SE511954C2 - Liner board - comprises a sulfate pulp surface layer with a specific basis weight and at least one short recycled fiber layer with a specific basis weight and Ambertec formation value - Google Patents

Abstract

The liner board includes a sulfate pulp surface layer with a specific basis weight and at least one short recycled fiber layer with a specific basis weight and Ambertec formation value. - An uncoated, non-bleached liner board material with a brightness value of less than 40 % and a basis weight of at least 100 g/m2 is made from sulfate pulp and recycled fiber, and comprises at least two layers. At least one of the surface layers has a basis weight of at least 20 g/m2 and comprises sulfate pulp with a maximum fines content of 2.5 %, and at least one of the other layers contains recycled fiber with a length of at least 0.9 mm, containing 3.5-12 % fines. The recycled fiber layer(s) comprise(s) at least 60 wt.% of the board basis weight. The maximum Ambertec formation value is 0.8 g/m for basis weights less than 150 g/m2, and 0.9 g/m for basis weights of 150 g/m2 and above. The liner board density is at least 700 kg/m3.

Description

10 15 20 25 30 511 954 2 The best test liner products indicate that sulphate substitutes provide better conditions for one good surface. Linerboard with a top layer of bleached pulp generally shows better surface roughness values than the best values for unbleached sulphate pulp. Too many applications however, the use of bleached pulp results in too expensive products. Another disadvantage is that the bleaching impairs the mechanical properties. You can also mix in the filling means to improve the surface properties, but it has a negative impact on the technical characteristics. Although sulphate pulp has a better surface roughness potential, it is also clear that by the use of sulphate pulp does not automatically obtain good surface properties. Firewood- the impact has an impact and in addition the process conditions interact with the raw material in a complex way.

The purpose and most important characteristics of the invention The object of the present invention is to provide an uncoated bleach linerboard, ie a lurninance <40% with a basis weight of at least 100 g / mz and with a high return content, which at the same time has an improved surface roughness. The linerboard shall in addition the good printability properties show good mechanical strength values.

This has been solved by at least one of the outer layers having a basis weight of at least 20 g / mz and contains sulphate pulp and has an ash content of not more than 2.5%, that at least one of the other layers contain return bers with a length of at least 0.9 mm and has an ash content between 3.5 and 12%, that the layer (s) with return fi ber represents at least 60% of the total basis weight of the linerboard and that the linerboard has a foundation number according to Ambertec at most: 0.80 v / g / m for basis weights <150 g / mz, 0.90 x / g / m for basis weights z 150 g / mz, and that the linerboard has a density of at least 700 kg / m3.

By utilizing the formation potential of the return mass with its relatively short fibers, and in that the layers with returnable content represent a major part of 10 15 20 25 30 511954 3 product, a good formation can be achieved in the product. A good formation reflects one even local basis weight distribution in the sheet, which is a prerequisite for a high evenness in the structure which in turn is a condition for good printability properties. A good forma- tion can also, depending on how it has been achieved, be related to good mechanical properties.

With a well-shaped and clean surface layer of sulphate pulp, conditions are provided at the same time for one low surface roughness and satisfactory mechanical properties. Furthermore, one is satisfactory density level a prerequisite for good surface properties and a high utilization of strength.

Thus, the density should be at least 700 kg / m3.

Preferably, the linerboard has a surface roughness according to Bendtsen of at most: 600 ml / min for basis weights <150 g / mz, 700 ml / min for basis weights 150-200 g / mz, 800 ml / min for basis weights> 200 g / mz.

Description of drawings F ig. 1 shows the formation number over the web width of a linerboard according to the invention prepared according to the examples presented below.

F ig. 2 shows the density over the web width of the same linerboard.

Fig. 3 shows the surface roughness over the web width of the linerboard.

Description of figures The measurement methods intended for determining those in the claims and the description specified parameters are: -Luminance (Y-value): SCAN P 43:95; Ash content: SCAN C 6:62; measured on the finished product after separation of the individual layers.

-Density I SCAN P 7:75; -Surface: Bendtsen's methodology according to SCAN P21: 67; -Formation figures: Direct emission of beta radiation according to the Ambertec method (Komppa, A. (1990), "The formation of paper and the measurement of formation", lO 15 20 25 511 954 4 Paper and Puu 72 (6): 566). The measured values specified in this document have been measured according to standard procedure with 3.5 mm center distance between the network points.

-Compression index (geometric mean in MD and CD): SCAN P 46:83; -F iberlength (length-weighted mean): T271 cm-98, eñer separation of the individual layers and folding.

The linerboard is manufactured by layering in two or two layers, with one or two surface layer consisting of sulphate pulp and one or fl your layers consisting mainly of returns and committees. Preferably, at least 80% of the dry weight is in the return layer (-n) of returns fi brers and committees fi from production. The generally shorter fiber length of recycled pulp compared to in particular softwood sulphate pulp gives a better formation potential, making it easier to achieve the critical foundation numbers for the linerboard.

However, the choice of forming technique is critical. At the same time, the economic and environmental benefits. However, it should be noted that in order to obtain sufficient good strength potential should use returns of good quality, preferably well return. MAN can, however, note that technical recyclable grades have higher ash contents than sulphate plenty. The ash content should not exceed 12% and the berl length should be at least 0.9 mm.

The return layer (-n) is formed by double wire roll forming or double wire roll forming. blade forming for good formation and advantageous mechanical properties obtained. The headbox concentration should be less than 0.9% (SCAN-C 17:64), preferably 0.7% or less.

For the sulphate layer (-n) sulphate pulp made of fi bres with a fi basis weight per length unit of not more than 200 mg / km (T 234 cm-82) for a satisfactory surface roughness, density and formation potential. Sulphate pulp made from Scandinavian pine, spruce and / or birch is favorable in this respect. The sulphate mass should not have been dried, as drying reduces the strength potential. 10 15 20 25 30 5 'I 1 9 5 4 5 In particular, the pulp used for the top layer should undergo a tailored and sufficient grinding in view of the structural pairs formation and density as in its turn is reflected in the surface roughness and the mechanical properties. For example, a speci fi k can load of 2 Ws / m and a net energy of 100 kWh / ton is applied during a grinding of a child's nose in a conquest. The degree of grinding of the top layer mass should be at least 18 SR (SCAN-C 19:65).

The sulphate layer is formed at a low concentration, preferably below 0.5% (weight concentration ration) to obtain a good formation and at the same time a high utilization of strength of mass. From a strength / formation point of view, double wire roll forming or fourdririiertekiiik.

The sulphate layer is formed to obtain maximum layer purity, which requires one high-grade separation of the backwater fi from the layer (s) containing return mass, which in in turn requires separate backwater systems (short circulations) in the paper machine. One high-grade layer purity further presupposes that the sulphate layer (-n) is dewatered by a clean wire from the return layer.

After molding, the pressing is performed in a pressing section with two or two nips, where at least a nip is a shoe press nip to obtain sufficient density potential and thus satisfactory surface roughness and strength utilization.

During the subsequent drying, a high return ratio contributes to a reduced one cross-shrinkage of the paper web, since recycled fibers generally have a lower shrinkage tendency than never dried sulfate mass. A low cross-shrinkage is favorable for a low one surface roughness.

After pressing and drying, the linerboard is calendered in one or more nips. IN in case a hard nip formed by two steel cylinders is used, the line load should preferably be over 70 kN / m. With a good foundation, a favorable result of the calendering is obtained. 10 15 20 25 511 954 6 In addition to the good printability properties, the linerboard should also show good results mechanical strength values. Thus, the geometric mean of the compression index in MD and CD be at least 20 kNm / kg, preferably at least 22 kNm / kg.

Example The connection is exemplified here with a linerboard with a basis weight of 177 g / mz, manufactured on a full-scale machine by SCA Packaging Obbola. It should be noted that it is industrial easier to achieve low formation numbers and surface trawl values at lower basis weights, as one as it can operate more easily at low feed concentrations at acceptable production levels.

F ormningsselcrionen The supply section consisted of two separate drainage units, a double-wire roller blade. forms for the base layer and a mini-fourdririíer for the top layer.

The top layer consisting of unbleached softwood sulphate pulp had a basis weight of 35 g / m 2. The base layer which 90% consisted of recycled fibers and committees and the rest unbleached sulphate pulp, had basis weight 142 g / mz.

The table below presents the conditions regarding the stocks and the form.

Chart. Stocks and shaping Chemicals No retention additives or strength additives. Hydrophobing only Malgrad top layer 14 SR * Malgrad bottom layer 38 SR Forming concentration, top layer 0.3% Forming concentration, bottom layer 0.9% Wire speed 500 m / min 10 15 20 25 511954 a higher level of nialgmden should have given even better results Press section The press section had three nips, a double salted nip followed by a single salted nip which in in turn was followed by a double-salted shoe press pinch.

T orksection The drying section was a conventional cylinder drying section.

Smoothing The smoothing was performed in a nip with two steel cylinders where the line load was 70 kN / m.

The winding speed was 516 m / min.

Compression strength S C T, geometric mean Drum average: 23.1 kNm / kg Ash content Base layer 5.0%, top layer 1.3%.

F iberlängcil, bass layer Length-weighted average value: 1.4 mm Formation numbers, density values and surface roughness values fi are given by the attached Figs. 1-3.

As can be seen from the fi gures, these values show a certain variation across the web width.

The deviation in the outermost edge portions of the web is particularly large, which is well known fact. It should therefore be pointed out that approx. ch of web width along each edge portion when calculating the various parameter values specified in patent claims and description text.

Claims (8)

10 15 20 25 30 35 511 954 8 Patent claims Uncoated unbleached linerboard with a luminarx <40%, a basis weight of at least 100 g / mz and made of sulphate pulp and return fi spreads in at least two layers, characterized in that at least one of the outer layers has a basis weight of at least 20 g / mz and contains sulphate pulp and has an ash content of not more than 2.5%, that at least one of the other layers contains return fi brer with a fi length of at least 0.9 mm and has an ash content between 3.5 and l2 ° / 0, that the layer (s) with return fi brer represents at least 60 % of the total basis weight of the linerboard and that the linerboard has a formation number according to Ambertec of not more than: 0.80 Jg / m for basis weights 0.90 t / g / m for basis weights 2150 g / mz, and that the linerboard has a density of at least 700 kg / m3. Uncoated linerboard according to Claim 1, characterized in that the linerboard has a surface roughness according to Bendtsen of at most: 600 ml / min for basis weights 700 ml / min for basis weights 150-200 g / m 2, 800 ml / min for basis weights> 200 g / m 2 . Uncoated linerboard according to Claim 2, characterized in that it has a surface roughness according to Bendtsen of at most: 550 ml / min for basis weights 650 ml / min for basis weights 150-200 g / m 2, 750 ml / min for basis weights> 200 g / m 2 . 4. An unobstructed linerboard according to claim 3, characterized in that it has a surface roughness according to Bendtsen of at most: 500 ml / min for basis weights 600 ml / min for basis weights 150-200 g / m 2, 700 ml / min for basis weights> 200 g / m . 10 15 20 25 511 954 9 Uncoated linerboard according to one or more of the preceding claims, characterized in that it has an Ambertec formation number of not more than: 0.75 t / g / m for weights <1000 g / m 2 0.85 x / g / m for basis weights z 150 g / m 2 . Uncoated linerboard according to one or more of the preceding claims, characterized in that it has a geometric mean compression index in MD and CD of at least 20 kNm / kg. Uncoated linerboard according to claim 6, characterized in that it has a geometrical mean compression index in MD and CD of at least 22 kNm / kg. Uncoated linerboard according to one or more of the preceding claims, characterized in that the ñbrema in the return fi top layer has a fiber length of at least 1.1 and preferably at least 1.3 mm.