Note: Descriptions are shown in the official language in which they were submitted.
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Description
PRIMED POLYOLEFIN S~R~ACES FOR EPO~Y ADZ~ESIVE5
Technical Fiel_
This invention relates to polyolefin substrates
5Z having a primed surface whZich provides improved boZnding of -.
~pOZxy resin adhesives thereto and a method for adhering
primed polyolefin substrates with epoxy resin adhesives.
BackZ~round
~or many years there has existed a desire fcZr
polyolefin materials which can be bonded to other maZterial~
e.g., metals, ceramics and wood, or to themselves with epoxy '
resin adhesZives~ Bonding of such material s wi~h epoxy resin
adhe~Zives is often dZesirable, particularly when the bonded
material iZ6Z to be subjected to conditions o~ high :
temperature and high humidity.
Z Vntreated polyolefin substrates, e.g.~ :
Z, polyethylenel polypropylene or polyallo~er which is a
copolymer of polyethylene and polypropylene, are generally
unreceptive to epoxy adhesives alnd much effort ha~ been
j 20 expended i~ the search for a technique which will easily and
reliably increase adhesion without siqni~icantly changing
the properties of the substrate. Surface modification
techni~ues for enhancing adhesive bonding ~hich have been
examined are treatment with helium gas plasma, oxygen gas
¦ 25 plasma and chromic acid. These treatments and other surface
modification procedures have a common shortcoming in poor
durability. Light rubbing of th~ surface causes a decrease
l in the effect, the altered surface being easily abraded.
'! Irradiation of pZolyolefin substrates, such as with
an elZlQlctron beam, to improve the adhesion of various
coatings i5 al o known and has been dZisclosed in U.S.
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Patents No. 4,041,192 (Heger et al.), No~ 4,148,839
(Fydelor), No. 3,252,880 (Magat et al.) and No. 4,179,401
(Garnett et al.)O
Polyolefin substrates have been pro~id2d with a
treated surface for improved adhesion of pre~sure-sensitive
adhesives. Such pressure-sensitive adhesive~ include
rubber-type adhesives sueh as those based on natural rubber::
and ~ynth2tie rubbers, e.g., styrene-butadiene, rhloroprene,
neoprene, and isobutylene rubbers and synthetic resin-type~ :~
adhesives such as acrylic, polyvinyl chloride, polyvinyl
acetate, and pslyvinyl butyral adhesives. U.S. Patent No.
3,628,987 (Nakata et al.) discloses a pressure-sensitive ~;
j adhe~ive film wherein the film surface to which the adhesiveis adhered has graft-polymerized thereto a vinyl monomer or
diene monomer, the adhesive havins a solubility para~eter
near that of polymers of the vinyl or diene monom~r. U.S.
Patent No. 4,563,388 (~onk et al.~ discloses a polyolefin
substrate having graft-polymeri:æed thereto at lea~t one
~, monomer s~lected from the group consisting of acrylic acid,
methacrylic acid and ester~ thereof; acrylamide;
j methacrylamide; 6terically non-hindered tertiary alkyl
acrylamide~ and methacrylamides having three or les~ carbon
atoms in the alkyl group; and N--vinyl pyrrolidone, and
firmly adherently bonded to the graft-polymerized monomer an
:!, 2s acrylic type normally tacky and pressure-sensitive adhesive.
:¦ A s~ries of articles, "Surface Modifica~ion ~fJ Polyethyle~e by Radiation-Induced Grafting for Adhe~ive .:
:l Bondlng. I. Relatlonship Between Adhesive Bond Strength and ::-
, Surface Composition," (S. Y~makawa, J. Ap~l, Polym Sci, 20,
;, 30 3057-3072 (1976J; "II. Relationship Between Adhesive Bond
Strength and Surface Structure," (S. Yamakawa et al.,
i Macror~olecu1ea, 9, 754-758, tl976); "III. Oxidativ~ . i
;' Degradation and Stabilization of Grafted Layer," (S. . J-
-I Yamakawa et al., J. Appln. Polym. Sci., 22, 2459-2470
~': 35 (1978~ IV. Improv~ment in Wet Peel Strength," (S. Yamakawa 'A'
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et al~, J. Appl~ Pol~m. Sci., 25, 25-39 (1980), and "V.
Comparison with Other Surface Treatments," (S. Yamakawa et
al., J. Appl. Po~ym. Sci., 25, 40-49 ~1980), disclose
grafting of methyl acrylate (followed by saponification),
vinyl acetate, acrylic acid, acrylamide, and
methylolacrylamide to polyethylene by vapor-phase mutual
grafting or liquid-phase preirradiation at thicknesses of
grafted ~onomer of more than 10 micrometers to improve -:
adhesion of epoxy adhesives.
1 0 SumM~y
The present invention provides a polyolefin first
substrate firmly adhered to a second substrate with an epoxy
resin adhesive, ~aid polyolefin first substrate having
graft-polymerized thereto at least one monomer selected from ~-
the group consisting of sulfonic and carboxylic acids and
alkyl ester~ thereof containing fewer than eight carbon
atoms in the 2ster group, amide~; and mono- and
di-~ubstituted amides, alcohols, amines, epoxides, and 5~, :
6-, and 7-membered heter w yclic rings having at least one
oxygen and/or nitrogen atom in the ring, with the proviso
tAat said monomer contain an ethylenically unsaturated
, poly~erizable moiety, and that t:he graft-polyme~ized
A~ monomers are in a layer less than 5 micromet~rs in thickn~ss
and eontactin~ said epoxy resin adhesive.
~he present invention also provides a method for
adhering a polyolefin ~irst substrate to a second substr~te
with an epoxy resin adhesive co~prising the steps of
a) coatin~ on said polyolefin first substrate a liquid
monomer selected from the group consisting of .
sulfonic and carboxylic acids and alkyl esters
'. ~hereof containing fewer than eight carbon atoms in
the ester group, amides and mono- and di-substituted
~ amides, alcohols, amines, epoxides, and 5-, 6-, and
., 7-membered heterocyclic rings having at least one
, 35 oxygen and/vr nitrogen atom in the ring, in a layer
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less than 5 micrometers in thickness with the ~-
proviso that said monomer contain an ethylenically
unsaturated polymerizable moiety;
b) irradiating the coated sub~trate with ioni2ing
radiation to graft polymerize said monomer to said
substrate;
c) coating an epoxy resin adhesive on at least one of
aid graft-polymerized monomer surface of said - --
first substrate and (ii) a surface of said second
~, 10 substrate;
d) contacting said surfaces (i) and tii~; and
e) curing said epoxy resin adhesive.
Surprisingly excellent peel values, i.e., greater
than 25 lb/in t440 N/dm), result when the grafted monomer
1, 15 layer is les than 5 micrometer~ thic~. Good peel adhesion
i~ also retained after exposure to water for a period of
about one week.
Detailed Description
The substrate o~ the invention is a polyolefin
material, i.e., polyethylene, polyalkyl-~-olefins, and
I blend~ thereof, uch a~ polyethy~lene, polypropylene, or
i polyallomer which i~ an ethylen~/propylene copolymer.
~hese polyolefin materials can also contain s~all a~ount~
'~ i.e., up to about 10 weight percent of modifying monomers,
0.g., ~ros~linkabl~ terpolymers, such a dicyclopentadiene
and norborneene~ a~d ionomers which enhance ~trength, such
as acrylic acid. These terpolymers and ionomer~ are~not .. -
3 present on the surface of the polyole~in material~ in
suficient~quantl~ties to affect epoxy adhe~iv~ adhesion to
303 ~the polyole in materials~
' :~ The thicknes~ og the polyolefin ~at2rial is
d*ter~ined by the end usç o~ the adhes~ve-coated product,
typical thicknesses being in the ranye of about 0.025 to
about~5.0 milli~eters. The polyole~in material may contain
~5~ additives, such as carbon black, calcium carbonate, silica,
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titanium dioxide, crosslinking agents, dispersants and
extrusion aids, which are known in the art.
Various specific monomers suitable for
graft-polymeriæation onto polyolefin substrates to promote
j 5 adherence of epoxy adhesives to the substrate include
acrylic acid, dimethylacrylamide, diethylacrylamide,
dipropylacrylamide, hydroxyethylacrylate,
butanedioldiacrylate, hexanedioldiacrylate,
diethylaminoethylacrylate, glycidylmethacrylate,
j 10 isobutylmethacrylate, cyclohexylmethacrylate,
trimethylolpropane triacrylate, trimethylolpropane
trimethacrylate, pentaerythritol triacrylate,
~3 pentaerythritol tetraacrylate, hydantoin hexacrylate,
~ 2-vinyl-4,4-dim~thylazlactone, ~nd N-vinyl-pyrrolidone.
3 15 The mGnOmer composition generally contains about
60 to about 100 weight percent monomer. The monomer
composition applied to the polyolefin substra~e may contain
various additive such as crosslinking agents, surfactant~,
alcohols, and acids.
~l 20 Crosslinking agents, some of which may also be
monomers suitable for grafting onto th0 substrate
themselv~s, may be added to further enhance heat resistance
of the product. Examples of useful crosslinking agents
include polyethyleneglycol diacrylate, pentaerythritol
tetraacrylate, tetr3ethylene glycol dimethacrylate,
trimethylolpropan~ tri~crylate, trimethylolpropane
trimethacrylate, allyl methacry:Late, 1,6-hexanediol
diacrylate, 1,6-hexanediol dimethacrylate, thiodiethylene
glycol diacrylate, and triallyl cyanurate. The preferred
I 30 crosslinking agents include polyethylene glycol diacrylate,
:~1, tetraethylene glycol dimethacrylate, trimethylol propane
~`~ triacrylate, and thiodiethylene glycol diacrylate.
;, Crosslinking agents may be present in monomer compositions
in amounts o~ about 0 to about 80 percent by weight,
'' 35 pref~rably 0 ts about 40 percent by weight.
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Surfactants may be present in the monomer
composition to improve the uniformity of the coating on the
substrate. ~-
The thickness of the monomer composition is
preferably less than about 5 micrometers, more preferably
le~s than about 1 micrometer and most preferably less than
about 0.5 micrometer. ~
For uniform application of the monomer to the ~-
polyolefin ~ubstrate, the substrate is preferably treated to
enable a polar liquid to wet the surface. This can be
achieved by treating the substrate with an oxidizing agent
such a~ nitric acid or chromic acid, or treating the
~ substrate with flame, plasma discharge or corona discharge.
j The preferred method of treatment is corona discharge.
The mono~er may be graft-polymerized to the
substrate by use of actinic radiation such as x-rays, beta
ray~, gamma rays, ultraviolet light, vi~ible light and
1ectron beam irradiation. The pre~erred method of
graft~polymerization is by irradiation with an electron
J 20 beam. The eleçtron beam dosag~ is typically greater th~n d -
! about 0.05 Mrads, preferaby greater than about 0.5 ~rads, I
and more preferably in the range of about 2 to about 10
Mrad~. -
The sub&trate to which the polyolefin material is
i 25 to be adhered can be any substrate which bonds well with
¦~ epoxy adhesive~. Such substrates include, for example, :-
metals such as aluminum, teel, galvanized ~teel, stainless
~teel, copper, and titanium, pla~tics, other than
polyolefins, uch as polycarbonate, polyvinyl chloride,
polyester and fiber-reinforced polye~ter,
pol~methylmethacrylat~, and acrylonitrile-butadiene-styrene,
and particularly those plastics which are high-temperature
impact modified, natural and synthetic rubbers, such as
polychloroprene, styren~-butadiene rubber, and nitrile
j~ 35 rubber, ceramics, wood, painted surfaces, glas~ primed with
silane and polyole~in having a monomer graft-polymerized
!~ thereto according to the present invention.
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Epoxy adhesives useful in the present invention
include any one- or two-part epoxy adhesives a~ long as the
curing temperature required does not exceed the softening
temperature of the polyolefin substrate. In use the epoxy
adhesive may be applied to either the polyolefin substrate
or to the substrate to which ~he polyolefin material iæ to
be adhered or to both substrates. ~ypical epoxy adhesives
include Scotch-Weld~ brand Epoxy Adhesives 1838 and 2216
~/A, each available from Minnesota Mining and Manufacturing
Company
The advantages of the invention are illustrated by
the following examples, it being understood that numerous
variations will be well wi~hin the ability of those skilled
in the art.
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`I 15 Example 1
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Into a polyallomer resin, available from ~ennessee
Ea6tman under the trade design~tion "Tenite" 5321E, was
l milled 1~ carbon black by weight. The composition was then:l extruded as a sheet having a thickness of about 0.5
millimeter, after which one surface was coron~-treated by
pas6ing the sheet through a 1 millimeter air gap between a
~ chlorinated polyethylene-coated electrode and a grounded
l aluminum cylinder. The frequency of the unit was 16 kHz,
the total input power being 1.5 kw and the exposure time of
the sample being on the order oE 0.6-1.0 sec. Ov~r the
.l corona-treated surface was then applied a blend of ~0 parts
j by weight N,N-dimethyl acrylamide, 20 part by weight
~I trimethylol propane triacrylate, and 0.5 part by weight of a
~`l fluorochemical acrylate oligomer ~a wetting and lev*ling
agent commercially available from 3M Company as "FC 430"). -::
The blend, which had a viscosity of 2D3 CpS at 25C, was
applied to the coro~a-treated polyallomer sur~ace using a
No. 20G quad knurled gravure roll in combination with a
i doctor blade, minimizing the coating thickness to less than ::
, ~ 35 one micrometer. The coated surface was then exposed to
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electron beam irradiation at a dosage of about 4 Mrads and a
voltage of 150-250 kV in a nitrogen atmosphere. The
thickness of the grafted layer was found to be less than 0.4
micrometer using attenuated total reflection-infrared -:-
spectro~copy. . : -~
A cold-rolled steel panel (4" x 12" x 0.32" (lO cm
x 30 cm x 0.8 cm), designated 80-730F cold-rolled steel,
40, unpolished? 17603001, available from ~dvanced Coating
Technologie~, Inc., Hillsdale, Michigan~ was wiped three ::.
times with methyl ethyl ketone to remove a~y surface oil
present. Scotch-Weld ~3brand Epoxy Adhesive 1838-L B/A
translucent was prepared ~y mixing together 6 parts by -- .
weight base and 5 par~s by weight accelerator. The adhesive
wa~ coated on the steel panel and a one-inch wide x six-inch
long strip of polyallomer having the N,N-dimethyl
acrylamide/tri~ethylolpropane triacrylat~ grafted thereto
wa~ placed on the adhe~ive with the grafted sur~ace :
contacting the adhesive and an end of the polyallomer
extending beyond the plate. A 4.5 lb (2 kg) roller was
¦ 20 rolled acros6 the ~teel plat0/adhesive/polyallomer zompo~ite ::
twice. The co~posite, in which the epoxy adhesive layer wa6 ..
about 0.004 inch (0.1 mm) thick, was placed in an oven at
170F (77C) or 2 hours. The oven was then turned of~ and
the compo6ite wa6 ~llowed to cool overnight (16 hour~).
Adhesion was determined by pulli.ng the polyallomer from
steel plate at a 90~ angle and a rate of 12 inches (30 cm)
per minute. No ~dhesive failure occurred~ The polyallomer
adherend failed at a force of about 40 lb/in (700 ~/d~
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Com~arative Exam~les 1-3
In Comparative Examples 1-3, untreated
polyallomer, polyallomer which had been corona-treated as in :
Example 1, and polyallomer which had been corona-treated and
subjected to electron beam radiation as in Example 1 but
with no monomer present, respectively were tested for
adhesion as in Example 1. The resultc are shown in Tablç 1.
¦ ~xample 2-19
n Examples 2-19, various monomers set forth in
. lO Table 1 were graft-polymerized onto polyallomer as described in Example 1 except that the monomer was applied by wiping
the polyallomer with a paper towel moistened with the
monomer and the dosage of electron beam irradlation was
j about 5 Mrads. In each of Examples 2-12 and 14-19, 95 parts
by weight of the indicated monomer was mixed with 5 parts by
weight trimethylolpropane triacrylate, as crosslinking agent
and in Example 13 the 'crimethylolpropane triacrylate was
applied as a 50 weight percent solution in acetone.
Composites were prepared as in E~xample 1 and tested ior
adhecion. ~he results are set t~orth in Table 1.
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Table 1 -;:-
Adhesion
Example Monomer ~/dm?
Comp 1 - 16 :
j 5Comp 2 - 17
Co~p 3 - 15 :::
2 acrylic acid PAB*
3 dimethylacrylamide PAB
4 diethylacrylamide PAB :::
dipropylacrylamide ~AB
6 hydroxyethylacrylate PAB
~ 7 butanedioldiacrylate PAB
:l 8 hexanedioldiacrylate PAB `~ g diethylaminoethylacrylate P~
1 15 10 glycidyl methacrylate P~B
1 , 11 i~obutylmethacrylate P~
¦ 12 cyclohexylmethacrylate PAB
3 13 trimethylolpropane triacrylate pAs
14 trimethylolpropane trimethacrylat~ 26
. 20 15 p~ntaerythritol triacrylate PA~
I 1~ pentaerythritol tetraacrylate PAB
.~ 17 hydantoin h~xacrylate 33
i 18 2-vinyl-4,4-dimethylazlactone PAB
:~ 19 N-vinylpyrrolidone PAB
* polyallomer adherend break
Examples 20 and 21 ..
j To 20 mil tO.S mm~ thick polyallomer sheet -.
.. ~ material wa~ gra~ted a monomer mixture of 80 parts by weight
di~thylacrylamide~ 20 parts by weight trimethylolpropane
triacrylate, and 0.5 parts FC 430 as in Example lo
Cold-roll2d mild ~teel plates (3" x 7" x 1/8" t7.5 cm x 17.5 ::
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cm x 2.2 cm) Type 1018 available from Paper Calmenson h Co.,
St. Paul, Minnesota) were abraded by hand using Grade 35
sandpaper, followed by Grade 80 sandpaper, and then a Grade
80 abrasive bristle brush, and then degreased with methyl
ethyl ketone. The steel plates were then coated with
Scotch-Weld~ brand Epoxy Primer 194~, available from
Minnesota Mining and Manufacturing Co., at a thickness of
about 1-2 mil (0.025-0.05 mm) and allowed to dry for about
ten minutes.
In Example 20, Scotch-Weld ~ brand Epoxy Adhesive
1838-L B/A Translucent, available from Minnesota Mining and
Manu~acturing Co. was prepared by mixing equal volumes of
base and accelerator. The adhesive was coated on the primed
steel plate. The grafted surface of a 1 inch x 8 inch piece
of th~ polyallomer was laid over the adhesive ~s in Example
l and a second steel plate was placed on top of the
polyallomer to effect uniform contact between the
polyallomer material and the adhesive. The thus-formed
composite was allowed to cure at room temp~rature (73F,
23C) for three days. The top steel plate was then removed
and the somposite was soaked in water ~t room temper~ture
for 13 days. When the compo~ite was tested using the 90D
peel test as in Example 1, the polyallomer adherend broke
I be~ore any bond failure occurred.
', In ~xample 21 a composite was prepared and tested
~, 25 as in Example 20 except that the adhesive used was
Scotch-Weld ~ brand 2216 B/A Structural Adhesive (2 part~ by
'~ volume base ~ixed with 3 parts by volume accelerator).
I Again, the polyallomer adherend broke before any bond
1 failure oocurred.
Various modifications and alterations of this
' invention wîll be apparent to those skilled in the art
- without dep~rting from the scope and spirit of this
! invention and this invention should not be restricted to
that set forth herein for illustrative purposes.
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