Image changeable sheet with water

An image changeable sheet with water characterized in that an opaque film comprising a transparent film and a water-absorbable coating layer formed on one side of the transparent film and containing a pigment composed mainly of a white pigment with a refractive index of not more than 1.7 is adhered to a base paper having an image on the colored surface, and a surface image is provided on the coating layer, said surface image being an image whose color matches the color of the colored surface and/or the image of the base paper seen through via water absorption.

TECHNICAL FIELD 
This invention relates to an image changeable sheet with water, and more 
specifically to an image changeable sheet with water wherein when the 
sheet is wetted with water, an image on the surface of the sheet 
disappears and a different image appears, and when the sheet is dried, the 
original image revives. 
BACKGROUND ART 
There has been so far known an image changeable film with water which is an 
opaque film having a white or light-colored appearance and composed of a 
transparent film and a coating layer formed on one side of the transparent 
film, wherein when the film is adhered to any printed matter and the 
surface of the coating layer is wetted with water, the coating layer 
becomes transparent and the printed image rises to the surface vividly 
through the film (Japanese Laid-open Patent Application No. 199185/83). 
The above image changeable film with water is white or light-colored 
throughout the surface, and no image is seen unless the film is wetted 
with water. Accordingly, said film has been a bit less amusing as a 
picture book or toy for children. Meanwhile, in recent years, a survival 
game that a target is shot at a fixed distance by a water pistol has 
appeared as an adult amusement. Ink is however used as a liquid being shot 
in this game or a printed matter easily broken when water strikes 
thereagainst is employed as a target, and there is thus a likelihood of 
making clothes dirty. Moreover, said film suffers problems with target 
designs and costs of materials. 
SUMMARY OF THE INVENTION 
An object of this invention is to resolve the aforesaid problems, that is, 
to provide an image changeable sheet with water that enables the image to 
appear with the aid of water, allows application of varying designs and 
makes possible the repetitive use said image changeable sheet with water 
being able to give different images to a person who observes it before or 
after water absorption in particular. 
The present inventors have made studies at the request of Buddy L. 
Corporation (200 Fifth Ave., New York, N.Y. 10010, U.S.A.), and 
consequently found that in a sheet wherein an image changeable sheet with 
water having a surface image on a surface of a coating layer is adhered to 
a printed matter, the surface image comes out of the sight in harmony with 
a background color seen through via water absorption when there is a 
specific color difference between the surface image and the printed 
matter. 
This invention is thus to provide an image changeable sheet with water 
characterized in that an opaque film comprising a transparent film and a 
water-absorbable coating layer formed on one side of the transparent film 
and containing a pigment composed mainly of a white pigment with a 
refractive index of not more than 1.7 is adhered to a base paper having an 
image on the colored surface, and a surface image is provided on the 
coating layer, said surface image being an image whose color matches the 
color of the colored surface and/or the image of the base paper seen 
through via water absorption.

BEST AND VARIOUS MODES FOR CARRYING OUT INVENTION 
The image changeable sheet with water in this invention is composed of an 
opaque film (hereinafter referred to as an "image changeable film with 
water") comprising a transparent film (1) and a water-absorbable coating 
layer (2) formed on one side of the transparent film (1) and containing a 
pigment composed mainly of a white pigment with a refractive index of not 
more than 1.7, a base paper (3), a colored surface (5) of the base paper, 
a surface image (4) and an image (6), i.e. an internal image on the 
colored surface. 
The image changeable film with water shows a white or light-colored, highly 
opaque appearance, and the coating layer is quite easy to absorb water and 
clarified via water absorption. However, the coating layer is not 
delaminated even by water absorption, returned to the original appearance 
through evaporation of water, and does not allow occurrance of wrinkles or 
blurs even by repetitive water absorption and drying. 
The image changeable film with water has to be prepared by using as a 
starting material a water-resistant transparent film or a transparent film 
with a water resistance imparted thereto. Examples thereof are 
polyethylene, polyvinyl chloride, polypropylene, polyesters, polyethylene 
terephthalate, polyvinyl alcohol, nylons, acetates, cellophane, etc. The 
higher clarity is better. The polypropylene film and the polyester film 
which are the most preferable films in this invention exhibit an 
opaqueness of not more than 5% measured by a Photovolt Reflector, Model 
670. 
The transparent film is required to have a surface tension of at least 35 
dyne/cm, preferably at least 40 dyne/cm. This is because the image 
changeable film with water is used repetitively in relation to water, and 
this necessitates a surface tension (delamination resistance) in both dry 
and wet conditions. Many of general-purpose resin films do not have the 
lowest surface tension in this invention. Consequently, in order to 
complete the image changeable sheet with water, the surface treatment of 
the transparent film is advisable. It is necessary to raise the surface 
tension to a desirous value by e.g. conducting the corona discharge 
treatment or thinly coating a solution of a solvent such as polyvinyl 
alcohol, acetyl cellulose or isocyanates. 
It goes without saying that the transparent film is colorless or 
light-colored with no pattern in view of the object of this invention. 
The coating layer in the image changeable film with water has to contain a 
pigment composed mainly of a white pigment with a refractive index of not 
more than 1.7. Examples of such white pigment are synthetic silica, talc, 
white clay and calcium carbonate (said pigment is hereinafter referred to 
as a "white pigment with a low refractive index"). Titanium oxide and 
other materials having a higher refractive index are not desirous for 
achieving the object of this invention, but they may be used as an aid. 
Binders are those having good affinity for films and providing transparency 
such as casein, starch, synthetic latexes and cellulose derivatives. Among 
others, acrylic latexes or SBR latexes are preferable. 
The coating layer is formed by coating the above pigments or the other 
pigments such as carbon black which will be later described. A coating 
layer having a two-layered structure of upper and lower coating layers is 
more preferable in this invention. A difference in component between the 
upper and lower coating layers is that a small amount of a black or dark 
pigment, e.g. carbon black, is contained in the lower coating layer. The 
dark color includes, for example, purple, light brown and dark blue 
colors. A ratio of the other pigments is 1.3 to 1.7%, preferably about 
1.5% based on the weight of the other solid contents (the white pigment 
with a low refractive index and the binder). These other pigments increase 
hiding properties. If the amounts thereof increase, a whiteness of the 
surface of the image changeable film with water decreases, and a clarity 
of the image appearing at the time of water absorption reduces. On the 
other hand, when the other pigments are not added at all, hiding 
properties are poor. Accordingly, the amounts of said other pigments may 
vary depending on the colored surface and the image of the base paper, 
etc. A mixing ratio of the white pigments with the low refractive index in 
both coating layers to the binder is set such that the surface strength of 
the image changeable film with water and the clarifying performance by 
water absorption can be best exhibited. That is, when the amount of the 
binder is smaller, the surface strength is lower. When the amount of the 
binder is larger, water absorption becomes difficult. Thus, the weight 
ratio of the white pigments with the low refractive index to the binder is 
1:0.4-1. 
The amount of the coating in the lower coating layer is 7 to 15 g/m.sup.2, 
and that in the upper coating layer is 8 to 25 g/m.sup.2. Where the total 
amount of the coatings in both layers is more than 40 g/m.sup.2, an 
internal adhesion decreases, causing crack in the coating layer. Where it 
is less than 15 g/m.sup.2, hiding properties notably decrease. 
The base paper (3) has the colored surface (5) with the image ((6): 
hereinafter referred to as an "internal image"). Said base paper supports 
the image changeable film with water and causes a colored surface (5b) and 
a water image (6b) to appear via water absorption of the coating layer. 
Examples of the base paper are water-resistant thick papers, opaque 
synthetic resin sheets and synthetic papers. The synthetic papers are most 
preferable because said paper lack water absorption properties and permit 
beautiful printing with high luster through various printing means. The 
base paper is colored in advance by coating or printing, and it is also 
advisable that the colored surface is water-resistant and lacks water 
absorption properties. This holds true of the internal image formed on the 
colored surface. 
The image on the surface of the coating layer, i.e. the surface image (4) 
matches the colored surface (5) or the internal image (6) via water 
absorption by [A] determining a given color difference between the surface 
image and the colored surface or the internal image and [B] using ink 
containing a white pigment with a refractive index of not more than 1.7 to 
form the surface image. These two means are described in detail below. 
[A] Determination of the color difference 
The coating layer is to have numerous fine pore channels thereon in view of 
the function. Besides, it is advisable in this invention to form the 
surface image such that water is absorbed from the surface image too, 
namely, the overall coating layer participates in water absorption. When a 
non-water-absorbable continuous coating is formed, waterdrops or a water 
film is further formed on the continuous coating in the water-absorbed 
state of the image changeable sheet with water, and the surface image 
becomes more vivid by reflection of light making it hard at times that the 
surface image matches the colored surface or the internal image of the 
base paper. In case the surface image is formed by usual printings, e.g. 
offset printing, a density of dots on a printing plate, an amount of ink, 
etc. can be so adjusted that water is immersed also from the image and the 
ink coated film does not cove the pore channels. On this occasion, if the 
same ink in the same amount as used in the colored surface or the internal 
image is employed in the printing of the surface image, the color of the 
surface image overlaps those of the colored surface or the internal image 
and becomes deep in the water-absorbed state. As a result, these colors do 
not match each other, making it impossible to achieve the object of this 
invention. Accordingly, when inks of colors of the same series are used in 
the surface image, the colored surface or the internal image in this 
invention, a specific color difference is required. As will be later 
described in EXPERIMENTAL EXAMPLE, the color difference has to be 40 to 60 
DNS unit. When the color depth of the surface image gets higher and the 
color difference is less than 40, the colors are hard to match each other 
by water absorption. When the color depth of the surface image gets lower 
and the color difference is more than 60, the colors are easy to match 
each other but the surface image in the dry state becomes hard to be seen. 
The aforesaid "colors of the same series" indicate a group of color names 
comprising a name of a basic color and modifiers, including an achromatic 
color as described in JIS Z 8102-1985. For instance, general names of 23 
colors such as blue, greenish blue, purplish blue, etc. are shown in the 
series of the blue color. In this invention, it is advisable to use inks 
of colors with a given color difference selected from colors of the same 
series. Incidentally, in the field of the color science, there is a 
combination of colors which is generally poor in legibility, as is the 
case with arrangement of greenish blue letters on a black background. The 
colors of different basic color names are, if meeting the above 
requirement, included in the technical idea of this invention. 
As the colored surface 5b and the water image 6b are seen through via the 
transparent film and the clarified coating layer, it usually tends to look 
dull. The color of the base paper surface is therefore set to be 
preferably lighter than that of the surface image. 
FIGS. 1 to 3 are examples wherein the surface image is formed by specifying 
the color difference as above. For the sake of explanation, an embodiment 
wherein the color of the surface image matches the color of the colored 
surface is shown in these figures. It is also possible to provide an 
embodiment wherein the color of the surface image matches the color of the 
internal image or an embodiment wherein the color of the surface image 
matches the colors of both the colored surface and the internal images. 
All commercial inks to form a water-resistant coating are available as ink 
of the surface image. A printing method is not limited in particular, but 
offset printing, gravure printing and screen printing are most preferable 
because a water-absorbable ink coating can easily be formed by selecting 
dots and mesh of a printing plate. 
[B] Specifying of blending inks 
A surface image printed by using as ink for surface refractive image, 
instead of an ordinary ink using a pigment with a high refractive index as 
a main pigment, an aqueous ink comprising the aforesaid white pigment with 
the low refractive index as a main pigment, the same binder as described 
in the aforesaid coating layer and a suitable amount of a color pigment, 
or a so-called oil ink to solidify a white pigment with a low refractive 
index and a color pigment by drying a known vehicle such as a linseed oil 
vehicle is clarified by water absorption and almost loses a color sense. 
The color pigment can be used in an amount of 3 to 10% by weight based on 
the solids content of ink. In this case, the surface image can be formed 
without being restricted by the colors of the colored surface and the 
internal image. More preferable is to select the colors having the above 
color difference. FIGS. 4 to 6 are examples wherein the surface image is 
formed by specifying the blending of ink as above, and show an embodiment 
that the surface image overlaps the colored surface and the internal 
image. 
The preferable embodiments of this invention have been thus far explained. 
However, this invention is not limited to these embodiments, and it is 
optionally possible to form two or more surface images different in rate 
of water absorption on the coating layer or to conjointly use a 
water-absorbable surface image and a non-water-absorbable surface image. 
The range of the color difference by which the color of the surface image 
effectively matches the color of the colored surface at the point of water 
absorption can be seen as in EXPERIMENTAL EXAMPLE below. 
EXPERIMENTAL EXAMPLE 
A single side cast coated paper (Esprit Coat.RTM.: a product of 
Sanyo-Kokusaku Pulp Co., Ltd.) having a basis weight of 127 g/m.sup.2 was 
used as a base paper, and the surface thereof was uniformly printed with 
black and red printing inks (No. 2 synthetic paper oil inks of Toka 
Shikiso Kagaku Kogyo K. K.) each in an amount of about 2.5 g/m.sup.2. A 
25-micron thick polyester film was used as a transparent film. A coating 
layer having a two-layered structure was formed using a coating shown in 
Table 1, and an image changeable sheet with water was thus formed. Parts 
referred to in Table 1 are all parts by weight. 
TABLE 1 
______________________________________ 
Composition of 
Lower coating 
Upper coating 
a coating layer (parts) 
layer (parts) 
______________________________________ 
Water 67.65 65.0 
Sodium hexa- 0.14 0.16 
methaphosphate 
Kaolin 7.92 8.70 
Synthetic 11.10 13.94 
silica 
Acrylic ester 12.67 12.20 
copolymer 
latex 
Carbon black* 0.52 -- 
Dry weight of 10 15 
coating (g/m.sup.2) 
______________________________________ 
*Mikuni SM Black C: a product of Mikuni Shikiso K. K. 
For convenience' sake, the same inks as used in the base paper were 
imployed in printing the surface image, and a letter indicated at (4) in 
FIG. 1 was printed with said inks by offset printing. Several types of 
surface images were formed with varying amounts of inks adhered. The 
resulting samples were tested for color difference in the following 
manner. 
A digital color difference meter (SM-3 Model: a device of Suga Shikenki K. 
K.) according to JIS Z 8722 was used as a measuring device. A color 
difference .DELTA.E (delta-E) was a color difference .DELTA.E (NBS units: 
National Bureau of Standard unit) by a Lab system among color differences 
shown in JIS Z 8730. .DELTA.E is calculated from .DELTA.a and .DELTA.b 
according to a Hunter color difference formula. L is a brightness, "ab" is 
a chromaticity showing a hue and a chroma. "a" and "b" are each a 
direction of a color. The order and the results of measurement are as 
follows. 
The samples were equilibrated in a room of 20.degree. C. and RH of 65%. 
Subsequently, colors of the samples were tested and a color difference 
.DELTA.E was measured. After the image changeable film with water was 
adhered to the base paper, water was absorbed in the surface of the 
coating layer, and a color difference .DELTA.E between the surface image 
and the colored surface seen through was measured. Meanwhile, the samples 
before and after water absorption were observed with an unaided eye at a 
distance of 2.5 m. The samples were selected which were legible in the dry 
state but actually illegible in the water-absorbed state. The results are 
shown in Tables 2 and 3. 
TABLE 2 
______________________________________ 
(black) 
L a b .DELTA.E 
______________________________________ 
Dry state 
Colored 8.37 -0.56 -1.16 -- 
surface 
Surface 49.68 -0.83 -2.12 41.32 
image 
Water- Colored 27.89 -3.31 -4.07 -- 
absorbed 
surface 
state Surface 23.04 -2.42 -2.19 5.28 
image 
______________________________________ 
L . . . brightness 
a . . . direction of green 
b . . . direction of blue 
TABLE 3 
______________________________________ 
(red) 
L a b .DELTA.E 
______________________________________ 
Dry state 
Colored 29.23 59.42 17.99 -- 
surface 
Surface 56.18 15.62 -3.00 55.54 
image 
Water- Colored 33.58 16.47 1.96 -- 
absorbed 
surface 
state Surface 31.21 21.42 2.52 5.53 
image 
______________________________________ 
L . . . brightness 
a . . . direction of red 
b(+) . . . direction of yellow 
b(-) . . . direction of blue 
In e.g. Table 3 (red), the color difference in the dry state was 55.54. 
There is a color difference of 5.53 in the water-absorbed state. With such 
color difference, the color cannot actually be discriminated at a distance 
of 2.5 m. This holds true of the other colors. In the image changeable 
sheet with water in this invention, the color of the colored surface on 
the base paper is usually lighter than the color of the surface image. 
Accordingly, the color difference in the usual case tends to be big 
compared to the results of this test using the same inks. Considering this 
point, the color difference required for the image changeable sheet with 
water in this invention can be 40 to 60 DNS unit. 
The following Examples illustrate this invention in more detail. Parts are 
on the weight basis. 
EXAMPLE 1 
A lower coating solution with a surface tension of 35 dyne/cm having the 
coating composition shown in Table 1 was coated (dry weight 10 g/m.sup.2) 
with a Mayer bar on a substrate whose surface tension was made 45 dyne/cm 
by previously subjecting a 30 micron-thick polypropylene film to corona 
discharge, and dried with hot air of 100.degree. C. An upper coating 
solution (Table 1) having almost the same surface tension as the lower 
coating solution was coated (dry weight 15 g/m.sup.2) thereon with a Mayer 
bar, and dried with hot air of 100.degree. C. There was formed an image 
changeable film with water. A greenish blue surface image was printed on 
the surface of the coating layer by offset printing. No. 2 synthetic paper 
ink made by Toka Shikiso Kagaku Kogyo K. K. was used for said surface 
image. When the image surface was observed with a 10X magnifier, dots of 
the printing plate were seen on the overall surface. A synthetic paper 
(Yupo.RTM.: a product of Oji Yuka Synthetic Paper Co., Ltd.) wherein an 
orange internal image was formed on an art ultramarine base was used as a 
base paper. A color difference between the surface image and the colored 
surface of the base paper was measured by a color difference meter, SM-3 
Model of Suga Shikenki K. K. The results are shown in Table 4. These were 
adhered by an acrylic adhesive. The structure is as shown in FIGS. 1 and 
2. 
TABLE 4 
______________________________________ 
(blue) 
L a b .DELTA.E 
______________________________________ 
Dry state 
Colored 23.96 -4.07 -56.44 
-- 
surface 
Surface 43.99 -2.42 -11.51 
49.51 
image 
Water- Colored 25.89 0.39 -11.33 
-- 
absorbed 
surface 
state Surface 21.48 -1.38 -11.75 
4.77 
image 
______________________________________ 
L . . . brightness 
a(-) . . . direction of green 
a(+) . . . direction of red 
b . . . direction of blue 
As shown in Table 4, the color difference between the colored surface of 
the base paper and the surface image was 49.51. The colored surface and 
the internal image were actually concealed in the resulting image 
changeable sheet with water in this invention. As soon as the sheet was 
wetted with water, the surface image matched the colored surface and 
almost disappeard, and the vivid internal image appeared with the colored 
surface, as shown in FIG. 3. The value 4.77 in column .DELTA.E of Table 4 
means that a slight color difference could be measured between the surface 
image and the colored surface in the water-absorbed state. 
The product was cut to a given size and used in a distance of a few meters 
as a target of a survival game, but the performance thereof was not 
decreased even by the repetitive use. 
EXAMPLE 2 
An image changeable film with water was formed using a 50 micron-thick hard 
vinyl chloride film (surface tension 40 dyne/cm) having an untreated 
surface and the same coating solution as in Example 1. A surface image was 
printed by flexographic printing with ink obtained by adding a yellowish 
green pigment (Hansa yellow . . . an azo pigment) to the coating of the 
same composition as in the coating solution described in Example 1. A 
weight ratio of the yellowish green pigment to the ink solids content was 
4.33%. A synthetic paper (Yupo.RTM. a product of Oji Yuka Synthetic Paper 
Co., Ltd.) was used as a base paper. The characteristics of both the 
images and the colored surface are shown in Table 5. 
TABLE 5 
______________________________________ 
L a b 
______________________________________ 
Dry state Colored surface 
52.60 -6.38 31.39 
(yellowish green) 
Internal image 
35.31 39.68 15.13 
(redish yellow) 
Surface image 
43.42 -2.07 15.05 
(yellowish green) 
______________________________________ 
L . . . brightness 
a(-) . . . direction of green 
a(+) . . . direction of red 
b . . . direction of yellow 
These were adhered with an acrylic adhesive. The structure is as shown in 
FIGS. 4 and 5. The colored surface an the internal image were actually 
concealed, and when the sheet was wetted with water, the surface image was 
clarified and came out of the sight, and the vivid internal image appeared 
with the colored image (FIG. 6). 
A tack sheet was formed by applying a rubber tackifier and a release paper 
to the opposite side of the image changeable sheet with water. A product 
obtained by delaminating the release paper from the tack sheet could be 
used as a target of a survival game as in Example 1. 
As is understandable from the foregoing explanation, the image changeable 
sheet with water in this invention allows the phenomena, disappearance of 
the surface image and appearance of the water image either simultaneously 
or successively. This brings forth an effect that the surface image is 
changeable with water, and said sheet finds various applications for not 
only children but also adults, accordingly.