Note: Descriptions are shown in the official language in which they were submitted.
CA 02219628 1997-10-29
,
Water-Resistant Barrier Material
The invention relates to a water-resistant barrier material
that is suitable in particular for the finishing, formation
or synthesis of protective, adhesive and intermediate layers
or films or for the production of unsupported foils having
outstanding sealing properties in relation to gaseous and/or
liquid ambient media, in particular o~ygen, air, water
vapour and the like.
The main fields of application of the planar substrates and
moulded articles or of the unsupported films that are
finished or coated with such material are to be found, inter
alia, in the following areas
- planar, optionally flexible packaging substrates for
foodstuffs and pharmaceutical products,
- automotive engineering, aviation industry and
shipbuilding
- construction engineering
- lacquering and painting sector.
With the barrier material according to the invention, both
planar substrates and moulded articles consisting of metal,
plastic, cellulose material and/or inorganic materials can
be finished or coated and also adhesion-bonded.
In engineering the finishing of planar substrates, the
coating of moulded articles with sealing layers or the
formation of sealing layers in connection with the synthesis
of composite materials or laminates by adhesion is a known
necessity, conditioned by the material, in order that
objects are protected against environmental influences and
in order that their lifespan is prolonged. Protection in
CA 02219628 1997-10-29
relation to environmental influences has a prominent status
in the national economy. In the case of packagings, in
particular for the foodstuff and pharmaceutical sector but
also for other high-quality goods, particularly high demands
are made of the barrier-medium finishes. Particularly in
the case of fillings stemming from the foodstuff and
pharmaceutical sector the barrier materials have to be
chemically and physically inert and must not give off any
toxic substances that influence taste or odour, or undergo
sensory changes as a result of such substances.
Furthermore, in the case of direct or indirect contacts with
fillings they must not trigger any so-called 'scalping'
effects. In order to be able to achieve this objective with
good sealing properties, particularly in relation to oxygen
and/or water vapour, using means pertaining to the state of
the art, predominantly use still has to be made of barrier
materials containing solvent, water and/or monomer, such as
coating compositions, lacquers. With these product groups
the solvents are important auxiliary substances, in order
for example to obtain barrier materials in liquid,
processable states of aggregation from solid polymers and/or
resins, in order thereby to be able to wet the surfaces of
the material to be coated with a view to the development of
adhesion.
The solvents that are necessary for this purpose are, unless
it is a question of water or monomers (reactive diluents),
of aliphatic and aromatic type, such as, for example,
esters, ketones, toluene, xylene and the like, and have to
be removed from the barrier materials after the
applications. According to emission legislation and German
technical regulations on clean air (TA-Luft), the released
solvents have to be disposed of or recycled by means of
cost-intensive techniques.
In the case of the so-called 'aqueous' barrier materials
there are added, moreover, to the solvent 'water' up to 20 %
CA 02219628 1997-10-29
of organic solvents, which according to German technical
regulations on clean air also have to be disposed of after
removal.
One of the biggest disadvantages with the use by way of
barrier material of polymer solutions and resin solutions
that contain solvent arises from the fact that with a view
to the development of sealing layers the solvent has to be
removed from said material by evaporation. The evaporation
or expulsion of the solvents is effected in this connection
almost exclusively via the pores which form in the process.
Since these pores are partly responsible for causing the
permeability in respect of oxygen and water vapour, in
practice, for this reason alone, several sealing layers have
to be laid on top of one another in order to achieve good
barrier properties. But such a processing technique for the
purpose of achieving sealing layers that have a low number
of pores or are non-porous is consequently exceptionally
cost-intensive.
Recently solvent-free coating compositions or barrier
compositions have also become known. Such compositions
contain, instead of inert solvents, so-called reactive
diluents or monomers that are integrated into the polymer
matrix in the course of curing or crosslinking. Since in
this connection it is a question of relatively low-molecular
compounds, they are not only physiologically questionable
but they also present characteristic, intense, negative
taste and odour difficulties. The degree of crosslinking
that can be achieved with them often amounts only to < 90 %,
so they are not suitable, inter alia, for the finishing of
packing materials for foodstuffs and pharmaceuticals. But
also in technical fields a degree of crosslinking that is
too low can result in problems, above all in the resistance
to environmental influences. Altogether the reactive
diluents have the disadvantage that if residues thereof,
also in the ppm range, are not incorporated by crosslinkage,
CA 02219628 1997-10-29
they have a negative influence on the adhesion at the
boundary surface because they may wander like inert
solvents.
Now, in order to accelerate polymerising or curing at high
rates of production, several years ago polymerisable barrier
materials also became known that are capable of being cured
by means of ionising radiation, in particular by means of
electron beams and UV rays.
To the UV-curable barrier compositions there are added
photoinitiators and possibly so-called synergists, in order
that they polymerise under UV rays. However, these
photosensitive additives remain in the barrier layers after
the curing and contaminate the environment both in the
course of stacking and also upon contact with fillings and
for this reason alone are also unsuitable for foodstuff and
pharmaceutical packing materials, since physiologically they
are to be regarded as questionable. In the case of curing
or crosslinking with ionising beams or rays, such
contamination problems do not exist.
However, the radiation-curable barrier compositions that are
known in the current state of the art have the disadvantage
overall that for processing reasons they have to contain a
relatively high proportion of monomers containing
(meth)acrylic groups by way of reactive diluents. These
(meth)acrylic monomers may be physiologically questionable
to a greater or lesser extent. Some of them are also
regarded as toxic. One of the biggest disadvantages,
however, is the taste- and odour-influencing component in
relation to the environment, the fillings, particularly in
the foodstuff and pharmaceutical sector, which is caused by
contents of residual monomer, also in the case of very low
ppm values.
CA 02219628 1997-10-29
The barrier materials described above will, either from an
economic or from a technical point of view, make it
difficult in future for the person skilled in the art to
produce sealing-layer finishes under environmentally
friendly conditions that are optimal as regards industrial
hygiene, because the state of the art offers no overall
solutions that comply with all requirements. Considerable
demands are made precisely in the field of packagings for
foodstuffs and pharmaceuticals, as can be gathered just from
the recommendations of the German Federal Public Health
Department (Bundesgesundheitsamt, BGA) entitled "Kunststoffe
im Lebensmittelverkehr" or from the legal regulations of the
Food and Drug Administration (FDA) and also from the
individual laws on the environment. The additives that are
necessary in conventional anti-corrosion agents may also
represent an additional problem, as is described in
Gachter/Muller, "Kunststoff-Additive", 2nd Edition, Hanser-
Verlag, Munchen, 1983, in Chapter 18 "Gewerbe- und
lebensmittelhygienische Aspekte von Kunststoff-Additiven".
These problems are made clear in particular by the article
by Piringer et al on the topic "Der Einflu~ von
Restlosemitteln und monomeren Acrylaten aus Verpackungen auf
die sensorischen Eigenschaften von Lebensmitteln",
Verpackungsrundschau, Issue 8/1986, pages 53-58, since
precisely the residual solvents and the acrylic monomers
have a particular influence on foodstuff fillings in sensory
respects. On the basis of the relative threshold values of
inert solvents, acrylates and methacrylates with respect to
odour and taste that are presented, it is made abundantly
clear that in the case where use is made of such low-
molecular compounds the latter remain beset by problems.
For instance, the relative odour threshold value amounts in
the case of n-butyl acrylate, for example, to around 0.002
and in the case of 2-ethylhexyl methacrylate to around
0.02 mg/kg.
CA 02219628 1997-10-29
.
Furthermore it may be said that evaluation of the legal
measures and directives as regards the environment,
industrial and food hygiene and the like in the European
Community and also in the North-American market and Japan
are ~vc~ very largely identical, if certain nuances in the
regulations to be implemented are disregarded. Synoptic and
comparative accounts have been published, inter alia, by
Keener R.L., Plamondon J.E. and West A.S.: "Recent
Developments in the Regulation of Industrial Chemicals in
the United States and Europe", lecture RADCURE EUROPE '85,
Basel/Switzerland, Organiser: AFP/SME, Dearborn, Mich.
48121, USA, and in the book by Ronald Brickman et al
entitled "Controlling Chemicals: The Politics of Regulation
in Europe and the United States", Cornell University Press,
Ithaca, N.Y., 1985.
Conventional barrier materials which are based on various
polymers and dissolved in solvent are described very
extensively in the literature, such as, for example, H
Kittel, "Lehrbuch der Lacke und Beschichtungen", Vols. 4, 5
and 7, Verlag W A Colomb Verlagsgesellschaft mbH, Berlin und
Oberschwandorf, and therefore this state of the art need not
be especially appraised.
The finishing with sealing layers of planar substrates
and/or moulded articles, in particular of metals and
cellulose materials, using coating agents that are free from
inert solvents is likewise sufficiently well-known in
industrial practice. For this purpose use has been made of
coating agents in which the backbone polymers are present
dissolved in reactive diluents or the base products are
present in such a liquid state of aggregation that they are
capable of being applied. Even if these reactive diluents
and/or other liquid coreactants are integrated into the
polymer matrix by curing or crosslinking, free residues are
still left over, depending on the degree of crosslinking.
In many cases these unincorporated residues cannot be
CA 02219628 1997-10-29
removed or reduced to such an extent that they conform to
the legal regulations, not even by means of additional
purification processes that add to the cost of the product.
Since they may in addition be physiologically questionable,
such barrier materials are only usable to a limited extent,
in which connection the foodstuff and pharmaceutical sector
has to be totally ruled out. This is necessary, in
addition, purely for the reason that the filling is
influenced in sensory respects - that is to say, as regards
taste and odour. Although qualitative improvements can
likewise be achieved by means of baking and/or post-curing
in the case of substrates that are not thermosensitive,
these improvements are often not sufficient to achieve the
required minimum standard. Besides, a further factor is the
additional cost burdens for end products as a result of such
aftertreatment measures. Therefore efforts have been made
to work out, with the aid of curing by beams or rays, better
technical solutions which at the same time also ensure
economic efficiency. On account of the minimum degree of
crosslinking which cannot be achieved under economic
conditions - as already mentioned above - the breakthrough
that was hoped for could not be achieved with these
radiation-curable coating agents.
In another European Patent Application, EP 0 184 345~
radiation-curable, thermoplastic coating compositions for
wood and other substrates are described that consist of
copolymerisable ethylenically unsaturated polyesters and
thermoplastic polymers. In order to be able to process them
as coating compositions, monomers or reactive diluents
and/or inert organic solvents are necessary. Hence coating
agents are presented which, although able to produce good
final properties, are beset with the problems of the
evaporation of the inert solvents and those associated with
the contents of residual solvent and of monomers.
CA 02219628 1997-10-29
For the purpose of forming sealing layers, so-called hot
melt coatings (Hei~schmelzmassen) that are synthesised on
the basis of inert resins, waxes, thermoplastics and/or
elastomers have furthermore also become known. In German
linguistic usage the use of the unconnected term 'hei~'
('hot') is advised against (see Rompps Chemie-Lexicon, 8th
Edition, Volume 3 (1983, page 1763), therefore only the term
'melt coatings' (Schmelzmassen) will subsequently be used.
Whereas the melt adhesives that are related to the melt
coatings have attained considerable importance in many
branches of industry, the melt coatings have remained
relatively insignificant, if certain fields of application
such as films for protection against corrosion are
disregarded. These films for protection against corrosion
are formed from a hot-dip coating consisting, inter alia, of
cellulose ester, plasticiser mixtures and mineral-oil
additives if, for example, tool parts, machine parts are
immersed in the hot composition and are then allowed to
cool. The film or coating that forms may later be pulled
off without leaving any residue.
Irrespective of whether it is a question of melt coatings
for coating purposes or for adhesive purposes, the
thermoplastic basic raw materials, including the resins and
plasticisers, are thermosensitive and subject to thermal
oxidation, particularly in the presence of atmospheric
oxygen. In this connection not only are the properties of
the product changed but cracking products which are
physiologically questionable are also formed. These
associated thermal problems are paraphrased in the
international jargon by the term 'heat history'. Whereas in
the case of the melt adhesives it is possible to work with
stabilisers and anti-oxidants, these can only be used in the
case of the melt coatings when they find application in the
technical field. Thermo-oxidative decomposition can also be
reduced by means of a covering with protective gases such as
nitrogen (N2), for example. Another disadvantage of the
CA 02219628 1997-10-29
.
thermoplastic melt coating compositions is constituted by
the relatively low softening-points, which preferably lie
below +150~ C, in particular below +120~ C. Another
disadvantage arises as a result of the fact that the
backbone polymers are already present in their final state
in the form of a macromolecule and therefore very high
processing temperatures of +180~ C to +270~ C are necessary
in order to achieve a sufficient wetting and hence adhesion
~ on the different substrate surfaces. Certainly compositions
yl do also exist that melt at lower temperature~ , but such
compositions possess no resistance to thermal distortion and
also their resistance to chemicals is not always adequate.
Those melt coating compositions which are formulated on the
basis of ethylene/vinyl-acetate copolymers are described,
inter alia, in DE-OS 24 25 395. Other melt coatings are
described in the monograph by R Jordan entitled
"Schmelzklebstoffe", Volume 4a (1985) and Volume 4b (1986),
HINTER-WALDNER-VERLAG, Munich. Listed among them are
polyester melt coatings which are synthesised on the basis
of linear copolyesters formed from terephthalic acid and/or
isophthalic acid and which may range from amorphous to
crystalline (DE-OS 24 14 287).
In DE-OS 19 17 788 and DE-OS 31 06 570 radiation-sensitive
telomerised and acryloxy-terminated or methacryloxy-
terminated polyesters are described which are preferably
produced from aliphatic and cycloaliphatic polycarboxylic
acids and only partially from aromatic polycarboxylic acids
and multivalent aliphatic alcohols. They are markedly
linear and may only be cured with beams or rays under
aggravated conditions. Since in the case of linear
molecules the relative spacings of the acrylic or
methacrylic groups become greater with increasing molecular
weights, the necessary energy demand that is needed for
crosslinking or curing also increases. Despite this higher
energy demand, a good thorough crosslinking, in order that a
degree of crosslinking less ~5~r~) than 90 % is achieved, is
CA 02219628 1997-10-29
not guaranteed. If, on the other hand, use is made of low-
molecular polymers or monomers, although a relatively
sufficient degree of crosslinking can be obtained, such
coatings are exceptionally brittle and therefore sensitive
to shocks and impacts and are not deformable. In addition,
stresses may arise in the coatings in the event of loads,
such stresses then resulting at least in the formation of
fine hairline cracks.
The situation is analogous as regards resistances also in
the case of high-molecular linear polyester, even though the
cured coatings may be more viscoplastic. One of the
essential main points of attack is constituted by the
uncrosslinked reaction groups that are still free.
A still more significant disadvantage consists in the
thermosensitivity and the rheological properties, above all
when it is a question of high-molecular linear polyesters,
for the latter decompose very strongly as a result of
oxidation with increasing temperature.
In order to keep a tighter hold on the critical parameters
associated with the 'heat history', on the one hand, and the
improvement in the final properties such as, for example,
resistance to thermal distortion, on the other hand,
reactive melt coatings have also been proposed already.
With these melt coatings it is preferably a question of
adhesives and sealants which are in fact processed from a
melt in analogous manner to a melt coating at temperatures
< 150~ C, in particular < 100~ C, and as a result are
functionally manageable at an early stage, but their
crosslinking function is triggered only by the ambient
moisture. In this connection it is preferably a question of
polyurethane systems that cure through the action of
moisture. Depending on the layer thickness and ambient
moisture, curing requires between 1 and 96 hours. For
industrial manufacture this is a curing phase that is out of
CA 02219628 1997-10-29
the question, quite apart from the fact that uncrosslinked
portions of curing agent may migrate.
In European Patent EP 0 270 831 solvent-free, low-monomer or
monomer-free, polymerisable melt coatings on the basis of
(meth)acrylated cellulose esters and polyesters are
described which may optionally, inter alia, be employed for
the formation of sealing layers on planar substrates.
However, in order now to be able to synthesise an effective
sealing layer in relation to oxygen and water vapour, layer
thicknesses of 2 50 ~m, in particular 2 100 ~m, are
required. Despite these layer thicknesses the oxygen
permeability, for example, falls only by a factor of 10 to
20 on substrates consisting of polyethylene and/or
polypropylene. In the case of substrates consisting of
polyesters (eg, Melinex), no improvement in the sealing
properties arises. These melt coatings were also conceived
for other tasks. Since these melt coatings are likewise
processed at temperatures 2 80~ C, in particular 2 140~ C,
they are likewise thermosensitive.
The reasons for the negative evaluation are certainly not to
be sought solely in the so-called 'heat history' but rather
in the lack of suitable raw materials on offer. In order to
comply with the legal directives on improving the
environment which have to be continually updated, to conform
to food and industrial hygiene and to do justice to the
sensory problems, more preventive measures are not
sufficient on their own, since they are associated, on the
one hand, with higher investment expenditure on
installations, measuring instruments and the like and, on
the other hand, with costly monitoring systems. Therefore,
both for a better ecology and also with regard to industrial
and food hygiene it is better to eliminate these existing
stated problems, and those which are approaching, by
removing the causes as far as possible and in the process
also ensuring a high degree of economic efficiency.
CA 02219628 1997-10-29
Regardless of these numerous efforts it has not hitherto
been possible to ascertain, from the extensive range of
products and processes in accordance with the state of the
art that are on offer, highly effective, foodstuff-resistant
sealing layers for planar substrates or moulded articles,
particularly in relation to oxygen and water vapour, that
are also economic.
Independently of the barrier compositions pertaining to the
state of the art which are described above and which are
processed from solutions, aqueous dispersions and melts, a
large number of additional barrier polymers are known in
industrial practice. According to Rompps Chemie-Lexicon,
9th Edition, Volume 1, page 349, the barrier polymers can be
classified as follows:
Barrier effect Plastic
high (lst class) .a. polyvinylidene chloride (PVDC),
copolymers of acrylonitrile with
styrene or acrylates
medium (2nd class) polyamides, polyesters, polyvinyl
chloride (PVC) and polyvinyl fluoride
(PVF)
low (3rd class) polystyrene and polyolefins
Processing of the barrier polymers is effected in accordance
with diverse processing techniques such as, for example, by
injection moulding, compression moulding, blow moulding,
rotation moulding, thermoforming and the like. Since
individual barrier polymers rarely possess multiple barrier
properties, so-called 'composite foils' or 'composite
laminates' have to be produced from different substrates by
co-extrusion and/or adhesion.
CA 02219628 1997-10-29
The specific properties of the individual barrier polymers
are adequately described in the relevant literature. A
current overview of the barrier polymers is provided by
William J. Korosin in "Barrier Polymers and Structures", ACS
Symposium Series 423, Washington D.C., 1990, ISBN 0-8412-
1762-9.
In EP-Al-O 547 551 edible films are described that consist
of modified starches, gelatin, plasticiser, lipids and
water. In the case of foodstuffs these films are intended
to possess physical or microbial barrier properties in
relation to water, dissolved substances, gas and water
vapour. Depending on the type, content and film thickness,
water-vapour permeabilities of 2 7 % are ascertained. In
this connection the starch/gelatin mixture still possesses a
value of 25 %. The gas-barrier properties are not
substantiated by any values. A further point is that the
basic materials for the films consist of multi-component
mixtures which are complicated and relatively expensive to
manufacture and apply. These barrier properties are
unacceptable for the packing industry, particularly in the
case of sensitive foodstuffs and pharmaceutical products.
For the keeping quality of perishable goods the permeability
of the barrier polymers with respect to water vapour and
gases is of particular importance. With this permeability
it is a question not of imperfect seals in the classical
sense of porosity and/or capillary holes but of so-called
'solution diffusion'. In this case the gas dissolves ln the
barrier polymer in a manner similar to dissolving in a
liquid, migrates though it and emerges again on the other
side in the form of gas. This diffusibility does not depend
on the thickness of the barrier layer but exclusively on the
barrier polymer. The thickness of the polymer sealing layer
represents only a time factor.
CA 02219628 1997-10-29
In the case of barrier polymers that absorb moisture, such
as, for example, polyamide, cellulose acetate, as a result
of an increased degree of moisture easier diffusing of gases
occurs, since the latter are also able to dissolve in the
moisture itself. The barrier polymers are assessed, inter
alia, in accordance with their permeability coefficients.
In connection with the summary of the state of the art which
has been partially described in brief, the person skilled in
the art will note that the use of barrier polymers is a very
complex field, both as regards processing and as regards
application. In addition there are the ecological,
environmental and recycling problems and the constant effort
to reduce the requisite volumes of barrier polymers.
The tabulation below is a characteristic example, taken from
the foodstuff and beverage sector, of the demands made of
barrier materials against oxygen and water vapour in order
to obtain a stability in storage of 1 year at 25~ C (Plastics
Engineering, May 1984, page 47).
CA 02219628 1997-10-29
Table 1
Foodstuff/Beverages Estimated maximum increase or
decrease in weight
Oxygen Water
ppm wt-%
Canned milk, meat, 1 to 5 - 3
baby food, beer ),
wine
Instant coffee 1 to 5 + 2
Canned vegetables, 1 to 5 - 3
canned soups and
canned spaghetti
Canned fruit 5 to 15 - 3
Nuts, snacks 5 to 15 + 5
Dried foods 5 to 15 + 1
Fruit juices 10 to 40 - 3
Oils 50 to 200 + 10
) less than 20 % loss of CO2
The known barrier polymers possess very different sealing
properties, particularly in relation to oxygen and water
vapour. Only in a few applications do they provide the
required sealing properties in the form of a single layer.
Now in order to be able to satisfy the catalogue of
requirements of the packing industry, amongst which not just
the sealing properties alone are numbered, predominantly so-
called multiple coatings, composite foils or laminates have
to be produced from the barrier polymers and/or the surfaces
of such coatings, foils or laminates have to be metallised.
Only with the aid of these measures can sealing properties
CA 02219628 1997-10-29
16
be achieved that are comparable to those of aluminium foils.
But technical and economic limits are laid down for such
multilayer composites, because
- the weight of packaging and hence the requirement for
barrier polymer rises
- disposal and/or recycling is made difficult and
- economic efficiency for the manufacturer and user is no
longer ensured.
Further aspects in connection with the selection of barrier
polymers, particularly for use by way of packing materials
for consumer commodities which are everyday necessities, are
the legal directives and/or self-restraints imposed on
manufacturer and consumer in relation to the ecology and the
environment. In so~e countries this fact has already
resulted in polyvinyl halides such as PVC and PVDC, for
example, no longer being permitted as barrier polymers in
packing materials. Although the number of usable barrier
polymers decreases by virtue of this measure, the range of
requirements existing in practice cannot be covered by the
remaining barrier materials. This is the case, above all,
when very superior sealing properties - ie, very low oxygen
and water-vapour permeability values, for example - are
required. So in practice there are a great many needs where
the requirements can no longer be satisfied - even by high-
quality barrier polymers.
But efforts are also being made to improve the barrier
properties of packing materials with the aid of transparent
evaporated films consisting of oxides of Si, Al and Mg.
However, not all the objectives that have been set by the
packing industry can be achieved in this way. See, on this
point, Coating, Volume No. 8, 1994, pages 274 to 280.
The state of the art described above concerning barrier
finishes and reasons arising from ecology, environment and
CA 02219628 1997-10-29
industrial hyglene are sufficient cause for the industry
that processes and uses barrier polymer, particularly in the
foodstuff and pharmaceutical sector, to seek technically and
economically simpler solutions having further improved
sealing properties in order to be able to produce packaging
substrates having very low area weights.
It is the object of the present invention to make available
barrier materials that avoid the aforementioned
disadvantages and satisfy the requirements defined in Table
1 with only a single layer.
In particular it is intended to provide remedies for
problems in connection with sensory perception, ecology,
disposal and/or recycling. In this regard the fields of
application in the foodstuff and pharmaceutical sectors and
in the sphere of industrial hygiene constitute, inter alia,
a main focus.
In accordance with the invention this object is achieved by
means of a water-resistant barrier material comprising
natural, biologically degradable hydrocolloids that are
substituted once or several times by ethylenically
unsaturated residues and/or by residues bearlng epoxide
groups, the hydrocolloids being cured and/or crosslinked by
means of a polyreaction that affects the residues.
Surprisingly it has now been found that high-quality barrier
materials having superior, advantageous properties can be
produced from hydrocolloids that are capable of being cured
or crosslinked by means of a polyreaction, in particular a
polymerisation and/or polyaddition, and are substituted with
singly or multiply (sic) ethylenically unsaturated residues
and/or residues bearing epoxide groups.
The adhesive primary materials according to the invention on
the basis of natural, biologically degradable hydrocolloids
CA 022l9628 l997-l0-29
18
that are substituted once or several times by ethylenically
unsaturated residues and/or by residues bearing epoxide
groups include water-soluble, biologically degradable
hydrocolloids or backbone polymers A which, inter alia,
originate from the following polymer families:
- Proteins
polypeptides, in particular those of collagenic origin,
such as, for example, gelatin; animal glues; collagens;
whey proteins, caseins; plant proteins, in particular
soybean, rape and grain proteins and/or their
hydrolysates.
- Polysaccharides
cellulose and its derivatives such as methylcellulose,
ethylcellulose, hydroxyethylcellulose,
carboxymethylcellulose, etc, starch and starch
derivatives, glycogen, alginic acid and derivatives
including salts, agar-agar, heteropolysaccharides,
heteroglycanes, hemicelluloses and their derivatives,
chitin, gum arabic and the like.
In the case of the barrier materials according to the
invention it is preferably a question of hydrocolloidal
compounds corresponding to the general formula (I)
(R - C - X)n - (R2)m - Y - A (I)
wherein A is a hydrocolloid having the above significance,
preferably with a molecular weight from about 500 to about
2,000,000r
R1 is the hydrocarbon residue of an ethylenically
unsaturated, optionally hydroxy-, nitrile-, halogen-
and/or C1-C4-alkyl-substituted carboxylic acid,
preferably of an acrylic, methacrylic and/or crotonic
CA 02219628 1997-10-29
acid and/or with an a-, ~-epoxide group having 2 to 10
C atoms,
X = -O-, -N(R2)-, -NH-C(O)- and/or the group R1 -C(O)-X-
stands for an ethylenically unsaturated residue of
dicarboxylic imide, preferably a residue of maleic
imide,
R2 is an optionally hydroxy-, amino-, multiply R1
-C(O)-X-, C1-C8-alkyl-, C1-C8-alkoxy- and/or oxyalkyl-
substituted, saturated or unsaturated hydrocarbon
residue, preferably an aliphatic hydrocarbon residue,
and optionally comprises -C(O)-O-, -O-C(O)-O-,
-O-C(O)-, -O-, -C(O)-, -NH-C(O)-NH-,
R3
I
- N -
and/or -NH-C(O) bridge-type links,
R3 may be = H, R-C(O)-, R2 _ y - A and/or C1-C4 alkyl,
Y = -O-, -O-C(O)-, C(O)-O-, -NH-C(O)- or -C(O)NH-
n = 1 to 5 and
m = O to 10.
The barrier materials according to the invention are based
on functionalised hydrocolloids. The primary materials are,
inter alia, known and conventional hydrocolloids or their
basic raw materials. The chemical modification of the
primary materials is effected through the introduction of
reactive and/or functional groups into the main molecular
chains without changing or damaging the colloidochemical and
water-soluble properties in the process.
The barrier materials according to the invention are
reactive, biologically degradable hydrocolloids or backbone
CA 02219628 1997-10-29
-
polymers. They are substantially conversion products
resulting from a non-radical reaction between polypeptides
and/or polysaccharides, whereby their functional groups, for
example hydroxyl, amino, imino, thiol and/or carboxyl
groups, are at least partially subjected to derivatisation
with a polymerised residue.
In the case of the barrier materials according to the
invention it is consequently a question of derivatives of
esters of unsaturated carboxylic acids and/or residues
bearing epoxide groups with hydrocolloids from the
aforementioned groups. Particularly preferred are those
hydrocolloidal compounds corresponding to the above formula
(I). In the hydrocolloidal compounds corresponding to
formula (I) Rl may be the hydrocarbon residue of, for
example, methacrylic acid, chloroacrylic acid, cyanoacrylic
acid and the like, the residues of acrylic and methacrylic
acid being particularly preferred. Furthermore, Rl may also
be a hydrocarbon residue bearing epoxide groups and having 2
to 10 C atoms, the epoxy groups preferably being arranged in
a or ~ position.
Quite particularly preferred are compounds in which X is
oxygen.
The residue R2 contains at least one Rl-C(O)-X group, wherein
Rl and X may have the above significance and in the case of
several Rl-(C)-X residues within one molecule the residues
and X may in each case be the same or different. Bridge-
type links of the residue R2 which are optionally present may
be arranged both within the residue, especially in the case
of aliphatic residues R2, and/or arranged terminally on one
side or on both sides as bridge-type links of the residue R2
in relation to X, Y or A. In a quite particularly preferred
embodiment R2 is an at least divalent, optionally
substituted, glycol or polyol residue having 2 to 6 C atoms,
the divalent residue of an aliphatic hydroxycarboxylic acid
CA 02219628 1997-10-29
having 2 to 18 C atoms or the divalent residue of a
carboxylic acid -C2-C6-glycol or C6-C80 polyalkylene glycol
ester. R2 may also, for example, be a C1-C4 alkylene group
which is optionally substituted with low alkyl groups. The
residue R2 is preferably linked to the residue Y or A via
ether, ester and/or imino groups (Y = -O-, -OCO-, -COO- or
NR4-). A further group of usable, well suited compounds that
are substituted in ethylenically unsaturated manner have the
general formula (II):
(R - X)n - (R2) - Y - A (II)
wherein R1 is an allyl or vinyl group and/or an a~
epoxide group having 2 to 10 C atoms, X, R2, Y, A, n and m
have the same significance as before.
In particularly preferred manner use is made of compounds
according to formula (I) in which - X - R2 _ may be
(O [CH2]p) m- ~ - , - O - [CH2] p) m ~ O ~ R4 -
and also residues corresponding to the general formulae
-O-C - _(-O-CH2-CH2)~m -O-C- / -o-R4-o-C-m -~4-0-
RS O
m+l
-O--(-CH2)2--lC~-- ~ O CH2--fH--CH2--O-Ii--R6-1CI--O-CH2--
O m OH O
--O- [CH2] P-l(~-O-- ~ -O- [CH2 ] p-C- o-R4-
O,m+l _ O m+l
H H
-O- [CH2~ P C O-R4-O- -N-R4- _1_R4_C6H4_R4_
~ O m+l
CA 02219628 1997-10-29
22
-N-C-N-R4- -R4-N-C- -I-f _ NH-R4
R5 m
CH3 - fH CH3
H ~H2 H
- N - C N - R
and/or - (CH2) m'
R4 may be the same or different and branched and
unbranched as well as cyclic alkylene residues having 1
to 20, preferably 1 to 10, carbon atoms, arylene
residues, aralkylene residues and/or acyl residues
having 1 to 20 C atoms,
R5 = H, Cl, CN, OH, C1-C4 alkyl,
R6 = ~ CH = CH -, -CH2 - CH2-,
m = 0 to 50
p = 1 to 20.
Another preferred group of compounds is constituted by those
corresponding to the formulae
CA 02219628 1997-10-29
O CH2
Z~ C~2- 1 - CH2--Y - A and/or z o-c~2-f cH2--O-Y-A
fH2 l H2
O O
Z 1 or 2 Z I c- 2
wherein
Z = RL _ C -
and/or - Y - A, but at least one of the residues
Z = R~ - C -
and A, Y and R1 have the above signi~icance.
The binding link Y between the residues from formula (I)
and/or ~II) and the main chain of the polymer results from
the reaction of the functional groups of the hydrocolloid A
with the corresponding reactive groups OL the aforementioned
polymerisable residue. In particular, Y has the same
meanings as the heterogroups of R2. Derivatisation may be
ef~ected by non-radical reaction or by graft re~ctions onto
the backbone polyr.er.
The reactive groups that are introduced into the main
molecular chains of the hydrocolloids A in acco dance with
CA 02219628 1997-10-29
24
the present invention are ethylenically unsaturated residues
and/or residues bearlng epoxide groups. These may be linked
to the hydrocolloids directly or via the residue R2, for
example a divalent, optionally substituted hydrocarbon
residue or polyol residue. Curing or polymerisation is
effected by means of the reaction initiators, curing agents
that are conventional for compounds of this type, and/or by
high-energy beams or rays. The barrier materials may
additionally contain other known components such as
accelerators, stabilisers, rheology-influencing agents,
fillers, pigments and/or other polymerisable compounds or
compounds that are capable of being copolymerised with the
aforementioned ethylenically unsaturated hydrocolloids
and/or hydrocolloids bearing epoxide groups, in particular
water-soluble compounds and/or compounds bearing active
hydrogen atoms and the like.
Preferred in accordance with the invention are, however, the
functionalised backbone polymers or hydrocolloids in which
the reactive groups have been introduced into the main
molecular chains via a non-radical reaction. They make a
significant contribution to a homogeneous barrier material,
as has surprisingly been found. The production of these
functionalised products is effected, inter alia, as
described in DE-A-42 10 334.
Functionalisation of the hydrocolloids A with one or more
reactive residues is effected in particular via their
hydroxyl, amino, imino, thiol and/or carboxyl groups. The
contents of functional residues in the hydrocolloid amount
to 2 0.1 mass-% (m-%). The particularly preferred contents
amount to between 1 and 50 m-%, in particular between 5 and
35 m-%. Those functionalised hydrocolloids which possess at
least 10 curable or crosslinkable groups per 1,000 amino-
acid or monosaccharide units prove to be particularly
advantageous barrier materials.
CA 02219628 1997-10-29
According to the invention a large number of ethylenically
unsaturated compounds and/or compounds bearing epoxide
groups in accordance with the above formulae are suitable
for the purpose of functionalising the hydrocolloids A.
Particularly preferred are those reactive residues which,
inter alia, are introduced into the hydrocolloid A from the
groups of the
- ethylenically unsaturated compounds such as, for
example, glycidyl acrylate, glycidyl methacrylate,
glycidyl acryloxypropionate, glycidyl
methacryloxypropionate, monomethylacryloxyethyl
maleate, urethane methacrylate, allyl glycidyl
carbonate, (meth)acrylamide, 2-acrylamido-2-
methylpropanesulphonic acid,
epoxydicyclopentenyloxyethyl methacrylate,
vinylcyclohexane epoxide, allyl glycidyl ether and/or
- compounds bearing epoxide groups, such as, for example,
epichlorohydrin, butyl diglycidyl ether, 1,6-hexanediol
diglycidyl ether, neopentylglycol diglycidyl ether,
polypropyleneglycol diglycidyl ether, vinylcyclohexene
diepoxide.
Particularly preferred for the functionalising are those
compounds which are water-soluble and/or capable of being
easily dispersed in water.
The polymerisation required for the curing may be effected
in the form of pure homopolymerisation of one of the
derivatives containing the above residues, but it may also
be effected by copolymerisation of a mixture of such
derivatives. But the hydrocollolds according to the
invention may also copolymerise with water-soluble or water-
dispersible unsaturated monomers, oligomers and/or polymers
or with monomers, oligomers and/or polymers bearing epoxide
groups. In this connection these coreactants have, inter
CA 02219628 1997-10-29
26
alia, the function of a crosslinker. These crosslinking
compounds may, for example, be those employed above for the
purpose of functionalisation or may be other compounds.
Suitable furthermore for the purpose of crosslinking
hydrocolloids bearlng epoxide groups are compounds that
possess active H atoms in the molecule and that, for
example, cure via polyaddition, unless a cationic
polymerisation is preferred. Such compounds are, inter
alia, polyamines, polyimines, polyamides, polyamidoamines,
polysulphides, silane compounds and the like. Also suitable
for the cationic polymerisation are polyols, in particular
water-soluble polyols, that additionally provide a
'softening' or 'plasticising' component in a cured polymer
matrix.
The curing or polymerisation of the barrier materials
according to the invention themselves is effected
a) in the case of ethylenically unsaturated residues by
free-radical polymerisation
- in the presence of reaction initiators selected
from
1. inorganic peroxides such as, for example, alkali-
metal peroxides and/or alkaline-earth metal
peroxides, and also hydrogen peroxide;
2. organic peroxides and/or hydroperoxides such as,
for example, benzoyl peroxides, cumene
hydroperoxides;
3. peroxo acids and the salts thereof, such as, for
example, peroxodisulphuric acid, sodium
peroxodisulphate (persulphate);
- actinic light, in particular UV rays in the
wavelength range from 380 to 100 nm in the
presence of photoinitiators such as, for example,
CA 02219628 1997-10-29
benzophenone, benzoin ether, Michler's ketone,
methylthioxanthone, ketone acetals and optionally
other synergists such as, for example, amines,
tert. amino alcohols and/or
- by means of electron beams in the low-energy
acceleration range from 50 to 300 keV and a
preferred effective depth of penetration from 3 to
400 g/m2 and also a dose distribution from 5 kGy to
100 kGy, in particular 10 to 70 kGy, and a dose
variance of about + 3 %.
b) in the case of residues bearing epoxide groups
- by means of polyaddition with compounds bearing
active H atoms such as already mentioned above in
connection with the crosslinkers, such as, for
example, isophoronediamine, diethylenetriamine,
4,4-diaminodiphenylmethane
- by means of cationic polymerisation and actinic
light in the presence of Lewis acids and Br~nsted
acids, carbonium ions and trialkyloxonium salts
such as, for example, bis-[4-(diphenylsulphono)-
phenyl]-sulphite-bis-hexafluorophosphate, ~-2,4-
(cyclopentadienyl)[1,2,3,4,5,6-~)-(methylethyl)-
benzene]-iron(II) hexafluorophosphate.
Furthermore, the polymerisation and copolymerisation may be
accelerated after addition of one or more reaction
initiators by addition of an accelerator, above all if
curing is effected at temperatures < 25~ C. Suitable for
this purpose are accelerators on the basis, inter alia, of
tertiary amines such as, for example, diethylaniline,
diethyl-p-toluidine, triethyleneamine, salts of heavy
metals, such as cobalt acetylacetonate, for example.
CA 02219628 1997-10-29
28
Particularly preferred are water-soluble or water-
emulsifiable accelerators such as triethanolamine.
The curing or crosslinking of the ethylenically unsaturated
residues in the barrier materials according to the invention
by means of free-radical polymerisation has to be effected,
particularly in the case of thin layers, in an inert
protective-gas atmosphere consisting of nitrogen (N2), carbon
dioxide (CO2) and/or noble gas with a view to forestalling
the inhibition of oxygen. If, on the other hand, layers,
coatings, films and foils or the like consisting of the
aqueous barrier materials according to the invention are
cured or crosslinked prior to the dehydration or drying, an
inert protective-gas atmosphere can be dispensed with, as
has surprisingly been found, for the content of water that
is present creates its own self-sufficient protective zones
in relation to molecular oxygen (~2)- Furthermore, this
manner of proceeding also offers the additional advantage
that the dehydration or drying that follows directly can be
made technically simpler and hence more economical.
Independently of the above explanatory remarks, in addition
other reactive groups can be crosslinked in the main
molecular chains of the hydrocolloids. Suitable for this
purpose are, inter alia, bifunctional and/or polyfunctional
isocyanates and the like, but also aldehydes such as
glutaraldehyde, for example. But dual curing and hybrid
curing may also be carried out with the barrier materials
according to the invention, provided that they have been
functionalised for this purpose with the suitable residues
and/or contain other reactive members in the main molecular
chain.
Particularly suitable crosslinkers for the copolymerisation
with the hydrocolloids according to the invention are, inter
alia, monomeric and/or oligomeric monofunctional,
CA 02219628 1997-10-29
-
29
bifunctional, trifunctional and polyfunctional (meth)acrylic
compounds, in particular those with molecular weights
(Mw) 2 500. This group includes, inter alia, aliphatic
and/or cycloaliphatic urethane (meth)acrylates, polyether
(meth)acrylates, acrylamido-2-methylpropanesulphonic acid.
If these compounds are not water-soluble, they are
advantageously added to the barrier materials according to
the invention in the form of aqueous dispersions. Additions
of just < 25.0 m-%, preferably < 10.0 m-%, in particular
< 5.0 m-%, of urethane (meth)acrylates again result in
significant reductions in permeation, particularly as
regards oxygen, as has surprisingly been found.
The barrier materials according to the invention may
optionally be modified by means of further additives. By
way of known conventional additives, mention should firstly
be made of pigments, in order to impart a coloured
appearance to the barrier materials. The term 'pigments' is
to be understood to encompass quite generally dyestuffs,
colouring compounds, fillers and extenders of all types
which supply additional solids to the barrier materials
according to the invention and optionally also make them
printable. At the same time they impart a number of
specific properties to the barrier materials.
In connection with the use of the pigments in barrier
materials that are later employed in the foodstuff and
pharmaceutical sector said pigments have to conform to the
respective legal regulations regarding foodstuffs and
pharmaceuticals. The particular properties and functions
are summarised in "Pigmente und Fullstoffe", 2nd Edition,
1980, M. and O. Luckert, Laatzen. The content of pigments
and fillers may amount to between 0.5 and 80 wt-%,
preferably between 1.0 and 70 wt-%.
Furthermore, the barrier materials may also contain
plasticisers. Especially suitable by way of plasticisers
CA 02219628 1997-10-29
are water-soluble products such as polyols, such as, for
example, diols, glycols, glycerin, sorbitol, inositol and
other sugar alcohols which may optionally possess reactive
groups according to the above formula.
For use in the technical field, further additives such as,
for example, stabilisers, anti-oxidants, flow-control agents
and wetting agents may be added to the barrier materials
according to the invention. The additives are sufficiently
described in the literature, so reference may be made to the
a-forementioned book by Gachter/Muller entitled "Kunststoff-
Additive", 2nd Edition, Hanser-Verlag, Munich, 1983. If, on
the other hand, additives that are used in the foodstuff and
pharmaceutical sector are required for barrier materials,
the legal regulations applying are to be observed. The
supplemental amounts are generally between 0.1 and 5.0,
preferably between 0.1 and 2.5 wt-% - relative to the solids
content. Since the physical characteristic data are not
altered by the derivatisation of the hydrocolloids, in
connection with the processing and production of sealing
layers and films the barrier materials according to the
invention offer an additional advantage by virtue of the
fact that they remain water-soluble or water-dispersible.
Only as a result of the curing or crosslinking are these
properties - depending on the content of reactive groups -
partially or entirely eliminated. Consequently the person
skilled in the art is provided with a barrier material, the
processing of which is familiar to him and the properties of
which he knows.
The barrier materials according to the invention are present
in solid form as powders, granulates and the like or as
aqueous gels, solutions and/or dispersions. With a view to
processing they have to be
CA 022l9628 l997-l0-29
31
- in the case of solid forms, previously wetted with
water, optionally swollen, then molten under heat
and/or dissolved in water and
- in the case of aqueous gels, molten by means of heat
and hence converted into the sol state.
Since processing is effected from aqueous solutions and/or
dispersions, the hydrocolloids according to the invention
are particularly environmentally friendly also from this
point of view.
The addition and incorporation of the crosslinking
coreactants, reaction initiators and optionally other
adjuvants and/or additives is effected likewise in an
aqueous, liquid phase in the case of the hydrocolloids
according to the invention. To this end, simple mixing
vessels with suitable mixing tools may be used which, where
required, have to be equipped so as to be heatable for the
purpose of melting the gels. Preparation and processing may
also be effected continuously, for which purpose extruders,
screw mixers are, inter alia, suitable.
If the barrier materials according to the invention contain
trapped gases, for example air, prior to application they
have to be degassed by means of a vacuum.
A further subject of the invention is the finishing of
substrates with the polymerisable barrier materials
according to the invention or the production of self-
supporting barrier films. The polymerisable barrier
materials according to the invention are suitable for the
formation of coatings for planar substrates and moulded
articles consisting, inter alia, of
- cellulose materials such as, for example, paper,
cardboard and paperboard of all types,
CA 02219628 1997-10-29
32
- plastics such as, for example, foils and sheets
consisting of, inter alia, polyvinyl alcohols,
polyethylene, polypropylene, polycarbonate, polyester,
polyvinyl ester, polyamides, polyvinyl halides and
their copolymers, as well as fibrous composite
materials formed from thermoplastics and thermosetting
plastics, but also
- for other materials such as metals, inorganic materials
such as, for example, glass and the like.
In particular they are suitable for porous substrates and/or
substrates that are not diffusion-proof, in order to impart
the necessary barrier properties to the latter. The barrier
materials according to the invention are also quite
particularly suitable, as has surprisingly been found, as
so-called topcoats of substrate surfaces that are finished
with evaporated films consisting of metals or oxides of
silicon (Si), aluminium (Al) and/or magnesium (Mg), because
they improve the gas and water-vapour permeability values
thereof again by very high factors.
The sealing properties of the barrier materials according to
the present invention may be varied within wide limits. In
addition to the
- contents of reactive residues or groups - according to
the above formula - and/or
- the respective layer thicknesses, optionally as a time-
dependent influencing factor,
the barrier properties are essentially partly determined by
the type of the hydrocolloids according to the invention and
their dehydration behaviour, as has surprisingly been found.
Particularly high reductions in permeation are produced by
CA 02219628 1997-10-29
those hydrocolloids which dehydrate or dry from their
aqueous solutions and/or gels not via pores or capillary
activities but via diffusion processes. These preferably
include, inter alia, those hydrocolloids according to the
invention which form gels or which in the uncrosslinked
state are subject to a sol/gel transformation and have a
content of reactive groups amounting to between 20 and
50 m-%. In particular, those hydrocolloids according to the
invention are suitable which are of collagenic origin - for
example, gelatin.
The sealing properties of the hydrocolloids according to the
invention can optionally be further improved if
- in addition to the curing or crosslinking the
aforementioned crosslinkers and/or other known
crosslinkers are used concomitantly and/or
- dual curing and/or hybrid curing are carried out.
The dehydration and drying of the uncrosslinked and
crosslinked layers, coatings, films, foils or the like also
have an influence on the polymer-network formations and
their sealing-layer properties. For this reason the
dehydration and drying are performed under air-conditioned
climates, predried air having a relative atmospheric
moisture < 40 % and low temperatures < 100~ C being
particularly preferred.
The cured or crosslinked barrier materials, films and/or
foils according to the invention possess differing barrier
properties and functions, depending on
- their hydrocolloid base,
- the respective degrees of crosslinking and crosslink
densities and
- the layer thicknesses chosen in each case.
CA 022l9628 l997-l0-29
34
Consequently they are able to form sealing layers having
outstanding functionalities in relation to a large number of
gases, vapours and/or liquids, in which connection gases and
vapours containing oxygen, for example, but also water
vapour and readily volatile vapours, constitute a main
focus.
Furthermore, the barrier materials according to the
invention also possess good resistances to organic solvents
such as, for example, alcohols; oils and fats; and also a
large number of weak acids and bases. In this connection
the chemical resistance is essentially influenced by the
base hydrocolloid, the degree of crosslinking and the
crosslink density. In relation to water or liquids
containing water, in the case of the cured or crosslinked
barrier materials according to the invention considerably
reduced reswelling capacities are obtained which in addition
may optionally have a positive influence on the sealing
properties, as has surprisingly been found.
With the barrier materials according to the present
invention it is possible for innovative, high-quality
sealing layers to be produced. These sealing layers
according to the invention provide barrier factors which in
comparison with their unmodified base hydrocolloids may be
higher by a factor of up to 10 . These potential
improvements were already surprising, because the barrier
factors of the unmodified hydrocolloids are generally < 102.
Hence, depending on the supporting material, the
pretreatment of the surface thereof and the barrier material
according to the invention that is employed, inter alia
permeation values can be achieved
- in the case of oxygen (~2)~ amounting to < 0.1 ml /
(m2 X 24 h x bar)
(ASTM D 3985-81)
CA 02219628 1997-10-29
- in the case of water vapour, amounting to < 0.3 g
(m2 x 24 hrs)
(ASTM 372-78).
The barrier materials according to the invention adhere to a
large number of substrate surfaces. With a view to
improving the wetting and adhesion of the surfaces to be
coated, a pretreatment of the surface may be necessary.
This is particularly the case when these surfaces are non-
polar, as in the case of polyolefinic substrates, for
example.
Suitable for the pretreatment of the surface are, inter
alia, singeing, corona discharges, low-pressure plasma
and/or adhesive primer.
Self-supporting barrier films and foils can be produced from
the barrier materials according to the invention by, inter
alia, pouring onto an adhesive backing sheet, subsequent
curing or crosslinking and dehydration. The processing
conditions are analogous to those above.
As a result of the curing, crosslinking and/or polymerising,
the hydrocolloids according to the invention lose their
hydrocolloidal properties. That is to say, the layers,
coatings, films, foils and the like produced with them are
no longer water-soluble and/or water-dispersible but they
produce, inter alia, network polymers that are resistant to
boiling water and optionally resistant to sterilisation.
Furthermore, the temperature-dependent reversi~le sol/gel
transformation turns into an irreversible transformation.
In water the polymer networks may still have a relatively
weak charactersitic swelling.
The new polymer networks are, inter alia, resistant to
water, media containing water, salt solutions, weak acids
CA 02219628 1997-10-29
and bases, sugar solutions, fruit juices, milk, alcoholic
beverages, soft drinks, milk and milk products, oils, fats,
organic solvents and are therefore particularly suitable for
the finishing of packing materials and packagings consisting
of different materials. Since they are diffusion-proof with
respect to a large number of aromatic media, the barrier
layers also offer outst~n~ ng protection to products that
are sensitive in sensory respects, such as, for example,
coffee, fruit powders and the like.
The cured barrier layers, coatings, films and foils are
neutral in sensory respects and do not produce or have any
so-called 'scalping effect' in relation to any fillings or
the like.
The barrier materials according to the invention that are
cured by means of W rays and electron beams are, in
addition, sterile.
The new polymeric networks that have formed as a result of
curing, crosslinking and/or polymerising the barrier
materials according to the invention have furthermore
remained biologically degradable, as has surprisingly been
found. By addition of enzymes the cured barrier materials
can be degraded in acid or'alkaline medium within a few
days. When the materials are buried in the ground or
composted, biological degradation requires a period from
several days to a few weeks.
Such substrates and others having a barrier protective film
are required in many sectors of the industrial economy and
in many branches of industry. These include, inter alia,
the packaging and wrapping industry, the vehicle industry,
aviation and aerospace, construction engineering, etc.
Particular fields of application for additive-free, monomer-
free, polymerisable barrier materials according to the
CA 02219628 1997-10-29
37
present invention are the packaging and wrapping sectors for
foodstuff and pharmaceutical products. In order to be able
to make packagings and wrappings available in future for
these fields of application, said packagings and wrappings
will have to be capable of being produced and processed not
only under more severe legal directives but they will also
have to satisfy in their physiological and sensory behaviour
the higher requirements of foodstuff and pharmaceutical
legislation. In order to achieve this objective, new
barrier materials are needed in the form of coating
compositions which are based on different, innovative, new
technologies. According to the present invention this
object can be achieved in technically and economically
successful manner with the polymerisable barrier materials,
which in particular are additive-free and monomer-free,
because
- their primary hydrocolloids are natural polymers and
predominantly foodstuffs and their properties and
technical characteristic data are not modified as a
result of derivatisation and
- only as a result of the curing, crosslinking and/or
polymerising are new, polymeric networks formed having
exceptionally high sealing properties in relation to
gases, water vapour and a large number of other media,
as has surprisingly been found. These polymeric networks
that form in accordance with the invention possess such
sealing properties already in very thin layers or films,
such as less than 10 ~m for example, that they can be
assigned to at least the 1st barrier class above.
Furthermore it was totally surprising that the already
outstanding sealing properties of the substrates that are
finished with evaporated films consisting of metals and
oxides of Si, Al and Mg can, after the application and
CA 02219628 1997-10-29
38
curing of the barrier materials according to the invention
as topcoats, be improved again by factors > 101.
Furthermore, porous and/or absorptive substrates such as,
for example, cellulose materials, in particular paper,
cardboard, paperboard, wood, derived timber products and the
like, can be impregnated with the barrier materials
according to the present invention in order to impart highly
functional sealing properties to said substrates.
According to the present invention new, innovative barrier
materials are created which are not comparable to the known
barrier polymers. As a result, not only can the described
disadvantages and other known disadvantages be very largely
eliminated but totally new barrier polymers and barrier
materials are made available which are better able to cope
with current and future aspects and requirements,
particularly in the foodstuff and pharmaceutical sector.
This new class of barrier polymers according to the present
invention offers, inter alia, the following advantages:
- natural polymers which are available from national
resources
- the primary hydrocolloids are preferably foodstuffs or
permitted additives for foodstuffs
- may be processed like their base colloids
- biological degradability
- after curing, crosslinking and/or polymerising,
monomer-free polymeric networks are formed which are
resistant to boiling water and to sterilisation
CA 022l9628 l997-l0-29
39
- high economic efficiency, as layers < 10 ~m already
possess high barrier functions in relation to gases and
liquids
- improvement of the barrier factors by up to 107.
In comparison with the barrier polymers described at the
outset and other barrier polymers according to the state of
the art, the barrier materials according to the present
invention are potentially superior and consequently make
essential contributions to improving the ecology, the
environment and the disposal of waste and are,
physiologically and toxicologically, generally acknowledged
to be many times safer.
The invention is elucidated in more detail by means of the
following Examples, without, however, being restricted
thereto.
~x~Dle 1
100 g derivatised high-bloom type A gelatin having a
methacrylate proportion of 14 mmol/100 g 20-% aqueous gel
were mixed at 50~ C with 0.5 ml 50-% aqueous triethanolamine
and 5 ml 10-~ Na2S208 solution. The formulation polymerised
after 40 seconds to form a gel that was resistant to boiling
water. An increase in temperature (60, 70~ C) resulted in
short reaction-times (10-20 s~co~c) - formulations without
addition of amine polymerised more slowly.
~X~Dle
Derivatised high-bloom type A gelatin having a methacrylate
proportion of 28 mmol/100 g 20-% aqueous gel was mixed at
50~ C with 0.5 ml 50-% aqueous triethanolamine and 5 ml 10-%
Na2S20~ solution. The formulation polymerised for an additional
CA 02219628 1997-10-29
25 seconds. As in Example 1, an increase in temperature
resulted in shorter reaction-times, whereas formulations
without addition of amine polymerised more slowly.
Example 3
Derivatised high-bloom type A gelatin having a methacrylate
proportion of 45 mmol/100 g 20-% aqueous gel was mixed with
a photoinitiator (Igracure 184 = 1-hydroxy-cyclohexyl-
phenyl-ketone). The concentration of photoinitiator
amounted to 0.5 wt-%. The mixture was applied onto paper
with a manual doctor blade and irradiated by means of a
high-pressure Hg lamp (power 120 W/cm2). At a throughput
speed of 13 m/min, solid layers that were resistant to
boiling water were produced.
Example 4
Derivatised high-bloom type A gelatin gels (sic) (20 % W/W)
of the types specified in Table 2 was applied onto 210 g/m2
cardboard by the manual doctor blade and irradiated with
180 keV electrons. The radiation dose amounted to 40 kGy.
The ~2 permeability and N2 permeability of the cardboard
coated with crosslinked gelatin were determined. By way of
barrier factor for ~2 the ratio
~2 permeability of the substrate
~2 permeability of the coated substrate
is specified
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Table 2
Methacry- Dry layer Barrier Permea- Permea-
latethickness factor ~2 bility bility
content,um ~2 (ml/m2.h.bar) N2
mmol/100 g
20-% gel.
Cardboard250 - 30.3 . 106
(cardboard)
6 2.5 . 106 12 10
14 8 8.8 . 105 34 . 34
18 1.2 . 106 25 27
28 24 4.1 . 105 73
Example 5
Derivatised high-bloom type A gelatin of the types specified
in Table 3 was applied by manual doctor blade onto
polypropylene (PP) foils with a thickness of 25 ~m and
irradiated with 180 keV electrons. The radiation dose
amounted to 40 kGy. Permeabilities and barrier factors were
measured.
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42
Table 3
Methacry- Dry layer Barrier Permea- Permea-
late thicknessfactOr ~2 bility bility
content ~m ~2 (ml/m2.h.bar) N2
mmol/100 g
20-% gel.
PP foil 25 (foil) - 74 21
7 264 0.28 0.18
7 62 1.2 0.25
7 93 0.8 0.25
7 123 0.8
Example 6
Derivatised high-bloom type A gelatin of the type specified
in Table 4 was applied by manual doctor blade onto polyester
foil that had been precoated with SiOx and was irradiated
with 180 keV electrons. The radiation dose amounted to
40 kGy. The oxygen permeability of the gelatin-coated foil
was measured.
Table 4
Methacrylate Dry layer Barrier factor Permeability
content thickness ~2 (ml/m2 . h.bar)
mmol/100 g ~m ~2
20-% gel.
PET SiOx foil 11.5 (foil) 2.5
6 < 0.1
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Example 7
Derivatised type A gelatin of the types specified in Table 5
was mixed with aqueous dispersions of various monomeric and
oligomeric acrylates such as TMPTA, polyether acrylates and
polyester acrylates. The acrylate concentration amounted to
between 1 and 10 wt-%. The mixtures were applied by manual
doctor blade onto 60 g/m2 paper and irradiated with 180 keV
electrons. The radiation dose amounted to 40 kGy. In Table
5 barrier factors and ~2 permeabilities of the coated
substrates are stated and compared with measured values for
pure gelatin coatings.
Table 5
Methacry- Acrylate Layer Barrier Permea-
late addition thickness factor O2 bility
content of % ~m o2 (ml/m2.h.bar)
derivatised
gelatin
mmol/100 g
20-% gel.
Base paper - 61 2.4 . 108
- 13.66 . 103 420
10l) 15.86.7 . 105 3.6
101~ 16.41.3 . 106 1.8
52) 18.11.6 . 104 150
l) urethane acrylates
2) polyether diacrylate
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44
Example 8
The biological degradabillty of the irradiated - that is to
say, crosslinked - coating material was investigated by
means of tests in vivo and in vitro.
The in-vitro test includes the treatment of the coating
material in the form of foils having a thickness of 20 ~m
with the protease pepsln at 37~ C over a period of 7 days.
Depending on the radiation intensity employed for the
crosslinking, different changes in mass result after the
enzymatic hydrolysis, relative to the initial mass.
Intensity of Irradiation
20 kGy 40 kGy 60 kGy
Relative change 15 % 32 % 45 %
in mass after 7
days
In a modification of the burial trial from DIN 53739,
according to process D, use was made of a soil-burial test
under anaerobic conditions for the in-vivo investigation.
This test enables qualitative and semi-quantitative
determination of the biological degradability by soil
bacteria and soil moulds of test samples consisting of
biological or synthetic polymers.
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IncubationRel. change in mass of foils Gelatin
periodirradiated with different type
days intensities
20 kGy 40 kGy 60 kGy
3 100 % 100 % 100 % B
3 100 % 100 % 60 % A
6 100 %
