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WO2002092910A1 - Multilayered fibrous product and a process for the production thereof - Google Patents

Multilayered fibrous product and a process for the production thereof Download PDF

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Publication number
WO2002092910A1
WO2002092910A1 PCT/FI2002/000342 FI0200342W WO02092910A1 WO 2002092910 A1 WO2002092910 A1 WO 2002092910A1 FI 0200342 W FI0200342 W FI 0200342W WO 02092910 A1 WO02092910 A1 WO 02092910A1
Authority
WO
WIPO (PCT)
Prior art keywords
ofthe
layer
filler
top layer
fibre
Prior art date
Application number
PCT/FI2002/000342
Other languages
French (fr)
Inventor
Petri Silenius
Leena Yliniemi
Jari Meuronen
Markku Leskelä
Original Assignee
M-Real Oyj
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by M-Real Oyj filed Critical M-Real Oyj
Priority to JP2002590164A priority Critical patent/JP4582998B2/en
Priority to US10/475,773 priority patent/US20040168779A1/en
Priority to CA2445100A priority patent/CA2445100C/en
Priority to NZ529159A priority patent/NZ529159A/en
Priority to EP02718226.0A priority patent/EP1392923B1/en
Priority to AU2002249300A priority patent/AU2002249300B2/en
Publication of WO2002092910A1 publication Critical patent/WO2002092910A1/en

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Classifications

    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
    • D21H17/63—Inorganic compounds
    • D21H17/67—Water-insoluble compounds, e.g. fillers, pigments
    • D21H17/69—Water-insoluble compounds, e.g. fillers, pigments modified, e.g. by association with other compositions prior to incorporation in the pulp or paper
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H27/00—Special paper not otherwise provided for, e.g. made by multi-step processes
    • D21H27/30—Multi-ply
    • D21H27/38—Multi-ply at least one of the sheets having a fibrous composition differing from that of other sheets
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H11/00—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only
    • D21H11/16—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only modified by a particular after-treatment
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H15/00—Pulp or paper, comprising fibres or web-forming material characterised by features other than their chemical constitution
    • D21H15/02—Pulp or paper, comprising fibres or web-forming material characterised by features other than their chemical constitution characterised by configuration
    • D21H15/10—Composite fibres
    • D21H15/12—Composite fibres partly organic, partly inorganic

Definitions

  • Multilayered fibrous product and a process for the production thereof
  • the present invention concerns a multi-layer fibrous product according to the preamble of claim 1.
  • This kind of a product comprises at least two overlapping fibrous layers, of which at least the layer forming the operating surface ofthe product is light and essentially opaque (non- transparent), covering the fibre layer under it.
  • the top layer contains filler and possibly conventional additives and auxiliary agents for paper.
  • the present invention relates also to a process according to claim 12 for producing of multi-layer fibrous product.
  • a multilayered fibrous product usually consisting of two or three layer is called a "liner".
  • a liner can be completely brown (kraft-liner) or partially white (white-lined liner) or its top layer can be coated.
  • the liner can be made of virgin fibre or recycled fibre or both.
  • a liner is used as a surface of a background liner in a corrugate board package.
  • the special characteristics of kraft-liners are strength, uniform quality and product safety. Strength is with kraft-liners a very important competitive advantage when comparing with recycled fibre-based products. The advantages of using test liners that contain recycled fibre are low price and the ecological values that support recycling.
  • the products called "Kemiart Graph” and “Kemiart Lite” and the uncoated “Kemiart Brite” of Oy Metsa-Botnia Ab can be mentioned as examples of commercial coated liners.
  • the liner product of Oy Metsa-Botnia Ab is a kraft-liner that has two fibre layers, the base layer being high yield softwood sulphate pulp and the top layer of bleached birch and softwood sulphate pulp. The fillers are used in the top layer to give the surface more brightness and smoothness, which improves the printability properties.
  • the coating is added to the coated products with an on-line coating unit.
  • the coating is, for example, a combination of kaolin, carbonate and latex which improves significantly the printability ofthe product.
  • the final gloss and smoothness ofthe final product are obtained with calendering.
  • the method of producing the top layer ofthe white lined linerboard (cover layer) is considerably more expensive than the method of producing brown back layer.
  • the product can be optimised by changing, for example, the strengths ofthe fibre layers. In that case it would be reasonable to produce the liner the top layer of which is as lightweight as possible. So far, however, the attempts to reduce the weight ofthe cover while maintaining a sufficient brightness of a liner without making the cover too weak, have been unsuccessful.. The amount ofthe white fibre cannot be decreased easily, without the brown fibre showing through.
  • the top layer does also need to have a good formation, which shows directly as good printability. Thus bad formation is visible especially well in grey scales of offset printing and as mottled print quality.
  • the present invention is based on the idea that a composite filler consisting of fibrils and mineral pigments is used as a filler ofthe top layer ofthe fibre product mentioned in the introduction.
  • Finnish Patent Specification No. 100729 discloses a papermaking filler comprising porous aggregates formed by precipitated calcium carbonate particles on the surface of fines. What characterises this new kind of filler is that, according to the patent specification, the calcium carbonate is precipitated on fine fibrils produced by refining cellulose fibres and/or mechanical pulp fibres. The size distribution ofthe fines fraction corresponds mainly to the wire screen fraction P 100.
  • the present invention it has been found that when the top layer of a multilayer product is filled with the filler described above, the opacity ofthe surface increases so drastically that the grammage ofthe cover can be reduced significantly.
  • the top layer containing the new filler covers very efficiently the brown background despite the lower grammage.
  • fillers consisting at least partly of cellulose or lignocellulose fibrils, over which light scattering material particles has been precipitated, can be used as fillers.
  • These particles are typically inorganic salts precipitating in an aqueous phase, such as calcium carbonate, calcium sulphate, barium sulphate and calcium oxalate.
  • GB Patent No. 628603 describes a multi-layer paper or board, the top layer of which contains modified fibre bulk.
  • the bulk has been produced by impregnating the pulp with calcium chloride, after which the manipulated bulk is put in contact with carbonate compound, which causes the calcium carbonate to precipitate on the fibres - not on the fibrils.
  • the bulk has considerably poor strength properties. It is stated in the publication, that it would not be possible to produce paper from this material. Moreover, the bulk has very poor retention.
  • the fibre product according to the present invention is mainly characterised by what is stated in the characterising part ofthe claim 1.
  • a white lined liner can be prepared with a lighter top layer without compromising the strength ofthe surface.
  • the proportions ofthe white and brown layers can be changed much more easily.
  • the filler content can be increased and as the filler is extremely white, the amount ofthe white layer can be significantly decreased.
  • the commercial manufactures of liners can also decrease the total grammage ofthe liner.
  • the grammage ofthe top layer according to the present invention can be at least about 5 % by weight, preferably at least 10 % by weight smaller than a top layer that has a corresponding opacity and formation and is prepared from the same fibre material and mineral pigment.
  • the filler has been found to improve the formation and stiffness ofthe top layer.
  • the better retention helps also to optimise/decrease the dosage of other paper making additives. Purity helps the operation of the machine and generally the operation efficiency ofthe machine improves, as the frequency of breaking down is smaller.
  • Figure 1 present a side view ofthe principal structure of a two-layer fibre product and Figure lb the corresponding four-layer fibre product,
  • Figure 2 shows the light scattering factor of a two-layer fibre product produced according to the present invention and two reference products as a function ofthe Mullen indices with two different filling factors
  • Figure 3 shows corresponding results as a function ofthe bonding power (ScottBond)
  • Figure 4 shows corresponding results as a function ofthe tensile index
  • the figure 5 uses bar graphs to present the brightness of four two-layer fibre products, wherein two has top layers that contain filler according to the present invention, and two other contain reference filler.
  • composite filler comprising cellulose fibrils, on which light scattering pigments have been precipitated, is added as filler to the top layer ofthe multi-layer fibre product.
  • Fibrils can originate from chemical pulp or mechanical pulp or mixtures thereof.
  • chemical pulp reference is herein made to a pulp, which has been treated with cooking chemicals to delignify cellulose fibres.
  • the fibrils are obtained by refining pulps produced with the sulphate process or with some other alkaline cooking method.
  • fibrils can originate also from chemi-mechanical or mechanical pulps.
  • the average thickness of cellulose or lignocellulose fibrils is smaller than 5 ⁇ m, conventionally smaller than 1 ⁇ m.
  • the fibrils are characterized by at least one ofthe following criteria: a. they correspond to a fraction which passes a 100-mesh screen; and b. their average thickness is 0.01 - 10 ⁇ m (preferably at maximum 5 ⁇ m and in particular at maximum 1 ⁇ m) and their average length is 10 - 1500 ⁇ m.
  • the source material for the fibrils i.e. the fines based on cellulose or other fibers, is fibrillated by beating it in a pulp refiner.
  • the desired fraction may, when necessary, be separated by using a screen, but fines need not always be screened.
  • Suitable fibril fractions include wire screen fractions P50 - P400.
  • refiners with grooved blades are used.
  • the light-scattering material particles in the filler are inorganic or organic salts that can be formed from their source materials by precipitation in an aqueous medium.
  • Such compounds include calcium carbonate, calcium oxalate, calcium sulphate, barium sulphate, and mixtures thereof.
  • the material particles are deposited on the fibrils.
  • the amount of an inorganic salt compound in proportion to the fibril amount is approx. 0.0001 - 95 % by weight, preferably approx. 0.1 - 90 % by weight, most suitably approx. 60 - 80 % by weight, calculated from the amount of filler, and approx. 0.1 - 80 % by weight, preferably approx. 0.5 - 50 % by weight, ofthe paper.
  • the filler is produced by precipitating a mineral pigment on the surface of fine fibrils prepared from cellulose fibres and/or mechanical pulp fibres.
  • the precipitation of calcium carbonate can be carried out by feeding into an aqueous slush of fibrils an aqueous calcium hydroxide solution which possibly contains a solid calcium hydroxide, and a compound which contains carbonate ions and is at least partly dissolved in water (e.g. sodium carbonate or ammonium carbonate). It is also possible to introduce into the aqueous phase carbon dioxide gas that, in the presence of calcium hydroxide, produces calcium carbonate. There are formed string-of-pearls-like calcium carbonate crystal aggregates, which are held together by fibrils, i.e.
  • the diameter ofthe calcium carbonate particles in the aggregates is about 0.1 to 5 ⁇ m, typically about 0.2 to 3 ⁇ m.
  • the fibrils correspond (at least to 55 %) to wire screen fractions P50 to P400.
  • filler 1 to 90 % by weight (dry weight), typically about 5 to 50 % by weight, of this kind of filler is added to the top layer of a multi- layer product.
  • the filler described forms at least 5 % by weight, most suitably from 10 to 100 % by weight ofthe filler ofthe bottom web and respectively 10 to 50 % by weight ofthe fibre material ofthe bottom web.
  • the present filler can form 1 to 100 % by weight of fibre material ofthe bottom web.
  • part ofthe filler can consist of conventional fillers, such as calcium carbonate. However, preferably at least 80 %, especially preferably at least 90 % ofthe precipitated light scattering pigment particles are attached into the fibrils.
  • Figures la and lb illustrate the structures ofthe multi-layer products containing two and four layers, respectively.
  • Figure la illustrates atypical white lined liner board and
  • Figure lb illustrates so called test liner.
  • the grammage ofthe fibre product according to the present invention is preferably about 50 to 500 g/m 2 , typically about 80 to 350 g/m 2 . Usually its grammage is over 125 g/m 2 , but products having a grammage below 100 g/m 2 qualify for small packages.
  • the liner according to the present invention comprises a two-layer product (see Figure la), that has a surface of a cover layer 1 and a back layer 2.
  • the top layer covers the back layer so that the back layer cannot be seen through the top layer.
  • the number of layers in a layer product has no upper limit, there can be even up to 5, 6 or 7 layers.
  • the top layer contains filler described more precisely hereinbefore, so that the top layer covers the layers under it, the layers that can be produced from raw materials of cheap costs.
  • test liner type four-layer products of Figure lb having a top layer 3, a layer 4 under the top layer, intermediate layer 5 and a back layer 6, are to be mentioned.
  • the virgin fibre can originate from softwood or hardwood (wood chips) or it can originate from cuttings.
  • Especially preferably virgin pulp is used in the top layer. This is most suitably produced by sulphate cooking (kraft pulp), because sulphate cooking gives a mass having especially good strength properties, as the name suggests.
  • the recycled fibre can originate e.g. from used corrugated board packages (OCC) or mixed fibres. Recycled fibres are used especially for the production of test liners.
  • the surface and back layer(s) can be produced from similar raw materials or from different source fibres.
  • the mass ofthe back layer can be cooked in high yield, after which a mild refining is performed on it.
  • the pulp ofthe back layer is cooked to a kappa value of 30 to 70 and the pulp ofthe top layer to lower kappa value of 25 (the kappa number ofthe unbleached pulp).
  • Bleaching can be performed in a manner known per se, e.g. as ECF of TCF bleaching.
  • Retention agents can be added to the slush e.g. in about 0.5 to 3 % ofthe amount ofthe fibre material.
  • the filler described here gives such a good retention that no retention agents are needed for the layer the and amount ofthe retention agents can be significantly decreased.
  • the liner is stuff or surface sized to improve the moisture resistance. If a low quality recycled fibre is used as raw material, it is preferable to use a surface-size press to produce a product that has sufficient strength.
  • the distribution ofthe base weight between the top and the back layer is about 20/80...40/60, typically about 30/70.
  • the grammage ofthe top layer is generally about 20 to 125 g/m 2 (see below).
  • the grammage ofthe top layer can be decreased over 10 %, up to 20 % or more, without deteriorating the optical or mechanical properties ofthe cover.
  • the layer product is produced in a manner known per se. According to one preferred embodiment both or all layers are produced first from slush of their own and spread on the Fourdriner wire. After this, the layers are couched fastened into each other. With regard to the production process, a reference is made to a text by Ari Kiviranta "Board Grades", in a book series Paper Making Science and Technology, Book 18, Paper and Board Grades, Fapet Oy, Jyvaskyla 2000, pages 68 and 69.
  • a planar fibre product according to the present invention can be used as a top layer of different corrugate board packages.
  • the solution according to the present invention is especially preferably suitable for white lined top liner and coated white lined liner, both of which are used for demanding printing works.
  • the surface of the liner according to the invention is extremely smooth and uniform, and has at the same time high opacity and brightness can be made use of.
  • the grammage ofthe top layer is about 20 to 125 g/m , most suitably about 50 to 80 g/m , especially preferably about 55 to 70 g/m 2 , and bleached chemical cellulose pulp is used ofthe top layer.
  • mainly hardwood is used in the top layer.
  • typically over 80 % of fibre material of pulp is hardwood and the rest softwood.
  • the fibre material of pulp can consist totally of hardwood.
  • Conventional coating mixtures can be used for coating ofthe coated white lined top layer product.
  • Precipitated calcium carbonate, ground calcium carbonate, calcium sulphate, calcium oxalate, aluminium silicate, kaolin (hydrous aluminium silicate), aluminium hydroxide, magnesium silicate, talc (hydrous magnesium silicate), titanium dioxide and barium sulphate, and mixtures thereof can be used as pigments. Synthetic pigments can also be used.
  • the main pigments are kaolin, calcium carbonate, precipitated calcium carbonate and gypsum, which in general constitute over 50 % ofthe dry solids in the coating mix.
  • Calcined kaolin, titanium dioxide, satin white, aluminium hydroxide, sodium silicoaluminate and plastics pigments are additional pigments, and their amounts are in general less than 25 % ofthe dry solids in the mix.
  • binders generally used in paper production can be used as binders in the coating composition.
  • binders include synthetic latexes made up of polymers or copolymers of ethylenically unsaturated compounds, e.g. copolymers ofthe butadienestyrene type, and polyvinyl acetate having comonomers that contain carboxyl groups.
  • synthetic latexes made up of polymers or copolymers of ethylenically unsaturated compounds, e.g. copolymers ofthe butadienestyrene type, and polyvinyl acetate having comonomers that contain carboxyl groups.
  • water-soluble polymers starch, CMC, hydroxyethyl cellulose and polyvinyl alcohol
  • additives and auxiliary agents such as dispersants, agents affecting the viscosity and water retention ofthe mix, lubricants, hardeners used for improving water-resistance, optical auxiliary agents, anti-foaming agents, pH control agents, and preservatives can be used in the coating composition.
  • the coating mix can be applied to the material web in a manner known per se.
  • the coating can be done before couching. Preferably it is done after forming the multi-layer structure.
  • the method according to the present invention for coating paper and/or board can be carried out with a conventional coating apparatus, in other words by blade coating, or by film coating or JET application. Coating can be done on-line or off-line.
  • the amount of grammage ofthe coating layer varies from 5 to 30 g/m . It has also been found in the context ofthe the present invention, quite surprisingly, that the above-described filler does not only improve opacity ofthe top layer but the filled layer is also very easy to be coated. The amount of pigment or amounts of coatings required for the desired brightness can be decreased with the filler.
  • the opacity is significantly improved with the filler.
  • Birch sulphate pulp was refined with a Valmet JC-01 refiner to produce pulp that is suitable for production of filler.
  • the consistency of refining was about 4 % and the total energy consumption was 343 kWh/t and specific edge load was 0.5 J/m.
  • Carbonating was performed in tap water according to the FI Patent Specification No. 100729. Water slurry that has dry matter content of 2.22 % was produced. The final product had CaCO 3 content of 69.7 % and a specific surface area of 10.6 m 2 /kg.
  • Fibre layers suitable for cover layer of two-layer white lined liner was produced from chemical pulp that contained 70 % by weight of birch pulp and 30 % by weight of pine pulp. Filler was added from the pulp in the slush in various amounts: 13 and 20 % by weight, respectively, of filler described in example 1 (SuperFill), 14 and 16 % by weight, respectively, precipitated calcium carbonate (PCC, Albacar LO, ref. 1) and 14 % by weight of mixture of chalk and calcined kaolin (ref. 2).
  • Figures 2 to 4 illustrate the light scattering ability ofthe obtained fibre layers as a function of mechanical strength properties.
  • the figures show that the light scattering factor is at least 25 % and about 20 % greater with the SuperFill filler when compared with references 1 and 2 in constant strengths.
  • Consequence of this is that the grammage ofthe surface can be decreased by about 20 %, which decreases significantly production costs of liner.
  • Ffigure 5 shows a result in which the above presented results are substantiated.
  • the result is from a liner test run made by pilot machine (FEX) of STFI in Sweden, wherein the grammage ofthe surface was decreased from the normal level of 75 g/m 2 to a level of 65 g m 2 .
  • FEX pilot machine
  • Figure 5 shows that the top layer lightened 10 g/m 2 with SuperfiU, generates brightness which is 4 brightness units greater as compared with the reference 2, in which the grammage is 75 g/m 2 .
  • the result is extremely good and it suggests that the grammage of the surface can be decreased even lower than 10 g/m 2 .

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  • Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Paper (AREA)

Abstract

The multi-layer fibrous product and a process for producing it. According to the present invention the fibre product comprises at least two overlapping fibre layers, whereby the one that forms the top layer of the product contains filler and is lighter than the layer under it and is at least essentially opaque. According tothe present invention the filler of the top layer consists at least partially of cellulose or lignocellulose fibrils, on which light scattering material particles have been precipitated. The present invention can be used, for example, to produce white surface liner with a lighter top layer without impairment of the strengthof the surface. Thus, the grammage of the layer can be at least about 5% by weight less than a top layer, which has the corresponding opacity and formation, and which has been produced from the same fibre material and mineral pigments.

Description

Multilayered fibrous product and a process for the production thereof
The present invention concerns a multi-layer fibrous product according to the preamble of claim 1.
This kind of a product comprises at least two overlapping fibrous layers, of which at least the layer forming the operating surface ofthe product is light and essentially opaque (non- transparent), covering the fibre layer under it. The top layer contains filler and possibly conventional additives and auxiliary agents for paper.
The present invention relates also to a process according to claim 12 for producing of multi-layer fibrous product.
A multilayered fibrous product usually consisting of two or three layer is called a "liner". A liner can be completely brown (kraft-liner) or partially white (white-lined liner) or its top layer can be coated. The liner can be made of virgin fibre or recycled fibre or both.
A liner is used as a surface of a background liner in a corrugate board package. The special characteristics of kraft-liners are strength, uniform quality and product safety. Strength is with kraft-liners a very important competitive advantage when comparing with recycled fibre-based products. The advantages of using test liners that contain recycled fibre are low price and the ecological values that support recycling.
The products called "Kemiart Graph" and "Kemiart Lite" and the uncoated "Kemiart Brite" of Oy Metsa-Botnia Ab can be mentioned as examples of commercial coated liners. The liner product of Oy Metsa-Botnia Ab is a kraft-liner that has two fibre layers, the base layer being high yield softwood sulphate pulp and the top layer of bleached birch and softwood sulphate pulp. The fillers are used in the top layer to give the surface more brightness and smoothness, which improves the printability properties. Other chemicals, such as retention agents, are also used in production of liner, in order to retain the noil material and filling agents in the product instead of cycling it in the water cycle, and AKD adhesives to improve water resistance. The coating is added to the coated products with an on-line coating unit. The coating is, for example, a combination of kaolin, carbonate and latex which improves significantly the printability ofthe product. The final gloss and smoothness ofthe final product are obtained with calendering.
The method of producing the top layer ofthe white lined linerboard (cover layer) is considerably more expensive than the method of producing brown back layer. The product can be optimised by changing, for example, the strengths ofthe fibre layers. In that case it would be reasonable to produce the liner the top layer of which is as lightweight as possible. So far, however, the attempts to reduce the weight ofthe cover while maintaining a sufficient brightness of a liner without making the cover too weak, have been unsuccessful.. The amount ofthe white fibre cannot be decreased easily, without the brown fibre showing through.
The top layer does also need to have a good formation, which shows directly as good printability. Thus bad formation is visible especially well in grey scales of offset printing and as mottled print quality.
It is an object ofthe present invention to eliminate the problems involved with the known methods and to provide a novel solution for producing multi-layer fibre products, such as liners.
The present invention is based on the idea that a composite filler consisting of fibrils and mineral pigments is used as a filler ofthe top layer ofthe fibre product mentioned in the introduction.
Finnish Patent Specification No. 100729 discloses a papermaking filler comprising porous aggregates formed by precipitated calcium carbonate particles on the surface of fines. What characterises this new kind of filler is that, according to the patent specification, the calcium carbonate is precipitated on fine fibrils produced by refining cellulose fibres and/or mechanical pulp fibres. The size distribution ofthe fines fraction corresponds mainly to the wire screen fraction P 100.
According to the present invention, it has been found that when the top layer of a multilayer product is filled with the filler described above, the opacity ofthe surface increases so drastically that the grammage ofthe cover can be reduced significantly. The top layer containing the new filler covers very efficiently the brown background despite the lower grammage.
Furthermore, within the scope ofthe present invention it has been found that also other similar fillers consisting at least partly of cellulose or lignocellulose fibrils, over which light scattering material particles has been precipitated, can be used as fillers. These particles are typically inorganic salts precipitating in an aqueous phase, such as calcium carbonate, calcium sulphate, barium sulphate and calcium oxalate.
According to the present invention it is, thus, possible to reduce the thickness ofthe multilayer paper without impairing the opacity by using a filler that comprises fibrils over which calcium carbonate has been precipitated. GB Patent No. 628603 describes a multi-layer paper or board, the top layer of which contains modified fibre bulk. The bulk has been produced by impregnating the pulp with calcium chloride, after which the manipulated bulk is put in contact with carbonate compound, which causes the calcium carbonate to precipitate on the fibres - not on the fibrils. In the case corresponding to that described in the GB Patent, the bulk has considerably poor strength properties. It is stated in the publication, that it would not be possible to produce paper from this material. Moreover, the bulk has very poor retention.
More specifically, the fibre product according to the present invention is mainly characterised by what is stated in the characterising part ofthe claim 1.
The process according to the present invention, for its part, is characterised by what is stated in the characterising part of claim 12.
The present invention provides considerable advantages. Thus, a white lined liner can be prepared with a lighter top layer without compromising the strength ofthe surface. With the help of a new kind of a composite filling agent, the proportions ofthe white and brown layers can be changed much more easily. As the filler content can be increased and as the filler is extremely white, the amount ofthe white layer can be significantly decreased. By decreasing the white fibre layer, the commercial manufactures of liners can also decrease the total grammage ofthe liner. For example, it should be mentioned, that the grammage ofthe top layer according to the present invention can be at least about 5 % by weight, preferably at least 10 % by weight smaller than a top layer that has a corresponding opacity and formation and is prepared from the same fibre material and mineral pigment.
The filler has been found to improve the formation and stiffness ofthe top layer. The filler described in the FI Patent Specification No. 100729, referred hereinafter with its product name "SuperFill", retains well, which makes it possible to reduce the dosage of retention agents and still maintain a purer process. The better retention helps also to optimise/decrease the dosage of other paper making additives. Purity helps the operation of the machine and generally the operation efficiency ofthe machine improves, as the frequency of breaking down is smaller.
The present invention will be examined below in greater detail with the help of a detailed description and some examples.
Figure 1 present a side view ofthe principal structure of a two-layer fibre product and Figure lb the corresponding four-layer fibre product,
Figure 2 shows the light scattering factor of a two-layer fibre product produced according to the present invention and two reference products as a function ofthe Mullen indices with two different filling factors, Figure 3 shows corresponding results as a function ofthe bonding power (ScottBond), Figure 4 shows corresponding results as a function ofthe tensile index, and The figure 5 uses bar graphs to present the brightness of four two-layer fibre products, wherein two has top layers that contain filler according to the present invention, and two other contain reference filler.
Filler and its preparation
As stated above, according to the present invention, composite filler comprising cellulose fibrils, on which light scattering pigments have been precipitated, is added as filler to the top layer ofthe multi-layer fibre product. Fibrils can originate from chemical pulp or mechanical pulp or mixtures thereof. By chemical pulp reference is herein made to a pulp, which has been treated with cooking chemicals to delignify cellulose fibres. According to a preferred embodiment the fibrils are obtained by refining pulps produced with the sulphate process or with some other alkaline cooking method. In addition to chemical pulps, fibrils can originate also from chemi-mechanical or mechanical pulps.
Typically, the average thickness of cellulose or lignocellulose fibrils is smaller than 5 μm, conventionally smaller than 1 μm. The fibrils are characterized by at least one ofthe following criteria: a. they correspond to a fraction which passes a 100-mesh screen; and b. their average thickness is 0.01 - 10 μm (preferably at maximum 5 μm and in particular at maximum 1 μm) and their average length is 10 - 1500 μm.
The source material for the fibrils, i.e. the fines based on cellulose or other fibers, is fibrillated by beating it in a pulp refiner. The desired fraction may, when necessary, be separated by using a screen, but fines need not always be screened. Suitable fibril fractions include wire screen fractions P50 - P400. Preferably refiners with grooved blades are used.
The light-scattering material particles in the filler are inorganic or organic salts that can be formed from their source materials by precipitation in an aqueous medium. Such compounds include calcium carbonate, calcium oxalate, calcium sulphate, barium sulphate, and mixtures thereof. The material particles are deposited on the fibrils. The amount of an inorganic salt compound in proportion to the fibril amount is approx. 0.0001 - 95 % by weight, preferably approx. 0.1 - 90 % by weight, most suitably approx. 60 - 80 % by weight, calculated from the amount of filler, and approx. 0.1 - 80 % by weight, preferably approx. 0.5 - 50 % by weight, ofthe paper.
In the following, the present invention is examined with particular reference to a product according to FI Patent Specification No. 100729, but it is clear that the present invention can be adapted for other products mentioned hereinbefore by changing appropriately the source materials ofthe light scattering pigment.
The filler is produced by precipitating a mineral pigment on the surface of fine fibrils prepared from cellulose fibres and/or mechanical pulp fibres. For example, the precipitation of calcium carbonate can be carried out by feeding into an aqueous slush of fibrils an aqueous calcium hydroxide solution which possibly contains a solid calcium hydroxide, and a compound which contains carbonate ions and is at least partly dissolved in water (e.g. sodium carbonate or ammonium carbonate). It is also possible to introduce into the aqueous phase carbon dioxide gas that, in the presence of calcium hydroxide, produces calcium carbonate. There are formed string-of-pearls-like calcium carbonate crystal aggregates, which are held together by fibrils, i.e. fine strands, and in which the calcium carbonate particles are deposited onto the fine fibrils and attached to them. The fine fibrils together with calcium carbonate form string-of-pearls-like strands, and the calcium carbonate aggregates primarily resemble strings of pearls in a pile. In water (slush) the ratio of the effective volume ofthe aggregates to the pulp is very high compared with the corresponding ratio of conventional calcium carbonate used as filler. By "effective volume" is meant, in this case, the volume required by the pigment.
The diameter ofthe calcium carbonate particles in the aggregates is about 0.1 to 5 μm, typically about 0.2 to 3 μm. In particular, the fibrils correspond (at least to 55 %) to wire screen fractions P50 to P400.
1 to 90 % by weight (dry weight), typically about 5 to 50 % by weight, of this kind of filler is added to the top layer of a multi- layer product. Usually the filler described forms at least 5 % by weight, most suitably from 10 to 100 % by weight ofthe filler ofthe bottom web and respectively 10 to 50 % by weight ofthe fibre material ofthe bottom web. In principle it is also possible to produce a bottom web the fibre material of which consist totally of fibrils ofthe filler, so, in general, the present filler can form 1 to 100 % by weight of fibre material ofthe bottom web.
In the slush used in the production ofthe bottom web, part ofthe filler can consist of conventional fillers, such as calcium carbonate. However, preferably at least 80 %, especially preferably at least 90 % ofthe precipitated light scattering pigment particles are attached into the fibrils.
Multi-layer structure
Figures la and lb illustrate the structures ofthe multi-layer products containing two and four layers, respectively. Figure la illustrates atypical white lined liner board and Figure lb illustrates so called test liner. The grammage ofthe fibre product according to the present invention is preferably about 50 to 500 g/m2, typically about 80 to 350 g/m2. Usually its grammage is over 125 g/m2, but products having a grammage below 100 g/m2 qualify for small packages.
Preferably the liner according to the present invention comprises a two-layer product (see Figure la), that has a surface of a cover layer 1 and a back layer 2. The top layer covers the back layer so that the back layer cannot be seen through the top layer.
It is also possible to produce three-layer or four-layer products. In principle the number of layers in a layer product has no upper limit, there can be even up to 5, 6 or 7 layers. What is essential in the present invention, is that the top layer contains filler described more precisely hereinbefore, so that the top layer covers the layers under it, the layers that can be produced from raw materials of cheap costs.
Among multi-layer products, the test liner type four-layer products of Figure lb, having a top layer 3, a layer 4 under the top layer, intermediate layer 5 and a back layer 6, are to be mentioned.
Different raw materials can be used for production of a fibre product according to the purpose of use. Both virgin fibres and recycled fibres can be used. The virgin fibre can originate from softwood or hardwood (wood chips) or it can originate from cuttings. Especially preferably virgin pulp is used in the top layer. This is most suitably produced by sulphate cooking (kraft pulp), because sulphate cooking gives a mass having especially good strength properties, as the name suggests. The recycled fibre can originate e.g. from used corrugated board packages (OCC) or mixed fibres. Recycled fibres are used especially for the production of test liners. The surface and back layer(s) can be produced from similar raw materials or from different source fibres. If virgin fibre, such as kraft pulp, is used for both, then the mass ofthe back layer can be cooked in high yield, after which a mild refining is performed on it. Mass that has been cooked to a lower kappa and also refined more than mass ofthe back layer, is used for the top layer. Typically the pulp ofthe back layer is cooked to a kappa value of 30 to 70 and the pulp ofthe top layer to lower kappa value of 25 (the kappa number ofthe unbleached pulp). Bleaching can be performed in a manner known per se, e.g. as ECF of TCF bleaching. Retention agents can be added to the slush e.g. in about 0.5 to 3 % ofthe amount ofthe fibre material. However, it has been found in connection with the present invention that the filler described here gives such a good retention that no retention agents are needed for the layer the and amount ofthe retention agents can be significantly decreased. The liner is stuff or surface sized to improve the moisture resistance. If a low quality recycled fibre is used as raw material, it is preferable to use a surface-size press to produce a product that has sufficient strength. According to the machine the distribution ofthe base weight between the top and the back layer is about 20/80...40/60, typically about 30/70. Thus the grammage ofthe top layer is generally about 20 to 125 g/m2 (see below). When operating according to the present invention, the grammage ofthe top layer can be decreased over 10 %, up to 20 % or more, without deteriorating the optical or mechanical properties ofthe cover.
The layer product is produced in a manner known per se. According to one preferred embodiment both or all layers are produced first from slush of their own and spread on the Fourdriner wire. After this, the layers are couched fastened into each other. With regard to the production process, a reference is made to a text by Ari Kiviranta "Board Grades", in a book series Paper Making Science and Technology, Book 18, Paper and Board Grades, Fapet Oy, Jyvaskyla 2000, pages 68 and 69.
A planar fibre product according to the present invention can be used as a top layer of different corrugate board packages. The solution according to the present invention is especially preferably suitable for white lined top liner and coated white lined liner, both of which are used for demanding printing works. In these objects the fact that the surface of the liner according to the invention is extremely smooth and uniform, and has at the same time high opacity and brightness can be made use of. Generally the grammage ofthe top layer is about 20 to 125 g/m , most suitably about 50 to 80 g/m , especially preferably about 55 to 70 g/m2, and bleached chemical cellulose pulp is used ofthe top layer. In order to obtain a very good formation in the preferred embodiment ofthe present invention, mainly hardwood is used in the top layer. Thus e.g. over 60 % by weight, typically over 80 % of fibre material of pulp is hardwood and the rest softwood. The fibre material of pulp can consist totally of hardwood. Conventional coating mixtures can be used for coating ofthe coated white lined top layer product. Precipitated calcium carbonate, ground calcium carbonate, calcium sulphate, calcium oxalate, aluminium silicate, kaolin (hydrous aluminium silicate), aluminium hydroxide, magnesium silicate, talc (hydrous magnesium silicate), titanium dioxide and barium sulphate, and mixtures thereof can be used as pigments. Synthetic pigments can also be used. Ofthe pigments mentioned above, the main pigments are kaolin, calcium carbonate, precipitated calcium carbonate and gypsum, which in general constitute over 50 % ofthe dry solids in the coating mix. Calcined kaolin, titanium dioxide, satin white, aluminium hydroxide, sodium silicoaluminate and plastics pigments are additional pigments, and their amounts are in general less than 25 % ofthe dry solids in the mix.
Special-quality kaolins and calcium carbonates, as well as barium sulphate and zinc oxide ofthe special pigments should be mentioned as examples.
Any known binders generally used in paper production can be used as binders in the coating composition. Besides the individual binders, it is also possible to use mixtures of binders. Examples of typical binders include synthetic latexes made up of polymers or copolymers of ethylenically unsaturated compounds, e.g. copolymers ofthe butadienestyrene type, and polyvinyl acetate having comonomers that contain carboxyl groups. Together with the materials mentioned above, it is possible to use , for example, water-soluble polymers, starch, CMC, hydroxyethyl cellulose and polyvinyl alcohol as binders. Furthermore, conventional additives and auxiliary agents, such as dispersants, agents affecting the viscosity and water retention ofthe mix, lubricants, hardeners used for improving water-resistance, optical auxiliary agents, anti-foaming agents, pH control agents, and preservatives can be used in the coating composition.
The coating mix can be applied to the material web in a manner known per se. The coating can be done before couching. Preferably it is done after forming the multi-layer structure. The method according to the present invention for coating paper and/or board can be carried out with a conventional coating apparatus, in other words by blade coating, or by film coating or JET application. Coating can be done on-line or off-line.
The amount of grammage ofthe coating layer varies from 5 to 30 g/m . It has also been found in the context ofthe the present invention, quite surprisingly, that the above-described filler does not only improve opacity ofthe top layer but the filled layer is also very easy to be coated. The amount of pigment or amounts of coatings required for the desired brightness can be decreased with the filler.
According to the present invention, the opacity is significantly improved with the filler.
The following non-restrictive examples illustrate the present invention. The measurement results indicated for the paper properties in the examples have been determined by the following standard methods :
Surface roughness: SCAN-P76:95
Porosity: SCAN-P60
Resistance of air permeability: SCAN-M8,P19
Example 1
Production of filler
Refining of chemical pulp
Birch sulphate pulp was refined with a Valmet JC-01 refiner to produce pulp that is suitable for production of filler. The consistency of refining was about 4 % and the total energy consumption was 343 kWh/t and specific edge load was 0.5 J/m.
Properties of the product are presented in Table 1.
Table 1. Fibre properties before and after refining
Before refining After refining
Fibre length (length), mm 0.86 0.58
Fibre length (weight), mm 1.00 0.77
SR° 16 86 Carbonating of pulp
Carbonating was performed in tap water according to the FI Patent Specification No. 100729. Water slurry that has dry matter content of 2.22 % was produced. The final product had CaCO3 content of 69.7 % and a specific surface area of 10.6 m2/kg.
Example 2
Fibre layers suitable for cover layer of two-layer white lined liner was produced from chemical pulp that contained 70 % by weight of birch pulp and 30 % by weight of pine pulp. Filler was added from the pulp in the slush in various amounts: 13 and 20 % by weight, respectively, of filler described in example 1 (SuperFill), 14 and 16 % by weight, respectively, precipitated calcium carbonate (PCC, Albacar LO, ref. 1) and 14 % by weight of mixture of chalk and calcined kaolin (ref. 2).
Figures 2 to 4 illustrate the light scattering ability ofthe obtained fibre layers as a function of mechanical strength properties. The figures show that the light scattering factor is at least 25 % and about 20 % greater with the SuperFill filler when compared with references 1 and 2 in constant strengths.
Consequence of this is that the grammage ofthe surface can be decreased by about 20 %, which decreases significantly production costs of liner.
Ffigure 5 shows a result in which the above presented results are substantiated. The result is from a liner test run made by pilot machine (FEX) of STFI in Stockholm, wherein the grammage ofthe surface was decreased from the normal level of 75 g/m2 to a level of 65 g m2. A two-layer fibre structure was produced for the test. The ISO brightness ofthe product was determined.
Figure 5 shows that the top layer lightened 10 g/m2 with SuperfiU, generates brightness which is 4 brightness units greater as compared with the reference 2, in which the grammage is 75 g/m2. The result is extremely good and it suggests that the grammage of the surface can be decreased even lower than 10 g/m2.

Claims

Claims:
1. A multi-layer fibrous product comprising of at least two overlapping fibre layers (1, 2;
3-6), of which the one (1; 3), which forms the top layer, contains filler and is lighter than the layer under it (2; 4-6) and it is at least essentially opaque, charactericed in that the filler ofthe top layer (1 ; 3) consists at least partially of cellulose or lignocellulose fibrils, on which light scattering material particles have been precipitated.
2. A fibrous product according to claim 1, charactericed in that the filler comprises cellulose or lignocellulose fibrils produced by refining and screening from plant fibres, the average thickness of which is less than 5 μm.
3. A fibrous product according to claim 2, charactericed in that the light scattering material particles has been precipitated over fibrils corresponding to a fraction that passes through a 50 mesh screen and/or having an average thickness of 0.01 to 5 μm and an average length of 10 to 1500 μm.
4. A fibrous product according to any of claims lto3, charactericed in that the light scattering material particles are inorganic salts that can be formed from their source materials by precipitating in an aqueous medium.
5. A fibrous product according to claim 4, charactericed in that the light scattering material particles are calcium carbonate, calcium oxalate, calcium sulphate, barium sulphate or mixtures thereof.
6. A fibrous product according to any ofthe preceding claims, characterised in that it comprises white lined top liner or coated white lined liner.
7. A fibrous product according to any ofthe preceding claims, characterised in that its grammage is preferably about 50 to 500 g/m2, typically about 80 to 350 g/m2, in which case the grammage ofthe top layer is about 20 to 125 g/m2, preferably about 50 to 70 g/m2.
8. A fibrous product according to any ofthe preceding claims, characterised in that the distribution ofthe grammage between the top and back layers are between about 20/80...40/60.
9. A fibrous product according to any ofthe preceding claims, characterised in that the top layer (1 ; 3) is produced from chemical cellulose pulp comprising hardwood pulp, softwood pulp or a mixture thereof.
10. A fibrous product according to any ofthe preceding claims, characterised in that the back layer comprises 1 to 5 layers (2; 4-6) that have been produced from virgin fibre or recycled fibre.
11. A fibrous product according to any ofthe preceding claims, characterised in that the grammage ofthe top layer is at least about 5 % by weight, preferably at least 10 % by weight, less than the top layer that has been produced from the same fibre material and mineral pigments and that has corresponding opacity and formation.
12. A process for producing a multi-layer product, according to which process a filler- containing fibre layer, which forms the surface (1; 3) ofthe fibre product and covers the back layer, is fitted on top of a backing layer (2; 4-6) that consists of at least of one fibrous layer, characterised in that the top layer (1; 3) is formed from slush of fibre material, to which a product comprising cellulose or lignocellulose fibrils, on which light scattering material particles have been precipitated, is added as a filler.
13. A process according to claim 12, characterised by using a filler that comprises cellulose or lignocellulose fibrils produced from plant fibres by refining and screening, having an average thickness of less than 5 μm.
14. A process according to claim 13, characterised by using a filler, in which the light scattering material particles have been precipitated on fibrils corresponding to a fraction that passes through a 50 mesh screen and/or having an average thickness of 0.1 to 10 μm and an average length of 10 to 1500 μm.
15. A process according to any of claims 12 to 14, characterised by using a filler in which at least 80 % ofthe precipitated light scattering pigment particles are attached to the fibrils.
16. A process according to any of the claims 12 to 15, characterisedin that the top layer is coated in a paper machine with a pigment-containing coating mixture.
17. A method according to any of claims 12 to 16, c h a r a c t e r i s e d in that the top layer (1; 3) and the back layer(s) (2; 4-6) are formed separately on the Fourdriner wire and couched when still wet.
PCT/FI2002/000342 2001-04-24 2002-04-24 Multilayered fibrous product and a process for the production thereof WO2002092910A1 (en)

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CA2445100A CA2445100C (en) 2001-04-24 2002-04-24 Multilayered fibrous product and a process for the production thereof
NZ529159A NZ529159A (en) 2001-04-24 2002-04-24 Multilayered fibrous product and a process for the production thereof
EP02718226.0A EP1392923B1 (en) 2001-04-24 2002-04-24 Multilayered fibrous product and a process for the production thereof
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US7491293B2 (en) * 2004-09-29 2009-02-17 Meadwestvaco Corporation White top paperboard
WO2007003697A1 (en) * 2005-07-01 2007-01-11 M-Real Oyj Method for coating cellulose particles, coated cellulose particles, and use thereof in paper and board production
WO2007100783A3 (en) * 2006-02-27 2008-01-03 Int Paper Co Reducing top ply basis weight of white top linerboard in paper or paperboard
WO2008052970A1 (en) * 2006-10-31 2008-05-08 Basf Se Method for producing a multi layer fiber web from cellulose fibers
WO2010018301A3 (en) * 2008-08-11 2010-09-02 Kemira Oyj Gypsum-fibre composite product and paper comprising such
CN102119126A (en) * 2008-08-11 2011-07-06 凯米罗总公司 Gypsum-fibre composite product and paper comprising such
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FI20010848A0 (en) 2001-04-24
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CN100396848C (en) 2008-06-25
US20040168779A1 (en) 2004-09-02
AU2002249300B2 (en) 2008-04-24
JP2004525282A (en) 2004-08-19
EP1392923B1 (en) 2018-07-25
FI117871B (en) 2007-03-30
FI20010848L (en) 2002-10-25
CA2445100A1 (en) 2002-11-21
CN1516770A (en) 2004-07-28
NZ529159A (en) 2005-07-29
EP1392923A1 (en) 2004-03-03

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