WO2006129086A1

WO2006129086A1 - The use of alginates in laser imaging

Info

Publication number: WO2006129086A1
Application number: PCT/GB2006/001982
Authority: WO
Inventors: Joseph Gaunt
Original assignee: Datalase Ltd.
Priority date: 2005-05-31
Filing date: 2006-05-31
Publication date: 2006-12-07
Also published as: JP2008542077A; GB0511096D0; JP4827920B2; EP1888348A1; JP2008545560A; WO2006129078A1; EP1888347A1

Abstract

A method for marking an object by directing a laser beam onto the areas of the object to be marked, wherein those areas at least comprise an alginate.

Description

THE USE OF ALGINATES IN LASER IMAGING Field of the Invention

This invention relates to the use of alginates in laser imaging. Background of the Invention WO02/068205 discloses a material that reacts with a separate metal compound on irradiation with a laser, such that a reaction product of contrasting colour to the reactants is formed. This reaction product is used to form an image on an object, e.g. an edible object.

The reaction of WO02/068205 allows printing to be conducted with low maintenance costs, and avoids the need for solvents, emissions, debris and extraction. It allows on-line, non-contact coding, with reduced down-time. There is no need for the purchase of stocking of materials associated with printing. Adhesion problems and smudging can be avoided, and it is possible to code in damp conditions. Summary of the Invention

The present invention is based on the ability of particular polysaccharide moieties to undergo internal reactions on irradiation with a laser, such that a reaction product of contrasting colour is formed. According to the present invention, a method for marking an object that comprises an alginate, comprises directing a laser beam onto the areas of the object to be marked.

Depending on the nature of the components that are used, and the nature of the resulting reaction product, the product may be physiologically acceptable, or in other words edible. This means that the invention can be used in the marking of foodstuffs and pharmaceutical products such as tablets and pills. Description of the Invention

In accordance with the invention, an object may comprise an alginate moiety and a metal ion. On irradiation with a laser, this moiety may undergo an internal elimination reaction so as to form a reaction product in situ which is a colourant, dye or chromophore. Generally, the elimination reaction is a dehydration reaction (i.e. elimination of water), and usually the elimination reaction results in charring of the functional group. In many instances, where appropriate starting materials are utilised, this process and its products are akin to caramelisation.

Usually the object comprises a substrate and, coated thereon, a coating. In this instance, the moiety is preferably contained within the coating, as are any additional chemical additives.

The object or substrate upon which the image or mark is to be made can be a foodstuff, for example confectionary, eggs or fruit, or a pharmaceutical dosage unit such as a tablet or pill. If the object or substrate is intended for consumption or (if pharmaceutical) oral administration, then the moiety and reaction product are edible. Alternatively, the object or substrate can be paper, polymer film, card or board, plastic containers, or any other item capable of bearing a printed image.

The reaction product (i.e. the colourant, dye or chromophore) can be of greater colour intensity than the unreacted moiety, and preferably the unreacted moiety is substantially transparent or substantially colourless.

Alginates are known as flavouring agents and are approved as food ingredients. They can be readily marked, by means of the invention.

The metal ion in a metal alginate is preferably a mono-, di- or tri-valent metal cation. Examples of preferred metal ions for use in the third embodiment include NH₄ ⁺, Li⁺, Na⁺, K⁺, Ca²⁺, Mg²⁺, Sr²⁺ and Al³⁺, where Na⁺ is particularly preferred. Cu²⁺ is generally less preferred, since its salts may be highly coloured. An exception is anhydrous CuSO₄ (which is colourless and non-toxic) which may be a desirable additive; its use may require anhydrous solvent and non-hygroscopic materials. Alternatively, the metal ion may comprise a divalent transition metal cation, preferably from the first row of the Periodic Table. Examples of particularly preferable metal ions include Mn²⁺, Co²⁺, Fe²⁺, Ni²⁺ and Cu²⁺. Of these, Mn²⁺ and Co²⁺ are most preferable as their salts are generally relatively pale in colour, and Fe²⁺ is often least preferred since yellow aqueous ferrous ion solutions are sometimes readily darkened by atmospheric oxygen to ferric ion.

A preferred embodiment of the invention is based on the ability to improve the intensity of an image or mark by adding a substance comprising a second metal ion to either the object or the coating. The second metal ion may react with functional groups on the moiety that do not undergo the internal elimination reaction, so as to give rise to a larger amount of product and hence a darker colour. It is believed that only some functional groups are capable of undergoing the internal reaction due to an excess of functional groups as opposed to metal ions in the original moiety. The extra metal ions provided by the additional substance therefore allow more functional groups to react.

Substances suitable for achieving this enhanced intensity effect include those containing a metal ion that may be the same as the metal ion present in the moiety. Such substances may be inorganic or organic in nature, and may also function as a binder. Methylcellulose salts of second metal ions are preferred. As an example, it has been shown that when sodium alginate is the moiety, sodium methylcellulose can be used to provide an enhanced intensity effect. Other preferred examples include sodium carbonate, sodium hydrogen carbonate and magnesium chloride.

Based on the above information, other suitable functional groups, metal ions and intensity enhancers will be known, or can be readily chosen or tested for their suitability, by those of ordinary skill in the art.

It is within the scope of the invention that objects or substrates to be marked may be pre-wrapped, provided that the wrapping is transparent to the applied energy; in other words, film-wrapped tablets, foodstuffs or other such products can be printed by means of the present invention. Many commonly available wrapping films have been found to be transparent to IR laser energy, including PE, PP, PET, PVC, cellulose and cellulose acetate. The space allocated on an object or substrate, or its wrapping, for the batch code, sell-by date, etc. is usually a small patch printed in a light colour to give good contrast to the (normally) black print. Using the system of the invention, this may be a white or lightly-coloured coating, which is printed with a laser-sensitive ink. On exposure to a threshold dose of laser energy, the ink changes colour to give the image.

The object to be marked may be formulated with the additional components that allow marking. In a preferred embodiment, these components are formulated and used to coat a substrate. For application to the substrate, the material or materials used in this invention may be formulated in an aqueous or non-aqueous system, as a solution or dispersion achieved by, for example, ball milling. Typically, the materials are formulated in an aqueous system comprising ethanol or a water/ethanol mix. Preferably, the materials are formulated to include a binder, for example polyvinyl alcohol or polyacrylic acid or cellulosic binder(s). Optionally the formulation also includes IR absorbers, which enhance the sensitivity of the coating to the wavelength of light emitted by a particular laser.

Since it may determine the clarity of the marking that can be achieved, coating may be done more than once, if desired. Further, on top of the coating, a protective layer of for example carnauba wax can be applied by a conventional coating process, provided the coatings are laser-markable through the protective layer, as is the case for carnauba wax.

The amounts of the components that are used in the invention can readily be chosen by one of ordinary skill, having regard to the intended use. For example, a coating composition may comprise 0.1 to 20% w/v of each component.

As indicated above, an image can be formed by the application of heat. Preferably, heat is applied locally, on irradiation with a laser. Suitable lasers include those emitting at high energy, including Nd-YAG lasers and CO₂ lasers, the latter typically at a wavelength of 10,600 nm. In many cases, it may be desirable to use a low-energy laser, such as diode laser, typically emitting light at a wavelength in the range of 800-1500 nm. In certain circumstances, this energy input may be insufficient to cause the desired reaction, and the composition to be irradiated then preferably comprises a suitable absorbent material.

Further additives that may be used are thus IR-absorbent materials, many of which are known. In general terms, any suitable such material may be incorporated, for the purposes of this invention, and can be chosen by one of ordinary skill in the art. The laser can operate in either the dot matrix mode or continuous- wave, scribing mode. In this latter mode, improved quality of print can be obtained. Because of the low output of the laser, highly reliable, approaching maintenance-free, operation is offered. The system can operate in a scribe mode, and coding onto moving lines at up to 200 m/min is possible. For higher speeds than this, dot matrix printing is suitable.

The system can be used for coding through packing film, or coding into film laminates. A low-power laser ensures that puncturing does not occur. The following Examples illustrate the invention.

Example 1

When a solid sample of sodium alginate was irradiated using a Videojet Focus S10 CO₂ laser, the material was marked black. Example 2 92 g ethanol was used to dissolve 8 g hydroxypropylcellulose; 25 g sodium alginate was added and the resulting suspension was ground for 48 hours. When this composition was applied to a lemon, orange, apple, egg or pharmaceutical tablet, a white coating was obtained. Irradiation using a Videojet Focus S10 CO₂ laser resulted in legible dark brown/black markings. Example 3

A mixture of 50 g ethanol and 50 g water was used to dissolve 4.5 g hydroxypropylcellulose; 25 g sodium alginate was added and the resulting mixtures was stirred vigorously for 20 minutes. When this composition was applied to a lemon, orange, apple, egg or pharmaceutical tablet, a clear coating was obtained. Irradiation using a Videojet Focus S10 CO₂ laser resulted in legible dark brown/black markings. Example 4

A mixture of 67.5 g ethanol, 6 g hydroxypropylcellulose, 1.5 g aerosil 200 (fumed silica), 5 g sodium carbonate and 20 g sodium alginate (Manugel DJX) was prepared. When this composition was applied to a lemon, orange, apple, egg or pharmaceutical tablet, an opaque coating was obtained. Irradiation using a Videojet Focus S10 CO₂ laser resulted in legible, dark brown/black markings at applied fluence less than examples without additional sodium carbonate (e.g. Example 2). Example 5

A mixture of 67.5 g ethanol, 6 g hydroxypropylcellulose, 1.5 g aerosil 200 (fumed silica), 5 g sodium hydrogen carbonate and 20 g of sodium alginate (Manugel DJX) was prepared. When this composition was applied to a lemon, orange, apple, egg or pharmaceutical tablet, an opaque coating was obtained. Irradiation using a Videojet Focus S10 CO₂ laser resulted in legible, dark brown/black markings at applied fluence less than examples without additional sodium hydrogen carbonate (e.g. Example 2). Example 6 A mixture of 83.95 g deionised water, 5 g glycerol, 0.05 g sodium dodecyl sulphate, 1 g sodium carbonate and 1O g of sodium alginate (Manucol LB) was prepared. When this composition was applied to a lemon, orange, apple, egg or pharmaceutical tablet, a clear coating was obtained. Irradiation using a Videojet Focus S10 CO₂ laser resulted in legible, dark brown/black markings.

Claims

1. A method for marking an object by directing a laser beam onto the areas of the object to be marked, wherein those areas at least comprise an alginate.

2. A method according to claim 1, wherein the alginate is a metal alginate.

3. A method according to claim 2, wherein the metal is sodium.

4. A method according to any preceding claim, wherein the object is a pharmaceutical or foodstuff, and the reaction product is physiologically acceptable.

5. A method according to any preceding claim, wherein the object comprises a substrate and, coated thereon, a coating comprising the alginate.

6. A method according to claim 5, wherein the substrate is a tablet or pill and the coating comprises a pharmaceutical agent.

7. A method according to any preceding claim, wherein the object is wrapped or covered in a filmic material.

8. A method according to any preceding claim, wherein the object or any coating further comprises a substance comprising a second metal ion that reacts with any functional group that does not undergo reaction on laser- irradiation.

9. A method according to claim 8, wherein the amount of said substance is sufficient to enable substantially all functional groups to undergo the elimination reaction.