Adhesive fastener article

This invention relates generally to an adhesive fastening device which includes a substantially flat base carrying on its undersurface a layer of heat activable adhesive. The fastening device may also include a section extending from the base designed as a secondary fastening feature, such as a stud, tab, clip or the like. Protuberances of limited surface area and height are formed adjacent the perimeter of the base in a pair of laterally spaced lines adapted to be associated with the end surfaces of a U-shaped core to slightly space the core from the base.

This invention relates generally to an article adapted to be secured to a 
support structure by an adhesive layer. 
The invention more particularly relates to an article adapted to be secured 
to a support layer through the use of a U-shaped induction core creating 
heat in a base which activates adhesive. 
The use of a U-shaped induction core to heat metal articles is becoming 
known in the art. Such a system, for use in adhesive fastening devices is 
used by placing the end surfaces of the core in abutting contact with 
laterally spaced surfaces on a ferromagnetic base of the fastener. A 
magnetic flux circuit is thus created by the bridging of the metal article 
between the faces of the core. The flux density formed in the metal 
article heats the base primarily through a hysteresis effect and thus 
effectively activates the adhesive. 
It is very important that the adhesive, in such a system, be heated in a 
uniform manner or there will be dissimilarities in the bonding strength 
over the faying surface of the bonded article. A typical limitation of 
U-shaped heating systems for use in activating adhesive carrying fasteners 
is that the core itself may become a heat sink by the conduction of heat 
back into the core as the flat metal base is heated. This will, obviously, 
reduce the efficiency of the system, increase the time of the heating 
cycle and quite frequently result in less heat being provided in the 
regions of the heat sink, creating a dissimilarity in the bonding strength 
across the adhesive layer. This problem is increased when the article 
being heated is of an irregular shape which inherently includes a heat 
sink in its configuration. Since adhesive bonds are weakest when subjected 
to a peel force, efforts should be taken to strengthen the bond adjacent 
the perimeter by an adhesive layer. 
Accordingly, it is a primary object of the invention to provide an adhesive 
carrying article which provides a uniform heating pattern to the adhesive 
layer when associated with a U-shaped induction core. 
A further object of the invention is to provide an article that carefully 
spaces all or most of the surface area of the end surfaces of the legs 
from conductive contact with the article. 
A still further advantage of the invention is to provide a particular 
adhesive fastening member which will have a uniform heating pattern even 
when the fastening member is of an irregular shape including a heat sink 
forming section. 
The various objects and advantages of the invention are accomplished by an 
adhesive fastening device which basically incorporates a flat base with a 
layer of heat activable adhesive formed on its undersurface. The upper 
surface of the flat base includes a plurality of protuberances of very 
limited surface area and height arranged in a pair of laterally spaced 
lines each being directly adjacent to the extremity of the heat activable 
adhesive and, therefore, close to the perimeter of the metal article. A 
more detailed embodiment of the invention includes an upstanding tab at 
one end of the article and contemplates protuberances of differing and 
increasing height from a region close to the tab to a region remote from 
the tab so that end faces of a U-shaped core are spaced from the base a 
distance which is greater at the region remote from the tab than in the 
region close to the tab to compensate for the loss of the heat into the 
tab. 
Other objects and advantages will become more apparent during the course of 
the following description when taken in connection with the accompanying 
drawings wherein like reference numerals are intended to designate similar 
elements.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings, reference numeral 10 denotes the fastening 
device which is the subject matter of the invention and which is 
designated particularly for use with a U-shaped induction heating core, 
such as 30. 
The device 10 basically includes a substantially flat base 12 and is 
conventionally provided with an upstanding fastening element, such as 
threaded stud 14, having threads 16 formed thereon and extending generally 
perpendicular to the base. This stud is shown to be positioned 
intermediate the side edges 20 and end edges 22 of the generally 
rectangular base 12. An adhesive layer 18 is formed beneath the base for 
association with a primary support surface 42, as more clearly shown in 
FIGS. 2 and 4. 
In operation, the adhesive carrying fastener 10 is effectively heated 
through operative association with U-shaped core 30. Core 30 will 
typically include a bridge section 32 and a pair of legs 34 with an 
exciter coil 38 wound about the bridge. The core may be configured so that 
the legs are inclined to the fastener base so as to accommodate various 
lengths of studs 14. End surfaces 36 at the extremities of the legs will 
be positioned in abutting relationship with the upper surface of the 
fastener. In such a manner, a magnetic flux circuit is completed between 
the legs of the core so that the flux density heats the base, primarily 
through a hysteresis effect. However, as noted earlier, it is important 
that the adhesive layer be heated uniformly and since the end surfaces 36 
of the core directly abut the ferromagnetic base 12, a certain amount of 
heat is conducted back into the low loss core legs. This situation 
minimizes the efficiency of the system and increases the time of the 
heating cycle as well as diluting heat from the regions of the adhesive 
which are adjacent the side edges 20. 
The invention incorporates a pair of lines of protuberances formed in the 
upper surface of the base 12. Each line should include at least two 
protuberances 24 and 25. These lines of protuberances are adapted to be 
aligned with the end surfaces of an appropriately sized core and are 
advantageously positioned closely adjacent the side edges 20 of the 
article. This positionment of the lines of protuberances will be related 
directly to the side extremities of the adhesive coating. It will be shown 
in FIG. 3 that these protuberances are of a very limited surface area and 
height, preferably not exceeding the thickness of the base. Thus, a slight 
spacing is created between the face of the core and the base to be heated. 
This slight spacing is not so great as to seriously effect the flux 
density entering the core but does eliminate the conduction of the heat 
into the core. 
In certain instances, it has been found appropriate to provide the end 
surfaces of the core with a very thin layer 36 of wear-resistant material 
which will protect the rather soft magnetically permeable laminations 
forming the legs of the core. 
It will be seen that the use of properly positioned protubernaces on an 
article to be heated may be varied to accommodate uniquely configured 
fastening devices which inherently create a heat sink when heat is 
provided to the base. For example, FIG. 5 shows an L-shaped fastener 10a 
comprising a generally flat base 12a and an upstanding tab region 14a 
including an aperture or secondary fastening means 16a. The tab 14a will 
extend from one end margin 22a of the device. In keeping with the 
invention, a pair of laterally spaced lines of protuberances are provided 
in the base 12a closely adjacent the side edges 20a. However, in this 
embodiment the protuberances 24a closest the tab region are of a smaller 
height than the protuberances 26a furthest from the tab region. This 
results in a tilting of the associated core 30a as shown in FIGS. 6 and 7 
and in more detail in FIG. 8. For example, protuberance 24a is a distance 
A above the surface while protuberance 25a is a distance B which is 
greater than A. These distances are not substantially greater than the 
thickness of the base and will, thus, not effect the ability of a U-shaped 
core to sufficiently heat the base. 
Thus, it is apparent that the flux density in the region adjacent the tab 
14a will be greater than the flux density in the region remote from the 
tab. The increase in flux density in the tab region thus will accommodate 
the heat sink situation formed by the tab and will, when carefully 
calibrated, insure that the adhesive layer 18a is heated uniformly. 
In an L-shaped fastener of the type described, uniform heating becomes 
important since the tab 14a is designed to secure a secondary element to 
the primary surface through the use of the fastener and its bonding layer. 
As noted above, since an adhesive bond is relatively weak when loaded in a 
peeling direction, an inadequate heating of the adhesive in the region of 
the tab 14a will create an inherently weak joint. 
While the invention has been described with particular reference to a 
preferred embodiment, it will be understood that it is not intended to 
limit the invention to that embodiment. On the contrary, it is intended to 
cover all alternatives, modifications and equivalents as may be included 
within the spirit and scope of the invention and as defined by the 
appended claims.