This invention relates to an embossing machine roller and to a method of producing an embossing roller for a machine, in particular for embossing microcopic relief images such as holographic images.

Sheet material which is embossed and metallized is often used nowadays for decorative purposes such as wrapping paper, greetings cards or decals. The patterns used are often complex, and may contain microscopic relief images displaying diffraction or holographic effects. For economical production, the sheet material needs to be embossed in rolls of considerable width and then sub-divided as necessary. It has however always been a problem to manufacture the embossing roller to do this, since the surface of the roller must carry many images side-by-side in order to cover the full width of the sheet material.

Experience has shown that in some circumstances the embossing surface wears too easily in use, and in particular is very susceptible to damage to its surface by careless handling. A single contact with a sharp hard object could ruin an entire roller.

Accordingly, the present invention further proposes a method of producing an embossing machine roller, characterised in that it comprises the steps of generating a master roller carrying an overall relief image casting an intermediate mould around the master roller to form an inverted relief image, and using the

intermediate mould to form a cylindrical outer layer of a relatively soft resilient material on a solid mandrel.

The invention further proposes an embossing machine roller for sheet material, characterised in that it comprises a solid cylindrical mandrel having an outer layer of a relatively soft resilient material, the layer carrying a relief image which is to be embossed.

The invention further proposes a method of embossing sheet material, characterised in that the material is softened by heating and a relief pattern is imparted to its surface by contact with an embossing roller carrying said pattern on an outer surface of a relatively soft resilient material.

The relatively soft resilient material may for example be rubber, synthetic rubber, or various plastics materials. It must be unaffected by the temperature at which it is used to emboss the sheet material. The relief pattern may be a holographic image produced first on a small nickel shim by methods well known in the art.

The master roller is preferably produced by the repetitive rolling method now to be mentioned but not necessarily so. Any method which produces a sufficiently accurate master is acceptable.

It has been known to prepare rollers by making an appropriate number of nickel shim images from a single photo-resist master of a laser generated image or any other desired complex profile. The shims are then

curved and stuck side-by-side in columns and rows on the outside of the roller. This has many difficulties and disadvantages. It takes a long time to produce shims; they are difficult to align, particularly when they must abut exactly to produce a continuous pattern; they tend to come unstuck in high speed use? and it is seldom possible to eliminate the witness lines (dividing lines) in a continuous pattern.

The present invention proposes a method of making an embossing machine roller, characterised in that it comprises the steps of rolling a blank roller having a metal outer surface against a harder metal die, carrying a desired relief image, under sufficient pressure to emboss the image on the roller, the die having an area which is a fraction of the area of the roller outer surface, indexing the roller and/or the die, and repeating the rolling operation until the desired number of images or apparent overall image appear on the roller.

Preferably, the roller is supported to prevent distortion during the rolling operation diametrically opposite to the die. The support may come from another die so that two images are embossed at once on the roller surface.

The image on the roller surface is extremely accurate and the witness lines are eliminated.

Finally, the invention proposes a method of producing an embr ^{■ ■} sing machine roller characterised in that it compriε the steps of: forming an adhesive layer on a mandrel, depositing a layer of granular material onto

the adhesive layer to form a master roller, casting an intermediate mould around the master roller, and using the intermediate mould to form a cylindrical outer layer of relatively soft resilient material on a solid, further mandrel.

Suitable granular materials are talc, sand, comminuted plastic chips, or chips of sheet material which have been embossed with a refractive or holographic reflective image.

The mandrel may be an already prepared embossing master roller, carrying microscopic relief images which are particularly covered by the granular material.

In order that the invention shall be clearly understood, an exemplary embodiment will now be described with reference to the accompanying drawing, in which:

Fig. l shows apparatus for producing a master roller.

Fig. 2 shows the first stage of producing an embossing roller;

Fig. 3 shows the second stage; and

Fig. 4 shows the completed embossing roller.

The apparatus has a rigid frame 10 which supports a roller 11 which is to be embossed with a repeated pattern, for example a microscopic relief image, for future use as a master roller. The roller 11 is mounted for rotation in bearings 12. Two other

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bearings 13,14 are positioned on diametrically opposite sides of roller 11 and support rotatable, cylindrical arcs 15,16. These arcs have a radius which is the same as that of the roller 11, and carry on their surface nickel shims 17 which carry a relief image which may be produced by any suitable means, for example by engraving, or etching, or electro forming. The dimensions of each shim 17 may be small relative to the dimensions of the roller: for example, one sixth of the roller circumference in height, by one twentieth of the roller length in width.

Means, not illustrated, are provided for rotating the roller 11 and the arcs 15,16 in unison in the directions of the arrows while maintaining contact between them at diametrically opposed axial lines on the circumference of the roller. The dimensions are accurately controlled so that for the duration of these rolling contacts the pressure between the contacting surfaces is of the order of many tons/square centimetre. Since the nickel shims are harder than the outer surface of the roller 11, the relief images are impressed in the outer surface. A single rolling impression is used, so that there is no danger of degradation of the impression by poor registration. The frame 10 is of a massive construction so that even the forces arising between the rolling members can lead to no distortion. The arcs 15,16 acting on opposite sides of the roller 11 ensure that the roller does not bend when the impression is effected midway along its length.

In addition to rotation, there is also provision for indexing of either the roller 11 or the arcs 15,16 in

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unison, both so that different arcs of the circumference of the roller, and different sections along its length, can be embossed. Thus, with shims of the size mentioned above, the full circumference of the roller can be embossed by accurately indexing the roller twice after the initial impression so that successive 60° arcs are embossed.

Indexing is in each case by 60° in the direction of the arrow. Alternatively, the arcs 15,16 can be indexed back 60° to their starting position each time. This procedure is then repeated twenty times along the length of the roller. Again either the roller or the arcs can be moved.

The roller 11 might be of aluminium, with its outer surface very highly polished. Alternatively, a steel core may be used with a copper intermediate layer and a highly polished tin outer surface layer. The latter has the advantage of being non-corroding, particularly non-oxidisable, so that neither the embossed pattern nor the polished surface become degraded. In a modification the arcs may be rollers.

When a master roller has been prepared as described it will be found that a perfectly precise and uniform relief decoration will have been applied. However, the surface of the cylinder being a soft metal, it is not durable enough for embossing purposes, and the processes now described are required to produce a substantial and durable embossing roller. Refer to Figures 2 and 4.

First, a sleeve 20 of metal or other suitable material which has internal dimensions greater than the external dimensions of the master roller 21 is placed over the original.

The void 23 between the master and the sleeve is then filled with silicone casting rubber or an alternative suitable casting material. When the casting material has set and cured, the master roller 21 can be extracted from the sleeve and casting material by cooling the master and/or heating the sleeve 20. If heating the sleeve is the option chosen, then it must be ensured that the casting material adheres to the sleeve 20, by application of a primer, but not to the master 21.

Once the master roller has been removed, the inner surface 25 of the casting material 24 will display a perfect replication of the relief decoration 22 on the master.

Second a mandrel 26 which will form the basis of the final embossing roller can now be inserted within and the casting material 24, and the sleeve 20 still attached to it. The mandrel must be smaller in external diameter than the internal diameter of the casting material 24, thereby creating a void 27.

A suitable heat resistant relatively soft resilient material, such as casting resin or casting rubber, which can be made to ad .ere to the mandrel 26 but which has no natural adhesion to the casting material 24, can now be inserted between the wandrel 26 and original casting material. When the second casting material has

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hardened and cured, the mandrel with its externally cast layer 28 can be removed from the sleeve 20 with its internally cast layer 24.

Removal can best be achieved by driving a lubricant between the two cast layers under pressure. Having injected the lubricant in this fashion, it will be found relatively easy to remove the mandrel with its external casting layer. It will be seen, if correct materials are chosen, that the casting layer 28 applied to the mandrel 26 displays an exact reproduction 29 of the master roller.

A holographic embossing roller produced by these means can be made to be extremely durable, show perfect registration, and exact replication of the original hologram concerned. Moreover, the embossing process carried out on a sheet material is greatly simplified and more efficient. Preferably, the embossing is carried out on a material which is softened by heating

(at least at the surface being embossed) . Even the relatively soft resilient material is then hard enough to emboss satisfactorily, but does not wear much in use, nor is it damaged easily. The hardness should be between 40 and 90 shore A, preferably about 70.

Moreover, silicone rubber is the preferred material since it has to adhesion for the surfaces to be embossed.

An alternative method of producing a master roller is to take a mandrel formed from a suitable material, and coat the mandrel with an adhesive substance. A layer of granular material is then deposited on the adhesive layer by sprinkling the granular material

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onto the mandrel, or by rolling the mandrel in the granular material. The coated mandrel forms a master roller which can be used to produce embossing machine rollers by the method described.

Suitable granular materials are talc, sand, or comminuted plastic chips. A particularly attractive "glitter-finish" embossing roller is produced if the granular material consists of small chips of a sheet material which has already been embossed with a refractive or holographic reflective image.

The method can be used to treat a master roller that has already been prepared by another method. The granular material can be deposited in stripes which obliterate the original pattern.

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