Q&A on Printing Paper (163-174)

163. What is the effect of paper acidity on the durability of paper?
A: Durability refers to the ability of long-term paper to retain important physical and mechanical properties, especially strength and whiteness. The pH value of the paper has a great influence on the durability of the paper. The lower the pH value (ie, the stronger the acidity), the more serious the discoloration and strength degradation of the paper, namely, the stronger the acidity of the paper and the shorter the service life. However, an excessively high pH value is also not conducive to improving the service life of the paper, because the fiber will also degrade faster under alkaline conditions.

164. How does the pH of the paper affect print quality?
A: The acidity and alkalinity of the paper mainly affect the drying speed of the ink, change the pH of the fountain solution and reduce the printing plate resistance to printing.
(1) The higher the pH of the paper, the faster the ink is dried. Because the paper is alkaline, hydroxide ions can accelerate the oxidation of the ink and promote ink drying; if the paper is acidic, the acid and desiccant The role of polyvalent metals in the formation of oil-insoluble substances, hinder the oxidation of the conjunctiva process, thereby extending the ink drying time.
(2) The pH value of the paper can also change the pH of the fountain solution. Under normal conditions, the fountain solution is acidic, but when the alkali of the paper is too strong, a neutralization reaction occurs with the acidic fountain solution to make it pH. The value is increased, which affects the normal transfer of the ink, causing the glossiness of the printed product to drop, and the color of the ink not to be bright. On the contrary, the paper is too acidic, which will make the fountain solution more acidic, which will seriously affect the drying speed of the ink. Moreover, a significant decrease in the pH of the fountain solution will accelerate the corrosion rate of the printing plate, thereby reducing the printing plate's resistance to printing.
In addition, the use of low pH paper printing gold ink, a long time gold ink graphic easy to change color. Therefore, trying to control the pH of paper in production should not deviate too far from neutrality.

165. What are the methods for measuring paper acidity?
A: First, measure the pH of the water extraction solution, that is, according to the standard method, use distilled water to extract the paper sample, determine the pH of the aqueous solution as the pH value of the paper sample, and secondly, measure the pH value of the surface of the paper, the electricity measurement method and the color indicator. Method, the resulting paper surface pH is more meaningful.

166. What is the appearance quality of paper? What is the importance?
A: The appearance quality of paper refers to the condition of paper quality that can be discerned and recognized by human senses alone without the use of equipment and equipment, including the appearance quality of paper sheets and the appearance quality of pieces of paper. The poor appearance quality will not only reduce the paper's use value and the printed product yield, but also cause the paper to be scrap when serious. Some serious paper defects in the paper, such as hard blocks, etc., will also squash the plates and rollers during printing, causing damage to the printing equipment. Therefore, both the manufacturer and the user must carefully check the appearance of the paper.

167. What are the contents of paper quality inspection?
A: (1) Check the quality of the paper, including: whether the shape of the paper is good, whether the size is qualified, the quality of the packaging, and the degree of damage.
(2) Master the basic properties of paper, including color, uniformity, flatness, flexibility, smoothness, and cleanliness.
(3) Sampling The percentage of the total number of paper sheets in the lithographic paper with significant paper disease.

168. What is the appearance quality of a piece of paper?
A: The appearance quality of a piece of paper is an intuitive impression of the entire piece of paper. For flat paper, it mainly refers to the regularity of paper stacking, the quality of the package, and the degree of damage, and for webs. , mainly refers to the paper rewinding quality, how many joints, packaging quality and extent of damage.

169. For lithographic paper, what are the conditions for good appearance quality?
Answer: Each ream of paper is neatly laid out, and the reams are separated or packaged separately by seals; the bottom and top of each piece of paper are lined with a moisture-proof paper and a thick paperboard, and then packaged; the paperboard must be completely solidified, Smooth and dry; pieces of paper without deformation, parts, broken or exposed white and other damage.

170. What is the appearance quality of the paper sheet? How to test?
A: The appearance quality of a paper sheet refers to the quality condition that a single sheet or paper strip can sense with human touch in a certain area. The method of checking the appearance quality of a roll paper sheet is generally to cut the outer circumference of the roll paper. 10 layers, remove the outermost 5 layers, use the remaining 5 layers as a pattern, check the quality of the web (each batch should generally take 2 to 3). The appearance quality of the flat paper is relatively easy to check. Generally, from the entire paper of the same shipment, a few samples are opened with the standard sampling method, and then 2 orders are taken from each piece to check the appearance quality. Through inspection, understand the main advantages and disadvantages of the appearance of the paper, find the missing rate of paper and all paper diseases. Specific inspection methods include reflected light head-up inspection, light-seeing inspection, oblique viewing inspection, hand touch inspection, and auditory inspection.

171. What is a reflected light head-shot inspection?
A: Spread the paper on the table or on the table, and observe the color, whiteness, evenness, and smoothness of the page at a distance of about 30cm from the surface of the paper; check the presence of dust, spots, and holes in the paper. Holes, creases, wrinkles, broken sheets, cracks, dirty spots, seersuckers, pulp blocks and other hard blocks. When the observation is generally in the ordinary indoor light, the eyes are facing the paper surface.

172. What is the fluoroscopy method?
A: The paper is directed against the light source (or placed on the glass with a reflector lamp), so that the light through the paper, with the eye to observe the quality of the paper, mainly to see the uniformity of the fibrous tissue and degree of opacity, check the paper There are no "cloud flowers", transparent spots, dirty spots, holes, and uneven light transmission lines.

173. What is the oblique inspection method?
A: Some appearances of paper diseases, such as glossy or dull scratches on paper, felt marks, roller shadows, etc., are not easily detected by hand-touch inspection methods, and must be observed with oblique inspection methods. One side of the paper is raised or lowered, and the paper is viewed obliquely from different angles, so as to find defects or deficiencies in the appearance quality of the paper.

174. What is the hand touch inspection method?
Answer: The hand-touch inspection method relies on the contact of the sensory organs to discover hidden paper diseases, such as the difference in paper thickness, high or low ration, and the presence of encrusted weeds, fiber bundles, and fine sand grains inside the paper sheet.

- "Printing Technology - Equipment and Special Printing"