CR-39
Encyclopedia
CR-39, or allyl diglycol carbonate (ADC), is a plastic
polymer
commonly used in the manufacture of eyeglass lenses
. The abbreviation stands for “Columbia Resin #39,” because it was the 39th formula of a thermosetting plastic developed by the Columbia Resins project in 1940.
The first commercial use of CR-39 monomer was to help create glass-reinforced plastic
fuel tanks for the B-17 bomber aircraft in World War II, reducing weight and increasing range of the bomber. After the War, the Armorlite Lens Company in California is credited with manufacturing the first CR-39 eyeglass lenses in 1947. CR-39 plastic has an index of refraction of 1.498 and an Abbe number
of 58. CR-39 is now a trade marked product of PPG Industries
.
An alternative use includes a purified version that is used to measure neutron radiation
, a type of ionizing radiation
, in neutron
dosimetry
.
CR-39 should not be confused with polycarbonate
, a tough homopolymer usually made from bis-phenol A.
. The presence of the allyl groups allows the polymer to form cross-link
s; thus, it is a thermoset resin. The monomer structure is
The polymerization schedule of ADC monomers using IPP is generally 20 hours long with a maximum temperature of 95°C. The elevated temperatures can be supplied using a water bath or a forced air oven.
Benzoyl peroxide
(BPO) is an alternative organic peroxide
that may be used to polymerize ADC. Pure benzoyl peroxide is crystalline and less volatile than diisopropyl peroxydicarbonate. Using BPO results in a polymer that has a higher yellowness index, and the peroxide takes longer to dissolve into ADC at room temperature than IPP.
and is almost completely opaque in the ultraviolet
range. It has high abrasion resistance, in fact the highest abrasion/scratch resistance of any uncoated optical plastic. CR-39 is about half the weight of glass
with an index of refraction only slightly lower than that of crown glass
, and its high Abbe number yields low chromatic aberration
, altogether making it an advantageous material for eyeglasses and sunglasses
. A wide range of colors can be achieved by dye
ing of the surface or the bulk of the material. CR-39 is also resistant to most solvent
s and other chemicals, gamma radiation, aging, and to material fatigue. It can withstand the small hot sparks
from welding
, something glass cannot do. It can be used continuously in temperatures up to 100 °C and up to one hour at 130 °C.
In the radiation detection application, raw CR-39 material is exposed to proton
recoils caused by incident neutrons. The proton recoils cause ion tracks, which are enlarged by an etching process in a caustic solution of sodium hydroxide. The enlarged ion tracks are counted under a microscope (commonly 200x), and the number of ion tracks is proportional to the amount of incident neutron radiation.
It is used in some photographic filter
s, such as the Cokin filter system.
A direct equivalent is produced by Acomon AG with the brand name RAV,
and another one by Danyang Yueda FineChemichal Co. Ltd in China.
Plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...
polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
commonly used in the manufacture of eyeglass lenses
Lens (optics)
A lens is an optical device with perfect or approximate axial symmetry which transmits and refracts light, converging or diverging the beam. A simple lens consists of a single optical element...
. The abbreviation stands for “Columbia Resin #39,” because it was the 39th formula of a thermosetting plastic developed by the Columbia Resins project in 1940.
The first commercial use of CR-39 monomer was to help create glass-reinforced plastic
Glass-reinforced plastic
Fiberglass , is a fiber reinforced polymer made of a plastic matrix reinforced by fine fibers of glass. It is also known as GFK ....
fuel tanks for the B-17 bomber aircraft in World War II, reducing weight and increasing range of the bomber. After the War, the Armorlite Lens Company in California is credited with manufacturing the first CR-39 eyeglass lenses in 1947. CR-39 plastic has an index of refraction of 1.498 and an Abbe number
Abbe number
In physics and optics, the Abbe number, also known as the V-number or constringence of a transparent material, is a measure of the material's dispersion in relation to the refractive index...
of 58. CR-39 is now a trade marked product of PPG Industries
PPG Industries
PPG Industries is a global supplier of paints, coatings, optical products, specialty materials, chemicals, glass and fiber glass. With headquarters in Pittsburgh, Pennsylvania, PPG operates in more than 60 countries around the globe. Sales in 2010 were $13.4 billion...
.
An alternative use includes a purified version that is used to measure neutron radiation
Neutron radiation
Neutron radiation is a kind of ionizing radiation which consists of free neutrons. A result of nuclear fission or nuclear fusion, it consists of the release of free neutrons from atoms, and these free neutrons react with nuclei of other atoms to form new isotopes, which, in turn, may produce...
, a type of ionizing radiation
Ionizing radiation
Ionizing radiation is radiation composed of particles that individually have sufficient energy to remove an electron from an atom or molecule. This ionization produces free radicals, which are atoms or molecules containing unpaired electrons...
, in neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
dosimetry
Dosimetry
Radiation dosimetry is the measurement and calculation of the absorbed dose in matter and tissue resulting from the exposure to indirect and direct ionizing radiation...
.
CR-39 should not be confused with polycarbonate
Polycarbonate
PolycarbonatePhysical PropertiesDensity 1.20–1.22 g/cm3Abbe number 34.0Refractive index 1.584–1.586FlammabilityV0-V2Limiting oxygen index25–27%Water absorption – Equilibrium0.16–0.35%Water absorption – over 24 hours0.1%...
, a tough homopolymer usually made from bis-phenol A.
Synthesis
CR-39 is made by polymerization of diethyleneglycol bis allylcarbonate (ADC) in presence of diisopropyl peroxydicarbonate (IPP) initiatorInitiator
An initiator can refer to:* A person that takes an initiative in making something happen.* Modulated neutron initiator, a neutron source used in some nuclear weapons...
. The presence of the allyl groups allows the polymer to form cross-link
Cross-link
Cross-links are bonds that link one polymer chain to another. They can be covalent bonds or ionic bonds. "Polymer chains" can refer to synthetic polymers or natural polymers . When the term "cross-linking" is used in the synthetic polymer science field, it usually refers to the use of...
s; thus, it is a thermoset resin. The monomer structure is
The polymerization schedule of ADC monomers using IPP is generally 20 hours long with a maximum temperature of 95°C. The elevated temperatures can be supplied using a water bath or a forced air oven.
Benzoyl peroxide
Benzoyl peroxide
Benzoyl peroxide is an organic compound in the peroxide family. It consists of two benzoyl groups bridged by a peroxide link. Its structural formula is [C6H5C]2O2. It is one of the most important organic peroxides in terms of applications and the scale of its production...
(BPO) is an alternative organic peroxide
Organic peroxide
Organic peroxides are organic compounds containing the peroxide functional group . If the R' is hydrogen, the compound is called an organic hydroperoxide. Peresters have general structure RCOOR. The O-O bond easily breaks and forms free radicals of the form RO·...
that may be used to polymerize ADC. Pure benzoyl peroxide is crystalline and less volatile than diisopropyl peroxydicarbonate. Using BPO results in a polymer that has a higher yellowness index, and the peroxide takes longer to dissolve into ADC at room temperature than IPP.
Applications
CR-39 is transparent in the visible spectrumVisible spectrum
The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. A typical human eye will respond to wavelengths from about 390 to 750 nm. In terms of...
and is almost completely opaque in the ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
range. It has high abrasion resistance, in fact the highest abrasion/scratch resistance of any uncoated optical plastic. CR-39 is about half the weight of glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
with an index of refraction only slightly lower than that of crown glass
Crown glass (optics)
Crown glass is type of optical glass used in lenses and other optical components. It has relatively low refractive index and low dispersion...
, and its high Abbe number yields low chromatic aberration
Chromatic aberration
In optics, chromatic aberration is a type of distortion in which there is a failure of a lens to focus all colors to the same convergence point. It occurs because lenses have a different refractive index for different wavelengths of light...
, altogether making it an advantageous material for eyeglasses and sunglasses
Sunglasses
Sunglasses or sun glasses are a form of protective eyewear designed primarily to prevent bright sunlight and high-energy visible light from damaging or discomforting the eyes. They can sometimes also function as a visual aid, as variously termed spectacles or glasses exist, featuring lenses that...
. A wide range of colors can be achieved by dye
Dye
A dye is a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and requires a mordant to improve the fastness of the dye on the fiber....
ing of the surface or the bulk of the material. CR-39 is also resistant to most solvent
Solvent
A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...
s and other chemicals, gamma radiation, aging, and to material fatigue. It can withstand the small hot sparks
Ember
Embers are the glowing, hot coals made of greatly heated wood, coal, or other carbon-based material that remain after, or sometimes precede a fire. Embers can glow very hot, sometimes as hot as the fire which created them...
from welding
Welding
Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...
, something glass cannot do. It can be used continuously in temperatures up to 100 °C and up to one hour at 130 °C.
In the radiation detection application, raw CR-39 material is exposed to proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
recoils caused by incident neutrons. The proton recoils cause ion tracks, which are enlarged by an etching process in a caustic solution of sodium hydroxide. The enlarged ion tracks are counted under a microscope (commonly 200x), and the number of ion tracks is proportional to the amount of incident neutron radiation.
It is used in some photographic filter
Photographic filter
In photography and videography, a filter is a camera accessory consisting of an optical filter that can be inserted in the optical path. The filter can be a square or oblong shape mounted in a holder accessory, or, more commonly, a glass or plastic disk with a metal or plastic ring frame, which...
s, such as the Cokin filter system.
A direct equivalent is produced by Acomon AG with the brand name RAV,
and another one by Danyang Yueda FineChemichal Co. Ltd in China.