EP1571258A1 - Package coated with a protection varnish against light - Google Patents

Abstract

Package (A) comprises a sheet of cardboard covered on the outside with a varnish (3) that contains at least one additive (I) that reduces light-induced degradation of the package. Independent claims are also included for: (1) method for preparing (A); and (2) sheet of cardboard for preparing (A).

Description

The present invention relates to packaging, especially cardboard.

The cardboard sheets generally used for packaging may be characterize by their weight and by the nature of their constituents.

"Cardboard sheet" denotes a sheet whose grammage is greater than 100 g / m ² , especially greater than or equal to 190 g / m ² , or even greater than 200 g / m ² .

We distinguish cartons based on conifers, or called cartons wood, and Cartons made of deciduous trees, also called cellulose cartons.

To make the pulp of the wooden boards , the bark of the conifers are mechanically chopped ( mechanical pulping ), which leads to rather long fibers.

Wood cartons generally have at least 80% by weight of conifers and are yellowish. These fibers contain lignin which darkens under the effect of ultraviolet radiation.

To improve surface appearance, printability or varnishing and to increase the whiteness, the cartons can be put down.

The term "coated cardboard sheet" thus refers to a sheet of cardboard which has a surface coating on one or both sides.

The yellowing of the lignin-rich cardboard sheets under the effect of the visible light and especially ultraviolet radiation is a very old problem that the manufacturers are struggling to solve because this yellowing greatly diminishes the appeal of packaging for the consumer.

"Visible light" means light of wavelength between 400 and 800 nm and by "ultraviolet light" that of wavelength included between 280 and 400 nm.

To avoid being confronted with the problem of yellowing related to the presence of lignin or minimize this one, it is possible to use cellulose cartons which are less rich in lignin since generally comprising less than 15% by weight of conifers.

However, these cartons that use less raw material in some parts of the world and require chemical pulping are usually more expensive than cartons.

In addition, the mechanical rigidity of these boxes is generally worse than that of wood cartons, so that the grammage must be higher at equal rigidity, which makes the use of cellulose boards reserved for expensive products.

It is known to retard the yellowing of lignin-rich cartons by incorporating into the surface coating an additive based on carbon black, iron or zinc, but this affects the whiteness of the coating and / or may food compatibility.

In addition, lignin eventually migrates into the surface coating and the yellowing is not permanently prevented.

It is also known to counter-glue a polymeric film containing titanium dioxide, but this changes the appearance and characteristics to the touch of the sheet of cardboard and may make it more difficult to recycle it.

In addition, the inks used to print packaging exist under several grades, which are more or less expensive depending on their resistance to ultraviolet. UV-resistant grades are preferentially used unless the product is intended to be sold quickly.

It is also known to incorporate brighteners in the cardboard sheets, in order to increase the whiteness, but these brighteners are sensitive to ultraviolet and efficiency and limited in time.

There is a need to reduce the cost of packaging without this reduction is to the detriment of the mechanical properties of the packaging or its appearance over time, especially under the effect of ultraviolet radiation.

According to the invention, the package comprises a sheet of cardboard covered externally of a varnish comprising at least one additive for reducing degradation packaging under the effect of light, for example the yellowing of the the effect of light and / or the alteration of an underlying impression.

By "cardboard sheet" is meant in the description and the claims a sheet of cardboard or a sheet of a similar material, composite or not, having substantially the same mechanical behavior as the cardboard. Such a composite material for example, comprises vegetable fibers, especially more than 40% by weight, better 50% or more, these vegetable fibers being for example mixed with fibers made of synthetic material.

The invention makes it possible to produce a package with a cardboard sheet rich in lignin while effectively retarding the yellowing thereof.

The invention thus makes it possible to use stiffer wood cartons than cartons cellulose and decrease the thickness of the cardboard sheet to equal stiffness, which decreases the amount of material used.

In addition, the presence of the varnish makes it possible to use underlying inks less resistant to ultraviolet, so less expensive.

The invention thus makes it possible to achieve significant savings on the cost of a cardboard packaging.

The invention is advantageously applied to cardboard sheets comprising by example more than 70%, better 80%, in mass of coniferous fibers, rich in lignin.

The invention also makes it possible to protect the packaging without this protection requires, where appropriate, to modify the composition or thickness of a coating of possible surface of the sheet, which allows to less affect, not to affect, its printability characteristics and its mechanical characteristics, including stiffness or compressive strength.

Thus, the existing processes and machines used for the manufacture of packaging or packaging of products in such packaging may be retained.

The invention does not apply exclusively to coated cardboard sheets but also relates to uncoated cardboard sheets.

In the case where the invention is applied to coated cardboard sheets, the surface coating may especially be white and contain for example at least one optical brightener, which may be for example in a proportion of between 0.05 and 0.5% by weight in the surface coating, better in a proportion between 0.1 and 0.3%.

For example, the surface coating may have a thickness of between 20 and 30 μm and contain calcium carbonate and / or clay, especially kaolin. In an exemplary implementation of the invention, the surface coating has calcium carbonate and clay substantially in the mass ratio 60/40.

The surface coating may also comprise a binder, in particular starch, to improve its cohesion.

The presence of calcium carbonate, which may include spheroidal fine grains, may be useful for surface smoothness.

The presence of clay, especially kaolin, which may have grains coarse prismatic, can be useful to achieve the desired density for the coating of surface.

The thickness of the varnish may be for example between 2 and 20 μm, better between 3 and 12 μm, the total thickness of the cardboard sheet being for example between 100 and 1000 μm, and preferably between 300 and 500 μm.

The additive (s) may be present in a total mass proportion by additives between 0.5 and 10% in the varnish, for example in a proportion between 1 and 6%.

The varnish may comprise an additive which may be a UV absorber compound, for example a UV absorber of formula

The varnish may also comprise an additive which may be a free radical scavenging compound, especially a hindered amine or an HALS amine, for example a free radical scavenger of formula

The varnish may be based on aqueous solvent, for example a varnish acrylic.

Alternatively, the varnish may be a crosslinkable varnish under the action of a UV radiation, which makes it possible not to have to evaporate water from the carton, which can keep its moisture. In this case, the additive (s) intended to combat the effects of the light are chosen to be compatible with such a varnish. In particular, it is preferable that the varnish does not have when it is crosslinkable under the action of a ultraviolet radiation of free radical sensors such as impermissible amines steric or amines HALS (Hindered Amine Light Stabilizer in French amine blocked stabilizing to light).

The varnish, when crosslinkable under the action of UV radiation, can for example, two ultraviolet absorbers whose absorption spectra are chosen so as to provide a range of wavelengths where the absorption is less, and the lamp used to cause the polymerization is then chosen to emit in this beach.

This makes it possible to prevent the ultraviolet absorbers present in the varnish fulfill their protective function without unduly hampering the polymerisation of the varnish.

The varnish may have a purple dye, which tends to increase the whiteness of the cardboard sheet.

The sheet may be covered for example by about 3 to 10 g / m ² of varnish before drying, including about 6 g / m ² of varnish.

The invention also relates to a method of manufacturing a package comprising a sheet of cardboard or the like, into which the sheet is applied to varnish containing at least one additive intended to reduce the degradation of the packaging the effect of light.

This additive may be a UV absorber compound and / or radical scavenger free.

The varnish can be applied by various techniques, in particular by offset, heliography, flexography or screen printing.

The sheet can be printed before or after the application some nail polish.

Preferably, the sheet is printed before depositing the varnish, which allows to protect the ink from ultraviolet rays and thus to use less expensive inks.

The invention thus also relates, in another of its aspects, to a sheet of cardboard comprising an impression of at least one ink with low resistance to ultraviolet, for example less than ... [ to be completed ], covered by a varnish comprising at least one ultraviolet absorber and / or one free radical sensor, in particular one of those mentioned above.

Another subject of the invention, according to another of its aspects, independently or in combination with the above, a crosslinkable varnish under the effect ultraviolet radiation, having at least two ultraviolet absorbers chosen so as to have absorption spectra sufficiently shifted to spare between them a range of wavelengths where the absorption is less, in order to the irradiation in this range during the crosslinking of the varnish.

The absorption peaks of the two additives are, for example, shifted by more than 40 nm and create between them a valley whose hollow corresponds for example to a absorption more than 30% less than the maximum absorption defined by one of the peaks.

The varnish may further comprise a violet dye.

The emission spectrum of the source can be centered for example on 310-330 about nm.

Another subject of the invention, according to another of its aspects, independently or in combination with the foregoing, a coated cardboard sheet a varnish comprising at least one UV absorber additive and / or radical scavenger free.

• la figure 1 représente de manière schématique, en perspective, un exemple d'emballage réalisé par pliage d'une feuille de carton ou analogue revêtue d'un vernis conforme à l'invention,
• les figures 2 à 4 sont des coupes schématiques et partielles d'une feuille de carton revêtue illustrant divers exemples de mise en oeuvre de l'invention, et
• la figure 5 représente de manière schématique l'absorption en fonction de la longueur d'onde pour un exemple de vernis susceptible d'être utilisé.

The invention will be better understood on reading the following detailed description, non-limiting examples of implementation thereof, and on examining the appended drawing, in which:

• FIG. 1 schematically represents, in perspective, an example of packaging made by folding a sheet of cardboard or the like coated with a varnish according to the invention,
• Figures 2 to 4 are schematic and partial sections of a coated cardboard sheet illustrating various examples of implementation of the invention, and
• Figure 5 schematically shows the absorption as a function of the wavelength for an example of varnish that can be used.

The invention applies to all types of packaging made by folding, gluing and / or rolling of one or more sheets of cardboard or the like, and in particular to boxes intended to contain containers containing cosmetic or care products.

Such a box may have for example a general shape parallelepiped as illustrated in FIG. 1, with at one end at least one folding tongue.

Of course, the invention is not limited to a particular form packaging and can be made with a sheet of cardboard or the like coated with a varnish according to the invention, packagings having very different shapes, and intended for example to contain cigarettes or other objects.

The packaging may include only the sheet of cardboard or the like and the varnish covering it on the outside and exposed side of the packaging, so as to facilitate its recyclability. The sheet of cardboard or the like may in particular be devoid of film polymer laminated.

The sheet used may comprise a base 1, preferably comprising coniferous fibers, therefore containing lignin, and at least the outer side of the packaging a surface coating 2 in the case where the sheet is a sheet of cardboard lying. When the sheet comprises cellulosic fibers, these may come from the Aspen tree for example.

The surface coating 2, the thickness of which is for example between 20 and 30 μm, can improve the printability and varnishing characteristics of the sheet of cardboard and improve its whiteness.

The coating layer 2 comprises, for example, calcium carbonate and clay, especially kaolin, in a mass ratio compatible with the processes used, for example 60/40.

The surface coating 2 may be devoid of protective compounds vis-à-vis light such as carbon black or an oxide of iron or zinc.

The surface coating 2 may comprise at least one optical brightener, for example example in a mass proportion of between 0.05 and 0.5%, better 0.1 and 0.3%.

According to the invention, the cardboard sheet is covered on the outside the package by a layer of varnish 3, the latter comprising at least one compound for protecting the leaf from the effects of light, especially yellowing due to visible and / or ultraviolet light, in particular wavelengths between 290 and 460 nm.

Varnish 3, which can be colorless and does not appreciably change the color of the underlying sheet, for example comprises at least one UV absorber compound and / or a free radical scavenging compound.

The varnish 3 can be applied by various known techniques, for example heliography, flexography, screen printing or offset.

The thickness of varnish 3 deposited may depend on the deposition technique used, about 2 microns for the offset to about 20 microns for flexography. Of preferably, the thickness deposited will be between 3 and 12 microns.

The varnish 3 is preferably applied after the printing of a decoration 4 on the sheet, as shown in Figure 3, but could alternatively be applied prior to the application of the decor 4, as illustrated in FIG.

When the varnish 3 is applied after printing a decoration 4 on the sheet, the varnish 3 can usefully protect the inks of the decor layer 4 from a change of color.

The varnish 3 then makes it possible to use light-sensitive inks, such as for example fluorescent inks unstable or sensitive to the phenomenon of metamerism.

Many additives can be incorporated in the varnish 3 in order to obtain the protection function sought.

This or these additives are in a concentration that may depend on their efficiency, the latter being proportional to the concentration and thickness of the coat of varnish according to the law of BEER LAMBERT. The layer of varnish 3 can by example absorb light of wavelengths between 290 and 460 nm in a proportion, for example to increase by at least 50%, better to double, the duration of exposure to light leading to the same effects of degradation of the packaging only in his absence.

Typically, the proportion of additive (s) may be between 0.5 and 10% in bulk in the varnish 3, and better between 1 and 6%, for example between 3 and 6%.

As usable additives, mention may be made especially of those marketed by GREAT LAKES and CIBA-GEIGY, and in particular derivatives of the family of benzotriazoles.

Such derivatives may be heterocycles of cyclo-benzene type, on which a carbon atom has been replaced.

By way of example of a UV absorber compound, mention may be made of that of formula

As an example of a free radical scavenger, mention may be made of that of formula

The free radical scavenger (s) used may be amines AES steric hindrance or HALS amines.

The free radical sensor (s) can stabilize the varnish and prevent its yellowing clean.

The nature of the varnish used may depend on the printing process and the Drying mode retained.

Preferably, varnish offsets fat that yell naturally by oxidation.

It is possible to use a water-based, acrylic-type varnish supplemented with an absorber UV and / or a free radical scavenger, for example added with the two compounds whose formulas have been given above.

We can still use a crosslinkable varnish under the action of radiation ultraviolet, preferably avoiding the inclusion of hindered amines, which would be partially annihilated by the crosslinking of the varnish.

When a UV curable varnish is used, this varnish comprises for example at least two UV absorbers, for example each at a concentration of less than 3% by weight, more preferably less than or equal to 2%, whose absorption spectra are chosen so as to provide a range of wavelengths where the additives absorb less and allow a UV source to cause crosslinking of the varnish.

One of the additives is for example at a concentration of 2% and the other of 1%, so as to have a total concentration of less than or equal to 3%.

By way of example, FIG. 5 shows the absorption spectrum of a varnish (for a path of 1 cm after dilution in toluene at 20 mg / l) comprising two additives whose absorption spectra have respective 10 and 11 sparing peaks between them a valley whose bottom 12 is for example centered on a wavelength emission of the source used to crosslink the varnish, for example 320 nm.

   et un dérivé de benzophénine tel que par exemple celui commercialisé par la société CIBA sous la référence CGL 477, de formule générale :

UV absorbers are for example
an aromatic triazine derivative such as that marketed by CIBA under the name TINUVIN 400, of general formula:

and a benzophenine derivative such as for example that marketed by CIBA under the reference CGL 477, of general formula:

The minimum absorption observed in the bottom 12 of the valley is, for example, less than 30% less than the maximum absorption A _max observed for one of the peaks 10 and 11.

The varnish may include a purple dye to increase the whiteness of the sheet, this dye being for example at a concentration less than or equal to 1%.

To highlight the protective effect against yellowing, conferred by a varnish 3 according to the invention, it is possible to carry out a test consisting in depositing a predefined quantity, for example 6 g / m ² , of varnish wet water on a sheet of cardboard with a total thickness of 350 μm, and then expose the sheet thus covered for a predefined period to a mercury vapor lamp. The concentration of additives in the varnish can for example reach 5% by weight. An "Anilox" cylinder with a volume of at least 13 cm ^{3 can be used} to apply the varnish.

Yellowing is measured on the Wool scale, which corresponds to a scale of blue of increasing holding in the light, normed from 1 to 8.

In the absence of varnish, measured yellowing can for example the scale of Wool value 3. In the presence of the varnish, measured yellowing can pass to a value at least equal to 4, which highlights the resistance to yellowing more large of the cardboard sheet coated with varnish. The change from value 3 to 4 corresponds to a doubling of the duration of the stability to light.

In the case where the varnish is a UV curable varnish, it is possible to observe a increased whiteness over time due to crosslinking of the varnish continuing in time, when exposure to the artificial source to cause the polymerization was not sufficient to polymerize the varnish as much as possible.

Of course, the invention is not limited to the examples that have just been other additives than those mentioned.

It is also possible to use cardboard sheets having coatings of surface of other composition, or even sheets of cardboard without surface coating.

Throughout the description, including the claims, the expression "Comprising one" should be understood as being synonymous with "comprising at least a ", unless the opposite is specified.

By "understood between", it is necessary to understand limits included, except specified other.

Claims (46)

Packaging comprising a sheet of cardboard covered externally a varnish (3) comprising at least one additive intended to reduce the degradation of packaging under the effect of light. Packaging according to claim 1, characterized in that the cardboard sheet comprises coniferous fibers. Packaging according to claim 2, characterized in that the paperboard sheet comprises more than 70%, better still more than 80% by weight of coniferous fibers. Packaging according to any one of claims 1 to 3, characterized in that the additive absorbs in a large proportion the light radiation of wavelength between 290 and 460 nm. Packaging according to any one of claims 1 to 4, characterized in that the cardboard sheet comprises a surface coating (2). Packaging according to claim 5, characterized in that the surface coating (2) is white. Packaging according to one of claims 5 and 6, characterized in that the surface coating contains at least one optical brightener. Packaging according to claim 7, characterized in that the mass proportion of optical brightener in the surface coating is between 0.05 and 0.5%. Packaging according to the preceding claim, characterized in that the proportion of optical brightener is between 0.1 and 0.3%. Packaging according to any one of claims 5 to 9, characterized in that the surface coating (2) has a thickness of between 20 and 30 microns. Packaging according to any one of claims 5 to 10, characterized in that the surface coating (2) contains calcium carbonate. Packaging according to any one of claims 5 to 11, characterized in that the surface coating (2) comprises clay, especially kaolin. Packaging according to the two immediately preceding claims, characterized in that the surface coating (2) comprises calcium carbonate and clay substantially in the weight ratio 60/40. Packaging according to any one of claims 5 to 13, characterized in that the surface coating (2) comprises starch. Packaging according to any one of the preceding claims, characterized in that the sheet has a basis weight greater than or equal to 100 g / m ² , better than or equal to 190 g / m ² , in particular greater than or equal to 200 g / m ² . Packaging according to any one of the preceding claims, characterized in that the thickness of varnish (3) is between 2 and 20 microns. Packaging according to the preceding claim, characterized in that the thickness of varnish (3) is between 3 and 12 microns. Packaging according to any one of the preceding claims, characterized in that the additive is in a mass proportion of between 0.5 and 10% in the varnish (3). Packaging according to the preceding claim, characterized in that the additive is in a mass proportion of between 3 and 6% in the varnish. Packaging according to any one of the preceding claims, characterized in that the additive is a UV absorber compound. Packaging according to the preceding claim, characterized in that the additive is a UV absorber of formula:

Packaging according to any one of claims 1 to 17, characterized in that the additive is a free radical scavenging compound. Packaging according to Claim 22, characterized in that the additive is a hindered amine or an HALS amine. Packaging according to Claim 22, characterized in that the additive is a free radical scavenger compound of formula:

Packaging according to any one of the preceding claims, characterized in that the varnish (3) is a varnish crosslinkable under the action of UV radiation. Packaging according to claim 25, characterized in that the varnish comprises at least two ultraviolet absorbers whose absorption spectra are chosen so as to provide a range of wavelengths where the absorption is less. Packaging according to any one of the preceding claims, characterized in that the varnish comprises a violet dye. Packaging according to claim 26, characterized in that the valley formed between the absorption peaks is substantially centered on 310-330 nm. Packaging according to any one of claims 1 to 24, characterized in that the varnish is based on aqueous solvent. Packaging according to the preceding claim, characterized in that the varnish is an acrylic varnish. Packaging according to claim 1, characterized in that the cardboard sheet is of the SBS type. Packaging according to any one of the preceding claims, characterized in that the sheet is covered with approximately 3 to 10 g / m ² of varnish (3) before drying. Packaging according to the preceding claim, characterized in that the cardboard sheet is covered with about 6 g / m ² of varnish. Packaging according to any one of the preceding claims, characterized in that the varnish (3) covers an impression (4) on the sheet. Packaging according to any one of claims 1 to 33, characterized in that it comprises an impression (4) on the varnish (3). Packaging according to claim 1, characterized in that the cardboard sheet comprises a base (1) comprising cellulose fibers, in particular from the Aspen. Packaging according to claim 1, characterized in that the cardboard sheet comprises lignin. Packaging according to any one of claims 1 to 35, characterized in that the grammage of the sheet is less than or equal to 320 g / m ² . A method of manufacturing a package comprising a sheet of cardboard, in which a varnish (3) containing at least one additive for to reduce the degradation of the leaf under the effect of light. Process according to Claim 39, characterized in that the additive is a UV absorber compound and / or free radical scavenger. Method according to one of the two immediately preceding claims, characterized in that the varnish (3) is applied by offset, heliography, flexography or screen printing. Process according to Claim 39 or 40, characterized in that the sheet is printed before the varnish (3) is applied. Process according to Claim 39 or 40, characterized in that the sheet is printed after the application of the varnish (3). A method according to claim 39, characterized in that the UV-curable varnish comprises at least two ultraviolet absorbers selected so as to have absorption spectra sufficiently offset to provide a range between them. wavelengths where the absorption is less and in that a source emitting in this place is used to cause the crosslinking of the varnish. Process according to Claim 39, characterized in that the absorption peaks of the two additives are shifted by more than 40 nm and form between them a valley whose hollow corresponds to an absorption (A _min ) of more than 30% lower than the maximum absorption (A _max ) defined by one of the peaks. Cardboard sheet for making a package as defined in one of the any of claims 1 to 38.

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