FIELD OF THE INVENTION

The present invention relates to a process for forming envelope blanks from a streaming length of material with a rotary knife. More particularly, but not exclusively, the present invention relates to forming envelope blanks having perforated fold lines. BACKGROUND OF THE INVENTION

Rotary knives have been previously used in envelope manufacturing processes to form envelope blanks from a streaming length of paper. Envelope blanks are trimmed pieces of paper that are yet to be folded to form the envelope. It can be difficult to use a rotary knife to form transverse cuts at right angles to the streaming length of paper due to the cutting action of the rotary knife, which operates in a similar manner to a guillotine.

It has also been previously proposed to form envelope blanks having lines of perforations for fold lines. Similar to transverse cuts, transverse perforations formed at right angles to the streaming length of paper can be difficult to form and have typically been formed using modified cut off knives which can limit the process speed.

Examples of the invention seek to solve, or at least ameliorate, one or more disadvantages of previous envelope manufacturing processes.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided a method of forming envelope blanks from a length of material with a rotary knife, comprising the steps of: streaming the length of material; providing a rotary knife; arranging the rotary knife so that an axis of rotation of the rotary knife is at a first acute angle to a transverse -axis of the length of material; and bringing the knife into contact with the length of material to form an envelope blank, wherein the knife has at least one cutting protrusion extending along an outer surface thereof for contacting the length of material, the at least one protrusion arranged in at least a partial outline corresponding to cuts to be made on the length of material to form the envelope blank, the outline being offset on the surface of the knife by an offset amount corresponding to said first angle so as to be generally aligned with a longitudinal axis of the length of material.

In preferred embodiments, the at least one protrusion includes a continuous projection corresponding to an outline of a section to be trimmed from the length of material. The cuts on the length of material can be a plurality of small holes or perforations. In this regard, the at least one protrusion can include a plurality of small, and preferably like, projections arranged to form lines of perforations on the length of material. Preferably, the first angle is approximately 1 degree. Preferably, the length of material is a length of paper.

According to another aspect of the present invention, there is provided an apparatus for forming envelope blanks from a streaming length of material, the apparatus comprising a rotary knife having at least one protrusion formed on an outer surface thereof for contacting the length of material, the at least one protrusion arranged in at least a partial outline corresponding to cuts to be made on the length of material to form the envelope blanks, wherein the knife is arranged so that an axis of rotation of the rotary knife is at a first acute angle to a transverse axis of the length of material, and the at least one protrusion is arranged so that the outline is offset on the surface of the knife by an offset amount corresponding to the said first angle so as to be generally aligned with a longitudinal axis of the length of material.

In preferred embodiments, the at least one protrusion includes a continuous projection corresponding to an outline of sections to be trimmed from the length of material. Preferably, the first angle is approximately 1 degree.

The at least one protrusion may be configured to form perforations. In this regard, the at least one protrusion can include a plurality of small, and preferably like, projections arranged so as to form lines of perforations on the length of material.

Each projection of the plurality of small projections can have a generally triangular cross section. Preferably, sides of the triangular cross section intersect at an angle of 60 degrees. The height of the projections, are preferably approximately 1mm high. Preferably, the projections have a length between 0.5 and 3mm and are separated by a distance between 0.5 and 3mm.

Preferably, the rotary knife includes a foil on which the protrusion is formed, the foil being configured to wrap around a drum of the rotary knife. Preferably, the drum is magnetised and the foil is metallic so as to be removably fixable to the drum. Alternatively, the drum is configured to permanently receive the foil. The drum may include a receptacle for receiving the foil.

According to another aspect of the present invention, there is provided a foil for use with an apparatus of the above described type, the foil being configured for fixing to the knife and having the at least one protrusion formed on an outer surface thereof.

BRIEF DESCRIPTION OF THE DRAWINGS Preferred embodiments of the invention will be further described, by way of non-limiting example only, with reference to the accompanying drawings in which:

Figure 1 is a plan view of an apparatus for cutting a streaming length of material of one embodiment of the invention, a rotating foil knife of the apparatus shown in an unwound condition;

Figure 2 is a rear view of the apparatus;

Figure 3 is a plan view of an unwound foil for use with the rotating foil knife; Figure 4 is side view of the apparatus;

Figure 5 is a sectional side view of a lower mounting plate used for mounting the apparatus;

Figure 6 is a top view of the lower mounting plate

Figure 7 is an end view of the lower mounting plate;

Figure 8 is an underneath view of the lower mounting plate;

Figure 9 is a sectional side view of an upper mounting plate used for mounting the apparatus;

Figure 10 is a top view of the upper mounting plate

Figure 1 1 is an end view of the upper mounting plate; and

Figure 12 is an underneath view of the upper mounting plate.

DETAILED DESCRIPTION An apparatus 10 according to a preferred embodiment of the present invention is shown in Figure 1. The apparatus 10 is configured for forming envelope blanks from a streaming length of material. In the described embodiment the length of material is a length of paper and envelope blanks are pieces of paper that are trimmed from the length of paper and are intended to be folded to form the envelope.

The apparatus 10 comprises a rotary knife 12 having a rotating drum 14 with at least one protrusion 16 formed on an outer surface thereof for contacting the length of paper. In the described embodiment, the rotary knife 12 includes a foil 18 on which the protrusion 16 is formed. The drum 14 is magnetised and the foil 18 is metallic so as to be removably fixed to the drum 14 by way of magnetism. Figure 1 illustrates the foil 18 in an unwound state so that the configuration of the protrusion 16 can be seen. It will be appreciated that in other embodiments the protrusion 16 may be formed directly onto the drum 14 of the rotary knife 12. The protrusion 16 is a cutting element which projects from an outer surface of the rotary knife 12 and is arranged in at least a partial outline corresponding to cuts to be made on the length of paper to form the envelope blanks. The cuts may be continuous or a plurality of individual cuts in the form of perforations. The cuts may also be made in multiple steps using multiple knives.

As illustrated in Figure 1, the knife 12 is arranged so that the axis of rotation x-x is at a first acute angle a to a transverse axis A of the length of paper. The at least one protrusion 16 is configured so that the outline is offset an offset amount or counter rotated on the foil 18 an amount corresponding to the first angle a so as to accommodate the rotation of the knife so that the outline is generally aligned with a longitudinal axis B of the length of paper. The offset amount or counter rotation, of the outline is generally of the same magnitude as the first acute angle a. The alignment can be seen in a plan view, such as that shown in Figure 4, and provides that the trimmed envelope blank, which is generally a right rectangle having parallel leading and trailing edges transverse to the length of paper and parallel side edges parallel to the length of paper, i.e. generally square with the length of paper and aligned with the longitudinal axis B. Although the envelope blank is generally square, a manufacturing variation in the range of 1 to 2 degrees may exist.

Arranging the knife so as to be rotated with respect to the length of paper allows transverse cuts to be more easily made on the length of paper without sacrificing processing speed, i.e. the speed at which the streaming material can be run. However, simply arranging the knife in this manner results in the envelope blanks being rotated and thus more difficult to handle after forming, thus compromising later manufacturing steps. Forming envelope blanks in this manner can also increase waste material which is trimmed from the length of paper. ^' By modifying the foil 18 as illustrated in Figure 1 , the offset, rotation or skewing of the knife 12 can be compensated for so that the envelope blank is generally maintained in the form of a parallelogram whilst remaining generally aligned with a longitudinal axis B of the length of paper. The at least one protrusion 16 includes a continuous projection 20 corresponding to an outline of sections to be trimmed from the length of paper. In this regard, the outline corresponds to an outline of the envelope blank to be trimmed from the length of paper. The at least one protrusion 16 also includes portions 22 which are configured to form perforations on the envelope blank. Incorporating lines of perforations into the envelope blank facilitates folding during later processes and provides a number of advantages when compared to conventional scoring and folding processes. In this regard, folding is improved and the process of forming perforations is less susceptible to speed variations, thereby improving process quality. Also, material when perforated exhibits less memory or rebound so that the demand of precision on subsequent steps of the process, such as gluing, is reduced.

It has also been found that by providing lines of perforations instead of score lines the stacking height of envelopes once folded is reduced, thereby reducing packaging volumes.

The portions 22 which are configured to form the perforations on the envelope blank include a plurality of small, and preferably like projections. Each projection of the plurality of small projections can have a generally triangular cross section, with side faces of the triangular cross section intersecting to form an angle of 60 degrees.

In the described embodiment, the projections are approximately 1mm high, with the height being measured from a base of the foil to a tip of the projection, with the thickness of the foil, which is approximately 0.2mm thick, being included in the height. Also in the preferred embodiment, the projections have a length between 0.5 and 3mm and are separated by a distance of 0.5 to 3mm.

The inventors have found that using an acute angle a of 1 degree provides particularly good results. It will be appreciated by those skilled in the art that small variances from this angle, such as those within a range of plus or minus 1 degree, may still provide acceptable results. Figure 2 illustrates a rear view of the apparatus. It can be seen that the rotary knife 12 is disposed above and generally parallel to a space 24 through which the length of paper will pass, sufficiently close to the rotary knife so that the protrusion 16 comes into contact with the length of paper to cut it.

Figure 3 further illustrates the foil 18. Similar to conventional foils, the foil 18 is formed from a thin material which is approximately 0.2mm thick so that it can be wound around the drum 14 of the rotary knife 12. It can be seen that the continuous projection 20 corresponds to an outline of the envelope blank to be formed from the length of paper and that the portions 22 are arranged to form lines of perforations to facilitate folding of the envelope blank.

It can be seen that the at least one protrusion 16 is offset or counter rotated on the foil 18 an offset amount corresponding to the first angle a so as to be generally aligned in use with a longitudinal axis B of the length of paper.

Although only transverse perforations are shown, it will be appreciated that perforations may be formed generally parallel with a longitudinal axis of the length of paper to facilitate forming of side tabs of the envelope blank.

Figures 4 to 12 illustrate how the apparatus 10 is fixed to a conventional envelope manufacturing machine 26. The apparatus 10 includes a top plate 28 and a bottom plate 30.

.

It can be seen from Figures 5 to 8 that the bottom plate 30 has a generally constant cross section, excluding mounting holes, along its length. The bottom plate 30 has a lower channel 32 which is formed in a surface which is lowermost is use and configured to accept a correspondingly shaped protrusion extending from the machine 26. The bottom plate 30 also has an upper channel 34 in which a protrusion 36 from the top plate 28 can be received. As illustrated in Figures 9 to 12, the top plate 28 has a lower protrusion 36 and an upper channel 38. So that the rotary knife 12 may be arranged at an angle to the length of paper, the upper channel 38, as illustrated in Figure 10, is formed in the top plate 28 at an angle a to a longitudinal axis of the top plate 28.

The rotary knife 12 has mountings 25 which have lower protrusions that are shaped to correspond with and be received in the upper channel 38 to fix the rotary knife 12 t the envelope manufacturing machine 26.

In use, envelope blanks are formed by streaming the length of paper, providing a rotary knife 12, arranging the rotary knife 12 so that the axis of rotation is at a first acute angle to a transverse axis of the length of paper and bringing the knife 12 into contact with the length of paper, and bringing the knife 12 into contact with the length of paper to form envelope blanks. As discussed above, the knife 12 has at least one cutting protrusion 16 extending along an outer surface thereof for contacting the length of paper and the at least one protrusion is arranged so as to form at least a partial outline corresponding to cuts to be made on the length of paper to form the envelope blank. The outline is counter rotated on the surface of the knife an amount corresponding to the first angle so as to be generally aligned with a longitudinal axis of the length of paper.

The cuts formed on the length of paper can be continuous and include a plurality of small holes or perforations. In this regard, the at least one protrusion can include a plurality of small, and preferably like, projections arranged to form lines of perforations on the length of paper. ₍

Folding of the envelope blank is performed using conventional means, such as by bringing the envelope blank into contact with guide bars for example. The described process has been described in relation to envelopes formed from a streaming length of paper, though it will be appreciated that it will also have application to different types of envelopes formed from other materials.

The embodiments have been described by way of example only and modifications possible within the scope of the invention disclosed.