U.S. patent application number 10/544144 was filed with the patent office on 2008-02-21 for pressure sensitive adhesive tape for the adhesion of printing plates and method for the production thereof.
Invention is credited to Marc Husemann, Torsten Runge, Stephan Zollner.
Application Number | 20080044611 10/544144 |
Document ID | / |
Family ID | 32826177 |
Filed Date | 2008-02-21 |
United States Patent
Application |
20080044611 |
Kind Code |
A1 |
Husemann; Marc ; et
al. |
February 21, 2008 |
Pressure Sensitive Adhesive Tape for the Adhesion of Printing
Plates and Method for the Production Thereof
Abstract
A pressure-sensitive adhesive tape made of a flat support
material provided with a pressure sensitive adhesive comprising a
polymer formed from a monomer mixture of acrylic acid ester and/or
methyl acrylic acid ester or free acids thereof of the formula
CH.sub.2=CH(R.sub.1)(COOR.sub.2), acrylic acid ester and/or methyl
acrylic acid ester having the formula
CH.sub.2=CH(R.sub.3)(COOR.sub.4) and acrylic aid ester and/or
methyl acrylic acid ester having the formula
CH.sub.2=CH(R.sub.3)(COOR.sub.5).
Inventors: |
Husemann; Marc; (Hamburg,
DE) ; Runge; Torsten; (Hamburg, DE) ; Zollner;
Stephan; (Hamburg, DE) |
Correspondence
Address: |
NORRIS, MCLAUGHLIN & MARCUS, P.A.
875 THIRD AVE, 18TH FLOOR
NEW YORK
NY
10022
US
|
Family ID: |
32826177 |
Appl. No.: |
10/544144 |
Filed: |
January 9, 2004 |
PCT Filed: |
January 9, 2004 |
PCT NO: |
PCT/EP04/00093 |
371 Date: |
October 4, 2006 |
Current U.S.
Class: |
428/41.5 ;
156/332; 528/271 |
Current CPC
Class: |
Y10T 428/1462 20150115;
C09J 2400/243 20130101; C09J 7/22 20180101; C09J 7/385 20180101;
B41N 6/02 20130101; C09J 7/38 20180101; C09J 133/08 20130101; C09J
2433/00 20130101; Y10T 156/1092 20150115; C09J 2301/124
20200801 |
Class at
Publication: |
428/41.5 ;
156/332; 528/271 |
International
Class: |
C09J 7/04 20060101
C09J007/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 29, 2003 |
DE |
103 03 538.9 |
Apr 1, 2003 |
DE |
103 14 898.1 |
Claims
1. A pressure-sensitive adhesive tape having a flat carrier
material which is coated on both sides with a pressure-sensitive
adhesive, wherein at least one side of the carrier material is
coated with a pressure-sensitive adhesive comprising polymers
formed from a monomer mixture of at least the following components:
i.a) 49.5%-89.5% by weight (based on the monomer mixture) of
acrylic esters and/or methacrylic esters and/or the corresponding
free acids with the following formula:
CH.sub.2=CH(R.sub.1)(COOR.sub.2), where R.sub.1=H or CH.sub.3 and
R.sub.2 is an alkyl radical having 1 to 10 carbon atoms or H and
the homopolymer possesses a static glass transition temperature of
<-30.degree. C.; i.b) 10% to 40% by weight (based on the monomer
mixture) of acrylic esters and/or methacrylic esters with the
following formula: CH.sub.2=CH(R.sub.3)(COOR.sub.4), where
R.sub.3=H or CH.sub.3 and R.sub.4 is a cyclic alkyl radical having
at least 8 carbon atoms or a linear alkyl radical having at least
12 carbon atoms and the homopolymer possesses a static glass
transition temperature of at least 30.degree. C.; i.c) 0.5%-10% by
weight (based on the monomer mixture) of acrylic esters and/or
methacrylic esters with the following formula:
CH.sub.2=CH(R.sub.3)(COOR.sub.5), where R.sub.3=H or CH.sub.3 and
R.sub.5=H or an aliphatic radical containing a functional group X,
X comprising COOH, OH, --NH, NH.sub.2, SH, SO.sub.3H, and the
homopolymer possesses a static glass transition temperature of at
least 30.degree. C.
2. The pressure-sensitive adhesive tape of claim 1, wherein the
polymers of the pressure-sensitive adhesive have a molar mass
M.sub.n of between about 10 000 and about 600 000 g/mol.
3. The pressure-sensitive adhesive tape of claim 1, wherein the
polymers of the pressure-sensitive adhesive are crosslinked.
4. The pressure-sensitive adhesive tape of claim 1, wherein said
polymers are present in a branched state as graft polymers.
5. The pressure-sensitive adhesive tape of claim 1, wherein said
pressure-sensitive adhesive comprises tackifier resins.
6. The pressure-sensitive adhesive tape of claim 5, wherein the
weight fraction of the tackifier resins as a proportion of the
polymer is up to 40% by weight.
7. The pressure-sensitive adhesive tape of claim 1, wherein the
pressure-sensitive adhesive comprises additives selected from the
group consisting of plasticizers, fillers, nucleators, expandants,
compounding agents, aging inhibitors, and light stabilizers.
8. The pressure-sensitive adhesive tape of claim 1, wherein the
carrier material is a film, of polyester, PET, PE, PP, BOPP or
PVC.
9. The pressure-sensitive adhesive tape claim 1, wherein the
carrier material is a polymer foam of PU, PVC or polyolefin.
10. The pressure-sensitive adhesive tape claim 1, wherein the
carrier material is a combination of a film and at least one foam
carrier, the film being connected by adhesive bonding to the at
least one foam carrier.
11. The pressure-sensitive adhesive tape of claim 8, wherein the
film is a film made of PET and has a thickness of 5 to 500
.mu.m.
12. The pressure-sensitive adhesive tape of claim 1, wherein the
carrier material is pretreated by flame, corona and/or plasma,
and/or chemically, and/or by provision with primer.
13. The pressure-sensitive adhesive tape of claim 1, having a liner
on one or both sides.
14. The pressure-sensitive adhesive tape of claim 1, wherein two
sides of the adhesive tape are coated with pressure-sensitive
adhesive, and the two sides of the adhesive tape have
pressure-sensitive adhesives differing in bond strength.
15. A free-radical polymerization method of producing the
pressure-sensitive adhesive tape of claim 1, wherein a reaction
solution of a monomer mixture comprising at least the following
components: i.a) 49.5%-89.5% by weight (based on the monomer
mixture) of acrylic esters and/or methacrylic esters and/or the
corresponding free acids with the following formula:
CH.sub.2=CH(R.sub.1)(COOR.sub.2), where R.sub.1=H or CH.sub.3 and
R.sub.2 is an alkyl radical having 1 to 10 carbon atoms or H and
the homopolymer possesses a static glass transition temperature of
<-30.degree. C.; i.b) 10% to 40% by weight (based on the monomer
mixture) of acrylic esters and/or methacrylic esters with the
following formula: CH.sub.2=CH(R.sub.3)(COOR.sub.4), where
R.sub.3=H or CH.sub.3 and R.sub.4 is a cyclic alkyl radical having
at least 8 carbon atoms or a linear alkyl radical having at least
12 carbon atoms and the homopolymer possesses a static glass
transition temperature of at least 30.degree. C.; i.c) 0.5%-10% by
weight (based on the monomer mixture) of acrylic esters and/or
methacrylic esters with the following formula:
CH.sub.2=CH(R.sub.3)(COOR.sub.5), where R.sub.3=H or CH.sub.3 and
R.sub.5=H or an aliphatic radical containing a functional group X,
X comprising COOH, OH, --NH, NH.sub.2, SH, SO.sub.3H, and the
homopolymer possesses a static glass transition temperature of at
least 30.degree. C., with the addition of an initiator having a
grafting activity of .epsilon.<5 and of an initiator having a
grafting activity of .epsilon.>5, is prepared and polymerized,
and the resulting polymers are crosslinked.
16. The method of claim 15, wherein first the initiator having a
grafting activity of .epsilon.<5 is added for a linear
polymerization and then the initiator having a grafting activity of
.epsilon.>5 is added for a graft polymerization of the reaction
solution.
17. The method of claim 16, wherein after the initiator having a
grafting activity of .epsilon.<5 is added and before the
initiator having a grafting activity of .epsilon.>5 is added,
initiation is repeated at least once with an initiator having a
grafting activity of .epsilon.<5.
18. The method of any one of claims 15 to 17, characterized in that
the reaction is controlled by diluting the reaction solution in
accordance with the viscosity of the polymer.
19. The method of any one of claims 15 to 17, wherein the
polymerization is carried out at a temperature of 50-90.degree.
C.
20. The method of any one of claims 15 to 17, wherein the initiator
having a grafting activity of .epsilon.>5 is used in an amount
of up to 2% by weight, based on the monomer mixture.
21. The method of any one of claims 15 to 17, wherein the initiator
having a grafting activity of .epsilon.>5 has a grafting
activity of.epsilon.>10.
22. The method of any one of claims 15 to 17, wherein the initiator
having a grafting activity of .epsilon.<5 is
2,2-azobis(2-methylbutyronitrile).
23. The method of any one of claims 15 to 17, wherein the
polymerization is carried out to a conversion of at least 90.
24. The method of any one of claims 15 to 17, wherein the method is
carried out as a controlled polymerization with the addition of
regulator substances.
25. The method of claim 24, wherein said regulator is selected from
the group consisting of 2,2,5,5-tetramethyl-1-pyrrolidinyloxyl
(PROXYL), 3-carbamoyl-PROXYL, 2,2-dimethyl-4,5-cyclohexyl-PROXYL,
3-oxo-PROXYL, 3-hydroxylimine-PROXYL, 3-aminomethyl-PROXYL,
3-methoxy-PROXYL, 3-t-butyl-PROXYL, 3,4-di-t-butyl-PROXYL;
2,2,6,6-tetramethyl-1-piperidinyloxyl-(TEMPO), 4-benzoyloxy-TEMPO,
4-methoxy-TEMPO, 4-chloro-TEMPO, 4-hydroxy-TEMPO, 4-oxo-TEMPO,
4-amino-TEMPO, 2,2,6,6-tetraethyl-1-piperidinyloxyl,
2,2,6-trimethyl-6-ethyl-1-piperidinyloxyl, N-tert-butyl
1-phenyl-2-methylpropyl nitroxide, N-tert-butyl
1-(2-naphthyl)-2-methylpropyl nitroxide, N-tert-butyl
1-diethylphosphono-2,2-dimethylpropyl nitroxide, N-tert-butyl
1-dibenzylphosphono-2,2-dimethylpropyl nitroxide,
N-(1-phenyl-2-methylpropyl) 1-diethylphosphono-1-methylethyl
nitroxide, di-t-butyl nitroxide, diphenyl nitroxide, and tert-butyl
tert-amyl nitroxide.
26. The method of claim 24, wherein the controlled polymerization
is a variant of the RAFT polymerization, in which the
trithiocarbonates TTC1 and TTC2 or the thio compounds THI1 and THI2
or the thioesters THE are used, .phi. ##STR00004## being an
unfunctionalized phenyl group or a phenyl group functionalized with
alkyl or aryl substituents attached directly or via ester or ether
bridges, a functionalized phenyl group, functionalized preferably
with halogen, hydroxyl, epoxy and/or nitrogen-containing or
sulfur-containing groups, a cyano group or a saturated or
unsaturated aliphatic radical, and where R.sup.$1 and R$.sup.2 are
chosen independently of one another and R.sup.$1 can be a radical
from one of groups i) to iv) below, and R$.sup.2 a radical from one
of groups i) to iii) below: i) C.sub.1 to C.sub.18 alkyl, C.sub.2
to C.sub.18 alkenyl, C.sub.2 to C.sub.18 alkynyl, each linear or
branched; aryl, phenyl, benzyl, aliphatic and aromatic
heterocycles. ##STR00005## ii) --NH.sub.2, --NH--R.sup.$3,
--NR.sup.$3R.sup.$4,
--NH--C(O)--R.sup.$3--NR.sup.$3--C(O)--R.sup.$4,
--NH--C(S)--R.sup.$3, --NR.sup.$3--C(S)--R.sup.$4, where R.sup.$3
and R.sup.$4 are radicals selected independently of one another
from group i). iii) --S--R.sup.$5 or --S--C(S)--R.sup.$5, R.sup.$5
preferably being a radical from one of groups i) or ii). iv)
--0--R.sup.$6 or --O--C(O)--R.sup.$6, R.sup.$6 preferably being a
radical from one of groups i) or ii).
27. The method of claim 24, wherein the controlled polymerization
is a variant of ATRP polymerization.
28. The method of claim 15, wherein radical stabilization is
effected using polymer-bonded or non-polymer-bonded nitroxides of
the type (NIT 1) or (NIT 2): ##STR00006## where R.sup.#1, R.sup.#2,
R.sup.#3, R.sup.#4, R.sup.#5, R.sup.#6, R.sup.#7 and R.sup.#8
independently of one another can denote the following groups: i)
halides, ii) linear, branched, cyclic and heterocyclic hydrocarbons
having 1 to 20 carbon atoms, which may be saturated, unsaturated or
aromatic; iii) --COOR.sup.#9 ,--OR.sup.#10 and
--PO(OR.sup.#11).sub.2, where R.sup.#9, R.sup.#10 and R.sup.#11
stand for radicals from group ii).
29. The method of claim 15, wherein crosslinkers selected from the
croup consisting of metal chelates, isocyanates, amines, alcohols
and epoxides are added.
30. The method of claim 15, wherein the polymers are crosslinked by
actinic radiation.
31. The method of claim 15, wherein the polymers are crosslinked by
UV radiation.
32. A method for mounting printing plates to printing cylinders or
sleeves which comprises mounting said printer Plates with the
adhesive tape of claim 1.
33. The method of claim 21, wherein said initiator having a
grafting activity of .epsilon.>10 is bis(4-tert-butylcyclohexyl)
peroxide dicarbonate or dibenzoyl peroxide.
Description
[0001] The invention relates to pressure-sensitive adhesive (PSA)
tapes and to a method of producing pressure-sensitive adhesives
(PSAs) for the adhesive bonding of printing plates, the PSA
possessing a very low peel increase on polar surfaces and being
easy to reposition, and, after the bonding on the printing
cylinder, exhibiting low edge lifting of the printing plate and of
the assembly formed from adhesive plate-mounting tape and printing
plate.
[0002] The printing industry knows of a variety of techniques for
transferring designs to paper, for example, by means of print
originals. One possibility is that known as flexographic printing.
One embodiment of flexographic printing, in turn, is the use of
multilayer photopolymer printing plates with a flexible
substructure, this type of printing having been part of the prior
art for a relatively long time. The printing plates in this case
are composed of a plurality of layers of different polymeric
materials each with specific functions. For example, the "nyloflex
MA" and "nyloflex ME" printing plates from BASF AG have three
layers, namely a light-sensitive relief layer, a stabilizing film
below it, and an elastic carrier layer.
[0003] In the flexographic printing process, flexible printing
plates are bonded adhesively to printing cylinders. This bonding is
generally carried out using double-sided PSA tapes, on which very
stringent requirements are imposed. For the printing process, the
PSA tape is required to have a certain hardness but also a certain
elasticity. These properties must be set very precisely in order
that the printed image produced yields the desired result in
accordance with the requirements. Further stringent requirements
are imposed on the PSA itself, where the bond strength must
likewise be high so that the printing plate does not detach from
the double-sided PSA tape or the PSA tape from the cylinder. This
must be so even at increased temperatures of.sub.--40 -60.degree.
C. and at high printing speeds. In addition to this property,
however, the adhesion properties of the PSA must also be
reversible, since it is often necessary to bond the printing plates
and then to detach them again for repositioning. This detachability
should also exist in the case of an adhesive bond over a prolonged
time period (up to six months). Moreover, it is desired that the
PSA tape and especially the printing plate can be removed again
without destruction thereof, i.e., without great application of
force. In addition, no residues should remain on the printing plate
or on the cylinder. In summary, then, very stringent requirements
are imposed on the double-sided PSA tapes that are suitable for
this utility.
[0004] U.S. Pat. No. 4,380,956 describes a process for mounting a
printing plate for the flexographic printing process. PSAs are
among the adhesives used for this process, but have not been
specified in any greater detail.
[0005] GB 1,533,431 claims a double-sided PSA tape including an
elastomeric layer which in turn is foamed by fragile air bubbles.
The air bubbles are destroyed under pressure during the
flexographic printing application.
[0006] U.S. Pat. No. 4,574,697 claims double-sided PSA tapes
comprising as their carrier material a flexible polyurethane foam
affixed to a PET (polyethylene terephthalate) film. The outer
layers are composed of pressure-sensitive adhesives.
The PSA tape described is to be reversible and to be removable from
the printing cylinder and from the printing plate. A similar
product structure has been described in EP 0 206 760. There, the
flexible foam carrier used was a polyethylene foam.
[0007] U.S. Pat. No. 4,574,712, in analogy to U.S. Pat. No.
4,574,697, describes a similar PSA tape construction. Here there is
a restriction on the PSAs, namely that the bond strength to the
printing plate and to the printing cylinder should be lower than to
the carrier film and the carrier foam.
[0008] U.S. Pat. No. 3,983,287 describes a laminate whose carrier
material comprises an incompressible elastomer. Compressibility is
achieved by means of beads which are destroyed under pressure and
which therefore produce flexibility.
[0009] U.S. Pat. No. 5,613,942 describes PSA tapes which are
especially suitable for bonds on wet surfaces. It is mentioned,
inter alia, that such tapes are suitable for bonding printing
plates.
[0010] U.S. Pat. No. 5,476,712 likewise describes a double-sided
PSA tape which is used in the flexographic printing process. This
PSA tape contains, in turn, a thermoplastic elastomer, the
structure present in this case being a cellular structure produced
by means of expanding microparticles.
[0011] In the cases mentioned above, a very large number of
different PSAs are used. Natural rubber adhesives possess good tack
properties but lack great shear strength at room temperature, and
age as a result of degradation via the double bonds present in the
polymer.
[0012] SIS-based or SEBS-based PSAs are generally very soft and
tacky and tend to soften at high temperatures as well. If the
printing plate is bonded to the printing cylinder under tension
using an SIS or SEBS PSA, the printing plate tends to detach,
despite the fact that the bond strength is high.
Acrylate PSAs, on the other hand, are very suitable for bonding
printing plates to printing cylinders but have to be crosslinked in
the preparation process following the coating operation. Moreover,
these PSAs, owing to the multiplicity of ester groups and the
resulting polarity, have a tendency toward high peel increase. As a
result the printing plates can be removed only with very high
application of force. Moreover, the PSA must exhibit a certain
hardness, so that, after bonding to the printing cylinder, the
printing plates do not tend toward edge lifting over a prolonged
time period.
[0013] There is therefore a need for a pressure-sensitive acrylate
adhesive which is suitable for bonding printing plates and which
meets the abovementioned requirements.
[0014] Surprisingly, and unforeseeably for the skilled worker, the
object is achieved by means of a pressure-sensitive adhesive having
the features specified in claim 1 and by a production method for
certain pressure-sensitive adhesives, having the method measures
specified in claim 15, the use of the pressure-sensitive acrylic
adhesives for bonding printing plates being included.
[0015] Advantageous embodiments of the invention are subject-matter
of the subclaims.
[0016] The invention accordingly provides a double-sided
pressure-sensitive adhesive tape for mounting printing plates,
especially multilayer photopolymer printing plates, on printing
cylinders or sleeves, the carrier of the pressure-sensitive
adhesive tape being a film, foam or composite of the two and there
being double-sidedly self-adhesive coatings applied to the
corresponding carrier or composite, with both, but at least the
side facing the printing plate, having been provided with a
pressure-sensitive adhesive system of the invention/inventive
pressure-sensitive adhesive system.
[0017] The pressure-sensitive adhesive tape of the invention with a
flat carrier material, are coated on both sides with a
pressure-sensitive adhesive, and consists in that at least one side
of the carrier material is coated with a polymer-based
pressure-sensitive adhesive which is preparable from a monomer
mixture comprising at least the following components: [0018] i.a)
49.5%-89.5% by weight (based on the monomer mixture) of acrylic
esters and/or methacrylic esters and/or the corresponding free
acids with the following formula:
[0018] CH.sub.2=CH(R.sub.1)(COOR.sub.2), [0019] where R.sub.1=H or
CH.sub.3 and R.sub.2 is an alkyl radical having 1 to 10 carbon
atoms or H and the homopolymer possesses a static glass transition
temperature of <-30.degree. C.; [0020] i.b) 10% to 40% by weight
(based on the monomer mixture) of acrylic esters and/or methacrylic
esters with the following formula:
[0020] CH.sub.2=CH(R.sub.3)(COOR.sub.4), [0021] where R.sub.3=H or
CH.sub.3 and R.sub.4 is a cyclic alkyl radical having at least 8
carbon atoms or a linear alkyl radical having at least 12 carbon
atoms and the homopolymer possesses a static glass transition
temperature of at least 30.degree. C.; [0022] i.c) 0.5%-10% by
weight (based on the monomer mixture) of acrylic esters and/or
methacrylic esters with the following formula:
[0022] CH.sub.2=CH(R.sub.3)(COOR.sub.5), [0023] where R.sub.3=H or
CH.sub.3 and R.sub.5=H or an aliphatic radical containing a
functional group X, X comprising COOH, OH, --NH, NH.sub.2, SH,
SO.sub.3H, and the homopolymer possesses a static glass transition
temperature of at least 30.degree. C.
[0024] The main claim relates correspondingly to a two-stage method
of producing pressure-sensitive adhesives based on a polymer with
the following monomer mixture comprising at least the following
components [0025] (i.a) 49.5% to 89.5% by weight (based on the
monomer mixture) of acrylic esters and/or methacrylic esters and/or
the corresponding free acids with the following formula:
[0025] CH.sub.2=CH(R.sub.1)(COOR.sub.2), [0026] where R.sub.1=H or
CH.sub.3 and R.sub.2 is an alkyl radical having 1 to 10 carbon
atoms or H and the homopolymer possesses a static glass transition
temperature of <-30.degree. C.; [0027] (i.b) 10% to 40% by
weight (based on the monomer mixture) of acrylic esters and/or
methacrylic esters with the following formula:
[0027] CH.sub.2=CH(R.sub.3)(COOR.sub.4), [0028] where R.sub.3=H or
CH.sub.3 and R.sub.4 is a cyclic alkyl radical having at least 8
carbon atoms or a linear alkyl radical having at least 12 carbon
atoms and the homopolymer possesses a static glass transition
temperature of at least 30.degree. C.; [0029] (i.c) 0.5% to 10% by
weight (based on the monomer mixture) of acrylic esters and/or
methacrylic esters with the following formula:
[0029] CH.sub.2=CH(R.sub.3)(COOR.sub.5), [0030] where R.sub.3=H or
CH.sub.3 and R.sub.5=H or an aliphatic radical containing a
functional group X, X comprising COOH, OH, --NH, NH.sub.2, SH,
SO.sub.3H, and the homopolymer possesses a static glass transition
temperature of at least 30.degree. C., [0031] and in a
polymerization process [0032] at least two thermally decomposing
initiators having a grafting activity of .epsilon.<5 and of
.epsilon.>10, polymerization first taking place linearly with
.epsilon.<5 and then, with .epsilon.>10, graft polymers being
prepared [0033] and the crosslinking of the polymers prepared by
the abovementioned process, with a fraction of 0.2% -1.0% by weight
of crosslinker
[0034] These pressure-sensitive adhesive systems are distinguished
by the fact that the abovementioned prerequisites are met and
exhibit in particular the following advantages: [0035] multiple
reusability (repositionability) of the PSA tapes [0036]
reversibility on different surfaces [0037] low peel increase even
on polar surfaces [0038] minimized edge lifting after bonding on
the printing cylinder
[0039] Glass transition temperatures are reported as results of
quasi-static techniques such as, for example, differential scanning
calorimetry (DSC).
[0040] In order to obtain the polymer glass transition temperature,
T.sub.G, in accordance with the comments made above and below, the
monomers are very preferably selected in such a way, and the
quantitative composition of the monomer mixture advantageously
chosen in such a way, that the polymer has the desired T.sub.G in
accordance with equation (E1) (in analogy to the Fox equation; cf.
T. G. Fox, Bull. Am. Phys. Soc. 1 (1956) 123).
1 T G = n W n T G , n ( E 1 ) ##EQU00001##
[0041] 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.
[0042] (Meth)acrylic monomers which can be used with great
preference as a component in the sense of (i.a) encompass acrylic
and methacrylic esters having alkyl groups consisting of 1 to 10
carbon atoms. Specific examples of such compounds, without wishing
to be restricted by this enumeration, are n-butyl acrylate,
n-pentyl acrylate, n-hexyl acrylate, n-heptyl acrylate, n-octyl
acrylate, n-nonyl acrylate, 2-ethylhexyl acrylate and isooctyl
acrylate.
[0043] (Meth)acrylic monomers which can be used with great
preference as a component in the sense of (i.b) encompass acrylic
and methacrylic esters with a cyclic alkyl radical having at least
8 carbon atoms or a linear alkyl radical having at least 12 carbon
atoms. Specific examples are, e.g., n-lauryl acrylate, stearyl
acrylate, isobornyl acrylate, isobornyl methacrylate and norbornyl
acrylate, this enumeration possessing no claim to completeness.
[0044] (Meth)acrylic monomers which can be used with great
preference as a component in the sense of (i.c) encompass the free
acids and also aliphatic radicals containing a functional group X,
X being COOH, OH, --NH, NH.sub.2, SH or SO.sub.3H. Specific
examples of such compounds, without wishing to be restricted by
this enumeration, are hydroxyethyl acrylate, hydroxypropyl
acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate,
n-methylolacrylamide, acrylic acid, methacrylic acid, allyl
alcohol, maleic anhydride, itaconic anhydride and itaconic
acid.
In a further favorable embodiment the monomers (i.c) are
functionalized such that a thermally initiated crosslinking can be
carried out. Crosslinkers which can be chosen favorably include the
following: epoxides, aziridines, isocyanates, polycarbodiimides and
metal chelates, to name but a few.
[0045] One preferred characteristic of the copolymers used for the
pressure-sensitive adhesive systems of the invention is that their
molar mass M.sub.n is between about 10 000 and about 600 000 g/mol,
preferably between 30 000 and 400 000 g/mol, more preferably
between 50 000 g/mol and 300 000 g/mol.
A further preferred characteristic is that the polymer chains are
present in a branched state as graft polymers.
[0046] To prepare the copolymers of the invention it is possible in
principle to use any free-radical or radical-controlled
polymerizations, including combinations of different polymerization
methods. Besides conventional free radical polymerization mention
may be made, for example, without possessing any claim to
completeness, of ATRP, nitroxide/TEMPO-controlled polymerization or
the RAFT process, in other words, in particular, those methods
which allow control of the chain lengths or the polymer
architecture.
[0047] As free-radical initiators for the free-radical
polymerization it is possible to use any customary initiators known
for this purpose for acrylates. The preparation of C-centered
radicals is described in Houben Weyl, Methoden der Organischen
Chemie, Vol. E 19a, pp. 60-147. These methods may be employed
analogously. Examples of radical sources are peroxides,
hydroperoxides, and azo compounds; as nonexclusive examples of
typical free-radical initiators mention may be made here of
potassium peroxodisulfate, dibenzoyl peroxide, cumene
hydroperoxide, cyclohexanone peroxide, di-t-butyl peroxide,
azodiisobutyronitrile, cyclohexylsulfonyl acetyl peroxide,
diisopropyl percarbonate, t-butyl peroctoate, and benzpinacol. In
one very preferred variant, the initiators are added in a number of
stages, so that the conversion is increased to more than 90%. The
residual monomer content of the polymer can in this way be
decreased to below 10% by weight; by virtue of a low residual
monomer content, the adhesive properties of the polyacrylate are
considerably improved in respect of the bonding of printing
cylinders.
[0048] The initiators added at the beginning are preferably chosen
for their low propensity to form side chains in the polymers; their
grafting activity is preferably below a level of .epsilon.<5 at
the temperature of the reaction mixture when the initiator is
added.
The absolute grafting activity (crosslink efficiency) is defined as
the number of chemical side chains formed per 100 mole units of
decomposed initiator. In analogy to van Drumpt and Oosterwijk
[Journal of Polymer Science, Polymer Chemistry Edition 14 (1976)
1495-1511], it is possible to specify a value for this number by
determining the dimers in a defined solution of the initiator; see
also DE 43 40 297 A1: A precisely 0.1 molar solution of the
initiator is decomposed in n-pentadecane under an He atmosphere.
The reaction time is chosen to correspond to ten times the
half-life of the respective initiator at the chosen temperature.
This ensures virtually complete decomposition of the initiator.
Subsequently, the fraction of dimeric pentadecane produced is
measured by means of GLC. The percentage fraction .epsilon. is
stated as a measure of the grafting activity. The reaction
temperature is normally chosen so that the half-life of the test
initiator at this temperature is 15 minutes.
High .epsilon. values for the grafting activity imply a high
propensity of the initiator to form side chains in the
polymerization, whereas small .epsilon. values result in
preferentially linear polymers.
[0049] In one preferred procedure, the process sequence is as
follows: [0050] the reaction solution used is an at least 50%
strength solution of the monomers with added initiator with an
.epsilon. value of <5, [0051] the free-radical polymerization is
conducted within a temperature range from 50.degree. C. to
90.degree. C., [0052] during the polymerization the batch is
reinitiated at least once using a free-radical polymerization
initiator with a low propensity to form side chains (grafting
activity .epsilon.<5 at the prevailing reaction temperature),
[0053] if desired, the reaction is controlled by diluting the
reaction solution according to the viscosity of the polymer, [0054]
controlled reinitiation is carried out with up to 2% by weight,
based on the monomer mixture, of an initiator with an increased
propensity to form side chains (grafting activity .epsilon.>10
at the prevailing reaction temperature), [0055] the polymerization
is conducted to a conversion >90%, preferably >95%.
[0056] Preferred initiators having a low .epsilon. value
(.epsilon.<5) are those whose radicals, owing to their low
energy content, cause infrequent, if any, abstraction of hydrogen
from the polymer chains. It is preferred here to use, for example,
azo initiators such as azoisobutyrodinitrile or derivatives
thereof, such as 2,2-azobis(2-methylbutyronitrile) (Vazo67,
DuPont).
[0057] Initiators having a high side-chain formation propensity
(high .epsilon. value >10) give high grafting yields even at
relatively low temperatures. Particular preference is given here to
using bis(4-t-butylcyclohexyl) peroxydicarbonate (Perkadox 16, Akzo
Chemie), dibenzoyl peroxide or the like.
[0058] The polymerization may be conducted in the presence of an
organic solvent or in the presence of water or in mixtures of
organic solvents and/or water. As solvents for the polymerization
it is possible to use all solvents which are suitable or commonly
used for free-radical polymerizations, with acetone, ethyl acetate,
petroleum spirit, toluene or any mixtures of these solvents being
particularly appropriate.
It is preferred to use as little solvent as possible. Depending on
conversion, temperature, and initiation, the polymerization time is
between 6 and 48 h.
[0059] For radical stabilization an advantageous procedure is to
use nitroxides of type (NIT 1) or (NIT 2):
##STR00001##
where R.sup.#1, R.sup.#2, R.sup.#3, R.sup.#4, R.sup.#5, R.sup.#6,
R.sup.#7 and R.sup.#8 independently of one another denote the
following compounds or atoms: [0060] i) halides, such as chlorine,
bromine or iodine, for example; [0061] ii) linear, branched, cyclic
and heterocyclic hydrocarbons having 1 to 20 carbon atoms, which
may be saturated, unsaturated or aromatic; [0062] iii) esters
--COOR.sup.#9, alkoxides --OR.sup.#10 and/or phosphonates
--PO(OR.sup.# ).sub.2, where R.sup.#9, R.sup.#10 and/or R.sup.#11
stand for radicals from group ii).
[0063] Compounds of structure (NIT 1) or (NIT 2) can also be
attached to polymer chains of any kind (primarily such that at
least one of the abovementioned radicals constitutes such a polymer
chain).
[0064] More preferred are controlled regulators for the
polymerization of compounds of the following type: [0065]
2,2,5,5-tetramethyl-1-pyrrolidinyloxyl (PROXYL),
3-carbamoyl-PROXYL, 2,2-dimethyl-4,5-cyclohexyl-PROXYL,
3-oxo-PROXYL, 3-hydroxylimine-PROXYL, 3-aminomethyl-PROXYL,
3-methoxy-PROXYL, 3-t-butyl-PROXYL, 3,4-di-t-butyl-PROXYL [0066]
2,2,6,6-tetramethyl-1-piperidinyloxyl pyrrolidinyloxyl (TEMPO),
4-benzoyloxy-TEMPO, 4-methoxy-TEMPO, 4-chloro-TEMPO,
4-hydroxy-TEMPO, 4-oxo-TEMPO, 4-amino-TEMPO,
2,2,6,6-tetraethyl-1-piperidinyloxyl,
2,2,6-trimethyl-6-ethyl-1-piperidinyloxyl [0067] N-tert-butyl
1-phenyl-2-methylpropyl nitroxide [0068] N-tert-butyl
1-(2-naphthyl)-2-methylpropyl nitroxide [0069] N-tert-butyl
1-diethylphosphono-2,2-dimethylpropyl nitroxide [0070] N-tert-butyl
1-dibenzylphosphono-2,2-dimethylpropyl nitroxide [0071]
N-(1-phenyl-2-methylpropyl) 1-diethylphosphono-1-methylethyl
nitroxide [0072] di-t-butyl nitroxide [0073] diphenyl nitroxide
[0074] t-butyl t-amyl nitroxide.
[0075] U.S. Pat. No. 4,581,429 A discloses a controlled-growth
free-radical polymerization process initiated using a compound of
the formula R'R''N--O--Y in which Y is a free radical species which
is able to polymerize unsaturated monomers. The reactions, however,
generally have low conversions. A particular problem is the
polymerization of acrylates, which proceeds only to very low yields
and molar masses. WO 98/13392 A1 describes open-chain alkoxyamine
compounds which have a symmetrical substitution pattern.
[0076] EP 735 052 A1 discloses a process for preparing
thermoplastic elastomers having narrow molar mass distributions. WO
96/24620 A1 describes a polymerization process using very specific
radical compounds such as, for example, phosphorus-containing
nitroxides which are based on imidazolidine. WO 98/44008 A1
discloses specific nitroxyls based on morpholines, piperazinones
and piperazinediones. DE 199 49 352 A1 describes heterocyclic
alkoxyamines as regulators in controlled-growth free-radical
polymerizations. Corresponding further developments of the
alkoxyamines or of the corresponding free nitroxides enhance the
efficiency for preparing polyacrylates (Hawker, paper to the
National Meeting of the American Chemical Society, Spring 1997;
Husemann, paper to the IUPAC World-Polymer Meeting 1998, Gold
Coast).
[0077] As a further controlled polymerization method it is possible
advantageously to use atom transfer radical polymerization (ATRP)
to synthesize the block copolymers, with preferably monofunctional
or difunctional secondary or tertiary halides being used as
initiators and, to abstract the halide(s), complexes of Cu, Ni, Fe,
Pd, Pt, Ru, Os, Rh, Co, Ir, Ag or Au (EP 0 824 111 A1; EP 826 698
A1; EP 824 110 A1; EP 841 346 A1; EP 850 957 A1). The different
possibilities of ATRP are further described in U.S. Pat. No.
5,945,491 A, U.S. Pat. No. 5,854,364 A and U.S. Pat. No. 5,789,487
A.
[0078] A very preferred preparation process conducted is a version
of RAFT polymerization (reversible addition-fragmentation chain
transfer polymerization). The polymerization process is described
in detail in, for example, WO 98/01478 A1 and WO 99/31144 A1. In
one very advantageous version, for example, the trithiocarbonates
(TTC1) and (TTC2) or the thio compounds (THI1) and (THI2) are used
for the polymerization, in which .phi. can be a phenyl ring, which
can be unfunctionalized or functionalized by alkyl or aryl
substituents attached directly or via ester or ether bridges, or
can be a cyano group, or can be a saturated or unsaturated
aliphatic radical.
[0079] Examples of possible functionalizations for the phenyl ring
.phi. include halogens, hydroxyl groups, epoxide groups, and groups
containing nitrogen or containing sulfur, without this list making
any claim to completeness.
##STR00002##
[0080] It is additionally possible to employ thioesters of the
general structure
R.sup.$1--C(S)--S--R.sup.$2 (THE),
particularly in order to prepare asymmetric systems. R.sup.$1 and
R.sup.$2 may be selected independently of one another and R.sup.$1
can be a radical from one of groups i) to iv) below, and R.sup.$2 a
radical from one of groups i) to iii) below: [0081] i) C.sub.1 to
C.sub.18 alkyl, C.sub.2 to C.sub.18 alkenyl, C.sub.2 to C.sub.18
alkynyl, each linear or branched; aryl, phenyl, benzyl, aliphatic
and aromatic heterocycles. [0082] ii) --NH.sub.2, --NH--R.sup.$3,
--NR.sup.$3R.sup.$4, --NH--C(O)--R.sup.$3,
--NR.sup.$3--C(O)--R.sup.$4, --NH--C(S)--R.sup.$3,
--NR.sup.$3--C(S)--R.sup.$4,
[0082] ##STR00003## [0083] where R.sup.$3 and R.sup.$4 are radicals
selected independently of one another from group i). [0084] iii)
--S--R.sup.$5, --S--C(S)--R.sup.$5, where R.sup.$5 can be a radical
from one of groups i) and ii). [0085] iv) --O--R.sup.$6,
--O--C(O)--R.sup.$6, where R.sup.$6 can be a radical selected from
one of groups i) and ii).
[0086] The inventive PSAs prepared by the methods described above
can be coated from solution or from the melt. In one embodiment of
the invention, the solvent is stripped off preferably in a
concentrating extruder under reduced pressure, it being possible to
use, for example, single-screw or twin-screw extruders for this
purpose, which preferentially distill off the solvent in different
or the same vacuum stages and which possess a feed preheater.
[0087] For advantageous further development in accordance with the
invention, tackifier resins may be admixed to the PSAs. In
principle, it is possible to use all resins soluble in the
corresponding polymer. Suitable tackifier resins include rosin and
rosin derivatives (rosin esters, including rosin derivatives
stabilized by, for example, disproportionation or hydrogenation)
polyterpene resins, terpene-phenolic resins, alkylphenol resins,
and aliphatic, aromatic and aliphatic-aromatic hydrocarbon resins,
to name but a few. Primarily, the resins chosen are those which are
compatible preferentially with the polymer. The weight fraction of
the resins in the block copolymer is typically up to 40% by weight,
more preferably up to 30% by weight.
[0088] It is also possible, optionally, to add plasticizers,
fillers (e.g., fibers, carbon black, zinc oxide, titanium dioxide,
chalk, solid or hollow glass beads, microbeads of other materials,
silica, silicates), nucleators, expandants, compounding agents
and/or aging inhibitors, in the form of primary and secondary
antioxidants or in the form of light stabilizers, for example.
[0089] A further constituent of the inventive method is the
increase in the internal strength (cohesion) of the
pressure-sensitive adhesive through the crosslinking with a
crosslinker. For this purpose, compatible crosslinker substances
are added to the acrylate PSAs. Examples of suitable crosslinkers
include metal chelates, such as Z. aluminum or titanium chelates,
polyfunctional isocyanates, polyfunctional amines, polyfunctional
alcohols or polyfunctional epoxides.
For the properties of the PSA it is of great advantage if the
weight-percentage fraction of the crosslinker relative to the
polymer is between 0.2% and 1%, with particular preference between
0.3% and 0.8%.
[0090] For a further inventive version, crosslinking is carried out
with actinic radiation. For this purpose it is advantageous to add
polyfunctional acrylates or methacrylates as crosslinkers.
[0091] For the optional crosslinking with UV light, UV-absorbing
photoinitiators are added to the acrylate PSAs employed in the
systems of the invention. Useful photoinitiators which can be used
to great effect are benzoin ethers, such as benzoin methyl ether
and benzoin isopropyl ether, for example, substituted
acetophenones, such as 2,2-diethoxyacetophenone (available as
Irgacure 651.RTM. from Ciba Geigy.RTM.),
2,2-dimethoxy-2-phenyl-1-phenylethanone,
dimethoxyhydroxyacetophenone, substituted .alpha.-ketols, such as
2-methoxy-2-hydroxypropiophenone, aromatic sulfonyl chlorides, such
as 2-naphthylsulfonyl chloride, and photoactive oximes, such as
1-phenyl-1,2-propanedione 2-(O-ethoxycarbonyl)oxime.
[0092] The abovementioned photoinitiators and others which can be
used, including those of the Norrish I or Norrish II type, can
contain the following radicals: benzophenone, acetophenone, benzil,
benzoin, hydroxyalkylphenone, phenyl cyclohexyl ketone,
anthraquinone, trimethylbenzoylphosphine oxide, methylthiophenyl
morpholinyl ketone, aminoketone, azobenzoin, thioxanthone,
hexarylbisimidazole, triazine or fluorenone, it being possible for
each of these radicals to be further substituted by one or more
halogen atoms and/or one or more alkyloxy groups and/or one or more
amino groups or hydroxyl groups. A representative overview is given
by Fouassier: "Photoinitiation, Photopolymerization and
Photocuring: Fundamentals and Applications", Hanser-Verlag, Munich
1995. For further details it is possible to consult Carroy et al.
in "Chemistry and Technology of UV and EB Formulation for Coatings,
Inks and Paints", Oldring (ed.), 1994, SITA, London.
[0093] In principle it is also possible to crosslink the PSAs using
electron beams alone or additionally. Typical irradiation devices
which may be employed are linear cathode systems, scanner systems,
and segmented cathode systems, in the case of electron beam
accelerators. A detailed description of the state of the art, and
the most important process parameters, are found in Skelhorne,
Electron Beam Processing, in Chemistry and Technology of UV and EB
Formulation for Coatings, Inks and Paints, Vol. 1, 1991, SITA,
London. The typical acceleration voltages are situated within the
range between 50 kV and 500 kV, preferably 80 kV and 300 kV. The
scatter doses used range between 5 to 150 kGy, in particular
between 20 and 100 kGy.
[0094] A further part of the invention is the side of the PSA that
faces the printing cylinder. Here it is possible to use all of the
PSAs that are known to the skilled worker. Suitable accordingly are
rubber-based PSAs, synthetic rubber PSAs, PSAs based on
polysilicones, polyurethanes, polyolefins or polyacrylates, without
this enumeration having any claim to completeness.
[0095] In one preferred version of the invention use is made of PSA
systems based on the PSA facing the printing plate. The PSA systems
may possess the same composition or a different composition. The
composition corresponds to the PSA that has already been described
and is facing the printing plate.
[0096] In one further, very preferred version, an acrylate PSA is
used for bonding on the printing cylinder or sleeve, particularly
polyurethane sleeves.
[0097] Suitable carrier materials for the PSA tapes include the
films which are customary and familiar to the skilled worker, such
as polyesters, PET, PE, PP, BOPP, PVC, etc., for example. This list
is not conclusive. A film of polyethylene terephthalate is used in
one particularly preferred version.
[0098] Also suitable as carrier materials for the double-sided PSA
tapes of the invention, however, are foam carriers. In preferred
versions, polymer foams are used, in which case the carrier foams
are composed, for example, of polyolefins--especially polyethylene
or polypropylene--or of polyurethanes or of polyvinyl chloride.
[0099] Through partial etching of the carrier material, in the form
of indicia, lines, dots or other designs, for example, it is
possible deliberately to strengthen the anchoring of the adhesive
at particular points. In this way, preset breakage points are
formed, at which the adhesive undergoes transfer when the adhesive
tape is demounted. The residues of adhesive, and the damaged
adhesive tape itself, thus disclose removal of the adhesive tape,
in the context, for example, of unauthorized opening of
cartons.
[0100] Generally speaking, an improvement in the anchoring of the
pressure-sensitive adhesive can be achieved by roughening the
carrier material. One way of roughening and of chemically modifying
the polymer structure proceeds via the wet-chemical etching of the
carrier material. Besides etching, pretreatment can be carried out
in other ways. For instance, for improving anchoring, the carrier
materials can be pretreated physically and chemically. For physical
treatment, the film is preferably treated by flame or corona or
plasma. For chemical pretreatment, the carrier material is given a
primer coat, with reactive primer coats being used in one
particularly preferred version. Examples of suitable primer
materials include reactive primers.
[0101] For its use as a double-sided PSA tape for bonding printing
plates, the PSA tape possesses, in one particularly preferred
version of the invention, the product structure in FIG. 1.
[0102] The adhesive tape is used for bonding a printing plate which
is composed of a PET film 2 and of a layer of a photopolymer 1.
[0103] The layers 3 to 9 form a double-sided adhesive
plate-mounting tape which is compressible and elastic by virtue of
its foamed carrier 8.
[0104] Beginning from the side by means of which the printing plate
is bonded, the adhesive tape consists of the following individual
sections: [0105] 3 pressure-sensitive adhesive for anchoring the
printing plate [0106] 4 the roughened top surface of the PET film 5
[0107] 5 film of polyethylene terephthalate (PET) [0108] 6 the
roughened bottom surface of the PET film 5 [0109] 7
pressure-sensitive adhesive for anchoring the foamed carrier 8 to
the polyethylene terephthalate (PET) film 5 [0110] 8 foamed carrier
[0111] 9 pressure-sensitive adhesive for anchoring on the printing
cylinder
[0112] Specifically in the printing industry it is of significance
if the adhesive tapes used here have a high flexibility; that is,
if they are able to a certain extent to change their thickness on
application of pressure and, when the load is removed, to take up
their original form again.
[0113] For this reason, in a further advantageous embodiment of the
double-sided adhesive tape, between the polyethylene terephthalate
(PET) film and at least one adhesive there is a foamed carrier, in
particular between the adhesive facing the printing cylinder or the
sleeve and the polyethylene terephthalate (PET) film, insofar as
the adhesive tape finds use in the printing industry.
It is advantageous, moreover, if the foamed carrier 8 is composed
of polyolefin(s), polyurethane or PVC. In one particularly
preferred embodiment, foamed polyethylenes and polypropylenes are
used. It is further preferred if the surfaces of the foamed carrier
have been physically pretreated, especially corona-pretreated.
[0114] With further preference, the film of polyethylene
terephthalate (PET) has a thickness of from 5 .mu.m to 500 .mu.m,
preferably 5 .mu.m to 60 .mu.m, with very particular preference 23
.mu.m.
[0115] In addition to the product structure depicted in FIG. 1, the
stabilizing film may also be composed of polyolefins, polyurethanes
or PVC, and besides etching may also have been pretreated in
another way. For instance, for improving anchoring, the stabilizing
films can be pretreated physically and chemically. For physical
treatment, the film is preferably treated by flame or corona or
plasma. For chemical pretreatment, the film is given a primer coat,
with reactive primer coats being used in one particularly preferred
embodiment. Examples of suitable primer materials include reactive
primers.
[0116] In one further preferred procedure, the stabilizing film of
PET or another material is printed on one or both sides. This
printing may take place under a pressure-sensitive adhesive for
later application.
[0117] For the pressure-sensitive adhesives 7, in preferred
versions acrylate PSAs are used.
[0118] In addition, the adhesive tape of the invention may be
provided on one or both sides with a lining of paper or of a
corresponding film, especially a double-sidedly siliconized liner,
in order to ensure longer storage and comfortable handling in the
course of service.
[0119] Owing to its special properties, the double-sided adhesive
tape of the invention is outstandingly suitable for mounting
printing plates, especially multilayer photopolymer printing
plates, on printing cylinders or sleeves.
[0120] In one version a weakly adhering acrylate adhesive 9 is
coated onto the side of the adhesive tape (see FIG. 1) which is
mounted on the carrier layer of the printing plate. The adhesive in
particular has a bond strength of 0.5 to 5.5 N/cm, preferably
<2.5 N/cm.
[0121] The other adhesive coating is then formed by a more strongly
adhering layer, preferably likewise based on acrylate. This coating
is characterized in particular by a bond strength of 1 to 6 N/cm,
preferably 4.5 N/cm. The bond strengths indicated are measured in
accordance with AFERA 4001.
[0122] Owing to its special configuration, and particularly with
the bond strengths attuned to the printing plate, the adhesive tape
of the invention is outstandingly suitable for bonding the printing
plates to the printing cylinders. On the one hand, it is possible
to reposition the printing plates as often as desired before
beginning printing; on the other hand, however, a secure bond of
the plate during the printing process is ensured.
[0123] The printing plate can be removed from the PSA tape without
any damage whatsoever. Peeling of the carrier layer of the plate or
the formation of unwanted creases in the plate during removal does
not occur. Moreover, no residues remain after the adhesive tape has
been removed from the printing cylinder.
[0124] In the text below, the advantages of the adhesive tape of
the invention are described in a number of experiments.
Experiments
[0125] The pressure-sensitive adhesive tapes of the invention are
described below by means of experiments.
[0126] The following test methods were employed to evaluate the
technical adhesive properties of the pressure-sensitive adhesives
prepared.
Test Methods
A. Bond Strength
[0127] The peel strength (bond strength) was tested in accordance
with PSTC-1. A PSA layer is applied at 20 g/m.sup.2 to a PET film
25 pm thick.
A strip of this specimen, 2 cm wide, is adhered to a steel plate by
rolling back and forth over the applied strip three times using a 2
kg roller. The plate is clamped in and the self-adhesive strip is
peeled off via its free end on a tensile testing machine under a
peel angle of 180.degree. and with a speed of 300 mm/min.
B. Thermal Storage-Bond Strength
[0128] A PSA layer is applied at 20 g/m.sup.2 to a PET film 25
.mu.m thick.
A strip of this specimen, 2 cm wide, is stored in a drying cabinet
at 60.degree. C. for 3 months. It is then adhered to a steel plate
by rolling back and forth over the applied strip three times using
a 2 kg roller. The plate is clamped in and the self-adhesive strip
is peeled off via its free end on a tensile testing machine under a
peel angle of 180.degree. and with a speed of 300 mm/min.
C. Bond Strength-Peel Increase
[0129] The peel strength (bond strength) was tested in accordance
with PSTC-1. A PSA layer 100 .mu.m thick is applied to a PET film
25 .mu.m thick.
A strip of this specimen, 2 cm wide, is adhered to a steel plate by
rolling back and forth over the applied strip three times using a 2
kg roller. After 72 h of adhesive bonding, the plate is clamped in
and the self-adhesive strip is peeled off via its free end on a
tensile testing machine under a peel angle of 180.degree. and with
a speed of 300 mm/min.
Production of Test Specimens
EXAMPLE 1
[0130] A 2 L glass reactor conventional for free-radical
polymerizations was charged with 8 g of acrylic acid, 272 g of
2-ethylhexyl acrylate, 120 g of isobornyl acrylate and 266 g of 1:1
acetone:special-boiling-point spirit 60/95. After nitrogen gas had
been passed through the reactor for 45 minutes with stirring, the
reactor was heated to 58.degree. C. and 0.2 g of
azoisobutyronitrile (AIBN, Vazo 64.TM., DuPont) in solution in 10 g
of acetone was added.
[0131] Subsequently the external heating bath was heated to
75.degree. C. and the reaction was carried out constantly at this
external temperature. After a reaction time of 1 h a further 0.2 g
of AIBN in solution in 10 g of acetone was added. After a reaction
time of 5 hours 0.8 g of bis(4-tert-butylcyclohexanyl)
peroxydicarbonate (Perkadox 16.TM., Akzo Nobel) in solution in 10 g
of acetone was added. After 6 hours the batch was diluted with 100
g of special-boiling-point spirit 60/95. After a reaction time of 7
hours 0.8 g of bis(4-tert-butyl-cyclohexanyl) peroxydicarbonate
(Perkadox 16.TM., Akzo Nobel) in solution in 10 g of acetone was
added. After 10 hours the batch was diluted with 150 g of
special-boiling-point spirit 60/95. After a reaction time of 24 h
the reaction was discontinued and the product cooled to room
temperature. Subsequently the polyacrylate was blended with 0.6% by
weight of aluminum(IIII) acetylacetonate (3% strength solution,
acetone) and the blend was diluted to a solids content of 30% with
special-boiling-point spirit 60/95 and then coated from solution
onto a PET film. After drying at 120.degree. C. for 30 minutes, the
application rate was 50 g/m.sup.2. The technical adhesive
properties were analyzed by carrying out test methods A, B and
C.
EXAMPLE 2
[0132] A 2 L glass reactor conventional for free-radical
polymerizations was charged with 8 g of acrylic acid, 312 g of
2-ethylhexyl acrylate, 80 g of isobornyl acrylate and 170 g of 1:1
acetone:special-boiling-point spirit 60/95. After nitrogen gas had
been passed through the reactor for 45 minutes with stirring, the
reactor was heated to 58.degree. C. and 0.2 g of
azoisobutyronitrile (AIBN, Vazo 64.TM., DuPont) in solution in 10 g
of acetone was added. Subsequently the external heating bath was
heated to 75.degree. C. and the reaction was carried out constantly
at this external temperature. After a reaction time of 1 h a
further 0.2 g of AIBN in solution in 10 g of acetone was added.
After a reaction time of 5 hours 0.8 g of
bis(4-tert-butylcyclohexanyl) peroxydicarbonate (Perkadox 16.TM.,
Akzo Nobel) in solution in 10 g of acetone was added. After 6 hours
the batch was diluted with 100 g of special-boiling-point spirit
60/95. After a reaction time of 7 hours 0.8 g of
bis(4-tert-butyl-cyclohexanyl) peroxydicarbonate (Perkadox 16.TM.,
Akzo Nobel) in solution in 10 g of acetone was added. After 10
hours the batch was diluted with 150 g of special-boiling-point
spirit 60/95. After a reaction time of 24 h the reaction was
discontinued and the product cooled to room temperature.
Subsequently the polyacrylate was blended with 0.6% by weight of
aluminum(IIII) acetylacetonate (3% strength solution, acetone) and
the blend was diluted to a solids content of 30% with
special-boiling-point spirit 60/95 and then coated from solution
onto a PET film. After drying at 120.degree. C. for 30 minutes, the
application rate was 50 g/m.sup.2. The technical adhesive
properties were analyzed by carrying out test methods A, B and
C.
EXAMPLE 3
[0133] A 2 L glass reactor conventional for free-radical
polymerizations was charged with 8 g of acrylic acid, 312 g of
2-ethylhexyl acrylate, 80 g of stearyl acrylate and 266 g of 1:1
acetone:special-boiling-point spirit 60/95. After nitrogen gas had
been passed through the reactor for 45 minutes with stirring, the
reactor was heated to 58.degree. C. and 0.2 g of
azoisobutyronitrile (AIBN, Vazo 64.TM., DuPont) in solution in 10 g
of acetone was added. Subsequently the external heating bath was
heated to 75.degree. C. and the reaction was carried out constantly
at this external temperature. After a reaction time of 1 h a
further 0.2 g of AIBN in solution in 10 g of acetone was added.
After a reaction time of 5 hours 0.8 g of
bis(4-tert-butylcyclohexanyl) peroxydicarbonate (Perkadox 16.TM.,
Akzo Nobel) in solution in 10 g of acetone was added. After 6 hours
the batch was diluted with 100 g of special-boiling-point spirit
60/95. After a reaction time of 7 hours 0.8 g of
bis(4-tert-butyl-cyclohexanyl) peroxydicarbonate (Perkadox 16.TM.,
Akzo Nobel) in solution in 10 g of acetone was added. After 10
hours the batch was diluted with 150 g of special-boiling-point
spirit 60/95. After a reaction time of 24 h the reaction was
discontinued and the product cooled to room temperature.
Subsequently the polyacrylate was blended with 0.6% by weight of
aluminum(IIII) acetylacetonate (3% strength solution, acetone) and
the blend was diluted to a solids content of 30% with
special-boiling-point spirit 60/95 and then coated from solution
onto a PET film. After drying at 120.degree. C. for 30 minutes, the
application rate was 50 g/m.sup.2. The technical adhesive
properties were analyzed by carrying out test methods A, B and
C.
EXAMPLE 4
[0134] A 2 L glass reactor conventional for free-radical
polymerizations was charged with 8 g of acrylic acid, 352 g of
2-ethylhexyl acrylate, 40 g of isobornyl acrylate and 170 g of 1:1
acetone:special-boiling-point spirit 60/95. After nitrogen gas had
been passed through the reactor for 45 minutes with stirring, the
reactor was heated to 58.degree. C. and 0.2 g of
azoisobutyronitrile (AIBN, Vazo 64.TM., DuPont) in solution in 10 g
of acetone was added. Subsequently the external heating bath was
heated to 75.degree. C. and the reaction was carried out constantly
at this external temperature. After a reaction time of 1 h a
further 0.2 g of AIBN in solution in 10 g of acetone was added.
After a reaction time of 5 hours 0.8 g of
bis(4-tert-butylcyclohexanyl) peroxydicarbonate (Perkadox 16.TM.,
Akzo Nobel) in solution in 10 g of acetone was added. After 6 hours
the batch was diluted with 100 g of special-boiling-point spirit
60/95. After a reaction time of 7 hours 0.8 g of
bis(4-tert-butyl-cyclohexanyl) peroxydicarbonate (Perkadox 16.TM.,
Akzo Nobel) in solution in 10 g of acetone was added. After 10
hours the batch was diluted with 150 g of special-boiling-point
spirit 60/95. After a reaction time of 24 h the reaction was
discontinued and the product cooled to room temperature.
Subsequently the polyacrylate was blended with 0.6% by weight of
aluminum(IIII) acetylacetonate (3% strength solution, acetone) and
the blend was diluted to a solids content of 30% with
special-boiling-point spirit 60/95 and then coated from solution
onto a PET film. After drying at 120.degree. C. for 30 minutes, the
application rate was 50 g/m.sup.2. The technical adhesive
properties were analyzed by carrying out test methods A, B and
C.
REFERENCE R1
[0135] A 2 L glass reactor conventional for free-radical
polymerizations was charged with 8 g of acrylic acid, 372 g of
2-ethylhexyl acrylate, 20 g of isobornyl acrylate and 170 g of 1:1
acetone:special-boiling-point spirit 60/95. After nitrogen gas had
been passed through the reactor for 45 minutes with stirring, the
reactor was heated to 58.degree. C. and 0.2 g of
azoisobutyronitrile (AIBN, Vazo 64.TM., DuPont) in solution in 10 g
of acetone was added. Subsequently the external heating bath was
heated to 75.degree. C. and the reaction was carried out constantly
at this external temperature. After a reaction time of 1 h a
further 0.2 g of AIBN in solution in 10 g of acetone was added.
After a reaction time of 5 hours 0.8 g of
bis(4-tert-butylcyclohexanyl) peroxydicarbonate (Perkadox 16.TM.,
Akzo Nobel) in solution in 10 g of acetone was added. After 6 hours
the batch was diluted with 100 g of special-boiling-point spirit
60/95. After a reaction time of 7 hours 0.8 g of
bis(4-tert-butyl-cyclohexanyl) peroxydicarbonate (Perkadox 16.TM.,
Akzo Nobel) in solution in 10 g of acetone was added. After 10
hours the batch was diluted with 150 g of special-boiling-point
spirit 60/95. After a reaction time of 24 h the reaction was
discontinued and the product cooled to room temperature.
Subsequently the polyacrylate was blended with 0.6% by weight of
aluminum(IIII) acetylacetonate (3% strength solution, acetone) and
the blend was diluted to a solids content of 30% with
special-boiling-point spirit 60/95 and then coated from solution
onto a PET film. After drying at 120.degree. C. for 30 minutes, the
application rate was 50 g/m.sup.2. The technical adhesive
properties were analyzed by carrying out test methods A, B and
C.
REFERENCE R2
[0136] A 2 L glass reactor conventional for free-radical
polymerizations was charged with 8 g of acrylic acid, 192 g of
2-ethylhexyl acrylate, 200 g of isobornyl acrylate and 170 g of 1:1
acetone:special-boiling-point spirit 60/95. After nitrogen gas had
been passed through the reactor for 45 minutes with stirring, the
reactor was heated to 58.degree. C. and 0.2 g of
azoisobutyronitrile (AIBN, Vazo 64.TM., DuPont) in solution in 10 g
of acetone was added. Subsequently the external heating bath was
heated to 75.degree. C. and the reaction was carried out constantly
at this external temperature. After a reaction time of 1 h a
further 0.2 g of AIBN in solution in 10 g of acetone was added.
After a reaction time of 5 hours 0.8 g of
bis(4-tert-butylcyclohexanyl) peroxydicarbonate (Perkadox 16.TM.,
Akzo Nobel) in solution in 10 g of acetone was added. After 6 hours
the batch was diluted with 100 g of special-boiling-point spirit
60/95. After a reaction time of 7 hours 0.8 g of
bis(4-tert-butyl-cyclohexanyl) peroxydicarbonate (Perkadox 16.TM.,
Akzo Nobel) in solution in 10 g of acetone was added. After 10
hours the batch was diluted with 150 g of special-boiling-point
spirit 60/95. After a reaction time of 24 h the reaction was
discontinued and the product cooled to room temperature.
Subsequently the polyacrylate was blended with 0.6% by weight of
aluminum(IIII) acetylacetonate (3% strength solution, acetone) and
the blend was diluted to a solids content of 30% with
special-boiling-point spirit 60/95 and then coated from solution
onto a PET film. After drying at 120.degree. C. for 30 minutes, the
application rate was 50 g/m.sup.2. The technical adhesive
properties were analyzed by carrying out test methods A, B and
C.
REFERENCE R3
[0137] A 2 L glass reactor conventional for free-radical
polymerizations was charged with 8 g of acrylic acid, 352 g of
2-ethylhexyl acrylate, 40 g of isobornyl acrylate and 170 g of 1:1
acetone:special-boiling-point spirit 60/95. After nitrogen gas had
been passed through the reactor for 45 minutes with stirring, the
reactor was heated to 58.degree. C. and 0.2 g of
azoisobutyronitrile (AIBN, Vazo 64.TM., DuPont) in solution in 10 g
of acetone was added. Subsequently the external heating bath was
heated to 75.degree. C. and the reaction was carried out constantly
at this external temperature. After a reaction time of 1 h a
further 0.2 g of AIBN in solution in 10 g of acetone was added.
After 6 hours the batch was diluted with 100 g of
special-boiling-point spirit 60/95. After 10 hours the batch was
diluted with 150 g of special-boiling-point spirit 60/95. After a
reaction time of 24 h the reaction was discontinued and the product
cooled to room temperature. Subsequently the polyacrylate was
blended with 0.6% by weight of aluminum(IIII) acetylacetonate (3%
strength solution, acetone) and the blend was diluted to a solids
content of 30% with special-boiling-point spirit 60/95 and then
coated from solution onto a PET film.
Bond Strength Determination of Examples 1-4 and Reference Examples
R1 and R2
TABLE-US-00001 [0138] TABLE 1 BS to steel instantaneous.sup.a BS to
steel after 72 h.sup.b BS after 60.degree. C..sup.c [N/cm] [N/cm]
[N/cm] Example Test A Test C Test B 1 5.0 5.2 5.5 2 3.8 4.2 4.4 3
2.4 2.7 2.9 4 3.0 3.4 3.7 R1 2.7 3.6 5.4 R2 2.2 2.6 6.0 .sup.aBS =
bond strength to steel at 23.degree. C. and 50% atmospheric
humidity, measured after bonding. .sup.bBS = bond strength to steel
at 23.degree. C. and 50% atmospheric humidity after 72 hours of
bonding. .sup.cBS = bond strength to steel at 23.degree. C. and 50%
atmospheric humidity after bonding; the PSA tapes were stored at
60.degree. C. for 3 months beforehand. 50 g/m.sup.2 application
rate to PET film 25 .mu.m thick.
[0139] From the figures from table 1 it can be inferred that the
inventive examples, even under very extreme storage conditions,
possess only a very low peel increase. In contrast, the examples R1
and R2 already exhibit a much greater peel increase, since in the
case of R1 the adhesive is already very soft and is therefore able
to flow out very well over a prolonged period of time. Reference
example R2, by contrast, is very hard and therefore
exhibits--especially at high temperatures--an improved flow-out and
hence a high peel increase in test C. For use for the bonding of
printing plates it is preferred to use pressure-sensitive adhesives
having a low peel increase preferably, in order that the PSA tape
can be removed again easily after the printing process. The bonds
may extend from several days through to several months, so that
test C in particular is very informative as regards the suitability
of a pressure-sensitive adhesive for bonding printing plates. Here,
the inventive adhesives produced according to the method show
themselves to be very advantageous as compared, for example, with
the systems containing only a very low fraction (R1) or a very high
fraction (R2) of isobornyl acrylate.
Production of the Double-Sided PSA Tape Assembly:
[0140] A PET film 25 .mu.m thick and etched on both sides with
trichloroacetic acid was coated with examples 1, 2, 3, 4, R1 or R2.
Following crosslinking and drying, the application rate was 20
g/m.sup.2. For this purpose the film was coated directly from
solution with the examples and dried at 100.degree. C. for 30
minutes. The specimens thus coated were lined with a double-sidedly
siliconized release paper. Subsequently, a commercially customary
acrylate PSA was laminated via a transfer carrier onto the uncoated
side of the existing assembly, with an application rate of 20
g/m.sup.2.
In the following step, a EVA foam with a thickness of 500 .mu.m and
a density of 270 kg/m.sup.3 was laminated on. Then, again via a
transfer carrier, a commercially customary acrylate PSA is
laminated onto this foam carrier, onto the uncoated side of the
existing assembly, at an application rate of 50 g/m.sup.2.
Adhesive Bonding of Printing Plates and Use:
[0141] The double-sided PSA tapes described above with the adhesive
side lying open (see FIG. 1, layer 9) were adhered to a steel
cylinder having a diameter of 110 mm. On top of this, a printing
plate from DuPont Cyrel.RTM. HOS with a thickness of 1.7 mm, with
layer 2 from the figure was bonded to the PSA (layer 3 in FIG. 1).
This steel cylinder with printing plate was subsequently inserted
into a printing machine where it was used for printing for 16 hours
with a print setting of 150 .mu.m.
For all of the examples, the printing plate was very easy to remove
by hand from the double-sided adhesive tape, without any
residue.
[0142] After 7-day storage at 23.degree. C. and 50% atmospheric
humidity, the edge lifting of the printing plate from the
double-sided PSA tape was ascertained. The values are reported in
mm, are averaged from three measurements, and are summarized in
table 2.
TABLE-US-00002 TABLE 2 Example Edge lifting of the printing plate
in mm 1 5 2 20 3 25 4 18 R1 55 R2 60 R3 35
[0143] A PSA tape suitable for printing-plate bonding ought to
exhibit edge lifting of less than 30 mm. The boundary is a function
of the fact that, at higher values, the printing process is
severely impaired.
Examples 1 to 4 meet this requirement on the one hand as a result
of the production method, which allows the formation of graft
copolymers. Example R3, without a graft initiator, demonstrates
that the edge lifting deteriorates markedly. On the other hand,
examples 1 to 4 in combination with the inventive method show that
edge lifting can be reduced to the degree necessary.
* * * * *