JP2007253565A - Ink-jet recording device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent defective discharge due to adhesion of an white inorganic pigment in a channel. <P>SOLUTION: An ink-jet recording device comprises a recording head which discharges at least white ink. The white ink contains a radiation polymer compound, a white inorganic pigment, and a fluorescent whitening agent. The recording head has a channel of the white ink. An organic coating containing polyparaxylene or a derivative thereof is formed on at least a part of an inner wall surface of the channel. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ink jet recording apparatus, and more particularly to an ink jet recording apparatus using a white pigment ink.

  Some recording heads (hereinafter simply referred to as “heads”) mounted on an ink jet recording apparatus eject ink containing a pigment as a colorant (coloring material). In such a recording head, it is known that the pigment component of the ink precipitates and accumulates in the ink flow path. The pigment deposited in the ink flow path causes ink ejection failure and causes image quality to deteriorate. In particular, a white ink containing a white inorganic pigment such as titanium oxide has a problem that the pigment component easily precipitates and accumulates in the ink flow path because of its specific gravity.

  In order to solve such a problem, for example, a method of temporarily increasing the ink flow rate and flow velocity in the ink flow path to values necessary for diffusing the pigment deposited in the ink flow path, Proposed a method to apply a negative pressure larger than the negative pressure applied to the colored ink discharge port to the white ink discharge port when suctioning and removing pigments and other foreign matter accumulated in the ink flow path by applying a negative pressure to the nozzle) (See Patent Documents 1 and 2).

On the other hand, for the purpose of improving the brightness and whiteness of a white image, an ink jet recording apparatus using a white ink containing not only a white pigment but also a fluorescent brightening agent is known (Patent Document 3,). 4).
JP-A-6-155757 JP 2005-153514 A JP 2005-1265884 A JP 2005-126585 A

  However, the inventions described in Patent Documents 1 and 2 are methods for removing the pigment deposited and deposited in the ink flow path, and are not methods for preventing the adhesion of the pigment in the ink flow path. For this reason, regular maintenance is required. Further, since it is a removing means that uses the flow of ink, it is difficult to remove it if serious pigment adhesion occurs in the ink flow path.

  The inventions described in Patent Documents 3 and 4 are intended to increase the brightness and whiteness of a white image, and do not improve the ink ejection stability due to the adhesion of the pigment into the flow path.

  The present invention has been made in view of such circumstances, and provides an ink jet recording apparatus capable of preventing discharge failure caused by adhesion of a white inorganic pigment in a flow path and performing good quality image recording. The purpose is to do.

  In order to achieve the above object, an invention according to claim 1 is an ink jet recording apparatus including a recording head that discharges at least white ink, wherein the white ink includes a radiation polymerizable compound, a white inorganic pigment, and fluorescent whitening. The recording head has a flow path for the white ink, and an organic coating containing polyparaxylene or a derivative thereof is formed on at least a part of the inner wall surface of the flow path. An inkjet recording apparatus is provided.

  According to the present invention, an organic coating containing polyparaxylene or a derivative thereof on at least a part of the inner wall surface of the white ink channel while adding a fluorescent brightening agent to a white ink containing a white inorganic pigment as a colorant By forming the (parellin film), adhesion of the white inorganic pigment in the flow path can be prevented, and ejection failure caused by this can be prevented. Thereby, it is possible to realize image recording with good quality using the white ink containing the white inorganic pigment. Further, maintenance for eliminating the adhesion of the pigment in the flow path is not necessary, and the running cost can be reduced.

  In addition, the present invention is suitable when a radiation curable ink that cures when irradiated with radiation such as ultraviolet rays, visible light, or an electron beam, preferably ultraviolet curable ink (UV ink) is used. The fixability of the white ink ejected on the recording medium can be improved, and the image quality can be improved.

  The “flow path” includes not only a pressure chamber filled with ink but also a flow path between the pressure chamber and the ejection port and a flow path for supplying ink to the pressure chamber.

  A second aspect of the present invention relates to the ink jet recording apparatus according to the first aspect, wherein the organic coating has a thickness of 1 μm or more and 10 μm or less.

  The thickness of the organic coating is preferably 1 μm or more and 10 μm or less, and stable ejection performance can be obtained.

  A third aspect of the present invention relates to the ink jet recording apparatus according to the first or second aspect, wherein the content of the fluorescent brightening agent is 5% by mass or more and 10% by mass with respect to the total mass of the white ink. It is characterized by the following.

  The content of the fluorescent brightening agent is preferably 5% by mass or more and 10% by mass or less with respect to the total mass of the white ink, and stable ejection performance can be obtained.

  A fourth aspect of the present invention relates to the ink jet recording apparatus according to any one of the first to third aspects, wherein at least a part of the partition walls of the flow path is made of a piezoelectric material, and the recording head includes: The white ink is ejected using shear deformation of the partition wall.

  The present invention is suitable for a so-called wall vent type recording head using a shear deformation mode of a partition wall (piezoelectric material) made of a piezoelectric material, and can provide particularly stable ejection performance.

  According to the present invention, an organic brightening agent is added to a white ink containing a white inorganic pigment as a colorant, and further, polyparaxylene or a derivative thereof is contained in at least a part of the inner wall surface of the white ink channel. By forming the film (parellin film), it is possible to prevent the white inorganic pigment from adhering in the flow path and to prevent ejection failure caused by this. Thereby, good image quality can be realized using a white ink containing a white inorganic pigment. Further, maintenance for eliminating the adhesion of the pigment in the flow path is not necessary, and the running cost can be reduced.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[Inkjet recording device]
FIG. 1 is an overall configuration diagram of an ink jet recording apparatus as an embodiment of the present invention. FIG. 2 is a principal plan view showing the periphery of the printing unit of the inkjet recording apparatus of the present embodiment.

  The ink jet recording apparatus 10 of the present embodiment is an apparatus using ultraviolet curable (UV curable) ink, and is characterized in that, in particular, white ink containing a white inorganic pigment and a fluorescent brightening agent is used.

  As shown in FIG. 1, the inkjet recording apparatus 10 includes a printing unit 12 having a plurality of heads 12W, 12K, 12C, 12M, and 12Y provided for each ink color, and each head 12W, 12K, 12C, 12M, An ink storage / loading unit 14 for storing ink to be supplied to 12Y, a paper feeding unit 18 for supplying recording paper 16, a decurling unit 20 for removing curling of the recording paper 16, and a nozzle of the printing unit 12 A suction belt transport unit 22 that is disposed to face a surface (ink ejection surface) and transports the recording paper 16 while maintaining the flatness of the recording paper 16, and a print detection unit 24 that reads a printing result by the printing unit 12, An ultraviolet irradiation unit 42 and a paper discharge unit 26 that discharges printed recording paper (printed matter) to the outside are provided.

  In FIG. 1, a magazine for rolled paper (continuous paper) is shown as an example of the paper supply unit 18, but a plurality of magazines having different paper widths, paper quality, and the like may be provided side by side. Further, instead of the roll paper magazine or in combination therewith, the paper may be supplied by a cassette in which cut papers are stacked and loaded.

  In the case of an apparatus configuration using roll paper, a cutter 28 is provided as shown in FIG. 1, and the roll paper is cut into a desired size by the cutter 28. The cutter 28 includes a fixed blade 28A having a length equal to or greater than the conveyance path width of the recording paper 16, and a round blade 28B that moves along the fixed blade 28A. The fixed blade 28A is provided on the back side of the print. The round blade 28B is arranged on the print surface side with the conveyance path interposed therebetween. Note that the cutter 28 is not necessary when cut paper is used.

  When multiple types of recording paper are used, an information recording body such as a barcode or wireless tag that records paper type information is attached to the magazine, and the information on the information recording body is read by a predetermined reader. Therefore, it is preferable to automatically determine the type of paper to be used and perform ink ejection control so as to realize appropriate ink ejection according to the type of paper.

  The recording paper 16 delivered from the paper supply unit 18 retains curl due to having been loaded in the magazine. In order to remove this curl, heat is applied to the recording paper 16 by the heating drum 30 in the direction opposite to the curl direction of the magazine in the decurling unit 20. At this time, it is more preferable to control the heating temperature so that the printed surface is slightly curled outward.

  After the decurling process, the cut recording paper 16 is sent to the suction belt conveyance unit 22. The suction belt conveyance unit 22 has a structure in which an endless belt 33 is wound between rollers 31 and 32, and at least a portion facing the nozzle surface of the printing unit 12 and the sensor surface of the printing detection unit 24 is flat. It is configured to make.

  The belt 33 has a width that is wider than the width of the recording paper 16, and a plurality of suction holes (not shown) are formed on the belt surface. As shown in FIG. 1, an adsorption chamber 34 is provided at a position facing the nozzle surface of the print unit 12 and the sensor surface of the print detection unit 24 inside the belt 33 spanned between the rollers 31 and 32. Then, the suction chamber 34 is sucked by the fan 35 to make a negative pressure, whereby the recording paper 16 on the belt 33 is sucked and held.

  The power of a motor (not shown) is transmitted to at least one of the rollers 31 and 32 around which the belt 33 is wound, so that the belt 33 is driven in the clockwise direction in FIG. The recording paper 16 is conveyed from left to right in FIG.

  Although a mode using a roller / nip transport mechanism instead of the suction belt transport unit 22 is also conceivable, when the print area is transported by a roller / nip, the roller comes into contact with the print surface of the paper immediately after printing, so that the image blurs. There is a problem that it is easy. Therefore, as in this example, suction belt conveyance that does not contact the image surface in the printing region is preferable.

  As shown in FIG. 2, the printing unit 12 is a so-called full-line type in which a line-type head having a length corresponding to the maximum paper width is arranged in a direction (main scanning direction) perpendicular to the paper transport direction (sub-scanning direction). It has become the head of. Each of the heads 12W, 12K, 12C, 12M, and 12Y constituting the printing unit 12 has a plurality of ink discharge ports (nozzles) over a length that exceeds at least one side of the maximum size recording paper 16 targeted by the inkjet recording apparatus 10. It is composed of arranged line type heads.

  Each color in the order of white (W), black (K), cyan (C), magenta (M), and yellow (Y) from the upstream side (left side in FIG. 1) along the conveyance direction (paper conveyance direction) of the recording paper 16 Heads 12W, 12K, 12C, 12M, and 12Y corresponding to ink are arranged. A color image can be formed on the recording paper 16 by ejecting the color inks from the heads 12W, 12K, 12C, 12M, and 12Y while conveying the recording paper 16, respectively.

  Thus, according to the printing unit 12 in which the full line head that covers the entire width of the paper is provided for each ink color, the recording paper 16 and the printing unit 12 are relatively moved in the paper transport direction (sub-scanning direction). It is possible to record an image on the entire surface of the recording paper 16 by performing this operation only once (that is, by one sub-scan). Thereby, high-speed printing is possible and productivity can be improved as compared with a shuttle type head in which the head reciprocates in a direction (main scanning direction) orthogonal to the paper transport direction.

  Here, the main scanning direction and the sub-scanning direction are used in the following meaning. That is, when driving the nozzles with a full line head having a nozzle row corresponding to the full width of the recording paper, (1) whether all the nozzles are driven simultaneously or (2) whether the nozzles are driven sequentially from one side to the other (3) The nozzles are divided into blocks, and one of the nozzles is driven sequentially from one side to the other for each block, and the width direction of the paper (direction perpendicular to the paper transport direction) ) Is defined as main scanning, in which nozzles that print one line (a line composed of one line of dots or a line composed of a plurality of lines of dots) are defined as main scanning. A direction indicated by one line (longitudinal direction of the belt-like region) recorded by the main scanning is called a main scanning direction.

  On the other hand, by relatively moving the above-described full line head and the recording paper, printing of one line (a line formed by one line of dots or a line composed of a plurality of lines) formed by the above-described main scanning is repeatedly performed. Is defined as sub-scanning. A direction in which sub-scanning is performed is referred to as a sub-scanning direction. After all, the conveyance direction of the recording paper is the sub-scanning direction, and the direction orthogonal to it is the main scanning direction.

  In this example, the five-color configuration of WKCMY is illustrated, but the combination of ink colors and the number of colors is not limited to this embodiment, and light ink and dark ink may be added as necessary. For example, it is possible to add a head for ejecting light-colored ink such as light cyan and light magenta.

  As shown in FIG. 1, the ink storage / loading unit 14 includes tanks for storing inks of the respective colors corresponding to the heads 12W, 12K, 12C, 12M, and 12Y. The heads 12W, 12K, 12C, 12M, and 12Y are communicated with each other. Further, the ink storage / loading unit 14 includes notifying means (display means, warning sound generating means, etc.) for notifying when the ink remaining amount is low, and has a mechanism for preventing erroneous loading between colors. is doing.

  An ultraviolet irradiation unit 42 is provided at the subsequent stage of the printing unit 12. The ultraviolet irradiation unit 42 irradiates the ink on the recording paper 16 discharged from the heads 12W, 12K, 12C, 12M, and 12Y with ultraviolet rays to fix the ink.

  Similarly to the heads 12W, 12K, 12C, 12M, and 12Y, the ultraviolet irradiation unit 42 has a length corresponding to the maximum paper width of the recording paper 16, and a direction (sub-scanning direction) substantially orthogonal to the paper conveyance direction (sub-scanning direction). It is fixed so as to extend in the main scanning direction). For example, as an ultraviolet light source (UV light source), light emitting elements such as an ultraviolet LED element and an ultraviolet LD element are arranged in a line. According to this configuration, light emission control can be selectively performed for each light emitting element, so that the light emitting element to be turned on and the amount of emitted light can be easily adjusted, and a desired irradiation range and light intensity (intensity) distribution can be realized for the ultraviolet irradiation area. it can.

  It is preferable that the arrangement is such that ultraviolet leakage light or reflected light emitted from each light emitting element is not irradiated to the nozzle surfaces of the heads 12W, 12K, 12C, 12M, and 12Y. Discharge defects such as nozzle clogging due to ultraviolet irradiation can be prevented. For example, a light shielding member may be provided in each head 12W, 12K, 12C, 12M, 12Y or the ultraviolet irradiation unit 42 so that ultraviolet leakage light or reflected light is not irradiated onto the nozzle surface.

  A print detection unit 24 is provided following the ultraviolet irradiation unit 42. The print detection unit 24 includes an image sensor (line sensor or the like) for imaging the droplet ejection result of the print unit 12, and means for checking nozzle clogging and other ejection defects from the droplet ejection image read by the image sensor. Function as.

  The print detection unit 24 of this example is composed of a line sensor having a light receiving element array that is wider than at least the ink discharge width (image recording width) by the heads 12W, 12K, 12C, 12M, and 12Y. The line sensor includes an R sensor row in which photoelectric conversion elements (pixels) provided with red (R) color filters are arranged in a line, a G sensor row provided with green (G) color filters, The color separation line CCD sensor includes a B sensor array provided with a blue (B) color filter. Instead of the line sensor, an area sensor in which the light receiving elements are two-dimensionally arranged can be used.

  The print detection unit 24 reads the test patterns printed by the heads 12W, 12K, 12C, 12M, and 12Y for each color, and detects the ejection of each head. The ejection determination includes the presence / absence of ejection, measurement of dot size, measurement of dot landing position, and the like.

  The printed matter generated in this manner is outputted from the paper output unit 26. It is preferable that the original image to be printed (printed target image) and the test print are discharged separately. The ink jet recording apparatus 10 is provided with sorting means (not shown) for switching the paper discharge path in order to select the print product of the main image and the print product of the test print and send them to the discharge units 26A and 26B. ing. Note that when the main image and the test print are simultaneously formed in parallel on a large sheet, the test print portion is separated by a cutter (second cutter) 48. The cutter 48 is provided immediately before the paper discharge unit 26, and cuts the main image and the test print unit when the test print is performed on the image margin. The structure of the cutter 48 is the same as that of the first cutter 28 described above, and includes a fixed blade 48A and a round blade 48B. Although not shown, the paper output unit 26A for the target prints is provided with a sorter for collecting prints according to print orders.

[Inkjet recording head]
Next, the structure of the heads 12W, 12K, 12C, 12M, and 12Y will be described. Since the structures of the heads 12W, 12K, 12C, 12M, and 12Y are common, in the following, the head is represented by reference numeral 50 as a representative thereof.

  3A and 3B are configuration diagrams of the head 50 of the present embodiment, in which FIG. 3A is a partial cross-sectional view parallel to the nozzle surface, and FIG. 3B is a cross-sectional view taken along line 3b-3b in FIG.

  The head 50 according to the present embodiment includes a nozzle 51 serving as an ink droplet ejection port, a pressure chamber 52 communicating with the nozzle 51 and filled with ink, and a supply port 53 for supplying ink to the pressure chamber 52. It is mainly composed of a substrate 54, a top plate 56, a nozzle plate 58 and a back plate 60. Although illustration is omitted, many nozzles 51 are formed on the nozzle surface of the head 50.

The piezoelectric substrate 54 is formed by bonding an upper substrate 54 a and a lower substrate 54 b made of lead zirconate titanate (Pb (Zr, Ti) O ₃ ), which is a piezoelectric material, with an adhesive 62. The upper substrate 54a and the lower substrate 54b are polarized in opposite directions in the directions of arrows A and A ′ in FIG. Thus, a substrate (PZT substrate) composed of lead zirconate titanate is preferable because it has excellent piezoelectric characteristics such as piezoelectric constant and high frequency response. As another piezoelectric material, BaTiO ₃ , PbTiO _3, or the like can be used.

  A groove 64 corresponding to the pressure chamber 52 is formed in the piezoelectric substrate 54 so as to open toward the upper substrate 54a. The groove portion 64 has a depth that extends between the upper substrate 54a and the lower substrate 54b, and is formed in a narrow groove shape so as to open opposite side surfaces of the piezoelectric substrate 54 (see FIG. 3B). .

  An electrode 66 is provided on the inner wall surface of the groove portion 64. The electrode 66 is a metal thin film made of, for example, gold, silver, aluminum, palladium, nickel, or titanium, and can be formed by a method such as plating, vacuum deposition, or sputtering.

  The top plate 56 is bonded to the piezoelectric substrate 54 via an adhesive 62 on the surface of the upper substrate 54a opposite to the lower substrate 54b so as to close the opening of the groove portion 64. The top plate 56 only needs to have high mechanical strength and ink resistance. In particular, it is preferable to use a ceramic substrate, and the top plate 56 is bonded to the piezoelectric substrate 54 that performs a predetermined displacement during ejection driving. Therefore, it is preferable to use a piezoelectric ceramic substrate. Specific examples include a substrate mainly composed of aluminum oxide, zircon oxide, silicon nitride, aluminum nitride, quartz, etc. Among them, a substrate mainly composed of aluminum oxide has excellent insulating properties and a thin substrate. However, it is particularly preferable because destruction due to thermal expansion and stress can be prevented.

  The nozzle plate 58 is made of, for example, a plastic material such as polyimide or polycarbonate, and a nozzle (through hole) 51 corresponding to the pressure chamber 52 is formed by perforation. The nozzle plate 58 is bonded by an adhesive 62 to one side surface of the piezoelectric substrate 54 where the groove 64 is opened in a state where the nozzle 51 is positioned at the approximate center of the groove 64 viewed from the nozzle surface side. (See FIG. 3B).

  A supply port (through hole) 53 corresponding to the pressure chamber 52 is formed in the back plate 60. As in the case of the nozzle plate 58, the other side surface (in which the groove portion 64 of the piezoelectric substrate 54 is opened) in a state where the supply port 53 is positioned at the approximate center of the groove portion 64 as viewed from the nozzle surface side. It is bonded to the surface opposite to the surface to which the nozzle plate 58 is bonded by an adhesive 62 (see FIG. 3B). The ink supply port 53 communicates with the ink storage / loading unit 14 shown in FIG. 1 via a supply path (not shown), and the ink stored in the ink storage / loading unit 14 shown in FIG. It is configured to be.

  The pressure chamber 52 is a flow path (space) configured by being surrounded by the piezoelectric substrate 54, the top plate 56, the nozzle plate 58, and the back plate 60. A protective film 68 is provided on the inner wall surface of the pressure chamber 52 (that is, the constituent surface of the pressure chamber 52 of each substrate).

  In the present invention, a parylene film is used as the protective film 68. The parylene film is an organic film made of polyparaxylene resin and / or a derivative resin thereof, and is formed by a CVD method (gas phase synthesis method) using solid diparaxylene dimer or a derivative thereof as a raw material. That is, the diradical paraxylene monomer generated by vaporization and thermal decomposition of the diparaxylene dimer is adsorbed on the substrate and undergoes a polymerization reaction to form a film. The thickness of the parylene film is preferably in the range of 1 μm to 10 μm from the viewpoint of ejection stability.

  With this configuration, when an electric field in a direction perpendicular to the polarization direction of the upper substrate 54a and the lower substrate 54b constituting the piezoelectric substrate 54 is applied, shear mode deformation due to thickness-slip displacement of the piezoelectric material causes deformation of FIG. As shown by the broken line, the partition between the adjacent pressure chambers 52, 52 is displaced in the direction of decreasing the volume of the pressure chamber 52. As a result, the ink inside the pressure chamber 52 is pressurized, and ink droplets are ejected from the nozzles 51 communicating with the pressure chamber 52. When the application of the electric field is released, the partition between the adjacent pressure chambers 52 and 52 returns to the original state, and ink is supplied into the pressure chamber 52 from the supply port 53.

  According to this embodiment, a predetermined amount of fluorescent brightening agent is added to white ink containing a white inorganic pigment as a colorant, and polyparaxylene resin or a derivative resin thereof as a protective film 68 on the inner wall surface of the pressure chamber 52. By forming an organic film (palerin film) having a predetermined thickness containing the white inorganic pigment on the inner wall surface of the pressure chamber 52 can be prevented. From the viewpoint of ejection stability, the content of the fluorescent brightening agent is preferably 5% by mass or more and 10% by mass or less with respect to the total mass of the white ink. From the same viewpoint, the thickness of the parelin film is preferably 1 μm or more and 10 μm or less. Thereby, ejection failure due to adhesion of the white inorganic pigment can be prevented, and good quality image recording can be realized using the white ink containing the white inorganic pigment. In addition, maintenance for eliminating the adhesion of the pigment to the inner wall surface of the pressure chamber 52 becomes unnecessary, and the running cost can be reduced.

  In the present embodiment, the embodiment in which the parylene film is formed as the protective film 68 on the inner wall surface of the pressure chamber 52 is illustrated, but the position of the protective film 68 is not particularly limited in the implementation of the present invention. Various flows such as a flow path between the pressure chamber 52 and the nozzle 51 and a flow path for supplying ink to the pressure chamber 52 (that is, a flow path between the ink storage / loading unit and the supply port 53 in FIG. 1). A protective film (parellin film) 68 may be formed on the path.

[Control system configuration]
Next, the control system of the inkjet recording apparatus 10 will be described.

  FIG. 4 is a principal block diagram showing the system configuration of the inkjet recording apparatus 10. The inkjet recording apparatus 10 includes a communication interface 70, a system controller 72, an image memory 74, a motor driver 76, a heater driver 78, a print control unit 80, an image buffer memory 82, a head driver 84, a light source driver 85, and the like.

  The communication interface 70 is an interface unit that receives image data sent from the host computer 86. A serial interface or a parallel interface can be applied to the communication interface 70. In this part, a buffer memory (not shown) for speeding up communication may be mounted.

  Image data sent from the host computer 86 is taken into the inkjet recording apparatus 10 via the communication interface 70 and temporarily stored in the image memory 74. The image memory 74 is a storage unit that temporarily stores an image input via the communication interface 70, and data is read and written through the system controller 72. The image memory 74 is not limited to a memory made of a semiconductor element, and a magnetic medium such as a hard disk may be used.

  The system controller 72 is a control unit that controls each unit such as the communication interface 70, the image memory 74, the motor driver 76, and the heater driver 78. The system controller 72 includes a central processing unit (CPU) and its peripheral circuits, and performs communication control with the host computer 86, read / write control of the image memory 74, and the like, as well as a transport system motor 88 and heater 89. A control signal for controlling is generated.

  The motor driver 76 is a driver (drive circuit) that drives the motor 88 in accordance with an instruction from the system controller 72. The heater driver 78 is a driver that drives the heaters 89 of the ultraviolet irradiation unit 42 and other units in accordance with instructions from the system controller 72.

  The print control unit 80 has a signal processing function for performing various processing and correction processing for generating a print control signal from the image data in the image memory 74 according to the control of the system controller 72, and the generated print A control unit that supplies a control signal (dot data) to the head driver 84. Necessary signal processing is performed in the print controller 80, and the ejection amount and ejection timing of the ink droplets of the head 50 are controlled via the head driver 84 based on the image data. Thereby, a desired dot size and dot arrangement are realized.

  Further, the print control unit 80 controls on / off of the ultraviolet light source (UV light source) of the ultraviolet irradiation unit 42, the irradiation amount, the irradiation time, and the like via the light source driver 85. It may be interlocked with the control of the head 50 and the conveyance control of the recording paper 16.

  The print control unit 80 includes an image buffer memory 82, and image data, parameters, and other data are temporarily stored in the image buffer memory 82 when image data is processed in the print control unit 80. In FIG. 4, the image buffer memory 82 is shown in a form associated with the print control unit 80, but it can also be used as the image memory 74. Also possible is an aspect in which the print controller 80 and the system controller 72 are integrated and configured with one processor.

  The head driver 84 generates a drive signal for driving the heads 50 of each color to be ejected based on the dot data given from the print control unit 80, and supplies the generated drive signal to the head 50. The head driver 84 may include a feedback control system for keeping the driving condition of the head 50 constant.

  The light source driver 85 generates a drive signal for driving the ultraviolet light source of the ultraviolet irradiation unit 42 based on the control signal sent from the print control unit 80 to the light source driver 85, and supplies the drive signal to the ultraviolet light source. . Similar to the head driver 84, the light source driver 85 may include a feedback control system in which the driving condition of the ultraviolet light source is kept constant.

  As described with reference to FIG. 1, the print detection unit 24 is a block including a line sensor, reads an image printed on the recording paper 16, performs necessary signal processing, and the like to perform a print status (whether ejection is performed, droplet ejection And the detection result is provided to the print control unit 80. The print controller 80 performs various corrections on the head 50 based on information obtained from the print detector 24 as necessary.

[Description of ink]
Next, the ink used in this embodiment will be described.

  The ink used in this embodiment is an ultraviolet curable ink that cures when irradiated with ultraviolet rays, and contains at least a polymerizable compound, a polymerization initiator, and a colorant as main components. In the present invention, in particular, a white ink containing a fluorescent brightener together with a white inorganic pigment is used as a colorant. The ultraviolet curable ink includes a radical polymerization type ultraviolet curable ink (radical polymerization type ink) containing a radical polymerizable compound as a polymerizable compound and a cationic polymerization type ultraviolet curable ink (cationic) containing a cationic polymerizable compound. And polymerization type ink). Hereinafter, each material constituting these inks will be described.

<Polymerizable compounds (radiation curable monomers and oligomers)>
The polymerizable compound used in the radical polymerization type ink preferably has a polymerizable group such as an acryloyl group, a methacryloyl group, an allyl group, a vinyl group, or an internal double bond group (such as maleic acid) in the molecule. Among these, a compound having an acryloyl group or a methacryloyl group is preferable because it can cause a curing reaction with low energy.

  Examples of the polymerizable compound used in the cationic polymerization type ink include compounds such as alicyclic epoxy compounds, aliphatic epoxy compounds, oxetane derivatives, and vinyl ethers.

  Only one type of polymerizable compound may be used in one liquid, or two or more types may be used in combination.

  As content rate of the polymeric compound contained in the liquid containing a coloring agent, the range of 50-99 mass% is preferable in a liquid, The range of 70-99 mass% is more preferable, The range of 80-99 mass% is further preferable.

<Polymerization initiator (curing initiator, reaction initiator)>
Examples of the polymerization initiator used in the radical polymerization type ink include compounds such as acetophenone derivatives, benzoin ether derivatives, benzyldialkyl ketal derivatives, and acylphosphine oxide derivatives.

  Polymerization initiators used in cationic polymerization type inks include aryldiazonium salts, diaryliodonium salts, triarylsulfonium salts, onium salt-based polymerization initiators such as phenacylsulfonium salts, or iron arene complexes, sulfonate esters, Nonionic polymerization initiators such as silanol / aluminum complexes are listed.

  The content of the polymerization initiator in the ink is preferably 0.5 to 20% by mass, more preferably 1 to 15% by mass, and more preferably 3 to 10% by mass from the viewpoints of stability over time, curability, and curing speed. Further preferred.

  A polymerization initiator can be used 1 type or in combination of 2 or more types. Further, as long as the effects of the present invention are not impaired, a known sensitizer can be used in combination for the purpose of improving sensitivity.

<Colorant (coloring material)>
In the present invention, a known white inorganic pigment is used as the colorant for the white ink. Examples of white inorganic pigments include barium sulfate, calcium carbonate, silica, calcium silicate, alumina, alumina hydrate, titanium oxide, zinc oxide, talc, and clay. Among these, it is particularly preferable to use titanium oxide from the viewpoints of concealability, colorability, and dispersibility.

  In the present invention, white inorganic pigments may be used alone or in combination of two or more.

  On the other hand, there is no particular limitation on the colorant of the color inks other than white (in this embodiment, black, cyan, magenta, and yellow inks) used in the present invention, and the hue and color suitable for the intended use of the ink As long as the concentration can be achieved, it can be appropriately selected from known water-soluble dyes, oil-soluble dyes and pigments. Among these, the liquid constituting the ink for ink jet recording of the present invention is preferably a water-insoluble liquid and does not contain an aqueous solvent from the viewpoint of ink droplet stability and quick drying, and from such a viewpoint It is preferable to use an oil-soluble dye or pigment that is easily dispersed and dissolved in a water-insoluble liquid.

  There is no particular limitation on the oil-soluble dye that can be used in the colored ink, and any one can be used. The content of the dye when using an oil-soluble dye as the colorant is preferably in the range of 0.05 to 20% by mass, more preferably 0.1 to 15% by mass, and more preferably 0.2 to 0.2% in terms of solid content. 6% by mass is particularly preferred. An embodiment in which a pigment is used as the colorant is also preferable from the viewpoint that aggregation easily occurs when a plurality of liquids are mixed.

  Moreover, as a pigment used for colored ink, both an organic pigment and an inorganic pigment can be used, but as a black pigment, a carbon black pigment etc. are mentioned preferably. In general, pigments of three primary colors of black and cyan, magenta, and yellow are used, but pigments having other hues such as red, green, blue, brown, white, gold, silver, etc. The metallic luster pigment, colorless or light-colored extender pigment, and the like can also be used depending on the purpose.

  In addition, particles having silica, alumina, resin, or the like as a core material and having a dye or pigment fixed on the surface, an insoluble raked product of a dye, a colored emulsion, a colored latex, or the like can also be used as a pigment.

  Furthermore, resin-coated pigments can also be used. This is called a microcapsule pigment, and is also available as a commercial product from Dainippon Ink and Chemicals, Toyo Ink, etc.

  The volume average particle diameter of the pigment particles contained in the liquid in the present invention is preferably in the range of 30 to 250 nm, more preferably 50 to 200 nm, from the viewpoint of balance between optical density and storage stability. . Here, the volume average particle diameter of the pigment particles can be measured by a measuring device such as LB-500 (manufactured by HORIBA).

  The content in the case of using a pigment as the colorant is preferably in the range of 0.1% by mass to 20% by mass in terms of solid content in the ink from the viewpoint of optical density and jetting stability, and is preferably 1% by mass. More preferably, it is in the range of -10% by mass.

  The colorant may be used alone or in combination of two or more. Further, different colorants may be used for each liquid, or the same may be used.

  There are no particular limitations on the material used for the colorant in both the radical polymerization type ink and the cationic polymerization type ink, and any oil-soluble dye and the above-described dye can be used as long as they can achieve a hue and color density suitable for the intended use of the ink. It can be appropriately selected from pigments.

<Fluorescent brightener>
Various known brightening agents can be used. Examples include benzoxazole, coumason, and pyrazoline, and it is particularly preferable to use benzoxazolinaphthalene and benzoxazolyl stilbene.

  In the present invention, the content of the fluorescent brightening agent in the white ink is preferably 5% by mass or more and 10% by mass or less with respect to the total mass of the white ink from the viewpoint of ejection stability.

  In the present invention, the optical brightener may be used alone or in combination of two or more.

<Other additives>
For both radical polymerization type ink and cationic polymerization type ink, other additives such as dispersants, solvents and polymers, surface tension adjusting agents, UV absorbers, antioxidants, anti-fading agents, pH adjusting agents, etc. An agent can be used in combination.

<Energy application process>
In the present invention, ultraviolet light, visible light, or the like can be used as an exposure light source for proceeding polymerization of the polymerizable compound. In addition, energy can be applied by radiation other than light, for example, α-ray, γ-ray, X-ray, electron beam, etc. Of these, ultraviolet rays and visible rays are used from the viewpoint of cost and safety. Preferably, ultraviolet rays are used. The amount of energy required for the curing reaction varies depending on the type and content of the polymerization initiator, but is generally about 1 to 500 mJ / cm ² .

  The radical polymerization type ink is one in which polymerization is initiated when a polymerization initiator generates radicals upon irradiation with light (UV), is inexpensive, and is currently generally used as an ink jet ink.

  Cationic polymerization type inks are those that start polymerization by generating an acid upon irradiation with light (UV), have little volume shrinkage upon curing, have little odor and skin irritation, but are expensive. It has the following features.

  Next, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

[Preparation of ink for evaluation]
The compositions shown in Table 1 were blended by a pressure kneader, and then kneaded and dispersed by a roll mill to obtain a white pigment dispersion 1.

  Next, after mixing the thing of the composition of Table 2, it filtered with the filter and prepared the white pigment dispersion 2 containing a white inorganic pigment, a polymeric compound, and a polymerization initiator.

  Further, fluorescent whitening agents represented by the following formula were mixed with the white pigment dispersion 2 at the ratios shown in Table 3 to prepare inks 101 to 106 as inks for evaluation (Table 3). These inks are all cationic polymerization type inks.

[Production of evaluation head]
As the evaluation heads, heads (evaluation heads) 201 to 209 shown in Table 4 were manufactured.

  Each of the evaluation heads 201 to 209 has the same structure except for the head 50 (see FIG. 3) of the present embodiment and the protective film 68. Similar to the head 50 of the present embodiment, the evaluation heads 201 to 207 are formed by forming a parylene film as the protective film 68 on the entire inner wall surface of the pressure chamber 52, and the thicknesses thereof are different. On the other hand, the evaluation head 208 is formed by forming a polyimide film (film thickness: 5.0 μm) as the protective film 68. The evaluation head 209 has no protective film 54 formed at all.

[Evaluation methods]
While appropriately combining each of the evaluation inks and the evaluation heads thus obtained, the evaluation head is filled with the evaluation ink, and then the PET film is conveyed at a constant speed while the evaluation head is fixed. Then, 10,000 droplets were continuously ejected from all nozzles of the evaluation head on the PET film, and 10 evaluation samples were prepared for each combination. And the presence or absence of non-ejection was visually confirmed with respect to each evaluation sample, and the non-ejection occurrence frequency was evaluated by totaling the results. In this evaluation experiment, the number of non-ejection occurrence nozzles / the total number of nozzles was taken as the non-ejection occurrence rate, and the average value of 10 evaluation samples was taken. As criteria for this evaluation experiment, a case where the non-ejection occurrence rate was 0 to 0.5% was evaluated as ◯, 0.5 to 1.0% as Δ, and 1.0% or more as ×. Table 5 shows the evaluation experiment results.

[Evaluation 1]
In Comparative Examples 1 to 5 and Example 1, the ink 101 containing no fluorescent whitening agent and the ink 103 containing 5 wt% of the fluorescent whitening agent, the head 209 where the protective film 68 is not formed, and a polyimide film as the protective film 68 are used. This is a combination of a head 208 to be formed and a head 204 on which a parylene film is formed.

  In the case where the protective film 68 is not formed (Comparative Examples 1 and 2), the non-ejection occurrence rate is considerably high at 2% or more, and it has been confirmed that non-ejection is likely to occur. Further, when a polyimide film was formed as the protective film 68 (Comparative Examples 3 and 4), it was confirmed that the non-ejection occurrence rate was increased although it was lower than that of Comparative Examples 1 and 2. Further, it was confirmed that the non-ejection occurrence rate was also increased in the case where a parylene film was formed as the protective film 68 and an ink containing no fluorescent brightening agent was used (Comparative Example 5).

  On the other hand, when a parylene film is formed as the protective film 68 and an ink containing a fluorescent brightening agent is used (Example 1), the non-ejection occurrence rate is considerably low at 0.25% and non-ejection is not caused. It was confirmed that it hardly occurred.

[Evaluation 2]
Comparative Examples 6 to 9 and Examples 2 to 4 are a combination of the ink 103 containing 5 wt% of the fluorescent brightening agent and the heads 201 to 207 in which the film thickness of the parylene film formed as the protective film 68 is different. It is.

  When the film thickness was less than 1 μm (Comparative Examples 6 and 7), the non-ejection occurrence rate was considerably high at 2% or more, and it was confirmed that non-ejection was likely to occur. This is because pinholes are likely to occur in the coating, and it is difficult to obtain a uniform coating, and it is considered that non-ejection is likely to occur. Moreover, when the film thickness was larger than 10 μm (Comparative Examples 8 and 9), it was confirmed that the non-ejection occurrence rate was extremely high. In particular, when the film thickness of Comparative Example 9 was 30 μm, no discharge was performed. This is because the film rigidity becomes excessively high and becomes a factor that hinders deformation of the piezoelectric substrate 54, and a sufficient ejection force cannot be obtained.

  On the other hand, when the film thickness was 1 to 10 μm (Examples 2 to 4), the non-ejection occurrence rate was less than 0.5%, and it was confirmed that almost no non-ejection occurred. In particular, the non-ejection occurrence rate when the film thickness is 5 μm is the lowest at 0.28%, and it was found that the combination as in Example 3 is preferable in order to obtain good image quality.

[Evaluation 3]
Comparative Examples 10 and 11 and Examples 5 to 7 are a combination of inks 102 to 106 having different optical brightener content ratios and a head 204 on which a 5 μm-thick parylene film is formed as the protective film 68. is there.

  When the content ratio of the optical brightener was less than 5 wt% of the whole (Comparative Example 10), it was confirmed that the non-ejection occurrence rate was slightly increased to 0.67%. This is presumably because the fluorescent whitening agent sufficient to obtain the pigment adhesion preventing effect is not contained in the ink. Further, when the content ratio of the fluorescent brightening agent was larger than 10 wt% of the whole (Comparative Example 11), the non-ejection occurrence rate was as high as 1.23%, and it was confirmed that non-ejection was likely to occur.

  On the other hand, when the content ratio of the fluorescent brightening agent is 5 to 10 wt% of the whole (Examples 5 to 7), the non-ejection occurrence rate is less than 0.5% and almost no non-ejection occurs. confirmed.

  From the above evaluation results, according to the example of the present invention, it was confirmed that even when a white ink containing a white inorganic pigment was used, the frequency of occurrence of defective ejection was reduced and stable ejection performance could be obtained. In addition, the radical polymerization ink has the same effect as the cationic polymerization ink.

  Although the ink jet recording apparatus of the present invention has been described in detail above, the present invention is not limited to the above examples, and various improvements and modifications may be made without departing from the gist of the present invention. Of course.

Overall configuration diagram of the inkjet recording apparatus of the present embodiment Main part plan view showing the periphery of the printing unit of the ink jet recording apparatus Partial sectional view of the head Main block diagram showing the system configuration of the inkjet recording apparatus

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Inkjet recording device, 42 ... Ultraviolet irradiation part, 50 ... Head, 51 ... Nozzle, 52 ... Pressure chamber, 53 ... Supply port, 54 ... Piezoelectric substrate, 56 ... Top plate, 58 ... Nozzle plate, 60 ... Back plate, 64 ... groove, 66 ... electrode, 68 ... protective film, 80 ... print control unit

Claims (4)

An inkjet recording apparatus including a recording head that discharges at least white ink,
The white ink contains a radiation polymerizable compound, a white inorganic pigment and a fluorescent brightening agent,
The recording head has a flow path for the white ink,
An ink jet recording apparatus, wherein an organic film containing polyparaxylene or a derivative thereof is formed on at least a part of an inner wall surface of the flow path.   The inkjet recording apparatus according to claim 1, wherein the organic coating has a thickness of 1 μm to 10 μm.   3. The inkjet recording apparatus according to claim 1, wherein the content of the fluorescent brightening agent is 5% by mass or more and 10% by mass or less based on the total mass of the white ink. At least a part of the partition wall of the flow path is made of a piezoelectric material,
4. The ink jet recording apparatus according to claim 1, wherein the recording head discharges the white ink by using shear deformation of the partition wall. 5.

Images