IE42162B1 - Thickening solutions of film-forming polymer - Google Patents

Abstract

Solns. of film forming polymers in solvents of dielectric constant 5-50 are thickened (made thixotropic) by addn of 0.5-5 wt. % of an alkali metal salt of 8-36C (pref. 12-22C) fatty acid at a temp. above ambient and allowing mixt. to cool while practically free from movement and/or stirring. Paints or adhesives which do not drain or drip from sloping or vertical surfaces are easily obtd.

Description

This invention relates to thickened solutions of film forming polymers, especially to thickened adhesive compositions.

Solutions of film forming polymers are widely used as -adhesives 5 and lacquers.( They can be applied by. the use of a spreading device to spread a portion of the solution in a thin film over a surface or they can be applied by extrusion from a collapsible tube or from a bottle with a rubber application orifice or the like. However, the standard liquid adhesive and lacquer compositions have a number of disadvantages, principally a tendency to run when applied to inclined or vertical surfaces, and a tendency to tail. Tailing is the name given to the tendency of the liquid adhesive or lacquer compositions to form strands or tails between the work surface and the application device, whether it be a hand held spreader, a tube or a bottle, as the device is removed from the work surface after application of tlie adhesive. Tailing is undesirable because it makes neat application, {essential for model work and many small20 scale domestic uses) very difficult.

This invention is based on the discovery that standard liquid adhesive and lacquer compositions can be improved, the tendency to run and tail being reduced, by incorporating a thickening or gelling agent in the composition.

Although thickening and gelling agents are commonly used in many areas of industry, the adhesives and lacquer industry is peculiar in that its range of solvents tend to be medium polar solvents such as methylacetate, ethylacetate, butylacetate, acetone, methylethylketone and methylisobutylketone. The standard thickening and gelling agents for highly polar solvents like water and for non-polar hydrocarbon solvents are generally unsuitable for use with medium polar solvents.

However, we have discovered that the addition of an alkali metal salt of a (preferably cj2-22^ acid> preferably as a solution in a lower aliphatic alcohol (e.g. methanol or ethanol), to standard liquid lacquer and adhesive compositions (e.g. to about 5-50'j by weight of the total composition) produces a thickened composition which has a reduced tendency to run and tail.

Accordingly, the present invention provides a method of thickening a solution of a film-forming polymer material in a solvent of dielectric constant in the range 5.0 to 50.0, comprising preparing a mixture of said solution and an alkali metal salt of a Cg_36 fatty acid, said mixture being at a temperature above room temperature, and allowing said mixture to cool without substantial agitation.

The degree of thickening achieved will naturally be related to the concentration of fatty acid salt (herein/··Iter called the soap) added. - 3 42162 In general the soap may comprise from 0.05 to 5% by weight of the total thickened composition.

The soap is preferably an alkali metal salt of a ^2-22 fatty acid, most preferably a sodium salt. Sodium stearate is a preferred soap.

Preferably the soap'is mixed with the solution of the filmforming polymer as a solution in a lower aliphatic alcohol, especially methanol or ethanol. The temperature at which the alcoholic soap solution is mixed with the solution of XO film-former may be in the range 30°C-80°C depending on the volatility of the solvents used. It may sometimes be possible to form the soap in situ by neutralising an added fatty acid.

The solvent of a dielectric constant in the range 5.0 to . 50.0 may be selected from the standard medium polarity solvents used in the past for adhesive and lacquer compositions, usually low molecular weight esters and ketones and mixtures thereof, sometimes with small amounts of lower alcohols. Examples of such solvents include 2q methylacetate, ethylacetate, butylacetate, dibutylphthalate, cyclohexanone, acetone, methylethylketone and methylisobutyl ketone. Methyl and ethyl alcohol may be mixed in minor proportions with these ester and ketone solvents. The solvent is usually a blend of individual solvents, chosen to give the desired rate of evaporation. Normally the dielectric constant will be in the range 5.0 to 30.0, e.g. 10.0 to 25.0. - 4 42162 The film-forming polymer material may be any of those used in the past for adhesive and lacquer compositions, for example, polyvinyl acetate, polyvinyl alcohol, polyvinyl chloride', polyurethane, polyacrylate or polymethacrylate or their esters, polyvinylpyrrolidone, or copolymers of these materials, as well as cellulose nitrate, cellulose ethers and esters.

If desired, small amounts of water may be included in the compositions of this invention, either as part of normal moisture content of the organic solvents or as added water. The water gives the thickened or gelled composition an attractive translucent appearance.

Although the compositions of this invention are generally satisfactory in that they have a reduced tendency to run and tail, we have found that with some film-forming agents, e.g. polyvinylacetate, especially in compositions containing water, the stability of the total thickened or gelled composition is rather less than that of the same composition without the soap or water and that occasionally metal surface adhesion properties may be worse. However, we find that in instances where the stability is unsatisfactory, the addition of buffers to keep the pH of the composition in the range from about 7.0 to about 9.0 (preferably inorganic salts (e.g. sodium salts) of weak organic or inorganic acids, as for example sodium tetraborate (borax), sodium acetate, sodium-p-hydroxybenzoicacid methylescer, sodium iodate, sodium formate and sodium succinate),in an amount of from 0.05% to 20% by weight of the whole composition (depending - 5 I 43162 on the pH required) restores stability with little or no adver-se effect on the adhesive or lacquering properties of the composition. The buffer substance may be incorporated in the solution as a saturated solution in water, alcohol·, or other solvents. At the same time we surprisingly find that these buffer additives, e.g. borax, sodium acetate, sodium-p-hydroxy-benzoicacid methylester, also tend to improve the metal surface adhesion of the composition.

The buffer substances also appear to increase the gelling temperature of the compositions of this invention (possibly due to a salting out effect which reduces the solubility of the gelling agent in its colloidal form). This increase in gelling temperature may also partly explain the stabilising effect of the buffers.

Hence, according to a preferred embodiment of the invention there is provided a method of thickening a solution of a film-forming polymer material in a solvent of dielectric constant in the range 5.0 to 50.0 comprising mixing with said solution a buffer substance in an amount to control the I • i final pH of the total composition within the range 7.0 to 9.0 and an alkali metal salt of fatty acid., preferably in alcoholic solution, said fatty acid salt being mixed with the solution of film-forming agent at a temperature above room temperature, and allowing the mixture to cool without substantial agitation. - 6 42162 The buffer substance is preferably added in an amount of from 0.05® to 20® by weight of the whole composition to control the pH at about 8.0. It may be added before, after or together with an alcohol solution of fatty acid salt. The temperature at which buffer is added is preferably at or above room temperature, and it may be added as an aqueous solution or in some cases may be formed in situ by the addition of a weak inorganic or organic acid followed by neutralisation e.g. with sodium hydroxide.

The following Examples illustrate the invention: EXAMPLE 1 15 Plexigum MB 319 (a trade mark of Messrs. Rbhm Darmstadt) a copolymerisate of polymethylmethacrylate and polyethylacrylate) 30 % by weight Methylacetate 45 % by weight Ethyl alcohol 24.7 % by weight Sodium stearate 0.3 % by weight 100.0 % by weight Procedure: Mix the methylacetate and ethyl alcohol in a vessel fitted with reflux condenser and add the Plexigum with stirring at room temperature. After about 1 hour the solution will be homogeneous. - 7 431®2 Now, add the sodium stearate and continue stirring for about 15 minutes at room temperature. Heat to 60°C and stir (about 5 minutes) until the composition appears homogeneous. The finished batch is pumped into containers and the resultant mix allowed to cool.

EXAMPLE 2 Polyvinyl acetate with a Mol. weight of 130,000 Methyl alcohol Methyl acetate Ethyl alcohol Sodium stearate % solution of borax in water % by weight % by weight % by weight 19.75 % by weight 0.25 % by weight 2% by weight 100.00 % by weight Procedure: Mix the methyl. acetate and ethyl alcohol in a vessel fitted with a reflux condenser. Add the polyvinyl acetate with stirring. After about 2.5 hours when the solution seems to be homogeneous, add the sodium stearate as a heated solution in the methyl alcohol and continue Stirring for about 15 minutes until it is dispersed. Then heat the whole mixture to about 60°C and add the 5S solution of borax in water. Allow the resultant mix to cool.

EXAMPLE 3 ' Linear linked polyurethane 20 % by weight Alkylphenol resin (Alresen^PA104) 10 % by weight Methylethylketone 40 % by weight *nAlresen is a Registered Trade Mark? - 8 42162 Ethanol 29.7 % by weight Sodium stearate 0.3_% hy wol ght 100.0 % by weight Procedure: Fill the methylethylketone into a vessel fitted with a reflux condenser; add the linear linked polyurethane with stirring. After about 2.5 hours when the solution seems to be homogeneous add the alkylphenol resin and continue stirring for % hour. Then add the hot solution (50°C) of sodium stearate in ethanol slowly under stirring and heat the whole mixture to about 60°C. After reaching a fully homogeneous solution allow the resultant mix to cool.

Claims (10)

CLAIMS:

1) A· method of thickening a solution of a film forming polymer material in a solvent of dielectric constant in the range 5.0 to 50.0, comprising preparing a mixture of said solution and an alkali metal salt of a c g_ 3 g fatty acid, said mixture being at a temperature above room temperature, and allowing said mixture to cool without substantial agitation.

2. ) A method as claimed in claim 1 wherein the added fatty acid salt comprises from 0.05 to 5.0-% by weight of the total composition.

3. ) A method as claimed in claim 1 or 2 wherein the fatty acid salt is an alkali metal salt of a C 12-22 fatty acid.

4. ) A.method as claimed in claim 3 wherein the fatty acid salt is sodium stearate.

5. ) A-method as claimed in any one of the preceding claims wherein the fatty acid salt is mixed 20 with the solution of film-forming polymer as a solution in a lower aliphatic alcohol.

6. ) A method as claimed in claim 5 wherein the alcohol is methanol or ethanol. - 10 42162

7. ) A method as claimed in any one of the preceding claims wherein the film-forming polymer is polyvinyl acetate, polyvinyl alcohol, polyvinyl chloride, polyurethane, polyacrylate or polymeth5 acrylate, polyvinylpyrrolidone, copolymers of the preceding substances, cellulose nitrate, cellulose ethers or cellulose esters.

8. ) A method according to any one of the preceding claims comprising mixing with the said solution 10 of a film-forming polymer a buffer substance in an amount to control the final pH of the total composition within the range 7.0 to 9.0 and the said alkali metal salt of a fatty acid, seiid fatty acid salt being mixed with 15 said solution at a temperature above room temperature, and allowing the mixture to cool wiUiout substantial agitation.

9. ) A method as claimed in claim 8 wherein the buffer substance is added in an amount of from 0.05 to 2q 20% by weight of the whole composition to control the pH at about 8.0.

10. ) A method as claimed in claim 8 or claim 9 wherein the buffer substance is sodium tetraborate, sodium acetate,, sodium-p-hydroxybenzcicacid 25 methyl ester, sodium iodate, sodium formate or sodium succinate.