U.S. patent application number 11/971980 was filed with the patent office on 2008-05-08 for adhesive-backed articles.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Patrick R. Fleming, Mieczyslaw H. Mazurek, Haruyuki Mikami.
Application Number | 20080105356 11/971980 |
Document ID | / |
Family ID | 23205409 |
Filed Date | 2008-05-08 |
United States Patent
Application |
20080105356 |
Kind Code |
A1 |
Mikami; Haruyuki ; et
al. |
May 8, 2008 |
ADHESIVE-BACKED ARTICLES
Abstract
Methods of preparing adhesive-backed articles and methods of
applying adhesives backed articles are described. The
adhesive-backed articles include a compliant film and a
pressure-sensitive adhesive having a microstructured surface
opposite the compliant film.
Inventors: |
Mikami; Haruyuki; (Tendo
City Yamagata, JP) ; Fleming; Patrick R.; (Lake Elmo,
MN) ; Mazurek; Mieczyslaw H.; (Roseville,
MN) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
23205409 |
Appl. No.: |
11/971980 |
Filed: |
January 10, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10357151 |
Feb 3, 2003 |
|
|
|
11971980 |
Jan 10, 2008 |
|
|
|
09311101 |
May 13, 1999 |
6524675 |
|
|
10357151 |
Feb 3, 2003 |
|
|
|
Current U.S.
Class: |
156/60 |
Current CPC
Class: |
B32B 2037/243 20130101;
B32B 2605/08 20130101; Y10T 428/2902 20150115; B44C 1/105 20130101;
C09J 2301/204 20200801; Y10T 156/10 20150115; C09J 7/38 20180101;
B32B 2405/00 20130101; Y10T 428/1476 20150115; B32B 38/0012
20130101; Y10T 428/2843 20150115; B32B 37/1284 20130101; Y10T
428/14 20150115; Y10T 428/1486 20150115; Y10T 428/24562 20150115;
Y10T 156/1023 20150115; Y10T 428/24959 20150115; B32B 3/30
20130101; Y10T 428/24479 20150115; Y10T 428/1471 20150115; C09J
7/403 20180101; B32B 37/24 20130101; Y10T 428/28 20150115 |
Class at
Publication: |
156/060 |
International
Class: |
B32B 37/12 20060101
B32B037/12 |
Claims
1. A method of preparing an adhesive-backed article, said method
comprising: embossing a release liner to form a microstructured
release liner; coating a pressure-sensitive adhesive layer onto the
microstructured release liner, wherein the pressure-sensitive
adhesive layer has a microstructured surface facing the
microstructured release liner; and laminating a compliant film to a
surface of the pressure-sensitive adhesive layer that is opposite
the release liner, wherein when the release liner is removed to
expose the microstructure surface of the pressure-sensitive
adhesive layer, said microstructure surface has channels that
define exit pathways providing a continuous fluid egress to a
periphery of said microstructured surface, said channels having a
volume of at least 1.times.10.sup.3 .mu.m.sup.3 per any 500 .mu.m
diameter circular area of the microstructured surface and having an
aspect ratio of about 0.1 to about 20.
2. The method of claim 1, wherein the channels have a
cross-sectional form of v-grooves, u-grooves, rectangles,
trapezoids, or combinations thereof.
3. The method of claim 1, wherein the microstructured surface
comprises a plurality of structures which at least partially define
the channels.
4. The method of claim 3, wherein the structures are selected from
hemispheres, prisms, pyramids, ellipsoids, or a combination
thereof.
5. The method of claim 3, wherein the structures are truncated.
6. The method of claim 3, wherein the structures are regularly
placed about the microstructured surface of the pressure-sensitive
adhesive.
7. The method of claim 3, wherein the structures are randomly
placed about the microstructured surface of said adhesive.
8. The method of claim 3, wherein the structures are arranged at a
pitch of about 400 .mu.m or less.
9. The method of claim 3, wherein the structures have a height of
about 3 .mu.m to about 50 .mu.m.
10. The method of claim 1, wherein the compliant film comprises a
primer layer on a surface laminated to the pressure-sensitive
adhesive layer.
11. The method of claim 1, wherein the compliant film has a
thickness of about 300 .mu.m or less.
12. The method of claim 1, wherein the release liner comprises a
thermoplastic film.
13. The method of claim 1, wherein the release liner comprises a
paper laminated or coated with a thermoplastic material.
14. The method of claim 1, wherein the release liner comprises a
polyethylene coated paper.
15. The method of claim 1, wherein the pressure-sensitive adhesive
comprises a solvent based acrylic pressure-sensitive adhesive.
16. A method of preparing an adhesive-backed article comprising:
providing a compliant film: coating the compliant film with a
pressure-sensitive adhesive layer; embossing the pressure-sensitive
adhesive layer to form to microstructured surface having channels
that define exit pathways providing a continuous fluid egress to a
periphery of said microstructured surface, said channels having a
volume of at least 1.times.10.sup.3 .mu.m.sup.3 per any 500 .mu.m
diameter circular area of the microstructured surface and having an
aspect ratio of about 0.1 to about 20.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S.
application Ser. No. 10/357,151, filed Feb. 3, 2003, now pending;
which is a continuation-in-part of U.S. application Ser. No.
09/311,101, filed May 13, 1999, now issued as U.S. Pat. No.
6,524,675, the disclosure of which is incorporated by reference in
its entirety herein.
FIELD OF THE INVENTION
[0002] The present invention relates to an adhesive-backed article,
more particularly to such an adhesive-backed article having an
adhesive with a microstructured surface bonded to a compliant film,
and even more particularly to channels, with a specific volume per
unit area, formed by the microstructured surface in the adhesive
which permit the desirable properties of positionability and fluid
egress to a periphery of the article without adversely affecting
the surface appearance of the film after application onto a
substrate.
BACKGROUND OF THE INVENTION
[0003] Films are often bonded to substrates utilizing
pressure-sensitive adhesives. The films are generally bonded to a
variety of different substrates including, for example, surfaces on
motor vehicles. The interface between the adhesive and the contact
surface of the substrate is important to the performance of the
film. The interface between the adhesive and the substrate is
affected by several factors. For example, the application may be
affected by the type of adhesive used, the size and type of the
films utilized, the surface of the substrate upon which the article
is applied, the application technique utilized, or combinations
thereof.
[0004] Adhesive-backed films are often used for decorative
purposes. The placement of a film into a specific position prior to
the formation of a bond between the adhesive and the substrate is
often difficult, but important for aesthetic reasons. Some
adhesive-backed articles are unable to slide on the surface of the
substrate and will adhere with the slightest contact on the surface
of the substrate. Such articles can often be particularly difficult
to reapply if they inadvertently adhere to the substrate. The
inability to slide the adhesive-backed article in place can
adversely affect the positioning of the article or cause damage to
the article upon attempted repositioning after adhesion.
[0005] The decorative articles also require that the
adhesive-backed article be able to evacuate air or other fluids
trapped underneath the adhesive during the bonding step. The
ability to bleed fluids and eliminate bubbles from underneath the
article improves the overall appearance of the article.
Additionally, bubbles under a film can adversely affect the
adhesive performance of the article.
[0006] Thin films are often utilized on surfaces so that the
adhesive film blends with the substrate upon which the film is
applied. Additionally, thinner films are generally more flexible
and therefore suited for application on contoured surfaces.
However, the utilization of thin films can create an appearance
problem. The thinner films have a tendency to show all surface
abnormalities or uneven portions of either the adhesive or the
substrate upon which the adhesive-backed article is applied.
SUMMARY OF THE INVENTION
[0007] The present invention relates to an adhesive-backed article.
The article includes a compliant film with a pressure sensitive
adhesive bonded to a lower surface of the film. The pressure
sensitive adhesive includes a microstructured surface opposite the
compliant film.
[0008] In accordance with the present invention, the
microstructured surface defines channels in the pressure sensitive
adhesive. The channels comprise a volume of at least
1.times.10.sup.3 .mu.m.sup.3 per any 500 .mu.m diameter circular
area in the adhesive. The channels are utilized to create exit
pathways for fluid egress to a periphery of the article when the
article is applied to a substrate. The adhesive-backed article
sufficiently bonds to a substrate as indicated by a wet out value
of at least 85%. The channels are substantially undetectable on an
upper surface after final application of the article onto a
substrate.
[0009] In general, the adhesive-backed article of the present
invention is positionable over a substrate prior to forceful
application of the article onto the substrate. The microstructured
surface of the adhesive permits the article to either slide over
the surface of a substrate, or be easily removed from the surface
of the substrate, until enough pressure is applied to enable a bond
between the adhesive and the surface of the substrate. The article
of the present invention also enhances the egress of fluid from the
interface between the adhesive and the substrate as a bonding force
is applied to the article. The microstructured features are
particularly suited for applications utilizing thin films, i.e.,
less than 300 .mu.m.
[0010] The channels of the present invention can take various
shapes or patterns. The channels are generally formed by structures
in the adhesive that create the microstructured surface. The
structures may be either placed randomly about the surface of the
adhesive or placed in regular patterns.
[0011] The microstructured surface can be formed by directly
embossing the pressure sensitive adhesive layer with the
structures. Alternatively, a liner or backing can be embossed first
and then coated with a pressure sensitive adhesive to impart the
structures to the adhesive. The film is typically laminated or
bonded to a side of the adhesive layer opposite the microstructured
features.
[0012] It is an advantage to provide an adhesive-backed article
that has pathways in the adhesive for fluid egress and permits
positioning of the article without adversely affecting the
appearance of the article. The channels define pathways to the
periphery of the article that permit the flow of fluid trapped
between the adhesive and the surface of the substrate.
Additionally, the microstructured surface of the present invention
enables the positioning of the article onto a substrate. Further,
the microstructured adhesive does not result in observable periodic
patterns on the exposed surface of the film after application of
the article onto a substrate.
[0013] For purposes of the present invention, the following terms
used in this application are defined as follows:
[0014] "microscopic" refers to structures of small enough dimension
so as to require an optic aid to the naked eye when viewed from any
plane of view to determine its shape. One criterion is found in
Modern Optic Engineering by W. J. Smith, McGraw-Hill, 1966, pages
104-105 whereby visual acuity, " . . . is defined and measured in
terms of the angular size of the smallest character that can be
recognized." Normal visual acuity is considered to be when the
smallest recognizable letter subtends an angular height of 5
minutes of arc on the retina. At typical working distance of 250 mm
(10 inches), this yields a lateral dimension of 0.36 mm (0.0145
inch) for this object;
[0015] "microstructure" means the configuration of structures
wherein at least 2 dimensions of the structures are microscopic.
The topical and/or cross-sectional view of the structures must be
microscopic;
[0016] "embossable" refers to the ability of a pressure-sensitive
adhesive layer or liner to have part of its surface raised in
relief, especially by mechanical means;
[0017] "wetting" or "wet out" means spreading out over and
intimately contacting a surface;
[0018] "positionable" or "positionability" refers to those
adhesive-backed articles that can easily slide over a substrate
without grabbing or bonding to the substrate absent the application
of a force, or adhesive-backed articles that upon light force are
capable of releasably bonding to a substrate and upon removal
retain at least some form of the original microstructured
surface;
[0019] "release liner", used interchangeably with the term "liner",
refers to a flexible sheet which after being placed in intimate
contact with pressure-sensitive adhesive surface may be
subsequently removed without damaging the adhesive coating;
[0020] "microstructured liner" refers to a liner with at least one
microstructured surface, which is suitable for contact with an
adhesive;
[0021] "backing" refers to a thin, flexible sheet which, after
being placed in intimate contact with pressure-sensitive adhesive
can not be subsequently removed without damaging the adhesive
coating;
[0022] "microstructured backing" refers to a backing with a
microstructured surface.
[0023] "substrate" refers to a surface to which the
pressure-sensitive adhesive coating is applied for an intended
purpose;
[0024] "tape" refers to a pressure-sensitive adhesive coating
applied to a backing.
[0025] "inelastic deformation" means the permanent set at a given
strain resulting from a film being stretched to 15% under tension
and dissipating that tension.
[0026] "compliant" refers to a polymeric film that is soft and
flexible as well as having sufficient inelastic deformation after
being stretched so that once stretched, the film does not recover
to its original length;
[0027] "bleedability" or "air-bleedability" refers to the egress of
fluids, particularly air, from the interface between the adhesive
and the surface of the substrate; and
[0028] "appearance" means the visual characteristics of the article
as viewed from the exposed surface of the film after application of
the article onto a substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] The invention will be more fully appreciated with reference
to the following drawings in which similar reference numerals
designate like or analogous components throughout and in which:
[0030] FIG. 1 is an enlarged, fragmentary, cross-sectional view of
an adhesive-backed article according to the invention;
[0031] FIG. 2a is a segmented planar view of a microstructured
adhesive surface according to the present invention;
[0032] FIG. 2b is a segmented view of the adhesive backed article
highlighting the microstructured features of the present
invention;
[0033] FIG. 3a is a perspective view of one embodiment of a
microstructured feature according to the present invention;
[0034] FIG. 3b is a perspective view of one embodiment of a
truncated microstructured feature according to the present
invention;
[0035] FIG. 4a is a perspective view of one embodiment showing a
double featured microstructured element according to the present
invention;
[0036] FIG. 4b is a perspective view of another embodiment showing
a double featured microstructured element according to the present
invention;
[0037] FIG. 5 is a sectional view showing the configuration of a
microstructured surface of an adhesive layer;
[0038] FIG. 6 is a sectional view showing a second configuration of
microstructured surface of an adhesive layer;
[0039] FIG. 7 is a sectional view showing an additional
configuration of a microstructured surface of an adhesive
layer;
[0040] FIG. 8 is a perspective view of a release liner suitable for
forming a microstructured surface in an adhesive according to the
present invention;
[0041] FIG. 9 is a graph indicating the surface roughness of the
article of the present invention after it is applied onto a
substrate; and
[0042] FIG. 10 is a graph indicating the surface roughness of a
comparative article after it is applied onto a substrate.
DETAILED DESCRIPTION
[0043] The present inventive article 10, as depicted in FIG. 1,
includes a compliant film 12 having opposing surfaces 14, 16. A
pressure sensitive adhesive 18 is bonded to surface 16 of the
compliant film 12. The pressure sensitive adhesive 18 includes a
surface 20 that can be bonded to a substrate (not shown). The
pressure sensitive adhesive 18 includes structures 22 which define
channels 24. A release liner 26 is releasably attached to the
pressure sensitive adhesive 18. The release liner 26 includes
protrusions 28 that are utilized to form corresponding channels 24
and structures 22 in the pressure sensitive adhesive 18. The
release liner 26, shown in a partially removed state, is fully
detachable and is used to protect the pressure sensitive adhesive
prior to application of the article 10 on a substrate.
[0044] The article of the present invention is an improvement over
structured adhesives that provide some degree of egress for
entrapped air. However, certain structured adhesives are not easily
positioned on a substrate. Further, the structures often show
through the outer surface of the film after forceful application of
the article onto the substrate. This is particularly true with thin
films that tend to highlight any underlying surface differences.
The present invention imparts a microstructured surface which
defines channels in a pressure sensitive adhesive with specific
rheological characteristics to address the issues associated with
conventional adhesive-backed articles. The channels in the adhesive
of the present invention have specific dimensions and
characteristics to improve the positionability and fluid egress to
a periphery of the article. Additionally, the characteristics of
the channels render the microstructured surface of the adhesive
substantially undetectable to the human eye when viewed from the
exposed surface of the article after application.
[0045] The compliant film utilized in the present inventive article
is generally made of various plastic materials used conventionally
by those skilled in the art. Suitable films include, for example,
vinyl, polyvinyl chloride, plasticized polyvinyl chloride,
polyurethane, polyethylene, polypropylene, fluororesin or the like.
The thickness film can vary widely according to a desired
application, but is usually within a range from about 300 .mu.m or
less, and preferably about 25 .mu.m to about 100 .mu.m.
[0046] A specific example of a suitable compliant layer is a
plasticized polyvinyl chloride film, and has sufficient inelastic
deformation after being stretched so that when stretched, the film
does not recover to its original length. Preferably, the film has
an inelastic deformation of at least 5% after being stretched once
to 115% of their original length. A typical formulation of the
vinyl film includes polyvinyl chloride resin, light and/or heat
stabilizer(s), plasticizer, and optionally, pigment. The amount of
plasticizer is generally less than about 40% by weight, and is
preferably composed of polymeric non-migratable plasticizers which
are compatible with the vinyl film and provide the necessary
flexibility and durability. A suitable plasticizer is a combination
of polymeric polyester elastomer and an ethylene vinyl acetate
copolymer (such as Elvaloy 742 made by DuPont Co.) soluble in
aromatic solvents and present in amounts of about 26 parts and 10
parts, respectively, per 100 parts vinyl resin.
[0047] Primers may optionally be used to enhance the bond between
the film and the adhesive. The type of primer will vary with the
type of film and adhesive used and one skilled in the art can
select an appropriate primer. Examples of suitable primers include
chlorinated polyolefins, polyamides, and modified polymers
disclosed in U.S. Pat. Nos. 5,677,376, 5,623,010; and those
disclosed in WO 98/15601 and WO 99/03907, and other modified
acrylic polymers. Typically, primers are dispersed into an adequate
solvent in very low concentrations, e.g., less that about 5%
solids, and coated onto the film, and dried at room or elevated
temperatures to form a very thin layer. Typical solvents used may
include water, heptane, toluene, acetone, ethyl acetate,
isopropanol, and the like, used alone or as blends thereof.
[0048] In accordance with the present invention, useful pressure
sensitive adhesives include those which are capable of retaining
microstructured features on an exposed surface after being embossed
with a microstructured molding tool, backing or liner, or after
being coated on a microstructured molding tool, backing or liner
from which it is subsequently removed. The particular pressure
sensitive adhesive selected for a given application is dependent
upon the type of substrate the article will be applied onto and the
microstructuring method employed in producing the adhesive-backed
article. Additionally, useful microstructured pressure sensitive
adhesives should be capable of retaining their microstructured
surfaces for a time sufficient to allow utilization of the
adhesive-backed article.
[0049] Any pressure-sensitive adhesive is suitable for the
invention. Adhesives are typically selected based upon the type of
substrate that they are to be adhered to. Classes of
pressure-sensitive adhesives include acrylics, tackified rubber,
tackified synthetic rubber, ethylene vinyl acetate, silicone, and
the like. Suitable acrylic adhesives are disclosed, for example, in
U.S. Pat. Nos. 3,239,478; 3,935,338; 5,169,727; RE 24,906; U.S.
Pat. Nos. 4,952,650; and 4,181,752. A preferred class of
pressure-sensitive adhesives are the reaction product of at least
alkyl acrylate with at least one reinforcing comonomer. Suitable
alkyl acrylates are those having a homopolymer glass transition
temperature below about -10.degree. C. and include, for example,
n-butyl acrylate, 2-ethylhexylacrylate, isoctylacrylate, isononlyl
acrylate, octadecyl acrylate and the like. Suitable reinforcing
monomers are those having a homopolymer glass transition
temperature about -10.degree. C., and include for example, acrylic
acid, itaconic acid, isobornyl acrylate, N,N-dimethylacrylamide,
N-vinyl caprolactam, N-vinyl pyrrolidone, and the like.
[0050] The adhesives may be polymers that are dispersed in solvent
or water and coated onto the release liner and dried, and
optionally crosslinked. If a solventborne or waterborne
pressure-sensitive adhesive composition is employed, then the
adhesive layer must undergo a drying step to remove all or a
majority of the carrier liquid. Additional coating steps may be
necessary to achieve a smooth surface. The adhesives may also be
hot melt coated onto the liner or microstructured backing.
Additionally, monomeric pre-adhesive compositions can be coated
onto the liner and polymerized with an energy source such as heat,
UV radiation, e-beam radiation.
[0051] The thickness of the adhesive is dependent upon several
factors, including for example, the adhesive composition, the type
of structures used to form the microstructured surface, the type of
substrate, and the thickness of the film. Those skilled in the art
are capable of adjusting the thickness to address specific
application factors. In general, the thickness of the adhesive
layer is greater than the height of the structures which comprise
the microstructured surface. Preferably, the thickness of the
adhesive layer is within a range from about 10 to about 50
.mu.m.
[0052] The pressure sensitive adhesive can optionally include one
or more additives. Depending on the method of polymerization, the
coating method, the end use, etc., additives selected from the
group consisting of initiators, fillers, plasticizers, tackifiers,
chain transfer agents, fibrous reinforcing agents, woven and
non-woven fabrics, foaming agents, antioxidants, stabilizers, fire
retardants, viscosity enhancing agents, coloring agents, and
mixtures thereof can be used.
[0053] The pressure sensitive adhesive of the present invention
includes a microstructured surface on an exposed surface of the
adhesive opposite the compliant film. The microstructured surface
defines channels in the adhesive. Channels are continuous open
pathways or grooves that extend into the adhesive from the exposed
surface. The channels either terminate at the peripheral portion of
the adhesive layer or communicate with other channels that
terminate at a peripheral portion of the article. Upon application
of the article onto a substrate, the pathways provide an egress to
a periphery of the article for fluid trapped at the interface
between the adhesive and the substrate.
[0054] The channels are created to define a specific volume per any
given area of the microstructured surface of the adhesive. The
minimum volume per unit area of the adhesive ensures adequate
egress for fluids at the interface of the substrate and the
adhesive. Preferably, the channels define a volume of at least
1.times.10.sup.3 .mu.m.sup.3 per any 500 .mu.m diameter circular
area in a two-dimensional plane of the adhesive. Most preferably,
the channels define a volume in the range of above
1.0.times.10.sup.3 .mu.m.sup.3 to about 1.times.10.sup.7
.mu.m.sup.3 on any 500 .mu.m diameter circular area.
[0055] The channels of the present invention at least partially
disappear upon final application of the article, in order to
provide a desirable adhesion to the exposed surface of the film.
The ability of the channels to at least partially disappear is
dependent upon the shape of the channel and the rheology of the
adhesive. In accordance with the present invention, the channel's
size and dimensions are selected for the specific pressure
sensitive adhesive compositions to obtain a result of at least 85%
according to the percent wet out test discussed in the "Examples"
section below. The proper wet out enables a sufficient seal between
the article and the substrate.
[0056] The shape of the channels can vary widely according to the
processing methods, but each preferably has a V-shaped, U-shaped,
rectangular or trapezoidal cross section on observation in a
transverse direction. FIGS. 2A and 2B show a segmented view of the
inventive article 30 highlighting trapezoidal channels 34 in the
adhesive 38. The adhesive-backed article 30 includes film 32 and
adhesive 38. The trapezoidal channels 34 and corresponding
structures 36 are formed in the adhesive 38. Side walls 35 of the
structures 36 define side walls for the channels 34.
[0057] The limits of dimensions of the channels can be described by
use of the aspect ratio. The aspect ratio is defined as the ratio
of the greatest microscopic dimension of the channel parallel to
the plane of the continuous layer of adhesive to the greatest
microscopic dimension of the channel perpendicular to the plane of
the continuous layer of adhesive. The aspect ratio is measured by
taking the cross-sectional dimensions of the channel at an angle
perpendicular to the wall of the channel. Depending on the specific
type of channel, the limits of the aspect ratio would be about 0.1
to about 20. For example, the structures of FIG. 7 would define
channels that would have a preferred aspect ratio of about 10 to
about 15.
[0058] Channels are generally created by embossing or forming a
plurality of structures into the adhesive. The structures may be
present in either a random array or in regular patterns. Individual
structures at least partially define a portion of a channel in the
adhesive. Selected patterns could include rectilinear patterns,
polar patterns and other conventional regular patterns. A plurality
of structures combine to create the continuous channels on the
surface of the adhesive.
[0059] The shape of the structures formed in the pressure sensitive
adhesive to create the microstructured surface can vary. Examples
of structure shapes include but are not limited to those selected
from the group consisting of hemispheres, prisms (such as square
prisms, rectangular prisms, cylindrical prisms and other similar
polygonal features), pyramids, or ellipsoids. Combinations of the
different structure shapes can be utilized. The preferred shapes
include those selected from the group consisting of hemispheres,
prisms, and pyramids. Each individual structure should typically
have a height of greater than about 3 micrometers but less than the
total thickness of the adhesive layer, and preferably about 3
micrometers to about 50 micrometers. Additionally, some of the
structures may be truncated to provide a surface for additional
structures, to control the contact surface of the adhesives, and to
improve the wet out of the adhesive. FIG. 3A illustrates a
quadrangle pyramid 40 as an illustration of one embodiment suitable
for use with the present invention. FIG. 3B depicts a truncated
quadrangle pyramid 41 that may also be embossed in the pressure
sensitive adhesive of the invention.
[0060] In the adhesive-backed article of the present invention, the
regular patterns or groups of structures have a specific shape and
a size to achieve the desired performance parameters. Therefore,
the structures are arranged at a pitch (average value of a distance
between similar structural points of adjacent structures) of about
400 .mu.m or less, and preferably about 300 .mu.m or less. A pitch
larger than 400 .mu.m may undesirably result in a pattern of the
features appearing on the surface of the film after application,
thereby causing deterioration in the quality of the article's
appearance.
[0061] Double featured structures are an additional embodiment that
are suitable for use in the present inventive article. The stacking
or use of two structures enhances the positionability of the
article by further reducing the initial contacting surface of the
adhesive. FIG. 4A illustrates a truncated, quadrangle pyramid 42
having an exposed surface 43. A second quadrangle pyramid 44,
having a base 45, is positioned on exposed surface 43. FIG. 4B
depicts another embodiment highlighting the double features of the
invention. A rectangular feature 46 provides a base 47 for
receiving a base 49 of a second smaller rectangular feature 48. In
general, the base surface of a second structure is smaller than the
exposed surface of the first feature. Additionally, different
configurations or shapes may be combined with base structures to
achieve the desirable positioning properties for the present
invention.
[0062] The positionability of the article is affected by the area
of the adhesive that initially contacts the substrate. Preferably,
the contact area of the microstructured features results in an
initial surface contact area of about 60% or less of the total area
of the adhesive in the plane parallel to the continuous layer of
adhesive. The positionability of the present invention is
determined by the test noted in the "Examples" section. Preferably,
the article of the present invention exhibits a positionability
test rating of 2 or better.
[0063] FIGS. 5-7 are utilized to demonstrate the various dimensions
and characteristics of the microstructured surface of the pressure
sensitive adhesive. The figures represent idealized shapes
corresponding to the liner. Those skilled in the art will recognize
the pressure sensitive adhesive cannot hold exact tolerances with
the scale of the structures utilized in the present invention. FIG.
5 is a segmented perspective view of a pressure sensitive adhesive
used in the present invention. The adhesive 50 has a plurality of
structures 52. The pitch P between the features 52 is not more than
400 .mu.m. The height h of each feature 52 from the channel 54 is
within a range from 3 to 30 .mu.m, the length W.sub.1 of the upside
of the channel 54 is within a range from 1 .mu.m to the size of the
pitch P and furthermore a length W.sub.2 of the base of the channel
54 is within a range from 0 .mu.m to the size enough to make a base
angle (of the feature to a value within a range from 1 to
90.degree.. The aspect ratio of the corresponding channel would be
no greater than 20.
[0064] FIG. 6 is an illustration of an adhesive 60 having a
truncated structure 62 with a second structure 64 positioned on an
upper surface 63 of the truncated structure 62. The pitch P
measured from corresponding edges of second structure 64 is not
more than 400 .mu.m. The height of each structure from the base of
the channel 66 is in a range of about 1 .mu.m to about 30 .mu.m.
The length W.sub.1 of the upside of the channel 66 is within a
range from 1 .mu.m to the size of the pitch P and furthermore a
length W.sub.2 of the base of the channel 66 is within a range from
0 .mu.m to the size enough to make a base angle .alpha..sub.1 of
the structure 62 to a value within a range from 1 to 90.degree.. A
base angle .alpha..sub.2 of the second structure 64 is within a
range from 1 to 90.degree..
[0065] FIG. 7 corresponds to the adhesive layer 70 having a
microstructured surface 72 in the shape of a quadrangular pyramid.
The pitch P between the structures 72 is equal to the length
W.sub.1 of the upside of the channel 74 and is not more than 400
.mu.m. The height h of each structure 72 from the base of the
channel 74 is within a range from 3 to 30 .mu.m. The length W.sub.2
of the base of the channel 74 is 0 .mu.m.
[0066] The use of a release liner or backing is one method suitable
for forming the microstructured adhesive of the present invention.
The release liner can be advantageously made of various materials.
Preferred materials which the microstructured liner may include,
but are not limited to plastics such as polyethylene,
polypropylene, polyesters, cellulose acetate, polyvinylchloride,
and polyvinylidene fluoride, as well as paper or other substrates
coated or laminated with such plastics. These embossable coated
papers or thermoplastic films are often siliconized or otherwise
treated to impart improved release characteristics. The thickness
of the release liner can vary widely according to the desired
effect. Furthermore, it is possible to afford structures to the
release liner by using various techniques, such as those disclosed
in U.S. Pat. No. 5,650,215 (Mazurek), herein incorporated by
reference in its entirety.
[0067] Suitable release liners as well as adhesive layers on
release liners are further described in U.S. application Ser. No.
09/808,636, filed on Mar. 14, 2001 by Fleming et al., herein
incorporated by reference in its entirety.
[0068] FIG. 8 depicts a liner 80 suitable for creating structures
on the surface of an adhesive. The liner 80 includes protrusions 82
that form channels in an adhesive as the adhesive is cast onto the
liner.
[0069] The article of the present invention is produced by
imparting the inventive microstructured surface onto an adhesive
with practices conventionally recognized in the art. The features
are imparted by embossing the adhesive directly through utilization
of molding tools or by coating the adhesive onto a liner or backing
previously embossed with the inventive features. Such methods and
practices are fully disclosed in U.S. Pat. No. 5,650,215,
previously incorporated by reference.
[0070] The above-described article can be applied to a variety of
substrates, including smooth air-tight surfaces. It is important to
match a specific pressure sensitive adhesive to a substrate in
order to achieve the desired level of adhesion. Examples of
suitable substrates include glass, metal, plastic, wood, and
ceramic substrates, and painted surfaces of these substrates.
Representative plastic substrates include polyvinyl chloride,
ethylene-propylene-diene monomer rubber, polyurethanes, polymethyl
methacrylate, engineering thermoplastics (e.g., polyphenylene
oxide, polyetheretherketone, polycarbonate), and thermoplastic
elastomers. The substrates are generally smooth substrates that
accentuate the need for an article with fluid egress. Substrates
with rough surface inherently provide an egress for fluids trapped
an interface of an applied article because the rough surface
permits fluid flow.
[0071] The application of the article requires the positioning of
the article over the substrate. The microstructured surface of the
present invention enable the movement of the adhesive-backed
article about the surface of the substrate until pressure is
applied to enable adhesive contact and wet out of the adhesive on
the surface of the substrate. The appropriate level of pressure and
resulting wet out will create a bond between the adhesive and the
substrate.
[0072] Upon forceful application of the article, the channels
permit any entrapped fluid to bleed out around the periphery of the
article, thereby eliminating air bubbles. Additionally, the
microstructured features of the present invention at least
partially collapse during application of the article and thereby
increase the amount of adhesive in contact with the substrate. The
at least partial disappearance of the channels is indicated through
the wet out test, described in the "Examples" below. The present
invention demonstrates wet out test results of at least 85%, and
preferably at least 95%. The at least partial disappearance of the
channels ensures that the article has a desirable level of adhesion
to the substrate.
[0073] In accordance with the present invention, the
microstructured surface of the article is substantially
undetectable from the surface of the film and therefore improves
the overall appearance of the article. One method for measuring the
appearance involves the use of the surface roughness test
procedure, fully described in the "Examples" section. The present
invention, upon application of the article onto a substrate,
exhibit, from the upper surface of the compliant film, an
appearance having no periodicity or repetitive pattern.
Additionally, the present invention has a surface roughness no
greater than the roughness of the film by itself.
[0074] The invention will now be described further by way of the
following non-limiting examples.
EXAMPLES
Surface Roughness Test
[0075] The surface topography of a film is measured using the RST
Plus surface profiling system available from Wyko Corporation in
the vertical scanning interferometer mode (VSI) at a magnification
of 1.2.times. and a pixel size of 13.64 .mu.m.
[0076] The system uses an interference microscope and a computer
algorithm to analyze the surface. In the system, a white light beam
passes through a microscope objective to the sample surface. A beam
splitter reflects half of the incident beam to a reference surface.
The beams from the sample and the reference surface recombine at
the beam splitter to form interference fringes which are
alternating light and dark bands that are visible when the surface
is in focus. The reference arm containing the interferometric
objective moves vertically to scan the surface at varying heights
using a linearized piezoelectric transducer to control the motion.
The interference fringes for white light are present only over a
very shallow depth for each focus position so the fringe contrast
at a single sample point reaches a peak when the point is in focus.
The system starts above the focus point and scans the surface at
evenly spaced intervals as the camera captures frames of
interference data which contain interference signals for each point
on the surface. A computer algorithm processes the data to
calculate surface heights.
[0077] A single line analysis of the surface, such as those
indicated in FIGS. 9 and 10, provides a plot of the surface heights
along a single line of the sample. The peaks on the plot show
whether or not the surface has any periodicity, i.e., a repeating
pattern of peaks. The analyses are performed with the tilt term
removed to eliminate extraneous data due to the interferometer
configuration. The magnification is 1.2.times. and the pixel size
is 13.64 .mu.m. Evidence of periodicity for an adhesive backed film
is generally apparent when the roughness of the adhesive-backed
film exhibits a surface roughness greater than the surface
roughness of the uncoated film. The surface roughness (Ra) is the
arithmetic average roughness for the area sampled.
Percent Wetout Test
[0078] This technique is used to study the wetting of an adhesive
having a microstructured surface onto a smooth transparent
substrate. The hardware used with this technique consists of a
stereo-microscope (Olympus Model SZH-ZB), a video-camera (Cohu
Model 4815) mounted on the microscope, a coaxial vertical
illuminator (Olympus Model TL2), and a computer (Hewlett-Packard
Vectra QS/20) with a video digitizing board (Imaging Technologies
PCVISIONplus) installed which allows the computer to capture and
digitize an image. Such an image can subsequently be stored and
analyzed by commercial software packages (Jandel JAVA). The coaxial
vertical illuminator provides light which is sent through the lens
(i.e., the optic axis) to illuminate the subject. This light passes
through a circular polarizer mounted on the end of the planar
objective lens of the microscope. In practice, the procedure is as
follows: [0079] 1. Apply the adhesive tape onto a glass (or other
optically clear and flat) surface with one pass of a 2 kg roller.
[0080] 2. Position the laminate so that the adhesive/glass
interface is viewed through the glass by a stereo microscope.
[0081] 3. Adjust the sample so that the glass is perpendicular to
the optic axis. [0082] 4. Adjust the circular polarizer to optimize
light intensity and contrast. [0083] 5. Using the image analysis
software, capture and digitize the image. [0084] 6. Set the
software grey value window of acceptance to accept only those grey
values (i.e., brightness levels) corresponding to the wet areas.
[0085] 7. Upon application of the tape, analyze the total wetted
area as a percentage of the total imaged area. Slide Test for
Positionability
[0086] A horizontal glass plate, at about 23.degree. C., was
cleaned with methyl ethyl ketone (MEK). A test sample (i.e.,
pressure sensitive adhesive on the indicated backing),
approximately 2.5 cm by 7.5 cm, was draped flat onto the glass
plate with the pressure sensitive adhesive side down for
approximately 10 seconds. The end edge of the sample was lifted and
pulled laterally. The test ratings are as follows: [0087] 1. sample
slid freely [0088] 2. sample slid easily with some resistance
[0089] 3. sample slid with considerable resistance because of
adhesion to the plate, but could be lifted without damage [0090] 4.
sample stuck to the plate and could not be repositioned without
damage Volume of Air Channels
[0091] The volume of the air channels were calculated based on the
sizes of the microstructures in a 500 micrometer diameter circle in
the liner. The results are reported in cubic microns per 500 .mu.m
circle. The volume of air channels is calculated and indicated in
Table 1.
Examples 1-11 and Comparative Examples C1-C5
[0092] Embossing rolls were cut with diamond tools or laser
machined to provide patterns having varying pitch, depth, widths at
the top of the channel and at the base of the channel, and base
angles. Polyethylene coated paper release liners having a silicone
coating over the polyethylenes, such as those available from Rexam
or Inncoat, were embossed between a heated rubber roll and each of
the embossing roll to produce microstructured liners with ridges.
The rubber roll was heated to a temperature of 110.degree. C. and
the polycoated paper was heated to a surface temperature of
110.degree. C. before entering the nip between the rubber roll and
the embossing roll. The liners traveled around approximately half
of the embossing roll, and then onto a cold can which cooled the
liner. The dimensions of the microstructures on the liners are
shown in Table 1 and have the shape of inverted square pyramids.
The pitch is the distance from one microstructure to the same point
on the adjacent microstructure, the height is the height of the
microstructure from the base of the channel, W1 is the length of
the top of the trapezoidal channel and W2 is the length of the
bottom of the trapezoidal channel.
[0093] A solvent based acrylic pressure-sensitive adhesive was
prepared according to the pressure sensitive adhesive (PSA)
copolymer procedure of U.S. Pat. No. 4,737,577, incorporated herein
by reference, using 90 parts isooctyl acrylate and 10 parts acrylic
acid. The PSA was diluted to about 25% solids with an aziridine
crosslinking agent, such as those disclosed in U.S. Pat. No.
5,648,425.
[0094] The pressure-sensitive adhesive solution was coated onto the
microstructured liners to a dried coating thickness of about 30
micrometers. The solution on each liner was dried at 100.degree. C.
for 10 minutes to form an adhesive film having a microstructured
surface defining trapezoidal channels with the approximate
dimensions calculated from the liner shown in Table 1.
[0095] The exposed adhesive side of each example was then laminated
at room temperature to a 50 micron thick primed white plasticized
flexible and compliant vinyl (PVC) film primed with an acrylic
polymer modified with 2-methylaziridine. The primer was an amine
functional acrylic polymer in ethyl acetate. The lamination was
made using a two roll nip to provide flat pressure-sensitive
adhesive coated PVC films. The films were tested for Appearance,
Air Bleed Capability, Slidability, and Wet-out according to the
above described Test Methods. Test results are shown in Table 1.
TABLE-US-00001 TABLE 1 Avg. Vol. (.mu.m.sup.3) Pitch Height W1 W2
Angle .alpha.1 per any 500 .mu.m Air Wet-out .mu.m .mu.m .mu.m
.mu.m .degree. circular area Appearance Bleedability Slidability %
1 126 16 34 17 62 1.1 .times. 10.sup.6 Good Good 3 2 198 21 67 3 39
1.1 .times. 10.sup.6 Good Good 3 90.4 3 198 22 28 3 62 6.1 .times.
10.sup.5 Good Good 3 93.5 4 197 15 18 1 60 2.8 .times. 10.sup.5
Good Good 3 98.4 5 200 15 200 0 9 1.9 .times. 10.sup.6 Good Good 2
98.7 6* 197 25 197 3 28 3.3 .times. 10.sup.5 Good Good 2 99.0 7 203
20 35 12 60 8.5 .times. 10.sup.5 Good Good 3 8 297 20 35 12 60 6.0
.times. 10.sup.5 Good Good 3 9 198 19 38 22 72 9.9 .times. 10.sup.5
Good Good 10 198 19 28 11 71 6.3 .times. 10.sup.5 Good Good 11 197
20 24 1 60 4.8 .times. 10.sup.5 Good Good 3 98.5 C1 1270 22 61 27
52 ** Poor Good 3 C2 770 20 143 96 40 ** Poor Good 3 C3 508 20 35
12 60 ** Poor Good 3 *Includes a secondary feature with a base
angle of 60.degree. **Volume indeterminate within a given 500 .mu.m
circle
Examples 1-11, produced in accordance with the present invention,
exhibit good appearance, good air bleedability, and at least fair
slidability. The appearance was determined by visual examination
with the unaided eye. A good appearance result indicates no
observable underlying structure. A poor appearance results if the
pattern is visible. With respect to Examples C1-C3, the average
volume per any 500 .mu.m diameter circular area is indeterminate
since some 500 .mu.m diameter circular areas do not have channels.
Additionally, Examples C1-C3 have poor appearance indicating that
patterns created by the channels are visible with the human eye
after application.
[0096] Samples from each Example measuring approximately 2.54 cm by
2.54 cm were then laminated to a clean glass plate using a plastic
squeegee. The samples were then analyzed for surface roughness and
periodicity according to the procedure described above. Example C4
is the vinyl film with no adhesive laminated to it, and C5 is the
vinyl film with a non-structured PSA laminated to it. Results are
shown in Table 2. TABLE-US-00002 TABLE 2 Ex R.sub.a Value - .mu.m
Single Line Analysis PSD 1 0.99 Irregular peaks, no No spikes
periodicity 2 0.50 Irregular peaks, no No spikes periodicity 5 0.85
Irregular peaks, no No spikes periodicity 6 0.54 Irregular peaks,
no No spikes periodicity C2 1.60 Definite repeating peaks C4 1.31
Irregular peaks, no periodicity C5 0.65 Irregular peaks, no
periodicity
[0097] Examples 1, 2, 5 and 6 have arithmetic average roughness
values comparable to that of a vinyl film (Example C5). Example 2,
as illustrated in FIG. 9, shows no periodicity or repeating
patterns. Example C2 has a higher arithmetic average roughness, but
more importantly a repeating pattern or periodicity as indicated by
the interferometer data. The periodicity of Example C2, as
illustrated in FIG. 10, corresponds to the pitch of the channels in
the structured surface of the adhesive. The patterns in C2 are
detectable with the human eye. Example C4 has a roughness greater
than the vinyl film (Example C5) due to microbubbles present in the
adhesive. Examples C4 exhibits no periodicity because the adhesive
is not structured.
[0098] From the above disclosure of the general principles of the
present invention and the preceding detailed description, those
skilled in this art will readily comprehend the various
modifications to which the present invention is susceptible.
Therefore, the scope of the invention should be limited only by the
following claims and equivalents thereof.
* * * * *