Note: Descriptions are shown in the official language in which they were submitted.
220~890
Use of aqueous dispersions as heat-sealing lacquer
The present invention relates to a method of heat-sealing
5 substrates.
Packaging i8 widely prepared by subjecting substrates to heat
sealing, with at least one of the two substrates to be joined
being coated with a meltable polymer, referred to as a sealing
10 lacquer.
The substrates are joined under temperature and pressure
conditions which do not deform or damage the substrates
themselves but under which the polymer coating melts and bonds
15 with the other substrate. After cooling, the substrates are
connected with one another in the region of the heated areas.
occasionally, only part of the area of one substrate that has
been coated with the meltable polymer is sealed with the other
20 substrate in dotwise or linear zones. Por example, an aluminum
foil coated with 8 heat-sealing lacquer is sealed as a lid on the
edge of the container made from thermoformed plastic film.
The literature recommends numerous meltable polymers as
25 heat-sealing lacquers.
In selecting them, a variety of criteria have a role to play;
these include the distance between their melting point and the
melting temperature of the substrates, adhesion to the
30 substrates, the strength of the sealed seam, and the coating
conditions under which the heat-sealing lacquer is applied to one
of the substrates, and these requirements must be satisfied for
widely differing substrates. In the case of food and drug
packaging, moreover, it i8 also necessary to ensure compliance
35 with foodstuffs law and pharmacological harmlessness,
respectively.
Since coating of the substrate and bonding are conducted in
different operations, the requirements to which heat-sealing
40 coatings are subject are sometimes contradictory.
The coated substrates must be able to be stacked without sticking
together (blocking resistance).
2200890
In the course of heat sealing, however, it is desirable not to
have to use excessive temperatures, and the bonds obtained are
required to show high strength (good heat-sealability).
5 DE-A 39 21 256 discloses heat-sealing lacquers based on an aqueous
dispersion which comprises two different free-radically
polymerized polymers.
The heat-sealing lacquers of US-A-5 385 967 also include two
10 different polymers, the difference in their glass transition
temperatures being at least 20~C.
EP-A-129 178 relates to heat-sealable coating compositions in an
organic solvent. The coating composition consists of 3 polymeric
15 constituents, including, for example, a polyolefin, a
polyacrylate and a copolymer.
The heat-sealing lacquers known to date do not adequate fulfil
the requirements set out above.
It is an object of the present invention to provide a method of
heat-sealing substrates using an aqueous heat-sealing lacquer,
while meeting the requirements set out above. In particular, the
method is intended to provide for good sealed-seam strength even
25 where the substrates to be heat-sealed are aluminum and polymers.
We have found that this object is achieved by a method of
heat-sealing substrates, which comprises coating a substrate with
an aqueous dispersion comprising an ethylene polymer A), with at
30 least 20 % by weight of ethylene and at least 5 % by weight of an
ethylenically unsaturated acid, and a free-radically polymerized
polymer B) and pressing the coated substrate with a second
substrate at elevated temperature. We have also found aqueous
dispersions suitable for this method.
The aqueous dispersions for the novel method include an ethylene
polymer A) and a free-radically polymerized polymer B).
The ethylene polymer comprises at least 20 % by weight, preferably
40 at least 40 % by weight and, with particular preference, at least
60 % by weight of ethylene and at least 5 % by weight, preferably
at least 10 % by weight and, with particular preference, at least
15 % by weight of an ethylenically unsaturated acid as its
structural components.
The ethylene polymer A) consists in particular of
2200890
a1) from 20 to 95 % by weight, preferably from 40 to 90 % by
weight and, with particular preference, from 60 to 85 % by
weight of ethylene,
5 a2) from 5 to 80 % by weight, preferably from 10 to 60 % by
weight and, with particular preference, from 15 to 40 % by
weight of an ethylenically unsaturated acid, and
a3) from 0 to 60 % by weight, preferably from 0 to 40 % by weight
and, with particular preference, from 0 to 20 % by weight of
further monomers that are different from a) and b).
Ethylenically unsaturated acids a2) are, in particular, acrylic or
methacrylic acid.
Possible examples of further monomers a3) which can be
copolymerized with ethylene are (meth)acrylates, especially Cl-C10
(meth)acrylates, such as methyl, ethyl, propyl, butyl or
ethoxylhexyl (meth)acrylate, (meth)acrylonitrile,
20 (meth)acrylamide or vinyl esters, such as vinyl acetate or vinyl
propionate.
The preparation techniques for the ethylene polymers A are
familiar to the skilled worker. Polymers of this kind are
25 prepared, for example, by (co)polymerizing ethylene in
continuously operated tubular polymerization systems under
pressures of 500-5000 bar and at 50-450~C in the presence of
polymerization initiators which break down with formation of free
radicals.
The densities of such copolymers are generally greater th'an
0.925 g/cm3 (T - 23~C). Their molecular weights are generally about
500-40,000 daltons, especially 5000-20,000 (Mn)~ Following
polymerization, the copolymers A used in accordance with the
35 invention are converted to an aqueous emulsion preferably by
pressure emulsification, with or without the addition of a
neutralizing agent.
This technique of pressure emulsification of polyethylene to form
40 aqueous (secondary) emulsions is familiar to the skilled worker.
Suitable neutralizing agents are preferably ammonia,
diethylamine, dimethylethanolamine, diethanolamine, etc.
2200890
To prepare the emulsion it is also possible to use customary
ionic and/or nonionic emulsifiers. Preference is given to highly
mobile, fine and light-colored emulsions of the polymer A with a
solids content of about 20-40 % and a pH of more than 8.
The polymer B) consists in particular of
bl) from 30 to 100 % by weight of monomers referred to as
principal monomers, selected from Cl-C20
alkyl (meth)acrylates, C8-Cl2 vinyl aromatic
compounds, vinyl esters of carboxylic acids
of 1 to 20 carbons, and ethylenically
unsaturated nitriles,
~5 b2) from 0 to 30 ~ by weight of an ethylenically unsaturated acid
or anhydride,
b3) from 0 to 20 % by weight of ethylenically unsaturated
compounds having a crosslinking action, and
b4) from 0 to 70 % by weight of further monomers that are
different from bl)-b3).
Preferably, the polymer B) consists of from 60 to 100 % by weight,
25 particularly preferably from 80 to 100 % by weight, of the
monomers b1), from 0 to 10 % by weight, particularly preferably
from 0 to 4 % by weight, of the monomers b2), from 0 to 10 % by
weight, particularly preferably from 0 to 5 % by weight, of the
monomers b3), and from 0 to 40 % by weight and , with particular
30 preference, from 0 to 20 % by weight of the monomers b4).
As monomers bl) mention may be made in particular of methyl,
ethyl, propyl, n-butyl and 2-ethylhexyl (meth)acrylate,
vinyl-aromatic compounds such as vinyltoluene, o and p-styrene
35 and preferably styrene, and vinyl laurate, stearate, propionate
and acetate.
The alkyl (meth)acrylates and the vinyl aromatic compounds, and
mixtures thereof, are particularly suitable.
Monomers b2) are, in particular, C3-C5 mono or dicarboxylic acids
and/or their anhydrides.
Monomers b2) are commonly employed in minor amounts, preferably in
45 amounts of less than 4 % by weight based on ~), and, with
particular preference, monomers b2) are absent from B).
- 220Q890
-
Examples of monomers b3), which have a crosslinking action (and
are therefore referred to below simply as crosslinkinq monomers)
are free-radically polymerizable monomers having at least one
epoxy, hydroxyl, N-alkylol, N-alkoxy or amidine group or at least
5 two nonconjugated ethylenically unsaturated double bonds. A
combination of such compounds is of course possible.
Examples of epoxy-functional monomers are glycidyl acrylate,
glycidyl methacrylate and vinyl glycidyl ether.
Preferred N-alkylol compounds are the N-alkylolamides of
ethylenically unsaturated carboxylic acids with 1 to 4 carbons in
the alkyl, such as N-methylolacrylamide, N-ethanolacrylamide,
N-propanolacrylamide, N-methylolmethacrylamide,
15 N-ethanolmethacrylamide, N-methylolmaleimide, N-methylolmaleamide
and N-methylolvinylbenzamide.
Suitable N-alkoxymethyl acrylates and methacrylates are primarily
compounds with 1 to 8 carbons in the alkoxy, such as
20 N-(methoxymethyl)acrylamide, N-(butoxymethyl)acrylamide,
N-(methoxymethyl)methacrylamide and
N-(butoxymethyl)methacrylamide, and methylolallyl carbamates
whose methylols can be etherified by Cl-C8 alkyl.
Carbonyl-cont~ini ng monomers are preferably acrolein,
25 diacetonacrylamide, formylstyrene, vinyl alkyl ketones and
(meth)acryloxyalkylpropanals as set forth in EP 0 003 516,
diacetone acrylate, acetonyl acrylate, diacetone methacrylate,
2-hydroxypropyl acrylate acetylacetate and 1,4-butanediol
acrylate acetylacetate.
A monomer which contains aziridine groups that may be me~tioned
is 2~ aziridinyl)ethyl methacrylate.
As crosslinking components having at least two acrylic,
35 methacrylic, alkyl or vinyl groups, or appropriate combinations,
mention may be made of alkylene glycol di(meth)acrylates, such as
ethylene glycol diacrylate, 1,3-butylene glycol diacrylate,
propylene glycol diacrylate and triethylene glycol
dimethacrylate, 1,3-glycerol dimethacrylate,
40 l,l,l-trimethylolpropane dimethacrylate, l,l,l-trimethylolethane
diacrylate, pentaerythritol trimethacrylate, sorbitol
pentamethacrylate, methylenebisacrylamide and -methacrylamide,
divinylbenzene, vinyl methacrylate, vinyl crotonate,
vinylacrylate and divinyl adipate, diallyl phthalate, allyl
45 methacrylate, allyl acrylate, diallyl maleate, diallyl itaconate,
diallyl malonate, diallyl carbonate, triallyl citrate, divinyl
- ' 220Q890
ether, ethylene glycol divinyl ether and cyclopentadienyl
(meth)acrylate.
In addition to the use of such crosslinking monomers, the
5 internal strength of the polymer films can under certain
circumstances be increased by adding metal salts, such as salts
of Ca, Mg and Zn, after polymerization has taken place, provided
they include groups capable of bonding with the salts, such as,
for example, carboxyl groups; it is also possible to add
10 hydrazine derivatives, aminooxyalkanes, and condensation products
based on formaldehyde, melamine, phenol and/or urea, after
polymerization has taken place.
Examples of further monomers b4) are vinyl halides, preferably
15 vinyl chloride and vinylidene chloride, nonaromatic Cz-C8
hydrocarbons with one or two olefinic double bonds, such as
butadiene, isoprene or chloroprene, esters of acrylic and
methacrylic acid with alcohols of 1 to 20 carbons which include
at least one heteroatom not counting the oxygen in the alcohol
20 group, and/or include an aliphatic or aromatic ring, such as
2-ethoxyethyl acrylate, 2-butoxyethyl (meth)acrylate,
dimethylaminoethyl (meth)acrylate, diethylaminoethyl
(meth)acrylate, aryl, alkaryl or cycloalkyl (meth)acrylates such
as cyclohexyl ~meth)acrylate, phenylethyl (meth)acrylate and
25 phenylpropyl (meth)acrylate, or acrylic esters of heterocyclic
alcohols, such as furfuryl (meth)acrylate.
Examples of other possible monomers b4) are (meth)acrylamide,
N-Cl-C4 alkyl derivatives, and hydroxy-functional comonomers such
30 as Cl-C15 alkyl (meth)acrylates substituted by one or two
hydroxyls. Particularly important hydroxy-functional comohomers
are Cl-C8 hydroxyalkyl (meth)acrylates, such as n-hydroxyethyl,
n-hydroxypropyl and n-hydroxybutyl (meth)acrylate.
35 Particularly preferred polymers B) comprise no
chlorine-containing compounds such as vinyl chloride and
vinylidene chloride.
In addition, the polymers B) include ethylene preferably in - at
40 best - minor amounts of, in particular, less than 20 % by weight,
particularly preferably less than 10 % by weight and, with very
particular preference, less than 5 % by weight. In particular,
there is no ethylene in B).
2200890
The polymer ~) preferably has a glass transition temperature
(calculated in accordance with Fox) of from -20 to +130,
preferably from 0 to +90, particularly preferably from +10 to
+70~C.
The glass transition temperature (Tg) can be calculated by the
method of Fox (T.G. Fox, Bull. Am. Phys. Soc. (Ser. II) 1, [1956]
123), according to which the Tg of copolymers is given in good
approximation by
Xl x2 xn
+ ....... +
Tg Tg1 Tg2 Tgn
where X1, x2 ... xn = mass fractions of the monomers 1, 2, ... n
and Tg1, Tg2 ... Tgn = glass transition temperatures of the
monomers 1, 2 ... n in kelvins.
20 Tg is known for major monomers and is given, for example, in
~J. Brandrup, E.H. Immergut, Polymer Handbook, 1st Ed.,
J. Wiley & Sons, New York 1966".
Polymer B) i8 prepared by free-radical polymerization.
25 Appropriate polymerization techniques, such as polymerization in
bulk, solution, suspension or emulsion, are known to the skilled
worker.
The copolymers are prepared in particular by solution
30 polymerization with subsequent dispersion in water ~seco~dary
dispersion) or, preferably, by emulsion polymerization.
In the course of the emulsion polymerization, the monomers are -
as is usual - polymerized in the presence of a water-soluble
35 initiator and an emulsifier at (preferably) from 30 to 95~C.
Suitable free-radical polymerization initiators are all those
capable of triggering a free-radical aqueous emulsion
polymerization. They may be peroxides, for example alkali metal
40 peroxodisulfates, dibenzoyl peroxide, butyl perpivalate, t-butyl
per-2-ethylhexanoate, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane
and cumene hydroperoxide, or azo compounds, for example
azobisisobutyronitrile or 2,2~-azobis(2-amidinopropane)
dihydrochloride.
- 2200890
Suitability extends to combined systems composed of at least one
organic reducing agent and at least one peroxide and/or
hydroperoxide, for example tert-butyl hydroperoxide and sodium
hydroxymethanesulfinate, or hydrogen peroxide and ascorbic acid.
5 Also suitable are combined systems which additionally include a
small amount of a metal compound which is soluble in the
polymerization medium and whose metallic component can exist in
two or more valency states, for example ascorbic acid/iron(II)
sulfate/hydrogen peroxide, where the ascorbic acid is frequently
10 replaced by sodium hydroxymethanesulfinate, sodium sulfite,
sodium hydrogen sulfite or sodium metabisulfite, and the hydrogen
peroxide by tert-butyl hydroperoxide or alkali metal
peroxodisulfates and/or ammonium peroxodisulfates.
15 In general, the amount of free-radical initiator employed, based
on the overall amount of monomers to be polymerized, is from 0.1
to 3 % by weight. With particular preference, ammonium and/or
alkali metal peroxodisulfates or tert-butyl hydroperoxide in
combination with a reducing agent are employed as initiator.
The manner by which the free-radical initiator system is added to
the polymerization vessel in the course of the novel free-radical
aqueous polymerization i8 familiar to the skilled worker. The
system can be included in its entirety in the initial charge to
25 the polymerization vessel, or else introduced continuously or in
portions in accordance with the rate of its consumption during
the free-radical aqueous emulsion polymerization. In each
individual case this will depend, as known to the skilled worker,
both on the chemical nature of the initiator system and on the
30 temperature of polymerization. Preferably, part is included in
the initial charge and the remainder is supplied to the
polymerization zone in accordance with the rate of its
consumption.
35 For the emulsion polymerization it is possible to use commonly
known ionic and/or nonionic emulsifiers and/or protective
colloids and stabilizers.
Suitable such surface-active substances are, in principle, the
40 emulsifiers and protective colloids commonly used as dispersants.
A detailed treatment of suitable protective colloids is given in
Houben-Weyl, Methoden der organischen Chemie, Volume XIV/I,
makromolekulare Stoffe [macromolecular substances],
Georg-Thieme-Verlag, Stuttgart, 1961, pp. 411 - 420. Suitable
45 emulsifiers include anionic, cationic and nonionic types. As
surface-active substances, preference is given to the exclusive
used of emulsifiers, whose relative molecular weights - unlike
2200890
those of the protective colloids - are usually below 1000. Where
mixtures of surface-active substances are used, the individual
components must of course be compatible with one another, and in
case of doubt this can be checked by means of a few preliminary
5 experiments.
Preference is given to anionic and nonionic emulsifiers as
surface-active substances. Common co ~ lsifiers are, for
example, ethoxylated fatty alcohols ~E0 units: 3 to 50, CB-
10 C36-alkyl), ethoxylated mono, di- and trialkylphenols (E0 units:
up to 50, C4-Cg-alkyl), alkali metal salts of dialkyl esters of
sulfosuccinic acid, and alkali metal and ammonium salt~ of
C8-C12-alkyl sulfates, of ethoxylated Cl2-C18-alkanol, (E0 units: 4
to 30), of ethoxylated alkylphenols (E0 units: 3 to 50,
15 C4-C9-alkyl), of C12-C18-alkylsulfonic acids and of
alkylarylsulfonic acids (Cg-Cl8-alkyl).
Further suitable dispersants are compounds of the formula II
R5 R6
S03X S03Y
where R5 and R6 are hydrogen or C4-C14-alkyl and are not both
30 hydrogen, and X and Y can be alkali metal ions and/or ammonium
ions. R5 and R6 are preferably linear or branched C6-C18-alkyl,
especially with 6, 12 or 16 carbons, or are hydrogen but not both
at the same time. X and Y are preferably sodium, potassium or
ammonium ions, the former being particularly preferred.
35 Particularly advantageous compounds II are those in which X and Y
are sodium, R5 is branched C12-alkyl and R6 iB hydrogen or is R5.
Use is frequently made of industrial mixtures contA;ning from 50
to 90 ~ by weight of the monoalkylated product, such as
Dowfax~ 2Al (trademark of Dow Chemical Company).
Further suitable emulsifiers are given in Houben-Weyl, Methoden
der organischen Chemie, Band XIV/l, Makromolekulare Stoffe, Georg
Thieme-Verlag, Stuttgart, 1961, (loc. cit) pp. 192 - 208.
45 To adjust the molecular weight it is possible to use regulators
in the polymerization. Examples of suitable compounds are those
containing -SH, such as mercaptoethanol, mercaptopropanol,
' 22~0890
thiophenol, thioglycol, ethyl thioglycolate, methyl
thioglycolate, tert-dodecyl mercaptan and mercaptoacetic acid.
The aqueous dispersion used in the novel method can be obtained,
5 simply, by mixing the aqueous dispersion of the ethylene polymer
A) with the aqueous dispersion of the polymer B).
However, it has proven particularly appropriate first to prepare
a dispersion of the ethylene polymer A) as described above and
10 then to polymerize the monomers of the polymer B) in the presence
of the ethylene polymer A). The monomers of B) can be included
entirely in an initial charge or can be metered continuously into
an initial charge cont~ining A). It is also possible, for
example, for both A) or portions of A) and the monomers of B) to
15 be metered continuously over identical or different periods into
an initial charge.
Since the content of acid groups and/or the corresponding salt
groups in the ethylene polymer A) endows it with an emulsifying
20 effect, it is possible when following the above procedure for
preparing B) in the presence of A) to do away with some of all of
the emulsifier. If desired, it is possible to use, for example,
from 0.05 to 3 % by weight of emulsifier, based on the total
weight of A) plus B).
The resultant aqueous dispersion of A) and B) preferably has a
solids content of from 20 to 70 % by weight.
The aqueous dispersion is used for sealable coatings, ie. as a
30 sealing lacquer, and may include additives customary for such
use, examples being wetting agents, thickeners, antifoam~ and
film formers.
For this use, the dispersion can first of all be applied to a
35 substrate, for example aluminum, printed or plain paper,
cardboard packaging, or films of polyvinyl chloride, polyethylene
terephthalate, polystyrene or polyolefins. The amount applied
~based on solids) is generally from 1 to 100 g, preferably from 10
to 15 g, per m2 of coated area.
The coated substrate is then pressed with a further, preferably
uncoated substrate (sealing or heat-sealing). Examples of
suitable uncoated substrates are, again, those indicated above.
Further candidate substrates are glass, metals and textiles.
11 220~8qO
With preference, at least one of the two substrates to be
heat-sealed is made from plastic. With particularly preference,
the substrate coated with a dispersion is made from aluminum. The
plastic i8 eBpecially polystyrene, polyethylene terephtalate,
5 PVC, polyethylene or polypropylene.
~y means of heat-sealing it i8 possible to package articles, for
example by coating an aluminum film with the heat-sealing lacquer
in the form of dots or zones, and subsequently pressing this
lO coated foil with, for example, a thermoformed plastic film so as
to enclose an item to be packaged.
In the course of heat sealing, the substrates are pressed
together by sealing jaws, which can be at 80-250~C. In the course
15 of this pressing operation, the pressures are generally from 0.1
to lO bar, in particular from 2 to 6 bar, with a pressing time
(contact time) of at least 0.5 second, generally from 1 to 5
seconds.
20 The novel dispersions are notable for the fact that they bring
about a seal of high sealed-seam strength, in particular between
aluminum foil and polystyrene, polyethylene terephthalate,
polyvinyl chloride and polyolefinic substances, including in
particular ~ubstances of polypropylene and polyethylene; at the
25 same time, the film of sealing lacquer on its own possesses good
blocking resistance.
Another notable feature of the novel dispersions is that they
possess good adhesion to aluminum foil without the need for any
30 further primer coat on the aluminum surface.
Comparison Examples
Comparison Examples 1 and 2 in accordance with US 5 385 967:
Copolymer I:
The copolymers I are water-soluble copolymers prepared by bulk
polymerization following the method of DE-A-3 225 876.
For this preparation, 60 parts by weight of styrene and 40 parts
by weight of acrylic acid were metered continuously into a 1 1
pressure vessel with a downstream pressure tube of twice the
capacity, with a pressure regulator. The system was heated to
45 310~. The pressure was kept at between 5 and 50 bar and once was
22û08~0
12
varied within this range by means of a periodic pressure
regulation over the course of one minute.
The residence time was 11 minutes; the copolymer melt was
5 discharged quantitatively at the same rate at fresh monomer
mixture was supplied. The copolymer had a mean molecular weight
Mn of 650 and a polydispersity U = MW/Mn -1 of 1.5.
Preparation of the copolymers II in the presence of the
10 copolymers I:
The amounts of an aqueous solution of the copolymers I as
indicated in Table 1 were charged to a 3 1 four-neck flask fitted
with reflux condenser, 2 feed vessels, a thermometer, a pilot
15 stirrer and gas inlet and outlet, the reaction vessel was flushed
with nitrogen, and the solution was heated to 85~C. 54 g of a
1.5 % strength aqueous sodium peroxodisulfate solution were
added, and then 1000 g of the monomers of copolymer II were run
in at 85~C with stirring over the course of 2 h. At the same time,
20 in a separate feed, 126 g of a 1.5 % strength sodium
peroxodisulfate solution were added dropwise over the course of
2.5 h. After the end of the two feeds, reaction was continued at
85~C for 1 h and then the reaction mixture was cooled to room
temperature.
The polymer dispersions obtained by this procedure were free from
coagulum. Their composition is shown in Table 1.
Comparison Examples 3 and 4 correspond to Examples 1 and 2 of
30 DE--A--39 21 256:
Mixture 1 was charged together with 260 g of isobutanol to a
reaction vessel, and the resulting mixture was heated to 105~C.
Then mixture 2 was added, and the batch was polymerized at reflux
35 for 2.5 hours. Subsequently, mixture 3 was metered in at about
105~C over the course of 3 hours.
The batch was then polymerized at 105~C for 4 hours, during which
it was diluted with 200 g of isobutanol. After it had cooled to
40 60~C, 35.4 g of 25 % strength by weight aqueous ammonia solution
and then 850 g of water were stirred in. An isobutanol/water
mixture was distilled off under reduced pressure until virtually
no more isobutanol passed over. During the distillation, an
amount of water corresponding to the amount of liquid removed by
45 distillation was added.
2200~90
13
Mixture 1:
Comp. Example 3 Comp. Example 4
5 Methyl methacrylate (g) 160 145
n-Butyl acrylate (g) 100 110
Acrylic acid (g) 20 25
Mixture 2:
tert-Butyl benzoate ~g) 1.5 1.5
15 tert-Butyl peroctoate (g) 1.5 1.5
Isobutanol (g) 30 30
20 Mixture 3:
Methyl methacrylate (g) 370 380
n-Butyl methacrylate (g) 350 340
tert-Butyl (g) 7.5 6.7
25 perbenzoate
tert-Butyl peroctoate (g) 4.5 6.0
Isobutanol (g) 150 140
The composition is given in Tab. 1.
Comparison Example 5
3S As Comparison Example 5, the product Plexisol~ PM 555 from Rohm,
Darmstadt was tested. This product is currently state of the art
in terms of sealability with respect to polypropylene. It is a
methacrylate/olefin-based emulsion in butyl acetate/methyl ethyl
ketone.
Products of thi~ type are described in EP 023 978 (to Rohm). To
ensure bond strength to aluminum foil, Rohm recommends a primer
of PVC copolymers (eg. Vinylite VMCH from Union Carbide).
' 22no890
14
CO .~ ~,~
U ~ . . .
~r ~ e
~ '' ~d ~ ~ ~ ~
a. U' O c~
.~ ~i
m
0 P
0 0
r~ ~P
C~ I ~ I
~
X
W ~ _~
U
L H
H O
O O o o CO
.C r
a~
O o
-
Ll O ~ 3 V~
~, 0 ~ m ~ ~ n
~J O C~ 0 3
:~: CO o 0
O _ ~ 0
C
G L. O O - a ~ ~ r
,- X Z t ) ~ U C~ U
- 2200890
Glass transition temperatures of the copolymers
The glass transition temperatures were determined by differential
5 canning calorimetry in accordance with ASTM 3418/82. They can also
be calculated approximately, using the Fox equation, from the
glass transition temperatures of the monomers (T.G. Fox, Bull. Am.
Phys. Soc. Ser. II 1, (1956) 123).
10 Table 2: Glas~ transition temperatures in ~C [DSC]
Example Copolymer ICopolymer II
Cl 125 -26
C2 125 -14
C3 35 12
C4 30 16
20 Examples
Polymer B was prepared in the presence of polymer A. The
composition of polymers is shown in Table 3.
25 To do this, ethylene polymer A was charged to a 3 1 reaction flask
with reflux condenser, 3 feed vessels, thermometer, pilot stirrer
and nitrogen inlet. Together with 90 % by weight of the total
amount of initiator system used (tert-butyl hydroperoxide, Na
hydroxymethylsulfinate) and after nitrogen flushing, this
30 solution was heated to 70~C with stirring.
Subsequently, the monomers and the remaining amounts of initiator
(0.8 % by weight t-BHP and 0.8 % by weight Na
hydroxymethylsulfinate, based on monomers of copolymer B) were
35 added continuously with stirring over the course of 1.5 h. In
Examples 1 to 10, the monomers were metered in in the sequence
indicated in Table 3.
The batch was subsequently stirred at 70~C for one hour more and
40 then cooled to room temperature, to give coagulum-free
dispersions whose composition and characteristic data are
summarized in Table 3.
To give coagulum-free dispersions whose composition and
45 characteristic data are summarized in Table 3.
' ' 2200890
16
Table 3: Composition of the copolymers from the Examples
Composition Quantitative Tg (~C)
ratio Copol. B
Copol. A:B
Ex. No. Copol. A/ SC
Copol. B (%)
1 A 60 E/20 EHA/20 AA; NH3 33.4:66.6 13.6 34.1
B 50 nBA/50 S
2 A 60 E/20 EHA/20 AA NH3 33.4:66.6 63.2 34.4
B 20 nBA/80 S
3 A 60 E/20 ERA/20 AA; NH3 33.4:66.6 44.8 34.1
B 30 nBA/70 S
4 A 60 E/20 EHA/20 AA; NH3 43:57 44.8 33.8
B 30 nBA/70 S
A 60 E/20 EHA/20 AA; NH3 43:57 13.6 34
B 50 nBA/50 S
6 A 80 E/20 AA; DMEA33.4:66.6 13.6 34.4
B 50 nBA/50 S
7 A 80 E/20 AA DMEA 43:57 13.6 30
B 50 nBA/50 S
8 A 80 E/20 AA; N~333.4:66.6 13.6 35
B 50 nBA/50 S
9l) A 80 E/20 AA; NH333.4:66.6 13.6 33.7
B 50 nBA/50 S
A 80 E/20 AA; NH3 43:57 13.6 34.6
B 50 nBA/50 S
30 Key:
DMEA:
E: Ethylene
EHA: Ethylhexyl acrylate
1) The polymers B were polymerized in the presence of an
additional 10 % by weight, based on B, of a vinyl
chloride-vinyl acetate-maleic acid copolymer from Union
Carbide ~Vinylite VMCH).
Performance testing
Description of the test methods:
1. Applying the lacquers
The aqueous dispersions were coated using a 36 ~m doctor
blade onto a 40 ~m thick aluminum (Al) foil, which is clean
and untreated, and the coated foils were dried at 130~C for 3
- - 2200890
17
minutes in a convection oven. The dry-film thickness was in
the range 10-15 ~m (- 10-15 g/m2).
2. Sealing
The coated Al foils were subjected to pressing with the
polymer films (film thickness 250-300 ~m) indicated in Table
4, which possess the surface tensions indicated in that
table, and are not treated further, in a welding apparatus of
type HSG/ETK 525 from Brugger, with the application of
pressure and temperature. The sealinq jaw~ were smooth and
measured 150xlO mm. In the course of sealing, the lower jaw
was adjusted to the stated temperature while the upper jaw
remained unheated (at room temperature). The heated jaw
contacted the Al foil while the cold jaw was against the
polymer film. Sealing was carried out at 230~C (4 kp for a
period of 4 seconds) and 220~C (4 kp, 1 second).
3. Sealed-seam strength
The strength of the bond was measured in a tear tester
from Frank, Model No. 81565, and is stated as the tear
strength in N/10 mm. The tear off rate was 150 mm/min. With
regard to tearing, two parameters are stated: Fmax, the
~; tearing force, and FM/N, the mean tear strength along
the sealed seam (about 10-12 cm). (Results in Table 4).
4. 81Ocking resistance
The blocking resistance was tested with the dry but unsealed
lacquer surface on the Al foil under the conditions stated in
the table (temperature, applied weight, duration). It was
determined face to face, ie. coating against coating (in the
Table c/c), then coating against uncoated Al foil (in the
Table c/r: coating/reverse) and coating against an Al film
coated with a nitrocellulose-based printing-ink binder (in
the Table c/PI8: coating against printing-ink binder). The
valuation is in accordance with a rating syctem: 1 = very
good blocking resistance: the surface~ come apart again after
weight is removed; 5 = very poor: the surfaces are stuck to
one another and can be removed only with difficulty (re~ults
in Table 5).
22008qo
18
5. Anticorrosion test
Here, a drop of an aqueous solution comprising 70 parts by
weight water, 20 parts by weight HCl (37 % strength) and
10 parts by weight CuS04 x H20 was allowed to fall on the
lacquers which have been applied to Al foil and then dried
(as described above). The test result is positive (+) if
after 30 minutes there is no visible hole in the Al foil;
otherwise it is negative (-). (Results in Table 5).
Table 4: Sealability
Sealing at 230~C Sealing at 220~C
Ex. No. PVC PET PS PS PS
(30-6 mN/m)* ~38.0 mN/M)* (29.8 mN/m)*(35.44 mN/m)*(35.44 mN/m)*
Fmax/FM/N Fmax/FM/N Fmax/FM/N Fmax/FM/N Fmax/FM/N
1 13.1/8.5 Rating: 3-4*** 17.0/14.5 7.3/5.5
2 none none 18.3/15.3 17.7/16.1 5.4/3.3
3 none none 19.8/15.3 7.2/4.3
4 none none 24.6/19.8 15.7/10.6 6.7/4.4
10.5/8.1 8.2/4.6 11.0/8.6Cohesion in PP II11.8/5.8
6 11.7/5.4 3.9/1.2 17.8/13.3 14.9/12.4 lO/3.6
7 9.4/3.3 Rating: 3-4 13.8/10.3 13.6/12.6 11.6/5.0
8 15.0/4.6 Rating: 4 20.0/16.3 12.5/10.9
9 21.7/7.9 4.9/2.0 22.2/16.7 12.6/10.8 4.1/3.1
7.9/4.1 Rating: 4 13.2/10.2 5.4/3.1
Comp. Ex. 13.3/2.9 4.5/3.3 4.9/3.0 9.1/5.3 4.1/2.7
Comp. Ex. 28.0/5.1 10.9/5.6 6.7/4.8 5.1/3.5 2.6/0.9
Comp. Ex. 33.8/2.9 2.8/2.0 6.2/4.5 Rating: 4 1.3/0.6 r~
Comp. Ex. 43.1/2.3 2.4/l.9 5.9/4.0 Rating: 4 l.0/0.4 O
PM 555 6.5/4.3 6.4/5.0 7.7/5.9 8.7/6.6 2.3/1.3 CX~
PM 555+Pr** 13.1/11.7 6.3/4.8 O
* Thi~ i~ the curface tension of the film
** A primer (adhesion promoter) wa~ used in addition to PM 555
*** Ratings of 3 to 5 are awarded if the tear strength F5n~ is < 1.0 N/10 mm (Rating 3 = poor,
Rating 5 = very poor)
Table 5: Blocking resistance and corrosion test
Blocking resistance Blocking resistance Corrosion test15 h, 50~C, 1500 g 15 h, 40~C, 100 g HCl/CuS04 30'/RT
Ex. No. c/c c/r c/c c/PIB Damage
1 S 3 4 2 +
2 2 1 1 1 +
3 3 2 1-2 1 +
4 3 2 2 1 +
S 4 4 2 +
6 5 . 3- 4-5 2 +
7 5 2- 4-5 2 +
8 5 2 4-5 2 +
9 5 2 4-5 2 +
2-3 3 2 +
Comp. Ex. 3 1-2 2 1- + r~
No. 1 r~
Comp. Ex. 5 4 5 4 + oNo. 2 CX~
Comp. Ex. 4-5 4-5 4_5 4_5 + ~5~
No. 3 O
Comp. Ex. 4-5 4-5 4_5 4_5 +
No. 4
PM 555 3 1 1 1 +/-
PM 555 + Pr. 3 1 1 1 +
