First, the performance of the ink:
1) Concentration: the ink with high density is used less in printing, and the ink color is better; the ink with lower concentration is used more in printing, and the ink color is lighter;
2) Fineness: the size of the ink particles, high ink fineness, large ink concentration, clear and full dots of the printed matter; low ink fineness, the dots of the printed matter are prone to hairiness, and the printing plate has a low durability;
3) The viscosity and viscosity are large, which is easy to cause uneven ink transfer, dot shaving and pattern, etc .; the low viscosity is easy to cause ink emulsification and scumming;
4) Fluidity: large fluidity will make the level of the picture and text unclear and the ink color is not full; the small fluidity will make the spread of the ink not smooth and uneven, and it is easy to cause the front and back to fade or the front to fade on the same printing surface Deep phenomenon
5) Lightfastness: Ink with good lightfastness, printed products with gorgeous color, full and strong graphic and graphic dots, full of three-dimensional sense, and can be stored for a long time; ink with poor lightfastness, the color of the printed product is easy to become lighter and darker;
6) Water resistance, acid resistance and alkali resistance: For offset printing inks, special attention should be paid to water resistance, acid resistance, alkali resistance, water acid resistance and alkali resistance inks. The printed products have bright colors, clear layers and clear dots. ; Water-resistant, acid-resistant, alkali-resistant, poor ink, the printed product is gray and weak, the level is unknown, and the dots are not smooth.
Second, fountain water
The pH of the dampening water is generally between 3.8 and 4.6. In actual production, it should be adjusted according to the specific conditions of the printing conditions. If the dampening water is too acidic, it will affect the oleophilic foundation of trachoma and graphics in the blank part of the layout. The corrosiveness will increase, which will easily cause patterning and reduce the printing durability of the printing plate. At the same time, the ink is easy to emulsify, the ink roller will deink, and the printed matter will be dull and dull.
If the dampening water has too weak acidity, it will weaken the hydrophilic and oil-repellent properties of the blank part of the printing plate, and the plate surface is easy to get dirty and the paste phenomenon will occur due to the expansion of the printed dots. The layout is easy to get dirty)
Three, color order
Color sequence refers to the sequence of overprinting of each color printing plate in multi-color printing. Different color sequences will produce a variety of different printing effects. It is important to arrange color sequences reasonably. But the color sequence is not absolute, the general arrangement of color sequence is:
Monochrome machine: yellow → magenta → cyan → black two-color machine: black → yellow, magenta → cyan (print landscape) or cyan → red (print characters);
When there are gold, silver, and full-page solid printing, it is generally necessary to first gold, silver, and full-page solid printing, and then set four-color ink after the ink is dry. 4. Batch printing
1) Check whether the specifications of the four-color film are consistent (whether the four films are complete)
2) Check whether the pictures are complete with reference to the proofs;
3) Stabilize the water and ink volume to reach the level of water and ink to ensure the consistency of the ink color of the same batch of printed products;
4) Minimize downtime or clean the blanket after downtime (some version paper can be placed)
4. When officially printing
When printing officially, the operator should concentrate on:
(1) Look: Look at the operation of the machine, check the ink color, registration and dot quality of the proofs;
(2) Listen: Listen for abnormal sounds of the machine, and hear noises in the vibration sensitive area of ​​the machine;
(3) Touch: Touch the parts of the machine that are easy to heat up due to wear, whether there is a significant temperature change;
(4) Smell: Smell whether there are burnt electrical appliances and other abnormal odors. (Please pay more attention to the power cord of the UV machine when printing with UV ink);
(5) Check: Check the condition of the printed product and the machine for abnormalities, find the problem, and eliminate it in time.
Five, how to identify the size of moisture
To identify the major problem of moisture, first look at the layout moisture. This point depends on the operator's experience. Generally speaking, the water content is large, the reflection light is strong on the layout, and the side view is bright; on the contrary, the reflection light is weak on the layout, and the side view is dark;
If the moisture is too large, it can be observed from the following points:
(1) Use jammed paper to shovel ink on the ink roller, and tiny water drops will be left on the jammed paper;
(2) There are tiny water droplets on the water roller, and there is deinking or water droplets in the ink roller group;
(3) After the water is turned off or the machine is shut down for a long time, the water content of the page has not dried up;
(4) The imprinted dots are empty and the ink color is dull and dull;
(5) There are water shadows or water droplets on the tip of the rubber roller.
Six, control water balance
Ink and water are not absolutely incompatible. In the actual printing process, the ink and water are squeezed by the rubber roller and the rubber roller, they will fuse together, emulsifying the ink. There are two emulsified states of the ink: when the water is large in ink, it forms "oil-in-water"; when the water is small and the ink is large, it forms "water-in-oil".
In the offset printing process, the mastery of water-ink balance is closely related to the normal transfer of the imprint, the shade of the ink color, the accuracy of the color registration, the drying of the printed matter and the stickiness, etc. Generally speaking, if the water is large, the ink will be emulsified and the color of the ink will be light; if the water is small, the blank part of the layout will adhere to the ink and produce stains. Therefore, the key to printing is to control the water-ink balance of offset printing.
Seven, control the water and ink balance
To control the balance of water and ink, it is generally necessary to master the principle of less water and thicker ink. Low water refers to the premise that the blank part of the layout is not sticky; thick ink refers to an appropriate increase in the amount of ink based on the lack of water. In the printing process, the most taboo point is the big ink. When considering the amount of water, the size and distribution of the graphic area of ​​the layout, the thickness of the printed ink layer, the nature of the printing paper, the performance of the ink, the speed of the machine, the temperature and humidity of the workshop, the PH value of the fountain solution, and the added Adjuvants and other circumstances.
8. Cleaning the blanket, the ink roller must be cleaned when changing colors
After a period of printing, the blanket will accumulate paper wool, paper powder, ink skin and other dirt, which reduces the quality of the printed matter, so the blanket should be cleaned in time, especially when the paper with low strength is printed. The accumulation of paper dust is more serious, so it is necessary to clean it more often.
If the ink roller set is not cleaned when changing colors, it will affect the purity of the new ink color, especially when changing from dark ink to light ink. For example, when the black ink is replaced by the yellow ink, if the black ink is not cleaned, the yellow ink will be black, which will affect the quality of the printed matter. Therefore, the ink roller set must be cleaned when changing colors.
Nine, the main factors of inaccurate overprint
Before and after overprinting is not allowed:
(1) Printing machine
a. The locking screw of the world adjustment disk is not fixed, or the M5 hex screw on the paper feed rocker arm is fixed tightly;
b. Whether the copper sleeve of the paper pusher is worn;
c. Paper feed teeth are worn;
d. The printing pressure is too low;
e. Gear wear;
f. The blanket is too loose and not tight.
(2) Paper
a. Paper cutting accuracy is not high;
b. The amount of water is too large during printing, and the paper has expansion and contraction.
(3) Other
a. There is a problem with the printing plate or the original;
b. The jammed paper stack is too high or the pressure plate is too heavy, causing the jammed paper to skew.
The left and right sets are not allowed:
a. Whether the left and right bezels are too tight or whether the screws of the left and right bezels are fixed;
b. The length of paper jam varies;
c. The drum moves left and right;
10. Reasons for oil contamination
Oil can be divided into two categories: one is because the blank part of the layout feels the ink and appears in a greasy state, commonly known as "greasy"; the other is because the ink is emulsified evenly distributed on the layout with very fine particles, commonly known as "greasy" Dirty ".
The causes of oil contamination are:
(1) Printing plate
a. The printed version is not of high quality (bad version or regenerated version);
b. Insufficient exposure time during printing and too low developer concentration;
c. The protective glue on the printing plate is not cleaned;
d. The blank part of the printing plate is oxidized;
(2) Printing machine
a. The pressure of the version is too light;
b. The pressure between the water rollers is too light;
c. Ink viscosity is too low;
d. The surface of the blanket is aging;
e. Paper powder and paper wool wear plate;
f. Improper PH value of fountain solution.
11. Reasons for the different shades of ink before and after
In actual printing, sometimes it is found that the ink color on the same screen has different shades before and after, and often the ink color is mostly dark before and then light, and the ink color is light before and after
The reasons for the different shades of ink before and after are:
(1) Drum part
a. Drum gears or bearing journals wear out over time.
b. The roller journal is not concentric with the roller shell.
c. The pressure between the plate roller and the printing plate is too heavy, which causes a jump
(2) Ink roller part
a. Aged roller surface aging
b. The ink roller has not been cleaned for a long time.
c. Ink viscosity is too high
12. How did the ink bar arise and how to eliminate it?
Ink bar refers to when printing flat screen or on-site printing, there are obvious deep streaks in the axial direction on the printing plate and the printing, commonly known as "black bar" or "black bar head".
The reason and elimination method of ink stick are:
(1) The drum gears wear out over time, and a new set of gears should be replaced;
(2) The printing pressure is too high or the pressure between the plate cylinder and the rubber cylinder is too large. The appropriate pressure should be adjusted;
(3) Paper wool, ink skin and other dirt are embedded between the gears. All kinds of dirt between gears should be removed, new gear oil should be added to strengthen the cleaning and maintenance of the machine;
(4) The pressure between the plate and the form roller is too large, and the pressure between the form plate and the plate should be adjusted;
(5) If the surface of the plate roller is uneven or the roller core is curved or not straight, a new ink roller should be replaced;
(6) If the ink is too thin, an appropriate amount of 0 # ink should be added to enhance the viscosity of the ink;
(7) The paper is rough and the surface strength is poor. Wash the blankets frequently, and add 6 # ink to the ink to reduce the viscosity of the ink and reduce the degree of paper powder and hair loss
13. How to solve the cause of water bar?
Water bar refers to the printing of flat screen or solid prints, the printing plate and printed parts have an axially obvious light streak, commonly known as "white bar" or "white bar head".
The water bar is generally caused by the water delivery part. The causes and solutions are:
(1) The pressure between the water supply roller and the main ink leveling is too large, the pressure between them should be readjusted to reduce the pressure properly;
(2) Ink emulsification, too much ink on the surface of the water roller;
(3) If the water content on the page is too large, the water supply should be reduced, the blanket should be cleaned, and the ink roller should be cleaned in severe cases;
(4) The acidity of dampening water is too strong, so the acidity of dampening water should be reduced.
14. How to eliminate the cause of the flower version?
The flower version refers to the shrinkage and emptiness of the dots on the printing plate, the fat sensitivity is weakened, the fine dots are lost, and the color is dull
The cause and elimination of the flower version are:
(1) The pressure between the plate cylinder and the rubber cylinder is too large, and the thickness of the cylinder lining should be reduced;
(2) The pressure between the water roller and the water roller is too small (the water is too large), the pressure of the water roller and the water roller should be adjusted appropriately;
(3) The dampening water is too acidic, so dilute the dampening water and reduce its acidity;
(4) If the water supply volume is too large, the water supply volume should be reduced;
(5) The viscosity of the ink is too large, a certain amount of ink adjustment oil should be added to the ink to reduce the viscosity of the ink;
(6) The printed version is already in the process of plate making and printing, and should be replaced with a new version.
Fifteen, what are the reasons for confusing? How to eliminate?
The causes and elimination methods of paste edition are:
(1) The pressure between the plate cylinder and the rubber cylinder is too large, the pressure between the plate cylinder and the rubber cylinder should be reduced;
(2) The pressure between the plate roller and the printing plate is too light, and the pressure should be readjusted (2.5-3mm);
(3) The pressure of the plate roller and the printing plate is too heavy, and the pressure should be reduced;
(4) The acidity of dampening water is too strong, so the acidity of dampening water should be reduced appropriately;
(5) If the ink is too thin, add "0 #" ink to the ink;
(6) The amount of ink is too large, the amount of ink supply should be reduced;
(7) If excessive amount of desiccant is added in the ink, the ink roller should be cleaned to reduce the amount of desiccant in the ink;
(8) The printed version is too thin for trachoma and should be replaced with a new version.
16. The causes and elimination methods of rubbing on the back
Smudged back refers to the stack of freshly printed sheets stacked together. The ink on the lower sheet rubs on the back of the upper sheet, causing contamination of the printed sheet.
The reasons for the back rubbing are as follows:
(1) If the ink does not dry well or the amount of ink is too large, an appropriate amount of desiccant and anti-sticking agent should be added to the ink or the amount of ink should be reduced;
(2) The stacking height of the paper is too high, the stacking height of the paper should be reduced;
(3) The ink is not dry and the pressure paper is too heavy;
17. Reasons for ghosting
There are two types of ghosting, commonly known as double printing and ghosting: axial ghosting, that is, the imprint of the ghosting part is approximately parallel to the axis of the roller; circumferential ghosting, that is, the imprint of the ghosting part is perpendicular to the axis of the roller.
Causes of axial ghosting:
(1) The precision of the machine is poor and the bearings are worn.
(2) Axial displacement of printing plate cylinder or rubber cylinder occurs.
(3) The axial movement of the ink roller (or the plate roller is not matched with the original machine)
(4) Paper "lotus leaf"
The causes of Zhou Xiang ghosting are:
(1) The blanket is not stretched tightly
(2) The roller pressure is not in place
(3) The machine has been used for many years, the roller gears, bearings are worn or the gap between the three rollers is too large
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