Adhesion Buildup

Fast adhesion buildup is an important property, since this will define the ability of the adhesive to be rapidly functional after application. For insulated glasses, for instance, manipulation of the insulated glass takes place directly after appli­cation and transportation often occurs within the first 24 h. Internal stresses due to temperature increase when stored in uncontrolled environments or dur­ing transportation within the first 24 h can also lead to pre-mature failure or weaknesses in interface adhesion which will affect the adhesion durability.

Tables 1 and 2 compare 180° peel adhesion (ASTM C974-2010 “Standard Test Method for Adhesion-in-Peel of Elastomeric Joint Sealants") [6] on differ­ent substrates used in glass assemblies; the peel strength was not measured but only the percentage of cohesive failure (% CF). When the result is denoted as CF, the failure is more than 90 % CF; when it is denoted as AF, the failure is more than 90 % AF. Mixed failures would be de noted as CF/AF. Such tests can easily be used on-site for a rapid qualitative evaluation of adhesion build-up. The substrates used are: float glass (Float), coated glass (Low E), anodized alu­minum (AA), aluminum mill finish (AMF), powder coated anodized aluminum (PCAA), stainless steel (SS) and galvanized steel (GS). It is well-known that the surface nature of the different substrates can vary depending on their origin but the aim of this work was to evaluate the effect of the adhesive and primer on standard substrates used in the building industry and therefore cohesive failure

TABLE 1—Peel adhesion tests on substrates used in the building industry.

Product/Surface Condition Treatment

Float

Low E

AA

AMF

PCAA

SS

GS

1 day cure DC 993

CF

AF

CF

AF

AF

CF

AF

DC opt

CF

CF

CF

CF

CF

CF

CF

DC 993 + 1200 OS

CF

CF

CF

CF

CF

CF

CF

DC 993 + Pyrosil

CF

CF

CF

CF

CF

CF

CF

1 day cure + 1 h WI

DC 993

CF

AF

CF

AF

AF

AF

AF

DC opt

CF

CF

CF

CF

CF

CF

CF

DC 993 + 1200 OS

CF

CF

CF

CF

CF

CF

CF

DC 993 + Pyrosil

CF

CF

CF

CF

CF

CF

CF

3 day cure + 1 week WI

DC 993

CF

CF

CF

CF

CF

CF

CF

DC opt

CF

CF

CF

CF

CF

CF

CF

DC 993 + 1200 OS

CF

CF

CF

CF

CF

CF

CF

DC 993 + Pyrosil

CF

CF

CF

CF

CF

CF

CF

TABLE 2—Peel adhesion tests on substrates for solar thermal applications.

Substrate

Treatment

1 Day Cure

1 Day + 1 Week WI (23 °C)

1 Day + 1 Week WI (55 °C)

AMF

None

AF

AF

AF

1200 OS

CF

CF

CF

Pyrosil

CF

CF

CF

AA

None

CF

CF

CF

1200 OS

CF

CF

CF

Pyrosil

CF

CF

CF

PCAA

None

CF

AF

AF

1200 OS

CF

CF

CF

Pyrosil

CF

CF

CF

on anodized aluminum, for instance, does not guarantee cohesive failure for all anodized aluminums on the market.

For Table 1, peel adhesions are given after a 1 day cure, a 1 day cure fol­lowed by 1 h 23° C water immersion, and a 3 day cure at room temperature fol­lowed by 1 week immersion in 55°C water. For all tests under water immersion (WI), peeling is performed directly after water immersion. For Table 2, peel adhesions are measured after a 1 day cure followed by one week water immer­sion, either at 23°C or 55°C. In Table 2, substrates used in the solar thermal industry were tested: those are similar substrates to the ones used in the build­ing industry (AMF, AA, PCAA) but their manufacturing origin differs.

Both Tables 1 and 2 show that adhesion buildup can be improved either by the use of a primer (dry or wet) or by modifying the product formulation. This adhesion survives 1 week of water immersion.

Table 3 evaluates the capability of the sealant/adhesive to maintain a glass- to-glass assembly (H-bar) under a 0.45 MPa constant stress applied for 10 min with the lower glass immersed in water. The adhesive thickness is 12 mm and the adhesive surface is 12 mm x 20 mm. This test is sometimes used in the insu­lated glass industry since those assemblies can be submitted to high stresses rapidly after production due to pressure buildup in the assembly with an increase in temperature. In the case of “soft" low E coatings, edge deletion is

TABLE 3—Adhesion on low E coated glass.

Coating

Sealant

Priming

Time to Failure (min)

Standard

DC 3362

None

<2

DC 3362

1200 OS

>10

DC 3362

Pyrosil

>10

DC opt

None

2-10

New

DC opt

None

>10

usually required before sealant application to avoid glass corrosion to take place in the long term [7]. Glass corrosion is due to the sensitivity of the low E coating towards hydrolysis. However, edge deletion often does not lead to the complete removal of the coating and adhesion is often also required on the coated layer. DC 3362 is a two component sealant used for insulated glass. Two low E coat­ings were evaluated: a standard low E (Standard) coating and a newly developed coating (New) with a lower sensitivity towards hydrolysis. With the standard coating, the optimized formulation did not pass this severe test, however, fast and strong adhesion buildup was obtained when using both the wet or the dry primers. The optimized formulation did, however, lead to good results with the new low E coating.

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