Note: Descriptions are shown in the official language in which they were submitted.
c; ~.~
2096643
PAT 90 281/fe
13.11.1990
- 1271Z -
BASF Lacke + Farben Aktiengesellschaft, Munster
Powder coating and the use thereof for the coating of
packaQina container interiors and of weld seams
The present invention relates to powder coatings, based
on epoxy resins and carboxyl-containing polyesters, for
the coating of packaging container interiors and weld
seams. In addition, the present invention relates to the
process of coating packaging container interiors and weld
seams as well as to the use of the powder coatings.
Packaging containers, such as food cans, two- and three-
part beverage cans and others, are provided on the inside
with a coating, the purpose of which is on the one hand
to protect the contents from contamination by dissolved
constituents of the metal sheeting and on the other hand
to prevent corrosion of the metal sheeting by aggressive
contents.
This coating of the packaging containers takes place in
practice mainly by means of organically dissolved
coatings. However, this causes high solvent
contamination of the environment on drying of the coating
films . Attempts ha~~e therefore been increasingly made to
.. 209fi643
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replace these coatings by low-solvent or solvent-free
coatings. Thus, for example, thermoplastic powder
coatings have frequently been used to coat can weld
seams. These products are produced from the
corresponding thermoplastics by an expensive cold
grinding process.
Furthermore, thermosetting powder coatings for the
coating of weld seams of metal containers used for
foodstuffs or beverages are known from EP-B-119,164.
These thermosetting powder coatings contain, as binder,
a mixture of an aromatic epoxy resin having on average
not more than 2 epoxide groups per molecule, and an
aromatic epoxy resin having on average more than 2
epoxide groups per molecule. The condensation product
of bisphenol A diglycidyl ether with bisphenol A and/or
an acid polyester based on trimellitic
anhydride/aliphatic polyol is used as curing agent.
However, EP-B-119,164 contains no information on suitable
particle sizes and particle size distribution of the
powder coatings. In addition, it is a drawback that
these powder coatings are only suitable for the coating
of weld seams.
Powder coatings for the coating of can interiors, which
contain a polyester having terminal carboxyl groups and
an OH value lower than 10 mg of ROH/g as well as an epoxy
resin, are known from EP-B-10,805. These powder coatings
contain choline derivatives as curing catalyst. The
2o9ss4~
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powder coatings have an average particle size between 20
and 150 um. However, EP-B-10,805 contains no information
on how to obtain can interior coatings which would
provide closed films even at film thicknesses of s 15 gym.
Furthermore, owing to the low OH value of the polyester,
these powder coatings have the drawback of having only
poor crosslinking. Correspondingly, this system has
drying times of 10 to 40 min. at 150 to 220°C which are
unacceptable in practice, while the drying time in
modern production lines is not more than 20 to 30 sec. at
an object temperature of 260 to 280°C.
Powder coatings for the coating of can interiors and can
lids which contain an epoxy resin and aromatic amines,
Lewis acids and acid anhydrides as curing agents, are
known from US Patent 4,497,837. The powder coatings have
an average particle size between 20 and 150 gym,
preferably 30 to 70 gym. The drawback of these systems is
the high minimum film thickness of 38 ~m for obtaining
coatings which are not excessively porous. Moreover,
these powder coatings have the drawback of oven dwell
times between 5 and 12 min. being required for the curing
of the systems described.
Furthermore, powder coatings which also contain an epoxy
resin and aromatic amines, epoxide-amine adducts or acid
anhydrides, for the coating of can interiors are known
from US Patent 3,962,486. By using the plasma spray
coating process it is possible to produce coatings which,
2096643
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at low film thicknesses of less than 13 gym, comply with
the requirements which are usually specified for interior
coatings of foodstuff containers. To ensure
applicability by the plasma spray process, only those
powder coatings which have a maximum particle size of
<_ 100 ~m and a sufficiently low melt viscosity should be
used.
However, the use of aminic curing agents leads to an
inadequate resistance to sterilization of the resultant
coatings. It is furthermore a drawback that amine-cured
epoxy resins tend to be brittle and have very poor
flexibility. Acid anhydride curing agents have the
disadvantage of being strongly irritant, thus requiring
special protective measures in the formulation of the
powder coatings.
Finally; powder coatings for the coating of can interiors
which contain an epoxy resin and an amine curing agent,
are known from US Patent 4,183,974. These powder
coatings have an average particle size between 1 and 100 gym,
preferably between 1 and 10 gym. It is true that the
resultant coatings have the required low porosity at film
thicknesses as low as s 13 gym, but the resistance to
sterilization of the resultant coatings is in the need of
improvement. Furthermore, it is a drawback that amine-
cured epoxy resins tend to be brittle and have very poor
flexibility.
209664
The object of the present invention is to make available
powder coatings which, with the same chemical compo-
sition, are suitable both for weld seam coating and for
the coating of packaging container interiors, in
5 particular metal container interiors. In addition, these
powder coatings, when used for the coating of packaging
container interiors and when applied at film thicknesses
as low as s 15 gym, should comply with the requirements
which are usually specified for can interior coatings.
In particular, these interior coatings should not be
porous (determined with the aid of a so-called enamel
rater test), they should possess good adhesion to the
substrate and good flexibility, and they should withstand
the customary pasteurization and sterilization
conditions. Furthermore, these powder coatings, when
used for weld seam coating, should lead to highly
flexible coatings which withstand the mechanical
deformations incurred in the flanging and of the cans
beading. Resistance to sterilization and pasteurization
is also required after the deformative treatment.
The powder coatings should be curable in the course of
the brief drying times which are customary in can
coating.
Surprisingly, this object is achieved by a powder coating
of the type referred to at the outset, wherein
2096643
1.) the powder coating contains
A) at least one polyester having an acid value of 25
to 120 mg of ROH/g and an OH value >_ 10 mg of
ROH/g and
B) at least one epoxy resin having an epoxide
equivalent weight of 400 to 3000, and
2.) the powder coating has such a particle size dis-
tribution that
a) at least 90% by mass of the powder coating
particles have a particle size between 1 and
60 gym,
b) the maximum particle size for at least 99% by
mass of the powder coating particles is s 100 gym,
c) the average particle size of the powder coating
particles is between 5 and 20 gym, and
d) the slope of the particle distribution curve at
the inflection point is greater than or equal to
100.
Furthermore, the invention relates to a powder coating
for the coating of packaging container weld seams based
on epoxy resins and carboxyl-containing polyesters,
CA 02096643 1999-09-16
wherein
1.) the powder coating contains
A) at least one polyester having an acid value of 25
to 120 mg of KOH/g and an OH value of >_ 10 mg of
KOH/g, and
B) at least one epoxy resin having an epoxide
equivalent weight of 400 to 3000, and
2.) the powder coating has such a particle size
distribution that
a) at least 90~ by mass of the powder coating
particles have a particle size between 1 and 100
Vim,
b) the maximum particle size for at least 99~ by mass
of the powder coating particles is <_ 150 Vim,
c) the average particle size of the powder coating
particles is between > 20 and 60 Vim, and
CA 02096643 1999-09-16
d) the slope of the particle distribution curve at
the inflection point is >_ 50.
In addition, the invention relates to processes for the coating
of packaging container interiors and weld seams
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~8~.6643
in which these powder coatings are applied. The invention
finally also relates to the use of the powder coatings for
the coating of packaging container interiors and weld seams .
It is surprising, and could not have been foreseen, that
the powder coatings according to the invention are
suitable, with the same chemical composition, for the
coating both of weld seams and of packaging container
interiors and that the property profile and hence the use
can be regulated simply by establishing a corresponding
particle size distribution. At the same time these
powder coatings are rapidly curable, simple to handle and
simple to apply.
Furthermore, the powder coatings according to the inven-
tion, when used for the coating of packaging container
interiors, are distinguished by the fact that coatings
with a very low film thickness of only s 15 ~m possess
the properties required by can manufacturers. In par-
ticular, these coatings have the required low porosity
at a film thickness as low as s 15 gym. Moreover, these
coatings possess good adhesion, high flexibility and good
resistance to pasteurization and sterilization.
Furthermore, the powder coatings according to the inven-
tion, when used for weld seam coating, have the advantage
of high flexibility, with the result that the weld seam
coating is able to follow the deformations of the packag-
ing container on further fabrication without peeling off
CA 02096643 1999-09-16
or cracking. Moreover, it is an advantage that, in contrast in
aminic curing agents, the powder coating according to the
invention attains good resistance to sterilization.
The individual components of the powder coatings
according to the invention are now elucidated in greater detail
below. The polyesters employed in the powder coatings according
to the invention (component A) have an acid value of 25 to 120
mg of KOH/g, preferably 30 to 90 mg of KOH/g and particularly
preferably 60 to 90 mg of KOH/g, and an OH value of at least 10
mg of KOH/g, preferably at least 15 mg of KOH/g and preferably
lower than or equal to 30 mg of KOH/g. Polyesters having a
functionality of >_ 2 are preferably employed. The number average
molecular weights of the polyesters are generally between 1000
and 10,000, preferably between 1500 and 5000. Polyesters
approved by the US FDA (FDA = Food and Drug Administration) are
preferably used. The carboxyl- and hydroxyl-containing
polyesters can be prepared by conventional methods (cf., for
example, Houben Weyl, Methoden der organischen Chemie, [Methods
of Organic Chemistry], 4th edition, volume 14/2, Georg Thieme
Verlag, Stuttgart 1961.)
Aliphatic, cycloaliphatic and aromatic dicarboxylic
and polycarboxylic acids, such as phthalic acid, terepthalic
acid, isopthalic acid, trimellitic acid, pyromellitic acid,
adipic acid, succinic acid, glutaric acid, pimelic
_ g _
~09fi6~~3
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acid, suberic acid, acelaic acid, sebacic acid and
others, are suitable as the carboxylic acid component in
the preparation of the polyesters. The acids can also be
used in the form of their derivatives capable of esterif-
ication (for example anhydrides) or transesterification
(for example dimethyl esters).
The commonly used diols and/or polyols, for example
ethylene glycol, 1,2- and 1,3-propanediol, butanediols,
diethylene glycol, triethylene glycol, tetraethylene
glycol, 1,6-hexanediol, neopentyl glycol, 1,4-dimethylol-
cyclohexane, glycerol, trimethylolethane, trimethylolpro-
pane, pentaerythritol, ditrimethylolpropane, diglycerol
and others, are suitable as the alcohol component in the
preparation of the polyesters. The polyesters obtained
in this manner can be used either individually or as a
mixture of different polyesters.
Any solid epoxy resin having an epoxide equivalent weight
between 400 and 3000, preferably between 600 and 900 and
particularly preferably between 700 and 800, is suitable
as the component B. Epoxy resins based on bisphenol A
and/or epoxidized novolak resins are preferably used.
The epoxy resins based on bisphenol A generally have a
functionality s 2, and the epoxidized novolak resins a
functionality of ~ 2.
Examples of suitable epoxy resins are products commer-
cially available under the following names: Epikote~ 154,
CA 02096643 1999-09-16
1001, 1002, 1055, 1004, 1007, 1009, 3003-4F-10 from Shell
Chemie, XZ 86 795* and DER* 664, 667, 669, 662, 642U and 672U
from Dow and Araldite* XB 4393, XB 4412, GT 7072, GT 7203, GT
7004, GT 7304, GT 7097 and GT 7220 from Ciba Geigy.
Epoxy resins approved by the FDA are preferably employed.
The polyester component A is normally used in an amount of 19 to
80 % by weight, preferably of 39 to 60 % by weight, based on the
total weight of the powder coating. The epoxy resin component B
is normally used in an amount of 19 to 80 % by weight,
preferably of 39 to 60 % by weight, based on the total weight of
the powder coating.
As a further component C, the powder coatings according to the
invention contain at least one curing catalyst, normally used in
an amount of 0.01 to 5.0 % by weight, preferably of 0.05 to 2.0
% by weight, in each case based on the total weight of the
powder coating.
The catalyst used is preferably imidazole, 2-methylimidazole,
ethyltriphenylphosphonium chloride or another salt of the same
compound, a quinoline derivative, such as that described in
*Trade-mark
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CA 02096643 1999-09-16
EP-B-10,805, a primary, secondary or tertiary aminophenol,
aluminum acetylacetonate or a salt of toluenesulfonic acid or a
mixture of different catalysts listed above.
The carboxyl- and hydroxyl-containing polyester resins available
commercially usually already contain the required curing
catalyst. Examples of such carboxyl- and hydroxyl-containing
polyesters available commercially which are particularly
preferably used are the products available commercially under
the following brand names: Crylcoat* 314, 340, 344, 2680, 316,
2625, 320, 342 and 2532 from UCB, Drogenbos, Belgium, Grilesta*
7205, 7215, 72-06, 72-08, 72-13, 72-14, 73-72, 73-93 and 7401
from Ems-Chemie and Neocrest* P 670, P 671, P 672, P 678 and P
662* from ICI.
In addition, the powder coatings according to the invention may
also contain 0 to 40 ~S by weight, preferably 15 to 25 ~S by
weight, of fillers (component D). Fillers approved by the FDA
are preferably used. In general, inorganic fillers, for example
titanium dioxide such as Kronos* 2160 from Kronos Titan, rutile
R 902 from Du Pont and RC 566 from Sachtleben, barium sulfate
and silicate-based fillers, such as talc, kaolin, magnesium
aluminum silicates, mica and others are used. Titanium dioxide
and fillers of the quartz sand type are preferably used.
*Trade-mark
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CA 02096643 1999-09-16
Furthermore, the powder coatings according to the invention may
also contain, where appropriate, 0.01 to 10 % by weight,
preferably 0.1 to 2 ~ by weight, based on the total weight of
the powder coating, of other auxiliary substances and additives.
Examples of these are flow control agents, spraying agents,
deaeration agents, such
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209664-3
- 13 -
as benzoin, pigments and others.
The preparation of the powder coatings is performed by
known methods ( cf . , for example, product information from
BASF Lacke + Farben AG, "Pulverlacke", ["Powder Coat-
ings"], 1990) by homogenization and dispersion, for
example by means of an extruder, worm kneader and others.
It is an essential part of the invention that the particle
size distribution of the powder coatings, following their
preparation, is adjusted to suit the application by
grinding and, if appropriate, by screening and sieving.
For use in the coating of packaging container interiors,
the particle size distribution (a) is adjusted in such a
way that at least 90 % by mass of the powder coating
particles have a particle size between 1 and 60 gym, i.e.
d 90 = 1 to 60 gym. Preferably 90 % by mass of the powder
coating particles have a particle size between 1 and
40 ~m (d 90 - 1 to 40 gym) and particularly preferably
between 5 and 25 ~m (d 90 = 5 to 25 gym). For at least
99 % by mass of the particles, the maximum particle size
of the powder coating particles is s 100 gym, preferably
s 60 ~m and particularly preferably s 40 gym). The
average particle size of the powder coating particles is
between 5 and 20 gym, particularly preferably between 5
and 12 gym. Furthermore, it is an essential part of the
invention that, when the powder coatings are used for the
coating of packaging container interiors, the particle
size distribution is adjusted in such a way that the
?Q96~4~3
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slope S of the particle distribution curve at the
inflection point is >_ 100, preferably >_ 150 and
particularly preferably >_ 200. To obtain coatings having
particularly good properties, it is most particularly
preferred to use powder coatings in which the slope S of
the particle distribution curve at the inflection point
is >_ 300. However, the production costs of powder
coatings increase considerably with increasing slope.
The slope S is defined as limit value for
f ( xz ) - f ( xl ) against zero of ( f ( xz ) - f ( xl ) ) / lg ( ( x2/xl ) )
at the inflection point of the particle distribution
curve. The particle distribution curve thus represents
the plot of the accumulated percentages by mass against
the absolute particle diameter (represented logarith-
mically). Accordingly, for use in the coating of
packaging container interiors, suitable powder coatings
are in particular those which contain only a small
proportion of very fine particles (particle size < 5 gym)
and also a very small proportion of coarse powder coating
particles (particle size > 25 gym), i.e. they have as
narrow a particle size distribution as possible.
For use in the coating of weld seams, the particle size
distribution (b) is adjusted in such a way that at least
90 % by mass of the powder coating particles have a
particle size between 1 and 100 gym. Preferred powder
coatings are those in which at least 90 % by mass of the
powder coating particles have a particle size between 5
and 100 gym. In this case the slope S, defined above, of
20966-3
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the particle distribution curve at the inflection point can
also be below 100. The slope is usually >_ 50, preferably
> 100. For at least 99 ~ by mass of the particles, the
maximum particle size of the powder coating particles is
<_ 150 gym, preferably <_ 100 gym. The average particle size of the
powder coating particles is preferably between > 20 and
60 gym, particularly preferably between 25 and 40 gym.
Accordingly, the powder coatings used for the coating of
packaging container interiors are in principle also suitable for
use in the coating of weld seams. However, powder coatings
preferred for use in the coating of weld seams are those which
contain a high proportion of coarse powder coating particles.
The adjustment of the particle size distribution of the
powder coatings is carried out in each case with the aid of
suitable grinding aggregates, if appropriate in combination
with suitable screening and sieving equipment, e.g. using a
fluidized bed opposed jet mill (AFG) from Alpine, Augsburg,
in combination with an ultra-fine classifier from Alpine,
Augsburg.
The packaging containers which are coated with the powder
coatings according to the invention, can be made of a .
variety of materials, can be of a variety of sizes and shapes
and can be produced by various processes. However, metal
containers in particular are coated by the powder
coatings according to the invention. These metal
containers can be prepared by first rolling and then
_~~~~ s ~
folding back the metal plate. The end pieces can then be
affixed to the cylinder produced in this way. The powder
coatings according to the invention are used for the
coating of the weld seam as well as for the coating of
the can body interiors, which generally are already
provided with a bottom. In addition, the interiors of
deep-drawn metal containers can also be coated with the
powder coatings according to the invention. The powder
coatings are of course also suitable for the coating of
can lids and can bottoms.
The packaging containers can be made from a variety of
materials, such as aluminum, black plate, tin plate, and
various ferrous alloys which are provided, if necessary,
with a passivation coat based on nickel, chromium and tin
compounds.
Containers of this type are usually used as containers
for foodstuffs and beverages, such as beer, juices, fizzy
drinks, soups, vegetables, meat dishes, fish dishes,
vegetables, but also, for example, for pet foods.
Application is carried out by known methods, for example
those described in US Patent 4,183,974. The electro-
static charging of the powder coating particles is
carried out by friction (triboelectricity~. Application
of the powder coating particles is performed with the aid
of special spray heads, known to a person skilled in the
art.
2095693
_ 1~ _
For the coating of packaging container interiors, the
powder coatings are normally applied at a film thickness
of <_ 15 gym, preferably of 10 to 14 gym. Even at these low
film thicknesses, the coatingscomply with the requirements
normally specified for such films. The powder coatings
can of course also be applied in higher film thicknesses.
For the coating of weld seams, the powder coatings are
normally applied at a film thickness of s 200 gym,
preferably s 80 gym. The packaging containers whose weld
seam or interior have been coated with the powder coating
according to the invention, are subsequently heat-treated
in order to cure the powder coating. This heat treatment
can be performed in a variety of ways. To this end the
containers in practice are often passed through a
continuous-heating oven. In general, the powder coatings
cure fully at object temperatures between 230 and 350°C
within 5 to 30 sec. The continuous-heating oven can by
operated at constant temperature or at a temperature
profile set to suit the particular circumstances.
The working examples given below elucidate the invention
in greater detail. All parts and percentages are by
weight, unless expressly stated otherwise. The pre-
paration of the powder coatings was carried out in each
case by weighing all components in canisters, premixing
them in a premixer, homogenizing the mixture by means of
an extruder at 60 to 80°C, cooling it as rapidly as
possible and adjusting it to the desired particle size
distribution using grinding aggregates.
20~~G4-3
Example 1
The following components were. processed to give powder
coating 1:
500 parts of a commercial polyester containing a
crosslinking catalyst, having an acid
value of 35 mg of ROH/g and an OH value of
mg of ROH/g (commercial product
Grilesta P 7401 from Ems-Chemie),
248 parts of a commercial epoxidized novolak resin
10 having an epoxide equivalent weight (EEW)
of 700 (commercial product DER 672 U from
Dow),
50 parts of a commercial epoxy resin based on
bisphenol A having an EEW of 800 (commer-
15 cial product Epikote 3003-4F-10 from Shell
Chemie),
200 parts of a finely divided silicate filler of the
quartz sand type, and
2 parts of a fluidization auxiliary agent based on
pyrogenic silicic acid.
Using grinding aggregates, the particle size distribution
was adjusted in such a manner that at least 90 % by mass
?016643
of the powder coating particles have a particle size
between 1 and 25 ~,m (d 90 - 1 to 25 gym). For at least
99 % by mass of the particles, the maximum particle size
is <_ 100 gym, the average particle size is about 9 gym. The
slope S is 250. This powder coating 1 was applied to a can
body (diameter of opening 73 mm, length of body = 110 mm)
using suitable equipment, baked for 30 sec. at an object
temperature of 280°C and then subjected to an enamel
rater test: The coated can was immersed in a Cu/Cd standard
solution S475 (conductance 2.2 + 0.2 mS/cm) and connected
as cathode. A voltage of 6.3 V was applied for a period
of 30 sec. and the amperage was measured. The amperage
I = 5 mA was not exceeded at a film thickness as low as
gym. In addition, this powder coating 1 was applied to
15 a tinned can body (deposit of 2.8 mg/m2) at a film
thickness of 15 ~m and baked for 30 sec . at an ob ject
temperature of 280°C. The coating obtained in this way
was subjected to a sterilization test (30 min., 1.6 bar,
128°C) in various test media. Water uptake, (visual)
adhesion and flexibility were tested after sterilization.
The results are summarized in Table 1.
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Table 1: Test results of the powder coating coat 1 (film
thickness 15 gym, d 90 = 1-25 gym)
r
3% 3% 2%
untreat- H20 NaCl HAc lactic
ed 3' a' " ac id 6' '
HZO uptake - none none none none
Adhesion l~ Gt 0 Gt 0 Gt 0 Gt 0. Gt 0
1
T-Bend Z' TO TO TO TO TO
Key to Table 1:
1) adhesion t esting by the crosshatch method
(DIN 53151)
2) testing by the ECCA (European
Coil
Coating
Association) procedures
3) examination of the untreated coating prior to
sterilization
4) test medium = 3% aqueoussodium chloride solution
5) test medium = 3% aqueousacetic acid
6) test medium = 2% aqueouslactic acid
?09~~43
a._ - 21 -
Example 2
Powder coating 2 was prepared in a manner similar to that
of Example 1 from the components listed in Example 1. In
contrast to Example 1, the particle size distribution was
adjusted in such a way that at least 90 % by mass of the
powder coating particles have a particle size between 1
and 100 ~m (d 90 - 1 to 100 gym). The maximum particle
size of at least 99 % by mass of the particles is
< 150 gym, the average particle size is about 35 gym. The
slope S is 100. This powder coating 2 was applied to a can
body (diameter of opening 73 mm, length of body = 110 mm),
baked for 30 sec. at an object temperature of 280°C and
then subjected to the enamel rater test described in
Example is A minimum film thickness of 35 ~m was required
to maintain the amperage I < 5 mA.
Furthermore, this powder coating 2 was applied to a
tinned (deposit of 2.8 mg/m2) panel (size 20 x 20 cm2) at
a film thickness of 80 gym, using suitable spray equip-
ment, and was baked for 30 sec. at an object temperature
of 280°C. The coating obtained in this manner was
subjected to a sterilization test (30 min., 1.6 bar,
128°C) in various test media. Water uptake (visual),
adhesion and flexibility were tented after sterilization.
The results are summarized in Table 2.
~ 9 ~ ~ ~-3
- 22 -
Table 2: Test results of the powder coating coat 2 (film
thickness 80 gym, d 90 = 1-100 gym)
3% 3% 2%
untreat- Hz0 NaCl HAc lactic
ed 3' ' S ~ ac id 6'
H20 uptake - none none none none
Adhesion 1' Gt 0 Gt Gt 0 Gt Gt 0
0 0
T-Bend Z' TO TO TO TO TO
Rey to Table 2:
1) adhesion testing by the crosshatch method (DIN 53151)
2) testing by the ECCA (European Coil Coating
Association) procedures
3) examination of the untreated coating prior to
sterilization
4) test medium = aqueous sodium chloride solution
3%
5) test medium = aqueous acetic acid
3%
6) test medium = aqueous lactic acid
2%
?09643
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Example 3
The following components were. processed to give powder
coating .3:
600 parts of a commercial polyester containing a
crosslinking catalyst, having an acid
value of 35 mg of ROH/g and an OH value of
15 mg of ROH/g (commercial product
Grilesta P 7401 from Ems-Chemie),
250 parts of a commercial epoxy resin based on
bisphenol A having an EEW of 600 (commer-
cial product DER 692 from Dow),
48 parts of a master batch of 10 parts of a flow
control agent based on an oligomeric
acrylate in 90 parts of a commercial epoxy
resin based on bisphenol A having an EEW
of 800 (commercial product E 3003-4F-10
from Shell Chemie),
100 parts of a finely divided silicate filler of the
quartz sand type, and
2 parts of a fluidization agent of the pyrogenic
silicic acid type.
~o~ss~~3
- 24 -
Using grinding aggregates, the particle size distribution
was adjusted in such a way that at least 90 % by mass of
the powder coating particles have a particle size between
1 and 25 ~m (d 90 - 1 to 25 gym). The maximum particle
size for at least 99 % by weight of the particles is
<_ 100 gym, the average particle size is about 11 gym. The
slope S is 200.
This powder coating 3 is applied to a can body (diameter
of opening 73 mm, length of body = 110 mm) by means of
spray aggregates, is baked for 30 sec. at an object
temperature of 280°C and then subjected to the enamel
rater test described in Example 1: the amperage I = 5 mA
was not exceeded at a film thickness of less than 15 gym.
In addition, this powder coating 3 was applied with the
aid of spray aggregates to a tinned can body (deposit of
2.8 mg/m2) at a film thickness of 15 ~m and was baked for
30 sec.. at an object temperature of 280°C. The coating
obtained in this way was subjected to a sterilization
test (30 min., 1.6 bar, 128°C in various test media.
Water uptake, adhesion and flexibility were tested after
sterilization. The results are summarized in Table 3.
2046643
- 25 -
Table 3: Test results of the powder coating coat 3 (film
thickness 15 gym, d 90 = 1-25 gym)
3% 3% 2%
untreat- HZO NaCl HAc lactic
ed " 5' fi' ac id
"
H20 uptake 1' - mod. mod. strong strong
Adhesion Z' Gt 0 Gt 0 Gt 0 Gt 0 Gt 0
T-Bend 3' TO TO TO TO TO
Rey to Table 3:
(mod. -
moderate)
1) visual assessment: exam inationfor turbidity or
similar
2) adhesion testing by the crosshatch method
(DIN 53151)
3) testing by the ECCA (European
Coil
Coating
Association) procedures
4) examination of the untreated coating prior to
sterilization
5) test medium = 3% aqueous sodium chloride solution
6) test medium = 3% aqueous acetic acid
7) test medium = 2% aqueous lactic acid
20~~~~-3
- 26 -
Example 4
Powder coating 4 was prepared in a manner similar to that
of Example 3 from the components listed in Example 3. In
contrast to Example 3, the particle size distribution was
adjusted in such a way that at least 90 % by mass of the
powder coating particles have a particle size between 1
and 100 ~m (d 90 - 1 to 100 gym). The maximum particle
size for at least 99 % by mass of the particles is
< 150 gym, the average particle size is about 40 gym. The
slope S is 90. This powder coating 4 was applied to a can
body ( diameter of opening 73 mm, length of body = 110 mm) ,
was baked for 30 sec. at an object temperature of 280°C
and then subjected to the enamel rater test described in
Example 1: A minimum film thickness of 35 ~m was required
to maintain the amperage I < 5 mA.
In addition, this powder coating 4 was applied to a
tinned (deposit of 2.8 mg/m2) panel (size 20 x 20 cm2) at
a film thickness of 80 ~.m and was baked for 30 sec. at an
object temperature of 280°C. The coating obtained in
this manner was subjected to a sterilization test
(30 min., 1.6 bar, 128°C) in various test media. Water
uptake (visual), adhesion and flexibility were tested
after sterilization. The results are sunanarized in
Table 4.
209~~'~3
- 27 -
Table 4: Test results of the powder coating coat 4 (film
thickness 80 gym, d 90 = 1-100 gym)
2% (sic) 3% 3%
untreat- H20 NaCl HAc lactic
ed 3~ a) 5~ aCid
H20 uptake - mod. mod. strong strong
Adhesion 1' Gt 0 Gt 0 Gt 0 Gt 0 Gt 0
T-Bend 2' T2 T2 T2 T3 T3
Key to Table 4:
(mod. =
moderate)
1) adhesion t esting by the crosshatch method
(DIN 53151)
2) testing by the ECCA (European Coil Coating
Association) procedures
3) examination of the untreated
coat prior
to
sterilizatio n
4) teat medium = 3% aqueoussodium chloride solution
5) test medium = 3% aqueousacetic acid
6) test medium = 2% aqueouslactic acid
2096643
Example 5
Powder coating 5 was prepared from the following com-
ponents:
400 parts of a commercial polyester containing a
crosslinking catalyst, having an acid
value of 80 mg of KOH/g, an OH value of
about 20 mg of ROH/g, synthesized from
terepthalic acid, trimellitic acid, adipic
acid, ethylene glycol and neopentyl glycol
(commercial product Grilesta V 72-6 from
Ems-Chemie),
400 parts of a commercial epoxy resin based on
bisphenol A, having an EEW of 750 (commer-
cial product XB 4393 from Ciba Geigy),
100 parts of titanium dioxide of the rutile type,
93 parts of a finely divided silicate filler of the
quartz sand type,
5 parts of a flow control agent based on an
oligomeric acrylate, and
2 parts of a fluidization auxiliary agent based on
S i02 .
2~~96643
Using grinding aggregates, the particle size distribution
was adjusted in such a way that at least 90 % by mass of
the powder coating particles have a particle size between
and 15 ~m (d 90 - 5 to 15 gym). The maximum particle
5 size for at least 99 % by mass of the particles is
s 100 gym, the average particle size is about 8 gym. The
slope S is 250.
This powder coating 5 was applied to a can body (diameter
of opening 73 mm, length of body = 110 mm), was baked for
30 sec. at an object temperature of 280°C and then
subjected to the enamel rater test described in
Example 1: The amperage I - 5 mA was not exceeded at a
film thickness of less than 15 ~cm.
In addition, this powder coating 5 was applied to a
tinned can body (deposit of 2.8 mg/m2) at a film thickness
of 15 ~m and was baked for 30 sec. at an object
temperature of 280°C. The coating obtained in this
manner was sub jected to a sterilization test ( 30 min. ,
1.6 bar, 128'C) in various test media. Water uptake
(visual), adhesion and flexibility were tested after
sterilization. The results are summarized in Table 5.
2 ~ '~ ~ ~i 4-3
- 30 -
Table 5: Test results of the powder coating coat 5 (film
thickness 15 gym, d 90 = 5-15 gym)
3% 3% 2%
untreat- H20 NaCl HAc lactic
ed 3' 4~ 5~ acid
HZO uptake - none none none none
Adhesion 1' Gt 0 Gt 0 Gt 0 Gt 0 Gt 0
T-Bend 2' TO TO TO TO TO
Key to Table 5:
1) adhesion testing by the crosshatch method
(DIN 53153)
2) testing by the ECCA (European Coil Coating
Association) procedures
3) examination of the untreated coat prior to
sterilization
4) test medium = 3% aqueous sodium chloride solution
5) test medium = 3% aqueous acetic acid
6) test medium = 2% aqueous lactic acid
2~9~~43
- 31 -
Example 6
Powder coating 6 was prepared in a manner similar to that
of Example 5 from the components listed in Example 5. In
contrast to Example 5, the particle size distribution was
adjusted in such a way that at least 90 % by mass of the
powder coating particles have a particle size between 1
and 100 ~m (d 90 - 1 to 100 um). The maximum particle
size for at least 99 % by mass of the particles is
s 150 gym, the mean particle size is about 40 gym. The
slope S is 100. This powder coating 6 was applied to a can
body (diameter of opening 73 mm, length of body = 110 mm),
was baked for 30 sec. at 280°C and then subjected to the
enamel rater test described in Example 1: A minimum film
thickness of 25 ~m is required to maintain the amperage
I < 5 mA.
In addition, this powder coating 6 was applied to a
tinned (deposit of 2.8 mg/m2) panel (size 20 x 20 cm2) at
a film thickness of 80 ~m and was baked for 30 sec. at an
object temperature of 280°C. The coating obtained in
this manner was subjected to a sterilization test
(30 min., 1.6 bar, 128°C) in various test media. Water
uptake (visual), adhesion and flexibility were tested
after sterilization. The results are summarized in
Table 6.
?~9~~4-3
- 32 -
Table 6 : Test results of the powder coating coat 6 ( film
thickness 80 gym, d 90 = 1-100 gym)
3% 3% 2%
untreat- ' H20 NaCl HAc lactic
ed 3' '~ 5~ acid
HZO uptake - none none none none
Adhesion 1' Gt 0 Gt 0 Gt 0 Gt 0 Gt 0
T-Bend Z' TO TO TO TO TO
Key to Table 6:
1) adhesion testing the crosshatch method
by
(DIN 53151)
2) testing by the ECCA (European
Coil
Coating
Association) procedures
3) examination of the untreated coating prior to
sterilization
4) test medium = 3% aqueous sodiumchloride solution
5) test medium = 3% aqueous aceticacid
6) test medium = 2% aqueous lacticacid
In addition, pack tests were carried out on cans whose
weld seams were coated with powder coating 6 ( application
by means of suitable spray aggregates, curing for 30 sec.
at an object temperature of 280°C, film thickness
60 - 80 gym, coating of the can interiors with a con-
ventional, commercial spray paint). The foodstuff cans
20964-3
- 33 -
were filled with water, 3$ acetic acid and 2% lactic acid
and sealed. The cans were sterilized for 30 min. at
1.6 bar and 128°C and then stored at 37°C.
No damage to the coating was apparent after 6 months'
storage.
Example 7
The following components were processed to give powder
coating 7:
425 parts of a commercial polyester containing an
esterification catalyst, having an acid
value of 80 mg of ROH/g and an OH value of
mg of ROH/g (commercial product
Grilesta V 72-6 from Ems-Chemie),
475 parts of a commercial epoxy resin based on
15 bisphenol A, having an EEW of 800 (commer-
cial product XZ 86795 from Dow),
50 parts of talc,
48 parts of a masterbatch of 10 parts of a flow
control agent based on an oligomeric
20 acrylate in 90 parts of the abovementioned
commercial polyester having an acid value
of 80 mg of ROH/g and an OH value of 20 mg
20~~&643
of KOH/g, and
2 parts of a fluidization auxiliary agent based on
pyrogenic silicic acid.
Using griding aggregates, the particle distribution was
adjusted in such a way that 90 % by mass of the powder
coating particles have a particle size between 1 and
25 um (d 90 = 1 to 25 ~cm) . The maximum particle size for
at least 99 % by mass of the particles is s 100 gym, the
average particle size is about 14 gym. The slope S is
200. This powder coating 7 was applied to a can body
(diameter of opening 73 mm, length of body = 110 mm),
baked for 30 sec. at an object temperature of 280°C and
then subjected to the enamel rater test described in
Example 1: A minimum film thickness of 15 ~m is required
to maintain an amperage I < 5 mA.
In addition, this powder coating 7 was applied to a
tinned (deposit of 2.8 mg/m2) panel (size 20 x 20 cm2) at
a film thickness of 30 ~m and baked for 30 sec . at an
ob ject temperature of 280 °C. The coating obtained in this
manner was subjected to a sterilization test (30 min.,
1.6 bar, 128°C) in various test media. Water uptake
(visual), adhesion and flexibility were tested after
sterilization. The results are summarized in Table 7.
20~~64-3
- 35 -
Table 7: Test results of the powder coating coat 7 (film
thickness 30 ~.m, d 90 = 1-25 gym)
3% 3% 2%
untreat- H20 NaCl HAc lactic
ed 3' w' S' ac id
6'
HZO uptake - strong strong strong strong
Adhesion 1' Gt 0 Gt 0 Gt 2 Gt 0 Gt 2
T-Bend 2' TO TO ~ TO TO TO
Rey to Table 7:
1) adhesion t esting by the crosshatch method
(DIN 53151)
2) testing by the ECCA (European
Coil
Coating
Association) procedures
3) examination of the untreated coating prior to
sterilizatio n
4) test medium = 3% aqueoussodium chloride solution
5) test medium = 3% aqueousacetic acid
6) teat medium = 2% aqueouslactic acid
Example 8
Powder coating 8 was prepared in a manner similar to that
of Example 7 from the components listed in Example 7. In
contrast to Example 7, the particle size distribution was
adjusted in such a way that at least 90 % by mass of the
20~~6~-3
- 36 -
powder coating particles have a particle size between
1 and 100 ~m (d 90 = 1 to 100 ~sm). The maximum particle
size for at least 99 $ by mass of the particles is <_ 150 gym,
the average particle size is about 35 gym. The slope S is
150. This powder coating 8 was applied to a can body
(diameter of opening 73 mm, length of body = 110 mm) , baked
for 30 sec . at an ob ject temperature of 280 °C and then sub-
jected to the enamel rater test. A minimum film thickness
of 35 ~m is required to maintain the amperage I < 5 mA.
In addition, this powder coating 8 was applied to a
tinned (deposit of 2.8 mg/m2) panel (size 20 x 20 cm2) at
a film thickness of 80 ~m and baked for 30 sec . at an
object temperature of 280°C. The coating obtained in
this manner was subjected to a sterilization test
(30 min., 1.6 bar, 128°C) in various test media. Water
uptake (visual) , adhesion and flexibility were tested after
sterilization. The results are summarized in Table 8.
~046~~3
- 37 -
Table 8 : Test results of the powder coating coat 8 ( film
thickness 80 gym, d 90 = 1-100 gym)
3% 3% 2%
untreat- HZO NaCl HAc lactic
ed 3' " 5' ac id
6'
HZO uptake - strong strong strong strong
Adhesion 1' Gt 0 Gt 0 Gt 2 Gt 0 Gt 2
T-Bend Z' T2 T2 T3 T3 T4
Key to Table 8s
1) adhesion testing the crosshatch method
by
(DIN 53151)
2) testing by the ECCA (European
Coil
Coating
Association) procedures
3) examination of the untreated coating prior to
sterilization
4) test medium = 3% aqueous sodium chloride solution
5) teat medium = 3% aqueous acetic acid
6) test medium = 2% aqueous lactic acid
