WO2009130383A2

WO2009130383A2 - Paper product and a method for the production of a paper product

Info

Publication number: WO2009130383A2
Application number: PCT/FI2009/050303
Authority: WO
Inventors: Markku Karlsson
Original assignee: Upm-Kymmene Oyj
Priority date: 2008-04-22
Filing date: 2009-04-21
Publication date: 2009-10-29
Also published as: WO2009130383A3; FI20085348A0

Abstract

The invention relates to a paper product (1) comprising a base paper (2). The base paper (2) consists of a base layer (3) and a surface layer (4) so that the base paper (2) has a surface side (5) formed by the surface layer (4) and a base side (6) formed by the base layer (3). The base layer (3) and the surface layer (4) have different stock compositions. The invention relates also to a method for producing a paper product (1). The method comprises a step for forming a base paper (2) consisting of a base layer (3) and a surface layer (4) so that the base paper (2) has a surface side (5) formed by the surface layer (4) and a base side (6) formed by the base layer (3), wherein the base layer (3) and the surface layer (4) have different stock compositions.

Description

Paper product and a method for the production of a paper product

Field of the invention

The invention relates to a paper product as defined in the preamble of independent claim 1. The invention also relates to a method for the production of a paper product as defined in the preamble of independent claim 9.

The invention relates especially to office or copy papers and to a method for the production of office or copy papers having a grammage between about 50 and about 90

0 0 0 0 0 g/m , for example about 50 g/m , about 60 g/m , about 70 g/m , about 80 g/m , or about 90 g/m². The term office paper is used in this application as a generic name of paper product used in offices and households including business forms, letterheads, copying papers, envelopes, postal papers, digital printing papers and computer printouts.

A major part of office and domestic documents produced are one-sided, which means that only one of the sides of the paper is used so that there is text and pictures only on one side of the paper. On the other hand it is required from standard office or copy paper that it is symmetrical in such a way that both sides can be printed on. In other words, an office or copy paper must be symmetrical in its characteristics and suitable for double- sided printing and copying. Choice of raw materials, optical, electrical and thermal characteristics, surface roughness etc must be identical on both sides of the paper. In the future flexibility is also required of papers suitable for copying ; a paper must be suitable for many different uses such as for black-and-white and color copying, offset printing and black-and-white and color ink-jet printing, which means that compromises must be made between the characteristics so that one paper can be used for many various purposes.

A normal office or copy paper is a single-layer product having a base paper or an interior made of bleached pulp and a suitable filling material. Office and copy papers produced from recycled fibers are also known. Important characteristics of an office or copy paper are rigidity and surface strength. To ensure a required rigidity of an office or copy paper, the weight of the papers is normally around 80 g/m , but also significantly lighter papers having a weight under 60 to 70 g/m are known. To ensure surface strength and to minimize dusting the paper must be surface sized on both sides.

3-layer office or copy papers are also known. A 3-layer paper has a base paper or interior consisting of three layers; two surface layers and a base layer between the surface layers.

An example of a 3-layer paper is IQ TRIOTEC^® produced by Mondi Group. The base layer between the surface layers may in this paper be of recycled fibers.

Objective of the invention The object of the invention is to provide a paper product of a new type which is easy to produce and which can be made of inexpensive raw material and which can fulfill the need of most users.

Short description of the invention The paper product is characterized by the definitions of independent claim 1.

Preferred embodiments of the paper product are defined in the dependent claims 2 to 8.

The method for the production of a paper product is correspondingly characterized by the definitions of independent claim 9. Preferred embodiments of the method are defined in the dependent claims 10 to 15.

The invention is based on the idea of making the base paper i.e. the furnish of the paper product so that the base paper consists of two layers: a base layer, which can be made of inexpensive raw material such as recycled fiber or mechanical pulp, and a surface layer made of raw material making possible for example a smooth surface having high whiteness and high opacity, which surface layer is made of for example virgin fiber, chemical pulp, CTMP, or corresponding wood-free stock.

The base layer of the base paper of the paper product of the invention gives the paper product its mechanical characteristics and the surface layer of the base paper of the paper product of the invention gives the paper product its required surface characteristics such as printability, whiteness, opacity, roughness, etc. Because achieving the required surface characteristics requires usage of raw materials which are more expensive than that which can be used in the base layer it is desired to make the surface layer as thin as possible i.e. so that the grammage of the surface layer is as low as possible taking the requirements for the surface layer at the same time into consideration. This can be achieved with a paper product and a method according to the invention.

A paper product of the invention is easier and less expensive to produce than a single layer double-sided or 3-layer paper product suitable for printing on both sides.

In a single layer double-sided paper product both surfaces of the base paper must have identical properties and this leads to the requirement that the base paper must be made of relatively expensive raw material such as chemical pulp, virgin fiber, or other wood-free stock in order to ensure identical surface properties on both sides of the paper.

A 3-layer paper product suitable for printing on both sides is more complicated to make than a paper product of the invention, because the making of a 3-layer paper product includes production of a 3-layer web i.e. a base paper having three layers. In addition, in order to ensure sufficient coverage of the surface layers on both sides of the base layer, the grammage of both surface layers must be at least about 30 g/m², which leads to that in a paper having a grammage of 80 g/m², the grammage of the base layer between the surface layer and which can be made of less expensive material than the base layer can be only 20 g/m². This does not result in any saving in raw material costs. In addition drainage of water from the base layer is not easy, because the water must be drained through the surface layers, which leads to that the optical cleanness of the surface layers suffers. A paper product of the invention makes possible to use a greater proportion of less expensive raw material in the base paper that in previously known office or copy papers. For example in a paper having a grammage of 80 g/m , the base paper could consist of a base layer having a grammage of 50 g/m²and a surface layer having a grammage of 30 g/m². In comparison to a corresponding 3-layer paper product having a grammage of 80 g/m², the base paper in a paper product of the invention can contain more than double the amount of cheap raw material and less than half the amount of expensive raw material.

One important feature of copy papers is that the copy papers retain their flatness also after copying. It is easier to retain the flatness of a one-sided paper than the flatness of a double-sided paper, because in a one-sided paper only drying of ink on one of the sides of the paper product must be managed.

Standard copy papers always show so called deletion problem in a certain amount. Deletion of toners is present only in two-sided copying and on the last copied side, regardless which side is copied first. This kind of quality problem is unknown for onesided office papers. If only one of the sides of a paper product of the invention is intended for use, it is sufficient that only the side to be used is surface finished, for example calendered.

The base paper can for example be formed using a multilayer head box and a multilayer former such as Metso Paper's ValFormer.

The paper product can be produced in a paper machine having a former or utilizing a former for treating only one of the sides of the base paper i.e. the surface side of the base paper, in cases where only the surface side of the paper product is intended to be used by the end user.

If the surface of a paper product is surface finished, for example calendered, surface sized, pigmented or coated, it is sufficient that only the surface side of the paper product is surface finished if only the surface side of the paper product is intended to be used by the end user.

In a preferred embodiment of the invention the paper product is a one-sided copy or office paper having a grammage of about 80 g/m . In this preferred embodiment of the invention the paper product comprises a base paper consisting of a base layer having a grammage of 50 g/m² and a surface layer having a grammage of 30 g/m². In this preferred embodiment the surface side of the paper product is surface finished to achieve the required surface requirements set by the needs of the end user for example for B/W inkjet printing, B/W laser printing, color copying, color inkjet printing, color laser printing, copying, or fax use. In this preferred embodiment the surface side of the paper product is in addition surface sized and the base side of the paper product is only surface sized to avoid dusting.

In a preferred embodiment of the invention the paper product is a paper having sides with different properties. It is for example possible that the paper product of the invention is in the form of a paper having sides that have one side suitable for ink-jet printing and one side suitable for laser copying or printing.

In a preferred embodiment of the invention the paper product is a two-sided copy or office paper having a grammage of about 80 g/m . In this preferred embodiment of the invention the paper product comprises a base paper consisting of a base layer having a grammage of 50 g/m² and a surface layer having a grammage of 30 g/m². In this preferred embodiment the surface side of the paper product is surface finished to achieve the required surface requirements set by the needs of the end user for B/W laser printing and color laser printing and the base side of the paper product is surface finished to achieve the required surface requirements set by the needs of the end user for example for B/W inkjet printing and color inkjet printing. In this preferred embodiment both the surface side of the paper product and the base side of the paper product are surface sized to avoid dusting.

List of figures

In the following the invention will be described in more detail by referring to the figures, of which

Figure 1 shows in detail view one preferred embodiment of the invention, and Figure 2 shows forming of a paper web.

Detailed description of the invention

Figure 1 shows a detail of a paper product 1 comprising a base paper 2 or so-called furniture.

The base paper 2 consists of a base layer 3 and a surface layer 4 so that the base paper 2 has a surface side 5 formed by the surface layer 4 and a base side 6 formed by the base layer 3.

The base layer 3 and the surface layer 4 have different stock compositions, which means that they contain different material.

The paper product 1 is preferably a office or copy paper having a grammage between about 50 and 90 g/m², for example about 50 g/m², about 60 g/m², about 70 g/m², about 80 g/m², or about 90 g/m².

The grammage of the base paper 2 is preferably, but not necessarily, between about

0 0 0 0 50 and about 90 g/m , for example about 50 g/m , about 60 g/m , about 70 g/m , about 80 g/m², or about 90 g/m². The grammage of the base layer 3 is between about 30 and about 60 g/m , preferably about 50 g/m in a paper product 1 in the form of an office or copy paper having a grammage of about 80 g/m².

The base layer 3 comprises preferably, but not necessarily, at least one of the following: recycled fiber, mechanical pulp, ground wood pulp, deinked recycled pulp (DIP), non-wood pulp and recycled pulp.

The grammage of the surface layer 4 is preferably, but not necessarily, between about 20 and about 40 g/m², preferably about 30 g/m² in a paper product 1 in the form of an office or copy paper having a grammage of about 80 g/m . The surface layer 4 comprises preferably, but not necessarily, a filler and at least one of the following: virgin fiber, chemical pulp, CTMP, or corresponding wood-free stock.

The base paper 2 is preferably, but not necessarily, produced using a multi-layer headbox so that the surface layer 4 is not substantially penetrated into the base layer 3 and vice versa.

The base side 6 of the base paper 2 may be calendered.

The surface side 5 of the base paper 2 is preferably, but not necessarily, calendered with an apparatus selected from the group consisting of a machine calender, a soft calender, a belt calender, a metal belt calender, a supercalender, a multi-roll calender with polymer rolls, a shoe calender, and a brush polisher.

The surface side 5 of the base paper 2 is preferably, but not necessarily, polished against a polishing roll of calender nip or against a Yankee cylinder or metal belt.

The paper product 1 may comprise a first surface sizing agent applied on the base side 6 of the base paper 2. The amount of a first surface sizing agent is preferably, but not necessarily, about 0.1 to 2 g/m² when calculated in dry matter.

The paper product 1 may comprise a second surface sizing agent applied on the surface side 5 of the base paper 2. The amount of a second surface sizing agent is preferably, but not necessarily about 0.1 to 2 g/m when calculated in dry matter.

The surface side 5 of the base paper 2 may be uncoated. The base side 6 of the base paper 2 may be uncoated.

The invention also relates to a method for producing a paper product 1. The method comprises a step for forming a base paper 2 consisting of a base layer 3 and a surface layer 4 applied on the base layer 3 so that the base paper 2 has a surface side 5 formed by the surface layer 4 and a base side 6 formed by the base layer 3, wherein the base layer 3 and the surface layer 4 having different stock compositions which means that they contain different material.

In a preferred embodiment of the method of the invention a paper product 1 is formed having a grammage between about 50 and about 90 g/m , preferably about 80 g/m . In a preferred embodiment of the method of the invention a base paper 2 is formed having a grammage between about 50 and about 90 g/m , preferably about 80 g/m .

In a preferred embodiment of the method of the invention a base layer 3 is formed having a grammage between about 30 and about 60 g/m , preferably about 50 g/m . In a preferred embodiment of the method of the invention the base layer 3 is formed of at least one of the following: recycled fiber, mechanical pulp, ground wood pulp, deinked recycled pulp (DIP), non-wood pulp and recycled pulp.

In a preferred embodiment of the method of the invention a surface layer 4 is formed having a grammage about 20 and about 40 g/m², preferably about 30 g/m². In a preferred embodiment of the method of the invention the surface layer 4 is formed of a filler and at least one of the following: virgin fiber, chemical pulp, CTMP, or corresponding wood-free stock.

Figure 2 shows a preferred embodiment of the method of the invention where the stock 7 forming the base layer 3 and the stock 8 forming the surface layer 4 are fed from a multi-layer headbox so that the surface layer 4 is not substantially penetrated into the base layer 3 and vice versa. In this preferred embodiment, the stock 8 forming the surface layer 4 is preferably fed from the multi-layer headbox on the wire 10 and the stock 7 forming the base layer 3 from the multi-layer headbox on the surface layer 4.

In a preferred embodiment of the method of the invention the stock consistency for base layer 3 can be higher, but not necessarily, than for surface layer 4. Elevated of high

(up to 3 %) stock consistency of base layer improves layer purity because of less mixing of layers during free jet and initial draining. In addition, pumping energy is saved with decreasing flow rates.

In a preferred embodiment of the method of the invention water is drained from the paper web to both sides either with a gap forming by means of a former having an at least partly curved dewatering element 9 and by sucking the paper web against said at least partly curved dewatering element to drain water from the paper web or with combined two-layer headbox -former unit having straight or slowly curved covering channel with layer separating vane or wedge reaching over initial draining zone. Metso Paper's ValFormer is preferably used to drain water from the paper web. In this embodiment water is preferably, but not necessarily, drained in the former from the paper web through the base layer 3 of the paper web. A combined headbox-former is also known from Metso Paper's pulp drying machines and resembles suitably modified ControFlowFormer (CFF) with pressurized forming chamber. In a preferred embodiment of the method of the invention the base side 6 of the base paper 2 is calendered.

In a preferred embodiment of the method of the invention the surface side 5 of the base paper 2 is calendered with an apparatus selected from the group consisting of a machine calender, a soft calender, a belt calender, a metal belt calender, a supercalender, a multi-roll calender with polymer rolls, a shoe calender, and a brush polisher.

In a preferred embodiment of the method of the invention the surface side 5 of the base paper 2 is polished against a polishing roll of calender nip or against a Yankee cylinder or metal belt.

In a preferred embodiment of the method of the invention a first surface sizing agent is applied on the base side 6 of the base paper 2. The amount of a first surface sizing agent is preferably, but not necessarily, about 0.1 to 2 g/m² when calculated in dry matter. In a preferred embodiment of the method of the invention a second surface sizing agent is applied on the surface side 5 of the base paper 2. The amount of a second surface sizing agent is preferably, but not necessarily, about 0.1 to 2 g/m when calculated in dry matter. In a preferred embodiment of the method of the invention the structural curl tendency caused by different stock compositions and fiber orientation between the base and surface sides is adjusted with the help of a combination of one-sided drying, one-sided moisturing at the post dryers and one-sided steaming before calendering. Especially, a different amount and consistency of the surface sizing agent dosed on the base and surface sides are also practicable to control curl.

In a preferred embodiment of the method of the invention the surface side 5 of the base paper 2 is left uncoated. In a preferred embodiment of the method of the invention the base side 6 of the base paper 2 is left uncoated.

Some tests have been made with the paper product according to the invention and the tests showed that the surface layer and the base layer did not mix together but maintained their layer purity. The test paper products were also measured and table 1 shows measurement values of a paper product according to the invention and comparable values of a commercial reference paper product. The paper product 1 according to the invention is made of a base layer 3 and a surface layer 4. The base layer 3 has a grammage of 40 g/m² and comprises deinked recycled pulp (DIP) made of recycled paper from Finnish households and about 10 % filler. The surface layer 4 also has a grammage of 40 g/m² and comprises milled birch pulp without a filler. The reference paper product is a commercial paper product UPM Office having a grammage of 80 g/m and filler content 23-25 %.

The reference paper, UPM Office from Kymi mill, was compared to the tested paper product 1 according to the invention which print quality was evaluated with different measurements. In print density measurement the bigger the value, the better, and in this measurement the paper product 1 according to the invention was at the same level as the reference paper. That was good especially when looking at the density of black (K) in which the aim is a high value since black text in inkjet is a preferred feature. In inkjet print through measurement the smaller the value, the better. In this measurement the acceptable limit of print through value is 0,1 which was well achieved with the paper product 1 according to the invention. The different values are for different colors, the codes being K for black, C for cyan, M for magenta, Y for yellow, R for red, G for green and B for blue.

In inkjet strike through measurement the reference paper is a shade better than the paper product 1 according to the invention.

With the paper product 1 according to the invention the vertical and horizontal inkjet line spreading and line roughness are more or less close to the reference paper's values.

Table 1

The paper product according to the invention can be used in a printer or in a copying machine for one sided printing or copying. The printer or copying machine is advantageously having a separate container for office paper used for one sided printing or copying.

It is apparent to a person skilled in the art that as technology advances, the basic idea of the invention can be implemented in various ways. The invention and its embodiments are therefore not restricted to the above examples, but they may vary within the scope of the claims.

Claims

1. A paper product (1), such as an office paper, a copy paper or a digital printing paper, comprising a base paper (2), characterized in that the base paper (2) consists of a base layer (3) and a surface layer (4) so that the base paper (2) has a surface side (5) formed by the surface layer (4) and a base side (6) formed by the base layer (3) , and in that the base layer (3) and the surface layer (4) have different stock compositions.

2. The paper product (1) according to claim 1, characterized in that the grammage of the base paper (2) is between about 50 and about 90 g/m , preferably about 80 g/m .

3. The paper product (1) according to claim 1 or 2, characterized in that the base layer (3) comprises at least one of the following: recycled fiber, mechanical pulp, ground wood pulp, deinked recycled pulp (DIP), and recycled pulp.

4. The paper product (1) according to any of the claims 1 to 3, characterized in that the grammage of the surface layer (4) is between about 20 and about 40 g/m , preferably about 30 g/m².

5. The paper product (1) according to any of the claims 1 to 4, characterized in that the surface layer (4) comprises filler and at least one of the following: virgin fiber, chemical pulp, CTMP, or corresponding wood-free stock.

6. The paper product (1) according to any of the claims 1 to 5, characterized in that the base paper (2) is produced using a multi-layer headbox so that the surface layer (4) is not substantially penetrated into the base layer (3) and vice versa.

7. The paper product (1) according to any of the claims 1 to 6, characterized in that the base side (6) of the base paper (2) and/or the surface side (5) of the base paper (2) is calendered.

8. The paper product (1) according to any of the claims 1 to 7, characterized in that the base side (6) of the base paper (2) and/or the surface side (5) of the base paper (2) is surface sized.

9. Method for producing a paper product (1), in which method comprises steps for forming a base paper (2) characterized in that a base paper (2) is formed consisting of a base layer (3) and a surface layer (4) so that the base paper (2) has a surface side (5) formed by the surface layer (4) and a base side (6) formed by the base layer (3), wherein the base layer (3) and the surface layer (4) have different stock compositions.

10. The method according to claim 9, characterized by forming a base paper (2) having a grammage between about 50 and about 90 g/m , preferably about 80 g/m .

11. The method according to claim 9 or 10, characterized by forming the base layer (3) of at least one of the following: recycled fiber, mechanical pulp, ground wood pulp, deinked recycled pulp (DIP), and recycled pulp.

12. The method according to any of the claims 9 to 11, characterized by forming the surface layer (4) of filler and at least one of the following: virgin fiber, chemical pulp,

CTMP, or corresponding wood-free stock.

13. The method according to any of the claims 9 to 12, characterized by feeding the stock forming the base layer (3) and the stock forming the surface layer (4) from a multi- layer headbox so that the surface layer (4) is not substantially penetrated into the base layer (3) and vice versa.

14. The method according to any of the claims 9 to 13, characterized in that the base side (6) of the base paper (2) and/or the surface side (5) of the base paper (2) is calendered.

15. The method according to any of the claims 9 to 14, characterized by applying a surface sizing agent on the base side (6) of the base paper (2) and/or on the surface side (5) of the base paper (2).