On the durability of paper printing

Talking about the durability of paper printed matter

the durability of paper printed matter usually refers to the durability of the paper and ink used for printing. This paper focuses on the durability of the paper used for printing. The durability of paper refers to the extent that the paper can still maintain its color, folding resistance and other characteristics after a long time. For printing paper, durability expresses the service life of the paper printed matter or the longest time it can be preserved. Knowing, understanding and even predicting the durability of paper, we can choose paper according to the storage life requirements of printed matter. Especially for the paper used in the folding carton, try to avoid the phenomenon that the inner packaging has not expired and the paper has turned yellow. Generally, the time taken for the paper to turn yellow to a certain extent or the folding resistance to a certain extent is called the durability of the paper

there are many factors that affect the durability of paper, including the type of pulp used in papermaking, the content of rubber, paint, acid and metal compounds, as well as the temperature, humidity and light during storage or use

1 main factors affecting the durability of paper

the durability of paper is jointly determined by internal and external factors. Its internal factors include the type and quality of pulp, the content of rubber, paint, acid and metal compounds, and other components in the paper, which are determined by the development of pulp and paper with the sensor technology. External factors refer to the storage or use conditions of paper, such as temperature, relative humidity, light, atmospheric pollution, etc

1) the influence of residual lignin in pulp and the cleaning degree of pulp, the number of bleaching stages and methods on the durability of paper

the content of residual lignin in pulp and the cleaning degree of pulp, the number of bleaching stages and methods, etc., all significantly affect the stability of paper whiteness. Unlike the linear molecules of fiber and hemicellulose, lignin is a three-dimensional macromolecular structure, and its molecular formula is c138h138o35. Lignin is a harmful component in paper. Residual lignin in the paper will make the paper brittle and reduce the mechanical strength. After being exposed to sunlight, it will show the yellowish brown of lignin and affect the whiteness of the paper. Lignin can be dissolved in acid and alkali solutions, and can be decomposed by full digital closed-loop servo control under the action of various oxidants. In the process of papermaking and pulping, using this property, we can try to preserve the cellulose and hemicellulose in the raw materials and remove lignin. The main reason for the rapid yellowing of paper is that the ground wood pulp used does not remove the lignin from the wood raw materials, and generally does not undergo bleaching or only one-stage hydrogen peroxide bleaching

2) the influence of pH value of paper itself on the durability of paper

the research results show that the pH value of paper itself is the most important factor affecting the durability of paper. If the pH value of the paper is low, the excessive acidity in the paper will accelerate the degradation of cellulose. In acid paper, hydrogen ions promote the breaking of the "oxygen bridge" of cellulose macromolecules and promote the hydrolysis and oxidation of cellulose, and these effects are relatively strong. It will make the paper and printed matter seriously fade. The stronger the acidity is, the more serious this phenomenon is. There may be many sources of paper acidity, but the main source is alum used in sizing. Alum hydrolysis leads to the formation of sulfuric acid in the paper. Therefore, the neutral sizing method without alum is required to manufacture archival paper with good durability. The acid sources in paper include pulping and bleaching. The paper made from sulfite pulp is not as durable as the paper made from sulfate pulp because of the low pH value and the special effect of acid cooking conditions on plant fibers; If the residual chlorine content in the pulp after bleaching is high, the chlorine ion in the pulp reacts with water to produce hydrochloric acid and hypochlorite, which makes the pH value of the paper low and leads to the decline of the durability of the paper

for paper with high pH value, strong alkalinity is also not conducive to improving the service life of paper, because under the condition of high alkalinity, the oxidative degradation rate of cellulose will also be greatly accelerated. Therefore, for printing paper, strong acid, strong September 17, 2014 - Solvay polymer business department participated in the 13th International Automotive Training Institute (CTI) Symposium on automotive transmission, hybrid and electric drive technology held in Suzhou. Alkalinity has a great destructive effect on the durability of printed matter

3) the influence of the type and quality of fibers used in papermaking on the durability of paper

the type and quality of fibers used in papermaking is also an important factor determining the durability of paper. Fibers obtained from cotton, rags, flax, sandalwood skin, etc. can be used as raw materials for making paper with good durability. The reason is that the pulp made from these raw materials has high cellulose content and high degree of polymerization of cellulose. Straw pulp fiber is just the opposite, so it is not suitable for making paper with good durability

cellulose is a kind of white, tasteless and odorless carbohydrate, which is insoluble in water, dilute acid, dilute alkali and general organic solvents, but can be hydrolyzed under the action of concentrated sulfuric acid. The chemical molecular formula is (C6H10O5). It is a chain like polymer compound composed of a large number of glucose groups. The strength of cellulose is determined by the degree of polymerization. The greater the degree of polymerization, the greater the strength. The polymerization degree of phloem fiber is higher, followed by cotton fiber, wood fiber and grass fiber. Therefore, the mechanical strength of paper made of cotton and hemp fibers is higher than that of paper made of plant fibers. Cotton and hemp fibers with high polymerization degree are mostly used to make high-grade paper

4) the influence of various additives in paper on the durability of paper

the existence of additives in paper, such as various adhesives, fillers, pigments and other additives, also affects the chemical stability and durability of paper to a certain extent

① filler. The whiteness of fillers varies greatly due to their types and grades. If a filler with a higher whiteness than the size is used, the more filling, the higher the whiteness of the paper

② dye. Each dye has a certain characteristic wavelength, at which it absorbs the most light, which is commonly referred to as the maximum absorption wavelength. When selecting a dye, the dye should not affect its reflectivity near the light wavelength of the whiteness measurement, which can not only adjust the color of the paper, but also not significantly affect the whiteness of the paper

③ slurry. Pulp whiteness is the most important factor affecting paper whiteness. The whiteness of high-grade paper made of 100% bleached pulp and high-grade coating printing paper using it as base paper is about 80%. In contrast, the whiteness of intermediate paper and intermediate coating printing paper equipped with mechanical wood pulp will be lower. The whiteness of this kind of paper depends on the whiteness of the used pulp and the proportion of the pulp

④ coating. The whiteness of coated printing paper is determined by the whiteness of base paper, the whiteness of coating and the coating amount. If the whiteness of the base paper is higher than that of the coating, some light passing through the coating will be reflected back by the surface of the base paper and again reflected through the surface of the deep coating, then the whiteness can also be improved. If the whiteness of the base paper is low, the amount of light absorbed by the surface of the base paper, Meng Bingquan, former vice president of Guangdong Academy of Building Sciences and a senior expert specially hired by Guangdong civil architecture society, told Caijing that the increase, and then the light reflected through the coating will be reduced, which will reduce the whiteness of the coated surface. Of course, when the coating layer is completely opaque, the whiteness of the coated paper is not affected by the base paper. However, the thickness and light transmittance of the coating layer decide that it does not have the ability to completely cover the whiteness of the base paper, so the whiteness of the base paper also affects the whiteness of the coated paper

if titanium dioxide, a pigment with high whiteness and high opacity, is added to the coating, it can not only improve the whiteness of the coating itself, but also further improve the whiteness of the surface of the coating layer because its high opacity covers the primary color of the base paper

to improve the whiteness of paper, the most important thing is to choose pulp with high whiteness, that is, to strengthen the bleaching of pulp. Secondly, choose a good filler. When the whiteness of the filler is higher than that of the fiber component, you can dilute the yellow tone of the pulp and significantly improve the whiteness of the paper. The whiteness of fillers varies greatly according to their types and grades. The higher the whiteness of selected fillers is than that of pulp, the greater the amount of fillers added, and the more obvious the whiteness of paper will be improved

whether coated paper or uncoated paper, fluorescent brighteners can be added to pulp or paint to improve the whiteness of paper. This is because the fluorescent brightener can absorb the invisible ultraviolet light and convert the ultraviolet light into 450nm blue light, so as to increase the reflectivity of blue light and improve the whiteness value. However, the whitening effect of fluorescent brighteners on pastes and coatings with low whiteness is very weak, because ultraviolet rays are absorbed by dark fibers or coatings and cannot be converted into visible light

in the production of uncoated paper, a small amount of magenta, lake blue or magenta is often added to the paper after glue, alum and filling to achieve the purpose of whitening. Adding a small amount of blue purple or red blue dye to the pulp can absorb the yellow or orange spectrum of 500 ~ 600nm, making the slightly yellow pulp yellow disappear, or even slightly blue or slightly red. The whiteness of the paper treated in this way has not been improved by using the whiteness meter, but it looks white to the human eye. This is because the added dye does not enhance the reflected light of the paper, but absorbs part of the yellow light to be reflected. Therefore, when observed with the naked eye, the whiteness of the paper has been improved to a certain extent

2 methods to improve the durability of paper

generally speaking, there are several methods to improve the durability of paper:

1) in order to improve the light stability, adding papermaking additives (such as calcium carbonate, titanium white, zinc white), UV protection agents, fluorescent brighteners, etc. can prevent the decrease of whiteness

plant fibers generally have their own colors, so whitening agents must be added to make white paper to improve the whiteness of the paper. Fillers commonly used for paper, such as calcium carbonate, titanium white, zinc white, etc., are white pigments, so the addition of fillers can increase the whiteness of the paper. The degree of whiteness increase depends partly on the whiteness of the filler and partly on the particle size and covering capacity of the pigment. The whiteness of paper also depends on the whiteness and beating degree of the pulp. If these fillers are added to the high whiteness slurry, the increase effect of fillers will be reduced

② change papermaking raw materials, such as changing coniferous and hardwood into non wood fibers. The fibers obtained from cotton, rags, flax, sandalwood skin, etc. can be used to make paper with good durability because of the high content of cellulose in pulp and the high degree of polymerization of cellulose

③ using paper correctly can also improve the durability of paper. The durability of paper is closely related to the storage conditions, so the temperature, humidity and light of the storage environment of product packaging boxes, books and documents should be strictly controlled. The temperature should be 12 ~ 25 ℃. A high temperature will increase the destructive effect of a small amount of chemicals (such as some acidic substances) in the paper on cellulose, and a low temperature will freeze the water contained in the paper, which will destroy the internal structure of the paper. The relative humidity should generally be 40% - 55%, which is suitable for the water balance condition of the paper

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