U.S. patent application number 15/102824 was filed with the patent office on 2016-10-27 for post-curable pressure-sensitive adhesive.
The applicant listed for this patent is 3M INNOVATIVE PROPERTIES COMPANY. Invention is credited to Peter Bissinger, Siegfried R. Goeb, Silke D. Mechernich, Mareike Richter, Kerstin Unverhau.
Application Number | 20160312080 15/102824 |
Document ID | / |
Family ID | 49880443 |
Filed Date | 2016-10-27 |
United States Patent
Application |
20160312080 |
Kind Code |
A1 |
Richter; Mareike ; et
al. |
October 27, 2016 |
POST-CURABLE PRESSURE-SENSITIVE ADHESIVE
Abstract
The present disclosure is directed to a curable precursor of a
pressure sensitive adhesive comprising: a) a (co)polymeric material
comprising the reaction product of a (co)polymerizable material
comprising a (meth)acrylate ester monomer; and optionally, a
co-monomer having an ethylenically unsaturated group and which is
different from the (meth)acrylate ester monomer; b) a
polyfunctional aziridine curing agent; and c) an acid generating
agent. The present disclosure is also directed to a method of
manufacturing such pressure sensitive adhesives and uses
thereof.
Inventors: |
Richter; Mareike;
(Dusseldorf, DE) ; Unverhau; Kerstin; (Neuss,
DE) ; Mechernich; Silke D.; (Neuss, DE) ;
Goeb; Siegfried R.; (Willich, DE) ; Bissinger;
Peter; (Diessen, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
3M INNOVATIVE PROPERTIES COMPANY |
Saint Paul |
MN |
US |
|
|
Family ID: |
49880443 |
Appl. No.: |
15/102824 |
Filed: |
December 5, 2014 |
PCT Filed: |
December 5, 2014 |
PCT NO: |
PCT/US2014/068723 |
371 Date: |
June 8, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09J 11/08 20130101;
C09J 9/00 20130101; C09J 4/06 20130101; C09J 2301/302 20200801;
C09J 2433/00 20130101; C09J 4/00 20130101; C09J 5/00 20130101; C07D
203/08 20130101; C08F 220/18 20130101; C09J 2479/02 20130101; C09J
133/08 20130101 |
International
Class: |
C09J 11/08 20060101
C09J011/08; C09J 9/00 20060101 C09J009/00; C09J 5/00 20060101
C09J005/00; C09J 133/08 20060101 C09J133/08 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 18, 2013 |
EP |
13198136.7 |
Claims
1. A curable precursor of a pressure sensitive adhesive comprising:
a) a (co)polymeric material comprising the reaction product of a
(co)polymerizable material comprising a (meth)acrylate ester
monomer; and optionally, a co-monomer having an ethylenically
unsaturated group, the co-monomer being a non-acid functional polar
monomer; b) a polyfunctional aziridine curing agent comprising at
least two aziridine functional groups; and c) an acid generating
agent selected from the group consisting of thermal acid generating
agents, photo acid generating agents, and any combinations or
mixtures thereof; and wherein the photo acid generating agent is
selected from the group consisting of ionic salts of organometallic
complexes, iodonium or sulfonium salts and any combinations or
mixtures thereof.
2. A curable precursor according to claim 1, wherein the
polyfunctional aziridine curing agent comprises two or three
aziridine functional groups.
3. A curable precursor according to claim 1, wherein the
polyfunctional aziridine curing agent has the following formula:
##STR00017## wherein R.sup.1 is a (hetero)hydrocarbyl group;
R.sup.2 is an H, C.sub.1-C.sub.12 alkyl group, or C.sub.6-C.sub.12
aromatic group; x is 0, 1 or 2; and y is at least 1.
4. A curable precursor according to claim 1, wherein the
polyfunctional aziridine curing agent has the following formula:
##STR00018## wherein R.sup.4 is a (hetero)hydrocarbyl group having
a valency of y; R.sup.5 and R.sup.6 are independently
(hetero)hydrocarbyl groups; R.sup.2 is an H, C.sub.1-C.sub.12 alkyl
group, or C.sub.6-C.sub.12 aromatic group; y is at least 1; x is 0,
1 or 2; and each of a and b are independently 0 to 6.
5. (canceled)
6. A curable precursor according to claim 1, wherein the acid
generating agent is a thermal acid generating agent selected from
the group consisting of quarternary blocked superacids, amine
blocked superacids, and any combinations or mixtures thereof.
7. (canceled)
8. A curable precursor according to claim 1, wherein the non-acid
functional polar monomer has a nitrogen-containing group or a salt
thereof.
9. A curable precursor according to claim 8, wherein the
nitrogen-containing group is selected from secondary amido groups
and tertiary amido groups.
10. A curable precursor according to claim 1, wherein the optional
co-monomer having an ethylenically unsaturated group is N-vinyl
caprolactam.
11. A curable precursor according to claim 1, wherein the
(co)polymeric material comprising the reaction product of a
(co)polymerizable material comprising a (meth)acrylate ester
monomer, is free of acid functional monomers.
12. A curable precursor according to claim 1, comprising: a) 100
parts by weight of a (co)polymeric material comprising the reaction
product of a (co)polymerizable material comprising a (meth)acrylate
ester monomer; and optionally, a co-monomer having an ethylenically
unsaturated group, the co-monomer being a non-acid functional polar
monomer; b) from 0.1 to 30 parts by weight of a polyfunctional
aziridine curing agent comprising at least two aziridine functional
groups; c) from 0.01 to 10 parts by weight of an acid generating
agent selected from the group consisting of thermal acid generating
agents, photo acid generating agents, and any combinations or
mixtures thereof; and wherein the photo acid generating agent is
selected from the group consisting of ionic salts of organometallic
complexes, iodonium or sulfonium salts and any combinations or
mixtures thereof; and d) optionally, from 1 to 20 parts by weight
of a filler material, preferably hollow glass microspheres.
13. A cured pressure sensitive adhesive obtainable by curing the
curable precursor according to claim 1, wherein the curing step is
performed by allowing acid to be released into the curable
precursor of a pressure sensitive adhesive.
14. A cured pressure sensitive adhesive according to claim 13,
wherein the curing step is performed by subjecting the curable
precursor of a pressure sensitive adhesive to a triggering energy
sufficient to allow the acid generating agent to release acid into
the curable precursor of a pressure sensitive adhesive, and wherein
the triggering energy is thermal energy or actinic radiation.
15. A method of applying a pressure sensitive adhesive to a
substrate, comprising the steps of: a) providing a curable
precursor of a pressure sensitive adhesive comprising: i. a
(co)polymeric material comprising the reaction product of a
(co)polymerizable material comprising a (meth)acrylate ester
monomer; and optionally, a co-monomer having an ethylenically
unsaturated group, the co-monomer being a non-acid functional polar
monomer; ii. a polyfunctional aziridine curing agent comprising at
least two aziridine functional groups; and iii. optionally, an acid
generating agent selected from the group consisting of thermal acid
generating agents, photo acid generating agents, and any
combinations or mixtures thereof; and wherein the photo acid
generating agent is selected from the group consisting of ionic
salts of organometallic complexes, iodonium or sulfonium salts and
any combinations or mixtures thereof; b) applying the curable
precursor of a pressure sensitive adhesive to at least part of the
surface of the substrate; and c) curing the curable precursor of a
pressure sensitive adhesive by allowing acid to be released into
it.
16. A method of applying a pressure sensitive adhesive to a
substrate, comprising the steps of: a) providing a curable
precursor of a pressure sensitive adhesive comprising: i. a
(co)polymeric material comprising the reaction product of a
(co)polymerizable material comprising a (meth)acrylate ester
monomer; and optionally, a co-monomer having an ethylenically
unsaturated group, the co-monomer being a non-acid functional polar
monomer and which is different from the (meth)acrylate ester
monomer; ii. a polyfunctional aziridine curing agent comprising at
least two aziridine functional groups; and iii. optionally, an acid
generating agent selected from the group consisting of thermal acid
generating agents, photo acid generating agents, and any
combinations or mixtures thereof; and wherein the photo acid
generating agent is selected from the group consisting of ionic
salts of organometallic complexes, iodonium or sulfonium salts and
any combinations or mixtures thereof; b) partially curing the
curable precursor of a pressure sensitive adhesive by allowing acid
to be released into it; c) applying the partially cured pressure
sensitive adhesive to at least part of the surface of the
substrate; and d) allowing the partially cured pressure sensitive
adhesive to fully cure onto the substrate.
17. A method according to claim 16, whereby the curing step is
performed by subjecting the curable precursor of a pressure
sensitive adhesive to a triggering energy sufficient to allow the
acid generating agent to release acid into the curable precursor of
a pressure sensitive adhesive, and wherein the triggering energy is
thermal energy or actinic radiation.
18. A method according to claim 16, whereby the curing step is
performed by contacting the curable precursor of a pressure
sensitive adhesive with a source of acid.
19. (canceled)
20. (canceled)
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of EP Patent Application
No. 13198136.7 filed Dec. 18, 2013, the disclosure of which is
incorporated by reference herein in its entirety.
TECHNICAL FIELD
[0002] The present disclosure relates generally to the field of
adhesives, more specifically to the field of pressure sensitive
adhesive (PSA). The present disclosure also relates to a method of
manufacturing such pressure sensitive adhesives and uses
thereof.
BACKGROUND
[0003] Adhesives have been used for a variety of marking, holding,
protecting, sealing and masking purposes. Adhesive tapes generally
comprise a backing, or substrate, and an adhesive. One type of
adhesive which is particularly preferred for many applications is
represented by pressure sensitive adhesives.
[0004] Pressure-sensitive tapes are virtually ubiquitous in the
home and workplace. In its simplest configuration, a
pressure-sensitive tape comprises an adhesive and a backing, and
the overall construction is tacky at the use temperature and
adheres to a variety of substrates using only moderate pressure to
form the bond. In this fashion, pressure-sensitive tapes constitute
a complete, self-contained bonding system.
[0005] Pressure sensitive adhesives (PSAs) are well known to one of
ordinary skill in the art, and according to the Pressure-Sensitive
Tape Council, PSAs are known to possess properties including the
following: (1) aggressive and permanent tack, (2) adherence with no
more than finger pressure, (3) sufficient ability to hold onto an
adherend, and (4) sufficient cohesive strength to be removed
cleanly from the adherend. Materials that have been found to
function well as PSAs include polymers designed and formulated to
exhibit the requisite viscoelastic properties resulting in a
desired balance of tack, peel adhesion, and shear holding power.
PSAs are characterized by being normally tacky at room temperature
(e.g., 20.degree. C.). PSAs do not embrace compositions merely
because they are sticky or adhere to a surface.
[0006] These requirements are assessed generally by means of tests
which are designed to individually measure tack, adhesion (peel
strength), and cohesion (shear holding power), as noted in A. V.
Pocius in Adhesion and Adhesives Technology: An Introduction,
2.sup.nd Ed., Hanser Gardner Publication, Cincinnati, Ohio, 2002.
These measurements taken together constitute the balance of
properties often used to characterize a PSA.
[0007] With broadened use of pressure-sensitive tapes over the
years, performance requirements have become more demanding. Shear
holding capability, for example, which originally was intended for
applications supporting modest loads at room temperature, has now
increased substantially for many applications in terms of operating
temperature and load. When used as attachment devices for a variety
of assembly and manufacturing applications, such as interior or
exterior automotive mounting of panels and molding, or in the
construction industry, pressure sensitive adhesives are
additionally required to provide good adhesion performance to rough
or irregular surfaces. In addition, many applications require
pressure sensitive adhesives to support a load at elevated
temperatures, typically in the range of from 70.degree. C. to
90.degree. C., for which high cohesive strengths are required.
So-called high performance pressure-sensitive tapes are those
capable of supporting loads at elevated temperatures for 10,000
minutes. Increased shear holding capability has generally been
accomplished by crosslinking the PSA, although considerable care
must be exercised so that high levels of tack and adhesion are
retained in order to retain the aforementioned balance of
properties.
[0008] It is therefore a recognized challenge in the adhesive tapes
industry to combine good adhesion and good cohesion properties. In
order to optimize the adhesion of a PSA to a particular substrate,
in particular an irregular substrate, an excellent surface wetting
is necessary.
[0009] Partial solutions have been described in the art, whereby a
non- or very low crosslinked adhesive is applied to a surface and
then post-cured, so that, after an adequate surface wetting, the
cohesive strength can be built up. In that context, the so-called
"semi-structural tapes" described e.g. in U.S. Pat. No. 5,721,289
(Karim et al.) have been used, as. These systems are based on
post-curable epoxy functionalities and specifically require using a
superacid which is activated by UV irradiation as triggering
energy. However, these known systems show undesired moisture
sensitivity as the superacid needed for UV-induced cationic curing
or crosslinking of the epoxy functionalities decomposes to
hydronium ion, rendering ineffective the ring-opening
polymerization of epoxies. Other known post-curable systems are
based on the so-called "DICY-chemistry" described e.g. in
EP-A1-0798354, wherein an epoxy-amine curing reaction is triggered
with heat. However, these systems require a continuous heating step
so as to maintain the curing reaction until the curing or
crosslinking step has been completed. Patent applications US
2011/0076493-A1 (Kavanagh et al.) and US 2011/0178248-A1 (Kavanagh
et al.) disclose pre-adhesive compositions comprising an aziridine
crosslinking agent.
[0010] The commonly known curing or crosslinking systems do not
often provide industrially viable solutions for the production of
pressure sensitive adhesives having acceptable characteristics.
Without contesting the technical advantages associated with the
curing or crosslinking systems known in the art for producing
pressure sensitive adhesives, there is still a need for a pressure
sensitive adhesive provided with an excellent and versatile balance
of adhesive and cohesive properties, in particular on uneven or
irregular substrates.
[0011] Other advantages of the pressure sensitive adhesives and
methods of the invention will be apparent from the following
description.
SUMMARY
[0012] According to one aspect, the present disclosure relates to a
curable precursor of a pressure sensitive adhesive comprising:
[0013] a) a (co)polymeric material comprising the reaction product
of a (co)polymerizable material comprising a (meth)acrylate ester
monomer; and optionally, a co-monomer having an ethylenically
unsaturated group and which is different from the (meth)acrylate
ester monomer; [0014] b) a polyfunctional aziridine curing agent;
and [0015] c) an acid generating agent.
[0016] In another aspect, the present disclosure relates to a
composite assembly comprising a substrate and a curable precursor
of a pressure sensitive adhesive as above described applied onto at
least part of the surface of the substrate, thereby forming a layer
of a curable precursor of a pressure sensitive adhesive.
[0017] According to still another aspect of the present disclosure,
it is provided a method of applying a pressure sensitive adhesive
to a substrate, comprising the steps of: [0018] a) providing a
curable precursor of a pressure sensitive adhesive comprising:
[0019] i. a (co)polymeric material comprising the reaction product
of a (co)polymerizable material comprising a (meth)acrylic acid
ester monomer; and optionally, a co-monomer having an ethylenically
unsaturated group and which is different from the (meth)acrylate
ester monomer; [0020] ii. a polyfunctional aziridine curing agent;
and [0021] iii. optionally, an acid generating agent; [0022] b)
applying the curable precursor of a pressure sensitive adhesive to
at least part of the surface of the substrate; and [0023] c) curing
the curable precursor of a pressure sensitive adhesive by allowing
acid to be released into it.
[0024] In still another aspect, the present disclosure relates to
the use of a curable precursor of a pressure sensitive adhesive as
above-described, for the bonding to an uneven or irregular
substrate. In yet another aspect, the present disclosure relates to
the use of a curable precursor of a pressure sensitive adhesive,
for industrial applications, in particular for automotive
applications, in particular for taped seal on body
applications.
DETAILED DESCRIPTION
[0025] According to a first aspect, the present disclosure relates
to a curable precursor of a pressure sensitive adhesive comprising:
[0026] a) a (co)polymeric material comprising the reaction product
of a (co)polymerizable material comprising a (meth)acrylate ester
monomer; and optionally, a co-monomer having an ethylenically
unsaturated group and which is different from the (meth)acrylate
ester monomer ; [0027] b) a polyfunctional aziridine curing agent;
and [0028] c) an acid generating agent.
[0029] In the context of the present disclosure, it has
surprisingly been found that a curable precursor of a pressure
sensitive adhesive as described above is outstandingly suitable for
producing post-cured pressure sensitive adhesives provided with an
excellent and versatile balance of adhesive and cohesive
properties, in particular on uneven or irregular substrates. The
curable precursor of a pressure sensitive adhesive according to the
disclosure is particularly suitable to perform on-demand
post-curing, i.e. activatable and delayed in-place curing. In the
context of the present disclosure, the acid generating agent for
use herein acts as an activatable latent source of acid catalysts
for cationic (ring-opening) polymerization of the polyfunctional
aziridine curing agent, resulting in curing of the precursor of a
pressure sensitive adhesive according to the disclosure.
[0030] Without wishing to be bound by theory, it is believed that
the curing mechanism used to build up inner strength of the
pressure sensitive adhesive involves the formation of an
interpenetrating network involving the (meth)acrylate ester based
(co)polymeric material and an aziridine network resulting from
acid-catalyzed cationic ring-opening polymerization of
polyfunctional aziridine monomeric units.
[0031] Still without wishing to be bound by theory, it is believed
that the particular combination of a polyfunctional aziridine
curing agent and an acid generating agent, allows providing an
excellent surface wetting characteristics to the precursor of a
pressure sensitive adhesive on its uncured state, in particular on
uneven or irregular substrates, which ultimately translates into
providing excellent adhesives and cohesive properties to the
pressure sensitive adhesive resulting from the curing of the
precursor of the pressure sensitive adhesive.
[0032] The curable precursor of a pressure sensitive adhesive of
the present disclosure may be (pre)polymerized and cured in-place
to produce a pressure sensitive adhesive provided with excellent
characteristics directly on the desired substrate or article.
[0033] The use of the curable precursor composition and method of
the present disclosure affords a number of advantages as compared
to conventional post-curable compositions, such as e.g. those based
on post-curable epoxy functionalities or on the so-called
"DICY-chemistry". These advantages include, but are not limited to,
insensitivity of the curable composition to moisture, and ability
to perform post-curing of the curable precursor by short initiation
with a suitable triggering energy (e.g. thermal energy or actinic
radiation) without the necessity to provide a continuous source of
triggering energy until the curing is completed.
[0034] In addition, the cured pressure sensitive adhesives exhibit
high peel strength, high cohesive strength, high temperature shear
strength, and excellent stress relaxation properties. The
pressure-sensitive adhesives according to the present disclosure,
i.e. in the cured state, provide the desired balance of tack, peel
adhesion, and shear holding power, and further conform to the
Dahlquist criteria; i.e. the modulus of the adhesive at the
application temperature, typically room temperature, is less than
3.times.106 dynes/cm at a frequency of 1 Hz.
[0035] The pressure sensitive adhesives according to the disclosure
may find particular use for adhering e.g. automotive body side
mouldings, weather strips, road signs, commercial signs,
constructions, electrical cabinets, shell moulds, machine parts,
junction boxes or backsheet solutions for photovoltaic modules. In
a particular advantageous aspect, the pressure sensitive adhesives
of the present disclosure provide excellent adhesion properties on
low surface energy substrates, such as polyolefin surfaces and
clear coat surfaces. More particularly, the pressure sensitive
adhesives disclosed herein may be advantageously bonded to
automotive clear coat surfaces.
[0036] In the context of the present disclosure, the expression
"low surface energy substrates" is meant to refer to those
substrates having a surface energy of less than 34 dynes per
centimeter. Included among such materials are polypropylene,
polyethylene (e.g., high density polyethylene or HDPE), and blends
of polypropylene (e.g. PP/EPDM, TPO).The surface energy is
typically determined from contact angle measurements as described,
for example, in ASTM D7490-08.
[0037] In the context of the present disclosure, the term "curing"
is not meant to designate crosslinking, but is rather meant to
refer to the formation of an interpenetrating polymer network
structure, e.g. the interpenetrating network involving the
(meth)acrylate ester based (co)polymeric network and the aziridine
polymeric network resulting from acid-catalyzed cationic
ring-opening polymerization of polyfunctional aziridine monomeric
units.
[0038] In the context of the present disclosure, and as well known
to those skilled in the art, the term "acid generating agent" is
meant to refer to a latent source of acid catalysts for performing
e.g. cationic (ring-opening) polymerization, and which is
activatable by exposure to a suitable triggering energy (such as
e.g. thermal energy or actinic radiation).
[0039] As used herein, the term "alkyl (meth)acrylate" and "alkyl
(meth)acrylate ester" are used interchangeably. The term
"(meth)acrylate" refers to an acrylate, methacrylate, or both. The
term "(meth)acrylic" refers to methacrylic, acrylic, or both. A
(meth)acrylic-based" material refers to one prepared from one or
more monomers having a (meth)acryloyl group, which is a group of
formula CH.sub.2.dbd.C(R)--(CO)-- where R is hydrogen or
methyl.
[0040] The term "alkyl" refers to a monovalent group which is a
saturated hydrocarbon. The alkyl can be linear, branched, cyclic,
or combinations thereof and typically has 1 to 32 carbon atoms. In
some embodiments, the alkyl group contains 1 to 25, 1 to 20, 1 to
18, 1 to 12, 1 to 10, 1 to 8, 1 to 6, or 1 to 4 carbon atoms.
Examples of alkyl groups include, but are not limited to, methyl,
ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl,
n-pentyl, n-hexyl, cyclohexyl, n-heptyl, n-octyl, 2-ethylhexyl,
2-octyl and 2-propylheptyl.
[0041] The terms "glass transition temperature" and "Tg" are used
interchangeably and refer to the glass transition temperature of a
material or a mixture. Unless otherwise indicated, glass transition
temperature values are determined by Differential Scanning
Calorimetry (DSC).
[0042] As used herein, the term "heteroalkyl" includes both
straight-chained, branched, and cyclic alkyl groups with one or
more heteroatoms independently selected from S, O, and N with both
unsubstituted and substituted alkyl groups. Unless otherwise
indicated, the heteroalkyl groups typically contain from 1 to 20
carbon atoms. "Heteroalkyl" is a subset of "hydrocarbyl containing
one or more S, N, O, P, or Si atoms" described below. Examples of
"heteroalkyl" as used herein include, but are not limited to,
methoxy, ethoxy, propoxy, 3,6-dioxaheptyl,
3-(trimethylsilyl)-propyl, 4-dimethylaminobutyl, and the like.
Unless otherwise noted, heteroalkyl groups may be mono- or
polyvalent.
[0043] As used herein, "aryl" is an aromatic group containing 6-18
ring atoms and can contain optional fused rings, which may be
saturated, unsaturated, or aromatic. Examples of an aryl groups
include phenyl, naphthyl, biphenyl, phenanthryl, and anthracyl.
Heteroaryl is aryl containing 1-3 heteroatoms such as nitrogen,
oxygen, or sulfur and can contain fused rings. Some examples of
heteroaryl groups are pyridyl, furanyl, pyrrolyl, thienyl,
thiazolyl, oxazolyl, imidazolyl, indolyl, benzofuranyl, and
benzthiazolyl. Unless otherwise noted, aryl and heteroaryl groups
may be mono- or polyvalent.
[0044] As used herein, "(hetero)hydrocarbyl" is inclusive of
hydrocarbyl alkyl and aryl groups, and heterohydrocarbyl
heteroalkyl and heteroaryl groups, the later comprising one or more
catenary oxygen heteroatoms such as ether or amino groups.
Heterohydrocarbyl may optionally contain one or more catenary
(in-chain) functional groups including ester, amide, urea,
urethane, and carbonate functional groups. Unless otherwise
indicated, the non-polymeric (hetero)hydrocarbyl groups typically
contain from 1 to 60 carbon atoms. Some examples of such
heterohydrocarbyls as used herein include, but are not limited to,
methoxy, ethoxy, propoxy, 4-diphenylaminobutyl,
2-(2'-phenoxyethoxy)ethyl, 3,6-dioxaheptyl,
3,6-dioxahexyl-6-phenyl, in addition to those described for
"alkyl", "heteroalkyl", "aryl", and "heteroaryl" supra.
[0045] In a typical aspect, the (co)polymeric material comprising
the reaction product of a (co)polymerizable material comprising a
(meth)acrylate ester monomer, comprises a polymer base material
selected from the group consisting of polyacrylates whose main
monomer component comprises a linear or branched alkyl
(meth)acrylate ester, preferably a non-polar linear or branched
alkyl (meth)acrylate ester having a linear or branched alkyl group
comprising preferably from 1 to 32, from 1 to 20, or even from 1 to
15 carbon atoms.
[0046] According to a particular aspect, the (co)polymeric material
for use herein comprises a polymer base material selected from the
group consisting of polyacrylates whose main monomer component
preferably comprises a linear or branched alkyl (meth)acrylate
ester, preferably a non-polar linear or branched alkyl
(meth)acrylate ester having a linear or branched alkyl group
comprising preferably from 1 to 32, from 1 to 20, or even from 1 to
15 carbon atoms.
[0047] According to a preferred aspect of the curable precursor of
a pressure sensitive adhesive of the present disclosure, the
(co)polymeric material for use herein comprises a polymer base
material selected from the group consisting of polyacrylates whose
main monomer component comprises a linear or branched alkyl
(meth)acrylate ester selected from the group consisting of methyl
(meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate,
isopropyl (meth)acrylate, n-butyl acrylate, isobutyl acrylate,
tert-butyl (meth)acrylate, n-pentyl (meth)acrylate, iso-pentyl
(meth)acrylate, n-hexyl (meth)acrylate, iso-hexyl (meth)acrylate,
cyclohexyl (meth)acrylate, phenyl (meth)acrylate, octyl
(meth)acrylate, iso-octyl (meth)acrylate, 2-octyl(meth)acrylate,
2-ethylhexyl (meth)acrylate, decyl (meth)acrylate, lauryl
(meth)acrylate, 2-propylheptyl (meth)acrylate, stearyl
(meth)acrylate, isobornyl acrylate, benzyl (meth)acrylate,
octadecyl acrylate, nonyl acrylate, dodecyl acrylate, isophoryl
(meth)acrylate, and any combinations or mixtures thereof.
[0048] In a more preferred aspect, the linear or branched alkyl
(meth)acrylate ester for use herein is selected from the group
consisting of iso-octyl (meth)acrylate, 2-ethylhexyl
(meth)acrylate, 2-propylheptyl (meth)acrylate, 2-octyl
(meth)acrylate, butyl acrylate, and any combinations or mixtures
thereof; more preferably from the group consisting of iso-octyl
acrylate (IOA), 2-ethylhexyl acrylate (2-EHA), 2-octyl acrylate
(2-OA) and 2-propylheptyl acrylate (2-PHA). In a particularly
preferred aspect, the linear or branched alkyl (meth)acrylate ester
for use herein comprises or consists of 2-ethylhexyl acrylate.
[0049] According to an alternative aspect, the linear or branched
alkyl (meth)acrylate ester for use herein is selected to comprise
2-octyl(meth)acrylate. Polymer base material derived from 2-octyl
(meth)acrylate provides comparable adhesive properties when
compared with other isomers of octyl (meth)acrylate, such as
n-octyl and isooctyl. Further, the pressure sensitive adhesive
compositions have lower inherent and solution viscosities when
compared to adhesive compositions derived from other octyl isomers,
such as isooctyl acrylate, at the same concentrations, and under
the same polymerization conditions.
[0050] The 2-octyl (meth)acrylate may be prepared by conventional
techniques from 2-octanol and (meth)acryloyl derivates such as
esters, acids and acyl halides. The 2-octanol may be prepared by
treatment of ricinoleic acid, derived from castor oil, (or ester or
acyl halide thereof) with sodium hydroxide, followed by
distillation from the co-product sebacic acid.
[0051] It is however preferred that the 2-octyl(meth)acrylate
monomer for use herein is at least partly, preferably completely
(i.e. 100 wt %) derived from biological material, more preferably
from a plant material. This may advantageously be used to provide
adhesive films/tapes which are at least partly derived from "green"
sources, which is ecologically more sustainable and also reduces
the dependency on mineral oil and the price development.
[0052] In the context of the present disclosure, the term "derived
from biological material" is meant to express that from a certain
chemical ingredient, at least a part of its chemical structure
comes from biological materials, preferably at least 50 wt % of its
structure. This definition is in principle the same as for
bio-diesel fuel, in which usually only the fatty acid part
originates from biological sources whereas the methanol may also be
derived from fossil material like coal or mineral oil.
[0053] Accordingly, in one specific aspect, at least 50 wt %, at
least 75 wt %, or even 100 wt % of the chemical structure of the
2-octyl(meth)acrylate is at least partly, preferably completely
(i.e. 100 wt %) derived from biological material, more preferably
from a plant material.
[0054] The (meth)acrylate ester monomer(s) for use herein may be
present in the (co)polymerizable material, in any suitable amounts.
In some exemplary aspects, the (meth)acrylate ester monomer(s) are
present in amounts up to 100 parts by weight, up to 90 parts by
weight, or even up to 80 parts by weight of the (co)polymerizable
material. In some other exemplary aspects, this amount is typically
of at least 50 parts by weight, or at least 60 parts by weight of
the (co)polymerizable material.
[0055] Accordingly, in some exemplary aspects, the (meth)acrylate
ester monomer(s) are present in amounts in a range of from 50 to
100 parts, from 60 to 95 parts by weight, from 65 to 90 parts, or
even from 65 to 80 parts by weight of the (co)polymerizable
material.
[0056] According to a particular aspect, the (co)polymeric material
for use herein may further comprise an optional co-monomer having
an ethylenically unsaturated group and which is different from the
(meth)acrylate ester monomer(s) described above. Suitable
co-monomer(s) having an ethylenically unsaturated group for use
herein will be easily identified by those skilled in the art, in
the light of the present description. As such, co-monomer(s) having
an ethylenically unsaturated group for use herein are not
particularly limited as long as they are different from the
(meth)acrylate ester monomer(s) described above.
[0057] In one preferred aspect, the co-monomer(s) having an
ethylenically unsaturated group include, but are not limited to,
the group of polar monomers, in particular non-acid functional
polar monomers.
[0058] In another aspect of the present disclosure, the
co-monomer(s) having an ethylenically unsaturated group are
selected from the group of non-acid functional polar monomers
having a single ethylenically unsaturated group and a
nitrogen-containing group or a salt thereof. In a typical aspect,
the nitrogen-containing group is selected from secondary amido
groups and tertiary amido groups, in particular those selected from
the group consisting of N-vinyl lactams.
[0059] Advantageoulsy, the co-monomer(s) having an ethylenically
unsaturated group may be selected from the group consisting of
N-vinyl lactams, in particular N-vinyl caprolactam, N-vinyl
piperidone, N-vinyl pyrrolidone; acryloyl morpholine, acrylamides
and substituted acrylamides; in particular t-butyl acrylamide,
dimethylamino ethyl acrylamide, N-octyl acrylamide, N,N-dialkyl
acrylamides, N-methyl acrylamide, N-ethyl acrylamide, N-isopropyl
acrylamide, tert-octyl acrylamide, N,N-dimethyl acrylamide,
N,N-diethyl acrylamide, N,N-dipropyl acrylamide, N,N-dibutyl
acrylamide; and any combinations or mixtures thereof. Preferably,
the co-monomer(s) having an ethylenically unsaturated group
comprise N-vinyl caprolactam. Preferably still, the co-monomer
having an ethylenically unsaturated is selected to be N-vinyl
caprolactam.
[0060] Without wishing to be bound by theory, it is believed that
the co-monomer(s) having an ethylenically unsaturated group
selected from the group of non-acid functional polar monomers
having a single ethylenically unsaturated group and a
nitrogen-containing group, and in particular those wherein the
nitrogen-containing group is selected from the group consisting of
N-vinyl lactams, do advantageously affect the curing mechanism. It
is further believed that the co-monomer(s) having an ethylenically
unsaturated group selected from the group of non-acid functional
polar monomers having a single ethylenically unsaturated group and
a nitrogen-containing group beneficially participate in the
formation of an interpenetrating network involving the
(meth)acrylate ester based (co)polymeric material and an aziridine
network resulting from acid-catalyzed cationic ring-opening
polymerization of polyfunctional aziridine monomeric units.
[0061] The co-monomer(s) having an ethylenically unsaturated group
for use herein may be present in the (co)polymerizable material, in
any suitable amounts. In some exemplary aspects, the co-monomer(s)
having an ethylenically unsaturated group are present in amounts up
to 40 parts by weight, up to 35 parts by weight, or even up to 30
parts by weight of the (co)polymerizable material. In some other
exemplary aspects, this amount is typically of at least 5 parts by
weight, or at least 10 parts by weight of the (co)polymerizable
material.
[0062] Accordingly, in some exemplary aspects, the co-monomer(s)
having an ethylenically unsaturated group are present in amounts in
a range of from 0 to 40 parts, from 5 to 35 parts by weight, or
even from 20 to 35 parts by weight of the (co)polymerizable
material. In some other exelplary aspects, the co-monomer(s) having
an ethylenically unsaturated group are present in amounts in a
range of from 0 to 20 parts, from 5 to 15 parts by weight, or even
from 5 to 10 parts by weight of the (co)polymerizable material.
[0063] In a particular aspect of the curable precursor of the
present disclosure, the (co)polymerizable material comprises:
[0064] a) from 60 to 100 parts by weight, from 65 to 95 parts by
weight, or even from 65 to 80 parts by weight, of a (meth)acrylate
ester monomer; and [0065] b) optionally, from 0 to 40 parts by
weight, from 5 to 35 parts by weight, or even from 20 to 35 parts
by weight, of a co-monomer having an ethylenically unsaturated
group.
[0066] In some exemplary aspects, the (co)polymerizable material
suitable for preparing the (co)polymeric material of the curable
precursor, comprises a second co-monomer having an ethylenically
unsaturated group. Suitable second co-monomer(s) having an
ethylenically unsaturated group for use herein will be easily
identified by those skilled in the art, in the light of the present
description. As such, the second co-monomer(s) having an
ethylenically unsaturated group for use herein are not particularly
limited.
[0067] In one exemplary aspect, the second co-monomer(s) having an
ethylenically unsaturated group include, but are not limited to,
the group consisting of high Tg monomers. In the context of the
present disclosure, the expression "high Tg monomer" is meant to
refer to monomers having a Tg of at least 25.degree. C., preferably
at least 50.degree. C. (wherein the Tg of a monomer is measured as
a homopolymer prepared from the monomer).
[0068] Suitable high Tg monomers for use herein include, but are
not limited to, those selected from the group consisting of t-butyl
acrylate, methyl methacrylate, ethyl methacrylate, isopropyl
methacrylate, n-butyl methacrylate, isobutyl methacrylate, s-butyl
methacrylate, t-butyl methacrylate, stearyl methacrylate, phenyl
methacrylate, cyclohexyl methacrylate, isobornyl acrylate,
isobornyl methacrylate, benzyl methacrylate, 3,3,5
trimethylcyclohexyl acrylate, cyclohexyl acrylate, N-octyl
acrylamide, propyl methacrylate, and any combinations or mixtures
thereof.
[0069] According to a particular aspect of the curable precursor
according to the disclosure, the (co)polymerizable material
comprises: [0070] a) from 50 to 100 parts by weight, from 60 to 90
parts by weight, or even from 65 to 80 parts by weight, of a
(meth)acrylate ester monomer; and [0071] b) optionally, from 0 to
20 parts by weight, from 5 to 15 parts by weight, or even from 5 to
10 parts by weight, of a co-monomer having an ethylenically
unsaturated group; and [0072] c) optionally, from 0 to 30 parts by
weight, from 5 to 25 parts by weight, or even from 15 to 25 parts
by weight, of a second co-monomer having an ethylenically
unsaturated group.
[0073] According to a particular aspect of the curable precursor
according to the disclosure, the (co)polymerizable material is free
of acid functional monomers.
[0074] In order to increase cohesive strength of the pressure
sensitive adhesive, a multifunctional (meth)acrylate may optionally
be incorporated into the blend of polymerizable monomers. Examples
of useful multifunctional (meth)acrylate include, but are not
limited to, di(meth)acrylates, tri(meth)acrylates, and
tetra(meth)acrylates, such as 1,6-hexanediol di(meth)acrylate,
poly(ethylene glycol) di(meth)acrylates, polybutadiene
di(meth)acrylate, polyurethane di(meth)acrylates, and propoxylated
glycerin tri(meth)acrylate, and mixtures thereof. The amount and
identity of multifunctional (meth)acrylate is tailored depending
upon application of the adhesive composition. Typically, the
multifunctional (meth)acrylate is present in amounts less than 5
parts based on total dry weight of adhesive composition. More
specifically, the crosslinker may be present in amounts from 0.01
to 5 parts, preferably 0.05 to 1 parts, based on 100 parts total
monomers (polymerized or unpolymerized) of the adhesive
composition.
[0075] Generally, the (co)polymerizable material
(pre-polymerization monomer mixture) used to prepare the
(co)polymeric material, includes an appropriate initiator. For
polymerization by ultraviolet light, a photoinitiator is included.
Useful photoinitiators include substituted acetophenones such as
benzyl dimethyl ketal and 1-hydroxycyclohexyl phenyl ketone,
substituted alpha-ketols such as 2-methyl-2-hydroxypropiophenone,
benzoin ethers such as benzoin methyl ether, benzoin isopropyl
ether, substituted benzoin ethers such as anisoin methyl ether,
aromatic sulfonyl chlorides, photoactive oximes and azo-type
initiators. The photoinitiator may be used in an amount from about
0.001 to about 5.0 parts by weight, preferably from about 0.01 to
about 5.0 parts by weight, more preferably in an amount from 0.05
to 0.5 parts by weight, and more preferably in an amount from 0.05
to 0.3 parts by weight per 100 parts by weight of total
monomer.
[0076] The pre-polymerization monomer mixture used to prepare the
acrylate the (co)polymeric material, may also be polymerized by
thermal polymerization or by a combination of thermal and radiation
polymerization. For thermal polymerization, a thermal initiator is
included. Thermal initiators useful in the present invention
include, but are not limited to azo, peroxide, persulfate, and
redox initiators. Azo-type initiators, such as e.g. the "Vazo"
line, commercially available from DuPont Chemical Co, are
particularly preferred. The thermal initiator may be used in an
amount from about 0.01 to about 5.0 parts by weight per 100 parts
by weight of total monomer, preferably from 0.025 to 2 weight
percent.
[0077] The (co)polymerizable material may optionally further
comprise chain transfer agents to control the molecular weight of
the resultant polymer. Examples of useful chain transfer agents
include but are not limited to those selected from the group
consisting of carbon tetrabromide, alcohols, mercaptans, and
mixtures thereof. When present, the preferred chain transfer agents
are isooctylthioglycolate and carbon tetrabromide. The emulsion
mixture may further comprise up to about 0.5 parts by weight of a
chain transfer agent, typically about 0.01 to about 0.5 parts by
weight, if used, preferably about 0.05 parts by weight to about 0.2
parts by weight, based upon 100 parts by weight of the total
monomer mixture.
[0078] The curable precursor according to the disclosure further
comprises a polyfunctional aziridine curing agent. Suitable
polyfunctional aziridine curing agents for use herein will be
easily identified by those skilled in the art, in the light of the
present description. As such, the polyfunctional aziridine curing
agents for use herein are not particularly limited. Suitable
polyfunctional aziridine curing agents for use herein are described
e.g. in US-A1-2011/0178248 (Kavanagh et al.), the content of which
is herewith incorporated by reference.
[0079] In one exemplary aspect, the polyfunctional aziridine curing
agents comprise at least two aziridine functional groups, in
particular two or three aziridine functional groups. In another
exemplary aspect, the polyfunctional aziridine curing agents
comprise at least one aziridine functional group and at least one
(meth)acryloyl functional group.
[0080] According to a particular aspect of the present disclosure,
the polyfunctional aziridine curing agent for use herein has the
following formula:
##STR00001##
[0081] wherein [0082] R.sup.1 is a (hetero)hydrocarbyl group;
[0083] R.sup.2 is an H or C.sub.1-C.sub.12 alkyl group,
C.sub.1-C.sub.8 alkyl group, C.sub.1-C.sub.6 alkyl group,
C.sub.1-C.sub.4 alkyl group, C.sub.1-C.sub.2 alkyl group,
C.sub.6-C.sub.12 aromatic group, C.sub.6-C.sub.10 aromatic group,
or even C.sub.6-C.sub.7 aromatic group; [0084] preferably R.sup.2
is H, CH.sub.2, C.sub.2H.sub.5 or even phenyl group; [0085] x is 0,
1 or 2, and [0086] y is at least 1, preferably 1 to 4, or even 2 to
3.
[0087] According to another particular aspect of the present
disclosure, the polyfunctional aziridine curing agent for use
herein has the following formula:
##STR00002##
[0088] wherein [0089] R.sup.3 is a (hetero)hydrocarbyl group;
[0090] R.sup.2 is an H or C.sub.1-C.sub.12 alkyl group,
C.sub.1-C.sub.8 alkyl group, C.sub.1-C.sub.6 alkyl group,
C.sub.1-C.sub.4 alkyl group, C.sub.1-C.sub.2 alkyl group,
C.sub.6-C.sub.12 aromatic group, C.sub.6-C.sub.10 aromatic group,
or even C.sub.6-C.sub.7 aromatic group; [0091] preferably R.sup.2
is H, CH.sub.2, C.sub.2H.sub.5 or even phenyl group; and [0092] x
is 0, 1 or 2.
[0093] According to another particular aspect of the present
disclosure, the polyfunctional aziridine curing agent for use
herein has the following formula:
##STR00003##
[0094] wherein [0095] R.sup.4 is a (hetero)hydrocarbyl group having
a valency of y; [0096] R.sup.2 is an H or C.sub.1-C.sub.12 alkyl
group, C.sub.1-C.sub.8 alkyl group, C.sub.1-C.sub.6 alkyl group,
C.sub.1-C.sub.4 alkyl group, C.sub.1-C.sub.2 alkyl group,
C.sub.6-C.sub.12 aromatic group, C.sub.6-C.sub.10 aromatic group,
or even C.sub.6-C.sub.7 aromatic group; [0097] preferably R.sup.2
is H, CH.sub.2, C.sub.2H.sub.5 or even phenyl group; [0098] y is at
least 1, preferably 1 to 4, or even 2 to 3; [0099] x is 0, 1 or 2;
and [0100] each of a and b are independently 0 to 6, 0 to 4, or
even 0 to 2.
[0101] According to still another particular aspect of the present
disclosure, the polyfunctional aziridine curing agent for use
herein has the following formula:
##STR00004##
[0102] wherein [0103] R.sup.4 is a (hetero)hydrocarbyl group having
a valency of y; [0104] R.sup.5 and R.sup.6 are independently
(hetero)hydrocarbyl groups; [0105] R.sup.2 is an H or
C.sub.1-C.sub.12 alkyl group, C.sub.1-C.sub.8 alkyl group,
C.sub.1-C.sub.6 alkyl group, C.sub.1-C.sub.4 alkyl group,
C.sub.1-C.sub.2 alkyl group, C.sub.6-C.sub.12 aromatic group,
C.sub.6-C.sub.10 aromatic group, or even C.sub.6-C.sub.7 aromatic
group; [0106] preferably R.sup.2 is H, CH.sub.2, C.sub.2H.sub.5 or
even phenyl group; [0107] y is at least 1, preferably 1 to 4, or
even 2 to 3; [0108] x is 0, 1 or 2; and [0109] each of a and b are
independently 0 to 6, 0 to 4, or even 0 to 2.
[0110] According to still another particular aspect of the present
disclosure, the polyfunctional aziridine curing agent for use
herein has the following formula:
##STR00005##
[0111] wherein [0112] R.sup.4 is a (hetero)hydrocarbyl group having
a valency of y; [0113] R.sup.7 is a (hetero)hydrocarbyl group, in
particular C.sub.2-C.sub.12 alkyl group, C.sub.2-C.sub.8 alkyl
group, C.sub.2-C.sub.6 alkyl group, or even
CH.sub.2--CHR'--O-group, with R' being H or CH3; [0114] R.sup.2 is
an H or C.sub.1-C.sub.12 alkyl group, C.sub.1-C.sub.8 alkyl group,
C.sub.1-C.sub.6 alkyl group, C.sub.1-C.sub.4 alkyl group,
C.sub.1-C.sub.2 alkyl group, C.sub.6-C.sub.12 aromatic group,
C.sub.6-C.sub.10 aromatic group, or even C.sub.6-C.sub.7 aromatic
group; [0115] preferably R.sup.2 is H, CH.sub.2, C.sub.2H.sub.5 or
even phenyl group; [0116] y is at least 1, preferably 1 to 4, or
even 2 to 3; [0117] x is 0, 1 or 2; and [0118] a is 0 to 100, 1 to
50, 1 to 20 or even 1 to 10.
[0119] According to still another particular aspect of the present
disclosure, the polyfunctional aziridine curing agent for use
herein has the following formula:
##STR00006##
[0120] wherein [0121] R.sup.4 is a hydrocarbyl group having a
valency of y; [0122] R.sup.2 is an H or C.sub.1-C.sub.12 alkyl
group, C.sub.1-C.sub.8 alkyl group, C.sub.1-C.sub.6 alkyl group,
C.sub.1-C.sub.4 alkyl group, C.sub.1-C.sub.2 alkyl group,
C.sub.6-C.sub.12 aromatic group, C.sub.6-C.sub.10 aromatic group,
or even C.sub.6-C.sub.7 aromatic group; [0123] preferably R.sup.2
is H, CH.sub.2, C.sub.2H.sub.5 or even phenyl group; [0124] y is at
least 1, preferably 1 to 4, or even 2 to 3; and [0125] x is 0, 1 or
2.
[0126] According to still another particular aspect of the present
disclosure, the polyfunctional aziridine curing agents for use
herein have the following formula:
##STR00007##
[0127] The curable precursor according to the disclosure further
comprises an acid generating agent. Suitable acid generating agents
for use herein will be easily identified by those skilled in the
art, in the light of the present description. As such, the acid
generating agents for use herein are not particularly limited.
Suitable acid generating agents for use herein are described e.g.
in U.S. Pat. No. 5,089,536 (Palazzotto), US-A1-2011/0178248
(Kavanagh et al.) and U.S. Pat. No. 5,721,289 (Karim et al.)
incorporated herein by reference.
[0128] In one typical aspect, the acid generating agents are
selected from the group consisting of thermal acid generating
agents, photo acid generating agents, and any combinations or
mixtures thereof. As will be apparent to those skilled in the art,
some acid generating agents may operate as both thermal- and photo
acid generating agents.
[0129] Without wishing to be bound by theory, it is believed that
the (super)acid generated by the acid generating agents initiates
the ring-opening homopolymerization of the polyfunctional aziridine
curing agents acting as monomeric units.
[0130] Suitable thermal acid generating agents are for example
selected from the group consisting of quarternary blocked
superacids, amine blocked superacids, and any combinations or
mixtures thereof. Exemplary quarternary blocked superacids for use
herein are quarternary blocked SbF.sub.6, quarternary blocked
triflic acid, and any combinations thereof. Exemplary suitable
thermal acid generating agents are for example commercially
available from King Industries under tradename K-Pure CXC and TAG
series.
[0131] In a particular aspect, the acid generating agents for use
herein are selected from the group consisting of quarternary
blocked SbF.sub.6, quarternary blocked triflic acid, quarternary
blocked fluorosulfonic acids, and any combinations or mixtures
thereof.
[0132] Suitable photo acid generating agents are for example
selected from the group consisting of ionic salts of organometallic
complexes and onium salts, in particular sulfonium and iodonium
salts. Exemplary organic onium salts for use herein are iodonium or
sulfonium or phenyliodonium salts of the anions SbF.sub.6--,
PF.sub.6--, CF.sub.3SO.sub.3--, C.sub.4F.sub.9SO.sub.3-- and
C.sub.8F.sub.17SO.sub.3--, and any combinations or mixtures
thereof. Exemplary suitable photo acid generating agents are for
example commercially available from Bluestar Silicones under
tradename Rhodorsil 2074, from Wako Chemicals under tradename WPI
113 (Iodonium salt), from Hampford Research Inc. under tradename FP
5386, or from BASF under tradenames CGI 1907 or Irgacure 290
(Sulfonium salt).
[0133] The curable precursor according to the disclosure, may in
some aspects further comprise a filler material which is preferably
selected from the group consisting of filler particles, in
particular expanded perlite, microspheres, expendable microspheres,
glassbeads, glass microspheres, silica type fillers, hydrophobic
silica type fillers, hydrophilic silica type fillers, hydrophobic
fumed silica, hydrophilic fumed silica, fibers, electrically and/or
thermally conducting particles, nanoparticles, in particular silica
nanoparticles, and any combinations or mixtures thereof. The
disclosure is however not that limited as alternative filler
material may be easily identified by those skilled in the art, in
the light of the present disclosure. In a particular aspect, the
filler material, in particular the particulate filler material
comprises hollow glass microspheres.
[0134] The filler material for use herein may be present in the
curable precursor of a pressure sensitive adhesive, in any suitable
amounts. In some exemplary aspects, the filler material is present
in amounts up to 30 parts by weight, up to 25 parts by weight, or
even up to 20 parts by weight of the curable precursor of a
pressure sensitive adhesive. In some other exemplary aspects, this
amount is typically of at least 1 part by weight, or at least 3
parts by weight of the curable precursor of a pressure sensitive
adhesive.
[0135] Accordingly, in some exemplary aspects, the filler material
is present in amounts in a range of from 1 to 20 parts, from 3 to
15 parts by weight, or even from 5 to 13 parts by weight of the
curable precursor of a pressure sensitive adhesive.
[0136] In the context of this disclosure, the (co)polymeric
material comprising the reaction product of a (co)polymerizable
material comprising a (meth)acrylate ester monomer is present in
the curable precursor of a pressure sensitive adhesive in an amount
of 100 parts by weight to calculate the amounts of the remaining
ingredients.
[0137] In a particular aspect, the curable precursor of the
disclosure comprises: [0138] a) 100 parts by weight of a
(co)polymeric material comprising the reaction product of a
(co)polymerizable material comprising a (meth)acrylate ester
monomer; and optionally, a co-monomer having an ethylenically
unsaturated group; [0139] b) from 0.1 to 30 parts by weight, from
0.5 to 25 parts by weight, from 1 to 20 parts by weight, from 1 to
15 parts by weight, or even from 5 to 15 parts by weight, of a
polyfunctional aziridine curing agent; [0140] c) from 0.01 to 10
parts by weight, from 0.1 to 8 parts by weight, from 0.2 to 6 parts
by weight, or even from 0.2 to 5 parts by weight, of an acid
generating agent; and [0141] d) optionally, from 1 to 20 parts by
weight, from 3 to 15 parts by weight, or even from 5 to 13 parts by
weight, of a filler material, preferably hollow glass
microspheres.
[0142] The curable precursor of a pressure sensitive adhesive may
also contain one or more conventional additives. Preferred
additives include tackifiers, plasticizers, dyes, antioxidants, and
UV stabilizers. Such additives can be used if they do not affect
the superior properties of the pressure sensitive adhesives.
[0143] If tackifiers are used, then up to about 50% by weight,
preferably less than 30% by weight, and more preferably less than
5% by weight based on the dry weight of the total adhesive polymer
would be suitable. The type and amount of tackifier can affect
properties such as contactability, bonding range, bond strength,
heat resistance and specific adhesion.
[0144] Suitable tackifying resins include, for example, terpene
phenolics, rosins, rosin esters, esters of hydrogenated rosins,
synthetic hydrocarbon resins and combinations thereof. Especially
suitable tackifying resins include the commercially available
tackifying resins: FORAL 85E (a glycerol ester of highly
hydrogenated refined gum rosin) commercially available from
Eastman, Middelburg, NL), FORAL 3085 (a glycerol ester of highly
hydrogenated refined wood rosin) commercially available from
Hercules Inc., Wilmington, Del.; ESCOREZ 2520 and ESCOREZ 5615
(aliphatic/aromatic hydrocarbon resins) commercially available from
ExxonMobil Corp., Houston, Tex.; and Regalite 7100 (a partially
hydrogenated hydrocarbon resin) commercially available from
Eastman, Kingsport, Tenn.
[0145] The curable precursor of a pressure sensitive adhesive may
contain a plasticizer, if desired. The plasticizer is typically
selected to be compatible with (i.e., miscible with) the other
components in the composition such as the polymerizable material
and any optional tackifier. Suitable plasticizers include, but are
not limited to, various polyalkylene oxides (e.g., polyethylene
oxides or propylene oxides), adipic acid esters, formic acid
esters, phosphoric acid esters, benzoic acid esters, phthalic acid
esters, and sulfonamides, or naphthenic oils.
[0146] The (co)polymeric material may be prepared by any
conventional free radical polymerization method, including
solution, radiation, bulk, dispersion, emulsion, solventless, and
suspension processes. Generally, the pre-polymerization monomer
mixture used to prepare the (co)polymeric material, includes an
appropriate initiator.
[0147] As will be apparent to those skilled in the art, the curable
precursor of a pressure sensitive adhesive according to the present
disclosure may further include a variety of additional additives
depending on the envisaged properties for the resulting cured
pressure sensitive adhesive. Exemplary additional additives
include, but are not limited to, one or more plasticizers, UV
stabilizers, antistatic agents, colorants, antioxidants,
fungicides, bactericides, organic and/or inorganic filler
particles, pigments, and any combinations thereof. Advantageously,
the additional additives for use herein are non-polymerizable
additives. As will be apparent to those skilled in the art,
additional additives for use herein may be included at appropriate
timing and in the appropriate polymeric or pre-polymeric
matrix.
[0148] One exemplary method of preparing a curable precursor of a
pressure sensitive adhesive comprises partially polymerizing
monomers to produce a syrup polymer comprising the (meth)acrylate
copolymer and unpolymerized monomers. Generally, the polyfunctional
aziridine curing agent, the acid generating agent, and optionally
the co-monomer having an ethylenically unsaturated group, are added
to the partially polymerized composition, then coated on a suitable
substrate and further polymerized. The syrup polymer composition is
polymerized to a useful coating viscosity, which may be coated onto
a substrate (such as a tape backing) and further polymerized.
Partial polymerization provides a coatable solution of the
(meth)acrylate copolymer.
[0149] In an alternative exemplary method of preparing a curable
precursor of pressure sensitive adhesive, the (meth)acrylate
copolymer is prepared by solution methods. A typical solution
polymerization method is carried out by adding the monomers, a
suitable solvent, and an optional chain transfer agent to a
reaction vessel, adding a free radical initiator, purging with
nitrogen, and maintaining the reaction vessel at an elevated
temperature, typically in the range of about 40 to 100.degree. C.
until the reaction is completed, typically in about 1 to 20 hours,
depending upon the batch size and temperature. Examples of the
solvent are methanol, tetrahydrofuran, ethanol, isopropanol,
acetone, methyl ethyl ketone, methyl acetate, ethyl acetate,
toluene, xylene, and an ethylene glycol alkyl ether. These solvents
can be used alone or as mixtures thereof. Generally, the
polyfunctional aziridine curing agent and the acid generating agent
are added to a solution of the (meth)acrylate copolymer thereby
forming a coating solution, then coated on a suitable substrate and
further dried in an oven.
[0150] The polymerizations may be conducted in the presence of, or
preferably in the absence of, suitable solvents such as ethyl
acetate, toluene and tetrahydrofuran which are unreactive with the
functional groups of the components of the syrup polymer.
[0151] Polymerization can be accomplished by exposing the syrup
polymer composition to energy in the presence of a photoinitiator.
Energy activated initiators may be unnecessary where, for example,
ionizing radiation is used to initiate polymerization.
[0152] A preferred method of preparation of the coatable syrup
polymer is photoinitiated free radical polymerization. Advantages
of the photopolymerization method are that 1) heating the monomer
solution is unnecessary and 2) photoinitiation is stopped
completely when the activating light source is turned off.
Polymerization to achieve a coatable viscosity may be conducted
such that the conversion of monomers to polymer is up to about 30%.
Polymerization can be terminated when the desired conversion and
viscosity have been achieved by removing the light source and by
bubbling air (oxygen) into the solution to quench propagating free
radicals. The solute polymer(s) may be prepared conventionally in a
non-monomeric solvent and advanced to high conversion (degree of
polymerization). When solvent (monomeric or non-monomeric) is used,
the solvent may be removed (for example by vacuum distillation)
either before or after formation of the syrup polymer. While an
acceptable method, this procedure involving a highly converted
functional polymer is not preferred because an additional solvent
removal step is required, another material may be required (the
non-monomeric solvent), and dissolution of the high molecular
weight, highly converted solute polymer in the monomer mixture may
require a significant period of time.
[0153] Useful photoinitiators include benzoin ethers such as
benzoin methyl ether and benzoin isopropyl ether; substituted
acetophenones such as 2,2-dimethoxyacetophenone, available as
Irgacure.TM. 651 photoinitiator (Ciba-Geigy Corp.; Ardsley, N.Y.),
2,2 dimethoxy-2-phenyl-1-phenylethanone, available as Esacure.TM.
KB-1 photoinitiator (Sartomer Co.; West Chester, Pa.), and
dimethoxyhydroxyacetophenone; substituted .alpha.-ketols such as
2-methyl-2-hydroxy propiophenone; aromatic sulfonyl chlorides such
as 2-naphthalene-sulfonyl chloride; and photoactive oximes such as
1-phenyl-1,2-propanedione-2-(O-ethoxy-carbonyl)oxime. Particularly
preferred among these are the substituted acetophenones.
[0154] Preferred photoinitiators are photoactive compounds that
undergo a Norrish I cleavage to generate free radicals that can
initiate by addition to the acrylic double bonds. The
photoinitiator can be added to the mixture to be coated after the
copolymer has been formed, i.e., photoinitiator can be added to the
syrup polymer mixture. Such polymerizable photoinitiators are
described, for example, in U.S. Pat. No. 5,902,836 (Bennett et al.)
and U.S. Pat. No. 5,506,279 (Babu et al.).
[0155] The syrup polymer composition and the photoinitiator may be
irradiated with activating UV radiation to polymerize the monomer
component(s). UV light sources can be of two types: 1) relatively
low light intensity sources such as Blacklights which provide
generally 10 mW/cm.sup.2 or less (as measured in accordance with
procedures approved by the United States National Institute of
Standards and Technology as, for example, with a UVIMAP.TM. UM 365
L-S radiometer manufactured by Electronic
[0156] Instrumentation & Technology, Inc., in Sterling, Va.)
over a wavelength range of 280 to 400 nanometers and 2) relatively
high light intensity sources such as medium pressure mercury lamps
which provide intensities generally greater than 10 mW/cm.sup.2,
preferably between 15 and 450 mW/cm.sup.2. Where actinic radiation
is used to fully or partially polymerize the syrup polymer
composition, high intensities and short exposure times are
preferred. For example, an intensity of 600 mW/cm.sup.2 and an
exposure time of about 1 second may be used successfully.
Intensities can range from about 0.1 to about 150 mW/cm.sup.2,
preferably from about 0.5 to about 100 mW/cm.sup.2, and more
preferably from about 0.5 to about 50 mW/cm.sup.2. Such
photoinitiators preferably are present in an amount of from 0.1 to
1.0 pbw per 100 pbw of the syrup polymer composition.
[0157] Accordingly, relatively thick coatings (e.g., at least about
1 mil or 25.4 micrometers) can be achieved when the extinction
coefficient of the photoinitiator is low.
[0158] The degree of conversion can be monitored during the
irradiation by measuring the index of refraction of the
polymerizing medium as previously described. Useful coating
viscosities are achieved with conversions (i.e. the percentage of
available monomer polymerized) in the range of up to 30%,
preferably 2-20%, more preferably from 5-15%, and most preferably
from 7-12%. The molecular weight (weight average) of the solute
polymer(s) is at least 100,000, preferably at least 500,000.
[0159] When preparing pressure sensitive adhesives, it is expedient
for the photoinitiated polymerization reactions to proceed to
virtual completion, i.e., depletion of the monomeric components, at
temperatures less than about 70.degree. C. (preferably at
50.degree. C. or less) with reaction times less than 24 hours,
preferably less than 12 hours, and more preferably less than 6
hours. These temperature ranges and reaction rates obviate the need
for free radical polymerization inhibitors, which are often added
to acrylic systems to stabilize against undesired, premature
polymerization and gelation. Furthermore, the addition of
inhibitors adds extraneous material that will remain with the
system and inhibit the desired polymerization of the syrup polymer
and formation of the cured pressure sensitive adhesives of the
disclosure. Free radical polymerization inhibitors are often
required at processing temperatures of 70.degree. C. and higher for
reaction periods of more than about 6 to 10 hours.
[0160] It is preferable to coat the curable precursor of pressure
sensitive adhesive soon after preparation. The curable precursor
composition of pressure sensitive adhesive, either as a syrup or
solution are easily coated upon suitable substrates, such as
flexible backing materials, by conventional coating techniques,
then further polymerized, and cured or dried, to produce adhesive
coated sheet materials. The flexible backing material may be any
material conventionally utilized as a tape backing, optical film or
any other flexible material.
[0161] Adhesive articles may be prepared by coating the curable
precursor composition of a pressure sensitive adhesive on a
suitable support, such as a flexible backing. Examples of materials
that can be included in the flexible backing include polyolefins
such as polyethylene, polypropylene (including isotactic
polypropylene), polystyrene, polyester, polyvinyl alcohol,
poly(ethylene terephthalate), poly(butylene terephthalate),
poly(caprolactam), poly(vinylidene fluoride), polylactides,
cellulose acetate, and ethyl cellulose and the like. Commercially
available backing materials useful in the invention include kraft
paper (available from Monadnock Paper, Inc.); cellophane (available
from Flexel Corp.); spun-bond poly(ethylene) and poly(propylene),
such as Tyvek.TM. and Typar.TM. (available from DuPont, Inc.); and
porous films obtained from poly(ethylene) and poly(propylene), such
as Teslin.TM. (available from PPG Industries, Inc.), and
Cellguard.TM. (available from Hoechst-Celanese).
[0162] Backings may also be prepared of fabric such as woven fabric
formed of threads of synthetic or natural materials such as cotton,
nylon, rayon, glass, ceramic materials, and the like or nonwoven
fabric such as air laid webs of natural or synthetic fibers or
blends of these. The backing may also be formed of metal, metalized
polymer films, or ceramic sheet materials may take the form of any
article conventionally known to be utilized with pressure sensitive
adhesive compositions such as labels, tapes, signs, covers, marking
indicia, and the like.
[0163] The above-described precursor compositions are coated on a
substrate using conventional coating techniques modified as
appropriate to the particular substrate. For example, these
compositions can be applied to a variety of solid substrates by
methods such as roller coating, flow coating, dip coating, spin
coating, spray coating, knife coating, and die coating. These
various methods of coating allow the compositions to be placed on
the substrate at variable thicknesses thus allowing a wider range
of use of the compositions. Coating thicknesses may vary as
previously described.
[0164] The syrup polymers may be of any desirable concentration for
subsequent coating, but is typically between 2 to 20 wt. % polymer
solids in monomer, preferably 5 to 15 wt. %. The desired
concentration may be achieved by further dilution of the coating
composition, or by partial drying.
[0165] The flexible support may also comprise a release-coated
substrate. Such substrates are typically employed when an adhesive
transfer tape is provided. Examples of release-coated substrates
are well known in the art and include, by way of example,
silicone-coated kraft paper and the like. Tapes of the invention
may also incorporate a low adhesion backing (LAB), which are known
in the art.
[0166] According to another aspect, the present disclosure relates
to a cured pressure sensitive adhesive obtainable by curing the
curable precursor as above-described. In this context, the curing
step is preferably performed by allowing acid to be released into
the curable precursor of a pressure sensitive adhesive.
[0167] In a preferred aspect of the cured pressure sensitive
adhesive according to the disclosure, the curing step is performed
by subjecting the curable precursor of a pressure sensitive
adhesive to a triggering energy sufficient to allow the acid
generating agent to release acid into the curable precursor of a
pressure sensitive adhesive, and wherein the triggering energy is
preferably selected from the group of thermal energy or actinic
radiation, more preferably UV radiation.
[0168] In still another aspect of the present disclosure, it is
provided a composite assembly comprising a substrate and a curable
precursor of a pressure sensitive adhesive, as above-described,
applied onto at least part of the surface of the substrate, thereby
forming a layer of a curable precursor of a pressure sensitive
adhesive.
[0169] According to an alternative execution of the composite
assembly, the layer of a curable precursor of a pressure sensitive
adhesive is cured, preferably by allowing acid to be released into
the curable precursor of a pressure sensitive adhesive.
[0170] In a preferred aspect of the composite assembly according to
the disclosure, the curing step is performed by subjecting the
curable precursor of a pressure sensitive adhesive to a triggering
energy sufficient to allow the acid generating agent to release
acid into the curable precursor of a pressure sensitive adhesive,
and wherein the triggering energy is preferably selected from the
group of thermal energy or actinic radiation, more preferably UV
radiation.
[0171] Advantageoulsy, the composite assembly according to the
present disclosure is an adhesive article, wherein the substrate is
preferably a flexible backing layer.
[0172] According to an advantageous aspect of the composite
assembly, the layer of a curable precursor of a pressure sensitive
adhesive takes the form of a polymeric foam layer. According to
this beneficial aspect, properties/requirements of the overall
composite assembly such as application issues, deforming issues and
energy distribution may be advantageously addressed by appropriate
formulation of this polymeric foam layer, while other properties
such as adhesion (quick adhesion) can be adjusted by the
formulation of other non-foam pressure sensitive adhesive layers
(also commonly referred to as skin layers).
[0173] In the context of the present disclosure, the term
"polymeric foam" is meant to designate a material based on a
polymer and which material comprises voids, typically in an amount
of at least 5% by volume, typically from 10% to 55% by volume or
from 10% to 45% by volume. The voids may be obtained by any of the
known methods such as cells formed by gas. Alternatively, the voids
may result from the incorporation of hollow fillers, such as hollow
polymeric particles, hollow glass microspheres or hollow ceramic
microspheres.
[0174] A polymeric foam layer for use herein has for example a
thickness comprised between 100 and 6000 .mu.m, between 200 and
4000 .mu.m, between 500 and 2000 .mu.m, or even between 800 and
1500 .mu.m. As will be apparent to those skilled in the art, in the
light of the present description, the preferred thickness of the
polymeric foam layer will be dependent on the intended
application.
[0175] A polymeric foam layer typically has a density comprised
between 0.45 g/cm.sup.3 and 1.5 g/cm.sup.3, between 0.45 g/cm.sup.3
and 1.10 g/cm.sup.3, between 0.50 g/cm.sup.3 and 0.95 g/cm.sup.3,
between 0.60 g/cm.sup.3 and 0.95 g/cm.sup.3, or even between 0.70
g/cm.sup.3 and 0.95 g/cm.sup.3. This density is achieved by
including voids or cells. Typically, the polymeric foam layer will
comprise at least 5% of voids by volume and for example between 15
and 45%, or between 20% and 45% by volume.
[0176] The voids or cells in the polymeric foam layer can be
created in any of the known manners described in the art and
include the use of a gas or blowing agent and/or including hollow
particles into the composition for the polymeric foam layer. For
example, according to one method to create a polymeric foam
described in U.S. Pat. No. 4,415,615, an acrylic foam can be
obtained by the steps of (i) frothing a composition containing the
acrylate monomers and optional comonomers, (ii) coating the froth
on a backing and (iii) polymerizing the frothed composition. It is
also possible to coat the unfrothed composition of the acrylate
monomers and optional comonomers to the backing and to then
simultaneously foam and polymerize that composition. Frothing of
the composition may be accomplished by whipping a gas into the
polymerizable composition. Preferred gasses for this purpose are
inert gasses such as nitrogen and carbon dioxide, particularly if
the polymerization is photoinitiated.
[0177] According to still another aspect, it is provided a
(post)curing system for pressure sensitive adhesives, comprising a
polyfunctional aziridine curing agent and an acid generating
agent.
[0178] According to yet another aspect, the present disclosure is
directed to a method of applying a pressure sensitive adhesive to a
substrate, comprising the steps of: [0179] a) providing a curable
precursor of a pressure sensitive adhesive comprising: [0180] i. a
(co)polymeric material comprising the reaction product of a
(co)polymerizable material comprising a (meth)acrylate ester
monomer; and optionally, a co-monomer having an ethylenically
unsaturated group and which is different from the (meth)acrylate
ester monomer; [0181] ii. a polyfunctional aziridine curing agent;
and [0182] iii. optionally, an acid generating agent; [0183] b)
applying the curable precursor of a pressure sensitive adhesive to
at least part of the surface of the substrate; and [0184] c) curing
the curable precursor of a pressure sensitive adhesive by allowing
acid to be released into it.
[0185] According to another aspect, the present disclosure is
directed to a method of applying a pressure sensitive adhesive to a
substrate, comprising the steps of: [0186] a) providing a curable
precursor of a pressure sensitive adhesive comprising: [0187] i. a
(co)polymeric material comprising the reaction product of a
(co)polymerizable material comprising a (meth)acrylate ester
monomer; and optionally, a co-monomer having an ethylenically
unsaturated group and which is different from the (meth)acrylate
ester monomer; [0188] ii. a polyfunctional aziridine curing agent;
and [0189] iii. optionally, an acid generating agent; [0190] b)
partially curing the curable precursor of a pressure sensitive
adhesive by allowing acid to be released into it; [0191] c)
applying the partially cured pressure sensitive adhesive to at
least part of the surface of the substrate; and [0192] d) allowing
the partially cured pressure sensitive adhesive to fully cure onto
the substrate.
[0193] In a preferred aspect of the methods of applying a pressure
sensitive adhesive to a substrate, as described above, the curing
step is performed by subjecting the curable precursor of a pressure
sensitive adhesive to a triggering energy sufficient to allow the
acid generating agent to release acid into the curable precursor of
a pressure sensitive adhesive, and wherein the triggering energy is
preferably selected from the group of thermal energy or actinic
radiation, more preferably UV radiation.
[0194] In an alternative execution of the methods of applying a
pressure sensitive adhesive to a substrate, as described above, the
curing step is performed by contacting the curable precursor of a
pressure sensitive adhesive with a source of acid.
[0195] Suitable source of acids for use herein may be easily
identified by those skilled in the art, in the light of the present
disclosure. Suitable examples of sources of acid are for example
selected from the group consisting of acid-containing compositions,
acid-containing layers, acid-containing priming compositions, and
any combinations or mixtures thereof.
[0196] In yet another aspect of the present disclosure, it is
provided a method of preparing a cured pressure sensitive adhesive,
comprising the steps of: [0197] a) providing a curable precursor of
a pressure sensitive adhesive comprising: [0198] i. a (co)polymeric
material comprising the reaction product of a (co)polymerizable
material comprising a (meth)acrylate ester monomer; and optionally,
a co-monomer having an ethylenically unsaturated group and which is
different from the (meth)acrylate ester monomer; [0199] ii. a
polyfunctional aziridine curing agent; and [0200] iii. optionally,
an acid generating agent; and [0201] b) curing the curable
precursor of a pressure sensitive adhesive by allowing acid to be
released into it.
[0202] In a preferred aspect of the method of preparing a cured
pressure sensitive adhesive, as described above, the curing step is
performed by subjecting the curable precursor of a pressure
sensitive adhesive to a triggering energy sufficient to allow the
acid generating agent to release acid into the curable precursor of
a pressure sensitive adhesive, and wherein the triggering energy is
preferably selected from the group of thermal energy or actinic
radiation, more preferably UV radiation.
[0203] In an alternative execution of the method of preparing a
cured pressure sensitive adhesive, as described above, the curing
step is performed by contacting the curable precursor of a pressure
sensitive adhesive with a source of acid.
[0204] Suitable source of acids for use herein may be easily
identified by those skilled in the art, in the light of the present
disclosure. Suitable examples of sources of acid are for example
selected from the group consisting of acid-containing compositions,
acid-containing layers, acid-containing priming compositions, and
any combinations or mixtures thereof.
[0205] In the context of the present disclosure, the curable
precursor of a pressure sensitive adhesives, the (co)polymeric
material comprising the reaction product of a (co)polymerizable
material comprising a (meth)acrylic acid ester monomer, the
(meth)acrylic acid ester monomers, the optional co-monomers having
an ethylenically unsaturated group, the polyfunctional aziridine
curing agents, and the optional acid generating agents for use in
the methods as described above are identical to those described
above with respect to the curable precursor of a pressure sensitive
adhesive according to another aspect of the present disclosure.
[0206] In still another aspect, the present invention relates to
the use of a combination of a polyfunctional aziridine curing agent
and an acid generating agent for preparing a cured pressure
sensitive adhesive comprising: [0207] a) a (co)polymeric material
comprising the reaction product of a (co)polymerizable material
comprising a (meth)acrylate ester monomer; and [0208] b)
optionally, a co-monomer having an ethylenically unsaturated group
and which is different from the (meth)acrylate ester monomer.
[0209] In yet another aspect, the present invention relates to the
use of a curable precursor of a pressure sensitive adhesive or a
cured pressure sensitive adhesive as above described, for the
bonding to an uneven or irregular substrate.
[0210] In another particular aspect, the present invention relates
to the use of a curable precursor of a pressure sensitive adhesive
or a cured pressure sensitive adhesive as above described, for the
bonding to a low surface energy substrate.
[0211] In yet another aspect, the present invention relates to the
use of a curable precursor of a pressure sensitive adhesive or a
cured pressure sensitive adhesive as above described, for
industrial applications, in particular for construction
applications and automotive applications. According to a particular
aspect, the curable precursor of a pressure sensitive adhesive or
the cured pressure sensitive adhesive as above described is used
for automotive applications, in particular for taped seal on body
applications for the automotive industry.
[0212] The curable precursor of a pressure sensitive adhesive or a
cured pressure sensitive adhesive of the present disclosure may be
used in any article conventionally known to use such assemblies
such as labels, tapes, signs, covers, marking indices, display
components, touch panels, and the like. Flexible backing materials
having microreplicated surfaces are also contemplated.
[0213] The pressure sensitive adhesive assembly according to the
present disclosure may be particularly useful for forming strong
adhesive bonds to low surface energy (LSE) substrates. Included
among such materials are polypropylene, polyethylene (e.g., high
density polyethylene or HDPE), blends of polypropylene (e.g.
PP/EPDM, TPO). Other substrates may also have properties of low
surface energy due to a residue, such as an oil residue or a film,
such as paint, being on the surface of the substrate.
[0214] The substrate to which the curable precursor of a pressure
sensitive adhesive or a cured pressure sensitive adhesive may be
applied is selected depending on the particular application. For
example, the curable precursor of a pressure sensitive adhesive or
a cured pressure sensitive adhesive may be applied to sheeting
products (e.g., decorative graphics and reflective products), label
stock, and tape backings. Additionally, the curable precursor of a
pressure sensitive adhesive or a cured pressure sensitive adhesive
may be applied directly onto other substrates such as a metal panel
(e.g., automotive panel) or a glass window so that yet another
substrate or object can be attached to the panel or window.
Accordingly, the curable precursor of a pressure sensitive adhesive
or a cured pressure sensitive adhesive of the present disclosure
may find a particular use in the automotive manufacturing industry
(e.g. for attachment of exterior trim parts or for weatherstrips),
in the construction industry or in the solar panel construction
industry.
[0215] Item 1 is a curable precursor of a pressure sensitive
adhesive comprising: [0216] a) a (co)polymeric material comprising
the reaction product of a (co)polymerizable material comprising a
(meth)acrylate ester monomer; and optionally, a co-monomer having
an ethylenically unsaturated group and which is different from the
(meth)acrylate ester monomer; [0217] b) a polyfunctional aziridine
curing agent; and [0218] c) an acid generating agent.
[0219] Item 2 is the curable precursor according to item 1, wherein
the polyfunctional aziridine curing agent comprises at least two
aziridine functional groups, in particular two or three aziridine
functional groups.
[0220] Item 3 is a curable precursor according to item 1, wherein
the polyfunctional aziridine curing agent comprises at least one
aziridine functional group and at least one (meth)acryloyl
functional group.
[0221] Item 4 is a curable precursor according to any of the
preceding items, wherein the polyfunctional aziridine curing agent
has the following formula:
##STR00008##
[0222] wherein [0223] R.sup.1 is a (hetero)hydrocarbyl group,
[0224] R.sup.2 is an H or C.sub.1-C.sub.12 alkyl group,
C.sub.1-C.sub.8 alkyl group, C.sub.1-C.sub.6 alkyl group,
C.sub.1-C.sub.4 alkyl group, C.sub.1-C.sub.2 alkyl group,
C.sub.6-C.sub.12 aromatic group, C.sub.6-C.sub.10 aromatic group,
or even C.sub.6-C.sub.7 aromatic group; [0225] preferably R.sup.2
is H, CH.sub.2, C.sub.2H.sub.5 or even phenyl group; [0226] x is 0,
1 or 2, and [0227] y is at least 1, preferably 1 to 4, or even 2 to
3.
[0228] Item 5 is a curable precursor according to any of the
preceding items, wherein the polyfunctional aziridine curing agent
has the following formula:
##STR00009##
[0229] wherein [0230] R.sup.3 is a (hetero)hydrocarbyl group;
[0231] R.sup.2 is an H or C.sub.1-C.sub.12 alkyl group,
C.sub.1-C.sub.8 alkyl group, C.sub.1-C.sub.6 alkyl group,
C.sub.1-C.sub.4 alkyl group, C.sub.1-C.sub.2 alkyl group,
C.sub.6-C.sub.12 aromatic group, C.sub.6-C.sub.10 aromatic group,
or even C.sub.6-C.sub.7 aromatic group; [0232] preferably R.sup.2
is H, CH.sub.2, C.sub.2H.sub.5 or even phenyl group; and [0233] x
is 0, 1 or 2.
[0234] Item 6 is a curable precursor according to any of the
preceding items, wherein the polyfunctional aziridine curing agent
has the following formula:
##STR00010##
[0235] wherein [0236] R.sup.4 is a (hetero)hydrocarbyl group having
a valency of y; [0237] R.sup.2 is an H or C.sub.1-C.sub.12 alkyl
group, C.sub.1-C.sub.8 alkyl group, C.sub.1-C.sub.6 alkyl group,
C.sub.1-C.sub.4 alkyl group, C.sub.1-C.sub.2 alkyl group,
C.sub.6-C.sub.12 aromatic group, C.sub.6-C.sub.10 aromatic group,
or even C.sub.6-C.sub.7 aromatic group; [0238] preferably R.sup.2
is H, CH.sub.2, C.sub.2H.sub.5 or even phenyl group; [0239] y is at
least 1, preferably 1 to 4, or even 2 to 3; [0240] x is 0, 1 or 2;
and [0241] each of a and b are independently 0 to 6, 0 to 4, or
even 0 to 2.
[0242] Item 7 is a curable precursor according to any of the
preceding items, wherein the polyfunctional aziridine curing agent
has the following formula:
##STR00011##
[0243] wherein [0244] R.sup.4 is a (hetero)hydrocarbyl group having
a valency of y; [0245] R.sup.5 and R.sup.6 are independently
(hetero)hydrocarbyl groups; [0246] R.sup.2 is an H or
C.sub.1-C.sub.12 alkyl group, C.sub.1-C.sub.8 alkyl group,
C.sub.1-C.sub.6 alkyl group, C.sub.1-C.sub.4 alkyl group,
C.sub.1-C.sub.2 alkyl group, C.sub.6-C.sub.12 aromatic group,
C.sub.6-C.sub.10 aromatic group, or even C.sub.6-C.sub.7 aromatic
group; [0247] preferably R.sup.2 is H, CH.sub.2, C.sub.2H.sub.5 or
even phenyl group; [0248] y is at least 1, preferably 1 to 4, or
even 2 to 3; [0249] x is 0, 1 or 2; and [0250] each of a and b are
independently 0 to 6, 0 to 4, or even 0 to 2.
[0251] Item 8 is a curable precursor according to any of the
preceding items, wherein the polyfunctional aziridine curing agent
has the following formula:
##STR00012##
[0252] wherein [0253] R.sup.4 is a (hetero)hydrocarbyl group having
a valency of y; [0254] R.sup.7 is a (hetero)hydrocarbyl group, in
particular C.sub.2-C.sub.12 alkyl group, C.sub.2-C.sub.8 alkyl
group, C.sub.2-C.sub.6 alkyl group, or even
CH.sub.2--CHR'--O-group, with R' being H or CH.sub.3; [0255]
R.sup.2 is an H or C.sub.1-C.sub.12 alkyl group, C.sub.1-C.sub.8
alkyl group, C.sub.1-C.sub.6 alkyl group, C.sub.1-C.sub.4 alkyl
group, C.sub.1-C.sub.2 alkyl group, C.sub.6-C.sub.12 aromatic
group, C.sub.6-C.sub.10 aromatic group, or even C.sub.6-C.sub.7
aromatic group; [0256] preferably R.sup.2 is H, CH.sub.2,
C.sub.2H.sub.5 or even phenyl group; [0257] y is at least 1,
preferably 1 to 4, or even 2 to 3; [0258] x is 0, 1 or 2; and
[0259] a is 0 to 100, 1 to 50, 1 to 20 or even 1 to 10.
[0260] Item 9 is a curable precursor according to any of the
preceding items, wherein the polyfunctional aziridine curing agent
has any the following formula:
##STR00013##
[0261] Item 10 is a curable precursor according to any of the
preceding items, wherein the acid generating agent is selected from
the group consisting of thermal acid generating agents, photo acid
generating agents, and any combinations or mixtures thereof.
[0262] Item 11 is a curable precursor according to any of the
preceding items, wherein the acid generating agent is a thermal
acid generating agent selected from the group consisting of
quarternary blocked superacids, amine blocked superacids, and any
combinations or mixtures thereof.
[0263] Item 12 is a curable precursor according to any of the
preceding items, wherein the acid generating agent is a thermal
acid generating agent selected from the group consisting of
quarternary blocked SbF.sub.6, quarternary blocked triflic acid,
quarternary blocked fluorosulfonic acids, and any combinations or
mixtures thereof.
[0264] Item 13 is a curable precursor according to any of items 1
to 11, wherein the acid generating agent is a photo acid generating
agent selected from the group consisting of ionic salts of
organometallic complexes and onium salts, in particular iodonium or
sulfonium salts, and any combinations or mixtures thereof.
[0265] Item 14 is a curable precursor according to item 13, wherein
the acid generating agent is a photo acid generating agent selected
from the group consisting of iodonium or sulfonium or
phenyliodonium salts of the anions SbF.sub.6--, PF.sub.6--,
CF.sub.3SO.sub.3--, C.sub.4F.sub.9SO.sub.3-- and
C.sub.8F.sub.17SO.sub.3--, and any combinations or mixtures
thereof.
[0266] Item 15 is a curable precursor according to any of the
preceding items, wherein the (co)polymeric material comprises a
polymer base material selected from the group consisting of
polyacrylates whose main monomer component comprises a linear or
branched alkyl (meth)acrylate ester, preferably a non-polar linear
or branched alkyl (meth)acrylate ester having a linear or branched
alkyl group comprising preferably from 1 to 32, from 1 to 20, or
even from 1 to 15 carbon atoms.
[0267] Item 16 is a curable precursor according to any of the
preceding items, wherein the (co)polymeric material comprises a
polymer base material selected from the group consisting of
polyacrylates whose main monomer component comprises a linear or
branched alkyl (meth)acrylate ester selected from the group
consisting of methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl
(meth)acrylate, isopropyl (meth)acrylate, n-butyl acrylate,
isobutyl acrylate, tert-butyl (meth)acrylate, n-pentyl
(meth)acrylate, iso-pentyl (meth)acrylate, n-hexyl (meth)acrylate,
iso-hexyl (meth)acrylate, cyclohexyl (meth)acrylate, phenyl
(meth)acrylate, octyl (meth)acrylate, iso-octyl (meth)acrylate,
2-octyl(meth)acrylate, 2-ethylhexyl (meth)acrylate, decyl
(meth)acrylate, lauryl (meth)acrylate, 2-propylheptyl
(meth)acrylate, stearyl (meth)acrylate, isobornyl acrylate, benzyl
(meth)acrylate, octadecyl acrylate, nonyl acrylate, dodecyl
acrylate, isophoryl (meth)acrylate, and any combinations or
mixtures thereof.
[0268] Item 17 is a curable precursor according to item 16, wherein
the linear or branched alkyl (meth)acrylate ester is selected from
the group consisting of iso-octyl (meth)acrylate, 2-ethylhexyl
(meth)acrylate, 2-propylheptyl (meth)acrylate, 2-octyl
(meth)acrylate, butyl acrylate, and any combinations or mixtures
thereof; more preferably from the group consisting of iso-octyl
acrylate, 2-ethylhexyl acrylate, 2-octyl acrylate, and
2-propylheptyl acrylate.
[0269] Item 18 is a curable precursor according to item 16 or 17,
wherein the linear or branched alkyl (meth)acrylate ester comprises
2-ethylhexyl acrylate.
[0270] Item 19 is a curable precursor according to item 16 or 17,
wherein the linear or branched alkyl (meth)acrylate ester comprises
2-octyl(meth)acrylate.
[0271] Item 20 is a curable precursor according to item 19, wherein
at least 25 wt %, at least 50 wt %, at least 75 wt %, or even 100
wt % of the chemical structure of the 2-octyl(meth)acrylate is at
least partly, preferably completely (i.e. 100 wt %) derived from
biological material, more preferably from a plant material.
[0272] Item 21 is curable precursor according to any of the
preceding items, wherein the optional co-monomer having an
ethylenically unsaturated group is selected from the group of
non-acid functional polar monomers.
[0273] Item 22 is a curable precursor according to any of the
preceding items, wherein the optional co-monomer having an
ethylenically unsaturated group is selected from the group of
non-acid functional polar monomers having a single ethylenically
unsaturated group and a nitrogen-containing group or a salt
thereof.
[0274] Item 23 is a curable precursor according to item 22, wherein
the nitrogen-containing group is selected from secondary amido
groups and tertiary amido groups, in particular those selected from
the group consisting of N-vinyl lactams.
[0275] Item 24 is a curable precursor according to item 22 or 23,
wherein the optional co-monomer having an ethylenically unsaturated
group is selected from the group consisting of N-vinyl caprolactam;
N-vinyl piperidone, N-vinyl pyrrolidone; acryloyl morpholine,
acrylamides and substituted acrylamides; in particular t-butyl
acrylamide, dimethylamino ethyl acrylamide, N-octyl acrylamide,
N,N-dialkyl acrylamides, N-methyl acrylamide, N-ethyl acrylamide,
N-isopropyl acrylamide, tert-octyl acrylamide, N,N-dimethyl
acrylamide, N,N-diethyl acrylamide, N,N-dipropyl acrylamide,
N,N-dibutyl acrylamide; and any combinations or mixtures
thereof.
[0276] Item 25 is a curable precursor according to item 24, wherein
the optional co-monomer having an ethylenically unsaturated group
is selected to be N-vinyl caprolactam.
[0277] Item 26 is a curable precursor according to any of the
preceding items, wherein the (co)polymerizable material comprises:
[0278] a) from 60 to 100 parts by weight, from 65 to 95 parts by
weight, or even from 65 to 80 parts by weight, of a (meth)acrylate
ester monomer; and [0279] b) optionally, from 0 to 40 parts by
weight, from 5 to 35 parts by weight, or even from 20 to 35 parts
by weight, of a co-monomer having an ethylenically unsaturated
group.
[0280] Item 27 is a curable precursor according to any of the
preceding items, wherein the (co)polymerizable material comprises a
second co-monomer having an ethylenically unsaturated group, which
is preferably selected from the group consisting of high Tg
monomers.
[0281] Item 28 is a curable precursor according to item 27, wherein
the high Tg monomer is selected from the group consisting of
t-butyl acrylate, methyl methacrylate, ethyl methacrylate,
isopropyl methacrylate, n-butyl methacrylate, isobutyl
methacrylate, s-butyl methacrylate, t-butyl methacrylate, stearyl
methacrylate, phenyl methacrylate, cyclohexyl methacrylate,
isobornyl acrylate, isobornyl methacrylate, benzyl methacrylate,
3,3,5 trimethylcyclohexyl acrylate, cyclohexyl acrylate, N-octyl
acrylamide, propyl methacrylate, and any combinations or mixtures
thereof.
[0282] Item 29 is a curable precursor according to item 27 or 28,
wherein the (co)polymerizable material comprises: [0283] a) from 50
to 100 parts by weight, from 60 to 90 parts by weight, or even from
65 to 80 parts by weight, of a (meth)acrylate ester monomer; and
[0284] b) optionally, from 0 to 20 parts by weight, from 5 to 15
parts by weight, or even from 5 to 10 parts by weight, of a
co-monomer having an ethylenically unsaturated group; and [0285] c)
optionally, from 0 to 30 parts by weight, from 5 to 25 parts by
weight, or even from 15 to 25 parts by weight, of a second
co-monomer having an ethylenically unsaturated group.
[0286] Item 30 is a curable precursor according to any of the
preceding items, wherein the (co)polymeric material comprising the
reaction product of a (co)polymerizable material comprising a
(meth)acrylate ester monomer, is free of acid functional
monomers.
[0287] Item 31 is a curable precursor according to any of the
preceding items, which further comprises a filler material which is
preferably selected from the group consisting of filler particles,
in particular expanded perlite, microspheres, expendable
microspheres, glassbeads, glass microspheres, silica type fillers,
hydrophobic silica type fillers, hydrophilic silica type fillers,
hydrophobic fumed silica, hydrophilic fumed silica, fibers,
electrically and/or thermally conducting particles, nanoparticles,
in particular silica nanoparticles, and any combinations or
mixtures thereof.
[0288] Item 32 is a curable precursor according to item 31, wherein
the particulate filler material comprises hollow glass
microspheres.
[0289] Item 33 is a curable precursor according to any of the
preceding items, comprising: [0290] a) 100 parts by weight of a
(co)polymeric material comprising the reaction product of a
(co)polymerizable material comprising a (meth)acrylate ester
monomer; and optionally, a co-monomer having an ethylenically
unsaturated group; [0291] b) from 0.1 to 30 parts by weight, from
0.5 to 25 parts by weight, from 1 to 20 parts by weight, from 1 to
15 parts by weight, or even from 5 to 15 parts by weight, of a
polyfunctional aziridine curing agent; [0292] c) from 0.01 to 10
parts by weight, from 0.1 to 8 parts by weight, from 0.2 to 6 parts
by weight,or even from 0.2 to 5 parts by weight, of an acid
generating agent; and [0293] d) optionally, from 1 to 20 parts by
weight, from 3 to 15 parts by weight, or even from 5 to 13 parts by
weight, of a filler material, preferably hollow glass
microspheres.
[0294] Item 34 is a cured pressure sensitive adhesive obtainable by
curing the curable precursor according to any of the preceding
items, wherein the curing step is preferably performed by allowing
acid to be released into the curable precursor of a pressure
sensitive adhesive.
[0295] Item 35 is a cured pressure sensitive adhesive according to
item 34, wherein the curing step is performed by subjecting the
curable precursor of a pressure sensitive adhesive to a triggering
energy sufficient to allow the acid generating agent to release
acid into the curable precursor of a pressure sensitive adhesive,
and wherein the triggering energy is preferably selected from the
group of thermal energy or actinic radiation, more preferably UV
radiation.
[0296] Item 36 is a composite assembly comprising a substrate and a
curable precursor of a pressure sensitive adhesive according to any
of items 1 to 33 applied onto at least part of the surface of the
substrate, thereby forming a layer of a curable precursor of a
pressure sensitive adhesive.
[0297] Item 37 is a composite assembly according to item 36,
wherein the layer of a curable precursor of a pressure sensitive
adhesive is cured, preferably by allowing acid to be released into
the curable precursor of a pressure sensitive adhesive.
[0298] Item 38 is a composite assembly according to item 37,
wherein the curing step is performed by subjecting the curable
precursor of a pressure sensitive adhesive to a triggering energy
sufficient to allow the acid generating agent to release acid into
the curable precursor of a pressure sensitive adhesive, and wherein
the triggering energy is preferably selected from the group of
thermal energy or actinic radiation, more preferably UV
radiation.
[0299] Item 39 is a composite assembly according to any of items 36
to 38, wherein the layer of a curable precursor of a pressure
sensitive adhesive takes the form of a polymeric foam layer.
[0300] Item 40 is a composite assembly according to any of items 36
to 39, which is an adhesive article, and wherein the substrate is
preferably a flexible backing layer.
[0301] Item 41 is a (post)curing system for pressure sensitive
adhesives, comprising a polyfunctional aziridine curing agent and
an acid generating agent. Item 42 is a method of applying a
pressure sensitive adhesive to a substrate, comprising the steps
of: [0302] a) providing a curable precursor of a pressure sensitive
adhesive comprising: [0303] i. a (co)polymeric material comprising
the reaction product of a (co)polymerizable material comprising a
(meth)acrylate ester monomer; and optionally, a co-monomer having
an ethylenically unsaturated group and which is different from the
(meth)acrylate ester monomer; [0304] ii. a polyfunctional aziridine
curing agent; and [0305] iii. optionally, an acid generating agent;
[0306] b) applying the curable precursor of a pressure sensitive
adhesive to at least part of the surface of the substrate; and
[0307] c) curing the curable precursor of a pressure sensitive
adhesive by allowing acid to be released into it.
[0308] Item 43 is a method of applying a pressure sensitive
adhesive to a substrate, comprising the steps of: [0309] a)
providing a curable precursor of a pressure sensitive adhesive
comprising: [0310] i. a (co)polymeric material comprising the
reaction product of a (co)polymerizable material comprising a
(meth)acrylate ester monomer; and optionally, a co-monomer having
an ethylenically unsaturated group and which is different from the
(meth)acrylate ester monomer; [0311] ii. a polyfunctional aziridine
curing agent; and [0312] iii. optionally, an acid generating agent;
[0313] b) partially curing the curable precursor of a pressure
sensitive adhesive by allowing acid to be released into it; [0314]
c) applying the partially cured pressure sensitive adhesive to at
least part of the surface of the substrate; and [0315] d) allowing
the partially cured pressure sensitive adhesive to fully cure onto
the substrate.
[0316] Item 44 is a method according to item 42 or 43, whereby the
curing step is performed by subjecting the curable precursor of a
pressure sensitive adhesive to a triggering energy sufficient to
allow the acid generating agent to release acid into the curable
precursor of a pressure sensitive adhesive, and wherein the
triggering energy is preferably selected from the group of thermal
energy or actinic radiation, more preferably UV radiation.
[0317] Item 45 is a method according to item 42 or 43, whereby the
curing step is performed by contacting the curable precursor of a
pressure sensitive adhesive with a source of acid, which is
preferably selected from the group consisting of acid-containing
compositions, acid-containing layers, acid-containing priming
compositions, and any combinations or mixtures thereof.
[0318] Item 46 is a method of preparing a cured pressure sensitive
adhesive, comprising the steps of: [0319] a) providing a curable
precursor of a pressure sensitive adhesive comprising: [0320] iv. a
(co)polymeric material comprising the reaction product of a
(co)polymerizable material comprising a (meth)acrylate ester
monomer; and optionally, a co-monomer having an ethylenically
unsaturated group and which is different from the (meth)acrylate
ester monomer; [0321] v. a polyfunctional aziridine curing agent;
and [0322] vi. optionally, an acid generating agent; and [0323] b)
curing the curable precursor of a pressure sensitive adhesive by
allowing acid to be released into it.
[0324] Item 47 is a method according to item 46, whereby the curing
step is performed by subjecting the curable precursor of a pressure
sensitive adhesive to a triggering energy sufficient to allow the
acid generating agent to release acid into the curable precursor of
a pressure sensitive adhesive, and wherein the triggering energy is
preferably selected from the group of thermal energy or actinic
radiation, more preferably UV radiation.
[0325] Item 48 is a method according to item 46, whereby the curing
step is performed by contacting the curable precursor of a pressure
sensitive adhesive with a source of acid, which is preferably
selected from the group consisting of acid-containing compositions,
acid-containing layers, acid-containing priming compositions, and
any combinations or mixtures thereof.
[0326] Item 49 is the use of a curable precursor of a pressure
sensitive adhesive according to any of items 1 to 30 or the cured
pressure sensitive adhesive according to item 31 or 32, for the
bonding to an uneven or irregular substrate.
[0327] Item 50 is the use of a curable precursor of a pressure
sensitive adhesive according to any of items 1 to 30 or the cured
pressure sensitive adhesive according to item 31 or 32, for the
bonding to a low surface energy substrate.
[0328] Item 51 is the use of a combination of a polyfunctional
aziridine curing agent and an acid generating agent for preparing a
cured pressure sensitive adhesive comprising: [0329] a) a
(co)polymeric material comprising the reaction product of a
(co)polymerizable material comprising a (meth)acrylate ester
monomer; and [0330] b) optionally, a co-monomer having an
ethylenically unsaturated group and which is different from the
(meth)acrylate ester monomer.
[0331] Item 52 is the use of a curable precursor of a pressure
sensitive adhesive according to any of items 1 to 30 or the cured
pressure sensitive adhesive according to item 31 or 32, for
industrial applications, in particular for construction
applications and automotive applications, in particular for taped
seal on body applications for the automotive industry.
EXAMPLES
[0332] The invention is further illustrated by the following
examples. These examples are merely for illustrative purposes only
and are not meant to be limiting on the scope of the appended
claims.
Test Methods Applied:
[0333] 90.degree.-Peel-Test at 300 mm/min (According to Test
Method, Finat No. 2):
[0334] Pressure sensitive adhesive assembly strips according to the
present invention and having a width of 10 mm and a length >175
mm are cut out in the machine direction from the sample material.
For test sample preparation, the liner is first removed from the
one adhesive side and placed on an aluminum strip having the
following dimension 22.times.1.6 cm. Then, the adhesive coated side
of each PSA assembly strip is placed, after the liner is removed,
with its adhesive side down on a clean test panel using light
finger pressure. Next, the test samples are rolled twice in each
direction with a standard FINAT test roller (weight 6.8 kg) at a
speed of approximately 10 mm per second to obtain intimate contact
between the adhesive mass and the surface. After applying the
pressure sensitive adhesive assembly strips to the test panel, the
test samples are allowed to dwell 24 hours at ambient room
temperature (23.degree. C..+-.2.degree. C., 50% relative humidity
.+-.5%) prior to testing. Half of the samples are then submitted to
peel testing (uncured version) whilst the other half of the samples
are placed in an oven for 20 minutes at 110.degree. C. (cured
samples). After sample removal from the oven, the samples are
allowed to cool down for a period of 24 hours at ambient room
temperature (23.degree. C..+-.2.degree. C., 50% relative humidity
.+-.5%).
[0335] For peel testing, the test samples are in a first step
clamped in the lower movable jaw of a Zwick tensile tester (Model
Z020 commercially available from Zwick/Roell GmbH, Ulm, Germany).
The pressure sensitive adhesive film strips are folded back at an
angle of 90.degree. and their free ends grasped in the upper jaw of
the tensile tester in a configuration commonly utilized for
90.degree. peel measurements. The tensile tester is set at 300 mm
per minute jaw separation rate. Test results are expressed in
Newton per 10 mm (N/10 mm) The quoted peel values are the average
of two 90.degree.-peel measurements.
Tensile Testing Using T-Block Geometry at 100 m/min
[0336] The test is carried out at ambient room temperature
(23.degree. C..+-.2.degree. C.) and 50%.+-.5% relative humidity.
First, the aluminum T-Block surface is roughened with a ScotchBrite
4774 cleaning sponge and afterwards cleaned with pure isopropyl
alcohol. The cleaned aluminum T-Block test surface is then further
pre-treated with a commercially available 3M Primer P94 to avoid
pop-off aluminum failures during testing. The liner is first
removed from one side of the test specimen. A first aluminum
T-Block is then brought onto the exposed adhesive surface of the
test specimen and the overstanding adhesive is cut at the edges of
the aluminum T-Block. The liner on the other side of the test
specimen is thereafter removed and a second, in the same way
cleaned and primed aluminum T-Block is brought then onto the open
adhesive surface and overstanding edges cut off. A force of 300
N.+-.5 N for 15 seconds is then applied onto the prepared test
sample. After a dwell time of at least 24 hours at ambient room
temperature (23.degree. C..+-.2.degree. C. and 55%.+-.5% relative
humidity) the test sample is tested in a Zwick tensile tester by
performing a tensile test at 100mm/min The complete stress-strain
curves as well as the adhesion energy and maximal forces are then
collected.
Tensile Testing in OLS (Overlap Shear) Geometry at 100 m/min (in
Accordance with ASTM D897)
[0337] Overlap shear strength is determined according to ASTM D897
using a tensile tester of the type ZWICK/ROELL Z020 (available from
Zwick GmbH & Co. KG, Ulm, Germany) at a crosshead speed of 100
mm/min.
[0338] For the test assembly preparation, two aluminium test panels
(as later described under point c.), are joined in a overlap
connection of 10 mm width and 25mm length using pressure sensitive
adhesive assemblies of the current invention and by pressing these
overlap shear test assemblies for 15 seconds with 300 N (.+-.5 N).
The test assemblies are then conditioned prior to testing for 24
hours at 23.degree. C..+-.2.degree. C. and 50%.+-.5% relative
humidity.
Test Panels/Substrates used for Testing:
[0339] a.) Stainless steel test panels according to EN1939:20,
surface 1.4301 mirror-like (commercially available from Rocholl
GmbH) having a dimension of 150 mm.times.50 mm.times.2 mm are the
selected panels for all 90.degree. peel tests.
[0340] Prior to testing the stainless steel panels are cleaned
according to the following described procedure. First, the
stainless steel panels are wiped once with heptane, then with MEK
followed by a last wipe with heptane and thereafter dried with a
paper tissue.
[0341] b.) Aluminum T-Blocks: AlMg.sub.3 (Int. 5754) T-Profile,
dimension of 25 mm.times.25 mm and a height of 25 mm with 10 mm
wide drilled hole; material thickness 3 mm.
[0342] The aluminium T-Blocks are cleaned as follows. First, the
aluminum T-Block surface is roughened with a ScotchBrite 4774
sponge (commercially available by 3M Deutschland GmbH, Germany) and
then cleaned with pure isopropyl alcohol. The cleaned aluminum
T-Block test surface is further pretreated with a commercially
available 3M Primer P94.
[0343] c.) Aluminum test panels in accordance with ASTM B211 having
a dimension of 50 mm.times.25 mm.times.1 mm. Prior to the
preparation of an OLS test assembly, the aluminium panels are
roughened using ScotchBrite 4774 (commercially available by 3M) and
afterwards wiped once with isopropyl alcohol. Drying is done using
a paper tissue. The cleaned aluminum test panel surface is then
further pretreated with a commercially available 3M Primer P94.
Raw Materials:
[0344] In the examples, the following raw materials are used:
[0345] 2-Ethyl hexyl acrylate (C8-acrylate, 2-EHA): is an ester of
2-ethylalcohol and acrylic acid which is obtained from BASF AG,
Germany. Tg value: -58.degree. C.
[0346] N-Vinyl caprolactam (NVC): monofunctional acrylic monomer
with an amide-group in the side-chain, commercially available from
BASF GmbH, Ludwigshafen, Germany.
[0347] Irgacure 651: 2.2-Dimethoxy-1,2-diphenylethan-1-one is an
initiator for radical polymerization, commercially available from
BASF GmbH, Ludwigshafen, Germany.
[0348] K-Pure CXC-1612: Quarternary amine blocked SbF6, thermal
acid generator, commercially available by King Industries Inc.,
Norwalk, U.S.A.
[0349] K-Pure CXC-1614: Quarternary amine blocked triflic acid,
thermal acid generator, commercially available by King Industries
Inc., Norwalk, U.S.A.
[0350] K-Pure CXC-1802: Quarternary amine blocked superacid similar
to CXC-1612 but without antimony, thermal acid generator,
commercially available by King Industries Inc., Norwalk, U.S.A.
[0351] Irgacure PAG 290: tetralis (2,3,4,5,6,-pentafluorophenyl)
boranide; tris(4-(4-acetylphenyl)sulfonylphenyl) sulfonium, photo
acid generator, commercially available from BASF GmbH,
Ludwigshafen, Germany.
[0352] Aziridine curing agent A: CX-100 Trimethylolpropane
tris(2-methyl-1-aziridinepropionate), trifunctional aziridine
curing agent, commercially available from DSM Neo Resins BV,
Waalwijk, Netherlands.
[0353] Aziridine curing agent C: Ethoxylated (4 EO) Bisphenol A
Bis[3-(2-Methyaziridino)-propanoate]
##STR00014##
synthesized as later described.
[0354] Aziridine curing agent B: Ethoxylated (14 EO)
Trimethylolpropane Tris[3-(2-Methyaziridino)-propanoate]
##STR00015##
wherein x+y+z=14, and synthesized as later described.
[0355] Aziridine curing agent D:
(2-(2-Methyl-acryloxy)-ethyl-carbamato)-Pentaerythritol
Tris[3-(2-Methyaziridino)-propanoate]
##STR00016##
synthesized as later described.
[0356] Omnirad BDK: 2,2-dimethoxy-2-phenylacetophenone is a
UV-initiator, commercially available from iGm resins, Waalwijk
Netherlands.
[0357] 3M Glass bubbles (K15) are hollow glass bubbles with a
diameter of 115 .mu.m, available from 3M, Germany.
[0358] 3M Glass bubbles (K37) are hollow glass bubbles with a
diameter of 85 .mu.m, available from 3M, Germany.
[0359] Aerosil R-972 are hydrophobic fumed silica particles,
available from Evonik, Germany.
[0360] Calcium Oxide: stabilizer, commercially available from Sigma
Aldrich, Seelze, Germany.
[0361] Primer 94 (P94): adhesion promoter for pressure sensitive
adhesives to surfaces such as polyethylene, polypropylene, ABS,
PET/PBT blends, concrete, wood, glass, metal and painted metal
surfaces, commercially available from 3M Deutschland GmbH,
Germany.
Preparation of Aziridine Curing Agent B:
[0362] In a round bottom flask,
1,1,1-Trishydroxymethylpropane-ethoxylate (.about.14 EO/3OH)
triacrylate (200 g=658 meq. C.dbd.C, e.g. Sartomer SR9035) is
placed. 2.14 g equaling 3 ml triethyl amine are added and the
mixture is stirred. To the clear solution, 2-methyl aziridine
(137.5 g=2408.4 mmol) is then added dropwise at ambient room
temperature (23.degree. C..+-.2.degree. C.) and 50%.+-.5% relative
humidity while continuously stirring. The temperature initially
remains at 23 to 24.degree. C. but rises to about 41.degree. C.
after about 30% of the addition of 2-methyl aziridine. In order to
keep the temperature of reaction mixture at 35 to 40.degree. C., an
ice bath is used. Entire dosing time is about 2 hours. After that,
the reaction mixture is stirred 96 hours at ambient room
temperature to ensure that there are no more traces of acrylate
double bonds visible in the .sup.1H NMR spectrum of the reaction
mixture. Excess 2-methyl aziridine together with triethyl amine are
removed by vacuum distillation at 40.degree. C. and 0.1 mbar. A
clear yellow oil in a yield of 97% (229 g) is obtained with a
kinematic viscosity of 24.9 mPa*s at 23.degree. C. and 50-100
l/s.
Preparation of Aziridine Curing Agent C:
[0363] In a round bottom flask, ethoxylated (4EO) bisphenol A
diacrylate (500 g=1927 meq. C.dbd.C, e.g. Sartomer SR601E) is
placed. 6.25 g equaling 8.6 ml triethyl amine are then added and
the mixture is stirred. To the clear solution 2-methyl aziridine
(137.5 g=2408.4 mmol) are added dropwise at ambient room
temperature (23.degree. C..+-.2.degree. C.) and 50% .+-.5% relative
humidity while continuous stirring. The temperature initially
remains at 23.degree. C. to 24.degree. C. but rises to about
41.degree. C. after about 20% of addition of 2-methyl aziridine. In
order to keep the temperature of reaction mixture at 35.degree. C.
to 40.degree. C., an ice bath is used. The entire dosing time is
approximately 4 hours. After that, the reaction mixture is stirred
48 hours at ambient room temperature. After that time, no more
traces of acrylate double bonds are visible in the .sup.1H NMR
spectrum of the reaction mixture. Excess 2-methyl aziridine
together with triethyl amine are then removed by vacuum
distillation at 40.degree. C. and 0.1 mbar. A clear colorless oil
in a yield of 99% (602 g) is obtained with a kinematic viscosity of
1.5 Pa*s at 23.degree. C. and 50-100 l/s.
Preparation of Aziridine Curing Agent D:
[0364] In a round bottom flask, 0.0800 g bismuth neodecanoate,
0.0068 g 4-methoxy phenol, 0.0068 g BHT
(2,6-Di-tert-butyl-p-cresole) and 50.0 g equaling 117 mmole PZ-33
(PolyAziridine, LLC--PO Box 637--Medford, N.J. 08055)
(CAS-#57116-45-7) are charged. The mixture is stirred until the
solid components are dissolved. Subsequently, 13.7 g equaling 88
mmole isocyanatoethyl methacrylate are added dropwise. The
temperature of the reaction mixture is kept below 35.degree. C.
using an ice bath. The addition of the isocyanatoethyl methacrylate
is completed within 15 minutes. Two hours after the addition is
completed, no more residual NCO-bands at 2130 cm.sup.-1 can be
detected. A clear, viscous, yellow resin is obtained. Yield is 59 g
(87%).
Preparation of the Curable Precursors and Comparative Examples
(C1/C2):
[0365] The curable precursors of C1, C2 and CP1-CP24 of the
pressure sensitive adhesives, are prepared by combining the C8
acrylate (2-EHA) and 0.04 pph of Omnirad BDK as a photoinitiator in
a glass vessel. Before the UV exposure is initiated, the mixture is
flushed 10 minutes with nitrogen and nitrogen is also bubbled into
the mixture the whole time until the polymerization process is
stopped by adding air to the syrup. All the time, the mixture is
stirred with a propeller stirrer (300 U/min) and the reaction is
stopped when a viscosity around 4500 mPas is reached (when measured
with a Brookfield viscosimeter, T=25.degree. C., spindle 4, 12
rpm). Additionally, the remaining amount of 0.16 pph Omnirad BDK,
the selected aziridine curing agent, the selected glass bubbles or
mixtures thereof and part of the NVC (10 g of NVC are put aside)
are added to the syrup and mixed until they have
dissolved/dispersed. Finally, the initiator--dissolved in the
residual 10 g NVC--is added under continuous stirring. The exact
formulations of the curable precursors are later listed (in pph) in
Tables 2 to 4 below.
[0366] For coating the curable precursors, the line speed of the
coater is set to 0.82 m/min. The resulting adhesive layer thickness
is about 800 .mu.m. Curing is accomplished in a UV-curing station
with a length of 300 cm at the line speed given above. The total
radiation intensity irradiated cumulatively from top and bottom and
the respective length of the three coating zones within the
UV-curing station are as follows:
TABLE-US-00001 TABLE 1 Zone 1 Zone 2 Zone 3 Total intensity 2.07
4.27 4.98 [mW/cm.sup.2]
Formulations of the Curable Precursors used for Making the Pressure
Sensitive Adhesives
[0367] The formulations of the curable precursors used for making
the pressure sensitive adhesives are listed in Tables 2, 3 and 4
below. Table 2 contains comparative examples 1 and 2, later
referred to as C1 and C2, which are curable precursors without acid
generating agent and without polyfunctional aziridine curing agent.
Curable precursors listed in Table 2 have different thermal acid
generators and/or varying amounts of a co-monomer having an
ethylenically unsaturated group.
TABLE-US-00002 TABLE 2 Curable BDK CXC- CXC- CXC- CX GB precursor
2-EHA NVC BDK I II 1612 1614 1802 100 K15 (CP) w % w % pph pph pph
pph pph pph pph C1 75 25 0.04 0.16 -- -- -- 9 C2 75 25 0.04 0.16 --
-- 5 9 CP1 70 30 0.04 0.16 0.6 -- 5 9 CP2 75 25 0.04 0.16 0.6 -- 5
9 CP3 70 30 0.04 0.16 -- 0.6 5 9 CP4 75 25 0.04 0.16 -- 0.6 5 9 CP5
70 30 0.04 0.16 -- -- 0.6 5 9 CP6 75 25 0.04 0.16 -- -- 0.6 5 9 CP7
70 30 0.04 0.16 -- 0.6 10 9 CP8 70 30 0.04 0.16 -- 0.6 5 9 CP9 70
30 0.04 0.16 -- 0.6 1 9
[0368] Curable precursors listed in Table 3 use different kinds of
polyfunctional aziridine curing agents.
TABLE-US-00003 TABLE 3 Initiator Filler Monomer BDK CXC- Aziridine
GB Curable 2-EHA NVC BDK I II 1614 A B C D K15 precursor w % w %
pph pph pph pph pph pph pph pph CP10 75 25 0.04 0.16 0.6 -- 10 --
-- 9 CP11 75 25 0.04 0.16 0.6 -- 5 -- -- 9 CP12 75 25 0.04 0.16 0.6
-- 1 -- -- 9 CP13 75 25 0.04 0.16 0.6 -- -- 10 -- 9 CP14 75 25 0.04
0.16 0.6 -- -- 5 -- 9 CP15 75 25 0.04 0.16 0.6 -- -- 1 -- 9 CP16 75
25 0.04 0.16 0.6 4 -- -- 1 9 CP17 75 25 0.04 0.16 0.6 -- 4 -- 1 9
CP18 75 25 0.04 0.16 0.6 -- -- 4 1 9
[0369] Table 4 below provides the formulations of curable
precursors having different kinds of aziridines, a photo acid
generating agent ("Photo Acid Generating agent") and which are
coated by either a solvent-based or a Hot Melt process.
TABLE-US-00004 TABLE 4 Monomer Initiator PAG Fillers 2- BDK
Aziridine Irgacure GB Aerosil Curable EHA NVC BDK I II 1 2 290 K37
R 972 CaO precursor w % w % pph pph pph pph pph pph pph pph CP19 70
30 0.04 0.16 20 -- 4 -- -- -- CP20 70 30 0.04 0.16 20 -- 4 -- --
0.06 CP21 70 30 0.04 0.16 20 -- 4 -- -- 0.60 CP22 70 30 0.04 0.16
-- 10 -- 10 3 0.06 CP23 70 30 0.04 0.16 -- 10 2 10 3 0.06 CP24 70
30 0.04 0.16 -- 10 4 10 3 0.06
Test Results:
90.degree. Peel Results on Stainless Steel Panels
[0370] The peel results of comparative examples C1 and C2, as well
as of the pressure sensitive adhesives made from curable precursors
CP1- CP9 are shown in Table 5 below.
TABLE-US-00005 TABLE 5 Peel value Curable Peel value Peel value
(N/cm), (cured precursor (N/cm), (N/cm), (cured on substrate for
used (uncured) 20 min at 110.degree. C.) 20 min at 110.degree. C.)
C1 13.9 10.6 11.4 C2 8.9 10.3 7.7 CP1 12.7 10.7 20.4 CP2 14.4 10.0
35.7 CP3 13.0 12.1 22.1 CP4 14.4 12.9 30.2 CP5 13.7 11.1 32.1 CP6
11.9 10.8 26.4 CP7 9.7 9.2 17.8 CP8 13.0 12.1 22.1 CP9 16.2 12.9
18.7
[0371] Comparative examples C1 and C2 show no increase in peel
behavior after curing, whereas the pressure sensitive adhesives
made from curable precursors according to the invention (C1-C9)
show surprisingly strong increases in their peel performance after
being cured on a substrate. This is applicable to all thermal acid
generating agents used.
OLS and T-Block Tensile Results
[0372] The results of the OLS tensile testing for the pressure
sensitive adhesives made from curable precursors CP1-CP9, as well
as comparative examples C1 and C2 are provided in Table 6. In this
table, the resulting forces at 2 mm and 4 mm elongation for uncured
and cured pressure sensitive adhesives are listed.
TABLE-US-00006 TABLE 6 Curable F (2 mm)/N F (4 mm)/N precursor F (2
mm)/N (cured 20 min F (4 mm)/N (cured 20 min used (uncured) at
110.degree. C.) (uncured) at 110.degree. C.) C1 74.2 64.9 111.1
96.2 C2 53.6 55.5 100.2 96.4 CP1 203.2 263.0 356.8 512.3 CP2 86.7
162.6 148.4 362.4 CP3 109.7 149.7 186.2 308.7 CP4 78.4 107.2 126.1
212.3 CP5 123.1 192.8 217.3 396.5 CP6 71.3 116.2 138.8 261.2 CP7
81.7 163.4 132.1 340.7 CP8 109.7 149.7 186.2 308.7 CP9 179.0 181.7
304.1 355.1
[0373] Tensile testing in OLS geometry shows for C1 and C2 no
curing effect after being treated with 110.degree. C. for 20
minutes. For the pressure sensitive adhesives made from curable
precursors according to the invention (CP1-CP9), the post-curing
effect of the pressure-sensitive adhesives can be clearly seen,
irrespective of which thermal acid generating agent is
selected.
[0374] The results of the T-block tensile testing for the pressure
sensitive adhesives made from curable precursors CP1-CP9, as well
as comparative examples C1 and C2 are provided in Table 7. In this
table, the resulting forces at 2 mm and 4 mm elongation of cured
and uncured pressure sensitive adhesives are listed.
TABLE-US-00007 TABLE 7 Curable F (2 mm)/N F (4 mm)/N precursor F (2
mm)/N (cured 20 min F (4 mm)/N (cured 20 min used (uncured) at
110.degree. C.) (uncured) at 110.degree. C.) C1 218.6 224.1 222.22
231.9 C2 170.1 201.7 178.1 237.3 CP1 487.8 835.7 150.6 -- CP2 262.4
-- 270.1 -- CP3 292.8 613.6 308.7 356.6 CP4 221.6 437.0 228.6 275.1
CP5 421.9 560.8 347.6 588.2 CP6 283.1 442.7 371.9 -- CP7 241.1
678.8 269.4 -- CP8 292.8 630.4 308.7 252.2 CP9 423.9 632.3 398.9
683.3
[0375] Similar to the results in Table 6, the results of the
mechanical tensile testing in T-block geometry also clearly show
the post-curing effects of the pressure sensitive adhesives when
compared to comparative examples C1 and C2.
[0376] The results of the OLS tensile testing for the pressure
sensitive adhesives made from curable precursors CP10-CP18 are
provided in Table 8. In this table, the resulting forces at 2 mm
and 4 mm elongation for uncured and cured pressure sensitive
adhesives are listed. These pressure sensitive adhesives have in
common that they all have the same thermal acid generating agent
but use different polyfunctional aziridine curing agents in varying
amounts.
TABLE-US-00008 TABLE 8 Curable F (2 mm)/N F (4 mm)/N precursor F (2
mm)/N (cured 20 min F (4 mm)/N (cured 20 min used (uncured) at
110.degree. C.) (uncured) at 110.degree. C.) CP10 93.7 111.0 156.1
203.6 CP11 89.1 108.6 141.1 189.3 CP12 101.1 120.0 160.6 211.7 CP13
92.9 150.6 153.0 308.8 CP14 92.5 127.1 156.3 257.3 CP15 95.2 128.0
155.1 247.6 CP16 127.5 194.1 248.8 118.7 CP17 143.0 208.8 305.1
212.5 CP18 123.3 227.3 267.9 --
[0377] The results of the T-block tensile testing for the pressure
sensitive adhesives made from curable precursors CP10-CP18 are
provided in Table 9. In the table, the resulting forces at 2 mm and
4 mm elongation of cured and uncured pressure sensitive adhesives
are listed.
TABLE-US-00009 TABLE 9 Curable F (2 mm)/N F (4 mm)/N precursor F (2
mm)/N (cured 20 min F (4 mm)/N (cured 20 min used (uncured) at
110.degree. C.) (uncured) at 110.degree. C.) C10 254.4 422.9 319.1
543.94 C11 234.6 300.6 274.8 359.8 CP12 229.4 403.2 246.8 441.2
CP13 292.9 566.8 319.6 662.1 CP14 256.9 549.4 273.8 357.0 CP15
267.0 468.5 280.3 576.7 CP16 440.6 81.1 291.2 -- CP17 392.1 265.1
-- -- CP18 322.9 217.2 -- --
[0378] The results of the mechanical tensile testing in OLS and
T-Block geometry from Tables 8 and 9 clearly show, that by varying
the number of aziridine functionalities, the molecular weight of
the selected aziridine curing agent and by modifying the chosen
amount of an aziridine curing agent, the properties of post-cured
tapes can be modified concerning such properties as elongation at
break and forces at break.
[0379] The results of the OLS tensile testing for the pressure
sensitive adhesives made from curable precursors CP19-CP24 are
provided in Table 10. In this table, the resulting forces at 2 mm
and 4 mm elongation for uncured and cured pressure sensitive
adhesives are listed. The pressure sensitive adhesives made from
curable precursors CP19, CP20 and CP21 are made by making a polymer
mixture of 2-EHA and NVC as previously described for all prior
listed precursors C1-C18. This polymer mixture is then solved in
ethyl acetate, in order to prepare a coating solution. The
aziridine and the photo acid generating agent are added to a 33%
solution of the polymer mixture. A coating thickness of 350 .mu.m
is coated onto a siliconized liner (commercially available as
Akrosil BR90GGLSILSILOX G1H/G7 Scotchcal from Akrosil Europe) and
dried at 80.degree. C. for 10 minutes in an oven. The pressure
sensitive adhesive layers obtained this way are then laminated on
top of each other 8 times and then pressed to a total thickness of
800 .mu.m with an heatable hydraulic table press (type no. TP400,
commercially available by Fortune, Holland) first at a pneumatic
pressure of 10 kN for 1 minute at 80.degree. C. followed by 30
minutes at 80.degree. C. using a pneumatic pressure of 40 kN.
[0380] The pressure sensitive adhesives made from curable
precursors CP22 to CP24 are obtained by making a polymer mixture of
2-EHA and NVC as previously described for all prior listed
precursors C1-C18. This polymer mixture is then kneaded at
170.degree. C. at a torque of 60 Nm in a kneader type Plastograph
350EHT (commercially available from Brabender GmbH & Co. KG,
Germany) together with fillers, the aziridine and the photo acid
generating agent. After that the hot melt mixture is pressed to a
thickness of 800 .mu.m using a heatable hydraulic table press (type
no. TP400, commercially available by Fortune, Holland) first at a
pneumatic pressure of 10 kN at 150.degree. C. followed by 5 minutes
at 150.degree. C. with a pneumatic pressure of 40 kN.
[0381] Curing of the pressure sensitive adhesives is done using a
UV-A lamp, type UVA lamp 250 commercially available from Dr. Honle
in Planegg, Germany.
TABLE-US-00010 TABLE 10 Curable F (2 mm)/N F (4 mm)/N precursor F
(2 mm)/N (cured 30 s F (4 mm)/N (cured 30 s used (uncured) UV-A)
(uncured) UV-A) C19 20.7 32.6 50.3 130.1 C20 23.2 36.4 52.9 139.5
CP21 22.2 35.1 49.3 136.1 CP22 120.1 230.1 118.7 210.3 CP23 128.7
232.7 150.5 306.0 CP24 152.8 274.8 219.7 384.2
[0382] The post-curing effect increases with an increasing amount
of the photo acid generating agent and polyfunctional aziridine in
the curable precursor and can be seen in the OLS tensile testing of
CP22 to CP24.
* * * * *