WO2009132857A1

WO2009132857A1 - Method to measure cloudiness of paints on test tables

Info

Publication number: WO2009132857A1
Application number: PCT/EP2009/003156
Authority: WO
Inventors: Georg Wigger; Klaus Holzapfel; Christian Bornemann; Ingo Raupach
Original assignee: Basf Coatings Ag
Priority date: 2008-05-02
Filing date: 2009-04-30
Publication date: 2009-11-05
Also published as: DE102008022013A1

Abstract

Method to measure cloudiness of paints on test tables by means of a measurement of the paint coordinates L*, a* and b* on at least 100 different measurement sites on the test table each under at least 2 different observation angles, wherein (i) the standard deviation is determined for each group of measured values which was obtained under a particular observation angle for a particular paint coordinate at different measurement sites, and (ii) the sum is formed from the standard deviations so obtained and used as a measure for the cloudiness of the paint.

Description

Method for measuring the cloudiness of coatings on test panels

The invention relates to a method for measuring the cloudiness of coatings on test panels. The invention further relates to the use of the method for measuring the cloudiness of automobile finishes.

In a paint job, especially in automotive painting, the surface quality in addition to the classic performance characteristics such as stone chip resistance, chemical resistance and scratch resistance is the primary quality criterion. It can particularly influence the purchase decision of the customer in the automotive sector, because the painted surface is crucial together with the shape the first impression that the customer wins, for example, from his new car.

For the development and quality control of paints and application processes, it is therefore necessary to analyze the surface quality of the paints that can be achieved with them. For this purpose, test coatings are usually made, for which the term "test panel" has become natural, since the sample-coated object is often plate-shaped. However, there are also variously curved "test panels", e.g. if parts of car bodies are used or if just the paint properties are to be examined in curved zones.

An important factor in the surface quality of a paint job is the extent of its cloudiness. The cloudiness of a paint job is understood in accordance with EN ISO

4618: 2006, the inconsistent appearance of a paint job, caused by irregular, arbitrarily distributed on the surface areas that differ in color and / or gloss. Such, stain-like inhomogeneity disturbs the uniform overall impression of the paint and is usually undesirable. The undesired cloudiness of the coating can be due, for example, to the properties of the coating composition (paint) used and / or the method of application used. Therefore, it is necessary to analyze the cloudiness of the coatings obtained in the development and quality control of paints and application processes.

Various methods are known from the prior art. Usually, a visual assessment of cloudiness takes place under defined lighting conditions. For example, the examiner attempts to grade different basecoat colors and / or patterns of the same color or to sort them into an order. To do this, he has to look at the test panels with the corresponding paintwork at different angles, evaluate the differences in brightness and color under each angle, and then determine his overall result. This process is very error prone and often leads to the misjudgment of resist patterns. Especially the evaluation of the color stability (color coordinates a *, b *) is very difficult visually, whereas brightness differences (color coordinate L *) can be visually perceived better.

The patent application WO 98/14778 A1 describes a method for measuring coated test panels, wherein the test panels are transferred from a gripping and moving device, for example a laboratory robot, to a measuring station. In the measuring station, a measurement of different coating properties is carried out by the laboratory robot with different measuring devices. For example, layer thickness, course, hue, the color coordinates L ^* (brightness), a * (red-green), b * (yellow-blue), hardness, haze and / or the gloss of the test panels can be measured. If, for example, cloud formation is to be determined in the case of metallic finishes, it is advantageous, according to WO 98/14778 A1, to use a color measuring device which supplies the color coordinates L *, a * b *, preferably at different observation angles. In the exemplary embodiment of WO 98/14778 A1, it is shown on the basis of the measurement of the brightness (color coordinate L *) of paint films that the visually clearly discernable differences in the cloudiness between the paint films could not be detected at an observation angle of 25 °, but only at viewing angles of 45 ° and / or 75 °. This result, according to WO 98/14778 A1, proves the need for complete measurement data determination. However, it is not stated in WO 98/14778 A1, in what way, the cloudiness a coating can now be reliably detected. In particular, it is not stated how a measure of the cloudiness of the coating can be obtained from the proposed "complete measurement data determination".

Voye (color and lacquer (2000), 106 (10), pp. 34-40) also notes the existence of this problem. The article describes an automated analysis system for determining surface data, e.g. the brightness (color coordinate L) and evaluation of paint surfaces. This particular paint batches can be checked. However, visually recognizable cloud formation is not sufficiently recognized in the automated process (p.39, last paragraph). In particular, the development of suitable evaluation algorithms for the analysis of the surface measurement data represents a further challenge (page 40, last column). The known methods for instrumental assessment of cloudiness thus do not yet provide reliable and satisfactory results.

The object of the present invention was therefore to solve the long-known problem and to provide a method by which the cloudiness of coatings on test panels can be determined instrumentally. The method is intended, in particular, for measuring the cloudiness of colorants and of effecting finishes, such as e.g. Metallic finishes, be suitable. Furthermore, the method should be automated and have a high reproducibility of the results.

This object is surprisingly achieved by a method for measuring the cloudiness of coatings on test panels by measuring the color coordinates L ^* , a * and b * at at least 100 different measurement locations on a test panel each having at least 2 different observation angles, where (i) to each group of measured values obtained at a certain angle of observation for a specific color coordinate at different measuring locations, the standard deviation is determined, and

(ii) from the thus obtained standard deviations the sum is formed and serves as a measure of the cloudiness of the paint dissolved. The color coordinates L ^* , a * and b * to be measured correspond to the coordinates of the ClELab color space of the CIE (Commission Internationale de l'eclairage). They are also called Farbmaßzahlen. The coordinate L ^* describes the brightness of the hue, ie the position of the hue on the brightness axis. The coordinates a ^* and b * describe the position of the hue in the color space on an axis between red and green (a *) or on an axis between blue and yellow (b *).

The measurement of the color coordinates L *, a * and b * can be carried out by means of methods known and suitable to the person skilled in the art. For example, spectrophotometers, in particular multi-angle spectrophotometers, can be used as colorimeters. Suitable instruments include the devices MA60 and MA68 from X-Rite ^®.

The measurement of the color coordinates L *, a * and b * is preferably carried out by means of an automated measuring method. This means that at least a part of the required measurements on the test panel in a corresponding technical device is carried out automatically, without the need for manual intervention in the measuring process. For example, the determination of the color coordinates can be carried out successively or simultaneously at different measurement locations on the test panel, without the test panel having to be removed from the measuring apparatus or manually reoriented for this purpose. This can be enabled by a suitable automatic measuring device (e.g., laboratory robot with measuring station), as described, for example, in patent application WO 98/14778 A1. The obtained measurement data are preferably acquired, stored, evaluated and / or displayed electronically.

The measurement of the color coordinates L * a * and b * is carried out in the inventive method at least 100 different measuring locations on the test panel. The measurement is preferably carried out in each case at at least 150 different measurement sites, preferably at least 184 in each case and very particularly preferably at in each case 500 to 800 different measurement sites on the test panel. The individual measuring locations have a minimum distance of 0.5 cm from each other. Preferably, the measuring points have a distance of 0.5 cm to 3.0 cm, especially preferably from 0.8 cm to 1, 2 cm from each other. Most preferably, the different measuring locations are arranged in a rectangular grid at a distance of 1 cm in each case in the direction of the two mutually perpendicular axes of the grid. The measuring locations are preferably within an area of 500 × 200 mm on the test panel.

The measurement of the color coordinates L *, a * and b * at the measuring locations takes place in the method according to the invention under at least two different observation angles, preferably at the observation angles of 15 ° and 25 °. Preferably, the measurement is carried out in each case at least 4 observation angles, preferably under at least 5 different observation angles. The individual observation angles differ by at least 10 ° each. Preferably, the measurement of the color coordinates takes place in each case at the observation angles of 15 ° and 25 °. Particularly preferably, the measurement of the color coordinates takes place at in each case 5 observation angles, preferably in each case under 10 ° -19 °, 20 ° -30 °, 40 ° -50 °, 70 ° -80 ° and 105 ° -115 °, very particularly preferably below 15 °, 25 °, 45 °, 75 ° and 110 °. The illumination is preferably directed at an illumination angle (angle of incidence) of 45 °.

For each group of n measured values, each having a specific one of a total of m different observation angles (wi, W ₂ , ...., w _m) for a specific color coordinate F * (F ^* = L *, a ^* or b *) obtained at different measuring locations, the standard deviation s (w, F *) is determined according to the formula (I):

s (w, F *) = ((1 / (n-1) * (Σ ⁿ i = i (Xi - x) ²⁾⁾ ° ^l5 (D

where n stands for the number of measured values X, which were obtained at a certain observation angle w for a certain color coordinate F * at different measuring locations, and x for the arithmetic mean of these measured values x, stands for (x = (Σ ⁿ _{i = 1} Xj ). From the standard deviations s (w, F ^* ) thus obtained, the sum S according to formula (II) is formed:

S = S (W ₁₁ L ^* ) + s (w ₂ , L ^* ) + + s (w _m , L *)

+ s (w ,, a ^* ) + s (w _2l a ^* ) + s (w _m , a *) (II)

+ S (W ₁ ^ ^* ) + S (W ₂ , b *) + .... + s (w _m , b *)

where Wi, W ₂ , ...., w _m stand for the m different observation angles under which the color coordinates L *, a * and b * were respectively measured.

The sum S of the standard deviations serves as a measure of the cloudiness of the coating. The larger S, the greater the cloudiness of the paint job.

The value of S as a measure of the cloudiness of a coating has a high reproducibility. In a repetition of the analysis with re-measurement of the color coordinates L *, a * and b * under the same observation angles and re-evaluation of the measured data, the deviation for the sum S of the standard deviations is usually below ± 0.15 units.

The inventive method thus enables the automatable, instrumental determination of the cloudiness of coatings on test panels with high reproducibility of the results. The method according to the invention is furthermore suitable for determining the cloudiness of coloring and of effecting coatings, such as e.g. Metallic finishes.

The finishes on the test panels are preferably coloring and / or effect finishes, particularly preferably effect-effecting metallic finishes. Coloring finishes are understood to mean finishes which have been obtained from a pigment-containing coating composition. They contain, for example, white, colored and / or black pigments. Effect-giving coatings accordingly contain effect pigments, such as pearlescent or metallic effect pigments. Both coloring and effect paint finishes can also be used as part of a Multicoat paint present. In this case, the color and / or effect coating can be the topmost layer of the multicoat system, or it can be below a clearcoat. In all these cases, the inventive method for determining the cloudiness of the coating is suitable.

Another object of the invention is the use of the method for measuring the cloudiness of automotive coatings.

Automobacking is understood to mean coatings obtained from coating compositions which are suitable for the automotive industry.

Original painting, in particular OEM painting, and / or automotive

Repainting are suitable. The automotive coatings can be present for example on test panels, body parts or bodies.

The automotive finishes are preferably dye-colored and / or effect-based finishes, particularly preferably metallic finishes. The

Coatings may also be present in the context of a multi-layer coating.

The process can be used, for example, in the development of improved coating materials, coating compositions or application processes for automotive finishing, in order to detect the cloudiness of the coatings achieved as a function of the altered experimental parameters. In addition, for example, the cloudiness of the paint achieved with a certain coating batch and / or a defined application process can be checked as part of a quality control.

In the following the invention will be explained in more detail by embodiments. Examples

Embodiment 1

On steel sheets which had been pretreated with an electrodeposition coating (layer thickness 12-15 μm) and a commercial filler (layer thickness 30-35 μm), either a dark blue or a silver, in each case commercially available metallic basecoat from BASF Coatings was applied in two steps in each case before a commercially available two-component clearcoat was applied by means of ESTA high-speed rotation to the intermediately dried basecoat (layer thickness of the clearcoat 40-45 μm).

The first application step of the basecoat was carried out by means of electrostatic spray application (ESTA) under high rotation atomization. The EcoBell device from Dürr was used with the following application parameters:

Nozzle: 1, 4 mm

Bell: 16010043

Speed: 45000 rpm

Outflow rate: 280 ml / min

Pulling speed: adjusted for nominal layer guide air: 160 NL (NL = standard liters)

Layer thickness: 7 - 9 μm

Flash off time: 1 min at room temperature

SB50%: 45 cm

Grid: 15 cm

On the basecoat layer obtained, the respectively same basecoat in the second application step was then applied with pneumatic atomization. The device AGMD-Gun from DeVillbis was used with the following application parameters:

Air cap: 797

Nozzle: 1, 4 mm

Center air: 240 NL

Homing air: 350 NL Outflow rate: 275 ml / min

Pulling speed: adjusted for nominal layer

SB50%: 40 cm

Layer thickness: 4 - 6 μm Flash off time: 3 min at room temperature

Intermediate drying: 10 min at 80 ⁰ C.

Grid: track spacing 8 cm for 5-fold overlapping, or track spacing 13 cm for 3-fold overlapping

The spray width SB50% is understood to mean the spray pattern diameter (in cm) at 50% of the maximum layer thickness. The track distance indicates the distance between the locations of the maximum layer thickness of two spray patterns in cm.

From the spray width SB50% and the spray bar (web spacing), the degree of overlap of the applied spray paths is consequently obtained. The overlap describes the ratio of SB50% and track distance (overlap = SB50% /

Stepover). For example, if a spray width of SB50% = 40 cm for the

Spray cone of the pneumatic atomization set, this results in a

Spray grid with a track distance of 8 cm an average overlap of 5 applied spray paths for each point of the painted surface. If, on the other hand, a larger web distance of 13 cm is set for the same spray width of SB50% = 40 cm, this results in an average overlap of only 3 applied

Spray paths for each point of the painted surface. It is up to date

Knowledge from visual evaluations known that with a lower degree of overlap usually the cloudiness of the resulting paint is more pronounced.

The dark blue or silver metallic basecoat was applied in each case with two different spray buttons (web spacing 8 cm and web spacing 13 cm), resulting in an average overlap of 5 or 3.

The cloudiness of the coatings obtained was detected after curing of the clearcoat by means of the method according to the invention. For this purpose, an automatic measuring device according to WO 98/14778 A1 with a Angle spectrophotometer from the company X-Rite ^® (MA60) used. The color coordinates L * a ^* and b * were each measured at 4 different observation angles (15 °, 25 °, 45 °, 75 °) at 675 different measurement points on the painted test panel. The measuring points were in a rectangular distance grid of 1, 0 cm x 1, 0 cm on an area of 15 x 45 cm. The standard deviations s were calculated from the 675 measured values obtained per combination of color coordinate F * (F * = L *, a * or b *) and observation angle w. Subsequently, the sum S of the standard deviations thus obtained was calculated as a measure of the cloudiness of the coating:

S = s (15 °, L *) + s (25 °, L *) + s (45 °, L ^* ) + s (75 °, L *) + s (15 °, a *) + s (25 °, a *) + s (45 °, a *) + s (75 °, a ^* ) + s (15 °, b *) + s (25 °, b *) + s (45 °, b *) + s (75 °, b ^* )

The results are shown in Table 1 below.

Color Overlap Cloudiness (S) Dark Blue 5 3.4 Dark Blue 3 4.12 Silver 5 2.24

Silver 3 2.62

It can be clearly seen that a smaller overlap leads to significantly higher sums S of the standard deviations and thus to higher cloudiness. This corresponds to the results of the visual inspection and proves that the cloudiness of the coatings can be determined by the method according to the invention over the sum S of the standard deviations.

Embodiment 2

Example 2 was carried out analogously to Example 1. The cloudiness of four different basecoats (dark blue, silver, gray, beige) was determined as a function of the outflow rate of the paint in the pneumatic application. Notwithstanding Example 1, the pneumatic atomization was carried out with the following parameters:

a) low outflow rate: 275 ml / min

Center air: 240 NL

Horn air: 350 NL

SB50%: 40 cm

Grid: track distance 10 cm (for 4-fold overlapping)

b) high effluent rate: 400 ml / min

Center air: 325 NL

Horn air: 300 NL

SB50%: 40 cm

Grid: track distance 10 cm (for 4-fold overlapping)

According to the current state of knowledge, it is known from visual evaluations that the cloudiness of the resulting coating is usually more pronounced at high outflow rates due to the "natter" atomization.

The cloudiness of the resulting coatings was measured after curing of the clearcoat by means of the method according to the invention as indicated in Example 1.

The results are listed in Table 2 below.

Color tone Discharge rate (ml / min) Cloudiness (S) dark blue 275 2.78 dark blue 400 4.12

Silver 275 1, 87

Silver 400 2,62 gray 275 2,19 gray 400 2,88 beige 275 2,30 beige 400 3,45 It can be clearly seen that a higher outflow rate leads to significantly higher sums S of the standard deviations and thus to higher cloudiness. This corresponds to the results of the visual examination and further proves that the cloudiness of the coatings can be determined by the method according to the invention over the sum S of the standard deviations.

Claims

claims

1. A method for measuring the cloudiness of coatings on test panels by measuring the color coordinates L *, a * and b ^* at at least 100 different locations on the test panel under at least two different observation angles, characterized in that

(i) for each group of measurements obtained at a given angle of observation for a particular color coordinate at different measurement locations, the standard deviation is determined, and (ii) the sum is formed from the standard deviations thus obtained and as a measure of the cloudiness of the coating serves.

2. The method according to claim 1, characterized in that the measurement of the color coordinates is carried out in each case at least at the observation angles of 15 ° and 25 °.

3. The method according to any one of the preceding claims 1 or 2, characterized in that the measurement of the color coordinates by means of an automated measuring method.

4. The method according to any one of the preceding claims 1 to 3, characterized in that the measurement of the color coordinates at 500 to 800 measurement locations is performed on the test panel.

5. The method according to any one of the preceding claims 1 to 4, characterized in that the measurement of the color coordinates is carried out under each 4 to 5 observation angles.

6. The method according to any one of the preceding claims 1 to 5, characterized in that the measurement of the color coordinates is carried out under each of 5 observation angles, preferably in each case under 10 ° - 19 °, 20 ° - 30 °, 40 ° - 50 °, 70 ° - 80 ° and 105 ° - 115 °, most preferably below 15 °, 25 °, 45 °, 75 ° and 110 °.

7. The method according to any one of the preceding claims 1 to 6, characterized in that the obtained measurement data are electronically recorded, stored, evaluated and / or displayed.

8. The method according to any one of the preceding claims 1 to 7, characterized in that it is a color and / or effect paint, preferably an effect metallic paint, is.

9. Use of the method according to any one of the preceding claims 1 to 8 for measuring the cloudiness of automotive finishes.