U.S. patent application number 12/174652 was filed with the patent office on 2008-11-06 for process and apparatus for microreplication.
Invention is credited to Rishikesh K. Bharadwai, Eng-Pi Chang, Hsiao Ken Chuanq, David N. Edwards, Robert J. Fermin, Ali R. Mehrabi, Reza Mehrabi, Ronald F. Sieloff, Chunhwa Wang, Philip Yi Zhi Chu.
Application Number | 20080274225 12/174652 |
Document ID | / |
Family ID | 32233316 |
Filed Date | 2008-11-06 |
United States Patent
Application |
20080274225 |
Kind Code |
A1 |
Bharadwai; Rishikesh K. ; et
al. |
November 6, 2008 |
PROCESS AND APPARATUS FOR MICROREPLICATION
Abstract
A method of embossing a sheet material includes: heating at
least a portion of the sheet directly or indirectly with radiant
energy from a radiant energy source; pressing a tool against the
heated portion of the sheet, thereby patterning a surface of the
sheet; and separating the sheet and the tool. The radiant energy
may travel through a solid material that is relatively transparent
to radiation, on its way to being absorbed by a
relatively-absorptive material. The relatively-transparent material
may be an unheated portion of the sheet, and the
relatively-absorptive material may be either the tool or the heated
portion of the sheet. Alternatively, the relatively-transparent
material may be the tool, and the relatively-absorptive material
may be all or part of the sheet. The method may be performed as one
or more roll-to-roll operations.
Inventors: |
Bharadwai; Rishikesh K.;
(Chino Hills, CA) ; Chang; Eng-Pi; (Arcadia,
CA) ; Yi Zhi Chu; Philip; (Monrovia, CA) ;
Chuanq; Hsiao Ken; (Arcadia, CA) ; Edwards; David
N.; (La Canada-Flintridge, CA) ; Fermin; Robert
J.; (La Verne, CA) ; Mehrabi; Ali R.;
(Glendale, CA) ; Mehrabi; Reza; (Tujunga, CA)
; Sieloff; Ronald F.; (Chardon, OH) ; Wang;
Chunhwa; (Diamond Bar, CA) |
Correspondence
Address: |
Jonathan A. Platt;RENNER, OTTO, BOISSELLE & SKLAR, LLP
1621 Euclid Avenue, 19th Floor
Cleveland
OH
44115
US
|
Family ID: |
32233316 |
Appl. No.: |
12/174652 |
Filed: |
July 17, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11047300 |
Jan 31, 2005 |
7416692 |
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12174652 |
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10634104 |
Aug 4, 2003 |
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11047300 |
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60400755 |
Aug 2, 2002 |
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60438194 |
Jan 6, 2003 |
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Current U.S.
Class: |
425/174.4 |
Current CPC
Class: |
B29C 35/0272 20130101;
Y10T 156/1023 20150115; Y10T 156/1041 20150115; B29C 2035/0822
20130101; B29C 59/04 20130101; Y10T 156/1737 20150115; B29C 59/02
20130101; B29C 35/0888 20130101 |
Class at
Publication: |
425/174.4 |
International
Class: |
B29C 35/08 20060101
B29C035/08 |
Claims
1. An embossing system, comprising: a plurality of rollers, arrayed
on opposite sides of a passage for receiving therein a sheet
material to be embossed; a radiant heater operatively configured to
heat the sheet material while in the passage; and a patterned belt
in the passage, for patterning the sheet material.
2. The system of claim 1, wherein the radiant heater includes
radiant energy sources; and wherein the radiant heater further
includes one or more reflectors operatively coupled to the at least
some of the radiant energy sources, to thereby direct radiant
energy from the radiant energy sources to the passage.
3. The system of claim 2, wherein in radiant energy sources and the
reflectors are in at least some of the rollers; and wherein the at
least some of the rollers include radiantly-transparent roller
material that allows radiant energy from the radiant energy sources
to pass therethrough.
4. The system of claim 1, wherein in radiant energy sources are in
at least some of the rollers; and wherein the at least some of the
rollers include radiantly-transparent roller material that allows
radiant energy from the radiant energy sources to pass
therethrough.
5. An embossing system, comprising: a pair of belts arrayed on
opposite sides of a passage for receiving therein a sheet material
to be embossed; and a radiant heater operatively configured to heat
the sheet material while in the passage.
6. The system of claim 5, wherein one of the belts includes a
radiantly-transparent material; and wherein the radiant heater is
configured to pass radiant energy into the passage through the
radiantly-transparent material.
7. The system of claim 6, wherein the other belt includes a
radiantly-absorptive material.
8. The system of claim 5, wherein the radiant heater includes: at
least one radiant energy source that produces radiant energy; and
at least one reflector; and wherein the at least one radiant energy
source and the at least one reflector are configured such that the
at least reflector directs at least some of the radiant energy
toward the passage.
9. An embossing system, comprising: a pair of press platforms
configured to press a sheet material therebetween; and a radiant
heater configured to deliver radiant energy between the press
platforms.
10. The system of claim 9, wherein one of the press platforms
includes a radiantly-transparent material; and wherein the radiant
heater is configured to pass the radiant energy through the
radiantly-transparent material.
11. The system of claim 10, further comprising a pressure-producing
device operatively coupled to the press platforms to press the
platforms together.
Description
[0001] This application is a divisional of U.S. application Ser.
No. 11/047,300, filed Jan. 31, 2005, which is a continuation of
U.S. application Ser. No. 10/634,104, filed Aug. 4, 2003, now
abandoned, which claims the benefit under 35 USC 119(e) of U.S.
Provisional Application No. 60/400,755, filed Aug. 2, 2002, and of
U.S. Provisional Application 60/438,194, filed Jan. 6, 2003. All of
the above applications are herein incorporated by reference in
their entireties.
TECHNICAL FIELD
[0002] The present invention relates to a process and apparatus for
embossing material with precise detail, and more particularly, to a
process and apparatus for making products having surfaces with
precision microstructures. The invention also pertains to sheeting,
such as synthetic resinous sheeting, especially adapted for use
with said process and apparatus.
BACKGROUND OF THE RELATED ART
[0003] Processes and apparatus for embossing precision optical
patterns such as microcubes, in a resinous sheet or laminate, are
well known as referenced in U.S. Pat. Nos. 4,486,363; 4,478,769;
4,601,861; 5,213,872; and 6,015,214, which patents are all
incorporated herein by reference. In the production of such
synthetic resin optical sheeting, highly precise embossing is
required because the geometric accuracy of the optical elements
determines its optical performance. The above referenced patents
disclose particular methods and apparatus for continuously
embossing a repeating retro-reflective pattern of fine or precise
detail on one surface of a transparent thermoplastic material film
to form the surface of the film into the desired microstructure
pattern.
[0004] Besides precision optical sheeting, various other
applications have been developed requiring the formation of highly
precise shapes and structures in resinous film. Such applications
include (in addition to optical applications) micro-fluidic,
micro-electrical, micro-acoustic, and micro-mechanical
applications. Such applications require the embossing of
thermoplastic material to provide precisely formed functional
geometric elements, or arrays of such functional geometric elements
on the film surface.
[0005] These geometric elements, or precision microstructures, are
defined by any or all of the following characteristics: precise
embossing depths; flat surfaces with precise angular orientation;
fine surface smoothness; sharp angular features with a very small
radius of curvature; and precise dimensions of the elements and/or
precise separation of the elements, within the plane of the film.
The precise nature of the formed surface is critical to the
functional attributes of the formed products, whether used for
microcubes or other optical features; or as channels for
microfluidics, or in fuel cells; or for accurate dimensions,
flatness and spacing when providing a surface for holding
nanoblocks in fluidic self assembly (FSA) techniques; or imparting
a microtextured surface that is not optically smooth.
[0006] U.S. patents describing some uses of precise microstructures
include: U.S. Pat. Nos. 4,486,363; 6,015,214 (microcubes);
5,783,856; 6,238,538 (microfluidics); and 6,274,508 (FSA).
[0007] As described in some of the above mentioned patents, such as
U.S. Pat. Nos. 4,486,363, 4,601,861, and 4,478,769, embossed
microstructure film may be made on a machine that includes two
supply reels, one containing an unprocessed film of thermoplastic
material, such as acrylic or polycarbonate, or even vinyl, and the
other containing a transparent and optically smooth plastic carrier
film such as Mylar, which should not melt or degrade during the
embossing process. These films are fed to and pressed against a
heated embossing tool that may take the form of a thin endless
flexible metal belt. The belt creates the desired embossed pattern
on one surface of the thermoplastic film, and the carrier film
makes the other surface of the thermoplastic film optically
smooth.
[0008] The belt moves around two rollers that advance the belt at a
predetermined linear controlled speed or rate. One of the rollers
is heated and the other roller is cooled. An additional cooling
station, e.g. one that blows cool air, may be provided between the
two rollers. Pressure rollers are arranged about a portion of the
circumference of the heated roller. Embossing occurs on the web as
it and the tool pass around the heated roller and while pressure is
applied by one or more pressure rollers causing the film to be
melted and pressed onto the tool. A backing film such as Mylar.RTM.
may be used in order to create an optically smooth surface on the
non-embossed surface of the film. The embossed film, (which may
have been laminated to other films during the embossing process),
is cooled, monitored for quality and then moved to a storage
winder. At some point in the process, the Mylar.RTM. film may be
stripped away from the embossed film.
[0009] The prior apparatus and process work well to produce rolls
of film that are effectively 48'' (122 cm) wide (52''/132 cm at
salvage), but such equipment and processes have several inherent
disadvantages. The process speed (and thus the volume of material)
is limited by the time needed to heat, mold and freeze the film.
Also, the pressure surface area and thus the time available to
provide adequate pressure by the pressure rollers, and then cooling
the material, impose certain special constraints.
[0010] The prior apparatus and process of U.S. Pat. Nos. 4,486,363,
4,601,861, and 4,478,769, and other embossing processes discussed
below, depend on heating a preformed synthetic resinous sheeting
above its glass transition temperature or melting temperature in
order to emboss the sheeting while in a molten state. The embossing
apparatus includes a heated roller with internal passages for
circulation of hot oil. Typical temperatures of the heated roller
are 425.degree. F. to 475.degree. F., possibly as high as
500.degree. F. U.S. Pat. No. 4,486,363 also includes a limited
disclosure (without explanatory details) of an alternative
embodiment using an infrared heater or other radiant heater.
[0011] One earlier prior device for forming microcubes while in a
planar condition is illustrated in U.S. Pat. No. 4,332,847, and
involves indexing of small (9''.times.9'' or 22.86 cm.times.22.86
cm) individual molds at a relatively slow speed (See Col. 11, lines
31-68). That process is not commercially practical because of its
perceived inability to accurately reproduce microstructures because
of indexing mold movement and the relatively small volume (caused
by mold size) and speed. Also, the equipment and process is
non-continuous. The '847 patent discloses the use of platens that
are heated by electric cartridge heaters, as well as platens that
are heated using hot oil.
[0012] U.S. Pat. No. 5,945,042 discloses an embossing apparatus in
which synthetic resin sheeting is fed to a thermoforming zone while
in a "flow temperature region" of the resinous material; this can
be accomplished by extruding molten resinous sheeting to feed to
the thermoforming zone, or by pre-heating preformed resinous
sheeting. The '042 patent discloses, as to means for pre-heating
the resinous sheeting, passing the sheeting between two heated
rollers. It is said that "indirect heating devices such as a hot
blast heater, a near-infrared lamp heater and a far-infrared lamp
heaters may be used in combination". The '042 patent also discloses
heating the thermoforming roll from within using dielectric heaters
or using a heated circulating medium. This heat source during
thermoforming can be supplemented by "auxiliary means . . . such as
a hot blast heater, a near-infrared lamp heater and a far-infrared
lamp heater". No specifics are given as to these heat sources and
their operation in heating the sheeting.
[0013] U.S. Pat. No. 6,096,247 discloses a process and apparatus
for making an embossed optical polymer film. A heat flux is
provided by either a flame burner or a flameless radiant burner to
soften at least one surface of a polymer film. The film then is
passed through an embossing nip to form embossments on the softened
surface of the film. This embossed surface is then cooled to fix
the structure of the embossments. It is said that the time required
to heat, emboss, and cool the embossed optical polymer film ranges
from about 0.05 to about 1 second, depending in part on the
temperature sensitivity of the optical film being embossed.
International patent application PCT/US01/18655 (publication no. WO
01/98066) discloses a process and apparatus for forming
thermoplastic products having precise embossed surfaces, using a
continuous double band press. This apparatus includes continuous
flat beds with two endless bands or belts, preferably of steel,
running above and below the product and around pairs of upper and
lower drums or rollers. An advantage of such presses is the mainly
uniform pressure that can be provided over a large area. This
machine forms a pressure or reaction zone between the two belts and
has the advantage that pressure is applied to a product when it is
flat rather than when it is curved.
[0014] The machine is based upon a fluid or air cushion press,
which uses a cushion of air to reduce friction between the belt and
the rest of the machine. It was conceived by applicants of the
above-identified application that this type of press may be
suitable for precision embossing of microstructures. The fluid
cushion press is sometimes associated with the term "isobaric." In
an isobaric press, heat generally does not come from rollers or
drums; rather the fluid, i.e. air, provides it. The fluid transfers
heat to the steel belts that in turn transfer the heat to the
material passing through the press. This provides one advantage
over certain prior art forms of embossing equipment--the ability to
heat the film to be embossed from both sides.
[0015] It will be appreciated from the above discussion that many
approaches have been undertaken with regard to embossing of
microstructures, and that there is further room for improved
microstructure methods and products.
SUMMARY OF THE INVENTION
[0016] According to an aspect of the invention, a method of
embossing a sheet material includes: heating at least a part of the
sheet; pressing a patterned tool against a surface of the at least
a part of the sheet, thereby patterning a surface of the sheet; and
separating the tool from the surface. The heating includes radiant
heating using radiant energy from a radiant energy source. The
heating includes passing the radiant energy from the radiant energy
source through a relatively radiantly-transparent solid material
before absorbing the radiant energy in a relatively
radiantly-absorptive solid material. The relatively
radiantly-transparent solid material has a lower absorptivity of
the radiant energy than does the relatively radiantly-absorptive
solid material.
[0017] According to another aspect of the invention, a method of
embossing a sheet material includes: radiantly heating a relatively
radiantly-absorptive portion of the sheet, using radiant energy
from a radiant energy source; pressing a patterned tool against a
surface of the relatively radiantly-absorptive portion of the
sheet, thereby patterning a surface of the sheet; and separating
the tool from the surface. The heating includes passing the radiant
energy through a relatively radiantly-transparent portion of the
sheet before absorbing the radiant energy in the relatively
radiantly-absorptive portion of the sheet. The relatively
radiantly-transparent portion has a lower absorptivity of the
radiant energy than does the relatively radiantly-absorptive
portion.
[0018] According to yet another aspect of the invention, a method
of embossing a sheet material includes: radiantly heating a
relatively radiantly-absorptive portion of the sheet, using radiant
energy from a radiant energy source; pressing a patterned tool
against the relatively radiantly-absorptive portion of the sheet,
thereby patterning a surface of the sheet; and separating the tool
from the surface. The sheet material is relatively radiantly
transparent. The heating includes passing the radiant energy
through the sheet before absorbing the radiant energy in the
patterned tool. The sheet material has a lower absorptivity than
the patterned tool. According to still another aspect of the
invention, a method of embossing a sheet material includes:
pressing a patterned tool against the sheet; and, while maintaining
the pressing, radiantly heating the sheet, using near-infrared
radiant energy from a radiant energy source. The radiantly heating
includes passing the radiant energy through a relatively
radiantly-transparent material in contact with the sheet.
[0019] According to a further aspect of the invention, an embossing
system includes a plurality of rollers, arrayed on opposite sides
of a passage for receiving therein a sheet material to be embossed;
and a radiant heater operatively configured to heat the sheet
material while in the passage.
[0020] According to a still further aspect of the invention, an
embossing system includes a pair of belts arrayed on opposite sides
of a passage for receiving therein a sheet material to be embossed;
and a radiant heater operatively configured to heat the sheet
material while in the passage.
[0021] According to another aspect of the invention, an embossing
system includes a pair of press platforms configured to press a
sheet material therebetween; and a radiant heater configured to
deliver radiant energy between the press platforms.
[0022] According to still another aspect of the invention, a method
of embossing a sheet material includes: radiantly heating the sheet
material, using radiant energy from a radiant energy source; and
pressing patterned tools against opposite major surfaces of the
sheet material.
[0023] According to yet another aspect of the invention, an
embossing system includes: a plurality of rollers, arrayed on
opposite sides of a passage for receiving therein a sheet material
to be embossed; a radiant heater operatively configured to heat the
sheet material while in the passage; and a patterned belt in the
passage, for patterning the sheet material.
[0024] According to a further aspect of the invention, an embossing
system includes: a pair of belts arrayed on opposite sides of a
passage for receiving therein a sheet material to be embossed; and
a radiant heater operatively configured to heat the sheet material
while in the passage.
[0025] According to a still further aspect of the invention, an
embossing system includes: a pair of press platforms configured to
press a sheet material therebetween; and a radiant heater
configured to deliver radiant energy between the press
platforms.
[0026] According to another aspect of the invention, a method of
embossing a sheet material includes the steps of radiantly heating
the sheet material, using radiant energy from a radiant energy
source; and pressing patterned tools against opposite major
surfaces of the sheet material.
[0027] According to an aspect of the invention, a method of
embossing an optical film includes: providing an optically
anisotropic, uniaxially oriented film; heating a patterned tool
using radiant energy from a radiant energy source, wherein the
pattern comprises a plurality of parallel raised microstructures
having a longitudinal direction; pressing the tool against the a
surface of the oriented film such that the longitudinal direction
of the raised microstructures is substantially parallel to the
direction of orientation of the polymer substrate, thereby
patterning a surface of the oriented film. In one aspect of the
invention, v-shaped grooves are embossed into the surface of the
oriented film.
[0028] In one form of the invention, the optical film comprises a
transparent embossed polymeric film having a plurality of v-shaped
microchannels therein. The term "transparent" as used throughout
the specification and claims means optically transparent or
optically translucent. The embossed film is a uniaxially oriented
film wherein the direction of orientation is substantially parallel
to the longitudinal direction of the v-shaped microchannels, and
wherein the orientation of the embossed polymer film is unchanged
throughout the polymer substrate and first major surface.
[0029] To the accomplishment of the foregoing and related ends, the
invention comprises the features hereinafter fully described and
particularly pointed out in the claims. The following description
and the annexed drawings set forth in detail certain illustrative
embodiments of the invention. These embodiments are indicative,
however, of but a few of the various ways in which the principles
of the invention may be employed. Other objects, advantages and
novel features of the invention will become apparent from the
following detailed description of the invention when considered in
conjunction with the drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0030] In the annexed drawings, which are not necessarily to
scale:
[0031] FIG. 1 is a timeline schematically illustrating an embossing
method in accordance with the present invention;
[0032] FIG. 1A is a chart showing energy emission characteristics
of a blackbody emitter;
[0033] FIG. 1B is a chart showing energy emissions characteristics
for various blackbody emitters;
[0034] FIG. 1C is a chart showing the spectral absorption of an
exemplary sheeting material for use in the present invention;
[0035] FIG. 1D is a chart showing the spectral absorption of an
exemplary tooling material over the same range of wavelengths shown
in FIG. 1D;
[0036] FIG. 2 is a schematic diagram illustrating radiant heating
according to one embodiment of the present invention;
[0037] FIG. 3 is a schematic diagram illustrating radiant heating
according to another embodiment of the present invention;
[0038] FIG. 4 is a schematic diagram illustrating radiant heating
according to yet another embodiment of the present invention;
[0039] FIG. 5 is a side view of an embossing system in accordance
with the present invention;
[0040] FIG. 6 is a detailed side view of parts of one embodiment of
the embossing system of FIG. 5;
[0041] FIG. 7 is a detailed side view of parts of another
embodiment of the embossing system of FIG. 5;
[0042] FIG. 7A is a detailed side view of parts of yet another
embodiment of the embossing system of FIG. 5;
[0043] FIG. 8 is a side view of parts of an alternate embodiment
embossing system in accordance with the present invention;
[0044] FIG. 9 is a side view of another alternate embodiment
embossing system in accordance with the present invention;
[0045] FIG. 10 is a side view of yet another alternate embodiment
embossing system in accordance with the present invention;
[0046] FIG. 10A is a side view of still another alternate
embodiment embossing system in accordance with the present
invention;
[0047] FIG. 10B is a side view of a further alternate embodiment
embossing system in accordance with the present invention;
[0048] FIG. 10C is a side view of a still further alternate
embodiment embossing system in accordance with the present
invention;
[0049] FIG. 11 is an isometric view of a sheet material with posts,
embossed in accordance with the present invention;
[0050] FIG. 12 is an isometric view of a sheet material with ribs,
embossed in accordance with the present invention;
[0051] FIG. 13 is an isometric view of a sheet material with
recesses, embossed in accordance with the present invention;
[0052] FIG. 14 is an isometric view of a sheet material with
faceted protrusions, embossed in accordance with the present
invention;
[0053] FIG. 15 is a side view of another alternate embodiment
embossing system, for embossing both sides of a sheet material, in
accordance with the present invention;
[0054] FIG. 16 is a side view of part of the system of FIG. 15,
illustrating the alignment process;
[0055] FIG. 17 is a side view of part of the system of FIG. 15,
illustrating the embossing process;
[0056] FIG. 18 is a side view of one embodiment of a product that
may be produced using the system of FIG. 15;
[0057] FIG. 19 is a side view of another embodiment of a product
that may be produced using the system of FIG. 15;
[0058] FIG. 20 is a side view of yet another one embodiment of a
product that may be produced using the system of FIG. 15;
[0059] FIG. 21 is a side view of still another embodiment of a
product that may be produced using the system of FIG. 15;
[0060] FIG. 22 is a side view of a first embodiment multi-layer
product that may be embossed according the present invention;
[0061] FIG. 23 is a side view of a second embodiment multi-layer
product that may be embossed according the present invention;
[0062] FIG. 24 is a side view of a third embodiment multi-layer
product that may be embossed according the present invention;
[0063] FIG. 25 is a side view of a part of one embodiment of an
embossing system that utilizes a stencil, in accordance with the
present invention;
[0064] FIG. 26 is a side view of a part of another embodiment of an
embossing system that utilizes a stencil, in accordance with the
present invention;
[0065] FIG. 27 is a plan view of a stencil for use with the systems
of FIGS. 25 and 26;
[0066] FIG. 28 is a plan view of sheet of material with selectively
applied radiation-absorbing material, in accordance with the
present invention;
[0067] FIG. 29 is a cross-sectional view of an embossed film in
accordance with the present invention
[0068] FIG. 30 is a perspective view of an embossed film in
accordance with the present invention; and
[0069] FIG. 31 is a cross-sectional view of a lightguide
incorporating the embossed film of the present invention.
DETAILED DESCRIPTION
[0070] A method of embossing a sheet material includes: heating at
least a portion of the sheet directly or indirectly with radiant
energy from a radiant energy source; pressing a tool against the
heated portion of the sheet, thereby patterning a surface of the
sheet; and separating the sheet and the tool. The radiant energy
may travel through a solid material that is relatively transparent
to radiation, on its way to being absorbed by a
relatively-absorptive material. The relatively-transparent material
may be an unheated portion of the sheet, and the
relatively-absorptive material may be either the tool or the heated
portion of the sheet. Alternatively, the relatively-transparent
material may be the tool, and the relatively-absorptive material
may be all or part of the sheet. The method may be performed as one
or more roll-to-roll operations. Alternatively or in addition, the
method may include one or more batch processes.
[0071] In the following description, first a general outline of
embossing methods is given. Then examples are given of several
apparatuses suitable for carrying out various embodiments of the
method.
[0072] The time chart of FIG. 1 shows the chronological sequence of
heat application, pressure application and other processing stages
within a cycle of a method 1 for molding or embossing precision
microstructures. (The terms "molding" and "embossing" are intended
here to identify the same process for forming molten sheeting under
heat and pressure). During an initial preparation stage 2, a
preformed polymeric film or sheeting to be molded or embossed may
be prepared, e.g., by cleaning. The sheeting or film is then
delivered (e.g., as a solid web or sheet) to the molding zone where
molding occurs in a molding stage 4, under conditions of elevated
temperature and elevated pressure. A freezing stage 5 to set the
molded pattern follows molding stage 4. Then the sheeting is
removed from the molding/embossing apparatus in a de-molding stage
6. Typically, during part or all of the molding stage 4, including
the possibility of multiple intervals within that stage (e.g. with
multiple pressure nips), the sheeting is subjected to high
pressure. In the schematic of FIG. 1, continuous application of
pressure is shown at 7. Likewise, during part or all of the molding
stage 4, including the possibility of multiple intervals within
that stage, the sheeting is subjected to high temperature (e.g.
above the glass transition temperature or melting temperature of a
thermoplastic material of the sheeting). In the schematic of FIG.
1, three heating intervals 8a, 8b, and 8c are shown with
intermediate "hold" (no heating or cooling) intervals 9a and 9b.
The chronological relationships of subprocesses may be different
from that illustrated in FIG. 1; for example, heating may commence
before or after application of pressure. During and/or after the
high pressure and heating conditions are terminated, the sheeting
is subjected to cooling in order to effect the freezing stage
5.
[0073] "Radiant energy" is broadly defined as radiation of whatever
wavelength, which transfers heat or energy by photons, as opposed
to by the mechanisms of other heat transfer modes such as
convection or conduction. The term "radiant energy source" is used
herein to denote a generator or other source of radiant energy,
while the terms "radiant heater" and "radiant heating system" are
used to denote radiant energy sources as well as other associated
components, such as reflectors.
[0074] The methods and systems described herein use radiant energy
as the sole or primary heat source in carrying out a heat plus
pressure embossing process of the type schematically illustrated in
FIG. 1; such a process can be used for example to emboss precision
microstructures that are difficult or impossible to mold or emboss
using more conventional processing techniques. Optionally the
sheeting also may be subjected to pre-heating prior to the molding
stage 4, i.e. during preparation, and this pre-heating may be
effected using any suitable process not necessarily involving
radiant energy.
[0075] The use of thermal radiation as the sole or primary heat
source in the embossing process described herein may offer one or
more various significant advantages: [0076] (a) Radiant energy heat
transfer, in comparison to conductive and convective heat transfer,
is capable of achieving significantly higher heat fluxes and
embossing temperatures. This opens up a broad range of process
capabilities, for example in the embossing of very high T.sub.g
thermoplastic polymers. [0077] (b) Radiant energy heating offers
various means precisely to control heat transfer to materials to be
embossed, and other elements of the system, that cannot be achieved
through conductive and convective heating. This includes for
example control of the thermal radiation source e.g. via
reflection, focusing, filtering, etc. to regulate the spectral and
geometric distribution of the radiation. Another example of
controlled radiant heat transfer is designing the material or
sheeting construction to be embossed, e.g. through doping or
multilayer structures, to regulate absorption of the thermal
radiation. Controlled radiant heating can achieve various process
improvements, such as reduction of the cooling requirements of the
system, and improved embossing precision via coordination between
localized heat and pressure during embossing. [0078] (c) Radiant
energy heating can be combined with other modes of heat transfer,
for example conductive heating, to achieve advantageous effects.
These effects can be achieved using only a radiant heat source,
since the thermal radiation heat transfer can heat structures of
the embossing system (particularly the embossing tooling) which in
turn may transfer heat to the material to be embossed via
conduction. [0079] (d) Radiant energy can provide extremely rapid
heating because of the high speed of light. [0080] (e) Radiant
energy heating can be incorporated in continuous and non-continuous
embossing systems, with effective interaction of key subsystems
including radiant heat source optics, embossing tooling,
pressurizing structures, and mechanisms for handling webstock or
sheetstock to be embossed.
[0081] In addition, numerical simulations indicate significant and
qualitative differences between radiation and other heating
methods, e.g. purely conductive heating. The surface temperature of
the sheet material (film) rises sharply in the conductive process
versus the smooth rise in for NIR or other radiative heating. In
the conductive process as the hot tool comes in contact with the
film, it raises the film surface temperature quickly. This causes a
large temperature gradient in the film; therefore, heat propagates
quickly into the thin film. As the temperature of the film rises
and temperature difference decreases, heat transfer slows. By
contrast, in the NIR or other radiative process, heat is
continually generated on the tool surface, so the temperature of
the tool surface rises as a function of time. Because of the
thermal resistance of the sheet material, the top (away from the
tool) temperature of the sheet material lags that of the bottom
(next to the tool). This temperature difference increases because
more heat is generated on the surface of the tool that can be
conducted away from it. As the tool is made thinner, the
temperature profile for conductive tool heating does not change
very much. The initial rise of the film surface temperature becomes
steeper for thinner tools because the heat resistance of the tool
is less. The effect of tool thickness is much more pronounced in
the case of radiative heating. The thinner the tool is, the higher
the maximum temperature of the film. As the tool is made thinner
and the surface temperature rises, the higher temperature
difference leads to larger conduction of the heat away from the
tool. Thus temperature will tend to increase faster initially and
more slowly later. In summary, radiant heating more readily adapts
heat output to the requirements of a given system, than does
conductive heating. Higher temperatures are made possible just by
increasing the duration of radiant heating. Also, it is possible to
change temperature by changing the thickness of the tool, i.e. its
thermal mass. Use of a thinner tool results in higher temperatures,
because the same flux is applied to less tool material.
[0082] The foregoing advantages derive from the physical
characteristics of radiant energy (thermal radiation). Whereas the
transfer of heat energy by conduction and convection depends on
temperature differences of locations approximately to the first
power, the transfer of energy by thermal radiation depends on
differences of individual absolute temperatures of bodies each
raised to a power of 4. Because of this characteristic, thermal
radiation effects are intensified at high absolute temperature
levels.
[0083] In a preferred embodiment, the radiant energy source is a
blackbody emitter that has an energy emission characteristic of the
type shown in FIG. 1A. Particularly preferred is high energy near
infrared radiant (NIR) heating systems. The preferred radiant
heating systems use near-infrared radiation operating at or above
2000K, preferably at or above 3000K. The energy outputs of these
emitters are several orders-of-magnitude larger than those of
short-wave and medium-wave infrared emitters, and provide high heat
fluxes that can be critical for effective heat-plus-pressure
precision embossing. Besides the peak wavelength of the output, the
emitter operating temperature affects the total energy output;
increasing the emitter temperature shifts the peak to a shorter
wavelength as well as provides a higher energy output. Various
blackbody emissions illustrating these variables are shown in FIG.
1B.
[0084] A preferred line of commercially available high-energy NIR
systems is supplied by AdPhos AG, Bruckmuhl-Heufeld, Germany
(AdPhos). AdPhos infrared heating systems provide durable, high
energy heating systems; and an AdPhos lamp acts as a blackbody
emitter operating at about 3200K. Other radiant heaters and
emitters that provide suitable thermal energy are available from
various major lamp manufacturers (including Phillips, Ushio,
General Electric, Sylvania, and Glenro). For example, these
manufacturers produce emitters for epitaxial reactors used by the
semiconductor industry. All of these emitters have temperatures
over 3000 K. More broadly, however, suitable NIR sources may be
emitters with temperatures over about 2000 K. An advantage of the
AdPhos system is that whereas most such high energy NIR lamps have
a rated life of less than 2000 hours, the AdPhos NIR systems are
designed for 4000 to 5000 hours of service life. The radiant energy
emissions of the AdPhos lamps have most of their energy in a
wavelength range of between 0.4 to 2 microns, which is shifted to a
lower wavelength than short-wave and medium-wave infrared sources,
providing a higher energy output and other advantages in absorption
of the thermal radiation as explained below. Advances in emitter
design, in terms of power spectrum, energy output, and durability
for industrial applications, have been realized in the past
decade.
[0085] Blackbody radiation heat sources offer total emissive powers
that have a power-of-4 relationship with the peak temperature.
Another significant characteristic is the spectral distribution of
the radiation. As illustrated below, the spectral distribution of
emissive power bears an important relationship to the spectral
distribution of absorption characteristics of the material to be
embossed, as well as the absorption characteristics of other parts
of the embossing system that are subjected to the emitted radiant
energy.
[0086] The output of a radiant energy source can be controlled in
various ways to improve system performance. Most notably, through
the use of reflectors (such as curved reflectors (parabolic or
elliptic) at the rear of the lamp, and side reflectors), the useful
radiant energy output can be significantly increased. Where it is
desired to focus the thermal radiation to a very limited geometric
area, this can be achieved through focusing optics and reflectors.
Another technique is selectively to mask the radiant energy. It is
also possible to change the spectral distribution of the emitted
energy through filtering.
[0087] As another alternative, radiant heating may be used to heat
rollers just prior to nipping of the sheet of film by the
rollers.
[0088] The spectral and spatial distribution of the thermal energy
emission from the radiant source can be significantly altered
between the source and a point in the system at which absorption of
energy and other effects are being considered. The emitted thermal
energy can be attenuated for example by absorption intermediate the
source and the point under consideration; by scattering; and by
other effects. Notwithstanding this attenuation of thermal energy,
the very high heat fluxes characteristic of the radiant heat
sources that are used here result in high heat fluxes incident on
other structures of the embossing system.
[0089] An important determinant of the radiant heat transfer
achieved by the embossing system described herein is the
absorptivities of the sheeting or other material to be embossed and
of other materials or objects of the system. In this regard, two
pertinent properties are the spectral absorptivities of these
materials, and their ratio of energy absorbed. Spectral absorptions
are illustrated in FIGS. 1C and 1D, which may be considered in
conjunction with FIG. 1A. FIG. 1A shows the spectral distribution
of the thermal radiation that is incident on the sheeting and/or on
the tooling (to simplify the illustration this is shown as a
blackbody radiation source, and attenuation of the thermal
radiation is ignored), over a range of wavelengths. FIG. 1C shows
the relative spectral absorption of an exemplary sheeting material,
Ardel sheeting (Ardel is a trademark of Amoco Polymers for a
polyarylate polymer), over the relevant range of wavelengths, and
FIG. 1D shows the relative spectral absorption of an exemplary
tooling material (electroformed nickel tooling) over the same range
of wavelengths (these are qualitative values for the sake of this
example). The overall absorptivity over the range of wavelengths,
which in this patent application is called "ratio of energy
absorbed", is the ratio of all absorbed radiant energy (e.g., from
the radiant source), to the total incident radiant energy from that
direction. The total absorbed energy depends on distribution of the
spectral absorptivity in relation to the spectral emissivity across
the relevant range of wavelengths. Thus, in the case of the
sheeting material, which has relatively low spectral absorptivities
at the high-energy wavelengths of the blackbody source, the ratio
of energy absorbed will be relatively low, whereas for tooling
material, which has relatively high spectral absorptivities at the
high-energy wavelengths of the blackbody source, the ratio of
energy absorbed will be relatively high.
[0090] In considering the total radiant energy absorbed by the
sheeting to be embossed, it is necessary to consider not only
energy incident from the radiant source, but also reflected thermal
radiation that may return to the sheeting. Thus, for example
reflections between reflectors that are arranged around the
sheeting can cause an "infinite series" of thermal radiation to be
absorbed by the sheeting that, despite a relatively high
transparency of the sheeting material, can cause significant
radiant heating of the sheeting.
[0091] As described in greater detail below, the radiant energy may
pass through a relatively-radiantly-transparent material before
impinging upon and being absorbed by a
relatively-radiantly-absorptive material. As used herein, a
relatively-radiantly-transparent material (also referred to a
"relatively-transparent material" or a "transparent material") is
defined as a solid material that is less absorptive to the radiant
energy than the relatively-radiantly-absorptive material (also
referred to as a "relatively-absorptive material" or an "absorptive
material"). Specifically excluded from the definition of
relatively-radiantly-transparent material are gasses, such as air,
through which the radiant energy may pass on its way from the
radiant energy source to the absorptive material. It will also be
understood that the term relatively-transparent material, as used
herein, does not include materials that are part of the radiant
heater or radiant energy source.
[0092] The above definitions involve two connections. First of all,
it will be appreciated that the above definition of materials as
"relatively transparent" or "relatively absorptive" is relative.
That is, a material is transparent or absorptive only relative to
another material in the case at hand. Furthermore, a material may
be relatively transparent in one device or system, and relatively
absorptive in another. The concept of relativity that is employed
in this definition is that involving specific absorptive properties
of a material, its absorptivity per unit volume or per unit
mass.
[0093] Second, the definition is tied to the spectral emissivity
distribution of radiant energy employed. It is possible that a
material may be relatively absorptive with regard to another
material with respect to a first source of radiant energy, and be
relatively transparent with regard to the same material with
respect to second radiant energy of a different spectral emissivity
distribution. For example, FIGS. 1B and 1C show that Ardel is
relatively transparent to a 3200 K source but not to a 1200 K
source.
[0094] A further note regarding the above terms is that it will be
appreciated that even a relatively transparent material may have
some level of absorptivity of the radiant energy. Thus, while the
radiant energy may be described here as passing through the
transparent material and as heating only the absorptive material,
it will be appreciated that some absorption in and heating of the
transparent material may in fact occur.
[0095] Relatively transparent and absorbent materials have been
defined above broadly in terms of which is more absorbent of the
radiant energy (i.e. greater ratio of energy absorbed from the
radiant energy source). However, it will be appreciated that the
materials of varying absorptivity may be characterized more
narrowly based on a relative ratio of their absorptivity. For
example, the relatively-absorptive material may have an
absorptivity that is seven times that of the relatively-transparent
material.
[0096] The relatively-transparent and the relatively-absorptive
materials are characterized by comparing their total rate of energy
absorption (total energy absorbed per time). The total energy
absorption of a material depends on the emission spectrum
(wavelengths) of the radiant energy source, the absorptivity
spectrum of the material, and the distance that the radiant energy
travels through the material. Therefore, the ratio of energy
absorbed of a material can be defined as an integral over the
volume (or distance) and over the emission spectrum (wavelengths)
of the radiant energy, of the product of the intensity spectrum of
the radiant energy (a function of wavelength) and the absorptivity
spectrum of the material, and an exponential decay function (a
function of absorptivity spectrum and distance. The ratio of energy
absorbed of the relatively-transparent material to the ratio of
energy absorbed of the relatively-absorptive material may be less
than 1, may be less than or equal to 0.7, may be less than or equal
to 0.5, may be less than or equal to 0.3, may be less than or equal
to 0.1, or may be nearly zero.
[0097] Having the radiant energy pass through the transparent
material to get to the absorptive material allows the radiant
energy to be preferentially absorbed in the vicinity of the part of
the sheet that is actually embossed. Thus only small portions of
the sheet and the tool need actually be heated to accomplish the
patterning on the sheet. It will be appreciated that many
advantages flow from being able to concentrate the radiant energy
where heating is most needed. First, overall energy consumption for
the process may be reduced. Second, localized heating may reduce
processing time, since times required for heating and cooling of
the sheet may be reduced. Further, material properties of the
resulting embossed sheet may be improved. Excessive heating, either
in terms of excessively elevated temperature or the amount of time
maintained at an elevated temperature, may have a deleterious
effect on material properties. One example is that prolonged
heating may alter orientated structures in a material. By providing
localized heating for only a short period of time, this degradation
of material properties may be avoided. Excessive heating may result
in exceeding the glass transition temperature, flow temperature,
and/or melting temperature of the material for a time longer than
is necessary to achieve the embossing. Similarly, excessive heating
may result in exceeding the glass transition temperature, flow
temperature, and/or melting temperature of the material in parts of
the material where such heating is not necessary to achieve the
embossing. These possible deleterious effects of excessive heating
may be reduced or avoided by using the systems and/or methods
disclosed herein.
[0098] As discussed further in the examples below, there are many
possible configurations for the transparent material and the
absorptive material. As one example, illustrated in FIG. 2, the
transparent material 20 and the absorptive material 22 may be
different layers of the sheet of material 24 to be embossed.
Radiant energy 30 from a radiant energy source 32 passing through
the transparent material layer 20 is absorbed by the absorptive
material layer 22. Such a configuration may allow localized heating
of the portion 34 of the sheet material 24 actually to be embossed.
It will be appreciated that sheet material with layers of various
absorptivity may be formed in a variety of ways, for example by use
of different materials joined together by co-extrusion.
Alternatively, the difference in absorptivity may be accomplished
by other means, such as by doping with suitable material, such as
NIR-absorbing additives or nano-silicates. The localized heating
may involve passing radiation back and forth through the material
multiple times, with the radiation selectively absorbed in the
absorptive material layer. This use of multiple passes of radiation
to accomplish the heating may advantageously result in even
heating, with small thermal gradients.
[0099] Another possible configuration, illustrated in FIG. 3, has
the radiant energy 30 pass through the transparent material 20 of
the sheet material 24 on its way to being absorbed by a
relatively-absorptive material tool 36. Heating may be thus
localized at the tool surface 40, and at the portion 34 of the
sheet material 24 in contact with the tool surface 40. This is an
example of indirect heating of the material to be embossed, in that
the radiant energy 30 does not directly heat the material embossed,
but only through the intermediary of the heated tool 36.
[0100] Yet another possible configuration, illustrated in FIG. 4,
has a tool 36 made of a transparent material 20 and the sheet
material 24 made of the absorptive material 22. Radiant energy from
the radiant energy source passes through the transparent tool and
is absorbed by the sheet material 24 to be embossed.
[0101] It will be appreciated that the transparent material 20 may
include two or more materials between the radiant energy source 32
and the absorptive material 22. For example, the system may be
configured such that the radiant energy 30 passes between
transparent material of both a tool and a portion of the sheet
material 24, before being absorbed by another portion of the sheet
material 24.
[0102] The heating may be sufficient to melt at least a portion of
the sheet material 24. Alternatively, the heating may only soften
the heated portion of the sheet material 24, for example by raising
the temperature of the heated portion above the glass transition
temperature for the material. In either case, the heating makes the
portion of the sheet more susceptible to formation of recesses
and/or protrusions along a surface of the heated portion of the
sheet.
[0103] Specific examples of relatively radiantly transparent and
relatively radiantly absorptive materials are discussed below, all
in relation to the emission spectrum of the AdPhos NIR emitters,
which have most energy output in the range from 0.7 to 1.5 microns
and a peak output at about 0.8 microns:
[0104] Quartz and Pyrex.RTM. (borosilicate glass) are nearly
transparent to the emitted energy, since these materials do not
absorb very much below about 2 microns. These materials have been
employed in hard rollers and other structures that can press
against the sheeting to be embossed (pressure source for embossing
process). These pressure structures permit the thermal radiation to
be transmitted through to the heating highly efficiently (cf. FIG.
1C).
[0105] Various thermoplastic polymeric sheeting or films can be
used as the material to be embossed, as discussed below. These
polymeric materials also are nearly transparent to the emitted
energy, since these polymers do not absorb very much below about 2
microns. In addition to films to be embossed, as well known in the
art of precision embossing, one may combine such a film or sheeting
with a carrier film, e.g. Mylar.RTM., which likewise is highly
transparent to the radiant energy. Thus the radiant energy can be
transmitted through the film to the tooling with limited
losses.
[0106] Nickel and nickel alloys, which are preferred materials used
in electroformed tooling for precision embossing, are highly
absorptive of the NIR radiation. The incident NIR radiation rapidly
heats the tooling to temperatures that can be well above the
500.degree. F. upper limit achieved by conventional circulatory oil
heating of embossing tooling. This results in improved conductive
heating of the sheeting to be embossed, which contributes to
desirable fluidity of the thermoplastic material at the sheeting
surface for the purpose of molding and freezing well formed,
defect-free precision microstructures.
[0107] These preferred structures may be combined in an embossing
system in which nickel tooling absorbs most of the emitted thermal
radiation to provide fast and efficient embossing. The film to be
embossed can be radiated when pressed against the tool using a
transparent pressure structure intermediate between the film and
the radiant emitter. The radiation passes rapidly through the film
and is absorbed at the surface of the embossing tooling. This
rapidly heats the tool, which in turn melts the film locally and
embosses the film. It should be emphasized that this functionality
is not necessarily dependent on the use of AdPhos NIR emitters as
the radiant energy source, but could be achieved using other
emitters if the total heat fluxes (radiant energy emission) and the
emission spectra are similar.
[0108] In the mold stage 4 of the method 1 (FIG. 1), the sheet
material 24 (FIGS. 2-4) is patterned by pressing the tool 36 (FIGS.
2-4) against the heated portion of the sheet. The tool 36 may have
a patterned surface, with recesses and/or protrusions. By pressing
the tool against the heated portion, the portion of the sheet is
patterned with a corresponding array of protrusions and/or
recesses.
[0109] The pressing of the tool 36 against the sheet material 24
may be accomplished by pressing the two together as part of a
roll-to-roll process. For example, a flexible patterned belt may be
used as a tool to impart a pattern of protrusions and/or recesses
on the sheet. Indeed, all of the steps of the method 1 may be
performed as part of a single roll-to-roll process.
[0110] The pressing of the tool against the sheet material 24 may
be commenced before the heating of the heated portion of the sheet
material 24, such that the tool 36 is first pressed against the
sheet material 24, and then the portion of the sheet material 24 is
heated. The heating of the portion while the tool 36 is pressed
against the sheet material 24 may be by conduction from the tool to
the sheet material 24, or may be direct heating by the radiant
energy.
[0111] Further, there may be continuous constraint of the sheet
material 24 while it is heated. The sheet material 24 may be
constrained, such as being between belts, during the heating and
embossing, until the embossed sheet material is cooled, for example
being cooled below the glass transition temperature or flow
temperature of the material.
[0112] Alternatively, the pressing may occur only after the heating
has been completed.
[0113] In the de-mold stage 6 of the method 1 (FIG. 1), the sheet
material 24 and the tool 36 are separated. The separation occurs
after the mold stage 4, and may be delayed to allow sufficient
cooling of the patterned heated portion of the sheet material 24,
so that the patterned sheet material maintains its shape after
separation. To that end, there may be a separate step of cooling
the sheet material 24 and/or the tool 36, such as the freeze stage
5 of the method 1 (FIG. 1).
[0114] It will be appreciated that the cooling cycle may be speeded
up and may use less energy, compared to prior systems using other
heating mechanisms. This is because heating may be more localized,
involving less heating of the sheet material 24 and less heating of
the tooling adjacent to the sheet material 24. In conventional
embossing systems, using electrical or oil heating, a large mass of
the machine, e.g., a heating drum, is heated and pressed against
material to be embossed. This large mass of heated machine makes
cooling of the embossed material more difficult, causing additional
time and/or energy to be expended to accomplish the desired
cooling. In order to practically effect the cooling in such
systems, separation of the embossed material from the heated
machinery may be required, which may adversely affect the quality
of the embossed product.
[0115] The embossing (or molding) methods described herein may be
used for embossing microstructures in any of a wide variety of
materials, to thereby form a precision microstructured material. As
used in the present application, "precision microstructured
material" or "precision microstructured film" generally refers to a
thin film or sheet of resinous thermoplastic material having an
embossed precise geometric pattern of very small elements or
shapes, and in which the precision of the formation is important to
the functionality of the product. The precision of the embossed
film is a function of both the precise geometry required of the
product, and the capability of the embossing tool, process and
apparatus to conserve the geometric integrity from tool to
article.
[0116] Typically at least one or more of the following features
will be formed in the film, (on one or both sides thereof:
[0117] (a) flat surfaces with angular slopes controlled to a
tolerance of 5 minutes relative to a reference value, more
preferably a tolerance of 2 minutes relative to a reference value;
or to at least 99.9% of the specified value;
[0118] (b) having precisely formed (often, very smooth) surfaces
with a roughness of less than 100 Angstroms rms relative to a
reference surface, more preferably with a roughness configuration
closely matching that of less than 50 Angstroms rms relative to a
reference surface; or, if the surface requires small irregularities
it may be greater than 100 Angstroms and less than 0.00004 inch (1
micron);
[0119] (c) having angular acute features with an edge radius and/or
corner radius of curvature of less than 0.001 inches (25 microns)
and controlled to less than 0.1% of deviation;
[0120] (d) having an embossing depth less than 0.040 inches (1000
microns), more preferably less than 0.010 inch (250 microns);
[0121] (e) precisely controlled dimensions within the plane of the
sheeting, in terms of the configuration of individual elements,
and/or the location of multiple elements relative to each other or
a reference point; and
[0122] (f) characteristic length scale (depth, width, and height)
less than 0.040 inch (one millimeter with an accuracy that is
better than 0.1 percent.
[0123] In certain embodiments of precision microstructured film,
discrete elements and/or arrays of elements may be defined as
embossed recessed regions, or embossed raised regions, or
combinations of embossed recessed and raised regions, relative to
the unembossed regions of the film. In other embodiments, all or
portions of the precision microstructured film may be continuously
embossed with patterns of varying depths comprising elements with
the characteristics described above. Typically, the discrete
elements or arrays of elements are arranged in a repetitive
pattern; but it will be appreciated that other, non-repetitive
arrays of precision microstructured shapes may also be
embossed.
[0124] Exemplary types of precision microstructured sheeting, and
their requirements of precision, are stated below in several
examples.
[0125] For retroreflective materials for road reflectors or
signage, and Fresnel lenses, in such optical sheeting applications,
precise flatness, angles and uniform detail are important.
Cube-corner type reflectors, to retain their functionality of
reflecting light back generally to its source, require that the
three reflective faces of the cube be maintained flat and within
several minutes of 90.degree. relative to each other. Spreads
beyond this, or unevenness in the faces, results in significant
light spread and a drop in intensity at the location desired. Also,
surface smoothness is required so light is not diffused.
[0126] Feature to feature accuracy is important for LCD display
systems in which adjacent embossed recesses not only have to be
precisely shaped, but the spatial relations of the array of
recesses must be closely adhered to.
[0127] Another feature that may be desirable is the ability to
manufacture microstructures with an edge radius of less than 0.001
inches (25 microns) and with very sharp points and sharp ridges
(less than 0.00028 inches (7 microns).
[0128] Yet another desirable attribute may be volumetric accuracy
for microfluidic and microwell applications with 90% or greater
accuracy of the cross sectional area being conserved through the
length of channel; and from channel to channel, and/or well to
well, in which dimensions range from 0.00020 to 0.008 inches (5-200
microns) depth; 0.00020 inches to 10 inches (5 microns to 25.4 cm)
length. The channels may have convoluted shapes and microtextured
shapes.
[0129] It also may be desirable to achieve surface roughness for
microfluidic applications that allow for low friction and minimal
surface drag, all resulting in smooth continuous non-diffusive
flow, allowing the laminar fluid flow.
[0130] The method described above allows avoidance of residual
stresses by providing essentially stress free microstructures. This
is critical for some optical, FSA, and for microfluidic
applications where the detection mechanisms use fluorescent
polarization technology. Materials with stress generally have
strand orientation, which acts like a polarizing lens. Materials
that contain residual stresses may relax that stress during
subsequent processing or during the life cycle of the product,
resulting in dimensional instability.
[0131] The precision microstructured pattern typically is a
predetermined geometric pattern that is replicated from the
tooling. It is for this reason that the tooling may be produced
from electroformed masters that permit the creation of precisely
designed structures. In contrast, high tensile stainless steel,
which has typically been used in the bands of double band presses,
is not well suited to creation of tooling for embossing of such
precisely controlled microstructures. Micromachining and
photolithography are methods that may be used to create masters.
The masters typically are replicated using electroforming to
generate multiple tools or can be used directly as embossing tools
themselves.
[0132] Considering now the sheet film material 24 in greater
detail; for purposes of this description, two temperature reference
points are used: T.sub.g and T.sub.e. T.sub.g is defined as the
glass transition temperature, at which plastic material will change
from the glassy state to the rubbery state. The material may need
to be hotter than T.sub.g before it can flow.
[0133] T.sub.e is defined as the embossing or flow temperature
where the material flows enough to be permanently deformed by the
continuous press or other processes described herein, and will,
upon cooling, retain form and shape that matches or has a
controlled variation (e.g. with shrinkage) of the embossing tool.
Because T.sub.e will vary from material to material and also will
depend on the thickness of the film material and the nature of the
dynamics of the continuous press, the exact T.sub.e temperature is
related to process conditions including the embossing pressure(s);
the temperature input of the continuous press and the press speed,
as well as the extent of both the heating and cooling sections in
the reaction zone.
[0134] The embossing temperature must be high enough to exceed the
glass transition temperature T.sub.g, so that adequate flow of the
material can be achieved to provide highly accurate embossing of
the film.
[0135] Numerous thermoplastic materials may be considered as
polymeric materials to provide precision microstructure film.
However, not all can be embossed on a continuous basis. Applicants
have experience with a variety of thermoplastic materials to be
used in continuous embossing under pressure at elevated
temperatures. These materials include thermoplastics of a
relatively low glass transition temperature (up to 302.degree.
F./150.degree. C.), as well as materials of a higher glass
transition temperature (above 302.degree. F./150.degree. C.).
[0136] Typical lower glass transition temperature (i.e. with glass
transition temperatures up to 302.degree. F./150.degree. C.)
include materials used for example to emboss cube corner sheeting,
such as vinyl, polymethyl methyacrylate, low T.sub.g polycarbonate,
polyurethane, and acrylonitrile butadiene styrene (ABS). The glass
transition T.sub.g temperatures for such materials are 158.degree.
F., 212.degree. F., 302.degree. F., and 140.degree. to 212.degree.
F. (70.degree. C., 100.degree. C., 150.degree. C., and 60.degree.
to 100.degree. C.).
[0137] Higher glass transition temperature thermoplastic materials
(i.e. with glass transition temperatures above 302.degree.
F./150.degree. C.) that have been found suitable for embossing
precision microstructures, are disclosed in a co-pending patent
application, U.S. Ser. No. 09/776,281, filed Feb. 2, 2001. These
polymers include polysulfone, polyarylate, cyclo-olefinic
copolymer, high T.sub.g polycarbonate, and polyether imide.
[0138] A table of exemplary thermoplastic materials, and their
glass transition temperatures, appears below as Table I:
TABLE-US-00001 TABLE I Symbol Polymer Chemical Name T.sub.g
.degree. C. T.sub.g .degree. F. PVC Polyvinyl Chloride 70 158
Phenoxy Poly (Hydroxyether) 95 203 PMMA Polymethyl methacrylate 100
212 BPA-PC Bisphenol-A Polycarbonate 150 302 COC Cyclo-olefinic
copolymer 163 325 PSF Polysulfone 190 374 Polyarylate Polyarylate
210 410 Hi-T.sub.g-PC High T.sub.g polycarbonate 260 500 PEI
Polyether imide 215 500 Polyurethane Polyurethane varies varies ABS
Acrylonitrile Butadiene Styrene 60-100 140-212
[0139] The thermoplastic sheeting also may comprise a filled
polymeric material, or composite, such as a microfiber filled
polymer, and may comprise a multilayer material, such as a
coextrudate of PMMA and BPA-PC.
[0140] A variety of thermoplastic materials such as those listed
above in Table I may be used for the formation of microstructures
using the systems and methods described elsewhere in this
description. Relatively low T.sub.g thermoplastic materials such as
polymethyl methyacrylate, ABS, polyurethane and low T.sub.g
polycarbonate may be used. Additionally, relatively high T.sub.g
thermoplastic materials such as polysulfone, polyarylate, high
T.sub.g polycarbonate, polyetherimide, and copolymers also may be
used in an embossing system or press. Applicants have observed as a
rule of thumb that for good fluidity of the molten thermoplastic
material in the reaction (embossing) zone, the embossing
temperature T.sub.e should be at least 50.degree. F. (28.degree.
C.), and advantageously between 100.degree. F. to 150.degree. F.
(55.degree. C. to 83.degree. C.), above the glass transition
temperature of the thermoplastic sheeting.
[0141] In addition to the amorphous thermoplastic materials
described above, suitable crystalline thermoplastic materials may
be utilized. Crystalline thermoplastic materials in general have a
low T.sub.g and a high melting point T.sub.m, relative to amorphous
thermoplastic materials. An example of a suitable crystalline
thermoplastic material is Nylon 6, which has a T.sub.g of
50.degree. C. and a T.sub.m of 210.degree. C. In embossing
crystalline thermoplastic materials, T.sub.m, rather than T.sub.g,
is the temperature to be exceeded.
[0142] With such thermoplastic materials the pressure range is
approximately 150 to 700 psi (1.03 to 4.82 MPa), and potentially
higher, depending on factors such as the operational range of the
machinery; the mechanical strength of the embossing belt or tool
(high pressure capacity); and the thermoplastic material and
thickness of the thermoplastic film.
[0143] Amorphous thermoplastic materials may react to heating
differently from crystalline thermoplastic materials. Upon
sufficient heating, amorphous thermoplastic materials eventually
exceed their glass transition temperature and reach a state in
which softening occurs. Further heating may cause the amorphous
thermoplastic material to reach a temperature at which flow of the
material occurs. Still further heating may cause the amorphous
material to reach a temperature at which it decomposes.
[0144] In contrast, heated crystalline thermoplastic materials may
melt without first undergoing any significant softening at a
temperature below the melting temperature. Therefore constraint of
the material may be important when embossing crystalline
thermoplastic materials.
[0145] Thermoplastic materials of thicknesses of up to 0.250 inches
(6.35 mm) may be embossed with precise formations in the range of
0.0004 to 0.040 inches (10 to 1000 microns) deep. It will be
appreciated that other thicknesses of thermoplastic material, for
example thickness greater than that listed above, may alternatively
be embossed.
[0146] The apparatus and processes described herein allow for the
thermoplastic film material to be relatively thick and yet still
have precision microstructures in one or both major surfaces. This
allows products as diverse as office light diffusers, reflective
signage, compact disks, flat panel displays, high-efficiency
lighting systems for internally illuminated signs and medical
diagnostic products to be efficiently, effectively and
inexpensively manufactured. Another exemplary application is
retroreflective lenses for road markers, which are more than 0.04
inches (1 mm) thick. The embossing is on the order of 0.008 inches
(0.2 mm) deep.
[0147] In embossing relatively thick thermoplastic sheeting, it
will be appreciated that at least some embodiments disclosed herein
may be used to emboss both sides of the sheet material 24 without
heating the center. Besides double sided embossing of a monolayer
sheet, the embossing processes described herein permit the
embossing of two sheets separated by a separator sheet, which are
later stripped apart; an example is a sandwich of PMMA, PET, and
PMMA films.
[0148] As a further variation, the thermoplastic film may be a
coextruded, peelable construction such as disclosed in U.S. Pat.
No. 4,925,714, wherein after embossing of the faces of the
sheeting, and cooling and removal of the sheeting from the
continuous press, two embossed films may be separated from each
other at a peelable interface. Care must be taken to avoid air
entrapment between the layers resulting in a less than perfect
optical surface under certain conditions.
[0149] Where it is required to register the images embossed on both
sides of the thermoplastic sheeting, a suitable mechanical and/or
electro-optical subsystem may be provided to ensure the
registration of the embossed images, as known in the art of
registration printing. In some applications, however, registration
of the embossed images would not be required. The use of
transparent constructions in radiative heating and embossing lends
itself to easy incorporation of optical registration devices.
[0150] The use of the phrase "thermoplastic material" in the
appended claims is intended to cover all of the foregoing
possibilities--single layer film; laminates; use of a strippable
carrier; and registered and unregistered embossing.
[0151] As noted above, parts of the sheet material 24 may be doped
to increase their absorptivity. Many plastics, e.g. polyolefins and
polystyrenes, have low absorption of suitable types of radiant
energy, such as near-infrared energy. Where the desired effect is
heating of the plastic, one does not want the plastic to reflect or
transmit all of the near infrared radiation or other type of
radiant energy, since there is then no interaction. Nor must
excessively strong absorption take place, since in this case the
high thermal gradients and high temperatures may lead to
decomposition of the plastics. The absorption of the near-infrared
or other radiant energy, and therefore the interaction with the
material, depends on the chemical structure of the plastic and on
the characteristics of the near-infrared radiation used. It may be
necessary to add appropriate additives, such as absorbers, in order
to render plastics able to absorb a suitable amount of the radiant
energy. Alternatively, one may chemically modify the base polymers
in order to render the polymeric material more absorbent of the
radiant energy, such as near-infrared energy.
[0152] Additives to the sheet material 24 may include suitable
dopants. The term dopant is broadly defined herein as relatively
absorbent material of the radiant energy, which is in or on the
sheet material. Thus a dopant may be actually within the polymer or
other material or component of the sheet material 24. Alternatively
or in addition, the dopant may be a coating on the sheet material
24. Such dopants may be dispersed through the sheet material 24;
may be chemically reacted throughout part or all of the sheet
material 24; and/or may be in a separate phase on or within the
sheet material 24.
[0153] The desirable concentration of the dopant in the plastic may
depend on the type of polymer material, and the wavelength and
energy of the radiant energy employed, among other factors. A small
proportion of dopant may not substantially alter the material
properties of the polymer sheet material 24, and hence may have
little or no effect on its processability.
[0154] Incorporation of a dopant within the thermoplastic can take
place by mixing the plastic pellets with the dopant, followed by
shaping with exposure to heat. Other conventional mixing
techniques, including compound extrusion, would be known to one of
ordinary skill in the art. During incorporation of the dopant, the
plastic pellets may, if desired, be treated with adhesion
promoters, polymer-compatible solvents, stabilizers and/or
surfactants resistant to the operating temperatures used. The doped
plastic pellets may be produced by placing the plastic pellets in a
suitable mixer, wetting these with any additives, and then adding
and incorporating the dopant. The resultant mixture may then be
directly processed in an extruder.
[0155] Extruded films may have a homogeneous dopant distribution.
On the other hand, a non-uniform distribution of the dopant may be
desired in order to localize the radiant heating effect within a
certain region of the polymeric substrate. One way this can be
achieved is by including dopant within one layer of a multilayer
coextrudate. Thus such localization, or non-uniform distribution of
the dopant, can be achieved by strata or layers across the
thickness dimension of the substrate. Localization of dopant also
may be achieved within the plane of the substrate, e.g., by
depositing or printing the dopant in a desired pattern, such as a
grid. The dopant may comprise particulate matter, and also may
comprise a coating. The coating may be a surface coating, or may be
an interfacial coating or layer between layers of a multilayer
substrate.
[0156] As a further alternative, the dopant may be impregnated into
the sheet material 24. The sheet material 24 may be impregnated by
swelling a surface of the sheet material 24 with a solvent,
allowing the dopant to migrate into the swollen structure, and then
removing the solvent, causing the swelling to reverse and trapping
the dopant within a polymer structure of the sheet material 24.
Further details regarding impregnation methods may be found in U.S.
Pat. Nos. 4,937,026 and 5,453,100, which are herein incorporated by
reference in their entireties.
[0157] The dopant may be placed in a pattern on or within the sheet
material 24. For example, the dopant may be placed at locations
within the sheet material 24 where deformation of the material is
to be greatest.
[0158] Examples of suitable dopants are Epolight 1125, 1178, and
3063 near-infrared absorbing dyes available from Epolin, Inc., of
Newark, N.J.
[0159] Turning now to FIGS. 5-7A, a system 100 is shown for
performing the method described above, in a roll-to-roll process.
The system 100 embosses the sheet material 24 as the sheet material
24 travels from a supply roll 102 to a take-up roll 104. A
patterned belt 106 travels around a pair of rollers 110 and 112.
Press rollers 116a-116d and 118a-118d press the sheet material 24
and the patterned belt 106 together. The sheet material 24 is
heated during this pressing, such that the pattern from the
patterned belt 106 is transferred to the sheet material 24.
[0160] FIGS. 6 and 7 show details of one of the rollers 116. The
roller 116, which may be typical of one or more of the rollers
116a-d, includes a radiant energy source 32 that directs radiant
energy 30 toward the sheet material 24 and the patterned belt 106.
A reflector 120 re-directs at least some of the radiant energy 30,
initially emanating from the radiant energy source 32 in a
direction away from the sheet material 24 and the patterned belt
106, toward the sheet material 24 and the patterned belt 106. The
reflector 120 thereby increases efficiency of the radiant heating.
The reflector 120 may also be configured to focus the radiant
energy 30 on a narrow area of the sheet material 24, providing
concentrated heating.
[0161] The roller 116 includes a transparent roller material 130
between the radiant energy source 32 and the sheet material 24. The
transparent roller material 130 allows the radiant energy 30 to
pass through, while being hard enough to press the sheet material
24 and the patterned belt 106 together to pattern the sheet
material 24. The transparent roller material 130 may be quartz, for
example. As another alternative, the transparent roller material
130 may be a glass material, such as that sold under the trademark
PYREX. More specifically, the roller material may be a glass able
to withstand thermal stress. It will be appreciated that other
alternatives may be used for the roller material, such as
transparent or translucent ceramic materials, and polymer materials
sold under the trademark TEFLON.
[0162] In one embodiment, shown in FIG. 6, the sheet material 24 is
a transparent material, which allows most of the radiant energy 30
to pass therethrough. The radiant energy 30 is then absorbed by an
absorbent material of the patterned belt 106. The patterned belt
106 may include a tooling surface 134 and a flexible backing 136.
The tooling surface 134 may include a material that is both
absorbent with respect to the radiant energy 30, and is
sufficiently hard so as to transfer its surface pattern to the
sheet material 24. The flexible backing 136 may provide cushioning
for the pressing together of the sheet material 24 and the
patterned belt 106. In addition, the flexible backing 136 may be a
thermal insulator, when compared with the material of the tooling
surface 134. By using a thermal insulator for the flexible backing
136, the heating from the radiant energy 30 may be concentrated in
the tooling surface 134, with little or no appreciable heat loss
through the flexible backing 136.
[0163] A suitable material for the tooling surface 134 is nickel,
and a suitable material for the flexible backing 136 is rubber.
However, it will be appreciated that other suitable materials may
alternatively be used. Examples of alternative tool materials that
may be suitable are nickel alloys, cobalt, chromium, manganese,
silicon, and suitable ceramics.
[0164] Tooling materials discussed in the preceding paragraph may
function as absorptive materials, while the thermoplastic materials
shown above in Table I may function as relatively transparent
materials. Alternatively, as discussed above, parts of the sheet
material may be made relatively absorptive, for example by use of
dopants or different sheet materials. The use of
relatively-transparent materials advantageously allows more
flexibility in configuring the locations of energy sources,
rollers, and sheet material.
[0165] The configuration shown in FIG. 6, that of a radiant energy
source 32 with a transparent roller material 130, may be used in
each of the rollers 116a-116d. Alternatively, one or more of the
rollers 116a-116d may be simple press rollers without a radiant
energy source. It will be appreciated that the radiant heating,
such as from the radiant energy source 32, may be combined with
other types of heating, such as heating from conventionally-heated
rollers, if desired. The possibility for combining different types
of heating may be employed as suitable for all of the embossing
systems described herein.
[0166] In another embodiment, shown in FIG. 7, the sheet material
24 includes a transparent upper layer 144, and an absorbent lower
layer 146. The lower layer 146 may include a suitable dopant, such
as those described above. The radiant energy 30 passes through the
upper layer 144 and is absorbed in the lower 146. This heats the
lower layer 146, softening or melting a portion of the sheet
material 24 along a lower surface 148 that is in contact with the
patterned belt 106.
[0167] In yet another embodiment, illustrated in FIG. 7A, the
transparent roller material 130 has a patterned outer surface that
patterns a top surface of the sheet material 24. The belt 106 may
include a reflective material that may be patterned for embossing
the bottom surface of the sheet material 24. The patterned belt 106
may include a reflective material, such as polished aluminum or
copper, that reflects at least some of the unabsorbed radiant
energy back through the sheet material 24. An additional reflector
150 may be utilized to reflect unabsorbed radiant energy further
times through the sheet material. This configuration of reflectors
(the belt 106 of reflective material and the additional reflector
150) allows multiple chances for the sheet material 24 to absorb
the incident radiant energy, which may advantageously improve the
efficiency and evenness of the radiant heating of the sheet
material 24. It will be appreciated that other variants on the
configurations shown in FIGS. 6-7A may be possible. For example, it
may be to have the radiant energy 30 absorbed in both the tool and
part of the sheet material 24. Further, the tool may act as a
reflector, allowing radiant energy not absorbed in the sheet
material 24 during its initial pass through the sheet material 24
to be reflected into the sheet material 24, to perhaps be absorbed
in the sheet material 24.
[0168] As noted above with regard to the embodiment shown in FIG.
7A, the system 100 (FIG. 5) may be used to pattern both surfaces of
the sheet material at the same time, for example by providing a
dimpled or otherwise suitable patterned surface on the outer
surface of the transparent roller material 130. In patterning both
surfaces of the sheet material 24, it may be desirable to suitably
dope the sheet material 24 so as to achieve heating at both
surfaces of the sheet material 24. For example, it may be desirable
to dope sections of the sheet material 24 to allow absorption of
the radiant energy 30 at both surfaces. Such doping may involve
different concentrations of dopants at the different surfaces.
[0169] Turning now to FIG. 8, a different type of radiant heating
system is illustrated. The embossing system 200 shown in FIG. 8
includes a radiant heating system 210 that is separate from the
press rollers 116a-116e and 118a-118e. The radiant heating system
210 includes radiant energy sources 32a-32d that transmit radiant
energy 30 from the sources 32a-32d to the sheet material 24,
between the press rollers 116a-116e. A reflector 216 may aid in
directing the radiant energy from the radiant energy sources
32a-32e to the sheet material 24 and/or to the patterned belt 106.
It will be appreciated that the radiant energy may pass through
part of the sheet material 24, and be absorbed by another part of
the sheet material 24, similar to the configuration described
above, particularly with regard to FIG. 7. Alternatively, the sheet
material 24 may be fully composed of transparent material, with the
bulk of the radiant energy 30 absorbed by the tooling surface 134
of the patterned belt 106, similar to the configuration described
above with regard to FIG. 6.
[0170] FIGS. 9 and 10 show further alternative embossing systems.
The embossing systems 300 and 400 each involve pressing the sheet
material 24 between a patterned belt 106, and an additional belt
320. Pairs of rollers 322, 324 and 332, 334 maintain pressure
against the belts 106 and 320, and thereby against the sheet
material 24. It will be appreciated that additional rollers and/or
fluid (e.g. air) pressure may be used for pressing the belts
against the sheet material.
[0171] While pressure is maintained against the sheet material 24,
a radiant heating system 340 heats the sheet material 24 and/or the
belts 106, 320, and a cooling system 350 cools the sheet material
24 and the belts 106, 320. The radiant heating system 340 may be
similar to the radiant heating system described above with regard
to FIG. 8. That is, the radiant heating system 340 may include one
or more radiant energy sources, and a reflector to direct the
radiant energy toward the sheet material 24 and/or the belts 106,
320. The cooling system 350 may be any of a variety of known
suitable systems for cooling the sheet material 24 suitable for
cooling the sheet material 24 sufficiently to allow it retain the
embossed pattern after the sheet material 24 is separated from the
belts 106 and 320. For example, the cooling system may include a
cooling roller. Alternatively, a suitable pressurized cooling
station, such as that discussed above, may be utilized.
[0172] In the embossing system 300 (FIG. 9), the belt 320 is
transparent, and radiant energy from the radiant heating system 340
passes through the belt 320, to be absorbed by the sheet material
24 and/or the patterned belt 106. The patterned belt 106 then
patterns one side of the sheet material 24. The cooling system 350,
which cools the sheet material 24, may be on either side of the
belts 106 and 320.
[0173] Another configuration, shown in FIG. 10, has the radiant
heating system 340 on an opposite side of the belts 106 and 320.
The system 400 thus has a flexible belt 106 at least part of which
is transparent, with radiant energy absorbed by the sheet material
24 or part of the flexible belt 106. Alternatively, the belts may
be both absorptive; in this case, the radiation is absorbed on the
backside of a belt and conducted through to the other side.
[0174] It will be appreciated that many alternative configurations
of the radiant heating system 340 and the cooling system 350 are
possible. For example, the cooling system 350 may be on both sides
of the belts 106 and 320.
[0175] It will be appreciated that both sides of the sheet material
24 may be patterned at the same time using the systems 300 and
400.
[0176] Turning now to FIG. 10A, a system 450 is shown in which a
single radiant heating system 340 heats a pair of rollers 452 and
454 on opposite respective sides of a sheet material 24. The sheet
material 24 is made of a relatively transparent material, which
allows radiant energy 456 to pass through the sheet material 24 and
heat the lower roller 454. Thus a single heating system 340 may be
utilized to heat rollers on both sides of the sheet material, for
example for patterning both sides of the sheet material 24.
[0177] Another embossing system, a press system 460, is illustrated
in FIG. 10B. The system 460 includes an air cylinder 462 having a
lower press platform 464, a platen 468 upon which the sheet
material 24 is placed, and an upper press 470, all held together by
a frame 474. In addition, the press system 460 includes a heating
system 340, for providing radiant energy to soften and/or melt the
sheet material 24.
[0178] The upper press 470 may be made of a relatively transparent
material, such as quartz, which allows radiant energy 478 emitted
by the heating system to pass therethrough for absorption by the
sheet material 24. The upper press 470 may be a tool that includes
a patterned lower surface for patterning the sheet material 24.
[0179] Operation of the press system 460 is as follows: the sheet
material 24 is arranged on the platen 468, which is then placed on
the lower press platform 464 of the air cylinder 462. The air
cylinder is then used to press the sheet material 24 against the
upper press 470. Once pressure has been applied, the heating system
340 may be activated for a set period of time, such as on the order
of seconds, to soften or melt the sheet material 24, with the
patterned surface of the upper press 470 thereby patterning the
sheet material 24. The sheet material 24 is then cooled, for
example by blowing cool air over the system, before the pressure of
the air cylinder is removed and the platen 468 and the sheet
material 24 are removed.
[0180] The press system 460 may include additional features, such
as pins on the lower press platform 464 to aid in alignment of the
platen 468 and the sheet material 24. The heating system 340 may be
movable, so that it can be raised and lowered relative to the rest
of the system.
[0181] In an exemplary embodiment, the press system 460 may be used
to pattern material pieces up to six inches (15.2 cm) in diameter.
The upper press 470 may be approximately one inch (2.54 cm) thick,
and the heating system 340 may be within about 1.5 inches (3.8 cm)
of the sheet material 24.
[0182] It will be appreciated that the press system 460 is only one
of a variety of press systems for patterning the sheet material 24.
Many variants are possible. For example, the platen 468 may be
patterned instead of or in addition to the upper press 470. The
platen 468 may be omitted, with the sheet material 24 pressed
between the upper press 470 and the lower press surface 464 of the
cylinder 462. Pressure-producing devices other than air cylinders
may be employed, although it will understood that the air cylinder
462 provides a means of evenly providing pressure along the sheet
material 24.
[0183] FIG. 10C illustrates yet another embodiment, an embossing
system 480. The system 480 utilizes a roller 482 of transparent
material to focus radiant energy from the radiant energy source.
The radiant energy emerges from the radiant energy source 32, and
may be reflected by the reflector 120 toward the sheet material 24.
The reflector 120 and the transparent roller 482 focus the radiant
energy, and the sheet material may focus the radiant energy
further. The radiant energy is absorbed in the tooling surface 134,
which along with the flexible backing 136 makes up the patterned
belt 106.
[0184] It will be appreciated that the system 480 shown in FIG. 1C
may be modified, if desired, to allow heating of an absorptive
portion of the sheet, such as an absorptive layer similar to the
absorbent lower layer 146 shown in FIG. 7, as opposed to or in
addition to heating the tooling surface 134.
[0185] FIGS. 11-14 show various types of patterned microstructures
that may be formed on the sheet material 24. The sheet material 24
may have an array of posts 510 (FIG. 11); may have an array of ribs
520 (FIG. 12); may have an array of recesses 530 (FIG. 13), such as
for receiving microstructure elements, also known as nanoblocks; or
may have an array of faceted protrusions 540 (FIG. 14). Further
details regarding the microstructure elements may be found in U.S.
Pat. Nos. 5,545,291 and 5,904,545, which are incorporated herein by
reference in their entireties. It will be appreciated that the
sheet material 24 may alternatively have other types of
microstructures embossed thereupon, and that the sheet material 24
may alternatively have larger structures patterned thereupon.
[0186] FIGS. 15-17 show an embossing system 600 for embossing both
sides of a sheet material 24. The system 600 may include parts,
such as a patterned belt 106, and rollers 622, 624, 632, and 634, a
heating system 636, and a cooling system 638, all of which may be
similar to corresponding parts of the systems 300 and 400 shown in
FIGS. 9 and 10 and described above. In addition, the system 600
includes a second patterned belt 640, allowing the sheet material
to be embossed on both sides (major surfaces) thereof. As shown in
FIGS. 16 and 17, the patterned belts 106 and 640 may have different
patterns. It will be appreciated that alternatively the belts 106
and 640 may have substantially the same pattern, or may have
patterns of complimentary shape.
[0187] The system 600 includes an alignment mechanism 650 for
obtaining suitable alignment between the patterned belts 106 and
640. The alignment mechanism 650 enables precise alignment between
the patterned belts 106 and 640, allowing a desired spatial
relationship between the patterns formed on the opposite sides of
the sheet material 24. The belts 106 and 640 may have respective
alignment marks 652 and 654 on them. The alignment mechanism 650
may use optical methods to align the alignment marks 652 and 654,
thereby assuring that the belts 106 and 640 are in the desired
relative spatial relationship. For example, the alignment mechanism
650 may shine a light through the belt 106 and the sheet 24, and
may include a light receiver, such a phototube or CCD, for
determining whether the alignment marks 652 and 654 are aligned.
The alignment marks 652 and 654 may be suitably configured so as to
create or avoid optical interference when aligned. Thus the belt
106 may be transparent to a suitable wavelength of visible or
non-visible light utilized by the alignment mechanism 650. If
necessary, the belt 640 may include a reflective coating or backing
to send light back to the alignment mechanism, in order to allow
checking of whether the alignment marks 652 and 654 are
aligned.
[0188] It will be appreciated that other sorts of alignment
mechanisms, such as suitable types of non-optical mechanisms may be
used in the alignment mechanism 650. For example, the sheet 24 may
have sprocket holes that engage protrusions on the belts 106 and/or
640, to mechanically align the sheet 24 and the belts 106 and
640.
[0189] The alignment mechanism 650 has been described above in
connection with a double band press. It will be appreciated that
alignment mechanisms such as the alignment mechanism 650 may be
even more suitably employed in connection with other embossing
processes, such as a batch or stepwise (step and repeat)
process.
[0190] The system 650 may be used to produce embossed sheets 24
with a variety of patterns. A few examples of suitable patterns are
shown in FIG. 18-21. FIG. 18 shows a micro-corrugated film 24a,
which may be used for example for optical applications, or to
increase surface area. FIG. 19 shows a sheet 24b with two-sided
through holes 660 to create an undercut structure. Optionally an
additional film may later be laminated onto the sheet 24b. FIG. 20
shows a sheet 24c having wells 662 on one major surface, and vias
664 placed in a desired location relative to the wells 662, either
in the center of the wells 662 or at another location relative to
the wells 662. FIG. 21 illustrates one example of a sheet 24d
having optical devices thereupon. The optical devices on the sheet
24d have one surface 670 that is an optical collector, and an
opposite surface 672 that directs and distributes the light in a
desired direction.
[0191] It will be appreciated that many other sorts of two-sided
embossed sheets may be produced using a suitable system such as the
system 600. The structure may have microfluidic channels with wells
for sample injection, for extraction, and/or for testing probe
insertion. As another example, the structure may be a two-sided
abrasive film. The two-sided embossing may be used to vary
bioreactivity of implants on the two sides. As another alternative,
high density interconnects for microelectronics may be formed, for
example including blind vias on both sides of the sheet. Heat
management devices may be created, with for example condenser
shapes on one side and evaporator shapes on the other side, with
through-holes linking the condensers and evaporators. Wells coupled
to through-holes may be utilized for heat management in electronic
systems, with integrated circuits placed in the wells and a channel
and/or through-hole structure used to the dissipate heat.
[0192] Turning now to FIGS. 22-24, one benefit of embossing using
the systems described above is that multilayered sheets may have
their integrity maintained during embossing, even though the
different materials of the different layers may have different
material properties, for example having different glass transition
temperatures and/or different melting temperatures. By
concentrating radiation-absorbing materials in layers or portions
of layers to be embossed, softening of materials by heating may be
localized, and heating may be minimized in other layers or portions
of layers, which may otherwise have their integrity and/or material
properties adversely affected.
[0193] FIG. 22 shows a multilayer sheet or film 24 having a first
layer 680 and a second layer 682. The layers 680 and 682 may be
made or different materials or may otherwise have different
material properties. The first layer 680 has conical protrusions
684 thereupon that are formed by embossing, using systems such as
those described above. The second layer 682 remains relatively
unheated during the embossing process, as radiant heat (such as
from a radiant heating system) is concentrated toward the embossed
portion. The radiant heat that is preferentially concentrated
toward all or a portion of the first layer 680 may be either
directly absorbed by all or a portion of the first layer 680.
Alternatively, the radiant heat may be absorbed by a suitable tool,
and then used to heat all or a portion of the first layer 680.
[0194] By concentration heating on all or a portion of the first
layer 680, undesired substantial heating of the second layer 682
may be avoided. This may reduce or eliminate problems that may
occur if uniform heating of the sheet 24 were to be used instead.
These problems may include softening of the second layer 682,
melting of the second layer 682, and/or mixing of the layers 680
and 682 or other breakdown of the integrity of the layers.
[0195] The first layer 680 may have a lower glass transition
temperature and/or melting temperature than the second layer 682.
The melting temperature of the first layer 680 may be lower than
the glass transition temperature of the second layer 682.
[0196] The second layer 682 may be less stiff than the first layer
680. Thus the protrusions 684 may be relatively stiff, with a more
flexible backing material, the second layer 682. The fist layer may
include a suitable polymeric material.
[0197] In a specific example embodiment, the first layer 680 may be
polysulfone that is 3 mils thick, and the second layer 682 may be a
co-extrusion of polypropylene and one of the following: styrene
butadiene styrene, styrene isopriene, or styrene ethylene butadiene
styrene, each 1 mil thick
[0198] It will be appreciated that a wide variety of structures may
be embossed on the first sheet 680.
[0199] FIG. 23 shows a multilayer film or sheet 24 that includes
first and second layers 690 and 692, both of which are embossed, on
opposite major surfaces of the sheet 24. The layers 690 and 692, or
portions thereof, may be suitably doped to provide the desired
heating for embossing. For example, the first layer 690 may have a
higher glass transition temperature than the second layer 692, and
thus may require more heating. The first layer 690 may thus have a
higher doping level of radiation-absorbing materials than the
second layer 692. This enables the first layer 690 to absorb more
radiant energy, and thus reach a higher temperature, than the
second layer 692.
[0200] It will be appreciated that the concentration or doping
level of radiation-absorbing material within each of the layers 690
and 692 may be non-uniform. For example, the concentration may be
limited to the portion of each of the layers nearest the embossed
surface. The radiation-absorbing material may be limited to half
the depth of each of the layers 690 and 692, for example.
[0201] FIG. 24 shows a multilayer sheet 24 having a first layer
700, a second layer 702, and a third layer 704, with the second
layer 702 between the first layer 700 and the third layer 704. The
first and third layers 700 and 704 may be heated using radiant
heating, while leaving the second layer 702 substantially unheated.
The radiant energy may pass through the second layer 702
substantially unabsorbed. The second layer 702 may be of a material
with a lower glass transition temperature than either the first
layer 700 or the third layer 704. Yet because of the selective
absorption of heat in the first and third layers, the second layer
702 may be substantially unheated. Thus a heat sensitive layer,
such as an adhesive layer, may be included in a material to be
embossed, without risk of damage from excessive heating in the
embossing process.
[0202] While the second layer 702 is described above as being
"substantially unheated," it will be appreciated that alternatively
the second layer 702 may undergo some sort of heating, albeit less
heating than the first layer 700 or the third layer 704. Put
another way, the second layer may be less absorptive of the
radiation of the heating system than the first layer 700 and the
third layer 704.
[0203] The layers of the various multilayer sheets of FIGS. 22-24
have been described as having their absorptivity of radiant energy
controlled by addition of different amounts of radiation-absorbing
material. It will be appreciated that the different materials in
the different layers may themselves have different
radiation-absorbing characteristics.
[0204] Selective heating and embossing of multilayer materials may
be used to produce a wide variety of types of products:
[0205] a) An embossed layer may overlie a layer that maintains its
orientation during the embossing process.
[0206] b) Embossing may be accomplished on one major surface while
maintaining structures, such as embossed structures, on the other
major surface.
[0207] c) One of the layers may include a ferromagnetic composite,
with the other layer including a conductive material.
[0208] d) Through holes or other structures may be embossed in the
hydrophobic layer of a hydrophobic/hydrophilic co-extruded film,
without affecting the hydrophilic nature of the underlying film,
and without causing the films to blend together.
[0209] e) A surface film over a holographic layer may be embossed,
without destroying the holographic characteristics.
[0210] f) A reflective film that overlies a peel layer may be
embossed.
[0211] g) A surface layer over a heat-activated film may be
embossed without activating the underlying film.
[0212] h) Microembossed structures may be formed over a
thermally-doped electrically conductive film, without disturbing
the electrically conductive properties of the conductive film.
[0213] i) A structure may be embossed on a plastic display
device.
[0214] j) A pattern, such as a waffle pattern, may be made atop a
layer with active ingredients. For example, the underlying layer
may contain a cleaning solution and the top layer may have
patterned hard material suitable for scrubbing.
[0215] With regard to preservation of film orientation in the
embossing process, the orientation to be maintained may be a
uniaxial or biaxial orientation, for example to be used in
orienting liquid crystals. For example the embossing processes such
as described herein may be used to create holes or other
microstructures in oriented film, while enabling the oriented film
to maintain its strength and/or other desirable properties.
Applications for such films include filtration, products that are
in contact with skin, and packaging.
[0216] Another potential application for the heating and embossing
processes described herein is in preservation of article or filler
distribution.
[0217] Yet another potential application for the heating and
embossing processes described herein is embossing
thermally-sensitive materials, while allowing them to retain
substantial thermally-sensitive properties. Such
thermally-sensitive materials may decompose or may react, when
heated excessively. For example, a sheet material may have a
subsurface material, such as a fragrance, that would be adversely
affected by heat. Other examples of material that would be
adversely affected or degraded by heat include certain surfactants
or pharmaceuticals.
[0218] It will be appreciated that some of the benefits described
above with regard to multi-layer films may also be applicable to
single-layer single-material sheets, where only part of the sheet
that is to be embossed is heated. A surface portion of the sheet
may be heated and embossed, while an underlying portion of the
sheet is substantially unheated, or is heated by a lesser amount.
The surface portion that is heated and embossed may extend from
about 0 to about 50 percent of the depth of the sheet, for example.
By selectively heating only a portion of the sheet, the properties
of the bulk part of the sheet may be maintained. The preferential
heating of the surface portion of the film may be accomplished by
selective placement of radiation-absorbing material along the
surface of the sheet. Alternatively, the sheet as a whole may
highly absorb radiant energy, with substantially all or most of the
radiant energy absorbed at the surface.
[0219] With reference now to FIGS. 25-28, embossing may be carried
out in a selective manner, on only a selected portion of a major
surface of a sheet 24. As shown in FIG. 25, an embossing system 720
includes a stencil 722 between a heating system 730 and a patterned
belt 734, which is made of a material that absorbs the radiant
energy. As shown in FIG. 26, an embossing system 760 includes a
stencil 762 between a heating system 770 and the sheet material 24
being embossed, wherein the sheet 24 includes a material that
absorbs the radiant energy. The stencils 722 and 762 include a
material that reflects the radiant energy, not allowing it to pass
therethrough. In both of the systems 720 and 760, the stencils 722
and 762 block radiant energy from impinging upon parts of the
patterned belt 734 and/or the sheet 24, thereby limiting heating to
parts of the belt 734 and/or the sheet 24. Thus embossing may be
limited to parts of the sheet 24 corresponding to openings in the
stencils 722 and 762.
[0220] An example of a stencil 722, with openings 774, is shown in
FIG. 27. The stencil 762 may have a similar configuration. It will
be appreciated that the stencils 722 and 762 may have a wide
variety of suitable configurations. For example, the stencil 722 or
762 may allow one or more words or symbols to be embossed on the
sheet 24 to form a retroreflective portion of the sheet 24, for
example for use in a traffic sign.
[0221] As shown in FIG. 28, selective embossing may be accomplished
by selectively doping or dyeing portions 780 of the sheet 24 with
radiantly-absorptive material. Such doped or dyed portions 780 are
preferentially heated with radiant energy relative to other
portions of the sheet 24, allowing the doped or dyed portions 780
to be selectively embossed.
[0222] Although the process has been described above as a selective
embossing process, it will be appreciated that the systems and
processes may be utilized for selective heating of the sheet 24 for
purposes other than embossing. For example, selective heating may
utilized to locally initiate a chemical reaction or locally change
material properties of the sheet 24.
[0223] It will be appreciated that the selectively heating and/or
embossing described above may be used in a variety of circumstances
to produce a variety of devices. For example, selective hot spots
may be created in a material to initiate a reaction with dopants
for bonding, or for generating voids through an out-gassing
reaction. As another example, selective heating may be used to
trigger nucleating agents in selected areas to enhance, for
example, localized crystallinity for change in refractive index,
light transmission, or other properties. As a further alternative,
an optically-sensitive or gas-sensitive region may be selectively
embossed. Selective embossing may also be used to emboss features
that require multiple embossing steps to produce different features
that are close together. Devices with patterned differences of
material properties, for example channels of crystalline vs.
amorphous polymer materials, may also be produced.
[0224] Systems described above may be used to emboss thicker
materials than may normally be embossed using conventional systems.
Thick materials may be difficult to emboss using bulk heating
methods such as flame heating, due to the difficulty of evenly
heating the material, and due to the relatively large amount of
energy involved in heating all or substantially all of a thick
material. With radiation heating of the sheet 24, especially with
the radiation passing into and/or being absorbed within parts of
the sheet 24, heating may be more localized. Embossing may thereby
be accomplished without overheating parts of the sheet, which
otherwise may need to be done to insure that the portions to be
embossed are sufficiently heated.
[0225] In addition, embossing of thick materials using conventional
heating may be cost-prohibitive because of the high energy costs
and low line speeds involved. Systems and methods using radiative
heating, such as those described herein, may allow less costly
embossing of thick materials, with energy costs and line speeds
that may be as low as or nearly as low as costs for thin materials.
This may be due at least in part to selective softening of only a
surface portion of the thick sheet material.
[0226] The thickness of materials embossed using the systems
described above may include materials that have a greater thickness
than the 5-7 mils (0.13-0.18 mm) thick materials normally embossed
using other systems or processes. For example, systems and methods
described above may be able to emboss materials that are greater
than about 1 inch (25.4 mm) thick, or even greater than about 2
inches (50.8 mm) thick. Examples of such thick materials may
include microfluidic assemblies, Fresnel lenses, retroreflective
markers, such as traffic markers.
[0227] Referring now to FIGS. 29 and 30, these figures show an
embossed oriented film, for example using systems and methods
described above. Optical film 910 comprises uniaxially oriented
film 912 with microchannels or grooves 914 embossed in its upper
surface. Microchannels 914 have a longitudinal direction (See FIG.
30) that is substantially parallel to the direction of orientation
of film 912. In the illustrated embodiment, microchannels 914 are
v-shaped grooves having a top angle .theta.. Each of the individual
microchannels 914 may be of substantially the same size and shape
as shown in FIG. 30, or of different sizes and shapes.
Microchannels 914 may have a cross-sectional shape that is
V-shaped, rectangular, trapezoidal, semi-circular or
sinusoidal.
[0228] In one embodiment, the individual microchannels 914 have a
depth in the range of about 1 micron to about 100 microns, and in
another embodiment, about 10 microns to about 100 microns. In yet
another embodiment, the depth of the microchannels is about 40
microns to about 60 microns. The width of the individual
microchannels 914, in one embodiment is within the range of about
0.2 microns to about 500 microns, and in another embodiment within
the range of about 10 microns to about 100 microns. Top angle
.theta. can be within the range of about 200 to about 120.degree.,
or about 60.degree. to about 90.degree..
[0229] Microchannels 914 may be spaced apart a distance of about
0.2 microns to about 500 microns in one embodiment, or about 100
microns to about 200 microns in another embodiment.
Oriented Films
[0230] Embossed uniaxially oriented film 912 comprises a
thermoplastic polymer. Oriented thermoplastic polymer films are
prepared by methods known in the art, such as by heating the
polymer to a temperature near or above the softening transition
temperature, followed by stretching in one direction (uniaxial
orientation) or two directions (biaxial orientation). Typically, a
polymer sheet is extruded and then oriented by rapid stretching at
a desired temperature to form an oriented film, followed by rapid
quenching. Quenching ensures that the orientation is not lost by
molecular relaxation. Orientation can occur in the direction of
film motion, referred to as machine direction (MD). Stretching in
the direction orthogonal to the machine direction is referred to as
transverse (TD) or cross direction.
[0231] Mechanical properties of oriented films vary depending upon
the direction and degree of orientation. Orientation brings out the
maximum strength and stiffness inherent in the polymer film. In
addition, orientation induces even higher levels of crystallinity
so that properties like barrier and chemical inertness are further
enhanced. Optical properties are generally superior, since
orientation leads to a crystalline structure that scatters much
less light than the crystalline domains formed in unoriented
films.
[0232] The embossed film described herein may be a uniaxially
oriented film, and not a biaxially oriented film. In one
embodiment, the stretch ratio of the oriented film is in the range
of about 4-5.times.MD and 1.times.TD. Amorphous glassy
thermoplastic films and semi-crystalline thermoplastic films are
suitable for use in making the embossed oriented film by the
methods described herein.
[0233] Suitable oriented amorphous glassy thermoplastic films
include those comprising acetates such as cellulose acetate,
cellulose triacetate and cellulose acetate/butyrate, acrylics such
as polymethyl methacrylate and polyethyl methacrylate, polystyrenes
such as poly(p-styrene) and syndiotactic polystyrene, and
styrene-based copolymers, vinylics such as polyvinyl chloride,
polyvinyl fluoride, polyvinylidene chloride, polyvinylidene
fluoride, polyvinylidone dichloride and mixtures thereof.
[0234] Suitable oriented semi-crystalline thermoplastic films
include those comprising polyolefin homopolymers such as
polyethylene and polypropylene, copolymers of ethylene, propylene
and/or 1-butylene; copolymers containing ethylene such as ethylene
vinyl acetate and ethylene acrylic acid; polyoxymethylene;
polyesters such as polyethylene terephthalate, polyethylene
butylrate, polybutylene terephthalate and polyethylene napthalate;
polyamides such as polyhexamethylene adipamide; polyurethanes;
polycarbonates; polyhexamethylene adipamide; polyurethanes;
polycarbonates; polyvinyl alcohol; ketones such as
polyetheretherketone; polyphenylene sulfide; and mixtures
thereof.
[0235] As used herein, the term "anisotropic" means that the
polymer film has different reflective properties along the
orthogonal in-plane axes. Anisotropic films are described in
International Publications WO02/48607 and WO01/90637. Particularly
suitable as the anisotropic optical film are polyethylene
terephthalate (PET) and polyethylene naphthalate (PEN).
[0236] In one embodiment, the anisotropic material is a
birefringent polymeric material. Such a birefringent polymer has an
extraordinary refractive index n.sub.e along its optical axis and
an ordinary refractive index no along the axes orthogonal thereto.
Dependent on the particular material, n.sub.e>n.sub.o or
n.sub.e<n.sub.o. The birefringence of the film, .DELTA.n, is the
difference between the ordinary refractive index and the
extraordinary refractive index. The birefringence of the
anisotropic material in this embodiment may be in the range of 0.1
to 0.5.
[0237] In one embodiment, a multilayer film may be used as the
embossed film. Examples of multilayer films include layers of films
that are formed by co-extrusion with one or more other polymers,
films coated with another layer, or films laminated or adhered
together. The surface of the multilayer film to be softened and
embossed is the anisotropic, uniaxially oriented film surface.
Isotropic Layer
[0238] In one embodiment, the anisotropic embossed film is coated
with an optically isotropic layer on its embossed surface. This
embodiment is illustrated in FIG. 31, in which lightguide 930
comprises embossed anisotropic film 932 having an isotropic coating
36 overlying its upper surface and embossed microchannels 934.
Isotropic materials are described in International Publications
WO02/48607 and WO01/90637. The refractive index of the isotropic
material is n.sub.i, which is substantially equal to one of the
refractive indices of the anisotropic layer n.sub.e or n.sub.o.
Suitable isotropic materials comprise, for example,
polymethylmethacrylate, polystyrene, polycarbonate, polyether
sulphone, cyclic olephine copolymers, crosslinked acrylates,
epoxides, urethane and silicone rubbers. In one embodiment, the
isotropic material comprises bisphenol A ethoxylated diacrylate
with a photoinitiator, which is UV cured.
[0239] In one embodiment, the refractive index of the isotropic
coating (n.sub.i) is equal to the ordinary refractive index
(n.sub.o) of the anisotropic film so that the emitted light is
linearly polarized.
Adhesives
[0240] The embossed film may be coated with an adhesive on its
unembossed surface to adhere the embossed film to another optical
layer or substrate. Suitable adhesives include hot-melt coated
formulations, water-based, and latex formulations, as well as
laminating, and thermally-activated adhesives. The adhesive layer
can be applied to the film by conventional techniques.
[0241] Examples of suitable adhesives include polyacrylate;
polyvinyl ether; diene-containing rubber such as natural rubber,
polyisoprene, and polyisobutylene; polychloroprene; butyl rubber;
butadiene-acrylonitrile polymer; thermoplastic elastomer; block
copolymers such as styrene-butadiene polymer; poly-alpha-olefin;
amorphous polyolefin; silicone; ethylene-containing copolymer such
as ethylene vinyl acetate, ethylacrylate, adn ethyl methacrylate;
polyurethane; polyamide; epoxy; polyvinylpyrrolidone and
vinylpyrrolidone copolymers; polyesters and mixtures of the above.
Additionally, the adhesives can contain additives, such as
tackifiers, plasticizers, fillers, antioxidants, stabilizers,
pigments, diffusing particles, curatives and solvents.
[0242] Suitable adhesives according may be pressure sensitive
adhesives. Pressure sensitive adhesive are normally tacky at room
temperature and can be adhered to a surface by application of, at
most, light finger pressure. A general description of useful
pressure sensitive adhesives may be found in Encyclopedia of
Polymer Science and Engineering, Vol. 13, Wiley-Interscience
Publishers (New York, 1988). Additional description of useful
pressure sensitive adhesives may be found in Encyclopedia of
Polymer Science and Technology, Vol. 1, Interscience Publishers
(New York, 1964).
[0243] The adhesive may be used to laminate the embossed film to a
substrate or to another optical layer, such as a waveguide plate.
Referring to FIG. 31, embossed film 932 has adhesive layer 938
adhered to its lower, unembossed surface. Adhesive layer 938
adheres the embossed film 932 to substrate 940, which can be a
conventional polymeric substrate such as polymethyl methacrylate.
The adhesive can be selected based on its refractive index so that
it does not interfere with the functioning of the waveguide
plate.
[0244] The adhesive layer on the embossed film may have a removable
liner adhered thereto. The liner protects the adhesive layer and
prevents inadvertent bonding prior to use. The liner that can be
used can be any release liner known in the art.
Embossing Method
[0245] A method of embossing an optical film includes: heating at
least a portion of the optical film indirectly with radiant energy
from a radiant energy source; pressing a tool against the heated
portion of the optical film, thereby patterning a surface of the
optical film; and separating the optical film and the tool. The
radiant energy may travel through a solid material that is
relatively transparent to radiation, on its way to being absorbed
by a relatively-absorptive material. The relatively-transparent
material may be an unheated portion or all of the optical film, and
the relatively-absorptive material may be the tool. The method may
be performed as one or more roll-to-roll operations. Alternatively
or in addition, the method may include one or more batch
processes.
[0246] The systems and methods described above may involve heating
and embossing processes that at least partially overlap in time,
and therefore to at least some extent are performed simultaneously.
By overlapping the heating and the embossing in time, several
advantageous process characteristics may be achieved, including
reducing energy losses and reducing unwanted changes in material
shape.
[0247] At least some of the systems and methods described above
also have the advantage of containing the sheet material 24 during
the heating and embossing processes. By containing the sheet
material 24, such as between a pair of belts, planarity of the
sheet material may be better maintained, when compared to processes
where the sheet material is not contained or constrained on both
sides.
[0248] Radiant heating using radiant heaters, such as NIR heaters,
provides several advantages compared to heating using flame
heaters. Flameless radiant heaters may provide a safety advantage,
in that they do not utilized open flames, and may thus be used in
environments where it would be unsafe to use an open flame. In
addition, NIR heaters and other flameless radiant heaters may
provide better output controllability than flame heaters. The
output of flame heaters may change based on environmental and other
conditions, such as changes in ambient temperature, pressure,
and/or humidity, and/or variations in fuel characteristics.
Contamination caused by combustion by-products of flame heaters may
also be avoided by use of flameless heaters. The heat produced by
flame heaters also tends to be relatively broad in its wavelength
range. Thus heat from a flame heater is well-absorbed by a wide
variety of materials, while heat from a flameless radiant heater
may be more selectively absorbed, allowing more localization in
heating. Of course, localization in heating enables embossing to be
performed with less energy and fewer undesirable side effects.
[0249] The radiant energy utilized in the above systems and/or
methods may be near-infrared energy, for example utilizing NIR-type
heaters available from Advanced Photonics Technologies AG. Other
suitable radiant heaters and emitters are available from Phillips,
Ushio, General Electric, Sylvania, and Glenro. The radiant energy
may have most of its energy in a wavelength range of between 0.4 to
2 .mu.m (microns).
[0250] Other types of radiant energy may alternatively or in
addition be utilized. Examples of some other types of radiation
that may be suitable include microwaves having a frequency of
approximately 7-8 GHz. Free water within a polymer structure may be
able to absorb such microwave radiation, as well as possibly
radiation of other frequencies or wavelengths. Radiation having a
peak wavelength of approximately 1-6 microns may also be suitable.
Such radiation may be produced by suitable quartz-tungsten lamps.
RF induction heating may also be employed, for example in the
heating of metal tooling for embossing. High power lasers with
suitable wavelength may also be used.
[0251] A variety of suitable power levels may be employed for the
radiant energy source. One example embodiment utilizes a power
level of approximately 14 kilowatts. However, it will be
appreciated that the amount of power involved is very dependent on
many factors of the process, such as the materials involved, size
of the materials to be embossed, process speed, etc.
[0252] Suitable combinations of heat sources, including
combinations of radiant heating with non-radiant heating, may be
employed in heating the sheet material 24.
[0253] It will be appreciated that the systems and methods
described above may provide significant advantages over prior
systems. First, selective heating may be accomplished, focusing the
heating where needed. Second, heat transfer to the material may be
provided by multiple mechanisms, for example radiation from an
energy source along with conduction from a tool. This may result in
high heat fluxes. Further, use of multiple heat transfer mechanisms
may increase flexibility of the system, by allowing the heat
transfer mechanisms to be independently manipulated. With variation
of such factors as tool mass and radiation time (as well as other
factors), the heating profile for the sheet material 24 may be
controlled, such that (for example) the film degradation is
minimized, and/or the cooling time is shortened.
[0254] In addition, many of the processes are described above in
terms of systems involving belts and rollers. It will be
appreciated that other types of processes may embody many of the
characteristics of the belt-and-roller processes. For example,
embossing using presses or patterned rollers may be used
alternatively or in addition to the belt processes disclosed.
[0255] Although the invention has been shown and described with
respect to a certain embodiment or embodiments, it is obvious that
equivalent alterations and modifications will occur to others
skilled in the art upon the reading and understanding of this
specification and the annexed drawings. In particular regard to the
various functions performed by the above described elements
(components, assemblies, devices, compositions, etc.), the terms
(including a reference to a "means") used to describe such elements
are intended to correspond, unless otherwise indicated, to any
element which performs the specified function of the described
element (i.e., that is functionally equivalent), even though not
structurally equivalent to the disclosed structure which performs
the function in the herein illustrated exemplary embodiment or
embodiments of the invention. In addition, while a particular
feature of the invention may have been described above with respect
to only one or more of several illustrated embodiments, such
feature may be combined with one or more other features of the
other embodiments, as may be desired and advantageous for any given
or particular application.
* * * * *