U.S. patent number 3,853,675 [Application Number 05/213,706] was granted by the patent office on 1974-12-10 for materials adapted to exhibit varying visual appearances.
This patent grant is currently assigned to Thomas de la Rue International Limited. Invention is credited to Christopher John Edwards.
United States Patent |
3,853,675 |
Edwards |
December 10, 1974 |
MATERIALS ADAPTED TO EXHIBIT VARYING VISUAL APPEARANCES
Abstract
Sheet material comprising two superimposed differently coloured
light-transmitting non-fibrous layers and between the layers and in
substantially intimate contact therewith a partially
light-transmitting layer is herein defined, the colors of the
light-transmitting layers being so selected that when either face
of the material is viewed by transmitted light from a source of a
substantially white light, the color observed is different from
that observed when either layer alone is viewed in like manner.
Inventors: |
Edwards; Christopher John
(Marlow, EN) |
Assignee: |
Thomas de la Rue International
Limited (London, EN)
|
Family
ID: |
10487354 |
Appl.
No.: |
05/213,706 |
Filed: |
December 29, 1971 |
Foreign Application Priority Data
|
|
|
|
|
Dec 30, 1970 [GB] |
|
|
61710/70 |
|
Current U.S.
Class: |
428/77; 40/1.6;
40/219; 40/581; 40/615; 428/138; 428/203; 428/337; 428/211.1 |
Current CPC
Class: |
B32B
3/266 (20130101); B44F 1/066 (20130101); B32B
27/08 (20130101); B32B 23/04 (20130101); B44F
1/10 (20130101); B32B 7/12 (20130101); Y10T
428/24868 (20150115); Y10T 428/266 (20150115); B32B
2305/026 (20130101); Y10T 428/24934 (20150115); B32B
2307/418 (20130101); Y10T 428/24331 (20150115); B32B
2307/412 (20130101); B32B 2307/40 (20130101) |
Current International
Class: |
B44F
1/00 (20060101); B44F 1/06 (20060101); B44F
1/10 (20060101); B44f 001/12 () |
Field of
Search: |
;161/1,228,229,232,408,409,410,166,3,6,4
;40/1.6,5,13B,13F,135,204,205,219 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Amsher; Harold
Assistant Examiner: Dixon, Jr.; William R.
Attorney, Agent or Firm: Baldwin, Wight & Brown
Claims
What is claimed is:
1. Sheet material comprising at least two superimposed colored
light-transmitting non-fibrous organic polymer film-forming layers,
each layer of a pair of layers being differently colored, and
between each adjacent pair of said layers and in substantially
intimate contact therewith a single substantially planar layer
which is partially light-reflecting and partially
light-transmitting with the ratio of the intensity of transmitted
light to the intensity of reflected light being dependent upon the
angle of incidence of the light and being a maximum when the angle
of incidence is normal to said layer, the colors of the
light-transmitting layers being so selected that when either face
of the composite material is viewed by transmitted light from a
source of substantially white light the color observed is different
from that observed when any light-transmitting layer alone is
viewed in like manner.
2. Sheet material as claimed in claim 1 in which each of the
light-transmitting layers has a thickness within the range 0.0001
inch to 0.1 inch.
3. Sheet material as claimed in claim 2 in which the thickness of
at least one light-transmitting layer is within the range 0.0005
inch to 0.05 inch.
4. Sheet material as claim in claim 1 in which the overall external
surfaces thereof comprise continuous light-transmitting layers.
5. Sheet material as claimed in claim 1 in which at least one
light-transmitting layer comprises a layer applied to said
partially light-reflecting and partially light-transmitting layer
as a coating.
6. Sheet material as claimed in claim 1 in which at least one of
light-transmitting layers is a discontinuous layers.
7. Sheet material as claimed in claim 6 in which the discontinuous
layer is a perforated layer.
8. Sheet material as claimed in claim 6 in which the discontinuous
layer comprises discrete organic polymer areas.
9. Sheet material as claimed in claim 1 in which all of the
light-transmitting layers are discontinous, said layer being so
disposed in relation to one another that at least some of the light
travelling substantially normal to the colored portions of any one
layer travels also substantially normal to at least some portions
of at least one other layer.
10. Sheet material as claimed in claim 1 including three
light-transmitting layers, the remotely disposed layers being of
the same color and the other layer being of a different color and
having partially light-reflecting and partially light-transmitting
layers between each pair of light-transmitting layers.
11. Sheet material as claimed in claim 1 in which said partially
light-reflecting and partially light-transmitting layer is formed
of a fibrous material.
12. Sheet material as claimed in claim 1 in which said partially
light-reflecting and partially light-transmitting layer is in the
form of a calendered material of the paper and fabric type.
13. Sheet material as claimed in claim 1 in which said partially
light-reflecting and partially light-transmitting layer is in the
form of a layer of spaced discrete particles of a light-reflecting
material.
14. Sheet material as claimed in claim 1 in which said partially
light-reflecting and partially light-transmitting layer is formed
of a transparent material having a surface finish which is highly
reflectant of light rays which are not normal thereto.
15. Sheet material as claimed in claim 14 in which the partially
light-reflecting and partially light-transmitting layer is in the
form of a transparent film printed on both sides with an ink
containing discrete particles of a highly light-refractive
pigment.
16. Sheet material as claimed in claim 1 in which there are
adhesive means bonding said partially light-reflecting and
partially light-transmitting layer to said adjacent
light-transmitting layers.
17. Sheet material as claimed in claim 1 in which said partially
light-reflecting and partially light-transmitting layer is
co-extensive with portions only of said adjacent light-transmitting
layers.
18. sheet material as claimed in claim 1 in which portions of said
partially light-reflecting and partially light-transmitting layer
are transparent.
19. Sheet material as claimed in claim 1 in which portions of said
partially light-reflecting and partially light-transmitting layer
are opaque.
20. A product comprising sheet material as claimed in claim 1
incorporated generally centrally within a paper base material with
the sheet material being viewable by light transmitted through said
product.
21. A product as claimed in claim 20 in which said paper base
material includes a layer of paper fibres having a minimum layer
thickness of 0.005 inch overlying each surface of the sheet
material.
22. A product as claimed in claim 21 in which at least that portion
of each layer of paper fibres overlying the sheet material are
transparent.
23. Sheet material as claimed in claim 1 wherein said film-forming
materials are thermoplastic resins.
24. sheet material as claimed in claim 1 wherein said film-forming
materials are regenerated cellulose.
25. Sheet material as claimed in claim 1 wherein said film-forming
materials are cellulose esters.
Description
This invention relates to improvements in sheet materials wherein
at least one portion thereof exhibits a visual appearance which
differs in color in accordance with the angle through which the
materials are viewed and/or illuminated.
The said materials have utility in areas such as, for example, the
construction of playthings, advertising and promotional media,
printed articles generally, teaching, the conveyance of
information, the identification of articles, and as artists' or
artistic materials per se.
It is desirable that certain printed and other articles, including
those above mentioned should incorporate or constitute one or more
features that attract the eye and attention of a viewer. By this
means, information may be brought to the notice of an observer more
emphatically than is the case with media not exhibiting such a
feature.
According to this invention a sheet material comprises at least two
superimposed differently colored light-transmitting non-fibrous
organic polymer layers and between each adjacent pair of the layers
and in substantially intimate contact therewith is a substantially
planar partially light-transmitting layer as hereinafter defined,
the colors of the light-transmitting layers being so selected that
when either face of the material is viewed by transmitted light,
from a source of substantially white light, the color observed is
different from that observed when either layer alone is viewed in
like manner.
By a partially light-transmitting layer it is meant a layer which
serves partially to reflect and partially to transmit light falling
upon it; the ratio of the intensity of the transmitted light to the
reflected light being dependent upon the angle of incidence of the
light and being a maximum when the angle of incidence is normal to
the partially transmitting layer.
The partially light-transmitting layer may be any suitable layer
having the properties defined above and may comprise for example, a
fibrillated plastics layer, a layer of tissue or similarly
structured paper, an alpha cellulose or similar paper, a layer of
particulate matter in spaced distribution, a layer of transparent
material having a surface finish adapted to confer a high degree of
reflectance upon the incidence thereupon of non-normal light rays
(for example, a transparent film printed on both sides with an ink
containing discrete particles of a white highly refractive pigment
such as titanium dioxide) or a web or mesh of textile fabric. The
partially transmitting layer may be an adhesive suitable for
bonding two light transmitting layers together and yet, when set,
possessing the transmission characteristics required of such a
layer. No particular limits are to be applied to the thickness of
the partially light-transmitting layer other than that preferably
it should be as thin as is commensurate with the exhibition of the
above defined characteristics.
The orgaanic polymer light-transmitting layers are preferably
selected from the group comprising thermoplastic resins,
regenerated cellulose and cellulose esters and transparent
compositions containing the same. However any colored non-fibrous
transparent organic polymer material will suffice. The layers,
which may be preformed or formed during the manufacture of articles
according to this invention, are preferably each of a thickness
within the range of 0.0001 inch to 0.1 inch and, preferably still,
within the range 0.0005 inch to 0.05 inch. A light-transmitting
layer may be continuous or non-continuous with respect to an
adjacent partially light-transmitting layer; a non-continuous layer
may be created by the application to a suitable partially
light-transmitting layer of organic polymer material by selective
coating, printing or like techniques.
Optionally also one or more of the light-transmitting layers may
comprise sheet materials converted to mesh-like configuration by a
punching or like operation; depending upon the desired effect to be
obtained from and the appearance desired of any given material, the
partially light-transmitting layer or layers may or may not be
perforated in accordance with the perforations of the associated
light-transmitting layers. If more than one of the
light-transmitting layers are perforated or comprise discrete
shapes the colored portions of each layer must be so positioned
that, in the sheet material, they are in at least partial register
with at least some of the colored portions of at least one of the
two other light-transmitting layers thus insuring that at least
some of the light travelling normally or nearly normally through
the colored portions of one of the layers also travels normally or
nearly normally through at least some of the colored portions of at
least one of the other light-transmitting layers.
The external surfaces of the light-transmitting layers may
optionally be further patterned or decorated by the application
thereto of light-transmitting printed or similarly applied
designs.
Materials according to this invention may be adapted to give
variegated effects overall. For example, a material may comprise
two adjacent portions, one in which the superimposed
light-transmitting layers are, for example, yellow and blue and the
other in which the superimposed layers are, for example, green and
violet; thus when viewed under transmitted light one portion of the
material will appear to be green and the adjacent portion will
appear as grey. Such materials may be readily constructed by
producing each element of such a composite separately and then
arranging portions of each in desired adjacent relationship. When
more than two light-transmitting layers are used they may each be
of a different color or, according to the total number employed,
two or more of them may be of the same color. However, in order to
obtain the desired colored effect under transmitted light (when
each is of a different color) three or more such layers must each
be of such a configuration that the composite effect of two layers
is not marred by the presence of any other layer; thus when using
three or more such layers one or more of them is preferably colored
in parts only or perforated to give an equivalent effect. By the
use of a plurality of colored light-transmitting layers with
uncolored portions or spaces between colored portions of each layer
according to a predetermined overall pattern, viewing by
transmitted light will produce a predetermined pattern, for
example, according to the relative positioning of the colored
portions of relevant layers, a recognizable pattern, word or legend
in the composite color.
According to the nature and intended use of materials according to
this invention, the partially light-transmitting layer may be
co-extensive with its adjacent light-transmitting layers or,
provided it is always present between portions of such layers
required to exhibit the desired effect under transmitted light, it
may be discontinuous in relation to other portions of the
light-transmitting layers; in areas where the partially
light-transmitting layer is not present the combined effect of two
adjacent light-transmitting layers, under transmitted light, will
be different from that obtained if the partially light-transmitting
layer were present. In any event, however, the partially
light-transmitting layer, when present between two differently
colored light-transmitting layers may be modified to create special
effects. For example, within an area of such a partially
light-transmitting layer smaller areas corresponding to the shapes
of, for example, letters may be created by stamping out or by
selective transparentization of the layer; in such an instance the
letters may appear, when viewed mainly by reflected light, as the
color of either of the outermost layers of the light-transmitting
layers (on the background of the combinative color of the two
layers) in dependence upon the side from which viewing takes place
-- when viewed under mainly transmitted light, the letters would
disappear, tend to disappear, or appear differently within the
entire area encompassed by the partially transmitting layer.
Conversely, by opacifying, e.g., by the application of opaque inks,
portions of the said area of the light-transmitting layer in
correspondence with, for example, the shapes of letters, the
reverse effect will be obtained, that is to say the lettering will
be weak under reflected light but will be seen more distinctly when
the material is viewed under mainly transmitted light.
The colored light-transmitting layers and the partially
transmitting layer may be firmly bonded together over substantially
the whole of their co-extensive surfaces or may be bonded only at
the peripheral regions thereof. It is preferred that the materials
be bonded together over substantially the whole of their
co-extensive surfaces in order to guarantee intimate contact and
thus to maximize the effect peculiar thereto. It is, however,
important when bonding the layers together to insure that the
properties necessary in the partially transmitting layer are
maintained therein and not to employ bonding means or tecniques
that deleteriously effect the defined properties of said partially
transmitting layer. When bonding agents, e.g., adhesives, are used
they must be only be compatible with and capable of bonding to the
material of the light-transmitting layers but also of such a nature
and present in such a quantity that they do not penetrate
substantially into the body of the partially light-transmitting
layer. To this end, when the partially light-transmitting layer is
paper, it is preferable to use a calendered product.
It is preferred that the bonding of the layers is so performed that
the bonded layers cannot be readily separated and more preferably
it is so performed that attempts to separate the bonded layers
results in the mechanical disruption of one or more of the layers.
Suitably, this preferred bonding is performed utilizing bonding
agents and/or bonding means such that the strength of the bonds
formed between light-transmitting layers and the partially
transmitting layer or layers exceeds the cohesive strength of the
partially transmitting layer or/layers and/or are at least as
strong as the cohesive strength of the colored light-transmitting
layer, For example, when preparing a material according to our
invention in which the partially transmitting layer is a paper
sheet or a fabric the material may be prepared by adhesively
bonding the preformed colored light-transmitting layers to the
paper or fabric sheet; alternatively the colored layers may be
prepared by extrusion techniques known per se for certain of the
suitable materials and by positioning and bonding the partially
transmitting layer during or immediately after the extrusion in
such a manner that the partially transmitting layer and the
light-transmitting layers become bonded together as a unitary
structure during that period wherein one or both of the colored
light-transmitting layers is in a flowable state.
The materials of the invention may be used alone or in combination
with other materials. For example, display cards may be fabricated
entirely of the materials of our invention suitably printed and/or
fashioned or a display card may be formed, from any suitable base
material known for such purpose, having affixed into the base
material, but selectively removable therefrom in a predetermined
and controllable manner, a material according to our invention.
Furthermore, printed articles can be fabricated in which the
materials are incorporated in a non-removable manner. For example,
if the base material for such articles is a thermoplastics material
the materials of our invention can be non-removably incorporated
therein by any suitable means such as, for example welding, solvent
bonding, extrusion or molding. If the base material is paper, our
novel materials may be incorporated into the paper during the
process of manufacturing the paper, preferably by laying materials
according to this invention on a layer of paper pulp in the
paper-making machine and then laying a further layer of paper pulp
thereover. Obviously, the thickness of such paper pulp layers must
not be such as to prevent the transmission of light through the
incorporated sheet material. The use of a perforated version of our
material facilitates the production of a coherent body as a result
of the penetration of the paper fibres through the holes in the
material so securing it firmly into the paper body.
When the novel materials are to be incorporated into a paper web
during its manufacture it is preferred that the thickness of the
material is not greater than and more preferably that the thickness
is less than the paper into which it is to be incorporated. When
the novel material is thinner than the paper, and is incorporated
therein during the paper-making process as described above, it is
thereby protected from mechanical abrasion and damage during use or
display of the article prepared therefrom. Paper materials are
available in a wide range of thicknesses but irrespective of the
thickness of the paper into which the novel materials are to be
incorporated it is preferred that the materials are so selected
that in the finished paper a layer of paper fibres at least 0.0005
inch thick overlays each surface of the material provided that the
thickness and/or opacity of the fiber layers does not prevent
transmission of light through the sheet material. However, this
restriction is not to be taken as limiting since, according to the
use for the finished product, materials according to this
invention, when incorporated in paper, may have still thinner
overlaying layers of paper fibre or may, in part, protrude through
the surfaces of the paper. Composite articles comprising the novel
materials may be printed and/or fashioned to bear any suitable
legend or message; they may include one or more materials according
to this invention and such materials may form a major or a minor
part of such composites.
It will be appreciated that, in order for the materials of the
invention to exhibit varying visual appearance, the manner in which
they are utilized must be such that light will pass through and
onto the materials and hence they must be so positioned that they
may be viewed alternatively by essentially transmitted or
essentially reflected light. The function of the partially
transmitting layer is such that at low angles of incidence of
viewing and/or illumination the ratio of transmitted light to
reflected light is low and hence the color observed by a viewer is
substantially that contained by the colored layer closer to his
eye; as the angle of incidence increases towards normal the
observed color changes until, at a normal angle of incidence, the
color observed is a composite of the two differently colored
light-transmitting layers so long as the degree of illumination
onto the surface farther away from the observer results in the
majority of light falling onto the observer's eye coming from that
source of illumination.
In that embodiment of our invention wherein the novel material is
incorporated within the body of a paper sheet the best effect is
obtained when using a transparent or transparentized region of
paper wherein the light entering or leaving the material through
the paper layers is dispersed to a leaser extent than when using
known papers. Conveniently, transparentization is effected
subsequent to the production of such paper composites by treating
the surfaces thereof or the portions of such surfaces which enclose
materials according to this invention with a suitable agent, for
example a melamine formaldehyde resin, a derivative thereof or
other cross-linkable compounds known per se as suitable for the
transparentization of paper.
In order that it may be more fully understood certain non-limiting
embodiments of the invention are exemplified below with reference
to the accompanying drawings of which
FIG. 1 is a diagrammatic exploded view of the components of the
material described in Example 1;
FIG. 2 is a plan view showing diagrammatically the disposition
within a paper web of the separately produced components of Example
II;
FIG. 3 shows an exploded view of the components of the material
described in Example III; and
FIG. 4 is an exploded view of the components described in Example
IV.
EXAMPLE I
This example describes a novel sheet material according to our
invention suitable for incorporation into a paper web during its
manufacture and also a method for preparing the materials.
As indicated hereinabove, for incorporation into a paper web during
its manufacture our novel materials are preferably at least 0.001
inch thinner than the finished paper. The material described in
this example is about 0.003 inch thick and thus is suitable for
incorporation into papers having a finished thickness of at least
0.004 inch.
The novel material according to this example is in perforated web
form (although for purposes of simplicity perforations are not
shown in the drawing) and comprises a central layer 1 of highly
calendered alpha cellulose paper about 0.002 inch thick having
adhered to one side thereof a blue dyed film 2 formed from
polyethylene terephthalate and to the other side a yellow dyed film
3 formed from polyethylene terephthalate, each layer of
polyethylene terephthalate being about 0.0005 inch thick.
The novel material was prepared as follows:
i. One surface of each of the films was coated with a two part
adhesive 4 of the polyester-isocyanate type and the adhesive
thoroughly dried by passage through an oven.
ii. The two films with their adhesive coated surfaces inwards were
then arranged on either side of the paper web and the assembly
passed through a hot nip laminator whereby the adhesive was
activated and the assembly consolidated to a unitary structure in
web form.
iii. The web was then passed between cooling rollers and then
perforated before being wound upon a take-up spool.
The perforated web was incorporated into paper during a
paper-making process by first laying down a layer of paper pulp,
positioning the perforated web thereon, and then applying to the
first down pulp layer and the tape further pulp to build up the
paper to the desired thickness of about 0.004 inch. After drying
and finishing the paper in the normal manner that area of the paper
web corresponding to the perforated web material was treated in a
known manner by a printing technique with a composition known for
the transparentization of paper.
The material according to this example was suitable for use per se
or in combination with materials other than paper-making pulp.
The novel material prepared as described exhibits, both alone and
when incorporated into the paper web, a visual appearance varying
in dependence upon the angle of the light path by which it was
viewed. When viewed under transmitted light conditions the material
appeared green while in reflected light the material appeared
either blue or yellow depending upon which side of the material was
being viewed.
EXAMPLE 11
Example I was repeated up to and including step (iii) save for the
use of a green dyed film of polyethylene terephthalate in place of
the blue film and a violet dyed film of the same polymer in place
of the yellow film.
A portion of the material so produced together with a portion of
the material produced in accordance with Example 1, was then
incorporated in paper in accordance with the further description of
Example 1. The portions of Example 1 and 11 materials were laid in
contiguous alignment with each other so that the finished product
over one area appeared green, and in an adjacent area appeared
grey, when viewed under transmitted light. In FIG. 2 the portion of
the finished product exhibiting the green composite color is
indicated at 5 and that giving a grey composite color is shown at
6.
This material was also suitable for use other than in the body of
paper pulp.
EXAMPLE 111
This example relates to a triple layer material for incorporation
into paper web or sheet, and may be considered to be a symmetrical
arrangement based on Example 1.
The novel feature of this example is to provide a first color when
paper incorporating the material is viewed from either side by
reflected light, and a second color when viewed from either side by
transmitted light.
Referring to FIG. 3 it will be seen that the constituents of the
material comprise a centrally disposed blue dyed film 8 formed from
polyethylene terephthalate of thickness 0.0005 inch and two
outwardly disposed yellow dyed films 9 and 10 (also of 0.0005 inch
thickness) of a similar material. Interposed between the dyed films
are disposed alpha cellulose paper sheets 11 and 12 having a
thickness of about 0.002 inch.
The method of preparing the material comprised coating both
surfaces of the film 8 and one surface each of film 9 and 10, with
adhesive 13. Thereafter, the adhesive was dried, the components
were than assembled in the manner shown in FIG. 3, and finally were
consolidated by heat and pressure.
The material so formed may be perforated if desired and then
incorporated into a paper web in the manner described in Example
1.
When theh paper is viewed from either side by reflected light the
material embedded therein will appear yellow, but when viewed by
transmitted light it will appear green (i.e., the combined effect
of all these films). The optical effect may be enhanced by
transparentization of the paper in the vicinity of the
material.
The material described above was suitable for uses other than in
the body of fibrous substances.
EXAMPLE 1V
This example relates to material comprising two continuous
differently colored light-transmitting layers having therebetween a
discontunuous partially transmitting layer which is co-extensive
with only portions of the light-transmitting layers, in order to
produce a special effect.
The materials are those referred to in Example 1. Referring now to
FIG. 4 layer 14 is yellow and layer 15 is blue. The adhesive layers
are indicated at 16. The alpha cellulose layer 17 is shorter in
length than either of the light-transmitting layers and is so
disposed that, at each end of the composite material the yellow and
blue layers, or rather the adhesive coatings thereof are in
intimate contact with each other.
The alpha cellulose layer is perforated at 18, said perforations
being representative of portions of letters, say D.L.R.
When material according to this example was viewed mainly by
reflected light the portions not encompassing the alpha cellulose
layer and those portions corresponding to the perforations in the
alpha cellulose layer appeared green viewed from either side, and
the portions of the light-transmitting layers having the alpha
cellulose layer therebetween appeared blue when viewed from the
blue side and yellow when viewed from the yellow side. Thus the
green lettering was clearly visible, on a yellow background when
viewed from one side and on a blue background when viewed from the
other side.
However, when the material was viewed under mainly transmitted
light, the lettering was discernable only with difficulty because
the effect overall was green or two difficulty separable shades of
green.
Material according to this Example was suitable or adaptable for
incorporation in paper-making pulps or for use per se or with other
materials.
EXAMPLE V
Material according to this invention was produced from three
superposed open-work webs of regenerated cellulose, one being
colored violet, one being colored green and one being colored
yellow and each having a thickness of 0.001 inch thick and two
layers of tissue paper, one between each adjacent pair of
regenerated cellulose webs and co-extensive therewith and each
having a thickness of 0.01 inch. The webs were arranged in the
above-mentioned order, that is with the green web centrally
placed.
The layers of regenerated cellulose were bonded to the layers of
the tissue paper by means of a nitrile rubber based adhesive
applied to the webs prior to their use for the purpose of this
invention.
Each web was initially a continuous sheet but each was converted to
open-work form by the stamping-out of predetermined portions in a
predetermined pattern. One portion of each element of the violet
layer was arranged to overlie an element of the green layer and
another portion of the violet layer was arranged to overlie an
element of the yellow layer.
When the resultant product was viewed by reflected light, one face
appeared of clear violet and diffused green areas and the other
face appeared of clear yellow and diffused green areas. When viewed
from either side by light transmitted through the material, the
appearance was a pattern of gray, green and brown areas.
Material according to this example was suitable for uses as a
material in its own right although it was also suitable for
incorporation within the body of a relatively thick paper fibre
body.
In alternative embodiments of the invention which may be applied to
any of the above examples or adaptations thereof, an equivalent
optical effect may be obtained by coating the surfaces of the
partially light-transmitting layer sheets with light-transmitting
color media, (for example by roller coating techniques). This
method serves to provide an extremely compact material, and
eliminates the need for adhesives.
Example V relates the use of a partially light-transmitting layer
with cut-out portions but in still further embodiments, which serve
to provide additional unique and artistic effects, and which are
also applicable to the above described examples, the partially
light-transmitting layers may be cut out to provide a pattern,
discretely transparentized or printed upon with opaque inks or dyes
in a predetermined manner before application of the layers or
coatings.
By way of an example applicable to advertising, words may first be
printed upon the partially light-transmitting layer in opaque ink
and subsequent to the production of material according to this
invention incorporating such a layer a second printing may be
applied to the frontal surface of a paper sheet enclosing the said
material. In use, a first source of illumination may be directed
upon the front of the sheet to display the second printed matter. A
further source of illumination may be positioned behind the
composite sheet, and a suitable switching means may be arranged to
render either or both sets of printing selectively visible.
* * * * *