ES2252357T3 - PAINT INSTALLATION FOR COATINGS WITH HIGH SOLID CONTENT. - Google Patents

Abstract

A paint installation for the use of paints with high solids content comprises a spray gun 1, at least one paint conduit 7 and one pressurized air conduit 6 leading to the spray gun 1, at least one heat exchanger 2, preheating the paint and the pressurized air. The heat exchanger is connected to a source of preheated air located outside the paint booth. The preheated air flows around the paint coils 24, 25 and said pressurized air coil 26. At least one temperature sensor controls the entry and/or exit temperature of paint and/or hot air. The output of the temperature sensor is sent to a PLC, which is regulating the supply of heat exchange medium. The invention is preferably applied in continuously operating closed automatic paint installations. <IMAGE>

Description

Paint installation for coatings with high solids content

The invention relates to equipment for painting, in particular to a spray painting equipment. The team to spray paint is located in a paint booth and is suitable for automatic operation, for example when using A painting robot Automatic operation requires that it be supply paint in sufficient quantity under process conditions controlled. The amount of paint fed to the nozzle of paint spray, paint temperature and pressure compressed air, are the parameters whose surveillance covers the maximum importance An increase in paint temperature usually reduces its viscosity and allows applying paints with higher solids content. Therefore, it is proposed to heat the paint and compressed air before the nozzle of spray.

In the prior art several have been proposed examples of paint equipment or spray equipment in that a preheating step of the paint is executed.

Document DE 4008466 describes a device for Paint from this class. The heating equipment (9) preheats the compressed air on its way to the spray nozzle of paint and compressed air preheats then the paint on the mouthpiece The heat transmission is limited because the time of contact between paint and air is very short. The painting is only preheated in the nozzle area where it mixes with the air hot, producing heat transmission by contact between air and paint spraying, according to theories of heat transfer by conduction.

Consequently, the paint cannot get hot enough to get a significant reduction in Amount of solvent used.

Document US3197168 describes a device liquid atomizer to dispense insecticides. The application of Heat reduces the viscosity of the liquid product. The decrease of viscosity reduces the forces required to atomize and break the liquid into smaller particles. The object of the invention is create an insecticide spray in the form of droplets or Very small particles in order to get a dense fog. In  this application, a temperature is not necessary precisely defined of the pulverized product since it is not necessary that the product adheres homogeneously on a solid surface; therefore, it is not necessary to use precise regulation of the temperature for this particular case.

Document US6183161 describes a device paint sprayer in which the paint is heated by the exhaust gases from an engine, so that the paint is missing in direct contact with the exhaust gases. Warming up paint reduces its viscosity and, therefore, the Amount of solvent added to the paint. The temperature of the paint is not controlled, making it difficult to get an application for high quality surfaces. With spray equipment described in document US6183161 it is impossible to work inside a paint booth.

In document GB707756 a heat exchanger that is not connected to the gun sprayer to keep the paint supply hose and the area before the nozzle, at a constant temperature. He intermittent manual operation of the spray gun requires a mechanism that ensures that the spray gun is feeds paint at constant temperature. Pressure difference resulting from the manual step of a spray operation to a inoperative position manipulating the spray gun, does operate a two position slide valve. In position which it adopts during the paint application operation, it you need a large amount of heating medium in the hose paint feed, while in the heat exchanger heat itself, only a quantity is needed Limited heat transmission. This situation is reversed when The spray gun stops working. The paint contained in The heat exchanger must be kept at a high temperature in order to avoid clogging, while in the hose just a small amount of heat to maintain the amount of paint contained in the feeding line -which is stationary- to operating temperature With this equipment it is possible overcome problems related to a batch supply of the paint, but its performance is limited to a fixed amount Of paint. For manual operation the fixed amount is desired because it allows the operator to apply the desired amount of paint according to the time it keeps the gun active.

In the case of automatic operation, which requires a continuous feed of paint, this valve switching is not necessary. Yes in automatic operation the amount of paint has to be altered, a valve is needed paint flow control and temperature control heating medium act simultaneously, since not only 2 cases can be presented, but a whole margin must be covered of supply quantities.

Document GB700595 represents the status of the technique and provides a possibility to heat paint for a continuous and intermittent operation. The painting goes through a coil in a bowl full of hot water. Parallel to paint coil, in the water bath are arranged a compressed air coil and a water vapor coil. The water can be heated by the water vapor that circulates through the coil or by an electric resistance heater. Due to the considerable amount of water contained in the container, the Water heating takes a long time. Due to the presence of the coils in the containers, no means are provided for stir the water in order to achieve a uniform distribution of temperature.

Document FR1252974 provides a solution alternative for preheating paints for a gun sprayer The paint is preheated by compressed air Coming from a compressor. Compressor hot air passes through coils around the paint before being introduced into the spray nozzle A similar concept is proposed in the document GB161738, in which the details are shown construction of a preheating system of this class. He Preheating of the paint is achieved, in the case of the document FR1252974, only in the area of the nozzle and, in the case of GB 161738, also in the paint tank connected to the spray gun. Neither document provides a control of the temperature of the air circulating in the area of the nozzle and / or around the paint reservoir. Consequently, the application of the paint on a large surface may not result uniform due to uncontrollable temperature variations.

There is a need for an application system of paint that provides controllable preheating of the paint, which can be used in a continuous process, giving as result a constant and repeatable surface quality.

In order to overcome the inconveniences of the prior art, this invention relates to equipment for application of paints, in particular for paints containing solvents It also applies to mixtures of various compounds different that constitute a mixture to paint. The painting or the Paint mixture is heated in order to reduce viscosity of the paint, which allows the use of higher viscosity paints. Consequently, the number of paint layers can be reduced - it is say, the number of repeated paint application passes.

An additional advantage of the application of paints that contain a higher percentage of solids is the reduction of solvent content. This not only relieves environmental problems associated with solvent evaporation, it also eventually reduces material costs for The painting itself.

Another advantage, compared to the technique above, it consists in the possibility of maintaining the temperature of the heating or cooling medium at a value similar to that of The temperature of the paint. A temperature difference of only 5 ° C between the paint and the heating or cooling medium can be achieved using air or other gas as a means of heating or cooling. Compared to a heat exchanger for liquids, such as a system of oil / paint heat exchange, the response to changes in temperature is much faster due to the minimum differences of temperature. The heater and pump required for a system heat exchange based on liquids, such as oil, not only increases the cost of the equipment but, also, can create problems in an environment subject to explosion risks. If the pump and heater must be installed outside the cab painting, which means covering a certain distance, any Paint temperature change can be signaled immediately to the control system, but the time needed to change the oil temperature and the time it takes to pump the oil to the heat exchanger, increase the time of response.

In order to reduce the response time, the Heat exchanger uses as medium air or other gas, substantially at the same temperature as the paint. In addition, the air flow controlled by a fan installed outside the cabin is subjected to much less inertia than the flow of liquid. Except for the fan motor and the compressor, in the Paint booth is not present any electrical equipment, which Completely eliminates the risks of explosion. Preferably, the compressors, fans and their motors, are installed, of all modes, outside the paint booth or at least in an enclosure separated from the paint booth.

Another advantage of the invention lies in the possibility of painting large surfaces with a constant and repeatable quality. Due to the precise control of the temperature, a constant thickness of the paint layer by a procedure Fully automated paint application. In said paint application process, this can be applied in a Paint booth using one or more robots. These conditions precise temperature and flow of paint, as well as air compressed, can only be achieved and maintained throughout large series of parts, through an automatic process.

All the cited solutions of the technique previous deal with the manual application or by batches of paint, so the problems related to continuous operation do not they are presented in the case of small series or have been sidelined by using elaborate valve equipment and of switches.

Consequently, the solutions of the technique above are not considered suitable for a painting operation continues, especially in the case of large surface parts, such as car exteriors.

In order to paint large surfaces with a constant and repeatable quality, the process of applying the Paint has to be fully automatic. The quality of the painted surface is determined by the thickness of the layer of paint, as well as the constant conditions of the operation when a batch of paint application is carried out. By therefore, the paint is advantageously applied in a booth of painting by one or more robots. Consequently, they can obtain precise temperature and flow conditions of the paint and compressed air. Since all the solutions of the prior art deal with the manual or batch application of the painting, it is difficult to meet quality requirements imposed on automotive painted surfaces, domestic applications or, even more, in work done on time Free or in the field of design items. The procedure of automatic application of the paint usually leads to Continuous application processes of painting. Can arise problems during the change of paint batch or composition of is. Critical situations may occur during commissioning. running and stopping the process, which requires careful batch size planning and geometry of pieces.

The painting process includes the following steps: load the conveyor means, for example, the skates; clean, usually with water-based cleaning agents; rinse with water and dry; increase the surface tension of the piece of thermoplastic by oxidation or fluorination to replace C-H by C-O or C-F by applying a flame; application of a corona discharge; treatment with plasma or fluorine gas as a subsequent step to the application of a primer, possibly together with an agent to favor adhesion (for example, for PP substrates); the application of the basic paint composition; heating by IR (infrared); application of the transparent coating; IR heating; Drying and final cooling.

During this process, the paint is applied, usually, at temperatures that differ substantially from those existing in ambient conditions. Heat exchanger provided for that purpose is arranged externally with respect to the paint spraying head and preferably outside the paint booth, to avoid the risk of explosion. The Heat exchanger dimensions are calculated depending on the amount of paint and determine the size and surface of heat exchange Heat transmission by conduction and / or by convection it can be achieved by air or water or with another heat transmitting fluid.

In a preferred embodiment, the earners of Temperature are connected to a PLC. The PLC compares the values of temperature with the previously programmed value for paint composition in use. Consequently, the PLC sends a signal to resistance heaters. Heaters by resistance generate heat by transforming electrical energy into heat, for example, by heating a coil or metal strip, so that the Electric power supply can become a series of current impulses The frequency of these impulses can change, which results in a variation of the heating capacity The PLC signal makes it possible, by so much, the change in frequency that, eventually, has as result the temperature change of the hot air entering The heat exchanger. Alternatively, the PLC can issue a signal to act on the flow of the exchange fluid thermal. The heat exchange fluid flow rate may be determined by a fan, driven by an electric motor with variable turning speed. Alternatively, the speed of turn can also be determined by pulsating signals (by example, in case of a stepper motor). The signal issued from the PLC results in a frequency change of engine speed and therefore a change in air flow. Changing the air supply flow rate changes the residence of the air in the heat exchanger. Air flow increased results in heat transfer improved

With 2K paints (two components), the components can be heated separately in it heat exchanger and can be mixed immediately before point of application For each of the components of the paint, a separate coil can be used, being arranged the coils in parallel, either because they are joined or because one or more coils are arranged to form another coil, so that the diameter of the coils for painting is smaller, or larger, than the diameter of the compressed air coil, depending on the total necessary length of the surface of heat exchange, which is equal to the surface of the coils

The invention is suitable for mounting on a robot Of paint. In the case of mixing more than one component, the Mixer can also be located on the robot arm.

If the equipment is designed for manual application, the heat exchanger may be connected to the means of spraying (spray nozzle) through flexible ducts such as thermally insulated hoses. In this case, the heat exchanger may also be located outside the paint booth, allowing better accessibility in case maintenance or if you have to change the color or paint composition

Heating the paint allows painting With high solids content. Consequently, the solvent content For this invention, paintings with a solids content of preferably between 60% and 70% is apply on parts in one or more process steps in the art Previously, the high viscosity of the paints required the use of high spray pressures, which caused difficulties when it comes to obtaining homogeneously painted surfaces. The resulting brightness parameters in the case of large paints viscosity did not reach a satisfactory level in the art previous when the application of the painting was done by spraying, especially in relation to large paint surfaces, such as auto parts. Another advantage is the reduction of the number of layers of paint in each painted part, being able to reduce, in many cases, the number of layers of paint applied to only a single coat of paint.

Working at high temperatures makes the Paint equipment is easier to clean, as it can be avoided paint is clogged due to reduced viscosity at High temperature. The temperature is constantly maintained at a value close to the operating temperature, so that the change to another product or composition of paint takes out at working temperature.

Due to the lower solvent content, it could an increase in brightness and a better coverage of the surface, as well as a reduction in the effect of "skin of orange ". Due to the reduced solvent content in comparison with the usual installations for painting, the quantity of solvent molecules that have to pass the paint layer before evaporation, it decreases, so it can be maintained at minimum disturbance of the paint surface, with the result that you get a more homogeneous surface that has, as a consequence, an improvement in brightness and appearance. Other advantages obtained thanks to the invention are a reduction of volatile compound emissions due to reduced solvent content and therefore overall compatibility Improved procedure with environmental and sanitary regulations. He procedure can be used with usual paint equipment and It can be applied for products with coatings based on solvent or water. The conditions of application, such as seasonal temperature changes, less affect the quality of the paint since the temperature can be controlled with much higher precision.

Fig. 1 is a schematic graph of the equipment of painting.

Fig. 2 illustrates the exchange equipment of hot.

Fig. 3 shows a detail of a coil of the heat exchanger.

Figs. 4a-4c represent the arrangement of coils in the heat exchanger.

Fig. 5 shows the spray equipment of painting mounted on a robot.

Fig. 6 illustrates the position of the perceivers of temperature in the heat exchanger equipment.

Fig. 1 shows the equipment for painting in a way schematic The equipment for painting consists of a gun 1, a heat exchanger 2, a hot air generator 3 and a 4 air compressor. The air compressor 4 and the generator 3 hot air are located outside the paint booth 5. The hot air is circulated through the exchanger of heat located inside the paint booth. The exchanger of heat houses tubes 6 for compressed air and conduit 7 of paint feed Driving paint feed transports paint from container 8 for paint. Driving paint feed enters the heat exchanger in point 9 and leave it by point 10.

The paint is stored in containers located outside the paint booth, in order to allow them to be filled and replace the heats without problems. The transport of the Paint is done by gravity or by pumping. In Fig. 1, schematically shows a pump 18 for driving paint 9 paint feed.

Fig. 2 shows the heat exchanger 2 with the hot air generator 3, in greater detail. He heat exchanger consists of a vessel 11, preferably a cylindrical vessel. The hot air supply tube 14 is welded or flanged to the vessel at one end of vessel 11, the hot air discharge tube 15 is welded or flanged to the vessel at the opposite end of vessel 11, in order to provide a counter current flow. Parallel to the hot air feed, 16 air feed compressed enters the heat exchanger in the area of the prechamber 13 and exits the heat exchanger in the area of the prechamber 12. Compressed air and paint circulate through ducts separated.

The ducts can have one or more coils, as shown in Fig. 3, so that the paint gets hot while circulating through the heat exchanger tubes. In In parallel, the compressed air for the spray nozzle is preheated in a separate coil. Depending on the temperature necessary to treat the paint, it can be enough with a straight tube, but if temperatures of up to 60 ° C are needed to reduce the viscosity of paints with high solids content, the heat exchanger would simply adopt a dimension longitudinal difficult and expensive to obtain, if not provided The coils

As the paint and compressed air pass through the heat exchanger continuously, it is necessary  get an exact temperature control. Therefore, in both prechambers 12 and 13 there are integrated temperature sensors in the path of passage of the paint and, preferably also, in the path of compressed air. Temperature values measured are sent to a control unit 19, such as a PLC. He PLC determines the air requirements to achieve the effect of desired heating and activates a variable flow limiter, such as a throttle valve 20, or change the speed of rotation of the fan motor 21. Alternatively, you can regulate the heater power 22 by electrical resistance. May be considered a combination of the control alternatives with the in order to respond to different demands on the speed of response to signals, depending on the variation of the temperature difference to regulate.

Fig. 3 shows a possible arrangement of the coils 23. The coils 23 are preferably made of stainless steel and, for the application of the paint, it must be ensured that the surface roughness of the inner face in contact with the paint , be low enough to prevent paint particles from clogging
ra.

Figs. 4a, b, c show a variety of coil arrangements. Depending on the amount of paint,  a whole range of different provisions of coils in the heat exchanger. The different heat exchangers can also be part of a team modular. For a different amount of paint or for a type of different paint, the spray gun is joined by a different heat exchanger. If the external dimensions of the Heat exchanger are fixed due to mounting limitations, the heat exchange surface can be modified by vary the length of the coils.

Fig. 4a shows an example in which the 24 coil for paint fills the interior space of the coil 26 for compressed air throughout the heat exchanger. The coil 24 for paint and the coil 26 for compressed air They are mounted in a mutually concentric way.

Fig. 4b illustrates an example in which the paint coil does not take up all the space inside of the heat exchanger. In this case, the heat transmission necessary to heat the paint is less than the transmission of heat required to heat compressed air. One possible application for this embodiment is the case of applying small amounts of paint or using paints with a high heat transfer coefficient.

Fig. 4c shows a heat exchanger with Multiple coils for painting. The two illustrated coils In this embodiment they only serve as an example. it's possible arrange more than two coils concentrically or use only a fraction of the space available for small coils.

Fig. 5 shows the equipment mounted on a robot Of paint. Heat exchanger 2 is mounted near the 1 paint spray gun. Hot air feed it is done by insulated tubes, not shown in the drawing, fixed, for example, to the robot arm or that are part of he.

If multiple are used simultaneously paint components, a mixer device 27 of the paint between heat exchanger and gun sprayer

Different types of heat exchangers, such as those illustrated in Figs. 4a, b, c. This allows to quickly change paint composition and makes it possible to clean the heat exchanger when it is not use, without interrupting production.

Fig. 6 shows the position of the perceivers of temperature in the heat exchanger 2. The sensors of temperature are located in the two chambers 12, 13 in the tube 9 paint feed, paint discharge tube 10, the air supply 16 and air discharge 17.

Temperature sensors 28 and 30 located at the paint and compressed air inlets they provide, respectively, information about the temperature at the entrance. The signal sent to PLC 19 is evaluated by a program and determines the quantity and temperature of the hot air to be fed. The value final amounts of paint and hot air is stored in the program. They can be programmed by a user or they can come from a process controller (not shown) that has stored all the parameters related to the application of Any type of paint. Temperature sensors 29 and 31 measure paint and air discharge temperatures compressed and feed the values to the PLC. PLC program controls the calculated temperature with reference to the temperatures measures and emits a visible or audible alarm if exceeded the tolerances established.

In a preferred example, the part to be painted, such like the outside or inside of a car, it It is coated with a transparent coating. Alternatively, you can apply a 2K coating. These paintings with "elevated solids content ", have low molecular weight and Narrow distribution of the same classic polyol resins. This leads to a solution with lower viscosity and, consequently, It allows to increase the solids content.

Normally, paints with high content of solids do not dry physically, the solvents evaporate slowly and the thickness of the dry film increases. In order to prevent these phenomena, the paint heats up to about 60ºC, resulting in a notable reduction in viscosity.

In a preferred example, the invention has been applied to usual paints or paints with high content of solids and, in particular, for the following compositions of painting.

Painting usual Hot paint that Painting hot contains the same covering transparent Parts by weight overlay transparent 100 100 100 Solids content of covering 44 44 65 transparent (% in weigh) Hardener content (parts in weight) 40 40 fifty

(Continuation)

Painting usual Hot paint that Painting hot contains the same covering transparent Content of hardener solids (% in weight) 68 68 75 Parts by weight of solvent twenty 0 0 Solids content of the mixture (% in weight) 44.4 50.8 68.3 Solvent content of the mixture (% in weight) 55.6 49.2 31.7 Solvent reduction (%) 11.5 43

The mixture called "usual paint" It consists of 100% transparent coating, 40% hardener and  20% solvent The solids content of the coating transparent is 40%, the solids content of the hardener is 68% and the solids content of the solvent is 0%.

The overall solids content can be calculated, Then, as follows:

Solids content of the mixture = (transparent coating \ times solids content of transparent coating + hardener \ times content of hardener solids + solvent \ times solids content of solvent) / (transparent coating + hardener + solvent)

The overall solvent content is calculated, then, as follows:

Solvent content of the mixture = (transparent coating x solvent content of the transparent coating + hardener \ times content of hardener solvent + solvent times content of solvent solvent) / (transparent coating + hardener + solvent)

The solids content of the coating transparent is usually in the range of 40 to 50%, while the solids content of the composition, as used in the invention, may preferably be in the margin from 60 to 70%.

Application parameters

Parameter value units method Density 20ºC 1.2-1.03 g / cm3 I04 Viscosity Ford cup 4 a 60ºC 20-24 s A02 Solids content (% in weight) 60.0-68 % 01.0 Solids content (% volumetric) 55% -60% % Q04 Lifetime of the mixture < 3 hours L04

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Dry coating characteristics

Parameter value tolerance units method Brightness twenty > 85 % D07 Coating thickness dry 35 \ pm5 \ mum E01

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List of parts

one

Spray gun

2

Heat exchanger

3

air generator

4

compressor

5

cabin Of paint

6

pipes compressed air

7

driving power painting

8

container with paint

9

point of paint input in HX

10

point HX paint output

eleven

cylindrical vessel

12

prechamber - paint output

13

prechamber - paint entrance

14

hot air supply

fifteen

hot air discharge

16

air supply compressed

17

compressed air discharge

18

bomb for paint

19

control unit (PLC)

twenty

limiter (choke) variable

twenty-one

fan

22

resistance heater electric

2. 3

coils

24

paint coil (component one)

25

paint coil (component 2)

26

compressed air coil

27

mixer device painting

28

temperature sensing point painting entrance

29

temperature sensing point paint output

30

temperature sensor compressed air supply

31

discharge temperature sensor compressed air

Claims (19)

1. A device for applying paint on a surface, comprising a spray gun (1), at least one duct (7) for paint and a duct (16) for compressed air leading to the spray gun (1), to the minus a heat exchanger (2) for changing the temperature of the paint and compressed air inside a paint booth comprising ducts (14) connecting the heat exchanger (2) with a source of exchange medium (3) thermal, whereby the heat exchange medium circulates around the heat exchange surfaces containing said paint and said compressed air, characterized in that said compressed air and said paint are fed in predetermined amounts that are regulated according to the output of At least one temperature sensor (28-31) disposed in the heat exchange area, whereby the heat exchanger (2) is located within the area of the paint booth. 2. The device of claim 1, characterized in that the temperature sensor (28-31) is located in a pre-chamber (12, 13). 3. The device according to claim 1, characterized in that the sensors (28-31) are connected to a PLC (19). 4. The device according to claim 3, characterized in that, based on the input of the temperature sensor (s) (28-31), the PLC (19) regulates the heat exchange medium supply. 5. The device according to claim 4, characterized in that the supply of thermal exchange medium is regulated by the variation of the current supply of the heaters (22) by electrical resistance
AC. The device according to claim 4, characterized in that the supply of heat exchange medium is regulated by the variation in the rotation speed of the fan motor (21). 7. The device according to claim 1 or claim 3, characterized in that the paint feed is regulated by the PLC (19). The device according to claim 1, characterized in that the heat exchanger (2) consists of multiple separate coils (23-26), said coils containing the paint (s) and the compressed air. 9. The device according to claim 1, characterized in that the heat exchanger (2) is mounted on a robot. The device according to claim 9, characterized in that the heat exchanger (2) is fixed in the robot so that it can be removed from it. 11. The device according to claim 1, characterized in that the heat exchange fluid is air. 12. The device according to claim 1, characterized in that the heat exchange fluid is water. 13. The device according to claim 1, characterized in that the paint has a solids content of not less than 40%. 14. The device according to claim 13, characterized in that the solids content can reach up to 70%. 15. The device according to claim 14, characterized in that the solids content is preferably in the range of between 60 and 70%. 16. The device according to claim 1, characterized in that the solvent content is not more than 20%. 17. The device according to claim 16, characterized in that the solvent content can be reduced to 0%. 18. The device according to claim 1, comprising a spray gun, a paint feed, a compressed air feed, a heat exchanger and a heat exchange fluid feed, characterized in that the heat exchanger is arranged between The paint feed and spray gun and heats the paint and compressed air simultaneously.

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19. Method for painting a piece of plastic, which It includes the operations of: feeding a painting or several components of a paint, from storage containers (8) to a heat exchanger (2), supply compressed air from a source (4) of compressed air to said heat exchanger (2), change the temperature of the paint and compressed air, to at the same time, in said heat exchanger (2), adjust the feed and / or temperature of the heat exchange medium to provide paint and compressed air at a temperature defined to the spray gun (1) or to an additional mixer located between the heat exchanger (2) and the gun sprayer (1), so the heat exchanger (2) is located within the area of the paint booth.