U.S. patent application number 09/844261 was filed with the patent office on 2002-10-31 for multi-layered magnetic pigments and foils.
This patent application is currently assigned to Flex Products, Inc.. Invention is credited to Coombs, Paul G., LeGallee, Charlotte R., Markantes, Charles T., Phillips, Roger W..
Application Number | 20020160194 09/844261 |
Document ID | / |
Family ID | 25292242 |
Filed Date | 2002-10-31 |
United States Patent
Application |
20020160194 |
Kind Code |
A1 |
Phillips, Roger W. ; et
al. |
October 31, 2002 |
Multi-layered magnetic pigments and foils
Abstract
Multilayered magnetic pigment flakes and foils are provided. The
pigment flakes can have a symmetrical coating structure on opposing
sides of a magnetic core, or can be formed with encapsulating
coatings around the magnetic core. The magnetic core can be a
magnetic layer between reflector or dielectric layers, a dielectric
layer between magnetic layers, or only a magnetic layer. Some
embodiments of the pigment flakes and foils exhibit a discrete
color shift so as to have distinct colors at differing angles of
incident light or viewing. The pigment flakes can be interspersed
into liquid media such as paints or inks to produce colorant
compositions for subsequent application to objects or papers. The
foils can be laminated to various objects or can be formed on a
carrier substrate.
Inventors: |
Phillips, Roger W.; (Santa
Rosa, CA) ; LeGallee, Charlotte R.; (Healdsburg,
CA) ; Markantes, Charles T.; (Santa Rosa, CA)
; Coombs, Paul G.; (Santa Rosa, CA) |
Correspondence
Address: |
WORKMAN NYDEGGER & SEELEY
1000 EAGLE GATE TOWER
60 EAST SOUTH TEMPLE
SALT LAKE CITY
UT
84111
US
|
Assignee: |
Flex Products, Inc.
|
Family ID: |
25292242 |
Appl. No.: |
09/844261 |
Filed: |
April 27, 2001 |
Current U.S.
Class: |
428/403 ;
428/404 |
Current CPC
Class: |
C09C 1/0078 20130101;
B41M 3/14 20130101; C09C 2200/1008 20130101; C01P 2006/65 20130101;
C09C 2200/1058 20130101; B42D 25/29 20141001; C01P 2004/52
20130101; C01P 2004/86 20130101; C09C 2200/1054 20130101; C09C
2200/301 20130101; C01P 2006/90 20130101; Y10T 428/2991 20150115;
Y10T 428/256 20150115; C09C 1/0015 20130101; Y10T 428/2993
20150115; B42D 2033/16 20130101; B42D 2035/24 20130101; C09C
2220/20 20130101; C01P 2006/60 20130101; C01P 2004/54 20130101;
C09C 2200/24 20130101; C01P 2004/61 20130101; Y10T 428/2982
20150115; Y10S 428/90 20130101; Y10T 428/254 20150115; Y10T 428/257
20150115; C01P 2006/42 20130101; C09C 2200/1091 20130101; B42D
25/369 20141001; C09C 2200/1025 20130101; C01P 2006/66 20130101;
Y10T 428/25 20150115; C09C 1/62 20130101 |
Class at
Publication: |
428/403 ;
428/404 |
International
Class: |
B32B 005/16 |
Claims
What is claimed and desired to be secured by United States Letters
Patent is:
1. A magnetic pigment flake, comprising: a central magnetic layer
having a first major surface, an opposing second major surface, and
at least one side surface; a first reflector layer on the first
major surface of the magnetic layer; and a second reflector layer
on the second major surface of the magnetic layer; wherein the
pigment flake exhibits a reflectivity corresponding to the
reflectivity of the reflector layers and exhibits magnetic
characteristics based on the relative magnetism of the magnetic
layer.
2. The pigment flake of claim 1, wherein the first and second
reflector layers are on each of the first and second major surfaces
but not on the at least one side surface of the magnetic layer.
3. The pigment flake of claim 2, further comprising a first
dielectric layer on the first reflector layer and a second
dielectric layer on the second reflector layer.
4. The pigment flake of claim 3, wherein the first and second
dielectric layers are selectively absorbing and provide additional
color effects to the pigment flake.
5. The pigment flake of claim 2, further comprising a dielectric
layer substantially surrounding the first and second reflector
layers and the magnetic layer.
6. The pigment flake of claim 5, wherein the dielectric layer is
selectively absorbing and provides additional color effects to the
pigment flake.
7. The pigment flake of claim 1, wherein the first and second
reflector layers form part of a contiguous reflecting layer
substantially surrounding the magnetic layer.
8. The pigment flake of claim 7, further comprising a dielectric
layer substantially surrounding the reflecting layer.
9. The pigment flake of claim 8, wherein the dielectric layer is
selectively absorbing and provides additional color effects to the
pigment flake.
10. The pigment flake of claim 1, wherein the magnetic layer
comprises a soft magnetic material.
11. The flake of claim 1, wherein the magnetic layer is composed of
a material with a coercivity of less than about 2000 Oe.
12. The flake of claim 1, wherein the magnetic layer is composed of
a material with a coercivity of less than about 300 Oe.
13. The pigment flake of claim 1, wherein the magnetic layer
comprises a material selected from the group consisting of iron,
nickel, cobalt, iron, gadolinium, terbium, dysprosium, erbium, and
alloys or oxides thereof.
14. The pigment flake of claim 1, wherein the magnetic layer
comprises a material selected from the group consisting of Fe/Si,
Fe/Ni, FeCo, Fe/Ni/Mo, and combinations thereof.
15. The pigment flake of claim 1, wherein the magnetic layer
comprises a hard magnetic material.
16. The pigment flake of claim 1, wherein the magnetic layer
comprises a material selected from the group consisting Of
SmCo.sub.5, NdCo.sub.5, Sm.sub.2Co.sub.17, Nd.sub.2Fe.sub.14B,
TbFe.sub.2, and combinations thereof.
17. The pigment flake of claim 1, wherein the magnetic layer
comprises a material selected from the group consisting of
Fe.sub.3O.sub.4, NiFe.sub.2O.sub.4, MnFe.sub.2O.sub.4,
CoFe.sub.2O.sub.4, YIG, GdIG, and combinations thereof.
18. The pigment flake of claim 1, wherein the magnetic layer h as a
physical thickness of about 200 .ANG. to about 10,000 .ANG..
19. The pigment flake of claim 1, wherein the reflector layers
comprise a reflective material selected from the group consisting
of aluminum, silver, copper, gold, platinum, tin, titanium,
palladium, nickel, cobalt, rhodium, niobium, chromium, and
combinations or alloys thereof.
20. The pigment flake of claim 1, wherein the reflector layers each
have a physical thickness of about 400 .ANG. to about 2,000
.ANG..
21. A magnetic colorant composition, comprising: a pigment medium;
and a plurality of pigment flakes dispersed in the pigment medium,
the pigment flakes having a multilayer structure substantially the
same as the pigment flake defined in claim 1.
22. The colorant composition of claim 21, wherein the pigment
medium comprises a material selected from the group consisting of
acrylic melamine, urethanes, polyesters, vinyl resins, acrylates,
methyl methacrylate, ABS resins, epoxies, styrenes, ink and paint
formulations based on alkyd resins, and mixtures thereof.
23. A magnetic color shifting pigment flake, comprising: a magnetic
core section including: a central magnetic layer having a first
major surface, an opposing second major surface, and at least one
side surface; and a first reflector layer on the first major
surface of the magnetic layer, and an opposing second reflector
layer on the second major surface of the magnetic layer; a first
dielectric layer overlying the first reflector layer, and a second
dielectric layer overlying the second reflector layer; and a first
absorber layer overlying the first dielectric layer, and a second
absorber layer overlying-the second dielectric layer; wherein the
pigment flake exhibits a discrete color shift such that the pigment
flake has a first color at a first angle of incident light or
viewing and a second color different from the first color at a
second angle of incident light or viewing.
24. The pigment flake of claim 23, wherein the magnetic layer
comprises a soft magnetic material.
25. The pigment flake of claim 23, wherein the magnetic layer
comprises a material selected from the group comprising iron,
nickel, cobalt, iron, gadolinium, terbium, dysprosium, erbium, and
alloys or oxides thereof.
26. The pigment flake of claim 23, wherein the magnetic layer
comprises a material selected from the group consisting of Fe/Si,
Fe/Ni, FeCo, Fe/Ni/Mo, and combinations thereof.
27. The pigment flake of claim 23, wherein the magnetic layer
comprises a hard magnetic material.
28. The pigment flake of claim 23, wherein the magnetic layer
comprises a material selected from the group consisting of
SmCo.sub.5, NdCos, Sm.sub.2Co.sub.17, Nd.sub.2Fe.sub.14B,
TbFe.sub.2, and combinations thereof.
29. The pigment flake of claim 23, wherein the magnetic layer
comprises a material selected from the group consisting of
Fe.sub.3O.sub.4, NiFe.sub.2O.sub.4, MnFe.sub.2O.sub.4,
CoFe.sub.2O.sub.4, YIG, GdIG, and combinations thereof.
30. The pigment flake of claim 23, wherein the reflector layers
comprise a reflective material selected from the group consisting
of aluminum, silver, copper, gold, platinum, tin, titanium,
palladium, nickel, cobalt, rhodium, niobium, chromium, and
combinations or alloys thereof.
31. The pigment flake of claim 23, wherein the first and second
dielectric layers comprise a dielectric material having an index of
refraction of about 1.65 or less.
32. The pigment flake of claim 23, wherein the dielectric material
is selected from the group consisting of silicon dioxide, aluminum
oxide, magnesium fluoride, aluminum fluoride, cerium fluoride,
lanthanum fluoride, neodymium fluoride, samarium fluoride, barium
fluoride, calcium fluoride, lithium fluoride, and combinations
thereof.
33. The pigment flake of claim 23, wherein the first and second
dielectric layers comprise a dielectric material having an index of
refraction of greater than about 1.65.
34. The pigment flake of claim 23, wherein the dielectric material
is selected from the group consisting of zinc sulfide, zinc oxide,
zirconium oxide, titanium dioxide, diamond-like carbon, indium
oxide, indium-tin-oxide, tantalum pentoxide, cerium oxide, yttrium
oxide, europium oxide, iron oxides, hafnium nitride, hafnium
carbide, hafnium oxide, lanthanum oxide, magnesium oxide, neodymium
oxide, praseodymium oxide, samarium oxide, antimony trioxide,
silicon monoxide, selenium trioxide, tin oxide, tungsten trioxide,
and combinations thereof.
35. The pigment flake of claim 23, wherein the first and second
dielectric layers have an optical thickness in a range from about 2
QWOT at a design wavelength of about 400 .mu.m to about 9 QWOT at a
design wavelength of about 700 nm.
36. The pigment flake of claim 23, wherein the first and second
dielectric layers have substantially the same optical
thickness.
37. The pigment flake of claim 23, wherein the first and second
dielectric layers are composed of the same material.
38. The pigment flake of claim 23, wherein the first and second
dielectric layers are each composed of a dielectric optical stack
having a plurality of alternating layers of a high index material
and a low index material.
39. The pigment flake of claim 38, wherein the dielectric optical
stack has a gradient index of refraction.
40. The pigment flake of claim 23, wherein the first and second
dielectric layers are each composed of a mixture or multiple
sublayers of dielectric materials selected from the group
consisting of low index materials, high index materials, and
combinations thereof.
41. The pigment flake of claim 23, wherein the first and second
absorber layers comprise materials that are uniformly absorbing in
the visible part of the electromagnetic spectrum.
42. The pigment flake of claim 23, wherein the first and second
absorber layers comprise materials that are non-uniformly absorbing
in the visible part of the electromagnetic spectrum.
43. The pigment flake of claim 23, wherein the first and second
absorber layers comprise an absorbing material selected from the
group consisting of chromium, nickel, aluminum, silver, copper,
palladium, platinum, titanium, vanadium, cobalt, iron, tin,
tungsten, molybdenum, rhodium, niobium, carbon, graphite, silicon,
germanium, and compounds, mixtures, or alloys thereof.
44. The pigment flake of claim 23, wherein the first and second
absorber layers comprise an absorbing material selected from the
group consisting of metal oxides, metal sulfides, metal carbides,
and combinations thereof.
45. The pigment flake of claim 23, wherein the first and second
absorber layers each have a physical thickness of about 30 .ANG. to
about 500 .ANG..
46. The pigment flake of claim 23, wherein the first and second
absorber layers have substantially the same physical thickness.
47. The pigment flake of claim 23, wherein the first and second
absorber layers are composed of the same material.
48. The pigment flake of claim 23, wherein the first and second
reflector layers are on each of the first and second major surfaces
but not on the at least one side surface of the magnetic layer.
49. The pigment flake of claim 23, wherein the first and second
reflector layers form part of a contiguous reflecting layer
substantially surrounding the magnetic layer.
50. The pigment flake of claim 23, wherein the first and second
absorber layers form part of a contiguous absorbing layer
substantially surrounding the first and second dielectric layers
and the magnetic core section.
51. The pigment flake of claim 23, wherein the first and second
absorber layers form part of a contiguous absorbing layer
substantially surrounding the first-and second dielectric layers,
and the first and second dielectric layers form a part of a
contiguous dielectric layer substantially surrounding the magnetic
core section.
52. A magnetic color shifting pigment composition comprising a
plurality of color shifting pigment flakes, each of the pigment
flakes having a multilayer structure substantially the same as the
pigment flake defined in claim 23.
53. A magnetic color-shifting colorant composition, comprising: a
pigment medium; and a plurality of color-shifting pigment flakes
dispersed in the pigment medium, the pigment flakes having a
multilayer structure substantially the same as the pigment flake
defined in claim 23.
54. The colorant composition of claim 53, wherein the pigment
medium comprises a material selected from the group consisting of
acrylic melamine, urethanes, polyesters, vinyl resins, acrylates,
methyl methacrylate, ABS resins, epoxies, styrenes, ink and paint
formulations based on alkyd resins, and mixtures thereof.
55. The colorant composition of claim 53, wherein the pigment
medium is a paint or ink vehicle.
56. The colorant composition of claim 53, wherein the pigment
flakes have a dimension on any surface thereof ranging from about 2
microns to about 200 microns.
57. The colorant composition of claim 53, wherein the pigment
flakes have an aspect ratio of at least about 2 to 1.
58. The colorant composition of claim 53, further comprising a
plurality of non-color-shifting pigment flakes dispersed in the
pigment medium.
59. A magnetic pigment flake, comprising: a central support layer
having a first major surface, an opposing second major surface, and
at least one side surface; a first magnetic layer on the first
major surface of the support layer; and a second magnetic layer on
the second major surface of the support layer; wherein the pigment
flake exhibits magnetic characteristics based on the relative
magnetism of the magnetic layers.
60. The pigment flake of claim 59, wherein the support layer
comprises a dielectric material.
61. The pigment flake of claim 60, wherein the dielectric material
is selected from the group consisting of mica, coated mica,
micaeous iron oxide, glass, talc, silicon dioxide, boron nitride,
boron carbide, alumina, carbon, graphite, bismuth oxychloride, and
combinations thereof.
62. The pigment flake of claim 59, wherein the first and second
magnetic layers are on each of the first and second major surfaces
but not on the at least one side surface of the support layer.
63. The pigment flake of claim 62, further comprising a first
dielectric layer on the first magnetic layer and a second
dielectric layer on the second magnetic layer.
64. The pigment flake of claim 63, wherein the first and second
dielectric layers are selectively absorbing and provide additional
color effects to the pigment flake.
65. The pigment flake of claim 59, wherein the first and second
magnetic layers form part of a contiguous magnetic layer
substantially surrounding the support layer.
66. The pigment flake of claim 65, further comprising a dielectric
layer substantially surrounding the contiguous magnetic layer.
67. The pigment flake of claim 66, wherein the dielectric layer is
selectively absorbing and provides additional color effects to the
pigment flake.
68. The pigment flake of claim 66, further comprising an absorber
layer substantially surrounding the dielectric layer.
69. The pigment flake of claim 68, wherein the dielectric layer is
selectively absorbing and provides additional color effects to the
pigment flake.
70. The pigment flake of claim 68, further comprising a reflector
layer interposed between the magnetic layer and the dielectric
layer.
71. The pigment flake of claim 59, wherein the magnetic layers
comprise a soft magnetic material.
72. The pigment flake of claim 59, wherein the magnetic layers are
composed of a material with a coercivity of less than about 2000
Oe.
73. A magnetic colorant composition, comprising: a pigment medium;
and a plurality of pigment flakes dispersed in the pigment medium,
the pigment flakes having a multilayer structure substantially the
same as the pigment flake defined in claim 59.
74. The colorant composition of claim 73, wherein the pigment
medium is a paint or ink vehicle.
75. A magnetic pigment flake, comprising: a central magnetic layer
having a first major surface, an opposing second major surface, and
at least one side surface; a first dielectric layer on the first
major surface of the magnetic layer; and a second dielectric layer
on the second major surface of the magnetic layer; wherein the
dielectric layers provide increased rigidity, durability, and
corrosion resistance to the pigment flake, with the pigment flake
exhibiting magnetic characteristics based on the relative magnetism
of the magnetic layer.
76. The pigment flake of claim 75, wherein the first and second
dielectric layers are selectively absorbing and provide additional
color effects to the pigment flake.
77. The pigment flake of claim 75, wherein the magnetic layer
comprises a soft magnetic material.
78. The pigment flake of claim 75, wherein the magnetic layer is
composed of a material with a coercivity of less than about 2000
Oe.
79. The pigment flake of claim 75, wherein the first and second
dielectric layers are on each of the first and second major
surfaces but not on the at least one side surface of the magnetic
layer.
80. The pigment flake of claim 79, further comprising a first
absorber layer on the first dielectric layer and a second absorber
layer on the second dielectric layer.
81. The pigment flake of claim 79, further comprising an absorber
layer substantially surrounding the first and second dielectric
layers and the magnetic layer.
82. The pigment flake of claim 75, wherein the first and second
dielectric layers form part of a contiguous dielectric layer
substantially surrounding the magnetic layer.
83. The pigment flake of claim 82, wherein the contiguous
dielectric layer is selectively absorbing and provides additional
color effects to the pigment flake.
84. The pigment flake of claim 82, further comprising an absorber
layer substantially surrounding the flake.
85. A color shifting pigment flake, comprising: a magnetic core
section having a top surface, a bottom surface, and at least one
side surface; a dielectric layer on the top surface and the bottom
surface but not on the at least one side surface of the magnetic
core section; and an absorber layer substantially surrounding the
dielectric layer and in contact with the at least one side surface
of the magnetic core section.
86. The pigment flake of claim 85, wherein the magnetic core
section includes a magnetic layer.
87. The pigment flake of claim 85, wherein the magnetic core
section comprises: a central magnetic layer having a first major
surface, an opposing second major surface, and at least one side
surface; and a first reflector layer on the first major surface of
the magnetic layer, and an opposing second reflector layer on the
second major surface of the magnetic layer.
88. The pigment flake of claim 87, wherein the first and second
reflector layers are on each of the first and second major surfaces
but not on the at least one side surface of the magnetic layer.
89. The pigment flake of claim 87, wherein the first and second
reflector layers form part of a contiguous reflecting layer
substantially surrounding the magnetic layer.
90. A magnetic pigment flake, comprising: a magnetic core having a
first major surface, an opposing second major surface, and at least
one side surface; a first colored layer on the first major surface
of the magnetic core; and a second colored layer on the second
major surface of the magnetic core.
91. The pigment flake of claim 90, wherein the magnetic core
comprises a monolithic magnetic layer.
92. The pigment flake of claim 90, wherein the magnetic core
comprises a multilayer magnetic structure.
93. The pigment flake of claim 92, wherein the multilayer magnetic
structure comprises the coating structure Al/Fe/Al.
94. The pigment flake of claim 90, wherein the first and second
colored layers are on each of the first and second major surfaces
but not on the at least one side surface of the magnetic core.
95. The pigment flake of claim 90, wherein the first and second
colored layers form part of a contiguous colored layer
substantially surrounding the magnetic core.
96. The pigment flake of claim 90, wherein the first and second
colored layers comprise an organic dye.
97. The pigment flake of claim 96, wherein the organic dye is
selected from the group consisting of copper phthalocyanine,
perylene-based dyes, anthraquinone-based dyes, azo dyes, azo metal
dyes, and combinations thereof.
98. The pigment flake of claim 96, wherein the colored layers each
have a physical thickness of about 0.05 .mu.m to about 5 .mu.m.
99. The pigment flake of claim 90, wherein the first and second
colored layers comprise an inorganic colorant material.
100. The pigment flake of claim 99, wherein the inorganic colorant
material is selected from the group consisting of titanium nitride,
chromium nitride, chromium oxide, iron oxide, cobalt-doped alumina,
colored metallics, and combinations thereof.
101. The pigment flake of claim 99, wherein the colored layers each
have a physical thickness of about 0.05 .mu.m to about 0.10
.mu.m.
102. The pigment flake of claim 90, wherein the first and second
colored layers comprise a sol-gel matrix holding a colored pigment
or dye.
103. A color shifting foil device, comprising: a magnetic layer; a
reflector layer overlying the magnetic layer; a dielectric layer
overlying the reflector layer; and an absorber layer overlying the
dielectric layer; wherein the foil exhibits a discrete color shift
such that the foil has a first color at a first angle of incident
light or viewing and a second color different from the first color
at a second angle of incident light or viewing.
104. The foil of claim 103, wherein the magnetic layer comprises a
soft magnetic material or a hard magnetic material.
105. The foil of claim 103, further comprising a web carrier with
either the magnetic layer or the absorber layer deposited on the
web carrier.
106. The foil of claim 105, wherein the web carrier further
comprises a release layer thereon disposed between the web carrier
and the magnetic layer, or the web carrier and the absorber
layer.
107. The foil of claim 105, further comprising an adhesive layer
for laminating the foil to a substrate.
108. The foil of claim 107, wherein the adhesive layer is selected
from the group consisting of a hot stampable adhesive, a pressure
sensitive adhesive, a permanent adhesive, a transparent adhesive,
and a UV curable adhesive.
109. The foil of claim 107, wherein the adhesive layer is overlying
the magnetic layer or the absorber layer.
110. An optical article comprising: a substrate having first and
second non-overlapping regions on a surface of the substrate; a
magnetic pigment coating structure overlying the first region, the
magnetic pigment coating structure including a plurality of
multilayer magnetic pigments dispersed in a solidified pigment
vehicle, the magnetic properties of the pigment coating structure
being provided by a non-optically observable magnetic layer within
each of the multilayer magnetic pigments; and a non-magnetic
pigment coating structure overlying the second region, the
non-magnetic pigment coating structure including a plurality of
multilayer nonmagnetic pigments dispersed in a solidified pigment
vehicle.
111. The article of claim 110, wherein the non-magnetic pigment
coating structure has a substantially identical color as the
magnetic pigment coating structure.
112. The article of claim 110, wherein one or both of the magnetic
pigment and non-magnetic pigment coating structures have discrete
color shifting effects.
113. The article of claim 110, wherein the magnetic pigment and
non-magnetic pigment coating structures have substantially
identical color shifting effects.
114. The article of claim 110, wherein the magnetic pigment and
non-magnetic pigment coating structure have different color
shifting effects.
115. An optical article comprising: a substrate having an upper
surface region; a magnetic pigment coating structure overlying the
upper surface region of the substrate, the magnetic pigment coating
structure including a plurality of multilayer magnetic pigments
dispersed in a solidified pigment vehicle, the magnetic properties
of the pigment coating structure being provided by a non-optically
observable magnetic layer within each of the multilayer magnetic
pigments; and a non-magnetic pigment coating structure overlying at
least a portion of the magnetic pigment coating structure, the
non-magnetic pigment coating structure including a plurality of
non-magnetic pigments dispersed in a solidified pigment
vehicle.
116. The article of claim 115, wherein the non-magnetic pigment
coating structure has a substantially identical color as the
magnetic pigment coating structure.
117. The article of claim 115, wherein one or both of the magnetic
pigment and non-magnetic pigment coating structures have discrete
color shifting effects.
118. The article of claim 115, wherein the magnetic pigment and
non-magnetic pigment coating structures have substantially
identical color shifting effects.
119. An optical article comprising: a substrate having an upper
surface region; a non-magnetic pigment coating structure overlying
the upper surface region of the substrate, the non-magnetic pigment
coating structure including a plurality of non-magnetic pigments
dispersed in a solidified pigment vehicle; and a magnetic pigment
coating structure overlying the magnetic pigment coating structure
including a plurality of multilayer magnetic pigments dispersed in
a solidified pigment vehicle, the magnetic properties of the
pigment coating structure being provided by a non-optically
observable magnetic layer within each of the multilayer magnetic
pigments.
120. The article of claim 119, wherein the non-magnetic pigment
coating structure has a substantially identical color as the
magnetic pigment coating structure.
121. The article of claim 119, wherein one or both of the magnetic
pigment and non-magnetic pigment coating structures have discrete
color shifting effects.
122. The article of claim 119, wherein the magnetic pigment and
non-magnetic pigment coating structures have substantially
identical color shifting effects.
123. An optical article comprising: a substrate having first and
second non-overlapping regions on a surface of the substrate; a
multilayer magnetic foil structure overlying the first region, the
magnetic properties of the foil structure provided by a magnetic
layer which is not optically observable; and a non-magnetic foil
structure overlying the second region.
124. The article of claim 123, wherein the non-magnetic foil
structure has a substantially identical color as the magnetic foil
structure.
125. The article of claim 123, wherein one or both of the magnetic
foil structure and the non-magnetic foil structure have discrete
color shifting effects.
126. The article of claim 123, wherein the magnetic foil structure
and the non1 magnetic foil structure have substantially identical
color shifting effects.
127. The article of claim 123, wherein the magnetic foil structure
and the non19 magnetic foil structure have different color shifting
effects.
128. An optical article comprising: a substrate having an upper
surface region; a multilayer magnetic foil structure overlying the
upper surface region of the substrate, the magnetic properties of
the magnetic foil structure provided by a magnetic layer which is
not optically observable; and a non-magnetic foil structure
overlying at least a portion of the magnetic foil structure.
129. An optical article comprising: a substrate having an upper
surface region; a non-magnetic foil structure overlying the upper
surface region of the substrate; and a multilayer magnetic foil
structure overlying at least a portion of the non-magnetic foil
structure, the magnetic properties of the magnetic foil structure
provided by a magnetic layer which is not optically observable.
130. A magnetic pigment flake, comprising: a magnetic core section
including: a central magnetic layer having a first major surface,
an opposing second major surface, and at least one side surface;
and a first reflector layer on the first major surface of the
magnetic layer, and an opposing second reflector layer on the
second major surface of the magnetic layer; and a first dielectric
layer overlying the first reflector layer, and a second dielectric
layer overlying the second reflector layer, the first and second
dielectric layers composed of dielectric optical stacks including
alternating high index and low index materials.
131. The pigment flake of claim 130, wherein the first and second
dielectric layers have coating structures selected from the group
consisting of (HL).sup.n, (LH).sup.n, (LHL).sup.n, and (HLH).sup.n,
where n=1-100 and the L and H layers are 1 QW at a design
wavelength.
Description
BACKGROUND OF THE INVENTION
[0001] 1. The Field of the Invention
[0002] The present invention relates generally to pigments and
foils. In particular, the present invention relates to multilayered
pigment flakes and foils which have magnetic layers, and pigment
compositions that incorporate multilayer pigment flakes having
magnetic layers.
[0003] 2. The Relevant Technology
[0004] Various pigments, colorants, and foils have been developed
for a wide variety of applications. For example, magnetic pigments
have been developed for use in applications such as decorative
cookware, creating patterned surfaces, and security devices.
Similarly, color shifting pigments have been developed for such
uses as cosmetics, inks, coating materials, ornaments, ceramics,
automobile paints, anti-counterfeiting hot stamps, and
anti-counterfeiting inks for security documents and currency.
[0005] Color shifting pigments, colorants, and foils exhibit the
property of changing color upon variation of the angle of incident
light, or as the viewing angle of the observer is shifted. The
color-shifting properties of pigments and foils can be controlled
through proper design of the optical thin films or orientation of
the molecular species used to form the flake or foil coating
structure. Desired effects can be achieved through the variation of
parameters such as thickness of the layers forming the flakes and
foils and the index of refraction of each layer. The changes in
perceived color which occur for different viewing angles or angles
of incident light are a result of a combination of selective
absorption of the materials comprising the layers and wavelength
dependent interference effects. The interference effects, which
arise from the superposition of light waves that have undergone
multiple reflections, are responsible for the shifts in color
perceived with different angles. The reflection maxima changes in
position and intensity, as the viewing angle changes, due to
changing interference effects arising from light path length
differences in the various layers of a material which are
selectively enhanced at particular wavelengths.
[0006] Various approaches have been used to achieve such color
shifting effects. For example, small multilayer flakes, typically
composed of multiple layers of thin films, are dispersed throughout
a medium such as paint or ink that may then be subsequently applied
to the surface of an object. Such flakes may optionally be
overcoated to achieve desired colors and optical effects. Another
approach is to encapsulate small metallic or silicatic substrates
with varying layers and then disperse the encapsulated substrates
throughout a medium such as paint or ink. Additionally, foils
composed of multiple layers of thin films on a substrate material
have been made.
[0007] One manner of producing a multilayer thin film structure is
by forming it on a flexible web material with a release layer
thereon. The various layers are deposited on the web by methods
well known in the art of forming thin coating structures, such as
PVD, sputtering, or the like. The multilayer thin film structure is
then removed from the web material as thin film color shifting
flakes, which can be added to a polymeric medium such as various
pigment vehicles for use as an ink or paint. In addition to the
color shifting flakes, additives can be added to the inks or paints
to obtain desired color shifting results.
[0008] Color shifting pigments or foils are formed from a
multilayer thin film structure that includes the same basic layers.
These include an absorber layer(s), a dielectric layer(s), and
optionally a reflector layer, in varying layer orders. The coatings
can be formed to have a symmetrical multilayer thin film structure,
such as:
[0009] absorber/dielectric/reflector/dielectric/absorber; or
[0010] absorber/dielectric/absorber.
[0011] Coatings can also be formed to have an asymmetrical
multilayer thin film structure, such as:
[0012] absorber/dielectric/reflector.
[0013] For example, U.S. Pat. No. 5,135,812 to Phillips et al.,
which is incorporated by reference herein, discloses color-shifting
thin film flakes having several different configurations of layers
such as transparent dielectric and semi-transparent metallic
layered stacks. In U.S. Pat. No. 5,278,590 to Phillips et al.,
which is incorporated by reference herein, a symmetric three layer
optical interference coating is disclosed which comprises first and
second partially transmitting absorber layers which have
essentially the same material and thickness, and a dielectric
spacer layer located between the first and second absorber
layers.
[0014] Color shifting platelets for use in paints are disclosed in
U.S. Pat. No. 5,571,624 to Phillips et al., which is incorporated
by reference herein. These platelets are formed from a symmetrical
multilayer thin film structure in which a first semi-opaque layer
such as chromium is formed on a substrate, with a first dielectric
layer formed on the first semi-opaque layer. An opaque reflecting
metal layer such as aluminum is formed on the first dielectric
layer, followed by a second dielectric layer of the same material
and thickness as the first dielectric layer. A second semi-opaque
layer of the same material and thickness as the first semi-opaque
layer is formed on the second dielectric layer.
[0015] With regard to magnetic pigments, U.S. Pat. No. 4,838,648 to
Phillips et al. (hereinafter "Phillips '648") discloses a thin film
magnetic color shifting structure wherein the magnetic material can
be used as the reflector or absorber layer. One disclosed magnetic
material is a cobalt nickel alloy. Phillips '648 discloses flakes
and foils with the following structures:
[0016] dyed superstrate/absorber/dielectric/magnetic
layer/substrate;
[0017] dyed superstrate/absorber/dielectric/magnetic
layer/dielectric/absorber/dyed superstrate; and
[0018] adhesive/magnetic layer/dielectric/absorber/releasable
hardcoat/substrate.
[0019] Patterned surfaces have been provided by exposing magnetic
flakes to a magnetic force to effect a physical alteration in the
structure of the pigment. For example, U.S. Pat. No. 6,103,361 to
Batzar et al. (hereinafter "Batzar") uses pigments made of
magnetizable materials to decorate cookware. In particular, Batzar
is directed toward controlling the orientation of stainless steel
flakes in a fluoropolymer release coating to make patterns where at
least some of the flakes are longer than the coating thickness. The
patterned substrate is formed by applying magnetic force through
the edges of a magnetizable die positioned under a coated base to
alter the orientation of the flakes within the coating, thereby
inducing an imaging effect or pattern. However, Batzar does not
discuss the use of optical thin film stacks or platelets employing
a magnetic layer. In addition, although the stainless steel flakes
used in Batzar are suitable for decorating cookware, they are
poorly reflecting.
[0020] U.S. Pat. No. 2,570,856 to Pratt et al (hereinafter "Pratt")
is directed to metallic flake pigments which are based on
ferromagnetic metal platelets. Like Batzar, however, Pratt uses
poorly reflecting metals and does not teach the use of thin film
optical stacks.
[0021] U.S. Pat. Nos. 5,364,689 and 5,630,877 to Kashiwagi et al.,
(hereinafter collectively "the Kashiwagi patents"), the disclosures
of which are incorporated herein by reference, disclose methods and
apparatus for creating magnetically formed painted patterns. The
Kashiwagi patents teach use of a magnetic paint layer, which
includes nonspherical magnetic particles in a paint medium. A
magnetic field with magnetic field lines in the shape of the
desired pattern is applied to the paint layer. The final pattern is
created by the different magnetic particle orientations in the
hardened paint.
[0022] One attempt at incorporating a magnetic layer into a
multilayer flake is disclosed in European Patent Publication EP
686675B1 to Schmid et al. (hereinafter "Schmid"), which describes
laminar color shifting structures which include a magnetic layer
between the dielectric layer and a central aluminum layer as
follows:
[0023]
oxide/absorber/dielectric/magnet/Al/magnet/dielectric/absorber/oxid-
e
[0024] Thus, Schmid uses aluminum platelets and then coats these
platelets with magnetic materials. However, the overlying magnetic
material downgrades the reflective properties of the pigment
because aluminum is the second brightest metal (after silver),
meaning any magnetic material is less reflective. Further, Schmid
starts with aluminum platelets generated from ballmilling, a method
which is limited in terms of the layer smoothness that can be
achieved.
[0025] Patent Publication EP 710508A1 to Richter et al.
(hereinafter "Richter") discloses methods for providing three
dimensional effects by drawing with magnetic tips. Richter
describes three dimensional effects achieved by aligning
magnetically active pigments in a spatially-varying magnetic field.
Richter uses standard pigments (barium ferrite, strontium ferrite,
samarium/cobalt, Al/Co/Ni alloys, and metal oxides made by
sintering and quick quenching, none of which are composed of
optical thin film stacks. Rather, the particles are of the hard
magnetic type. Richter uses electromagnetic pole pieces either on
top of the coating or on both sides of the coating. However,
Richter uses a moving system and requires "drawing" of the image.
This "drawing" takes time and is not conducive to production type
processes.
[0026] U.S. Pat. No. 3,791,864 to Steingroever (hereinafter
"Steingroever") describes a method for patterning magnetic
particles by orienting them with a magnetic pattern generated in an
underlying prime coating that has previously been patterned by a
magnetic field. The prime coat contains magnetic particles of the
type MO.times.6Fe.sub.2O.sub.3 where M can be one or more of the
elements Ba, Sr, Co, or Pb. After coating a continuous sheet of
liquid coating of the primer, it is hardened and then areas of the
primer are magnetized by a magnetic field. Next, a pigment vehicle
with magnetic particles suspended therein is then applied. The
magnetic particles suspended therein are finally oriented by the
magnetic force from the magnetic pattern in the primer, creating
the final pattern. However, Steingroever suffers from a diffuse
magnetic image in the prime coat, which in turn passes a diffuse
image to the topcoat. This reduction in resolution is because high
magnetic fields are limited in the resolution they can create. This
limitation is due to high magnetic field lines surrounding the
intended magnetic image, thereby affecting untargeted magnetic
particles in the prime coat and blurring the image.
[0027] Accordingly, there is a need for improved multilayer pigment
flakes and foils with magnetic properties that overcome or avoid
the above problems and limitations.
SUMMARY AND OBJECTS OF THE INVENTION
[0028] It is an object of the invention to provide durable magnetic
flakes and foils.
[0029] It is another object of the invention to provide magnetic
color shifting flakes and foils with high chroma.
[0030] It is a further object of the invention to provide pigment
flakes and foils with security features that are not visually
perceptible.
[0031] It is yet another object of the invention to provide pigment
flakes and foils capable of providing three dimensional like
images.
[0032] To achieve the foregoing objects and in accordance with the
invention as embodied and broadly described herein, pigment flakes
and foils are provided which have magnetic properties. The pigment
flakes can have a symmetrical stacked coating structure on opposing
sides of a magnetic core layer, can have an asymmetrical coating
structure with all of the layers on one side of the magnetic layer,
or can be formed with one or more encapsulating coatings around a
magnetic core. The coating structure of the flakes and foils
includes at least one magnetic layer and optionally one or more of
a reflector layer, dielectric layer, and absorber layer. In color
shifting embodiments of the invention, the coating structure
includes the dielectric layer overlying the magnetic and reflector
layers, and the absorber layer overlying the dielectric layer. Non
color shifting embodiments of the invention include a magnetic
layer between two reflector layers or encapsulated by a reflector
layer, a magnetic layer between two dielectric layers or
encapsulated by a dielectric layer, a dielectric layer between two
magnetic layers or encapsulated by a magnetic layer, and a magnetic
layer encapsulated by a colorant layer. The color shifting
embodiments exhibit a discrete color shift so as to have a first
color at a first angle of incident light or viewing and a second
color different from the first color at a second angle of incident
light or viewing. The pigment flakes can be interspersed into
liquid media such as paints or inks to produce colorant
compositions for subsequent application to objects or papers. The
foils can be laminated to various objects or can be formed on a
carrier substrate.
[0033] These and other objects and features of the present
invention will become more fully apparent from the following
description and appended claims, or may be learned by the practice
of the invention as set forth hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] In order to illustrate the manner in which the above-recited
and other advantages and features of the invention are obtained, a
more particular description of the invention briefly described
above will be rendered by reference to specific embodiments thereof
which are illustrated in the appended drawings. Understanding that
these drawings depict only typical embodiments of the invention and
are not therefore to be considered limiting of its scope, the
invention will be described and explained with additional
specificity and detail through the use of the accompanying drawings
in which:
[0035] FIG. 1 is a schematic representation of the coating
structure of a magnetic flake according to one embodiment of the
invention;
[0036] FIG. 2 is a schematic representation of the coating
structure of a magnetic flake according to another embodiment of
the invention;
[0037] FIG. 3 is a schematic representation of the coating
structure of a magnetic flake according to an alternative
embodiment of the invention;
[0038] FIG. 4 is a schematic representation of the coating
structure of a magnetic flake according to another embodiment of
the invention;
[0039] FIG. 5 is a schematic representation of the coating
structure of a magnetic flake according to a further embodiment of
the invention;
[0040] FIG. 6 is a schematic representation of the coating
structure of a magnetic flake according to a further embodiment of
the invention;
[0041] FIG. 7 is a schematic representation of the coating
structure of a magnetic flake according to an alternative
embodiment of the invention;
[0042] FIG. 8 is a schematic representation of the coating
structure of a magnetic flake according to a further embodiment of
the invention;
[0043] FIG. 9 is a schematic representation of the coating
structure of a magnetic flake according to yet a further embodiment
of the invention;
[0044] FIG. 10 is a schematic representation of the coating
structure of a magnetic flake according to another alternative
embodiment of the invention;
[0045] FIG. 11 is a schematic representation of the coating
structure of a magnetic flake according to another embodiment of
the invention;
[0046] FIG. 12 is a schematic representation of the coating
structure of a magnetic flake according to a further embodiment of
the invention;
[0047] FIG. 13 is a schematic representation of the coating
structure of a magnetic foil according to one embodiment of the
invention;
[0048] FIG. 14 is a schematic representation of the coating
structure of a magnetic foil according to another embodiment of the
invention;
[0049] FIG. 15 is a schematic representation of the coating
structure of a magnetic foil according to a further embodiment of
the invention;
[0050] FIG. 16 is a schematic representation of the coating
structure of an optical article according to an additional
embodiment of the invention; and
[0051] FIG. 17 is a schematic representation of the coating
structure of an optical article according to a further embodiment
of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0052] The present invention relates to multilayer pigment flakes
and foils which have magnetic layers, and pigment compositions
which incorporate the magnetic flakes. The flakes and foils can be
used both to create security features which are not visually
perceptible, and to create three dimensional-like images for
security devices or to add decorative features to a product. The
nonvisual security features are provided by burying the magnetic
layer between other layers within a flake or foil so that only the
overlying layers are exposed.
[0053] The three dimensional-like effects can be provided by
exposing the flake or foil to an external magnetic force, thereby
orienting the plane of some of the pigments normal to the surface
of the coating. The un-oriented pigments lie with their planar
surface parallel to the surface of the coating. The three
dimensional-like effect is due to the alignment of the particles
such that the aspect ratio is oriented with the magnetic field,
i.e. the longest part of the pigment aligns itself along the
magnetic field lines. In such case, the face of the pigment is
turned away from the observer to various extents depending on the
magnitude of the magnetic force. In the limit or maximum
orientation, the coating appears black in color. As one moves off
the black, one moves slowly toward the color of the planar surface
of the pigment, i.e., color shifting, non-color shifting, such as
the color blue, or silver as for example, aluminum. The result is a
colored three dimensional-like effect, similar to that of a
holographic effect, that appears to move as the viewing angle
changes. Methods of creating three dimensional-like images using
the magnetic pigments disclosed herein are described in further
detail in a copending U.S. Patent Application, bearing attorney
docket No. 13676.167, and entitled Methods For Producing Imaged
Coated Articles By Using Magnetic Pigments, the disclosure of which
is incorporated herein by reference.
[0054] Unlike many prior magnetic flakes, the presently disclosed
flakes are not composed only of magnetizable materials, but include
both magnetizable and nonmagnetizable materials. For example, the
invention encompasses pigment flakes wherein a magnetic layer is
buried within one or more reflector layers. In another embodiment
the pigment flakes comprise a magnetic core surrounded by
dielectric layers. In yet a further embodiment, the pigment flakes
include a dielectric core surrounded by magnetic layers.
[0055] In the case of magnetic layers buried between or within
overlying reflector layers, the present invention presents a
significant improvement over the prior art by substantially
achieving higher chroma and brightness. By putting the duller
magnetic material inside the reflector, the present invention
accomplishes two objectives: 1) the reflectivity of the reflector
layer is maintained; and 2) color shifting pigments without the
inner core of magnetic material cannot be distinguished by an
observer from such pigment with the core of magnetic material. For
example, two coated objects viewed side by side, one with and one
without the magnetic material in the coating, would look the same
to the observer. However, the magnetic color shifting pigment
provides a covert security feature in addition to the color
shifting effect. Thus, with a magnetic detection system, a magnetic
covert signature in the pigment could be read by a Faraday rotator
detector, for example.
[0056] In various embodiments of the present invention, the pigment
flakes and foils have substantial shifts in chroma and hue with
changes in angle of incident light or viewing angle of an observer.
Such an optical effect, known as goniochromaticity or "color
shift," allows a perceived color to vary with the angle of
illumination or observation. Accordingly, such pigment flakes and
foils exhibit a first color at a first angle of incident light or
viewing and a second color different from the first color at a
second angle of incident light or viewing. The pigment flakes can
be interspersed into liquid media such as paints or inks to produce
various color shifting colorant compositions for subsequent
application to objects or papers. The foils can be laminated to
various objects or can be formed on a carrier substrate.
[0057] Generally, the color shifting pigment flakes can have a
symmetrical stacked coating structure on opposing sides of a
magnetic core layer, can have an asymmetrical coating structure
with a majority of the layers on one side of the magnetic layer, or
can be formed with one or more encapsulating coatings which
surround a magnetic core. The coating structure of the flakes and
foils generally includes a magnetic core, which includes a magnetic
layer and other optional layers, a dielectric layer overlying the
magnetic core, and an absorber layer overlying the dielectric
layer.
[0058] The color shifting flakes and foils of the invention can be
formed using conventional thin film deposition techniques, which
are well known in the art of forming thin coating structures.
Nonlimiting examples of such thin film deposition techniques
include physical vapor deposition (PVD), chemical vapor deposition
(CVD), plasma enhanced (PE) variations thereof such as PECVD or
downstream PECVD, sputtering, electrolysis deposition, and other
like deposition methods that lead to the formation of discrete and
uniform thin film layers.
[0059] The color shifting pigment flakes of the invention can be
formed by various fabrication methods. For example, the pigment
flakes can be formed by a web coating process in which various
layers are sequentially deposited on a web material by conventional
deposition techniques to form a thin film structure, which is
subsequently fractured and removed from the web, such as by use of
a solvent, to form a plurality of thin film flakes.
[0060] In another fabrication method, one or more thin film layers
including at least the magnetic layer is deposited on a web to form
a film, which is subsequently fractured and removed from the web to
form a plurality of pigment preflakes. The preflakes can be
fragmented further by grinding if desired. The preflakes are then
coated with the remaining layer or layers in a sequential
encapsulation process to form a plurality of pigment flakes. A
similar process is disclosed in further detail in copending U.S.
application Ser. No. 09/512,116, filed on Feb. 24, 2000, the
disclosure of which is incorporated by reference herein.
[0061] In another fabrication method, magnetic particles can be
coated in a sequential encapsulation process to form a plurality of
pigment flakes. When an encapsulation process is used for forming
the outer layers of the flakes, it will be appreciated that each
respective encapsulating layer is a continuous layer composed of
one material and having substantially the same thickness around the
flake structure. In some embodiments of the invention, the
encapsulating layer can be a colored dielectric material or an
organic layer with added colorant.
[0062] Referring now to the drawings, wherein like structures are
provided with like reference designations, the drawings only show
the structures necessary to understand the present invention. FIG.
1 depicts a reflective magnetic flake ("RMF") 20 according to one
embodiment of the invention. The RMF 20 is a three layer design
having a generally symmetrical thin film structure with a central
magnetic layer 22 and at least one reflector layer on either or
both of the opposing major surfaces of the central magnetic layer.
Thus, RMF 20 comprises a magnetic layer interdisposed between a
reflector layer 24 and an opposing reflector layer 26. By inserting
the magnetic layer between the highly reflective reflector layers,
such as aluminum, the optical properties of the reflector layers
are not degraded and the flake remains highly reflective. The RMF
20 can be used as a pigment flake or can be used as a core section
with additional layers applied thereover such as in a color
shifting pigment. In the case of color shifting pigments,
maintaining the high reflective layer is extremely important to
preserve high brightness and chroma. Each of these layers in the
coating structure of RMF 20 is discussed below in greater
detail.
[0063] The magnetic layer 22 can be formed of any magnetic material
such as nickel, cobalt, iron, gadolinium, terbium, dysprosium,
erbium, and their alloys or oxides. For example, a cobalt nickel
alloy can be employed, with the cobalt and nickel having a ratio by
weight of about 80% and about 20%, respectively. This ratio for
each of these metals in the cobalt nickel alloy can be varied by
plus or minus about 10% and still achieve the desired results.
Thus, cobalt can be present in the alloy in an amount from about
70% to about 90% by weight, and nickel can be present in the alloy
in an amount from about 10% to about 30% by weight. Other examples
of alloys include Fe/Si, Fe/Ni, FeCo, Fe/Ni/Mo, and combinations
thereof. Hard magnetics of the type SmCo.sub.5, NdCo.sub.5,
Sm.sub.2Co.sub.17, Nd.sub.2Fe.sub.14B, Sr.sub.6Fe.sub.2O.sub.3,
TbFe.sub.2, Al--Ni--Co, and combinations thereof, can also be used
as well as spinel ferrites of the type Fe.sub.3O.sub.4,
NiFe.sub.2O.sub.4, MnFe.sub.2O.sub.4, CoFe.sub.2O.sub.4, or garnets
of the type YIG or GdIG, and combinations thereof. The magnetic
material may be selected for its reflecting or absorbing properties
as well as its magnetic properties. When utilized to function as a
reflector, the magnetic material is deposited to a thickness so
that it is substantially opaque. When utilized as an absorber, the
magnetic material is deposited to a thickness so that it is not
substantially opaque. A typical thickness for the magnetic material
when utilized as an absorber is from about 2 nm to about 20 nm.
[0064] Although this broad range of magnetic materials can be used,
the "soft" magnets are preferred in some embodiments of the
invention. As used herein, the term "soft magnets" refers to any
material exhibiting ferromagnetic properties but having a remanence
that is substantially zero after exposure to a magnetic force. Soft
magnets show a quick response to an applied magnetic field, but
have very low (coercive fields (Hc)=0.05-300 Oersteds (Oe)) or zero
magnetic signatures, or retain very low magnetic lines of force
after the magnetic field is removed. Similarly, as used herein, the
term "hard magnets" (also called permanent magnets) refers to any
material that exhibits ferromagnetic properties and that has a long
lasting remanence after exposure to a magnetizing force. A
ferromagnetic material is any material that has a permeability
substantially greater than 1 and that exhibits magnetic hysteresis
properties.
[0065] Preferably, the magnetic materials used to form magnetic
layers in the flakes and foils of the invention have a coercivity
of less than about 2000 Oe, more preferably less than about 300 Oe.
Coercivity refers to the ability of a material to be demagnetized
by an external magnetic field. The higher the value of coercivity,
the higher the magnetic field required to de-magnetize the material
after the field is removed. In some embodiments of the invention,
the magnetic layers used are preferably "soft" magnetic materials
(easily demagnetized), as opposed to "hard" magnetic materials
(difficult to demagnetize) which have higher coercivities. The
coercivities of the foils, pigments or colorants of the magnetic
color shifting designs according to the invention are preferably in
a range of about 50 Oe to about 300 Oe. These coercivities are
lower than in standard recording materials. Thus, preferred
embodiments of the invention which use soft magnets in magnetic
color shifting pigments and magnetic non color shifting pigments
are an improvement over conventional technologies. The use of soft
magnetic materials in pigment flakes allows for easier dispersion
of the flakes without clumping.
[0066] The magnetic layer 22 can be formed to have a suitable
physical thickness of from about 200 angstroms (.ANG.) to about
10,000 .ANG., and preferably from about 500 .ANG. to about 1,500
.ANG.. However, it will be appreciated by those skilled in the art,
in view of the disclosure herein, that the optimal magnetic
thickness will vary depending on the particular magnetic material
used and the purpose for its use. For example, a magnetic absorber
layer will be thinner than a magnetic reflector layer based on the
optical requirements for such layers, while a covert magnetic layer
will have a thickness based solely on its magnetic properties.
[0067] The reflector layers 24 and 26 can be composed of various
reflective materials. Presently preferred materials are one or more
metals, one or more metal alloys, or combinations thereof, because
of their high reflectivity and ease of use, although non-metallic
reflective materials could also be used. Nonlimiting examples of
suitable metallic materials for the reflector layers include
aluminum, silver, copper, gold, platinum, tin, titanium, palladium,
nickel, cobalt, rhodium, niobium, chromium, and combinations or
alloys thereof. These can be selected based on the f desired. The
reflector layers 24, 26 can be formed to have a suitable physical
thickness of from about 400 .ANG. to about 2,000 .ANG., and
preferably from about 500 .ANG. to about 1,000 .ANG..
[0068] In an alternative embodiment, opposing dielectric layers may
optionally be added to overlie reflector layers 24 and 26. These
opposing dielectric layers add durability, rigidity, and corrosion
resistance to RMF 20. Alternatively, an encapsulating dielectric
layer may be formed to substantially surround reflector layers 24,
26 and magnetic layer 22. The dielectric layer(s) may be optionally
clear, or may be selectively absorbing so as to contribute to the
color effect of the pigment flake. Examples of suitable dielectric
materials for the dielectric layers are described hereafter.
[0069] FIG. 2 depicts a magnetic color shifting pigment flake 40
based upon a RMF according to one embodiment of the invention. The
flake 40 is a generally symmetrical multilayer thin film structure
having layers on opposing sides of a RMF 42. Thus, first and second
dielectric layers 44 and 46 are disposed respectively on opposing
sides of RMF 42, and first and second absorber layers 48 and 50 are
disposed respectively on each of dielectric layers 44 and 46. The
RMF is as discussed hereinabove for FIG. 1 while the dielectric and
absorber layers are discussed below in greater detail.
[0070] The dielectric layers 44 and 46 act as spacers in the thin
film stack structure of flake 40. These layers are formed to have
an effective optical thickness for imparting interference color and
desired color shifting properties. The dielectric layers may be
optionally clear, or may be selectively absorbing so as to
contribute to the color effect of a pigment. The optical thickness
is a well known optical parameter defined as the product .eta.d,
where .eta. is the refractive index of the layer and d is the
physical thickness of the layer. Typically, the optical thickness
of a layer is expressed in terms of a quarter wave optical
thickness (QWOT) that is equal to 4.eta.d/.lambda., where .lambda.
is the wavelength at which a QWOT condition occurs. The optical
thickness of dielectric layers can range from about 2 QWOT at a
design wavelength of about 400 nm to about 9 QWOT at a design
wavelength of about 700 nm, and preferably 2-6 QWOT at 400-700 nm,
depending upon the color shift desired. The dielectric layers
typically have a physical thickness of about 100 nm to about 800
nm, depending on the color characteristics desired.
[0071] Suitable materials for dielectric layers 44 and 46 include
those having a "high"index of refraction, defined herein as greater
than about 1.65, as well as those have a "low" index of refraction,
which is defined herein as about 1.65 or less. Each of the
dielectric layers can be formed of a single material or with a
variety of material combinations and configurations. For example,
the dielectric layers can be formed of only a low index material or
only a high index material, a mixture or multiple sublayers of two
or more low index materials, a mixture or multiple sublayers of two
or more high index materials, or a mixture or multiple sublayers of
low index and high index materials. In addition, the dielectric
layers can be formed partially or entirely of high/low dielectric
optical stacks, which are discussed in further detail below. When a
dielectric layer is formed partially with a dielectric optical
stack, the remaining portion of the dielectric layer can be formed
with a single material or various material combinations and
configurations as described above.
[0072] Examples of suitable high refractive index materials for the
dielectric layer include zinc sulfide (ZnS), zinc oxide (ZnO),
zirconium oxide (ZrO.sub.2), titanium dioxide (TiO.sub.2),
diamond-like carbon, indium oxide (In.sub.2O.sub.3),
indium-tin-oxide (ITO), tantalum pentoxide (Ta2O5), ceric oxide
(CeO.sub.2), yttrium oxide (Y.sub.2O.sub.3), europium oxide
(Eu.sub.2O.sub.3), iron oxides such as (II)diiron(III) oxide
(Fe.sub.3O.sub.4) and ferric oxide (Fe.sub.2O.sub.3), hafnium
nitride (HfN), hafnium carbide (HfC), hafnium oxide (HfO.sub.2),
lanthanum oxide (La.sub.2O.sub.3), magnesium oxide (MgO), neodymium
oxide (Nd.sub.2O.sub.3), praseodymium oxide (Pr.sub.6O.sub.11),
samarium oxide (Sm.sub.2O.sub.3), antimony trioxide
(Sb.sub.2O.sub.3), silicon monoxide (SiO), selenium trioxide
(Se.sub.2O.sub.3), tin oxide (SnO.sub.2), tungsten trioxide
(WO.sub.3), combinations thereof, and the like.
[0073] Suitable low refractive index materials for the dielectric
layer include silicon dioxide (SiO.sub.2), aluminum oxide
(Al.sub.2O.sub.3), metal fluorides such as magnesium fluoride
(MgF.sub.2), aluminum fluoride (AlF.sub.3), cerium fluoride
(CeF.sub.3), lanthanum fluoride (LaF.sub.3), sodium aluminum
fluorides (e.g., Na.sub.3AlF.sub.6 or Na.sub.5Al.sub.3Fl.sub.4),
neodymium fluoride (NdF.sub.3), samarium fluoride (SmF.sub.3),
barium fluoride (BaF.sub.2), calcium fluoride (CaF.sub.2), lithium
fluoride (LiF), combinations thereof, or any other low index
material having an index of refraction of about 1.65 or less. For
example, organic monomers and polymers can be utilized as low index
materials, including dienes or alkenes such as acrylates (e.g.,
methacrylate), perfluoroalkenes, polytetrafluoroethylene (Teflon),
fluorinated ethylene propylene (FEP), combinations thereof, and the
like.
[0074] It should be appreciated that several of the above-listed
dielectric materials are typically present in non-stoichiometric
forms, often depending upon the specific method used to deposit the
dielectric material as a coating layer, and that the above-listed
compound names indicate the approximate stoichiometry. For example,
silicon monoxide and silicon dioxide have nominal 1:1 and 1:2
silicon:oxygen ratios, respectively, but the actual silicon:oxygen
ratio of a particular dielectric coating layer varies somewhat from
these nominal values. Such non-stoichiometric dielectric materials
are also within the scope of the present invention.
[0075] As mentioned above, the dielectric layers can be formed of
high/low dielectric optical stacks, which have alternating layers
of low index (L) and high index (H) materials. When a dielectric
layer is formed of a high/low dielectric stack, the color shift at
angle will depend on the combined refractive index of the layers in
the stack. Examples of suitable stack configurations for the
dielectric layers include LH, HL, LHL, HLH, HLHL, LHLH, or in
general (LHL).sup.n or (HLH).sup.n, where n=1-100, as well as
various multiples and combinations thereof. In these stacks, LH,
for example, indicates discrete layers of a low index material and
a high index material. In an alternative embodiment, the high/low
dielectric stacks are formed with a gradient index of refraction.
For example, the stack can be formed with layers having a graded
index low-to-high, a graded index high-to-low, a graded index
[low-to-high-to-low].sup.n, a graded index
[high-tolow-to-high].sup.n, where n=1-100, as well as combinations
and multiples thereof. The graded index is produced by a gradual
variance in the refractive index, such as low-to-high index or
high-to-low index, of adjacent layers. The graded index of the
layers can be produced by changing gases during deposition or
co-depositing two materials (e.g., L and H) in differing
proportions. Various high/low optical stacks can be used to enhance
color shifting performance, provide antireflective properties to
the dielectric layer, and change the possible color space of the
pigments of the invention.
[0076] The dielectric layers can each be composed of the same
material or a different material, and can have the same or
different optical or physical thickness for each layer. It will be
appreciated that when the dielectric layers are composed of
different materials or have different thicknesses, the flakes
exhibit different colors on each side thereof and the resulting mix
of flakes in a pigment or paint mixture would show a new color
which is the combination of the two colors. The resulting color
would be based on additive color theory of the two colors coming
from the two sides of the flakes. In a multiplicity of flakes, the
resulting color would be the additive sum of the two colors
resulting from the random distribution of flakes having different
sides oriented toward the observer.
[0077] The absorber layers 48, 50 of flake 40 can be composed of
any absorber material having the desired absorption properties,
including materials that are uniformly absorbing or non-uniformly
absorbing in the visible part of the electromagnetic spectrum.
Thus, selective absorbing materials or nonselective absorbing
materials can be used, depending on the color characteristics
desired. For example, the absorber layers can be formed of
nonselective absorbing metallic materials deposited to a thickness
at which the absorber layer is at least partially absorbing, or
semi-opaque. Nonlimiting examples of suitable absorber materials
include metallic absorbers such as chromium, aluminum, nickel,
silver, copper, palladium, platinum, titanium, vanadium, cobalt,
iron, tin, tungsten, molybdenum, rhodium, and niobium, as well as
their corresponding oxides, sulfides, and carbides. Other suitable
absorber materials include carbon, graphite, silicon, germanium,
cermet, ferric oxide or other metal oxides, metals mixed in a
dielectric matrix, and other substances that are capable of acting
as a uniform or selective absorber in the visible spectrum. Various
combinations, mixtures, compounds, or alloys of the above absorber
materials may be used to form the absorber layers of flake 40.
[0078] Examples of suitable alloys of the above absorber materials
include Inconel (Ni--Cr--Fe), stainless steels, Hastalloys (e.g.,
Ni--Mo--Fe; Ni--Mo--Fe--Cr; Ni--Si--Cu) and titanium-based alloys,
such as titanium mixed with carbon (Ti/C), titanium mixed with
tungsten (Ti/W), titanium mixed with niobium (Ti/Nb), and titanium
mixed with silicon (Ti/Si), and combinations thereof. As mentioned
above, the absorber layers can also be composed of an absorbing
metal oxide, metal sulfide, metal carbide, or combinations thereof.
For example, one preferred absorbing sulfide material is silver
sulfide. Other examples of suitable compounds for the absorber
layers include titanium-based compounds such as titanium nitride
(TiN), titanium oxynitride (TiN.sub.xO.sub.y), titanium carbide
(TiC), titanium nitride carbide (TiN.sub.xC.sub.z), titanium
oxynitride carbide (TiN.sub.xO.sub.yC.sub.z), titanium silicide
(TiSi.sub.2), titanium boride (TiB.sub.2), and combinations
thereof. In the case of TiN.sub.xO.sub.y and
TiN.sub.xO.sub.yC.sub.z, preferably x=0 to 1, y=0 to 1, and z=0 to
1, where x+y=1 in TiN.sub.xO.sub.y and x+y+z=1 in
TiN.sub.xO.sub.yC. For TiN.sub.xC.sub.z, preferably x=0 to 1 and
z=0 to 1, where x+z=1. Alternatively, the absorber layers can be
composed of a titanium-based alloy disposed in a matrix of Ti, or
can be composed of Ti disposed in a matrix of a titanium-based
alloy.
[0079] It will be appreciated by one skilled in the art that the
absorber layer also could be formed of a magnetic material, such as
a cobalt nickel alloy. This simplifies the manufacture of the
magnetic color shifting device or structure by reducing the number
of materials required.
[0080] The absorber layers are formed to have a physical thickness
in the range from about 30 .ANG. to about 500 .ANG., and preferably
about 50 .ANG. to about 150 .ANG., depending upon the optical
constants of the absorber layer material and the desired peak
shift. The absorber layers can each be composed of the same
material or a different material, and can have the same or
different physical thickness for each layer.
[0081] In an alternative embodiment of flake 40, an asymmetrical
color shifting flake can be provided which includes a thin film
stack structure with the same layers as on one side of RMF 42 as
shown in FIG. 2. Accordingly, the asymmetrical color shifting flake
includes RMF 42, dielectric layer 44 overlying RMF 42, and absorber
layer 48 overlying dielectric layer 44. Each of these layers can be
composed of the same materials and have the same thicknesses as
described above for the corresponding layers of flake 40. In
addition, asymmetrical color shifting flakes can be formed by a web
coating process such as described above in which the various layers
are sequentially deposited on a web material to form a thin film
structure, which is subsequently fractured and removed from the web
to form a plurality of flakes.
[0082] In a further alternative embodiment, flake 40 can be formed
without the absorber layers. In this embodiment, opposing
dielectric layers 44 and 46 are formed of high/low (H/L) dielectric
optical stacks such as described previously. Thus, dielectric
layers 44 and 46 can be configured such that flake 40 has the
coating structures: (HL).sup.n/RMF/(LH).sup.n,
(LH).sup.n/RMF/(HL).sup.n, (LHL).sup.n/RMF/(LHL).sup.n,
(HLH).sup.n/RMF/(HLH).sup.n, or other similar configurations, where
n=1-100 and the L and H layers are 1 quarterwave (QW) at a design
wavelength.
[0083] FIG. 3 depicts a reflective magnetic flake or particle
("RMP") 60 according to another embodiment of the invention. The
RMP 60 is a two layer design with a reflector layer 62
substantially surrounding and encapsulating a core magnetic layer
64. By inserting the magnetic layer within the reflector layer, the
optical properties of the reflector layer are not downgraded and
the reflector layer remains highly reflective. The RMP 60 can be
used as a pigment particle or can be used as a core section with
additional layers applied thereover. The magnetic layer and
reflector layer can be composed of the same materials discussed
with respect to RMF 20.
[0084] In an alternative embodiment, a dielectric layer may
optionally be added to overlie reflector layer 62, to add
durability, rigidity, and corrosion resistance to RMP 60. The
dielectric layer may be optionally clear, or may be selectively
absorbing so as to contribute to the color effect of the pigment
flake.
[0085] FIG. 4 depicts alternative coating structures (with phantom
lines) for a magnetic color shifting pigment flake 80 in the form
of an encapsulate based upon either the RMF or the RMP according to
other embodiments of the invention. The flake 80 has a magnetic
core section 82, which is either a RMF or a RMP, which can be
overcoated by an encapsulating dielectric layer 84 substantially
surrounding magnetic core section 82. An absorber layer 86, which
overcoats dielectric layer 84, provides an outer encapsulation of
flake 80. The hemispherical dashed lines on one side of flake 80 in
FIG. 4 indicate that dielectric layer 84 and absorber layer 86 can
be formed as contiguous layers around magnetic core section 82.
[0086] Alternatively, the magnetic core section 82 and dielectric
layer can be in the form of a thin film core flake stack, in which
opposing dielectric layers 84a and 84b are preformed on the top and
bottom surfaces but not on at least one side surface of magnetic
core section 82 (RMF), with absorber layer 86 encapsulating the
thin film stack. An encapsulation process can also be used to form
additional layers on flake 80 such as a capping layer (not shown).
The pigment flake 80 exhibits a discrete color shift such that the
pigment flake has a first color at a first angle of incident light
or viewing and a second color different from the first color at a
second angle of incident light or viewing.
[0087] In a further alternative embodiment, flake 80 can be formed
without the absorber layer. In this embodiment, dielectric layer 84
is formed of contiguous high/low (H/L) dielectric optical coatings
similar to the dielectric optical stacks described previously.
Thus, dielectric layer 84 can have the coating structure
(HL).sup.n, (LH).sup.n, (LHL).sup.n, (HLH).sup.n, or other similar
configurations, where n=1-100 and the L and H layers are 1 QW at a
design wavelength.
[0088] FIG. 5 depicts another alternative coating structure for a
color shifting pigment flake 100 according to the present
invention. The flake 100 includes a magnetic core section 82 and a
single dielectric layer 84, which extends over top and bottom
surfaces of magnetic core section 82 to form a dielectric-coated
preflake 86. The core section 82 can be an RMF, RMP, or a magnetic
layer. The dielectric-coated preflake 86 has two side surfaces 88
and 90. Although side surface 90 is homogeneous and formed only of
the dielectric material of dielectric layer 84, side surface 88 has
distinct surface regions 88a, 88b, 88c of dielectric, magnetic core
section, and dielectric, respectively. The dielectric-coated
preflake 86 is further coated on all sides with an absorber layer
92. The absorber layer 92 is in contact with dielectric layer 84
and magnetic core section 82 at side surface 88.
[0089] The structure of pigment flake 100 typically occurs because
of a preflake coating process similar to the one disclosed in U.S.
application Ser. No. 09/512,116 described previously. The preflakes
can be a dielectric-coated flake, in which a dielectric coating
completely encapsulates an RMF or RMP (see FIG. 4), or a magnetic
layer (see FIG. 10). The preflakes are broken into sized preflakes
using any conventional fragmentation process, such as by grinding.
The sized preflakes will include some sized preflakes having top
and bottom dielectric layers with no dielectric coating on the side
surfaces of the preflake, such as shown for the embodiment of flake
40 in FIG. 2 in which RMF 42 is coated with top and bottom
dielectric layers 44 and 46. Other sized preflakes will have a
single dielectric layer extending over both top and bottom surfaces
of the magnetic core flake section, leaving one side surface of the
magnetic core flake section exposed, such as shown for
dielectric-coated preflake 86 in FIG. 5. Because of the
fragmentation process, substantially all of the sized preflakes
have at least a portion of a side surface exposed. The sized
preflakes are then coated on all sides with an absorber layer, such
as shown in the flakes of FIGS. 4 and 5.
[0090] FIG. 6 depicts a composite magnetic flake ("CMF") 120 which
comprises a central dielectric support layer 122 with first and
second magnetic layers 124, 126 on opposing major surfaces thereof.
By inserting the dielectric layer between the magnetic layers, the
CMF 120 is significantly stabilized and strengthened, having
increased rigidity. Additional dielectric layers (not shown) may
optionally be added to overlie magnetic layers 124, 126. These
additional dielectric layers add durability, rigidity, and
corrosion resistance to CMF 120. The CMF 120 can be used as a
pigment flake by itself or can be used as a magnetic core section
with additional layers applied thereover. The magnetic layers 124,
126 can be formed of any of the magnetic materials described
previously.
[0091] The dielectric material used for support layer 122 is
preferably inorganic, since inorganic dielectric materials have
been found to have good characteristics of brittleness and
rigidity. Various dielectric materials that can be utilized include
metal fluorides, metal oxides, metal sulfides, metal nitrides,
metal carbides, combinations thereof, and the like. The dielectric
materials may be in either a crystalline, amorphous, or
semicrystalline state. These materials are readily available and
easily applied by physical or chemical vapor deposition processes.
Examples of suitable dielectric materials include magnesium
fluoride, silicon monoxide, silicon dioxide, aluminum oxide,
titanium dioxide, tungsten oxide, aluminum nitride, boron nitride,
boron carbide, tungsten carbide, titanium carbide, titanium
nitride, silicon nitride, zinc sulfide, glass flakes, diamond-like
carbon, combinations thereof, and the like. Alternatively, support
layer 122 may be composed of a preformed dielectric or ceramic
preflake material having a high aspect ratio such as a natural
platelet mineral (e.g., mica peroskovite or talc), or synthetic
platelets formed from glass, alumina, silicon dioxide, carbon,
micaeous iron oxide, coated mica, boron nitride, boron carbide,
graphite, bismuth oxychloride, various combinations thereof, and
the like.
[0092] In an alternative embodiment, instead of a dielectric
support layer 122, various semiconductive and conductive materials
having a sufficient ratio of tensile to compressive strength can
function as a support layer. Examples of such materials include
silicon, metal siicides, semiconductive compounds formed from any
of the group III, IV, or V elements, metals having a body centered
cubic crystal structure, cermet compositions or compounds,
semiconductive glasses, various combinations thereof, and the like.
It will be appreciated from the teachings herein, however, that any
support material providing the functionality described herein and
capable of acting as a rigid layer with glass-like qualities would
be an acceptable substitute for one of these materials.
[0093] The thickness of support layer 122 can be in a range from
about 10 nm to about 1,000 nm, preferably from about 50 nm to about
200 nm, although these ranges should not be taken as
restrictive.
[0094] FIG. 7 depicts a composite magnetic particle ("CMP") 140
according to another embodiment of the invention. The CMP 140 is a
two layer design with a magnetic layer 142 substantially
surrounding and encapsulating a central support layer 144 such as a
dielectric layer. By inserting the support layer within the
magnetic layer, CMP 140 is significantly stabilized and rigid. The
support layer adds rigidity and durability to the pigment flake.
The magnetic layer 142 can be formed of any of the magnetic
materials described previously. The support layer 144 can be formed
of the same materials described hereinabove for support layer 122
of CMF 120. The CMP 140 can be used as a pigment particle by itself
or can be used as a magnetic core section with additional layers
applied thereover. For example, an outer dielectric layer may be
added to overlie and encapsulate magnetic layer 142. This outer
dielectric layer adds durability, rigidity, and corrosion
resistance to CMP 140.
[0095] FIG. 8 depicts a coating structure for a color shifting
pigment flake 160 in the form of an encapsulate. The flake 160 has
a thin core layer 162, which can be formed of a dielectric or other
material as taught hereinabove for support layer 122. The core
layer 162 is overcoated on all sides with a magnetic layer 164,
which can be composed of the same materials as described above for
magnetic layer 22 of RMF 20. Optionally, a reflector layer 168 can
be applied over magnetic layer 164. Suitable materials for
reflector layer 168 include those materials described for reflector
layer 24 of RMF 20. The reflector layer effectively provides the
reflective function of flake 160, shielding magnetic layer 164 from
being optically present. The core layer 162 and magnetic layer 164
can be provided as a CMP 166 which is overcoated with the other
layers. Alternatively CMP 166 can be replaced with a CMF such as
shown in FIG. 6. An encapsulating dielectric layer 170
substantially surrounds reflector layer 168 and magnetic layer 164.
An absorber layer 172, which overlays dielectric layer 170,
provides an outer encapsulation of flake 160.
[0096] Various coating processes can be utilized in forming the
dielectric and absorber coating layers by encapsulation. For
example, suitable preferred methods for forming the dielectric
layer include vacuum vapor deposition, sol-gel hydrolysis, CVD in a
fluidized bed, downstream plasma onto vibrating trays filled with
particles, and electrochemical deposition. A suitable SiO.sub.2
sol-gel process is described in U.S. Pat. No. 5,858,078 to Andes et
al., the disclosure of which is incorporated by reference herein.
Other examples of suitable sol-gel coating techniques useful in the
present invention are disclosed in U.S. Pat. No. 4,756,771 to
Brodalla; Zink et al., Optical Probes and Properties of
Aluminosilicate Glasses Prepared by the Sol-Gel Method, Polym.
Mater. Sci. Eng., 61, pp. 204-208 (1989); and McKiernan et al.,
Luminescence and Laser Action of Coumarin Dyes Doped in Silicate
and Aluminosilicate Glasses Prepared by the Sol-Gel Technique, J.
Inorg. Organomet. Polym., 1(1), pp. 87-103 (1991); with the
disclosures of each of these incorporated by reference herein.
[0097] Suitable preferred methods for forming the absorber layers
include vacuum vapor deposition, and sputtering onto a mechanically
vibrating bed of particles, as disclosed in commonly assigned
copending patent application Ser. No. 09/389,962, filed Sep. 3,
1999, entitled "Methods and Apparatus for Producing Enhanced
Interference Pigments," which is incorporated by reference herein
in its entirety. Alternatively, the absorber coating may be
deposited by decomposition through pyrolysis of metal-organo
compounds or related CVD processes which may be carried out in a
fluidized bed as described in U.S. Pat. Nos. 5,364,467 and
5,763,086 to Schmid et al., the disclosures of which are
incorporated by reference herein. If no further grinding is carried
out, these methods result in an encapsulated core flake section
with dielectric and absorber materials therearound. Various
combinations of the above coating processes may be utilized during
manufacture of pigment flakes with multiple encapsulating
coatings.
[0098] In one method of forming the absorber coating, powdered
flakes or other coated preflakes are placed on a square-shaped
vibrating conveyor coater in a vacuum coating chamber as disclosed
in U.S. application Ser. No. 09/389,962, discussed above. The
vibrating conveyor coater includes conveyor trays which are
configured in an overlapping inclined arrangement so that the
powdered flakes travel along a circulating path within the vacuum
chamber. While the flakes circulate along this path they are
effectively mixed by constant agitation so that exposure to the
vaporized absorber coating material is uniform. Efficient mixing
also occurs at the end of each conveyor tray as the flakes drop in
a waterfall off of one tray and onto the next tray. The absorber
can be sequentially coated on the flakes as they repeatably move
under a coating material source.
[0099] When using vibrating conveyer trays to coat the absorber, it
is important that the powdered flakes tumble randomly under the
coating material source such as sputter targets and do not become
subject to "metal welding" or sticking. Such metal welding or
sticking can occur between two flat surfaces of reactive metals
when such metals are deposited in a vacuum. For example, aluminum
has a high propensity to stick to itself, whereas chromium does
not. Suitable absorber materials can be applied as either a single
material or as an outer capping layer over an underlying different
absorber material.
[0100] FIG. 9 depicts a dielectric coated magnetic flake ("DMF")
180 according to a further embodiment of the invention. The DMF 180
is a three layer design having a generally symmetrical thin film
structure with a central magnetic layer and at least one dielectric
layer on either or both of the opposing major surfaces of the
central magnetic layer. Thus, as shown, DMF 180 includes a magnetic
layer 182 sandwiched in between a dielectric layer 184 and an
opposing dielectric layer 186. By inserting the magnetic layer
between the dielectric layers, the DMF has increased rigidity and
durability.
[0101] FIG. 10 depicts a dielectric coated magnetic particle
("DMP") 200 according to another embodiment of the invention. The
DMP 200 is a two layer design with a dielectric layer 202
substantially surrounding and encapsulating a central magnetic
layer 204.
[0102] Each of the layers in the coating structures of DMF 180 and
DMP 200 can be formed of the same materials and thickness as
corresponding layers described in previous embodiments. For
example, the dielectric layer in DMF 180 and DMP 200 can be formed
of the same materials and in the same thickness ranges as taught
hereinabove for dielectric layer 44 of flake 40, and the magnetic
layers in DMF 180 and DMP 200 can be formed of the same materials
and in the same thickness ranges as taught hereinabove for magnetic
layer 22 of flake 20. The DMF 180 and DMP 200 can each be used as a
pigment flake or particle, or can be used as a magnetic core
section with additional layers applied thereover. FIG. 11 depicts a
color shifting pigment flake 220 according to another embodiment of
the invention which does not use a reflector (with high
reflectance, i.e., an optical metal). The flake 220 is a
three-layer design having a generally symmetrical multilayer thin
film structure on opposing sides of a magnetic core section 222,
which can be a DMF or a DMP. Thus, first and second absorber layers
224a and 224b are formed on opposing major surfaces of magnetic
core section 222. These layers of flake 220 can be formed by a web
coating and flake removal process as described previously.
[0103] FIG. 11 further depicts an alternative coating structure
(with phantom lines) for color shifting flake 220, in which the
absorber layer is coated around magnetic core section 222 in an
encapsulation process. Accordingly, absorber layers 224a and 224b
are formed as part of a continuous coating layer 224 substantially
surrounding the flake structure thereunder.
[0104] Thus, pigment flake 220 may be embodied either as a
multilayer thin film stack flake or a multilayer thin film
encapsulated particle. Suitable materials and thicknesses for the
absorber, dielectric, and magnetic layers of flake 220 are the same
as taught hereinabove.
[0105] Some flakes of the invention can be characterized as
multilayer thin film interference structures in which layers lie in
parallel planes such that the flakes have first and second parallel
planar outer surfaces and an edge thickness perpendicular to the
first and second parallel planar outer surfaces. Such flakes are
produced to have an aspect ratio of at least about 2:1, and
preferably about 5-15:1 with a narrow particle size distribution.
The aspect ratio of the flakes is ascertained by taking the ratio
of the longest planar dimension of the first and second outer
surfaces to the edge thickness dimension of the flakes.
[0106] One presently preferred method of fabricating a plurality of
pigment flakes, each of which having the multilayer thin film
coating structure of flake 40 shown in FIG. 2, is based on
conventional web coating techniques used to make optical thin
films. Although flake 40 is described hereinbelow, the other flake
structures taught herein can also be fabricated with a procedure
similar to the one described hereinbelow. Accordingly, a first
absorber layer is deposited on a web of flexible material such as
polyethylene terephthalate (PET) which has an optional release
layer thereon. The absorber layer can be formed by a conventional
deposition process such as PVD, CVD, PECVD, sputtering, or the
like. The above mentioned deposition methods enable the formation
of a discrete and uniform absorber layer of a desired
thickness.
[0107] Next, a first dielectric layer is deposited on the absorber
layer to a desired optical thickness by a conventional deposition
process. The deposition of the dielectric layer can be accomplished
by a vapor deposition process (e.g., PVD, CVD, PECVD), which
results in the dielectric layer cracking under the stresses imposed
as the dielectric transitions from the vapor into the solid
phase.
[0108] The magnetic core is then deposited. In the case of
reflector layers, a first 1 reflector layer is then deposited by
PVD, CVD, or PECVD on the first dielectric layer, taking on the
characteristics of the underlying cracked dielectric layer.
Magnetic layers are then applied by e-beam evaporation, sputtering,
electrodeposition, or CVD, followed by a second reflector layer
being deposited.
[0109] This is followed by a second dielectric layer being
deposited on the second reflector layer and preferably having the
same optical thickness as the first dielectric layer. Finally, a
second absorber layer is deposited on the second dielectric layer
and preferably has the same physical thickness as the first
absorber layer.
[0110] Thereafter, the flexible web is removed, either by
dissolution in a preselected liquid or by way of a release layer,
both of which are well known to those skilled in the art. As a
result, a plurality of flakes are fractured out along the cracks of
the layers during removal of the web from the multilayer thin film.
This method of manufacturing pigment flakes is similar to that more
fully described in U.S. Pat. No. 5,135,812 to Phillips et al., the
disclosure of which is incorporated by reference herein. The
pigment flakes can be further fragmented if desired by, for
example, grinding the flakes to a desired size using an air grind,
such that each of the pigment flakes has a dimension on any surface
thereof ranging from about 2 microns to about 200 microns.
[0111] In order to impart additional durability to the color
shifting flakes, an annealing process can be employed to heat treat
the flakes at a temperature ranging from about 200-300.degree. C.,
and preferably from about 250-275.degree. C., for a time period
ranging from about 10 minutes to about 24 hours, and preferably a
time period of about 15-60 minutes.
[0112] Other pigment flake structures, methods of forming them, and
additional features compatible therewith can be found in Phillips
'648, U.S. Pat. No. 4,705,356 to Berning et al., and U.S. Pat. No.
6,157,489 to Bradley et al.; U.S. Patent Application Nos.
09/685,468 to Phillips et al, 09/715,937 to Coombs et al.,
09/715,934 to Mayer et al., 09/389,962 to Phillips et al., and
09/539,695 to Phillips et al., the disclosures of which are each
incorporated herein by reference. One skilled in the art will
recognize, in light of the disclosure herein, that the magnetic
layers discussed previously can be combined with the coating
structures disclosed in the above patents and applications, such as
by replacing a reflector layer with the RMF or RMP disclosed herein
to obtain additional useful coating structures.
[0113] Referring now to FIG. 12, pigment flake 240 is deposited
according to another embodiment of the invention. As illustrated,
flake 240 is a multilayer design having a generally symmetrical
thin film structure on opposing sides of a magnetic layer such as a
reflective magnetic core 242, which can be any non-color shifting
magnetic pigment flake or particle having reflective properties
described herein or known in the art. For example, reflective
magnetic core 242 can be a single reflective magnetic layer such as
a monolithic layer of Ni or other magnetic reflective metal, or can
be a multilayer magnetic structure such as Al/Fe/Al. A first
colored layer such as selective absorber layer 244a and a second
colored layer such as selective absorber layer 244b are formed on
opposing major surfaces of reflective magnetic core 242. These
colored layers of flake 240 can be formed by a web coating and
flake removal process as described previously.
[0114] FIG. 12 further depicts an alternative coating structure
(with phantom lines) for flake 240, in which a colored layer such
as selective absorber layer 244 is coated around reflective
magnetic core 242 in an encapsulation process. Accordingly,
selective absorber layers 244a and 244b are formed as part of a
contiguous coating layer 244 substantially surrounding the flake
structure thereunder. Suitable encapsulation methods for forming
flake 240 are as described in a copending U.S. Application Serial
No. 09/626,041, filed Jul. 27, 2000, the disclosure of which is
incorporated by reference herein. Thus, pigment flake 240 may be
embodied either as a multilayer thin film stack flake or a
multilayer thin film encapsulated particle. Suitable materials and
thicknesses for use in the reflective magnetic core of flake 240
are the same as taught hereinabove, so long as both reflective and
magnetic properties are maintained.
[0115] The colored layers of flake 240 can be formed of a variety
of different absorbing and/or reflecting materials in one or more
layers. Preferably, the colored layers such as selective absorber
layers are formed to have a thickness of from about 0.05 .mu.m to
about 5 110 .mu.m, and more preferably from about 1 .mu.m to about
2 .mu.m, by conventional coating processes for dye stuffs, when an
organic dye material is utilized to form the selective absorber
layers. Preferably, the colored layers are formed to have a
thickness of from about 0.05 .mu.m to about 0.10 .mu.m when colored
metallics or other inorganic colorant materials are utilized.
[0116] Examples of suitable organic dyes that can be used to form
the selective absorber layers of flake 240 include copper
phthalocyanine, perylene-based dyes, anthraquinone17 based dyes,
and the like; azo dyes and azo metal dyes such as aluminum red
(RLW), aluminum copper, aluminum bordeaux (RL), aluminum fire-red
(ML), aluminum red (GLW), aluminum violet (CLW), and the like; as
well as combinations or mixtures thereof. Such dyes can be applied
by conventional coating techniques and even by evaporation.
[0117] The colored layers of flake 240 can also be formed of a
variety of conventional organic or inorganic pigments applied
singly or dispersed in a pigment vehicle. Such pigments are
described in the NPIRI Raw Materials Data Handbook, Vol. 4,
Pigments (1983), the disclosure of which is incorporated by
reference herein.
[0118] In another embodiment, the selective absorber layers of
flake 240 comprise a solgel matrix holding a colored pigment or
dye. For example, the selective absorber layer can be formed of
aluminum oxide or silicon dioxide applied by a sol-gel process,
with organic dyes absorbed into pores of the sol-gel coating or
bound to the surface of the coating. Suitable organic dyes used in
the sol-gel coating process include those available under the trade
designations Aluminiumrot GLW (aluminum red GLW) and
Aluminiumviolett CLW (aluminum violet CLW) from the Sandoz Company.
Aluminum red GLW is an azo metal complex containing copper, and
aluminum violet CLW is a purely organic azo dye. Examples of
sol-gel coating techniques useful in the present invention are
disclosed in the following: U.S. Pat. No. 4,756,771 to Brodalla
(1988); Zink et al., Optical Probes and Properties of
Aluminosilicate Glasses Prepared by the SolGel Method, Polym.
Mater. Sci. Eng., 61, pp. 204-208 (1989); and McKieman et al.,
Luminescence and Laser Action of Coumarin Dyes Doped in Silicate
and Aluminosilicate Glasses Prepared by the Sol-Gel Technique, J.
Inorg. Organomet. Polym., 1(1), pp. 87-103 (1991); the disclosures
of all of these are incorporated herein by reference.
[0119] In a further embodiment, the colored layers of flake 240 can
be formed of an inorganic colorant material. Suitable inorganic
colorants include selective absorbers such as titanium nitride,
chromium nitride, chromium oxide, iron oxide, cobalt-doped alumina,
and the like, as well as colored metallics such as copper, brass,
titanium, and the like.
[0120] It should be understood that various combinations of the
above dyes, pigments, and colorants may also be employed to achieve
a desired color characteristic for flake 240. The organic dyes,
pigments, and colorants discussed herein can be used in the
invention to achieve pigments with bright colors having magnetic
properties.
[0121] Various modifications and combinations of the foregoing
embodiments are also considered within the scope of the invention.
For example, additional dielectric, absorber, and/or other optical
coatings can be formed around each of the above flake or particle
embodiments, or on a composite reflective film prior to flake
formation, to yield further desired optical characteristics. Such
additional coatings can provide additional color effects to the
pigments. For example a colored dielectric coating added to a color
shifting flake would act as a color filter on the flake, providing
a subtractive color effect which changes the color produced by the
flake.
[0122] The pigment flakes of the present invention can be
interspersed within a pigment medium to produce a colorant
composition which can be applied to a wide variety of objects or
papers. The pigment flakes added to a medium produces a
predetermined optical response through radiation incident on a
surface of the solidified medium. Preferably, the pigment medium
contains a resin or mixture of resins which can be dried or
hardened by thermal processes such as thermal cross-linking,
thermal setting, or thermal solvent evaporation or by photochemical
cross-linking. Useful pigment media include various polymeric
compositions or organic binders such as alkyd resins, polyester
resins, acrylic resins, polyurethane resins, vinyl resins, epoxies,
styrenes, and the like. Suitable examples of these resins include
melamine, acrylates such as methyl methacrylate, ABS resins, ink
and paint formulations based on alkyd resins, and various mixtures
thereof. The flakes combined with the pigment media produce a
colorant composition that can be used directly as a paint, ink, or
moldable plastic material. The colorant composition can also be
utilized as an additive to conventional paint, ink, or plastic
materials.
[0123] The pigment medium also preferably contains a solvent for
the resin. For the solvent, generally, either an organic solvent or
water can be used. A volatile solvent can also be used in the
medium. As for the volatile solvent, it is preferable to use a
solvent which is both volatile as well as dilutable, such as a
thinner. In particular, faster drying of the pigment medium can be
achieved by increasing the amount of the solvent with a low boiling
point composition such as methyl ethyl ketone (MEK).
[0124] In addition, the flakes can be optionally blended with
various additive materials such as conventional pigment flakes,
particles, or dyes of different hues, chroma and brightness to
achieve the color characteristics desired. For example, the flakes
can be mixed with other conventional pigments, either of the
interference type or noninterference type, to produce a range of
other colors. This preblended composition can then be dispersed
into a polymeric medium such as a paint, ink, plastic or other
polymeric pigment vehicle for use in a conventional manner.
[0125] Examples of suitable additive materials that can be combined
with the flakes of the invention include non-color shifting high
chroma or high reflective platelets which produce unique color
effects, such as MgF.sub.2/Al/MgF.sub.2 platelets, or
SiO.sub.2/Al/SiO.sub.2 platelets. Other suitable additives that can
be mixed with the magnetic color shifting flakes include lamellar
pigments such as multi-layer color shifting flakes, aluminum
flakes, graphite flakes, glass flakes, iron oxide, boron nitride,
mica flakes, interference based TiO.sub.2 coated mica flakes,
interference pigments based on multiple coated plate-like silicatic
substrates, metal-dielectric or all-dielectric interference
pigments, and the like; and non-lamellar pigments such as aluminum
powder, carbon black, ultramarine blue, cobalt based pigments,
organic pigments or dyes, rutile or spinel based inorganic
pigments, naturally occurring pigments, inorganic pigments such as
titanium dioxide, talc, china clay, and the like; as well as
various mixtures thereof. For example, pigments such as aluminum
powder or carbon black can be added to control lightness and other
color properties.
[0126] The magnetic color shifting flakes of the present invention
are particularly suited for use in applications where colorants of
high chroma and durability are desired. By using the magnetic color
shifting flakes in a colorant composition, high chroma durable
paint or ink can be produced in which variable color effects are
noticeable to the human eye. The color shifting flakes of the
invention have a wide range of color shifting properties, including
large shifts in chroma (degree of color purity) and also large
shifts in hue (relative color) with a varying angle of view. Thus,
an object colored with a paint containing the color shifting flakes
of the invention will change color depending upon variations in the
viewing angle or the angle of the object relative to the viewing
eye.
[0127] The pigment flakes of the invention can be easily and
economically utilized in paints and inks which can be applied to
various objects or papers, such as motorized vehicles, currency and
security documents, household appliances, architectural structures,
flooring, fabrics, sporting goods, electronic packaging/housing,
product packaging, etc. The color shifting flakes can also be
utilized in forming colored plastic materials, coating
compositions, extrusions, electrostatic coatings, glass, and
ceramic materials.
[0128] Generally, the foils of the invention have a nonsymmetrical
thin film coating structure, which can correspond to the layer
structures on one side of an RMF in any of the above described
embodiments related to thin film stack flakes. The foils can be
laminated to various objects or can be formed on a carrier
substrate. The foils of the invention can also be used in a hot
stamping configuration where the thin film stack of the foil is
removed from a release layer of a substrate by use of a heat
activated adhesive and applied to a countersurface. The adhesive
can be either coated on a surface of the foil opposite from the
substrate, or can be applied in the form of a UV activated adhesive
to the surface on which the foil will be affixed.
[0129] FIG. 13 depicts a coating structure of a color shifting foil
300 formed on a substrate 302, which can be any suitable material
such as a flexible PET web, carrier substrate, or other plastic
material. A suitable thickness for substrate 302 is, for example,
about 2 to 7 mils. The foil 300 includes a magnetic layer 304 on
substrate 302, a reflector layer 306 on magnetic layer 304, a
dielectric layer 308 on reflector layer 306, and an absorber layer
310 on dielectric layer 308. The magnetic, reflector, dielectric
and absorber layers can be composed of the same materials and can
have the same thicknesses as described above for the corresponding
layers in flakes 20 and 40.
[0130] The foil 300 can be formed by a web coating process, with
the various layers as described above sequentially deposited on a
web by conventional deposition techniques to form a thin film foil
structure. The foil 300 can be formed on a release layer of a web
so that the foil can be subsequently removed and attached to a
surface of an object. The foil 300 can also be formed on a carrier
substrate, which can be a web without a release layer.
[0131] FIG. 14 illustrates one embodiment of a foil 320 disposed on
a web 322 having an optional release layer 324 on which is
deposited a magnetic layer 326, a reflector layer 328, a dielectric
layer 330, and an absorber layer 332. The foil 320 may be utilized
attached to web 322 as a carrier when a release layer is not
employed. Alternatively, foil 320 may be laminated to a transparent
substrate (not shown) via an optional adhesive layer 334, such as a
transparent adhesive or ultraviolet (UV) curable adhesive, when the
release layer is used. The adhesive layer 334 is applied to
absorber layer 332.
[0132] FIG. 15 depicts an alternative embodiment in which a foil
340 having the same thin film layers as foil 320 is disposed on a
web 322 having an optional release layer 324. The foil 340 is
formed such that absorber layer 332 is deposited on web 322. The
foil 340 may be utilized attached to web 322 as a carrier, which is
preferably transparent, when a release layer is not employed. The
foil 340 may also be attached to a substrate such as a
countersurface 342 when the release layer is used, via an adhesive
layer 334 such as a hot stampable adhesive, a pressure sensitive
adhesive, a permanent adhesive, and the like. The adhesive layer
334 can be applied to magnetic layer 326 and/or to countersurface
342.
[0133] When a hot stamp application is employed, the optical stack
of the foil is arranged so that the optically exterior surface is
adjacent the release layer. Thus, for example, when foil 340 in
FIG. 15 is released from web 322, absorber layer 332 is optically
present on the exterior. In one preferred embodiment, release layer
324 is a transparent hardcoat that stays on absorber layer 332 to
protect the underlying layers after transfer from web 322.
[0134] Further details of making and using optical stacks as hot
stamping foils can be found in U.S. Pat. Nos. 5,648,165, 5,002,312,
4,930,866, 4,838,648, 4,779,898, and 4,705,300, the disclosures of
which are incorporated by reference herein.
[0135] Referring now to FIG. 16, another embodiment of the
invention is depicted in the form of an optical article 400 having
paired optical structures. The optical article 400 includes a
substrate 402 having an upper surface 404 and a lower surface 406.
The substrate 402 can be flexible or rigid and can be formed of any
suitable material such as paper, plastic, cardboard, metal, or the
like, and can be opaque or transparent. Non-overlapping paired
first and second coating structures 408, 410 are disposed on upper
surface 404 so as to overlie non-overlapping first and second
regions on surface 404. Thus, first and second coating structures
408, 410 are not superimposed but are physically separated from
each other on surface 404, although in an abutting relationship.
For example, in one embodiment, first coating structure 408 can be
in the form of a rectangle or square and is disposed within a
recess 412 formed by second coating structure 410, also being in
the form of a rectangle or square that forms a border or frame that
surrounds first coating structure 408. Thus, when optical article
400 is viewed from above, coating structures 408, 410 can be viewed
simultaneously.
[0136] The first coating structure 408 has a first pigment 414
formed of magnetic pigment flakes or particles, such as color
shifting magnetic flakes, constructed in the manner hereinbefore
described to provide a magnetic signature. The magnetic properties
of pigment 414 are provided by a non-optically observable
magnetic-layer within one or more of the magnetic flakes or
particles. The second coating structure 410 has a second pigment
416 formed of non-magnetic pigment flakes or particles, such as
color shifting non-magnetic flakes. Alternatively, the second
coating structure 410 could be formed to contain the magnetic
pigments and the first coating structure 408 could be formed to
contain the non-magnetic pigments. The pigments 414, 416 are
dispersed in a solidified liquid pigment vehicle 418, 420 of a
conventional type so that the pigments 414, 416 produce the desired
optical characteristics. For example, the liquid vehicle can be a
conventional ink vehicle or a conventional paint vehicle of a
suitable type.
[0137] In an alternative embodiment, optical article 400 can be
formed by using a suitable magnetic foil structure, such as the
color shifting magnetic foils disclosed hereinabove, in place of
coating structure 408, and by using a non-magnetic foil structure
such as a conventional color shifting foil in place of coating
structure 410. The magnetic properties of the magnetic foil
structure are thus provided by a magnetic layer which is not
optically observable. Non-overlapping paired first and second foil
structures, one magnetic and one non-magnetic, would be disposed on
upper surface 404 of substrate 402 so as to overlie non-overlapping
first and second regions on surface 404.
[0138] Other optical articles with paired optically variable
structures, which could be modified to include magnetic layers in
one of the paired structures such as disclosed herein, are taught
in U.S. Pat. No. 5,766,738 to Phillips et al., the disclosure of
which is incorporated by reference herein. Referring now to FIG.
17, another embodiment of the invention is depicted in the form of
an optical article 450 having overlapping paired optical
structures. The optical article 450 includes a substrate 452 having
an upper surface region 454. The substrate 452 can be formed of the
same materials as described for substrate 402 shown in FIG. 16. A
magnetic pigment coating structure 456 overlies upper surface
region 454 of substrate 452. The magnetic pigment coating structure
456 includes a plurality of multilayer magnetic pigments 458, such
as those described previously, which are dispersed in a solidified
pigment vehicle. The magnetic properties of the pigment coating
structure 456 are provided by a non-optically observable magnetic
layer within each of the multilayer magnetic pigments 458. A
non-magnetic pigment coating structure 460 overlies at least a
portion of magnetic pigment coating structure 456. The non-magnetic
pigment coating structure 460 includes a plurality of non-magnetic
pigments 462 dispersed in a solidified pigment vehicle.
[0139] In an alternative embodiment of optical article 450, a
non-magnetic pigment coating structure can be used in place of
magnetic pigment coating structure 456 overlying upper surface
region 454 of substrate 452. A magnetic pigment coating structure
is then used in place of non-magnetic pigment coating structure
460.
[0140] In a further alternative embodiment, optical article 450 can
be formed by using a suitable magnetic foil structure, such as the
color shifting magnetic foils disclosed hereinabove, in place of
coating structure 456. A non-magnetic foil structure such as a
conventional color shifting foil is then used in place of coating
structure 460. Alternatively, a non-magnetic foil structure can be
used in place of coating structure 456, and a magnetic foil
structure is then used in place of coating structure 460.
[0141] The respective pigment coating or foil structures in optical
articles 400 or 450 can be selected to provide identical coloring
or identical color shifting effects to articles 400 and 450, or can
be selected to provide different colors or different color shifting
effects. Of course, one skilled in the art will recognize that a
variety of combinations of optical features can be used by
selecting appropriate coatings or foils with the desired optical
characteristics to add various security features to optical
articles 400 and 450.
[0142] Although the pigment coating or foil structures used in
articles 400 and 450 may have substantially the same color or color
effects, e.g., the same color shifting effects, only one of the
pigment coating or foil structures in the articles carries a covert
magnetic signature. Therefore, although a human eye cannot detect
the magnetic features of the pigment coating or foil structure, a
magnetic detection system such as a Faraday rotator detector can be
used to detect the magnetic covert signature in the pigment or foil
and any information magnetically encoded therein.
[0143] From the foregoing it can be seen that there have been
provided thin film structures which have both magnetic, and
optionally, color shifting properties, which have many different
types of applications, particularly where additional security is
desired.
[0144] For example, a structure or device formed with the pigments
of the invention can be placed in a bar code pattern which would
produce a color shifting bar code device that can appear on a label
or on an article itself. Such a bar code would function as a color
shifting bar code that could be read by both optical and magnetic
readers. Such a bar code color shifting device would provide three
security features, the bar code itself, the color shifting
characteristic, and the magnetic characteristic. In addition,
information can be encoded in the magnetic layers of the pigments
of the invention. For example, the magnetic layers could record
typical information which is carried by a credit card in a magnetic
stripe. In addition, pigments of the invention could be utilized
for putting the numbers on the bottoms of checks so that the
information carried by the check could be read magnetically as with
present day checks while also providing an optical variable
feature.
[0145] The following examples are given to illustrate the present
invention, and are not intended to limit the scope of the
invention.
EXAMPLE 1
[0146] A three layer magnetic coating sample was prepared with 1000
.ANG. Aluminum, 1000 .ANG. Iron, and 1000 .ANG. Aluminum
(Al/Fe/Al). The coating sample was prepared in a roll coater, using
a 2 mil polyester web coated with an organic release layer (soluble
in acetone). After stripping the three layer coating from the web
to form pigment flake particles, the particles were filtered and
sized by exposing the particles in isopropyl alcohol to ultrasonic
agitation for 5 minutes using a Branson sonic welder. Particle size
was determined using a Horiba LA-300 particle sizing instrument
(laser scattering based system). The mean particle size was
determined to be 44 .mu.m (22 .mu.m standard deviation) in the
planar dimension, with a gaussian distribution. Following the
sizing, the pigment particles were filtered and dried.
[0147] A dry weight of magnetic pigment to binder (Du Pont auto
refinish paint vehicle) in the ratio of 1:4 was drawn down onto a
thin cardboard sheet (Leneta card). A "drawdown" is a paint or ink
sample spread on paper to evaluate the color. Typically, a drawdown
is formed with the edge of a putty knife or spatula by "drawing
down" a small glob of paint or ink to get a thin film of the paint
or ink. Alternatively, the draw-down is made using a Mayer rod
pulled across a Leneta card and through a small glob of paint. A
conventional sheet magnet was placed underneath the card while the
drawing down was occurring and left in place until the paint
vehicle dried. The result of the magnetic fields on this pigment
sample was to create parallel bright and dark areas in the pigment.
By using an ultra small area viewer (USAV, 2.3 mm) on a SF-600
DataColor spectrophotometer, the bright aluminum areas of the
pigment sample had a reflective luminance, Y, of 53% whereas the
dark areas had a reflective luminance of 43%. However, it was
difficult to fit the aperture within the dark and bright lines
suggesting that the difference in brightness may actually be larger
than these measurements.
EXAMPLE 2
[0148] A magnetic ink sample was prepared by mixing a 0.5 g sample
of the magnetic pigment of Example 1 (Al/Fe/Al) with 3.575 g of
standard Intaglio ink vehicle (high viscosity ink vehicle) and
0.175 g of an ink dryer. The ink sample was drawn down onto paper
using a flat putty knife. A magnetic strip with the word "FLEX" cut
out from it was placed beneath the paper during the drawing down
step. The pattern of the magnetic lines in the dried magnetic ink
was readily visible as black and white (silver color) strips with
the word "FLEX" readily apparent. The optical image of the word
"FLEX" in the ink sample was visible at normal incidence and at
approximately a 45 degree angle of viewing.
EXAMPLE 3
[0149] A magnetic ink sample was prepared as in Example 2 using an
Intaglio ink vehicle and coated over paper having a sheet magnet
placed behind it. The magnet had a cut out of a stylized letter
"F." In addition to the magnetic pigment (Al/Fe/Al) orienting along
the magnetic field lines, the cut out "F" was embossed upward away
from the paper and was bright silver in appearance. The "F" stood
out over the surrounding area by about 6 microns. This was caused
by the paper pushed slightly into the "F" recess of the magnet by
the force of the putty knife drawing down the highly viscous
Intaglio ink. Alter the paper relaxed, the "F" area remained bright
with the Al/Fe/Al flakes oriented parallel to the surface of the
paper but in a stepped-up height above the surrounding coating.
EXAMPLE 4
[0150] A stylized letter "F" was cut out of a flexible sheet magnet
using an exacto knife. A draw-down card was placed on top of and in
contact with the sheet magnet. A magnetic color shifting pigment
according to the invention was mixed with an acrylic resin based
vehicle and applied to the card with a #22 wire metering rod. The
resultant draw-down had striped superimposed black lines that
replicated the field pattern outside of the stylized "F" in the
sheet magnet below the card. The entire surface of the drawn-down
card exhibited color shifting effects. Where the pattern of the
stylized "F" was observed, the stylized "F" only had color shifting
effects, while the background had both color shifting effects and
the superimposed black lines.
[0151] The cut out stylized letter "F" pieces from the sheet magnet
were used in another draw-down with the same magnetic pigment and
vehicle described previously in this example. The resultant
draw-down had striped superimposed black lines that replicated the
field pattern within the cutout stylized "F" magnet pieces. The
entire surface of the drawn-down exhibited a color shifting effect.
Where the pattern of the stylized "F" was observed, the stylized
"F" had both color shifting effects and the superimposed black
lines, while the background had only color shifting effects.
[0152] Thus, in both instances the entire surface of the draw-down
cards exhibited color shifting effects, while the areas directly
above the magnets additionally had superimposed striped black lines
due to the magnetic field pattern.
[0153] The present invention may be embodied in other specific
forms without departing from its spirit or essential
characteristics. The described embodiments are to be considered in
all respects only as illustrative and not restrictive. The scope of
the invention is, therefore, indicated by the appended claims
rather than by the foregoing description. All changes which come
within the meaning and range of equivalency of the claims are to be
embraced within their scope.
* * * * *