Information
-
Patent Grant
-
6436240
-
Patent Number
6,436,240
-
Date Filed
Friday, March 3, 200024 years ago
-
Date Issued
Tuesday, August 20, 200222 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
- Caesar, Rivise, Bernstein, Cohen & Pokotilow, Ltd.
-
CPC
-
US Classifications
Field of Search
US
- 162 348
- 162 3582
- 162 900
- 162 902
- 162 903
- 442 32
- 428 217
-
International Classifications
-
Abstract
Papermachine clothing comprises a base fabric comprising at least two superimposed perforated non-woven membranes (11, 12), the upper or paper side one of which (11), has a lower maximum creep modulus and is less hard than the lower or machine side membrane (12).
Description
This invention relates to papermachine clothing, particularly, but not exclusively to clothing for use in the press section of a papermaking machine.
WO 92/17643 discloses papermachine clothing of the kind for use in the press sections of a papermaking machine which includes a base fabric composed of superimposed layers of synthetic thermoplastics material in mesh form which are secured together. The superimposed layers have apertures of different respective sizes and the base fabric formed by the superimposed layers provides support and reinforcement to a fibrous batt. The lower (machine contacting) layer may have a coarser mesh than the upper (batt contacting) layer.
It has been found that when resilient membranes are used, as at present, in such structures, the flexibility of the material under the pressures exerted in press nip causes the membrane material to deform and thus reduce or even close the mesh apertures. This in turn creates problems with re-wetting of the paper web with water which has entered the mesh being squeezed back through the batt into paper from which it has previously been extracted.
An object of the invention is to provide papermachine clothing with improved dimensional stability and strength, whereby the tendency towards closure of mesh apertures under nip pressure is much reduced and rewetting, and marking, of the paper web alleviated.
In accordance with the invention, papermachine clothing includes a base fabric comprised of at least two superposed membrane layers of synthetic thermoplastics material in mesh form, characterised in that the lower (machine side) membrane layer consists of a harder material than the upper (paper side) membrane layer which has a lower maximum creep modulus than the lower membrane layer.
Preferably, said upper membrane layer is of a thermoplastic polyurethane matrix material, with a Shore A hardness of, for example, between 65 and 85. The lower membrane preferably comprises a polyamide matrix material with a Shore D hardness of, for example, between 40 and 45.
A sandwich layer of batt staple fibre may be provided between the membrane layers.
The base fabric will normally in use support a fibrous batt of known form and materials, for example as described in WO 92/17643.
The effect of using a very hard lower membrane as envisaged is to create a large number of pockets into which water expelled from the paper sheet can be accepted. This can significantly increase the dewatering capacity of the felt.
The base fabric may of course be composed of three or more superimposed layers of perforated membrane and these may increase in hardness from the uppermost to the lowermost layer and similarly the sizes of the apertures may increase from the uppermost to the lowermost layer. Preferably at least one membrane layer contains parallel reinforcing yarns extending in at least one direction, and the fabric may comprise two such layers. These membranes may be made in accordance with GB-A-2254288. The base fabric may contain one or more woven base cloth layers either between or on an outer face of the membrane layers.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings, wherein:
FIG. 1
is a cross-section of a first embodiment of papermachine clothing according to the invention;
FIG. 2
is a cross-section of a second embodiment of papermachine clothing according to the invention; and
FIG. 3
is a cross-section of a third embodiment of papermachine clothing according to the invention.
DETAILED DESCRIPTION
Referring first to
FIG. 1
, a first embodiment of papermachine clothing according to the invention comprises a fibrous batt
10
of known type supported by a base fabric which is composed of two superimposed membrane layers, an upper layer
11
and a lower layer
12
.
The upper layer
11
is of a thermoplastic matrix material such as a thermoplastic elastomer, e.g. thermoplastic polyurethane with a Shore A hardness of from 65-85. The layer
11
is in the form of a mesh grid having substantially square or rectangular apertures
13
defined between machine direction lands
14
and cross machine direction strips not shown. In accordance with the teaching of WO 92/17643, at least some of the machine direction lands
14
are reinforced with load bearing yarns
15
embedded in and extending along the lands
14
.
The lower layer
12
is secured to the upper layer
11
by thermal fusion of the abutting surfaces, or by means of an appropriate adhesive or by ultrasonic welding or needling. The lower layer
12
is of a thermoplastic material, e.g. a polyester, silicone or nylon such as PA6, PA6.6 or PA6.10 or a blend containing one or more of these. This material has a Shore D hardness of 40-45. The Shore D scale is used for this as the values available on the Shore A scale do not go high enough to provide a range for the layer
12
.
Layer
12
is similar in configuration to layer
11
and also comprises square or rectangular apertures
16
defined by machine direction lands
17
and cross machine direction lands (not shown) to produce a similar mesh or reticulate structure. However, the apertures
16
are longer in size than the apertures
13
in the upper layer
11
.
By way of example, the layer
11
may be from 0.75-1.25 mm in thickness, the apertures
13
have an individual means area of from 0.6-1.2 mm
2
and a pitch (centre to centre spacing of the apertures
13
) of from 1.25 to 1.75 mm. The corresponding dimensions of the lower layer
12
are: thickness in the range 0.5-1.0 mm, mesh apertures
16
mean area from 1.21-1.8 mm
2
and pitch in the range of 1.75 mm-2.25 mm. In other words, the lower layer is much harder than the upper layer, somewhat thinner, with larger more widely spaced apertures.
FIG. 2
is a variant of
FIG. 1
wherein an upper layer
21
is separated from a lower layer
22
by a batt layer
23
. The upper and lower layers have similar dimensions to layers
11
and
12
in FIG.
1
and their properties and materials are also the same as or similar to those respective layers
11
,
12
. The batt layer
23
is needled into the lower membrane layers
22
and then the upper membrane layer
21
is placed on top of the batt layer and the entire structure is needled together to effect a bond between the layers.
In
FIG. 3
is shown a further variant, wherein papermachine clothing comprises an upper batt layer
30
, supported by a base fabric comprised of three superimposed layers
31
,
32
,
33
. Upper layer
31
and lower layer
33
have the same or similar properties and materials to those of layers
11
and
12
respectively of FIG.
1
. Intermediate layer has hardness and dimensional properties which are intermediate between those of layers
31
and
33
. This may be achieved by choosing an appropriate plastics material such as a polyamide/polyurethane blend or a less plasticised polyurethane.
Flexibility may be determined by meaning the converse, i.e. stiffness as defined by maximum creep modulus. This is measured at 120° C. and under 0.13 MPa applied load. The creep modulus of the softer layers
11
,
21
,
31
in the above embodiments may be in the range 2-10 MPa, and the harder layers
12
,
22
,
33
may be in the layer 15-25 MPa. The intermediate layer
32
of
FIG. 3
may have an intermediate value of e.g. 8-16 MPa.
The above embodiments are described by way of example only and the invention includes a variety of other embodiments within its scope. For example, any suitable combination of relatively resilient and relatively hard materials may be used, including metals for the hard membrane and natural or synthetic rubber as well as other plastics.
Any form of mesh of perforated sheet or foraminous structure may be used with any desired shape of aperture, including honeycomb structures and sheets with circular apertures, metal or plastics wire grids and meshes and the like.
Claims
- 1. Paper machine clothing including a base fabric comprising at least two superposed perforated non-woven membrane layers of material in mesh form, characterised in that the lower (machine side) membrane layer consists of a harder material than the upper (paper side) membrane layer, which has a lower maximum creep modulus than the lower membrane layer, wherein said upper membrane layer is a thermoplastic polyurethane matrix material that has a Shore A hardness of between 65 and 85 and wherein said lower membrane comprises a polyamide matrix material with a Shore D hardness of between 40 and 45.
- 2. Papermachine clothing according to claim 1, wherein a sandwich layer of batt staple fibre is provided between the membrane layers.
- 3. Papermachine clothing according to claim 1, comprising three or more superimposed layers of perforated membrane, said layers being arranged in order of increasing maximum creep modulus from the uppermost layer to the lowermost layer.
- 4. Papermachine clothing according to claim 1, wherein at least one of said membrane layers comprises parallel reinforcing yarns extending in at least one direction.
- 5. Papermachine clothing according to claim 1, wherein said base fabric supports a fibrous batt layer.
- 6. Papermachine clothing according to claim 1, wherein the base fabric includes one or more woven layers between or on an outer face of the membrane layers.
- 7. Papermachine clothing according to claim 1, wherein the harder, membrane layer of higher maximum creep modulus comprises a perforated member having apertures or perforations of larger size and more widely spaced than corresponding apertures in the upper softer membrane layer of lower maximum creep modulus which is also a mesh or perforated member.
- 8. Papermachine clothing according to claim 1, wherein the softer membrane layer has a maximum creep modulus of from 2-10 MPa, and the harder membrane layer has a maximum creep modulus of from 15-25 MPa.
Priority Claims (1)
Number |
Date |
Country |
Kind |
9712113 |
Jun 1997 |
GB |
|
PCT Information
Filing Document |
Filing Date |
Country |
Kind |
PCT/GB98/01544 |
|
WO |
00 |
Publishing Document |
Publishing Date |
Country |
Kind |
WO98/56982 |
12/17/1998 |
WO |
A |
US Referenced Citations (6)
Foreign Referenced Citations (3)
Number |
Date |
Country |
0 576 115 |
Dec 1993 |
EP |
2 254 288 |
Oct 1992 |
GB |
9217643 |
Oct 1992 |
WO |