U.S. patent application number 17/051074 was filed with the patent office on 2022-02-17 for latent reactive adhesive film.
This patent application is currently assigned to tesa SE. The applicant listed for this patent is tesa SE. Invention is credited to Thilo Dollase, Matthias Koop, Marco Kupsky, Philipp Preuss.
Application Number | 20220049139 17/051074 |
Document ID | / |
Family ID | 1000006122305 |
Filed Date | 2022-02-17 |
United States Patent
Application |
20220049139 |
Kind Code |
A9 |
Kupsky; Marco ; et
al. |
February 17, 2022 |
LATENT REACTIVE ADHESIVE FILM
Abstract
The invention relates to an adhesive film which comprises a
layer of an adhesive that comprises one or more polymers and at
least one peroxide, characterized in that the adhesive comprises at
last 50% by weight of thermoplastic polymers that do not have
C.dbd.C multiple bonds, in that at least one peroxide has the
general structural formula R--O--O--R', wherein R and R' each
represent organyl groups or together represent a cyclic organyl
group, and in that the peroxide in solution has a 1-minute
half-life temperature of less than 200.degree. C. In a preferred
embodiment, the thermoplastic polymer is a polyurethane and the
peroxide is a dicumyl peroxide.
Inventors: |
Kupsky; Marco; (Quickborn,
DE) ; Dollase; Thilo; (Hamburg, DE) ; Koop;
Matthias; (Norderstedt, DE) ; Preuss; Philipp;
(Norderstedt, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
tesa SE |
Norderstedt |
|
DE |
|
|
Assignee: |
tesa SE
Norderstedt
DE
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20210214593 A1 |
July 15, 2021 |
|
|
Family ID: |
1000006122305 |
Appl. No.: |
17/051074 |
Filed: |
April 26, 2019 |
PCT Filed: |
April 26, 2019 |
PCT NO: |
PCT/EP2019/060780 PCKC 00 |
371 Date: |
October 27, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09J 175/04
20130101 |
International
Class: |
C09J 175/04 20060101
C09J175/04 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 27, 2018 |
DE |
10 2018 206 632.9 |
Claims
1.-18. (canceled)
19. An adhesive film, comprising: a layer of an adhesive, the
adhesive comprising one or more polymers and at least one peroxide,
wherein the one or more polymers comprises at least 50% by weight
of thermoplastic polymers having no C.dbd.C multiple bonds, wherein
the at least one peroxide has the general structural formula
R--O--O--R' where R and R' each represent organyl groups or
collectively represent a cyclic organyl group, and further wherein
the at least one peroxide in solution has a 1 minute half-life
temperature of less than 200.degree. C.
20. The adhesive film according to claim 19, wherein the at least
one peroxide is dicumyl peroxide.
21. The adhesive film according to claim 19, wherein an amount of
the at least one peroxide in the adhesive is chosen within the
range from 0.1% to 10% by weight.
22. The adhesive film according to claim 19, wherein at least one
of the thermoplastic polymers is a polyurethane.
23. The adhesive film according to claim 19, wherein at least one
of the thermoplastic polymers is semicrystalline.
24. The adhesive film according to claim 23, wherein the
thermoplastic polymers have a maximum softening temperature of not
more than 25.degree. C.
25. The adhesive film according to claim 19, wherein the one or
more polymers have a maximum glass transition temperature of not
more than -25.degree. C., as determined by dynamic differential
calorimetry (DSC).
26. The adhesive film according to claim 19, wherein the adhesive
film is curable by thermal activation.
27. The adhesive film according to claim 19, wherein at least one
of the thermoplastic polymers is a thermoplastic elastomer.
28. The adhesive film according to claim 19, further comprising: at
least one adhesion promoter.
29. The adhesive film according to claim 28, wherein the at least
one adhesion promoter is at least one silane functionalized by one
or more alkoxy groups.
30. The adhesive film according to claim 29, wherein the one or
more alkoxy groups comprises methoxy and/or ethoxy groups.
31. The adhesive film according to claim 19, wherein an adhesive
strength of the adhesive film, as disposed on a substrate surface,
after curing, and after storage at 23.degree. C., 50% relative
humidity (RH) for eighteen weeks, is at least 90% of an adhesive
strength of the adhesive film, as disposed on a substrate surface,
after curing, and after storage for not more than one day at
23.degree. C., 50% RH.
32. The adhesive film according to claim 19, wherein an adhesive
strength of the adhesive film, as disposed on a substrate surface,
after curing, and after storage at 40.degree. C. for eighteen weeks
in a drying cabinet under standard climatic conditions (23.degree.
C./50% relative humidity (RH)), is at least 90% of an adhesive
strength of the adhesive film, as disposed on a substrate surface,
after curing, and after storage for not more than one day at
23.degree. C., 50% RH.
33. The adhesive film according to claim 19, wherein a force that
acts perpendicularly and completely parts an adhesive bond
established with the adhesive film, as having a thickness of 100
.mu.m and stored beforehand at 23.degree. C., 50% relative humidity
(RH) for six weeks, is at least 90% of a force that acts
perpendicularly and completely parts an adhesive bond established
with the adhesive film, as also having a thickness of 100 .mu.m and
stored for not longer than one day beforehand, wherein each of the
adhesive bonds has been established by a pressurized bonding of a
polycarbonate disk (Makrolon 099) with a frame made of anodized
aluminum (E6EV1) by means of a layer of the adhesive film, wherein
the pressurized bonding is effected at a temperature of 190.degree.
C. and a pressure of 10 bar for 10 s with an effective bond area of
282 mm.sup.2, and further wherein the force is measured at
23.degree. C. and 50% RH.
34. The adhesive film according to claim 19, wherein a force that
acts perpendicularly and completely parts an adhesive bond
established with the adhesive film, as having a thickness of 100
.mu.m and stored beforehand at 23.degree. C., 50% relative humidity
(RH) for eighteen weeks, then stored at 85.degree. C. and 85% RH
for 72 h and reconditioned at 23.degree. C., 50% RH for 24 h, is at
least 50% of a force that acts perpendicularly and completely parts
an adhesive bond established with the adhesive film, as also having
a thickness of 100 .mu.m and stored for not longer than one day
beforehand, wherein each of the adhesive bonds has been established
by a pressurized bonding of a polycarbonate disk (Makrolon 099)
with a frame made of anodized aluminum (E6EV1) by means of a layer
of the adhesive film, wherein the pressurized bonding is effected
at a temperature of 190.degree. C. and a pressure of 10 bar for 10
s with an effective bond area of 282 mm.sup.2, and further wherein
the force is measured at 23.degree. C. and 50% RH.
35. The adhesive film according to claim 19, wherein a force that
acts perpendicularly and completely parts an adhesive bond
established with the adhesive film, as having a thickness of 100
.mu.m and stored beforehand at 40.degree. C. in a drying cabinet
under standard climatic conditions (23.degree. C./50% RH) for
eighteen weeks and then stored at 85.degree. C. and 85% RH for 72 h
and reconditioned at 23.degree. C., 50% RH for 24 h, is at least
50% of a force that acts perpendicularly and completely parts an
adhesive bond established with the adhesive film, as also having a
thickness of 100 .mu.m and stored for not longer than one day
beforehand, wherein each of the adhesive bonds has been established
by a pressurized bonding of a polycarbonate disk (Makrolon 099)
with a frame made of anodized aluminum (E6EV1) by means of a layer
of the adhesive film, wherein the pressurized bonding is effected
at a temperature of 190.degree. C. and a pressure of 10 bar for 10
s with an effective bond area of 282 mm.sup.2, and further wherein
the force is measured at 23.degree. C. and 50% RH.
36. A method of joining two substrates with the adhesive film
according to claim 19.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a national stage application under 35
U.S.C. .sctn. 371 that claims the benefit of priority under 35
U.S.C. .sctn. 365 of International Patent Application Serial No.
PCT/EP2019/060780, filed on Apr. 26, 2019, designating the United
States of America, which in turn claims the benefit of priority
under 35 U.S.C. .sctn. 119 of German Patent Application No. 10 2018
206 632.9, filed Apr. 27, 2018, the contents of which are relied
upon and incorporated herein by reference in their entirety.
FIELD OF THE DISCLOSURE
[0002] The invention relates to an adhesive comprising one or more
polymers and at least one peroxide, and to a latently reactive
adhesive film comprising at least one layer of such an
adhesive.
BACKGROUND
[0003] Adhesive films are a means that has long been known for
bonding of two substrates to one another, in order to get around
the disadvantages of liquid adhesives. Among the advantages of
adhesive films are good storability and transportability, good
configurability, and easy applicability on use. According to the
adhesive used for the adhesive film, it is possible to achieve good
repositioning properties with nevertheless ultimately very high
bonding forces.
[0004] Adhesive tapes are used in various forms nowadays, for
example as aids in processes and for bonding of different objects.
Many self-adhesive tapes containing pressure-sensitive adhesives
have permanent tack. They can typically perform their bonding
function immediately after bonding without further curing. Such
self-adhesive tapes can therefore sometimes achieve very high bond
strengths. Nevertheless, in particular applications, there is the
need for bonding solutions that permit even higher bond strengths
than conventional self-adhesive tapes.
[0005] Many such bonding systems that lead to high-strength bonds
are applied in a hot compression step. The adhesives used--that are
frequently not self-adhesive at room temperature--then melt, wet
the bonding substrate and build up strength through solidification
during cooling. Such bonding systems may additionally have chemical
reactivity. By virtue of such reactions, it is possible to increase
the cohesion of the adhesive and hence further optimize the bond
strength. Furthermore, such reactions can have a positive effect on
chemical stability and weathering stability.
[0006] Some reactive adhesives comprise a polymer composition which
is reactive with a curing agent and a corresponding curing agent.
The polymer here has functional groups that can be made to react
with corresponding groups of the curing agent under appropriate
activation. The term "curable adhesive composition" in the prior
art therefore covers those formulations that contain functional
groups which, through the action of a corresponding curing
component in combination with elevated temperature as an additional
stimulus, can participate in a reaction that leads to an increase
in molar mass and/or crosslinking of at least one formulation
constituent and/or covalently binds different formulation
constituents to one another.
[0007] Peroxides are known as curing agents for unsaturated polymer
systems. For example, EP 0 650 987 A discloses a tacky fluorinated
polymer which, in a grafting operation, can be bound to molecules
that have been prepared from different organic materials or
inorganic materials and have at least one functional linking group
capable of grafting onto the fluorinated polymer. The fluorinated
polymer may be a thermoplastic. Peroxides are mentioned as
free-radical initiators for the reaction with the fluorinated
polymer.
[0008] U.S. Pat. No. 4,725,637 describes nitrile rubber-containing
formulations that can be crosslinked with peroxides. EP 287 928
describes EVA-containing formulations that can be crosslinked with
peroxide, especially for cable sheathing. Very small amounts of
peroxide are disclosed as being suitable. There is no mention of
adhesive films.
[0009] US 2003/0178138 A discloses electrically conductive,
reactive adhesive films for bonding of two electrodes. Adhesive
compositions used are mixtures of adhesives and
pressure-sensitively adhesive conductive polymers, especially
polyphthalide. The adhesive may, inter alia, be an irreversibly
hot-curing adhesive (thermoset) or a thermoplastic adhesive
(hotmelt).
[0010] The adhesive tape comprising the hot-curing adhesive may
consist of a film-forming matrix polymer and a reactive system
composed of an unsaturated polymerizable compound and a
polymerization initiator. The polymerization initiator for such
unsaturated compounds may be a dialkyl peroxide.
[0011] There is no disclosure or suggestion of the curing or
crosslinking of thermoplastic polymers, especially in the absence
of free-radically polymerizable and unsaturated systems, by
peroxides.
[0012] DE 10 2013 222 739 discloses adhesive films containing a
thermoplastic polyurethane, acrylate monomers and a free-radical
initiator, e.g. a hydroperoxide. Cumene hydroperoxide is mentioned
specifically.
[0013] It is an object of the invention to provide particularly
storage-stable but thermally reactive adhesive films based on
thermoplastic polymers. The adhesive films are advantageously also
storage-stable at elevated temperatures. Further advantageously,
the bonds established with the adhesive films have good
moisture/heat stability. They are to feature rapid curability.
[0014] A further, preferably additional advantage desired is that
the adhesive films do not exude any volatile constituents as a
result of the curing reaction under the bonding conditions
employed, especially in order to avoid blistering.
SUMMARY OF THE DISCLOSURE
[0015] It has now been able to be found in accordance with the
invention that adhesives--synonymous with "adhesive
compositions"--based on a polymer component comprising at least 50%
by weight of thermoplastic polymers, are suitable for establishment
of the desired adhesive films in the presence of peroxides even
when thermoplastic polymers lacking C--C multiple bonds are used.
These polymers thus do not have any free-radically polymerizable
groups.
[0016] According to another aspect of the disclosure, a method of
joining two substrates using the adhesive film of the disclosure is
provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] In the drawings:
[0018] FIG. 1 is a plot of push-out results of example adhesive
films bonded to substrates after storage under various conditions
and after storage under various conditions with an additional
moisture and heat exposure, according to embodiments of the
disclosure;
[0019] FIG. 2 is a dynamic differential calorimetry (DSC) plot of
example adhesive films, according to embodiments of the disclosure;
and
[0020] FIG. 3 is a DSC plot of example adhesive films, according to
embodiments of the disclosure.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] Accordingly, the invention relates to an adhesive film
comprising at least one layer of an adhesive, wherein the adhesive
comprises a polymer component and at least one peroxide, wherein
the polymer component comprises at least 50% by weight of those
thermoplastic polymers having no C.dbd.C double bonds and no
C.ident.C triple bonds.
[0022] Peroxides chosen are those for which the 1 minute half-life
temperature T(t.sub.1/2=1 min) in solution (0.1 molar in
monochlorobenzene) does not exceed 200.degree. C., preferably not
exceeding 190.degree. C., very preferably not exceeding 180.degree.
C.
[0023] The peroxides are especially those which--apart from
satisfying the above definition--also bear an organyl group on each
oxygen atom. Peroxides used are accordingly compounds of the
general structure R--O--O--R' where the R and R' radicals are
organyl groups that may be chosen independently or else be
identical, and where R and R' may also be bonded to one another, so
as to form a cycle via the peroxy group (--O--O--), resulting in a
structure of the
##STR00001##
type.
[0024] Organyl groups refer to organic radicals--irrespective of
which functional group is present therein--having one or less often
more free valences on one carbon atom. Examples of these are
acetonyl groups, acyl group (for example acetyl groups, benzoyl
groups), alkyl groups (for example methyl groups, ethyl groups),
alkenyl group (for example vinyl groups, allyl groups), alkynyl
groups (propargyl groups), aminocarbonyl groups, ampicilloyl groups
(radicals derived from ampicillin), aryl groups (for example phenyl
groups, 1-naphthyl groups, 2-naphthyl groups, 2-thiophenyl groups,
2,4-dinitrophenyl groups), alkylaryl groups (for example benzyl
groups, triphenylmethyl groups), benzyloxycarbonyl groups (Cbz),
tert-butoxycarbonyl groups (Boc), carboxy groups,
(fluoren-9-ylmethoxy)carbonyl groups (Fmoc), furfuryl groups,
glycidyl groups, haloalkyl groups (for example chloromethyl groups,
2,2,2-trifluoroethyl groups), indolyl groups, nitrile groups,
nucleosidyl groups, trityl groups, to name just a few.
[0025] Peroxides of the general structure R--O--O--R' (including in
cyclic form) have the advantage, for example, by comparison with
the hydroperoxides that they do not eliminate water in the manner
of primary cleavage products on thermal activation of the adhesive
composition. What is desired in accordance with the invention is
the greatest possible reduction in, preferably complete avoidance
of, volatile constituents having boiling points above 150.degree.
C., preferably having boiling points above 120.degree. C., in order
especially to avoid blistering at the bonding site and hence
weakening thereof. Accordingly, R and R' in the peroxides of the
invention should especially preferably be chosen such that these do
not lead to formation of volatile primary cleavage products
either--for example carbon dioxide, isopropanol.
[0026] The adhesive films of the invention have excellent
prelaminatability and have been found to be activatable in the hot
compression step to develop the ultimate bond strength, meaning
that they have the ability to react chemically, especially in a
rapid crosslinking and/or curing reaction, after appropriate
activation. The activation is especially effected thermally, i.e.
by supply of heat. In principle, other activation methods--for
example by induction, by microwaves, by irradiation with UV
radiation, laser treatment, plasma treatment--are also known for
latently reactive adhesive tapes. For the purposes of the present
invention, however, the activation very preferably takes place by
supply of thermal energy, and the further activation methods may
especially be used and optionally additionally (additively), for
instance by mixing UV photoinitiators into the adhesive. This is a
particular execution of the invention, but not the general
case.
[0027] During the supply of heat, the adhesive melts and can
excellently wet the substrate surfaces to be bonded, and the
crosslinking or curing reaction results in an increase in cohesion
of the adhesive. This is achieved by use of thermoplastic base
polymers.
[0028] By virtue of the reactive bonding, the adhesive films of the
invention are thus capable of generating high bond strengths to the
substrates on which they are bonded. The bond strengths here may
assume for example orders of magnitude that exceed those of
customary pressure-sensitive adhesive compositions by a factor of
10 or more.
[0029] The adhesives used in accordance with the invention and the
corresponding adhesive films are latently reactive. "Latently
reactive" in the context of this invention refers to those
activatable adhesive systems that can be stored in a stable manner
over prolonged periods without activation. Latently reactive
adhesive films are those that do not cure, or cure only over a
period of months, under standard climatic conditions (23.degree. C.
[296.15 K]; 50% RH) and especially at elevated storage temperatures
(especially up to 40.degree. C. [316.15 K]) and hence are
storage-stable, but which are activatable and cure and/or crosslink
at much higher temperatures. Latent reactivity offers the advantage
that these adhesive films can be stored, transported and processed
further (for example configured) under standard climatic conditions
and especially at elevated temperatures up to 40.degree. C. before
they are then used and cured at the bonding site. There should be
no significant change in the adhesives during the storage time,
such that there is no significant difference in the bonding
properties of an adhesive system freshly employed after the
establishment of the bond and of an adhesive system employed after
prolonged storage for otherwise comparable bonding.
[0030] It is a feature of the compositions of the invention that
they are firstly latently reactive and secondly rapidly curable at
elevated temperature.
[0031] Adhesive Components
[0032] According to the invention, the at least one peroxide, or
the multiple peroxides used, is chosen such that it has
comparatively high breakdown rates or short half-lives [t.sub.1/2]
at elevated temperatures--temperatures above their activation
temperature. The breakdown rate of the peroxides is a
characterizing criterion for the reactivity thereof and is
quantified by the reporting of the half-lives at particular
temperatures [t.sub.1/2(T)], where the half-life, as usual, is the
time after which half of the peroxide has broken down under the
given conditions. The higher the temperature, in general, the
shorter the half-life of breakdown. Thus, the higher the breakdown
rate, the shorter the half-life.
[0033] The half-life temperature [T(t.sub.1/2)] refers to the
temperature at which the half-life corresponds to a given value;
for example, the 10 hour half-life temperature [T(t.sub.1/2=10
h)]is the temperature at which the half-life of the substance
examined is just 10 hours, the 1 minute half-life temperature
[T(t.sub.1/2=1 min)] is that temperature at which the half-life of
the substance examined is just 1 minute, and so forth.
[0034] According to the invention, the person skilled in the art
would not have expected it to be possible to utilize peroxides in
accordance with the invention, since the demands on sufficient
storage stability at low and at moderately elevated temperatures
(i.e. very minor breakdown, see also below) but sufficiently
significant breakdown at the compression temperature (i.e. the
activation of the adhesive film) and hence the provision of
adequate reactivity in the curing of the adhesive film are
fundamentally at odds. However, it has been able to be found that
the use of the peroxides utilized in accordance with the invention
was successful and it was additionally possible to provide products
stable to heat and moisture.
[0035] In the context of this invention, the at least one peroxide,
or the multiple peroxides used, is chosen such that the 1 minute
half-life temperature T(t.sub.1/2=1 min) in solution does not
exceed 200.degree. C., preferably does not exceed 190.degree. C.,
very preferably does not exceed 180.degree. C.
[0036] The above condition is considered to be satisfied especially
when the peroxide in question has a corresponding half-life
temperature at least in monochlorobenzene (0.1 molar solution).
[0037] Such half-lives can be ascertained experimentally
(determination of concentration by means of DSC or titration) and
can also be found in the relevant literature. The half-lives are
also obtainable by calculation from the Arrhenius frequency factor
constant and breakdown activation energy constant for the
respectively specified conditions that are specific to the
respective peroxide. The following relationships set forth in
Equations [1] to [4] are applicable:
-dc/dt=kc [1]
ln(c.sub.1/c.sub.0)=-kt [2]
t.sub.1/2=ln2/k for c.sub.t(t.sub.1/2)=c.sub.0/2 [3]
k=Ae.sup.-Ea/RT [4]
[0038] where c.sub.0=starting concentration [0039]
c.sub.t=concentration at time t [0040]
c.sub.t(t.sub.1/2)=concentration at half-life [0041]
t.sub.1/2=half-life [0042] k=breakdown constant [0043] A=Arrhenius
frequency factor [0044] Ea=activation energy for peroxide breakdown
[0045] R=universal gas constant (R=8.3142 J/(molK)) [0046]
T=absolute temperature
[0047] The half-lives specified in this document and the half-life
temperatures are each based on a 0.1 molar solution of the
corresponding peroxide in monochlorobenzene, unless stated
otherwise in the individual case.
[0048] Using the Arrhenius frequency factor constant and breakdown
activation energy constant that can be found by searching for the
respective conditions--for instance the solvent used--or can be
calculated from values that can be found by searching, it is
possible to convert the half-lives and the half-life temperatures
to other conditions in each case--for instance in different
solvents--and hence make them comparable.
[0049] With appropriate choice of the peroxides, it has been
possible to crosslink even saturated thermoplastic polymer systems
in spite of good latency--i.e. storage stability without
significant crosslinking or curing under storage conditions with
temperatures up to 40.degree. C. More particularly, it was not to
be expected here that with the peroxides used in accordance with
the invention, especially dicumyl peroxide, as crosslinkers for
saturated thermoplastic polymers lacking C--C multiple bonds, it is
possible to create latently reactive adhesive films having
particularly positive properties that are even superior to those
systems that are hot-curable via reactive groups. Correspondingly,
the invention can provide the advantage arising from the hotmelt
properties of the thermoplastic polymer systems, in combination
with the possibility of excellent crosslinking of the polymer by
means of peroxide in spite of the absence of free-radically
reactive groups.
[0050] Preference is given to using those peroxides that
additionally have high half-lives at moderate
temperatures--especially those well below their activation
temperatures. It is thus possible to achieve good latency
characteristics, i.e. good storage stability, of the thermally
activatable adhesive films comprising the peroxides.
Correspondingly, the at least one peroxide, or the multiple
peroxides used, is chosen such that its half-life is, or their
half-lives are, at 80.degree. C.--i.e., for instance, after a
prelamination process--at least 13.5 hours, especially at least
22.5 hours, preferably at least 69 hours, especially preferably at
least 700 hours. This makes it possible for the thermally
activatable adhesive tape at 80.degree. C. still to have sufficient
processing and application time in that at least 95% of the
peroxide originally used is still present after one hour
(corresponding to t/2=13.5 h), especially still at least 97%
(corresponding to t/2=22.5 h), preferably still at least 99%
(corresponding to t/2=69 h), especially preferably still at least
99.9% of the peroxide used, and was thus not yet available for
reaction.
[0051] In order to guarantee a storage-stable system, the half-life
under customary storage conditions--that may typically, for
instance, be up to 40.degree. C.--should be high. Therefore, the
peroxides used should preferably be chosen such that their
half-life at the storage temperature, preferably up to 40.degree.
C., is sufficiently great that, after 9 months (274 days), at least
75%, preferably 85%, especially preferably 95% or very especially
preferably more than 95% of the peroxide is still available for
crosslinking. The corresponding half-lives can be ascertained by
the relationships given above.
[0052] Peroxides suitable in accordance with the invention are, for
example, representatives from the following groups: dialkyl
peroxides, diacyl peroxides, peroxy esters, peroxydicarbonates,
peroxy ketals, cyclic peroxides, for which the values mentioned in
respect of 1 minute half-life temperature, preferably also in
respect of half-life at 80.degree. C., further preferably also in
respect of half-life at 40.degree. C., are achieved.
[0053] Listed by way of example hereinafter are some
representatives for which this is true from the different groups
that are usable advantageously in accordance with the invention:
dialkylperoxides: di-tert-amyl peroxide, di-tert-butyl peroxide,
tert-butyl cumyl peroxide, dicumyl peroxide,
2,5-dimethyl-2,5-di-(tert-butylperoxy)hexane,
2,5-dimethyl-2,5-di(tert-butylperoxy)-hexyne-3,
di-(2-tert-butylperoxyisopropyl)benzene; diacyl peroxides:
dibenzoyl peroxide, dilauroyl peroxide, diisobutyryl peroxide,
didecanoyl peroxide, di(3,5,5-trimethylhexanoyl) peroxide; ketone
peroxides: acetylacetone peroxide, cyclohexanone peroxide, methyl
ethyl ketone peroxide, methyl isobutyl ketone peroxide; peroxy
esters: tert-butyl peroxyacetate, tert-butyl peroxybenzoate,
tert-butyl peroxydiethylacetate, tert-amyl
peroxy-2-ethylhexylcarbonate, tert-butyl peroxyisopropylcarbonate,
tert-butyl peroxy-2-ethylhexylcarbonate, tert-amyl
peroxy-2-ethylhexanoate, tert-butyl peroxy-2-ethylhexanoate,
1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate,
tert-butylperoxy-3,5,5-trimethylhexanoate,
tert-butylperoxyisobutyrate, tert-butyl monoperoxymaleate,
tert-amyl peroxyneodecanoate, tert-butyl peroxyneodecanoate, cumene
peroxyneodecanoate, 1,1,3,3-tetramethylbutyl peroxyneodecanoate,
tert-butyl peroxyneoheptanoate, tert-amyl peroxypivalate,
tert-butyl peroxypivalate, 1,1,3,3-tetramethylbutyl peroxypivalate,
2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane;
peroxydicarbonates: di-n-peroxydicarbonate, di(2-ethylhexyl)
peroxydicarbonate, di-n-butyl peroxydicarbonate, dicetyl
peroxydicarbonate, dimyristyl peroxydicarbonate,
di(4-tert-butylcyclohexyl) peroxydicarbonate; peroxyketals:
1,1-di-(tert-butylperoxy)-3,3,5-trimethylcyclohexane,
1,1-di-(tert-butylperoxy)-cyclohexane,
2,2-di-(tert-butylperoxy)butane; and cyclic peroxides:
3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane.
[0054] Particularly advantageously in accordance with the
invention, dicumyl peroxide (bis(1-methyl-1-phenylethyl) peroxide)
is used, which has the following half-lives: 812 h at 80.degree. C.
(corresponding to less than 0.1% of the original amount of peroxide
at 80.degree. C. within one hour), 10 h at 112.degree. C.; 1 h at
132.degree. C.; 0.1 h=6 min at 154.degree. C.; 1 min at 172.degree.
C.; all aforementioned values in solution (0.1 molar
monochlorobenzene). Dicumyl peroxide is selected with particular
preference since it can give particularly storage-stable and also
moisture/heat-stable adhesive films. It is also possible to use two
or more peroxides. In a preferred procedure, in that case, dicumyl
peroxide is chosen as one of the two or more peroxides.
[0055] The peroxide(s) used, especially dicumyl peroxide,
are--especially depending on their reactivity--preferably chosen in
an amount that the resulting bond brought about with the adhesive
film has the desired properties and especially satisfies the
specifications defined below in the push-out tests (as a fresh
sample at least 4 MPa, preferably even after defined moisture/heat
storage at least 3 MPa, further preferably not more than 10% losses
after storage under standard climatic conditions for six weeks,
even further preferably not more than 10% losses even after storage
and moisture/heat storage for six weeks; see the respective
specifications further down for the details). In order to meet
these demands, the amounts of peroxide--for example the amount of
dicumyl peroxide--of not less than 0.5% by weight, advantageously
not less than 1% by weight, particularly advantageously not less
than 2% by weight, very particularly advantageously not less than
3% by weight, and of not more than 10% by weight, preferably not
more than 8% by weight, very preferably not more than 7% by weight,
have been found to be very advantageous.
[0056] Peroxides that do not meet the demands according to the
present invention are, for example, a multitude of hydroperoxides,
i.e. compounds of the general formula R--O--O--H in which R is an
organyl group. The list of hydroperoxides that do not lead to the
desired success in accordance with the invention includes, for
example, cumene hydroperoxide, tert-butyl hydroperoxide, p-menthane
hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, tert-amyl
hydroperoxide, diisopropylbenzene monohydroperoxide. It has been
found in accordance with the invention that these hydroperoxides
are incapable of developing good crosslinking within a sufficiently
short processing time in the thermal activation of the adhesives,
and of bringing about the desired advantages. Moreover,
hydroperoxides under thermal stress can exude volatile primary
cleavage products (see also above).
[0057] The adhesive further includes a polymer component that
consists of a single polymer or is composed of multiple polymers.
At least one of the polymers that form the polymer component is a
thermoplastic polymer having no carbon-carbon double bonds, i.e. is
a saturated polymer. Saturated thermoplastic polymers account for
at least 50% by weight of the polymer component and may amount up
to 100% by weight of the polymer component, such that said polymer
component is formed in the latter case exclusively by one or more
saturated thermoplastic polymers. If just one thermoplastic polymer
is present, it is present in the polymer component at from 50% by
weight to 100% by weight.
[0058] The adhesive here in the first embodiment variant may be
composed exclusively of the polymer component and the
peroxide(s).
[0059] Very preferably, polymers used are those having a glass
transition temperature of not more than -25.degree. C., especially
preferably not more than -35.degree. C. All glass transition
temperature figures in the context of this document relate to the
determination of the static glass transition temperature TG by
means of dynamic differential calorimetry (DSC) to DIN 53765,
specifically to the glass transition temperature value Tg to DIN
53765:1994-03, unless stated otherwise in the individual case. Low
glass transition temperatures of the polymers used had advantageous
effects on good shock resistance properties of the composites
produced with the corresponding adhesive films.
[0060] Suitable saturated thermoplastic polymers may advantageously
be chosen from the group of the polyolefins (for example
ethylene-vinyl acetate copolymers (EVA)), the polyethers, the
copolyethers, the polyesters, the copolyesters, the polyamides, the
copolyamides, the polyacrylic esters, the acrylic ester copolymers,
the polymethacrylic esters, the methacrylic ester copolymers, the
thermoplastic polyurethanes and chemically or physically
crosslinked substances formed from the aforementioned compounds.
Furthermore, it is also possible to use blends of various
thermoplastic polymers, especially from the above compound classes.
Particular preference is given to using semicrystalline
thermoplastic polymers.
[0061] Preferred examples are polyolefins--especially
semicrystalline polyolefins. Preferred polyolefins are prepared
from ethylene, propylene, butylene and/or hexylene, it being
possible to polymerize the pure monomers in each case or to
copolymerize mixtures of the monomers mentioned. It is possible
through the polymerization method and through the selection of
monomers to control the physical and mechanical properties of the
polymer, for example the softening temperature and/or specific
mechanical properties.
[0062] Thermoplastic polymers used may preferably be thermoplastic
elastomers, alone or else in combination with one or more
thermoplastic polymers from the aforementioned compound classes.
Particular preference is given to using saturated semicrystalline
thermoplastic elastomers.
[0063] Particular preference is given to thermoplastic polymers
having softening temperatures lower than 100.degree. C. In this
connection, the term "softening point" represents the temperature
from which the granular thermoplastic sticks to itself. It is
advantageously a feature of semicrystalline thermoplastic polymers
that they have not only their softening temperature (which
correlates with the melting of the crystallites)--especially as
characterized above--but also a glass transition temperature of not
more than 25.degree. C.
[0064] Very advantageous examples of thermoplastic elastomers in
the context of the thermoplastic polymers are thermoplastic
polyurethanes (TPU). Polyurethanes are polycondensates that are
typically formed from polyols and isocyanates and contain soft and
hard segments. The soft segments consist, for example, of
polyesters, polyethers, polycarbonates, each preferably aliphatic
in nature in the context of this invention, and hard polyisocyanate
segments. According to the nature and use ratio of the individual
components, it is possible to obtain materials that can be used
advantageously in the context of this invention. Raw materials
available to the formulator for this purpose are specified, for
example, in EP 894 841 B1 and EP 1 308 492 B1.
[0065] In a preferred embodiment of the invention, a thermoplastic
polyurethane lacking C--C multiple bonds is used. The thermoplastic
polyurethane preferably has a softening temperature of less than
100.degree. C., especially less than 80.degree. C.
[0066] In a further preferred embodiment of the invention, a
mixture of two or more saturated thermoplastic polyurethanes is
used. The mixture of the thermoplastic polyurethanes preferably has
a softening temperature of less than 100.degree. C., especially
less than 80.degree. C.
[0067] In a particularly preferred embodiment of the invention,
Desmomelt.RTM. 530 is used as saturated thermoplastic polymer.
Desmomelt.RTM. 530 is a largely linear, thermoplastic, highly
crystallizing polyurethane elastomer commercially available from
Covestro AG (formerly Bayer MaterialScience AG). Desmomelt can also
be used together with other polymers--especially saturated
thermoplastic polymers, preferably further saturated thermoplastic
polyurethanes.
[0068] In a preferred execution of the invention, at least one
adhesion-boosting additive--also referred to as adhesion
promoter--is added to the adhesive. Adhesion promoters are
substances that improve the bonding force of the adhesive film on
the substrate to be bonded. This can especially be accomplished by
an increase in the wettability of the substrate surfaces and/or the
formation of chemical bonds between the substrate surface and the
adhesive or components of the adhesive.
[0069] An advantageous execution of the invention relates to an
adhesive composed exclusively of the polymer component, the
peroxides and the adhesion promoter--the latter especially in the
form of the silanes described hereinafter, and here especially in
such a way that the polymer component used is exclusively one or
more saturated thermoplastic polymers--especially semicrystalline
saturated thermoplastic polymers.
[0070] Adhesion promoters used may advantageously be silane
adhesion promoters. Silane adhesion promoters utilized are
especially compounds of the general form
RR'.sub.aR''.sub.bSiX.sub.(3-a-b) where R, R' and R'' are chosen
independently and each denote a hydrogen atom bonded to the silicon
atom or an organic functionalized radical bonded to the silicon
atom, X denotes a hydrolyzable group, a and b are each 0 or 1, and
where R, R' and R'' or two representatives from this group may also
be identical.
[0071] Adhesion promoters utilized may also be compounds in which,
in the presence of multiple hydrolyzable groups, X are not
identical but differ from one another [corresponding to the formula
RR'.sub.aR''.sub.bSiXX'.sub.cX''.sub.d with X, X', X'' as
independently chosen hydrolyzable groups (of which it is again
alternatively possible for two to be identical), c and d are each 0
or 1, with the proviso that a+b+c+d=2].
[0072] Hydrolyzable groups utilized are especially alkoxy groups,
such that alkoxysilanes in particular are used as adhesion
promoters. The alkoxy groups of a silane molecule are preferably
the same, but they may in principle also be chosen differently.
Alkoxy groups chosen are, for example, methoxy groups and/or ethoxy
groups. Methoxy groups are more reactive than ethoxy groups.
Methoxy groups may therefore have a better adhesion-promoting
effect through faster reaction with the substrate surfaces and it
may therefore be possible to reduce the amount used. Ethoxy groups,
by contrast, have the advantage of having a smaller influence
(possibly a negative one) on the processing time owing to their
lower reactivity, especially also with regard to the desired
moisture/heat stability.
[0073] Adhesion promoters used with preference are:
trialkoxysilanes R--SiX.sub.3. Examples of trialkoxysilanes
suitable in accordance with the invention are
trimethoxysilanes--such as
N-(2-aminoethyl)-3-aminopropyltrimethoxysilane,
N-cyclohexyl-3-aminopropyltrimethoxysilane,
3-aminopropyltrimethoxysilane, 3-ureidopropyltrimethoxysilane,
vinyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane,
3-methacryloyloxypropyl-trimethoxysilane,
methacryloyloxymethyltrimethoxysilane,
N-methyl-[3-(trimethoxysilyl)propyl]carbamate,
N-trimethoxysilylmethyl-O-methylcarbamate,
tris[3-(trimethoxysilyl)propyl] isocyanurate,
3-glycidoxypropyltrimethoxysilane, methyltrimethoxysilane,
isooctyltrimethoxysilane, hexadecyltrimethoxysilane,
3-mercaptopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane,
N-(2-aminoethyl)-3-aminopropyltrimethoxysilane,
N-phenyl-3-aminopropyltrimethoxysilane,
N-ethyl-3-aminoisobutyltrimethoxysilane,
bis[3-(trimethoxysilyl)propyl]amine,
3-isocyanatopropyltrimethoxysilane,
2-(3,4-epoxycyclohexyl)ethyl-trimethoxysilane;
3-methacryloyloxypropyltrimethoxysilane,
3-methacrylamidopropyl-trimethoxysilane, p-styryltrimethoxysilane,
3-acryloyloxypropyltrimethoxysilane,
N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane
hydrochloride, triethoxysilanes--such as
N-cyclohexylaminopropyltriethoxysilane,
3-aminopropyl-triethoxysilane, 3-ureidopropyltriethoxysilane,
3-(2-aminomethylamino)propyltriethoxysilane, vinyltriethoxysilane,
3-glycidoxypropyltriethoxysilane, methyltriethoxysilane,
octyltriethoxysilane, isooctyltriethoxysilane,
phenyltriethoxysilane, 1,2-bis(triethoxysilane)ethane,
3-octanonylthio-1-propyltriethoxysilane;
3-aminopropyltriethoxysilane, bis[3-(triethoxysilyl)propyl]amine,
3-isocyanatopropyltriethoxysilane,
2-(3,4-epoxycyclohexyl)ethyltriethoxysilane,
3-methacryloyloxypropyltriethoxysilane,
3-methacrylamidopropyltriethoxysilane,
3-triethoxysilyl-N-(1,3-dimethylbutadiene)propylamide,
triacetoxysilanes--such as vinyltriacetoxysilane,
3-methacryloyloxypropyltriacetoxysilane, triacetoxyethylsilane, and
mixed trialkoxysilanes--such as
3-methacrylamidopropylmethoxydiethoxysilane,
3-methacryl-amidopropyldimethoxyethoxysilane.
[0074] Examples of dialkoxysilanes suitable in accordance with the
invention are: dimethoxysilanes--such as
N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane,
vinyldimethoxymethylsilane,
(methacryloyloxymethyl)methyldimethoxysilane,
methacryloyloxymethylmethyldimethoxysilane,
3-methacryloyloxypropylmethyldimethoxysilane,
dimethyldimethoxysilane, (cyclohexyl)methyldimethoxysilane,
dicyclopentyldimethoxysilane,
3-glycidoxypropylmethyldimethoxysilane,
3-mercaptopropylmethyldimethoxysilane, diethoxysilanes--such as
dimethyldiethoxysilane, gamma-aminopropylmethyldiethoxysilane;
3-glycidoxypropylmethyldiethoxysilane, and
3-methacryloyloxypropylmethyldiethoxysilane. One example of a
monooxysilane is trimethyloxysilane.
[0075] The amount of added adhesion promoters may in principle be
chosen within a wide range, according to the desired properties of
the product and taking account of the raw materials chosen for the
adhesive film. However, it has been found to be very advantageous
in accordance with the invention when the amount of the adhesion
promoter used, based on the adhesive used, is in the range from
0.5% to 20% by weight, preferably in the range from 1% to 10% by
weight, especially preferably from 1.5% to 5% by weight, very
especially preferably in the range from 2.5% to 3.5% by weight.
[0076] Very high amounts of adhesion promoters used can have a
strong plasticizing effect, such that it can be
advantageous--especially with regard to adequate stability of
films--to choose as small an amount as possible of adhesion
promoter such that the desired positive effect on moisture/heat
stability is sufficiently large on the one hand, without having an
adverse effect on the properties of the adhesive film with regard
to dimensional stability and stability thereof on the other
hand.
[0077] Adhesive Films
[0078] The adhesive of the invention in layer form more preferably
forms an adhesive film or is--alongside one or more further
layers--part of an adhesive film. The invention thus also
encompasses adhesive films composed of the adhesive of the
invention and adhesive films comprising a layer of the adhesive of
the invention.
[0079] The adhesive films of the invention may be of single-layer
construction--i.e. composed solely of the layer of the parent
adhesive--or else of multilayer construction, for instance provided
with a reinforcing or carrier layer. Single-layer systems are
advantageous, called transfer adhesive tapes.
[0080] Carriers utilized may in principle be any layers composed of
the materials suitable for the purpose that are known to those
skilled in the art, according to the desired properties of the
product and stability in the thermal activation. For example, it is
possible to use carrier material such as textile materials, weaves,
nonwovens, papers, polymer films, for example mono- or biaxially
stretched, optionally oriented polyolefins, polyvinylchloride films
(PVC), polypropylene films, polyethylene (PE) films, such as HDPE
and LDPE films, polyethylene terephthalate films (PET), polylactide
films, and foams and weaves. Carrier materials may have high or low
extensibility and/or flexibility and be chosen, for example, to be
tear-resistant or slightly tearable. Carriers utilized may in
principle be especially cohesive rubber films or adhesive
composition layers that are likewise suitable, for instance
pressure-sensitive adhesives or activatable adhesives that provide
appropriate intrinsic stability and meet the demands on the bonding
conditions for the adhesive films.
[0081] The adhesive films may be covered with a protective material
on one or both sides, called "liners". Liners serve for temporary
protection and for handling of the adhesive tape and are removed
again for the application. In the context of the present invention,
such liners are considered to be procedural aids, but not to be an
actual part of the adhesive films of the invention. Liners may be
paper or films, equipped with a release agent at least on the side
facing the adhesive film of the invention. The papers or films in
question may thus also have been modified to be slightly
pressure-sensitively adhesive (called tacky liners).
[0082] According to the invention, it is also possible to provide
laminate adhesive tapes, i.e. adhesive tapes composed of a
multitude of adhesive layers arranged one on top of another.
Laminates are advantageous, for example, when thicker carrier-free
adhesive tapes are to be produced by simple processes, since it is
generally simpler to produce thin adhesive layers and then to
laminate them with one another than to coat adhesive layers of the
resulting total thickness directly to give a uniform homogeneous
product.
[0083] Adhesive layers, transfer adhesive tapes and laminate
adhesive tapes of the invention may be configured from very thin
designs--in the region of a few micrometers--up to very thick
layers--in the region of several centimeters. Accordingly,
multilayer adhesive tapes--especially also those that comprise
further layers as well as the adhesive layers--may vary in their
thickness resulting from the respective thickness of the adhesive
layers--as described above--and of the further layers used, such as
carrier layers, pressure-sensitive adhesives, functional (e.g.
thermally or electrically conductive) layers, primer layers and the
like.
[0084] Typical layer thicknesses for single-layer adhesive films of
the invention are in the range from 1 to 250 .mu.m, for example 5,
20, 25, 50, 75, 100, 125, 150, 175 or 200 .mu.m. Correspondingly
higher layer thicknesses are possible in the case of laminate
adhesive tapes, for example in the range from 5 .mu.m to 5 mm or
even more.
[0085] The adhesive films of the invention are self-supporting and
hence independent products, meaning that they can be readily
stored, transported and applied. This distinguishes them
significantly from "adhesive films" composed of liquid adhesives,
i.e. adhesive layers that exist only after they have been applied
to the respective substrate to be bonded, where they are solidified
in the course of their application in use, but are not removed
again from the substrate as an independent product. For instance,
adhesive films of the invention can be wound up together to give a
roll or supplied as sections, blanks or die-cuts. Accordingly, the
invention also provides any blanks and die-cuts of adhesive films
of the invention.
[0086] The adhesive films of the invention have a very broad
application window in order to achieve bonds having the desired
qualities. Compared to those adhesive films activatable at low
temperatures as disclosed by the prior art--cf., for instance, WO
93/25599 A and DE 10 2010 013 145 A--it is possible to achieve very
much shorter cycle times, at the limits of which the prior art
adhesive films no longer lead to the required performance.
[0087] Effective bonding by means of the adhesive films with
activation thereof means an interaction of temperature, time (cycle
time); the lower the level chosen for one of the parameters, the
higher the level that can or has to be chosen for another
parameter. With higher temperatures, it is possible, for instance,
to achieve shorter cycle times. If the cycle time can be extended,
it is possible to work at lower temperature.
[0088] The compression pressure in this connection is primarily a
process parameter and is dependent on the raw materials used in the
formulation, in combination with the cycle time. For instance, an
elevated pressure can promote adaptation to the substrates and the
wetting of the substrates in the case of formulations having
elevated melt viscosity in combination with short cycle times. In
the case of formulations having a relatively low melt viscosity,
especially in combination with relatively long cycle times, a lower
pressure may be advantageous in order to avoid unwanted "oozing" of
the adhesive out of the bonded joint. For the advantageous and
inventive formulations ascertained here, it was advantageously
possible, for example, to work with a compression pressure of 10
bar, although the invention is not limited to this compression
pressure.
[0089] Particularly the contact time in the activation of the
adhesive film (the activation time) can be considerably reduced by
possible variations in the other parameters within the parameter
limits available, which arise from the stability of the substrates
to be bonded.
[0090] In principle, the maximum permitted temperature is
determined by the substrates to be bonded. For many of the desired
applications (for instance the bonding of plastics and/or anodized
substrates), the temperature chosen should not be higher than
200.degree. C. in order not to damage the substrates. It is
fundamentally the case here that the higher the temperature chosen,
the shorter cycle time should be, in order to expose the substrates
to a minimum damaging heat exposure. According to the invention, it
has been possible to reduce the cycle time to less than 10 s at a
temperature of 200.degree. C., and to 10 s at 190.degree. C.
(pressure 10 bar in each case). At temperatures below 170.degree.
C., by contrast, maximum cycle times of up to one minute,
advantageously up to 30 s, may be acceptable. In general, a minimum
cycle time at a maximum possible temperature, depending on the
sensitivity of the substrates to be joined, is advantageous in
order to increase productivity in the processing operation.
[0091] The adhesive films of the invention have good storability
without losing their positive properties as adhesive films. More
particularly, it has been found that the adhesive films of the
invention, even after storage for six weeks, are capable of
establishing bond strengths to a substrate that are still at least
90% of the bond strengths of the freshly produced adhesive
films--which have especially been stored for not longer than one
day.
[0092] Moreover, it has been found that the adhesive films of the
invention provide a further advantage: the bonds by means of
latently reactive adhesive films--including those based on
polyurethane--according to the prior art, as described, for
instance, in the already cited WO 93/25599 A and DE 10 2010 013 145
A, regularly have limited stability under moist/hot conditions.
This is connected to the fact that moisture is capable of
penetrating into the adhesive bond between substrate surface and
adhesive film with time and hence weakens the adhesive bond. The
adhesive films of the invention, by contrast, can achieve bonds
that have excellent stabilities under moist/hot conditions even
over a prolonged period of time.
[0093] Moisture/heat stability can be optimized in that one or more
adhesion promoters are added to the adhesive which is utilized for
production of the latently reactive adhesive film of the invention.
Adhesion promoters used here may be substances that improve the
adhesion of the adhesive film to the substrate surface.
[0094] A quantitative criterion for the bonding properties of an
adhesive film is considered to be what is called the push-out test
in particular. For the push-out test, a substrate in disk form is
bonded to a second substrate in frame form with an adhesive film
sample and then the force that has to be applied in order to
separate the two substrates from one another again is ascertained
(cf. the further details further down in this document; Test Method
A).
[0095] In a preferred manner, the adhesive films of the invention
have good bond strength. The bond strength is quantified by the
result of the push-out test. Preferably, the adhesive films of the
invention, as a fresh sample (freshly-coated adhesive film after
drying at 70.degree. C. for 30 min in a suitable air circulation
drying cabinet and subsequent conditioning under standard climatic
conditions (23.degree. C./50% RH) for 24 h), have, in the push-out
test (measurement of force to part an adhesive bond of a
polycarbonate disk (Makrolon 099) with a frame made of anodized
aluminum (E6EV1) by means of a layer of the adhesive film to be
examined, of thickness 100 .mu.m, with an effective bond area of
282 mm.sup.2 [for further details see also tests A and B]) a force
value of at least 3 MPa, preferably at least 4 MPa, preferably
after bonding under the Bonding Condition I., further preferably
also by the Bonding Condition II., and even further preferably also
under the Bonding Condition Ill. Bonding Condition I. is as
follows: pre-lamination 70.degree. C., 15 s; final bonding
(compression conditions) 190.degree. C., 10 s; 10 bar; conditioning
of the adhesive bond at 23.degree. C. for 24 h/50% RH [RH stands
for relative humidity]; and testing in each case at 23.degree. C.,
50% RH. Bonding Condition II. is as follows: pre-lamination
70.degree. C., 15 s; final bonding (compression conditions)
180.degree. C., 12 s; 10 bar; conditioning of the adhesive bond at
23.degree. C. for 24 h/50% RH; and testing in each case at
23.degree. C., 50% RH. Bonding Condition Ill. is as follows:
pre-lamination 70.degree. C., 15 s; final bonding (compression
conditions) 170.degree. C., 30 s; 10 bar; conditioning of the
adhesive bond at 23.degree. C. for 24 h/50% RH; and testing in each
case at 23.degree. C., 50% RH.
[0096] In a further very preferred manner, the adhesive films of
the invention additionally have good moisture/heat stability. For
quantification of moisture/heat stability, it is likewise possible
to employ the push-out test, specifically after defined storage (72
h at 85.degree. C. and 85% RH) of the adhesive bond to be examined,
established by means of the adhesive film of the invention. The
details of this test are described in detail in the experimental
section below (Test Methods A and B).
[0097] The adhesive films of the invention have, in the push-out
test, even after moist/hot storage (measurement of force to part an
adhesive bond of a polycarbonate disk (Makrolon 099) with a frame
made of anodized aluminum (E6EV1) by means of a layer of the
adhesive film to be examined, of thickness 100 .mu.m, with an
effective bond area of 282 mm.sup.2), a force value of at least 3
MPa, preferably in all three cases by bonding under the
aforementioned Bonding Conditions I., II. and III.
[0098] In addition--in combination with the aforementioned minimum
values--the bond strength--meaning the aforementioned push-out
force value--of the adhesive bond that has been stored under
moist/hot conditions should preferably be more than 50% of the
adhesive bond that has not been stored under moist/hot conditions;
more preferably, the bond strength of the adhesive bond stored
under moist/hot conditions should be more than 75% of the adhesive
bond not stored under moist/hot conditions; and very preferably,
the bond strength of the adhesive bond stored under moist/hot
conditions should be more than 90% of the adhesive bond not stored
under moist/hot conditions or even exceeds the value of the bond
not stored under moist/hot conditions.
[0099] Latently reactive adhesive systems refer to those
activatable adhesives that are storable in a stable manner over
prolonged periods of time without activation. Preferred latently
reactive adhesive films are those that do not cure, or cure only
over a period of months, under standard climatic conditions
(23.degree. C. [296.15 K]; 50% RH) and hence are storage-stable,
but which--for example at much higher temperatures--are activatable
(cf. also the "latency" test in the experimental) and cure and/or
crosslink. The latent reactivity offers the advantage that these
adhesive films can be stored, transported and processed further
(for example configured) under standard climatic conditions before
they then arrive at the bonding site and are cured.
[0100] The adhesives here should not change significantly during
the storage time, such that there is no material difference in the
bonding properties of an adhesive system employed freshly after the
establishment of the bond and of an adhesive system employed after
prolonged storage for otherwise comparable bonding. The latent
reactivity (also referred to as latency in the context of the
document) of the adhesive films can also be quantified via the
push-out test.
[0101] For the purposes of the present document, adhesive films are
considered to be latently reactive especially when an adhesive film
sample stored after 18 weeks a) under standard laboratory
conditions (23.degree. C. [296.15 K]; 50% RH), preferably also an
adhesive film sample stored b) at 40.degree. C. in a suitable
commercial air circulation drying cabinet (drying cabinet under
standard climatic conditions), by comparison with otherwise
identical fresh sample in the push-out test (measurement of force
to part an adhesive bond of a polycarbonate disk (Makrolon 099)
with a frame made of anodized aluminum (E6EV1) by means of a layer
of the adhesive film to be examined at an effective bonding area of
282 mm.sup.2), has not more than 10% losses, preferably in all
three cases after bonding under the aforementioned Bonding
Conditions I., II. and Ill.
[0102] Further preferably, the adhesive films are also stable in
relation to moisture/heat characteristics, i.e. have, in the
push-out test of the adhesive bond, even after prolonged storage of
the adhesive film prior to establishment of the bond [at least
after storage a) for 18 weeks under standard laboratory conditions
(23.degree. C. [296.15 K]; 50% RH), preferably also after
alternative storage b) at 40.degree. C. in a suitable commercial
air circulation drying cabinet (drying cabinet under standard
climatic conditions)], and after further moisture/heat storage (72
h at 85.degree. C. and 85% RH) of the adhesive bond established,
only admissible variances from the corresponding values for an
adhesive bond of adhesive films stored correspondingly but without
moisture/heat storage of the composite.
[0103] The adhesive films after prolonged storage are also
considered to have moisture/heat stability--in accordance with
criteria already specified above--when the bond strength of the
adhesive bond stored under moist/hot conditions is more than 50% of
the adhesive bond not stored under moist/hot conditions, and to
have good moisture/heat stability when the bond strength of the
adhesive bond stored under moist/hot conditions is more than 75% of
the adhesive bond not stored under moist/hot conditions, and to
have very good moisture/heat stability when the value of the bond
strength of the composite stored under moist/hot conditions exceeds
at least 90% of the value of the unstored sample. The determination
of bond strength corresponds here to the push-out test already
specified.
[0104] The adhesive films of the invention are suitable in
principle for bonding of all substrates, both of rigid and of
flexible materials. The substrates to be bonded may have various
configurations, thicknesses and the like. Examples here include
glass, all kinds of plastics, metal, ceramic, textiles, all kinds
of materials, artificial leather . . . in each case with the same
material and also with one another.
[0105] It is optionally possible to add tackifier resins to the
adhesive used for the adhesive films of the invention. The term
"tackifier resin" is understood by the person skilled in the art to
mean a resin-based substance that further increases bond strength.
Tackifiers used may be the standard tackifier resins, for example
hydrocarbon resins, polyterpene resins and terpene-phenol resins,
and also rosin and rosin derivatives. Formulation is in accordance
with the general rules. Reference is made to the description of the
state of knowledge relating to tackifier resins in the "Handbook of
Pressure Sensitive Adhesive Technology" by Donatas Satas (van
Nostrand, 1989) (chapter 25). Any combinations of these or other
tackifier resins may be used in order to adjust the properties of
the resulting adhesive and of the adhesive films obtainable
therefrom as desired.
[0106] The adhesive may additionally contain further formulation
constituents. Examples of these include fillers and/or additives,
for example thermally and/or electrically conductive additives,
pigments, dyes, catalysts, aging stabilizers, light stabilizers,
processing auxiliaries and further substances for establishment of
specific adhesive properties, although this enumeration should not
be considered to be conclusive.
EXPERIMENTAL
[0107] The test methods described hereinafter are used to evaluate
the adhesive film samples of the invention and the comparative
samples.
[0108] Push-Out Test (Test Method A):
[0109] The push-out test enables conclusions as to the bond
strength of an adhesive product in the direction of the adhesive
layer normal. The following are provided: a circular first
substrate (1) (polycarbonate, Macrolon 099, thickness 3 mm) with
diameter 21 mm, a second substrate (2) (anodized aluminum, E6EV1,
thickness 1.5 mm)--for example square with side length 40 mm--with
a circular opening disposed in the center (bore) of diameter 9 mm,
and the adhesive film sample to be examined, likewise in circular
configuration with diameter 21 mm (cut to size or punched).
[0110] The three aforementioned components are used to establish a
test specimen by pre-laminating the adhesive product with the open
surface accurately fitting the substrate (1) (at 70.degree. C. for
15 s). Then the temporary carrier is removed and this composite is
concentrically pre-laminated by the now exposed side of the
adhesive product onto the substrate (2) (likewise at 70.degree. C.
for 15 s), i.e. in such a way that the circular cutout of the
substrate (2) is arranged exactly in the middle above the circular
first substrate (1) (bonding area thus 282 mm.sup.2). It is ensured
that the total thermal contact time (70.degree. C.) in the
pre-lamination process does not exceed 30 s. Subsequently, the
overall composite is compressed thermally under pressure, giving
rise to the test specimen. The compression conditions are specified
in the evaluation.
[0111] After the compression, the test specimens are stored
(reconditioned) at 23.degree. C. and 50% relative humidity (RH)
(standard climatic conditions) for 24 h.
[0112] The testing is effected as follows: a tensile tester is
equipped with a cylindrical ram (steel, diameter 7 mm) and the test
specimen is clamped into a holder of the tensile tester above
substrate (2), such that substrate (1) is held solely by the
adhesive bond and can be detached through sufficient pressure by
parting of the bond. The sample is fixed in such a way that bending
of substrate (2) which is possible by application of force during
the testing is minimized. The cylindrical ram pushes
perpendicularly through the hole in substrate (2) (i.e. parallel
oppositely to the normal vector of the adhesive product surface)
and centrally onto the exposed area of the adhesive product at a
constant speed of 10 mm/s; the tests take place under standard
climatic conditions (23.degree. C. at 50% RH).
[0113] The force recorded is that at which the bond fails and
substrate (1) is parted from substrate (2) (parting of the adhesive
bond, apparent from the abrupt pressure drop). The force is
normalized to the bond area (N/mm.sup.2 or MPa). Owing to the
naturally high scatter of the individual results, as a result of
the adhesive failure that usually occurs (failure at the
substrate-adhesive film interface), the arithmetic mean is
calculated from three individual tests.
[0114] Moisture/Heat Stability (Test Method B):
[0115] Test specimen preparation and testing are effected
analogously to the push-out test, except that the test specimens,
after compression at 23.degree. C. and 50% relative humidity (RH)
(standard climatic conditions) for 24 h, are stored and then
subjected while in the upright position (on one of the 40 mm
longitudinal sides of the base plate) to moist/hot storage (at
85.degree. C. and 85% RH for 72 h) and conditioned again prior to
testing at 23.degree. C. and 50% RH for 24 h.
[0116] Should substrate (1) slide off substrate (2) during the
moist/hot storage (or the substrates recognizably slip with respect
to one another), the sample has failed and moisture/heat stability
is inadequate.
[0117] The abovementioned criteria for moisture/heat stability are
employed as a scale (moisture/heat stability: push-out value of the
adhesive bond stored under moist/hot conditions is more than 50% of
the adhesive bond not stored under moist/hot conditions; good
moisture/heat stability: push-out value of the adhesive bond stored
under moist/hot conditions is more than 75% of the adhesive bond
not stored under moist/hot conditions; very good moisture/heat
stability: push-out value of the adhesive bond stored under
moist/hot conditions is more than 90% of the adhesive bond not
stored under moist/hot conditions or even exceeds the value of the
composite not stored under moist/hot conditions).
[0118] Latency:
[0119] One portion of the latently reactive adhesive films is
stored prior to the establishment of the bonded test specimens at
40.degree. C. in a drying cabinet under standard climatic
conditions for 18 w; another portion is stored under standard
climatic conditions and then the push-out test and the
moisture/heat stability are assessed. The abovementioned criteria
for latency and moisture/heat stability are employed as a
scale.
[0120] Process/Application Window:
[0121] The reactive adhesive films are assessed under various
compression conditions (variation of cycle time=activation time and
temperature) with regard to push-out performance. The process
window is defined by a time-temperature window in which the
push-out values ascertained vary by not more than 25% from the
maximum push-out value ascertained. The maximum activation time
actually achievable can extend beyond the maximum cycle time
envisaged for establishment of the maximum value.
[0122] Shock Performance:
[0123] The heat-activatable adhesive film to be examined is used to
bond a test specimen produced from substrates (1) and (2) as
described under "push-out test" and under defined conditions using
a hot press (see the individual measurements).
[0124] The pre-lamination to the polycarbonate disk (substrate (1);
Makrolon 099, machined burr-free, diameter 21 mm, thickness 3 mm)
takes place by means of a hotplate at 70.degree. C.
[0125] The single-sided covered, heat-activatable adhesive film is
placed onto the hotplate with the covered side downward.
[0126] The heating on the hotplate makes the heat-activatable films
pressure-sensitively adhesive/tacky, and the substrate (1) can be
pre-laminated onto the adhesive film with gentle applied pressure
within 3 to 5 s, with the total period of thermal stress not
exceeding 30 s. After cooling, the composite of substrate (1) and
adhesive film is cut out very accurately with scissors.
[0127] Substrate (2) (base plate--40 mm.times.40 mm anodic aluminum
sheet with a central burr-free bore diameter 9 mm, thickness 1 mm)
is then placed onto the hotplate for preheating for 1-2 minutes and
removed for pre-lamination.
[0128] The remaining liner is pulled off the substrate (1)-adhesive
film composite and placed onto the preheated aluminum base plate
(substrate (2)) in an exactly centered manner and fixed by means of
gentle contact pressure. The finished pre-laminated test specimen
is then pressed with a suitable laboratory press with appropriately
set parameters (time, pressure, temperature), with introduction of
heat through the aluminum base plate facing downward.
[0129] After the compression, the test specimens are conditioned at
23.degree. C./50% relative humidity for 24 hours.
[0130] Immediately after storage, the adhesive bond is clamped to a
sample holder in a way that the composite is aligned
horizontally.
[0131] The test specimen is introduced into the sample holder with
the polycarbonate disk (substrate (1)) downward. The sample holder
is then inserted centrally into the envisaged receptacle of the
DuPont Impact Tester. The impact head, of weight 360 g, is used in
such a way that the circularly rounded impact geometry with the
diameter of 5 mm lies centrally and flush against the bonding side
of substrate (1).
[0132] A weight having a mass of 800 g guided on two guide rails is
allowed to fall vertically from a height of 5 cm onto the composite
composed of sample holder, sample and impact head in this
arrangement (measurement conditions: 23.degree. C., 50% relative
humidity). The height from which the weight falls is increased in 5
cm steps until the impact energy introduced breaks the sample as a
result of the impact stress and the polycarbonate disk (substrate
(1)) becomes detached from the base plate (substrate (2)).
[0133] In order to be able to compare experiments with different
samples, the energy is calculated as follows:
E[J]=height [m]*mass of weight [kg]*9.81 kg/m*s.sup.2
[0134] Five samples per product are tested, and the energy average
is reported as the index for impact resistance.
[0135] Instrument: DuPont Impact Tester (from Cometech, TAIWAN,
Model QC-641)
EXAMPLES
[0136] Adhesive Films Examined
[0137] Commercially available products are used as obtainable in
January 2018.
[0138] Desmomelt.RTM. 530 is a largely linear, thermoplastic,
highly crystallizing polyurethane elastomer. Reference is made to
the following product data sheet: Desmomelt.RTM. 530 product data
sheet, 2016-01-19 edition, Covestro AG, Leverkusen.
[0139] Desmocoll.RTM. 530/1 and Desmocoll.RTM. 540/3 are likewise
largely linear, thermoplastic, elastic hydroxy polyurethanes having
significant tendency to crystallization, available from Covestro
AG. The Desmocoll.RTM. 540/3 product has a higher crystallization
rate and higher solution viscosity than the Desmocoll.RTM.530/1
product.
[0140] Example 1: 100% by weight of Desmomelt.RTM.530 (Covestro
AG)
[0141] Example 2: 100% by weight of Desmocoll 530/1 (Covestro
AG)
[0142] Example 3: 100% by weight of Desmocoll 540/3 (Covestro
AG)
[0143] Example 4: 95% by weight of Desmomelt.RTM.530 (Covestro AG)
[0144] 5% by weight of dicumyl peroxide (CAS 80-43-3)
[0145] Example 5: 95% by weight of Desmocoll 530/1 (Covestro AG)
[0146] 5% by weight of dicumyl peroxide (CAS 80-43-3)
[0147] Example 6: 95% by weight of Desmocoll 540/3 (Covestro AG)
[0148] 5% by weight of dicumyl peroxide (CAS 80-43-3)
[0149] Example 7: 92% by weight of Desmomelt.RTM.530 (Covestro AG)
[0150] 5% by weight of dicumyl peroxide (CAS 80-43-3) [0151] 3% by
weight of 3-methacryloyloxypropytriethoxysilane (CAS
21142-29-0)
[0152] Example 8: 92% by weight of Desmomelt.RTM.530 (Covestro AG)
[0153] 5% by weight of dicumyl peroxide (CAS 80-43-3) [0154] 3% by
weight of 3-methacryloyloxypropyltrimethoxysilane (CAS
2530-85-0)
[0155] Example 9: 92% by weight of Desmomelt.RTM.530 (Covestro AG)
[0156] 5% by weight of dicumyl peroxide (CAS 80-43-3) [0157] 3% by
weight of [3-(2,3-epoxypropoxy)propyl]triethoxysilane (CAS
2602-34-8)
[0158] Example 10: 92% by weight of Desmomelt.RTM.530 (Covestro AG)
[0159] 5% by weight of dicumyl peroxide (CAS 80-43-3) [0160] 3% by
weight of 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane (CAS
10217-34-2)
[0161] Example 11: 92% by weight of Desmomelt.RTM.530 (Covestro AG)
[0162] 5% by weight of dicumyl peroxide (CAS 80-43-3) [0163] 3% by
weight of vinyltriethoxysilane (CAS 78-08-0)
[0164] Example 12: 72% by weight of Desmomelt.RTM.530 (Covestro AG)
[0165] 20% by weight of tris[2-(acryloyloxy)ethyl] isocyanurate
(CAS 40220-08-04) [0166] 5% by weight of dicumyl peroxide (CAS
80-43-3) [0167] 3% by weight of
3-methacryloyloxypropyltrimethoxysilane (CAS [0168] 2530-85-0)
[0169] Example 13: 94% by weight of Desmomelt.RTM.530 (Covestro AG)
[0170] 5% by weight of dicumyl peroxide (CAS 80-43-3) [0171] 1% by
weight of 3-methacryloyloxypropyltriethoxysilane (CAS
21142-29-0)
[0172] Example 14: 93% by weight of Desmomelt.RTM.530 (Covestro AG)
[0173] 5% by weight of dicumyl peroxide (CAS 80-43-3) [0174] 2% by
weight of 3-methacryloyloxypropyltriethoxysilane (CAS
21142-29-0)
[0175] Example 15: 94% by weight of Desmomelt.RTM.530 (Covestro AG)
[0176] 5% by weight of dicumyl peroxide (CAS 80-43-3) [0177] 1% by
weight of 3-methacryloyloxypropyltrimethoxysilane (CAS
2530-85-0)
[0178] Example 16: 93% by weight of Desmomelt.RTM.530 (Covestro AG)
[0179] 5% by weight of dicumyl peroxide (CAS 80-43-3) [0180] 2% by
weight of 3-methacryloyloxypropyltrimethoxysilane (CAS
2530-85-0)
[0181] Examples 1 to 3 (above) are comparative examples (without
addition of dicumyl peroxide); and Examples 4 to 16 (above) are
inventive examples.
[0182] The respective components were dissolved homogeneously in
methyl ethyl ketone (CAS 78-93-3) corresponding to the respective
composition, such that the total content of the aforementioned
compositions (Examples 1 to 12; sum total of the components
mentioned in each case) in the solvent was 25% by weight. The
solution was then coated in each case by known methods onto a
release paper known by the person skilled in the art to be suitable
for silane-containing compositions and dried in a suitable air
circulation drying cabinet at 70.degree. C. for 30 min, so as to
result in each case in an adhesive film of 100 .mu.m (dry film
thickness).
[0183] The corresponding adhesive films are examined by the test
methods cited above as fresh specimens (within . . . after the
above drying, reported as "initial") or after defined storage in a
drying cabinet in a climate-controlled room (see details in the
individual experiments in the table), which led to the following
results (a: standard deviation from multiple measurements):
TABLE-US-00001 TABLE 1 Push-out test/moisture/heat stability test
results Push-out Moisture/heat stability Example MPa .sigma. MPa
.sigma. 1 4.7 0.48 failed -- 2 4.5 0.16 failed -- 3 4.0 0.55 failed
-- 4 4.3 0.13 3.2 0.84 5 4.4 0.05 3.1 0.74 6 4.4 0.20 3.1 0.69 7
5.8 0.54 7.8 0.34 8 6.7 0.42 7.8 0.45 9 6.1 0.53 4.0 0.32 10 4.6
0.24 4.4 0.36 11 6.2 0.46 4.0 0.44 12 6.8 0.24 3.8 0.27 13 4.6 0.67
6.9 0.53 14 5.4 0.47 7.1 0.37 15 5.0 0.82 6.8 0.20 16 6.1 0.63 6.8
0.33 Adhesive films corresponding to the respective examples;
initial testing (fresh sample without further storage). Compression
conditions (production of the test specimens): 12 s @ 180.degree.
C. @ 10 bar Moisture/heat stability: 72 h @ 85.degree. C. @ 85% RH
Failure: slippage of substrate (1), blistering
[0184] The test results in Table 1(see above) show that only
inventive Examples 4 to 16 with use of dicumyl peroxide meet the
demands set in accordance with the invention (push-out value at
least 4 MPa, after moist/hot storage still >3 MPa), whereas
comparative examples 1 to 3without use of peroxides failed in the
moist/hot storage.
[0185] The use of silane compounds as adhesion promoters (Examples
7 to 16) can further improve moisture/heat resistance compared to
the examples without silane (Examples 4 to 6).
TABLE-US-00002 TABLE 2 Latency test results Push-out Moisture/heat
stability Storage MPa .sigma. MPa .sigma. initial 5.12 1.02 5.91
0.56 8 w @ RT 5.87 0.21 5.76 0.18 18 w @ RT 5.94 0.33 6.30 0.38 4 w
@ 40.degree. C. 5.06 0.47 5.58 0.37 10 w @ 40.degree. C. 5.56 0.24
5.87 0.87 18 w @ 40.degree. C. 5.36 0.76 5.12 0.48 Adhesive film
according to Example 8. Storage of the adhesive films prior to
production of the test specimens as specified in the table.
Compression conditions (production of the test specimens): 10 s @
190.degree. C. @ 10 bar For results in graph form, see FIG. 1.
[0186] It is apparent from the results in Table 2 (see above) that
both initial force values and those after defined storage in the
push-out test in the region of 5 MPa or more can be achieved, and
the requirements of the invention are thus met.
TABLE-US-00003 TABLE 3 Push-out and Moisture/heat stability test
results Compression Push-out Moisture/heat stability Example Time
MPa .sigma. MPa .sigma. 7 12 s 6.3 0.56 5.6 0.03 30 s 6.7 0.06 6.6
0.25 60 s 6.6 0.15 6.2 0.47 8 12 s 6.8 0.25 5.8 0.32 30 s 6.8 0.1
7.1 0.1 60 s 6.5 0.17 6.5 0.37 Storage: 18 w @ 40.degree. C.
Compression conditions (production of the test specimens):
180.degree. C. @ 10 bar for the time specified in each case
Moisture/heat stability: 72 h @ 85.degree. C. @ 85% RH
[0187] All the samples of the invention examined in Table 3 (see
above) have been shown to meet the demands made (push-out value at
least 4 MPa, after moist-hot storage still >3 MPa.
TABLE-US-00004 TABLE 4 Process window results Compression Push-out
Example Time Temperature MPa .sigma. 8 30 s 100.degree. C. 5.21
2.97 60 s 100.degree. C. 7.28 0.43 120 s 100.degree. C. 8.18 0.60
30 s 125.degree. C. 8.07 0.35 60 s 125.degree. C. 8.43 0.29 120 s
125.degree. C. 8.67 0.45 30 s 150.degree. C. 8.38 0.25 60 s
150.degree. C. 8.55 0.34 120 s 150.degree. C. 8.71 0.20 12 s
180.degree. C. 6.70 0.42 30 s 180.degree. C. 6.80 0.33 60 s
180.degree. C. 6.54 0.35 120 s 180.degree. C. 6.00 0.26 Adhesive
film according to Example 8; initial testing (fresh sample without
further storage). Compression conditions (production of the test
specimens): 5 bar, cycle time and temperature as specified.
[0188] It was found in the testing shown in Table 4 (see above)
that compression conditions at 100.degree. C. for 30 s and at
180.degree. C. for 120 s are outside the process window since the
push-out values are below the target value of 6.53 MPa
[=0.75*maximum push-out value=0.75*8.71 MPa, maximum push-out value
under compression conditions 120 s; 150.degree. C.].
TABLE-US-00005 TABLE 5 Shock performance Compression conditions E
[J] .sigma. 30 s @ 170.degree. C. @ 10 bar 57 4.45 10 s @
190.degree. C. @ 10 bar 55 4.32 Adhesive film according to Example
8, film thickness 100 .mu.m. Initial testing (fresh sample without
further storage) at room temperature (23.degree. C.). Compression
conditions as specified in Table 5 (see above).
[0189] The samples examined in Table 5 (see above) have been found
to be very shock-resistant.
[0190] DSC Analyses
[0191] Examples 5, 7, 8 and 13 to 16 were used to conduct DSC
analyses in order to examine the effect of the amount of silane on
the crosslinking characteristics (i.e. the curing of the adhesive
film). The results are shown in FIGS. 2 and 3.
[0192] DSC Analysis:
[0193] Instrument: DSC 204 F1 Phoenix, from Netzsch
[0194] Crucible: Al crucible, lid manually perforated
[0195] Temperature program: 20.degree. C..fwdarw.-140.degree. C.;
140.degree. C..fwdarw.200.degree. C. (first heating curve)
[0196] Temperature rate: 10 K/min (cooled with liquid N.sub.2)
[0197] Method/SOP: DSC-01
[0198] FIG. 2 shows Examples 7, 13 and 14 with use of
3-methacryloyloxypropytriethoxysilane (CAS 21142-29-0), and FIG. 3
shows Examples 8, 15 and 16 with use of
3-methacryloyloxypropyltrimethoxysilane (CAS 2530-85-0). For
comparison, FIG. 2 also shows Example 4 without the use of
silane.
[0199] In a second heating curve conducted for each of the two
measurements (200.degree. C..fwdarw.-140.degree. C.; -140.degree.
C..fwdarw.250.degree. C., not shown), it is not possible to observe
any post-crosslinking.
[0200] The curves are labeled in FIGS. 2 and 3 in accordance with
the Example numbers. The symbols "+" symbolize the positions of the
values as specified in the two tables below, Tables 6 and 7.
TABLE-US-00006 TABLE 6 DSC values in FIG. 2: Glass transition
Position of Position of Example T.sub.G [.degree. C.] peak 1
[.degree. C.] peak 2 [.degree. C.] 7 -42.8 44.1 180.7 14 -43.3 44.4
180.3 13 -44.4 44.6 179.9 5 -44.4 44.9 180.0
TABLE-US-00007 TABLE 7 DSC values in FIG. 3: Glass transition
Position of Position of Example T.sub.G [.degree. C.] peak 1
[.degree. C.] peak 2 [.degree. C.] 15 -42.2 45.3 180.5 16 -42.8
45.4 178.9 8 -43.4 46.8 180.4
[0201] These DSC traces (as shown in FIGS. 2 and 3) show that the
maximum exothermicity is fairly constant at 180.degree. C. and the
enthalpy of reaction is virtually independent of the silane
content. The addition of silane thus has a positive effect on
moisture/heat resistance as shown further up in the tests, but no
significant effect on the crosslinking reaction (curing) of the
adhesive film.
* * * * *