Plastics include plastic films and plastic products. Plastic film printing includes process of plate making, blow molding, corona treatment, printing, compounding, slitting, heat sealing and bag making; printing of plastic products includes plate making, flame treatment and printing. Plastic printing is not a process, but a printing type that is divided by the substrate.
Plastic printing features
Plastic printed substrates are plastic films and plastic products. Their molecular structure contains polar substances, good chemical stability, and resistance to most acid and alkali corrosion. At room temperature, it is insoluble in common solvents, and antioxidants are added during the production process. Due to the poor affinity of the plastic substrate with the ink, the ink is not easily dried after printing. At the same time, plastic substrates do not have the porosity of the paper surface and cannot absorb the ink binder. Therefore, the plastic substrates must be processed before printing so that they can be well-affixed to the ink, and the ink can be well adsorbed during printing. After printing, the ink layer does not separate from the substrate. Plastic printing inks are different from paper inks, and they cannot be mixed.
Plastic printing ink features
In order to meet the requirements of plastic substrates for inks, plastic printing inks mainly consist of synthetic resins, organic solvents and colorants. After being fully dispersed and grinded, they have good colloidal fluid properties. Plastic printing inks are volatile inks. Good printability, fastness, fast drying, etc.
The key to printing inks for plastic film printing is the adhesion of ink and plastic film, and this has a lot to do with the choice of binders.
There are several methods for selecting the binder for plastic film inks:
1. Use the same resin as the substrate, or resin that can dissolve with the substrate material. After the substrate is inked, due to the effect of the solvent, the interface between the ink and the substrate will dissolve and adhere to each other.
2, the use of ink with the printing material can occur in chemical reaction materials;
3, the use of adhesive material can form a similar surface layer of the substrate;
4, using the same material and substrate polar material.
Therefore, the ink used for plastic printing varies depending on the type of substrate material. Generally selected to be immiscible with the printed material of the binder, such as polyolefin plastic film ink ethylene copolymer used as a binder. Plastic film is generally used rotogravure printing, ink is solvent-based ink. This type of ink can meet the needs of high-speed printing, but its volatile organic solvents are also quite a lot, and the environment is also very serious pollution. Plastic films can also be screen-printed. Their inks are used as a binder to synthesize dispersions in aqueous media. Although the problem of solvent contamination is avoided, the print quality is not very good. In addition, plastic films can also be printed with flexographic printing.
The performance and role of ink components
Printing ink is a paste colloid that is uniformly mixed with components such as colorants, binders, and fillers. As a viscous fluid ink, due to the different properties of its varieties are also different, that is, thick and thin; the difference in viscosity, the drying speed is not the same situation. Therefore, the correct understanding and understanding of the role of the constituent components of the ink in the ink is of great significance in accurately adjusting the characteristics of the ink and improving the quality of the product.
1, the role of pigment in the ink.
Pigments include pigments and dyes. The colored materials used in printing inks are usually pigments, but also some dyes. They are all very fine colored materials. Pigments are insoluble in water and do not dissolve in the binder, and are mostly suspended in solution; dyes are generally soluble in the vehicle. The relative density, transparency, heat resistance, lightfastness, and chemical resistance of inks are all related to pigments. Its color determines the hue of the ink; its amount determines the concentration of the ink; its use affects the drying of the ink to a certain extent, and the oxidative polymerization and drying of the ink is particularly prominent.
2, the role of the link material in the ink.
The binder is a fluid with a certain viscosity and viscosity. Its role is multifaceted. As a carrier of the pigment, solid particles such as a powdery pigment are mixed and connected, and the pigments that are adhered to each other can finally be attached to the print. The quality of the linking material will directly affect its gloss, abrasion resistance and viscosity flow.
3, the role of additives.
The use of auxiliaries will be more effective for printing. Commonly used additives are diluting agents, additives, detackifiers, anti-adhesive agents, ink transfer and so on. Therefore, the reason why the printing ink is good in printability, strong adhesion and dispersibility, is inseparable from the additives.
Printing on the table and India
The so-called surface printing refers to the process of printing the plastic film on the surface of the finished product after the process of bag making and printing.
The surface-printed plastic film requires good ink adhesion and has considerable wear resistance, light resistance, freeze resistance, and temperature resistance. In recent years, some ink merchants have developed special heat-resistant surface-printing alcohol-soluble inks, such as Yip's ink (Shanghai) Co., Ltd. has successfully developed GYP-L series surface-printing high-temperature inks, which are resistant to abrasion and light. Sex, adhesion and color luster are all excellent.
The surface printing range is mostly polyethylene, polypropylene and other polyolefin films as substrates. There are two types of polyolefin film processed and untreated, and the ink is also divided into three types: dedicated, untreated, and general-purpose. The untreated special ink is an ink with cyclized rubber as the main link material. Its gloss, heat resistance, and sealability are good, and it is mainly suitable for packaging such as pasta. Due to the disadvantages of slow printing speed, residual solvents, and poor oil resistance, there is currently a tendency to reduce the use. The treatment of special inks with polyamide resin and nitrocellulose as the main link material, the heat resistance, oil resistance, chemical resistance are good. Plastic surface printing inks other than polyolefins include styrene inks using acrylic resin as the main binder, and vinyl chloride inks using salt acetate resin as the main binder. However, they all require high gloss and stable printing effects.
Liyin refers to the use of reverse-image printing plates to transfer the ink to the inside of the transparent printing material, so as to display the image-like printing method on the front side of the substrate. Its advantages are bright colors, no fading, no fading, moisture-proof and wear-resistant. After the printing ink is printed, the ink is coated with a curing agent (AC agent) or a bonding agent, which can be attached to the sealing film or the aluminum foil. With the development of composite packaging materials, many kinds of inks have entered the market. Currently, representative inks are mainly high-performance general-purpose inks with alkane resin as the linking material and polypropylene inks with the largest amount of composite packaging films. These inks are printed at high speed. Adaptability is good, and there is good level reproducibility and lamination processing suitability.
Sheet printing is often printed in reverse order, with white ink in the first place, while black ink is printed in the last unit. In India, on the other hand, the reverse order of ordinary two-sided printing is reversed. For example, the background color of a common surface printing is printed first, and the background color is printed last. Of course, a special printing item should be treated specially depending on its condition.
The difference between the printed ink and the printing solvent
The role of the solvent is to dilute the viscosity of the ink, making it more excellent in leveling and dispersion of the ink, and adjusting the volatilization rate to make it more suitable for printing. The thinner is determined by the temperature, humidity, and speed of the car. The diluent is often mixed solvent. The mixed solvent is better than the single solvent. No matter if it is printed or printed, the added solvent must not contain water exceeding the standard (not more than 2%), otherwise it will affect the printability, and the ink will appear thickened. Rough, precipitate decomposition and other undesirable phenomena. In chlorinated polypropylene inks, benzenes and esters are the true solvents for inks, and the ratio of the amount used is not limited. Isopropanol is a spurious solvent, and isopropyl alcohol is added to reduce the surface tension of the ink, prevent static electricity, and improve ink transferability. However, it cannot be added separately when it is added, and it is generally added by mixing. The amount should be controlled at 5 to 15%. In polyamide inks, benzenes and alcohols are true solvents, while ethyl acetate is a false solvent. When they are added together, the amount of ethyl acetate should not exceed 20%. Otherwise, the ink layer is easy to be white and has no color.
(Chen Quandong)
Source: "Chinese Packaging"