When it comes to light-curing 3D printing technology, we have to talk about photosensitive resin. The principle of light curing is to use ultraviolet light or other light beams to cure liquid photosensitive resin. The finished products of 3D printing with photosensitive resin materials have good details and high surface quality, and can be colored by spray painting and other processes. This material is mostly used to print fine models and complex design models that require high model accuracy and surface quality, such as prototypes, figurines, jewelry or precision assembly parts, etc.
What is photosensitive resin?
The photosensitive resin used in 3D printing mainly adopts the free radical polymerization acrylate system. Photosensitive resin is one of the earliest materials used in 3D printing and is suitable for photocuring. The main component is a small molecule resin (prepolymer, monomer) that can undergo polymerization reaction, to which photoinitiators, inhibitors, leveling agents and other additives are added. It can undergo polymerization reaction under specific light (usually ultraviolet light) to achieve curing.
Photosensitive resin characteristics
In general, photosensitive resins for 3D printing have the following requirements:
(1) The performance is stable before curing, and generally no curing occurs under visible light;
(2) Fast reaction speed. Higher reaction rate can achieve high-efficiency forming;
(3) Moderate viscosity to match the re-coating requirements of photocuring equipment;
(4) Small curing shrinkage to reduce deformation and internal stress during forming;
(5) Having sufficient mechanical strength and chemical stability after curing;
(6) Low toxicity and irritation to reduce harm to the environment and human body.
In addition, there are some other requirements in some special applications. For example, photosensitive resins used in casting require low ash content or even no ash. Resins used in the manufacture of dental orthotics or implants require properties such as non-toxicity to the human body or biodegradability.
But again, photosensitive resin is relatively expensive, and lacks toughness and strength, making it easy to break. At the same time, printed parts are also prone to bending and deformation under high temperature conditions, and their load-bearing capacity is insufficient.
Types of photosensitive resin
There are many different types of photosensitive resin materials. The subdivided photosensitive resin materials show different properties according to different formulas or production methods, and are suitable for application in different fields. At present, the main companies researching photosensitive material 3D printing technology are 3D Systems of the United States and Object of Israel.
01High -strength resin
In view of the shortcomings of photosensitive resins, such as insufficient strength and easy fracture, many companies have begun to produce tougher and more durable resins. High-strength resins have strength comparable to ABS. Such materials have achieved a balance between strength and elongation, making 3D printed products have better impact resistance and strength, and are suitable for automotive, industrial and consumer product manufacturing.
02Elastic resin
Elastic resin materials are highly flexible and elastic after molding, and show excellent elasticity under high-intensity extrusion and repeated stretching. Its application possibilities are endless. This new material will be used to make perfect hinges, shock absorption, contact surfaces, and other engineering applications, suitable for those who are interested in interesting creative and personalized designs.
03Flexible resin
Flexible resin is not as elastic as elastic resin. The performance of this resin is a medium hardness, wear-resistant, and repeatedly stretchable material. Suitable for occasions requiring toughness and resistance to repeated stress. This type of material provides high impact strength and is used in hinges and friction devices that require repeated stretching.
04Casting resin
This resin is introduced together with elastic resin. The expansion coefficient of this type of resin is not high. During the burning process, all the polymer will burn away, leaving only the shape of the final product. This material can be used to make jewelry, metal products, etc., and the surface of the printed object is relatively smooth.
05High temperature resin
High-temperature resin is a research and development direction that many resin manufacturers are keeping a close eye on, because we know that in the field of liquid resin curing, the aging problem of these plastics has long been a problem that has plagued the resin's move towards consumer and industrial applications.
High temperature resistant resins have excellent dimensional stability and can be used to manufacture exhibition models, faucets, pipes and furniture and electrical appliance prototypes that withstand strong light. They can also be used to manufacture components that require long-term thermal stability inside automobiles, aerospace and other industrial equipment.
06Ceramic resin
Most of the ceramic light-curing technologies on the market add ceramic powder to a light-curable solution, and disperse the ceramic powder evenly in the solution through high-speed stirring to prepare a ceramic slurry with high solid content and low viscosity. The ceramic slurry is then directly cured layer by layer on a light-curing molding machine to obtain a ceramic part blank, and finally the ceramic part is obtained through drying, degreasing and sintering.
The high-temperature ceramic 3D printing technology in California, USA, has developed preceramic monomers—“precursor conversion polymers”—for rapid prototyping of ceramics through ultraviolet light curing. The ceramics made from these polymers shrink uniformly and have almost no porosity. This resin can be fired after 3D printing to produce dense ceramic parts. The super-strong ceramic materials 3D printed using this technology can withstand temperatures exceeding 1,700 degrees Celsius.
07Medical resin
Medical resins are designed for components in medical systems, skin contact devices, drug contact devices and disposable medical device applications to produce safe and reliable end-use products for patients.
At the same time, medical resins have different high-specification requirements depending on their different uses. Ordinary medical products require them to have sterilization compatibility and chemical resistance, while dental resins also need to have good mechanical properties and biocompatibility.
08Transparent resin
A highly transparent stereolithography resin that is easy to use and can be quickly made. This material can produce colorless, precise functional parts with an appearance similar to organic glass, with excellent high temperature resistance, especially suitable for applications such as prototypes, concepts and functional models. This material also provides refractive values similar to engineering plastics, allowing functional testing of light transmission operations.
09Daylight resin
Daylight resins are different from resins that cure under ultraviolet light. They can cure under ordinary sunlight, so they no longer rely on UV light sources. An LCD screen can be used to cure such resins. This type of resin is expected to significantly reduce the cost of DLP 3D printing, and the prospects are very good.
There are many types of photosensitive resins that can be used for 3D printing. Many companies and research institutions are also constantly researching new materials. For example, the University of California, Berkeley, has developed a photosensitive environmentally friendly resin, which is a high-performance material that is completely safe for both people and the environment. There are many such examples, so I won’t introduce them one by one here. You can choose the type of material that suits you according to your needs.
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