TWI855664B - Color adjustment method for digital inkjet printer of high pressure laminates decorative paper - Google Patents

Abstract

A color adjustment method for digital inkjet printer of high pressure laminates decorative paper is disclosed. The method includes: a four-color standard confirmation stage, an ink loading confirmation stage and a multi-color standard confirmation stage. Each stage has more than one execution step. The present invention does not take the color blocks printed on the decorative paper as the basis for correcting inkjet traditionally but uses the color patches on the completely manufactured pressure laminates decorative board as the basis for correcting inkjet. In this way, all the objective causes of printing color variation can be eliminated at one time, and the purpose of perfectly color correction control of the digital inkjet printer can be achieved.

Description

Color calibration method for melamine decorative paper digital inkjet printer

The present invention relates to a color calibration method, in particular to a color calibration method for a melamine decorative paper digital inkjet printer.

Melamine board is a kind of man-made board, usually made of wood fiber or other natural fiber mixed with resin, with the advantages of moisture resistance, corrosion resistance, flame resistance, wear resistance, etc. The production method of melamine board mainly includes raw material mixing, extrusion molding, drying, polishing and other steps. In life, melamine board is widely used in the production of products such as construction, interior decoration, furniture, kitchen utensils, pencil cases, audio, etc. Melamine board is widely popular because of its smooth surface, diverse colors and good durability. In addition, melamine board can also be used to create special material effects, such as imitation stone, imitation wood, imitation marble, etc., for decorative wall panels, floors, etc., making interior decoration more textured and beautiful.

Generally speaking, the layered structure of melamine board includes surface paper, decorative paper, kraft paper layer and bottom layer. The surface paper plays the role of protecting melamine board and forming surface texture, and the decorative paper underneath is mainly used to display the design pattern of melamine board. Since the light first passes through the surface paper film and then reflects the color on the decorative paper, and the material and texture of the surface paper itself deteriorate after high temperature and high pressure, the color of the reflected light no longer meets the original standard of the decorative paper before making melamine board. Therefore, many melamine board manufacturers are often complained by customers about color deviation in production after delivery, and serious cases may even lead to returns.

Decorative paper must be able to withstand high temperature and high pressure without causing itself to crack or bubble. In Taiwan, most melamine board manufacturers currently use imported high-grade decorative paper. Because the carriers that use melamine board as the surface are generally large in size, these high-grade decorative papers are packaged and transported in bundles to facilitate the printing of various pattern sizes and cut after printing. Naturally, the machine for printing high-grade decorative paper will not be a traditional printer or screen printer. The current mainstream printing equipment is a digital inkjet printer. The digital inkjet printer uses more than four spot colors, combined with the color separation image file output by the computer, to spray back and forth on the decorative paper to form the pattern on the surface of the melamine board. Since the pressing of decorative paper and surface paper will inevitably cause color deviation, the color printed on the decorative paper needs to take color conversion into consideration and "deviate" from the correct color standard in advance, so that the nature of the peritoneal film and the effect of heat pressing can be used to make the final color combination of the melamine board consistent with the sample. The digital inkjet printer can accept operation or automatically correct the ink jet amount according to the color deviation effect, so that the printed product can present the most correct color. However, the traditional correction steps are not applicable to the decorative paper of melamine board. No matter how close the pattern on the decorative paper is to reality, the appearance color of the melamine board will deviate after pressing. Therefore, for the existing digital inkjet printer used for melamine board decorative paper, there needs to be a color adjustment method to solve the current common problem of color deviation.

This paragraph extracts and compiles certain features of the invention. Other features will be revealed in subsequent paragraphs. Its purpose is to cover various modifications and similar arrangements within the spirit and scope of the attached patent application.

In order to solve the above-mentioned problems, the present invention proposes a color calibration method for a melamine decorative paper digital inkjet printer. The method includes: a four-color standard confirmation stage, an ink loading confirmation stage and a multi-color standard confirmation stage. In the four-color standard confirmation stage, the steps are as follows: a) each color of the four primary colors is divided into N color levels, and a digital inkjet printer is used to sequentially print the colors representing these color levels in continuous square frames on a decorative paper; b) a closed colorimeter is used to read the three-color stimulation values of the colors in these square frames, and the three-color stimulation values of each square frame color are compared with the three-color stimulation values of the corresponding color level representative color to correct the ink spraying amount of each color nozzle of the digital inkjet printer; c) dividing each of the four primary colors to be printed into 2N color scales, and using the digital inkjet printer to sequentially print the colors representing the color scales in continuous frames on the decorative paper; d) reading the three-color stimulation values of the colors of the frames with the closed colorimeter, and comparing the three-color stimulation values of each frame color with the three-color stimulation values of the corresponding color scale representative colors to correct the ink spraying amount of each color nozzle of the digital inkjet printer; and e) repeating step c) and step d). The ink loading confirmation stage includes the steps of: f) printing the four primary colors on the decorative paper with the digital inkjet printer, and measuring the maximum ink loading amount of each color ink of the decorative paper. The multi-color standard confirmation stage includes the following steps: g) selecting a plurality of color combinations formed based on different percentages of the four primary colors, and using the digital inkjet printer to print the color combinations in an array on the decorative paper; h) sandwiching the decorative paper on which the color combinations are printed between a matte surface paper and a plurality of kraft papers, and hot pressing to form a melamine board; and i) using an open colorimeter to read the three-color stimulus values of the color combinations of the melamine board through the matte surface paper, comparing the three-color stimulus values of each color combination with the three-color stimulus values of the corresponding standard color combination to correct the ink spraying amount of each color nozzle of the digital inkjet printer, and controlling the ink spraying amount per unit area of each color nozzle to be no greater than the minimum value of the maximum ink loading amount of the four primary colors. Where N is a positive integer not less than 10.

According to the present invention, when printing, the digital inkjet printer uses standard cyan (C) ink and light cyan (LC) ink for the cyan part, uses standard magenta (C) ink and light magenta (LC) ink for the magenta part, uses standard yellow (Y) ink for the yellow part, and uses standard black (K) ink, light black (LK) ink and light light black (LLK) ink for the black part.

According to the present invention, N can be 10 or 20.

According to the present invention, when N is 20, the N color scales of each of the four primary colors include the darkest color scale when the dot percentage of the color is 100%, 18 decreasing color scales with the dot percentage decreasing by 5% in sequence, and the lightest color scale when the dot percentage of the color is 5%.

According to the present invention, when N is 20, the 2N color scales of each of the four primary colors printed include the darkest color scale when the dot percentage of the color is 100%, 38 decreasing color scales with the dot percentage decreasing by 2.5% in sequence, and the lightest color scale when the dot percentage of the color is 2.5%.

Unlike the traditional method of using color blocks printed on decorative paper as the basis for inkjet calibration, this invention uses color blocks on fully manufactured melamine boards as the basis for inkjet calibration. This can eliminate all objective reasons that cause color deviation in printing at one time, achieving the purpose of perfectly calibrating the inkjet control of the digital inkjet plotter.

1: Box

2: Box

3: Box

1a: Box

2a: Box

3a: Box

L1: Four-color standard confirmation stage

L2: Ink loading confirmation stage

L3: Multicolor standard confirmation stage

S01~S09: Steps

Figure 1 is a phase flow chart of a color calibration method for a melamine decorative paper digital inkjet printer according to an embodiment of the present invention.

Figure 2 is a flow chart of several steps involved in a four-color standard confirmation phase.

Figure 3 shows the steps involved in an ink level confirmation phase.

Figure 4 is a flow chart of several steps involved in a multicolor standard confirmation phase.

Figure 5 shows a digital inkjet printer printing out the four primary colors in sequence. Each color is divided into 20 color shades, and these color shades represent colors in continuous frames on a decorative paper.

Figure 6 shows that the digital inkjet printer prints out the four primary colors in sequence, each of which is divided into 40 color shades, and the color shades represent the colors in the continuous frames on the decorative paper.

FIG. 7 shows the state of selecting a plurality of color combinations formed by different percentages of the four primary colors when the digital inkjet printer is used to print arrays on the decorative paper.

The present invention will be described in more detail with reference to the following embodiments.

The purpose of the present invention is to propose a method for correcting the amount of ink sprayed by each nozzle of a digital inkjet printer before each nozzle of the digital inkjet printer sprays ink according to a predetermined image file, that is, a method for color adjustment so that the final image on the decorative paper can be closest to the original image based on a certain color management specification. Here, the digital inkjet printer to which the present invention is applied has the following features: first, it can use at least one color management specification as a standard. After receiving a digital printing image file, it can control the amount of ink ejected by its nozzle according to the color standard definition of each pixel on it, so as to achieve the function of printing the color closest to the pixel; second, it can adjust the amount of ink ejected by each nozzle in accordance with the color values actually detected by the color calibrator for multiple color points, such as the difference between the measured tristimulus values and the values of the standard color definition, so as to achieve the function of printing the color closest to the color standard recognized by the color calibrator in a manner that has a color deviation with the standard color definition used by the digital inkjet printer. Third, when printing, the digital inkjet printer uses standard cyan (C) ink and light cyan (LC) ink for the cyan part, standard magenta (C) ink and light magenta (LC) ink for the magenta part, standard yellow (Y) ink for the yellow part, and standard black (K) ink, light black (LK) ink, and light light black (LLK) ink for the black part.

Regarding the first feature mentioned above, the color management standards, such as but not limited to Japan Color 2001 Coated, U.S. Sheetfed Coated, U.S. Web Coated, etc., are used in different digital inkjet printers. As for the adjustment of the amount of ink ejected by the nozzle, as long as the aforementioned purpose is achieved, the present invention does not limit the principle of its use. Regarding the second feature mentioned above, the following explains why the digital inkjet printer should have the ability to abandon the standard to adapt to the detection results of the colorimeter. As mentioned above, even if a decorative paper is used by a perfectly functioning digital inkjet printer to accurately print out each pixel on a picture file according to the corresponding color definition, the decorative paper will eventually be combined with the surface paper due to heat pressing, and the pattern displayed on the melamine board and the original image will inevitably have color differences. If the pattern of melamine board is to be as close to the original as possible, the digital inkjet printer must systematically offset the custom standard printing. In addition, the difference between the pattern of melamine board and the original image also occurs when the ink expires (or deteriorates), the decorative paper ages (yellowing), the digital inkjet printer is not calibrated, and there may even be problems with the colorimeter itself. When it is necessary to accept mass-produced melamine board according to a standard, the printing method that systematically meets the standard must be used by the digital inkjet printer for reference. Regarding the third characteristic mentioned above, general digital inkjet printers use four spot colors for printing, that is, using four spot color inks of cyan (Cyan, C), magenta (Magenta, M), yellow (Yellow, Y) and key plate (Key plate, K) to simulate full-color printing. According to the present invention, the applicable digital inkjet printer can be a higher specification printing head combination. That is to say, in addition to the color combination based on CMYK, there are also light cyan, light magenta, light black and light light black inks. The two cyan inks are used to print all the parts that need cyan by the ratio between them and the overall dot percentage, and the two magenta inks are used to print all the parts that need magenta by the ratio between them and the overall dot percentage. As for yellow, since the human eye has poor recognition ability, one yellow ink can be used. As for black, three different inks are used, and all the parts that need black are printed by using the ratio and the overall dot percentage. This method of using 8 spot colors to simulate the printing of four primary colors can obtain a more realistic feeling of the printed pattern, less graininess and a smoother gradient effect.

Please see Figure 1, which is a phase flow chart of a color calibration method (hereinafter referred to as the method) for a melamine decorative paper digital inkjet printer according to an embodiment of the present invention. The method includes three implementation phases: a four-color standard confirmation phase (L1), an ink loading confirmation phase (L2) and a multi-color standard confirmation phase (L3). Each phase includes at least one step. The steps of each phase are described below.

Please refer to FIG. 2, which is a flow chart of several steps included in the four-color standard confirmation stage. The first step of the four-color standard confirmation stage is to divide each color of the four primary colors into N color levels, and use a digital inkjet printer to sequentially print out the color levels representing the colors in a continuous frame on a decorative paper (S01). In order to have a better understanding of this step, please also refer to FIG. 5, which shows that the digital inkjet printer sequentially prints out the color levels representing the colors of each color of the four primary colors divided into 20 color levels in a continuous frame on a decorative paper. According to the present invention, N is a positive integer not less than 10. The larger N is, the more color frames of different shades appear for the same four primary colors, and the greater the chance that the digital inkjet printer can perform fine adjustments. In practice, N can be 10 or 20. For example, when N is 20, each color of the four primary colors in step S01 is evenly divided into 20 color shades. The 20 color shades of each color of the four primary colors include the darkest shade when the dot percentage of the color is 100%, 18 descending shades with the dot percentage decreasing by 5% in sequence, and the lightest shade when the dot percentage of the color is 5%. On the decorative paper of FIG5, the rows are divided from left to right into 20 representative colors of black shades, 20 representative colors of yellow shades, 20 representative colors of magenta shades, and 20 representative colors of cyan shades. In FIG5, the cyan series is used as an example for explanation. The cyan color printed by the digital inkjet printer in the bottom box 1 of the cyan series is the darkest color when the dot percentage is 100%. There are 18 boxes 2 above box 1, and each box 2 prints a color with a decreasing color gradation. The decreasing color gradation in the box 2 closest to box 1 is printed using 95% dot percentage cyan, and the box 2 adjacent to the previous box 2 is printed using 90% dot percentage cyan, and so on. The top box 3 is the lightest color gradation when the dot percentage is 5%. Similarly, the black gradation, yellow gradation, and magenta gradation are also printed according to the above method. Because the digital inkjet printer does not print as expected for colors with a higher dot percentage before it is turned on for color calibration (for example, due to the influence of the heat level of the machine), the colors in box 2 close to box 1 in Figure 2 are almost the same, especially in yellow. Therefore, further calibration of the digital inkjet printer needs to be carried out more carefully.

The second step of the method is to read the three-color stimulus values of the box colors with a closed colorimeter, and compare the three-color stimulus values of each box color with the three-color stimulus values of the corresponding color scale representative color to correct the ink jetting amount of each color nozzle of the digital inkjet printer (S02). The colorimeter can read the objective detection data of the color in any area on a printed product, such as the three-color stimulus value (expressed as X, Y, Z, expressed as X (red primary color stimulus amount), Y (green primary color stimulus amount) and Z (blue primary color stimulus amount)), to identify the standard definition of the color of the area, thereby comparing it with the target color, and the comparison result can provide the digital inkjet printer with a method for correcting ink jetting. Since step S01 can use a smaller decorative paper, such as a printing area of 11.5cm x 2.5cm, the decorative paper under test can be placed in a closed test environment of a closed colorimeter, and the decorative paper under test can be tested with a test light that is not affected by external light to obtain three-color stimulus values. This result is more accurate. Taking the cyan color scale as an example, 20 sets of three-color stimulus values for printing box colors with different cyan depths can be obtained in Figure 5. There must be a difference between these three-color stimulus values and the standard three-color stimulus values corresponding to the cyan color scale recognized by the digital inkjet printer. After receiving the difference between the measured tri-color stimulus values and the standard tri-color stimulus values, the digital inkjet printer can fine-tune the amount of ink sprayed so that the color printed subsequently can be closer to the 20 cyan standards recognized by the closed colorimeter to meet the acceptance standards of melamine products.

Next, the third step of the method is to divide each of the four primary colors into 2N color shades, and use the digital inkjet printer to print out the color shades in succession on the decorative paper (S03). Step S03 is the same as step S01, except that the number of color shades for each of the four primary colors is doubled. The 2N color shades for each of the four primary colors include the darkest shade when the dot percentage of the color is 100%, 38 descending shades with a dot percentage of 2.5% decreasing in sequence, and the lightest shade when the dot percentage of the color is 2.5%. For a better understanding of this, please refer to FIG. 6 simultaneously, which shows that the digital inkjet printer sequentially prints out each of the four primary colors, which are divided into 40 color levels (N is 20), and the color levels represent the colors in the continuous frames on the decorative paper. FIG. 6 also uses the cyan level as an example for explanation. As the number of frames to be printed increases, in order to reduce the aspect ratio of the printed pattern and facilitate the closed colorimeter test, FIG. 6 is not printed in the form of 40 frames in a row. In FIG. 6, there are only 32 frames in each row, and the remaining 8 cyan-level color frames are printed on the next row, while the color frames of the other color level (magenta in this embodiment) continue to expand from the 9th color frame in the next row. The upper right box 3a is the lightest color when the dot percentage is 2.5%, the second box 2a from the top is printed with a dot percentage of 5%, the third box 2a from the top is printed with a dot percentage of 7.5%, and so on. The eighth box 1a in the second row on the right is the darkest color when the dot percentage is 100%. Compared with Figure 5, the color difference between the boxes in Figure 6 is more obvious because the digital inkjet printer has been adjusted for the first time, but the colors closer to the darkest color are still very close.

The fourth step of the method is to use the closed colorimeter to read the three-color stimulus values of the box colors, and compare the three-color stimulus values of each box color with the three-color stimulus values of the corresponding color gradation representative color to correct the ink spray volume of each color nozzle of the digital inkjet printer (S04). This step is the same as step S02, except that the number of color frames of the same color gradation is doubled. After step S04, the digital inkjet printer has undergone two inkjet calibrations. Then, the fifth step of the present invention is to repeat step S03 and step S04 (S05), that is, to perform the third inkjet calibration on the digital inkjet printer. At this point, if the inkjet calibration is continued, the effect is not obvious and it is also a waste of time.

Next, the present invention enters the ink loading confirmation stage. Please see FIG. 3, which shows the steps included in the ink loading confirmation stage, which is the fifth step of the method: using the digital inkjet printer to print four primary colors on the decorative paper, and measuring the maximum ink loading of the decorative paper for each color ink (S05). The maximum ink loading is the maximum loading capacity of each type of paper for a specific ink. If the maximum ink loading is exceeded, the ink will escape to places outside the edge, affecting the neatness of the pattern, and may even cause mutual rendering between the two inks, resulting in worse performance. Since the decorative paper used by the digital inkjet printer each time has different aging degrees, different batches, and even different product sources, and the characteristics of the ink itself vary, the maximum ink loading of each color ink will also change during printing. Therefore, recording the maximum ink loading of each color ink on decorative paper is helpful for controlling the ink volume during production printing.

Next, the present invention enters the multi-color standard confirmation stage. Please see Figure 4, which is a flow chart of several steps included in the multi-color standard confirmation stage. The first step of the multi-color standard confirmation stage, that is, the seventh step of the present method, is to select a plurality of combination colors formed based on different percentages of the four primary colors of printing, and use the digital inkjet printer to array-print these combination colors on the decorative paper (S07). After the inkjet calibration of the single-color ink is calibrated, the combination colors need to be calibrated next. Since the combination colors contain at least two or more ink colors of different color systems, they can also be detected to obtain three-color stimulation values. Please see Figure 7, which shows the state of using a digital inkjet printer to array-print on decorative paper to select a plurality of combination colors formed based on different percentages of the four primary colors of printing. The English or digital symbols in Figure 7 are numbers given to the colors to be printed. It can be seen from Figure 7 that the printing of the color blocks of the combination colors in step S07 is random. In practice, there can be more than a thousand color combinations. The more there are, the better the calibration effect. Therefore, the decorative paper used in this step will be larger, such as a size of B4 or above. Figure 7 only shows a part of the pattern of the printed decorative paper.

Next, the second step of the multi-color standard confirmation stage, which is the eighth step of the method, is to sandwich the decorative paper printed with the combined colors between a matte surface paper and several sheets of kraft paper, and heat press to produce a melamine board (S08). This step is to produce a standardized melamine board using the color sample formed by printing the decorative paper, and to perform the final calibration using the combined color blocks displayed on the melamine board.

The third step of the multi-color standard confirmation stage, that is, the ninth step of the method, is to use an open colorimeter to read the three-color stimulus values of the color combinations of the melamine board through the matte surface paper, compare the three-color stimulus values of each color combination with the three-color stimulus values of the corresponding standard color combination to correct the ink spray volume of each color nozzle of the digital inkjet printer, and control the ink spray volume per unit area of each color nozzle to be no greater than the minimum value of the maximum ink load of the four primary colors (S09). As mentioned above, because the decorative paper used in step S07 has a large area, the closed colorimeter is not applicable. An open colorimeter can also read the three-color stimulus values of the color combinations of melamine board through the matte surface paper, but it is slightly less accurate than a closed colorimeter. As you can imagine, the three-color stimulus values of the color combinations read by the open colorimeter are different from the three-color stimulus values of the digital inkjet printer itself for each color combination through a heat-pressed matte surface paper. Since the open colorimeter can read the difference between the three-color stimulus values of each color combination and the standard three-color stimulus values, this difference can provide the digital inkjet printer with a final calibration opportunity before printing decorative paper. This calibration may change the calibration effect of the monochrome level, but it can better meet the final quality requirements of melamine board. The ink volume per unit area of each color nozzle is no more than the minimum value of the maximum ink load of the four primary colors, ensuring that all inks will not exceed an upper limit value, resulting in ink overflow.

Although the present invention has been disclosed in the form of implementation as above, it is not intended to limit the present invention. Anyone with ordinary knowledge in the relevant technical field can make some changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of the patent application attached hereto.

Claims (5)

A color calibration method for a digital inkjet printer for melamine decorative paper includes: a four-color standard confirmation stage, including the steps of: a) dividing each color of the four primary colors into N color levels, using a digital inkjet printer to sequentially print the colors representing these color levels in continuous square frames on a decorative paper; b) using a closed colorimeter to read the three-color stimulus values of the colors of these square frames, and comparing the three-color stimulus values of each square frame color with the three-color stimulus values of the corresponding color level representative color to correct the color. The method comprises the steps of: adjusting the ink jetting amount of each color nozzle of the digital inkjet printer; c) dividing each color of the four primary colors for printing into 2N color scales, and using the digital inkjet printer to sequentially print the colors representing the color scales in continuous square frames on the decorative paper; d) using the closed colorimeter to read the three-color stimulus values of the colors of the square frames, and comparing the three-color stimulus values of each color of the square frame with the three-color stimulus values of the corresponding color scale representative colors to correct the ink jetting amount of each color nozzle of the digital inkjet printer; and e) repeating step c once. ) and step d); an ink loading confirmation stage, including the steps of: f) printing four primary colors on the decorative paper with the digital inkjet printer to measure the maximum ink loading of the decorative paper for each color ink; and a multi-color standard confirmation stage, including the steps of: g) selecting a plurality of combination colors formed based on different percentages of the four primary colors printed, and printing the combination colors in an array on the decorative paper with the digital inkjet printer; h) sandwiching the decorative paper printed with the combination colors between a matte surface paper and a A plurality of kraft papers are heat-pressed to form a melamine board; and i) an open colorimeter is used to read the three-color stimulation values of the combination colors of the melamine board through the matte surface paper, and the three-color stimulation values of each combination color are compared with the three-color stimulation values of the corresponding standard combination colors to correct the ink spraying amount of each color nozzle of the digital inkjet printer, and the ink spraying amount per unit area of each color nozzle is controlled not to be greater than the minimum value of the maximum ink loading amount of the four primary colors, wherein N is a positive integer not less than 10. A color calibration method for a melamine decorative paper digital inkjet printer as described in claim 1, wherein the digital inkjet printer uses standard cyan (C) ink and light cyan (LC) ink for the cyan part, standard magenta (C) ink and light magenta (LC) ink for the magenta part, standard yellow (Y) ink for the yellow part, and standard black (K) ink, light black (LK) ink and light light black (LLK) ink for the black part during printing. A color calibration method for a melamine decorative paper digital inkjet printer as described in claim 1, wherein N is 10 or 20. A color calibration method for a melamine decorative paper digital inkjet printer as described in claim 1, wherein when N is 20, the N color scales of each of the four primary colors include the darkest color scale when the dot percentage of the color is 100%, 18 decreasing color scales with the dot percentage decreasing by 5% in sequence, and the lightest color scale when the dot percentage of the color is 5%. A color calibration method for a melamine decorative paper digital inkjet printer as described in claim 1, wherein when N is 20, the 2N color scales of each of the four primary colors to be printed include the darkest color scale when the dot percentage of the color is 100%, 38 decreasing color scales with the dot percentage decreasing by 2.5% in sequence, and the lightest color scale when the dot percentage of the color is 2.5%.