U.S. patent application number 11/691574 was filed with the patent office on 2007-08-23 for shock indicator.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Kevin W. Anderson, Russell D. Birkholz, Marco Bommarito, Richard L. Crone, Robert C. Fitzer, Jeffrey W. McCutcheon, Zhiming Zhou.
Application Number | 20070194943 11/691574 |
Document ID | / |
Family ID | 29736518 |
Filed Date | 2007-08-23 |
United States Patent
Application |
20070194943 |
Kind Code |
A1 |
Fitzer; Robert C. ; et
al. |
August 23, 2007 |
SHOCK INDICATOR
Abstract
A shock indicator is described comprising (A) a base having a
first side and a second side; (B) an indicator associated with the
first side of the base, the indicator comprising a plurality of
indicator subparts, the subparts comprising solid material arranged
(i) in a first configuration when the shock indicator is in a first
state prior to a shock event, and (ii) in a second configuration
when the shock indicator is in a second state following a shock
event; and (C) means associated with the second side of the base
for attachment of the shock indicator to a surface. A method of
manufacture is also provided.
Inventors: |
Fitzer; Robert C.; (North
Oaks, MN) ; Bommarito; Marco; (Stillwater, MN)
; Crone; Richard L.; (Woodbury, MN) ; McCutcheon;
Jeffrey W.; (Baldwin, WI) ; Anderson; Kevin W.;
(St. Paul, MN) ; Birkholz; Russell D.; (Maplewood,
MN) ; Zhou; Zhiming; (Woodbury, MN) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
29736518 |
Appl. No.: |
11/691574 |
Filed: |
March 27, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10517685 |
Dec 10, 2004 |
7219619 |
|
|
PCT/US03/19014 |
Jun 13, 2003 |
|
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11691574 |
Mar 27, 2007 |
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60388684 |
Jun 14, 2002 |
|
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Current U.S.
Class: |
340/686.1 |
Current CPC
Class: |
G01P 15/06 20130101;
G01P 15/036 20130101; H04M 1/18 20130101 |
Class at
Publication: |
340/686.1 |
International
Class: |
G08B 21/00 20060101
G08B021/00 |
Claims
1. A shock indicator, comprising: (A) A base having a first side
and a second side; (B) an indicator associated with the first side
of the base, the indicator comprising a plurality of indicator
subparts, the subparts comprising solid material arranged (i) in a
first configuration when the shock indicator is in a first state
prior to a shock event, and (ii) in a second configuration when the
shock indicator is in a second state following a shock event; and
(C) means associated with the second side of the base for
attachment of the shock indicator to a surface.
2. The shock indicator of claim 1 wherein the subparts of the
indicator comprise material selected from the group consisting of
toner powder particles, talc, flour, pigment, clay, ceramics,
alumina, metals, and combinations of the foregoing.
3. The shock indicator of claim 2 wherein the subparts are surface
modified.
4. The shock indicator of claim 2 wherein the subparts comprise a
first size and the indicator further comprises another component
comprising a second subpart larger than the first subpart.
5. The shock indicator of claim 1 further comprising a containment
member disposed on the first side of the base and enclosing the
indicator therein, the containment member being transparent,
thereby facilitating the visual determination of the indicator in
either its first or second configuration.
6. The shock indicator of claim 5 further comprising an impingement
object within the containment member and positioned to impact the
indicator during a shock event to aid in transitioning the
indicator from the first state to the second state, the impingement
object selected from the group consisting of glass beads, plastic
beads, ceramic beads, ball bearings and combination thereof.
7. The shock indicator of claim 1 wherein the indicator comprises
dry materials and the shock indicator further comprises means to
indicate exposure to wetness.
8. The shock indicator of claim 1 wherein the base is a film, the
base further comprising a differentiating component on the first
side, the differentiating component comprising a film material to
enhance the visual contrast between the differentiating component
and the indicator.
9. The shock indicator of claim 1 wherein the indicator comprises
an agglomerated powder in the first state prior to a shock event
and a dispersed powder in the second state following a shock event,
the indicator subparts comprising particles of the powder.
10. The shock indicator of claim 1 wherein the indicator and the
first side of the base comprise different colors to provide a
visual contrast therebetween.
11. The shock indicator of claim 1 wherein the indicator comprises
a solid and a liquid.
12. The shock indicator of claim 11 wherein the solid comprises a
clay and the liquid is mineral oil.
13. The shock indicator of claim 11 wherein the solid is selected
from the group consisting of exfoliated organophilic clay fillers,
silica particles, glass particles, inorganic pigments, and
combinations of the foregoing and the liquid at 23.degree. C. has a
surface tension within the range from about 10.times.10.sup.-3 N/m
to about 80.times.10.sup.-3 N/m, a density from about 0.5 to about
2 grams/cm.sup.3, and a zero rate shear viscosity from about
1.times.10.sup.-3 to about 1.times.10.sup.6 Pa-s.
14. The shock indicator of claim 13 wherein the fluid comprises a
liquid selected from the group consisting of silicone fluids and
oils, saturated hydrocarbon-based oils, silicone gums, mineral oil,
glycerols, water and combinations of the foregoing.
15. The shock indicator of claim 11 further comprising a
differentiating component associated with the first side of the
base, the differentiating component comprising a first side and a
second side and an annulus extending through the differentiating
component from the first side to the second side, the indicator
positioned within the annulus, at least one of the first side or
the second side of the differentiating component comprising a
structured surface.
16. The shock indicator of claim 15 wherein the structured surface
comprises a microstructured surface, the microstructured surface
associated with the first side of the base and defining a plurality
of channels arranged in a predetermined pattern, the channels
comprising an opening to permit the ingress of fluid when the
indicator is in a second state.
17. The shock indicator of claim 16 wherein the microstructured
surface comprises a regular array of precise structures having a
shape selected from the group consisting of symmetrical shapes and
asymmetrical shapes.
18. The shock indicator of claim 1 wherein the means for attachment
is selected from the group consisting of adhesives and mechanical
fasteners.
19. The shock indicator of claim 1 wherein the means for attachment
comprises a material that reduces, maintains or increases the shock
force transmitted to the indicator during a shock event
20. The shock indicator of claim 1, further comprising a
transmission layer positioned on the first side of the base between
the base and the indicator, the transmission layer comprising a
material to reduce, maintain or increase shock force transmitted to
the indicator during a shock event.
21. The shock indicator of claim 20, wherein the transmission layer
comprises a material capable of changing the threshold at which the
indicator experiences a shock event.
22. The shock indicator of claim 20, wherein the transmission layer
comprises a viscoelastic material having a storage modulus of at
least about 1.0 psi (6.9.times.10.sup.3 Pascals) and a loss factor
of at least about 0.01 at the temperature and frequency at which
the shock indicator is used.
23. The shock indicator of claim 22, wherein the viscoelastic
material is selected from the group consisting of urethane rubbers,
silicone rubbers, nitrile rubbers, butyl rubbers, acrylic rubbers,
fluorine-based elastomers, fluorine-based rubbers,
styrene-butadiene rubbers, and combinations of the foregoing.
24. The shock indicator of claim 20, wherein the transmission layer
comprises a material selected from the group consisting of
acrylates, epoxy-acrylates, silicones, cyanate esters, polyesters,
polyurethanes, polyamides, ethylene-vinyl acetate copolymers,
polyvinyl butyral, polyvinyl butyral-polyvinyl acetate copolymers,
epoxy-acrylate interpenetrating networks and combinations of the
foregoing.
25. The shock indicator of claim 20, wherein the transmission layer
comprises a thermoplastic material selected from the group
consisting of polyacrylates, polycarbonates, polyetherimides,
polyesters, polysulfones, polystyrenes,
acrylonitrile-butadiene-styrene block copolymers, polypropylenes,
acetal polymers, polyamides, polyvinyl chlorides, polyethylenes,
polyurethanes, and combinations of the foregoing.
26. The shock indicator of claim 20, wherein the transmission layer
comprises a thermosetting resin.
27. The shock indicator of claim 1 further comprising a plurality
of indicators associated with the first side of the base, each
indicator comprising a plurality of indicator subparts, the
subparts comprising solid material arranged (i) in a first
configuration prior to a shock event, and (ii) in a second
configuration following a shock event.
28. The shock indicator of claim 27 wherein each of the plurality
of indicators is constructed to transition from the first state to
the second state at shock events of different severity.
29. The shock indicator of claim 1 further comprising: A
containment member disposed on the first side of the base and
enclosing the indicator therein, the containment member being
transparent, thereby facilitating the visual determination of the
indicator in either its first or second configuration; and An
impingement object disposed within the containment member that
allows the impingement member to impact the indicator during a
shock event.
30. The shock indicator of claim 29 wherein the containment member
further comprises surface structures.
31. The shock indicator of claim 1 wherein the subparts of the
indicator further comprise a primary subpart of a first average
size and secondary subparts of a second average size, the second
average size being less than the first average size, the secondary
subparts agglomerated around one or more primary subparts to form
the indicator.
32. The shock indicator of claim 31 wherein the primary subpart is
associated with the base so that the primary subpart will dislodge
from the base upon the occurrence of a shock event.
33. The shock indicator of claim 1 wherein the indicator is
positioned within the shock indicator so that a shock event from
any direction will impart substantially the same shearing,
compression, tension, cleavage and/or peel forces into the
indicator.
34. The shock indicator of claim 33 wherein the indicator is
positioned within the shock indicator using more than one
attachment point.
35. The shock indicator of claim 1 further comprising a containment
member disposed on the first side of the base and enclosing the
indicator therein and wherein single or multiple masses are
associated with the interior and/or exterior surfaces of the
containment member to further modify the response of the shock
indicator to a shock event.
36. The shock indicator of claim 1 wherein the indicator comprises
a viscous liquid with one or more shear plane surfaces within the
liquid.
37. An assembly comprising the shock indicator of claim 1
associated with an electronic device selected from the group
consisting of cellular telephone, personal digital assistant, hand
held computers and digital cameras.
38. A method for the manufacture of a shock indicator, comprising:
(A) providing a base comprising a first surface and a second
surface, the second surface of the base associated with an
attachment means; and (B) placing an indicator in association with
the first surface of the base, the indicator comprising a plurality
of indicator subparts, the subparts comprising solid material
arranged (i) in a first configuration when the shock indicator is
in a first state prior to a shock event, and (ii) in a second
configuration when the shock indicator is in a second state
following a shock event.
39. The method of claim 38 further comprising: providing a
differentiating component associated with the first side of the
base the differentiating component comprising a first side and a
second side and an annulus extending through the differentiating
component from the first side to the second side, one of the first
side or the second side comprising a structured surface; and
placing an indicator in association with the first surface of the
base further comprises placing the indicator within the
annulus.
40. The method of claim 39 wherein the structured surface comprises
a microstructured surface associated with the first side of the
base, the microstructured surface comprising a regular array of
precise structures having a shape selected from the group
consisting of symmetrical shapes and asymmetrical shapes, the
precise structures defining a plurality of channels arranged in a
predetermined pattern, the channels comprising an opening to permit
the ingress of fluid within the channels when the indicator is in a
second state.
41. The method of claim 38, further comprising providing a
transmission layer in association with the first side of the base
between the base and the indicator, the transmission layer
comprising a material to reduce, maintain or increase shock force
transmitted to the indicator during a shock event.
42. The method of claim 38 wherein placing an indicator in
association with the first surface of the base is accomplished by
screen printing the indicator onto the first surface.
43. The method of claim 38 wherein the shock indicator is provided
in a first condition to transition from a first state to a second
state at a first shock force; and further treating the shock
indicator to a second condition such that after the further
treatment, the shock indicator will transition from a first state
to a second state at a second shock force.
Description
[0001] Pursuant to 35 U.S.C. .sctn. 120, this continuation
application claims the benefit of U.S. nonprovisional patent
application Ser. No. 10/517,685 filed on Dec. 10, 2004 which claims
the benefit under 35 U.S.C. .sctn.371 of International Application
PCT/US03/19014 filed on Jun. 13, 2003 designating the United States
of America, which claims the benefit of U.S. provisional patent
application No. 60/388,684 filed on Jun. 14, 2002.
FIELD OF THE INVENTION
[0002] The present invention relates to a shock indicator device,
assemblies that include the shock indicator device, and a method
for the manufacture of the shock indicator device.
BACKGROUND OF THE INVENTION
[0003] Shock indicators are devices that may be applied to other
devices within any of a variety of different industries. Shock
indicators are useful in detecting significant vibration or
mechanical shock experienced by an associated device such as an
electronic device, including hand held electronic devices. Cellular
phones, personal digital assistants, hand held computers, battery
chargers, small electric appliances, digital cameras (e.g., video
and still cameras) are exemplary of devices that may be used in
association with a shock indicator. Shock indicators may be placed
on the electronic device in a suitable manner, either on the outer
surfaces of the device or on an internal surface such as adjacent
electronic components within the device, in the battery compartment
or the like. If the electronic device experiences a severe shock as
may occur if the device is dropped onto a hard surface from a
significant height, the shock indicator should be activated to
thereafter indicate the occurrence of the shock. Such information
could be useful to a manufacturer and/or a service organization
charged with repair or replacement of the device.
[0004] The vibration or shock history of an electronic device can
be important. For example, recent developments in electronic
equipment and components have provided a technological revolution
in display technology. Previous monochrome displays made of
polymeric film and the like have been relatively forgiving when
mistreated or otherwise subjected to conditions of extreme handling
(e.g., dropping or other shock inducing events). More recent
developments in color displays have not yet evolved to such a level
of durability. Many color systems still require glass panels which
may be damaged when dropped or otherwise subjected to a shock
force.
[0005] It would, therefore, be desirable to provide a shock
indicator that can be affixed to or otherwise associated with a
device, such as an electronic device including a cellular phone, a
personal digital assistant, a hand held computer and the like. It
would be especially desirable to provide such a shock indicator
device in a construction that allows for activation of the
indicator when an associated apparatus or device experiences a
significant shock event, regardless of the direction of the
force.
SUMMARY OF THE INVENTION
[0006] In one aspect, the invention provides a shock indicator,
comprising: [0007] (A) A base having a first side and a second
side; [0008] (B) an indicator associated with the first side of the
base, the indicator comprising a plurality of indicator subparts,
the subparts comprising solid material arranged (i) in a first
configuration when the shock indicator is in a first state prior to
a shock event, and (ii) in a second configuration when the shock
indicator is in a second state following a shock event; and [0009]
(C) Attachment means associated with second side of the base for
attachment of the shock indicator to a surface.
[0010] The subparts of the indicator may comprise material selected
from the group consisting of toner powder particles, talc, flour,
pigment, clay, ceramics, alumina, metals, and combinations of the
foregoing, and the subparts may be surface modified. In another
aspect, the subparts of the indicator may comprise a first size and
the indicator may further comprise another component comprising a
second subpart having a second size larger than the first subpart
such as glass beads, for example. Typically, the shock indicator
will also comprise a containment member disposed on the first side
of the base and enclosing the indicator therein, the containment
member being transparent, thereby facilitating the visual
determination of the indicator in either its first or second
configuration. The indicator and the first side of the base may be
provided in different colors to provide a visual contrast
therebetween.
[0011] In another aspect, the shock indicator may further comprise
a differentiating component associated with the first side of the
base the differentiating component comprising a film material to
enhance the visual contrast between the differentiating component
and the indicator. The differentiating component may comprise a
first side and a second side and an annulus extending through the
differentiating component from the first side to the second side,
the indicator positioned within the annulus, at least one of the
first side or the second side of the differentiating component
comprising a structured surface. The structured surface may be a
microstructured surface which is associated with the first side of
the base to define a plurality of channels arranged in a
predetermined pattern, the channels comprising an opening to permit
the ingress of fluid when the indicator is in a second state. The
microstructured surface typically comprises a regular array of
precise structures having a shape selected from the group
consisting of symmetrical shapes and asymmetrical shapes.
[0012] In still another aspect, the shock indicator may further
comprise an impingement object within the containment member and
positioned to impact the indicator during a shock event to aid in
transitioning the indicator from the first state to the second
state, the impingement object can be a material selected from the
group consisting of glass beads, glass bubbles, ceramic beads,
plastic beads, ball bearings and combination thereof.
[0013] In another aspect, the indicator comprises dry materials and
the shock indicator further comprises means to indicate exposure to
wetness.
[0014] In still another aspect, the indicator comprises an
agglomerated powder in the first state prior to a shock event and a
dispersed powder in the second state following a shock event, the
indicator subparts comprising particles of the powder. Also, the
indicator may comprise a solid (e.g., powder) and a liquid wherein
the solid may be selected from the group consisting of exfoliated
organophilic clay fillers, silica particles, glass particles,
inorganic pigments, and combinations of the foregoing and the
liquid at 23.degree. C. has a surface tension within the range from
about 10.times.10.sup.-3 N/m to about 80.times.10.sup.-3 N/m, a
density from about 0.5 to about 2 grams/cm.sup.3, and a zero rate
shear viscosity from about 1.times.10.sup.-3 to about
1.times.10.sup.6 Pa-s. Some suitable fluids comprise liquids
selected from the group consisting of silicone fluids and oils,
saturated hydrocarbon-based oils, silicone gums, mineral oil,
glycerols, water and combinations of the foregoing.
[0015] In still another aspect, the shock indicator further
comprises a transmission layer positioned on the first side of the
base between the base and the indicator, the transmission layer
comprising a material to reduce, maintain or increase shock force
transmitted to the indicator during a shock event. In other aspects
the transmission layer comprises a viscoelastic material having a
storage modulus of at least about 1.0 psi (6.9.times.10.sup.3
Pascals) and a loss factor of at least about 0.01 at the
temperature and frequency at which the shock indicator is used.
[0016] In still another aspect the invention provides an assembly
comprising the above mentioned shock indicator associated with an
electronic device selected from the group consisting of cellular
telephone, personal digital assistant, and hand held computers.
[0017] In another aspect, the invention provides a method for the
manufacture of a shock indicator, comprising: [0018] (A) providing
a base comprising a first surface and a second surface, the second
surface of the base associated with an attachment means; and [0019]
(B) placing an indicator in association with the first surface of
the base, the indicator comprising a plurality of indicator
subparts, the subparts comprising solid material arranged (i) in a
first configuration when the shock indicator is in a first state
prior to a shock event, and (ii) in a second configuration when the
shock indicator is in a second state following a shock event.
[0020] The step of placing an indicator in association with the
first surface of the base may further comprise placing a plurality
of indicators in association with the first side of the base, each
indicator comprising a plurality of indicator subparts, the
subparts comprising solid material arranged (i) in a first
configuration prior to a shock event, and (ii) in a second
configuration following a shock event.
[0021] In another aspect, placing an indicator in association with
the first surface of the base is accomplished by screen printing
the indicator onto the first surface.
[0022] In still another aspect, the invention provides the
foregoing method and further comprises placing a containment member
over the first side of the base and over the indicator, the
containment member being transparent, thereby facilitating the
visual determination of whether the indicator is in the first
configuration or the second configuration.
[0023] In still another aspect, the invention provides the
foregoing method and further comprises providing a differentiating
component associated with the first side of the base the
differentiating component comprising a first side and a second side
and an annulus extending through the differentiating component from
the first side to the second side, one of the first side or the
second side comprising a structured surface; and placing an
indicator in association with the first surface of the base further
comprises placing the indicator within the annulus. The structured
surface can comprise a microstructured surface associated with the
first side of the base, the microstructured surface comprising a
regular array of precise structures having a shape selected from
the group consisting of symmetrical shapes and asymmetrical shapes,
the precise structures defining a plurality of channels arranged in
a predetermined pattern, the channels comprising an opening to
permit the ingress of fluid within the channels when the indicator
is in a second state.
[0024] In another aspect, the method will also comprise providing a
means for attaching the indicator to another surface such as by an
adhesive or a mechanical fastener, for example, herein the means
for attaching may comprise a material to reduce, maintain or
increase shock force transmitted to the indicator during a shock
event
[0025] In still another aspect, the invention provides the
foregoing method and further comprises providing a transmission
layer in association with the first side of the base between the
base and the indicator, the transmission layer comprising a
material to reduce, maintain or increase the shock force
transmitted to the indicator during a shock event.
[0026] In still another aspect, the invention provides the
foregoing method and further comprises associating an electronic
device with the shock indicator, the device selected from the group
consisting of cellular telephone, personal digital assistant and
hand held computer.
[0027] Additional details of the invention will be more fully
appreciated by those skilled in the art upon further consideration
of the remainder of the disclosure, including the detailed
description of the preferred embodiment in conjunction with the
various figures herein and the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] In describing the preferred embodiment of the invention,
reference is made to the various figures in which the features of
the preferred embodiment are generally designated by reference
numerals and wherein like reference numerals indicate like
structure, wherein:
[0029] FIG. 1 is a perspective view of one embodiment of a shock
indicator according to the present invention;
[0030] FIG. 2 is a cross sectional side elevation view of the shock
indicator of FIG. 1;
[0031] FIG. 3 is a top plan view of the shock indicator of FIG. 1
in a first state prior to a shock event;
[0032] FIG. 4 is a top plan view of the shock indicator of FIG. 1
in a second state following a shock event;
[0033] FIG. 5 is a side elevation view of a material useful as a
base in the shock indicator of the present invention; and
[0034] FIG. 6 is a schematic illustrating a method for the
manufacture of the shock indicator of the present invention;
[0035] FIG. 7 is an exploded view, in a side elevated cross
section, of another embodiment of a shock indicator according to
the present invention;
[0036] FIG. 8 is a cross sectional side elevation view of the shock
indicator of FIG. 7 in a first state prior to a shock event;
[0037] FIG. 9 is a cross sectional side elevation view of the shock
indicator of FIG. 7 in a second state following a shock event;
and
[0038] FIG. 10 is a cross sectional side elevation view still
another embodiment of a shock indicator according to the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0039] The present invention provides a shock indicator suitable
for use on any of a variety of shock-sensitive machines, electronic
components, electronic equipment or other devices that may be
subjected to inertial and vibrational forces during use. The shock
indicator device of the present invention provides a passive means
to determine whether an associated apparatus or the like has been
subjected to a mechanical shock event. The shock indicator device
of the invention is initially provided in a non-activated condition
and is transitioned to an activated condition upon the application
of sufficient force or shock caused by, for example, the
deceleration of an associated device dropped onto a floor or other
hard surface from a significant distance.
[0040] Various features and embodiments are contemplated within the
scope of the invention and are generally described below.
[0041] Referring now to the drawings, FIGS. 1 and 2 show a shock
indicator 10 according to the present invention. The shock
indicator 10 may be affixed to a surface 30 (see FIG. 1) of another
device, as mentioned herein. The shock indicator 10 includes a base
member 12 having a first side 22 and a second side 24. The first
and second sides 22 and 24 of the base member 12 comprise,
respectively, the first and second major surfaces of the base
member 12. An indicator 14 is associated with the first side 22 of
the base 12. As shown, the indicator 14 can comprise a spherically
configured agglomerated powdered material. The indicator member 14
may comprise a colored powder and/or one or more coloring agents to
provide the indicator 14 with a visually discernable appearance. If
desired, portions of the indicator 14 may be provided in one or
more colors while other portions of the indicator 14 may be
provided in another color or colors.
[0042] The indicator 14 is an agglomerated powder which, when so
agglomerated, indicates a first or non-activated configuration
prior to the occurrence of a shock event. In the depicted
embodiment, a domed containment member 18 is provided over the
first side 22 of the base member 12 and enclosing the indicator 14.
As is described below, at least a portion of the domed containment
member 18 is typically transparent in order to facilitate the
visual observation of the indicator 14. The containment member 18
functions to protect the agglomerated powder material of the
indicator 14 from prematurely dispersing or smearing due to
handling, incidental bumping, and the like. It will be appreciated
that, in some embodiments, the containment member 18 may be
considered an optional component such as when the shock indicator
10 is incorporated within a device that includes a structure or
structures equivalent to containment member 18, or where the
indicator 14 is bound together in sufficient strength to withstand
smearing or activation during the normal and expected use of the
associated device. Additionally, the containment member may be
provided in any of a variety of shapes and sizes as may be required
due to spatial constraints in a particular application or as may be
desired for any other reason. An attachment means 16 is also
provided and is associated with the second side 24 of the base
member 12. In the depicted embodiment of the shock indicator 10,
the attachment means 16 is a pressure sensitive adhesive. Other
means for the attachment of the devices of the invention to a
surface are also contemplated as within the scope of the
invention.
[0043] It should be appreciated that the design and material
selection for the attachment means 16 may affect the level of force
that actually acts upon the indicator 14 and the associated parts
of the shock indicator device 10. The indicator 14 will respond to
a level of force that causes the subparts of the indicator 14 to
disperse. The shock event can lead to shear, compression, tensile,
peel or cleavage stress forces acting on the indicator and on the
attachment means. The shock stresses imparted through, into or onto
the indicator 14 will exceed the structural strength of the
indicator 14 and/or the attachment means, causing the structure of
the agglomerated indicator 14 to collapse, fail, break-apart,
disintegrate, implode, explode, disperse or change to thus indicate
that a significant shock event has occurred. In the embodiment of
FIG. 2, a release liner or liner material 26 may be provided to
protect the adhesive surface of the attachments means 16 prior to
the shock indicator 10 being applied to a surface.
[0044] In the embodiment of FIG. 2, a release liner or liner
material 26 may be provided to protect the adhesive surface of the
attachments means 16 prior to the shock indicator 10 being applied
to a surface.
[0045] An additional differentiating component 20 is may be
provided over at least a portion of the first surface 22 of the
base member 12. The differentiating component 20 may comprise a
film material overlying the first side 22 of the base member 12.
Most typically, the differentiating component 20, when present, is
provided with a suitable surface color to enhance the visual
contrast between the differentiating component 20 and the indicator
14. In this manner, the activation of the indicator 14 is more
readily observable where the contrast between the indicator 14 and
the differentiating component 20 have been selected to facilitate
the visual determination of the activation state of the indicator
14. Alternatively, the base 12 can be provided as a colored film to
provide the same color contrast effect in conjunction with the
color selected for the indicator 14.
[0046] Referring to FIGS. 3 and 4, the shock indicator 10 may
comprise an additional component in the form of a conductive layer
122 configured to act as a circuit upon the application of charge
thereto. The conductive layer 122 is constructed of a conductive
metal or other material capable of providing an electrostatic
charge to powder particles positioned within the innermost portion
of the differentiating component 20. The presence of a conductive
layer 122 provides a means by which the powdered indicator 14 may
be agglomerated during the manufacture of the shock indicator 10 by
providing sufficient electrostatic charge to coalesce individual
powder particles into a cohesive mass to thereby form the
spherically agglomerated indicator 14 in a first configuration or
first state prior to the occurrence of a shock event.
[0047] Referring to FIG. 4, the shock indicator 10 is depicted
following activation due to a shock event. Accordingly, the
subparts (e.g., powder particles) of the indicator 14 are in a
second configuration dispersed across differentiating component 120
on the first side of the base member 12, thereby visually exposing
more of the conductive layer 122. The conductive layer 122 of the
shock indicator 10 provides one manner by which the powdered
indicator 14 may be agglomerated in an appropriate position to
indicate a first state for the shock indicator prior to a shock
event. It will be appreciated by those skilled in the art that
other means are available to provide an agglomerated powder
indicator, some of which are described herein. The present
invention is not to be limited in any way by the use of a
conductive layer 122. For example, a binder composition and/or a
diluent liquid may be mixed with an appropriate powder suitable for
use as an indicator. The diluent liquid may be any of a variety of
suitable organic liquids, especially those capable of wetting the
powder and thereby displacing entrapped air. Most typically, such a
diluent liquid or binder will be selected so as to hold the powder
in an agglomerated state for a period long enough to position the
indicator in a first configuration within the shock indicator.
Thereafter, the diluent liquid may be evaporated and the binder
used, if any, will not be of sufficient strength to prevent the
powdered indicator from dispersing to a second configuration
following a shock event.
[0048] A principal starting material for the manufacture of the
shock indicator comprises a web 210, depicted in FIG. 5. The web
210 may compromise a multilayered film or a number of different
film and adhesive layers associated with one another. A number of
film layers may be desired or needed to support the indicator and
the containment member, if present. Additionally, one or more
adhesives or other attachment means may be utilized to adhere the
layers of the web 210 to one another as well as providing an
attachment means for affixing the shock indicator to another
device. In the depicted embodiment of the web 210, differentiating
component layer 220 overlies silicone release coating 222. The
differentiating layer 220, when present, may be colored where it is
desirable to provide a visual contrast with the indicator in the
finished shock indicator. Release coating 222 is provided as a
convenience during the manufacture of the shock indicator to
facilitate the removal of excess background film 220 when the web
210 is used to make a plurality of shock indicators. In this
manner, the excess background film 220 may be removed as "weed" in
the manner described below.
[0049] A polymeric backing 224 is provided as a film associated
with the silicone release coating 222 by an adhesive layer 226
disposed along a major surface of the polymer film backing 224.
Along the opposite side of the polymer film backing 224, another
layer of adhesive 228 provides an attachment means for affixing the
finished shock indicator to the surface of another device or the
like. Release liner 230 may overlay the surface of the adhesive 228
to at least temporarily protect the surface of the adhesive layer
228.
[0050] Referring now to FIG. 6, a process for the manufacture of
the shock indicator of the present invention will be described. The
aforementioned web 210 is conveyed along a converting line 300. A
first rotary die 302 is positioned along the converting line 300.
The die 302 is configured to cut a plurality of circular base
members in the web 210. It will be appreciated that the
configuration of the shock indicator, although depicted herein as
circular, may comprise any of a variety of shapes and sizes
including circular, square, rectangular, oval, polygonal, and the
like. Following die cutting by rotary die 302, the web 210 advances
along the converting line to roller 304 where the unneeded portions
of the layer 220 (see FIG. 5) are removed as "weed" 306 which is
directed to take up roll 308, leaving the web 210 to comprise a top
layer of circular background film 220 that will serve as a
differentiating component in an article of the invention.
[0051] In this embodiment, a rotary screen printing roll 310 is
positioned along the web converting line 300 to screen print the
powdered indicator onto the die cut circular portions on the web
210. The use of a rotary screen printing process for the deposition
of indicator materials is typically accomplished using a suitable
indicator material mixed with an appropriate amount of a binder
material and/or diluent liquid. Such materials may comprise
materials that are not normally considered as binders in many
applications. For purposes of the present invention, suitable
binders include mineral oil, for example, as well as other solvents
or materials that will aid in the agglomeration of the indicator
material without evaporating. Additionally, organic (e.g.,
hydrocarbon) liquids may be added to the binder to facilitate the
formation of a slurry that can then be deposited, printed or
otherwise placed on the base member. A diluent liquid may also be
an active solvent for a binder without being a solvent for the
indicator material. In this manner, a diluent liquid can assist in
initially holding the indicator powder materials to each other.
Following the deposition of a slurry onto the base member or web
210, the liquid is allowed to evaporate while the binder remains
associated with the powder and continues to hold the agglomerated
powder in a cohesive mass until it is disturbed by a shock event.
Additionally, the foregoing diluent liquids may be used without
binder so that, following the evaporation of the liquid, the
powdered agglomerate is maintained in a cohesive mass by
electrostatic attraction or van der Waals forces. Other embodiments
of the indicator as well as the other features of the shock
indicator of the invention are also contemplated, and at least some
of those are described herein including indicators that incorporate
liquids with powder particles and those that incorporate solid
materials other than powder particles or solid materials (other
than powder particles) that are used with powder particles, for
example. The present invention is not to be construed as limited to
any particular indicator composition or construction other than
those constructions that are capable of transitioning from a first
configuration to a second configuration in response to a shock
event. Moreover, the construction of the shock indicator device of
the invention can be customized in order to provide the device with
a sensitivity to shock events of a certain threshold value or
minimum magnitude.
[0052] In various embodiments, a containment member will be placed
over the aforementioned backing pieces and indicator materials. The
containment material 312 is typically a polymeric material.
Suitable materials for the containment material include materials
capable of being vacuumed formed such as polycarbonate,
polystyrene, polyolefin, acrylic polymers and also polyester
polymers and copolymers. The containment material 312 is supplied
from feed roll 314 to the vacuum forming roll 316. As mentioned,
the containment member may be supplied as a dome or in some other
configuration. In the depicted process, the configuration of the
containment structure is formed on a forming roll 316 and
thereafter applied over the above-described based members and the
rotary screen printed indicator materials. The containment material
312 is applied over the backing material and is affixed thereto by
adhesive layer 226 (FIG. 5) provided as a layer of the web material
210. A second rotary die 318 is provided to die cut through the
containment material 312 and the remaining layers of the web 210 so
that individual shock indicators are thereby formed and are carried
on a common backing. The backing may comprise a liner 230 to hold
all of the shock indicators on a sheet until further cutting or
slitting of the web 210 occurs. The "weed" from the containment
material 312 is then taken up on take up roll 328. In the depicted
embodiments, the take up roll 328 picks up the weed from the
conveyor line with guide rolls 322 and 324 to guide the weed to the
take up roll. A slitter 326 is then provided to slit the web 210
into elongate strips having a plurality of shock indicator buttons
aligned thereon in a longitudinal manner. These longitudinal strips
may then be further cut or packaged, as desired for convenient
dispensing or for automated dispensing such as from a dispenser
fitted with a magazine cartridge.
[0053] Regarding materials, the base 12 (FIGS. 1 and 2) may
comprise any of variety of suitable materials such as polymeric
film materials, woven and nonwoven materials, paper, spun bonded
materials and the like. The indicator material is typically
comprised of a solid material that further comprises a number of
solid indicator sub-parts. Most typically, the indicator material
is a powder material capable of forming an agglomerated mass.
Suitable materials for the indicator include conventional toner
powders, talc, flour, pigments, clays, ceramic powders (boron
nitride, silicon carbide, alumina, etc), spherical alumina, powered
metals, other finely ground materials and the like. The powders
particles can be surface modified with various chemical treatments
or coatings to modify their agglomerating ability and/or to improve
mixing, compounding and/or delivery to a location. The powders or
particulates can be provided in any of a variety of shapes, such as
platelets, spherical, pole like all with various feature aspect
ratios. The powder or particulate component can be hollow, porous,
solid or a mixture of these. Combination of these features permits
unique blending of particles and powders with optional larger
particles and polymer or resin matrixes. The agglomerates can also
be made using larger "seed" bodies or a resin starved matrix design
comprising particles or beads such as glass bubbles or microbubbles
and the like. When seed bodies are used, the smaller powder
particles will be attached to or associated with the larger seed
particle to form an agglomeration of the smaller particles around
the larger seed bodies.
[0054] Other materials are also mentioned herein in the discussion
of individual embodiments, and it is not intended that the
invention be limited to any particular selection of materials for
the indicator.
[0055] Regarding the attachment means, any of a variety of
materials may be used to affix the shock indicators of the present
invention to the surface of another device or apparatus. Adhesives
as well as reclosable fasteners such as hook and loop components,
and mechanical fasteners such as snaps, hooks, clips, clamps, and
rivets may be used in affixing the shock indicator of the invention
to a device such as, for example, a cellular telephone, a hand held
computer, or the like. Adhesives suitable for use as the attachment
means may be selected from any of a variety of adhesive materials
such as pressure sensitive adhesives, thermally bonded adhesives
(e.g., hot melts), ultra-violet activated adhesives, room
temperature curable adhesives, cold seal adhesives, self fusing
adhesives, epoxies, thermoplastics, thermosets and the like.
Typically, pressure sensitive adhesives are used to adhesively bond
the shock indicator to a device.
[0056] It will be appreciated that the selection of the specific
attachment means may take into account how the attachment means
will affect the shock indicator's response to a shock event.
Different attachment means can effect how the indicator will
respond to a shock event. For example, the attachment means can
provide damping and/or isolation to the shock indicator. The
geometry of the attachment means (e.g., whether it is a solid
material, has holes or other cut-outs, and its thickness, width,
and/or length), its configuration, materials used, modulus, and the
like can effect the properties of the attachment means such as the
stiffness, softness or spring constant and the resultant damping
can change how the shock indicator responds to a shock event. A
soft and low modulus attachment means (such as a double coated
foam) will change how a shock indicator responds to a same shock
event as compared with a stiff, high modulus attachment means (such
as an epoxy adhesive with a high modulus or high glass transition
temperature, Tg). A pressure sensitive adhesive (PSA) can have a
degree of damping and isolation performance depending on the
polymer's Tg and the application geometry used. Moreover, different
pressure sensitive adhesives (or other attachment means) can change
the transmissibility of the same shock force.
[0057] Pressure sensitive adhesives generally possess (1)
aggressive and permanent tack, (2) adherence to a substrate upon
the application of finger pressure, (3) the ability to hold onto a
substrate or adherend and (4) sufficient cohesive strength to be
substantially cleanly removed from the adherend for ease of rework.
Additives may be added to the pressure sensitive adhesive to impart
and/or improve these properties. Suitable pressure sensitive
adhesives will typically include the foregoing properties and the
actual attachment means used in the shock indicator of the
invention may comprise a single pressure sensitive adhesive or a
combination of adhesives. Suitable pressure sensitive adhesives
include those based on natural rubbers, synthetic rubbers, styrene
block copolymers, polyvinyl ethers, poly(meth)acrylates,
polyolefins and silicones, for example. Tackifiers may be added to
the adhesive for improved tack. Suitable tackifiers may comprise
rosin ester resins, aromatic hydrocarbon resins, aliphatic
hydrocarbon resins and terpene resins. Oils, plasticizers,
antioxidants, UV stabilizers, hydrogenated butyl rubber, pigments,
curing agents and combinations thereof may also be found in the
pressure sensitive adhesive useful herein.
[0058] A useful pressure sensitive adhesive may be based on at
least one poly(meth)acrylate derived from, for example, at least
one alkyl(meth)acrylate ester monomer such as isooctyl acrylate,
isononyl acrylate, 2-methyl-butyl acrylate, 2-ethyl-hexyl acrylate
and n-butyl acrylate; and at least one co-monomer component such as
(meth)acrylic acid, vinyl acetate, N-vinyl pyrrolidone,
(meth)acrylamide, vinyl ester, fumarate, styrene macromer, or
combinations of the foregoing. A suitable poly(meth)acrylate for
use in the invention may be derived from about 0 to about 30 wt. %
acrylic acid and about 100 to about 70 wt. % of at least one of
isooctyl acrylate, 2-ethyl-hexyl acrylate or n-butyl acrylate. More
typically, the suitable poly(meth)acrylate is derived from about 2
to about 10 wt. % acrylic acid and between about 90 and about 98
wt. % of at least one of isooctyl acrylate, 2-ethyl-hexyl acrylate
or n-butyl acrylate.
[0059] Referring generally to FIGS. 7, 8 and 9, a shock indicator
410 according to another embodiment of the invention is shown and
will now be described. The shock indicator 410 comprises a base
member 412 having a first side 422 and a second side 424. The first
and second sides 422 and 424 of the base member 412 comprise,
respectively, the first and second major surfaces of the base
member 412. An indicator 414 is associated with the first side 422
of the base 412. In the embodiment of the invention illustrated in
FIGS. 7 and 8, the indicator 414 comprises a liquid in addition to
the solid materials previously described herein. It is contemplated
that the indicator 414 may comprise, for example, a suspension of
exfoliated organophilic clay fillers or the like dispersed in a
liquid phase material such as, for example, mineral oil. One
suitable combination of materials for the indicator 414 is
exfoliated organophilic clay dispersed in mineral oil at about 16%
by weight. Other materials are described below.
[0060] The indicator 414 depicted in FIGS. 7 and 8 is in a first
configuration prior to the occurrence of a shock event. Domed
containment member 418 covers the first side 422 of the base member
412 and the indicator 414. Differentiating component 420 is
provided over at least a portion of the first surface 422 of the
base member 412. In this embodiment, the differentiating component
420 comprises sheeting or material having optical properties that
enable a viewer of the material to readily witness changes in color
caused by liquid released from the indicator 414 as it travels
along surface 422. Suitable materials for this application are
discussed herein.
[0061] In this embodiment, the differentiating component 420 is
typically cut (e.g., die cut) in an annular shape to surround the
indicator 414 within annulus 430 in which the indicator 414 nests
when the indicator is in its first configuration prior to a shock
event. The differentiating component 420 is provided with both a
structured surface 420a and a non-structured surface 420b. The
non-structured surface 420b may be laminated to, adhesively affixed
to, or otherwise associated with the domed containment member 418.
The structured surface 420a of the component 420 is textured, and
typically comprises a microstructured surface, wherein the
microstructured surface defines a plurality of channels 421 with a
predetermined channel pattern when the surface 420a is laminated to
the base member 412. The maximum depth and width of the channels is
typically less than about 1,000 microns. The channels may or may
not be interconnected. The channels may, optionally, be formed from
a series of projections on the surface 420a. The description of the
surface 420a is not meant to exclude webs, fabrics, porous
materials, porous papers, porous membranes, etc., which may have
channels, but which may be considered as not being of a
predetermined pattern. Typically, the channel portion of the
substrates of the invention is regular, orderly, and non-random,
and the channels are in an array. In some embodiments, each channel
would be substantially identical or identical to an adjacent
channel. In some embodiments, one may wish to have differing
channel geometries and/or sizes, either widthwise across the
channel surface or lengthwise down the channeled surface.
[0062] The substrates comprising the optical differentiating
component 420 may be flexible, and therefore easier to attach to an
intended surface. However, semi rigid and rigid substrates also may
be useful according to the invention. The differentiating component
420 may or may not be retroreflective depending on the particular
embodiment. Examples of useful non-retroreflective substrates
include, but are not limited to, microstructured substrates. The
use of a retroreflective microstructured substrate may provide a
number of advantages to the articles of the invention such as
providing a highly visible fluid flow front in which the fluid
frustrates total internal reflection in the retroreflective
substrate. It will also be appreciated that the differentiating
component may be provided with dual textured surfaces or dual
smooth surfaces (e.g., differentiating component 20, FIGS. 1 and 2)
as may be desired for a particular application of the shock
indicator of the invention.
[0063] The flow of the fluid through the microchannels is generally
passive in that it is typically accomplished via capillary action.
Gravitational effects may also influence the flow of fluid to at
least a minor extent. The microstructured surface of the
differentiating component can comprise different shapes including
symmetrical or asymmetrical shapes such as, for example,
rectangular, square, trapezoidal, ring, triangular, etc.
Optionally, markings (not shown) may be placed on the shock
indicator 410 to indicate the magnitude of a shock event. The
markings may, for example, be placed along the surface 419 of the
containment member 418 at calibrated intervals. Such markings may
or may not be evenly spaced depending on the construction of the
microstructured surface 420a and the channels created thereby.
Typically, the channel openings are located on at least one edge or
side of a substrate and the channels extend through the entire
substrate surface to another end or edge of the substrate
(typically an opposite end or edge). The channels 421 may be
interconnected to promote a more even fluid flow front.
[0064] Although the channels 421 may be provided using a textured
surface 420a laminated to a relatively flat surface of the base
member 412, it is also possible to provide channels that are
internal to the substrate by joining together two microstructured
surfaces to provide channels that will accommodate a desired fluid
flow. The resulting substrate may or may not be retroreflective
depending on the patterns joined together. These sheets can be held
together by a variety of means including adhesives, hot-melt
bonding, and the like. Depending on the substrate shape and channel
design, it may be desirable to seal the edges or sides of the
substrate to prevent leakage of fluid therefrom. The channels of
the microstructured substrate can have a variety of shapes.
Typically the channels within the substrate are similarly shaped.
Examples of useful channel cross-sectional shapes include, but are
not limited to, the following: v-shaped channels, u-shaped
channels, semi-circle-shaped channels, and square u-shaped
channels. The channels when viewed from above, can be linear or
non-linear. For example, they may be straight, curved, twisted,
crooked, tortuous, etc. The channels may optionally be formed by a
series of geometric projections, wherein the paths between the
projections become the channels. This would be the case for
retroreflective cube-corner sheeting discussed later herein.
Preferably the channels of the substrate are planar.
[0065] The depth of the channels normally will range from about 5
to less than about 1,000 microns, typically from about 10 to about
500 microns, more typically from about 25 to about 200 microns, and
often from about 25 to about 100 microns. The width of the channels
normally range from about 5 to about less than about 1,000 microns,
typically from about 10 to about 500 microns, more typically from
about 25 to about 250 microns. The spacing of the channels is such
that a channel is generally within about 5 to less than about 1,000
microns of another channel, typically from about 10 to about 500
microns, and often from about 10 to about 250 microns. The shape,
length, and number of channels on the substrate can vary depending
on a number of factors such as the length of time desired for the
fluid to run through the substrate, the particular fluid to be used
with the substrate. A microstructured substrate tends to retain its
geometry and surface characteristics upon exposure to the fluids
used in the articles of the invention. One suitable material is a
retroreflective diamond grade sheeting available from 3M Company
under the designation "DG307."
[0066] Examples of useful non-retroreflective substrates include,
but are not limited to, those disclosed in U.S. Pat. No. 5,728,446
(Johnston) and U.S. Pat. No. 5,514,120 (Johnston). These substrates
provide for liquid management films that facilitate desired rapid
and uniform anisotropy or directionally dependent distribution of
liquids and absorbent articles using these films. These liquid
management films have at least one microstructured surface with a
plurality of primary grooves to promote the unidirectional
spreading of the liquids. These primary grooves may also contain
secondary grooves as in U.S. Pat. No. 5,728,446.
[0067] The microstructured flow channels of non-retroreflective
microstructured substrates are, in some embodiments, substantially
parallel and linear over at least a portion of their length. The
channels can be easily formed from thermoplastic materials by
casting, profile extrusion or embossing, preferably by casting or
embossing.
[0068] The non-retroreflective microstructured substrates are
preferably formed from any thermoplastic materials suitable for
casting, profile extrusion, or embossing including, for example,
polyolefins, polyesters, polyamides, poly(vinyl chloride),
polymethyl methacrylate, polycarbonate, nylon, etc. Polyolefins are
often used, particularly polyethylene or polypropylene, blends
and/or copolymers thereof, and copolymers of propylene and/or
ethylene with minor proportions of other monomers, such as
ethylene/vinyl acetate. Polyolefins have excellent physical
properties, are relatively easy to process, and typically are lower
in cost than other thermoplastic materials having similar
characteristics. Moreover, polyolefins readily replicate the
surface of a casting or embossing roll and are also readily profile
extruded. They are tough, durable and hold their shape well, thus
making such films easy to handle after the casting or embossing
process. Alternatively, the microstructured substrate can be cast
from curable resin materials such as acrylates or epoxies, and
cured by exposure to heat, ultraviolet (UV), or E-beam radiation.
Most likely, the microstructured substrates having retroreflective
and/or other optical properties discussed in greater detail below
can also be made by the procedures described above.
[0069] Another class of microstructured substrates useful in
embodiments of this invention are retroreflective substrates.
Retroreflective materials have the property of redirecting light
incident on the material back toward its originating source. In
situations where the retroreflective sheeting may need to flex or
conform to a surface, a sheeting may be selected, to permit flexing
without sacrificing retroreflective performance.
[0070] There are two common types of retroreflective sheeting:
microsphere-based sheeting and cube-corner sheeting.
Microsphere-based sheeting, sometimes referred to as "beaded"
sheeting, is known and employs a multitude of microspheres,
typically at least partially embedded in a binder layer and having
associated specular or diffuse reflecting materials (e.g., pigment
particles, metal flakes or vapor coats, etc.) to retroreflect
incident light. Illustrative examples of such retroreflectors are
disclosed in U.S. Pat. No. 3,190,178 (McKenzie), U.S. Pat. No.
4,025,159 (McGrath), and U.S. Pat. No. 5,066,098 (Kult).
Microsphere based sheeting does not have a regular predetermined
channel pattern.
[0071] Basic cube-corner retroreflective sheeting is known and may
be used as a differentiating component 420 in the articles of the
invention. Such sheeting is frequently used on road signs, safety
garments and the like. The sheeting comprises a substantially
planar base surface and a structured surface comprising a plurality
of cube-corner elements opposite the base surface. Each cube-corner
element comprises three mutually substantially perpendicular
optical faces that intersect at a single reference point, or apex.
Light incident on the planar base surface of the sheeting is
refracted at the base surface of the sheeting, transmitted through
the sheeting, reflected from each of the of the three perpendicular
cube-corner optical faces, and redirected toward the light source.
The symmetry axis, also called the optical axis, extends through
the cube-corner apex and forms an equal angle with the three
optical surfaces of the cube-corner element. Cube-corner elements
typically exhibit the highest optical efficiency in response to
light incident on the base of the element roughly along the optical
axis. The amount of light retroreflected by a cube corner
retroreflective surface drops as the incidence angle deviates
significantly from the optical axis.
[0072] Manufacturers of retroreflective sheeting are known to
design retroreflective sheeting to exhibit its peak performance in
response to light incident on the sheeting at a specific angle of
incidence. The term "entrance angle" is used to denote the angle of
incidence, measured from an axis normal to the base surface of the
sheeting, of light incident on the sheeting. See, e.g. ASTM
Designation: E 808-93b, Standard Practice for Describing
Retroreflection. Retroreflective sheeting for signing applications
is typically designed to exhibit its optimal optical efficiency at
relatively low entrance angles (e.g. approximately normal to the
base surface of the sheeting). See, e.g. U.S. Pat. No. 4,588,258 to
Hoopman.
[0073] Other applications such as, for example, pavement marking or
barrier marking applications, require retroreflective sheeting
designed to exhibit its maximum optical efficiency at relatively
high entrance angles. For example, U.S. Pat. No. 4,349,598 to White
('598 patent), discloses a retroreflective sheeting design wherein
the cube-corner elements comprise two mutually perpendicular
rectangular faces disposed at 45 degrees to the cube-corner
sheeting base and two parallel triangular faces perpendicular to
the rectangular faces to form two optically opposing cube-corner
elements. U.S. Pat. No. 4,895,428 to Nelson et al. ('428 patent)
and U.S. Pat. No. 4,938,563 to Nelson et al. ('563 patent) disclose
a retroreflective sheeting wherein the cube-corner elements
comprise two nearly perpendicular tetragonal faces and a triangular
face nearly perpendicular to the tetragonal faces to form a
cube-corner. The cube-corner elements further include a non
perpendicular triangular face, all of the aforementioned
cube-corner sheeting would be expected to be useful in the articles
of the present invention. The manufacture of retroreflective
cube-corner element arrays is typically accomplished using molds
made by different techniques, including those techniques known as
pin bundling and direct machining. Molds manufactured using pin
bundling are made by assembling together individual pins that each
have an end portion shaped with features of a cube-corner
retroreflective element. U.S. Pat. Nos. 3,632,695 (Howell) and
3,926,402 (Heenan et al.) disclose illustrative examples of pin
bundling. The direct machining technique, also known generally as
ruling, comprises cutting away portions of a substrate to create a
pattern of grooves that intersect to form structures including
cube-corner elements. The grooved substrate is typically used as a
master mold from which a series of impressions, i.e., replicas, may
be formed. In some instances, the master itself may be useful as a
retroreflective article. More commonly, however retroreflective
sheeting or retroreflective articles are formed in a polymeric
substrate using the master mold or using replicas of the master
mold.
[0074] Direct machining techniques are a useful method for
manufacturing master molds for small microcube arrays. Small
microcube arrays are particularly beneficial for producing thin
retroreflective sheeting having good flexibility. Microcube arrays
are also more conducive to continuous manufacturing processes. The
process of manufacturing large arrays of cube-corners is also
relatively easy using direct machining methods rather than pin
bundling or other techniques. An illustrative example of direct
machining is disclosed in U.S. Pat. No. 4,588,258 (Hoopman).
[0075] Master molds suitable for use in forming cube-corner
sheeting in accordance with the '598 patent, the '428 patent, and
the '563 patent may be formed using direct machining techniques as
described above. However, the cube-corner geometries disclosed in
these patents require two different machining tools to produce a
master mold. This reduces the efficiency of the master mold
manufacturing process. Additionally, master molds manufactured
according to these patents comprise surfaces that extend
substantially perpendicular to the base surface of the master mold.
Such perpendicular surfaces can be detrimental to the process of
producing exact replicas of the master mold.
[0076] It is believed that all cube-corner sheeting discussed in
the aforementioned patents would be useful in the articles of the
present invention. Other microstructured retroreflective substrates
which have projections other than cube-corners would also be useful
in the articles of the invention. The substrates useful according
to the invention may optionally have one or more of the following
optical characteristics: retroreflectivity, total internal
reflection, and partial internal reflection. These include
refractive and/or diffractive properties, for example. The
microstructured substrate itself can have specular or diffusive
properties to improve the visibility of the fluid on the
microstructured substrate. As the fluid wets the microstructured
surface, the difference between the refractive index of the
microstructured surface and the fluid decreases, resulting in
frustration of the optical characteristics of the microstructured
substrate and improving its transparency.
[0077] As previously mentioned, the indicator 414 of the shock
indicator 410 may comprise a suspension of exfoliated organophilic
clay or other solid filler material with a fluid. Regarding the
solid filler material useful in the formulation of the indicator
414, suitable solids can be selected and obtained from commercial
resources providing the exfoliated clay such as Nanocor of
Arlington Heights, Ill. or Southern Clay Products, Inc. of
Gonzalez, Tex. Other useful solid filler materials may comprise
silica particles including hydrophobic silica particles, fumed
silica particles; bubble and microbubble glass particles; hollow
and solid glass spheres; inorganic pigments including titanates and
zirconates. Also included would be solid filler materials whose
surfaces are chemically and/or physically modified to improve their
compatibility with the fluid phase of the suspension.
[0078] Regarding the fluids available for use in the formulation of
the indicator 414, suitable fluids can comprise a variety of
materials. These material typically have certain properties that
may be beneficial in their use as an indicator material. For
example, the surface tension of the fluid can vary such that the
surface tension of the fluid at 23.degree. C. may range from about
10.times.10.sup.-3 N/m to about 80.times.10.sup.-3 N/m, typically
from about 10.times.10.sup.-3 N/m to about 60.times.10.sup.-3 N/m,
and often from about 10.times.10.sup.-3 N/m to about
50.times.10.sup.-3 N/m. Most commonly, the surface tension of the
fluid may range from about 10.times.10.sup.-3 N/m to about
40.times.10.sup.-3 N/m. The density of the fluid can vary.
Typically the density of the fluid at 23.degree. C. ranges from
about 0.5 to about 2 grams/cm.sup.3, commonly from about 0.5 to
about 1.5 grams/cm.sup.3, and often from about 0.8 to about 1.5
grams/cm.sup.3. Likewise, the zero rate shear viscosity of the
fluid can vary at 23.degree. C. from about 1.times.10.sup.-3 to
about 1.times.10.sup.6 Pa-s, typically from about 0.1 to about
1.times.10.sup.5 Pa-s, and often from about 1 to about 10,000
Pa-s.
[0079] The fluid selected for use in the indicator 414 is typically
an innocuous and relatively non-reactive liquid to minimize or even
eliminate undesired reactions or other potentially damaging and/or
non-useful interactions with the other components of the article.
Examples of useful relatively innocuous and non reactive fluids
include, but are not limited to, the following: silicone fluids
such as polydimethylsiloxane fluids, saturated hydrocarbon-based
oils, silicone oils and gums, mineral oils, glycerols, water, and
aqueous based fluids.
[0080] The fluid may or may not be colored. In an embodiment, such
as that shown in FIG. 9, where the differentiating component 420 is
retroreflective, or where the substrate may have the optical
characteristics as discussed herein, the fluid is typically clear
and colorless. As the fluid fills the channels, it causes the total
internal reflection to become frustrated. In other words, the
substrate that appeared opaque now appears clear in those areas
where the channels are filled, allowing a viewer (represented by
"A") to observe the colored cover layer below. The fluid typically
has an index of refraction within about 0.4 of the index of
refraction of the microstructured substrate surface and more
typically substantially the same index of refraction. However, the
exact nature of the fluid can vary as long as, when it is used in
an application where it is intended to render the substrate
transparent, it does so sufficiently so one can identify the fluid
flow front by, for example, viewing any color and/or graphics
beneath the substrate.
[0081] When the substrate is not retroreflective or when the
substrate is retroreflective but one does not intend to use it in a
manner that causes it to become transparent, the fluid typically
contains pigment(s) and/or dye(s) (such as blue organic dye, for
example) and the substrate is selected to provide a contrast to the
fluid flow (such as a white opaque substrate, for example).
[0082] The selection of the fluid and the differentiating component
and the positioning thereof in the shock indicator articles of the
invention is accomplished to allow an observer to view the progress
of the fluid over time as it migrates through the aforementioned
channels 421. Depending on the particular embodiment of the article
of the invention an observer may find that the fluid is more
readily visible by changing the viewing angle. An observer can
readily manipulate the article or change his/her viewing position
to find a preferred viewing angle.
[0083] Suitable fluids according to the present invention include,
for example, viscoelastic and viscous fluids and combinations
thereof that provide the desired properties for migration into the
channels of the microstructured surface in response to a shock
event of a given magnitude. For capillary action to primarily drive
the migration of the fluid into the channels of the microstructured
substrate, the surface energies of the article components should
preferably cause the local contact angle of the fluid on the
microstructured surface of the substrate to be less than about 90
degrees, more preferably less than about 25 degrees, within the
range of intended use temperatures. The contact angle is a function
of the surface energy of the microstructured surface, the surface
energy of the fluid (e.g. liquid), and the interfacial energy
between the two.
[0084] A viscous material can be defined by analogy to classic
viscous fluids. If an external stress is applied to a viscous
fluid, it will deform and continue to deform as long as the stress
is present. Removal of the stress will not result in a return of
the fluid to its undeformed state. Such a response is called
viscous flow and defines a viscous material or fluid. When there is
a direct proportionality between the stress and the rate of
deformation in a viscous fluid, the fluid is a Newtonian fluid.
There are also viscous fluids that are non-Newtonian and which
exhibit a non-linear dependence between the stress and the rate of
deformation. In the articles of the invention, stress results from
a shock event of a given magnitude.
[0085] Materials that exhibit both elastic and viscous properties
simultaneously are called viscoelastic materials. Elastic
properties can be explained with reference to classic elastic
solids. Elastic solids respond to external stress by deforming and,
upon removal of the stress, respond by returning to their original
shape. Such a response is called elastic. Some elastic materials
exhibit a direct proportionality between the stress and the
deformation, thereby conforming to what is known as Hooke's Law.
There are also elastic materials that do not obey Hooke's Law and
that exhibit a non-linear relationship between stress and
deformation. Viscoelastic materials are sometimes classified as
either viscoelastic solids, i.e., elastic solids that exhibit some
viscous effects during deformation, or viscoelastic liquids, i.e.,
viscous liquids that exhibit some elastic effects. A viscoelastic
liquid can be identified as a viscoelastic material that continues
to deform indefinitely when subjected to a stress.
[0086] A viscoelastic material may exhibit a transition from an
immobile, glassy state to a viscoelastic liquid state at a
temperature known as the glass transition temperature, T.sub.g. It
may also exhibit a transition from a partially crystalline state to
an amorphous state at the temperature at which the crystalline
material melts, T.sub.m. Often, such a material will behave as a
viscoelastic solid below T.sub.m. The properties and the analysis
of viscoelastic materials are discussed in John D. Ferry,
Viscoelastic Properties of Polymers, (John Wiley & Sons, Inc.
1980). Fluids selected for use in the articles of the invention
normally have T.sub.g and T.sub.m below the temperatures at which
the article of the invention is intended for use.
[0087] In an article of the present invention, when a viscoelastic
material has been selected for use, it is preferred to use a
viscoelastic liquid exhibiting small elastic effects, such that it
behaves essentially as a viscous fluid in a liquid state at all
anticipated temperatures to which the article of the invention will
be exposed. An illustrative, non-limiting, list of viscoelastic and
viscous materials that may be suitable for use as an indicator
material in the articles of the present invention includes natural
rubber; butyl rubber; polybutadiene and its copolymers with
acrylonitrile and styrene; poly(alpha-olefins) such as polyhexene,
polyoctene, and copolymers of these and others; polyacrylates;
polychloroprene; polydimethylsiloxane; silicone oils and gums;
mineral oils; and block copolymers such as styrene-isoprene block
copolymers; and mixtures of any of the above.
[0088] The viscoelastic materials may, for example, comprise
elastomers conventionally formulated as pressure sensitive
adhesives. Examples thereof include, but are not limited to,
polyisoprene, atactic polypropylene, polybutadiene,
polyisobutylene, silicone, ethylene vinyl acetate, and acrylate
based elastomers and can typically include a tackifying agent
and/or a plasticizing agent.
[0089] Monomers useful in making fluids useful in the articles of
the invention include, but are not limited to, those that have a
homopolymer glass transition temperature less than about 0.degree.
C. Useful alkyl acrylates include, but are not limited to,
unsaturated monofunctional (meth)acrylic acid esters of
non-tertiary alkyl alcohols having from 2 to 20 carbon atoms in the
alkyl moiety, typically from 4 to 18 carbon atoms, and often from 4
to 12 carbon atoms. Examples of useful alkyl acrylate monomers
include, but are not limited to, n-butyl acrylate, hexyl acrylate,
octyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate, isononyl
acrylate, decyl acrylate, dodecyl acrylate, lauryl acrylate,
octadecyl acrylate, and mixtures thereof.
[0090] An example of an optional reinforcing co-monomer is a
monoethylenically unsaturated monomer having a homopolymer glass
transition temperature greater than about 25.degree. C. and is
preferably co-polymerized with the acrylate monomers. Examples of
useful co-polymerizable monomers include, but are not limited to,
meth(acrylic) acid, N-vinyl pyrrolidone, N-vinyl caprolactam,
substituted (meth)acrylamides such as N,N-dimethyl acrylamides,
acrylonitrile, isobornyl acrylate, and mixtures thereof. When a
copolymerizable monomer is used, the alkyl acrylate is typically
present in the composition in amounts from about 50 to 99 parts by
weight and the co-polymerizable monomer is typically present in
corresponding amounts from 50 parts to 1 part by weight, wherein
the total amount by weight is 100.
[0091] The elastomer can optionally include a tackifier and/or
plasticizer in a tackifier to elastomer base weight ratio or a
plasticizer to elastomer base weight ratio of typically up to about
2:1. Suitable tackifiers include, but are not limited to,
hydrogenated rosin esters commercially available under the trade
designations "Foral 85", "Foral 105", or "Abitol E" and hydrocarbon
tackifiers such as those known as "Regalrez", all available from
Eastman Chemical Company of Kingsport, Tenn. Suitable plasticizers
include, but are not limited to, hydrocarbon oils such as those
available under the trade designation "Shellflex" (available from
Shell Chemical Co., Houston, Tex.), USP grade mineral oil, and
phthalates including alkyl phthalates such as dioctyl phthalate,
diisononyl phthalate, and allyl phthalates.
[0092] The article of the invention is preferably designed to
provide sufficient fluid to fill the channels of the
microstructured surface as the fluid migrates along the channels.
The components of the article are normally chosen to provide a
desired rate of migration of the fluid into the channel structure
of the microstructured substrate. In a shock indicator, the fluid
such as a viscous liquid, for example, will migrate through the
aforementioned channel structure at a rate that is roughly
proportional to the magnitude of the shock event. By controlling
the properties of the liquid, the indicating device can be
constructed to provide a visually observable indication that the
article has experienced a shock event exceeding a given magnitude.
Accordingly, it is desirable to be able to select a liquid having
suitable characteristics for the contemplated magnitude of the
shock event. Preferably, the viscous fluid also exhibits a yield
stress such that the stress created by the shock event exceeds this
yield stress allowing the fluid to flow into the channel structure.
Such a viscous fluid would also stop flowing when this stress is
removed (i.e. when the shock event is over). The viscous fluid with
a yield stress effectively provides and on/off behavior that is
desirable in this embodiment. One way of generating a viscous fluid
exhibiting a yield stress is to use the solid filler materials
described above along with the appropriate viscous liquid to create
a suspension--i.e., a viscous fluid exhibiting a yield stress or a
suspension of exfoliated organophilic clay or other solid filler
material with a fluid such as mineral oil. Other suitable solid
filler materials may comprise silica particles including
hydrophobic silica particles, fumed silica particles; bubble and
microbubble glass particles; hollow and solid glass spheres;
inorganic pigments including titanates and zirconates. Also
included would be solid filler materials whose surfaces are
chemically and/or physically modified to improve their
compatibility with the fluid phase of the suspension.
[0093] The textured or microstructured surface 420a may be adhered
to the base member 412 using a suitable adhesive which may also
comprise a pigment or other coloring agent. In one such
application, a pressure sensitive adhesive filled with carbon black
may be applied to the textured surface 420a to partially cover the
texture-imparting structure thereof. Lamination of the textured
surface 420a to the base member 412 creates a series of
interconnected microchannels 421 between the laminated layers and
surrounding but not initially in contact with the indicator 414.
The channels 421 are initially filled with air when the device 410
is in a first configuration (e.g., see FIG. 8), and the properties
of the differentiating component 420 are such that the resulting
laminated structure will not reveal the adhesive color under the
material 420. As an alternative to using a colored adhesive layer,
the base member 412 can be supplied as a colored material. In such
a construction the adhesive or other laminating material should be
transparent.
[0094] When the device 410 is in a second configuration (e.g., FIG.
9) following the occurrence of a shock event, liquid from the
indicator 414 is released into the annular space 430 of the
differentiating component 420 where the liquid is then drawn into
the microchannels 421 that are provided between the base member 412
and the surface 420a. The liquid is pulled into the microchannels
421 by capillary action, and the presence of the liquid within the
microchannels 421 causes a change in the optical properties of the
material 420 to thereby provide a color change that can be readily
seen by an observer. Such a color change may be taken an indication
that a shock event has occurred.
[0095] It will be appreciated that the containment member 418 and
the optical indicator material 420 can be integrated by
manufacturing a single film serving both functions. Those skilled
in the art will appreciate that a suitable manufacturing process to
produce an integrated top film could comprise thermo- or vacuum
forming with embossing to produce the protective dome structure and
the diamond grade microstructure in a single pass for a continuous
process. Such a construction is contemplated within the scope of
the invention.
[0096] Still another embodiment of a shock indicator device 510
according to the invention is illustrated in FIG. 10. In the
depicted device 510, a transmission layer 530 is provided to
reduce, maintain or increase the force transmitted from or by the
shock event. The transmission layer 530 is provided and positioned
on the base layer 512. The transmission layer 530 can be designed
to have a damping and/or isolation effect by using materials that
provide adherence of the indicator 514 as well as additionally
providing damping and/or isolation properties. In the depicted
embodiment, the base member 512, containment member 518, release
liner 526, and adhesive 516 are as previously described. The layer
530 may be included in a shock indicator device of the invention to
alter the threshold vibrational frequency and/or the magnitude of
force at which the device 510 will transition from a first
condition to a second condition to indicate that a shock event has
occurred. Suitable materials for the transmission layer 530 include
those that will provide a desired degree of damping and/or
isolation. The selection of materials for the transmission layer
and/or the attachment means will also change the natural frequency
of the indicator 514. The selection of materials for the
transmission layer and/or the attachment means will combine to
effect the level of force that the indicator experiences. In such a
construction, the transmission layer 530 will change the level of
shock force that the indicator 514 experiences upon the occurrence
of a shock event.
[0097] The shock indicator 514 can be made from materials with high
or low damping potential, which will affect the amplification
factor. Exemplary materials for the transmission layer 530 include
those described in U.S. Pat. No. 6,456,455, the disclosure of which
is incorporated in its entirety herein by reference thereto. In
general the vibration damping material of the transmission layer
530 will comprise a viscoelastic material or combination of
different viscoelastic materials. Suitable viscoelastic materials
include those having a storage modulus of at least about 1.0 psi
(6.9.times.10.sup.3 Pascals) and a loss factor of at least about
0.01 at the temperature and frequency of use (typically about -60
to 100.degree. C.). Those skilled in the art will appreciate that a
viscoelastic material is viscous and capable of dissipating energy,
yet exhibits certain elastic properties that make it capable of
storing energy in a manner similar to a spring and thus can also
have isolation or amplification characteristics based on the
material's Tg, geometry, application, and the like.
[0098] Those skilled in the art will also appreciate that the
transmission layer 540 may comprise materials selected to have a
certain viscoelastic ratio, depending on the ultimate use of the
finished shock indicator. For example, a high Tg epoxy at room
temperature will have a high modulus or elastic portion and a very
low viscous portion (loss factor less than about 0.15). Or the
layer could be a material with a higher loss factor at room
temperature with a lower modulus. Viscoelastic materials for use in
the vibration damping materials normally will have a loss factor,
i.e., the ratio of energy loss to energy stored, of at least about
0.01, often at least 0.15. The loss factor is a measure of the
material's ability to dissipate energy and depends on the frequency
and temperature experienced by the damping material. More
typically, the loss factor for the vibration damping materials is
at least about 0.3, normally at least about 0.5, and may reach
about 0.7-10 in the frequency and temperature range where damping
is required (generally in the range of about 1-10,000 Hz and from
-60 to about 100.degree. C., typically in the range of about
50-5,000 Hz and about 0-100.degree. C., and more often in the range
of about 50-1500 Hz and about 20-80.degree. C.). As an example of a
specific type of material, a crosslinked acrylic polymer at a
frequency of 100 Hz, the loss factor at 68.degree. F. (20.degree.
C.) is typically about 1.0, while at 158.degree. F. (70.degree.
C.), the loss factor is about 0.7.
[0099] It should be appreciated that the present invention utilizes
principles known in the art including, without limitation, the
relationship between force, mass and acceleration--i.e.,
Force=(mass)(acceleration). Properties such as, for example, the
mass of the indicator or the subparts thereof, the frequency of the
shock event, acceleration, damping, the loss factor, the storage
modulus, the loss modulus, isolation, the spring constant,
stiffness, the natural frequency, the resonant frequency, the
geometry, the configuration of the indicator, and the point of
placement on a surface for an end use of the shock indicator can
all effect or can influence the design of the shock indicator of
the invention. Additionally, environmental conditions (e.g.,
temperature and humidity) can influence the selection of materials
that impact the performance of the shock indicator across the range
of end-use environments. In selecting an approach to the design of
a particular shock indicator device, it may be appropriate to
consider these various concepts and/or properties and how they may
impact the performance of the device.
[0100] Useful viscoelastic damping materials can be isotropic as
well as anisotropic, particularly with respect to elastic
properties. As used herein, an "anisotropic material" or
"nonisotropic material" is one in which the properties are
dependent upon the direction of measurement. Specific viscoelastic
materials useful herein include urethane rubbers, silicone rubbers,
nitrile rubbers, butyl rubbers, acrylic rubbers, natural rubbers,
fluorine-based elastomers and rubbers, styrene-butadiene rubbers,
synthetic rubbers, and the like. Other useful damping materials
include acrylates, epoxy-acrylates, silicones, acrylate-silicone
mixtures, cyanate esters, polyesters, polyurethanes, polyamides,
ethylene-vinyl acetate copolymers, polyvinyl butyral, polyvinyl
butyral-polyvinyl acetate copolymers, epoxy-acrylate
interpenetrating networks and the like. Specific examples of useful
materials are also described in or referenced in U.S. Pat. Nos.
5,183,863; 5,262,232; and 5,308,887. Examples of thermoplastic
materials suitable for use as the vibration damping material
include, but are not limited to, those selected from the group
consisting of polyacrylates, polycarbonates, polyetherimides,
polyesters, polysulfones, polystyrenes,
acrylonitrile-butadiene-styrene block copolymers, polypropylenes,
acetal polymers, polyamides, polyvinyl chlorides, polyethylenes,
polyurethanes, and combinations thereof. Useful viscoelastic
materials can also be crosslinkable to enhance their strength
and/or temperature resistance. Such viscoelastics are classified as
thermosetting resins. During the manufacturing process, the
thermosetting resin is cured and/or crosslinked typically to a
solid state, although it could be a gel upon curing, as long as the
cured material possesses the viscoelastic properties described
above. Depending upon the particular thermosetting resin employed,
the thermosetting resin can include a curing agent, e.g., catalyst,
which, when exposed to an appropriate energy source (such as
thermal energy), the curing agent initiates polymerization of the
thermosetting resin.
[0101] It will be appreciated that the properties of the
transmission layer can be changed by the curing process used for
the particular polymer system employed. This could enable a shock
indicator to have one set of performance criteria during
manufacturing and shipping and an alternate set of performance
criteria when attached to an end use application. The system could
be designed to have high damping and isolation during manufacturing
and shipping to safe-guard the shock indicator from premature
activation and once applied to the end use application, the polymer
system may be further, or more fully, cured so that the damping and
isolation properties are changed and the indicator will thereafter
activate upon the occurrence of shock event of a predetermined
threshold level. Examples of polymer systems for use as
transmission layers according to the foregoing criteria include
pressure sensitive adhesive layers with at least one epoxy mixture
or resin in the layer. In this combination, the PSA provides
damping and isolation during assembly and shipment. Once the shock
indicator is applied to an end use application, the epoxy system in
the transmission layer can be exposed to a curing method for the
epoxy and the Tg is changed to thereby change the damping and
isolation performance of the shock indicator.
[0102] It will be further appreciated that the transmission layer
and the external attachment means can both be selected and designed
to provide the same, similar or different damping and isolation
characteristics. The shock indicator enclosure construction plus
it's attachment means and the agglomeration construction and its
attachment means inside the enclosure can affect the amplification
of the vibration or shock force to the agglomeration in the shock
indicator. Likewise, the shock indicator of the invention may be
constructed to take advantage of many or only a few different
material properties inherent in the materials selected for each of
the individual components to thereby change the amplification
factor that the indicator experiences and the threshold value for
the shock event that will cause the shock indicator to transition
from a first condition to a second condition. Additionally, the
geometry of the components, environmental conditions (temperature,
etc.) and the like can all contribute to the threshold at which a
shock event will trigger the shock indicator to indicate the
occurrence of the shock event, as described herein. Thus, it will
be understood that the materials and components used in the
construction of the shock indicator device of the present invention
can all be used to change the
isolation-damping-amplification-transmissibility properties of the
shock indicator device, thus changing how the indicator responds to
a particular shock event.
[0103] The vibration damping material used in the transmission
layer can optionally include additives such as fillers (e.g., talc,
etc.), colorants, toughening agents, fire retardants, antioxidants,
antistatic agents, and the like. The vibration damping material can
optionally contain fibers and/or particulates additives that are
designed to provide an increased thermal and/or electrical
conductive path through the vibration damping material.
[0104] It will be appreciated that the manufacture of the foregoing
embodiment can be accomplished according to the above described
manufacturing method by incorporating another line for the
lamination or attachment of the transmission layer to the base
layer or to the differentiating component described herein. As
mentioned, the materials used for the transmission layer may be
provided as a pressure sensitive adhesive or other form of adhesive
material that provides the means for attaching the transmission
layer to the base or the differentiating layer. Other materials may
require additional means for affixing these components to one
another such as the application of additional adhesive layer(s),
calendaring with heat and pressure, and the like. Such methods are
well within the skill of those practicing in the field and are not
further described herein.
[0105] Regarding applications, the shock indicator of the present
invention may be applied to any of a variety of devices where it
may be appropriate or desired to monitor in a passive mode any and
all shock events experienced by the device. In particular, cellular
telephones and other hand-held electronic devices are particularly
suited to be equipped with the shock indicator of the invention.
One particular application involves the placement of the indicator
of the invention in a cellular telephone. Current warranty
practices within the cellular industry preclude warranty coverage
where the user has abused the device. Hence, the shock indicator of
the invention may be used in conjunction with cellular telephones
as a means to determine whether the telephones have experienced a
shock event caused, for example, by dropping the telephone from a
significant height onto a hard surface such as concrete or the
like. Similar applications also exist for other hand-held devices
as well as any variety of electronic components and equipment. In
view of the foregoing applications, it will be appreciated that the
size of the shock indicator may be an important feature. Use of the
shock indicator inside of a hand-held device will typically require
that the indicator be relatively small.
[0106] When placed in association with a device, consideration
should also be given to the hardness of the surface to which the
shock indicator is being affixed because the placement of the shock
indicator in an end use application will also affect the shock
indicator's apparent performance. If the shock indicator is placed
onto a very rigid portion of a rigid structure, the shock indicator
will perform differently than if the indicator is attached to
another portion of the structure that is isolated from the stiff
structure that is encountering the shock or vibration event.
[0107] In still another embodiment of the invention, multiple
levels of activation may be indicated within a single shock
indicator. As mentioned herein, the cohesive character of the
agglomerated indicator can be modified by the presence of a small
amount of an oil or other organic diluent or agglomeration aid.
Mineral oil, for example, may be used as an agglomeration aid in
agglomerating the powder indicators of the invention. Levels of the
agglomeration aid in the agglomerated powder are typically very
low, and as little as about 2 wt. % mineral oil has been used. As
the mineral oil concentration in increased, the threshold level of
force also increases (e.g., the minimum amount of force required to
transition the indicator from the first state to the second state).
The maximum level of mineral oil in the particle agglomeration is
limited by the volume ratio of the oil and the solid particulate at
which the particles become a discontinuous phase while the liquid
becomes a continuous phase. In providing multiple levels of shock
indication in a single indicator, it has been found that varying
the concentration of the agglomeration aid can change the threshold
level at which the indicator transitions from a first configuration
to a second configuration following a vibrational shock so that the
shock indicator can be observed in a second or activated state.
[0108] In the contemplated embodiment, two, three or more colored
indicator compositions of an agglomerated powder can be used to
indicate different levels of vibrational or inertial shock. In this
embodiment each of the agglomerated powder indicators is typically
formulated to comprise the same powder materials with each of the
indicators having different levels of mineral oil therein. In the
manufacture of such an embodiment, a dispersion of the powder and
mineral oil may be placed in discrete independent dots around a
central area on a base member and thereafter covered with a
containment member such as a protective dome. An organic (e.g.,
hydrocarbon) diluent may be added to the mixture of powder and oil
to allow for the preparation of a slurry with binder and powder.
The diluent is typically selected to be volatile so that it will
evaporate after the slurry is deposited on the base member,
thereafter leaving the agglomerated powder indicator. The base
member may be treated in a manner that enhances the color or visual
differences between the powder and the materials of the base
member. For example, polyester film may be treated with a black
aluminum oxide evaporation process, such as that described in U.S.
Pat. Nos. 4,430,366 and 5,766,827, to produce a black film that
will serve as a base member with sufficient color contrast to
permit a quick visual confirmation of the state of each of the
agglomerated indicator powders. In such a construction, a device
associated with the shock indicator may then be subjected to
vibrational shocks of different magnitudes. The agglomerated
indicator comprising the lowest amount of mineral oil will be the
first to transition to a second configuration. On subsequent
increasing shock treatments the other agglomerated indicators will
also disperse at progressively greater vibrational shock
levels.
[0109] In addition to the inclusion of multiple indicators within
the same shock indicator, it is within the scope of the invention
to include more than one shock indicator, such as the shock
indicator embodiments shown in the various Figures herein, in
association with a single device. Each of the different shock
indicators may be constructed to transition from the agglomerated
or first state to a dispersed or second state upon the occurrence
of shock events of different magnitudes.
[0110] In still another embodiment of the invention, a wetness
indicator may be combined with the shock indicator of the invention
to provide a combined device capable of passively showing exposure
of the shock indicator to vibrational or inertial shocks as well as
showing whether an associated device has been exposed to water or
other forms of moisture. A suitable wetness indicator that can be
incorporated into the shock indicator of the invention include
conventional wetness indication paper comprising a white paper
base, an indicator dye and pressure sensitive adhesive. Where the
powdered agglomerated indicators do not contain water, the
indicator can be applied to a white paper base in the same way as
it would otherwise be applied to the above described polymeric
film. A suitable wetness indicator that may be combined with the
shock indicator of the present invention includes that described in
co-pending U.S. patent application Ser. No. 09/972,124, filed Oct.
1, 2001, entitled "Water Contact Indicator," the disclosure of
which is incorporated in its entirety herein by reference
thereto.
[0111] In still another embodiment, the protective film structure
of the containment member may comprise dimples, intrusions,
protrusions, multiple layers and/or different material layers that
change the optical characteristics of the protective film. The
inclusion of these features can also be, at least in part, for the
purpose of changing the strength of the protective film
structure.
[0112] In still another embodiment, the indicator can comprise
primary and secondary matrices wherein the first matrix is an
agglomeration of powder particles and the second matrix is
comprises larger glass bubbles or beads (or other similar objects).
The larger components of the secondary matrix provides a structure
for the smaller primary agglomerated powders to further attach and
also can provide a structure with greater X-Y-Z dimensions and
stability with a larger primary agglomeration overall versus a
agglomeration with no secondary matrix. This construction can also
be designed so that the larger matrix will "break free" from the
attachment location within the enclosure while the smaller powder
particles become fractured from the secondary matrix. In a
variation of the foregoing embodiment, the smaller powder particles
break free of the larger secondary matrix upon experiencing a first
level of shock while the larger matrix can be positioned within the
indicator device to break free at its attachment points upon the
occurrence of a second (e.g., higher) level of shock. The secondary
matrix can comprise one or more larger particles of any of a
variety of geometries and sizes including larger those mentioned
herein such as beads, (e.g., glass, plastic or ceramic) as well as
metal beads (e.g., ball bearings).
[0113] In still another embodiment, the containment member of the
shock indicator is attached to a desired location with an
attachment means such as an adhesive provided in a discontinuous
coating or one that utilizes a smaller or larger area than actual
base of the shock indicator. In this construction, attachment can
occur with one, two, three or more individual attachment points
between the base of the shock indicator and the surface of the
desired object.
[0114] In still another embodiment, the shock indicator contains
the above described indicator comprising agglomerated particles of
powder or the like. Additionally, one or more objects may can be
attached (loose or firmly) or be free to move about the enclosure,
so that the objects impact the agglomerated powder during a shock
event to aid in the fracture of the powder agglomeration and the
indication of a desired shock event. The impingement objects could
be glass beads, bubbles, BB's and the like, and the masses, sizes
and shapes of the objects can be changed to achieve a desired
movement within the containment member of the shock indicator. If
the containment member is provided with dimples or other surface
structures, these structures can help to direct the objects in
striking the agglomerated powder when a shock event occurs.
Moreover, the additional objects can be designed or selected to
provide a significant force when accelerated within the confines of
the containment member during a shock event.
[0115] In another embodiment of the invention, the indicator can
include primary and secondary subparts wherein the primary subparts
are larger objects and the secondary subparts are smaller objects
such as the powder particulates described herein. The secondary
subparts agglomerate around one or more primary subparts to form a
single mass useful as an indicator. The primary subpart(s) may be
attached to the base with the secondary subparts agglomerated
therearound. A shock event causes the primary subparts to dislodge
from the base and the associated movement of the mass breaks apart
the associated secondary subparts, providing shock indication. The
primary subparts could comprise one or more masses with an
associated agglomeration of the secondary subparts agglomerated
around the primary subpart(s). Each primary subpart(s) could be the
same or different as other primary subparts.
[0116] In another embodiment of the invention, the indicator can be
positioned within the containment member so that a shock event from
any direction will impart substantially the same shearing,
compression, tension, cleavage and/or peel forces into the
indicator. A means for positioning the indicator within the device
might be to have more than one attachment point for positioning the
indicator within the device. Attachment points may be provided to
facilitate the attachment of the indicator to the base member
and/or to the other components of the device such as an attachment
point to the internal surface of the containment member, for
example. Such a means for attaching the indicator might be
considered a multi-axis attachment.
[0117] In another embodiment of the invention, single or multiple
masses may be added to the shock indicator enclosure interior
and/or exterior surfaces to further modify the response of the
shock indicator to a shock event. The modified response of the
shock indicator may be determined by the amount and/or number of
additional mass added to the device as well as the position of the
masses within the containment member of the shock indicator
device.
[0118] In another embodiment of the invention, the indicator
comprises a viscous liquid with one or more shear plane surfaces
within the liquid. The liquid is as described elsewhere herein
along with one or more masses or added shear plane geometries
(glass beads, bubbles, BB's, pins, posts, etc.) that can be of
various sizes and shapes that aid in the shear thinning of the
liquid in response to a shock event. The masses increase the shear
force into the fluid and provides additional shear thinning planes
or surfaces.
[0119] In still another embodiment of the invention, the indicator
can comprise a combination of colored materials that will
facilitate the visual determination of whether the indicator has
transitioned form the first state to the second state following a
shock event. For example, the indicator may comprise a first
agglomerated powder present at a low concentration in a first color
and the second agglomerated powder present at a high concentration
in a second color. In a first state prior to a shock event, the
colors of the two agglomerated powders appear distinct and both
colors are visually observable to an observer. In a second state
following a shock event, the two agglomerated powders become
dispersed and, in the dispersed state, will appear as a single
color, typically as the second color due to the lower concentration
of the first powder and the mixing of the powder particles that
occurs when the particles are dispersed.
[0120] While various embodiments of the invention have been
described in detail, it should be appreciated that the invention is
not limited to the specific constructions that have been described.
Changes to the basic construction are possible such as by adding
additional film layers to the base member that serve one or more
additional functions in the operation of the finished shock
indicator device. For example, a tamper-indicating shock indicator
device may comprise layers of (a) a planar, light-transmissive
layer; (b) a light-transmissive imaged release coating; and (c) an
adhesive layer; in which (i) the image is not visible until
becoming permanently visible when the release coating is separated
from the other layer(s); and (ii) the assembly cohesive strength of
the indicator device ensures that the device remains as a single
unit after the release coating is separated and the image is seen.
Such layers are described in U.S. Pat. No. 5,770,283 to Gosselin et
al. Additionally, the exact ordering of the components and the
order of the manufacturing steps in the above described method may
be changed without changing the basic construction of the
invention--i.e., a base and an indicator that is capable of being
presented in one configuration prior to the experience of a shock
event and which presents itself in a second configuration in
response to a shock event to indicate to an observer that the
device has experienced such a shock event. The indicator device of
the invention can be constructed to increase or to decrease the
sensitivity of the device to customize the device to transition for
the first configuration to a second configuration only when the
predetermined threshold shock has been experienced by the device.
In this manner, the invention provides a shock indicator that can
be customized for a particular application where shock indication
is appropriate only for shock events exceeding a threshold value at
which components or the like of the associated electronic or other
device are more likely to experience damage or harm from such a
shock event. Additional unforeseen changes and modifications to the
described embodiments may also be possible which also may be
equivalents to the components described herein. All such
modifications are contemplated as being within the scope of the
invention, as generally set forth in the following claims.
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