SE500472C2 - Printing paper overcoming problem of fluffy appearance - comprising coating on one of base paper produced from pulp-fibre mixt. consisting of exchange pulp - Google Patents

Abstract

The paper is coated at least on one side, and comprises a base paper with a surface wt. of 35-65 g/m2 produced from a pulp- fibre mixt. comprising high exchange pulp, with an exchange exceeding 80 per cent, and with a freeness in the formation of the paper of 25-350 CSF, chemical pulp, and a coating layer with a surface wt. of 5 - 18 g/m2. The high exchannge pulp is produced from timber which up to at least 90 per cent comes from the genus Populus (poplar). The coating layer is formed by a layer with a synthetic and/or natural binder of 7 - 25 parts per 100/parts pigment, and with a content of wet strength medium of 0.1-1 part per 100 parts pigment.

Description

Prior Art Said base paper is usually made from a stock containing; 1) chemical pulp in an amount of 30-70% (w / w) and 2) high-yield pulp in an amount of 70-30% (w / w).

An example of a suitable chemical pulp is bleached long-fiber sulphate pulp, such as pine sulphate pulp. Other chemical pulps, such as bleached or unbleached sulphite pulp, can also be used.

By high-yield pulp is meant pulps with a yield in excess of 80%. Examples of such pulps are abrasive pulp (GW), pressure abrasive pulp (PGW and Super-PGW), thermomechanical pulp (TMP), refiner pulp where the wood is impregnated with alkaline peroxide (APMP) and chemithermomechanical pulp (CTMP). Usually the said masses of long-fiber wood are produced, i.e. softwood, for example in the form of spruce.

The two types of pulp give the base paper special properties. The chemical pulp contributes in the first place to reinforcing the paper. i.e. give it sufficient strength leading to good runnability of both the paper machine and the coating plant and in subsequent printing. The high yield pulp is added to give the paper high bulk and high opacity.

As for the chemical pulp, it is always ground before the paper is formed. In most cases, the high-yield pulp is also ground before the paper is formed, and usually the pulps are ground together, although it is possible to grind them separately. As for the high yield pulp, it is important that it has a freeness of 25-350 ml CSF measured according to SCAN-C 21:65, (which method applies to all freeness values specified in this patent application) when forming the paper. If the high-yield pulp already has a pulp within this range when it leaves the pulp mill, the pulp in question does not need to be ground, even if it is possible to do so, especially at high freeness values within the specified range.

In addition to the previously stated quantitatively, the ingredients dominated 1 the base paper, i.e. cellulose pulp and fillers, are included in varying amounts, for example retention aids, adhesives, alkalis and dyes. 10 15 20 25 30/1 -. ~ _- ~ a f f; il: r k All these ingredients are thus included in the stock which is fed to the paper machine via the headbox, whereupon the base paper is formed.

After the base paper is finished. including dried to a dry content in the range 93-96%, the paper is coated, usually on both sides, with a batter.

Very varied batter recipes were used in practice and examples of ingredients are pigments. binders and minor additives, including, for example, a dye.

Disclosure of the Invention Technical Problem Coated papers of the type described above have a number of disadvantages, primarily caused by the high-yield pulp part, since it is usually made of wood with long and rigid fibers. A problem is that a relatively large number of fibers rise from the plane or surface of the paper when handling, for example moistening, the paper. For example, in offset printing and when a large amount of color is used, said fiber erection gives the printed paper surface a fuzzy and slightly frizzy impression. By increasing the amount of coating paste, expressed for example in g / m2, the printing properties of the paper can be improved. However, this means that the manufacturing cost of the coated paper increases and further the flexural stiffness of the paper is negatively affected if the amount of smear applied is too large in relation to the amount of cellulosic pulp fiber. The coated paper becomes slippery and its runnability in, for example, printing presses deteriorates.

The Solution The present invention is a solution to the said problem and relates to paper coated on at least one side, comprising base paper in a basis weight of 35-65 g / m 2 prepared from 10 ø-Ary - ,,., V; ... u -.f-'J - <1 I »3:» Lf. a pulp fiber mixture consisting of high yield pulp, with a yield exceeding 80% and with a freeness in the formation of the paper of 25-350 ml CSF, and chemical pulp and a coating layer having a basis weight of 5-18 g / m 2, characterized in that the high-yield pulp contained in the paper is made from wood, which at least 70% comes from tree species belonging to the Populus family (poplar genus).

Examples of such tree species are aspen, hybrid aspen and poplar.

When producing high-yield pulp, it is not uncommon to use several types of wood, including both hardwood (eg birch, beech, etc.) and softwood (eg spruce, pine, etc.). For the production of the paper according to the invention, it is necessary that the pulp part of the cellulose pulp fiber mixture comes from trees to at least 70% of the fibers in the high-yielding poplar genus.

As for the chemical pulp, any such can be used for the manufacture of the paper according to the invention. However, a semi-bleached or fully bleached softwood sulphate pulp with a brightness of at least 80% ISO is preferred. Bleached or unbleached sulphite pulp can also be used. As for the quantitative ratio in the paper between high-yield pulp and chemical pulp, it can be varied mainly according to the prior art, for example of 100 parts, 30-80 parts can consist of high-yield pulp. The properties of the paper are improved with an increasing proportion of aspen fibers in the high-yield pulp part of the cellulose pulp fiber mixture, and it is preferred that at least 90% of the high-yield pulp fibers come from tree species belonging to the Populus family.

The stock from which the base paper is formed contains, in addition to the specific cellulosic pulp mixture specified above, traditional ingredients such as fillers, binders, dyes and alkalis. crayons and clays of various kinds. If, for example, a clay retention aid, Examples of fillers are of some kind used as fillers, it usually only needs to be added explicitly (even then) at the start of papermaking, because after the coating plant is running so As a rule, the committee arising from the coated paper is involved in the stock which is introduced into the paper machine and in this way a part of the clay applied during the coating is recovered and constitutes a filler in the base paper production.

The paper according to the invention has a brightness. measured according to SCAN-C 17:75, which exceeds 75% ISO and preferably exceeds 78% ISO. With an increasing proportion of aspen fibers in the high-yield pulp, it is possible to achieve high brightnesses of the finished coated paper.

The properties of the paper (including its lightness) are also affected in addition to the thickness of the coating layer, for example expressed as basis weight in g / m2. of the coating layer composition and therefore it is suitable that the coating layer is formed of a batter with a content of synthetic and / or natural binder of 7-25 parts per 100 parts of pigment and with a content of wet strength agent of 0- 1.5 parts per 100 parts of pigment and it is preferred that the coating layer is formed of a batter with a content of synthetic and / or natural binder of 9-20 parts per 100 parts of pigment and with a content of wet strength of 0.1-1 part per 100 parts pigment. Examples of pigments are crayons and clays of various kinds. In addition to the ingredients listed above, the batter may contain harder and more dye.

The coated paper according to the invention can then be post-processed, for example calendered to achieve the desired gloss of the paper.

Advantages The paper according to the invention has several advantages.

By, for example, offset printing of the paper according to the invention, it has been found possible to obtain a good printing result even on surfaces with a large amount of color. The problems with fiber rising of this type of paper have greatly reduced- At the same time the paper according to cerats. For example, the drivability of the invention in, for example, printing presses is good as a result of the fact that the specific cellulosic pulp fiber mixture contained in the paper allows the use of a comparatively thin coating layer.

Prior art problems with the brightness and brightness stability of paper of this type can be largely eliminated by the paper according to the invention.

Best Embodiment Two exemplary embodiments are presented below, and in connection with these, more precise information is given about the structure of the paper according to the invention.

Example 1 In order to evaluate the printing properties of both the paper according to the invention and a traditional paper, base papers of both types have been manufactured at a Swedish paper mill and both papers have subsequently been coated in a pilot coater at a Swiss company.

Both base papers were prepared on the same paper machine and in the preparation of the paper according to the invention the pulp fiber mixture consisted of: a) 70% chemithermomechanical pulp (CTMP) made from exclusively aspen wood with a freeness of 235 ml CSF and with a brightness of 84.0% ISO b) 30% bleached pine sulphate pulp with a brightness of 90.0% ISO c) 8% filler in the form of clay (English China Clay) with the trade name SPS.

Normally the filler is not included in the pulp fiber mixture, ie. in the pulp suspension that was subjected to a first grinding step. In these two cases the addition of the filler took place before the first grinding step and therefore the filler c) is indicated here as part of the pulp fiber mixture. In the preparation of the traditional paper, the pulp fiber mixture consisted of: a) 70% spruce pulp with a freeness of 63 ml CSF and with a brightness of 78.5% ISO b) 30% bleached pine sulphate pulp with a brightness of 90.0% ISO c ) 8% filler in the form of clay (English China Clay) with the trade name SPS.

As can be seen, there is agreement on points (b) and (c) of the pulp fiber mixture, while there is a difference in point (a).

In both cases, dried pulp in the form of bales was used and a number of bales with a uniform weight of the respective pulp type (in the ratio 7 to 3) were stored in a bale dissolver. The filler was also added to the bale dissolver.

The respective pulp fiber mixture including the filler was ground in two steps, first in a grinder i. Mainly immediately after beating and mixing and then, after the addition of the substances listed below, 1 a grinder (machine grinder) before the introduction of the resulting stock on the paper machine, with a total energy input of 90 kWh / ton of pulp of the pulp fiber mixture for the production of the paper according to the invention and 120 kWh / ton of pulp of the pulp fiber mixture for the production of the traditional paper. Said amounts of energy were controlled from a certain numerical value by the vacuum in the gusma roller at the beginning of the paper machine.

The final stock was completed in each case by adding the following substances in specified amounts.

Retention aid in the form of cationic polyacrylamide with the trade name Polymin KE 40 = 0.l2% Stock glue of the trade name Aquapel = l.0% Starch of the trade name Empressol NE 25 = 0.63% Sodium bicarbonate = 0.35% Dyes of the trade names Levanyl violet BNZ Eisenoxydschwarz 31 250 ml / ton paper 280 g / ton paper 17 g / ton paper 10 15 20 25 30 The percentages given above refer to the percentage of the dry weight of the cellulose pulp fiber mixture in the stock.

Said sieve with a pH of 7.5 was introduced at each time via the inlet drawer on the paper machine. The machine speed was 390 m / minute and the basis weight of the paper in dried and conditioned form was 40 g / m2. Two paper rolls (tamboures) with a weight of 3 tons were driven by each quality. The first roll 1 and case, respectively, were advanced to achieve equilibrium in the paper machine, and said roll was not further processed.

A roll of paper of each quality was transported to the previously mentioned pilot coater. on each side of the respective paper, a coating layer of a basis weight of 12 g / m2 was applied in dried and conditioned form.

The coating batter consisted of the following components: Pigment; 70 parts of chalk with the trade name Hydrocarb 90 MH and 30 parts of clay with the trade name Hydragloss E powder Binder; 10 parts styrene butadiene latex with the trade name Dow DL 685 and 0.5 parts carboxymethylcellulose with the trade name CMC FF5 and 0.5 parts polyvinyl alcohol with the trade name Polyviol LL 603.

Otherwise, the batter contained 0.6 parts harder of the urea formaldehyde resin type with the trade name Urecoll S and 0.0025 parts of a dye with the trade name Levanyl violet BNZ.

The dry matter content was 68% and the pH was adjusted with sodium hydroxide (NaOH) to 9.0.

The basis weight of the coated papers was thus 40 + 2 x 12 = 64 g / m 2.

The two papers were then calendered in a pilot calendar at a speed of 400 m / min. The line pressure was 130 kN / m and the temperature was 8S ° C. 10 15 20 25 30 35 '-0 (i I (f) C) f »l" J The brightness of the paper according to the invention in calendered form was 80.6% ISO, while the brightness of the calendered traditional paper was 77.5% ISO. An aging test was also performed and consisted of irradiating the papers with light from a xenon lamp for 2 hours The paper according to the invention lost 3.2% units in brightness, lost 3.6% units in brightness.

The paper according to the invention was test printed together with the paper of traditional composition and a commercial LWC paper available on the market in a roll-offset printing press of the Zirkon brand from the company Polygraph in Leipzig. The printing press was equipped with a hot air drying system with subsequent cooling rollers from the company Butab. while the reference paper Falsverket after the printing press was also of the 'Zirkon' brand.

The color sequences at the time of printing were black, cyan, magenta and yellow. Manufacturer of the colors. which were of the heat-set color type, was the Hartmann company. Product numbers for each color were 808-9201 (black), 805-9200 (cyan), 801-9173 (magenta) and 803-9198 (yellow). The moist water in the dye plants contained 4% moisture concentrate with the trade name HET 86 from the company Nordic AB. The color densities were adjusted manually by the operators after visual assessment against a model.

A subjective ranking of the printed samples was performed and showed good printing properties for all papers.

The paper according to the invention showed the smoothest printing surface coupled with the least tendency to fiber rise. In the case of paper produced in the traditional way, the fiber rise was much more marked. The commercial reference had the most marked surface structure and thus the most fiber erection.

The better print quality that the paper according to the invention exhibits also appears from the surface structure measured as surface roughness with a prototype of the instrument FIBRO 1000 delivered from the company FIBRO System AB. Measurement on five test strips gave an average value of 1.4 '10 mmz for the paper according to the invention a 3.3 ° 1o "2 and 3.2' 1o'2 mmz for the paper produced in the traditional way and the commercial paper respectively. 10 15 20 25 30 10 Example A paper in accordance with the invention was produced by initially producing base paper in a test run in a Swedish paper mill.

The pulp fiber mixture consisted of: 67% chemithermomechanical pulp (CTMP) made from a wood mixture consisting of 80% aspen and 20% spruce with a friness of 56 ml CSF and with a brightness of 83.0% ISO. 33% bleached pine sulphate pulp with a brightness of 90.02 ISO. l2.5% filler in the form of kaolin from English China Clay, grade C. a) b) After storage of the said cellulose pulps and mixing of the filler in the pulp suspension, it was first ground in the mill in a grinder and after the addition of the following substances as a finish before the paper machine also in a grinder. The total grinding energy amounted to 50 kWh / tonne of pulp.

The final stock was completed by adding the following substances in specified amounts.

Retention aid in the form of cationic polyacrylamide with the trade name Percol 1243 = 0.036% Stock glue 1 form of cationic resin glue with the trade name T-glue 23 = 0.9% Alum = 1.2% Sodium bicarbonate = O.52% Dyes with the trade names Pigmosolblau 6900 B36 Flexonyl violet RL VLV17 bleach with the trade name Blankophor P 3.1 1 / ton of paper The percentages given above refer to the percentage of the dry 2.6 g / ton of paper 1.6 g / ton of paper the weight of the cellulose pulp fiber mixture in the stock. 10 15 20 25 30 ll: eg xïf Oulu «: r_ When the stock was introduced on the paper machine, its pH = 5.0.

The machine speed was 240 m / minute and the basis weight of the resulting paper. in dried and conditioned form, was 60 g / m 2.

Said base paper is then coated in a commercial coating plant. The following batter recipes. which is common for offset paper, was used.

Pigmentz 70 parts clay trade name SPS 30 parts chalk with the trade name Hydrocarb 90 HH 9 parts styrene butadiene latex: with the trade name Dow DL 685 and 1.2 parts carboxymethylcellulose with the trade name CMC FF5.

(English China Clay) with Binder: In addition, 0.8 parts of hardener of the urea formaldehyde resin hardener with the trade name Urecoll S and 0.8 parts of optical brightener with the trade name Blankophor P. were added to the batter. The batter dry content was 60% and the pH was adjusted to 8.5 with ammonia (NH3).

The coating machine was run at a speed of 650 m / minute and a coating layer of 15 g / m2, 1 dried and conditioned mold. was placed on each side of the paper.

The basis weight of the coated paper thus became 60 + 2x15 = 90 g / m2.

Thereafter, the coated paper 1 was calendered a supercalender at a line pressure of 175 kN / m and a temperature of 45 ° C to 65% gloss measured according to Lehmann - LGDL - 02.

The brightness of the calendered paper was 82.6% ISO.

The paper according to the invention was proof printed in a 4-color sheet-off offset printing press of the brand Roland Favorit with IR drying after the last dye. The water in the humidifier contained 8% isopropyl alcohol and. 4% moisturizing water additive with the trade name Combifix. The printing took place with a normal color sequence, ie. black, cyan, magenta and yellow. The inks were manufactured by the company Hartmann with the trade name Irocart.

The color density for each color was kept at 2.20, 1.60, 1.50 and 1.08 measured according to Grapho Metronic.

The print result was assessed visually and was found to be in line with the print result achieved by existing wood-free glossy papers on the market, ie. such coated papers where the pulp fiber mixture is entirely based on chemical pulp. The fiber erection and associated problems from a print quality point of view which is common in paper with a certain content of high yield pulp based on softwood fibers could not be observed in the paper according to the invention.

Claims (6)

10 15 20 25/3 VLL. EIÄEIÄKR be. Paper coated on at least one side, comprising base paper with a basis weight of 35-65 g / m2 made from a pulp fiber mixture consisting of high-yield pulp, with a yield exceeding 80% and with a freeness in the formation of the paper of 25-65 g / m2 350 ml CSF. and chemical pulp and a coating layer with a basis weight of 5-18 g / m2, characterized in that the high-yield pulp contained in the paper is made from wood, which at least 70% comes from tree species belonging to the family Qgpglgg (poplar genus). Paper according to claim 1, characterized in that the high-yield pulp contained in the paper is produced from wood, which at least 90% comes from tree species belonging to the Populus family (poplar genus). Paper according to claims 1-2, characterized in that the brightness measured according to ISO exceeds 75%. Paper according to claims 1-2, characterized in that the brightness measured according to ISO exceeds 78%. Paper according to claims 1-4, characterized in that the coating layer is formed of a batter with a content of synthetic and / or natural binder of 7-25 parts per 100 parts of pigment and with a content of wet strength agent. of 0.1-5 parts per 100 parts of pigment. Paper according to claims 1-4, characterized in that the coating layer is formed of a batter with a content of synthetic and / or natural binder of 9-20 parts per 100 parts of pigment and with a content of wet strength agent of 0.1-l part per 100 parts pigment.