Ink additives

Details Ink additives Ink additives

1999-12-23

2001-11-20

Klemanski, Helene (Department: 1755)

Compositions: coating or plastic

Coating or plastic compositions

Marking

C106S031350, C106S031430, C106S031580, C427S466000, C428S195100

Reexamination Certificate

active

06319309

ABSTRACT:

The present invention relates to the use of additives in an ink, to aqueous ink compositions, and to substrates printed with the inks.
It is desirable for ink jet printing inks to give images having high water fastness and good optical density. Clogging of the ink jet nozzle during the printing process is often reduced or prevented by using ink colorants having a high solubility in the ink medium. However, when the inks are aqueous, highly soluble dyes can result in printed images having poor water fastness because the dye remains water-soluble on the printed substrate.
WO 95/27759 discloses aqueous inks containing a colorant and a binder material capable of ionically or physically entrapping the colorant.
EP 648 821 discloses inks containing a colorant and certain aromatic monobasic acids and non volatile polyamine derivatives.
EP 356 080 discloses aqueous inks containing dyes and an ammonium salt of a monobasic acid.
We have found that the use of a polybasic acid and a volatile base in inks give a surprising increase in water fastness. In addition, the optical density of resultant prints is retained and, in some cases, there is less bronzing.
The term “water fastness” refers to the resistance of a printed dye to running or smudging on contact with water on a printed substrate.
The term “bronzing” refers to an undesirable metallic bronze appearance that can detract from the true black colour desired for many inks.
According to a first aspect of the present invention there is provided the use of a polybasic acid and a volatile base, or a salt formed by the said acid and base, in an aqueous ink to increase the water fastness of a water-soluble dye contained in the ink.
The polybasic acid can be any compound having two or more acidic protons. By way of illustration H
2
SO
4
, 1,4-dicarboxybenzene and phenylphosphonic acid are all dibasic acids and H
3
PO
4
and 1,3,5-tricarboxy benzene are tribasic acids. Preferably the polybasic acid free from chromophoric groups, more preferably it is colourless or substantially colourless because coloured polybasic acids can alter the colour of the ink.
The polybasic acid may be an organic or an inorganic acid, preferably with a first pKa in the range of from 2.0 to 6.0, more preferably from 2.8 to 5 and a second pKa in the range of from 3.5 to 8, more preferably from 4 to 6.
When the polybasic acid is inorganic, it is preferably phosphoric acid, pyrophosphoric acid, a polyphosphoric acid or molybdic acid. Preferably the polybasic acid is an organic polybasic acid because we have found that these give a higher waterfastness than inorganic acids. In addition, the buffering effect of a weak organic polybasic acid with the base reduces corrosion of the ink jet print head which can occur if strong acids are used. Preferred organic polybasic acids have groups selected from carboxy, sulpho, phosphato, phosphono, a monobasic phosphate ester, a monobasic phosphonic ester, —COSH and thiol, more preferably carboxy and sulpho, especially carboxy.
The organic polybasic acid is preferably an aromatic or aliphatic polybasic acid, more preferably of Formula (1):
Z—X
n
  (1)
wherein:
Z is an aliphatic or aromatic group;
each X independently is an acidic group;
n is 1, 2, 3 or 4;
provided that the acid is polybasic.
X may be any of the hereinbefore mentioned acidic groups present on the organic polybasic acid.
Preferably X is —COOH, —SO
3
H, phosphato (—OP(O)(OH)
2
), a phosphono (—P(O)(OH)
2
), a phosphate ester group of the formula —OP(O)(OR)(OH) or a phosphonic ester group of the formula —P(O)(OR)(OH), wherein R is optionally substituted C
1-6
-alkyl or optionally substituted phenyl. Preferred substituents on R include, for example, —OH, —NH
2
, —NO
2
, halogen, (especially F and Cl) and C
1-4
-alkyl, especially methyl and ethyl.
Aromatic Polybasic Acids
Preferred aromatic polybasic acids are of the Formula (1) wherein Z is an aromatic group Ar. Ar is preferably an optionally substituted monocyclic or polycyclic aromatic group containing up to 10 carbon atoms and optionally containing one or more heteroatoms.
Preferred monocyclic aromatic groups represented by Ar are optionally substituted phenyl, pyridyl, pyridonyl, thiophenyl and furanyl groups.
When Ar is a polycyclic aromatic group it is preferably a polycyclic aromatic group wherein the cyclic rings are fused together or linked by a single covalent bond or a linker group. Suitable linker groups include ether, thioether, amino, carbonyl, alkyl and alkenyl groups.
Preferred polycyclic aromatic groups wherein the cyclic rings are fused together include optionally substituted naphthyl, quinolinyl, indolinyl, benzothienyl and benzofuranyl.
Preferred polycyclic aromatic groups wherein the cyclic rings are linked by a single covalent bond or a linker group include biphenyl, stilbenyl and diphenylmethane.
The optional substituents which may be present on Ar are preferably selected from halogen (especially F or Cl); —NO
2
; —CF
3
; —CN; a C
1-6
-alkyl, C
2-6
-alkenyl, C
5-8
-cycloalkyl or C
1-6
-alkoxy group optionally substituted by —OH, —NH
2
, —NO
2
or halogen; a group of the formula —SR
1
, or —COOR
1
wherein R
1
is H, C
1-4
-alkyl, C
5-8
-cycloalkyl or phenyl; and groups of the formula —OR
2
, —COR
2
; —NR
2
R
3
, —SO
2
NR
2
R
3
, —SOR
2
, —SO
2
R
2
, —NR
2
COR
3
, —CONR
2
R
3
, or —OCOR
2
, wherein R
2
and R
3
each independently represent H, C
1-4
-alkyl, C
5-8
-cycloalkyl, phenyl or R
2
and R
3
together with the nitrogen to which they are attached form a 5 or 6 membered ring, for example piperazine or morpholine.
Preferably Ar is optionally substituted phenyl.
Preferred acidic groups present in the aromatic polybasic acid are —SO
3
H and —COOH, more preferably —COOH.
As hereinbefore defined, the acid must be a polybasic acid. Accordingly, when n is 1 in Formula (1) X will be a polybasic acidic group, for example phosphato or phosphono.
Preferably n is 2, 3 or 4, more preferably 2 or 3, especially 2.
Preferred aromatic polybasic acids for use in the present invention include aromatic tetrabasic acids, for example pyromellitic acid, aromatic tribasic acids, for example trimesic acid, trimellitic acid, 4-sulphophthalic acid, 3,5-disulphobenzoic acid and aromatic dibasic acids, for example phthalic, isophthalic and terephthalic acid, thiosalicylic acid and p-mercaptobenzoic acid. Especially preferred aromatic polybasic acids are optionally substituted dibenzoic acids, for example phthalic acid, isophthalic acid and terephthalic acid, more especially terephthalic acid.
Aliphatic Polybasic Acids
Preferred aliphatic polybasic acids contain up to 20 carbon atoms. Preferably the aliphatic polybasic acids contain 2 to 8, more preferably 2 to 6, especially 2 or 3 and more especially 2 acid groups. The aliphatic polybasic acid may be saturated or unsaturated.
Preferred acid groups in the aliphatic polybasic acids are as hereinbefore defined for the aromatic polybasic acids. More preferably the acid groups are carboxy or sulpho, especially carboxy.
Preferred saturated groups are alkanes and preferred unsaturated groups are alkenes and alkynes. The alkane, alkene and alkyne groups may be straight chain, branched chain or cyclic and are optionally interrupted by one or more groups or heteroatoms, for example —O—, —S—, —NR
4
—, optionally substituted phenyl, piperazine and —C(O)—, wherein R
4
is H, optionally substituted alkyl, or optionally substituted aryl. The alkane and alkene groups optionally contain further substituents, preferably selected from —SH, or —OR
2
, wherein R
2
is as hereinbefore defined, more preferably —OH.
When the alkane, alkene or alkyne group is interrupted by an optionally substituted phenyl group, it is preferred that the optional substituents on the phenyl are selected from —OH, —NO
2
, —NH
2
, C
1-4
-alkyl, —SH, —COOH and —SO
3
H.
Preferably R
4
is H, optionally substituted C
1-4
-alkyl or optionally substituted phenyl, more preferably H, C
1-4
-alkyl, C
1-4
-alkyl substituted by —OH, phenyl or phenyl substituted by —OH, —NH
2
, —NO
2
, C
1-4
-alkyl or C
1-4
-alkyl subs

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