The important role of photosensitive resin materials in 3D printing technology

Update:28 Dec 2020
Summary:

Light-curing materials were used in the making of mummi […]

Light-curing materials were used in the making of mummies by the ancient Egyptians more than 4000 years ago. According to records, the ancient Egyptians encapsulated mummies with linen strips soaked and coated with asphalt. As the asphalt contains unsaturated compounds, it can be cured in the sun. The folks in my country use tung oil to dip-coated wooden utensils and place them in the sun to cure, which can also form a waterproof and leak-proof wear-resistant protective layer on the surface of the wooden utensils. In fact, this is also the application of light curing technology.
Resin is a raw material for the production of plastic products, and there are many types, including natural resin and artificial resin. If it is limited to resins that are sensitive to ultraviolet light (photosensitive resins), the selectivity of resins is not much. Photosensitive resin materials are suitable for photopolymerization molding 3D printing technology, mainly including light curing molding (SLA), digital light processing (DLP), polymer jetting (PolyJet), as well as the emerging continuous liquid world manufacturing technology (CLIP), two-photon 3D Printing (TPP).
Photosensitive resin, also known as UV resin, is a special resin with many advantages. It is composed of photosensitive prepolymer, active diluent and photosensitizer. The photosensitive resin is generally liquid, and it immediately initiates a polymerization reaction and completes curing when irradiated with a certain wavelength of ultraviolet light (250nm ~ 400nm). The photosensitive resin has a wide range of uses. It can be used to make high-strength, high-temperature resistant, and waterproof materials. It has the characteristics of energy saving, low pollution, fast curing speed, and high production efficiency. ...
Qualified photosensitive resin suitable for 3D printing needs to meet the following requirements. ...
    1. High sensitivity to specific wavelength light sources. 3D printing mostly uses a light source of a specific wavelength as the light source to initiate the reaction, which requires the photosensitive resin material to have high sensitivity to the light source.
 2. Appropriate light curing speed. 3D printing photosensitive resin must have a high curing speed to ensure that the next layer of resin and the upper layer of resin can be cured quickly, but the curing speed should not be too fast. The photosensitive resin used as a binder must ensure that the curing speed is lower than the resin penetration speed to avoid the resin being cured before it has penetrated into place and the resin cannot continue to flow, resulting in poor bonding performance. ...
Currently, common photosensitive resins are divided into two categories, acrylates and epoxy resins. ...
1. Epoxy resin
Epoxy Resin (EP for short) is a common photosensitive resin in 3D printing*. In 1930, epoxy resin was first synthesized by Pierre Castan in Switzerland and S.Q. Greenlee in the United States, and it was a thermosetting plastic. Our country has been studying epoxy resin since 1958, and it has been put into industrial production at a very fast speed. These resins can be widely used in various sectors of national defense and national economy as casting, impregnation, laminating materials, adhesives, coatings, etc. use.
Epoxy resin is used as a material for 3D printing, nano-clay flakes can be used to enhance viscosity, in addition to silicon carbide and carbon fiber as fillers. By changing the combination of these fillers, scientists can freely control the strength of the material to meet various needs. This new material can be used to make lighter cars or airplanes, or used as a structural component in lightweight buildings, so it is an ideal material. ...
3D printed honeycomb structure with epoxy resin and about 1% volume of carbon fiber composite material
Another important use of epoxy resin in 3D printing is as a bonding agent. Epoxy resin has good compatibility with inorganic and metal powder materials and can quickly infiltrate the surface of inorganic or metal powder. As a photosensitive coating, epoxy resin has been widely researched and applied in people's daily life. There are many types of products and a wide range of applications. Corresponding epoxy resin photosensitive materials can be found in different systems.
2. Acrylic
Acrylic ester has the characteristics of light color, light resistance, heat resistance, and chemical resistance. Therefore, coatings made of acrylic ester have a wide range of uses and varieties. When 3D printing technology is used in combination with acrylate monomers, the acrylate monomer can be mixed with a photoinitiator, and the photoinitiator absorbs a certain wavelength of energy in the ultraviolet region, and the initiator generates free radicals. The advantage of free radical polymerization is its fast reaction speed and short curing time. However, free radical polymerization is affected by oxygen: free radicals will react with oxygen in the air and will be consumed, resulting in hindered polymerization. The macroscopic performance is that the cured surface of the photosensitive resin is not fully cured, and the hand feels sticky.
In addition, ceramics and metals can also be used as printing materials. After mixing ceramic powder with acrylate in a ratio of 1:1, the resin can act as a binder. The resin added with ceramic powder will be cured to a certain extent, and its hardness is just enough to maintain the actual shape. After that, the finished product added with ceramic powder is fired in a furnace to remove the polymer and bond the ceramic components together, so that the ceramic content in the final product is as high as 99%. This method is also applicable to acrylic resins containing metal powder.

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