Synthesis and applications of near-infrared absorbing additive copper hydroxyphosphate
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Research Letter
Synthesis and applications of near-infrared absorbing additive copper hydroxyphosphate Elena Pérez-Barrado, School of Chemical and Physical Sciences, Keele University, Staffordshire ST5 5BG, UK; Keeling & Walker Ltd, Whieldon Rd, Stoke-on-Trent ST4 4JA, UK Richard J. Darton, School of Chemical and Physical Sciences, Keele University, Staffordshire ST5 5BG, UK Dieter Guhl, Keeling & Walker Ltd, Whieldon Rd, Stoke-on-Trent ST4 4JA, UK Address all correspondence to Richard J. Darton at [email protected] (Received 22 May 2018; accepted 16 July 2018)
Abstract The use of copper hydroxyphosphate (Cu2PO4OH), also called libethenite, as a near-infrared (NIR) absorbing additive has been investigated. Samples were synthesized by using a hydrothermal treatment or simple wet chemical processing, which was later easily upscaled. All synthesized samples showed a strong absorption in the NIR region. Trials were conducted to produce laser-marked plastic plates and security IR ink printing tests. It was found that when incorporated in plastic and ink formulation, Cu2PO4OH added good NIR absorption properties without influencing other finished product properties too much, which confirms that it is a suitable additive that can be readily manufactured at room temperature and without pressured equipment.
Introduction Materials that either absorb or reflect near-infrared (NIR) radiation have numerous applications. This type of material, often used as an additive in polymers, can be found in a variety of products and places that are part of our daily lives: in cars, mobile phones, plastic bottles, buildings, passports. . ..[1–4] It is an important market for many businesses due to the large number of applications, such as in heat retention films, laser marking and laser welding, IR security inks, 3D-Moulded Interconnect Devices (3D-MID) and glazing, amongst others. For the particular case of laser-marking, where a laser interacts with a surface that by itself would insufficiently absorb NIR radiation, these additives are appropriately dispersed (e.g. in a polymer or coated film) and function as absorbers for the laser light.[5] Dispersed in security inks, these types of additives can be found in banknotes, which include numerous security features such as IR marks, easily detected by commercial banknote detectors. The color of these additives is an important property to be considered before their use. For some applications, the color of the additive is not determinant but for others, it is necessary to have flexibility in the coloring. Regarding the elemental composition of these additives, in the last few years, there has been a trend in the industry towards the use of compounds that are free of toxic metals (such as Cd, Ni or Sb) and also a need to keep production costs low. All these requirements demand new materials that should be easy to manufacture. Copper hydroxyphosphates have attracted attention due to their applications mainly in catalysis, but also in material and
intercalation chemistry. A number of copper hydro
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