A KRAFT LINER IN MULTI-LAYER CONSTRUCTION

Abstract: A presentation liner, i.e. a kraft liner, comprised of several layers, preferably of 2-3 layers, wherein from 50-100 % of the pulp forming the top layer consists of a bleached hardwood sulphate pulp which contains no chlorine chemical and to which there is added 0-15 % pigment, calculated on absolutely dry pulp. The remainder of the pulp forming the top layer is comprised of unbleached softwood sulphate pulp or of bleached softwood sulphate pulp that contains no chlorine chemical. The top surface of the liner has a luminance (Y-value, SCAN-method P 8:75) of 45-85 %, or measured as brightness 32-85 % (SCAN-method P 3:75).

Description: A Kraft Liner in Multi-layer Construction The present invention relates to a presentation liner, i.e. a kraft liner, in multi-layer construction. By presentation liner is meant an improved liner quality which gives good printability with respect to reproduc¬ tion, and uniformity in print, brilliance, contrast and sharpness. Presentation liners are used when desiring high print quality, half-tone print and multicolour print. The liner is also used for printing bar codes and informa¬ tion which includes small type faces. A presentation liner shall have a high degree of smooth¬ ness, adapted luminance, uniform absorption and a high degree of purity. Kraft liners which form the flat sheets in corrugated fibreboard, also referred to as facing paper, are traditionally produced primarily from kraft pulp in two or three layers to a surface weight of 2 100-440 g/m and are included generally in kraft papers. Kraft liners, or facing papers, are normally produced from softwood sulphate pulp and hardwood sulphate pulp, the composition of the pulp depending on the particular requirements of a given pulp quality. Hardwood pulp provides a better surface than softwood pulp, and is slightly cheaper than softwood pulp. It is also known to admix secondary fibres in kraft liners, in at least one layer, wherein fine printing waste is normally used as a starting material. The Swiss Patent Specification CH 633 482 describes a method of manufacturing high strength outerply for corrugated board, i.e. a liner which is comprised of at least two layers, of which one layer is a waste paper semimanufacture, while the other layer, or the other layers, is/are produced from chemimechanical softwood pulp (CMP) . It is said that this method of manufacture will reduce drastically or completely obviate the use of kraft pulp or kraft recycled fibres, and therewith improve the use of the wood starting material. The patent specification also describes as part of the known art a method of extending kraft pulp with a modi¬ fied ther omechanical pulp (MTMP) or with a chemithermo- mechanical pulp (CTMP) respectively. As before mentioned, the present invention relates to a so-called presentation liner, i.e. a kraft liner, which is characterized in that the liner comprises a plurality of layers, preferably 2-3 layers, in that from 55-100% of the pulp forming the outer layer or layers is com¬ prised of a bleached hardwood sulphate pulp which is free from chlorine chemical and which includes an addi¬ tion of 0-15% pigment, e.g. calcined clay, said concen¬ trations being calculated in percent on absolutely dry pulp; and in that the remainder of the pulp in the outer layer (the top layer) is comprised of unbleached soft- wood sulphate pulp or of bleached softwood sulphate pulp that is free from chlorine chemicals. It has been found that the outer layer (top side) of the inventive liner has a luminance (Y-value, SCAN-method P 8:75) of 45-85%, or expressed as brightness 32-85% (SCAN-method P 3:75). According to one particular embodiment of the invention, at least 80% of the hardwood pulp in the top layer consists of birch. The hardwood pulp may be bleached with oxygen in one or more stages, or bleached in known combinations of oxygen and peroxide stages. ( The surface weight of the outer layer, or top layer, is ♦ 2 preferably from 30-90 g/m and the pulp which forms this 5 layer is preferably refined to a degree of refinement of 20-40 SR. According to one particular embodiment of the invention, the pulp in the remaining layers of the liner consists 10 of unbleached softwood sulphate pulp in mixture with 0- 10% unbleached hardwood sulphate pulp and 0-50% recycled fibres. The surface of the top layer preferably has a Bendtsen roughness number beneath 1000 ml/min. (SCAN-P 21:67) . 15 Example A liner according to the present invention was produced with existing machinery and by means of generally tradi- 20 tional techniques. The liner comprised two layers, of which the top layer was produced from oxygen-gas bleached hardwood sulphate pulp (> 80% birch) with kappa number 12. The pulp was purchased from another manufac¬ turer. The pulp was clean and had been refined to SR- 25 number 24-25. The top layer had a surface weight of 2 about 60 g/m . The base layer was produced from softwood sulphate pulp having a kappa number of about 75. The pulp was refined 30 to an SR-number of about 21-22, with the addition of 10% recycled corrugated fibreboard pulp. The manufactured product had a total surface weight of 2 186 g/m . The Bendtsen roughness number (SCAN-P 21:67) 35 was below 1000 ml/min. and the luminance of the presen¬ tation liner was 54% (Y-value, SCAN-P 8:75).

Claims: Claims 1. A presentation liner in multi-layer construction, preferably a construction consisting of 2-3 layers, c h a r a c t e r i z e d in that the top layer is formed from pulp of which 50-100% is comprised of hard¬ wood sulphate pulp free from chlorine chemicals and admixed with 0-15% pigment, e.g. calcined clay, calcu- lated on absolutely dry pulp; in that the remainder of the pulp forming the top layer consists of unbleached softwood sulphate pulp or of bleached softwood sulphate pulp free from chlorine chemicals; and in that the top surface of the liner has a luminance (Y-value, SCAN- method P 8:75), of 45-85%, or measured as brightness of 32-85% (SCAN-method P 3:75). 2. A liner according to Claim 1, c h a r a c ¬ t e r i z e d in that the top layer is comprised of pulp in which more than 80% of the hardwood consists of birch. 3. A liner according to Claim 1, c h a r a c ¬ t e r i z e d in that the hardwood sulphate pulp has been bleached with oxygen in one or more stages. 4. A liner according to Claim 1, c h a r a c ¬ t e r i z e d in that the hardwood sulphate pulp has been bleached in a combination of oxygen and peroxide stages. 5. A liner according to Claim 1, c h a r a c ¬ t e r i z e d in that the top layer has a surface 2 weight of 30-90 g/m . 6. A liner according to Claim 1, c h a r a c ¬ t e r i z e d in that the pulp in the top layer has been refined to 20-40 SR. 7. A liner according to Claim 1, c h a r a c ¬ t e r i z e d in that layers other than the top layer are formed from unbleached softwood sulphate pulp and 0-10% unbleached hardwood sulphate pulp and 0-50% recycled fibres. 8. A liner according to Claim 1, c h a r a c ¬ t e r i z e d in that the top layer has a Bendtsen roughness number beneath 1000 ml/min. (SCAN-P 21:67). AMENDED CLAIMS [received by the International Bureau on 22 June 1992 (22.06.92); original claim. 1 amended; other claims unchanged (2 pages)] 1. Λ presentation liner in multi-layer construction, preferably a construction consisting of 2-3 layers, c h a r a c t e r i z e d in that the top layer is formed from pulp of which 50-100% is comprised of bleached hard¬ wood sulphate pulp free from chlorine chemicals and admixed with 0-15% pigment, e.g. calcined clay, calcu- lated on absolutely dry pulp; in that the remainder of the pulp forming the top layer consists of unbleached softwood sulphate pulp or of bleached softwood sulphate pulp free from chlorine chemicals; and in that the top surface of the liner has a luminance (Y-value, SCΛN- method P 8:75), of 45-85%, or measured as brightness of 32-85% (SCAN-method P 3:75). 2. Λ liner according to Claim 1, c h a r a c ¬ t e r i z e d in that the top layer is comprised of pulp in which more than 80% of the hardwood consists of birch. 3. Λ liner according to Claim 1, c h a r a c ¬ t e r i z e d in that the hardwood sulphate pulp has been bleached with oxygen in one or more stages. 4. Λ liner according to Claim 1, c h a r a c ¬ t e r i z e d in that the hardwood sulphate pulp has been bleached in a combination of oxygen and peroxide stages. 5. Λ liner according to Claim 1, c h a r a c ¬ t e r i z e d in that the top layer has a surface 2 weight of 30-90 q/m . 6. A liner according to Claim 1, c h a r a c ¬ t e r i z e d in that the pulp in the top layer has been refined to 20-40 SR. 7. A liner according to Claim 1, c h a r a c ¬ t e r i z e d in that layers other than the top layer are formed from unbleached softwood sulphate pulp and 0-10% unbleached hardwood sulphate pulp and 0-50% recycled fibres. 8. A liner according to Claim 1, c h a r a c ¬ t e r i z e d in that the top layer has a Bendtsen roughness number beneath 1000 ml/min. (SCAN-P 21:67)

Inventors: BACKLUND STURE, DOELLING RAGNHILD, HAGEN NILS, BACKLUND, STURE, DOELLING, RAGNHILD, HAGEN, NILS
Applicants: SCA NORDLINER AB
Application year: 1992
Main classification: D21H27
IPC codes: D21H11, D21H17, D21H27