U.S. patent application number 10/363005 was filed with the patent office on 2003-10-09 for process for controlling the brightness of paper products.
Invention is credited to Tindal, Alec.
Application Number | 20030188393 10/363005 |
Document ID | / |
Family ID | 9898605 |
Filed Date | 2003-10-09 |
United States Patent
Application |
20030188393 |
Kind Code |
A1 |
Tindal, Alec |
October 9, 2003 |
Process for controlling the brightness of paper products
Abstract
A process for shading white paper characterized in that a
mixture comprising at least one direct dye or pigment and at least
one optical brightener is used, is claimed as well as the mixture
and the paper dyed with this method.
Inventors: |
Tindal, Alec; (Yorkshire,
GB) |
Correspondence
Address: |
CLARIANT CORPORATION
INTELLECTUAL PROPERTY DEPARTMENT
4000 MONROE ROAD
CHARLOTTE
NC
28205
US
|
Family ID: |
9898605 |
Appl. No.: |
10/363005 |
Filed: |
February 26, 2003 |
PCT Filed: |
August 31, 2001 |
PCT NO: |
PCT/IB01/01608 |
Current U.S.
Class: |
8/532 |
Current CPC
Class: |
D21H 21/28 20130101;
D21H 17/72 20130101; D21H 21/30 20130101 |
Class at
Publication: |
8/532 |
International
Class: |
D06P 003/82 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 1, 2000 |
GB |
0021404.9 |
Claims
1. A process for shading white paper by using a mixture comprising
at least one direct dye or pigment and at least one optical
brightener characterised in that the mixture consists of one or
more direct dyes and one or more optical brighteners in a ratio of
25/75 to 90/10 percent by weight, preferably 50/50 percent by
weight.
2. A process according to claim 1 characterized in that C.I. Direct
Violet 51, C.I. Direct Blue 267, C.I. Direct Violet 35 and/or C.I.
Direct Red 253 are used.
3. A process according to claim 1 characterized in that C.I.
Pigment Violet 23, C.I. Pigment Violet 3 and/or C.I. Pigment Blue
15 are used.
4. Mixture for adding fluorescence to shading dyes for paper
comprising one or more direct dyes and one or more optical
brighteners in a ratio of 25/75 to 90/10 percent per weight.
5. Mixture for adding fluorescence to shading dyes for paper
comprising one or more pigments and one or more optical brighteners
in a ratio of 25/75 to 90/10 percent per weight.
6. A process according to any one of claims 1 to 3 or a composition
according to claim 4 or 5, characterized in that the optical
brightener are Wet-end OBA's, Size-press OBA's and/or Coating
OBA's.
7. A process according to claim 6, characterized in that the
optical brightener C.I. Fluorescent Brightener 220, C.I.
Fluorescent Brightener 28 and/or C.I. Fluorescent Brightener
264.
10. Paper obtained by the process of claim 1 or 2 or 3 or 6 or 7.
Description
[0001] This invention relates to a process for controlling the
Brightness of paper products while using shading dyes.
[0002] In the paper industry Brightness is the technical term used
to describe the reflectance of the paper or pulp at a specific
wavelength, e.g. TAPPI Brightness, ISO Brightness etc.
[0003] There are several definitions for Brightness, Whiteness and
color of paper samples.
[0004] a) CIE Whiteness and CIE Tint
[0005] CIE Whiteness and CIE Tint are calculated from the
chromaticity co-ordinates and the color coordinates. CIE Whiteness
gives an impression of the whiteness of a sample including OBA and
shading dye elements. The tint value is used to describe the
particular shade of white. This gives fairly close correlation with
the human eye and undoubtedly the best method of measuring
whiteness available. In addition the Tint value is useful since two
whites can have the same whiteness but have different shades. CIE
Whiteness and Tint are defined in ISO 11475 as:
1 CIE Whiteness W.sub.10 = Y.sub.10 + 800(x.sub.n .multidot. 10 -
x.sub.10) + 1700(y.sub.n .multidot. 10 - y.sub.10)
[0006]
2 CIE Tint T = 900(x.sub.n .multidot. 10 - x.sub.10) - 650(y.sub.n
.multidot. 10 - y.sub.10)
[0007] b) CIELAB L*, a*, b* Values
[0008] The CIELAB L*, a*, b* values are used to describe color
space, they are the three axis of a three dimensional system of
describing a color. L* represents the difference between black and
white, a* is the red-green co-ordinate and b* is the blue yellow
co-ordinate. They are particularly useful for describing and
controlling the effect of shading dyes in white papers. Another
similar system is L, C, H where C and H represent the Chroma and
the Hue. Whilst the a* and b* value are very useful for describing
and controlling shade, the L* value again does not take into
account shading dyes. When shading dyes are added the L* value is
decreased. It should be noted also that OBA's effect a* and
particularly b* values.
3 CIELAB L*, a*, b* values L* value: Lightness (White-Black
co-ordinate) 0 = perfect black 100 = perfect white a* value
Red-green co-ordinate b* value Yellow-blue co-ordinate
[0009] Note that in today's paper industry, shading dyes are not
only added to achieve a whitening effect, but they are also added
to control the color. Control of the color is often achieved
through the use of a* and b* target values. This can be done
manually, on-line or by on-line closed-loop color control. Violet
and reddish blue dyes are used to improve whiteness, other colors
are used to control the shade of the white paper, for example,
reds, blues and yellows. Black colors are also used in very small
amounts to control the opacity of white papers.
[0010] c) Brightness
[0011] Brightness is a term used in the paper and pulp industry,
which refers to a reflectance factor, usually around 460 nm. It is
defined in ISO 2470 and 3688, though there are other definitions
(e.g. Scandinavian Pulp, Paper & Board testing committee
SCAN-test C11:75 & TAPPI standard test method T452). When small
amounts of shading dye are added to white papers they reduce
Brightness to a greater or lesser extent depending on the dye and
concentration used. This occurs because dyes absorb light and
therefore reduce reflectance. Optical Brighteners increase
Brightness as they are fluorescent and therefore increase the
Brightness value.
[0012] Optical brighteners are colorless to weakly colored organic
compounds that, in solution or applied to a substrate, absorb
ultraviolet light (e.g., from daylight at ca. 300-430 nm) and
re-emit most of the absorbed energy as blue fluorescent light
between ca. 400 and 500 nm.
[0013] In daylight optical brighteners can thus compensate for the
aesthetically undesirable yellowish cast found in white industrial
substrates, such as textiles, papers, or plastics. Furthermore,
since a portion of the daylight spectrum not perceived by the eye
is converted to visible light, the brightness of the material is
enhanced to give a dazzling white.
[0014] The first method of compensating for the yellowish cast was
the use of a blue dye such as ultramarine or indigo. Bluing lowers
the reflectance of the sample in the long-wavelength part of the
visible spectrum. As a result, the sample takes on a neutral white
appearance, which appears more appealing to the eye.
[0015] Optical brighteners lower the reflectance mainly in the UV
and near visible by absorption; at visible wavelengths (mostly with
a maximum at 435-440 nm), they greatly increase the Brightness
through fluorescence. The optical brightener acts as a
supplementary emission source. Optical brighteners are more
effective the cleaner and whiter the substrate is.
[0016] In a typical white paper production process many color
parameters are controlled, those in use include:
[0017] CIE Whiteness
[0018] ISO Brightness
[0019] CIELAB a* value
[0020] CIELAB b* value
[0021] CIELAB L* value
[0022] Fluorescence (usually obtained by measuring Brightness or
Whiteness with UV component and subtracting the value measured
without the UV component in the illuminant)
[0023] The problem for the paper maker is that the two types of
components used to control these parameters are:
4 a) one or more shading dyes b) one or more OBA's
[0024] (Shading dyes are typically added at the wet-end or in
coatings and rarely in the size-press. OBA's are added in the
wet-end, size-press and or coating.) These components have an
effect on each of the measured values, sometimes the desired
addition rate required to adjust a required parameter has a
negative influence on another parameter which must then be
corrected, for example:
[0025] Reddish Violet Shading dye (e.g. C.I. Direct Violet 51, C.I.
Direct Blue 267) or pigment (e.g. C.I. Pigment Violet 23): Used to
adjust a* and b* values, has a negative effect on Brightness and a
positive effect on Whiteness, no effect on fluorescence.
[0026] Bluish/Neutral Violet Shading dye (e.g. C.I. Direct Violet
35) or pigment (e.g. C.I. Pigment Blue 15, C.I. Pigment Violet 3)):
Used to adjust b* value, has a negative effect on Brightness and a
positive effect on Whiteness, little or no effect on a* value, no
effect on fluorescence.
[0027] Red Shading dye (e.g. C.I. Direct Red 253): Used to adjust
a* value, has a negative effect on Brightness and no effect on
Whiteness, little or no effect on b* value,, no effect on
fluorescence.
[0028] OBA (e.g. C.I. Fluorescent Brightener 220, C.I. Fluorescent
Brightener 28, C.I. Fluorescent Brightener 264): Used to increase
Fluorescence and Whiteness and Brightness, also influences a* and
b* values.
[0029] In the case of the production of a high white paper
involving a violet, red or blue shading dye and an OBA added at the
wet-end and possibly another OBA added at the size-press, the
decision making process to adjust the additions to get the right
target parameters for process control can be seen to be very
complicated, especially when an increase or a decrease in the
shading dyes or OBA's must be considered. When any shading dye
dosage is increased the Brightness goes down, therefore the paper
maker must compensate by adding more OBA to regain the Brightness
target, vice-verca when the shading dye dosage is decreased. The
components must often be adjusted together to achieve all of the
target parameters.
[0030] The problem of the decrease of the Brightness* while using
shading dyes is a widely known problem.
[0031] In the state of the art this problem was solved by adding
additional optical brighteners. Until now a typical procedure for
doing it was:
[0032] adding first the solution containing the dyestuff and
afterwards adding the solution containing optical brighteners.
[0033] The color control in a white paper dyeing process is
difficult to obtain. When increasing the concentration of the
shading dye to achieve the correct color, the concentration of the
OBA then has to be increased to obtain the right Brightness, since
the increase in shading dye addition causes a decrease in
Brightness. This complicated and delicate procedure has to be done
either manually or by closed loop color control.
[0034] The goal of the present invention is to provide an easier
method to control the Brightness in paper products while using
shading dyes by using a one step procedure which will help to save
not only time but also reduce the necessary amount of the dyestuff
and the OBA.
[0035] A process for shading white paper is provided, characterized
in, that a mixture comprising at least one direct dye or pigment
and at least one optical brightener is used.
[0036] Preferably the inventive process is characterized in that
the mixture consists of one or more direct dyes and one or more
optical brighteners in a ratio of 25/75 to 90/10 percent by weight,
preferably 50/50 percent by weight.
[0037] Also a part of this invention is a mixture for adding
fluorescence to shading dyes for paper comprising one or more
direct dyes and one or more optical brighteners in a ratio of 25/75
to 90/10 percent per weight.
[0038] The OBA's for the present invention are Wet-end OBA's,
Size-press OBA's and/or Coating OBA's.
[0039] Preferred OBA's are C.I. Fluorescent Brightener 220, C.I.
Fluorescent Brightener 28 and/or C.I. Fluorescent Brightener
264.
[0040] Paper obtained by the inventive process is also a part of
this invention.
[0041] With this method the shading dye dosage can now be adjusted
without affecting the Brightness value and allowing only one
adjustment to be made, to the shading dye, without needing to also
adjust the optical brightening agent dosage to regain
Brightness.
[0042] For this invention all known OBA's for paper can be used.
Preferred optical brighteners are Wet-end OBA's (Leucophor.RTM. AP,
AL, U etc.), Size-press OBA's
[0043] (Leucophor.RTM. U, NS, SHR, TC etc) Coating OBA's
(Leucophor.RTM. U, AP, AL, NS, SHR, TC etc.). Leucophor is a
registered trademark of Clariant.
[0044] The OBA is added to the shading dye in the form of a mixture
so that, when added to the paper the fluorescence of the OBA
compensates for the loss in Brightness due to the absorbance of the
dye and the Brightness of the paper is not reduced by the addition
of the shading dye. Therefore process control is made more simple
as only one component needs to be adjusted to achieve a color
target and the Brightness is not reduced, therefore a compensatory
adjustment of the OBA is not needed.
[0045] An additional benefit is that the amount of the shading dye
used is reduced since the mixture of OBA and shading dye has a
greater effect on the color co-ordinates (a*,b*) than the dye
alone.
[0046] Pigments (e.g. C.I. Pigment Violet 23, C.I. Pigment Blue 15,
C.I. Pigment Violet 3) are also used in the shading of white papers
(for example in coatings).
[0047] Shading dyes and OBA's are also used in size-press and
coating applications as well as wet-end applications.
[0048] The following example illustrates the present invention.
EXAMPLE 1
[0049] A standard preparation of paper stock consisting of 50%
bleached softwood pulp and 50% bleached pulp are prepared at
20.degree. Schopper Riegler, 20% CaCO.sub.3 are added (ash by
weight of dry fiber). Handsheets are prepared from the above stock
containing various amounts of a 1:1 mixture of a liquid anionic
direct paper dye (containing 13% C.I. Direct Violet 35) and a
mixture of a liquid optical brightening agent (containing 25%
C.I.F. Br. 290) and, as a control a 50% dilution of the same liquid
paper dye (C.I. direct Violet 35). A sizing agent is added (1.7%
Aquapel.RTM. 360X) and a retention aid is used to retain the chalk
filler (0.003% Cartaretin.RTM. 20CE). The following additions are
made of the dye and the dye/optical brightening agent-mixture, by
weight of liquid product on dry fiber:
[0050] 0.0%, 0.001%, 0.003%, 0.006% and 0.100%.
[0051] Afterwards the hand-sheets are pressed and dried. The
following table shows the results of the measurements, made on a
Minolta CM-3700d Spectrometer, with the UV component included.
5 CIE Sample Whiteness Brightness a* b* 0.0% (Blank) 71.7 85.7 0.1
4.4 0.001% (Dye only) 74.0 86.0 0.0 3.7 0.001% (50% dye/50% Optical
74.3 86.0 0.0 3.6 brightener agent) 0.003% (Dye only) 76.4 85.8 0.1
2.8 0.003% (50% dye/50% Optical 77.4 86.0 0.1 2.6 brightener agent)
0.006% (Dye only) 79.4 85.4 0.1 1.7 0.006% (50% dye/50% Optical
83.1 86.3 0.2 0.9 brightener agent) 0.100% (Dye only) 114.9 79.4
2.2 -9.7 0.100% (50% dye/50% Optical 134.1 84.5 3.6 -13.7
brightener agent)
* * * * *