Note: Descriptions are shown in the official language in which they were submitted.
CA 02363482 2001-09-14
WO 00/55265 PCT/EP00/01065
s BADGE-FREE CAN COATING
Background of the Invention
Metal containers for receiving foods and beverages generally have one
or more coatings to prevent contact between the filled product and metal.
This is to prevent or minimize corrosion to the metal by the product and any
disadvantageous influences on the quality of the product. For producing
containers of this type, such as steel or tin cans, metal sheets are used
which,
prior to their shaping (such as for three-piece can production) or deformation
~s (such as for deep drawing process), are coated with suitable coating
compositions. In producing cans for foods and beverages, coatings are
required which are extremely flexible and have a low order of toxicity.
Epoxy phenolic type coatings have been applied as lacquers onto metal
can stock (e.g., for three-piece cans) and baked to provide coatings having
2o good resistance to aggressive filled products, mechanical performance and
metal adhesion. However, many of these incorporate 2,2'-bis(4-
hydroxyphenyl) propane-bis(2,3-epoxypropyl)-ether (or homologues thereof),
otherwise known as bisphenol-A-diglycidyl-ether or "BADGE" (Bisphenol-
A-DiGlycidyl-Ether).
2s One objective of the present invention is to provide a novel can coating
which is substantially free of BADGE (and BADGE-type components).
BADGE-containing formulations do not meet approval in some countries for
use in food canning. Currently available polyester type coatings, such as
those cross-linked with amino-type or isocyanate-type resins, are used on the
3o exterior of three-piece cans, but do not resist processing when in contact
with
food, or do not comply with food laws, and therefore do not yet provide an
alternative coating formulation. In view of the foregoing disadvantages of the
prior art, a novel can coating is need which is substantially BADGE-free (and
PVC-free as well).
CA 02363482 2001-09-14
WO 00/55265 PCT/EP00/01065
Summary of the Invention
In surmounting the disadvantages of the prior art, the present
invention provides a coating for metal sheet substrates, such as metal cans or
metal can stock, which is substantially BADGE-free.
1 o Another objective of the present invention to provide a coating which
is substantially free of polyvinyl chloride (PVC).
A further objective of the invention is to provide metal can coatings
that have suitable flexibility and are safe when processed in contact with
food.
The coatings should be suitable for three-piece cans as well as deep-drawn
1 s metal cans.
An exemplary coating of the invention comprises (a) a polyester resin
(20-50% wt.); (b) a resol resin (1-15% wt.); and (c) a solvent component (35-
79 % wt.), all weight percentages based on total coating weight, the coating
being substantially free of bisphenol-A-diglycidyl-ether and bisphenol-F-
2o diglycidyl ether (e.g., "BADGE" or "BADGE-type' components), and
preferably also substantially free of polyvinyl chloride. In further preferred
embodiments, the coating comprises a lubricant (0.1-2% wt.) and acid catalyst
(0-2% wt.).
Further advantages and features of the present invention are discussed
25 hereinafter.
Detailed Description of the Invention
All weight percentages provided herein are based on the total weight
of the coating composition including solvent.
3o As summarized above, exemplary coating compositions of the
invention comprise: (a) a polyester resin in the amount of ~0-50% wt.; (b) a
resol resin in the amount of 1-15% wt. and comprising a condensation product
made from a phenol or homologue thereof and formaldehyde; and (c) a
solvent in the amount of 35-79% wt., all weight percentages being based on
35 the total weight of said coating, the coating compositions being
substantially
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CA 02363482 2001-09-14
WO 00/55265 PCT/EP00/01065
s free of bisphenol-A-diglycidyl-ether ("BADGE") and bisphenol-F-diglycidyl
ether (a "BADGE-type' component).
The phrase "substantially free" as used within the context of this
application means that the coating compositions of the invention have no
BADGE, BADGE-type component, or PVC, or at least no more than a de
t o minimus amount of these components, e.g., less than 0.001 % by total wt..
An exemplary polyester resin component of the invention comprises
(a) trimethylolpropane in the amount of 0.1-10% wt. and more preferably 1-
7% wt.; neopentylglycol in the amount of 15-30% wt. and more preferably 20-
25% by wt.; at least one other polyol (e.g., ethylene glycol, propylene
glycol)
1s in the amount of 5-20% wt. and more preferably 10-15% wt.; phthalic acid
(including iso- and tere-) in the amount of 20-60% wt. and more preferably 20-
25% wt.; and adipic acid in the amount of 10-35% wt. and more preferably 15-
20 % wt. A commercially available polyester resin, available from DSM Resins
of Zwolle, The Netherlands under the tradename URALAC XP 8481 SN, is
2o believed to be suitable for use as polyester resin component (a) in the
present
invention.
Resol resin component (b) may be characterized as a condensation
resin made from a phenol or phenolic homologue (phenol, butyl phenol,
cresol, xylenol, Bisphenol A) and formaldehyde. Preferably, the resol resin
2s comprises Bisphenol A, butyl phenol, xylenol, or a mixture thereof, and
formaldehyde. Commercially available resol resins believed to be suitable for
use in the present invention are available from Vianova Resins, Germany,
under the tradename PHENODUR PR 401 and from Deutsche Shell Chemie,
Germany, under the tradename EPICURE DX 200.
3o The resins can be solvated in a solvent or solvent mixture, for example,
n-butanol and/or butylcellusolve, or other conventional solvents used for can
coatings. The resin can be etherified with an alcohol (e.g., butanol) and
solvated in the solvent or solvent mixture. Other known solvents that can be
used for solvating the polyester and resol resins include aromatic
3s hydrocarbons (e.g., aromatic 100 or aromatic 150), glycolether/glycolether
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WO 00/55265 PCT/EP00/01065
acetate (e.g., methoxypropanol butylcellusolveacetate,
methoxypropylacetate,), alcohols (e.g., isobutanol, diacetone alkohol), ketons
(e.g., methylisobutylketon, isophorone) or esters (e.g., butyl acetate,
dibasic
esters). In other exemplary coating compositions of the invention, at least
two
different solvents are used, preferably having different boiling ranges.
1o Preferably, the coating composition further comprises a lubricant
which is in a solid form dispersed in solvent. The lubricant may be present in
the coating composition in the amount of 0.1-2% wt., and more preferably 0.1-
1 % wt. Exemplary lubricants may comprise polyethylene (PE),
polypropylene (PP), PTFE, lanoline, carnauba wax and petrolatum.
Preferably, the lubricant comprises PE, PP or PTFE or a mixture of these.
Preferred coating compositions also comprise at least one catalyst,
preferably an acidic catalyst, such as sulfonic acid (e.g., paratoluene
sulfonic
acid and dodecyl benzenesulfonic acid), phosphoric acid and phosporic acid
ester (e.g., phosphoric acid monobutyl ester), in the amount of 0.05-2.0% wt.,
2o and more preferably in the amount of 0.05-1.0% wt.
Accordingly, a preferred coating composition of the invention
comprises polyester resin (solid) (20-50% wt); resol resin (solid) (1-15% wt);
a
lubricant (solid) (0.1-2% wt); an acidic catalyst (0-2% wt); and a solvent (35-
79% wt), all percentages based on the total weight of the coating composition.
The coating may be applied to a metal substrate or metal plate for a
can, such as by roller coating or spray coating, or it may be applied by these
means to a formed can. Preferred application is by roller coating to the flat
metal before formation of the can. Preferred coating layer weights are 2-15
gsm (grams/square meter), and more preferably 3-8 gsm. After application,
3o the coating should be cured at 180°C - 210°C, and more
preferably at 190°C -
205°C for 6 to 20 minutes, and more preferably 8-13 minutes.
CA 02363482 2001-09-14
WO 00/55265 PCT/EP00/01065
s Example 1
An exemplary can coating composition of the invention may be
prepared and applied as follows. A coating batch may be formulated as
follows, using a blender that can mix the following components into a
sufficiently homogeneous composition. The polyester resin, comprising
1 o trimethylolpropane, neopentylglycol, and other polyols, as previously
discussed, is preferably added first into the blender in the amount of 40-85%
wt and more preferably 69-80% wt (based total weight of coating
composition). The polyester resin was URALAC XP 8481 SN (from DSM
l;esins) which was solvated in a solvent mixture that comprised SOLVESSO
1 s 150 and butyl cellosolve (which solvents were used in a 4:1 weight ratio).
SOL~1ESS0 150 aromatic hydrocarbon solvent is available from Exxon
Chemical, and is believed to have a boiling range of 186-210°C.
Butyl
cellosolve is otherwise known as butyl glycole (e.g., ethylene glycol mono
butyl ether).
2o Thus, once the polyester resin is introduced into the blender, then the
other components can be introduced thereafter during mixing, as follows:
Preferred More PreferredComponent Description of
Range % Range % (total Component
(total
wei ht) wei ht
40-SS 60-80 Polyester Resin~c ~ ~1 (which
is
about 503'o resin
components in
Solvesso ISOButyl
Cellosolve
4:1
4-25% 6-ls% ResolResin PHENODURPR401,70%
in butanol
0-25 % 3-8 % metho ro 1 optional additional
acetate solvent
0-25% 3-8% bu 1 cellosolveoptional additionat
acetate solvent
0-25 % 3-10 % aromatic hydrocarbonoptional additional
solvent
solvent (e.g., SOLVESSO
100 from
Exxon
0-5 % 0.5-2.0 % mixture of optional additional
methozy solvent
propanole and Wherein these
components
hos horic acidare preferably
used 4:1
O.s-s.0% 0.8-3.0% lubricant in lubricant such
solvent as PTFE
(solid) can be
used if
solvated in solvents,
e.g,
SOLVESSO 100
and butyl
cellosolve in
1:1:1 ratio
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CA 02363482 2001-09-14
WO 00/55265 PCT/EP00/01065
s Exemplary lubricants which are suitable for use in the present
invention are PFTE (polytetrafluoroethylene) modified with polyethylene
wax, micronised (e.g., specially fine), and are available from Lanco Wax under
the designations "TF 1780 EF." Also available from Lanco Wax is a
polyethylene/polypropylene lubricant under the designation "PP 1350 FF"
Io which may also be suitable in the present invention. The lubricant, which
is
in solid form, should be mixed with a suitable solvent or solvents, such as
SOLVESSO 100 (an hydrocarbon based solvent from Exxon) and butyl
cellosolve, in amounts sufficient to prevent agglomeration of the lubricant in
the mixture.
1 s Once a homogeneous mixture of the coating components is obtained,
this may be roller coated onto steel or aluminum can stock, for example, and
baked at about 200°C for preferably 12-15 minutes. A BADGE-free can
coating is thus obtained.
The foregoing discussion is provided by way of illustration only and is
2o not intended to limit the scope of the invention as set forth in the
claims.
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