ES2368920T3 - PACKAGING COVERED 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

Packaging coated with a light protection varnish.

The present invention relates to packaging, in particular cured.

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

Through the expression " cardboard sheets " a sheet whose weight is greater than 100 g / m2, in particular greater than or equal to 190 g / m2, even greater than 200 g / m2 is designated.

The coniferous-based cartons, or also called wooden caons, are distinguished, and the cartons based on deciduous trees, also called cellulose cartons.

To make the pulp of the wooden cartons, the conifer barks are mechanically crushed (mechanical pulping) which leads to quite long fibers.

Wood cartons generally have at least 80% by mass of coniferous fibers and are yellowish. These fibers comprise lignin that darkens under the effect of ultraviolet radiation.

To improve surface appearance, printing or varnishing and increase whiteness, cartons can be coated.

The expression " coated cardboard sheet " thus designates a cardboard sheet comprising a surface coating on one or both sides.

The yellowing of cardboard sheets rich in lignin under the effect of visible light and especially of ultraviolet radiation is a very old problem that manufacturers strive to solve, since this yellowing greatly decreases the attractiveness of the packaging for the consumer.

For " visible light " the light of wavelength between 400 and 800 nm is designated and by "ultraviolet light" the wavelength between 280 and 400 nm.

To avoid facing the problem of yellowing related to the presence of lignin or to minimize it, it is possible to use cellulose cartons that are less rich in lignin since they generally comprise less than 15% by mass of coniferous fibers.

However, these cartons that use a less widespread raw material in certain regions of the world and need a chemical treatment (chemical pulping) are usually more expensive than wooden cartons.

In addition, the mechanical stiffness of these cartons is generally less good than that of wooden cartons, so that the weight must be higher at the same stiffness, which makes the use of cellulose cartons reserved for expensive products. .

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

In addition, lignin ends up migrating in the surface coating and yellowing is definitely not prevented.

It is also known to countersink a polymeric film containing titanium dioxide, but this modifies the appearance and touch characteristics of the cardboard sheet and can make recycling difficult.

On the other hand, the inks used to print the packages exist under various degrees, which are more or less expensive depending on their resistance to ultraviolet. The UV-resistant grades are preferably used unless the product is intended to be sold quickly.

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

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

According to the invention, the packaging comprises a cardboard sheet externally coated with a varnish comprising at least one additive which aims to reduce the degradation of the packaging under the effect of light, for example the yellowing of the sheet under the effect of light and / or degradation of an underlying impression.

For the expression " cardboard sheet " in the description and in the claims a cardboard sheet or a sheet of an analogous material, composite or not, is designated which has substantially the same mechanical behavior as the cardboard. Said composite material also comprises, for example, vegetable fibers, in particular more than 40% by mass, better 50% or even more, these vegetable fibers being for example mixed with fibers of synthetic material.

The invention allows packaging with a sheet of cardboard rich in lignin, effectively delaying its yellowing.

The invention thus allows using stiffer wood cartons than cellulose cartons and decreasing the thickness of the cardboard sheet to the same 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, therefore less expensive.

The invention thus allows significant savings in the cost of a corrugated packaging.

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

The invention also makes it possible to protect the packaging without this protection needing, if necessary, modifying the composition or thickness of a possible surface coating of the sheet, which makes it possible to less affect, even affect nothing, its printing characteristics and its mechanical characteristics, in particular stiffness or compressive strength.

Thus, the existing procedures and machines used for the manufacture of the packaging or the conditioning of the products in these packages can be preserved.

The invention does not apply exclusively to cardboard sheets " coated ", but also refers to cardboard sheets not " stuccoed ".

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

The surface coating may, for example, have a thickness between 20 and 30 µm and contain calcium carbonate and / or clay, in particular kaolin. In an exemplary embodiment of the invention, the surface coating comprises calcium carbonate and clay substantially in the 60/40 mass ratio.

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

The presence of calcium carbonate, which may in particular comprise spheroidal fine grains, may be useful for surface smoothing.

The presence of clay, in particular kaolin, which can have prismatic coarse grains, can be useful to obtain the desired density for the surface coating.

The thickness of the varnish can be comprised 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 1,000 µm, and preferably between 300 and 500 µm.

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

The varnish can comprise an additive that can be a UV absorbing compound, for example a UV absorber of formula

The varnish may also comprise an additive that can be a free radical scavenging compound, in particular an amine with steric hindrance or a HALS amine, for example a free radical scavenger of formula

The varnish can be based on aqueous solvent, for example being an acrylic varnish.

As a variant, the varnish can be a crosslinkable varnish under the action of UV radiation, which allows not having to evaporate the water from the cardboard, which can retain its moisture. In this case, the additive or additives intended to combat the effects of light are selected to be compatible with said varnish. In particular, it is preferable that the varnish does not comprise, when crosslinkable under the action of ultraviolet radiation, no free radical scavenger, such as amines with steric hindrance or HALS amines (Hindered Amine Light Stabilizer, ie blocked amine which it stabilizes with light).

The varnish, when crosslinkable under the action of UV radiation, can comprise, for example, two ultraviolet absorbers whose absorption spectra are selected such that a range of wavelengths is available in which the absorption is less, and the Lamp used to cause polymerization is then selected to emit in this range.

This allows to avoid that the ultraviolet absorbers present in the varnish fulfill their protective function, without preventing the polymerization of the varnish too much.

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

The sheet can be coated, for example, by about 3 to 10 g / m2 of varnish before drying, in particular about 6 g / m2 of varnish.

The present specification also describes a method of manufacturing a package comprising a cardboard sheet or the like, in which a varnish containing at least one additive is applied on the sheet which aims to reduce the degradation of the packaging under the effect of the light.

This additive can be a UV absorbing compound and / or a free radical scavenger.

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 varnish application.

Preferably, the sheet is printed before varnish deposition, which allows the ink to be protected from ultraviolet rays and therefore use less expensive inks.

The present specification also describes a cardboard sheet comprising an impression of at least one ink of low ultraviolet resistance, coated with a varnish comprising at least one ultraviolet absorber and / or a free radical scavenger, in particular one of those mentioned above.

The present specification also describes a crosslinkable varnish under the effect of ultraviolet radiation, comprising at least two ultraviolet absorbers selected so as to obtain absorption spectra sufficiently displaced to have a range of wavelengths between them. that the absorption is lower, with a view to irradiation in this interval during crosslinking of the varnish.

The absorption peaks of the two additives are for example displaced by more than 40 nm and have between them a valley whose gap corresponds, for example, to an absorption lower than 30% to the maximum absorption defined by one of the peaks .

The varnish may also comprise a violet dye.

The emission spectrum of the source may be centered, for example, at approximately 310-330 nm.

This specification also describes a cardboard sheet coated with a varnish comprising at least one UV absorbing additive and / or a free radical scavenger.

The invention will become more clearly apparent from the following detailed description, from non-limiting embodiments thereof and from the examination of the attached drawing, in which:

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Figure 1 schematically represents, in perspective, an example of packaging made by folding a cardboard sheet or the like coated with a varnish according to the invention,

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Figures 2 to 4 are schematic and partial sections of a coated cardboard sheet illustrating various embodiments of the invention, and

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Figure 5 schematically represents absorption as a function of wavelength for an example of varnish that can be used.

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

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

Obviously, the invention is not limited to a particular form of packaging, and can be made with a sheet of cardboard or the like coated with a varnish according to the invention, packages that have very different shapes, and intended, for example, to contain tobacco or other objects.

The packaging may comprise only the cardboard or similar sheet and the varnish that covers it on the outer and exposed side of the packaging, so that recycling is facilitated. The cardboard sheet or the like can be in particular devoid of countercoated polymer film.

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

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

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

The surface coating 2 may be devoid of lightning protection compounds such as carbon black or an iron or zinc oxide.

The surface coating 2 may comprise at least one optical bluish, for example in a mass proportion between 0.5 and 0.5%, better between 0.1 and 3%.

According to the invention, the cardboard sheet is coated on the outer side of the packaging by a layer of varnish 3, the latter comprising at least one compound intended to protect the sheet from the effects of light, in particular from yellowing due in visible and / or ultraviolet light, in particular wavelengths between 290 and 460 nm.

The varnish 3, which can be colorless and not substantially modify the color of the underlying sheet, comprises, for example, at least one UV absorbing compound and / or a free radical scavenging compound.

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

The thickness of the deposited varnish 3 may depend on the deposition technique used, from approximately 2 µm for offset to approximately 20 µm for flexography. Preferably, the deposited thickness will be between 3 and 12 µm.

The varnish 3 is preferably applied after printing a decoration 4 on the sheet, as illustrated in Figure 3, but could, as a variant, be applied previously to the application of the decoration 4, as illustrated in the figure 4.

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

The varnish 3 then allows the use of light-sensitive inks, such as, for example, fluorescent inks that are unstable or sensitive to the phenomenon of metamerism. 10 Numerous additives can be incorporated into varnish 3 in order to obtain the protection function sought.

This or these additives are in a concentration that could depend on their effectiveness, the latter being proportional to the concentration and thickness of the varnish layer according to the law of BEER LAMBERT. Varnish layer

15 3 may, for example, absorb light of wavelengths comprised between 290 and 460 nm in a large proportion, so that, for example, it increases by at least 50%, better double, the duration of exposure to the light it leads for the same purposes of packaging degradation as in its absence.

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

As additives that can be used, those marketed by the GREAT LAKES and CIBA-GEIGY companies and in particular those derived from the benzotriazole family can be mentioned.

Said derivatives may be cyclobenzene heterocycles, in which a carbon atom has been substituted.

As an example of a UV absorbing compound, one can cite the formula

As an example of a free radical scavenger, the formula one can be mentioned

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

The free radical scavenger can stabilize the varnish and prevent yellowing. 40 The nature of the varnish used may depend on the printing procedure and the drying mode chosen.

Preferably, fatty offset varnishes that are naturally yellowed by oxidation will be avoided.

An acrylic varnish with water can be used, added with a UV absorber and / or with a free radical scavenger, for example added with the two compounds whose formulas have been previously provided.

A crosslinkable varnish can also be used under the action of ultraviolet radiation, preferably avoiding incorporating sterile hindered amines, which would be partially annihilated by crosslinking the varnish.

When a crosslinkable varnish is used under the action of ultraviolet radiation, this varnish comprises, for example, at least two UV absorbers, for example each in a concentration of less than 3% by weight, better than or equal to 2%, whose absorption spectra are selected so that they are available among them

a range of wavelengths in which the additives absorb less and allow a source of UV to cause crosslinking of the varnish.

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

By way of example, the absorption spectrum of a varnish (for a path of 1 cm after dilution in toluene to 20 mg / l) is shown in Figure 5, comprising two additives whose absorption spectra have respective peaks 10 and 11 that leave between them a valley whose bottom 12 is centered for example on

10 an emission wavelength of the source used to crosslink the varnish, for example 320 nm.

UV absorbers are, for example

a derivative of aromatic triazine such as that sold by the CIBA company under the name TINUVIN 15 400, of general formula:

and a benzophenine derivative such as that sold by the CIBA company under the reference CGL 20 477, of general formula:

The minimum absorption observed at the bottom 12 of the valley is, for example, more than 30% lower than the maximum Amax absorption 25 observed for one of the peaks 10 and 11.

The varnish may comprise a violet dye in order to increase the whiteness of the sheet, this dye being for example in a concentration less than or equal to 1%.

To demonstrate the effect of protection against yellowing, conferred by a varnish 3 according to the invention, a test can be carried out consisting of depositing a predefined amount, for example 6 g / m2, of wet water varnish on a sheet of cardboard of total thickness 350 µm, and then to expose to a mercury vapor lamp the sheet thus coated for a predefined time. The concentration of additives in the varnish can, for example, reach 5% by mass. You can use a cylinder " Anilox " of volume at least equal to

35 13 cm3 to apply the varnish.

Yellowing is measured on the Laine scale, which corresponds to a scale of blues growing in the light, normalized from 1 to 8.

40 In the absence of varnish, the measured yellowing can, for example, reach the value of 3 on the Laine scale. In the presence of the varnish, the measured yellowing can pass at a value at least equal to 4, which demonstrates the resistance to the largest yellowing of the cardboard sheet coated with the varnish. The passage of the value 3 to 4 corresponds to a duplicate of the duration of the light stability.

45 In the case where the varnish is a UV crosslinkable varnish, an increase in whiteness can be observed over time related to a crosslinking of the varnish that continues over time, when exposure to the artificial source for causing the polymerization has not been sufficient to polymerize the varnish to the maximum.

Obviously, the invention is not limited to the examples just provided and in particular other additives other than those mentioned can be used.

You can also use cardboard sheets that have surface coverings of different composition, even cardboard sheets without any surface coating.

Throughout the description, including the claims, the expression "comprising" It should be understood as a synonym for "which comprises at least one", unless otherwise specified.

By the expression "within", it should be understood that the limits are included, unless otherwise specified.

Claims (42)

one.

Packaging comprising a cardboard sheet coated externally with a varnish (3) comprising at least one additive that aims to reduce the degradation of the packaging under the effect of light.

2.

Packaging according to claim 1, characterized in that the cardboard sheet comprises coniferous fibers.

3.

Packaging according to claim 2, characterized in that the cardboard sheet comprises more than 70%, better more than 80% by mass of coniferous fibers.

Four.

Packaging according to any of claims 1 to 3, characterized in that the additive absorbs in a wide proportion the light radiation of wavelength between 290 and 460 nm.

5.

Packaging according to any of claims 1 to 4, characterized in that the cardboard sheet comprises a surface coating (2).

6.

Packaging according to claim 5, characterized in that the surface coating (2) is white.

7.

Packaging according to one of claims 5 and 6, characterized in that the surface coating contains at least one optical bluish.

8.

Packaging according to claim 7, characterized in that the mass proportion of optical bluish in the surface coating is between 0.05 and 0.5%.

9.

Packaging according to the preceding claim, characterized in that the proportion of optical bluing is between 0.1 and 0.3%.

10.

Packaging according to any of claims 5 to 9, characterized in that the surface coating (2) has a thickness between 20 and 30 µm.

eleven.

Packaging according to any of claims 5 to 10, characterized in that the surface coating (2) contains calcium carbonate.

12.

Packaging according to any of claims 5 to 11, characterized in that the surface coating (2) comprises clay, in particular kaolin.

13.

Packaging according to the two immediately preceding claims, characterized in that the surface coating (2) comprises calcium carbonate and clay substantially in the 60/40 mass ratio.

14.

Packaging according to any of claims 5 to 13, characterized in that the surface coating (2) comprises starch.

fifteen.

Packaging according to any of the preceding claims, characterized in that the sheet has a weight greater than or equal to 100 g / m2, better than or equal to 190 g / m2, in particular greater than or equal to 200 g / m2.

16.

Packaging according to any of the preceding claims, characterized in that the thickness of the varnish (3) is between 2 and 20 µm.

17.

Packaging according to the preceding claim, characterized in that the thickness of the varnish (3) is between 3 and 12 µm.

18.

Packaging according to any of the preceding claims, characterized in that the additive is in a mass proportion between 0.5 and 10% in the varnish (3).

19.

Packaging according to the preceding claim, characterized in that the additive is in a mass proportion comprised between 3 and 6% in the varnish.

twenty.

Packaging according to any of the preceding claims, characterized in that the additive is a UV absorbing compound.

twenty-one.

Packaging according to the preceding claim, characterized in that the additive is a UV absorber of the formula:

22

Packaging according to any of claims 1 to 17, characterized in that the additive is a compound

free radical scavenger 5 23. Packaging according to claim 22, characterized in that the additive is an steric hindered amine or a HALS amine. 24. Packaging according to claim 22, characterized in that the additive is a free radical scavenger compound of the formula: 26. Packaging according to any of the preceding claims, characterized in that the varnish (3) is a crosslinkable varnish 15 under the action of UV radiation. 26. Packaging according to claim 25, characterized in that the varnish comprises at least two ultraviolet absorbers whose absorption spectra are selected such that a range of wavelengths is available in which the absorption is less. 27. Packaging according to any of the preceding claims, characterized in that the varnish comprises a violet dye. 28. Packaging according to claim 26, characterized in that the valley formed between the absorption peaks is substantially centered over 310-330 nm. 29. Packaging according to any of claims 1 to 24, characterized in that the varnish is based on aqueous solvent. 30. Packaging according to the preceding claim, characterized in that the varnish is an acrylic varnish. 31. Packaging according to claim 1, characterized in that the cardboard sheet is of the SBS type. 32. Packaging according to any of the preceding claims, characterized in that the sheet is coated with approximately 3 to 10 g / m2 of varnish (3) before drying. 33. Packaging according to the preceding claim, characterized in that the cardboard sheet is covered by approximately 6 g / m2 of varnish. 34. Packaging according to any of the preceding claims, characterized in that the varnish (3) covers a print (4) on the sheet. 35. Packaging according to any of claims 1 to 33, characterized in that it comprises an impression (4) on the varnish (3). Four. Five 36. Packaging according to claim 1, characterized in that the cardboard sheet comprises a base (1) comprising cellulose fibers, in particular from Aspen. 37. Packaging according to claim 1, characterized in that the cardboard sheet comprises lignin. fifty 38. Packaging according to any one of claims 1 to 35, characterized in that the weight of the sheet is lower or equal to 320 g / m2. 39. Procedure for manufacturing a package comprising a cardboard sheet, in which a varnish (3) containing at least one additive is applied on the sheet which aims to reduce the degradation of the sheet under the effect of the light. 40. Method according to claim 39, characterized in that the additive is a UV-absorbing compound and / or free radical scavenger. 41. Method according to one of the two immediately preceding claims, characterized in that the varnish (3) is applied by offset, by heliography, by flexography or by screen printing. A method according to claim 39 or 40, characterized in that the sheet is printed prior to varnish application (3). 43. Method according to claim 39 or 40, characterized in that the sheet is printed subsequently to the varnish application (3). fifteen 44. Method according to claim 39, characterized in that the varnish is crosslinkable under the effect of ultraviolet radiation and comprises at least two ultraviolet absorbers selected so as to obtain absorption spectra sufficiently displaced to have a range between them of wavelengths in which the absorption is less, and because a source that emits in this range is used 20 to cause crosslinking of the varnish. 45. Method according to claim 39, characterized in that the absorption peaks of the two additives are displaced by more than 40 nm and have between them a valley whose gap corresponds to an absorption (Amin) lower by 30% at the maximum absorption ( Amax) defined by one of the peaks.