FI59608C - FOER FARING FRAMSTAELLNING AV ETT PULVERFORMIGT BELAEGGNINGSMATERIAL - Google Patents

Description

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Patent and * registered (44) Nihtlvlluipsflen j «kuL | uUul * m date. -

Patent · och registsrstyrelMn 'AiwekM uti «fd och uti. * Krtft» «pubiicarad 29.05.8l (32) (33) (31) Requested this year — Begird prtorltet 05.10.71 USA (US) I86695 (71) Grow Group, Inc. , PanAin Building, 200 Park Avenue, New York,

New York 10017, USA (72) Ivan Hsieh-An Tsou, Pontiac, Michigan, James William Garner,

Detroit, Michigan, USA (7) +) Berggren Oy Ah (5I +) Method for the preparation of a powder coating material - Förfarande för framställning av ett pulverformigt beläggningsmaterialial

The invention relates to a process for preparing a powder coating material.

The use of powder coating materials such as powder coating has greatly increased in the last few years. There are many advantages to using powder coatings instead of liquid coatings, but there are many drawbacks to current methods of making powder coatings, especially paint powders.

Today, powder coatings are made by methods that involve the attraction of solid paint or paint component pieces, i. hankausjauhatus. First, the equipment used for grinding requires large investments, and the obsolescence of the equipment used for the production of paint by certain methods significantly increases the cost of powder coatings. Second, in mechanical abrasive grinding, it is not possible to precisely control the size or size distribution of the paint powder particles. Third, mechanical grinding does not produce smooth, rounded paint particles, but particles with sharp edges and an irregular shape. These irregularly shaped particles reduce efficiency when used in electrostatic spraying steps because they require higher voltages, resulting in a greater increased risk of sparking. When paint powders are used for coating, the properties of the finished coating often depend greatly on the physical properties of the powder, such as particle size and shape, uniformity of composition, and uniformity of size.

According to the present invention, there is provided a method of manufacturing a powder paint comprising mixing a liquid paint having a solvent portion miscible with the coagulating liquid, the at least most of the non-solvent portion of the liquid paint precipitating as a powder, and removing the powder paint thus precipitated from the mixture.

In the case of the present invention, standard paint preparation equipment can be used to produce a conventional paint, where only the solvent may be different from conventional paint compositions. Although some additional equipment is needed, the technology used requires only a minimum amount of additional machinery. In addition, the particle size can be controlled with reasonable accuracy and the particles are substantially uniform in shape.

In adjusting the particle size of the precipitated powder, the rate at which the liquid paint and the coagulating liquid are mixed and the completeness of the mixing of the two liquids are very important. It has been found that the size of the particles generated is proportional to the rate at which the paint solvent is diluted, and that the size of the particle size range is directly proportional to the completeness of the mixing, i. the slower the paint solvent is diluted from the moment just before coagulation, i.e. the onset of precipitation until most of the non-solvent part has precipitated, the larger the powder paint particles formed, and the less complete the coagulation liquid and liquid paint mix, the wider the resulting powder. The particle size distribution.

The invention is shown, by way of example only, in the accompanying drawing, in which:

Figure 1 is a flow chart of the process, including many optional steps, Figures 2 and 3 show typical paint systems using liquids A and B to determine the percentage of solvent added, Figure 4 shows the particle size distribution in powders prepared at the points indicated in Figure 2.

In conventional liquid paints, the choice of solvent is determined by the purpose of the paint and the conditions of that use.

Since the powder paint is a substantially solvent-free coating agent, the use of solvents during the manufacture of the powder does not affect the deposition of the powder. As a result, the choice of solvent can be adapted to the requirements of the preparation of a powder with advantageous physical properties. The term "powder" is used in this specification to genetically refer to fine paint particles, each of which is substantially free of solvent but otherwise encompasses a complete paint system with film formers and pigments. The powder can be either in dry form or wet from a liquid in which the particles are insoluble. The powder can be either hydrophilic or hydrophobic. When preparing the powder, as explained below, it can either be dried to a dry powder or it can be left wet from a liquid that is not a solvent in the paint system. This latter form is preferred in those applications where the paint is deposited as a slurry, since no drying step is required during the manufacture of the paint powder.

The term "paint" is intended to include both powder coatings and conventional paints.

The first step is to prepare a conventional paint using a solvent belonging to a selected group of solvents as a liquid carrier, as described below. The common property of solvents that makes them suitable for the production of powder paint is that they are good solvents for both the paint system and the precipitating or coagulating liquid.

The second step is to suddenly dilute the paint uniformly with a liquid medium that is miscible with the paint solvent and is not the solvent for the rest of the paint system - the pigments and film formers. Dilution can be performed in many ways, as explained below, depending on the desired physical properties of the powder and the economics of the production process. In addition, there are a number of optional steps such as washing and treating the precipitated powder paint by one of a number of known methods.

According to Figure 1, film formers and pigments are prepared as is normally done in normal paint production. The solvent portion of a liquid paint is referred to herein as a liquid A. Film formers are defined herein as all paint components that are soluble in liquid A. Likewise, pigments are all components of a paint that are insoluble in liquid A. Pigments must be ground so finely that they remain homogeneously suspended to liquid A. Although liquid A is referred to in the unit, it is clear that it can also be a solvent mixture.

In addition to the choice of the solvent for the liquid paint so as to obtain the desired powder, the amount of solvent in the paint must also be adjusted, i. the paint must be made thinner or thicker before precipitation so that the resulting powder has optimum properties and the manufacturing process is as economical as possible. Thus, it will be apparent to those skilled in the art that the only difference between the paint in question and a regular paint is the amount and type of solvent.

Once the paint has been prepared, an optional step which, although not necessary for the use of the invention, nevertheless alters the properties of the resulting powder is to gradually and uniformly mix the coagulating liquid B with the liquid paint until the desired amount of liquid B is present. Liquid B is miscible with liquid A but is not a solvent for pigments. If it is desired to keep the powder particles as small as possible, it is preferable to increase the concentration of the liquid B almost to the concentration necessary to effect coagulation, as indicated by the broken line 8 in Fig. 2. In any case, however, the uniformly mixed concentration of liquid B must not be on the other side of the coagulation line 4 in Fig. 2, or otherwise premature coagulation will occur.

Returning to Figure 1. After liquid B has been added (if added), the paint is suddenly diluted and mixed with liquid B.

This step is important for adjusting the properties of the powder particles.

Once the initial condition of the paint and its solvent is met, the method of dilution and coagulation and the rate at which it is performed determine the particle size and size distribution.

One way is to stir the liquid paint in the tank and then quickly pour in a large amount of coagulation liquid until the non-solvent portion of the paint coagulates. This method gives a wide range of particle sizes and is suitable for batch production. However, with this method, the size of the obtained powder particles is difficult to control.

Another method which is also suitable for batch production is that the coagulating container containing the second liquid is agitated and the prepared paint is slowly poured into this agitated second liquid. As each drop of paint strikes another liquid, the paint pigments and film formers coagulate out of the solvent because the solvent becomes infinitely thin in the volume of this second liquid in which the solvent is miscible but in which the pigments and film formers are insoluble. This results in a somewhat narrower distribution of powder particle sizes, although the average size tends to be large. Even now, adjusting particle sizes proves difficult, but this method is most convenient for preparing small amounts of powder for the laboratory.

The third method, which is also the preferred embodiment, is well suited for continuous production and allows more precise control of both the particle size and the particle size distribution than the other two methods described above. In this method, the tank of liquid B, to which liquid B is fed at a point below the point of entry of the paint, is vigorously agitated by a rapidly rotating vane stirrer. Below the surface of the liquid B, close to the agitation wing where the agitation of the liquid B is at its highest, a paint mixture feed nozzle is attached. The paint mixture is then sprayed under high pressure through a nozzle into the agitated liquid B. This spraying causes the paint stream to disintegrate into small droplets in the blink of an eye. The solvent in these droplets, because it is miscible with liquid B, is removed from the droplet, causing the droplet to coagulate into small particles containing non-solvent parts of the paint (because these parts are insoluble in liquid B) which then form a powder.

Due to the confusion, the coagulated particles are on the surface as foam. Since fresh liquid B is constantly fed into the tank, the overflow from above takes with it the foamed powder as it emerges from the paint. As the product liquid B is fed into the tank below the paint nozzle, the mixture of liquid B and paint solvent (liquid A) also flows out as an overflow, so that the liquid in the tank cannot get saturated with the solvent.

Although this method is the preferred embodiment for the continuous preparation of a powdered substance, it is clear that any coagulation method can be used, provided that liquid A is removed, for example by dilution, from fine droplets of paint and liquid A is sufficiently diluted with liquid B to redissolve and precipitate particles. is prevented.

Once coagulation has occurred, the powder particles are removed from the liquid mixture by filtration or some other method of separating the solid particles from the liquid.

Particle entrapment, i. in order to prevent several small particles from sticking together into larger particles, it is preferable to wash all traces of solvent (i.e. liquid A) away from the wet powder.

This can be done either by using fresh liquid B or some other liquid that is miscible with liquid A and is not a solvent for the paint powder. This second liquid may be the liquid which is sent to transport the powder} if the powder is packed wet as explained below.

The mixture of liquids A and B or the liquid used to wash the powder can then be recycled back in a closed system.

The great advantage of this method is that very little or no solvent is lost to the atmosphere, so that no air pollution occurs.

As a result, there is no restriction on the choice of solvents other than the restrictions imposed by the properties of the powder paint to be prepared. This makes it economically possible to use solvents that would be unsuitable for use in liquid paints.

Once washed, the powder can be screened to remove particles of inappropriate size. For example, only particles smaller than 40 microns in diameter may be desired for wet spraying.

Electrostatic spraying is more effective if the powder does not contain very large or very small paint particles. Thus, it may be desirable to screen out particles smaller than 20 and greater than 80. This wet screening can be performed using any conventional method. The advantage of wet screening is that fine paint particles do not enter the atmosphere as dust.

Particles that have been screened off and are not desired for any other use can be recycled back to the original paint by redissolving them in liquid A, which is easy because no irreversible change has occurred in this manufacturing process.

If the powder is to be finally used in liquid form, the powder can be stored and packaged without drying, as the powder is already wet and its final use is wet.

If the powder is to be deposited dry, such as by electrostatic spraying, or as a fluidized bed, the powder can be dried by any conventional method such as air drying or spray drying.

In order to control the particle sizes obtained from the coagulation step, both the paint mixture and the physical conditions of the coagulation must be precisely adjusted.

Figures 2 and 3 are typical diagrams that have been found to be helpful in determining the composition of the paint composition necessary to achieve a predetermined particle size distribution. The first axis x represents the amount of the non-solvent part of the paint, i.e. the substance, by its weight, which part includes both parts soluble and insoluble in the solvent A. Soluble moieties usually include plasticizers, resins, and other organic compounds; the insoluble part includes pigments. It is not essential that the paint have insoluble parts, but if they do, they can act as precipitation cores for the soluble part during coagulation, thus promoting the homogeneity of the mixture. The second axis y represents the amount of solvent, named for convenience A, as weight J6. Although, for simplicity, only one solvent is normally used, it will be appreciated that in some substance systems, a mixture of more than one solvent may be preferred to produce a powder having a certain size distribution. The third axis z represents a coagulation liquid called liquid B. Liquid B can also be either a single liquid or a liquid mixture. Liquid A must be a solvent for at least some of the solids in the solvent paint, but liquid B must not be a solvent for any solids in the paint or at least be a very poor solvent. In addition, liquids A and B must be miscible with each other, and the easier they mix with each other, the easier it will be to adjust the particle size of the coagulated powder.

In Figure 2, line 4 represents the point at which coagulation begins to occur for each liquid paint mixture containing a certain percentage of paint solids, liquid A (i.e., solvent), and coagulation liquid B. The straight Q represents the point where most, e.g. 95% of the paint solids are coagulated as liquid B is further added slowly. Similarly, in Figure 3, line 5 represents the onset of coagulation of the second paint system and line 7 represents the almost finished, i. 95% coagulation.

It should be noted that as the percentage of liquid A increases, the lines representing the beginning and end of coagulation converge. The distance between these lines where liquid A is low depends on the elements of the resin or paint solid system. In general, the more complex the resin system, the farther the two lines differ. And the further the two lines differ, the longer it will take for a particular mechanical system to cross these lines when diluted with liquid B. And the longer it takes from the onset of coagulation to the end of this process, the larger the resulting powder particles. Thus, if, as is usually the case, it is desired to obtain particles that are as small in size as possible, the solvent content must be increased (i.e., the paint must be thinned).

However, as the solvent content of the paint increases, the process becomes less efficient in that more solvent must be used and then recovered from the coagulating liquid, liquid B. In addition, the more solvent in the paint, the less solids it can contain and the amount of paint powder developed by a particular system. decreases. Thus, a balance must be found between the desired production capacity and the desired particle size of the manufactured powder.

Using the system of Figure 2, samples having the solvent content of points 10, 20, 30, 40 and 50 of the figure were prepared by way of example using the same mechanical system. The coagulated powders were analyzed and the particle size distributions obtained are shown in Fig. 4, where curve 10 'corresponds to the powder prepared at point 10 in Fig. 2, etc. The logarithmic horizontal scale (pm) in Fig. 4 59608 indicates the having a particle diameter greater than the appropriate size in microns. It is obvious that if particles smaller than 30 microns are desired, this system should use a point of 50.

Similarly, after the presentation of Figures 2 or 3 and the analysis of the particle size distributions obtained as in Figure 4, the optimum amount of liquid A to coagulate the paint can be determined. This analysis concerned a mechanical system that is constant and predetermined liquids A and B When these factors are changed, the calculation must be performed again.

The size of the powder coagulated with a given paint, liquid A and liquid B, can be quite widely adjusted by selecting a suitable mechanical system. An essential feature of a mechanical system is the rate at which the liquid paint is completely mixed with liquid B. This in turn is likely to depend to some extent on the size of the liquid paint droplets because the smaller droplets appear to mix faster and more completely than the larger droplets. Further, the droplet size appears to be related to the final particle size.

Thus, the faster the mixing and the smaller the size of the paint droplets, the smaller the paint particles obtained.

In the preferred embodiment described above as the third method, the smaller the average nozzle size at a given pressure and agitation, the smaller the average size of the powder obtained. Similarly, the average pressure of the powder particles will be smaller the higher the pressure, although this dependence is not as obvious as the nozzle size effect. Confusion also has some effect on particle size, but this is not of great significance, provided the confusion is sufficiently intense. Thus, it can be seen that a powder made from a particular system using higher pressure and smaller nozzles for spraying paint into liquid B has the same particle sizes as a powder made from paint with relatively more liquid A compared to non-solvent parts of paint, using lower pressure and larger nozzles.

One limitation on the types of paint that can be prepared as powders by this method is due to the fact that some film-forming ingredients (plasticizers) are liquid at normal manufacturing and storage temperatures. When prepared with powdered soil containing these plasticizers and the powder remaining in the liquid medium, no difficulty occurs. This restriction therefore does not apply to powders that are stored and used wet. However, if it is desired to dry a powder paint containing these 9 59608 film formers into a dry powder, the liquid film former tends to act so that the paint powder particles become sticky, i.e., precipitate into unusable masses. This problem can be alleviated by limiting the amount of liquid film formers below a predetermined critical percentage. For example, if dioctyl phthalate (DOP) is used in the paint, there is no problem unless more than 10-15% y of D0P is present in the finished dry powder when the powder is prepared and stored at room temperature. Another way to alleviate this problem is to prepare and store a dry powder paint at a low temperature where the film former, which is liquid at normal temperature, solidifies.

In Figure 1 of the drawing, the preparation of the liquid paint used in the process is denoted by the words "paint preparation" and includes the conventional steps of liquid paint preparation, modified only in that the solvent part is selected from liquid A which is immiscible with liquid B. The thus prepared liquid paint can then be directly added to the liquid B koaguloimiskammiossa as cat-koviivanuolella 100 is shown in which the fluid B is fed to the direction of arrow 102 by, or liquid paint, and the liquid B may be mixed in advance near the coagulation and then the collapse of the mixture by adding it to a large amount of the liquid B of the arrow 104 by. It has been found that liquid A may suitably be acetone for many liquid paint compositions, and liquid B may be water.

After coagulation, i.e. the precipitate, the wet powder can be collected and led to a filtration step in which the wet powder is separated from the liquid mixture by conventional means and the liquids A and B are then separated for reuse. This separation can be performed by distillation or other suitable techniques. The filtered powder can be washed with either additional amounts of liquid B or some other liquid that is not a solvent for the powder, and then screened to size. Particles of inappropriate size can be returned to the original liquid paint fabrication step for a new cycle. After screening, the approved particles can either be packaged wet or dried and packaged dry.

The following examples are provided to demonstrate the versatility and wide scope of this method.

Example I

A conventional liquid paint was prepared by grinding 25 g of carbon pigment, 50 g of Rohm & Haas "Acryloid A-101" acrylic ester resin and 125 g of acetone in a steel ball mill for 40 hours to give a pigment dispersion with a fineness of 7 as measured by a Hegman grinding gauge. This was then added together with 1000 g of acetone to a coagulated resin prepared by mixing 1500 g of Rohm & Haas "Acryloid B-66" acrylic ester resin * with 500 g of VM&P naphtha. After stirring in a food mixer for 1 hour, the paint became homogeneous. Continuing to stir the liquid paint, water was added as a coagulation liquid in 500 g portions until coagulation began.

At this time, an additional 2000 g of additional water was added immediately to precipitate the powder. The powder was then collected and separated from the liquid mixture, filtered, washed and dried.

Example II

50 g of the liquid paint of Example I was manually poured into 500 g of water which was stirred with a high speed stirrer such as a Waring Blender Model 1120. The coagulated paint was then filtered and air dried for 16 hours. Screening analysis showed that approximately 21% of the powder particles were less than 50 microns in size.

Example III

A liquid paint was prepared by grinding 500 g of titanium dioxide and 50 g of gas soot, 25 g of talc, 250 g of Vincal's 150 "thermoplastic resin and 600 g of acetone in a steel ball mill for 16 hours to give a pigment dispersion with a fineness of 7 on a Hegman grinder. Hercules' Vinsaly's 150 "resin and 400 g of acetone and this mixture was stirred until homogeneous. This liquid paint was then pumped at a pressure of 7 <^ Tri through a 0.71 mm diameter nozzle into a 115 liter barrel containing about 75 liters of water stirred with a serrated 15 cm vane rotated at 2000 rpm by a high speed mixer such as the Shar Model S-20, and a serrated the wing and nozzle were very close to each other, immersed under the surface of the water. The coagulated powder was filtered, washed and dried, whereby analysis showed that at least 50% of the powder paint particles were less than 50 .mu.m in size.

Example IV-VIII

In this exemplary series, 70 wt.% Thermoplastic acrylic polymer resin was dissolved in 50 wt% JC "Ethyl Cello Solvent" from Union Carbide. No pigment was added to the resin. To this solution was then added acetone according to Table I below. These mixtures are indicated in Figure 2 using the relevant references to this table. Water used as liquid B was then added uniformly to these mixtures to bring the mixture to points 11, 21, 51, 41, 51 on line 3, just before coagulation. Each paint was then pumped into a drum of the type described in Example III with a nozzle diameter of 1.65 mm at a pressure of 56 atm and a blade speed of 3200. The resulting powder was dried, and the particle size and particle size distribution analysis of each powder is shown in Table I below. with the corresponding reference numeral referring to Fig. 4.

Table I

70 Resin and 30% “Ethyl Cellosolve” Acetone Reference Number

Weight- # Weight- in the figure 2 80 20 12 66 2/3 33 1/3 22 50 50 32 33 1/3 66 2/3 42 20 80 52

Example IX

100 g of Neville Chemical Co.'s "LXIOOO" petroleum hydrocarbon resin was dissolved in 50 g of VM & P naphtha. This mixture was poured by hand into a high speed mixer containing acetone as coagulating liquid B. The coagulated powder was filtered, washed and dried. A fine powder was obtained with particle sizes substantially similar to those shown in Figure 4.

Example X

Same as Example IX, except that isopropyl alcohol was used as the coagulant (liquid B).

Example XI

A lacquer powder was prepared by dissolving 45 kg of Neville Chemical Co.'s "LX1000" petroleum hydrocarbon resin in 38 liters of linseed oil by heating the oil at 288 ° C for 40 minutes. After cooling to 38 ° C, 0.454 g of cobalt naphthanate (6%) and 23 kg of VM & P-naphtha were added and mixed thoroughly. This mixture was coagulated using the equipment of Example III at a pressure of 56 atm from a nozzle 1.42 mm in diameter to a drum containing isopropyl alcohol which was stirred by rotating the vane at 2000 rpm. The resulting powder was washed and dried, after which the diameters of the powder particles were found to be between 40 and 50 μm.

Table II shows the groups of miscible solvents and coagulants. These groups are required that liquid A be a solvent for at least part of the paint or resin system and that it be miscible with liquid B, which in turn is not a solvent for any part of the paint or resin.

12 59608

Table II

Solvent A Solvent B Use xylene hexane or alkyd, polyesters, stytoluene other paraffinic rhenium and vinyl toluene ketone hydrocarbons nimodified polyesters alcohol xylene low molecular weight hydrocarbon resins, toluene alcohols varnishes such as oil hexane and ketones resins water-soluble alcohol alkaline acids such as paints especially hydrogen chloride or phosphoionic latexes acetic acid acetone water due to its most important cheapness and easy separation

Claims (9)

1. Process for Preparing a Powder Coating Material According to Which a Liquid Coating Material is Prepared Containing a Solvent Part and a Film Forming Part Containing a Pigment, A Coagulant Liquid Compatible with the Solvent, but Not Solvent for the Film Forming Part, is used , for the precipitation of the filing part in the form of powdery particles, and the coating particles are separated from the mixture of the solvent part and the coagulating liquid, characterized in that the liquid coating material is atomized in the presence of the droplet and the droplet liquid together with the a sufficient amount of coagulant to remove the solvent from them to precipitate the film-forming part in the form of powdery coating particles. Process according to claim 1, characterized in that the precipitated powdery coating particles are dried. Method according to claim 1 or 2, characterized in that the separated coating material particles are washed and screened according to size. 4. A process according to claim 3, characterized in that the powdered coating particles are washed with coagulating liquid. Process according to any of the preceding claims, characterized in that the ratio of the solvent to the film-forming part of the liquid coating material is inversely proportional to the desired sorrel of the powdery coating particles.