DE2247695B2 - Process for the production of powdery coating materials - Google Patents

Description

30th

The invention relates to a method for producing powdery coating materials.

The use of powdery coating materials, for example fulver paints (»powder lacquers«), has increased more and more in recent years. Although the use of coating agents in powder form has many advantages over liquid coating materials Disadvantages due to the current manufacturing processes for coatings in powder form, in particular for Powder paints.

At present, powdery coating materials are manufactured by processes which are mechanical Include comminution, namely grinding pieces of solid color or the components more firmly Colour. Obtaining the equipment necessary for grinding requires a great deal of material Effort that is increased by the fact that the usual equipment for conventional production of colors is often not suitable for this purpose. Second, mechanical crushing does not allow any precise control over the grain size and the distribution of the grain sizes of the powder paint. Third Milling does not produce smooth, rounded particles, but rather sharp-edged and irregular ones Particles generated. These irregularly shaped particles put the effectiveness of the process in action Use of electrostatic spray comes down because higher voltages are required, the one pose a greater risk of electric arcs occurring. When using powder paints the properties of the coating produced often depend very much on the physical properties of the Powder, such as B. Size and shape of the particles, homogeneity of the mixture and uniformity of the Grain size.

From DE-OS 20 08 711 is a method for Production of pigmented synthetic resin powder known, in which a synthetic resin solution in water introduces and thereby separates the powder by lowering the solubility

It has been shown, however, that powders of this type have a strong tendency to stick together, therefore caking and adhere to the walls of the reaction vessel.

The aim of the invention is to provide a method for producing powder paints from the most diverse Materials such as those used for the production of the usual liquid paints that the does not have the above-mentioned disadvantages and wherein the powder paints produced have the desired physical Properties regarding grain shape and size as well as homogeneity of the mixture and color consistency should have. Furthermore, to carry out this process, the usual equipment for the production of liquid colors, possibly with only minor changes or additions.

According to the invention this is achieved in the manner shown in the claims

In the preferred embodiment of the method, the liquid paint becomes one by something less than the coagulation-triggering amount of the coagulation liquid is added and the mixture then with a further amount of the coagulation liquid until most of the coagulation has taken place of the color solid mixed.

In contrast to the previously known processes for the production of powder paints, in which a solid color cake or solid color components have been ground to produce a powder, you walk according to the invention from a conventional liquid paint, from which the color powder by coagulation or precipitation of the color body is obtained. To carry out the process, the solvent fraction The color is chosen so that it can be used with a coagulation liquid that is not a solvent for the Color solid is, is miscible. To control the grain size of the powder to be precipitated, the speed with which the liquid paint and the coagulation liquid are mixed together, and the completeness of the degree of mixing of the two liquids is of great importance. It was found that the grain size of the particles produced is inversely proportional to the speed with that the solvent of the paint is diluted and that the grain size distribution is directly dependent on the Completeness of mixing. The slower the color in the period from the beginning or shortly before The start of coagulation or precipitation, the larger the particles produced Powder color, and the less complete the mixing of the coagulating liquid and the liquid Color is, the more so is the grain size distribution in the powder produced.

The invention is explained in more detail with reference to the drawings

F i g. 1 a process scheme with possible additional process steps,

F i g. 2 and 3 typical color system diagrams with liquids a and b to determine the percentage of the solvent to be added,

4 shows the particle size distribution for colored powder according to the method shown in FIG. 2 marked points.

For conventional liquid paints, the choice of solvent is determined by the type of application Color and its conditions. Because powder paint is an essentially solvent-free coating material

touches the use of any solvents during the manufacture of the powder paint not their use. Consequently, the choice of a solvent can be according to the exact requirements for the production of powder with the desired physical Properties are made. The term "powder" in this context generally means one Amount of fine paint particles that are essentially solvent-free, but otherwise complete Color body made from binder and, if necessary, pigment represent. The color powder can be in dry form or by a liquid that is suitable for this particle is not a solvent, be wetted. The powder may be either hydrophilic or hydrophobic. In the manufacture of the powder it may, as will be explained below, either to a dry one Dried powder or as a moist powder with a liquid that is a nonsolvent for the color body is to stay wetted. This latter form is preferred for areas of application in which the color is applied in the form of a slurry, as the powder then dries during manufacture can be omitted.

The first step in the process is to produce common paints using one of the for Process possible solvents as described below. The common property of these solvents, which are suitable for the production of powder paints is that both the color body as well as the precipitation or coagulation liquid must be easily soluble therein.

The second essential process step consists in the sudden and even dilution of the Paint in a medium that is miscible with the solvent of the paint and a nonsolvent for the The rest of the paint - the pigments and binders - represents.

Further procedural steps are not mandatory, such as B. washing and processing the failed Powder paint by one of the many known processes.

According to FIG. 1 the binder and the pigment are produced according to a conventional manufacturing process for paints. The solvent fraction of the liquid paint is referred to here as liquid a . The term "binder" is used here for all elements of the paint that are soluble in the liquid a. Similarly, the term "pigment" denotes all the components that are not soluble in liquid a. The pigment must be ground down to a sufficiently small particle size in order to produce a homogeneous suspension in the liquid a. Although the singular liquid a is spoken of, it should be noted that it can be a mixture of solvents.

Besides the choice of solvent for the liquid paint, it is for the manufacture of a powder of the desired quality also necessary to adjust the content of the solvent in the paint, d. h., for Achievement of the optimal properties of the powder to be produced with the greatest economic efficiency of the Manufacturing process to make the color thinner or thicker before precipitation. Thus the only difference in color compared to conventional colors in the amount and type of f> 5 Solvent.

After the production of the paint, the properties of the powder to be produced can be influenced by a further, but not absolutely necessary, process step by slowly and evenly mixing the liquid paint with a liquid b until a required concentration of the liquid b is present in the mixture If a powder color that is as fine-grained as possible is desired, it is expedient to increase the concentration of the liquid b almost to the point at which coagulation occurs, which is indicated by the dashed line 8 in FIG. 2 is indicated, however, the concentration of the liquid b with uniform mixing can in no case go beyond the coagulation line 4 of FIG. 2, since otherwise premature coagulation would occur.

After the liquid b has optionally been added in the manner described, the paint is mixed and diluted at high speed with a further quantity of the liquid b . This step is important for achieving the desired properties of the paint particles. After the preconditions for paint and solvent have been met, the size and size distribution of the paint particles depends on the type and speed of dilution and coagulation.

According to a third and preferred variant of the method, which is well suited for continuous production and a stronger influence on the particle size and particle size distribution enables than the two methods described above, is that the fluid b in a container in the liquid b (z. B. Water) is entered below the paint inlet and stirred at high speed with the aid of a (rotating paddle) mixer. An outlet nozzle for the color mixture is arranged under the surface of the liquid b near the mixer blade where the circulation of the liquid b reaches the maximum. The color mixture a is then injected under high pressure through the nozzle into the moving liquid b Almost instantaneous division of the color flow into small drops. The solvent contained in these drops, since it is miscible with the liquid b, is withdrawn from the drops and causes the drop to coagulate into small pigment particles which, since they are not soluble in the liquid b , form the powder.

The coagulated particles normally float as a foam because of the movement of the liquid on its surface. Since more liquid b is supplied to the container, the foamed powder is discharged through an overflow as it arises. Since the fresh liquid b is fed into the container below the paint nozzle, the mixture of liquid b and the solvent of the paint (liquid a) also flows out via the overflow, thereby avoiding an increase in the concentration of the solvent in the liquid contained in the container will.

This continuous type of process represents the preferred mode of implementation for the continuous one Manufacture of the powdery material.

After coagulation has occurred, the powder particles are removed from the liquid mixture by filtration or removed by another method of separation of solids and liquids.

In order to avoid agglomeration of the particles, ie the agglomeration of numerous small particles to form larger ones, it is desirable to remove any residues of the solvent {or the liquid a) from the

to wash off wet powder. For this purpose, either fresh liquid b or another liquid can be used which is miscible with the liquid a and which is a nonsolvent for the colored powder. This other liquid can be the transport liquid for the powder when the powder is wet packed, as described below.

The mixture of liquids a and b or the liquid used to wash the powder can be circulated in a closed system. The great advantage of this is that little or no solvent is lost to the atmosphere, thus avoiding air pollution. There are therefore no other limits in the choice of solvents than those which are given by the properties of the powder paint to be produced. This allows the economical use of solvents which would be unacceptable for liquid paints.

If the powder is to be used later in liquid form, it can be stored without drying because the powder is already moist.

When the powder is to be used in dry form, such as that in electrostatic spraying or is the case in the fluidized bed process, the powder may in any known manner, e.g. B. in an air or Spray dry method are dried.

To control the grain sizes produced in the coagulation process step, it is necessary to set the color mixture and the physical conditions of the coagulation. The F i g. 2 and 3 show typical diagrams which are useful for determining the composition of the color or color mixture and which are necessary for achieving a predetermined particle size distribution. The X-axis shows the content of color bodies in percent by weight, in which both the part which is soluble in the solvent or in the liquid a is contained. The part which can be dissolved usually consists of plasticizers, resins and other organic compounds; the insoluble part consists of the pigments.

It is not essential that the paint contain an insoluble portion, but if such is present, its particles can act as nuclei for the dissolvable component to settle during coagulation and thus promote the homogeneity of the mixture. The second - the V-axis shows in percent by weight the proportion of solvent, which is referred to here as liquid a. While it is usually easiest to use a single solvent, for some materials a mixture of more than one solvent is desirable to produce a powder with a particular particle size distribution. The third - the Z-axis shows the proportion of coagulation fluid, which is referred to as fluid b . The liquid b can also consist of a single liquid or a combination of several liquids. While liquid a must be a solvent for at least a portion of the color solid, liquid b must not be a solvent or at least must be a very poor solvent for each of the constituents of the color solid. Further, the liquids a and b must be miscible with each other, and the easier they mix with each other, the easier it is to control the particle size of the coagulating powder.

Line 4 of FIG. For each mixture of the liquid color with a certain percentage of color body liquid a (or solvent) and coagulation liquid b corresponds to the point at which coagulation begins. The line 6 corresponds to the point at which the predominant part, for example about 95% of the color body has coagulated with the slow addition of further portions of the liquid b. Correspondingly, in FIG. 3, line 5 indicates the start of coagulation and line 7 indicates the almost completed, B. 95% coagulation in a different color mixture. It can be seen that as the proportion of liquid a increases, the lines significant for the onset and completion of coagulation converge. The size of the distance between these lines where there is little liquid a depends on the type of resin or solid. In general, the more complex the binder system, the more divergent the two, and the farther apart the two lines are, the longer it takes for a given system to cross this line when diluted by the liquid b . However, the longer it takes from the beginning to the completion of coagulation, the larger the powder particles that are produced. When, as is usually the case, it is desirable. To produce particles as small as possible, the solvent content must be increased (the paint diluted). However, as the solvent content of the paint increases, the process becomes less economical because more solvent has to be used and then recovered from the coagulating liquid, liquid b. Furthermore, the more solvent the paint contains, the fewer color bodies there can be and the lower the yield of powder paint in a given system. A balance must therefore be found between the desired production capacity and the particle size of the powder produced.

For example, according to the system shown in FIG. 2, samples were produced with a solvent content indicated by points 10, 20, 30, 40 and 50. The same color system was used in each case. The powders produced by coagulation were analyzed. The resulting particle size distribution is shown in FIG. 4, where 10 'corresponds to the powder prepared according to point 10 of FIG. 2, etc. The logarithmically divided horizontal axis (μ) of FIG. 4 shows the diameter of the powder particles in μ, while the vertical axis shows the amount of powder in percent with a larger diameter than the specified size in μ.It can be seen that if particles with sizes below 30 μ are desired, a mixture according to point 50 is used should. Accordingly, after creating diagrams according to FIG. 2 or 3 and analyzing the resulting grain sizes according to FIG. 4 possible to determine the optimal content of liquid a for ie coagulation of the color.

This analysis can be used for a specific process system and for predetermined liquids a and b . If these factors are changed, a new calculation must be made.

For a certain color and certain liquids a and b , the coagulation of the powder can largely be determined by the type of process used. The main characteristic of the different types of process is the speed with which the liquid paint is completely mixed with the liquid b. This in turn depends to a certain extent on the tropical size of the liquid color, since smaller drops move faster and

mix more completely than larger ones. The drop size in turn corresponds to the size of the resulting Particles. Consequently, the faster the mixing and the smaller the particles, the smaller the particles Drop size of color is.

The average grain size of the powder produced is smaller, the smaller the nozzle opening is at a certain pressure and a certain liquid circulation. Correspondingly, the higher the pressure, the smaller the average grain size of the powder particles. although the effect is not as pronounced as that achievable by the size of the nozzle opening. The stirring effect also has an influence on the grain size. However, this factor is of no great importance provided that the agitation speed is sufficiently high. It follows that a powder made using higher pressure and smaller nozzles for injecting the paint into the liquid b has the same particle size distribution as a powder made from a paint with a relatively larger proportion of liquid a under lower pressure and with a larger nozzle arrangement .

A narrowing of the types of paint from which powders are made according to the proposed method can, results from the fact that certain film-forming substances or plasticizers in normal Manufacturing and storage temperatures are liquid. When powder paint is made, use such plasticizers and the powder remains in a liquid medium, there is no problem. Therefore the restriction does not apply to powders that are stored and used in a moist state. If it however, it is necessary to convert the liquid paint containing such film-forming agents into a dry powder, the liquid film former tends to make the particles of the powder paint sticky or causes them Agglomeration to useless masses. This problem can be partially solved by limitation the amount of liquid film formers up to a predetermined critical percentage. Is z. B. If dioclyl phthalate (DOP) is used in one color, the problem mentioned will not occur, if not more as 10 to 15% DOP are contained in the finished, dry powder, if this is at room temperature is manufactured and stored.

In Fig. 1 the production of the liquid paint to be used in the proposed process is referred to as "paint production" and contains the usual process steps for the production of liquid paint, modified only in the choice of solvent, liquid a, which must be miscible with liquid b. The liquid color produced in this way can then be added directly to the liquid b in the coagulation chamber, as indicated by the dashed arrow 100 , further liquid b being added as indicated by the arrow 102 , or the liquid color can be mixed with the Liquid b premixed until a state shortly before coagulation is reached and the coagulation of the mixture can then be triggered by adding a large amount of liquid b , as indicated by arrow 104.For numerous liquid colors, acetone can be used as liquid a and water as liquid b to be used.

After coagulation or precipitation, the moist powder can be collected and fed to a filtration stage, where the moist powder is separated from the liquid mixture in a known manner and the mixture of liquids a and b is separated into its components for reuse. Such a separation can be carried out by distillation or another suitable process. The filtered powder can either be washed with a further quantity of liquid b or another liquid which is a non-solvent for the powder, and the powder can then be sieved according to particle size. Particles with undesirable grain sizes can be returned to the liquid paint production stage. After sieving, the usable fractions can be packed either wet or after drying.

ι - B e i s p i e I A

A conventional liquid paint was made by grinding 25 grams of carbon pigment, 50 grams of commercially available Acrylic ester resin in the form of a 40% solution of methyl methacrylate with a glass transition temperature

-'Ii temperature of 100 ° C in methyl ethyl ketone and 125 g of acetone 40 hours in a steel ball mill to achieve a pigment of the fineness 7 according to the grinding scale ground according to Hegman. This mixture was coagulated together with 1000 g of acetone

-i resin added, which by mixing 1500g Acrylic ester resin, consisting of a methyl methacrylate-butyl methacrylate copolymer with a glass transition temperature of 50 ° C and 4500 g of white spirit. After mixing in

in a food mixer the color was homogeneous. With further stirring of the liquid paint, water was used as the coagulation liquid in aliquots of 500 g each are added until the start of coagulation. Suddenly another 2000 g of water were added to the

)> Precipitation of the powder added. The powder was then collected, separated from the liquid mixture, filtered, washed and dried.

Example B.

4 (i 50 g of the same liquid paint as in Example 1 described, were entered by hand in 300 g of water, the water being blown through a puff Mixer was stirred. The coagulated paint was then filtered and left in the air for 16 hours

· »"> Dried. The sieve analysis shows that about 21% the powder particles had a size of less than 50 μ.

example 1

"> <> A liquid paint became through sixteen hours Milling 300 g of titanium dioxide with 50 g of lamp black, 25 g of talc, 250 g of thermoplastic resin consisting of a mixture of oxidized tall oil pitch and vinsol resin (mp ~ 120 ° C) and 600 g of acetone in a steel ball mill up to the production of a pigment of size 7 according to Hegman a further 600 g of the same thermoplastic resin and 400 g of acetone were added and the mixture up to Stirred to achieve homogeneity. The liquid paint

bo was then passed through a nozzle at a pressure of 7 at with a diameter of 0.7 mm placed in a 120-liter container containing 80 liters of water, The water is added through a 15 cm long, saw-like toothed blade of a high-performance mixer 2000 rpm was stirred and the stirring blade and the nozzle in close proximity under the water surface were arranged. After filtering, washing and drying the coagulated powder, the

Analysis that at least 50% of the powder paint consisted of particles smaller than 50 μ in size.

Examples 2 Lis 6

In this series of examples, 70% by weight of a thermoplastic acrylic polymer resin was dissolved in 30% by weight of 2-ethoxyethanol. No pigment was added to the resin. Acetone was added to parts of this solution as shown in Table 1. The resulting mixtures correspond to those in FIG. 2 specified. Water was used as liquid b , and these mixtures

10

Big added to bring the mixtures into a near pre-coagulation equilibrium according to the Bring points 11, 21, 31, 41, 51 of line 8. then Each color was placed in a container according to Example 3, using a nozzle of 1.65 mm in diameter was used and a pressure of 56 at was applied. The speed of rotation of the stirring blade was 3200 rev / min.

The powder produced was dried. Analysis of grain sizes and grain size distribution each Powder is the fig. 4 can be found.

Table 1

Weight percent
70% resin and
30% 2-ethoxyethanol acetone Reference point
in Fig. 2 80 20th 12th 66-2 / 3 33-1 / 3 22nd 50 50 32 33-1 / 3 66-2 / 3 42 20th 80 52

Example 7

A powder coating was prepared by dissolving 45 kg of a commercial petroleum hydrocarbon resin in 38 liters of linseed oil by heating the oil in 40 minutes at 290 ⁰ C. After cooling the mixture to 38 ° C 450 g Cobaltonaphthenat were (6% strength) together with 22 , 5 kg of white spirit added and mixed in. This mixture was coagulated using the device according to Example 3. The pressure was 56 atm, the nozzle had a diameter of 1.4 mm, the container contained isopropyl alcohol which was stirred by a stirring blade at 2000 rpm. After washing and drying, the powder produced had particles with diameters between 40 and 50 μ.

Miscible solvents and coagulants assigned to one another are shown in Table 2. The assignment condition is that the liquid a must be a solvent for at least part of the color body and be miscible with the liquid b , which in turn must be a nonsolvent for each of the constituents of the color body.

Table 2

Liquid a Liquid b (Solvent) (Coagulant) Xylene Hexanes or paraffinic toluene Hydrocarbons Ketones Alcohols Xylene low molecular weight alcohols or toluene Ketones Hexane water water-diluted mineral acid, alcohol such as B. hydrochloric or phosphoric acid acetone water

use

Alkyd, polyester, styrene and vinyl toluene
modified polyester

Hydrocarbon resins, varnishes such as e.g. ß. resinified oil varnishes and alcohol varnishes

suitable for water-soluble paints, especially anionic latices

of the utmost importance because it is not very complex and
easily separable

The selection of liquids a and b depends on the binders used.

For this purpose 3 sheets of drawings

Claims (4)

Patent claims: 1. Process for the production of powdery coating materials optionally containing pigment by precipitating a synthetic resin solution with a medium containing the synthetic resin solvent miscible, but not a solvent for the synthetic resin, characterized that the resin solution is suddenly and evenly diluted with the medium by the Inject synthetic resin solution into the turbulent moving medium 2. The method according to claim 1, characterized in that the medium is in a stirrer provided vessel and the synthetic resin solution in the immediate vicinity of the running stirrer brings in below the surface 3. The method according to claim 1-2, characterized in that the synthetic resin solution is before premixed with the medium upon introduction into the medium 4. The method according to claim 3, characterized in that the synthetic resin solution with a such an amount of medium is premixed that no precipitation occurs.