How to use post-press processing to control print color and gloss

"Chinese character information processing and printing revolution" was rated as China's major engineering and technological achievements in the 20th century, marking that China has successfully completed the second printing technology revolution from lead line printing, lead printing to photocopying and offset printing. The large-scale technological transformation covering the entire printing industry and related industries was nearly a millennium away from the first printing revolution in our country, which resembles the printing of engravings and the invention of movable type printing. “In the past thousands of years, some traditional industries have disappeared under the impact of new technologies, and the printing industry has always been able to quickly integrate with the new technologies of various dynasties and gain new opportunities for development from the use of new technologies” ( Excerpted from the Director of the Press and Publication Administration, Mr. Shi Zongyuan, at the 7th World Printing Conference on the theme of "The Challenge of the 21st Century Knowledge Economy on the Printing Industry".

The surface purification process is to generate strong ionization and excitation on the printed matter by the electrostatic electric field, which can automatically absorb dust, fluff, accelerate the oxidation of the ink, and impact the surface of the crystallized conjunctiva.

The color and gloss of prints are reflected by the surface of the printing medium, the thickness of the ink layer, and the degree of ink drying. When its amount has been timed, through innovative surface purification technology, it can improve the effect of prints and enhance the color and luster of prints.

The printing surface is the general name for the surface of the printing carrier and the ink layer, and is also the material basis for the color and gloss performance of the printed matter. In today's rapid development of modern printing, printing carriers are mainly paper and polymeric film two categories.

The smoothness and gloss of paper are mainly determined by the papermaking raw materials and the papermaking process. When the surface smoothness and gloss of the paper are high, no pressure is required to carry out embossing, and the contact area between the printing plate and the blanket can be maximized, and the transfer of the dots can be completed more uniformly and completely. Clear, rich levels, soft tone, full color, bright gratifying.

In order to improve the smoothness and gloss of the paper, paper mills apply water-based paint to the surface of the base paper and heat and dry it. In general, the heating and drying methods for water-based paints include hot-air drying and dry-cast drying. Coating papers have great differences in the mechanisms and processing methods used to remove water from applied coatings. The hot air surface is volatilized and dried. In the drying stage, hot air is used to force drying from the surface. Most of the water is evaporated on the coated surface. The molecular structure of the coating is arranged in an ordered manner along the evaporation direction toward the surface under the effect of heat, and the backside of the cast coating is infiltrated and dried. The drying stage is when the coating is in a wet state, it is pressed with a roller and pressed against a mirror hot cylinder for drying. The moisture of the coating is transmitted through the pores of the fiber. The molecular structure of the coating under the thermal action also follows the evaporation direction, but it is back-facing. Ordered. Regardless of the molecular structure that is arranged on the surface or on the back, there are always some more active molecules that are more active under heating conditions, and there is considerable energy to break away from the attraction of other molecules to the direction of the original row or in the opposite direction. Disorderly movement.

When these coating molecules free from intermolecular gravitational motion reach the working surface of the applicator roll or cast coating cylinder, the enormous pressure generated by the application roller or the working interface of the cast coating cylinder forces them to continue to move and escape the coating in the coating. Stay on the surface. This kind of static on the surface of the coating is exactly the same as that of the application roller or the cast coating cylinder, although it is chrome-plated and throws off the river, but there are still fine lines and uneven positions of rough marks, which results in the absence of molecules when the hot-press coating layer is dried. As a result of the sequence movement, the surface of the paper should have a slight dent in the smooth surface, or increase some of the powder peaks, and thus appear different rough. When the light propagates to the surface of the paper, which is not so conspicuously noticeable, the uneven surface makes the reflection angle change, and the visual signal from the paper surface is weakened, ie, the glossiness is not strong.

At the same time, since the recessed portion of the paper surface needs the ink to reach the surface of the paper before it is dried, the thickness of the ink layer is actually reduced, the density of the ink layer is changed, and the thickness of the ink layer is different from that of the original layer. This actual working condition will also cause the paper fiber to absorb the binder in the ink, and the uneven surface will increase the surface area and increase the surface area, so that the ink will reflect from the surface of the pigment particles and the binder material will be greatly contained in the pores of the paper fiber. After absorption, the refractive index of the pigment suspended between them is poor, resulting in a decline in the transparency of the ink. When performing color printing, if the transparency of the bottom layer ink is poor, it will affect the light transmission on the paper surface and reflect the gloss of the paper surface; when the transparency of the top layer ink is poor, it will affect the light through the upper layer ink and penetrate into the bottom layer ink. , Can not be fully absorbed by the lower layer of ink, the performance of the color should not be formed after the overprint.

A large number of high-speed printing presses at home and abroad, in order to avoid the paper entering a new process when the ink blots are not dry, can easily cause the back side of the printed sheets to be adhered, resulting in the destruction of the surface of the imprinted imprints, and the occurrence of defects in the backing and sticking of the backside of the printed sheets. In the printing press delivery process, a powder spraying device is provided. Commonly used air dusting devices (other electrostatic powder spraying devices and liquid powder spraying devices, because the device cost is higher or only for special blocks, currently used less), is the powdered particulate matter with the compressed air Spray on the printing surface, so that these powder particles adhere to the imprinted layer of viscous ink on the surface of the surface of the imprint.

Based on the theory of particle-size Jones-Higgins,

LaJones and CChiggins use the value of the density ifferences between neighbors to express the granularity, and according to the formula of SΔD=IDa-IDa1, the density difference between adjacencies is obtained. The application of the theory to prints is consistent with the grainy reflection of continuous tone photographs made from silver particles, which creates a coarser, lighter reflection of the light's surface by the particulate new surface of the print. The pulverized particles remaining on the surface of the print not only affect the gloss of the printed product, but also become an isolated layer of granular structure. The penetration of light due to the presence of the coated particles causes obstacles. If we print a layer of yellow (Y) ink on white paper, we spray it for stickiness. On this basis, a layer of magenta (M) ink was printed, and the standard inter-color red (Y+M=R) was originally obtained after the same amount of ink was used twice. Due to the influence of dusting particles, the color of the entire print is caused, and at the same time, the ideal red light appears. The resident permanent opaque mineral particles block only the magenta light reflecting the color of the upper layer ink, and the cyan color just touching the surface of the underlying ink. After the particles, it penetrates the ink on the upper layer, which is reflected by three primary colors, such as white light and the like, thus affecting the adhesion of the next color sequence superimposition and the color of the dot overlap. Similarly, print on the white paper firstly. After the color is sprayed and the other color is printed, the printed dots are inconsistently colored due to the influence of the color and transparency of the dusting particles, which causes the change in transmission density of the other color to change the transmittance and reflectance. Phenomenon, so there are various forms of color change. In addition, the barrier properties of dust particles make the surface energy of the imprint change, which will further affect other processing after printing.

Polymeric thin products such as PE, BOPP, PET and other high-molecular materials are new-type printing carriers that have been rapidly applied in the past 20 years. For example, the biaxially-stretched polypropylene BOPP film causes the microcrystallizing effect of the crystals in the stretching direction (stretching of the plastic melt during the recrystallization process) to cause plastic sliding of the crystals in the film. Arrangement, surface structure change, turbidity from non-oriented (NO) of 0.078-0. 117% mm, reduced to biaxially oriented (BO) of 0.039-0.078% mm, so that increased refractive index, with high transparency (≥ 95 %) and high gloss (≥ 85%) surface gloss.

Plate making

The printing plate production process can be roughly divided into three processes of raw material processing, writing, and engraving.

Raw material processing:

The printing plates of the Dege Printing Institute use red birch wood, which is abundant in Dege, Baiyu and Jiangda counties. It is said that at the time of the creation of the Degas Printing Institute, the birch used was produced on the nearby Mount Oplon. In the early spring of each year, the demand for birch in the printing plate was carved by the Degebuk Institute's budget for the year and submitted to Dege Toast. Dege Toast distributed the amount of materials to the poor people who had amassed birch area by means of a pay difference. After the autumn harvest, the poor people will cut down the birch trees and select the tree trunk that is straight and uncrossed. The sections are cut into sections according to the required size. Then they are cut into pieces of 4-5 cm, and then they are dehumidified and smoked on the floor. After being dried, they will be brought home and placed in a stockpile (or pool). Until the next March or March of the following year, after the wooden properties of the boards have receded, they will be taken out of boiled water, dried, planed, and finally become finished. After processing, the embryonic board is transported to the printing house by livestock and checked into the warehouse after passing inspection.

write:

Before the plates were carved, the Tibetan writer wrote the “Tibetan Documentary Standard 40” written by Dege's famous calligraphers, Ban Bo and Chi Pengwa, and the size and content of the plates. There are generally two methods for writing a printing plate. One is to directly reverse the Tibetan script onto the embryonic board, and it must be strictly proofread before engraving. Another method is to cut the thin upper grade paper into a sample size paper with the same size as the blank board, and then write (or draw) the Tibetan (or portrait) on the sample paper. After careful proofreading, the book will be typed. The paper is paste on the embryonic board with a clear paste. The traces (or images) will naturally penetrate the embryonic board. When the paper is dried to a certain extent, it is soaked with water and the sample paper, handwriting (or portrait) is removed. It will clearly show itself.

Engraved version:

The engraved craftsmen of the Degeban Printing Academy are all trained with teachers and followers. After a strict examination and selection, the engravers are not only highly skilled, but also have a good basis for Tibetan and painting. “In order to ensure deep carving, accurate carving, and good carving, it is stipulated that each person can only engrave a one-inch layout every day. When the edition is first carved out, it is carefully proofread and dug and make mistakes.” After absolutely correcting, put batches of engravings into ghee The pot is brewed, soaked for one day, and then dried out. The roots of a plant called "Suba" are washed with water and dried and put into the storage. In the whole process of engraving, the Printing Academy has attached great importance to the quality of engraving, and from the time of writing to the completion of the engraving, it has undergone about 12 repeated proofreadings. Therefore, the printing plate of Degei Printing & Printing Institute enjoys “the most The classic version of the standard" reputation. Once the engraved version and the version of the layout specification have been determined, no one has the right to make changes without the permission of Degas. At ordinary times, we must also inspect the printing plates and find that plates that are worn out or have jumping or jumper lines must be promptly filled.

Source: pack.cn