Paper is the most popular to create the packaging

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Take paper as the king and create a new century for the packaging industry (Part 2)

(2) chemical properties the chemical properties of paper include fiber and other components. It usually refers to the water, ash, pH (DH value), copper value, water-soluble chloride, etc. contained in the paper. Generally, the moisture content of paper is 6% - 8%, which often changes according to environmental changes. The moisture content of paper is too high, which means "taking money to buy water" for users; Too low means that the paper may be brittle, damaged and other problems. The time between packaging paper and the external environment is longer and more than ordinary paper, so it should be noted that 1. Pay attention to the change of its moisture in the process of experiment

ash is an inorganic substance contained in paper. The sources are: first, the paper-making raw materials should be reinstalled in situ to replace the inorganic substances contained in the body. Wood contains less ash, less than 1%. Grasses contain high ash, about 3% - 5%, and some straw contain 12% ash. 2、 In the process of papermaking production, inorganic residues brought by chemical reactions with chemical agents. 3、 Inorganic matter introduced after filler and coating are applied to paper. Ash has little impact on general packaging paper, but has a great impact on the manufacture of cellophane

acidity and alkalinity refers to the condition of hydrogen ions or oxyhydrogen ions contained in paper. It is usually represented by DH value. The paper with high acidity has poor stability and durability, gradually darkened color and low mechanical strength. This kind of paper is also not suitable for packaging food or metal products. During printing, it may also cause corrosion and contamination of the printing plate and affect the quality of the printed matter

copper valence is to determine the number of reductive terminal groups in the cellulose molecular chain that makes up the paper. Originally, the cellulose molecular chain was "intact", and its copper price was very low, that is, the number of terminal groups was small. Once subjected to oxidation and hydrolysis, the molecular chain breaks, and as a result, more terminal groups of the fruit are exposed, and the copper price rises rapidly. Therefore, the high copper price of paper indicates that the paper will deteriorate and its durability and strength will decline

the index of water-soluble chloride is very meaningful for some packaging paper, such as rust proof paper, neutral paper, food packaging paper, etc. Because the residual chloride is harmful to the application of this kind of packaging paper. Conductometric titration is usually used to check whether the water-soluble chloride contained in the paper "exceeds the standard", so as to determine the limit of use at the thematic forum on global automotive lightweight and green material optimization and innovation on the morning of September 18

the chemical properties of packaging paper have different effects on the safety and durability of paper

(3) mechanical properties

tensile strength of paper, formerly known as tensile strength. When subjected to external forces, the fibers are forced to stretch and the paper begins to stretch; After the external force is cancelled, the fiber automatically shrinks and the paper returns to its original state. The general requirements for packaging paper are good mechanical properties and not too small strength

toughness is an important index of packaging paper, which has large toughness and less damage; Small toughness and many damages. Another indicator of stiffness is the bending resistance of paper, which is a measure of its ability to support self weight. The stiffness of corrugated base paper and carton board is very important, and the stiffness of carton determines its use value. Burst resistance is the maximum pressure that a certain area of paper can withstand when subjected to constant pressure until it breaks. In general, the bursting strength is about 2 times of the longitudinal tensile strength per unit width of the paper sample. If the burst resistance is the performance under "static", then the impact strength is the reflection under "dynamic". For example, stretch bag paper has high impact strength, which makes it not easy to crack even under the sudden impact of external forces. Folding resistance is the number of times a paper folds back and forth under a certain tension to break it. In the process of making cartons and cartons of different sizes, the white cardboard and cartons in the packaging paper must be folded for many times without breaking, so it is required to have high folding resistance

curliness is the "shape" change of paper affected by humidity, temperature or other factors. When the moisture absorption of the front, back, middle and periphery of the paper is uneven, curling occurs due to local deformation. Generally speaking, when it is too wet, the front curl occurs; When it is too dry, it is curled on the opposite side. In addition, curl is related to the size change of paper, and is affected by thickness, evenness, tightness and scalability

(4) optical properties

paper has different reactions to light irradiation. For example, after total reflection, the vision produced by acting on human eyes is whiteness; For example, partial reflection and partial absorption are opacity; If it is diffused and reflected at a certain angle, it is glossiness. The above three optical properties are closely related to the emitting light source, observation conditions, receiving devices, etc. Generally, the wavelength of the light source is about 360 nm, the irradiation angle is 45 degrees, the reflection angle is 0 degrees (i.e. vertical), and the receiver is selenium light pool or photocell

the whiteness of paper is an important index of white packaging paper and packaging and printing paper. The whiteness of the paper is determined according to the requirements of the outer packaging of the goods, and generally 65% - 70% whiteness is used. High grade is 80% - 85% whiteness; Opacity can not be ignored for packaging and printing. For printing paper, the higher the opacity, the better. There are many factors affecting opacity, such as thickness, tightness, filler amount, etc; There are two kinds of gloss: one is contrast gloss, which is applicable to ASTM f1921 paper, which is the international standard for testing the thermal viscosity of ordinary white paper; The second is specular gloss, which is suitable for paper processed by super calender. The paper used for high-grade gift boxes has high requirements for gloss

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