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1. What is coated white paper coating Whiteboard paper belongs to the category of packaging paperboard. It is a processed paperboard made by coating and finishing after coating white paper on the raw paperboard. Its basis weight is generally above 200g/m2 and the thickness is 0.1mm. The above is mainly used for making a packaging box after one-sided color printing.
2. Performance characteristics of coated whiteboard paper The whiteness of the coated whiteboard coating surface is high, and the smoothness, ink absorption and printing gloss are all very good. The paperboard itself has good stiffness and folding resistance, so it can carry out High-quality color offset printing and gravure printing, which can meet the requirements of packaging, are high-quality materials for middle and high-end commodity packaging.
3. The type of coated white paper The coated white paper is divided into A, B, and C according to the quality level. When selecting, the product type, specifications, and quality grade should be taken into consideration.
A type whiteboard paper: Bleached chemical wood pulp is used on the surface, sulphate wood pulp, mechanical wood pulp, fine waste paper, etc. are used for the core and the bottom layer, and its folding endurance is good, and it is used for producing small carton boxes.
Type B white paper: Bleached chemical pulp or fine white waste paper is used on the surface, and waste paper pulp is used on the core and bottom layer.
Type C whiteboard paper: The use of lower grade raw materials than Type B whiteboard paper is no longer in production.
4. Structure of coated white paper The coated white paper consists of a secondary coating layer, a top layer, a core layer, and a bottom layer. The primary or secondary coating layer is composed as shown in Fig. 1 : 1 layer and 5 layers are coating layers, whose role is to improve the whiteness and printing effect of coated whiteboard paper; 2ã€4 layers are sulphate wood pulp, Mechanical pulp, deinked newsprint pulp, its role is to maintain the strength and whiteness of white paper; 3 layers of mixed newsprint pulp, waste magazines. Waste corrugated paper pulp is used to increase the thickness of white paper, reduce the cost of white paper, and improve the ink absorption of white paper.
5. Technical requirements for coated white paper (1) High strength. High strength is the basic performance that packaging materials should have. Carton made of white paper must have a stable shape and a certain hardness in order to protect the contents. For example, the frequent opening and closing of the lid of the medicinal paper carton will cause the fold line to break, which is related to the folding strength.
(2) has a good processing performance. In the die-cutting machine and the folder-gluer, the whiteboard paper is required to have a suitable hardness, easy to die-cut, and easy to bond, so as to meet the process requirements of the box-making.
(3) Excellent printing adaptability. Adapt to offset printing. Gravure and other printing methods.
(4) Light weight, with proper cushion die cut properties. Whiteboard paper has these characteristics and is very advantageous for protecting contents and improving transport performance.
Second, the troubleshooting process in the printing coating coated white paper is usually used embossing, offset printing and gravure printing process, embossing, offset printing used for printing a single sheet of white paper, gravure and more for printing roll white paper. There are mainly the following problems in the process of printing whiteboard paper.
1. Dirty phenomenon In the offset printing process, the coated whiteboard paper with an overly alkaline coating layer is liable to cause dingy phenomenon.
the reason:
(1) Hydrophilic gum arabica membranes that are not in the graphic part (the part that does not contain ink) are easily removed by alkali, and the resin ink is gradually absorbed by the non-graphic part, causing the Plate to accumulate dirt and cause a floating phenomenon.
(2) Fatty acids and bases in the ink binder produce soap (unlike the type of household soap, but the principle of formation is the same), destroy the balance between the ink binder and the fountain solution, and make the ink gradually adhere to non-graphics. section.
Solution: Increase the acidity of the fountain solution, to a certain extent, can alleviate the floating phenomenon.
2 ink uneven reason:
(1) During the printing process, the white paper coating layer is dross, causing uneven absorption of ink.
(2) The uneven distribution of pigments and binders on the coated surface of white paper produces partial ink absorption unevenness.
(3) Ink absorption unevenness is related to the coating process of whiteboard paper and the composition of the coating pigment. In the drying process, drying often leads to adhesive migration. In winter, the temperature of the wet paper is particularly low before drying. Rapid temperature rise in the drying process can easily cause the migration of the adhesive. This is the reason why the ink layer in winter is more scarred.
Solution:
(1) Replace the paper, or cover the surface of the paper with oil and fill the gap on the surface of the paper.
(2) The winter wet paper must not be dried too quickly to avoid the migration of the adhesive.
3. Ink Pulverization After the ink film layer printed on the surface of the white paper is dried, the pigment encounters a slight friction and becomes powdery and falls off. This phenomenon is called ink pulverization.
the reason;
(1) The binder in the ink is too dilute or uses too much non-volatile, immiscible solvent.
(2) The moisture content of the paper is too low, the coating layer absorbs the ink too quickly, and the link material in the ink penetrates too deeply.
(3) The ink drying is too slow and promotes the penetration of the binder.
(4) The quality of the link material is too bad.
Solution:
(1) Improve the structure and consistency of the binder.
(2) Use of non-reactive resin and linseed oil, cooked oil or medium viscosity varnish.
(3) Add a small amount of varnish or varnish to the ink: When designing the ink formulation, substitute pigments with small specific gravity and large amount of oil absorption for the pigments with large specific gravity and small oil absorption, for example, replace the chrome yellow with Hansha yellow, benzidine yellow, etc. .
(4) The composition of the coating layer can be slightly changed (using a different whiteboard paper).
4. Dirty and back stains When the ink is not sufficiently dry, the prints are stacked on the printer's paper feeder. Under the pressure of its own weight, the back of the paper is glued with printing ink, and the ink on the underside of the paper is also printed. It is transferred and the printed matter is in a variegated shape. This kind of malfunction is dirty and back stained.
the reason:
(1) The printing surface is uneven, and the protrusions are strong, making it easy to transfer the ink. Especially when the printed matter is in a high pile, the stacking pressure can cause sticking and back rubbing.
(2) The pH value of the paper surface of coated white paper is too low, resulting in poor ink drying.
(3) Absorption of ink is poor due to poor oil absorption of the coated surface of white paper.
(4) Offset printing is more likely to result in dirty and back stain than offset printing, because in offset printing, the fountain solution tends to emulsify the ink and reduce the color concentration, especially when the amount of ink is too much.
Solution: Use a high concentration ink ink desiccant to speed up ink drying.
5. Paste stencil refers to the phenomenon that paper hairs and pigments are attached to the surface of the printing plate. It causes many taints in the non-graphic area of ​​the printed matter. Printed words such as "mouth", "product", "crystal", etc. are filled with ink in a solid state. Or even a salty outlet, are the performance of paste version.
the reason:
(1) The surface strength of the paper is weak or the viscosity of the ink is too high, so that the offset roller of the offset printing machine peels off the coating layer from the surface of the paper and then transfers to the printing plate to cause a paste plate. When performing multi-color offset printing, the fountain solution is added once for each color, the surface strength of the paper is also reduced once, and the faster the printing speed is, the more severe the peeling of the surface coating layer of the paper is.
(2) During the offset printing process, the printing pressure may destroy the blank surface film layer of the printing plate to expose the metal. Exposed areas are traces of surfactant in the fountain solution. Polar substance. After the free fatty acid acts, it becomes lipophilic and absorbs ink, resulting in taints in non-graphic areas.
(3) The yield value of the ink is too high, the water's acidity is too weak, or the ink absorption by the water roller can also cause a paste plate.
Solution:
(1) Before printing on the machine, use a brush or a vacuum cleaner to remove the paper on the paper.
(2) Use appropriate inks. For example, if the ink is too thick, some of the thinner varnish may be added to increase the ink dispensing performance.
(3) If you paste in a high profile, you can reduce the pressure.
(4) Select inks with good fineness, high color concentration, and low oil content; use fast-drying resin inks; add some thick binders to offset inks: increase the acidity of fountain solution; increase the amount of water supply; Use fountain solution with high surface tension.
6. Ink accumulation When the surface strength of the white paper is insufficient and the coating layer is powdered off, the fibers and filler particles from the paper surface are mixed with the ink and gradually pile up on the blanket or printing plate to form a stack of ink. . Stacking ink will hinder the transfer of ink, so that the image is not bright colors, dot gain, reduced clarity. Occasionally, the surrounding area of ​​the stack of ink on the printing plate is not in contact with the paper, and an irregular ring-shaped white spot is formed on the printed matter, resulting in that the dots on the image are not full and irregular, and the graphics and text appear defective and various spots.
Solution:
(1) Replace paper or reduce ink viscosity.
(2) Apply varnish to the paper surface. If the ink absorption is not good, use an oily, sticky ink.
7. Ink agglomerates The phenomenon that a grain is hardened on a printing plate is called ink agglomeration.
the reason:
(1) The pigment is not uniformly dispersed in the ink binder.
(2) Insufficient link material in the ink, too high or low ink viscosity can also cause this failure.
Solution:
(1) Replace the ink after the plate wash or adjust the viscosity of the ink.
(2) reduce the amount of ink supply.
First, know coated white paper