Carton production enterprises often buy high-speed printing machines, but they operate at low speeds. If encountering multi-color or four color stacked printing, it becomes slower, and there are always phenomena such as deinking, inaccurate overprinting, high production losses, and poor product printing quality, which can be solved.
case
An enterprise in Jiangsu has 5 printing presses, mainly for Fast-moving consumer goods. The company's equipment is a well-known domestic brand 4-color printing slotting machine. At that time, the company's production speed was all at 120 sheets/minute, but after process improvement, it reached 200 sheets/minute. How did this happen?
Production conditions
Printing machine: a domestic brand 4-color printing slotting machine, machine specification: 2400mm * 1200mm, maximum speed: 250 sheets/minute, four groups are all scrapers, Anilox is 250 meshes, 4-color is all;
Carton: Four colors: red (with text added on site), green, yellow, and black. Carton size: 1480mm * 650mm; Corrugated type: B, cardboard thickness: 2.9mm;
Printing transmission method: vacuum adsorption transmission.
Firstly, if you want to increase the speed of production, you are most afraid of the problems of printing deinking and color stacking. The first step is to solve the problem of deinking.
Before improvement, after on-site inspection, the ink viscosity and pH value were adjusted to:
First color: Red viscosity for 12 seconds, pH value: 8.6;
Second color: green viscosity 13 seconds pH value: 8.3;
Third color: yellow viscosity 12 seconds pH value: 8.5;
Fourth color: Black viscosity 14 seconds pH value: 8.7 (black has overlapping colors with red and yellow).
When the production speed exceeds 120 sheets per minute, the deinking process occurs, so the factory operates 120 sheets per minute. There is no way to increase the speed, there is clearly a problem with the ink here. If the viscosity and pH value of the ink are not controlled, there may be problems with poor printing performance and deinking.
After improvement, the ink viscosity and pH value were adjusted to:
First color: Red viscosity for 8 seconds, pH value: 8.9 (and requires a high color concentration of the ink);
Second color: green viscosity for 9 seconds, pH value: 8.5;
Third color: yellow viscosity for 10 seconds, pH value: 8.2;
Fourth color: Black viscosity for 12 seconds, pH value: 8.0 (black has overlapping colors with red and yellow).
After on-site improvement, the printing locomotive speed can reach 160 sheets per minute, but the deinking phenomenon and overprinting effect are still some poor, and there are still some problems with color registration. The color registration accuracy can only be controlled at 1.5mm. At this point, the problem of overprinting and color stacking can be solved by measuring the thickness of the cardboard.
step
1. Firstly, measure the thickness of the cardboard, with a measurement value of 2.9mm;
2. After the cardboard enters the paper feeding wheel, it is measured again, and the thickness of the cardboard is 2.7 mm;
3. Through the first color printing unit, the thickness of the cardboard is 2.65mm, but the thickness of the red printing surface cardboard is 2.4 mm;
4. Through the second color, the thickness of the cardboard is 2.65 mm, and the printing surface is 2.6mm;
5. Through the third color, the thickness of the cardboard is 2.65 mm, and the printing surface is 2.45 mm;
6. Through the fourth color, the cardboard thickness is 2.6mm and the printing surface is 2.3mm.
From here, it can be seen that the cardboard has been crushed, and the thickness of the cardboard has lost 0.2mm since the paper was fed. The pressure on the first color is too heavy, resulting in a loss of thickness on the cardboard and printing surface, resulting in poor overprinting effect. So if you want to overprint well in the future, you must increase the printing pressure. Excessive printing pressure can cause deinking and printing paste, so it is necessary to reduce the printing pressure and paper feeding pressure.
All pressure readjustments
1. Firstly, measure the thickness of the cardboard, with a measurement value of 2.9mm;
2. Adjust the paper feed gap and measure again. The thickness of the cardboard is 2.85mm;
3. Through the first color printing unit, the thickness of the cardboard is 2.85mm, but the thickness of the red printing surface cardboard is 2.75mm;
4. Through the second color, the thickness of the cardboard is 2.85mm, and the printing surface is 2.75mm;
5. Through the third color, the thickness of the cardboard is 2.85 mm, and the printing surface is 2.73 mm;
6. Through the fourth color, the cardboard thickness is 2.82mm and the printing surface is 2.7mm.
Readjust the printing plate pressure
Firstly, adjust the printing plate pressure to maximum, and then gradually reduce the plate pressure. When the printing surface appears on the cardboard, some of the printing plate is not coated with ink. Therefore, it is necessary to apply tape to the back of the printing plate to make it flat. Reducing the plate pressure can reduce the amount of ink on the printing plate.
After the above adjustments, the vehicle speed can be set at 200 sheets per minute, and the printing deinking phenomenon has been resolved. However, the printing displacement is still 1.5mm. Then, through on-site investigation, it was found that the problem lies in the paper feeding unit. When the vehicle speed is too fast, the rear paper loading personnel pile up too much paper in the feeding section, and the paper feeding guide rod is not used. The gap between the upper and lower knives of the slotting knife group is 5mm.
Paper feeding unit adjustment
1. Adjust the width of the rear baffle of the paper feeding section to 652mm, and the width of the cardboard to 652mm to prevent the cardboard from moving back and forth.
2. When the width of the cardboard decreases, the paper guide rod has already caught the cardboard above the paper feeding section, causing an angle to form on the paper feeding surface. This means that one piece of paper is transported out, with the next piece coming down from above. This way, the conveyed cardboard will not be delayed due to the excessive weight of paper being pressed on top, causing inaccurate color matching or skewed paper output.
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Install a paper sponge at the edge of the slotted knife holder to reduce the slot gap. After adjustment, the gap between the upper and lower knife holders is 2mm.
After several adjustments to the printing machine and increasing the speed to 200 sheets per minute, the printing and color matching were all normal, but the printing effect was better than that of low-speed printing. When printing at low speeds, the ink layer is relatively thick, but the color is not beautiful enough. Through further improvement in the later stage, the number of times the printing machine stops and erases the plate has been reduced, with an average production of over 10000 sheets per hour.