Conditions and types of the hottest synthetic pape

Conditions and types of synthetic paper

synthetic paper printing synthetic paper refers to a flat material made of high molecular organic compounds (such as polystyrene, polypropylene, polyethylene and other plastic fibers), artificial short synthetic fibers, wood pulp and other raw materials with synthetic resin as the basic component through calendering or extrusion. In the process of forming synthetic paper, in order to make it have good whiteness, opacity, printability and writability, various inorganic fillers (such as clay, talc powder, calcium carbonate, iron oxide, barium sulfate, etc.), tackifiers, stabilizers and antioxidants are added according to the different raw materials used. After the paper is formed, it is also treated with water, inorganic acid solution, phosphate solution, aluminum sulfate and hydrated lime solvent, It can be used only after being oxidized by oxidants (hydrogen peroxide, sodium oxide, ozone, air, etc.). The composition and structure of synthetic paper not only retains the appearance, whiteness, stiffness, opacity, printability and writing of natural fiber paper, but also has the excellent characteristics of polyolefin plastic film, such as lightness, moisture resistance, oxygen resistance, acid resistance, alkali resistance, pollution prevention and so on. Therefore, synthetic paper has become a popular high-end new material for printing, packaging and decoration in the world market. （1） The conditions for synthetic paper as a printing material, synthetic paper should have the following conditions: ① white and opaque appearance; ② It must meet the operation suitability of the printing machine; ③ And printing inks. These three conditions are not controlled independently, but affect each other. How to make these elements cooperate with each other is the key to its quality design. 1. The appearance shall be white and opaque except in special cases. White paper can be obtained only after the wood pulp is treated with drugs, the utilization rate is low, and the relative molecular weight of cellulose is reduced. In contrast, it is easy to make synthetic paper only white and opaque. That is, after filling with white filler or designing foaming layer and porous layer, we can not only get high whiteness, but also get white products with higher purity than natural paper. At the same time, the opacity can also be changed by changing the above treatment conditions. 2. Adaptability of printing operation (1) static electricity when printing with a sheet fed printer, static electricity often occurs and causes faults, so it is necessary to prevent electrification. In the case of low humidity in Dongxiu, electrostatic barriers often occur in ordinary paper, so when using synthetic polymers that are inherently easy to be charged as raw materials, full attention should be paid. The ratio h0/d of diameter D is related to adding or coating anti electrification agent, but if it is used too much or selected incorrectly, the following adverse effects will occur. First of all, there will be seepage printing when taking notes, and plate pasting when film printing, and even become the cause of ink discoloration. In addition, the added inhibitor will lose its function if it volatilizes on the surface, so long-term stability is also one of the key requirements. (2) As we all know, cellulose is basically constructed by an extremely hard molecular skeleton. In contrast, the polymers used in synthetic paper raw materials are soft. Therefore, compared with natural paper of the same thickness, the hardness of general film is small. If the polymers used in synthetic paper are arranged according to the young's modulus, polystyrene and PVC are almost the same, followed by polypropylene and polyethylene. Needless to say, polypropylene and polyethylene are only films made as is, and their hardness is not enough, so measures should be taken to improve them. Adding fillers also has an effect, which varies according to the type of polymer, the type and amount of fillers, for example, in (1.2 × 104) after adding 30% glass, 40% asbestos and 40% talc into polypropylene with bending coefficient of kg/cm2, they are increased to (4.9, 2.8 and 2.5) respectively × 104kg/cm2。 Of course, even if the resin with high Young's modulus is used or extended and filled, the hardness of general synthetic paper is still worse than that of natural paper, but this is not related to the difficulty of paper feeding. The operability of paper feeding is controlled by the skilled procedures of the printer and the operator. For example, the products of Japan Synthetic Paper Company: with the same thickness of coating (about 120 μ m) Taking the same filler as an example, the printing plant initially used can print without failure at the speed of 120 sheets/min. on the contrary, some printing plants only maintain the speed of 60 sheets/min despite various adjustments. (3) Dimensional stability any kind of synthetic paper, from the nature of the selected materials, its dimensional stability to humidity changes is much better than natural paper, with almost no expansion. It is not only unnecessary to adjust the humidity of the printing workshop, but also unnecessary to dry the paper before printing. However, generally speaking, compared with other materials, plastic has a higher thermal expansion rate, so it may be considered that its size changes due to temperature changes. The linear expansion rate of polymers used as synthetic paper raw materials after heating, such as polystyrene is () ×、 HDPE is () × Wait, roughly () × Scope of. In the printing workshop without temperature regulation, if there is a temperature change of 10 ℃, the expansion rate can be calculated as 0.05% - 0.3%. From the standard state of relative humidity of about 60% to the expansion and contraction of natural paper caused by the humidity change of ± 0%, coated paper is 0.5%-0.9%, and glass fiber mixed paper is 0.15%-0.3%. Compared with this value, it can be seen that the size change of synthetic paper due to temperature change is within the allowable range. In terms of dimensional stability, it should be noted that its resistance to dynamic tension during printing is extremely small, and natural paper is easy to extend. Nowadays, almost all synthetic papers improve their dimensional stability through the above methods of improving stiffness and filling fillers. However, under normal printing conditions, even if they are generally met, the printing process requiring more stringent conditions in terms of tension or higher accuracy, such as stereoscopic printing, will also bring unsatisfactory results. (4) Flat natural paper and synthetic paper are no exception. If the surface of the paper is wavy and severely deformed, inaccurate overprint or even wrinkle will occur when passing through the printing cylinder, which will become a major fault. The corrugated state of natural paper can be restored to normal by drying, but synthetic paper will stretch due to humidity changes, which cannot be corrected by this method. The ripple of synthetic paper is mainly attributed to the material creep caused by uneven tension during rewinding, so this phenomenon can be prevented as long as we pay attention to the rewinding method. That is, reduce the thickness error in the width direction when manufacturing the film, disperse the difference in the width direction with a rotary table, rewind slowly, etc., and take different measures according to the manufacturing method. In addition, synthetic paper used for printing food packaging should also meet the following conditions: a. the synthetic paper used must fully meet the hygienic standards for food packaging. That is, there is no migration of toxic substances, non-toxic and odorless. b. With the appearance similar to natural fiber paper, the surface is smooth, white and opaque. c. It has good moisture-proof, waterproof, heat-resistant, cold resistant, corrosion-resistant, moth proof and UV penetration resistance. 3. Relationship with printing ink the surface of natural paper has the property of absorbing printing ink. Offset printing or relief printing ink has a certain degree of penetration and solidification on the surface of the paper immediately after printing, followed by polymerization and solidification. Synthetic paper is only required to have the adaptability of single sheet offset printing and letterpress printing, so its surface is expected to have the properties similar to natural paper. That is, the most important point of the so-called paper processing goal is to make it have a surface that this ink can penetrate. In order to achieve this goal, there are several methods, which are only briefly explained here. However, it is not to say that these methods have their own shortcomings. The manufacturers need to master the adjustment of their advantages and disadvantages. (1) Fillers filled with iron oxide, calcium carbonate and other fillers have strong compatibility with printing ink, but we must pay attention to the following points: only mixing about 20% - 30% of this kind of fillers can not obtain permeability, because at this time, the polymer is covered around the fillers, there is no necessary capillary, and if we only rely on filling fillers to get the effect, Either the content must be increased, or the surface layer must be washed off with solvent to expose the filler. (2) When the polyolefin film containing a large amount of filler is filled and extended, micro cracks will occur. By adjusting the occurrence of such cracks, it is conducive to penetration. (3) Pigment coating is a method of coating clay, titanium dioxide, calcium carbonate, etc. on the surface together with adhesives. The principle is the same as that of coated paper and coated paper in natural paper. With this method, we can not only get the same permeability as natural paper, but also have excellent smoothness, so we can get more ink compatibility and printing effect than natural paper. Jinan assaying is a household name. In addition, when the film is extruded and its surface is not completely cured, the paint effect can also be obtained by evenly dispersing the pigment. (4) Drug treatment here there is a method of treating the surface of the film with a mixture of solvent and non solvent; The method of solidifying it after treatment with bentonite or solvent; There are several ways to make the surface layer foam by soaking it in foaming agent. Either way, the permeability is adjusted through the control of treatment conditions and convenient disassembly. (5) The destruction of foaming unit can also be treated with the above drugs. The permeability can be obtained by treating the surface of independent bubble membrane with drugs or destroying the foaming unit with extension method to make continuous or semi continuous bubble membrane. (6) After extracting and mixing the soluble substances into a film, and removing them, a porous film can be obtained. The size of the capillary tube can also be adjusted by selecting the additive. (7) The porous film obtained by sintering polymer fine powder has ink permeability. （2） Types of synthetic paper the types of synthetic paper are divided into film method and fiber method. One kind of thin film method is to thin film resin and meta machine additives, which is called "internal paper method", and the other is to coat pigments on the surface of resin film, which is called "surface coating method". The fiber method includes spraying the dissolved resin from the nozzle, which is similar to spinning and made into a film. It is divided into "fiber glue method" and "synthetic pulp method". The representative Japanese film synthetic paper Yupo is introduced below. The manufacturing process of Po Yupo is to add inorganic fillers and a small amount of additives into the main raw material polypropylene resin, mix it, extrude it into a film shape with an extruder, and then draw it into a film by biaxial stretching. This is a typical internal paper synthesis method. Yupo is characterized by its stretched film, fine gap between additive and resin, and light weight. The resin composition structure is complex, and there are many tiny voids in each layer. The polypropylene film is stretched in uniaxial. Then, the resin containing additives is bonded on both sides of it. The film is composed of a uniaxial stretching intermediate layer and a resin film stretched at right angles to it. During the stretching process, many tiny pores are formed in the resin film, which are cracked near the surface, which can improve the printing and writing performance, increase whiteness, opacity and softness

reprinted from: printed in China