Full Answer
What is photopolymerization?
Photopolymerization is a technique that uses light (visible or ultraviolet; UV) to initiate and propagate a polymerization reaction to form a linear or crosslinked polymer structure. Eujin Pei, ... Axel Nordin, in Additive Manufacturing with Functionalized Nanomaterials, 2021
What is vat photopolymerization?
Vat Photopolymerization Photopolymerization, that is, light-induced polymerization, is a form of 3D printing where materials (photopolymers, radiation-curable resins, and liquid) collected in a vat are successively cured into layers one layer at a time by irradiating with a light source thereby providing a 2D patterned layer.
What are the most common 3D printing processes that support photopolymerization?
Some of the most common 3D printing processes that support photopolymerization include the following: 1 Digital light processing 2 Continuous liquid interface production 3 Stereolithography More ...
What is the mechanism of UV light polymerization?
This mechanism involves strong interactions between a donor and acceptor when both species are exposed to a UV source, leading to the formation of an intermediate. This intermediate species then breaks down to form free radicals, which initiate polymerization.
What is photopolymerization used for?
Free radical photopolymerization is still the most widely used process both in popular applications (e.g., adhesives, lithography, coating industry) and in advanced high-technology purposes (microelectronics and optoelectronics, holographic data storage, microlithography, and nanolithography, etc.).
What is photopolymerization in 3D printing?
Photopolymerization is the curing process that's characterized by the use of ultraviolet (UV) light. In 3D printing, it's used to cure the deposited material. When exposed to UV light, the deposited material cures.
What is photopolymerization in additive manufacturing?
Share. Vat photopolymerization is a category of additive manufacturing (AM) processes that create 3D objects by selectively curing liquid resin through targeted light-activated polymerization. Stereolithography, the first AM process to be patented and commercialized, is a vat photopolymerization technique.
What is the form of material used by vat photopolymerization?
Materials. The Vat polymerisation process uses Plastics and Polymers.
Is SLA and vat photopolymerization?
Stereolithography (SLA), the first patented and marketed AM process, is a vat photopolymerization technology. Dr Hideo Kodama, a Japanese researcher, created the contemporary layered stereolithography technique in the early 1970s, employing ultraviolet radiation to cure photosensitive polymers.
Is SLS powder bed fusion?
The Powder Bed Fusion process includes the following commonly used printing techniques: Direct metal laser sintering (DMLS), Electron beam melting (EBM), Selective heat sintering (SHS), Selective laser melting (SLM) and Selective laser sintering (SLS).
What chemical is 3D resin?
In essence, 3D printer resin is a liquid solution that's made of a variety of monomers and oligomers. Photopolymerisation ensures that the short carbon chains that make up monomers and oligomers cross-link and form polymers - a material that is composed of repeating units that make up large molecules.
What is photopolymer resin made from?
The mixture consists of monomeric styrene and oligomeric acrylates. Most commonly, photopolymerized systems are typically cured through UV radiation, since ultraviolet light is more energetic.
How do DLP printers work?
DLP (Digital Light Processing) is a 3D printing technology used to rapidly produce photopolymer parts. It's very similar to SLA with one significant difference -- where SLA machines use a laser that traces a layer, a DLP machine uses a projected light source to cure the entire layer at once.
What does vat stand for in 3D printing?
Overview of VAT Polymerization VAT polymerization is a group of 3D printing processes that's characterized by its use of UV light for curing purposes. 3D printers generally don't deposit solid material.
What is the difference between SLA and DLP 3D printing?
The primary difference between DLP and SLA is the light source; SLA uses a UV laser beam while the DLP uses UV light from a projector. In DLP, the UV light source remains stationary and it cures the complete layer of resin at a time. In SLA, the laser beam moves from point to point tracing the geometry.
Where is vat polymerization used?
3D printingVat Polymerization is a method in 3D printing to print 3D objects by using photopolymerization, which is the process of exposing liquid polymers to ultraviolet (UV) light to turn liquid into solids. Digital light processing technology is used for the process.
How do photopolymers work?
The term photopolymer refers to a class of light-sensitive resins that solidify when exposed to ultraviolet (UV) light. When the liquid photopolymer resin comes into contact with a UV light source — typically a lamp, laser, or projector — photoinitiators transform that light energy into chemical energy.
What is material jetting?
Material jetting creates objects in a similar method to a two dimensional ink jet printer. Material is jetted onto a build platform using either a continuous or Drop on Demand (DOD) approach. Material is jetted onto the build surface or platform, where it solidifies and the model is built layer by layer.
What is the result of polymerization?
Polymerization is the process to create polymers. These polymers are then processed to make various kinds of plastic products. During polymerization, smaller molecules, called monomers or building blocks, are chemically combined to create larger molecules or a macromolecule.
What are the materials used in SLS system?
Commercially-available materials used in SLS come in powder form and include, but are not limited to, polymers such as polyamides (PA), polystyrenes (PS), thermoplastic elastomers (TPE), and polyaryletherketones (PAEK).
What is photopolymerization?
Photopolymerization allows for obtaining 3D-printed objects with complex shapes and a high spatial resolution, together with a smooth surface finish, which are provided by the spot size of the laser beam (Vaezi et al., 2013;
Why is photopolymerization important?
For instance, it is solvent-free and energy-efficient and can be used for heat-sensitive substances. Composites are materials consisting of two organic and inorganic compounds collecting the process ability of organic materials as well as hardness and ductility of inorganic materials.
How does photopolymerization work without PI?
The mechanism for the initiation of the photopolymerization process without PI involves a donor/acceptor pair in the presence of UV light [157]. This mechanism involves strong interactions between a donor and acceptor when both species are exposed to a UV source, leading to the formation of an intermediate. This intermediate species then breaks down to form free radicals, which initiate polymerization. A significant advantage of using a donor/acceptor pair in the initiation process is that it has the dual function of acting as an initiator as well as forming a copolymer. For example, photopolymerization of N -vinylpyrrolidinone (NVP) within the CS matrix can be initiated by a donor/acceptor pair with NVP as the donor and N -hydroxymethylmaleimide (HMMI) and 2-hydroxyethyl methacrylate (HEMA) as the acceptors, under the influence of a UV source. HMMI and HEMA each possess an electron-withdrawing group adjacent to the double bond in their structures, thus contributing to the electron-accepting property in these monomers [50].
What is the role of photopolymer in ceramics?
Upon curing by UV light, the photopolymer acts as a matrix for the ceramic particles and provides shape, cohesion, and strength to the green part. The green body is subjected to a binder burnout heat treatment to ensure complete removal of the polymer matrix and then sintering to yield the final ceramic part.
What happens to the rate of polymerization in the presence of a strong hydrogen donor?
In the presence of a strong hydrogen donor the rate of polymerization is found to be increased [158]. Hydrogen donors are compounds which contain abstractable hydrogens located adjacent to heteroatoms such as oxygen, nitrogen, and sulfur. When N -substituted maleimides (MI) (an acceptor) and vinyl ethers (donors) are subjected to UV radiation in the presence of a hydrogen donor, the excited state MI can undergo intermolecular hydrogen abstraction. After hydrogen abstraction, these donors bear free radicals that are capable of initiating polymerization. Thus the hydrogen abstraction process involving intermolecular abstraction will enhance the rate of polymerization to a greater degree as a result of the production of more free radical species [157].
What is a photoinitiated radical polymerization?
Without question, the photoinitiated radical polymerizations of acrylates and methacrylates comprise the most well-studied and commercially important class of active center photopolymerizations. Contributing significantly to the commercial and academic success of this chemistry has been the development of a wide range of highly sensitive radical photoinitiators. A photoinitiator is a compound that becomes electronically excited through absorption of light within a given spectral range, and undergoes subsequent reactions to afford reactive species capable of inducing an addition polymerization reaction.
Which compounds are used as radical photoinitiators?
In addition to the above two classes of commonly used radical photoinitiators, a wide assortment of azo, sulfur, and heterocyclic compounds, organometallic compounds, and charge transfer complexes are known to generate radicals on irradiation with light.
What is photopolymerization?
Photopolymerization is a special form of free-radical polymerization where light is used to initiate polymerization. This method has many advantages over conventional polymerization in terms of less energy consumption, reduced waste, higher productivity (fast cure) and lower reaction temperature. The primary limitation of light-induced polymerization is the limited light penetration depths which will depend on the wave length and spectral distribution but does not exceed a few millimeters. Since polymerization stops when the light source is removed, photopolymerization techniques are only useful for thin film applications.
How does photochemical initiation occur?
The photochemical initiation is usually achieved by subjecting suitable photoinitiators to UV irradiation. The absorption of light (photons) converts the absorbing molecules (PI) to their activated form which rapidly disintegrate into radicals or ions (I). These molecule fragments then initiate polymerization and/or crosslinking reactions in a subsequent step. In the case of photosensitizers (S), the light-activated molecules (S *) transfer their energy directly to an energy acceptor molecule which then produces radicals by either hydrogen abstraction (II) or by photocleavage (III):
What are the two classes of photoinitiators?
Photoinitiators can be divided into two major classes: The first class are initiators that undergo intramolecular bond scission (PI1) , and the second class are molecules that undergo intermolecular hydrogen abstraction (PI2).
How does light absorption occur?
The absorption of light occurs only if the energy difference between the activated state and ground state of the in initiator molecule is equal to the energy of the photon. Its energy is proportional to its frequency ν or wave length λ and can be calculated with the Planck-Einstein relation:
Do sensitizers undergo chemical changes?
Sensitizers do not undergo any chemical changes whereas photoinitiators are consumed during the initiation step.
What is the process of photopolymerization?
Photopolymerization is the curing process that’s characterized by the use of ultraviolet (UV) light. In 3D printing, it’s used to cure the deposited material. When exposed to UV light, the deposited material cures. Curing results in physical changes to the deposited material, turning it from a liquid or semi-solid state to a solid state.
How does photopolymerization work?
Photopolymerization works by leveraging the UV-sensitive properties of photopolymer materials. For most 3D printing processes, layers of deposited material are cured via a UV light. After the 3D printer has completed a layer, a UV light is projected over it. The UV light triggers a reaction within the deposited material, essentially solidifying it.
How effective is photopolymerization?
Photopolymerization is highly effective at solidifying deposited materials. It’s able to change the physical properties of the deposited material so that it’s stronger and better protected against damage. With photopolymerization, entire layers of deposited material can be cured at once.
What is the curing method for 3D printing?
Of course, there are other curing methods available for 3D printing materials. Some 3D printing processes use a laser, for instance. The laser moves across the top of the print bed while curing the underlying material. When compared to lasers, as well as other curing methods, photopolymerization offers several advantages.
Why do 3D printers release heated material?
Doing so allows the 3D printer to release an even and consistent amount of material, thereby reducing the risk of defects like ghosting. Finished objects, however, must be solid, which is where photopolymerization comes into play. Photopolymerization is used to harden the deposited material so that the finished object achieves a solid state.
What is a photopolymer?
A photopolymer material is a type of resin material that hardens under UV light. Other types of materials are generally unaffected by UV light. For photopolymerization to work, a photopolymer material must be used in the 3D printer.
What happens when UV light is used in a 3D printer?
The UV light triggers a reaction within the deposited material, essentially solidifying it. The cured material changes to a solid state, allowing for the production of a solid and finished object by the 3D printer.
How does vat photopolymerization work?from fastradius.com
Vat photopolymerization creates parts with excellent surface finishes by curing a liquid photopolymer resin one layer at a time using light. First, the build platform is lowered into the vat of resin. Then, UV light, typically from a laser or projector, causes a reaction within the resin. The photopolymer’s molecules bond together to form a solid, and the build platform moves away from the light source to allow additional layers to be built on top of the previous ones. After the part is fully formed, the resin is drained and the part is removed.
How does a photopolymer build platform work?from fastradius.com
The photopolymer’s molecules bond together to form a solid, and the build platform moves away from the light source to allow additional layers to be built on top of the previous ones. After the part is fully formed, the resin is drained and the part is removed.
What was the first additive manufacturing process?from fastradius.com
Vat photopolymerization was the first additive manufacturing process to be successfully commercialized, and it remains a popular technique some forty years after its market debut. Let’s take a deep dive into the original additive manufacturing process.
What are the advantages and disadvantages of vat photopolymerization?from fastradius.com
Vat photopolymerization has remained popular among manufacturers over the years because it is ideal for manufacturing highly detailed parts and is often faster than other manufacturing processes in terms of pure volume.
What is DLP in resin?from fastradius.com
Instead of using a laser, this process uses a digital light projector screen that flashes a single image of each layer of the part into the resin all at once. As a result, the printing process is accelerated.
What is additive manufacturing?from fastradius.com
Additive manufacturing, commonly referred to as 3D printing, is a manufacturing method that lays down successive layers of material driven by the contours of a 3D model to create physical objects. The field of additive manufacturing has witnessed steady growth in both technological development and adoption over the years.
What is a photopolymer?
A photopolymer or light-activated resin is a polymer that changes its properties when exposed to light, often in the ultraviolet or visible region of the electromagnetic spectrum. These changes are often manifested structurally, for example hardening of the material occurs as a result of cross-linking when exposed to light.
What is the purpose of photopolymer?
A wide variety of technologically useful applications rely on photopolymers, for example some enamels and varnishes depend on photopolymer formulation for proper hardening upon exposure to light. In some instances, an enamel can cure in a fraction of a second when exposed to light, as opposed to thermally cured enamels which can require half an hour or longer. Curable materials are widely used for medical, printing, and photoresist technologies.
What is photoinitiator in biology?
Photoinitiators are compounds that upon radiation of light decompose into reactive species that activate polymerization of specific functional groups on the oligomers. An example of a mixture that undergoes cross-linking when exposed to light is shown below.
What is a free radical photopolymer?
Dentistry is one field in which free radical photopolymers have found wide usage as adhesives, sealant composites, and protective coatings. These dental composites are based on a camphorquinone photoinitiator and a matrix containing methacrylate oligomers with inorganic fillers such as silicon dioxide. Resin cements are utilized in luting cast ceramic, full porcelain, and veneer restorations that are thin or translucent, which permits visible light penetration in order to polymerize the cement. Light-activated cements may be radiolucent and are usually provided in various shades since they are utilized in esthetically demanding situations.
How do changes in structural and chemical properties occur?
Changes in structural and chemical properties can be induced internally by chromophores that the polymer subunit already possesses, or externally by addition of photosensitive molecules. Typically a photopolymer consists of a mixture of multifunctional monomers and oligomers in order to achieve the desired physical properties, ...
Why are monomers used in radiation curable systems?
The monomers used in radiation curable systems help control the speed of cure, crosslink density, final surface properties of the film, and viscosity of the resin.
How do photocurable materials form?
Photocurable materials that form through the free-radical mechanism undergo chain-growth polymerization, which includes three basic steps: initiation, chain propagation, and chain termination. The three steps are depicted in the scheme below, where R• represents the radical that forms upon interaction with radiation during initiation, and M is a monomer. The active monomer that is formed is then propagated to create growing polymeric chain radicals. In photocurable materials the propagation step involves reactions of the chain radicals with reactive double bonds of the prepolymers or oligomers. The termination reaction usually proceeds through combination, in which two chain radicals are joined together, or through disproportionation, which occurs when an atom (typically hydrogen) is transferred from one radical chain to another resulting in two polymeric chains.
What are the most common photopolymerization reactions?
There are multiple photopolymerization reactions with various mechanisms. Radically polymerized (meth)acrylate may be the most popular, but cationic epoxide and vinyl ether photopolymerizations and radical thiol-ene and thiol-yne polymerizations are also very prevalent. Anionic photopolymerizations of thiols with acrylates or thiols with isocyanates and even photoinitiated azide alkyne cycloaddition are other examples. Asking how photopolymerization work is a little like asking how chemistry works.
What do you need for photopolymerization?
For A photopolymerization you need a UV-lamp and a photoinitiator that absorbs in the same region as the UV emitted from the lamp. This photoinitiator then will generate radicals that can start the polymerization.
What type of polymer to use for emulsion?
For emulsion polymerization you will mainly use monomers, but when applying a coating onto a substrate you want to have a higher viscosity and you then would use oligomers.
Who wrote the book "Photoinitiation, photopolymerization and photocuring: Fundamentals and Applications"?
There's a book by JP Fouassier called, "Photoinitiation, photopolymerization and photocuring: Fundamentals and applications" which is great.