FIELD OF TECHNOLOGY
[0001] This invention relates to a pressure-sensitive recording material which can produce
multiple copies by pressures such as printing or writing pressure. More specifically,
it relates to a pressure-sensitive recording material having a surface coated layer
of a novel structure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0002] Figures 1 to 3 are examples of prior art pressure-sensitive recording materials in
which two color-forming components are coated on the surfaces of supports in a face-to-face
relationship; Figures 4 and 5 show examples of coated layers in the present invention;
and Figure 6 shows an example of a spot-type pressure-sensitive recording business
form which utilizes the pressure-sensitive recording materials of this invention.
All of these drawings are cross-sectional views.
[0003] In the drawings, 1 represents a support; 2, a microcapsular layer containing a liquid
comprising a color-forming agent; 3, a layer of a solid containing a coloring agent;
4 and 5, layers formed by spot-coating only the desired portions with a hot-melt type
coating containing a color-forming agent; 5', a layer formed by coating the entire
surface with the hot-melt type coating, and 6, a layer having absorbent micropores
consisting of microcapsules, a fine powder and a binder.
BACKGROUND TECHNOLOGY
[0004] Pressure-sensitive recording materials having two color-forming components coated
on the surfaces of separate supports, which have conventionally gained widespread
use, are of the type shown in Figure 1. Specifically, one of the color-forming components
is encapsulated in microcapsules (2) and coated on the undersurface of an upper support
(1), and the other color-forming component is present as a coated layer (3) on the
top surface of a lower support (1). When a printing or writing pressure is applied
to such a pressure-sensitive material, the liquid contained in the microcapsules (2)
flows out and is transferred to, and absorbed by, the coated layer (3), and simultaneously,
the two color-forming components react with each other to form a colored substance
and thus to form an image on the receptive surface of the coated layer (3).
[0005] When in the material of the type shown in Figure 1, the upper support and the lower
support are superimposed and cut or bent, colored stains occur at the parts to which
pressure is applied. There is known a pressure-sensitive recording sheet in which
microcapsules (2) containing a color-forming component are spot-coated on the undersurface
of the upper support, as shown in Figure 2, in order to inhibit or avoid the occurrence
of such an inconvenience. In practice, however, the spot-coating of microcapsules
is difficult, because tough capsules which withstand spot-coating are difficult to
obtain, and creases form on the coated support because of the use of a water-base
coating, etc.
[0006] It was thus proposed to form a transferable spot-coated layer (4) by spot-coating
a so-called hot-melt ink resulting from the dispersion of a color-forming conponent
in a hot-melt type wax on the undersurface of the upper support (1), as shown in Figure
3. Although in this type, the color-forming components contained in the transferable
coated layer (4) and the receptive coated layer (3) are enveloped by another component
(e.g., wax, binder, etc.), when the upper support and the lower support are handled
in the superimposed state, colored stains occur under an unexpected exterior force.
Furthermore, when a printing or writing pressure is applied, the transferable coated
layer (4) is transferred to the receptive coated layer (3), and conversely, the receptive
layer (3) is transferred to the transferable layer (4). This results in the formation
of an image on both coated layers, and the rate of color formation and the density
of the color formed in the receptive coated layer are frequently reduced. If, in an
attempt to remove such an inconvenience, the formulation is changed so that the transferable
coated layer (4) may not easily be transferred, color formation upon the application
of a printing or writing pressure is poor so that a clear image cannot be obtained.
DISCLOSURE OF THE INVENTION
[0007] As a material which removes these inconveniences, the present invention provides
a pressure-sensitive recording material comprising a transferable coated layer of
a hot-melt type coating containing one color-forming component and a receptive coated
layer having absorbent micropores and consisting of microcapsules which contain another
color-forming component, a fine powder and a binder. Figures 4 and 5 illustrate this
invention. Figure 4 shows a material in which a transferable coated layer (5) is spot-coated
on the undersurface of an upper support (1), and Figure 5 shows a material in which
a transferable coated layer (5) is coated on the entire undersurface of the upper
support (1). In these figures, (6) represents a layer having absorbent micropores
-and consisting of the microcapsules, a fine powder and a binder, which is applied
to the top surface of the lower support (1).
[0008] As stated above, many pressure-sensitive recording sheets are of the type in which
microcapsules containing one color-forming component as a liquid are kept present
in the transferable coated layer when the liquid in the capsules is caused to be transferred
to the opposite receptive surface to form a color thereon. In this case, not all of
the liquid in the capsules is transferred to the receptive surface, and some remains
on the transfer surface without contributing to color formation. In contrast, the
present invention is based on the theory that microcapsules are caused to be present
in the receptive layer and the liquid therein is flowed out and absorbed in the layer,
instead of causing microcapsules containing a color-forming component to be present
in'the transferable coated layer and transferring them to the receptive coated layer.
Because the color-forming component in the capsules changes effectively to a colored
substance which directly forms an image on the receptive surface, both the rate of
color formation and the density of the color formed increase. For the same reason,
it is not necessary to incorporate a large amount of the coloring component. Thus,
the first feature of the present invention is that microcapsules containing one color-forming
component are included in the recentive coated layer.
[0009] The second feature of the present invention is the use of a hot-melt type coating
containing a color-forming component in the transferable coated layer. As is well
known, the hot-melt type coating is called a hot-melt ink or hot-melt wax, and has
the advantage that this coating is easy to spot-coat and needs only to be cooled after
coating without the need for drying, and moreover, the coating head is simple and
the rate of coating can be increased. When the hot-melt coating is used in the construction
shown in Figure 3, inconveniences are caused. However, when in accordance with this
invention, the transferable coated layer composed of such a hot-melt coating containing
a color-forming component is combined with the structure in which the microcapsules
are included in the receptive coated layer, i.e. the first feature described above,
the advantages of the two cooperate with each other to give good results.
[0010] The combination of the first and second features alone is still inconvenient, however.
If the microcapsules are ruptured immediately before the hot-melt type coating of
the transferable coated layer is transferred upon the application of printing pressure
to the surfaces of the microcapsules in the receptive coated layer, the liquid comes
out and is transferred to the transferable coated layer to form a color. Or because
the hot-melt type coating cannot be transferred, an image is not formed well. Hence,
the results are undesirable.
[0011] Thus, according to this invention, the receptive coated-layer is formed as a layer
of the structure having absorbent micropores and composed of microcapsules, a fine
powder and a binder, and the liquid which comes out upon the application of pressure
is instantaneously and completely absorbed in the receptive coated layer. By so doing,
the hot-melt type coating is completely transferred, and back-transferring of the
liquid does not occur. The layer of the structure having absorbent micropores also
has an action of protecting the microcapsules against an external force.
[0012] In preparing the receptive coated layer, appropriate conditions corresponding to
the size of the capsules, the amount of the binder, and the shape, size and size distribution
of the fine powder should be selected so that the volume of the pores is larger than
the total volume of the liquid in the capsules to provide absorbent micropores having
the aforesaid function. The following table shows experimental examples which show
the relation of the blending proportions of the capsules, the fine powder and the
binder in the preparation of a receptive layer to the function of the receptive layer
formed. In these experiments, a hot-melt coating containing 30% of Silton Clay (a
product of Mizusawa Kagaku) was used as the transferable layer.
[0013] The formation and effect of absorbent micropores _are described further.
[0014] Generally, in order for a liquid to penerate into a capillary and reach a distant
point, the diameter of the capillary should be as small as possible. However, in order
for a large amount of the liquid to be absorbed within short periods of time, the
diameter of the capillary should be as large as possible. In the receptive coated
layer in this invention, it is desirable for the liquid which has flowed from the
microcapsules to be instanta--neously and completely absorbed by the aforesaid coated
layer. Consequently it is desirable that the diameter of absorbent micropores should
br large. However, since the size of the microcapsules is usually about 1 to 10 microns
and the amount of the liquid contained in the microcapsules is small, if the diameter
of pores existing in the neighborhood is too large, the liquid does not at all move
along the pores, that is, it is not absorbed. Accordingly, the diameter of the absorbent
micropores should be smaller than about 10 microns. Furthermore, in order to increase
the ability of absorbing liquid, the total volume of the pores should be large.
[0015] Usually, the microcapsules are spherical when they are dispersed in a liquid, but
when they are coated and dried, they form a nearly continuous phase with not so much
interstices left among the microcapsules. Thus, the interstices are filled with the
powder or a fine fibrous powder in order to leave fine spaces after drying.
[0016] Generally speaking, when spheres of the same diameter are filled in a box, 26% of
space remains in the closest packing and 50% of the space remains in the bulky packing.
In a cylindrical filament, 22% of the space likewise remains. Thus, if a coated layer
is formed on a support by means of a coating composed of microcapsules and various
fine powders and dried, the aforesaid space should remain. However, if a binder is
added to prevent picking of the dried coated layer, the amount of the space decreases
according to the amount of the binder blended. If the amount of the binder increases-beyond
the amount of the space, no absorbent micropore will remain.
[0017] The above is based on presumption from calculated values. The fine powders in actual
use are not spherical or cylindrical but irregularly-shaped. Thus, the particle size
distribution exists continuously, and there may be a deviation from the calculated
values. The above table shows a part of this situation. When the receptive layer and
the transferable layer are set opposite to each other and letters are printed, an
image appears in the transferable layer upon the migration of the color-forming component
in the microcapsules to the color-forming component of the transferable layer. This
shows that the liquid contained in the ruptured microcapsules cannot be fully absorbed
by the receptive layer and the excess of the liquid is transferred to the transferable
surface. In the above experiments, when the amount of the microcapsules in the receptive
coated layer is less than 20%, the liquid in the microcapsules is all absorbed by
the receptive coated layer to prevent coloration at the transferable coated layer.
[0018] The total volume of the absorbent micropores which gives such an effect has to do
not only with the amount of a fine powder to be blended, but also directly with the
amount of the binder added. The total pore volume decreases when the binder is added
in a large amount, and increases when it is added in a small amount. Moreover, when
the support is absorbent, it absorbs the binder incorporated in the coating, and changes
the amount of the binder remaining in the dried coated layer. Accordingly, the absorbency
of the support also affects the total pore volume.
[0019] In the examples of coating formulations shown in the above table, wood-free paper
having a basis weight of 43 g/m
2 is used as a support, and precipitated calcium carbonate and polyvinyl alcohol are
added to microcapsules. Depending upon the materials used, for example upon the selection
of the support, microcapsules, fine powder or binder, the same results are not always
obtained. Usually, good results can be obtained by adjusting the proportions of the
individual components in the coated layer as follows:
[0020] Of course, the proportions of the fine powder and the binders should be selected
properly within the aforesaid ranges in order to form absorbent micropores of the
desired volume. In short, in the present invention, the amounts of the fine powder
and binder should be selected properly so that the total amount of the liquid in the
microcapsules does not exceed the total pore volume of the absorbent micropores formed
in the receptive coated layer.
[0021] The support in this invention is mainly paper. However, since in this invention the
receptive coated layer is given the ability to absorb a liquid, a non-absorbent material
such as plastic films and metal foils may optionally be used. Thus, there is no particular
limit to the material for the support.
[0022] As the color-forming components, various combinations of compounds which react with
each other to form a colored substance can be used. Since in this invention, one component
of the combination is used in the form of a hot-melt type coating, substances having
strong valatility at about 100°C or substances which are liquid at room temperature
are undesirable. There can be used combinations of colorless dyes of the triphenylmethane
phthalide, fluoran, phenothiazine, indolyl phthalide, leuco auramine, spiropyran,
triphenylmethane, triazene, naphtholactam, benzopyrane, azomethine, hydroxyphthalane
types, etc. with inorganic color developing agents such as activated clay, colloidal
silica or zeolite and various organic color developing agents. The compounds in these
combinations may be used interchangeably in the transferable coated layer and the
receptive coated layer. A combination of a ferric salt of a fatty acid with a higher
alcohol ester of gallic acid, and a combination of a vanadium compound such as stearyl
trimethyl ammonium vanadate and a higher alcohol ester of gallic acid are also used.
If desired, these combinations may be used as mixtures.
[0023] The fine powder, as used in the present invention, denotes various inorganic and
organic white pigments, starch particles, wood cellulose powder, etc. It should not
be the one which forms a color upon contact with the microcapsules containing a color-forming
component. This is because even when the color-forming component is kept inside the
microcapsules, it is by no means sure that the color-forming component does not at
all adhere to the outside wall of the capsules. For example, for capsules containing
crystal violet lactone, etc., fine powders which do not cause color formation, such
as calcium carbonate or aluminum hydroxide are desirable.
[0024] In addition, the shape, size and size distribution of the fine powder have to do
with the formation of absorbent micropores, and become factors which determine the
rate and amount of absorbing the liquid in the capsules. Although it is difficult
to express these parameters by numerical figures, desirable fine powders are those
which exhibit a nearly spherical shape and have a particle diameter of 0.5 to 20 microns
and a particle size distribution which is concentrated as much as possible on one
point. The wood cellulose powder desirably has a size of less than 300 mesh.
[0025] Natural and synthetic polymers which do not form a color with the color-forming component
are used as the binder. Since the amount of the binder added is an important factor
in forming absorbent micropores, it should be determined so as to maintain a balance
against the amount of the capsules by considering the aforesaid calculated values
of the remaining space at the time of filling spherical bodies into a box and the
shape, size and size distribution of the fine powder used.
[0026] Since the hot-melt type coating should be transferable, it is desirable to form a
primer layer before its coating. As the primer, the above-exemplified polymers used
as binders may be used. Those having good effect of sealing are selected.
[0027] Materials for the hot-melt type coating other than the color-forming component include,
for example, high-melting natural waxes such as carnauba wax, candelilla wax and montan
wax, oils and fats, hardened oils, higher fatty acids, polyvalent metal salts of higher
fatty acids, petroleum waxes, and other involatile high-melting substances. If desired,
minor amounts of involatile solvents may be added. Furthermore, stabilizers such as
antioxidants and ultraviolet absorbents may be added as required.
POSSIBILITY OF UTILIZATION IN INDUSTRY
[0028] A stack of a plurality of the pressure-sensitive recording materials of this invention
can'be used as a pressures-sensitive recording business form.
BEST MODE OF PRACTICING THE INVENTION
[0029] The present invention is illustrated specifically by the following Examples. These
Examples are for the purpose of illustrating preferred modes of practicing the invention,
and the invention is not limited thereto.
Example 1
[0030] Microcapsules containing colorless dyes were prepared in the following manner.
[0031] Crystal violet lactone (50 g) and 30g of benzoyl leuco methylene blue were dissolved
in alkylnaphthalene (KMC-113, Kureha Chemical) to form 1000g of a solution. The solution
was dispersed in a solution of 200g of gelatin in 1500g of water with stirring at
high speed by a homomixer. Then, a solution of 40g of carboxy methyl cellulose in
3000g of water was added. Furthermore, 2000g of water was added. Then, 90g of 10%
acetic acid was added to adjust the pH of the mixture to 4.0. The solution was then
cooled with ice to 7°C, and 150g of 37% formaldehyde was added, and then 300g of 4%
sodium hydroxide was added to adjust the pH of the mixture to 9.0. The mixture was
maintained at 50
0C for 1 hour, and 200g of wood cellulose powder (KC Flock-300, Sanyo Kokusaku Pulp)
was added. The mixture was then stored at room temperature. If desired, some amount
of an ultraviolet absorbent may be added to the alkylnaphthalene.
[0032] The formulation (parts by weight) of a coating for the receptive coated layer was
as follows:
[0033] An aqueous dispersion of the above formulation having a solids concentration of 18%
was coated by an air knife at a rate of 3.5 g/m
2 on wood free paper having basis weight of 40 g/m
2 and consisting of 70% LBKP and 30% NBKP. An 8% polyvinyl alcohol solution had been
coated on the back surface of the paper by a Meyer bar to prevent curling and give
barrier property as a primer for the transferable coated layer. Then, a hot-melt type
coating for the transferable coated layer consisting of the following formulation
was spot-coated at a rate of 3.0 glm2 by a hot-melt transfer gravure technique to
that surface of the paper which had been given barrier property as above. The formulation
(parts by weight) of the hot-melt coating was as follows:
[0034] The above ingredients were melt-mixed by a kneader at 80°C, and used as the hot-melt
type coating.
[0035] Ten paper sheets coated both at the top and back surfaces in the above manner were
superimposed to form a pressure-sensitive recording business form of the structure
shown in Figure 6 (the illustration of six intermediate sheets is omitted). When letters
were printed on the resulting assembly by an electric typewriter, blue clear letters
could be rapidly printed even on the lowermost sheet (lOth sheet).
[0036] When relief printing was performed on the surface of the receptive coated layer,
troubles were not seen as was the case with relief printing on wood free paper.
[0037] When a pressure-sensitive recording business form was made in the same way as above
using the receptive coated layer obtained in Run No.7 in the above table, the same
good results as above were obtained.
Example 2
[0038] In the same way as in Example 1, microcapsules containing an iron compound were prepared.
That is, 80g of a ferric salt of mixed coconut oil fatty acid was dissolved in oxyethylene
lauryl ether (Actinol, Matsumoto Kosan) to form 1000g of a solution. Using the resulting
solution, microcapsules were prepared.
[0039] A coating for a receptive coated layer was also prepared in accordance with Example
1.
[0040] The formulation (parts by weight) of a hot-melt type coating for a transferable coated
layer opposite thereto was as follows:
[0041] Ten coated sheets obtained in accordance with Example 1 were superimposed and letters
were printed on the assembly, The rate of color formation was somewhat lower than
in Example 1, but a black image having good fastness to light was obtained.