Effect of surface purification treatment on color and gloss of printed matter
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The surface purification treatment is to generate strong ionization and excitation of the electrostatic electric field on the printed matter, which can automatically adsorb dust, fluff, accelerate the oxidation of the ink, and impact the surface of the crystallized conjunctiva in central China.
The color and gloss of the printed matter are the printing tools reflected by the surface of the printing carrier, the thickness of the ink layer, and the degree of drying of the ink. When the amount has been timed, through the innovative surface purification treatment technology, the effect of printed matter can be improved, and the printing and color rendering of the printed products can be enhanced.
1 printing surface with color, gloss
The printing surface is the general name of the substrate and the surface of the ink layer, and is also the material basis of the color and gloss of the printed matter. In the rapid development of modern printing, the printing carrier mainly has two major types of equipment consumables: paper and polymeric film.
a, paper
The smoothness and gloss of the paper depends mainly on the papermaking material and the papermaking process. When the surface smoothness and gloss of the paper are high, it is not necessary to increase the pressure when imprinting, and the contact area with the printing plate or the blanket can reach the maximum, and the transfer of the dots can be completed more uniformly and completely. Clear, rich in layers, soft tones, full of color, bright and grateful printing alliance.
In order to improve the smoothness and gloss of the paper, the paper mills apply water-based paint on the surface of the base paper and heat dry the printing alliance. Generally speaking, the heating and drying methods for water-based paints include hot air drying and drying of the cylinder surface by drying and drying. The mechanism and processing method of the coated paper to remove moisture from the applied coatings are quite different. The hot air surface is volatilized and dried. In the drying stage, the hot air is forced to dry from the surface. Most of the water is evaporated by the surface of the coating. The molecular structure of the coating is arranged under the action of the heat in the direction of evaporation, and the surface of the cast coating is permeated and dried. In the drying stage, when the coating is in a wet state, the pressure roller is pressed against the mirror surface drying cylinder for drying. The coating moisture is transported through the pores of the fiber, and the molecular structure of the coating is under the action of heat and also toward the back side. Orderly print the league. Regardless of the molecular structure arranged on the surface or the back, there will always be some more active molecules that are more active under heating conditions, and have considerable energy to break away from the attraction of other molecules and do more complicated directions in the original or opposite directions. Disordered sports printing market. When these coating molecules that move freely from the intermolecular gravitational force reach the application interface of the application roller or the casting coating cylinder, the enormous pressure generated by the application roller or the casting coating cylinder is forced to continue to move and escape the coating. The surface stays down the material market. This kind of static on the surface of the coating, just like the application roller or the casting coating cylinder, is chrome-plated, but there are still fine marks, rough and convex rough positions, which causes the molecules of the hot-pressed coating layer to dry. As a result of the sequential motion, the surface of the paper should have some pitted dents on the smooth surface, or some powder peaks may be added, so that the rough middle printing of different performances appears. When the light propagates to the rough surface of the paper surface which is not noticeable to the surface, the uneven surface changes the reflection angle, and the visual signal from the paper surface is weakened, that is, the gloss is not strong.
At the same time, because the concave portion of the paper surface needs to be filled before the paper surface is dried, the actual thickness of the ink layer is reduced, so that the density of the ink layer changes accordingly, and the middle portion of the original layer is different from the light reflection performance. print. This actual working state also causes the absorption of the binder in the ink by the paper fiber, which is increased by the surface of the uneven surface, so that the surface of the ink is reflected from the surface of the pigment particles and the pores of the paper fiber are large due to the binder. The difference in refractive index of the pigment suspended during absorption is caused by the deterioration of the transparency of the ink. In the case of color printing, if the transparency of the underlying ink is poor, it will affect the reflection of light transmitted through the surface of the paper and the gloss on the surface of the paper; when the transparency of the upper layer of ink is poor, it will affect the penetration of light into the lower layer of ink and penetrate into the lower layer of ink. It can't be fully absorbed by the underlying ink, and it can't express the color of central China that should be formed after overprinting.
A large number of high-speed printing machines at home and abroad, in order to avoid the paper entering a new process when the ink imprint is not dry, it is easy to cause adhesion on the back side of the printed sheet, which causes the surface of the printed sheet to be damaged, and the back surface of the printed sheet is smeared and stuck. In the process of receiving the printing press, a dusting device printing tool is provided. The commonly used air dusting device (another electrostatic powder spraying device and liquid dusting device, because of the higher cost of the device or only for special blocks, currently used less), is to mix powdery particulate matter with compressed air. Sprayed on the printing surface, so that these powder particles adhere to the viscous dry ink printing layer under the strong action of compressed air, forming a new new particle granular structure surface printing alliance on the printing surface.
According to the theory of particle size Jones-Higgins, LaJones and CCHiggins use the value of density differences between adjacent points to represent the particle size. According to the formula of SΔD=IDa-IDa1, the density difference between adjacent parts is obtained. . Applying its theory to prints and by matching the grainy reflections of successively tuned photographs made of silver particles, the new grainy surface of the print on the surface of the print produces a rough central China that reflects light. The powdery particles remaining on the surface of the imprint not only affect the gloss of the printed matter, but also become an isolation layer of the granular structure, and the penetration of the light causes the obstacle equipment consumables due to the presence of the coated particles. If we print a layer of yellow (Y) ink on a white paper, spray the equipment consumables for anti-sticking. On this basis, a layer of magenta (M) ink was printed, and the standard color red (Y+M=R) printing technique was originally obtained after two equal amounts of ink. Due to the influence of the powder particles, the color of the whole print is produced, and at the same time, the ideal red light appears. The resident opaque mineral particles block and only reflect the magenta light of the upper ink color, and the cyan color of the underlying ink surface. After the particles, the upper layer of ink is penetrated, and the reflected light of the white light and the like after the three primary colors are mixed, thereby affecting the adhesion of the subsequent color sequence overprint and the color of the dot overlap. Similarly, a white paper is printed first. After the color is sprayed, and another color is printed, due to the influence of the color and transparency of the powder particles, the printing density of the other color is changed, and the printing dots whose transmittance changes and the reflectance change are inconsistent. Phenomenon, therefore, appears in various forms of color change printing alliance. In addition, the barrier properties of the dust particles can change the surface energy of the imprint, which will further affect the post-press processing and printing market.
b, polymeric film
Polymerization thin such as PE, BOPP, PET and other polymer materials, is a new printing carrier printing technology that has been rapidly applied in the past 20 years. For example, a biaxially stretched polypropylene BOPP film, in addition to causing macromolecules to undergo microcrystallization in the direction of stretching (stretching of the plastic recrystallization process), causing plastic sliding of crystals in the film, orientation Arrangement, surface structure changes, turbidity by non-oriented (NO) 0.078-0 printing technique. 117% mm, reduced to 0.039-0.078% mm in biaxially oriented orientation (BO), resulting in increased refractive index, high gloss (≥95%) and high gloss (≥85%) surface gloss in central China.
The commonly used polymeric film BOPP, which has no polar groups in its molecule, is a typical non-polar polymer material in central China. After biaxial stretching, the crystalline molecules are thermodynamically stable, but the surface energy of the film is usually very low in printing. The critical surface tension of the polypropylene (BOPP) film is 3. 4 x 10-2 N/m printing technology. When the ink is transferred from the printing plate to the film, the viscoelastic fluid ink drives away the original air between the film surface and the printing plate, but the high surface energy ink cannot wet the surface of the low surface energy film. Wet printing technology. This unattached attachment causes the viscoelastic fluid ink to be covered between the upper surface air states and the lower back solid film to be suspended. The molecular density of the viscoelastic fluid liquid ink is much larger than the molecular density of the gas phase, so the molecules on the upper and lower surfaces of the ink are more attracted by the viscoelastic liquid phase ink molecules than the gravitational force of the gas phase or solid phase molecules. A considerable amount of value and pointing to the inside of the ink mark forms a central pull of the material that is self-aggregating. When the pressure of the printing plate is removed, the ink layer on the surface of the film cannot be wetted, and the in-situ auxiliary layer on the surface of the film cannot have the stress of automatically shrinking to make the surface become spherical, and the transferred ink layer is broken. , printing failed in central China.
At the same time, since the plastic film is rubbed between stretching, slitting, winding and multi-pass flattening rolls of various equipments, or when the film is rewinded, the film itself has 2.0-2.6× 106/cm high-volume electricity rent, the generated static charge can not be timely discharged to the earth and stored in the printing market. The presence of static charge not only makes the film appear electrical, but also easily adsorbs dust, moisture, oil and other substances in the air medium, and hinders the wetting of the surface of the plastic film by inks, adhesives, and the like.
2 imprint status and color, luster
The color of a print is a print union represented by a specific relationship between ink layer density and reflectivity. The reflectance is equal to the ratio of reflected light to incident light; the density is equal to the product of the ratio of log10 to 1 and the reflectance. When the density of the ink layer reaches a certain limit within a certain limit, the color begins to saturate and the density cannot rise again. The standard density can get the maximum contrast, so that the color of the printed matter is close to the original, the layer is distinct, the bright area reflects the bright level, and the dark area can truly reproduce the texture of the fine and trace, and the whole printed product shines on the printing market. Otherwise, the ink is too thick, the color is deep, and the level is dull; the ink layer is too thin, the color is light, and the layers are gray and dull in central China.
The gloss of the printed matter comes from the fact that the conjunctiva after blotting can have a strong amount of reflected light in one direction when exposed to light. This is to ensure that the ink layer is to maintain a proper dryness printing market. In order to control the optimal color density of the ink to achieve the best color performance, there should be a certain thickness of the ink layer (for example, when printing on coated paper, the optimum ink layer thickness is: black ink is 1.8-2.0 μm, cyan ink It is 1.45-1.7μm, magenta ink is 1.25-1.5μm, yellow ink is 0.9-1.05μm) printing alliance.
Under the high-speed working efficiency of the printing press and the production conditions of the high-speed collecting and stacking of the paper, the dry conjunctiva of the ink is undoubtedly not provided with a time-time printing tool which is effective in contact with air. The reflection density of the ink will decrease with the slow drying of the ink (the binder is gradually absorbed by the paper fiber or the coating layer, and the oxidized conjunctiva is behind), which is often referred to as the "dry-densification phenomenon" printing tool. Taking black ink as an example, when the coated paper is just printed, the solid reflection density is 1.9, the reflection density measured after 3 days is only 1.55, and the attenuation rate is 18.42%; when the offset paper is just printed, the solid reflection density is 1.35, measured after 3 days. The resulting reflection density was 1.16 and the decay rate was 14.07% for the printing tool. To ensure the timely drying of the ink printing layer without crystallization, it is necessary to rely on the surface purification treatment technology to ensure the color, gloss and subsequent re-processing of the printing tools.
3 purification treatment with color, luster
The fixing of the anti-adhesive sprayed powder particles on the surface of the printing process not only affects the color and gloss of the printed product, but also adds trouble to the printing alliance for post-press lamination processing and glazing treatment. Commonly used inks are printed in the middle of different fixing times and drying times due to different manufacturers.
For dusting, in the past, the method of manual wiping and removal was used to print the alliance. Even the use of feather dusters or soft cloths can cause paint particles with a certain hardness to cause scratches on the surface of the ink print. And because of the incomplete overlap of the contact surfaces, and the angle of the initial touch and the angle of termination, the force of the wiping process is not evenly uniform, and it is impossible for the dust to completely remove the central printing.
In order to improve the brightness of the ink, dry vegetable oil such as linseed oil is commonly used for printing in the middle of the binder. When these materials are in contact with air, the unsaturated fatty acid reacts with oxygen in the air to polymerize the original linear structure of the viscoelastic fluid phase liquid ink into a network structure, which gradually becomes thick and finally becomes a solid equipment consumable. This oxidative filming process, although having the required time standard, does not have the actual conditions of full contact with the air, can only be slowly completed in the later stages of printing, and does not meet the gloss printing tools that should be available in the production quality standard. If too much desiccant is added to the ink, the hue performance of the ink will be affected, and the resulting gloss will not satisfy the printing tool. Therefore, the color assurance ink thickness under high-speed printing conditions - reflected light rate - dry state - gloss performance equipment supplies. It is always in a state of materiality that must be followed, practiced, and difficult to satisfactorily resolve conflicts. The various efforts that have been made to this end have always had some kind of profit, and still have quite flawed central printing.