing dispersant for the pigment). The dispersion took place at ambient temperature to a particle size of a maximum of 20 pm. 50 g of this paste is mixed at ambient temperature for approx. 10 minutes with 200 g of 100% (solvent-free) linseed oil alkyd with an oil length of approx. 80%, which acts as a binder, 12 g of nonylphenol dodecaethoxylate (sterically stabilizing non-ionic emulsifier), 1.2 g of cobalt naphthenate (6% Co-siccativ), 0.8 g of a 38%

o-phenanthroline solution in butyl glycol "activ 8" - sold by Vanderbilt Corp. (stabilizer for siccative against hydrolysis) as well as 2 g of methyl ethyl ketoxime (volatile antioxidant that acts as an anti-skin-forming agent).

The thus obtained mixture of 266 g, which can be perceived as a thin oil paint, is dispersed at ambient temperature for approx.

10 minutes in a mixture of 210 g demineralized water and 30 g 1 5%

polyvinylmaleic acid alkyl glycol ester ammonium salt ("Thickner LN"), which is an anionic stabilizer, which further acts as'

complexing agent and thickener, which are first mixed in approx.

5 min. with a further 60 g of demineralised water. This is achieved

566 g of pigment dispersion which has the character of an emulsion paint, and to which, while stirring, h^ k g of demineralized water is added,

to which biocides and other protective agents may have been added.

The stain thus obtained (1000 g) has at 20°C a viscosity of 12 cP, pH 7.8, specific gravity 1.083. It is cheap and can be produced easily, has excellent penetration when applied to wooden surfaces and causes no air pollution when used. It is stable when left standing and has no tendency for the pigment to settle, even after a storage period of

months The stain also has excellent freeze-thaw ■ stability. Thus, no changes to the product are observed after a standard sample comprising 3 freezings to -18°C with intermediate thawings.

In the same way, stains have been produced using pigments with other colors, such as "VN 088", which is a yellow

iron oxide pigment and "VN 288" which is a rbdt iron oxide pigment, further "carbon-black" and phthalocyanin blue,' and other dispersing aids, such as e.g. "Texaphor 963" which is an electroneutral pigment humectant, and lecithin, as well as other dispersants, such as e.g. tall oil alkyds. Stains of the same excellent quality are obtained.

For comparison, identical mordants have been produced, omitting the dispersing aid characteristic of the invention. In all cases, the pigments settled after a short period of time.

The protective effect of a number of

stains produced as stated above when treating wooden

surfaces. Under accelerating test conditions with regard to weather resistance, the products in question have shown a surprisingly high degree of weather resistance, and have, among other things, been shown to surpass common stain types on both an alkyd-solvent basis and an acrylic dispersion basis, under otherwise identical conditions with regard to degree of pigmentation , binder concentration, etc.

EXAMPLE 2

Manufacture, of pigmented stain.

By dispersing on ball mold, a black paste was produced from 15 parts by weight "carbon-black" ("Printex 300"), h parts by weight bentonite (thickening agent, 10% in mineral turpentine),

1 part by weight dispersing aid ("Disperbyk"), 35 parts by weight

linol jealky-d (dispersant) and h$ parts by weight of mineral turpentine (specific weight equalizing agent).

50 g of this paste was treated analogously to that in example 1

produced paste, and a stable stain was obtained with a . ^ specific gravity of 1.03, pH 7.8 and viscosity 1'2 cP. This stain also exhibits excellent penetration and is stable even with further high dilution.

EXAMPLE

A polishing agent was prepared by grinding together 1 part by weight diatomaceous earth, 8 parts by weight dearomatized turpentine, a 1 part by weight, alkyd, 0.1 part by weight linoleyltrimethylenediamine dioleate (dispersing aid), 0.5 part by weight polyethylene glycol dioleate (PEG ^00 - dioleate), which then was emulsified in 89.0 parts by weight of water containing 0.0025 parts by weight of polyacrylic acid ammonium salt "Acrysol ASE95" (anionic stabilizer). The odorless agent obtained was stable after a longer period of standing without a tendency to settle.

Claims (11)

1. Method for producing a stable suspension of finely divided solid particles in the oil phase in an oil-in-water emulsion, such as e.g. a pigmented stain, a pigmented paint, an abrasive or a polish, characterized in that the finely divided solid particles are triturated in an oil phase in the presence of one or more dispersing aids, which can make the surface of the particles oleophilic, as well as one or more sterically and/or electrostatically stabilizing dispersing agents to form a stabilized suspension, after which this is emulsified in an aqueous medium in the presence of one or more emulsifiers of such a type that they do not affect the stability of the oil phase caused by the said dispersing agent or dispersing aids. 2. Method as stated in claim 1, characterized in that one or more surface-active agents selected from among non-ionic agents, such as e.g. alkyl polyethoxylates and alkyl aryl polyglycol ethers, ampholytic agents such as e.g. electroneutral salts of cation-active and anion-active groups, e.g. salts of fatty amines with fatty acids or polycarboxylic acids, further anionic agents such as e.g. fatty alcohol sulfonates, sulfimides, alkylaryl sulfonates, especially alkylbenzene and -naphthalene sulfonates, phosphate esters, metal naphthenates and metal salts of fatty acids, as well as cationic agents such as e.g. quaternary ammonium compounds, alkylimidazole salts and. lecithin, and as stabilizing dispersants one or more of the above-mentioned surface-active agents or one or more surface-active soluble polymers of a polar nature are used, such as e.g. polymers of oxidized unsaturated fatty acids and esters or ethers thereof, partially polymerized esters of polycarboxylic acid such as e.g. alkyds, and styrene-, isocyanate- and silicone-modified versions thereof, acrylic-modified and/or epoxidized oils and resins, aldehyde condensation products with amines and/or phenols, as well as polyethers and polyvinyl derivatives. 3. Method as stated in claim 1 or 2, characterized in that a compound containing a hydrophobic group of cation-active character, such as an amine, possibly in the form of an amine salt, especially with a hydrophobic anion (electron neutral salt) is used as an oleophiling dispersing aid or an amine ester, such as lecithin, and that it. A sterically stabilizing surface-active polymer with a molecular weight of approx. 1500 - 10,000. h. Procedure as stated in claims 1-3, characterized in that, to stabilize the emulsion, "a non-ionic emulsifier is added to the oil phase and a smaller amount of an anionic surface-active agent of the protective colloid type is added to the water phase. 5. Method as specified in claim 1 - h, characterized by the fact that an agent is also added to the oil phase which balances the specific weight difference between the inner and outer phase. 6. Method as specified in claims 1-55, characterized in that one or more pigments are used as finely divided solid particles. 7. Method as stated in claim 6, characterized in that an oil-soluble pigment binder is also added to the oil phase. 8. Method as stated in claim 7, characterized in that an optionally modified oil which dries by oxidation is used as pigment binder. 9- Method as stated in claim 6, characterized in that a water-soluble or water-dispersible pigment binder is also added to the emulsion. 10. Method as stated in claim 9, characterized in that an acrylic-based pigment binder is used. 11. Method as stated in claims 1 - 10, characterized in that an oxidation catalyst (siccative) is further added which is complexed in such a form that the equilibrium concentration of the free catalyst in the outer phase is so small that the emulsion's stabilization system is not significantly affected by it .