Plastisols are widely used for protecting metallic surfaces from corrosion. In particular in the automotive sector, plastisols are used for the waterproofing, bonding and sealing of seams and joints, and for protecting external surfaces, such as underbodies and sills.

These applications mostly use plastisols based on PVC polymers or on PVC copolymers.

These plastisols are composed of fine polymer particles which have been dispersed in a non-volatile plasticizer. At room temperature, the polymer particles are insoluble in the liquid phase. At a higher temperature (gelling temperature), the polymer particles dissolve in the plasticizer. On cooling, the homogeneous solution hardens to give a flexible or rigid coating.

The main methods used to apply these coatings to the materials to be protected are brushing, rolling or spraying.

The formulation of plasticized polyvinyl chloride coating compositions (plastisols), and their preparation and use is extensively described in: Krekeler/Wick, Kunststoff-Handbuch [Plastics Handbook] (1963), Volume II, Part 1, pp. 396 ff.

A significant criterion for the quality of plastisols applied in this way is their adhesion to the coated material. Relatively low adhesion of the protective layer increases the risk of penetration of aggressive fluids. For example, water can migrate under the coating and corrode the metal. This becomes increasingly possible as the adhesion of the protective film to the metal becomes lower. To increase the adhesion of these coatings, therefore, industry adds adhesion-improving additives to the plasticized polyvinyl chloride. The function of the adhesion promoters is to bring about lasting adhesion to the surfaces of commonly encountered materials, such as non-degreased untreated steel, galvanised metal sheet or tin-coated metal sheet, electrocoated metal sheet, etc.

There are previously-developed adhesion promoters for PVC plastisols. Examples of these adhesion promoters are polyamines, epoxy resins, capped isocyanates, organofunctional silanes, and esters of acrylic or methacrylic acid.

In most cases, the adhesion promoters used comprise polyaminoamides containing imidazoline groups. These give good adhesion to the substrate, even if the concentrations in the plastisol are relatively small. These polyaminoamides are prepared from what are known as polymerized fatty acids and an excess of polyethylene polyamines, by polycondensation.

The expression polymerized fatty acids encompasses polymerized fatty acids prepared from unsaturated, naturally occurring or synthetic, monobasic, aliphatic acids having from 12 to 22 carbon atoms, preferably 18 carbon atoms. The fatty acids may be polymerized by a well- known process (for example as in DE 25 06 211 A1). These adhesion promoters are described by way of example in DE 26 54 871 A1 and in DE 32 01 265 A1. DE 44 00 509 A1 describes plastisol compositions in which the addition of secondary adhesion promoters in the form of trihydric or higher-functionality aliphatic alcohols and/or alkanolamines, in addition to the conventional adhesion promoters based on polyaminoamides, to PVC plastisols improves their adhesion properties, in particular on sheets coated by a cataphoretic process. In the experimental section of that specification, glycerol is used as secondary adhesion promoter. However, these secondary adhesion promoters have to be added in addition to the primary polyaminoamide adhesion promoters, the amount of which incorporated into the plastisol is usually about 1% by weight (based on the total amount of plastisol). The viscosity of the polyaminoamides used is moreover generally very high, and incorporation into the plastisol is therefore rendered difficult.

In order to lower the viscosity and thus provide good processability of the adhesion promoter, e. g. for the mixing of the adhesion promoter into the plastisol, and also to lower the price of these adhesion promoters, the adhesion promoters, which are generally of very high viscosity, are often formulated with plasticizers. However, plasticizers have an adverse effect on the adhesion of the PVC plastisol to the substrate in most cases. Plasticizers often used are phthalic esters, e. g. dibutyl phthalate, dioctyl phthalate or dinonyl phthalate. One adverse effect which has been observed is their low effectiveness in diluting the adhesion promoter. Relatively high amounts of these phthalate have to be used if sufficient processability is to be provided.

However, larger amounts of these plasticizers have an adverse effect on adhesion to the substrate. In addition, dialkyl phthalate used as plasticizers in adhesion promoters bring about a rise in viscosity of the adhesion promoter over the course of time, this being explicable via cleavage of the ester and reaction with the free amine groups in the polyaminoamide/imidazoline. The usefulness of these adhesion promoters is therefore subject to a time limit, because after some time incompatibility arises, and finally gelling occurs. In addition, the toxicological risks posed by the dialkyl phthalates class of product have recently caused their use to be criticized. DE 694 02 959 T2 claims a process for the preparation of specific polyamide resins which, according to Claim 9, comprise dioctyl phthalate, benzyl alcohol, and diisopropylnaphthalene as plasticizers. EP 0 658 574 A1 describes the use of amidoamines, imidoamines and ester amines based on a) copolymers of monounsaturated carboxylic acids and ethylenically unsaturated compounds and b) polyamines as adhesion promoters, likewise using the abovementioned compounds as plasticizers. However, as the proportion in the adhesion promoter rises, the use of these plasticizers again leads to impairment of adhesion of the plastisol to the substrate.

It is therefore an object of the invention to provide an additive which is intended for adhesion promoters in PVC plastisols and which is compatible with the polyaminoamide, has good effectiveness in diluting the adhesion promoter, and is stable with respect to viscosity, and, finally, has minimum effect on the adhesion of the PVC plastisols to the substrate.

According to the invention, this object is achieved by using adhesion promoters which comprise not only a polyaminoamide but also propylene glycol monophenyl ether (phenoxypropanol). Depending on the adhesion behaviour and on the amount of the respective polyaminoamide used, the amount of phenoxypropanol advantageously used may vary within a very wide range. However, on the basis of the commonly used proportions of adhesion promoter, from 0.5 to 2% by weight in the respective plastisol composition, the amount of phenoxypropanol used, based in each case on the total amount of the adhesion promoter, should advantageously be at least 10% by weight and at most 60% by weight, preferably from 25 to 55% by weight, particularly preferably from 40 to 50% by weight.

Surprisingly, these compounds (phenoxypropanol) have no adverse effect on the adhesion of the PVC plastisol to the substrate, even in these very large amounts of from 40 to 50% by weight in the adhesion promoter. It would have been expected that the adhesion of the PVC plastisols to the substrate would fall off as the amount of additive in the adhesion promoter rises, because the proportion of the adhesion promoter itself becomes smaller. However, even when the proportion of phenoxypropanol in the adhesion promoter is 50%, there is no, or at least hardly any, effect on the adhesion of the PVC plastisol to the substrate. The viscosity of the adhesion promoters is low, and the adhesion promoter is stable in terms of viscosity.

This invention therefore provides adhesion promoters for PVC plastisols, characterized in that they comprise not only a polyaminoamide but also phenoxypropanol, the amount of phenoxypropanol present in the adhesion promoter, based on the total amount of adhesion promoter, being at least 10% by weight and at most 60% by weight, preferably from 25 to 55% by weight, particularly preferably from 40 to 50% by weight.

The invention also provides a process for the production of coatings and adhesive bonds for materials by applying plastisols based on fine-particle polyvinyl chloride or, respectively, vinyl chloride copolymers, which comprise conventional fillers, additives, plasticizers and adhesion promoters, characterized in that use is made of adhesion promoters which comprise not only a polyaminoamide but also phenoxypropanol in amounts, based on the total amount of adhesion promoter, of at least 10% by weight and at most 60% by weight, preferably from 25 to 55% by weight, particularly preferably from 40 to 50% by weight.

The adhesion promoters are added in proportions of from 0.3 to 5% by weight, preferably from 0.5 to 2% by weight, particularly preferably 1 % by weight, based on the weight of the plastisol, and the mixture is homogenized, and the plastisols thus prepared are stoved on the material at temperatures of 90°C or above, preferably at from 120°C to 160°C.

The invention also provides plastisols for the production of coatings on materials, comprising fine-particle polyvinyl chloride or, respectively, vinyl chloride copolymers, conventional plasticizers, fillers, additives and adhesion promoters, characterized in that an adhesion promoter of the invention is present.

Examples In examples 2 to 5 below, the polyaminoamide adhesion promoter Euretek 563 from example 1 is heated with stirring to about 100°C and the appropriate additives are added, and the mixture is then homogenized.

Example 1 (comparative example) : Eureteko 563 (commercial adhesion promoter based on a polyaminoamide from the company Vantico AG).

Example 2 (comparative example) : 60% Euretek 563; 40% of dioctyl phthalate.

Example 3: 60% Euretek 563; 40% of phenoxypropanol.

Example 4: 50% Euretek 563; 50% of phenoxypropanol.

Example 5 (comparative example) : 80% Euretek 563; 20% of glycerol.

Preparation of plastisols : 1 % of the abovementioned polyaminoamide of examples 1 to 5, based on the entire mixture, is added as adhesion promoter to a plastisol composed of: 35% of diisononyl phthalate ; 25% of paste PVC (e. g. SolvicX 347 MB); 16.0% of coated chalk (Socals 312) ; 16.5% of naturally occurring chalk (Juraperle) ; 2. 0% of CaO ; 0.2% of ZnO and 4.3% of Exxsols 80.

Of course, the adhesion promoters may also be added to conventional plastisol formulations other than those given above in order to obtain the self-adhesive plastisols of the invention.

The adhesion achievable using the plastisols of the invention is determined manually. For this, use is made of Cathoguard 400 CEC sheets from the company BASF. Dimensions of adherends 25 x 100 mm.

Method: A spatula is used to apply a strip of the PVC plastisol, about 1.5 cm in width and about 5 cm in length, to the CEC strip, and a doctor is used to spread the plastisol to give a test strip of width 1.5 cm with a thickness of 1.5 mm. The test specimen is placed in the temperature- controlled drying cabinet and stoved at 140°C for 30 minutes. After stoving, the test specimen is removed from the drying cabinet. After cooling (for at least 2 hours), the adhesion test can be carried out. For this, a knife is used to make an incision to a width of about 0.5 cm in both sides of the test strip. The test strip is then tested manually for peelability.

The following classification system is used for assessment: No adhesion at all O Strip can easily be peeled ; slight film of plastisol remaining on the CEC layer 33 Strip difficult to peel ; slight film of plastisol remaining on the CEC layer + Strip difficult to peel and breaks on peeling ; significant film of plastisol remaining on the CEC layer ++ Strip cannot be peeled The results of the measurements are listed in table 1 below.

Table 1: Example Viscosity at Viscosity at Manual Viscosity at 75°C Appearance 25°C [mPa. s] 75°C [mPa. s] Adhesion [mPa's] after storage after storage 30 30 days/50°C days/50°C 1 n. m* 16500 ++ 16600 clear 2 22300 1300 + 6000 cloudy/ incompatible 3 16200 810 ++ 815 clear 4 11900 500 ++ 505 clear 5 n. m*) 12000 (D 12600 clear *) not measurable at 25°C (viscosity too high) The viscosities were measured using a VT 550 Haake rotary viscosimeter in accordance with the manufacturer's instructions.

Interpretation of results: As can be seen from the table, the adhesion promoters of the invention (examples 3 and 4) have low viscosity and are therefore easier to process. In contrast with comparative example 2, the adhesion promoters of the invention are storage-stable, even after storage at relatively high temperatures, and therefore remain available for use by the user even after a prolonged storage time. Surprisingly, use of the inventive adhesion promoters with 40% (example 3) and even 50% (example 4) content of phenoxypropanol, based on the total amount, gives excellent adhesion of the plastisols to the substrate. Use of the adhesion promoter from comparative examples 2, and in particular 5, gives adhesion which can sometimes carry marked reduction as dilution increases. The adhesion of the plastisols to the substrates would also have been expected to fall when phenoxypropanol is used in the adhesion promoter, as the proportion of phenoxypropanol rises. Surprisingly, even with 50% of phenoxypropanol in the adhesion promoter the adhesion is not reduced and remains good.

This result was not foreseeable.