U.S. patent application number 11/285003 was filed with the patent office on 2007-05-24 for method for coating vehicle bodies and parts thereof with rust-preventive ionomeric coatings.
Invention is credited to Albert Gordon Anderson, Walter Mahler.
Application Number | 20070114131 11/285003 |
Document ID | / |
Family ID | 37831734 |
Filed Date | 2007-05-24 |
United States Patent
Application |
20070114131 |
Kind Code |
A1 |
Anderson; Albert Gordon ; et
al. |
May 24, 2007 |
Method for coating vehicle bodies and parts thereof with
rust-preventive ionomeric coatings
Abstract
The present invention is directed to a method for coating car or
truck bodies, or part thereof, with a rust-preventive ionomer
coating composition as the car or truck body is being conveyed
along the assembly line as at the vehicle assembly plant. The
method of the present invention is used as a replacement for the
electrodeposition priming process used today at vehicle assembly
plants.
Inventors: |
Anderson; Albert Gordon;
(Wilmington, DE) ; Mahler; Walter; (Wilmington,
DE) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY;LEGAL PATENT RECORDS CENTER
BARLEY MILL PLAZA 25/1128
4417 LANCASTER PIKE
WILMINGTON
DE
19805
US
|
Family ID: |
37831734 |
Appl. No.: |
11/285003 |
Filed: |
November 22, 2005 |
Current U.S.
Class: |
204/471 |
Current CPC
Class: |
C09D 5/002 20130101;
C09D 5/08 20130101; B05D 7/50 20130101; C09D 123/0876 20130101;
B05D 7/14 20130101; B05D 7/51 20130101 |
Class at
Publication: |
204/471 |
International
Class: |
C25B 7/00 20060101
C25B007/00 |
Claims
1. A coating method for applying a rust-preventive primer coating
to an automotive substrate comprising: (a) applying to at least one
surface of an automotive substrate, a coating liquid comprising an
aqueous dispersion of an ionomer resin; (b) flash drying or baking
said coating liquid on the substrate to form a rust-preventive
primer layer; and, (c) optionally, applying over said
rust-preventive primer layer, a primer surfacer and/or an
automotive topcoat finish such as a basecoat/clearcoat finish.
2. The method according to claim 1 wherein the substrate is a car
or truck body or part thereof.
3. The method of claim 1 wherein the automotive substrate is in
continuous movement throughout the primer paint application process
steps (a) and (b) as it travels along an automotive assembly
line.
4. The method according to claim 1 wherein the coating liquid is an
aqueous dispersion of an ionomer resin partially or fully
neutralized with a cation or mixture of cations.
5. The method according to claim 4 wherein the ionomer resin is
fully neutralized or partially neutralized with a mixture of
divalent metal ions and ammonium ions.
6. The method according to claim 5 wherein the ionomer resin is an
ethylene-unsaturated carboxylic acid copolymer having an acid
content of 10-35 wt %.
7. The method according to claim 5 wherein the ionomer resin is an
ethylene-acrylic or methacrylic acid copolymer having an acid
content of 10-35 wt %.
8. The method according to claim 6 wherein the divalent metal ion
is selected from Zn.
9. The method according to claim 8 wherein the dispersion has a
solids content of 10 to 45 wt %.
10. The method according to claim 5 wherein the dispersion further
contains a non-water-soluble vapor phase corrosion inhibitor.
11. A rust-preventive treated automotive substrate coated by the
method of claim 1.
12. A rust-preventive treated car or truck body substrate coated by
the method of claim 1.
13. An apparatus for applying a rust-preventive liquid ionomeric
primer coating to an car or truck body, comprising an
electrocoating tank at a vehicle assembly plant wherein the cathode
or anode has been disabled.
Description
TECHNICAL FIELD
[0001] This invention relates to a method for coating vehicle
bodies, such as car and truck bodies and parts thereof, with
rust-preventive ionomeric coatings to provide corrosion protected
bodies having good smoothness, appearance, and corrosion
resistance.
BACKGROUND OF THE INVENTION
[0002] Electrodeposition of rust-preventive primers on metal
automotive substrates is widely used in the automotive industry. In
this process, a conductive article, such as an autobody or an auto
part, is immersed in a bath of an electrodepositable coating
composition comprising an aqueous emulsion of a film forming
polymer and the article acts as an electrode in the
electrodeposition process. A high voltage electric current is then
passed between the article and a counter-electrode in electrical
contact with the coating composition until a coating of a desired
thickness is deposited on the article. In a typical cathodic
electrocoating process, the article to be coated is the cathode and
the counter-electrode is the anode.
[0003] After the electrodeposition process is complete, the
resulting coated article is removed from the bath and is rinsed
with deionized water and then cured typically in an oven at
sufficient temperature to form a crosslinked finish on the article.
Once the electrodeposition rust-preventive primer is applied to the
automotive substrate, the vehicle is then top coated with a
multi-layer automotive exterior finish to provide chip resistance
properties and an attractive aesthetic appearance such as gloss and
distinctness of image.
[0004] One disadvantage associated with conventional
electrodeposition processes is that coating defects tend to form on
the surface of the coated article, such as pinholes and cracks,
which can compromise the corrosion protective properties of the
electrodeposited film and produce other deleterious effects such as
a rough film surface. The high voltage baths required in
electrodeposition coating processes use up large amounts of
electricity and are also expensive to maintain. Furthermore, the
multiple deionized water rinses are undesirable, as they present
significant waste handling and water treatment problems.
[0005] Accordingly, there is a desire to eliminate the
electrocoating process altogether and find new coating methods and
compositions which can replace the electrodeposition process, while
still maintaining the desired coating properties for automotive
rust-preventive primer finishes such as a high degree of corrosion
resistance and paint adhesion to both underlying rust-preventive
pretreatments on the metal surface and to paint applied thereover
during exterior automotive finishing operations.
[0006] Various ionomeric coating compositions comprising aqueous
dispersions of ionomer resins made from ion-neutralized
ethylene-acrylic acid or ethylene-methacrylic acid copolymers have
been proposed for rust-preventive treatment of metal surfaces, for
example, as disclosed in JP 2000-198949 A2 to Akimoto et al., WO
00/50473 A1 to Nakata, et al., and U.S. Pat. No. 6,458,897 to
Tokita, et al. issued Oct. 1, 2002. However, none of these have
been used to treat entire vehicle bodies being conveyed along a
vehicle assembly line, especially using the electrocoat tank
emptied of electrocoat composition as the holding/dip tank for
these ionomer resin dispersions.
[0007] Diverse properties are required for a coating formed from an
ionomer resin dispersion in order for it to be a suitable
commercial replacement for an electrocoat bath. Good edge
protection, bath stability and uniformity and corrosion resistance,
water impermeability, film smoothness and ease of use are desired
to produce a high performance rust-preventive coating of automotive
quality. The present invention provides a method of coating ionomer
resin dispersions onto a vehicle body as it is being conveyed on a
continuously moving automotive assembly line in the vehicle
manufacturer's plant, without adversely impacting upon the
operation of the coating operation and the level of corrosion
protection when compared to a standard electropriming process.
[0008] The method of the present invention is capable of forming a
rust-preventive primer finish on vehicle bodies, such as car and
truck bodies, or parts thereof, that meets the high performance
requirements of automotive finishes. This method is therefore a
suitable commercial replacement for conventional electrodeposition
primers and electopriming processes used nowadays in automotive
assembly plants. The process of the present invention can be
applied to typical car body steel such as galvanized steel, but
since it is robust enough, it can also be applied to untreated
metal to provide direct contact corrosion protection, which
provides substantial savings to the automakers, since most vehicle
bodies today are constructed of costly Zn plated (galvanized) steel
everywhere except the roof area.
SUMMARY OF THE INVENTION
[0009] A method is provided for coating a vehicle body, such as a
car or truck body, or part thereof, with a rust-preventive
ionomeric coating composition, as the vehicle is being conveyed on
a vehicle assembly line during its original manufacture. The
coating method is preferably used as a replacement for
electrocoating car and truck bodies. The method comprises:
[0010] (a) applying to at least one surface of an automotive
substrate, such as a vehicle body or part thereof, a coating liquid
comprising an aqueous dispersion of an ionomer resin;
[0011] (b) flash drying or baking said coating liquid on the
substrate to form a rust-preventive primer layer; and,
[0012] (c) optionally, applying over said rust-preventive primer
layer, a primer surfacer and/or an automotive topcoat finish such
as a basecoat/clearcoat finish;
[0013] wherein the automotive substrate is, preferably, in
continuous movement throughout the primer paint application process
along a vehicle assembly line.
[0014] Preferably, the ionomer resin coating liquid is housed in
the existing electrocoat tank that has been emptied of
electrocoating composition and is being used as a complete
replacement for the standard automotive electrodeposition coating
composition. The old electrocoating tank is preferably used as a
coating dip tank for the new ionomer resin. The tank is preferably
stripped of electrodes and applied voltage and is preferably
operated as a non-electrophoretic coating process.
[0015] Treated articles such as vehicle bodies or parts thereof
treated with the same, also form part of this invention.
[0016] The ionomer resin dispersion employed as the coating liquid
preferably comprises ethylene-acrylic acid or methacrylic acid
copolymer having an acid content of 5-40 weight percent neutralized
with a mixture of ammonium ions and at least one divalent metal
cation selected from the group consisting of alkaline earth metals
and Zn, and water as the volatile liquid carrier.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The forgoing summary, as well as the following detailed
description of the preferred embodiments, will be better understood
when read in conjunction with the appended drawings, in which:
[0018] FIG. 1 is a schematic diagram of an exemplary process
according to the present invention for applying an ionomer resin
coating composition to an automotive substrate on a continuously
moving assembly line during vehicle manufacture.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] In this disclosure, a number of terms and abbreviations are
used. The following definitions are provided.
[0020] "Ionomer" or "ionomeric resins" are polymers or copolymers
of ethylene and acrylic or methacrylic acid that have optionally
been partially or completely neutralized with a base, such as a
metal hydroxide or oxide or acetate, ammonium hydroxide, or amines.
The resulting polymer is capable of forming or behaving as though
crosslinks are formed between polymer chains under curing
conditions, creating tough flexible films.
[0021] "Copolymer" means polymers containing two or more
monomers.
[0022] All "molecular weights" disclosed herein are determined by
gel permeation chromatography "GPC" using polystyrene as the
standard.
[0023] A method according to the present invention for applying a
rust-preventive ionomer coating liquid to an automotive substrate
to form a rust-preventive coating layer thereon as part of an
automotive coating process will now be discussed with reference to
an exemplary continuous automotive coating process described in
detail below. By "continuous process" is meant that the substrate
is in continuous movement along an assembly line. However, it is to
be understood that this exemplary continuous coating process is
provided simply as one example of a process in which the invention
can be practiced and the invention should not be considered as
limited thereto. One skilled in the art would understand that the
present invention could also be used, for example, in
non-continuous, e.g., semi-continuous or indexing coating
processes, or batch coating processes. Additionally, while the
following discussion is directed primarily to coating automotive
bodies, it is to be understood that the invention could be
practiced on any automotive substrate at any point along the
coating line or off-line.
[0024] Referring now to FIG. 1, there is shown a schematic diagram
of a portion of an exemplary continuous automotive coating process
(indicated generally as 10) for applying a rust-preventive primer
over one or more surfaces of an automotive substrate, for rinsing
the coated substrate, if desired, with one or more rinsing
compositions, and for flash drying or baking the substrate in a
continuous oven.
[0025] Useful substrates that can be coated include those formed
from metallic materials, for example ferrous metals such as iron,
steel, and alloys thereof, non-ferrous metals such as aluminum,
zinc, magnesium and alloys thereof, and combinations thereof.
Preferably, the substrate is formed from cold-rolled steel,
electrogalvanized steel such as hot-dipped electrogalvanized steel,
aluminum or magnesium.
[0026] The substrates can be used as components to fabricate
automotive vehicles, including but not limited to automobiles,
trucks, and tractors. The substrates can have any shape, e.g., in
the form of automotive body components, such as bodies (frames),
hoods, doors, fenders, bumpers and/or trim, for automotive
vehicles. A coating system incorporating the concepts of the
present invention first will be discussed generally in the context
of coating a metallic automobile body. One skilled in the art would
understand that a coating process incorporating the present
invention also is useful for coating other automotive as well as
non-automotive components.
[0027] The substrate is typically first cleaned to remove grease,
dirt, or other extraneous matters. This is typically done by
employing conventional cleaning procedures and materials. Such
materials include mild or strong alkaline cleaners, such as those
commercially available and conventionally used in metal treatment
processes. Examples of alkaline cleaners include Chemkleen 163 and
Chemkleen 177, both of which are available from PPG Industries,
Pretreatment and Specialty Products. Such cleaners are generally
followed and/or preceded by water rinse(s). Optionally, the metal
surface may be rinsed with an aqueous acidic solution after
cleaning with the alkaline cleaner and before contact with a
subsequent coating composition. Examples of rinse solutions include
mild or strong acidic cleaners, such as the dilute nitric acid
solutions commercially available and conventionally used in metal
treatment processes.
[0028] The metal substrate may also optionally be phosphated.
Suitable phosphate conversion coating compositions may be any of
those known in the art. Examples include zinc phosphate, iron
phosphate, manganese phosphate, calcium phosphate, magnesium
phosphate, cobalt phosphate, zinc-iron phosphate, zinc-manganese
phosphate, zinc-calcium phosphate, and layers of other types, which
may contain one or more multi-valent cations. Phosphating
compositions are known to those skilled in the art and are
described, for example, in U.S. Pat. Nos. 4,941,930; 5,238,506; and
5,653,790.
[0029] The substrate can also be contacted with one or more
conventional passivating compositions to improve corrosion
resistance. Such passivating compositions are typically dispersed
or dissolved in a carrier medium, usually an aqueous medium. The
passivating composition may be applied to the metal substrate by
any known application techniques, such as by dipping or immersion,
spraying, intermittent spraying, dipping followed by spraying,
spraying followed by dipping, brushing, or by roll-coating. An
exemplary passivating composition is described in U.S. Pat. No.
6,217,674.
[0030] Referring now to FIG. 1, in the rust-preventive primer
coating portion 12 of the process 10, a coating liquid in the form
of a liquid ionomer resin coating composition 14 is applied to a
surface 16 of an automobile body 18 in a first step 20. The coating
composition 14 can be applied, for example, by dipping the
automobile body 18 into a container or bath 22 containing the
liquid ionomer resin coating composition 14. Preferably, the
container being used is the existing electrodeposition coating dip
tank located along the assembly line at a vehicle assembly
plant.
[0031] As indicated above, the existing electrocoating tank will
not be used for electrodeposition in view of the present invention.
Instead, it is used as the dip tank 22 for the ionomer resin
coating composition which serves herein as a replacement or
substitute for the electrodeposition coating composition and
process. The liquid ionomer resin coating composition 14 has a top
surface 24, the location of which top surface 24 in the bath 22 may
vary between a maximum level and a minimum level depending upon the
quantity of coating composition 14 in the bath 22 and whether the
automobile body 18 is in or out of the bath 22. The liquid ionomer
resin coating composition 14 can be applied to the surface 16 of
the automobile body 18 by any suitable dip coating process well
known to those skilled in the art.
[0032] In the primer coating process of the present invention, the
electrically conductive anode or cathode (not shown) previously
used in the electrodeposition process will preferably be turned off
in the tank and essentially no voltage will be passed between this
electrode and its counter-electrode (the electrically conductive
surface 16 of the automobile body 18) to deposit the coating film
on the automobile body. Instead, in the present invention, the
automobile body merely enters the dip tank 22 and following contact
with the liquid ionomer resin coating composition, an adherent film
26 of the coating composition 14 is deposited on the automobile
body 18. The conditions under which film deposition is conducted
can be varied depending on the environmental conditions at the
assembly plant, the nature of the liquid coating materials, and the
desired final film thickness of the adherent coating film, as will
be apparent to those skilled in the art. It is generally desired to
keep the automobile body 18 in the dip tank 22 for about 1 to 300
seconds, more preferably about 1 to 60 seconds, at a bath
temperature of 18 to 60.degree. C., at atmospheric pressure.
[0033] Of course, the rust-preventive ionomer treatment can be
conducted by any other known manner such as spray, curtain, flow
coater, roll coater, brush coating, and the like. In automotive
applications, the dipping method, as described above, is generally
preferred.
[0034] Generally, any type of conventional ionomer resin coating
composition can be used in the practice of the present invention.
Preferably, the ionomer resin coating composition 14 comprises an
aqueous dispersion of ionomer resin in water. The ionomer resin
coating composition can also be dispersed in an aqueous medium
which can include an admixture of water with coalescing solvents,
if desired. The ionomer resin coating composition is also
preferably supplied as a one-component system with all ingredients
dispersed and neutralized in aqueous medium prior to incorporation
into the dip tank.
[0035] The ionomer resin coating composition used herein generally
comprises an aqueous dispersion of one or more film-forming ionomer
resins, such as an ethylene-unsaturated carboxylic acid copolymer,
and one or more neutralizing agents therefore. The amount of
film-forming material in the composition generally ranges from
about 5 to 50 weight percent on a basis of total weight solids of
the composition.
[0036] As for the components of the aqueous dispersion, the ionomer
resin is typically a polymer comprising a polymeric main chain
mainly consisting of hydrocarbon, and having carboxyl groups at
side chains, wherein at least a part of the carboxyl groups is
neutralized with cationic neutralizing agents. Preferably, the
ionomer resin employed in the present invention is an
ethylene-unsaturated carboxylic acid copolymer ("ethylene-acid
copolymer"), comprising a partially neutralized product obtained by
neutralizing at least a part of the carboxyl groups contained in
the copolymer with either polyvalent metal cations, alkali metal
cations, ammonium ions, or a mixture of any of the above.
[0037] The ethylene-unsaturated carboxylic acid copolymer that
constitutes the main skeleton of the ionomer resin may be a random
copolymer of ethylene and unsaturated carboxylic acid or a graft
copolymer in which unsaturated carboxylic acid is graft bonded to
the main chain comprising polyethylene. In particular, the
ethylene-unsaturated carboxylic acid random copolymer is
preferable. Further, this ethylene-unsaturated carboxylic acid
copolymer may contain one kind of unsaturated carboxylic acid only,
or two kinds or more of unsaturated carboxylic acids.
[0038] The unsaturated carboxylic acid that is the component of the
ethylene-unsaturated carboxylic acid copolymer includes an
unsaturated carboxylic acid having 3-8 carbon atoms or the like.
Specific examples of the unsaturated carboxylic acid having 3-8
carbon atoms include acrylic acid, methacrylic acid, maleic acid,
fumaric acid, itaconic acid, crotonic acid, isocrotonic acid,
citraconic acid, allylsuccinic acid, mesaconic acid, glutaconic
acid, nadic acid, methylnadic acid, tetrahydrophthalic acid, and
methylhexahydrophthalic acid. Of those, acrylic acid and
methacrylic acid are preferable from the standpoint of film-forming
property.
[0039] Further, the ethylene-unsaturated carboxylic acid copolymer
may contain a third component in the main skeleton such as a
softening monomer in addition to ethylene and the unsaturated
carboxylic acid. This third component includes unsaturated
carboxylic acid esters such as methyl (meth)acrylate, ethyl
(meth)acrylate and isobutyl (meth) acrylate, and vinyl esters such
as vinyl acetate. If these monomers are included, it is generally
desirable for the content to be set in the range of 20 wt % or
less, preferably 10 wt % or less, since larger amounts tend to
cause the melting point of a coating film to fall and the heat
resistance to be unacceptable. Preferably, the ethylene acid
copolymer is a dipolymer (no third comonomer).
[0040] As for the ethylene-unsaturated carboxylic acid copolymer,
when considering the feasibility of manufacture of an aqueous
dispersion, the dispersion stability and the physical properties of
the coating film obtained with the aqueous dispersion, it is
generally desirable for the ethylene-unsaturated carboxylic acid
copolymer to have an unsaturated carboxylic acid content of 5-40
wt. %, preferably 10-35 wt %, and more preferably 15-25 wt. %. In
the case of using a copolymer containing an unsaturated carboxylic
acid in an amount that is less than the above-mentioned range, it
is difficult to obtain a composition having good dispersion
stability. In the case of using a copolymer containing an
unsaturated carboxylic acid in an amount more than the
above-mentioned range, a stable dispersion composition can be
obtained and both the waterproofness (imperviousness to water) and
mechanical strength of the coated film are reduced.
[0041] At least a part of the carboxyl groups on the
ethylene-unsaturated carboxylic acid copolymer is neutralized with
a base such as a metal hydroxide or oxide, ammonium hydroxide, or
amines, or any mixtures thereof, to form crosslinks comprising
association of carboxylic acid anions with various metal cations,
and ammonium ions. However, in order to obtain a coating film
especially excellent in water resistance and film quality, it is
more desirable to use a mixture of divalent metal cations and
ammonium ions as the neutralizing agent. The divalent metal ions
which remain in the film, provide the desired corrosion resistance
to the coating formed therefrom. The ammonium ions evanesce as
ammonia on heating and thus provide the desired water
impermeability, especially in comparison to alkali metal ions.
[0042] As for divalent metal cations, alkaline earth metals, such
as Mg and Ca, and Zn are preferred. Of those, the ionomer resins
having Zn is preferable in the point that the production is easy.
It should be understood that compounds containing these divalent
metal cations, when used at the levels desired herein, will
typically cause the aqueous dispersion to coagulate. Therefore, for
example, when zinc is used, to avoid coagulation, it is desirable
to introduce it in the dispersion as an ammonia (or amine) complex
preferably in the presence of excess aqueous ammonia (i.e., using
an amount of ammonia in excess of the amount that would be needed
to neutralize the carboxylic acid groups). Failure to complex the
divalent cation prior to contact (i.e., mixing) with the ionomeric
resin will generally cause the mixture to coagulate and form an
unusable and inferior coating.
[0043] Thus, in order to form the desired divalent metal
(preferably divalent zinc oxide)/ammonia complex, the divalent
metal oxide (e.g., zinc oxide) is preferably milled, such as ball
milled, with a large amount of (i.e., excess) aqueous ammonia (10
to 50 moles of ammonia for each mole of zinc oxide) for several
hours, preferably at least 5 hours, at room temperature. The
resulting slurry can then be added to ionomer resin which may or
may not be pre-dispersed with aqueous ammonia. Of course, other
techniques may also be used to introduce the divalent metals into
the dispersion without coagulation, as will be apparent to those
skilled in the art.
[0044] Since the metal cations remain in the final film, it is
preferred to discuss levels of neutralization in terms of the metal
ion. As will be appreciated by one skilled in the art, the
preferred degree of neutralization by the metal, i.e., the
preferred ratio of metal ion to carboxylic acid anion, of course
will depend on the ethylene-acid copolymers and the ions employed
and the properties desired. However, the preferred proportion of
carboxyl groups neutralized with divalent metal cations to all of
carboxyl groups that the ethylene-unsaturated carboxylic acid
copolymer has on the side chain, that is, degree of neutralization
by the metal, is generally about 20-100%, and preferably 25-50%, so
that a coating having excellent corrosion resistance is obtained.
Since excess ammonia is preferably used, this typically translates
to a mole ratio of metal cation to ammonia in the final mixture of
generally about 2 to 100, and preferably 10 to 20.
[0045] As will be appreciated by one skilled in the art based on
the teachings herein, the preferred level of neutralization will
depend on the ethylene-acid copolymers and the ions employed and
the properties desired. In particular, where the aqueous dispersion
composition of the present invention is used as a rust-preventive
coating liquid, the above ranges are effective in the point that a
rust-preventive layer having excellent corrosion resistance and
water resistance can be formed.
[0046] The production of ionomer resins used herein can be
conducted according to various methods well known in the art, for
example, a method of copolymerizing ethylene, unsaturated
carboxylic acid, and a third component used according to the need,
by a high pressure radical polymerization method, and neutralizing
carboxyl groups of the ethylene-unsaturated carboxylic acid
copolymer obtained with a cationic compound; or a method of graft
polymerizing unsaturated carboxylic acid onto polyethylene, and
neutralizing carboxyl groups of the graft copolymer obtained with a
cationic compound. Further, this production may be conducted by
supplying predetermined components into an extruder and melt
kneading to conduct reaction, or may be conducted in water or an
appropriate organic solvent.
[0047] Rather than preparing the ethylene-unsaturated carboxylic
acid copolymer, Nucrel.RTM., which is a
poly(ethylene-co-methacrylic acid) copolymer, sold by DuPont,
Wilmington, Del., can be used as the starting material. This
material is typically sold pre-dispersed in ammonia water.
[0048] As for the other components, a compound having desired
divalent metal cations which can be used to neutralize the resin
includes divalent metal oxides or hydroxides and simple
water-soluble salts such as the acetates, sulfates and nitrates of
zinc, calcium, or magnesium. A compound having the desired ammonium
ions which can be used to neutralize the resin is ammonia
(NH.sub.3) or aqueous ammonia (which is also referred to herein as
"ammonium hydroxide" or "ammonia water").
[0049] Typically, the coating composition is made by introducing
ionomer resin, and neutralizing agents, such as aqueous ammonia
(ammonium hydroxide), one or more metal cations, and the like and
water into a vessel, then stirring or shaking the mixture at a
temperature above the melting temperature of the ionomer resin,
typically about 100-200.degree. C., for a sufficient time to heat,
melt and uniformly disperse the ionomer resin, preferably about 10
minutes to 2 hours.
[0050] A suitable aqueous dispersion for rust-preventive coating of
automotive bodies comprises an aqueous dispersion of ethylene-acid
copolymer having an acid content of 18-30 wt. % and containing
25-50 mole % divalent metal cations and 75-600 mole % ammonia based
on the carboxyl groups of copolymer.
[0051] A suitable aqueous dispersion for rust-preventive coating
preferably also has its average diameter of dispersed particles in
the range of about 0.1 .mu.m or less, and preferably 0.05 .mu.m or
less and its solid content concentration in the range of 10-45 wt
%, and preferably 15-35 wt %, and more preferably 15-30 wt. %. A
suitable aqueous dispersion typically also has a pH of 7 or more
and a viscosity of about 30-2,000 mPas, and particularly about
50-1,500 mPas, at the time of application for good workability.
[0052] Various other additives can be blended into the dispersion
to provide additional coating attributes, depending on need, within
the range that the object of the present invention is not impaired.
For example, various other film-forming and/or crosslinking resins
such as water-soluble polyester polyols, acrylics, and
water-soluble covalent curing agents such as amino resins and the
like. The water-soluble amino resin is used in particular to
improve strength of the coating, and examples thereof include
water-soluble melamine resin, hexamethoxymelamine, methylolated
benzoguanamine resins and methylolated urea resins. Examples of the
other components include organic and inorganic thickeners to adjust
viscosity, surface active agents to improve stability,
water-soluble polyvalent or monovalent metal salts and other
rust-preventive assistants, vapor phase corrosion inhibitors,
mildew proofing agents, fungicides, biocides, ultraviolet
absorbers, heat stabilizers, foaming agents, rheology control
agents, pigments, fillers, and extenders. In addition to the
forgoing materials, in order to obtain a coating film with
sufficient water resistance for automotive applications (i.e.,
impervious to agents which can cause corrosion of metal), it is
generally desired to include at least one non-water soluble, vapor
phase corrosion inhibitor such as dicyclohexylamine in the
dispersion.
[0053] The thickness of the coating applied to the substrate can
vary based upon such factors as the type of substrate and intended
use of the substrate, i.e., the environment in which the substrate
is to be placed and the nature of the contacting materials.
Generally, the coating is applied such that the final thickness of
the coating formed on the substrate ranges from about 0.1-20 .mu.m,
and more preferably to coat in a thickness of 0.3-10 .mu.m.
[0054] Referring again to FIG. 1, the coating composition in the
bath 22 can be recycled in conventional manner, such as by a
recycling system 28 having a pump P1 that prevents the solids of
the coating composition from settling to the bottom of the bath 22.
Further, the temperature of the coating composition 14 may be
controlled by use of a heat exchanger (not shown) in flow
communication with the bath 22 in any conventional manner, such as
through pipes or conduits.
[0055] The coating composition 14 from the bath 22 also may be in
flow communication with a conventional ultrafiltration system (not
shown) to remove soluble impurities and the filtered material
recycled to the ionomer bath 22. In the ultrafiltration system, the
coating composition 14 flows over a membrane permeable to water and
small particles, e.g., those less than about 1,000 Mw, such as
salts. The ultrafiltrate or "permeate", i.e., the portion of the
coating composition which passes through the membrane, can be used
in further subsequent rinsing operations (if employed) and a
portion of the permeate, e.g., about 20 weight percent, may be
discarded. The "non-permeate" portion of the coating composition is
directed back into the bath 22, e.g., through one or more conduits
or pipes.
[0056] After conveying from the ionomer coating bath 22, the coated
automobile body 18 is preferably exposed to air to permit excess
deposited coating composition to drain from the interior cavities
and surfaces of the automobile body 18 back into the bath 22.
[0057] After coating the rust-preventive ionomer coating
composition on a substrate and rinsing (if employed), the agent may
be spontaneously dried (i.e., flash dried under ambient or slightly
elevated temperature conditions, preferably at an air temperature
ranging from about 10.degree. C. to about 40.degree. C.), but it is
preferable to conduct baking in a conventional continuous oven 30
typically located after the ionomer resin dip tank along the
automotive assembly line. The oven baking temperature is about
60-250.degree. C. The coated automotive body 18 is preferably
conveyed to the continuous oven 30 and heated in the above
temperature range for about 1 second to 30 minutes to drive off the
volatile components such that a rust-preventive layer comprising a
coating having good corrosion resistance can be formed.
[0058] The thickness of the rust-preventive coating layer formed on
the substrate is appropriately selected according to the purpose of
use of rust-preventive treated metal products, rust-preventive
treating agent used, kind, thickness or the like of a over coat
paint, and the like, and is not particularly limited thereto.
Generally, in order to exhibit sufficient rust-preventive ability
without causing breakage in the rust-preventive layer when drying
after coating the rust-preventive treating agent, it is preferable
to coat in a thickness of about 0.3 to 2.5 mils (7 to 60 .mu.m),
preferably 0.5 to 1.5 mils (12 to 36 .mu.m).
[0059] The rust-preventive coating layer this formed on the
automobile body has excellent corrosion resistance and also good
adhesion to an over coat paint, such as an automotive primer,
filler or basecoat paint.
[0060] The rust-preventive coating method of the present invention
is also especially useful over unplated metal, which is
particularly desirable in the automotive industry when the metal is
used to construct vehicle bodies, such as car and truck bodies.
[0061] In the rust-preventive treatment method of the present
invention, after the rust-preventive primer coating layer is dried,
it is traditionally overcoated or topcoated with a primer surfacer
to provide a smooth film free of surface imperfections over which
an automotive topcoat finish such as a basecoat/clearcoat finish
can be applied.
[0062] The overcoat paint that is coated on the rust-preventive
coating layer formed herein can be any automotive primer surfacer,
filler or colored basecoat paint or basecoat/clearcoat paint. The
nature of the primer surfacer, filler, or basecoat or
basecoat/clearcoat composition employed in the method of the
present invention is in no way critical. Any of a wide variety of
commercially available automotive primer surfacer, fillers,
basecoats, clearcoats may be employed in the present invention.
[0063] Typically, a primer-surfacer is next applied (not shown) to
smooth the surface and provide a thick enough coating to permit
sanding to a smooth, flat finish, and then baked. Then a top-coat
system (not shown) is applied, sometimes as a single colored coat,
more often now as a pigmented basecoat with solid color or flake
pigments followed by a transparent protective clear coat, to
protect and preserve the attractive aesthetic qualities of the
finish on the vehicle even on prolonged exposure to the environment
or weathering.
[0064] It has become customary, particularly in the auto industry,
to apply a clear topcoat over the basecoat by means of a
"wet-on-wet" application, i.e., the clear coat is applied to the
basecoat without curing or completely drying the basecoat. The
coated substrate is then heated for a predetermined time period to
allow simultaneous curing of the base and clear coats.
[0065] Conventional coating methods such as spraying, electrostatic
spraying, high rotational electrostatic bells, and the like, can be
used to apply any of these three overcoatings. The preferred
techniques for applying all three coatings are air atomized
spraying with or without electrostatic enhancement, and high speed
rotary atomizing electrostatic bells, since these techniques are
typically employed in modern automobile and truck assembly
plants.
[0066] When the primer surfacer coating material is applied to
automotive bodies according to the present invention, any of the
above techniques can be used.
[0067] The primer-surfacer coating material preferably forms a dry
coated layer having a thickness of about 0.3 to 2.5 mils (7 to 60
.mu.m), preferably 0.5 to 1.5 mils (12 to 36 .mu.m), but it may
vary according to the intended use.
[0068] The primer after application is typically flash dried at
ambient temperatures and then baked in an oven 100-150.degree. C.
for about 15-30 minutes to form a cured primer surfacer layer on
the substrate.
[0069] After the primer surfacer layer is formed on the automobile
body, the layer may be cooled and sanded as desired. Then colored
base coating material which may contain solid color, metallic
flake, pearlescent and/or other effect pigments and a transparent
clear coating material are the typically applied in the wet-on-wet
manner to form a base coated layer and a clear coated layer.
[0070] The base coating material may be applied, like the primer
surfacer coating material, with using air-electrostatic spray
coating or a rotary atomizing electrostatic bell so as to have a
dry thickness of 0.1 to 1.6 mils (3 to 40 .mu.m). The basecoating
is typically flash dried for a short period at ambient or slightly
elevated temperatures before the automobile body is
clearcoated.
[0071] The clear coated material is then applied on the base coated
layer, for the purpose of smoothing roughness or glittering which
occurs due to the presence of luster color pigment and for
protecting a surface of the base coated layer. The clear coated
material may be applied, like the base coating material, with using
the rotary atomizing electrostatic bells.
[0072] The clear coated layer is preferably formed so as to have a
dry thickness of about 1.0 to 3.0 mils (25-75 .mu.m).
[0073] The basecoat and clearcoat obtained as described above are
then cured simultaneously in an oven 100-150.degree. C. for about
15-30 minutes to form a desired multi-layer finish on the
automobile body.
[0074] The process of the invention may also include a subsequent
cooling step (not shown) to cool the finish to ambient temperatures
before the vehicle is further worked on during its manufacture.
[0075] The overall thickness of the dried and cured composite
multi-layer finish is generally about 40-150 .mu.m (1.5-6 mils) and
preferably 60-100 .mu.m (2.5-4 mils).
[0076] The rust-preventive treated automobile body obtained by the
rust-preventive coating method of the present invention contains a
rust-preventive layer having excellent water resistance and
rust-preventive property, and therefore can suitably be used as
parts for automobiles
[0077] Coatings formed from the method of this invention have
excellent rust-preventive properties and provide high level of
adhesion to treated or untreated metals and are tough, flexible,
stone-chip resistant, and are relatively impermeable to moisture
and other corrosive agents, and can provide rust preventive
coatings having properties desirable for automotive finishes.
[0078] The following Examples illustrate the invention. All parts
and percentages are on a weight basis unless otherwise
indicated.
EXAMPLE 1
Preparation of Aqueous Dispersion
[0079] Into a 1000 ml bottle is charged 8.6 g of zinc oxide, 20 g
of conc. ammonium hydroxide, 2.0 g of dicyclohexylamine, and ten
0.5 in. long.times.0.5 in. diam. high density alumina
(Burundum.RTM.) ceramic grinding stones (manuf. by U.S. Stoneware,
East Palestine, Ohio). The bottle was sealed, placed on a roller
mill (manuf. by U.S. Stoneware, East Palestine, Ohio), and rolled
at 53 rpm for 18 hours. Then 800 g of Michem Prime.RTM. 4983R
(ethylene/21% acrylic acid (Nucrel.RTM.)copolymer at 25% solids in
ammonia water manuf. by Michelman, Inc., Cincinnati, Ohio), 10 g of
ammonium hydroxide, and 70 g of water was added to the bottle. The
contents were placed on the roller mill and rolled for 24 hours.
The dispersion was filtered through a Nylon stocking to give an
ionomeric dispersion having 23% solids and 38% neutralization of
the carboxylic acid groups by zinc.
EXAMPLE 2
Preparation of Rust-Preventive Treated Metal Plate
[0080] Cold rolled steel plates, 3 in..times.5 in., (32 guage)
(manuf. by ACT Laboratories, Inc, Hillsdale Mich.) were cleaned by
dipping them in a 1:1 v/v solution prepared from dichloromethane
and acetone. After removing the cleaning solvent by air drying, the
plates were dipped in the dispersion of Example 1 and then heated
in an 95.degree. C. oven for 25 to 30 minutes. The plates were then
removed from the oven and allowed to cool to room temperature. The
thickness of the coating was found to be approx. 1.0 mils. using a
Permascope.RTM. ES thickness meter (manuf. by Twin City Testing
Corp., North Tonawanda, N.Y.).
Test Results
[0081] Coating Adhesion was determined by cutting the coating with
a razor to create a cross-hatched design with cut-lines spaced 2 mm
apart. Five lines were cut in each direction to form 16 squares. A
piece of Scotch tape was firmly pressed over the cross-hatched
design and the pulled off at an angle of 90 degrees. Perfect
adhesion results in no loss of coating within the 16 squares and is
given a score of 16/16. Loss of all squares is given a score of
0/16. The coating of Example 2 had an adhesion score of 16/16.
[0082] Corrosion resistance was determined by placing the coated
steel sheets prepared in Example 2 in 3% sodium chloride solution
for 10 days and noting the appearance of rust. Prior to the
corrosion test, the edges of the coated steel panels were painted
with an oil-based alkyd paint. Coatings prepared as in Example 2
that are 0.5 mil or greater in thickness displayed no corrosion,
which is a significant improvement in corrosion resistance.
[0083] Various other modifications, alterations, additions or
substitutions of the components of the processes and compositions
of this invention will be apparent to those skilled in the art
without departing from the spirit and scope of this invention. This
invention is not limited by the illustrative embodiments set forth
herein, but rather is defined by the following claims.
* * * * *