WO2000015902A1

WO2000015902A1 - Method of manufacturing paper

Info

Publication number: WO2000015902A1
Application number: PCT/FI1999/000752
Authority: WO
Inventors: Vesa Huovila
Original assignee: Metso Paper Inc.
Priority date: 1998-09-15
Filing date: 1999-09-14
Publication date: 2000-03-23
Also published as: AU5749499A

Abstract

A method of manufacturing paper, the method comprising feeding pulp into a former, where a fiber web is formed. Moisture is pressed from the fiber web, the fiber web is dried and reeled with a reel. When the fiber web is being dried, its temperature is raised sufficiently high for a sufficiently long time so that the paper to be manufactured by the process is substantially free from bacteria and germs.

Description

METHOD OF MANUFACTURING PAPER

The invention relates to a method of manufacturing paper, the method comprising feeding pulp into a former, where a fiber web is formed, pressing moisture from the fiber web, drying the fiber web and reeling it with a reel.

A conventional paper machine comprises at least a headbox, former, dryer and reel. Pulp is fed from the headbox into a former, where a fiber web is formed of the pulp. The fiber web formed in the former is further led to a dryer for drying, as a result of which a paper web is obtained. The thus formed paper web is reeled with a reel for further processing, such as calendering or coating.

Paper typically contains a rather large amount of bacteria and germs. When paper is used in connection with foodstuffs and hygiene products, the influence of the bacteria and germs in the paper of the package on the contents of a package has to be restricted. The amount of bacteria is monitored carefully during the manufacturing process of paper and paper board to be used in connection with foodstuffs and the like, and if necessary, overgrowth is controlled with suitable toxins. The influence of the bacteria is also restricted by subjecting the paper or paper board to a special sterilization treatment before using it for its final purpose. Paper to be used in connection with foodstuffs is typically laminated, for example with plastic or aluminium, one of the purposes of lamination being to prevent bacteria and germs from coming into contact with foodstuffs. Lamination and other treatments are, however, rather difficult to carry out and constitute an additional process stage, which raises the price of the paper used in connection with foodstuffs and hygiene products to rather a high level.

The object of the present invention is to provide a method of manufacturing paper which is more suitable for use in connection with foodstuffs and hygiene products.

The method of the invention is characterized in that the temperature of a fiber web is raised sufficiently high for a sufficiently long time during the drying of the fiber web so that the paper manufactured by the process is substantially free from bacteria and germs. The basic idea of the invention is that in the paper making process the temperature of a fiber web is raised sufficiently high for a sufficiently long time during the drying of the fiber web so that the paper to be manufactured is substantially free from bacteria and germs.

An advantage of the invention is that the paper manufactured by the method is free from bacteria and germs even without any additional treatments, which allows the paper to be utilized in a more versatile and simpler manner in connection with foodstuffs and hygiene products.

In this specification the term "paper" also refers to paper board and tissue. Furthermore, the expression "paper substantially free from bacteria and germs" refers to paper which has so low content of bacteria and germs that the amount of bacteria and germs in the paper does not substantially prevent the use of the paper in connection with foodstuffs and hygiene products.

The invention will be described in greater detail in the accompanying drawing, in which

Figure 1 is a schematic side view of an apparatus suitable for implementing the method of the invention, and

Figure 2 is a schematic and partially cross-sectional side view of a drying apparatus suitable for use in connection with the method of the invention.

Figure 1 illustrates an apparatus for manufacturing paper. The apparatus comprises a headbox 1 , from which pulp is fed into a former 2, where a fiber web 3 is formed of the pulp. After the former 2 the fiber web is led to a drying apparatus. A press section 5 may be provided between the former 2 and the drying apparatus 4. After the drying apparatus 4 the fiber web 3 is led to a reel 6. The paper machine may also comprise size presses, calender and coating units, which are not illustrated in the accompanying figure for the sake of clarity.

In the drying apparatus 4 the fiber web 3 is dried and during the drying the temperature of the fiber web is raised so that substantially along the whole thickness of the fiber web its temperature rises so high for so long a time that the paper to be reeled with the reel 6 is substantially free from bacteria and germs. Preferably the temperature of the fiber web 3 is raised to over 100 °C for more than 1 second. The content of bacteria and germs in the paper to be manufactured can be decreased further if the temperature of the fiber web 3 is raised even more, i.e. the temperature of the fiber web 3 is raised e.g. to over 140 °C for more than 1 second. Figure 2 illustrates a drying apparatus 4 by means of which the temperature of the fiber web 3 can be raised sufficiently high for a sufficiently long time for manufacturing paper free from bacteria and germs. The drying apparatus 4 comprises a first band 7, i.e. an upper band, and a second band 8, i.e. a lower band, which are endless, air impermeable, conduct heat well and are preferably made of metal. A fine wire or felt 9, coarse wire 10 and fiber web 3 run between those surfaces of the bands that face each other. The first band 7 is arranged to turn around first turning rolls 11a and 11b located at the ends of the drying apparatus 4. Correspondingly, the second band 8 is arranged to turn around second turning rolls 12a and 12b also located at the ends of the drying apparatus 4, below the first turning rolls 11 a and 11b. The wires 9 and 10 are supported and guided by guide rolls 13. Since the pressure prevailing in the pressure zone in the area between the bands 7 and 8 is usually different from the pressure prevailing outside or on the sides of the bands 7 and 8, seals are arranged on both sides of the apparatus between or at the edges of the bands 7 and 8, the seals preventing liquid or gas from moving out of the area between the bands 7 and 8 sidewards, or vice versa. To effect the pressure between the bands the drying apparatus 4 comprises a pressure chamber 14, which is located above the first band 7. The first band 7 is sealed with the seals to the body of the pressure chamber 14 so that the pressure of the steam in the pressure chamber remains at a suitable pressure. Below the second band 8 there is a water chamber 15 containing a cooling medium, such as water, which cools the second band 8. At the edges of the water chamber there are seals, with which the second band 8 is sealed to the body of the water chamber 15.

The operation of the drying apparatus 4 is based on heating the first band 7, which is in contact with the fiber web 3, by hot steam contained in the pressure chamber 14. The temperature of the first band 7 causes the water in the web 3 to vaporize and to be transferred through the wires 9 and 10 towards the second band 8. The second band 8 is in turn continuously cooled with the water located below it, whereby the steam coming on its surface condenses into water and is removed with the band 8 and wire 10. Pressure is also directed to the fiber web 3 in the pressure zone between the pressure chamber 14 and the water chamber 15. The heating of the first band 7 and the pressure in the pressure zone make it possible to raise the temperature of substantially the whole fiber web 3 so high for so long a time during the drying that most of the bacteria and germs in the fiber web 3 are killed.

The temperature of the heated first band 7 may be e.g. approximately 100 to 200 °C and the temperature of the cooled second band 8 e.g. approximately 50 to 90 °C. The pressure in the pressure zone vary for example from two to ten bars.

The drawing and the related description are only intended to illustrate the inventive concept. The details of the invention may vary within the scope of the claims. Thus it is not relevant which pressure medium is used in the pressure chamber 14 and water chamber 15. Thus the pressure medium used in the pressure chamber 14 may be for example steam, air, hot combustion gases or water. In addition to water, for example air can be used as the pressure medium in the water chamber 15. In addition to the heating with the pressure chamber 14, the first band 7 may also be heated in other positions of the process in manners known per se. The first band 7 may also be heated completely outside the pressure chamber 14. Furthermore, the second band 8 can be cooled outside the water chamber 15.

Claims

1. A method of manufacturing paper, the method comprising feeding pulp into a former, where a fiber web is formed, pressing moisture from the fiber web, drying the fiber web and reeling it with a reel, wherein the temperature of the fiber web is raised sufficiently high for a sufficiently long time during the drying of the fiber web so that the paper to be manufactured by the process is substantially free from bacteria and germs.

2. A method according to claim 1 , wherein the temperature of the fiber web is raised to over 100┬░C for at least 1 second during the drying process.

3. A method according to claim 1 , wherein the temperature of the fiber web is raised to over 140┬░C for at least 1 second during the drying process.

4. A method according to claim 1 , wherein the fiber web is dried with a drying apparatus, comprising two endless air impermeable bands, first turning rolls, the first band being arranged to turn around the first turning rolls, and second turning rolls, the second band being arranged to turn around the second turning rolls, whereby the first band and the second band are arranged to run part of the way parallel with each other in such a way that they form a drying zone between them, the first band being heated with a pressure chamber and the second band being cooled with a cooling chamber, and whereby the fiber web and at least one felt or wire are led between the bands in such a way that the fiber web is in contact with the heated first band, and the felt or the wire is located between the fiber web and the cooled second band, respectively.