Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-06-29
2002-04-16
Pezzuto, Helen L. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S558000, C156S278000, C156S280000, C156S307500, C156S309600, C156S312000, C156S313000, C156S324400
Reexamination Certificate
active
06372827
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to establishing a seal between two substrates, particularly where at least one of the substrates is glass.
Many applications exist where it is necessary to secure a glass substrate within a frame such as a metal, plastic or wood frame, which may be painted. For example, glass windshields are secured within the metal or plastic frame of a motor vehicle both during vehicle manufacture and following manufacture to replace the windshield in the event that it cracks or breaks.
It is difficult to establish a strong bond to glass using conventional sealants and adhesives such as polyurethane pastes. To enhance adhesion, the glass surface is typically primed prior to inserting it into the frame.
Polyurethane pastes are conventionally used to establish a seal between the primed glass and the frame. Such pastes, however, are difficult to apply uniformly and reproducibly. Another problem is that pushing the glass into the frame causes the paste to flow and squeeze out of the bond line. This creates bond lines of uneven thickness and glass-frame contact points that can act as failure points because any stress applied to the frame is transmitted directly to the glass at these points. This is particularly a problem when a motor vehicle windshield is installed into a frame that has a highly uneven surface. To address this problem, discontinuous “spacers” are typically placed at various points around the perimeter of the frame. While these spacers help avoid creating glass-frame contact points, they also act as stress concentration points because while the sealant shrinks during cure, the spacers do not. It is then necessary to use extra sealant to accommodate the spacers.
Another problem is encountered in the case of polyurethane sealant pastes that require a relatively long time to cure and build bond strength such as those which are moisture-curable. During this vulnerable curing period, the glass can vibrate within the frame, making the seal and the glass susceptible to damage. Gaps in the seal can form, giving rise to wind noise and compromising seal integrity. The noise associated with the vibrations is also undesirable. Moreover, the reliance on ambient moisture means that the cure process varies depending upon ambient conditions.
SUMMARY OF THE INVENTION
In a first aspect, the invention features an article (e.g., in the form of a tape) that includes (a) a conformable, compressible, melt flow-resistant foam core layer having first and second major surfaces, and (b) a thermosettable sealant layer on said first major surface of the core layer. The sealant layer has a surface available for contacting a substrate.
A “sealant composition” or a “sealant layer” is a gap-filling material. Consequently, at the time of seal formation, sealant compositions according to the invention have an elasticity that is sufficiently low such that the sealant composition is able to flow into and fill gaps in the substrate to which it is applied and, after the sealant has cured (in the case of thermosetting sealant compositions) or solidified upon cooling (in the case of thermoplastic sealant compositions), still sufficiently fill the gaps so as to seal the substrate. Both the surface of the sealant layer available for contacting a substrate and the bulk composition of the sealant layer meet these criteria. Sealant compositions useful in the invention are non-tacky (i.e., they are not tacky to the touch) once they have cured (in the case of thermosetting sealant compositions) or solidified upon cooling (in the case of thermoplastic sealant compositions).
In addition, the sealant compositions do not meet the definition of a pressure sensitive adhesive as established by the Pressure Sensitive Tape Council (PSTC), Glenview, Ill. According to the PSTC Glossary of Terms (August, 1985 revision), pressure sensitive adhesives are aggressively and permanently tacky at room temperature and firmly adhere to a wide variety of dissimilar surfaces upon mere contact and without the need for more than finger or hand pressure. They require no activation by water, solvent or heat in order to exert a strong adhesive holding force toward materials such as paper, plastic, glass, wood, cement and metals. They have a sufficiently cohesive holding and elastic nature so that, despite their aggressive tackiness, they can be handled with the fingers and removed from smooth surfaces without leaving a residue.
A “'thermosetting” or “thermosettable” composition is one which can be cured (i.e., crosslinked), for example by exposure to, preferably, heat or actinic radiation (although exposure to moisture or other chemical means may also suffice), to yield a substantially infusible (i.e., thermoset) material. Combinations of these various curing means may also be used (e.g., a combination of heat and actinic radiation). Such compositions may include a curing agent (e.g., a thermal or photo-active curing agent).
A “thermoplastic” composition is one which is capable of being repeatedly softened by heat and hardened by cooling.
A “melt flow-resistant” material is a material that resists undergoing macroscopic mass flow under conditions at which the sealant layer exhibits macroscopic flow. Typically, the melt flow-resistant material resists undergoing macroscopic mass flow when subject to temperatures of up to about 200° C.
A “conformable, compressible” material is a material that readily deforms when subjected to an applied stress, but will tend to elastically recover when the stress is removed within the time frame that it takes to establish a seal between two substrates of interest, although some permanent set or deformation may occur depending on the stress to which the material is subjected in a given application.
In one embodiment, the thermosettable sealant layer includes a blend of (a) an epoxy resin, (b) a resin selected from the group consisting of polyacrylates, semi-crystalline polyesters, and combinations thereof, and (c) a curing agent selected from the group consisting of (i) thermally activated curing agents characterized by a thermal activation temperature and (ii) photo-active curing agents characterized by a thermal decomposition temperature.
In another embodiment, the thermosettable sealant layer substantially retains its shape when heated to a temperature greater than the softening temperature of the composition, but less than about 200° C., until acted upon by an external force other than gravity. Such force includes the pressure exerted during sealing by pushing two substrates together. One test for determining whether a given composition exhibits this behavior involves placing a sample of the composition on a plate maintained at an angle in an oven, heating the sample to the desired temperature, and observing the extent to which the sample loses its initial shape and flows down the surface of the plate within a set period of time. Because the test is conducted in the absence of an applied external force, any such flow is attributable to the combined effect of temperature and gravity alone. This test is described in greater detail in the “Examples” section below.
In another embodiment, the sealant layer includes a thermosetting sealant composition that includes a curing agent selected from the group consisting of (a) thermally activated curing agents characterized by a thermal activation temperature, and (b) photo-active curing agents characterized by a thermal decomposition temperature. The sealant composition is characterized in that, prior to cure, the composition substantially retains its shape when heated to a temperature greater than the softening temperature of the composition, but less than (a) the thermal activation temperature of the curing agent, where the curing agent is a thermally activated curing agent, or (b) the thermal decomposition temperature of the curing agent, where the curing agent is a photo-active curing agent, until acted upon by an external force other than gravity, measured according to the test procedure generally described above.
An exa
Boettcher Robert J.
George Clayton A.
Johnson Michael A.
3M Innovative Properties Company
Pezzuto Helen L.
Skolnick Steven E.
Szymanski Brian E.
LandOfFree
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