Note: Descriptions are shown in the official language in which they were submitted.
7437
` LC-2026-A TITLE
Polyurethane-Based Adhesive Composition
BAC~G~OUND OF THE IN~7ENTION
This invention relates to a polyurethane-
based adhesive, which is particularly well suited forbonding shoe soles to shoe uppers in footwear manu-
facturing.
Modern shoe industry employs machines capable
of producing large quantities of the necessary shoe
parts. Those parts must be joined together to form the
final product. In industrial manufacturing processes,
joining of shoe parts is often accomplished by adhesive
bonding. This step must produce adequate strength
bonds in a short time to avoid slowing down the produc-
;15 tion lines. The most critical bonding operation is the
attachment of the shoe uppers to the sole. The sole
can be made of a variety of natural or synthetic plas-
tic or elastomeric materials, such as polyvinyl
chloride, thermoplastic rubber, styrene/butadiene co-
polymers, and thermoset polyurethanes.
The adhesives currently most widely used are
; solvent solutions of synthetic elastomers, such as
polychloroprene or polyurethane. The bonding process
involves coating the substrates with an adhesive solu-
tion, evaporating the solvent, then "reactivating" the
~1~7437
':
adhesive film by the application of mild heat before
assembly. Activation temperatures above about 70C
must be avoided because they cause distortion of many
heat-sensitive shoe materials.
It would be advantageous to replace the sol-
vent solutions with solvent-free adhesives. Suitable
systems are known and are used in other bonding opera-
tions. They comprise fluid isocyanate-terminated pre-
polymers that can be chain-extended or "cured" by
admixture with diamine curing agents such as methylene-
dianiline. The combination of curing agent and an
isocyanate-terminated prepolymer should have adequate
potlife after mixing but sufficiently high reaction
rate for continuous line applications. Unmodified
methylenedianiline, when used with typical urethane
prepolymers, gives adhesives having too short a potlife
to be applicable in sole attaching operations. A com-
plex of methylenedianiline with sodium chloride in a
mole ratio of 3:1 is a known curing agent for urethane
prepolymers. A typical dispersion of this complex is
available from E. I. du Pont de Nemours & Co,
Wilmington, Delaware, under the name "Caytur 21"*.
Mixtures of "Caytur 21" with urethane prepolymers have
a very long potlife but are slow to cure unless acti-
vated at temperatures above 120C, that would destroy
: many typical shoe materials. The activation tempera-
; ture of methylenedianiline/sodium chloride complexes
can be reduced to about 90C by addition of certain
active hydrogen compounds including urea, according to
the teachin~s of U.S. 3,891,606, but this is still too
high a temperature for most shoe materials. Therefore,
a polyurethane-based adhesive capable of producing in a
short time and at a moderate temperature bonds having
good strength is greatly needed.
SUMMARY OF THE INVENTION
According to this invention, there is now
` * denotes trade mark
J'
11~7437
provided a polyurethane adhesive based on an isocyanate-
terminated prepolymer made from 1.2-2.0 moles of
tolylene diisocyanate containing at least 65% of the
2,4-isomer, 1 mole of poly(tetramethyleneoxy) glycol
having a number average molecular weight of about 400
to 3000,and a polytethyleneoxy) compound having a num-
ber average molecular weight of about 310-4000 and con-
taining 7-30 (-CH2-CH2O-) groups and 1 or 2 hydroxyl
groups, its (-CH2-CH2O-) groups providing 0.5-4% of the
combined weight of thepoly(ethyleneoxy) compound and
poly(tetramethyleneoxy) glycol, while the poly(tetra-
methyleneoxy) glycol provides no less than 80% of said
combined weight. A mixture of a methylenedianiline/
sodium chloride complex with finely ground urea can be
used as the curing agent for the isocyanate-terminated
prepolymer to form an adhesive suitable for show sole
attaching operations.
DETAILED DESCRIPTION OF THE INVENTION
While the isocyanate-terminated prepolymer
based on tolylene diisocyanate and poly(tetramethylene-
oxy) glycol alone can be cured with a dispersion of a
methylenedianiline/sodium chloride complex containing
powdered urea at a temperature of about 90C, a pre
polymer additionally containing the poly(ethyleneoxy)
~5 aompound can be cured with the same agent at a tempera-
ture of 70C. The adhesive bond forms fast and has
high strength. This lower temperature does not damage
the usual shoe sole materials or deform the molded shoe
bottoms.
The isocyanate-terminated prepolymer can be
readily made by those skilled in the art. Preparation
of prepolymers of the present invention will suitably
follow the teachings of U.S. Patents 2,929,8~0 (to
Hill) and U.S. 3,755,261 (to Van Gulick) modified by
the incorporation of the poly(ethyleneoxy) compound.
,
- li07437
The order of addition of the ingredients is not
critical. The preferred proportion of the poly-
(ethyleneoxy) compound is such that its (-CH2-CH2O-)
groups provide 1.0 to 3.0% of the combined weight of
poly(ethyleneoxy) compound and poly(tetramethyleneoxy)
glycol. It is critical for the success of this inven-
~ tion that the prepolymers be based on a poly(tetra-
- methyleneoxy) glycol, which must constitute at least
80% of the combined weight of poly(ethyleneoxy) com-
pound and poly(tetramethyleneoxy) glycol. Poly-
(ethyleneoxy) glycols and polyester glycols, for
example, have been found to produce inferior results.
The poly(ethyleneoxy) compound is the product
of addition of ethylene oxide to a suitable compound
having one or two active hydrogens. Representative
starting materials from which the poly(ethyleneoxy)
compounds of this invention are prepared incIude, for
example, the following.
A. Alcohols such as methanol, ethanol, butanol,
octanol, decanol, dodecanol, octadecanol and
cyclohexanol.
B. Diols such as ethylene glycol, butanediol, hexane-
diol, cyclohexanediol, diethylene glycol, dipropy-
lene glycol and poly(propyleneoxy) glycols.
C. Phenols such as phenol, cresol, naphthol, octyl-
phenol, nonylphenol and dodecylphenol.
D. Monocarboxylic acids such as acetic, butyric,
lauric, palmitic, stearic and benzoic acids.
E. Dicarboxylic acids such as succinic, glutaric,
sebacic, dodecanedioic, isophthalic and tere-
phthalic acids.
F. Amides o~ any monocarboxylic acids of the type
~ described under D, above.
; G. Mercaptans and thiophenols such as butyl mercaptan,
dodecylmercaptan, and thiophenol.
:
- .
" 11a!7437
The preferred poly(ethyleneoxy) compounds are
the readily available and highly effective oxyethylated
alcohols, phenols, and diols; for example, octylphenoxy-
poly(ethyleneoxy) ethanols, nonylphenoxypoly(ethyleneoxy)
ethanols, poly(ethyleneoxy) glycol, and oxyethylated
poly(propyleneoxy) glycols. Because of their basic
character, which may adversely affect the stability of
the adhesive compositions of the present invention,
amines are not suitable starting materials.
The ethylene oxide reaction products will have
, repeating units (-CH2-CH2-0-~. Some commercial products
suitable in the practice of the present invention are
made by adding both ethylene oxide and propylene oxide
to the base compound having one or two active hydrogens.
Usually, these alkylene oxide adducts contain both poly-
(,ethyleneoxy) and poly(propyleneoxy) blocks. For the
purpose of this invention, the number of propyleneoxy
units is not critical, so long as the total number of
ethyleneoxy groups (-CH2-CH2-0-) in the molecular is
within the 7-30 range, the total molecular weight is no
more than 4000, and the mole ratio of ethyleneoxy units
to propyleneoxy units is not less than 0.2.
Commercial products suitable in the practice ,-
of the present invention are available from several
sources under trade names such as, for example,
"Pluronic"*, BASF Wyandotte Corp., and "Triton"*, Rohm
and Haas. Other suitable poly(ethyleneoxy) compounds
can be made, for example, according to the process
described in U.S. Patent 2,674,619.
The methylenedianiline/sodium chloride com-
plex usually is sold as a dispersion in an inert
liquid. Such dispersions can be prepared following the
general procedure of U.S. 3,876,604 (to Caruso et al).
Finely powdered urea i5 best added to methylenediani-
line/sodium chloride complex as a dispersion. The
* denotes trade mark
, 5
''` , ~ .
.
74~7
urea dispersion can be made by ball-milling urea with an
inert liquid of U.S. 3,876,604 until proper particle
size is obtained (usually, less than 20 microns). The
amount of urea used should be 2-5 parts per 100 parts by
weight of complex.
The proportion of the methylenedianiline/
sodium chloride complex to the prepolymer is such that
the amine -NH2/-NCO mole ratio is about 0.95:1 to
1.50:1, ratios of 1.00:1 to 1.30:1 being preferred.
Below 0.95, the bond development is too slow for most
industrial applications, while above 1.50 the ultimate
bond strength is often too low. It is interesting to
note that the compositions of the present invention can
be used not only as heat-activated adhesives but also
as casting or liquid injection-molding compositions.
Should the present system be used for casting or
molding, rather than as an adhesive, the lower limit of
the -NH2/-NCO range can be as low as 0.70, the preferred
range being 0.85-1.20. Within the preferred range,
cured articles having best physical properties are
obtained.
In the practice of the present invention, the
adhesive is used as a two-part system. The isocyanate-
terminated prepolymer which contains the poly(ethylene-
oxy) compound is mixed with the curing agent shortlybefore use. The composition has at room temperature a
potlife in excess of 8 hours; preferred compositions,
in excess of 24 hours. The adhesive is applied by
suitable means such as brushing, doctoring or transfer
coating onto one or both surfaces which are to be
bonded; the adhesive surface or surfaces are heated to
initiate reaction, and the parts joined in a press for
at least 10 seconds. The bonded assembly is suffi-
ciently strong to be subjected to the remaining steps
of footwear finishing. The strength of the bond
11~D7437
,
increases with time, approaching its maximum within
several hours after bonding.
The adhesive composition of the present
invention can be also used, if desired, in other
applications, including those where parts to be joined
are coated with the adhesive composition, assembled
together, and then heated to full cure. Such appli-
cations require, of course, heat-stable parts to be
joined.
10This invention is now illustrated by the
following examples of certain representative embodi-
- ments thereof, wherein all parts, proportions, and
percentages are by weight unless otherwise indicated.
EXAMPLE 1
15To 100 g o~ an isocyanate-terminated Prepoly-
mer A containing 4.1% free isocyanate groups (prepared
by a reaction of 1.0 mole poly(tetramethyleneoxy)
glycol of molecular weight 1000 with 1.6 moles of 2,4-
tolylene diisocyanate for 3 hours at 80C) is added
3.25 g of octylphenoxypoly(ethyleneoxy) ethanol having
an average molecular weight of about 756 and a poly-
(ethyleneoxy) block of 12-13 (-CH2-CH2O-) units. These
proportions provide a (-CH2-CH2O-) content of 2.93% by
: weight and a poly(tetramethyleneoxy) glycol content of
97.1% based on the total weight of poly(ethyleneoxy)
compound and poly(tetramethyleneoxy) glycol. After 3
- days at 25C, the resulting reaction product (Prepoly-
mer B) contains 3.7% free isocyanate groups.
Both Prepolymer A and Prepolymer B are made
into adhesives by combining with either curing agent C
consisting of a 1:1 dispersion of methylenedianiline/
sodium chloride complex in di(2-ethylhexyl) phthalate
;or curing agent D which is prepared by adding 4.5 parts
per 100 parts of curing agent C of a 50% dispersion of
finely divided urea in di(2-ethylhexyl) azelate.
7437
The proportions used are as follows:
(a) Prepolymer A 100 parts
Curing Agent C 26.7 parts
(b) Prepolymer B 100 parts
Curing Agent C 25.6 parts
(c) Prepolymer A 100 parts
Curing Agent D 27.9 parts
(d) Prepolymer B 100 parts
; Curing Agent D 26.7 parts
All four adhesive compositions are still
workable 24 hours after preparation. The four compo-
sitions are used as adhesives by coating 5 mils (0.13
mm) of the aZhesive on roughed 0.3 cm thick slabs of
cured styrene-butadiene copolymer. The slabs are
immediately heated by radiant heat using a Compo
Industries, Inc. 220 volt adhesive activator so that
the adhesive reaches a surface temperature of 73C.
Immediately after heating, the adhesive coating is
placed in contact with the vinyl surface of a vinyl-
coated fabric containing about 30~ dioctyl phthalateas a plasticizer in the vinyl coating and the combined
assembly is pressed at 0.41 MPa for 20 sec. The com-
bined pieces are then peel tested as described in
ASTM D2558-69 section 8.1 at a jaw separation rate of
5 cm/min. The results are shown in the following
table:
Peel Strength, kN/m - With Curing Agent C
1 Min After Release 3 Hrs After Release
Prepolymer from Press from Press
-
A < 0.02 0.02
B 0.2 3.0
Peel Strength, kN/m - With Curing Agent D
1 Min After Release 3 Hrs After Release
Prepolymer from Press from Press
A 0.2 1.6
B 1.1 5.8
:
743~
., g
The above results show the improved bonding
performance of the modified Prepolymer B with both
curing agents. When Prepolymer B is used with curing
agent D, the resulting adhesive gives high-strength
bonds.
Similar results are obtained using chemically
equivalent amounts of nonylphenoxypoly(ethyleneoxy)
ethanols having number average molecular weights of
600-900.
10EXAMPLE 2
To 100 g of Prepolymer A (used in Example 1)
is added 6.05 g of an oxyethylated poly(propyleneoxy)
glycol derived by end-capping poly(propyleneoxy)
glycol with poly(ethyleneoxy) groups. The glycol has
an average molecular weight of 2750 and contains about
25% by weight of ethyleneoxy units, which corresponds
; to 16 ethyleneoxy units total. For this composition
the (-CH2-CH2O-) fraction is 1.84~ and the poly(tetra-
methyleneoxy) glycol content is 92.8% of the combined
weight of both glycols. After standing for 3 days at
25C, the resulting Prepolymer E contains 3.6% free
isocyanate groups.
The results of adhesion tests using the pro-
cedure and curing agent D (from Example 1) are shown
below. The proportions used are as follows:
;(a) Prepolymer A 100 parts
Curing Agent D 26.8 parts
(b) Prepolymer E 100 parts
Curing Agent D 25.9 parts
30 Peel Strength, kN/m
1 Min after Removal 3 Hrs After Removal
- Prepolymer from Press from Press
.
A 0.09 1.1
E 1.2 5.3
:`
, 9
~ `` 11.(3 743'7
EXAMPLE 3
To 100 g of Prepolymer A (used in Example 1)
is added 2.0 g of poly(ethyleneoxy) glycol of molecular
` weight 1000 (degree of polymerization 22~23) to form
Prepolymer F with a free isocyanate content of 3.6%.
The proportion of (-CH2-CH2O-) units is 2.49%, and the
proportion of polyttetramethyleneoxy) glycol is 97.5%
, of the total weight of both glycols.
The results of adhesion tests using the pro-
cedure and curing agent D (from Example 1) with Pre-
polymers A and F are shown below. The proportions used
are as follows:
(a) Prepolymer A 100 parts
Curing Agent D 27.3 parts
15 (b) Prepolymer F 100 parts
Curing Agent D 24.5 parts
Peel Strength, kN/m
1 Min After Release 8 Hours After Release
Prepolymer from Press from Press
A 0.04 2.1
~` F 0.9 6.7
The effect of degree of polymerization of the
poly(ethyleneoxy) diol of the general formula
HO-(CH2-CH2-O)n-H on the peel strength of the finished
adhesive is shown below using diols with degrees of
polymerization 13-22. The various glycols are all used
in amounts of 2.0 millimoles per 100 g of Prepolymer A.
Peel Strenqth, kN/m
- (-CH2CH2O-) PTMEG 2 Min After Release
30 Prepolymer % % From Press
A 0.14
F where n=13 1.44 98.5 1.2
17 1.88 98.1 1.4
22-23 2.49 97.5 1.6
~, .
, 10
;37
. 11
EXAMPLE 4
A series of prepolymers (Bx) was prepared, to
show the effect of the number of ethyleneoxy groups, by
mixing 4.3 millimoles of octylphenoxypoly(ethyleneoxy)
ethanols of the general formula:
17 8 ~ O-(CH2-CH2-O)n-H
with 100 g of Prepolymer A from Example 1.
The results of adhesion tests using one day-
old adhesives made from 100 g of prepolymers Bx and26 g of curing agent D are shown below. An adhesive
prepared from unmodified Prepolymer A is included as
a control.
(-CH2CH2O-) PTMEG 8 Hr Bond Strength,
15 Prepolymer % ~ kN/m
A 0.04
Bx where n=l0.24 98.6 0.09
30.71 98.2 0.18
51.18 97.8 1.2
7-8 1.76 97.1 2.1
9-10 2.23 96.7 2.8
12-132.91 96.0 7.0
The above Examples 2-4 further illustrate
the exceptionally good results obtained with adhesive
systems of the present invention.
EXAMPLE 5
A series of four modified prepolymers were
prepared by the proceduxe of Example 1 by adding in-
creasing amounts of an oxyethylated poly(propyleneoxy)
glycol derived by end-capping poly(propyleneoxy)
glycol with poly(ethyleneoxy) units to 100 g portions
of Prepolymer A. The oxyethylated poly(propyleneoxy)
glycol had a molecular weight of about 2650 and con-
tained about30~ by weight of -CH2-CH2O- units. The
modified prepolymers were made into adhesives by the
addition of curing agent D. The resulting adhesives
` 11
.
12
were evaluated by bonding slabs of styrene-butadiene
copolymer to vinyl-coated fabric as described in
Example l. The pot-life of the adhesiveswas deter-
mined by measuring their viscosities 8 hours and 24
hours after preparation.
Proportions and test results are presented in
the following table along with results for a control
adhesive to which no polyethyleneoxy compound was added.
Preparation
10 Control 5-A 5-B 5-C 5-D
Poly(oxyethylene) -- 2.94 7.7610.3 19.4
compound, g/lO0 g
Prepolymer A
Poly(tetramethy-100.0 96.392.0 88.079.5
leneoxy) glycol, %*
Ethyleneoxy -- 0.932.00 3.01 5.12
units, ~*
Curing Agent D,27.9 26.624.5 22.519.1
parts/100 parts
modified prepolymer
Peel Strength, kN/m 0.35 .88 .88 .53 --
1 min after release
from press
Adhesive viscosity,
Pa s, 26C, 8 hr. 35 33 74 135 **
after preparation
Pa-s, 26C, 24 hr. 64 73 486 ** **
; after preparation
* Based on the sum of the weights of poly(tetramethy-
leneoxy) glycol and poly(ethyleneoxy) compound.
** Too viscous to measure.
,:
7437
13
The results show that the addition of poly-
(ethyleneoxy) compound increases peel strength. How-
ever, in preparation S-D where the level of poly-
(ethyleneoxy) compound was high enough to provide 5%
ethyleneoxy units and to reduce the concentration of
poly(tetramethyleneoxy) glycol below 80%, the adhesive
was too viscous for use. Preparation 5-D is outside
the limits of this application.
EXAMPLE 6
Three prepolymers were prepared by the proce-
dure used for Prepolymer A of Example 1 with the excep-
tion that poly(tetramethyleneoxy) glycol (MW 1000) was
replaced by an equal weight of
A. poly(ethylene adipate) glycol (MW 1000),
: 15 B. poly(ethyleneoxy) glycol (MW 1000), or
C. poly(l,2-propyleneoxy) glycol (MW 1000).
Prepolymers A and B were made into adhesive
compositions by the addition of 27.9 parts of curing
agent D per 100 parts of prepolymer. In less than 8
hours both of these adhesive compositions became too
viscous for use.
A portion of Prepolymer C was modified by the
addition of 3.25 g of octylphenoxypoly(ethyleneoxy)-
ethanol having an average molecular weight of 756
following the procedure of Example 1 to form a prepoly-
mer designated as Prepolymer C'. Prepolymers C and C'
were converted to adhesives by the addition of 27.9 and
26.7 parts per 100 parts prepolymer, respectively, of
curing agent D. The resulting adhesives were tested by
bonding styrene-butadiene copolymer and vinyl-coated
fabric as in Example 1. Peel strengths 1 minute after
release from the press were less than 0.02 kN/m which
is inadequate for use as a shoe adhesive.
None of the above preparations is within the
scope of this application. They are provided to
:
~ 13
~'
~ ... . .
:' .
. . . .
' ' ' ' ' ' ' '
.
~1~7q~3~7
14
illustrate the criticality of using poly(tetra-
- methyleneoxy) glycol in preparing the present ad-
hesives.
