Carton manufacturers often buy high-speed printing machines, but they are all produced at low speeds. If it encounters multi-color or four-color multi-color printing, it becomes slower, and there will always be deinking, inaccurate overprinting, large production losses, and poor product printing quality. In fact, these can be solved.
Case
An enterprise in Jiangsu, the company has 5 printing machines, mainly for FMCG customers. The company's equipment is a 4-color printing and slotting machine of a well-known domestic brand. At that time, the company produced a speed of 120 sheets / minute, but after the process improvement, it reached 200 sheets / minute. How does this work?
Production conditions
Printing machine: a 4-color printing and slotting machine made by a domestic brand, machine specifications 2400mm * 1200mm, maximum speed: 250 sheets / min, four groups are scrapers, anilox roller: 250 mesh, all 4 colors;
Carton: four colors: red (text on the ground), green, yellow, black, carton size: 1480mm * 650mm; corrugated type: B, cardboard thickness: 2.9mm;
Printing transmission method: vacuum adsorption transmission.
First of all, if you want to increase the speed of production, the most fear is the problem of printing deinking and poor color stacking. The first step is to solve the problem of deinking.
Before improvement, the ink viscosity and PH value were adjusted to:
The first color: red viscosity 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 and red and yellow have overlapping colors).
Deinking occurs when the production speed exceeds 120 sheets / minute, so the factory opens 120 sheets / minute. There is no way to increase the speed of the vehicle, and there is obviously a problem with the ink. If the ink viscosity and PH value are not controlled, then the problems of poor printing effect and deinking will exist.
After improvement, the ink viscosity and PH value are adjusted to:
The first color: red viscosity 8 seconds, PH value: 8.9 (and requires the color density of the ink to be higher);
Second color: green viscosity 9 seconds, PH value: 8.5;
Third color: yellow viscosity for 10 seconds, PH value: 8.2;
Fourth color: black viscosity 12 seconds, PH value: 8.0 (black and red and yellow have overlapping colors).
After the on-site improvement, the speed of the printing machine can be opened to 160 sheets / minute, but the deinking phenomenon and the overprint effect are still somewhat poor, and the color registration still has some problems. The color registration accuracy can only be controlled at 1.5mm. At this time, it is possible to solve the problem of overprinting and overlapping by measuring the thickness of the cardboard.
step
1. First measure the thickness of the cardboard, the measured value is: 2.9mm;
2. After the cardboard enters the paper feed wheel, the measurement is performed again. The thickness of the cardboard is 2.7 mm;
3. Through the first color printing unit, the cardboard thickness is 2.65mm, but the red printed surface cardboard thickness is 2.4mm;
4. Through the second color, the cardboard thickness is 2.65 mm and the printing surface is 2.6 mm;
5. Through the third color, the cardboard thickness 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.
Here we see that the cardboard has been crushed. The thickness of the cardboard has been lost by 0.2mm from the beginning of the paper feeding. The pressure of the first color is too heavy in the back, and the thickness of the cardboard and the printing surface is lost, causing poor overprinting. Therefore, if you want to overprint in the future, you must increase the printing pressure. Higher printing pressure will cause deinking and printing paste, so reduce printing pressure and paper feed pressure.
All pressures are readjusted
1. First measure the thickness of the cardboard, the measured value is: 2.9mm;
2. Adjust the paper feed gap and then measure it. The cardboard thickness is 2.85mm;
3. Through the first color printing unit, the cardboard thickness is 2.85mm, but the red printed cardboard thickness is 2.75mm;
4. Through the second color, the cardboard thickness is 2.85mm and the printing surface is 2.75mm;
5. Through the third color, the cardboard thickness 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.
Printing plate pressure readjustment
First adjust the printing plate pressure to the maximum, and then gradually reduce the plate pressure. When the printing surface appears on the cardboard, some printing plates are not stained with ink, you need to stick tape on the back of the printing plate to make up the printing plate surface, reducing the plate pressure can reduce the amount of ink on the printing plate.
After the above adjustments, the vehicle speed can be driven at 200 sheets / minute, and the phenomenon of printing deinking is solved, but the printing position is still 1.5mm. Then through the on-site search and found that the problem lies in the paper feed unit. When the vehicle speed is too fast, the paper feeder at the rear stacks the paper in the paper feed section too high, and the paper feed guide is not used. The slotted Knife Set has a gap of 5mm between the upper and lower knife.
Paper feed unit adjustment
1. Adjust the width of the rear baffle of the paper feed section to a width of 652mm, and the width of the cardboard to 652mm, so as to prevent the cardboard from moving back and forth.
2. When the width of the paperboard becomes smaller, the paper guide bar has caught the paperboard above the paper feed section, so that the paper feed surface forms ∠, that is, one sheet of paper is sent out, and the next one on top. Pressing too much paper causes the paper to be delayed, causing inaccurate color registration or skewed paper output.
Slotted unit adjustment
Add a paper-drawing sponge to the edge of the slotted knife holder, which reduces the slotting gap. After adjustment, the gap between the upper knife holder and the lower knife holder is 2mm.
After several times of printing machine debugging, and then increase the printing machine speed to 200 sheets / minute, printing and register all normal, but the printing effect is better than low-speed printing. The ink layer is thicker when printing at low speed, but the color is not beautiful enough. In the later stage, through further improvement, the number of printing downtimes was reduced, and the average production per hour was more than 10,000 sheets.
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