Note: Descriptions are shown in the official language in which they were submitted.
CA 02257963 1998-12-11
A METHOD FOR THE PREPARATION OF A LAMINATE AND A
LAMINATE OBTAINABLE THEREBY
The present invention relates to a method for the
preparation of a quick-curing laminate and a laminate
obtainable thereby.
Plastic film is a frequently used material for the
packaging of numerous articles and products. Within
many fields of application, the requirements for such
plastic films are of a character that cannot be met by
one film alone. Consequently, various laminates of
films have been developed with properties that in many
respects meet the requirements better.
Usually, adhesives are used to attach separate
films to each other, thus generating a laminate.
Various requirements are made for such adhesives, e.g.
adherence, heat resistance, transparency, and it has
been proved that, inter alia, polyurethane-containing
adhesives may be used for the adhesion of the separate
films of a laminate, thus obtaining the requested pro-
perties of the laminate.
As far as polyurethane adhesives are concerned, it
is problematic, however, that the curing time is long
and that a laminate has to age, possibly at a compara-
tively high temperature and in a properly ventilated
room, to ensure the adhesive curing.
In order to reduce the curing time of the ad-
hesives employed, various methods have been used,
including the addition of a catalyst for the curing
reaction.
When using a catalyst, the simplest way to accel-
erate the curing of a polyurethane adhesive is to add
the catalyst directly into the polyurethane adhesive,
immediately before the adhesive is applied to a film
that is to be attached to another film. On an indus-
trial scale, this is not efficient, however, since to
AMENDED SHEET
CA 02257963 1998-12-11
2
some extent the adhesive composition will have cured
before use. The curing will cause an increased viscos-
ity and a subsequently more difficult application to
the film, whereby the application quantity cannot be
controlled. A limited space of time is available for
the administration of the adhesive composition, the so-
called pot-life, and, in consequence, production
disturbances may cause glue vessels and application
devices having to be cleared of cured adhesives.
To overcome said problem of the low pot-life, in
EP-Al-0152102 it is suggested to use a urethane ad-
hesive containing micro capsules with a catalyst for
the curing. Such micro capsules will be destroyed when
the laminate film is attached by means of pressure
rollers, whereby the encapsulated catalyst will be
released.
The disadvantage of this method is that a
homogenous distribution of the catalyst in the glue
layer cannot be obtained, since the catalyst concentra-
tion will peak in the immediate vicinity of the
destroyed capsule. Furthermore, such capsules will
remain in the adhesive as a suspension and therefore
precipitate when stored.
Another suggestion to bring a polyurethane adhes-
ive into contact with the catalyst is disclosed in EP-
Al-0586843. In this, a method for the preparation of a
laminate film is disclosed, wherein at least two films
are attached to each other by means of a polyurethane
adhesive, the adhesive layer or the adhesive-free film
being humidified with an aqueous solution bearing at
least one catalyst, which accelerates the curing
reaction of polyurethane adhesives. The catalyst
solution humidification is problematic, however, since
it will be difficult to obtain a homogenous distribu-
tion of the solution on a film, e.g. a polyethylene or
AMENDED SHEET
CA 02257963 1998-12-11
3
polypropylene film, even when using an surfactant in
the solution. Inter alia, because a suitable equipment
for a homogenous application of the catalyst solution
all over the film is not available, so that in certain
sections of the prepared laminate water will accumu-
late, which leads to an isocyanate conversion to the
corresponding amine compound, thus involving the risk
of a subsequent amine compound migration. Therefore,
whenever preparing a laminate according to the method
disclosed in EP-Al-0586843, it is necessary to age the
said laminate before use, in particular when foreseen
for the packaging of food.
In international patent application No. PCT/DK
96/00319, publication No. WO-A-97/03821 (which was not
available to the public on the priority date of the
present application), the present applicant suggested
to bring the catalyst into contact with the adhesive by
incorporating the catalyst in one of the films to be
attached to each other by means of the adhesive.
Although this reduces the curing time considerably and
result in a low migration of amine compounds so far as
laminates with no ink between the films are concerned,
the suggestion is not recommendable when the catalyst-
containing film has to be printed with ink, because the
layer of ink will prevent a diffusion of catalyst from
the film to the adhesive.
The object of the present invention is to provide
a method for the preparation of a laminate having ink
on one or both films to be attached to each other,
whereby the laminate is ready for further treatment
comparatively soon after its preparation, without any
long-lasting ageing period.
According to the invention, this is achieved by
a) providing an ink comprising a catalyst suitable for
accelerating the curing of an adhesive for films,
AMENDED SHEET
CA 02257963 1998-12-11
4
b) applying to a first film one or more completely or
partially covering layers of the said ink,
c) laminating a second film to the first film inked
surface, using an adhesive, the curing of which is
accelerated by the catalyst.
The present invention relates to the laminate
obtainable by this method as well. Furthermore, the
invention relates to the film being coated with one or
more entirely or partially covering layers of ink
obtainable after step b) of the method.
Soon after the preparation of the laminate accord-
ing to the invention, the measurable amine migration is
comparatively low, and, in addition, a fairly satisfac-
tory mutual adherence of the films is obtained shortly
after the preparation of the laminate. Due to the
quick-curing of the adhesive used as well as the low
amine migration, the laminate prepared needs no or only
moderate ageing before further treatment. Especially
within the food industry a low amine migration is in
great demand, and, when in use, the laminate should
show no amine migration at all. The fact that the
laminate prepared may be exposed to further treatment
shortly after its preparation is advantageous from a
producer's point of view, inter alia, because this will
reduce the need for storage room, and, sales of the
laminate prepared can start sooner after production.
Moreover, a laminate according to the invention
has a reduced tendency to telescoping, i.e. shear of
the films relative to each other.
The term "ink" used in the present description and
claims refers to both pigmented and un-pigmented inks
and varnishes as well as clear and coloured varnishes.
For the application of the inks methods known from the
prior art, e.g. gravure, flexography or offset print-
ing, may be used.
l~ENDEU btic;; I'
CA 02257963 1998-12-11
The ink employed may be of any suitable type, e.g.
nitrocellulose, PVB or acryl or combinations thereof.
In addition, the inks may be offset inks, e.g. oil-
based or water-based. The ink may have any colour or be
5 uncoloured.
The inks may be based on any solvent, in particu-
lar, they may be dilutable in ethanol, isopropanol,
ethylacetate, methylethylketon, acetone, water or
combinations thereof. Furthermore, solvent-free inks
may be used.
The inks used according to the invention may be
single-component, dual-component and/or even three-
component inks. Single-component inks are immediately
employable for printing, possibly after having been
diluted by a suitable solvent. Dual-component inks are
foreseen to be mixed immediately before use, whereby
the first component comprises a standard ink and the
second component the catalyst suitable for accelerating
the curing of an adhesive for films.
Any adhesive curing in the presence of a catalyst
may be used. Preferred adhesives are of the poly-
urethane type and alcohol-based or water-based imine-
epoxy systems. Polyurethane adhesives may be single-
component systems or dual-component systems. A poly-
urethane adhesive comprises at least one organic poly-
isocyanate and at least one polyol, the polyisocyanate
comprising two or more isocyanate groups, and the
polyol two or more hydroxy groups. The polyol may be a
polyester polyol, a polyether polyol or a polyether-
esterpolyol. The polyisocyanate may be a pre-polyTner.
Typical examples of diisocyanates for polyurethane
adhesives are 1,6-hexanediisocyanate, 1,10-
decanediisocyanate, 1,3-cylopentanediisocyanate, 1,4-
cyclohexanediisocyanate, 1-isocyanat-3,3,5-trimethyl-3
or 5-isocyanatomethancyclohexane, 4,4'-, 2,4'- and
p,N1ENDED SHEE~
CA 02257963 1998-12-11
6
2,2'-di-isocyanate diphenylmethane, 1,5-naphta-
lenediisocyanate, 4,4'-diisocyanate-dicyclohexyl-
methane, 1,4-di-isocyanate-benzene and/or 2,4- or 2,6-
diisocyanate-tolu-ene. Pre-polymers of polyisocyanates
may be achieved by reacting the above diisocyanates
with a polyvalent alcohol.
Typical examples of polyols for polyurethane ad-
hesives are alkanediols with linear or branched carbon
chains, e.g. ethylene glycol, 1,2-dihydroxypropane,
1,3-dihydroxypropane, 1,4-dihydroxybutane, 1,6-
dihydroxyhexane and neopentylglycol. In case of the
polyol being a polyetherpolyol, this is usually
obtained by adding ethylene oxid to a compound compris-
ing two or more active hydrogen atoms in a molar ratio
of 30 to 90%. Suitable examples of compounds comprising
two or more active hydrogen atoms are ethylene glycol,
diethylene glycol, propylene glycol, dipropylene
glycol, glycerin, trimethylol-propane, pentaerythritol,
sorbitol, saccharose or the like. Instead of
ethylenoxid e.g. propylenoxid and butylenoxid may be
used. In general, polyetherpolyol has a molecular mass
in the range from 1,000 to 20,000, especially between
1,000 and 5,000.
Polyurethane adhesives used for single-component
systems comprise e.g. pre-polymers of polyisocyanates
and polyols, the said adhesive curing when reacted with
water. Examples of this may be found in German patent
No. 2549227 and European patent application No. 0586843
Al.
Dual-component systems either consist of pre-
polymers with free isocyanate groups curing by means of
a hydroxy group bearing cross-linking agent, or of pre-
polymers with free hydroxy groups, curing by means of
isocyanate group bearing cross-linking agents. Examples
of the first type of dual-component systems are dis-
AMENDED SHEE'
CA 02257963 1998-12-11
7
closed in German laid-open publication No. 4021113 and
in European patent No. 150444. Examples of the latter
type of dual-component systems are listed in European
patent No. 176726. No matter the type of polyurethane
adhesive, these may comprise a solvent, be free of
solvents or water-based. For the method according to
the present invention, it is preferred to use a dual-
component system, in which the various components are
mixed immediately before their application to the first
f.ilm.
The catalysts accelerating the curing of the
polyurethane adhesives are known from the prior art.
Various substance groups are proved active catalysts,
inter alia Lewis bases and Lewis acids. The most
important Lewis bases are tertiary amines, e.g. dia-
zabicyclooctane, triethylamine, dimethylbenzylamine,
bisdimethylaminoethylether, tetramethylguanidine and
bisdimethylaminomethylphenol. The most important
catalytically effective Lewis acids are metallo-organic
compounds, especially tin organic compounds, like tin-
diethylhexanoate, dibutyltindilaurate, dibutyltinbis-
dodecylmercaptide and lead-phenylethyldithiocar-
baminate. Presumerably, the metallo-organic compounds
are activating the isocyanate groups thus making these
electrophile, whereas the bases first and foremost
increase the nucleophile properties of the OH group.
Other known catalysts are alkaline salts of
organic acids and phenols, like phenol-Mannich-bases,
phosphine and phospholinoxide.
Also e-caprolactam have catalytic properties, and
in the present invention the use of E-caprolactam,
which is available as a powder, flakes or in a fluid
form, is preferred as a catalyst.
AMIEKIDED
~~i~~
CA 02257963 1998-12-11
8
The catalyst itself may be an appropriate mixture
of several different catalysts so as to obtain an
optimal curing in relation to various types of adhesive
Usually, the catalyst content of ink is up to 20%,
however, a catalyst content of approximately 5% of the
solid content of the ink proved to be particularly
suitable.
The catalyst, per se, may be added to the ink
immediately or, as a pre-solution, optionally with use
of a surfactant to obtain a homogenous distribution in
the ink. The catalyst preferred, E-caprolactam, is
preferentially added to the ink as a pre-solution.
Appropriately, the pre-solution comprises equal parts
of E-caprolactam and isopropanol and/or water.
The first film may partially or entirely be made
of a plastic material, preferably chosen from poly-
esters, in particular orientated polyesters; polyole-
fines, e.g. polyethylenes and orientated polypropylenes
or cast polypropylenes; polyamides, in particular cast
polyamides or orientated polyamides; and cellophane.
The second film may be of the same type as the
first film. Preferentially, however, the second film
consists entirely or partially of aluminium-containing
materials, metallized plastics, paper, metallized
paper, or plastic materials, in particular poly-
ethylene and polypropylene.
Both the first and the second film may incorporate
a catalyst for an adhesive. Using a film with an
incorporated catalyst is particularly recommendable in
case of only partial application of ink to the film. In
this way, a catalyzed curing also takes place outside
the areas of the film covered with catalyst-containing
ink.
In cases when a film without an incorporated
catalyst is used along with partial application of a
AMENDED SHEET
CA 02257963 1998-12-11
9
catalyst-containing coloured ink it is recommendable to
apply a completely covering layer of clear varnish or
unpigmented catalyst-containing ink to the first film.
In this way, a catalyzed curing is ensured outside the
areas of the film originally covered with the coloured
ink as well.
Multi-colour printing is well-known in the prior
art, i.e. applying several layers of different inks
consecutively or on top of each other. All applied inks
may contain a catalyst, so that catalyzed curing is
taking place within all areas of the laminate. If at
last a completely covering ink is applied, a so-called
background colour, only that ink needs to contain a
catalyst to ensure a catalyzed curing within all areas
of the laminate.
The first and/or the second film may be a lami-
nate, per se. In particular when using a metallo-film
in the laminate, it may be advantageous to coat the
metallo-film with a plastic film prior to applying the
ink.
When the catalyst-containing ink has been applied
to the first film this is laminated to the second film.
The adhesive may either be applied to the first or the
second film, prior to their being attached together or
be added simultaneously. Preferably, the adhesive is
applied to the first ink covered film.
The laminates prepared may be used for the wrap-
ping and packaging of food, i.e. they get into immedi-
ate contact with food. Therefore, it must be ensured
that no noxious substances are transferred to the food,
or at least the extent of the transfer must be non-
toxic. E-caprolactam is a comparatively non-toxic
compound, which is released for the market by the
authorizies for use in materials getting into contact
with food. Since the catalyst is placed between the two
AMENDED SHEET
CA 02257963 1998-12-11
films of the laminate, it will not get into immediate
contact with the food.
Without any intention of limiting the invention to
any specific theoretical explanation, it is assumed,
5 that the catalyst in the ink diffuses and penetrates
the adhesive layer thus accelerating the curing of the
adhesive.
In the following, the present invention will be
illustrated by means of examples, however, these
10 examples are not to be considered as a limitation of
the scope of the protection.
Example 1
Two inks, one with and one without a catalyst,
were applied to separate areas of a first film. After
a few days of storage, an adhesive was applied to the
first film, and a second film was laminated thereto.
After the lamination, the adherence and the amine
migration was measured at certain intervals.
The first film was a corona-treated 30 m
polypropylene film (Mobil MB400), and the second film
was a 50 micron polyethylene film (Borealis 0601
standard) . The adhesive was a MorFree 403a/C79 mixed in
the ratio 100:65 and applied in a density of 1.5 g/m2.
The ink was a white "Resino Reversal 142" type
from Resino A/S having a solid content of 60% (w/w).
The catalyst-containing ink labelled "A1" was prepared
by adding a solution of 300 g E-caprolactam flakes
dissolved in 300 ml of isopropanol into 10 kg of the
above ink. During 14 days of storage, the viscosity of
the catalyst-containing ink remained essentially
unchanged. The ink without any catalyst was labelled
B1. Both inks were applied in a layer of 1.5 m.
The adherence was measured according to DIN 53357
(unit: N per 15 mm), whereas the amine migration was
CA 02257963 1998-12-11
11
measured as the migration of primary aromatic amines
(e.g. 2,4-toluenediamine and 4,4'-diamino-diphenyl-
methan), by a process wherein the amine is coupled to
N-(l-naphthyl)-ethylenediamine-dihydrochloride for the
formation of a coloured addition product. The formation
of the addition product was measured as the absorbance
at a wave length of 550 nm. The concentration was
measured in g/dm2.
The results are indicated in Table Ia and Ib
below:
Table Ia
ADHERENCE 2 hours 4 hours 6 hours 1 day 3 days 8 days
Al ink 0.02 0.15 1.10 4.00 4.50 4.60
B1 ink 0.01 0.04 0.09 1.80 4.00 4.00
Table Ib
AMINE 1 day 3 days 5 days 9 days
MIGRATION
Al ink 32 10 1.0 0.3
21 ink 63 26 9.5 4.5
The tables show that the use of a catalyst-con-
taing ink accelerates the curing of the laminates and
makes the amine migration decrease sooner. Furthermore,
considerably lower amine migration values are obtained
when using a catalyst-containing ink compared to the
results obtainable when using an ink without a cata-
lyst, at least within the observed time period.
AMENDED SHEET
CA 02257963 1998-12-11
12
Example 2
The same procedure was adopted as in Example 1,
only an unpigmented ink (trademark: Resino Reversal)
having a solid content of 30% (w/w) was used. The
catalyst-containing ink was labelled A2 and prepared by
adding a solution of 62.5 g E-caprolactam flakes
dissolved in 62.5 g isopropanol to 10 kg of the ink.
The ink without any catalyst was labelled B2. The
adhesive is as stated in Example 1.
Measurement of the adherence and the amine migra-
tion followed as described in Example 1. The results
are indicated in Table IIa and IIb below:
Table IIa
ADHERENCE 2 hours 4 hours 6 hours 1 day 3 days 8 days
Al ink 0.05 1.00 2.10 3.40 4.10 4.50
El ink 0.01 0.06 0.11 2.20 3.30 3.90
Table IIb
AMINE 1 day 3 days 5 days 9 days
MIGRATION
Al ink 24 6 0.9 0.3
131 ink 60 26 10.5 3.6
The tables show that the use of a catalyst-con-
taining ink accelerates the curing of the laminates and
makes the amine migration decrease sooner. Furthermore,
considerably lower amine migration values are obtained
when using a catalyst-containing ink compared with the
results obtained when using an ink without a catalyst,
at least within the observed time period.
AMENDED SHEET
CA 02257963 1998-12-11
13
Example 3
In this example, the adherence effect from various
concentrations of E-caprolactam in the ink was studied
at room temperature and at an elevated temperature, at
various time intervals after the lamination.
The first film was an oriented 30 m polypropylene
film from UCB, whereas the second was a 50 m
polyethylene film (trademark Sengewald FC-203). The
adhesive was a Novacote SF 782 A and CA 375 mixed in
the ratio 100:36. The adhesive was applied in a layer
of 1.7-1.9 g/m2 to the first ink-treated film.
The ink was white (Resino Reversal 142) and
supplemented with various concentrations of E-caprolac-
tam.
Two samples from each run were stored at room
temperature and for 6 hours at 35 C, followed by room
temperature, respectively, whereupon the adherence was
measured according to DIN 53357. The results are listed
in Tables IIIa and IIIb.
Table IIIa
Storing at Room Temperature
Adherence
Concentration of after after after after after
e-caprolactam 1 2 4 6 24
~(w/w) hour hours hours hours hours
0.0 <0.3 0.5 1.6 2.3 4.7 T
1.25 0.6 1.3 2.5 4.7 T 3.5 T
2.5 1.7 2.7 3.1 T 3.5 T 4.7 T
4.8 3 0 5.0 3.5 4.7 T 4.8 T T 3.5 T
P + T
T = Tear
P = Peel
AMENDED SriEtq
CA 02257963 1998-12-11
14
Table IIIb
Storing for 6 hours at 35 C,
Followed by Storing at Room Temperature
Adherence
Ccncentration of after after after after after
e-caprclactam 1 2 4 6 24
%(w/w) hour ccurs hours hours hours
0.0 0.6 2.0 4,3 T 5,0 T 4.5 T
1.25 2.0 4,6 T 4,2 T 3.2 T 4.6 T
2.5 3.8 T 4.7 T 4.9 T 4.9 T 4.7 T
5.0 3.7 T 4.1 T 4.8 T 4.4 T 4.8 T
T = Tear
From the tables IIIa and IIIb it may be deduced
that an increased concentration of E-caprolactam
accelerates the curing of the laminates produced.
Furthermore, also storing at increased temperatures
results in curing acceleration. One hour after produc-
tion, the adherence of the laminates containing 2.5 and
5.0% (w/w) E-caprolactam, respectively, is adequate for
further treatment of the laminates. By way of compari-
son, laminates with no e-caprolactam must be stored at
least 4 hours before use.
Example 4
A first polyester-type film and a second film,
which is a laminate between an aluminium film and a
polyethylene film, was provided.
The first film was coated with a transparent ink
("Resino Reversal" without pigment) in a 1.5 m layer,
whereupon an adhesive ("Novacote SF 782A" and "CA 375",
mixed in the ratio of 100:40) was applied in
i:.. :r.flwL~ ~ ~ JH7
CA 02257963 1998-12-11
an amount of 1.7-1.9 g/m2. With the aluminium side
against the adhesive, the second film was laminated
thereto.
5 Using increasing amounts of E-caprolactam, the
adherence was measured after storing at room tempera-
ture (Table IVa) as well as after storing 6 hours at
35 C followed by room temperature (Table IVb) The
results are shown in the tables below.
Table IVa
Storing at Room Temperature
Adherence (N/15 mm)
Concentration of after after after after after
e-caprolactam 1 2 4 6 24
% w/w hour hours hours hours hours
0.0 0.2 0.5 2.0 1.9 3.4
P+T
1.25 0.5 1.0 2.3 2.9 4.9
P+T
2.5 0.6 2.1 2.8 3.7 3.1
P+T P+T
5.0 2.0 3.3 4.0 3.0 3.6 T
P+T P+T
-ij
T = Tear
P = Peel
~_.
i=: ~~~..~ ~~. _~.
CA 02257963 1998-12-11
16
Table IVb
Storing for 6 hours at 35 C,
Followed by Storing at Room Temperature
Adherence (N/15 mm)
Concentration of after after after after after
c-caprolactam 1 2 4 6 24
%(w/w) hour hours hours hours hours
0.0 0.5 2.1 2.8 3.2 3.2
P+T P+T
1.25 0.7 2,5 5,3 3.4 T 4.9 T
P+T
2.5 1.8 2.7 3.3 3.0 3.0
P+T P+T P+T
5.0 2.8 4.0 3.4 3.5 3.6 T
P+T P+T P+T
P = Peel
R = Tear
From the tables IVa and IVb it may be deduced that
an increased concentration of E-caprolactam accelerates
the curing of the laminates produced. Furthermore, also
storing at increased temperatures results in curing
acceleration.
The laminate produced has a metallic appearance.
It may be used for packaging aromatic products, e.g.
coffee.
