U.S. patent application number 14/114964 was filed with the patent office on 2014-03-27 for method for increasing the adhesive properties of pressure-sensitive adhesive compounds on substrates by way of plasma treatment.
This patent application is currently assigned to Tesa SE. The applicant listed for this patent is tesa SE. Invention is credited to Arne Koops, Sarah Reich, Thomas Schubert.
Application Number | 20140083608 14/114964 |
Document ID | / |
Family ID | 46026826 |
Filed Date | 2014-03-27 |
United States Patent
Application |
20140083608 |
Kind Code |
A1 |
Schubert; Thomas ; et
al. |
March 27, 2014 |
METHOD FOR INCREASING THE ADHESIVE PROPERTIES OF PRESSURE-SENSITIVE
ADHESIVE COMPOUNDS ON SUBSTRATES BY WAY OF PLASMA TREATMENT
Abstract
A process increases adhesion between a layer of
pressure-sensitive adhesive and a substrate, wherein the layer of
pressure-sensitive adhesive has a first surface facing away from
the substrate and a second surface facing toward the substrate and
a third surface of the substrate. The process treats (i) the second
surface of the layer of pressure-sensitive adhesive that faces
toward the substrate and (ii) the third surface of the substrate
with atmospheric-pressure plasma, and adhesive bonds the layer of
pressure-sensitive adhesive to the third surface of the
substrate.
Inventors: |
Schubert; Thomas; (Hamburg,
DE) ; Koops; Arne; (Neu-Lankau, DE) ; Reich;
Sarah; (Hamburg, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
tesa SE |
Hamburg |
|
DE |
|
|
Assignee: |
Tesa SE
Hamburg
DE
|
Family ID: |
46026826 |
Appl. No.: |
14/114964 |
Filed: |
May 4, 2012 |
PCT Filed: |
May 4, 2012 |
PCT NO: |
PCT/EP2012/058286 |
371 Date: |
December 13, 2013 |
Current U.S.
Class: |
156/272.6 |
Current CPC
Class: |
C09J 2301/302 20200801;
C09J 2301/208 20200801; C08G 18/3206 20130101; C08G 18/4812
20130101; C09J 123/16 20130101; B32B 27/32 20130101; B29B 7/485
20130101; B29B 7/82 20130101; B32B 27/308 20130101; C08J 5/128
20130101; B32B 27/08 20130101; B32B 27/40 20130101; C09J 175/08
20130101; B29B 7/86 20130101; B32B 27/16 20130101; C09J 2423/00
20130101; C08G 2170/40 20130101; C09J 2301/1242 20200801; C08G
18/6674 20130101; C09J 7/10 20180101; C09J 5/02 20130101; C08G
18/12 20130101; C08G 18/755 20130101; B32B 2405/00 20130101; C09J
2301/304 20200801; C09J 2433/00 20130101; C08G 18/4829 20130101;
Y10T 428/2826 20150115; C08J 2323/16 20130101; C08G 18/227
20130101; C09J 2423/10 20130101; C09J 2475/00 20130101; C08G
18/4825 20130101; C08G 18/12 20130101; C08G 18/758 20130101 |
Class at
Publication: |
156/272.6 |
International
Class: |
C09J 7/02 20060101
C09J007/02 |
Foreign Application Data
Date |
Code |
Application Number |
May 6, 2011 |
DE |
10 2011 075 468.7 |
May 6, 2011 |
DE |
10 2011 075 470.9 |
Claims
1. A process for increasing the-adhesion between a layer of
pressure-sensitive adhesive and a substrate, wherein the layer of
pressure-sensitive adhesive has a first surface facing away from
the substrate and a second surface facing toward the substrate and
a third surface of the substrate, the process comprising: treating
(i) the second surface of the layer of pressure-sensitive adhesive
that faces toward the substrate and (ii) the third surface of the
substrate with atmospheric-pressure plasma; and adhesive bonding
the layer of pressure-sensitive adhesive to the third surface of
the substrate.
2. The process according to claim 1, further comprising a treatment
atmosphere for treating the second and third surfaces, wherein the
treatment atmosphere comprises the following pure process gases, or
mixtures of: N.sub.2, compressed air, O.sub.2, H.sub.2, CO.sub.2,
Ar, He, ammonia, and ethylene, and, optionally, N.sub.2 and
compressed air.
3. The process according to claim 1, wherein treatments of the
second and third surfaces with the atmospheric-pressure plasma take
place at or in the vicinity of atmospheric pressure.
4. The process according to claim 2, wherein reactive aerosols are
present in the treatment atmosphere or are added to the treatment
atmosphere.
5. The process according to claim 1, wherein the plasma is applied
by of one or more nozzles.
6. The process according to claim 1, wherein the plasma is applied
by of a rotary nozzle, using compressed air.
7. The process according to claim 1, wherein the second and third
surfaces are treated immediately prior to the adhesive bonding of
the layer of pressure-sensitive adhesive to the substrate.
8. The process according to claim 3, wherein (i) for a treatment
directly prior to the adhesive bonding, a chronological separation
between the treatment and the adhesive bonding is <1 s, (ii) for
an in line treatment prior to the adhesive bonding, the
chronological separation is in a first range from seconds to
minutes, (iii) for an off-line treatment, the chronological
separation is in a second range from hours to days, and (iv) for a
treatment in a production process of an adhesive tape, the
chronological separation is in a third range from days to
months.
9. The process according to claim 3, wherein wherein the treatments
of the second and third surfaces comprise a first treatment and a
second treatment, wherein the first treatment initially takes
place, and then the second treatment takes place with chronological
separation from the first treatment immediately prior to the
adhesive bonding of the layer of pressure-sensitive adhesive to the
substrate.
10. The process according to claim 9, wherein at least one of the
first and second treatments comprises a plurality of individual
treatment steps.
11. The process according to claim 1, wherein chronological
separation between multiple treatments varies from about 0.1 s up
to 1 year.
12. The process according to claim 9, wherein a pretreatment of one
of the second and third surfaces uses a first plasma generator, and
at a subsequent juncture a different second plasma generator is
used to supplement or refresh the first or second treatment.
13. The process according to claim 3, wherein the treatments of the
second and third surfaces are identical.
14. The process according to claim 1, wherein the layer of
pressure-sensitive adhesive is based on natural rubber, synthetic
rubber, or polyurethanes, and the layer of pressure-sensitive
adhesive is composed mostly of acrylate.
15. The process according to claim 1, wherein the layer of
pressure-sensitive adhesive forms a carrierless, single-layer,
double-sided adhesive tape.
16. The process according to claim 1, wherein the layer of
pressure-sensitive adhesive has been applied on a carrier
comprising a foil, a foam, a nonwoven, and/or a textile, or a
viscoelastic carrier.
17. The process according to claim 1, wherein a the thickness of
the layer of pressure-sensitive adhesive or of the adhesive tape
formed thereby is .gtoreq.20 .mu.m and/or at most .ltoreq.1500
.mu.m.
18. The process according to claim 1, wherein the substrate is
selected from steel, aluminum, polyester, PVC, PC, PE, PP, EPDM,
ABS, rubber, glass, ceramic, coating materials and coatings, CEC,
composite materials, wood-composite products, coated paperboard
packaging materials, foils, bottles, plastics containers,
packaging, and housing parts.
19-20. (canceled)
Description
[0001] The invention relates to a process for enhancing the
adhesive properties of pressure-sensitive adhesives on substrates
by means of plasma treatment.
[0002] Pressure-sensitive adhesives are in principle subject to the
problem of simultaneous requirement for volume optimization and
surface optimization, i.e. cohesion and adhesion. In many
instances, the weakness of an adhesive bond is found at the
surface, i.e. the adhesion.
[0003] The term "adhesion" usually means the physical effect by
which two phases brought into contact with one another are held
together at their interface by virtue of intermolecular
interactions arising there. The adhesion therefore determines the
extent of bonding of the adhesive on the substrate surface, and can
be determined in the form of what is known as "tack" and in the
form of bond strength. Plasticizers and/or "tackifies" resins are
often added to the adhesive in order to exert a controlled effect
on its adhesion.
[0004] Adhesion can be defined in simple terms as "the interaction
energy per unit of area" [in mN/m], but this is not measurable
because of experimental restrictions, for example lack of knowledge
of the actual contact areas. Surface energy (SE) is also often
described by using "polar" and "nonpolar" components. This
simplified model is now well accepted for practical purposes. This
energy and its components are often measured by measuring the
static contact angle of various test liquids. The surface tensions
of these liquids are divided into polar and nonpolar components.
The polar and nonpolar components of the surface energy of the test
surface are determined from the observed contact angles of the
droplets on the test surface. The OWKR approach can by way of
example be used here. An alternative method conventionally used in
industry is determination by means of test solutions in accordance
with DIN ISO 8296.
[0005] In the context of discussions of this type, the terms
"polar" and "high-energy" are often treated as equivalent, as also
are the terms "nonpolar" and "low-energy". This derives from the
fact that polar dipole forces are large in comparison with what are
known as "disperse" or nonpolar interactions, which do not involve
permanent molecular dipoles. The basis for this approach to surface
energy and surface interactions is the assumption that polar
components interact only with polar components and nonpolar
components only with nonpolar components.
[0006] However, it is also possible that a surface has small or
moderate polar surface energy components without "high" surface
energy. A guideline that can be used is: as soon as the polar
component of the SE is greater than 3 mN/m the surface is to be
designated "polar" for the purposes of this invention. This
corresponds approximately to the practical detection limit.
[0007] In principle, there are no specific boundaries for terms
such as "high-energy" and "low-energy". For the purposes of
discussion, the limit is set at 38 mN/m or 38 dyn/cm. At this and
higher values by way of example the printability of a surface is
mostly adequate. The surface tension (=surface energy) of pure
water can serve for comparison, and is about 72 mN/m (being inter
alia temperature-dependent).
[0008] In particular on low-energy substrates such as PE, PP, or
EPDM, but also on many coating materials, major problems arise in
achieving satisfactory adhesion when pressure-sensitive adhesives
or other adhesives or coatings are used.
[0009] Equally, it is known that polar pressure-sensitive adhesives
such as the acrylates class exhibit satisfactory behavior on
high-energy substrates, but often fail on very low-energy
substrates. There are other compositions for example based on
natural or synthetic rubber which provide improved adhesive bonds
on both low- and high-energy substrates.
[0010] Acrylates in particular moreover also exhibit the typical
"delayed maturity" behavior, i.e. a process which often takes some
days to establish "flow-contact" with the substrate before the
adhesive bond achieves its final strength. In most instances this
behavior is undesirable.
[0011] And even if fewer problems are generally encountered with
adhesive bonding on high-energy or polar substrates such as steel,
there are still many pressure-sensitive adhesives that fail to
achieve a fully satisfactory level of interaction. This is apparent
from peel tests where many pressure-sensitive adhesives fail to
exhibit cohesive fracture on steel, indicating that adhesion is
failing.
[0012] In this connection, it is often considered desirable to
develop adhesives which exhibit comparable behavior across
different substrates.
[0013] Adhesive bonding of different substrates to one another
(polar to nonpolar), for example in the case of double-sided
adhesive tapes, in particular requires optimization specifically on
different substrates.
[0014] Problems of this type could also arise during the adhesive
bonding of two substrates with different properties in one plane
(for example placed alongside one another or on top of one another)
by a single-sided adhesive tape.
[0015] In particular for the sector covering high-performance
adhesive tapes and adhesive assembly tapes, there are carrierless,
viscoelastic adhesive tapes. In this context, the term
"carrierless" means that there is no layer that is necessary merely
for structural integrity, and therefore that the adhesive tape has
sufficient intrinsic cohesion for the specified use. There is no
need to use a carrier foil or the like, for example nonwoven or
textile. These adhesive tapes, too, are mostly based on highly
crosslinked acrylate adhesives. These pressure-sensitive adhesive
tapes are moreover mostly relatively thick, typically thicker than
300 .mu.m.
[0016] Such a "viscoelastic" polymer layer can be regarded as a
very high-viscosity liquid which when subjected to pressure
exhibits flow behavior (also termed "creep"). When these
viscoelastic polymers are exposed to a slow-acting force they have
a particular ability to provide relaxation of the forces to which
they are exposed, and the same applies to a polymer layer of this
type: they are able to dissipate the forces into vibration
phenomena and/or deformation phenomena (which can also in
particular--at least to some extent--be reversible), thus providing
a "protective buffer" against the forces to which they are exposed
and preferably avoiding any mechanical destruction by said forces,
but advantageously at least mitigating same, or else at least
delaying the occurrence of the destruction. When exposed to a very
fast-acting force, viscoelastic polymers usually exhibit elastic
behavior, i.e. fully reversible deformation, and forces which
extend beyond the elastic capability of the polymers here can cause
fracture. Contrasting with this are elastic materials, which
exhibit the elastic behavior described even on exposure to
slow-acting forces. The properties of these viscoelastic adhesives
can also be varied greatly by using admixtures, fillers, foaming or
the like.
[0017] In particular, it is often advantageous to produce a
syntactic foam. If this is achieved by way of example by adding
expandable microballoons which expand only after addition, the term
used for the purposes of this disclosure is "foaming". If, instead
of this, preexpanded or non-expandable hollow fillers such as
hollow glass beads are added, the term used for the purposes of
this disclosure is "foaming" or "filling". Both "foaming" and
"filling" produce a syntactic foam.
[0018] By virtue of the elastic properties of the viscoelastic
polymer layer which in turn make a substantial contribution to the
adhesive properties of adhesive tapes using this type of
viscoelastic carrier layer, it is not possible to achieve complete
dissipation of the stress caused by way of example by exposure to
tension or to shear. This is expressed via the relaxation capacity,
which is defined as ((stress(t=0)-stress(t)/stress (t=0))*100%. The
relaxation capacity of viscoelastic carrier layers is typically
more than 50%.
[0019] To the extent that any adhesive is viscoelastic, for
high-performance carrierless adhesive tapes it is preferable to use
adhesives which exhibit these particular relaxation properties.
[0020] A problem that is particularly difficult to solve is the
simultaneous optimization of adhesion and cohesion for single-layer
carrierless self-adhesive tapes, there is no possibility here of
specific coating of the sides of the adhesive tape for the
respective substrates.
[0021] However, it is not then possible to proceed simply changing
the chemical formulation of a pressure-sensitive adhesive in a
desired manner in order to optimize adhesion, since many
volume-related properties are influenced concomitantly. By way of
example, these can be viscosity, resistance to dynamic shocks,
solvents, or temperature change, or the problem can simply be
limitations of the production/polymerization process. In practice
there is therefore often restriction to a particular underlying
chemistry which then has to be used to ensure, inter alia,
adhesion.
[0022] It is moreover possible that a pressure-sensitive adhesive,
for example a viscoelastic thick-layer product, fails both at high
and at low temperatures. A typical reason for failure at low
temperatures is that the glass transition point has been reached
and that resultant hardening occurs. In that case, fracture is
often caused by adhesive failure. At the same time, the product can
also soften at high temperatures with resultant inadequate strength
or durability in shear tests again with fracture caused by adhesive
failure.
[0023] The physical pretreatment of substrates (for example by
flame, corona, or plasma) to improve adhesive bond strengths is
especially customary with liquid reactive adhesives. One function
of this physical pretreatment can also be cleaning of the
substrate, for example to remove oils, or roughening to enlarge the
effective area.
[0024] The term mostly used for physical pretreatment is
"activation" of the surface. This mostly implies a non-specific
interaction, contrasting by way of example with a chemical reaction
using the key-in-lock principle. Activation mostly implies an
improvement in wettability, printability, or anchoring of a
coating.
[0025] In the case of self-adhesive tapes, it is customary to apply
an adhesion promoter to the substrate. However, this is often a
complicated manual step that is susceptible to error.
[0026] Use of physical pretreatment of the substrate (flame,
corona, or plasma) to improve the adhesion of pressure-sensitive
adhesives has not achieved universal success, since nonpolar
adhesives such as natural or synthetic rubber typically do not
profit from that process.
[0027] DE 10 2007 063 021 A1 describes activation of adhesives by
means of filamental corona treatment. The effect of the corona
treatment was in essence restricted to increased values for holding
power (HP). No improvement of other adhesive properties was
achieved. This is probably attributable to the formation of
degradation products through electron bombardment in a corona
discharge. In particular bond strength observed was unaltered or
indeed reduced. In fact it is also clear to the person skilled in
the art that any assumption that increased values for holding power
of a pressure-sensitive adhesive mean that bond strength has also
been increased would be an over-simplification. Nor is it likely
that the oxidative-polar modification that is taught for the
adhesive can provide any improvement on nonpolar substrates. Corona
treatment is moreover associated with a large number of other
restrictions, as will be described hereinafter.
[0028] The solutions available hitherto in the teaching of the
prior art for increasing the bond strength of a shaped layer of
viscoelastic pressure-sensitive adhesive relate to addition of one
or more layers of an adhesive by lamination, thus giving a
multilayer structure. The obvious disadvantages of a multilayer
structure are the increased manufacturing cost and the number of
steps in the process. This type of solution is in principle
susceptible to problems of delamination between the layers, since
interlaminate adhesion is not based on strong covalent chemical
interactions but instead on nonspecific interactions of general
polar type. In this context, corona treatments on interior
interfaces of adhesive tapes are described in order to improve
interlaminate adhesion, for example in WO 2006/027389 A1, DE 10
2006 057 800 A1, or EP 2 062 951 A1.
[0029] Chemico-physical modifications of substrates are also in
principle known, with subsequent application of adhesive tapes,
where the adhesive tapes themselves are not modified. DE 695 31 394
T2 describes by way of example how chemico-physical oxidation of a
polymer surface can be used in combination with application of a
coupling agent in an electrical field in order to improve adhesion
of a surface. The application of an unmodified adhesive tape to the
surface thus modified is also claimed.
[0030] A process for improving the adhesion of pressure-sensitive
adhesives is therefore desirable, where the process: [0031] should
ideally have a favorable effect on all aspects of adhesion such as
bond strength, shear resistance, and flow-contact, [0032] should
not be restricted to particular classes of substrates or
pressure-sensitive adhesives, and [0033] should have good technical
suitability for achieving the object.
[0034] It is an object of the invention to find the stated
favorable effects on physical surface modification of
pressure-sensitive adhesives and substrates, in order to achieve
high-strength bonds. The main object is to achieve a high level of
anchoring between the pressure-sensitive adhesive layer and the
substrate.
[0035] Said objects are achieved via a process as described in the
main claim. The dependent claims here provide advantageous
embodiments of the subject matter of the invention.
[0036] Accordingly, the invention provides a process for increasing
the adhesion between a layer of pressure-sensitive adhesive which
has a surface facing away from the substrate and which has a
surface facing toward the substrate and the surface of a substrate,
where that surface of the layer of pressure-sensitive adhesive that
faces toward the substrate and the substrate surface covered with
the layer of pressure-sensitive adhesive are respectively treated
with atmospheric-pressure plasma.
[0037] A surprising feature of the process of the invention is that
a significant increase both of bond strength and of shear
resistance and of other adhesion properties is observed for very
many adhesive-tape-substrate combinations. In particular, this is
also true for low-energy substrates. This improvement is obtained
irrespective of whether the substrate is very smooth or rough, or
even structured/textured.
[0038] Surprisingly, the process of the invention is robust and
easy to use.
[0039] The plasma is preferably applied by means of one or more
nozzles, preferably operating with compressed air or N.sub.2.
[0040] It is particularly preferable that the plasma is applied by
means of a rotary nozzle, particularly preferably operating with
compressed air.
[0041] Modern indirect plasma techniques are often based on a
nozzle system. These nozzles can be of round or linear design and,
without any intention of introducing a restriction here, rotary
nozzles are sometimes used. This type of nozzle system is
advantageous because it is flexible and inherently suitable for
single-side treatment. Nozzles of this type, for example from
Plasmatreat, are widely used in industry for the pretreatment of
substrates prior to adhesive bonding. Disadvantages are the
indirect treatment, which is less efficient because it is
discharge-free, and the resultant reduced web speeds. However, the
customary design of a round nozzle is especially suitable for
treating narrow webs of product, for example an adhesive tape which
is a few cm in width.
[0042] Various plasma generators are available in the market, and
differ in the method of plasma generation, in nozzle geometry, and
in the gas atmosphere used. Although the treatments differ inter
alia in their efficiency, the fundamental effects are mostly
similar and are determined especially via the gas atmosphere used.
Plasma treatment can take place in a variety of atmospheres, and
this atmosphere can also comprise air. The treatment atmosphere can
be a mixture of various gases selected inter alia from N.sub.2,
O.sub.2, H.sub.2, CO.sub.2, Ar, He, and ammonia, where water vapor
or other constituents may also have been admixed. This list of
examples does not constitute any restriction.
[0043] In one advantageous embodiment of the invention, the
following pure, or mixtures of, process gases form a treatment
atmosphere: N.sub.2, compressed air, O.sub.2, H.sub.2, CO.sub.2,
Ar, He, ammonia, ethylene, where water vapor or other volatile
constituents may also have been added. Preference is given to
N.sub.2 and compressed air.
[0044] In principle, it is also possible to admix coating
constituents or polymerizing constituents in the form of gas (for
example ethylene) or liquids (atomized in the form of aerosol) with
the atmosphere. There is almost no restriction on the aerosols that
can be used. Plasma techniques involving indirect operation are
particularly suitable for the use of aerosols, since there is no
risk here of contamination of the electrodes.
[0045] Since the effects of plasma treatment are chemical in
nature, and alteration of surface chemistry is of prime importance,
the methods described above can also be described as
chemico-physical treatment methods. Although there can be
differences in the detail, there is no intention to emphasize any
particular technique for the purposes of this invention, either in
terms of the method of plasma generation or in terms of
engineering.
[0046] Preference is further given to the application of plasma jet
by means of rotation of the nozzle tip. The plasma jet then passes
in a circle across the substrate at a predetermined angle and
advantageously provides a good treatment width for adhesive tapes.
Given an appropriate advance rate, the rotation causes the
treatment jet to pass repeatedly across the same locations, and
therefore implicitly to achieve repeated treatment.
[0047] In an equally preferred variant of the plasma treatment, a
fixed plasma jet is used without any rotary nozzle.
[0048] In an equally preferred plasma treatment, a lateral
arrangement of a plurality of nozzles, offset if necessary, is used
to provide treatment over an adequate width with no gaps and with
some overlaps. A disadvantage here is the necessary number of
nozzles, and typically it is necessary to use from two to four
non-rotating round nozzles instead of one rotary nozzle.
[0049] The design of a round nozzle is generally preferred for
adhesive bonding of narrow adhesive tapes. However, linear nozzles
are also suitable.
[0050] In another advantageous embodiment of the invention, the
treatment distance is from 1 to 100 mm, preferably from 3 to 50 mm,
particularly preferably from 4 to 20 mm.
[0051] It is further preferable that the treatment velocity is from
0. to 200 m/min, preferably from 1 to 50 m/min, particularly
preferably from 2 to 20 m/min.
[0052] Particular preference is given to universal treatment by
means of a rotary nozzle with from 9 to 12 mm of distance between
nozzle and the surface requiring treatment with a relative lateral
movement of from 4 to 6 m/min between nozzle and substrate.
[0053] The treatment must, of course, take place within a range
within which the gas is reactive or, respectively, within a
distance (for example from a nozzle) within which the gas remains
reactive. In the case of a nozzle, said range comprises the
effective range of the plasma jet.
[0054] The plasma treatment of the surfaces can also be
repeated.
[0055] A treatment can be repeated in order to achieve the desired
intensity. This always occurs in the case of the preferred rotary
treatment or in the case of nozzle arrangements which overlap to
some extent.
[0056] The required treatment intensity can by way of example be
achieved via a plurality of passes under a nozzle or via
arrangement of a plurality of nozzles in series. The repeated
treatment can also be utilized in order to refresh the
treatment.
[0057] Division of at least one of the treatments into a plurality
of individual treatments is another possibility.
[0058] In principle, both surfaces are treated, i.e. adhesive tape
and substrate. In the case of double-sided adhesive tapes this can
be true for both sides.
[0059] There is no prescribed juncture, but a juncture briefly
prior to adhesive bonding is preferred.
[0060] In the case of treatment directly prior to the adhesive
bonding the chronological separation from the adhesive bonding can
be <1 s, in the case of in-line treatment prior to the adhesive
bonding it can be in the range from seconds to minutes, in the case
of off-line treatment it can be in the range from hours to days,
and in the case of treatment in the production process of the
adhesive tape it can be in the range from days to many months.
[0061] Plasma treatment can, like most physical treatments, become
less effective over the course of time. However, this phenomenon
can be greatly dependent on the details of the treatment and of the
substrate and of the adhesive tape. During any possible decrease of
effectiveness, adhesion obviously remains improved in comparison
with the untreated condition. The improved adhesion during said
period is in principle also part of this teaching.
[0062] A repeated treatment can in principle be used to supplement
or refresh a treatment.
[0063] The chronological separation between the multiple treatments
can therefore vary from about 0.1 s (during the rotation of the
nozzle) up to about 1 year (when a product is treated before
delivery and there is a refreshment treatment prior to use).
[0064] The treatments of the two surfaces are in principle
independent of one another, spatially and chronologically.
[0065] By way of example, it is possible that one treatment takes
place in a first step and that the second treatment takes place in
a second step.
[0066] One or both of said treatments can take place in-line with
the adhesive bonding.
[0067] There is no restriction on the number of individual nozzles
or other plasma generators used for a single treatment or for all
of the treatments.
[0068] There is no restriction on the number of individual
treatments carried out with the plasma generator(s).
[0069] By way of example, it would be conceivable to use a
particular plasma generator for the pretreatment of one of the
relevant surfaces, and at a subsequent juncture to use a different
plasma generator to supplement or refresh this treatment.
[0070] By way of example, the surface could also have been flame-
or corona-pretreated before it is treated with the process taught
here. By way of example, foils or plastics parts are sometimes
provided with a physical pretreatment by the producer.
[0071] In one variant of the invention, the plasma is applied by a
plasma nozzle unit with additional introduction of a precursor
material into the operating gas stream or into the plasma jet. In
this case, contact can take place at different times or
simultaneously.
[0072] An atmospheric-pressure plasma (and surface treatment by
means of same) differs substantially from a corona discharge (and
surface treatment by means of same).
[0073] Corona treatment is defined as a surface treatment which
uses filamental discharges and which is generated via high
alternating voltage between two electrodes, whereupon the discrete
discharge channels come into contact with the surface requiring
treatment, in which connection see also Wagner et al., Vacuum, 71
(2003), pp. 417 to 436. The process gas can be assumed to be
ambient air unless otherwise stated.
[0074] The substrate is almost always placed within or passed
through the discharge space between an electrode and an opposing
electrode, this being defined as "direct" physical treatment.
Substrates in the form of webs here are typically passed between an
electrode and a grounded roll.
[0075] In particular, the term "corona" mostly means a "dielectric
barrier discharge" (DBD). At least one of the electrodes here is
composed of a dielectric, i.e. of an insulator, or has a coating or
covering of same.
[0076] The treatment intensity of a corona treatment is stated as
"dose" in [Wmin/m.sup.2], where the dose D=P/b*v, where
P=electrical power [W], b=electrode width [m], and v=web speed
[m/min].
[0077] The substrate is almost always placed within, or passed
through the discharge space between an electrode and an opposing
electrode, this being defined as "direct" physical treatment.
Substrates in web form here are typically passed between an
electrode and a grounded roll. Another term that is also sometimes
used is "ejected corona" or "single-side corona". This is not
comparable with an atmospheric-pressure plasma, since very
irregular discharge filaments are "ejected" together with a process
gas, and it is impossible to achieve stable, well-defined,
efficient treatment.
[0078] "Atmospheric-pressure plasma" is defined as an electrically
activated, homogeneous, reactive gas which is not in thermal
equilibrium, with a pressure close to ambient pressure. Electrical
discharges and ionizing processes in the electrical field activate
the gas and generate highly excited states in the gas constituents.
The gas used or the gas mixture is termed process gas. In
principle, it is also possible to admix coating constituents or
polymerizing constituents in the form of gas or aerosol with the
plasma atmosphere.
[0079] The term "homogeneous" indicates that there are no discrete,
inhomogeneous discharge channels encountering the surface of the
substrate requiring treatment (even though these may be present in
the generation space).
[0080] The "not in thermal equilibrium" restriction means that the
ion temperature can differ from the electron temperature. In a
thermally generated plasma these would be in equilibrium (in which
connection see also by way of example Akishev et al., Plasmas and
Polymers, Vol. 7, No. 3, September 2002).
[0081] When atmospheric-pressure plasma is used for the physical
treatment of a surface, the electrical discharge mostly takes place
in a space separate from the surface. The process gas is then
passed through said space and electrically activated, and then in
the form of plasma mostly passed through a nozzle onto the surface.
The reactivity of the plasma jet mostly decreases rapidly with time
after discharge: in spatial terms typically after millimeters to
centimeters. An English term often used for the decreasing
reactivity of the plasma as it is discharged is "afterglow". The
lifetime of the plasma discharged, and the distance over which it
remains effective, depend on molecular details and on the precise
method of plasma generation.
[0082] This type of physical treatment is termed "indirect" when
the treatment is not undertaken at the location of generation of
the electrical discharges. The treatment of the surface takes place
at or in the vicinity of atmospheric pressure, but there may be
increased pressure in the electrical discharge space.
[0083] However, there are also by way of example known generation
systems for carrying out indirect plasma treatments in which
electrical discharges take place in the gas stream outside of a
nozzle and likewise provide a plasma-jet treatment.
[0084] Equally, there are known homogeneous atmospheric-pressure
plasmas in which the treatment takes place in the discharge space
at atmospheric pressure, the term used being "glow discharge
plasma", see for example T. Yokoyama et al., 1990 J. Phys. D: Appl.
Phys. 23 1125.
[0085] Constituents of the atmospheric-pressure plasma can be:
[0086] highly excited atomic states [0087] highly excited molecular
states [0088] ions [0089] electrons [0090] unaltered constituents
of the process gas.
[0091] It is preferable to use commercially available systems for
the generation of atmospheric-pressure plasma. The electrical
discharges can take place between metal electrodes, or else between
metal dielectric, or else are generated via piezoelectric discharge
or other methods. Some examples of commercial systems are
Plasma-Jet (Plasmatreat GmbH, Germany), Plasma-Blaster (Tigres
GmbH, Germany), Plasmabrush and Piezobrush (Reinhausen, Germany),
Plasmaline (VITO, Belgium), or ApJet (ApJet, Inc., USA). The
systems mentioned operate with different process gases, for example
air, nitrogen or helium, and different resultant gas
temperatures.
[0092] Preference is given to the process from Plasmatreat GmbH
(Steinhagen, Germany) described by way of example in the following
quotation from WO 2005/117507 A2:
[0093] "The prior art of EP 0 761 415 Al and EP 1 335 641 A1
discloses a plasma source in which by means of a with application
of a high-frequency high voltage in a nozzle tube between a pin
electrode and an annular electrode by means of a nonthermal
discharge from the operating gas a plasma jet is generated, which
is discharged from the nozzle aperture. At a suitably adjusted flow
rate, said nonthermal plasma jet comprises no electrical streamers,
and it is therefore possible to direct only the high-energy, but
low-temperature plasma jet onto the surface of a component.
Streamers here are the discharge channels along which the
electrical discharge energy proceeds during the discharge.
[0094] The plasma jet can also be characterized via the high
electron temperature, the low ion temperature, and the high gas
velocity."
[0095] In the case of a corona discharge as defined above, the high
voltage applied causes formation of filamental discharge channels
with accelerated electrons and ions. The low-mass electrons in
particular encounter the surface at high velocity with energies
that are sufficient to break most of the molecular bonds. The
reactivity of the other reactive gas constituents produced is
mostly a subordinate effect. The broken bond sites then react
further with constituents of the air or of the process gas. An
effect of decisive importance is the formation of short-chain
degradation products via electron bombardment. Treatments of higher
intensity also cause significant ablation of material.
[0096] The reaction of a plasma with the substrate surface promotes
the direct "incorporation" of the plasma constituents.
Alternatively, it is possible that an excited state or an open bond
site is produced on the surface and that these then undergo
secondary further reaction, for example with atmospheric oxygen. In
the case of some gases, such as noble gases, no chemical bonding of
the process gas atoms or process gas molecules to the substrate is
to be expected. The activation of the substrate here takes place
exclusively by way of secondary reactions.
[0097] The significant difference is therefore that in the case of
the plasma treatment there is no direct exposure of the surface to
discrete discharge channels. The effect therefore takes place
homogeneously and non-aggressively primarily by way of reactive gas
constituents. Free electrons are possibly present during indirect
plasma treatment, but these are not accelerated electrons, since
the treatment takes place outside of the generating electrical
field.
[0098] The plasma treatment is therefore less destructive than a
corona treatment, since no discrete discharge channels encounter
the surfaces. Amounts produced of short-chain degradation products
are smaller, where these can form a layer with adverse effect on
the surface. Better wettability values can therefore often be
achieved after plasma treatment than after corona treatment, with
longer-lasting effect.
[0099] The reduced extent of chain degradation and the homogeneous
treatment via use of a plasma treatment make a substantial
contribution to the robustness and effectiveness of the process
taught.
[0100] The adhesive of the invention is a pressure-sensitive
adhesive, i.e. an adhesive which can give a durable bond with
almost all adhesion substrates even when the pressure applied is
relatively weak, and after use can in essence in turn be peeled
from the adhesion substrate to leave no residue. A
pressure-sensitive adhesive has a permanent pressure-sensitive
adhesive effect at room temperature, i.e. because its viscosity is
sufficiently low and its tack is high it wets the surface of the
respective adhesion substrate even when the pressure applied is
low. The adhesive bonding capability of the adhesive derives from
its adhesive properties, and the peelability derives from its
cohesive properties.
[0101] It is preferable that the layer of pressure-sensitive
adhesive is based on natural rubber, synthetic rubber, or
polyurethanes, and the layer of pressure-sensitive adhesive here is
preferably composed exclusively of acrylate or mostly of acrylate
(hotmelt or UV), in particular being viscoelastic, or else blends
and copolymers.
[0102] The pressure-sensitive adhesive can have been blended with
tackifiers in order to improve adhesive properties.
[0103] Suitable tackifiers, also termed tackifier resins, are in
principle any of the known classes of substance. Examples of
tackifiers are hydrocarbon resins (for example polymers based on
unsaturated C.sub.5- or C.sub.9-monomers), terpene-phenolic resins,
polyterpene resins based on raw materials such as .alpha.- or
.beta.-pinene, aromatic resins such as coumarone-indene resins or
resins based on styrene or .alpha.-methylstyrene, for example
colophony and its downstream products, e.g. disproportionated,
dimerized or esterified colophony, e.g. reaction products with
glycol, glycerol, or pentaerythritol, to mention just a few.
Preference is given to resins without readily oxidizable double
bonds, for example terpene-phenolic resins, aromatic resins, and
particularly preferably resins produced via hydrogenation, for
example hydrogenated aromatic resins, hydrogenated
polycyclopentadiene resins, hydrogenated colophony derivatives, or
hydrogenated polyterpene resins. Preference is given to resins
based on terpene-phenolics and on colophony esters. Equally,
preference is given to tackifier resins with softening point above
80.degree. C. in accordance with ASTM E28-99 (2009). Particular
preference is given to resins based on terpene-phenolics and on
colophony esters with softening point above 90.degree. C. in
accordance with ASTM E28-99 (2009). Typical amounts used are from
10 to 100 parts by weight, based on polymers of the adhesive.
[0104] In order to achieve a further improvement in cable
compatibility, the adhesive formulation can optionally have been
blended with light stabilizers or primary and/or secondary
antioxidants.
[0105] Antioxidants that can be used are UV absorbers, sterically
hindered amines, thiosynergists, phosphites, or products based on
sterically hindered phenols.
[0106] It is preferable to use primary antioxidants such as Irganox
1010 (tetrakis(methylene
(3,5-di(tert)butyl-4-hydrocinnamate))methane; CAS No. 6683-19-8
(sterically hindered phenol), BASF) or Irganox 254, alone or in
combination with secondary antioxidants such as Irgafos TNPP or
Irgafos 168.
[0107] The antioxidants here can be used in any desired combination
with one another, and mixtures that exhibit particularly good
antioxidant effect here are those of primary and secondary
antioxidants in combination with light stabilizers such as Tinuvin
213.
[0108] Antioxidants that have proven very particularly advantageous
are those in which a primary antioxidant has been combined with a
secondary antioxidant in one molecule. These antioxidants involve
cresol derivatives whose aromatic ring has substitution by
thioalkyl chains at any desired two different sites, preferably in
ortho- and meta-position with respect to the OH group, where the
bonding of the sulfur atom on the aromatic ring of the cresol unit
can also be by way of one or more alkyl chains. The number of
carbon atoms between the aromatic system and the sulfur atom can be
from 1 to 10, preferably from 1 to 4. The number of carbon atoms in
the alkyl side chain can be from 1 to 25, preferably from 6 to 16.
Particular preference is given here to compounds of the following
type: 4,6-bis(dodecylthiomethyl)-o-cresol,
4,6-bis(undecylthio-methyl)-o-cresol,
4,6-bis(decylthiomethyl)-o-cresol,
4,6-bis(nonylthiomethyl)-o-cresol, or
4,6-bis(octyl-thiomethyl)-o-cresol. Antioxidants of this type are
supplied for example by Ciba Geigy as Irganox 1726 or Irganox
1520.
[0109] The amount of the antioxidant or antioxidant package added
should be in the range from 0.1 to 10% by weight, preferably in the
range from 0.2 to 5% by weight, particularly preferably in the
range from 0.5 to 3% by weight, based on total solids content.
[0110] In order to improve processing properties, the adhesive
formulation can moreover have been blended with conventional
processing aids such as antifoams, deaerators, wetting agents, or
flow control agents. Suitable concentrations are in the range from
0.1 up to 5 parts by weight, based on solids.
[0111] Fillers (reinforcing or nonreinforcing) such as silicon
dioxides (spherical, acicular, lamellar, or irregular, for example
the fumed silicas), glass in the form of solid or hollow beads,
non-expandable, organic microspheres made of in particular phenolic
resins, chalk, calcium carbonates, zinc oxides, titanium dioxides,
aluminum oxides, or aluminum oxide hydroxides, carbon blacks,
fibers, carbon nanotubes (CNTs), can serve to improve
processability or adhesion properties. Suitable concentrations are
in the range from 0.1 to 70 parts by weight, based on solids, in
particular up to 40 parts by weight, particularly preferably from 1
to 20 parts by weight.
[0112] Fibers that can be used are (chemically derived) fibers
(staple fibers or continuous filaments made of synthetic polymers,
also known as synthetic fibers, made of polyester, polyamide,
polyimide, aramid, polyolefin, polyacrylonitrile, or glass,
(chemically derived) fibers made of natural polymers, for example
cellulosic fibers (viscose, modal, lyocell, cupro, acetate,
triacetate, Cellulon), or for example rubber fibers, or for example
vegetable-protein fibers and/or for example animal-protein fibers
and/or natural fibers made of cotton, sisal, flax, silk, hemp,
linen, coconut, or wool. Yarns manufactured from the stated fibers
are moreover equally suitable. Staple fibers are individual fibers
of restricted length. Filaments (continuous fibers) are the
opposite of staple fibers. Preference is given to stable
pressure-resistant hollow microspheres of which the shell is not
based on polymers.
[0113] In particular, particular preference is also given to the
combination of filling and resin addition. As can be seen from the
data sets in the examples, addition of resin and of a filler can
permit high maximal force in peel tests, at the same time as high
shear resistance in terms of good holding power and a small value
for shear under static load.
[0114] It is moreover possible to add the following, or to
incorporate them by compounding: low-flammability fillers, such as
ammonium polyphosphates, and also electrically conductive fillers,
such as conductive carbon black, carbon fibers and/or silver-coated
beads, and also ferromagnetic additives, such as iron(III) oxides,
antioxidants, light stabilizers, antiozonants, before or after
increasing the concentration of the polyacrylate.
[0115] Particular preference is given to expandable microballoons,
because these permit foaming of the adhesive.
[0116] Microballoons involve resilient hollow spheres which have a
thermoplastic polymer shell. Said spheres have a filling of
low-boiling-point liquids or liquefied gas. Shell material used is
in particular polyacrylonitrile, PVDC, PVC or polyacrylates.
Particularly suitable as low-boiling-point liquid are hydrocarbons
of the lower alkanes, such as isobutane or isopentane, enclosed in
the form of liquefied gas under pressure within the polymer shell.
Exposure of the microballoons, in particular exposure to heat,
firstly softens the exterior polymer shell. At the same time, the
liquid blowing gas present in the shell is converted to its gaseous
state. During this process, the microballoons expand irreversibly
and three-dimensionally. The expansion ends when the internal and
external pressures are equal. The polymeric shell is retained, and
the result here is therefore a closed-cell foam.
[0117] A wide variety of types of microballoon is available
commercially, for example the Expancel DU products (dry unexpanded)
from Akzo Nobel, which differ in essence in their size (from 6 to
45 .mu.m diameter in the unexpanded state) and in the temperature
at which they begin to expand (from 75 to 220.degree. C.). If the
type of microballoon and, respectively, the foaming temperature
have been adjusted appropriately for the temperature profile
required for the compounding of the material and the machine
parameters, compounding of the material and foaming can also take
place simultaneously in a single step.
[0118] Unexpanded types of microballoon are moreover also available
in the form of aqueous dispersion with about 40 to 45% by weight
content of solids or of microballoons, and also moreover in the
form of polymer-bound microballoons (masterbatches), for example in
ethyl-vinyl acetate with about 65% by weight microballoon
concentration. The microballoon dispersions and the masterbatches
are as suitable as the DU products for the foaming of adhesives in
accordance with the process of the invention.
[0119] In particular for "foam-in-place" applications, it can be
advantageous to use expandable microballoons, in preexpanded form
(expanded by the producer, and sometimes also further expandable
subsequently, for example the DE products from Expancel), in
incipiently expanded form (partially expanded in the process of
production of the adhesive tape), or in unexpanded form. In the
case of "foam-in-place" applications, the foaming of the adhesive
tape is initiated or continued after adhesive bonding.
[0120] Other possible variants for the foaming of the adhesive can
be chemical foaming with substances that cleave to give a gas, or
the physical foaming that is known from the literature, via
mechanical incorporation of gases such as air or nitrogen.
[0121] If the hollow bodies (in particular microballoons)
introduced to form the foam are destroyed subsequently, it is
nevertheless possible to obtain a non-syntactic foam of high
quality.
[0122] In relation to the preferred adhesives, it must be noted
that not every arbitrarily selected test can demonstrate the
improvement of adhesion via the invention. If by way of example the
fracture in a bond strength test was 100% cohesive fracture without
the treatment taught, the increased adhesion cannot provide any
measurable gain, since the weakest bond is provided by the bulk
properties of the adhesive tape. The increased adhesion can thus be
hidden.
[0123] In particular cases, a complex mixed fracture with
components of adhesive and cohesive failure can generate a high
force in the peel test. If adhesion is improved by the treatment
taught, the force measured in the peel test can fall, because by
way of example the type of fracture changes to pure cohesive
fracture. The improved adhesion could be demonstrated in such cases
by way of example via the increased amount of residues of the
composition on the substrate.
[0124] In principle, the decisive factor for ability to increase
the practical performance capability of the adhesive tape via
increased adhesion is the combined effect of pressure-sensitive
adhesive and carrier.
[0125] The preferred properties mentioned below lead to a
particularly large improvement in adhesion (tested for example via
bond strength measurement) through the process taught, since the
bulk properties of the adhesive tape then permit this. However,
this particular increase is surprising, since the good bulk
properties are not so clearly discernible when adhesion is
weak.
[0126] A suitable filler, for example using hollow glass beads, can
markedly increase the pressure- and shear-resistance of a
pressure-sensitive adhesive. However, this favorable bulk property
cannot be utilized until adhesion is sufficiently high. Very many
different ideas have been disclosed and described for the filling
of pressure-sensitive adhesives. Most of them improve aspects of
cohesion, but not of adhesion. Because of the poor adhesion, the
maximal performance capability of the products is often not fully
utilized (or even known). The invention is therefore particularly
suitable for these filled pressure-sensitive adhesives, in
particular highly filled pressure-sensitive adhesives, in
particular syntactic foams.
[0127] The adhesive treated in the invention can have been applied
on a carrier material, in particular a foil carrier (made of PE,
PP, PS, or polyester, such as PET), foam carrier, textile carrier,
nonwoven carrier, or paper carrier, or a composite carrier.
[0128] The carrier can comprise one or more layers of foils or of
foam carriers.
[0129] The adhesive tape formed from carrier and adhesive can
moreover comprise one or more functional layers such as barrier
layers, layers of material that can form a hotmelt, or other
functional layers.
[0130] The carrier preferably has viscoelastic properties.
[0131] On that side of the carrier that faces away from the
substrate there can moreover be a second adhesive present, which
does not have to be identical with the first, and which can have
been treated but has not necessarily been treated by the process of
the invention.
[0132] The uncovered side of the second adhesive layer can have
been treated with atmospheric-pressure plasma. This also applies to
the "second" substrate on which the second adhesive is
adhesive-bonded.
[0133] Preference is given to double-sided self-adhesive tapes,
preferably on a foil carrier or foam carrier.
[0134] Advantageous embodiments of the invention comprise the
adhesive tapes K1 to K8 described in the examples.
[0135] Preference is moreover given to double-sided carrierless
adhesive transfer tapes.
[0136] It is particularly preferable that the thickness of the
layer of pressure-sensitive adhesive or of the adhesive tape formed
thereby is .gtoreq.20 .mu.m, preferably .gtoreq.100 .mu.m, very
particularly preferably .gtoreq.300 .mu.m, and/or at most
.ltoreq.1500 .mu.m, preferably .ltoreq.1000 .mu.m.
[0137] Preference is in particular given to a single-layer
structure made of a viscoelastic layer. No weaknesses can arise
here at the inner interfaces, and the product is simple and
inexpensive. The greatest compromises between adhesion and cohesion
in the design of the product are typically involved here, since no
specific external layers are used to ensure adhesion. These
products therefore profit particularly from subsequently increased
adhesion.
[0138] In particular, preference is given to a single-layer
structure of a filled and resin-blended viscoelastic
pressure-sensitive adhesive tape, and particular preference is
given here to a syntactic foam.
[0139] Preference is equally given to a multilayer structure of
viscoelastic layers.
[0140] In principle, a suitable substrate is any of the substrates
that can actually be treated with the selected plasma. The
substantial exceptions in the case of most atmospheric plasma
treatments are fluoropolymer-based plastics, and among these
primarily the fully fluorinated plastics. However, even these
materials can be treated with suitable intensive plasmas.
[0141] In particular, the concept underlying the invention includes
not only high-energy materials but also low-energy materials, or
polar and nonpolar materials.
[0142] Particular preference is given to the substrates mentioned
in the examples.
[0143] Particular preference is given to steel, aluminum,
polyesters such as PET, PVC, PC, PMMA, PE, PP, EPDM, glass, ABS,
coating materials and coatings (inter alia acrylate- or PU-based),
CEC, composite materials such as CFC, wood-composite products,
coated paperboard packaging materials, foils, bottles, plastics
containers, but this list is not to be interpreted as
exclusive.
[0144] Treatment with atmospheric-pressure plasma therefore
differs--as already mentioned--essentially from corona treatment.
Indirect treatment with atmospheric-pressure plasma by means of
nozzles is particularly suitable here for the process taught.
[0145] A plasma nozzle with a stable plasma jet can still achieve a
homogeneous effect from a distance of some cm. In contrast, a
typical traditional corona gap has a maximal aperture of from 2 to
3 mm, and at greater distances either discharge becomes impossible
or the discharges become very inhomogeneous. Treatment giving good
results from thick irregularly shaped substrates or components is
therefore possible only by using a plasma nozzle.
[0146] A plasma nozzle is particularly suitable for treatments of
narrow materials with the width of an adhesive tape. Plasma nozzles
are available with various geometries: round, linear, etc. The
design of a round nozzle is generally suitable for treatment of
narrow adhesive tapes. However, linear nozzles are also suitable.
The plasma has low potential and can be rendered practically
potential free by taking an appropriate measure. It is therefore
also possible to treat sensitive electronic components by the
process taught.
[0147] Plasma treatment in air can be ozone-free (TUV Nord, Report
No. 34 268 8, for a plasma generator from Plasmatreat GmbH).
Another price advantage is obtained when no ozone destructor is
required.
[0148] Indirect plasma treatment by means of nozzles does not
damage the reverse side of the substrate or adhesive tape, because
no reverse opposing electrode is used. Self-adhesive tapes
typically have a release liner or release coating (e.g.
siliconized) which would be damaged by unintended corona discharges
on the reverse side. A potential-free plasma-nozzle treatment is
very particularly suitable for preventing reverse-side
discharges.
[0149] The process of the invention provides a wide variety of
advantages.
[0150] The process can achieve an increase not only in bond
strength but also in shear strength, over a wide range of
pressure-sensitive adhesives and substrates. The surface energy of
the substrate prior to treatment is of no significance.
[0151] The process is robust and not dependent on optimized
treatment for each composition and/or on optimized treatment for
each substrate.
[0152] In many cases, the process can generate a comparable final
bond strength with a given adhesive tape across a plurality of
classes of substrate, frequently via cohesive fracture. This
"universal tape" provides particular advantages, for example in the
design of adhesive bond with different adhesive-bonding
partners.
[0153] The effect of the process taught is synergistic, i.e.
[0154] more than the sum of the individual effects of treatment of
substrate or adhesive.
[0155] In particular, the frequent lack of success with treatment
of one side alone renders the treatment of both sides
non-obvious.
[0156] The invention can combine the following desirable properties
in a single adhesive tape (with the precondition of suitable bulk
properties): [0157] high peel strength [0158] high initial adhesion
[0159] high shear resistance [0160] high temperature resistance
[0161] suitability for substrates with low surface energy
(LSE).
[0162] The process is so robust and simple that it can achieve
maximization of adhesion with a single parameter set (for example
in accordance with the process PV1 explained in the examples) for
most of the adhesive tapes and substrates studied. "Maximization"
is defined here as an increase up to the measurable limit. Either
the material encounters its cohesion limit or the measured time in
holding-power tests is too long. A further increase in adhesion
cannot then provide any further gain in terms of strength of
adhesive bond. However, measurable differentiation when other
analytical methods are used is not excluded.
[0163] The process taught can therefore be a "universal treatment".
This is a particular feature of the invention.
[0164] An adhesive tape thus treated and adhesive-bonded exhibited
the same or at least comparable performance on all substrates. By
virtue of the process taught, the adhesive bonds became independent
of the substrate. In this sense, the adhesive tapes described
therefore assumed the character of "universal adhesive tapes". This
is equally a particular feature of the invention.
[0165] This is particularly surprising when acrylate adhesives are
used.
[0166] In particular because the invention permits equivalent
adhesive bonding on different substrates: it is particularly
desirable to avoid any necessity of developing a specific
pretreatment method for each substrate and each adhesive in order
to obtain an adequate adhesive bond.
[0167] The process also generates good resistance to nonpolar
solvents.
[0168] Test Methods
[0169] Bond Strength, Steel, 90.degree.
[0170] The bond strength tests were carried out by methods based on
PSTC-101 by peeling the adhesive tapes from the substrates at 300
mm/min at an angle of 90.degree. between peel direction and
substrate. For the test, the substrates were inserted into a
specific holder which permits perpendicular upward peeling of the
sample at an angle of 90.degree.. A Zwick tensile tester was used
to measure the bond strength. The test results have been averaged
over a peel distance of at least 75 mm, are stated in N/cm after
standardization for the width of the adhesive tape, and have been
averaged from three tests.
[0171] The double-sided carrierless adhesive tapes were laminated
to a 36 .mu.m etched PET foil, which gives a very good bond to the
surface of the adhesive. The other adhesive tapes have a carrier
with good tensile strength.
[0172] Shortly after adhesive bonding, a 2 kg roller was used 5
times to apply pressure to the test samples, the velocity of roller
application being 10 m/min. Unless otherwise stated, this was
followed by three days of aging at 23.degree. C. and 50% +/-5% rel.
humidity prior to the test. The test conditions used for bond
strength determination were 23.degree. C. +/-1.degree. C.
temperature and 50% +/-5% rel. humidity. The bond strength test
applied tension either to the laminated PET foil or to the carrier
of the adhesive tape.
[0173] Unless otherwise stated, the expression "bond strength" in
this invention is used for the parameters mentioned here, in
particular peel angle 90.degree. and peel velocity 300 mm/min. In
particular, the aging time of three days at 23.degree. C. and 50%
+/-5% rel. humidity after adhesive bonding and prior to the test is
also included here.
[0174] Holding Power
[0175] Holding power gives the strength of the adhesive bond for a
loading force acting parallel to the adhesive-bonded tape. It is
the time required for shear load to remove an adhesive tape
completely from a steel plate.
[0176] To determine the values for holding power, a double-sided
adhesive tape is adhesive-bonded between two polished steel plates
with an adhesive-bonding area of 25 mm.times.20 mm. The steel
plates have holes suitable for the suspension of the test sample
and for attachment of a suspended weight. After adhesive bonding,
pressure is applied for one minute to the test samples by using a
force of 600 N. Unless otherwise stated, the test samples are aged
for 14 days at 23.degree. C. and 50% +/-5% rel. humidity after
adhesive bonding and prior to testing. Unless otherwise stated, the
test samples are tested at constant 70.degree. C. in a
temperature-controlled chamber and with static loading with a
weight of 1 kg. The time to failure in minutes [min] is stated as
result.
[0177] Static Glass Transition Temperature
[0178] Static glass transition temperature was determined by
dynamic scanning calorimetry in accordance with DIN 53765. Unless
otherwise stated in any individual case, the glass transition
temperature T.sub.g information relates to the glass transition
temperature T.sub.g in accordance with DIN 53765:1994-03.
[0179] Molecular Weights
[0180] Average molecular weight M.sub.W and polydispersity D were
determined by means of gel permeation chromatography (GPC). THF was
used as eluent with 0.1% by volume of trifluoroacetic acid. The
measurement was made at 25.degree. C. The precolumn used was
PSS-SDV, 5 .mu.m, 103 .ANG. (10-7 m), ID 8.0 mm.times.50 mm. The
separation columns used were PSS-SDV, 5 .mu.m, 103 .ANG. (10-7 m),
105 .ANG. (10-5 m) and 106 .ANG. (10-4 m) with in each case ID 8.0
mm.times.300 mm. Sample concentration was 4 g/l, and flow rate was
1.0 ml per minute. Measurements were made against PMMA
standards.
[0181] Solids Content
[0182] Solids content is a measure of the proportion of
constituents that cannot be vaporized in a polymer solution. It is
determined gravimetrically by weighing the solution, then removing
the vaporizable fractions in a drying oven at 120.degree. C. for 2
hours, and weighing the residue.
[0183] K Value (FIKENTSCHER Method):
[0184] The K value is a measure of the average molecular size of
highly polymeric substances. It is measured by producing one
percent (1 g/100 ml) polymer solutions in toluene and determining
their kinematic viscosities with the aid of a VOGEL-OSSAG
viscometer. After standardization to the viscosity of toluene, the
relative viscosity is obtained, and the K value can be calculated
from this by the method of Fikentscher (Polymer 8/1967, 381
ff.).
[0185] Density Determination by Means of Pyknometer:
[0186] The principle of measurement is based on the displacement of
the liquid present in the pyknometer. The empty pyknometer and the
liquid-filled pyknometer are first weighed, and then the body on
which the measurement is to be made is placed in the vessel.
[0187] The density of the body is calculated from the weight
differences:
[0188] If [0189] m.sub.0 is the mass of the empty pyknometer,
[0190] m.sub.1 is the mass of the water-filled pyknometer, [0191]
m.sub.2 is the mass of the pyknometer with the solid, [0192]
m.sub.3 is the mass of the pyknometer with the solid, with water
added until it is full, [0193] .rho..sub.W is the density of water
at the appropriate temperature, [0194] .rho..sub.F is the density
of the solid.
[0195] The density of the solid is then given by:
.rho. F = ( m 2 - m 0 ) ( m 1 - m 0 ) - ( m 3 - m 2 ) .rho. W
##EQU00001##
[0196] Three determinations are carried out for each sample. It
should be noted that this method gives the envelope density (in the
case of porous solids, here a foam, the density based on the volume
inclusive of the pore spaces).
[0197] A number of examples will be used below for further
explanation of the invention, without any intention of resultant
restriction of any type.
[0198] Plasma Process PV1
[0199] Plasma process PV1 used a RD1004 plasma generator with an
FG5001 plasma generator from Plasmatreat GmbH (Steinhagen,
Germany). The plasma jet generated was passed out at a slightly
oblique angle through a nozzle tip rotating at 2800/min, so that
the treatment describes a circle. The nozzle here had been attached
fixedly and vertically at an angle of 90.degree. to the substrate,
and a moving table on which the samples (substrates) had been
placed was passed under the nozzle.
[0200] With uniform movement of the nozzle relative to the
substrate at constant distance from the substrate, the treatment is
carried out over a width corresponding to the diameter of the
plasma cone at the given distance. In particular, this diameter is
greater than the diameter of the plasma jet itself. In the case of
the distance selected here between nozzle and substrate, this
corresponds to a treatment width of about 25 mm.
[0201] In process PV1 (unless otherwise stated): [0202] both the
substrate and the adhesive were treated [0203] treatment of
substrate and treatment of adhesive to be adhesive-bonded thereto
took place in direct succession [0204] treatment velocity was 5
m/min [0205] treatment used compressed air as process gas [0206]
the distance from the moving table during treatment was 12 mm.
[0207] The distance of 12 mm from the moving table gives a
different distance between nozzle and treated surface, depending on
substrate thickness. The distance of nozzle from the substrate
surface can be calculated from the stated data for the substrates
(substrates and adhesive tapes). If the distance between nozzle and
substrate surface was adjusted to a particular value, this has been
explicitly noted.
[0208] The capability of achieving treatment with the same effect
at varying distances is one of the main features of the
invention.
[0209] Adhesives and Self-Adhesive Tapes Used
TABLE-US-00001 TABLE 1 Adhesive tapes used Thickness of Adhesive
Pressure-sensitive adhesive tape adhesive Structure tape K1
acrylate (hotmelt), viscoelastic 905 .mu.m syntactic foam with
single-layer microballoons product K2 acrylate (hotmelt),
viscoelastic 900 .mu.m pure acrylate single-layer product K3
acrylate (hotmelt), viscoelastic 1105 .mu.m syntactic foam with
single-layer microballoons and product with added resin K4 acrylate
(hotmelt), viscoelastic 990 .mu.m syntactic foam with single-layer
hollow glass product microbeads and with added resin K5 acrylate
(UV viscoelastic 800 .mu.m technology), single-layer syntactic foam
with product hollow glass microbeads K6 natural rubber adhesive on
280 .mu.m textile carrier K7 synthetic rubber adhesive on foil 100
.mu.m carrier K8 polyurethane, viscoelastic 1000 .mu.m syntactic
foam with single-layer microballoons product
[0210] The following descriptions provide details and precise
data.
TABLE-US-00002 TABLE 2 Raw materials used Chemical compound Trade
name Producer CAS No. bis(4-tert-butylcyclohexyl) Perkadox 16 Akzo
Nobel 15520-11-3 peroxydicarbonate
2,2'-azobis(2-methylpropionitrile), Vazo 64 DuPont 78-67-1 AlBN
2,2'-azobis(2-methylbutyronitrile) Vazo 67 DuPont 13472-08-7
pentaerythritol tetraglycidyl ether Polypox R16 UPPC AG 3126-63-4
Denacol EX-411 Nagase Chemtex Corp. 3,4-epoxycyclohexylmethyl 3,4-
Uvacure 1500 Cytec 2386-87-0 epoxycyclohexanecarboxylate Industries
Inc. N'-(3-(dimethylamino)propyl)-N,N- Jeffcat .RTM. Z-130 Huntsman
6711-48-4 dimethyl-1,3-propanediamine triethylenetetramine Epikure
925 Hexion 112-24-3 Specialty Chemicals microballoons (MB) Expancel
051 DU Expancel Nobel (dry-unexpanded microspheres, 40 Industries
diameter from 9 to 15 .mu.m, temperature for start of expansion
from 106 to 111.degree. C., TMA density .ltoreq.25 kg/m.sup.3)
hollow glass microbeads (HGM) Q-CEL 5070S OMEGA (borosilicate
glass, effective MINERALS density 0.7 g/cm.sup.3, size distribution
from 10 to 100 .mu.m with d.sub.50 = 35 .mu.m, compressive strength
24.1 MPa terpene-phenolic resin (softening Dertophene T110 DRT
resins 25359-84-6 point 110.degree. C.; M.sub.w = 500 to 800 g/mol;
D = 1.50) resorcinol bis(diphenyl phosphate) Reofos RDP Chemtura
57583-54-7 aqueous carbon black dispersion Levanyl Black Lanxess
(aqueous, solvent-free, organic N-LF pigment preparation) n-butyl
acrylate n-butyl Rohm & Haas 141-32-2 acrylate acrylic acid
pure acrylic BASF 79-10-7 acid 2-ethylhexyl acrylate Brenntag
103-11-7 methyl acrylate BASF 96-33-3 SIS/SI block copolymer Vector
4113 Dexco Polymers hydrocarbon resin Escorez 1310LC Exxon
technical white mineral oil Tufflo 6056 Citco 8042-47-5 antioxidant
Irganox 1010 BASF
[0211] The expansion capability of the microballoons can be
described via determination of TMA density [kg/m.sup.3] (Stare
Thermal Analysis System from Mettler Toledo; heating rate
20.degree. C./min). TMA density here is the minimal achievable
density at a certain temperature T.sub.max under atmospheric
pressure prior to collapse of the microballoons.
[0212] Adhesive M1 and Adhesive tape K1
[0213] Production of Main Polymer for M1
[0214] 30.0 kg of 2-ethylhexyl acrylate, 67.0 kg of butyl acrylate,
3.0 kg of acrylic acid, and 66.7 kg of acetone/isopropanol (96:4)
are charged to a reactor conventionally used for free-radical
polymerization processes. After nitrogen gas had been passed
through the system for 45 minutes, with stirring, the reactor is
heated to 58.degree. C., and 50 g of Vazo.RTM. 67, dissolved in 500
g of acetone, were added. The exterior heating bath was then heated
to 70.degree. C., and the reaction was carried out at this constant
external temperature. After 1 h, a further 50 g of Vazo.RTM. 67,
dissolved in 500 g of acetone, were added, and after 2 h the
mixture was diluted with 10 kg of acetone/isopropanol mixture
(96:4). After 5.5 h, 150 g of
bis(4-tert-butylcyclohexyl)peroxydicarbonate, dissolved in 500 g of
acetone, were added; after 6 h 30 min, a further 10 kg of
acetone/isopropanol mixture (96:4) were used for dilution. After 7
h, a further 150 g of bis(4-tert-butylcyclohexyl)peroxydicarbonate,
dissolved in 500 g of acetone, were added, and the heating bath was
controlled to a temperature of 60.degree. C.
[0215] After 22 h of reaction time, the polymerization was
terminated and the system was cooled to room temperature. The
solids content of the product was 50.2%, and this was dried. The K
value of the resultant polyacrylate was 75.2, its average molar
mass was M.sub.W=1 370 000 g/mol, its polydispersity D (Mw/Mn) was
17.13, and its static glass transition temperature Tg was
-38.0.degree. C.
[0216] Process 1: Concentration Increase/Production of Polyacrylate
Hotmelts
[0217] The acrylate copolymers (main polymers M1 and M2) are very
substantially freed from the solvent by means of single-screw
extruders (vented extruders, BERSTORFF GmbH, Germany) (residual
solvent content .ltoreq.0.3% by weight; cf. the individual
examples). The parameters for concentration-increase of main
polymer M1 are shown here by way of example. The rotation rate of
the screw was 150 rpm, the motor current was 15 A and the liquid
output achieved was 60.0 kg/h. Concentration was increased by
applying a vacuum at three domes. The reduced pressures were in
each case from 20 mbar to 300 mbar. The discharge temperature of
the concentrated hotmelt is about 115.degree. C. Solids content
after this step to increase concentration was 99.8%.
[0218] Process 2: Production of Foamed Composition
[0219] Foaming is carried out in an experimental system
corresponding to the depiction in FIG. 2.
[0220] The appropriate main polymer K (M1 to M5) is melted in a
feed extruder 1 (single-screw conveying extruder from Troester GmbH
& Co KG, Germany) and conveyed thereby in the form of polymer
melt by way of a heatable hose 11 into a planetary-gear extruder 2
(PGE) from ENTEX (Bochum); (in particular, a PGE with four modules
T.sub.1, T.sub.2, T.sub.3, T.sub.4 that could be heated
independently of one another was used). By way of the feed aperture
22, the molten resin is then added. There is moreover the
possibility of introducing additional additives or fillers, for
example color pastes, by way of other feed locations that are
present. At point 23 the crosslinking agent is introduced. All of
the components are mixed to give a homogeneous polymer melt.
[0221] By means of a melt pump 24a and a heatable hose 24b, the
polymer melt is transferred into a twin-screw extruder 3
(BERSTORFF) (input position 33). At position the accelerator
component is added. The entire mixture is then freed from all gas
inclusions in a vacuum dome V at a pressure of 175 mbar; (see above
for criterion for freedom from gas). On the screw, the vacuum zone
is followed by a blister B, permitting pressure increase in the
subsequent segment S. By suitable control of extruder rotation rate
and of the melt pump 37a, a pressure greater than 8 bar is
generated in the segment S between blister B and melt pump 37a, and
the microballoon mixture (microballoons embedded into the
dispersion aid in accordance with the data in the series of
experiments) is added at the feed point 35 and incorporated
homogeneously into the premix by means of a mixing element. The
resultant melt mixture is transferred into a die 5.
[0222] The incorporated microballoons expand after leaving the die
5, i.e. after pressure reduction, and by virtue of the pressure
reduction here the polymer composition is cooled under low-shear
conditions, in particular without shear. This gives a foamed
self-adhesive composition S, which is then formed into a layer
between two release materials, in particular between a release
material which can be reused after removal (process liner), the
composition then being shaped by means of a calender 4 into the
form of a web.
[0223] An alternate process can be found in DE 10 2009 015 233
A1.
[0224] Production of K1
TABLE-US-00003 TABLE 3 Components for K1 Components main polymer M1
[% by 94.85 Expancel 051 DU 40 weight] 1.93 Levanyl N-LF 2.15
Polypox R16 0.22 Jeffcat Z-130 0.19 Reofos RDP 0.66 Structure
Thickness [.mu.m] 905 Density [kg/m.sup.3] 650
[0225] The components mentioned were blended in accordance with
process 2 and extruded to produce the foamed adhesive tape K1.
[0226] Adhesive M2 and Adhesive Tape K2
[0227] Production of Main Polymer M2:
[0228] 54.4 kg of 2-ethylhexyl acrylate, 20.0 kg of methyl
acrylate, 5.6 kg of acrylic acid, and 53.3 kg of
acetone/isopropanol (94:6) are charged to a reactor conventionally
used for free-radical polymerization processes. After nitrogen gas
had been passed through the system for 45 minutes, with stirring,
the reactor was heated to 58.degree. C., and 40 g of Vazo.RTM. 67,
dissolved in 400 g of acetone, were added. The exterior heating
bath was then heated to 75.degree. C., and the reaction was carried
out at this constant external temperature. After 1 h, another 40 g
of Vazo.RTM. 67, dissolved in 400 g of acetone, were added, and
after 4 h the mixture was diluted with 10 kg of acetone/isopropanol
mixture (94:6).
[0229] After each of 5 h and 7 h, 120 g of
bis(4-tert-butyl-cyclohexyl)peroxydicarbonate, in each case
dissolved in 400 g of acetone, were used for post-initiation. After
22 h of reaction time, the polymerization was terminated and the
system was cooled to room temperature. The solids content of the
product was 55.9%, and this was dried. The K value of the resultant
polyacrylate was 58.8, its average molar mass was M.sub.W=746 000
g/mol, its polydispersity D (Mw/Mn) was 8.9, and its static glass
transition temperature Tg was -35.6.degree. C.
[0230] Concentration Increase/Production of Polyacrylate Hotmelts
in Accordance with Process 1 (See Above)
[0231] Production of K2
TABLE-US-00004 TABLE 4 Components for K2 Components main polymer M2
[% by 99.45 Polypox R16 weight] 0.4 Jeffcat Z-130 0.15 Structure
Thickness [.mu.m] 900 Density [kg/m.sup.3] 1015
[0232] The components mentioned were blended in accordance with
process 2 and extruded to produce the adhesive tape K2.
[0233] Adhesive Tape K3
[0234] Production of K3
TABLE-US-00005 TABLE 5 Components for K3 Components Main polymer M2
[% by wt] 69.6 Dertophene T110 28.3 Expancel 051 DU 40 0.7 Levanyl
N-LF 0.5 Polypox R16 0.14 Epikure 925 0.14 Structure Thickness
[.mu.m] [.mu.m] 1105 Density [kg/m.sup.3] [kg/m.sup.3] 780
[0235] The components mentioned were blended in accordance with
process 2 and extruded to produce the foamed adhesive tape K3.
[0236] Adhesive tape K4
[0237] Production of K4
TABLE-US-00006 TABLE 6 Components for K4 Components Main polymer M2
[% by wt] 48.7 Dertophene T110 19.8 Q-Cel 5070S 31.0 Polypox R16
0.21 Jeffcat Z-130 0.28 Structure Thickness [.mu.m] 990 Density
[kg/m.sup.3] 1010
[0238] The components mentioned were blended in accordance with
process 2 and extruded to produce the filled adhesive tape K4.
[0239] Adhesive tape K5
[0240] Adhesive tape K5 is GT6008, which is a filled single-layer
acrylate foam without resin addition from 3M with density 700
kg/m.sup.3 and thickness 800 .mu.m. It comprises hollow glass
microbeads (HGM) as filler in order to provide a syntactic foam.
The adhesive tape is produced by UV-polymerization, the process
being based by way of example on DE 40 02 834 A1.
[0241] Adhesive M6 and Adhesive Tape K6
[0242] Adhesive M6 is a natural rubber composition:
TABLE-US-00007 Constitution Weight of solids Raw material [% by
wt.] V145 natural 41.90 rubber HIKO RES 41.40 MS 40 chalk 12.70
filler Powder premix 3 4.00 for NR
[0243] Powder premix 3 is composed of 50% by weight of chalk, 25%
by weight of TiO.sub.2, and 25% by weight of antioxidants.
[0244] HIKO RES involves a C.sub.5-based hydrocarbon resin.
[0245] This natural rubber composition is applied at 50 g/m.sup.2
to a textile carrier equipped with a reverse-side release
system.
[0246] Adhesive M7 and Adhesive tape K7
[0247] Content of Adhesive M7
TABLE-US-00008 TABLE 7 Components for M7 Quantity Component 100 g
Vector 4113 125 g Escorez 1310LC 10 g Tufflo 6056 1.5 g Irganox
1010
[0248] Adhesive M7 in accordance with this formulation was applied
at a layer thickness of 50 g/m.sup.2 to an MOPP foil (thickness 85
.mu.m) (adhesive tape K7).
[0249] Adhesive M8 and Adhesive Tape K8
[0250] The polyurethane-based polymer M8 and the adhesive tape K8
were produced in accordance with WO 2009/138402 A1, and
specifically in accordance with example 4 in that document.
Furthermore, reference may also be made to EP 2 325 220 A1 in
connection with the production process. It is a viscoelastic
syntactic foam using preexpanded microballoons as filler. The
product was produced with a thickness of 1000 .mu.m.
[0251] Substrates Used
[0252] For Bond Strength Testing:
TABLE-US-00009 TABLE 8 Substrates used in bond strength testing
Substrate Description Thickness EPDM LyondellBasell (HX TRC 135X/4
Black), 3.5 mm smooth PE, PP, ABS, Standard plastics sheets made of
3 mm PET polyethylene, polypropylene, acrylonitrile-
butadiene-styrene, polyethylene terephthalate ASTM steel Standard
steel test plates in accordance with 1 mm ASTM standard Coating
BASF FF79-0020 (based on polyurethane) 1 mm material 1 coated onto
metal sheet with basecoat Coating BASF FF99-0778 (based on acrylate
resin) 3.5 mm material 2 coated on thin metal sheet, mounted onto
plastics sheet CFC Carbon fiber composite 2.3 mm CEC Cathodic
electrocoat on metal sheet 0.8 mm
DATA, EXAMPLES
[0253] Demonstration of the Advantageous Nature of the Process of
the Invention for Acrylate-Based Adhesives
[0254] (Plasma treatment in accordance with process PV1 or based on
PV1 on the stated surfaces, adhesive bonding immediately after
treatment)
TABLE-US-00010 TABLE 9 Bond strength [N/cm] ASTM Coating Coating
Adhesive tape Treatment EPDM PE ABS steel material 1 material 2 K1
PV1 42.16 42.98 42.55 44.41 39.99 40.54 No treatment 1.93 0.62
13.70 5.38 3.21 4.87 Only substrate 5.78 5.78 3.90 5.30 4.44 4.25
treated Only adhesive 1.10 0.71 11.47 43.22 2.85 4.00 treated K2
PV1 35.69 17.05 33.97 33.26 26.71 30.82 No treatment 1.95 1.78
11.90 12.39 6.34 10.70 Only substrate 18.61 14.16 13.66 13.19 12.61
12.19 treated Only adhesive 0.96 1.93 8.75 19.54 6.35 8.11 treated
K3 PV1 87.53 76.85 84.87 84.65 81.76 83.81 No treatment 3.11 2.38
38.11 49.67 11.91 30.21 Only substrate 61.65 64.85 43.25 73.14
37.47 39.20 treated Only adhesive 3.63 2.80 65.86 83.01 5.57 26.45
treated K4 PV1 68.61 62.80 71.62 71.53 74.18 73.36 No treatment
1.62 2.07 12.52 25.74 8.66 17.27 Only substrate 30.42 28.05 30.63
32.55 33.2 33.17 treated Only adhesive 3.36 2.02 10.27 69.17 9.63
17.57 treated K5 PV1 39.25 30.17 37.80 39.38 38.20 38.10 No
treatment 0.69 0.63 9.95 28.25 2.15 17.17 Only substrate 24.04
22.69 25.70 30.90 24.69 27.37 treated Only adhesive 0.60 0.56 1.51
38.74 2.15 2.76 treated
[0255] This demonstrates, for various acrylate compositions, that
the bond strength increased by this invention can be rendered
substantially independent of the substrate, in particular also on
substrates with low surface energy.
[0256] In individual cases, bond strength on a substrate with high
surface energy, for example steel, can also be in the vicinity of
the maximum for the adhesive provided, even without this invention.
This is not inimical to the invention.
[0257] A possibility that cannot be excluded in individual cases is
that the adhesive bond on a substrate does not achieve the maximum
possible bond strength with every treatment setting after aging for
three days at 23.degree. C. This can be compensated by adjusting
treatment parameters appropriately or by using a longer maturing
time.
[0258] A particularly important discovery is that in almost all
cases revealed here the sum of the bond strength increases from
individual treatment of substrate OR adhesive does not reach the
value achieved from treatment of substrate AND adhesive. (The "bond
strength increase" is defined here as the difference between the
value "after treatment" and "prior to treatment".) The effect due
to the process taught is in most cases synergistic, i.e. more than
the sum of the individual effects.
[0259] In particular, the often unsatisfactory effect of treatment
of one side alone renders the treatment of both sides non-obvious.
Adhesive bonding of K1 on PE can be taken as an example: [0260]
Bond strength without treatment was 0.62 N/cm. [0261] After
treatment only of the substrate, bond strength was 5.78 N/cm, i.e.
the increase achieved was disappointing: 5.16 N/cm. [0262] After
treatment only of the adhesive, bond strength was 0.71 N/cm, i.e.
the increase achieved was negligible: 0.09 N/cm. [0263] The sum of
these increases is therefore low: 5.25 N/cm. [0264] In contrast,
the increase due to the process taught is remarkable: 42.36
N/cm.
[0265] Relative Increase and Maximal Bond Strength
[0266] (due to process PV1)
TABLE-US-00011 TABLE 10 Average values on 6 substrates (EPDM, PE,
ABS, ASTM steel, coating material 1, coating material 2) Average
maximal Adhesive Particular feature Average improvement bond
strength tape of adhesive of bond strength [N/cm] K1 Foam 2055%
42.11 K2 Pure acrylate 675% 29.58 K3 Foam with resin 1233% 82.97 K4
Foam with resin 1567% 70.35 K5 Foam 2166% 37.15
[0267] This shows that particularly high relative increases in bond
strength are obtained by using a filler or by foaming. In
particular, the combination with resin addition leads not only to a
large relative increase but also to high absolute bond
strength.
[0268] Demonstration on Other Substrates with Adhesive Tape K1
[0269] (Plasma treatment in accordance with process PV1, adhesive
bonding immediately after treatment)
TABLE-US-00012 TABLE 11 Adhesive Bond strength tape K1 [N/cm]
Treatment: PP PET CFC CEC PV1 45.53 47.10 38.16 37.58 Without 3.95
9.61 7.16 3.97 treatment Only 17.71 12.11 12.47 14.81 substrate
treated Only 2.98 25.85 37.16 36.98 adhesive treated
[0270] The effect is demonstrated here for other substrates. In
particular, the effect is revealed for a carbon fiber composite
(CFC) and cathodic electrocoat (CEC).
[0271] These substrates and the substrates in the preceding
examples are particularly relevant for automobile construction.
EPDM is a typical material for seals, and CEC and coating materials
1 and 2 are used for coatings on bodywork. CFC is a material with
future relevance for lightweight construction.
[0272] Demonstration of the Advantageous Nature for Other
Adhesives
[0273] (Plasma treatment in accordance with process PV1, adhesive
bonding immediately after treatment)
TABLE-US-00013 TABLE 12 Underlying Bond strength chemistry of
[N/cm] Adhesive pressure-sensitive ASTM tape adhesive Treatment PE
steel K6 Natural Rubber PV 1 9.40 8.80 no treatment 5.56 8.22 K7
Synthetic rubber PV 1 8.80 7.96 no treatment 4.04 6.72 K8
Polyurethane PV 1 18.98 17.01 no treatment 3.51 3.61
[0274] The effect is demonstrated here for adhesives based on
different chemistry. In principle, the favorable effect can be
seen, but, by virtue of the restricted maximal bond strength of the
adhesives, the increase of bond strength is less significant. This
demonstrates the restricted performance capability of these
self-adhesive tapes, despite increased adhesion due to the process
corresponding to the present teaching.
[0275] Demonstration of Improved Shear Resistance
[0276] (Plasma treatment in accordance with process PV1, adhesive
bonding immediately after treatment)
TABLE-US-00014 TABLE 13 (Average max. bond strength Max. in
accordance HP, 70.degree. 1 kg [min] shear with table 10 Adhesive
Without [mm] [N/cm]) tape plasma PV1 PV1 PV1 K2 100 10 000 1 mm
29.58 K3 200 10 000 10 mm 82.97 K4 150 10 000 1 mm 70.35
[0277] Here, the improvement of adhesion for the adhesive tapes
based on the polymer M2 is demonstrated by improved holding power
(HP) at 70.degree. C. The adhesive tapes K2 to K4 used are based on
the main polymer M2 and differ in resin addition and filler
addition. Without the plasma treatment taught, the values for HP at
70.degree. C. are unsatisfactory, but after treatment they are
fully satisfactory. In particular, the combination of use of hollow
microspheres as filler and addition of resin (adhesive tape K4)
exhibits good holding power with a small value for shear under
load, and also with high bond strength (see table above).
[0278] Demonstration of High Bond Strengths After Short Time
[0279] (Plasma treatment in accordance with process PV1, adhesive
bonding immediately after treatment)
TABLE-US-00015 TABLE 14 Aging time after adhesive bonding prior to
measurement as Adhesive stated, at Bond strength [N/cm] ASTM tape
Treatment 23.degree. C./50% rh EPDM PE ABS steel Coating 2 K1 none
3 days 1.93 0.62 13.70 5.38 4.87 PV1 5 min 45.99 37.27 25.65 32.32
29.17 PV1 3 days 42.16 42.98 42.55 44.41 40.54 K2 none 3 days 1.95
1.78 11.90 12.39 10.70 PV1 5 min 19.09 25.10 17.72 14.37 23.07 PV1
3 days 35.69 17.05 33.97 33.26 30.82 K3) none 3 days 3.11 2.38
38.11 49.67 30.21 PV1 5 min 51.63 47.82 86.45 90.37 84.82 PV1 3
days 87.53 76.85 84.87 83.01 83.81 K5 none 3 days 0.69 0.63 9.95
28.25 17.17 PV1 5 min 21.09 34.47 42.90 43.74 42.59 PV1 3 days
39.25 30.17 37.80 39.38 38.10
[0280] Here, it is demonstrated that this process does not require
long maturing times. In the examples, the bond strengths always
reach at least 14 N/cm after 5 min.
[0281] Remarkably, the values reached by the bond strengths due to
treatment by PV1 in the examples are already higher after 5 min
than those after three days of maturing time without treatment.
Particularly suitable adhesives reach >40 N/cm after 5 min.
[0282] The bond strength achieved after 5 min. on steel by the
adhesive tape K3 by virtue of our invention was 90 N/cm, an
exceptionally high value.
[0283] Demonstration of Alternate Treatment Parameters
[0284] (Plasma treatment based on process PV1, changes from PV1 as
stated, adhesive bonding immediately after treatment)
TABLE-US-00016 TABLE 15 Distance Distance from from surface of
surface of Adhesive adhesive substrate F Substrate tape Process gas
[mm] [mm] [N/cm] ASTM steel K2 no treatment -- -- 10.70 ASTM steel
K2 air 5 8 33.14 ASTM steel K2 air 8 8 35.85 ASTM steel K2 air 11 8
33.69 ASTM steel K2 air 14 8 32.87 ASTM steel K2 air 17 8 32.67 PP
K3 no treatment -- -- 4.48 PP K3 N2 5 6 83.55 PP K3 N2 11 12 82.63
PP K3 N2 17 18 82.86 PP K3 air 5 6 79.85 PP K3 air 8 9 83.90 PP K3
air 11 12 83.21 PP K3 air 17 18 57.52
[0285] Here, it is demonstrated that the process is robust in
respect of variation of distances and operating gas. Process
latitude is surprisingly great.
[0286] Remarkably, the treatment distance available when operating
with N2 is greater than that when operating with air.
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