Note: Descriptions are shown in the official language in which they were submitted.
CA 02273493 1999-06-02
WO 98/28378 - 1 - PCT/EP97/07106
Composite paper material with a pressure-sensitive
adhesive coating finished to be resistant to repulping
The invention relates to a composite paper
material, especially labels, with a pressure-sensitive
adhesive coating finished to be resistant to repulping,
and to a process for the production thereof.
A high percentage of waste paper is collected and
recycled. This waste paper contains a number of non-
cellulosic "impurities", such as, for example, adhesive
tapes, film materials, composite materials and adhesive
films. For recycling, the collected waste paper is
disintegrated in a pulper (defibrator) in water, at a
neutral to alkaline pH, by mechanical action as far as
possible down to the individual cellulose fibres. This is
followed by cleaning in a multi-stage process with the
object of obtaining a pulp of cellulose fibres which is
as pure as possible and which can be used on the paper
machine without causing faults. The cleaning steps
virtually always comprise a screening, usually by means
of screens with slotted holes, for example of about 0.15
mm hole width. Occasionally, an additional flotation is
carried out subsequently, especially if printing inks are
to be removed (de-inking) in order to reach better paper
qualities.
In the processing of fibre pulps, obtained from
waste paper, on high-speed paper machines, faults occur
again and again due to the formation of so-called
"stickies", for example owing to residues of pressure-
sensitive adhesive layers from labels which have not been
separated off during the processing step. "Stickies" are
to be understood here as lumps or clusters of
preferentially polymers which are themselves tacky and
which become noticeable in the newly produced paper by
"fatty" spots and by individual sheets sticking together.
Moreover, stickies deposit, for example, on rolls and
screens of the paper machines and thereby cause faults in
the operating sequence, for example wet tearing. Both
problems cause high costs. The increasing introduction of
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closed water circulation systems in waste paper processing
and the increasing quantity of adhesive fractions in
waste paper, especially of pressure-sensitive adhesives
due to the wider use of pressure-sensitive adhesive paper
labels, have in recent years caused the sticky problem to
become substantially more serious.
Methods of separating off adhesive residues from
the fibre pulp in the recycling of waste paper in order
to solve this problem are therefore being sought. This
turns out to be difficult especially in the case of films
of pressure-sensitive adhesives, since these disintegrate
into small pieces during defibration. Due to the size of
the pieces and the softness or flexibility of these self
adhesive masses, these can be removed by screening only
to a very restricted extent.
In WO-A 93/08239, it is proposed to use
recyclable labels with a repulpable layer of pressure-
sensitive adhesive, the layer of pressure-sensitive
adhesive consisting of an acrylate polymer with a content
of 10 to 20% of comonomer units containing carboxyl
groups. WO-A 94/17998 follows a similar approach, with
the difference that 10 to 20% of hydroxyethyl
methacrylate units are copolymerized. In WO-A 96/08539,
repulpable labels are described which are finished with
two layers of different pressure-sensitive adhesives. The
repulping resistance of the pressure-sensitive adhesive
component is obtained by applying to the paper carrier a
water-dispersible layer of pressure-sensitive adhesive,
which is then laminated to a layer of pressure-sensitive
adhesive which is not redispersible in water.
It is a disadvantage that redispersed particles
of the dispersible layer of pressure-sensitive adhesive
concentrate during repulping, involving the risk of the
formation of stickies, and must be removed at a high
cost, for example by an additional flotation step. If no
additional flotation step is carried out, the effluent
must be cleaned in treatment plants or it would pollute
the receiving water.
In EP-A 438,781, labels are claimed which are
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composed of a paper layer, a polymer film resistant to
repulping and a pressure-sensitive adhesive resistant to
repulping. In this case, the plastic film is extruded
onto the paper or applied in the liquid state as a melt.
If desired, the layer of pressure-sensitive adhesive is
anchored on the film by means of an additional primer
layer. The disadvantage is that, when the polymer film is
applied in the liquid state, the paper fibres are
enveloped and bonded by liquid polymer. The fibres are
therefore no longer set free on repulping and are lost
for recycling. A further disadvantage is that a pulping-
resistant pressure-sensitive adhesive is applied, even
though pressure-sensitive adhesives are in general not
pulping-resistant.
' It was therefore the object to provide labels
based on a paper carrier and conventional pressure-
sensitive adhesives which are finished in such a way that
the layer of pressure-sensitive adhesive does not com-
pletely disintegrate on pulping, but is obtained in the
form of screenable particles, and that the paper fibre is
completely set free on repulping.
The object has been achieved by a moisture-
resistant, non-repulpable but hydrophilic interlayer
which is applied in the form of an aqueous dispersion.
The invention relates to a composite paper
material with a pressure-sensitive adhesive coating
finished to be resistant to repulping, comprising a paper
carrier and a layer of pressure-sensitive adhesive,
characterized in that an interlayer comprising a disper-
sion polymer film containing a protective colloid and/or
an emulsifier and having a glass transition temperature
Tg from -20°C to +40°C has been applied between the paper
carrier and the layer of pressure-sensitive adhesive.
The invention furthermore relates to a process
for producing a composite paper material with a pressure
sensitive adhesive coating finished to be resistant to
repulping, characterized in that
a) in a first process step for producing the inter-
layer, an aqueous dispersion of a homo- or copolymer,
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stabilized by a protective colloid and/or an emulsifier
and having a glass transition temperature Tg from -20C
to +40C, from the group consisting of homo- or
copolymers of vinyl esters of alkylcarboxylic acids
having 1 to 15 C atoms, homo- or copolymers of esters
of
(meth)acrylic acid with alcohols having 1 to 12 C atoms,
and styrene/ butadiene copolymers, is applied and dried,
and
b) in a second process step, a pressure-sensitive
adhesive composition is applied to the polymer layer from
the first process step and, if appropriate, is dried.
The paper carriers employed can be the unsized or
sized paper grades that are particularly common in the
production of labels.
Suitable polymers for the moisture-resistant
interlayer with the hydrophilic surface are homo- or
copolymers, stabilized. by a protective colloid and/or
emulsifier, from the group consisting of homo- or
copolymers of vinyl esters of alkylcarboxylic acids
having 1 to 15 C atoms, homo- or copolymers of esters
of
acrylic acid or methacrylic acid with alcohols having
1
to 12 C atoms, if appropriate in combination with
styrene, and styrene/butadiene copolymers.
Moisture-resistant here is taken to mean that the
interlayer survives the repulping step without disinte-
grating completely into non-screenable particles. The
hydrophilic surface is provided by the content of protec-
tive colloid or emulsifier, if necessary by auxiliary
monomers, and it facilitates the detachment of the
interlayer from the paper fibre.
Preferred vinyl esters are vinyl acetate, vinyl
propionate, vinyl 2-ethylhexanoate, vinyl laurate,
1-methylvinyl acetate, vinyl pivalate and vinyl esters
of
alpha-branched monocarboxylic acids having 5 to 10
C atoms, for example WSR, VeoVa9R or VeoValOR. Vinyl
acetate is particular preferred.
Preferred methacrylic esters or acrylic acid
esters are methylacrylate, methylmethacrylate, ethyl
acrylate, ethyl methacrylate, propyl acrylate, propyl
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methacrylate, n-butyl acrylate, n-butyl methacrylate,
iso-butyl acrylate, iso-butyl methacrylate, t-butyl
acrylate, t-butyl methacrylate, 2-ethylhexyl acrylate and
2-ethylhexyl methacrylate. Methyl acrylate, methyl
methacrylate, n-butyl acrylate and 2-ethylhexyl acrylate
are particularly preferred.
In a preferred embodiment, water-soluble,
ethylenically unsaturated monomers can, if appropriate,
also have been copolymerized in a proportion of up to 5%
by weight, relative to the total weight of polymer.
Examples of these are acrylic acid, methacrylic acid,
acrylamide, methacrylamide, hydroxyethyl acrylate,
hydroxyethyl methacrylate, hydroxypropyl acrylate,
hydroxypropyl methacrylate and acrylamidopropanesulphonic
acid.
Examples of suitable vinyl ester polymers which,
if appropriate, also contain water-soluble or cross-
linkable, ethylenically unsaturated monomers, are:
vinyl acetate homopolymer, vinyl acetate/ethylene
copolymers, vinyl acetate/ethylene/vinyl chloride
copolymers, vinyl acetate copolymers with the vinyl ester
of an alpha-branched carboxylic acid having 5 to 10
C atoms and vinyl acetate/n-butyl acrylate copolymers.
Examples of suitable (meth)acrylic acid polymers
are:
copolymers of methyl methacrylate with n-butyl acrylate
and/or 2-ethylhexyl acrylate and also copolymers of
n-butyl acrylate or 2-ethylhexyl acrylate with styrene.
The selection of monomer or the selection of the
proportions by weight of the comonomers is made here in
such a way that the homo- and co-polymers have a glass
transition temperature Tg from -20°C to +40°c, preferably
-15°C to +25°C, especially -5°C to +10°C. If a
particularly stiff composite paper material is desired,
the use of polymers having a high Tg is preferred. The
glass transition temperature Tg of the polymers can be
determined in the known manner by means of differential
scanning calorimetry (DSC). The Tg can also be approxi-
mately precalculated by means of the Fox equation.
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According to Fox T. G., Bull. Am. Physics Soc. 1, 3, page
123 (1956), the following applies: 1/Tg =_ xl/Tgi + xz/Tgz
+ ... + xa/Tgn, xn being the mass fraction (% by
weight/100) of the monomer n, and Tgn being the glass
transition temperature in degrees Kelvin of the homo-
polymer from the monomer n. Tg values for homopolymers
are listed in Polymer Handbook, 2nd Edition, J. Wiley &
Sons, New York (1975).
To improve the repulping resistance, the
dispersion polymers of the interlayer can, if desired,
also contain one or more auxiliary monomer units for
crosslinking, preferably 0.1 to 5% by weight thereof, in
each case relative to the total weight of the polymer.
Examples of these are N-methylolacrylamide, N-methylol
methacrylamide, N-(alkoxymethyl)acrylamides or N-(alkoxy-
methyl)methacrylamides having a C1- to C6-alkyl radical,
such as N-(isobutoxymethyl)acrylamide (IBMA), N-(iso-
butoxymethyl)methacrylamide (IH1~IA), N-(n-butoxymethyl)-
acrylamide (NBMA) and N-(n-butoxymethyl)methacrylamide
(NBI~iA). In the case of these comonomers, the cross-
linking can, if appropriate, also be promoted by the
addition of acidic hardeners, for example metal salts of
Al(III) such as A1 nitrate, A1 chloride, Cr(III) salts
such as chromiumnitrate and Zr(IV) salts such as
zirconiumoxychloride. The quantity of metal salt amounts
in general to 0.5 to 5.0% by weight, relative to the
total weight of the polymer.
Further examples of comonomers having a cross
linking action are ethylenically polyunsaturated
comonomers such as ethylene glycol diacrylate,
1,3-butylene glycol diacrylate, 1,4-butylene glycol
diacrylate, propylene glycol diacrylate, divinyl adipate,
divinylbenzene, vinyl methacrylate, vinyl acrylate, allyl
methacrylate, allyl acrylate, diallyl maleate, diallyl
phthalate, diallyl fumarate, methylenebisacrylamide,
cyclopentadienyl acrylate or triallyl cyanurate. The
repulping resistance can also be improved by external
crosslinking by means of the addition of di- or poly-
functional crosslinking agents, for example di- or poly-
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functional isocyanates such as hexamethylene diisocyanate
or 2,4- and 2,6-toluylene diisocyanate. Comonomers
containing carbonyl groups, such as diacetoneacrylamide
or crotonaldehyde, which are converted for crosslinking
or anchoring with the addition of crosslinking agents
containing hydrazide groups, such as adipic acid
dihydrazide, or of crosslinking agents containing amino-
oxy groups, such as 1,4-diaminooxybutane or 2-amino-
oxypropionic acid hydrazide, are also suitable. The
content of the said comonomers containing carbonyl groups
or of the crosslinking agents amounts in general to 0.1
to 3.0% by weight, relative to the polymer.
The hydrophilic character of the interlayer is
effected above all by the content of emulsifier and/or
protective colloid. The emulsifiers used can be any
commercially available ionic and nonionic emulsifiers. In
particular, these can be: block copolymers of ethylene
oxide and propylene oxide, ethoxylated alkylphenols,
ethoxylated fatty alcohols and also alkali metal salts
and ammonium salts of long-chain alkyl sulphates (C8- to
Clz-alkyl radical), of sulphuric acid half-esters of
ethoxylated alkanols and ethoxylated alkylphenols, of
alkylsulphonic acids and of alkylarylsulphonic acids.
Examples of suitable protective colloids are
celluloses such as hydroxyethylcellulose, hydroxypropyl
cellulose and carboxymethylcellulose, starches and
dextrins, cyclodextrins, fully or partially saponified
polyvinyl alcohols, polyethylene glycol, polyvinyl
pyrrolidone, and homo- and copolymers of acrylamido
propanesulphonic acid.
The emulsifier content is preferably 0.1 to 5% by
weight, relative to polymer. The protective colloid
content is preferably 0.1 to 15% by weight, relative to
polymer. Mixtures of emulsifier and protective colloid
can also be present. Preferably, the interlayer contains
partially saponified polyvinyl alcohols having a degree
of hydrolysis from 60 to 95 mol %, preferably as a
mixture with emulsifier(s).
Preferably, the interlayer comprises vinyl
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acetate/ethylene copolymers, if appropriate with a
content of N-methylolacrylamide and/or the said water-
soluble ethylenically unsaturated comonomers, and
polyvinyl alcohol and/or emulsifier. An interlayer is
also preferred which contains vinyl acetate homopolymers
or copolymers of vinyl acetate with VeoValO and also
polyvinyl alcohol and/or emulsifier and which, if
appropriate, has been externally plasticized.
The preparation of the dispersion polymers of the
interlayer is preferably carried out by the emulsion
polymerization process in aqueous phase and is initiated
by the water-soluble free-radical formers normally used
for the emulsion polymerization. The dispersants used are
the emulsifiers and/or protective colloids mentioned
above which are normally used in emulsion polymerization.
Preferably, the polymerization is carried out at a
temperature between 30 and 100°C and at a pressure of
below 100 bar. The polymerization is carried out at a pH
of preferably 2 to 7.
The interlayer can have any desired thickness,
and this is preferably 4 to 40 Vim, particular preferably
4 to 20 ~Cm.
For the layer of pressure-sensitive adhesive, all
conventional pressure-sensitive adhesives or pressure
sensitive adhesive compositions based on polymer
dispersions, hot-melt adhesives and radiation-
crosslinkable systems are suitable. Examples of these are
acrylic acid ester copolymers, copolymers of acrylic acid
esters with vinyl esters and, if appropriate, ethylene,
3.0 copolymers of acrylic acid esters or vinyl esters with
malefic and fumaric acid esters, or thermoplastic rubbers
such as styrene/butadiene block copolymers and
styrene/isoprene block copolymers. The acrylic acid ester
copolymers and the copolymers of acrylic acid esters with
vinyl ester and, if appropriate, ethylene are preferred.
Suitable acrylic acid esters and vinyl esters are
the abovementioned preferred vinyl esters such as vinyl
acetate, vinyl propionate, vinyl 2-ethylhexanoate, vinyl
laurate, 1-methylvinyl acetate, vinyl pivalate and vinyl
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esters of alpha-branched monocarboxylic acids having 5 to
C atoms, for example W5R, VeoVa9R or VeoValOR, and the
already mentioned acrylic acid esters such as methyl
acrylate, ethyl acrylate, propyl acrylate, n-butyl
5 acrylate, iso-butyl acrylate, t-butyl acrylate, 2-ethyl
hexyl acrylate and n-octyl acrylate. For the layer of
pressure-sensitive adhesive, the copolymer composition is
selected such that the glass transition temperature Tg of
the copolymers is below -20°C, preferably from -60°C to
10 -30°C.
The conventional pressure-sensitive adhesive
dispersions usually contain a proportion of water
soluble, ethylenically unsaturated auxiliary monomers of
the abovementioned type in quantities of up to 10% by
weight, relative to polymer.
To improve the tack, pressure-sensitive adhesive
compositions containing tackifier can also be used.
Examples of tackifiers are the colophony resins which are
also known as balsamic resins or tall resins, as well as
their derivatives such as dimerized, disproportionated
and hydrogenated colophony. Further examples are the
glycol esters, glycerol esters and pentaerythritol esters
of the balsamic resins such as colophony diethylene
glycol ester, hydrocarbon resins, polyterpene resins,
coumarone/indene resins and terpene/phenol resins.
The pressure-sensitive adhesive layer can have
any desired thickness, preferably 10 to 40 ~Cm, particu-
larly preferably 10 to 25 E.cm.
In a preferred embodiment, the film of pressure
sensitive adhesive is anchored to the polymer film of the
interlayer by chemical crosslinking. The crosslinking can
be effected, for example, by using mixtures of the
pressure-sensitive adhesive or of the pressure-sensitive
adhesive composition with di- or polyfunctional cross
linking agents (2-component systems). Suitable cross-
linking agents are the conventional crosslinking agents
which react with hydroxyl-, amide- or carboxyl-functional
. polymers, such as the polyvinyl alcohol fraction of the
interlayer or the functional monomer units of the polymer
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of the interlayer and of the layer of pressure-sensitive
adhesive.
Examples of conventional crosslinking agents are
aziridines, melamine resins, preferably di- or poly-
functional isocyanates such as methylenediphenyl diiso-
cyanate (ICI) or isophorone diisocyanate. Water-
emulsifiable, oligomeric polyisocyanates, which give a
pot life of the adhesive system of several hours, are
particularly preferred. The content of these crosslinking
agents is in general 0.5 to 10% by weight, preferably 0.5
to 5% by weight, in each case relative to the total
weight of the pressure-sensitive adhesive composition.
A further preferred embodiment of the film of
pressure-sensitive adhesive, for anchoring the latter on
the dispersion polymer film of the interlayer, is the use
of pressure-sensitive adhesive copolymers based on the
abovementioned monomers which contain crosslinkable
comonomer units. Examples of such comonomer units are
monomers containing epoxy groups, such as glycidyl
methacrylate. Further examples are N-methylol-functional
monomer units such as N-methylolacrylamide, N-methylol-
methacrylamide, N-(alkoxymethyl)acrylamides or
N-(alkoxymethyl)methacrylamides having a C1- to C6-alkyl
radical, such as N-(isobutoxymethyl)acrylamide (IBMA),
N-(isobutoxymethyl)methacrylamide (IBI~iA), N-(n-butoxy-
methyl)acrylamide (NBMA) and N-(n-butoxymethyl)methacryl-
amide (NBI~tA). Comonomers containing carbonyl groups,
such as diacetoneacrylamide or crotonaldehyde, which are
converted for crosslinking or anchoring with the addition
of crosslinking agents containing hydrazide groups, such
as adipic acid dihydrazide, or of crosslinking agents
containing aminooxy groups, such as 1,4-diaminooxybutane
or 2-aminooxypropionic acid hydrazide, are also suitable.
Preferably, the content of the comonomer units is 0.1 to
3% by weight, relative to the pressure-sensitive adhesive
polymer.
The production of the composite paper material
can be carried out in known coating units. The polymer
forming the interlayer is applied in the form of an
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aqueous dispersion with a solids content of 30 to 75% by
weight, preferably 50 to 75% by weight and particularly
preferably 58 to 75% by weight, to the paper carrier, for
example by means of a blade. The procedure can here also
be such that the dispersion is applied to a release
material, for example a paper provided with a silicone
release layer, and dried, and is transferred directly to
the paper by laminating it to the paper carrier. Prefe-
rably, the polymer layer is produced by direct applica-
tion of the appropriate aqueous dispersion to the paper
carrier and subsequent drying in a drying duct. The
drying temperature is here in general between 50°C and
200°C.
To produce a crosslinked interlayer, copolymer
dispersants with crosslinkable comonomer units or a
mixture of aqueous copolymer dispersion and the external
crosslinking agent are used. The application takes place
analogously to the procedure for producing the uncross-
linked interlayer. The crosslinking occurs during the
drying step. For accelerating the crosslinking, drying
temperatures above 100°C, preferably up to 170°C can also
be used here if desired, or the abovementioned hardeners
can be added.
In the second process step, the layer of
pressure-sensitive adhesive is applied to the interlayer.
This can be carried out with a time offset after the
application of the interlayer (off-line), or preferably
directly after the application of the polymer layer in
one working step (in-line). The latter method requires a
suitable design of the coating unit.
The pressure-sensitive adhesive composition
which, if appropriate, also contains tackifier,
processing aids such as antifoams or wetting agents or
external crosslinking agents, can here be applied in the
form of an aqueous dispersion having a preferred solids
content of 50 to 75% by weight or as a melt. If
appropriate, the pressure-sensitive adhesive composition
is crosslinked by radiation, for example W radiation or
electron beams. The application of the layer of pressure-
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sensitive adhesive takes place in the usual manner either
by direct application to the interlayer, for example by
means of a blade or roller application, or by coating a
release material, preferably siliconized release paper,
with the pressure-sensitive adhesive, if appropriate
drying it, preferably at 50°C to 200°C, or radiatively
crosslinking it and subsequently laminating it to the
paper carrier provided with the interlayer. In this case,
the layer of pressure-sensitive adhesive is transferred
to the polymer film forming the interlayer. If necessary,
a backing material or release material, preferably
siliconized release paper, is fed in during the subse-
quent winding-up of the resulting composite paper
material.
During the coating with pressure-sensitive
adhesive compositions with an external crosslinking agent
or during the coating with pressure-sensitive adhesives
based on copolymers with crosslinkable monomer units, the
pressure-sensitive adhesive is preferably applied as an
aqueous dispersion directly to the interlayer, for
example by means of a blade. For crosslinking, the drying
takes place at room temperature or elevated temperature,
preferably at temperatures from 100°C to 200°C.
Subsequently, a backing material or release material,
25 preferably siliconized release paper, is fed in during
the winding-up of the composite paper material obtained.
In the composite paper material according to the
invention, the introduction of the moisture-resistant and
hydrophilic interlayer provides a composite which, on
repulping, almost completely sets the paper fibre free
and minimizes the fibre loss. During repulping, the
adhesive layer arises together with the interlayer in
such large pieces that almost complete screening of these
pieces by means of the screens usual in paper recycling
is possible. Consequently, no specific cleaning step, for
example flotation, is necessary for separating the
particles of pressure-sensitive adhesive from the pulp.
Concentrating of polymer in the water circulation of the
paper machine is effectively prevented. The risk of the
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formation of stickies is minimized and the content of
organic constituents, especially polymer, in the effluent
is greatly reduced.
The examples which follow serve for further
explanation of the invention,
Test method:
For repulping, 250 g of water were put into a
400 ml beaker, and 4 g of coated label paper (80 g/ms
vellum paper) was torn into pieces of about 2 x 2 cm and
suspended in water, free of lumps as far as possible. The
water and the label paper were transferred into a kitchen
mixer (type D 70 Mouline~l")and defibrated for 20 minutes
at speed stage 3. The content of the mixer was then put
into a 1 1 beaker and made up to a total quantity of
400 g of water and fibre pulp. The mixture was then
homogenized for 1 minute using a wing stirrer at about
1200 rpm. About 5 g were taken from the homogeneous
mixture and distributed on an absorbent paper over a
surface area of about 5 x 5 cm.
The size of the adhesive particles was measured.
The detachment of the layer of pressure-sensitive
adhesive from the interlayer and the adhesion of the
paper fibre to the interlayer were assessed
qualitatively.
The dispersion for producing the interlayer and
the pressure-sensitive adhesive were coloured by the
addition of small quantities (< 0.5%) of different dyes
(for example helizarin blue). In this way, it was
possible to distinguish the interlayer and the layer of
pressure-sensitive adhesive in the pulp.
Example 1:
An aqueous dispersion of a copolymer of vinyl
acetate and ethylene (ethylene content about 18% by
weight; Tg (DSC) - 3°C) with 4% by weight of polyvinyl
alcohol (degree of hydrolysis 88%) and 0.5% by weight of
an alkylalcoholethoxylate emulsifier, each relative to
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the polymer content, was applied by means of a wire blade
to 80 g/m' vellum paper in a layer thickness of 15 ~.m
(dry). An aqueous dispersion of a pressure-sensitive
adhesive composition consisting of an acrylic acid ester
5 copolymer (Tg - -57°C; 40% by weight), a copolymer of
vinyl acetate, ethylene and acrylic acid ester (Tg
-35°C; 30% by weight) and disproportionated colophony as
tackifier (30% by weight relative to dry mass) as well as
wetting agent and antifoam was applied in a layer thick
ness of 18 ~.m (dry) to the dry interlayer.
After repulping of the composite material thus
obtained, the paper fibres were completely separate from
the polymer layer. The interlayer and the pressure-
sensitive adhesive were in the form of a composite. More
than 95% of the total polymer area was present in
particles greater than 2 mm.
Comparison Example 1:
The procedure was analogous to that in Example 1,
with the difference that no interlayer was applied, but
the pressure-sensitive adhesive composition from
Example 1 was applied directly to 80 g/m' vellum paper in
a layer thickness of 22 Vim. After repulping, more than
50% of the layer of pressure-sensitive adhesive were
present in non-screenable particles smaller than 0.5 mm.
Example 2:
The procedure was analogous to Example 1, with
the difference that, for producing the interlayer, an
aqueous dispersion of a vinyl acetate/ethylene copolymer
with 2% by weight of N-methylolacrylamide, stabilized
with 5% by weight of polyvinyl alcohol (degree of
hydrolysis 88%) and 1% by weight of alkylphenol-
ethoxylate emulsifier, each relative to the polymer
content, which also contained 3% by weight, relative to
the dispersion, of a 50% aqueous solution of aluminium
chloride 6-hydrate as a hardener, was applied. The
thickness of the dry interlayer was 15 fcm. The pressure-
sensitive adhesive applied was that from Example 1 in a
CA 02273493 1999-06-02
15 -
film thickness (dry) of about 17 N.m.
After repulping of the composite material thus
obtained, the paper fibres were completely separate from
the polymer layer. The interlayer and pressure-sensitive
adhesive were in the form of a composite. More than 95%
of the total polymer area was in the form of screenable
particles larger than 2 mm.
Example 3:
The procedure was analogous to Example 1, with
the difference that, for producing the interlayer, an
aqueous dispersion of a copolymer of vinyl acetate,
ethylene, n-butyl acrylate and N-methylolacrylamide (Tg
about -14°C) stabilized with alkylphenol ethoxylate
emulsifier was applied in a thickness of 12 ~.m (dry) . The
pressure-sensitive adhesive applied was that from
Example 1 in a thickness (dry) of about 15 ~Cm.
After repulping of the composite material thus
obtained, the paper fibres were completely separate from
the polymer layer. The interlayer and the pressure-
sensitive adhesive were in the form of composite. More
than 95% of the total polymer area was present in the
form of screenable particles larger than 3 mm.
Example 4:
The procedure was analogous to Example l, with
the difference that, for producing the interlayer, an
aqueous dispersion of a copolymer of vinyl acetate and
N-methylolacrylamide (Tg about 35°C) stabilized with
polyvinyl alcohol (degree of hydrolysis 88%), which also
contains 2.5% by weight of butyldiglycol acetate as a
film-forming auxiliary and 2% by weight of aluminium
nitrate 9-hydrate, each relative to the dispersion, was
applied in a thickness of 20 ~,m (dry). The pressure-
sensitive adhesive applied was that from Example 1 in a
thickness (dry) of about 20 Vim.
After repulping of the composite material thus
obtained, the paper fibres were completely separate from
the polymer layer. The interlayer and pressure-sensitive
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adhesive were in the form of a composite. More than 95%
of the total polymer area was present in the form of
screenable particles larger than 1 mm.
Example 5:
The interlayer was produced using an aqueous
dispersion, containing a film-forming auxiliary, of a
styrene/butyl acrylate copolymer (Tg about 10°C), which
had been stabilized with alkylethoxylate emulsifier, in
a layer thickness of 18 ~Cm. The pressure-sensitive
adhesive used was an aqueous copolymer dispersion of
2-ethylhexyl acrylate, n-butyl acrylate, vinyl acetate
and acrylic acid, having a Tg of about -45°C. Before the
application to the interlayer, 3% by weight, relative to
the dispersion, of a water-emulsifiable, polyfunctional,
oligomeric isocyanate were mixed with the dispersion of
pressure-sensitive adhesive. The pot life of the mixture
was about 8 hours.
After the application and drying of the layer of
pressure-sensitive adhesive, repulping was carried out.
The interlayer and the pressure-sensitive adhesive were
anchored to one another and were in the form of a
composite. More than 95% of the total polymer area was
present in the form of screenable particles larger than
3 mm.
Example 6:
The production of the composite paper material
was carried out analogously to Example 5, with the
difference that no isocyanate was mixed into the
dispersion of pressure-sensitive adhesive.
After repulping, about 50% of the polymer area
was in the form of screenable particles. The particle
size was greater than 1 mm.
Example 7:
The production of the interlayer was carried out
analogously to Example 1. The pressure-sensitive adhesive
used was an aqueous dispersion of a copolymer of 2-ethyl
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hexyl acrylate, n-butyl acrylate and vinyl acetate with
2% by weight of N-methylolacrylamide (Tg _ -45°). The
layer of pressure-sensitive adhesive was dried at above
130°C; the thickness was 20 fcm (dry) .
5 After repulping of the composite material thus
obtained, the paper fibres were completely separate from
the polymer layer. The interlayer and pressure-sensitive
adhesive were in the form of a composite. More than 95%
of the total polymer area was in the form of screenable
particles larger than 2 mm.
Example 8:
The composite paper material was produced
analogously to Example 7, with the difference that the
copolymer of the dispersion of pressure-sensitive
adhesive did not contain any N-methylolacrylamide. After
drying of the layer of pressure-sensitive adhesive
applied to the interlayer in a thickness of 20 hem (dry),
repulping was carried out.
After repulping, detachment of the layer of
pressure-sensitive adhesive from the interlayer was
observed on about 50% of the polymer area. The particle
size was about lmm.
Example 9:
The interlayer was produced analogously to
Example 1. The pressure-sensitive adhesive used was a
hot-melt pressure-sensitive adhesive consisting of 45% of
a polystyrene/polybutadiene/polystyrene block copolymer,
53% of a colophony resin ester as tackifier and 2% of an
antioxidant as an anti-ageing additive, and this was
applied with a blade to the silicone side of a
siliconized separating paper in a layer thickness of
20 um. The paper carrier provided with the dry interlayer
was then laminated to the separating paper coated with
the hot-melt pressure-sensitive adhesive. The layer of
pressure-sensitive adhesive was thus transferred to the
interlayer. After repulping of the composite material
thus obtained, the paper fibres were completely separate
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from the polymer layer. The interlayer and hot-melt
pressure-sensitive adhesive were present as a composite.
More than 95% of the total polymer area was in the form
of screenable particles larger than 3 mm.
Comparison Example 2:
The procedure followed was analogous to
Example 1, with the difference that, for producing the
interlayer, an aqueous dispersion of a copolymer of vinyl
acetate, ethylene and 2-ethylhexyl acrylate, having a Tg
of only -35°C and stabilized with alkylphenol-ethoxylate
emulsifier, was applied in a thickness of 14 N.m (dry) .
The pressure-sensitive adhesive applied in a thickness of
about 18 ~m (dry) was that from Example 1.
After repulping of the composite material thus
obtained, far more than 50% of the total polymer area was
in the form of non-screenable particles smaller than
0.5 mm.
