Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2002-02-01
2004-09-28
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S593000, C524S594000
Reexamination Certificate
active
06797752
ABSTRACT:
The present invention relates to the use of whitening pigments for whitening paper coating compositions.
Aqueous coating compositions are used extensively in the production of coated papers and cardboards. For the purpose of whitening, the coating compositions generally comprise anionic fluorescent whitening agents, the action of which is highly dependent on the amount and nature of co-binders used. The use of cationic coating compositions, for example for ink-jet papers, results in a loss of effect, for example poor fastness to light, bleeding in food packaging and a deterioration in printability. Similar problems can also occur in the case of pulp or size press applications.
It has now been found, surprisingly, that certain whitening pigments that comprise melamine-formaldehyde resin and a water-soluble fluorescent whitening agent significantly improve the properties of the coating compositions.
The present invention accordingly relates to the use of whitening pigments comprising
(a) a melamine-formaldehyde or phenol-formaldehyde polycondensation product and
(b) a water-soluble fluorescent whitening agent, for whitening paper coating compositions.
Condensation products of melamine and formaldehyde, also referred to as melamine-formaldehyde (MF) resins, are aminoplastic resins.
The said condensation products are prepared by acid- or base-catalysed reaction of melamine in a methylolation reaction with aqueous formaldehyde solutions to form N-methylol compounds. On extending the reaction time or increasing the temperature, the methylol groups then react with further melamine, forming methylene bridges or—when metnylol groups react with one another—methylol ether bridges.
The reaction is usually halted at the stage where preliminary condensation products, which are still soluble or meltable, are present, in order for fillers to be added i desired. To improve the solubility of those preliminary condensation products, some of the methylol groups still remaining may, in addition, be etherified.
The substance from that initial stage may also be formulated as an aqueous solution in which the fluorescent whitening agent can then be incorporated.
Etheritication of the N-methylol compounds may also be carried out, after azeotropically distilling off the water with alcohols or by spray-drying, by etherifying the practically water-free methylol-melamines with lower alcohols, with the addition of acid or alkaline catalysts, neutralising after etherification and, where appropriate, distilling off the excess alcohol.
In a further embodiment, polycondensation of the formaldehyde with the aminoplast-former melamine or phenol is carried out in the presence of the fluorescent whitening agent.
Fluorescent whitening agents corresponding to component (b) that are suitable for use according to the invention correspond to formula
wherein
R
1
and R
2
are each independently of the other —OH, —Cl, —NH
2
, —O—C
1
—C
4
alkyl, —O-aryl, —NH—C
1
—C
4
alkyl, —N(C
1
—C
4
alkyl)
2
, —N(C
1
—C
4
alkyl)(C
1
—C
4
hydroxyalkyl), —N(C
1
—C
4
hydroxyalkyl)
2
or —NH—aryl, for example anilino, aniline-mono- or -di-sulfonic acid or an anilinesulfon-amide, morpholino, —S—C
0
—C
4
alkyl(aryl), or a radical of an amino acid, for example aspartic acid or iminoacetic acid, which radical is substituted at the amino group, and
M is hydrogen; sodium; potassium; calcium; magnesium; ammonium; mono-, di-, tri- or tetra-C
1
—C4alkylammonium; mono-, di- or tri-C
1
—C4hydroxyalkylammonium; or ammonium di- or tri-substituted by a mixture of C
1
—C
4
alkyl and C
1
—C
4
hydroxyalkyl groups
Especially suitable fluorescent whitening agents of formula (1) are those wherein the group R
1
is an anilino radical, more especially those wherein the group R
2
is NH—C
1
—C
4
alkyl, —N(C
1
—C4alkyl)2, —N(C
1
—C
4
alkyl) (C
1
—C
4
hydroxyalkyl), —N(C
1
—C
4
hydroxyalkyl)
2
, morpholino, or a radical of an amino acid, for example aspartic acid or iminoacetic acid, which radical is substituted at the amino group, and
M is hydrogen; sodium or potassium.
C
1
—C
4
alkyl radicals are branched or unbranched and are, for example, methyl, ethyl, propyl, isopropyl or n-butyl; they may be unsubstituted or substituted by halogen, for example fluorine, chlorine or bromine, C
1
—C
4
alkoxy, for example methoxy or ethoxy, phenyl or carboxyl, C
1
—C
4
alkoxycarbonyl, for example acetyl, mono- or di-(C
1
—C
4
alkyl)amino or by —SO
3
M.
The compounds of formula (1) are used preferably in neutral form, that is to say: M is preferably a cation of an alkali metal, especially sodium.
The fluorescent whitening agents corresponding to component (b) are present in the whitening pigment for use according to the invention in an amount of from 0.05 to 10% by weight, preferably from 0.1 to 5% by weight.
The whitening pigments used in accordance with the invention may also comprise, in addition to the melamine-formaldehyde or phenol-formaldehyde resin, further copolymers (component (c)) with, for example, aromatic sulfonamides, cyanuric acids, urea, cyclised ureas, for example ethylene urea, or glyoxalic acid.
Preferably, the whitening pigments used in accordance with the invention additionally comprise a copolymer with an aromatic sulfonamide.
Preferably, a melamine-formaldehyde polycondensaton product is used as component (a).
The whitening pigments for use according to the invention are prepared in various ways.
In one process variant, they can be prepared in a melting process, the procedure for which is as follows:
The aromatic sulfonamide is melted in a suitable reaction vessel. The formaldehyde is then added slowly to the molten sulfonamide. A low-melting resin forms. When that reaction is complete, this resin is allowed to react further with the melamine. Cocondensation occurs, a resin having a relatively high melting point of from 115 to 135° C. being formed. At the end of the reaction the fluorescent whitening agent is added to the reaction mixture. The resinous reaction mixture is dispensed in droplets at a temperature of from 150 to 175° C. into a suitable storage container and is left to cool.
The glassy resin material is then comminuted, using a suitable appliance, into pieces about 3 mm in size. The resulting material is then introduced into a suitable grinding apparatus, for example a ball, hammer or vibration mill, in which the resin is ground to a size of from 5 to 6 &mgr;m.
In a further variant, the whitening pigments can be prepared in a water-based process, the procedure for which is as follows:
The whitening pigment used in accordance with the invention can be prepared by mixing components (a) and (b), preferably in the presence of a solvent especially water. Component (a) is preferably used in the form of a preliminary condensation product or a low-molecular-weight N-methylol derivative. After mixing, the solvent can optionally be removed.
The pigments are then dried, ground and optionally re-dispersed in aqueous media for further use.
The whitening pigments used in accordance with the invention preferably comprise
(a) from 75 to 99% by weight, preferably from 85 to 95% by weight, of a melamine-formaldehyde or phenol-formaldehyde polycondensation product,
(b) from 0.05 to 5% by weight, preferably from 0.1 to 5% by weight, of a water-soluble fluorescent whitening agent, and
(c) from 0 to 20% by weight, preferably from 5 to 10% by weight, of an aromatic sulfonamide.
The finely particulate whitened whitening pigments can, after dry-grinding, be incorporated in powder form directly in the paper coating composition, the particle size being from 0.05 to 40 &mgr;m, preferably from 0.3 to 10&mgr;m and especially from 0.5 to 5 &mgr;m.
In most instances, however, it will probably be more convenient to disperse the finely particulate whitening pigments in an aqueous phase and to incorporate the resulting aqueous dispersion in the paper coating compositions.
The amount of whitening pigments for use according to the invention employed in the paper coating composition depends on the desired whitening effect it is usually from 0.01 to 5% by weight of pure active su
Ciba Specialty Chemicals Corporation
Lipman Bernard
Mansfield Kevin T.
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