MXPA01008286A

MXPA01008286A - Method of coating silicic acid with waxes.

Info

Publication number: MXPA01008286A
Application number: MXPA01008286A
Authority: MX
Inventors: Schubert Jurgen
Original assignee: Degussa
Priority date: 2000-08-23
Filing date: 2001-08-16
Publication date: 2003-05-09
Also published as: DE10122861A1; NZ511223A; DE50103519D1; RU2001123440A; SG164273A1

Abstract

A method for coating silicic acid with wax involves applying the coating to the silicic acid in air at a temperature above the melting range but below the decomposition point of the wax.

Description

Procedure for coating silicic acids with waxes The present invention relates to a process for coating silicic acids with waxes and the use of these silicas. Matting agents for lacquers based on silicic acids impregnated with waxes are known and described, for example, in DE 10 06 100, DE 15 92 865 and EP 0 922 691. Here, a wax emulsion, in some cases using a dispersant, with a suspension of silicic acid. Subsequently, the silicic acid impregnated and coated in this way dries expensively and, in addition, often still contains the dispersant. In addition, for many applications the application of wax on silicic acid is not enough. Another process for the coating of silicic acid with waxes is described in patent EP 0 442 325. Here, in a first step, the silicic acid is coated with a polyol which facilitates the application of the hydrophobic wax on the hydrophilic silicic acid. Lacquers containing impregnated silicic acid according to EP 0 442 325 have a viscosity to such a high degree that it is not desirable. In comparative examples of the patent EP 0 442 325 it is shown that silicic acids which are not coated or coated only with wax without the addition of polyol significantly reduce the viscosity of a lacquer. It is assumed that this is due to the hydrophilic surface of the silica particles compared to the hydrophobic lacquer. Therefore and in order to avoid this effect, a polyol must be added. The above represents an additional step of the procedure. For the purpose of processing silica gels or silica sols, a thermal process according to DE 10 06 100 is known. Here and in a first step, silicic acid hydrogels are prepared, dried and, in an additional step, activated. The dried gel is activated by heating to a temperature of about 468-532 ° C and is reacted with a molten and microcrystalline wax at a temperature of 371 ° C, using 15 to 30% by weight of wax with respect to the hydrosol. The very fine hydrosol particles have a reticular gel structure with a very high water content and, therefore, can only be satisfactorily coated by applying the described high temperatures, that is, very large wax fractions. The very high thermal load prevents the use of many waxes (color change). In addition, for rapid cooling of the silica gel coated in this way should be ensured a temperature lower than the decomposition temperature of the wax. Silicic acid coating is described in DE 10 06 100. Silicic acids and silica gels have different structures due to the different preparation processes. Silic acids are prepared by alkaline precipitation and often have an open structure of the particles. The water can be easily extracted from the open pore particles. Silica gels, however, are obtained by acid precipitation and have a more closed structure from which water is only extracted with difficulty. Therefore, the object of the present invention is to provide a method for the coating of silicic acids that is easy to use and that allows good stability of sedimentation and dispersibility with a minimum use of wax, for example, in lacquers . Therefore, the object of the present invention is a process for the coating of silicic acid with wax, wherein the coating of the silicic acid is carried out at a temperature above the melting area and below the decomposition temperature of the wax in the air. The coating of the silicic acid is preferably carried out together with grinding, for example, in an impact mill. In any case, it is advantageous that the wax and silicic acid components are mixed before the coating step in a suitable mixing apparatus (e.g., an Eirich mixer). The melting and decomposition ranges of the waxes used, according to the present invention, are between 40 and 250 ° C, preferably between 60 and 200 ° C, particularly preferably between 70 and 130 ° C. Preferably, the process, according to the present invention, is carried out at these temperatures. It is possible to work with preheated air in a corresponding way or with heated inert gases. Suitable silicic acids are the precipitated silicas described in the examples. However, the corresponding aerosols are also suitable. In the process, according to the present invention, polyethylene (PE) waxes, Fischer-Tropsch waxes or silicone-based waxes can be used. In practice, the silicic acid coating has been seen as advantageous 2 to 15% by weight, preferably 5 to 10% by weight of wax, with respect to silicic acid. The silicic acids coated according to the present invention can be used as matting agents for lacquers such as alkyd resin lacquers or any other baking varnish. General description of the process In a mixer (for example, an Eirich mixer) a precipitated silica and a coating agent (wax) are intimately mixed in a ratio of 3% by weight to 15% by weight. This mixture is milled and separated in a ball mill for air separation (for example, 50 ZPS or similar) or a jet mill.

During grinding, the grinding chamber is heated by introducing hot air through nozzles (60 to 160 ° C) in such a way that the air present at the mill outlet still has a temperature of 40 to 140 ° C. The product is separated by means of a filter or a cyclone decanter. The product coated with the coating agent has a carbon content of 2 to 18% by weight, preferably 3 to 10% by weight and particularly preferably 3 to 6% by weight. The grain fraction can be adjusted by means of a subsequent classification.

Embodiment example: The data of the silicic acid and the coating agent used: Table 1 Example: The precipitated silica of Table 1 is mixed with 6% by weight of PE wax (Table 1). The mixture is mixed, varying the parameters of the process such as the number of rotations of the separator or the mill or the grinding air (measured at the exit of the mill). The test parameters, the physical-chemical data and the technical results of the lacquer obtained in black lacquer for drying in the oven are listed in table 2.

Table 2 Example 2 - Silicic acid variant and coating temperature A precipitated silicic acid, for example Sipernat 50, is intimately mixed with a PE wax, for example AF 30 (from BASF), in a proportion of 6 parts of wax and 94 parts of silicic acid. This mixture is dosed to a rebound separation mill (ZPS 50). This rebound sorting mill is operated during grinding with preheated grinding air. The exit temperature of the grinding air is varied from the mill. The settings of the grinding (number of revolutions of the separating wheel and the mill) are not decisive for the coating of the acid With the wax, however, these values are chosen in such a way that the product has a suitable distribution for the desired opacification efficiency.

Characteristic values of the silicic acid used BET surface [m2 / g] 450 Average particle size [micron] 27 (measuring device: Coulter LS 230) Stamping density [g / 1] 180 (non-sifted) Loss on drying [%] 6.0 (2 hours at 105 C) Loss on calcination [%] 5.0 (2 hrs at 1000 ° C) pH value 6.0 (concentration of 5% in water) DBP adsorption [g / lOOg] 335.0 Table 3 * Measuring device: Coulter LS 230 ** Standard: Acematt HK 460, Company Degussa AG Example 3 - Variation of the wax, that is, of the softening temperature of the wax The test is carried out as described for example 2. Waxes with a softening point lower than the softening point of example 2 are used. 4 Table 5 Table 6 Table 7 Methods of analysis: Sedimentation A quantity of approximately 40 g of shaded varnish is introduced into glass bottles and the bottles are closed with a screw cap. The samples are stored for 10 days at a temperature of 50 +/- 2 ° C in a drying cabinet. For evaluation, the glass bottles are cooled to room temperature. In order to evaluate the consistency of the sediment, the glass bottles are turned upside down and it is observed how the phase containing the shading agent is drained. Then the glass bottles are shaken twice by hand. In the case that no sediment is visually determined, it is scratched with a needle on the bottom. Through this treatment, even very fine and unwanted precipitation can be determined. The consistency of the sediment is evaluated as follows: Release of the wax 1 g of the shading agent and 35 g of ethoxypropyl acetate are weighed in a bottle with a screw cap and a wide neck. The lid closes and the bottle is shaken by hand. During the night, the bottle is stored at a temperature of 50 ° C. If under these conditions the wax is released from the shading agent, then the wax floats on the solvent and the shading agent precipitates to the bottom. If the wax does not come off, then only a sediment of shading agent appears on the bottom.

The examples show that the application, according to the present invention, must be carried out at temperatures above the melting point of the wax. Here, the concepts "melting range" and "softening point" should be understood as synonyms.

Claims

1. A process for coating silicic acid with wax, characterized in that the coating of the silicic acid is carried out at a temperature above the melting area and below the decomposition temperature of the wax in the air.

2. A method according to claim 1, characterized in that a grinding is carried out together with the coating at the same time.

3. A method, according to any of claims 1 or 2, characterized in that the coating is carried out at a temperature of 40 ° C to 200 ° C.

4. A process according to any of claims 1 to 3, characterized in that 2 to 15% by weight of the wax is used, with respect to the silicic acid.

5. A process according to any of claims 1 to 4, characterized in that polyethylene wax, Fischer-Tropsch wax or silicone-based waxes are used for the coating.

6. The use of the coated silicic acid, according to any of claims 1 to 5, as an agent for lacquer matting.