MULTILAYERED PAPER

Abstract: The present invention furnishes a paper that includes at least two layers in the z direction, which in turn are, in the y direction, divided into at least two fields with properties that differ from each other and that extend in the x direction. These properties can be optical or tactile, preferably optical. Such a paper is secure against forgery as it has one appearance when looked down upon, yet displays another hidden pattern that becomes apparent when looking through the paper. An arrangement for producing such paper includes means of arranging stocks in exact positions on the roll screen, both in the y and x directions of the paper. The present invention also includes a method for producing such paper.

Description: Multi-layered paper The present invention concerns an arrangement and a method for the production of paper, in particular paper for bank notes and other valuable documents. The arrangement and a method make it possible to produce single or multi-layered sheet compositions with several fields running in the direction of the paper web. The present invention also includes paper produced according to the method as well as valuable documents produced with the paper. The prior art / Background to the invention The development of colour photocopiers has made it easier to copy bank notes and other valuable documents such as securities and bonds. At the same time, the development of security measures intended to simplify verifying the authenticity of, for example, bank notes, is taking place. Such measures include traditional security measures such as water marks, intricate patterns and hidden symbols, for example, microscopic text. Numbered among the more modern security measures are security fibres in plastic and metal, with or without printed text or patterns. Another way of tackling the problem is to give the paper itself characteristics that cannot be imitated by copying, for example, varying the transparency or including a specific content of marker substances, for example, an optical, electrical or magnetic content of specific substances that can be read. The mixing in of magnetically readable substances, e.g. metal shavings, is known from US-P- 59 281. The drawback of these previously named methods, and thus the documents of value, is that their authenticity cannot be proven without the use of technical aids. Visible strings or fields of differing transparency can be achieved by means of a method according to SE 500 384. Multi-layered paper, for example, filter paper, as well as the production of this, are described in WO 92/01112 and 92/01113. The arrangement of optically differing paper-making stock or pigment on or in a paper web is also known, for example, via EP Al 580 363 and GB 696 673. Nevertheless, the problem of producing paper with a good and uniform durability that at the same time is simple to demonstrate optical or tactile variations in three dimensions, i.e. the paper web's x, y and z directions, still remains. In this respect, y relates to width, z to thickness or height and x to the longitudinal direction of the paper web. Brief description of the invention The present invention provides a solution to this problem and makes possible the production of paper with a good and even durability and with easy-to-demonstrate security measures. The present invention concerns a paper, an arrangement and a method according to the invention that are distinguished by the characteristics of the enclosed claims. Description of the drawings The invention will be described in greater detail as follows by means of examples of embodiments and references to the enclosed drawings, whereby Fig. 1 A shows schematically one embodiment of the invention where the paper comprises two layers 1 and 2, each including two fields, 3 and 4 and 5 and 6 respectively, each one with different optical properties, for example, one field has a lower (4 and 5) and one a higher (3 and 6) light transmission. Fig. 1 B shows an embodiment very similar to the previous one, but where fields 3 and 6 do not overlap one another. The numerical designations are the same as in fig. A. Fig. 2 shows schematically one embodiment of the invention where the upper layer 1 and the lower layer 3 are produced of a uniform paper-making stock 4, while one or more inner layers 2 include one or more fields 5 and 6. In this paper, the extent of the fields 5 and 6 is visible when looking through it, but when glancing down at it, the paper displays a uniform appearance. Fig. 3 shows schematically one further embodiment of the invention with two fields 5 and 6 arranged in the upper and lower layers of the paper (1 and 2 respectively) and which differ in optical properties from the surrounding paper 4. By arranging the extended fields 5 and 6 in this way so that they partly overlap one another, and by suitable choice of the colour of the field or another property, one can achieve the following: The paper displays differing appearances on its upper and lower sides when glancing down on it and, when looking through it, a third, hidden pattern that is formed by the interaction of the fields is seen. Fig. 4 shows schematically one embodiment of the invention where a multi- layered paper includes two uniform outer layers 1 and 2 plus two inner layers 2a and 2b. The inner layers contain two or more fields with different optical properties 5 and 6. The inner layers' fields are hidden when viewed from above but, when looking through them, together form a tactile pattern of lighter and darker areas (7 and 8). Fig. 5 shows schematically a side view of a flow chamber connected to a roll screen paper-making machine where the flow chamber includes sections for the simultaneous input of several stock mixtures. Fig. 6 shows schematically a side view of a system with several flow chambers, 11, 14 and 15, where the flow chamber 14 is sectioned into two levels so that two layers can be applied simultaneously. Fig. 7 shows schematically as a perspective view how a flow chamber can be divided into several levels with rows of diffusers arranged in the form of a matrix. Fig. 8 shows schematically a cut-away view of a flow chamber divided into three levels, A, B, and C, separated by a divider. Fig. 9 shows schematically a cut-away view from above of one embodiment where a diffuser, displaceable in a sideways direction, is arranged with one or more sections for the input of one or more stock mixtures whereby the displaceable diffuser is supplied with stock mixture B, whose properties differ from the surrounding stock mixture A. Fig. 10 shows a sketch illustrating the principle of a device that can be used for the input of a stock that differs from surrounding stock mixtures. Description of the invention The paper according to the invention includes at least two layers, which in turn are divided into longitudinal continuous or discontinuous fields of paper with properties that differ from the surrounding paper. Continuous fields are well suitable. The properties that can be allowed to vary according to the invention are suitably those that can easily be demonstrated without further auxiliary assistance, e.g. optical or tactile properties. Examples of optical properties include transparency or the transmission of visible light, reflection or colours that can be demonstrated in visible light or with the help of ultraviolet light. Examples of tactile properties include a glossy or rough finish, stiffness and thickness, which can easily be demonstrated by manually handing the paper or the printed document of value, e.g. a bank note. The term "layer" is used for the distinct layers in the paper, each with an area weight of about 3 g/m 2 or more. Bank note paper with an area weight of about 80 g/m 2 and a thickness of 120 μ can, in theory, contain up to 25 distinct layers. The paper according to the invention includes a number of layers so that the sought-after effects are achieved with, in practice, 2 to 10 layers, preferably 3 to 5 layers. An embodiment with two layers is illustrated in fig. 1A and IB and in fig. 3, while embodiments with three or four layers are illustrated in fig. 2 and fig. 4. In fig. 1A and IB, 1 and 2 designate the different layers in the paper, which in turn are divided into longitudinal fields with different optical properties. According to one embodiment shown in fig. 1 A, fields 4 and 5 have a lower transmission of light or transparency, while fields 3 and 6 have a higher transmission of light. The lanes between the fields in the upper and lower layers consist of lines with a regular pattern, e.g. sinusoidal curves, whereby the fields are arranged so that they partially overlap one another. When looked upon, the paper has a uniform surface but, when looked through, a pattern with a lower transmission of light becomes visible. The fields can naturally be given reversed properties, whereby, when looking through the paper, the hidden pattern is seen as a lighter element in the paper. According to another embodiment illustrated in fig. IB, fields 3 and 6 do not overlap. Looking through this instead reveals a pattern with a higher transmission of light 7 that borders an area with a lower transmission of light 8. Once again, these fields can be given reversed properties, whereby the opposite effect is achieved. Figs. 2, 3 and 4 illustrate further embodiments of the invention where the paper has different appearances when looked down upon and when looked through. An interesting combination of effects can be achieved by producing the patterned paper with a high degree of precision in the pattern and then printing and cutting out documents of value, such as bank notes, that 100% fit in with the pattern. To accomplish the variations in properties according to the invention, different paper-making stocks mixed with suitable fibres, pigments, fillers and binding agents are used. Examples of suitable fibres include material of both natural and synthetic origin, e.g. cotton fibres, cellulose fibres or fibres of polymers or thermoplastics such as viscose fibres and polyethane fibres. Such fibres are particularly suitable since they give the paper noticeable optical or tactile properties without reducing the robustness of the paper. Examples of suitable pigments are conventionally used pigments, e.g. titanium dioxide. Examples of suitable filling and binding agents are those that are used conventionally during the making of paper and which can be considered to be well known for a skilled person in the area. The device according to the invention includes means for building up a three dimensional structure, including layers arranged on top of one another, and, within these layers, fields running in a longitudinal direction. See, for example, fig. 2, where the layers are designated 1, 2 and 3, and the fields running in a longitudinal direction, 5 and 6. According to one embodiment of the invention, the device is arranged as in fig. 5, where a sectioned flow pipe 11 is shown in cross-section. The flow pipe 11 includes a number of feed pipes, here exemplified as pipes for feeding in paper-making stock A and B that open into diffuser 12. Flow pipe 11 is arranged adjacent to a cylinder or roll screen paper- making machine 9 equipped with sectioned vacuum suction chambers. By means of the divider 13, the different stocks are fed onto the roll screen paper-making machine and are prevented from being mixed together prior to the water being removed. Fig. 6 shows one embodiment of the invention where three separate flow pipes 11 , 14 and 15 are arranged around a cylinder with sectioned vacuum suction chambers. An initial layer of paper is applied with the use of the flow pipe 11, while the following flow pipe 14 is separated by a dividing element 13 and can thus feed two separate paper-making stocks to the zone where water is removed. Flow pipe 15 is used to apply the final layer of paper. In this context, the term "flow pipe" means a general means of feeding the stock to the water removal zone. A flow pipe can include several feed pipes that suitably open into diffusers, ideally into what is known as step diffusers intended to achieve a flow with a uniform rate of flow profile. The feed pipe can be made up of branches from a common feed channel but can also be supplied individually with special stocks. According to the present invention, the flow pipe is sectioned in longitudinal groups of feed pipes that are equivalent to the horizontal layer intended to be achieved on the paper. This embodiment is exemplified in fig. 7. Within each longitudinal group or "plane", one or more feed pipes can be supplied with a stock that differs from that supplied to the surrounding feed pipes. From fig. 7, it is evident how the "planes" are separated by the dividing elements, which prevents the different stocks mixing prior to the removal of water and the forming of the distinct layers. Fig. 6 shows an alternative embodiment of an arrangement according to the invention. Here three flow pipes 11, 14 and 15 are arranged beside a cylinder 9 equipped with a sectioned vacuum suction chamber. Each one of these flow pipes is able to achieve a layer of paper on the cylinder and the flow pipes are so arranged that the layer is formed before the following layer is applied. At least on of the flow pipes is sectioned, i.e. it includes several feed pipes. In fig. 6, the centre flow pipe 14 is sectioned by dividing element 13. The flow pipes intended to provide a field in the layer with differing properties are equipped with one or more feed pipes that have their own feed input for stock that differs from the stock that makes up the main constituent component of the current layer or paper. Alternatively, one or more of the flow pipes can be divided into levels, whereby two or more layers can be applied by the same flow pipe. In such a case, the flow pipe is equipped with flexible dividers in the z-direction, which essentially runs forward to the surface of the cylinder or the roll screen. One essential characteristic of these flow pipes is that they are not in direct contact with the surface of the cylinder, but are separated by a gap of about 2-3 mm between the upper edge of the flow pipe and the surface of the cylinder or roll screen. This means that the flow of stock cannot be under pressure and that the formation of the layer in the sheet is essentially controlled wholly by the removal of water. According to one preferred embodiment of the invention, one or more of the feed pipes in a flow pipe is equipped with moveable dividers in the x-direction, which essentially runs forward to the surface of the cylinder or the roll screen. By controlling these dividing elements and, for example, giving them an oscillating movement, a pattern can be reproduced on the surface. This principle is illustrated in fig. 9, where a flow chamber 11 is shown in cut-away view as seen from above. A feed pipe or diffuser 12 has been equipped with a separate feed input B and with the moveable divider 16. These dividing elements are preferably flexible elements that extend essentially all the way forward to the surface of the cylinder or the roll screen. By causing these elements to move, a field of the desired design can be formed in a layer, preferably a layer located in the middle of the finished paper. According to one preferred embodiment, the flow of stock B is regulated in relation to the flow of surrounding stock A so that the dividing elements 16 alternately approach and retreat form each other. By increasing the flow of B in relation to the surrounding flow, the dividing elements are pushed further apart from one another and the resulting field becomes broader. By decreasing the flow of B in relation to the surrounding flow, the dividing elements are brought closer to one another and the resulting field becomes narrower. A plane can even be divided into two fields so that one dividing element 16 is arranged between a number of diffusers 12 that are provided with a stock with certain properties and other diffusers in the same plane that are supplied with a stock with properties that differ from those of the adjacent stock. The dividing elements can even be arranged in a connected manner as exemplified in fig. 10, whereby they can be connected to a means that brings about their movement, e.g. an oscillating movement. By setting the width of the field that differs and the frequency of the oscillating movement, a visual or tactile presence of a pattern can be achieved in the paper or on its surface. According to another embodiment of the invention, the arrangement can include several flow chambers, whereby at least one is sectioned with permanently fixed or moveable dividing elements for feeding in the special stocks, and the associated absorbent screen. Following formation, the layers from all the flow chambers are combined on one paper web, which continues running for dying in the conventional manner. Example of an embodiment Stocks with different optical properties, e. g. two stocks with high and low transparency respectively, are prepared in separate containers. Examples of the composition and treatment of the stocks are given below. Stock A: 60-80 % combed cotton, 20-40 % cotton loops, approx. 6 % titanium dioxide, pigments for toning the shade of the paper, chemicals for increasing the strength. Stock Bl : 60 % polyvinyl alcohol fibres, e.g. Kurarai VPB101 plus 40 % combed cotton or 40 % acrylic fibre, softeners, e.g. glycerol, glycerine. Stock B2: 100 % acrylic fibre, e.g. Asahi A104. Stock B3: 100 % combed cotton plus impregnation as in stock B2. Normally, the finished paper is coated with a surface glue, e.g. polyvinyl alcohol. Fields produced with stock B2 can, in addition, be impregnated or coated with binding agents, e.g. UN-hardened acrylics, water-based acrylate latex, polyvinyl alcohol or viscose. A paper with three layers including a pattern, hidden when looked down upon but visible when looked through, produced when stock A is applied by a cylinder with sectioned vacuum suction chambers, whereby, immediately following the removal of water from this layer, stock Bl is applied in the form of a field with oscillating edges surrounded by stock A. Following water removal from this layer, a fresh layer of stock A is applied. The finished paper displays a uniform surface when glanced upon while a lighter pattern appears when examined by looking through the paper, i.e. a field with a greater transparency.

Claims: Claims 1. A method for the production of multi-layered paper by forming suspensions of fibres deposited in layers upon each other on a roll screen in a paper-making machine, characterised in that at least two layers (1; 2) are formed each divided in side-by-side located fields (3, 4; 5, 6) with paper properties that differ from each other by the simultaneous deposition onto the roll screen of fibre suspensions laterally separated from each other, and in that the field in one (3 , 4) of the said at least two layers forms in a manner that is laterally displaced with respect to the field in another (5, 6) of the said at least two layers. 2. The method according to claim lcharacterised in that at least one pair of adjacently located fields (3, 4) is formed with varying widths. 3. An arrangement for carrying out the method according to any of the above claims, including a number of inlets arranged on top of each other for forming the fibre suspensions deposited in layers upon each other on a roll screen in a paper-making machine, characterised in that at least two inlets each include a number of inlet pipes (12) lying side-by-side for dividing up the respective inlet-formed layers into side-by-side located fields (3, 4; 5, 6) with paper properties that differ from each other by the simultaneous deposition onto the roll screen of fibre suspensions laterally separated from each other. 4. The arrangement according to claim 3, characterised in that inlets and inlet pipes located adjacent to each other are separated by a dividing element (13, 16) that prevents the mixing of the adjacent fibre suspensions prior to the removal of water from the roll screen. 5. The arrangement according to claim 3, characterised in that the dividing element (16) that separates the inlet pipes is arranged in a moveable manner to allow the possibility of adjusting the width of the associated field. 6. A multi-layered paper produced by a method or arrangement according to any of the above claims.

Inventors: BERGSTROEM JAN, BERGSTROEM, JAN
Applicants: BERGSTROEM JAN, TUMBA BRUK AB, AB TUMBA BRUK, BERGSTROEM, JAN
Application year: 1998
Main classification: D21H21
IPC codes: D21F1, D21F11, D21H11, D21H13, D21H21, D21H27