Table of Contents
What is Optical Plastic?
In the field of modern optics, optical plastics are rapidly emerging due to their excellent performance and wide range of applications. Optical plastics, also known as optical resins, are plastic materials specifically designed for use in optical applications. Compared with traditional optical materials, such as optical glass, optical plastics are becoming one of the main forces in optical lens manufacturing due to their unique advantages.
Optical plastics are cheaper to manufacture and can be formed in one pass through injection molding, compression molding or cast molding. This material has excellent optical, mechanical, thermal and chemical properties that make it outstanding in numerous optical applications.
This article will delve into the properties of optical plastics, discuss their preparation processes, and several common plastic materials such as polymethyl methacrylate, polystyrene, polycarbonate, allyl diglycol carbonate, and cyclic olefin copolymers wait. With the wide application of optical plastics in lenses, camera lenses, organic optical fibers and other fields, it is redefining the future of modern optics with its low cost, lightweight and superior performance.
Advantages and Disadvantages of Optical Plastics
As an emerging optical material, optical plastics have obvious advantages, which make them widely used in many applications.
Advantages of optical plastics:
- Mass production to reduce manufacturing costs: Optical plastics are suitable for industrial mass production and contribute to effective cost control.
- Designing complex shapes: Plastic products can be flexibly designed, making it possible to manufacture very complex optical shapes, meeting the needs of some special optical systems.
- Light weight and impact resistance: Plastic is lighter than glass and has better impact resistance, providing an ideal solution for some scenarios that require weight and safety.
- Simultaneous pressing of optical surfaces and positioning surfaces: During the manufacturing process of optical plastics, the pressing of optical surfaces and positioning surfaces can be completed at the same time, which helps to reduce the assembly cost of the system.
- Consistent part quality: Plastic products can maintain high quality consistency through industrialized production processes, ensuring the stability and reliability of optical systems.
However, in addition to the above advantages, the application of optical plastics is also limited by its shortcomings
Disadvantages of optical plastics:
- Sensitive to environmental changes: Optical plastics are more sensitive to environmental changes such as temperature and humidity. Their thermal expansion coefficients and refractive index temperature coefficients are large, which limits their application in some extreme conditions.
- Molding process affects surface accuracy: During the injection molding process, the surface accuracy of plastic parts is easily affected by factors such as flow patterns, cooling and solidification shrinkage, which may affect the accuracy of optical parts.
- Presence of birefringence: Optical plastic parts may have varying degrees of birefringence due to molecular orientation during polymerization and internal stress during molding, which may cause problems in some high-precision optical applications.
Therefore, when selecting materials, it is necessary to weigh their advantages and disadvantages and make an appropriate choice based on the specific application scenario.
Optical Plastic Processing Methods
Plastic optical components can be manufactured and processed in a variety of processing methods. The following are several common processing methods:
- Plastic Injection Molding: Plastic injection molding is a common method of manufacturing optical components. The process involves injecting molten plastic material into an optical mold, which is then cooled and solidified to obtain the desired shape. Plastic injection molding enables high-precision and mass production and is suitable for manufacturing optical components such as lenses, prisms, windows, etc.
- Precision machining: Precision machining is a processing method performed by CNC (computer numerical control) machine tools, which can perform cutting, turning, milling, grinding and other operations on optical plastics. This processing method is suitable for manufacturing complex-shaped optical components, such as aspheric lenses, optical prisms, etc.
- Thermoforming: Thermoforming is a method in which thermoplastic materials are heated to a softened state and then shaped through pressure and mold shape. This process is commonly used to create optical components of specific shapes such as optical waveguides and fiber optic connectors.
- 3D printing: 3D printing technology is gradually used in the field of optics, including the manufacturing of optical plastic components. With appropriate optical-grade materials and high-precision 3D printing equipment, optical components with complex shapes and structures, such as microlens arrays, optical waveguides, etc., can be manufactured.
Each of these processing methods has its own advantages and scope of application. According to the specific optical component requirements and manufacturing needs, the appropriate processing method can be selected. Sometimes, multiple processing methods can also be used in combination to obtain more complex or special requirements optical components.
Classification of optical plastics
Plastic materials are generally divided into thermoplastics and thermoset plastics. Thermoplastic plastics refer to polymer materials that can be repeatedly heated and softened without changing their chemical composition, that is, plastics that have the characteristics of softening flow when heated and hardening when cooled. Most of the optical plastics are thermoplastics. The most commonly used ones include polymethylmethacrylate (PMMA), polystyrene (PS), polycarbonate (PC), etc. Among them, PMMA is the most widely used in the field of optical lenses.
Thermoplastic materials can be directly processed to form optical components through injection molding technology, or they can be cast into blocks first, and then optical components can be obtained through subsequent processing and polishing techniques.
Thermoset plastic refers to a material that can soften and flow when heated initially. After being heated to a certain temperature, a chemical reaction occurs and the plastic hardens, but this change is irreversible. The commonly used material, allyl diglycol carbonate (CR-39), is a thermosetting plastic.
Most Commonly Used Optical Plastics
Although there are dozens of types of optical plastics, the most commonly used optical plastics mainly include the following 9 types, such as polymethyl methacrylate, polystyrene, polycarbonate, allyl diglycol carbonate and cyclic olefins Copolymers, etc.
1. Polymethacrylate (PMMA)
Polymethyl methacrylate (PMMA), also known as methyl acrylate or methyl acrylate polymer, is a common transparent optical plastic widely used in the optical field. Its density is about 1.19 g/cm³, nd=1.491, dispersion coefficient Vd=57.2, transmittance is about 92%, and has excellent optical properties and weather resistance. The tensile strength of PMMA is generally between 50-80 MPa, and its linear expansion coefficient is 8.3 × 10^-5 K^-1, which is better than the optical memory performance of glass. The material’s refractive index change with temperature (dn/dt) is -8.5 × 10^-5, which is approximately 30 times greater than that of ordinary glass, although it is negative. Its thermal conductivity is 0.192 W/(m·K) and specific heat capacity is 1465 J/(kg·K). The glass transition temperature of PMMA is about 85-165℃, and the melting temperature is between 160-180℃. Because of its excellent transparency and shape plasticity, PMMA is widely used in the manufacturing of cameras, military optical systems, aspheric lenses and other fields.
2. Polystyrene (PS)
Polystyrene, referred to as PS, is a flint-type thermoplastic optical plastic with a transmittance of 88% and a large birefringence. Although its anti-ultraviolet radiation performance and anti-scratch performance are not as good as PMMA, it has a high refractive index, nd=1.59-1.660, and a small Abbe coefficient Vd=30.8, so when it is combined with PMMA, it can become a perfect match for F and C spectra. For achromatic lenses that perform line correction, the correction of the secondary spectrum is generally better than that of glass achromatic lenses. In addition to being able to form achromatic lenses with PMMA, PS is also used in grating components, optical instruments, laboratory consumables and display devices.
PS is one of the types of resin that is easy to mold and process. It has the characteristics of large difference between molding temperature and decomposition temperature, low melt viscosity, and stable size. It can be used for molding and injection molding. However, it is more brittle than other optical plastics. , so it is easy to crack, and care should be taken to prevent cracking when cutting the gate. It can also be machined with general metal or wood processing tools, such as drilling, sawing, cutting, etc.
3. Copolymer of styrene and acrylate (NAS)
A copolymer of 70% styrene and 30% acrylic resin, its properties are better than polystyrene. The transmittance can reach 90%, the refractive index nd can vary between 1.533-1.567, vd=35, it can It is used as a second material for positive chromatic aberration, but it is generally only used for thin lenses.
4.SAN
SAN (styrene-acrylonitrile copolymer) is a plastic widely used in the optical field. Its highly transparent properties make it ideal for manufacturing optical lenses, display coverings and optical components. SAN has excellent optical transparency and good mechanical properties, and is resistant to chemical corrosion. It can meet the requirements for clarity and durability of optical devices and is suitable for a variety of optical applications.
5.Polycarbonate （PC）
Polycarbonate (PC), commonly referred to as PC, is a thermoplastic known for its excellent overall properties. With excellent heat and cold resistance, PC maintains high mechanical strength and dimensional stability over a wide temperature range (-135°C to +120°C). Its linear dimension only increases by 0.07% when the temperature increases to 105°C. PC shows excellent impact strength and ductility, has uniform molding shrinkage, low water absorption, and only gains 0.13% weight after being soaked in water for 24 hours. However, PC is relatively difficult to machine, and injection molding is its most common processing method.
The density of PC is 1.20 kg/m³, and its original color is light yellow. Colorless and transparent products can be obtained by adding light blue. Its refractive index is 1.586, its dispersion coefficient is 34.0, and its transmittance reaches 88%. Among thermoplastics, PC’s unnotched impact strength ranks among the best, and its molding shrinkage is stable between 0.5% and 0.7%.
Since the optical constants of PC are similar to those of polystyrene (PS), it can be combined with polymethylmethacrylate (PMMA) to form an achromatic lens to give full play to their optical synergy.
6.TPX
TPX is a polymer of 4-methylpentene (4-methylpentene-1) produced by Mitsui Chemicals Co., Ltd. of Japan. TPX is its trade name. Its chemical name is Methylpentene copolymer, or PMP for short.
Poly-4-methyl pentene-1 is a highly crystalline transparent plastic with density: 0.82-0.83; water absorption: 0.01%; melting point: 240℃; Vicat softening point: 160℃～170℃; shrinkage rate: 1.5%～ 3.0%; light transmittance: 90% ~ 92% (the only crystalline polymer among currently commercialized high-transparency resins)
7.Allgl Diglycol Carbonate (ADC)
Allgl diglycol carbonate (ADC), referred to as ADC or CR-39, is a thermosetting material with excellent optical properties and strong chemical stability. It has excellent high temperature resistance and can withstand 100℃ for a long time and even 150℃ in the short term. The surface hardness of ADC is 40 times higher than PMMA, making it the hardest material among current optical plastics. Its refractive index is 1.498, its dispersion coefficient is between 53 and 57, and its white light transmittance is as high as 92%. ADC not only has wear resistance and impact resistance, but also shows strong resistance to chemical corrosion.
Since ADC has a shrinkage rate of 14% during curing, it is mainly used in the manufacture of spectacle lenses. Usually, ADC is formed by casting, poured in a glass mold, and cured at a temperature of 140°C for 17 hours. ADC is widely used in the optical field because of its excellent performance.
8.Polyethylene terephthalate （PET）
PET (polyethylene terephthalate) has excellent optical properties, its molecular chains are regular and orderly, and it has high crystallinity, resulting in a large density range between 1.2 and 1.38g/cm³. PET molecular chain has strong rigidity, exhibits superior strength and rigidity, has good barrier properties to non-polar gases and resistance to decay, and has a small expansion coefficient and high dimensional stability.
PET is a highly crystalline polymer with a melting point between 225 and 260°C and a glossy surface that is milky white or light yellow. PET exhibits excellent physical and mechanical properties over a wide temperature range and can withstand long-term use temperatures up to 120°C. It has good electrical insulation and maintains good electrical performance under high temperature and high frequency conditions. PET has excellent optical properties, and amorphous PET exhibits good optical transparency. These advantages make PET widely used in the optical field, such as optical lenses, optical lenses and other applications that require high optical performance.
9.PSU
Polyphenylene ether sulfone (PSU) is a high-performance plastic that excels in optical applications. Its high transparency and high temperature resistance make it ideal for manufacturing optical lenses, optics and high temperature optical components. PSU also has excellent mechanical strength and dimensional stability, making it suitable for optical applications that require high precision and stable performance, such as laser systems, medical optics, etc.
These are common plastic materials used in optical applications, and they have different properties and applicability. When selecting optical plastics, you need to make a reasonable choice based on specific application needs and performance requirements.
Optical Plastic Vs Optical Glass
Optical plastics and optical glass are the two mainstream materials for optical devices, each with unique characteristics and application advantages. First of all, from the perspective of material properties, the refractive index of optical plastics usually ranges from 1.42 to 1.69, the Abbe number ranges from 18.8 to 65.3, and the relative density ranges from 0.83 to 1.46g/cm³. In contrast, optical glass has a wider range of refractive index and dispersion, but optical plastics come at the expense of relatively low heat resistance, high moisture absorption, and a large coefficient of thermal expansion.
Although optical plastics are relatively disadvantaged in some aspects, such as poor heat resistance and chemical stability, they have clear advantages. Optical plastics are lightweight and have strong impact resistance. Their relative density is only half that of glass, and their manufacturing and processing costs are far lower than 1/10 to 1/30 of optical glass. The impact resistance of optical plastic lenses is about 10 times that of glass, making it an ideal choice for scenarios that require high device weight and safety. In addition, optical plastics have good shape adaptability and can flexibly prepare complex shapes such as aspheric lenses, providing more possibilities for optical system design.
However, optical plastics also have some limitations. It has relatively low heat resistance and may soften or deform in high temperature environments. The surface has relatively poor abrasion and chemical resistance and may require additional protective measures. In contrast, optical glass has higher heat resistance, better wear resistance and chemical stability.
In practical applications, optical system designers need to choose optical plastics or optical glasses according to specific needs, or use them in clever combinations to achieve the best performance balance. For high-demand application scenarios, optical glass may be preferred, while in applications that emphasize lightweight and cost, optical plastics appear to be more competitive.
Conclusion
With a decade-long presence in the optical industry, Noni is a trusted supplier that excels in delivering high-precision optical lenses tailored to customers’ specific requirements and designs. Our vast experience in the field enables us to provide optimal solutions based on customers’ samples and drawings. Our expertise includes the production of optical PMMA, PC aspheric lenses, aspheric magnifying lenses, and 3D optical lenses. We also provide molding production for various optical plastics such as polystyrene, silicone, olefin, PMMA, and PS.