GB2410208A

GB2410208A - Method of producing photographically marked micro particles

Info

Publication number: GB2410208A
Application number: GB0501430A
Authority: GB
Inventors: Michael Cleary
Original assignee: Smartwater Ltd
Current assignee: Detertech Holdings Ltd
Priority date: 2004-01-23
Filing date: 2005-01-22
Publication date: 2005-07-27
Anticipated expiration: 2025-01-22
Also published as: GB0501430D0; GB2410208B; GB0401541D0

Abstract

The Present invention provides a method for producing batches of micro particles, comprising four basic steps. The first step involves creating a photographic film having a plurality of codes marked thereon as well as markings for aligning a laser for cutting. The second step involves placing said film on a support layer. The third step involves cutting the film by means of a laser device according to said aligning markings on said film to define a plurality of micro particles, each micro particle containing said code. The final step involves removing the micro particles from the support. The method of the present invention facilitate the production of large batches of micro particles with a repeated unique marking, such as a number, on each micro particle.

Description

24 1 0208

METHOD OF PRODUCING PHOTOGRAPHICALLY MARKED

MICRO PARTICLES

Field of the Invention

The present invention relates to a method for producing large batches of micro particles marked in such a manner as to uniquely identify each batch.

Background of the Invention

The use of micro particles as a security device is well understood in the field of product security marking. The application of micro particles with unique markings to goods is generally used to prove ownership of the goods, to provide a means of tracking, and even in brand protection.

Known methods for producing batches of identically and uniquely marked micro particles are based on a code formed from a plurality of digits, said digits being reproduced on a substrate by means of photo reduction, the substrate then being cut to form a batch of micro particles. The required numerical code is one sequence of multiple sequences of numbers. This results in the particles being excessively large due to the inclusion of irrelevant information.

Earlier UK Patent 2369078 discloses an improved method of producing large batches of marked micro particles. The improved method utilises lasers to both mark the micro particles, and to cut up the substrate into individual micro particles. The use of a single laser, or a combination of lasers, to mark and cut the micro particles provided a much more accurate and efficient way of producing large batches of micro particles for use in security applications.

The level of resolution required to form good quality characters at the size required is such that the preferred laser system would be an Excimer.

However, such laser systems are still, to a large extent, research tools that are operated by highly qualified expert staff. In addition, these lasers have quite high running costs.

In view of the fact that micro particles are required in very large quantities, there is a need to provide ways of reducing the costs of manufacture without compromising on the efficiency and accuracy that is provided by the above method.

Summary of the Invention

The present invention seeks to provide a viable alternative for producing large batches of marked micro particles. To this end, the present invention provides a method for producing batches of micro particles, comprising the following steps: creating a photographic film having a plurality of codes marked thereon as well as markings for aligning a laser for cutting; placing said film on a support layer; cutting the film by means of a laser device according to said aligning markings on said film to define a plurality of micro particles, each micro particle containing said code; and removing the micro particles from the support.

By using photographic images to provide the high resolution characters on the individual micro particles, the present invention enables the use of relatively simple, far less expensive, C02 laser systems to carry out the step of forming the particles from the substrate.

Such laser systems are well understood, have good reliability and are the workhorses in several industries were high throughput and continuous output is required. As a result these laser systems can be left to operate, with little intervention, on a 24 hours a day, 7 days a week basis. In addition, C02 laser systems also have minimal running costs, which normally equate to an exchange, re-gassed laser every 2-3 years.

The flim used in the present method is preferably microfilm as this is available in significant lengths.

Preferably the step of creating the photographic film may comprise creating a spreadsheet on a computer, the spreadsheet having a plurality of cells, each of which contains one code. Once created the spreadsheet is converted to a printable file and then printed onto the photographic film.

Preferably, the arrangement of the spreadsheet is set up to maximise the number of cells printed on the film.

Advantageously, the step of cutting may comprise the alignment of the laser on the film by using count marks on each frame of the film to locate the frame under the laser. Also, the blacking out of cells at pre- set positions on the spreadsheet enables the use of a vision system to control the laser by detecting the blacked out cells and making adjustments to the laser so that the laser cuts precisely around each code.

Preferably the method may further include the step of laminating the photographic film with a white backing. This provides the contrast needed to ensure that the black characters on the film, which is the middle layer can be read irrespective of the colour of the background upon which the micro particles may be resting.

Preferably a backing layer is laminated onto the photographic film. This backing layer, which is preferably not cut by the laser during the present method, provides a base for the film layer and the white backing layer as they move through the system.

In situations where the above form of support layer is used it should be appreciated that the step of removing the micro particles from the support may preferably remove the micro particles from the base layer as well.

Preferably, the step of removing the micro particles from the support layer may involve the use of a solvent.

Brief Description of the Drawings

In the drawings, which illustrate a preferred embodiment of the present invention: Figure 1 shows an example of a spreadsheet with an arrangement of cells that would be transposed onto photographic film; Figure 2 shows the arrangement of the various layers of the support layer and the film; Figure 3 shows an example of a frame with laser alignment points; and Figure 4 shows an example of the micro particles produced by the present method.

Description of the Preferred Embodiment of the Invention The first stage of the method of the present invention is the creating of a photographic film that has a plurality of repeats of a unique know code. In order to ensure that the same code is accurately repeated in an arrangement that will allow the convenient cutting up of the film into individual micro particles, a computer is used to generate the template that is to be applied to the photographic film.

Thus that creation of the marked photographic film is carried out by the following events.

Number Generation Unique codes were generated and stored in a Computer database. A block of numbers sufficient to fill a reel of film, approximately 2000, was taken form the table one at a time and transferred into a computer spreadsheet program such as Microsoft Excels.

Spreadsheet Generation and Format A default format was set up in the spreadsheet as the basis for the photographic frame. A spreadsheet consisting of 18 rows and 28 columns was found to be optimal for the laser processing of the subsequent photographic frame produced However, it will be appreciated that alternative numbers of rows and columns may be appropriate in situations where the size of the photographic film varies. The cell size with the film used in the preferred embodiment was, to some extent, determined by our requirement to obtain approximately 500 cells/spreadsheet.

The digit size within each cell was a variable and could be changed depending upon the amount of space available after laser cutting. In practice Small Fonts 4 gave the best results. The font was used "bold" and the 9 digit number was "wrapped" within the cell to produce a block of digits similar to the shape of the cell. An example of a spreadsheet produced by the above method is shown in figure 1.

In order to form a border around the text it was necessary to write the digits in two blocks separated with gaps. These gaps then provided the space around the digits to allow for the cutting line width of the laser and the heat effected zone. The number shown in figure 1 was written: 1 234 56789 A code from the database was then transferred using a macro to this empty default spreadsheet and filled to occupy all the cells. This image was then digitally transferred to the film, after which the process was repeated with the next code until ail the frames of the photographic film had been filled in this way.

In this manner most of the roll of microfilm may be used to hold approximately 2000 frames, each one being a spreadsheet and each one containing a large number of cells. Given a 12 second/batch production rate means that once started the device can be left to run for approximately 7 hours before any intervention is required.

Image Formation The image was taken from the spreadsheet and written to microfilm digitally, at no point was any hard copy ever involved. In the presently described method KodakO 1 6mm microfilm was used. However, it is appreciated that any similar microfilm would be suitable. The image was written and developed using a Kodak Archive WriterO.

Once the image has been transferred to photographic film, the next step is to place the photographic film onto a support layer so that it can be more easily handled during the rest of the process. In a preferred embodiment of the present method two different layers where applied to the photographic film.

In order to provide a contrast to assist reading of the digits on the micro particle, a white polymer layer was applied over the film. Whilst several such entities were tested, a white P.E.T., 20 micron film was found to be best suited.

In terms of forming the laminate of the white layer and the film various adhesive systems were tested. Polyurethane, two pack epoxy and heat activated adhesive all gave a good bond and the final choice is dependent upon the final application.

For ease of use we chose a heat activated adhesive. A lamination temperature of 150 C was used to form an initial bond between a 0.5m wide roll of white P.E.T. film to a 0.5m wide roll of the adhesive. Both rolls were 500m in length. This 0.5m wide roll of adhesive backed P.E.T. was then slit down to 1 5mm wide and 33m meter long rolls. These smaller rolls were then laminated directly to the microfilm.

Although higher temperatures produced a better bond they also caused distortion and shrinkage in the film and so 1 50 C was the maximum temperature used.

Both the film layer and the white background layer are cut during laser processing, thus a support layer was required to provide the base on which these two layers are moved along the processing line.

A clear pressure sensitive tape was used with a heat resistant silicone adhesive. The laser energy was set such that whilst the other two layers of the laminate were cleanly cut, this tape was only slightly scored by the cutting action but otherwise remained intact.

The pressure sensitive tape has a very low tack adhesive such that when a solution of product polymer in solvent is applied and allowed to partly dry, the whole frame of particles will simply lifted off this backing tape. Whilst a preferred tape is made by 3M@, having part number 8901, it is appreciated that alternative tapes would be equally suitable for use in the present method.

The preferred laminate structure is as shown in figure 2 of the drawings. In figure 2 the three layers are at the top the White P.E.T. layer 3, then the microfilm layer 4, and at the bottom the base layer of clear backing tape 5. The laser 1 is positioned above the laminate and cuts through the top two layers 3 and 4. The vision system 6 is located on the reverse side of the laminate so that it can detect the alignment markings 10 (see fig. 3) on the microfilm 4 through the clear backing tape 5.

Once the photographic film has been placed onto a suitable support layer the whole laminate is ready to be cut up into individual micro particles. In the present method this step is carried out using a relatively cheap laser system such as a C02 laser. The use of a cheaper laser is made possible by the removal of the need for a high resolution level to mark the unique characters on to the individual micro particles.

In order to ensure the accurate cutting of the micro particles there was a need to ensure that the laminate and the cutting laser are correctly aligned with one another. In this regard the transposed spreadsheet frame also contains the alignment information required to accurately cut the particles.

This is in the form of a two step process, the first crude alignment uses the frame count marks along the film to reel the film into approximately the correct position.

Next the laser vision system aligns the laser head exactly with respect to the frame through the use of cells 20 placed within the frame at specific positions which are entirely black. These provide information on the size of the frame, exact position and any rotational displacement of the frame on the film. Given this alignment information the laser then cuts the film into diced sections based on a preloaded cutting programme designed to cut around each cell or block of digits. An example of a frame with alignment points 10 is shown in figure 3 of the drawings.

The laser cutting was performed on the laminate shown in figure 2, from the top downwards (i.e. through the white P.E.T. and microfilm).

However the vision system allowing alignment for cutting, viewed the laminate from the bottom upwards (i.e. through the clear backing tape). As mentioned above, the laser was arranged so that only the top two layers were cut through entirely, with the bottom layer being left intact to maintain the structural stability of the laminate until the next step of the present method. It should also be appreciated that in this arrangement the support layer (not shown) would also need to be transparent to the vision system, in this regard suitable forms of support layer will be appreciated by the skilled man.

In order to maximise the efficiency in laser cutting and the overall approach, two tracks were fitted to allow simultaneous alignment and cutting of two separate rolls of film. In this arrangement the vision system providing alignment information for the first track which allows the laser to cut the specified frame of the first track. Then, whilst the laser was cutting first track, the vision system can move on to gather and store alignment information for the second track. In this way, as soon as the laser 1 finishes cutting the first track it would have all the information it required to begin cutting the second track. This alternating approach allows continuous laser cutting with no stoppage time for alignment. It gave a processing time of 12 seconds/frame and as there are in the order of 2000 frames/roll, two rolls being processed simultaneously would give 4000 batches of particles in approximately 7 hours.

At the start of each film three frames were repeated to give the laser system time to line up accurately on the frames. The first two of these frames were subsequently scrapped. The final stage of the present method is the removal of the micro particles from the support layer/backing tape. The particles can be freed from the both the support layer and the backing tape using the solvenVpolymer mix as previously described or by simply lifting off in solvent such as propan-2-ol.

In order to avoid possible cross contamination from frame to frame, each frame is coated with a polymer/solvent mixture, such that as the solvent evaporates the polymer left behind holds the particles in place and these are removed as one, wrapped in the soft polymer. This is then added to the product wherein the solvent dissolves the polymer liberating the particles.

Photographic film was used as the basis for the digits, because as yet direct writing onto plastic using YAG laser systems does not give the same level of resolution and clarity.

The particles produced using the present method preferably have an edge length of between 300 and 500 microns. Character clarity and general appearance are both excellent. An example of the particles produced by the present method are shown in figure 4.

Claims

1. A method for producing batches of micro particles, comprising the following steps: a) creating a photographic film having a plurality of codes marked thereon as well as markings for aligning a laser for cutting; b) placing said film on a support layer; c) cutting the film by means of a laser device according to said aligning markings on said film to define a plurality of micro particles, each micro particle containing said code; and d) removing the micro particles from the support.

2. The method of claim 1, wherein the photographic film is a microfilm with a plurality of frames.

3. The method of claim 1 or 2, wherein the step of creating the film comprises creating a spreadsheet on a computer, said spreadsheet having a plurality of cells, each cell containing one code, converting the spreadsheet to a printable film and printing said file onto the film.

4. The method of claim 3, wherein the spreadsheet is created so that a maximum number of cells are printed on said film.

5. The method of any of claims 2, 3 or 4, wherein the step of cutting the film comprises: aligning the laser on the film using count marks on each of frame of the film to locate the frame under the laser; and blacking out cells at pre-set positions so that a vision system controlling the laser can detect the blacked out cell and make a final adjustment to the laser so that the laser cuts precisely around each code.

6. The method according to any of the preceding claims, further comprising an additional step of laminating the photographic film with a white backing to increase the contrast between the markings on the film and the film.

7. The method according to any of the preceding claims, further comprising an additional step of laminating the photographic film with a clear backing layer, which is optionally a clear pressure sensitive tape, to provide a structural base for the film as it is being processed.

8. The method according to any of the preceding claims, wherein the step of removing the micro particles from the support layer is carried out using a solvent.

9. The method according to any of claims 2 to 8, whereby continuous cutting of the film is facilitated by simultaneously cutting a film frame at the same time as the alignment information for the next film frame in the cutting order is being collected and stored.

10. A method for producing batches of micro particles, substantially as described herein, with reference to the drawings.