GB2036649A - Embossing in register with printing - Google Patents

Abstract

A method and apparatus for embossing a pattern on a web, e.g. of wallpaper, in register with an existing printed pattern on the web utilises a tensioning device, e.g. a pair of tensioning rollers 12, to tension and stretch the web 16 upstream of the embossing station. The tension and degree of stretch is adjusted in response to scanner 18, which measures the speed of the web by counting marks thereon, so as to achieve perfect registration of the stretched printed pattern with the fixed dimension of the embossed pattern. The tension may be adjusted by moving the point of action of tensioning rollers 12 with respect to the embossing station, or by varying the speed of embossing cylinder 13. <IMAGE>

Description

SPECIFICATION Printing in register The invention relates to a method of forming a three-dimensional deformation repeat-pattern on a web, in particular a wallpaper web, in particular embossing by means of a raised embossing cylinder, in register with a pre-printed repeated pattern on the web. Additionally the invention relates to an apparatus for carrying out this method.

A great number of widely varying wall-covering patterns are on the market today. Various printing processes are used to print the coloured patterns but, in particular, the so-called photogravure or intaglio process is used. Furthermore, embossed wall coverings are known in which, in production, the wall-covering web passes through an embossing cylinder, whereupon it is embossed with the corresponding relief pattern. Similarly, in a multi-colour printing process it is known to print the multiply repeating pattern image, i.e. a so-called repeated pattern or pattern repeat, with a variety of colours in register with one another.

Moreover, it is known to print and emboss a wall-covering web simultaneously. As in known printing processes, ink is applied to the raised points of the embossing cylinder, or else into the hollows, before the embossing process is performed by said cylinder. During the passage of the wall-covering web through the embossing/coiour-printing station, the wall-covering web is embossed and printed in a single operation. However, this process is neither very accurate nor dimensionally stable; moreover, in this way only a single colour can be printed. Using the known processes and techniques it is not possible for a pre-printed web, which may be printed with a multi-colour print, to be subsequently deformed, in particular embossed, three-dimensionally inaccurate alignment with the pattern repeat of the web.

Accordingly, the present invention provides a method for forming a three-dimensional deformation pattern on a web in register with an existing printed repeat pattern on the web which method comprises tensioning and stretching the web between an upstream tensioning means and a downstream deforming station and adjusting the amount of stretch so that the deformation pattern is printed in register.

Thus between a web-tensioning point and the succeeding deforming station which forms the reference point for the accurate alignment of pattern repeat, the web is subjected to a tensile stress and, according to the deviation from proper alignment of the deformation pattern from the pre-printed pattern, the web is either lengthened by increasing the tensile stress or is shortened by reducing the tensile stress. In this way the web can be subjected to tensile stress and only lengthened and thus can be deformed elastically, semi-elastically or partly plastically.

The outstanding advantage of the method according to the invention over the known printing and embossing process lies in the fact that it enables a web already provided with a pre-printed pattern repeat, in particular a wall-covering web, to be subsequently provided with a three-dimensional deformation pattern aligned accurately with the pattern repeat. Most advantageously, the printing process is completely independent from and unaffected by the three-dimensional deforming process, e.g. embossing process. It has been found in an extremely surprising and astonishingly simple manner that precise registration can be obtained by subjecting the web of material to tensile stress.

A basic tensile stress can be so chosen that the web can be additionally lengthened by increasing the tension above the basic or the web can be relatively shortened by reducing the tensile stress below the basic. Accordingly, it is possible to apply to the web a basic tensile stress, said basic tensile stress representing a reference tension from which one can deviate either by increasing or reducing the tensile stress to maintain alignment. It is also possible for the web only to be lengthened, in which case the web can be deformed elastically, semielastically or partly plastically.

In an advantageous development of the invention, for the purpose of increasing the stretch limit of the web material, it is possible to moisten or saturate the web before applying the tensile stress. The elongation of the web can advantageously be increased thereby, since the web expands through being wet.

In principle, the method of the invention may of course be used both with dry elongation and with wet expansion.

The decisive factor is merely to bring about the lengthening or shortening of the web, which most simply is effected by applying a tensile stress to the web. In a further development of the invention it is also possible to moisten or dry the web locally in response to deviation from proper alignment. In this case the elongation is controlled by way of the water absorption of the web and the web can also be shortened by way of local drying, so that by moistening and drying it is possible to achieve variable stretching and shortening of the web and, therefore, variation of the tensile stress itself. In this case it is also possible to impart a certain basic humidity to the web, so that it exhibits a definite stretch limit.

The invention includes an apparatus for performing the above method comprising a deforming station for forming a three-dimensional deformation pattern on a web, tensioning means upstream of the deforming station for tensioning and stretching the web, and means for adjusting the amount the web is stretched to cause the deformation pattern to be printed in register.

An apparatus according to the invention for carrying out the method may comprise a webtensioning cylinder assembly and a succeeding deforming cylinder whose patter registers accurately with the pre-printed pattern repeat of the web, the speed of the deforming cylinder being infinitely variable.

In a further embodiment of the method in accordance with the invention, in connection with the aforementioned apparatus, for the purpose of creat ing both a basic tensile prestressing and and increased or reduced tensile stress, according to the deviation from alignment, it is possible for the speed of rotation of the deforming cylinder to varied be the same as or higher or less than that of the webtensioning cylinder assembly depending on the change in tension needed from moment to moment.

Advantageously, the deforming or embossing cylinder is simply controlled in such a way that its speed is slightly higher than or is the same as the speed of the web-tensioning cylinder assembly. Alternatively or additionally, the variation in tensile stress may be achieved by use of a web-tensioning cylinder assemblywhich is simultaneously a length-compensating device. This may be accomplished, for example, by shifting the point of action e.g. the centre axis or centre axes of the web-tensioning means.

The web-tensioning means may be one or more pairs of opposed rollers which may be driven or non-driven and may be mounted to be moveable as an assembly to vary the distance to the embossing station.

In principle, the elongation of the web may thus be carried out by varying the tension thereof or by varying the water content thereof or may be carried out thermally.

The method according to invention makes available for the first time a method which makes possible an accurately aligned embossing of a web with a pre-printed pattern repeat, wherein the printing process and embossing process proceed com pletely independently and unaffected by one another.

The invention is illustrated in detail in the follow ing description of the embodiment illustrated in the drawing. The method according to the invention is described with reference to the production of a wallpaper web from two webs of paper, which are bonded by means of a water based adhesive and are laminated together. The method according to the invention is likewise suitable for other webs, such as plastic webs or fabric webs with three-dimensional deformation carried out under the application of heat.

In accordance with the drawing, a wall-covering web 1 passes through a first set of feed rollers 2, 3.

At the same time a second wall-covering web 4 passes through a set of rollers 7, one of which rollers is immersed in a tank 5 containing a water based adhesive 6. The wall-covering web 4 is coated with adhesive 6 therefrom and at the same time passes through the set of feed rollers 2,3 in which both wall-covering webs 1 and 4 are laminated together.

Subsequently, the now laminated web passes through a soaking-in section 8 in which it is dis posed, for example, in meanderlike fashion, in which case the water contained in the adhesive diffuses into the two paper webs which have been laminated together. In this way the web is uniformly saturated and also becomes uniformly elastic. After the soak ing-in section 8, the web is then directed through a set of feed rollers 9 and through another set of rollers 10. The web additionally passes through a set of rollers 11 to reach a web-tensioning cylinder assembly 12, this latter being shown here as only one pair of opposed driven cylinders. The axis of rotation of this cylinder assembly 12 can be shifted in accordance with the arrows in the drawing plane, so that varying tensile stress can be imparted to the web by means of the cylinder assembly 12.The web 16 now passes over a pressure cylinder 14 which is positioned opposite the actual deforming or embossing cylinder 13. The embossing of the web so as to accurately match the pattern repeat now takes place between the deforming cylinder 13 and the pressure cylinder 14. The finished embossed wall-covering web is drawn off and wound on by way of a set of cylinders 15.

In the drawing the portion 16 of the wall-covering web is the part thereof which undergoes a controlled elongation. A sensor 18 senses the speed of the wall-covering web via markings thereon and compares this speed with the angular velocity of the deforming cylinder 13. A specific pretension can now be imparted to the web 16 via the cylinder 12.If the web speed in terms of markings detected per unittime is found notto match the peripheral speed ofthe deforming cylinder 13, i.e. the number of register marks per second counted by the sensor does not exactly tally with the number of marks corresponding to a length of web equal to that printed by the embossing cylinder in a second, the tension of the cylinder assembly 12 is increased or reduced accordingly by the centre point of the cylinder assembly being disposed translationally.

The variation in tension may also be effected by slightly increasing the peripheral speed of the deforming cylinder 13 relative to the speed of the web, whereby it is also possible to control the proper pattern-repeat alignment.

This causes a change in the elongation of the portion 16 of the web and thus a change in the register mark spacing. A given length of web taken by the embossing cylinder may thereby be made to contain fewer (increased tension) or more (decreased tension) register marks to maintain the correct elongation of the web to give correct registration with the pattern on the embossing cylinder.

The reference numeral 17 designates an additional moistening and/or drying station, since it is likewise possible to effect the elongation of the web portion 16 by way of water absorption andlor thermal drying.

Claims (17)

1. A method for forming a three-dimensional deformation pattern on a web in register with an existing printed repeat pattern on the web which method comprises tensioning and stretching the web between an upstream tensioning means and a downstream deforming station and adjusting the amount of stretch so that the deformation pattern is printed in register.

2. A method as claimed in claim 1 wherein the three-dimensional deformation pattern is an embossed pattern and the deforming station is an embossing station.

3. A method as claimed in claim 1 or claim 2 wherein the web is a web of wall-covering material.

4. A method as claimed in any preceding claim wherein registration marks are provided at intervals along the web, means is provided to count the rate of passage of the registration marks between the tensioning means and the deforming station and to compare the rate with the rate of operation of the deforming station and to vary the said stretch to match the two said rates.

5. A method as claimed in any preceding claim wherein the tensioning means comprises one or more pairs of driven or undriven opposed rollers.

6. A method as claimed in any preceding claim wherein the deformation station comprises a pair of opposed cylinder, at least one of which bears a raised pattern.

7. A method as claimed in any preceding claim wherein the web is moistened or saturated before being tensioned, to increase the stretch limit of the material.

8. A method as claimed in any preceding claim wherein the web is locally moistened or dried in the region between the tensioning means and the deforming station to further adjust the tension of the web.

9. A method as claimed in any preceding claim wherein the tension of the web is adjusted by movement of the point of action of the tensioning means relative to the deforming station.

10. A method as claimed in any preceding claim wherein the tension of the web is adjusted by speeding or slowing the motion of the web through the deforming station.

11. A method of embossing in register with a pre-printed pattern as a web substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.

12. Apparatus for use in a method as claimed in any preceding claim comprising a deforming station for forming a three-dimensional deformation pattern on a web, tensioning means upstream of the deforming station for tensioning and stretching the web, and means for adjusting the amount of web is stretched to cause the deformation pattern to be printed in register.

13. Apparatus as claimed in claim 12, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.

14. Awes when printed buy a method claimed in any one of claims 1 to 9.

15. A method of registering a pre-printed repeated pattern of a web, in particular a paper wallcovering web, with a repeat-pattern threedimensional deformation of the web, especially a pattern embossed by means of a raised embossing cylinder, characterised in that between a webtensioning location and a succeeding deforming station which forms the reference point to the proper alignment of pattern repeat, the web is subjected to a tensile stress and, according to the deviation in the proper pattern-repeat alignment of the deformation from the pre-printed pattern repeat, the web is lengthened by increasing the tensile stress or is shortened by reducing the tensile stress.

16. A method as claimed in claim 15, characterised in that the web is subjected to a tensile stress and is only lengthened and thus is deformed elastically, semi-elastically or partly plastically.

17. Apparatus for carrying outthe method as claimed in any one of claims 1 to 11, characterised by a web-tensioning cylinder assembly and a succeeding deforming cylinder whose pattern repeat registers accurately with the pre-printed repeated pattern of the web, the speed of the deforming cylinder being infinitely variable.