JP2006240734A - Packaging material coated with varnish for protection against light - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a packaging material, particularly a cardboard method material.
[Solution]
The present invention relates to a packaging material including a cardboard sheet having a varnish containing one or more additives for reducing deterioration of the packaging material applied to the outer surface thereof. The present invention makes it possible to produce a packaging material with the sheet while effectively delaying yellowing of the cardboard sheet rich in lignin. The present invention allows the use of wood pulp cardboard that is more rigid than cellulose cardboard, thereby reducing the thickness of equivalent rigid cardboard sheets and reducing the amount of material used. The additive can be a UV absorbing compound and / or a free radical scavenger.
[Selection] Figure 1

Description

  The present invention relates to packaging materials, particularly cardboard packaging materials.

Cardboard sheets commonly used for packaging materials are characterized by their mass and the type of their components.
The term “cardboard sheet” refers to a sheet of 100 g / m ² or more, such as 190 g / m ² or more, or 200 g / m ² or more.
Cardboard mainly composed of coniferous trees, also called wood pulp cardboard, and cardboard mainly composed of deciduous trees, also called cellulose cardboard, are distinguished.
In order to produce wood pulp cardboard pulp, the conifer bark is mechanically pulped into fairly long fibers.
Wood pulp cardboard generally has at least 80% by weight of coniferous fibers and is yellowish. The fiber contains lignin that becomes dark under the action of ultraviolet light.
Cardboard can be coated to improve surface appearance, printability, or varnish treatment, and to increase whiteness.
Thus, the term “coated cardboard sheet” refers to a cardboard sheet having a surface coating on one or both of its surfaces.
The yellowing of lignin-rich cardboard sheets under the action of visible light and especially UV radiation greatly reduces the attractiveness of such yellowing to consumers of packaging materials, so manufacturers try to solve it. It is a very old problem.
The term “visible light” refers to light having a wavelength of 400 to 800 nm, and the term “ultraviolet light” means light having a wavelength of 280 to 400 nm.
To avoid facing the yellowing problem associated with the presence of lignin, or to minimize this problem, it is possible to use cellulose cardboard that does not contain much lignin because it is generally This is because it contains lignin lower than 15% by mass of coniferous fibers.

However, cardboard using raw materials that are not widely spread in some parts of the world and that require chemical pulping is usually more expensive than wood pulp cardboard.
In addition, the mechanical stiffness of such cardboard is generally not as good as that of wood pulp, so it must be heavier to obtain the equivalent stiffness, which reduces the use of cellulose cardboard. Limited to expensive products.
Although it is known to retard yellowing of lignin-rich cardboard by surface coatings containing carbon black additives or additives based on iron oxide or zinc oxide, this reduces the whiteness of the coating. And / or make it difficult to be compatible with food.
Furthermore, since lignin eventually moves to the surface coating, yellowing cannot be prevented permanently.
Laminating polymer films containing titanium oxide is also known, but this can change the appearance and feel characteristics of the cardboard sheet and make it more difficult to recycle the cardboard sheet.
In addition, inks used for printing on packaging materials exist in several grades that are expensive depending on their UV resistance. If the product does not sell quickly, it is preferable to use a grade with a very high UV resistance (value of 5 or more for light resistance according to Blue Wool scale ISO 105-B).
It is also known to add bleach to cardboard sheets to increase whiteness, but such bleach is sensitive to ultraviolet light and therefore its effectiveness is limited over time.

  There is a need to reduce the price of the packaging material without compromising the mechanical properties of the packaging material, or in particular under the action of ultraviolet radiation, without compromising its appearance over time.

In the present invention, the packaging material has on its outer side at least one for reducing deterioration of the packaging material under the action of light, for example yellowing of the sheet under the action of light and / or damage to the underlying printing. Includes cardboard sheets coated with varnish containing seed additives.
In the description and claims, the term “cardboard sheet” refers to a sheet of similar material that is a cardboard or paperboard, or optionally a composite material, having a mechanical behavior substantially similar to that of cardboard or paperboard. To do. By way of example, such a composite material comprises in particular more than 40% by weight, preferably more than 50% by weight of plant fibers, said plant fibers being mixed, for example, with fibers made from synthetic substances.
The present invention makes it possible to produce a packaging material with the sheet while effectively delaying yellowing of the cardboard sheet rich in lignin.
Thus, the present invention allows the use of wood pulp cardboard that is stiffer than cellulose cardboard, thereby reducing the amount of material used by reducing the thickness of equivalently rigid cardboard sheets. .
In addition, the presence of the varnish makes it possible to use inks with lower UV resistance and therefore lower costs.
Thus, the present invention allows for significant savings with respect to the cost of the coated packaging material.
The invention is advantageously applied to cardboard sheets comprising, for example, more than 70% by weight, preferably more than 80% by weight of lignin-rich coniferous fibers.
The invention also makes it possible to protect the packaging material, without which it is inevitably necessary to change the composition and thickness of the surface coating of the sheet, which protects its printing and mechanical properties, In particular, its rigidity or its compressive strength is little or not affected.
Thus, it is possible to continue using existing methods and machines for manufacturing packaging materials or for packaging products in such manufacturing materials.

The invention applies not only to coated cardboard sheets but also to uncoated cardboard sheets.
When the present invention is applied to a coated cardboard sheet, the surface coating may be white or may contain, for example, one or more fluorescent brighteners, which may be included in the surface coating, for example, 0. It may be present at a concentration in the range of 05 to 0.5% by weight, preferably in the range of 0.1 to 0.3% by weight.
The surface coating is for example 20-30 μm thick and may contain calcium carbonate and / or clay, in particular kaolin. In one aspect of the invention, the surface coating comprises calcium carbonate and clay in a mass ratio of substantially 60/40.
The surface coating may also contain a binder, in particular starch, to improve its binding strength.

The presence of calcium carbonate, which can contain particularly fine oval particles, is useful for achieving a flat surface.
The presence of clay, particularly kaolin, that may be present in coarse prismatic particles is useful to obtain a surface coating of the desired density.
The thickness of the varnish is, for example, in the range of 2 to 20 μm, preferably in the range of 3 to 12 μm. The thickness of the entire cardboard sheet is, for example, in the range of 100 to 1000 μm, preferably in the range of 300 to 500 μm.
In the varnish, the concentration of the one or more additives is in the range of 0.5 to 10% by weight, for example 1 to 6% by weight.
Varnishes contain additives that are UV absorber compounds, for example UV absorbers having the formula:

The varnish may also contain an additive which is a radical scavenger compound, in particular a sterically hindered amine or a Hindered Amine Light Stabilizer (HALS), for example a radical scavenger having the formula:

The varnish may be based on an aqueous solvent, and the varnish is, for example, an acrylic varnish.
In one variant, the varnish may be a varnish that is crosslinkable under the action of UV irradiation, thereby eliminating the need to evaporate water from cardboard where moisture may remain. In that case, one or more additives that oppose the action of light are selected to be compatible with such varnishes. In particular, it is preferred that the varnish does not contain a radical scavenger such as a sterically hindered amine or HALS.
When crosslinkable under the action of UV irradiation, the varnish may contain, for example, two UV absorbers having an absorption spectrum that is selected to form a lower wavelength range of absorption, thus polymerizing The lamp used to cause the light is selected to emit light in the range.
This makes it possible to prevent the UV absorber present in the varnish from realizing its protective function without unduly preventing the polymerization of the varnish.

The varnish may contain a purple dye that tends to increase the whiteness of the cardboard sheet.
As an example, the sheet may be coated with about 3 to 10 g / m ² varnish, in particular about 6 g / m ² varnish, before drying.
The present invention is also a method for producing a packaging material including a sheet such as cardboard, and the method comprises a step of coating the sheet with a varnish containing at least one additive for reducing deterioration of the packaging material under the action of light. I will provide a.
The additive may be a UV absorbing compound and / or a radical scavenger.
Varnishes can be applied using various techniques, in particular by offset printing, photolithography, flexographic printing, or silk screen printing.
The sheet can be printed before applying the varnish or after applying the varnish.
The sheet is preferably printed before the varnish is deposited, thereby allowing the ink to be protected from UV irradiation and allowing the use of low cost inks.

Accordingly, in another aspect, the present invention provides a low UV resistance, such as Blue, coated with a varnish comprising one or more UV absorbers and / or free radical scavengers, particularly one of those previously described. A cardboard sheet is provided that includes one printed with one or more inks having a Wool lightfastness scale of 4.
In another aspect alone or in combination with another aspect and the aforementioned aspect, the present invention also provides a varnish that is crosslinkable under the action of UV radiation, and the varnish absorbs at least two UV absorbers. These absorbers are selected so that they have an absorption spectrum that is sufficiently far away to form a region of low absorption wavelength between the absorption spectra, in which case the varnish crosslinks into the wavelength region The purpose is to irradiate.
The absorption peaks of the two additives are separated, for example, by more than 40 nm, and between them, a valley is formed whose absorption minimum is at least 30% lower than the maximum absorption defined by, for example, one of the peaks.

The varnish can also contain a purple dye.
The center of the emission spectrum of the light source can be, for example, in the range of about 310 to 330 nm.
In another single aspect, or in combination with another aspect and the aforementioned aspect, the invention also covers a varnish comprising at least one additive that constitutes a UV absorber and / or a free radical scavenger. Provided cardboard sheets.
The invention can be better understood on reading the following detailed description of its non-limiting embodiments and on examining the accompanying drawings.

The present invention applies to any type of packaging material produced by folding, sizing and / or rolling one or more sheets of cardboard or the like, and in particular a box for containing containers containing cosmetics or care products Applies to
As an example, such a box is generally rectangular in shape with one or more folding cage lids at one end, as shown in FIG.
Of course, the present invention is not limited to a packaging material having a specific shape, and a wide variety of packaging materials can be produced according to the present invention using a sheet of cardboard or the like coated with varnish, Designed to include, for example, tobacco or other items.
The packaging material may include only a varnish covering a sheet such as cardboard and the exposed outer surface of the packaging material to facilitate recycling. In particular, a sheet such as cardboard need not include any laminated polymer film.

The sheet used preferably has a base layer (1) of coniferous fibers (and thus lignin) and, if the sheet is a coated cardboard sheet, a surface coating (2) on at least the outer surface of the packaging material. May be included. When the sheet contains cellulose fibers, the fibers can be derived from, for example, poplar trees.
For example, a surface coating (2) with a thickness in the range of 20 to 30 μm can improve the printability and varnish properties of the cardboard sheet and can also improve its whiteness.
As an example, the coating layer (2) comprises calcium carbonate and clay, in particular kaolin, in a mass ratio compatible with the production method used, for example a mass ratio of 60/40.
The surface coating (2) need not contain carbon black or any protective compound such as iron oxide or zinc oxide to provide light resistance.
The surface coating (2) may contain one or more optical brighteners, for example in a concentration in the range of 0.05 to 0.5% by weight, preferably in the range of 0.1 to 0.3% by weight.

According to the invention, the cardboard sheet is coated with a layer of varnish (3) on the outer surface of the packaging material, said varnish acting on the light, in particular visible and / or ultraviolet light, in particular in the wavelength range of 290 to 460 nm. Contains one or more compounds to protect the sheet from yellowing by light.
The varnish (3), which may be colorless and does not need to change the color of the underlying sheet, for example comprises at least one UV absorber compound and / or a free radical scavenger compound.
The varnish (3) can be applied using various known techniques such as photolithography, flexographic printing, silk screen printing, or offset printing.
The thickness of the varnish to be deposited depends on the deposition technique used and can range from about 2 μm for offset printing to about 20 μm for flexographic printing. The thickness to be deposited is preferably in the range of 3 to 12 μm.
The varnish (3) is preferably applied after the pattern or design (4) is printed on the sheet, as shown in FIG. 3, but in a variant the pattern (3) is shown in FIG. It may be applied before applying 4).
When the varnish (3) is applied after the pattern (4) is printed on the sheet, the varnish (3) can effectively protect the ink of the pattern layer (4) from being discolored.
The varnish (3) thus allows the use of light sensitive inks such as fluorescent inks that are unstable or sensitive to the phenomenon of metamerism.

A number of additives can be added to the varnish (3) to obtain the desired protective function.
The concentration of additives depends on their potency, which is proportional to their concentration and the thickness of the varnish layer according to the BEER LAMBERT law. As an example, the layer of varnish (3) increases the time during which the packaging material can be exposed to light before it reaches the same degree of degradation as the packaging material without varnish application, for example by at least 50%, preferably 100%. Therefore, it can absorb much of light with a wavelength in the range of 290 to 460 nm.
In the varnish (3), the concentration of the one or more additives is typically 0.5 to 10% by weight, preferably 1 to 6% by weight, for example 3 to 6% by weight.
Suitable additives include in particular those marketed by GREAT LAKES and CIBA-GEIGY, in particular the derivatives of the benzotriazole family.
Such derivatives can be cyclo-benzene type heterocyclic compounds in which the carbon atom is substituted.

An example of a UV absorber compound may include the following structural formula:

An example of a free radical scavenger may include the following structural formula:

The free radical scavenger used is sterically hindered amine (SHA) or HALS.
Free radical scavengers can stabilize the varnish and prevent the varnish itself from yellowing.
The type of varnish used can depend on the printing and drying method used.
Long oil offset printing varnishes that naturally turn yellow upon oxidation are preferably avoided.
A water-based acrylic type varnish to which a UV absorber and / or a free radical scavenger, for example, two compounds of the above structural formula are added may be used.
Varnishes that can be cross-linked under the action of UV radiation can also be used, but preferably they are avoided from being added to the varnish because sterically hindered amines are destroyed to some extent by cross-linking of the varnish.
When using varnishes that can be cross-linked under the action of UV radiation, the varnishes are, for example, less than 3% by weight, preferably less than 2% by weight, with little additive absorption and UV The source includes two or more UV absorbers having an absorption spectrum selected between them to form a range of wavelengths that can cause varnish crosslinking.

In one example, one of the additives has a concentration of 2% and the other has a concentration of 1% to have a total concentration of 3% or less.
As an example, FIG. 5 shows, for example, peaks (10) and (10) respectively forming valleys with absorption minimums (12) centered at the wavelength of the light source used to crosslink the varnish, eg 320 nm. 11 shows the absorption spectrum of a varnish containing two additives having an absorption spectrum providing 11) (1 cm path after dilution with toluene at a concentration of 20 mg / l).
As an example, UV absorbers are
Derivatives of aromatic triazines such as those commercially available from CIBA under the name TINUVIN 400 having the general formula:

である。 And a derivative of benzophenine having the general formula: e.g. commercially available from CIBA under the designation CGL 477,

It is.

As an example, the absorption minimum observed at the bottom (12) of the valley is at least 30% lower than the maximum absorption A _max observed at one of the peaks (10) and (11).
The varnish may contain a purple dye, for example in a concentration not exceeding 1%, in order to increase the whiteness of the sheet.

In order to show the protective effect against yellowing imparted by the varnish (3) of the present invention, a cardboard sheet having a total thickness of 350 μm of a predetermined amount, for example, a varnish based on 6 g / m ² of moist water. A test can be performed in which the sheet deposited on it and then exposed in this way is exposed to a mercury lamp for a predetermined time. The concentration of the additive in the varnish can reach, for example, 5% by weight. “Anilox” cylinders with a volume of 13 cm ³ or more can be used for varnish application.
Yellowing is measured on a blue wool scale corresponding to an increasing lightfast blue scale normalized to 1-8.
Without varnish, the measured yellowing can reach a value of 3, for example on a wool scale. With varnish, the measured yellowing reaches a value of 4 or more, indicating that the cardboard sheet coated with varnish is more resistant to yellowing. The progression from 3 to 4 corresponds to a doubling of the light resistance duration.

In the case of varnishes where the varnish is UV crosslinkable, if exposure to an artificial light source causing polymerization is insufficient to fully polymerize the varnish, the reduction in yellowing will be reduced in the time associated with subsequent varnish crosslinking. Can be observed after the course.
Of course, the present invention is not limited to the above-described embodiments, and in particular, those other than the above-mentioned additives can be used.
It is also possible to use a cardboard sheet having a surface coating film of another composition or a cardboard sheet having no surface coating film.
In the description of this specification, including the claims, the term “comprising” is understood to have the same meaning as “comprising one or more”, unless expressly specified otherwise. Should.
The term “within range” should be understood to include boundaries unless otherwise specified.

It is a perspective view which shows an example of the packaging material by this invention manufactured by bending sheets, such as cardboard which coat | covered the varnish. It is a fragmentary sectional view which shows the coated cardboard sheet | seat which shows the aspect of this invention. It is a fragmentary sectional view which shows the coated cardboard sheet | seat which shows the aspect of this invention. It is a fragmentary sectional view which shows the coated cardboard sheet | seat which shows the aspect of this invention. Fig. 6 is a graph showing absorption as a function of wavelength for an example of a suitable varnish.

Claims (46)

  A packaging material comprising a cardboard sheet having a varnish (3) containing at least one additive for reducing deterioration of the packaging material under the action of light applied to the outer surface.   The packaging material according to claim 1, wherein the cardboard sheet contains softwood fibers.   3. Packaging material according to claim 2, wherein the cardboard sheet comprises more than 70% by weight, preferably more than 80% by weight, of coniferous fibers.   4. A packaging material according to claim 1, wherein the additive absorbs most of the light irradiation at a wavelength in the range of 290 to 460 nm.   The packaging material according to any one of claims 1 to 4, wherein the cardboard sheet includes a surface coating (2).   The packaging material according to claim 5, wherein the surface coating is white.   The packaging material according to claim 5 or 6, wherein the surface coating contains at least one fluorescent brightening agent.   8. A packaging material according to claim 7, wherein the optical brightener in the surface coating is present at a concentration in the range of 0.05 to 0.5% by weight.   9. A packaging material according to claim 8, wherein the optical brightener is present at a concentration in the range of 0.1 to 0.3% by weight.   The packaging material according to any one of claims 5 to 9, wherein the thickness of the surface coating (2) is in the range of 20 to 30 µm.   The packaging material according to any one of claims 5 to 10, wherein the surface coating (2) contains calcium carbonate.   12. A packaging material according to claim 5, wherein the surface coating (2) contains clay, in particular kaolin.   The packaging material according to claim 11 or 12, wherein the surface coating (2) contains calcium carbonate and clay in a mass ratio of substantially 60/40.   The packaging material according to any one of claims 5 to 13, wherein the surface coating (2) contains starch. Packaging material according to any one of the mass of the sheet exceeds the 100 g / m ^2, to preferably more than 190 g / m ^2, claims 1, especially exceeding 200g / m ² 14.   The packaging material according to any one of claims 1 to 15, wherein the thickness of the varnish (3) is in the range of 2 to 20 µm.   The packaging material according to claim 16, wherein the varnish (3) has a thickness in the range of 3 to 12 µm.   The packaging material according to any one of claims 1 to 17, wherein the additive is present in the varnish (3) at a concentration in the range of 0.5 to 10% by mass.   19. A packaging material according to claim 18, wherein the additive is present in the varnish at a concentration in the range of 3 to 6% by weight.   The packaging material according to any one of claims 1 to 19, wherein the additive is a UV absorber compound. The packaging material according to claim 20, wherein the additive is a UV absorber having the following structural formula:

  The packaging material according to any one of claims 1 to 19, wherein the additive is a free radical scavenger compound.   The packaging material according to claim 22, wherein the additive is a sterically hindered amine or HALS. The packaging material according to claim 22, wherein the additive is a free radical scavenger compound having the following structural formula:

  The packaging material according to any one of claims 1 to 24, wherein the varnish (3) is a varnish that can be crosslinked under the action of UV irradiation.   26. The packaging material of claim 25, wherein the varnish comprises at least two ultraviolet absorbers having an absorption spectrum selected to form a lower wavelength range of absorption.   The packaging material according to any one of claims 1 to 26, wherein the varnish contains a purple dye.   27. The packaging material of claim 26, wherein the center of the valley formed between the absorption peaks is substantially in the range of 310 to 330 nm.   The packaging material according to any one of claims 1 to 24, wherein the varnish is based on an aqueous solvent.   30. A packaging material according to claim 29, wherein the varnish is an acrylic varnish.   The packaging material according to claim 1, wherein the cardboard sheet is of SBS type. 32. A packaging material according to claim 1, wherein the sheet is coated with about 3 to 10 g / m < ² > of varnish (3) before drying. 33. The packaging material of claim 32, wherein the cardboard sheet is coated with about 6 g / m < ² > varnish.   34. A packaging material according to claim 1, wherein the varnish (3) covers the printing (4) on the sheet.   34. A packaging material according to any of claims 1 to 33, comprising printing (4) on the varnish (3).   The packaging material according to claim 1, wherein the cardboard sheet has a base layer (1) comprising cellulose fibers derived from poplar trees in particular.   The packaging material according to claim 1, wherein the cardboard sheet contains lignin. Packaging material according to any one of 35 to the mass of the sheet claims 1 to not exceed 320 g / m ^2.   A method for producing a packaging material comprising a cardboard sheet, wherein the sheet is coated with a varnish (3) containing at least one additive for reducing deterioration of the sheet under the action of light.   40. The method of claim 39, wherein the additive is a UV absorber compound and / or a free radical scavenger.   41. A method according to claim 39 or 40, wherein the varnish (3) is coated by offset printing, photolithography, flexographic printing or silk screen printing.   41. A method according to claim 39 or 40, wherein the sheet is printed before applying the varnish (3).   41. A method according to claim 39 or 40, wherein the sheet is printed after applying the varnish (3).   At least two UV absorptions selected such that the varnish is crosslinkable under the action of UV irradiation and has an absorption spectrum that is sufficiently separated to form a lower wavelength range of absorption between absorption spectra 40. The method of claim 39, wherein a light source comprising an agent and emitting in this range of light is used to crosslink the varnish. The absorption peaks of the two additives are separated by 40 nm or more, and a trough is formed between them where the absorption minimum (A _min ) is at least 30% lower than the maximum absorption (A _max ) defined by one of the peaks. 40. The method of claim 39.   A cardboard sheet for producing the packaging material according to any one of claims 1 to 38.

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