FI113789B - Method and apparatus for making sheet paper or board - Google Patents

Description

1 113789

A process for making laminated paper or board

The invention relates to a process for the production of layered paper or board, wherein the paper or board is formed from at least two superimposed feed streams, which are different from each other and whose components are from the same pulp source.

Multilayer paper or paperboard is usually formed by feeding overlapping streams from a multilayer headbox to a wire section where the web begins to form as the water is drained by superimposed suspensions. There are at least two mass streams, for example two or three, and at least two of these streams have different compositions which may have different fiber compositions or the same fiber composition but differ with respect to other added substances of different quality and / or proportions.

It is known in the paper and board making technology that by influencing the position of the various raw material components in the pulp stock in the paper or board web thickness direction, significant quality changes are achieved. One general application example is to improve the rigidity of a product by imitating a so-called. I-beam structure. In this case, the high layer (i.e. low density) raw material is directed to the middle layer of the product. Hereby, the surface layers of the product are obtained. , spaced apart, and by directing a high-elastic feedstock to the surface layer, the stiffness of the product can be improved by in a situation where the various raw material components are evenly distributed; paper or paperboard in the z-direction.

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The layered structure is almost invariably utilized in carton machines where the web is formed by separate web units and the layers are combined into one carton web. With the advancement of paper machine sandwich boxes and guitar pads, paper sandwiching has also become possible. In this way, new opportunities have also been opened to influence the quality properties of paper by utilizing different layered structures 35.

When applying the layering technique, completely different pulp components can be used for the middle layer of the paper; · · · and the surface layers • · 2 113789 (pulping). Alternatively, different fiber fractions of a pulp may be used provided that fractionation techniques have been utilized in pulp processing. The deposition of different pulp compositions is characterized by the separation of the treatment of pulps from different layers. In order to avoid confusion between the middle layer and the surface layer 5, there must also be separate short turns for each layer. The disadvantage of this technology is the high investment costs due to the complexity of the process.

Thus, it is known to use different pulps in different layers by applying at least two different pulps to different multi-layered headbox along different fresh masonry lines, whereby they are brought separately from their own pulp containers or similar sources through different processing steps.

Another possibility for utilizing the layering technique is to add an additional 15 layers of material in the short cycle of a papermaking machine described in Häggblom-Ahnger, U., Layering of office paper, Paper and Wood 80 (1998) 7, 508-513. The aim is to influence the use of different process control chemicals, e.g. fine and filler distribution in the z-direction of the paper. The process required by the additive coating is significantly simpler and less expensive compared to the process required by the bulk coating, but the possibilities to influence the quality of the product and the production economy are also limited.

. Different types of pulp have different fiber dimensions and properties, but there are also differences between different fibers in the same pulp. Fractionation text-. the ankle can be used to separate the different fiber fractions, whereby the quality of the paper can also be affected by varying the location of the different fiber fractions in the paper web. Fractionation in the bulk processing area results in a complex and expensive process solution. : 30 Also, fractionation in a short cycle of a paper or board machine can easily lead to overly complex process solutions.

L: Finnish Patent 92729, which is the European Patent Publication No. 651092, and European Patent Publication 745721, 35 disclose a multilayer headbox mass feeding system using different layers of the same fresh bulk container. but the required feed additives, such as chemicals and fillers, are fed separately to each of the feed streams branched from the same fresh stock container. In this way, a simple pulp cycle with only one starting mass can be used and at least two different pulp concepts can be obtained by suitable additions.

In International Application Publication WO 98/17860, it is proposed to incorporate fractionation into this single-pulp system such that, after the machine screen, each line branched from the same basic pulp line has a pulp fractionator capable of dividing the pulp into fractions of different fiber lengths. The long fibers separated in the fractionators can then be transferred to the middle layer forming flow and the short fibers can be transferred to the surface layer forming flows. The rejects of the mass flows of the surface layers, which are separated by the sieves in the corresponding mass lines and consist of long fibers, are led to the mass flow forming the middle layer before the 15 fractionating sieves in this mass line. The accept of this screen consists of long fibers which are allowed to flow along the line to the corresponding manifold, and the sieve reject fractions consisting of short fibers are again divided into mass flows to the surface layers.

The above solution requires fractionation devices between the machine screens and the headbox manifolds. When three different pulp feed lines are used to form triple-layer paper, fractionation devices must be used on the pulp feed lines of at least both surface layers if long fibers are to be transferred to the middle layer. Branching and combining streams near the headbox causes management problems in the process.

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Finnish Patent Publication 75200, corresponding to U.S. Patent 4,781,793, discloses a process for making a multilayer paper comprising mixing two different pulps, v: 30 chemical and mechanical, with different fiber contents in a pulp treatment step. From the mixing type, the pulp is led to fractionation by a pressure screen, followed by: further refining and fractionation of the long-fiber fraction, from which ly; the more fluid fraction is mixed with the short fiber fraction obtained in the first fractionation to form the middle layer of the paper '··· *. 35 multilayer headbox into which the long fiber fraction is directed into surface layers. The starting point here is the existence of two different pulps, of which • · 4 113789 can be mixed to form a base mixture which can be fractionated in a pulping system. The system requires multiple spacers and fractionators.

Fractionation techniques have also been utilized in U.S. Patent Nos. 5,916,417 and 5,503,710, which describe the manufacture of multilayer board. At least one fractionation is performed on the same mass so that the fibers of the separated fractions end up in different layers.

The object of the invention is to eliminate the above-mentioned drawbacks and to provide a method for producing multilayer paper, in which the same pulp can be obtained with parallel streams of different fiber composition, which can be formed into two or more layers of paper. To accomplish this purpose, the method of the invention is essentially characterized in what is set forth in the characterizing part of the appended claim 1.

The various fiber and fines fractions are formed and separated in a short rotation of a paper or board machine by suitable fractionators and are introduced into an intermediate container so that they remain substantially different. The fractions are preferably formed and separated into different fractions by means of a vortex cleaning technique in a process entity formed by a decoder and a vortex cleaner in a short paper or board machine. ·. cycle, which can largely utilize existing equipment.

: 25 *. It is a prerequisite for the practice of the invention that the pulp or blend to be fractionated contains different fibers differing in at least one of the following fiber properties: fiber content, fiber width, fiber wall thickness, longitudinal mass, fine:: content.

: Various fiber fractions are created by vortex cleaning technology, which ·, is capable of separating different fractions based on differences in fiber density, specific surface area and in some cases fiber length differences. To this end, a known process solution can be applied in which the first (normally 2-4) steps of the vortex purification plant are in communication with the decoder and the acceptances of these steps are led to the decoder.

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The vortex cleaners are dimensioned such that the acceptors of the vortex cleaning steps introduced into the decalber produce the desired fiber fractions. Fiber fractions are formed in vortex cleaners 5, whose accents are led to spaces for the top and middle layers of the decollator. Fiber fractions.

10 Many types of paper or board have the objective of directing the filler and / or fines and the shorter fiber fraction to the surface layers. This improves the properties of the surface layer of the paper with respect to certain further processing processes. Among other things, this type of layering has a positive effect on the quality of printed matter. The invention improves the conditions for the deposition of fines compared to current technology and enables the deposition of different fiber fractions by a simpler process.

The differences in surface and middle layer masses created by the process solution of the invention can be characterized by the following differences in fiber dimensions:

Top layer Middle layer

The finer the larger the smaller the smaller

Fiber length smaller larger; '25 Fiber wall thickness smaller larger \. Longitudinal mass smaller larger *; The invention will now be described in more detail with reference to the accompanying silicon drawings, in which 0 ': 30 is a schematic diagram of the main principle of the method, 1': Fig. 2 is a more detailed diagram of the invention for the separation step. and Figure 3 shows a more detailed diagram of another embodiment of the invention for the separation step.

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Figure 1 shows the basic principle of the method. The diagram shows a short cycle of a papermaking machine in which the pulp comes from the same source and is led to a first separation step 1 from which the first fraction D is derived as a pulp stream M diluted with short circulating circulating water, typically at a consistency of about 0.2-1.5%. the intermediate container 2, which is a known decalcifier 2, and the second fraction is further introduced into a second separation step 1, from which the first fraction B is led to the decalcifier 2 and the second fraction is removed. The decoller is a deaerator used in a short cycle of a papermaking machine, which removes 10 pulps of air based on the vacuum in the reservoir and the pulp temperature. The vacuum pump generating the vacuum is denoted by the reference numeral 7. The fractions D, B obtained in the separator steps leading to the decollerator 2 are kept separate, at least to the extent that their composition remains different in terms of fiber properties and fines content. From decoder 2, the fractions D and B are fed in their respective streams to the multilayer headbox 4 of the papermaking machine at a consistency substantially equivalent to the paper forming consistency. Small amounts of dilution water can be added to these streams. Before the headbox, the fraction D separated in the first step is further divided into two identical fractions A and C, which are led in parallel with fraction B to the headbox in their own flows, so that the fractions still pass through the machine screens 3. From the fractions D, A, C obtained in the first separation step 1, a layered paperboard is formed. and from fraction B obtained in the second separation step 1

25, a middle layer of layered paper is formed. The fractions are derived. in a multilayer headbox 4 where they form: 'overlapping streams according to the principle described above. Multi- *; the structure of the bed headbox 4 is known per se and is not described in further detail herein, and in this respect reference is made, for example, to the aforementioned publications. Mass pumping pumps are marked with a letter P.

: I ': The first separation step 1 is dimensioned such that a fines and a fiber fraction with an average standing · · direction is directed to the surface layer fraction. 35 such thickness and fiber length is less than the starting mass. Correspondingly, less fines and fiber fractions, respectively, are directed to the middle layer with a mean wall thickness and fiber content greater than the starting mass. Applying fines and fiber fractions with a smaller fiber dimension to the surface layers reduces roughness and average surface pore size. The advantage of using pulp pulps is also the higher modulus of elasticity of the surface layer, which increases the stiffness of the paper.

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Fig. 2 is a more detailed diagram of the above principle according to an embodiment of the invention. As the separation steps 1, vortex cleaners are used, the lighter fraction of which is always fed to the decalcifier 2, from which the pulp is taken out and passed as a suitable fraction to the size of the headbox. The finer material separated in the first step is directed to the decoder 2 into its own compartment 2a, which is separated by a partition 5 from the thigh compartment 2b, to which the finer material obtained from the reject of the first separation step 1 'is removed. Fractions B1 and B2, or '' accept '', separated from the same mass flow, are introduced into compartment 2b in two 15 successive separation steps. The second compartment 2b of the desiccator is separated by a partition 5 from a third compartment 2c connected to an overflow 6 which is led to a wire well. From the first compartment 2a, a finer fraction is introduced into the headbox as the surface layer forming fraction D, which is branched into similar fractions A and C before the headbox. From the second compartment 2b, a mass flow is led to the headbox as a middle layer forming fraction B having coarser fibers. The flows generated by the different fractions are kept separate and led to their own manifolds 4a, 4b and 4c 25 in the headbox 4. The mass flows from the manifolds are led as separate streams along known headbox liners to the lip cone: 4d, after which they separate. From the headbox 4, the mass is led to the wire section where it begins to form a layered product. The water drained off by the wire section ends up in a known manner;: 30 as part of a short circulation into the wire well.

Figure 3 shows another embodiment which also has three pe-; a stepwise separation step 1 such that the first step separates a finer fraction of decolor 2 from the same mass flow M

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'**. 35 to 2a, and the remaining fraction is controlled through two successive separation steps 1, in which the finer fractions B1, B2 separated form a coarser fraction, which ends up in its own compartment 2b with a decolor 2 forming the middle layer mass fraction B.

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Between the compartments 2a, 2b there is a third compartment 2c separated from them by partitions 5, which is connected to the overflow 6 which is led into the wire well. The solution of Fig. 3 has the advantage that the mass fractions D and B separated in successive separation steps are not mixed because there is a compartment 2c between the decoder 2 5 to which they are both communicating through the flow through the partition 5.

Figures 2 and 3 further show, with a full line L1, how the wire trunk can be derived from the uptake of fine and filler-containing dilution water into the first obtained fraction D into the desiccator 2 into compartment 2a, and dashed how this can also be derived from the following fraction B into the decollector compartment 2b. In addition, Fig. 2 shows with a dashed dotted line L2 how, if necessary, a small portion of the short circulation mass flow M can be controlled before separation

15 directly from either the first fraction D or the next fraction B

which also increases the ability to adjust the compositions of the pulp fractions.

The invention facilitates the utilization of fractionation techniques in the layering of 20 paper or board. In addition, the double mass processing themes and short rotations normally required for pulp rusting are avoided. The present invention can be applied with minor modifications to existing short pulp cycles. In particular, if vortex cleaners and a decolorizer are already used in the short rotation, fractionation can be accomplished by properly coupling the vortex cleaners to the decoupler. a separator for forming partitions for decomposing different decompositions.

| *: · 'Each fraction can also be provided with its own decalcifier, where: 30 is an overflow, and each is taken as a corresponding fraction for a multi-layer headbox of a paper or board machine.

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The invention is not limited to the use of any particular pulp, but may be used for all pulps and alloys which can be separated into fractions of different composition in a short cycle.

For example, coniferous sulphate pulp typically contains various fiber fractions. The softwood pulp spring and summer wood fibers differ by 9 113789 mm. fiber wall thickness, and also the fibers from different parts of the wood frame differ in fiber wall thickness and fiber content. Thus, the same wood raw material may already contain different fibers which are separable into different fractions of fiber composition.

In addition to softwood sulphate pulp, the pulp mixture often also contains short pulp which differs in fiber dimensions from that of softwood pulp used as reinforcing pulp. Because the pulp blend 10, which is often used in papermaking, contains fibers of different fiber dimensions, the invention is also extensively applicable to different pulp blends whose fibers are derived from at least two different wood raw materials and / or two different pulp production processes. Examples include: the following pulp mixtures: 15 - softwood sulphate / hardwood sulphate, - softwood sulphate / grit (grit, pressurized grit), - softwood sulphate / grit (grit, hot pulp), - CTMP.

These mixtures can be used to make e.g. the following types of multi-ply paper: - wood-based and wood-free base papers, coated with downstream processes, - wood-free uncoated and coated paper, Γ * 25 - wood-based uncoated and coated printing paper (SC, LWC, MWC), .

»- * The term" same source of pulp ", as used herein, generally means: a fibrous pulp of the same wood raw material or vegetable raw material, a mixture of pulps of various kinds mentioned above, e.g. because of the desirable properties of the end product, paper or cardboard, or a mixture of pulps from different pulping processes with raw materials

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35 may be the same or different.

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Claims (10)

10 1 13789 A process for the production of layered paper or paperboard, wherein the paper is formed from at least two superimposed feed streams, which are different from each other and whose components are from the same pulp source, characterized in that the fractions (A, B, C) for different layers are obtained separating two fractions (B, D) from at least one separation step (1) from the pulp (M) of the short circulation paper or board machine, each of which is fed to an intermediate container (2) so that the fractions remain substantially different; different layers of cardboard. Process according to claim 1, characterized in that the fractions are separated from the same mass flow (M) in at least two successive separation steps (1). Process according to Claim 2, characterized in that at least one fraction (B) is formed in fractions (B1, B2) from the same mass flow (M) in at least two successive separation steps. Method according to Claim 2 or 3, characterized in that the finer fraction which is always separated in successive separation steps is introduced into an intermediate container (2). »T · A method according to any one of the preceding claims, characterized by; This means that the obtained fractions (B, D) are completely separated by means of one or more intermediate containers (2). : 30 Process according to any one of the preceding claims, characterized in that the fractions are introduced into the same intermediate container (2), where they are kept substantially different in one or more partitions (5) or the like. with the help of tava. \ 35 1 »» » A method according to claim 6, characterized in that ··; between the at least two different fractions (B, D), the intermediate container (2) has a compartment ·: (2c) which receives the overflow flow of each fraction (B, D). 11 113789 Method according to one of the preceding claims, characterized in that vortex cleaning is used as the separation step (s) (1). 5 Method according to one of the preceding claims, characterized in that a decalcifier is used as the intermediate container (2). A process according to any one of the preceding claims, characterized in that paper or paperboard of at least three layers is produced, wherein the finer fraction is led to the surface layers and the coarser fraction is introduced into the middle layer. I »1 • · · • ·» · 12 1 13789