U.S. patent application number 17/124382 was filed with the patent office on 2021-04-08 for film and stylus system for emulating pen-on-paper tactile feedback.
The applicant listed for this patent is Tactus Technology, Inc.. Invention is credited to Brian Flamm, Ryosuke Isobe, Curtis Takagi, Justin Virgili, Micah Yairi.
Application Number | 20210103349 17/124382 |
Document ID | / |
Family ID | 1000005287627 |
Filed Date | 2021-04-08 |
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United States Patent
Application |
20210103349 |
Kind Code |
A1 |
Virgili; Justin ; et
al. |
April 8, 2021 |
FILM AND STYLUS SYSTEM FOR EMULATING PEN-ON-PAPER TACTILE
FEEDBACK
Abstract
A feedback-enhancing film includes: an elastic layer comprising
a first polymer exhibiting optical transparency and elasticity; and
an interface layer arranged across an upper surface of the elastic
layer comprising a second polymer exhibiting optical transparency,
impact resistance, UV resistance, and smoothness to touch.
Additionally, the interface layer and the elastic layer mutually
deform to resist transverse movement of a stylus tip across the
interface layer in response to an application of writing force to
the interface layer via the stylus tip. The film can also comprise
a system including: the film; a stylus including a stylus tip; and
a touch-sensitive screen.
Inventors: |
Virgili; Justin; (Fremont,
CA) ; Yairi; Micah; (Fremont, CA) ; Takagi;
Curtis; (San Jose, CA) ; Isobe; Ryosuke;
(Westminster, CO) ; Flamm; Brian; (Los Altos
Hills, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Tactus Technology, Inc. |
Fremont |
CA |
US |
|
|
Family ID: |
1000005287627 |
Appl. No.: |
17/124382 |
Filed: |
December 16, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16379733 |
Apr 9, 2019 |
10895922 |
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17124382 |
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15227726 |
Aug 3, 2016 |
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16379733 |
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15895971 |
Feb 13, 2018 |
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16379733 |
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62655125 |
Apr 9, 2018 |
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62200231 |
Aug 3, 2015 |
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62458458 |
Feb 13, 2017 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G06F 3/03545 20130101;
G06F 3/041 20130101; G06F 3/0202 20130101 |
International
Class: |
G06F 3/041 20060101
G06F003/041; G06F 3/0354 20060101 G06F003/0354; G06F 3/02 20060101
G06F003/02 |
Claims
1. A feedback-enhancing film comprising: an elastic layer,
comprising a first polymer exhibiting optical transparency, bulk
elasticity, and a first elastic recovery rate; an interface layer
arranged across an upper surface of the elastic layer comprising a
second polymer exhibiting optical transparency, impact resistance,
UV resistance, smoothness to touch, and a second elastic recovery
rate, the second elastic recovery rate less than the first elastic
recovery rate; and wherein, in response to an application of a
first writing force via a stylus tip, the interface layer and the
elastic layer mutually deform to exhibit a first dynamic
coefficient of friction substantially similar to a second dynamic
coefficient of friction exhibited by paper in response to an
application of the first writing force via a pen.
2. The feedback-enhancing film of claim 1, wherein the interface
layer and the elastic layer exhibit elastic deformation greater
than 10% engineering strain of the interface layer and the elastic
layer when a writing force is applied to the interface layer and
the elastic layer via the stylus tip.
3. The feedback-enhancing film of claim 1, wherein the first
elastic recovery rate and the second elastic recovery rate is
characterized by a peak tan delta ratio less than 2.5.
4. The feedback-enhancing film of claim 1, wherein the interface
layer and the elastic layer exhibit the first dynamic coefficient
of friction between 0.2 and 0.3.
5. The feedback-enhancing film of claim 4, wherein the interface
layer and the elastic layer exhibit the first dynamic coefficient
of friction between 0.20 and 0.23 in response to the application of
the first writing force of 1.0 Newtons and exhibit a second dynamic
coefficient of friction between 0.22 and 0.28 in response to an
application of a second writing force of 3.0 Newtons.
6. The feedback-enhancing film of claim 4, wherein the interface
layer and the elastic layer exhibit the first dynamic coefficient
of friction between 0.2 and 0.3 in response to the application of
the first writing force via a 1.5-millimeter stylus tip across the
interface layer.
7. The feedback-enhancing film of claim 1, wherein the elastic
layer comprising the first polymer is chemically crosslinked with
the interface layer comprising the second polymer at the upper
surface of the elastic layer.
8. The feedback-enhancing film of claim 7, wherein the elastic
layer comprising the first polymer is chemically crosslinked with
the interface layer comprising the second polymer by: combining a
prepolymer, a solvent, a cross-linking agent, and a chain extender
to define a viscous material; advancing the elastic layer;
depositing the viscous material through a deposition head across
the elastic layer, the viscous material flowing across the elastic
layer to form a thin layer of substantially uniform thickness; and
heating the thin layer and the elastic layer to initiate
polymerization of the thin layer into the interface layer and
crosslinking between the interface layer and the elastic layer.
9. The feedback enhancing film of claim 1, wherein: the first
polymer comprises polyurethane; and the second polymer comprises
self-healing acrylic polyurethane.
10. The feedback-enhancing film of claim 1, further comprising a
distribution of microparticles comprised of a hard polymer
suspended within the interface layer, the microparticles
characterized by optical transparency.
1. feedback-enhancing film of claim 1: wherein the elastic layer
defines a continuous layer; and wherein the interface layer defines
a set of discontinuous regions across the elastic layer.
12. The feedback-enhancing film of claim 11, wherein each
discontinuous region in the set of discontinuous regions: spans an
area less than 1 square millimeter; and is separated from an
adjacent discontinuous region by a distance greater than 10
micrometers.
13. The feedback-enhancing film of claim 1, wherein the elastic
layer comprises a textured upper surface approximating the surface
roughness of paper.
14. A system for enhancing writing feedback comprising: a stylus
comprising a stylus tip; and a film comprising: an elastic layer,
comprising a first polymer exhibiting optical transparency and bulk
elasticity; an interface layer arranged across an upper surface of
the elastic layer comprising a second polymer exhibiting optical
transparency, abrasion resistance, impact resistance, UV
resistance, and smoothness to touch; a distribution of
microparticles comprised of a hard polymer suspended within the
interface layer, the microparticles characterized by optical
transparency and an average distance between adjacent
microparticles less than a diameter of the stylus tip; and wherein
the interface layer and the elastic layer mutually deform to resist
transverse movement of the stylus tip across the interface layer in
response to an application of writing force to the interface layer
via the stylus tip.
15. The system of claim 14, wherein: the first polymer comprises
polyurethane; the second polymer comprises self-healing acrylic
polyurethane; and the stylus tip comprises polyoxymethylene.
16. A system for enhancing writing feedback comprising: a stylus
comprising a stylus tip; a film comprising: an elastic layer,
comprising a first polymer exhibiting optical transparency and bulk
elasticity; an interface layer arranged across an upper surface of
the elastic layer comprising a second polymer exhibiting optical
transparency, abrasion resistance, impact resistance, UV
resistance, and smoothness to touch; and wherein the interface
layer and the elastic layer mutually deform to resist transverse
movement of the stylus tip across the interface layer in response
to an application of writing force to the interface layer via the
stylus tip; and a touch sensitive display: arranged across a bottom
surface of the elastic layer; bonded to the elastic layer via a
layer of optically clear adhesive; and configured to detect the
stylus tip at a distance substantially equal to a film thickness of
the film.
17. The system of claim 16, wherein: the first polymer comprises
polyurethane; the second polymer comprises self-healing acrylic
polyurethane; and the stylus tip comprises polyoxymethylene.
18. A system for enhancing writing feedback comprising: a stylus
comprising a stylus tip; and a film comprising: an elastic layer,
comprising a first polymer exhibiting optical transparency and bulk
elasticity; an interface layer arranged across an upper surface of
the elastic layer comprising a second polymer exhibiting optical
transparency, abrasion resistance, impact resistance, UV
resistance, and smoothness to touch; and wherein the interface
layer and the elastic layer mutually deform to resist transverse
movement of the stylus tip across the interface layer in response
to an application of writing force to the interface layer via the
stylus tip; and wherein the film defines a film thickness between
50 micrometers and 200 micrometers and the elastic layer defines a
thickness between two and three times a thickness of the interface
layer.
19. The system of claim 18, wherein: the first polymer comprises
polyurethane; the second polymer comprises self-healing acrylic
polyurethane; and the stylus tip comprises polyoxymethylene.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This Application is a continuation application of U.S.
patent application Ser. No. 16/379,733, filed on 9 Apr. 2019, which
claims the benefit of U.S. Provisional Application No. 62/655,125,
filed on 9 Apr. 2018, both of which are incorporated in their
entireties by this reference.
[0002] U.S. patent application Ser. No. 16/379,733, filed on 9 Apr.
2019, is a continuation-in-part application of U.S. patent
application Ser. No. 15/227,726, filed on 3 Aug. 2016, which claims
the benefit of U.S. Provisional Application No. 62/200,231, filed
on 3 Aug. 2015, both of which are incorporated in their entireties
by this reference.
[0003] U.S. patent application Ser. No. 16/379,733, filed on 9 Apr.
2019, is also a continuation-in-part application of U.S. patent
application Ser. No. 15/895,971, filed on 13 Feb. 2018, which
claims the benefit of U.S. Provisional Application No. 62/458,458,
filed on 13 Feb. 2017, both of which are incorporated in their
entireties by this reference.
TECHNICAL FIELD
[0004] This invention relates generally to the field of
touch-sensitive interfaces, and more specifically to a system for
emulating pen-on-paper tactile feedback in the field of
touch-sensitive interfaces.
BACKGROUND
[0005] Enabled by the increased resolution and performance of
capacitive touchscreens (and styluses capable of interacting with
them) and by the emergence of the tablet market, consumers are
increasingly demanding the fine precision and capability of
interaction afforded only by the use of a stylus or other writing
implement in conjunction with the ability to provide touch input to
a screen interface.
[0006] However, stylus-capable touch interfaces of modern computing
devices still resemble those of previous finger-centric devices.
Often hard, slick, and formed of glass or glasslike material, these
interfaces provide a stylus experience incapable of providing the
same high accuracy and tactile feedback that consumers experience
with pens or pencils on paper.
[0007] Manufacturers have attempted to address this issue by
focusing on the stylus--manufacturing styluses with soft,
deformable tips, which provides some improvements to feel, but at a
significant cost to durability and accuracy.
[0008] The present application is directed to a system for
enhancing stylus tactile feedback that provides stylus users with
the feel of traditional writing without the accuracy tradeoffs
taken by stylus manufacturers.
BRIEF DESCRIPTION OF THE FIGURES
[0009] FIGS. 1A and 1B are schematic representations of a
feedback-enhancing film;
[0010] FIGS. 2A and 2B are schematic representations of a
touch-sensitive system including the feedback-enhancing film;
[0011] FIGS. 3A and 3B are schematic representations of variations
of the feedback-enhancing film;
[0012] FIGS. 4A and 4B are schematic representations of variations
of the feedback-enhancing film;
[0013] FIG. 5 is a graphical representation of the dynamic
coefficient of friction of the feedback-enhancing film over a range
writing forces;
[0014] FIG. 6 is a schematic representation of a manufacturing
method of the feedback-enhancing film;
[0015] FIG. 7 is a schematic representation of a manufacturing
method of the feedback-enhancing film; and
[0016] FIG. 8 is a flowchart representation of the manufacturing
method of the feedback-enhancing film.
DESCRIPTION OF THE EMBODIMENTS
[0017] The following description of embodiments of the invention is
not intended to limit the invention to these embodiments but rather
to enable a person skilled in the art to make and use this
invention. Variations, configurations, implementations, example
implementations, and examples described herein are optional and are
not exclusive to the variations, configurations, implementations,
example implementations, and examples they describe. The invention
described herein can include any and all permutations of these
variations, configurations, implementations, example
implementations, and examples.
1. Feedback-Enhancing Film
[0018] As shown in FIG. 1A, a feedback-enhancing film 100
(hereinafter "the film") includes an elastic layer 120, comprising
a first polymer exhibiting optical transparency and elasticity; an
interface layer 110 arranged across an upper surface of the elastic
layer 120 comprising a second polymer exhibiting optical
transparency, impact resistance, UV resistance, and smoothness to
touch. Additionally, the interface layer 110 and the elastic layer
120 mutually deform to resist transverse movement of a stylus tip
across the interface layer 110 in response to an application of
writing force to the interface layer 110 via the stylus tip.
[0019] As shown in FIG. 2A the film 100 can also comprise a system
200 including: the film 100; a stylus 210 including a stylus tip;
and a touch-sensitive screen. Additionally, the interface layer 110
and the elastic layer 120 mutually deform to resist transverse
movement of the stylus tip across the interface layer 110 in
response to an application of writing force to the interface layer
110 via the stylus tip.
2. Applications
[0020] Generally, the film 100 is a multilayer film including an
elastic layer 120 and an interface layer 110 and is configured to
interact with a stylus 210 and/or human fingers as part of a system
200 for enhancing stylus 210 tactile feedback while maintaining the
expected optical transparency/clarity, durability, and touch
sensitivity/feel of a typical capacitive and/or resistive
touchscreen installed on a mobile computing device (e.g., a
smartphone or tablet). When a typical writing force (e.g., 0.5 to
3.0 Newtons) is applied to the film 100 by a user via the stylus
210, the film 100 emulates the tactile feeling of writing with a
pen on paper by exhibiting similar deformation characteristics and
a similar dynamic coefficient of friction to those exhibited by
several sheets of paper when written on by a pen. In particular,
the interface layer 110 functions as a protective and visually
appealing top layer to prevent damage (e.g., mechanical or UV) to
the underlying elastic layer 120 or touch screen while also being
able to macromolecularly deform under pressure without separating
from the elastic layer 120. The elastic layer 120 more accurately
mimics the deformation characteristics of multiple sheets of paper.
Thus, by including a protective interface layer 110, the film 100
enables the selection of materials for the elastic layer 120 that
can be more finely tuned to the mechanical properties of paper but
may not be sufficiently stable, durable, or visually appealing to
function as a single-layer film for a touchscreen display.
Furthermore, by more accurately mimicking the macromolecular
deformation that occurs around a pen when applied to paper, the
film 100 also enables the inclusion of a stylus 210 with a small
tip diameter (e.g., 1.5 millimeters), which further improves
writing precision for the user and facilitates accurate detection
of the stylus 210 by an underlying touchscreen.
[0021] More specifically, the film 100 exhibits significantly
different deformation and surface friction characteristics in
response to an application of localized force (e.g., such as via
tip of a stylus 210) versus an application of distributed force
(e.g., via a touch of a finger). This property is an emergent
quality of careful tuning of the relative elasticity of each layer
and the relative thickness of each layer, wherein the elastic layer
120 is thicker (e.g., 60%-80% of the total thickness of the film
100) and more elastic than the interface layer 110, while the
interface layer 110 is thin enough to deform to the same degree as
the elastic layer 120 while exhibiting surface hardness and
smoothness (e.g., substantially similar to glass). The film 100 can
exhibit elastic deformation characteristics through at least 10%
engineering strain of the film 100, thereby exhibiting consistent
elastic recovery upon indentation by the stylus 210 (e.g., an
indentation of 30 to 60 micrometers). Additionally, at 10%
engineering strain and during the application of typical writing
force, the film 100 exhibits a dynamic coefficient of friction of
between 0.2 and 0.3 (indicating a friction force equal to 20%-30%
of the normal force applied via the stylus 210). These
characteristics are similar to those exhibited by several sheets of
paper when pressed upon by the tip of a ballpoint pen, as shown in
FIG. 5. However, as is further described below, the film 100 can
also be tuned to mimic a pencil-on-paper feel with the addition of
subsurface texturing or suspended particles within the film
100.
[0022] The film 100 exhibits durability on par with similar polymer
touchscreen coatings despite being capable of repeated deformation
by a stylus 210 due to tuning of the elastic recovery rate of the
interface layer 110 relative to the elastic recovery rate of the
elastic layer 120. Although, the interface layer 110 and the
elastic layer 120 differ in elasticity and thickness, the elastic
layer 120 can exhibit an elastic recovery rate equal to or greater
than the elastic recovery rate of the interface layer 110, thereby
preventing separation of the interface layer 110 from the elastic
layer 120. Additionally, a specialized manufacturing method S100 of
the film 100 further improves the film's durability by chemically
crosslinking the interface layer 110 to the elastic layer 120
during curing of the interface layer 110.
[0023] Although the composition of the interface layer 110 and the
composition of the elastic layer 120 can vary depending on the
desired tactile feedback from the film 100, the film 100 can
include an elastic layer 120 composed of a soft, optically-clear
polymer characterized by elastic and/or viscoelastic properties and
an interface layer 110 composed of a medium durometer polymer with
a smooth surface finish, UV resistance, and the ability to
crosslink with the polymer of the elastic layer 120. In one
implementation, the elastic layer 120 includes an optically-clear
polyurethane cast elastomer, while the interface layer 110 includes
a self-healing, optically-clear acrylic polyurethane cast
elastomer. In a second implementation, the elastic layer 120
includes an optically-clear thermoplastic polyurethane, while the
interface layer 110 includes a self-healing, optically--clear
acrylic polyurethane cast elastomer.
3. Example
[0024] In one example implementation of the film 100, the film 100
is included in a touchscreen and stylus system 200, which can be
installed on a mobile computing device. Upon visual examination of
the touchscreen 220 on the mobile computing device, a user may
notice no significant difference in the appearance of the
touchscreen 220, which has a similar optical clarity and gloss to a
normal touchscreen. The user may then interact with the touchscreen
220 using their fingers and perceive a smooth tactile surface with
minimal deformation under load. However, upon applying writing
force (e.g., a concentrated/localized force) to the surface of the
touch screen, the user may experience a slight depression of the
stylus 210 into the film 100 and a drag force resisting transverse
motion of the stylus 210 across the film 100. Thus, a touchscreen
and stylus system 200 including the film 100 can provide desired
tactile feedback through touch and through a stylus 210
feedback.
4. Interface Layer
[0025] Generally, the film 100 includes an interface layer 110
including a polymer exhibiting optical transparency, impact
resistance, UV resistance, and smoothness to touch. The film 100
includes an interface layer 110 that: presents a smooth tactile
surface to a user of touchscreen underlying the film 100; provides
a glossy surface finish consistent with typical hard coatings for
touchscreens; and provides impact, abrasion, and UV resistance to
the elastic layer 120 and underlying touchscreen. Additionally, the
interface layer 110 minimally deforms in response to distributed
force applied over a larger area of the film (e.g., in response to
touch or press of a finger over an area on the order of a square
centimeter) but elastically deforms in response to localized force
applied over a smaller area (e.g., in response to writing force
applied to the film 100 via a stylus 210 over an area on the order
of a square millimeter). Thus, the interface layer 110 is
characterized by a low surface roughness (e.g., comparable to
tempered glass), a low static/kinetic coefficient of friction, and
a medium durometer/hardness and an elastic modulus higher than an
elastic modulus of the elastic layer 120.
[0026] The film 100 can include an interface layer 110 with a
surface roughness similar to tempered glass, which contributes to
the desired surface friction and surface gloss characteristics of
the interface layer 110. In one implementation, the surface
roughness of the interface layer 110 is less than 0.15 micrometers
R.alpha. root-mean-squared (hereinafter "RMS").
[0027] The interface layer 110 includes a polymer with a greater
durometer/hardness and elastic modulus when compared to the elastic
layer 120. The interface layer 110 can therefore include polymers
such as polyurethanes with higher crosslinking densities and
shorter polyol chains. In one implementation the interface layer
110 includes a self-healing (e.g., at room temperature) acrylic
polyurethane.
[0028] Because the interface layer 110 deforms to the same extent
as the elastic layer 120, which has a lesser elastic modulus, the
film 100 includes an interface layer 110 with a thickness less than
the thickness of the elastic layer 120. In one implementation, the
film includes an interface layer 110 that comprises 10%-35% of the
overall thickness of the film 100. Typically, in order for an
underlying (capacitive) touch screen to function, the film 100 is
characterized by a thickness between 50 and 200 micrometers.
Therefore, the film 110 can include an interface layer 110
characterized by a thickness between 5 and 70 micrometers. In one
implementation, the interface layer 110 is characterized by a
thickness of 25 micrometers and the elastic layer 120 is
characterized by a thickness of 50 micrometers. In a second
implementation, the interface layer 110 is characterized by a
thickness of 25 micrometers and the elastic layer 120 is
characterized by a thickness of 75 micrometers.
[0029] In one implementation, the interface layer 110 includes an
oleophobic coating applied over the tactile surface of the
interface layer 110 to prevent fingerprinting on the tactile
surface of the interface layer 110.
4. Interface Layer Composition
[0030] The film 100 can include an interface layer 110 with
properties tuned such that, upon an application of writing force
the film 100 exhibits a dynamic coefficient of friction similar to
a ball-point pen writing on four sheets of paper. The interface
layer 110 can include a polyurethane chemistry characterized by an
acrylic polyol, as a primary polyol and an aliphatic isocyanate
(hereinafter "antiscratch coating" or "ASC"). The film 100
including ASC in the interface layer 100 can exhibit significantly
increased dynamic coefficient of friction when compared to coated
glass, as shown in TABLE 1 Example 6. However, various
compositional characteristics of the interface layer 110 can be
further adjusted in order to better achieve the abovementioned film
properties. More specifically, the properties of the interface
layer 110 can be modified: by adjusting the stoichiometric ratio of
aliphatic isocyanate groups to isocyanate-reactive groups
(hereinafter "stoichiometric ratio" of "[NCO/OH]"); by modifying
the polyol chemistry of the thermoplastic polyurethane; or by
adding reactive fluoropolymer additives.
[0031] In one implementation, the film 100 includes an interface
layer 110 characterized by a stoichiometric ratio between 0.8 and
1.6, which results in a dynamic coefficient of friction between
0.13 and 0.20, as shown in TABLE 1 Examples 1-3. Thus, the film 100
can approximate the dynamic coefficient of friction exhibited by a
ball point pen on four sheets of paper, as shown in TABLE 1 Example
7.
[0032] In a second implementation, the interface layer 110 can
include a secondary polyol with a non-acrylic backbone comprised of
a polyether, polyester, or polycarbonate mixed with the primary
acrylic polyol to reduce the dynamic coefficient of friction (as
shown in TABLE 1, Example 4).
[0033] In a third implementation, the interface layer 110 can
include a fluoropolymer additive containing at least one
isocyanate-reactive functional group is mixed with the acrylic
polyol, such as trimethylolpropane (TMP) or ethoxylated TMP to
modify the dynamic coefficient of friction (as shown in TABLE 1,
Example 5). Therefore, the interface layer 110 can include reactive
fluoropolymer additives, such as fluoroethylene/alkyl vinyl ether
copolymers, perfluoropolyethers, polyvinylidene fluoride,
tetrafluoroethylene copolymer, polyhexafluoropropylene,
polytetrafluoroethylene and combinations thereof. Furthermore, in
implementations of the interface layer 110 including a reactive
fluoropolymer additive, the reactive fluoropolymer additive can be
modified to include at least one isocyanate-reactive functional
group. The dynamic coefficient of friction was measured using the
amount of indentation experienced for a 1.9 mm diameter POM stylus,
20 mm/s tip speed, and 300 gram-force specific writing force using
a customized friction testing instrument.
[0034] TABLE 1 indicates the dynamic coefficient of friction of
exemplary interface layer compositions as a component in the film
100 measured with a 1.9 mm diameter POM stylus oriented
perpendicular (90.degree.) to the interface layer 110 using a 20
mm/s tip speed and 300 g force. Measurements were recorded using a
customized friction testing instrument comprised of an Instron 5942
equipped with a 10 N load cell and low friction rail system. In all
cases, the Interface and Elastic layer thicknesses are 25 and 75
um, respectively.
TABLE-US-00001 Interface Surface Dynamic Layer Roughness
Coefficient Example Composition (R.sub.a, nm) of Friction 1 ASC 1.6
[NCO/OH] 31 .+-. 2 0.20 .+-. 0.01 2 ASC 1.4 [NCO/OH] 29 .+-. 3 0.15
.+-. 0.01 3 ASC 0.8 [NCO/OH] 27 .+-. 2 0.13 .+-. 0.01 4 ASC w/2.3%
31 .+-. 5 0.08 .+-. 0.01 polycarbonate polyol 5 ASC w/2.2% 27 .+-.
3 0.09 .+-. 0.01 tetrafluoroethylene additive 6 Anti-fingerprint
coated n.d. 0.04 .+-. 0.01 glass (comparative) 7 4 stacked sheets
20# 1724 .+-. 133 0.23 .+-. 0.01* paper (comparative) *Measured
using ball point pen in place of a stylus.
5. Elastic Layer
[0035] Generally, the film 100 includes an elastic layer 120
including a polymer exhibiting elasticity and optical transparency
that replicates the feeling of writing with a pen on several sheets
of paper. The elastic layer 120 can exhibit an elastic modulus such
that the elastic layer 120 (and therefore the film 100 as a whole)
deforms by 10% to 20% strain and experiences elastic deformation
throughout this intended deformation range. Additionally, the
elastic layer 120 is characterized by a thickness that is 65%-90%
of the total thickness of the film 100. Thus, the elastic layer 120
can deform significantly when force is applied by the stylus 210
while distributing the force across the underlying touchscreen
thereby preventing damage to the touchscreen 220.
[0036] In one implementation, the film 100 includes an elastic
layer 120 of a low durometer polyurethane. However, the elastic
layer 120 can be manufactured from any polymer composition that
exhibits the appropriate elastic and optical properties described
herein.
[0037] Furthermore, the elastic layer 120 is configured to exhibit
an elastic recovery rate equal to or greater than the elastic
recovery rate of the interface layer 110. Therefore, the force of a
stylus 210 mutually deforms the interface layer 110 and the elastic
layer 120 downward and, upon removal of the stylus 210 from the
film 100, the interface layer 110 does not retract upward from the
elastic layer 120. Instead the elastic layer 120 can function to
push the interface layer 110 upward, preventing delamination of the
elastic layer 120 from the interface layer 110.
5.1 Elastic Layer Composition
[0038] The film 100 can include an elastic layer 120 with
properties tuned such that, upon an application of writing force
the film 100 exhibits a dynamic coefficient of friction similar to
a ball-point pen writing on four sheets of paper. More
specifically, dynamic coefficient of friction of the film 100 can
be modified: by adjusting hardness of the elastic layer 120; and by
modifying the thickness of the elastic layer 120.
[0039] In one implementation, the elastic layer 120 is composed of
a thermoplastic polyurethane (TPU), which can be obtained via the
reaction of polyisocyanates, polyols, and optional chain extenders.
Non-limiting examples of suitable polyisocyanates include aliphatic
isocyanates, such as hexamethylene diisocyanate (HDI), isophorone
diisocyanate (IPDI), or hydrogenated methylene diphenyl
diisocyanate (H12MDI), or aromatic isocyanates, including methylene
diphenyl diisocyanate (MDI), or toluene diisocyanate (TDI).
Non-limiting examples of suitable polyols include polyether,
polyester, or polycarbonate polyols. Non-limiting examples of
suitable chain extenders include diols (ethylene glycol, diethylene
glycol, alkane diols, such as 1,4-butanediol and 1,6-hexanediol,
and aromatic diols, such as hydroquinone bis(2-hydroxylethyl)
ether) and diamines (tetramethylene diamine and hexamethylene
diamine).
[0040] The elasticity of the interface layer 110 and elastic layer
120 is characterized using Dynamic Mechanical Analysis (Mettler
Toledo DMA1, 1 Hz@0.1 N in tension, 2.degree. C./min). The
elasticity of single layers is given by the glass transition
temperature (T.sub.g) determined using peak tan delta and the value
of tan delta at 20.degree. C. (td.sub.T=20.degree. C.). The
similarity of the elastic recovery rates of the interface layer 110
and elastic layer 120 is parameterized by .DELTA.T.sub.g
(T.sub.g,Interface-T.sub.g,Elastic) and the ratio of the interface
layer and elastic layer's td.sub.T=20.degree. C., R.sub.td,
20.degree. C. (td.sub.Interface/td.sub.Elastic). In implementations
of the film 100 exhibiting commensurate elastic recovery rates in
the interface layer 110 and the elastic layer 120 are characterized
by a .DELTA.T.sub.g wherein 0.degree.
C..ltoreq..DELTA.T.sub.g.ltoreq.50.degree. C. and R.sub.td,
20.degree. C. wherein 0.1.ltoreq.R.sub.td, 20.degree.
C..ltoreq.2.5. The dynamic coefficient of friction was measured
using a 1.9 mm diameter POM stylus oriented perpendicular
(90.degree.) to the Interface Layer using a 100 mm/s tip speed and
300 g force. Measurements were recorded using a Nanovea T50
Tribometer.
[0041] As shown in TABLE 2, by modifying the thickness and
durometer hardness of the elastic layer 120 characteristics of the
film 100 can be tuned in order to exhibit a desired .DELTA.T.sub.g
(between 0.degree. C. and 50.degree. C.), a desired R.sub.td,
20.degree. C. (between 0.1 and 2.5); and a desired dynamic
coefficient of friction that is sufficiently similar to the dynamic
coefficient of friction exhibited by a pen on paper.
[0042] TABLE 2 indicates the dynamic coefficient of friction of
exemplary elastic layer compositions as a component in the film
100. In all cases, the interface layer thickness is 25 um and the
film structure includes a PET substrate layer 130 (50 um) and
adhesive layer 140 (20 um). Films were laminated to soda lime glass
prior to measurement.
TABLE-US-00002 Elastic Elastic Layer Layer Dynamic Durometer
Thickness T.sub.g .DELTA.T.sub.g Coefficient Example Hardness (um)
(.degree. C.) (.degree. C.) td.sub.T=20.degree. C. R.sub.td,
20.degree. C. of Friction 1 78A 50 -18 50 0.10 2.5 0.17 .+-. 0.01 2
80A 40 19 13 1.20 0.2 0.23 .+-. 0.01 3 54D 40 32 0 0.25 1.0 0.17
.+-. 0.01 4 PET only n/a 81 -49 10.sup.-2 12.5 n/a (comparative) 5
ASC only n/a 32 n/a 0.25 n/a 0.13 .+-. 0.01 (comparative) 6 4
stacked sheets n/a -- n/a -- n/a 0.22 .+-. 0.01* 20# paper
(comparative) *Measured using ball point pen in place of a
stylus.
6. Substrate Layer
[0043] The film can include a substrate layer 130, which functions
as a supportive backing for the film 100 in order to maintain the
desired pen-on-paper feel of the film 100 by separating the elastic
layer 120 from the adhesive layer 140 that attaches the film 100 to
the touchscreen 220. Because the adhesive layer 140 typically has a
soft durometer and generally undesirable viscoelastic properties
the substrate layer 130 can provide the film 100 with consistent
mechanical properties independent of the touchscreen to which the
film 100 is adhered. In one implementation, the substrate layer 130
is composed of polyethylene terephthalate (hereinafter "PET").
7. Adhesive Layer
[0044] The film can include an adhesive layer 140 attaching the
substrate layer 130 to the touchscreen 220. In one implementation,
the adhesive layer 140 is composed of an optically clear adhesive,
thereby maintaining the optical properties of the film and
preventing aberration of images displayed by the touchscreen 220.
Alternatively, the film 100 can include a self-wetting adhesive as
the adhesive layer 140.
8. Film Mechanics
[0045] The combination of the elastic layer 120 and the interface
layer 110 provide the film 100 with properties that are
substantially similar to the transverse "drag" or resistive force
of paper to a writing force (e.g., between 0.5 Newtons and 3.0
Newtons) applied normal to the surface of the paper. In particular,
the film 100, in response to the application of writing force from
stylus 210, exhibits an indentation creating "pile-ups" of film
material on either side of the indentation. Subsequently, upon
translation of the stylus 210 across the surface of the film 100,
the film 100 exhibits a resistive force to the motion of the stylus
210 via macromolecular displacement of a "pile-up" on one side of
the indentation across the surface of the film 100. Thus, in order
to exhibit pen-on-paper feel, the film 100 can indent by up to 20%
of its initial thickness under 3 Newtons of writing force (e.g., 20
to 80 micrometers depending on the total thickness of the film
100).
[0046] Tests have indicated that the just-noticeable difference in
dynamic coefficient of friction for human users is .+-.0.03. Thus,
the film 100 exhibits a dynamic coefficient of friction that is
"similar" to paper if the film 100 exhibits a dynamic coefficient
of friction within 0.03 of paper under comparable testing
conditions. However, in some implementations, the film 100 can
exhibit a dynamic coefficient different than the dynamic
coefficient of friction exhibited by paper in order to comply with
user preferences for a touchscreen device.
[0047] The force resulting from the elasticity of the film can be
characterized as the dynamic coefficient of friction, which is
expressed as a ratio of normal force applied to the film 100 to the
transverse/resistive force generated by the film 100. As is
indicated in FIG. 5, the film 100 can resist transverse movement of
the stylus tip across the interface layer 110 according to a
dynamic coefficient of friction between 0.2 and 0.3 for the writing
forces indicated. The dynamic coefficient of friction exhibited by
the film 100 can be between the dynamic coefficient of friction
exhibited by two sheets of paper and four sheets of paper at all
levels of writing force. Furthermore, the dynamic coefficient of
friction for any material can vary based on the applied writing
force (e.g., as a function of the writing force). In one
implementation, the film 100 exhibits a dynamic coefficient of
friction curve of similar to a dynamic coefficient of friction
curve for a ball-point pen applied to four sheets of paper. The
similarity between the dynamic coefficient of friction curves is
shown in FIG. 5. In on implementation, the film 100 exhibits a
dynamic coefficient of friction greater than that of paper at
normal applied writing forces between 0.5 Newtons and 3 Newtons
[0048] In one implementation, the film 100 can exhibit a
shear-thickening property, wherein the dynamic coefficient of
friction of the film 100 increases as the normal force incident to
the film 100 increases. the film 100 can also resist transverse
movement of the stylus tip across the interface layer 110 according
to a dynamic coefficient of friction between 0.22 and 0.26 in
response to an application of 1.0 Newton and resist transverse
movement of the stylus tip across the interface layer 110 according
to a dynamic coefficient of friction between 0.26 and 0.30 in
response to application of 3.0 Newtons.
[0049] Furthermore, the film 100 can be adapted to exhibit the
above properties in response to the application of writing force
via a stylus 210 of a particular size and or shape. In one
implementation, the film 100 can resist transverse movement of a
1.5-millimeter stylus tip across the interface layer 110 according
to a dynamic coefficient of friction between 0.2 and 0.3 in
response to an application of writing force to the interface layer
110 via the stylus tip.
[0050] The relationship between the elastic layer 120 and the
interface layer 110 that enables the abovementioned properties can
be parameterized by the peak tan delta ratio, R.sub.td, 20.degree.
C., between the interface layer 110 and the elastic layer 120.
R.sub.td, 20.degree. C. compares the viscoelastic response of the
interface layer 110 to the viscoelastic response of the elastic
layer 120. In one implementation, the film 100 is characterized by
R.sub.td, 20.degree. C. less than 2.5. Alternatively, the film 100
is characterized by R.sub.td, 20.degree. C. less than 1.
9. Layer Texturing
[0051] In one variation, shown in FIG. 3A, the film 100 includes an
elastic layer 120 including a textured upper surface, while the
interface layer 110 includes a smooth tactile surface that is
exposed to the fingers of the user. Therefore, the "subsurface"
texture of the film may only be noticeable to the user via tactile
feedback through the stylus 210 while applying a writing force to
the film 100. This texturing can provide a grainy feel to the user
when the user applies a writing force to the film 100 in order to
better mimic a pen-on-paper feel or a pencil-on-paper feel. The
subsurface texture of the elastic layer 120 can include an applied
surface roughness. Alternatively, the subsurface texture can define
a grid of larger bumps (e.g., 5 micrometers in height) arranged
across the surface of the elastic layer 120. Furthermore, the
subsurface bumps can be spaced proportional the tip diameter of the
stylus 210, causing the stylus 210 to perturb vertically as it
translates across the film 100.
[0052] In another variation, shown in FIG. 3B, the film 100
includes a distribution of microparticles (e.g., on the order of
micrometers in diameters) or nanoparticles (e.g. on the order of
nanometers in diameter) suspended within the interface layer 110 or
between the interface layer 110 and the elastic layer 120, thereby
causing the film 100 to exhibit a grainy feel approximating dynamic
friction forces caused by the surface roughness of paper as a pen
or pencil is drawn across it. In one implementation, the
microparticles are manufactured from a hard polymer or inorganic
compound that provides noticeable disruption to the elastic
characteristics of the interface layer 110, thereby causing
perturbations in the tactile feedback experienced by the user.
[0053] In a second implementation, the microparticles are comprised
of a hard polymer. For example, the interface layer can include 0.1
to 5% (w/w) of Ultra High Molecular Weight Polyethylene (UHMWPE)
microparticles suspended within the interface layer 110 (TABLE 3,
Examples 3 and 4). The UHMWPE microparticles possess a mean
particle size of 3.5 micrometers and a particle size range of 2 to
7 micrometers as determined by dynamic light scattering.
TABLE-US-00003 TABLE 3 In all cases, the film structure is
comprised of a PET Substrate Layer (50 um) and Adhesive Layer (25
um) laminated to soda lime glass prior to measurement.
Microparticle Interface Elastic Elastic Loading Layer Layer Layer
Surface Dynamic (Interface Thickness Durometer Thickness Roughness
Coefficient Example Layer) (um) Hardness (um) (R.sub.a, nm) of
Friction 1 0 25 PET n/a 24 .+-. 2 0.12 .+-. 0.01 (substrate) 2 0 25
78 50 22 .+-. 3 0.16 .+-. 0.01 3 2% 30 PET n/a 44 .+-. 5 0.15 .+-.
0.01 (substrate) 4 3% 41 78 50 50 .+-. 5 0.18 .+-. 0.01
[0054] Additionally, the suspended nanoparticles or microparticles
can exhibit the same or similar index of refraction to the
interface layer 110 and/or the elastic layer 120.
10. Layer Patterning
[0055] In one implementation, the film 100 includes an elastic
layer 120 that defines a continuous layer; and an interface layer
110 that defines a set of discontinuous regions across the elastic
layer 120. Additionally, the film 100 can include an interface
layer 110 that defines a set of discontinuous regions across the
elastic layer 120, wherein the set of discontinuous regions: spans
an area less than 1 square millimeter; and is separated from an
adjacent discontinuous region by a distance greater than 10
micrometers. The interface layer 110 can be spatially patterned to
result in thinner film areas or even in discontinuities in the
interface layer 110, as shown in FIGS. 4A and 4B. This can enable
the film 100 to include an interface layer 110 characterized by
increased hardness and/or elastic modulus while still allowing
substantial deformation in response to writing force applied via a
stylus 210. Thus, the interface layer 110 can include a set of
sub-sections that are preferably small enough to enable deformation
around the contour of a stylus tip (e.g., <1 mm 2). Likewise,
the gap between sections is preferably large enough to enable
deformation, but small enough to not have a substantial effect on
friction (e.g., due to the stylus 210 running over ridges); for
example, 10-100 microns.
[0056] The interface layer 110 (or any other layer of the film 100)
may be patterned, divided, shaped, or otherwise structured in any
manner.
11. Optical Properties
[0057] The film 100 is optically transparent and therefore includes
two optically transparent layers. Additionally, to prevent optical
aberration of an image displayed on the underlying touch screen,
the film 100 can include an interface layer 110 and an elastic
layer 120 with substantially the same index of refraction.
Therefore, the film 100 does not cause reflection and/or distortion
of the underlying image.
12. UV Resistance
[0058] The film 100 also exhibits resistance to UV degradation over
time as a result of its two-layer structure. In many
implementations, polymers exhibiting desired mechanical properties
for the elastic layer 120 exhibit yellowing in the presence of UV
light. Thus, the interface layer 110 can function to block incident
UV light to the film 100 and prevent yellowing of the elastic layer
120, thereby expanding potential material choices for the elastic
layer 120 composition
13. Hardness/Durability
[0059] The film 100 exhibits hardness and durability, which can be
characterized according to a variety metrics including Shore
hardness, tensile strength at 50% engineering strain, and/or
tensile set.
[0060] In a first example of layer characterization, the film 100
is characterized by Shore hardness. In this example, the interface
layer 110 is preferably of a hardness of 80 Shore A to 75 Shore D,
more preferably of a hardness of 85 Shore A to 65 Shore D, and most
preferably of a hardness of 90 Shore A to 60 Shore D; while the
elastic layer 120 is preferably of a hardness of 60 Shore A to 65
Shore D, more preferably of a hardness of 75 Shore A to 55 Shore D,
and most preferably of a hardness of 80 Shore A to 50 Shore D.
Further, the interface layer 110 is preferably of greater hardness
than the elastic layer 120. Alternatively, the layers of the film
100 may be of any hardness.
[0061] In a second example of layer characterization, the film 100
is characterized by tensile strength at 50% strain (as measured
according to ASTM D638 using a Type V sample geometry). In this
example, the interface layer 110 is preferably of a tensile
strength of 5 to 15 MPa, more preferably of a tensile strength of 5
to 10 MPa, and most preferably of a tensile strength of 5 to 8 MPa;
while the elastic layer 120 is preferably of a tensile strength of
1 to 10 MPa, more preferably of a tensile strength of 1 to 5 MPa,
and most preferably of a tensile strength of 2 to 4 MPa. Further,
the interface layer 110 is preferably of greater tensile strength
than the elastic layer 120. Alternatively, the layers of the film
100 may be of any tensile strength.
[0062] In a third example of layer characterization, the film 100
is characterized by tensile set at 50% engineering strain (as
measured according to ASTM D638 using a Type V sample geometry). In
this example, the interface layer 110 is preferably of a tensile
set of 0 to 25%, more preferably of a tensile set of 0 to 15%, and
most preferably of a tensile set of 0 to 8%; while the elastic
layer 120 is preferably of a tensile set of 0 to 20%, more
preferably of a tensile set of 0 to 10%, and most preferably of a
tensile set of 0 to 5%. Further, the interface layer 110 is
preferably of greater tensile set than the elastic layer 120.
Alternatively, the layers of the film 100 may be of any tensile
set.
14. Stylus
[0063] The stylus 210 of the system 200 can include any stylus 210
capable of interacting with a touch sensor. For example, the stylus
210 can include a pen-shaped element constructed of plastic, metal,
ceramic, or some other material that can slide easily across the
tactile surface of the interface layer 110. The stylus 210 can
include a tip configured to interface with any type of touchscreen
(e.g., capacitive, resistive, FTIR). The stylus 210 preferably has
a rigid tip (e.g., manufactured of polyoxymethylene) but may
additionally or alternatively have any type of tip. Furthermore,
the stylus 210 can be characterized by a tip diameter similar to
that of a typical pen or pencil (e.g., 1.5 millimeters), thereby
providing a similarly precise user-experience to drawing with the
aforementioned traditional writing instruments. In one
implementation, the coefficient of kinetic friction of the stylus
210 and the tactile surface of the interface layer 110 can be
calibrated in order to adjust the scratch and/or dynamic
coefficient of friction, thereby better approximating the scratch
and/or dynamic coefficient of friction of a pen moving over a sheet
of paper. Additionally or alternatively, the coefficient of static
friction between the stylus tip and the tactile surface of the
interface layer 110 can also be controlled to prevent stick-slip
motion of the stylus tip across the film 100.
15. Touchscreen
[0064] In one implementation, the system 200 includes a
touch-sensitive screen (i.e. a touchscreen): arranged across a
bottom surface of the elastic layer 120; bonded to the elastic
layer 120 via a layer of optically clear adhesive; and configured
to detect the stylus tip at a distance substantially equal to a
film thickness of the film 100. Thus, the system 200 can function
to detect the tip of the stylus 210 upon contact of the stylus 210
with the tactile surface of the film 100, thereby enabling a mobile
computing device to register writing inputs applied to the tactile
surface of the film 100.
16. Manufacturing
[0065] Generally the film 100 can be manufactured according to a
manufacturing method S100 executed by a manufacturing system 300 in
order to imbue the film 100 with the durability characteristics and
mutual elasticity described above. The manufacturing method S100
enables chemical crosslinking between the elastic layer 120 and the
interface layer 110 that prevent separation of the two-layer film
100.
16.1 Mixing Prepolymer
[0066] Block S110 of the method S100 recites combining a
prepolymer, a solvent, and a catalyst to define a viscous material.
Generally, the manufacturing system 300 can dissolve one or more
base components of the interface layer 110 (e.g., urethane
prepolymer) with solvent (e.g., MEK) in Block S110 to form a
viscous material (i.e., a liquid) of a particular viscosity
configured to allow the viscous material to flow across and
self-level on the elastic layer 120 within a prescribed period.
[0067] In one implementation, the manufacturing system 300 can mix
the prepolymer, the solvent, and the catalyst within a mixing
vessel and/or mixing head 310. As described below, the
manufacturing system 300 can mix a TDI-terminated polyester
prepolymer and a solvent, such as methyl ethyl ketone or
cyclohexanone, to form a liquid viscous material. Additionally or
alternatively, the manufacturing system 300 can heat the viscous
material to dissolve the prepolymer. (The TDI-terminated polyester
prepolymer can form a solid at ambient temperatures). The
manufacturing system 300 can heat the prepolymer further and/or
dilute the prepolymer with MEK and/or cyclohexanone to form the
liquid viscous material of a viscosity (e.g., less than 3500
centipoise or "cP") desired for distribution through a slot-die as
described below. In particular, the manufacturing system 300 can
heat the prepolymer to a temperature at which the polymer and
solvent are soluble (e.g., between seventy and a hundred degrees
Celsius). In this implementation, the manufacturing system 300 can
also define the viscous material to exhibit a viscosity such that,
after distribution of the viscous material onto the elastic layer
120, the viscous material flows across the elastic layer 120 at a
rate sufficient to facilitate self-leveling within a period of time
and to limit formation of flow lines (i.e., lines that appear in
the interface layer 110 after curing and indicate direction of flow
of the viscous material across the elastic layer 120).
[0068] Similarly, the manufacturing system 300 can also mix curing
agents, such as catalysts (e.g., dibutyltin dilaurate), chain
extenders, and/or cross-linking agents with a solvent within a
mixing vessel and/or mixing head 310. In one implementation, the
manufacturing system 300 can heat the curing agent-solvent
combination to facilitate dissolution of the curing agents. For
example, a chain extender aromatic diamine curative for
polyurethane can remain a liquid at room temperature (e.g., 35
degrees Celsius) while a cross-linking agent DiTMP remains a solid
at room temperature. Therefore, the manufacturing system 300 can
heat the aromatic diamine curative for polyurethane and DiTMP and
combine with solvent (e.g., MEK) to a temperature at which DiTMP is
soluble (e.g., greater than sixty degrees Celsius). As described
below, the manufacturing system 300 (and/or operators of the
manufacturing system 300) can select the catalyst, the
cross-linking agent, and/or the chain extender to define a
particular cure time, a particular percentage or rate of
cross-linking of polymer chains, etc. Therefore, the manufacturing
system 300 can select and mix catalysts, cross-linking agents,
and/or chain extenders to generate a substantially transparent
interface layer 110 exhibiting the aforementioned surface
roughness, elastic modulus, and UV resistance.
[0069] The manufacturing system 300 can combine any combination of
prepolymer, solvent, and/or curing agent (i.e., catalyst,
cross-linking agent, and/or chain-extender). As described below,
the manufacturing system 300 can combine components of the
interface layer 110 to define a viscous material within the mixing
head 310 including --by weight percentage of the viscous material
as a whole--between sixty and ninety percent prepolymer; between
two and four percent chain extender; between one and three percent
cross-linking agent; between zero and 0.5 percent catalyst; and
between five and thirty-five percent solvent.
[0070] In another implementation shown in FIG. 6 and FIG. 8, the
manufacturing system 300 can mix a prepolymer and solvent to form
"Part A" and mix curing-agents to form "Part B", independently. The
system can then combine Part A and Part B within a mixing head 310.
In this implementation, the manufacturing system 300 can heat
and/or add additional solvent to the viscous material of Part A and
Part B. For example, the manufacturing system 300 can define a
maximum allowable viscosity of combined components of the viscous
material. Due to a difference in viscosities of Part A and Part B,
the manufacturing system 300 can heat and/or add additional solvent
to equilibrate viscosities of the (final) and define a viscous
material with a viscosity remaining below a maximum allowable
viscosity suitable for distribution through a slot-die coater 320.
In particular, the manufacturing system 300 can measure viscosities
of Part A and Part B and, in response to a viscosity of one of Part
A and/or Part B exceeding a threshold viscosity, heat and/or add
solvent to the appropriate viscous material.
[0071] Additionally or alternatively, to encourage mixing of
components (i.e., Part A and Part B), the manufacturing system 300
can define a threshold (acceptable) deviation between viscosities
of components of the viscous material. For example, the
manufacturing system 300 can define a threshold deviation of
viscosities of the components at twenty-percent deviation, such
that the viscosity of Part A remains within twenty percent of the
viscosity of Part B.
[0072] Once Part A and Part B are suitably mixed individually
and/or dissolve, the manufacturing system 300 can combine Part A
and Part B within a mixing head 310. For example, the manufacturing
system 300 can store Part A and Part B individually in storage
vessels. Then the manufacturing system 300 can subsequently meter
each component from their respective storage vessel at a known flow
rate into a mixing chamber. The manufacturing system 300 can then
mix Part A with Part B within the mixing chamber. In this example,
the manufacturing system 300 can include a static mixing head 310
with a series of crossing elements to create turbulence over which
streams of Part A and Part B flow to induce mixing prior to a
material forming process, such as slot-die coating.
[0073] In one variation, the manufacturing system 300 can select
the solvent to react with the elastic layer 120 onto which the
manufacturing system 300 casts the viscous material. In this
variation, the solvent can be selected to dissolve a portion of the
elastic layer 120 to improve adhesion (and promote cross-linking)
between the elastic layer 120 and the interface layer 110 formed by
casting the viscous material onto the elastic layer 120. In this
variation the solvent can form a permanent bond between the
interface layer 110 and the elastic layer 120, such that the
elastic layer 120 cannot be easily removed from the interface layer
110 and therefore deforms with the interface layer 110 when writing
force is applied to the film 100 via a stylus 210.
[0074] However, the manufacturing system 300 can mix any other
component to form the interface layer 110 in any other suitable
way.
16.2 Casting
[0075] As shown in FIG. 1A, Blocks S120 and S130 of the method S100
recite: advancing an elastic layer 120 from a first roll across a
surface continuously at a first speed in Block S120; and depositing
the viscous material through a deposition head at a first viscosity
onto the elastic layer 120 in Block S130, the viscous material
flowing laterally across the elastic layer 120 to form an interface
layer 110 of substantially uniform thickness over the elastic layer
120 over a period of time while the elastic layer 120 advances
along the surface. Generally, after mixing components of the
interface layer 110 (e.g., prepolymer, solvent, catalyst,
cross-linking agents, and/or chain extenders) into a viscous
material within a mixing head 310, the manufacturing system 300 can
cast or dispense the viscous material through a slot-die coater 320
or nozzle onto an elastic layer 120 advancing on the conveying
system beneath the slot-die coater 320.
[0076] In particular, after component parts of the interface layer
110 are combined within a static mixing head 310 to define a liquid
viscous material, a material forming processor can dispense the
viscous material onto an elastic layer 120, on which the interface
layer 110 can form. In this implementation, component materials of
the viscous material enter the slot-die coater 320. Clamping
components of the slot-die coater can apply pressure to the viscous
material to conform with a particular shape. The clamping
components then force the viscous material to flow out from an
interstitial space between the clamping components onto an elastic
layer 120 translating below the slot-die coater 320.
[0077] In the foregoing implementation, the manufacturing system
300 can include a conveyor and/or other component configured to
translate an elastic layer 120 (e.g., PET and/or urethane) under
the slot-die coater 320 to facilitate even and continuous
distribution of viscous material across the elastic layer 120
during dispensation of the viscous material onto the elastic layer
120. The conveying system can be configured to unspool a roll of
the elastic layer 120 and translate the elastic layer 120 over a
surface, such as a mirror-finish or approximately flat and uniform
plate.
[0078] The conveyor can cooperate with the slot-die coater 320 to
translate--or otherwise progress--the elastic layer 120 to pass
over a surface (e.g., a mirror-finish plate) underneath outflowing
viscous material at a translation rate proportional to a flow rate
of the viscous material dispensed through the slot-die coater 320
onto the elastic layer 120. Therefore, the slot-die coater 320 can
deposit sufficient viscous material onto the elastic layer 120 to
define a continuous layer of viscous material. Furthermore, the
conveyor and the slot-die coater 320 can cooperate to determine
thickness of the interface layer 110 (e.g., between five
micrometers and seventy micrometers) as described below.
[0079] However, the manufacturing system 300 can deposit the
viscous material onto the elastic layer 120 in any other suitable
way.
16.3 Leveling
[0080] As shown in FIG. 3, Block S120 of the method recites:
advancing an elastic layer 120 from a first roll 330 across a
surface continuously at a first speed in Block S120. Generally, the
conveyor can continue to translate the elastic layer 120 and the
deposited viscous material over the surface (e.g., the
mirror-finished plate described above) over a distance sufficient
for the viscous material to flow to define a uniform thickness film
distributed across the elastic layer 120.
[0081] As described above, the manufacturing system 300 can combine
components of the viscous material of a viscosity sufficient to
flow to uniform thickness across the elastic layer 120--laterally
and/or longitudinally--within a period (e.g., one minute)
corresponding to a distance between the deposition head and point
of entry into a curing device. In one implementation, the
manufacturing system 300 can access a known viscosity and/or
measure a viscosity of the viscous material prior to dispensation
from the slot-die coater 320 onto the elastic layer 120. Based on
the viscosity of the viscous material, the manufacturing system 300
can define an approximate distance from dispensation of the viscous
material until the viscous material levels across the elastic layer
120 to form the interface layer 110 of substantially uniform
thickness. (The manufacturing system 300 can also include a
vibratory and/or agitation module to facilitate self-leveling of
the viscous material to form the interface layer 110.) For example,
the manufacturing system 300 can cast the viscous material onto the
elastic layer 120 (e.g., a continuous extruded elastomer film)
translating a direction during deposition of the first viscous
material. Following deposition of the viscous material, the first
viscous material can flow across the continuous film elastic layer
120, such as through capillary action between the elastic layer 120
and the viscous material in order to form an interface layer 110 on
top the elastic layer 120.
[0082] However, the manufacturing system 300 can facilitate
self-leveling of the viscous material and uniform distribution of
the viscous material across the elastic layer 120 by any other
suitable means.
16.4 Curing
[0083] Block S140 of the method S100 recites, at a distance from
the deposition head of the viscous material onto the elastic layer
120 corresponding to a duration of time for the viscous material to
flow laterally across the elastic layer 120 to form the interface
layer 110, heating the interface layer 110 to evaporate solvent
from the interface layer 110 and to induce a reaction between the
catalyst and the prepolymer to cure the interface layer 110 in
Block S140. Generally, the manufacturing system 300 can implement
Block S140 to heat the interface layer 110 in order to drive off
excess solvent from the interface layer 110 and, therefore,
facilitate curing of the interface layer 110 and formation of
polymer cross-links desired for applications of the film 100.
[0084] In particular, the conveyor can translate the elastic layer
120 and the interface layer 110 of viscous material toward a curing
device, such as an oven 352, an ultraviolet-curing oven, etc.
However, the curing device can include any device capable of
applying heat, ultraviolet radiation, a curing solution, and/or any
combination thereof to cure the interface layer 110 to an initial
cured state. The manufacturing system 300 can access properties of
the viscous material, such as cure time and curing parameters, and
desired curing level upon exit from the curing device (i.e., from a
local database and/or remote lookup table) to calculate a duration
and other curing parameters to output from the curing device to
achieve a desired curing level (e.g. 50% cured, 75% cured, 100%
cured). For example, the manufacturing system 300 can calculate the
desired curing level of the interface layer 110 as 80% cured upon
exiting the curing device. In this example, the manufacturing
system 300 can perform additional processes and/or apply additional
coatings (e.g., such as oleophobic coatings) following initial
curing within the device--further down the manufacturing line.
After these additional coatings and/or materials or other processes
are applied to the interface layer 110, the manufacturing system
300 can fully cure the interface layer 110 (and additional
coatings) to a final cured state (e.g., 100% cured).
[0085] In one implementation, the curing device can output
conditions configured to evaporate approximately 90-95% of the
solvent and, therefore facilitate curing of the interface layer
110. By removing the solvent to this extent, the manufacturing
system 300 can induce reaction of components in the interface layer
110 and promote cross-linking between the polymers of the interface
layer 110. Additionally, removal of the solvent also prevents
bubble formation in the interface layer 110, thereby mitigating
optical defects and/or aberrations formed at uncured regions of the
interface layer 110, regions of unreacted prepolymer and/or
catalyst, and/or regions of the interface layer 110 of non-uniform
thickness.
[0086] In one example, the manufacturing system 300 can include a
curing oven 352. The curing oven 352 can output heat over a time
window and at a target temperature (e.g., 100 degrees Celsius) to
evaporate solvent off the interface layer 110 and, therefore,
facilitate reaction between the prepolymer and the curing agents.
The oven can heat the film 100 to the temperature over a
predetermined duration in order to yield a desired level of
tackiness (or percent of uncured viscous material) of the interface
layer 110 when the interface layer 110 exits the oven. In this
example, the conveyor can cooperate with the curing oven 352 to
progress the film 100 through the oven 352 during a time window
corresponding to the duration defined for the film 100. In this
example, the interface layer 110 can remain with the oven 352 for a
longer duration to lessen tackiness of the interface layer 110 when
the interface layer 110 exits the oven 352. Alternatively, the
interface layer 110 can remain within the oven 352 for a shorter
duration to increase tackiness of the interface layer 110 when the
interface layer 110 exits the oven 352. Therefore, the conveyor and
the oven 352 can cooperate to sufficiently cure the interface layer
110 to yield: a desired level of tackiness corresponding to a
desired material performance and a sufficient curing level such
that the manufacturing system 300 can spool the film 100 without
sticking to itself when rolled.
[0087] In one variation, the manufacturing system 300 can define a
final curing level for the interface layer 110 upon completion of
all processes performed by the manufacturing system 300 (e.g.,
deposition, leveling, initial curing, and rolling onto a spool). In
this variation, the interface layer 110 can be partially uncured at
a time when the manufacturing system 300 spools the film 100--which
includes the interface layer 110 and the elastic layer 120--onto a
roll. The interface layer 110 can continue to cure on the roll
after spooling.
[0088] However, the manufacturing system 300 can drive off solvent,
induce polymerization of the prepolymer and cross-linking between
polymers, and/or cure the interface layer 110 in any other suitable
way.
16.5 Multiple Layers
[0089] In one variation, the manufacturing system 300 can execute
the foregoing Blocks of the method S100 to produce the elastic
layer 120 (e.g., over a removable backing) before a second
iteration of the foregoing Blocks of the method S100 to deposit the
interface layer 110 onto the partially cured elastic layer 120. In
this variation, the manufacturing system 300 can tune chemical
composition and curing parameters for each layer to control
adhesion (and polymer cross-linking) between layers and define the
film 100 that is resistant to impacts, deformable via a stylus 210,
and optically clear. In particular, the manufacturing system 300
can first deposit a first viscous material of prepolymer, curing
agents, and solvent onto an adhesive backing (e.g., a continuous
elastomer film unspooled from a roll 330) and cure the first
viscous material to define the elastic layer 120 on top of the
adhesive backing as described above. After exiting the curing
device, the manufacturing system 300 can translate the elastic
layer 120 under a slot-die coater 320, which can deposit the
interface layer 110 of the viscous material (or of another viscous
material of prepolymer) onto the partially cured elastic layer
120.
[0090] In this implementation, the solvent of the viscous material
deposited onto the first interface layer 110 can facilitate
adhesion and/or cross-linking of polymers between layers of the
film 100. Therefore, the interface layer 110 can be physically and
chemically cross-linked with the elastic layer 120 in order to
provide durability and mutual elasticity to the film 100.
16.5.1 Layer Texturing
[0091] One variation of the multilayer implementation of the method
S100 includes texturing the upper surface of the elastic layer 120
to provide subsurface texture approximating a surface roughness of
paper. As described above, the film 100 can approximate the grainy
tactile feel caused by the surface roughness of paper by exhibiting
a subsurface texture on the upper surface of the elastic layer 120.
In one implementation the manufacturing system 300 includes a
textured roller arranged along the conveyer behind the curing oven
352. The manufacturing system 300 can then apply a predetermined
pressure to the textured roller thereby imprinting the (partially
cured) elastic layer 120 with a texture. Alternatively, the
manufacturing system 300 can apply a textured film to the surface
of the elastic layer 120 after the elastic layer 120 has been
partially cured. The elastic layer 120 can then cure over time,
thereby receiving the texture of the textured film. However, the
manufacturing system 300 can apply texture to the surface of the
elastic layer 120 in any other way.
17. Composition Alternatives
[0092] As described above, the method S100 can be implemented to
manufacture and process a film 100 that is durable,
optically-clear, and elastic such that it mimics the previously
described pen-on-paper feel, such as for application over a
touchscreen 220. As described above he film 100 can exhibit
properties such as specifically tuned elasticity (e.g., for the
elastic layer 120 and the interface layer 110), high elastic
recovery (for the elastic layer 120), durability (for the interface
layer 110), optical clarity, and scratch resistance, which can
result from chemical composition of the film and process parameters
implemented by the manufacturing system 300 in Blocks of the method
S100.
[0093] In one implementation, a primary base component of the film
100 is a prepolymer at an intermediate stage of polymerization.
While in one implementation, the prepolymer includes TDI-terminated
polyester prepolymer, other prepolymers can be mixed in combination
with or in lieu of TDI-terminated polyester prepolymer. These
additional or alternative prepolymers include: isocyanate
containing prepolymers having low molecular weight; or
isocyanate-containing polymers that contain aliphatic, aromatic, or
isocyanate groups. The manufacturing system 300 can also implement
other prepolymers, such as prepolymers with low concentrations of
free isocyanates ("low free"). However, both conventional and "low
free" materials can be utilized. Prepolymer backbones can include
polyester, polyether, polycarbonate, polyacrylic, or mixtures
thereof. (The prepolymer component can be an isocyanate-containing
compound that will slowly react with water and other alcohols. The
manufacturing system 300 can therefore pump a nitrogen gas blanket
over the prepolymer and other solids in the viscous material to dry
them prior to mixing with other components of the thin layer
140.)
[0094] The viscous material applied to the substrate 120 can also
include a chain extender, such as an aromatic diamine curative for
polyurethane. However, one or more other chain extenders can be
applied to the viscous material in combination with or in lieu of
the aromatic diamine curative for polyurethane, including classes
of materials with small molecules and two isocyanate reactive end
groups that include aliphatic amines, aromatic amines, and
hydroxyls. In one implementation, the viscous material includes a
combination of chain extenders or curatives to balance processing
characteristics, such as pot life and tack time, and material
performance characteristics of the interface layer 110, such as
optical properties, UV resistance properties, elastic recovery,
scratch resistance, and/or compressibility. Examples of chain
extenders/curatives that can be used in the viscous materials of
chain extenders include: ethylene glycol, diethylene glycol, 1,3
propanediol, 1,4 butanediol, 1,5 pentanediol, 1,6 hexanediol,
aromatic diamine curative for polyurethane 90, aromatic diamine
curative for polyurethane of various molecular weights (e.g., 100,
or 300), polyoxypropylenediamine of various molecular weights
(e.g., 230, 400, or 2000), Hydroquinone bis(2-Hydroxyethyl) or
"HQEE", and/or ethoxylated HQEE.
[0095] The viscous material also includes a cross-linking agent,
such as DiTMP. However, one or more other cross-linking agents can
be mixed with DiTMP. For example, isocyanate reactive end groups
include aliphatic amines, aromatic amines, and hydroxyls. In one
implementation, the viscous material can contain a combination of
cross-linking agents and chain extenders to balance processing
characteristics, such as pot life and tack time, and material
performance characteristics such as optical properties, UV
resistance properties, elastic recovery, scratch resistance, and
indentation/compressibility. Examples of these cross-linking agents
include TMP, DiTMP, Ethoxylated TMP, Ethyoxylated DiTMP.
[0096] The viscous material also includes a catalyst (e.g.,
Dibutyltin dilaurate). However, other catalysts that exhibit snap
cure capabilities include organo-metallic containing compounds with
one or more of the following ligands: Sn, Ti, Zn, Hg, and/or Bi.
Alternatively, catalysts can include an organic catalytic moiety,
such as a tertiary amine (e.g., stannous octoate or dibutyltin
dilaurate)
[0097] An appropriate snap-cure catalyst that is compatible with
Part A and Part B can be selected such that Part A and Part B do
not begin to react upon mixing in the static mixing head.
Therefore, the manufacturing system can dispense the mixture
through the mixing head and slot-die, and the mixture can
self-level before curing begins. In this implementation, the
manufacturing system can: 1) tune the non-catalyzed reactivity of
the Part B mixture with isocyanate groups in Part A to minimize
reaction and associated enthalpy of reaction at room temperature;
2) dilute the viscous material with solvent to reduce concentration
of isocyanate and isocyanate-reactive groups; and/or 3) select a
snap-cure catalyst that is inactive at temperatures below the
drying/curing temperature of the viscous material.
[0098] In this implementation, the manufacturing system can combine
a prepolymer, such as a TDI-terminated polyester prepolymer, a
chain extender, such as an aromatic diamine curative for
polyurethane, and a cross-linker, such as DiTMP to form the mixture
that can be cast according to the method S100 for the elastomer
layer 14. Once base components of the elastomer are thus selected,
the manufacturing system can identify an appropriate amount--by
weight or by volume--of each component to achieve an optimal
composition mixture for forming a film layer with the appropriate
optical properties, durability properties, and mechanical
properties.
[0099] Once the base components of the elastomer are identified,
the manufacturing system 300 can identify an appropriate amount (by
weight or by volume) of each component to achieve an optimal
composition viscous material for forming a film layer with the
appropriate optical properties, durability properties, and
mechanical properties.
[0100] The solvent can include an OH terminated chain extender,
such as including diol chain extenders (e.g., butanediol or "BDO"
or hydroquinone ether or "HQEE"). In the mixture of base components
described above, a portion of the aromatic diamine curative for
polyurethane component of the base components can be substituted
with solvent since aromatic diamine curative may also function as a
chain extender for polyurethane.
[0101] TDI-terminated polyester prepolymer typically forms 70%-86%
of the composition of the film 100 whereas aromatic diamine
curative for polyurethane, DiTMP, catalyst, and solvent form
2-2.9%, 1.5-2%, 0.1-0.2%, and 9-33%, respectively, of the film 100.
In this implementation, the weighted percentage of the components
can vary to achieve specific performances of the film 100 described
below. Furthermore, the composition can also enhance or lengthen
shelf-life stability of Part A and Part B (as described above) in
viscous materials with solvent. For example, the manufacturing
system can increase a volume of cross-linking agent within the
viscous material to improve durability of the thin layer.
[0102] In another implementation, the manufacturing system Soo can
replace or substitute a portion or all of the aromatic diamine
curative for polyurethane chain extender with an OH terminated
chain extender, such as BDO and/or HQEE, to increase pot life for
the material composition. Thus, the manufacturing system 300 can
vary a volume and a type of the OH terminated chain extender
substituted into the material composition according to an amount of
pot life desired for manufacturing a film using the material
composition. For example, by substituting at least 50% of the
aromatic diamine curative for polyurethane chain extender with 50%
BDO or 50% HQEE, the manufacturing system 300 can extend the pot
life by one minute (1 min.) or eight minutes (8 min.),
respectively. In another example, by replacing the aromatic diamine
curative for polyurethane component with a diol chain extender,
such as BDO or HQEE, the manufacturing system Soo can extend the
pot life of the material composition by thirty minutes (30 min.) or
by more than sixty minutes (60 min.).
[0103] The manufacturing system 300 can then add the chain extender
to the prepolymer component at one or more times during
manufacture. For example, the manufacturing system Soo can add the
chain extender at the outset of the mixing of the base components
of the viscous material in order to aid in the dissolution of one
or more of the base components, including the prepolymer.
Alternatively or additionally, the manufacturing system 300 can add
the chain extender composition continuously throughout one or more
aspects of manufacture of the material to control the dissolution
and viscous material of the base components. Additionally or
alternatively, amounts of the chain extender can be added at a
first time (e.g., before mixing for purposes of dissolving the
prepolymer, etc.) and at a second time to enhance the dissolution
of the composition materials prior to a slot-die coating.
[0104] The film 100 can include an interface layer 110 and an
elastic layer 120 that are fabricated to achieve desired material
properties. Examples of materials that may be used in the film 100
include urethanes, ureas, olefins, polyesters, plasticized
polyvinyl chloride, polyesters (e.g., polyethylene terephthalate
(PET) and/or polyethylene naphthalate (PEN)), polycarbonate,
acrylic, silicones etc. Additionally, the layers of the film 100
can include different types of urethanes, such as those based on
aromatic or aliphatic isocyantes and urethanes based on ether,
ester, carbonate, or acrylic polyols. In one example, the interface
layer 110 includes self-healing material (e.g., self-healing
urethane) that enable the layer 110 to be soft while still proving
resistant to abrasion, wherein the self-healing polyurethane has an
acrylic backbone instead of a typical polyol backbone, thereby
increasing its durometer.
[0105] Variants of the film 100 can exhibit tuned material
properties varying the crosslinking density within the layers. A
layer with a high-crosslinking density exhibits decreased
flexibility, increased modulus, increased hardness, and increased
melting point. Conversely, a layer with a lower crosslinking
density exhibits increased flexibility, decreased modulus,
decreased hardness, and decreased melting point. Thus, by tuning
the crosslink densities for each layer, the film 100 can converge
to the aforementioned desired material properties. In addition to
crosslinking density, the same type of variable mechanical property
gradient can be achieved by varying the amount of an inorganic
filler such as nanoparticles, nanorods, etc. A high filler content
may correspond to a high modulus, etc.
[0106] Furthermore, the crosslinking density and/or filler variance
can vary as function of depth within a layer of the film 100 to
achieve desired elasticity and/or texture characteristics.
[0107] Similar strategies to those used to vary crosslink density
may additionally or alternatively be used to generate layers with
customized shear properties (e.g., by varying the amount of curing
agent present in a polymer as a function of depth).
[0108] As a person skilled in the art will recognize from the
previous detailed description and from the figures and claims,
modifications and changes can be made to the embodiments of the
invention without departing from the scope of this invention as
defined in the following claims.
* * * * *