JPH03137956A - Method and device for coating liquid film product - Google Patents

Abstract

PURPOSE: To obtain a good coating film even if the change of weather conditions is fast by changing the ratio of at least one diluents according to at least one parameters among the weather conditions near the object under coating. CONSTITUTION: While the coating film raw materials from coating film raw material distribution circuits 22a to 22c are measured with a flow meter 27 by a pump 25, the materials are forcibly fed. The diluents (for example, xylene and toluene) are supplied from mixing means 34a, 34b and are mixed and diluted with a manifold 35. The diluted mixture is sprayed toward the coating object 14 from an electrostatic sprayer 12. A computer 30 regulates pressure regulators 37a, 37b and changes the addition ratio of at least one kind of the diluents in accordance with the environmental conditions in a booth 11 detected by a temp. sensor 40 and a relative humidity sensor 41 and the viscosity of the coating film detected by a viscosity measuring instrument 43 with temp. compensation, thereby changing the addition ratio of at least one diluents.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of applying a liquid coating product, usually a paint or a varnish, to an object to be painted. This invention relates to an improvement for better controlling the drying state of a coating product when applied. Moreover, the present invention
It also relates to an apparatus for carrying out the method.

BACKGROUND OF THE INVENTION It is known that the quality and appearance of the coating of a coating product applied to an object, such as an automobile body, depends inter alia on the drying state of the applied coating product. "Dry state"
means the viscosity of the droplets of the applied coating product as they pass through the air and reach the object to be applied. If the fluidity of the droplets is too high, the coating product will run off the surface of the object before the desired coating thickness is achieved and/or, in the case of metallic coatings, it will cause coating unevenness (marbling). ) may occur.

If the viscosity of the droplets is too high, the droplets will not stick to each other well,
The occipital membrane exhibits the so-called "orange peel" phenomenon, or
Otherwise, the result will be a dull finish. The parameters that affect the drying state mentioned above include the following.

Temperature of the object - Temperature of the droplets of the coating product after passing through the air - Dilution of the coating product before coating - Relative vapor partial pressure in the air near the coating - Formation of the coating film The present invention is based on the observations and analyzes described below.

The temperature of the object is usually determined to a large extent by the treatment to which the coating product is applied before it is applied. If the object has a large mass, a high heat source is required to control its temperature. This is especially the case for car bodies.

On the other hand, when the droplets of the coating film product reach the object to be painted, the temperature of the droplets depends exclusively on the ambient temperature near the object (specifically, the temperature inside the coating booth through which the object passes). temperature). The heat capacity of the droplet is too small relative to its initial temperature, ie the temperature of the coating product before it is applied, to play an equally decisive role. moreover,
The atomization and/or the air jet forming the atomization introduces too much air relative to its own temperature;
Even in rotating bowl atomizers it is not possible to have an equally significant effect. Very high heating capacities are required to control the ambient temperature.

This is because the paint booth must be continuously ventilated, even though some of such heat may be reused in some instances. It has previously been proposed to vary the dilution of the coating product in order to control the viscosity of the droplets as they reach the object.

However, in known devices, this modification takes place over a relatively long period of time, at least one day, or even more, depending on the prediction of weather conditions. If these predicted conditions do not materialize, or if weather conditions change quickly, the coating product is no longer compatible with the conditions, resulting in worsening application conditions. It turns out.

The present invention proposes an improvement that allows more effective control of at least the dilution and/or volatility of coating products.

(Means for Solving the Problems and Their Effects) In terms of aspects, the present invention provides a method for applying a liquid coating product to an object to be coated by adding at least one diluent to a coating product raw material. The mixing ratio of the at least one diluent described above is changed depending on at least one weather condition parameter in the vicinity of the object being coated.

In practice, these so-called weather conditions prevail in at least one coating booth through which the objects to be coated pass. Relevant parameters are, for example, temperature and/or relative humidity. The expression "coating product raw material" is used because the coating product has an excessively high viscosity compared to what is desirable to be applied under optimal conditions. , irrespective of the ambient temperature and relative humidity at the painting site, as the -layer needs to be diluted. Addition of one type of diluent can reduce the viscosity of the coating product to a suitable value. This solution provides good results if the changes in atmospheric conditions are small enough and the range of changes in ζ dilution is not excessive.

If the application conditions also remain unchanged, reducing the viscosity will result in a finer spray. For example, it has been observed that as the degree of dilution increases (the viscosity decreases and therefore a finer spray is obtained), while traveling through the air, Evaporation of the diluent is accelerated, and adjusting the viscosity of the liquid layer when it reaches the object may not be as important as expected.

According to another important feature of the invention, the volatility of the coating product is determined by adding at least two diluents of different viscosities to the coating product raw material described above under the conditions described above. The relative proportions of the diluent may be varied immediately prior to application by adjusting the relative proportions of the diluent in response to at least one weather condition parameter.

The two diluents may be added, for example, in different proportions ranging from 0 to 100% each. Preferably, these diluents are chosen such that their diluting capacities, themselves and their mixtures, do not differ significantly. The viscosity of the final coating product obtained by adding these diluents is then relatively independent of the mixing ratio.

In a variation of this method, the mixing ratio and the total flow rate of added diluent can be varied simultaneously.

In yet another variant, the relative proportions of the diluents are adjusted depending on the temperature of the object to be painted.

By way of example, similar diluents such as xylene and toluene, methylisoamyl ketone and methylisobutyl ketone, or butyl alcohol and isopropyl alcohol may be mixed. These "sets" of diluents have sufficiently different volatilities that it is not necessary to change the proportions of said diluents so as to significantly affect the viscosity of the final coating product before application. It is possible to change the volatility of the entire mixture without changing it. If necessary, diluents selected from different families, in order to widen the volatility range of the mixture,
They need to be in harmony, but
may be mixed in the same way.

In the case of electrostatic coating, the components of the various mixtures are selected in such a way that they do not impair, and in particular do not reduce, the durability of the final product.

The basic principle of the present invention described above can be
It may be employed at various locations in the coating equipment.

For example, if the installation has only one paint booth or a small number of paint booths, all of which have approximately the same temperature and relative humidity,
The diluent may be added at the outlet from one storage tank storing the coating product feedstock described above. The temperature sensor and the relative humidity sensor may be installed at positions where signals representative of the ambient temperature and relative humidity inside the booth can be obtained. for example,
They may be located in one booth or in one of several booths.
It can be installed in several places. These sensors can be integrated into a control system that controls the flow rate of each of the 2Fli class diluents and the flow rate of the coating product feedstock.

Viewed from another aspect, the invention features an apparatus for applying a liquid coating product to an object to be painted, comprising at least one atomizer for said coating product; and said at least one atomizer. mixing means connected to the substrate, said mixing means comprising means for supplying at least one coating product feedstock, means for regulating and supplying at least one diluent, is connected to at least one sensor for detecting one parameter of atmospheric conditions in the vicinity of the air conditioner. Preferably, the adjusting means includes means for adjusting the flow rates of each of the at least two types of diluents supplied to the mixing means.

In practice, at least one temperature sensor and/or at least one relative humidity sensor and/or at least one object temperature sensor will be used.

For more complex installations with multiple booths located generally at different temperatures and/or relative humidity (different distances from the drying oven, closer to the north or south wall of the building, etc.), A growing number of systems can be equipped with specific temperature and relative humidity sensors. In one example of such a system, each booth is provided with an individual control system, each booth is supplied with at least IFf1 coating product feedstock from a common storage tank, and each booth is supplied with at least IFf1 coating product feedstock as previously described. At least one diluent having the following characteristics is provided. In the case of installations in which the coating product is changed rapidly, a suitable number of stores may be provided by closed-loop circuits supplying the various booths and associated coating product exchange units in a manner known per se. Just connect the tank.

The invention will be better understood, and other advantages thereof will become clearer, from the following description, given by way of example only, with reference to the accompanying drawings, in which: FIG.

(Example) In carrying out the present invention in its complete form, the following observations are fundamental. For some coating products, the volatility of the diluent contained in the coating product to be applied must be reduced in proportion to the temperature of the coating site;
It must be increased proportionately to its relative humidity. As shown in the graph of FIG. 1, this is represented by a nearly linear relationship. In this graph, T is temperature and H is F
1 indicates humidity, and ■ indicates volatility. At point A, which represents warm, dry conditions (eg, near the oven), the volatility vA is low. At point B, which represents a hot, humid condition of 1 (eg, a summer storm), or 0, which represents a cold, dry condition (eg, winter), volatility is moderate. Point D represents a state of low temperature and high humidity (for example,
In spring), volatile VD is high.

For other coating products, on the other hand, volatility must be reduced in proportion to relative humidity, as shown in the graph of FIG. This difference in properties is, to some extent,
This may be due to the hydrophilic nature of the coating product.

Since the partial pressure of water vapor and diluent and the evaporation rate are largely independent, the effect of humidity can be explained by the following fact. That is, the heat of vaporization of the diluent (approximately 150 ca
l/g), the temperature of the liquid layer of the coating product is lowered. For example, radius 15 microns, specific heat approximately 0.6
For a cal/g/deg droplet, there is a drop of approximately 20° and 10% of its mass is lost. This droplet surface and immediate temperature drop around the droplet causes some water vapor to condense.

At 25° C. and 80% relative humidity, ie for a water vapor partial pressure of 25 mb, a temperature drop of 20″ reduces the saturated vapor pressure to about 9 mb, which is much lower than its partial pressure. The resulting supersaturation will result in rapid condensation of water vapor. Only 10% of the heat absorbed by diluent evaporation will contribute to the condensation of water vapor; the remaining heat will be absorbed by radiation, conduction, convection, etc. Even assuming that the temperature of the ambient air is reduced by Since the ratio of the mass of the coating product to the mass of the total ambient air (total ambient air) is of the order of 10%, the resulting mass of condensate corresponds to 0.025% of the mass of flowing air, and the condensate Low compared to possible steam.It has a partial pressure of 25 m
This is because b corresponds to the mass of water vapor that is 1.5% of the mass of air, whereas the mass of water vapor at saturated vapor pressure is only 0.5% of the mass of the same air.

Thermal agitation of the water vapor molecules is more than sufficient to condense this small amount of water available as the coating product travels between the atomizer and the object being painted.
In the case of electrostatic painting, condensation is promoted by ions in the atmosphere, the charge released by the droplets, and the presence of an electric field.
It has been shown that along with the coating product droplets, they can even generate slightly charged water droplets around these ions that are deposited on the object.

For example, if the coating product is hydrophobic because the diluent or solvent is hydrocarbon-based, water will be repelled at the surface because of its high surface tension. Also, the surface still prevents the evaporation of the diluent (
Most coating products contain at least 50% diluent. ), the coating product flows due to its high fluidity, or the diluent is trapped, resulting in a large number of pores or blowholes when it evaporates. This occurs after the diluent has evaporated if its volatility is relatively low. In this case, the use of volatile diluents would inevitably lower the temperature of the coating product droplets, causing such a phenomenon.

If the coating product is hydrophilic, for example because it contains a polar diluent or solvent, such as an alcohol,
The use of volatile diluents would be free of such risks and therefore would be feasible.

Therefore, in a humid atmosphere, polar diluents may be preferred and beneficial in adjusting the viscosity of the coating product, provided they do not contain significant amounts of water.

As shown in the above discussion, in implementing the method according to the invention it may be advantageous to select a diluent that is more or less polar, depending on the surrounding relative humidity.

The apparatus shown in FIG. 3 is an example in which each booth is provided with dilution means. By way of example, at least one electrostatic sprayer 12 spraying a coating product (paint and/or varnish)
A single booth 11 is shown. conveyor 1
3 passes through the booth and transports the object 14 to be painted. In this example, the object is the body of a car. In addition, booth 11 is equipped with a conventional coating product exchange unit 16 having a set of selectively operable valves connected to manifolds. The valves 17a, 17bs17c are
Connected to a circuit distributing different coating product feedstocks. A selectively operable valve 18 is connected to a cleaning agent distribution circuit 19. A selectively operable valve 20 is connected to a compressed air distribution circuit 21 . The coating product feedstock distribution circuits 22 a % 22 b 122 c are connected to respective storage tanks 23 a s 23 b arranged together in a part of the plant that may be located remotely from the coating booth.
It is a normal closed loop circuit fed from s 23 c. Storage tanks and distribution circuits are connected to the coating product exchange units in all booths. The outlets of the previously described selectively operable valves are all connected to a first manifold 24, and the manifold outlets are connected to a positive displacement gear pump 25 driven by a motor 26. The outlet of the pump is connected to a flow meter 27, which has a similar structure to a gear pump. All the devices mentioned so far are known per se and constitute means for feeding the atomizer or atomizers 12 with coating product raw material. The valves 17, 18, 20 are controlled by a computer 30 which manages the entire operating sequence of the device. This computer receives signals sent from the flow meter 27,
- For example, data is input, such as a signal generated by one or more sensors 32 in conjunction with the conveyor 13, indicating the position of objects in the booth.

According to the invention, a mixing device is provided on the inlet side of the atomizer 12 which is connected to the outlet of the coating product raw material supply means and to the means 34 for supplying at least two diluents of different volatility. It is completed by means 33. More precisely, the mixing means comprises a second manifold 35 connected to the outlet of the flow meter 27 and a static mixer 35a connected to the outlet of this manifold 35. The supply means 34 have two similar branches 3 each receiving a pressurized diluent.
4a and 34b. Each branch is equipped in series with a selectively operable pressure regulator 37a or 37b, a venturi flow meter 38a or 38b, and a selectively operable valve 36a or 36b, respectively. The outlet of each valve is connected to a second manifold 35. The equipment provided in these branches, together with the computer 30,
A flow rate WJ adjustment means for two types of diluents is formed. The valves and pressure regulators mentioned above are controlled by computer 30. The data received by computer 30 includes flow meter 38
The signals generated by a or 38b are included. The flow rates of the two diluents are controlled by controlling pressure regulators in each branch to provide the necessary flow adjustment. The flow rate of the coating product feedstock is controlled by controlling the gear pump 25. Alternatively, the branches 34a, 34b may be provided with positive displacement gear pumps and sensors.

The outlet of static mixer 35a is connected to atomizer 12 via a valve 38 controlled by computer 30.

A temperature sensor 40 and a relative humidity sensor 41 are provided at positions where the ambient temperature and relative humidity near the object to be painted can be measured. Also provided opposite the object to be painted is a remote temperature sensor 48, such as an infrared sensor suitable for measuring the temperature of the object 14.

In this embodiment, these sensors are provided inside the booth 11, and their outputs are connected to the data input of the computer 30. In particular, the combiator, according to the information sent by the sensor 40.41.48,
It is programmed to adjust the ratio of flow rates in the two branches 34a134b. Finally, the temperature compensated viscosity, '
The 111 constant device 42 may be provided on the inlet side of the atomizer 12, in this example, between the valve 38 and the mixer 35a. The signals generated by this device also provide input data to the computer 30, allowing continuous monitoring of the viscosity of the final coating product just prior to application, thereby allowing optimization of coating conditions.

If the apparatus has a number of booths, it is advantageous for each booth to be provided with its own mixing means, coating product supply means, diluent supply means and flow regulating means.

Similarly, temperature sensors, relative humidity sensors, and remote temperature sensors may be provided in each booth, preferably within each booth. However, if the booths in a group always operate at the same temperature and relative humidity as each other, use only three sensors for the entire group and place them in one of the booths. is practical.

Here, the operation of the device will be explained. computer 3
0 receives a signal from the production control center specifying the work to be performed on the vehicle body entering the booth 11. The coating product is then selected and the flow rate of the coating product raw material necessary to paint a particular portion of the moving vehicle body is adjusted in accordance with information sent by a sensor 32 in conjunction with the conveyor.

This is primarily done by controlling the flow rate of pump 25. At the same time, the computer
Based on the temperature information and relative humidity information sent from 0.41.48, the ratio of flow rates of two types of diluents with different volatilities to be added to the coating product raw material in the mixing means 33 is determined. This diluent flow rate determines the dryness of the coating product applied to the object. Of course, the flow rate of diluent in each branch 34a % '34b depends on the flow rate of the coating product feed determined by pump 25.

The flow ratio of the two diluents is kept constant for a given temperature and relative humidity. The signal sent by the viscosity measuring device may be used to modify the total flow rate of the diluent if the viscosity of the final coating product differs from the desired value without having to create individual flow rates of the diluent. .

The computer memory contains, for each coating product, the viscosity of the diluted coating product, the relationship between volatility and temperature and relative humidity as deduced from the graph in Figure 1, for example, and the graph in Figure 4. The relationship between the ratio D% (horizontal axis) of the two types of diluents and the volatility V of the finally obtained mixture, etc., shown in , is stored.

This latter relationship is not always a one-to-one relationship and may characterize a maximum or minimum value, as in the graph shown here. Therefore, it is necessary to determine the selection criteria by taking economic efficiency or control stability into consideration, for example. Finally, the overall function relating temperature to humidity and the flow rate of each added diluent can only be approximated as a general principle and must be modified by trial and error on a case-by-case basis.

[Brief explanation of the drawing]

1 and 2 are graphs plotting the volatility of coating products as a function of weather conditions for different types of coating products; FIG. 3 is a graph plotting coating product volatility as a function of weather conditions for different types of coating products; FIG. 4, a schematic diagram of a rapidly changing coating product application apparatus, is a graph plotting the diluent ratio as a function of the volatility of the final mixture. 11...Booth 12...Electrostatic sprayer 13...Conveyor 14...Object to be painted 16...Coating film product exchange unit 17 a,
17 b, 17 c----Valve 18...
Valve 19...Detergent distribution circuit 20...Valve 21...Compressed air distribution circuit 22a, 22b, 22c...Coating film product raw material distribution circuit 23 ' a % 23 b s 23 c...
Storage tank 24... First manifold 25... Positive displacement gear pump 26... Motor 27... Flow meter 30... Computer 32 ...Sensor 33...Mixing means 34...Diluent mixing means 35...Second manifold 35a...Static mixers 36a, 36b... ... Valve 37a, 37b ... Pressure crab J8 regulator 38 ...
...Valves 38a, 38b...Venturi flowmeter 40.
...Temperature sensor 41 ...Relative humidity sensor 42 ...Temperature compensated viscosity flllJ constant device 48
・・・・・・Remote temperature sensor

Claims (18)

[Claims] (1) at least one diluent is added to the coating product feedstock, and the proportion of the at least one diluent is such that at least one of the weather conditions in the vicinity of the object being coated
A method of applying a liquid coating product to an object to be painted, which is varied according to two parameters. 2. The method of claim 1, wherein at least one parameter of the weather conditions is temperature. 3. The method of claim 1, wherein at least one parameter of the weather conditions is relative humidity. (4) at least two diluents are added to the coating product before being sprayed, the ratio of the at least two diluents being at least one of the weather conditions in the vicinity of the object being painted; 2. The method of claim 1, wherein the method is modified according to one parameter. 5. The method of claim 4, wherein the diluents are selected such that when they are mixed, the mixture has approximately the same diluting capacity regardless of relative mixing ratio. (6) The degree of polarity of the at least one diluent is:
2. The method of claim 1, wherein the temperature is selected according to the relative humidity in the atmosphere. (7) at least one atomizer for coating product;
mixing means connected to said at least one atomizer;
at least one sensor for detecting parameters of weather conditions in the vicinity of the object being painted, the mixing means comprising means for supplying at least one coating product raw material and at least one dilution Apparatus for applying a liquid coating product to an object to be coated, the apparatus being connected to means for supplying a liquid agent and regulating its flow rate, said sensor controlling said flow rate regulating means. (8) The device according to claim 7, comprising a temperature sensor and/or relative humidity sensor suitable for controlling the flow rate regulating means. 9. The device according to claim 7, further comprising means for supplying at least two diluents with different volatilities and/or polarities. (10) Regarding multiple painting booths and each booth,
8. The apparatus according to claim 7, comprising separate mixing means, supply means, and flow rate adjustment means. (11) Claim 8 comprising a plurality of paint booths and a temperature sensor and/or relative humidity sensor for each booth.
The device described. (12) The apparatus according to claim 11, wherein the temperature sensor and/or relative humidity sensor is provided inside the booth. (13) The apparatus according to claim 7, wherein the flow rate adjustment means includes means for adjusting the flow rate of each of the diluents supplied to the mixing means. 14. The apparatus of claim 7, wherein the flow rate regulating means constitutes a closed loop control system suitable for controlling the flow rate of the one or more diluents. 15. The apparatus of claim 14, wherein the control system is responsive to the flow rate of the coating product feedstock. (16) The apparatus according to claim 7, wherein the outlet of the mixing means is connected to the atomizer by a viscosity measuring device connected to the flow rate adjusting means. (17) at least two diluents are added to one coating product feed, the relative proportions of the at least two diluents being varied according to at least one parameter representative of the temperature of the object; , a method of applying a liquid coating product to an object to be painted. (18) at least one atomizer for the coating product, mixing means connected to the at least one atomizer, and at least one sensor responsive to the temperature of the object, the mixing means comprising: said sensor is connected to means for supplying at least one coating product feedstock and means for supplying and regulating the flow rates of at least two diluents having different volatilities and/or polarities; An apparatus for applying a liquid coating product to an object to be coated, wherein the flow rate adjusting means is controlled.