METHOD OF CONTROLLING FILM THICKNESS OF MIXTURE LIQUID LAYER OF OIL MATERIAL AND WATER IN PRINTING MACHINES

Abstract: A method of controlling film thickness of a mixture liquid layer of oil material and water in a printer such as, for example, an offset printer is disclosed wherein the mixture liquid layer of the oil material containing printing ink, printer's varnish and the like and water such as, for example, dampening water attached to one roller of a roller group carrying the mixture liquid layer is alternately irradiated by infrared rays which are most strongly absorbed into the oil material and the water and by infrared rays which are hardly absorbed into the oil material and the water. Film thicknes­ ses of the oil material and the water are detected on the basis of infrared absorption characteristics of the oil material and the water. The detected film thicknesses of the oil material and the water are compared with the respective predeter­ mined target values and supply of the oil material and the water is controlled so that differences between the detected film thicknesses and the respective target values are mini­ mized. Thus, printing failure such as so-called greasing and water stain occurring in a prior art printing is prevented and printing quality is improved, so that spoilages can be reduced.

Description: BACKGROUND OF THE INVENTION (i) FIELD OF THE INVENTION The present invention relates to a method of automatically controlling film thickness of a mixture emulsion layer in a device, which supplies mixture emulsion of printing ink and damping water, such as an ink and dampening water feeder and a varnish coating device for use in a printer, particularly an offset printer. (ii) PRIOR ART STATEMENT In an offset printer, it is necessary to make printing while supply of ink and dampening water is optimally maintained as well known. However, thickness of the ink and the dampening water is greatly varied depending on variation of speed of a printing machine and ambient temperature. When film thickness of ink is varied, ink density on a printed matter is changed. When the balance of ink and dampening water is changed, printing failure such as so-called greasing and water stain occurs. A printed matter having the printing failure is treated as a spoilage and if a percentage of the spoilages is increased, a printing cost goes up. Various manners for reduction of the spoilages caused by the variation of supply of the ink and the dampening water have been proposed heretofore. One of them is disclosed in the EP-A-0 000 689, in which infrared rays auf two different wavelength are used. One wavelength is used which is hardly absorbed by water and one wavelength is used which is strongly absorbed by water. By this way the thickness of a layer can be determined in order to maintain a constant water-ink ratio. Also according to this reference for the measurement of the film thickness a special sampling roller in the printing machine is provided . Such a method involves the following drawbacks: Complicated processing steps are required such as the formation of several hydrophylic and oily affinitive portions by division on the surface of the measuring roller, thus requiring hight cost. The maintenance of hydrophylic properties over a long period of time is generally difficult and a treatment of restoring hydrophylic properties is necessary so that preservation (or maintain) becomes worsened. By adding such a roller to a group of ordinary rollers, the flow of ink or damping water leads to the tendency of lowering of printing quality. The use of infrared rays of different wavelength is also known from GB-A-2 016 678 and GB-A-2 127 541. According to the first reference it is known to determine the thicknesses of several superposed layers by using one reference IR wavelength which is hardly absorbed by any of the layers and several IR wavelength which each correspond to the wavelength absorbed by one layer. And from GB-A-2 127 541 a method is known to determine the amount of water in ink or oil material by using one infrared wavelength which is strongly absorbed by water and one reference wavelength which is hardly absorbed by water. In the Japanese Patent Publication No. 52-37402, the film thickness of the ink is determined by the absorption characteristic of the light having the range of visible rays but the absorption characteristic is different depending on types of ink, particularly color of the ink. Accordingly, the measured value of the film thickness is widely different depending on types of the ink and it takes much time to control the film thickness. Further, the measured value is greatly influenced by outside light leaking into a measuring portion from the outside and hence it is difficult to determine the film thickness of the ink exactly. Furthermore, a conventional varnish coating device does not control film thickness of the varnish to be constant by detecting the film thickness of the varnish being fed. Operators change a rotational number of a feeding roller properly on the basis of their own experience and judgment to adjust the film thickness. Accordingly, variation of the film thickness due to change of environmental conditions such as temperature can not be followed exactly. SUMMARY OF THE INVENTION The present invention is made in view of the above defficiencies. (I) It is an object of the present invention to provide a method of controlling film thickness of a mixture emulsion layer in which the film thickness of the mixture emulsion layer of printing ink and damping water in a printing machine is exactly measured so that the same measured values are always obtained regardless of types of the printing ink and variation thereof is correctly determined in a short time so that the film thickness can be controlled reliably. (II) It is another object of the present invention to provide a method of controlling film thickness of a mixture emulsion layer in which supply of printing ink or varnish and dampening water fed to a printer is always maintained to an optimum state to prevent printing failure such as so-called greasing and water stain occurring due to variation of supply of the printing ink or the varnish and the dampening water. In order to achieve the above objects, the present invention is configured as follows. The method of controlling film thickness of a mixture emulsion layer of printing ink and damping water in a printing machine is characterized in that the mixture emulsion layer of the oil or varnish and the damping water attached on one roller made of material having a surface which is difficult to absorb infrared rays, of a roller group carrying the mixture emulsion layer of the printing ink and the damping water is alternately irradiated by infrared rays of three different wavelengths in a range of 2.5 µm to 10 µm. The first are strongly absorbed in the printing ink and the second are strongly absorbed in the damping water and the third are hardly absorbed in both printing ink and damping water. Then the quantity of reflected light of said first second and third infrared rays respectively from said one roller is detected. The film thickness and percentage of water content of printing ink and damping water are calculated by calculating means from said detected signals and said calculated film thickness and water content is compared with previously determined target values for controlling the supply amount of printing ink and damping water on said one roller so that devation thereof from said target values can be reduced to a minimum. The present invention possesses the following effects since the above configuration is provided. The film thickness of the mixture emulsion layer of the printing ink and the water in the printing machine is detected in no contact manner irrespective of types of the printing ink and the film thickness can be automatically controlled to be a predetermined target value. Supply of the printing ink or varnish and supply of the damping water to the printer can be always maintained to an optimum state and printing failure such as so-called greasing and water stain occurring due to variation of supply of the printing ink and supply of the water can be prevented, so that spoilages can be reduced. Further, a predetermined film thickness can be stably obtained at all times regardless of variation of environmental conditions such as temperature. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 schematically illustrates an embodiment implementing the present invention in automatic control of film thickness of ink and dampening water in an offset printer; Fig. 2 is a graph showing a relation of wavelength of infrared rays and transmittances of ink and water; Fig. 3 schematically illustrates another embodiment implementing the present invention in automatic control of film thickness of varnish and water in a varnish coating device; Fig. 4 is a graph of a relation of wavelength of infrared rays and transmittances of varnish and water; and Fig. 5 is an enlarged side view of a portion of a film detection apparatus for use in the above embodiments of the automatic control. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Preferred embodiments of the present invention are now described on the basis of the drawings. (First Embodiment) An embodiment implementing the present invention in automatic control of film thickness of a mixture emulsion layer of printing ink and dampening water in an offset printer is described with reference to Figs. 1, 2 and 5. Describing the offset printer with reference to Fig. 1, the offset, printer comprises an impression cylinder 30, a blanket cylinder 31, a plate cylinder 33, an inking device including a form roller 34, inking rollers 36, an ink ductor 37, an ink fountain roller 38 and an ink fountain 39, and a damping water device including a damping water tank 41, a water fountain roller 42, a roller 43 and a form damping roller 44. Thus, printing is made on printing paper 32. In the automatic control apparatus, while a metal roller 35 or 40 of the inking rollers 36 measures the film thickness of the ink and the dampening water, the metal roller may be replaced with other ink roller formed of material which is difficult to absorb infrared rays. Further, a sampling roller may be provided in the inking rollers 36 to measure the film thickness of the ink and the dampening water. The automatic control apparatus is decribed with reference to Figs. 1 and 5. In Fig. 5, numeral 10 denotes an infrared emitting element, 11 a lens, 12 an interference filter, 13 a light guide pipe, 14 the mixture liquid layer of the ink and the dampening water existing on the metal roller 35, 15 a photoelectric element (a measuring device or a detector) disposed in the vicinity of the metal roller 35, 16 an amplifier, 18 a synchronizer, 19 an A/D converter, 20 a computer and 21 a plotter. In Fig. 1, numerals 23 and 24 denote D/A converters, 25 a motor for driving the ink fountain roller and 26 a motor for driving the water fountain roller. Operation is now described. First of all, description is made to a reason why the infrared rays are used to detect the film thickness of the printing ink and the dampening water. When light illuminates on a material, the material absorbs light having a particular wavelength and remaining light is accordingly observed as a color of the material. The absorption of light having the particular wavelength is effected to not only a range of visible rays but also a range from ultraviolet rays to infrared rays. Since an infrared absorption spectrum in the wavelength range of 2.5 µm to 10 µm has clear correlation of the absorption characteristic and the molecular structure, it is most suitable to obtain knowledge concerning compound structure. Curves 1 ○ and 2 ○ of Fig. 2 show infrared absorption spectra of the ink and the dampening water in the wavelength range of 2.5 µm to 10 µm measured by an infrared spectrophotometer. Representative absorption zones for the ink in the above spectrum exist in three wavelengths of 3.40 µm (see 3 ○ of Fig. 2), 5.40 µm (see 4 ○ ) and 6.84 µm (see 5 ○ ). The facts are due to the molecular structure of vehicle in the ink and is not related to a color of pigment. That is, an offset ink generally used exhibits the almost same absorption characteristic and measurement can be performed in the same absorption zone independently of types of ink. Absorption zones for the water exist in three wavelengths of 2,96 µm (see 6 ○ of Fig. 2), 4.80 µm (see 7 ○ ) and 6.10 µm (see 8 ○ ). An actual measurement uses the wavelengths most strongly absorbed, of these absorption wavelengths, that is, the wavelength of 3,40 µm for the ink and the wavelength of 2.96 µm for the water. Description is now made to a rate of the absorbed infrared rays into material. The rate is related to thickness and density of a layer of a material. An index representing the rate of the absorption generally uses transmittance represented by a ratio of intensity Io of incident light and intensity I of transmitted light and the transmittance is proportional to the thickness and the density of the layer. Using this principle, if light having particular wavelength passing through a filter, of the infrared rays illuminates on ink roller to measure quantity of light reflected from a surface of the roller, the film thickness of the ink and the percentage of water content can be detected. Fig. 5 shows a configuration of a detection device of film thickness of the printing ink and the water for use in an embodiment of the present invention. While the detection device is a percentage meter of water content in film thickness of ink described in Japanese Patent Application No. 58-124418, since the infrared spectrum characteritic of printing ink of the embodiment and varnish of a second embodiment is almost identical, the detection device can be applied to both the embodiments. The automatic control apparatus for ink and dampening water shown in Figs. 1 and 5 utilizes the above principle. Infrared rays emitted from the infrared emitting element 10 forming a light source are condensed by the lens 11 and then pass through the interference filter 12. The interference filter 12 is provided with three types filters of a filter for infrared rays absorbed into the ink, a filter for infrared rays absorbed into the dampening water and a filter for reference rays which are not absorbed into the ink and the dampening water. The infrared rays passing through the reference filter are used to correct a measured value in absorption of the infrared rays on a basic material of the roller and to correct the measured value in accordance with variation of a measurement distance between the light guide pipe 13 and the roller 35 due to mechanical vibration. The three types of filters are mounted in a chopper wheel so that infrared rays alternately illuminate the roller 35 by rotation of the chopper wheel. Light passig through the interference filter illuminates emulsified ink 14 (that is, a mixture emulsion layer of ink and dampening water) on the roller 35 through the light guide pipe 13. A portion of this light is absorbed into the emulsified ink while remaining light is reflected and condensed to the photoelectric element 15. The remaining light is converted to an electric signal by the photoelectric element 15 and the signal amplified by the amplifier 16 is supplied to the A/D converter 19. At this time, the rotational number of the roller 35 and the rotational number of the interference filter 12 are detected and the detected signals are supplied to the A/D converter 19 through the synchronizer 18. The digitized signals of the A/D converter 19 are supplied to the computer 20 together with other necessary signals to calculate the film thickness of the ink and the percentage of water content, which are supplied to the plotter 20. Further, control signals are applied from the computer 20 through the D/A converters 23 and 24 to the motor 25 for driving the ink fountain roller and the motor 26 for driving the water fountain roller to control the rotational numbers of the motors 25 and 26. At this time, control is made so that deviation |ki - ki'| between a value ki representing the film thickness of the ink and a target value ki' for optimum printing quality and deviation |kw - kw'| between a value kw representing the percentage of water content and a targer value kw' for optimum printing quality are minimized. As describe above, supply of the ink and the dampening water fed to the printer are always maintained to the optimum condition. Further, printing failure such as so-called greasing and water stain occurring due to variation of supply of the ink and the dampening water can be prevented and hence spoilages can be reduced. (Second Embodiment) Another embodiment implementing the present invention in automatic control of film thickness of a mixture emulsion layer of varnish and water in a varnish coating device of a printer is now described with reference to Figs. 3, 4 and 5. Referring to Fig. 3, the varnish coating device comprises a roller group composed of a rubber blanket cylinder 137, an intermediate cylinder 138, an impression cylinder 139, a delivery shaft 140, a varnish saucer 133, a fountain roll 134, an intermediate roller 135 and a form roller 136 and a varnish feeding unit composed of a varnish tank 130, a mixture tank 131, a water tank 132 and pumps 128, 129 and 127. Thus, coating is effected on a surface of printing matter. A detection device 22 for varnish and water, which is the same as the device shown in Fig. 5 described in the first embodiment, is provied in the vicinity of the roller 136 and output signals from the detection device 22 are supplied to the computer 20 through the A/D converter 19 to be processed in the computer 20. Data produced from the computer 20 are displayed in the plotter 21 and supplied as control signals through D/A converters 123, 124 and 125 to a rotation control motor 126, which drives the fountain roller 134 when the film thickness of the varnish is changed. Further, when density of the varnish is changed, the pumps 127 and 128 are operated. When liquid level in the mixture tank goes down, the pumps 127 and 128 are also operated. Fig. 4 shows infrared absorption spectra of varnish and water in a wavelength range of 2.5 µm to 10 µm measured by an infrared spectrophotometer. As seen from the spectra, while representative absorption zones of the varnish exist in three wavelengths of 3.40 µm, 5.40 µm and 6.85 µm, varnish used in a printer exhibits similar characteristic independently of types of varnish and hence measurement can be made in the absorption zones having the same wavelengths. Absorption zones of water exist in three wavelengths of 2.96 µm, 4.80 µm and 6.10 µm. An actual measurement uses the wavelengths most strongly absorbed, of these absorption wavelengths, that is, the wavelength of 3.40 µm for the ink and the wavelength of 2.96 µm for the water. The index representing the rate of the absorpted infrared rays into material generally uses transmittance as described above, and the transmittance is proportional to the thickness and the density of the layer. Using this principle, if light having particular wavelength passing through a filter, of the infrared rays illuminates the varnish roller to measure quantity of light reflected from a surface of the roller, the film thickness of the ink and the percentage of water content can be detected. In other words, the film thicknesses of varnish and water on the surface of the roller are detected on the basis of infrared rays of wavelengths absorbed into and reflected by varnish and water. The detection device of film thickness of varnish and water used in the present embodiment uses the film thickness detection device shown in Fig. 5 in the same manner as in the first embodiment. Accordingly, operation and processing of electric signals of the detection device are the same as those of the first embodiment and description thereof is omitted. In Fig. 5, numeral 14' denotes a mixture liquid layer of varnish and water. The film thickness of the varnish is controlled so that deviation K = |k - k'| between the measured value k of the varnish film thickness and the target value k' representing an optimum coating condition is minimized. The density of the varnish is also controlled so that deviation D = |d - d'| between the measured value d of the varnish density and the target density d' representing an optimum coating condition is minimized. By effecting control in this manner, that is, by sending a deviation up signal Dup when the density is increased and a deviation down signal Dn when the density is decreased, variation of the film thickness and the density of the varnish due to variation of printing speed of the printing machine, ambient temperature and humidity can be minimized and stable coating with high quality is effected. The measuring roller used in the present invention is not limited to the metal roller and may be other roller having small absorption for infrared rays. Further, measuring and control can be effected if the sampling roller is mounted in the roller group. As described above, the varnish and the water on The roller in the printer are detected in non-contact manner to automatically control the rotational number of the feeding roller and the ratio of the varnish and the water, and the stable film thickness of the varnish an be obtained independently of environmental conditions.

Claims: A method of controlling film thickness of a mixture emulsion layer of printing ink and dampening water in a printing machine, by means of infrared rays of different wavelength to determine the thickness of the emulsion layer and then using this information to maintain a constant water-ink ratio, characterised in (a) carrying the mixture emulsion layer of said printing ink and dampening water in the printing machine by a group of ink rollers (36, 134, 135) where by one ordinary roller (35, 136) (no sampling roller) of said group of ink rollers (36, 134, 135) having a surface capable of reflecting almost all infrared rays of a wavelength in a range of 2.5 µm to 10 µm; (b) irradating said surface with infrared rays of 3 different wavelengths in a range of 2.5 µm to 10 µm; (c) the first infrared rays having a wavelength strongly absorbed in the printing ink; (d) the second infrared rays having a wavelength strongly absorbed in the dampening water; (e) the third infrared rays having a wavelength hardly absorbed in both said printing ink and dampening water; (f) detecting the quantity of reflected light of said first, second and third infrared rays respectively from said one roller (35, 136) ; (g) calculating film thickness and percentage of water content of said printing ink and dampening water by calculating means from said detected signals and comparing said calculated film thickness and water content with previously determined target values for controlling the supply amount of said printing ink and dampening water on said one roller so that deviation there of from said target values can be reduced to a minimum. A method of controlling film thickness, as claimed in Claim 1, wherein said printing ink is varnish.

Inventors: ISONO, HITOSHI HIROSHIMA TECHNICAL INSTITUTE, ITO, YOSHIFUMI HIROSHIMA TECHNICAL INSTITUTE, SHIMOYAMA, MAKOTO HIROSHIMA TECH. INSTITUTE
Applicants: MITSUBISHI JUKOGYO KABUSHIKI KAISHA
Application year: 1985
Main classification: B41F33
IPC codes: B41F31, B41F33