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The present invention relates to a hot melt adhesive composition, to method
of filling voids with the adhesive composition and to articles filled or
coated with the hot melt adhesive composition. More particularly, it
refers to block copolymers containing glass fibers and a finely divided
metal powder, to a method of filling voids with such compositions and to
articles, filled or coated with the compositions.
Hot melt adhesives are well known in the prior art. These materials are
conveniently applied to a substrate in the molten state and upon cooling
form an adhesive bond. However, a deficiency common to most of the hot
melt adhesives of the prior art is their tendency to soften and flow at
elevated temperature, as, for example, 70.degree. to 100.degree. C. with a
resulting loss of bond strength. Consequently, these materials are not
suitable for use over a broad temperature range.
Attempts to upgrade the softening and flow temperatures have involved using
very high molecular weight resinous materials and/or crosslinking of the
resin. These methods have resulted in materials with higher softening
points and flow temperatures. However, in most cases the resulting
material was not adapted to thermal processing because its higher
molecular weight and/or crosslinked structure engendered extremely high
application viscosity. Thus, these materials were not suitable for use as
hot melt adhesives.
In the manufacture and repair of metal bodies such as automobiles and
appliances, solder compositions containing lead are frequently used to
fill cavities and voids. These lead solders are extremely dense and can
add a significant increment to the weight of the metal body. They present
a health hazard which mandates special handling to protect workers engaged
in the soldering and cavity filling operations. Curable adhesives such as
epoxies are generally unsatisfactory for such cavity and void filling
applications because they require careful metering of the components to
provide good physical properties and bond strength, because they take too
long to cure a sandable state and because they have rather poor weather
resistance. Conventional hot melt adhesives are also unsatisfactory for
cavity and void filling applications because they cannot be sanded rapidly
at assembly line speed, they do not readily accept paint, exhibiting
"bleed-through", and they do not withstand the high temperatures necessary
for the subsequent cure of paint overcoats. "Bleed-through" or
"telegraphing" is the term used to describe the revelation of difference
in composition of the substrate when it has been painted, caused by a
difference in reflectivity between the painted metal and the painted
adhesive composition.
U.S. Pat. No. 3,650,999 discloses block copolymer comprising hard polyester
segments and soft polyamide segments having improved adhesion and high
temperature performance obtained by reacting a crystalline polyester, a
C.sub.18 to C.sub.54 polycarboxylic acid and a primary diamine. This
poly(ester-amide) in common with other hot melt adhesives has deficiencies
in creep resistance at temperatures above 150.degree. C. in the range up
to 205.degree. C. and above and in shrinkage when the hot melt is cooled
to room temperature after application. These deficiencies have been
overcome to a considerable degree by incorporating a metal powder into the
block copolymer to yield a cavity filling composition which possesses good
sandability and paint acceptance. However, the metal powder copolymer
composition can lack adequate impact resistance especially at low
temperatures and can sag excessively at elevated temperatures. Attempts to
improve the impact resistance by introducing an energy-absorbing rubber
reinforcement were generally unsuccessful and added a further complication
of binding of the sanding disc, making sanding extremely difficult.
The present invention is directed to an adhesive composition of improved
impact resistance at low temperatures, which is less dense and toxic than
lead solder, forms a strong bond to metal and painted metal substrates,
withstands extremes of humidity and temperature, has sag resistance at
elevated temperatures, is readily trowelled to fill a cavity, sets rapidly
to a sandable state, is easily sanded smooth and accepts paint without
"bleed-through".
The adhesive composition comprises a block copolymer, aluminum powder, and
glass fiber; wherein the block copolymer is selected from the group
consisting of copolyesters, copolyamides, copoly(esteramides) and
copoly(ether-esters) melting at a temperature of at least about
150.degree. C., having from about 30 to about 70 weight percent of hard
segments and from about 70 to about 30 weight percent of soft segments,
wherein the weight ratio of block copolymer to aluminum powder and glass
fiber is in the range of about 3:7 to about 3:2, wherein the weight ratio
of block copolymer to glass fiber is at least about 2:1 and wherein the
weight ratio of glass fiber to aluminum powder is at least about 1:9.
Another aspect of the invention is directed to substrates coated or filled
with the adhesive composition and yet another aspect is directed to a
method of filling a cavity in a substrate which comprises applying the
adhesive composition as a hot melt to fill the cavity, cooling the
adhesive composition below the crystallization temperature of the block
copolymer and sanding the adhesive composition to provide a surface even
with the surrounding substrate.
The block copolymer of the adhesive compositions of the present invention
is selected from the group consisting of copolyesters, copolyamides,
copoly(ester-amides) and copoly(ether-esters) melting at a temperature of
at least about 150.degree. C., having hard segments and soft segments to
provide a balance of physical properties and processability. These are
considered to exist in microscopic domains within the bulk mass of
copolymer resin to provide a heterophase system in which the copolymer
will have physical properties reflecting the properties which the
respective segments would manifest independently. By control of the
relative size, proportions, crystallinity and crystal melting points of
the segments, the tack, open time and bond strength of the adhesive can be
controlled. The hard segments contribute crystalline blocks to the
copolymer so that optimum bulk physical properties such as tensile
strength and stiffness can be achieved without incurring the disadvantage
of high processing viscosity.
The hard or crystalline segments can be polyester or polyamide of weight
average molecular weight of from about 400 to about 16,000 to ensure that
the segment will contribute the optimum ordered structure to the final
polymeric product. Polyesters and polyamides with a weight average
molecular weight of less than about 400 have a short chain length and
cannot contribute the necessary ordered structure to the final polymeric
product which also comprises soft segments. Polyesters and polyamides with
a weight average molecular weight of greater than about 16,000 may require
excessive reaction times or temperatures to form the final block copolymer
leading to degradation of the polymer and a subsequent loss in adhesive
properties. To ensure that the final polymeric product has excellent
thermal properties such as resistance to flow at elevated temperatures the
melting point of the hard polyester or polyamide segment should be at
least about 180.degree. C. Preferably, the melting point is in the range
of from 200.degree. C. to 270.degree. C.
The hard or crystalline polyester segments of the block copolymer are
condensed from at least one aliphatic or alicyclic diol having from 2 to
10 carbon atoms and at least one alicyclic or aromatic dicarboxylic acid
having from 8 to 20 carbon atoms selected to give a melting point in the
desired range.
Representative examples of such acids are terephthalic acid, isophthalic
acid, hexahydroterephthalic acid, the naphthalic acids, such as 2,6-,
2,7-, 2,8-, 1,5- and 1,4-naphthalene dicarboxylic acids and other such
acids which form high melting polyester resins. Examples of glycols are
ethylene glycol, propylene glycol, tetramethylene glycol, neopentylene
glycol, 1,4-cyclohexane diol, 1,4-cyclohexane dimethanol and other such
glycols. High melting polymers containing components such as
2,2-dimethylpropane diol, form polyesters which have melting points above
234.degree. C. Mixtures of the foregoing polyesters can also be used.
Preferably, a polyester from the following group can be used to provide the
hard segments of the block copolymer:
Poly(ethylene terephthalate/isophthalate), 100/0 to 75/25;
Poly(ethylene/hexamethylene terephthalate), 100/0 to 75/25;
Poly(ethylene/neopentylene terephthalate), 100/0 to 75/25;
Poly(tetramethylene terephthalate/isophthalate), 100/0 to 75/25;
Poly(tetramethylene/hexamethylene terephthalate), 100/0 to 75/25;
Poly(tetramethylene/neopentylene terephthalate), 100/0 to 75/25;
Poly(ethylene/propylene terephthalate), 100/0 to 60/40; and
Poly(tetramethylene 2,6-naphthalate/terephthalate), 100/0 to 75/25; etc.
When the hard polyester segments comprise polyethylene terephthalate, the
molecular weight range corresponds to an inherent viscosity range of about
0.05 to about 0.7 determined at 25.degree. C. with a solution of 0.5 g/100
ml in a solvent pair consisting of phenol and sym-tetrachloroethane in the
weight ratio of 60:40.
The hard or crystalline polyamide segments of the block copolymer can be
condensed from at least one aliphatic or alicyclic diamine having from 2
to 12 carbon atoms and at least one aliphatic or alicyclic dicarboxylic
acid having from 2 to 12 carbon atoms selected to provide a polyamide with
a melting point in the desired range. Examples of diamines include
ethylene diamine, 1,3-propane diamine, 1,4-butane-diamine, 1,5-pentane
diamine, hexamethylene diamine, 1,10-decanediamine, cyclohexanediamine,
etc. Examples of acids include oxalic, malonic, succinic, glutaric,
adipic, pimelic, suberic, azelaic, and sebacic acids. The hard or
crystalline polyamide segments of the block copolymer can be obtained by
polymerization of .omega.-aminocarboxylic acids containing from 2 to 10
carbon atoms such as aminoacetic acid, 3-aminopropionic acid,
4-aminobutyric acid, 6-aminohexoic acid, 10-aminodecanoic acid, etc.
Polymerization of lactams such as .epsilon.-caprolactam provides a route
to several of such polyamides. Among the preferred polyamides are
poly(hexamethylene adipamide) and poly(.epsilon.-caprolactam).
The soft, amorphous or low melting segments of the block copolymer
contribute wettability, elasticity and rubber character to the copolymer.
They can be polyester, poly(ether-ester) or polyamide and are generally of
weight average molecular weight in the range of about 300 to about 16,000
and possess a glass transition temperature less than about 50.degree. C.
and more preferably in the range of about -30.degree. to about 40.degree.
C.
The soft polyester segments of the block copolymer can be condensed from an
aliphatic or alicyclic diol having from 4 to 10 carbon atoms and an
aliphatic, alicyclic or aromatic dicarboxylic acid having from 4 to 54
carbon atoms selected to provide a polyester with a glass transition
temperature in the desired range. They can be formed by reacting a
polylactone diol of number average molecular weight in the range of about
350 to 6000 with an aliphatic, alicyclic or aromatic dicarboxylic acid
having from 4 to 54 carbon atoms. Poly(ether-ester) segments can be
prepared by condensing a poly(alkylene ether) glycol of number average
molecular weight in the range of about 350 to 6000 in which the alkylene
groups have from 2 to 10 carbon atoms with an aliphatic, alicyclic or
aromatic dicarboxylic acid having from 4 to 54 carbon atoms. Polyamide
segments can be prepared by condensing an aliphatic or alicyclic diamine
having from 2 to 12 carbon atoms with a mixture of an aliphatic or
alicyclic dicarboxylic acid having from 4 to 54 carbon atoms and at least
40 weight percent of an aliphatic dicarboxylic acid having from 18 to 54
carbon atoms.
The block copolymers are prepared by a one step or two step method. In the
one step method the components which form the hard or soft segments are
polymerized in the presence of a prepolymer of the soft or hard segments
respectively. In the two step method the hard segments and soft segments
are prepared separately as prepolymers and then condensed together.
The preferred block copolymer component of the present invention contains
about 30 to about 70 percent by weight of hard segments and conversely
about 70 to about 30 percent by weight of soft segments. It is further
characterized as having a weight average molecular weight in the range of
about 5500 to about 30,000, more preferably in the range of about 8000 to
about 20,000 for an optimal balance of physical properties and
processability. The melting point of the copolymer component is above
about 150.degree. C. and is preferably in the temperature range of about
155.degree. to about 225.degree. C. for ease of processing without
degradation of the copolymer. The glass transition temperature associated
with the soft segments of the copolymer is generally less than about
50.degree. C. and is preferably in the range of about -30.degree. to
40.degree. C. to contribute wettability, elasticity, and rubber character
to the copolymer. The melting point and glass transition temperature are
conveniently determined with a duPont differential thermal analyzer Model
DTA 900 with the scanning calorimeter attachment, employing a 5 to 25 mg
sample heated at a rate of 20.degree. C. per minute, in a nitrogen
atmosphere. The melt viscosity of the copolymer at 232.degree. C. is
preferably less than 150,000 centipoise at a shear rate of 4 sec.sup.-1
and is preferably in the range of about 25,000 to 100,000 centipoise.
The most preferred group of block copolymers are block copoly(ester-amides)
of the type described in U.S. Pat. No. 3,650,999. They comprise hard
segments of polyester as described hereinabove, and soft segments of
polyamide formed by condensing a C.sub.18 to C.sub.54 dicarboxylic acid
and a C.sub.2 to C.sub.10 aliphatic or alicyclic primary diamine. The
dicarboxylic acids include the "dimer acids" from dimerization of
unsaturated aliphatic monocarboxylic acids, e.g., linoleic acid, available
commercially as mixtures of monobasic, dibasic and tribasic acids
containing up to 10 weight percent of monobasic and tribasic acids. The
aliphatic or alicyclic diamines include ethylene diamine, 1,3-diamine,
1,4-butanediamine, 1,5-pentane diamine, hexamethylene diamine,
1,10-decane-diamine, cyclohexanediamine, 2,2-dimethyl-1,3-propane diamine,
etc.
Optionally up to 60 percent by weight of a linear aliphatic dibasic acid
having from 4 to 17 carbon atoms may be substituted for a corresponding
amount of the C.sub.18 to C.sub.54 polycarboxylic acid used to prepare the
soft polyamide segments of the polyesteramide. Examples of these acids
include oxalic, succinic, adipic, pimelic, suberic, azelaic, sebacic,
dodecanedioic and thapsic acids. The advantage of substituting the C.sub.4
to C.sub.17 acids for the C.sub.18 to C.sub.54 acids is to provide a more
heterogeneous character to the polyamide segments of the polymer and to
modify the glass transition temperature.
The second component of the adhesive composition is a finely divided
aluminum powder added to improve the creep resistance of the block
copolymer and the sandability. It may be of average particle size in the
range of about 0.2 micron to about 150 microns and is preferably of
average particle size in the range of about 4 to about 50 microns. It is
preferred to use an atomized aluminum of generally spheroidal shape
particularly when the adhesive composition is used for cavity filling
since it allows the hot melt composition to be readily smoothed and
burnished when it is sanded. In general, plate-like, acicular or
multi-faceted granular aluminum powders are unsatisfactory, surprisingly
causing high viscosity in the hot melt and "blinding" or filling and
occlusion of sand paper when the adhesive composition is sanded.
In addition to improving the creep resistance and sandability of the
adhesive composition, the aluminum powder improves the rate of melting of
the adhesive composition, allows the composition to be applied and spread
or trowelled more easily with less pressure, imparts longer "open" time
between application of the hot melt and closing of the bond and higher
"green" strength of faster onset of bond strength, and reduces the degree
of shrinkage of the adhesive composition when it is cooled from the hot
melt temperature to ambient temperature.
When the adhesive composition comprises only the block copolymer and the
aluminum powder, the impact resistance tends to be low particularly at low
temperatures such as -30.degree. C. and the molten composition tends to
sag at the elevated temperatures at which it is applied. Addition of glass
fiber as the third component of the adhesive composition improves the
impact resistance at low temperatures, reduces the tendency of the
adhesive composition to sag at elevated temperatures and permits greater
latitude in overcoming shrinkage and minimizing coefficient of expansion
differences with the substrate. The glass fiber is of the type
conventionally used for reinforcement of thermoplastic resins. It is
preferred to use relatively soda-free glasses comprising lime-aluminum
borosilicate glass such as types "C" and "E" glass. The glass fiber should
preferably be in the form of milled fibers or chopped fibers of average
length in the range of about 1/32 inch (0.8 mm) to about 1/4 inch (6.4 mm)
and longer, and of diameter in the range of about 2 to about 20 microns.
The preferred average length is in the range of about 1/16 inch (1.6 mm)
to about 1/4 inch (6.4 mm).
The inorganic components of the adhesive composition may optionally be
treated with an effective amount of coupling agent by methods well known
to those skilled in the art before or while being blended into the block
copolymer. Such coupling agents include organosilane coupling agents
exemplified by triethoxy vinylsilane, vinyl methyl dichlorosilane,
2-(trimethoxysilyl)ethyl methacrylate, 3-amino-1-triethoxysilyl-propane,
etc.; organotitanium coupling agents such as the alkyl alkanoyl titanates
exemplified by C.sub.1 to C.sub.40 alkyl stearyl titanates; fatty acids
exemplified by oleic and stearic acid; fatty amides exemplified by
oleamide and stearamide and chromium compounds exemplified by methacrylato
chromic chloride. These coupling agents can cause a significant reduction
in the melt viscosity of the polymer filler mix, can improve the wetting
and dispersion of filler, and can enhance the physical properties of the
adhesive composition.
The ratio of the three components of the adhesive composition is selected
so that the desired balance of adhesion, sag resistance, workability,
impact resistance and sandability is achieved. Excessive amounts of glass
fiber should be avoided since they contribute to very high melt viscosity,
cause poor workability as manifested by the difficulty with which the
composition can be spread or trowelled and feathered onto a substrate and
decrease the adhesion of the adhesive composition to the substrate. It is
therefore, preferred to select the components so that the weight ratio of
block copolymer to inorganic components, i.e. to the sum of aluminum
powder and glass fiber, is in the range of about 3:7 to about 3:2 and is
preferably in the range of about 1:2 to about 1:1; the weight ratio of
block copolymer to glass fiber is at least about 2:1, and is preferably in
the range of about 2:1 to 10:1; and the weight ratio of glass fiber to
aluminum powder is at least about 1:9 and is preferably in the range of
about 1:4 to about 1:1. The component ratios are preferably selected so
that the melt viscosity of the hot melt composition is less than about
300,000 and preferably less than 150,000 cps. at a temperature of
250.degree. C. and a shear rate of 4 sec.sup.-1 measured in a Brookfield
Thermocel Unit Model HBT. Above 300,000 centipoise melt viscosity, the hot
melt is difficult to apply and spread, and tends to be dragged from the
point of application.
The hot melt composition is formed by mixing the aluminum powder and the
glass fiber with the melted polymer in any convenient way such as by melt
blending in a blender-extruder. A good mix is considered to have been
obtained if the filler particles are evenly distributed through the melt.
In poor mixes, the filler particles are not adequately wet by the melt,
and tend to be unevenly distributed, remaining aggregated within the melt.
Melt stability of the mix is determined by maintaining the mix at
216.degree. C. for two hours. If the melt viscosity changes less than
.+-.10 percent during this time, the mix is considered to have melt
stability.
Creep resistance of the compositions of the present invention is determined
by observing the sag of a 10 to 15 gram sample of the composition placed
on an aluminum plane inclined at 60.degree. to the vertical. The
observations are carried out at 175.degree. C. and 205.degree. C. Creep or
sag in less than 60 minutes at the designated temperature is recorded as a
failure to meet the test.
Impact strength is determined by applying the composition as a hot melt at
500.degree. F. (260.degree. C.) to a smooth steel panel 7.5 cm.times.22.5
cm to provide a strip 4 cm wide and in the range of 25 to 250 microns
thick. The panels are conditioned for 24 hours at -30.degree. C. One lb.
(454 g) steel balls are dropped onto the strip of composition from heights
of 18 inch (46 cm) and 36 inch (92 cm). The impact is repeated three times
at 15 minute intervals. If chipping or cracking of the composition or
separation from the steel panel occurs, the composition is considered to
have failed the test.
Similar test panels are prepared for testing of the sandability of the
composition. In the preparation of the panels, the ease of flow of the hot
melt composition is observed and its ability to be spread or trowelled to
provide a smooth cohesive strip is noted. The panel is cooled to room
temperature and a disc sander, 12.5 cm diameter, with 80 grit medium
tungsten carbide abrasive, is applied to the composition at 1000 rpm to
smooth and feather the composition. If the surface of the composition
becomes smooth enough to accept paint without "telegraphing" or showing a
difference in reflectivity between the painted steel and the painted
composition, and without blinding or blocking the abrasive surface of the
sander, the composition is rated sandable.
Depending upon the particular substrate and especially when the substrate
is bare metal, it can be advantageous to apply a primer coat to improve
the adhesion of the hot melt composition. Suitable primers include the
commercially available primer coatings, and the etherified
methylolmelamines described in U.S. Pat. No. 4,053,682. Also suitable, can
be organic solvent solutions and aqueous dispersions of the block
copolymer component of the hot melt adhesive composition.
The hot melt adhesive compositions of the present invention find widespread
utility in a wide variety of applications. They are especially valuable in
those applications where resistance to creep at elevated temperatures is a
necessary requirement. The adhesive compositions of the present invention
may be used to great advantage to bond a variety of substrates including
metal, glass, synthetic and natural textiles, leathers, synthetic
polymeric sheet material wood, paper, etc.
The present invention also includes the concept of incorporating various
ingredients into the adhesive composition to improve processing and/or
performance of these materials. These additives and adjuncts include
antioxidants, thermal stabilizers, extenders, dyes, pigments, adhesion
promoters, plasticizers, etc.
The following examples are set forth in illustration of the invention and
should not be construed as a limitation thereof. Unless otherwise
indicated, all parts and percentages are by weight.
EXAMPLE 1
A block copolymer which is approximately 65 percent by weight crystalline
polyethylene terephthalate segments and 35 percent by weight amorphous
polyamide made from dimer acid and hexamethylene diamine, is prepared in
two steps. In the first step 157.5 parts (0.272 mol) of a C.sub.36 dibasic
acid and 30.8 parts (0.266 mol) of hexamethylene diamine are charged to a
reaction vessel and heated with agitation at about 215.degree. C. for one
hour to form a polyamide resin. During the first 30 minutes the pressure
rises to 1000 kPa after which time the reaction vessel is vented to reduce
the pressure to 600 kPa. At the end of one hour the pressure is released
and 332 parts of a crystalline polyethylene terephthalate (M.P.
=260.degree. C./inherent viscosity 0.147) and 7.5 parts (0.095 mol) of
ethylene glycol are charged to the vessel along with a minor amount of an
antioxidant. The vessel is flushed with nitrogen and the mixture is heated
to about 280.degree. C. while maintaining a nitrogen pressure of 240 kPa.
After 0.5 hour the vessel is vented and vacuum applied and the reaction is
continued under full vacuum (0.1 to 5 mm. of mercury) for two hours. At
the end of this time the resulting molten poly(ester-amide) is discharged
under pressure into a water bath to quench the material. The polymer
obtained melts at 205.degree. C. and the inherent viscosity is 0.50.
A filled composition of block copolymer, aluminum powder and glass fiber in
the weight ratio of 50:37.5:12.5 is prepared by the following procedure:
To a stainless steel reactor fitted with an anchor agitator and a jacketed
hot oil heating system is added 100 parts by weight of the
poly(ester-amide) and heating is begun. When the contents have reached
250.degree. C., agitation is begun at 60 rpm and 100 parts by weight of a
mixture of dry aluminum powder (Alcoa Atomized Powder 123 of average
particle size about 17 microns) and milled glass fiber of average length
1/16 inch (1.59 mm) is fed into the mass at a rate of 10 parts by weight
per minute. The agitation is continued and the temperature raised to
266.degree. C. under a nitrogen blanket. Agitation is continued for 15
minutes after the addition of the mixture is complete and the molten mass
is discharged under slight N.sub.2 pressure (250 kPa), quenched in a bath,
ground and redried. This material is used as a hot melt to fill dents and
orifices in a metal plate. After application it is cooled to room
temperature, sanded smooth with 80 grit tungsten carbide abrasive and
painted with an automotive surface coating. No "telegraphing" is observed.
The filled adhesive composition is excellent in flow at 260.degree. C., is
spread or trowelled well, and passes the 18 in.lb. and 36 in.lb. impact
tests at -30.degree. C.
EXAMPLES 2-7
Filled adhesive compositions are prepared in the manner set forth in
Example 1 with the same ratio of block copolymer to filler and with
various ratios of aluminum powder to glass fiber. The compositions are
evaluated for flow at 260.degree. C., workability and impact strength. The
data are presented in Table 1.
TABLE 1
______________________________________
EFFECT OF RATIO OF ALUMINUM POWDER TO
GLASS FIBER IN FILLED POLYESTERAMIDE
COMPOSITION
Ex- Impact Test,-30.degree. C.
am- Weight ratio
Flow at Work- 18 in.lb.
36 in.lb.
ple Al:glass 260.degree. C.
ability
(2.03J)
(4.07J)
______________________________________
1 3:1 excellent
good pass pass
2 1:1 good fair pass --
3 1:2 good v.good fail --
4 4:1 good good pass pass/fail
5 9:1 excellent
good pass fail
6 9.5:1 excellent
excellent
fail fail
7 1:0 excellent
good fail fail
______________________________________
Examples 1, 2, 4 and 5 are within the scope of the invention and
demonstrate the improved impact resistance at -30.degree. C. of the hot
melt adhesive and cavity filling compositions containing glass fiber in a
weight ratio of glass to aluminum in the range of 1:9 to 1:1. In contrast
Example 3 with a high glass fiber:aluminum ratio of 3:2, Example 6 with a
low glass fiber:aluminum ratio and Example 7 without glass fiber, fail the
low temperature impact test. Examples 1, 2 and 4 further show that an
optimum in impact resistance at -30.degree. C. occurs when the ratio of
glass fiber to aluminum is in the range of about 1:4 to 1:1. Lap bond
tensile strength (ASTM D-1002-72) of Examples 1 and 4 are 185 and 171
kg/cm.sub.2.
EXAMPLE 8
A hot melt adhesive composition is prepared by mixing 150 parts by weight
of dry aluminum powder (Alcoa Atomized Powder 123) and 50 parts by weight
of milled glass fiber of average length 1/16 inch (1.59 mm), with 100
parts by weight of the block copolymer of Example 1 by the procedure set
forth in Example 1. The composition is used as a hot melt to fill dents
and orifices in a metal plate. The hot melt flows rather poorly and is
trowelled smooth with some difficulty. After application, it is cooled to
room temperature, sanded smooth with 80 grit tungsten carbide abrasive and
painted with an automotive surface coating. No "telegraphing" of the
composition through the coating is observed.
When the hot melt adhesive composition is subjected to the impact test at
-30.degree. C., it passes the 18 inch-pound (2.03 J) and 36 inch-pound
(4.07 J) tests.
EXAMPLE 9
A hot melt adhesive composition is prepared as in Example 8 with a weight
ratio of glass fiber to aluminum powder of 1:1. The hot melt proves to be
impossible to flow or trowel except at temperatures which degrade the
polymer.
EXAMPLE 10
A hot melt adhesive composition is prepared by the method set forth in
Example 1 from 100 parts of the block copolymer of Example 1, 112.5 parts
of aluminum powder (Alcoa Atomized Powder 123) and 37.5 parts of milled
glass fiber of average length 1/32 inch (0.8 mm). The composition passed
the 18 inch-pound (2.03 Joule) impact test at -30.degree. C., but failed
the 36 inch-pound (4.07 Joule) test.
EXAMPLES 11-13
Hot melt adhesive compositions similar to the composition set forth in
Example 10 were prepared from milled glass fiber of average lengths 1/16
inch (1.6 mm), 1/8 inch (3.2 mm) and 1/4 inch (6.4 mm). The data for
impact tests carried out on the compositions at -30.degree. C. are
presented in Table 2 and show that the impact resistance is superior when
the fiber length is 1/16 inch or greater.
TABLE 2
______________________________________
Impact Tests
Glass Fiber Length
18 inch-pounds
36 inch-pounds
Example
in (mm) (2.03 Joule)
(4.07 Joule)
______________________________________
10 1/32 (0.8) pass fail
11 1/16 (1.6) pass pass
12 1/8 (3.2) pass pass
13 1/4 (6.4) pass pass
______________________________________
EXAMPLES 14-15
A series of hot melt adhesive compositions are prepared by the procedure of
Example 1 reinforced with polymeric reinforcing agents. The weight ratio
of block copolymer to aluminum powder (Alcoa Atomized Powder 123) and
polymeric reinforcing agent is 2:3. The compositions are subjected to the
impact test at -30.degree. C. and to the sandability test and are found to
be greatly inferior to compositions such as Example 11, reinforced with
glass fiber. The data are presented in Table 3.
TABLE 3
______________________________________
EFFECT OF POLYMERIC
REINFORCING AGENTS ON IMPACT RESISTANCE
Ex- Ratio of Impact Resistance
am- Reinforce- Al:Rein- 18 in. lbs.
86 in. lbs.
Sand-
ple ment forcement (2.03 J)
(4.07 J)
Ability
______________________________________
11 glass fiber 3:1 pass pass pass
14 amorphous
polypropylene
4:1 fail fail --
15 SBR rubber 14:1 pass fail fail
______________________________________
EXAMPLE 16
A block copolyester of inherent viscosity about 0.6 containing 65 weight
percent of polyethylene terephthalate as the hard segments interlinked by
means of terephthaloyl bis-N-butyrolactam with 35 weight percent of
copoly(hexamethylene isophthalate-terephthalate) (I:T, 80:20), as the soft
segments, is melt blended with aluminum powder and glass fiber as
described in Example 1. The blend is used as a hot melt to fill dents and
orifices in a metal plate.
EXAMPLE 17
A block copoly(ether-ester) of inherent viscosity about 0.6 containing 65
weight percent of polybutylene terephthalate as the hard segments and 35
weight percent of the copolyisophthalate-terephthalate (I:T, 80:20) of
polytetramethylene ether glycol (having a number average molecular weight
about 600) as the soft segments, is melt blended with aluminum powder and
glass fiber as described in Example 1. T | | |
