FR2808540A1 - TRANSPARENT AND / OR TRANSLUCENT PAPER OF FLUORESCENT COLOR - Google Patents

Abstract

Process for manufacturing a translucent and / or transparent paper having an intense fluorescent color, characterized in that: - a cellulose or a 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.

Description

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  TRANSPARENT AND / OR TRANSLUCENT PAPER

FLUORESCENT COLOR

  The present invention relates to a transparent and / or translucent paper of fluorescent color, more particularly a tracing paper of fluorescent color, but also to other transparent or translucent papers such as greaseproof papers, papers transparentized by impregnation or so-called "crystal" papers. , which have been given a

  fluorescent color by the means described below.

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

FLUORESCENT COLORING MATERIALS

  "Fluorescent dyestuffs" are dyestuffs, generally synthetic, which differ from conventional dyestuffs in that they absorb certain frequencies of the light spectrum (in particular 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 polychromatic light source, these materials present in the spectrum of visible frequencies 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. For this

  frequency matter can therefore emit more light than it receives.

  This is impossible for conventional coloring matter, which reflects or transmits only part of the light

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  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 greatly exceed 100% maximum re-emission. This property gives them extremely pure and bright colors,

  therefore an extraordinary visual effect.

DYES - PIGMENTS

  Regardless of their own chemical nature or their origin, the 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, one

will talk about dye.

  When the coloring matter is used as a powder dispersed in

  the material to be colored, we will speak of pigment.

  The dyes can be soluble in water or in an organic medium. Most pigments can be used in both media. There is currently no true fluorescent pigment on the market, but only fluorescent dyes, the most interesting of which are organosoluble. Pigment producers circumvent the difficulty by introducing these dyes into resins which 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.

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  The pigments industry, which targets many industries, but more particularly that of paints and inks, provides

  colored products for which opacity is an essential quality.

  (When transparency is sought for 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 fluorescent color pigments, are therefore considered as materials

opaque dyes.

  TRANSPARENT MATERIAL - TRANSLUCENT - OPAQUE

  A transparent material is a material that light can pass through without great loss. Some transparent transparent material is passed through by certain frequencies of visible light without great loss, 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 small foreign particles, opaque or transparent but with a different refractive index are disseminated there, it is no longer perfectly transparent. From a certain thickness we 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 vast majority of light rays can no longer pass through the material without being absorbed or reflected. The material is then opaque. This can happen when the number of foreign particles per unit volume is high,

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  or when the thickness of the translucent material to be crossed is large enough.

  TRANSPARENT AND / OR TRANSLUCENT PAPER

  We will consider that a paper is 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 a commonly held idea, a transparent paper can be intensely colored without losing its transparency because a black text remains perfectly visible when such a paper is placed on it. We will consider that a paper is translucent if under 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 hindered by the text on the following pages. Only certain technical papers have transparency (crystal or parchment paper for packaging, tracing paper for the creation of superimposable and reproducible plans by the diazo process). Those skilled in the art of making paper for printing / writing therefore have not hitherto sought to produce transparent colored papers. The invention of transparent and / or translucent bright-colored papers intended for printing / writing has been 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 brightness L such that the ratio of c to L is greater than 50%, or L

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  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 for printing and / or writing. The paper described in this document also includes a

  fluorescent dye soluble in water, in bulk or in size press.

  The present invention therefore constitutes an improvement to this

previous invention.

  In fact, when a dye is used, the fluorescence obtained is not always satisfactory and the present invention seeks to

  improve the quality of fluorescence.

  There is also known an extra white transparent paper comprising a whitening agent in combination with an opacifying agent. Such transparent paper is described in European patent application No. 0 919 664 filed by the applicant. This paper does not have an intense color. The optical brightener is a fluorescent dye which is soluble in water and which emits a bluish light when it is 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.

  New FR-A-2 348 317 (CIBA-GEIGY) has described new optical brighteners insoluble in aqueous medium which are used in suspension to coat an opaque paper. These brighteners are intended to give a superior whiteness appearance

with opaque paper.

  Document GB-A-1 369 202 (CIBA-GEIGY) describes a process for bleaching an opaque paper using an acid solution of an optical brightener. 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.

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  Document EP-A1-0 712 960 describes a liquid composition containing an optical brightener dissolved in polyethylene glycol of low molecular weight in the range of 150 to 500. This composition

  is used for coating conventional opaque paper.

  There are currently opaque papers on the market which have an intense fluorescent color. These papers are mainly intended for the manufacture of posters or labels for which 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 and / or transparent paper which has a fluorescent, intense and usable color.

  in the field of printing and / or writing.

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

  usable for printing and / or writing.

  The present invention further aims to provide a method of manufacturing a translucent and / or transparent paper having a

intense fluorescent color.

  A person skilled in the art in the field of papermaking knows that in order to obtain a coloring thereof, it is possible either to introduce dyes or pigments in bulk during the making of the paper, or to cover the paper with a composition containing dyes or

pigments in suspension.

  Since the paper is made in suspension in water, it is convenient to use a water-soluble dye in bulk. Some of these dyes spontaneously fix on cellulose while others require the intervention of additives for their fixation. The pigments, insoluble in an aqueous medium, can also be used so as to carry out the mass coloring of the paper, but a fixing agent must be added which makes it possible to retain the pigments on the fibers. This does not prevent a

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  some loss of pigments in the water discharged from the paper machine. Those skilled in the art for coloring paper therefore have on the one hand a range of transparent dyes soluble in water and on the other hand

  share a range of opaque pigments insoluble in water.

  A person skilled in the art who seeks to produce fluorescent color paper can find commercially available water-soluble fluorescent dyes. These products are transparent but not very fluorescent; moreover, their range of colors is poor, that is to say that there are very few fluorescent dyes soluble in water on the market. 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 commercially available organosoluble fluorescent dyes of bright and varied colors. Since these dyes are not usable in water, they cannot be used either en masse in the manufacture of paper, or on the surface in a water-soluble coating. They can be used only in varnishes or inks in solvents applicable on paper, and because of their reduced power of reflection they do not give the paper a satisfactory color,

  especially in terms of fluorescence.

  On the contrary, a person skilled in the art has commercially available fluorescent pigments with very bright and saturated colors in a varied range. Being insoluble pigments and not soluble dyes, these products are considered opaque. To impart fluorescent coloring to paper, those skilled in the art who wish to produce a range of colors therefore have pigments of

  varied but opaque fluorescent colors.

  Also known are paints based on fluorescent pigments which consist of transparent resin particles. However, in the technical sheet P.P.V. No. 166 of PAINTS-Pigments-varnishes,

  it is mentioned that these pigments must be deposited on a sub-

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  white layer to make the most of their brightness and purity and ensure that the light rays which have passed through the layer of fluorescent paint are not absorbed by the substrate but reflected by it and pass through the fluorescent layer to participate in I ' visual effect. According to the prior art, it is therefore accepted that to obtain good fluorescence, it is necessary that the background be as white and opaque as possible so as to reflect light as much as possible. Consequently, the person skilled in the art believed before the realization of the present invention that it was not possible to obtain a transparent paper of bright fluorescent color and moreover in a range of varied colors. This prejudice stems from the fact that if a variety of fluorescent colors is to be obtained, those skilled in the art are obliged to use fluorescent pigments which 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 those skilled in the art to suppress the transparency of the paper. Another prejudice of a person skilled in the art is that to obtain fluorescence

  effective it is essential that the background is reflective and not transparent.

  So the skilled person believes that it is not possible to obtain a paper

  transparent with some fluorescence.

  However, the present inventors have surprisingly found that it was possible to give transparent and / or translucent paper an intense fluorescent color by using fluorescent pigments in certain proportions, without these pigments reducing

  significant transparency of the paper finally obtained.

  The present inventors have also surprisingly found that by depositing, by coating and / or printing, an aqueous composition of fluorescent pigments on a transparent background, namely, inter alia a conventional transparent paper, one obtains both an intense fluorescent color and good transparency. They also

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  surprisingly found that by massively introducing fluorescent pigments into the pulp of a transparent paper, the transparency of the

  paper obtained is not reduced significantly.

  The present invention therefore relates to a paper characterized in that it simultaneously 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 the DIN 53237 standard, such that the ratio of c to L is greater than 50%, it has for a given wavelength Xmax an AR reflection coefficient greater than 100%, when the measurement is made on a resting paper

on a white background.

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

  paper from cellulose processing.

  According to one of the embodiments of the invention, the transparent or translucent paper receives on each face a surface layer

  comprising a fluorescent pigment insoluble in water.

  The layer, when applied to the paper contains

  about 20 to 30% of fluorescent pigment by weight.

  The dry layer resulting from this application comprises from 1 to, preferably from 3 to 6 g / m2 of fluorescent pigment on each side.

paper.

  According to another embodiment of the present invention, a non-water-soluble fluorescent pigment is introduced in bulk and

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  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 is chosen from the group formed by tracing paper, parchment paper, crystal paper (or "glassine"), paper transparentized by impregnation. The present invention, with reference to the figures and examples appended without limitation, will allow a better understanding of 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) by placing 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,

  ie a saturation c, and a brightness L measured in CIELAB units according to DIN 53237, such that the ratio of c to L is greater than%, it has for a given wavelength Xmax a higher reflection coefficient AR 100%, when the measurement is made on paper

  resting on a curved white background A).

  Transparent and / or translucent paper consists of very refined fibers to a very high Schoper degree, at least greater than 80 or a paper transparentized by means of a chemical composition. The transparent and / or translucent paper can also be a paper called "parchment paper" or "vegetable parchment" made transparent by immersing an opaque base paper in a bath of sulfuric acid which dissolves part of the cellulose of the fibers. This bath is followed by numerous rinses at

  the water eliminates the excess acid is eliminated.

  The transparent and / or translucent paper according to the present invention can also be a so-called "glassine" paper. Such paper has a Bekk smoothness greater than 2000 s and is obtained by extensive calendering of an opaque paper. 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 standard 53237, such that the 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 is furthermore as it comprises

  a surface layer of water-insoluble fluorescent pigment.

  Therefore, the paper according to the invention has, for a given wavelength range 2max a reflection coefficient AR greater than%. The paper according to the invention is further characterized in that it is obtained by depositing on an transparent paper an aqueous composition which does not

  not comprising or comprising a minute quantity of charges.

  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 / m2, by dry weight. If the quantity is less than 3 g / m2, the transparency of the paper is good, while the fluorescence and color intensity are insufficient. If the amount of pigment is more than 6 g / m2, the transparency of the paper is insufficient, without however the fluorescence and the intensity of color

  are increased remarkably.

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  The transparency of the paper according to the invention can be conveniently measured using a device designed by the applicant (represented in FIG. 1), in the following manner: On a transparent rigid tape 1, 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 light in color to the naked eye. The second circle 2b, filled with a grid of tighter lines, appears darker to the naked eye than the circle 2a. The third circle 2c, filled with a grid of tighter lines, appears darker to the naked eye than 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 circle 2d, etc. The grid lines are adjusted so that if the paper according to the invention 1 lets see only the circle 2e, it will be noted 5, if it lets see the lighter circle 2d, it will be noted 4, etc., the paper leaving appear 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.

  FIG. 2 shows a schematic curve of the reflection coefficient (or reflectance) on the ordinate and the wavelength of the reflected light (nm), on the abscissa. The reflectance or coefficient of reflection is measured by spectrocolorimetry using a

DATACOLOR CS3 device.

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

fluorescent.

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  FIG. 3 shows a curve actually obtained, curve A being obtained when the paper according to the invention is placed on a white support 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 / m2 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 whose average particle size is between 2 and 3 μm. 4.5 g / m2 are applied per layer face by dry weight and the amount of pigment in the layer

  by dry weight is approximately 3 g / m2 per side.

Examples 2 to 5

  The same layers are deposited as that of Example 1, but the colorant is changed, as indicated in the following table. The results

  measurements are given in this table.

Board

  Ex. No. Pigment L * a * b * C * H * C / L% imax transparency AR% measured with (nm) the device described 1 Yellow 96.02 -40.72 110.55 117.83 110.25 122 , 71 I 520 146 2 Orange-yellow 82.91 54.02 102.75 116.08 62.27 140.01 I 590 176 3 Orange-red 68.16 83.48 74.60 11.95 41.78 164 , 25 1,610 180 4 Pink 61.21 87.01 10.19 87.60 6.68 143.11 I 620 148 Green 82.93 -74.62 84.66 112.85 131.39 136.08 1,520 124

  In addition to its fluorescent color, the pigment is characterized by an average particle size of between 2 and 3 μm.

OD o ce oC

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Example 6

  A roll of tracing paper of 92 g / m2 is coated on each side on both sides with a composition containing a small quantity of silica and a fluorescent pigment content of 24% by dry weight. The dry weight layer is 5.5 g / m2 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 / m2 per side,

  about 4 g / m2 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 / m2 per side of pigment and binder, i.e. 2.45 g / m2 per side

of pigment.

  All the examples above allow to obtain a paper

  bright and fluorescent transparent.

  Furthermore, although the layers of fluorescent pigment do not contain fillers, the paper according to the invention is easily printable, which proves that the fillers are not necessary. This constitutes an additional advantage of the invention, because in this way the formulation of the layers of fluorescent pigment are easier to carry out.

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Claims (10)

  1. Paper characterized in that it simultaneously 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 standard DIN 53237, such that the ratio of c to L is greater than 50%, it has for a given wavelength Xmax a reflection coefficient AR greater than 100%, as measured on a paper placed on a white background. This paper is obtained from a transparent and / or translucent paper which is colored by means of fluorescent pigments. 2. Paper according to claim 1, characterized in that it consists of a transparent paper which has on each side a layer   surface of water-insoluble fluorescent pigment.   3. Paper according to claim 1 or 2, characterized in that the surface layer on each side comprises by dry weight from 1 to 10, of   preferably 3 to 6 g / m2 of fluorescent pigment.   4. Paper according to claim 1 or 2, characterized in that it comprises by mass a fluorescent pigment in an amount of 5 to 20% by weight   dry pigment relative to the dry weight of paper.   5. Paper according to any one of claims 1 to 4, characterized in   what transparent paper is chosen from the group formed by tracing paper obtained with cellulose fibers having a Schopper refining degree greater than 80, parchment paper, "crystal" or "glassine" paper, chemically transparent paper or the like paper   chemically and / or mechanically transparent. 17 2808540   6. Paper according to any one of claims 1 to 4, characterized in   what is obtained by depositing on transparent paper an aqueous composition containing a fluorescent pigment, in an amount of about 20 to % by wet weight.   7. Paper according to claim 6, characterized in that it is obtained by depositing on a transparent paper an aqueous composition does   not comprising or comprising a minute quantity of charges.   8. Paper according to any one of the preceding claims,   characterized in that it is obtained by depositing an aqueous composition containing a fluorescent pigment by coating, printing   heliographic, flexographic, offset or screen printing.   9. Application of a paper according to any one of the claims   previous, printing and / or writing.   10. A method of manufacturing a translucent and / or transparent paper having an intense fluorescent color, characterized in that: - a cellulose or a 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 from cellulose processing.