Stock material or miscellaneous articles – Structurally defined web or sheet – Including variation in thickness
Reexamination Certificate
1999-08-04
2001-09-11
Copenheaver, Blaine (Department: 1772)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including variation in thickness
C428S198000, C296S208000, C277S644000, C277S650000, C277S654000
Reexamination Certificate
active
06287669
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to sealing discontinuities, for example, of the type found in motor vehicles.
Motor vehicles such as automobiles and trucks have metal surfaces that are typically painted “on-line” using an electrostatic spray process. The paints used are relatively brittle because they are formulated to be hard, durable and to approximate the low coefficient of thermal expansion characteristic of metal surfaces.
These motor vehicles also have joints that must be sealed. One example is a generally non-planar overlap joint formed by welding together the roof and side panel of the vehicle to create a U-shaped trough called a roof ditch. Water collects in the roof ditch and then is drained away from the vehicle.
To prevent water from seeping through the joint it is necessary to seal it. It is often difficult to obtain a good seal, however, because the joint is not planar. In addition, the width of the roof ditch typically varies along its length, further complicating the ability to provide a good seal.
In practice, roof ditch joints are typically sealed using a paste-like plastisol which is then painted, baked and cooled to room temperature. The surface of the sealant may be covered with a plastic or rubber molding having a flexible top surface, which molding may be painted, for example to match or complement the color of the vehicle exterior. Alternatively, a metal molding may be used. The molding is typically attached to the sealant surface using a mechanical fastener or a pressure sensitive adhesive.
The plastic or rubber molding cannot be painted “on-line” along with the rest of the vehicle because the brittle, electrostatically applied paint will crack and flake off the surface owing to poor adhesion and a mismatch in the coefficients of thermal expansion between the molding surface and the paint. Therefore, the plastic or rubber molding is painted “off-line” in a separate operation using specially formulated paints.
SUMMARY OF THE INVENTION
In one aspect, the invention features a method and an article for sealing a discontinuity in the surface of a substrate. Examples of discontinuities include overlap seams or joints, butt seams or joints, depressions or indentations, holes, spot welds, and manufacturing defects. The method includes the steps of: (a) placing over the discontinuity an article that includes (i) a melt-flowable composition (i.e., a composition that exhibits mass flow upon heating) characterized by a first width, and (ii) a shaped, polymeric cap having a pre-selected, cross-sectional profile characterized by a second width, and a shape in which the thickness of the cap across its width, the width of the cap, or both the width and the thickness of the cap vary; (b) heating the article to cause the melt-flowable composition to flow and seal the discontinuity; and (c) allowing the article to cool while substantially retaining the pre-selected cross-sectional profile of the cap. The method is particularly useful for sealing seams or joints formed in the floor of a recessed area such as the roof ditch on a motor vehicle.
The cap controls the melt-flow behavior of the melt-flowable composition to substantially confine the melt-flowable composition to the area underneath the cap. To aid in accomplishing this purpose, it is generally preferred that the width of the cap exceed the width of the melt-flowable composition, a characteristic that relates to another aspect of the invention.
The shape of the cap is selected based upon the particular discontinuity which the article is designed to seal. A configuration particularly useful in the case of seams or joints formed in the floor of recesses such as motor vehicle roof ditches is one in which the cross-sectional profile is characterized by a pair of laterally extending, opposed extensions, at least one of which is tapered in the thickness direction. Preferably, both opposing extension portions are tapered in the thickness direction.
The cap is designed to substantially retain its shape during the melt-sealing operation. It may contain one or more layers of material. A preferred material for the cap is a B-staged thermosetting composition such as a B-staged epoxy-polyester blend. “B-staged” refers to an intermediate state in a thermosetting resin reaction in which the material softens when heated, and swells, but does not dissolve in certain liquids, as described in ASTM Standard D907-91b. Consequently, a B-staged material is partially cured (i.e., partially cross-linked) and dimensionally stable (i.e., it substantially retains it shape during the heat curing cycle of the melt-flowable composition, e.g., at about 110-200° C. for 20-40 minutes). Another suitable material is a thermoplastic composition having a high heat deflection temperature such as polyetheretherketone, polyphenyleneoxide, and polyesters such as polybutylene terephthalate and blends thereof with polycarbonates.
The stiffness of the article may be further enhanced by including a stiffening member such as a metal or a dimensionally stable plastic insert in the cap, in the melt-flowable composition, or between the cap and the melt-flowable composition.
The cap preferably includes a paint-receptive surface such that it can be painted either following cooling or prior to heating. Preferably, the paint-receptive surface is paintable to a substantially Class A finish. A “substantially Class A finish” is an exterior finish, particularly of the type found in the automotive industry, that is substantially free from pits, porosity and swirls. In this way, both scaling and painting can be accomplished in a single operation. Preferably, the paint-receptive surface is sufficiently electrically conductive to permit the cap to be electrostatically painted. In this way, in the case of motor vehicle manufacture, the molding can be painted “on-line” along with the rest of the vehicle.
A variety of melt-flowable compositions can be used. Examples of preferred compositions include semi-crystalline, thermosetting epoxy-polyester blends, thermosetting epoxy-acrylate blends, and thermosetting ethylene vinyl acetate-elastomer blends. The composition may include one or more melt-flowable layers, and may be covalently bonded to the cap.
In a different aspect, the invention features a method for scaling a discontinuity in the surface of a substrate in which a sealant and a cap are provided separately. The method includes steps of: (a) placing a sealant composition over the discontinuity; (b) placing over the composition a shaped, polymeric cap having a pre-selected, cross-sectional profile in which the thickness of the cap across its width, the width of the cap, or both the width and the thickness of the cap vary; (c) heating the sealant composition to cause the composition to seal the discontinuity; and (d) allowing the composition and the cap to cool while substantially retaining the pre-selected cross-sectional profile of said cap. The cap controls the behavior of the composition to substantially confine the sealant to the area underneath the cap. Examples of suitable sealants include the above-described melt-flowable materials, as well as conventional sealants such as urethanes and polyvinyl chloride plastisols.
In other aspects, the invention features a shaped, electrostatically paintable, preferably B-staged, polymeric cap having a pre-selected, cross-sectional profile in which the thickness of the cap across its width, the width of the cap, or both the width and the thickness of the cap vary, said cap substantially retaining its profile upon exposure to temperatures of at least about 110° C., and, more preferably, temperatures encountered during an automotive paint-bake cycle. In addition to sealing applications, the cap may be used in applications involving motor vehicle body side moldings and decorative moldings. In such applications, the cap is combined with a bonding material such as a pressure sensitive adhesive, e.g., in the form of a tape such as Structural Bonding Tape No. 9245 commercially available from 3M Company, St. Paul, Minn
George Clayton A.
Johnson Michael A.
Willett Peggy S.
3M Innovative Properties Company
Chevalier Alicia
Copenheaver Blaine
Knecht III Harold C.
LandOfFree
Sealing method and article does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Sealing method and article, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Sealing method and article will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2513488