WO2015062996A1

WO2015062996A1 - Method of forming a high gloss metallic coating

Info

Publication number: WO2015062996A1
Application number: PCT/EP2014/072917
Authority: WO
Inventors: Bodo-Werner Lutzig; Joachim KLETT; Timothee CAILLEAUX
Original assignee: Philip Morris Products S.A.
Priority date: 2013-10-28
Filing date: 2014-10-24
Publication date: 2015-05-07

Abstract

A method of applying a metallic coating to a surface of a substrate material (10) comprises providing a substrate material (10) having a first surface (12) and applying a solvent based lacquer to the first surface (12). The solvent based lacquer is dried to form a layer of dried lacquer (16) and a metallic material is applied over the layer of dried lacquer (16) to form a metallic layer (18).

Description

METHOD OF FORMING A HIGH GLOSS METALLIC COATING

The present invention relates to a method of applying a metallic coating to a surface of a substrate material and substrates comprising such a coating. The present invention also relates to the use of a solvent based lacquer to reduce the surface roughness of a substrate prior to the application of a metallic material.

It is often desirable to modify a surface of a substrate material to provide a metallic appearance. For example, consumer goods may be packaged in many different types of containers formed from a variety of materials and in some cases, it may be desirable to provide such containers with a metallic appearance. However, it is often impractical or too expensive to form containers from a metal substrate. Therefore, containers for consumer goods are typically formed from substrate materials that are cheaper and easier to process on high speed packaging machinery and the substrate materials receiving a surface treatment to provide a metallic appearance. Typical substrate materials include paper, cardboard, plastic and such like.

Existing surface treatments for providing a metallic appearance on a non-metallic substrate include hot foil stamping or lamination for example with a metalised PET film. However, such foils and films may become wrinkled upon application to the substrate. Furthermore, foils and films must normally be applied in an offline process which may require a complex registration between the foil or film and the substrate material and can result in expensive waste where the registration is insufficient or only a small amount of the metal material is transferred to the substrate material. Additionally, metal foils and films may fail to provide satisfactory visual integration with non-metallic printed portions of any artwork or design printed onto surrounding areas of the substrate.

An alternative surface treatment is the application of a metallic ink to the substrate.

However, when printed directly onto paper and cardboard metallic inks will provide a matt finish which does not replicate the high gloss finish of a polished metal. This is believed to be due to the size and shape of the metal particles in the metallic ink and the orientation of the particles on the surface. In particular, small metallic particles or a random distribution of the metallic particles may result in an achromatic scattering of the light that looks grey and dull to the eye.

International patent application WO-A-2012/099698 describes a metallic surface treatment comprising an energy-cured coating, for example using ultra violet light. However, this process may be expensive as it typically would require at least a dedicated curing station and may require complex photo-initiators. JP H01 192895 A and WO 96/31649 A1 also describe methods of applying a metallic coating by first applying a radiation cured base layer. It would be desirable to provide a novel and cost effective method of applying a metallic coating to a substrate that can simulate the high gloss effect of a polished metal.

The present invention provides a method of applying a metallic coating to a surface of a substrate material, the method comprising providing a substrate material having a first surface and applying a solvent based lacquer to the first surface. The solvent based lacquer is then dried to form a layer of dried lacquer and a metallic material is applied over the layer of dried lacquer to form a metallic layer.

As used herein the term "solvent based lacquer" means a coating which is converted from a liquid to a solid form using only a drying step to evaporate the solvent. A solvent based lacquer may dry at room temperature by natural evaporation of the solvent (depending on the solvent), although the drying step may be shortened by heating the lacquer. This is in contrast to a curable lacquer, which must be converted from a liquid to a solid state using a dedicated curing process in which polymer cross-linking is induced using chemical additives, UV radiation, electron beam, and other means of energy curing.

As used herein, the term "metallic material" is a material that comprises metal particles, metal flakes, or both. A metallic material may comprise between about 10 percent and 100 percent of metal by weight, preferably between about 20 percent and about 50 percent metal by weight. In some embodiments the metallic material is a metallic ink.

Advantageously, the application of the solvent based lacquer reduces the surface roughness of the first surface of the substrate material that would otherwise be presented on a typical printing surface such as cardboard, coated paper or uncoated paper. This may provide a smooth surface onto which the metallic material is applied. The smooth surface provided by the lacquer results in a smooth and uniform metallic layer so that light incident on the metallic layer is reflected in a specular manner rather than being randomly scattered. Therefore, metallic coatings applied in accordance with the present invention provide a high gloss effect that simulates a polished metal.

Furthermore, the method according to the present invention can be implemented as an inline process so that the solvent based lacquer and the metallic material can be applied at subsequent stages of the same printing press as printed inks, for example. This may greatly simplify the registration step between the applied metallic layer and preceding or subsequent applications of ink, as a registration between printing stations in printing presses is well established and generally significantly more precise and easier to achieve than overprinting a metallic surface area that has been created in an offline process, such as for example hot foil stamping. Using a solvent based lacquer also eliminates the need for a separate curing station. Further complex and expensive photo initiators required by the curable coatings described in the prior art are not required. Preferably, before the drying step, the solvent based lacquer comprises a solvent in an amount of about 60 percent by weight of the solvent based lacquer. A solvent based lacquer having a solvent content in this range advantageously comprises sufficient non-solvent material to smooth any microscopic irregularities on the surface of the substrate material, thus optimising the high gloss finish of the overlying metallic layer. Additionally, or alternatively, the solvent based lacquer has a viscosity of between about 12 seconds and 40 seconds, before the drying step, preferably between about 20 seconds and 35 seconds when measured using a German Industry Norm DIN 4 cup, according to International Standard IS02431 , before the drying step.

Preferably, the thickness of the lacquer layer on the substrate is between about 0.1 grams per square meter and about 10 grams per square meter, preferably, the thickness of the lacquer layer on the substrate is between about 0.2 grams per square meter and about 3 grams per square meter, most preferably, the thickness of the lacquer layer on the substrate is between about 0.3 grams per square meter and about 1 gram per square meter.

Exemplary solvents include for example water, ethanol, propanol, iso-propanol or ethoxy- propanol.

The solvent based lacquer may comprise at least one of a binder, an additive, a pigment and combinations thereof. For example, in some embodiments, the solvent based lacquer comprises at least one pigment in an amount of between about 1 percent by weight of the solvent based lacquer and about 20 percent by weight of the solvent based lacquer, before the drying step. The pigment may have a desirable visual effect on the overlying metallic layer. The pigment may aid in registration of the substrate material during application of the metallic layer.

The solvent based lacquer can be applied using conventional printing processes, such as gravure printing or flexographic printing. The solvent based lacquer can be left to dry naturally. Alternatively or in addition, the drying process can be assisted, for example by the application of heat or air streams. In some embodiments, the drying step comprises heating the solvent based lacquer to a temperature between about 50 degrees Celsius and about 200 degrees Celsius, preferably, between about 90 degrees Celsius and about 120 degrees Celsius for between about 0.5 seconds to about 1 second.

After the drying step, the layer of lacquer preferably has a basis weight of between about

1 gram and about 6 grams per square meter.

As discussed above, the solvent based lacquer functions to smooth the surface of the substrate material prior to the application of the metallic material. Thus, the applied metallic layer also has a smooth surface that results in a high gloss effect. Therefore, in some embodiments, the Parker-Print-Surface roughness of the metallic layer is between about 0.1 micrometers and about 1 micrometre, preferably, less than about 0.6 micrometres measured according to International Standard IS08791 -4.

The substrate material may include any suitable material, such as paper, cardboard or plastic. In some embodiments, the substrate material includes a blank which may be folded to form a container for consumer goods. For example, the substrate material may be a blank that, when folded, forms a container for elongate smoking articles, such as a hinged lid box, as for example a Flip-Top® box.

The present invention extends to substrate materials having a metallic coating applied thereon in accordance with any of the embodiments of the method described above. Therefore, the present invention also provides a substrate having a metallic coating comprising a layer of a dried solvent based lacquer on a first surface of the substrate, and a layer of metallic material on the layer of dried solvent based lacquer.

A substrate having a metallic coating thereon in accordance with the present invention may include any of the preferred features described above with respect to the method of applying such a coating. For example, in some embodiments, the Parker-Print-Surface roughness of the layer of metallic material is less than about 0.6 micrometres. Additionally, or alternatively, the solvent based lacquer may include at least one of a binder, an additive, a pigment, or combinations thereof. Suitable binders, additives and pigments include those described above with respect to the method of applying the metallic coating.

The invention will now be further described, by way of example only, with reference to the accompanying drawing, Figure 1 , which shows a substrate material 10 comprising a sheet of cardboard having a first surface 12. The first surface 12 comprises microscopic irregularities 14 that result in a Parker-Print-Surface roughness on the first surface 12 of approximately 1.2 micrometres.

To smooth the first surface 12 of the substrate material 10, a layer of solvent based lacquer is applied to the first surface 12. The solvent based lacquer is applied to the first surface 12 of the substrate material 10 using a printing process, such as gravure printing or flexographic printing. The solvent based lacquer is dried to form a lacquer layer 16 on the first surface 12 of the substrate material 10. The lacquer layer 16 has a Parker-Print-Surface roughness of approximately between 0.1 micrometres and 0.6 micrometres.

Finally, a layer of metallic material 18, for example silver or aluminium is applied over the lacquer layer 16, the layer of metallic material 18 having a Parker-Print-Surface roughness of approximately between 0.1 micrometres and 0.6 micrometres. The combination of the lacquer layer 16 and the layer of metallic material 18 forms a metallic coating on the substrate material 10. The combined smoothness of the two layers results in specular reflection of incident light so that the metal coating has a high gloss appearance.

Claims

1. A method of applying a metallic coating to a surface of a substrate material, the method comprising:

providing a substrate material having a first surface;

applying a solvent based lacquer to the first surface of the substrate material;

drying the solvent based lacquer to form a layer of dried lacquer; and

applying a metallic material over the layer of dried lacquer to form a metallic layer.

2. A method according to claim 1 , wherein, before the drying step, the solvent based lacquer comprises a solvent in an amount of less than 50 percent by weight of the solvent based lacquer.

3. A method according to claim 1 or 2, wherein, before the drying step, the solvent based lacquer comprises at least one pigment in an amount of at least 15 percent by weight of the solvent based lacquer.

4. A method according to any preceding claim, wherein the Parker-Print-Surface roughness of the metallic layer is less than 0.6 micrometres.

5. A method according to any preceding claim, wherein, before the drying step, the solvent based lacquer has a viscosity of between about 12 seconds and about 40 seconds, measured using a DIN 4 cup.

6. A method according to claim 5, wherein, before the drying step, the solvent based lacquer has a viscosity of between about 20 seconds and about 35 seconds, measured using a DIN 4 cup.

7. A method according to any preceding claim, wherein the basis weight of the lacquer layer on the substrate is between about 0.1 grams per square meter and about 10 grams per square meter.

8. A method according to any preceding claim, wherein the solvent based lacquer comprises a binder, an additive and a pigment.

9. A method according to any preceding claim, wherein the metallic material comprises a metallic ink.

10. A substrate having a metallic coating applied thereon in accordance with the method of any preceding claim.

1 1. A substrate having a metallic coating comprising:

a layer of a dried solvent based lacquer on a first surface of the substrate; and a layer of metallic material on the layer of dried solvent based lacquer.

12. A substrate according to claim 1 1 , wherein the Parker-Print-Surface roughness of the layer of metallic material is less than 0.6 micrometres.

13. A substrate according to claims 1 1 or 12, wherein the solvent based lacquer comprises a binder, an additive and a pigment.

14. A substrate according to any of claims 1 1 to 13 , wherein the basis weight of the lacquer layer on the substrate is between about 0.1 grams per square meter and about 10 grams per square meter.

15. Use of a solvent based lacquer to reduce the surface roughness of a substrate prior to the application of a metallic material to the substrate.