U.S. patent application number 12/221923 was filed with the patent office on 2009-03-19 for adhesive sheet.
Invention is credited to Jan Vetrovec, Katerina Vetrovec.
Application Number | 20090075055 12/221923 |
Document ID | / |
Family ID | 36181108 |
Filed Date | 2009-03-19 |
United States Patent
Application |
20090075055 |
Kind Code |
A1 |
Vetrovec; Jan ; et
al. |
March 19, 2009 |
Adhesive sheet
Abstract
An adhesive sheet is disclosed including a flexible substrate
and an adhesive layer formed on at least one of the main surfaces
of the flexible substrate. The adhesive sheet further includes a
plurality of microscopic holes connecting the opposing surfaces of
the sheet and being generally perpendicular to them. Such adhesive
sheet is permeable by air and allows good bubble escapability when
the sheet is applied to an article. Sufficient permeability of the
sheet to air is achieved with microscopic size holes installed in
modest areal densities, hence the appearance and functionality of
the film surface are not significantly adversely impacted. One
intended use of the subject invention is for tinting films used to
reduce light transmission in windows for use in buildings and
automobiles. In this application visual appearance of the film is
paramount. Another intended application of the subject invention is
for antireflective film which is applied to electronic computer
displays (flat panel, cathode ray tube) to reduce unwanted ambient
light reflection and to improve contrast.
Inventors: |
Vetrovec; Jan; (Larkspur,
CO) ; Vetrovec; Katerina; (Larkspur, CO) |
Correspondence
Address: |
Aqwest, LLC
P.O. BOX 468
Larkspur
CO
80118
US
|
Family ID: |
36181108 |
Appl. No.: |
12/221923 |
Filed: |
August 7, 2008 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10969114 |
Oct 20, 2004 |
7413787 |
|
|
12221923 |
|
|
|
|
Current U.S.
Class: |
428/315.9 ;
427/207.1; 427/540; 427/555; 428/315.5 |
Current CPC
Class: |
B32B 37/003 20130101;
B32B 2307/724 20130101; B32B 38/145 20130101; C09J 2301/18
20200801; B32B 2038/047 20130101; Y10T 428/24331 20150115; B32B
2457/20 20130101; B29C 63/0047 20130101; Y10T 428/14 20150115; Y10T
428/24273 20150115; C09J 7/22 20180101; Y10T 428/24322 20150115;
C09J 2301/124 20200801; B29C 2049/2433 20130101; B29L 2031/744
20130101; Y10T 428/24998 20150401; B29C 2049/2425 20130101; B32B
37/1292 20130101; C09J 2301/204 20200801; Y10T 428/15 20150115;
Y10T 428/249978 20150401; Y10T 428/24802 20150115; Y10T 428/1486
20150115; B29L 2031/3475 20130101; Y10T 428/2495 20150115 |
Class at
Publication: |
428/315.9 ;
428/315.5; 427/207.1; 427/540; 427/555 |
International
Class: |
B32B 3/26 20060101
B32B003/26; B05D 5/10 20060101 B05D005/10; B05D 3/06 20060101
B05D003/06; B05D 3/14 20060101 B05D003/14 |
Claims
1. An adhesive film comprising a flexible substrate and a
pressure-sensitive adhesive coating, wherein a. Said flexible
substrate has a first surface and a second surface; b. Said first
and second surfaces are opposing each other and being generally
parallel; c. Said pressure-sensitive adhesive coating being adhered
to said first surface; and d. A plurality of microscopic holes are
installed each extending at least through said substrate.
2. Adhesive film of claim 1 further comprising a layer of material
selected from the family of: printing ink, protective coating, or
decorative coating; said material being applied to said second
surface of said substrate; and wherein said microscopic holes
penetrate through said material.
3. An adhesive film comprising: a) A flexible substrate with
opposing sides; b) Pressure sensitive adhesive which is
discontinuously coated on at least one side of said substrate to
provide areas of the pressure sensitive adhesive interspersed with
areas of uncoated substrate; the areas of said substrate which are
not coated by adhesive being 5 to 80 percent of the area of one
side of said substrate; wherein, i) said substrate has a plurality
of microscopic holes connecting said substrate sides and being
generally perpendicular thereto; ii) transverse dimension of said
holes being between about 1 and about 300 micrometers; iii) and the
size and the areal density of said holes installed in the portions
of the substrate uncoated by said adhesive are chosen so that the
adhesive film has an air permeability in the range of 1 to 1000
Gurley seconds.
4. Adhesive film of claim 3 further including a release liner
attached to said adhesive.
5. Adhesive film of claim 3 wherein said adhesive is applied to
only one side of said substrate and the other side has a finish
layer applied onto it; and wherein said microscopic holes penetrate
through said finish layer.
6. A porous transparent adhesive film; said film comprising a. a
substrate having a plurality of microscopic holes installed
therethrough; and b. a layer of pressure sensitive adhesive applied
to one side of said substrate.
7. A method for fabricating a porous adhesive film comprising the
acts of: a) Presenting a flexible film substrate having a first
surface and a second surface; said first and said second surface
opposing each other and being substantially mutually parallel; b)
Applying a layer of adhesive to said second surface; c) Installing
microscopic holes in said substrate by a method selected from a
family consisting of mechanical piercing, electric discharge, and
laser drilling. wherein said flexible substrate further comprises a
finish layer attached to said second surface.
8. The method of claim 1 wherein said adhesive is a pressure
sensitive adhesive.
9. The method of claim 1 wherein said adhesive is a water soluble
adhesive.
10. The method of claim 1 wherein said adhesive is substantially
porous and permeable by air.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Not Applicable
FEDERALLY SPONSORED RESEARCH
[0002] Not Applicable
SEQUENCE LISTING OR PROGRAM
[0003] Not Applicable
FIELD OF THE INVENTION
[0004] The present invention relates to an adhesive film in a form
of a sheet, strip, tape, label, tag, and the like which is
perforated with microscopic holes to provide good air bubble
escapability while maintaining good appearance and functionality of
the film surface after being adhered to an article.
BACKGROUND OF THE INVENTION
[0005] Various types of adhesive films comprising a flexible
substrate and an adhesive layer have been heretofore available.
Such films are provided in the form of sheets, tapes, strips,
labels, tags, and the like. Those films having a pressure sensitive
adhesive layer generally are mounted on some type of release liner
or other releasable support to protect the pressure sensitive
adhesive until the film is ready to be applied to an intended
article. The film is then stripped from the release liner and
applied.
[0006] Typically, the substrate for such a film is a
self-supporting web or a sheet of paper, cardboard, plastic, or
metal. One major face of the substrate has a pressure sensitive
adhesive while the other major face can be further coated and/or
printed on. Such coating and/or printing can be accomplished either
before or after the application of adhesive to the first major
face. Other versions of adhesive film have adhesive coating on both
faces of the substrate and are known as "double sided" or
"two-sided.". Adhesive films of this basic construction are
manufactured for a variety of commercial and consumer uses
including labels, tags, and stickers for industrial and consumer
products, decorative films for furniture finish and wall covering,
tinting films for building and automotive windows, and antiglare
films for computer displays. Such films constructed in accordance
with prior art are substantially impervious to air and liquids.
This condition is due to a variety of practical considerations
including the choice of materials and manufacturing processes used,
and requirements for appearance and function.
[0007] Problem: When an adhesive film according to the prior art is
applied to an article, air tends to become entrapped between the
adhesive and the article surface. This condition is shown in FIG.
1. To prevent such entrapment and the resulting bubble, a
considerably high level of skill is necessary during the
application step. Consequently, a great amount of labor and time
are necessary to perform the bonding application step. Tolerance
for errors during the bonding step is very low because the bond
strength rises with the passage of time, which makes it more
difficult to peel the adhesive sheet from the substrate article and
reposition it at later time. When air bubbles are trapped between
the adhesive layer and adherent article surface, the appearance of
the film is negatively impacted. This condition is highly
undesirable especially when the film is used for decorative
purposes.
[0008] Even when the film is applied to the article surface and
trapped air bubbles are avoided, lifting and formation of bubbles
can occur at the bond interface when the film is exposed to
environment such as heat and light. Exposure to ultraviolet light
is considered especially deleterious. This is particularly
detrimental to the appearance and functionality of transparent
films such as employed for tinting of windows used in buildings and
automobiles, and antiglare films used for electronic and computer
displays (flat panel, cathode ray tube).
[0009] REVIEW OF PRIOR ART: Prior art discloses several approaches
to the design of adhesive films that avoid the trapping of air when
adhesive film is applied to article. These prior art approaches can
be grouped as follows: 1) use of permeable film substrate, 2) use
of permeable adhesive structure, and 3) use of permeable surface
structure of the adherent article.
[0010] 1) Use of permeable substrate: Substrate materials for
construction of adhesive films having physical characteristics
which allow for significant air permeability are well known and are
generally referred to as being porous. Porous substrate materials
typically have woven, non-woven, knitted, or foamed constructions,
or are formed as microporous sheets.
[0011] Adhesive films with porous substrate have many applications
and are particularly useful as tapes in the medical field. See for
example, Lucast et al., in U.S. Pat. No. 5,613,942 and Dunshee et
al., in U.S. Pat. No. 5,914,282. When porous substrate is used in
construction of adhesive film, one should generally avoid using
adhesives which readily migrate into the interstices of the porous
substrate, thus filling the pores. Another limitation of films with
porous substrate is that when a coating or an ink for decoration is
applied to the second, non-adhesive face of the substrate, it tends
to close the pores of the porous substrate and initial performance
cannot be obtained. This condition is particularly problematic when
a coating with sealing properties is highly desirable as the means
for protecting the non-adhesive surface of the adhesive film from
dust, dirt, moisture, liquids, or human touch, or when such a
coating is used to improve the performance, prepare the surface for
printing, or protect the print ink. Furthermore, many desirable
substrate materials including plastics and metals are not naturally
porous and permeable by air. Hence, the usefulness of permeable
substrate of prior art for construction of adhesive films is very
restricted.
[0012] 2) Use of permeable adhesive structure: Abe in U.S. Pat. No.
6,015,606 discloses adhesive film having structured adhesive
including raised portions. Such raised portions are generated by
elastic microspheres included in the adhesive. During the
application step, the raised portions on the adhesive layer allow
formation of passages which communicate with the atmosphere and
through which bubbles trapped between the adherent article and the
adhesive layer escape to the atmosphere. This situation is shown in
FIG. 2a. However, as the film is pressed onto the article, the
raised portions are gradually flattened thereby closing off the
passages. Hence, initial performance is degraded. This situation is
shown in FIG. 2b. Therefore, a precise sequencing is required to
assure that all of the trapped air is expelled before the passages
are closed off. Such sequencing is, however, difficult to achieve
in practice. Furthermore, formation of structured adhesive layer
requires special equipment. In addition, once the film is applied
to an article, gasses generated at the bond interface when exposed
to environment such as heat and light cannot escape and, as a
result, cause bubbles and lifting. A more complex adhesive
structure disclosed by Abe in U.S. Pat. No. 6,294,250 has the same
limitations.
[0013] 3) Use of permeable adherent surface structure: Kurtz in the
U.S. Pat. No. 4,548,846 discloses an adherent article with a
specially prepared grooved surface. When adhesive film is applied
to such grooved surface, the grooves provide channels for
communication with outside atmosphere and allow trapped air to
escape. This condition is shown in FIG. 3. However, this approach
is not suitable for general use as it requires special preparation
of adherent article surface. Such surface preparation is costly and
impractical in most situations, especially when the adherent
article is a glass window or computer display. In addition, the
need for surface preparation greatly restricts the choice of
adherent materials and limits the selection of sites on the surface
of substrate article that are suitable for receiving adhesive
film.
[0014] Permeability of materials by air can be quantified in terms
of Gurley value. Gurley value (also known as Gurley seconds) for
porosity is measured on a Gurley porosity tester (Gurley Precision
Instruments, Troy, N.Y.) and it represents the time (in seconds)
for 100 cubic centimeters (about 6.1 cubic inches) of air to flow
through 1 square inch area of test material under pressure gradient
of 1.2 kilo-Pascals (about 4.9 inches of water). The Gurley value
actually represents air resistance, but popularly is referred to as
permeability or porosity. A low Gurley value indicates high
porosity material, while a high Gurley value indicates a low
porosity material. For comparison purpose, 50 pound smooth paper
for offset printing has a Gurley value around 20.
SUMMARY OF THE INVENTION
[0015] To overcome the limitations of prior art, the present
inventors made an extensive study, and as a result, they have
discovered a novel construction and a method for manufacture for
adhesive film having good air bubble escapability. The invention is
based on experimental evidence indicating that very modest air
permeability of the film is sufficient to prevent trapping pockets
of air between the film and an adherent article when the film is
applied to the article surface. The inventors have determined that
appropriate air permeability can be achieved by perforating the
film with microscopic holes at relatively low areal density. Using
this approach, the film is rendered permeable without significantly
affecting its appearance or functionality.
[0016] The present invention is an adhesive film which is permeable
by air. The film comprises a thin flexible substrate such as a
sheet, strip, tape, tag, or the like, coated with a layer of
adhesive on at least one side. Substrate materials suitable for use
with the subject invention include paper, cardboard, plastics, and
metal. The substrate may also include a print and/or protective
coating on its other surface opposite to the surface coated with
adhesive layer. The substrate is perforated by a number of
microscopic holes generally perpendicular to its surfaces. Such
holes are generally 1 to 300 micrometers in transverse dimension.
Size and areal density of the microscopic holes are chosen to
provide appropriate permeability by air while avoiding degradation
in appearance and functionality of the film. For example, if the
subject invention is used as an antireflective film for computer
screens such as disclosed by Kishioka et al., in the U.S. Pat. No.
6,599,967, the microscopic holes should be preferably less than
about 10 micrometers in size and applied with areal density about
100 to about 1000 per square inch. When used for wall covering, the
microscopic holes from about 30 to about 100 micrometers in size
and areal density of about 1 to about 100 per square inch can be
employed in many cases without adversely affecting the film
appearance. For comparison, a typical human hair has a diameter
around 70 micrometers. This is also considered the limit of optical
resolution of human eye. Objects smaller than 10 micrometers are
generally indistinguishable by naked human eye.
[0017] In one embodiment of the subject invention, the adhesive is
applied over less then 100% of each substrate surface. In
particular, adhesive may be applied in regular or irregular
patterns that provide predetermined coverage (typically 20 to 90%)
of the coated substrate face. The desired level of air permeability
is obtained by installing microscopic holes in the substrate so
that when averaged over the surface area, a sufficient number of
these holes are in locations where the substrate surfaces are not
covered by adhesive. The microscopic holes can be installed in the
substrate prior to coating with adhesive or after the coating
process. Suitable methods for production of microscopic holes
include mechanical piercing, perforation by electric discharge
(spark), and laser drilling. The microscopic holes can be applied
in patterns that are coordinated with the adhesive coating patterns
so as to preferentially perforate the substrate in areas not having
adhesive coating. Alternately, the holes can be applied in regular,
irregular, or even random patterns with sufficient areal density to
assure that a sufficient quantity of the holes penetrates the
substrate in areas not covered with adhesive coating. If the film
substrate also has an ink print and/or decorative/protective
coating on the face opposite to that of the adhesive, the holes are
installed therethrough so that the desired permeability is
achieved.
[0018] In another embodiment of the subject invention, the adhesive
is applied over generally 100% area of at least one surface. In one
variant of this embodiment, the adhesive has microscopic voids
forming passages, with some of the passages connecting to the
microscopic holes in the substrate. In another variant, the
microscopic holes are generated after the adhesive has been applied
to the film and penetrate through the adhesive layer with
sufficient spatial frequency to achieve the desired level of air
permeability.
[0019] In each embodiment of the subject invention, the microscopic
holes provide a path for air to permeate through the adhesive film
of the subject invention. When the film of the subject invention is
applied to a substrate, pockets of air trapped between the film and
the substrate surface are relieved to outside atmosphere. As a
result, formation of bubbles of trapped air is avoided. When
adhered film is exposed to environment such as light and heat that
cause the materials in the vicinity of adhesive bond interface
generate gas, such gas is readily relieved through the microscopic
holes to the atmosphere.
[0020] In many instances, most notably in consumer articles, it is
desirable to remove the product label after the product has been
purchased. Yet, very often the adhesive employed (usually pressure
sensitive or water soluble type) adheres very well to the article
and the label substrate is too weak to carry the force required to
peel off the label without breaking. Softening the adhesive with
suitable solvent requires great amount of time since the solvent
has to penetrate the adhesive layer starting from the edge. In
contrast, when the product label is fabricated in accordance with
the subject invention, the solvent can readily permeate through the
film substrate via microscopic holes and soften the adhesive,
thereby making it possible to remove the label shortly after the
solvent it applied.
OBJECTS OF THE INVENTION
[0021] One object of the invention is to allow removal and venting
of air entrapped between adhesive films and surface of adherent
article when the film is applied to the article.
[0022] Another object of the invention is to allow venting of gases
evolved at the bond interface after an adhesive film has been
applied to an adherent article.
[0023] Yet another object of the invention is to allow for easier
removal of adhesive film after it has been adhered to an adherent
article.
[0024] Yet another object of the invention is to improve appearance
of adhesive film adhered to an article.
[0025] Yet another object of the invention is to make easier
installation of adhesive film onto an article.
[0026] Features and advantages of the invention will emerge in the
discussion of the embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 shows a side cross-sectional view of a prior art
adhesive film applied to an article wherein a bubble is formed by
entrapped air;
[0028] FIG. 2a shows a side cross-sectional view of a prior art
adhesive film applied to an article wherein a permeable adhesive
structure forming passages is used to relieve trapped air;
[0029] FIG. 2b shows an adhesive film of FIG. 2a wherein passages
used to relieve trapped air have significantly collapsed;
[0030] FIG. 3 shows a side cross-sectional view of a prior art
adhesive film applied to an adherent surface having relieve
passages;
[0031] FIG. 4 shows a side cross-sectional view of a first
embodiment of the subject invention with adhesive layer applied
discontinuously to one face of the substrate;
[0032] FIG. 5 shows a side cross-sectional view of a variant of a
first embodiment of the subject invention with adhesive layer
applied discontinuously to both faces of the substrate;
[0033] FIG. 6 shows a side cross-sectional view of a second
embodiment of the subject invention using porous adhesive;
[0034] FIG. 7 shows a side cross-sectional view of a third
embodiment of the subject invention with holes installed through
the adhesive layer.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0035] Referring now to FIG. 4, there is shown a side
cross-sectional view of an adhesive film 10 in accordance with a
first embodiment of subject invention. The film 10 comprises a
flexible substrate 21 having surfaces 32 and 33. The substrate 21
is a thin flexible member that can be in a form of a sheet, strip,
tape, label, or alike. Typical thickness of substrate 21 is 10 to
1500 micrometers. Suitable materials for fabrication of the
substrate include paper, cardboard, plastics, and metals. More
specifically, suitable plastics include polyethylene, polyvinyl
chloride (PVC), polyester, polyurethane, polyacrylate, etc. PVC
resin is particularly suitable for the construction of substrate 21
because it can be easily printed onto. In addition, PVC is
economical and has good weatherability, which makes it suitable for
outdoors use. Furthermore, in the present invention it is possible
to use those film substrates to which surface treatment such as
printing, embossing, and protective layers is applied. Surface 32
of substrate 21 is coated with a pressure sensitive adhesive 24,
which is applied in a discontinuous manner so that portions 32a of
the surface 32 are generally free of the adhesive material.
Preferably, the adhesive 24 covers less than 90% of the surface 32.
The pressure sensitive adhesive 24 may be applied in regular,
irregular, or entirely random patterns. Examples of suitable
patterns are straight lines, stripes, wavy lines, curves, dots,
shapes, checkered, crosshatched, and any combination thereof. A
variety of pressure sensitive adhesives can be used with the
subject invention including the types that contain elastic
microospheres as for example disclosed by Date in U.S. Pat. No.
6,294,250.
[0036] The substrate 21 is further perforated by microscopic holes
27 which are installed generally perpendicular to the surface 32.
The pattern for placement of the microscopic holes 27 can be
coordinated with the pattern of the adhesive 24 to yield a high
percentage of the microscopic holes placed in the portions 32a of
surface 32. This percentage can be 100% if the adhesive pattern and
hole pattern are well coordinated. Holes terminating in surface
portion 32a which is not coated by adhesive are open and available
for transport of air through the film 10. Hole 27a is an example of
an open hole. Unless porous adhesive is used, microscopic holes
terminating into the adhesive 24 are deemed substantially blocked
by the adhesive and not significantly contributing to air transport
through the film. Hole 27b is an example of a blocked hole.
Alternate to coordinated patterns, the pattern for microscopic
holes 27 can be uncoordinated with the patterns for adhesive 24,
and can be regular, irregular, or random. Whichever the choice, the
areal density and the size of microscopic holes should be chosen so
that the permeability of the film 10 rendered by the unblocked
holes is in the range of 1 to 1000 Gurley seconds when measured
under the already described conditions. Appropriate size and areal
density of microscopic holes 27 can be estimated using the theory
of air flow through microscopic holes in thin sheets.
Example 1
[0037] Table 1 shows theoretical predictions of air flow through
smooth holes with diameters of 10, 32, and 100 micrometers
installed in a 75 micrometer thick sheet impervious to air and
operated with a pressure differential of 1.2 kilo Pascals (4.9
inches of water). (Note that this is the same pressure differential
normally used in the Gurley tester.) This data is based on
theoretical predictions found in "Effect of Pinholes on Sterile
Barrier Properties," by Earl T. Hackett, Jr. presented at the
HealthPak Conference, St. Petersburg, Fla., in March 2001.
TABLE-US-00001 TABLE 1 Hole Diameter [micrometers] 10 .mu.m 32
.mu.m 100 .mu.m Flow velocity [cm/sec] 400 3500 5500 Flowrate per
hole [cubic cm/sec] 0.000314 0.028 0.039 Porosity produced by 1
hole per 318000 3571 256 inch square [Gurley seconds] Areal density
of holes necessary 3,180 36 2.6 to produce porosity of 100 Gurley
seconds [per square inch]
Example 2
[0038] Table 2 shows several suitable choices of diameter and areal
density for microscopic holes suitable to relieve 1 cubic
centimeter air bubble to atmosphere in less 5 seconds assuming a
constant pressure differential of 1.2 kilo Pascals. Sheet thickness
is 75 micrometers. Expectedly, the data shows that smaller holes
must be applied with greater areal density to meet the specified
venting time during installation of adhesive film to an article.
Note that even for a 10 micrometer diameter hole the required areal
density of 1,000 to 10,000 holes per square inch is realistic and
technically attainable.
TABLE-US-00002 TABLE 2 Time (seconds) required to relieve 1 cubic
centimeter air Areal density of microscopic bubble for hole
diameters holes [per square inch] 10 .mu.m 32 .mu.m 100 .mu.m 1 2.6
10 3.6 0.26 100 0.36 1,000 3.2 10,000 0.32
[0039] As already noted, after the film is applied to the article
surface and trapped air bubbles are avoided, gas evolution can
still occur at the bond interface when the film is exposed to
environment such as heat and light. Such gas is relieved by
microscopic holes 27 and lifting and formation of bubbles are
avoided. Since the rates at which such gas is evolved are very low,
microscopic holes 27 can be very small (typically 1 to 10
micrometers) and installed with low areal density (1 to 1000 per
square inch).
[0040] Referring further to FIG. 4, the adhesive film 10 may also
include a layer 29 attached to surface 33 of substrate 21. Layer 29
can be a print ink, protective coating, or decorative coating.
Alternately, layer 29 may be a composite layer comprising separate
sublayers which may include print ink, protective coating, or
decorative coating. Whichever the case, microscopic holes 27
penetrate through the layer of material 29 to provide air
permeability for the film 10.
[0041] Microscopic holes 27 may be installed either before or after
the adhesive 24 is applied to the substrate 21. Preferably, the
holes are installed after providing the substrate 21 with the
finish layer 29. When the holes are installed after coating the
substrate with adhesive 24, some of the holes 27 may actually
penetrate through the adhesive. Depending on the process for
production of the holes 27 and the nature of the adhesive 24, holes
27 penetrating through adhesive 24 may become at least partially
closed with passage of time. Holes that remain at least partially
open increase the air permeability of the film 10. Adhesive film 10
may also include a release liner attached to surface 43 the
adhesive 24. Furthermore, the substrate 21 of adhesive film 10 may
be also embossed for decorative or other beneficial purposes.
[0042] Suitable techniques for installation of the holes 27 include
mechanical piercing, electric discharge, and laser drilling.
Mechanical piercing method and apparatus suitable for production of
holes in the manufacture of the subject adhesive sheet is disclosed
by Silverstein in the U.S. Pat. No. 3,789,710. Silverstein's method
and apparatus use a heat assisted piercing and are particularly
effective for use on substrates made of thermoplastic material.
Mechanical piercing can produce holes down to about 0.020 inch
diameter.
[0043] The use of electric discharge for perforation of dielectric
sheet materials has been practiced commercially since the 1940's.
Devices and methods for electric discharge perforation have been
disclosed by Meaker in the U.S. Pat. No. 2,340,546; Menke in the
U.S. Pat. No. 2,528,157; Bancroft et al. in the U.S. Pat. No.
3,385,951; Martin in the U.S. Pat. No. 4,029,938; and Whitman in
the U.S. Pat. No. 4,447,709. Electric discharge can produce holes
down to about 0.030 inch diameter.
[0044] Laser drilling has become a well established commercial
practice since its initial introduction in the 1970's. General
review of the state of the art in laser drilling is presented by
Leo Rakowski in "Non-Traditional Methods for Making Small Holes,"
published in Modern Machine Shop, June 2002 issue, pages 76-83.
Devices and methods for laser drilling have been disclosed by Lilly
et al. in the U.S. Pat. No. 4,410,785; Kimbara et al., in the U.S.
Pat. No. 4,568,815; Fukuchi in the U.S. Pat. No. 5,403,990;
Steadman in the U.S. Pat. No. 6,344,256; and Hamada in the U.S.
Pat. No. 6,720,524. Equipment for laser drilling of the holes
suitable for use with the subject invention may also include means
for detecting adhesive free portions of surface 33 and
preferentially installing the hole (s) at such locations. Laser
drilling is particularly suitable for production of
precision-located holes smaller than 30 micrometers and as small as
about 1 micrometer in diameter.
[0045] Referring now to FIG. 5, there is shown a side
cross-sectional view of an adhesive film 10' in accordance with a
variant of first embodiment of the subject invention. In this
variant, the substrate 21 is coated with pressure sensitive
adhesive on both faces: surface 32 is coated with adhesive 24 and
surface 33 is coated with adhesive 24'. In each case, the adhesive
coating is applied discontinuously so that portion 32a of surface
32 and portion 33a of surface 33 remain generally free of the
adhesive. Preferably, the adhesive covers less than 90% of each the
surface 32 and 33. The adhesive may be applied in regular,
irregular, or entirely random patterns. Examples of suitable
patterns are straight lines, stripes, wavy lines, curves, dots,
shapes, checkered, crosshatched, and any combination thereof. If
regular patterns are employed, preferably they should be
coordinated and well aligned so that a high percentage of uncoated
portions 32a and 33a lay directly opposite to each other. A pattern
for microscopic holes 27 is preferably chosen so that a large
percentage of the holes are at locations where they connect
opposing uncoated portions 32a and 33a. Adhesives 24 and 24' can be
both of the same type or different types. An example of two
different types of adhesives that may be simultaneously used with
adhesive film 10' are permanent pressure sensitive adhesive and a
temporary pressure sensitive adhesive. Adhesive film 10' may also
include a release liner attached to surface 42 the adhesive 24
and/or surface 43 of adhesive 24'.
[0046] Referring now to FIG. 6, there is shown a side
cross-sectional view of an adhesive film 11 in accordance with a
second embodiment of subject invention. This embodiment is similar
to the first embodiment except that 1) pressure sensitive adhesive
124 is applied substantially continuously over the surface 32 of
substrate 21, and 2) the pressure sensitive adhesive 124 is porous
and permeable by air. Suitable porous pressure sensitive adhesive
has been disclosed in prior art for example by Copeland in the U.S.
Pat. No. 3,121,021. Holes 27 can be installed in any suitable
pattern either before or after the adhesive 124 is applied to
substrate 21. Since the adhesive 124 is porous, a large percentage
of the holes 27 will connect to one or more pores in adhesive 124
leading up to surface 43. Air trapped between the adhesive film 11
and adherent article is then relieved by first passing through the
adhesive 124 and then through holes 27 into the atmosphere.
[0047] Referring now to FIG. 7, there is shown a side
cross-sectional view of an adhesive film 12 in accordance with a
third embodiment of subject invention. This embodiment is similar
to the first embodiment except that 1) the adhesive 224 is applied
substantially continuously over the surface 32 of substrate 21, 2)
the adhesive 224 can be either pressure sensitive or solvent
activated, and 3) holes 27 penetrate through the adhesive 224.
[0048] Those skilled in the art can now appreciate from the
foregoing description that the broad teachings of the subject
invention can be implemented in a variety of forms. Therefore,
while this invention has been described in connection with
particular examples thereof, the true scope of the invention should
not be limited since other modifications will become apparent to
the skilled practitioner upon a study of the drawings and the
following claims.
* * * * *