GB2121358A - Production of embossing members - Google Patents

Abstract

An embossing member such as a sleeve 2 is produced from a destructible former 1 which is a replica of sleeve 2. Former 1 is produced of a material which in easy to form into the desired replica. Moulding material is built up around the former 1 which may then be destroyed to leave a mould 6 into which a solidifiable material (e.g. molten metal 7) is poured. The mould is then removed to yield the sleeve 2. <IMAGE>

Description

SPECIFICATION Production of embossing members This invention relates to the production of embossing plates, cylinders, rollers, sleeves and the like, hereinafter referred to simply as embossing members.

The production of embossed patterns on paper and like materials by means of embossing members is well known. The surface of an embossing member is a relief surface so that the desired embossed pattern may be produced on the paper or the like.

Embossing members are conventionally produced of metal and their relief surfaces have to be provided by engraving or machining which are expensive and time consuming processes.

Additionally the machining or engraving has to be accurate. This is particularly so in the case where the embossing is performed by passing the paper or the like through a nip between two embossing cylinders with raised surface portions on one cylinder and complementary recessed portions on the other cylinder (i.e. mated embossing cylinders) such that the paper is pressed by the raised portion into the recesses to produce the embossed pattern. In this case, the raised portions and the recesses must be machined or engraved accurately so as to a complementary.

It is an object of the invention to obviate or mitigate the abovementioned disadvantages.

According to the present invention there is provided a process of producing an embossing member comprising forming a mould around a destructible former having a surface pattern corresponding to that desired for the embossing member, destroying the former to leave the mould, pouring a solidifiable material into the mould and removing the mould to leave the embossing member.

The invention also provides a method of embossing a material by using an embossing member as defined in the preceding paragraph.

The invention is based on the use of a destructible former produced of a material which may be readily formed with the surface pattern required for the embossing member. Methods by which the former may be produced as described more fully later. A mould may then be built up around the former which may then be destroyed to leave a mould into which the solidifiable material is introduced and solidified. The mould may then be removed to leave the embossing member.

The invention allows the accurate reproduction of the surface characteristics of the former in the finished embossing member. Additionally the invention allows embossing members to be produced more quickly and cheaply than using the prior art processes described above.

The invention is particularly suitable for the production of embossing members in the form of rollers or sleeves, although it is not limited to such forms.

Preferably the mould is produced from a refractory material and preferably also the former is heat destructible, e.g. it is melted or vaporised by heat so that it may easily be removed from the mould. Preferabiy the embossing member is cast with molten metal, e.g. steel, bronze etc. When molten metal is used, the destructible former, and thus the mould produced therefrom, should be larger than the desired final size of the embossing member. This is to allow for contraction of the metal as it solidifies, thereby allowing the required size embossing member to be obtained.

The invention may be carried out by the process known as investment casting. Applying investment casting to the invention, the destructible former is "invested" and stuccoed to build up the mould, and the embossing member is produced as described previously.

The destructible former is conveniently produced of a plastics material since the plastics formers may be produced cheaply and easily with the surface relief pattern required for the embossing member.

The plastics former is preferably produced in a photographic process from a photo-hardenable polymer material which is capable of being hardened in various degrees depending on light intensity and/or time of exposure to the light.

Suitable photo-hardenable polymers are those hardened by exposure to U.V. light.

in the photographic process there is used a photographic master (e.g. a negative or a positive) having light transparent and light opaque areas in a pattern corresponding to that required for the embossing member, i.e. light transparent areas corresponding to recesses, grooves or the like to be formed on the embossing member and opaque areas corresponding to the raised surface pattern for the embossing member. It will be appreciated that the pattern may be a grey scale negative having different degrees of light transparency depending on the depth of recesses, grooves or the like required for the embossing member.

To produce the plastics former, the photographic master is positioned over the polymer, which will be of suitable shape, e.g. flat plate, and the assembly irradiated for a suitable period of time. Subsequently the areas of unexposed polymer are removed from the polymer to leave the finished former which may then be used in the casting method described above. The destructible former may of course by produced by other methods, as given below by way of example: (1) by cutting the profile required for the embossing surface in a blank of suitable material, e.g. wax or plastics; (2) by machining a blank suitable material (e.g.

wax or plastics), by scanning a grey scale negative representing depths and moving a cutting tool automatically in response to the scan to cut the desired surface pattern with the required depths; (3) by chemically eating away areas of a blank of suitable material to produce the desired surface pattern for the former; (4) by treating a blank of suitable material which becomes swollen when chemically treated.

A stencil may be used to apply the chemical only to those areas of the polymer which are to be swollen; and (5) by producing the former in a mould which has itself been produced from an existing embossing member.

One method according to the invention for producing an embossing cylinder (in this case a sleeve) will be described by way of example only with reference to the accompanying flow diagram.

The illustrated process utilises a tubular heat destructible former 1 which, save for its dimensions, is a replica ofthe embossing cylinder or sleeve 2 which it is desired to produce (as represented by the arrow-headed dotted line). The dimensional difference is to allow for contraction effects, as explained previously.

Former 1 is firstly provided at on end thereof with a ceramic, cup 3 and a wax cup 4 for forming a pouring spout as will be appreciated from the subsequent description.

A refractory coating is now applied to the outer and inner surfaces of the former 1, including around the free end thereof, as well as around the outer surface of cup 4 and inner surface of cup 3.

In this way, a refractory mould is built up around the former 1.

Subsequently, heat is applied to destroy the former 1 and cup 4 by vaporisation or melting, thereby allowing them to be removed, as illustrated by the up-turned representation of the finished mould 6.

It should at this point be noted that the inner surface of the mould 6 which correspond with the outer surface of the original former 1 accurately reproduces the features (e.g. recesses, contours etc.) of that surface.

Molten metal 7 is now teemed into the mould 6, this operation being facilitated by the pouring spout which has been formed from the wax cup 4.

The metal 7 is allowed to solidify and subsequently the mould is removed. In fact, the mould may partially break away during cooling and contraction of the metal.

There is left a metal casting 8 which still includes cast flash which is removed by well known techniques to produce the finished embossing sleeve 2.

This sleeve 2 may be located over a suitable suppoftand used as a convectional embossing roller.

Whilst the drawing illustrates the production of an embossing cylinder, it will be appreciated that the process is equaliy applicable to the production of flat embossing plate.

It will be seen therefore that the method of the invention provides a simple, quick, and inexpensive way of producing embossing members.

Claims (11)

1. A process of producing an embossing member comprising forming a mould around a destructible former having a surface pattern corresponding to that desired for the embossing member, destroying the former to leave the mould, pouring a solidifiable material into the mould and removing the mould to leave the embossing member.

2. A process as claimed in claim 1 wherein the former is of wax or plastics.

3. A process as claimed in claim 1 or 2 wherein the former is destroyed by heat.

4. A process as claimed in any one of claims 1 to 4 wherein the mould is of a refractory material.

5. A process as claimed in any one of claims 1 to 4 wherein the solidifiable material is molten metal.

6. A process as claimed in any one of claims 1 to 5 wherein the embossing member is a sleeve or a roller.

7. A process as claimed in claim 6 for producing an embossing member in the form of a sleeve wherein the former is tubular and the mould is formed by providing a particulate moulding material around the inner and outer surfaces thereof and around the end thereof.

8. A process as claimed in claim 7 wherein the tubular former is provided with a destructible cup for forming a mouth for the mould.

9. A process for producing an embossing member substantially as hereinbefore described with reference to the accompanying drawing.

10. An embossing member produced by the process of any one of claims 1 to 9.

11. A method of embossing a material by using an embossing member as claimed in claim 10.