Note: Descriptions are shown in the official language in which they were submitted.
This invention relates -to a method of obtaining
improved adhesion be-tween acrylate plastic compo~itions per
se and/or metals, polyes-ters or other structural plastics.
More specifically, this invention relates to a method of
treating -the surface o~ an acrylate plastic composition which
may contain glass fiber reinforcement to enhance the effec-
tiveness of the adhesive bond.
Here-tofore, in makin~ laminates between acrylate
plastic compositions per se and/or metals, polyesters and
other structural plastics, it has been customary to clean the
surface to be bonded with a suitable solvent to remove
greases and other contaminants. This treatment has frequen-t- -
ly resulted in a surface that gives relatively low bond -
strength, usually less than 50 pounds per square inch tpsi).
Where the bond strength is no greater than 50 psi the bond
is then the weakest link in -the assembly or laminate. There-
fore, it is desirable to improve -the adhesive bond to a value
higher than 100 psi to give the assembly or laminate greater
structural strength.
Therefore, it is an object of this invention to pro-
vide a method for obtaining improved adhesion be-tween an acry-
late plastic composition per se and/or metals and a polyester
composition and other structural plastics. This object and
other advantages may be obtained by the practice of this in-
vention as will be evident from the ensuing discussion.
The surface of the acrylate plastic composition is
subjected to a treatment with a suitable first and second
treating agent more fully described hereinafter, or preferably
dissolved in a solvent. A suitable adhesive of the acrylate
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plastic composition to be bonded or laminated and the
acrylate class adhesive is allowed to set or cure.
An embodiment of the invention is a method for
improving the adhesion between an adhesive of the
polyurethane class and acrylate plastic composition
comprising treating the surface of the acrylate plastic
composition with a first and second treating agent without
regard to se~uence and then applying an adhesive of the
polyurethane class and curing said adhesive, said first
treating agent being an organic polyisocyanate and the
second treating agent being a tertiary amine with the
polyurethane class adhesive preferably being selected from
the class of isocyanate prepolymer and a polyol curative.
More specifically, the acrylate plastic
compositions are those utilized as rod, extrusions and
sheets such as constructing panels or built-up objects of
substantial rigidity. For instance, the use of solid
acrylate plastic compositions containing glass fiber
reinforcements such as those used in making roof or wall
panels, automobile parts, and related objects are some
of the ones to which this invention has its primary benefit.
The acrylate plastic compositions useful in this
invention are available as sheets, rods, extrusions and
related structural shapes, either filler loaded or unloaded,
and their nature is specifically described in "The
Technology of Plastics and Resins" by J. Phillip Mason,
PhD., fourth printing, in Chapter 8 under the heading
"Synthetic Plastics-Acrylic Resins".
In essence the acrylate resins are polymers or
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copolymers of acrylic or methacrylic acid or their alkyl
or aryl esters, where alkyl radical contains one to about
20 carbon atoms. These acrylate plastics are a~ailable
under a wide range of trade names as listed in Dr. Mason's
book.
As indicated heretofore, the objects and
advantages of this invention are obtained by applying
in succession a treatment with two different treating
agents to the clean surface of the acrylate plastic -
composition and/or metal polyester or other structural
plastic, which then is brought into laminating contact -
with another acrylate plastic composition until the
adh-sive has set-or cured. ~
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For convenience, the different treating agents will
be referred to as first and second treating agents, respect
ively, as this designated sequence of treatment gives pre-
ferred results. It should be appreciated the order or se-
quence of treatment can be reversed. Thus,the treatment insome instances can be referred to as without sequence.
Hereinafter, the term "first treating agent" will
be used to designate an organic polyisocyanate or a solution
of an organic polyisocyanate.
Any of the organic polyisocyanates may be used as
the first treating agent to pretreat the composition surface
to enhance the adhesion. Representative classes of these are
the aromatic, aliphatic, and cycloaliphatic diisocyanates and
the triisocyanates such as those listed in U~S. Patents
2,917,489 and 3,102,875.
Since the organic polyisocyanates of higher molecu-
lar weight and higher isocyanate content are more viscous than
the lower molecular weight or even solids, the use of a sol-
vent as a vehicle to dissolve, dilute or lower the viscosity
aids the control application during the pretreatment to the
acrylate plastic composition or metal surface. Suitable and
representative vehicles for the organic polyisocyanates are
the ketones such as methyl ethyl ketone, acetone, the hydro-
carbon distillates, chlorinated solvents as hydrocarbons and
other solvents boiling below about 300F. and preferably be-
low 250F. Preferably, the solvent used should not dissolve
or effect the surface appearance of the acrylate composition.
The acrylate plastic composition, preferably in the
~orm of a sheet or thin film, although rods and other struc-
1(38838~
tural shapes can be used, is treated with the first treatingagent by applying the treati.ng agent preferably dispersed or
dissolved in a solvent to the surface by brushing, spraying, .
rolling or other suitable techniques, then allowing.the sol-
vent to evaporate-to leave the treating agent deposited on
the surface of the desired composition.
It has been discovered that the benefits of this
invention are obtained if the second treatment immediately
follows the first treatment or if considerable time is al-
lowed to elapse. Usually an elapse of one to several days is .desirable as it gives greater freedom in scheduling the work ~ ~ .
in the plant.
The second treating agent is applied to the surface
of the acrylate plastic composition by brushing, spraying,
rolling or other suitable techniques and allowed to dry. Then
the acrylate plastic composition whose surface has been so
prepared is treated with a polyurethane class adhesive and
the two surfaces to be joined are placed in contact until the .-
adhesive has had time to laminate or bond the two compositions
together.
The second treating agent for treating the surface
of the acrylate plastic composition is a tertiary amine of the :
aliphatic, cycloaliphatic, or heteroaromatic hydrocarbon class.
Representative tertiary amines are triethylene diamine, alkyl
piperazines, alkyl morpholines, and dialkylated lower amines
such as triethylamine. The agent or treating agent is prefer-
ably dissolved in a suitable solvent such as the ketones or .
halogenated hydrocarbon solvents, although any of the low boil-
ing inert organic liquids in which the amine is soluble may
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be used. Usually about 0.5 to 5 or more parts of the agent
is dissolved in 100 parts of solvent, and depending on the
specific activity of the tertiaryamine abou-t one to three
parts is preferred. This concentration of the treating agent
in the solvent allows adhesion to be obtained with the usual
application methods. Of course, it should be appreciated
that higher concentrations, viz. 5 or lO parts to even lO0
percent liquid tertiaryamine can be used, but difficulty may
be experienced in getting a uniform application of the ter-
tiary amine to t7ne acrylate plastic composition surface at
concentrations above 10 percent, and the cost of the treat-
ment tends to become uneconomical.
In general, washing of the acrylate plastic compo-
sition-or the metals, for example, steel, copper, aluminum,
magnesium and related alloys or polyester or related struc-
tural plastics, is not necessary since the solvent in the
first treating agent can function to loosen the grease and
other surface contaminants to permit the isocyanate to bond
to the solid acrylate plastic composition, viz fiberglass
filled acrylate panel or mat. Likewise, in some instances,
it is preferred to treat metals, the polyester or other struc-
tural plastics, with the amine treating agent before using the
isocyanate treating agent. It should be noted that some of
the chlorinated solvents tend to react with some tertiary-
amines to form a precipitate. Consequently, the solvent solu-
tion sometimes has limited pot life and is made immediately
before its use.
The acrylate class adhesive useful in this invention
includes isocyanate class adhesive such as those described in
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UOS. Patents 3,812,003 and 3,935,051 to Bender and Larson,
and generally are the reaction product of an organic polyiso-
cyanate at 2 to 6 mols per mol of a 500 to above 5000 molecu-
lar weight reactive hydrogen compound, such as the usual poly-
ester or polyether with a monomeric polyol such as the lower
glycols of ethylene, propylene, butylene, pentylene or deca-
methylene to give a cured pol~rethane adhesive.
An adhesive of the isocyanate class can be prepared
by reacting the reactive hydrogen containing materials of
about 500 to 4000 with an organic polyisocyanate, a low mole-
cular weight polyamine containing material and preferably an
inert filler. The adhesive of the isocyanate class is pre-
pared by forming a prepolymer and then mixing the prepolymer
with a curative, the prepolymer being formed by the reaction
f the reactive hydrogen containing material. Preferably a
polypropylene ether polyol of about 1000 to 3000 molecular
weight and an organic polyisocyanate containing at least two
and preferably more than an average of two isocyanates per
molecule. mis prepolymer can contain about five to as much ~ -
as 70 percent by weight of a filler based on the reactive hy-
drogen containing material. One of the prime functions of
the inert filler such as clays, silica, etc. is to act as a
viscosity increaser and also to hasten the building of green -
strength or tack in the adhesive. The curative may contain
polyhydroxyl terminated materials of relatively low molecular
weight, usually less than about 600. Representative of these
materials are N,N,N',N'-(2-hydroxylpropyl) ethylene diamine
or the adduct formed by reacting a material such as pentaery- ;
thritol, trimethylol, propane, trimethylol ethane and the hy-
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droxylated sugars with alkylene oxides such as propylene
oxide. These curatives may also contain in addition to the
low molecular weight hydroxyl terminated or amine terminated
materials, a small amount of catalysts such as the tertiary
amines or the organic tin c~mpounds. Usually the adhesives
of the isocyanate class of a relatively high isocyanate to
reactive hydrogen material ratio is in excess of 2.5 and
preferably about 5 to 7 moles per mole. The nature of the
isocyanate adhesive and the first and second treating agents
is also described in U. S. Patents 3,647,513 and 3,703,426.
The nature of this invention may be more specifical-
ly exemplified by the following examples wherein all parts
are by weight unless otherwise indicated:
EXAMPLE A
A suitable adhesive of the isocyanate class was pre-
pared by reacting the following ingredients: 100 parts of a
- polypropylene ether glycol of about 2000 molecular weight
having dispersed therein 60 parts of talc coated with zinc
stearate and an organic polyisocyanate mixture comprising
28 parts of a polyisocyanate A and 32 parts of toluene di-
isocyanate where polyisocyanate A is the phosgenated mixture
obtained by phosgenation of the rearrangement product of the
reaction of aniline and formaldehyde as taught in U. S.
Patent 2,683,730.
This prepolymer was then mixed in a two-compartment
pressure adhesive gun with a curative comprising 30.8 parts
N,N,N',N'-(2-hydroxylpropyl) ethylene diamine and 13.2 parts
of a propylene oxide adduct of pentaerythritol of about 400
molecular weight to form the adhesive.
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EXAMPLE B
Another adhesive of the isocyanate class was pre-
pared by reacting 100 parts polypropylene ether glycol of
2000 molecular weight having dispersed therein 63 parts of
zinc stearate coated talc with an isocyanate mixture com-
prising 29.8 parts of a polyisocyanate A and 33.7 parts of
toluene diisocyanate. This prepolymer was mixed with a cura-
tive to form an adhesive. The curative was formed by mix-
ing 49.6 parts of a propylene oxide adduct of ethylene dia-
mine of about 500 molecular weight with 12.4 parts of a
propylene oxide adduct of pentaerythritol of about 500 mole- --
cular weight.
EXAMPLE I
A five percent by weight solution of polyphenyl me-
thane polyisocyanate (available from the supplier under the
name PAPI) in a chlorinated nephtha having a boiling point
below 250F. was spray applied to clean dry acrylate fiber
glass filled test panels and allowed to dry at room tempera-
ture for 30 minutes.
Then the test panels were spray coated with a one
percent by ~eight solution of triethylene diamine in methyl
ethyl ketone. The panels were allowed to dry at room tem-
perature for 30 minutes before being coated with the isocya-
nate adhes1ve of Example A. The panel containing the isocya-
nate adhesive was covered with a second panel in cross rela-
tionship and held in this relationship for 24 hours to develop
the overlap laminate bond.
The laminate specimens were subjected to a pull test
in an "Instron" test machine at test temperatures indicated
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below:
Test Temperature Bond Failure, P.S.i.
75F. 970
180F. 410
250F. 250
-40F. 1010
These bond strengths represent approximately an
appreciable improvement in bond strength over those where no
primer treatment was used.
~he sequence of primer use above can be reversed,
but Example I exemp~i~ies ~he pre~erred sequence. Also, the
chlorinated hydrocarbon organic polyisocyanate solutions o~
2 to 10 percent are normally used.
While certain representative embodiments and details
have been shown for the purpose of illustrating the invention,
it will be apparent to those skilled in this art that various
changes and modifications may be made therein without depart-
ing from the spirit or scope o~ the invention~
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