What is a Photopolymer? | Your Definitive Guide to Photopolymer 3D Printing

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Photopolymer Defined

By definition, a photopolymer is a light-sensitive material that changes physical properties when exposed to light. Photopolymers are common in 3D printing because of their versatility and compatibility with a variety of 3D printing processes. 3D printed photopolymers go from a liquid resin composed of monomers and oligomers to a solid polymeric network with a defined shape when exposed to light of specific wavelengths. Beginning with stereolithography (SLA) technology in 1984 and progressing with digital light processing (DLP) and polyjet printing over the past several decades, photopolymers offer a distinct advantage for product developers, engineers and researchers.

Alternative 3D printing processes utilize thermoplastic materials via filament or pellet extrusion. In contrast, photopolymers are thermosets, meaning the material—or resin—is cured and hardened to develop specific mechanical properties. When exposed to UV light, the photopolymer resin layers adhere together to create a homogenous part. This typically requires strategic material jetting or highly advanced UV light placement to create solid, 3D printed parts. The most commonly used photopolymer resins for 3D printing technologies on the market are SLA and DLP. Both technologies operate with a vat of resin, however SLA uses pinpoint laser technology while DLP operates with a digital projector screen to flash-cure an entire layer.

SLA vs DLP

The type of photopolymer 3D printing you use depends on a range of factors. Here is a basic overview of when to use SLA vs DLP, and vice versa.

When to use SLA

When resolution and build size matter most. The ability to print parts with 25 micron XY resolution with SLA provides a slight advantage compared to DLP. When it comes to build size, SLA has higher resolution for larger parts that take up more of the build platform. Examples include:

  • Dental Applications
  • Investment Casting Patterns
  • Optical Models
  • Rapid Prototyping

When to use DLP

For specific use cases that require high accuracy or throughput. For example, tiny models and smaller part builds are ideal with DLP technology. Additionally, DLP produces parts faster compared to SLA. It’s also important to consider surface finish and other factors when determining which solution works for your application. DLP is ideal for the following:

  • Jewelry Applications
  • Biocompatible & healthcare
  • Medical Devices
  • ESD (Static Dissipative) Applications

Ultimately, these two technologies are closely related and the differences can sometimes be negligible. Arguably, the most significant advantage that SLA vs DLP photopolymer resin 3D printing provides is the ability to print highly accurate and aesthetically pleasing models. If you’re still not sure which method is ideal for your application, you can always request a photopolymer design consultation with our team.

Historical Benefits of Photopolymer Resins

Liquid photopolymer resins contain monomers, oligomers and photoinitiators that polymerize when exposed to UV light. As defined above, the 3D printing process cures the photopolymer to form solid objects with specified mechanical properties. For many years, engineers used 3D printing technology as a means to rapidly produce prototypes to test the form, fit and function of their designs. Compared to conventional methods that were highly manual and less repeatable, 3D printing quickly became a viable alternative to many industries, specifically healthcare, automotive, consumer products and electronics. It is still widely used in rapid prototyping today.

Types of photopolymers in 3D printing

There are many different photopolymer resins available for 3D printing. They vary in strength, heat resistance, static dissipative qualities and other mechanical properties that allow engineers to produce unique parts for niche applications. In addition, it’s possible to produce flexible materials that range in shore values for soft touch applications. However, traditional 3D printed photopolymer resins are scientifically limited because it’s based on photoradical or photoacid chemistries, with the photocrosslinkable moiety being acrylate, methacrylate, or epoxy functionalities. The properties of typical photopolymer resins are fundamentally limited by the nature of these moieties. Limitations include lack of toughness, increased brittleness, low heat resistance, and shrinkage. While recent resins are highly engineered to overcome some of these issues, the printed part property is still fundamentally limited by the nature of the photochemistry.

For example, timing is very important within the polymerization process so it requires multi functional components that make the network brittle and diminish select mechanical properties. In addition, shrinkage is problematic when converting from a single monomer to polymer.

polySpectra addresses these limitations by ruggedizing properties for advanced 3D printing applications that were previously impossible. The process is not based on conventional acrylates. Our proprietary chemistry, combined with a unique olefin metathesis catalyst that creates a network of more durable bonds, yields stronger mechanical properties. Simply put, the raw materials are tougher and the polymerization process is unique compared to conventional 3D printed photopolymers.

Next Generation Advantages of Photopolymer Resins

The days of brittle photopolymer parts used only for aesthetically pleasing models or highly niche applications are over.

Traditional 3D printed photopolymer resins lack true functionality, and as such, are uncommon in manufacturing applications. polySpectra’s COR Alpha, addresses the limitations of conventional photopolymers by offering engineering grade materials and solutions for true production parts. We’ve accomplished this by boosting the isotropic strength capabilities that enhance the development of materials with tailored properties for advanced functionality. We refer to it as functional lithography.

polySpectra photopolymer COR alpha enhances the isotropic strength of manufactured 3d printed parts Figure 1: electrical connectors printed with COR Alpha.

Do materials drive applications, or is it the other way around?

The next generation of advanced additive manufacturing relies on material development, which will undoubtedly lead to new applications and market penetration. The inherent benefits of additive manufacturing enable engineers to redefine new product development by embracing complexity that leads to higher performance. Combine that with advanced materials that improve functionality, and the opportunities are endless. Here are several advantages of using COR Alpha:

  • Increased Toughness & Temperature Stability: Most photopolymer resins available on the market today measure XY tensile strength and are less likely to publish Z-axis characteristics. COR Alpha materials have true isotropic values that overcome conventional limitations of SLA and DLP 3D printing technology. COR Alpha has been thoroughly tested and approved for advanced engineering applications. Watch the video to see how it compares to other photopolymers.
  • Improved Chemical Resistance: COR Alpha photopolymer resins are resistant to most organic solvents, salt water, and even jet fuel. This opens the door to new industries including transportation, aerospace, heavy machinery and energy. Download the Spec Sheet.
  • Enhanced Biocompatibility: Hearing aids, dental applications, medical devices and healthcare applications benefit from a material with enhanced cytotoxicity grades. In addition, the improved thermal ductility of COR Alpha photopolymer resins enable medical device manufacturers to autoclave and sterilize products without fear of warping or degradation. Watch the video: