RU2176600C2 - Method for printing and printer - Google Patents

Abstract

FIELD: highly efficient printers that can produce polychromatic products, whose quality of reproduction of image is similar to color photography on a wide class of medium (paper, plastic, polyethylene, etc.). SUBSTANCE: method consists in exposure of the printing ink applied onto a transparent backing to pulses of ultra-violet radiation used for control of intensity and position and directed to the regions of printing ink subject to transfer to the information carrier, selecting the characteristics of ultra-violet radiation and coordinating them withy the parameters of printing ink so that in the region of radiation incidence would arise a process of photochemical reaction causing a decomposition of part of the printing ink and its transfer to the information carrier. The printer has a source (sources) of ultra-violet radiation, elements of formation and control of radiation, printing ink carrier that is transparent for ultra-violet radiation, information carrier and members providing for movement of the carriers, application of printing ink and fixation of printing ink after printing. EFFECT: enhanced quality of printing. 30 cl, 4 dwg

Description

 The invention relates to printing methods and devices using radiation energy for transferring ink (ink) directly from an ink carrier to an information medium (paper, plastic card, polyethylene, etc.) without intermediate real-time operations, i.e. for printing on the principle of Computer to print.

 SUMMARY OF THE INVENTION The method is carried out by acting on a paint (hereinafter referred to as viscous ink) applied to a transparent substrate with ultraviolet radiation pulses, which are controlled in intensity and position and sent to the ink areas to be transferred to the information carrier from the side opposite to the applied ink side choosing the characteristics of UV radiation and matching them with the paint parameters, so that in the areas of radiation incidence a photochemical reaction occurs, leading to decomposition part of the paint adjacent to the substrate and the occurrence of pressure ejecting part of the paint from the area of UV radiation to the intermediate, or directly to the final storage medium.

 A printing device for implementing the method comprises a source (s) of UV radiation, a device for generating and controlling radiation, a carrier for paint transparent to UV radiation, a storage medium and elements for supporting the movement of carriers, applying ink, removing ink and fixing ink after printing.

 The invention relates to the class of high-performance analog or digital printing devices, such as Computer to print, which can create multicolor printed products, the quality of image reproduction is close to color photography, on a wide class of media (paper, plastic, polyethylene, etc.).

Known printing methods that use the energy of light radiation to transfer ink (ink) from an ink carrier (printing form) to an information carrier. The general principle is to use light energy to create pressure that ejects or squeezes paint (ink is usually water or alcohol based) from the ink carrier to the information carrier. To achieve this goal in the known printing methods use two physical phenomena:
- heating by ink radiation followed by evaporation and ejection of ink from the cells, similarly to ink-jet printers, in which electric current is used for heating;
- a light-hydraulic effect (Opening diploma N 65 BI N 19, 1969) that occurs in a liquid under the action of laser radiation and is accompanied by characteristic features: self-focusing, the formation of acoustic waves, etc.

 In known methods using the above effects for ink transfer, a laser is used as a radiation source. In order to increase the efficiency of the device for energy concentration in small volumes, optical focusing methods and elements made of highly absorbing laser radiation material are used.

 In the known method and device using the laser heating effect described in US patent N 3798365 US CL 178/6 6a. Int. Cl G 03 G 15/04, published March 19, 74. Laser radiation is focused using a mosaic of microlenses into small volumes (grid cells) filled with ink. The laser intensity is increased to a heating level at which ink ejection is observed.

 Another method of applying laser radiation to eject ink based on the photohydraulic effect is described in Russian patents: RU N 2096183 C1, published on 11/20/97. Bull. N 32, RU 2082615 C1, published on 06.27.97. Bull. N 12 and RU 2088411 C1, published on 08.27.97. Bull. N 24. In the patent RU N 2096183 it is proposed to use a light-hydraulic effect for ejecting ink from a nozzle of an inkjet print head. In the patent RU N 2082615 C1, the printing machine contains a printing form in the form of a grid, and the means for selectively forcing the ink is made in the form of a laser with a device for focusing it to the size of the mesh cell and a device for deflecting the laser beam along the rows of cells.

 Closest to the proposed printing device is the patent RU N 2088411 C1. A distinctive feature of this patent is the reduction of the threshold energy of laser radiation by converting light into acoustic radiation by applying a matrix of metal, semiconductor films, or superlattices with quantum wells to the surface of the printing form. In addition, for the same purpose, it is proposed to use electrodes in the gap between the printing form and the image carrier.

All existing methods of using laser radiation to eject paint (ink) by heating, or using the photohydraulic effect, have a number of common disadvantages such as:
- low efficiency associated with energy losses during heating, or the achievement of light-hydraulic effect;
- the need to use special light-absorbing elements and optics to increase the heating efficiency, or the occurrence of light-hydraulic effect;
- the occurrence of significant difficulties when working with viscous colored inks, the viscosity of which is ten times higher than the viscosity of water-based inks. The latter circumstance is very significant, because viscous inks, including UV inks, which polymerize under the influence of UV radiation, are widely used in offset printing, are characterized by high color saturation, resistance to various influences, etc.

 The aim of this invention is to provide a printing method and a printing machine of the type "Computer to print", which allow highly efficient printing with various inks (inks), which include polymers or plastic. The method and device are reliable, easy to implement and devoid of the disadvantages of previously developed methods.

 The problem is solved by the signs presented in paragraphs. 1-30 claims.

The basis of the proposed method is the decomposition reaction of polymers and plastics, stimulated by UV radiation. The advantage of the method is that with appropriate coordination of the radiation characteristics of the UV radiation source (wavelength, intensity, duration) with the characteristics of the paint (absorption coefficient, activation energy), the conditions for the condensate-gas phase transition in a depth of 10 ^-4 -10 ^{- 5} cm, as a result of which there is a pressure impulse sufficient for transferring paint to the information carrier at low threshold energies of UV radiation. This circumstance makes it possible to use a source of low-power UV radiation to eject paint of any color without additional elements, absorbing coatings, sources of acoustic waves, electric field, etc. The advantage of the proposed method is the possibility of using non-laser gas-discharge point or linear sources of UV radiation, which allows you to simplify, reduce dimensions and reduce the cost of the printing device.

Another advantage is the small depth of the paint layer (10 ^-4 -10 ^-5 cm), in which a "cold" decomposition reaction occurs, which allows you to apply a thin layer of paint - up to several microns thick, and achieve savings in ink consumption.

 The use of short-wave radiation also allows for sharp focusing of the laser beam and thus allows to increase the limiting resolution to several thousand dpi, i.e. really get closer to the quality of color photography.

 In the case of the use of paint polymerizing under the influence of UV radiation, the intensity of which is below the threshold of complete decomposition, it is possible to use the same radiation source to eject and subsequently fix the paint on the information carrier. To this end, the duration of the radiation pulse is slightly increased, and after transferring the ink, the decay (tail) of the pulse is used to polymerize the transferred ink. The same effect can be achieved by additionally turning on the UV source in the pause between print strokes.

In FIG. 1 schematically shows the relationship of the basic elements of a UV printing device for implementing the proposed method. As a UV radiation source, lasers and other types of sources can be used. Such sources include solid-state, gas lasers and semiconductor lasers, including those with multiplication of the radiation frequency using nonlinear crystals, as well as metal vapor lasers and semiconductor lasers pumped by an electron beam based on wide-gap compounds of type A _II B _VI and A _III B _vi . When using high-power pulsed lasers, such as nitrogen, on metal vapor, excimer, etc., paint can be transferred to the storage medium in arrays, for example, line by line. The required radiation power in this case can reach tens of kilowatts with durations of tens of nanoseconds.

 As a pulsed UV radiation source, a gas discharge lamp with a point or linear glow body can be used. These types of sources in the UV range are highly efficient, compact and relatively low cost.

For the effective implementation of the method, it is necessary that the characteristics of UV radiation are consistent with the characteristics of the paint. The source of UV radiation and the forming elements must ensure the intensity of the radiation incident on the paint
I ₀ ≥ V _cr / α [J • cm ^-2 ],
where V _cr is the specific energy of the phase transition at which the decomposition of the paint occurs [J • cm ³ ];
α is the absorption coefficient of the paint UV radiation [cm ^-1 ].

In the range λ = 0.4-0.2 μm, α can reach 10 ⁴ - 10 ⁵ cm ^-1 .

Taking V _cr ≈ 10 ^-3 J • cm ^-3 , α = 10 ⁵ cm ^-1 , we can estimate the possible energy density necessary for the transfer of the image element
I _{o min} = 10 ^{3/10 5} = 10 ² J cm ^-2 •
The energy required to print an image element
E = SI ₀ ,
where S is the area of the image element transferred to the storage medium. For example, if the diameter of the minimum image element - pixel is 20 microns, which corresponds to a resolution of 1250 dpi, then the minimum energy for printing one pixel
E _min = I _0min S _p = 10 ^-2 • 3.14 • 4 • 10 ^-6 / 4 ≈ 3 • 10 ^-8 J.

The second important parameter of radiation is the pulse duration. The duration at which the minimum ink transfer energy is achieved must satisfy the condition
τ ₀ ≤ 1 / α ² χ,
where χ is the thermal diffusivity of the paint. For α = 10 ⁵ cm ^-1 , χ = 10 ^-3 cm ² • s ^-1 , τ ₀ ≤ 10 ^-7 s. Accordingly, the minimum power of the light pulse incident on the paint, P _min can be estimated as
P _min = E _min / τ ₀ = 3 • 10 ^-8 / 10 ^-7 = 0.3W.
Thus, to implement the method, it is necessary that the radiation sources and paint are consistent and meet a number of the listed basic conditions, namely, provide the necessary intensity, duration and absorption coefficient.

 Formative optics. The forming optics serves to form a light beam of the required diameter and divergence for its subsequent modulation and control by the position on the ink carrier. To implement the device, it is possible to use traditional optical elements - reflectors, condensers, mirrors, projection lenses, microlens rasters, etc.

 Radiation control system. To implement a control system of the light beam (s) of the printing device, one can give preference to acousto-optical and mirror devices for modulating and deflecting the laser beam, as well as spatial modulation systems using the principle of reflection of light from mirror surfaces that change their relief or angle of incidence due to electrostatic forces. Such spatial modulators, for example, include the microscopic mirror matrix developed by Texas Instruments — the spatial DMD (Digital micromirror Device) modulator.

 Paint carrier. The paint carrier must be made of a material that weakly absorbs UV radiation, and can be made in the form of a rotating disk 1 (Fig. 2a), cylinder 3 (Fig. 2b), a moving plate (Fig. 2c), tape (Fig. 2d) on which the paint 2 is applied from the side opposite to the incident UV radiation. In the case of a cylinder or an endless (closed) tape, paint is applied on the outside of the cylinder or tape, and radiation pulses can be applied to the inner surface of the cylinder or tape using, for example, optical fibers. Materials that are weakly absorbing radiation can be used as a material for a paint carrier: dielectrics, glass, quartz, sapphire, etc.

 Intermediate image carrier. An intermediate image medium is placed between the ink medium and the information medium and serves to transfer the image to the information medium in a contact manner. The intermediate information carrier allows you to more accurately capture the gap through which the ink is transferred, which is especially important when the information carrier (paper, cardboard, plastic, etc.) has an insufficiently flat surface.

The device of two main options that implement the proposed printing method, is given in Fig 3 a, b. The first option (Fig. 3A), direct transfer of ink from the ink carrier 1 to the information medium 3. The ink carrier, in this case, can be made in the form:
- the rotating disk of FIG. 2a
- the rotating cylinder of FIG. 2b
- the moving plate of FIG. 2c,
- the moving belt of FIG. 2g

 Another option is the transfer of paint through an intermediate medium in the form of a moving tape (Fig. 3b) or a rotating cylinder (Fig. 3c). The ink carrier in this case can be made in the form of one of the above options.

 In FIG. 4 shows an embodiment of an array printing device operating with a pulsed UV light source 1 (laser, lamp), comprising forming optics 2 with a digital light modulator 3 based on miniature mirrors 4, a grid for transmitting light rays 5, a rotating disk 6 with paint 7 , information carrier 8, tape 9, conveyor rollers 10, engine 11, device for applying paint 12 and control unit 13. The device operates as follows. From the control unit 13, signals are received that change the angle of inclination of the mirrors of the modulator 3 so that part of the radiation passes through the holes in the grid 5. After installing all the mirrors on the modulator 3 from the radiation source 1, a radiation pulse (lamp or laser) formed by optics 2 is supplied The light beams from the spatial modulator pass through a transparent disk 6 to the paint 7 and transfer it to the storage medium 8, which is mounted on a conveyor belt 9 moving along the rollers 10. The disk is driven by the engine 11. Speed l the rotation of the disk is chosen so that during the period between the radiation pulses there is a shift to a new area of paint. Areas with used (transferred) paint are filled again using device 12.

 In the case of applying a scheme with an intermediate image carrier, elements 9 and 10 are replaced by elements 3, 4 (Fig. 3b, c) - conveyor, rotating cylinder.

Claims (30)

1. The printing method, which consists in the use of radiation energy for transferring ink from an ink carrier, made in the form of a substrate transparent for radiation to the information carrier from the side opposite to the ink side, characterized in that the ink is influenced by UV pulses controlled by intensity and position, directing to the areas to be transferred to the information carrier, and the characteristics of UV radiation are selected, matching them with the paint parameters in such a way that in the areas of incidence In the process of radiation, a photochemical reaction occurs, which leads to the decomposition of a part of the paint adjacent to the substrate and the appearance of a pressure pulse that ejects a part of the paint from the area of UV radiation exposure to the intermediate or directly to the final information carrier, and the intensity and optimal duration of the UV source radiation are selected from the condition :
I ₀ ≥ V _cr / α [J • cm ^-2 ], τ ₀ ≤ 1 / α ² χ,
where V _cr is the specific energy of the condensate-gas transition, J • cm ^-3 ;
α is the absorption coefficient of radiation, cm ^-1 ;
χ - thermal diffusivity of the ink (ink), cm ² • s ^-1 .  2. The method according to claim 1, characterized in that they use continuous laser UV radiation, controlled by intensity and position.  3. The method according to claim 1, characterized in that they use pulsed UV radiation, which is controlled using a spatial radiation modulator.  4. The method according to claim 2, characterized in that they use an acousto-optical control system for UV radiation in intensity and position.  5. The method according to claim 1, characterized in that the carrier with the paint is rotated or moved, substituting under the UV radiation with each subsequent exposure to the carrier with paint new areas of paint for transferring them to the information carrier.  6. The method according to claim 1, characterized in that the paint from the ink carrier to the information carrier is transferred in arrays, acting simultaneously on the ink patches with a large number of light pulses.  7. The method according to claim 1, characterized in that the paint from the ink carrier is transferred to an intermediate image carrier, from which the image is then transferred to the information carrier by a contact method.  8. The method according to p. 1, characterized in that the quality of the paint use paint, polymerized by UV radiation.  9. The method according to claim 7, characterized in that a color image is formed sequentially by paints of various colors onto an intermediate image carrier and then transferred to the information carrier by a contact method.  10. The method according to claim 8, characterized in that the UV paint applied to the storage medium is polymerized, increasing the radiation duration necessary for ejecting the paint.  11. The method according to claim 10, characterized in that for the polymerization of the paint transferred to the information carrier, in the interval between the clock pulses use the radiation of a UV source. 12. A printing device containing an ink carrier, an ink applicator, an information carrier, a system for generating and controlling light radiation, characterized in that a UV radiation source and ink are used, the parameters of which are consistent with the characteristics of UV radiation, the intensity and optimal duration radiation of a UV source is selected from the condition:
I ₀ ≥ V _cr / α [J • cm ^-2 ], τ ₀ ≤ 1 / α ² χ,
where V _cr is the specific energy of the condensate-gas transition, J • cm ^-3 ;
α is the absorption coefficient of radiation, cm ^-1 ;
χ - thermal diffusivity of the paint, cm • s ^-1 .  13. The device according to p. 12, characterized in that the ink carrier is made in the form of transparent to UV radiation rotating around the axis of the disk, on which a thin layer of paint is applied.  14. The device according to p. 12, characterized in that the ink carrier is made in the form of a cylinder rotating around its axis, inside which along the axis of rotation there is a system of optical fibers and microlenses that transmit and focus the radiation of a controlled radiation source onto a paint deposited on the outer surface of the cylinder in the place of the minimum distance of the paint from the surface of the information carrier.  15. The device according to p. 12, characterized in that the ink carrier is made in the form of a moving tape, on the surface of which a paint is applied from the side facing the information carrier.  16. The device according to p. 12, characterized in that the ink carrier is made in the form of a moving plate.  17. The device according to p. 12, characterized in that for transferring to the media information paint and its subsequent polymerization contains one source of UV radiation.  18. The device according to p. 12, characterized in that between the ink carrier and the storage medium is an intermediate image carrier in the form of a rotating cylinder, from which the applied image is transferred by contact (contact) to the storage medium.  19. The device according to p. 18, characterized in that the intermediate image carrier is made in the form of an endless ribbon.  20. The device according to p. 18, characterized in that the intermediate image carrier is made in the form of a moving plate.  21. The device according to p. 12, characterized in that the source of UV radiation is a gas laser.  22. The device according to p. 12, characterized in that the source of UV radiation is a solid-state laser with frequency multiplication on nonlinear crystals.  23. The device according to p. 12, characterized in that the source of UV radiation is a metal vapor laser.  24. The device according to p. 12, characterized in that the source (s) of radiation is (are) a semiconductor (s) laser (s) made on the basis of gallium nitride compounds.  25. The device according to p. 12, characterized in that the radiation source is a semiconductor (s) laser (s) pumped by an electron beam.  26. The device according to p. 12, characterized in that the radiation source is a pulsed gas discharge with a forming optical system and a mirror spatial modulator of radiation.  27. The device according to p. 12, characterized in that the radiation source is a continuous UV laser with an acousto-optic system for modulating and deflecting the laser beam.  28. The device according to p. 12, characterized in that the source of UV radiation is a pulsed UV laser with a mirror spatial modulator of radiation.  29. The device according to p. 12, characterized in that it has successively arranged ink carriers of different colors and one information carrier.  30. The device according to clause 29, wherein the intermediate medium (s) of the image is located between the ink carriers and the information carriers.

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