Please contact us for help and advice on choosing the most suitable product solution for your needs

Plastic Parts can be Found on Vehicles such as

  • Building machines.
  • Special-purpose vehicles (Border control, Police).
  • Light-weight construction vehicles.
  • Race cars.


Typical materials are PMMA (Polymethylmethacrylate) and PC (Polycarbonate). In the manufacturing process, many polycarbonate sheets are coated with a scratch resistant surface. Unlike standard float glass, plastic parts have a much higher coefficient of thermal expansion, resulting in greater movement (expansion and contraction of the window).
In addition, plastic parts do not have the ceramic coating of glass windshields, which provides UV-protection for the adhesive bond-line. For these reasons, the following procedures must be followed when bonding plastic parts.

Permanent Glazing

Pre-treatment of PC or PMMA; If there is an unknown coating, the surface should be tested before bonding (contact Sika); otherwise, use the following procedure:

Step 1
Abrade bonding area with siavlies speed abrasive pad. Remove scratch resistant coating.
Step 2

Remove dust

Note: Use only oil free compressed air or wipe with Sika®Cleaner G+P and dry with a clean paper towel.

Clean surface of dust.
Step 3
Apply Sika® Primer-207. Flash-off for 10 minutes. Clean and prime the surface.
Step 4

Application of Sikaflex®-223. Layer thickness according to table below.

Sikaflex®-223 PowerCure can be used when fast curing is required.

Bonding.

 

Sika® Primer-207 must be used for bonding plastic parts. Black primerless bonding is not possible. 

 

Adhesive

Due to the high thermal expansion specified a low modulus adhesive/sealant should be used. The adhesive accommodates the movements and the part can expand without causing too much stress. A standard windscreen adhesive is usually too stiff and could lead to detachments in the long run. Curing should be done in a controlled environment as for example a temperature change outside in winter could already shrink the part size and increase the risk of detachments in warm conditions.

A small and high triangular bead should be applied and a minimum of 5mm thickness in compressed stage should be secured. If the bead is compressed too much it loses its elastic behaviour and does not compensate thermal expansion.
For elastic bonded parts the following urethane is recommended:

  • Sikaflex®-223
  • Sikaflex®-223 PowerCure (for accelerated curing)

Surrounding Conditions and Safe Drive-Away Time

Plastic parts have a very high thermal expansion factor which means every degree of temperature change the size of the plastic part changes. Therefore the installation and curing has to be carried out in-house at 15 - 25 °C.  

Remarks

Any anti-scratch hard coating can be difficult to be removed. The removal of coating damages the original design and protection of the plastic. Application of primer and adhesives (solvents, plasticizers) and stresses (internal/external) could lead to ESC (Environmental Stress Cracking) as known from other unprotected plastic parts.

Using a low modulus adhesive can deviate from the car design (if designed for mineral glass and all in one modulus) and needs to be communicated and carried out in accordance to OE instructions. It must be considered that a car body structure is calculated based on its standard design. If mineral glasses are replaced by organic parts the body stiffness cannot be guaranteed any longer. (E.g. Police car or similar applications) For example drive comfort or crash behaviour (roll over) can be different and are in Installers responsibility.

Sikaflex®-223 is recommended for the durable bonding of plastic windshields. This adhesive has a low modulus (soft) and can handle the thermal expansion of windshield without resulting in mechanical overload. Since PMMA is particularly sensitive to stress cracks, windshields should remain flat during the bonding process. If there are larger-than-specified dimensions of PC or PMMA to be bonded, please contact Sika before beginning work.

Temperature changes during curing can cause stresses and increase the risk of detachments.
Engine covers (Porsche, Ferrari, etc.) are highly sensitive applications as high temperatures are causing big changes of dimensions.

UV-Protection

Depending on the type of organic glass, UV protection is provided, but not given in all cases. To ensure a durable bond, transparent windshields must be surface-protected against UV. Sika® UV Shielding Tape or trims can be used in cases where no protection is given. Sika Primer (and most glass primers from other manufacturers) are organic materials and will be destroyed by UV radiation within a very short time and therefor provide no durable protection.
Any anti-scratch hard coating can be difficult to be removed. The removal of coating damages the original design and protection of the plastic. Application of primer and adhesives (solvents, plasticizers) and stresses (internal/external) could lead to ESC (Environmental Stress Cracking) as known from other unprotected plastic parts.

Possible solutions are:

  • Suitable print color
  • Protective metal or opaque plastic trim
  • Sika® UV Shielding Tape*

Without this protection, Sika® Primer-207 will eventually detach from the plastic windshield. The exact period until failure depends largely on the weather, the synthetic material quality, and the general load.
* Availability depends on the local Sika Organisation.

Alternatives

Substrate Process
Old PU

Cut back old Polyurethane

Sika® Cleaner G+P

Optional Sika®Aktivator-309 P

Paint

Sika® Cleaner G+P

Sika®Primer-207 or Sika®Aktivator-309 P

Fresh paint

Abrasive pad

Sika® Cleaner G+P

Sika® Primer-207 or Sika®Aktivator-309 P

FRP

Abrasive pad

Sika® Cleaner G+P

Sika® Primer-207

Corrosion treatment Sika® Primer-207