Quality Assurance in IG Production

Despite the fact that insulating glass panes manufactured using organic adhesives/sealants have been available on the market for almost 40 years, wrong ideas regarding the function of the products used still exist. In spite of the generally adopted usage of the word 'insulating glass sealants', this term is only correct when it refers to the PIB inner seal, since this product is definitely capable of offering limited resistance to all mechanical influences and has almost no recovery properties. The outer seal is more exactly defined as an 'adhesive/sealant', owing to the structural adhesive function it has besides the sealing function. The insulating glass edge sealing system is a structural bond and not a typical movement joint.

Joint sealing technology:

• Absorption of relatively large movements of the joint
  
• Adherence of the sealant only on the two flanks opposite to each other
  
• Sealants with high elongation and low modulus.

Insulating glass outer seal (adhesive/sealant):

• Prevention of high deformation, i.e. tolerance of only relatively small movements of the structure
  
• Adherence of the sealant to all relevant surfaces of the structure
  
• Adhesives/sealants with low elongation and high modulus.

This comparison makes clear that two completely different tasks are concerned whose structural details and functions must under no circumstances be mixed.

From the functions and properties of the two products used in the insulating glass edge sealing system, the following aspects result:

PIB inner seal:

• Plasto-elastic sealant with extremely low moisture vapour transmission (MVT)
  
• Largely irreversible deformation under the influence of forces acting upon it
  
• Almost no recovery
  
• No structural properties of the adhesive (low tensile strength).

Outer seal:

• Elastic adhesive/sealant with low MVT
  
• Reversibly deformed under the influence of forces acting upon it
  
• High recovery
  
• Structural properties of the adhesive owing to low elongation under the influence of forces acting upon it (high tensile strength).

From these properties and functions, the following results for the design of the edge sealing system:

• The inner seal accounts for an essential part of the tightness of the edge sealing system and is also, but not exclusively, an aid for assembly.
  
• Owing to its plasto-elastic properties, the inner seal adopts the deformations to which the glass unit is exposed.
  
• The outer seal (adhesive/sealant) must adhere to all relevant structural surfaces (i.e. the two surfaces of the glass panes and the surface of the spacer profile between the panes as well), so as to ensure mechanical coherence.
  
• The high modulus and the recovery of the outer seal ensure the functionability of the inner seal and prevent it from being damaged on account of mechanical and/or climatic influences, owing to the all-over adherence of the structural bond.

As a consequence of the lack of adherence of the outer seal (adhesive/sealant) to the spacer profile, the following problems can be expected to materialise:

• Over-elongation of the structure under climatic stress and, as a result, detachment of the inner seal. This increases water vapour permeation which reduces the service life of the insulating glass unit.
  
• Weakened resistance of the edge sealing system to shear forces, should the insulating glass unit be stressed unilaterally, for example during re-packaging, loading, transport and installation; this results in prior damage caused to the system and, once again, reduces the service life of the unit.

Monitoring standards
It is essential that the following methods should be used as standards in the monitoring of sealants:

Inner seal:

1. Monitoring of the quantity applied to the spacer profile (equally to both sides)
   
2. Verification of the adherence of the inner seal to the profile
   
3. Verification of the adherence of the inner seal to the glass.

Outer seal (Adhesive/sealant):

1. Verification of the mixture's homogeneity (compression of the mixture applied between two sheets of glass)
   
2. Rough evaluation of the potlife/processing time using the 'stringing method'
   
3. Rough evaluation of the chemical curing behaviour (verification if mechanical strength is developed or final strength built up following curing), by measuring the Shore-A hardness (according to DIN EN ISO 868)
   
4. Verification of the product's adherence to the glass (according to EN 1279-6, Annex F)
   
5. Verification of the product's adherence to the spacer profile (according to EN 1279-6, Annex F, see fig. 4).

Definitions of quality
Desirable definitions of quality and test provisions for the purpose of internal or external monitoring of the adherence of the sealant to the spacer profile in the production of insulating glass, are for the most part stipulated in EN 1279-6, Annex F. However, they could be made clearer (see below), in order to define the method in a more precise manner and limit the rank growth of interpretations:

• Definition of the specimen in accordance with EN 1279-6, Annex F
  
• Load criteria: 0.30 MPa for 10 minutes in accordance with EN 1279-6, Annex F
  
• Unambiguous definition of the result. The sealant is not allowed to detach from the profile, in accordance with EN 1279-6, Annex F
  
• Definition of the terms of conditioning of the specimens: Defined time and climatic conditions, for well-known, conventional technologies (relevant clauses of agreement in line with EN 1279-6, Annex F only make sense for other, i.e. different or new technologies (such as ThermoPlastic Spacer (TPS) systems for instance)
  
• Definition of the interaction between the test result and the state of the insulating glass units produced.

Uniform technical regulations which are equally binding for all concerned, have always been a sensible basis for concerted action to the benefit of all parties concerned.