EP0395496B2 - Sheet suitable for exposure to light, with an identification and security mark, and use of such a sheet - Google Patents

Abstract

The invention concerns a sheet intended for prolonged exposure to light. It carries one at least light-resistant imprint having a first colour in natural light with a wavelength between 400 and 700 nanometres and a second colour, different from the first, in an artificial light with a wavelength of less than 400 nanometres and greater than 700 nanometres. The imprint is produced by photogravure printing with liquid ink containing at least one luminescent pigment capable of withstanding temperatures above 100 DEG C for at least 10 minutes. Use especially as a decorative sheet for laminates.

Description

The invention relates to a decorative sheet usable for the manufacture of laminated panels, this sheet further comprising means of recognition and security. The invention further relates to a composition to print such a sheet.

We know that there are mainly two kinds of laminated panels: so-called high pressure panels and so-called low pressure panels.

For many years, laminates have been used as materials in dwellings and premises commercial and industrial. Typical applications of such laminates are the surface coating of walls, table tops, furniture and more.

The so-called high pressure laminates are produced from a core consisting of sheets impregnated with resin. The sheets are generally sheets of kraft paper which has been impregnated with a thermosetting resin and more particularly of a phenolic resin.

When the kraft paper has been impregnated with resin, the sheets are dried, cut, then stacked on top of each other. The number of sheets in the stack depends on the applications and can vary between 3 and 9, but can be higher.

Then placed on the pile of sheets constituting the core, a decorative sheet which is generally a sheet of paper bearing a printed or light-colored pattern, and impregnated with a non-blackening thermosetting resin not heat, for example melamine-formaldehyde resins, benzoguanamine-formaldehyde resins, unsaturated polyester resins. In general, we place above the decorative sheet, a protective cover sheet, devoid of pattern and transparent in the final laminate. In terms by trade, this protective sheet is called "over-lay". We then face the stack of sheets impregnated in a press fitted with a sheet conferring the surface condition. The pile is then densified by heating and pressing to get a unitary structure.

During densification, thermosetting resins are transformed into thermoset form and obtains an extremely hard material with a decorative effect.

We produce so-called low pressure laminates in a similar way to that of high pressure laminates, but we laminate the decorative sheet directly on a wood particle board or any other basic support.

The decorative sheet is traditionally made in the following manner. We make a sheet of paper by draining an aqueous suspension of long and / or short cellulose fibers on a flat canvas, bleached and / or unbleached, fillers, binders. The sheet thus formed is drained, pressed and dried to form a sheet of paper. This sheet is then printed. The usual impression is a rotogravure printing using engraved rollers. The engraving technique consists of making a drawing, for example reproducing a wood or a purely fancy artistic drawing. Then we take the photograph of this drawing and from the films obtained, one or more printing rollers are engraved. Each cylinder then passes through an ink bath, and the indentations or imprints engraved in the cylinder are filled ink which is then transferred to the paper. Typically one to five separate prints are made and successive using one to five rollers.

It is understood that the gravure printing process allows from a drawing to print a sheet of paper. However, this poses a problem for the printer of the decorative sheet. Indeed, if the drawing is a original drawing, created by the printer, any other printer, from a printed decorative sheet, may have photographs taken of this sheet and have cylinders engraved for the same impression. Counterfeits can therefore be numerous and it is generally not possible to detect them or have intangible proof that these are counterfeits.

The invention therefore aims to solve this problem.

Another problem that arises is the identification of the laminate manufacturer. Indeed, the sheet maker decorative can sell the same authentic sheet to several laminate manufacturers. Each manufacturer of laminate generally bears its mark on the laminate, by means of a more or less removable label. Here again, there is the problem of identifying the manufacturer of a particular laminate. The invention aims to solve this second problem.

Another problem which arises is that the sheets which are generally used for the manufacture of furniture are subjected for prolonged periods to natural or artificial light.

An object of the invention is therefore to provide a decorative sheet for laminated panels, comprising means of recognizing the origin of laminates.

• comportant une impression au moins résistant à la lumière,
• présentant une première teinte à la lumière d'onde de longueur d'onde comprise entre 400 et 700 nanomètres et une seconde teinte différente de la première à la lumière de longueur d'onde inférieure à 400 nanomètres et supérieure à 700 nanomètres,
• portant une impression héliographique à l'aide d'encre liquide, l'encre comportant au moins un pigment luminescent résistant à des températures supérieures à 100°C pendant au moins 10 minutes et résistant à une action prolongée de la lumière.

To this end, the invention relates to the use as a decorative sheet of laminated panels used as materials in homes and commercial and industrial premises, a sheet intended to be subjected to the prolonged action of light as well as to heat for a period of several tens of minutes during the preparation of said laminates, said sheet:

• comprising a print at least resistant to light,
• having a first shade in the wavelength of wavelength between 400 and 700 nanometers and a second shade different from the first in the light of wavelength less than 400 nanometers and greater than 700 nanometers,
• carrying a gravure printing using liquid ink, the ink comprising at least one luminescent pigment resistant to temperatures above 100 ° C for at least 10 minutes and resistant to a prolonged action of light.

Preferably, the first design is invisible to natural light and the second design is visible to light artificial. By natural light is meant a light source whose wavelengths are included between 400 and 700 nanometers and by artificial light, a light source whose wavelengths are less than 400 nanometers and more than 700 nanometers.

We know that certain pigments and dyes are luminescent. These materials are commonly called "phosphorus". These pigments can be fluorescent or phosphorescent. The feeling of color produced by conventional pigments or dyes which are not luminescent results from selective absorption wavelengths in the visit part of the spectrum. Wavelengths that are not absorbed are reflected or transmitted, which gives the feeling of color. This feeling of color is absent when there is no visible light source, because there is no energy to reflect or transmit.

Unlike conventional dyes or pigments, luminescent pigments do not reflect light, but they are sources of light themselves. They have the property of absorbing certain wavelengths, generally wavelengths less than 400 nanometers and invisible to the eye, and transform these wavelengths into visible wavelengths. The wavelengths thus emitted produce a feeling of color. When the emission of light continues for a significant period of time, after the excitation energy source has been switched off, the material is said to be phosphorescent. We have described zinc sulfide pigments in the Kirk-Othmer documenet: Encyclopedia of Chemical Technology, 3rd ed. volume 17. These pigments are described as chemically stable.

Many publications have described the synthesis of such luminescent materials.

The following publications will be cited as references: EP-A-15382, EP-A-21342, EP-A-123947.

We also know that it is known to introduce pigments inside the paper, in particular by publications. FR-A-2 478 695 and EP-A-226367. These pigments are dispersed in the paper and the latter is used as security paper for checks, banknotes, etc.

Document EP-A-147252 describes a mixture of a luminescent substance and an anti-storage substance. Such a mixture can be used for marking documents to prevent counterfeiting, for example example of bank notes, fiduciary papers. The compositions can be introduced on paper and can be introduced into printing inks. These inks are fatty inks, i.e. containing an oil and the printing is done by offset or intaglio. So far, the problem of marking heat resistant sheets that can be used to decorate laminates have never been laid.

Document AU-A-518 156 describes a sheet of paper comprising at least one printing light-resistant having a first light shade of wavelength between 400 and 700 nm and a second shade different from the first at a wavelength less than 400 nm, printing being an intaglio print. However, it is not a paper usable for the manufacture of laminates.

Document DE-A-2 910 176 describes a method for characterizing disc packaging using a fluorescent print.

GB-2,147,542 describes an article printed using fluorescent or synthetic material.

The document EP 0253 543 describes a printing ink comprising a metallic compound, a compound luminescent and one or more inert compounds. Such ink is used for credit cards.

The document "Research Disclosure" n ° 160, August 1977, HAVANT GB, page 60 years, describes a printed document using fluorescent ink and non-fluorescent ink.

None of these documents describes a paper printed using at least one fluorescent ink, usable for the manufacture of laminated panels obtained by low or high pressure and subjected to temperatures high during stratification.

However, an essential technical problem to be solved is the fact that the sheets are intended to be submitted with heat, for a period of several tens of minutes, or even several hours. When he these are laminate sheets, during densification the sheet is subjected to temperatures of more than 100 ° C, for 20 minutes. Likewise, when manufacturing paper covered with metal or metallized, these papers are subjected to high temperatures, especially when hot stamping is carried out.

Marking sheets, for example for laminates, also poses different and additional problems marking paper for banknotes and other security documents.

In fact, the decorative sheets for laminates are necessarily impregnated with a thermosetting resin. When carrying out the densification, the impregnated sheet is placed on a particle board or a stack of impregnated kraft paper sheets. Then we press the assembly against a sheet. Now a problem technique posed is that the prints should not transfer from the decorative sheet onto the sheet which must remain sharp.

A second technical problem to be solved is that during the impregnation, the decorative sheet passes in an impregnation bath. The prints should therefore not migrate into the impregnation bath and should not must not pollute it. Indeed, if the impregnation resin is polluted by printing, during lamination posterior, the thermosetting resin creeps under the action of heat and pressure and if it contains luminescent printing substances, these flow at the same time and cause a smear of the final impression.

Another technical problem to solve is that when rubbing the printed sheet, it should not be the luminescent substance comes off. The friction resistance must therefore be high. In addition, the impregnation decorative sheet should be kept.

Finally, it is essential that the luminescent substances used have a very good resistance to light. Indeed, these sheets can be used for panels used as materials in homes and above furniture and so they are intended to be subjected to the action of light during periods of extended times.

The Applicant has tried many commercially available luminescent substances and has found that the ones that work well are mineral pigments. Indeed, organic molecules are very sensitive to outdoor conditions and degrade easily in light, as well as in heat.

The Applicant has been able to use mineral pigments having a very good resistance to light and withstand high temperatures for long periods of time, i.e. higher temperatures at 100 ° C, preferably between 140 and 200 ° C, for example 140-150 ° C for at least 10 min at 2 hours, for example 20 to 30 minutes.

It has surprisingly been found that luminescent substances used according to the invention such that the zinc sulfides or their mixture with other metallic sulfides are heat resistant, for time periods of more than 10 min.

More preferably, the luminescent substances are pigments based on zinc sulfide in mixture with cadmium sulfide. These pigments can have a particle size of less than 40 micrometers.

Pigments of zinc sulfide or zinc sulfide and cadmium which are activated by copper can be used. Their preparation method is known and is for example described in H.W. Leverenz, An introduction to luminescence of solids: S. John, Wiley & Sons, Inc. New York, Chapman & Hall Ltd London, 1950.

Pigments based on zinc sulfide emitting in various wavelengths have been described in the Patent applications EP-A-34059, EP-A-78538, EP-A-91184 filed by the Japanese company KASEI OPTONIX. Pigments which are well suited are also pigments based on zinc sulphide, produced by the German company RIEDEL DE HAEN.

Of course, according to the invention, mixtures of luminescent substances can be used, provided that they are resistant to light, heat, pressure, as mentioned above.

The following description, with reference to the examples, will make it possible to understand how the invention can be put into practice.

EXAMPLE 1

18,9

parties de pigment vendu par la société RIEDEL DE HAEN sous la référence Lumilux CD 704. Il s'agit d'un sulfure de zinc.

9

parties d'eau

3

parties d'alcool, de préférence l'éthanol

8,8

parties de vernis ou liant pour encre 992209 vendu par SICPA

26,9

parties de vernis 991129 vendu par SICPA

33,5

parties d'un mélange éthanol (2/3) eau (1/3).

We mix successively

18.9

parts of pigment sold by RIEDEL DE HAEN under the reference Lumilux CD 704. It is a zinc sulfide.

9

parts of water

3

parts of alcohol, preferably ethanol

8.8

parts of varnish or binder for ink 992209 sold by SICPA

26.9

parts of varnish 991129 sold by SICPA

33.5

parts of an ethanol (2/3) water (1/3) mixture.

This mixture is applied to a sheet of white paper of 90 g / m2 by gravure printing.

The cylinder was etched by electronic etching, the cells having a depth of 37 micrometers, the height of the frame being 190 micrometers, and the width of the frame being 210 micrometers.

The size of the pigment particles is approximately 0.1 to 40 micrometers, which allows printing with such cells. You get a paper that is white in daylight, but when it is illuminated by rays ultraviolet, a blue print appears when the white paper turns brown because it does not reflect and does not does not transmit light.

This sheet is subjected to a temperature of 160 ° C. by placing it between two hot plates for 15 minutes. Then we illuminate the paper with UV rays. The blue print appears again.

COMPARATIVE EXAMPLE

The same mixture is made as in Example 1, but the mineral pigment is replaced by an organic pigment which is an N-substituted anthranilic acid of the type described in document DE-A-3225966. When we subjects the paper to the temperature of 200 ° C for 0.5 seconds, the fluorescent print no longer appears.

EXAMPLES 2 to 9

The same mixture is made as in Example 1, with pigments sold by the company OPTONIX, under different numbers.

The light resistance is 3 to 6 measured according to the Wool scale test and the rays resistance ultraviolet is 5 to 6.

The Wool scale test corresponds to standards NF T 51056 and NF T 51058. It consists in lighting up a sample including printing with a xenon lamp for 90 hours or 300 hours and at compare the sample obtained with strands of wool with shades ranging from 1 to 8, the number 1 corresponding to the degradation of shade, the number 8 corresponding to a non-degradation.

EXAMPLE 10

Paper is printed by heliography, using one to five color prints in the traditional way. This paper is then decorated and has this decorative aspect and visible by lighting in natural light. We then makes a heliography printing by making one to three prints using the mixtures ink from examples 1 to 9. The original drawing is not changed in natural light. When we light the paper in ultra-violet light, the initial drawing disappears and it is the superimposed drawing that becomes visible.

The invention relates not only to a means of marking and recognizing subject sheets at temperature, and / or pressure and light, for long periods of time, but also concerns a new means of decoration of these leaves. You can also print polyvinyl chloride plates which are laminated to particle board by bonding and pressure. These plates used for furniture must be resistant to light. You can also print sheets of polyethylene, polypropylene, possibly coated and possibly impregnated with a resin.

Claims (8)

1. Use, as decorative sheet of laminated panels used as materials in residences and commercial and industrial premises, of a sheet intended to be subjected to the prolonged action of light as well as heat for a period of several tens of minutes during the preparation of said laminated panels, said sheet:

   comprising a print at least resistant to light,

   having a first tone in light of wavelength between 400 and 700 nanometres, and a second tone, different from the first, in light of wavelength less than 400 nanometres and higher than 700 nanometres,

   bearing a heliographic print with the aid of liquid ink, the ink comprising at least one luminescent pigment resistant to temperatures higher than 100°C for at least 10 minutes and resistant to a prolonged action of light.
2. Use according to claim 1, characterised by the fact that the pigment is resistant to temperatures of 140 to 200°C for 20 to 30 minutes.
3. Use according to one of claims 1 and 2, characterised by the fact that the pigment is a zinc sulphide.
4. Use according to one of claims 1 to 3, characterised by the fact that the pigment contains at least one zinc sulphide, a second metal sulphide and optionally at least one activating agent.
5. Use according to one of claims 1 to 4, characterised by the fact that the pigment is a mixture of zinc sulphide and cadmium sulphide activated by copper.
6. Use according to one of claims 1 to 5, characterised by the fact that the pigment has a resistance to ultra-violet rays greater than 5, preferably 6.
7. Use according to one of claims 1 to 6, characterised by the fact that the pigment has a particle size smaller than 40 micrometres.
8. Use according to one of claims 1 to 7, characterised by the fact that said sheet is constituted by paper or polyvinyl chloride or polyethylene or polypropylene, said sheet being optionally coated and optionally impregnated with a thermosettable resin.