FI117801B - Method and arrangement for making cardboard - Google Patents

Description

117801

Method and arrangement for making cardboard

The present invention relates to a method of making cardboard according to the preamble of claim 1. In particular, the invention is applicable to the manufacture of folding boxboard.

The invention also relates to an arrangement for applying the invention.

The differences between paper and board are difficult to pinpoint, but usually board has a basis weight greater than paper, typically greater than 150 g / m. Cardboard often also consists of several layers, which are intended to achieve the desired properties of the final product. This invention relates to cartons for printing. The cardboard 10 to be printed must be flat, even and smooth, and have exactly the same thickness in all cross-sections. The minimum surface quality requirements required will be determined by the intended use of the product. The main purpose of cartonboard is for various packaging applications, ie boxes, boxes and liquid packaging. By definition, printable board grades include carton board, which includes 15 folding boxboard (FBB), white lined chipboard (WLC), (SBS), (SU S) and liquid packaging board (LPB).

Nordic folding boxboard is used in many packaging applications. Typical comprehensive products include cosmetics, cigarettes, pharmaceuticals, confectionery and food. Folding boxboard is usually made of three and sometimes four layers: ***, the top layer and the backing layer are made of bleached chemical pulp and some mechanical pulp or wreckage may be used for the middle layer or layers. . The cardboard can be surface glued and, depending on the intended use, it can be coated one or more times on both sides or only on one side. Määrä (| "The number of layers and composition of the coating mixture is determined by the normal printing process and the good print quality required. * Because folding boxboard * \ # is used for demanding packaging, its printing properties have must be: ***: Good The commonly used printing method for folding boxboard is sheet offset The most important properties of board * t ·; \ * m are thickness, bending stiffness and Scott bond, i.e. strength in the direction of z- * * · i * «·, ···. On the other hand, since smoothness is important to support printability, the most critical feature pair is smoothness-flexural strength, which cannot be achieved simply by calendering (Papermaking Science and Technology, book 18, Paper and Board Grades). , printed on 2000, ISBN 952-5216-18-7) For calendering, high line pressure must be used to achieve good si in particular, the bending stiffness is reduced relative to the amount of raw material used. For this reason, folding boxboard machines use an MG dryer, or Yankee cylinder, to achieve a good surface layer smoothness. The Jenk race cylinder provides a smooth surface and also seals the surface structure very effectively for coating.

In a modern, Nordic-type folding boxboard machine, the various 10 layers are made with separate fourdrinier type web formers. The press section usually has two or three presses, one of which is a shoe press to ensure a good sweat, followed by a pre-dry section followed by a Yankee cylinder and an end-dry section. The next is typically surface sizing, calendering and coating with the necessary dry ingredients. With respect to coating, calendering and surface sizing, the structure of the machine 15 varies considerably depending on the type of calendering used and the number of times the cardboard is coated and one or two sided coating is required. Surface sizing is usually always used because it advantageously provides additional strength.

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The White Lined Chipboard (WLC) is designed for folding boxboard in • * · 20 countries. The major differences are the use of different coating compositions and the use of a primer under the topcoat. This saves expensive surface • • • · material. Recycled fiber is also often used in this carton, so it is not suitable for • * · '! "Foods. The same qualities are important for this carton grade as for folding carton and the same are used for the production board. Solid 25 Bleached Cardboard (SBS) single ply paperboard using sulphate pulp.

t · · • · · · · · · · · · · · · · · · · · · · · · · · ·, Board can also be made as a multi-layer structure. In order to achieve sufficient smoothness of the cardboard, it may be calendered by a wet calendering method with a calendar * * * *; water is fed to the nipple. In this way, good smoothness is achieved, but bulk and at the same time stiff. diminished capacity. Solid Unbleached Cardboard (SUS) is usually a multi-layer composite and is used in high strength consumer packaging. The printability must also be reasonably good. The unbleached sulphate mass 3: 117801 is used as the pulp and the surface of the board is coated to provide a printing surface of sufficient quality. Surface sizing may be used to increase strength. Good coverage and opacity due to unbleached base material is required. In order to achieve sufficient smoothness, the web formed is calendered prior to coating with a wet calender and, if necessary, also after coating with a suitable calender. Even this kind of paperboard does not achieve very good surface smoothness by mere pre-calendering.

Printable board also includes liquid packaging board (LPB). Sufficient impermeability is achieved mainly by coating the base board. The coating and the properties of the bottom board have an effect on printability and in the production of liquid packaging board, the field of the invention mainly involves the production of the bottom board. Impermeable treatment, e.g. lamination, can be considered as a separate manufacturing step.

European Patent Publication No. 0 815 319 discloses a method of fish-15 coating of a coated paperboard in which the coated web is processed in a long nip calender. Prior to coating, the web may not be calendered. The publication does not describe how to make a paperboard web. In DE 102 06 333, prior to winding, the web is calendered first with a long nip calender and then with a hard and short calender nip for thickness. cycle.

A disadvantage of the methods described above is that multiple calendering or a combination of Yankee cylinder and calendering is not achieved without sufficient smoothness.

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The Yankee cylinder is an expensive and large device and limits the maximum running speed of the machine. Normally, when using a Yankee cylinder, the maximum speed is limited to 600 m / min. If, on the other hand, pre-calendering before coating and final calendering after coating 25 are used, the cost of the hardware will increase. At each calendering step, the web is • • · • · · compressed, thereby increasing its density and decreasing its thickness, i.e., loss of sweat. Since • · * t t one of the most important properties of the board is good stiffness, loss of the sweat • * • * * *. "is extremely detrimental, since it will then be necessary to use * '* more web raw material to achieve the same stiffness. Thus, it would be advantageous to provide a method that can ensure sufficient web smoothness without the use of a Yankee cylinder and minimized sweat reduction.

More specifically, the process for producing a printed board according to the invention is characterized in what is set forth in the characterizing part of claim 1.

The invention also relates to an arrangement according to claim 6.

The invention provides considerable advantages.

The main advantage of the invention is the good end product quality obtained by simple devices. The print is good without an expensive Yankee cylinder. When using a long nip calender, the calendering parameters can be adjusted in a very versatile way, thus affecting the product characteristics. The invention provides a good weight-10 surface and, thanks to the hard nip, the profile of the web becomes smooth, which facilitates further processing of the web, especially coating and winding. The speed of the machine can be increased and the calendering method does not limit the achievable speed for board machine speeds. For the long nip, it is essential that the bulk of the treated product remains good, so that the consumption of the base raw material is reasonable.

The invention will now be illustrated by means of examples and test results.

Figures 1-10 show the experimental results graphically.

,. In a board machine, a mass of water and fibers is formed by one or more plurality of fourdrinier • · · i <«.1 1 web forming sections wires using a headbox! a layer from which water is gradually removed. Some of the water is already removed by the wire. The partial webs are joined together to form a single layered web. In the next step, drying of the pulp • · • · is continued with a press section through which one or more presses are applied, ···. through the tinnip. When pressed, water is removed from the web mechanically under nip pressure. A subsequent web is passed to a dryer section to dewater it by heating the web. of dryer. ♦ · · • · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·. Depending on the type of tea and the properties, the fracture head section size, the nipple into the forming part, pu. the cross section and the dry section apply in principle to all machine solutions. In the manufacture of printable paperboard, the web continues to be processed at various stages here. In the method of the invention, the web is calendered before applying the first coating layer.

· 5 117801 posts. Calendering takes place in two steps, first with a long nip calender and then with a hard nip. The long nip calender consists of at least one press shoe which is mounted against the counter roll by a strap running around the press shoe, the characteristics of which influence the calendering result. Polymer or steel straps are most commonly used. The length of the nip is typically 30 to 280 mm. Modern long-nip calendars have nip pressure adjustable by zone. Another characteristic of long nip calendars is that the nip pressure can be kept lower due to the compensating effect of the nip length. The calendering effect is more pronounced on the surface of the web and the web is not compressed, so that the shrinkage of the blanket is negligible compared to other methods providing similar smoothness. If only one side of the web is to be treated as a printing surface, only one long nip is sufficient for the calender. If both sides of the web are to be treated in the same way, separate nipples are needed for each surface of the web.

Following the long nip calender is followed by a hard nip consisting of two hard steel rolls. In this nip, the surface of the web is further smoothed and at the same time the web thickness and thickness profile are constant. Both calendering must be done before or after surface sizing and before applying the first coating layer on the dry part of the machine. The calenders must thus be placed in the machine between the last dewatering device and the first coating station. It has been found that calendering is preferably carried out in an area of the dry portion where the web moisture content is less than 10%. The · · V. * 20 web so treated has good printing properties.

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After calendering, the following surface sizing, * *. ** ·, according to the type of cardboard to be manufactured, follows. coating one or both web surfaces one or more times and, if necessary, final calendering. One or more of the coating steps may be cardboard ····; ***. treatments impermeable either before or after final calendering. The invention * ·· 25 is applicable to all at least one surface-coated printable: · *; for the production of cardboard grades.

The printability of the carton made by the invention was experimentally investigated by comparing it. * different cardboard samples made after test printing. The test results showed that the correct stiffness of the long-nip calender and hard nip * *· ϊ.ϊ ϊ 30 is particularly important. In order to ensure good print quality, it is particularly important that the nipples are in accordance with the present invention.

6 117801

Inductive heating of hard rolls can be used with calender nipples. The induction coils can be positioned outside the rolls and inductively heat the rolls, allowing the calender to profile the properties of the product.

5

As a folding cardboard pre-calender, the order of the shoe and hard nip calendars should be first the shoe calender (OD) and then the hard nip calender (OH) for best results. The trial program variables included shoe load, shoe length, hard nipple load, and order between shoe calender and hard nipple. Print marks were evaluated both visually in the print jury and by the mottling program developed by Stfin. The print was analyzed for blue and gray inks. In addition, the visual assessment was done according to the overall impression, which included mottling and topography. The following are the results that can be used to draw the conclusion.

Figure 1 shows the effect of pre-calendering variables and their interaction (t-value) on visually estimated print quality (mottling and topography). From the figure it can be seen that the interaction between the load and the order of the shoe has the greatest effect on the print. The shoe load also plays a major role.

,. Figure 2 shows the effect of variables on the visually estimated printout. The higher the · · · * 1 1 print, the worse the print. From the figure, it can be seen that the order of the main effects is most significant (0 = OH + OD, 1 = OD + OH). The order * # 1 1, ···, is a hard nip + shoe calender.

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Figure 3 shows the effect of pre-calendering variables and their interaction * 1 1: ... · visually on blue ink for estimated mottling. From the figure, it can be seen that the interaction between shoe load and order has the greatest effect on ♦ * 1 1 * "2 25 prints. Shoe load also matters.

• · • · • · 1 /. Figure 4 shows the effect of variables visually on the blue · ink · estimated print result. The higher the print number, the worse the print.

• «· _ From the image it can be seen that the order of the main effects is most significant (0 = OH + OD, • ·« • 1 «* 30

ITM

2 • · '' 7 117801 l = OD + OH). With the stiffness of the shoe calender + hard nip, a better print quality is achieved than with the hard shoe + shoe calender.

Figure 5 shows the effect of pre-calendering variables and their interaction on visually gray ink on estimated mottling. From the figure, it can be seen that the order has the greatest effect on the print. The load on the shoe also matters.

Figure 6 shows the effect of the variables on the visually estimated gray print. The higher the print number, the worse the print. From the figure it can be seen that the order of the main effects is the most significant 10 (0 = OH + OD, 1 = OD + OH). With order in shoe calender + hard nip, a better print quality is achieved than in order in shoe caliber + shoe calender.

Figure 7 shows the effect of pre-calendering variables and their interaction on the mottling measured by blue ink in the mottling program. The image can be searched; claim that shoe load and order are most influenced by print. 15 The length of the shoe and the load of the hard nipple are also important.

Figure 8 shows the effect of variables from blue ink to mottling measured by the mottling program. The higher the print number, the worse the print. From the figure it can be seen that the order of the main effects is the most significant j **: (0 = OH + OD, 1 = OD + OH). With the stiffness of the shoe calender + hard nip: # ί l 20 better print than in the case of the hard caliper + shoe calender.

··· • · "! Figure 9 shows the effect of pre-calendering variables and their interactions" · *, mottling measured from gray ink to mottling. From the image it can be stated that the load of the shoe has the greatest effect on the print. The order and the interaction of the heavier load are also important.

* 25 * Figure 10 shows the effect of variables on blue ink using the mottling program M .....

J * .. to the measured mottling. The higher the print index, the worse it is! hard nipple ·· «· j *** · r achieves a better print quality than hard nip + shoe calender.

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Claims (11)

A process for making cardboard which is suitable as a printing surface, wherein: - a base web is produced from a water-containing fiber pulp and water is removed from it first by pressing and then by heating the web, - the web is calendered to equalize at least one surface of the web, - at least one of the web surfaces is coated by at least one coating layer, 10. the web is calendered at a long nip after the water removal, which is carried out by pressing and heating, and in the long nip and prior to application of the first coating layer, characterized in that the web is calendered in that phase of manufacture where its water content rises to a maximum of 10% and the base web is made of at least two layers. 2. A method according to claim 1, characterized in that the length of the long Itt: nip runs to 30 - 280 mm. ··· * · • · ·· * Method according to any of the preceding claims, characterized in that the hardened nip consists of two earth rollers. ·· ♦ 20 4. A method according to any of the preceding claims, characterized in that the web is calendered in at least two consecutive long nips for processing the two sides of the web. • · · • · »** ···. * · *. Method according to any of the preceding claims, characterized in that the two sides of the web are coated with at least one coating layer. * · *: * "25 A carton manufacturing apparatus comprising: 117801 π - a web forming portion for forming at least one aqueous fibrous web, - a pressing portion for removing water from the web, - a drying portion for removing the water from the web by heating, - at least one coating station for spreading the coating smear onto at least one surface of the web, and - at least two between the press portion and a first coating station arranged calender type, the first one being a long nip and the second a hard nip, characterized in that the calender type is arranged. in an area of the machine where the water content of the web produced is at most 10% and the web forming portion comprises at least two web forming devices for producing at least two fiber layers. 7. Device according to claim 6, characterized in that the length of the long nip extends to 30 - 280 mm. SS '15 8. Device according to any one of the preceding claims 6 - 7, can be used. characterized in that the hardened nip is a nip between two ground rolls. • a • · • Φ * 9. Device according to any of the preceding claims 6-8, characterized in * at least two long nips, which are arranged before the hardened nip. • · · * ··· *. · **. Device according to any of the preceding claims 6-9, characterized in that it comprises at least two coating stations. * · · 11. Device according to any of the preceding claims 6-10, characterized in that it comprises at least one calender type after the coating stations. φφφ • Φ φ # ... * ··· .. · * # φ φ • # φ «φ φ φ φ · φ · Φ • * '