The hottest screen printing ink for polyethylene p

Printing inks for polyethylene and polypropylene plastics

I. Introduction to plastics

organic high molecular polymers can be molded under heating and pressure, and materials that can maintain a fixed shape under normal temperature and pressure are called plastics. The main component of plastic is synthetic resin, which is a product synthesized by artificial methods from organic polymers. Its performance is similar to that of natural resin. In order to change some properties, some auxiliary materials can be added, such as fillers, plasticizers, stabilizers and colorants. All components of plastic are uniformly bonded together by synthetic resin. Plastics can be divided into thermoplastic and thermosetting plastics according to their different properties after heating

polyethylene and polypropylene are two kinds of general plastics, mainly urea formaldehyde plastics. Because of their large output and low price, they are widely used

1. polyethylene (PE) plastic

polyethylene plastic has many uses, and can be made into various finished products through extrusion, injection and other molding processes. The molecular chain of polyethylene is a long chain composed of methylene, which contains a certain amount of side groups. According to the chemical principle, the more side groups in the polymer chain, the longer, the lower the crystallinity of the polymer, that is, the higher the density of polyethylene, the less conducive to surface finishing. Generally, polyethylene is insoluble in many solvents, but when the temperature exceeds 70 ℃, a small amount of polyethylene can be dissolved in toluene, amyl acetate and other solvents. This property of polyethylene provides conditions for surface finishing. We can soak the plastic with heating solvent to make its surface swell and destroy some crystals, so as to improve the adhesion of printing ink film on the plastic surface. The mixture of concentrated nitric acid, chromic acid, fuming sulfuric acid and sulfuric acid can slowly act on polyethylene at room temperature; The mixture of sulfuric acid and nitric acid at 90 ~ 100 ℃ can quickly destroy polyethylene; Soaking polyethylene plastic with a mixture of potassium dichromate, sulfuric acid and distilled water at 70 ~ 75 ℃ is conducive to enhancing the adhesion of the ink film on the plastic surface

2. Polypropylene (PP) plastic

for many years, polypropylene has been one of the important varieties in the development of plastics. It is suitable for all molding methods, and can be used as all kinds of pipes, building materials, sewer pipes, all kinds of boxes, films, fibers, etc. Industrial polypropylene has high crystallinity, and its isotactic index is as high as 89% - 95%. At the same time, it also contains a small amount of macromolecular chains with amorphous random structure and low crystalline cubic block structure. When the melting point of plastic is in the range of 170 ~ 175 ℃, the glass transition temperature of isotactic polymer is -13 ~ 0 ℃, while the glass transition temperature of syndiotactic polymer is reported to be 0 ℃. Concentrated nitric acid and fuming sulfuric acid can etch polypropylene. At higher temperatures, polypropylene can dissolve in aromatics and oxidized hydrocarbons, but at room temperature, it can only expand. Acids and esters also have a certain corrosion effect on it. With the increase of isotactic polymer content, the solvent resistance will be improved accordingly

in general, polyethylene and polypropylene are non-polar molecular polymer materials with high crystallinity and low surface tension. There are no polar groups such as carbonyl, carboxyl and hydroxyl in their molecular structure. However, compared with polyethylene, the surface coating of polypropylene is easier

for polyolefin materials, in order to ensure the adhesion of ink film, the plastic surface must be treated. One method is to increase the surface tension of plastic solids. The method is to increase the molecular weight of the low molecular layer on the plastic surface by using ultraviolet light in the presence of photosensitizer, so as to improve the surface tension of solids. Another method is to oxidize the molecules on the surface of polyolefin plastics and generate some polar groups such as carboxyl, hydroxyl and carbonyl groups on the surface, so as to improve the critical surface tension of the plastic surface and the adhesion of ink and paint to the plastic surface. Flame, chromic acid mixture, discharge oxidation, ozone oxidation and other treatment methods can be used

II. Polyethylene and polypropylene plastic printing inks

Plastic printing inks are also known as coatings or printing materials. The following briefly introduces the performance requirements of plastic printing materials for inks and the process requirements of printing operations for inks:

1. Performance requirements of plastic printing materials for inks

① the appearance of printing ink film is flat and bright

② the ink should have good adhesion on the plastic surface

③ the ink film should have greater hardness and wear resistance

④ the ink film should have certain water resistance and heat resistance

⑤ the ink film should have certain alkali resistance, acid resistance, and resistance to alcohol and other organic solvents

⑥ the ink film has certain weather resistance and has little influence when the temperature and humidity change

2. Process requirements for printing ink

① thickening is allowed in the printing process, but the service life should exceed 4H; ② The ink used in plate printing is easy to operate, and the scraping operation is convenient and free. The printing plate does not draw and stick when leaving; Clear imprinting and good leveling

③ silk and other utensils are easy to clean

in actual production, we should select appropriate PE and PP plastic printing inks according to the above performance requirements and process requirements. Although phenolic, alkyd and other coatings are easy to operate, their adhesion, hardness, wear resistance and other properties can not meet the requirements. Nitrocellulose paint, perchloroethylene paint and acrylate paint have good properties. However, through the plate printing test, it is found that due to the rapid volatilization of the solvent, it is necessary to frequently supplement the solvent in the scraping process, and the wiredrawing phenomenon will also occur when the printing plate is separated. The paint film is not easy to level, and it is easy to block in the scraping process, so it is not suitable for PE and PP plastic plate printing

since plastic printing materials are not allowed to be baked, it is only allowed to use Chang 7. Do not wipe the reflector and spectroscope of the instrument as much as possible. The isothermal catalytic curing ink is easy to get at room temperature. The catalytic curing coatings include polyurethane coating, acid curing amino coating, amine curing epoxy coating, etc. Polyurethane coating is easy to react with moisture (water) in the air, so it is not allowed to expose and scrape the coating on the printing plate for a long time; However, the acid catalyst in the acid curing paint has a corrosive effect on the wire, and the acid curing paint has a strong smell of formaldehyde, which cannot be scratched manually; Amine cured epoxy ink can be made into coatings with high solid content and low viscosity. Because the resin has a certain amount of hydrocarbon and epoxy groups, it can also form chemical bonds with hydrocarbon and carbonyl groups on the treated plastic surface, which can improve the fixation fastness of the plastic surface. Of course, epoxy coatings also have shortcomings, but due consideration is given to the formulation design, it is still a better choice for inks with certain chemical and physical properties. Amine cured epoxy coatings are suitable polyolefin plastic printing coatings

epoxy resin and different pigments can be processed into inks with different colors, which can quickly break the supply and demand pattern and inherent mechanism of the upstream and downstream industries. According to the requirements of product performance, appropriate use of fillers can also be made into inks with different gloss. In order to improve the performance of ink, additives can also be used appropriately, such as driers, leveling agents, defoamers, etc

source: ink information