EP1152085A1 - Transparent and/or translucent paper having a fluorescent colour - Google Patents

Abstract

The transparent and/or translucent paper contains at least one fluorescent pigment, giving a color intensity or saturation and a luminescence to give a color intensity:luminescence ratio of ≥ 50. It has a reflection coefficient ( DELTA R) of ≥ 100% at a given wavelength ( lambda max), measured when the paper is on a white surface. The paper can be coated on at least one surface with a covering of a fluorescent pigment which is insoluble in water, and preferably on both surfaces. The fluorescent pigment coating is applied at a rate of 1-10 g/m<2> and preferably 3-6 g/m<2>. The paper composition can have a content of dry pigment of 5-20 wt.% in relation to the paper dry weight. The transparent/translucent paper is a tracing paper derived from cellulose fibers refined to a Schoepper degree of ≥ 80, a sulfured paper, a crystal or glassine paper, a paper treated chemically to render it transparent or other chemical and/or mechanical papers. The paper is treated with a watery coating with a fluorescent pigment at a rate of 20-30 wet wt.%. The coating has little or no additives. The fluorescent coating is applied by spreading, or by printing using a heliogravure or flexographic or offset or silk-screen printing.

Description

The present invention relates to transparent paper and / or translucent fluorescent color, more particularly paper layer of fluorescent color, but also other transparent papers or translucent like greaseproof paper, transparentized paper by impregnation or the so-called "crystal" papers, to which a fluorescent color by the means described below.

The terms used in the field of color as in that of transparency sometimes lending to ambiguity, the inventors specify below the meaning they assign to them:

FLUORESCENT COLORING MATERIALS

"Fluorescent dyestuffs" are materials dyes, generally synthetic, which differ from materials conventional dyes in that they absorb certain frequencies of the light spectrum (especially in blue and ultraviolet) and restore part of the light energy in narrow bands visible frequencies (especially yellow, orange and red).

When illuminated by a light source polychromatic, these materials present in the frequency spectrum visible a particular re-emission curve, characterized by the presence of an acute maximum whose value can exceed 100% of the light intensity received for the frequency considered. At these frequencies, matter can therefore emit more light than it does receives. This is impossible for conventional coloring matters, which reflect or transmit only part of the light incident. Only a perfect mirror reaches 100% in reflection, a medium perfectly transparent 100% in transmission. Most of the fluorescent dyes currently on the market market far exceed 100% maximum reissue. This property gives them extremely pure and bright colors, therefore an extraordinary visual effect.

DYES - PIGMENTS

• lorsque la matière colorante est dissoute dans la matière à colorer, on parlera de colorant,
• lorsque la matière colorante est utilisée à l'état de poudre dispersée dans la matière à colorer, on parlera de pigment.

Regardless of their own chemical nature or their origin, coloring matters can be classified into two families according to the form in which they are used:

• when the coloring matter is dissolved in the matter to be colored, we will speak of dye,
• when the coloring matter is used in the form of a powder dispersed in the matter to be colored, we will speak of a pigment.

The dyes can be soluble in water or in medium organic. Most pigments can be used as well aqueous medium than in organic medium.

There is currently no fluorescent pigment on the market true, but only fluorescent dyes, the most interesting of which are organosoluble. Pigment producers bypass the difficulty in introducing these dyes into resins they polymerize before grinding them. The fine powder obtained, brilliantly colored, is insoluble in water and in certain solvents, and can therefore be assimilated to a pigment. The fluorescent pigments of which it is question in the invention are of this type.

The pigment industry, which caters to many industries but more particularly to that of paints and inks, provides colored products for which opacity is an essential quality. (When transparency is sought for the color, the user turns to dyes which are naturally transparent). All the means that can be used to improve this opacity are used by manufacturers, in particular the increase in the fineness of grinding. In all industries, pigments, and among them pigments of fluorescent color, are therefore considered as materials opaque dyes.

TRANSPARENT MATERIAL - TRANSLUCENT - OPAQUE

A transparent material is a material that light can cross without great loss. A colored transparent material is crossing without great loss by certain frequencies of light visible, while other frequencies are strongly absorbed. The color transmitted by transparency is the result of the frequencies which cross matter.

When the material is not homogeneous and only small particles foreign, opaque or transparent but with a different refractive index are scattered there, it is no longer perfectly transparent. From of a certain thickness one can no longer distinguish the contours of an object located on the other side because the light is blurred when passing through it. We then speaks of translucent matter. When the quantity of particles exceeds a certain threshold, the large majority of light rays can no longer pass through matter without being absorbed or reflected. The material is then opaque. This can happen when the number of foreign particles per unit volume is high, or when the thickness of the translucent material to pass through is enough big.

TRANSPARENT AND / OR TRANSLUCENT PAPER

A paper is considered to be transparent if, when a sheet of this paper is placed on a document containing text or drawing with a minimum of contrast, we can distinguish the drawing or read the text across the paper.

Contrary to popular belief, a paper transparent can be intensely colored without losing its transparency because black text remains perfectly visible when such paper is placed above.

We will consider that a paper is translucent if in the same conditions it does not allow the reading of the text but if we can distinguish light and dark areas of the drawing.

The printing / writing paper industry has always sought to produce opaque papers, because the readability of the texts should not be bothered by the text on the following pages. Only some technical papers have a transparency (crystal paper or greaseproof for packaging, tracing paper for making plans superimposable and reproducible by the diazo process). The man of trade, in the field of paper making for printing / writing, so far did not seek to produce colored transparent papers. The invention of transparent papers and / or translucent in bright color intended for printing / writing made the subject of a patent application by the applicant (PCT / FR / 9800930). These tracing papers are characterized in that they have a color intensity (or saturation) c and a luminosity L such that the ratio of c to L is greater than 50%, or L is less than or equal to 60, or the ratio of c to L is greater than 50%, and L is less than or equal to 60. These papers are intended printing and / or writing. The paper described in this document additionally includes a bulk water soluble fluorescent dye or in size press.

The present invention therefore constitutes an improvement to this previous invention.

Indeed, when using a dye, the fluorescence obtained is not always satisfactory and the present invention seeks to improve the quality of fluorescence.

We also know an extra white transparent paper comprising a bulk brightener in combination with an agent cloudy. Such transparent paper is described in the patent application European No. 0 919 664 filed by the plaintiff. This paper has not an intense color. The optical brightener is a fluorescent dye which is water soluble and emits a bluish light when excited by daylight or under a UV lamp. It does not provide an intense color. It increases the luminance L of the papers whites and therefore reduces the c / L ratio.

Document FR-A-2 348 317 (CIBA-GEIGY) has described new optical whiteners insoluble in aqueous medium which are used suspended to coat an opaque paper. These whiteners are intended to impart a superior whiteness appearance with opaque paper.

GB-A-1 369 202 (CIBA-GEIGY) describes a method of bleaching of opaque paper with an acidic solution of a brightener optical.

Document FR-A-2 660 944 describes a coating composition for opaque paper containing an optical brightener dissolved in polar organic solvents such as ethylene glycol, diethylene glycol, propylene glycol, dimethylformamide.

Document EP-A1-0 712 960 describes a liquid composition containing an optical brightener dissolved in polyethylene glycol Low molecular weight in the range of 150 to 500. This composition is used for coating conventional opaque paper.

There are currently opaque papers in the trade which have an intense fluorescent color. These papers are mainly intended for the manufacture of posters or labels for which the transparency would constitute an annoying defect; manufacturers strive therefore to make them opaque. These papers are therefore not transparent.

There is therefore currently no translucent paper and / or transparent which has a fluorescent color, intense and usable in the field of printing and / or writing.

The present invention therefore aims to provide a translucent paper and / or transparent which has an intense fluorescent color and usable for printing and / or writing.

The present invention further aims to provide a method of manufacture of a translucent and / or transparent paper having a intense fluorescent color.

Those skilled in the art of papermaking know that to obtain a coloring of it, one can either introduce dyes or pigments in bulk when making paper, either cover the paper with a composition containing dyes or pigments in suspension.

The paper being made in suspension in water, it is convenient mass use of a water-soluble dye. Some of these dyes are spontaneously fix on cellulose while others ask the intervention of additives for their fixation. Pigments, insoluble in aqueous medium, can also be used in order to carry out the mass coloring of the paper, but a fixing agent must be added which retains the pigments on the fibers. This does not prevent a some loss of pigments in the water discharged from the paper. Those skilled in the art for coloring a paper therefore have a a range of water-soluble transparent dyes and other share a range of opaque pigments insoluble in water.

The skilled person who seeks to make colored paper fluorescent can commercially find fluorescent dyes soluble in water. These products are transparent but, rather little fluorescent; moreover, their color gamut is poor, i.e. that there are very few soluble fluorescent dyes on the market in water. With these soluble fluorescent dyes it is not possible to obtain a range of bright and saturated, fluorescent colors, having a c / L ratio greater than 50.

Those skilled in the art can also find in the trade organosoluble fluorescent dyes of bright and varied colors. These dyes which cannot be used in water cannot be used or mass in papermaking, nor on the surface in a coating water soluble. They can only be used in varnishes or inks in solvents applicable on paper, and because of their power to reduced reflection they do not give the paper a satisfactory color, especially in terms of fluorescence.

On the contrary, the skilled person has, at his disposal in the trade, very bright and saturated fluorescent pigments in a varied range. Being insoluble pigments and not soluble dyes, these products are considered opaque. For impart a fluorescent coloring to the paper the skilled person who wishes to achieve a range of colors therefore has pigments of varied but opaque fluorescent colors.

We also know paints based on pigments which consist of transparent resin particles. Gold, in the P.P.V. No. 166 of PAINTS-Pigments-varnishes, it is mentioned that these pigments must be deposited on an undercoat white to make the most of their brightness and purity and making sure that the light rays that have passed through the layer of fluorescent paint are not absorbed by the substrate but reflected by him and cross again the fluorescent layer to participate in the visual effect. According to the prior art, it is therefore accepted that for obtain good fluorescence, the background must also be white and opaque as possible so as to reflect as much as possible the light.

Consequently, the person skilled in the art estimated before carrying out the present invention that it was not possible to obtain a paper transparent in bright fluorescent color and further in a range of various colors. This prejudice stems from the fact that if we want to obtain a variety of fluorescent colors, the skilled person is in the obligation to use fluorescent pigments that are not soluble in water, which can be deposited on the surface of the paper or incorporated without the mass of the paper. However, fluorescent pigments are considered by skilled in the art as removing transparency from paper. A other prejudice of those skilled in the art is that, to obtain a effective fluorescence, it is essential that the background be reflective and not transparent. So the skilled person believes that it is not possible to obtain a transparent paper having a certain fluorescence.

The present inventors have surprisingly found that was possible to give transparent and / or translucent paper a intense fluorescent color using fluorescent pigments, without that these pigments significantly reduce the transparency of the paper finally obtained.

The present inventors have further found in a manner surprising that by depositing by coating and / or printing a aqueous composition of fluorescent pigments on a transparent background, know among other things a classic transparent paper, we get both a intense fluorescent color and good transparency.

They also surprisingly found that by introducing by mass of fluorescent pigments in the pulp of a transparent paper, the transparency of the paper obtained is not reduced in a way significant.

• il est transparent et/ou translucide,
• il possède une intensité de couleur (ou saturation) c et une luminosité L, mesurées en unités CIELAB selon la norme DIN 53237, telles que le rapport de c à L soit supérieur à 50%,
• il possède, pour une longueur d'onde λ_max donnée, un coefficient de réflexion ΔR supérieur à 100%, tel que mesuré sur un papier placé sur un fond blanc.

The present invention therefore relates to a paper characterized in that it comprises at least one fluorescent pigment and that it has the following physical characteristics:

• it is transparent and / or translucent,
• it has a color intensity (or saturation) c and a brightness L, measured in CIELAB units according to DIN standard 53237, such that the ratio of c to L is greater than 50%,
• for a given wavelength λ _max , it has a reflection coefficient ΔR greater than 100%, as measured on a paper placed on a white background.

• on choisit une cellulose ou un papier que l'on traite de manière à obtenir un papier transparent et/ou translucide ;
• on choisit un pigment de la longueur d'onde souhaitée, que l'on mélange à la cellulose ou que l'on dépose à la surface du papier issu du traitement de la cellulose.

The present invention also relates to a process for manufacturing a translucent and / or transparent paper having an intense fluorescent color, characterized in that:

• a cellulose or paper is chosen which is treated so as to obtain a transparent and / or translucent paper;
• a pigment of the desired wavelength is chosen, which is mixed with the cellulose or which is deposited on the surface of the paper resulting from the treatment of the cellulose.

A paper according to the invention can be used for writing or for print, in particular, typographical characters.

According to one of the embodiments of the invention, the paper transparent or translucent receives a surface layer on each side comprising a fluorescent pigment insoluble in water.

The layer, when applied to the paper, can contain about 20 to 30% fluorescent pigment by weight.

The dry layer resulting from this application can comprise from 1 to 10 g / m ² , preferably from 3 to 6 g / m ² of fluorescent pigment on each side of the paper.

According to another embodiment of the present invention, bulk introduction of a fluorescent pigment that is not soluble in water and opaque in an amount of 5 to 20% by dry weight of pigment by ratios dry weight of paper.

The paper according to the invention can be chosen from the group formed by tracing paper, parchment paper, crystal paper (or "glassine"), transparentized paper by impregnation.

The present invention, with reference to the figures and examples appended without limitation, will better understand how the invention can be put into practice.

Figure 1 is a scale for convenient measurement transparency of a paper.

Figure 2 is a schematic curve of the coefficient of transmission as a function of the wavelength of the reflected light.

Figure 3 is a curve according to Figure 2 obtained (curve A) in laying a paper according to Example 2 of the invention on a white background and obtained (curve B) by placing the paper according to Example 2 of the invention on a black background.

The paper according to the present invention is a paper which is transparent and / or translucent, which has a color intensity, that is to say a saturation c, and a brightness L measured in CIELAB units according to DIN standard 53237, such that the ratio of c to L is greater than 50%, it has, for a given wavelength λ _max, a reflection coefficient ΔR greater than 100%, when the measurement is made on a paper resting on a white background (curve A ).

The transparent and / or translucent paper can be a tracing paper obtained with cellulose fibers refined to a high Schöpper degree, at least greater than 80 or a paper transparentized by means of a chemical composition. Transparent and / or translucent paper can also be a paper called "parchment paper" or "vegetable parchment" rendered transparent by immersing an opaque base paper in a bath sulfuric acid which dissolves part of the cellulose from the fibers. This bath is followed by numerous rinses with water eliminates the acid excess is eliminated.

The transparent and / or translucent paper according to the present invention can also be a paper called "glassine". Such paper has a smoothness Bekk greater than 2000 s and is obtained by extensive calendering of a paper opaque. A transparent paper can be provided by any other means chemical and / or mechanical known or which will be known in the future.

The transparent and / or translucent paper according to the present invention has a color intensity (or saturation c) and a brightness L, measured in CIELAB units according to DIN 53237, such as c / L ratio is greater than 50%. The paper according to the invention therefore has an intense color.

The paper according to the present invention may consist of a transparent and / or translucent paper which comprises, on at least one of its faces, a surface layer of fluorescent pigment insoluble in the water.

This layer of fluorescent pigment may be present on each side of the paper.

The paper according to the invention has, for a given wavelength range λ _max , a reflection coefficient ΔR greater than 100%.

The paper according to the invention is further characterized in that it can be obtained by depositing on a transparent paper a composition aqueous not containing or comprising a minute quantity of charges.

The fluorescent pigments that can be used in the context of the present invention can be chosen from those sold by the company CIBA under the brand MIGLO® ^, by the company RADIANT COLOR under the brand Jst® or the pigments of the SX series sold by NOVAGLO company.

The amount of pigment deposited is adjusted to maintain the transparency of the paper while obtaining a desired bright color and sufficient fluorescence. The amount of pigment deposited on the paper is comprised, per side, according to the invention, between 3 and 6 g / m ² , by dry weight. If the quantity is less than 3 g / m ² , the transparency of the paper is good, while the fluorescence and the color intensity are insufficient. If the quantity of pigment is greater than 6 g / m ² , the transparency of the paper is insufficient, without however the fluorescence and the intensity of color being remarkably increased.

The transparency of the paper according to the invention can be measured conveniently using a device designed by the applicant (shown in Figure 1), as follows:

On a transparent rigid tape 1, we draw circles 2 of 1 cm in diameter which are filled with a grid of lines. A first circle 2a has a slight grid to appear clear to the eye bare. The second circle 2b, filled with a grid of tighter lines, appears darker to the naked eye than circle 2a. The third circle 2c, filled with a grid of tighter lines, appears darker to the eye naked as the circle 2b. The fourth circle 2d, filled with a grid of tighter lines, appears darker to the naked eye than the circle 2c. The fourth circle 2e, filled with a grid of tighter lines, appears darker to the naked eye than the 2d circle, etc. Gridlines are set so that if the paper according to the invention 1 shows only the circle 2nd, it will be noted 5, if it lets see the lighter circle 2d, it will be noted 4, etc., the paper showing the circle 2a being the best in transparency, and therefore noted 1.

You can also measure the opacity of the paper by the method according to a DIN 53147 standard or a standard such as JIS P 8138 or ISO 2469.

In FIG. 2, a schematic curve of the coefficient of reflection (or reflectance) on the ordinate and the length of reflected light (nm), on the abscissa. We measure the reflectance or reflection coefficient by spectrocolorimetry using a DATACOLOR CS3 device.

We obtain a curve with a peak. The coefficient of reflection is more important in this area and the curve forms a peak. The reflection coefficient is greater than 100% in the case of a pigment fluorescent since there is light emission by the pigment fluorescent.

In Figure 3, there is shown a curve actually obtained, the curve A being obtained when the paper according to the invention is placed on a support of white color and curve B being obtained when the paper is placed on a black support.

On curve A we see that the reflectance reaches almost 180%.

EXAMPLES Example 1

A tracing paper of 92 g / m ^{2 is} coated on each side with a Meyer bar. The layer formulation contains 22.5% by dry weight of water-insoluble fluorescent pigment dispersed in an aqueous mixture containing a dispersing agent, a thickening agent and a wetting agent, and an acrylic binder. These agents and this binder are analogous to those commonly used in the art for coating paper. The pigment is a commercial fluorescent yellow pigment with an average particle size of between 2 and 3 μm. 4.5 g / m ^{2 are} deposited per layer face by dry weight and the amount of pigment in the layer by dry weight is approximately 3 g / m ² per face.

Examples 2 to 5

We deposit the same layers as that of Example 1, but we changes color, as shown in Table I below. The measurements of the color of the papers obtained were carried out with a measuring device marketed by HUNTERLAB.

Such a device makes it possible to measure Cartesian coordinates in three directions a, b, L of a point P of a color. So the point P is spotted according to the four colors blue, red, yellow and green. If a is positive, the color draws towards red, if a is negative, the color is more green. If b is positive, the color turns yellow, if b is negative, the color is more blue.

The HUNTERLAB device can also measure coordinates polar of point P. The distance between the center O and the point P is c and called chroma. It represents the intensity of the color. The angle H allows to locate the point P in relation to the four colors yellow, red, Blue green.

The transparency was measured using the device designed by the applicant, described above, and represented in FIG. 1.

Example 6

A 92 g / m ² roll of tracing paper is coated on each side on both sides with a composition containing a small amount of silica and a fluorescent pigment content of 24% by dry weight. The layer deposited by dry weight is 5.5 g / m ² per side.

Example 7

The same composition is applied as that of Example 6, but on parchment paper. The dry weight layer is 7.4 g / m ² per side, or approximately 4 g / m ² per side of pigment.

Example 8

The same composition is applied as that of Example 1, and under the same conditions, but on glassine paper. The dry weight layer is 3.5 g / m ² per side of pigment and binder, or 2.45 g / m ² per side of pigment.

All the examples above allow to obtain a paper bright and fluorescent transparent.

Furthermore, although the fluorescent pigment layers do not contain no fillers, the paper according to the invention is easily printable, which proves that the charges are not necessary. This constitutes an additional advantage of the invention, because in this way the formulation of the fluorescent pigment layers are easier to achieve.

Claims (11)

Paper characterized in that it comprises at least one fluorescent pigment and that it has the following physical characteristics: it is transparent and / or translucent, it has a color intensity (or saturation) c and a brightness L, measured in CIELAB units according to DIN standard 53237, such that the ratio of c to L is greater than 50%, for a given wavelength λmax, it has a reflection coefficient ΔR greater than 100%, as measured on a paper placed on a white background. Paper according to claim 1, characterized in that it consists of a transparent paper which comprises, on at least one of its two faces, a surface layer of fluorescent pigment insoluble in water. Paper according to claim 2, characterized in that it has a layer of water-insoluble fluorescent pigment on each of its faces. Paper according to one of claims 2 and 3, characterized in that the surface layer on each side comprises, by dry weight, from 1 to 10 g / m ² , preferably 3 to 6 g / m ² of fluorescent pigment. Paper according to claim 1, characterized in that it comprises, by mass, a fluorescent pigment in an amount of 5 to 20% by dry weight of pigment relative to the dry weight of paper. Paper according to any one of Claims 1 to 5, characterized in that the transparent paper is chosen from the group formed by tracing paper obtained with cellulose fibers having a Schopper refining degree greater than 80, a parchment paper, a "crystal" or "glassine" paper chemically transparent paper or other chemically and / or mechanically transparent paper. Paper according to any one of claims 1 to 4, and 6, characterized in that it is obtained by depositing on transparent paper an aqueous composition containing a fluorescent pigment, in an amount of about 20 to 30% by wet weight. Paper according to claim 7, characterized in that it is obtained by depositing on an transparent paper an aqueous composition not comprising or comprising a minute quantity of fillers. Paper according to any one of claims 1 to 4, 6 and 7, characterized in that it is obtained by depositing an aqueous composition containing a fluorescent pigment by coating, heliographic, flexographic, offset or screen printing. Application of a paper according to any one of claims 1 to 9, printing and / or writing. Process for manufacturing a translucent and / or transparent paper having an intense fluorescent color, characterized in that : a cellulose or paper is chosen which is treated so as to obtain a transparent and / or translucent paper; a pigment of the desired wavelength is chosen, which is mixed with the cellulose or which is deposited on the surface of the paper resulting from the treatment of the cellulose.

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