U.S. patent application number 09/207814 was filed with the patent office on 2002-07-25 for multilayer adhesive tape.
Invention is credited to KARMANN, WERNER, KLUGE-PALETTA, WORNER, SZONN, BODO.
Application Number | 20020098347 09/207814 |
Document ID | / |
Family ID | 7853108 |
Filed Date | 2002-07-25 |
United States Patent
Application |
20020098347 |
Kind Code |
A1 |
SZONN, BODO ; et
al. |
July 25, 2002 |
MULTILAYER ADHESIVE TAPE
Abstract
A single- or double-sided pressure-sensitive adhesive tape
having an elastomeric backing layer, characterized in that a) the
framework substance of the backing layer consists of natural rubber
or of a mixture of natural rubber and at least one
styrene-butadiene rubber, b) an essential constituent of the
backing layer is an electron beam-crosslinkable, polyfunctional
crosslinker, c) a pressure-sensitive adhesive is applied to one or
both sides of the backing layer, and d) between backing layer and
pressure-sensitive adhesive there is an interlayer of a polyamide
or of a mixture of polyamides.
Inventors: |
SZONN, BODO; (WASBEK,
DE) ; KLUGE-PALETTA, WORNER; (BUCHHOLZ, DE) ;
KARMANN, WERNER; (HAMBURG, DE) |
Correspondence
Address: |
William C. Gerstenzang
Norris, McLaughlin & Marcus, P.A.
220 East 42nd Street - 30th Floor
New Y ork
NY
10017
US
|
Family ID: |
7853108 |
Appl. No.: |
09/207814 |
Filed: |
December 9, 1998 |
Current U.S.
Class: |
428/343 ;
427/208; 428/354 |
Current CPC
Class: |
C09J 2433/00 20130101;
Y10T 428/28 20150115; B32B 25/12 20130101; Y10T 428/2891 20150115;
B32B 2270/00 20130101; C09J 7/29 20180101; B32B 27/34 20130101;
C09J 7/241 20180101; C09J 2409/006 20130101; Y10T 428/31725
20150401; Y10T 428/2848 20150115; B32B 25/08 20130101; B32B 2405/00
20130101; B32B 27/308 20130101; C09J 133/08 20130101; Y10T 428/2809
20150115; B32B 2250/24 20130101; C09J 2301/122 20200801; C09J
2301/124 20200801; B32B 25/14 20130101; C09J 2301/162 20200801;
C09J 2407/006 20130101; C09J 2477/006 20130101; C09J 2407/006
20130101; C09J 2409/006 20130101 |
Class at
Publication: |
428/343 ;
428/354; 427/208 |
International
Class: |
C09J 007/02; B32B
007/12 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 23, 1997 |
DE |
197 57 426.2 |
Claims
1. Single- or double-sided pressure-sensitive adhesive tape having
an elastomeric backing layer, characterized in that a) the
framework substance of the backing layer consists of natural rubber
or of a mixture of natural rubber and at least one
styrene-butadiene rubber, b) an essential constituent of the
backing layer is an electron beam-crosslinkable, polyfunctional
crosslinker, c) a pressure-sensitive adhesive is applied to one or
both sides of the backing layer, and d) between backing layer and
pressure-sensitive adhesive there is an interlayer of a polyamide
or of a mixture of polyamides.
2. Adhesive tape according to claim 1, characterized in that the
polyfunctional crosslinker is an oligoacrylate or oligovinyl ether
consisting of a polyol, oligoether or oligourethane having at least
two terminal vinyl groups.
3. Adhesive tape according to claims 1 and 2, characterized in that
the vinyl-terminal polyol admixed to the backing is
ethoxylated.
4. Adhesive tape according to claims 1 to 3, characterized in that
the vinyl-terminal, ethoxylated oligoether admixed to the backing
is ethoxylated trimethylolpropane triacrylate.
5. Adhesive tape according to claims 1 to 4, characterized in that
the electron beam-crosslinkable, polyfunctional crosslinker is
present in an amount of from 5 to 20% by weight, especially 7% by
weight, relative to the framework substance of the backing
layer.
6. Adhesive tape according to claims 1 to 5, characterized in that
the interlayer consists of a polyamide which comprises alicyclic
segments or of a mixture of polyamides whose excess component
comprises alicyclic segments.
7. Adhesive tape according to claims 1 to 6, characterized in that
the interlayer has a thickness of from 5 to 40 .mu.m, especially 8
.mu.m.
8. Adhesive tape according to claims 1 to 7, characterized in that
the interlayer is produced by extrusion with or without auxiliary
supports.
9. Adhesive tape according to claims 1 to 8, characterized in that
the interlayer is prepared from dissolved form on an auxiliary
support.
10. Adhesive tape according to claims 1 to 9, characterized in that
the pressure-sensitive adhesive coating consists of a copolymer of
2-ethylhexyl acrylate and/or butyl acrylate with methyl acrylate
and acrylic acid, with or without further comonomers.
11. Adhesive tape according to claim 10, characterized in that the
pressure-sensitive adhesive coating has the following
composition:
5 from 50 to 70% by weight of 2-ethylhexyl acrylate and/or butyl
acrylate, from 20 to 40% by weight of methyl acrylate, from 0 to
10% by weight of acrylic acid with or without further
comonomers.
12. Adhesive tape according to claims 1 to 11, characterized in
that the combination product of backing layer and interlayer with
or without pressure-sensitive adhesive coat is crosslinked with
electron beams at a radiation dose of from 10 to 200 kGy, in
particular from 50 to 100 kGy.
13. Process for producing an adhesive tape according to at least
one of the preceding claims, characterized in that the backing
layer, the one or two interlayers and the one or two coats of the
pressure-sensitive adhesive are brought together by a laminating
process, especially a cold laminating process.
14. Process for producing an adhesive tape according to at least
one of the preceding claims, characterized in that the backing
layer is shaped by a calendering process on the ready-formed
interlayer, which is supported by an auxiliary support, if desired,
the backing layer is covered on the other side by a second
interlayer, together, if desired, with auxiliary support, the
backing layer and the interlayer(s) are irradiated with electrons,
the auxiliary support or supports is or are then peeled off, and a
self-adhesive coating is applied to each of the one or two
interlayers.
Description
[0001] The invention relates to an adhesive tape which has been
given a pressure-sensitive adhesive coating, having an elastomeric
backing layer, a single- or double-sided energy-elastic interlayer
and a pressure-sensitive adhesive layer on one or both sides.
[0002] The use of interlayers between the actual backing layer and
the pressure-sensitive adhesive coating is known. One of the
purposes of these interlayers is to prevent or lessen the migration
of constituents from the backing layer into the pressure-sensitive
adhesive. Migration of this kind may lead to structural alterations
in the pressure-sensitive adhesive layer and/or to deposits on the
surface of the pressure-sensitive adhesive, and hence to a
reduction in the adhesion. A further function of the interlayers is
to smooth out uneven backing surfaces.
[0003] In the case of the bonded adhesive tape,
interlayers--especially if they are energy-elastically
deformable--may have the function of absorbing stress peaks greater
than the average force acting on the bond area and of distributing
such peak stresses over the area of the bond in order thereby to
counter fracture of the bond.
[0004] For example, it is known for this application to use thin
layers of polymers which are in an energy-elastic state
thermodynamically owing to their high glass transition temperature
and/or their partial crystallinity. Polyamides in particular meet
the requirements that are placed on an interlayer.
[0005] A disadvantage of the interlayers consisting of polyamides,
however, is that, while they often fulfil the barrier, smoothing
and force-absorbing function, at the same time their adhesion to
the underlying backing is inadequate. At relatively high stress
levels, especially in the case of stresses in which peel forces
become active, there is a possibility that the adhesive tape might
suffer delamination, instances of which may lead to complete
failure of the bond.
[0006] The object of the invention, therefore, was to provide an
adhesive tape which, with an elastomeric backing layer, has an
energy-elastic interlayer anchored securely on the backing
layer.
[0007] To achieve this object the invention proposes an adhesive
tape which has been given a single- or double-sided
pressure-sensitive adhesive treatment and has an elastomeric
backing layer, the polymeric framework of the backing layer
consisting essentially of natural rubber or of a mixture of natural
rubber with at least one styrene-butadiene rubber.
[0008] The styrene-butadiene rubber of the backing layer can be a
random copolymer having a styrene content of about 23% by weight.
The natural rubber or mixture of natural rubber with
styrene-butadiene rubber that is used for the backing layer is
crosslinkable by means of electron beams.
[0009] In accordance with the invention the backing layer comprises
an electron beam-crosslinkable, polyfunctional crosslinker,
preferably oligoacrylate or oligovinyl ether, which is partially
soluble in the polymeric framework and whose physical forces of
interaction with the polymeric framework are so low that it tends
towards diffusion to the surface of the backing layer where,
together with its fraction which is not dissolved in the polymeric
framework, it forms a thin film which contacts the entire area of
the polyamide interlayer.
[0010] In that case the electron beam-crosslinkable polyfunctional
crosslinker is at least partially soluble in the polyamide and is
therefore able to diffuse into it. Irradiation with electrons
crosslinks the pure framework of the backing, the framework of the
backing together with the crosslinker, the pure crosslinker
dispersed in the backing, the crosslinker present like a film on
the surface of the backing, and those fractions of the crosslinker
that have diffused into the polyamide interlayer, this crosslinking
possibly taking place with attachment to the polyamide, so that an
indissoluble, predominantly covalent attachment of the interlayer
to the backing is achieved.
[0011] It is advantageous if the combined product composed of
backing, crosslinker film and polyamide is irradiated with
electrons before the latter has diffused to that side of the
polyamide which is opposite the rubber backing.
[0012] The combined product can be irradiated, for example, with an
electron accelerator of the scanner type at a radiation dose of
from 10 to 200 kGy, preferably from 50 to 100 kGy and, with
particular preference, 80 kGy. The required acceleration voltage
depends on the thickness of the combined product that is to be
crosslinked. To achieve sufficient homogeneity of crosslinking, the
combined product can be irradiated from both sides.
[0013] The crosslinked combined product composed of backing,
crosslinker film and polyamide interlayer preferably carries, on
the interlayer, a polyacrylate-based pressure-sensitive adhesive,
which may or may not be crosslinked.
[0014] The pressure-sensitive adhesive can be crosslinked
separately on an auxiliary support or in combination with
interlayer and backing by means of a chemical reaction, via an
inherent mechanism and/or physically by irradiation with electrons
in the course of the crosslinking of the backing with the
interlayer.
[0015] The crosslinker which is supplied to the backing, diffuses
onto its surface as a soluble fraction and is deposited there,
inter alia, as an insoluble fraction, and which, following partial
diffusion into the adjacent polyamide interlayer, brings about
anchorage of the interlayer to the backing following its
crosslinking with electron beams, is a polyfunctional--especially
di-, tri- or tetrafunctional--oligoacrylate or an oligovinyl ether
having terminal, electron beam-crosslinkable vinyl groups. The base
compound carrying the vinyl groups may, for example, be an
ethoxylated or non-ethoxylated polyol, an oligoether, or an
oligourethane having terminal OH groups.
[0016] In accordance with the invention the crosslinker can be
admixed alone or in a blend with one or more other crosslinkers of
the same or different functionality to the backing formulation.
[0017] For example, a bifunctional urethane acrylate having an
average molecular weight of 5000 or a tetrafunctional oligoether
acrylate having an average molecular weight of 1000 or a
trifunctional oligoether acrylate, such as ethoxylated
trimethylolpropane triacrylate, can be employed per se. It is also
possible, however, to blend the bifunctional urethane acrylate or
the tetrafunctional oligoether acrylate in equal or unequal parts
with the trifunctional ethoxylated trimethylolpropane
triacrylate.
[0018] Preferably, the crosslinker or the mixture of different
crosslinkers is added to the backing formulation in an amount of
from 5 to 20% by weight, especially 7% by weight.
[0019] To increase the durability of the backing it can be admixed
with customary anti-ageing agents, which, depending on the
particular application, may originate from the class of the
discolouring or non-discolouring anti-ageing agents, in particular
in the range from 0 tp 10 phr, and also with known light
stabilizers or ozone protectants. Blending with plasticizers is
also possible.
[0020] In order establish specifically the desired properties of
the backing it is possible if desired to use fillers. For instance,
the natural rubber or the mixture of natural rubber and
styrene-butadiene rubber can be admixed with reinforcing,
semi-reinforcing or non-reinforcing carbon blacks, in particular at
from 0 to 50 phr, with zinc oxide, in particular at from 0 to 50
phr, and/or with other fillers, such as silica, silicates or chalk.
Fillers other than those mentioned can also be used. It is possible
in addition to add resins from the class of the phenolic resins
and/or hydrocarbon resins, in the range, in particular, of from 0
to 50 phr. Depending on the intended application of the adhesive
tape, all of these additives referred to can be employed either
alone or in any desired combination with one another to produce the
backing, in order to obtain optimum tailoring to the utility.
Through the use of these additives it is also readily possible to
provide the black coloration of the backing which is generally
required by the industry.
[0021] The backing layer has a thickness of from 400 to 3000 .mu.m,
in particular from 500 to 1400 .mu.m.
[0022] The backing mixture is preferably prepared in an internal
mixer of the kind typically used for elastomer compounding.
Processing takes place preferably without solvent. The electron
beam-crosslinkable polyfunctional crosslinker and the desired
fillers may be added to the natural rubber or to the mixture of
natural rubber with styrene-butadiene rubber at the same time. The
resulting mixture can subsequently be extruded or calendered to the
desired thickness on customary commercial machines. This gives a
backing layer thickness that is within the ranges set out
above.
[0023] In a preferred embodiment the interlayer consists of a
polyamide or of a mixture of polyamides in which polyfunctional
oligoacrylates are partly soluble; for example, it consists of an
amorphous ternary copolyamide having alicyclic units, which
copolyamide may have been blended with minor amounts of a partially
crystalline polyaminoamide. In that case it is possible to use a
polyamide which includes alicyclic segments or a mixture of
polyamides whose excess component includes alicyclic segments.
[0024] In this context, the interlayer can be produced in a
separate operation from the solution or without solvent, by
extrusion with or without an auxiliary support, specifically in a
thickness of from 5 to 40 .mu.m, especially 8 .mu.m. If an
auxiliary support is used, the interlayer can be peeled from this
support again with no restrictions.
[0025] The pressure-sensitive adhesive consists preferably of
copolymers of 2-ethylhexyl acrylate, butyl acrylate, methyl
acrylate and acrylic acid, preferably with a composition of from 50
to 70% by weight 2-ethylhexyl acrylate and/or butyl acrylate, from
20 to 40% by weight methyl acrylate, and from 0 to 10% by weight
acrylic acid.
[0026] The addition of further, known components is possible in
order to obtain certain properties, especially the addition of
further comonomers, crosslinkers, tackifier resins and anti-ageing
agents. The pressure-sensitive adhesive can be processed as a
solution, dispersion or melt. It can be applied directly or by the
transfer technique to the interlayer. Chemical crosslinking of the
pressure-sensitive adhesive with crosslinking agents and/or
physical crosslinking with electron beams is advantageous. The
applied weight of the pressure-sensitive adhesive can likewise be
chosen arbitrarily in dependence on the intended use, within the
range from 10 to 250 g/m.sup.2, preferably from 40 to 150
g/m.sup.2. Furthermore, one or both pressure-sensitive adhesive
layers may be covered with a release paper, preferably with a
double-sidedly anti-adhesively coated masking paper or with a
polyolefin-based film. The film can have been antiadhesively
treated on both sides.
[0027] Also embraced by the concept of the invention are processes
for producing an adhesive tape of the invention.
[0028] In one preferred production process the backing layer, one
or both interlayers and one or both coats of the pressure-sensitive
adhesive are brought together by a laminating process.
[0029] In a second preferred process, the backing layer is first of
all shaped by a calendering process on the ready-formed interlayer,
which is supported by an auxiliary support. The other side of the
backing layer is then covered, if desired, with a second
interlayer, including auxiliary support, or, in the case of an
auxiliary support provided on both sides with an interlayer, is
joined with the second interlayer on the other side while the
laminate is being wound up into a roll. As soon as the crosslinker
film on the backing surface has come into contact with the
polyamide of the interlayer, the dissolution and diffusion of the
crosslinker into the polyamide begins. Experience has shown that
the unreacted crosslinker present on the surface of the interlayer
is able to diffuse into the pressure-sensitive adhesive and bring
about a deterioration in the force of its adhesion to substrates
encountered in practice. Likewise, fractions of the crosslinker
which have already been crosslinked, on the surface of the
interlayer, may reduce the spontaneous adhesion of the
pressure-sensitive adhesive on the interlayer. It is therefore
advantageous for the laminate composed of backing and interlayer to
be irradiated with electrons before the crosslinker has diffused to
the interlayer surface opposite the backing. In the next step of
the process the auxiliary support or supports is or are peeled off,
and, finally, the pressure-sensitive adhesive is applied directly
or by the transfer technique to one or both interlayers.
[0030] The present invention describes the construction of a
self-adhesive tape which exploits the electron beam
crosslinkability of a polyfunctional (at least bifunctional)
crosslinker which is partially soluble, and therefore diffuses to
the surface of the backing, and is partially insoluble, and
therefore becomes deposited, inter alia, on the surface of the
backing, this crosslinker being in uninterrupted contact with that
fraction that has remained in the backing as well as with that
fraction which has diffused into the interlayer. The self-adhesive
tape backing of the invention consists of natural rubber or of a
mixture of natural rubber with a styrene-butadiene rubber, and the
interlayer of the invention consists of polyamide which comprises
alicyclic segments and in which the polyfunctional crosslinker is
soluble. The firm connection of the two layers, brought into
contact with one another preferably by dry lamination, is brought
about essentially by the electron-beam curing of the polyfunctional
crosslinker. The resulting anchorage of the interlayer on the
backing ensures that there is no delamination of the adhesive tape,
even under high stresses.
[0031] The diffusion of the crosslinker to the surface of the
backing and further into the polyamide interlayer, this diffusion
preceding irradiation with electrons, takes place spontaneously at
room temperature and can be accelerated by elevated temperature.
The highest level of adhesion of the pressure-sensitive adhesive on
the interlayer is obtained when irradiation with electrons is
carried out before the crosslinker has diffused to the interlayer
surface facing the pressure-sensitive adhesive. The time required
by the crosslinker to reach that surface is of course influenced by
the composition and thickness of the interlayer, by the structure
of the crosslinker, by its solubility in the interlayer and by the
temperature. Experience has shown that, with an adhesive tape
construction in the preferred embodiment of the invention, there is
no adverse effect on the adhesion of the pressure-sensitive
adhesive in the above sense until the uncrosslinked combination
product of backing and interlayer with free, diffusable crosslinker
is stored at a temperature of up to 40.degree. C. for more than 4
weeks.
[0032] In the text below the invention will be elucidated further,
with examples, without wishing thereby to restrict the invention
unnecessarily.
EXAMPLES
Example 1
[0033] The basis was a backing layer having the composition in
Table 1.
1TABLE 1 Composition of the backing layer for Example 1
Constituents Parts by weight Natural rubber (standard Malaysian
rubber CV 50) 41 Polyisoprene having a molecular weight of 2900, 8
as plasticizer Liquid hydrocarbon resin having a viscosity of 7
from 20 to 40 Pas at 25.degree. C., as plasticizer Prepared chalk
30.7 Semi-active furnace black N 772 6.5 Anti-ageing agent
2,2'-methylenebis(4-methyl-6- 0.8 tert-butylphenol) Polyfunctional
crosslinker 6
[0034] The framework polymer used was a viscosity-stabilized
standard Malaysian rubber CV 50, the following being employed
alternatively as the polyfunctional crosslinker:
[0035] a) a bifunctional urethane acrylate having an average
molecular weight of 5,000 and a viscosity of 40 Pas at 25.degree.
C. (Ebecryl 230 from UCB Chemicals),
[0036] b) a trifunctional oligoether acrylate based on a
trimethylolpropane having a viscosity of 80 mPas at 25.degree. C.
(Ebecryl 160 from UCB Chemicals),
[0037] c) a mixture of equal parts of both of these
[0038] d) a tetrafunctional oligoether acrylate having an average
molecular weight of 1,000 and a viscosity of 3.5 Pas at 25.degree.
C. (Ebecryl 80 from UCB Chemicals)
[0039] e) a tetrafunctional oligoether acrylate having an average
molecular weight of 1000 and a viscosity of 3.5 Pas at 25.degree.
C. in a mixture with the ethoxylated trimethylolpropane triacrylate
(Ebecryl 160 from UCB Chemicals) in equal parts.
[0040] Also used were the fillers chalk and carbon black, and also
two plasticizers and a phenolic anti-ageing agent.
[0041] The constituents were mixed together in an internal mixer
under the conditions customary in the rubber industry.
[0042] The interlayer was prepared from an aqueous/alcoholic
solution of a mixture of 65 parts by weight of an amorphous ternary
copolyamide having alicyclic units (Ultramid 1C from BASF) and 35
parts by weight of a partially crystalline polyiminoamide (Platamid
M 1276 from Atochem) by spreading and drying in a coat thickness of
8 .mu.m on a polyethylene terephthalate film.
[0043] The backing mixture was shaped and applied by means of a
calender to an auxiliary support coated on both sides with the
interlayer, the resulting assembly being 0.5 mm thick and being
wound up into a roll so that the reverse side of the backing comes
into contact with the interlayer that was facing away from the
backing during its shaping. The auxiliary support employed was a 25
to 50 .mu.m thick polyethylene terephthalate film. In the course of
storage in roll form, there is partial diffusion of the crosslinker
from the backing into the interlayer on both sides of the
laminate.
[0044] Both sides of the laminate of backing and interlayers were
then crosslinked with electron beams over the course of 24 hours
with a radiation dose of 100 kGy.
[0045] The crosslinked samples produced in this way were examined
for the adhesion of the interlayer to the backing, which was
compared with that of uncrosslinked samples. For this purpose, the
auxiliary support for the interlayers was first of all removed.
Then one side of the laminate was reinforced with a
pressure-sensitive adhesive tape. On the other side of the sample,
a 30 mm wide strip of a filament-reinforced pressure-sensitive
adhesive tape which is obtainable commercially as tesapack 4588 was
stuck onto the interlayer, avoiding air-inclusion bubbles, and a
roller weighing 5 kp was rolled over the assembly 4 times. On test
strips cut to a width of 20 mm, the peeled strength of the
interlayer--now bonded to the filament-reinforced
pressure-sensitive adhesive tape--from the backing was measured
using a tensile testing machine at a peel rate of 300 mm/min.
2TABLE 2 Peel force of interlayer from backing Peel force [N/cm]
Non-EB- Backing/interlayer crosslinked laminate EB Crosslinker with
which backing/interlayer crosslinked the backing was blended
laminate at 100 kGy None 0.2 0.4 Ebecryl 230 0.6 2 Ebecryl 160 0.3
>6 1 part by wt. Ebecryl 160 + 0.2 >6 1 part by wt. Ebecryl
230 1 part by wt. Ebecryl 160 + 0.4 >6 1 part by wt. Ebecryl
80
[0046] The crosslinked backing described above, which is now
attached firmly on both sides to an interlayer, was coated on both
sides with a pressure-sensitive adhesive. The pressure-sensitive
adhesive was applied in a dry film thickness of 50 .mu.m to an
anti-adhesively treated auxiliary support and was dried at a
temperature of more than 100.degree. C. in order to induce
crosslinking.
[0047] To produce the adhesive tape of the invention the dried,
crosslinked pressure-sensitive adhesive was laminated by the
transfer technique onto the interlayer exposed after the backing
had been unrolled, following removal of the auxiliary support for
the interlayer.
[0048] The pressure-sensitive adhesive employed was a copolymer of
methyl acrylate with 2-ethylhexyl acrylate and acrylic acid which
crosslinks at a temperature upwards of 100.degree. C. with 0.5% of
an acetylacetone-based chelate formed with titanium. The copolymer
described has the following composition:
[0049] 30% by weight methyl acrylate
[0050] 60% by weight 2-ethylhexyl acrylate
[0051] 10% by weight acrylic acid
Example 2
[0052] A double-sided pressure-sensitive adhesive tape was produced
by the procedure described in Example 1. The backing used was a
mixture having the following composition:
3TABLE 3 Composition of the backing layer for Example 2
Constituents Parts by weight Natural rubber (standard Malaysian
rubber CV 50) 62.7 Prepared chalk 24.7 Semi-active furnace black N
772 6.2 Anti-ageing agent 2,2'-methylenebis(4-methyl-6- 1.4
tert-butylphenol) Polyfunctional oligoacrylate 5
[0053] The polyfunctional oligoacrylate used was ethoxylated
trimethylolpropane triacrylate having a viscosity of 25.degree. C.
of 80 mPas (Ebecryl 160 from UCB Chemicals).
[0054] The interlayer employed is again the mixture of two
polyamides described in Example 1.
[0055] The pressure-sensitive adhesive employed was an
acrylate-based copolymer having the composition described in
Example 1.
[0056] In order to study the time effect in the diffusion of the
uncrosslinked oligoacrylate through the interlayers to their
surfaces, the uncrosslinked laminate comprising the backing and the
interlayers was stored for different periods of time at 20.degree.
C. and 40.degree. C., and only then was crosslinked with electron
beams.
[0057] The pressure-sensitive adhesive was then laminated by the
transfer technique onto the interlayers and the overall
construction was stored at 70.degree. C. for one week in order, for
the purpose of optimum adhesion, to allow the pressure-sensitive
adhesive to flow onto the interlayers. The samples produced in this
way were subjected to a shear load at 70.degree. C. For this
purpose one pressure-sensitive adhesive side of a sample was
reinforced with a 50 .mu.m thick aluminium foil. From this assembly
there was cut a 13 mm wide and over 20 mm long strip which along a
length of 20 mm of its pressure-sensitive adhesive, free side was
bonded to a finely polished steel plate and rolled firm 4 times
with a roller weighing 2 kp. The end of the vertically positioned
sample that protrudes beyond the steel plate was subjected to a
weight of 10 N. The test was conducted in a drying cabinet at
70.degree. C. The fracture behaviour of the samples under load was
observed.
4TABLE 4 Shear stabilities at 70.degree. C. of backing/interlayer
laminates stored for different periods in the uncrosslinked state.
Storage period of the backing/interlayer laminate prior to Shear
stability [min] EB crosslinking Storage at 20.degree. C. Storage at
40.degree. C. no storage >20,000 min 2 weeks >20,000 min
>20,000 min 4 weeks >20,000 min >20,000 min 12 weeks 800
min 900 min adhesive fracture adhesive fracture between PSA and
between PSA and interlayer interlayer
[0058] The table shows that a significant drop in the shear
stability occurs only when the laminate composed of backing and
interlayer is stored for more than 4 weeks at a temperature of up
to 40.degree. C. prior to electron beam (EB) crosslinking, so that
it can be assumed that in the case of the exemplary construction
the diffusion of the oligoacrylate to the surface of the interlayer
takes more than 4 weeks. Before this time, no reduction is expected
in the adhesion of the pressure-sensitive adhesive (PSA) on the
interlayer as a result of crosslinked oligoacrylate in the case of
the exemplary construction.
* * * * *