GB2133027A - Printing ink pigments - Google Patents

Abstract

Printing ink pigments are resin- impregnated with non-drying alkyd resins which are modified with oils, fatty acids, and/or fatty alcohols with an iodine number less than 95, e.g. coconut oil. The pigments may be used in inks for offset printing. The printing ink pigments may be impregnated by applying, for instance spraying, the non-drying alkyd resins in the form of an emulsion or solution during the pigment-drying procedure.

Description

SPECIFICATION Printing ink pigments itis known to load printing ink pigments with different substances for improving their dispersion behaviour, for controlling crystal growth and for improving bleed resistance and viscosity stability.

Some ofthese pigments, including in particular4 B toner or Lithol ruby, receive their basic pigment properties only bytheformation of so-called lakes in that they are precipitated, i.e. laked, with heavy-metal ions, in particular alkaline earth metal ions. In orderto obtain further improved product properties, in another procedure, the diazo coupling product is precipitated in suitable manner, with the addition of resins, these including in particular rosin or colophony resins or derivatives thereof.

The fundamental processes and the production of specific colour properties are described in numerous patents. One ofthe more recent methods is described in German Offenlegungsschrift specifications 2834 028 and 2803990. Here, for example, hydrogenation rosin types are used to improve the storage stability of pigments.In French Patent Specification 7528524 resins ofwidely va rying type are disclosed as aids to disperson and as additives, in quantities of below 10 to above 50% in relation to the pigment The application of loading substances on to the pigments can be effected in this case both by precipitation of the pigment in the presence of substances influencing the properties thereof and intheformofanafter- treatment of the finished pigment with solutions or dispersions of the loading material.

The processes are described in averywidevariety of embodiment; this is also the case in French Application 1 091 201.

Furthermore, British PatentSpecification 1 313 147 discloses the production of azo pigments (calcium 4 B toner) with the special advantages of easy dispersibilityforintaglio inks. Besides this improved dispersibility, emphasis is placed particularly on the greater depth of colour and the improved rheological properties of the printing inks produced with the pigments.

Synthetic and natural resins, esters and amines are disclosed as resins for attaining these properties.

In another process, German Offenlegu ngssch rift 20 01 505 discloses precipitation in the presence of rosin derivatives with the additional ofnon-ionicsurface- active agents.

In addition to having excellent colouring power and high transparency, this pigment is intended to be very easily dispersible in alkyd ink media.

However, if the pigments described in these processes are used for the production of offset inks, deleterious properties of the finished printing ink become evident, which can be clearly attributed to the special pigment properties. In the processing ofthese printing inks in conventional offset-printing machines, white coatings are formed on the rollers which can seriously affect the printing process.

Such findings are described in the literature (I. Najda I. C. Schutze, Polygraph 17(81)1296 etseq).

In addition to calcium ions, originating from adherent calcium chloride from the production process, inter ails the calcium resinate ofthe pigment is responsiblefortheformation of this coating. The lipophilic/hydrophilic properties of the entire system are altered. As a result of interaction with the anions of the moistening medium or dampening solution,tha calcium compounds in the pigmentform insoluble deposits on the rollers, possibly on the printing plate and on the rubber blanket.

Thus the present invention sets otto make available a pigment which, whilst retaining the pigment-improving action ofthe original resin-impregnation in respect of transparency, the desired bluish tint and dispersibility, does not have any properties with a detrimental effect on printing inks, especially from the lithographic aspect. Moreover, afar as possible the quality of the printing inks, also including the quality of the product produced therewith, should be increased and improved.

In accordance with the invention,there are provided printing ink pigments in which the resin-impregnation pa rtly contains non-drying alkyd resins which are modified with oils,fatty acids and/orfatty alcohols with an iodine number lower than 95, preferably lower than 20.

Thus, according to the invention, printing ink pigments are resin-impregnated with non-drying alkyd resins which are modified with oils, fatty acids and/orfatty alcohols with an iodine number lower than 95.

As regards the alkyd resins it is mostly a question of phthalate resins (ortho-, iso-terephthalic acid ester) and/or urethane-containing alkyd resins. They are composed of dicarboxylic acids of polyhydric alcohols, such as glycerine, pentaerythritol, sorbitol, trimethylol propane, or of multifunctional isocyanates, on the one hand, and oils, natural or synthetic fatty acids offatty alcohols, on the other hand, and are produced in known manner.

Coconut oil (iodine number about 9) in particular and palm-kernel oil (iodine number about 10-18) are suitable as modifying oils. Instead of or in addition to oils, it is possible forthe alkyd resins also to be modified with fatty acids, for example with synthetic fatty acids, and/orwith fatty alcohols having the aforementioned iodine numbers. The modifying agents should generally be substantially free of multiple double bonds.The amount of modifying agent (oil,fatty acid and/orfatty alcohol) contained in the alkyd resin lies generally within the range of40- 70% by weight, in the case of dicarboxylic-acid or isocyanate amounts within the range of 2035% by weight and in the case of polyhydric alcohols within the range of 5 to 15% by weight. Examples of natural and synthetic fatty acids orfatty alcohols which can be used in accordance with the invention are hexanoic acid, iso-octanoic acid and other derivatives or their hydrogenated derivatives (oxo-alcohols) (Ca rstens, Lackrohstofftabellen 1978,46; Rormpp's Chemie Lexikon, 2nd edition 1103). It has also proven to be an advantage if the alkyd resins contained in the pigments according to the invention have a pure hydroxyl number (withoutacid number) of higherthan 10, preferably higherthan 15 upto a maximum of about 40. Alkyd resins with a hydroxyl numberwithin the range of about 20 to about35 have proven to be particularly successful. The acid number ofthe alkyd resins may also be ofadvantageous influence. In particular, alkyd resins with an acid number of lower than approximately 25, in particularly of about 612, have proven to be successful.

Advantageously, the non-drying alkyd resins contained in the pigments according to the invention have a weight average molecular weight (Mw) of from 9,000 to 30,000, preferably about 12,000 to about 22,000 or a number average molecularweight (Mn) of from 3,000 to 5,000, preferably about 3,500 to about 4,500. The dispersion factor mostly lies within the range offrom 3 to 6, preferablyabout3.5to 5. The determination of molecularweightcan be effected by means of gel chromatography. In particular, those alkyd resins have proven to be successful whose molecular weights Mw lie within the range of approximately 14,000 to 16,000 and whose molecularweights Mn lie within the range of approximately3,500 to 4,000, corresponding to a dispersion factor of approximately 4.

In this case it is not at all necessary (as has been surprisingly demonstrated) for all the loading resins, in the manner according to the invention, to be replaced by the non-drying alkyd resins. On the contrary, in orderto attain the particularly desired colour properties of the calcium 4 B-toner, only a part ofthe resinate has to be replaced.

Satisfactory results can be achieved if 550% by weight, preferably 1530% by weight, of the other loading resins are replaced by the non-drying alkyd resins. Experience has shown that itis in fact sufficient for about 50% of the total resin content to consist of the non-drying alkyd resins, it being possibleforthe content of non-drying alkyd resins to be substantially higherwithoutdetriment.

Itwas especially remarkable that by only partial replacement of the resinate it was possible to eliminate or reduce the disadvantageous properties ofthe printing ink produced from the pigments. The ex planation for this is that, as a result of the enveloping ofthe individual pigment crystallite by the alkyd resin, there is achieved the necessarycompatibilitywith the customary binding agent constituents of offset inks.

As a result of this, access of the moistening medium or dampening solution to the interface (lipophilic) of mineral oil/binding agentandthepigmentsurface (hydrophilic) is obviated.

The subject-matter ofthe invention is also a method fortheproduction ofprinting-inkpigments,forwhich purpose the non-drying alkyd resins, optionally together with the other loading substances, are applied, preferably by spraying, on the the pigments in theform of an emulsion orsolution, during the pigment-drying procedure. Such a mode of procedure is preferabletothe simultaneous precipitation of the pigments in the presence ofthe non-drying alkyd resins, which may also be used.

Finally,the invention also relates to printing inks, in particular offset-printing inks, which in addition to the conventional printing ink constituents also contain resin-loaded pigments, the resin-impregnation of which contains non-drying alkyd resins which are modified with oils, fatty acids and/orfatty alcohols with an iodine number lowerthan 95, in particular lower than 20. Preferably, the non-drying alkyd resins are modified with coconut oil. For the most part, the non-drying alky resins amountto 550% by weight, preferably 30% by weight, ofthetotal resin loading.

The printing ink pigments according to the invention, as well as the printing inks of the invention containing these pigments, are distinguished by higher colour depth yield, greatertransparency ofthe produced printing inks quality after printing, improved water stability in offset, more rapid separation properties and shorter dispersion times. Moreover, as a resultofthe contentofnon-drying alkyd resins, non-powdery, lustrous pigments can be obtained.

The following examples serve to illustratethe invention.

Example I 93.5 parts of p -toluidine - 3 - sulphonic acid were dissolved in 2,00 parts of water, with the addition of 67 parts of an NaOH solution (10 N). After adding 350 parts of 5 N - hydrochloric acid and 1,300 parts of ice, diazotization was carried out with 260 parts of an 2 N-sodium nitrate solution, with agitation attemperatures of between 0 and 5"C.

After adding a solution of 78 parts ofcalcium chloride in 500 parts of water, there was added a solution of 409 rosin in 1,000 parts of water and additionally 159 of 10 N NaOH solution.

Thiswasleftto reactfor30 min. at 0-50C with agitation and then mixed rapidly with a solution of 97.59 ss-oxynaphthoic acid, dissolved in 2,500 parts of waterwith the addition of 2009 of 25% ammonia.

The suspension was agitated futherfor one hour at a temperature of 10 --15"C, then heated to 70"C and maintained atthistemperatureforfinal particle formation. Subsequently, 250g of the pigment was filtered off, wahsed out, then dried at 70" and triturated (pigment 1).

Example Il The production ofthe pigment ofthis Example followed that ofthe foregoing example, however,the solution containing 409 of rosin was replaced by a solution which contained only 259 of rosin, dissolved in 1,000 parts of water with 10 parts of 10 normal NaOH solution.

After the grinding, the pigment was mixed drop by drop, with agitation, with a mixture of 1 0g ofthe alkyd resin according to German Patent 30 23 118 and 5 - 89 of mineral oil. After all the drops had been added, agitation was continued for 30 minutesto effect homogenization.

Offset inks were formulated in conventional manner from the pigments according to Example I and II, with the addition of 10 - 13% pigment, 25 - 35% of usual mineral oils and 45 - 55% of conventional offset binding agent consisting of hard resin and alkyd resin.

Printing inks produced in accordance with Example II do not exhibit, even after a protracted run on conventional offset-printing machines, any coating formation which could lead to interference with the printing process.

Claims (12)

1. A resin-impregnated printing ink pigment, wherein the resin comprises a non-drying alkyd resin which is modified with an oil, fatty acid and/orfatty alcohol with an iodine number lowerthan 95.

2. A printing ink pigment as claimed in Claim 1 wherein the modifying oil(s), fatty acid(s) and/or alcohols have an iodine number lowerthan 20.

3. A printing ink pigment as claimed in Claim 1 or claim 2 wherein the non-drying alkyd resin is modified with coconutoil.

4. A printing ink pigment as claimed in any one of the preceding claims wherein the non-drying alkyd resin is present in an amount offrom 5-50% by weight ofthetotal resin content.

5. A printing ink pigment as claimed in Claim 4 wherein the non-drying alkyd resin is present in an amountoffrom 15-30% by weight ofthe total resin content.

6. A printing ink pigment as claimed in Claim 4 or Claim 5 wherein the remainder ofthe resin content is rosin and/or a rosin derivative.

7. A printing ink pig ment as claimed in Clai m 1 substantiallyas hereinbefore described.

8. A printing ink pigment as claimed in Claim 1 substantially as hereinbefore described in Example I or Example II.

9. A printing ink pigment as claimed in any one of the preceding claimswhich isan offset printing ink pigment.

10. A method forthe production of a printing ink pigmentwherein a non-drying alkyd resin is defined in any one of Claims 1 to 8, optionally together with other loading substances, is applied,on to the pigment in the form of an emulsion or solution, during the pigment-drying procedure.

11. A method as claimed in Claim 10 wherein the application is by spraying.

12. Aprinting inkwhich comprises a pigment as claimed in any one of Claims 1 to 9 or prepared by a method as claimed in Claim 10 or Claim 11.