U.S. patent application number 11/580382 was filed with the patent office on 2007-04-19 for method of making a privacy film.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Graham M. Clarke, Paul D. Graham.
Application Number | 20070084549 11/580382 |
Document ID | / |
Family ID | 37947069 |
Filed Date | 2007-04-19 |
United States Patent
Application |
20070084549 |
Kind Code |
A1 |
Graham; Paul D. ; et
al. |
April 19, 2007 |
Method of making a privacy film
Abstract
A method of making a privacy film includes generally the
following steps: providing a polymeric material, depositing the
polymeric material onto a microstructured mold comprising a
plurality of substantially parallel, elongated channels with
specific geometry; inducing the polymeric material to flow into the
channels of the microstructured mold; solidifying the polymeric
material inside the channels to yield a plurality of light
directing elements that are connected with one another via a
polymeric base sheet; and separating the privacy film from the
microstructured mold.
Inventors: |
Graham; Paul D.; (Woodbury,
MN) ; Clarke; Graham M.; (Woodbury, MN) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
37947069 |
Appl. No.: |
11/580382 |
Filed: |
October 13, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11250676 |
Oct 14, 2005 |
|
|
|
11580382 |
Oct 13, 2006 |
|
|
|
Current U.S.
Class: |
156/245 ;
264/239; 264/240 |
Current CPC
Class: |
Y10T 428/2457 20150115;
G02B 5/00 20130101; Y10T 428/14 20150115; B29C 33/424 20130101;
Y10T 428/25 20150115; B29C 2059/023 20130101; Y10T 428/24372
20150115; Y10S 428/916 20130101; Y10S 283/901 20130101; Y10S
283/902 20130101; B29C 59/022 20130101 |
Class at
Publication: |
156/245 ;
264/239; 264/240 |
International
Class: |
B29C 47/00 20060101
B29C047/00; B27N 3/08 20060101 B27N003/08; B29C 33/00 20060101
B29C033/00 |
Claims
1. A method of making a privacy film comprising the steps of:
providing a polymeric material; depositing the polymeric material
onto a microstructured mold comprising a plurality of substantially
parallel, elongated channels, wherein each channel is slanted and
is separated from the next channel by a land region, wherein each
channel has a base disposed adjacent to and a tip disposed distal
to the land region, wherein each channel has a minor axis that runs
from the base to the tip; inducing the polymeric material to flow
into the channels of the microstructured mold; solidifying the
polymeric material inside the channels to yield a plurality of
light directing elements that are connected with one another via a
polymeric base sheet having a first surface from which the light
directing elements protrude and an opposing second substantially
planar surface; and separating the privacy film from the
microstructured mold.
2. The method of claim 1, wherein the channels of the
microstructured mold are tapered at their tips.
3. The method of claim 1, wherein the polymeric material is a
thermoplastic polymer.
4. The method of claim 3, wherein the thermoplastic polymer is
selected from the group consisting of polypropylene, polyethylene,
polystyrene, polycarbonate, polymethyl methacrylate, ethylene vinyl
acetate copolymers, acrylate-modified ethylene vinyl acetate
polymers, ethylene acrylic acid copolymers, nylon,
polyvinylchloride, and combinations thereof.
5. The method of claim 1, wherein the polymeric material comprises
a light reflecting material.
6. The method of claim 5, wherein the light reflecting material is
selected from the group consisting of titanium dioxide, zinc oxide,
zinc sulfide, zinc phosphate, calcium carbonate, alumina, silica,
antimony oxide, barium sulfate, lithopene, calcined kaolin, lead
carbonate, magnesium oxide, and combinations thereof.
7. The method of claim 6, wherein privacy film comprises less than
20% by weight of the light reflecting material, based on the total
weight of the film.
8. The method of claim 1, wherein each channel has a height h,
which is the distance from its base to its tip along its minor
axis, and two adjacent channels have a center-to-center spacing P,
and wherein the ratio of h to P is from about 0.5 to 5.
9. The method of claim 1, wherein two adjacent channels are placed
such that the tip of one channel, as viewed from an imaginary line
normal to the land region, overlaps the base of the adjacent
channel.
10. The method of claim 1, wherein the polymeric material is molten
resin.
11. The method of claim 10, wherein the inducing step comprises
heating the microstructured mold.
12. The method of claim 1, wherein the polymeric material is a
liquid resin or a thermoplastic film.
13. The method of claim 12, wherein the inducing step comprises
applying heat and pressure to the liquid resin.
14. The method of claim 1, wherein the separating step results in
substantially no distortion on the light directing elements of the
privacy film.
15. The method of claim 1 further comprising laminating a light
transmissive adhesive to the second surface of the polymeric base
sheet.
16. The method of claim 1, wherein the light transmissive adhesive
is a repositionable pressure sensitive adhesive.
17. The method of claim 1, wherein the channels of the
microstructured mold are slanted at an angle greater than about
15.degree. and less than about 90.degree., the angle being formed
between the intersection of the minor axis of the channel and a
line lying in the plane of the land region.
18. The method of claim 1, wherein two adjacent channels are placed
such that the tip of one channel, as viewed from an imaginary line
normal to the land region, is coincident with the base of the
adjacent channel.
19. The method of claim 1 further comprising applying a light
absorbing coating to a top portion of the light directing
elements.
20. The method of claim 1, wherein the polymeric material comprises
a light absorbing material.
21. The method of claim 1, wherein the polymeric material comprises
light absorbing and light reflecting materials.
22. The method of claim 1, wherein the polymeric material comprises
at least two layers, wherein a first layer is substantially free of
light absorbing and light reflecting materials, and wherein a
second layer comprises light absorbing material, light reflecting
materials, or a combination thereof.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] The present application is a continuation-in-part of U.S.
patent application Ser. No. 11/250,676 filed on Oct. 14, 2005,
which is incorporated by reference in its entirety.
FIELD OF INVENTION
[0002] The present invention relates to a privacy film. In
particular, the present invention relates to a polymeric based
privacy film having a plurality of light directing elements each
element being disposed substantially parallel to the next adjacent
light directing element, the film being well suited for use with
documents.
BACKGROUND
[0003] Products capable of providing privacy for the consumer have
increased. For example, it is very common today for most personal
computers and automatic teller machines to include a privacy screen
allowing the user to view the image on the monitor while
simultaneously limiting the view for bystanders, or at least those
not in the viewing angle of the screen. Some have used light
control films to provide privacy to a user who has documents
containing sensitive material. The idea is similar in that the user
can view the image on the document but bystanders are limited in
viewing the document's content.
[0004] The art discloses various light control films that also
serve the purpose of providing privacy to the user. However, as
document privacy is becoming more and more of a desire for
consumers, those skilled in the art seek different solutions to
provide this desired feature. Thus, there is a continuing need for
new privacy film constructions.
SUMMARY
[0005] The present invention provides for a privacy film that can
be used with documents to limit the angle at which a viewer can
read the information on the document. In particular, when the
privacy film is placed in the use orientation such that the viewing
angle is coincident with the user's line of sight, the user will be
able to see the contents of the documents while others will only
have a limited view of the document's content.
[0006] In one aspect, the present invention pertains to a privacy
film comprising a light transmissive, polymeric base sheet
comprising (i) a first polymeric material, the base sheet having
opposing first and second surfaces; and (ii) a plurality of light
directing elements comprising a second polymeric material, wherein
each element has a base, a height h, and a minor axis disposed
along the height, wherein the elements protrude from the first
surface of the base sheet, and wherein each element is disposed
such that the minor axis of one element is substantially parallel
to the minor axis of the next adjacent element and the base of one
element is not joined with the base of the next adjacent element.
In another aspect, the privacy film comprises elongated light
directing elements.
[0007] In another aspect, the present invention pertains to a
method of making a privacy film comprising the steps of (i)
providing a polymeric material; (ii) depositing the polymeric
material onto a microstructured mold comprising a plurality of
substantially parallel, elongated channels, wherein each channel is
slanted and is separated from the next channel by a land region,
wherein each channel has a base disposed adjacent to and a tip
distal from the land region, wherein each channel has a minor axis
that runs from the base to the tip; (iii) inducing the polymeric
material to flow into the channels of the microstructured mold;
(iv) solidifying the polymeric material inside the channels to
yield a plurality of light directing elements that are connected
with one another via a polymeric base sheet having a first surface
from which the light directing elements protrude and an opposing
second substantially planar surface; and (iv) separating the
privacy film from the microstructured mold.
[0008] As used herein, the term "light transmissive" means the
ability to transmit visible light. In one embodiment, the light
transmissive base sheet has an opacity of 90 or less, as measured
using a Lab Scan 6000 Tester with a HuterLab Master Color Data
Program, commercially available from Hunter Associates Laboratory,
Inc., Reston, Va. With reference to the light directing element,
the term "elongated" generally means that the element has a
rail-like appearance. The rails can be continuous along the entire
length of the privacy film or they can be discontinuous. In one
embodiment, the discontinuous light directing elements are discrete
bodies having an appearance of a stem, such as, e.g., a stem of a
mushroom.
[0009] One advantage of the present invention is that it provides
the privacy feature with flexible construction that is relatively
easy to manufacture. The privacy film can be quickly attached to
the document in a non-permanent manner. Furthermore, the privacy
film is durable so that it can be used repeatedly.
[0010] In this document, the term "about" is presumed to modify all
numerical values.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The invention can be better understood with reference to the
following drawings, wherein:
[0012] FIG. 1 is a perspective view of one exemplary embodiment of
a privacy film;
[0013] FIG. 2 is a cross-sectional view of the privacy film of FIG.
1 taken along line 2-2;
[0014] FIG. 3 is a cross-sectional view of another exemplary
embodiment of a privacy film showing light directing elements with
multiple sections;
[0015] FIG. 4 is a cross-sectional view of another exemplary
embodiment of a privacy film showing the tip portions of the light
directing elements being covered with a light absorbing
coating;
[0016] FIG. 5 is a cross-sectional view of another exemplary
embodiment of a privacy film showing light directing elements at
varying cant angles;
[0017] FIG. 6 is a cross-section view of another exemplary
embodiment of a privacy film showing the tip portions of the light
directing elements being elongated in a direction parallel to the
base layer;
[0018] FIG. 7 is a perspective of another exemplary embodiment of a
privacy film showing a combination of elongated light directing
elements; and
[0019] FIGS. 8a to 8c are schematic views of an exemplary process
that can be used to make the privacy film.
[0020] These drawings are not drawn to scale and are intended only
for illustrative purposes.
DETAILED DESCRIPTION
[0021] FIG. 1 is a perspective view of one exemplary embodiment of
the present invention showing privacy film 10 having elongated
light directing elements 18 disposed on substrate 50 that may
contain sensitive information. In one embodiment, the privacy film
can be attached using a light transmissive adhesive (not shown).
The elements have a major axis L and a minor axis l. One exemplary
substrate is a document bearing confidential information that the
document owner wants limited viewing access.
[0022] In use the privacy film of the present invention is disposed
on the document so that the major axis L lies substantially
parallel to the image or lines of text on the document. For
example, on 81/2 by 11 inch paper in portrait orientation where the
text lies substantially parallel to the 81/2 inch side of the
paper, the privacy film would be oriented so that the major axis
also lies along the same direction. The privacy film can be
disposed on the document temporarily, meaning that the film can be
removed from the substrate without damage thereto, or permanently,
meaning that removal of the privacy film will most likely cause
damage to the document. There exists a variety of means for
attaching or disposing the privacy film to the document. For
example, an adhesive can be used. The adhesive can be pressure
sensitive or hot melt. The adhesive can be a repositionable
adhesive, meaning that it can be applied and removed from the
substrate multiple times without damage to the substrate and
without significant loss in adhesion of the repositionable
adhesive. In another application, the privacy film is formed as a
pocket, where the privacy film forms a front, a polymeric backing
or the privacy film forms a back, and the privacy film and the back
are attached on three sides, leaving the fourth, typically top
side, open for insertion and removal of a document. Other
configurations can be used.
[0023] The light directing elements interfere with light
transmission thereby providing the privacy feature of the present
inventive film. Optically active materials, such as light
reflecting and or light absorbing materials, may be included. The
light directing elements geometry, spacing, and the optically
active materials are discussed below in detail.
[0024] In one exemplary embodiment, the heights of the light
directing elements are substantially the same on the privacy film.
There may be some variation in the elements' heights due to the
manufacturing conditions. In another exemplary embodiment, the
heights of the elements vary from one region of the privacy film to
another region and even from one element to the next adjacent
element. By variation in height, it is generally meant that one
element will be from 75% to 95% in height of another element. FIG.
3 generally illustrates the embodiment having light reflecting
elements with varying heights.
[0025] FIG. 2 shows a cross-section of the privacy film in FIG. 1
taken along line 2-2. The privacy film includes base sheet 12
having opposing first surface 14 and second surface 16 and
demarcation line 13. Light directing elements 18 protrude from the
first surface of the base sheet. While FIG. 2 shows that
demarcation line 13 is collinear with first surface 14, the line
can be at a different location. Each light directing element has a
height h, a width W, and a center-to-center spacing from one
element to the next adjacent element P. The height h is measured
along the minor axis l from the first surface 14 of the base sheet
to tip 20. The width W is measured perpendicular to the minor
axis.
[0026] In one exemplary embodiment the h to P ratio (h:P) is
greater than 0.5. In another embodiment, the h:P ratio is less than
5. In one embodiment, the width of the light directing element, as
measured proximate to the first surface of the base sheet is
greater than 25 microns. In another embodiment, the width is less
than 750 microns. In the embodiment of FIG. 2, the light directing
elements are disposed on the base sheet at a cant angle .theta..
The cant angle is the angle between first surface 14 and the minor
axis of each light directing element. In one embodiment, the cant
angle is greater than 15.degree.. In another embodiment, the cant
angle is less than 90.degree.. In yet another embodiment, the cant
angle ranges from 40.degree. to 85.degree.. In yet another
embodiment, the cant angle ranges from 55.degree. to 75.degree.. If
desired, adhesive 22 is provided on the second surface of the base
sheet, for attachment to a substrate. While the light directing
elements of this particular embodiment are substantially uniform in
its cross-sectional dimension, there can be a slight draft (i.e., a
slight narrowing) to the elements towards tip 20. Also, as shown in
FIG. 2, the placement of two adjacent light directing elements is
such that the tip of one element, taken along an imaginary line
normal to the first surface of the base sheet (shown as dotted line
N), lies next to the base (shown as reference letter b) of the next
element. Other placement configurations can be used, so long as the
light directing elements provide the privacy feature and provided
that the h:P ratio falls within the established range. In this
particular embodiment, the light directing element includes either
light absorbing materials or light reflecting materials.
[0027] Suitable light reflecting materials include, e.g., titanium
dioxide, zinc oxide, zinc sulfide, zinc phosphate, calcium
carbonate, alumina, silica, antimony oxide, barium sulfate,
lithopene (a co-precipitate of barium sulfate and zinc oxide),
calcined kaolin, lead carbonate, magnesium oxide, and combinations
thereof. Suitable light absorbing materials include, e.g., carbon
black, spinel black, rutile black, iron black, and combinations
thereof. When a light reflecting material is used, 1 to 50 parts by
weight, based on 100 parts by weight total, is added to the polymer
resin to form the light directing elements. In some embodiments, 1
to 15 parts by weight is used. In other embodiments, 2 to 10 parts
by weight is used. When a light absorbing material is used, 0.1 to
50 parts by weight, based on 100 parts by weight total, is added to
the polymer resin to form the light directing elements. In some
embodiments 1 to 15 parts by weight of light absorbing material is
used. In other embodiments, 1 to 5 parts by weight is used. A
combination of light reflecting material and light absorbing
material can be used to form an individual light directing element,
as further discussed below. In other embodiments, color pigments,
fluorescent colors, and glitter can be added to the light directing
elements.
[0028] FIG. 3 shows a cross-sectional view of another embodiment of
the invention, where privacy film 100 includes base sheet 112
having opposing first surface 114 and second surface 116. Light
directing elements 118 protrude from the first surface of the base
sheet. Demarcation line 113 resides slightly within the light
directing element. In this particular embodiment, the light
directing element include first portion 119 disposed distal to the
first surface of the base sheet, second portion 117 disposed
proximate to the first surface, and third portion from the first
surface to line 113. In some embodiments, the composition of the
base sheet and the third portion will be similar, and may even be
the same. Line 115 demarcates the first portion from the second
portion. The first portion includes a light absorbing material and
the second portion includes a light reflecting material. The height
of the first portion is denoted as l.sub.119, and is the distance
along the minor axis of the element between line 115 and the tip.
The height of the second portion is denoted as l.sub.117 and is the
distance along the minor axis of the element between line 113 and
115. In one embodiment, the ratio of l.sub.119 to l.sub.117 is 3 to
0.1. The placement of two adjacent light directing elements is such
that the tip of one element, taken along imaginary line N overlaps
with the base of the next adjacent element. While the light
directing element of FIG. 2 includes a tip that is has
substantially straight edges, the tips can be rounded as shown in
FIG. 3. Other geometry can be used, so long as the light directing
elements interfere with light transmission so as to provide the
privacy feature.
[0029] FIG. 4 shows a cross-sectional view of another embodiment of
the present invention where privacy film 200 includes base sheet
212 having opposing first surface 214, second surface 216, and
demarcation line 213. Light directing elements 218 protrude from
the first surface. At the tips of the light directing elements,
light absorbing coating 219 has been applied. The coating may
migrate down the sides of the light directing elements. In this
particular embodiment, the light directing element could include
light reflecting materials. The coating can be applied to the
elements using known coating techniques. In one embodiment, the
coating is 0.01 to 1.0 mm in dry thickness. In one embodiment, the
light absorbing coating is applied to the tips using digital
printing methods, such as inkjet printing, color inkjet printing,
laser printing, and dye or mass transfer printing or by
conventional printing techniques, such as offset lithography,
flexography, and gravure. The tips of the elements are receptive to
the ink or the dyes used in the printing process.
[0030] FIG. 5 shows a cross-sectional view of another embodiment of
the present invention, where privacy film 300 includes base sheet
312 having opposing first surface 314 and second surface 316. Light
directing elements 318 protrude from the first surface of the base
sheet. For ease of understanding, only the cross-sections of five
light directing elements are shown. In this particular embodiment,
the cant angle of each light directing element differs from the
next adjacent element. For example, cant angle .theta..sub.1 will
be similar to cant angle .theta..sub.2. For example, .theta..sub.1
may be 90.degree. while .theta..sub.1 may be 88.degree.. Thus,
these two light directing elements will be substantially parallel
to one another. The cant angle for the fifth light directing
element, .theta..sub.5, however, may be very different than that of
the first light directing element. In this figure, if .theta..sub.1
is 90.degree., .theta..sub.5 may be 60.degree., so that the first
light directing element will not be considered to be parallel to
the fifth light directing element. The magnitude of the varying
change in cant angles has been exaggerated in this figure to
illustrate the varying cant angles.
[0031] FIG. 6 shows a cross-sectional view of yet another
embodiment of the present invention, where privacy film 400
includes base sheet 412 having opposing first surface 414, second
surface 416 and demarcation line 413. Light directing elements 418
protrude from the first surface. Each light directing element has
first portion 419 distal to the first surface of the base sheet and
second portion 417 proximate to the first surface. Line 415
demarcates the first portion from the second portion. Line 413
demarcates the second portion from a third portion. The first
portion has one-sided extension, similar to an upside down "L". The
extensions can all be on the same side, e.g., all left facing or
all right facing (as shown in the figure), or they can alternate
between left facing and right facing. The extensions can also be
randomly oriented to the left or to the right or at any angle
between the left and the right side. In other words, if one were to
take a top view of the embodiment of FIG. 6 so that all that would
be seen is first portion 419, it can be rotated at any of the
various angles along a 360.degree. path. In one embodiment, at
least one of the first and second portion includes light reflecting
materials. In another embodiment, the first portion includes light
absorbing materials and the second portion includes light
reflecting materials. In yet another embodiment, a combination of
different light directing elements, such as, e.g., the elements
shown in FIGS. 2, 3, and 6 are used together to form a privacy
film.
[0032] FIG. 1 shows the light directing elements as elongated rails
that run continuously along the length of a document. In other
embodiments, the elements can include interruptions, either of a
specified length to create uniform interruptions, or of a random
length to create non-uniform interruptions. Among all the various
elements, there could be light directing elements that are
continuous over the length of the entire substrate. For example,
FIG. 7 shows an illustrative privacy film 500 disposed on substrate
550. The privacy film includes light directing elements 518 having
uniform interruptions on the left hand side and non-uniform
interruptions on the right hand side. Interspersed in between are
light directing elements that are continuous over the entire length
of the film.
[0033] While the base sheet in all of the embodiments is light
transmissive, it may include light reflecting materials. The
quantity of light reflecting materials used in the base sheet can,
but does not have to, be similar to that used in the light
directing elements. The advantage of using similar amounts is that
the process of making the privacy film, as further described below,
can be simplified to using a single extruder instead of multiple
extruders. In the case where substantially the same amount is used,
care should be taken to select a sufficient amount to impart the
privacy feature to the film without adversely affecting the
readability of the underlying document.
[0034] Suitable materials for use in forming the privacy film
include thermoplastic polymers and elastomers. Suitable
thermoplastic polymers include, e.g., polyolefins such as
polypropylene or polyethylene, polystyrene, polycarbonate,
polymethyl methacrylate, ethylene vinyl acetate copolymers,
acrylate-modified ethylene vinyl acetate polymers, ethylene acrylic
acid copolymers, nylon, polyvinylchloride, and engineering polymers
such as polyketones or polymethylpentanes. Suitable elastomers
include, e.g., natural or synthetic rubber, styrene block
copolymers containing isoprene, butadiene, or ethylene (butylene)
blocks, metallocene-catalyzed polyolefins, polyurethane, and
polydiorganosiloxanes. Mixtures of thermoplastic polymers and
elastomers may also be used.
[0035] The inventive light directing element can be made in various
ways. In a first exemplary method, the privacy film of the present
invention can be formed by extruding a polymeric web through a die
having an opening cut, for example, by electron discharge
machining. The web would include the base sheet and the light
directing elements disposed thereon.
[0036] The shape of the die opening is designed to generate a web
with a desired cross-sectional shape or profile. The web can be
quenched after leaving the die opening by pulling it through a
quenching material such as water. A wetting agent may be added to
the quenching medium to wet the entire surface of the extruded web,
including spaces between the light directing elements. The extruded
web may be further processed, e.g., by applying a light absorbing
coating to the tips of the elements (as shown in FIG. 4) or by
cutting the extruded elements and stretching the web to form
discontinuous light directing elements.
[0037] When the inventive privacy film contains multiple different
layers, as when the base sheet and the light directing elements are
of different materials or as when the light directing elements
contain multiple sections (see, e.g., FIGS. 3 and 6), the film can
be formed by co extrusion techniques as described, e.g., in PCT
application WO 99/17630. The coextrusion technique may involve
passing different melt streams from different extruders into a
multiple-manifold die or multiple-layer feed block and a film die.
The individual streams merge in the feed block and enter the die as
a layered stack that flows out into layered sheets as the material
leaves the die.
[0038] A second exemplary method of making the privacy film is
shown schematically in FIGS. 8a, 8b, and 8c. In the method depicted
in FIG. 8a, polymeric material 801 and microstructured mold 800 are
provided. The microstructured mold includes a plurality of
elongated, slanted channels 808, each channel being separated from
the next by land region 806. Each channel has a base 808a disposed
adjacent to the land region and a tip 808b disposed distal to the
land region. In this embodiment, the channel may have substantially
linear walls with distinct sharp edges at the tip. Each channel
includes minor axis l that runs from the base to the tip. Each
channel is slanted at an angle of greater than 15.degree. and less
than 90.degree.. In another embodiment, each channel is slanted at
angle of greater than 40.degree. and less than 85.degree.. In yet
another embodiment, each channel is slanted at angle of greater
than 55.degree. and less than 75.degree.. The angle is formed
between the intersection of the minor axis of the channel and a
line lying in the plane of the land region. Similar to the light
directing element as discussed in FIG. 2, each channel in the mold
has a height h, as measured its base to its tip along the minor
axis. Two adjacent channels have a center-to-center spacing of P.
In one embodiment, the mold has h to P ratio of 0.5 to 5.
[0039] Two adjacent channels are placed such that, as viewed from
an imaginary line normal to the land region, the tip of one channel
coincides with the base of the next channel. This feature is
similar to that shown in FIG. 2. In an alternative embodiment, two
channels are placed such that, as viewed from the imaginary line,
the tip of one channel overlaps the base of the next channel. The
polymeric material is deposited onto the microstructured mold. FIG.
8a also shows schematically, by use of plunger 804, that the
polymeric material is induced into the channels of the
microstructured mold by use of heat and or pressure.
[0040] FIG. 8b shows a subsequent step in the process where the
polymeric material has flowed into and filled the channels thereby
replicating the shape of the channels. The replicated polymeric
material solidifies in the mold. The term "solidifies" means
generally that the polymeric material cools and hardens
sufficiently to allow it to be separated from the mold. In one
process, the polymeric material includes light reflecting material,
such as the ones listed above. When used, the light reflecting
material constitutes less than 20%, and in some embodiments, less
than 5% of the total weight of the polymeric material.
[0041] FIG. 8c shows yet another step in the process where the
replicated polymeric material has been separated from the mold to
yield privacy film 810 having a plurality of distinct light
directing elements 818, each connected to another by a polymeric
base sheet 812 having first surface 812a from which the light
directing elements protrude and opposing second substantially
planar surface 812b. The separation step results in substantially
no distortion on the light directing elements of the privacy film.
That is, when the replicated polymeric material is separated from
the mold, each light directing elements of the resulting privacy
film is nearly an exact replica of its corresponding channel, so
that there would be less than 20% and preferably less than 10%
variation in the dimensions of the light directing element as
compared to the dimensions of the corresponding channel. FIG. 8c
further shows light transmissive adhesive 819 is disposed on the
second substantially planar surface of the polymeric base
sheet.
[0042] The polymeric material can be in the form of a thermoplastic
material, such as a thermoplastic film, a molten resin, or a liquid
resin. When in the thermoplastic film form, a combination of heat
and pressure can be used to induce the polymeric material to flow
into the channels. Such a method can be generally described as
compression molding and are discussed in publications such as U.S.
Pat. No. 4,244,683 (Rowland) and U.S. Pat. No. 4,601,861 (Pricone
et al.). In the molten resin state, the heat of the molten resin,
along with heating the mold are useful steps in inducing it to flow
into the channels. U.S. Pat. No. 4,097,634 (Bergh) discloses an
exemplary extrusion cast and embossing method. In a liquid resin
state, heat and or pressure can be used to induce the polymeric
material to flow into the channels. Useful liquid resins are light
curable resins, such as an ultraviolet light curable resin. In such
a case, the solidifying step will involve exposing the light
curable resin to a light source. U.S. Pat. No. 3,869,346 (Rowland);
U.S. Pat. No. 4,576,850 (Martens); and U.S. Pat. No. 5,183,597 (Lu
et al.) disclose exemplary liquid cast and light curing processes.
These patents are incorporated by reference in their entirety.
[0043] The polymeric material may include at least two layers,
i.e., it may be of a multilayer construction. In one embodiment,
the polymeric material includes a first layer that is substantially
free of light absorbing and light reflecting materials and a second
layer that comprises light absorbing materials, light reflecting
materials, or a combination thereof. In such cases, the channels of
the microstructured mold contacts the layer containing the light
absorbing and/or light reflecting materials.
EXAMPLE
Example 1
[0044] A privacy film, made generally according to FIGS. 8a to 8c
as follows. A microstructured tool was made by machining a copper
plate to impart channels thereto. Each channel had a height
dimension of 19.3 mil (0.5 mm) measured along its minor axis and
slanted at an angle of 63.1 degrees. The tip of each channel had a
dimension of 3.8 mil. The base of each channel had a dimension of
6.9 mil (0.18 mm), as measured along a line that lies in the same
plane as the land region. As measured near the base along a line
that is parallel to the tip, the base had a dimension of 5.5 mil
(0.14 mm). The land region distance between one edge of a channel
to the nearest edge of the next adjacent angle was 4.9 mil (0.12
mm).
[0045] A polypropylene film containing 2% by weight of TiO.sub.2
pigment was used as the thermoplastic polymeric film. The
polypropylene film was 5 mil (0.13 mm) thick. The film was induced
to flow into the channels using a heat press set at 170.degree. C.
under a pressure of 160 pounds per square inch (psi) for 30
seconds. The compression molded film was cooled to 100.degree. C.
under the same pressure, after which time it was separated from the
mold to yield a privacy film having a plurality of light directing
elements connected to one another by a base substrate. A small
amount of black ink was applied to the top of the light directing
elements.
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