As a thermoplastic engineering plastic with excellent performance, polycarbonate (PC) has many advantages such as high strength, high transparency, heat resistance, impact resistance, etc., and has been widely used in many fields. As an important plastic molding method, PC material can be thermoformed into various shapes and sizes to meet the needs of different industries.
Thermoforming Polycarbonate Sheet Physical and Chemical Properties
| Performance Classification | Specific Performance | Index |
|---|---|---|
| PC Physical Properties | Density | 1.18 – 1.22 g/cm³ |
| Light Transmittance | The colorless and transparent polycarbonate sheet has a light transmittance of up to 92%, and the 3mm transparent sheet has a light transmittance of up to 87%. | |
| Refractive Index | Relatively high, with specific values varying depending on the product. | |
| Coefficient of Linear Expansion | 3.8×10⁻⁵ cm/cm°C | |
| Heat Deflection Temperature | Around 135°C, which can be increased with glass fiber reinforcement. | |
| Brittleness Temperature | As low as -100℃ | |
| Long-term Service Temperature Range | -60℃ – 120℃ | |
| Water Absorption | Relatively low | |
| Shrinkage Rate | Relatively low | |
| Weight | Its specific gravity is only half that of ordinary glass. | |
| Sound Insulation Performance | It can effectively reduce noise. The 10mm hollow sheet can reduce noise by 20 decibels, the 6mm solid sheet by 35 decibels, and the 3mm granular sheet by 28 decibels. | |
| Impact Resistance | It has the best impact resistance among thermoplastics, with a cantilever beam notch impact strength of 600 – 900 J/m. | |
| Hardness | The surface hardness is relatively low, but it can be improved by surface treatment. For example, a hard coating can increase the surface hardness to HB – H1. | |
| Abrasion Resistance | Poor, and the surface is prone to scratches, but it can be improved by special treatment. | |
| PC Chemical Properties | Acid Resistance | It can resist the erosion of various organic and inorganic acids at room temperature. |
| Alkali Resistance | It is resistant to weak alkalis but not to strong alkalis. | |
| Oil Resistance | It has excellent oil resistance to neutral oils. | |
| Solvent Resistance | It is soluble in chlorinated alkanes, slightly soluble in aromatic hydrocarbons and ketones, and will swell in thinner and methanol. | |
| Hydrolysis Stability | It has relatively good hydrolysis resistance, but it cannot be used for products that repeatedly withstand high-pressure steam. | |
| Oxidation Resistance | It is not resistant to oxidizing acids, amines, and ketones. | |
| Flame Retardancy | Good, reaching the difficult-to-burn B1 level. The self-ignition point of the sheet is 630℃. During combustion, no toxic gases are produced, and it is self-extinguishing after leaving the fire source. |
Thermoforming Polycarbonate Process Overview
The PC plastic absorption molding process is to heat the spreading PC plastic sheet to the softening temperature, make it above the mold through the vacuum adsorption or positive pressure pressure, etc., tightly affixed to the mold surface, and then through the cooling and shaping, and ultimately form the required shape and size of the product.
Thermoforming PC Process Flow :
Mold design and production:
According to the shape, size and precision requirements of the product, use computer-aided design software to design the mold, and use the corresponding processing technology to make the mold. The quality and precision of the mold directly affects the quality and dimensional accuracy of the blister products.
Material Preparation:
Choose suitable PC plastic sheet, generally require the sheet thickness is uniform, the surface is flat, no obvious defects. Before use, it is necessary to dry the PC sheet to remove the moisture, to prevent bubbles or hydrolysis and other problems in the heating process, usually the drying temperature of 110 ℃ -120 ℃, drying time of about 8 hours.
Heating softening:
put the dried PC sheet into the heating device of the blister machine and heat it to the softening temperature, the softening temperature of PC material is generally between 180℃-220℃, the specific temperature depends on the thickness of PC sheet, molecular weight and other factors. During the heating process, the heating temperature and time need to be strictly controlled to ensure that the sheet can be softened uniformly, to avoid localized overheating leading to a decline in material performance or deformation and other problems.
Thermoforming molding:
When the PC sheet reaches the softening temperature, it is quickly moved to the top of the mold, and the air between the mold and the sheet is extracted through the vacuum system, so that the sheet is tightly adhered to the surface of the mold under atmospheric pressure to form the desired shape. For some complex shapes of products, it may also need to use positive pressure or positive and negative pressure combination for molding to ensure the molding quality of the products.
Cooling and shaping:
After the blister molding, keep the mold and the sheet in the close state, and cool the products through the cooling device, so that they can be shaped quickly. The cooling method can be air-cooled, water-cooled or natural cooling, etc. Different cooling methods will affect the internal stress and dimensional accuracy of the products. Generally speaking, water-cooled cooling speed is fast, but the product internal stress is large; natural cooling speed is slow, but is conducive to eliminating internal stress, improve the impact resistance of the product.
Demolding and post-processing:
After the products are cooled down to room temperature, they will be taken out from the molds for necessary post-processing, such as trimming of flying edges, surface treatment, assembly and so on, in order to get the final blister products.
Advantages and disadvantages of PC Thermoforming
High molding accuracy:
PC material can completely fit the shape of the mold after heating and softening, so the size and shape of the products can be precisely controlled to meet the demand for products with high dimensional accuracy, such as electronic product shells, medical equipment components, etc..
Good surface quality:
The surface of PC products after blister molding is smooth, no need for secondary processing, you can get good appearance quality, saving time and cost.
Abrasion and corrosion resistance:
PC plastic has high hardness and abrasion resistance, able to resist scratches and abrasion in daily use, and also has good corrosion resistance, suitable for a variety of harsh environments.
High degree of freedom in design:
The blister process can be used to design and produce various shapes and complex structures of molds according to different product requirements, thus realizing diversified product design and meeting the requirements of personalized customization.
High production efficiency:
PC blister process is a kind of efficient production method, can produce the same specification products in large quantities in a short period of time, suitable for large-scale industrialized production, can effectively improve the production efficiency and reduce the production cost.
Thermoforming Polycarbonate Disadvantages:
High material cost:
the price of PC material is relatively high, resulting in the cost of PC blister products is also high, to a certain extent, limiting its application in some cost-sensitive areas.
Processing difficulty:
PC materials have high melt viscosity, the molding process requires high temperature and pressure, and the temperature and pressure control requirements are more stringent, otherwise it is easy to crack, deformation and other defects, so it requires professional equipment and technical personnel to operate.
High mold requirements:
Due to the high precision requirements of PC blister products, the precision and surface quality of the molds also put forward higher requirements, mold production costs and cycle time is relatively long.
Internal Stress:
During the process of PC blister molding, due to the rapid cooling and deformation of the material, it is easy to produce internal stress, which leads to cracking and deformation of the products in the process of use, etc. It is necessary to take appropriate measures to eliminate or reduce the internal stress, such as optimizing the cooling process and annealing treatment.
Factors affecting the PC thermoformed Products
Material Factors:
Molecular weight:
The molecular weight of PC material has an important influence on its absorption and plasticity properties. If the molecular weight is too high, the viscosity of the melt will be high, the fluidity will be poor, and the molding will be difficult; if the molecular weight is too low, the mechanical properties and heat-resistant properties of the products will be reduced.
Therefore, it is necessary to choose PC materials with appropriate molecular weight according to specific product requirements.
Moisture content:
PC material is easy to absorb water, high moisture content will lead to bubbles, hydrolysis and other problems in the heating process, affecting the quality of products.
Therefore, the PC sheet must be fully dried before blistering, so that its moisture content is controlled below 0.02%.
Process parameter factors:
Heating temperature:
Heating temperature is one of the key factors affecting PC blister molding. If the temperature is too low, the sheet can not be fully softened, and it is difficult to fit the surface of the mold, resulting in poor molding; if the temperature is too high, it will make the PC material degradation and reduce the performance of the products.
Therefore, according to the thickness of the PC sheet, molecular weight and other factors, we need to reasonably determine the range of heating temperature, and strictly control the stability of the heating temperature.
Heating time:
The heating time is closely related to the heating temperature, the heating time is too short, the softening of the sheet is not uniform, which will affect the molding quality of the products.
Heating time is too long, which will lead to excessive softening of the PC material, or even decomposition, which will also affect the performance of the products. Therefore, according to the specific heating temperature and sheet thickness and other factors, reasonable adjustment of the heating time.
Vacuum or pressure:
The size of the vacuum or pressure directly affects the degree of adhesion between the PC sheet and the mold. Insufficient vacuum or pressure will result in the sheet not being able to closely fit the surface of the mold, bubbles, wrinkles and other defects.
Too high a vacuum or pressure may make the sheet overstretched, resulting in uneven wall thickness or rupture of the product and other problems. Therefore, according to the shape, size and complexity of the products and other factors, reasonable choice of vacuum or pressure, and precise control.
Cooling speed:
Cooling speed has an important effect on the internal stress and dimensional accuracy of PC blister products. If the cooling speed is too fast, the internal stress of the product is large, and cracking and deformation are easy to occur.
If the cooling speed is too slow, the production efficiency is low, and the dimensional stability of the product may be affected. Therefore, according to the requirements of the products and material properties, choose the appropriate cooling method and cooling speed.
Mold factors:
Mold precision:
The precision of the mold directly determines the dimensional accuracy and shape accuracy of the blister products. The dimensional tolerance of the mold, surface roughness and other parameters should be in line with the design requirements of the products, otherwise it will lead to dimensional deviation of the products, surface unevenness and other problems.
Mold structure:
The structure design of the mold should be reasonable, taking into account the thermal expansion coefficient of PC sheet, shrinkage and other factors, to avoid deformation, cracking and other defects due to unreasonable mold structure.
For example, when designing the mold, the slant of demolding should be increased appropriately so as to facilitate the demolding of the products.
Mold materials:
The selection of mold materials should be based on the requirements of the blister process and the production batch of products and other factors for comprehensive consideration.
Commonly used mold materials are gypsum, copper, aluminum, etc., different materials have different strength, wear resistance, thermal conductivity and other properties of the mold, should be based on the specific circumstances of the selection of suitable mold materials.
Application and Development Trend of Thermoforming Polycarbonate
Application:
Electronic products:
Such as cell phone shell, computer shell, display protective cover, etc., the use of PC blister molding process can produce high-precision, high-strength, beautiful appearance of the product, to meet the requirements of electronic products on the appearance and performance.
Automotive parts:
Such as automotive lampshades, instrument panels, interior parts, etc., PC plastic absorbing products have good heat resistance, impact resistance and optical properties, can improve the quality and safety of automotive parts.
Medical devices:
Such as medical device shells, petri dishes, surgical instrument trays, etc., PC materials, non-toxic, tasteless, disinfection-resistant and other characteristics of the medical device field has been widely used, blister molding process can be manufactured in line with the health standards of medical devices and precision requirements of the product.
Packaging industry:
Such as food packaging, cosmetic packaging, pharmaceutical packaging, etc., PC blister packaging has good transparency, barrier and impact resistance, can effectively protect the product, while improving the product display effect.
Lighting industry:
Such as blister light cover, light box, etc. PC blister light cover has excellent light transmittance, weather resistance and impact resistance, which can provide good lighting effect and service life.
Development trend:
High precision:
With the increasing requirements for product precision in electronic products, medical devices and other industries, the PC blister process will develop in the direction of higher precision, and more advanced mold manufacturing technology and molding process will be developed to meet the market demand for high-precision blister products.
Multi-functional:
Future PC blister products will not only be limited to a single function, but will develop in the direction of multifunctionalization. For example, the development of anti-bacterial, anti-static, electromagnetic shielding and other functions of the PC plastic material, as well as the combination of plastic technology and other processing technology, the manufacture of composite products with a variety of functions.
Green environmental protection:
In the environmental protection awareness of the background, PC plastic absorption molding process will pay more attention to green environmental protection. On the one hand, the research and development of more environmentally friendly PC materials, reduce its impact on the environment; on the other hand, optimize the blister process, reduce energy consumption and waste emissions, improve the environmental friendliness of the production process.
Intelligent:
With the continuous development of intelligent manufacturing technology, PC blister molding process will gradually realize intelligent production. For example, the use of automated equipment and robotics to achieve automated operation and online inspection of the blister production process, improve production efficiency and product quality; the use of big data, artificial intelligence and other technologies to optimize and predict the parameters of the blister process, reduce production costs and scrap rate.
Conclusion
As an important plastic molding method with the advantages of high molding precision, good surface quality, high design freedom and high production efficiency, the polycarbonate PC thermoforming molding process has been widely used in many fields, such as electronic products, automotive parts, medical devices, packaging, lighting and so on.
However, PC plastic absorbing process also exists in high material cost, processing difficulty, high mold requirements, internal stress problems and other shortcomings, which require in-depth research and optimization in the selection of materials, process parameter control, mold design and manufacturing and other aspects.
With the continuous progress of science and technology and the constant change of market demand, PC plastic absorbing process will move towards the direction of high precision, multi-functionality, green environmental protection, intelligent development, for the development of related industries to provide more high-quality, efficient, environmentally friendly technical support.