Ford Kuga

 Service Manual

Paint - General Information » Painting Plastic Parts
Plastic groups

Thermoplastics

When warmed these undergo a reversible transformation into a plastic deformable state and once cooled they maintain their shape. They consist of string-like (linear) or only slightly branched molecular chains.

Thermosets

Thermosets are hard and have the form of a close-meshed network in all directions. They do not undergo plastic deformation, are especially resistant to chemicals, are difficult to swell and are insoluble. At normal temperatures they are hard to brittle. At first the material does not undergo any change when heated, but when it reaches a critical point, the thermoset is totally destroyed.

Elastomers

Elastomers are characterized by high elasticity over a wide temperature range. They have properties like rubber or a sponge and after compression or distension they return to their original state.

Types of plastic

The plastics used in the automotive area:

• ABS - Acrylonitrile butadiene styrene (polymer)
• PA - Polyamide
• PC - Polycarbonate
• PE - Polyethylene
• PP - Polypropylene
• PP/EPDM - Polypropylene/ethylene propylene diene copolymer
• PC/PBT - Polycarbonate/Polybutylene terephthalate
• PBT/PC - Polybutylene terephthalate/Polycarbonate
• PUR - Polyurethane
• GRP - Glass reinforced plastic

NOTE: PE and PP are plastics which cannot be painted, or can only be painted using special techniques.

As well as the pure plastics, so-called 'blends' are also used. This means combinations of different plastics. If we were dealing with metals they would be called alloys.

Plastic identification

Normally the identifier is marked on the plastic components used in vehicle construction.

One method to determine the plastic group is the sanding test. In this a place is chosen which will not be visible later, and the finger belt sander is used to sand the plastic.

The plastic group can be determined using the pattern left by the sanding and the dust:

• Thermosets produce a white dust.
• Thermoplastics smear and do not produce dust.

The plastic group can be determined by a sound test:

• Degree of hardness - the higher-pitched the sound, the harder the plastic.
• Elasticity - the more muffled the sound, the higher the elasticity of the plastic.

Cleaning plastic

Plastic components are manufactured using complicated moulds and presses or other highly engineered tools, mostly using an injection moulding process or reactive injection moulding process.

In order to be able to remove the component from a particular tool, a separating agent is used, which in some cases adheres very strongly to the plastic.

This separating agent on the plastic components must be completely removed before any surface coating is applied.

Warm storage (tempering) before actual cleaning brings the following advantages:

• The separating agent sweats out of the plastic
• Tensions in the plastic are released.
• Air inclusions can be recognized and removed.

Intensively clean the item several times using a pad and fresh cleaning agent.

NOTE: A single wipe, even with cleaning agent, is not usually sufficient in most cases. Clean textured components with the aid of a soft brush. After cleaning, it is absolutely vital that cleaning agent absorbed by the plastic should be expelled by tempering again. If the ventilation is good and the room temperature is about 20C the solvent can be evaporated away by overnight storage.

General

Plastic groups

Painting new components

Unknown primer

Paint faults on plastic substrates