Baking varnish filling is the core link in the production of baking varnish badges that determines the color reproduction and visual texture. It is necessary to strictly control aspects such as color separation accuracy, pigment properties, and operation techniques. The following are the key details and technical points to note during the baking varnish filling process:
I. Pretreatment of the color separation tank: Ensure that the color boundaries are clear
Control of slot depth and width
The depth of the color separation slot (the metal partition reserved during stamping) should reach 0.3-0.5mm, and the width should be ≥0.2mm to ensure that the pigment filled in will not overflow to the adjacent area due to excessive thickness.
Example: If the badge design has a red circular outer circle and a blue inner circle, the color separation slot needs to completely isolate the two to avoid the formation of a purple edge when the red and blue are mixed during coloring.
Treatment of the smoothness of the groove wall
The wall of the color separation tank after stamping may still have metal burrs, which need to be removed by fine sandpaper (800 mesh or above) or ultrasonic cleaning; otherwise, it will cause the pigment to adhere to the wall or the filling to be uneven.
Detection method: Observe the slot wall from the side with strong light. If there are reflective bright spots, it needs to be re-polished.
Ii. Pigment Properties and Blending: Precise Reproduction of Design colors
Color number matching and pre-test
The baking varnish pigments (such as Pantone 200C bright red and 3292C dark blue) must be precisely mixed using the Pantone International color card to avoid relying on the RGB color values of the screen.
For the first color matching, a sample color card needs to be made (fill the color on the metal sheet and bake it). After confirming with the customer that there are no errors, mass production can be carried out to prevent color deviation caused by batch differences in the color paste.
Pigment viscosity control
The paint for baking varnish should maintain a paste-like texture (similar to the consistency of toothpaste). If it is too thin, it will flow out of the color separation tank; if it is too thick, it will be difficult to fill fine lines (such as 0.5mm wide strokes of text).
Adjustment method:
When it is too thin, add silica thickener (in a ratio of ≤5%). If it is too thick, add thinner (butyl acetate) and stir evenly. After each adjustment, test the smoothness of color filling.
Multi-color layering sequence
If the badge has a layering effect (such as gold at the bottom and transparent red at the top), the bottom color should be filled in and solidified first, and then the top color should be filled in.
When making the “golden border + red center” badge, first fill in the red area and bake it, then fill in the golden border to avoid the golden border covering the red edge and causing color mixing.
Iii. Coloring Tools and Techniques: Meticulous operation to avoid flaws
Tool selection
Needle tube dropper: Suitable for fine lines with a width of 0.3-1mm (such as strokes of characters, logo Outlines), the diameter of the tube opening should be less than half of the line width to ensure precise injection.
Chisel (color filling knife) : It is used for filling large areas of color blocks (such as background color). The blade should be thin and smooth (thickness ≤0.1mm) to avoid scratching the electroplating layer.
Toothpick/fine brush: Assist in correcting the paint that overcomes from the edges. Dip a small amount of thinner and gently rub. Do not scrape hard.
Coloring intensity and speed
When filling the color, it is necessary to advance at a constant speed along the edge of the color separation slot with moderate force (to avoid breaking the electroplating layer). For example, when filling a circular color block with a diameter of 2cm, it can be filled in a spiral manner from the center to the edge to ensure there are no air bubbles in the middle.
Prohibited action: Repeatedly applying back and forth in the same area can easily cause the pigment to churn (the undried pigment at the bottom layer is stirred), resulting in uneven granular texture.
Micro-area processing
For hollowed-out patterns (such as the star-shaped hollowed-out holes on badges), it is necessary to first stick tape on the back to cover them. When filling in the color, prevent the pigment from seeping into the holes. After it has cured, remove the tape.
For extremely fine lines under 0.2mm (such as hair strands or gear lines), screen printing should be used to assist in coloring instead of manual operation to ensure the integrity of the lines without any breaks.
Iv. Standing and bubble treatment: Enhance surface flatness
After coloring, let it stand for defoaming
After coloring is completed, the badge should be left to stand for 5 to 10 minutes to allow the air in the paint to naturally escape. If baked immediately, the bubbles will expand and burst at high temperatures, forming surface pits.
Key observation points: Large color blocks (such as solid color areas exceeding 3cm²) are prone to accumulate air bubbles. It is necessary to gently poke the surface with a toothpick to release the gas.
Bubble remediation methods
If there are still tiny bubbles (with a diameter < 0.1mm) after standing still, they can be punctured with a fine needle and a small amount of pigment can be replenished. If the bubble diameter is greater than 0.3mm, it should be wiped clean with alcohol and recolored to avoid obvious blemishes after baking.
V. Environmental Control: Temperature, Humidity and Cleanliness Management
Temperature and humidity requirements
The coloring workshop needs to maintain a temperature of 20-25℃ and a humidity of 40%-60% RH. When the humidity is higher than 70%, the pigment is prone to absorbing water vapor, causing the surface to turn white after curing. When the temperature is below 15℃, the drying speed of the pigment slows down, which may stick to the tool and affect the filling accuracy.
Cleanliness management
Dust particles in the air (such as impurities ≥5μm) will form “particle defects” if they fall into uncured pigments. The workshop needs to be cleaned regularly. The coloring area is equipped with a dust-free operation table (with a cleanliness level of 10,000), and the operators must wear masks and finger cots.
Vi. Quality Inspection and Rework: Timely correct and fill defects
Visual inspection after coloring
Observe the following content with a 5-10 times magnifying glass:
Whether the color separation boundary is clear, and whether there are any “rough edges” or color mixing;
Whether the fine lines (such as the strokes of characters) are complete and whether there is any missing color;
Check if the surface is smooth and free of bubbles, depressions or pigment accumulation.
Rework operation specifications
If the wrong color needs to be removed, it should be soaked in a thinner for 30 minutes to soften the pigment, and then removed with an ultrasonic cleaner. Do not forcibly scrape to avoid damaging the metal base.
The reworked badges need to be re-electroplated (as the thinner may damage the adhesion of the electroplating layer), and then undergo secondary coloring to avoid uneven secondary filling due to a rough base.
Post time: May-08-2025