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Why is there a color difference on the surface of the Prepainted Galvanized Steel Coil?

Why is there a color difference on the surface of the Prepainted Galvanized Steel Coil?

(paint, paint film thickness, viscosity,  temperature, cooling water, curing oven, paint uneven or unstirred )

  1. Paint

  • Refers to the paint color difference  between different batches or different barrels (light color)

  • All pigments and fillers of the paint are different

  • When changing a new batch or a new paint, it extends from the direction of the feeding port to the direction of the return port, causing different colors.

  • Features: It extends from the side of the feeding port to the direction of the return port, is distributed in a belt shape, and gradually widens

  • Solution: find the reason for the paint.

  • Confirmation: From the laboratory scraper sheet, compare two different Prepainted Galvanized Steel Coil.

2. Paint film thickness

  • The different colors are caused by the different paint thickness.

  • Pressure change by paint viscosity, coating rollers, and sticking rollers

  • There is no apparent change, but there is a big difference between each coil.

  • Solution: strictly control the paint consumption

  • Confirm: pay attention to the change of paint consumption.

3. Viscosity

  • Refers to the different colors caused by the low or high viscosity of the machine

  • The viscosity in the barrel is quite different from the viscosity of the paint in the barrel.

  • A few minutes after changing the paint, there is a band-like color difference from the side of the feeding port.

  • The same as the previous paint film thickness change, in essence, the high or low viscosity will eventually cause the paint film thickness.

  • Solution:  after changing the paint a few minutes, there is a band-like color difference from the side of the feeding port

  • Pay attention to the paint consumption.

4. Steel sheet temperature

 The color difference caused by the high or low temperature of the fingerboard

The furnace temperature setting is unreasonable and uses the wrong material.

Phenomenon: The gloss of the sheet is not high, and MEK is not qualified

There is no problem with the same sheet, but different coils with a big gap.

Solution: measure the sheet temperature from time to time, and change the specifications (the difference is significant) to measure the board temperature.

Confirm: MEK test glossy.

5. Cooling water

  • 2# The color difference caused by the lack of water quality

  • The quality of 2# water and cold water is not good, and the drying effect of the squeezing roller is not good.

  • Phenomenon: the board surface is black, and the gloss is not high

  • Features: surface dirt can be wiped off with cotton yarn

  • Solution: replace the water-cooled water in time to enhance the squeezing effect of the squeezing roller

  • Confirm: the surface gloss is not high, but the surface dirt can be wiped off with cotton yarn to restore the original gloss

6. Curing furnace

  • The different colors are on both sides of the fingerboard.

  • The temperature of the transmission side and the operation side of the curing furnace is not uniform.

  • Features: There is no obvious chromatic aberration in the vertical direction, and the lateral chromatic aberration is large (similar to the difference in film thickness on both sides)

7. The paint is not evenly stirred or not stirred

  • Distributed on the board in a strip shape

  • The paint is delaminated, resulting in poor viscosity.