Means of coating substrates with a paint-proof layer.

0001In many cities, especially in large cities, public and private structures and vehicles, in particular railroad and subway cars, spray paint, so-called "Grafitti", are appearing increasingly. Although the Grafitti have developed into an independent art form on the one hand and are often desired for the optical design of dreary urban concrete landscapes, on the other hand there are mostly artless smearings as well as political and social slogans in the cities that are perceived as soiling the cityscape. To remove such paint sprays from spray cans, the public sector and private homeowners have to spend large sums annually to restore buildings and railway and subway cars to their original state, whereby the penetration of the spray paints into surface pores often even causes irreparable damage to buildings, which only can be eliminated by costly coats of paint, which in turn often impair the visual impression of a building.

0002As a prophylactic measure against such contamination, wax-based coating compositions are already known, which are applied, for example, in the lower areas of buildings which are particularly at risk of graphite. Such coatings are to a certain extent repellent to paint and can be removed by spraying paint together with water vapor, which softens the coating and detaches it from the surface. A disadvantage of such wax-based coating compositions is, in particular, the fact that the coatings have to be renewed again and again after the graphite removal, which is an expensive matter.

0003The object on which the invention is based was therefore to obtain an improved agent for coating-repellent coating of substrates which allows spraying of paint to be removed as easily as possible without having to be applied again to the substrate afterwards. This object is achieved with the agent according to the invention.

0004This agent according to the invention for the coating-repellent coating of substrates is characterized in that it<ul id="ul0001" list-style="none"><li>a) a hydroxyl-containing branched saturated polyester with a hydroxyl number (mg KOH / g solid resin) from 180 to 320, with a hydroxyl content, based on solid resin, from 6 to 10% and with an acid number of at most 6,</li><li>b) at least one polyisocyanate,</li><li>c) a polysiloxane-modified polyisocyanate,</li><li>d) a curing catalyst for polyurethanes and</li><li>e) at least one organic solvent</li></ul> contains.

0005Polyurethanes are formed from the agents according to the invention, the surprising effect of the easy removability of paint spraying being in particular due to the combination of components a) and c). The modified polyurethanes resulting from the agent according to the invention adhere firmly and permanently to the substrate. When spraying with paint colors, you get a double effect. On the one hand, the substrate takes on the paint colors poorly and allows the colors to partially coagulate and run off the surface, which prevents the sprayers from spraying on such surfaces from the start. On the other hand, paint sprays can easily be removed from the coating after it has dried, without the coating itself being attacked or even removed.

0006The hydroxyl number is expediently in the range from 210 to 290, in particular in the range from 240 to 280, the hydroxyl content in the range from 7 to 9% and the acid number at a maximum of 4.5.

0007In order to obtain an increased water vapor permeability of the coating, which is particularly important for bridge structures and civil engineering structures that come into contact with the groundwater, it is preferred to replace a part of component a) by a hydroxyl-containing branched saturated polyester with a hydroxyl number of 120 to less than 180 and with a hydroxyl content of 3 to less than 6% and / or by a hydroxyl-containing branched saturated polyether with a hydroxyl content of 8 to 14%. Advantageously, 10 to 50% by weight of component a) is replaced by the other polyester or polyether, particularly preferably 20 to 40% by weight. By adding such a polyester with a lower hydroxyl content or a polyether with a hydroxyl content in the range mentioned, the removability of the paint spraying is practically or hardly impaired, while the water vapor permeability is increased significantly.

0008If this additional component is a polyester, its hydroxyl number is preferably 150 to 170 and its hydroxyl content is preferably 4 to 5.5%. The hydroxyl content of the polyether is preferably 10 to 12%. If the description and the claims refer to percentages in relation to the hydroxyl content, this means percentages by weight, based on the solids content of the particular polyester or polyether.

0009Component b) can in principle be any of the polyisocyanates customary for polyurethanes, in particular diisocyanates, but also tri- and tetraisocyanates or prepolymers thereof. The polyisocyanates can be aromatic, aromatic-aliphatic, aliphatic or cycloaliphatic in nature. However, since the agents according to the invention are generally used outdoors and aromatic polyisocyanates give coatings with poor weather resistance, it is preferred to use aliphatic polyisocyanates, in particular diisocyanates, or their prepolymers in the agents according to the invention.

0010Conventional blocked polyisocyanates may also be used. These are commercially available compounds which, for blocking the isocyanate groups, can be reacted, for example, with an alcohol, with caprolactam, with a phenol or with a glycol. Blocked polyisocyanates are particularly suitable if the agent according to the invention contains components a) to e) in a uniform mixture with one another. In the case of unblocked polyisocyanate, it is expedient to pack and store the agent as two components, component a) being contained in one package and components b) and c) being contained in the other.

0011Component c) is a polysiloxane-modified polyisocyanate and can in turn be a di-, tri- or tetra-isocyanate, but is preferably a diisocyanate and in particular such an aliphatic nature. This is polymerized into the polyurethane so that the polysiloxane modification is fixed in the polyurethane polymer. Moisture-curing systems are also suitable, which are stable in storage when moisture is excluded and only harden when exposed to atmospheric moisture.

0012Component d) consists of a conventional curing catalyst for the production of polyurethanes. Such curing catalysts are, for example, and in particular tertiary amines, quaternary ammonium salts and ester amines, and various metal compounds, such as zinc octoate or dibutyltin dilaurate.

0013The organic solvent is added in an amount necessary for easy handling. In many cases, the individual components are contained in solvents, so that with the individual components such solvents automatically get into the agents according to the invention. When stored in two separate containers, both contain an organic solvent. Basically, all organic solvents are considered which are inert towards the polyester component and the polyisocyanate components. Aromatics such as xylenes, solvent naphtha or the like and / or esters such as butyl acetate, methoxypropyl acetate, ethoxyethyl acetate or ethyl glycol acetate and ketones such as methyl isobutyl ketone or methyl ethyl ketone are preferred.

0014A particularly favorable paint-repellent effect is obtained if, in addition to components a) to e), component f) includes a polyester-modified hydroxy-functional polysiloxane, preferably a polyester-modified hydroxy-functional polydimethylsiloxane. This is expediently mixed in an amount of 0.5 to 5, preferably 1 to 3 parts by weight per 100 parts by weight of component a).

0015Furthermore, the agents according to the invention can contain further additives that are common in coating agents, such as leveling agents, pigments, dyes, UV absorbers or the like, provided that these agents do not impair the desired properties of the agent.

0016The optimal composition by weight can be determined by series tests. It is expedient that the agent contains 10 parts by weight of component a) 50 to 120, preferably 60 to 90 parts by weight of component b), 0.5 to 5, preferably 1 to 3 parts by weight of component c) and 0.01 to 1, preferably contains 0.1 to 0.5 part by weight of component d). Overall, regardless of whether it is present as a uniform mixture or in two separate containers, the agent according to the invention expediently contains 50 to 500 parts by weight of component a), preferably 100 to 250 parts by weight, particularly 140 to 180 parts by weight of component e).

0017The agents according to the invention can be applied to the substrates in different ways, for example by spraying, brushing, rolling or in any other usual way.

example 1

Component A

0018<tables id="tabl0001" num="0001"><img file="EP0442272A2_D0001.tif" /></tables>

Component B

0019<tables id="tabl0002" num="0002"><img file="EP0442272A2_D0002.tif" /></tables>

0020Components A and B were mixed together in a weight ratio of 2: 1 and applied as a coating on concrete. After curing, paint colors were sprayed on from standard spray cans. These were poorly accepted by the coating and partially expired. After drying, the paint coatings could be easily and completely removed using conventional cleaning agents.

Example 2

0021In the formulation of Example 1 in component A, 30% by weight of the 65% solution of hydroxyl-containing, highly branched, saturated polyester was replaced by a 75% solution of a hydroxyl-containing, highly branched, saturated polyester which had been modified with a low molecular weight fatty acid, in xylene replaced. This polyester had a hydroxyl number of about 165, a hydroxyl content of about 5% and an acid number of about 15. The coatings obtained with this agent were distinguished by increased water vapor permeability.

Example 3

0022The recipe of Example 1 was repeated with the modification that 20% of the 65% solution of the hydroxyl-containing branched saturated polyester by a solvent-free hydroxyl-containing branched polyether with a hydroxyl content of about 11.5%, an equivalent weight of about 148, an acid number of less than 0.5 and a density at 20 ° C according to DIN 51757 of 1.03 g / cm³ were replaced.

0023The composition gave a paint-repellent coating with approximately the same paint-repellency properties as the coatings of Examples 1 and 2, but with a water vapor permeability which was superior to that of Example 1.