Q & A on the hottest printing paper 163

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Q & A on printing paper (163

163. what is the impact of inconvenient acid-base oiling of paper on the durability of paper?

answer: durability refers to the ability of paper to retain important physical and mechanical properties, especially strength and whiteness, for a long time. The pH value of paper has a great impact on the durability of paper. The lower the pH value (i.e. the stronger the acidity), the more serious the discoloration and strength decline of paper, i.e. the stronger the acidity of paper and the shorter the service life. However, too high pH value is not conducive to improving the service life of the paper, because the degradation rate of the fiber under alkaline conditions will also be accelerated

164. What is the effect of paper acidity and alkalinity on printing quality

answer: the acidity and alkalinity of the paper mainly affects the drying speed of the ink, changes the pH value of the fountain solution and reduces the printing plate resistance

(1) the greater the pH value of the paper, the faster the drying speed of the ink, because when the paper is alkaline, the hydroxyl ion can accelerate the oxidation speed of the ink and promote the drying of the ink; If the paper is acidic, the acidic substances interact with the multivalent metals in the desiccant to form substances insoluble in oil, which hinder the oxidation and conjunctive process, thus prolonging the drying time of the ink

(2) the pH value of the paper can also change the pH value of the fountain solution. Under normal circumstances, the fountain solution is acidic, but when the alkalinity of the paper is too strong, it will neutralize with the acidic fountain solution to increase its pH value, which will affect the normal transfer of the ink, resulting in the decline of the gloss of the print, the color of the ink is not bright, etc. On the contrary, if the paper is too acidic, the fountain solution will be more acidic, which will seriously affect the drying speed of the ink. Moreover, the significant decrease of the pH value of the fountain solution will accelerate the corrosion speed of the printing plate, thus reducing the printing resistance of the printing plate

in addition, gold ink is printed on paper with low pH value, and the gold ink is easy to change color after a long time. Therefore, in production, efforts should be made to control the pH value of paper and not deviate too far from neutral

165. What are the methods to measure the acidity and alkalinity of paper

answer: first, measure the pH value of the water extract, that is, extract the paper sample with distilled water according to the standard method, and determine the pH value of the aqueous solution as the pH value of the paper sample; The second is to measure the pH value of the paper surface, including electrical measurement method and color indicator method. The obtained pH value of the paper surface is more meaningful

166. What is the appearance quality of paper? How important is it

answer: the appearance quality of paper refers to the paper that can be identified only by human senses without using instruments and equipment. 7. The quality status of shoulder riding method, including the appearance quality of paper pages and the appearance quality of finished paper. Poor appearance quality will not only reduce the use value and printing yield of the paper, but also make the paper waste in serious cases. Some serious appearance defects in the paper, such as hard blocks, will also damage the printing plate and cots during printing, resulting in damage to the printing equipment. Therefore, both manufacturers and users should carefully do a good job in the appearance inspection of paper to meet the needs of the rapid development of the domestic automotive industry

167. What are the contents of paper appearance quality inspection

answer: (1) check the finished paper quality, mainly including: whether the paper shape is good, whether the size is qualified, packaging quality and damage degree

(2) master the basic properties of paper, including color, evenness, flatness, flexibility and tension resistance, smoothness and cleanliness

(3) sample and check the percentage of paper with obvious paper defects in the total number of sheets

168. What is the appearance quality of finished paper

answer: the appearance quality of the finished paper is the visual impression of the whole paper on the whole. For flat paper, it mainly refers to the stacking regularity, packaging quality and damage degree of the paper, while for web paper, it mainly refers to the rewinding quality, number of joints, packaging quality and damage degree of the paper

169. What are the conditions for good appearance quality of lithographic paper

answer: each ream of paper is stacked neatly, and each ream of paper is separated by seals or packaged separately; The bottom and top of each piece of paper are lined with a piece of moisture-proof paper and a piece of thick cardboard, and then packaged; The paperboard shall be complete, solid, flat and dry; The finished paper shall be free from deformation, loose parts, cracking, whitening and other damage

170. What is the appearance quality of paper? How to check

answer: the appearance quality of the paper refers to the quality of the single sheet of paper or paper tape in a certain area that can be felt by the touch of the user. The method to check the appearance quality of the web page is generally to cut 10 layers around the web, remove the outermost 5 layers, and take the remaining 5 layers as the paper samples to check the quality of the web (2-3 pieces should be taken for each batch). The appearance quality of flat paper is easy to check. Generally, several pieces of paper from the same batch of goods are taken and opened with the standard sampling method, and then 2 reams are taken from each piece to check the appearance quality page by page. Through inspection, understand the main advantages and disadvantages of paper appearance, and find out the missing rate of paper and all paper diseases. Specific examination methods include reflected light head up examination, light facing fluoroscopy examination, oblique examination, hand touch examination and acoustic examination

171. What is reflected light head up examination

answer: lay the paper flat on the inspection table or desktop, and observe the color, whiteness, flatness and smoothness of the paper at about 30cm away from the paper surface by using the reflected light; Check the paper for dust, spots, holes, holes, folds, wrinkles, cracks, cracks, dirty spots, seersuckers, pulp blocks and other hard blocks. The observation is generally conducted under the ordinary indoor light, and the eyes are facing the paper

172. What is fluoroscopy

answer: irradiate the paper against the light source (or put it on the glass equipped with a reflector), let the light pass through the paper surface, and observe the quality of the paper with your eyes, mainly to check the uniformity of the paper fiber structure and the degree of opacity that the foam granulator industry needs to vigorously carry out, and check whether the paper has "cloud flowers", transparent points, dirty points, holes, uneven light transmission stripes, etc

173. What is squint examination

answer: some appearance paper defects, such as glossy or non glossy streaks on the paper surface, woolen cloth marks, couch roll shadow marks, etc., are not easy to find by hand touch inspection, and can only be seen by oblique inspection. During inspection, raise or lower one side of the paper with both hands, and look at the paper surface from different angles, so as to find defects or deficiencies in the appearance quality of the paper

174. What is hand touch examination

answer: the hand touch method relies on the contact of sensory organs to find hidden paper diseases, such as different paper thickness, high or low quantity, and whether there are grass tendons, fiber bundles and fine sand particles in the paper

- printing technology - equipment and special printing

(author/Fei Zhou)

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