ADHESIVES, GLUES AND SEALANTS
Do you know that adhesives or glues that cure by ultraviolet light are used in a wide variety of objects around you?, Watches, sunglasses, electronics devices, glass tables and even tooth fillings are made possible by the development and implementation of the ultraviolet-curing adhesives.
The ultraviolet curing adhesives are defined as adhesives / glues able to cure, solidify or harden only when it exposed to one source of ultraviolet radiation with an intensity and wavelength well defined previously.
One of the main disadvantages of use adhesives and glues as bonding materials is the waiting time in which we have to still and fixed the joint due the cure time of the adhesive. This is no problem with the use of adhesives cured by ultraviolet light, due its cured mechanism allows solidify the adhesive in seconds, so this type of adhesives are widely used in the manufacture of products in bulk , especially in automated processes which require high accuracy of dosage and short curing times.
You can find the following adhesives with UV curing technology;
Cured mechanism of UV light curing adhesives
The common feature with all UV cure adhesives is that they contain photoinitiator molecules which are activated and / or decompose when they absorb the energy emitted by the ultraviolet light; producing free radicals which initiate and accelerate the curing process of the adhesive achieving solidify state in order of seconds.
As we mentioned above the key or secret of this type of glue is to activate the curing reaction by supplying energy in the form of ultraviolet light, ultraviolet light energy is determined by their wavelength, so that ultraviolet light with a long wavelength has lower energy compare the same ultraviolet light but with a shorter wavelength. The selection of the correct wavelength is determined by the type of photoinitiator that adhesive contain, so long wavelengths cannot activate the photoinitiator inside of the adhesive doing that the adhesive don’t cure, and short wavelengths can be decomposed and / or reduce the mechanical characteristics of the adhesive.
Ultraviolet light curing adhesives considerations
The use of such adhesives requires suitable u.v. radiation equipment so that we ensure to dosage and apply the right wavelength (energy), each manufacturer of adhesive has their technical data sheet where you can find and select suitable ultraviolet equipment.
The rate of curing of these adhesives depends on:
The intensity or quantity of ultraviolet light applied
Time of application of ultraviolet
Distance of application of the ultraviolet to the adhesive
Thickness of the adhesive
Permeability of the substrate which has to pass through the ultraviolet
Permeability of the substrate must be take into account if you want bond with this kind of adhesives, due to activate the cure process the adhesive need to absorb ultraviolet light and is necessary that at least one substrate must be permeable to ultraviolet, the variation of the substrate (especially plastic) produce different cure times as well as different chemical and mechanical behavior, for example exist transparent glass substrates that absorb ultraviolet radiation preventing their passage into the adhesive, so that no curing adhesive occurs.
Furthermore there are ultraviolet combined curing adhesives which allow continue it curing after applying the ultraviolet light by applying heat, moisture or absence of oxygen, solidifying the adhesive in those dark / hidden areas where light has not reached or reducing cure time when the adhesive thickness is high. Finally we must take into account that these products are very sensitive to light, so we store in a suitable condition reducing their exposure to sun and artificial light.
Advantages of the ultraviolet light curing adhesives
High speed curing, reducing curing times and eliminating fastening and fixation tools increased efficiency, productivity and reducing the cost of the process.
1 component adhesive, not need to be mixed with another component, eliminating the possibility of error during the mixing process as well as the equipment for mixing, these adhesives do not have pot life.
Quick and easy verification of the joint by fluorescence of the adhesive, economic Non-destructive test and easily automated (online continuous inspection)
Possibility of combined cured adhesives (temperature, humidity, activators...) in order to cure the adhesive in areas where ultraviolet does not reach.
Solvent-free adhesives, improving environmental and health issues.
Adhesive suitable for bonded joints mass produced, easily automated process.
Adhesives transparent, allowing “invisible" joints improving aesthetics issues.
Disadvantages of the ultraviolet light curing adhesives
Need special equipment for generate the radiation of ultraviolet light as well as dispensing and verification equipment in production in mass.
Need permeable substrates to ultraviolet radiation; the variation of substrates involves changes in the mechanical and chemical properties of the adhesive.
Low range of adhesives available with this technology compared to conventional adhesives, reducing possible applications.
Adhesives cured by ultraviolet light are more expensive compared to conventional adhesives of the same family.
Applications of UV curing adhesives
Many sectors using these adhesives in its processes, optical industry for bonding lenses to the frame of the glasses, the electronics sector uses it for bonding and sealing components in electronic boards, decorative sector uses it to build tables and glass furniture, lamps, jewelry, earrings, and other decorative items, automotive uses it to seal sensors ...
Some of the areas where you use these types of adhesives / glues is the medical sector, because they do not emit hazardous solvents or compounds for health, these adhesives are widely used in the manufacture of medical devices such as syringes, tweezers, capsules, scalpels ...
Other fields where this type of adhesives used is the dental restoration, because of their curing time in seconds and non-emission of solvents or health hazardous compounds, these adhesives are used by most dentists during realization of tooth fillings.
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