JP2006264258A - Color printer and color printing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form an edgeless print by performing a printing as far as the end of a recording sheet so that a heating element may not be disconnected due to overheating. <P>SOLUTION: The heating element of a thermal head does not turn overheated even if the element is made to be heated in the state that the recording sheet does not come to contact with the element at a print density of 50% when the print density at performing a printing of black color on a color thermal recording sheet is defined to be 100%. Therefore, a correction is made so that the print density of a pixel by which a printing is performed on the side end of the color thermal recording sheet may become 50% or less. With this correction, each print density of Y, M, C of a target pixel is compared, then the color with the highest print density is defined as a high-density color. If the print density of the high-density color is higher than 50%, correction is made so that the print density of the high-density color may become 50%. The print density of other two colors are reduced to 50% or less without loosing a color balance by making correction using a correction ratio applied at making the print density of the high-density color corrected to 50%. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a color printer and a color printing method, and more particularly, to a color printer and a color printing method for preventing damage due to air heating of a thermal head during borderless print creation.

  In the production of color prints by a color printer, it is desired to be able to create a green-free print having no margin around the entire recording surface. In order to create this borderless print, it is a common technique to print so that it protrudes outside the recording paper. For example, in an inkjet printer described in Patent Document 1 that forms a color image by ejecting ink onto recording paper, printing is performed so as to protrude outside the recording paper in order to create a borderless print.

  However, the ink jet printer has a problem that the ink printed out of the recording paper adheres to the recording drum and stains the recording paper to be printed later. Also, a known color thermal printer is not suitable for printing that extends beyond the recording paper described above.

  The color thermal printer has a thermal head pressed against a color thermal recording paper having a yellow thermal coloring layer, a magenta thermal coloring layer, and a cyan thermal coloring layer, and in that state, the color thermal recording paper is conveyed in the sub-scanning direction. A three-color thermosensitive coloring layer is developed in a surface sequence to form a full-color image. The thermal head includes a heating element array in which heating elements as printing elements are arranged in a main scanning direction orthogonal to the sub scanning direction, and records an image on color thermal recording paper conveyed in the sub scanning direction. . Each heating element is provided so as to correspond to one pixel of a recorded image.

  When the heat generating element generates heat in a state where it is not in contact with the recording paper (hereinafter, such heat generation is referred to as idle heat generation), the temperature rises above the normal use temperature at the time of printing. It becomes. When the heating element is overheated, the color thermal recording paper protective layer, etc. will adhere, the attached protective layer, etc. will burn and the temperature of the heating element will rise further, and finally the heating element will break. It becomes impossible to generate heat. When the heat generating element is disconnected, the pixels in charge of the heat generating element are not printed, and hence the subsequent color print has a background color streak of color thermal recording paper, a so-called white streak.

Therefore, in a conventional color thermal printer, the generation of empty heat generation is prevented by performing printing so that a margin of one dot, that is, a width of one heating element (for example, 80 μm) is generated on the outer periphery of the color print. is doing. For example, as described in Patent Document 2, the margins at the leading and trailing edges of the color thermal recording paper are set to a predetermined width by controlling the timing of starting printing and the timing of ending printing. It has gained. Further, as described in Patent Document 3, the margin of the side edge in the transport direction is obtained by limiting the heat generating elements that are driven by detecting the width of the color thermal recording paper with a line sensor. I am doing so. When a borderless print is created by this color thermal printer, as described in Patent Documents 4 and 5, the entire circumference of the color thermal recording paper after printing is cut with a cutter.
JP 2001-317690 A Japanese Utility Model Publication No. 63-117159 JP 2004009611 A Japanese Patent Laid-Open No. 2001-063166 JP 2001-219610 A

  In the color thermal printer described in Patent Document 3, the positions of the thermal head and the line sensor are adjusted at the time of manufacture, and the respective heating elements and photoelectric elements are associated with each other. This adjustment operation is performed under an environmental condition of, for example, 23 ° C., which is an average use environment temperature of the printer. However, color thermal recording paper and thermal heads expand and contract with changes in temperature and humidity, and slightly change in size. When the size of the color thermal recording paper or the heat generating element is changed, the heat generating element near the side edge that is originally in contact with the color thermal recording paper may be disposed outside the color thermal recording paper to generate heat.

  Also, in order to create a borderless print, cutting the entire circumference of the color thermal recording paper after printing is time consuming and expensive, and it takes time to dispose of cutting waste. In addition, there is a demand for a color thermal printer capable of obtaining borderless prints.

  The present invention has been made in order to solve the above-described problem. By printing to the end of the color thermal recording paper so that the heating element is not overheated, the edge is formed without causing white streaks due to disconnection. The purpose is to create a print without.

  In order to solve the above problems, the color printer of the present invention compares the print densities of a plurality of colors constituting pixels printed near the side edge of the recording paper, and determines the color with the highest print density as the high density color. The print density of the high density color is compared with the preset print density set in advance, and if the print density of the high density color is equal to or higher than the prescribed print density, the print density of the high density color is defined. Density correction means for correcting the print density to the print density and correcting the print density of other colors using the correction ratio at this time is provided. As a result, the print density of the pixels printed near the side edge of the recording paper is lowered, so that various problems that occur when printing is performed so as to protrude from the recording paper can be reduced.

  In addition, since the correction of the print density is performed on the pixel corresponding to the side edge of the recording paper and the adjacent pixels adjacent to the pixel in the main scanning direction, the positional deviation between the recording head and the recording paper. Even if it occurs, a borderless print can be created.

  When color thermal recording paper is used as the recording paper and thermal head is used as the line printing head, the life of the heating element is generated when the heat generating element generates heat when the heating element is not in contact with the color thermal recording paper. Since the upper limit of the print density that does not affect the print density is set as the specified print density, disconnection or the like due to overheating of the heating element does not occur. As the specified print density, when the print density when printing black on color thermal recording paper is set to 100%, the print density of 50% is set to the specified print density, which shortens the life of the heating element. There is no.

  In the color printing method of the present invention, the recording paper is transported in the sub-scanning direction, the side edge of the recording paper being transported is detected, and the print position in the main scanning direction with respect to the recording paper is determined based on the detection result. Compare the print densities of multiple colors that make up the pixels printed near the side edge of the recording paper, determine the color with the high print density as the high density color, and set the print density of this high density color in advance. Compared with the specified print density, if the print density of the high density color is equal to or higher than the specified print density, the print density of the high density color is corrected to the specified print density. The print density of other colors is corrected using the ratio, and a plurality of printing elements arranged along the main scanning direction orthogonal to the sub-scanning direction are different colors for a predetermined recording area set on the recording paper. A single screen color image is recorded in a frame sequential manner. To form. As a result, the print density of the pixels printed near the side edge of the recording paper is lowered, so that various problems that occur when printing is performed so as to protrude from the recording paper can be reduced.

  According to the color printer and the color printing method of the present invention, it is possible to reduce various problems that occur when printing is performed so as to protrude from the recording paper. Specifically, in an ink jet printer, the amount of ink that protrudes from the recording paper can be reduced, so that the contamination of the recording paper due to the protruding ink can be reduced. Further, in a color thermal printer, disconnection due to overheating of the heating element can be prevented. Furthermore, since a marginless print with no margin can be created, a troublesome process of cutting the entire circumference of the recording paper after printing can be omitted.

  1 and 2 are a schematic diagram and a block diagram showing the configuration of a color thermal printer embodying the present invention. A recording paper roll 3 is set in the color thermal printer 2. The recording paper roll 3 is formed by winding a long color thermal recording paper 4 in a roll shape. The recording paper roll 3 is rotated by a paper feed roller 5 in contact with the outer periphery, and the color thermal recording paper 4 is fed from the recording paper roll 3 to the left in the drawing or rewound by this rotation.

  As shown in FIG. 3 showing the layer structure of the color thermal recording paper 4, the color thermal recording paper 4 has a cyan (C) thermal coloring layer 9, a magenta (M) thermal coloring layer 10, and a yellow (Y ) A thermosensitive coloring layer 11 and a protective layer 12 are sequentially formed. As shown in FIG. 4, which is a graph showing the relationship between the color density of each thermosensitive coloring layer and the applied thermal energy, the yellow thermosensitive coloring layer 11 has the highest thermal sensitivity and develops yellow with small thermal energy. The cyan thermosensitive coloring layer 9 which is the lowermost layer has the lowest thermal sensitivity and develops cyan with a large thermal energy. The yellow thermosensitive coloring layer 11 loses its coloring ability when irradiated with near ultraviolet rays of 420 nm. The magenta thermosensitive coloring layer 10 develops magenta with intermediate heat energy between the yellow thermosensitive coloring layer 11 and the cyan thermosensitive coloring layer 9 and loses the coloring ability when irradiated with 365 nm ultraviolet rays.

  A conveyance roller pair 15 is disposed downstream of the color thermal recording paper 4 in the feeding direction with respect to the recording paper roll 3 so as to sandwich and convey the upper and lower surfaces of the color thermal recording paper 4. The conveyance roller pair 15 includes a capstan roller 17 that is rotationally driven by a conveyance motor 16 and a pinch roller 18 that is in pressure contact with the capstan roller 17. The carry motor 16 is driven by a motor driver 19.

  The pinch roller 18 is movable in the vertical direction by a shift mechanism (not shown). When the color thermal recording paper 4 is fed, the pinch roller 18 is moved upward so that the color thermal recording paper 4 can pass between the capstan roller 17. A clear gap. After passing the color thermal recording paper 4, it is moved downward and the color thermal recording paper 4 is sandwiched together with the capstan roller 17. The color thermal recording paper 4 is reciprocally conveyed by the conveying roller pair 15 in the left A direction (feeding direction) in the drawing and the right B direction (rewinding direction) in the drawing.

  A thermal head 22 and a platen roller 23 are arranged on the upstream side in the A direction of the conveying roller pair 15 so as to sandwich the upper and lower surfaces of the color thermal recording paper 4. As shown in FIG. 5, the thermal head 22 has a C direction (mainly a large number of heating elements 26 on the lower surface of a head substrate 25 formed of a metal having good thermal conductivity, which is orthogonal to the conveyance direction of the color thermal recording paper 4. The heating element array 27 is arranged in a line along the scanning direction. The heating element array 27 is provided longer than the width of the color thermal recording paper 4 in order to perform printing on the entire area of the color thermal recording paper 4 in the width direction.

  The platen roller 23 is rotatably disposed below the heating element array 27. The platen roller 23 is movable in the vertical direction by a shift mechanism (not shown), and is shifted downward when the color thermal recording paper 4 is fed and rewound to form a gap with the thermal head 22. At the time of printing, it is shifted upward and pressed against the thermal head 22.

  The thermal head 22 is driven by the head driver 30 and is pressed against the color thermal recording paper 4 conveyed in the A direction by the conveying roller pair 15 to generate heat in each of the heating elements 26 of the heating element array 27 to thereby generate each thermal coloring layer 9. Develop ~ 11. As a result, a plurality of rows of printing lines are printed along the A direction on the color thermal recording paper 4 to form an image. The platen roller 23 is driven and rotated in accordance with the conveyance of the color thermal recording paper 4 to assist the sliding contact between the color thermal recording paper 4 and the heating element array 27.

  A leading edge detection sensor 33 that detects the leading edge in the feeding direction of the color thermal recording paper 4 at the time of feeding is disposed on the downstream side in the A direction of the pair of conveying rollers 15. The leading edge detection sensor 33 includes, for example, a photo interrupter including a light projecting unit that irradiates inspection light onto the leading end of the color thermal recording paper 4 and a light receiving unit that receives the inspection light reflected by the color thermal recording paper 4. It is used.

  As shown in FIG. 5, on the upstream side in the A direction of the thermal head 22, below the conveyance path of the color thermal recording paper 4, the side edge detection sensor is located at a position facing both side edges 4 a and 4 b of the color thermal recording paper 4. 36 and 42 are arranged symmetrically. The side edge detection sensor 36 includes a line-shaped LED 37 that irradiates the side edge 4a of the color thermal recording paper 4 with inspection light, and a CCD line sensor 38 that images the side edge 4a of the color thermal recording paper 4 illuminated by the inspection light. Are arranged in parallel on one substrate and detect the position of the side edge 4a of the color thermal recording paper 4 in the main scanning direction. The CCD line sensor 38 includes a plurality of imaging elements 39 arranged in the main scanning direction. Further, the imaging elements 39 of the CCD line sensor 38 and the heating elements 26 of the heating element array 27 are arranged in the same pitch in the main scanning direction. Therefore, the main scanning direction position of the side edge of the color thermal recording paper 4 can be detected in units of heating elements.

  The other side edge detection sensor 42 is the same as the side edge detection sensor 36 and includes an LED 43, a CCD line sensor 44, and an image sensor 45, and the position of the side edge 4b of the color thermal recording paper 4 in the main scanning direction. Is detected. These side end detection sensors 37 and 42 are driven by sensor drivers 48 and 49.

  The positions of the thermal head 22 and the side edge detection sensors 36 and 42 are adjusted so that the heating element 26 and the imaging elements 39 and 45 are aligned in the main scanning direction when the color thermal printer 2 is manufactured. Further, at the time of this position adjustment, the heating element 26 and the imaging elements 39 and 45 are associated with each other. For example, it is assumed that the center line CL in the width direction of the standard color thermal recording paper 4 having no dimensional error matches the center HC of the heating element array 27. At this time, the color thermal recording paper 4 In the figure, the image pickup device 39 facing the left side end 4a is SL1, and the image pickup device 45 facing the right side end 4b is SR1. The heating elements 26 corresponding to these imaging elements SL1 and SR1 are denoted as HL1 and HR1. The imaging elements SL1 and SR1 and the heating elements HL1 and HR1 are recorded in the print position determining unit 50 as the reference imaging element and the reference heating element.

As shown in FIG. 6, when the color thermal recording paper 4 is actually transported and printing is performed, if the transport position of the color thermal recording paper 4 is shifted in the main scanning direction, the printing position determining unit 50 is used. Thus, the heating element to be driven is determined in the following procedure. First, the image sensors that detect the side edges 4a and 4b of the color thermal recording paper 4 are identified as SL1 ′ and SR1 ′. It is immediately known how many dots are separated in which direction the image pickup devices SL1 ′ and SR1 ′ are located with respect to the reference image pickup devices SL1 and SR1, and further, the image pickup device and the heating element are in the main scanning direction. If the difference between the image pickup devices SL1 ′, SR1 ′ and the reference image pickup devices SL1, SR1 is added to the reference heating elements HL1, HR1, as shown in the following formulas 1 and 2, It is possible to easily specify the heating elements HL1 ′ and HR1 ′ at both ends which are driven when printing is performed on the color thermal recording paper 4 whose position is shifted in the scanning direction.
HR1 ′ = HR1 + (SR1-SR1 ′)... Formula 1
HL1 ′ = HL1 + (SL1-SL1 ′)... Formula 2

  An optical fixing device 52 is disposed on the downstream side in the A direction of the thermal head 22 and above the conveyance path. The optical fixing device 52 includes a yellow fixing lamp 53 and a magenta fixing lamp 54. The yellow fixing lamp 53 emits near ultraviolet rays having an emission peak of 420 nm, and the yellow thermosensitive coloring layer of the color thermosensitive recording paper 4 is used. 11 is fixed. The magenta fixing lamp 54 fixes the magenta thermosensitive coloring layer 10 by emitting ultraviolet rays of 365 nm. The optical fixing device 52 is driven by a lamp driver 55.

  A cutter 58 for cutting the long color thermal recording paper 4 for each recording area is provided on the downstream side of the optical fixing device 52 in the A direction. A paper discharge port 59 for discharging the cut sheet-like color thermal recording paper 4 is disposed on the downstream side of the cutter 58.

  As shown in FIG. 2, the color thermal printer 2 is entirely controlled by a system controller 63. The system controller 63 is a microcomputer composed of, for example, a CPU, a program ROM, a work RAM, and the like. The PU controls each part of the printer 2 according to a control program stored in the program ROM, and temporarily occurs temporarily. Data is stored in the work RAM and used for printer control.

  An interface circuit (I / F) 66 is connected to the system controller 63. The I / F 66 is provided with various connectors, and a personal computer (PC), a digital still camera, a card reader for reading the recorded contents of a memory card, and the like are connected to input image data.

  The image data input via the I / F 66 is recorded in the image memory 69. The image data recorded in the image memory 69 is read into the print data forming unit 70 via the system controller 63. The print data forming unit 70 includes a data conversion unit that converts the read RGB image data into YMC print data, a frame memory that records YMC print data, and print data for one line read from these frame memories. A line memory or the like is recorded. The print data for one line read from the line memory is input to the head driver 30, and the head driver 30 drives each heating element 26 of the thermal head 22 based on the print data for one line.

  The density correction unit 73 corrects the print data of the pixels corresponding to the side edges 4a and 4b of the color thermal recording paper 4 and changes the print density. As a result of experiments by the present applicant, the lifetime of the heat generating element 26 is about 3000 when no idling is performed. Further, when the heat generation is performed with the heat energy that causes the color thermal recording paper 4 to develop a black color, the service life is extremely shortened to about 200 sheets. On the other hand, it was found that the life is not shortened when the heat is generated by the heat energy for coloring gray on the color thermal recording paper 4. Note that when black is developed on the color thermal recording paper 4, 100% of the thermal energy of each thermal coloring layer is applied during printing of Y, M, and C, and when gray is developed, Y, M , C, approximately 50% of black thermal energy is applied to each thermosensitive coloring layer.

  From the above experimental results, the print density that is developed with 100% thermal energy, that is, the idling heat generation with 100% print density shortens the life of the heating element 26, but 50% that is developed with 50% thermal energy. In the case of the idling heat generation with the print density of 1, the life of the heating element 26 is not affected. The density correction unit 73 corrects the print density of the pixels corresponding to the side edges 4a and 4b of the color thermal recording paper 4 to be 50% or less using the experimental result. Specifically, the print density of the color of the maximum print density (hereinafter referred to as a high density color) is 50% among the Y, M, and C print data of the pixels corresponding to the side edge 4a of the color thermal recording paper 4. If the color density exceeds 50%, it is corrected to 50%, and the print density of the other colors is corrected using the ratio when the high density color is corrected to 50% so that the color balance is not lost.

For example, as shown in FIG. 7, when the print density of each color before correction of the pixel Px1 corresponding to the side edge 4a of the Nth print line PLn is as shown in Examples 1 and 2, the high density color Correction is performed so that the print density is 50%, and the print density of other colors is corrected using the correction ratio. As a result, the corrected print density of the pixel PL1 corresponding to the side edge 4a is always 50% or less. For this reason, even if the heating element HL1 for printing the pixel Px1 generates heat due to the expansion and contraction of the color thermal recording paper 4 or the thermal head 22, the lifetime is not shortened.
Example 1
Before correction After correction Y density = 100% → Y density = 50%
M concentration = 60% → M concentration = 30%
C concentration = 80% → C concentration = 40%
Example 2
Before correction After correction Y density = 40% → Y density = 26.6%
M concentration = 75% → M concentration = 50%
C concentration = 30% → C concentration = 20%

  Further, the density correction described above is performed on the recording surface of the color thermal recording paper 4 and the pixel Px1 corresponding to the outer side of the color thermal recording paper 4 with respect to the pixel Px1 corresponding to the side edges 4a and 4b of the color thermal recording paper 4. This is also performed for the -1 dot pixel Px1-1. That is, in FIG. 5, the print density is corrected for the pixels on which the printing is performed by HL1, HL1 + 1, HL1-1 and HR1, HR1 + 1, HR1-1 of the heating element 26. As a result, the color thermal recording paper 4 and the thermal head 22 expand and contract due to changes in temperature and humidity, and even if the position of the color thermal recording paper 4 and the thermal head 22 is slightly shifted, the side edge 4a of the color thermal recording paper 4 is reached. , 4b are always printed with low print density pixels, so that a borderless print can be created without being affected by the printing environment. Further, since the peripheral pixels are low-density images having a lower print density than the normal image inside, the pixels are not conspicuous and a natural borderless print can be created.

  Next, the operation of the above embodiment will be described with reference to the flowcharts of FIGS. For example, when a printing operation is performed on a PC connected to the color thermal printer 2, image data is input to the color thermal printer 2 together with a signal instructing printing. The system controller 63 records the image data input from the I / F 66 in the image memory 69.

  The print data forming unit 70 reads RGB image data from the image memory 69 via the system controller 63 and converts it into YMC print data. This print data is recorded in a frame memory in the print data forming unit 70. The density correction unit 73 is adjacent to the pixels of each print line printed on the side edges 4a and 4b of the color thermal recording paper 4 in the print data recorded in the frame memory in the main scanning direction. Correct the print density of the pixel.

  As shown in FIG. 9, the density correction unit 73 compares the Y, M, and C print densities of the pixel Px1 shown in FIG. 7, for example. Among the compared colors, the color having the highest print density is specified as the high density color, and it is determined whether the print density of the high density color is 50% or more. When the high density color is 50% or less, the life of the heat generating element 26 is not reduced even if the heat is generated, so that the print density is not corrected.

  For example, when the print density of each color of the pixel Px1 is Y density = 100%, M density = 60%, and C density = 80%, the print density of yellow, which is a high density color, is set to 50%. Then, the print density of magenta and cyan is corrected according to the correction ratio of yellow. As a result, the print density of each color is Y density = 50%, M density = 30%, and C density = 40%. Therefore, the life of the heat generating element 26 is not shortened even if air heat is generated. The density correction is also performed on pixels corresponding to the side edges 4a and 4b of each print line, for example, Px1 and Px1 + 1 and Px1-1 adjacent to the pixel Px1.

  Along with the input of the image data, the system controller 63 feeds the color thermal recording paper 4 in the A direction by rotating the carry motor 16 forward. During feeding, the platen roller 23 is moved downward and the pinch roller 18 is moved upward, so that a passage path for the color thermal recording paper 4 is secured. When the leading edge of the color thermal recording paper 4 is detected by the leading edge detection sensor 33, the rotation of the transport motor 16 is temporarily stopped, and the pinch roller 18 and the platen roller 23 are moved to come into pressure contact with the color thermal recording paper 4. Further, the side edge detection sensors 36 and 42 detect the positions of the side edges 4a and 4b of the color thermal recording paper 4 in the C direction, and the printing position determination unit 50 determines the range of the heating elements driven during printing. .

  As shown in FIGS. 6 and 10, the side edge 4 a is printed at the time of printing based on the imaging elements SL1 ′ and SR1 ′ in which the side edges 4 a and 4 b are detected, the reference imaging elements SL1 and SR1, and the reference heating elements HL1 and HR1. , 4b, the heating elements HL1 ′, HR1 ′ are determined. Printing is performed by a plurality of heating elements 26 between the heating elements HL1 '+ 1 and HR1' + 1 adjacent to the heating elements HL1 'and HR1'.

  By resuming the rotation of the transport motor 16, the color thermal recording paper 4 is transported again in the A direction. At the same time, print data for one line of the yellow image is read from the frame memory in the print data forming unit 70 to the line memory, and is input to the head driver 30 from this line memory. The thermal head 22 generates heat on the heating element array based on print data for one line, and prints a one-line yellow image on the color thermal recording paper 4. At the time of printing, since the print density of the pixels corresponding to the side edges 4a and 4b and the pixels adjacent thereto are corrected, the color thermal recording paper 4 and the thermal head 22 expand and contract due to changes in temperature and humidity. Even if the positions of the thermal recording paper 4 and the thermal head 22 are slightly shifted, a borderless print can be created without reducing the life of the heating element 26.

  Along with the start of printing of the yellow image, the yellow fixing lamp 53 of the optical fixing device 52 is turned on. As a result, the yellow thermosensitive coloring layer 11 on which the yellow image is printed is fixed so as not to develop color by subsequent heating.

  After the yellow image is printed, the yellow fixing lamp 53 is turned off. Further, the platen roller 23 moves downward and separates from the color thermal recording paper 4. The system controller 63 reverses the conveyance motor 16 and conveys the color thermal recording paper 4 in the B direction until the leading edge of the color thermal recording paper 4 is detected by the leading edge detection sensor 33, and rewinds the recording paper roll 3.

  After the color thermal recording paper 4 has been rewound, the platen roller 23 is moved upward again, and the conveyance motor 16 is rotated forward to convey the color thermal recording paper 4 in the A direction. Further, the thermal head 22 is driven to print a magenta image line by line, and the magenta thermosensitive coloring layer 10 is fixed by using the magenta fixing lamp 54 as a point. Even when this magenta image is printed, the print density of the pixels corresponding to the side edges 4a and 4b and the pixels adjacent thereto are corrected, so that a borderless print can be created without reducing the life of the heating element 26. Can do.

  After the printing of the magenta image is completed, the color thermal recording paper 4 is rewound again, and the cyan image is printed. Even when the cyan image is printed, the print density of the pixels corresponding to the side edges 4a and 4b and the pixels adjacent thereto are corrected, so that a borderless print can be created without reducing the life of the heating element 26. Can do.

  After the cyan image is printed, the front end and the rear end of the recording area of the color thermosensitive recording paper 4 are cut by the cutter 58 so as not to generate a margin, and a sheet-like color print is completed. The pixels at the side edges of the color print are low-concentration images with a lower print density than the normal image inside the color prints, so that they are not conspicuous and are natural borderless prints. This color print is discharged out of the printer from the paper discharge port 59.

  In the above-described embodiment, the density correction is performed according to the color having the highest print density among the Y, M, and C images. However, the print density of the cyan image having the highest coloring heat energy is 50%. As long as it is below, the lifetime of the heat generating element 26 is not reduced by the air heat generation. Therefore, the print density correction may be performed only when the print density of the cyan image exceeds 50%.

  Although the above embodiment has been described by taking a color thermal printer as an example, it can also be applied to other types of printers using a thermal head, such as a thermal transfer printer, a thermal melting printer, and the like. It can also be employed in an ink jet printer. In this case, the amount of ink that protrudes outside the recording paper can be reduced.

1 is a schematic diagram illustrating a configuration of a color thermal printer embodying the present invention. It is a block diagram which shows the structure of a color thermal printer. It is explanatory drawing which shows the layer structure of a color thermal recording paper. It is a graph which shows the color development characteristic of each thermosensitive coloring layer. It is explanatory drawing which shows the position adjustment state of a thermal head and a side edge detection sensor. FIG. 6 is a plan view showing a state in which color thermal recording paper is conveyed during printing. FIG. 6 is an explanatory diagram illustrating an example of a pixel on which print density correction is performed. 6 is a flowchart illustrating a printing procedure. 6 is a flowchart illustrating a procedure for correcting a print density. It is a flowchart which shows the procedure which specifies the heat generating element driven at the time of printing.

Explanation of symbols

2 Color Thermal Printer 4 Color Thermal Recording Paper 22 Thermal Head 26 Heating Element 27 Heating Element Array 36, 42 Side Edge Detection Sensor 50 Print Position Determination Unit 73 Density Correction Unit

Claims (5)

Conveying means for conveying the recording paper in the sub-scanning direction;
It has a plurality of printing elements arranged along the main scanning direction orthogonal to the sub-scanning direction, and records a plurality of images of different colors for a predetermined recording area set on the recording paper in a frame sequential manner. A line print head for forming a color image of the screen;
Detecting means for detecting a side edge of the recording paper being conveyed;
Based on the detection result, print position determining means for determining the print position in the main scanning direction with respect to the recording paper,
Compare the print density of multiple colors that make up the pixels printed near the side edge of the recording paper,
The color with the highest print density is determined as the high density color,
Compare the print density of this high density color with the preset print density set in advance,
If the print density of the high density color is equal to or higher than the specified print density, the print density of the high density color is corrected to be lowered to the specified print density.
A color printer comprising density correction means for correcting the print density of another color using the correction ratio at this time.   2. The color printer according to claim 1, wherein the pixels printed in the vicinity of the side edge are pixels corresponding to the side edge and pixels adjacent to the pixel in the main scanning direction.   The recording paper is a color thermosensitive recording paper provided with a thermosensitive coloring layer that develops a different color on a support, and the line printing head is a thermal printer provided with a heating element that heats the thermosensitive coloring layer as a printing element. The specified print density is an upper limit of the print density that does not affect the life of the heat generating element when performing the idling heat generation when the heat generating element is not in contact with the color thermal recording paper. The color printer according to claim 1 or 2.   4. The color printer according to claim 3, wherein the specified print density is 50% when the print density when printing black on color thermal recording paper is 100%. Transport the recording paper in the sub-scanning direction,
Detect the side edge of the recording paper being conveyed,
Based on the detection result, the print position in the main scanning direction with respect to the recording paper is determined,
Compare the print density of multiple colors that make up the pixels printed near the side edge of the recording paper,
The color with the highest print density is determined as the high density color,
Compare the print density of this high density color with the preset print density set in advance,
If the print density of the high density color is equal to or higher than the specified print density, the print density of the high density color is corrected to be lowered to the specified print density.
Use the correction ratio at this time to correct the print density of other colors,
With a plurality of printing elements arranged along the main scanning direction orthogonal to the sub-scanning direction, a plurality of images of different colors are recorded on a predetermined recording area set on the recording paper in a frame sequential manner. A color printing method comprising forming a color image.

Images