Fluorescent Whitening Pigments

Abstract

A whitening pigment comprising the reaction product of (a) a melamine-formaldehyde and/or a melamine-urea poly-condensation product and (b) a water-soluble fluorescent whitening agent of the formula (1), wherein each of the two R1 groups, independent of the other, represents a C1-C6alkyl or C1-C4alkyl-O—C1-C4alkyl residue, which is substituted by one or two —CONH2, —CONHC1-C4alkyl, —COOH, —SO2NH2, —SO2NHC1-C4alkyl or —NH2 groups, each of the two R2 groups, independent of the other, represents hydrogen, C1-C4alkyl, C2-C4hydroxyalkyl or C1-C4alkoxyC1-C4alkyl, or R1 and R2 together with the nitrogen atom complete a piperazine ring, each of the two X1 groups, independently, represent —OH, —OC1-C4alkyl, —Oaryl or the group —NR3R4, wherein R3 and R4 each, independently, represent hydrogen, C1-C4alkyl, C2-C4hydroxyalky, C1-C4alkoxyC1-C4alkyl, a phenyl, phenyl mono- or disulphonic acid residue or, R3 and R4, together with the nitrogen atom to which they are attached, complete a morpholino, piperidino or pyrrolidino ring or, alternatively, X1 represents an amino acid residue from which a hydrogen atom has been abstracted from the amino group and M is hydrogen, an alkaline or alkaline earth metal ion, ammonium, mono- di-, tri- or tetra-substituted C1-C4alkylammonium or C2-C4hydroxyalkylammonium or mixtures thereof, a process for preparation of the pigments and the use thereof for the fluorescent whitening of paper.

Description

EXAMPLE 1

To a stirred solution of 252 g of a 59.7% aqueous pentamethylol-melamine (LYOFIX™ CHN) and 7.5 g of the compound of formula

in 900 ml of water, 37% aqueous hydrochloric acid is added to adjust the pH to 3.9. The solution is heated to 70° C., the pH adjusted to 2.0 by the addition of further 37% aqueous hydrochloric acid and stirred at this temperature for 4 hours. After cooling to room temperature, the pH is adjusted to 9.5-10 by addition of 32% aqueous sodium hydroxide solution, the precipitated solids filtered, washed with water and dried under vacuum at 80° C. There are obtained 89 g of a white pigment incorporating 8% of the fluorescent whitening agent of formula (101).

EXAMPLE 2

By reaction of 335 g of a 59.7% aqueous pentamethylol-melamine (LYOFIX™ CHN) with 5.0 g of the compound of formula (101), as described in Example 1, there are obtained 119 g of a white pigment incorporating 4% of the fluorescent whitening agent of formula (101).

EXAMPLE 3

By reaction of 76.4 g of a 59.7% aqueous pentamethylol-melamine (LYOFIX™ CHN) with 4.58 g of the compound of formula (102)

as described in Example 1, there are obtained 27.7 g of a white pigment incorporating 16% of the fluorescent whitening agent of formula (102).

EXAMPLE 4

By reaction of 100 g of a 59.7% aqueous pentamethylol-melamine (LYOFIX™ CHN) with 11.9 g of the compound of formula (102), as described in Example 1, there are obtained 40.2 g of a white pigment incorporating 28% of the fluorescent whitening agent of formula (102).

EXAMPLE 5

By reaction of 168 g of a 59.7% aqueous pentamethylol-melamine (LYOFIX™ CHN) with 7.0 g of the compound of formula (103)

as described in Example 1, there are obtained 61 g of a white pigment incorporating 11% of the fluorescent whitening agent of formula (103).

EXAMPLE 6

By reaction of 100 g of a 59.7% aqueous pentamethylol-melamine (LYOFIX™ CHN) with 3.0 g of the compound of formula (103), as described in Example 1, there are obtained 57 g of a white pigment incorporating 5% of the fluorescent whitening agent of formula (103).

EXAMPLE 7

By reaction of 268.8 g of a 59.7% aqueous pentamethylol-melamine (LYOFIX™ CHN) with 32.0 g of the compound of formula (103), as described in Example 1, there are obtained 117 g of a white pigment incorporating 24% of the fluorescent whitening agent of formula (103).

EXAMPLE 8

By reaction of 168 g of a 59.7% aqueous pentamethylol-melamine (LYOFIX™ CHN) with 10.0 g of the compound of formula (104)

as described in Example 1, there are obtained 63.7 g of a white pigment incorporating 16% of the fluorescent whitening agent of formula (104).

B. Application Examples

1). Preparation of Dispersions

6.0 g of each of the dried pigments, obtained as described in the above Examples 1-8, are added to 21.5 g of deionised water containing 2.5 g of dispersing agent (Pluronic™ F 108) and wet milled using 50 g of glass beads of 2 mm in diameter for a period of 15 hours. Following the milling process, the dispersions are separated from the glass beads by filtration through a coarse wire filter.

2). Preparation of Coating Mixture

To a coating colour having a solids content of 60% and consisting of 100 parts of a mixture of 60% calcium carbonate and 40% clay, 0.2 parts of polyvinyl alcohol and 9 parts of SBR binder followed by 4 parts of the whitening pigments obtained as described in Examples 1-8 and dispersed as described under Pt 1) above, based on the total weight of the coating pigment, are added. After stirring for 15 minutes to homogenize the coating colour, a base paper free of fluorescent whitening agent is coated using a laboratory drawdown coater with a coating speed of 5 m/min. such that a coat weight of approximately 28 g/m² results.

After drying, the ISO-fluorescence and CIE Whiteness values are measured by means of a Datacolor Elrepho 3000 spectrophotometer and the results are summarized in Table 1 below:

TABLE 1
	Percentage	Pigment		CIE
Example Nr.	FWA1	Example	Fluorescence	Whiteness
	None		0	75
9	8	1	10.9	110
10	4	2	8.3	103
11	16	3	13.1	114
12	28	4	13.8	115
13	11	5	11.9	112
14	5	6	8.1	102
15	24	7	14.0	115
16	16	8	12.6	114
1Percentage of fluorescent whitening agent incorporated into whitener pigment of the respective Examples.

In a further series of experiments, coating compositions containing sufficient of the appropriate pigments of the invention to provide 0.075, 0.15 and 0.3 parts of the fluorescent whitening agents incorporated into the pigments, based on the total weight of inorganic pigment, were prepared and coated as described above.

The resulting ISO fluorescence and CIE Whiteness values are summarized in Table 2 below:

TABLE 2
		Pigment		CIE
Example Nr.	Parts FWA1	Example	Fluorescence	Whiteness
	None		0	75
17	0.075	1	5.4	93
18	0.15	1	7.4	100
19	0.3	1	10.6	109
20	0.075	2	5.3	94
21	0.15	2	8.0	102
22	0.3	2	11.3	112
23	0.075	3	3.8	86
24	0.15	3	6.4	94
25	0.3	3	9.4	103
26	0.075	5	4.6	90
27	0.15	5	6.4	96
28	0.3	5	9.6	105
1parts of the fluorescent whitening agents incorporated into the pigments, based on the total weight of inorganic pigment

The results summarized in the above Tables 1 and 2 clearly demonstrate both the excellent whitening effects of the fluorescent pigments of the invention and also their build-up characteristics, whereby no undesirable greening tendency is observed with increasing concentrations of fluorescent whitening agents.

Claims

1. A whitening pigment comprising the reaction product of (a) a melamine-formaldehyde and/or a melamine-urea polycondensation product and(b) a water-soluble fluorescent whitening agent of the formula

2. A whitening pigment according to claim 1, wherein the component (a) is a melamine-formaldehyde polycondensation product.

3. A whitening pigment according to claim 1, wherein, in the compound of formula (1), each of the two R1 groups, each of the two R2 groups and each of the two X1 groups are the same.

4. A whitening pigment according to claim 1, wherein, in the compound of formula (1), R1 represents a C1-C4alkyl residue which is substituted by one —CONH2 or —CONHC1-C4alkyl group.

5. A whitening pigment according to claim 1, wherein, in the compound of formula (1), R2 represents hydrogen, C1-C4alkyl or C2-C4hydroxyalkyl.

6. A whitening pigment according to claim 1, wherein, in the compound of formula (1), X1 represents the group —NR3R4, whereinR3 represents hydrogen, C1-C4alkyl, C2-C4hydroxyalky, C1-C4alkoxyC1-C4alkyl, a phenyl, phenyl mono- or disulphonic acid residue,R4 represents hydrogen C1-C4alkyl or C2-C4hydroxyalkyl or,R3 and R4, together with the nitrogen atom to which they are attached, complete a morpholino ring or, alternatively,X1 represents an amino acid residue from which a nitrogen atom has been abstracted from the amino group.

7. A whitening pigment according to claim 1, wherein, in the compound of formula (1), M represents hydrogen, sodium or potassium.

8. A process for the preparation of whitening pigment according to claim 1, whereby a melamine-formaldehyde or melamine-urea polycondensation product is reacted with a fluorescent whitening agent of formula (1) in aqueous medium, in the presence of mineral acid, and subsequently treated with base.

9. A method for the fluorescent whitening of paper which comprises applying to paper an effective whitening amount of a whitening pigment according to claim 1.

10. A paper coating composition comprising, in addition to 0.01 to 10 parts by weight of the whitening pigment according to claim 1, per 100 parts of inorganic pigment, (i) from 3 to 25 parts by weight of binder and co-binder,(ii) 0 to 1 part by weight of rheology modifier and(iii) 0 to 2 parts by weight of wet-strength agent.

11. A method for the fluorescent whitening of paper which comprises applying to paper an effective whitening amount of a paper coating composition according to claim 10.

12. Paper which has been treated with a whitening pigment composition according to claim 1.

13. Paper which has been treated with a coating composition according to claim 10.