KR100800933B1 - Process for controlling the brightness of paper products - Google Patents

Abstract

The present invention relates to a shading method of white paper, a mixture and paper dyed with the method, characterized in that it uses a mixture comprising at least one mordant-free dye or pigment and at least one fluorescent brightener.

Description

PROCESS FOR CONTROLLING THE BRIGHTNESS OF PAPER PRODUCTS}             

The present invention relates to a method of controlling the brightness of a paper product while using shading dyes.

Luminance in the paper industry is a technical term used to represent the reflectance of paper or pulp at a specific wavelength, for example TAPPI (technical association of pulp and paper industry) luminance, ISO (International Organization for Standardization) and the like.

Some definitions of brightness, whiteness and color of paper samples are as follows.

a) CIE whiteness and CIE hue

CIE whiteness and CIE hue are calculated from chromaticity coordinates and color coordinates. CIE whiteness refers to the whiteness of a sample comprising a fluorescent brightener (hereinafter abbreviated as OBA) and a shading dye component. Tint values are used to indicate the degree of specific contrast of white. Since this figure is so closely correlated with human vision, it is undoubtedly the best method of measuring the available whiteness. In addition, since the two whites may have the same whiteness but different degrees of contrast, the color tone value is usefully used to distinguish them. CIE whiteness and hue are defined in Equations 1 and 2 in ISO 11475, respectively:

b) CIELAB L ^* , a ^* , b ^*  shame

CIELAB L ^* , a ^* , b ^* Numbers are used to describe the color space and are the three axes of a three-dimensional system for representing color. L ^* represents the difference between black and white, a ^* represents the red-green coordinates, and b ^* represents the blue-yellow coordinates. These are particularly useful for displaying and controlling the effects of shading dyes on white paper. Another similar system is L, C, H, where C and H represent saturation and color, respectively. The a ^* and b ^* values are very useful for controlling and indicating the degree of contrast, but the L ^* values do not reconsider the shading dye. When the shading dye is added, the L ^* value drops. It should also be noted that OBA also affects a ^* and especially b ^* levels.

CIELAB L ^* , a ^* , b ^* values L ^* value: brightness (white-black coordinates), 0 = full black, 100 = full white a ^* number: red-green coordinates b ^* number: yellow-blue coordinates

It should be noted that in the current paper industry, shading dyes are added not only to achieve the white effect but also to control the color. Color is often adjusted using target values of a ^* and b ^* . This method can be done manually, on-line or on-line closed-loop color control. Purple dyes and reddish blue dyes are used to enhance whiteness, while other colors, such as red, blue and yellow, are used to control the degree of contrast of white paper. Also, black is used in very small amounts to control the opacity of white paper.

c) luminance

Luminance is a term used in the paper and pulp industry that typically refers to a reflectance factor near 460 nm. There are other definitions of this term (eg Scandinavian pulp, paper and board test committee SCAN-test C11: 75 and TAPPI standard test method T452), but are defined as above in ISO 2470 and 3688. When a small amount of shading dye is added to the white paper, the luminance decreases somewhat depending on the dye used and its concentration. This occurs because the dye reduces the reflectance by absorbing light. Fluorescent brighteners increase brightness because they are fluorescent and increase brightness levels.

Fluorescent brighteners are colorless to weakly colored organic compounds that, when present in solution or applied to a substrate, absorb ultraviolet light (e.g., from daylight from about 300 to 430 nm) and absorb most of the absorbed energy from about 400 to about Re-emission with blue fluorescence between 500 nm.

Thus, fluorescent brighteners can correct aesthetically undesirable yellowish colors in white industrial substrates such as textiles, paper or plastics under sunlight. In addition, since part of the daylight spectrum that is not visible to the naked eye is converted into visible light, the luminance of the material is enhanced to show a dazzling white color.

The first way to calibrate conventional yellowish colors was to use blue dyes such as ultramarine blue or indigo blue. This bluening method lowers the reflectance of the sample to the long wavelength portion of the visible light spectrum. As a result, the sample has an intermediate white appearance and is visually more interesting.

Fluorescent whitening agents lower the reflectance by absorbing mainly in the ultraviolet and near visible range. They greatly increase the brightness by fluorescence at visible light wavelengths (mostly peaking at 435-440 nm). Fluorescent brighteners act as secondary light sources. Fluorescent brighteners are more effective with clean, whiter substrates.

In a typical white paper manufacturing process, many color parameters are controlled, including CIE whiteness, ISO brightness, CIELAB a ^* value, CIELAB b ^* value, CIELAB L ^* value and fluorescence (typically when there is an ultraviolet component in the light source). Obtained by subtracting the measured value when the ultraviolet component or the ultraviolet component is not present).

The problem for papermakers is that the two types of components that have controlled these variables are a) one or more shading dyes and b) one or more OBAs. (Shading dyes are typically added at wet-ends or coatings, and rarely at size-compressions. OBA is added at wets, size-compressions and / or coatings.) These components affect each measurement, and sometimes other variables need to be modified later, since the desired addition rate required to adjust the necessary parameters negatively affects another variable. For example:

Reddish purple shading dye (e.g. C.I. Direct Violet 51, C. i. Direct Blue 267) or pigment (e.g. C. Pigment Violet 23): used to adjust the a ^* and b ^* values, which has a negative effect on brightness, a positive effect on whiteness, and no effect on fluorescence.

Bluish / medium purple shading dye (e.g. C. direct violet 35) or pigment (e.g. C. pigment blue 15, c.i. pigment violet 3): b ^* value It has a negative effect on brightness, a positive effect on whiteness, little or no effect on a ^* values, and no fluorescence at all.

Red shading dyes (e.g. C. I. Direct Red 253): used to adjust a ^* values, which negatively affects brightness, has no effect on whiteness, and rarely affects b ^* values Or does not affect at all, and does not affect the fluorescence at all.

OBA (e.g., C. Fluorescent Brightener 220, C. Fluorescent Brightener 28, C. Fluorescent Brightner 264): Enhances fluorescence, whiteness and brightness It also affects the a ^* and b ^* values.

When producing highly white, white paper containing purple, red or blue shading dyes added in the wet zone and OBAs, and possibly other OBAs added in the size-compression zone, obtain the correct target parameters to control the process. Decisions on the process of adjusting the hazardous additives can appear very complex, especially when an increase or decrease in the shading dye or OBA is to be considered. When any shading dye increases its usage, the brightness drops. Therefore, the papermaker must compensate by adding more OBA to restore the brightness target, and conversely reduce the amount of OBA added when reducing the amount of shading dye used. These components often have to be adjusted together to achieve all target variables.

The problem of reduction in brightness while using shading dyes is well known.

In the art, this problem could be solved by adding additional fluorescent brighteners. The typical procedure used to date has been to first add a solution containing dyeing material followed by a solution containing fluorescent brightener.

It is difficult to control the color in the white paper dyeing process. Then, when increasing the concentration of the shading dye to reach the correct color, the concentration of the OBA must be increased to obtain the correct brightness because the brightness decreases as the amount of added shading dye is increased. This complex and precise procedure must be done manually or through a closed-loop color control scheme.

It is an object of the present invention to provide an easier method of controlling the brightness of paper products during the use of shading dyes, using a one-step procedure that will help save time and reduce the amount of dyestuff and OBA required.

The present invention provides a method for shading white paper, characterized in that it uses a mixture comprising at least one mordant-free dye or pigment and at least one fluorescent brightener.

Preferably, the invention is characterized in that the mixture consists of at least one mordant-free dye and at least one fluorescent brightener in a ratio of 25/75 to 90/10% by weight, preferably 50/50% by weight. .

Also part of the present invention are mixtures for imparting fluorescence to paper shading dyes comprising at least one mordant-free dye and at least one fluorescent brightener in a ratio of 25/75 to 90/10 weight percent.

The OBAs used in the present invention are wetted OBAs, size-compressed parts OBAs and / or coated OBAs.

Preferred OBA is C. I. Fluorescent Brightner 220, C.I. Fluorescent brightener 28 and / or C.I. Fluorescent brightener 264.

The paper obtained by the process of the invention is also part of the invention.

By this method, the amount of shading dye used can be adjusted without affecting the luminance value, only the shading dye needs to be adjusted, and it is not necessary to adjust the amount of fluorescent brightener to recover the brightness.

In the present invention, all OBAs known for paper making can be used. Preferred fluorescent brighteners are wetted OBAs (Leucophor® AP, AL, U, etc.), size-compressed parts OBAs (Leucophor U, NS, SHR, TC, etc.) and cladding OBAs (Leucophor U). , AP, AL, NS, SHR, TC, etc.). Leukovopor is a registered trademark of Clariant.

OBA is added to the shading dye in the form of a mixture so that its fluorescence, when added to the paper, compensates for the loss of brightness due to absorption of the shading dye so that the brightness of the paper is not reduced by the addition of the shading dye. Thus, only one component needs to be adjusted to achieve the color target, and there is no need for supplemental adjustment with OBA as the luminance is not reduced, making the process simpler.                 

A further advantage is that the mixture of OBA and shading dye has a greater influence on the color coordinates (a ^* , b ^* ) than the dye alone, thus reducing the amount of shading dye used.

In addition, pigments (e.g., C. Pigment Violet 23, C. I. Pigment Blue 15, C. I. Pigment Violet 3) are also used to shade (e.g., coat) white paper. .

Shading dyes and OBAs are also used in wet-pressing processes as well as size-compression and coating processes.

The following examples illustrate the invention.

Example 1

A standard preparation of paper stock consisting of 50% bleached conifer pulp and 50% bleached pulp was prepared in a 20 ° Shopper Riegler and 20% CaCO ₃ was added (weight of anhydrous fibers). Batch based on). 1: 1 mixture of liquid anionic mordant-free paper dye (including 13% C. I. direct violet 35) and liquid fluorescent brightener (including 25% C. F. Br. 290), And a handsheet comprising 50% dilution of the liquid paper dye (C.I. direct violet 35) as a control in various amounts. A focusing agent (1.7% Aquapel® 360X) was added and a retention filler (0.003% Cataretin® 20CE) was used to hold the chalk filler. 0.0 wt%, 0.001 wt%, 0.003 wt%, 0.006 wt% and 0.100 wt% of the dye and dye / fluorescent brightener-mixture were added based on the weight of the liquid product on the dry fibers.

Thereafter, the handsheet was compressed and dried. Table 2 below shows the results measured on a Minolta CM-3700d spectrometer when the ultraviolet component was included in the light source:

sample CIE whiteness Luminance a ^* b ^* 0.0 wt% (black) 71.7 85.7 0.1 4.4 0.001% by weight (dye only) 74.0 86.0 0.0 3.7 0.001% by weight (50% dye / 50% fluorescent brightener) 74.3 86.0 0.0 3.6 0.003% by weight (dye only) 76.4 85.8 0.1 2.8 0.003% by weight (50% dye / 50% fluorescent brightener) 77.4 86.0 0.1 2.6 0.006% by weight (dye only) 79.4 85.4 0.1 1.7 0.006% by weight (50% dye / 50% fluorescent brightener) 83.1 86.3 0.2 0.9 0.100% by weight (dye only) 114.9 79.4 2.2 -9.7 0.100% by weight (50% dye / 50% fluorescent brightener) 134.1 84.5 3.6 -13.7

Claims (12)

A method of shading white paper by using a mixture of one or more mordant-free dyes or pigments and one or more fluorescent brighteners, the mixture comprising one at a ratio of 25/75 to 90/10% by weight. And at least one mordant-free dye and at least one fluorescent brightener. The method of claim 1, Mr. Child. C.I.Direct Violet 51, C.I. Direct Blue 267, C.I. Direct Violet 35 and C.I. Using at least one dye selected from the group consisting of Direct Red 253. The method of claim 1, Mr. Child. Pigment Violet 23, C.I. Pigment Violet 3 and C.I. Pigment Blue 15, characterized in that using at least one pigment selected from the group consisting of. A mixture for imparting fluorescence to a paper shading dye comprising one or more mordant-free dyes and one or more fluorescent brighteners in a ratio of 25/75 to 90/10 weight percent. A mixture for imparting fluorescence to a paper shading dye comprising at least one pigment and at least one fluorescent brightener in a ratio of 25/75 to 90/10 weight percent. The method of claim 1, Wherein the at least one fluorescent brightener is selected from the group consisting of wet-end fluorescent brighteners, size-compression fluorescent brighteners and coating fluorescent brighteners. The method of claim 6, At least one fluorescent brightener is C. eye. Fluorescent Brightener 220, C.I. Fluorescent brightener 28 and C.I. Fluorescent brightener 264 selected from the group consisting of. delete delete Paper obtained by the method according to claim 1. The method according to claim 4 or 5, At least one fluorescent brightener is selected from the group consisting of wet fluorescent brighteners, size-compression fluorescent brighteners and coating fluorescent brighteners. The method of claim 11, At least one fluorescent brightener is C. eye. Fluorescent Brightner 220, C.I. Fluorescent brightener 28 and C.I. A mixture characterized in that it is selected from the group consisting of fluorescent Brightner 264.