U.S. patent application number 11/290725 was filed with the patent office on 2006-05-04 for front face erasable microcapsule magnetophoretic display sheet, erasing magnet and writing magnet.
This patent application is currently assigned to A SON ENTERPRISE, INC.. Invention is credited to Sadatoshi Igaue, Takashi Iwasaki, Kenji Nonaka, Takuya Yashuhara.
Application Number | 20060093858 11/290725 |
Document ID | / |
Family ID | 19188650 |
Filed Date | 2006-05-04 |
United States Patent
Application |
20060093858 |
Kind Code |
A1 |
Iwasaki; Takashi ; et
al. |
May 4, 2006 |
Front face erasable microcapsule magnetophoretic display sheet,
erasing magnet and writing magnet
Abstract
Disclosed herein is a front face erasable microcapsule
magnetophoretic display sheet having a support and a solid
dispersion layer provided on one surface of the support and
composed of microcapsules having an average particle diameter of 50
to 650 .mu.m, in which a liquid dispersion, a white pigment,
additives and magnetic particles are encapsulated, and a binder.
The magnetic particles include at least two kinds of magnetic
particles different in particle diameter from each other. An
erasing magnet for front face erasing and a writing magnet for
front face erasable microcapsule magnetophoretic display sheet are
also disclosed.
Inventors: |
Iwasaki; Takashi;
(Hanno-shi, JP) ; Yashuhara; Takuya; (Iruma-shi,
JP) ; Nonaka; Kenji; (Tokyo, JP) ; Igaue;
Sadatoshi; (Tokyo, JP) |
Correspondence
Address: |
BROUSE MCDOWELL LPA
388 SOUTH MAIN STREET
SUITE 500
AKRON
OH
44311
US
|
Assignee: |
A SON ENTERPRISE, INC.
TOKYO
JP
TOCOM CORPORATION
|
Family ID: |
19188650 |
Appl. No.: |
11/290725 |
Filed: |
November 30, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10323181 |
Dec 18, 2002 |
|
|
|
11290725 |
Nov 30, 2005 |
|
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Current U.S.
Class: |
428/692.1 |
Current CPC
Class: |
G09F 9/375 20130101;
B43L 1/008 20130101; B43L 19/0031 20130101; Y10T 428/25 20150115;
B43L 1/045 20130101; G02F 1/094 20210101; Y10T 428/2991 20150115;
Y10T 428/254 20150115; Y10T 428/2984 20150115; Y10S 428/90
20130101; Y10T 428/32 20150115; G02F 1/09 20130101; B43L 21/00
20130101 |
Class at
Publication: |
428/692.1 |
International
Class: |
B32B 15/00 20060101
B32B015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 25, 2001 |
JP |
2001-392561 |
Claims
1-18. (canceled)
19. An erasing magnet/display sheet apparatus for front face
erasing, which is adapted to slide over at least a part of the
front face of the front face erasable microcapsule magnetophoretic
display sheet, wherein the apparatus comprises: at least one
magnetic portion; at least one non-magnetic portion, the
non-magnetic portion creating a clearance between the front face
erasable microcapsule magnetophoretic display sheet and the
magnetic portion; and, a magnetic field comprising multiple
magnetic lines, wherein portions of the magnetic lines are almost
horizontally acting on the magnetic portion at a position somewhat
distant from the magnetic portion.
20. The apparatus of claim 19, wherein the type of magnetization of
the magnet is double-sided magnetization IP.
21. The apparatus of claim 20, wherein the magnet further comprises
a surface magnetic flux density of 100 to 750 G.
22. The apparatus of claim 21, wherein the clearance is a
non-magnetic layer.
23. The apparatus of claim 19 wherein the the non-magnetic portion
is selected from an air layer, resin, sponge, sponge resin, rubber,
wood, corrugated board, paper, fiber, glass, or metal.
24-42. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] This application claims priority to Japanese patent
application no. 2001-392561 filed on Dec. 25, 2001.
[0002] 1. Field of the Invention
[0003] The present invention relates to a front face erasable
microcapsule magnetophoretic display sheet, an erasing magnet and a
writing magnet for the sheet, and particularly to a front face
erasable microcapsule magnetophoretic display sheet, by which a
magnetic record magnetically recorded on the front face of the
sheet can be erased wholly or partially from the front face side
thereof by a magnet, an erasing magnet which can erase a record
from the front face side of a recorded sheet, and a writing magnet
for the sheet.
[0004] 2. Related Background Art
[0005] There has heretofore been known a magnetic recording system
that a magnetic recording is conducted on the front face of a
microcapsule magnetophoretic display sheet. This magnetic recording
system is generally a system that an erasing magnet is slid on the
whole rear face of the microcapsule magnetophoretic display sheet
to make the front face thereof clean, writing is then conducted on
the front face with a writing magnet or magnet pen to obtain a
magnetic record, and the magnetic record recorded thereon is
optionally erased from the rear face side by sliding an erasing
magnet on the whole rear face thereof. When such a magnetic record
is erased, the erasing magnet is slid on the rear face of the
microcapsule magnetophoretic display sheet, thereby erasing the
record recorded on the front face of the magnetophoretic display
sheet. According to an erasing method heretofore used, however, the
magnetically recorded display recorded on the microcapsule
magnetophoretic display sheet is erased at the whole portion slid
by the erasing magnet when the erasing is conducted from the rear
face side. Therefore, only a desired portion of the magnetically
recorded display cannot be erased, which is very inconvenient. The
uses thereof are thus limited.
SUMMARY OF THE INVENTION
[0006] Once characters, diagrams and/or the like magnetically
recorded can be erased from the front face side under the foregoing
circumstances, the record can be partially erased, to say nothing
of the whole surface erasing, so that not only such inconvenience
as described above can be eliminated, and such a microcapsule
magnetophoretic display sheet becomes easy to use, but also
excellent merits that the sheet can be applied to various uses, for
example, chalk boards, and used by attaching it on surfaces of
walls, lockers, etc. or for production of machine readable magnetic
records and as inspection materials of steel products or the like
can be achieved. The present inventors have paid attention to this
regard and continued to carry out various investigations. As a
result, it has been found that the microcapsule magnetophoretic
display sheet is improved, and the erasing magnet and the writing
magnet or magnet pen is devised, whereby printing of recorded
characters and the like or erasing of the print can be partially
and easily conducted from the front face of the magnetic display
sheet. It is therefore a first object of the present invention to
provide a front face erasable microcapsule magnetophoretic display
sheet, by which characters, diagrams and/or the like magnetically
recorded on the front face of the magnetic recording sheet can be
simply and easily erased wholly or partially from the front face
side thereof.
[0007] A second object of the present invention is to provide an
erasing magnet for front face erasing, which has a simple structure
and can wholly or partially erase characters, diagrams and/or the
like from the recording surface side of a recorded sheet.
[0008] A third object of the present invention is to provide a
writing magnet for front face erasable microcapsule magnetophoretic
display sheets, by which fine characters, diagrams and/or the like
can be clearly displayed.
[0009] The above objects of the present invention can be achieved
by the respective aspects of the present invention described
below.
[0010] According to the present invention, there is thus provided a
front face erasable microcapsule magnetophoretic display sheet
comprising a support and a solid dispersion layer provided on one
surface of the support and composed of microcapsules having an
average particle diameter of 50 to 650 .mu.m, in which a liquid
dispersion, a white pigment, additives and magnetic particles are
encapsulated, and a binder, wherein the magnetic particles include
at least two kinds of magnetic particles different in particle
diameter from each other.
[0011] In the front face erasable microcapsule magnetophoretic
display sheet described above, at least one kind of magnetic
particles having a particle diameter ranging from 0.1 .mu.m to 1.0
.mu.m and at least one kind of magnetic particles having a particle
diameter greater than the above particles ranging from greater than
1.0 .mu.m to 20 .mu.m may be used as the magnetic particles.
[0012] In the front face erasable microcapsule magnetophoretic
display sheet described above, the proportion of the magnetic
particles may be the sum total of 100% by weight of said at least
one kind of magnetic particles having a particle diameter ranging
from 0.1 .mu.m to 1.0 .mu.m and 10 to 200% by weight of said at
least one kind of magnetic particles having a particle diameter
greater than the above particles ranging from greater than 1.0
.mu.m to 20 .mu.m.
[0013] In the front face erasable microcapsule magnetophoretic
display sheet described above, the support may be a releasing
member, and the display sheet is composed of only a support-free
solid dispersion layer from which the releasing member has been
released and removed.
[0014] In the front face erasable microcapsule magnetophoretic
display sheet described above, a solvent in the liquid dispersion
may be composed of at least one low-boiling solvent selected from
the group consisting of toluene, xylene, ethylbenzene,
methylcyclohexane, ethylcyclohexane and cyclohexane and at least
one high-boiling solvent selected from the group consisting of
dodecylbenzene, dipentylbenzene, diphenyl ether, dibenzyl benzoate,
phenylxylylethane, diethylbenzene, pentylbenzene, ethyl phthalate
and butyl phthalate, and a proportion of the high-boiling solvent
to the low-boiling solvent may be 10 to 250 parts by weight per 100
parts by weight of the low-boiling solvent.
[0015] According to the present invention, there is also provided
an erasing magnet for front face erasing, which is adapted to slide
it over at least a part of the front face of a front face erasable
microcapsule magnetophoretic display sheet, wherein the magnet is
arranged and used in such a manner that a clearance is made between
the front face erasable microcapsule magnetophoretic display sheet
and the magnet, whereby a magnetic field different from the case
where the magnet is brought into direct contact with the sheet acts
on microcapsules in the sheet.
[0016] According to the present invention, there is further
provided a writing magnet for front face erasable microcapsule
magnetophoretic display sheets, wherein a magnet is covered with a
metal to control a magnetic field.
[0017] In the front face erasable microcapsule magnetophoretic
display sheet according to the present invention, comprising the
support and the solid dispersion layer provided on one surface of
the support and composed of the microcapsules having an average
particle diameter of 50 to 650 .mu.m, in which the liquid
dispersion, the white pigment, the additives and the magnetic
particles are encapsulated, and the binder, the magnetic particles
may include at least two kinds of magnetic particles different in
particle diameter from each other, whereby the magnetic sheet can
exhibit a particularly marked effect that characters, diagrams
and/or the like magnetically recorded on the magnetic recording
sheet can be wholly or partially erased simply and easily from the
recording surface side thereof.
[0018] In the magnetophoretic display sheet according to the
present invention, at least one kind of magnetic particles having a
particle diameter ranging from 0.1 .mu.m to 1.0 .mu.m and at least
one kind of magnetic particles having a particle diameter greater
than the above particles ranging from greater than 1.0 .mu.m to 20
.mu.m may be used as the magnetic particles, whereby the magnetic
sheet can exhibit a particularly preferred effect for wholly or
partially erasing the magnetically recorded characters, diagrams
and/or the like simply and easily from the recording surface
side.
[0019] In the magnetophoretic display sheet according to the
present invention, the proportion of the magnetic particles may be
the sum total of 100% by weight of said at least one kind of
magnetic particles having a particle diameter ranging from 0.1
.mu.m to 1.0 .mu.m and 10 to 200% by weight of said at least one
kind of magnetic particles having a particle diameter greater than
the above particles ranging from greater than 1.0 .mu.m to 20
.mu.m, whereby the magnetic sheet can exhibit an excellent effect
that the magnetically recorded characters, diagrams and/or the like
can be wholly or partially erased simply and easily from the
recording surface side.
[0020] In the magnetophoretic display sheet according to the
present invention, the support may be a releasing member, and the
display sheet may be composed of only a support-free solid
dispersion layer from which the releasing member has been released
and removed, whereby the uses of the sheet can be variously widened
without using any writing magnet pen in that it can be used for
production of machine readable magnetic records and as inspection
materials of steel products or the like.
[0021] In the magnetophoretic display sheet according to the
present invention, a solvent in the liquid dispersion may be
composed of at least one low-boiling solvent selected from the
group consisting of toluene, xylene, ethylbenzene,
methylcyclohexane, ethylcyclohexane and cyclohexane and at least
one high-boiling solvent selected from the group consisting of
dodecylbenzene, dipentylbenzene, diphenyl ether, dibenzyl benzoate,
phenylxylylethane, diethylbenzene, pentylbenzene, ethyl phthalate
and butyl phthalate, and a proportion of the high-boiling solvent
to the low-boiling solvent may be 10 to 250 parts by weight per 100
parts by weight of the low-boiling solvent, whereby the dispersoids
can be more stably dispersed.
[0022] In the erasing magnet for front face erasing according to
the present invention, which is adapted to slide it over at least a
part of the front face of a front face erasable microcapsule
magnetophoretic display sheet, the magnet may be arranged and used
in such a manner that a clearance is made between the front face
erasable microcapsule magnetophoretic display sheet and the magnet,
whereby a magnetic field different from the case where the magnet
is brought into direct contact with the sheet acts on microcapsules
in the sheet. As a result, an erasing magnet for front face
erasing, which has a simple structure and can partially erase
characters, diagrams and/or the like from the recording surface
side of a recorded sheet can be provided.
[0023] In the writing magnet according to the present invention for
front face erasable microcapsule magnetophoretic display sheets
(hereinafter referred to as "writing magnet for front face erasable
sheet"), the magnet may be covered with a metal to control a
magnetic field, whereby the writing magnet can exhibit an excellent
effect that fine characters, diagrams and/or the like can be
clearly displayed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The above and other objects, features and advantages of the
present invention will become apparent from the following
description and the appended claims, taken in conjunction with the
accompanying drawings, in which:
[0025] FIGS. 1A and 1B are a plan view and a cross-sectional view,
respectively, illustrating an erasing magnet for front face erasing
according to an embodiment of the present invention;
[0026] FIGS. 2A and 2B are a plan view and a cross-sectional view,
respectively, illustrating an erasing magnet for front face erasing
according to another embodiment of the present invention; and
[0027] FIGS. 3A and 3B are a plan view and a cross-sectional view,
respectively, illustrating a writing magnet for front face erasable
sheet used in the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] The present invention will hereinafter be described in
detail.
[0029] In the front face erasable microcapsule magnetophoretic
display sheets according to the present invention, at least two
kinds of magnetic particles different from each other in at least
any of particle diameter and material are contained. As these
magnetic particles, any magnetic particles may be used so far as
they are ordinarily used in this technical field. Examples thereof
include fine particles of black iron oxide, porous iron oxide,
manganese dioxide-containing iron oxide, chromium dioxide, ferrite,
iron and nickel, and magnetic particles to which no hydrophilic
treatment is subjected, such as iron-nickel alloys, with synthetic
magnetic iron oxide being particularly preferred. These magnetic
materials may be used either singly or in any combination thereof.
Examples of commercially available products include Todacolor
KN-320 (magnetite, product of Toda Kogyo Corporation and Tarox
BL-50 (synthetic iron oxide, product Titan Kogyo K.K. Magnetic iron
oxide represented by Fe.sub.3O.sub.4 is preferred.
[0030] The particle diameter of these magnetic particles are
preferably not greater than 20 .mu.m, more preferably 0.1 .mu.m to
20 .mu.m. In the magnetic particle groups different from each other
in particle diameter, a group of magnetic particles having a
smaller particle diameter has a particle diameter ranging from 0.1
.mu.m to 1.0 .mu.m, and one or more kinds of such magnetic
particles are used. On the other hand, a group of magnetic
particles having a greater particle diameter has a particle
diameter ranging from greater than 1.0 .mu.m to 20 .mu.m, and one
or more kinds of such magnetic particles are used. These groups of
magnetic particles are not separately used, but used in
combination, whereby the greater magnetic particles act so as to
aid and facilitate the action of the smaller magnetic particles
upon erasing of the resulting magnetophoretic display sheet in such
a manner that the greater magnetic particles are temporally
attracted by the smaller magnetic particles upon migration and
dispersion thereof to migrate in a state attached to the smaller
magnetic particles, and the smaller magnetic particles migrate in a
state included in the greater magnetic particles. As a result,
clean erasing is feasible without leaving the blackness of the
smaller magnetic particles. According to the present invention,
therefore, the present invention cab exhibit a particularly marked
effect that characters, diagrams and/or the like magnetically
recorded on such a magnetic recording sheet can be partially erased
simply and easily from the recording surface side. As described
above, in the present invention, such actions and effects as
described above are brought about by using, in combination, the
magnetic particles having a particle diameter ranging from 0.1
.mu.m to 1.0 .mu.m as a group of the smaller magnetic particles and
the magnetic particles having a particle diameter ranging from
greater than 1.0 .mu.m to 20 .mu.m as a group of the greater
magnetic particles. The effects of the present invention cannot be
achieved if this range is departed.
[0031] With respect to the microcapsules used in the present
invention, in which a liquid dispersion, a white pigment, additives
and the magnetic particles are encapsulated, the average particle
diameter is 50 to 650 .mu.m, preferably 50 to 400 .mu.m. If the
average diameter is smaller than 50 .mu.m, the effects of the
present invention cannot be achieved. If the average particle
diameter exceeds 650 .mu.m on the other hand, economical
disadvantage is incurred. The microcapsules themselves can be
easily produced by means of any publicly known production
technique. The liquid dispersion used in the present invention is
composed of solvents stable to the production of the microcapsules
and compatible with each other. As the liquid dispersion, a
low-boiling solvent and a high-boiling solvent may preferably used
in combination for the purpose of facilitating the movement
(migration) of a magnetic material (for example, magnetic
particles) and improving contrast. As described above, examples of
the low-boiling solvents used in the present invention include
toluene, xylene, ethylbenzene, methylcyclohexane, ethylcyclohexane
and cyclohexane. These low-boiling solvents may be used either
singly or in any combination thereof. Examples of the high-boiling
solvents used in the present invention include dodecylbenzene,
dipentylbenzene, diphenyl ether, dibenzyl benzoate, diethyl
phthalate, phenylxylylethane, diethylbenzene, pentylbenzene, ethyl
phthalate and butyl phthalate. These high-boiling solvents may be
used either singly or in any combination thereof. A proportion of
the high-boiling solvent to the low-boiling solvent is 10 to 250
parts by weight per 100 parts by weight of the low-boiling solvent,
preferably 20 to 200 parts by weight per 100 parts by weight of the
low-boiling solvent, more preferably 20 to 150 parts by weight per
100 parts by weight of the low-boiling solvent, still more
preferably 40 to 100 parts by weight per 100 parts by weight of the
low-boiling solvent. If the proportion of the high-boiling solvent
to the low-boiling solvent is lower than 10% by weight, the
divergence of the low-boiling solvent cannot be prevented. Although
mixing in a ball mill or the like is necessary for dispersing the
magnetic material and the white pigment in a solvent, only the
low-boiling solvent high in volatility cannot be used in the
mixing, and so it is necessary to mix at least 10% by weight of the
high-boiling solvent. If the proportion of the high-boiling solvent
exceeds 250% by weight on the other hand, the movement of the
magnetic particles becomes poor.
[0032] The white pigment used in the present invention is composed
of nonmagnetic particles. Examples thereof include white pigments
such as titanium oxide, lithopone, zinc white, white lead and zinc
sulfide. The titanium oxide used may be either anatase type and
rutile type. Rutile type titanium oxide is preferred from the
viewpoint of covering property. These pigments are preferably small
in specific gravity. Further, those having relatively high oil
absorption (meaning that a solvent is absorbed in the interior of
particles) are preferred. No particular limitation is imposed on
the particle diameter of the nonmagnetic particles so far as they
can be sufficiently dispersed. However, it is generally 0.1 to 20
.mu.m, preferably 0.1 to 10 .mu.m, more preferably 0.1 to 5 .mu.m,
still more preferably 0.1 to 1 .mu.m. When the particle diameter of
the magnetic particles is great, and the particle diameter of
titanium oxide is small, the blackness is not developed though the
movement of the magnetic particles becomes fast, so that contrast
is deteriorated. When the particle diameter of the magnetic
particles is small, and the particle diameter of titanium oxide is
great, the movement of the magnetic particles becomes extremely
poor though the blackness is developed, and contrast is improved.
Thus, such a combination is not preferred. From these facts, it has
been found that the size of the nonmagnetic particles is preferably
smaller than the magnetic particles.
[0033] A proportion of the nonmagnetic particles used in the
present invention is 5.0 to 50.0% by weight, preferably 10.0 to
40.0% by weight, more preferably 15.0 to 35.0% by weight based on
the weight of the liquid dispersion. If the proportion of the
nonmagnetic particles to the liquid dispersion is lower than 5.0%
by weight, the resulting sheet becomes blackish as a whole in the
case of a thin type in particular, and so contrast is not fully
developed, and moreover clear characters and/or images cannot be
displayed. If the proportion of the nonmagnetic particles exceeds
50.0% by weight on the other hand, the resulting sheet becomes
whitish as a whole on the contrary, and so contrast is not fully
developed. In view of these respects, the proportion of the
nonmagnetic particles to the magnetic particles is preferably 4 to
30 times, more preferably 5 to 20 times, still more preferably 6.0
to 15.0 times. The resulting sheet can thereby display clear images
excellent in contrast even in the case of a thin type.
[0034] Examples of the additives used in the present invention
include fine particle thickeners and dispersing agents. Examples of
the fine particle thickeners include silicic anhydride, hydrous
silicic acid, silicates (sodium silicate, potassium silicate,
aluminum silicate, calcium silicate, etc.), finely particulate
alumina, silica powder, diatomaceous earth, kaolin, hard clay, soft
clay, bentonite, ultrafine calcium carbonate, ultrafine activated
calcium carbonate, calcium hydrogencarbonate, hydrous basic
magnesium carbonate, barium sulfate and benzidine Yellow. These
thickeners may be used either singly or in any combination thereof.
The amount of the fine particle thickener added to the liquid
dispersion varies according to the kind of the liquid dispersion.
However, it generally 0.2 to 5% by weight, preferably 0.4 to 2% by
weight based on the weight of the liquid dispersion. If the amount
of the fine particle thickener added to the liquid dispersion is
less than 0.2% by weight, the adjusting effect of such a thickener
on the magnetic particles and the nonmagnetic particles cannot be
exhibited. On the other hand, any amount exceeding 5% by weight
interferes with the movement of solid particles such as the
magnetic particles. It is hence not preferable to add the thickener
in such a little or great amount.
[0035] The dispersing agent used in the present invention is used
in dispersing the magnetic particles and the like. Examples of
preferable dispersing agents include polyoxyethylene lauryl ether,
polyoxyethylene cetyl ether, polyoxyethylene stearyl ether,
polyoxyethylene oleyl ether, anionic fatty acid ester mixtures,
polycarboxylic acid amine salts, sorbitan trioleate, sorbitan
monolaurate and sorbitan monostearate. The amount of the dispersing
agent added may be an amount ordinarily added as a dispersing
agent. However, it is generally 0.2 to 10% by weight, preferably
0.4 to 3.0% by weight based on the liquid dispersion. If the amount
of the dispersing agent added is less than 0.2% by weight,
sufficient dispersing effect cannot be achieved. If the amount
exceeds 10% by weight on the other hand, the viscosity of the
liquid dispersion becomes high, and so the properties of the liquid
dispersion are impaired.
[0036] In addition, colorants may be added to the liquid dispersion
as needed. As the colorants, dyes and pigments are generally used.
Examples of the dyes and pigments include dyes such as Methylene
Blue, Congo Red and Benzo Yellow TZ, and besides Oil Blue, Oil
Green, Oil Yellow and Benzidine Yellow. Such a colorant may be
contained in any of a gelatin film of a microcapsule, a transparent
aqueous additive in a microcapsule coating layer and a transparent
film, to say nothing of the liquid dispersion in the microcapsules,
whereby the microcapsules can be colored proper color. A back
surface or background of a magnetic display panel can be thereby
colored various colors.
[0037] In the front face erasable microcapsule magnetophoretic
display sheets described above, the proportion of the magnetic
particles is the sum total of 100% by weight of at least one kind
of the magnetic particles (hereinafter referred to as "small
particles") having a particle diameter ranging from 0.1 .mu.m to
1.0 .mu.m and 10 to 200% by weight of at least one kind of the
magnetic particles (hereinafter referred to as "large particles")
having a particle diameter greater than the above particles ranging
from greater than 1.0 .mu.m to 20 .mu.m. A proportion of the large
particles to the small particles is preferably 50 to 150% by
weight, more preferably 80 to 120% by weight per 100% by weight of
the small particles. If the proportion of the large particles is
lower than 10% by weight, the movement of the small particles
cannot be sufficiently aided. If the proportion of the large
particles exceeds 200% by weight on the other hand, blackness
cannot be sufficiently developed, so that clear characters and/or
diagrams cannot be displayed. Accordingly, the present invention
can exhibit an excellent effect that characters, diagrams and/or
the like magnetically recorded can be simply and easily erased
partially from the recording surface side by adjusting the
proportions of the small particles and the large particles to 10 to
200% by weight per 100% by weight of the small particles,
particularly 50 to 150% by weight per 100% by weight of the small
particles.
[0038] In the front face erasable microcapsule magnetophoretic
display sheets according to the present invention, the support is a
releasing member, and the display sheet is composed of only a
support-free solid dispersion layer from which the releasing member
has been released and removed, whereby the uses of the sheets can
be variously widened without using any writing magnet pen in that
they can be used for production of machine readable magnetic
records and as inspection materials of steel products or the
like.
[0039] In the erasing magnet for front face erasing according to
the present invention, which is adapted to slide it over at least a
part of the front face of the front face erasable microcapsule
magnetophoretic display sheet, the magnet is arranged and used in
such a manner that a clearance is made between the front face
erasable microcapsule magnetophoretic display sheet and the magnet.
The principle of the erasing magnet for front face erasing
according to the present invention will hereinafter be described.
The erasing magnet for front face erasing means a magnet capable of
erasing characters, diagrams and/or the like magnetically recorded
on the front face of the front face erasable microcapsule
magnetophoretic display sheet by sliding the erasing magnet over
the front face of the display sheet from the displayed surface
side. This magnet emits countless magnetic lines from its N pole
toward its S pole to form a magnetic field. In these magnetic
lines, there are portions almost horizontally acting on the magnet
at a position somewhat distant from the magnet. A region of the
almost horizontally acting magnetic lines is caused to act on the
microcapsules in the microcapsule magnetophoretic display sheet,
whereby the magnetic particles in the microcapsules are moved and
dispersed by the action of the magnetic lines. As a result, the
nonmagnetic particles composed of the white pigment particles are
substitutively gathered in plenty at the surface on the front, face
side to exhibit a white color. The present inventors have paid
attention to the fact that this almost horizontally acting magnetic
field is generated only by selecting an erasing magnet having the
desired nature, and this nature is very weak.
[0040] According to the erasing magnet of the present invention, by
taking such the construction as described above, an erasing magnet
which has a simple structure and can wholly or particularly
partially erase characters, diagrams and/or the like from the
recording surface side of a recorded sheet with ease by causing a
magnetic field different from the case where a magnet is brought
into direct contact with the sheet, i.e., with the generation of a
magnetic field controlled, to act on the microcapsules in the sheet
can be provided. As a material for the magnet, ferrite, rare earth
metals, Alnico alloy or the like may be used. However, the material
for the magnet is not limited to these materials.
[0041] The erasing magnet for front face erasing according to the
present invention will be described in more detail. An erasing
magnet having a property value of 100 to 750 G in terms of surface
magnetic flux density is preferably used. A magnet used herein
varies according to the uses of the display sheet, and so it is
widely selected according to the uses thereof without any
particular limitations. Its form may be any form of cylinder, coin,
rod, prism and the like, and its size may be suitably selected. As
erasing magnets used in front face erasing, are preferred ferrite
magnets, rare earth magnets such as rare earth cobalt magnets (for
example, samarium.cobalt magnet) and rare earth iron magnets
(neodymium.iron magnet, etc.), and bond magnets. As the kind of
magnetization of the magnet, is prepared double-side magnetization
IP (the surface magnetic flux density amounts to 100 to 750 G under
these conditions). As a particularly preferable magnet, may be used
an isotropic or anisotropic rare earth magnet or ferrite magnet.
Clear erasing is feasible by selecting a magnet and the kind of
magnetization of such conditions. In the erasing magnet for front
face erasing used in the present invention, it is preferred to
control the generation of a magnetic field by providing a
clearance. A clearance distance is often determined by the material
of the magnet used. No particular limitation is imposed on a method
for providing the clearance. For example, either an air layer or a
nonmagnetic material may be provided between the front face
erasable microcapsule magnetophoretic display sheet and the magnet
of the erasing magnet. In the present invention, a method of
uniting the magnet to the nonmagnetic material is preferred.
[0042] No particular limitation is imposed on the nonmagnetic
material. However, preferable examples thereof include resins,
sponge or sponge resins, rubber, wood, corrugated board, paper,
fibers, glass and metals. These materials may be preferably capable
of smoothly sliding on the magnetic display sheet. As a method for
uniting the magnet to the nonmagnetic material, may be either
bonding or fitting, or integral molding between different materials
in the case of resins or rubber. The clearance may also be provided
either on the erasing surface side alone or on both sides thereof.
When the clearance is provided on both sides, there is no need to
distinguish the erasing side of the magnet. When the clearance is
provided on all the surfaces of the magnet, recesses conformed to
fingers or a lug or handle may preferably be provided to make
handling easy.
[0043] FIGS. 1A and 1B are a plan view and a cross-sectional view,
respectively, illustrating an erasing magnet for front face erasing
and a front face erasable microcapsule magnetophoretic display
sheet according to an embodiment of the present invention, in which
FIG. 1A is a plan view showing the erasing magnet for front face
erasing, and FIG. 1B is a cross-sectional view showing the erasing
magnet for front face erasing and the front face erasable
microcapsule magnetophoretic display sheet. FIGS. 2A and 2B are a
plan view and a cross-sectional view, respectively, illustrating
the front face erasable microcapsule magnetophoretic display sheet
and an erasing magnet for front face erasing according to another
embodiment of the present invention, in which FIG. 2A is a plan
view showing the erasing magnet for front face erasing according to
another embodiment, and FIG. 2B is a cross-sectional view showing
the front face erasable microcapsule magnetophoretic display sheet
and the erasing magnet for front face erasing. FIG. 1A illustrates
the erasing magnet I for front face erasing having a circular
section and a diameter, .phi..sub.1 of 10 to 100 mm. As illustrated
in FIG. 1B, the erasing magnet I for front face erasing has a
clearance 3 on a lower surface of a magnet 2 for erasing and comes
into contact with a front face 1a of the front face erasable
microcapsule magnetophoretic display sheet 1 through the clearance
3. In this embodiment, the thickness, z of the magnet 2 for erasing
is 2 to 20 mm, and the thickness, z' of the clearance is expressed
by 0.2Z to 20Z. Similarly, FIG. 2A illustrates the erasing magnet
II for front face erasing having a rectangular section and a size
of 10 to 100 mm in breadth, x and 10 to 100 mm in length, y. As
illustrated in FIG. 2B, the erasing magnet II for front face
erasing has a clearance 3 on a lower surface of a magnet 2 for
erasing. In this embodiment, the values of z and z' are the same as
in FIG. 1B.
[0044] As illustrated in FIGS. 1A to 2B, the diameter, .phi..sub.1
is 10 to 100 mm, x is 10 to 100 mm, and y is 10 to 100 mm, and no
particular limitation is imposed on the shape and size of the
erasing magnets I and II for front face erasing so far as the
dimensions fall within the respective ranges described above. The
values of .phi..sub.1, x and y are can be determined can be
determined according to the sizes of the front face erasable
microcapsule magnetophoretic display sheet 1 used and characters to
be written thereon. Z is 2 to 20 mm, and z' is 0.2Z to 20Z,
preferably 0.2z to 5.0z, more preferably 0.5z to 2.0z, most
preferably 0.5z to 1.0z. If z is out of the range of 2 to 20 mm,
handling is difficult in view of the size, weight, etc. If z' is
smaller than 0.2z, a magnetic field applied to the front face
erasable microcapsule magnetophoretic display sheet 1 comes near to
perpendicular, and so the surface of the sheet becomes blackish. If
z' exceeds 20z on the other hand, no magnetic field can be applied
to the front face erasable microcapsule magnetophoretic display
sheet 1, and so written characters cannot be erased. Such a small
or great clearance is hence not preferred. In these limitations, z'
is particularly important from the viewpoint of causing the
magnetic field to suitably act on the magnetic display sheet.
[0045] FIGS. 3A and 3B illustrate a writing magnet III for front
face erasable sheet according to the present invention. As
illustrated in FIG. 3A, a writing magnet 21 is covered with a metal
5 to control a magnetic field. More specifically, it is a publicly
known technique to cover a magnet with a metal such as brass or
iron to partially control the generation of a magnetic field,
whereby fine and clear written characters can be formed on a
magnetic display sheet like the conventional writing magnet. In the
writing magnet III for front face erasable sheet used for the front
face writable and erasable magnetic display sheet (i.e. the front
face erasable microcapsule magnetophoretic display sheet) according
to the present invention, however, the generation of a magnetic
field must be more severely controlled than the front face writable
and rear face erasable magnetic display sheet. In the writing
magnet III used in the present invention, as a material of a magnet
21 for writing, ferrite, rare earth metals, Alnico alloy or the
like may be used. However, the material for the magnet 21 is not
limited to these materials. More specifically, as the kind of
magnetization of the magnet 21 for writing, is prepared double-side
magnetization IP (the surface magnetic flux density amounts to at
least 750 G under these conditions). In order to produce the
writing magnet III for front face erasable sheet using such a
magnet 21 for writing, the tip of the magnet 21 for writing is
coated with a metal 5 composed of a ferromagnetic material. A
magnetic force distribution can be thereby more concentrated, and
so a clear record can be effectively provided. As the coating metal
5, is generally preferably used brass or iron excellent in working
ability and stability. However, the material is not limited to
these metals so far as it can easily control a magnetic field.
[0046] The writing magnet for front face erasable sheet according
to the present invention will be described in more detail. FIGS. 3A
and 3B are a plan view and a cross-sectional view, respectively,
illustrating the writing magnet for front face erasable sheet used
in the present invention. As illustrated in FIGS. 3A and 3B, the
writing magnet III for front face erasable sheet is composed of a
rod magnet 21 having a diameter of .phi..sub.2, and coated with the
metal 5 under such conditions that an angle formed between a
diameter, .phi..sub.2' of a coating on the tip portion and a
diameter of a coating on the rear end is .theta..
[0047] With respect to the shape and size of the magnet for writing
used in producing the writing magnet III for front face erasable
sheet, .phi..sub.2 is 0.2 to 2.0 mm, preferably 0.8 to 1.2 mm.
.phi..sub.2' is 1.0.phi..sub.2 to 4.0.phi..sub.2 mm, preferably
2.0.phi..sub.2 to 30.phi..sub.2. If .phi..sub.2 is smaller than 0.2
mm, and .phi..sub.2' is smaller than 1.0.phi..sub.2, working is
difficult, strength becomes insufficient, and no preference is
given even from the viewpoint of safety. If .phi..sub.2 exceeds 2.0
mm on the other hand, a magnetic field generated by such a magnet
becomes too great, and so characters written by the resulting
writing magnet becomes thick. In FIG. 3B, z is 5.0 to 10.0 mm, and
z' is -0.3 to 1.0 mm, preferably 0.0 to 0.5 mm. If .phi..sub.2' is
out of the range of 1.0.phi..sub.2 to 4.0.phi..sub.2 mm, and z' is
out of the range of -0.3 to 1.0 mm, it is impossible to control the
magnetic field to a desired value, and so written characters become
unclear. Any z' greater than 1.0 mm is not preferred even from the
viewpoint of safety. No particular limitation is imposed on z, and
z is preferably matched to a pen body. No particular limitation is
also imposed on .theta.. In these requirements, z' is particularly
important from the viewpoint of controlling the magnetic field. By
satisfying these conditions, the writing magnet III for front face
erasable sheet can exhibit an excellent effect that fine
characters, diagrams and/or the like can be clearly displayed.
Incidentally, the metal coating 5 is provided for the purpose of
concentrating a magnetic force distribution, and so the coating
form of the metal 5 can be optionally determined by tests and the
like.
[0048] The front face erasable microcapsule magnetophoretic display
sheets according to the present invention can be used in various
application fields, for example, cards such as cash cards, cashless
cards, credit cards and prepaid cards, and besides general uses,
for example, illustrated books for little children, toys for little
children, character drills, panels for various games, boards for
penmanship, sheets and boards having an adhesive layer on their
rear faces, boards for writing memos, black boars for meeting,
various information boards in clean rooms, sign boards with lamp,
display panels for personal computers, etc. As special uses, they
can be used for production of machine readable magnetic records and
as inspection materials of steel products or the like.
[0049] The present invention will hereinafter be described in more
detail by the following examples. However, the following examples
are intended to explain the present invention, and so the present
invention is not limited to these examples.
EXAMPLE 1
[0050] (1) Preparation Process of Microcapsules: TABLE-US-00001
[Formulation of Liquid Dispersion A to be encapsulated in
microcapsule] Smaller magnetic particle (synthetic 1.5 wt. % iron
oxide, 0.3 .mu.m) Greater magnetic particle (synthetic 1.5 wt. %
iron oxide, 3 .mu.m) Nonmagnetic particle (white titanium 12.0 wt.
% oxide powder, R-820, 0.26 .mu.m, product of Ishihara Sangyo
Kaisha, Ltd.) High-boiling solvent (dibutyl phthalate) 40.0 wt. %
Low-boiling solvent (toluene) 43.6 wt. % Antifoaming agent (Dappo
SN-350, 0.2 wt. % silicone, product of San Nopco Limited)
Suspending agent (finely particulate 0.5 wt. % silicic acid,
Aerosil, product of Nippon Aerosil Co., Ltd.) Dispersing agent
(Nopcosanto K963 0.7 wt. % product of San Nopco Limited)
[0051] A 3.6% aqueous solution of gum arabic was added to a 3.6%
aqueous solution of gelatin adjusted to pH 6 to prepare an aqueous
solution for microcapsule film. After the solution was heated to
about 50.degree. C., and the pH of the solution was adjusted to 5,
Liquid Dispersion A formulated above was added, and the resultant
mixture was stirred in such a manner that the average droplet
diameter of droplets of the dispersion amounts to 100 .mu.m. After
the desired dispersion droplets were obtained, the dispersion was
slowly cooled to 10.degree. C. to gel a polymer film of gelatin/gum
arabic deposited interfaces between the dispersion droplets. A 25%
aqueous solution of glutaraldehyde was added to cure the polymer
film to obtain gelatin microcapsules. The microcapsule thus
obtained were classified through a screen to remove particles of a
size exceeding 250 .mu.m, thereby obtaining microcapsules having a
particle diameter of 250 .mu.m or smaller.
(2) Production of Front Face Erasable Microcapsule Magnetophoretic
Display Sheet:
[0052] An aqueous solution of a urethane resin as a aqueous binder
was added to a group of microcapsules obtained by removing water
from the microcapsules obtained above, and the resultant mixture
was fully stirred to form an inky product for coating. The
viscosity of this inky product for coating was 4,000 cPs. The
thus-obtained inky product for coating was applied to the surface
of a transparent film having a thickness of 75 .mu.m and dried with
hot air of 70.degree. C. for 40 minutes. The thickness of the
microcapsule-containing coating layer was 250 .mu.m. As a
protective member, a polyethylene terephthalate film having a
thickness of 50 .mu.m was further bonded to the
microcapsule-containing coating layer with an adhesive to produce a
microcapsule magnetic display sheet.
(3) Production of Erasing Magnet for Front Face Erasing:
[0053] An erasing magnet was formed in the shape of a coin as
illustrated in FIG. 1A using ferrite as a material of the magnet.
The diameter .phi..sub.1 and thickness z thereof were determined to
be 30 mm and 3.0 mm, respectively. On the other hand, an ABS resin
(acrylonitrile-butadiene-styrene resin) was used as a material of a
clearance to form a clearance having a diameter .phi..sub.1 of 30
mm and a thickness z' of 2.0 mm in the shape of a coin. The
coin-shaped ferrite and the coin-shaped ABS resin were then
integrally bonded to each other to provide an erasing magnet I for
front face erasing.
(4) Production of Writing Magnet for Front Face Erasable Sheet:
[0054] A circular rod-shaped ferrite magnet 21 was coated with
brass 5 as illustrated in FIGS. 3A and 3B, thereby producing a
writing magnet III for front face erasable sheet. A diameter of the
magnet .phi..sub.2 and a diameter .phi..sub.2' of a coating on the
tip portion were 1.0 mm and 2.5 mm, respectively, and z and z' were
7.0 mm and 0.0 mm, respectively. A handle was attached thereto to
provide a writing magnet pen for front face erasable sheet.
(5) Evaluation of Front Face Erasable Microcapsule Magnetophoretic
Display Sheet:
[0055] The erasing magnet I for front face erasing was slid on the
whole display surface of the front face erasable microcapsule
magnetophoretic display sheet 1 to erase the whole display surface
into a uniform clear white surface. Characters were written on this
surface with the writing magnet pen for front face erasable sheet.
As a result, both greater magnetic particles and smaller magnetic
particles migrated on the front face side to obtain a black clear
written display. In order to erase a part of the recorded
characters, the erasing magnet I for front face erasing was brought
into contact with the written display and scanned on a portion to
be erased. As a result, the characters of the scanned region were
able to be cleanly erased to make the scanned region a uniform
clear white surface.
EXAMPLE 2
[0056] (1) Preparation Process of Microcapsules: TABLE-US-00002
[Formulation of Liquid Dispersion B to be encapsulated in
microcapsule] Smaller magnetic particle (synthetic 1.5 wt. % iron
oxide, 0.3 .mu.m) Greater magnetic particle (synthetic 1.0 wt. %
iron oxide, 3 .mu.m) Greater magnetic particle (synthetic 0.5 wt. %
iron oxide, 10 .mu.m) Nonmagnetic particle (white titanium 12.0 wt.
% oxide powder, R-820, 0.26 .mu.m, product of Ishihara Sangyo
Kaisha, Ltd.) High-boiling solvent (dibutyl phthalate) 40.0 wt. %
Low-boiling solvent (toluene) 43.6 wt. % Antifoaming agent (Dappo
SN-350, 0.2 wt. % silicone, product of San Nopco Limited)
Suspending agent (finely particulate 0.5 wt. % silicic acid,
Aerosil, product of Nippon Aerosil Co., Ltd.) Dispersing agent
(Nopcosanto K963 0.7 wt. % product of San Nopco Limited)
(2) Production of Front Face Erasable Microcapsule Magnetophoretic
Display Sheet:
[0057] Microcapsules were prepared in the same manner as in Example
1 except that Liquid Dispersion B was used, and a front face
erasable microcapsule magnetophoretic display sheet was produced in
the same manner as in Example 1 except that the microcapsules
obtained above were used.
(3) Evaluation of Front Face Erasable Microcapsule Magnetophoretic
Display Sheet:
[0058] Such an erasing magnet II for front face erasing as
illustrated in FIG. 2A was slid on the whole display surface of the
front face erasable microcapsule magnetophoretic display sheet 1 to
erase the whole display surface into a uniform clear white surface.
Characters were written on this surface with the writing magnet pen
for front face erasable sheet. As a result, a black clear written
display was obtained. In order to erase the whole of the recorded
characters, the erasing magnet II for front face erasing was
brought into contact with the display surface and scanned over the
whole surface. As a result, the whole display surface was able to
be made a uniform clear white surface. The conventional erasing
magnet was also slid on the whole display surface of the front face
erasable microcapsule magnetophoretic display sheet 1. As a result,
the surface did not become white and entirely remained blackish
(blackish gray).
COMPARATIVE EXAMPLE 1
[0059] (1) Preparation Process of Conventional Microcapsules:
TABLE-US-00003 [Formulation of Liquid Dispersion C to be
encapsulated in microcapsule] Smaller magnetic particle (synthetic
3.0 wt. % iron oxide, 0.3 .mu.m) Nonmagnetic particle (white
titanium 12.0 wt. % oxide powder, R-820, 0.26 .mu.m, product of
Ishihara Sangyo Kaisha, Ltd.) High-boiling solvent (dibutyl
phthalate) 40.0 wt. % Low-boiling solvent (toluene) 43.6 wt. %
Antifoaming agent (Dappo SN-350, 0.2 wt. % silicone, product of San
Nopco Limited) Suspending agent (finely particulate 0.5 wt. %
silicic acid, Aerosil, product of Nippon Aerosil Co., Ltd.)
Dispersing agent (Nopcosanto K963 0.7 wt. % product of San Nopco
Limited)
(2) Production of Conventional Microcapsule Magnetophoretic Display
Sheet:
[0060] Microcapsules were prepared in the same manner as in Example
1 except that Liquid Dispersion C was used, and a conventional
microcapsule magnetophoretic display sheet was produced in the same
manner as in Example 1 except that the microcapsules obtained above
were used.
(3) Evaluation of Conventional Microcapsule Magnetophoretic Display
Sheet:
[0061] An erasing magnet II for front face erasing (see FIGS. 2A
and 2B) was slid on the whole rear face of the conventional
microcapsule magnetophoretic display sheet. As a result, the front
face exhibited a white color. When characters were then written on
this surface with the writing magnet pen for front face erasable
sheet, a black clear written display was obtained like Example 1.
When the erasing magnet II for front face erasing was brought into
contact with the whole display surface and scanned over the whole
surface, however, the display surface was extremely blackish
(blackish gray). When characters were then written on this surface
with the writing magnet pen for front face erasable sheet, written
characters were very poor in contrast, and so the resultant written
display was entirely poor in utility. Characters were further
written with a conventional writing magnet pen after the erasing
magnet II for front face erasing was slid on the whole rear face of
the conventional microcapsule magnetophoretic display sheet to
erase the display surface clean. As a result, the resultant written
display slightly had an unclear portion, but caused no problems in
practical use.
COMPARATIVE EXAMPLE 2
[0062] (1) Preparation Process of Conventional Microcapsules:
TABLE-US-00004 [Formulation of Liquid Dispersion D to be
encapsulated in microcapsule] Greater magnetic particle (synthetic
3.0 wt. % iron oxide, 3 .mu.m) Nonmagnetic particle (white titanium
12.0 wt. % oxide powder, R-820, 0.26 .mu.m, product of Ishihara
Sangyo Kaisha, Ltd.) High-boiling solvent (dibutyl phthalate) 40.0
wt. % Low-boiling solvent (toluene) 43.6 wt. % Antifoaming agent
(Dappo SN-350, 0.2 wt. % silicone, product of San Nopco Limited)
Suspending agent (finely particulate 0.5 wt. % silicic acid,
Aerosil, product of Nippon Aerosil Co., Ltd.) Dispersing agent
(Nopcosanto K963 0.7 wt. % product of San Nopco Limited)
(2) Production of Conventional Microcapsule Magnetophoretic Display
Sheet:
[0063] Microcapsules were prepared in the same manner as in Example
1 except that Liquid Dispersion D was used, and a conventional
microcapsule magnetophoretic display sheet was produced in the same
manner as in Example 1 except that the microcapsules obtained above
were used.
(3) Evaluation of Conventional Microcapsule Magnetophoretic Display
Sheet:
[0064] An erasing magnet II for front face erasing was slid on the
whole display surface of the conventional microcapsule
magnetophoretic display sheet. As a result, the surface exhibited a
blackish gray color. When characters were then written on this
surface with the writing magnet pen for front face erasable sheet,
only a written display very low in contrast was obtained. The same
result was obtained even when characters were written with a
conventional writing magnet pen. A conventional erasing magnet was
slid on the whole display surface of the conventional microcapsule
magnetophoretic display sheet to wholly erase the display surface.
However, the display surface remained black as a whole. Characters
were written on this display surface with the writing magnet pen
for front face erasable sheet and the conventional writing magnet
pen. In any case, however, no character was unable to be
written.
EXAMPLES 3 AND 4
Production of Erasing Magnet (Coin Shape) for Front Face
Erasing:
[0065] Erasing magnets were respectively produced with materials
and in sizes shown in Table 1 in the form of a coin as illustrated
in FIG. 1A. They are shown in Table 1 together with Comparative
Examples. TABLE-US-00005 TABLE 1 Ex. 3 Comp. Ex. 3 Ex. 4 Comp. Ex.
4 Coin-shaped Component of magnet Erasing magnet A Erasing magnet C
Erasing magnet E Erasing magnet G Material of magnet Ferrite
Ferrite Ferrite Ferrite Diameter .phi..sub.1(mm) 30 30 30 30
Thickness z(mm) 3.0 3.0 3.0 3.0 Material of clearance ABS resin --
ABS resin ABS resin Diameter .phi..sub.1 (mm) 30 -- 30 30 Thickness
z'(mm) 3.0 0 (direct contact) 0.6 63 Uniting method of both Bonding
-- Bonding Bonding
[0066] When the erasing magnet A for front face erasable sheet
according to the present invention was used to erase a written
display recorded on a front face erasable microcapsule
magnetophoretic display sheet, the written display was able to be
very clearly erased, the display surface was visually observed
becoming clear white. In addition, no unevenness occurred. When the
comparative erasing magnet E was used, a written display was able
to be erased, but the surface was somewhat blackish. Therefore,
contrast was slightly lowered. However, no problem was offered in
practical use though unevenness slightly occurred. On the other
hand, the comparative erasing magnet G failed to erase a written
display. The comparative erasing magnet C was able to erase a
written display, but the display surface became very blackish, and
so contrast was very lowered, which caused a problem in practical
use. In addition, unevenness was heavy.
EXAMPLES 5 AND 6
Production of Erasing Magnet (Rectangle) for Front Face
Erasing:
[0067] Erasing magnets were respectively produced with materials
and in sizes shown in Table 2 in the form of a rectangle as
illustrated in FIG. 2A. They are shown in Table 2 together with
Comparative Examples. TABLE-US-00006 TABLE 2 Ex. 5 Comp. Ex. 5 Ex.
6 Comp. Ex. 6 Coin-shaped Component of magnet Erasing magnet B
Erasing magnet D Erasing magnet F Erasing magnet H Material of
magnet Rare earth Rare earth Rare earth Rare earth Breadth x(mm) 50
50 50 50 Length y(mm) 30 30 30 30 Thickness z(mm) 15 15 15 15
Material of clearance Syn. rubber -- Syn. rubber Syn. rubber
Breadth x(mm) 50 50 50 50 Length y(mm) 30 30 30 30 Thickness z'(mm)
15 0 (direct contact) 3.0 330 Uniting method of both Integral
molding -- Integral molding Integral molding
[0068] When the erasing magnet B for front face erasable sheet
according to the present invention was used to erase a written
display recorded on a front face erasable microcapsule
magnetophoretic display sheet, the written display was able to be
very clearly erased, the display surface was visually observed
becoming clear white. In addition, no unevenness occurred. When the
comparative erasing magnet F was used, a written display was able
to be erased, but the surface was somewhat blackish. Therefore,
contrast was slightly lowered. However, no problem was offered in
practical use though unevenness slightly occurred. On the other
hand, the comparative erasing magnet H failed to erase a written
display. The comparative erasing magnet D was able to erase a
written display, but the display surface became very blackish, and
so contrast was very lowered, which caused a problem in practical
use. In addition, unevenness was heavy.
EXAMPLE 7
Production of Writing Magnet for Front Face Erasable Sheet:
[0069] Writing magnets for front face erasable sheet were
respectively produced with materials and in sizes shown in Table 3
by coating each writing magnet with a metal as illustrated in FIGS.
3A and 3B. A handle was attached to each writing magnet to provide
a writing magnet pen for front face erasable sheet. TABLE-US-00007
TABLE 3 Component of magnet Writing magnet A Writing magnet B
Writing magnet C Brass Material of magnet Ferrite Rare earth
Ferrite Diameter .phi..sub.2 (mm) 1.0 1.2 1.0 Diameter .phi..sub.2'
(mm) 2.5 2.4 2.5 z (mm) 7.0 6.0 7.0 z' (mm) 0.0 0.2 No coated
Component of magnet Writing magnet D Writing magnet E Writing
magnet F Brass Material of magnet Rare earth Ferrite Rare earth
Diameter .phi..sub.2 (mm) 1.2 1.0 1.2 Diameter .phi..sub.2' (mm)
2.4 2.5 2.4 z (mm) 6.0 7.0 6.0 z' (mm) No coated 2.0 1.8 Component
of magnet Writing magnet G Writing magnet H Writing magnet I Brass
Material of magnet Ferrite Rare earth Rare earth Diameter
.phi..sub.2 (mm) 1.0 1.2 2.5 Diameter .phi..sub.2' (mm) 2.5 2.4 4.5
z (mm) 7.0 6.0 6.0 z' (mm) -0.5 -0.4 0.0
[0070] The writing magnets A and B for front face erasable sheet
were respectively used to conduct recording on a front face
erasable microcapsule magnetophoretic display sheet. As a result,
both large characters and small characters recorded thereon were
very clear. When the writing magnets E, F, G, H and I for front
face erasable sheet were respectively used to conduct recording on
a front face erasable microcapsule magnetophoretic display sheet,
large characters were clear, but small characters were somewhat
unclear. However, they caused no problem in practical use. When the
writing magnets C and D for front face erasable sheet were
respectively used to conduct recording, both large characters and
small characters were unclear. In particular, intersecting portions
of the characters were indistinct.
[0071] According to the present invention, as described above, in
the front face erasable microcapsule magnetophoretic display sheet,
comprising the support and the solid dispersion layer provided on
one surface of the support and composed of the microcapsules having
an average particle diameter of 50 to 650 .mu.m, in which the
liquid dispersion, the white pigment, the additives and the
magnetic particles are encapsulated, and the binder, the magnetic
particles include at least two kinds of magnetic particles
different in particle diameter from each other, whereby the
magnetic sheet can exhibit a particularly marked effect that
characters, diagrams and/or the like magnetically recorded on the
magnetic recording sheet can be wholly or partially erased simply
and easily from the recording surface side thereof.
[0072] In the erasing magnet for front face erasing according to
the present invention, which is adapted to slide it over at least a
part of the front face of a front face erasable microcapsule
magnetophoretic display sheet, the magnet is arranged and used in
such a manner that a clearance is made between the front face
erasable microcapsule magnetophoretic display sheet and the magnet,
whereby a magnetic field different from the case where the magnet
is brought into direct contact with the sheet acts on microcapsules
in the sheet. As a result, an erasing magnet for front face
erasing, which has a simple structure and can partially erase
characters, diagrams and/or the like from the recording surface
side of a recorded sheet can be provided.
[0073] In the writing magnet for front face erasable sheet
according to the present invention, the magnet is covered with a
metal to control a magnetic field, whereby the writing magnet can
exhibit an excellent effect that fine characters, diagrams and/or
the like can be clearly displayed.
* * * * *