Synthetic paper should have the conditions and types

Synthetic paper refers to the use of synthetic organic resin-based high-molecular organic compounds (such as: polystyrene, polypropylene, polyethylene, and other plastic fibers), synthetic short synthetic fibers and wood pulp and other raw materials, by calendaring or extrusion The flat material.

During the molding process, the synthetic paper is added with various inorganic fillers (such as clay, talcum powder, calcium carbonate) according to different raw materials, in order to make it have good whiteness, opacity, printing property and writing property. , iron dioxide, barium sulfate, etc.), tackifiers, stabilizers, and antioxidants. After the paper is formed, it is treated with water, inorganic acid solution, phosphate solution, aluminum sulfate, and slaked lime, followed by an oxidant ( Hydrogen peroxide, sodium oxide, ozone, air, etc. can only be used for oxidation treatment.

The composition structure of synthetic paper not only retains the appearance, whiteness, stiffness, opacity, printability, and writing properties of natural fiber paper, but also has the lightness, moisture resistance, oxygen resistance, acid resistance, alkali resistance, and the like of polyolefin plastic film. Pollution and other excellent features. Therefore, synthetic paper has become a popular high-end new material for printing, packaging and decorating in the world market.

(A) Synthetic paper should have the conditions

The main conditions for synthetic paper used as a printing material are:

1 white opaque appearance;

2 must meet the operating adaptability of the printing press;

3 There is a good relationship between printing inks and so on. These three conditions are not independently controlled by each other, but affect each other. How to make these elements work together is the key to quality design.

1. Appearance

Except under special circumstances, it should have a white and opaque appearance. Wood pulp obtained white paper after being treated with drugs, with a low utilization rate and a decrease in the relative molecular mass of cellulose. In contrast, synthetic paper is only white and opaque is very easy. That is, after filling or designing a foamed layer or a porous layer with a white filler, not only a high degree of whiteness can be obtained, but also a white finished product with higher purity than natural paper is obtained. At the same time, the opacity can also be changed by changing the above processing conditions.

2. Suitability of printing operations

(1) When static electricity is printed on a sheet-fed printing press, static electricity often causes failure, and it is necessary to prevent the electrification. In the case of winter and low humidity, static paper often suffers from electrostatic obstacles. Therefore, when using a paper made of a synthetic polymer that is easily charged, it should be fully noted.

The method of preventing the electrification is to add or apply an antistatic agent, but if it is used excessively or the selection is wrong, the following adverse effects will occur. First of all, bleed-in occurs when taking notes, and it also causes stencils during film printing, and even causes discoloration of the ink. In addition, the added inhibitors lose their effect if volatilized on the surface, so having long-term stability is also one of the requirements.

(2) Hardness It is well known that cellulose is made of a very hard molecular skeleton with its basic structure. Contrary to this, the polymers used in the raw materials used by people are soft. Therefore, the general film has a lower hardness than natural paper of the same thickness.

When the polymer used for the synthetic paper is arranged according to the Young's modulus, polystyrene and polyvinyl chloride are almost the same, followed by polypropylene, and the smallest is polyethylene. The first two needless to say, polypropylene, polyethylene, just as the film made of the original, its hardness is not enough, should take measures to be improved.

The addition of filler also has an effect, and the effect is different depending on the kind of polymer, the type and amount of the filler, for example, adding 30% of glass, 40% of asbestos, and talc 40 to a polypropylene having a (1.2×104) kg/cm 2 bending coefficient. After %, they were increased to (4.9, 2.8, 2.5) x 104 kg/cm2, respectively.

Of course, even if a resin with a high Young's modulus or a stretch and filler is used, the general synthetic paper is inferior in hardness to natural paper, but this is not related to the difficulty of paper feeding.

The workability of paper feeding is determined by the skilled procedures of the printer and the operator. For example, in Japan Synthetic Paper's product: the same thickness coating (about 120μm), the same filler material, for example, the first used printer can be printed without any trouble at a speed of 120 sheets/min. Although various adjustments were made, only 60 sheets/min were maintained.

(3) Dimensional stability For any kind of synthetic paper, from the nature of the materials used, it is much more superior to natural paper in terms of dimensional stability in terms of humidity change, with almost no stretching. Not only does it not need to adjust the humidity in the press room, it does not even require paper to be printed before printing.

However, in general, plastics have a higher coefficient of thermal expansion than other materials. Therefore, it may be necessary to consider the dimensional change caused by changes in temperature, and the linear expansion coefficient value of a polymer used as a synthetic paper raw material after heating, such as polystyrene. Yes (6-8) x 10-5, high-density polyethylene is (10-16) x 10-5, etc., and is roughly in the range of (5-30) x 10-5. In a temperature-controlled printing plant, if there is a temperature change of 10°C, the expansion rate can be calculated as 0.05%-0.3%. From the standard state of about 60% relative humidity to about ±0% of the field, the natural paper is stretched, the coated paper is 0.5%-0.9%, and the glass fiber mixed paper is 0.15%-0.3%. Judging from this value, it can be seen that the size change of the synthetic paper due to temperature changes is within the allowable range.

In terms of dimensional stability, it should be noted that it is less resistant to dynamic tension during printing than natural paper and is easily extended. Nowadays synthetic papers almost all improve the dimensional stability by the above-mentioned methods for increasing the stiffness and filling fillers. However, under normal printing conditions, even if it is substantially satisfied, more stringent conditions are required in terms of tension or printing processes such as three-dimensional printing require higher accuracy, and unsatisfactory results are also brought about.

(4) Flat natural paper, synthetic paper without exception, if the surface of the paper is corrugated and deformed seriously, overprinting will occur when the printing cylinder passes through, and even wrinkles may become major problems.

The corrugated state of natural paper can be returned to normal by the paper, but the synthetic paper will be stretched due to humidity changes and cannot be corrected by this method. The corrugation of the synthetic paper is mainly due to the creep of the material caused by the uneven tension during rewinding, so it is possible to prevent this phenomenon by paying attention to the rewinding method. That is, the thickness error in the width direction at the time of manufacturing the thin film is reduced, the difference is dispersed in the width direction by the turn table, the slow rewinding, etc., and different measures are taken according to the manufacturing method.

In addition, the synthetic paper used for printing food packaging should also meet the following conditions: a. The synthetic paper used must fully comply with food packaging hygiene standards. That is, no migration of toxic substances occurs by itself, and it is non-toxic and odorless. b. Has the appearance of a similar natural fiber paper with a smooth, white and opaque surface. c. Has good moisture-proof, waterproof, heat-resistant, cold-resistant, anti-corrosion, anti-aging and anti-UV penetration properties.

3. The relationship between printing inks

The surface of the natural paper absorbs the properties of the printing ink. After the printing, the offset printing or letterpress ink has a certain degree of penetration and solidification on the surface of the paper immediately followed by polymerization and curing. Synthetic paper is only required to have the suitability of sheet-fed offset printing and relief printing, and it is hoped that its surface will have natural paper-like properties. That is, the most important point of the so-called paper processing target is to make this ink-permeable surface.

In order to achieve this goal, there are several ways, only a brief description here. However, it does not mean that these methods all have their own shortcomings. The adjustment of their advantages and disadvantages requires that the manufacturers master them.

(1) Fillers Filling with iron dioxide, calcium carbonate, and other fillers themselves has a high tolerance for printing inks, but it must be noted that only 20% to 30% of such fillers are mixed, and permeability cannot be obtained because At this time, the polymer is covered around the filler, there are no necessary capillaries, and if the effect is achieved only by filling the filler, either the content must be increased, or the surface layer must be washed away with the solvent to expose the filler.

(2) Fine cracks may occur when the filler is filled and extended and a polyolefin film with a large amount of filler is stretched. By adjusting the occurrence of this crack, penetration is facilitated.

(3) Pigment coating This is a method of coating clay, titanium dioxide, calcium carbonate and the like together with a binder on the surface. The principle is the same as that of coated paper and coated paper in natural paper. In this way, not only can Natural paper has the same permeability and excellent smoothness, so it can get more ink acceptability and printing effect than natural paper.

In addition, when the film is extruded and the surface is not completely cured, the pigment can be evenly dispersed therein, and the coating effect can also be obtained.

(4) Drug treatment There is a method of treating a film surface with a solvent-non-solvent mixture, a method of solidifying it with a swelling agent or a solvent, and a method of impregnating a surface layer with a foaming agent to foam it. . Either way, the permeability is adjusted by controlling the processing conditions.

(5) The destruction of the foaming unit can also be treated with the above-mentioned medicine, and the permeation can be obtained by treating the surface of the closed cell membrane with a drug or breaking the cell with an extension method to form a continuous or semi-continuous cell membrane.

(6) Extraction After the soluble substances were mixed into a thin film, they were extracted and removed to obtain a porous film. The size of the capillary can also be adjusted by selecting the added substance.

(7) A porous film obtained by powder sintering and sintering of a polymer fine powder having ink permeability.

(b) types of synthetic paper

The type of synthetic paper is classified into a film method and a fiber method. One of the thin film methods is to thin film the resin and the machine additives, called "internal paper method", and the other is to coat the surface of the resin film with the pigment, which is called "surface coating method". The fiber method involves spraying a molten resin from a nozzle, like spinning, into a film. Divided into "Fibre glue legal" and "Synthetic pulp law."

The following is a representative YUPO of Japan's thin-film synthetic paper.

1. YUPO manufacturing process

YUPO is made by adding inorganic filler and a small amount of additives to the main raw material polypropylene resin, mixing and stirring, then extruding into a film by an extruder, and then making a film by biaxial stretching. This is a typical internal paper synthetic paper. YUPO is characterized by the fact that it is a stretched film, and there is a fine gap between the additive and the resin, and the weight is light. The resin composition is complex and there are many tiny gaps in each layer.

The polypropylene resin film was uniaxially stretched. A resin containing an additive is further laminated on both sides of the film, and the film is composed of a uniaxially drawn intermediate layer and a three-layered resin film stretched at right angles thereto. In the stretching process, a lot of tiny pores are formed inside the resin film and cracked at the adjacent surface, which can improve the printing and writing performance, increase whiteness, opacity, and softness.

Reprinted from: Printed in China