3D printing is a new technology developed in recent decades. Light curing rapid prototyping Stereolithography technology (SLA) is the earliest and most mature technology in 3D printing. Photosensitive resin plays a very important role in 3D printing, it refers to a resin material that can exhibit special functions under the excitation of ultraviolet light.

3D Printing

3D printing is additive manufacturing technology or rapid prototyping technology (RP). It is based on digital and uses micron-level powder shape metals, thermoplastics or liquid photosensitive resins, and other bondable materials to print layer by layer. The technology of forming three-dimensional objects by forming.

In 1986, American Charels W. Hull. Chareles designed a system that can automatically manufacture parts, called Stereolithography, which is the prototype of 3D printing. Since then, various molding methods have been developed one after another. Compared with forced forming (forging forming), and removing forming (cutting forming). 3D printing is formed based on the principle of material dispersion/stacking and the layered processing method of the data model. First, the physical object is transformed into a digital three-dimensional solid that can be recognized by a computer. Information model, use computer software to slice the input digital three-dimensional model. Divide the model into a number of approximate plane models with a certain thickness. Turn the original three-dimensional digital model into a series of thin-layer films. Computer-controlled related software guides the printer to work on the basis of the digital information of the slices, manufactures samples by layer by layer.

3D Printing Applications

Mechanical manufacturing: 3D printing technology can directly manufacture parts applied to airplanes, high-strength bicycles, rifles, and racing parts.

Medical industry: In the medical industry, 3D printing plays a unique advantage in medical equipment, for instance, dentures, femoral heads, and knees printing technologies are widely used, the technologies are becoming more mature.

Automobile manufacturing industry: 3D printing technology has begun to manufacture experimental housings on automatic gearboxes. It is used in preliminary tests for automobile companies, they will test the gearboxes of the experimental samples under different conditions. Find out the deficiencies of the design. There are still many parts made with 3D printing technology in the car test phase. After passing the test, the model is finalized and manufactured. Mass standardized production is carried out according to the traditional manufacturing method. In this way, the R&D cycle is shortened and the R&D cost is reduced.

Photosensitive Resin Composition

Photosensitive resin refers to a resin material that can exhibit special functions under the excitation of ultraviolet light. The photosensitive resin refers to the liquid raw material used in the light-curing rapid prototyping technology. In general, reactive oligomers, reactive diluents, photoinitiators, fillers, pigments, and other additives together constitute photosensitive resins.

Photoinitiator (PI) is a molecule that creates reactive species (free radicals, cations, or anions) when exposed to radiation (UV or visible). It is an important part of photosensitive resin, and it plays a decisive role in the reaction speed of photosensitive resin. Usually, the amount of photoinitiator added is 3-8% in mass of the photosensitive resin matrix (the sum of the oligomer and the diluent).  

Free Radical Photoinitiators

1. 2-Methyl-1-(4-methylmercaptophenyl)-2-morpholine-1-acetone, Photoinitiator 907 is white to light brown powder, can be quickly dissolved in common diluents. Decomposed to produce p-methylmercaptobenzoyl radicals and morpholinoisopropyl radicals after being irradiated with ultraviolet light. Both have higher priming activity. 907 has poor yellowing resistance, and its application in colorless photosensitive resins is limited. However, it can be used together with thioxanthone (ITX) photoinitiators in colored curing systems to achieve good coordination effects.
2. 2,2-Dimethoxybenzyl ketal (1065 or 651, BDK), Photoinitiator 651. White powder appearance with a melting point of 64°C-67°C. It has good solubility in common diluents. After 651 absorbs ultraviolet light, it will be cleaved to generate benzoyl radicals and dimethoxy phenyl radicals.
3. 1-Hydroxycyclobenzophenone, Photoinitiator 184. White to moon-white crystalline powder appearance with good solubility. 184 will generate benzoyl radicals and hydroxycyclohexyl radicals after being irradiated with ultraviolet light. Both of which are highly reactive free radicals. 184 has excellent thermal stability. 184 has good yellowing resistance and is widely used in light-curing varnishes.
4. 2,4,6-Trimethylbenzoyl diphenyl phosphine oxide, Photoinitiator TPO. Light yellow powder appearance with excellent solubility in reactive diluents. It can be decomposed into two kinds of active radicals when exposed to light, diphenylphosphonyl and trimethyl benzoyl.