WO1999009247A1

WO1999009247A1 - Paper making felts

Info

Publication number: WO1999009247A1
Application number: PCT/GB1998/002415
Authority: WO
Inventors: Ian Christison Sayers
Original assignee: Scapa Group Ltd
Current assignee: Scapa Group Ltd
Priority date: 1997-08-15
Filing date: 1998-08-11
Publication date: 1999-02-25
Anticipated expiration: 2000-02-15
Also published as: AU8739398A; GB9717215D0

Abstract

A papermaking fabric (10) for producing paper with a pattern embossed thereon, the fabric (10) comprising a base layer (11), in the form of a woven substrate, and a fibrous batt layer (12) with a paper contacting surface (13). Raised patterns (14) are provided in the paper contacting surface (13) by needling selected areas of the surface (13) by forked needles (15).

Description

PAPERMAKING FELTS

This invention relates to papermaking felts and in particular to press

and marking felts for use in producing paper with a pattern embossed

thereon.

Marking felts are used for example to produce paper including

tissues, which requires a pattern to be embossed thereon. This may be

achieved by means of an embossed pattern on the felt surface, or by harder

yarns disposed as required just below a fibrous face layer of the felt.

Embossed felts may also be used in the web pick-up arrangement of a

Yankee machine which transfers the formed web to a press felt.

WO 96/25555 discloses a forming or dryer fabric for a papermaking

machine which has patterned resin surface with openings through which air

and/or water is conveyed during formulation or drying of the paper.

Manufacture of such a fabric is time consuming and expensive.

In co-pending application No. 96261 53.2 we disclose a method of

making such a fabric wherein a batt of fibres is at least partially melted

using ultrasonic energy and a pattern is imprinted into the batt whilst the

fibres are in a molten state, by means for example of an engraving wheel

or roller.

This last method is only usable with batts of thermoplastic and similar

synthetic fibres which are susceptible to melting with the use of ultrasonic energy.

The present invention is concerned with an alternative method of

providing a felt having relatively raised and relatively depressed areas which

is useable with fibres of any material, thermoplastic, natural or otherwise.

In accordance with the present invention, a papermaking felt has a

paper contacting surface provided by a fibrous batt layer, wherein the

surface batt fibres are needled selectively to provide raised patterns.

The batt may comprise a blend of two or more fibres with

significantly different melting points, eg polypropylene and polyamide 6.

The felt may be heat set after needling which causes the lower melting

point fibres to melt and then resolidify at the end of heat setting to act as

a rigidising polymer material which reinforces the patterns formed of higher

melting point fibres and improves resistance to the elevated patterned

regions to compaction.

The blended fibres may be provided in one or more layers within the

fabric, at least one of which is at or close to the surface of the felt which

is to be embossed.

Alternatively, at least one batt layer predominantly or wholly

comprising relatively low melting point fibres may be used close to or at the

surface to be embossed. In this case structured needling with forked

needles may ensure that the raised pattern regions will have a high content of low melting point fibre whilst the main surface in the lower plane will be

mainly higher melting point fibres, forming an embossed surface with rigid

compaction resistant raised patterns.

Needling may be carried out by known needling machines, in

accordance with a pattern applied e.g . electronically to controls of the

needling machine, selected areas being needled in such a manner as to

provide raised regions, the remainder of the surface being needled so as to

leave relatively depressed regions.

An embodiment of the invention is now described by way of example

with reference to the accompanying drawing, which is a diagrammatic cross

section of a paper making felt in accordance with the invention.

A paper making felt 10, such as an embossing felt or a press felt,

comprises a base layer 1 1 , in the form of a woven substrate, which carries

in the simplest form of the invention, a fibrous batt layer 1 2 which provides

a paper contacting surface 1 3 on its side opposite the base layer 1 1 .

Batt layer 1 2 comprises a mixture of relatively high melting point

polyamide 6 fibres, and relatively low melting point polypropylene fibres.

To produce raised areas such as 14, selected areas of the surface 1 3

are needled, such as by forked needles 1 5. This produces a raised area of

pulled fibres and fibrils which is then bonded by heat treatment of the

sur ace 13 which melts the low melting point polypropylene fibres creating a matrix towards the surface 13 at least which embeds the higher melting

point polyamide fibres, and also consolidates the raised areas, forming an

embossed surface with rigid compaction resistant raised patterns.

Suitable machines for use in the needling step include Fehrer AG's

NL21 and NL9/S needling machines.

The pattern applied to the surface 13 will depend upon the desired

characteristics of the paper or tissue to be carried by the felt - e.g. to

produce spot embossings on tissues to maintain tissue coherence without

substantial reduction of porosity will necessitate relatively small well spaced

raised spots on the felt.

The base layer 1 1 may be any form of fabric substrate or base layer

used in the art, such as a perforated membrane, a non-woven layer, or a

spiral link fabric.

The fabric may comprise more than a single batt layer, and may

comprise other layers apart from the surface layer which is adapted for

embossing and heat treatment, to impart other desired properties, such as

resilience, porosity or mechanical strength.

Claims

1 . A papermaking felt, said felt having a paper contacting surface

provided by a fibrous batt layer, characterised in that the surface batt fibres

are needled selectively to provide raised patterns.

2. A papermaking felt according to claim 1 wherein the fibrous batt layer

comprises a blend of two or more fibre types with significantly different

melting points.

3. A papermaking felt according to claim 2 wherein the blended fibres

are provided in one or more layers within the fabric, at least one said layer

being at or close to said paper contacting surface which is to be embossed.

4. A papermaking felt according to claim 1 wherein at least one batt

layer comprised predominantly or wholly by relatively low melting point

fibres is located at or close to said paper contacting surface.

5. A papermaking felt according to claim 2 wherein said batt layer

comprises a mixture of relatively high melting point polyamide 6 fibres, and

relatively low melting point polypropylene fibres.

6. A papermaking felt according to any preceding claim, wherein said

paper contacting surface comprises one or more raised areas of pulled fibres

and fibrils which is heat bonded to provide a matrix embedding higher

melting point fibres and forming an embossed surface with relatively

compaction resistant raised areas.

7. A process for making a papermaking felt, comprising selectively

needling an exposed paper contacting surface of a fibrous batt layer to

provide raised areas.

8. A process according to claim 7 wherein said batt comprises a blend

of two or more fibre types with significantly different melting points.

9. A process according to claim 7 or 8 wherein the felt is heat set after

needling, causing the lower melting point fibres to melt and resolidify to act

as a rigidising polymer material which reinforces the raised areas.

10. A process according to claims 7, 8 or 9 wherein the needling is

carried out with forked needles.

1 1 . A process according to any one of claims 7, 8, 9 or 10 wherein the

needling is carried out in accordance with a pattern controlling a needling

machine, selected areas being needled to provide raised regions, the

remainder of the surface being treated to leave relatively depressed regions.

12. A papermaking felt made by a process according to any of claims 7

to 1 1 .