Background of the invention In this specification, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date: (i) part of common general knowledge; or (ii) known to be relevant to an attempt to solve any problem with which this specification is concerned.

While the present invention will be describe with reference to the production of sheets of paper, such as paper in the form of sheets of cellulosic fibre web having patterned effects it will be appreciated that the invention is not so limited but also relates to the production of patterned sheets of other material, such as polymer, plastic, metal or laminate.

Paper can be formed in two basic ways, both of which have a number of variants.

The first way of making paper, specifically hand made paper usually commences with the formation of a very dilute slurry or suspension of fibres in a vat. Some of this slurry or suspension is then drained through a mesh or filtration means which is supported by a peripheral frame (the mesh or filtration means together with the peripheral frame is commonly called a deckle mould) so as to produce a web of fibres which can be pressed and dried to produce a sheet of paper. Most commonly, the fibres are cellulosic fibres derived from wood or non-woody plant species.

Various means are known for producing patterned effects in or on such sheets.

One method for achieving a patterned effect is to produce a watermark by including a pattern element on the mesh or filtration means or by impressing a patterned element onto the web prior to or during pressing. This approach is limited in its effect to producing regions of different transparency and the result is normally only clearly visible when an observer views the watermark using light transmitted from behind the sheet.

Another method is to have two or more vats containing fibre slurries or suspensions of fibres of different colours, lengths and/or textures and to blank off different portions of the deckle mould prior to processing slurry or suspension from different vats. A sheet produced in this way has regions of different colour or texture. The method is very time consuming.

Still another method is to include small quantities of additives in the slurry or suspension. The additives are usually in the form of elements which are large relative to the size of the fibres. A sheet formed from such a slurry or suspension will have an internal texture of randomly arranged features. This technique is commonly used by hobbyist papermakers and by some makers of specialty decorative papers. There is very limited scope to control the technique, and the sheet produced has the elements usually arranged substantially at random both over the plane of the sheet and through its thickness.

The second way of making paper is by means of a paper machine. In this method a slurry or suspension of fibres is more or less continuously spread over a continuously moving mesh or filtration means, the web of fibres so formed passing over a series of devices for removing water, for pressing or compacting the web and for drying to form the sheet of paper. This method has the advantages of economically producing paper in large quantities and can be worked with more concentrated slurries or suspensions of fibres than are practical with the hand made method. However, paper making by means of a paper machine is not well adapted to producing patterned effects. The only such effects that are commonly produced on a paper machine are watermarks and additive inclusions.

Object of the invention It is an object of the present invention to provide an alternative means of producing patterned sheets of paper, plastic, metal or laminate.

Summary of the invention According to one form of the invention there is provided a method for forming a patterned sheet comprising the steps of a) adding patterning material in a controlled or semi-controlled manner to the upper surface of a sheet, b) optionally pressing the sheet, and c) drying the sheet Preferably, but not essentially, step (a) precedes step (b).

According to another form of the invention there is provided a patterned sheet produced by the method.

According to a preferred embodiment of the invention a web of cellulosic fibre is used to produce a sheet of patterned paper. Specifically, a web of cellulosic fibre is produced on a paper machine by known means and then, before the web is pressed or dried, patterning material comprising a slurry or suspension of patterning elements, including fibre and/or a pigment is applied at least once to the web. Under these circumstances any fibre or element of high aspect ratio in said patterning material will tend to bond with or become entangled in the fibres in the web and the resulting sheet of paper will bear a pattern. Further if the said application includes pigment, this will tend to penetrate the web.

According to another preferred form of the invention, a sheet of non-woven fabric is produced by known means and then patterning material is applied at least once to the sheet.

Under these circumstances any fibre in said patterning material will tend to bond with the sheet. Further if the said application includes pigment, this may tend to penetrate the sheet.

According to another preferred form of the invention, a sheet of metal film is produced by known means and then one or more applications of patterning material is made to the sheet.

Under these circumstances any fibre in said patterning material may tend to bond or chemically react with the sheet. Further if the said application includes pigment or reactive materials, these may tend to colour and/or patinate the sheet..

According to another preferred form of the invention, a laminated sheet is produced by known means and then one or more applications of patterning material is made to the sheet.

Under these circumstances any fibre in said patterning material will tend to bond with the sheet. Further if the said application includes pigment, this may tend to penetrate the sheet.

The word'pigment'and forms of the word'pigment'as used in this description refers to any coloured material suitable for the invention herein described, and includes but is not limited to dyes and slurries or suspensions of solid colourant material.

The word'pattern'and forms of the word'pattern'as used in this description refers to any differentiable feature which can be distinguished from other areas of the sheet whether that distinguishing feature displays a repeating form or not.

The sheet produced by means of this invention can be used for any suitable purpose. For example, the sheet of paper may be decorative (such as wall coverings) structural (such as for

use in architectural screens) or for security purposes (to produce a distinctive sheet which is difficult to copy), or it may perform some combination of these functions.

Description of the method The invention will now be further explained by reference to some specific means of performing the method.

The examples given here are generally directed to machine made sheets of paper but, as will be apparent to one skilled in the art, most of the methods are equally applicable to sheets of non- woven fabric, metal film or laminate any of which may incorporate additional surface coatings that enhance the bonding of the patterning material.

Typically, the pattern is not distributed right across the width of the sheet. Therefore in a preferred embodiment the patterning material will be applied to the sheet or web of cellulosic fibres comprising the sheet by means of one or more conduits that deliver the patterning material to only a portion of the width of the sheet.

The sheet may be moving relative to the conduits. The delivery ends of the conduits may be adapted so that the force of impact of the patterning material onto the sheet is controlled to obtain a desired effect. Further, the orientation and open area of the ends of the conduits may be varied so that the velocity of the emerging stream of patterning material relative to that of the sheet can be adjusted.

In a further embodiment, the conduit is adapted so that its delivery end is capable of being moved in a direction substantially parallel to the plane of the sheet and perpendicular to the direction of movement of the sheet. This arrangement will permit the position at which the patterning material is applied to change relative to the edge of the paper. This movement can be caused by mechanical or manual means.

In an alternative embodiment, multiple conduits with fixed delivery ends are provided and the flow of patterning material through each delivery end is capable of being controlled. Typically, the conduits may be individually controlled. In this way a pattern can be produced by a process analogous to that employed by an ink-jet printer.

In a still further embodiment, multiple conduits having delivery ends are provided and at least some of the delivery ends are capable of being moved in a direction substantially parallel to the plane of the web and perpendicular to the direction of movement of the web. This enables comparatively complex patterns to be produced without requiring an excessive number of

conduits. The movement of the conduits may be individually controlled or controlled in groups.

In another preferred embodiment, a number of different patterning materials are provided to one or more conduits such that only one patterning material is supplied at a time, or different combinations of patterning materials are supplied at different times. By use of this arrangement it would be possible to make, for example, a pattern consisting of a stripe on the sheet which changes in colour along the direction of movement of the paper machine.

It will be apparent that all or most of these facilities can be combined. However it may be inconveniently complicated or expensive to provide all of the effects simultaneously.

It will be noted that the way in which these patterns are applied can be changed to suit the particular purpose for which the sheet of paper produced is to be used. For example, if a paper sheet is to be used for producing secure documents, then the pattern will preferably be repeated over a short distance (for example every 50-250 mm). Alternatively, if paper is to be used as wall paper or for some analogous purpose, then it might be desired for the pattern to repeat over a relatively long distance (for example every 2-4 m) or be non-repeating. If the paper is to be used for an artistic display, then it may be preferred that there is no repetition of the pattern, in which case the pattern could be randomly generated (e. g. by use of a computer) or the pattern could be manually generated by the direct intervention of the user of the invention.

The patterning material can be one or more of various different types of material, depending on the effect that is desired.

Typically the patterning material is a colouring substance such as dye, pigment or a formulation including one of these or a texture creating substance such as a fibrous, granular or pulpy material. In the particular case of a paper sheet, by introducing the colouring substance whilst the sheet or web is still wet, the colouring substance will tend to penetrate the sheet and cause colouring through part or all of the depth. This may even occur with sheets which resist the penetration of inks when they have been dried. Therefore this effect may be useful in making papers for both decorative and security purposes.

Where the patterning material is cellulosic fibre pulp it may be introduced together with a colouring agent. The pulp may be introduced in small quantities so as to produce a different colour or texture over part of the surface of the sheet. In this case the pulp may be introduced as a slurry or suspension of similar fibre content to that normally used in paper making.

Alternatively, the pulp may be introduced in larger quantities so as to produce relief effects. In latter case it may be found advantageous to introduce the pulp at somewhat higher fibre content and/or with longer fibre lengths than is usually used in paper making.

The patterning material may be applied in any convenient form such as a liquid, slurry or suspension or solid. For example, in the case of a paper sheet where the patterning material is slurry or suspension it may contain at least one solid material other than normal papermaking fibres. Examples of such materials include: Very long fibres and/or plant fragments so as to produce effects similar to those in some traditional Japanese papers. Such papers show a pattern in transmitted light and are useful for making paper screens for use in windows or room dividers.

Materials which give texture or optical effects such as granular or reflective material.

Security features, such as fibres which can only be distinguished by illumination with ultra-violet or infra-red light or other non-visible electromagnetic radiation. If these are placed predominantly at surface regions, then in addition to their normal function, their absence in some areas would indicate that information has been erased from the sheet.

It will be apparent that multiple additions of patterning material may be made to produce particular effects.

When the patterning material includes fibre or other solid, it may be useful to include a binding agent such as an adhesive to improve bonding between the patterning agent and the sheet.

When the invention is used for manufacture of patterned sheets on a paper machine, the patterning material may be applied to the fibre web at different points during its passage through the paper machine depending on the effect required.

Typically the patterning material will be applied in the forming region of the paper machine onto a formed fibre web, for example just after the point where the sheet is'set'. If a patterning material containing solids is added in this region there will be comparatively little intermingling of the solids of the sheet and the patterning agent, but good bonding between the patterning material and the fibre web may be achieved.

For some purposes preferably the patterning material is applied to the web of fibres in the region prior to where the web is fully formed-or set. In this case there may be some intermingling of the patterning material and the fibres from which the sheet is formed in the upper portion of the web. This embodiment is particularly useful when the patterning material includes very long fibres and/or plant fragments as such patterning material cannot be conveniently processed in a conventional paper machine.

When making relief or textured effects, it may be desirable to press the sheet prior to adding some or all of the patterning materials. This reduces the subsequent need for drying and gives a stronger base sheet.

The word'comprising'and forms of the word'comprising'as used in this description does not limit the invention claimed to exclude any variants or additions.

Modifications and improvements to the invention will be readily apparent to those skilled in the art. Such modifications and improvements are intended to be within the scope of this invention.