The use of equipment, consumables, see carton printing problems

At present, the packaging carton printing is booming, and the customer's requirements for product quality are also getting higher and higher. How to avoid problems in production and improve product quality has become the company's goal. Printing is a systematic project, and it is also a dynamic process. The condition of equipment, the level of technicians, ink and printing materials are all factors that affect product quality.

There are mainly three types of carton printing methods: first offset printing and then printing, flexo printing, preprinting and offset printing. With the improvement of printing technology, flexographic printing has been adopted by various cartons companies with its high quality and high efficiency. This requires companies to start small and improve printing.

Printing Equipment

Printing equipment is one of the five major elements of printing. Good equipment is the prerequisite for the production of high-quality products. The use of equipment, precision adjustment, and good or bad maintenance directly affect product quality.

Pay attention to the adjustment of pressure

The ink transfer and printing section of the flexographic printing press has four rollers, an inking roller, an anilox roller, a plate cylinder, and an impression cylinder. The following figure shows the schematic diagram of the ink transfer section of the flexographic printing press. Whether the pressure between the four is appropriate or not has a direct impact on the transmission of ink, which in turn affects the quality of the product.

n Printing pressure

The printing pressure is the pressure between the plate cylinder and the impression cylinder. Its main function is to evenly transfer the ink on the plate to the substrate. Many problems in the printing process are caused by improper pressure adjustments, such as too much or too little ink.

If the printing pressure is too heavy, on the one hand, it is easy to make the lines thicker on the substrate, the dot is enlarged, and the precision of the graphic and text is reduced. In addition, excessive embossing force can also deform the tile and reduce the strength of the cardboard. If the pressure is too light, the proper amount of ink cannot be transferred on the substrate, and the ability to reproduce graphic images is poor. Lines are prone to break. Lines are prone to false imprints, directly affect the printing effect, and printing may not be performed properly. .

The adjustment of the printing pressure is to make the ink even and medium, and the ink is clear. The tile surface has no dents and flatness is not deformed. Once the pressure is determined, do not adjust casually.

n Printing ink pressure

Printing ink pressure is the pressure between the anilox roller and the printing plate. Its main function is to evenly transfer the ink of the anilox roller to the printing plate. In actual operation, the influence of the printing pressure of the printing plate on the printing quality is very important. If the printing pressure is too heavy, the plate is easy to insert ink, which affects the quality of the product and also affects the printing rate of the printing plate; if the pressure of the printing ink is too light If the plate is not inked, it cannot be printed. Therefore, during the printing process, adjustments should be taken to ensure that printing can proceed smoothly.

n Ink control pressure

This pressure is the pressure between the ink roller and the anilox roller. It controls the thickness of the ink, which is the size of the ink, and evenly transmits the ink. The pressure is inversely proportional to the thickness of the ink layer, and the pressure is too large. The ink layer will be too thin, otherwise it will make the ink layer too thick. If a change in the amount of ink is found during the printing process, first check whether the pressure has changed and carefully adjust it.

These three pressures are related to the entire transfer process of ink from the ink tank to the cardboard. It is the key to the amount of ink on the board and the uniformity of printing.

Pay attention to the adjustment of equipment accuracy

In the printing process, the plate cylinder, impression cylinder, anilox roller, ink roller, and transmission gears of the printing press, due to various factors, may change their own precision and adjustment accuracy, thus affecting Printed image accuracy and quality. During the printing process, careful inspection should be carried out and problems should be discovered and solved in a timely manner.

The precision adjustment between the drums mainly has the problems of concentricity and parallelism. The concentricity mainly consists of the concentricity between the drum body and the supporting journal and between the rollers. The two concentricities must be adjusted. When the printing press is in normal operation, the vibration error cannot exceed 0.01mm, otherwise there will be ink transmission and dot printing failures. The main idea is to expand, but the image dot print is not clear or printed. The accuracy of gears is the basis for ensuring the concentricity of the rollers. The accuracy of the transmission gears changes, and mechanical defects such as micro-vibration are generated, which brings certain difficulties to the printing of the network cable, and the entire printing cannot obtain an ideal pressure. Mechanical vibration can also cause damage to the anilox roller and plate, affecting the service life and product quality.

The parallelism mainly refers to the relative position of the axes of the two rollers parallel to each other. If the axes of the two rollers are not parallel, the size of the gap at both ends will be different, resulting in the difference in the pressure between the rollers and affecting the amount of ink transfer. Taking an impression cylinder and a printing plate cylinder as an example, the pressure at the small end of the gap is large, and the amount of ink in the printed matter is sufficient. At the large gap end, the printing pressure is small, the amount of ink transfer is small, and the amount of printing ink is light. In the same printing surface, a failure occurs when one end is dark and the other end is light. Similarly, the unevenness of the gap also causes inconsistencies in ink transfer between the ink roller and the anilox roller, between the anilox roller and the plate cylinder.

In addition, pay attention to the condition of the ink roller and the anilox roller. If the surface of the roller has grinded lines or scratches, in the case of printed dot products, the ink is uneven and the color is uneven. The printed cable is more visible. Found worn silk or scratches should be replaced in time.

In the daily production process, in addition to maintenance, the cleanliness of the workshop environment should also be noted. If the surface of the transmission gear is not clean and there is dirt, the transmission accuracy will also be affected.

Note the choice of anilox roll

The anilox roller can be regarded as the core of the ink transfer system of the flexographic printing machine. The quality of the anilox roller can be directly affected by the quality of the anilox roller. In addition, the depth, shape, and surface finish of the cells also affect the ink transfer performance of the anilox roll.

The number of lines of the anilox roller is not as high as possible. According to the type of printing press, printed graphics, substrates and economic factors to consider. In general, the higher the number of anilox roller lines, the smaller the amount of ink transferred, and the lower the number of lines, the greater the amount of ink transferred. In actual operation, the slower the printing speed is, the larger the ink transfer amount is, and the larger the viscosity is, the larger the ink transfer amount is. It can be seen that the lower number of anilox rollers can be considered when performing on-site printing or block printing, the use of larger-viscosity inks and the combination of slightly slower printing speeds. In contrast, high-line and color-level dot printing is performed. A higher number of anilox rolls can be used, with lower viscosity inks and faster printing speeds. Of course, this can be used in conjunction with the actual situation.

The accuracy of corrugated cartons printing graphics is generally not very high, and the corrugated board surface roughness and other factors also determine that the need for expensive anilox ceramic anilox rolls and general metal anilox rolls are sufficient. The number of corrugated box printing lines is generally 55-65 lines/in, and some are as high as 85 lines/in. According to the optional relationship between the anilox roller and the printing plate network line 4:1, 200 lines/in, 300 lines/in can be used. The anilox roller can be provided with an anilox roller of 150 threads/in if there is a product for coating or large field printing. Therefore, 150 lines/in anilox roller can be considered for large field printing, 200 lines/in for daily general corrugated box printing, and 300 lines/in for high-precision color overprinting. If during the printing process, the number of anilox roller screens does not match the quality requirements of the printed material, it should be replaced in time.

The darkness of the anilox roller on the sculpted hole on the Internet creates a large amount of ink, and the printed ink is thick and deep, with a bright color. However, excessive ink should pay attention to the dryness of the ink layer to prevent the product from sticking to the ink. On the contrary, the engraved network cable is shallow, the amount of ink transferred to the printing plate on the anilox roller is small, and the printed product lacks a certain amount of ink and the color is poor. At present, the depth of the general anilox roller network engraving is between 22μ and 30μ. In the production, according to the different nature of the substrate, the ink and the product adopt the corresponding network line depth.

The anilox roller has a good finish, and the ink is even and delicate, forming a good spot. Especially in the flat-screen printing is more obvious, otherwise it will make the ink uneven, dot-tone tone formed after the dot printing is not ideal to restore the level of clarity will be damaged. Attention should be paid to the maintenance of the anilox roller during production, and the ink should be carefully filtered to prevent scratches caused by particles.

In flexographic printing, in addition to improperly angling the angles of the screens of various colors, the relationship between the angles and the number of lines of the anilox roll and the printing plate lines may cause moire. If a flexible version is used to make the film, Avoid this phenomenon during plate making. However, the phenomenon of hitting the turtle in actual production occurs from time to time. The net holes on the anilox roller are generally sculpted at an angle of 45 degrees with the axis. Therefore, in the printing process, the angle of the 45-degree cable is avoided.

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printing material

Ink

Ink selection is appropriate

Printing is to receive ink and transfer ink through the printing plate, and then reproduce the pattern and the image through the color of the ink. The printability of the ink is closely related to the quality of the printed matter. The printing ink for board printing is water-based ink. The quality of the printing ink is related to the pure, bright, uniform transmission and adhesion of the printing color. Special attention must be paid during the selection and use.

There are no significant differences between high-quality inks and color marks, and the touch is delicate, viscous, and has high fineness of ink particles, and has no corrosion or corrosivity to the printing plate. Add water or alcohol solvent to dilute without precipitation, coagulation and other abnormal phenomena, stirring without foam, mixed with other ink color, mutual solubility is good, the ink color is pure, good fluidity, high adhesion to the substrate. If the inks undergo some changes in their suitability during the printing process, they will directly affect the printing effect.

For example, a high-quality carton print with a line number of 80 to 100 lines/inch is selected, and the corresponding number of screen lines of the metal anilox roller must be 240 lines to 300 lines/inch before the metal anilox roller and the plate screen cable are used. The ratio is 3:1. That is, a dot on the printing plate needs to be supplied with ink by nine dots on the metal anilox roller so as to achieve the purpose of uniformly transferring the ink volume and ensure the correct color and sharpness of the printed article. If the ink's grain size becomes coarse and indelible, a satisfactory product cannot be obtained.

Based on this factor, it is required that the printing ink must be delicate so that each screen on the metal anilox roller can obtain an even amount of ink and be correctly delivered to each dot on the printing plate. Printing products printed in this way have uniform outlets and clear gradations. On the contrary, ink fineness does not meet the requirements, the dots on the metal anilox roller to eat ink uneven, easy to string ink between nodes, resulting in dirty spots, affecting the appearance and level of image, color reproduction is easy to distort, easy to lose the tone level area.

Additives to pay attention to

Auxiliaries are used as adjusting liquids for inks. They play an important role in the printability of inks in printing. Additives can adjust the shade of ink, control the color balance, and the drying speed of ink. At the same time, various additives are used for printing plates. The Indian print rate also has an effect.

The flexographic printing solvent is generally formulated with alcohol-soluble and water-soluble solvents. The formula should be based on various factors such as the production conditions, temperature and humidity, printing speed, printing area, and ink thickness. When preparing, it should be noted that the ink is dry and normal in the printing process, and there should be no sticky ink or piled ink phenomenon. In addition, the solubility of the auxiliaries is better, and the inks that are dispensed are more fluid and uniform. In this way, the color of ink delivered is uniform, and the printed image can be uniform in color, clear in dots, rich in gradation, and bright in brightness.

There should not be too much defoamer in the ink, too much defoamer in the original ink itself, or too much defoamer in the ink. After printing, India