1. Field of the Invention
An adhesive stick based on starch ethers
This invention relates to an adhesive stick consisting of a water-based preparation of starch derivatives and a soap gel as the shaping gel-forming component and, optionally, other auxiliaries. The invention also relates to a process for the production of such sticks and to their use.
2. Discussion of Related Art
Adhesive sticks (=stick-like adhesives which are displaceably mounted in a closeable tube which leave behind a tacky film when rubbed onto a receiving surface) are now part of everyday life. They contain in particular (see DE-PS 18 11 466) water-soluble or water-dispersible synthetic high polymers of adhesive character, more particularly polyvinyl pyrrolidone (PVP), dissolved in an aqueous/organic liquid phase together with a shaping gel-forming component. The gel-forming component is selected in particular from alkali metal or ammonium salts of aliphatic carboxylic acids, more particularly containing from about 12 to 22 carbon atoms. If the basically high-tack water-based preparations of the polymer substances of adhesive character are heated together with small quantities of the gel-forming component based on fatty acid soaps to relatively high temperatures, more particularly above 50.degree. C., and if this solution is subsequently left standing to cool, the mixture solidifies to a more or less stiff soap gel in which the shaping and comparatively rigid micelle structure of the soap gels is predominantly in evidence at first. This provides for the known production and handling of such adhesives in stick form in closeable tubes. When the stick is rubbed onto a receiving surface, the micelle structure if destroyed so that the rigid mixture is converted into a paste-like state in which its adhesive character is predominant.
Numerous attempts have been made to modify adhesive sticks of this type by changing the shaping gel-forming component and/or by changing the solvent-activated adhesive-forming component. DE-OS 22 04 482 uses the reaction product of sorbitol and benzaldehyde as the shaping gel-forming component. According to DE-OS 26 20 721, salts of substituted terephthalic acid amides are said to be used as the gelling agent. According to DE-OS 20 54 503, free long-chain aliphatic acids or esters thereof are said to form the gel-forming component instead of the alkali metal salts of aliphatic carboxylic acids. DE-OS 22 19 697 seeks to improve adhesive sticks of the type in question by incorporation of anionic non-soap-like wetting agents in the stick, particularly with a view to improving its rubbing onto the substrate. According to DE-OS 24 19 067, a reaction product of aromatic diisocyanates with monoalkanolamines and/or dialkanolamines is said to be used as the gel-forming agent.
Despite all these proposals, the oldest form of adhesive sticks of the type in question based on soap gels, which are described in DE-PS 18 11 466 cited at the beginning, are still in use to by far the predominant extent to this day. A solution of PVP in an aqueous organic solvent mixture is converted into the form of the soft-rubbing adhesive stick by incorporation of alkali metal soaps of aliphatic carboxylic acids.
Gelman patent application DE 36 06 382 describes an improved adhesive stick which, to improve its soft-rubbing characteristics, additionally contains a limited quantity of lactams of lower aminocarboxylic acids and/or the corresponding ring-opened aminocarboxylic acids.
Other patents and patent applications relating to adhesive sticks include DE 39 21 554, DE 37 02 871, DE 33 28 099, DE 26 13 935, DE 30 15 268 and DE 20 53 674. According to the last of these documents, film-forming, natural and synthetic polymers are used as the adhesive component. Among a number of compounds, carboxymethyl starch is mentioned as an Example of starch derivatives. Water-soluble or water-dispersible adhesives such as, for example, ethoxylated and propoxylated starch derivatives are known from DE 18 11 466 as a constituent of adhesive sticks. If compounds such as these are used in their commercial form as the predominant or sole adhesive component of adhesive sticks, the adhesive stick may be useable in principle, but is not satisfactory in regard to dimensional stability, soft rubbing and minimum tackiness because it is generally friable in its constitution, is difficult to apply and lacks sufficient tack.
The problem addressed by the present invention was to remedy these deficiencies and to provide an adhesive stick which would be dimensionally stable and easy to rub onto substrates and which would show sufficient adhesive power although it was to be formulated without solvents on the basis of ecologically safe raw materials of native origin. However, the necessary changes would not make it any more difficult to produce, but on the contrary would facilitate its production.