BRPI0621286A2 - process to produce optically brightened paper - Google Patents

Abstract

PROCESS TO PRODUCE OPTICALLY SHINY PAPER. The present invention relates to a process for the production of optically brightened paper by treating the pulp suspension with an optically brightened filler composition comprising optically brightened plastic fibers, preferably polyester fibers, which leads to surprisingly high light fixation resulting paper.

Description

Report of the Invention Patent for "PROCESS FOR PRODUCING OPTICALLY OPENED PAPER".

The present invention relates to a process for producing optically brightened paper by treating the pulp suspension with an optically brightened filler composition.

High gloss is a desirable property of paper and cardboard articles. The most important raw material in the papermaking industry is pulp, which naturally absorbs blue light and is therefore yellow in color and gives the paper a dull appearance. Optical brighteners are used in the papermaking industry to compensate for the absorption of blue light by absorbing UV light with a maximum wavelength of 350-380 nm and converting it to visible blue light with a maximum wavelength of 440 nm. .

Triazinylamino stilbene-type optical brighteners have been used almost exclusively to brighten paper by application to the pulp or surface of the paper. However, it is well known that light fixation of such brighteners is no better than weak to moderate, or from 1 to about 3 on the "Blue Wool Scale". (See "Optische Aufheller - Neuer Erkenntnisse zu Eigenschaften und Verhalten im Papier" by F. Müller, D. Loewe and B. Hunke in Wochenblatt f Papierfabrikation 1991, 6, pages 191-203.). There is therefore a need to protect optimally brightened papers from yellowing by light.

In order to provide high light fixation optically brightened papers, it is generally recognized that brighteners other than those of the triazinylamino stilbene type should be used; in particular, brighteners typically used for optical brightening of textiles, such as those of benzoxazole, naphthalimide, triazolylcoumarin, or triazinylpyrene types. Such brighteners are, however, typically much more expensive, and can only be applied with difficulty to either the pulp or the paper surface.

EP-A-801 700 overcomes some of these problems by describing the use of optically brightened polyacrylonitrile powder to prepare white paper coating strips. Preferred optical brighteners are those typically used to provide high light fixation on textiles, for example triazolylcoumarin or benzoxazole. Papers prepared using such coating strips show excellent brightening effects with high light fixation. However, there is no suggestion that this approach could be used to prepare papers optically brightened by a more economical pulp application.

Therefore, the economical use of textile brighteners to prepare optically brightened papers is a difficult problem for which a satisfactory solution has not yet been found.

Surprisingly, it has now been found that by treating a pulp suspension with a filler composition comprising finely divided optically brightened plastic fibers, an optically brightened high light fixation paper is obtained in an economical manner.

Therefore, an object of the present invention relates to a process for optical brightening of paper, wherein a filler composition comprising optically brightened plastic fibers is added to the pulp suspension.

Said fibers may be made of polyester, polyethylene, polypropylene or polyamide. More preferably, the fibers are made of polyester.

The fibers have a fineness between 1 and 10 dtex and are cut to a length between 0.1 and 1 mm, preferably they have a fineness between 1 and 2 dtex and a length between 0.2 and 0.6 mm.

The preparation of polyester fibers is well known and is described, for example, in the "Handbook of Fiber Chemistry" by Menachem Lewin, published in 1998 by Mareei Dekker, page 18.

The production of optically brightened polyester is also well known and is described, for example, in GB 835,898 and EP-A-1 379 5885.

For the purpose of the present invention, the fibers are preferably optically brightened with compounds of formulas (1) to (4) <formula> formula see original document page 4 </formula>

wherein in formula (1) R1 to R8 are independently hydrogen, C1-C20-alkyl or groups of formula -COOR9, where R9 is hydrogen, C1-C20-alkyl or phenyl, or R1 to R8 are a group of the formula -SO 2 R 10. wherein R10 is hydrogen, C1-C10-alkyl or C1-C10-hyroxyalkyl, and A is stilbene, naphthalene, phenylene, thiophenylene or biphenylene, or mixtures of said compounds.

More preferred optical brighteners are compounds of formula (1), wherein R 1 to R 8 are independently hydrogen or C 1 -C 4 alkyl, and A is stilbene, naphthalene, phenylene, thiophenylene or biphenylene.

Most preferred optical brighteners are compounds of formula (1), wherein R1-R8 are independently hydrogen or methyl, and A is stilbene.

The optically brightened plastic fiber contains between 10 and 500 ppm optical brightener, preferably between 20 and 250 ppm.

The pulp can be any conventional pulp for producing paper, for example, stone crushed wood pulp, thermomechanical pulp, chemothermomechanical pulp, semi-chemical pulp, sulfite pulp or kraft pulp, or a mixture thereof.

In general, the pulp suspension is treated with 2 to 60%, preferably 10 to 40% by weight, based on the weight of the dried pulp of the present filler composition.

The filler composition may be added to the pulp suspension in either dried form or preferably as an aqueous dispersion. It may be useful to add a dispersing agent, particularly suitable dispersing agents which are of the type described in EP-A-964 015. Finally, the paper is formed onto a wire mesh of a conventional pressed and dried paper machine.

The present invention provides an optically brightened paper produced in accordance with the present process and which comprises 2 to 60%, preferably 10 to 40% by weight, based on the dry pulp weight of the filler composition of the present invention. .

Optically brightened paper may also contain other additives commonly employed in the papermaking industry, examples of such additives include sizing agents (eg rosin, starch, alkyl ketene dimer, alkenyl succinic anhydride), moisture resistant resins (e.g. polyaminoamide-epichlorohydrin resins), retention and drainage aids (eg poly (aluminum chloride), poly (diallyl dimethyl ammonium chloride), and tinting pigments.

The following example further serves to illustrate the invention. All parts and percentages are by weight unless otherwise indicated. EXAMPLE

Five parts of 1,7 dtex fineness polyester fibers, made by known methods, containing 0,014% of a mixture of optical brighteners of 5a-c structure in an approximate ratio of 30:50:20 and cut 0.5 mm parts are stirred with 0.025 parts dispersant (Cartaspers® PSM1 commercially available from Clariant) and 1,000 parts water for 5 minutes to form a 0.5% dispersion of optically spun fibers.

<formula> formula see original document page 6 </formula>

χ parts of the 0.5% dispersion of optically brightened fibers are then added to (1,000-x) parts of a 0.5% aqueous suspension of a 50:50 mixture of birch wood pulp and spruce up to a Schopper-Riegler degree (release) of 35 °. A sheet of paper is then made by dragging the dispersed suspension through a wire mesh. After being pressed and dried, the optically brightened paper contains between 5% (x = 50) and 30% (x = 300) of optically brightened polyester fibers, equivalent to an optical brightener content of between 7 ppm and 42 ppm.

Each sheet of paper is measured to an R457 brightness on a calibrated Minolta 3270D spectrophotometer.

Accelerated aging experiments are conducted by exposing the papers to a Xenotest device. R457 brightness measurements are made at 70, 140 and 280 hour intervals. Results are shown in tabular (Table 1) and graphical (Figure 1) forms. Table 1

<table> table see original document page 7 </column> </row> <table>

(Brightness R457; Exposure time in hours)

Figure 1: Effect of light exposure for 280 hours on R457 Brightness of papers containing 5-30% optically brightened polyester fibers.

It is clear from the results that the present invention provides a high light fixation optically brightened paper, with the added advantage that a surprisingly low concentration (7-42 ppm) of optical brightener is required to achieve a high degree of brightness.

COMPARATIVE EXAMPLES

Comparative example 1: Brightened Polyester Fibers

A sheet of paper is made as in the example, containing 25% (x = 250) of optically brightened polyester fibers. Comparative example 2: Unpolished pulp

A sheet of paper is made as in the example but without the addition of optically brightened polyester fibers. Comparative Example 3: Unpolished Polyester Fibers

A sheet of paper is made as in the example but containing 25% (x = 250) unbleached polyester fibers in place of the optically brightened polyester fibers.

Comparative Example 4: Non-Brightened Polyester Fibers and Optical Brightener (5a-c)

A sheet of paper is made as in the example but containing 25% (x = 250) unpolished polyester fibers and - separately added to 1,000 parts aqueous suspension to the 5% fibers - 0.000175 part one optical structure brighteners (5a c) in a ratio of approximately 30:50:20, all in place of optically brightened polyester fibers.

Comparative Example 5: Unpolished Polyester Fibers and Optical Brightener (6)

<formula> formula see original document page 8 </formula>

A sheet of paper is made as in the example but containing 25% (x = 250) unpolished polyester fibers and - separately added to 1,000 parts of a 0.5% aqueous fiber suspension - 0.004 parts of a optical brightener of structure (6), all in place of optically brightened polyester fibers.

Accelerated aging experiments are conducted as in the example. The results are shown below in tabular (table 2) and graphical (figure 2) form.

Table 2

<formula> formula see original document page 8 </formula> <table> table see original document page 9 </column> </row> <table>

(Brightness R457; Exposure time in hours; Comparative Example 1)

Figure 2: Effect of light exposure for 280 hours on R457 paper brightness.

Comparative examples demonstrate the advantage of the invention in providing a white paper with excellent light fixation.

It is clear that the addition of optically brightened polyester fibers (Comparative example 1) provides a much whiter paper than the addition of unbleached polyester fibers (Comparative example 3). It is also clear that the optical brightener should be incorporated into the polyester fiber rather than added separately (example 4). Whereas the separate addition of a triazinylamino stilbene type optical brightener (6) provides a particularly white paper whose fixation to light is poor (Comparative Example 5).

Claims (14)

1. Optical brightening paper process, wherein a filler composition comprising optically brightened plastic fibers is added to the pulp suspension. A process according to claim 1 wherein the fibers are made of polyester, polyethylene, polypropylene or polyamide. A process according to claim 2, wherein the fibers are made of polyester. Process according to claim 3, wherein the fibers have a fineness between T and 10 dtex and are cut to a length of between 0.1 and 1 mm. Process according to claim 4, wherein the fibers have a fineness between 1 and 2 dtex and are cut to a length between 0.2 and 0.6 mm. A process according to any preceding claim wherein the fibers are optically brightened with compounds of formulas (1) to (4) <formula> formula see oR1ginal document page 11 </formula> and wherein formula (1) R 1 to R 8 are independently from each other hydrogen, C 1 -C 20 alkyl or groups of the formula -COORg, R 9 is hydrogen, C 1 -C 20 alkyl or phenyl, or R 1 to R 8 are a group of the formula -SO 2 R 10. wherein R10 is hydrogen, C1-C10-alkyl or C1-C10-hydroxyalkyl, and A is stilbene, naphthalene, phenylene, thiophenylene or biphenylene, or mixtures of said compounds. A process according to claim 6 wherein the fibers are optically enhanced with a compound of formula (1) wherein R 1 to R 8 are independently hydrogen or C 1 -C 4 alkyl, and A is stilbene, naphthalene, phenylene, thiophenylene or biphenylene. A process according to claim 7 wherein Rr R6 are independently one of gold, hydrogen or methyl, and A is stilbene. A process according to any one of claims 2 to 8, wherein the optically brightened plastic fibers contain between 10 and -500 ppm optical brightener. Process according to claim 9, wherein the optically brightened plastic fibers contain between 20 and 250 ppm optical brightener. A process according to any preceding claim wherein 2 to 60% by weight, based on the weight of the dried pulp, of the optically brightened filler composition is added to the pulp suspension. A process according to claim 11 wherein 10 to -40% by weight based on the weight of the dried pulp of the optically brightened filler composition is added to the pulp suspension. A process according to claim 11 or 12, wherein the optically brightened filler composition is added to the pulp suspension as an aqueous dispersion. Optically brightened paper produced by a process as defined in any one of the preceding claims.