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Claims  |
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What is claimed is;
1. A method of filling a cavity in a substrate which comprises applying
excess adhesive composition as a hot melt into the cavity, spreading the
adhesive composition to fill the cavity, cooling the adhesive composition
below its crystallization temperature and sanding the adhesive composition
to provide a surface even with the surrounding substrate, wherein the
adhesive composition comprises a block copolymer, aluminum powder, glass
fiber and hollow inorganic silicate microspheres, wherein the block
copolymer is selected from the group consisting of copolyesters,
copolyamides, copoly(esteramides) and copoly(ether-esters) melting at a
temperature of above 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 copolymerto
aluminum powder, glass fiber and silicate microspheres 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, wherein the weight ratio of glass fiber
to aluminum powder is at least about 1:9 and wherein the volume percentage
of silicate microspheres is less than about 10.
2. The method of claim 1 wherein the hard segments of the block copolymer
are polyester condensates of an aliphatic or alicyclic diol having from 2
to 10 carbon atoms and an alicyclic or aromatic dicarboxylic acid having
from 8 to 20 carbon atoms, or polyamide condensates of an aliphatic or
alicyclic diamine having from 2 to 12 carbon atoms and an aliphatic or
alicyclic dicarboxylic acid having from 2 to 12 carbon atoms, or polyamide
condensates of an .omega.-aminocarboxylic acid having from 2 to 12 carbon
atoms; and wherein the soft segments of the block copolymer are polyester
condensates of an aliphatic or alicyclic diol having from 4 to 10 carbon
atoms or a polylactone diol of molecular weight in the range of about 350
to 6000 and an aliphatic, alicyclic or aromatic dicarboxylic acid having
from 4 to 54 carbon atoms, or poly(ether-ester) condensates of a
poly(alkylene ether) glycol of molecular weight in the range of about 350
to about 6000 in which the alkylene groups have from 2 to 10 carbon atoms
and an aliphatic, alicyclic or aromatic dicarboxylic acid having from 4 to
54 carbon atoms, or polyamide condensates of an aliphatic or alicyclic
diamine having from 2 to 12 carbon atoms and a mixture of an aliphatic or
alicyclic dicarboxylic acid having from 4 to 54 carbon atoms containing at
least 40 weight percent of an aliphatic dicarboxylic acid having from 18
to 54 carbon atoms.
3. the method of claim 1 wherein the block copolymer is a copolyester
wherein the hard segments are condensed from an aliphatic or alicyclic
diol having from 2 to 10 carbon atoms and an alicyclic or aromatic
dicarboxylic acid having from 8 to 20 carbon atoms and the soft segments
are condensed from an aliphatic or alicyclic diol having from 4 to 10
carbon atoms or a polylactone diol of molecular weight in the range of
about 350 to about 6000 or a poly(alkylene ether) glycol of molecular
weight in the range of about 350 to about 6000 in which the alkylene
groups have from 2 to 10 carbon atoms and an aliphaticm alicyclic or
aromatic dicarboxylic acid having from 6 to 54 carbon atoms.
4. The method of claim 1 wherein the block copolymer is a copolyamide
wherein the hard segments are condensed from an aliphatic or alicyclic
diamine having from 2 to 12 carbon atoms and an aliphatic or alicyclic
discarboxylic acid having from 2 to 12 carbon atoms or from an
.omega.-aminocarboxylic acid having from 2 to 12 carbon atoms and the soft
segments are condensed from an aliphatic or alicyclic diamine having from
2 to 12 carbon atoms and a mixture of aliphatic and alicyclic dicarboxylic
acids having from 4 to 54 carbon atoms containing at least 40 weight
percent of an aliphatic dicarboxylic acid having from 18 to 54 carbon
atoms.
5. The method of claim 1 wherein the block copolymer is a
copoly(ester-amide) wherein the hard segments are condensed from an
aliphatic or alicyclic diol having from 2 to 10 carbon atoms and an
alicyclic or aromatic dicarboxylic acid having from 8 to 20 carbon atoms
and the soft segments are condensed from an aliphatic or alicyclic diamine
having from 2 to 12 carbon atoms and a mixture of aliphatic or alicyclic
dicarboxylic acids having from 4 to 54 carbon atoms containing at least 40
weight percent of an aliphatic dicarboxylic acid having from 18 to 54
carbon atoms.
6. The method of claim 5 wherein the polyester is selected from the group
consisting of poly(ethylene terephthalate), poly(tetramethylene
terephthalate), co-poly(butylene terephthalate(-(ethylene terephthalate),
co-poly(ethylene terephthalate)-(ethylene isophthalate), and
copoly(ethylene terephthalate)-(propylene terephthalate) and wherein the
polyamide segments are condensed from a C.sub.36 dimer acid and
hexamithylene diamine.
7. The method of claim 1 wherein the block copolymer is a
copoly(ester-amide) wherein the hard segments are condensed from an
aliphatic or alicyclic diamine having from 2 to 12 carbon atoms and an
aliphatic or alicyclic dicarboxylic acid having from 2 to 12 carbon atoms
or from an .omega.-aminocarboxylic acid having from 2 to 12 carbon atoms
and the soft segments are condensed from an aliphatic or alicyclic diol
having from 4 to 10 carbon atoms or a poly(alkylene ether) glycol of
molecular weight in the range of about 350 to about 6000 in which the
alkylene groups have from 2 to 10 carbon atoms and an aliphatic, alicyclic
or aromatic dicarboxylic acid having from 6 to 54 carbon atoms,
8. The method of claim 1 wherein the adhesive composition has a melt
viscosity at 250.degree. C. of less than about 600,000 centipoise at a
shear rate of 4 sec..sup.-1.
9. The method of claim 1, 5 or 7, wherein the hard segment prior to
incorporation in the block copolymer has a weight average molecular weight
in the range of about 400 to about 16,000 and a melting point in the range
of about 180.degree. to about 270.degree. C.
10. The method of claim 9 wherein the block copolymer has a weight average
molecular weight in the range of about 5500 to about 30,000 and a glass
transition temperature in the range of about -30.degree. to 40.degree. C.
11. The method of claim 10 wherein the aluminum powder is spheroidal and
has an average particle size in the range of about 0.2 to about 150
microns.
12. The method of claim 11 wherein the glass fiber is milled glass fiber of
average length at least about 0.8 mm.
13. The method of claim 12 wherein the silicate microspheres comprise from
about 2 to about 8 volume percent of the adhesive composition and are of
averge particle size in the range of about 10 to about 150 microns.
14. The method of claim 10 wherein the aluminum powder is spheroidal and
has an average particle size in the range of about 4 to about 50 microns.
15. The method of claim 14 wherein the glass fiber is milled glass fiber of
average length at least about 0.8 mm.
16. The method of claim 15 wherein the silicate microspheres comprise from
about 2 to about 8 volume percent of the adhesive composition and are of
average particle size in the range of about 50 to about 100 microns.
17. A method of filling a cavity in a substrate which comprises applying
excess adhesive composition as a hot melt into the cavity, spreading the
adhesive composition to fill the cavity, cooling the adhesive composition
below its crystallization temperature and sanding the adhesive composition
to provide a surface even with the surrounding substrate, wherein the
adhesive composition comprises:
(a) a poly(ester-amide) block copolymer of weight aveage molecular weight
in the range of about 5500 to about 30,000 and of melting point in the
range of about 155.degree. C. to about 225.degree. C., having from about
30 to 70 percent by weight of hard polyester segments selected from the
group consisting of poly(ethylene terephthalate), poly(tertramethylene
terephthalate), co-poly(butylene terephthalate(-(ethylen terephthalate),
co-poly(ethylene terephthalate(-(ethylene isophthalate) and
co-poly(ethylene terephthalate)-(propylene terephthalate) which prior to
incorporation in the poly(ester-amide), have a weight average molecular
weight in the range of about 400 to about 16,000 and a melting point in
the range of about 180 to about 270.degree. C., and from about 70 to about
30 percent by weight of soft polyamide segments of glass transition
temperature in the range of about -30.degree. to 40.degree. C., condensed
from a C.sub.18 to C.sub.54 dibasic acid and an aliphatic or alicyclic
diamine containing from 2 to 10 carbon atoms;
(b) spheroidal aluminum powder of average particle size in the range of
about 4 to about 50 microns;
(c) milled glass fiber of average length in the range of about 1.6 mm to
about 6.4 mm; and
(d) hollow inorganic silicate microspheres of average particle size in the
range of about 10 to about 150 microns;
wherein the weight ratio of block copolymer to aluminum powder, glass fiber
and silicate microspheres is in the range of about 1:2 to about 1:1,
wherein the weight ratio of block copolymer to glass fiber is in the range
of about 2:1 to about 10:1 wherein the weight ratio of glass fiber to
aluminum powder is in the range of about 1:4 to about 1:1, and wherein the
silicate microspheres comprise from about 2 to about 8 volume percent of
the adhesive composition.
18. The method of claim 17 wherein the adhesive composition has a melt
viscosity at 250.degree. C. of less than about 600,000 centipoise at a
shear rate of 4 sec..sup.-1.
19. The method of claim 17 wherein the dibasic acid is a C.sub.36 dimer
acid and the diamine is hexamethylene diamine.
20. The method of claim 19 wherein the crystalline polyester segments are
poly(ethylene terephthalate). |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
The present invention relates to a hot melt adhesive composition, to a
method of filling voids with the adhesive composition and to articles
filled or coated with the hot melt adhesive composition. More
particularly, it relates to block copolymers containing glass fibers,
aluminum powder and hollow inorganic silicate microspheres, 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 temperatures, 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 of 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 to 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
"telegraphing" or "bleed-through", and they do not withstand the high
temperatures necessary for the subsequent cure of paint overcoats.
"Telegraphing" or "bleed-through" are terms used to describe the
revelation of difference in composition of the substrate when it has been
painted, because of 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(esteramide) 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
reinforcement were generally unsuccessful and added a further complication
of blinding of the sanding disc, making sanding extremely difficult.
SUMMARY OF THE INVENTION
The present invention is directed to a method of filling a cavity in a
substrate which comprises applying excess adhesive composition, comprising
a block copolymer, 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 adhesive composition has improved impact resistance at low
temperatures, 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,
glass fiber and hollow inorganic silicate microspheres; 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, glass fiber and silicate microspheres 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, wherein the weight ratio
of glass fiber to aluminum powder is at least about 1:9 and wherein the
volume percentage of silicate microspheres is less than about 10.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
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-, 1,4- and 1,5- 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, from 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 dl/g.sup.-1 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-butanediamine, 1,5-pentane
diamine, hexamethylene diamine, 1,10-decanediamine, cyclohexanediamine,
etc. Examples of acids includes 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 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 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 a 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 determined 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 1000,000
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" obtained by dimerization of
unsaturated aliphatic monocarboxylic acids, e.g., linoleic acid, available
commercially as mixtures of monobasic, dibasic and tribasic acids. The
aliphatic or alicyclic diamines include ethylene diamine, 1,3-propane
diamine, 1,4-butanediamine, 1,5-pentane diamine, hexamethylene diamine,
1,10-decanediamine, 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 the 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, allows longer working time or
longer "open" time between application of the hot melt and closing of the
bond and higher "green" strength or 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 1/4inch (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 1/4inch (6.4 mm).
The introduction of glass fiber into the adhesive composition comprising
block copolymer and aluminum powder can cause an undesirable decrease in
the flow and workability particularly at higher weight ratios of these
inorganic components and can require such higher temperatures for
application and smoothing of the composition that decomposition of the
block copolymer may tend to occur. The addition of a minor amount of
inorganic silicate microspheres can cause a further increase in melt
viscosity and hence sag resistance but surprisingly the pressure required
to extrude the adhesive composition is not appreciably affected and the
flow and workability of the hot melt extrudate are not impaired and indeed
in the preferred compositions are actually improved. Consequently, a
sufficient amount of inorganic silicate microspheres is included in the
adhesive composition to obtain this increase in melt viscosity but the
amount is limited so that the flow and workability are not impaired.
Generally up to about 10 volume percent and preferably from about 2 to
about 8 volume percent of the total composition is required. The silicate
microspheres are hollow synthetic inorganic silicate microspheres of
average particle size in the range of about 10 to about 150 microns, and
preferably in the range of about 50 to about 100 mincrons. Their average
effective particle density is in the range of about 100 g per liter to
about 400 g per liter and is preferably in the range of about 150 g per
liter to about 250 g per liter. Such microspheres are sold for example by
the Philadelphia Quartz Company under the registered trademark Q-Cel.
Because of the low density of the silicate microspheres, they comprise
less than 2:5 weight percent of the adhesive composition, and preferably
less than 1.5 weight percent depending upon the effective particle density
of the microspheres. In contrast to the effect obtained with the hollow
microspheres, when an equivalent volume of solid microspheres is added to
the adhesive composition significant increases in melt viscosity and the
pressure required to extrude the melt are observed and the flow and
workability of the hot melt composition is impaired.
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 vinyl silane, vinyl methyl dichlorosilane,
2-(trimethoxysilyl)ethyl methacrylate, 3-amino-1-triethoxysilylpropane,
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
methacrylato chromic chloride. These coupling agents can cause a
significant reduction in the melt viscosity of the blend, can improve the
wetting and dispersion of the inorganic components (i.e. the aluminum
powder and the glass fiber) and can enhance the physical properties of the
adhesive composition.
The ratio of the components of the adhesive composition is selected so that
the desired balance of flow and workability, adhesion, sag resistance,
impact resistance and sandability is achieved. Excessive amounts of glass
fiber and silicate microspheres 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, glass fiber and inorganic
silicate microspheres, 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 about 10:1; 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; and the inorganic silicate microspheres comprise
up to about 10 volume percent of the adhesive composition. The component
ratios are preferably selected so that the melt viscosity of the hot melt
composition is less than about 600,000 centipoise and preferably less than
about 300,000 centipose at a temperature of 250.degree. C. and a shear
rate of 4 sec.sup.-1 measured in a Brookfield Thermocel Unit Model HBT.
When the melt viscosity is greater than 600,000 centipoise, 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, the glass
fiber and the hollow inorganic silicate microspheres 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 throughout 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. 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 height
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 pressure needed to
extrude the hot melt composition at 260.degree. C. through a 3/16 (4.76
mm) nozzle is noted, and the ease of flow of the hot melt extrudate and
its ability to be worked by spreading, trowelling and feathering it to a
smooth cohesive strip is observed. The panel is cooled to room temperature
and a disc sander, 12.5 cm. diameter, wlith 80 grit medium tungsten
carbide abrasive, is applied to the composition at 1000 rpm to further
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 segements 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 viscostiy 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 viscostiy is 0.50.
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 200 parts by weight of a
mixture of 149 parts dry aluminum powder of average particle size about 17
microns, sold by the Aluminum Company of America under the tradename
Atomized Powder 123, 49 parts milled glass fiber of average length 1/16
inch (1.59 mm), and 1.8 parts hollow inorganic silicate microspheres sold
by Philadelphia Quartz Company under the registered tradename Q-Cel 300,
of average particle size 75 microns, 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. The melt viscosity of the
composition at 250.degree. C. is 198.times.10.sup.3 centipoise. The
pressure required to extrude the hot melt at 260.degree. C. through an
orifice of 3/16 inch diameter (4.76 mm) is 70 psi (482 kPa).
The adhesive composition is used as a hot melt to fill dents and orifices
in a metal plate. It flows and is readily trowelled to yield a smooth
coherent mass. 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 composition passes the 18 inch
pound (2.03 Joule) and the 36 inch pound (4.07 Joule) impact tests.
EXAMPLES 2-11
Hot melt adhesive compositons are prepared by the procedure of Example 1
from the block copolymer of Example 1. The weight ratio of block copolymer
to inorganic components in Examples 2-7 is 1:2 and in Examples 8-11 is
2:3. The weight ratio of aluminum powder to glass fiber is 3:1. In
Examples 2-4, 10 and 11 hollow inorganic silicate microspheres are
incorporated into the adhesive composition. Examples 5 and 8 contain no
microspheres and Examples 6, 7 and 9, included for comparative purposes,
contain solid glass microspheres of average particle size 25 microns. The
processability of the hot melt adhesive compositions is evaluated by
determining the melt viscosity, the pressure required to cause flow
through a 3/16 inch (4.76 mm) orifice and the ease of flow and workability
of the hot melt composition applied at a temperature of 260.degree. C. The
data including results of Example 1 are presented in Table 1. Examples 4,
9 and 11 show the increase in melt viscosity obtained with the hollow
micropsheres. Examples 1, 3 and 10 containing hollow microspheres in the
volume percentage range of about 2 to about 6 show improved flow and/or
workability in comparison with Examples 5 and 8 without microspheres. In
contrast when the microspheres are solid (Examples 6, 7 and 9) or when the
concentration is greater than 10 volume percent (Examples 4 and 11) a very
significant increase in pressure for melt extrusion accompanies the
increase in melt viscosity and the flow and workability of the hot melt
composition is substantially impaired.
The lap bond tensile strength of the adhesive composition of Example 10,
determined by ASTM Test Method D-1002-72 is 149 kg cm.sup.2 .
TABLE I
__________________________________________________________________________
EFFECT OF MICROSPHERES ON PROCESSABILITY OF HOT MELT COMPOSITIONS
Pressure
Melt needed
Weight Ratio Viscosity
for flow
Flow Workability
Block Copolymer:
Weight %
Volume %
at 250.degree. C.
at at (applied at
Example
Inorganic Compounds
Microspheres
Microspheres
cps .times. 10.sup.-3
260.degree. C.
260.degree. C.
260.degree. C.)
__________________________________________________________________________
1 1:2 0.61 (h)
5 198 70 good v.good
2 1:2 0.14 (h)
1.2 228 75 poor poor
3 1:2 0.30 (h)
2.5 208 75 fair fair
4 1:2 1.5 (h)
11.7 >4000 100 v.poor
untrowelable
5 1:2 0 0 216 70 fair poor
6 1:2 6.1 (s)
4.8 452 95 poor v.poor
7 1:2 30 (s) 10.4 >4000 100 v.poor
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