Method for operating an inkjet printing machine

Abstract

In a method for operating an inkjet printing machine, a condition of an ink is determined. A sedimentation and/or agglomeration of a pigmented ink is determined by refractometry, i.e. the value of the refractive index of the ink is measured with a refractometer and compared with a stored value with computer assistance.

Claims

1. A method for operating an inkjet printing machine, which comprises the steps of: providing a refractometer; determining a condition of a pigmented ink by performing the further steps of: measuring a value of a refractive index of the pigmented ink with the refractometer; determining a sedimentation and/or agglomeration of the pigmented ink based on a deviation of the value of the refractive index from a reference value of the refractive index of the pigmented ink by comparing the value of the refractive index with a stored reference value with a computer; initiating a corrective measure in the printing machine for reducing the refractive index when the deviation exceeds a selected deviation; comparing a measured, sedimentation-dependent and/or agglomeration-dependent refractive index with at least one stored type-specific refractive index for determining a type of ink; starting a print job by applying ink with a print head of the printing machine when the deviation is below an acceptable level.

2. The method according to claim 1, which further comprises carrying out a measurement directly after stirring the pigmented ink.

3. The method according to claim 1, which further comprises measuring the sedimentation and/or agglomeration in a liquid phase of the pigmented ink.

4. The method according to claim 1, which further comprises measuring the sedimentation and/or agglomeration in an ink tank or an ink storage container or an ink line.

5. The method according to claim 1, which further comprises measuring the sedimentation and/or agglomeration continuously or quasi-continuously.

6. The method according to claim 1, wherein depending on a value of a deviation obtained from a comparison, one of the following steps is taken: printing with the pigmented ink without stirring; printing with the pigmented ink with simultaneous stirring; printing with the pigmented ink after the stirring; intensifying the stirring, namely longer and/or faster stirring; outputting a warning upon detection of a high sedimentation; computer-aided gathering of a decision for or against an ink change; emptying an ink tank and/or an ink storage container; flushing the ink tank and/or the ink storage container and/or an ink line and/or an inkjet print head with a cleaning liquid; and changing out the pigmented ink.

7. The method according to claim 1, which further comprises determining a sedimentation-dependent and/or agglomeration-dependent refractive index of a white ink in the inkjet printing machine for printing three-dimensional objects.

8. A method for operating an inkjet printing machine, which comprises the steps of: providing a refractometer; determining a condition of a pigmented ink by performing the further steps of: measuring a value of a refractive index of the pigmented ink with the refractometer; determining a sedimentation and/or agglomeration of the pigmented ink based on a deviation of the value of the refractive index from a reference value of the refractive index of the pigmented ink by comparing the value of the refractive index with a stored reference value with a computer; initiating a corrective measure in the printing machine for reducing the refractive index when the deviation exceeds a selected deviation; comparing a measured, sedimentation-dependent and/or agglomeration-dependent refractive index with at least one stored color-specific refractive index for determining a color of the pigmented ink; starting a print job by applying ink with a print head of the printing machine when the deviation is below an acceptable level.

9. A method for operating an inkjet printing machine, which comprises the steps of: providing a refractometer; determining a condition of a pigmented ink by performing the further steps of: measuring a value of a refractive index of the pigmented ink with the refractometer; determining a sedimentation and/or agglomeration of the pigmented ink based on a deviation of the value of the refractive index from a reference value of the refractive index of the pigmented ink by comparing the value of the refractive index with a stored reference value with a computer; initiating a corrective measure in the printing machine for reducing the refractive index when the deviation exceeds a selected deviation; comparing measured, sedimentation-dependent and/or agglomeration-dependent refractive index with at least one stored age-specific or aging-specific refractive index for determining an age of the pigmented ink; starting a print job by applying ink with a print head of the printing machine when the deviation is below an acceptable level.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 is a flow chart showing a preferred exemplary embodiment of a method according to the invention;

(2) FIG. 2 is a flow chart showing a preferred exemplary embodiment of a method according to the invention; and

(3) FIG. 3 is an illustration showing a device during the performance of a preferred exemplary embodiment of a method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(4) Referring now to the figures of the drawings in detail and first, particularly to FIG. 1 thereof, there is shown a flowchart of a series of method steps of a preferred exemplary embodiment of a method according to the invention. The method steps will be explained below (with regard to the designations, reference is also made to FIG. 3).

(5) Step 1 (optional): An ink supply device 17 of an inkjet printing machine 18 or its ink tank 20 and/or ink storage container and possibly its ink lines 22a, 22b, 25 and 31a is/are emptied of liquid ink 21, 24.

(6) Step 2: Liquid ink 24 is provided, i.e. the ink is put into storage container 23 (or an already filled storage container is provided).

(7) Step 3: The ink 24 from the storage container 23 is brought or put into the ink tank 20, preferably pumped, and is present there as ink 21. Optionally, the ink 21 is stirred by using a stirrer 27. The ink is brought, preferably pumped, via an ink line 22a to at least one inkjet print head 22 and back to the ink tank 20 via an ink line 22b.

(8) Step 4: A starting value n.sub.Start of a refractive index n of the ink is measured. The measurement can be carried out at one of the following points: preferably with a refractometer 30 in the storage container 23 or with the refractometer 31 in an ink line 31a, 31b (bypass) on the storage container 23; or with the refractometer 32 in the ink line 22a, 22b; or with the refractometer 33 in the ink tank 20. The measured value n can be stored.

(9) Step 5: The measured starting value n.sub.Start of the refractive index n is compared by computer with apreferably likewise stored (see step 6)reference value of the refractive index n.sub.Ref. Preferably, a difference is formed.

(10) Step 6: Thepreferably storedreference value of the refractive index n.sub.Ref is provided for the comparison by computer. The reference value can, for example, originate from the ink manufacturer or can be determined from previous measurements (e.g. by means of averaging).

(11) Step 7: Depending on or in the event of an excessively high value of a deviation n of n relative to n.sub.Ref that is obtained from the comparison, one of the following measures is taken: intensified stirring (longer and/or faster; with stirrer 27 and/or 28), after that step 4: emptying (the ink tank 20 and/or the ink storage container 23), optionally combined with flushing with a cleaning liquid, after that step 2.

(12) Step 8: Depending on or in the event of a value that is not excessively high (or is suitable) of a deviation n of n relative to n.sub.Ref that is obtained from the comparison, the measured starting value n.sub.Start of the refractive index n is stored, i.e. preferably stored by computer.

(13) Step 9: The printing of a print job is started, i.e. the inkjet print head 22 transfers the image to be printed in the form of ink drops to the surface 19 (of a three-dimensional object or a flat substrate). Optionally, the ink 21 is stirred by using a stirrer 27.

(14) FIG. 2 shows a flowchart of a series of further method steps of a preferred exemplary embodiment of a method according to the invention.

(15) Step 10 (optional): After a print job has been completed, an ink change is made. The steps to be carried out for this purpose can coincide with steps 1 to 3 (see FIG. 1).

(16) Step 11: The inkjet print head 22 prints and a print job is carried out. During the printing, the ink 21 and/or 24 can optionally be stirred or recirculated.

(17) Step 12: During the printing, a determination or measurement of the value of the refractive index n.sub.current of the ink is carried out (continuously or quasi-continuously).

(18) Step 13: The measured value of the refractive index n.sub.current is compared by computer with apreferably stored (see steps 6, 8 and 14)starting value n.sub.Start or reference value of the refractive index n.sub.Ref. The difference is preferably formed.

(19) Step 14: Thepreferably storedstarting value of the refractive index n.sub.Start (or alternatively the reference value of the refractive index n.sub.Ref) is provided for the comparison by computer.

(20) Step 15: Depending on or in the event of an excessively high value of a deviation n of n.sub.current relative to n.sub.Start (or alternatively n.sub.Ref) that is obtained from the comparison, one of the following measures is taken: outputting a warning against excessively high sedimentation (possibly with the recommendation to change the ink); computer-aided gathering of a decision for or against an ink change. Depending on the reaction of the operator, an ink change can be carried out (further with step 10), or printing can be continued (further with step 11). The decision can also be made by computer, for example by predefining a limiting value for the deviation n. Alternatively, the following can also be initiated: intensified stirring (longer and/or faster; with stirrer 27 and/or 28), after that or simultaneously, step 11.

(21) Step 16: Depending on or in the event of a value that is not excessively high (or is suitable) of a deviation n of n.sub.current relative to n.sub.Start (or alternatively n.sub.Ref) that is obtained from the comparison, printing is continued and, possibly, stirring is continued. Then, a measurement according to step 12 can be carried out again.

(22) FIG. 3 shows a device during the performance of a preferred exemplary embodiment of a method according to the invention. Liquid ink 21 is accommodated in an ink tank 20. The ink is led to an inkjet print head 22 and non-printed ink is led back to the tank (via ink lines 22a, 22b). Ink 24 is likewise accommodated in a storage container 23. The storage container can preferably accommodate more ink than the tank; it can be formed, for example, as a can or a barrel. The ink is led to the tank 20 (via a line 25). A stirrer 26 is provided in the container 23, a stirrer 27 in the tank 20. Alternatively, it is also possible for only one of the two stirrers to be provided. The stirrers are intended to prevent or re-mix sediments 34, 35.

(23) FIG. 2 additionally shows the locations at which measuring devices or sensors can be arranged: a refractometer 30 in the container 23, a refractometer 31 in a line 31a, 31b, a refractometer 32 in the line 22b (or alternatively in the line 22a) and/or a refractometer 33 in the tank 20.

(24) The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention: 1 to 16 Method steps 17 Ink supply device 18 Inkjet printing machine 19 Surface 20 Ink tank 21 Ink 22 Inkjet print head 22a, 22b Ink lines 23 Ink storage container 24 Ink 25 Ink line 26, 27 Stirrer 30, 31 Refractometer 31a, 31b Ink line 32, 33 Refractometer 34, 35 Sediments