ACADEMY

Cataphoresis Paint Controls and Analysis

Paint content in cataphoresis plating; decreases due to transportation, consumption (adhesion to the metal surface), and solvent evaporation that occurs with heat.

Missing chemical paint components; It should be returned to the bathroom at regular intervals every day by making regular analyzes.

Cataphoresis Paint Controls and Analysis

For a quality cataphoresis paint application; Pay attention to the pigment and resin P/B ratio.

Theoretically, the percentage of P/B in the paint on the metal surface is higher than the percent P/B in the paint in the tank.

We experience the problem of the decrease of the electrolytic chemical reactions in the paint in the tank, acidity caused by the water carried from consumption and rinsing, especially solvent reduction due to reaction and heating.

As a result of the physical and chemical effects mentioned above, we experience reductions in the percentages of the formulations of different chemical components in the paint.

To control these natural losses, we have to do some chemical analysis regularly.

Determination of Solids Content

Tare the aluminum foil container with a diameter of 50 mm and a side height of 5 mm brought to a constant weight. (A)

A 1.0 – 2.0 gr paint sample is put on the tared foil container. It is weighed again and the full weight is recorded. (B)

The sample is kept in the oven at 110 °C for 60 minutes.

The sample is cooled down to 20–25 °C in a desiccator.

The sample removed from the desiccator is reweighed.

The amount of solids is determined

It is preferred that the amount of solids to be between 14–18%.

Determination of ash amount

Tare a porcelain crucible brought to a constant weight. (A)

A 1.5–2.0 g sample is placed on the tared porcelain crucible. It is weighed again and the full weight is recorded. (B)

The sample is first left in the oven at 110 °C for 60 minutes to dry.

Then 30 minutes at 250 °C for 30 minutes at 450 °C, respectively.

The sample is allowed to burn in the muffle furnace at 750 °C for 20 minutes.

Cooled to 20–25 °C in desiccator.

The sample removed from the desiccator is reweighed.

The result of the analysis is requested to be between 1.3–2.1%.

P/B (Solid / Ash Resin)

The ratios of solid and ash samples are found.

The following formula calculates the P/B ratio.

P/B = Ash /Solid-Ash (2.23)

As a result of the analysis, it is desired that the P/B ratio be between 0.090–0.140.

PH Determination

pH determines the balance of the paint in the tank, which is particularly disturbed by electrolytic chemical reaction and transport.

The pH in cataphoresis paint is between 5.7 – 6.0. When the pH value rises, the resin solubility decreases and the emulsion becomes unbalanced, causing the paint to clump in the tank, filters and membranes.

When PH value drops; Corrosion in pipes releases iron ions to the environment. It causes blockages in the membranes.

The reason why the cataphoresis system is so dependent on pH is that Hydroxyl groups (OH-) are formed on the cathode surface during the reaction and the pH rises, so the flocculated paint settles and adheres to the surface.

Analyses are recorded once a day.

Conductivity check

Paint conductivity indicates the paint's ability to pass current. Affects coating thickness.

Conductivity in a running bath always tends to increase due to the release of soluble salts, polarized solvents and acids.

Conductivity is stabilized by removal of acid ions from the system or removal of UF.

To change the conductivity of the bath, the amount of solvent is increased or the cationic groups (NH+) is increased or the bath temperature is increased.

Measurement should be made with a calibrated conductivity meter. It is desirable that the conductivity be in the range of 800–2500 mS.

Analyses are recorded at least once a day.

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