How to choose resins compatible with different light-curing 3D printers

I. Characteristics of different light-curing 3D printers and their resin requirements

(1) LCD light-curing 3D printers

1. Printer characteristics
   • Simple principle and structure: LCD light-curing 3D printers use the imaging principle of LCD screens. The optical projection passes through the red, green, and blue color filters to filter out infrared and ultraviolet rays, and then projects the three primary colors through three liquid crystal panels to synthesize a projection image, which then cures the photosensitive resin. Its core components are relatively inexpensive and the technology is open source.
   • Scope of application: Suitable for individual makers and entertainment purposes, as well as for printing small-sized models. The price is relatively affordable, and the printing accuracy is lower than that of DLP and SLA printers, but it can meet general needs within its applicable scope.
   • Component lifespan issue: Since LCD screens are sensitive to ultraviolet rays, they have to withstand heat resistance, high-temperature heat dissipation tests, and high-intensity baking (baked by dozens of watts of 405 LED lamp beads for several hours) during use. Therefore, their service life is relatively short. If used frequently, the core component, the LCD screen, may be damaged within one to two months.
2. Characteristics in terms of resin requirements
   • Diverse resin types: LCD light-curing 3D printers can use various types of resins. For example, the environmentally friendly plant-based resins, low-odor water-washable resins, ABS-like resins, and rigid resins produced by Gezhi Weidu can be used on mainstream LCD printers without complicated testing to ensure the printing success rate. Moreover, high-transparency, tough, hard, high-toughness, resin for figurines, dental resin, and resin for jewelry casting on the market can also be used in LCD printers.
   • Relatively low requirement for resin fluidity: Compared with other high-precision printers, LCD printers have relatively low precision, so they are less sensitive to resin fluidity. However, the resin still needs to maintain a certain degree of fluidity to evenly cover the printing area.
   • Resin compatibility affected by short lifespan: Due to the short service life of the LCD print head or screen, the resin needs to have less chemical corrosion and wear on the printing equipment. Otherwise, within the limited service life of the equipment, the damage to the equipment may be aggravated.

(2) DLP light-curing 3D printers

1. Printer characteristics
   • High precision and speed: Based on the digital light processing rapid prototyping technology, DLP projectors are used to project the sliced models layer by layer onto the resin. It has excellent printing precision and quality, and the printing speed is fast, faster than the SLA molding process. It is suitable for high-precision and high-efficiency small-batch production, scientific research and education, and rapid verification and small-batch production of small-sized products in the field of industrial design.
   • Convenient operation: It has a simple and easy-to-operate interface and a one-touch control touch panel, providing an efficient and fast overall 3D printing experience.
   • Mature molding technology: The DLP light-curing molding technology has a high level of technological maturity, an intelligent and automated molding process, good surface quality of the constructed objects, and high composite production efficiency (multiple independent and complex models can be printed and produced at one time).
2. Characteristics in terms of resin requirements
   • High matching degree of resin to light wavelength: Manufacturers specify the compatible resin wavelengths for their DLP printers, and the wavelengths of these resins are usually relatively large. During the photo-induced curing process, the resin needs to be quickly and efficiently cured within a specific wavelength range. For example, when printing a model of a special color or function, the light wavelength absorption and excitation of the resin need to exactly match the spectral characteristics of the DLP light source to ensure good curing effects and high-quality printed products.
   • Diverse requirements for resin physical properties: DLP light-curing 3D printers are equipped with a variety of resin consumables for flexible selection. There are various colors of consumables, and the physical properties range from flexible to hard with multiple models. Standard resins, wax-based resins, and other special resins can be selected according to the usage requirements of the model to meet the high requirements of the constructed objects. For example, when printing flexible joints, resins with good flexibility are needed, while when printing delicate jewelry models, resins with high hardness and good transparency may be required.

• • Requirements for resin thermal stability and mechanical properties: Since DLP printers are widely used in the commercial and industrial fields, especially in the preparation of some high-precision models. To meet these application scenarios, the resin should have good thermal stability to prevent thermal deformation during the printing process or deformation in different temperature environments after printing. At the same time, good mechanical properties (such as impact resistance and compression resistance) are also important to ensure that the printed models have sufficient strength and stability.

(3) SLA light-curing 3D printers

1. Printer characteristics
   • High precision: SLA light-curing 3D printers are based on the light-curing molding principle. A laser beam is used to draw the object image on the resin tank (similar to the writing process of lithography), and the liquid photosensitive resin is cured layer by layer into the final product. Its vertical accuracy can reach 0.008mm, and it can easily print parts with complex shapes. For example, when printing a human bone model, it can accurately restore the complex structure of the bone, which is a very important advantage in the medical field.
   • Good surface effect: The surface of the printed model parts is smoother. It has better surface smoothness than models made of PLA material, and it does not require a lot of time and effort for grinding in the later stage to achieve a very delicate effect.
   • Printing speed and cost: The printing speed can reach 7m/s, and the product can be integrally formed, effectively reducing redundant steps. Moreover, since it uses the concept of adding materials rather than subtracting materials, there is almost no material waste during the printing process, and the printing cost is relatively low. It can print large-sized models to meet the customer’s needs for printing large-sized models, and it can accurately print various complex models and parts. It can handle models with hollow or openwork structures that cannot be made by traditional processes, meeting the needs of personalized customization.
2. Characteristics in terms of resin requirements
   • High requirement for wavelength accuracy: SLA printers use lasers to cure materials. Usually, the laser wavelength is specific, such as ultraviolet lasers with a wavelength of 355nm or 405nm as the light source. This requires the resin to be efficiently cured at this specific laser wavelength. If the resin does not match the laser wavelength, problems such as incomplete curing or excessive curing time may occur.
   • High strength and stability: Since SLA printers are often used for industrial and precise model printing, such as models of medical equipment and automobile accessories. Therefore, the resin needs to have high strength to ensure the integrity of the printed model during transportation and use. Moreover, it should maintain stable performance under different environmental conditions (such as changes in temperature and humidity) and not deform or become brittle.
   • Requirement for resin uniformity: To ensure that the laser can uniformly cure the resin, the uniformity of the resin is crucial. If there are uneven components or physical states inside the resin (such as inconsistent density or anisotropy), defects or uneven strength may occur in the cured model.

II. Types of resins compatible with LCD light-curing 3D printers

1. Standard resin
   • Characteristics and advantages: This type of resin is the most common and widely used in the market. Almost all manufacturers develop standard resins. They are affordable and available in a variety of colors. The parts printed with this resin have a relatively smooth and delicate surface, high hardness, and only require simple post-processing, such as painting and sanding. For example, when printing prototypes of some household decorations or small figurines, standard resin can meet the basic requirements for hardness and appearance. At the same time, the cost is low, making it suitable for beginners or users who are sensitive to cost.
   • Limitations: It is relatively brittle and prone to breakage and cracking. Therefore, in use scenarios, it is necessary to avoid situations where it may be subjected to large external impacts or pressures. For example, it cannot be used to make mechanical parts that bear high-intensity tensile or impact forces.
2. Transparent resin
   • Characteristics and advantages: Similar in texture to standard resin, but it has semi-transparent and colorless characteristics, which are convenient for sanding and painting, and can create a glass-like effect for decorations. Although it is not recommended for use in the food field, it has certain application prospects in the waterproof field. If you want to make transparent decorations, such as models of crystal ornaments or some art decorations with a light-transmitting effect, transparent resin can achieve good results, and its transparency and refractive index can meet certain appearance requirements.
   • Disadvantages and precautions: It also has the problem of brittleness, and when making parts with large sizes or uneven thicknesses, there may be problems such as inconsistent transparency or cracking due to internal stress.

1. Water-washable resin
   • Characteristics and advantages: Generally, 3D printed parts made of resin need to be post-processed with isopropyl alcohol (IPA) to remove supports and excess resin, while water-washable resin can remove these parts by washing with water. After washing with water, the parts can obtain a smoother and more comfortable touch, reducing the stickiness unique to resin and the odor associated with standard resin. This is very advantageous for making parts that have requirements for surface touch and odor, such as prototypes of some hand-operated tools or children’s toys, which can reduce the residue of harmful chemicals and improve the safety of use.
   • Disadvantage: Affected precision: An obvious disadvantage of this resin is that its precision may be affected. Therefore, for parts with extremely high precision requirements, such as models of micro-precision instruments, water-washable resin may not be the most suitable choice.
2. Flexible resin
   • Characteristics and advantages: The Shore hardness of flexible resin is about 80A, and it has rubber-like qualities. These types of 3D printing resins can bend and compress without deformation and can create high-strength, bendable objects. It can return to its original shape after being compressed and has a long service life. It can be used to create parts that require elasticity and flexibility, such as shock absorbers, handles, prototypes of moving parts, and seals. For example, in the production of prototypes of some shock absorbers in automobile parts or handles of hand-held tools, flexible resin can simulate the elastic effect during actual use.
   • Limitations: In structures that require high hardness support or when subjected to the extrusion of sharp objects, excessive deformation or damage may occur. Its low hardness limit restricts its application in scenarios that require both hardness and flexibility but have relatively high requirements for hardness.
3. Industrial resins (including heat-resistant, combustible, dental resins, etc.)
   • Overall characteristics and applicability in LCD printers: Industrial photopolymers (rigid resins) have high mechanical properties and are ideal for harsh application environments. For LCD printers, if you need to print some small industrial prototypes or conceptual models in industrial design, these resins can also be used. Although the precision of LCD printers is relatively low among light-curing printers, in the initial design and verification stages of industrial applications where the precision requirements are not extremely high, these resins can also play a certain role.
   • Characteristics of subdivided resins
     • Heat-resistant resin: It can withstand temperatures of up to 230°C without affecting its shape and performance. It can be used to manufacture models of casting tools, tools exposed to hot liquids, and equipment exposed to strong heat. For example, in the preliminary model production of some casting processes, if the heat resistance of the mold needs to be verified, using an LCD printer with heat-resistant resin can initially achieve model production. Although the final precision mold may still require a more advanced printer and better resin, this combination can provide a preliminary test prototype.
     • Combustible resin: From the beginning of model design and printing, a high level of detail can be achieved. In subsequent metal casting, the combustible resin will evaporate without leaving ash or residue, making the surface of the final object clean and smooth. It has application value in the fields of jewelry and dental restoration, such as making preliminary models of jewelry molds or temporary restoration models for dental restoration.
     • Dental resin: It is composed of non-toxic organic elements and can be used in dental applications without endangering the patient’s health. It is suitable for manufacturing models for retainers, dental crowns, dental bridges, surgical models, dentures, or anatomical models and other dental applications. In some oral medicine teaching or preliminary treatment plan discussions, using an LCD printer and dental resin can quickly and cost-effectively produce tooth models for reference.

III. Characteristics of resins compatible with DLP light-curing 3D printers

1. In terms of physical properties
   • Diverse hardness: The resins suitable for DLP printers range from highly flexible to very hard. When printing some items that require elasticity, such as prototypes of silicone products, resins with good flexibility can be selected; while when printing items that require structural support or a delicate surface, such as precision mechanical parts or high-end jewelry, resins with high hardness are more suitable. For example, in the field of jewelry design, some jewelry shapes require both strong support and the ability to present exquisite carving effects on the surface. At this time, high-hardness resins that can be precisely cured are needed to cooperate with the high-precision performance of DLP printers.
   • Rich and controllable colors: In addition to common colors such as black, red, blue, and gray, various customized colors of resins can be obtained according to different needs. This is very useful for some fields with high requirements for color matching, such as color design research and the model production of products with specific brand colors. For example, to make a product model of a well-known brand’s specified color, it can be accurately achieved through a DLP printer and the corresponding color resin.
2. Related to optical characteristics
   • Specific light absorption and excitation characteristics: DLP printers use digital light processing technology, and the resin needs to have good absorption and excitation conversion capabilities for its specific light source wavelength to achieve fast and efficient curing. Only when the photochemical characteristics of the resin are perfectly matched with the optical parameters such as the wavelength and intensity of the printer’s light source can high-quality parts be printed. If the light absorption efficiency is low, it may cause some of the resin to not be completely cured, affecting the strength and precision of the parts; if the excitation conversion process is unstable, it will lead to uneven curing speed and make the surface of the parts uneven.
   • Characteristics related to the wavelength difference compared with SLA resins: Generally speaking, the wavelength of DLP resins is longer than that of SLA resins. This wavelength difference means that they are suitable for different curing light sources, that is, DLP printers and SLA printers need to use the corresponding resin types respectively. If SLA resin is misused in a DLP printer (or vice versa), due to the wavelength mismatch, the resin cannot be normally cured in the given printer light environment, and the expected printing result cannot be obtained.
3. From the perspective of application characteristics
   • High precision and detail restoration characteristics: The high precision of DLP printers requires the resin to be able to achieve precise polymerization and curing at a microscopic level. Only in this way can it be ensured that when printing very delicate models, such as micro-medical devices or high-end figurines, there will be no problems such as blurring,delamination, or missing details. The molding ability of the resin at the microscopic level directly affects the quality and precision of the printed product. Therefore, the resins directly related to DLP need to perform well in this regard.
   • Meeting the needs of specific industries
     • In the dental field: For dental models, the resin needs to have good biocompatibility (if the model is used for direct contact inside the oral cavity, such as a temporary dental crown model) and high precision to accurately restore the shape and occlusal relationship of the teeth. The dental resin used in DLP printers can meet these requirements and can print dental models with accurate dimensions and smooth surfaces, whether it is a dental crown, a dental bridge, or an orthodontic model.
     • In the field of industrial design and testing: When making industrial product prototypes, in addition to being able to withstand certain pressure, impact, and other conventional mechanical properties, the resin also needs to meet some special testing requirements. For example, some prototypes need to undergo permeability tests, and the corresponding resin needs to have good optical transparency; if electrical performance tests are required, the resin also needs to have appropriate insulation or conductivity and other special properties. DLP printers can use resins that meet these diverse needs to make prototypes.

IV. Analysis of resins suitable for SLA light-curing 3D printers

1. Resins compatible with laser wavelengths
   • Requirement for specific response to laser wavelengths: SLA light-curing 3D printers usually use lasers with specific wavelengths, such as ultraviolet lasers with a wavelength of 355nm or 405nm, as the light source. Therefore, the suitable resin must have an efficient photo-induced curing reaction at these specific wavelengths. The components in the resin, such as photoinitiators, monomer polymers, and prepolymers, need to have good absorption and conversion capabilities for this specific wavelength of laser, converting light energy into chemical energy to promote the rapid curing of the resin. For example, resins containing specific aromatic components may have a good response to 355nm ultraviolet lasers and can be cured in a short time. If the resin does not match the laser wavelength, problems such as incomplete curing, excessive curing time, and insufficient strength of the printed parts may occur.
   • Relationship between resin components and wavelength compatibility: The proportion of each component in the resin also affects its adaptability to the laser wavelength. For example, different contents and types of photoinitiators will change the overall absorption and conversion efficiency of the resin to laser energy. When the content of the photoinitiator is too low, even if other components of the resin have good absorption ability for the laser wavelength, it may not be able to be quickly cured due to the lack of sufficient initiating active species; on the contrary, if the content is too high, it may lead to an overly fast reaction speed, making it difficult to control the curing precision and quality.
2. Resins meeting the requirements of strength and stability
   • Occasions and reasons for high-strength mechanical performance requirements: Since SLA printers are often used to print parts that require high strength, such as industrial parts and prototypes of medical implants. Therefore, the suitable resin needs to have high strength, whether it is tensile strength or compressive strength. For example, when making a prototype of an automobile engine part, the model printed with resin needs to have sufficient strength to withstand various external forces during the testing process without breaking or deforming; when making a medical implant (such as an initial model of a bone fixation bracket), the biomechanical environment inside the human body after implantation also needs to be considered, and the resin must have sufficient strength to ensure safety and effectiveness.
   • Significance and requirements of stability in different environments: The resin needs to remain stable under different environmental conditions, including changes in temperature and humidity, and should not become brittle, soften, or deform. In a high-temperature environment, such as in some high-temperature industrial environments or in the disinfection process of medical device models, the resin should maintain its mechanical performance stability; in a humid environment, such as test part models in a water immersion experiment, performance degradation due to water absorption should be avoided.
3. Analysis of resins suitable for SLA printers from the perspective of uniformity
   • Importance of uniformity for printing: SLA printers cure the resin layer by layer with a laser. If the uniformity of the resin is poor, uneven curing will occur. For example, if there are uneven particles or uneven component ratios inside the resin, during the laser curing process, it may cause local areas of the model to be incompletely cured or over-cured, resulting in problems such as uneven strength and uneven surface of the model.
   • Resin component factors to ensure uniformity: The components in the resin, such as monomer polymers, prepolymers, and photoinitiators, need to be evenly dispersed to avoid precipitation or aggregation. At the same time, during the resin production process, the mixing ratio and mixing process of each component need to be precisely controlled to ensure the uniformity of the components and the consistency of the physical and chemical properties from the initial resin liquid to the final printing process.

V. How to judge the compatibility between resin and light-curing 3D printer

1. Judgment from the optical aspect
   • Resin wavelength matching: Different light-curing 3D printers use different types of light sources. For example, SLA uses lasers (specific wavelengths such as 355nm or 405nm), and DLP and LCD use light displays (corresponding to different wavelengths). Manufacturers usually specify the compatible wavelength range of their resins. Therefore, the first step is to check whether the recommended wavelength of the resin matches the light source wavelength of the printer. If they do not match, the resin may not be effectively cured. For example, if the resin suitable for a DLP printer (with a longer wavelength) is used in an SLA printer (with a shorter wavelength), due to the wavelength difference, the resin cannot absorb enough energy and thus cannot be normally cured, directly affecting the printing success rate and quality.
   • Light absorption and curing efficiency: In addition to wavelength matching, the light absorption efficiency and curing speed of the resin for the printer’s light source also need to be considered. This is closely related to components such as the photoinitiator in the resin. Some resins may match the wavelength, but due to a low content of photoinitiator or an unsuitable type, they cannot quickly and effectively convert light energy into chemical energy to cure the resin under the specific light intensity of the printer. In actual tests, small-scale printing tests can be carried out to observe whether the curing speed of the resin meets the normal requirements of the printer. If the curing is too slow, it will prolong the printing time and may even lead to incomplete curing; if the curing is too fast, it may be difficult to control the precision and cause problems such as deformation of the parts.
2. Consideration from the aspects of mechanical performance and stability
   • Strength of the printed parts: The resin should cooperate with the printer to make the printed parts meet the expected strength requirements. This needs to be judged according to the usage scenario of the printed parts. For example, when printing a prototype of a part for a mechanical component, the cured part of the resin needs to be able to withstand certain tensile, compressive, and shear forces. If the strength is insufficient, the part is likely to be damaged during subsequent testing or actual use. This requires a certain understanding of different printers and different types of resins. When selecting a resin, it is necessary to refer to the strength test data or reports of similar parts produced by previous printer and resin combinations. If there is a lack of data, some sample tests can be carried out first.
   • Stability in different environments: Considering that the printed parts may face changes in temperature, humidity, and contact with chemicals in different usage environments, the compatibility between the resin and the printer is also reflected in the adaptability to the usage environment. For example, for parts used outdoors, they need to remain stable in different temperature, humidity, and even ultraviolet radiation environments. Some resins may seem normal during the printing process, but after being placed for a period of time, they may become brittle, soften, or change color in a specific environment. This requires an understanding of the chemical stability of the resin, checking its technical manual or conducting environmental simulation tests to ensure that the resin has the required environmental stability under the specific molding process of the printer.