NO146677B - PROCEDURE FOR THICKNESSING A SOLUTION OF A MOVIE-MAKING POLYMER MATERIAL - Google Patents

Description

The invention relates to a method for thickening a solution of a film-forming polymer material in a solvent with a dielectric constant in the range 5.0-50.0.

Solutions of film-forming polymers are widely used as adhesives and varnishes. They can be applied using a spreading device which can spread a quantity of the solution in a thin film over a surface, or they can be applied by extruding from a collapsible tube or from a bottle with a rubber applicator nozzle or the like. However, the standard types of liquid adhesive and varnish mixtures have a number of disadvantages, mainly a tendency to run when applied to inclined or vertical surfaces, and they tend to create "tails". "Tailing" is the term given to the tendency of the liquid adhesive or varnish mixtures to form strings or "tails" between the work surface and the application device, whether a hand-held spreader, tube or bottle, when the device is removed from the work surface after the adhesive has been applied. "Tailing" is undesirable, as it makes neat application (which is essential for model work and many small-scale household purposes) very difficult.

The invention is based on the discovery that standard types of liquid adhesive and varnish mixtures can be improved, while the tendency to flow and form "tails" is reduced, by incorporating a thickening or smoothing agent into the product.

Although thickening and gelling agents are commonly used in many areas of industry, the adhesive and varnish industry is special in that the solvents used there are often medium polar solvents, e.g. methyl acetate, ethyl acetate, butyl acetate, acetone, methyl ethyl ketone and methyl isobutyl ketone. The standard types of thickening and gelling agents for highly polar solvents such as water and for non-polar hydrocarbon solvents are generally unsuitable for use with medium polar solvents.

Accordingly, the invention provides a method for thickening a solution of a film-forming polymer material in a solvent with a dielectric constant in the range 5.0-50.0, comprising low molecular weight esters and ketones or mixtures thereof, and the method is characterized in that the solution above room temperature is mixed with 0.05-5.0% by weight sodium stearate, calculated on the entire mixture, which is then allowed to cool without significant agitation. Optionally, the solvent contains small amounts of lower alcohols.

The degree of thickening that is achieved will of course depend on the concentration of sodium stearate (hereinafter called "Soap") that is added.

The soap is preferably mixed with the solution of the film-forming 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 film former can be in the range 30-80°C, depending on the volatility of the solvents used. It may occasionally be possible to form the soap in situ by neutralizing added fatty acid.

The solvent with a dielectric constant in the range 5.0-50.0 can be selected from among the standard solvents with medium polarity that have been used up to now for adhesive and varnish mixtures, usually low molecular weight esters and ketones and mixtures thereof, occasionally with small amounts of lower alcohols. Examples of such solvents are methyl acetate, ethyl acetate, butyl acetate, dibutyl phthalate, cyclohexanone, acetone, methyl ethyl ketone and methyl isobutyl ketone. Methyl and ethyl alcohol can be mixed in small quantities with these ester and ketone solvents. The solvent is usually a mixture of single solvents selected to give the desired evaporation rate. Normally, the dielectric constant will lie in the range 5.0-30.0, e.g. 10.0-25.0.

The film-forming polymer material can be any of those that have been used up to now for adhesive and varnish mixtures, e.g. 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 can be included in the method according to the invention, either as part of the normal moisture content of the organic solvents or as added water. The water gives the thickened or gelled product an attractive translucent appearance.

Although the method according to the invention generally gives products with the advantage that they have a reduced tendency to flow and form "tails", it has been found that in the case of some film-forming agents, e.g. polyvinyl acetate, especially in products containing water, the stability of the overall thickened or gelled product is rather poorer than for the same product without the soap or water, and that occasionally metal surface addition properties may be poorer. However, it has been shown that in cases where the stability is unsatisfactory, the addition of buffers to keep the product's pH value in the range from approx. 7.0 to approx. 9.0 (preferably inorganic salts, e.g. sodium salts, of weak organic or inorganic acids, e.g. sodium tetraborate (borax), sodium acetate, sodium p-hydroxybenzoic acid methyl ester, sodium iodate, sodium formate and sodium succinate), in an amount of from 0.05 to 20% by weight of the entire mixture (depending on the required pH value) again stability with little or no adverse effect on the adhesive or varnish properties of the product. The buffer substance can be incorporated into the solution as a saturated solution in water, alcohol or other solvents.

At the same time, it has surprisingly been found that these buffer additives, e.g. borax, sodium acetate, sodium p-hydroxybenzoic acid methyl ester, also tend to improve the metal surface addition to the product. The buffer substances are also found to increase the gelation temperature of the products (possibly due to a "salting out" effect which reduces the solubility of the gelling agent in its colloidal form). This increase in gelation temperature can also partly explain the buffers' stabilizing effect.

From Dr. J. Gartner's article "Verwendung von Fett-derivaten als Hilfsmittel in Anstrichstoffen" in "Fette, Seifen, Anstrichmittel", volume 73, 1971, pages 496-502, it appears that i.a. aluminum stearate is known as a thickening agent in non-aqueous systems, but such a metal soap is however considered to be completely different from the alkali soap used in the method according to the present invention, i.e. sodium stearate. Metal soaps are of no value in thickening solvents of medium or high polarity.

From BRD-off.skrift no. 1 811 466 it is known to use sodium stearate as a thickener for aqueous dispersions of polymers. It is also proposed to use solvents that fall within the scope of the invention, see p.2, 3rd section in the official document. However, no practical examples of this have been given. Thus, none of the examples deal with any anhydrous preparation, only solvents that are strongly polar, not medium polar as the present invention deals with. The specialist in the field would therefore, by reading the description in the official document, believe that alkali metal soaps must only be used to thicken strongly polar/aqueous solvent systems.

The following examples illustrate the invention:

EXAMPLE 1

Approach:

. Mix the methyl acetate and ethyl alcohol in a vessel fitted with a reflux condenser and add the "Plexigum" while stirring at room temperature. After approx. After 1 hour, the solution will be homogeneous.

Add the sodium stearate and continue stirring for approx. 15 minutes at room temperature. Heat to 60°C and stir (approx. 5 minutes) until the mixture appears homogeneous. The finished batch is pumped into containers and the resulting mixture is allowed to cool. The dielectric constant of the solvent was 13.3.

EXAMPLE 2

Dielectric constant of the solvent was 17.6.

Approach:

Mix the methyl acetate and ethyl alcohol in a vessel fitted with a reflux condenser. Add the polyvinyl acetate while stirring. After approx. 2.5 hours, when the solution appears to be homogeneous, add the sodium stearate as a heated solution in the methyl alcohol and continue stirring for approx. 15 minutes until dispersed. Then heat the whole mixture to approx. 60°C and add to it a 5% solution of borax in water. Allow the resulting mixture to cool.

EXAMPLE 3

Approach:

Fill the methyl ethyl ketone into a vessel fitted with a reflux condenser; add the linear bonded polyurethane while stirring. After approx. 2.5 hours, when the solution appears to be homogeneous, add the alkylphenol resin and continue stirring for half an hour. Then add the hot solution (50°C) of sodium stearate in ethanol slowly while stirring and heat the whole mixture to approx. 60°C. After it has become a completely homogeneous solution, allow the resulting mixture to cool.

Dielectric constant of the solvent was 19.2.

Comparative example

Control experiments were carried out to determine the effect of a number of known thickeners on an adhesive mixture in a solvent with intermediate polarity, i.e. with a dielectric constant between 5 and 50, first an experiment according to the invention.

An adhesive mixture was prepared with the following content of ingredients:

The polyvinyl acetate components constituted the film-forming polymer material, and the methyl acetate/methanol/ethanol solvent system had a dielectric constant of 16.

To this mixture was added 0.25% sodium stearate and 0.25% sodium acetate. The result was a smooth thickened gel adhesive that had no tendency to string or drip.

Instead of the sodium stearate/sodium acetate thickening system, it was used:

I) thickeners that were suitable for non-polar adhesive solvents, and

II) thickeners suitable for polar solvents (those with a dielectric constant above 50).

The amount of thickener in each case was 1%, i.e. twice the amount of sodium stearate/sodium acetate.

The following non-polar solvent thickeners were used:

I) aluminum stearate,

II) hydrogenated castor oil,

III) modified Montmorillonite (Bentone 38),

IV) lithium palmitate, and

V) amorphous silicon dioxide (Aerosil 380).

In each case, the thickener was substantially insoluble and formed a slurry-like precipitate in the adhesive mixture. The thickeners were clearly unsuitable for the intermediate polarity solvent system used in the experiments.

The following polar solvent thickeners were used:

I) Polymerized acrylic acid neutralized with various alkalis (sodium hydroxide, potassium hydroxide, ammonium hydroxide, octylamine, dodecylamine, dibutylamine and

triamylamine).

II) Polymerized acrylic acid (Carbopol 940)

III) Methyl cellulose

IV) Carboxymethyl cellulose

V) Polyvinyl pyrrolidone

VI) Synthetic clay (Laponite RP - Laporte)

With thickener (I) a muddy, lumpy mass was produced. Thickener (II) was soluble and gave a slightly thickened, transparent adhesive, but the adhesive did not gel and tended to string and drip. The thickeners (III) and (IV) were insoluble and gave muddy precipitates. Thickener (V) was partially soluble, but did not produce a thickening effect. Thickener (VI) gave a muddy precipitation product and had no thickening effect.

These experiments clearly show that the specific nature of the thickener is critical when a solvent of intermediate polarity is used, and that the particular type of thickener useful for this purpose could not be predicted.

It is noted that sodium acetate is included in these comparative examples to buffer the system and thereby ensure maximum shelf life by preventing degradation of pH sensitive materials.

Claims (3)

1. Process for thickening a solution of a film-forming polymer material in a solvent with a dielectric constant in the range 5.0-50.0 comprising low molecular weight ester or ketone solvent or a mixture thereof, and which optionally contains small amounts of lower alcohols , characterized in that the solution, at a temperature above room temperature, is mixed with sodium stearate, in an amount of 0.05-5.0% by weight, calculated on the entire mixture, and that the mixture is allowed to cool without significant agitation. 2. Method as stated in claim 1, characterized in that the sodium stearate is mixed with the solution of film-forming polymer as a solution in a lower aliphatic alcohol. 3. Method as stated in claim 2, characterized in that methanol or ethanol is used as alcohol.