Patent Application
20080135805
The present invention relates to novel fluorescent pigments obtained by treatment of a melamine-formaldehyde and/or melamine-urea polycondensate with a distyryl biphenyl fluorescent whitening agent (FWA) and, optionally, at least one additional FWA, a process for preparation of the whitening pigments and their use for the fluorescent whitening of paper, especially in coating.
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 such anionic fluorescent whitening agents in cationic coating compositions, for example for ink-jet papers, results in a loss of primary effect and poor fastness to light. Bleeding can also be a problem for water-soluble fluorescent whitening agents, particularly in paper and board intended for use in food packaging.
One approach to solving such problems has been disclosed in WO 01/11140 A1, whereby mechanical mixtures of melamine-formaldehyde or phenol-formaldehyde polycondensation products together with water-soluble fluorescent whitening agents are used as whitening pigments for coating compositions. However, such mixtures suffer from the disadvantage that only minor quantities of fluorescent whitening agents are incorporated into large amounts of the polycondensate, thus leading to difficulties in dosage and resulting in large quantities of the polycondensate being present in the coating composition, which may be undesirable.
Surprisingly, it has now been found that coating compositions possessing superior properties, especially with regard to light fastness, bleed fastness and also whitening effect, result by the incorporation of a whitening pigment resulting from treatment of a melamine-formaldehyde polycondensate with a distyryl biphenyl fluorescent whitening agent and, optionally, at least one additional FWA, since the fluorescent whitener is protected from environmental influences.
Accordingly, the present invention relates to a fluorescent pigment comprising
Polycondensation products of melamine and formaldehyde, component a) of the composition, 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 methylol 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 if desired. To improve the solubility of those preliminary condensation products, some of the methylol groups still remaining may, in addition, be etherified.
Etherification of the N-methylol compounds may also be carried out after azeotropically distilling off the water with alcohols or glycols, or by spray-drying, by etherifying the practically water-free methylol-melamines with lower alcohols or glycols, with the addition of acid or alkaline catalysts, neutralising after etherification and, where appropriate, distilling off the excess alcohol or glycol.
Most preferred resins are tri- or penta-methylolmelamines which may be etherified with, for example, methanol or methanol/diethylene glycol mixtures.
Preferred distyryl biphenyl fluorescent whitening agents, component b) of the composition, are those selected from the compounds of formulae
in which
M′ represents hydrogen, lithium, potassium or sodium, whereby the 2,2′-disulphonic acid derivatives of formula (2) are most preferred.
Where a further FWA, component c) of the composition, is present, this may be selected from a wide range of known compounds. Thus, for example, the additional fluorescent whitening agent, component c), is preferably selected from the compounds of formulae (6) to (18), i.e. a bis-triazinylamino stilbene of the formula
in which
in which
R6 and R7 each, independently, represent hydrogen, C1-C4alkyl, phenyl or a phenyl sulphonic acid residue and
M is as previously defined;
a 4,4′-distyryl-biphenyl or 4,4′-distyryl-phenyl fluorescent whitening agent of the formula
in which
in which
in which
R12 and R13, independently, are hydrogen, C1-C4alkyl, —Cl or —SO3M and
M is as previously defined;
a stilbenzyl-naphthotriazole of the formula
in which
R14 is hydrogen or chlorine,
R15 is —SO3M, —SO2N(C1-C4alkyl)2, —SO2O-phenyl or —CN,
R16 is hydrogen or —SO3M and
M is as previously defined;
a bis-(benzoxazol-2-yl) derivative of the formula
in which each of
a bis-(benzimidazol-2-yl) derivative of the formula
in which each
R19, independently, represents hydrogen, C1-C4alkyl or —CH2CH2OH,
R20 is hydrogen or —SO3M,
X1 is —CH═CH— or a 2,5-furanyl residue and
M is as previously defined;
a coumarin derivative of the formula
in which
R21 is hydrogen, C1-C4alkyl, chlorine or —CH2CO2H,
R22 is hydrogen, phenyl, —CO2C1-C4alkyl or a group of the formula
in which
An− is an anion of an organic or inorganic acid or a mixture thereof,
R23 is —OC1-C4alkyl, —N(C1-C4alkyl)2, —NHCOC1-C4alkyl or a group of the formula
in which each
R24 and R25, independently, represent phenyl, mono- or disulphonated phenyl, phenylamino, mono- or disulphonated phenylamino, morpholino, —N(CH2CH2OH), —N(CH3)(CH2CH2OH), —NH2, —N(C1-C4alkyl)2, —OCH3, —Cl, —NHCH2CH2SO3H or —NHCH2CH2OH,
R27 is hydrogen, C1-C4alkyl or phenyl, and each
R28 and R29, independently, represent hydrogen, C1-C4alkyl, phenyl or monosulphonated phenyl;
a pyrazoline derivative of the formula
in which
in which
in which
R38 is C1-C4alkoxy, each
R39 and R40, independently, is C1-C4alkyl or benzyl and
An− is an anion of an organic or inorganic acid;
a 2-styrylbenzoxazole or 2-styrylnaphthoxazole of the formula
in which
R41 is —CN, chlorine, —CO2C1-C4alkyl or phenyl,
R42 and R43 are the atoms required to form a fused benzene ring or each
R43 and R45, independently, are hydrogen or C1-C4alkyl and
R44 is hydrogen, C1-C4alkyl or phenyl and
a fluorescent whitening agent that is a pyrenyl-1,3,5-triazine, in addition to
mixtures of such fluorescent whitening agents.
Of the compounds of classes (6) to (18), most suitable for use as component c) of the composition are those bis-triazinylaminostilbene disulphonic acids of the formula (6) in which R2 and R4 are identical and R3 and R5 are identical and are each independently represent —NH2, —NHC1-C4alkyl, —N(C1-C4alkyl)2, —N(C1-C4alkyl)(C2-C4hydroxyalkyl), —N(C2-C4 hydroxyalkyl)2, —NHaryl, in which aryl is unsubstituted phenyl or phenyl which is substituted by one or two —SO3M groups, a morpholino residue or an amino acid or amide residue from which a hydrogen atom has been abstracted from the amino group.
Preferred amino acid or amino acid amide residue from which a hydrogen atom has been removed are those derived from glycine, alanine, serine, cysteine, phenylalanine, tyrosine (4-hydroxyphenylalanine), diiodotyrosine, tryptophan (β-indolylalanine), histidine ((β-imidazolylalanine), α-aminobutyric acid, methionine, valine (α-aminoisovaleric acid), norvaline, leucine (α-aminoisocaproic acid), isoleucine (α-amino-β-methylvaleric acid), norleucine (α-amino-n-caproic acid), arginine, ornithine (α,δ-diaminovaleric acid), lysine (α,ε-diaminocaproic acid), aspartic acid (aminosuccinic acid), glutamic acid (α-aminoglutaric acid), threonine, hydroxyglutamic acid and taurine, as well as mixtures and optical isomers thereof, glycine and aspartic acid being especially preferred.
A further preferred example of an amino acid from which an amino acid residue may be derived is iminodiacetic acid or the mono- or diacid amide thereof, whilst a suitable amino acid amide is 2-hydroxyethylaminopropionamide.
Most especially preferred fluorescent pigments of the invention are those comprising
Since, however, the additional FWA component c) of the fluorescent pigment is optional, a further preferred pigment may also comprise
Within the scope of the definitions of the substituents in the compounds of formulae (1) to (18), C1-C4alkyl radicals are branched or unbranched and are, for example, methyl, ethyl, propyl, isopropyl or n- sec- or tert-butyl; they may be unsubstituted or substituted by halogen, for example fluorine, chlorine or bromine. C1-C4Alkoxy is, for example, methoxy, ethoxy, propoxy, isopropoxy or n-butoxy whilst C2-C4hydroxyalkyl may, for example, be hydroxyethyl, hydroxypropyl or hydroxybutyl.
The anionic radical An− as an anion of an organic or inorganic may be selected from the group consisting of halide, e.g. chloride, bromide or iodide, sulphate, methyl sulphate, boron tetrafluoride, aminosulphonate, perchlorate, carbonate, bicarbonate, phosphate, phosphoromolybdate, phosphorotungstate, phosphorotungstomolybdate, benzenesulphonate, naphthalenesulphonate, 4-chloro-benzenesulphonate, oxalate, maleate, acetate, propionate, lactate, succinate, chloroacetate, tartrate, methanesulphonate or benzoate. Preferable examples of such anions are chloride, hydrogensulphate, sulphate, methosulphate, phosphate, formate, lactate or acetate, especially chloride and methosulphate. The anion can be exchanged in a known manner for another anion.
The ratios of the FWA components b) and c) of the fluorescent pigments may vary over wide ranges depending on the requirements of the final product. Since component c) of the fluorescent pigment is optional, this may comprise from 0 to 90% by weight, based on the total weight of fluorescent whitening agents present in the pigment, of the fluorescent whitening agent, component c) of the composition.
However, when the additional FWA, component c) of the fluorescent pigment is present, this may comprise from 5 to 90%, preferably from 10 to 80% and, most preferably, from 30 to 70%, by weight, based on the total weight of fluorescent whitening agents present in the pigment, of the composition.
Similarly, the total amount of FWA present in the fluorescent pigment may vary over a large range, depending on the degree of whiteness required. Thus, the fluorescent pigment of the invention may comprise a total weight of from 0.2 to 25%, preferably from 0.5 to 20% and, most preferably, from 2.0 to 15%, by weight, based on the total weight of fluorescent pigment, of the fluorescent whitening agents, components b) and, optionally, c) of the composition.
A further aspect of the invention is a process for the preparation of the fluorescent pigments of the invention, whereby the melamine-formaldehyde polycondensation product is reacted with a fluorescent whitening agent of formula (1) and, optionally, at least one further fluorescent whitening agent, component c), in aqueous medium, in the presence of mineral acid, and subsequently treated with base.
More specifically, the fluorescent pigments of the invention may be prepared by addition of the compound of formula (1) and, optionally, at least one further fluorescent whitening agent, component c), to an excess of the melamine-formaldehyde polycondensate in aqueous media under acidic conditions resulting from the addition of strong mineral acid, for example, concentrated hydrochloric acid. The mixture is then stirred, preferably at elevated temperature, for example, at between 50 and 90° C., preferably 65 to 75° C. until reaction is complete and, subsequently, basifying the reaction mixture with strong inorganic base, for example, an alkali metal hydroxide such as sodium hydroxide. The resulting aqueous suspension may be used directly in the coating colour or, preferably, is filtered, the resulting whitening pigment dried and then ground to a suitable particle size.
The fluorescent whitening agents of formulae (1) to (18) are known compounds or may be obtained by known procedures.
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 μm, preferably from 0.3 to 10 μm and especially from 0.5 to 5 μm.
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 substance, based on the melamine-formaldehyde polycondensation product used.
The paper coating compositions generally have a solids content of from 35 to 80% by weight, preferably from 40 to 70% by weight. In addition to 0.01 to 10 parts by weight of the fluorescent pigment of the invention, they generally comprise, per 100 parts of inorganic pigment,
The whitening pigments according to the invention are excellently suitable for whitening the optionally pigmented coating compositions customarily used in the textile, paint, adhesives, plastics, wood and paper industries. Such coating compositions comprise, as binders (co-binders), plastics dispersions based on copolymers of butadiene and styrene, of naphthalene sulphonic acids and formaldehyde, of polyethylene and polypropylene oxides, of acrylonitrile, butadiene and styrene, of acrylic acid esters, of ethylene and vinyl chloride and of ethylene and vinyl acetate, or homopolymers, such as polyvinyl chloride, polyvinylidene chloride, polyethylene, polyvinyl acetate, polyvinyl alcohol, or polyurethane.
If desirable, the coating composition may, in addition to the fluorescent pigment, contain further fluorescent whitening agents, whereby these may also be selected from the compounds of formulae (1) to (18).
For the purpose of pigmenting the coating compositions there are generally employed aluminium silicates, such as China clay or kaolin, and also barium sulphate, satin white, titanium dioxide or calcium compounds for paper. These are described by way of example in J. P. Casey “Pulp and Paper; Chemistry and Chemical Technology”, 2nd Ed. Vol. III; p. 1648-1649 and in Mc Graw-Hill “Pulp and Paper Manufacture”, 2nd Ed. Vol. II, p. 497 and in EP-A-0 003 568.
The whitening pigments according to the invention may be used especially for the coating of paper, more especially ink-jet and photographic paper, wood, foils, textiles, non-woven materials and suitable building materials. Special preference is given to use on paper and cardboard and on photographic and ink-jet papers.
Consequently, a further aspect of the invention is paper, which has been treated with a coating composition as described above.
The coatings or coverings so obtained have, in addition to a high degree of fastness to light, an excellent degree of whiteness. Evenness, smoothness, volume and printability properties are also improved because the whitening pigments used in accordance with the invention remain in the paper matrix as additional filler and have a favourable effect on the printability of the paper. Furthermore, due to their excellent bleed-fastness, such coatings are eminently suitable for use in food packaging.
The following Examples illustrate the invention, without intending to be restrictive in nature; parts and percentages are by weight unless otherwise stated.
To a solution of 84 g of a 59.7% aqueous pentamethylol-melamine (LYOFIX™ CHN) and 300 ml of water, are added 5.2 g of an aqueous slurry containing 30% of the compound of formula
and the mixture stirred until a homogenous solution is obtained. The pH of the solution is adjusted to 3.9 by addition of 37% aqueous hydrochloric acid and heated to 70° C. with stirring. Further hydrochloric acid is then added to adjust the pH to 2.0 and the solution stirred for 4 hours at 70° C. After cooling to room temperature, the pH is adjusted to 9.5-10.0 by addition of 32% aqueous sodium hydroxide solution and the mixture stirred for a further 30 minutes. The precipitated solids are filtered, washed thoroughly with water and dried at 80° C. for 16 hours. There are obtained 32.7 g of a white solid polymeric material incorporating 4.8% of the compound of formula (101).
By following the procedure described in Example 1, but replacing the 5.2 g of the slurry of compound (101) by a mixture consisting of 4.17 g of an aqueous slurry containing 30% of the compound of formula (101) and 0.31 g of the compound of formula
there are obtained 31 g of a white solid incorporating 4.0% of the compound of formula (101) and 1.0% of the compound of formula (102).
By following the procedure of Example 2, but replacing the 0.31 g of the compound of formula (102) by 0.31 g of the compound of formula
there are obtained 29.9 g of a white solid incorporating 4.2% of the compound of formula (101) and 1.0% of the compound of formula (103).
By following the procedure of Example 2, but replacing the 0.31 g of the compound of formula (102) by 0.31 g of the compound of formula
there are obtained 29.9 g of a white solid incorporating 4.1% of the compound of formula (101) and 1.0% of the compound of formula (104).
To a solution of 150.7 g of a 59.7% aqueous pentamethylol-melamine (LYOFIX™ CHN) and 525.8 g of water, are added 16.7 g of an aqueous slurry containing 29.9% of the compound of formula (101) and 16.5 g of an aqueous slurry containing 30.3% of the compound of formula
and the mixture stirred until a homogenous solution is obtained. The pH of the solution is adjusted to 3.9 by addition of 37% aqueous hydrochloric acid and heated to 72° C. with stirring. After stirring for 2 hours, further hydrochloric acid is added to adjust the pH to 2.2, the solution stirred for 2 hours, again treated with hydrochloric acid to lower the pH to 1.4 and stirring continued for a further 2 hours at 72° C. After cooling to room temperature, the pH is adjusted to 9.5-10.0 by addition of 32% aqueous sodium hydroxide solution and the mixture stirred for a further 30 minutes. The precipitated solids are filtered, washed thoroughly with water and dried at under vacuum at 80° C. There are obtained 56.5 g of a white solid polymeric material incorporating 8.8% of the compound of formula (101) and 8.8% of the compound of formula (105).
By following the procedure described in Example 5, but replacing the 16.5 g of the slurry of compound (105) by 32.2 g of an aqueous solution containing 15.5% of the compound of formula
there are obtained 61.2 g of a white solid incorporating 8% of the compound of formula (101) and 8% of the compound of formula (106).
By following the procedure described in Example 5, but replacing the 16.5 g of the slurry of compound (105) by 32.2 g of an aqueous solution containing 15.5% of the compound of formula
there are obtained 56.8 g of a white solid incorporating 8.8% of the compound of formula (101) and 8.8% of the compound of formula (107).
By following the procedure described in Example 5, but replacing the 16.5 g of the slurry of compound (105) by 22.0 g of an aqueous solution containing 22.8% of the compound of formula
there are obtained 68.9 g of a white solid incorporating 7.2% of the compound of formula (101) and 7.2% of the compound of formula (108).
By following the procedure described in Example 5, but employing 10.0 g of an aqueous slurry containing 29.9% of the compound of formula (101) and replacing the 16.5 g of the slurry of compound (105) by 8.2 g of the compound of formula
having an active content of 85.8%, there are obtained 61.4 g of a white solid incorporating 4.9% of the compound of formula (101) and 11.5% of the compound of formula (109).
By following the procedure described in Example 5, but employing 23.4 g of an aqueous slurry containing 29.9% of the compound of formula (101) and replacing the 16.5 g of the slurry of compound (105) by 3.5 g of the compound of formula (109) having an active content of 85.8%, there are obtained 68.9 g of a white solid incorporating 10% of the compound of formula (101) and 4.3% of the compound of formula (109).
To a solution of 301.5 g of 59.7% aqueous pentamethylol-melamine (LYOFIX™ CHN) and 1109 g of water, are added 67.6 g of an aqueous slurry containing 18.9% of the compound of formula (101) and 11.1% of the compound of formula (109). The solution is stirred and the pH adjusted to 3.9 by addition of 37% aqueous hydrochloric acid. The reaction mass is heated to 73° C. and, after adjusting the pH to 2.0 with 37% hydrochloric acid, the mixture is stirred for 2 hours. The pH is then adjusted to 1.5 with 37% hydrochloric acid and stirring continued for a further 2 hours. After cooling to room temperature, 32% aqueous sodium hydroxide solution is added to pH 9.5-10.0. The precipitated solids are filtered, washed with water and dried under vacuum at 100° C. There are obtained 113.1 g of a whitening pigment incorporating 11.3% of the compound of formula (101) and 6.6% of the compound of formula (109).
Coating colours having a solids content of 62% and consisting of 100 parts of inorganic pigment (60% calcium carbonate and 40% clay), 0.2 parts (based on the weight of inorganic pigment) of polyvinyl alcohol, 9 parts (based on the weight of inorganic pigment) of SBR latex and 0.25 parts (based on the weight of inorganic pigment) of rheology modifier (Coatex® RT5) are prepared by homogenising the components.
Dispersions of the whitening pigments of Examples 1-11 are prepared by wet milling approximately 20 g of the pigment with glass beads of approximately 2 mm diameter in the presence of a dispersant (e.g. 25 g of a 10% aqueous solution of Pluronic® F 108) in 75 ml of water during approximately 17 hours.
To the coating colour, prepared as described above, sufficient of the whitening pigment dispersions are added to result in a solid content of 4 parts, based on the weight of inorganic pigment, and the mixtures stirred for 10 minutes.
Each of the resulting coating colours is then applied to an FWA-free base paper by means of a draw down rod, such that a coat weight of approximately 12 g/m2 results. After drying, the CIE Whiteness and Iso-fluorescence values are recorded using a Datacolor Elrepho 3000 spectrophotometer and are summarized in Table 1 below.
In a further series of experiments, the bleed fastness's of the FWA's incorporated into the melamine/formaldehyde polycondensates, towards water, 1.5 g/l aqueous sodium carbonate and 1.5% aqueous acetic acid are measured according to EN 648 and the results summarized in the following Table 2, whereby bleed fastness is measured on a scale of 0-5 (a value of 5 corresponds to zero bleeding).
As is apparent from the above results, the fluorescent pigments of the invention exhibit excellent whitening effects when applied as coatings to paper and, furthermore, the FWA's incorporated therein mostly exhibit excellent bleed fastness.
| Number | Date | Country | Kind |
|---|---|---|---|
| 04103884.5 | Aug 2004 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP05/53789 | 8/3/2005 | WO | 00 | 10/17/2007 |
