BOOK PRINTING PAPER

Abstract

The present invention provides a book paper suitable for both inkjet and offset printing. The inventive printing paper comprises a base substrate with a grammage of below 100 gsm comprising at least 50 wt % mechanical cellulosic pulp fibers and having a total filler content of below 15 wt %. The substrate is surface treated with a composition comprising pigments in a range of 15-30 wt %, starch in a range of 20-40 wt %, latex in a range of 10-20 wt % and a multivalent metal salt in a range of 10-30 wt %.

Claims

1. A paper suitable for inkjet and offset printing, said paper comprising: a base substrate having a first and a second surface and a grammage of below 100 gsm, wherein said base substrate comprises at least 50 wt % mechanical cellulosic pulp fibers and a has total filler content of below 15 wt %, all percentages calculated on a total amount of solids of said base substrate, and a surface treatment composition applied on at least the first surface of said base substrate, wherein said surface treatment composition comprises pigments in a range of 15-30 wt %, starch in a range of 20-40 wt %, latex in a range of 10-20 wt %, and a multivalent metal salt in a range of 10-30 wt %, all percentages calculated on a total solid contents of said surface treatment composition, and wherein the paper has a bulk of at least 1.3 cc/g.

2. A paper according to claim 1, wherein the surface treatment composition is applied on the first surface of the substrate in an amount of less than 2 gsm.

3. A paper according to claim 2, wherein the surface treatment composition is applied on the second surface in an amount of less than 2 gsm.

4. A paper according to claim 2, wherein the Bendtsen roughness of the paper is below 1100 ml/min (ISO 8791-2).

5. A paper according to claim 1, wherein the multivalent metal salt is selected from a group consisting of: calcium chloride, poly-aluminum chloride (PAC), magnesium chloride, magnesium bromide, calcium bromide, barium chloride, calcium nitrate, magnesium sulphate, magnesium nitrate, barium nitrate, calcium acetate, magnesium acetate, barium acetate, and mixtures thereof.

6. A paper according to claim 1, wherein the pigments comprise round-like pigments,

7. A paper according to claim 1, wherein the starch is non-ionic starch.

8. A method of manufacturing a paper with a bulk of at least 1.3 cc/g and which is suitable for both inkjet and offset printing, said method comprising the steps of: providing a base substrate having a first and a second surface and a grammage of below 100 gsm, wherein said base substrate comprises at least 50 wt % mechanical cellulosic pulp fibers and has a total filler content of below 15 wt %, all percentages calculated on a total amount of solids of said substrate, applying a surface treatment composition on at least the first surface of said base substrate, wherein said surface treatment composition comprises pigments in a range of 15-30 wt %, starch in a range of 20-40 wt % latex in a range of 10-20 wt %, and a multivalent metal salt in a range of 10-30 wt %, all percentages calculated on a total solid contents of said surface treatment composition, and wherein the paper has a bulk of at least 1.3 cc/g.

9. A method according to claim 8, wherein the surface treatment composition is applied onto the base substrate by use of a film coating application.

10. The method of claim 8, wherein said surface treatment composition comprises starch in a range of 30-40 wt %.

11. The method of claim 8, wherein the surface treatment composition is applied on the first surface of the substrate in an amount of less than 2 gsm.

12. The method of claim 11, wherein the surface treatment composition is applied on the second surface in an amount of less than 2 gsm.

13. The method of claim 8, wherein the multivalent metal salt is selected from a group consisting of: calcium chloride, poly-aluminum chloride (PAC), magnesium chloride, magnesium bromide, calcium bromide, barium chloride, calcium nitrate, magnesium sulphate, magnesium nitrate, barium nitrate, calcium acetate, magnesium acetate, barium acetate, and mixtures thereof.

14. The method of claim 8, wherein the pigments comprise round-like pigments.

15. The method of claim 14, wherein the pigments comprise calcium carbonate, titanium dioxide, or both.

16. The method of claim 8, wherein the starch is non-ionic starch.

17. The paper of claim 1, wherein said surface treatment composition comprises starch in a range of 30-40 wt %.

18. The paper of claim 6, wherein the pigments comprise round-like pigments.

Description

DETAILED DESCRIPTION

[0023] The present invention provides a paper suitable for both inkjet and offset printing. In accordance with the invention, a base substrate is provided with a surface treatment composition comprising pigments, starch, latex and multivalent metal salt.

[0024] The base substrate has a grammage of below 100 gsm, preferably between 55-90 gsm, comprises at least 50 wt %, preferably at least 70 wt % or at least 80 wt % of mechanical cellulosic pulp fibers and a total filler content of below 15 wt %, or below 10 wt % (calculated on the total amount of solids of said substrate). The fillers may be e.g. inorganic fillers such as clay, talc, silica and/or calcium carbonate. In addition to mechanical pulp, the substrate may also comprise chemical cellulosic pulp fibers. It may further comprise recycled pulp, deinked pulp, coated or uncoated broke or mixture of various pulps. The cellulosic pulp fibers may be hardwood and/or softwood fibers. The substrate may further comprise further additives well known in the art for papermaking such as dyes, optical brightening agents, wet strength chemicals, strength chemicals, fixatives, biocides sizing agents, drainage and retention agent etc. In one embodiment, the base substrate comprises a total amount of internal sizing agents of less than 500 g/ton. Such low amount of internal sizing agents ensures that the water applied with the aq. surface treatment suspension is absorbed in the paper and does not interfere with the print quality.

[0025] The surface treatment composition comprises pigments in an amount of 15-30 wt %, preferably 20-30 wt %, starch in an amount of 20-40 wt %, preferably 30-40 wt %, latex in a range of 10-20 wt % and multivalent metal salt in a range of 10-30 wt %, preferably 15-25 wt %, all percentages calculated on the total solid contents of said surface treatment composition. The latex could be e.g. Styrene-Acrylate latex (SA latex) or Styrene-Butadiene latex (SB latex), preferably SB latex. The surface treatment could comprise further additives, such as 0-10 wt % or 0-5 wt % additives including but not limited to cross linkers, hardeners and dispersing agents.

[0026] The paper produced in accordance with the invention is preferably made by applying a pulp comprising cellulosic fibers and optionally additives onto a wire forming a web followed by dewatering and/or drying said web in a number of steps. The surface treatment suspension may be applied onto one or both of the surfaces of the paper web on-line or off-line the papermaking machine. The surface treatment suspension is preferably applied onto one or both of the surfaces of the paper web by use of any well-known coating methods, such as blade coating, film coating, curtain coating, spray coating etc. Preferably, film coating technologies is used. The surface treatment suspension may be applied on one or both sides of the paper in an amount of less than 2 gsm, or less than 1.7 gsm or even less than 1.5 gsm. The surface suspension is preferably applied at a consistency of 2-50 wt %, more preferably 7-20 wt %.

[0027] The bulk is defined as the thickness (ISO 534) divided with the grammage (ISO 536). The bulk of the paper according to the invention is at least 1.3 cc/g, or preferably at least 1.5 cc/g or 1.7 cc/g.

[0028] The Bendsten roughness as used in the claims and throughout the description is measured in accordance with ISO 8791-2.

Example

[0029] A trial was performed to evaluate the printing properties of the paper of the invention.

[0030] As a base substrate, an uncoated paper with a grammage of 70 gsm, comprising 87 wt % of mechanical pulp, 10 wt % of chemical pulp and 3 wt % fillers were used. A surface treatment composition was prepared in accordance with table 1, “surface treatment composition 1”.

TABLE-US-00001 TABLE 1 Surface treatment composition 1 Raw material [6% dry weight] REF SB Latex 16.0% 13.0% Starch 39.5% 12.5% Calcium carbonate 24.0% 74.0% Calcium chloride 20.0% 0.0% Dispersing agent 0.5% 0.5% and hardener

[0031] The base substrate was coated with said surface treatment composition in an amount of 2 gsm/side by use of film coating.

[0032] As a reference, the same base substrate was coated by coating color containing starch, latex, calcium carbonate, dispersant agent and hardener, “REF” in table 1. Application amount was 2 gsm/side by use of film coating.

[0033] Samples of the surface treated substrate of the invention and samples of the reference were printed by Albert Frankenthal A 101 S HSWO press and Sunmag HV ink serie at KCL and Kodak Prosper S10 4 color inkjet engine by using Prosper S-serie pigment inks. Speed was 50 m/min, droplet size 12.3 pl and resolution 600×600 dpi. The dusting tendency of the offset printed paper and the print quality of both the offset and inkjet printed samples of the invention (offset printed paper A and inkjet printed paper B) as well as that of the reference samples (offset paper ref. and inkjet paper ref.) were evaluated. The results and test methods can be seen in table 2.

TABLE-US-00002 TABLE 2 Offset Offset Inkjet Inkjet printed* printed* printed printed Ref. Paper A Ref. paper B Dusting tendency in 17.6 12.6 Not Not offset printing after evaluated evaluated 15000 printed copies in the 1.sup.st unit(black), summary of ink and water areas (ts + bs), [g/m.sup.2] Mottling Cyan 50% 5.7 5.6 4.6 4.6 Print density NA NA 1.2 1.7 [K100] Bleeding sharpness, NA NA 0.78 0.38 [mm.sup.2] Bulk [cm.sup.3/g] 1.8 1.8 1.8 1.8 Bendtsen roughness 320 390 320 390 [ml/min] Caliper [mm] 128 128 128 128 *15 000 copies printed

[0034] The print mottling was measured by use Pap Eye mottling measurement at KCL. The print density was measured by ISO 13655M1. The roughness was measured by using ISO 8791-1.

[0035] As can be seen in table 2, the inventive concept gives rise to a paper that gives excellent print qualities when printed with inkjet printing and offset as well as low dusting tendency in offset heat set printing.