CH663363A5 - METHOD FOR PRODUCING A DRY AND / OR CURED COATING ON A SUBSTRATE. - Google Patents

Description

The invention relates to a method for producing a dry and / or cured coating on a substrate, which is defined in claim 1, and devices for carrying out this method, which are defined in claims 11 and 12. According to the invention, drying can be carried out more effectively than before.

The invention is applied in the drying of paints, lacquer paints, clear lacquers, printing agents and printing inks, liquid adhesives, coating agents, sealants and the like. With the above definition, note the following:

1. In the context of coating, film or the like, the term "drying and / or curing" means that the coating is either free of "stickiness" and insoluble in solvent and has a high degree of integrity or adequate abrasion or pressure without damage can withstand. It will also be appreciated that in some cases a dry coating can have all of the above. If the term “coating” is used as a noun in the context of this invention, it is to be understood as a synonym for “film” (or the like).

2. The term “substrate” is to be understood in the broadest possible sense and includes any surface to which the agent can be adhered and on which it is held while the treatment with the drying agent takes place. So different materials such as cardboard, metal foil, steel plates, plastic material, heat-sensitive material, etc. can be used (depending on other circumstances).

3. The term coating medium includes in its meaning the colors etc. which were mentioned individually above.

4. The expression “drying and / or curing agent denotes the at least one chemical compound which effects the curing and / or drying of the coating agent. Alternatively, it may occasionally be referred to as a catalytic agent or simply a catalyst in this text.

In one form of the invention, the coating agent can be of the type containing free isocyanate groups. The term "free isocyanate groups" includes such potentially free groups, the meaning of which is that the prepolymer has isocyanate groups which can be released or are available for reaction with another compound which has active hydrogen sites (for the purpose of polymer spreading and / or film formation). The term compounds with free isocyanate groups is to be understood to include all of these compounds. Consequently, this includes not only isocyanates with a urethane structure and polyisocyanates, but also those with a poly-isocyanurate, biuret and allophanate structure.

The drying and / or curing agent (or catalytic agent) which can effect the vapor phase treatment can be ammonia or an amine or any other compound such as organometallic or inorganic

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Metal salts, which can accelerate the desired course of the reaction. The term »amine« includes not only those with a simple primary aliphatic monofunctional structure, but also amines that are characterized by (i) polyfunctionality and (ii) a higher degree of hydrogen substitution. The expression "vapor phase" indicates that the desiccant - i.e. ammonia, an amine etc. - is in the gas, vapor or other form carried in the air (e.g. dispersion, mist or aerosol) in which it is used Response is available.

The amine itself can be very different. Typical examples include Mono compounds such as methylamine, ethylamine, propylamine, isopropylamine and the numerous isomers of butylamine and polyfunctional amines such as hydrazine, ethylenediamine, propylenediamine and diethylenetriamine. Further examples are diethylamine, triethylamine and diethylethanolamine (DMEA) and di-tertiary amines such as N, N, N ', N'-tetramethylethylenediamine (TMEDA) and N, N, N', N'-2-pentamethyl-1,2-propanediamine ( PMT) - and in fact any combination of such amines that have been proportioned to the required extent, which makes it possible to take advantage of the synergistic effect of such a combination.

There are also numerous examples of organometallic compounds. Typical examples are dibutyltin dilaurate, lead tetraethyl, titanium acetyl acetonate, dimethyltin dichloride and tin and zinc octoates. The effective inorganic metal salts include Bismuth nitrate and ferric chloride. The synergistic effect of these compounds can also be used in interaction with one another and with the amines mentioned above.

The coating agent may be a one or two component paint, etc. containing free isocyanate groups (as defined above). A typical such paint - which can be applied electrostatically or otherwise to a substrate to be coated and quickly dried by a drying agent in the vapor phase, as will be explained further below - is a two-component preparation that consists of a first hydroxyl-bearing synthetic resin component and a second one an isocyanate-terminated prepolymer component. It is obvious that there are numerous exemplary embodiments for these components themselves.

Such a suitable color is a white two-component polyurethane preparation in which the pigment dispersion was carried out using a coconut alkyd-based resin, which is then mixed with an XDI-based prepolymer ending in an isocyanate (xylene diisocyanate). In alternative preparations, the XDI-based prepolymer ending in an isocyanate can be replaced by one or more prepolymers based on MDI, TDI, HDI, H, 2MDI, IPDI and H6XDI (the standard abbreviations were used) - or the reaction products thereof Diisocyanate monomers with corresponding polyols, polycarboxy or polyamine intermediates. The first component can also be selected as an alternative, e.g. made of acrylic, epoxy, polyether, polyester and polysiloxane resins (using the type designations).

Another example of a coating agent which can be applied to the substrate electrostatically or in another way and which can be quickly dried and / or cured according to the invention is a two-component agent, the first component consisting of a polyepoxide resin which contains hydroxyl groups , and the second component consists of a resin containing free polyamide groups.

The drying and / or curing agent or catalytic agent can be electrostatically deposited in such a way that the evaporated drying and / or curing agent is exposed to an generated electrostatic field. In one embodiment of the invention, the electrostatic field can be established in an orthodox manner, typically by an electrostatic gun of the type generally known for this purpose.

In one exemplary embodiment of the invention, the electrostatic deposition of the drying and / or curing agent (catalyst) can follow a previous step of applying the coating agent to the substrate. A code position, including the electrostatic code position - i.e. the simultaneous application of the coating and drying and; or curing agent due to the effect of an electrostatic field - is also within the scope of the invention. According to a further aspect of the method, the invention thus provides a process as defined above in the general sense, and which is also characterized in that the steps of applying the coating agent to the substrate and electrostatically depositing the drying and / or curing agent simultaneously be carried out. In a related aspect, the invention provides an apparatus for performing this method, as will be described.

In preparation for the definition of the device mentioned, reference is made to the manner in which the coating agent is applied to the substrate. Thus, the coating agent, typically a paint, can be applied by hand painting (using a brush), dipping or spraying, or by using a device in which the paint is applied electrostatically to the substrate. This electrostatic application of the paint can be done with an electrostatic spray gun.

The device for executing the code position of coating agent and drying and / or curing agent can (as mentioned above) operate using an electrostatic field. According to this aspect of the invention, the invention provides a device which consists of a combination of a device for directing the electrostatically charged coating agent, for example a paint, onto the substrate to be coated, and a device for simultaneously conducting an electrostatically charged drying and / or Hardening agent, typically in the vapor phase, on the substrate, the first-mentioned device and the second-mentioned device being arranged concentrically to one another. This device, which can also be used to direct only the drying and / or curing agent onto the substrate, is described in more detail below.

The drying and / or curing agent in the vapor phase can be produced in various ways, including evaporation or injection methods. The device according to which the drying and / or curing agent is effectively generated in the vapor phase forms a further aspect of the invention. From this point of view, the invention provides a device which consists of a combination of a device for evaporating a liquid drying and / or curing agent, a device for controllably supplying the evaporated drying and / or curing agent to a necessary location - for example to the device mentioned as the second the pre-defined 5

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direction - and there is a measuring device which is inserted into the feed path and ensures that the concentration of the evaporated drying and / or curing agent supplied is kept within defined limits. When the vaporized drying and / or curing agent is supplied to said second device, the steam generating components and the code position components combine and work as a single device.

The invention will now be described in order with reference to the accompanying drawings and some specific examples denoted by numerals. It goes without saying that the following description is intended to illustrate the features of the invention and is not intended to restrict it in any way. In the drawings:

Figure 1 is a perspective view of the device for creating (generating) the drying and / or curing agent in the vapor phase;

Figure 2 is a perspective view of the device for effecting the precipitation of the drying and / or curing agent or to code position of the coating agent and drying and / or curing agent.

The device of FIG. 1 (which is denoted overall by the number 1) consists of a box-like outer structure 2 which contains a container 3 for the liquid catalyst. The catalyst is atomized in an inner chamber 4, which is located under the container 3, by atomizing nozzles 5, which receive the catalyst from the container 3 by gravity. Air enters chamber 4 via an air inlet filter 7 in one side 8 of the construction. A turbulent air flow is generated in chamber 4 to facilitate mixing and atomization therein. This is achieved by a turbulence-generating fan 6 in the base of the chamber.

While the atomizing nozzles 5 are supplied with catalyst from the container 3, they receive compressed air via a hose 9, which serves to generate a fine atomizing mist at the nozzle 5.

In order to remove the catalyst in the vapor phase from the chamber 4, a turbulence blower 10 with adjustable speed is located in a side 11 of the construction opposite the side 8 containing the air filter 7, the operation of which is controlled by a mechanism 16. The blower 10 directs the vapor phase catalyst to a desired location via a flexible line 12 - in a special case to the code position device as defined above and described below with reference to FIG. 2. In a cover 13, which is arranged around the blower 10, there is a catalyst sensor 14. This sensor measures the concentration of the vapor-phase catalyst which passes through the line and generates a concentration reading which is returned to a scale 15 and displayed on it becomes.

By adjusting the atomization and evaporation of the liquid catalyst stored in the container 3, which can be controlled within defined limits via the scale 15, the concentration of the vapor phase catalyst which is supplied by the device can be controlled to the required extent. In addition, as already mentioned, the delivery speed of the catalyst is controlled by the operation of the controllable fan 10. In this way, specified concentrations of the catalyst can be precisely adhered to.

In the case of a molecular solution of the catalyst in the vapor phase in air, the concentrations naturally fluctuate between zero and the saturation concentration for the particular catalyst used at the corresponding temperature. This restriction does not apply to an aerosol mist.

As stated above, from the device of Figure 1 via the flexible conduit 12, vapor phase catalyst can be fed to the device shown in Figure 2 (generally designated by the number 20). This device can be used for the electrostatic deposition of only the catalyst or for the electrostatic codeposition of the catalyst and a coating agent - typically a paint.

The device 20 consists of a standard electrostatic gun 21 with a barrel 22 from which the electrostatic charge emerges. In the rear of the gun 21, a feed line 23 is introduced, which brings the paint into the barrel 22 of the gun, from which it is also released with an electrostatic charge. A power line 24 ensures the energy supply for the generation of the electrostatic charge in the gun 21. In this respect, it is a conventional gun, as is generally known in the art.

As stated above, the flexible line 12 can connect the device of FIG. 1 to the gun 21. The catalyst in the vapor phase is passed into the barrel of the electrostatic gun by the pressure difference generated by the blower 10 of FIG. 1. In the device of FIG. 2, a barrel jacket 25, which is arranged concentrically around the barrel 22, ensures that the catalyst in the vapor phase does not emerge from the gun 21 before the tip 26 of the barrel is reached. In this way, the catalyst is also charged by the electrostatic field generated at the tip of the barrel 22 and it is charged to a sufficient extent that the vaporized and now charged catalyst can deposit itself on a grounded substrate on which the Gun is aimed.

If the gun is used in an execution module for electrostatic deposition of only the drying and / or curing agent (which follows the previous painting of the substrate), this is achieved by actuating a trigger mechanism 27. In another embodiment, when code position is required, the gun 20, which is controlled by the actuation of the trigger mechanism 27, is simultaneously sprayed with paint via line 23, vapor-phase catalyst via line 12 (and electrostatic charge via line 24 ) fed. In this embodiment, when the trigger mechanism 27 is pressed, paint from the barrel 20 and catalyst from the barrel jacket 25 are electrostatically charged at the same time. The color flow as well as the flow and the concentration of the catalyst can be controlled in order to achieve a desired ratio in the codeposition of color and catalyst. It is of course easy to see that the components assigned to one another in this way, when the components of FIG. 1 deliver the drying agent in the vapor phase to the components of FIG. 2 via the flexible line 12, work as the only device.

The method by which the electrostatically charged catalyst is applied to prepainted products (on all surfaces thereof) or by which the code position of the electrostatically charged catalyst and the electrostatically charged paint (on all surfaces) is carried out leads to a substantial acceleration in the curing of the color film , which makes drying times of obviously commercial importance 4

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tion can be achieved. The manner in which the application or code position is carried out on all surfaces is clear from FIG. 2, which shows the diverging path of the drying and / or curing agent and the coating agent when the drying and / or curing agent and the coating agent leave the device.

The invention will now be described with reference to five numbered examples. Please note the following.

The paint used in these examples is a white two-component polyurethane preparation, as mentioned above.

As far as the electrostatic spray gun has a known structure, the electrostatic spray gun shows three basic types of construction, which for the sake of simplicity are referred to below as types I, II and III. Briefly, in the Type I gun, the paint (or other coating agent) is electrostatically applied by a rotating disc that atomizes the paint within an electrostatic field created at the tip of a filament that has been attached for this purpose (The paint loaded in this way is then applied to the substrate to be coated). The Type II gun creates an electrostatic field using a filament located at the end of a barrel through which the paint to be conducted by the electrostatic charge is passed (the paint is guided to and through the barrel by air assistance) ). The Type III pistol works essentially like Type II, the electrostatically charged color is the. However, barrel fed hydraulically.

Example 1 (sequential application):

A metal plate that is suitably grounded is painted on both surfaces as described above using a Type I electrostatic spray gun. Air containing about 2000 ppm vaporized dimethylethanolamine and generated in the apparatus of Figure 1 is directed at right angles to the painted plate and within two minutes the vapor phase catalyst is sprayed using a Type III electrostatic gun loaded, whereby the gun is supplied with no paint and only a charge is generated. The gun is positioned opposite the plate so that the charged field can cut the catalyst flow. The catalyst in the vapor phase and the electrostatic field emerge from the type III pistol continuously for about two minutes, after which the supply of the catalyst and the electrostatic charge are interrupted. After a further eight minutes of post-curing time in slightly turbulent air, it was found that the drying of the film on both sides of the plate was accelerated sufficiently to obtain a sufficiently dried film.

Example 2 (sequential application):

Vaporized dimethylethanolamine (hereinafter referred to as DMEA) from the device of FIG. 1 is fed through the flexible line 12 to the barrel casing 25 made of plastic around the barrel 22 of an electrostatic spray gun. This is the device of Figure 2, in which case a Type II electrostatic spray gun is used. Painted panels prepared in the same manner as in Example 1 are exposed to a stream of the vapor phase catalyst from the spray gun, as illustrated in Figure 2. The catalyst in the vapor phase is fed in at a concentration of approx. 2500 ppm for a period of approx. 60 s after painting. This catalyst flow is maintained for about two minutes, then switched off, and the plate is exposed to slightly turbulent air for about eight minutes. After this post-curing period, it was found that the drying of the ink film on both sides of the plate was accelerated considerably.

Example 3 (code position):

An application gun, as described in Example 2 and shown in FIG. 2, is set up and connected to the device in FIG. 1. Paint is then passed through the gun as described above, and at the same time the vapor phase catalyst (DMEA) is introduced in a concentration of approximately 4000 ppm DMEA as a molecular solution in air. Correspondingly earthed plates were painted by the simultaneous use of paint and catalyst. Under these conditions, the coated panels quickly reached a touch dry condition and overall commercial dryness.

Example 4:

This example corresponds to the case described in Example 3 above, i.e. the same process steps were repeated, but in this case the vapor phase catalyst was PMT (all other parameters remained unchanged). The degree of accelerated drying was even greater than that of DMEA, and commercial dryness was achieved even faster.

Example 5:

In this example, the vapor phase catalyst was lead tetraethyl. All other conditions were identical to those mentioned in Example 3. In this case, too, an equally pronounced acceleration of the curing of the paint was achieved.

Finally, it is repeated that the foregoing detailed description is only intended to illustrate the invention. While respecting the basic criteria, details that are not themselves critical can be changed in accordance with the needs of the situation.

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Claims (12)

663 363 PATENT CLAIMS 1. A process for producing a dry and / or cured coating on a substrate, characterized in that a coating agent and a drying and / or curing agent are used for this purpose and at least the drying and / or curing agent is brought onto the substrate by electrostatic deposition. 2. The method according to claim 1, characterized in that the application of the coating agent and the electrostatic precipitation of the drying and / or curing agent is carried out either sequentially or simultaneously. 3. The method according to claim 1 or 2, characterized in that the drying and / or curing agent carries out the drying and / or curing treatment in the vapor phase. 4. The method according to any one of claims 1 to 3, characterized in that the coating agent is a one- or two-component agent which contains free or potentially free isocyanate groups. 5. The method according to claim 3 or 4, characterized in that the drying and / or curing agent is selected from ammonia, an amine, an organometallic catalyst or from any combination thereof. 6. The method according to claim 5, characterized in that the drying and / or curing agent is an alkanolamine. 7. The method according to any one of claims 3 to 6, characterized in that the drying and / or curing agent is produced in the vapor phase by controlled atomization of a prepared liquid drying and / or curing agent. 8. The method according to claim 1, characterized in that the coating agent is applied to the substrate and the coating agent is subjected to a treatment with the drying and / or curing agent in the vapor phase, the drying and / or curing agent on the coating agent is electrostatically deposited and (i) the step of applying the coating agent to the substrate is carried out before the step of electrostatically depositing the drying and / or curing agent in the vapor phase, or (ii) the step of applying the coating agent to the substrate and the step of electrostatically depositing the drying and / or curing agent in the vapor phase are carried out simultaneously. 9. The method according to claim 8, characterized in that the coating agent is a one- or two-component agent which contains free or potentially free isocyanate groups. 10. The method according to claim 8 or 9, characterized in that the coating agent is applied to the substrate by electrostatic deposition. 11. The device for carrying out the method according to claim 1 or 8, characterized in that in combined form a device for guiding the electrostatically charged coating agent on the substrate to be coated and a device for simultaneously guiding an electrostatically charged drying and / or curing agent in the vapor phase are present on the substrate, the first and the second mentioned devices being arranged concentrically to one another. 12. The apparatus for carrying out the method according to claim 1 or 8, characterized in that, in combined form, a device for evaporating a liquid drying and / or hardening agent, a device for controllably supplying the evaporated drying and / or hardening agent and one in the Sensor device provided supply path, which guarantees that the concentration of the vaporized coating agent supplied is kept within predetermined limits.