The invention relates to a tissue membrane felt, and has particular, though by no

means exclusive, reference to a tissue membrane felt to be used as a pick-up felt in a Yankee cylinder drying process A Yankee machine forms, presses and dries thin paper webs and consists of a forming

section, a web pick-up arrangement which transfers the formed web to a press felt, known

as a pick-up felt, and one or more press rolls, over which the felt with the web is turned so that the web is pressed directly against a heated Yankee cylinder

Conventionally, a Yankee machine utilises a woven base pick-up felt in order to pick

up a formed web from a forming section and transfer the formed web from the forming

section to a heated Yankee cylinder for drying and creping Due to the critical limits at high

machine speeds of a Yankee machine, which can reach speeds of about 2000m/min when the web grammage is about 17g/m ² , the characteristics and quality of the pick-up felt are

significant. Traditionally, the pick-up felt has a smooth surface. It must have the requisite

density and water content in order to function properly The pick-up function is affected by the water quantity, permeability and surface characteristics of the felt Large quantities of water in the felt may improve its pick-up function, but this creates problems at the drying

cylinder

The primary object of this invention is to provide an alternative pick-up felt which has

enhanced performance over previous pick-up felts, particularly in the areas of enhanced bulk

and softness of the paper web.

It is a further object to provide a pick-up felt having uniquely resilient and compressible reinforcing elements disposed in the matrix of the felt with resistance to abrasive, chemical or heat degradation.

According to the present invention there is proposed a membrane felt for use in a Yankee machine, the membrane felt comprising a supporting base structure and a non-woven membrane, wherein the non-woven membrane comprises a polymeric matrix and yarns extending in the intended running direction thereof

The yarns may be monofilament or multifilament yarns

The supporting base structure may be a woven basecloth. Alternatively it may be a composite membrane structure comprising a polymeric matrix and load bearing yarns therein

In a preferred embodiment of the invention a batt fibre layer is secured, preferably

needled, between the supporting base structure and the non-woven membrane layer onto the

supporting base structure thus rbr ing a base structure-batt fibre-membrane assembly

Preferably the batt fibre layer is manufactured from polyamide or polyoleftn The non-woven membrane may be secured to the top of the uppermost staple fibre layer

Additionally, one or more layers of staple fibre may be needled onto the membrane- fibre-basecloth assembly at the paper contacting side of the felt, namely the membrane

surface, whilst ensuring that the amount of staple fibre used in this regard is kept to a

minimum so as not to mask the mesh pattern of the membrane.

Batt staple fibre may be needled into the base structure and membrane from the

surface of the base structure which is opposite to the membrane side of the felt.

The staple fibre used in the present invention may be between 3 - 15 denier,

- -> - preferably 3 - 6 denier, in order to provide the required strength to keep the woven basecloth

and non-woven membrane intact when being used at performance critical limits and high machine speeds

The non woven membrane may be of mesh form wherein the mesh layer includes yarns in the intended running direction thereof

The membrane surface in contact with the web may be planar However, preferably, it has a ribbed profile, so that at least some of the cross machine direction lands of the mesh membrane are raised with respect to the main plane of the mesh membrane As an alternative or in addition to the raised cross machine direction lands of the mesh membrane, some of the

machine direction lands may be raised with respect to the main plane of the mesh membrane forming a ribbed profile The machine direction lands are raised by needling the membrane into the base structure so that the yam containing machine direction lands are retained on the web-contacting surface of the felt whilst those machine direction lands with no yarns are

displaced in the body of the felt In a further preferred embodiment of the invention the membrane surface in contact with the web may have a rectangular pattern In such a construction some of the machine direction lands are raised above the main surface plane of the membrane, whilst others are depressed with respect to the plane The raised machine direction lands contain multifilament or monofilament core yams, and are raised as in the method described above Thus, the raised machine direction lands, in combination with the transverse ribs in the cross machine direction, as mentioned above, create a rectangular mesh pattern on the surface of the

membrane This is illustrated in the drawings

Preferably, two in every four of the running machine direction mesh lands are depressed with respect to the web-contacting surface of the felt, the remaining two running mesh lands containing yams are raised with respect to the web-contacting surface of the felt,

as described above The yarn-containing pattern, together with the raised transverse cross

machine lands which are preferably spaced apart at 2 5 mm intervals create a square or approximately rectangular mesh pattern on the surface of the membrane This network of cells allow regions of bulked and unbulked paper fibres of the web to be formed

The advantages of this arrangement are that the high surface contact area presented by the membrane improves adhesion of the web to the Yankee cylinder Furthermore, the yam-containing machine direction lands are slightly rigid in relation to the main surface plane of the membrane due to their relative inflexibility The cross machine direction lands are also slightly rigid due to the fact that more membrane polymer is present, making them less flexible than the machine direction lands containing no yarns This results in enhanced creping of the web which leads to an increase in web bulk and softness The bulk is further improved by the differential specific pressure at the membrane ribs which are under high load when compared with the non-ribbed surface regions which are under much reduced load.

The supporting base structure may comprise a membrane structure of mesh form wherein the mesh layer includes yams in one direction thereof The membrane structure may be manufactured in accordance with the method described in GB 2202873 -A The edges of

the membrane may be joined in accordance with the method described in GB 2254287

The matrix material to be used in the present invention may be selected from a wide variety of polymeric materials A preferred material is thermoplastic polyurethane in terms

of resilience and compressibility The compressible nature of such an elastomeric membrane material means that creping of the web is enhanced, thus contributing to the desired increase

in web bulk and softness Another advantage of the membrane when its surface is ribbed or

rectangular is that it confers grid-like or ribbed symmetrical patterns into the web, thus creating an aesthetically pleasing product

In a further preferred embodiment of the invention the membrane felt comprises a supporting base structure comprising a composite membrane structure, a second layer of up to 450 g/πr of needled batt fibre (6 - 15 denier), a third layer comprising a ribbed membrane

on the web contacting side of the felt and an extra 50 - 150 g/πr fine surface batt fibre (3 - 6 denier) needled onto the base structure-batt fibre-membrane assembly

The invention will now be described further, by way of example only, with reference to the accompanying drawings in which -

Fig 1 is a diagrammatic perspective view of a cut away portion of membrane felt in accordance with the invention Figs. 2 and 3 are enlarged sections taken on lines II-II and III-III respectively of Fig

1

Fig 4 is a plan view of the membrane layer of a membrane felt as illustrated in Fig 1

Referring now to the drawings, and particularly to Fig 1 thereof, a membrane felt which may be used in a Yankee machine comprises a membrane layer 1 1 and a woven basecloth 12 secured together with batt staple fibre 13

As illustrated in Figs 1, 2 and 3, membrane layer 1 1 presents longitudinally extending

raised land areas 14 and transversely extending raised land areas 15 to give rectangular areas

16 Land areas 14 contain load bearing yams 17 in the intended running direction of the

membrane felt

The differential specific pressure at land areas 14 and 15, which are under high load when the membrane felt is in use in a Yankee machine, is much higher than the pressure at rectangular areas 16 which are under reduced load Consequently there is enhanced creping

of the web which leads to an increase in web bulk and softness as well as less fibre compression in the low pressure areas

The fibrous batt layer 13 is secured on one side thereof to the membrane layer 1 1 The other side of the fibrous batt layer 13 is secured to a woven basecloth by thermal bonding, by an adhesive, ultrasonic welding by needling or any conventional or other method Ordinarily the fibres in the batt will be randomly oriented, but in some circumstances length orientation may be preferred

Whilst in the embodiment under consideration, land areas 14 and 15 give rectangular areas 16 thus creating a square pressure pattern on the web-contacting membrane surface, this is not essential and the membrane may have a planar surface Furthermore, the membrane may be ribbed in one direction only, for instance, the lands 14 containing the ya s

17 may be raised above the main surface plane whilst those containing no such reinforcing members are depressed with respect to the plane, with no raised transverse ribs, but instead depressed transverse ribs with respect to the main plane of the mesh membrane.

The membrane layer of the embodiment in consideration may be conveniently

manufactured in accordance with the method described in GB-A-2202873, although other

methods may be preferred, such as, for example, a powder dispersal technique

The woven basecloth may be of conventional form and matenals, capable of providing stability and water handling to the pick-up felt

The batt may be secured to the woven basecloth, alternatively, the batt may be built

up in situ on the woven basecloth by means of a melt-blown technique wherein fibres are extruded onto the woven basecloth and, by virtue of their semi-molten state, adhere at their boundary surfaces to the basecloth The degree of fineness of the fibres may be varied during batt build-up according to the specific requirements of the pick-up felt It is to be

appreciated that spun laced, spun bonded or other non-woven web creating techniques may also be used to create the batt

It is to be appreciated that the thickness of the membrane, woven basecloth and batt staple fibre layer, if such a layer is used for securing the membrane/basecloth assembly, may

be modified to accommodate the requirements of the web being formed, dπed and creped in the Yankee machine It is to be understood that the above descπbed embodiment is by way of illustration only Many modifications and variations are possible