Multiple-layer covering lid and method of making same

The present invention relates to a cardboard cover lid having a radiation curable varnish covering a print. This type of structure protects the graphic signs printed on the cardboard lid so that they are not distorted and / or damaged.

For attaching the cardboard lid to the tray after filling with the product, pressure sealing is usually used. The advantages of this method are more uniform seals, simpler tooling operation, and the ability to seal without contaminating food. The main disadvantage of this method is that the heated platen can damage the outer surface of the lid, which contains important sales marks and in some cases UPC symbols. A distorted or damaged surface determines the unsatisfactory appearance of the packaging and in some cases the UPC symbols that cannot be read.

In coating systems, it is known to use a varnish layer to protect the printed surface. An example of this is the solution known from US Pat. No. 4,170,681, entitled "Method of applying a varnish layer to a printed surface and the resulting product." However, this description discloses the use

179 985 varnish layers to obtain a smooth protective surface for printed graphic signs, however, the nature of this varnish layer is such that it is not heat resistant (mass stable) to temperatures above 163 ° C, and the varnish is not cured by radiation. Thus, the preferred varnish covering the print is one that is both heat resistant and radiation cured.

Therefore, there is a need to develop varnish on the print, which is suitable for protecting graphic signs printed on the lid, and which is both heat-resistant and radiation-hardened.

According to the invention, these goals were achieved by developing a multilayer lid having a varnish covering the print, which consists of a cardboard substrate having a first and second side a coating of molecular minerals placed on the outside of the first side of this substrate, a layer of printed graphic marks placed on the outside of said coating and of molecular minerals , a coating of radiation-hardened heat-resistant varnish, placed on the outside of the layer of printed graphic characters and a layer of heat-seal barrier material placed on the outside of the other side of said substrate.

In the preferred solutions, the molecular minerals are clays. The varnish coating is cured by electron beam or ultraviolet radiation.

The next recommended solution, radiation-cured varnish cover protects printed graphic signs against distortion and / or damage.

The lid according to the invention is light, easy to assemble, has good stability, good durability, has excellent protection for printed graphic signs and is very economical. In many recommended solutions, this ease of assembly, protection of graphic symbols and economy are optimized to a much greater extent than obtained so far in known multilayer ages.

The subject of the invention will be seen in the embodiment of the drawing showing a multilayer lid with a cured varnish covering the print according to the invention.

Cartons used to distribute, sell and in some cases heat prepared portions of prepared food are made from a cardboard substrate. The basic carton design includes a container to contain the product and a lid that is at least partially sealed to peripheral flanges protruding from the container sidewalls.

An example is the solution according to US Patent No. 5,356,070, entitled "Carton food tray with compartments", incorporated herein by reference. In some cases, the lid may form a whole with the container, as in the solution of US Patent No. 5,228,272, entitled "Product and method of heat sealing of cardboard cardboard having a polymer coating on one side",

The main substrate material in the present invention is machine-made cardboard with a thickness in the range from 0.178 mm to 0.889 mm. The cardboard substrate can be covered on one or both sides with a layer of molecular minerals. The surface of the lid just after the food product must be coated with a material that forms a barrier and is heat-sealed to the flanges of the container. Coatings that do this are commonly extruded polymers such as polyethylene terephthalate (PET), polypropylene (PP) and polyethylene (PE). The outer surface of the lid may be printed with sales graphic signs so that these graphic signs are printed on a layer of molecular minerals placed on the primary substrate.

The figure shows the multilayer lid 2, which contains a conventional cardboard substrate 4, a conventional barrier coating 6, a conventional layer of molecular minerals 8, a conventional layer of printed graphic signs 10 and a covering printing, radiation-cured varnish layer 12.

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As mentioned above, the barrier coating 6 must be a barrier and must be heat-sealed to the container flanges (not shown - see, for example, Figures 1 and 3 of the above-mentioned patents, '0.70 and -2.02 respectively). Preferably, the barrier is formed made of PET, PP or PE The layer of molecular mineral 8 is preferably made of clays The graphic characters are printed on the layer of molecular mineral 8 by any conventional printing technique.

It is important that the graphic signs 10 are not deformed or damaged when attaching or sealing the lid to the container. To this end, a radiation-hardened varnish layer 12 is placed over the layer of printed graphic signs 10, such that layer 12 does not stick to the heated platen and remains mass-stable above 163 ° C.

Two processes can be used to produce the radiation-curable print covering varnish layer 12, namely electron beam (EB) and ultraviolet (UV) cure. In the EB process, a coating (containing 100% solids) is applied to the substrate in a liquid state, just after printing a layer of 10 sales graphics. The coating is then exposed to highly accelerated electrons and a reaction occurs in which the chemical bonds in the coating are broken and a modified layer of varnish 12 is formed above the print. This process is referred to as polymerization. Polymerization causes significant physical changes in the processed product and gives it many desirable properties such as heat and abrasion resistance.

The UV process is similar in that the coating (containing 100% solids) is applied in a liquid state to a layer of 10 printed graphic signs. The coating is then exposed to a UV light source. These photochemical initiators in the coating form released radicals. This liberated radical initiates the crosslinking of monomers and oligomers, which causes rapid hardening of the print covering layer 12. As in the EB process, a durable varnish layer 12 covering the print is produced, suitable for sealing systems with a heated platen.

The better quality of the coatings according to the present invention (RAD) compared to conventional coatings (STD) as a result of using radiation cured varnish is shown below.

The temperature range used is typical of the applications previously described. The sealing pressure can be much larger. Increased pressure intensifies the problems indicated for the standard coating. Residence times cover a typical range depending on the type of polymer being sealed and the size of the carton (thickness).

Test conditions

Equipment: Sample location: Tested samples:

Pressure:

Residence time: Scaling:

25.4 mm rod sealant

Printed surface next to the heated one

STD = Standard water based ink and varnish,

RAD = Cured by radiation of carcasses and varnish,

0.414 MP 1 and 3 seconds

- Lack of destruction

- Slightly matt surface

- Matte surface and slight ink lifting

- Matte surface, ink rising and slight discoloration

- Serious discoloration, mascara rising and matte surface

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GRADE

<td></td><td colspan="2">Residence time 1.0 seconds</td><td colspan="2">Residence time 3.0 seconds</td>

<td>Temp. ° C</td><td>STD.</td><td>RAD.</td><td>STD.</td><td>RAD.</td>

<td> 163</td><td> 2</td><td> 1</td><td> 2</td><td> 1</td>

<td> 176</td><td> 2</td><td> 1</td><td> 3</td><td> 1</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>

<td colspan="5">After the above disclosure, various other characteristics become apparent to those skilled in the art, mo</td>

specifications or improvements. Such features, modifications or improvements are therefore to be regarded as part of this invention, the scope of which is defined by the appended claims.

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HARDENED ROOM_T

PRINTED GRAPHIC CHARACTERS WITH MOLECULAR MINERALS CARDBOARD BANKING SUBSTRATE

UP Department of Publications. Circulation of 60 copies Price PLN 2.00