U.S. patent number 3,908,267 [Application Number 05/453,802] was granted by the patent office on 1975-09-30 for method of applying an insulating connector.
This patent grant is currently assigned to Stone Industrial Corporation. Invention is credited to Patrick V. Loyd, Samuel M. Mills.
United States Patent |
3,908,267 |
Loyd , et al. |
September 30, 1975 |
Method of applying an insulating connector
Abstract
A laminated tubular connector for splicing or terminating
electric conductors, comprising an outer layer of a heat shrinkable
dielectric material, e.g., polyethylene terephthalate, and an inner
layer of a relatively soft, self-adhesive, low temperature flowable
thermoplastic material, preferably a polyvinyl acetate composition.
When heat is applied to the connector, the outer layer shrinks and
the inner layer functions as a sealant and a cushioning agent. The
adhesiveness of the inner layer may be used to hold the connector
in place during subsequent operations by pinching the connector so
that the depressed portions of the tube adhere to each other prior
to heating the connector to shrink the outer layer.
Inventors: |
Loyd; Patrick V. (West Laurel,
MD), Mills; Samuel M. (University Park, MD) |
Assignee: |
Stone Industrial Corporation
(College Park, MD)
|
Family
ID: |
26961799 |
Appl.
No.: |
05/453,802 |
Filed: |
March 22, 1974 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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282977 |
Aug 23, 1972 |
3814139 |
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Current U.S.
Class: |
29/887; 29/872;
29/828 |
Current CPC
Class: |
H01R
4/72 (20130101); B29K 2067/00 (20130101); Y10T
29/49123 (20150115); Y10T 29/49201 (20150115); B29K
2029/00 (20130101); Y10T 29/49227 (20150115) |
Current International
Class: |
H01R
4/70 (20060101); H01R 4/72 (20060101); H01B
019/00 () |
Field of
Search: |
;29/631,628,629,63R,63A,63F,447 ;174/DIG.8,84R ;138/141
;339/276R,276T,201,213R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lanham; C. W.
Assistant Examiner: Duzan; James R.
Attorney, Agent or Firm: Laurence, Stokes & Neilan
Parent Case Text
CROSSREFERENCE TO RELATED APPLICATION
This application is a division of our copending application Ser.
No. 282,977 filed Aug. 23, 1972, now U.S. Pat. No. 3,814,139.
Claims
We claim:
1. A method for insulating an electrical joint having at least one
conductive wire, comprising the steps of inserting the joint into a
laminated tubular connector having a relatively rigid,
heat-shrinkable dielectric outer layer and an adhesive inner layer,
pinching a portion of said connector to seal portions of said inner
layer to itself whereby a desired relative positioning of said
joint and said connector may be maintained during assembly
operations, and subsequently heating said connector to shrink said
outer layer and to cause said inner layer to flow about said
joint.
2. A method according to claim 1, wherein the pinching step
comprises pinching an end of said connector prior to the step of
inserting the joint into the connector.
3. A method according to claim 1, wherein the pinching step
comprises pinching an end of said connector after the step of
inserting the joint into the connector.
4. A method according to claim 1, wherein the pinching step
comprises pinching an intermediate portion along the length of the
connector.
5. A method according to claim 1, wherein said adhesive inner layer
comprises a synthetic polymeric pressure sensitive adhesive.
6. A method according to claim 1, wherein the pinching step also
bonds portions of said inner layer to said electrical joint.
Description
BACKGROUND OF THE INVENTION
The present invention relates to use of electrical connectors and
more particularly to use of laminated synthetic resin electrical
connectors which are initially in the form of tubes or sleeves and
which can be slipped onto electric conductors to splice or
terminate the conductors.
The use of such connectors is known in the art. One type of prior
art connector which has met with some success comprises a tubular
connector having elastic memory so that upon application of heat
the connector shrinks onto the electric conductor. The use of
various fusable inserts including solder inserts and polymeric
inserts has also been proposed in an effort to improve such known
connector structures.
The prior art approaches have not been fully satisfactory
particularly when the connectors are to be utilized within systems
in which insulating varnishes which should be subjected only to
relatively low temperatures, for example, 200.degree.F., are
employed. Other problems inherent in prior approaches involve the
possibility of breaking fine electric wires when the connector is
shrunk onto the wires and, in some manufacturing operations,
difficulties are experienced in keeping the connectors properly in
place upon the electric conductors before the connectors have been
heated to contract them down onto the conductors.
SUMMARY OF THE INVENTION
A primary object of the present invention is to provide a novel
method for assembling insulating connectors onto electric
conductors.
Other objects and advantages of the present invention will become
more apparent as this description proceeds.
Briefly, a presently preferred embodiment of the invention employs
an insulating connector initially in a tubular form having a heat
shrinkable, dielectric outer layer which is preferably spirally
wound polyethylene terephthalate tubing, and a continuous inner
layer of a soft, flowable, adhesive synthetic polymeric material
such as appropriately compounded polyvinyl acetate or polyvinyl
alcohol. In use, the connector is slipped onto the joint or splice
of the electric conductor(s) with a portion of the connector
extending along and around the conductor, whether insulated or not,
adjacent the splice or termination of the conductor. In some cases,
particularly in certain assembly line operations, it is desirable
to secure the connector relative to the conductor prior to the time
that the connector is heated to shrink it onto the conductor. This
initial securement of the connector may be accomplished by
squeezing the connector so that opposed portions of the inner layer
contact and adhesively unite to each other and may also bond to the
conductors. This squeezing may take place either at an end of a
connector or at an intermediate point along the length of the
connector. Thereafter, the units comprised of the electric
conductors and the connectors adhesively secured in place may be
transported to another operating station such as an oven or other
heating station in which heat is applied to the connectors to
shrink the heat shrinkable outer layer and at the same time soften
the inner layer so that when the outer layer shrinks the inner
layer flows and fully encases the splice or terminal at the ends of
the conductors.
The laminated connectors of the invention are produced by spirally
winding a thin strip of polyethylene terephthalate which has been
conditioned to make it heat shrinkable into tubular form while at
the same time extruding a continuous, soft inner layer onto the
inside of the spirally wound tube. The inner layer is applied by a
solution extrusion technique which is known per se. The polymer
constituting the inner layer is applied in a solvent carrier
combined with a thickener and a surfactant. If the amount of
thickener is too great, the tackiness and flowability of the inner
layer of the final product may be insufficient to allow the inner
layer to adhere to itself or to allow the inner layer to flow when
heat is applied to shrink the outer layer.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial perspective view showing a three wire electric
connection about to be inserted into a tubular connector of the
present invention.
FIG. 2 is a longitudinal cross sectional view of another embodiment
of the invention in which the connector is initially secured to the
electrical conductor by pinching an intermediate portion of the
connector.
FIG. 3 is a longitudinal cross sectional view in which one end of
the connector of the invention has been pinched closed.
FIG. 4 is a view similar to FIG. 3 illustrating the position of the
parts after the connector has been subjected to heat to shrink the
outer layer.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the drawing and more particularly to FIG. 1,
reference numeral 10 generally designates a laminated connector in
accordance with the present invention which is comprised of a
relatively rigid, outer sheath or layer 12 of dielectric material
and a relatively soft, continuous inner layer 14.
The relatively rigid outer layer 12 consists of a plurality of
spirally wound polyethylene terephthalate strips forming an
integral outer sheath. Polyethylene terephthalate which is
commercially available under the trademark Mylar is an excellent
dielectric material and can be obtained in a form which has been
treated to be heat shrinkable. In view of the high dielectric
properties of polyethylene terephthalate, use of this material
enables the wall thickness of the outer layer 12 to be quite thin,
for example, a few mils while still giving the final product the
desired electrical insulation properties.
The relatively soft inner layer 14 must satisfy a number of
requirements. These requirements include that the layer 14 have
relatively low temperature flow characteristics so that it does not
restrict heat shrinkage of the outer layer 12 and so that the inner
layer will flow around and encapsulate the conductors when the
outer layer shrinks. Another reason why the inner layer should be
capable of flowing at relatively low temperature is that in many
instances there are requirements that the electrical junctions be
subjected to temperatures of no more than 200.degree.F., the design
maximum temperature to which insulating varnish on the conductors
should be subjected. The inner layer should also have
pressure-sensitive, self-adhesive properties so it will unite to
itself when the connector is squeezed so that portions of the inner
layer contact one another. The material constituting the inner
layer should also be capable of being solution extruded onto the
inner surface of the outer layer 12.
Polyvinyl acetate has been found to be particularly suitable for
satisfying the above-mentioned diverse requirements. Although
presently less preferred, polyvinyl alcohol is also suitable for
some uses in which the water solubility of polyvinyl alcohol is not
objectionable. The polymer is dissolved in a suitable solvent which
will not deleteriously attack the polyethylene terephthalate outer
layer. Methyl alcohol is the presently preferred solvent for
polyvinyl acetate although other solvents including other lower
alcohols such as ethyl alcohol and isopropyl alcohol may also be
employed. Water is the solvent for polyvinyl alcohol. The total
polymer content of the composition at the time of extrusion is in
the range of about 50-70 weight percent. In the event that the
polymer is obtained commercially in the form of a solution,
additional solid polymer may be added while keeping the polymer
content in the above-mentioned range. A thickener, preferably fumed
silica, Cab-o-sil, is added to the solution in an amount of about
4.0 to 8.0 weight percent on a wet basis in order to thicken the
solution but the amount of thickener added is controlled so that it
is insufficient to reduce the flowability of the polymer or to
function as an antiblocking agent, i.e., prevent the polymer from
being adhesive after removal of the solvent. Other conventionally
employed additives such as dyes, surfactants and plasticizers are
also used in the composition. Plasticizers of the phthalate ester
class have been found to be particularly useful. The presently
preferred surfactant is Adogen, n-oleyl propylene diamine, which
functions to reduce the amount of thickener required which is
employed in a ratio of approximately 5:1 based on the amount of
thickener. As will be appreciated by those skilled in the art, the
optimum amounts of each component will vary somewhat depending upon
such factors as the molecular weight of the polymer, e.g., higher
molecular weight polymers generally require less thickener, and
optimum amounts can be determined by routine experimentation
consistent with the above disclosure.
While other polymers meet one or more of the requirements
enumerated above, they do not have all the advantages of the
polymers of the invention. For example, polyethylene which is used
for many purposes in the electronics industry does not flow at low
temperature and thus is not suitable use as the inner layer of the
connectors of the present invention.
Referring to FIG. 1, the connector 10 is shown about to be inserted
around a three-wire connection comprised of a crimped sleeve 16
which holds the ends of wires 18 and 20 which are covered with an
insulating varnish and the exposed wire 22 of an insulated
conductor 24 in electrical contact with each other.
After the connector 10 is slipped onto the wires at an assembly
station, it is frequently desirable to maintain the relative
positions of the electric connection and of the connector. This may
be accomplished in simple fashion utilizing the tackiness of the
inner layer 14.
FIG. 2 illustrates one application of the tackiness of the inner
layer in which an intermediate section along the length of the
connector 10 is pinched down in the region A around the conductors
so that portions of the soft, adhesive inner layer 14 unite to each
other usually also to the conductors, and temporarily fix the
connector is position.
FIG. 3 illustrates another embodiment of the invention in which the
connector 10 is temporarily fixed in position relative to the
conductors by providing the connector with a pinched end B so that
opposed upper and lower portions of the inner layer 14 bond to each
other. In some assembly operations, the end B will be pinched
closed after insertion of the conductors into the connector 10. In
other instances, it will be more convenient to previously form the
closed end B on the conductor. This is particularly true when the
assembly operation is so designed that the conductors and the
connector when in position would be elevated at an angle to the
horizontal so the connector tends to slide downwardly due to the
gravity.
After the connector is in place, the unit is transported to a
heating station which may be an oven, a bank of infrared heating
lamps, or other heating means. At the heating station, the
heat-shrinkable outer layer 12 is heated and contracts inwardly
while at the same time the inner layer 14 flows under the combined
action of the heat and the contraction of the outer layer and
completely encases the electric joint as seen in FIG. 4. In
addition to acting as a sealant, the inner layer being relatively
soft functions as a cushioning layer for electrical wires. In the
event that fine wires 18, 20 and/or 22 are utilized, these wires
might break if there was no cushioning material, i.e., if only a
heat-shrinkable layer was present without the soft inner layer
14.
As pointed out previously, it is a feature of the invention that
the amount of heat imparted to the connector 10 in the heating
station is insufficient to raise the temperature of the connector
and the encased conductors to the maximum design temperature for
the wires which, in the case of some electrical wiring employing
insulating varnish is as low as 200.degree.F.
The tubular laminated connectors of the invention may be produced
utilizing apparatus generally similar to that disclosed in Mills et
al, U.S. Pat. No. 3,347,274 which discloses apparatus for winding
three narrow film strips about the periphery of a mandrel employing
a winding belt wrapped about the strips and mandrel and driven by a
driving wheel. In order to provide the continuous inner layer 14,
minor modifications are made in the extrusion apparatus shown in
said Mills et al patent so that a continuous inner layer is
solution extruded onto the inner surface of the spirally wound
outer layer.
The invention will be further illustrated by the following
non-limiting example.
EXAMPLE
A formulation for preparing a soft inner layer 14 was produced by
mixing the following components:
Polyvinyl acetate-methyl alcohol solution 77.12% (50% solids) Solid
polyvinyl acetate polymer 6.28% Plasticizer, phthalate ester 9.93%
Adogen, No. 572, n-oleyl propylene diamine 0.95% Cab-o-sil, silica,
thickener 6.47% Red dye 0.05%
This formulation was solution extruded onto the inner surface of a
spirally wound polyethylene terephthalate tube just after the point
of tube formation utilizing a mandrel and a winding belt to produce
the spirally wound tube. The methyl alcohol solvent was evaporated
leaving a laminated tubular product having a spirally wound
polyvinyl terephthalate outer layer and a relatively soft inner
layer consisting essentially of polyvinyl acetate. After being cut
to suitable lengths, the resulting laminated tubes are useful as
electrical connectors in the manner described previously in this
specification.
While presently preferred embodiments of the invention have been
shown and described with particularity, it will be appreciated that
various changes and modifications may readily suggest themselves to
those of ordinary skill in the art upon being apprised of the
present invention. It is intended to encompass all such changes and
modifications as fall within the scope and the spirit of the
appended claims.
* * * * *