[0001] The present invention relates to a printing apparatus which can efficiently print
a small to large number of copies in two printing modes and, besides, is excellent
in drying characteristics of ink and causes less set-off of ink.
[0002] The "digital printing machines" have already become popular as printing machines
which are high in printing speed and low in running cost. In the digital printing
machines, a heat-sensitive stencil sheet composed of a thermoplastic film is molten
and perforated by a heating means such as a thermal head which emits heat in the form
of dots in accordance with image information of electric signals into which images
such as letters, figures and photographs are transformed, then the stencil sheet is
wound around a printing drum containing a stencil printing ink, and the printing ink
is transferred through perforations of the stencil sheet onto a printing paper.
[0003] However, when the heat-sensitive stencil sheet is perforated in these digital printing
machines, there often occur deficient perforation, failure of conveying and wrinkling
of the stencil sheet due to unevenness of pressure exerted to press the stencil sheet
to the thermal head. Furthermore, the conventional digital printing machines are useful
to obtain a large number of the same prints, but they rather require higher cost for
obtaining a small number of prints.
[0004] Under the circumstances, it is considered that printing machines are equipped with
heat-sensitive recording paper or thermal transfer recording paper for obtaining a
small number of prints. However, in this case, the printing machines become larger
in size and, further, operation becomes complicated because both the printing paper
and the recording paper must be prepared for the operation.
[0005] Furthermore, printing machines have been proposed according to which one kind of
paper may be printed by electrophotographic process when a small number of prints
are to be obtained or by stencil printing process using a heat-sensitive stencil sheet
when a large number of prints are to be obtained. However, the printing system as
a whole is expensive and is large in size.
[0006] On the other hand, when color prints are obtained by a digital printing machine,
printing drums containing a stencil printing ink must be prepared for the respective
colors. In partial color printing, printing drums must also be changed every one color
printing. Thus, the operation is complicated and working efficiency is deteriorated.
[0007] Furthermore, conventionally employed emulsion inks for stencil printing require much
time to be dried, and if printed paper is taken in hands, the ink is transferred to
hands or if printed pieces of paper are superposed in continuous printing, set-off
of the ink occurs, and this phenomenon is conspicuous in the case of postcard papers
which are poor in permeability to ink. This is because drying of the emulsion ink
is carried out only by permeation of oil phase and evaporation of water phase. In
addition, such emulsion ink changes in its viscosity depending on the environmental
temperature of use, and, for example, in the case of high temperature, the ink becomes
soft to cause seep through and so-called side or end leakage (that is, a phenomenon
of the ink leaking from edge or end portions of a stencil sheet wound around the printing
drum).
[0008] The object of the present invention is to provide a printing apparatus which does
not cause deficient perforation, wrinkling or failure in conveying at the time of
perforation of heat-sensitive stencil sheets, can efficiently print a small to large
number of copies at low running cost, and, besides, is excellent in drying characteristics
of ink and can inhibit set-off or seep through of ink.
[0009] According to the present invention, the above object can be achieved by a printing
apparatus which comprises
a liquid ejecting means for ejecting a photothermal conversion material contained
in a liquid onto a heat-sensitive stencil sheet in accordance with image information,
so that the photothermal conversion material is transferred to the stencil sheet to
reproduce thereon an image based on the image information;
a light irradiation means for irradiating the heat-sensitive stencil sheet to which
the photothermal conversion material has been transferred, with a visible or infrared
ray to perforate the stencil sheet;
a cylindrical printing drum having an ink-permeable circumferential surface, which
is rotated about a central axis thereof with the heat-sensitive stencil sheet wound
around the circumferential surface;
a heating means for heating a stencil printing ink which reversibly changes in its
phase from solid state to liquid state in said printing drum;
a squeeze means for internally contacting with the circumferential surface of said
printing drum and feeds the ink to the surface; and
a pressing means for pressing at least one of said printing drum and a printing sheet
which moves synchronously with the rotation of said printing drum, thereby to bring
them into close contact with each other, so that the stencil printing ink in liquid
state which is fed to the circumferential surface of said printing drum is transferred
to the printing sheet through the perforated heat-sensitive stencil sheet;
wherein said liquid ejecting means further ejects a photothermal conversion material
and/or a colorant contained in a liquid onto the printing sheet in accordance with
image information, whereby an image based on the image information can be directly
printed on the printing sheet.
[0010] That is, the first feature of the printing apparatus of the present invention, which
is different in stencil sheet perforation system from conventional rotary stencil
printing apparatuses, is that it employs a method for perforating a heat-sensitive
stencil sheet which comprises a first step of transferring a photothermal conversion
material to a heat-sensitive stencil sheet by ejecting a liquid containing the photothermal
conversion material onto the heat-sensitive stencil sheet from a liquid ejecting means
and a second step of perforating the heat-sensitive stencil sheet specifically at
sites to which the photothermal conversion material has been transferred, by irradiating
the heat-sensitive stencil sheet with a visible or infrared ray.
[0011] The liquid ejecting means may be a device which comprises an ejecting head of nozzle,
slit, porous material, porous film or the like having 10-2000 openings per inch (i.e.,
10-2000 dpi) which is connected to piezoelectric elements, heating elements, liquid-conveying
pumps or the like so as to eject the liquid containing the photothermal conversion
material intermittently or continuously, that is, in the form of dots or lines in
accordance with electric signals of letter images.
[0012] The first step can be performed, for example, by moving the ejecting head slightly
spaced from a heat-sensitive stencil sheet and in parallel with the heat-sensitive
stencil sheet and simultaneously controlling the liquid ejecting means so as to eject
the liquid containing the photothermal conversion material onto the heat-sensitive
stencil sheet from the ejecting head in accordance with image information previously
converted to electric signals, and evaporating the liquid transferred to the heat-sensitive
stencil sheet, thereby to reproduce the image as solid adherends mainly composed of
the photothermal conversion material on the heat-sensitive stencil sheet.
[0013] In the second step, when the heat-sensitive stencil sheet to which the photothermal
conversion material has been transferred is irradiated with a visible or infrared
ray, the photothermal conversion material absorbs light to emit heat. As a result,
the thermoplastic film of the heat-sensitive stencil sheet is molten and perforated
to obtain a master directly from the stencil sheet itself. Irradiation of the stencil
sheet with the visible or infrared ray can readily be carried out using xenon lamps,
flash lamps, halogen lamps, infrared heaters or the like.
[0014] In this way, the present printing apparatus does not require the stencil sheet to
contact any materials such as an original or a thermal head to make a master, but
only requires the stencil sheet itself to be irradiated with a visible or infrared
ray. Thus, no wrinkling occurs on stencil sheets in making masters.
[0015] Furthermore, in the present invention, the first and second steps mentioned above
may be carried out before the heat-sensitive stencil sheet is wound around the printing
drum or after the heat-sensitive stencil sheet has been wound around the printing
drum. Since the present printing apparatus employs an ink which reversibly changes
in its phase from solid state to liquid state, the printing apparatus is especially
useful for carrying out perforation of the heat-sensitive stencil sheet in a state
of being wound around the printing drum before heating and fluidizing the ink by a
heating means. That is, when the ink in the cylindrical printing drum is in solid
state and the ink on the outer circumferential surface of the cylindrical printing
drum is still in solid state, an air layer is present between the outer circumferential
surface of the cylindrical printing drum and the heat-sensitive stencil sheet wound
around the printing drum, and the air layer exhibits a substantial heat insulation
effect. Therefore, when the sites to which the photothermal conversion material has
been transferred are irradiated with a visible or infrared ray, heat energy generated
by photothermal conversion material is accumulated in the thermoplastic film, and,
as a result, the thermoplastic film is heated and efficiently molten and perforated.
[0016] On the other hand, in a stencil printing machine which uses an ink which is liquid
at room temperature, when the heat-sensitive stencil sheet is wound around the cylindrical
printing drum, the space between the outer circumferential surface of the printing
drum and the heat-sensitive stencil sheet is filled with the liquid ink and no air
layer is formed in the space. Therefore, even if the sites to which the photothermal
conversion material has been transferred are irradiated with a visible or infrared
ray in this state, heat energy generated by the photothermal conversion material diffuses
towards the liquid ink from the thermoplastic film, and, as a result, the temperature
of the thermoplastic film does not rise, and sometimes melting and perforation are
insufficiently performed.
[0017] The second feature of the present invention is that the printing apparatus is a printing
apparatus which can perform printing in two modes of stencil printing and ink jet
printing in which said liquid ejecting means further ejects a photothermal conversion
material and/or a colorant contained in a liquid onto a printing sheet in accordance
with image information previously transformed to electric signals, whereby images
based on the image information can be directly printed on the printing sheet.
[0018] In such a printing apparatus, the liquid ejecting means may have a single ejecting
head which can turn to different directions of the heat-sensitive stencil sheet and
the printing sheet and can eject the photothermal conversion material and/or a colorant
onto both the heat-sensitive stencil sheet and the printing sheet selectively, or
it may have separately an ejecting head which can eject the photothermal conversion
material onto the heat-sensitive stencil sheet and an ejecting head which can eject
the colorant onto the printing sheet. Furthermore, in order to make multicolor printing
possible, the liquid ejecting means may have a plurality of ejecting heads each of
which ejects each a colorant of a different color onto the printing sheet, or it may
have a single ejecting head which can eject a plurality of colorants of different
colors onto the printing sheet.
[0019] Thus, according to the present printing apparatus, a large number of copies can be
printed with stencil printing by ejecting a photothermal conversion material and/or
a colorant onto a heat-sensitive stencil sheet from a liquid ejecting means and perforating
the stencil sheet by a light irradiation means, and a small number of copies can be
simply printed by ejecting the photothermal conversion material and/or colorant directly
onto the printing sheet. Therefore, both the printing of a small number of copies
and that of a large number of copies can be efficiently performed only by providing
one kind of printing sheet and heat-sensitive stencil sheet in the printing apparatus
and controlling the liquid ejecting means in the printing appatatus. Moreover, overlay
printing and multicolor printing can also be effected by ejecting a photothermal conversion
material and/or a colorant in layers onto a printing sheet which has been printed
by stencil printing. Furthermore, printing in black, which is frequently demanded,
may be effected by stencil printing and printing in red, blue and yellow, which is
not frequently demanded, may be effected by printing directly from the liquid ejecting
means to increase efficiency of multicolor printing.
[0020] Photothermal conversion materials used in the present invention are those which can
transform light energy into heat energy, and are preferably those efficient in photothermal
conversion, for example, inorganic pigments such as carbon black, silicon carbide,
silicon nitride, metal powders, and metal oxides, and, besides, organic pigments and
organic dyes. Carbon black includes furnace black, channel black, lampblack, acetylene
black and oil black. Among organic dyes, particularly preferred are those having a
high light-absorbency within a specific range of wavelength, such as anthraquinone,
phthalocyanine, cyanine, squalirium and polymethine dyes.
[0021] Colorants used in the present invention may be the same as the photothermal conversion
materials if the photothermal conversion materials have colors. Examples of the colorants
are organic or inorganic pigments such as carbon black, Phthalocyanine Blue, Victoria
Blue, Brilliant Carmine 6B, Permanent Red F5R, Rhodamine Lake B, Benzidine Yellow,
Hansa Yellow, Naphthol Yellow, titanium oxide, and calcium carbonate, and azo, anthraquinone,
quinacridone, xanthene and acridine dyes.
[0022] The liquid in which the photothermal conversion material and the colorant are contained,
may be solvents such as aliphatic hydrocarbons, aromatic hydrocarbons, alcohols, ketones,
esters, ethers, aldehydes, carboxylic acids, amines, low molecular weight heterocyclic
compounds, oxides, and water. Specific examples thereof are hexane, heptane, octane,
benzene, toluene, xylene, methyl alcohol, ethyl alcohol, isopropyl alcohol, n-propyl
alcohol, butyl alcohol, ethylene glycol, diethylene glycol, propylene glycol, glycerin,
acetone, methyl ethyl ketone, ethyl acetate, propyl acetate, ethyl ether, tetrahydrofuran,
1,4-dioxane, formic acid, acetic acid, propionic acid, formaldehyde, acetaldehyde,
methylamine, ethylenediamine, dimethylformamide, pyridine, and ethylene oxide. These
liquids may be used alone or in combination, and are preferably those which evaporate
quickly after having been ejected from the liquid ejecting means onto the heat-sensitive
stencil sheet. To the liquid, may be added dyes, pigments, fillers, binders, hardening
agents, preservatives, wetting agents, surfactants, pH-adjusting agents, or the like,
as required.
[0023] Thus, compositions for perforating heat-sensitive stencil sheets or coloring can
be prepared by appropriately dispersing or mixing the above photothermal conversion
material and/or colorant in the above liquid in a form readily ejectable from the
liquid-ejecting means.
[0024] The heat-sensitive stencil sheet may be a stencil sheet to at least one side of which
the photothermal conversion material can be transferred and which can be molten and
perforated by heat emitted by the photothermal conversion material. The stencil sheet
may be made of a thermoplastic film only, or may be a thermoplastic film laminated
to a porous substrate.
[0025] The thermoplastic film includes a film made from polyethylene, polypropylene, polyvinyl
chloride, polyvinylidene chloride, polyethylene terephthalate, polybutylene terephthalate,
polystyrene, polyurethane, polycarbonate, polyvinyl acetate, acrylic resins, silicone
resins, and other resinous compounds. These resinous compounds may be used alone,
in combination, or as a copolymer. Suitable thickness of the thermoplastic film is
0.5 - 50 µm, preferably 1 - 20 µm. If the film is less than 0.5µm in thickness, it
is inferior in workability and strength. If the film is greater in thickness than
50 µm, it is not economical to be perforated requiring a great amount of heat energy.
[0026] The above porous substrate may be a thin paper, a nonwoven fabric, a gauze or the
like, which is made from natural fibers such as Manila hemp, pulp, Edgeworthia, paper
mulberry and Japanese paper, synthetic fibers such as of polyester, nylon, vinylon
and acetate, metallic fibers, or glass fibers, alone or in combination. Basis weight
of these porous substrates is preferably 1 - 20 g/m
2, more preferably 5 - 15 g/m
2. If it is less than 1 g/m
2, the stencil sheet is weak in strength. If it is more than 20 g/m
2, the stencil sheet is often inferior in ink permeability upon printing. Thickness
of the porous substrate is preferably 5 - 100 µm, more preferably 10 - 50 µm. If the
thickness is less than 5 µm, the stencil sheet is weak in strength. If it is more
than 100 µm, the stencil sheet is often inferior in ink permeability in printing.
[0027] The heat-sensitive stencil sheet used in the present invention preferably has a liquid
absorbing layer laminated to a side of the stencil sheet to which the liquid is ejected,
in order to prevent the liquid from blurring on the stencil sheet or to accelerate
drying of the liquid on the stencil sheet. In this case, perforations faithful to
the image information are obtained when a stencil sheet is irradiated with light,
and thus sharp image can be printed.
[0028] The liquid absorbing layer is preferably formed on the outermost surface of the heat-sensitive
stencil sheet as a resin layer which is molten and perforated similarly to the thermoplastic
film upon irradiation with light to obtain a master. The liquid absorbing layer can
be made of any materials so long as they can prevent the liquid from spreading in
a planar direction and fix the photothermal conversion material on the stencil sheet.
Preferably, the liquid absorbing layer is made of a material high in affinity with
the liquid used. For example, if the liquid is aqueous, the liquid absorbing layer
can be made of polymer compounds such as polyvinyl alcohol, methyl cellulose, carboxymethyl
cellulose, hydroxyethyl cellulose, polyvinyl pyrrolidone, ethylene-vinyl alcohol copolymers,
polyethylene oxide, polyvinyl ether, polyvinyl acetal, and polyacrylamide. These resinous
compounds may be used alone, in combination or as a copolymer. If the liquid is an
organic solvent, the liquid absorbing layer can be made of polymer compounds such
as polyethylene, polypropylene, polyisobutylene, polystyrene, polyvinyl chloride,
polyvinylidene chloride, polyvinyl fluoride, polyvinyl acetate, acrylic resins, polyamide,
polyimide, polyester, polycarbonate, and polyurethane. These resinous compounds may
be used alone, in combination, or as a copolymer.
[0029] Further, organic or inorganic particulates may be added to the liquid absorbing layer.
Such particulates include organic particulates such as of polyurethane, polyester,
polyethylene, polystyrene, polysiloxane, phenolic resin, acrylic resin, and benzoguanamine
resin, and inorganic particulates such as of talc, clay, calcium carbonate, titanium
oxide, aluminum oxide, silicon oxide, and kaolin.
[0030] The liquid absorbing layer can be obtained by coating a liquid containing the above
polymer compound and, if necessary, the above particulates on a heat-sensitive stencil
sheet by a coating means such as gravure coater and wire bar coater.
[0031] The third feature of the printing apparatus of the present invention is to use an
ink which reversibly changes its phase from solid state to liquid state at a certain
temperature as a stencil printing ink supplied into a cylindrical printing drum. Since
this ink becomes liquid having a certain viscosity by a heating means at the time
of stencil printing, it can be passed through perforations of stencil sheets and transferred
to printing sheets. Furthermore, the liquid ink that has been transferred to a printing
sheet instantaneously changes into a solid ink during conveyance of the printing sheet,
and, thus, the ink can be allowed to adhere to the printing sheet and fix thereon
in a short time. Accordingly, even if prints obtained by the method of the present
invention is touched with hand, the hands are not stained with ink, and besides no
set-off of ink occurs even if continuous printing is carried out. Furthermore, the
ink used in the present invention does not permeate into printing sheets, and thus
no seep-through occurs. Moreover, according to the present invention, since the ink
instantaneously changes in its phase from liquid to solid, not only usual printing
sheets and postcards which are poor in permeability to ink, but also films or metals
can be printed.
[0032] Stencil printing inks used in the present invention are desirably printing inks having
a phase-change temperature of 30 - 150°C, preferably 40 - 120°C. The solid state here
means a state of ink which loses fluidity to such an extent that the ink does not
stick to materials which touch the ink. The liquid state means a state of ink higher
in fluidity than in the solid state, preferably, a state of ink having a viscosity
of such an extent that the ink can flow through perforations of stencil sheets. The
phase-change temperature of ink means a maximum temperature at which the ink can keep
the above-mentioned solid state. If the phase-change temperature is too low, when
the inside temperature of the printing apparatus or environmental temperature becomes
lower than 30°C, the ink is fluidized to cause staining of a printing apparatus or
occurrence of so-called side or end leakage. If the phase-change temperature is higher
than 150°C, a heating means of large scale is needed for changing the ink from solid
to liquid to often cause loss of heat energy, and a long time is required for changing
the ink from solid to ink to prolong the waiting period before starting of printing.
[0033] The stencil printing ink used in the present invention can be obtained by mixing
a colorant and a reversibly phase-changeable component which reversibly changes in
phase from solid state to liquid state at a temperature in the range of 30 - 150°
C, preferably 40 - 120°C. For example, it can be obtained by melting the reversibly
phase-changeable component and mixing this component with a colorant and, if necessary,
a dispersing agent.
[0034] As the reversibly phase-changeable component, mention may be made of, for example,
waxes, fatty acid amides, fatty acid esters, and resins, such as carnauba wax, microcrystalline
wax, polyethylene wax, montan wax, paraffin wax, candellila wax, shellac wax, oxidized
wax, ester wax, beeswax, Japan wax, spermaceti, stearic acid amide, lauric acid amide,
behenic acid amide, caproic acid amide, palmitic acid amide, low molecular polyethylene,
polystyrene, α-methylstyrene polymer, vinyltoluene, indene, polyamide, polypropylene,
acrylic resin, alkyd resin, polyvinyl acetate, ethylene-vinyl acetate copolymer, and
vinyl chloride-vinyl acetate copolymer.
[0035] The colorants include, for example, organic or inorganic piqments such as furnace
carbon black, lampblack, Cyanine Blue, Lake Red, Cyanine Green, titanium oxide, and
calcium carbonate and dyes such as of azo, anthraquinone and quinacridone.
[0036] As the dispersing agents, anionic, cationic and nonionic ones can be used, and examples
of them are sorbitan fatty acid esters, fatty acid monoglycerides and quaternary ammonium
salts.
[0037] The stencil printing ink used in the present invention may be in a form of oil ink
and W/O type emulsion. The oil ink can be prepared by dissolving and mixing the reversibly
phase-changeable component, the colorant, and, if necessary, the dispersing agent.
The W/O type emulsion ink can be prepared by by dissolving and mixing the reversibly
phase-changeable component, the colorant, and, if necessary, the dispersing agent
and emulsifying the mixture with addition of an aqueous phase component under stirring,
and when the emulsion is cooled, a solid ink of W/O type is obtained. The colorant
may be contained in the aqueous phase component.
[0038] The stencil printing ink is rendered liquid by heating to higher than the phase-change
temperature at the time of printing, and the ink is preferably heated to such an extent
that the ink has a viscosity in a range of 10 - 1,000,000 cps, preferably 100 - 100,000
cps. If viscosity of the ink at the time of printing is lower than 10 cps, this is
too low and the ink is apt to leak from between the printing apparatus and an edge
of a stencil sheet to cause so-called side leakage or end leakage of the ink, and,
besides, the ink rapidly permeates a printing sheet from the surface to the inside
to cause seep-through. If the viscosity is higher than 1,000,000 cps, the ink passes
through the perforations of the perforated stencil sheet with difficulty to result
in decrease of printing density and uneven printing.
[0039] The cylindrical printing drum used in the present invention may be a printing drum
conventionally used for rotary stencil printing apparatuses, such as a metallic drum
having pores on the circumferential surface through which inks are passed. The circumferential
surface of the drum may be formed of porous members used for conventional stencil
printing apparatuses, such as metallic fibers, synthetic fibers, metallic porous bodies,
and polymeric porous bodies.
[0040] Furthermore, the printing apparatus of the present invention is provided with a heating
means which heats the stencil printing ink fed into the printing drum and a squeeze
means which internally contacts with the inner circumferential surface of the printing
drum and feeds the ink to the circumferential surface of the printing drum.
[0041] The heating means may be such as directly heating the stencil printing ink or heating
the squeeze means to generate heat by which the ink is heated. The heating means may
be either a contact type or a non-contact type. Examples of the heating means are
a nichrome wire heater, plate heater, ceramics heater, electrically conductive carbon
heater, magnetic induction heater, infrared heater, halogen lamp, xenon lamp, and
microwave heater.
[0042] Preferably, the heating means is arranged so as to heat the squeeze means preferentially
to the ink in order to improve heating efficiency for the stencil printing ink and
attain high speed printing. For example, the heating means may be provided near the
squeeze means or in contact with the squeeze means, or may be housed in the squeeze
means, or may be integrated with the squeeze means.
[0043] The squeeze means is provided internally contacting with the inner circumferential
surface of the printing drum and acts to squeeze out of the drum the ink which has
been changed in phase from solid to liquid by the heating means. Therefore, the squeeze
means must be sufficiently heated at the time of printing. The squeeze means may be
formed of heat resistant members comprising rigid body or elastic body, such as metallic
roller, metallic pipe, plastic blade and plastic belt.
[0044] Thus, according to the present invention, a perforated heat-sensitive stencil sheet
is wound around the outer circumferential surface of an ink-permeable cylindrical
printing drum rotated about its axis as in the case of conventional rotary stencil
printing apparatuses, and the stencil printing ink is molten by the heating means.
Then, in such a state that the printing sheet is moving synchronously with rotation
of the printing drum, the printing ink fed to the inner circumferential surface of
the printing plate is allowed to pass through perforations of the stencil sheet and
transferred to the printing sheet by the squeeze means with the assistance of a pressing
means which presses at least one of the printing drum and the printing sheet to bring
them into close contact. Thus, stencil printing is attained.
[0045] The pressing means is provided, for example, outside and opposite to the printing
drum, and may be a press roller which presses the outer circumferential surface or
may be a squeeze roller or blade which internally contacts with a flexible circumferential
surface of a printing drum and expands the wall of the printing drum outwardly thereby
to press the printing drum to another drum provided outside and opposite to the printing
drum. This squeeze roller or blade may also serve as the squeeze means mentioned above.
When an ink in liquid state is passed through perforations of a perforated stencil
sheet to transfer the ink to a printing sheet by the pressing means, the stencil sheet
and the printing sheet are pressed together under a pressure of 0.01 - 10 kg/cm
2, preferably 0.05 - 5 kg/cm
2 and printing is carried out for 0.001 - 10 seconds, preferably 0.005 - 5 seconds.
If the pressure is lower and the time is shorter, the ink in liquid state is difficult
to pass through the perforated stencil sheet, and, hence, amount of the ink transferred
to the printing sheet is small to result in low printing density and uneven printing.
On the other hand, if the pressure is higher and the time is longer, amount of the
ink passing through the stencil sheet is large and amount of the ink transferred to
the printing sheet is increased to result in indistinct prints having blotting or
blurring and to cause seep through or set-off of ink. Therefore, in the present printing
apparatus, when the pressure is low, the printing time should be prolonged, and when
the pressure is high, the printing time should be shortened for obtaining good prints.
Hereinafter, the present invention will be explained in more detail by way of the
following examples with reference to the accompanying drawings in which:
Fig. 1(a) is a sectional side view which diagrammatically shows a state in which a
liquid containing a photothermal conversion material is ejected from a liquid ejecting
means to a liquid absorbing layer of a heat-sensitive stencil sheet,
Fig. 1(b) is a sectional side view which diagrammatically shows a state in which a
photothermal conversion material is transferred onto a heat-sensitive stencil sheet,
Fig. 1(c) is a sectional side view which diagrammatically shows a state in which a
heat-sensitive stencil sheet onto which a photothermal conversion material has been
transferred is irradiated with light,
Fig. 1(d) is a sectional side view which diagrammatically shows a state in which a
heat-sensitive stencil sheet is perforated by irradiation with light,
Fig. 2 is a side view which schematically shows the printing drum of the printing
apparatus of the present invention with circumferential devices, and
Fig. 3 is a side view which schematically shows an internal structure of an example
of the printing apparatus of the present invention.
[0046] It should be construed that the following examples are presented for only illustrative
purpose, and the present invention is not limited to the examples.
[0047] A mechanism of perforating a heat-sensitive stencil sheet to make a master by the
apparatus of the present invention will be explained, referring to Fig. 1. Fig. 1(a)
shows a heat-sensitive stencil sheet 13 of three-layer structure comprising a liquid
absorbing layer 21, a thermoplastic film 22 and a porous substrate 23. Droplets of
liquid 26 containing a photothermal conversion material is ejected from an ejecting
head 25 of the liquid ejecting means onto the liquid absorbing layer 21 of the heat-sensitive
stencil sheet 13 in a form of letter images so that the photothermal conversion material
28 is transferred onto the heat-sensitive stencil sheet 13 as shown in Fig. 1(b).
[0048] Then, when the image portions on the stencil sheet which comprise the photothermal
conversion material 28 transferred and fixed are irradiated with a visible or infrared
ray 31 by a light irradiation means 30 with a reflector 29 as shown in Fig. 1(c),
only the fixed photothermal conversion material 28 generates heat to melt the liquid
absorbing layer 21 and the thermoplastic film 22, thereby forming perforations 32
as shown in Fig. 1(d). Thus, a master is formed.
[0049] Next, a mechanism of stencil printing in the printing apparatus of the present invention
will be explained, referring to an example illustrated in Fig. 2. In Fig. 2, numeral
5 indicates a cylindrical printing drum of the present invention, the outer circumferential
surface of which is constituted of a porous member. The heat-sensitive stencil sheet
13 perforated as shown in Fig. 1 is wound around the outer circumferential surface
of the printing drum 5 by a known method. Inside the cylindrical printing drum 5,
squeeze means 51 comprising a metallic pipe is provided in contact with the inner
surface of the printing drum 5 so that it can be rotated about its axis parallel to
the central axis of the printing drum 5, and the squeeze means 51 is rotated in the
same direction as the rotation of the printing drum at the time of rotating the drum.
Heating means 52 of a halogen lamp is provided in the squeeze means 51 so as to positively
heat the metallic pipe, whereby the metallic pipe can be efficiently heated with light
53. When the temperature of the outer circumference of the squeeze means 51 reaches
the phase-change temperature of ink 54 used for printing, the ink 54 changes from
solid state to liquid state, and the ink 54 in liquid state is forced out of the inner
surface of the printing drum 5 to the outside by the squeeze means 51 at the time
of rotation of the printing drum 5.
[0050] Printing sheet 14 fed synchronously with the rotation of the printing drum 5 is pressed
to the heat-sensitive stencil sheet 13 on the outer circumferential surface of the
printing drum 5 by press roller 6 provided outside the printing drum 5 and opposite
to the squeeze means 51, whereby ink 54 is transferred onto the printing sheet 14
through the perforations of the heat-sensitive stencil sheet 13. Temperature of the
transferred ink instantaneously becomes lower than the phase-change temperature, and
the ink is fixed as a solid ink 55.
[0051] Next, the printing apparatus of the present invention will be explained, referring
to an example illustrated in Fig. 3. Fig. 3 is a schematic side view which shows the
internal structure of the printing apparatus of the present invention, and printing
drum 5 is placed inside the casing C. The printing drum 5 has the same construction
as shown in Fig. 2, and a rotatable metallic pipe which contacts with the inner surface
of the drum is provided inside the drum as squeeze means 51. The squeeze means 51
is provided with a heating means 52 comprising a halogen lamp and is positively heated
by the lamp. The heated squeeze means 51 heats and fluidizes the phase-changeable
ink in the printing drum 5 and simultaneously squeezes the ink out of the printing
drum 5 at the time of rotation of the printing drum 5. Furthermore, a press roller
6 which can move up and down so as to touch to or be detached from the outer surface
of the printing drum 5 is provided just below the printing drum 5 at the position
opposite to the metallic pipe of the squeeze means 51. A clamping means 55 which clamps
one end portion of the stencil sheet wound around the outer circumferential surface
of printing drum 5 and which can be opened and closed is provided at a part of the
outer circumferential surface of the printing drum 5.
[0052] The printing drum 5 is rotated counterclockwise as shown in Fig. 3, and a paper feeding
tray 8 for printing sheets 14 is provided on the left side of the casing C. A paper
feeding means 11 which comprises a pair of rollers between which an endless belt is
stretched and which feeds one by one printing sheets 14 on the paper feeding tray
8 towards the printing drum 5 is provided above the paper feeding tray 8. Adjacent
to the paper feeding means 11, there is provided a paper feeding timing rollers 12a
comprising a pair of the upper and lower rollers which feed printing sheets 14 delivered
from the paper feeding means 11 to between printing drum 5 and press roller 6 with
timing to the rotation of printing drum at printing. On the right side of the printing
drum 5, there are provided paper discharging rollers 12b comprising a pair of the
upper and lower rollers which carry printed sheets 15 delivered after printed between
the printing drum 5 and the press roller 6 to paper discharging tray 9 disposed on
the right side of casing C.
[0053] In Fig. 3, a cover S is provided above the casing C, and an image sensor 1 is provided
on the back side of the cover S. An original feeding roller 19 is provided opposite
to the image sensor 1 and on the upper surface of the casing C, so that an original
is fed between the original feeding roller 19 and the image sensor 1 from the outside
of the cover S to scan the images on the original and transform them into image information
of electric signals. In the casing C, a roll of heat-sensitive stencil sheet 13 is
placed below the original feeding roller 19 and supported in a state of being rotatable
about an axis by a suitable stencil sheet holding means. In order to carry the heat-sensitive
stencil sheet therefrom toward the printing drum 5, there are provided stencil sheet
feeding rollers 10 comprising a pair of the upper and lower opposing rollers. On the
opposite side of the printing drum 5, a stencil sheet disposal box 7 is provided for
disposal of the stencil sheet after use. Furthermore, a cutter 20 which cuts the heat-sensitive
stencil sheet upon completion of carrying of the heat-sensitive stencil sheet for
one printing to the printing drum 5 is provided between the printing drum 5 and the
stencil sheet feeding roller 10.
[0054] According to the present invention, in the printing apparatus of Fig. 3, in order
to eject the photothermal conversion material onto the heat-sensitive stencil sheet,
for example, an ejecting head as shown by 2a of the liquid ejecting means can be provided
being directed to the stencil sheet 13 and near the stencil sheet carrying route A
on which the stencil sheet 13 is carried to the printing drum 5, and, besides, the
ejecting head as shown by 2b can be provided being directed to the printing drum 5.
[0055] Furthermore, in order to perforate a stencil sheet to make a master by the printing
apparatus shown in Fig. 3, for example, a light irradiation means as shown by 4a can
be provided being directed to the stencil sheet and near the stencil sheet carrying
route A on which the stencil sheet 13 is carried to the printing drum 5. Alternatively,
the light irradiation means as shown by 4b can be provided being directed to the printing
drum 5.
[0056] Moreover, in order to directly print the image on the printing sheet 14 by the printing
apparatus shown in Fig. 3, an ejecting head as shown by 3a of the liquid ejecting
means can be provided downstream the printing drum 5 and being directed to the printing
sheet on the printing sheet carrying route B. Alternatively, an ejecting head as shown
by 3b can be provided upstream the printing drum 5 and being directed to the printing
sheet on the printing sheet carrying route B.
[0057] In the printing apparatus shown in Fig. 3, the liquid ejecting means may have one
or both of the ejecting heads 2a and 2b for the perforation of the heat-sensitive
stencil sheet, and may have one or both of the ejecting heads 3a and 3b for the direct
printing on the printing sheet. Furthermore, for example, if the direction of the
ejecting head 2b can be turned to the printing drum and the printing sheet, and both
the perforation of the heat-sensitive stencil sheet and the direct printing on the
printing sheet can be performed only by a single ejecting head 2b.
[0058] In order to directly duplicate an original by the printing apparatus of Fig. 3, the
original is inserted below the cover S, and while the original is being fed by the
original feeding roller 19, images on the original are scanned by the image sensor
1 and transformed into image information of electric signals, and movement of the
ejecting head and ejection of the liquid are controlled based on the image information,
whereby the images can be reproduced on the stencil sheet or the printing sheet. It
is also possible to reproduce the images by controlling the operation of the ejecting
head directly by a personal computer (not shown) based on the image information stored
therein.
[0059] Printing of a small number of copies on printing sheet 14 is carried out in the following
manner. Printing drum 5 and press roller 6 are detached from each other, and during
the printing sheet 14 on the paper feeding tray 8 being carried by the paper feeding
means 11 and the paper feeding timing roller 12a and the paper discharging roller
12b, the liquid ejecting means is controlled so that a liquid containing a colorant
and/or a photothermal conversion material is directly ejected onto the printing sheet
14 from the ejecting head 3a or 3b to reproduce images. The printed sheets 15 are
stocked on the paper discharging tray 14.
[0060] In order to carry out color printing on printing sheet 14, the liquid ejecting means
is provided with a plurality of ejecting heads, and the ejecting means is controlled
so that colorants of different colors are ejected from the respective ejecting heads
onto the printing sheet 14. For example, two-color printing can be performed by ejecting
colorants of different colors from ejecting heads 3a and 3b, respectively.
[0061] When a large number of copies are printed on printing sheets 14, while the heat-sensitive
stencil sheet 13 is fed to printing drum 5 by feeding rollers 10, the liquid ejecting
means is controlled so that the liquid containing the photothermal conversion material
is ejected from ejecting head 2a onto the stencil sheet 13 to reproduce images, and
then the stencil sheet is irradiated with a visible or infrared ray by a light irradiation
means 4a to perforate the stencil sheet 13 and the perforated stencil sheet is wound
around the printing drum 5. This perforation may be carried out by the irradiation
with a visible or infrared ray from a light irradiation means 4b after the stencil
sheet 13 is wound around the printing drum 5. Furthermore, since the heat-sensitive
stencil sheet of the present invention can be perforated in the non-contact state,
the perforation may be carried out in the following manner. For example, after the
heat-sensitive stencil sheet 13 is wound around the printing drum 5, the liquid ejecting
means is controlled so that the liquid containing the photothermal conversion material
is ejected onto the stencil sheet 13 wound around the printing drum 5 to reproduce
images before the phase-changeable ink in the printing drum 5 changes from solid state
to liquid state by heating, and then the stencil sheet 13 is irradiated with a visible
or infrared ray by the light irradiation means 4b to perforate the stencil sheet.
[0062] The printing drum 5 having the stencil sheet 13 wound around the outer circumferential
surface thereof is rotated counterclockwise about its axis as shown, and simultaneously
a stencil printing ink changed from solid to liquid in its phase by squeeze means
51 heated by a heating apparatus 52 is fed to the inner circumferential surface of
the printing drum. Printing sheet 14 which is carried by the paper feeding means 11
and timing rollers 12a synchronously with the rotation of the printing drum is pressed
against the printing drum 5 by the press roller 6, whereby the stencil printing ink
which passes through the perforations of the stencil sheet 13 is transferred to the
printing sheet 14 to complete printing. Then, the printing paper 14 is carried to
the paper discharging tray 9 by the paper discharging rollers 12b, where it is stocked
as printed paper 15 on which the ink has been dried.
[0063] In order to obtain a piece of paper which is printed by both the stencil printing
and the direct printing with a liquid containing a colorant, the direct printing on
the printing paper 14 is carried out by ejecting means 3a or 3b in addition to the
above-mentioned stencil printing carried out by pressing the printing paper 14 against
printing drum 5 by press roller 6. In this case, the liquid ejecting means may have
a single ejecting head which can move to the position of the ejecting head 2a in the
stencil printing and to the position of the ejecting head 3a in the direct printing,
or may have a rotatable single ejecting head which can turn to the ejecting head 2b
in the stencil printing and to the ejecting head 3b in the direct printing. However,
it is advantageous for obtaining multicolor prints to provide a plurality of the ejecting
heads. In this case, the order of printing is, for example, as follows. First, either
one of the direct printing or the stencil printing is carried out on printing paper
14, the printed paper is stocked on the paper discharging tray 9 as printed paper
15, this paper 15 is again placed on the paper feeding tray 8, and then another printing
is carried out on the paper 15. If the direct printing is carried out by ejecting
heads 3a and/or 3b before and/or after printing paper 14 is stencil-printed by the
printing drum 5, both the stencil printing and the direct printing can be performed
during one step of the printing paper 14 being carried from the paper feeding tray
8 to the paper discharging tray 9.
[0064] According to the present invention, there is no need to allow the heat-sensitive
stencil sheet to contact with any matters such as originals and thermal heads, and
the heat-sensitive stencil sheet can be merely irradiated with a visible or infrared
ray. Therefore, no wrinkling of the stencil sheet occurs and no failure in conveyance
of the stencil sheet is caused.
[0065] Moreover, since printing of a large number of copies can be carried out by stencil
printing and that of a small number of copies can be carried out by direct printing
on printing paper, it is sufficient to provide only one kind of printing paper and
a heat-sensitive stencil sheets in the printing apparatus as in conventional rotary
stencil printing apparatuses, and, thus, an efficient printing can be performed by
one small printing apparatus at a low running cost.
[0066] Furthermore, since an ink which can reversibly change in its phase from solid to
liquid by heating is used, clear prints with neither set-off of ink nor seep through
can be obtained. In addition, because the ink spontaneously changes from liquid to
solid on the prints, not only usual printing paper, but also plastic films or metal
sheets can be printed.
[0067] Furthermore, overlay printing and multicolor printing can also be performed by carrying
out direct printing on printing paper which has been stencil-printed. The present
invention can also be applied to color printing.