U.S. patent number 3,810,707 [Application Number 05/170,193] was granted by the patent office on 1974-05-14 for joint structure and method.
This patent grant is currently assigned to Minnesota Mining and Manufacturing Company. Invention is credited to James A. Lindlof, Barry F. Tungseth.
United States Patent |
3,810,707 |
Tungseth , et al. |
May 14, 1974 |
JOINT STRUCTURE AND METHOD
Abstract
A semi-rigid flat cover strip, having permanently bonded over
one of its major surfaces a tacky, self-sealing, and
shock-resistant adhesive composition, is applied with its adhesive
covered surface over the adjoined edges of adjacent structural
members to provide a permanent joint structure which is useful, for
example, as a highway construction joint.
Inventors: |
Tungseth; Barry F. (St. Paul,
MN), Lindlof; James A. (St. Paul, MN) |
Assignee: |
Minnesota Mining and Manufacturing
Company (St. Paul, MN)
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Family
ID: |
26865820 |
Appl.
No.: |
05/170,193 |
Filed: |
August 9, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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852256 |
Aug 22, 1969 |
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Current U.S.
Class: |
404/67; 52/395;
404/74 |
Current CPC
Class: |
E01C
11/10 (20130101) |
Current International
Class: |
E01C
11/02 (20060101); E01C 11/10 (20060101); E01c
011/02 () |
Field of
Search: |
;94/18 ;14/16
;52/395,396 ;404/67 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Byers, Jr.; Nile C.
Attorney, Agent or Firm: Alexander, Sell, Steldt &
Delahunt
Parent Case Text
This application is a continuation-in-part of our prior copending
application Ser. No. 852,256, filed Aug. 22, 1969.
Claims
What is claimed is:
1. In a joint structure comprising adjacent structural members
having coplanar surfaces and separated to define a narrow opening
and a cover strip coextensive with the length of said opening and
overlapping its edges, the improvement comprising a weakly cohesive
self-sealing polymeric adhesive composition covering said opening
and adherently bonding together said strip and members, said
adhesive composition having adhesion greater than cohesion and the
following properties when tested as described in the
specification:
whereby said structure is capable of precluding moisture from
entering said narrow opening under damp conditions, permitting
temporary failure caused by separation of said structural members,
and thereafter resealing when said members return to sufficiently
close proximity.
2. The structure of claim 1 wherein said cover strip is a strip of
organic plastic.
3. The structure of claim 2 wherein said organic plastic cover
strip has a plurality of longitudinally aligned pleats spaced
interior from its edges.
4. The structure of claim 1 wherein said structural members are
sections of a concrete highway and said structure forms a highway
expansion joint.
5. The structure of claim 1 wherein said structural members are
sections of a concrete highway and said structure forms a highway
expansion joint.
6. The structure of claim 5 wherein said narrow opening is
channeled to provide a shallow groove having dimensions
substantially the same as those of said strip and being capable of
receiving said adhesive coated strip to bring the outer surface of
said strip into coplanar relationship with said highway strip.
7. The structure of claim 1 including an asphalt covering layer
over said cover strip.
8. The structure of claim 1 wherein said adhesive composition is a
self-healing tacky composition comprising: a major proportion of an
aromatic hydrocarbon process oil having a viscosity of at least
about 250 (SSU/210.degree. F.), an initial boiling point of at
least about 700.degree. F., and an aromatic content (clay-gel
method) of at least about 50%; and a minor proportion of a block
copolymer having an average molecular weight of at least about
85,000 and having the type formula A-B-A wherein the A components
acoount for about 10-40 percent of the total, each A represents a
non-elastomeric vinyl arene polymer block having an average
molecular weight of about 5,000 to about 125,000, and B represents
an elastomeric conjugated diene polymer block having an average
molecular weight of about 75,000 to about 250,000; the amount of
said copolymer being between about 25 and about 50 parts per 100
parts of said oil.
9. The structure of claim 8 wherein said adhesive comprises between
about 35 to about 45 parts of said copolymer per 100 parts of said
oil.
10. The structure of claim 8 wherein said adhesive composition
includes a polyolefin polymer in an amount up to about 30 parts per
100 parts of said copolymer.
11. The structure of claim 8 wherein said adhesive composition
includes a tackifier resin.
12. The structure of claim 8 wherein said adhesive composition
includes a paraffinic mineral oil.
13. In a method of sealing a concrete highway contraction joint
comprising the steps of abrading a shallow channel in the surface
of said highway along both sides of the joint area, placing
adhesive in said channel and pressing a cover strip into said
channel to bring the outer surface of said cover strip into
coplanar relationship with said highway surface, the improvement
comprising using as an adhesive a weakly cohesive self-sealing
polymeric adhesive composition covering said opening and adherently
bonding together said strip and members, said adhesive composition
having adhesion greater than cohesion and the following properties
when tested as described in the specification:
14. The method of claim 13 including the additional step of
covering said cover strip with a layer of asphalt in a thickness
sufficient to obscure said strip and provide a smooth roadway
surface.
Description
This invention relates to sealing of cracks between structural
members and to novel joint structures formed thereby. In one
particular aspect the invention relates to the sealing of highway
contraction joints with semi-rigid flat strip coverings permanently
held in place at the plane of the highway surface by a tacky,
self-sealing and shock-resistant adhesive.
Sealing joints between adjacent structural members such as the
concrete slabs that form a highway has heretofore been a difficult
problem. The problems attendant with such joint sealing could
easily be solved if they were not aggravated by environmental
fluctuations in temperature. In cold weather the concrete slabs
will contract, increasing the width of the opening between them.
This will cause seals formed with many known adhesive compositions
to pull apart. Other adhesive compositions are inadequate for other
reasons, e.g., because they are subject to fracture especially
during cold weather upon being subjected to continuous impact
caused by traffic on the highway, or they are insufficiently tacky
to provide a good seal to such structural materials as
concrete.
It has now been found that a superior joint structure is formed by
applying a strip coated with an adhesive composition provided by
highly aromatic, high-boiling, viscous oils, modified by the
incorporation of restricted amounts of certain block copolymers of
non-elastic vinyl arene and elastic conjugated diene polymers,
together with small amounts of other modifiers as desired. These
adhesive compositions have physical properties which provide
excellent adhesion to concrete, wood, metal, glass, plastics and
other structural materials, and which are particularly useful in
highway construction and maintenance. Unlike the adhesive
compositions employed in pressure-sensitive adhesive tapes, these
adhesives are more adhesive than cohesive.
The adhesive composition has a tacky, self-sealing, and
shock-resistant nature and an adhesion value of at least 10
gm./sq.cm., tensile of at least 4 psi, elongation of at least 100
percent, brittle point of not above 20.degree. F., and slump of not
more than 1/8 inch. This balance of physical properties has been
found to provide a joint structure that is useful under
environmental conditions including the extreme temperature
variations as experienced in the northern states.
The adhesion value of at least about 10 gm./sq.cm. is required for
effective use as a highway sealant. Adhesives having lower adhesion
values could be used in some similar applications but they have a
tendency to part from the surface to which they are applied when
pulled away from such surface. The tensile strength must be at
least 4 psi to prevent excessive flow of the adhesive under
pressure such as would be encountered in highway joint sealing
applications. An adhesive which exhibits excessive flow is forced
out from between the strip and the surface to which it is applied
to leave an insufficient amount of adhesive causing the joint to
fail. Elongation of at least about 50 percent is required if
brittleness is to be avoided; preferably elongation of at least 100
percent is desired. Brittleness is also determined by the brittle
point which must be below about 20.degree. F. Brittle adhesives
will not be sufficiently shock-resistant to provide an adequate
seal for highway use. The adhesive should also have appreciable
resistance to viscous flow (i.e., have no appreciable slump) up to
a temperature of about 140.degree. F., preferably up to about
160.degree. F. Adhesives that have appreciable viscous flow at
these temperatures are easily displaced from the joint structure
causing it to fail. Furthermore, the adhesive of the invention
preferably is more adhesive than cohesive and has a self-sealing
nature, i.e., if it fails temporarily at isolated areas by internal
splitting or separation, e.g., during cold weather when the opening
of the joint widens, it will reseal, upon narrowing of the opening,
to form a continuous adhesive mass. An adhesive composition having
the above specified adhesion value, tensile strength, elongation,
brittle point and slump will inherently have a tacky and
shock-resistant nature.
In the preferred adhesive compositions, the aromatic oils found
useful are high-boiling viscous materials having an initial boiling
point of at least about 700.degree. F. and an SSU viscosity at
210.degree. F. of at least about 250. Analysis by the clay-gel
method indicates an aromatic content of at least about 55 percent.
Many of the "Dutrex" aromatic hydrocarbon process oils of Shell
Chemical Company fall within such classification.
Useful as modifiers of the aromatic oils are block copolymers
having the type formula A-B-A, wherein each A is a non-elastomeric
polymer block of a vinyl arene and having an average molecular
weight of about 5,000 to about 125,000 or even higher, and B is a
polymer block of a conjugated diene and having an average molecular
weight of about 75,000 to about 250,000. The total A component is
between about ten and about forty percent, with preferred examples
being between about fifteen and about thirty percent of polystyrene
A blocks and the balance being polyisoprene or polybutadiene B
blocks. Certain of the Shell "Kraton" block copolymers are typical
examples of such materials. The amount of such copolymer is between
about 25 to 50, preferably 35 to 45 parts per 100 parts of the
process oil.
The styrene-diene block copolymers are soluble in the aromatic
process oils and may be dissolved therein by prolonged heating and
mixing, but with degradation of the polymer. Some means of
protecting the latter component is therefore required. The hindered
phenol antioxidants are useful for this purpose, and they offer
continued protection of the composition during subsequent exposure.
Amounts of approximately 1 percent by weight on the weight of the
polymer are ordinarily adequate, but greater or lesser amounts may
be used. Furthr protection during mixing and compounding may be
achieved by accomplishing these operations under an inert
atmosphere of nitrogen or carbon dioxide.
The tendency of the aromatic process oils to crystallize at low
temperatures and to cause embrittlement or loss of shock resistance
in the adhesive mass may be reduced by selection of the lower
viscosity oils or by addition of minor proportions of
non-crystallizing parafinic oils or polymers. The amount of such
additives must be small in order to avoid excessive softening and
flow of the adhesive at high use temperatures, a tendency which
results also when using the lower molecular weight or low styrene
content block copolymers.
The addition of small amounts of compatible low molecular weight
polyolefin polymers, e.g. polyethylene, serves also as a means of
overcoming softening and plastic flow in these compositions, but
has a tendency to reduce the adhesion and elongation values. The
proportion of such polyolefin additive is therefore to be
restricted to not greater than 30 parts, or preferably 25 parts,
per 100 parts of the copolymer.
The aromatic process oils are ordinarily adequately tacky and
provide good adhesion to most surfaces. Where additional tackiness
is required it may be achieved by the incorporation of small
amounts of compatible tackifier resins such for example as
polyterpene resin or other non-crystallizing resinous tackifiers,
of which a number are included in the list of tackifying resins
given in U.S. Pat. No. 3,239, 478.
In the drawing,
FIG. 1 is a view in perspective of a cover-strip product useful for
the highway joint structures of this invention,
FIG. 2 is a partial cross-sectional elevation of a highway
contraction joint area of FIG. 1, and
FIG. 3 is a partial cross-sectional elevation of another embodiment
of a highway joint.
The cover-strip 10 consists essentially of a semi-rigid thin
plastic or metal strip 11 having chamfered longitudinal edges and
coated over one surface with a coterminous uniform layer of
adhesive 12. A removable liner or cover-strip 13 having a surface
release coating 14 covers the adhesive surface during storage and
shipping.
FIG. 2 illustrates abutting sections 15 of a concrete highway
separated by a narrow crack-like opening which may or may not have
been filled with an asphalt-based filler 16. The upper surface of
the highway carries a thin water-resistant layer 17 which is ground
away, together with a thin layer of the concrete, to form a shallow
trench 18. The cover-strip 10, with liner 13 removed, is laid along
this trench and is pressed into place. The adhesive layer is
thereby brought into full adhesive contact with the surfaces
defining the trench and with the edges of the coated strip.
In another aspect of the joint structure of the invention,
illustrated by FIG. 3, cover-strip 10 is applied directly to a
narrow crack between abutting concrete sections 15 which were
previously one but have broken apart. Adhesive covered cover-strips
are applied to all such cracks in a section of highway and layer of
asphalt 19 is applied thereon to obscure the cover-strips and
provide a smooth roadway surface.
In warm weather the adhesive is sufficiently firm to resist further
flow under heavy traffic, and the vinyl strip protects the adhesive
from excessive localized pressures and from pickup of loose pebbles
or sand. The assembly is also fully waterproof and permits no entry
of water through the crack-like opening. In cold weather the
concrete slabs contract, increasing the width of the opening and
pulling away from the filler 16. Plastic flow of the adhesive is
sufficient to avoid breakage or loss of the protective vinyl strip.
In extremely cold weather the adhesive may fail temporarily, but
its self-sealing properties are such that subsequent traffic
recoheres the surfaces and renews the bond. During the next period
of warmer temperatures the slabs again expand. The protective cover
is maintained throughout repeated cycles.
The adhesive may be spread directly on the surface of the vinyl
strip or on any other desired substrate either at an elevated
temperature or suspended or dissolved in a volatile vehicle. A
preferred procedure involves coating the adhesive on a removable
carried sheet, e.g. by hot spreading using a heated spreader bar
and base plate, and then transferring the adhesive layer to any
desired surface and removing the carrier.
The following specific Examples, in which all proportions are in
parts by weight unless otherwise noted, will further illustrate the
invention.
EXAMPLE 1
A preferred adhesive composition is prepared by first heating to
270.degree. C. 70 parts of aromatic hydrocarbon process oil boiling
above 700.degree. F. and having an SSU viscosity at 210.degree. F.
of 478 and analyzing 57.6 percent aromatics by the clay-gel method
("Dutrex No. 957" oil). Under an inert atmosphere and with
continued agitation there is then added 0.3 part of liquid hindered
phenol antioxidant ("Wingstay T") followed by 30 parts of an A-B-A
type styrene-isoprene block copolymer containing 28% polystyrene
("Kraton 1108"). Solution of the copolymer in the hot oil is
accomplished in about 3 hours of mixing at the elevated
temperature. There is then added 6 parts of high melting
polyterpene resin tackifier ("Piccolyte S-115"), followed by 5
parts of powdered polyethylene resin having a melt index of 22
("Microthene MN 725-20") and 1 part of carbon black.
The adhesive composition is tested as hereinafter described for
adhesion value, tensile strength, elongation, brittleness and
resistance to viscous flow, with results as follows:
Adhesion 20 gm./sq.cm. Tensile 160 psi Elongation 1500% Brittle
Point 5.degree. F. Slump none (10 min. at 160.degree. F.)
the well-mixed plastic adhesive composition is then smoothly spread
over the surface of a silicone-treated paper liner using a knife
coater and at a temperature of about 250.degree. F., which is
sufficient to maintain a spreadable consistency. After cooling, the
coating has a thickness of approximately 0.06 inch.
While the coating is still at a relatively high temperature, or
after reheating the cooled material to about 150.degree. F., the
coated web is pressed against flat strips of rigid pigmented
unplasticized extruded vinyl chloride resin having cross-sectional
dimensions of 0.096 .times. 3.0 inch and chamfered edges. The
coating adheres firmly to the strips and after cooling the treated
paper liner may be stripped away, leaving a smooth glossy tacky
surface.
A highway contraction joint structure is prepared on a section of
concrete highway containing a contraction joint area by first
grinding away the surface to a width of 31/8 inch and depth of 0.15
inch along the joint area. The area is blown free of loose dust,
leaving a clean flat freshly exposed concrete surface extending
equally from both sides of the joint, which in this instance
contains residual asphalt filler material. The strips of coated
vinyl resin as laid end-to-end along the groove and are pressed in
place by rolling with a 3 inch diameter, 3 inch width
smooth-surfaced steel roller weighted to a total of 300 lbs. The
adhesive composition adheres firmly to the concrete. It flows
beyond the edges of the vinyl strip to fill the edge voids between
the strip and the edges of the groove, leaving the upper surface of
the strip in the plane of the highway surface. The highway is
immediately opened to traffic. The seal is highly resistant to
traffic and maintains a water-proof joint under prolonged service
under both summer and winter conditions as experienced in the
northern states.
EXAMPLE 2
Seventy parts of process oil having an SSU viscosity at 210.degree.
F. of 516, an initial boiling point of 740.degree. F., and an
aromatics content of 61.8 weight percent by the clay-gel method
("Dutrex 959") is heated to 240.degree. F. To the hot oil is added
0.25 part of antioxidant, 25 parts of styrene-isoprene block
copolymer containing 14% styrene ("Kraton 1107"), 5 parts of
rubbery polyisobutylene ("Vistanex"), and 3 parts of low mol. wt.
polyethylene ("Microthene 702"), each polymer in turn being
completely dissolved before the next addition. The composition
exhibits the following properties:
Adhesion 10 gm./sq.cm. Tensile 5 psi Elongation 1900 % Brittle
Point -30.degree. F. Slump none
It is applied to silicone-treated paper liner and transferred to
strips of rigid vinyl resin which are then applied over a suitably
prepared one inch width partially asphalt-filled contraction joint
in a concrete highway, all as described under Example 1. The seal
affords complete protection under all extremes of weather and
traffic except for occasional slight water penetration between
abutting strip ends.
EXAMPLE 3
The adhesive composition of Example 2 is similarly applied in
0.04-inch thickness to extruded strips of filled polypropylene
containing 30% asbestos and having substantially the thermal
expansion of concrete. The strips are 0.04 .times. 5 .times. 240
inches. The strips are laid over contraction joints and midpanel
cracks in a concrete highway, being adhered to the wire-brushed
cleaned surface. The highway is then resurfaced with bituminous
concrete or "blacktop." The blacktop coating is protected from
moisture normally rising through the cracks in the substrate and
which loosens the blacktop layer at such areas. Highway maintenance
requirements are greatly reduced.
EXAMPLE 4
A mixture of 52.5 parts of the process oil as used in Example 2 and
17.5 parts of a process oil having an SSU viscosity at 210.degree.
F. of 294, an initial boiling point of 700.degree. F., and an
aromatic content of 57.6 percent ("Dutrex 916") is heated to
270.degree. F. To the mixture is added 0.3 part of the antioxidant
and 30 parts of the styrene-isoprene block copolymer of Example 1,
and 3 parts of polyethylene. The following test values are
obtained:
Adhesion 35 gm./sq.cm. Tensile 180 psi Elongation 1800 % Brittle
Point -11.degree. F. Slump none
A 0.008 inch coating of the adhesive is transferred to a 0.002 inch
polyvinyl fluoride film. The coated film in widths of 3 inches is
laid over 3/4 inch junction line areas between concrete slabs
forming a factory roof. No leakage of water during heavy rains is
observed after prolonged exposure, whereas severe leakage occurs
through comparable joints sealed with conventional neoprene-based
sealing compositions after a single seasonal cycle.
EXAMPLE 5
A composition containing 67 parts of process oil as in Example 2,
and 0.3 part of antioxidant, 30 parts of block copolymer, 3 parts
of polyethylene and 6 parts of terpene resin all as defined in
Example 1, is further modified by the addition of 3 parts of heavy
mineral oil ("Nujol"). The compounding and coating procedures are
as described in the previous Examples. The properties are as
follows.
Adhesion 79 gm./sq.cm. Tensile 150 psi Elongation 1700 % Brittle
Point 12.degree. F. Slump none (trace in 15 min. at 160.degree.
F.)
An 0.008 inch coating is applied to 0.004 inch flexible vinyl resin
film which is then employed as a repair covering over cracks and
joints in a concrete swimming pool, the painted concrete surface
being first wire-brushed and washed. The strip is applied so as to
extend at least 1/2 inch beyond each side of the opening. In those
areas where the surface cannot first be dried due to excessive
ground water, a priming mixture consisting of one part of the
adhesive composition in 3 parts of a 4:1 mixture of methylethyl
ketone and ethyl alcohol and to which is added 5 percent of wetting
agent is first painted over the surface. Hydroxylated soybean
lecithin is a preferred example of a suitable wetting agent. The
pool is effectively sealed and the seals remain intact under long
continued operation.
The same priming composition is useful in forming an adherent
water-proof seal between vinyl resin moldings and glass or metal,
as in automotive window construction. The composition may
alternatively but less desirably be applied from solution in
aromatic or chlorinated aliphatic hydrocarbon solvents or from
aqueous suspension. The solvent-free adhesive is also useful in
extruded rod or flat strip form as a sealing or caulking strip for
windows and other applications.
EXAMPLE 6
A blend of 65 parts of process oil, 0.25 part of anti-oxidant, and
10 parts of mineral oil all as identified in Example 5, together
with 25 parts of styrene-butadiene block copolymer containing 28%
styrene ("Kraton 1101"), is prepared by mixing at 260.degree. F.
and in accordance with previously described procedures. The
properties of the composition are as follows:
Adhesion 22 gm./sq.cm. Tensile 4 psi Elongation 100% Brittle Point
-4.degree. F. Slump 1/8 inch
Used as a coating on rigid polyvinyl chloride strips to seal
concrete highway contraction joints, this composition flows
slightly under traffic pressure in hot weather but is otherwise
satisfactory. Reduction or elimination of the mineral oil content
increases the adhesion and resistance to flow but results in
brittleness at low temperature. Either composition is fully
effective when not subjected to extremes of temperature.
EXAMPLE 7
Seventy two parts of process oil having an SSU viscosity at
210.degree. F. of 478 and analyzing 57.6 percent aromatics by the
clay-gel method ("Dutrex No. 957") is heated to 240.degree. F. To
the hot oil is added 0.25 parts of antioxidant, 75 parts of
styrene-isoprene block copolymer containing 28% polystyrene
("Kraton 1108"), 3 parts white mineral oil, 6 parts of polyester
gum ("Vinsol"), and 3 parts of low molecular weight polyethylene
("Microthene 725-20"), each polymer in turn being completely
dissolved before the next addition, producing an adhesive
composition having the following properties:
Adhesion 40 gm./sq.cm. Tensile 160 psi Elongation 1500% Brittle
point -20.degree. F. Slump None
A flat ribbon, 4 inches wide and 0.040 inch thick, of completely
amorphous, fully cross-linked, carbon-black-filled, polyether
polyurethane having a softening point of 200.degree. F., melt
temperature of 390.degree. F., ultimate tensile strength of 5,500
psi, ultimate elongation of 250-300%, and flexibility of
-100.degree. F., ("Estane" 58300) is extruded at 325.degree. F. The
hot ribbon is formed on matched chill rolls to provide a pleated
structure having three centrally located longitudinally aligned
pleats measuring 1/4 inch on a side, leaving a 11/4 inch flat area
on each edge of the ribbon.
A 1 inch wide, 0.040 inch thick layer of the above-described
adhesive was coated on a silicone-treated paper liner and
transferred to the flat edge areas on the same side of the ribbon.
The adhesive bearing pleated strip was applied in a 72-foot length
to concrete roadway expansion joint that normally underwent unusual
expansion daily due to its thin nature. The opening between the
adjacent concrete structural members have a daily change from 1/2
inch in width to 11/2 inch in width. The sharp edges of the ribbon
are sloped by application thereon of a viscous moisture curing
polyurethane ("Deck Coating" Nos. 4833 and 5875). A waterproof
joint structure was maintained for a period of 30 days under low
speed traffic conditions. The joint structure, because of the
nature of the adhesive, was capable of accommodating lateral
movement of the ribbon caused by differential expansion of the
ribbon and of the cement to which it was applied, as well as the
dynamic movement of the concrete segments.
ADHESIVE TESTING
The adhesion value is obtained at room temperature by carefully
placing the smooth flat end of a steel rod against the surface of
the adhesive coating under defined conditions and measuring the
force required to lift the rod from the adhesive mass, a portion of
which is found to remain adhered to the rod. The rod is 1/16 inch
in diameter, is applied at a weight of two grams, and is removed
slowly after a dwell time of one second. An adhesive coating
thickness of 0.02 inch is employed in critical determinations.
Tensile and elongation at room temperature (about 72.degree. F.)
are determined at break, using a narrow flat strip of the adhesive
produced by spreading on a release liner to a thickness of
approximately 1/8 inch, removing the coating by careful hand
manipulation after first cooling if necessary, powdering the
surface to permit cutting, and cutting to a dumb-bell shape having
a central section of 1/8 inch width, for testing on an Instron
tensile test machine using an initial marked length of 1/2 inch and
a machine speed of 12 in./minute. Results are calculated to the
initial effective dimensions of the strip. Tensile strength must be
at least about 4 psi if excessive flow under pressure is to be
avoided.
Brittleness is also determined on a narrow unsupported strip of the
composition, by determining the temperature at which a sudden
change occurs in the ability of the strip to overcome twisting. As
defined for the Gehman test, similar to ASTM test procedure D 1053,
the specimen is 0.1 .times. 0.125 .times. 1.5 inches in dimensions.
It is clamped between jaws spaced 1 inch apart and is brought to
constant temperature. The upper jaw is supported on a torsion wire
from a rotatable support which is rotated 180.degree. to rotate a
pointer attached to the jaw through an arc of between 120.degree.
and 170.degree.. The pointer slowly returns toward its former
position and its position at 10 seconds is determined as the Gehman
value. The test is repeated over an appropriate range of
temperatures, and a graph of temperature vs. Gehman value is drawn.
The point of intersection of the two straight portions of the graph
is taken as the brittle point.
For the slump test, a narrow strip of the adhesive composition is
pressed against a flat wooden surface and supported at an angle of
60.degree. to the horizontal in an oven under specified time and
temperature conditions, and the extent of flow along the panel
between the initial and final positions of the lower edge is
determined to the nearest 1/64 inch. The strip is 1/8 inch thick
and 1/2 inch wide and heating is continued for 10 minutes at
140.degree. F. unless otherwise indicated.
* * * * *