Transparent plastics

Transparent plastics refer to a class of polymer materials with an ordinary light transmittance of more than 80%. The indicators to measure the performance of transparent plastics are: light transmittance, haze, refractive index, double which involves dispersion, etc.
Transmittance is the percentage (%) of the luminous flux through the material and the luminous flux incident on the surface of the material. The higher the light transmittance of the material, the better its transparency. The light transmittance of optical glass is about 95%, and the light transmittance of PMMA is 93%.
Haze is the percentage of scattered luminous flux and transmitted luminous flux of transparent material, it is an indicator of the degree of turbidity of transparent or translucent materials, the greater the haze, the worse the clarity of the material.
The refractive index is an optical indicator of transparent materials. The material used for the lens should be made with a larger refractive index to reduce the thickness of the lens. The refractive index of plastic is around 1.5.
Birefringence is the difference between the parallel and perpendicular refractive indices of a material, which characterizes the degree of anisotropy of the material's optical properties. Materials used for optical purposes require as little birefringence as possible to prevent image variation.
Dispersion is also a loss of light, expressed in Abbe number, which is related to the refractive index of the material, the greater the refractive index, the smaller the Abbe number.
The requirements for a good transparent material are: high light transmittance, low haze, high refractive index, small birefringence, and small dispersion.
Transparent plastics include: plexiglass (PMMA), polycarbonate (PC), polystyrene (PS), PET, PEN, polyethersulfone (PES), K resin (BS), AS, NAS, PMP, EVOH, J.D, HEMA, CR-39, mPP, mPE, polynorbornene, transparent nylon, transparent epoxy resin, etc. The following is an introduction to several varieties of transparent plastics that have not been mentioned before.
1,PMP
The scientific name of PMP is poly4-methyl-1-pentene, and the trade name is TPX, therefore, it is also customarily called TPX.
With a relative density of 0.83, PMP is the least dense of thermoplastics. The transparency is very good, and the light transmittance is 90%, which is between PMMA and PS. Its ultraviolet transmittance is second only to glass, the refractive index is 1.463, which is low, and the Abbe number is 56.4, which is somewhat large. Very low water absorption and good water resistance.
The rigidity of PMP is high, exceeding that of PP at temperatures above 100°C and of PC at temperatures above 150°C. Its mechanical properties vary little with temperature, and it still has usable mechanical strength at 250°C, and it can still maintain shape stability when it is close to the melting point. Its products are used at low temperature to room temperature (below 30 °C), the elongation at break is small, the impact performance is poor, and the strength is roughly the same as that of PE; when used above 30 °C, its flexibility increases, and the elongation at break and impact strength increase.
PMP has excellent electrical properties and is better than other polyolefin plastics.
PMP has good drug resistance and can resist inorganic acids, alkalis and other chemicals, but it is susceptible to strong oxidants, and light hydrocarbons and chlorinated hydrocarbons will make it swell. The UV resistance is not good, and it will turn yellow over time.
The specific uses of PMP include medical devices, laboratory supplies, food containers, automotive parts, lighting fixtures, high-voltage cables, etc.
2. BS or K resin
BS is a styrene/butadiene copolymer, and is also commonly known as K resin.
The biggest feature of BS is good transparency, and its light transmittance can reach 90%~95%, which is close to PS. BS poly has the physical properties of GPPS, and the impact resistance is much better than PS, ester is slightly worse than ABS and HIPS, and the thermal denaturation temperature is slightly lower than GPPS.
BS is used in large quantities for transparent packaging materials. It can be used for transparent covers for vending machines, transparent boxes with hinges, decorations, toys, etc. It can also be used in medical devices due to its unchanged performance during the sterilization process.
3,AS
The scientific name of AS is styrene/acrylonitrile copolymer, also known as SAN. It is an excellent transparent material. AS has an aqua white appearance and can be transparent, translucent, or opaque. Innocuity. The relative density is 1.06~1.08, the light transmittance is 87%~94%, the refractive index is 1.57, and the molding shrinkage is 0.2%~0.5%.
AS has good impact resistance, but is sensitive to notching, mechanical strength and transparency are comparable to PS, stress crack resistance is better than GPPS, scratch resistance, high rigidity, and high dimensional stability.
AS has high chemical stability to non-polar substances such as gasoline, kerosene and other aromatic compounds, and is resistant to water, inorganic acids, alkalis, detergents, chlorinated hydrocarbons, etc., but can be swollen by organic compounds and dissolved in ketone solvents.
AS has medium weather resistance and yellows after aging.
Most of the applications of AS are to make use of its transparency, such as lamps, pens, lenses, signal lamps and lamp housings, lighters, speedometer glass, toys, wine glasses, handicrafts, decorations and packaging materials. It can also be used for home appliance accessories, instrument panels, electrical parts, battery housings, and daily necessities.
4. Polynorbornene
Polynorbornene is a cyclic olefin polymer with the following properties:
(1) Excellent optical properties The light transmittance and refractive index of polynorbornene are 92% and 1.51, which are close to PMMA and higher than PC.
(2) High heat resistance The heat deflection temperature of polynorbornene is 162 °C, which is a high heat resistance temperature in plastics, 80 °C higher than PMMA and 20 °C higher than PC.
(3) Low water absorption: Its water absorption rate is 1/5 of PMMA, which is similar to that of PC. The size change after water absorption is only 0.04%.
(4) High surface hardness The surface hardness of polydegradable bornene is higher than that of PMMA and PC, and it has high scratch resistance.
(5) Good adhesion and easy coating treatment.
Polydegradable bornene is especially suitable for the manufacture of lenses, because it has high transparency, high temperature resistance, good humidity resistance, and is not sensitive to temperature changes.
5. Cellulose transparent plastics
(1) Cellulose acetate
Cellulose acetate can be divided into two types: cellulose triacetate and cellulose diacetate, which is abbreviated as CA in English.
Cellulose acetate is a white granular, powdery or cotton-like solid, which has the advantages of hardness, transparency and good luster. The refractive index is 1.49% and the light transmittance is 87%. The tensile strength is 13~61MPa, and the impact strength of the cantilever beam is 21~277J/m. The heat deflection temperature is 43~98°C. The volume resistivity is 1013Ω•cm, the dielectric constant (106Hz) is 3.2~7, and the dielectric loss tangent (1MHz) is 0.01~0.1.
Cellulose triacetate is stronger than cellulose diacetate, and its tensile strength is almost twice as high. It has high heat resistance and is suitable for the manufacture of motion picture films. Cellulose diacetate is more soluble in concentrated hydrochloric acid and acetone but insoluble in dichloromethane and chloroform, while cellulose triacetate is insoluble in hydrochloric acid and acetone, but soluble in dichloromethane and chloroform.
Cellulose triacetate is widely used in films, films and tapes, and cellulose diacetate is used in cigarette filters, handles, bicycle handlebars, pen barrels and spectacle frames.
(2) Nitrocellulose
Nitrocellulose, abbreviated as CN, is the world's first naturally modified plastic material, also known as "celluloid".
Nitrocellulose is a white odorless solid with a relative density of 1.38, tough and brightly colored. Good transparency, refractive index of 1.5, light transmittance of 88%. Low water absorption, high dimensional stability, continuous use temperature of 60°C. The tensile strength is 48~55MPa, the dielectric constant is 7.0~7.5, and the tangent of the dielectric loss is 0.09~0.12.
Nitrocellulose can be used to make stationery and educational items such as table tennis balls, triangular rulers, pen barrels and musical instrument shells. Everyday items such as toys, cosmetic boxes, eyeglass frames, umbrella handles, bicycle handlebars and knife handles, etc.
6. Other transparent plastics
(1)CR-39
CR-39 is a thermoset resin, but it can be cast.
CR-39 has a relative density of 1.32 and a water absorption rate of 0.2%. It has excellent optical properties. It has a high light transmittance of 91%, a refractive index of 1.50, which can be increased to 1.546 when copolymerized with diallyl phthalates, and an Abbe number of 58 with low birefringence. Good heat resistance, heat deflection temperature up to 140°C. It has high hardness and good impact resistance.
The disadvantage of CR-39 is that the wear resistance is not good, which can be improved by the coating method, and the refractive index is slightly lower, which can be improved by the copolymerization method.
CR-39 is a high-grade optical material that is very suitable for the manufacture of spectacle lenses.
(2)J.D
J.D is a derivative of polyethersulfone, which is a thermosetting plastic and can be molded by casting method.
The relative density of J.D is 1.19 and the water absorption is only 0.06%. The optical performance is very good, the light transmittance reaches 92%, the refractive index is adjustable, and the maximum refractive index can reach 1.62, which is the largest among transparent plastics, and the dispersion is small, and the Abbe number is only 27.
The hardness of J.D is larger, the Rockwell hardness is in the range of 138~332, and the Mohs hardness can reach 6H. Its cost is only 1/2 of PMMA and 1/6 of CR-39, and it is an optical material that can compete with CR-39.
J,D is mainly used in the manufacture of lenses, and due to its large refractive index, the thickness of the lens can be greatly reduced, and it is a promising optical material.
(3)HEMA
HEMA is a commonly used transparent plastic material for contact lenses, specifically composed of hydroxyethyl methacrylate. Contact lenses have high requirements for the performance of materials, in addition to the performance required by general lenses, they also require good water absorption, oxygen permeability, elasticity, toughness and physiological compatibility with the human body.
The water absorption rate of HEMA is as high as 39%~60%, which can effectively provide the water required by the human eye, its light transmittance reaches 97%, which is higher than that of optical glass, and the physiological compatibility with the human body is good, the refractive index is 1.43~1.45, and the relative density is 1.16~1.17.