RADIATION-CURABLE COMPOSITIONS OF PIGMENT VIOLET 23 WITH IMPROVED REMOVABILITY FROM SURFACES, METHOD OF MAKING A RADIATION-CURABLE COMPOSITION AND INK CONTAINING A RADIATION-CURABLE COMPOSITION

Abstract

Radiation-curable compositions of Pigment Violet 23 are described which can be used advantageously in UV inks for inkjet printing machines. Soiling containing such UV inks, especially within inkjet printing machines, can be removed particularly easily in a contactless procedure with conventional cleaners. The radiation-curable compositions described contain at least one modified Pigment Violet 23 which carries at least one polar functional group of the formula (I):

X-E (I) where X is a bridging group and E is a polar molecule radical.

Claims

1. A radiation-curable composition, comprising: a) at least one Pigment Violet 23, containing at least one functional group of formula (I)
X-E (I) where: X is a bridging group; and E is a polar molecule radical; b) at least one dispersant; and c) a nonaqueous dispersion medium.

2. The radiation-curable composition according to claim 1, wherein E in the formula (I) is
(Z).sub.m(A).sub.n where: Z is identical or different and is at least one polar functional group; A is identical or different and is a short-chain apolar molecule radical or a counteraction; m is 1 or 2; and n is 1, 2, 3 or 4.

3. The radiation-curable composition according to claim 2, wherein: Z is identical or different and is selected from the group consisting of polar acid groups, hydroxylate, and carbonyl radical; and A is identical or different and is selected from the group consisting of C.sub.1-C.sub.5 alkyl radical, proton, metal cations, and ammonium ion.

4. The radiation-curable composition according to claim 2, wherein: Z is identical or different and is selected from the group consisting of sulfonate radical, carboxylate radical, phosphate radical, and phosphonate radical; and A is identical or different and is selected from the group consisting of proton, metal cation, and ammonium ion.

5. The radiation-curable composition according to claim 1, wherein: X is an aliphatic, aromatic or araliphatic hydrocarbon group having 1 to 12 carbon atoms and may be linear or branched, and X may comprise at least one heteroatom selected from O, S, N, and P.

6. The radiation-curable composition according to claim 2, wherein: X is phenylene or methylenephenylene; Z is at least one sulfonate radical, carboxylate radical or phosphonate radical; A is at least one proton, alkali metal cation, alkaline earth metal cation or an ammonium ion; and m is 1 or 2.

7. The radiation-curable composition according to claim 1, wherein the at least one functional group of the formula (I) is selected from: ##STR00002## and alkali metal salts, alkaline earth metal salts, and ammonium salts of these functional groups.

8. A method for producing a radiation-curable composition, which comprises the steps of: i) providing at least one Pigment Violet 23 containing at least one functional group of the formula (I):
X-E (I) where: X is a bridging group; and E is a polar molecule radical; and ii) dispersing the at least one Pigment Violet 23 in a nonaqueous dispersion medium, using at least one dispersant.

9. The method for producing a radiation-curable composition according to claim 8, wherein the at least one Pigment Violet 23 containing the at least one functional group of the formula (I) is used in acid form in step i), the acid form having been obtained by the following method: a) providing an aqueous dispersion of at least one salt; b) treating the aqueous dispersion provided in step a) with acid; and c) isolating the acid form of the at least one Pigment Violet 23 containing the at least one functional group of the formula (I).

10. The method for producing a radiation-curable composition according to claim 8, wherein the at least one salt is an alkali metal salt.

11. An ink for inkjet printing, containing: a radiation-curable composition, containing: a) at least one Pigment Violet 23, containing at least one functional group of formula (I)
X-E (I) where: X is a bridging group; and E is a polar molecule radical; b) at least one dispersant; and c) a nonaqueous dispersion medium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0023] The radiation-curable compositions of the invention contain the at least one Pigment Violet 23, containing at least one functional group of the formula (I), preferably in an amount of 1 to 40 wt %, more preferably in an amount of 5 to 30 wt %, based on the overall radiation-curable composition.

[0024] In one preferred embodiment the radiation-curable composition is curable with UV radiation or electronic radiation, more preferably with UV radiation.

[0025] The radiation-curable composition of the invention comprises a nonaqueous dispersion medium. The radiation-curable composition preferably comprises at least 10 wt %, more preferably at least 20 wt %, and very preferably at least 30 wt % of a nonaqueous dispersion medium, based on the overall radiation-curable composition. In one preferred embodiment the radiation-curable composition comprises 10 to 90 wt %, more preferably 20 to 80 wt %, and very preferably 30 to 70 wt % of a nonaqueous dispersion medium, based on the overall radiation-curable composition.

[0026] The nonaqueous dispersion medium comprises one or more radiation-curable organic compounds. Suitable in principle for the compositions of the invention are all radiation-curable organic compounds which are normally used in UV inks. Such compounds are known fundamentally to the skilled person. They comprise, in general, polymerizable monomers, which may have different degrees of functionalization and may be doubly, triply or more highly functionalized, for example. Preferred radiation-curable organic compounds are selected from acrylates, as for example 1,6-hexanediol diacrylate or dipropylene glycol diacrylate, methacrylates, as for example 1,1,1-trimethylolpropane trimethacrylate, vinyl ethers, as for example triethylene glycol divinyl ether, and N-vinylamides, as for example N-vinylformamide.

[0027] The radiation-curable compositions of the invention comprise at least one dispersant, which may also be referred to as a dispersing assistant. This is at least one interface-active substance which is intended to facilitate the dispersing of the Pigment Violet 23 solid in the liquid, nonaqueous dispersion medium, by reducing the interfacial tension between the two components. Suitable in principle are all dispersants which are normally used for UV inks with solid pigment constituents. Such dispersants are known fundamentally to the skilled person. The at least one dispersant is selected for example from oligomeric titanates and silanes, oligomeric and polymeric carboxylic acids, polyamines, salts of long-chain polyamines and polycarboxylic acids, soylecithin, and the like. Dispersants of these kinds are available commercially from, for example, Lubrizol Advanced Materials, Inc., Brecksville, USA, under the brand name Solsperse; from BASF SE, Ludwigshafen, Germany under the brand name Efka; or from BYK-Chemie GmbH, Wesel, Germany, under the brand name BYKJET.

[0028] In the compositions of the invention the weight ratio of at least one Pigment Violet 23 of the invention to the at least one dispersant is preferably in the range from 1:10 to 10:1, more preferably in the range from 1:5 to 5:1, and very preferably in the range from 1:2 to 2:1.

[0029] The compositions of the invention comprise the at least one dispersant preferably in an amount of 1 to 30 wt %, more preferably in an amount of 5 to 20 wt %, based on the overall radiation-curable composition.

[0030] The radiation-curable compositions of the invention may additionally comprise further substances, which may also be referred to as additives. Preferred additives are those which are normally used in UV inks for inkjet printing, examples being photoinitiators, stabilizers, fillers, wetting agents, antistatic agents, lubricants, and the like. Besides the modified Pigment Violet 23, the radiation-curable compositions of the invention may also comprise further colorants such as organic or inorganic pigments, for example.

[0031] The surfaces which may become soiled with the UV ink, containing the radiation-curable composition of the invention, in conventional inkjet printing machines and which can be cleaned particularly easily in a contactless procedure preferably comprise silicon, fluorinated silicon materials, or stainless steel. More preferably the surfaces comprise fluorinated silicon materials. Such surfaces are encountered particularly in the region of the inkjet printheads.

[0032] A further subject of the invention is a method for producing a radiation-curable composition as specified herein, more particularly as specified herein as being preferred, wherein:

i) at least one Pigment Violet 23 containing at least one functional group of the formula (I) as defined herein is provided, and
ii) the at least one Pigment Violet 23 containing at least one functional group of the formula (I) which is provided in step i) is dispersed in a nonaqueous dispersion medium, using at least one dispersant.

[0033] As the at least one dispersant and the nonaqueous dispersion medium, preference is given in the method of the invention to the dispersants stated as preferred and the nonaqueous dispersion media stated as preferred above for the radiation-curable compositions of the invention.

[0034] The dispersing in step ii) may take place according to methods known fundamentally to the skilled person, as for example using agitator mills, dissolvers, rotor-stator mills, ball mills, and the like.

[0035] A further subject of the invention is a method for producing a radiation-curable composition as specified herein, more particularly as specified herein as being preferred, wherein at least one Pigment Violet 23 containing at least one functional group of the formula (I) as defined herein is used in acid form in step i), the acid form having been obtained by the following method:

Ia) providing an aqueous dispersion of at least one salt, more particularly alkali metal salt, of at least one Pigment Violet 23 containing at least one functional group of the formula (I) as defined herein,
IIa) treating the aqueous dispersion provided in step Ia) with acid, and
IIIa) isolating the acid form of the at least one Pigment Violet 23 containing at least one functional group of the formula (I).

[0036] Examples of suitable aqueous dispersions for step Ia) are aqueous dispersions available commercially from Cabot Corporation, Boston, USA.

[0037] The treating of the aqueous dispersion with acid in step IIa) may take place according to methods known fundamentally to the skilled person, as for example in reactors or using ion exchangers. Examples of suitable acids for the method of the invention are hydrochloric acid, sulfuric acid, organic sulfonic acids, and the like.

[0038] The isolating of the acid form in step IIIa) may take place according to methods known fundamentally to the skilled person, as for example by filtration, centrifugation or evaporation.

[0039] In a further preferred embodiment of the method of the invention for producing a radiation-curable composition as specified herein, more particularly as specified herein as being preferred, at least one Pigment Violet 23 containing at least one functional group of the formula (I) as defined herein is used in step i) in salt form, the salt form having been obtained by the following method:

Ib) providing an aqueous dispersion of at least one salt, more particularly alkali metal salt, of at least one Pigment Violet 23 comprising at least one functional group of the formula (I) as defined herein,
IIb) drying the aqueous dispersion provided in step Ib), and
IIIb) optionally grinding the at least one salt, more particularly alkali metal salt, of the at least one Pigment Violet 23 as obtained in step IIb).

[0040] The drying of the aqueous dispersion in step IIb) may take place according to methods known fundamentally to the skilled person, as for example by evaporation of the water with supply of heat. The grinding carried out optionally in step IIIb) may take place in principle by any grinding methods known in principle to the skilled person, as for example using ball mills.

[0041] A further subject of the invention is an ink, more particularly UV ink, for inkjet printing, comprising a radiation-curable composition of the invention.

[0042] UV inks for inkjet printing that comprise the radiation-curable compositions of the invention with the modified Pigment Violet 23 can be removed particularly easily using conventional cleaning products from the surfaces in inkjet printing machines, as for example the Labelfire inkjet printing machine from Heidelberger Druckmaschinen AG, Heidelberg, Germany, without any need for mechanical cleaning.