Many beginners want to quickly understand injection molding material. As an industry leader, we have involved injection molding product engineers and wrote this latest ultimate guide in 2023, which can guide everyone to quickly understand injection molding material.
The manufacturing process of plastic injection molding, sometimes called injection molding, is a manufacturing technique used to produce various dimensions, shapes, and colors of plastic parts in large quantities. Selecting the appropriate injection molding materials is essential in the operational steps, it will influences product performance and operation directly.
The detailed study shows that there are many factors that should be considered when choosing the right plastic material for a particular application. Physical performance of the Material, resistance to Impact, tensile Power, resistance to Wear, Functioning temperature of a product, resistance to Wear, strength, stiffness of the material Cost restrictions, and Weight restrictions all affect the final result.
1) Material cost
When it comes to making different products, you need to make sure you invest in the right plastic materials for the injection molding workers out there. Your choice of material is important because choosing the right material can save additional processing costs.
2) Avoid expensive mold adjustment costs
Each material has a different shrinkage rate, and all injection molds are made to handle a specific amount of shrinkage. Once the mold cavity shape is established, it cannot be changed. Making the proper material choice is essential to any successful injection molding project since injection molds are designed to shrink to a specified extent. Making the right material choice before starting production will save you from having to make expensive tooling adjustments.
You'll have to spend money on a different mold design if you deal with the incorrect material. This will result in extra expenses, some of which can be extremely high.
3) Manufacturing costs
The difficulty of forming determines the cost of production. So the type of plastic material selected may directly determine whether the final price of the product is high or low, of course, you must choose appropriate materials in order to meet the design requirements of the product, not in order to save costs, and choose materials that can not meet the requirements.
1) Thermosetting plastics VS Thermoplastics
Thermosets undergo a chemical reaction in the molding process that changes the material's molecular structure and causes it to "set" in shape. In thermosetting plastics, melting and curing are chemical changes (crosslinking) and are irreversible. Burning hydrogen (H 2) in the air (O 2) produces water (H 2 O), a chemical change that cannot be reversed by heating or cooling. These plastics can’t be reheated and softened. Mean is they can’t be reused. They are usually heat resistant, but too much heat can usually cause them to burn up.
Thermoplastics, on the other hand, are easily re-molded. They can be reheated and softened again (even into liquid). Thermoplastics like polyvinyl chloride and polyethylene are often called "plastics.". Thermoplastics are synthetic polymers that become pliable or moldable above a specific temperature, but they harden once cooled. They retain their chemical properties after cooling and can be melted down and utilized again.
Thermosetting plastics
● Generally very dimensionally stable
● Resistance to heat
● Can have thicker and thinner wall sections together
● Cannot be recycled
Thermoplastics
● Less resistant to heat
● Chemical resistance
● Harder or softer rubbery surface finishes
● Can be recycled
2) Thermoplastics - Semi-crystalline and Amorphous
Within the range of thermoplastic materials, there are two main types. Semi-crystalline polymers and amorphous polymers. The significant difference between these two types is how the polymer chains will be arranged when the resin is processed. The semi-crystalline polymer has a high melting point and creates stronger bonds, while the amorphous polymer has a lower melting point and can create weaker bonds.
Whether semi-crystalline or amorphous, each relies on the same melting energy source: barrel, screw and heating belt. Most of the energy (about 80%) comes from the friction between the particle and the cylinder wall and the compression of the screw transition zone. The rest comes from the heating belt around the barrel. The energy transfer mechanism of amorphous and semi-crystalline resin is the same. However, this is where melting these plastics is similar.
◆ Semi-crystalline plastics
The structure of these polymers is similar to that of amorphous polymers, but in some sections, called "crystalline regions," the chains are organized into compact, orderly packets. The crystalline regions of the polymer eventually break when it warms up, and the structure resembles that of an amorphous kind.
Semi-crystalline thermoplastics have good strength and wear resistance as well as good chemical resistance, but they generally lack impact resistance. A Semi-crystalline polymer with a sharp melting point remains solid until it absorbs a specified amount of heat. The polymer then undergoes a low viscosity liquid. Tightly packed chains of molecules produce more defined melting points. Semi-crystalline polymers are anisotropic in flow, as opposed to amorphous, meaning that they undergo an inhomogeneous contraction. These polymers shrink less in the flow direction than in the transverse direction. Common semi-crystalline thermoplastics include acetal, PE, PP, PEEK, and nylon etc.
The main characteristics of this family are:
● These materials show higher densities
● High chemical resistance, higher tensile strength, better creep
● High-temperature resistance and good stability
● Have a sharp melting point called Tm
● They are generally transparent
● High shrinkage rate
● With different shrinkage in flow and cross-flow direction, easy to warpage
◆ Amorphous plastic
Amorphous thermoplastics can be highly transparent and have good formability with a lower melting temperature range. While amorphous thermoplastics have poor chemical resistance, this provides an easier bond to other materials using adhesives or solvents. They have excellent mechanical properties and thermal stability, which makes it possible to mold shapes into most products.
The molecular structures of these polymers are entangled like spaghetti. When heated to the melting point, the polymer chains weaken and eventually flow freely. They freeze in place when the resin solidifies and cools. Entangled structures are not as tightly packed together, which allows light to pass through. Therefore, these polymers are transparent. Amorphous polymers have randomly arranged molecular structures that result in a range of melting temperatures. This also makes them relatively easy to thermoform, as the molecules become mobile when heated. The more heat you apply, the more mobile the molecules become.
Because of their random molecular arrangement, these thermoplastics are isotropic in flow. This gives them better dimensional stability and a smaller tendency to warp. They also often have excellent impact strength. They are more prone to stress cracking than semi-crystalline polymers and have poor fatigue resistance. They also tend to have lower chemical resistance and higher friction than their semi-crystalline counterparts.
Some major characteristics of this family are:
● No fixed melting point
● Have a range of temperatures where the chains start to slide, increase in temperature can facilitate plastic flowability.
● In many instances can be transparent
● Lower tensile strength and higher impact strength
● Much lower shrinkage rate
● Uniform shrinkage in all directions
Common examples of amorphous plastics are Polycarbonates (PC), Acrylic – Polymethyl methacrylate (PMMA), ABS, Polystyrenes (PS), etc.
◆ Between Semi-crystalline plastics and amorphous plastic
The below should be can help you:
◆ Thermoplastic elastomer (TPE)
Thermoplastic elastomer (TPE), also known as thermoplastic rubber, is a copolymer or compound with thermoplastic and elastomer properties that can be injection molding like other plastics and can be recycled. TPE is a true thermoplastic that doesn't require vulcanization or curing. When used within its design temperature range, TPE exhibits elastic behavior without cross-linking during manufacturing.
Thermoplastic elastomers use different types of cross-linking bonds with thermosetting elastomers in their structures, among which the cross-linking bonds in TPE are the key factors that confer elastic properties. Unlike more rigid materials, TPE can be stretched and returned to close to its original shape, providing a longer service life and better physical range.
Thermoplastic elastomers can be injected, extrude molding and blow molding. TPE is often used for overmolding. It can provide design flexibility and nice bonding to other thermoplastic substrates.
The most common plastic injection molding materials are listed below.
1) Nylon
● Nylon is often referred to by its chemical name, PA (Polyamide). Nylon is a thermoplastic injection molding material with high mechanical properties and excellent elasticity.
● NYLON can be used for various applications since it has a high toughness threshold and excellent resistance to damage and tear. It is frequently used to make durable mechanical components such as bushings, gears, and bearings.
● Due to its durability, low production costs, and ability to help reduce weight, it is also often used in automotive applications.
2) ABS (Acrylonitrile Butadiene Styrene )
● With a relatively low melting point and a high technical grade, ABS is a thermoplastic that is simple to mold.
● This opaque polymer allows for the addition of colorants and comes in various textures and surface coatings.
● ABS is famous for its durability and resistance to impacts. The styrene gives injection-molded products a bright, appealing surface, while the butadiene gives outstanding durability even at low temperatures.
3) Polystyrene (PS)
● Polystyrene is a commodity plastic that comes in two basic types: general-purpose polystyrene (GPPS) and high-impact polystyrene (HIPS).
● GPPS is brittle, with less dimensional stability than HIPS.
● Because both forms of polystyrene shrink uniformly and effectively, they are ideal materials for injection molding.
4) Polycarbonate (PC)
● This thermoplastic substance is transparent and has a glass-like ability to transmit interior light.
● Polycarbonate (PC) is an impact-resistant synthetic plastic, with a very low coefficient of expansion. Because of this, the PC is an ideal material for long-term use with resistance to temperature fluctuations, thermal shock, and cracking.
● It is a good choice when the product requires transparency and also needs to be impact resistant.
5) POM (Polyoxymethylene)
● Polyoxymethylene (POM) is a high-performance engineering plastic that offers excellent dimensional stability, low friction, and high stiffness.
● It is suitable for injection molding products that require a low coefficient of friction, higher strength, and good dimensional stability.
6) PMMA (Acrylic)
● Acrylic plastic is a clear, versatile substance that looks and feels like glass. It enables more light transmission than glass and has a high degree of durability.
● It is often used to make plastic products with high light transmission, car headlights, magnifying glasses, etc.
7) Polyethylene (PE)
● Polyethylene allows a wide range of flexibility at a low price, which suits its applications in consumer products and plastics.
● There are three basic classes of polyethylene: high-density polyethylene (HDPE), low-density polyethylene (LDPE), and Medium-density polyethylene.
● High-density polyethylene (HDPE) is used in plastic bottles, food containers, and utensils. Vessels made from HDPE resist chemical reactions such as oxidation, hydrolysis, and plasticizers.
8) PVC
● PVC is made from polyvinyl chloride (PVC) polymers, similar to other plastics it’s an ideal plastic for packaging items that must withstand wear and tear and high temperatures.
● PVC is non-toxic and has low volatility, making it safe to use in food preparation areas.
● When Injection PVC materials are particularly prone to corrode the mold, it’s very important. so this material injection mold must use mold steel resistance.
◆ Common Injection molding material physical performance, including advantages and considerations.
| Material | Description | Benefits | Applications | Considerations |
| ABS | Common thermoplastic with good impact resistance and toughness. | ● Good impact resistance with toughness and rigidity | ● Computer housings | ● Thick area easy shrinkage |
| ● Metal coatings have excellent adhesion to ABS | ● Musical instruments (recorders & plastic clarinets) | ● Flowability low | ||
| ● Excellent processability and appearance | ● Telecom devices | ● Suggestion wall thickness 1.5-3mm | ||
| ● Small appliances (enclosures) | ||||
| ● Automotive (interior trim, wheel covers, emblems) | ||||
| ● Medical components | ||||
| PP(Polypropylene) | Thermoplastic polymer used for a wide number of applications. | ● Excellent moisture resistance | ● Packaging | ● Flowability high |
| ● Food grades available | ● Industrial components for fluid processing | ● Soft, easy shrinkage and warping | ||
| ● Mold–in hinge possible | ● Household goods | ● Low temperature resistance | ||
| ● Good impact strength | ● Automotive | |||
| ● Electrical hardware | ||||
| Polyoxymethylene (POM) | Dimension stability thermoplastic with high stiffness and low friction | ● High tensile strength with rigidity and toughness | ● Mechanical automotive | ● Molding high quality appearance difficult |
| ● Good impact and solvent resistance | ● Business machines | ● High hardness | ||
| ● Glossy molded surface | ● Household appliance | |||
| ● Low static and dynamic coefficients of friction (slippery) | ● Gears | |||
| ● Many grades have FDA and NSF approvals on food and water contact | ● Bushings | |||
| ● Replace die-cast metal components | ● Door handles | |||
| ● Seat belt parts | ||||
| PC(Polycarbonate) | Thermoplastic material with good temperature resistance and impact strength. | ● High impact resistance | ● Automotive headlights | ● Low chemical resistance |
| ● Transparent | ● Business machines | ● Molding cost high | ||
| ● Dimensional stability | ● Consumer products | ● Perhaps molding need mold temperature | ||
| ● Telecommunications | ● Prone to formation of bubbles | |||
| ● Medical products | ||||
| ● Mechanical goods | ||||
| PC+ ABS | Blend of PC and ABS that creates strong parts for a variety of applications. | ● Nice impact resistance, toughness and rigidity | ● Automotive exterior and interior components | ● Molding cost high |
| ● Excellent adhesion | ● Medical hardware | ● Nice mechanical performance | ||
| ● UV light stability | ● Electrical housings | |||
| ● High light appearance parts ideal material | ● Computers | |||
| ● Monitors | ||||
| ● Business equipment housings | ||||
| ● Enclosures | ||||
| PVC | PVC is a polymer with good insulation properties, high hardness, and good mechanical properties. | ● Wide range of flexibility | ● Medical/healthcare products | ● Easily corroded mold |
| ● Flame retardant | ● Automotive applications | ● Mold cost high | ||
| ● Dimensional stability | ● Household items | |||
| ● Low cost | ● Electronic extruded wire covering | |||
| Nylon | Polymer material that is durable with high elongation and good abrasion resistance. | ● Temperature capability 80℃ | ● Automotive components | ● Big shrinkage |
| ● Excellent chemical resistance | ● Bearings | ● Mechanical performance fine | ||
| ● High resistance to abrasion | ● Electronic connectors | |||
| ● Tough and withstands repeated impact | ● Gears | |||
| ● Consumer products | ||||
| ● Industrial products | ||||
| Nylon 10-30% Glass Fiber | Polymer with excellent mechanical stiffness and elevated temperature resistance. | ● Good impact resistance with toughness and rigidity | ● Automotive components | ● Low shrinkage |
| ● High resistance to abrasion | ● Machine accessories | ● Poor toughness | ||
| ● Strength less than Nylon | ● Mechanical components | |||
| ● Low shrinkage rate | ||||
| Acrylic (PMMA) | strong, clear thermoplastic that provides a lighter-weight, shatter-resistant alternative to glass | ● Excellent optical clarity | ● Automotive transparent items such as head/tail lenses and trim | ● Brittle |
| ● Nice impact and rigid resistance | ● Household light fixtures and decorative items shell | ● Cheap | ||
| ● Nice light transmission | ● Safety equipment and shields | ● Low UV resistance | ||
| ● No release Bisphenol A | ● Impact resistance less than PC | |||
| ● Optical plastic parts ideal choice | ||||
| PS (Polystyrene) | Light weight material popular for its high impact strength and toughness. | ● Optical clarity | ● Household goods | ● Brittle |
| ● High gloss | ● Containers | ● poor UV resistance, very susceptible to hydrocarbon solvents | ||
| ● FDA grades available | ● Furniture | |||
| ● Low cost | ● Housings | |||
| ● Dimension stability | ● Packaging | |||
| ● High rigidity | ||||
| PEI( Polyetherimide) | An amorphous thermoplastic with high mechanical strength and rigidity | ● High heat resistance | ● Commercial aircraft interiors | ● Very expensvie |
| ● Exceptional strength and impact modulus | ● Healthcare products | ● High Injection molding temperature | ||
| ● High dielectric strength | ● Cooking utensils | ● Injection molding difficult | ||
| ● Broad chemical resistance | ● Fiber optics | |||
| ● Biocompatible | ● Electrical products | |||
| ● Excellent machinability and finishing characteristic | ● Electronic parts | |||
| ● Outstanding processability on conventional molding equipment | ||||
| ● Flame resistance with low smoke evolution | ||||
| PPS | A partially crystalline, high temperature performance polymer | ● Chemically resistant | ● Connectors, contact rails, heat shields | ● Molding temperature high |
| ● High mechanical strength | ● Automotive under the hood | ● Cost high | ||
| ● Nice dimensional stability | ● Slide bearings, chain guides | ● Molding technology high | ||
| ● Excellent electrical properties | ● Valves, taps, bushings, pumps | |||
| ● Creep resistance | ||||
| ● High mechanical strength | ||||
| ● Dimensional stability | ||||
| PEEK | unique semi crystalline, engineering thermoplastic that also offers excellent chemical compatibility. | ● Self-lubricating | ● Automotive components | ● Molding performance highly |
| ● Excellent friction | ● Aerospace components | ● Price very expensive | ||
| ● Wear characteristics | ● Medical device | ● Low halogens and acids resistance | ||
| ● Flame retardant(V0) | ● Orthopedics | ● Low resistance to UV light | ||
| ● High strength | ||||
| ● Dimensional stability | ||||
| ● High Chemical resistance | ||||
| ● Fatigue wear resistance | ||||
| ● FDA | ||||
| PAI | It recognized around the world as being the highest performing thermoplastic material that is melt processable | ● High wear resistance | ● Automotive components | ● Very expensive |
| ● Compressive strength | ● Aerospace components | ● Molding difficult | ||
| ● Low friction | ● Semiconductor | |||
| ● Excellent electrical insulation | ● Oil & gas | |||
| ● Resistant to acid and strong chemicals | ● Precision & specialty industrial | |||
| ● Electrical & electronics | ||||
| PES(PESU) | High temperature engineering thermoplastic, translucent and has a amber transparent | ● high mechanical strength and rigidity | ● Aerospace | ● Very expensive |
| ● low notch sensitivity | ● Medical | ● Molding cost high | ||
| ● Nice chemical compatibility | ||||
| ● Hydrolysis resistance | ||||
| ● High dimension stability | ||||
| ● Good electrical insulating properties | ||||
| PPSU | Translucent and light brown thermoplastic, high temperature plastics | ● Good radiation resistance | ● Valve spools, flanges, inspection windows | ● Very expensive |
| ● Good electrical insulation | ● Microwave dishes | ● Molding cost high | ||
| ● High mechanical strength | ● Oil level indicators | ● Thick parts are likely to have bubbles and voids. | ||
| ● High rigidity | ● Connectors, high frequency insulators, lamp sockets | ● Less resistant to organic solvents and organic chemicals | ||
| ● High dimensional stability | ● Medical | |||
| PVDF | opaque, semi crystalline, thermoplastic fluoropolymer | ● Dimensional stability | ● Valves | ● Price high |
| ● Chemical resistance | ● Automotive parts | ● Molding difficult | ||
| ● Hydrolysis resistance | ● Aerospace | |||
| ● UV resistance | ||||
| ● Radiation resistance | ||||
| ● High abrasion resistance | ||||
| ● Nice electrical insulation | ||||
| PSU | A family of sulfur-containing thermoplastics, closely related to polyethersulfone (PES) | ● Temperature Resistance | ● Electrical & Electronic | ● Low weather ability |
| ● Chemical Resistant | ● Medical & Healthcare | ● Subject to stress cracking | ||
| ● Flame Retardant | ● Mechanical Equipment accessories | ● Molding difficulties | ||
| ● Dimensional Stability | ● Outdoor Applications | ● Very expensive | ||
| ● Creep Resistant | ● Structural Parts | |||
| ● Nice Toughness | ||||
| ● Acid Resistant | ||||
| ● Thermal Stability | ||||
| ● Hydrolysis Resistant | ||||
| LCP(Liquid Crystal Polymer | halogen-free high-performance polymers | ● Low Warpage | ● Connectors | ● Hygroscopic property |
| ● Temperature Resistance | ● Electrical & Electronic parts | ● High molding cost | ||
| ● High Flowability | ● Automotive parts | ● Excellent moldability in thin sections | ||
| ● High Strength | ● Camera | ● replace such materials as ceramics, metals, composites | ||
| ● Flame Retardant | ● Computer Components | |||
| ● Chemical Resistance | ● Optical Applications | |||
| ● High Stiffness | ||||
| ● High dimension stability | ||||
| ● UV Stabilized | ||||
| ● V0 flame retardation |
◆ Resins by Highest Tensile Strength
◆ Resins by Highest Impact Strength
◆ Resins by Highest Dielectric Strength
5. Key considerations for injection molding material selection
Material selection starts with an understanding of the application. There are several factors to consider when selecting the proper materials. First, understand the application and the process. Then consider the application and whether need to select a bonding material (TPE).
What is the part's application? Whether operation in a high-temperature environment? What will be the aesthetics for appearance treatment, texture or polish, and color? If the product requires overmolding, the easiest way to select an ideal material is to start with comprehensive product application knowledge. Multiple key factors decide the efficient selection of cost-optimal molding materials to meet the needs of the industry.
To select the best molding material for your project, thinking about the questions below will help guide you to the right material during the parts design stage:
● What’s the intended end use of the part?
● Are there any distinct criteria for appearance?
● Do any regulations apply? (REACH, FDA, etc.).
● Is plating, printing, or painting necessary?
● What mechanical and environmental conditions will affect the product?
● Is the product suitable for indoor or outdoor use?
● What cost constraints do you have for your product？
In the following paragraph, we will see a few fundamental indicators for choosing materials:
◆ Flowability or viscosity
It is essential to take flowability into account while selecting materials. Flowability is critical for thin-walled parts or large parts. Good flowability will decrease the processing time and make it easier to mold thin wall plastic parts by varying the speed of the feeder/dispenser in the molding operation.
Flowability resins help make thin-wall plastic parts, like a cellphone's battery housing and food container. As we know, the hotter the temperature is, the better it will be for flowability. The higher the viscosity of a resin, the harder it will become to extrude.
● High flowability resins material: LCP, NYLON, PE, PS, and PP
● Medium flowability resins material: ABS, AS, PMMA, and POM
● Low flowability resins material: PEEK, PPO, PPS, PFA, PEI, PSU, etc high-temperature resins
The melt flow rate is commonly used to measure the flow of material during the molding process. The value of the melt flow rate depends on its relation to the average molecular weight of the polymer. The lower the melt flow rate, the higher the average molecular weight of the material. The higher molecular weight in turn provides better performance, especially in terms of resistance to impact, creep and fatigue.
The determination of the viscosity of plastics in the actual molding is very important. The most common method to measure this is the Melt Flow Rate (MFR) or Melt Flow Index (MFI). This is measured by ASTM D1238 and is the flow in grams of material in 10 minutes through an orifice 0.0825 in diameter under a certain force and at a certain temperature.
◆ Dimensional stability
"Dimensional stability" describes the plastic's changing shape when heated or cooled. When making a plastic component, how tightly a part should fit with the other parts must be considered. Choose a plastic with strong dimensional stability, such as PC, ABS, or POM, to ensure an exact fit. Since the material design requires mating to fit other components, neither PA nor PP would be a good option in this case due to their shrink ratio, strength, and flexibility.
Adding the additives also will improve the dimension stability of the resin in situations when PA or PP are required.
◆ Impact Strength (mechanical properties requirement)
The impact strength of plastic is the property that measures its hardness. Plastic materials have good impact strength and can withstand heavy shocks without any damage. They also have good toughness and elasticity, which improve their properties and quality.
Mixed with resin, glass, and carbon fiber, it will reduce the impact strength and increase the load and wear strength. When designing a new plastic component, it is crucial to consider the type of force applied, its magnitude, and how often it will occur.
PC plastic is a thermoplastic with almost the highest impact strength of common engineering plastics.
◆ Wear resistance
Wear-resistant plastics are designed to maintain their appearance and reduce costs associated with maintenance, wear and subsequent system downtime.
Friction is the resistance to relative motion between two surfaces. The lower the coefficient of friction, the easier it is for the two surfaces to slide against each other. Friction causes wear and tear, which shortens the service life of the material. PEEK, UHMW, POM, and POM are all good examples of low-friction high wear resistance.
These materials have a relatively high coefficient of friction compared to other plastics, making them ideal for use in applications requiring high performance and superior mechanical properties such as gears and screws.
◆ Toughness
Toughness is the ability of the material to resist permanent deformation, fracturing, and cracking. It can be best measured using the stress-strain curve. The material should be brittle and ductile to withstand the toughness.
Brittle materials with low ductility but high strength (like ceramics) are not rigid; similarly, very ductile materials with high strength are also not tough. The material must be able to sustain high stresses and strains to be considered tough. In general, strength refers to how much force a material can withstand, while toughness refers to how much energy it can absorb before it breaks.
◆ Resistance to decomposition
Decomposition is the breaking down of material by biological, chemical, or mechanical actions. Temperature, light, moisture content, and storage all contribute to decomposition.
All materials are at risk of decomposition over time. When choosing a material, it is critical to examine its resistance to decomposition in the climate zone where the construction will occur, especially for the products that will operation in an outdoor environment.
◆ Flame Resistant
Electrical and electronic plastic products typically use flame-retardant materials. The standards used by UL94 for classifying flame-resistant plastics are:
From HB, V-2, V-1, to V-0, the flame-retardant quality of plastic is significantly rising.
1) HB: UL94 standard in the lowest flame retardant grade. Requires a burn rate of less than 40 mm per minute for samples 3 to 13 mm thick. Samples less than 3 mm thick, a burning rate less than 70 mm per minute, Or put it out in front of a 100mm sign.
2) V-2: After two 10-second combustion tests on the sample, the flame will be extinguished within 60 seconds. You can have things fall.
3) V-1: After two 10-second combustion tests on the sample, the flame will be extinguished within 60 seconds. No combustibles should fall.
4) V-0: After two 10-second combustion tests on the sample, the flame will be extinguished within 30 seconds. No combustibles should fall.
◆ Assembly requirement
The assembly requirements of plastic parts differ from those of other materials, such as metal and wood. Adhesive manufacturers recommend ABS and PC materials for plastic part assembly using adhesives. Nylon and HDPE, however, need special adhesives. PP and ABS are easy to ultrasonic welding compared to Nylon and PC.
◆ Weather Resistance or UV Resistance
One of the main requirements for manufacturing outdoor operation plastic parts is that the material should have good weather and UV resistance. The material should resist cracking and splitting due to exposure to cold, heat, sunlight, and other environmental conditions.
Adding UV stabilizers and weatherized to the resin is also an option. No matter which plastic resin is used, it should be thoroughly tested before use to ensure that it will meet the requirements of the product. With excellent weather and UV resistance, ASA resin is functional in low and high-temperature applications.
◆ Appearance or aesthetic considerations
Appearance and aesthetics are essential in selecting a material for the final project. Different materials have a visual effect; for example, PVC gives off a glossy finish, whereas ABS plastic is softer and has a more matte finish.
Different materials have different effects, for example, PP material, and ABS material, have the same color, but the visual effect will be different, and the finish also can affect the visual effect, grinding or polishing effect will be different, even if the same finish, the same color, not of the same material, the final visual effect will be different.
◆ Materials cost
In order to properly analyze costs, it is essential to consider the market economy. We should look for inexpensive plastics as much as possible to increase our products' competitiveness based on the assumption that they fit the abovementioned parameters.
When material properties are unavailable in commercial-grade resin or a custom blend, adding fillers can improve the properties of various resins. Additives are added as powder or liquid and mixed into the binder during production by a mixing machine such as a ball mill or pan mixer.
Fillers can also be added multi types and proportions during the process to achieve various effects. The most common fillers used in plastic injection molding are glass, carbon, and talc. Compared to fillers, additives can affect the quality of plastic without significantly changing the material's makeup. The high amount of filler impacts the finished quality of the products.
1) What are plastic additives?
Plastic additives are compounds added during the formulation of a polymer to improve its mechanical properties. Whether it is about heat resistance, structural integrity, lubricity, or other properties, plastic additives are a great way to add new attributes to preexisting plastics.
2) Why using plastic additives?
Additives help in manipulating plastic parts in a variety of ways. Thermoplastics can be colored by adding pigmentation or new properties, such as self-lubrication or antistatic capabilities, that can be introduced with other chemicals. With foaming agents, it is easy to convert polystyrene into Styrofoam.
Car surfaces can be protected from wear and tear, and airplane components undergo creep resistance with the help of additives.
Alternatives that are less expensive than redesigning or retooling are available. When problems arise after the construction of the tool, when material and grade alternatives do not yield satisfactory results, then resin additives can improve the resin flow, mold release, scratch reduction, coefficient of friction, and dispersion.
Adapting plastic material to injection molding is a complex process that relies on the proper selection of additives, fillers, and the composition of the melt. It can have a dramatic effect on the material's properties and its impact on the end-user applications.
3) Common types of plastic additives
● Glass fiber
Glass fibers are one of the most commonly used fillers for injection molding. Glass fibers are an essential means of reinforcing and strengthening materials. They are helpful in many industries, improving stiffness and enhancing the flow of liquid materials while reducing warping, shrinkage, and thermal stress. It is also one of the most important ways to reduce costs. Our common glass fiber material like PA6/66+10%GF, PA6/66+20%GF... PA6/66+60%GF.
● Carbon fibers
Carbon fibers are an expensive filler, Because of the chemical inertness of carbon, Carbon fiber reinforced polymer has high chemical and corrosion resistance, and also increase the continuous service temperature and thermal deformation temperature. Carbon fiber has a higher strength-to-weight ratio and stiffness-to-weight ratio, which can produce stronger and stiffer products at a lighter weight. So many automotive industry companies use carbon fiber fillers to produce lightweight parts because they can improve strength and durability. And they are valuable as a colorant, pigment, UV barrier, and antioxidant.
● Antimicrobial
The purpose of antibacterial is achieved by adding a combination of active ingredients to plastics that inhibit microbial growth. These ingredients are called antimicrobial additives. They can resist the growth of a variety of microorganisms, such as algae, bacteria and fungi. They protect the polymer surface and provide a sterile environment. This extends their life, maintains their good appearance, and reduces the surface biological load. Polymer plastics with this antimicrobial additive are called antimicrobial plastics.
They are helpful in food-related applications or high-contact consumer products. Also, they are helpful in reducing the likelihood of discoloration, offensive odors, and material deterioration. Scientifically established antimicrobial technology will offer long-lasting and effective protection against hazardous bacteria, mold, and fungi by up to 99.99%.
● Talc
Talc is one of the mineral fillers compatible with polypropylene (PP). Adding talc to PP can significantly enhance its properties, including higher stiffness/rigidity, Higher impact strength (especially at sub-zero temperatures)， Better temperature resistance, creep resistance and chemical resistance; In particular, it improves dimensional stability when injection molding.
● Antistatic
Antistatic additives are chemicals that minimize electrostatic buildup on plastic materials. Antistatic agents can be applied to product surfaces or added during plastic manufacturing. Antistatic additives are often used for aesthetic reasons as well as (electrical and electronic) safety and performance reasons, depending on the end use.
An external antistatic agent is applied to the surface of the plastic parts. The antistatic effect of such compounds is of short duration because they wear out under the influence of mechanical factors. These compounds become inactive after a few weeks.
Internal antistatic additives added to plastics during processing are the same as other types of polymer additives. After 24-48 hours of extrusion, they migrate to the surface of the material and form a hygroscopic film that absorbs water. The layer created is conductive because it releases static electricity and reduces the level of plastic charge. The antistatic effect of internal antistatic agents is long-lasting (usually over a year). The migration of internal antistatic agents ensures their longer activity.
The use of antistatic agents in plastic production not only facilitates the production process and prevents dangerous spark discharges, but also provides additional benefits, such as limiting dust accumulation on plastic objects attracted by excessive charges. Because of the various mechanisms of action of antistatic agents, they can be adjusted according to the specific conditions of the production process and maximize the final effect.
● Conductivity Additives and Fillers
Pure plastics are classic insulators and often can‘t be used to meet the new requirement which needs to balance temperature stress or even avoid overheating to ensure process stability, safety and performance.
By adding graphite powder to the plastic, for a given amount of fill, the thermal conductivity of thermoplastics is higher than using any other additive material. Moreover, the addition of graphite powder doesn’t change the fundamental advantages and properties of plastics, whose cost-effective molding and high design freedom make it a universally applicable material for a wide variety of applications.
● Plasticizers
Plasticizers are chemical additives that are often used to improve the flexibility and durability of plastics when add to the raw polymer. Plasticizers bridge the gaps between polymer molecules and weaken their intermolecular forces, thus providing more freedom of movement for each molecular chain. This lowers the glass transition point of polymers and gives them flexibility, and they are used in many plastics.
In fact, plasticizers are non-volatile solvents. The most common plasticizers are phthalates, metaphenolate, benzoates, and adipate. These low molecular weight compounds act as spacers between polymer chains and lower rotational energy barriers, thereby improving plastic flexibility. Plasticizers can also reduce processing temperatures and alter many other physical and mechanical properties. For example, they reduce the glass transition temperature and melt viscosity.
● Optical brighteners / Whitening Agents
Optical brighteners improve whiteness and make the products more reflective, making them more easily visible in low-light conditions. Optical brighteners are sometimes called optical brightening agents (OBAs), fluorescent brightening agents (FBAs), or fluorescent whitening agents (FWAs). Optical brighteners are additives that reduce yellowing, increase whiteness and enhance the brightness of the product. These reagents work based on a "fluorescence effect"; They absorb light in the ultraviolet spectrum and emit light in the blue region of the visible spectrum, giving the plastic a brighter, fresher appearance. Whitening agent/fluorescent whitening agent is often used in engineering plastics, such as PVC, PC, etc.
● Flame retardants
Flame retardants reduce the flammability of plastics. They can be classified as inorganic compounds and organic compounds. Flame retardants are added to polyolefins, polycarbonate, polyamides, and other polymers to increase flame resistance, reduce flame spread, inhibit smoke formation, and prevent polymer dripping. The main goal is to delay the ignition and combustion of the material, giving people more time to escape the affected area. A secondary concern is limiting property damage.
The most common inorganic flame retardants are aluminum hydroxide (also known as aluminum trihydrate or ATH), magnesium hydroxide, zinc borate, antimony oxide, and magnesite (the mineral magnesium carbonate hydrate). The most common organic flame retardants are chlorinated and brominated compounds. Their effectiveness increases with the halogen content, which can be up to 80% by weight of the halogen. Other common organic flame retardants are organophosphates and organic phosphonates. Sometimes a combination of two flame retardants is used to improve their efficiency.
● Mineral fillers
Filler is an important additive. They are usually inexpensive inert inorganic materials that reduce raw material costs by reducing resin consumption. However, mineral fillers have other benefits, For example, they can improve the formability and stability of resins. In addition, they increase the thermal deformation temperature and reduce thermal expansion upon heating. The most common minerals used as fillers include calcium carbonate, talc, silica, clay, mica, kaolin, calcium sulfate, alumina trihydrate, and wollastonite, etc.
● Teflon/PTFE
Teflon/PTFE is a commonly used additive for all types of plastic. This additive reduces friction in components with heavy stress, such as engines, screws, and gears. Teflon can improve the lubricity of plastic by increasing its molecular bonding with other components and reducing friction and ultimately improving durability.
7. Conclusion
Developing a plastic product involves many risks but can be reduced to an acceptable level with careful collaboration and communication. The customer and the provider must communicate the possibilities, tradeoffs, priorities, restrictions, and needs to achieve the best result.
There is no perfect polymer. The key is determining which features are most important to you and which features you absolutely do not want. We hope this injection molding material selection guide was useful. If you would like assistance choosing the right resin for your application, We help select and recommend suitable injection molding materials according to the requirements of the design. With our manufacturing expertise, we can create a custom quote that will protect the bottom line while providing the best value for the selected material. our engineers would be more than happy to help.
