U.S. patent application number 13/203903 was filed with the patent office on 2012-02-02 for method for creating a foamed mass system.
This patent application is currently assigned to Tesa SE. Invention is credited to Axel Burmeister, Franziska Czerwonatis, Volker Lass, Stephan Schonbom.
Application Number | 20120029105 13/203903 |
Document ID | / |
Family ID | 42237217 |
Filed Date | 2012-02-02 |
United States Patent
Application |
20120029105 |
Kind Code |
A1 |
Czerwonatis; Franziska ; et
al. |
February 2, 2012 |
METHOD FOR CREATING A FOAMED MASS SYSTEM
Abstract
A method for producing a foamed mass system comprising thermally
sensitive substances, wherein the mass system is foamed at a first
temperature in a first step, and the thermally sensitive substances
are added to the mass system in a subsequent step at a second
temperature lower than the first temperature
Inventors: |
Czerwonatis; Franziska;
(Hamburg, DE) ; Schonbom; Stephan; (Tornesch,
DE) ; Burmeister; Axel; (Buchholz, DE) ; Lass;
Volker; (Elmenhorst, DE) |
Assignee: |
Tesa SE
Hamburg
DE
|
Family ID: |
42237217 |
Appl. No.: |
13/203903 |
Filed: |
March 18, 2010 |
PCT Filed: |
March 18, 2010 |
PCT NO: |
PCT/EP10/53541 |
371 Date: |
October 12, 2011 |
Current U.S.
Class: |
521/170 |
Current CPC
Class: |
B29K 2105/0097 20130101;
B29C 44/321 20161101; C09J 2301/412 20200801; C08J 2207/02
20130101; B29C 44/569 20130101; C08J 2203/22 20130101; C08J 9/32
20130101; B29K 2105/0002 20130101; C08J 9/36 20130101; B29K
2105/0076 20130101; C09J 7/38 20180101; C09J 7/10 20180101; B29K
2105/04 20130101; C09J 133/08 20130101; B29K 2033/04 20130101; B29K
2105/24 20130101; C08J 2333/08 20130101 |
Class at
Publication: |
521/170 |
International
Class: |
C09J 175/04 20060101
C09J175/04 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 1, 2009 |
DE |
102009015233.4 |
Claims
1. A method for producing a foamed mass system comprising thermally
sensitive substances, in which the mass system is foamed in a first
step at a first temperature, and the thermally sensitive substances
are added to the mass system in a following step at a second
temperature, which is lower than the first temperature.
2. The method of claim 1, wherein the first temperature, at which
the mass system is foamed, corresponds to or lies above the
expansion temperature of the microballoons, and the second
temperature, at which the thermally sensitive substances are added
to the mass system, lies below the expansion temperature of the
microballoons.
3. The method of either claim 1, wherein in a first mixing
assembly, expandable microballoons, and optionally further
additives, are introduced into a mass system; the mass system with
the microballoons added is heated under superatmospheric pressure
to a temperature of at least the expansion temperature of the
microballoons under atmospheric pressure, the microballoons are
expanded on emergence from the first mixing assembly, the mass
system is introduced into a second mixing assembly wherein the mass
system is at a temperature which lies below the expansion
temperature of the microballoons, the thermally sensitive
substances are added in the second mixing assembly, where it is
blended with the mass system the mass system thus blended is
shaped.
4. The method of claim 1, wherein in a first mixing assembly
expandable microballoons and optionally further additives are
introduced into a mass system; the mass system with the
microballoons added is heated under superatmospheric pressure in a
first mixing zone of the mixing assembly to a temperature of at
least the expansion temperature of the microballoons under
atmospheric pressure, the mass system is subsequently transferred
from the first mixing zone into a second mixing zone of the first
mixing assembly, at a temperature below the expansion temperature
of the microballoons, the thermally sensitive substances are added
during transfer of the mass system to the second mixing zone and/or
after transfer to the second mixing zone, where it is blended with
the mass system, the mass system thus blended is shaped.
5. The method of claim 1, wherein the mass system is or comprises a
self-adhesive.
6. The method of claim 1, wherein the thermally sensitive
substances or a portion of the thermally sensitive substances are
thermal crosslinkers.
7. The method of claim 1, wherein the thermally sensitive
substances or a portion of the thermally sensitive substances are
accelerators and/or regulators for a thermal crosslinking
reaction.
8. The method of claim 1, wherein the mass system, on addition of
the thermally sensitive substances, is present in a noncrosslinked
state.
9. The method of claim 3, wherein the foamed mass system provided
with the thermally sensitive substances is shaped to form a layer
on a carrier material or release material.
10. The method of claim 6, wherein the mass system is thermally
crosslinked.
11. The method of claim 9, wherein the thermal crosslinking
reaction or a major part of the thermal crosslinking reaction takes
place after the shaping to form the layer on the carrier material
or release material.
12. A foamed mass system produced by the method of claim 1.
13. A self-adhesive, for a single- or double-sidedly
(self-)adhesive tape, comprising the foamed mass system of claim
12.
Description
[0001] The invention relates to a method for producing thermally
crosslinked mass systems foamed with microballoons, more
particularly self-adhesives, and also to foamed masses thus
produced.
[0002] For a multiplicity of applications, foamed mass systems are
important. Foams are able, for example, to perform mechanical
buffering, by absorbing kinetic energy, or else to compensate
unevennesses, since they can easily deform.
[0003] As a result of this, foamed mass systems are being used
increasingly in adhesives processing as well. For example, in
adhesive tape production, more particularly in self-adhesive tape
production, it is possible for both foamed carrier materials and/or
foamed (self-)adhesives to be employed. In the adhesive bonding of
substrates to one another, use may then be made more particularly
of the advantages specified above, the adhesive tapes being
capable, for example, of compensating unevennesses in the surfaces
to be bonded.
[0004] Methods for producing microballoon-foamed self-adhesives and
carrier layers have been known for some considerable time.
[0005] EP 0 257 984 A1 discloses adhesive tapes which on at least
one side have a foamed adhesive coating. Contained within this
adhesive coating are polymer beads which in turn contain a fluid
comprising hydrocarbons, and expand at elevated temperatures. The
scaffold polymers of the self-adhesives may consist of rubbers or
polyacrylates. The hollow microbeads here are added either before
or after the polymerization. The self-adhesives comprising
microballoons are processed from solvent and shaped to form
adhesive tapes. The foaming step takes place consistently after
coating. Accordingly, microrough surfaces are obtained. This
results in properties such as, in particular, nondestructive
redetachability and repositionability. The effect of the better
repositionability through microrough surfaces of
microballoon-foamed self-adhesives is also described in other
specifications such as DE 35 37 433 A1 or WO 95/31225 A1.
[0006] The microrough surface is used in order to generate a
bubble-free adhesive bond. This use is also disclosed by EP 0 693
097 A1 and WO 98/18878 A1.
[0007] This described method, i.e., the processing from solvent and
the expansion of the incorporated microballoons after the web-form
shaping of the adhesive layer, is unsuitable, however, for the
production of permanently bonding foamed adhesive systems.
[0008] The advantageous properties of the microrough surface are
always opposed, therefore, by a distinct reduction in the bond
strength or peel strength. DE 197 30 854 A1 therefore proposes a
microballoon-foamed carrier layer which, for the purpose of
preventing the loss of bond strength, proposes the use of unfoamed
pressure-sensitive self-adhesives above and below a foamed
core.
[0009] The carrier mixture is preferably prepared in an internal
mixer typical for elastomer compounding. The mixture here is
adjusted in particular to a Mooney value ML.sub.1+3 (100.degree.
C.) in the range from 10 to 80. In a second, cold operation,
possible crosslinkers, accelerators, and the desired microballoons
are added to the mixture. This second operation takes place
preferably at temperatures less than 70.degree. C. in a kneading
apparatus, internal mixer, roll mixer or twin-screw extruder. The
mixture is subsequently calendered and/or extruded to the desired
thickness on machines. The carrier is then provided on both sides
with a pressure-sensitive self-adhesive. This is followed by the
steps of thermal foaming and, where appropriate, crosslinking.
[0010] The microballoons may be expanded either before they are
incorporated into the polymer matrix, or only after the polymer
matrix has been shaped to form a carrier.
[0011] In expanded form, the casing of the microballoons has a
thickness of only 0.02 .mu.m. Accordingly, the proposed expansion
of the microballoons prior to incorporation into the polymer matrix
of the carrier material is disadvantageous, since in that case, as
a result of the high forces during incorporation, many balloons
will be destroyed and the degree of foaming, accordingly, will be
reduced. Furthermore, partly damaged microballoons lead to
fluctuations in thickness. A robust production operation is barely
achievable. Preference is given, accordingly, to carrying out
foaming after the web-form shaping in a thermal tunnel. In this
case too, however, substantial deviations in the average carrier
thickness from the desired thickness are a likely occurrence, owing
to a lack of precisely constant conditions in the overall operation
prior to foaming, and to a lack of precisely constant conditions in
the thermal tunnel during foaming. Specific correction to the
thickness is no longer possible. Similarly, considerable
statistical deviations in the thickness must be accepted, since
local deviations in the concentration of microballoons and of other
carrier constituents as well are manifested directly in
fluctuations in thickness.
[0012] A similar route is described by WO 95/32851 A1. There it is
proposed that additional thermoplastic layers be provided between
foamed carrier and self-adhesive.
[0013] Both routes do comply with the requirement for high peel
strength, but also lead automatically to products having a
relatively high susceptibility, since the individual layers lead to
anchoring breaks under load. Furthermore, desired conformability of
such products is significantly restricted, because the foamed
component of a construction is necessarily reduced.
[0014] EP 1 102 809 B1 proposes a process in which the
microballoons undergo partial expansion prior to exit from a
coating die and, if desired, are brought to complete expansion by
means of a downstream step.
[0015] This process, however, is greatly limited in terms of its
function with respect to the viscosity of the mass. Highly viscous
mass systems lead inevitably to a high nip pressure in the die,
which compresses or deforms the expanded microballoons. Following
exit from the die, the microballoons regain their original shape
and puncture the surface of the adhesive. This effect is
intensified by increasing viscosity of the mass, decreasing layer
thickness, and falling density or rising microballoon fraction.
[0016] Microballoon-foamed (self-)adhesives or carrier layers are
distinguished by a defined cell structure with a uniform
distribution of foam cell sizes. They are closed-cell microfoams
without cavities, as a result of which they are able to seal
sensitive goods more effectively against dust and liquid media by
comparison with open-cell versions.
[0017] As a result of their flexible, thermoplastic polymer shell,
such foams possess greater conformity than foams filled with
unexpandable, nonpolymeric hollow microbeads (hollow glass beads).
They are better suited to the compensation of manufacturing
tolerances of the kind which are the rule, for example, with
injection moldings, and on account of their foam character they are
also better able to compensate thermal stresses.
[0018] Furthermore, the mechanical properties of the foam can be
influenced further by the selection of the thermoplastic resin of
the polymer shell. Thus, for example, it is possible to produce
foams having a higher cohesive strength than with the polymer
matrix alone, even when the density of the foam is lower than that
of the matrix. Hence typical foam properties such as conformability
to rough substrates can be combined with a high cohesive strength
for PSA foams.
[0019] Conventionally chemically or physically foamed materials, in
contrast, are more susceptible to irreversible collapse under
pressure and temperature. The cohesive strength here is lower as
well.
[0020] DE 21 05 877 C presents an adhesive tape composed of a
carrier which is coated on at least one side with a microcellular
pressure-sensitive adhesive and whose adhesive layer comprises a
nucleating agent, the cells of the adhesive layer being closed and
being distributed completely in the adhesive layer. This adhesive
tape has the ability to conform to the irregular surface to which
it is applied, and hence may lead to a relatively durable adhesive
bond, yet on the other hand exhibits only minimal recovery when
compressed to half its original thickness. The voids in the
adhesive offer starting points for the entry of solvents and water
into the glueline from the side, which is highly undesirable.
Furthermore, it is impossible to rule out the complete penetration
of solvents or water through the entire adhesive tape.
[0021] A disadvantage of the methods known from the prior art is
that thermally sensitive materials or substances, more particularly
those which have a decomposition temperature or reaction
temperature that lies below the expansion temperature of the
microballoons, cannot be processed, since these substances would
undergo decomposition during the expansion procedure or would react
in an uncontrolled way during the expansion procedure.
[0022] It is an object of the invention to overcome the
disadvantages of the prior art and more particularly to provide a
method that allows thermally sensitive substances to be
incorporated into a foamed pressure-sensitive adhesive, preferably
without thereby adversely affecting the degree of foaming.
[0023] The invention is achieved by means of a method in which the
mass system is first foamed in a first step at a first temperature,
and the thermally sensitive substances are added to the mass system
in a following step at a second, lower temperature than the first
temperature.
[0024] The mass system is advantageously foamed in a first step,
more particularly through expansion of microballoons at the
temperature necessary for that purpose, and the thermally sensitive
substances are to be admixed only in a following method step at a
lower temperature, thus more particularly a temperature which lies
below the expansion temperature of the microballoons, especially
advantageously at a temperature which is not critical for the
thermally sensitive substances.
[0025] In this respect it is advantageous, in particular, if the
first temperature, at which the mass system is foamed, corresponds
to or lies above the expansion temperature of the microballoons,
and if the second temperature, at which the thermally sensitive
substances are added to the mass system, lies below the expansion
temperature of the microballoons.
[0026] The procedure according to the invention is also suitable
for substances of great thermal sensitivity. If cooling to a lower
temperature does not produce a temperature which is already not
critical for the thermal substances, then the time from the
addition of the thermally sensitive substances until the shaping of
the mass system can be minimized, however, and so secondary
reactions, decomposition of the thermally sensitive substances or
other kinds of unwanted reactions of these substances can be
reduced to a minimum. As a result of the method of the invention,
it is possible to prevent the thermally sensitive substances being
subjected to the method step of microballoon expansion and to the
temperature conditions that are required for such expansion.
[0027] To the skilled person it was surprising and unforeseeable
that in the second mixing assembly there is no loss of foaming rate
on cooling of the foam and on addition of the further substances.
The cooling causes an increase in the viscosity of the mass system,
and so, in the case of processing in a mixing assembly, an
increased shear is likely. In accordance with expectation, the
processing of foamed mass systems in mixing assemblies therefore
leads, in the case of foamed mass systems at low temperatures, to
"destructive beating" of the foam and hence to a significant
decrease in the degree of foaming.
[0028] It has emerged, surprisingly, that microballoon-foamed mass
systems are good at withstanding processing after cooling in a
system in which the mass is subject to shearing, more particularly
in a mixing assembly. As a result, it has been made possible to
admix heat-sensitive additives in a method step downstream of the
foaming operation, without any significant decrease in the degree
of foaming.
[0029] In accordance with the invention it is possible to perform
the cooling of the mass system and the admixing of the
heat-sensitive substances in the same mixing assembly in which the
mixing of the mass system with the as yet unexpanded microballoons
has already been carried out.
[0030] The method of the invention opens up a route allowing foamed
mass systems--that is, systems after the expansion of the
microballoons as well--to be processed further. In other words, in
particular, additional thermally sensitive adjuvants, fillers or
additives, such as fragrances or crosslinker components, for
example, can be incorporated, without destroying the expanded
microballoons present in the polymer matrix.
[0031] With the method of the invention, success has been achieved
in particular in opening up access for thermal crosslinking to
foamed mass systems such as foamed self-adhesives, for example,
where the foaming is realized by means of supply of thermal energy,
without the mass system undergoing uncontrolled crosslinking in the
process.
[0032] Accordingly, therefore, it is possible to uncouple the
expansion procedure from the crosslinking operation. In other
words, the choice of the crosslinking system can be made completely
independently of the choice of the type of microballoon to be
expanded, and vice versa.
Microballoons
[0033] Microballoons are elastic hollow spheres which have a
thermoplastic polymer casing. These spheres are filled with
low-boiling liquids or with liquefied gas. Casing materials used
are, in particular, polyacrylonitrile, PVDC, PVC or polyacrylates.
Suitable low-boiling liquids are, in particular, hydrocarbons of
the lower alkanes, for example isobutane or isopentane, which are
enclosed as liquefied gas under pressure in the polymer casing. The
exposing of the microballoons, more particularly their exposure to
heat, has the effect on the one hand of softening the outer polymer
casing. At the same time, the liquid propellant gas within the
casing converts to its gaseous state. Here, the microballoons
undergo irreversible extension and expand three-dimensionally. The
expansion is at an end when the internal pressure and the external
pressure compensate one another. Since the polymeric casing is
retained, the result is a closed-cell foam.
[0034] A multiplicity of types of microballoon are available
commercially, such as, for example, from the company Akzo Nobel,
the Expancel DU products (dry unexpanded), which differ essentially
in their size (6 to 45 .mu.m in diameter in the unexpanded state)
and in the initiation temperature they require for expansion (75 to
220.degree. C.). When the type of microballoon or the foaming
temperature has been harmonized with the temperature profile
required for the compounding of the mass, and with the machine
parameters, it is also possible for mass compounding and foaming to
take place simultaneously in one step.
[0035] Furthermore, unexpanded microballoon products are also
available in the form of an aqueous dispersion having a solids
fraction or microballoon fraction of approximately 40% to 45% by
weight, and also, furthermore, in the form of polymer-bound
microballoons (masterbatches), for example in ethyl-vinyl acetate,
with a microballoon concentration of approximately 65% by weight.
Not only the microballoon dispersions but also the masterbatches
are suitable, like the DU products, for the foaming of adhesives in
accordance with the method of the invention.
Mass Base
[0036] The mass system is with particular preference a polymeric
system of a kind which can be used as an adhesive, especially
advantageously as a self-adhesive or pressure-sensitive
adhesive.
[0037] With the method of the invention it is possible in principle
to carry out solvent-free processing of all existing adhesives
components that are described in the literature, more particularly
those of self-adhesives.
[0038] The selection of a suitable adhesive base for the
implementation of the method of the invention is not critical. It
may be selected from the group of thermoplastic elastomers
constituting natural rubbers and synthetic rubbers, including block
copolymers and blends thereof, or else from the group of the
polyacrylate adhesives, as they are called.
[0039] Adhesives used may additionally be based on polyurethane,
silicone rubbers and/or polyolefins.
[0040] In accordance with the invention it is also possible to
employ mixed systems of adhesives having different bases (blends
based on two or more of the following chemical classes of compound:
natural rubbers and synthetic rubbers, polyacrylates,
polyurethanes, silicone rubbers, polyolefins and/or others; and/or
copolymers of the corresponding monomers of the above polymer
classes, and/or further monomers).
[0041] The base for the rubber-based adhesives is advantageously a
nonthermoplastic elastomer selected from the group of natural
rubbers or synthetic rubbers, or it is composed of any desired
blend of natural rubbers and/or synthetic rubbers, the natural
rubber or rubbers being selectable in principle from all available
grades such as, for example, crepe, RSS, ADS, TSR or CV products,
depending on required purity and viscosity, and the synthetic
rubber or synthetic rubbers being selectable from the group of
randomly copolymerized styrene-butadiene rubbers (SBR), butadiene
rubbers (BR), synthetic polyisoprenes (IR), butyl rubbers (IIR),
halogenated butyl rubbers (XIIR), acrylate rubbers (ACM),
ethylene-vinyl acetate copolymers (EVA) and polyurethanes, and/or
blends thereof.
[0042] With further preference it is possible to select
thermoplastic elastomers as a base for the adhesive.
[0043] As representatives, mention may be made at this point of the
styrene block copolymers and especially of the
styrene-isoprene-styrene (SIS) and styrene-butadiene-styrene (SBS)
products.
[0044] With further preference, the adhesive may also be selected
from the group of polyacrylates.
[0045] It is advantageous in this case if at least a portion of the
monomers have functional groups which are able to react in a
thermal crosslinking reaction and/or which promote a thermal
crosslinking reaction.
[0046] For the method of the invention it is preferred to use a
polyacrylate which on the following reactant mixture, comprising,
in particular, softening monomers, additionally monomers with
functional groups capable of entering into reactions with the
crosslinker substances or with some of the crosslinker substances,
more particularly addition reactions and/or substitution reactions,
and also, optionally, further copolymerizable comonomers, more
particularly hardening monomers. The nature of the polyacrylate to
be prepared (pressure-sensitive adhesive; heat-sealing composition,
viscoelastic nontacky material, and the like) may be influenced in
particular via a variation in the glass transition temperature of
the polymer, through different weight fractions of the individual
monomers.
[0047] For purely crystalline systems there is a thermal
equilibrium between crystal and liquid at the melting point
T.sub.m. Amorphous or partially crystalline systems, in contrast,
are characterized by the transformation of the more or less hard
amorphous or partially crystalline phase into a softer (rubberlike
to viscous) phase. At the glass point, particularly in the case of
polymeric systems, there is a "thawing" (or "freezing" in the case
of cooling) of the Brownian molecular motion of relatively long
chain segments. The transition from the melting point T.sub.m (also
"melting temperature"; really defined only for purely crystalline
systems; "polymer crystals") to the glass transition point T.sub.g
(also "glass transition temperature", "glass temperature") can
therefore be considered to be a fluid transition, depending on the
proportion of the partial crystallinity of the sample under
analysis.
[0048] In the sense of the remarks above, when the glass point is
stated, the reference for the purposes of this specification
includes the melting point as well--in other words, the glass
transition point (or else, synonymously, the glass transition
temperature) is also understood to include the melting point for
the corresponding "melting" systems. The statements of the glass
transition temperatures relate to the determination by means of
dynamic mechanical analysis (DMA) at low frequencies.
[0049] In order to obtain polymers, as for example
pressure-sensitive adhesives or heat-sealing compositions, having
desired glass transition temperatures, the quantitative composition
of the monomer mixture is advantageously selected such that, in
accordance with an equation (E1) in analogy to the Fox equation
(cf. T. G. Fox, Bull. Am. Phys. Soc. 1 (1956) 123), the desired
T.sub.g value for the polymer is produced.
1 T g = n W n T g , n ( E1 ) ##EQU00001##
[0050] In this equation, n represents the serial number of the
monomers used, W.sub.n represents the mass fraction of the
respective monomer n (% by weight), and T.sub.g,n represents the
respective glass transition temperature of the homopolymer of each
of the monomers n, in K.
[0051] It is preferred to use a polyacrylate which can be traced
back to the following monomer composition: [0052] a) acrylic and/or
methacrylic esters of the following formula
[0052] CH.sub.2.dbd.C(R.sup.I)(COOR.sup.II)
[0053] where R.sup.I.dbd.H or CH.sub.3 and R.sup.II is an alkyl
radical having 4 to 14 C atoms, [0054] b) olefinically unsaturated
monomers having functional groups of the type already defined for
reactivity with crosslinker substances or some of the crosslinker
substances, [0055] c) optionally further acrylates and/or
methacrylates and/or olefinically unsaturated monomers which are
copolymerizable with component (a).
[0056] For the use of the polyacrylate as a pressure-sensitive
adhesive (PSA), the fractions of the corresponding components (a),
(b), and (c) are selected such that the polymerization product more
particularly has a glass transition temperature .ltoreq.15.degree.
C. (DMA at low frequencies).
[0057] For the preparation of PSAs it is very advantageous to
select the monomers of component (a) with a fraction from 45% to
99% by weight, the monomers of component (b) with a fraction from
1% to 15% by weight, and the monomers of component (c) with a
fraction from 0% to 40% by weight (the figures are based on the
monomer mixture for the "base polymer", i.e., without additions of
any additives to the completed polymer, such as resins etc.).
[0058] For the application of a hotmelt adhesive, in other words of
a material which acquires its pressure-sensitive tack only by
virtue of heating, the fractions of the corresponding components
(a), (b), and (c) are selected more particularly such that the
copolymer has a glass transition temperature (T.sub.g) of between
15.degree. C. and 100.degree. C., preferably between 30.degree. C.
and 80.degree. C., more preferably between 40.degree. C. and
60.degree. C. The fractions of components (a), (b), and (c) should
be selected accordingly.
[0059] A viscoelastic material, which, for example, may typically
be laminated on both sides with pressure-sensitive adhesive layers,
has a glass transition temperature (T.sub.g) in particular of
between -50.degree. C. to +100.degree. C., preferably between
-20.degree. C. to +60.degree. C., more preferably 0.degree. C. to
40.degree. C. Here again, the fractions of components (a), (b), and
(c) should be selected accordingly.
[0060] The monomers of component (a) are, in particular, softening
and/or apolar monomers. For the monomers (a) it is preferred to use
acrylic monomers which comprise acrylic and methacrylic esters with
alkyl groups consisting of 4 to 14 C atoms, preferably 4 to 9 C
atoms. Examples of monomers of this kind are n-butyl acrylate,
n-butyl methacrylate, n-pentyl acrylate, n-pentyl methacrylate,
n-amyl acrylate, n-hexyl acrylate, hexyl methacrylate, n-heptyl
acrylate, n-octyl acrylate, n-octyl methacrylate, n-nonyl acrylate,
isobutyl acrylate, isooctyl acrylate, isooctyl methacrylate, and
their branched isomers, such as 2-ethylhexyl acrylate, 2-ethylhexyl
methacrylate, for example.
[0061] The monomers of component (b) are, in particular,
olefinically unsaturated monomers (b) having functional groups, in
particular having functional groups which are able to enter into a
reaction with the epoxide groups.
[0062] Preference for component (b) is given to using monomers
having those functional groups which are selected from the
following listing: hydroxyl, carboxyl, sulfonic acid or phosphonic
acid groups, acid anhydrides, epoxides, amines.
[0063] Particularly preferred examples of monomers of component (b)
are acrylic acid, methacrylic acid, itaconic acid, maleic acid,
fumaric acid, crotonic acid, aconitic acid, dimethylacrylic acid,
.beta.-acryloyloxypropionic acid, trichloroacrylic acid,
vinylacetic acid, vinylphosphonic acid, itaconic acid, maleic
anhydride, hydroxyethyl acrylate, hydroxypropyl acrylate,
hydroxyethyl methacrylate, hydroxypropyl methacrylate,
6-hydroxyhexyl methacrylate, allyl alcohol, glycidyl acrylate,
glycidyl methacrylate.
[0064] For the purposes of component (c) it is possible in
principle to use all compounds with vinylic functionalization which
are copolymerizable with component (a) and/or component (b), and
which may also serve to adjust the properties of the resultant
PSA.
[0065] Monomers named by way of example for component (c) are as
follows: methyl acrylate, ethyl acrylate, propyl acrylate, methyl
methacrylate, ethyl methacrylate, benzyl acrylate, benzyl
methacrylate, sec-butyl acrylate, tert-butyl acrylate, phenyl
acrylate, phenyl methacrylate, isobornyl acrylate, isobornyl
methacrylate, t-butylphenyl acrylate, t-butylphenyl methacrylate,
dodecyl methacrylate, isodecyl acrylate, lauryl acrylate, n-undecyl
acrylate, stearyl acrylate, tridecyl acrylate, behenyl acrylate,
cyclohexyl methacrylate, cyclopentyl methacrylate, phenoxyethyl
acrylate, phenoxyethyl methacrylate, 2-butoxyethyl methacrylate,
2-butoxyethyl acrylate, 3,3,5-trimethylcyclohexyl acrylate,
3,5-dimethyladamantyl acrylate, 4-cumylphenyl methacrylate,
cyanoethyl acrylate, cyanoethyl methacrylate, 4-biphenyl acrylate,
4-biphenyl methacrylate, 2-naphthyl acrylate, 2-naphthyl
methacrylate, tetrahydrofurfuryl acrylate, diethylaminoethyl
acrylate, diethylaminoethyl methacrylate, dimethylaminoethyl
acrylate, dimethylaminoethyl methacrylate, 2-butoxyethyl acrylate,
2-butoxyethyl methacrylate, methyl 3-methoxyacrylate,
3-methoxybutyl acrylate, phenoxyethyl acrylate, phenoxyethyl
methacrylate, 2-phenoxyethyl methacrylate, butyldiglycol
methacrylate, ethylene glycol acrylate, ethylene glycol
monomethylacrylate, methoxy polyethylene glycol methacrylate 350,
methoxy polyethylene glycol methacrylate 500, propylene glycol
monomethacrylate, butoxydiethylene glycol methacrylate,
ethoxytriethylene glycol methacrylate, octafluoropentyl acrylate,
octafluoropentyl methacrylate, 2,2,2-trifluoroethyl methacrylate,
1,1,1,3,3,3-hexafluoroisopropyl acrylate,
1,1,1,3,3,3-hexafluoroisopropyl methacrylate,
2,2,3,3,3-pentafluoropropyl methacrylate,
2,2,3,4,4,4-hexafluorobutyl methacrylate,
2,2,3,3,4,4,4-heptafluorobutyl acrylate,
2,2,3,3,4,4,4-heptafluorobutyl methacrylate,
2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctyl methacrylate,
dimethylaminopropylacrylamide, dimethylaminopropylmethacrylamide,
N-(1-methylundecyl)acrylamide, N-(n-butoxymethyl)acrylamide,
N-(butoxymethyl)methacrylamide, N-(ethoxymethyl)acrylamide,
N-(n-octadecyl)acrylamide, and also N,N-dialkyl-substituted amides,
such as, for example, N,N-dimethylacrylamide,
N,N-dimethylmethacrylamide, N-benzylacrylamide,
N-isopropylacrylamide, N-tert-butylacrylamide,
N-tert-octylacrylamide, N-methylolacrylamide,
N-methylolmethacrylamide,
acrylonitrile, methacrylonitrile, vinyl ethers, such as vinyl
methyl ether, ethyl vinyl ether, vinyl isobutyl ether, vinyl
esters, such as vinyl acetate, vinyl chloride, vinyl halides,
vinylidene chloride, vinylidene halides, vinylpyridine,
4-vinylpyridine, N-vinylphthalimide, N-vinyllactam,
N-vinylpyrrolidone, styrene, a- and p-methylstyrene,
a-butylstyrene, 4-n-butylstyrene, 4-n-decylstyrene,
3,4-dimethoxystyrene, macromonomers such as 2-polystyrene-ethyl
methacrylate (molecular weight Mw from 4000 to 13 000 g/mol),
poly(methyl methacrylate)-ethyl methacrylate (Mw from 2000 to 8000
g/mol).
[0066] Monomers of component (c) may advantageously also be
selected such that they contain functional groups which support
subsequent radiation crosslinking (by electron beams, UV, for
example). Suitable copolymerizable photoinitiators are, for
example, benzoin acrylate and acrylate-functionalized benzophenone
derivatives. Monomers which support crosslinking by electron
irradiation are, for example, tetrahydrofurfuryl acrylate,
N-tert-butylacrylamide, and allyl acrylate, this enumeration not
being conclusive.
[0067] The mass system may further be selected such that it may be
used as a carrier layer--more particularly for an adhesive tape.
The above remarks relating to the chemical nature apply analogously
for this purpose, although a carrier layer of this kind need not
necessarily have adhesive or self-adhesive properties (though of
course it may do so).
Additives
[0068] As tackifying resins it is possible without exception to use
all tackifier resins already known and described in the literature.
Representatives that may be stated are the rosins, their
disproportionated, hydrogenated, polymerized, and esterified
derivatives and salts, the aliphatic and aromatic hydrocarbon
resins, terpene resins and terpene-phenolic resins. Any desired
combinations of these and additional resins may be used in order to
adjust the properties of the resultant adhesive in accordance with
requirements.
[0069] As plasticizers it is possible to use all of the
plasticizing substances known from adhesive tape technology. These
include, among others, the paraffinic and naphthenic oils,
(functionalized) oligomers such as oligobutadienes, oligoisoprenes,
liquid nitrile rubbers, liquid terpene resins, vegetable and animal
oils and fats, phthalates, functionalized acrylates, low molecular
mass polyacrylates, water-soluble plasticizers, plasticizing
resins, phosphates, polyphosphates, and citrates.
[0070] Optionally it is also possible to add powder- and
granule-form fillers, dyes, and pigments, including, in particular,
abrasive and reinforcing types, such as, for example chalks
(CaCO.sub.3), titanium dioxides, zinc oxides, and carbon blacks.
With great preference it is possible to use various forms of chalk
as a filler, and Mikrosohl chalk is employed with particular
preference.
[0071] It is also possible for low-flammability fillers, such as,
for example, ammonium polyphosphate, and also electrically
conductive fillers (such as, for example, conductive carbon black,
carbon fibers and/or silver-coated beads), and also thermally
conductive materials (such as, for example, boron nitride, aluminum
oxide, silicon carbide), and also ferromagnetic additives (such as,
for example, iron(III) oxides), and also additives for volume
increase, especially for producing foamed layers (such as, for
example, expandants, solid glass beads, hollow glass beads,
microbeads made of other materials, silica, silicates, organically
renewable raw materials, for example sawdust, organic and/or
inorganic nanoparticles, fibers), and also aging inhibitors, light
stabilizers, ozone protectants, compounding agents and/or
expandants, to be added or compounded in. As aging inhibitors it is
possible with preference for primary aging inhibitors, e.g.,
4-methoxyphenol, and secondary aging inhibitors, e.g., Irgafos.RTM.
TNPP from Ciba Geigy, to be used, either alone or in combination
with one another. Reference is to be made only at this point here
to further corresponding Irganox.RTM. products from Ciba Geigy and
Hostano.RTM. from Clariant. As further outstanding agents against
aging it is possible to use phenothiazine (C-radical scavenger) and
also hydroquinone methyl ether in the presence of oxygen, and also
oxygen itself.
Thermally Sensitive Substances
[0072] Thermally sensitive substances may be, for example,
crosslinker substances and/or crosslinker accelerator substances
that are to be used for thermal crosslinking of the mass system
(the adhesive or pressure-sensitive adhesive). At the temperatures
of the kind needed for expansion of the microballoons, such
substances would already result in an uncontrollable crosslinking
reaction ("gelling") in the mixing assembly--depending on the
degree of uncontrollable crosslinking, such reaction may lead to
sporadic aggregation or even complete caking. In that case, shaping
of the mass system, more particularly its uniform and homogeneous
coating, as is important for adhesives and PSAs, can no longer be
carried out, and with too high a degree of crosslinking, the mass
system loses any suitability as a pressure-sensitive adhesive or
self-adhesive.
[0073] Thermally sensitive substances may also, for example, be
colorants or fragrances, especially those which at elevated
temperatures undergo decomposition or otherwise lose their coloring
or fragrancing properties, respectively.
[0074] It is also possible for the crosslinker system to be
composed of thermally sensitive and thermally insensitive
components; for example, the crosslinkers themselves may be
thermally insensitive, but the crosslinker accelerators may be
thermally sensitive, or vice versa. It is also possible, for the
purpose of the thermally induced chemical crosslinking, in the
method according to the invention, for all existing thermally
activatable chemical crosslinkers such as accelerated sulfur
systems or sulfur donor systems, isocyanate systems, reactive
melamine resins, formaldehyde resins and (optionally halogenated)
phenol-formaldehyde resins and/or reactive phenolic-resin or
diisocyanate crosslinking systems, with the corresponding
activators, or epoxidized polyester resins and acrylate resins, and
also combinations thereof, to be employed.
[0075] The crosslinkers are advantageously crosslinkers which are
activatable at temperatures above 50.degree. C., more particularly
at temperatures of 100.degree. C. to 160.degree. C., very
preferably at temperatures of 110.degree. C. to 140.degree. C.
[0076] The thermal excitation of the crosslinkers may take place,
for example, by in-process heat (active heating, heat of shearing),
IR radiation or high-energy alternating fields.
[0077] In one very advantageous embodiment, the added thermal
crosslinker is an isocyanate, preferably a trimerized isocyanate.
With particular preference, the trimerized isocyanates are
aliphatic isocyanates and/or isocyanates that are deactivated with
amines. Examples of suitable isocyanates include trimerized
derivatives of MDI [4,4-methylenedi(phenyl isocyanate)], HDI
[1,6-hexylene diisocyanate] and/or IPDI [isophorone diisocyanate,
5-isocyanato-1-isocyanatomethyl-1,3,3-trimethylcyclohexane] and
also--especially trimerized--polyisocyanates and/or polyfunctional
isocyanates and/or polyfunctional polyisocyanates.
[0078] Reference may be made here in particular to thermal
crosslinkers which are emphasized as being advantageous in WO
2006/027387 A1.
[0079] Additionally, and very advantageously, it is possible to use
a crosslinker-accelerator system for the thermal crosslinking
particularly of polyacrylates, comprising at least one substance
containing epoxide groups--as crosslinker--and at least one
substance ("accelerator") which has an accelerating effect on the
linking reaction at a temperature below the melting temperature of
the polyacrylate, more particularly at room temperature;
polyfunctional amines especially. The crosslinker-accelerator
system is used in particular in the presence of functional groups
in the building blocks of the mass that are able to enter into a
linking reaction with epoxide groups, particularly in the form of
an addition or substitution reaction. In the course of the thermal
crosslinking, therefore, there is preferably linking of the
building blocks that carry the functional groups with the building
blocks that carry the epoxide groups (more particularly in the
sense of a crosslinking of the corresponding polymer building
blocks carrying the functional groups, by way of the substances
carrying the epoxide groups, as linking bridges). Substance having
an accelerating effect means that the substance supports the
crosslinking reaction insofar as it ensures an inventively
sufficient reaction rate, whereas the crosslinking reaction in the
absence of the accelerator, with selected reaction parameters, here
more particularly a temperature which lies below the melting
temperature of the polyacrylates, would not proceed at all or would
proceed only with insufficient slowness. The accelerator, then,
ensures a substantial improvement in the kinetics of the
crosslinking reaction. This may take place catalytically, in
accordance with the invention, or else by coupling into the
reaction event.
[0080] Reference may be made in particular to
crosslinker-accelerator systems as presented in DE 10 2007 016 950
A1.
Carrier
[0081] As carrier material for the single-sided or double-sided
adhesive tape it is possible to use all known textile carriers such
as a loop product or a velour, scrim, woven fabric or knitted
fabric, more particularly a woven PET filament fabric or a woven
polyamide fabric, or a nonwoven web; the term "web" embraces at
least textile fabrics according to EN 29092 (1988) and also
stitchbonded nonwovens and similar systems.
[0082] It is likewise possible to use spacer fabrics, including
wovens and knits, with lamination. Spacer fabrics are matlike layer
structures having a cover layer composed of a fiber or filament
fleece, an underlayer, and individual retaining fibers or bundles
of such fibers between these layers, the said fibers being
distributed over the area of the layer structure, being needled
through the particle layer, and joining the cover layer and the
underlayer to one another. The retaining fibers that are needled
through the particle layer hold the cover layer and the underlayer
at a distance from one another and are joined to the cover layer
and the underlayer.
[0083] Suitable nonwovens include, in particular, consolidated
staple fiber webs, but also filament webs, meltblown webs and
spunbonded webs, which generally require additional consolidation.
Known, possible consolidation methods for webs are mechanical,
thermal and chemical consolidation. Whereas with mechanical
consolidations the fibers are held together purely mechanically,
usually by entanglement of the individual fibers, by the
interleafing of fiber bundles or by the stitching-in of additional
threads, it is possible by thermal and by chemical techniques to
obtain adhesive (with binder) or cohesive (binderless) fiber-fiber
bonds. Given appropriate formulation and an appropriate process
regime, these bonds may be restricted exclusively, or at least
predominantly, to the fiber nodal points, so that a stable,
three-dimensional network is formed while retaining the loose, open
structure in the web.
[0084] Webs which have proved to be particularly advantageous are
those consolidated more particularly by overstitching with separate
threads or by interlooping.
[0085] Consolidated webs of this kind are produced, for example, on
stitchbonding machines of the "Malifleece" type from the company
Karl Mayer, formerly Malimo, and can be obtained from companies
including Naue Fasertechnik and Techtex GmbH. A Malifleece is
characterized in that a cross-laid web is consolidated by the
formation of loops from fibers of the web.
[0086] The carrier used may also be a web of the Kunit or Multiknit
type. A Kunit web is characterized in that it originates from the
processing of a longitudinally oriented fiber web to produce a
fabric which has loops on one side and on the other has loop feeds
or pile fiber folds, but possesses neither threads nor
prefabricated fabrics. A web of this kind as well has been produced
for a relatively long time on, for example, stitchbonding machines
of the "Kunitvlies" type from the company Karl Mayer. A further
characterizing feature of this web is that, as a longitudinal fiber
web, it is able to accommodate high tensile forces in the
longitudinal direction. The characteristic feature of a Multiknit
web relative to the Kunit web is that the web is consolidated on
both the top and bottom sides by virtue of the double-sided needle
punching.
[0087] Finally, stitchbonded webs are also suitable as an
intermediate for forming an adhesive tape of the invention. A
stitchbonded web is formed from a nonwoven material having a
multiplicity of stitches extending parallel to one another. These
stitches come about through the incorporation, by stitching or
knitting, of continuous textile threads. For this type of web,
stitchbonding machines of the "Maliwatt" type are known from the
company Karl Mayer, formerly Malimo.
[0088] And then the Caliweb.RTM. is outstandingly suitable. The
Caliweb.RTM. consists of a thermally fixed Multiknit spacer web
with two outer mesh layers and an inner pile layer which is
disposed perpendicular to the mesh layers.
[0089] Also particularly advantageous is a staple fiber web which
is mechanically preconsolidated in the first step or is a wet-lay
web laid hydrodynamically, in which between 2% and 50% of the web
fibers are fusible fibers, more particularly between 5% and 40% of
the fibers of the web.
[0090] A web of this kind is characterized in that the fibers are
laid wet or, for example, a staple fiber web is preconsolidated by
the formation of loops from fibers of the web or by needling,
stitching or air-jet and/or water-jet treatment.
[0091] In a second step, thermofixing takes place, with the
strength of the web being increased again by the melting-on or
partial melting of the fusible fibers.
[0092] The web carrier may also be consolidated without binders, by
means, for example, of hot embossing with structured rollers, in
which case pressure, temperature, dwell time and the embossing
geometry can be used to control properties such as strength,
thickness, density, flexibility and the like.
[0093] Starting materials envisaged for the textile carriers
include, more particularly, polyester fibers, polypropylene fibers,
viscose fibers or cotton fibers. The present invention, though, is
not restricted to the materials stated; instead it is possible to
use a multiplicity of other fibers to produce the web, this being
evident to the skilled person without any need for inventive
activity. Use is made more particularly of wear-resistant polymers
such as polyesters, polyolefins or polyamides or fibers of glass or
of carbon.
[0094] Also suitable as carrier material are carriers made of paper
(creped and/or uncreped), of a laminate, of a film (for example
polyethylene, polypropylene or monoaxially or biaxially oriented
polypropylene films, polyester, PA, PVC and other films) or of foam
materials in web form (made of polyethylene and polyurethane, for
example).
[0095] On the coating side it is possible for the surfaces of the
carriers to have been chemically or physically pretreated, and also
for their reverse side to have undergone an anti-adhesive physical
treatment or coating.
[0096] Finally, the weblike carrier material may be a
double-sidedly anti-adhesively coated material such as a release
paper or a release film, also called a liner.
Method
[0097] The introduction of the expandable, but as yet unexpanded,
microballoons into the mass system may be accomplished in
particular by mixing the microballoons with the other constituents
needed to form the mass system (these are, more particularly, the
polymers and, optionally, resins and/or fillers). Alternatively the
microballoons can be added to the already melted mass system.
[0098] In this phase of the method--especially when the sensitive
substances are thermal crosslinkers or include or constitute a
thermal crosslinker system--it is possible to add components--more
particularly, this very same crosslinker system--which do not yet
react thermally in this phase, because, for example, a further
component of the system is not yet present here. It is possible,
accordingly, in this phase already to add crosslinkers which only
undergo substantial reaction in the presence of accelerator
substances.
[0099] It is of advantage, particularly when adding thermal
crosslinkers or a thermal crosslinker system, if the mass system on
addition of the thermally crosslinked substances is present in a
noncrosslinked state or in a state only of very slight
crosslinking. By this means, effective shaping of the mass is
possible.
[0100] Suitable mixing assemblies include, in particular,
continuously operating mixing assemblies, such as a planetary
roller extruder, for example.
[0101] In this extruder, the components for producing the mass
system can be introduced and, in particular, melted. In accordance
with the invention it is possible to introduce pre-prepared,
solvent-free mass into the slurrying assembly, more particularly
the planetary roller extruder, by means of injection, through
conveying extruders, such as single-screw extruders, for example,
or through a drum melt, and to meter the microballoons into this
initially introduced system in the intake zone of the planetary
roller extruder.
[0102] Microballoon foamed masses do not in general need to be
degassed prior to coating, in order to obtain a uniform, continuous
coating pattern. The expanded microballoons displace the air
included in the adhesive in the course of compounding. In the case
of high throughputs, however, it is still advisable to degas the
masses prior to coating, in order to obtain a uniform reservoir of
mass in the roll nip. Degassing is ideally accomplished immediately
ahead of the roll applicator, at mixing temperature and under a
pressure difference from ambient pressure of at least 200 mbar.
[0103] In accordance with the invention it is possible for the
cooling of the mass system following expansion of the
microballoons, and the admixing of the heat-sensitive substances,
to be performed in the same mixing assembly in which the mixing of
the mass system with the as yet unexpanded microballoons has
already been carried out. In accordance with the invention,
however, this operation may also take place in a second mixing
assembly.
[0104] The blended mass system may be shaped in particular to form
a layer, and with particular advantage this step takes place in a
roll applicator. In principle, however, foamed bodies of different
forms may also be shaped.
[0105] For the case in particular where the mass system is a
(self-)adhesive, it is possible in this way to produce
(self-)adhesive tapes. It is particularly advantageous for this
purpose if the (self-)adhesive is applied to a web-form carrier or
release material.
[0106] The mass system, foamed and provided with thermally
sensitive substances, is thermally crosslinked in an advantageous
procedure; especially when the thermally sensitives are thermal
crosslinkers and/or accelerators or constitute a thermal
crosslinker system or comprise the aforesaid components. Thermal
crosslinking may advantageously, in particular, take place after
the operation of shaping to form the layer, more particularly on a
carrier or release material.
[0107] The method of the invention is elucidated in more detail
below with reference to two advantageous variant embodiments,
without any intention to impose any unnecessary restriction through
the choice of the method variants depicted.
[0108] A first very advantageous procedure is characterized by a
method sequence (cf. also FIG. 1) in which [0109] in a first mixing
assembly, first of all, expandable microballoons--and optionally
further additives--are introduced into a mass system; [0110] the
mass system with the microballoons added is heated--more
particularly under superatmospheric pressure--to a temperature
which at least corresponds to, and is advantageously higher than,
the expansion temperature of the microballoons under atmospheric
pressure, [0111] the microballoons are expanded in particular on
emergence from the first mixing assembly, [0112] the mass system is
introduced into a second mixing assembly, and so in this second
mixing assembly the mass system is at a temperature which lies
below the expansion temperature of the microballoons, [0113] the
thermally sensitive substances are added in the second mixing
assembly, [0114] the mass system thus blended is shaped.
[0115] The cooling of the mass system to a temperature below the
expansion temperature of the microballoons takes place in this case
during the transfer of the mass system to the second mixing
assembly and/or following its transfer to the second mixing
assembly. Accordingly, the addition of the sensitive substances
takes place during and/or after the cooling of the mass system,
more particularly after its cooling.
[0116] A further very advantageous procedure is characterized by a
method sequence (cf. also FIG. 2) in which [0117] in a first mixing
assembly, first of all, expandable microballoons--and optionally
further additives--are introduced into a mass system; [0118] the
mass system with the microballoons added is heated--more
particularly under superatmospheric pressure--in a first mixing
zone of the mixing assembly to a temperature which at least
corresponds to, and is advantageously higher than, the expansion
temperature of the microballoons under atmospheric pressure, [0119]
the mass system is subsequently transferred from the first mixing
zone into a second mixing zone of the first mixing assembly, and so
in this second mixing zone the mass system is at a temperature
which lies below the expansion temperature of the microballoons,
[0120] the thermally sensitive substances are added during transfer
of the mass system to the second mixing zone and/or after transfer
to the second mixing zone, [0121] the mass system thus blended is
shaped.
[0122] The cooling of the mass system to a temperature below the
expansion temperature of the microballoons takes place in this case
during the transfer of the mass system to the second mixing zone
and/or after its transfer to the second mixing zone. Accordingly,
the addition of the sensitive substances takes place during and/or
after the cooling of the mass system, more particularly after its
cooling.
[0123] Below, the methods described above that lie within the
concept of the invention are illustrated in particularly
outstandingly embodied variants, without any intention to impose
any unnecessary restriction through the choice of the figures
shown.
[0124] FIG. 1 shows the method with two mixing assemblies, the
expansion of the microballoons taking place in the first mixing
assembly followed by addition of thermally sensitive additives or
fillers in the second mixing assembly
[0125] FIG. 2 shows the method with one mixing assembly, the
expansion of the microballoons and the addition of thermally
sensitive additives or fillers taking place in one mixing
assembly.
[0126] FIG. 1 shows one particularly advantageously embodied method
for producing a foamed mass system.
[0127] The reactants E which are intended to form the mass system
to be foamed, and the microballoons MB, are fed to a continuous
mixing assembly, such as a planetary roller extruder (PWE) 2, for
example.
[0128] Another possibility, however, is to introduce pre-prepared
solvent-free mass K into the planetary roller extruder (PWE) 2 by
means of injection 23 through conveying extruders, such as a
single-screw extruder (ESE) 1, for example, or through a drum melt
5, and to meter in the microballoons MB in the intake zone of the
PWE 2.
[0129] The microballoons MB are then mixed with the solvent-free
mass K or with the reactants E to form a homogeneous mass system in
the PWE 2, and this mixture is heated, in the first heating and
mixing zone 21 of the PWE 2, to the temperature necessary for the
expansion of the microballoons.
[0130] In the second injection ring 24, further additives or
fillers 25, such as crosslinking promoters, for example, may be
added to the mass system S comprising expanded microballoons.
[0131] In order to be able to incorporate thermally sensitive
additives or fillers 25, the injection ring 24 and the second
heating and mixing zone 22 are preferably cooled.
[0132] The foamed mass system is subsequently transferred to a
further continuous mixing assembly, such as a twin-screw extruder
(DSE) 3, for example, and can then be blended with further fillers
or additives, such as crosslinking components, such as catalysts,
for example, at moderate temperatures, without destroying the
expanded microballoons MB. The microballoons MB break through the
surface of the mass at the die exit of DSE 3, as they also did
before at the die exit of PWE 2.
[0133] With a roll applicator 4, this foamlike mass S is calendered
and coated onto a web-form carrier material 44 such as release
paper, for example; in some cases there may also be subsequent
foaming in the roll nip. The roll applicator 4 is composed of a
doctor blade roll 41 and a coating roll 42. The release paper 44 is
guided to the latter roll via a pick-up roll 43, and so the release
paper 44 takes the foamed mass S from the coating roll 42. At the
same time, the expanded microballoons MB are pressed again into the
polymer matrix of the foamed mass S, thereby producing a smooth
and, in the case of the foaming of self-adhesives, a permanently
(irreversibly) adhesive surface, with very low densities of up to
150 kg/m.sup.3.
[0134] FIG. 2 shows a further particularly advantageously embodied
method for producing a foamed mass system.
[0135] The reactants E and the microballoons MB, which are intended
to form the mass system to be foamed, are fed to a continuous
mixing assembly, such as a planetary roller extruder (PWE) 2, for
example.
[0136] Another possibility, however, is to introduce pre-prepared
solvent-free mass K into the planetary roller extruder (PWE) 2 by
means of injection 23 through conveying extruders, such as a
single-screw extruder (ESE) 1, for example, or through a drum melt
5, and to meter in the microballoons MB in the intake zone of the
PWE 2.
[0137] The microballoons MB are then mixed with the solvent-free
mass K or with the reactants E to form a homogeneous mass system in
the PWE 2, and this mixture is heated, in the first heating and
mixing zone 21 of the PWE 2, to the temperature necessary for the
expansion of the microballoons.
[0138] In the second injection ring 24, further additives or
fillers 25, such as crosslinking promoters, for example, may be
added to the mass system S comprising expanded microballoons.
[0139] In order to be able to incorporate thermally sensitive
additives or fillers 25, the injection ring 24 and the second
heating and mixing zone 22 are cooled.
[0140] The expanded microballoons MB break through the surface of
the mass at the die exit of the PWE 2.
[0141] With a roll applicator 4, this foamlike mass S is calendered
and coated onto a web-form carrier material 44 such as release
paper, for example; in some cases there may also be subsequent
foaming in the roll nip. The roll applicator 4 is composed of a
doctor blade roll 41 and a coating roll 42. The release paper 44 is
guided to the latter roll via a pick-up roll 43, and so the release
paper 44 takes the foamed mass S from the coating roll 42. At the
same time, the expanded microballoons MB are pressed again into the
polymer matrix of the foamed mass S, thereby producing a smooth
and, in the case of the foaming of self-adhesives, a permanently
(irreversibly) adhesive surface, with very low densities of up to
150 kg/m.sup.3.
Adhesive/Adhesive Tape
[0142] The invention also provides an adhesive, more particularly
self-adhesive, obtained by the method of the invention. The
invention more particularly provides a thermally crosslinked,
microballoon-foamed adhesive, more particularly self-adhesive.
[0143] The benefit of foamed adhesives lies on the one hand in cost
reduction. A saving can be made on raw materials, since coat
weights can be reduced by a multiple for given layer thicknesses.
For a given throughput or quantity production of adhesive, in
addition, the coating speeds can be increased.
[0144] An advantage of thermal crosslinking is that it produces an
adhesive which has no crosslinking profile--in particular,
therefore, in the case of layers of adhesive, no crosslinking
profile through the layer. In the case of crosslinking by actinic
radiation, such a profile is always formed to a greater or lesser
extent, owing to the limited depth of penetration of the radiation,
and all the more so in the case of thick layers, for which foamed
systems are frequently employed.
[0145] Moreover, the foaming of the adhesive produces improved
technical adhesive properties and performance properties.
[0146] The reduction of the drop in bond strength is favored by the
high surface quality generated as a result of the pressing of the
expanded microballoons back into the polymer matrix during the
coating operation.
[0147] Moreover, relative to the unfoamed mass having the same
polymer basis, the foamed self-adhesive gains additional
performance features, such as, for example, improved impact
resistance at low temperatures, enhanced bond strength on rough
substrates, greater damping and/or sealing properties and
conformability of the foam adhesive on uneven substrates, more
favorable compression/hardness characteristics, and improved
compressibility.
[0148] Further elucidation of the characteristic properties and
additional functions of the self-adhesives of the invention takes
place to some extent in the examples.
[0149] A foamed adhesive from the preferred hotmelt adhesive has a
smooth, adhering surface, since, during coating, in the roll nip,
the expanded microballoons are subsequently pressed back into the
polymer matrix, and the adhesive, accordingly, has a preferred
surface roughness R.sub.a of less than 10 .mu.m. Determination of
surface roughness is appropriate only for adhesive tapes which are
based on a very smooth carrier and themselves have a surface
roughness R.sub.a of only less than 1 .mu.m. In the case of
carriers that are relevant in practice, such as creped papers or
nonwovens and woven fabrics, for example, having a greater surface
roughness, the determination of the surface roughness of the
product is not suitable, accordingly, for describing the advantages
of the method.
[0150] According to one preferred embodiment of the invention, the
fraction of the microballoons in the adhesive is between greater
than 0% by weight and 30% by weight, more particularly between 0.5%
by weight and 10% by weight.
[0151] With further preference, the microballoons at 25.degree. C.
have a diameter of 3 .mu.m to 40 .mu.m, more particularly 5 .mu.m
to 20 .mu.m, and/or after temperature exposure have a diameter of
20 .mu.m to 200 .mu.m, more particularly 40 .mu.m to 100 .mu.m.
[0152] In all existing methods for producing microballoon-foamed
adhesive systems, the adhesive develops a rough surface which has
little or no adhesion.
[0153] With a self-adhesive coated from solvent, bond strength
(peel strength) losses of more than 40% can be obtained even
starting from a low microballoon content of 0.5% by weight. As the
microballoon content goes up, the bond strengths fall further
still, and the cohesion is increased.
[0154] At a fraction of just 1% by weight of microballoons, the
adhesion of the adhesive is already very low.
[0155] This is underlined by comparative examples 1.1 and 1.2 and
by table 3.
[0156] The ratio of the weight per unit volume of the adhesive
foamed by the microballoons to the weight per unit volume of the
adhesive of identical basis weight and formula, defoamed through
the destruction of the cavities formed by the expanded
microballoons, is preferably less than 0.9.
[0157] This behavior is also shown in the case of solvent-free die
coating, in which case the microballoons foam following emergence
from the extruder/die, with pressure equalization, and break
through the adhesive matrix.
[0158] Further encompassed by the concept of the invention is a
self-adhesive tape produced with the aid of the adhesive by
application of the adhesive to at least one side of a web-formed
material. In a double-sidedly adhesive tape, both adhesive coatings
may be in accordance with the invention. An alternative provision
is for only one of the two coatings to be in accordance with the
invention, while the second can be selected arbitrarily (adapted to
the tasks to be fulfilled by the adhesive tape).
[0159] As carrier material it is preferred to use a film, woven
fabric or paper, to which the (self-)adhesive is applied on one
side.
[0160] Furthermore, preferably, the (self-)adhesive is applied to a
release paper or release film, producing a carrier-less adhesive
tape, also referred to for short as a tab.
[0161] The thickness of the adhesive in an adhesive tape on the
web-formed carrier material may be between 20 .mu.m and 3000 .mu.m,
preferably between 40 .mu.m and 150 .mu.m.
[0162] Furthermore, the adhesive may be applied in a thickness of
20 .mu.m to 3000 .mu.m to a release material, if the layer of
adhesive, more particularly after crosslinking, is to be used as a
carrierless, double-sided self-adhesive tape.
Experimental Investigations
[0163] The following test methods are employed in order to
determine the stated measurement values, in the examples as
well.
Test Methods
Determination of Surface Roughness
[0164] The PRIMOS system consists of an illumination unit and a
recording unit.
[0165] The illumination unit, with the aid of a digital micromirror
projector, projects lines onto the surface. These projected
parallel lines are diverted or modulated by the surface
structure.
[0166] The modulated lines are recorded using a CCD camera arranged
at a defined angle, referred to as the triangulation angle.
Size of measuring field: 14.5.times.23.4 mm.sup.2 Profile length:
20.0 mm Areal roughness: 1.0 mm from the edge (Xm=21.4 mm; Ym=12.5
mm) Filtering: 3rd order polynomial filter
[0167] Measuring instruments of this kind can be purchased from
companies including GFMesstechnik GmbH at Teltow.
Peel Strength (Bond Strength) BS
[0168] The peel strength (bond strength) was tested in a method
based on PSTC-1.
[0169] A strip of the (self-)adhesive tape under investigation is
adhered in a defined width (standard: 20 mm) to a ground steel
plate or to another desired adhesion/test substrate such as, for
example, polyethylene or polycarbonate, etc., by rolling over it
ten times using a 5 kg steel roller. Double-sided adhesive tapes
are reinforced on the reverse side with an unplasticized PVC film
36 .mu.m thick. Thus prepared, the plate is clamped into the
testing instrument, the adhesive strip is peeled from its free end
on a tensile testing machine at a peel angle of 180.degree. and at
a speed of 300 mm/min, and the force needed to accomplish this is
measured. The results are reported in N/cm and are averaged over
three measurements. All measurements are conducted in a
controlled-climate room at 23.degree. C. and 50% relative
humidity.
Quantitative Determination of Shear Strength: Static Shear Test
HP
[0170] An adhesive tape is applied to a defined, rigid adhesion
substrate (in this case steel) and subjected to a constant shearing
load. The holding time in minutes is measured.
[0171] A suitable plate suspension system (angle 179.+-.1.degree.)
ensures that the adhesive tape does not peel from the bottom edge
of the plate.
[0172] The test is intended primarily to yield information on the
cohesiveness of the composition. This is only the case, however,
when the weight and temperature parameters are chosen such that
cohesive failure does in fact occur during the test.
[0173] Otherwise, the test provides information on the adhesion to
the substrate or on a combination of adhesion and cohesiveness of
the composition.
[0174] A strip, 13 mm wide, of the adhesive tape under test is
adhered to a polished steel plaque (test substrate) over a length
of 5 cm by rolling over it ten times using a 2 kg roller.
Double-sided adhesive tapes are lined on the reverse side with a 50
.mu.m aluminum foil and thus reinforced. Subsequently a belt loop
is mounted on the bottom end of the adhesive tape. A nut and bolt
is then used to fasten an adapter plaque to the facing side of the
shear test plate, in order to ensure the specified angle of
179.+-.1.degree..
[0175] The time for development of strength, between roller
application and loading, should be between 10 and 15 minutes.
[0176] The weights are subsequently hung on smoothly using the belt
loop. An automatic clock counter then determines the point in time
at which the test specimens shear off.
Density
Density Determination by Pycnometer:
[0177] The principle of the measurement is based on the
displacement of the liquid located within the pycnometer. First,
the empty pycnometer or the pycnometer filled with liquid is
weighed, and then the body to be measured is placed into the
vessel.
[0178] The density of the body is calculated from the differences
in weight:
Let
[0179] m.sub.0 be the mass of the empty pycnometer, [0180] m.sub.1
the mass of the pycnometer filled with water, [0181] m.sub.2 the
mass of the pycnometer with the solid body, [0182] m.sub.3 the mass
of the pycnometer with the solid body, filled up with water, [0183]
.rho..sub.W the density of the water at the corresponding
temperature, [0184] .rho..sub.F the density of the solid body; the
density of the solid body is then given by:
[0184] .rho. F = ( m 2 - m 0 ) ( m 1 - m 0 ) - ( m 3 - m 2 ) .rho.
W ##EQU00002##
[0185] One triplicate determination is carried out for each
specimen.
Quick Method for Density Determination from the Coatweiht and Film
Thickness:
[0186] The weight per unit volume or density of a coated
self-adhesive is determined via the ratio of the basis weight to
the respective film thickness:
.rho. = m V = MA d [ .rho. ] = [ kg ] [ m 2 ] [ m ] = [ kg m 3 ]
##EQU00003##
MA=coatweight/basis weight (excluding liner weight) in [kg/m.sup.2]
d=film thickness (excluding liner thickness) in [m]
Basis of the Examples
[0187] The invention is elucidated in more detail below, with
reference to comparative examples and to inventive examples,
without thereby wishing to impose any restriction on the subject
matter of the invention.
[0188] Comparative examples 1.1. and 1.2. below show the advantages
of the foaming of a self-adhesive by the inventive hotmelt method
as opposed to foaming from solvent.
[0189] The advantages resulting from the method of the invention
can be demonstrated most simply on a completed, foamed
self-adhesive tape, as shown in the additional comparative example
2.
[0190] For the sake of brevity, in the examples, the term "hotmelt"
is equated with the term "hotmelt process", as a method according
to the invention.
Raw Materials Used:
[0191] The raw materials used in the subsequent examples were as
follows:
TABLE-US-00001 TABLE 1 Raw materials used Manufacturer/ Trade name
Raw material/UPAC supplier Voranol P 400 .RTM. Polypropylene
glycol, diol Dow Voranol 2000L .RTM. Polypropylene glycol, diol Dow
Voranol CP 6055 .RTM. Polypropylene glycol, triol Dow MPDiol .RTM.
2-Methyl-1,3-propanediol Lyondell Vestanat IPDI .RTM. Isophorone
diisocyanate Degussa Desmodur N 3300 .RTM. Aliphatic polyisocyanate
based Bayer on hexamethylene diisocyanate Tinuvin 292 .RTM.
Sterically hindered amine, light Ciba stabilizer and aging
inhibitor Tinuvin 400 .RTM. Triazine derivative, UV Ciba protectant
Coscat 83 .RTM. Bismuth trisneodecanoate Caschem CAS No. 34364-26-6
Aerosil R 202 .RTM. Fumed silica, hydrophobized Evonik n-Butyl
acrylate Acrylic acid n-butyl ester Rohm & Haas Acrylic acid,
pure Acrylic acid BASF N-tert-Butylacrylamide
N-(1,1-Dimethylethyl)-2- Linz Chemie propenamide 2-Ethylhexyl
acrylate 2-Ethylhexyl acrylate Brenntag Bisomer HEMA 2-Hydroxyethyl
methacrylate IMCD Deutschland Methyl acrylate Acrylic acid, methyl
ester BASF Maleic anhydride 2,5-Dihydro-2,5-furandione, Condea- MAA
Huntsman Expancel 051 DU 40 .RTM. Microballoons (MB) Expancel Nobel
Industries
Base Formulas of the Ready-Prepared Base Masses:
TABLE-US-00002 [0192] Adhesive Preparation Fraction K H Raw
materials [% by weight] K1 H1 n-Butyl acrylate 44.2 2-Ethylhexyl
acrylate 44.7 Methyl acrylate 8.6 Acrylic acid, pure 1.5 Bisomer
HEMA 1.0 K2 H1 n-Butyl acrylate 44.9 2-Ethylhexyl acrylate 44.9
N-tert-Butylacrylamide 6.2 Acrylic acid, pure 3.0 Maleic anhydride
1.0 K3 H2 Voranol P400 17.23 Voranol CP 6055 48.88 MP Diol 3.60
Voranol 2000L 8.09 Tinuvin 400 0.21 Tinuvin 292 0.10 Coscat 83 0.41
Aerosil R202 2.06 Vestanat IPDI 19.42
Preparation Variants of the Ready-Prepared Base Masses:
Preparation H1:
[0193] The above monomer mixtures (amounts in % by weight) are
copolymerized in solution. The polymerization batches consist of
60% by weight of the monomer mixtures and 40% by weight of solvents
(such as benzine 60/95 and acetone). The solutions are first freed
from oxygen by flushing with nitrogen in customary reaction vessels
made of glass or steel (with reflux condenser, stirrer, temperature
measurement unit and gas inlet tube) and then heated to
boiling.
[0194] Polymerization is initiated by addition of 0.2% to 0.4% by
weight of a customary radical polymerization initiator such as
dibenzene peroxide, dilauroyl peroxide or
azobisisobutyronitrile.
[0195] During the polymerization time of approximately 20 hours,
dilution may take place a number of times with further solvent,
depending on viscosity, and so the completed polymer solutions have
a solids content of 35% to 55% by weight.
[0196] Concentration is accomplished by lowering the pressure
and/or raising the temperature.
Preparation H2:
[0197] The branched, thermoplastically processable,
hydroxyl-functionalized polyurethane hotmelt prepolymer was
prepared by homogeneously mixing and hence reacting the stated
starting materials in the stated proportions:
[0198] First of all, all of the starting materials listed, apart
from the MP Diol and the Vestanat IPDI, were mixed at a temperature
of 70.degree. C. and a pressure of 100 mbar for 1.5 hours. Then the
MP Diol was mixed in over 15 minutes, followed by the Vestanat
IPDI, likewise over a period of 15 minutes. The resultant heat of
reaction caused the mixture to heat to 100.degree. C., and part of
the mixture was then dispensed into storage vessels. Another part
was processed further directly in substep B).
[0199] The resulting prepolymer was solid at room temperature. The
complex viscosity .eta.* at room temperature (23.degree. C.) was 22
000 Pas and at 70.degree. C. was 5500 Pas.
[0200] The weight-averaged average molecular weight M.sub.w was 125
000 g/mol; the number-averaged average molecular weight M.sub.N was
17 800 g/mol.
Formulas of the Inventive Foamed Mass Systems Based on the
Ready-prepared Base Masses K:
TABLE-US-00003 [0201] Fraction According Exper- Base of the to
imental adhe- additives inventive specimen sive [% by preparation S
K Additives weight] process S1 K1 Polypox R16 0.01 V1 Epikure 925
0.1 Expancel 051 DU 40 3 S2 K1 Polypox R16 0.01 V1 Epikure 925 0.1
Expancel 051 DU 40 5 S3 K1 Polypox R16 0.01 V1 Epikure 925 0.1
Expancel 051 DU 40 8 S4 K2 Polypox R16 0.01 V1 Epikure 925 0.1
Expancel 051 DU 40 5.6 S5 K2 Polypox R16 0.01 V1 Epikure 925 0.1
Expancel 051 DU 40 5.6 Dertophene T110 10 S6 K2 Polypox R16 0.01 V1
Epikure 925 0.1 Expancel 051 DU 40 5.6 Dertophene T110 20 S7 K2
Polypox R16 0.013 V1 Epikure 925 0.13 S8 K2 Polypox R16 0.005 V2
Epikure 925 0.05 Expancel 051 DU 40 1 S9 K2 Polypox R16 0.013 V1
Epikure 925 0.13 Sylvares TP115 25 S10 K2 Polypox R16 0.005 V2
Epikure 925 0.05 Expancel 051 DU 40 1 Sylvares TP115 10 S11 K3
Coscat 83 0.41 V1 Expancel 051 DU 40 3 S12 K3 Coscat 83 0.41 V1
Expancel 051 DU 40 5 S13 K3 Coscat 83 0.41 V1 Expancel 051 DU 40 8
S14 K3 Coscat 83 0.41 V1
Inventive Preparation Processes V:
Process V1:
[0202] Preparation takes place as described in the disclosure
relating to FIG. 1.
[0203] The temperature profiles and machine parameters are adapted
to the mass system under preparation, such as the polymer matrix to
be compounded, the crosslinking system, the microballoon type
and/or further additives and fillers of any kind, and are given in
detail in the examples.
Process V2:
[0204] Preparation takes place as described in the disclosure
relating to FIG. 2.
[0205] The temperature profiles and machine parameters are adapted
to the mass system under preparation, such as the polymer matrix to
be compounded, the crosslinking system, the microballoon type
and/or further additives and fillers of any kind, and are given in
detail in the examples.
EXAMPLES
Example 1
Graduated Microballoon Contents with the Same Mass Basis
TABLE-US-00004 [0206] BS steel 90.degree. 3 d HP Coat- Film peel HP
RT 70.degree. C. Experimental weight thickness Density increase 10N
10N specimen [g/m.sup.2] [.mu.m] [kg/m.sup.3] [N/cm] [min] [min] S1
498 873 570 13.4 1524 40 S2 458 953 481 14.9 4722 149 S3 378 1048
361 11.7 >10 000 702
Example 2
Graduated Resin Contents with the Same Mass Basis and Constant
Microballoon Content
TABLE-US-00005 [0207] BS steel 90.degree. 3 d HP Coat- Film peel HP
RT 70.degree. C. Experimental weight thickness Density increase 10N
10N specimen [g/m.sup.2] [.mu.m] [kg/m.sup.3] [N/cm] [min] [min] S4
606 1030 588 8.7 2210 21 S5 438 1038 422 >17.6 >10 000 76 S6
404 1010 400 >22.1 >10 000 399
Example 3
Comparison Unfoamed/Foamed
Resin-Free/Resin-Containing
TABLE-US-00006 [0208] BS steel 90.degree. 3 d HP Coat- Film peel HP
RT 70.degree. C. Experimental weight thickness Density increase 10N
10N specimen [g/m.sup.2] [.mu.m] [kg/m.sup.3] [N/cm] [min] [min] S7
994 915 1086 13.8 325 13 S8 563 955 589 24.1 1386 105 S9 954 910
1048 18.9 831 30 S10 614 955 643 23.9 >3000 25
Specimens S7 and S9 in accordance with process 1, since unfoamed
mass requires subsequent degassing. Foamed mass, in contrast, does
not, and so specimens S8 and S10 prepared by process 2.
Example 4
Polyurethane Masses with Graduated Microballoon Content
TABLE-US-00007 [0209] BS steel 90.degree. 3 d HP Coat- Film peel HP
RT 70.degree. C. Experimental weight thickness Density increase 10N
10N specimen [g/m.sup.2] [.mu.m] [kg/m.sup.3] [N/cm] [min] [min]
S11 547 1010 542 24.4 492 3 S12 402 990 406 >21.4 1723 14 S13
397 1073 370 >29.7 1125 9
Example 5
Experimental Specimens S11 to S14 Subsequently Laminated on Both
Sides with 50 G/M.sup.2 of Aftercoat Mass
Three-Layer Construction
TABLE-US-00008 [0210] Film BS steel 90.degree. 3d HP RT
Experimental Coatweight thickness Density peel increase 10N
specimen [g/m.sup.2] [.mu.m] [kg/m.sup.3] [N/cm] [min] S11 + 50
g/m.sup.2 647 1110 583 29.2 782 S12 + 50 g/m.sup.2 502 1090 461
42.7 2336 S13 + 50 g/m.sup.2 497 1173 424 34.2 911 S14 + 50
g/m.sup.2 1150 1045 1100 20.8 150
* * * * *