Types, uses, processes and surface treatment of plastics


“The beauty of materials is divided into three categories: the beauty of the original state; the beauty of the re-creation; the beauty of the recombination. The material itself has no emotional color. Its original color gives people an emotional guide. The material itself is only functional. “

Plastic overview:
Plastic refers to a material with plastic behavior. The so-called plasticity refers to deformation when subjected to an external force, and after the external force is removed, it can still maintain the state under the force. Plastics are usually composed of resin and auxiliary additives. The resin accounts for about 40% to 100% of the total weight of the plastic.
The basic properties of plastics are mainly determined by the nature of the resin, and the name is often named by the name of its raw material resin. But additives also play an important role in changing performance defects.
Plastic is a representative of modern materials, and its advantages and disadvantages are as distinct. However, with the advancement of science and technology, the performance of plastics is becoming more and more easy to control. In almost all industries, plastics are used more and more widely. The trend of “plastic instead of wood” also reminds designers of the status of plastic as a material. There are many types of plastics, and this article cannot count them one by one, but a comprehensive summary of basic materials and basic craftsmanship can also improve designers’ control over product manufacturability.


Plastic performance-type recommendation table
When designers use materials, they should first consider whether the performance of the materials meets the requirements, rather than starting from the vision. How to match the performance and aesthetics of materials to serve the product is the key to CMF design.
Plastic Selection Reference Manual
High corrosion resistance
Low cost to quality ratio
Urea formaldehyde, phenol formaldehyde, polystyrene, polyethylene, polypropylene, PVC
Compressive strength
Polyterephthalamide, glass fiber reinforced phenolic, epoxy, melamine, nylon, glass fiber reinforced thermoplastic polyester, polyimide
Low cost to volume ratio
PE, PP, urea formaldehyde, phenol formaldehyde, PS, PVC
High dielectric constant
Phenolic, PVC, fluoroplastic, melamine, allyl plastic, nylon, polyterephthalamide, epoxy
High dielectric strength
PVC, fluoroplastics, PP, polyphenylene ether, phenolic, thermoplastic polyester, glass fiber reinforced nylon, polyolefin, PE
High loss factor
PVC, fluoroplastics, phenolic, thermoplastic polyester, nylon, epoxy, allyl terephthalate, polyurethane
Good bearing and deformation resistance
Thermosetting laminate
High elastic modulus
Melamine, urea formaldehyde, phenol formaldehyde
Low modulus of elasticity
PE, PC, fluoroplastics
High resistance
PS, fluoroplastics, PP
High elongation at break
PE, PP, silicone, ethyl hexene acetate
Low elongation at break
PES, glass fiber reinforced PC, glass fiber reinforced PP, thermoplastic polyester, polyetherimide, vinyl ester, polyetheretherketone, epoxy, polyimide
Flexural modulus
PPS, epoxy, glass fiber reinforced phenolic, glass fiber reinforced nylon, polyimide, diallyl terephthalate, polyterephthalamide, thermoplastic polyester
Bending yield strength
Glass fiber reinforced polyurethane, epoxy, carbon fiber reinforced nylon, glass fiber reinforced PPS, polyterephthalamide, PEEK, carbon fiber reinforced PC, etc.
Low friction coefficient
Fluoroplastics, nylon, polyoxymethylene
High hardness
Melamine, glass fiber or cellulose reinforced phenolic, polyimide, epoxy
High impact strength
Phenolic, epoxy, PC, ABS
High humidity resistance
PE, PP, fluoroplastics, PPS, polyolefin, thermoplastic polyester, polyphenylene ether, PS, PC, (glass fiber or carbon fiber reinforced PC)
PE, silicone, PVC, thermoplastic elastomer, polyurethane, ethylene acetate
High tensile strength at break
Epoxy, glass fiber or carbon fiber reinforced nylon, polyurethane, glass fiber reinforced thermoplastic polyester, polyterephthalamide, PEEK, carbon fiber reinforced PC, PEI, PES
High tensile yield strength
Glass fiber or carbon fiber reinforced nylon, polyurethane, glass fiber reinforced thermoplastic polyester, PEEK, PEI, polyterephthalamide, glass fiber or carbon fiber reinforced PPS
Low thermal conductivity
PP, PVC, ABS, PPO, polybutene, acrylic, PC, thermoplastic polyester, nylon
Low expansion coefficient
Carbon fiber or glass fiber reinforced PC, glass fiber reinforced phenolic, carbon fiber or glass fiber reinforced nylon, glass fiber reinforced thermoplastic polyester, glass fiber or carbon fiber reinforced PPS, PEI, PEEK, polyterephthalamide, allyl plastic, melamine
Permanent high transparency
Acrylic, PC
Excerpted from 2003.10 “Product Design Material Handbook” by Machinery Industry Press
Plastic selection
Under normal circumstances, the process of selecting materials for product development can be divided into the following steps:
1. The key requirement to define the product is CTQ, such as: V0 flame retardant, long-term use temperature is higher than 80 degrees, tensile modulus is greater than 10Gpa… The requirements should be specific, and it is better to have detailed data definitions.
2. Preliminary screening of material types based on CTQ, such as nylon 66, glass fiber reinforced PC, POM, etc. At this time, not only the product manual issued by the material manufacturer, but also the application case of the material should be checked. Reference to the requirements and reasons of selecting materials for similar products from other manufacturers can reduce the trial and error cost of the project at this step and shorten the project development cycle.
Third, select specific material specifications based on the material types determined in the previous step. When selecting specifications, you should not only refer to the application case of the material, but also the reference price in the material property table to understand the cost of raw materials and the procurement channels in advance.
Fourth, after selecting specific material specifications, it is necessary to conduct a feasibility analysis before opening the mold. Perform mold flow analysis to optimize mold design for more complex structural components, and even some products need to be 3D printed models for more verification.


Use classification
Generally, plastics can be divided into thermoplastics that are melted by heating and thermosets that are not melted by heating. But it is more meaningful in design to classify it into general plastics, engineering plastics and special plastics by use.
General Plastic
General-purpose plastics are the most common in daily life.
General-purpose plastics refer to plastics with large production volume, wide supply, low price and suitable for a large number of applications, including polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile -Butadiene-styrene copolymer (ABS). General-purpose plastics generally have good molding processability, and a variety of molding processes can be used to make products with various uses, including plastic bags, cling film, lunch boxes, furniture, electrical appliances, etc.
Polyethylene (PE) is the product with the largest consumption of the five general-purpose plastics. The consumption of pipes made by extrusion molding process and film products made by calendering process account for the highest consumption, and there is also hollow made by blow molding process. Products include bottles, cans, barrels, etc.; the injection molding process can be made into more forms of barrels, basins, and daily gadgets according to the shape of the mold; high-density polyethylene can also be used as a high-frequency electrical insulating material for radar And TV.
PE plastic is odorless, non-toxic, feels like wax, has low temperature resistance (the lowest operating temperature can reach -100~-70°C), has good chemical stability, and can withstand most acids and alkalis (not resistant to oxidizing properties) The acid), insoluble in general solvents at room temperature, low water absorption, excellent electrical insulation and other characteristics. When not dyed, low-density polyethylene is transparent, while high-density polyethylene is opaque.


Polypropylene (PP) is a thermoplastic resin made by polymerizing propylene. Polypropylene is a non-toxic, odorless, and tasteless milky white highly crystalline polymer, and it is currently one of the lightest varieties of all plastics. PP has good water stability, stable chemical composition, good anti-corrosion effect, and good heat resistance. Although polypropylene has good moldability, thick-walled products are easy to dent due to large shrinkage (1%~2.5%), and it is difficult to meet the requirements for some parts with high dimensional accuracy, but the surface of the products has good gloss.
Polypropylene is often used in the production of disposable tableware and is easy to recycle, but it should be noted that recycled plastic products cannot be used in the production of tableware. At the same time, because of the high temperature resistance of PP plastic, it can be applied to plastic products that require microwave heating. The PS material that is also commonly used in disposable lunch boxes is mostly used in the direction of cold drink packaging.


Polyvinyl chloride (PVC) plastic ranks second in the global synthetic materials consumption. PVC plastic is not flammable, has high strength, high hardness, friction resistance, and excellent geometric stability, but it is not resistant to high temperatures and is easy to soften at high temperatures.
In terms of color, PVC itself is slightly yellowish, translucent and shiny, but the stability of the finished product is poor, it will turn yellow after long-term use, and whitening will appear in the twists and turns.
Polyvinyl chloride is generally used in plastic wrap, plastic shoes and leather products, films, cables, and plastic bags.


Polystyrene (PS) refers to a polymer synthesized from styrene monomer through radical addition polymerization. It is a colorless and transparent thermoplastic with a glass transition temperature higher than 100°C, so it is often used Make various disposable containers that need to withstand the temperature of boiling water, and disposable foam lunch boxes. In addition, polystyrene is also used in combs, boxes, ballpoint pen holders, children’s toys, plastic shopping bags, etc.


ABS is acrylonitrile-butadiene-styrene copolymer. ABS is a thermoplastic polymer material structure with high strength, good toughness, and easy processing and forming. It has good comprehensive performance, good chemical stability, and good electrical properties. It has the characteristics of high impact resistance, high heat resistance, flame retardancy, reinforcement and transparency. At the same time, ABS plastic has good formability. The processed product has a smooth surface and can be electroplated or painted.
Because of the excellent performance of ABS plastics, it is often used in structural parts that require strength and hardness, such as automobiles, electronic appliances, office equipment, and communication equipment, and is often used as 3D printing materials, which is one of the most stable of 3D printing materials. Kind.


Engineering plastics
Engineering plastics refer to plastics that can be used as engineering materials and substitute for metal manufacturing and its parts. Compared with general plastics, engineering plastics can accept stronger external forces, and have good mechanical properties, high temperature resistance, low temperature resistance, good dimensional stability, and can meet higher requirements for use.
Engineering plastics can be divided into general engineering plastics and special engineering plastics. The former mainly includes five general engineering plastics: polyamide, polycarbonate, polyoxymethylene, modified polyphenylene ether and thermoplastic polyester; the latter mainly refers to heat resistance Engineering plastics with a resistance of over 150 degrees Celsius.
Generally speaking, “plastic to replace steel” and “plastic to replace wood” refer to engineering plastics, which are often used in electronic appliances, automobiles, construction, office equipment, machinery, aerospace and other fields.
Special plastics
Generally refers to plastics with special functions that can be used in special applications such as aviation and aerospace. For example, fluoroplastics and silicones have outstanding high temperature resistance, self-lubricating and other special functions, and reinforced plastics and foam plastics have special properties such as high strength and high cushioning. These plastics belong to the category of special plastics.


Processing technology
The first step after selecting design materials
Select the molding process according to different materials and different needs


Injection molding
Injection molding, also known as injection molding, is an important method for processing thermoplastic molded products.
The thermoplastic or thermosetting molding compound is heated and plasticized in a barrel with a controllable temperature, enters the gate through the nozzle under pressure, and the runner enters the mold cavity. After rapid curing, the mold is opened and the product is ejected.
In an improved process-runnerless molding, the runner is part of the cavity.
There are many varieties of injection molded products, such as plastic products for daily use, plastic parts for machinery and electrical appliances, etc. In addition to fluoroplastics, almost all thermoplastics can be processed by injection molding. In addition, injection molding can also be used to form some thermoset plastics.


Extrusion molding
Extrusion molding, also known as extrusion molding, is a method of continuously processing thermoplastics into products with various cross-sectional shapes using an extruder.
The thermoplastic or thermosetting molding compound is charged into the hopper, and then into the barrel, heated and plasticized in the barrel, and the material is pushed forward by the screw placement, and passes through the nozzle with the required cross-section.
This method is mainly used to produce plastic plates, sheets, rods, profiled materials, and cable sheaths. At present, extruded products account for about 40% to 50% of thermoplastic products.


Blister molding
Blister molding is also called thermoforming. During forming, the thermoplastic plastic sheet or sheet is clamped, fixed on the mold, and heated with a radiant heater. When heated to the softening temperature, a vacuum pump is used to extract the air between the sheet and the mold. Under atmospheric pressure, the sheet Stretching deformation fits to the surface of the mold, and after cooling, it is shaped into a product.
    Blister forming can be used to form packaging products, such as pharmaceutical packaging, disposable lunch boxes, electronic products such as button battery packaging, etc., thicker plates can also be formed into shell products such as refrigerator liners, bathroom mirror boxes, etc.
Commonly used materials for vacuum forming are polyethylene, polypropylene, polyvinyl chloride, ABS, polycarbonate and other materials.


Blow molding
Blow molding is also called hollow molding, which originated from the ancient glass blowing process. According to the different methods of preparing plastic tubular blanks, blow molding can be divided into two categories: extrusion blow molding and injection blow molding.
Put the heated thermoplastic extruded tube between the two halves of the open mold, apply gas pressure, make it expand against the side wall of the closed mold, open the mold, and eject the product.
Blow molding is commonly used in the daily-use industry to form car fuel tanks, car heating ducts, chemical packaging containers, portable tool suitcases, etc.


Usually after preforming with thermoplastic resin or partially polymerized thermosetting resin, the material is put into a heated cavity, the mold is closed, and heated and pressurized to make the material flow and fill the cavity, heat to make it fully polymerized, and open the mold. Take out the product.
Calendering and rolling by tandem heating or cooling rolls make the dough-type thermoplastic melt into a plate with uniform thickness. It can also be used to laminate plastic covers to the backside of other materials.
Calendering is a forming method for producing polymer material films and sheets, which can be used for plastics and rubber. If the processed paper or fabric is passed between the last pair of rollers at the same time, the hot plastic or rubber film can be laminated with these substrates only under the pressure of the rollers to produce composite products. This method is called calendering, and for rubber, it is also called glueing. The familiar artificial leather, floor leather, wallpaper, etc. are all composite products of plastic and substrate.


Foam molding
In the foaming molding process or foamed polymer materials, a honeycomb or porous structure is formed through the addition and reaction of a physical foaming agent or a chemical foaming agent.
(1) Chemical foaming. The specially added chemical foaming agent, the gas generated by thermal decomposition or the chemical reaction between the raw material components, makes the plastic melt fill the cells. The gases released by chemical blowing agents when heated are carbon dioxide, nitrogen, ammonia, etc.Chemical foaming is often used in the production of polyurethane foam. 
(2) Physical foaming. Physical foaming is a method of dissolving gas or liquid in plastic and then expanding or vaporizing it. There are many types of plastics suitable for physical foaming. 
(3) Mechanical foaming. The gas is mixed into the liquid mixture by the mechanical stirring method, and then the foamed plastic with the cells is formed through the shaping process. This method is often used for urea-sleeping formaldehyde resin, and other such as polyvinyl formal, polyvinyl acetate, polyvinyl chloride sol, etc. are also suitable.
Almost all thermosetting and thermoplastic plastics can produce microporous structures to make foam plastics. Commonly used resins are polystyrene, polyurethane, polyvinyl chloride, polyethylene, urea formaldehyde, phenolic and so on.


Laminating molding requires pre-impregnation of thermoplastic or thermosetting resin or spraying reinforcement materials such as cloth, paper, foil, etc., and molding them into sheets, rods, pipes or other simple shapes under pressure.


Pouring molding
The liquid plastics (except acrylic plastics, usually thermosetting plastics) are poured into the mold, cured and formed (without pressure), and then fall off from the mold after forming. Thermoplastics are deposited on a highly polished support surface in the form of a melt or a hot melt to form a thermoplastic film.
Pouring molding can produce large-scale products with thick sections, and the surface quality of the products is good, which is suitable for mass production.
Transfer molding
The thermosetting plastic enters the transfer box from the hopper, is heated and plasticized, and then enters the cavity through the closed mold gate and runner with a plunger, solidifies and forms, and then opens the mold to eject the product.
This technology has developed rapidly in recent years, and has been widely used in the aircraft industry, automobile industry, shipbuilding industry and other fields, and has developed a variety of branches to meet the application needs of different fields.


Hand lay-up
Hand lay-up molding is also called manual pasting molding and contact molding. It refers to the manual operation on the mold coated with the release agent, that is, while laying the reinforcing material, while painting the resin until the thickness of the required plastic product, and then curing and This process of demoulding and obtaining plastic products.
Fused Deposition Modeling
This process is by extruding filamentous materials such as thermoplastics, waxes or metal fuses from a heated nozzle, and depositing the melt at a fixed rate in accordance with the predetermined trajectory of each layer of the part.


CNC Forming
CNC computer numerical control machine tool is an automatic machine tool equipped with a program control system.
The control system can logically process the program with control codes or other symbolic instructions, and decode it, so that the machine tool can operate and process parts.


Surface treatment
The surface treatment of plastic is not only to improve the visual beauty, but also affects the appearance, texture, function and other three factors. Through the surface treatment, the color, gloss, feel, roughness, service life, and scratch resistance of the material can be changed. Performance, anti-fingerprint and other properties.
In-mold decoration technology (IMD)
In-Mold Decoration-IMD, also known as coating-free technology, is to put a film with a printed pattern into a metal mold, and inject the molding resin into the metal mold to join the film to print A molding method in which a patterned film is integrated with resin and cured into a finished product.
This kind of surface decoration technology, the surface hardened transparent film, the middle printing pattern layer, the back injection layer, and the ink middle, can make the product resistant to friction, prevent the surface from being scratched, and can keep the color bright and not easy to fade for a long time.
IMD includes IML (no stretch, small curved surface), IMF (high stretch product, 3D), IMR (surface film is removed, leaving only the ink on the surface).
At present, IML and IMF are collectively referred to as IML in the industry.
The advantages of the in-film decoration technology are: 1. Exquisite decorative graphics and signs are hidden, and will not disappear from friction or chemical corrosion; 2. The graphics, signs and color designs can be changed at any time without changing the mold; 3. Three-dimensional three-dimensional For shape products, the printing accuracy is accurate, with an error of ±0.05mm; 4. It can provide graphics and text, logo back light transmittance and high light transmittance window effect; 5. Function buttons have uniform convex bubbles, good hand feeling, and life of up to 1 million More than two times; 6. Three-dimensional changes can increase the designer’s freedom of product design; 7. Compound molding processing achieves a seamless effect. It should be noted that the yield rate of this technology is not high.
(IMD) Plastic products suitable for 3C, home appliances, LOGO nameplates and auto parts, especially the popular mobile phone casings and various instrument panels.


Spraying is a coating method in which the paint is atomized by spray tools such as a spray gun and sprayed on the workpiece. Process flow: injection molding → primer → drying → top coat → drying.
The advantages of this technology are 1. Rich colors; 2. Processing in a liquid environment, which can realize surface treatment with complex structures; 3. Mature technology and mass production; 4. Unique transparency and high gloss.
The disadvantages are 1. The cost is too high, and low-cost positioning products are not suitable for this process; 2. The process is relatively complicated and the yield is low.


Electroplating can make the plastic get a metal effect surface with higher yield and lower cost. Electroplating methods are mainly divided into vacuum plating and water plating.
The advantages of this technology are 1. weight reduction; 2. overall cost savings; 3. fewer processing procedures; 4. simulation of metal parts.
The disadvantage is that there is a fire hazard when electroplated plastic is used in certain types of household appliances.


Printing can be divided into many types according to different printing conditions.
Plastic parts printing is a process in which the required patterns are printed on the surface of plastic parts by means of pad printing, screen printing, and transfer printing.
Pad printing is an indirect gravure head printing technology. The designed pattern is first etched on the printing plate, the etching plate is coated with ink, and then most of the ink is transferred to the printed object through the silicone head .
Screen printing is one of the main printing methods in stencil printing: the printing plate is in the form of a mesh, and the ink on the printing plate is leaked from the through-hole part of the plate to the substrate under the squeeze of the squeegee during printing. Usually the wire mesh is made of nylon, polyester, silk or metal mesh.
The transfer technology in printing can be divided into water transfer and thermal transfer.
Water transfer printing is a kind of printing that uses water pressure to hydrolyze the transfer paper/plastic film with color patterns; heat transfer printing is to print patterns or patterns on heat-resistant adhesive paper, by heating and pressing A technique for printing the pattern of the ink layer on the finished material.


Laser carving
Laser engraving: also called laser engraving or laser marking. It is a process of surface treatment using optical principles. It is similar to screen printing. Through laser engraving, you can type or pattern on the product surface.
Laser technology has the advantages of wide application range, safety and reliability; precise and meticulous, safe and fast; low cost, saving and environmental protection.


Bite the flower
Flower biting is a process in which chemicals such as concentrated sulfuric acid are used to corrode the inside of the plastic molding mold to form lines in the form of snakes, etched, and plowed fields. After the plastic is molded through the mold, the surface has corresponding lines.
Process flow: mold receiving → sand blasting → chemical cleaning (pickling) → decals → upper bitumen powder → heating → Shangyang → dry paint → chemical corrosion → chemical cleaning → sand blasting → quality inspection
The advantages of biting are that it can improve the visual effect and feel of the product; it is non-slip; increases the surface area, which is good for heat dissipation; it is good for demoulding and easy to form.

Design case analysis
Finally, take the application of plastics in home appliances as an example. Please experience the CMF design results.


Take the microwave oven as an example
The plastic parts on the microwave oven are mainly external parts, such as shell, base, handle, knob, etc., which require heat resistance. The selected plastics are PBT/PET+GF, PBT+GF, PC/ABS, heat-resistant ABS, HIPS, heat-resistant PP, PP, etc.
In addition, the materials that can be used for the appearance of home appliances are:
ABS: high gloss, easy to spray, but not high temperature resistance;
PP: low cost, good fluidity, but poor dimensional stability;
PC: High strength, high temperature resistance, good transparency, but easy to crack;
PC/ABS alloy: Excellent overall performance, but higher price.
The main materials used for decoration are:
Transparent materials: transparent ABS, PMMA, PC, etc.;
Electroplating material: electroplating grade ABS;
Membrane material: PET film, PC film.
The materials that meet the core requirements of 3C key components are:
Flame retardant PBT, flame retardant PP, flame retardant PPO.
The materials that meet the core requirements of other key structural parts are:
POM, glass fiber reinforced nylon, PPS, PPA, PEI.


Summary: There are many types of plastic raw materials, and the application environment is also very different. How to select materials in specific work is a process of repeated analogy. It is necessary to consider factors such as product use environment, performance characteristics, safety performance, appearance and cost in turn

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