Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
I O~o/4~
~ ' ' ' 220022q''
Adhesive coatings containing superabsorber particles
.
The present invention relates to a process for the production of
5 substrates coated with water-absorbing solid particles, wherein
a) a substrate is coated with pressure sensitive adhesive and
then
10 b) the water-absorbing solid particles are applied and the
pressure sensitive adhesive is crosslinked by exposure to
high-energy radiation before or after application of the
water-absorbing solid particles.
15 The present invention furthermore relates to unwindable adhesive
tapes comprising these coated substrates, the use of the coated
substrates for the production of hygiene products and for
protection against moisture.
20 Textile sheeting having superabsorbing properties for absorbing
liquids are being more and more widely used. Typical applications
are disposable diapers for babies, sanitary towels or products
for adult incontinence. Usually, these superabsorbing articles
contain a more or less bulky layer of cellulose (fluff) into
25 which superabsorber (SA) particles are sprinkled. If a liquid
enters this layer, it i~ absorbed by the SA particles, the liquid
being conveyed to the particles by the hydrophilic fluff fibers.
The water absorptivity may be several times the weight of the
material itself. The design described here and usually used hide,s ,~
30 the disadvantage that it leads to hygiene products which are
severall mm to cm thick and therefore often do not adequately
meet the requirements for as much discretion as possible when
these articles are worn on the human body. This applies in
particular to adult incontinence.
There is a need to produce a sheet-like material which has high
water absorptivity, is suitable for the design of hygiene
products, such as incontinence articles, disposable diapers for
babies or sanitary towels and is substantially thinner than the
40 conventional fluff-cont~; n; ng products.
There is also a need to use water-ret~;n;ng layers in other
areas. For example, superabsorber particles are used for
sheathing marine cables to protect the conductive material from
AMENDED SHEET
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u u ~ ~
220022q
~ the penetration of water. Here, the SA particles swell, form a
water-impermeable layer and thus isolate the inside of the
sheath, preventing the penetration of further moisture. Coating
with SA particles is usually effected by immersing the cable in a
S liquid containing SA particles. This process is of course not
feasible when repairs are re~uired. A portable system which is
self-adhesive and provides protection from moisture and water
would be desirable here. This portable system could of course
also be used in other areas in which water barrier layers are
10 desired for protection from moisture, for example in the building
industry.
The non prior published German Patent Application P 4411896.1
~o.z. 44788) describes the binding of superabsorber particles to
15 nonwovens with the aid of the binder of the nonwovens. The
resulting products are suitable for the production of thin
hygiene articles but not as a portable system for protection from
moisture, as described above.
20 It is an object of the present invention to provide
water-absorbing materials which are suitable for the production
of thin hygiene produc~s and as a portable system for protection
from moisture.
25 We have found that this object is achieved by the process
defined at the outset.
The substrates coated according to the invention are in general
sheet-like substrates. In particular, they are, for example
30 paper, foils or films, for example of metal or plastic, or fabric
of natural or synthetic fibers. Plastics films comprising
polyesters, such as polyethylene terephthalate, or polyolefins,
such as polyethylene, polypropylene or oriented polypropylene, or
polyamides are preferred. Preferred fabrics are those comprising
35 plastic, for example polyolefins or polyamides.
The substrates are coated on at least one side with a pressure
sensitive adhesive. The pressure sensitive adhesive layer
preferably has a thickness of less than 1 mm, in particular from
40 1 to 200 ~m.
A11 conventional pressure sensitive adhesives may be used.
Preferred ones are pressure sensitive adhesives based on a
polymer obtained by free radial polymerization and composed of
45 monomers capable of free radical polymerization.
~M~NDED SHEET
3 2200229
The polymer consists, preferably at least partially, of main
monomers selected from C1-C20-alkyl (meth)acrylates, vinyl esters
of carboxylic acids of up to 20 carbon atoms, vinyl aromatics of
up to 20 carbon atoms, ethylenically unsaturated nitriles, vinyl
5 halides, vinyl ethers of alcohols of 1 to 10 carbon atoms,
aliphatic hydrocarbons having 2 to 8 carbon atoms and 1 or 2
double bonds or mixtures of these monomers. The polymer contains
preferably at least 40, particularly preferably at least 60,
particularly preferably at least 75, % by weight of the~e main
10 monomers or of mixtures thereof.
Examples are alkyl (meth)acrylates having a Cl-C10-alkyl radical,
such as methyl methacrylate, methyl acrylate, n-butyl acrylate,
ethyl acrylate and 2-ethylhexyl acrylate.
Mixtures of the alkyl (meth)acrylates are also particularly
suitable.
.
Vinyl esters of carboxylic acids of 1 to 20 car~on atoms are, for
20 example, vinyl laurate, vinyl stearate, vinyl propionate, vinyl
versatate and vinyl acetate.
Suitable vinyl aromatic compounds are vinyltoluene, a- and
p-methylstyrene, a-butylstyrene, 4-n-butylstyrene,
25 4-n-decylstyrene and preferably styrene~ Examples of nitriles are
acrylonitrile and methacrylonitrile.
The vinyl halides are ethylenically unsaturated compounds
substituted by chlorine, fluorine or bromine, preferably vinyl
30 chloride-and vinylidene chloride.
Examples of vinyl ethers are vinyl methyl ether and vinyl
isobutyl ether. Vinyl ethers of alcohols of 1 to 4 carbon atoms
are preferred.
Examples of hydrocarbons having 2 to 8 carbon atoms and two
olefinic double bonds are butadiene,- isoprene and chloroprene.
In addition to these main monomers, further monomers, for example
40 hydroxyl-cont~;n;ng monomers, in particular Cl-C10-hydroxyalkyl
(meth)acrylates, (meth)acrylamide, ethylenically unsaturated
acids, in particular carboxylic acids, such as (meth)acrylic acid
or itaconic acid, dicarboxylic acids and anhydrides or
half-esters thereof, for example maleic acid, fumaric acid and
45 maleic anhydride, may be present in the polymer.
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4 2200229
~ The polymer can, if required, also contain crosslinking monomers
having 2 or more than two double bonds as further monomers. If at
all desirable, the crosslinkin~ monomers are present in general
in an amount of from ~.05 to 5% by weight, based on the polymer.
In the case of polymers crosslinkable by UV radiation,
copolymerizable, ethylenically unsaturated photoinitiators, for
example acetophenone derivatives or benzophenone derivatives, are
also suitable as further monomers, as disclosed, for example, in
10 EP-A-246 848 or DE-A-3 844 445. Where they are concomitantly
used, the amount is in general from 0.05 to 5, preferably from
0.1 to 3, ~ by weight.
The preparation of the polymers, for example by free radical
15 polymerization, can be carried out in solution, for example in an
organic solvent (solution polymerization), in an aqueous
dispersion (emulsion polymerization, suspension polymerization)
or essentially in the absence of water or organic solvents (mass
polymerization).
The emulsion polymerization may be carried out, for example,
batchwise, without or without the use o~ seed latices, initially
taking all or individual components of the reaction mixture, or
preferably initially taking some of the or individual components
25 of the reaction mixture and subsequently metering in the
remainder, or by the metering method without initially taking
components.
In the emulsion polymerization, the monomers can be polymerized
30 in a conventional m~nner in the presence of a water-soluble
initiator and of an emuIsifier at, preferably, from 30 to 95 C.
Examples of suitable initiators are sodium persulfate, potassium
persulfate, ammonium persulfate, tert-butyl hydroperoxides,
35 water-soluble azo compounds and redox initiators, such as
H202/ascorbic acid.
Examples o~ emulsifiers used are alkali metal salts of relatively
long-chain fatty acids, alkyl sulfates, alkylsulfonates,
40 alkylated arylsul~onates or alkylated diphenyl ether sulfonates.
Other suitable emulsifiers are reaction products of alkylene
oxides, in particular ethylene oxide or propylene oxide, with
fatty alcohols, fatty acids or phenol or alkylphenols.
45 In the case of aqueous secondary dispersions, the copolymer is
~irst prepared by solution polymerization in an organic solvent
and then dispersed in water without the use of an emulsifier or
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dispersant and with the addition of salt formers, for example of
ammonia to carboxyl-contA; n; ng copolymers. The organic solvent
can be distilled off. The preparation of aqueous secondary
dispersions is known to a person skilled in the art and
5 described, ~or example, in DE - A - 37 20 860.
Regulators may be used in the polymerization in order to
establish the molecular weight. For example, -SH-containing
compounds su~h as mercaptoethanol, mercaptopropanol, thiophenol,
10 thioglycerol, ethyl thioglycolate, methyl thioglycolate and
tert-dodecyl mercaptan, are suitable.
The solids content of the polymer emulsions obtained i5
preferably from 40 to 80, particularly preferably from 45 to 75,
15 % by weight. High polymer solids contents can be obtained, for
example, by methods described in German Patent Application
P 4 307 683.1 or EP 37 923.
A preferred polymerization method is solution polymerization. The
20 solution polymerization can be carried out continuously,
batchwise as a batch process or, preferably, semicontinuously by
the feed process. In the last-mentioned case, some o~ the
monomers initially taken are heated to polymerization temperature
and the remainder of the monomers are fed in continuously.
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Solvents which may be used for the free radical solution
polymerization are, for example, alcohols, such as isobutanol or
isopropanol, aromatics, such as toluene or xylene, ethers, such
as dioxane or tetrahydrofuran, ketones, such as acetone or
30 cyclohexanone, or esters, such as ethyl acetate or n-butyl
acetate.
Examples of preferred initiators are dibenzoyl peroxide,
tert-butyl perpivalate, tert-butyl per-2-ethylhexanoate,
35 tert-amyl 2-ethylhexyl peroxide, di-tert-butyl peroxide,
tert-butyl hydroperoxide, cumyl hydroperoxide, dilauroyl
peroxide, tert-butyl peroxymaleate, tert-butyl peroxybenzoate,
dicumyl peroxide, didecanoyl peroxide, methyl ethyl ketone
peroxide, 2,2'-azobis(2,4-dimethylvaleronitrile),
40 2,2'-azobis(2,3-dimethylbutyronitrile) and
2,2'-azobisisobutyronitrile.
In the mass polymerization, some of the polymerization batch is
in general initially taken and heated to the polymerization
45 temperature, after ~hich the remainder is fed in continuously.
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2200229
~ Depending on the polymerization method chosen, the polymer is
obtained in the form of an aqueous dispersion of the polymer or
of a solution in an organic solvent or in an essentially
anhydrous and solvent-free form.
The polymers can be used in these forms as pressure sensitive
adhesives. If necessary, additives, such as rheology assistants,
thickeners, and tackifiers, for example rosin, may also be added.
10 In the case of an aqueous dispersion or organic solution of the
polymer, the water Qr the organic solvent is removed after
application, so that only the dry polymer film r~m~;n~ behind.
Aqueous polymer systems have the disadvantage that water must be
15 removed very substantially before application of the
water-absorbing solid particles, in order to prevent premature
swelling of the water-absorbing solid particles.
Anhydrous polymer systems, for example organic solutions of the
20 polymer, are therefore preferred.
Polymer melts (hotmelt pressure sensitive adhesives) which are
essentially free of water and organic solvents are particularly
preferred. In this case, no drying step for removing the water or
25 solvent is required after application of the polymer melt as a
pressure sensitive adhesive. Hotmelt pressure sensitive adhesives
can be solid, highly viscous or fluid at 20~C. They are preferably
applied as a melt at from 50 to 200 C, particularly preferably
from 80 to 180~C.
After coating with the pressure sensitive adhesive and, if
necessary, drying of the coating, the water-absorbing solid
particles can then be applied, for example by simply sprinkling
them onto the pressure sensitive adhesive layer.
Examples of suitable water-absorbing solid particles are silica
gel and superabsorber particles.
Preferred superabsorbers are, for example, homopolymers of
40 (meth)acrylic acid or copolymers cont~;ning at least 30,
particularly preferably at least 50, % by weight of (meth)acrylic
acid.
The mean particle size of the water-absorbing solid particles is
45 not important for the principle o~ the invention. Usually,
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~ weight-average particle sizes are from 10 to 2000 ~m. The mean
particle size is preferably less than the thickness o~ the
pressure sen~itive adhesive layer, particularly preferably less
than half the thickness of said layer.
The amount of water-absorbing solid particles is preferably
chosen so that from 0.1 to lO0 mg of water-absorbing solid
particles are fixed on 1 cm2 of substrate coated with pressure
sensitive adhesive.
Before or after application of the water-absorbing solid
particles, crosslinking of the polymers in the pressure sensitive
adhesive layer is carried out.
15 The crosslinking is carried out by exposure to high-energy
radiation, for example to electron beams or UV light. In the case
of UV light the polymer preferably contains copolymerizable
ethylenically unsaturated photoinitiators, as mentioned above.
However, suitable photoinitiators may also be mixed with the
20 polymersj although this is less preferable. The abovementioned
hotmelt pressure sensitive adhesives are particularly suitable
~or crosslinking with high-energy radiation.
For example, commercial UV lamps, which preferably emit radiation
25 in a wavelenyth range from 250 to 400 nm, may be used for the
exposure. Medium pressure mercury lamps having a radiant power of
~rom 80 to 120 W/cm are, for example, suitable.
By means o~ crosslinking with high-energy radiation, after
30 application of the particles, the desired amount of
water-absorbing solid particles are particularly readily fixed,
rapidly and firmly, in or on the pressure sensitive adhesive
layer.
35 The coated substrates obtained according to the invention may be
coated with pressure sensitive adhesive on one or both sides, and
the water-absorbing solid particles may also be applied to one or
both sides.
40 The pressure sensitive adhesive layer containing the
water-absorbing solid particles may be provided with a
water-permeable covering. Such coverings are preferably fabrics
of plastic or natural materials such as cellulose. The fabric
preferably has a mesh size which is smaller than the
45 weight-average diameter of the water-absorbing particles. The
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2200229
fabric may, for example, be adhesively bonded to the pressure
sensitive adhesive layer at the edges of the substrate. The edges
are suitably free of water-absorbing solid particles over the
bonded width.
In a preferred embodiment, the substrates are coated on one side
(defined as the upper side) with pressure sensitive adhesive and
water-absorbing particles fixed therein and on the other side
~defined as the lower side) only with pressure sensitive
10 adhesive, without fixed water-absorbing particles.
The substrates coated in this manner are particularly suitable as
a portable system for protection from moisture. The substrates
can be adhesively bonded to the lower side on objects to be
15 protected from moisture, for example cables. The substrates
coated on both sides can be used in particular in the form of
unwindable adhesive tapes. In these adhesive tapes, the lower
side coated with pressure sensitive adhesive may be provided with
a release paper, as is otherwise generally the case with adhesive
20 tapes. The upper side carries the pressure ~ensitive adhesive
layer cont~; n; ng the fixed water-absorbing particles and
preferably, but not necessarily, a covering which, as described
above, is adhesively bonded to the edges of the adhesive tape.
25 The coated substrates are suitable for the production of hygiene
products, for example incontinence articles, disposable diapers
for babies or sanitary towels. They are also suitable for
protecting, for example, articles in the electrical, electronics
or building industry from moisture.
They may be used in the form of adhesive tapes and, in this or
another form, constitute a suitable portable system, for example
for protecting objects from moisture.
35 Examples
Example 1
A polyester film tHostaphan~ RN 36) was coated with UV-
40 crosslinkable hotmelt pressure sensitive adhesive Acronal~ DS 3458(coating weight 70 g/m2). The superabsorber (Aqualic AL 76 LF) was
then sprinkled on. After SA particles which were not fixed had
been shaken off, the film was exposed to UV light (30 mW/cm2,
5 min).
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0050/45233 2 2 0 0 2 2 9
g
~ The exposed film was placed in water to swell. Even after
swelling had occurred, the superabsorber still adhered firmly to
the film.
5 Data for the film coated with Uv hotmelt pressur ~ e
adhesive:
UV-crosslinked
10 Weight of the film 0.11 g
Weight after application of hotmelt 0.34 g
pressure sensitive adhesive
Weight after coating with superabsorber 0.64 g
Weight after swelling in water 7.57 g
15 Water absorption (based on superabsorber) 2210 %
Example 2
20 A polyester film (Hostaphan~ RN 36) was coated with UV-
crosslinkable hotmelt pressure sensitive adhesive Acronal~DS 3458
(coating weight 70 g/m2). Thereafter, the superabsorber (Aqualic
CAL 76 LF ) was sprinkled on so that a zone about 2 cm wide at the
edge of the film remained free of superabsorber. After
25 superabsorber (SA) particles which were not fixed had been shaken
off and exposure had been effected, a polypropylene fabric having
a mesh size of 118 ~m was placed on top and adhesively bonded to
the edge without the use of additional adhesive.
30 The composite had good water swellability as above, the covering ~ ~
fabric not becoming detached.
Example 3
35 A polypropylene fabric having a mesh size of 118 ~m was coated
with UV-crosslinkable hotmelt pressure sensitive adhesive
Acronal~DS 3458 (coating weight 70 g/m2). The porosity of the
material resulted in hotmelt pressure sensitive adhesive being
present on both sides of the fabric. While one side was exposed
40 and then laminated with release paper, the superabsorber (Aqualic
CAL 76 LF) was sprinkled onto the other side so that a zone about
2 cm wide at the edge of the film remained free of superabsorber.
After SA particles which were not fixed had been shaken off and
the composite had been exposed, a second polypropylene fabric
45 having a mesh size of 118 ~m was stuck on without the use of
additional adhesive. After removal of the release paper from the
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lower side, this composite could be fixed to any desired
surfaces. This composite too had very good water swellability.
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