The marks left on the printed matter are formed by ink, which is the colorant for printing and the main raw material for printing. Ink is crucial to the quality of printing. When the performance of the ink is not suitable for printing, it will cause a series of technical processes. Failures seriously affect the progress of production and product quality. The printing operator must change some properties of the ink to meet the needs of printing, but some failures are not only caused by the ink, but also related to other factors, so the printing operator must carefully analyze the correct handling. This article discusses the faults and processing methods caused by the ink post-printing process, hoping to help.
1. Slow drying of blotting
Phenomenon and reason: After the imprint is transferred from the printing plate to the paper through the blanket, it is generally required to be dried in about 10 hours to facilitate the later color printing or finished product inspection and delivery. Once the imprint is slow to dry, it not only makes the next color impossible Overprint, and it is easy to make the back of the printed matter sticky and dirty. There are three factors in the drying of blots, such as oxidized conjunctiva, paper absorption, and water evaporation. We must correctly grasp the operation and prevent it in advance. The common causes of slow drying are as follows:
(1) The PH value of the paper is below 6.
(2) The PH value of the water bucket is below 3.
(3) The water on the plate is large, and the ink is large, which causes serious emulsification of the ink.
(4) The workshop temperature is low. The relative humidity is higher than 75%.
(5) The absorption of paper is poor.
(6) There are too many auxiliary materials such as ink-adjusting oil and debonding agent mixed into the ink.
(7) Too little dry oil.
Approach:
(1) In order to prevent the slow drying of the printed matter, the height of the stacked prints should be reduced, the paper stack should be shaken, and the semi-finished product ventilation can allow air to penetrate into the stacked paper and shorten the time of oxidation and conjunctiva.
(2) If the printing is urgently needed, the original graphic printing plate is used for dry oil overprinting, the formula is 70% of Wei Li oil and 30% of dry oil.
(3) In order to prevent the factors of unfavorable drying, add an appropriate amount of dry oil. The amount of dry oil is: winter is more than summer, the latter color is more than the previous color, and the diluted ink is added more than the undiluted ink.
Second, the color is not printed
Phenomenon and reason: Excessive dry oil is added to the ink or the stacking time of the semi-finished products is too long, which causes excessive drying and makes the imprinted surface vitrified. The imprinted surface is too smooth and loses its ability to absorb. The latter color cannot be printed. This kind of failure is common in the full version of the field, especially the yellow version (ink) or line pattern printing.
Approach:
(1) For prevention, add appropriate amount of auxiliary materials such as Viley oil, Kangbang, magnesium carbonate powder to the yellow ink that is easy to vitrify in advance to make the surface conjunctiva rough or prolong the drying time.
(2) If the vitrification phenomenon has occurred and the next color cannot be printed, if the number of products is small, use a soft cloth dipped in magnesium carbonate powder to gently wipe the surface ink film of each sheet, and then apply the next color, if Large quantity, it can be printed by coloring while caustic soda.
Third, the back is sticky and dirty
Phenomenon and reason: dirty on the back means that the semi-finished product or finished product enters the receiving pile, and the back is dirty with the ink on the next printed sheet. The reason for the sticky backside is.
(1) The surface of the paper is too smooth.
(2) The ink is too thin.
(3) The layout is large in water and ink.
(4) The ink quality is too light.
(5) The printing pressure is too light.
Approach:
(1) During the printing process, there should be no large water and ink phenomenon. Control the water content of the layout, the ink color becomes darker, and the ink delivery volume of the ink fountain is reduced. If the greasy or paste version is produced after reducing the water content, the water roller should be cleaned or replaced with a new water roller, or the acidity of the water bucket syrup should be appropriately strengthened and some gum arabic should be placed.
(2) The ink is adjusted too thin and easily sticks to the back of the dirty product. New ink should be replaced or some new ink should be added to increase the viscosity of the ink.
(3) The use of light double-color ink is commonly used in the preparation of light red, light blue, light tea, and light gray ink. It should be adjusted deeper to improve its color quality and avoid the printer from feeling that the ink color is too light. In order to achieve the sample hue To increase the amount of ink required, the ink layer is printed too thick and the back of the printed product is sticky.
(4) During the printing process, the rubber cylinder must ensure sufficient printing pressure when transferring graphics to text on the paper, so that the ink is completely transferred on the surface of the blanket to avoid the back of the printed matter from being dirty.
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Four, powdering
Phenomenon and reason: Ink powdering means that after the semi-finished product or finished product is dried, the ink layer cannot be well combined with the paper surface and is slightly rubbed, and the pigment particles on its surface fall off like powder. This pulverization phenomenon has a great relationship with the properties of paper and ink, except that the acidity of the water hopper liquid is too high and there are too many surfactants. Common ink powdering has the following reasons:
(1) The adhesion of the ink is too small and the paper surface is relatively smooth, so that the ink layer and the paper surface cannot be well combined, resulting in the ink layer rubbing off the paper surface.
(2) The ink is too thin, the binding material is easily absorbed by the paper, and a large amount of the binding material penetrates into the paper, which promotes the separation of the binding material and the pigment in the ink, causing the pigment particles to float on the paper surface, the pigment loses the binding material Adhesion, the degree of connection is reduced, so it can not be well adhered to the paper surface, causing shedding.
(3) The ink used is seriously emulsified, not only reduces the viscosity, drying speed, and increases the amount of penetration, more importantly, the emulsified ink cannot be well combined with the paper surface after film formation, the adhesion is poor, and the film layer is strong Very poor, slight rubbing will cause the film layer to rupture and fall off.
(4) Coated paper is made by coating paint on base paper. The paint and base paper have strong absorption, and the paper is thick, which can absorb a large amount of bonding material. In addition, the coating surface is smooth and the pores are very fine. The pigment may be sucked together, which acts as a filter layer, causing the pigment particles to float on the paper surface and fall off due to the lack of wrapping of the binding material.
Approach:
(1) Do not use highly absorbent coated paper (absorbency is less than 30 seconds) to print products, otherwise it must be printed with resin ink with strong adhesion.
(2) Add proper amount of No. 0 ink or adhesive to increase the adhesion of the ink to the paper.
(3) To control the emulsification of ink, the water consumption of the layout should be small. Frequently measure the PH value of the water bucket solution and adjust it to the required value. Dry oil should be added with use to reduce ink emulsification so as to master the drying time.
(4) Fine products that have been powdered can be solved by coating or filming.
Five, ink flooding
Phenomenon and reason: Ink flooding means that the hue of the ink changes and the color changes, causing the printed matter to lose its due artistic value. The common ones are golden red and black, sky blue and blue, peacock blue and light blue.
The yellow ink and transparent yellow luster disappear, and the semi-finished products or finished products are piled up due to heat generation. The causes of the above ills are:
(1) The ink pigment itself is unstable.
(2) After the acidic syrup penetrates into the ink, it will develop color.
(3) Oxidative fever reaction.
Approach:
(1) When the oily gold red ink is used, the pigment powder meets iron to produce a chemical reaction, and the hue is very easy to blacken. Switch to a resin ink to avoid the phenomenon of flooding.
(2) Tianlan ink will turn red after printing on paper for a few days, and the ink color looks darker than the original. This phenomenon should be noted that when encountering batches of products to be printed in batches, the formulation of the ink color must be consistent Can not be changed at will, so as not to cause inconsistency of product hue.
(3) Peacock orchid, light blue ink meets chromic acid bucket liquid, the color of ink is very easy to yellow, and white medicine can be used instead.
(4) Sunlight can fade the finished product, which can be solved by printing or pasting on the printed paper.
(5) During the stacking process of semi-finished products or finished products, it is easy to generate great heat, and the middle is also deficient in oxygen. The time will be a little longer. The product will become hot and dark. It should be mainly prevention. Ventilate once every -6 hours to accelerate the air flow between the papers, help it diffuse heat and shorten the time to oxidize the conjunctiva.
(6) Reduce the use of cobalt dry oil (that is, 402 red dry oil), because the red dry oil is easy to darken the hue of the ink after heating.
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Six, ink through printing
Phenomenon and reason: The ink part of the printed part penetrates to the back of the paper, and there are obvious imprinting patterns or oil stains on the back of the paper, especially for products that require double-sided printing, which is more harmful. It affects the quality of the product and causes the printing through of the product. In addition to the paper itself being too thin or having transparency, the reasons for common ink through printing are as follows:
(1) The ink is too thin and contains too much binder. A large amount of binder is absorbed by the paper and penetrates the back of the paper.
(2) There are too many non-drying binders in the ink. Too much non-drying binder will slow down the oxidative film formation on the surface of the paper, and the penetration and drying will accelerate. A large amount of binder will penetrate into the paper and print through to the back .
(3) The ink is printed too thick, and the drying is too slow, which also makes the linking material penetrate into the paper and print to the back.
(4) The oily pigment contained in the ink is dissolved in the connecting material. During the printing process, the pigment and the connecting material are printed through the paper together and through the back of the printed product.
Approach:
If through-printing has already appeared on the printed product, there is no way to remedy it, only prevent it in advance to prevent the occurrence of through-printing.
(1) Add No. 0 adjusting ink to the ink to increase its viscosity.
(2) Do not use non-drying oil as the linking material, and reduce the proportion of non-drying or highly permeable auxiliary materials.
(3) Increase the color value of the ink, thin the printed ink layer, and accelerate drying.
(4) If the pigment is oil-soluble, it is better to use resin ink for printing.
7. Printed Matte
Phenomenon and reason: The printed matter is the reproduction of artistic reproduction. It should have bright color, distinct layers, strong texture, space and material sense. Otherwise, the printed matter will lose its due value.
Common reasons that affect the gloss of printed products are as follows:
(1) Low-grade ink is used for printing, and the gloss is poor after coloring (except low-grade products).
(2) The surface of the paper is rough, the larger the gap between the fibers, the stronger the absorption capacity of the connecting material. After the ink is transferred to the paper, the connecting material is absorbed by most of the paper fibers without film formation, leaving the ink pigment The particles are attached to the surface of the paper, thus making the product dull and dull.
Approach:
How to make the printed products have better gloss, the actual operation experience tells us that the printing gloss can be obtained from the following aspects:
(1) The gloss of the ink itself is the most basic element. When printing high-end fine products, the ink should be printed with high-end quick-drying and bright ink to obtain the best gloss.
(2) Add dry oil to the ink properly during printing to help the good conjunctiva on the surface of the ink, so that the product can obtain a proper gloss. To correctly grasp the performance and dosage of red and white dry oil, the type and dosage of dry oil have a certain influence on the gloss. No. 402 red dry oil is mainly composed of cobalt citrate. The drying effect is based on the surface oxidized conjunctiva. The drying speed is about 23 times that of white dry oil. Generally, it is added in red ink and black ink, and medium blue and deep blue can also be used. Especially in the latter colors of the same kind of printed matter, if the red and dry oil can be added to the maximum, this will have a good effect on increasing the gloss of the printed matter. When the yellow version is used as the first color sequence, it is not advisable to add red dry oil, because the color of the red dry oil will change the hue of the yellow ink, followed by the largest amount of yellow ink, and excessive drying is prone to vitrification. White dry oil is a mixture of metal salts of cobalt, manganese, and lead. It has a comprehensive drying effect, but it is not as strong as red dry oil. The correct amount of white dry oil added will have an effect on increasing the gloss of the printed matter.
(3) Apply varnish or film to the surface of the finished product.
Ink is a colloid with a complex structure formed by mixing and grinding pigments, binders and additives. Its properties are mainly determined by the characteristics of the pigments and binders. It completes the drying of printed prints through three forms: volatilization, penetration, and oxidation of the conjunctiva. As the main material for printing, understanding the ink composition, familiarizing with the performance of the ink, and correctly mastering the use of the ink are the necessary conditions to ensure the printing quality.
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