EP0043290A1

EP0043290A1 - Process and apparatus for producing non-woven fibrous cellulosic sheet material

Info

Publication number: EP0043290A1
Application number: EP81302998A
Authority: EP
Inventors: Brian William Attwood
Original assignee: BLACK-CLAWSON INTERNATIONAL Ltd
Current assignee: BLACK-CLAWSON INTERNATIONAL Ltd
Priority date: 1980-07-02
Filing date: 1981-07-01
Publication date: 1982-01-06
Also published as: FI812061L; JPS5739300A; FI812061A7

Abstract

A process and apparatus for the production of webs of fibrous cellulosic material combine defibering of moist cellulosic material with dry-forming of a web of the defibered material and subsequent press-drying of the web. Hence, defibered cellulosic material having a moisture content, for example, of from 30-40% by weight, is dry-formed to produce a non-woven web which is then consolidated by feeding it through a press-drying stage. In the press-drying stage, the web is advanced through a plurality of heated pressure nips (13) provided between a rotating heated cylinder (14) and cooperating pressure rollers (15). The web (16) is retained in contact with the heated cylinder between the pressure nips by means of the forming band (11) on which the web is initially dry-formed and which is advanced through the nips together with the web.

Description

The present invention relates to the production of non-woven sheets or webs of fibrous cellulosic material suitable for the manufacture of paper, paperboard, folding boxboard or carton board.
From one aspect, the present invention consists in a process for the production of a non-woven web of fibrous cellulosic material, characterised by the steps of defibering moist cellulosic material, dry-forming a web of said defibered material, and consolidating the web by advancing said web through one or more heated pressure nips provided between one or more rotating heated cylinders and one or more cooperating pressure rollers, and retaining the web in contact with at least a part of the circumference of the or each heated cylinder by means of a supporting band.
From another aspect, the invention consists in apparatus for producing a non-woven web of fibrous cellulosic material, characterised by means for defibering moist cellulosic material, means for dry-forming a web of said defibered cellulosic material, and press-drying means for consolidating said web including one or more heated pressure nips provided between one or more rotating heated cylinders and one or more cooperating pressure rollers, and a supporting band guided through the pressure nip or nips for retaining the web in contact with at least a part of the circumference of the or each heated cylinder.
In a preferred embodiment, the supporting band is constituted by a travelling foraminous forming band on which the web of cellulosic material is initially formed, this forming band being advanced through the pressure nip(s), together with the web, and retaining or or pressing the web continuously in contact with the heated cylinder(s) during advance of the web through the nip(s) and about the cylinder(s).
The defibered cellulosic material may have a moisture content of 30-40% by weight. Preferably, the moisture content is brought to at least 40% by weight before dry-forming, and the forming is effected by entraining the moist defibered material in an air stream and depositing it on a forming band.
The linear nip pressure in the press-drier may be of the order of 25-45kg/cm, preferably 35kg/cm, and the nip temperature may be in the range from 65-180°C, preferably about 110°C.
The invention may also be utilised for the production of a multi-ply web of cellulosic material. In such a process, a second web of fibrous cellulosic material is wet-formed and the dry-formed web is deposited on this second web so as to produce a second ply thereon. A third wet-formed web of cellulosic material is then deposited on the second ply to form a third ply thereon, and the resulting three-ply web is consolidated by press-drying, as hereinbefore described. Preferably, the second web is wet-formed on a foraminous forming band and this forming band, together with the three-ply web deposited thereon, is advanced through the pressure nip(s) and about the heated cylinder(s) and the forming band serves as the supporting band to retain the three-ply.web pressed in contact with at least a part of the circumference of.. the or each cylinder.
The invention enables the production of paper, paperboard, folding boxboard or carton board from wood or cellulosic rag fibre in a continuous process on a single manufacturing installation, thus resulting in significant economies in space requirements, energy utilisation and usage of water.
In order that the present invention may be more readily understood, reference will now be made to the accompanying drawings in which:-

Fig. 1 is a diagrammatic side elevation of apparatus constructed in accordance with the invention, and
Fig. 2 is a block diagram illustrating a process according to the invention for making a multi-ply web.

Referring to Fig. 1 of the drawings, moist wood pulp is defibered in suitable defibering equipment, such, as a hammer mill (not shown), its moisture content being about 40% by weight. The moist defibered pulp is entrained in an air stream and laid by means of a distributor head 10 onto an endless foraminous forming band or wire 11 travelling over a vacuum box 12 disposed immediately beneath the distributor head so as to form a non-woven web of the defibered pulp. The resulting web is.consolidated by feeding it through a press-drying section whilst supported by the forming band 11. Hence, it is advanced together with the band 11 through three pressure nips 13 spaced around approximately half the circumference of a rotating heated drying cylinder 14 and defined by three pressure rollers 15 cooperating with the cylinder. The cylinder 14 may, for example, be 3.5m in diameter and be steam heated to a surface temperature of about 110°C. The linear nip pressure exerted by each pressure roller 15 may be about 35kg/cm. The web is pressed into contact with the heated cylinder during and between its travel through the pressure nips by the forming band 11. As a result, the moisture content of the web is reduced to within a range of from 15-20%. The web 16 is separated from the cylinder 14 and the band 11 at the final nip 13 by a take- off roller 17 and is then fed to further driers, size presses and other treatment units (not shown) before passing, as finished web, to reel-up units. Upon leaving the final nip 13, the band 11 is returned to the distributor head 10 via guide and tensioning rollers 18.
The web so formed is virtually "square" in that the ratio of its physical properties, such as, stiffness in the cross-machine direction and the machine direction is substantially 1:1. The same ratio is applicable to the physical characteristics of the web taken in any two mutually perpendicular directions in the plane of the web thus providing an "homogenous" sheet material. The sheet material has good dimensional stability `when subjected to changes in atmospheric humidity.
Referring now to Fig. 3, this illustrates a method of producing a multi-ply web using the process and apparatus of Fig. 1 in combination with known wet-forming techniques. Hence, in a first step 21, a cellulosic fibre first ply of wood fibre pulp containing about 1-2% solids by weight is wet-laid on a travelling forming band using a known wet-forming technique, such as, that disclosed in British Patent No. 1548924 issued to St. Anne's Board Mill Company Limited.
In a second step.22, moist wood pulp is defibered in equipment, such as a hammer mill at a moisture content of about 30-40% by weight and, in a third step 23, the moist defibered pulp is entrained in an air stream and deposited on the first ply, as a second ply. In a fourth step 24, a further wet-laid cellulosic fibre ply is formed in a similar manner to the wet-forming of the ply at 21 and is deposited on the second ply. Thus, the dry-laid second ply is sandwiched between the two wet-laid plies. Thereafter, in a fifth step 25, the multi-ply web is consolidated by the press-drying procedure described above with reference to Fig. 1. The resultant product is found to have its strength and stiffness concentrated in its outermost wet-laid plies.
Whilst particular embodiments have been described it will be appreciated that modifications can be made without departing from the scope of the invention as defined by the appended claims. For example, in the consolidation procedure described with reference to Fig. 1, the linear nip pressure may be varied between 26-45kg/cm and the surface temperature of the cylinder 14 may be in the range from 65-180⁰C. In an alternative process to that described with reference to Fig. 3, the multi-ply sheet may be made by forming the plies on separate forming bands and combining them by the use of transfer rollers and the like.

Claims

₁. A process for the production of a non-woven web (16) of fibrous cellulosic material, characterised by the steps of defibering moist cellulosic material, dry-forming a web of said defibered material, and consolidating the web by advancing said web through one or more heated pressure nips (13) provided between one or more rotating heated cylinders (14) and one or more cooperating pressure rollers (15), and retaining the web in contact with at least a part of the circumference of the or each heated cylinder (14) by means of a supporting band (11).

2. A process as claimed in claim 1, characterised in that the supporting band is a foraminous forming band (11) on which the web is dry-formed, said forming band being advanced through the pressure nip or nips together with the web.

3. A process as claimed in claim 1 or 2, characterised in that the moisture content of the defibered material is from 30-40% by weight, the linear nip pressure is about 25-45kg/cm, and the nip temperature is about 65-180°C.

4. A process as claimed in claim 1, characterised in that the moisture content of the defibered material is brought to at least 40% by weight before the dry-forming step, and the dry-forming step is effected by entraining the defibered material in an air stream and depositing said material on a foraminous forming band (11) to form the web thereon, and further characterised in that the web is advanced through a plurality of pressure nips (13) in the consolidating step, the linear nip pressure being about 35kg/cm, and the nip temperature being about 110⁰C.

5. A process as claimed in any preceding claim, characterised by the steps of wet-forming a second web of fibrous cellulosic material, depositing said first-mentioned, dry-formed web on said second web to form a second ply thereon, wet-forming a third web of fibrous cellulosic material, depositing said third web on said second ply to form a third ply thereon, and consolidating the resulting.three ply web in the consolidating step,

6. A process as claimed in claim 5, characterised in that the second web is wet-formed on a travelling foraminous forming band and, in the consolidating step, said forming band is advanced through the pressure nip or nips together with the three ply web to retain the web in contact with the heated cylinder or cylinders.

7. Apparatus for producing a non-woven web (16) of fibrous cellulosic material, characterised by means for defibering moist cellulosic material, means (10,12) for dry-forming a web of said defibered cellulosic material, and press-drying means for consolidating,said web including one or more heated pressure nips (13) provided between one or more rotating heated cylinders (14) and one or more cooperating pressure rollers (15), and a supporting band (11) guided through the pressure nip or nips for retaining the web in contact with at least a part of the circumference of the or each heated cylinder.

8. Apparatus as claimed in claim 7, characterised in that the supporting band is a foraminous forming band (11) on which the web is initially formed.

9. Apparatus as claimed in claim,7, characterised by means (21) for wet-forming a second web of fibrous cellulosic material, means (23) disposed upstream of the press-drying means (25) for depositing said first-mentioned, dry-formed web on said second web to form a second ply thereon, means (24) disposed upstream of the press-drying means (25) for wet-forming a third web of fibrous cellulosic material and depositing said third web on the second ply to form a three-ply web.

1.0. Apparatus as claimed in claim 9, characterised in that the supporting band is a foraminous forming band on which the second web is wet-formed.