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UV-curing technology is characterized by less environmental pollution, fast curing speed, low energy consumption. It is the fastest growing market segment in the ink, coating, printing and packaging fields. UV-curing resin system is mainly composed of photoinitiator, reactive oligomer, active diluent and other additives.
Photoinitiator is the key component of uv-curing resin system, which plays a decisive role in curing rate. According to different reaction mechanism, photoinitiators can be divided into free radical type and cationic type. In this post, we will introduce you the application of different free radical photoinitiators.
Common free-radical photoinitiators
Main free-radical photoinitiator introduction
KIP-100F and KIP-150 Photoinitiator
KIP-100F和KIP-150特別適用于需要極低固化氣味和顏色穩定性的UV固化體系的光聚合。當在與水相容的溶劑中預稀釋時，它適用于水基 UV 固化體系。主要應用包括粘合劑、印刷油墨、地板涂料、木材、塑料、紙張、金屬和光纖的清漆。最佳濃度為0.5%至5%（重量），具體取決于系統組成、厚度和所需的固化速度。
KIP-100F is particularly indicated for the photopolymerisation of UV curable systems when very low curing odor and colorstability are required. It is suitable for water based UV curable systems when prediluted in a water compatible solvent. Main applications include adhesives, printing inks, coatings for flooring,clear lacquers for wood, plastic, paper, metal and optical fibers. Optimum concentration is between 0.5 and 5% by weight and depending on system composition, thickness, and desired cure speed.
KIP-150 is a polymeric photoinitiator with good miscibility with resin systems, which provides low volatility and low migration. It can also be made into water emulsion and used as water-based photocuring initiator. The molecular chain of KIP-150 contains multiple initiator units, which can simultaneously form multiple free radicals on one macromolecule when irradiated by light, and the local free radical concentration can be very high. The local high concentration effect can effectively deal with oxygen inhibition and accelerate photopolymerization, but the probability of mutual coupling termination of active free radicals in macromolecules will also increase. By designing molecular structure, intramolecular free radical coupling can be reduced.
The photoinitiator KIP-100F produced by Synasia is composed of 1173 and KIP-150. Due to the characteristics of high reactivity, low odor and good color stability, KIP-100F is generally used in various coatings and adhesives, etc. It involves in industries like plastics, wood, metal, etc.
1173 is a high-efficiency, non-yellowing UV photoinitiator. The UV curing system of unsaturated polyester system has the characteristics of low odor, non-yellowing and good color stability.
1173 is a multifunctional liquid photoinitiator, which can be used for the acrylicseries of UV-curable varnishes on paper, metal and plastic surfaces. It is especially recommended for UV coatings that require only slight yellowing even when exposed to sunlight for a long time. 1173 has good compatibility and can be easily mixed with other photoinitiators and prepolymers.
TPO has excellent performance and is often used in combination with secondary amine and tertiary amine. It has been widely used in coatings, inks, adhesives, corrosion inhibitors, solders and other industries. Since 21st century, TPO initiator has been widely promoted and applied in the field of UV curing.
TPO has a wide range of long UV wavelength absorption. Its effective absorption peak is 350nm ~ 400 nm, and absorbs all the way to 420 nm wavelength. Its absorption peak is longer than that of conventional initiator. Because of this, TPO photoinitiator is widely used in many applications, such as ultraviolet curing coatings, printing inks, ultraviolet curing adhesives, optical fiber coatings, etc. And because of its function of photobleaching, TPO is specially used in thick film and white systems. It can be completely cured on the pigmented surface of white or high titanium dioxide. TPO initiator can also be used for transparent coatings, especially for products with low odor requirements.
819 is one of BAPO type photoinitiators, which absorbs longer wavelength UV light in the near visible region above 430nm. Light of this wavelength penetrates deeper into the thicker layers of the coating, thus enabling the through curing effect. Shorter wavelength light, around 230nm, is of higher photon energy but is less penetrating than that of longer wavelengths. Light of this shorter wavelength is particularly useful for surface curing.
As a new type of photoinitiator, acylphosphine oxides, such as photoinitiator 819, have been widely used in coatings, inks, adhesives and other industries for their excellent properties. They have greater absorption in the ultraviolet andvisible regions, and can initiate curing more effectively than other photoinitiators for coatings containing pigments. Acyl phosphine oxide photoinitiators hardly yellows after curing and long-term light radiation, sothey can be used in occasions where yellowing requirements are stricter, suchas white, light ink and paint. In addition, acylphosphine oxides have bleaching effect on light, which can penetrate the coating and help the thick film to be cured thoroughly.
In addition, photoinitiator 819 can also be used in colored UV curable plastic coatings. Because of its excellent performance and efficient production, UV coatings have been widely used in plastic shells of various electronic and household appliances products. However, the deep curing of UV coatings after color addition is not good, resulting in poor film adhesion, and the dispersion and arrangement of UV resins to pigments is poor, seriously affecting the appearance of the film, so the traditional construction process is to first coat solvent-based colored primer for coloring, after baking and then coated with UV varnish to improve the physical properties of the film surface.
ITX is a highly effective free radical type II photoinitiator, which uses for UV curing of corresponding resin and tertiary amine.
ITX用于絲網印刷油墨、清漆、平版油墨、柔版油墨、電子產品和木器涂料。也可用作光敏劑，增強UV 907的固化性能。吸收峰為258-382 nm。推薦用量為 0.2-2%。
ITX is used in screen printing inks, varnishes, lithographic inks, flexo inks, electronic products, and wood coatings. It can also be used as a photosensitizer to enhance the curing properties of UV 907. The absorption peak is 258-382 nm. Recommended amount is 0.2-2%.
The more popular name of 1-Hydroxycyclohexyl Phenyl Ketone is photoinitiator 184. As one of the most commonly used photoinitiators, 1-Hydroxycyclohexyl Phenyl Ketone has good yellowing resistant ability and low oddor. Its absorption peak in methanol solution is 246nm, 280nm, 333nm, so it mainly absorbs short wavelength UV light. 1-Hydroxycyclohexyl Phenyl Ketone is used to initiate the photopolymerisation of chemically unsaturated prepolymers – e.g. acrylates – in combination with mono- or multifunctional vinyl monomers.
Experimentshows that: the longer the wavelength of the UV light is, the stronger the penetrability is, the easier it is to reach the deep layer of the film, while the shorter the wavelength is, the harder it is to reach the deep layer of the film. So 1-Hydroxycyclohexyl Phenyl Ketone is good for surface curing. If for thicker film formulation, it often co-initiates with photoinitiator 819 to achieve the balance effect both on surface and base.
Nantong Synasia New Material Co., Ltd. produces cycloaliphatic epoxy resins and various UV photoinitiators such as KIP, 1173, etc. in high quality with competitive price. Please contact us for more information.
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