JPS5993761A - Method of tackifying aqueous latex composition - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a process for thickening aqueous latex compositions, and more particularly to a process for thickening aqueous latex compositions containing tannic acid in conjunction with a film-forming polymeric latex. The invention also relates to the thickened aqueous latex compositions thus produced.

It is known to use acidic aqueous solutions of tannic acid to treat and protect rusted ferrous substrates (eg, wire-brushed rusted steel). Tannic acid forms a complex with iron salts on the surface of the rusted substrate, and this appears to not only bind and fix the rust particles but also protect them to a certain extent from further rusting. . The reaction of tannic acid to remove rust and form a protective layer on the surface of a ferrous substrate is manifested by the typical appearance of a dark, substantially black coating layer.

It is also known to use tannic acid in combination with paints containing acidic aqueous latexes of film-forming polymers, thereby providing greater retention of treated substrates (GBP 826,564). (as described in the book).

It would be highly desirable to be able to increase the viscosity of compositions containing tannic acid with film-forming latexes.

If the viscosity does not increase appropriately, it is difficult to achieve sufficient coating thickness, and furthermore, the coating composition has a tendency to flow down from non-horizontal surfaces, thereby making it difficult to ensure proper application by brush. make it difficult.

In practice, by simply adding a water-soluble thickener, a film-forming latex containing tannic acid and a desired viscosity and the required storage stability (i.e., does not irreversibly settle on storage or It is difficult to achieve a composition that has both (no hardening) and no hardening. In many common commercially available polymer latices (which, of course, do not contain tannic acid), which are often prepared by using ionic (cationic or anionic) surfactants, the addition of thickeners to the polymer latex Destabilization of the system often occurs; as a result, agglomeration occurs (making the latex unsuitable as a film-forming agent) and the polymer precipitates out of the latex. However, thickened commercially available polymeric compositions with the required stability and containing thickeners (and of course not containing tannic acid) do not contain non-ionic compounds either during polymerization or subsequently. This can often be achieved by incorporating surfactants (eg surfactants based on polyethylene oxide, cellulose derivatives or polyvinyl alcohol). Unfortunately, polymeric latex/thickener systems in which tannic acid is additionally present and non-ionic surfactants are incorporated, in the inventor's experience, show that the combination of tannic acid and non-ionic surfactants is as a result of which the stabilizing effect of the surfactant is destroyed; furthermore, said interaction reduces the ability of tannic acid to complex with the treated substrate, thereby Protection of the substrate is not very effective.

This interaction between tannic acid and nonionic surfactants is found virtually elsewhere in the literature. For example, Example 6 of British Patent Publication No. 2,075,538 shows that when a latex containing a nonionic surfactant based on polyethylene oxide is added to a tannic acid solution, coagulation occurs violently. has been done. In this British Patent Publication, a storage-stable, film-forming latex composition containing tannic acid (for use as a rust-inhibiting/rust-removal primer) is defined as a film-forming latex composition containing covalently bonded acid groups. Coalescing (e.g. carboxylated polymers)
This is accomplished by using an ion-stabilized latex. According to this British Patent Publication, thickened latexes can inter alia be achieved without impairing storage stability by adding thickeners to such latex compositions. However, the inventor's experience has shown that the solution to this problem by using a thickening agent is that the preferred thickening agent of GB 2,075,538
Even when using other ionically stabilized polymer latexes containing tannic acid (acid salts of alginate), this is generally not a successful solution as destabilization still occurs, either rapidly or eventually.

The inventors therefore sought another solution to this problem.

The present inventor has discovered that by using a thickening agent introduced as a component of an aqueous dispersion of finely divided fumed silica (SiO2) particles, it becomes stable even in the absence of a nonionic surfactant. Thickened latex compositions can be produced.

According to the invention, therefore, in a method for thickening an acidic aqueous coating composition comprising tannic acid and a latex of film-forming compound and substantially free of nonionic surfactants. , incorporating into said aqueous coating composition a water-soluble thickener for aqueous latices that is non-complexing with tannic acid in the form of a gel-like aqueous dispersion containing uniformly dispersed particles of fumed silica; A method of thickening acidic aqueous coating compositions is provided, characterized in that said thickening agent is also compatible with the tannic acid used in the aqueous coating composition.

According to another aspect of the invention, a thickened acidic aqueous coating composition comprising tannic acid and a latex of a film-forming polymer and substantially free of nonionic surfactants. In the aqueous coating composition, the aqueous coating composition is a gel-like aqueous coating composition comprising a water-soluble thickener for an aqueous latex which is non-complexing with tannic acid and which contains uniformly dispersed particles of fumed silica. a thickening composition comprising a dispersion, wherein said thickening agent is also compatible with the tannic acid used in the aqueous coating composition. A coating composition is provided.

The thickening composition may optionally also contain tannic acid, and in a preferred embodiment all the tannic acid to be used in the acidic aqueous coating composition is incorporated with the thickening composition. In other words, in this preferred embodiment, all of the tannic acid used in the aqueous coating composition is introduced into the aqueous coating composition as a component of the gel-like aqueous dispersion of the thickener.

Gel-like aqueous dispersions containing thickeners and dispersed silica particles act to thicken tannic acid-containing polymer latexes, often at relatively high temperatures (e.g. 60°C).
(below) makes the polymer latex storage stable for long periods of time. The silica particles described above “structure” the gel-like dispersion.
It is believed that the thickening agent can be adsorbed onto the silica particles (which acts as a carrier for the thickening agent); as a result, the thickening agent is thus It cannot be in a form that causes aggregation or coagulation.

The fumed silica used in this invention is a very finely divided form of silica having submicron sized particles. Various grades of fumed silica are sold by the company Degussa under the general quality name "Aerosil" and these grades range from 7 to 1, for example.
It has an average major particle size in the range of 6 nm and a very high purity (>99.8%) with respect to silica content. "Aerosil" fumed silica is said to be coagulated silicon dioxide obtained by hydrolyzing silicon tetrachloride in an oxygen-hydrogen flame.

Polymers that can be used as film-forming polymers in the aqueous latex used in the present invention include homopolymers and copolymers of the following components: vinyl chloride; vinylidene chloride; 1 to 18 in the alkyl group.
vinyl esters of alkanoic acids with 1 to 18 carbon atoms, especially vinyl acetate; acrylic and methacrylic esters of alkanoic acids with 1 to 18 carbon atoms in the alkyl group, especially 1 to 12 carbon atoms in the alkyl group esters such as methyl, butyl or 2-ethylhexyl esters; acrylonitrile, methacrylonitrile; monoethylenically unsaturated hydrocarbons such as ethylene, isobutene, styrene and α-methylstyrene.

The polymers described above may also optionally contain small amounts of one or more α,β-unsaturated carboxylic acids.

The proportion of such one or more carboxylic acids can be, for example, from 0.2 to 10 parts by weight per 100 parts of the total monomer component of the polymer. α,β-unsaturated carboxylic acids that can be used include acrylic acid, methacrylic acid, itaconic acid and citraconic acid.

The invention is particularly advantageous when the polymer in the aqueous latex is derived from one or more chlorine-containing monomers, for example (i
It is particularly advantageous when it is a copolymer of) vinyl chloride, (ii) vinylidene chloride and (iii) one or more alkyl acrylates or alkyl methacrylates having 1 to 12 carbon atoms in the alkyl group; The polymer may optionally contain one or more aliphatic α,β-unsaturated carboxylic acids, with typical proportions and representative acids of such acids being as described above. Examples of such copolymers are those described generally and specifically in the specification of the applicant's British Patent No. 1,558,411.

The production of polymeric aqueous latexes is described, for example, in British Patent No.
No. 558,411, well-established emulsion polymerization techniques can be used. It will be appreciated that the use of nonionic surfactants should be avoided since, as discussed above, nonionic surfactants interact with tannic acid. However, it is not harmful to use ionic, especially anionic, surfactants during polymerization, and in fact it may be advantageous to incorporate additional ionic surfactants into the thickened aqueous composition after polymerization. could be. This is because the surfactants can enhance the infiltration of aqueous compositions onto rusted substrates.

The suitability of a particular water-soluble thickener can be easily evaluated by a simple test. Clearly unsuitable thickeners are those that form water-insoluble complexes with tannic acid, and such thickeners do not contain the thickener at the concentrations envisaged for use in the preparation of coating compositions. This can be recognized by the formation of flocs or precipitates (often black or dark blue) when an aqueous solution of tannic acid is mixed with an aqueous solution of tannic acid. Examples of such complexing thickeners are polyethylene oxide, polyvinyl alcohol and starch.

A thickener is also unsuitable if it is incompatible with tannic acid as used in the composition; incompatibility means that the thickener solution is homogeneously dispersed with the tannic acid solution. For example, instead of this, precipitation of the thickener takes place or separation of the thickener and the tannic acid solution takes place to produce a separate layer. Such incompatible thickeners can be prepared by simply thoroughly mixing an aqueous solution of the thickener with an aqueous solution of tannic acid at the concentrations contemplated for use in the preparation of the coating composition, and then separation or separation as described above occurs. It can usually be recognized by the occurrence of precipitation. Examples of such immiscible thickeners are polyurethanes, polyacrylic acids, polyacrylamides and cellulosic derivatives such as hydroxypropylmethylcellulose. Sometimes, mixing the thickener solution and the tannic acid solution will give a homogeneous dispersion, but when fumed silica is additionally present, a heterogeneous dispersion will be obtained (this is because the thickener is in the coating composition). An example of another such unsuitable thickening agent is deuterone santagalactomannene gum) and alginic acid (its sodium salt).

Water-soluble thickeners suitable for use in the present invention include the linear polysaccharide xanthan gum (e.g. "Kelza").
n)S") and maleic anhydride/methyl vinyl ether copolymers (eg "thickener" LN).

The relative proportions of tannic acid, film-forming polymer latex, thickener, and silica carrier material will depend on a number of factors, such as the particular polymer latex used, the desired viscosity, and the stability required. can vary within a wide range.

In the inventor's general experience, it is appropriate to use at least 0.5% (by weight of film-forming polymer) of tannic acid to ensure adequate minimum rust removal and rust protection. . The normal range of tannic acid concentration is 3~
It is 15%. The fumed silica is present, for example, in the range 1-5% (by weight of the film-forming polymer) and the thickener is present, for example, in the range 0.05-0.8% (by weight of the film-forming polymer). exists in

The pH of the thickened latex composition is, for example, in the range 1-4.

The thickened aqueous coating compositions of the present invention may contain other additives such as stabilizers, fillers, pigments, dyes, plasticizers and fungicides.

Although the thickened coating compositions of the present invention are primarily intended for use in providing a subbing layer for subsequent painting, it is of course possible to use the treated substrate as is without further treatment. .

The present invention will be illustrated by the following examples and comparative examples.

Example 1 Dissolve 20 g of tannic acid in water (71 g).

A mixture of 8 g of fumed silica ("Aerosil" 300, average major particle size 7 nm) and 1 g of xanthan gum thickener ("Kelzan" S) is added to the tannic acid solution,
Mixing with high speed stirring yields a thick, smooth, gel-like brown dispersion.

15 g of the gel-like dispersion was prepared with sodium lauryl sulfate (0.15% by weight on total monomers) as an emulsifying surfactant.
) prepared using vinylidene chloride/vinyl chloride/2-
Ethylhexyl acrylate/acrylic acid copolymer (
100 g of an aqueous latex (containing 60% solids by weight) having a viscosity of about 15 centipoise; the mixture is prepared by tumbling the ingredients together for about 5 hours. The tannic acid concentration obtained is therefore 5% by weight (per weight of copolymer), the concentration of silica is 2% by weight (per weight of copolymer) and the concentration of xanthan gum is 0.25% by weight (per weight of copolymer). (per polymer weight).

The viscosity of the resulting thickened latex was 35 centipoise (measured immediately after manufacture using a Roto-Pisco viscometer at 180 revolutions/second), and the thickened latex remained stable even after storage at 60°C for one month. It is stable.

The thickened latex can be applied in one thick layer by brushing onto a wire-brushed rusted steel plate, which after drying is typical of ferrous substrates treated with tannic acid. A blackish coating layer was formed.

Example 2 Example 1 is repeated with largely the same results. The viscosity of the resulting thickened latex was 33 centipoise after standing overnight, and the thickened latex was stable upon storage at 40°C for 6 months with no observed decrease in viscosity.

Examples 3 and 4 The method of Example 2 is used except that in Example 3 the amount of tannic acid used is 6.6% by weight (per copolymer weight)
The amount of fumed silica was 2.7% by weight (based on the weight of the copolymer), and the amount of xanthan rubber used was 0.
．． 3% by weight (based on the weight of the copolymer); in Example 4, the amount of tannic acid used was 8.3% (based on the weight of the copolymer) and the amount of fumed silica used was 3.3% by weight (based on the weight of the copolymer).
% by weight (based on the weight of the copolymer) and the amount of xanthan gum used is 0.4% by weight (based on the weight of the copolymer).

(These amounts are achieved by adding 20 g and 30 g of the gel-like dispersion in Examples 3 and 4, respectively, to 100 g of latex instead of 15 g as in Example 2.) The viscosities of the thickened latexes obtained are 67 and 72 centipoise, respectively, after standing overnight. Additionally, both latexes were easily applied by brush to rusted steel plates to produce a typical blackish coating layer, and both remained stable even after storage for 6 months at 40°C, with no decrease in viscosity. Not found.

Examples 5, 6 and 7 These examples repeat the methods of Examples 2, 3 and 4, except that in each case the anionic surfactant "Dowfax"2A; sodium salt of benzene disulfonate) at a concentration of 0.1% by weight (per weight of the thickening gel-like dispersion to be mixed with the copolymer latex) during the preparation stage of the gel-like thickening dispersion. Add to thickened latex. With the addition of this anionic surfactant, the thickening also obtained for gel-like dispersions, other than the fact that the thickened coating composition appreciably wets the rusted steel substrate. There are no differences between the copolymer latexes prepared, in particular the viscosity and storage properties are the same.

Examples 8, 9 and 10 The procedure of Examples 2, 3 and 4 is repeated, but instead of xanthan gum as thickener methyl vinyl ether/
A 15% w/w aqueous solution of maleic anhydride copolymer (“
Thickener LN) 2g is used. Examples 8, 9 and 1
The concentrations of thickener LN in 0 are therefore 0.07%, 0.10% and 1.24% by weight, respectively, based on the weight of the copolymer, and the concentrations of tannic acid and silica are substantially respectively as in Example 2. , 3 and 4.

Similar to Examples 2, 3, and 4, the gel-like thickening dispersions prepared in Examples 8, 9, and 10 were thick, smooth, gel-like brown dispersions, and the resulting thickened The latexes had viscosities of 30, 58 and 65 centipoise, respectively, after standing for 24 hours and were storage stable for 6 months at 40°C, although only a very slight decrease in viscosity was found.

Examples 11, 12 and 13 These examples repeat the methods of Examples 8, 9 and 10, except that in each case a gel-like thickening dispersion is prepared as in Examples 5, 6 and 7. Add anionic surfactant "Dowfax"2A' (0.1%) during the step.
Also, the inclusion of this surfactant makes no difference to the gel-like dispersion other than the fact that the thickened coating composition wets the rusted copper stock more easily, and the resulting thickened coating composition There is little difference to the copolymer latex, in particular the viscosity and storage properties are the same.

Examples 14 and 15 These examples follow the method of Example 3, except that instead of Aerosil 300 (average major particle size 7 nm) the following ingredients are used as thickeners: Example 14; Aerosil
200 fumed silica (average major particle size 12 nm), Example 15; "Aerosil" 150 fumed silica (
A smooth, thick, gel-like thickening dispersion was obtained in each case, with an average major particle size of 14 nm), and the thickened copolymer latex obtained after standing for 24 hours was 55 centipoise in Example 14, Example 14. 15 for 4
It has a viscosity of 2 centipoise.

It was found that when these latexes were stored for one month at 40° C., the viscosity or stability was not affected.

Similar results were obtained when Thickener LN was used in place of the Kelzan S rubber thickener used in these examples.

Examples 16 and 17 Examples 16 and 17 follow the methods of Examples 3 and 9, respectively, except that instead of 8 g of Aerosil 300, in both cases 85% by weight of fumed silica and 15% by weight of alumina are used. "Aerosil" COK8, which is a mixture of
Use 8g of 4.

Similar results were achieved, with the thickened copolymer latexes obtained in Examples 16 and 17 each having a viscosity of about 60 centipoise, whereas the unthickened latex had a viscosity of about 15 centipoise. , the thickened latex is storage stable at 40° C. for one month at the time of writing these examples.

Example 18 This example follows the method of Example 3, except that instead of 8 g of Aerosil 300, 4 g of Aerosil 300
and 4 g of barite (BaSO4) particles,
20 g of thickening dispersion are used with 200 g of copolymer latex. The resulting thickened latex was found to have a viscosity of 32 centipoise and to be storage stable at 40°C.

Comparative Examples 1 and 2 These comparative examples follow the method of Example 3, with the exception that 8
In Comparative Example 1, instead of g of Aerosil 300, 8 g of precipitated silica (not fumed silica; average major particle size 40 n) was used in Comparative Example 1.
m), and in Comparative Example 2, 8 g of barite (BaSO4) was used.
Use particles.

In each case no thickening of the copolymer latex was achieved.

Comparative Example 3 In this comparative example, a series of experiments are conducted to investigate potential alternative water-soluble thickeners for use in the present invention. It has been found that all thickeners are unsuitable because they complex with or are incompatible with tannic acid as used in the compositions of the present invention.

In each case a 2% w/w aqueous solution of a potential thickener 1
0 g are mixed with 50 g of a 20% w/w aqueous solution of tannic acid and the mixture is shaken for 1 hour on an electric shaker. The results with various potential thickeners are as follows: Potential thickeners Reasons for unsuitability Polyethylene oxide Complexing polyvinyl alcohol Complexing starch
Complex forming polyurethane Incompatible polyacrylic acid
Incompatible polyacrylamide
Incompatible Hydroxypropyl Methyl Cellulose Incompatible Comparative Example 4 This comparative example attempts to thicken the copolymer latex used in Example 1 in the presence of tannic acid without using fumed silica. To 86.2 g of copolymer were added 12.9 g of a 20% w/w aqueous solution of tannic acid and 0.9 g of "Kelzan" S thickener (xanthan gum), and the mixture was tumbled overnight. Ensure good dispersion. The mixture was examined after standing for 2 hours; agglomeration was observed;
When left to stand further, this aggregation increased and hard sedimentation occurred.

Comparative Example 5 In this comparative example, an attempt is made to use the copolymer latex of Example 1 and the technique described in GB 2,075,538.

Tannic acid (2.61g) and alginate sodium salt (
Copolymer latex (86.9
5 g; 60% solids). The mixture solidified within 3 hours. In a series of experiments, the above formulation is repeated, but in each case between 1 and 4% w/w (w/w) before addition of the tannic acid/alginic acid (sodium salt) dispersion in an attempt to stabilize the resulting dispersion. Anionic surfactants (for copolymers) are added to the latex. Anionic surfactants include "Dowfax"2A' (sodium salt of dodecylated oxydibenzenesulfonate), "Nansa" AS40 (ammonium dodecylbenzenesulfonate) and "Empico".
LZV (medium cut
t) lauryl alcohol sulfate). In all experiments, the mixture was still unstable and solidification occurred within 3 hours.

In another formulation, tannic acid (3.08 g) was mixed with water (31 g).
65 g) at 40°C, and the coagulation aid (2.57 g)
alginic acid (sodium salt) premixed with (0.41
g) is added to the tannic acid solution with stirring. Copolymer latex (60
62.28 g of % solids latex) are added to the mixture with further stirring.

The resulting mixture did not thicken at all. There was slight agglomeration and sedimentation after storage at 40°C for 72 hours.

Comparative Example 6 This experiment shows the adverse effects of using nonionic surfactants in the presence of tannic acid.

Nonionic surfactant (Synperonic PE39/70
; 6.50 g as a 30% w/w aqueous solution) was added to the copolymer latex (60% solids) 81 used in Example 1.
．． Tannic acid solution (12.20 g as a 20% w/w aqueous solution) is added to this stabilized dispersion. Global coagulation occurred. Increasing the amount of nonionic surfactant from 3% to 7% increased the coagulation rate.

Claims (2)

[Claims] 1. In a method for thickening an acidic aqueous coating composition comprising tannic acid and a latex of a film-forming polymer and substantially free of nonionic surfactants, the tannic acid is A water-soluble thickener for the aqueous latex, which is a polypropylene, is incorporated into said aqueous coating composition in the form of a gel-like aqueous dispersion containing uniformly dispersed particles of fumed silica, said thickener also being incorporated into said aqueous coating composition. A process for thickening an acidic aqueous coating composition, characterized in that it is compatible with the tannic acid used in the aqueous coating composition. 2. A thickened acidic aqueous coating composition comprising tannic acid and a film-forming latex and substantially free of nonionic surfactants, wherein said aqueous coating composition is a thickening composition comprising a gel-like aqueous dispersion comprising a water-soluble thickener for aqueous latex which is non-complexing with tannic acid and contains uniformly dispersed particles of fumed silica. A thickened acidic aqueous coating composition, characterized in that the thickening agent is also compatible with the tannic acid used in the aqueous coating composition.