FI117871B - Multilayer fiber product and process for its preparation - Google Patents

Description

ί J f ,. 1 1 7871

Multilayer fiber product and process for its manufacture

The present invention relates to a multilayer fiber product according to the preamble of claim 1.

Such a product comprises at least two overlapping layers of fiber, of which at least the layer forming the working surface of the article is light and substantially opaque (opaque), thereby covering the underlying fiber layer. The topsheet contains a filler and possibly conventional paper additives and additives.

The invention also relates to a process for the manufacture of a multilayer fibrous product according to claim 12.

"Liner" is called a multilayer, usually two or three-ply fiber-15 product. The liner may be completely brown (kraft liner) or partially white (white surface liner) or may be coated with a surface layer. The liner can be made of virgin fiber or recycled fiber, or both.

The liner is used as a surface or backing liner in corrugated packaging. The special features of kraftliners 20 are strength, uniformity and product safety. Strength is an especially important competitive advantage in kraft liners • · '' * * * compared to recycled fiber based products.

• * · • * j The use of recycled fiber testliners is supported by low cost and eco values, ie J · '»*.; * Support for recycling.

Examples of commercial coated liners include Oy Metsä-Botnia Ab's '' Kemiart Graph '' and '' Kemiart Lite '' products and uncoated '' Kemiart ,, #t. Brite ". The liner product of Oy Metsä-Botnia Ab is a kraftliner with two layers of fiber, • ·. · ·. whereby the base layer is high yield high sulfate pulp and the surface layer consists of bleaching. birch and softwood pulp. The topcoat uses fillers to add »·· 30 lightness and smoothness to the surface, improving printability. Other chemicals, such as retention agents, are also used to make the liner, to keep the fines and II · fillers in the product and not circulate in the water, and AKD adhesives to improve water resistance. Coated products are added with an on-line coating unit. For example, the coating is a combination of kaolin, carbonate, and latex, $ 2,117,771, which significantly improves the printability of the product. Calendering provides the final shine and smoothness of the end product.

The surface layer (cover layer) of white liner board is significantly more expensive than the 5 brown backing. For example, the product can be optimized by changing the strength of the fiber layers. In this case, it would be wise to make the liner as light as possible in its surface layer. So far, however, lightening of the surface layer has been limited by the fact that the lighter lightness of the liner has not been achieved without reducing the strength of the lid. The amount of white fiber cannot be reduced very easily, because then the brown fiber layer shines through.

The top layer is also required for good formation, which is directly reflected in good printability. Thus, poor formatting is particularly evident in offset printing in gray and as a patchy print.

15

The object of the present invention is to overcome the drawbacks of the prior art and to provide a novel solution for the manufacture of multilayer fiber products, such as liners.

The invention is based on the idea that a composite filler consisting of fibrils and mineral pigments is used as a filler for the surface layer of the fiber product mentioned in the introduction.

From U.S. Patent No. 100729 is known a papermaking filler comprising • 9 ** · * porous aggregates formed from calcium carbonate particles precipitated on the surface of a fines. A characteristic of this novel filler is the patent publication. according to the fact that calcium carbonate is precipitated on pulp fibrils made from pulp / • mechanical pulp fiber. The fines fraction *! * Essentially corresponds to the wire mesh screening grade P100.

♦ ··· ···· 30 · * · * * * ·; · 'According to the present invention, when the surface layer of a multilayer product is filled with the filler described above, the opacity of the surface increases to such an extent that the lid. the basis weight can be significantly reduced. With a new filler, the 3 117871 topcoat covers the brown background very effectively despite its lower basis weight.

It has further been found in the invention that, in addition to the aforementioned 5 preferred fillers, other similar fillers may be used which consist at least in part of cellulose or lignocellulosic fibrils deposited on light scattering material particles. These particles are typically inorganic salts precipitating in the aqueous phase, such as calcium carbonate, calcium sulfate, barium sulfate or calcium oxalate.

More specifically, the fiber product of the invention is essentially characterized by what is stated in the characterizing part of claim 1.

The method according to the invention, in turn, is characterized by what is disclosed in the characterizing part of claim 12.

The invention provides considerable advantages. Thus, a white surface liner can be made with a lighter surface layer so that the surface strength is not impaired. The new composite filler makes it much easier to change the proportions of the white 20 and brown layers. Because the filler content can be increased and the filler is very light, the amount of white layer can be significantly reduced. : A: Reducing the white fiber layer also allows commercial liner manufacturers to calculate the total liner weight. By way of example, the product of the invention may have a basis weight of at least about 5% by weight, preferably at least about 10% by weight, less than a surface layer of similar opacity and formation made of the same fibrous material and mineral pigment.

The filler has been found to improve the formation and stiffness of the surface layer. The filler described in FT- ··· · · '**, patent specification 100729, hereinafter also referred to as the brand name "SuperFill", is well-retained, thus reducing retention agent administration while still providing a cleaner system. Better retention also helps others

• M

optimization / reduction of dosing aids for papermaking. Purity · * · ,; promotes machine runnability and generally improves the machine's running efficiency by reducing the number of breaks · *: ···.

4117871

The present invention will now be explored in more detail with the aid of a detailed description and a few embodiments.

Fig. 1a is a side view of the principal structure of a two-layered fiber product and Fig. 1b showing the structure of a corresponding four-layer fiber product; Fig. 2 10 shows the corresponding results as a function of the tensile index, and FIG. 5 shows the bar graphs of the brightnesses of four double-layered fiber products, two having surface layers containing the filler of the invention, and two with reference fillers.

15 Filler and its preparation

As stated above, according to the invention, a composite filler comprising cellulose fibrils with light scattering pigments adhered thereto is added to the surface layer of the multilayer fiber product. The fibrils can be derived from chemical pulp or mechanical pulp or a mixture thereof. Chemical pulp, as used herein, is defined as pulp treated with cooking chemicals to delignify cellulose: V: fibers. According to a preferred embodiment, the fibrils are obtained by grinding the pulps prepared by a sulfate process or other alkaline cooking process. In addition to chemical pulps, the fibrils may also be derived from kernel ** · 25 mechanical and mechanical pulps, and typically have an average cellulose or lignocellulosic fibril thickness of less than 5 µm, usually less than 2 pm. Fibrils are characterized by one or both of the following criteria: * 30 · a. Correspond to a fraction passing through a 100 mesh sieve; and b. Have an average thickness of 0.01 to 10 µm. (preferably not more than 5 µm, preferably less than 1 µm) and an average length of 10 to 1500 µm.

ft.:;· • · ft ft · '·. ·.

• ♦ · t ft ft ft ft ft · '• · 117871 5

The starting material for the fibrils, i.e., the cellulose or other fiber-based fines, is fibrillated by means of a pulverizer. If desired, the desired fraction can be separated by a sorter, but the fines need not always be sorted. Suitable fibril fractions are the P50 -P400 screen screen fractions. Preferably, refiners with grooved blades are used.

5 · 'The light scattering material particles of the filler are inorganic or organic salts which can be formed from their starting materials by precipitation in an aqueous medium. Such compounds include calcium carbonate, calcium oxalate, calcium sulfate, barium sulfate, and mixtures thereof. The particles of material are deposited on the fibers. The amount of inorganic salt compound relative to the amount of fibrils is about 0.0001 to about 95% by weight, preferably about 0.1 to about 90% by weight, preferably about 60 to about 80% by weight based on the amount of filler and about 0.1 to about 80% by weight. %, preferably about 0.5 to 50% by weight based on the dry weight of the surface layer.

In the following, the invention is considered in particular with respect to the product 15 of U.S. Patent No. 100729, but it is clear that the invention can be applied to the other products mentioned above by appropriate modification of the light scattering pigment precursors.

The filler is prepared by precipitating a mineral pigment on the surface of fine pulp fibrils made of cellulose fiber / pulp. For example, the precipitation of calcium carbonate 20 can be accomplished by feeding an aqueous mixture of calcium hydroxide, optionally containing solid calcium hydroxide, into the aqueous fibril stock

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* "; at least partially dissolved in water containing carbonate ions. The aqueous phase may also be supplied with carbon dioxide gas which, in the presence of calcium hydroxide, produces calcium carbonate. • · 25 pearl-like aggregates of fibrils, or fine strands, are formed, with calcium carbonate crystal aggregates where calcium carbonate particles are deposited on * ··. * Fines. The fines strands, together with calcium carbonate, form pearl-like straps that resemble the pearl strands closest to the pile.

. * * ·. In water (sludge), the ratio of effective volume to mass of aggregates is very high *. compared to the corresponding ratio of conventional calcium carbonate filler • * 30. By effective volume is meant the volume required by the pigment.

The diameter of the calcium carbonate particles in the aggregates is from about 0.1 to about 5 µm, typically from about 0.2 to about 3 µm. The fibrils are essentially (at least about 55%) similar to the P50-P400 of the screen sorter.

6 117871

Such a filler is added to the surface layer of the multilayer product in an amount of 1 to 90% by weight of the fibers (dry weight), typically about 5 to 50% by weight. Typically, the disclosed filler comprises at least 5% by weight, preferably 10-100% by weight of the base web filler and 5-10-50% by weight of the base web fiber material, respectively. In principle, it is also possible to fabricate a base web whose entire fibrous material consists of filler fibrils, so that in general the present filler may comprise from 1 to 100% by weight of the fibrous material of the base web.

In the stock used to produce the topsheet, some of the filler may consist of conventional fillers, such as calcium carbonate. Preferably, however, at least 80%, particularly preferably at least 90%, of the precipitated light-scattering pigment particles are adhered to the fibrils.

15 Multilayer structure

Figures 1a and Ib show a side view of the structure of fibrous layer products having two and four layers respectively. Figure 1a shows a typical white surface liner board and Figure Ib shows a test liner.

. . The fiber product of the invention preferably has a basis weight of from about 50 to about 500 g / m 2, *. **. typically about 80-350 g / m2. Usually it has a basis weight of over 125 g / m2 but for small • * • * 11 ... p. ···. products weighing less than 100 g / m are also suitable for packaging.

• * • - ·····.

Preferably, the liner according to the invention comprises a two-layer product (see Fig. 1a) having a surface or cover layer 1 and a backing layer 2. The backing layer covers the backing layer so that the backing layer is not visible through the surface layer.

··· • · ·· ♦

It is also possible to produce three or four layer products. In principle, • * · ·. ** ·. There is no upper limit to the number of layers of 30 sandwich products, up to 5, 6 or 7, ♦ ·· * *. it is essential for the invention that the surface layer contains the ··· ** [*. filler, with the top layer covering the underlying layers, which can be made from economically advantageous raw materials.

7 117871

Of the multilayer products, the so-called "testliner" 4-layer products of Figure 1b, having a surface layer 3, a surface layer 4, an intermediate layer 5 and a backing layer 6, are to be mentioned.

5 Various raw materials may be used to make the fiber product, depending on its intended use. Both virgin and recycled fibers can be used. The virgin fiber may be derived from coniferous or hardwood (chips) or may be derived from sawdust. Particularly preferably virgin fiber pulp is used for the top layer. This is most preferably produced with sulphate soup (kraft pulp), since the sulphate soup gives 10 pulp with very high strength properties, as the name implies. The recycled fiber may be derived, for example, from used corrugated packaging (OCC) or mixed fibers. Recycled fiber is used especially for the production of test liners. The surface and backing layer (s) may be made from the same raw material or different starting fiber. If virgin fiber, such as kraft pulp, is used for both, the mass of the backing layer can be cooked in a high yield, followed by a slight refining. The top layer is made of pulp which has been cooked in a lower cup and which has also been ground in excess of the backing mass. Typically, the mass of the backing layer is boiled to about a kappa value of 30 to 70 and the mass of the top layer to less than a kappa value of 25 (kappa number of unbleached mass). The bleaching can be carried out in a manner known per se, e.g. as ECF or TCF bleaching.

♦ ♦ · • • · ““ ‘‘ ‘‘ Retention agents may be added to the stock, e.g.

• · «• · *

However, in the context of the invention, it has been found that the filler described herein provides such good retention that retention agents need not be applied to the layer or can be substantially reduced. The liner is mass or surface glued to improve moisture resistance.

* * * · «

If the raw material is low quality recycled fiber, it is preferable to use an adhesive press to produce a product having sufficient strength. According to the machine, the basis weight distribution. * ··, between the top and bottom layers is about 20/80 to .40 / 60, typically about 30/70. Thus, · * ♦ * generally has a basis weight of about 20 to 125 g / m2 (see below). According to the invention, when operating the surface layer, the basis weight can be reduced by more than 10%, up to 20% or more, without compromising the optical or mechanical properties of the lid.

··· * ·· * 4 · * The layered product is made in a manner known per se. According to a preferred embodiment, each or all of the layers are first produced from their own stock and applied to 8117871 flat wire. The layers are then felted together. As regards manufacturing technology, reference should be made to Ari Kiviranta's paper "Paperboard Grades" in Papermaking Science and Technology, Book 18, Paper and Board Grades, Fapet Oy, Jyväskylä 2000, pages 68 and 69.

5

The planar fibrous product according to the invention can be used as the top layer of various corrugated board packages. Particularly preferably, the solution of the invention is suitable for a white surface liner and a coated white surface liner, both of which are used for demanding printing jobs. These objects take advantage of the fact that the liner of the invention has a very smooth and even surface, while having high opacity and brightness. Generally, the surface layer has a basis weight of from about 20 to about 125 g / m 2, most preferably from about 50 to about 80 g / m 2, particularly preferably from about 55 to about 70 g / m 2, and bleached chemical pulp is used. In order to achieve a very good formation in the preferred embodiment of the invention, the hardwood 15 is used mainly in hardwood. Thus, for example, more than 60% by weight, typically more than 80% by weight of the fibrous material is hardwood and the rest is softwood. The fibrous material of the pulp may consist entirely of hardwood.

Conventional coating compositions may be used to coat the coated white surface layered product. The pigments may include doped calcium carbonate, calcium carbonate, calcium sulfate, calcium oxalate, aluminum silicate, kaolin (hydrous aluminosilicate), aluminum hydroxide, magnesium silicate, t ·, ···. (anhydrous magnesium silicate), titanium dioxide and barium sulphate, and mixtures of these. Synthetic pigments may also be considered. Of the above • *. ** ·. Of the pigments, the main pigments are kaolin, calcium carbonate, precipitated calcium carbonate and gypsum, which generally make up more than 50% of the dry weight of the coating composition. ·; ·· ♦ Calcined kaolin, titanium dioxide, satin white, aluminum hydroxide, sodium · * “: Silico-aluminate and plastic pigments are additional pigments and are generally present in amounts less than 25% of the dry matter of the mixture. Of the special pigments we can mention the special ones ** ··. * ··. 30 kaolins and calcium carbonates, as well as barium sulphate and zinc oxide.

• * · * * ·· * *] * · [*. Any known binders commonly used in papermaking can be used as binders for the coating composition. In addition to the individual binders, binder mixtures may also be used. Examples of typical binders include synthetic 9117871 latexes formed from polymers or copolymers of ethylenically unsaturated compounds, e.g., butadiene-styrene-type copolymers, and polyvinyl acetate having carboxyl group-containing comonomers. For example, water-soluble polymers, starch, CMC, hydroxyethylcellulose and polyvinyl alcohol may also be used as binders with the above materials. Conventional additives and adjuvants such as dispersants, admixtures, viscosity and water retention agents, lubricants, hardeners to improve water resistance, optical auxiliaries, anti-foaming agents, pH adjusting agents, and anti-pollution agents may still be used in the coating composition.

The coating composition may be applied to the web of the surface-forming material in a manner known per se. The coating can be done before felting. Preferably, however, this is done only after forming the multilayer structure. The method of coating the paper and / or board according to the invention can be carried out by conventional coating equipment, i.e., blade coating, or by film coating or by surface spraying (JET application). The coating can be done on-line or off-line.

The coating layer generally has a basis weight of 5 to 30 g / m.

The present invention has surprisingly found that not only does the filler described above improve the opacity of the surface layer, but the filled layer is also very easy to coat. The filler can be used to reduce the amount of light required * 4; ***. amount of pigment or coatings.

* 44 ·· * * 25 In accordance with the invention, the filler also significantly improves opacity.

The following non-limiting examples illustrate the invention. The 4 · a measurement results for paper properties reported in the examples are determined by the following standard methods ··; * • 44: * · *: 30 4 * ·

Surface roughness: SCAN-P76: 95: Porosity: SCAN-P60 • · * • 4

Permeability Resistance: SCAN-M8, P19 10 1 17781

Example 1 Preparation of filler

Pulp grinding 5 '.r

Birch sulphate pulp was milled with a Valmet JC-01 grinder to produce a pulp suitable for making filler. The refining consistency was about 4% and the total energy consumption was 343 kWh / t and the specific edge load was 0.5 J / m.

10 The product characteristics are given in Table 1.

Table 1. Fiber properties before and after milling

Before grinding After grinding 15

Fiber length (length), mm 0.86 0.58

Fiber length (weight), mm 1.00 0.77 20 SR ° 16 86

Carbonization of Fiber Pulp * · * · * · *: * * Carbonization was performed in tap water as disclosed in Fl Patent 100729.

An aqueous slurry of 2.22% solids was obtained. The final product had a CaCl3 content of 69.7% and a specific surface area of 10.6 m / g.

* ♦ • · · * ... * Example 2 * «« «* · 30 Fiber layers of 70% by weight of pulp of birch pulp and 30% by weight of pulp were prepared for a double-layer white liner cover layer. Various amounts of filler were added to the pulp: 13 and • ♦ · respectively 20 wt.% of the filler described in Example 1 (SuperFill), 14 and 16 wt.%, respectively, of precipitated calcium carbonate (PCC, Albacar LO, ref. 1) and 14. % chalk and 35 calcined kaolin (ref. 2).

i! π 117871

Figures 2 to 4 show the light scattering capacity of the resulting fiber layers as a function of mechanical strength properties. From the figures it can be seen that the light scattering coefficient with SuperFill filler is at least 25% and about 20% higher compared to references 1 and 2 in the constants.

It follows that the basis weight of the surface can be reduced by about 20%, which significantly reduces the cost of manufacturing the liner.

Figure 5 shows a result in which the above is still verified. The result is a liner test run on an STFI pilot-10 machine (FEX) in Stockholm, where the surface weight was reduced from a standard level of 75 g / m2 to 65 g / m2. For the experiment, a two-layer fiber structure was prepared. The ISO brightness of the product was determined.

Figure 5 shows that SuperFill 10 g / m 2 lightweighted surface layer achieves an additional 4 brightness units for 15 liners compared to Reference 2, which has a surface weight of 75 g / m 2. The result is very good, suggesting that the basis weight of the surface can be reduced by up to 10 g / m2.

* · (• · * 1 · • 1 · t · 1 · · »* 1 t · 1 * · *» »t ·« • · · · 1 ·· 1 • · • ·% ··· * · ·· 1: • 1 * ·· * · · • · · · * ··. ··.

• · • · • 1 «* • 1 · Λ • 1 ·» · »··. · '·

Claims (17)

A multilayered fiber product comprising at least two superposed liver layers (1,2; 3-6), one of which (1; 3) forming the surface layer of the product contains a filler and is lighter than that layer ( 2; 4-6), which are located below the same, and are at least substantially backpacked, characterized by the filler of the surface layer (1; 3) consisting at least partially of cellulose or lignocellulose fibrils, whereby light-scattering material particles are precipitated. Fiber product conformity with claim 1, characterized in that the filler comprises cellulose or lignocellulose fibrils made from plant fibers by grinding and sieving, the average thickness of the tibrillars being less than 5 microns. Fiber product according to claim 2, characterized in that the light-scattering material particles are deposited on fibrils, which correspond to a fraction passing a 50 mesh screen and / or whose average thickness ranges from 0.01 to 15. µm and average length to 10 - 1500 pm. Fiber product according to any of claims 1-3, characterized in: Y: that the light-scattering material particles are inorganic salts which can be formed from their starting materials by precipitation in an aqueous medium. • · * t 5. Fiber product according to claim 4, characterized in that the light-dispersing material particles are calcium carbonate, calcium oxalate, calcium sulfate, barium sulfate or a mixture thereof. : J *: 6. Fiber product according to any of the preceding claims, characterized in that it comprises a white surface or a white surface coated liner. m · * * · * · • · ·. *. 25 Fiber product according to any of the preceding claims, characterized in that its surface weight is preferably up to about 50-500 g / m, typically to • * * * · The surface weight of the surface layer is about 20 - 125 g / m2, preferably about 50 - 70 g / m2. 8. Fiber product in accordance with some of the preceding claims, characterized in that the distribution of the surface weight between the surface and the backing layers is approximately 5 20/80 ... 40/60. Fiber product according to any of the preceding claims, characterized in that the surface layer (1; 3) is made of chemical cellulose pulp containing plywood, softwood pulp or a mixture thereof. 10. Fiber product according to any of the preceding claims, characterized in that a cartoon-type backing layer comprises 1-5 layers (2; 4-6), which are made of virgin fiber or recycled fiber. 11. Fiber product according to any of the preceding patent claims, characterized in that the surface weight of the surface layer is at least about 5% by weight, preferably at least 10% by weight, less than a surface layer of corresponding opacity and formation, which is made from the same fiber material and mineral pigments. . ':; A process for producing a multi-layered fiber product, wherein a process comprising a backing layer (2; 4-6) consisting of at least one fiber layer provides an additional M: V: second, fiberglass-containing fiber layer. which forms the surface (1; 3) of the fiber product * 2 and covers the backing layer, characterized in that the surface layer (1; 3) is formed of fiber · material material which is supplied as a filler to a product comprising cellulose * 2 or lignocellulosic fibrils, where light scattering material particles are precipitated. Method according to claim 12, characterized in that a filling agent is used which comprises cellulose or lignocellulosic fibrils made from plant fibers by grinding and sieving, the average thickness of the fibrils being ♦. : 3: 25 less than 5 pm. · · 1 {* · · 2 Method according to claim 13, characterized in that a filler is used where the light-scattering material particles are deposited on fibrils, which correspond to a fraction passing a 50 mesh screen and / or whose through average thickness ranges from 0.1 to 10 pm and average length to 10 to 1500 pm. 15. A method according to any one of claims 12 to 14, characterized in that a filler is used, wherein at least 80% of the precipitated light-scattering pigment particles are adhered to the fibrils. Method according to the non-patent claims 12-15, characterized in that the surface layer is coated by means of a paper machine with a pigment-containing coating layer. • '· · · eel A method according to any of claims 12-16, characterized by the abrasive layer (1; 3) and the backing layer (s) (2; 4-6) of the image assay on a planar wire or cushioned moist. • · t · · · 1 · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · - • 1 ··· • 1 ♦ • · · «· · * · · • 1 • · • · · · • · · • · ♦ ♦ 2 '• I · 1 · {• · * • ·' '. • 1 · · · · · · · · · · · · · · · 2 · ·