WO1997010957A1

WO1997010957A1 - Peelable coating

Info

Publication number: WO1997010957A1
Application number: PCT/US1995/012062
Authority: WO
Inventors: Oliver Crowhurst
Original assignee: Eckart-Werke Standard Bronzepulver-Werke Carl Eckart Gmbh & Co.
Priority date: 1995-09-21
Filing date: 1995-09-21
Publication date: 1997-03-27
Also published as: AU3681295A

Abstract

The invention relates to a security element (2) comprising an arrangement of a substrate (4) carrying an information (8) and a coating (10) applied to this substrate in the form of an opaque layer (10) covering at least the information (8) carrying portion (6) of the substrate (4). In order to overcome the disadvantages often encountered when the opaque layer (10) is scratched off and brittles, a security element (2) according to the invention is characterized in that the coating layer (10) is a lacquer layer and that depending on the adhesion of the coating to the substrate (4) and on the tensile strength of the coating layer (10) the thickness of the coating layer (10) is determined such that a releasing force exceeding the adhesion but inferior to the tensile strenght of the coating (10) can be applied to an edge of the coating layer (10) so that it allows peeling off with the integrity of the coating layer (10) being substantially maintained. The lacquer layer (10) is prepared from a dispersion containing an aliphatic polyester polyurethane and an opacifying pigment.

Description

PEELABLE COATING

Background of the Invention

The invention relates to a security element comprising an arrangement of a substrate carrying an information and a peelable coating applied to this substrate in the form of an opaque layer covering at least the information carrying portion of the substrate.

The opaque coating layer of known security elements such as lottery tickets or the like can be scratched off using the edge of a coin- the finger nail or similar implements thereby forming a plurality of small flakes. The opaque coating layer is sufficiently tough and shows enough basis adhesion to the substrate to prevent flaking-off or off-setting until it is forcibly removed to render the information visible. The known security elements, however, exhibit several drawbacks and disadvantages. When scratching off the opaque coating layer in the way described, the layer brittles into flakes which adhere to the fingers or to the security element or simply fall down wasting the environment. It is almost impossible to remove or sample all the flakes scratched off because they tend to fall down or to adhere to the fingers thereby providing the risk of getting transferred to a person's face or eyes and thus being harmful. When used in connection with food or in a place where also food is handled or sold scratching off the coating can lead to contamination of the food with the scratched off flakes falling there into. Brief Description of the Invention

It is therefore an object of the underlying invention to provide for a security element of the kind with the opaque coating layer effectively hiding the information but being easily removable without showing the foregoing disadvantages. When removed, the coating layer cannot be reapplied to the security element.

This object is attained with a security element of the kind characterized in that the coating layer is a lacquer layer and that, depending on the adhesion of the coating to the substrate and on the tensile strength of the coating layer, the thickness of the coating layer is determined such that a releasing force exceeding the adhesion but inferior to the tensile strength of the coating can be applied to an edge of the coating layer so that it allows peeling off with the integrity of the coating layer being maintained. A lacquer layer is broadly described as a layer which dries or cures primarily by evaporation of the solvent therefrom.

According to the invention it has thus been discovered that it was possible to obtain a coating which allows peeling off in one or several pieces without brittling or flaking of the coating as waε the case with known scratch-off coatings. For this purpose the force necessary to release the coating layer from the substrate has to exceed the adhesion of the coating to the substrate and must not lead to breakage of the coating layer. The releasing force is strongly dependent on the angle the layer is pulled or peeled off with respect to the substrate. With increasing angle (maximum 180 degrees) the releasing force (per unit length or width of a liner of the coating) which is necessary to exceed the adhesion decreases. However, the thickness of the coating layer has to be deter¬ mined such that the tensile strength of the coating (per unit length or width or by unit cross-section area of the coating layer) is sufficiently high and the coating therefore does not break when being peeled off. The security element according to the invention allows peeling off of the opaque coating layer in one piece and does therefore not show the disadvantages of known security elements. The removed one piece of layer can easily and completely be transferred to waste products and does not pollute the environment.

According to one embodiment of the invention the thickness of the coating layer is reduced upon drying of the coating. Such reduction is due to e.g. evaporation of solvents, etc. and therefore tends to decrease the total volume of the coating. However, the decrease of volume substantially takes place in reduction of the thickness of the coating because due to the adhesion of the coating to the substrate the coating cannot shrink horizontally that is in the direction parallel to the substrate. However, when peeling off the coating there is a tendency for horizontal shrinkage with the effect, that the peeled off layer will curl and/or shrink making it impossible to replace the peeled off portions on the substrate.

It may also be preferred to use a release coating layer located between at least the information carrying portion of the substrate and the opaque coating layer to be peeled off.

Using or selecting a suitable release coating layer, the adhesion of the opaque coating layer can be chosen voluntarily. For example, it may be desirable that the thickness of the opaque coating be small so that the adhesion of the coating to the substrate or to the release coating layer accordingly has to be small, too, which can be achieved by selecting a certain release coating layer.

The opaque coating layer preferably has a thickness of about 5 to 50 microns. The release coating layer preferably has a thickness of 5 to 20 microns.

The opaque coating layer preferably is a pigmented layer. The pigment preferably is a metallic, inorganic or organic pigment.

Brief Description of Drawings FIGURE 1 shows a perspective view of a security element according to the invention wherein a peelable coating applied to a carrier substrate is shown partly peeled off; and

FIGURE 2 shows a sectional view of an embodiment of the security element according to the present invention.

Detailed Description of the Invention Figure 1 shows a security element 2 in the form of a lottery ticket or the like. The security element 2 comprises a carrier substrate 4, e.g. a sheet of paper, cardboard, a plastic card or the like, having an information carrying portion 6 with an information 8 printed thereon. The security element 2 further comprises an opaque coating layer 10 covering at least the information carrying portion 6 of the carrier substrate 4. This coating layer 10 printed onto at least the information carrying portion 6 of the carrier substrate in order to render the information 8 invisible is designed according to the invention so as to be peelable so that a user can lift an edge of the opaque coating layer 10 with a coin or a finger nail to grip the coating layer to easily peel it off with the integrity of the coating layer 10 being substantially maintained.

Figure 2 shows a sectional view of a security element 12 according to the invention again comprising a carrier substrate

14 having an information 16 printed thereon. At least the information carrying portion of the carrier substrate 14 is covered by a clear release coating layer 18. An opaque coating layer 20 is comprised of a pigmented coating. The peelable coating layer 20 may easily be peeled off with the integrity of the coating layer being substantially maintained. Preferred peelable coatings exhibit a decrease in volume upon drying and therefore, show a tendency for shrinkage and will curl when peeled off so that replacement of the coating will not be possible.

The opaque layer of the present invention comprises a pigmented film of an aliphatic polyester polyurethane. The film is compounded with additives which contribute to the integrity of the film and which give sufficient tensile strength to permit removal of the film along with the peelable layer. Dispersing and wetting agents, and flow-control agents for the polymeric film are also added as needed. Thus, various diols in a glycol such as ethylene glycol can be used as wetting agents for the pigment dispersion. Various dispersing agents such as the alkali metal sulfosuccinates can be used in small amounts. Opacifying agents such as metallic pigments are used. Examples are copper, silver, gold, bronze, brass, and aluminum, in powder or flake form. Metal oxides such as titanium dioxide and oxides of iron may be used instead of or in admixture with the metals. Other inorganics such as carbon black, cadmiums, chromates and the like may be used to achieve the requisite degree of opacity. Among the organic colorants are the benzidines, diarylides, azos, and diazos. Generally, non-toxic colorants are preferred. A polymeric wax may be added to the blend to improve the scuff resistance of the opaque coating. An organic amine such as dimethylethanolamine may be added to the coating composition in small amounts to raise the pH thereby improving the flow characteristics of the coating.

The opaque peelable coating layer of the present invention comprises in percent per weight:

Broad % Preferred %

Aliphatic polyester polyurethane 50-75 63.8

2, 4, 7, 9-tetramethy1, 5-decyn, 0. 1-3 0.5 4-diol (75% in ethylene glycol) Sodium dioctyl-sulfosuccinate 0.5-4 2.0

Aluminum paste in water (65%) 15-45 30.0

Polyethylene/polypropylene wax 0. 1-2 1.5

Dimethylethanolamine (DMEA) 0.1-0.5 0 .2

Water 1-10 2.0

100%

A particularly useful resin is an aqueous dispersion of an anionic polyester polyurethane possessing ' the requisite elongation and tensile properties.

The release coating layer may comprise an acrylic or modified acrylic resin. The layer typically is prepared by compounding the acrylic resin with an organic or a water base solvent or carrier and a release agent such as zinc stearate. Wetting agents and coalescing agents such as glycol ethers are added as needed.

A preferred release coating layer is comprised of:

Broad % Preferred %

Styrenated acrylic emulsion 0.1-70 54.5 Styrenated acrylic solution 0.1-30 15.0 Water 1-10 3.0

2, 4, 7, 9-tetramethy1, 5-decyn, 0.1-2 0.5 4-diol

Propylene glycol mono ethyl ester 0.5-4 2.0

Zinc stearate 15-35 25.0

100%

However, other types of release coatings can be used, such as silicone based or other polymeric film forming release coatings containing zinc stearate, talc, or other organic or inorganic release agent. The release coating preferably is clear. However, semi-transparent and tinted coatings may be used as well.

The substrate can be comprised of any suitable material, useful for its intended purpose. Examples are cardstock, plastic film, paper, metal, cloth, and wood.

The release coating and the peelable layer are applied by any of the methods useful for applying thin air-curable polymeric coatings. Among these are well known methods such as rotogravure, flexographic printing, roll coating, dip coating, spraying, brushing, knife coating, and curtain coating.

The peelable coating is applied from a dispersion having a viscosity between about 100 and about 1500 centipoise, preferably between about 100 and 300 centipoise. After the resin film is completely cured, preferably it has a percent elongation at break of at least about 600%. The pencil hardness of the opaque coating generally is in the range of about IB to 3B.

As previously mentioned, the opaque peelable coating has a thickness between about 5 and about 50 microns. Generally, the peelability characteristics of the coating improve as the thickness increases. Furthermore, multiple thin coatings typically can be applied to the substrate and dried more quickly with no sacrifice in peelability as compared to a single coating having the same total thickness. If a thin (e.g. 5-10 micron) opaque coating is preferred, the overall peela¬ bility of the coating may be enhanced by applying a 5-10 micron clear or semi-transparent coating of the polyester urethane between the release layer and the opaque layer or on top of the opaque layer. Except for the absence of the opacifying agent, the clear coating may be prepared from the same composition used for the opaque coating.

Claims

Having thus described the invention, what is claimed is:

1. Security element comprising an arrangement of a substrate carrying an information and a peelable coating applied to this substrate in the form of an opaque layer covering at least the information carrying portion of the substrate, wherein the coating layer comprises an opaque lacquer layer, and WHEREIN depending on the adhesion of the coating to the substrate and on the tensile strength of the coating layer, the thickness of the coating layer is determined such that a releasing force exceeding the adhesion but inferior to the tensile strength of the coating can be applied to an edge of the coating layer so that it allows peeling off with the integrity of the coating layer being substantially maintained.

2. Security element according to claim 1, wherein said peelable coating shrinks as it is peeled from the substrate.

3. Security element according to claim 1, wherein a release coating layer is located between at least the informa¬ tion carrying portion of the substrate and the opaque coating layer to be peeled off.

4. Security element according to claim 3, wherein the adhesion of the opaque coating to the substrate is controlled using a suitable release coating layer exhibiting such adhesion properties with the coating that it allows peeling off of the coating with its integrity being substantially maintained.

5. Security element according to claim 1, wherein the opaque coating layer has a thickness of between about 5 and about 50 microns.

6. Security element according to claim 3, wherein the release coating layer has a thickness of between about 5 and about 20 microns.

7. Security element according to claim 1, wherein the opaque coating layer is a pigmented layer.

8. Security element according to claim 7, wherein the pigment is a metallic pigment.

9. Security element according to claim 7, wherein the pigment is an organic pigment.

10. The security element according to claim 7, wherein the opaque coating layer includes an air-cured aliphatic polyester polyurethane resin.

11. Security element according to claim 10, wherein the opaque layer comprises aliphatic polyester polyurethane; 2, 4, 7, 9-tetramethyl, 5-decyn, 4-diol (75% in ethylene glycol); sodium dioctyl-sulfosuccinate; aluminum paste in water (65%); polyethylene/polypropylene wax; DMEA; and water.

12. An opaque coating adhered to a substrate, said coating containing as a film forming polymer an air-cured aliphatic polyester polyurethane resin, said coating having a tensile strength that is greater than the force of adhesion between the coating and the substrate whereby a releasing force greater than the adhesion but less than the tensile strength when applied to an edge of the coating will allow the coating to be peeled off of the substrate while maintaining the integrity of the peeled coating.

13. The coating of claim 12 wherein a pigment is used as an opacifying agent.

14. The coating of claim 12, wherein the percent elonga¬ tion of the coating at break is at least about 600%.

15. The coating of claim 12, wherein the pencil hardness of the coating is between about IB and about 3B.

16. The opaque coating according to claim 13, prepared from an aqueous dispersion having the following composition: between about 50 and about 75% of the aliphatic polyester polyurethane; between about 0.1 and about 3% of a wetting agent; between about 0.5 and 4% of a dispersing agent; between about 15 and about 45% of the opacifying pigment dispersed in water; between about 0.1 and about 2% of a scuff resistant agent; between about 0.1 and 0.5% of a flow control agent; and between about 1 and about 10% water.

17. The opaque coating according to claim 16, wherein the wetting agent comprises 2, 4, 7, 9-tetramethyl, 5-decyn, 4- diol, (75% in ethylene glycol); the dispersing agent comprises sodium dioctyl-sulfosuccinate; the pigment comprises aluminum paste; the scuff resistant agent comprises polyethylene/ polypropylene wax; and the flow control agent comprises dimethylethanolamine.

18. A dispersion composition useful for preparing an opaque coating for use on a substrate for concealing informa¬ tion contained thereon, and wherein the coating may be peeled from the substrate while maintaining the integrity of the peeled coating, said composition having the following composi¬ tion: between about 50 and about 75% of the aliphatic polyester polyurethane; between about 0.1 and about 3% of a wetting agent; between about 0.5 and 4% of a dispersing agent; between about 15 and about 45% of an aqueous dispersion of the opacifying pigment; between about 0.1 and about 2% of a scuff resistant agent; between about 0.1 and 0.5% of a flow control agent; and between about 1 and about 10% water.

19. The composition according to claim 18, wherein the wetting agent comprises 2, 4, 7, 9-tetramethyl, 5-decyn, 4- diol, (75% in ethylene glycol); the dispersing agent comprises sodium dioctyl-sulfosuccinate; the pigment comprises aluminum paste; the scuff resistant agent comprises polyethylene/ polypropylene wax; and the flow control agent comprises dimethylethanolamine.

20. The composition according to claim 18, wherein the viscosity of the dispersion is between about 100 and about 1500 centipoise.