Plastic for injection moulding

The raw material is the main ingredient in any manufacturing process. Plastic injection molding raw materials are the key element in the plastic injection molding manufacturing process. This blog post covers the Plastic for injection moulding, types of plastic injection molding raw material and the usage of each raw material.

Plastic injection molding materials

In the plastic injection molding process varieties of thermoplastic materials are used. Let’s understand different types of thermoplastic materials.

Varieties of thermoplastic materials used in the industry for manufacturing injection molded parts eg. acrylic, nylon, Teflon, polyvinyl chloride, polypropylene, polyvinyl chloride, Epoxy, and Phenolic.

Thermoplastics are mainly classified as crystalline or amorphous.

Acrylonitrile butadiene styrene (ABS)

Polycarbonate (PC)

Polyethyelene (PE)

Acrylic (PMMA),

Thermoplastic polyurethane (TPU)

Polyoxymethylene (POM)

Polystyrene (PS)

Thermoplastic elastomer (TPE)

Nylon,

Teflon,

Polyvinyl chloride (PVC)

Polypropylene (PP),

Polyvinyl chloride,

Epoxy,

Phenolic,

Selection criteria of plastic injection molding materials

Wide varieties of plastic resin materials are available in the market, selection of resin materials is based on the end application of the part/component. Following key criteria helps to identify the correct raw materials.

1. Physical Property
2. Thermal Property
3. Dimensional Stability
4. Cost
5. Injection Molding Parameters
6. Application
7. Environmental Factor
8. Food or Water Contact
9. Post Injection Molding Process
10. Regulatory Requirements

Physical Property:

Following physical properties must be considered for selection of any resin / plastic raw materials (not limited to)

• Tensile Modulus
• Yield strain
• Yield stress
• Charpy notched impact strength
• Charpy impact strength
• Poisson’s ratio
• Tensile creep modulus
• Hardness, Rockwell, M & R scale

Thermal Property:

Following thermal properties are considered for the selection of resin/plastic raw materials (not limited)

• Melting Temperature
• Burning Behavior
• Burning Rate
• Temp. of deflection under load
• Vicat softening temperature
• Coeff. of linear therm. expansion

Dimensional Stability:

Following dimensional properties is essential to consider while selecting raw material depending on the application.

• Dimensional accuracy and close tolerance
• Better form and fit

Cost:

The cost of materials depends on market value and demand or monthly or yearly consumption. In mass production, it’s easy to meet minimum order quantity (MOQ) whereas in batch production or for trial run it’s a bit challenging to meet MOQ. A high-cost resin and low-cost resin usage decisions are based on production volume, application, and customer requirements.

Injection Molding Parameters:

Following molding, parameters are considered for the selection of resin/injection molding,

• Cylinder temperature
• Screw speed
• Screw feed rate
• Molding cycle
• Nozzle temperature
• Injection pressure
• Cooling time
• Clamping force
• Hold time and pressure

Application:

Injection molded parts/components used in various applications such as

• Automotive industry
• Agricultural industry
• Oil and Gas
• Chemical industry
• Pharma
• Food packaging
• Aviation
• Aerospace
• Consumer goods
• Laptop / Tablet / Cellphone
• Electronics & Electrical

Various grades of plastic resin material are available and the selection of this material is depended on the end application.

Application of plastic raw material is further sub-divided into the following categories,

• Impact Load
• Fatigue
• Repeated/Cyclic load
• Static load
• Heat / Thermal Shock (High temperature exposure)
• Abrasion Resistance
• Paint Ability
• Chemical Resistance
• Moisture Resistance
• UV Stabilized

Food and Water Contact:

If the end product is going to be in contact with water and food contact, it must be BPA-free. BPA means bisphenol A which is an industrial chemical that exists in a few plastic materials. Bisphenol A content in a plastic bottle or milk bottle is health hazardous as bisphenol A seeps into food material.

Bisphenol A affects the brain, infant, and child’s health. Much research also increases the risk of high blood pressure and cardiovascular diseases.

Environmental Factor:

Central Pollution Control Board (CPCB) of India has launched guidelines on single-use plastic guidelines which restrict usage of single-use plastic. Similarly, many other countries restrict the usage of plastic materials and stringent rules applicable to the plastic recycling process. No doubt, plastic waste is harmful to the earth, water, human beings, and animals, hence stringent law is necessary to restrict the usage of plastic materials.

The selection of plastic material is not only dependent on waste management but also on plastic material behavior in various environmental challenges,

• UV Light exposure
• Moisture
• Fluctuating Temperature (High temperature or low temperature)
• Abrasion Resistance
• Water absorption rate
• Humidity absorption rate

Prolonged exposure to UV light / sun-light causes a change in plastic color or crack on plastic surfaces.

Regulatory Requirements:

Following regulatory requirements must be followed while selecting and ordering plastic raw materials.

• Australian Inventory of Chemical Substances (AICS)
• Canadian Domestics Substances List (DSL)
• India Plastic Waste Management Rules, 2016
• Japanese Existing and New Chemical Substances (ENCS)
• Korean Existing Chemicals Inventory (KECI)
• Taiwan Chemical Substance Inventory (TCSI)

It’s not required to follow all country regulations however it’s better to consider,

a. Host country regulation (country of origin)

b. Home country regulation (country of product manufacture and distribution)

VDA 277

Analysis of Volatile Contaminants from Polymers is most widely used in the automotive industry to analyze volatile contaminants in plastic interior components such as dashboard, and A-B-C pillar trim.

Post Injection Molding Process:

Various processes are used in the industry post-injection molding. Eg.

• Trimming
• Assembly
• Plastic Machining
• Laser Marking
• Laser trimming
• Ultrasonic welding
• Painting
• Heat Stacking

It’s a wise decision to consider plastic raw materials based on the post-injection molding process. Additional post-injection molding process will add on an additional cost.