Causes and Countermeasures of FAQ in Tinplate Spreader

gear stripe failure

Phenomenon and reasons: The gears of the coating machine are not well meshed and cannot rotate smoothly, resulting in uneven coating film, and striped spots appear in tinplate coating. In addition, this situation will also occur when the coating roller used is too large or too small compared to the specified size.

Countermeasure: Check whether it is the cause of the gear or the coating roller. If the gear is worn, it needs to be replaced with a new one; if the coating rubber roller is not suitable, it needs to be replaced with a suitable specification coating rubber roller.

uneven coating

Phenomenon and cause: Under normal circumstances, the paint passing between the feed roller and the leveling roller during coating operations should be evenly distributed between the two rollers. However, when the coating roller has too much paint, the paint will be transferred to the coated tinplate in the form of spraying. The faster the coating operation is, the more obvious this phenomenon will be.

Countermeasures: You can reduce the privacy of the paint, or replace the solvent with low surface tension. In addition, because the paint supply is not carried out in one place, we can also adopt the method of opening holes and use the conduit to evenly distribute the coating amount of the entire roller. This also helps to solve the problem.

Flying ink

Phenomenon and reasons: the speed of the coating machine is generally above 4000r/m, because the speed is faster, when the coating layer between the coating roller and the feeding roller is divided into two, the coating is drawn and chopped into drops shape and fly apart under the action of centrifugal force. Generally speaking, the paint with high drillability has a higher probability of flying ink.

Countermeasures: reduce the drill degree of the paint or add surfactants to reduce the surface tension, this method is often very effective. If it is a white paint, the concentration or content of the pigment can be increased. The thickness of the coating film layer in the wet state can be reduced, and it can also be used as a method to prevent the formation of droplets during separation.

Stolen

Phenomenon and reasons: After scraping by the scraper, a small amount of paint remaining on the embossing roller is applied to the back of the coated tinplate and other materials, becoming "back dirty". The main reason is due to the dunning of the scraper blade. In addition, if the embossing roller is coated. In addition, if the surface of the embossing roller is rough and has scars, it will also make it impossible to scrape off the paint and cause back dirt.

Countermeasure: Regrinding the blade can also increase the surface tension of the coating, making its wettability with the roller worse. In addition, in order to reduce the wear of the blade, the embossing roller is often wetted with paint before applying the scraper. At this time, the paint can be used as a lubricant, and it is more likely to be stained when white paint is applied. This is because the white paint The particles are coarser, and the wear on the blade is greater.

crepe

Phenomenon and reasons: When the temperature is low in winter, the part that is rapidly heated in the drying room (near the hot air blowing out) will form a round and thick paint film around the moon-shaped crater. This is because the movement of molecules in the coating is relatively slow at low temperature. At high temperature, the molecules are in a state of rapid movement, and the low-boiling-point solvent is evaporated quickly, and the high-boiling-point solvent in the resin is not easy to evaporate and remains. If the temperature is further raised, the resin will be in a molten state and condensed under the action of surface tension, forming a circular creeping pattern.

Countermeasures: When choosing a mixed solvent, the problem may be solved if the solvent with a small difference in surface tension value is selected.

Adhesive

Phenomenon and reasons: Insufficient drying temperature or insufficient cooling after drying. Sheets of tinplate sheets are stacked together at high temperature and tend to stick together. At the same time, there is a phenomenon of dirt on the back of the coating film.

Countermeasures: Improve the drying conditions and adjust the cooling system of the drying room.

phantom

Phenomenon and reasons: When drying, stripes in the shape of iron bars like flower iron frames will be formed on the surface of the tinplate coating. The hue of the coating becomes lighter, and the phenomenon of stripes in the shape of iron bars can be vaguely seen. This is because the heat is absorbed by the flower iron frame, which causes the solvent to evaporate slowly and the drying is insufficient, and other coating parts are affected. The entire coating layer becomes thinner and the hue becomes lighter. The larger the coating amount, the easier it is to see this phenomenon.

Countermeasure: It is better to preheat the flower iron frame before putting it in the drying room.

eye hole

Phenomenon and reasons: The area is very small, which also becomes a "pinhole". Due to the influence of the environment, the small holes of the coating film have the advantage of a very thin coating film, and the advantage will be to expose the surface of the tinplate. There are several reasons for this.

(1) There are holes or damages on the coating roller.

(2) There is an oil film on the tinplate plate, and the paint cannot be applied.

(3) There are impurities on the paint and tin plate.

(4) Electrostatic charge due to contact with conveyor belts, etc.

(5) There are problems in paint manufacturing, such as insufficient dehydration during phenol manufacturing.

Countermeasures:

(1) The coating rubber roller needs to be replaced.

(2) Bake the tinplate plate at a high temperature of about 200°C before coating, or when the situation is not serious, reduce the coating drill degree and increase the coating amount.

(3) Filter the paint with a fine mesh, while the tinplate sheet can be wiped clean one by one and reproduced. Or replace the paint and tin plate.

(4) Improve the paint drilling degree. Or replace the conveyor belt with an anti-static conveyor belt.

(5) Replace the paint.

flower iron frame iron bars pattern

Phenomenon and causes: The pattern of iron bars and bars on the iron frame is easy to occur in winter when the temperature is low. It may be that the paint on the tinplate plate is in contact with the flower iron frame before drying, and imprints are produced on the surface; it may also be that the tinplate plate jumps due to the bending of the tinplate plate and the hot air is too strong. Or the drive of the flower iron frame is unbalanced and intermittent The vibration causes the tinplate plate to contact the flower iron frame: In addition, the temperature difference between the tinplate plate is large and the paint privacy is too low. This failure is also prone to occur when the coating amount is too large.

Countermeasures:

(1) Preheat the flower iron frame. Eliminate the temperature difference between it and the tinplate sheet. In addition, in the absence of preheating equipment, it is necessary to consider heating the flower iron frame before coating. You can let the flower iron frame idle in the drying room for a circle to heat up.

(2) Pay more attention to the adjustment of paint privacy. If you use a quick-drying solvent, although it can reduce the incidence of failure to a certain extent, it will cause the paint to flow`} and cause a bad story. You must do a good test before using it.

(3) Check whether the amount of coating is appropriate before construction.

heavy leather

Phenomenon and reasons: When the coating roller has a cut, the paint accumulated at the cut flows out, and the paint "dripping" state is formed above the cut, especially white paint is prone to this phenomenon. The following two aspects are likely to cause heavy skin phenomenon.

(1) The coating rubber roller is too hard.

(2) Too much paint is attached and the drill bit of the paint is too low.

Countermeasures:

(1) Observe the effect after replacing the new coating roller.

(2) Be careful not to drop too low when adjusting the privacy of the paint. Using a quick-drying thinner can help solve the problem.

(3) Adjust the coating amount of paint to prevent the accumulation of paint at the incision.

(4) Properly control the temperature of the paint. Do not make the paint temperature too low.

Zebra stripes

Phenomenon and causes: Streaks like mat entries appear on the coated surface. The coating is transferred from the coating roller to the tinplate sheet, and cannot be smoothly extended on the tinplate surface due to high drilling of the coating or excessive evaporation of the solvent. The paint is fixed in the shape of a "mountain" when it leaves the applicator roller. The temperature is low in winter. The paint is too cool, which is easy to cause this phenomenon. The surface temperature of the coating rubber roller is too high, and this failure will also occur. In addition, when incompatible paints are mixed, one can also cause this failure.

Countermeasures: first use slow-drying solvents to try to reduce the drill degree of the paint. Always pay attention to observe the temperature of the coating. If the temperature is too low, it should be heated slightly but not too high. Sometimes it is necessary to replace the new coating roller: when using a coating with poor compatibility, you should check whether there is any Paint remains in the circulation channel, if any, all paint needs to be replaced.

wrinkled

Phenomenon and reason: The coating position should be uniform and smooth. If the local gloss of the dried coating layer disappears and a wrinkled surface is formed, it is called "air crack (wrinkle)". When there is cold air in the drying room and the hot air does not flow sufficiently, wrinkles of various shapes will appear, such as spider nests, dots, and frost.

Countermeasure: Let the coated tinplate plate pass through under the condition of sufficient exhaust and ventilation in the drying room. Check whether the surface of the tinplate plate is too cold. Of course, there is also such a special process. The baking temperature is deliberately lowered. Only the surface of the coating layer of the plate is dried, and then the temperature is raised to produce a wrinkled surface.

Pitting

Phenomenon and reasons: The coating layer after drying is not uniform and smooth, forming an orange peel-like pockmarked surface. First coated in the paint on the inner side. If there are wax components (such as lubricants in varnishes), stearic acid (such as aluminum in silver paints), etc. The backside is dirty during accumulation, and the numbness caused by this reason Dots are also referred to as paint rejection. No backside smudging but only pitting may be due to too high abrading of the paint, similar to the phenomenon of zebra stripes.

Countermeasure: On the basis of checking whether there is dirt on the back. Re-select silver paint and varnish.

Faults caused by unbalanced paint and ink

Phenomenon and reasons: Since the paint and ink cannot adapt to each other, the following problems will be caused.

(1) Bleeding. The pigment in the ink dissolves into the varnish in the last process and oozes out around the printed graphics.

(2) Color reduction. Not only the pigment, but also the linking material is easy to dissolve and cause exudation.

(3) Uplift. The printing surface is evenly coated with varnish, but accumulations are formed along the periphery of the printing screen

(4) Mat pattern. Mottled phenomenon like mat strips appear on the printing screen

Countermeasures: In most cases, it is necessary to replace the solvent component in the paint, or to improve the binder or pigment of the ink.