SIZER

Abstract

 The invention relates to a sizer (10), which comprises at least one hard-surfaced sizing roll (11; 12), application means (22) configured to apply a sizing agent layer (A) onto the surface of the hard-surfaced sizing roll (11), an application element (20) configured to smoothen the sizing agent layer (A) to a smooth sizing agent layer (AS). The application element (20) is a soft-surfaced application element (20) and hardness of the soft-surfaced application element (20) is substantially lower than hardness of the hard-surfaced sizing roll (11).

Description

Technical field

[0001] The present invention relates to fiber web production. More especially the invention relates to a sizer according to the preamble part of claim 1.

Background

[0002] The fiber webs are produced in a fiber web producing process. As known from the prior art in fiber web producing processes typically comprise an assembly formed by a number of apparatus arranged consecutively in the process line. A typical production and treatment line comprise a head box, a wire section and a press section as well as a subsequent drying section and a reel-up. The production and treatment line can further comprise other devices and/or sections for finishing the fiber web, for example, a pre-calender, a sizer, a final-calender, a coating section. The production and treatment line also typically comprise at least one slitter-winder for forming customer rolls as well as a roll packaging apparatus.

[0003] In production of fiber webs, for example in production of paper or board webs, sizing is used to alter the properties of the fiber web, in particular water resistance, water absorption properties, strength, internal strength, surface strength and bending stiffness, as well as to improve adherence of coating color to the surface of the fiber web, by adding sizing agents, for example starch and/or other sizing agents. In addition, runnability as well as dusting tendency can be affected favorably. Sizing can be divided to internal sizing and surface sizing. In internal sizing the sizing agent is added to pulp in the wet end of the fiber web machine before forming. In surface sizing the sizing agent is added in a sizer onto the surface of the fiber web typically at the dry end of the fiber web machine. The present invention relates to surface sizing in a sizer, which surface sizing is used in production of many fiber web grades, for example of uncoated fine papers and of several board grades. In surface sizing the sizing substance is added in the sizer onto the surface of the fiber web directly or in-directly via a roll at the dry end of the fiber web machine. In connection with the sizer different kinds of sizing technologies are employed, for example pond sizing technology or film-transfer technology or spray sizing technology. In a sizer of a size press type, sizing rolls are used to press the sizing agent into the web in nip formed between these rolls and through which nip the fiber web is guided.

[0004] In sizing an application element can be used. The application element can be for example a rod or a doctor or a blade. In the sizing based on rod technology a rod or a doctor is used functioning as dosing element of the sizing agent for scraping off the excessive sizing agent quantity. In the sizing the rod or the doctor functions against the surface of the sizing roll. The fiber web can be surface sized using film-transfer or blade technology, wherein the fiber web being sized is passed through the sizing nip between two sizing rolls. The sizing agent is applied with the help of a suitable applicators to the surface of one or both of the nip-forming rolls, wherefrom the substance is transferred to the surface of the fiber web being sized in the sizing nip between the sizing rolls. The thickness and cross-machine profile of the sizing agent layer applied to the roll surface is controlled by the application element. Generally, in these sizing agent application methods soft-surfaced sizing rolls are used and the rod-types of grooved rods or smooth rods are used. The grooved rods are grooved surfaced and the dosing is based on volumetric dosing. The smooth rods are smooth surfaced and the dosing is based on hydrodynamic force. The application of a good quality sizing agent layer onto the surface of the sizing roll, which can function as an application roll or as a transfer roll or as a sizing nip roll, is based on a short nip forming a smooth and even sizing agent layer. In this nip onto the surface of the roll the sizing agent is, thus, dosed and evened out. In the arrangements of these types known from prior art the roll is soft-surfaced, typically comprising a soft roll coating of rubber or polyurethane, which is always softer than the application element, which typically is of steel and hard-surfaced. Thus, loading the application element, it is pressed partially into the soft roll coating and thus, a nip of desired length is formed between the roll and the application element.

[0005] It is also known from prior art to use hard-surfaced sizing rolls, for example hard-coated composite, ceramic or steel rolls, but they are not suitable for this type of application as dosing and evening out of the sizing agent layer is non-functional. Additionally, even small grooves or other defects on the roll surface may cause unevenness in the sizing agent layer, which further causes defects to the fiber web surface. Contact between surfaces moving in respect of each other always causes wear, especially if the surfaces are hard.

[0006] An object of the invention is to create a sizer, in which the disadvantages and problems of prior art are eliminated or at least minimized.

[0007] An object of the invention is to create an improved sizer comprising at least one hard-surfaced sizing roll.

Summary

[0008] In order to achieve the above objects and those that will come apparent later the sizer according to the invention is mainly characterized by the features of the characterizing part of the independent claim 1. Advantageous aspects and features of the invention are presented in the dependent claims.

[0009] According to the invention the sizer comprises at least one hard-surfaced sizing roll, application means configured to apply a sizing agent layer onto the surface of the hard-surfaced sizing roll, an application element configured to smoothen the sizing agent layer to a smooth sizing agent layer, wherein the application element is a soft-surfaced application element and hardness of the soft-surfaced application element is substantially lower than hardness of the hard-surfaced sizing roll.

[0010] According to an advantageous feature the hardness of the soft-surface of the soft-surfaced application element is at a maximum 90%, advantageously at a maximum 70%, of the hardness of the hard-surface of the hard-surfaced sizing roll.

[0011] According to an advantageous feature of the invention in the sizer an application nip is formed between the soft-surfaced application element and the hard-surfaced sizing roll.

[0012] According to an advantageous feature of the invention the sizer comprises two sizing rolls, in between of which a sizing nip is formed.

[0013] According to an advantageous feature of the invention the sizing rolls are both hard-surfaced sizing rolls.

[0014] According to an advantageous feature of the invention both of the sizing rolls are provided with the application means and the soft-surfaced application element.

[0015] According to an advantageous feature of the invention the application element is an application rod with circular cross-section or the application element is an application bar with rectangular cross-section or the application element is a doctor-type application bar with triangular cross-section.

[0016] According to an advantageous feature of the invention the application means are a separate structure from the application element or the application means and the application element are integrated to a same, one unit.

[0017] Advantageously as the hard-surface roll is used a roll produced of hard material or provided with a hard coating or cover. Advantageously, as the hard roll is used a ceramic or metallic roll or advantageously, a roll with a hard-polymeric roll cover (rubber, polyurethane or composite) having surface hardness 50 - 100 shoreD, advantageously 80 - 95 shoreD.

[0018] Advantageously as the soft-surfaced application element is used an application element produced of soft material or provided with a soft coating or cover. For example, the material of the soft-surface application element or the material of the soft coating or cover is polymeric based material with or without reinforcements.

[0019] Advantageously, the sizing agent comprises for example starch. The sizing agent may also be a two-component sizing agent, for example lignin with acidic activator, and/or polymers, for example polyethene and/or polypropylene, and/or mineral fillers and/or particles, for example kaolin in platy particle shape. Also, sizing agents comprising cross-linking substances can be used. The sizing agent may also comprise fibers and/or pigments.

[0020] According to an advantageous aspect of the invention in the sizer comprising at least one hard-surfaced sizing roll a soft-surfaced application element is used. The hardness of the soft surface of the soft-surfaced application element is lower than that of the hard surface of the hard-surfaced sizing roll. Thus, in the nip between the hard-surfaced sizing roll and the soft-surfaced application element the surface of the application element yields, when it is loaded against the surface of the sizing roll and a nip with desired length is provided for forming smooth sizing agent layer. This prevents, that possible small defects on the surface of the roll would cause defects to the sizing agent layer.

[0021] By the invention and its advantageous features several advantages are achieved: The nip between the hard-surfaced sizing roll and the soft-surfaced application element can be provided to have the desired length as the surface of the application element yields, when it is loaded against the surface of the sizing roll. The sizing agent layer formed by the application element is smooth and evened out. Good quality of the finished fiber web is achieved as the possibility, that possible small defects on the surface of the roll would cause defects to the sizing agent layer and further to the fiber web surface is eliminated. Additionally, wear of the surfaces moving against each other is decreased due to the soft surface of the soft-surfaced application element.

Brief description of the drawings

[0022] Aspects of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of some example embodiments when read in connection with the accompanying drawings and in the following the invention is described in more detail referring to the accompanying drawing, in which

In figure 1 is schematically shown an advantageous example of a sizer according to the invention.

In figure 2 is schematically shown another advantageous example of a sizer according to the invention.

In figure 3 is schematically shown an advantageous example of an application element of a sizer according to the invention.

In figure 4 is schematically shown another advantageous example of an application element of a sizer according to the invention.

In figure 5 is schematically shown further an advantageous example of an application element of a sizer according to the invention.

In figure 6 is schematically shown further another advantageous example of an application element of a sizer according to the invention.

Detailed description

[0023] During the course of this description like numbers and signs will be used to identify like elements according to the different views which illustrate the invention. Repetition of some reference signs may have been omitted in the figures for clarity reasons.

[0024] In the figure 1 schematically shown example the sizer 10 comprises two sizing rolls 11, 12 in between of which a sizing nip SN is formed, through which sizing nip SN the fiber web W runs in running direction SW, in the example of the figure 1 substantially vertically downwards. The sizing rolls 11, 12 are rotatable. Rotation direction S of the sizing roll 11 is indicated in the figure 1. At least one of the sizing rolls is a hard-surfaced roll 11. The running direction SW of the fiber web W can also be substantially vertically upwards, in which case the rotation direction S of the sizing roll 11 is opposite to that shown in figure 1. Also, the other sizing roll 12 is advantageously a hard-surface roll 12. The sizing agent A is applied by application means 22 onto the surface of the hard-surfaced sizing roll 11 as a sizing agent layer A. The application means 22 are advantageously spray application means. The sizer 10 further comprises an application element 20 forming an application nip AN with the hard-surfaced sizing roll 11, which in this example is an application rod 20, by which the sizing agent layer A is smoothened and evened out to a smooth sizing agent layer AS, which is transferred by the roll surface to the sizing nip SN to be applied onto the fiber web W. The application element 20 is supported by a support structure 21, for example by an application beam 21. The hardness of the soft surface of the soft-surfaced application element 20 is lower than that of the hard surface of the hard-surfaced sizing roll 11. Thus, in the application nip AN formed between the hard-surfaced sizing roll Hand the soft-surfaced application element 20 the surface of the application element 20 yields, when it is loaded against the surface of the hard-surfaced sizing roll 11 and the application nip AN with desired length is provided for forming the smooth sizing agent layer AN. In the example of figure 1 only one side of the fiber web W is sized but the sizer 10 may comprise means to size the other side of the fiber web W as well, advantageously the means correspond substantially to those shown in the figure for sizing one side of the fiber web for the other side for sizing the other side of the fiber web.

[0025] In the figure 2 schematically shown example in the sizer 10 the distance from the application means 22 to the application element 20 is shorter than in the example of figure 1 and the running direction SW is inclined in respect of the vertical direction but the fiber web W runs substantially downwards as in the example of the figure 1. The running direction SW can also be inclined in respect of the vertical direction such that he fiber web W runs substantially upwards, in which case the rotation direction S of the sizing roll 11 is opposite to that shown in the figure 2. In the figure 2 schematically shown example the sizer 10 comprises two sizing rolls 11, 12 in between of which the sizing nip SN is formed, through which sizing nip SN the fiber web W runs in the running direction SW. The sizing rolls 11, 12 are rotatable and the rotation direction S of the sizing roll 11 is indicated in the figure. At least one of the sizing rolls is a hard-surfaced roll 11. Also, the other sizing roll 12 is advantageously a hard-surface roll 12. The sizing agent A is applied by application means 22 onto the surface of the hard-surfaced sizing roll 11 as a sizing agent layer A. The application means 22 are advantageously spray application means. The sizer 10 further comprises an application element 20 forming an application nip AN with the hard-surfaced sizing roll 11, which in this example is an application rod 20, by which the sizing agent layer A is smoothened and evened out to a smooth sizing agent layer AS, which is transferred by the roll surface to the sizing nip SN to be applied onto the fiber web W. The application element 20 is supported by a support structure 21, for example by an application beam 21. The hardness of the soft surface of the soft-surfaced application element 20 is lower than that of the hard surface of the hard-surfaced sizing roll 11. Thus, in the application nip AN formed between the hard-surfaced sizing roll 11 and the soft-surfaced application element 20 the surface of the application element 20 yields, when it is loaded against the surface of the hard-surfaced sizing roll 11 and the application nip AN with desired length is provided for forming the smooth sizing agent layer AN. In the example of figure 2 only one side of the fiber web W is sized but the sizer 10 may comprise means to size the other side of the fiber web W as well, advantageously the means correspond substantially to those shown in the figure for sizing one side of the fiber web for the other side for sizing the other side of the fiber web.

[0026] In figures 3 - 6 is schematically shown examples in which different types of the application element 20 is used. In figure 3 the application element 20 is the application rod 20 with circular cross-section as in the examples of figures 1-2. In figure 4 the application element 20 is an application bar 20 with rectangular cross-section and a short side against the hard-surfaced sizing roll. In figure 5 the application is a doctor-type application bar 20 with triangular cross-section and one of the points of the triangular form against the hard-surfaced sizing roll 11. In figure 6 the application element 20 is an application bar 20 with rectangular cross-section and a long side against the hard-surfaced sizing roll 11.

[0027] In the examples of figures 1-6 the application element 20 is supported onto the application beam 21. In the examples of figures 1-5 the application means 22 are a separate structure from the application element 20 and in the example of figure 6 the application means 22 and the application element 20 are integrated to a same, one unit.

[0028] The application element 20 may be produced of the soft material forming also the soft surface of the soft-surfaced application element 20 or the application element may be provided with a soft coating or a soft material layer forming the soft surface of the soft-surfaced application element 20.

[0029] In the description in the foregoing, although some functions have been described with reference to certain features, those functions may be performable by other features whether described or not. Although features have been described with reference to certain embodiments or examples, those features may also be present in other embodiments or examples whether described or not. Above the invention has been described by referring to some advantageous examples only to which the invention is not to be narrowly limited. Many modifications and alterations are possible within the invention as defined in the following claims.

Claims

1. Sizer (10), which comprises at least one hard-surfaced sizing roll (11; 12), application means (22) configured to apply a sizing agent layer (A) onto the surface of the hard-surfaced sizing roll (11), an application element (20) configured to smoothen the sizing agent layer (A) to a smooth sizing agent layer (AS), characterized in that the application element (20) is a soft-surfaced application element (20) and hardness of the soft-surfaced application element (20) is substantially lower than hardness of the hard-surfaced sizing roll (11).

2. Sizer according to claim 1, characterized in that the hardness of the soft-surface of the soft-surfaced application element is at a maximum 90%, advantageously at a maximum 70%, of the hardness of the hard-surface of the hard-surfaced sizing roll.

3. Sizer according to claim 1 or 2, characterized in that in the sizer (10) an application nip (AN) is formed between the soft-surfaced application element (20) and the hard-surfaced sizing roll (11).

4. Sizer according to any of the previous claims, characterized in that the sizer comprises two sizing rolls (11, 12), in between of which a sizing nip (SN) is formed.

5. Sizer according to claim 4, characterized in that the sizing rolls are both hard-surfaced sizing rolls (11, 12).

6. Sizer according to claim 4 or 5, characterized in that both of the sizing rolls (11, 12) are provided with the application means (22) and the soft-surfaced application element (20).

7. Sizer according to any of the claims 1-6, characterized in that the application element (20) is an application rod (20) with circular cross-section.

8. Sizer according to any of the claims 1-6, characterized in that the application element (20) is an application bar (20) with rectangular cross-section.

9. Sizer according to any of the claims 1-6, characterized in that the application element (20) is a doctor-type application bar (20) with triangular cross-section.

10. Sizer according to any of claims 1-9, characterized in that the application means (22) are a separate structure from the application element (20).

11. Sizer according to any of claims 1-10, characterized in that the application means (22) and the application element (20) are integrated to a same, one unit.

Drawing