A photopolymer is a polymer that cures, or becomes solid, when exposed to light. The word polymer means “many parts” and is defined as any material, synthetic or organic, consisting of small simple molecules chained together to form a larger molecule. The photo in photopolymer denotes its sensitivity to light.
A photopolymer is kept in a liquid state prior to use. Upon exposure to light, the photopolymer transforms into a solid state. The light, or actinic radiation, can be emitted from a laser or a lamp. Compounds that become solid upon exposure to a certain radiation are known as radiation-curable; a photopolymer will only cure under light, but other compounds may be similarly sensitive to microwave or heat radiation. Typically, a photopolymer consists of a complex mixture of compounds, rather than a single element.
One common use of the photopolymer is stereolithography, a three-dimensional printing process that fabricates a solid object from a computer image. Photopolymer is used in conjunction with this process to make stamps, as it is less expensive than real rubber. This is achieved with a metal plate coated with photopolymer film and an impression or print of the desired image on a transparent surface. The photopolymer plate and image are exposed together in light, usually ultraviolet. The photopolymer is effectively “engraved” with the image.
Photopolymer is also used to print type and art. A printing plate made of photopolymer can be used in a letterpress, and also has some advantages over traditional lead or magnesium plates. Photopolymer plates are easier to design than metal. In addition, they require less maintenance, they are more environmentally friendly because they are not etched with acids, and their surface is resistant to abrasion and therefore will not wear down - making for a longer useable life and more consistent type. A consumer can use computer design software to set type, as well as incorporate any images or artwork, and then send a scan to a professional platemaker.
Photopolymer products are also used to make photoresists, which are patterned impressions such as those on a circuit board. These photoresists are used in applications such as flat panel displays, printed or integrated circuits, and microelectromechanical systems.
A photopolymer product can also be used to make considerably larger models, as in rapid prototyping. Rapid prototyping is the automated building of a prototype from a three-dimensional drawing. A three-dimensional CAD drawing is loaded onto a computer and optically scanned, and an ultraviolet laser beam solidifies two-dimensional sections of photopolymer liquid in a vat according to instructions from the computer. The solidified area is then covered with another layer of photopolymer liquid, and the process is repeated until a three-dimensional prototype is complete.