NO122157B - - Google Patents

Description

Non-precipitating black lacquer and coating agent.

It is common knowledge that coating agents which have added color pigments or other organic powdery fillers have a much greater durability than coating agents which only consist of a film-forming binder. If you e.g. would coat an iron construction with linseed oil varnish, the rust protection effect would only be of short duration. If, however, the linseed oil varnish is mixed with color pigments to create a paintable color and the iron structure is coated with this mixture, the durability of the coating is many times better. This is because the breakdown of the binder film as a result of the effects of irradiation. and other atmospheric influences are greatly slowed down as a result of the color pigments. For this reason, currently only pigment-containing coating substances are generally used as rust protection agents.

However, this does not apply to the tai-tuminous smears. Here, it is even often common to use pure binders, i.e. solutions of bitumen or coal tar pitch in suitable solvents, as a coating agent. However, the coal tar coating solutions have the disadvantage that the film easily cracks under the influence of the weather (commonly known as "crocodile skin").

In connection with the bitumen solutions, it has partly already become common to use inorganic fillers, but in the case of the tar pitch solutions this presents particular difficulties. The inorganic fillers, i.e. e.g. stone flour, asbestos, lime flour and the like, have the property that the bituminous binders in these have a strong tendency to precipitate. This has the consequence that, within a short time, such coating agents have a hard impact on the bottom, so that it is only possible under the greatest difficulties to get this bottom deposit stirred out and again get it evenly distributed in the binder.

In the case of bitumen solutions, this can be remedied with the help of suitable dispersants, such as e.g. metal soaps of fatty acids that are added. These cause a significant reduction in the precipitation tendency. However, the problem is more difficult in the case of tar pitch solutions. The tar-bekopp solutions are substances which — considered colloidally chemically — are close to a critical limit. Coal tar pitch is a substance that can only be brought into homogeneous solution with difficulty, and only a few highly effective solvents are able to dissolve coal tar pitch completely and evenly. If solvents that only have an insignificantly lower dissolving power are used, disturbances occur in the tar pitch solution, which is shown by the high molecular weight components of the coal tar pitch separating out in the form of grain-like precipitates. This danger is increased by the addition of the otherwise usual dispersants, and in reality it is hardly possible to mix one of the usual dispersants with a coal tar pitch solution in sufficient quantity without such disturbances occurring in the colloidal structure of the tar pitch solution.

Up until now, people have mostly sought to remedy this by using the fillers without the addition of dispersants, but this has the consequence that after a relatively short time a bottom deposit forms which is very difficult to stir out again. If such colors are processed on a construction site with the inevitable lack of embarrassing accuracy, first the upper, filler-poor tar solution will be consumed and finally the thicker material at the bottom of the container, the last amount being mostly diluted due to its thick consistency. However, this results in a dissolution of the pitch and thus a reduction in the quality of the coating agent.

In view of the above-mentioned advantages of the pigment-containing coating materials, a homogeneous distribution of mineral fillers, such as rock flour, asbestos, lime flour, in coal-coal solutions is an important problem in the production of such coating materials.

With the invention, a new one has been found

way to prevent such fillers from settling, even when it concerns substances that have this tendency to a particularly strong degree. This has partly been made possible by the fact that a particle system is provided in the coal tar tar coating solution, with the help of which the filler parts that have the strongest tendency to sink to the bottom are kept in an even distribution. Such a particle system can be provided by e.g. to the coal tar ærebe solution, adding soot in such a large amount of soot gives a cream-like consistency, saturated with soot. While a normal coal tar solution has a consistency such as e.g. oil, the addition of a certain amount of soot will give a cream-like consistency, which becomes visible in that this soot-filled coal-tar solution does not flow out completely smoothly as a liquid when drained, but remains standing. This is obviously due to the fact that the hard coal oil solution itself has an evenly distributed system of soot particles which reduce the viscosity.

As already indicated, this is achieved

effect only with a specific soot addition. If too little soot is added, the tar peat solution still shows its normal viscosity, and if such a material is allowed to stand for a longer time, the soot will precipitate out and form a firmer layer in the lower part of the container.

Furthermore, it was ascertained that such a coal tar pitch solution, which contains so much soot that the mixture acquires the aforementioned cream-like consistency, can be added with mineral fillers which prevent

to split out. This does not only apply to the fine fillers that have less tendency to precipitate, such as e.g. shale flour, but also for fillers of a crystalline nature, such as quartz flour, tungspar etc.,

which, in terms of experience, is extremely easy to precipitate.

With the right amount of soot addition, it is easy to prepare stone coal tar pitch solutions with stone flour as a filler, which do not tend to precipitate even when stored for a longer period of time. Such a spreading substance has the appearance of a stiff, paste-like mass which, after stirring, changes to a liquid, cream-like consistency and can easily be processed in this state.

According to the invention, the possibility of keeping fillers which have a tendency to precipitate suspended by adding soot can also be achieved and improved by providing a soot-like material in the tar-beak solution itself.

As is well known, hard coal tar contains, depending on its origin, varying amounts of so-called free carbon. This free carbon consists of high-molecular coal-water substances that strongly resemble soot and are contained in their finest form in tar and coal-tar pitch, which can easily be detected under the microscope. However, the amount of such free carbon in ordinary coal tar pitch and the coal tar pitch solutions produced therefrom is much less than is necessary to achieve a cream-like consistency of the pitch solution as described above. One can, however, by blowing in air at a higher temperature and by other suitable, per se known precautions, change the coal tar tar base so that its content of free carbon increases extremely strongly. While a normal coal tar pitch only contains approx. 15 per cent free carbon, such a special pitch contains up to 50 per cent free carbon. If, however, one tries to dissolve such so-called special pitches in solvents of the kind that are otherwise suitable for the production of pitch pitch solutions (cf. G. J. P. Winkler, Der Steinkohlenteer und seine Aufarbeitung, 1951, p. 214), it turns out that it is impossible to bring these highly carbon-containing pitches into homogeneous solution, as the pitch even splits during the dissolution, after which the free carbon which was initially finely distributed in the pitch, clumps together into grain-like lumps. This is because the inherently very fine carbon particles coalesce into fairly large particles during the mixture with the solvent. Thereby, the material becomes less usable for ironing purposes because the coating produced from such an inhomogeneous mixture,

■becomes non-uniform with a large number of knot-like aggregations. The cream-like nature that is achieved by adding a certain amount of soot does not occur in this case either, even when the amount of free carbon is the same because the particles clump together.

In this case, however, you can also provide the desired cream-like consistency, as with the addition of soot by dissolving a correspondingly carbon-rich special beaker, by not melting the beaker and then adding the solvents, whereby the precipitates occur, but by grinding the beaker and thereby mixing it into brought pitch powder in a cold state with suitable solvents. In this way, it is avoided that the carbon particles clump together, as instead a cream-like mass is obtained with the same properties as when the normal tar peat solutions are added to soot.

The idea is close to adding the mentioned mineral fillers to such cream-like solutions of carbon-containing special beakers in order to provide in this way filled tar beaker solutions that do not form sediment. However, it has been shown in practice and during tests in the laboratory that this does not lead to the goal, and the reason lies primarily in the fact that these special beakers contain too little tar resins. in the production of special pitch, the tar resin originally found in the pitch is converted to a large extent into so-called free carbon and thus into solid substances. For this reason, an application of special pitch will adhere poorly to the substrate, apart from the film's bonding power being insufficient, as the tar resins which cause bonding to the substrate and the necessary film strength, are present in far too small a quantity.

In order to avoid these disadvantages, it is not appropriate to use these carbon-containing special pitches alone for the production of tar pitch solutions, but in a mixture with normal hard coal tar pitch. The normal coal tar pitch, which contains significant amounts of tar resin, will thus ensure that the film adheres well to the substrate and has a good binding force, while the high carbon content in the special pitch provides the desired particle system. You can, however, avoid the use of two beakers, choosing one that stands between the normal coal tar pitch and the usual special pitch. This is achieved by not driving the polymerization process as far as with normal special pitch, but only so far that a pitch is produced which, in terms of composition, corresponds to a mixture of normal coal tar pitch and special pitch.

It is true that bituminous coatings which contain soot are already known. However, the addition of soot cannot exert the same effect with these spreaders as according to the invention, since with the known spreaders no addition of inorganic fillers takes place. According to the invention, the soot or the soot-like components have the task of making the inorganic fillers stay suspended. Lacquer colors are also known, where carbon black (Rebenschwarz) is used as a pigment to provide a specific tint. Even in this case, however, the effect sought in accordance with the invention, namely the formation of a carbon particle system in the iron-on paint, is not achieved.

With regard to the inorganic fillers, it has been shown that it is appropriate to use coal meal and other substances of a crystalline nature with a small internal surface, such as e.g. quartz flour, silicon carbide, etc. These give, in connection with the soot respectively the free carbon which is suspended in the carbon solution and which both show a very large surface, a hetero-disperse filler mixture which has particularly favorable properties as a result of the gradual distribution of the particle sizes. The otherwise common fillers, such as e.g. shale flour, asbestos powder, etc., which mostly have a large internal surface, are less suitable as they absorb too much binder and for this reason give an application layer that has poor adhesion and is brittle.

Examples:

1) 85 parts of normal coal tar pitch with a softening point of 70° C in heavy benzene, which consists of 55 parts pitch and 45 parts heavy benzene, are mixed intensively with 15 parts of gas soot, whereby a mass is obtained

with a cream-like consistency. This is mixed in a ratio of 2 parts copper solution-soot mixture and 1 part finely ground silicon carbide. While the silicon carbide sinks rapidly in normal coal tar e-becoup solutions, it remains well distributed in the new solution.

2a) 30 parts normal coal tar pitch with a softening point of approx. 70° C (Kra-mer & Sarnow) is mixed with 20 parts blown special pitch. softening point approx. 130° C, which is melted and then diluted with 10 parts of anthracene oil and 40 parts of heavy benzene. When the solvent is added, the mixture takes on a grainy nature so that an applied film produced from it becomes rough and uneven.

b) 20 parts blown special pitch, softening point 130° C, grind to a fine

powder and dissolve in a mixing device in 5 parts amracenol oil and 20 parts heavy benzene. This results in a firm, cream-like paste. In addition, 20 parts of ordinary coal tar pitch, softening point 70° C, are melted, which in a hot liquid state are mixed with 5 parts of anthracene oil and 25 parts of heavy benzene. This results in a homogeneous tar bee solution which forms a glossy film after application. Both bekopping solutions are mixed, whereby a cream-like, easy-to-iron material is obtained.

c) 70 parts of the mixture of special roof solution and coal tar coating solution according to b) is mixed with 30

parts finely ground quartz flour. This gives a material which has a cream-like consistency and which, even after longer storage, shows no tendency to settle.

Claims (3)

1. Non-precipitating black lacquer and coating agent consisting of coal tar pitch solutions with inorganic fillers, characterized in that the dispersant for these fillers contains soot or soot-like components of the so-called special beakers in such quantities that the finished mixture acquires thixotropic properties and by stirring cream-like consistency. 2. Black lacquer and coating agent according to claim 1, characterized in that it contains the special pitch in a ground state and treated with solvent in a cold way. 3. Black varnish and coating agent according to claims 1 and 2, characterized in that it contains as fillers mineral stone flour with only a small surface, i.e. crystalline material.