Plastics:Injection Moulding in the POP Industry

Plastics seminar 2010

Presented byGeorge Kessler CBEGroup Deputy Chairman

The 4 Whys

• Why use plastic as part of POP?

• Why Injection moulding?

• Why pick your plastic in advance?

• Why worry which plastic to use?

Why use plastic to form your POP solutions?

• Permanence / semi-permanence

• Can be easy to colour

• Comparatively environmentally friendly

• Range of colour and transparency

• Range of strength

• Cost effective

Introduction to Injection Moulding

Why Injection Moulding?

There are 5 main plastic production methods used in our industry and one up and coming method;

• Injection Moulding

• Thermoforming

• Extrusion

• Fabrication

• 3D Printing

Why Injection Moulding?

• Fastest technique

• Most consistent technique

• Most cost effective once tool paid for

• Great variety of design options

• Can use less material for objective

BUT

• Tool cost and lead time

• Process design restrictions

Plastic: some background information

90 Classes• 400 Sub Groups• 50,000 Commercial grades and growing

• 3 Main GroupsThermosettingThermoplastic Elastomers

This can be simplified for POP

The main plastics used in injection moulding

• Acrylic (PMMA)- a- 2 types

• Polypropylene - c – 2 types and fillers

• Polystyrene –a - 2 basic types

• Nylon (PA) –c- 2 types

• Acetyl – lots of types

• Polycarbonate – a –

• ABS –a-

• Combination e.g. SAN

Why pick plastic in advance for injection moulding?

• Different Shrinkage

• Different tool techniques

• Different colours required

• Strength, cost, surface finish, printability and many other factors defined at this stage

What happens if the wrong plastic is used when injection moulding?

• Early toys – cheap plastic

• Toyota problems

• Scratching

• Colour

• Feel

• Strength

• Friction

• Assembly issues

Two types of Plastic - Thermoplastics

2 types: Amorphous (A)Semi-crystalline (C)

Amorphous polymer structure

No ordered structures or defined polymer chains

Amorphous (A)

Two dimensional representation of molecules in a crystalline

Semi- Crystalline (C)

Semi –Crystalline (C) polymer structure

Semi Crystalline

• Semi-crystalline materials are best used where chemical contact, mechanical abuse and repeated / cyclic loading is required.

- PP- PA- POM

• PP and PA are typically used where toughness is required. Due to the crystalline matrix and better packing of the polymer chains increased shrinkage is often seen and dimensional stability is more variable.

• Transparency is also quite poor.

• Crystalline materials tend to have a lower aesthetic quality when compared to amorphous materials.

.

Amorphous

Physical Characteristics

• As a general rule, amorphous plastics exhibit better creep resistance (constant static load over time) whereas semi-crystalline materials are better in fatigue than amorphous plastics.

• Amorphous plastics are best used where the following properties are required…good transparency, low mechanical abuse and low/no chemical contact.

- PMMA- PS- PC- PETG- ABS

• PC is particularly good when high transparency is required though UV stabilisers are usually required to ensure discolouration is minimised over time.

• Generally little water absorption therefore reasonable dimensional stability.

Finishes

• Amorphous materials tend to have a higher perceived quality because high gloss “glass” finishes are easier to achieve than with crystalline materials.

• Surface treatments such as park finishes and chemical etching are usually employed upon crystalline components to mask surface deformation due to shrinkage.

Examples of injection moulded displays

Plastics: elements to define for P-O-P

• Transparency

• Strength

• UV resistance

• Colour and colour criticality

• Gloss level

• Scratch ability

• Cost level acceptable

• Secondary operations – e.g. print, glue and chemical resistance

A few basics to remember

• The semi-crystalline (C) plastics are hard to glue / print

• Unless treated all plastics scratch but acrylic followed by SAN are best for scratch resistance in transparent, ABS is not bad in solid colour

• Polycarbonate followed by impact acrylic is strongest in transparent

• Acetyl and nylon have the most naturally low friction

Colouring

• Transparent plastics are easiest to colour but some pigments degrade when at high temperatures, and now quite a lot of traditional pigments are outlawed

• Polycarbonate processing at 300 degrees rather than styrene at 180 can be awkward for reds

• Some basic colours can vary or restrict

• 3 methods of colouring in normal use

- Masterbatch- Liquid- Compound

Costs

Remember • Initial high end cost for tooling • Density as well as cost per kilo• Commodity prices vary

Ratio SG Adjusted

0.00

0.50

1.00

1.50

2.00

2.50

PP PS

ABS PC PAPMMA

PVC

POM

RatioSGR

Summary

• Injection mounding has a number of benefits for POP manufacturing;- strong ability to colour match- versatility of shape and design - cost effective to produce on mass

• There are a number of elements to take into consideration in the design and manufacturing process