A lid having a cured overprint varnish

BACKGROUND OF THE INVENTION The present invention relates to a cardboard-based lid with a lacquer coating for printed graphics, and to a method for producing a lid comprising printing a graphic onto a substrate covered with a coating to protect the graphic.

Trays closed with cardboard-based lids are widely used for packaging articles. The advantage of these is that, in a simple and universally applicable manner, a heated pressure plate can be used to seal the trays filled with the goods, even when the sealing rim of the tray becomes contaminated with the material of the goods when it is being loaded. The disadvantage of this solution is that the heated sheet may damage the outside surface of the lid, which contains printed graphics with information about the goods and possibly with bar code (UPC symbols). The surface defect caused by the printing sheet degrades the appearance of the packaging and, in many cases, renders the graphics or bar code illegible.

In batches, plastic or cardboard trays, which are sealed with cardboard-based lids, which are sealed at the edges of the lids by means of gluing, usually by sealing thermoplastic layers with snow, are commonly used for packaging pre-packaged foodstuffs and other articles. Such a solution is described in U.S. Patent No. 5,356,070 to Rigby. The US 5,228,272 (Calvert) also discloses a solution in which the tray and lid are formed in one piece, one piece.

A known method for protecting printed graphics is to coat the graphics with lacquer. U.S. Patent No. 4,170,681 to Edwards et al. Discloses such a varnish for protecting print graphics, the object of which is primarily to achieve a sufficiently smooth surface. The material of the lacquer described herein is not heat-resistant, i.e. is no longer stable at 163 ° C, is not resistant to curing and has not been subjected to radiation treatment.

SUMMARY OF THE INVENTION It is an object of the present invention to overcome these shortcomings of the prior art by providing a lid and a method for making the lid which is able to withstand the heat demand of the closure without damage and to provide aesthetically suitable sealed lid packaging.

SUMMARY OF THE INVENTION An object of the present invention is to provide a lid with a lacquer coating for printed graphics in which one side of a carrier cardboard carrier is covered with a mineral layer overlaid with printed graphics covered with a radiation-cured heat-resistant lacquer on printed paper; material is provided with a closing cover.

Preferably, an additional layer of mineral material is formed between the paperboard and the thermoplastic barrier.

Preferably, the material of the mineral layer is clay.

Preferably, the material of the second mineral layer is also clay.

Preferably, the radiation-cured heat-resistant lacquer material is solid at 163 ° C.

On the other hand, the present invention provides a method for producing a cover, wherein a substrate is printed with a graphic which is coated with a lacquer layer. In the process, a surface of a cardboard carrier according to the present invention is coated with a layer of mineral material which is printed on and printed with a heat-resistant lacquer layer which is cured by radiation and a thermoplastic barrier on the other side of the paperboard.

Preferably the material of the lacquer layer when cured is stable at 163 ° C.

Preferably, the curing of the lacquer layer is effected by electron beam or ultraviolet irradiation.

Advantages of the present invention include low weight, good stability and durability, economical, easy manufacturing, good handling, and above all, excellent protection and advantageous presentation for printed graphics. By optimizing production and application, it provides significantly better features than those known above.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail with reference to the following drawing. In the drawing it is

First Arrangement of the cover layers of FIG.

In the figure, a cardboard support layer 2 with a sufficient strength is shown. The thickness of the cardboard used in the lid is selected from 0.178 to 0.899 mm. The paperboard is covered with a layer 8 of mineral particles on one or both sides of the cardboard. The inner layer of the lid laminate contacting the packaged goods is a thermoplastic, health-sealing barrier layer 6 which is an extruded polymeric material, most notably polyethylene terephthalate (PET), polypropylene (PP) or polyethylene (PE). A commercial graphic 10 is applied over the surface of the mineral layer (generally clay) 8, which covers the cover support carrier paper 4, which is coated with a radiation-cured heat-resistant lacquer layer 12.

In the figure, the lid structure 2 is shown with its first outer surface facing up and the second side facing downwards inside the package. From the inside to the outside, the cover layers are as follows: known weldable sealing cover 6, known cardboard 4, known mineral layer 8, known print graphics 10, radiation cured heat resistant lacquer 12.

The sealing layer 6 provides, on the one hand, the sealing of the packed goods with the packaging materials and the environment and, on the other hand, the sealing of the packing with the material welded to the edge of the tray.

It is a prerequisite for the sealing that the outer surface of the lid, especially the graphics, is not damaged in its texture or aesthetic appearance. Damage to the graphic 10 could be caused by the lacquer layer 12 adhering to a sealing tool heated to the melting temperature of the material of the barrier layer 6. To prevent this, a radiant-cured heat-resistant lacquer layer of the invention is formed over the graphic 10, which is still a solid solid at 163 ° C (325 ° F).

The lacquer layer 12 may be cured by ultraviolet (UV) irradiation or electron beam (EB).

HU 217 876 Β

By electron beam, the 100% solid layer in the liquid phase is formed by subjecting the liquid phase layer to high speed accelerated electron beam upon printing of the graphic 10, during which the chemical bonds of the liquid layer material are broken and modified by polymerization. lacquer 12 is formed. Polymerization significantly changes many of the properties of the material, such as heat resistance and abrasion resistance.

UV treatment produces a similar effect: the 100% solid lacquer layer is formed by irradiating the liquid applied material with ultraviolet radiation. The photochemical initiators of the material form free radicals, the free radicals initiating the crosslinking of monomers and oligomers, resulting in rapid cure.

The results of comparative tests with the inventive lacquer coat and the conventional lacquer coat, which illustrate the advantages of the present invention, are set out below.

The temperatures used in the tests are the values ​​that occur regularly during the described application and occur during packaging and use. The closing pressure can be much higher. At higher barrier pressures, the behavior of conventional lacquer coatings is even more unfavorable. The closing time depends on the polymer used and the thickness of the cardboard.

Test conditions:

Equipment: Sentinel Bar 25.4 mm sealing device,

Sample position: printed surface toward heated bar, Patterns: STD = water based ink and lacquer,

RAD = ink and varnish treated with radiation,

Pressure: 0.414 MPa

Operation time: 1 and 3 114 microprocessors,

Grades: 1 - no adhesion

- slight dimming,

- glossy surface and slight ink defects,

- glossy surface, defects in ink, slight discoloration,

- severe discoloration, ink defects, glossy surface.

T results:

seconds cure 3 seconds cure30 cure time

RAD STD RAD

2 1

3 1 time ° C STD

163 2

176 2

<td></td><td colspan="2">1 second cure time</td><td colspan="2">3 seconds cure time</td>

<td> 190</td><td> 3</td><td> 1</td><td> 3</td><td> 1</td>

<td> 204</td><td> 3</td><td> 1</td><td> 3</td><td> 1</td>

<td> 218</td><td> 3</td><td> 1</td><td> 4</td><td> 1</td>

<td> 232</td><td> 4</td><td> 1</td><td> 5</td><td> 1</td>

<td> 246</td><td> 4</td><td> 1</td><td> 5</td><td> 1</td>

<td> 260</td><td> 5</td><td> 1</td><td> 5</td><td> 2</td>

From the foregoing description, a person skilled in the art may make a number of further improvements based on the present invention, which should be considered as part of the present invention.