Measuring method and apparatus for measuring printing properties of printing

The invention relates to a measuring method and a measuring apparatus for printing properties of a printing product, such as paper or board, comprising a roll and a roll counter part.

Technical background

As a consequence of increased use of recycled paper as raw material for paper stock, the absorption properties of produced paper are more and more difficult to control, which in turn causes a lot of problems during printing.

Recycled paper stock made of recycled paper can contain fibers, fillers and chemicals of various qualities, the ratios of which are not necessarily precisely known, and the raw materials used for paper influence, for their part, the absorption properties of paper.

Due to the paper properties it is possible that wood fibers and parts of wood fibers as well as inorganic material used as a filler release as dust from the paper manufactured in a paper machine during the printing performed in a printing machine. Various types of linting cause problems during printing and can occur separately or simultaneously.

Offset printing is based on the surface-chemical characteristics and interaction of the color and fluid, or so-called dampening fluid, used in printing. The purpose of the dampening fluid in offset printing is to attach to the unprinted surfaces of the printing plate preventing thus spreading of the printing ink upon these. The activity of the dampening fluid has an essential purpose in the offset procedure. In practice, some dampening fluid always shifts during the printing process to the pressing surfaces of the printing plate and to the color equipment. In case the dampening fluid fails to work as it should, this causes problems for printing, such as impaired print quality and/or printing machine runnability problems.

By adjusting the balance between the dampening fluid and color it is attempted to influence on that printing problems would not occur. The product to be printed, in turn, should uniformly absorb the dampening fluid and printing inks used in connection with printing, i.e. the paper should have similar and uniform absorption properties on both of its sides, when examining the paper in both the machine direction and also in the cross direction, for ensuring the print quality. The

performance of the dampening fluid, the absorption properties of the printing product, and the linting property play an important role also as regards the printing machine runnability. Problems arise particularly if the absorption properties of the printing product vary during printing.

If the absorption properties of the printing product vary and if the printing product occasionally absorbs less dampening fluid, there is a risk of having an excessive amount of dampening fluid in the non-pressing areas, which leads to spreading of parts of color to the surface of the dampening fluid resulting in scumming, i.e. toning of the unprinted parts of the printing product. On the other hand, if the amount of dampening fluid is excessive in the non-pressing areas, dissolution of color in the dampening fluid may occur, and since the printing product is wetted by the dampening fluid, this may lead to spreading of parts of the color onto the unprinted surfaces of the printing product. In both cases soiling of printing surfaces is also possible.

If the printing product occasionally absorbs too much dampening fluid from the printing surfaces, i.e. the printing surfaces dry excessively, in this case it is also possible that the color coming over to the printing product from the non-pressing surfaces of the impression cylinder causes toning, or scumming, of the printing product. In addition, dust releases more easily from an excessively dry printing product, which when sticking to the surfaces of the impression rollers and/or printing plates leads to impaired print quality.

The known methods presently used for determining the absorption properties of a printing product are dependent on the specific point at which the test is taken, and thus do not provide a wider overview of the absorption properties of the printing product and the possible changes occurring in them. Furthermore, the known techniques presently used for measuring the linting property of a printing product are dependent on the person performing the linting property test on the printing product's linting property, and even the tests taken by one and the same person are not always comparable with each other.

Patent publication US2002120410 (Apparatus and method for analyzing liquid absorbency/desorbency, pore volume distribution and in-plane wicking/absorption) discloses a technique in which the paper's ability to absorb fluids is examined spotwise. Related to the determination of the paper's linting product, there are patent publications EP0335522 (Paper web surface cleaner or tester)) and

US5628228 (Device for applying pressure to a swatch for detecting debris on rolls of paper).

Description of invention

It has now been invented a method and apparatus for measuring the printing properties of a printing product, which measure the printing properties extremely reliably.

To achieve this object, the invention is characterized by the features specified in the independent claims. Some of the advantageous embodiments of the invention are set forth in the other claims.

The absorption and linting properties of a printing product, such as paper or board, are measured with a measuring apparatus, which comprises a roll and a roll counter part, including at least the following steps:

- feeding the printing product to the nip between the roll and the roll counter part,

- supplying fluid to the nip, supplying fluid to the roll, and/or supplying fluid to the printing product to be fed to the nip,

- measuring the absorption and/or linting properties of the printing product fed through the nip on the roll, on the roll counter part, on the printing product and/or on the fluid that has remained unabsorbed in the printing product.

It is now possible to examine reliably the absorption properties or linting properties of a printing product in conditions that are subjected to the printing product as it passes through the nip.

The objective of the measuring method is to enable inspecting ready paper rolls, for example, ensuring in this way that such paper rolls are delivered to printing whose paper absorption properties meet the customer's requirements and the printing product contained therein has such a quality that no dust releases from it, or that the quantity and quality of the releasing dust do not cause problems in the printing machine.

The measuring method allows, by measuring and testing, to find for example optimum operating methods for the paper machine, paper raw materials and raw material dosing positions in the process, and the dosing ratios, in which case

desired uniform absorption properties are achieved for the paper produced in the paper machine, and no dust releases from the printing product being manufactured, or the amount of releasing dust is so low that it does not lead to problems in printing.

The measuring apparatus and method of the invention can be used for measuring and determining the changes in the absorption properties and in the linting property of the printing product. The measuring apparatus and method of the invention can be used for inspecting separately both sides of the produced printing product determining in this way the absorption properties of both sides of the printing product as well as the fact whether dust releases from only one side of the printing product or from both sides and how much. With the measuring apparatus and the testing method it is possible to examine the absorption properties of paper or a similar product manufactured in a paper machine or similar as well as the quantity and quality of dust releasing from the printing product, immediately upon completing the paper production. The measurements and testing can be performed both at the paper mill and in the printing house.

According to one object of the invention, a known amount of fluid is supplied to the printing product and the amount of water absorbed in the printing product after the nip is measured directly from the printing product or indirectly using a fluid collection arrangement.

According to one object of the invention, the measuring apparatus comprises an optical measuring apparatus, such as on optical reading device or an optical scanning device or a camera, for measuring the amount of dust released from the printing product.

According to one object of the invention, the measuring apparatus comprises after- nip collection of the fluid unabsorbed in the printing product.

According to one object of the invention, both sides of the printing product are measured at different times and/or simultaneously for measuring the absorption and/or dusting properties of both sides of the printing product.

According to one object of the invention, samples of a desired kind are cut from the printing product for measuring the printing properties of the printing product.

According to one object of the invention, the method for measuring the printing properties of the printing product comprises an arrangement for supplying fluid to the nip.

According to one object of the invention, the measuring method for the printing properties of the printing product comprises an arrangement for supplying fluid to the printing product, such as a spraying system.

According to one object of the invention, the volume of fluid absorbed by the printing product is determined relative to the travel speed of the printing product, surface area, and the quality values of the printing product, such as the basis weight and ash content.

According to one object of the invention, the performance of various fluids is defined, such as when using different fluids, differences in dust conveyance with the fluid and/or differences in sticking of the dust that releases from the printing product to the test apparatus are studied.

According to one object of the invention, the amount of releasing dust, fillers and the fiber content are determined for the printing product.

According to one object of the invention, a quality value is calculated for: the absorption properties of the printing product tested, amount of releasing dust and the material distribution of dust, ash content of the printing product tested, basis weight, travel speed and total surface area of the printing product.

According to one object of the invention, the measurements are performed at a paper mill or in a similar plant.

According to one object of the invention, the measurements are performed in a printing house or a similar location.

The feeding method of the printing product may vary. Feeding of the printing product tested can be vertical, for example.

According to one object of the invention, the fluid used for testing is water.

According to one object of the invention, the fluid used for testing is fluid used in offset printing.

According to one object of the invention, the counter part is transparent and filming is carried out through it for determining the conveyance of fluids and dust in the nip during testing.

According to one object of the invention, the printing product is directed through an analysis apparatus prior to the dust measuring apparatus for determining the quality values, such as the basis weight and ash content, of the product tested.

According to one object of the invention, offset printing is modelled with the measuring method. Recycled paper is used a lot as raw material for newsprint. Thus the paper quality can vary widely. The presently developed method is indeed very useful in modelling the offset printing of newsprint.

According to one object of the invention, both the diameter and/or positioning of the roll are adjusted and/or the curvature and/or positioning of the. counter part are adjusted.

According to one object of the invention, the positioning of the slide comprised in the apparatus is adjusted and/or the surface roughness of the slide is modified.

According to one object of the invention, the positioning and/or the diameter of the guide roller are adjusted for changing the feed angles α, β of the printing product.

According to one object of the invention, the measuring apparatus is examined as a whole by means of a monitoring system, such as on optical monitoring system, which can be used for examining the progress of testing as a whole, and particularly the performance of the fluid used in testing, as well as the conveyance of dust releasing from the printing product during the testing process and its sticking to the surfaces of the test apparatus.

According to one object of the invention, smaller parts are cut from the printing product with a cutter and these are tested with an apparatus that simulates the printing conditions/situation of the printing machine. Here it is essential that the printing product under testing is wetted. As the printing product gets wet and as the stress conditions of the fibers and fillers contained therein consequently change, dust releases in a different way compared to a dry product. That is, to determine the impacts of the absorption properties of the printing product in connection with offset printing, it must be possible to test the printing product in a similar way as is actually effected for the printing product and in the printing product in connection with printing, such as offset printing. Specifically, it must be

possible to examine the absorption properties of the printing product and any changes occurring therein in both the machine and cross directions, which allows defining if changes occur in the absorption properties of the printing product and thus finding possible causes of the variations to be able to find process settings, whereby it is possible to achieve a desired kind of printing product. Also, due to differences between the various printing processes, it would be important to produce for example paper which would have the printing properties requested by the customer in each case.

Detailed description of invention

The invention is described below using an example by making reference to drawings 1.1 , 1.2, 2.1 , 2.2, 3, 4, 5, 6, 7 and 8.

The parts related to the apparatuses according to the figures are the following:

1 - sample to be tested,

2 - fluid container,

3 - fluid used for testing,

3.1, 3.2 - unabsorbed fluid

4 - supply arrangement of fluid used for testing,

5 - analyzing arrangement of fluid used for testing,

6 - rubber coated roll,

7 - counter part of roll, such as a counter roll

8 - guiding arrangement of the printing product,

9 - feeding of the printing product and feed speed arrangement,

10 - alternative wetting nozzle for the printing product,

11 - camera system developed for monitoring the progress of testing,

12, 12.1 , 12.2 - collection containers for unabsorbed fluid,

13 - slide for leading the fluid to be used

14 - arrangement for supplying the fluid 3 to the printing product, such as a fluid spraying system,

15 - laboratory analysis equipment

Web feeding of the test apparatuses shown in Figures 1.1 , 1.2, 2.1, 2.2, 3, 4, 5, 6, 7, and 8 through the test apparatus can be performed as a linear arrangement, in which case the tested web travels on the same plane relative to the floor level of the test room. Web feeding can also be performed as a vertical arrangement, in which case the arrangement shown in figure is viewed from above compared to the floor level of the test room. In connection with the latter, i.e. the vertical test, fluid/color is conveyed to the printing product, or directly to the nip formed by the roll and the counter part, over the entire testing width or over a desired width by means of a roll wetting apparatus 10 / rolls. When feeding the printing product through the nip formed by the roll 6 and the counter part 7 even by other arrangements than the vertical one, the roll 6 can be wetted with fluid 3 using the wetting apparatus 10, whereby also the printing product to be tested gets wet.

The device and method as shown in Figure 1.1 are used to guide a printing product 1 from a sample roll through a device, in which the printing product 1 gets wet in the same way as in offset printing. In this way it is possible to determine the volume of fluid absorbed by the printing product 1 relative to the travel speed and surface area of the printing product, i.e. the absorption properties of the printing product in connection with offset printing. The apparatus comprises an arrangement which is used to guide the printing product 1 to be tested through the nip N formed by the roll 6 and its counter part 7. The camera system 11 can be used to monitor the progress of testing as a whole as well as the conveyance of dust releasing from the printing product with the fluid used in testing. The camera system 11 can be used to examine the performance of the fluid used and the conveyance of dust releasing from the printing product, as well as sticking of dust to the surfaces of the roll 6 and the counter part 7 during and after the test procedure. In the method, dust releasing from the printing product to the fluid is inspected during the test by calculating the number of particles releasing from the printing product to the fluid 3, 3.1 used in testing. In addition, dust accumulated in the fluid 3.1 is filtered and analyzed. The amount of dust and the quality of dust releasing from the printing product reveal the linting property of the printing product tested in connection with offset printing.

Figure 1.2 shows an arrangement in which the fluid infiltration properties of a printing product, in turn, are analyzed as well as the absorption properties of the printing product. The apparatus comprises an arrangement which is used to guide the printing product 1 to be tested through the nip N formed by the roll 6 and its counter part 7. A known volume of fluid 3 and/or color can be dosed using a fluid/color dosing arrangement 2 according to Figure 1.2. The volume of unabsorbed fluid 3.1 can be determined by weighing the collection container 12 allowing thus to determine the volume of fluid/color absorbed in the printing product 1 , that is, the absorption properties of the printing product are defined in this way. On the contrary, when a known volume of fluid is dosed with the dosing arrangement 10, by weighing the collection container 12 it is possible to determine the volume of fluid conveyed to the container through the printing product 1 and in this way define the volumes of fluid absorbed in the printing product and, on the other hand, of that infiltrated through the printing product. The travel direction of the printing product tested can be towards or against the direction of the arrow.

Figures 2.1 and 2.2 show test apparatuses according to Figure 1.1 , which can be used to test both sides of a printing product at once. The printing product gets wet when passing through the nip N1 , N2 of the test device. When it is desired to measure simultaneously the differences of the printing product relative to the absorption properties and/or the linting property, in connection with the arrangements such as shown in Figures 2.1 and 2.2 it is possible, if required, to wet the web cyclically. In Figures 2.1 and 2.2, reference numbers 12.1 and 12.2 are used for the fluid collection containers 3.1 and 3.2.

Figure 3 shows a more detailed illustration of the method and apparatus according to Figures 1.1 , 2.1 and 2.2, in which the web is guided through the nip N formed by the roll and its counter part, to where fluid 3 used in testing is simultaneously led along the slide 13, whereby the printing product gets wet in the same way as in connection with offset printing. The flow speed of fluid 3 along the slide 13 can be adjusted by changing the position, i.e. the predetermined angle α, of the slide and/or by changing the flow VOL1 of the fluid used in testing. By changing the diameter of the roll 6 and/or the roll cover and/or the magnitude and/or the direction of force F applied to the nip and/or the roll diameter H1 and/or the cover and/or the curvature R of the counter part 7, it is possible to influence the nip geometry allowing thus detecting the effects of the differences in geometries of the test apparatus, and thereby in those present in the printing machines, on the printing procedure. In addition, by changing the angle α and/or the diameter H2

and/or the location of the guide roller 9, it is possible to influence the magnitude of the angle β, i.e. in what angle the printing product is guided to and from the nip.

In the nip formed by the roll and its counter part, part of the fluid absorbs into the printing product, and the part that does not absorb into the printing product is conveyed to the collection container 12 located after the nip. When the volume VOL1 of the fluid 3 led to the nip is known and the volume VOL2 of the fluid 3.1 accumulating in the collection container 12 per time unit is measured, it is possible to calculate the volume VOL_ABS of fluid absorbed in the printing product per time unit using equation 1.

Equation 1 : VOL1 - VOL2 = VOL_ABS

Figure 4 shows a more detailed illustration of the method and apparatus according to Figures 1.1 , 2.1 and 2.2, in which a camera K1.1 is used to monitor possible changes in the volume VOL2 of fluid 3.1 conveyed to the collection container 12 during testing, whereby it is possible to identify possible changes occurring in the volume VOL_ABS of fluid absorbed in the printing product in the nip N per time unit. The camera K1.1 and/or multiple cameras K1.1 , K1.2 are also used to monitor the amount of particles collected in the fluid 3.1 relative to the amount of the printing product tested and to the flow VOL1 of fluid 3 used in testing, whereby the amount of dust releasing during testing from the printing product to the fluid relative to the quality of fluid 3 used in testing and/or relative to the volume VOL1 of fluid 3 used for testing, and relative to the amount of the printing product tested and/or relative to the volume VOL_ABS of fluid absorbed into the printing product.

Figure 5 shows a more detailed illustration of the method according to Figures 1.1 , 2.1 and 2.2, in which the camera K2.1 and/or multiple cameras K2.1 , K2.2 of the camera system 11 are used during testing for monitoring dust releasing from the printing product and its amount on the surface of the roll 6, such as can occur during offset printing. The printing product under testing can be guided through the test apparatus 15 for the printing product located prior to and/or after the test apparatus for the absorption properties of the printing product, as shown in Figure 5. Thus it is possible to obtain as accurate information as possible on the quality values of the printing product tested, such as the basis weight and ash content, which are used when calculating the quality value/values reflecting the absorption properties and the linting property of the printing product.

Figure 6 shows a more detailed illustration of the arrangement in which the product tested is wetted by spraying 14 fluid 3, after which the printing product passes through the nip. The absorption properties of the printing product and its linting property are determined in the same way as described above. In addition, it is possible to lead fluid 3 to the nip along a slide, which has been illustrated in more detail in Figures 3 and 4. In an arrangement according to Figure 6, it is possible to study the effect of nozzles of various types and/or the pressure used for pumping relative to the quality and/or volume of sprayed fluid 3 absorbing in the printing product or relative to the amount of dust releasing from the printing product.

Figure 7 shows an arrangement which can be used to examine the progress of testing and particularly the conveyance of dust releasing from the printing product during the testing procedure. A camera K3.1 and/or multiple cameras K3.1 , K3.2 (not shown in figure) are used to film through the roll counter part 7, which is made of a translucent material, for example glass. With this arrangement, it is possible to monitor the conveyance of dust during testing in the nip formed by the roll and its counter part and its possible sticking to the surfaces, as well as the performance of the fluid used in testing in the nip.

Figure 7 also shows an arrangement in which fluid 3 used in connection with testing is supplied either along a slide 13 and/or by spraying 14 the fluid 3 either to one or both sides of the printing product, and/or by leading/spraying 14 the fluid used during testing to the roll 6.

Figure 8 shows an arrangement, in which it is possible to monitor the progress of testing with a camera K4.1 and/or multiple cameras K4.1 , K4.2. In this case the product is wetted either on one side or on both sides prior to the nip formed by the roll and its counter part either by using a spraying system 14 and/or by leading fluid 3 used for testing along a slide 13. The camera K4.1 and/or cameras K4.1 , K4.2 can be used to monitor the passage of the fluid used for testing and of the printing product through the nip as well as the point of time when the fluid 3.2 starts dripping from the printing product. In this way it is possible to detect the point of time at which the printing product is saturated, i.e. fluid starts dripping from it to the collection container 12.1 , and/or how much fluid is conveyed to the collection container 12.2.

When the surface area A1 of the roll 6 used in the test apparatus and the surface area A2 of the counter part 7 are known, the camera system 11 can be used to

monitor, at the end of and/or during testing, the relative total amount D _to t _a i of dust D1 and D2 released from the printing product and stuck to the surfaces A1 A2, which can be calculated using equations 2, 3 and 4, when calculating as remainder the total surface area of the known surface areas A1 A2 and, at the end of and/or during testing, Explodel of the subarea still visible of the surface area of the roll 6 and/or Explode2 of the subarea still visible of the surface area of the counter part 7. In this way, the volumes of dust D1 , D2 and D _tota i covering the surfaces A1 A2 of the roll 6 and the counter part 7 can be determined.

Equation 2 can be used to determine the relative total volume of dust stuck to the roll 6 and its counter part 7. Equation 3, in turn, can be used to determine the relative amount of dust stuck to the roll 6, while equation 4 can be used to determine the relative amount of dust stuck to the counter part 7.

Roll 6 area = A1

Subarea visible from roll 6 = Explodel

Area of dust covering the surface of roll 6 = D1

Area of counter part 7 = A2

Subarea visible from counter part 7 = Explode2

Area of dust covering the surface of counter part 7 = D2

Total area = A1 + A2 = A _to tai

Still visible total area = Explode _to tai

Relative total amount of stuck dust = D1 + D2 = Dtotai

Equation 2: Atotai - Explode _to tai = D _to tai

Equation 3: A1 - Explodel = D1

Equation 4: A2 - Explode2 = D2

In addition, the quality and quantity of dust accumulated in the test apparatus can be analyzed for example in a laboratory, whereby it is possible to accurately determine the quality of dust released from the printing product, and by weighing the roll 6 and its counter part 7 prior to and during/after testing, the amounts of

dust stuck to the roll 6 and its counter part 7 can be determined using the equations 5 and 6.

Equation 5:

Weight ₆ before - Weight ₆ after = Weight of dust stuck to roll 6 from printing product

Weight ₆ before ⁼ Roll weight prior to testing

Weight ₆ after = Roll weight after testing

Equation 6:

Weight ₇ before - Weight 7 after = Weight of dust stuck to counter part 7 from printing product

Weight 7 before = Roll weight prior to testing

Weight 7 after = Roll weight after testing