JP2007111941A - Apparatus and method for forming image - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming method for forming an image which has no image density variation even if using a recording medium having no ink receiving layer such as industrial printing paper, and also has high image density and no bleeding. <P>SOLUTION: A preprocessing liquid S is discharged to a recording medium P from a preprocessing liquid applicator, as shown in Fig. (1), before an ink droplet I is discharged to the recording medium P from print heads 21 to 24. In this case, an amount of the preprocessing liquid S is made such that the liquid S completely penetrate into the recording medium P as shown in Fig. (2) before the ink droplet I lands on the recording medium P. By thus controlling the amount of the preprocessing liquid S, the preprocessing liquid S has completely penetrated into the recording medium when the ink droplet I lands on the recording medium P. As a result, a dot shape D ideal for forming an image is formed in the recording medium P as shown in Fig. (3), so that a high quality image is formed as shown in Fig. (4). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and an image forming apparatus that apply a pretreatment liquid to a recording medium that is being conveyed in a predetermined conveyance direction, and subsequently form an image by ejecting ink onto the recording medium to which the pretreatment liquid has been applied. Regarding the method.

  2. Description of the Related Art Inkjet image forming apparatuses that form a desired image on a recording medium (print medium) such as paper, resin film, fabric, or metal by discharging ink from an ink discharge port of a print head (recording head) are widely used. Yes. In this inkjet image forming apparatus, since the print head is not in contact with the recording medium, it is excellent in quietness, high image formation speed (printing speed) is possible, and high-density printing is possible. There are advantages such as being easy. Taking advantage of such advantages, there is an increasing need for industrial image forming apparatuses.

  When an inkjet image forming apparatus is used as an industrial image forming apparatus, printing is often performed (forming an image) on a large number of recording media. For this reason, the demand for higher printing speed is particularly high. In order to increase the printing speed in this way, usually, an image forming apparatus using a so-called full-line type print head in which ink discharge ports are arranged over the entire width of the image forming area of the recording medium (full line). Type ink jet printer).

  This full-line type ink jet printer is usually configured such that the ejection direction of ink droplets ejected from the ink ejection ports of the print head is perpendicular to the surface of the recording medium. Further, image formation (printing operation) can be performed while continuously moving (conveying) the recording medium. For this reason, a full line type ink jet printer can perform a printing operation at a higher speed than a so-called serial type ink jet printer that forms an image while scanning the print head in a direction intersecting the conveyance direction of the recording medium.

  By the way, in inkjet printing used for industrial use, an image is often formed on plain paper (a recording medium having no ink receiving layer) from the viewpoint of running cost. Thus, when an image is formed on a recording medium called plain paper, the water resistance of the image is insufficient because there is no ink receiving layer. In addition, when forming color images on plain paper, both high-density images that do not cause feathering (a phenomenon in which ink bleeds along the fibers of the paper) and images that do not cause intercolor bleeding are compatible. And a color image with good image fastness and good quality cannot be formed.

  As a technique for improving the water resistance of an image, an ink in which a color material contained in the ink has water resistance has been put into practical use in recent years. However, this water resistance is inadequate and, in principle, it is an ink that is difficult to dissolve in water after drying, so the nozzles of the print head are likely to be clogged, and the apparatus configuration becomes complicated to prevent this. There is a problem.

  As a technique for solving the above problems, a technique capable of forming a high image density without ink bleeding on the paper surface by using an ink (recording liquid) containing aggregate particles formed from water, a colorant, and an aggregating agent. Is known (for example, see Patent Document 1). However, in this technique, the flocculant in the ink causes nozzle clogging, and there is a problem in long-term storage stability.

Further, as a technique for solving the above problem, in a serial type ink jet printer, a coating unit that scans in a predetermined scanning direction while applying a pretreatment liquid containing a substance that insolubilizes or aggregates a coloring material in ink to a recording medium. An ink jet recording apparatus having recording means for forming an image by discharging ink containing a color material onto a recording medium is known (for example, see Patent Document 2). This technique corresponds to a serial type ink jet printer, and a plurality of nozzles for discharging a pretreatment liquid are formed in the coating means. The coating unit discharges the pretreatment liquid from the plurality of nozzles onto the recording medium while scanning in the scanning direction. Even when some of the plurality of nozzles are clogged and the pretreatment liquid is not discharged, the pretreatment liquid can be discharged and applied to the entire surface of the image forming area of the recording medium by reciprocating in the scanning direction.
JP-A-10-298469 JP 2000-218772 A

  By the way, in the ink jet printer, the printing speed is increased and the apparatus is made compact. When downsizing or the like is achieved in this way, the time from when the pretreatment liquid is applied to the recording medium to when the ink is ejected to the applied portion (application portion) (ink landing) is short. Become. As a result, before the pretreatment liquid completely penetrates into the application portion, ink is ejected to the application portion. In such a case, the ink is solidified in the form of droplets inside the pretreatment liquid remaining (residual) on the surface of the application part. As a result, a so-called “medama” phenomenon occurs, causing unevenness in image density, and an ideal dot shape cannot be obtained on the recording medium. The medama phenomenon will be described later.

  SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides an image forming apparatus and an image forming apparatus that can form an image having high image density and no bleeding overflow even with a recording medium having no ink receiving layer such as industrial printing paper. It aims to provide a method.

In order to achieve the above object, an image forming apparatus of the present invention includes a pretreatment liquid applicator for applying a predetermined pretreatment liquid to a recording medium being conveyed in a predetermined conveyance direction, In an image forming apparatus comprising a print head that discharges ink to a recording medium coated with a treatment liquid,
(1) The image forming apparatus includes a control unit that controls the amount of the pretreatment liquid applied to the recording medium being conveyed based on a conveyance speed at which the recording medium is conveyed in the conveyance direction.

here,
(2) The control means allows all of the pretreatment liquid in this portion to be discharged from the print head to a portion of the recording medium to which the pretreatment liquid is applied by the pretreatment liquid applicator. The amount of the pretreatment liquid may be controlled so as to penetrate into the recording medium.

further,
(3) The control means reduces the amount of the pretreatment liquid when the conveyance speed is high, and increases the amount of the pretreatment liquid when the conveyance speed is low, thereby increasing the amount of the pretreatment liquid in the recording medium. The amount of the pretreatment liquid may be controlled so that the pretreatment liquid completely penetrates into the recording medium before the ink is ejected from the print head to the portion where the liquid is applied.

Furthermore,
(4) The pretreatment liquid applicator is formed with a plurality of nozzles from which the pretreatment liquid is discharged by electric pulses from each.
(5) The control means may control the amount of the pretreatment liquid discharged from the pretreatment liquid applicator by controlling the electric pulse.

Furthermore,
(6) The control means may control the amount of the pretreatment liquid by selecting a nozzle that discharges the pretreatment liquid from the plurality of nozzles.

Furthermore,
(7) The pretreatment liquid applicator may have the same resolution as that of the print head.

Furthermore,
(8) The time until ink is ejected from the print head to a portion of the recording medium to which the pretreatment liquid has been applied by the pretreatment liquid applicator may be within 10 seconds.

In addition, the image forming method of the present invention for achieving the above object is a recording method in which a predetermined pretreatment liquid is applied to a recording medium being conveyed in a predetermined conveyance direction, and then the pretreatment liquid is applied. In an image forming method for forming an image by ejecting ink onto a medium,
(9) The amount of the pretreatment liquid applied to the recording medium being conveyed is controlled based on a conveyance speed at which the recording medium is conveyed in the conveyance direction.

here,
(10) The amount of the pretreatment liquid is controlled so that all of the pretreatment liquid in this portion penetrates into the recording medium before ink is ejected to the portion of the recording medium to which the pretreatment liquid is applied. May be.

further,
(11) When the transport speed is fast, the amount of the pretreatment liquid is reduced, while when the transport speed is slow, the amount of the pretreatment liquid is increased to apply the pretreatment liquid in the recording medium. The amount of the pretreatment liquid may be controlled so that the pretreatment liquid completely penetrates into the recording medium before ink is ejected to the portion.

Furthermore,
(12) The pretreatment liquid may be ejected from the pretreatment liquid applicator having the same resolution as the resolution of the print head that ejects ink.

Furthermore,
(13) The time until ink is ejected to the portion of the recording medium to which the pretreatment liquid has been applied may be 10 seconds or less.

  The pretreatment liquid refers to, for example, a treatment liquid that insolubilizes or aggregates the color material contained in the ink ejected from the print head.

  Here, the pretreatment liquid used in the present invention will be described. The pretreatment liquid used in the present invention contains at least a cationic substance. The cationic substance used may be (1) a low molecular weight cationic compound or (2) a high molecular weight cationic compound, but more preferably (3) a cationic property measured using GPC. A cationic compound in which at least one peak of the molecular weight distribution of the substance exists in a region having a molecular weight of 1,000 or less and a region having a molecular weight of 1,500 or more and 10,000 or less is used.

  Specific examples of the low molecular weight cationic compound (1) above include, for example, primary, secondary and tertiary amine salt type compounds, specifically hydrochlorides such as dodecylamine, coconutamine, stearylamine and rosinamine. Quaternary ammonium salt type compounds, specifically dodecyltrimethylammonium chloride, dodecylbenzyltrimethylchloride, dodecyldimethylbenzylammonium chloride, stearyltrimethylammonium chloride, benzyltributylammonium chloride, benzalkonium chloride, Cetyltrimethylammonium chloride, etc .; pyridinium salt type compounds, specifically cetylpyridinium chloride, cetylpyridinium bromide, etc .; imidazoline type cationic compounds, specifically 2-heptadece Le - hydroxyethyl imidazoline, and the like; ethylene oxide adducts of higher alkyl amines, dihydroxyethyl stearylamine, and the like in particular.

  Furthermore, in the present invention, an amphoteric surfactant exhibiting a cationic property in a certain pH region can also be used in this case. More specifically, amino acid type amphoteric surfactant; R—NH—CH 2 —CH 2 —COOH type compound; betaine type compound, specifically carboxylate type such as stearyldimethylbetaine, dodecyldihydroxyethylbetaine, etc. In addition to amphoteric surfactants, amphoteric surfactants such as sulfate ester type, sulfonic acid type, and phosphate ester type may be mentioned. Of course, when these amphoteric surfactants are used, the treatment liquid is adjusted so as to have a pH lower than their isoelectric point, or when mixed with ink on a recording medium, the lower than the isoelectric point. It is necessary to take any method of adjusting to pH. As mentioned above, although the example of the low molecular weight cationic compound was given, it cannot be overemphasized that the compound which can be used by this invention is not necessarily limited to these.

  Specific examples of the high molecular weight cationic compound (2) include, for example, polyallylamine, polyaminesulfone, polyvinylamine, chitosan, and neutralized or partially neutralized products of acids such as hydrochloric acid or acetic acid. Of course, it is not limited to these.

  In the present invention, a compound obtained by cationizing a part of the high molecular weight nonionic compound may be used as the high molecular weight cationic compound. Specific examples of such compounds include copolymers of vinyl pyrrolidone and aminoalkyl alkylate quaternary salts, copolymers of acrylamide and aminomethyl acrylate quaternary salts, and the like. Of course, it goes without saying that these compounds are not limitative. Furthermore, the above-described polymer substance and cationic polymer substance are satisfactory as long as they are water-soluble, but may be a dispersion such as latex or emulsion.

  Hereinafter, the cationic compounds listed in the above (3) will be specifically described. The cationic compound having a molecular weight distribution peak in a region having a molecular weight of 1,000 or less can be appropriately selected from the low molecular weight cationic compounds mentioned in the above (1). In the present invention, as the low molecular weight cationic compound having a molecular weight distribution peak of 1,000 or less, those having a molecular weight distribution close to monodispersion can be used. For compounds having no molecular weight distribution, the molecular weight obtained from the usual chemical formula is considered as the peak position of the molecular weight distribution.

  As the cationic compound having a molecular weight distribution peak in the molecular weight range of 1,500 to 10,000, it can be appropriately selected from the high molecular weight cationic compounds described in (2). . The action and effect of the present invention of a high molecular weight cationic compound having a molecular weight distribution peak in the molecular weight range of 1,500 to 10,000, for example, a high molecular weight polyallylamine, is as described above. That is, as the second stage of the reaction between the treatment liquid and the ink, the high molecular weight cationic compound is a molecular weight of an aggregate of an anionic compound and a low molecular weight cationic compound or an aggregate of the pigment in the dye or pigment ink. By making them adsorb inside and further increasing their size, it becomes difficult for them to enter the gaps in the fibers of the recording paper, which is the recording medium, and only the liquid part that has undergone solid-liquid separation is immersed in the recording paper. To achieve both printing quality and fixing performance. In this case, if the molecular weight distribution peak is a high molecular weight cationic compound having at least one molecular weight in the range of 1,500 to 10,000, the effects of the present invention are sufficiently exhibited. . These cationic compounds are used in the treatment liquid in an amount of 1 to 10% by weight, preferably 1 to 5% by weight.

  Examples of the ink that can be used in the present invention include direct dyes, acid dyes, food dyes, basic dyes, reactive dyes, disperse dyes, vat dyes, soluble vat dyes, reactive disperse dyes, oil dyes, and pigments. A water-based ink is preferable from the viewpoint of safety according to the application to be used, and a water-based pigment ink is more preferable in consideration of weather resistance. The content of these recording agents is determined depending on the type of the liquid medium component, the characteristics required for the ink, etc., but is generally 0.2 to 20% by weight with respect to the total weight of the ink, preferably It is the ratio which occupies 0.5 to 10 weight%, More preferably, it is 1 to 5 weight%. Examples of the organic solvent that can be used in the present invention include amides such as dimethylformamide and dimethylacetamide, ketones such as acetone and diacetone alcohol, or ethers such as tetrahydrofuran and dioxane, diethylene glycol, triethylene glycol, and tetraethylene. Oxyethylene or oxypropylene addition polymers such as glycol, dipropylene glycol, tripropylene glycol, polyethylene glycol, polypropylene glycol, ethylene glycol, propylene glycol, trimethylene glycol, butylene glycol, 1,2,6-hexanetriol, hexylene Alkylene glycols such as glycol, thiodiglycol, glycerin, ethylene glycol monomethyl (or ethyl) ether Polyalkyl alcohol lower alkyl ethers such as diethylene glycol monomethyl (or ethyl) ether, triethylene glycol monomethyl (or ethyl) ether, triethylene glycol dimethyl (or diethyl) ether, tetraethylene glycol dimethyl (or diethyl) ether, etc. And lower alcohols such as lower dialkyl ethers, sulfolane, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone. The content of the organic solvent is generally in the range of 1 to 50% by weight, preferably 2 to 30% by weight with respect to the total weight of the ink. Although the above organic solvents can be used alone or as a mixture, the most preferable liquid medium composition is composed of water and one or more organic solvents, and the solvent is at least one water-soluble high-boiling solvent such as diethylene glycol. , Containing polyhydric alcohols such as triethylene glycol and glycerin. Further, it may contain a resin for dispersing the pigment, a neutralizing agent and the like.

  According to the present invention, when the transport speed is high, the amount of the pretreatment liquid is reduced, while when the transport speed is slow, the amount of the pretreatment liquid is increased so that the ink is deposited on the recording medium before the ink reaches the recording medium. The pretreatment liquid can be completely infiltrated. In this way, since the image is formed by ejecting ink from the print head onto the recording medium into which the pretreatment liquid has completely penetrated, the “medama phenomenon” due to the incomplete penetration of the pretreatment liquid can be prevented.

  The present invention has been realized in a printing apparatus that forms an image after applying a pretreatment liquid that insolubilizes a coloring material to a recording medium such as cardboard.

  An example of the image forming apparatus of the present invention will be described with reference to FIGS.

  FIG. 1 is a side view showing a schematic configuration of a printing apparatus which is an example of an image forming apparatus of the present invention. FIG. 2 is a perspective view showing the printing apparatus of FIG.

  The printing apparatus 10 includes a print head unit 20 on which print heads 21, 22, 23, and 24 that form images by ejecting ink onto a recording medium P such as cardboard, and a pretreatment liquid onto the recording medium P. And a transport unit 40 for transporting the recording medium P in the direction of arrow A (recording medium transport direction). The print head 21 ejects black ink, the print head 22 ejects cyan ink, the print head 23 ejects magenta ink, and the print head 24 ejects yellow ink. The print head unit 20 includes a head lifting / lowering motor (not shown) that moves the print heads 21 to 24 to a cap position, a print position, and a wipe position, and dust and residual droplets attached to the ink ejection surfaces of the print heads 21 to 24. Wiper blades for wiping off, a capping mechanism for sealing the print heads 21 to 24, and the like. The print head unit 20 is fixed to a plate-shaped engine base 28 and moves up and down (lifts and lowers) together with the engine base 28.

  The transport unit 40 includes four transport belts 42 so that the recording medium passes below the print head unit 20. The conveyor belt 42 is stretched around driven rollers 44, 45, 46, an encoder roller 47, and a driving roller 48. The conveyor belt 42 is tensioned by a tensioner 49. In addition, the conveying belt 42 is configured to rotate in the recording medium conveying direction (arrow A direction) by the timing belt 53 rotating around by the driving motor 50 rotating the driving roller 48.

  The engine base 28 to which the print head unit 20 is fixed has a rectangular shape, and its four corners are fixed to nuts 52. The nuts 52 are fitted into the screw shafts 54, and the nuts 52 move up and down as the screw shafts 54 rotate. Sprockets 56 are fixed to the lower part of four screw shafts 54 (only two are shown in the figure), and a chain 58 is stretched around these four sprockets 56. By rotating the chain 58 with a drive motor (not shown), the screw shaft 54 rotates synchronously, and the print head unit 20 moves up and down together with the engine base 28.

  As shown in FIG. 2, the print heads 21, 22, 23, 24, the pretreatment liquid applicator 31, and the transport unit 40 of the printing apparatus 10 are transmitted with print data, operation start and end commands, and the like. The processing device 12 is connected by a USB cable 14, and print data, operation start and end commands, etc. are transferred to the print head 21 and the like. Further, the information processing apparatus 12 and the transport unit 40 exchange a signal for cueing the recording medium P and synchronizing the transport speed and printing via the USB cable 14.

  The pretreatment liquid applicator 31 applies the pretreatment liquid to the recording medium P in a state of extending and fixing in the paper width direction (arrow B direction) orthogonal to the transport direction. Since the pretreatment liquid is uniformly applied to the recording medium P by the pretreatment liquid applicator 31, ink is ejected onto the recording medium P on which the pretreatment liquid has been uniformly applied, and an image is formed. Images are obtained. Two or more pretreatment liquid applicators may be arranged. When two or more pretreatment liquid applicators are arranged, they are arranged in the transport direction. The pretreatment liquid applicator 31 is connected to a pretreatment liquid tank 33 in which the pretreatment liquid is stored. The pretreatment liquid applicator 31 is an ink jet type that discharges and applies a droplet-like pretreatment liquid onto a recording medium. Therefore, the adjustment of the application amount and the application part can be limited only to the image forming area (printing part).

  The length in the paper width direction of the portion where the pretreatment liquid applicator 31 applied the pretreatment liquid to the recording medium P is the width direction of the portion where the print heads 21, 22, 23, 24 ejected ink to the recording medium P. Longer than the length of. For this reason, all of the ink ejected from the print heads 21, 22, 23, and 24 land on the portion of the recording medium P to which the pretreatment liquid has been applied, so that a good image is formed. Further, the resolution of the inkjet pretreatment liquid applicator 31 is the same as that of the print heads 21, 22, 23, and 24. However, these may have different resolutions. The pretreatment liquid applicator 31 is controlled by a pretreatment liquid applicator control circuit 35 (see FIG. 3) as will be described later.

  The print heads 21, 22, 23, and 24 are connected to the ink tanks 21a, 22a, 23a, and 24a via the tubes 21b, 22b, 23b, and 24b, respectively. Ink is supplied from ink tanks 21a, 22a, 23a, and 24a, respectively. Each print head 21, 22, 23, 24 is capped by a capping mechanism (not shown) when not in an image forming operation. Drying and clogging are prevented. In some cases, an adsorption mechanism (not shown) for adsorbing the recording medium P such as cardboard to the conveyance belt 42 by a vacuum pump or the like may be provided below a media stage (not shown) to which the recording medium P is conveyed. .

  The control system of the printing apparatus 10 will be described with reference to FIG.

  FIG. 3 is a block diagram illustrating a control system of the printing apparatus. 3, the same components as those shown in FIGS. 1 and 2 are denoted by the same reference numerals.

  Print data (record data) is transmitted from the information processing apparatus 12 to the interface controller 62 via the USB cable 14. After analyzing the command received from the USB interface, the CPU 64 instructs the VRAM 66 to render the image data of each color component of the recording data into a bitmap. In response to this instruction, the memory controller 68 writes the image data from the interface controller 62 into the VRAM 66 at a high speed. Simultaneously with this writing, the processing liquid application range and the application amount corresponding to the image data of each color component of the recording data are read, and a drawing instruction for bitmap development is given to the VRAM 66. In response to this instruction, the memory controller 68 writes the image data from the interface controller 62 into the VRAM 66 at a high speed.

  From the transport unit 40, a cueing signal of the recording medium P and a position pulse signal synchronized with the movement of the recording medium P are transmitted to the synchronization circuit 70. The synchronization circuit 70 synchronizes the received cue signal and position pulse signal with a system clock (not shown). Data in the VRAM 66 is read at high speed by the memory controller 68 in synchronization with the position pulse, and the read data passes through the pretreatment liquid applicator control circuit 35 (an example of the control means in the present invention). And transferred to the pretreatment liquid applicator 31. The pretreatment liquid applicator 31 discharges the pretreatment liquid based on the transferred data. That is, the pretreatment liquid applicator 31 is controlled by the pretreatment liquid applicator control circuit 35 to discharge the pretreatment liquid.

  The data read by the memory controller 68 is transferred to the print heads 21 to 24 via the print head control circuit 72. In the print heads 21 to 24, ink is ejected onto the recording medium P based on the transferred data. Thereby, an image is formed on the recording medium P. The operation of the CPU 64 is executed based on the processing program stored in the program ROM 74 in synchronization with the position pulse signal. This processing program is, for example, a program corresponding to the procedure shown in the flowchart of FIG. The CPU 64 uses a work RAM 76 as a working memory.

  As described above, the pretreatment liquid applicator 31 is controlled by the pretreatment liquid applicator control circuit 35 to discharge the pretreatment liquid. The pretreatment liquid applicator control circuit 35 performs preprocessing that is discharged from the pretreatment liquid applicator 31 based on the conveyance speed of the recording medium P being conveyed in the conveyance direction (the direction of arrow A in FIGS. 1 and 2). Control the amount of liquid. Further, the pretreatment liquid applicator control circuit 35 is arranged in front of this portion until ink is ejected from the print heads 21 to 24 to the portion of the recording medium P where the pretreatment liquid is applied by the pretreatment liquid applicator 31. The amount of the pretreatment liquid is controlled so that all of the treatment liquid penetrates into the recording medium P. Specifically, when the conveyance speed of the recording medium P is high, the amount of the pretreatment liquid is reduced, while when the conveyance speed is low, the amount of the pretreatment liquid is increased, so that the pretreatment liquid in the recording medium P is increased. The amount of the pretreatment liquid is controlled by the pretreatment liquid applicator control circuit 35 so that the pretreatment liquid completely penetrates into the recording medium P before the ink is ejected from the print heads 21 to 24 to the coated portion.

  The pretreatment liquid applicator 31 has the same structure as the print heads 21 to 24, and the pretreatment liquid applicator 31 is formed with a plurality of nozzles that each discharge the pretreatment liquid. Each of the plurality of nozzles is provided (formed) with a heating element (not shown) controlled (turned on and off) by the pretreatment liquid applicator control circuit 35. The heating element generates heat from the nozzles. The pretreatment liquid is discharged. The pretreatment liquid applicator control circuit 35 can independently control the heating elements of the plurality of nozzles. In other words, the pretreatment liquid applicator control circuit 35 can control the pretreatment liquid applicator 35 so that the pretreatment liquid is ejected from only an appropriate nozzle (from only the selected nozzle) of the plurality of nozzles. By controlling in this way, the amount of the pretreatment liquid discharged from the pretreatment liquid applicator 35 is controlled.

  The effect of controlling the amount of pretreatment liquid discharged as described above will be described with reference to FIGS.

  FIG. 4 schematically shows how the ink is ejected after the pretreatment liquid is ejected onto the recording medium. FIG. 4A shows the case where the ink is ejected after the pretreatment liquid has completely penetrated into the recording medium. 2A is a top view of (a-1) after ejecting ink onto a recording medium, and (b-1) is a comparative example. FIG. 4 is a cross-sectional view schematically showing an example in which ink is ejected before the pretreatment liquid completely penetrates into the recording medium, and (b-2) is a diagram (b-2) after ejecting ink onto the recording medium. It is a top view of -1). FIG. 5 is a schematic diagram showing an example in which the amount of the pretreatment liquid is reduced when high-speed printing is performed.

  In (a-1) and (b-1) of FIG. 4, the same amount (same thickness) of pretreatment liquid was applied to the recording medium. The application here refers to the pretreatment liquid from all the nozzles of the pretreatment liquid applicator 35 (see FIG. 1 etc.) that selectively discharges the pretreatment liquid from a plurality of nozzles as in the ink jet method. It means discharging.

  4A-1 and 4A-2 illustrate a case where the conveyance speed of the recording medium P is low, and before the ink droplets I are ejected from the print heads 21 to 24 to the recording medium P, (a As shown in (1-1), the pretreatment liquid S is discharged onto the recording medium P from the pretreatment liquid applicator 35 (see FIG. 1 and the like). Since the transport speed of the recording medium P is slow, the discharged pretreatment liquid S is completely applied to the recording medium P when the ink droplet I reaches the recording medium P as shown in (a-1-2). Has penetrated. In other words, the pretreatment liquid S completely penetrates the recording medium P before the ink droplets I land on the recording medium P. As a result, as shown in (a-1-3), an ideal dot shape D is formed on the recording medium P because an image is formed. An image can be formed.

  On the other hand, as shown in FIGS. 4B-1 and 4B-2, when the conveyance speed of the recording medium P is high, the ink droplets I are ejected from the print heads 21 to 24 onto the recording medium P. , (B-1-1), the pretreatment liquid S is discharged from the pretreatment liquid applicator 35 (see FIG. 1 and the like) onto the recording medium P. Since the transport speed of the recording medium P is fast, the ejected pretreatment liquid S is completely applied to the recording medium P when the ink droplets I land on the recording medium P as shown in (b-1-2). It has not penetrated. That is, the pretreatment liquid S has not completely penetrated into the recording medium P before the ink droplets I land on the recording medium P. As a result, as shown in (b-1-3), the ideal dot shape D for forming an image is not formed on the recording medium P, as shown in (b-2). A so-called “medama phenomenon” M occurs.

  By reducing the amount of the pretreatment liquid S discharged from the pretreatment liquid applicator 35 (see FIG. 1 and the like) to the recording medium P even at the same conveyance speed as that shown in FIG. As shown in FIG. 5, it is possible to prevent the occurrence of the “spot phenomenon” M. Prior to the ink droplets I being ejected from the print heads 21 to 24 onto the recording medium P, as shown in FIG. 5 (1), the pretreatment is applied to the recording medium P from the pretreatment liquid applicator 35 (see FIG. 1 and the like). Liquid S is discharged. The amount of the pretreatment liquid S in this case is an amount that completely penetrates into the recording medium P as shown in FIG. 5B before the ink droplet I reaches the recording medium P. By controlling the amount of the pretreatment liquid S in this way, the pretreatment liquid S completely penetrates the recording medium P when the ink droplets I land on the recording medium P. As a result, an ideal dot shape D for forming an image is formed on the recording medium P as shown in FIG. 5 (3), and a high-quality image is obtained as shown in FIG. 5 (4). Can be formed.

  An example of a method for controlling the amount of the pretreatment liquid as described above will be described with reference to FIG.

  FIG. 6 is a flowchart showing an example of a procedure of a method for controlling the amount of the pretreatment liquid. In the method shown in FIG. 6, the pretreatment liquid is applied by the pretreatment liquid applicator 31 (see FIG. 1, etc.) of the recording medium P as a guide for the conveyance speed (printing speed) of the recording medium P (see FIG. 4, etc.). As a guideline, it is determined whether the time until the ink is ejected from the print heads 21 to 24 (see FIG. 1 and the like) (the time from the landing of the pretreatment liquid to the landing of the ink) is 10 seconds or less. did.

  6 starts before print data is transmitted from the information processing apparatus 12 (see FIG. 3) via the USB cable 14 to the interface controller 62. This activation timing is when the user presses the print button or when an instruction is sent from the information processing apparatus 12 (see FIG. 3).

  The information processing apparatus 12 reads the distance d (m) from the pretreatment liquid applicator 31 to the print head 21 before sending the print data to the interface controller 62 (prior to sending) (S601). This distance d is stored in the printing apparatus 10 in advance. Subsequently, the conveyance speed (printing speed) s (m / second) is read (S602). Subsequently, the time until the portion of the recording medium P that has passed the pretreatment liquid applicator 31 reaches the print head 21 is calculated in d / s (seconds), and it is determined whether or not this time is within 10 seconds. (S603). The portion of the recording medium P that has passed through the pretreatment liquid applicator 31 is a portion of the recording medium P that has been applied with the pretreatment liquid by the pretreatment liquid applicator 31 (see FIG. 1 and the like). Further, that this portion has reached the print head 21 means that ink has been ejected to this portion.

  When the above time is within 10 seconds, the conveyance speed of the recording medium P is fast, so that the preprocessing of this part is performed before the ink is ejected from the print head 21 to the part of the recording medium P where the pretreatment liquid is applied. In order to permeate all of the liquid into the recording medium P, the amount of the pretreatment liquid discharged from the pretreatment liquid applicator 31 to the recording medium P is controlled (adjusted) (S604). That is, the thickness of the pretreatment liquid applied to the recording medium P is adjusted. Control of how much the amount of the pretreatment liquid is made according to the conveyance speed will be described later with reference to FIGS. Further, how to control the amount of the pretreatment liquid will be described later with reference to FIG.

  The amount of the pretreatment liquid adjusted in S604 is transmitted to the pretreatment liquid applicator control circuit 35 (see FIG. 3) of the printing apparatus 10 (S605). If it is determined in S603 that the above time exceeds 10 seconds, the conveyance speed of the recording medium P is low, and ink is ejected from the print head 21 to the portion of the recording medium P where the pretreatment liquid is applied. By this time, all of the pretreatment liquid in this portion has completely penetrated into the recording medium P, so the flow proceeds to S605 without controlling the amount of the pretreatment liquid. Subsequently, the print data is transmitted from the information processing device 12 to the printing device 10 (S606), and the printing operation is executed in the printing device 10 based on the print data. 12 is transmitted. The information processing apparatus 12 receives the print end status from the printing apparatus 10 (S609), and then ends this flow.

  In the above example, the amount of the pretreatment liquid is controlled by the information processing apparatus 12. However, the control pattern may be input in advance to the program ROM 74 of the printing apparatus 10 to execute the control. When printing is performed at high speed (when the recording medium is transported at a high speed), it is preferable to perform the printing with the printing apparatus 10 because it can cope with high speed.

  With reference to FIG. 7, how to control the amount of the pretreatment liquid discharged from the pretreatment liquid applicator 31 will be described.

  FIG. 7A is a schematic diagram showing an example in which the amount of the pretreatment liquid when the recording medium conveyance speed is low is set to 100 and the amount is 75% (75% duty), and FIG. FIG. 5C is a schematic diagram illustrating an example in which the duty is set to 50%, and FIG. 5C is a schematic diagram illustrating an example in which the duty is set to 25%. Here, the duty (pretreatment liquid duty) is a numerical value of the number of ejected dots / (vertical resolution × horizontal resolution) × 100%, and the case where the conveyance speed of the recording medium is low is the case of S603 in the flow of FIG. The case where it is determined that the time exceeds 10 seconds.

  As described above, the structure of the pretreatment liquid applicator 31 (see FIG. 1 and the like) is the same as that of the print head, and the pretreatment liquid applicator 31 is formed with a plurality of nozzles for discharging the pretreatment liquid. Has been. Each of the plurality of nozzles is provided with a heating element (not shown) that is controlled (turned on and off) by the pretreatment liquid applicator control circuit 35 (see FIG. 3). A pretreatment liquid is discharged from the nozzle. The pretreatment liquid applicator control circuit 35 can independently control the heating elements of the plurality of nozzles. In other words, the pretreatment liquid applicator control circuit 35 can control the pretreatment liquid applicator 35 so that the pretreatment liquid is ejected from only an appropriate nozzle (from only the selected nozzle) of the plurality of nozzles. By controlling in this way, the amount of the pretreatment liquid discharged from the pretreatment liquid applicator 35 is controlled.

  The heating elements arranged in the plurality of nozzles of the pretreatment liquid applicator 31 are selectively heated based on the pretreatment liquid application control data (see FIG. 6). When the duty is set to 75%, as shown in FIG. 7A, the pretreatment liquid is ejected from 75% of all the plurality of nozzles. Further, when the duty is set to 50%, as shown in FIG. 7B, the pretreatment liquid is discharged from 50% of the entire plurality of nozzles. When the duty is 25%, as shown in FIG. 7C, the pretreatment liquid is discharged from 25% of the plurality of nozzles as a whole. In this way, a desired coating amount can be obtained by selecting one of the plurality of nozzles according to the amount of the pretreatment liquid discharged from the pretreatment liquid applicator 31. As a result, after the pretreatment liquid has completely penetrated into the recording medium P, the ink is landed on this portion. Therefore, there is no unevenness in the image density even in a recording medium without an ink receiving layer such as industrial printing paper. An image having an image density and no bleeding overflow can be formed.

  The relationship between the conveyance speed and the amount of pretreatment liquid will be described with reference to FIGS.

  FIG. 8 is a graph showing the relationship between the conveyance speed of the recording medium and the amount of pretreatment liquid applied when the pretreatment liquid is applied with a liquid sprayer. FIG. 9 is a graph showing the relationship between the conveyance speed of the recording medium and the duty of the pretreatment liquid when the resolution of the pretreatment liquid applicator and the print head is 600 dpi. FIG. 10 is a graph showing the relationship between the recording medium conveyance speed and the pretreatment liquid duty when the resolution of the pretreatment liquid applicator and the print head is 300 dpi. The graph of FIG. 8 is created based on the data of Table 1, the graph of FIG. 9 is created based on the data of Table 2, and the graph of FIG. 10 is based on the data of Table 3. It was created. “Pre-processing to printing distance” described in FIGS. 8, 9, 10 and Tables 1, 2, and 3 is printed from the pre-treatment liquid applicator 31 (see FIG. 1 etc.). This is the distance to the head 21 (see FIG. 1 etc.).

As shown in FIG. 8, the longer the “distance between pre-processing and printing” is, and the slower the conveyance speed is, the more time it takes for ink to land on the recording medium P. The treatment liquid easily penetrates completely into the recording medium. For this reason, the application amount of the pretreatment liquid can be increased as the “distance between pretreatment and printing” is longer and the conveyance speed is slower.

Further, as shown in FIG. 9, the longer the “distance between pretreatment and printing” and the slower the conveyance speed, the more time it takes for ink to land on the recording medium P. The pretreatment liquid easily penetrates into the recording medium. For this reason, the duty at the time of discharging the pretreatment liquid can be increased as the “distance between pretreatment and printing” is longer and the conveyance speed is slower. In this case, when the conveyance speed is low, the pretreatment liquid is ejected in the same position on the recording medium P, so the duty may exceed 100%. The example shown in FIG. 9 is an example when the resolution of the pretreatment liquid applicator and the print head is 600 dpi. In this case, the conveyance speed is the same as when the resolution is low (for example, 300 dpi in FIG. 10). However, the amount of pretreatment liquid applied can be increased.

Further, as shown in FIG. 10, the longer the “distance between pre-processing and printing” is, and the slower the conveyance speed is, the more time is required for ink to land on the recording medium P. The pretreatment liquid easily penetrates into the recording medium. For this reason, the duty at the time of discharging the pretreatment liquid can be increased as the “distance between pretreatment and printing” is longer and the conveyance speed is slower. In this case, when the conveyance speed is low, the pretreatment liquid is ejected in the same position on the recording medium P, so the duty may exceed 100%. The example shown in FIG. 10 is an example when the resolution of the pretreatment liquid applicator and the print head is 300 dpi. In this case, the conveyance speed is the same as when the resolution is high (for example, 600 dpi in FIG. 9). However, the amount of pretreatment liquid applied is reduced.

  In the above-described embodiment, the pre-treatment liquid applicator 31 and the printing apparatus 10 including four print heads arranged in the transport direction (the direction of arrow A in FIG. 1 and the like) are exemplified. The present invention can be adopted even if the number and arrangement of the treatment liquid applicator and the print head are changed.

  Other examples of the number and arrangement of the pretreatment liquid applicator and the print head will be described with reference to FIGS.

  FIG. 11 is a top view schematically showing another example of the number and arrangement of pretreatment liquid applicators and print heads.

  As shown in FIG. 11, the printing apparatus 210 includes a pretreatment liquid applicator unit 220 that can uniformly apply a pretreatment liquid even on a wide recording medium, and an image forming area (an image is formed on the recording medium). A print head unit 230 for discharging ink is provided in the portion. The pretreatment liquid applicator unit 220 includes pretreatment liquid applicators 31 and 32 that are slightly shifted in the transport direction (arrow A direction) and aligned in a direction orthogonal to the transport direction (paper width direction and arrow B direction). ing.

  The print heads 21, 22, 23, 24 corresponding to the pretreatment liquid applicator 31 are positioned on the right side in the paper width direction (arrow B direction) on the paper surface of FIG. Ink is ejected from the print heads 21, 22, 23, 24 to the portion where the treatment liquid is applied. Similarly, the print heads 21, 22, 23, and 24 corresponding to the pretreatment liquid applicator 32 are located on the left side in the paper width direction (arrow B direction) on the paper surface of FIG. Ink is ejected from the print heads 21, 22, 23, 24 to the portion where the pretreatment liquid is applied. By arranging the two pretreatment liquid applicators 31, 32 and the two sets of print heads 21, 22, 23, 24 in this way, a high-quality image can be formed even on a wide recording medium. .

  FIG. 12 is a top view schematically showing still another example of the number and arrangement of pretreatment liquid applicators and print heads.

  As shown in FIG. 12, the printing apparatus 310 includes a pretreatment liquid applicator unit 320 that can uniformly apply a pretreatment liquid even on a wide recording medium, and an image forming area (image formation on the recording medium). A print head unit 330 that discharges ink is provided in a portion). The pretreatment liquid applicator unit 320 includes pretreatment liquid applicators 31 and 32 arranged in the paper width direction (arrow B direction).

  The print heads 21, 22, 23, 24 corresponding to the pretreatment liquid applicator 31 are located on the left side in the paper width direction (arrow B direction) on the paper surface of FIG. Ink is ejected from the print heads 21, 22, 23, and 24 to the portions where the ink is applied. Similarly, the print heads 21, 22, 23, 24 corresponding to the pretreatment liquid applicator 32 are located on the right side in the paper width direction (arrow B direction) on the paper surface of FIG. Ink is ejected from the print heads 21, 22, 23, 24 to the portion where the pretreatment liquid is applied. By arranging the two pretreatment liquid applicators 31, 32 and the two sets of print heads 21, 22, 23, 24 in this way, a high-quality image can be formed even on a wide recording medium. .

  FIG. 13 is a top view schematically showing still another example of the number and arrangement of pretreatment liquid applicators and print heads.

  As shown in FIG. 13, the printing apparatus 410 includes a pretreatment liquid applicator unit 420 that can uniformly apply a pretreatment liquid even on a wide recording medium, and an image forming area (an image is formed on the recording medium). A print head unit 430 for discharging ink is provided in the portion. The pretreatment liquid applicator unit 420 includes pretreatment liquid applicators 31 and 32 that are slightly shifted in the transport direction (arrow A direction) and aligned in the paper width direction (arrow B direction). The pretreatment liquid applicator 31 is located on the left side in the paper width direction (arrow B direction) on the paper surface of FIG. 13, and the pretreatment liquid applicator 32 is slightly downstream in the transport direction from the pretreatment liquid applicator 31. 13 and is located on the right side in the paper width direction on the paper surface of FIG.

  The print heads 21, 22, 23, 24 corresponding to the pretreatment liquid applicator 31 are located on the left side in the paper width direction (arrow B direction) on the paper surface of FIG. Ink is ejected from the print heads 21, 22, 23, and 24 to the portions where the ink is applied. Similarly, the print heads 21, 22, 23, 24 corresponding to the pretreatment liquid applicator 32 are located on the right side in the paper width direction (arrow B direction) on the paper surface of FIG. Ink is ejected from the print heads 21, 22, 23, 24 to the portion where the pretreatment liquid is applied. By arranging the two pretreatment liquid applicators 31, 32 and the two sets of print heads 21, 22, 23, 24 in this way, a high-quality image can be formed even on a wide recording medium. .

1 is a side view illustrating a schematic configuration of a printing apparatus which is an example of an image forming apparatus of the present invention. It is a perspective view which shows the printing apparatus of FIG. 3 is a block diagram illustrating a control system of the printing apparatus. FIG. FIG. 5 schematically illustrates how ink is ejected after the pretreatment liquid is ejected onto the recording medium. FIG. 5A schematically illustrates an example in which ink is ejected after the pretreatment liquid has completely penetrated the recording medium. (A-2) is a top view of (a-1) after ejecting ink onto the recording medium, and (b-1) shows a comparative example, FIG. 7B is a cross-sectional view schematically illustrating an example in which ink is ejected before the pretreatment liquid completely penetrates into the medium, and (b-2) is a diagram of (b-1) after ejecting the ink to the recording medium. It is a top view. It is a schematic diagram which shows the example which reduced the quantity of the pre-processing liquid in the case of high-speed printing. It is a flowchart which shows an example of the procedure of the method of controlling the quantity of a pre-processing liquid. (A) is a schematic diagram showing an example in which the amount of pretreatment liquid when the conveyance speed of the recording medium is slow is set to 100 and the amount is 75% (75% duty). It is a schematic diagram which shows the example made into% duty, (c) is a schematic diagram which shows the example made into 25% duty. It is a graph which shows the relationship between the conveyance speed of a recording medium when the application of a pretreatment liquid is performed with a liquid sprayer, and the application amount of a pretreatment liquid. 6 is a graph showing the relationship between the recording medium conveyance speed and the pretreatment liquid duty when the resolution of the pretreatment liquid applicator and the print head is 600 dpi. 6 is a graph showing the relationship between the recording medium conveyance speed and the pretreatment liquid duty when the resolution of the pretreatment liquid applicator and the print head is 300 dpi. FIG. 6 is a top view schematically showing another example of the number and arrangement of pretreatment liquid applicators and print heads. FIG. 10 is a top view schematically showing still another example of the number and arrangement of pretreatment liquid applicators and print heads. FIG. 10 is a top view schematically showing still another example of the number and arrangement of pretreatment liquid applicators and print heads.

Explanation of symbols

10, 210, 310, 410 Printing devices 21, 22, 23, 24 Print heads 31, 32 Pretreatment liquid applicator 35 Pretreatment liquid applicator control circuit

Claims (12)

A pretreatment liquid applicator that applies a predetermined pretreatment liquid to a recording medium that is being conveyed in a predetermined conveyance direction, and a print head that ejects ink onto a recording medium on which the pretreatment liquid has been applied by the pretreatment liquid applicator In an image forming apparatus comprising:
An image forming apparatus comprising: control means for controlling the amount of the pretreatment liquid applied to the recording medium being conveyed based on a conveyance speed at which the recording medium is conveyed in the conveyance direction. The control means includes
Before the ink is ejected from the print head to the portion of the recording medium to which the pretreatment liquid has been applied by the pretreatment liquid applicator, the pretreatment liquid in this portion penetrates into the recording medium. 2. The image forming apparatus according to claim 1, wherein the amount of the pretreatment liquid is controlled. The control means includes
When the transport speed is fast, the amount of the pretreatment liquid is reduced, while when the transport speed is slow, the amount of the pretreatment liquid is increased so that the portion of the recording medium to which the pretreatment liquid is applied is reduced. 3. The image according to claim 1, wherein the amount of the pretreatment liquid is controlled so that the pretreatment liquid completely penetrates into the recording medium before ink is ejected from the print head. Forming equipment. The pretreatment liquid applicator is formed with a plurality of nozzles from which the pretreatment liquid is discharged by electric pulses from each.
The said control means controls the quantity of the said pretreatment liquid discharged from the said pretreatment liquid applicator by controlling the said electric pulse, The Claim 1, 2, or 3 characterized by the above-mentioned. The image forming apparatus described. The image forming apparatus according to claim 4, wherein the control unit controls the amount of the pretreatment liquid by selecting a nozzle that discharges the pretreatment liquid from the plurality of nozzles. 6. The image forming apparatus according to claim 1, wherein the pretreatment liquid applicator has the same resolution as that of the print head. The time until the ink is ejected from the print head to a portion of the recording medium to which the pretreatment liquid has been applied by the pretreatment liquid applicator is within 10 seconds. The image forming apparatus according to claim 1. In an image forming method in which a predetermined pretreatment liquid is applied to a recording medium being conveyed in a predetermined conveyance direction, and then an image is formed by ejecting ink onto the recording medium coated with the pretreatment liquid.
An image forming method, wherein the amount of the pretreatment liquid applied to the recording medium being conveyed is controlled based on a conveyance speed at which the recording medium is conveyed in the conveyance direction. The amount of the pretreatment liquid is controlled so that all of the pretreatment liquid in this portion penetrates into the recording medium before ink is ejected to the portion of the recording medium to which the pretreatment liquid is applied. The image forming method according to claim 8. When the transport speed is fast, the amount of the pretreatment liquid is reduced, while when the transport speed is slow, the amount of the pretreatment liquid is increased so that ink is applied to a portion of the recording medium coated with the pretreatment liquid. The image forming method according to claim 8, wherein the amount of the pretreatment liquid is controlled so that the pretreatment liquid completely penetrates into the recording medium before the ink is discharged. 11. The image forming method according to claim 8, wherein the pretreatment liquid is ejected from the pretreatment liquid applicator having the same resolution as that of a print head that ejects ink. . The image according to any one of claims 8 to 11, wherein the time until ink is ejected to a portion of the recording medium to which the pretreatment liquid has been applied is 10 seconds or less. Forming method.

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