Note: Descriptions are shown in the official language in which they were submitted.
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ADHESIVE COMPOSITION AND LOW
TEMPERATURE APPLICABLE ADHESIVE SHEET
Background Of The Invention
Technical Field
The present invention relates to an adhesive composition and an adhesive
sheet,
and in more detail to an adhesive composition having pressure sensitivity
including an
adhesive polymer and a nonadhesive polymer, and to an adhesive sheet.
Related Art
An adhesive sheet equipped with an adhesive layer comprising a pressure
sensitive
adhesives on at least one of main surfaces of a substrate (surface side or
back side) may be
easily and strongly stuck only by pressure being applied, and thus since
sticking work to
adherend can be easily done manually, these adhesive sheets are used widely.
Conventionally, as pressure sensitive adhesives constituting adhesive layers
of
adhesive sheets, a pressure sensitive adhesive having adhesive polymers as
principal
component is widely known, and various types have been developed.
For example, a pressure sensitive adhesives including a) acrylate copolymer
100
mass parts obtained from a monomer mixture including one or more kinds of mono
functional acrylates having non-tertiary alkyl group having 1 to 14 carbons
about 70 to 98
2 0 percent by weight, and a polar monomer of approximately 30 to 2 percent by
weight, b) a
plasticizes of 2 to 10 mass parts are known.
Typically, pressure sensitive adhesives, wherein acrylate copolymers included
as
monomer units (repetition units) originating in mono functional acrylates at
comparatively
large percentage in molecule, almost all copolymers show a glass transition
point (Tg) by
2 5 a dynamic viscoelasticity measuring method of -5°C or less.
Furthermore plasticizers,
such as polyethylene oxides and adipates, may also be added, the pressure
sensitive
adhesives are excellent in low-temperature performance as low-temperature
adhesive
property. For the above reason when adhesive layers arranged on back side of
an
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adhesive sheet that is used out in the fields for advertising object, such as
graphics display
sheets, are constituted with this pressure sensitive adhesives, even in the
case where they
are used in a low-temperature environment as at 20°F (-7°C),
sufficient adhesive property
(releasing strength and holding power) is realized.
However, because plasticizers usually have low crystallinity, tack
(hereinafter,
referred to as a property with which sticking is carried out with slight
power) of an
adhesive layer may not be controlled. Therefore, even when an adhesive coated
article
was stuck to adherend surface lightly, adhesive sheet could not be released
easily after
adhesion, so that there occurred a problem that difficulty was induced in
accurate
positioning of site for sticking.
On the other hand, adhesive films are known wherein tack of adhesive layers is
suppressed. For example, an adhesive film in which good positioning property
at
ordinary temperature is realized by covering a part of the adhesive layer
surface by
non-tacky grains, such as inorganic grains and glass beads.
A pressure sensitive adhesive is known in which a nonadhesive polymer
comprising substantially linear polycaprolactones having a molecular weight of
approximately 3,000 to approximately 342,000 etc. is included in addition to
pressure
sensitive adhesive basic resin comprising adhesive polymers, such as acrylic
derived
polymers, and non-tacky grains comprising inorganic grains, such as silica, is
included to
2 0 mitigate tack at ordinary temperature effectively and to improve
positioning property in
sticking process.
An adhesive composition with thermo sensitive adhesiveness is known in which
an
adhesive polymer having two functional groups, hydroxy group and phenyl group,
in a
molecule, and crystalline polycaprolactone serving as a nonadhesive polymer
are included.
2 5 Compatibility between the adhesive polymer and the polycaprolactone are
improved and
tack on a surface of the adhesive at ordinary temperature is effectively
mitigable.
However, in these conventional adhesive compositions, although adhesive films
constituted with these adhesive layers were generally used outdoors for an
object, such as
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advertisement, pressure sensitivity under low-temperature conditions was not
necessarily
enough.
Namely, in these conventional adhesive compositions, since nothing was taken
into
consideration regarding pressure sensitivity at low-temperature (especially
low
temperature of less than 0°C) conditions, when tack at ordinary
temperature is suppressed
a tendency was observed that low-temperature adhesive property is decreased,
and in
some case there occurred a problem that little pressure sensitivity is
demonstrated under
low-temperature conditions as whole composition.
Summary of the Invention
Briefly, the present invention provides an adhesive composition that
effectively
enhances pressure sensitive adhesivity at low temperatures and tack
suppression effect at
the same time, which makes easy an accurate positioning of the site for
sticking, and
which can be easily stuck by press fitting even in an environment of low
temperature less
than 0°C, and at providing an adhesive sheet constituted with the
composition as an
adhesive layer.
Advantageously, when an adhesive composition is constituted with a adhesive
polymer and a nonadhesive polymer, viscoelasticity behavior of the adhesive
polymer has
direct influence over pressure sensitivity required for adhesive composition,
and that
selection of a composition having a glass transition point obtained from
viscoelasticity
2 0 behavior in a specific range demonstrates appropriate pressure sensitivity
even at low
temperature.
Moreover, in a nonadhesive polymer, it was found that a degree of restraint of
molecular motion resulting from crystalline grade of a polymer directly
affected tack
suppression effect required for adhesive composition, and that appropriate
tack
2 5 suppression effect was demonstrated even at low temperature by selecting a
composition
having a glass transition point obtained from degree (directly affected by
thermal property
of polymer) of restraint of this molecular motion in a specific range. And
furthermore, it
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was found out that coexistence of the both polymer was enabled, without
spoiling these
performances, if the nonadhesive polymer had compatibility with the adhesive
polymer in
uncrystallized state, and thus the present invention was attained.
According to present invention, an adhesive composition is provided having
pressure sensitivity including an adhesive polymer and a nonadhesive polymer,
wherein
the adhesive polymer has a glass transition point by a dynamic viscoelasticity
measuring
method of -60°C to -5°C, and the nonadhesive polymer has a glass
transition point by a
differential scanning calorimeter of -5°C or less, and a fusing point
of higher than 25°C by
a differential scanning calorimeter, and also has compatibility with the
adhesive polymer
in uncrystallized state.
A first solution in which the above described adhesive polymer is dissolved,
and a
second solution in which the above described nonadhesive polymer is dissolved
are mixed
almost uniformly, and then resulting mixed solution is dried to give an
adhesive
composition of the present invention.
Preferrably, an adhesive composition of the present invention has a probe tack
lower than 7N, measured by a method based on ASTM D2979 under conditions of
25°C,
contact pressure of 100 g/cmz, contact time of 1 second, and releasing speed
of 10
mm/second is lower than 7N, and a 180 degrees releasing strength measured at a
releasing
speed of 300 mm/minute, in -S°C environment is 20 N/25 mm or more,
after being stuck
2 0 to a melamine baking finish plate and being left to stand for 5 minutes
under -5°C
environment.
Moreover, in the present invention an adhesive polymer preferably has at least
one
alkyl group having 4 to 8 carbons including at least one butyl group, and at
least one
carboxyl group, and monomer units including alkyl groups having 4 to 8 carbons
in a
2 5 percentage of 60 to 99 mole % in all molecules.
And in the present invention an adhesive polymer preferably has a
polycaprolactone skeleton or a polycarbonate skeleton in the molecule.
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A method for manufacturing an adhesive composition is also provided, wherein
the
method comprises the steps of (a) preparing a first solution by dissolving an
adhesive
polymer whose glass transition point by a dynamic viscoelasticity measuring
method is
-60 to -5°C in a solvent, (b) preparing a second solution by dissolving
in a solvent a
nonadhesive polymer in which a glass transition point by a differential
scanning
calorimeter is -5°C or less, a fusing point by a differential scanning
calorimeter is higher
than 25°C, and the nonadhesive polymer being compatible with the
adhesive polymer in
uncrystallized state, (c) mixing the first solution and the second solution
approximately
uniformly, and (d) drying an obtained mixed solution.
According to the present invention, a low temperature applicable adhesive
sheet
comprising a substrate, and an adhesive layer comprising the above described
adhesive
composition arranged at least on one main surface of the substrate is
provided.
In a low temperature applicable adhesive sheet of the present invention, it is
preferable that the substrate includes a polymer film, and has a breaking
elongation of
50% or more at -5°C at an elastic stress rate of 300 mm/min and a 50%
elongation stress
of 10 to 200 MPa at an elastic stress rate of 300 mm/min at -5°C.
Detailed Description of Preferred Embodiment
Hereinafter, embodiments of the present invention will be described
concretely.
1. Adhesive Composition
2 0 An adhesive composition of the present invention is characterized by that
the
composition includes an adhesive polymer and a nonadhesive polymer, a glass
transition
point of the adhesive polymer by a dynamic viscoelasticity measuring method is
-60 to
-5°C, a glass transition point of the nonadhesive polymer by a
differential scanning
calorimeter is -S°C or less, a fusing point by a differential scanning
calorimeter is higher
2 5 than 25°C, and also has compatibility with the adhesive polymer in
uncrystallized state.
Thereby an adhesive sheet with an adhesive layer constituted by the above
described composition concerned may easily be released after stuck to adherend
face
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lightly to enable an easy accurate positioning to a site for sticking, and at
the same time
may easily be stuck by being stuck by press fitting towards an adherend face
in an
environment of comparatively wide temperature range (a range of -S to
25°C included)
including low temperatures of 0 or less °C.
In addition, although in the present invention an adhesive polymer and a
nonadhesive polymer are specified by glass transition points based on
different basis,
respectively, a reason is that in an adhesive composition of the present
invention, pressure
sensitivity is appropriately reflected by a glass transition point based on
viscoelasticity
behavior of an adhesive polymer, and tack suppression effect is appropriately
reflected by
a glass transition point based on thermal property of a nonadhesive polymer
according to a
knowledge of the present inventors. Hereinafter, practical description will be
given.
(1) Adhesive polymer
As mentioned above, a glass transition point (Tgl) of an adhesive polymer in
the
present invention by a dynamic viscoelasticity measuring method is -60 to -
5°C.
If a glass transition point (Tgl) of an adhesive polymer by a dynamic
viscoelasticity measuring method exceeds -5°C, low-temperature adhesive
property,
especially pressure sensitivity at temperature of less than 0°C will
fall, and on the other
hand tack effect cannot be effectively suppressed if a glass transition point
(Tgl) by a
dynamic viscoelasticity measuring method is less than -60°C, and as a
result after being
2 0 stuck toward adherend face lightly, it does not release easily to make
accurate positioning
of site for sticking difficult.
Adhesive polymers whose glass transition point (Tgl) by a dynamic
viscoelasticity
measuring method is -60 to -S°C involved, for example, polymers, such
as acrylic derived
polymes, nitrile-butadiene derived copolymers (NBR etc.), styrene-butadiene
derived
2 5 copolymers (SBR etc.), uncrystallized polyurethanes, and silicone derived
polymers, or
polymers with two or more of the above described kinds mixed.
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As an adhesive polymer of the present invention, a polymer having one or more
alkyl groups having 4 to 8 carbons including at least one butyl groups, and
one or more
carboxyl groups is preferable among polymers having the above described
characteristics.
Since an adhesive polymer having such substituents has a very high
compatibility
with a nonadhesive polymers at temperatures higher than fusing point of the
nonadhesive
polymers, and thus phenyl group is not needed to increase compatibility with
nonadhesive
polymer, a glass transition point (Tgl) by a dynamic viscoelasticity measuring
method is
easily controlled in the above described range.
And, in the present invention, in order for a glass transition point (Tg2) of
an
adhesive polymer to be controlled very easily in a range of -S°C or
less, it is preferable
that many butyl groups are included in all alkyl groups having 4 to 8 carbons,
and
specifically, it is preferable that 50 to 100 mol % in alkyl group having 4 to
8 carbons are
butyl groups.
Furthermore, as an adhesive polymer in the present invention, monomer units
including alkyl group having 4 to 8 carbons is preferably include 60 to 99 mol
% in all of
molecules, more preferably 65 to 98 mol % in all of the molecules, and still
more
preferably 70 to 95 mol % in all of the molecules.
In the case where a percentage of the monomer unit including alkyl group
having 4
to 8 carbons is less than 60 mol %, low-temperature adhesive property of the
adhesive
2 0 composition may not be effectively raised. On the other hand, when a
content of the
monomer unit including alkyl group having 4 to 8 carbons exceeds 99 mol %, a
content
percentage of a monomer unit including active hydrogen containing group may be
decreased, and so that compatibility between the nonadhesive polymer and the
adhesive
polymer may be decreased.
2 5 Although there is no specific limitation about a molecular weight, if an
adhesive
polymer used in the present invention is in a range where predetermined
adhesive strength
is demonstrated, usually it may be set to have a weight average molecular
weight of
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10,000 to 1,000,000. As used in this application "weight average molecular
weight"
means a styrene converted molecular weight by a GPC method.
A cross-linked polymer may be used as an adhesive polymer to increase heat
resistance, and to prevent adhesive deposit.
Cross linkage may be formed through functional groups, such as hydroxyl groups
other than alkyl group and carboxyl group in the adhesive polymer, epoxy
groups, and
radiation-induced cross linking property functional groups, and may be formed
through
carboxyl groups.
A cross linkage structure is typically formed using cross-linking agents, and
it is
preferable that a structure is formed by reacting suitable cross-linking
agents based on
types of cross-linking functional groups of an adhesive polymer so that
sufficient cross
linking density to increase heat resistance as an adhesive and adhesive
deposit prevention
effect may be obtained. For example, when a cross-linking functional group
utilized in
cross-linking is a carboxyl group, it is preferable that a cross linkage
structure is formed
using bis amide derived cross-linking agents or epoxy resin derived cross-
linking agents as
cross-linking agents. But a cross linkage structure may also be formed using
isocyanate
derived cross-linking agents in a range that does not impair effect of the
present invention.
Epoxy resin derived cross-linking agents, for example, bisphenol A type epoxy
resins, bisphenol F type epoxy resins, cresol novolak type epoxy resins,
phenol novolak
2 0 type epoxy resins, etc. also be used. The epoxy equivalent of epoxy resin
derived
cross-linking agents is usually 70 to 400, and preferably 80 to 300.
Bis amide derived cross-linking agents, for example, bisaziridine derivatives
of
dibasic acid, such as iso phthaloyl bis(2-methyl aziridine), etc. may also be
used. In
addition, since bisamide derived cross-linking agents may react at
comparatively low
2 5 temperature with adhesive polymer having carboxyl groups, it is especially
preferable to
easily obtain sufficient cross-linking density.
In an adhesive composition of the present invention, in order to increase heat
resistance of the adhesive it is preferable that cross-linking component unit
is included at
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0.01 to 20 mass % in the adhesive composition, and is more preferable that
0.05 to 10
mass %.
In an adhesive polymer used in the present invention tackifiers may also be
used
with adhesive polymers as in conventional pressure sensitive adhesives.
An adhesive polymer used in the present invention may be prepared by methods
known to those skilled in the art. For example, acrylic derived adhesive
polymer may be
obtained by polymerizing a mixed monomer including (a) (meth)acrylic monomer
that has
alkyl group having 4 to 8 carbons in molecule, and (b) (meth)acrylic monomer
that has
carboxyl group in molecule. In this case, copolymerization may be carried out
by
standard methods of polymerization, such as solution polymerization. Moreover,
in
order to raise compatibility with a nonadhesive polymer, it is preferable that
large amounts
of the above described components (a) and (b) are included in all monomers,
and
specifically it is preferable that the above described components (a) and (b)
are included
65 mol % or more in sum total in all monomers, and more preferable that 70 mol
% or
more.
(2) Nonadhesive Polymer
A glass transition point (Tg2) of a nonadhesive polymer by a differential
scanning
calorimeter used for the present invention is -5°C or less.
If a glass transition point (Tg2) by a differential scanning calorimeter
exceeds -5°C,
2 0 low-temperature adhesive property, and particularly the pressure
sensitivity at a
temperature of less than 0°C will decline, and therefore application to
adhesive film used
outdoors for an object, such as advertisement, will become difficult. In the
present
invention, although there is no limitation in lower limit of a glass
transition point (Tg2),
when the glass transition point (Tg2) is too low, there is a possibility that
adhesive
2 5 property (releasing strength and holding power) of adhesive composition
obtained may
decline. Therefore, a glass transition point (Tg2) is preferably -70°C
or more.
Moreover, in the present invention, a glass transition point as determined by
a
differential scanning calorimeter of a nonadhesive polymer (Tg2) is preferably
no more
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than a glass transition point (Tg~) as determined by a dynamic viscoelasticity
measuring
method of an adhesive polymer, and more preferably a Tg difference (Tgl- Tg2)
that is in a
range of 20 to 65°C. Tack suppression effect can be increased easily,
almost without
disturbing adhesive property including low-temperature adhesive property of
the adhesive
polymer, if the glass transition point of both polymers is in such a
relationship.
Further, a nonadhesive polymer as used in the present invention is a
crystalline
polymer with a fusing point by a differential scanning calorimeter higher than
25°C.
When a fusing point as determined by a differential scanning calorimeter is
25°C
or less, tackiness is substantially demonstrated at ordinary terriperatures
and tack of the
composition obtained may not be suppressed effectively. In the present
invention, there
is no particular limitation in an upper limit of a fusing point of a
nonadhesive polymer.
However, there is a possibility that compatibility with an adhesive polymer
may fall when
the fusing point is too high, and it is preferable that the fusing point of
the nonadhesive
polymer be 100°C or less.
Furthermore, a nonadhesive polymer in the present invention has compatibility
with an adhesive polymer in uncrystallized state.
A nonadhesive polymer having no compatibility with an adhesive polymer will
interfere with the low-temperature performance of the adhesive polymer, and,
as a result,
the low-temperature adhesive property of a composition will fall.
2 0 As used in this specification, "compatibility" may be determined by three
factors,
(1) change of transparency, (2) solution transparency and (3) transmittance of
polarized
light by a polarization microscope.
(1) Change of transparency (Haze) of adhesive composition
For example, in a film adhesive (film-like adhesive) comprising an adhesive
2 5 composition used in the present invention, and having a thickness in a
range of 20 to 60
Vim, a film adhesive is heated at a temperature no less than a fusing point of
an
nonadhesive polymer and compared with a film adhesive that is heated at a
temperature
less than the fusing point. In a case of where it is heated at a temperature
less than the
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fusing point, the nonadhesive polymer usually forms a plurality of fine
crystals. A phase
of the nonadhesive polymer is dispersed in matrix phase including the adhesive
polymer.
Although, it shows comparatively highly transparency, haze value measured
using a color
difference meter shows at least S% (usually 20% or less). On the other hand,
at a
temperature of the fusing point or more of the nonadhesive polymer, the
nonadhesive
polymer melts, and so that a state where the nonadhesive polymer and the
adhesive
polymer are melted mutually is shown to lower the haze value and the film
adhesives
seem to be almost transparent. Moreover, even if the nonadhesive polymer
melts, when
the nonadhesive polymer and adhesive polymer do not mutually melt, a haze
value hardly
changes. In such a case, smaller haze value means better compatibility.
Therefore, in
the case that the nonadhesive polymer and the adhesive polymer melt mutually,
a haze
value measured using a color difference meter is preferably 2% or less, and
especially
preferably 2% or less.
(2) Whether a solution including a nonadhesive polymer and an adhesive
polymer is transparent or not
In simple, when a first transparent solution including an adhesive polymer
dissolved therein, and a second transparent solution including a nonadhesive
polymer
dissolved therein are mixed, it can be judged by whether resulting mixed
liquor is
transparent or not.
2 0 (3) Transmittance of polarized light by a polarization microscope
As is known well, if polarization axes of two polarizing plates are made to
intersect perpendicularly, light will no longer be transmitted to give almost
black view.
Thus, a film adhesive comprising an adhesive composition of the present
invention is
placed between two polarizing plates made to intersect perpendicularly and
observation is
2 5 performed. At ordinary temperature, micro crystal of nonadhesive polymer
rotates
polarization plane of light coming into the film adhesive, and the light is
transmitted
through two polarizing plates. Since the direction of crystal axis is usually
random, a
crystal that works to transmit incident light through two polarizing plates by
rotating
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polarization plane of light by exactly 90 degrees and a crystal through which
light cannot
transmit may exist at the same time. Finer dispersion of micro crystal of the
nonadhesive
polymer gives higher compatibility between the nonadhesive polymer and the
adhesive
polymer. Therefore, finer crystal size displays whole of film half light
within a
microscopic field (magnification 100 to 200 times) if compatibility between
both of the
polymers is high. When the compatibility between both of the polymers is low,
the
crystal size is large, and therefore crystalline strucutre can be recognized
as a bright point
dotted on dark background. In addition, in the state where the nonadhesive
polymer
melts, and the adhesive polymer and nonadhesive polymer melt together, the
mixture of
these polymers included in the film adhesive is optically isotropic, and gives
a dark view
compared with a mixture at room temperature.
Non-limiting examples of a nonadhesive polymer used in the present invention
has
a glass transition point (Tg2) as determined by a differential scanning
calorimeter of -5°C
or less and a fusing point measured by a differential scanning calorimeter
being higher
than 25°C. Such polymers are compatible with the adhesive polymer in an
uncrystallized
state, and include but are not limited to polyester polyols, such as poly
caprolactones;
polyols, such as polycarbonate polyols, or crystalline polyurethanes obtained
by
polymerizing these polyols and diisocyanate compounds. In addition, these
polymers
may be used independently or may be used in combination.
2 0 Additional nonadhesive polymers used in the present invention include, a
polymer
that has an alkylene skeleton of 4 to 6 carbon atoms in the molecule with the
promise that
the polymer has (1) a high degree of crystallinity, and (2) an effective
fuming point such
that the polymer is not tacky at room temperature (3 is soluble in organic
solvents and (4)
is compatible with the adhesive polymer. Furthermore, a nonadhesive polymer
having
2 5 poly caprolactone skeleton or polycarbonate skeleton is more preferable. A
nonadhesive
polymer having a polycarbonate skeleton in molecule is preferable and
generally, water
resistance and anti-hydrolysis property of an adhesive composition.
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Moreover, compatibility with an adhesive polymer having functional groups
including OH group in molecule is effectively improved, when a nonadhesive
polymer
preferably has functional groups (hydroxyl group, carboxyl group, etc.)
including OH
groups.
Although there are present no limitation about molecular weight, are molecular
weight is usually in the range 2,000 to 200,000 as weight average molecular
weight, and
more preferably in the range of 3,000 to 100,000.
(3) Adhesive Composition
An adhesive composition in the present invention includes the above described
adhesive polymer and nonadhesive polymer, wherein tack suppression and
low-temperature adhesive property of the adhesive composition are
simultaneously
attained.
An adhesive composition in the present invention specifically has a probe tack
measured by a method based upon ASTM D2979 under conditions of 25°C, a
contact
pressure of 100 g/cm2, a contact time of 1 second, and a releasing speed of 10
mm/sec
(hereinafter referred to as "probe tack" simply) that is preferably lower than
7 N, and more
preferably is 6N or less, and especially preferably is 5 N or less.
A probe tack in this range provides for easier release of an adhesive sheet
and also
makes it easier to attain accurate positioning of the adhesive sheet.
2 0 In the present invention, although lower limit of a probe tack is not
especially
limited as long as pressure sensitivity at low temperature is not impaired, it
is preferably 2
N or more in view of easy temporary sticking process obtained, and more
preferably 3 N
or more.
An adhesive composition of the present invention preferably has a 180 degrees
2 5 releasing strength (hereinafter referred to as simply "-5°C
releasing strength") of 20 N/25
mm or more measured at a 300 mm/minute releasing speed at -S°C after
being left as it is
for 5 minutes while adhering to a melamine baking finish plate at -5°C,
more preferably
22 N/25 mm or more, and especially preferably 23 N/25 mm or more.
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When the release strength is in the range of -5°C, sufficient pressure
sensitivity is
demonstrated in an environment at low temperatures less than 0°C, and
application to an
adhesive sheet used out in fields for the purpose, such as an advertisement.
In the present invention, although an upper limit of a -5°C release
strength is not
especially limited, preferably it is 50 N/25 mm or less in view of making tack
control
easier.
In an adhesive composition in the present invention, it is preferable that a
suitable
combination of a nonadhesive polymer and an adhesive polymer may suitably be
selected
so that the above described characteristics, such as tack suppression and low-
temperature
pressure sensitivity, may be demonstrated.
In a combination of a nonadhesive polymer and an adhesive polymer, for
example,
(i) a probe tack ratio (TAf/TB~ that is a ratio of a probe tack (TAf) of an
adhesive
composition including a nonadhesive polymer 10 mass parts to an adhesive
polymer 90
mass parts, to a probe tack (TBf) of an adhesive composition including the
adhesive
polymer concerned independently is less than 0.9, and preferably 0.88 or less,
and (ii) a
-5°C releasing strength ratio (PAf/PB~ that is a ratio of a -S°C
releasing strength (PAfJ of
the adhesive composition including a nonadhesive polymer 10 mass parts to an
adhesive
polymer 90 mass parts to a -5°C releasing strength (PBfJ of an adhesive
composition
including the adhesive polymer concerned independently is 0.7 or more, and
preferably
2 0 0.8 or more.
In a combination in which a probe tack ratio (TAf/TBfJ exceeds 0.9, tack
suppression effect at normal temperature may not necessarily be enough, and
accurate
positioning of the site for sticking of an adhesive sheet may become
difficult. On the
other hand, in a combination in which a -5°C releasing strength ratio
(PAf/PBf) becomes
2 5 less than 0.7, low-temperature adhesiveness of a composition, especially
pressure
sensitivity at a temperature less than 0°C in an environment at low
temperature falls, and
sometimes sticking of an adhesive sheet may become difficult.
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In an adhesive composition in the present invention, it is preferable that an
adhesive polymer and a nonadhesive polymer are present in a ratio so that
effective tack
suppression and low-temperature press fitting nature may be demonstrated.
It is preferable that an adhesive polymer is included 70 to 97 mass % in an
adhesive composition, it is more preferable 75 to 95 mass %, and it is
especially preferable
80 to 94 mass %. There is a possibility that a pressure sensitivity,
especially pressure
sensitivity at low temperature may fall when a content rate of an adhesive
polymer is less
than 70 mass %, on the other hand if it exceeds 97 mass %, there is a
possibility that a
normal temperature tack may not be controlled low.
The nonadhesive polymer is preferably included 2 to 29 mass % in an adhesive
composition, more preferably 4 to 24 mass %, and especially preferably S to 19
mass %.
When a content of a nonadhesive polymer is less than 2 mass %, there is a
possibility that a normal temperature tack may not be controlled at low
temperatures and
when it exceeds 29 mass % on the contrary, there is a possibility that
pressure sensitivity
may fall.
In an adhesive composition of the present invention, a first solution with the
above
described adhesive polymer dissolved therein, and a second solution with a
nonadhesive
polymer dissolved therein are mixed to obtain a mixed solution with the
adhesive polymer
and the nonadhesive polymer almost uniformly dispersed therein. Subsequently,
this
2 0 mixed solution is preferably dried to obtain the adhesive composition.
In an adhesive composition obtained by such a manufacturing method, when an
adhesive polymer and a nonadhesive polymer form mutual phase separated
structure at a
temperature less than a fusing point of a nonadhesive polymer, a phase
separated structure
where phase including large amount of the nonadhesive polymer is finely and
uniformly
2 5 dispersed is obtained, and thereby a nonadhesive polymer may exist almost
without
blocking adhesive property (low-temperature releasing strength etc.) of an
adhesive
polymer, and tack control effect is easily improved.
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Preferably, the adhesive polymer and nonadhesive polymer can be dissolved low
molecular organic solvent having 4 to 8 carbons that has alkyl groups
conjugating with
benzene ring or carbonyl group in a molecule. Such organic solvents included
but are
not limited to for example, methyl ethyl ketone, ethyl acetate, toluene, etc.
Mixing process of a first solution and a second solution may be performed by
conventional methods using mixing equipments, such as a homogeneous mixer and
a
planetary mixer, and thus each polymer may be uniformly dissolved or
dispersed.
Drying process of mixed solution obtained may usually be performed at
temperatures of 60 to 180°C for dozens of seconds to several minutes.
In addition, when an adhesive composition is a cross-linkable polymer, a third
solution containing a cross-linking component is added to a mixed solution of
the first
solution and the second solution, and then all solutions are mixed together
uniformly.
Other additives may be included, provided the additives do not diminish the
effectiveness of the adhesive composition. If such additives are used, they
are present in
amount consistent with the use as known to those skilled in the art. Such
additives
include but are not limited to viscosity regulators, defoaming agents,
leveling agents, UV
absorbents, antioxidants, pigments, anti-mold agent, elastic minute balls
comprising an
adhesive polymer or nonadhesive rubber derived polymer, tackifiers, catalysts
promoting
cross-linking reaction, etc.
2 0 2. Low Temperature Applicable Adhesive Sheet
A low temperature applicable adhesive sheet in the present invention comprises
a
substrate and an adhesive layer made of an adhesive composition and such
adhesive
composition is disposed on at least one of major surface of the substrate.
Substrates used in the present invention, include for example, a substrate
made
2 5 from paper, coated paper, metal films, and polymer films. Substrates
comprising a
polymer film are preferred.
Polymer films comprising one or more synthetic polymer including at least one
kind selected from a group of non-crystalline polyesters, plasticized
polyesters,
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polyurethanes, polyolefins, and ethylene-acrylate copolymers etc. are
preferable.
Furthermore, polyolefms, especially ionomers, or ethylene-vinyl acetate
copolymer
modified polyolefins are more preferable.
A substrate used in the adhesive sheet of the present invention preferably has
50%
or more of low-temperature elongation at -5°C and by elastic stress
rate of 300 mm/minute,
more preferably 60% or more, and especially preferably 70% or more.
In the present invention, although there is no particular limitation about the
upper
limit of the above described low-temperature elongation, as long as there is
no possibility
that a wrinkle may occur on a sheet, or a sheet may fracture by a hand work at
ordinary
temperature, it is preferable that the above described low-temperature
elongation is
1,000% or less.
In addition, "low-temperature elongation" represents a ratio of an elongation
of the
substrate at breaking by strain to a length of a strain direction of a
substrate before
straining.
It is preferable that a substrate used in an adhesive sheet of the present
invention
further has SO% elongation stress of 10 to 200 MPa at -5°C and in 300
mm elastic stress
rate, it is more preferable that 12 to 150 MPa, and it is especially
preferable that 15 to 100
MPa.
If the above described 50% elongation stress is 200 MPa or more, there is a
2 0 possibility that neither irregularity of an adherend nor curve may not be
followed at a low
temperature of -5°C, and on the other hand, if the above described 50%
elongation stress
is less than 10 MPa, the elongation of a substrate will become excessively
large, and there
is a possibility that wrinkle may be given on a sheet or a sheet may fracture
by an ordinary
temperature hand work. "50% elongation stress" represents a stress when a
substrate is
2 5 elongated by 50%.
In the present invention, although there is no particular limitation about a
thickness
of a substrate, suitable thickness is generally based on the application and
such thickness
is generally 5 to S00 pm, and preferably 10 to 300 pm.
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Furthermore, a substrate used in an adhesive sheet of the present invention
may
transmit visible light and ultraviolet radiation, and may also be a substrate
reflecting light,
such as a retroreflection sheet. It may be colored, or the sheet may contain
one or more
images and such an adhesive sheet may be used as an ornamental sheet or a
marking film.
Although a substrate used in an adhesive sheet of the present invention may
include an adhesive layer on at least one main surface, a liner may also be
included on at
least one main surface of the substrate, and the adhesive layer may be
indirectly prepared
via this liner.
A liner having paper or plastics film as principal component may be included.
The paper liner usually has releasing coatings (releasing layer), such as a
polyethylene
coat and a silicone coat on a surface of paper. When the releasing coating of
a silicone
coat is laminated, it is typical that under coats, such as clay coat and a
polyethylene coat,
are present between the paper and the releasing coating layer.
Liners with fine irregularity formed on the stripping face are preferable as
liners
used in the present invention. In an adhesive sheet with such a liner formed
thereon,
irregularity transferred from the irregularity of a liner stripping face can
be prepared on a
surface (adhesion face) of an adhesive layer prepared on a liner. Furthermore,
minute
glass beads etc. can be disposed in a predetermined position of an adhesive
layer by giving
a desired pattern to the irregularity of a liner releasing face. And, after
the minute glass
2 0 beads have been disposed on the liner, an adhesive layer may be formed on
the liner and
the minute glass beads will be diffused onto the adhesive layer.
In addition, irregularity of a liner stripping face may be arranged with
regularly
repeated pattern, and may be irregularity having a rough surface with
irregular pattern.
When a first solution containing an adhesive polymer is in dissolved state and
a
2 5 second solution similarly including a nonadhesive polymer is in dissolved
state are mixed
together, the mixed solution is applied on a substrate or a liner. This
mixture is dried to
form an adhesive layer on the liner. In addition, when adding a cross-linking
component,
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predetermined quantity of a third solution comprising a cross-linking
component may be
added to the mixed solution obtained by mixing first solution and the second
solution.
Moreover, as solvents dissolving an adhesive polymer and a nonadhesive
polymer,
a solvent dissolving each polymer is preferably a comparatively low molecular
organic
solvent having 4 to 8 carbons that has benzene ring or carbonyl group, and
alkyl group
conjugating to the benzene ring or the carbonyl group in a molecule so that it
may have a
good compatibility to both of an adhesive polymer and a nonadhesive polymer
used in an
adhesive composition of the present invention and an adhesive polymer and a
nonadhesive
polymer can be uniformly dissolved in a mixed solution.
Moreover, as such organic solvents, for example, methyl ethyl ketone, ethyl
acetate, toluene, etc. may be mentioned.
When such an organic solvent is used, an adhesive polymer has one or more
alkyl
groups having 4 to 8 carbons, and one or more caxboxyl groups in a molecule, a
percentage of a monomer unit comprising the alkyl groups having 4 to 8 carbons
included
in the adhesive polymer molecule is 60 to 99 mol %, and it is preferable that
the one or
more alkyl groups having 4 to 8 carbons always include a butyl group, and that
a
nonadhesive polymer has alkylene skeleton having 4 to 6 carbons in a molecule.
In an
applied film formed from a coating material by such combination, an adhesive
polymer
and a nonadhesive polymer have uniform and minute phase separated structure,
and
2 0 thereby a nonadhesive polymer may exist almost without blocking adhesive
property of an
adhesive polymer, and tack control effect is easily improved in an adhesive
composition
comprising such an applied film.
A coating material that forms an adhesive layer can be formed by dissolving or
dispersing each material uniformly using mixing equipments, such as a
homogeneous
2 5 mixer and a planetary mixer. Drying process at a time of forming an
adhesive layer is
usually performed at a temperature of 60 to 180°C. Drying time is
usually dozens of
seconds to several minutes. An adhesive layer usually has a thickness of 5 to
1,000 Vim,
preferably 10 to 500 pm, and especially preferably 15 to 100 p,m. Well-known
means,
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such as a knife coater, a roll coater, a die-coater, and a bar coater, may be
used for an
application means. In addition, a nonvolatile component in a first solution, a
second
solution, and a mixed solution that mixes these solutions approximately in a
uniform state,
is preferably 10 to 70 mass %.
As adherend to which an adhesive sheet of the present invention is stuck,
materials
having adhering face formed by (1) metals, such as aluminum, stainless steel,
steel, and
zinc steel plate; (2) resins, such as polyimides, acrylate resins,
polyurethanes, melamine
resins, epoxy resins, and vinyl chlorides; (3) inorganic oxide materials, such
as ceramics
and glass etc. may be used. Moreover, materials having a coated face as an
adhering face
may be used.
Examples
Examples of the present invention will be described hereinafter.
A glass transition temperature (Tgz) and a fusing (or melting) point (Tm) of a
nonadhesive polymer of each Example and Comparative example were specified
from
endotherm peak temperature of the obtained chart, by measuring a quantity of
heat, using
a differential scanning calorimeter (type number) DSC-2CC manufactured by
PerkinElmer,
Inc., in a temperature range of -60°C to 180°C, at temperature
rising velocity for
10°C/minute.
When measuring a glass transition temperature (Tgl) of an adhesive polymer, an
2 0 adhesive polymer solution was applied on a release coated paper, and the
dried film (about
30 ~m in thickness) was cylindrically rounded to be used as a specimen. An
elastic loss
(tan8) was measured using a dynamic viscoelasticity spectrum meter
(manufactured by
Rheometric Scientific F.E. Ltd., type number: RDA-H) under the conditions of a
temperature region of -60 to 200°C, the share mode in torsion mode, and
the frequency of
one rad/s to give a glass transition temperature (Tg~).
Example 1
As a nonadhesive polymer, a polycaprolactone having a carboxyl group
(manufactured by DAICEL CHEMICAL INDUSTRIES, LTD., Placcel (TM) item number
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220BA, Mw = 4,900 by GPC measurement, Tg2 = -60°C, fusing point =
55°C
(abbreviated to "NTP1" hereafter)) was used. This nonadhesive polymer was
dissolved
in toluene and a nonadhesive polymer solution having nonvolatile matter
concentration of
20 mass % was prepared.
Next, a mixed monomer containing butyl acrylate SO mass parts, 2-ethyl hexyl
acrylate 33 mass parts, methyl acrylate 10 mass parts, and acrylic acid 7 mass
parts was
polymerized in solution in a mixed organic solvent of toluene and ethyl
acetate (mass ratio
3 : 7) to give an adhesive polymer (may be abbreviated to "SAP1" hereafter),
and thus an
adhesive polymer solution having solid content concentration of 30 mass % was
prepared.
A glass transition temperature by a dynamic viscoelasticity method of this
adhesive
polymer was -22°C, and a weight average molecular weight (Mw) by GPC
measurement
was 480,000.
Next, the nonadhesive polymer (NTP 1 ) solution and adhesive polymer (SAP 1 )
solution prepared as described above, respectively, were mixed and stirred so
that a mass
ratio of a nonvolatile matter may be set to 90 : 10. As a cross-linking agent,
0.2 mass
parts iso-phthaloyl-bis(2-methyl aziridine) was added to the obtained mixed
solution 100
mass parts and stirred, and the adhesive composition solution was obtained.
Obtained
adhesive composition solution was transparent.
Next, on the releasing face of a liner, the obtained adhesive composition
solution
2 0 was applied using a knife coater, dried under a condition at 90°C
and for S minutes, and
the adhesive layer comprising an adhesive composition having a thickness of 35
~,m was
formed on the liner. Subsequently, a substrate having a thickness of 80 ~m and
comprising ethylene vinyl acetate copolymer modified polyolefin film was dry-
laminated
onto the adhesive layer to obtain an adhesive sheet having an adhesive layer
at one side.
2 5 In addition, in the used substrate, the low-temperature elongation
measured under a
condition at -5°C and 300 mm/minute of elastic stress rate showed 200%,
and 50%
elongation stress measured under a same condition at -5°C showed 21
MPa. Evaluation
results of the obtained adhesive sheet are collectively shown in Table 1.
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(Example 2)
As a nonadhesive polymer, a poly carbonate diol (manufactured by DAICEL
CHEMICAL INDUSTRIES, LTD., Placcel (TM) item number CD220, Mw = 7,300 by
GPC measurement, Tg2 = -60°C, fusing point = 53°C (abbreviated
to "NTP2" hereafter))
was used. This nonadhesive polymer was dissolved in toluene and a nonadhesive
polymer solution having nonvolatile matter concentration of 20 mass % was
prepared.
Next, a mixed monomer containing butyl acrylate 93 mass parts, acrylnitrile 3
mass parts, and acrylic acid 4 mass parts was polymerized in solution in a
mixed organic
solvent of toluene and ethyl acetate (mass ratio 3 : 7) to give an adhesive
polymer (may be
abbreviated to "SAP2" hereafter), and thus an adhesive polymer (SAP2) solution
having
solid content concentration of 30 mass % was prepared. A glass transition
temperature
by a dynamic viscoelasticity method of this adhesive polymer was -21
°C, and a weight
average molecular weight (Mw) by GPC measurement was 590,000.
In other conditions, the same method as Example 1 was used, and an adhesive
sheet was manufactured. Evaluation results of the obtained adhesive sheet are
collectively shown in Table 1.
(Example 3)
As a nonadhesive polymer, the polycarbonate diol used in Example 2 and
isophorone diisocyanate was polymerized in toluene to prepare a crystalline
polyurethane
2 0 (Mw = 15,000 by GPC measurement, Mw/Mn = 2.8, Tg2 = -60°C, a fusing
point = 49°C
(may be abbreviate to "NTP3" hereafter)). Except that this polyurethane was
used as a
nonadhesive polymer (NTP3) solution, an adhesive sheet was manufactured as in
Example
1. In addition, a nonvolatile matter concentration of this solution showed 20
mass %.
Evaluation results of the obtained adhesive sheet are collectively shown in
Table 1.
2 5 (Example 4)
An adhesive sheet was manufactured as in Example 1, except that as a
nonadhesive
polymer, a polycaprolactone (manufactured by DAICEL CHEMICAL INDUSTRIES,
LTD., Placcel (TM) item number 220, Mw = 5,700 by GPC measurement, Mw/Mn =
2.0,
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Tg2 = -60°C, fusing point = 59°C (abbreviated to "NTP4"
hereafter)) was used, and this
nonadhesive polymer (NTP4) was dissolved in toluene and a nonadhesive polymer
solution having nonvolatile matter concentration of 20 mass % was prepared.
Evaluation
results of the obtained adhesive sheet are collectively shown in Table 1.
Comparative example 1
An adhesive sheet was manufactured as in Example 1, except that as a
nonadhesive
polymer, a non-crystallized polymer (manufactured by Hercules Incorporated,
Hydrogenated pentaerythritol resin ester, Foral (TM), item number 105, Mw =
970,
Mw/Mn =1.1, Tgz = -57°C, (may be abbreviated to "NTPS" hereafter)) was
used, and this
nonadhesive polymer was dissolved in mathyl ethyl ketone and a nonadhesive
polymer
solution having nonvolatile matter concentration of 20 mass % was prepared.
Evaluation
results of the obtained adhesive sheet are collectively shown in Table 1.
Reference Examples 1 and 2
In order to show adhesive properties of each of the independent adhesive
polymer
used in each Example and Comparative example, adhesive sheets were prepared as
in
Example 1 and Example 2, respectively, except having not used the nonadhesive
polymer
solution. Evaluation results of the obtained adhesive sheet are collectively
shown in
Table 1.
For reference, in addition, for, a glass transition temperature (Tg2) of the
adhesive
2 0 polymers (NTP 1 and NTP2) used in Example 1 and Example 2 was measured
from
endotherm peak temperature of the obtained chart, by measuring a quantity of
heat, using
a differential scanning calorimeter (type number) DSC-2CC manufactured by
PerkinElmer,
Inc., in a temperature range of -60°C to 180°C, at temperature
rising velocity for
10°C/minute, and the adhesive polymer (NTP1) used in Example 1 showed -
29°C, and the
2 5 adhesive polymer (NTP2) used in Example 2 showed -36°C.
(Evaluation method)
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Adhesive sheets obtained in each Example, Comparative example, and Reference
example were estimated by following test methods. Evaluation results are
collectively
shown in Table 1.
( 1 ) Crystallinity
S Samples were observed at 25°C using a polarization microscope, and a
sample in
which crystal was confirmed was given "observed", and a sample in which no
crystal was
confirmed was given "not observed".
(2) 20°C releasing strength
The adhesive sheets obtained in each Example, Comparative example, and
Reference example were cut by 200 mm x 25 mm, ant the cut sheet was stuck to a
melamine baking finish plate by PALTEC Co., Ltd. as an adherend under
20°C
environment using a press fitting roller to prepare a test specimen. Adhesion
of a sheet
was performed by a method according to JIS 20237 8.2.3. The releasing strength
in a
direction of 180 degrees at 300 mm/minute releasing speed was measured using a
Tensilon after kept standing for 48 hours under a same temperature after
completion of
adhesion.
(3) -S°C releasing strength
The adhesive sheets obtained in each Example, Comparative example, and
Reference example were cut by 200 mm x 25 mm, ant the cut sheet was stuck to a
2 0 melamine baking finish plate by PALTEC Co., Ltd. as an adherend under -
5°C
environment using a press fitting roller to prepare a test specimen. Adhesion
of a sheet
was performed by a method according to JIS 20237 8.2.3. The releasing strength
in a
direction of 180 degrees at 300 mm/minute releasing speed was measured using a
Tensilon after kept standing for 5 minutes under a same temperature after
completion of
2 5 adhesion.
(4) Probe tack
Based on ASTM D2979, measured using a probe tack tester with a thermostat
manufactured by TESTER SANGYO CO., LTD. Measurement conditions were
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WO 03/020842 PCT/US02/27334
temperature of 25°C, contact pressure 100 g/cm2, contact time 1 second,
and releasing
speed 10 mm/second. In addition, as evaluation values, an average by five
measurements
(N = 5) was used.
(5) The rate of tack attenuation
Calculated by a relational expression shown below.
Rate of tack attenuation = { 1-[probe tack of composition comprising
nonadhesive
polymer] = [probe tack of adhesive polymer itself) } x 100.
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CA 02458646 2004-02-24
WO 03/020842 PCT/US02/27334
U t~''
4~
O
r-0' o 0 0 0 0 0 0
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M ~D 0001 ~ M
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i3, C/~C/~C/~C/~CJ~ C/~ C/~
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CA 02458646 2004-02-24
WO 03/020842 PCT/US02/27334
Evaluation
In adhesive sheets in Examples 1 to 4, excellent pressure sensitive adhesion
was
possible in a temperature range of 20 to -5°C. Moreover, low tack was
given, and
outstanding positioning property and outstanding re-sticking performance were
demonstrated compared to a case where an adhesive polymer was used
independently
(reference example). And, sticky touch was also mitigated and it was able to
respond
easily also to quick handwork by the expert. On the other hand, in the
adhesive sheet by
Comparative example 1, although excellent pressure sensitive adhesion was
possible at
20°C, -S°C pressure sensitivity was low, and was estimated that
low-temperature
applicability was low as compared to samples in Example. And, tack suppression
effect
by addition of a nonadhesive polymer was not observed, and positioning
property and
re-sticking performance have not improved.
As described above, according to the present invention, there is provided an
adhesive composition which enables to effectively enhance pressure sensitive
adhesivity at
low temperatures and tack suppression effect at the same time, which makes
easy an
accurate positioning of the site for sticking, and which can be easily stuck
by press fitting
even in an environment of low temperature of lower than 0°C and an
adhesive sheet
constituted with the composition as an adhesive layer.
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