How a led uv ultraviolet light cure coatings inks paints ?

UV curing (ultraviolet curing) included led uv curing and mercury uv curing are the process by which ultraviolet light are used to initiate a photochemical reaction that generates a crosslinked network of polymers. UV curing is adaptable to printing, coating, paintings, paints , decorating, stereolithography, and in the assembly of a variety of products and materials. In comparison to other technologies, curing with UV energy may be considered a low-temperature process, a high-speed process, and is a solventless process, as cure occurs via direct polymerization rather than by evaporation. Originally introduced in the 1960s, this technology has streamlined and increased automation in many industries in the manufacturing sector.

A primary advantage of curing with ultraviolet light is the speed at which a material can be processed. Speeding up the curing or drying step in a process can reduce flaws and errors by decreasing time that an ink or coating spends wet. This can increase the quality of a finished item----printing paper various effect and wood finishing products, and potentially allow for greater consistency. Another benefit to decreasing manufacturing time is that less space needs to be devoted to storing items which can not be used until the drying step is finished.

Because LED UV energy has unique interactions with many different materials, LED UV curing allows for the creation of products with characteristics not achievable via other means. This has led to UV curing becoming fundamental in many fields of manufacturing and technology, such as printing ink, wood coatings where changes in strength, hardness, durability, chemical resistance, and many other properties are required for matching led uv curing character.
UV LED technology has seen sustained growth in the UV curing marketplace. Generating energy most efficiently in the 365-405 nm 'UVA' wavelengths, continued technological advances, have allowed for improved electrical efficiency of UV LEDs as well as significant increases in output. Benefiting from lower-temperature operation and the lack of hazardous mercury, UV LEDs have been main option in many printing ink /electric glue/adhesive / wood coats/paints applications.

How a led uv ultraviolet light cure coatings inks paints ?

Firstly, let us know one material, photosensitive polymer
Photosensitive polymer or light-activated resin is a polymer that changes its properties when exposed to light, usually in the ultraviolet or visible region of the electromagnetic spectrum. These changes are usually manifested in the structure, for example, the hardening of the material is due to cross-linking when exposed to light. An example is shown below, describing a mixture of monomers, oligomers, and photoinitiators that form a hardened polymer material through a process called curing.

Various technically useful applications rely on photopolymers; for example, some enamels and varnishes depend on photopolymer formulations in order to properly harden during exposure. In some cases, when exposed to light,coats/paints/varnishes can be cured in a fraction of a second, while heat-curing enamel/coats/paints may take half an hour or more. Curable materials are widely used in medical, printing ,wood finishes and photoresist technologies.

Changes in structural and chemical properties can be induced internally by chromophores that the polymer subunit already possesses, or externally by addition of photosensitive molecules. Typically a photopolymer consists of a mixture of multifunctional monomers and oligomers in order to achieve the desired physical properties, and therefore a wide variety of monomers and oligomers have been developed that can polymerize in the presence of light either through internal or external initiation. Photopolymers undergo a process called curing, where oligomers are cross-linked upon exposure to light, forming what is known as a network polymer. The result of photo-curing is the formation of a thermoset network of polymers. One of the advantages of photo-curing is that it can be done selectively using high energy light sources, for example lasers, however, most systems are not readily activated by light, and in this case a photoinitiator is required. Photoinitiators are compounds that upon radiation of light decompose into reactive species that activate polymerization of specific functional groups on the oligomers. An example of a mixture that undergoes cross-linking when exposed to light is shown below. The mixture consists of monomeric styrene and oligomeric acrylates.

Monomeric styrene and oligomeric acrylates can be used to produce crosslinked polymeric structures through photopolymerization.

UV curing technology

LED curing is a new and environmentally-friendly curing technology, namely UV curing, which uses the ultraviolet light emitted by a UV curing machine to trigger an instant photochemical reaction of UV coatings, forming bright light with a network-like chemical structure on the surface of printed matter or wood coating. At present, UV curing machines have become the choice of many UV coating manufacturers. They are widely used in many industries such as offset printing, inkjet printing, lithography, and wood coating curing. Electronic glue curing technology is also quite mature.

How to cure UV varnish? Principle analysis

The basic principle of UV curing technology is to use the instant chemical reaction triggered by ultraviolet light in the 365nm, 385nm, 395nm, 405nm wavelength bands to form a transparent glossy coating on the surface of the printed matter. At present, the UV varnishes used in the industry basically use free radical (also called free radical) polymerizable acrylate materials, including acrylate oligomers with polymerizable double bonds and acrylates with unsaturated double bonds. Class monomers and photoinitiators, etc. After UV varnish is irradiated by ultraviolet rays, the photoinitiator in its component first absorbs the light energy, generates free radicals upon excitation, initiates and leads to the photopolymerization and crosslinking reaction of unsaturated acrylate oligomers and reactive monomers, forming Curing the coating.

UV curing means that under the irradiation of ultraviolet light, the photoinitiator absorbs photons of a specific wavelength and is excited to an excited state to form free radicals or cations. Then through the transfer of energy between molecules, the polymerizable prepolymer and photosensitive monomer are made When it becomes an excited state, a charge transfer complex is produced. These complexes are continuously cross-linked and polymerized to produce high molecular polymers that solidify into a three-dimensional network structure in a very short time.

Among them, absorbing radiation energy, initiating the crosslinking and curing of unsaturated double bonds of monomers and oligomers, is a key part of the UV curing system. UV light curing technology is a new technology in the green industry. It was once rated as an industrial technology with "5E" characteristics by the North American Radiation Curing Committee, which fully demonstrated the characteristics of this technology.

The so-called 5E:

Efficient, is highly efficient. UV curing can achieve complete curing within a few seconds, and the production efficiency is higher;

Energy saving, energy saving, UV products are fast curing at room temperature, and their energy consumption is generally only 1/10 to 1/5 of thermal curing;
Environmentally friendly, the UV curing material contains no or only a small amount of solvents, and the energy used for UV curing is electricity, no fuel or gas, and no CO2 generation, so UV curing is known as "green technology";
Economy, economical, compact UV curing device, assembly line production, fast processing speed, thus saving space, high labor productivity, UV curing process ensures thinner film, and has excellent performance to reduce raw material consumption, which is conducive to reducing economic costs;
Enabling, wide adaptability, the UV product can be adapted to a variety of substrates, such as paper, wood, plastic, metal, leather, stone, glass, ceramics and almost all hard and soft materials.

Features of UV curing:
(1) Wide application range. In addition to paper prints, UV coating can also be applied to many substrates, such as aluminum foil, gold and silver cardboard, vacuum aluminized film, laser film, plastic, synthetic paper, metal, wood and other printing media.

(2) Excellent film-forming properties. After UV curing, it not only has high gloss, flat and smooth, but also after UV curing, it has excellent wear resistance, water resistance, heat resistance, scratch resistance, and chemical resistance due to the formation of a strong body network structure. The performance of chemicals and solvent resistance is unmatched by other glazing coatings.

(3)Using a UV curing machine can increase the production efficiency, which is higher than the general mercury lamp curing efficiency, more energy-saving, and no heat. Stable coating performance. Because UV varnish does not contain volatile solvents, it is not easy to cause viscosity changes in the coating process, so the coating stability is better, and the dosage is less.

(4) Product adhesion can be avoided. The resin used in solvent-based glazing coatings is mostly thermoplastic resins, which are greatly affected by factors such as temperature, humidity, coating thickness and drying conditions, which are likely to cause adhesion of varying degrees of products, and UV coatings as long as the light conditions meet the requirements , You don’t have to worry about adhesion problems at all, and you can stack them at will or perform post-processing operations after glazing.

(5) LED UV curing solutions Can replace plastic composite. The use of UV coating to replace the plastic film composite process has been widely used in many fields at home and abroad. It can completely avoid the edge curling, blistering, wrinkling, delamination and other phenomena that often occur in the laminating process, and it can be recycled for papermaking and reduce laminating. Environmental pollution caused by products that cannot be regenerated.

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