WO2007135306A1

WO2007135306A1 - Method of observation and of measurement of the dripping capability in products used as electrophoresis bath and its implementation.

Info

Publication number: WO2007135306A1
Application number: PCT/FR2007/051124
Authority: WO
Inventors: Johanne Sornin
Original assignee: Renault S.A.S
Priority date: 2006-05-18
Filing date: 2007-04-17
Publication date: 2007-11-29
Also published as: FR2901359A1; FR2901359B1

Abstract

The invention concerns a method of observation and of measurement of the dripping capability in products used as electrophoresis bath - notably for automobile structures - which is representative of the defects observed on structures at the end of an electrophoresis paint application chain, simple to implement and which allows a classification of the products according to their capability to drip under the conditions of a predetermined industrial application. The invention also concerns the implementation of this method to the comparison of products used in electrophoresis baths notably in the automobile industry.

Description

METHOD OF OBSERVING AND MEASURING THE FLOWABILITY OF PRODUCTS USED AS CATAPHORESE BATHS AND ITS APPLICATION.

The invention relates to a method for observing and measuring the flowability of products used as cataphoresis baths, in particular for automobile structures.

During a cataphoresis treatment process, a structure, such as a motor vehicle body, is immersed in a tank containing a bath of electrically conductive paint. Under the influence of a direct current flowing between an anode and a cathode immersed in the bath, a cationic type paint is deposited on the structure connected to the cathode.

The structure is then removed from the bath, rinsed, drained and placed in an oven to cook the paint. This process of cataphoresis treatment is automated and takes place in the chain. The structures emerging from these treatment chains sometimes show sagging of the product used for the bath. In particular, sagging with extra thickness or bubbles are sometimes observed in a visible area by the customer, which is not acceptable. It is then necessary to sand these runs in order to erase them.

The evaluation of the flowability of products used as cataphoresis baths would make it possible to improve the knowledge of the behavior of these products and to select the products for which no or few coulure phenomena are observed under industrial application conditions. that we want to use.

Two leak tests are currently known. A first test involves assembling two phosphate plates parallel to each other with a difference of 100 micrometers in order to simulate a docking. The assembled plates are submitted to a cataphoresis painting application in vertical position, followed by the usual rinsing, draining and firing steps. A visual observation of the coulures generated during the cooking is then carried out. This test makes it possible to observe the coulures due to a docking. However, it has the disadvantage of being non-reproducible, the position and the size of the coulures being random and their cause being unknown. In addition, the amount of product at the origin of the coulure is unknown. Finally, this test is representative only of the coulures due to a docking, and not the different types of coulures that can be observed on a structure. Thus, this test is not representative of the global phenomenon observed and not very exploitable. A second test is to perform a cataphoresis painting application on a phosphate plate, followed by dewatering for 10 minutes, then a drop of cataphoresis bath product drops on the plate in a horizontal position. Generally drops of different known volumes are deposited. The plate is then subjected to a cooking step, always in a horizontal position. The bubbling and the thickness of the drops are then evaluated visually. This test makes it possible to accurately deposit different volumes of drops and has good repeatability. However, it has the disadvantage of being difficult to handle, and allow only the observation of drops and not drips. In addition, few differences are observed between the different products, so it is difficult to determine which product produces the least run-off for a given application.

The aim of the invention is to overcome these drawbacks by proposing a method for observing and measuring the flowability of products used as cataphoresis baths, in particular for automobile structures, which is representative of the defects observed on the structures leaving the a cataphoresis painting application chain, simple to implement, and which allows a classification of the products according to their ability to flow under the conditions of a predetermined industrial application.

To this end, the object of the invention relates to a method for observing and measuring the flowability of products used as cataphoresis baths intended to coat structures for a predetermined industrial application, under conditions comparable to those said industrial application, comprising the following successive steps:

(i) applying a layer of paint to a plate by cataphoresis by immersion in a bath of an electrically conductive paint to be tested under conditions making it possible to obtain a paint deposit of a pre-determined thickness comparable to the thickness obtained with said industrial application, (ii) rinsing the paint-coated plate with a rinse aid to remove excess non-deposited conductive paint during cataphoresis,

(iii) removing the rinsing product from the paint-coated plate,

(iv) depositing on a test surface of the plate covered with paint and placed horizontally at least two drops of said conductive paint of a predetermined volume, the drops may have different volumes, (v) place the plate inside an oven in an inclined position relative to the horizontal, the test face being oriented upwards,

(vi) cook the plate thus inclined under the same conditions of temperature and duration as said industrial application, (vii) observe and measure the shape, appearance and size of the drops deposited after cooking.

The conditions of the observation and measurement method are thus very close and representative of the conditions of the industrial application for which it is desired to study the flowability of an ionic paint.

In particular, this method is representative of the conditions of application in the automotive industry, but not limited thereto. The application of automotive structure cataphoresis paint indeed comprises the steps (i), (ii), (iii), (v), and (vii) of the method according to the invention, the plate corresponding to a surface of the automobile structure to be coated which is in an inclined position, which can cause the dripping of paint drops that have not been removed during the rinsing step.

Advantageously, the observation and measurement step comprises one or more of the following steps:

- measurement of the width, and / or the length and / or the thickness of the coulures observed,

measuring the thickness of the retention drops observed at the lower ends of the coulures. - measurement of the diameter and the thickness of the drops which have not sunk, observation of bubbles at the level of the coulures, and / or drops which have not sunk, and / or drops of retention,

- Observation of the differences in color between the first drops, and / or retention drops and / or drops that have not flowed, and the other the rest of the surface of the plate.

The measurement and / or the systematic observation of one or more of the parameters listed above makes it possible to compare the different products tested under the same conditions.

Preferably, during the firing step, the test face of the inclined plate is protected by a cover so as to protect the drops from the movements of air. This makes it possible to prevent the ventilation systems that usually exist in the ovens from disturbing the flow of the drops, which would distort the observations.

Advantageously, the volume of at least one drop deposited during step (iv) and the inclination of the plate chosen during step

(vi) is determined so that said drop flows during cooking without flowing out of the plate. It is thus possible to measure the length of the run.

(vi) are determined in such a way that said drop does not flow. It is then possible to observe the behavior of this drop and in particular the possible formation of bubbles, or the difference in color observed relative to the rest of the plate. Advantageously, during step (iv), the volume of drops is chosen from about 30 to 80 microliters for an inclination of the plate from 10 ° to about 20 ° relative to the horizontal. These values are to be determined by tests for each type of industrial application for which it is desired to test a paint. Preferably, the rinse aid used in the rinsing step is demineralized water, but other suitable rinse agents may be employed.

Also preferably, the rinsing product is removed from the plate by heating the plate, the plate being in an inclined position relative to the horizontal. This inclination makes it possible to promote the elimination of the rinsing product. This elimination is indeed necessary in order to avoid any dilution of the drops of paint to be tested in traces of rinsing product, which would distort the study of the behavior of the paint.

The invention also relates to the application of the observation and measurement method according to the invention to the comparison of the flowability of different ionic paints used for cataphoresis painting of automobile structures, in which each paint is tested in the same conditions. The observation and measurement of the plates obtained for each painting thus allow the user to choose the most appropriate paint for its application. Advantageously, in an application in which the automotive structures have undergone one or more prior surface treatments, the plate used in the method has also undergone the same surface treatment or treatments as said structures.

For some applications, particularly in the automotive industry, the test plate is, for example, phosphated.

The invention is now described with reference to the accompanying drawings, in which: FIG. 1 is a view from above of a test plate at the time of depositing the paint drops, in a horizontal position before inclination; Figure 2 is a schematic side view of a support of a test plate for carrying out the method according to the invention, the plate being inclined; Figure 3 is a top view of a test plate at the end of the test method according to the invention.

An exemplary implementation of an observation and measurement method according to the invention is described below for an application to the automotive industry. More specifically, the industrial application for which it is desired to observe the behavior of paints for cataphoresis baths corresponds to the conditions for coating the external skin structures of a vehicle.

For this type of application, the thickness of paint that it is desired to obtain by cataphoresis on the structure is typically of the order of 20 microns, with an error of ± 2 microns. Of course this thickness may vary depending on the applications.

A first step of the method according to the invention consists in producing a paint deposit on a test plate 1 measuring by Example 9 cm wide and 19 cm long, in a cataphoresis bath under conditions allowing to obtain a paint thickness of 20 ± 2 microns. For this purpose, the following parameters: application temperature, voltage rise time, voltage and application time are adjusted to obtain this thickness.

Since automotive structures have a phosphated surface, a test plate identical to the structures of this particular application is used: the plate is therefore phosphated in this example. In a second step, the test plate, now coated with a coat of paint 20 ± 2 microns thick, is rinsed with demineralized water as a rinse, for example by means of a jet. This step makes it possible to remove the surplus of cataphoresis bath which has not deposited on the surface of the plate at the exit of the preceding step.

The test plate is then dried to remove any trace of the rinse.

This drying step can be performed in an oven heated at 40 ° for about 10 minutes, the test plate being inclined with respect to the horizontal of about 70 ° to promote drainage.

Of course, the temperature and duration of heating may vary, provided that the plate is fully dried at the end of this step, the rinse having been removed by evaporation. It is also not necessarily necessary to tilt the plate, provided that at least one side of the plate, intended to serve as a test surface, can be completely dried.

On the paint application line, the automobile structure drips during its transport from the rinsing line to the oven for cooking the paint due to the movements induced by its movement.

A specific quantity of the ionic paint which has been used as a cataphoresis bath is then removed by means of a micropipette. Drops of predetermined volumes are deposited on the test plate placed horizontally by means of the micropipette: these drops are deposited along a horizontal line located near an edge of the plate, as shown in FIG. Three drops G of paint with volumes of 30, 50 and 80 μl (at ± 1%), respectively, are deposited in this order on the test face (upper face) of the plate.

The test plate is then inclined at an angle α of approximately 15 ° with respect to the horizontal, its test face being directed upwards, by means of a suitable support, as represented in FIG. plate is oriented so that its end on which are dropped drops G is higher than its other end.

This support consists for example of a plate 2 provided with inclined grooves 3 in which are inserted two support lugs 4 and 5 respectively, one of which serves as a stop at the lower end of the test plate 1 (on the opposite side the drops G deposited), and the other 5 supports the underside of the test plate 1, the length of the latter tab 5 being chosen so as to obtain the desired angle α.

The test plate 1 thus inclined is then placed in an oven, a cover 6 being placed above the test face of the plate in order to prevent the air movements from disturbing the flow of the drops on this face. test. Preferably, this cover 6 is in the form of a bell placed above the test plate and its support 2. This bell may have for example a rounded or parallelepiped shape.

In the oven, the plate is mounted in 18 minutes at a temperature of 180 ⁰ C, then is maintained for 20 minutes at this temperature. These baking conditions of the deposited paint correspond to the conditions used for the application envisaged in this example, namely for the application of paint on the outer skin of a vehicle.

The plate is then removed from the oven, and the appearance, shape and dimensions of the drops are observed and measured, namely:

- width, length and thickness of the observed drips, (by running, is meant a trail of paint on the plate from a drop),

the thickness of the retention drops observed at the lower ends of the drips (by retention drop, the drop located at the lower end of a run, in which the cast product has accumulated). - diameter and thickness of the drops that have not flowed,

- observation of bubbles at the level of the coulures, drops not having poured, and drops of retention,

- Observation of color differences between the first drops, retention drops and drops that have not flowed, and the other part of the surface of the plate. One can also take into account the yellowing of the color.

The various dimensions listed above are measured by means of a millimeter scale and a thickness measuring device, for example a palmer.

These different criteria are summarized in Table 1 below.

Table 1: Measurement and Observation Criteria

Figure 3 shows a plate obtained with a typical paint A used for the application of paint on a vehicle.

We can observe bubbles formed on the drops of 30 .mu.l and 50 .mu.l, these drops having not generated sag during cooking.

The drop of 80 .mu.l caused a run, the length L, measured from the lower end of the mark of the initial drop to the lower end of the drop at the end of the run (retention drop) is 110 mm. Bubbles are also observed at the drop of retention, while the mark of the initial drop is also visible. The following table 2 indicates the criteria measured for the 80 μl drop for the plate obtained with product A, as well as those measured for product B.

Table 2: Observations after baking drops of 80 μl for two products A and B (inclination of the plate: α = 15 °)

It is clear from reading the results presented in Table 2 that product B gives rise to much less visible and important defects than product A. The user will thus prefer to use product A rather than product B.

Claims

A method of observing and measuring the pourability of products used as cataphoresis baths for coating structures for a predetermined industrial application, under conditions comparable to those of said industrial application, comprising the following successive steps:

(i) applying a layer of paint to a plate by cataphoresis by immersion in a bath of an electrically conductive paint to be tested under conditions making it possible to obtain a paint deposit of a pre-determined thickness comparable to the thickness obtained with said industrial application,

(ii) rinse the paint-coated plate with a rinsing agent to remove excess conductive paint not deposited during cataphoresis, (iii) remove the rinsing product from the paint-coated plate,

(Iv) depositing on a test surface of the plate covered with paint and placed horizontally at least two drops of said conductive paint of a predetermined volume, the drops may have different volumes,

(v) place the plate inside an oven in an inclined position relative to the horizontal, with the test face facing upwards,

(vi) cooking the plate thus inclined under the same temperature and duration conditions as said industrial application,

(vii) observe and measure the shape, appearance and size of the drops deposited after cooking.

The method of observation and measurement according to claim 1, wherein the step of observing and measuring comprises one or more of the following steps:

3. Method of observation and measurement according to claim 1 or 2, wherein, during the firing step, the test face of the inclined plate is protected by a cover so as to protect the drops of the movements of air.

4. Method of observation and measurement according to one of claims 1 to 3, wherein the volume of drops deposited in step (iv) and the inclination of the plate chosen during step (vi ) are determined in such a way that at least one drop flows during cooking without flowing out of the plate.

5. Method of observation and measurement according to one of claims 1 to 4, wherein the volume of at least one drop deposited during step (iv) and the inclination of the plate chosen during the step (vi) are determined in such a way that said drop does not flow.

6. Observation and measurement method according to claim 4 or

5, in which, during step (iv), the volume of the drops is chosen from about 30 to 80 microliter for an inclination of the plate of about 10 ° to 20 ° relative to the horizontal.

7. Method of observation and measurement according to one of claims 1 to 6, wherein the rinsing product is removed from the plate by heating the plate, the plate being in an inclined position relative to the horizontal.

8. Application of the observation and measurement method according to one of claims 1 to 7 to the comparison of the flowability of different ionic paints used for cataphoresis painting of automobile structures, in which each paint is tested in the same conditions.

9. Application according to claim 8, wherein the automotive structures having undergone one or more surface treatments prior, the plate used in the method has also undergone the same surface treatment or treatments as said structures.