EP0927279A1

EP0927279A1 - Colour tracing paper

Info

Publication number: EP0927279A1
Application number: EP98924408A
Authority: EP
Inventors: Emeric Thibierge; Jean-François Loeillot
Original assignee: Thibierge & Comar Sa; Thibierge and Comar; Arjo Wiggins Fine Papers Ltd
Current assignee: Thibierge and Comar; Arjo Wiggins Fine Papers Ltd
Priority date: 1997-07-10
Filing date: 1998-05-07
Publication date: 1999-07-07
Anticipated expiration: 2018-05-07
Also published as: KR20010029461A; FR2765899B1; ES2241144T3; AU7661698A; US6630056B1; KR100588860B1; CA2265450A1; CA2265450C; GB2333303B8; AU742530B2; JP4592834B2; DE98924408T1; FR2765898B1; DE69829636T2; DE69829636D1; GB2333303A8; GB9905536D0; JP2002503297A; EP0927279B8; GB2333303B

Abstract

The invention concerns a translucent and/or transparent paper with an intense colour, having an colour intensity c and luminosity L, as measured with a Hunterlab apparatus, measuring the cartesian co-ordinates a, b, L from a colour point P and its polar co-ordinates H and c. The paper is such that the ratio c to L is greater than 30 %, preferably greater than 50 %. The paper comprises a colouring agent in its volume, preferably from 5 to wt. 10 % of liquid colouring agent relative to the weight of the finished paper. The colouring agent is a dye which fixes itself directly on cellulose. The invention is applicable to paper used in the field of printing or writing.

Description

COLOR TRACK PAPER

The present invention relates to a transparent and / or translucent paper of intense color, more particularly a tracing paper of intense color or a transparentized paper of intense color.

Tracing papers are already known which are obtained with very refined cellulose fibers. These papers are transparent and are used in the field of industrial design or by architects. Such papers have a grayish color. Transparent papers are also known which are obtained by transparentization of opaque papers using chemical compositions, based on a non-volatile liquid or a wax. These papers are commonly called transparentized papers.

Also known are transparent or translucent papers colored or not obtained from initially opaque paper by means of a very thorough hot calendering.

This kind of paper, called "crystal paper" or "glassine" is easily recognizable by the very high smoothness of its surface. Said smoothness being the direct consequence of the crushing to which it was subjected in the grille to make it transparent. Bekk smoothness measurement generally exceeds 2,000 seconds for papers of this kind.

The technique used to make the base paper does not require very sophisticated refining of the fibers before the sheets are formed.

When such a paper is colored, the fixing of the dyes on the fibers is not favored and it is difficult to obtain a paper having an intense color.

Also known are transparent or translucent papers, colored or not obtained from paper initially opaque by the sulfurization process. This kind of paper, called "parchment paper" or "vegetable parchment" is made transparent by chemical means. The opaque base paper is immersed in a sulfuric acid bath which dissolves part of the cellulose from the fibers. This bath is followed by numerous rinses with water during which the cellulose recrystallizes while the excess acid is removed. The fixing of the dyes is not favored and it is therefore difficult to obtain colored papers having a pronounced tint.

Tracing papers are also known which have a slightly bluish color and which are used by architects in conjunction with "diazo" paper, these papers being used for the reproduction of plans. Likewise, tracing papers are known which have a slightly pink color and which are used for industrial drawing.

Document DE-C-603 554 describes a process for manufacturing printing paper, cardboard for printing or other cardboard by assembling sheets of unfinished, wet paper containing dyes or fillers with layers of usual paper. This process is such that fillers or dyes are added in an amount of once or twice the dry weight of the fibers and the paper layers are thus laminated. This document therefore relates to the manufacture of paper or cardboard which comprise several layers of fibers. In no way does this document relate to the manufacture of colored tracing paper.

Document EP-A-0 097 371 relates to a process for manufacturing paper or other similar products by suspending fibrous material in a pulper, grinding the pulp to shorten, fibrillate and hydrate the fibers, optionally the mixture of the mass of fibers obtained with additives, dyes and / or binders, and passage over a grid, this process being characterized in that 10 to 35% by weight of cellulose is replaced by reinforcing agents. These reinforcing agents can be reinforcing agents based on corn, rice and wheat. Therefore, this document is absolutely not about making a layer. It only describes the manufacture of a paper, optionally with bulk dyes and with additives based on corn, rice, etc. Document US-A-2 128 739 relates to a laminated paper made from two sheets of paper between which a film of wax is interposed. The result is a laminated sheet that resists grease and moisture. A colored or tinted product can optionally be introduced into the fiber suspension. This document describes the coloring of a paper during the papermaking process by adding a dye. It is well mentioned that the gloss and the opacity of the paper are maintained. The coloring of the paper is checked with the brightness value L, the value a of color difference between red and green and the value b which is the difference value between yellow and blue. This document absolutely does not describe the making of colored tracing paper. It only describes how we can adjust colorings of a paper by measuring L, a and b.

Document DE-C-250 533 relates to a process for coloring paper in bulk. The dye solution from there is brought to the headbox using a pipe.

Document JP-A-49 125 614 describes the reduction of wood pulp in the presence of a hydrosulfite reducing agent and sodium hydroxide. The pulp is mixed with a water-soluble dye. It is therefore not a process for manufacturing tracing paper.

The present invention aims to provide a translucent and / or transparent paper made up of very refined fibers at a very high Schoper degree, at least greater than 80 or a paper transparentized by means of a chemical composition which has an intense color and which has a Bekk smoothness less than 2000 seconds, preferably less at 30 seconds, the cellulose of which is 100% in the form of fibers and which can be used in the field of printing and / or writing.

The present invention also aims to provide a tracing paper comprising a high percentage of dye. The present invention also aims to provide a very colored tracing paper having a good look.

The invention also aims to provide a method of manufacturing a very colored tracing paper or a very colored transparentized paper.

A person skilled in the art of stationery knows that there are several solutions for coloring non-transparent paper.

A first way is to perform a double-sided printing on the paper. The inventors have carried out numerous tests consisting in carrying out such a printing on the upper face and the lower face of a translucent / and / or transparent paper, more particularly a tracing paper obtained with very refined fibers. However, when printing is performed on the faces of a sheet of tracing paper, whether it is a flexographic, heliographic or offset printing, the transparency is greatly impaired and the printability is degraded.

A second means for coloring a paper is to carry out a coating on the upper face and the lower face, this coating being carried out with a composition containing dyes, fillers and a binder. The inventors have therefore coated a translucent / and / or transparent paper with a colored composition. However, the more the percentage of dye is increased, the more transparency is lost.

A third way to color a paper is to introduce a dye into the aqueous suspension of cellulosic fibers. This technique can only be used if the dye is introduced into the upstream part of the circuits where the paper pulp is mixed with water and the other traditional constituents of the paper. Indeed, it is necessary that the dye remains in contact with the cellulosic fibers for a sufficient time for the dye to attach to the fibers. Those skilled in the art know that if the amount of dye is increased, only a certain portion of dye is fixed on the fibers, because once the sites of the fibers are occupied by the dye, no additional dye can be fixed. Those skilled in the art therefore believe that it is impossible to fix more than about 5% by weight of liquid dye relative to the finished paper. In addition, the more colorant is introduced, the more it is rejected into the drip water, which causes pollution of the machine circuits and the environment.

A fourth way is to color the tracing paper after the drying rollers, in size-press. However, such a method does not make it possible to obtain an intense shade of the paper.

Therefore, the inventors had to solve the following problems:

. obtain a transparent and / or translucent colored paper which has a pronounced or intense tint;

. obtain a transparent and / or translucent colored paper which retains its transparency although having an intense color; . obtain a transparent and / or translucent colored paper which has a good look, that is to say a homogeneous look;

. obtain a transparent and / or translucent colored paper which has a Bekk smoothness of less than 2000, preferably less than 30 seconds;

. obtain a transparent and / or translucent colored paper whose cellulose fibers are 100% in the form of fibers or fibrils;

. obtain a transparent and / or translucent colored paper which has a printability as good as that of an uncolored tracing paper;

. obtain a transparent and / or translucent colored paper by a manufacturing process which causes low pollution of the machine circuits; . obtain a transparent and / or translucent colored paper by a manufacturing process which causes only a slight coloration of the drainage water discharged by the paper machine.

Technically, all these problems seemed to be incapable of being solved by a person skilled in the art, since increasing the color of the paper should have greatly reduced the transparency of the paper and increased the pollution. In addition, those skilled in the art thought that increasing the amount of dye beyond about 5% would not make it possible to increase the tint of the paper since the excess of the dye could not be fixed on the cellulose fibers.

However, the inventors, contrary to the prejudices of a person skilled in the art, were able after many attempts to obtain a transparent and / or translucent paper, namely a paper comprising very refined fibers (tracing paper) or a paper transparentized by a chemical composition, having a good look and an intense shade. To this end, the inventors have produced a transparent and / or translucent paper comprising very refined fibers with a Schόpper degree at least greater than 80 or obtained by transparentization, having a Bekk smoothness less than 2000, preferably less than 30 seconds, of which the cellulose is 100% in the form of fibers and / or fibrils, by mass introduction of a dye. This paper has a defined intense or dark color and is such that the color intensity c (or chroma) and the brightness L measured on a Hunterlab or Datacolor type device are as follows: - either the ratio of c to L is greater than 50%, preferably greater than 60% and more preferably slightly greater than 70%,

-or L is less than or equal to 60, preferably less than or equal to 50, -or the ratio of c to L is greater than 50%, preferably greater than 60% and more preferably greater than 70% and L is less than or equal to 60, preferably less than or equal to 50.

The inventors have surprisingly obtained such paper by refining the pulp to a Schoper degree at least greater than

80, and by introducing the dye just before the headbox, that is to say well downstream of the pulper, contrary to what has always been done in the traditional way for intense coloring.

Without wishing to be bound by theory, the inventors believe that because the fibers are very refined, that is to say that they contain many fibrils, the number of dye binding sites is increased and that for a same weight of paper obtained with unrefined fibers, the amount of fixed dye can be increased, up to 4 times. Furthermore, since the fibers are very refined, the dye can be introduced in the headbox, since the contact time between the fibers and the dye does not have to be very long, the fibers having numerous sites fixing the dye, due to the presence of numerous fibrils. In addition, during the manufacture of a transparent and / or translucent paper, the temperature of the fibrous suspension is adjusted between approximately 80 and 100 ° C. to allow better drainage of the paper sheet. However, these relatively high temperatures are very favorable for fixing the dyes on the fibers. During the production of a paper transparentized by a chemical composition, the chemical phenomena different from those mentioned above unexpectedly lead to a transparentized paper having an intense color.

The inventors have surprisingly prepared an intense colored transparentized paper by producing an aqueous suspension. of fibers and of a water-soluble dye, by depositing the said suspension on a flat table of a paper machine, removing the water by gravity, then drying the sheet between drying rollers, depositing on the thus dried sheet a chemical composition of transparency and finally drying the sheet.

Thus, the introduction of the dye into the headbox avoids polluting the part of the machine between the pulper and the headbox. As the dye is retained by the fibrils, the water leaving the drip contains very little dye, and therefore the pollution is reduced. Furthermore, as the finished paper is transparent and / or translucent, each particle of dye plays a visible role. The dye which is in the mass of the paper is visible. On the contrary, for non-transparent papers, only the dye which is on the surface of the paper is visible, and therefore, to have an intense shade, it is necessary to introduce a lot more dye.

The invention further relates to a transparent and / or translucent paper comprising a bulk dye introduced into the headbox on which a dye has been deposited in an aqueous medium in size press, in order to obtain an increase in intensity when the same dye and material effects when using a different dye.

The invention further relates to a transparent and / or translucent paper comprising in mass or in size press a fluorescent dye and optionally one or more other dyes soluble in water. The following description, with reference to the Figures and Examples appended without limitation, will make it possible to understand how the invention can be put into practice.

Figure 1 is a diagram representing the coordinates obtained with a color measuring device for the papers according to the invention. FIG. 2 is a diagram showing on the abscissa the values of L and on the ordinate the values of c for papers according to the invention and papers of the prior art.

As can be seen in the Figures, the hues are characterized by a polar coordinate system L, c, H. It is also possible to use an orthogonal coordinate system L, a, b.

The first parameter L is the luminance of the tint. It is between 0 and 100 and indicates whether the tint is dark (0) or light (100).

The second parameter c is the saturation (or purity) of color. It also varies from 0 to 100. When c is low, the hue varies from absolute black (L = 0) to absolute white (L = 100) by browsing the gray range.

When c increases, the hue becomes more colorful, regardless of the shade, c = 100 corresponds to the purest and most intense colors. H is the shade, that is to say the color itself. This parameter is between 0 and 360 °. It indicates the position in degrees of the shade in the chromatic circle: 0 = red, 90 = yellow, 250 = blue, 300 = purple.

To define the shades of tracing or transparentized papers according to the present invention, the luminance L is noted on the abscissa and the saturation c on the ordinate.

According to the present invention, papers comprising very refined fibers (or tracing papers) or colored transparentized papers are such that the color intensity c and the brightness L are defined as follows:

either the ratio of c to L is greater than 50%, preferably greater than 60% and more preferably greater than 70%,

The white papers as well as the papers of light colors and little saturated are located in the sector at the bottom right of the graph of Figure 2 and are represented by squares. They are not part of the present invention. The tracing papers or transparencies having vivid and very saturated colors which are the subject of the present invention are found in the area at the top right of the graph in FIG. 2; tracing papers or transparencies having dark tints according to the present invention are found on the left side of the graph. The papers according to the present invention are represented by dots on the graph of Figure 2.

Comparative Example 1 Long fibers of a paper pulp obtained from conifers are suspended in water in a pulper, and they are refined in a refiner, until a schopper degree of 60 is obtained. temperature of the aqueous fiber suspension at a temperature of 80-100 ° C. Then, the aqueous suspension of fibers is deposited on the canvas of a paper machine with a flat table, the water is removed by gravity. The relatively high temperature of the aqueous suspension is necessary to remove water by gravity, the fibers having a great affinity for water due to the presence of numerous fibrils. Then the sheet is pressed to remove the residual water. The sheet is then dried between drying rollers. We then obtain a transparent paper. This paper is a traditional greyish colored tracing paper.

An ink composed of a binder, a solvent and 15% by weight of a blue dye is prepared. The tracing paper obtained above is printed by flexographic printing, on both sides. We get a blue colored paper. The paper has lost its transparency. It may have certain appearance defects due to printing. The coloring is not uniform. Printing ink on paper changes the surface finish, and therefore printability. Tracing paper printed with fatty ink including the dye is more difficult to print.

Comparative example 2

A tracing paper is prepared as in Comparative Example 1. An aqueous composition is then prepared containing the dye, fillers and a latex. This composition is then deposited by coating on both sides. There are many machinability problems. The coloring of tracing paper by coating also makes it lose its transparency. In addition, coating a tracing paper would cause very significant curling of the paper.

Example 1

Long fibers of a paper pulp from coniferous trees are suspended in water in a pulper, and they are refined in a refiner, until a shόpper degree of 60 is obtained. The temperature of the aqueous suspension of fibers at a temperature of 80-100 ° C. Then, just before the headbox of a paper machine, a blue dye in aqueous solution is introduced into the aqueous fiber suspension, the amount of dye being such that it is 6% by weight relative to the weight of the finished dry paper. The dye is a dye

® direct which attaches directly to cellulose, CARTASOL brand, blue reference 3RF, manufactured and sold by the company Clariant (Switzerland). The suspension of fibers and dye is deposited on a canvas of a flat table paper machine, the water is removed by gravity. The water coming out of the machine is very little colored, which shows that the dye has fixed well on the fibers. Then, the sheet is dried between drying rollers. We obtains a transparent and / or translucent paper which has a dark blue color. The weight of dye relative to the weight of finished paper is greater than 5%.

The color of the paper obtained is measured using, for example, an apparatus manufactured by the company Hunterlab. Such a device makes it possible to measure the Cartesian coordinates in three directions a, b, L of a point P of a color. Thus, point P is identified according to the four colors blue, red, yellow and green. If a is positive, the color turns red, if a is negative, the color is greener. If b is positive, the color turns yellow, if b is negative, the color is more blue. In the figure, point P represents a fairly red and a little yellow color, so it is an orange color. The third coordinate, perpendicular to the plane of a and b, represents the brightness of the color.

The Hunterlab device also makes it possible to measure the polar coordinates of the 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 makes it possible to locate the point P in relation to the four colors yellow, red, blue, green.

The values obtained with the Hunterlab apparatus are given in Table I which follows.

Example 2

A transparent paper is prepared in the same manner as in Example 1, but a red dye is added to the headbox, which is a dye from the company Clariant, of the same brand as that of Example 1 and of reference 2RF . The amount of dye is 10% by weight relative to the weight of the finished paper. We obtain a transparent red paper of dark color. The color of the paper is measured as in Example 1. The values are given in Table I which follows. Examples 3 to 5

Papers are made in the same manner as in Example 1, using yellow dyes 5GFN and RF from the company Clariant and of the same brand as those of the previous examples. They are mixed with the red 2RF dye to obtain a yellow, or orange or carmine hue. The color of the papers obtained is measured in the same way as in the previous examples. The results are given in the following Table I.

Table I

From the table, we see that the ratio of color intensity (chroma) to brightness is much higher than 50% and even more than 70%.

EXAMPLES 6 TO 16

Papers are made in the same manner as in Example 1, using other dyes mentioned in Table II below. Table II

Color N ° Contact Lab

L * a ^* b * c * h ^* % c / L

7 Azur 62.51 -6.47 -31.01 01 31.68 258.21 50.68

8 Turquoise 76.46 -38.12 -5.46 38.51 188.15 50.36

9 Anise 76.77 -10.96 73.83 74.63 98.44 97.21

10 Yellow 84.34 6.70 87.21 87.47 85.61 103.71

11 Orange 73.81 34.14 83.01 89.76 67.64 121, 60

12 Vermillon 47.56 59.59 38.01 70.68 32.53 148.61

13 Indigo 33.61 10.07 -35.38 36.79 285.89 109.45

14 Carmine 32.37 28.16 12.08 30.64 23.22 94.66

15 Fir 29.52 -6.09 7.08 9.34 130.70 31, 64

16 Black 23.91 0.63 -0.03 0.63 357.27 2.64

Comparative example 3

A traditional tracing paper is prepared as in Comparative Example 1. Then, a blue dye from Clariant, reference 3RF, is deposited in an aqueous solution in size press. The paper obtained has a bluish color. We measure with a Huntelab device and we obtain a c / L ratio of 10%.

Example 6.

A paper is prepared as in Example 2 by introducing the dye into the headbox. Then in size press, a red dye is deposited in an aqueous solution. A red-colored paper is obtained, the c / l ratio of which is 90%, of a more intense shade than in Example 2.

Consequently, according to the invention, transparent and / or translucent papers can be obtained whose color intensity c is very high compared to the papers of the prior art. In addition, these papers are obtained according to a new process which avoids pollution of paper machine circuits, which rejects only very little colored water.

In Figure 2, the first line A represents the values c / L = 60%. the second line B represents the values c / L = 70%. the third line C represents the values L = 60 (c = 0 at infinity), the fourth line D represents the values L = 50.

We see that the papers according to the invention are located in the upper left from the right A and the right C, and preferably from the right B and the right D.

Papers such as L> 60 and c / L <50% simultaneously are located in the lower right of the diagram and are papers of the prior art.

Claims

1. Paper characterized in that it is transparent and / or translucent, namely that it comprises fibers having a high degree of refinement or that it consists of an opaque paper transparentized by a chemical composition, having a smoothness Bekk less than 2000 seconds, preferably less than 30 seconds, in which the cellulose is 100% in the form of fibers and / or fibrils, and in that it has an intense or dark color defined by the intensity of color c and the brightness L as follows:

-or L is less than or equal to 60, preferably less than or equal to 50,

-or the ratio of c to L is greater than 50%, preferably greater than 60% and more preferably greater than 70% and L is less than or equal to 60, preferably less than or equal to 50.

2. Paper according to claim 1, characterized in that it comprises a bulk dye.

3. Paper according to claim 1 or 2, characterized in that it comprises from 5 to 10% by weight of liquid dye relative to the weight of finished paper.

4. Paper according to one of claims 1 to 3, characterized in that the dye is a dye which is fixed directly on the cellulose.

5. A method of manufacturing a paper according to one of claims 1 to 4, characterized in that an aqueous suspension of a paper pulp is refined to a Schoper degree of 50 to 80. a dye is introduced into headbox, at the same time as the aqueous suspension of fibers, the aqueous suspension of fibers and dye is deposited on a flat table of a paper machine, the water is removed by gravity and then the sheet obtained is dried between drying rollers.

6. Method according to claim 5, characterized in that the temperature of the aqueous suspension of fibers and dye is maintained just before the headbox at a temperature between about 80 and 100 ° C.

7. Method according to one of claims 5 or 6, characterized in that the liquid dye is introduced in an amount of 5 to 10% relative to the weight of finished paper.

8. Method according to one of claims 5 or 6, characterized in that a dye is further deposited in an aqueous medium in size press.

9. A method of preparing a paper according to one of claims 1 to 5, characterized in that an aqueous suspension of fibers and a water-soluble dye is produced, said suspension is deposited on a flat table of a paper machine, the water is removed by gravity, then the sheet is dried between drying rollers, a chemical composition of transparency is deposited on the thus dried sheet and the sheet is finally dried.