Method for printing on absorbent printing material using inks and dampening fluids

Abstract

A method prints on a printing material using inks and dampening fluids. An ink printing machine uses ink print heads to apply an image to a front side of the printing material and a dampening fluid print head to apply a dampening fluid image, thus reducing or avoiding water-related cockling of the printing material. The method includes: providing the image to be printed, calculating n different color separation matrices, calculating n ink amount matrices A.sub.n from the color separation matrices, and calculating a total ink amount matrix A. For every element of the total ink amount matrix: calculating a matrix B as B=G*A, with a weighting matrix G and determining the maximum of the matrix B, calculating a dampening fluid matrix C, calculating the dampening fluid image from the dampening fluid image matrix C, and printing the ink image and the dampening fluid image.

Claims

1. A method for printing on an absorbent printing material using inks and dampening fluids, wherein both the inks and the dampening fluids contain water as a solvent and a dampening fluid is colorless, wherein an ink printing machine having at least two ink print heads and at least one dampening fluid print head is provided, wherein the at least two ink print heads apply an ink image to be printed to a front side of the absorbent printing material and the at least one dampening fluid print head applies a dampening fluid image, to be printed to the front side of the absorbent printing material, thus reducing or avoiding water-related cockling of the absorbent printing material, and wherein a computer is provided, which method comprises the following steps of: a) providing the ink image to be printed onto the front side of the printing material; b) calculating n different color separation matrices of the ink image with n and n2; c) calculating n ink amount matrices A.sub.n from the n different color separation matrices of the ink image; d) calculating a total ink amount matrix A as A=A.sub.1+A.sub.2+ . . . +A.sub.n; e) calculating a matrix B.sub.i,j as B.sub.i,j=G*A for every element A(i, j) of the total ink amount matrix A, by multiplying the total ink amount matrix A with a provided weighting matrix G, and determining a maximum Max.sub.i,j of a matrix B; f) calculating a dampening fluid amount matrix C as C(i,j)=MaxB.sub.i,A(i,j); g) calculating the dampening fluid image to be printed onto the front side of the absorbent printing material from the dampening fluid image matrix C; h) screening the n different color separation matrices of the ink image using a raster image processor; i) screening the dampening fluid image using the raster image processor; j) printing the ink image; and k) printing the dampening fluid image.

2. The method according to claim 1, wherein the n different color separation matrices of the ink image are calculated as CMYK or CMYKOGV matrices.

3. The method according to claim 1, which further comprises calculating the n ink amount matrices A.sub.n, using a relationship T.sub.1 between intensity or optical density and layer thickness.

4. The method according to claim 1, wherein a respective weighting g1.sub.n of the n ink amount matrices A.sub.n is factored in when the total ink amount matrix A is calculated.

5. The method according to claim 4, wherein in terms of progression of values of elements G(i,j) thereof, the weighting matrix G is provided as a matrix that is cone-shaped at a center and filled with zeroes at margins.

6. The method according to claim 1, wherein a weighting g2 of the maximum MaxB.sub.i,j of the matrix B and the elements A(i,j) of the total ink amount matrix A in accordance with a respective water content of the dampening fluid and the inks is factored in when the dampening fluid matrix C is calculated.

7. The method according to claim 1, which further comprises calculating the dampening fluid image using a provided relationship T.sub.2 between intensity and layer thickness.

8. The method according to claim 1, which further comprise: repeating steps a)-g) for a further image to be printed onto a back side of the absorbent printing material; comparing the ink image or a dampening image value of the front side image and a corresponding back-side value of ink or the dampening fluid image on the back side at every printing material location to be printed on; and transferring a greater value obtained in a comparison for one image to a corresponding other image.

9. The method according to claim 1, wherein the dampening fluid print head has a lower print resolution than the ink print heads.

10. The method according to claim 1, wherein the computer is provided to carry out calculating, determining, and comparing steps.

11. The method according to claim 1, wherein: the dampening fluid image surrounds; and the ink image is an RGB image.

12. The method according to claim 3, wherein the step of calculating the ink amount matrices A.sub.n using the relationship T.sub.1 between the intensity or the optical density and the layer thickness uses a Tollenaar curve.

13. The method according to claim 7, which further comprises calculating the dampening fluid image using a Tollenaar curve or an inverse thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A is a flow chart illustrating a preferred exemplary embodiment of a first part of a method of the invention;

(2) FIG. 1B is a flow chart illustrating a preferred exemplary embodiment of a second part of a method of the invention;

(3) FIG. 2 is an illustration of a preferred exemplary embodiment of an ink amount matrix A;

(4) FIG. 3 is an illustration of a preferred exemplary embodiment of a weighting matrix G;

(5) FIG. 4 is an illustration of a preferred exemplary embodiment of a total ink amount matrix B; and

(6) FIG. 5 is an illustration of a preferred exemplary embodiment of a dampening fluid amount matrix C.

DETAILED DESCRIPTION OF THE INVENTION

(7) Referring now to the figures of the drawings in detail and first, particularly to FIGS. 1A and 1B thereof, there is shown a preferred exemplary embodiment of a method of the invention in accordance with steps 1 to 15. The individual steps of the method will be described in detail below with further reference to the further FIGS. 2 to 5.

(8) In step 1, an ink printing machine is provided. The machine has at least two ink print heads, preferably four or seven print heads as well as at least one dampening fluid print head for printing on a side of an absorbent printing material, preferably paper, cardboard, or any other natural-fiber-containing material. To print on and dampen the back side, further heads may optionally be provided. The inks and dampening fluid to be applied contain water as a solvent and the dampening fluid is essentially colorless or transparent. The at least two ink print heads apply a multicolor ink image to be printed onto a front side of the printing material. Correspondingly, the at least one dampening fluid print head transfers a dampening fluid image to be printed onto the front side of the printing material. The transfer of the dampening fluid reduces or avoids water-related cockling of the absorbent printing material.

(9) In a step 2, a computer is provided. The computer is in particular used to carry out some of the steps indicated below, in particular steps of calculating, determining, or comparing. The computer is preferably part of a machine control unit and includes a memory for saving data, in particular matrices.

(10) In a step 3, the image to be printed onto the front side of the printing material is provided. The image may in particular be a two- or multicolored image such as an RGB image provided as what is known as a bitmap. The image may be saved on the computer or may be supplied to the computer as a matrix. The image corresponds to the print job to be printed or produced, i.e. the physical print that is actually visible (on the printing material).

(11) In a step 4, color separations of the image that has been provided are created. In this process, n different color separation matrices of the image are calculated with n and n2. The color separation matrices of the image may be calculated as CMYK matrices or as CMYKOGV matrices (cyan, magenta, yellow, black, orange, green, violet). Thus in the former case, four matrices would be calculated. Every matrix would correspond to one of the four color separations C, M, Y, K. The color separation matrices correspond to the color separations of the multicolor print, which, once printed on top of one another, form the print job.

(12) In a step 5a, a relationship T.sub.1 between the intensity or optical thickness of the respective elements of the color separation matrices and a corresponding layer thickness or ink amount is provided. The T.sub.1 relationship may in general be provided as a function or as a discrete allocation. The T.sub.1 relationship may in particular be provided in the form of what is known as the Tollenaar curve. The T.sub.1 relationship may be provided jointly for all inks or colors or separately for every ink or color (T.sub.1n). Thus a calculation may be made in accordance with step 5b using the provided relationship T.sub.1 from the individual elements of the color separation matrices (intensity values or optical density values). In this process, a corresponding number of ink amount matrices A.sub.n is calculated from the n different color separation matrices of the image. The ink amount matrices thus contain elements that are values of the layer thickness to be created or rather of the ink amounts required for this purpose and not intensity values or optical density values like the color separation matrices. The ink amount matrices correspond to the ink amounts of the respective printing colors that are to be transferred to the printing material for the print job to be produced.

(13) In a step 6, the previously calculated ink amount matrices A.sub.n are used to calculate a total ink amount matrix A. This may preferably be done by forming a total out of the matrices A.sub.n: A=A.sub.1+A.sub.2+ . . . +A.sub.n. The calculation may optionally be made factoring in a respective weighting g1.sub.n of the respective ink amount matrices A.sub.n. An example of a total ink amount matrix A is shown in the upper half of FIG. 2 (matrix having lines i and columns j and elements (i, j)). The lower half of FIG. 2 is a graphic representation of the same matrix. The illustrated lines represent values of the matrix that have the same absolute value (corresponding to contour lines in a mountain range corresponding to the matrix). The total ink amount matrix corresponds to the distribution of the total ink amount to create the print job on the printing material, i.e. the total ink amount at every location on the printed printing material.

(14) In step 7a, a weighting matrix G is provided. FIG. 3 shows an example of such a matrix G. The figure shows that the matrix has an essentially cone-shaped structure, i.e. the progression of the absolute values of the matrix elements (i, j) is cone-shaped at the center of the matrix G. The tip of the cone is at the center of the matrix. At the margin, the matrix G is filled with zeroes. Other progressions are likewise possible, but tests have shown such a conical shape to be particularly advantageous. In a step 7b, a matrix B is calculated. Such a matrix B is shown in FIG. 4. The calculation is made as follows: For every value A(i,j) of the total ink amount matrix A, a respective matrix Bi,j is calculated by multiplying the total ink amount matrix A by the provided weighting matrix G, which is centered (that is to say whose center, in particular its cone tip, is disposed) at A(i,j). The calculation may be made as a convolution of the matrices. In accordance with a step 7c, the maximum MaxB.sub.i,j of all elements of the respective matrix B.sub.i,j is determined for every such matrix B.sub.i,j.

(15) In a step 8, a dampening fluid amount matrix C is calculated. In this process, every element (i,j) of the matrix C results from subtracting the value (i,j) of the matrix A from the maximum MaxB.sub.i,j: C(i,j)=MaxB.sub.i,jA(i,j). The values of MaxE.sub.i,j and A(i,j) may be weighted, i.e. a weighting by a factor g2 may be made in the aforementioned subtraction. The value of the weighting g2 may be selected in accordance with the respective water content of the dampening fluid and the inks. The dampening fluid amount matrix C corresponds to the amount of dampening fluid to be transferred to the printing material. This amount has been adapted, in accordance with the invention (in view of reducing or avoiding cockling), to the total ink amount to be transferred.

(16) In a step 9a, a relationship T.sub.2 between the intensity and the layer thickness (or rather the amount of dampening fluid) is provided. The T.sub.2 relationship may in general be provided as a function or as a discrete allocation. The T.sub.1 relationship may in particular be provided in the form of what is known as the Tollenaar curve. The relationship T.sub.2 may be provided for the dampening fluid, i.e. it may differ from the relationship T.sub.1 (or T.sub.1n). In a step 9b, the dampening fluid image to be printed onto the front side of the printing material is calculated from the dampening fluid matrix C. The dampening fluid image may be calculated using the relationship T.sub.2 that has been provided. The dampening fluid image and the term image are to be understood as corresponding to the (print) image: an (i,j) distribution of intensity values for a fluid to be transferred even though it is colorless.

(17) If only the front side of the printing material receives a print, the method continues at step 12. However, if the back side of the printing material is to receive a print, too, steps 2 to 9b are carried out in a corresponding way for the print to be applied to the back side. If both sides of the printing material are to be printed on, an additional step 11 is carried out. This step is to compare the front side value of the ink image or dampening fluid image and the corresponding back-side value of the ink image or dampening fluid at every location to be printed on the printing material. The greater one of the two values obtained by the comparison is transferred from one image to the corresponding other image.

(18) In a step 12, the color separation matrices of ink image are screened using a raster image processor. In a step 13, the dampening fluid image is likewise screened using the raster image processor. If the printing material is to be printed on both sides, the screening steps are carried out both for the front side and for the back side of the printing material.

(19) In a step 14, the ink image is printed onto the front side of the printing material. The same is done for the back side of the printing material if the back side is to be printed on, too.

(20) In a step 15, the dampening fluid image is printed onto the front side of the printing material. Again, the same is done for the back side of the printing material if the back side is to be printed on.

(21) The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention: 1 providing a printing machine including print heads 2 providing a computer 3 providing an image calculating color separation matrices 5a providing relationship T.sub.1 5b calculating ink amount matrices calculating total ink amount matrix A 7a providing weighting matrix G 7b calculating matrix B 7c determining maximum Max.sub.i,j 8 calculating dampening fluid amount matrix C 9a providing relationship T.sub.2 9b calculating dampening fluid image 10 decision 11 comparing and transmitting 12 screening the color separation matrices 13 screening the dampening solution image 14 printing the ink image 15 printing the dampening fluid image