CA1096982A - Aqueous printing ink transfer characteristics - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A composition and method for improving the ink transfer properties of aqueous printing inks are dis-closed. The composition is an aqueous ink containing from 0.1 to 1.5 percent by weight of a polyethylene oxide resin having a molecular weight in the range of from 100,000 to 350,000.

Description

BACRGROUND OF THE INVEN_ION
ii Th1s invention is directed to a composit1on and -11 method for improved aqueous printing. ~
12~ A printing process involves the distribution o - ink in a uniform film, the provision of a substrate lg having a uniform surface, and the transfer of the ink to the substrate. The final transfer of ink from the printin~
l~ surface is accomplished by means of Pressure; the final 17 force on the ink film is heavy pressure against a porous 18 surface followed by a tension sufficient to split the l9 ink film.
Flexogr~phic printing is a ~orm of "relief"
21 printing, in which an impression is taken from the raised 22 par~s of a prin~ing surface. Flexographic printingm2chin_s

2 are essentially high-speed web or sheet fed rotary presse8, 24 which print with liquid inks from curved plates, usually made of rubber or other plastic material, attachea to a ~6 cylinder. ~n importan~ advantage of flexogxaphic printing 27 is tha~ a uniform film o ink can be printed even on 28 rough paDers, because the surface of the rubber plate is suf~iciently resilient to be forced into the hollows in the paper.
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10~698Z s-13B66 l ¦ Flexographic printing can be used to produce a 2 ¦ wide variety of printed material, including waxed or deco ative wrappers, aluminum foil, plastic films, news-¦ print and corru~ated papers and cartons. The inking ¦ system used in ~lexoyraphic printing consists essentially ~; of an enclosed duct to limit the evap~ration o the 7 solvent, and a simple train of rollers. Ink control is ~: 8 usually done by pressure on the end bearings oE the inking rollers, which tends to force the rollers apart at the center. Because of this, continuous fine control and ll correct alignment o~ rollers is considered to be essential - 12 to produce acceptable printing. Although the pressure 13 on the inking rollers may vary appreciably in letter press l4 printing, in contrast, flexographic printinq requires ~5 maintenance of pressure on inking rollers at practically l~ zero. Because of the importance of maintaining this -17 critical inking roller Pressu~e, flexographic inks must 18 be carefully tailored to have appropriate viscosity or l9 fluidity. In addition the ink must be sufficientl~ volatile ZO or penetrative to dry within seconds or less, adhere well to ~l the printing surface, and be odorless when dry. The ink 22 must be free of any solvents which would attack the ru~ber ; 23 or plastic print plates.
24 In the case of pigmented inks, which are exten-2~ sively used because of the color effects and eye appeal of 28 the printed product, the ink should be stable ana any - 27 pigment which settles out should be readilv dispersible by , ., - , ., 1 s-13866 l ¦ stirring. A great amount of research has been expendea in 2 ¦ attempting to maintain satisfactory ~low properties whiie ¦ at ~he same time maximizing the degree of pigmentation and improving the ink transfer properties~
¦ Another widel~ used printing technique is intaglio 8 ¦ printing, which involves taking impressions ~rom recesses 7 ¦ engraved or etched below the surface of a plate or cylinder.
8 ¦ Presently, the most important of this group is rotogravure 9 ¦ printing from polished copper electro-deposited on an iron, ¦-stee1 or aIuminum base. The design is etched into the coppsr 11 1 by photoengraving means. Gravure inks rely for drying 12 ¦ mainly on solvent evaporation, and, there~ore, gravure 1 inks usually contain large amounts of hydrocarbon solvents.
1~ ¦ Not only are these solvents highly inflammable, forming 1 explosive miY.tures wi~h the atmosphere, but the vapors axe also l~ 1 extremely toxic. Because these undesirable properties involve 17 ¦ significant expendituxes for flameproo~ electrical equipment ¦ and hoods and duct work f~r containment and recovery o~
l9 the solvent, an aqueous rotogravure ink which has suitable ink transfer properties has long been an industry need.
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SU~ ARy 3~)~69~;~
The instant invention involves the discovexy that polyethylene oxide resins can be added to aqueous printing inks to improve ink trans~er properties. Spec-ifically, from 0.1 to 1.5 percent by weight o~ a polyethylere oxide having a molecular weight in the range of from lOQ,000 to 350,000 is added to an aqueous printi~g ink It is, therefore, an object of the instant invention to provide an aqueous printing ink composition having improved transfer properties.
It is a further object of the instant inventio~
to provide an aqueous pig~ented flexographic ink which prints out stronger, has increased brilliance, increased intensity of color, and increased clarity.
It is still another object-of the instant inven-tion to pro~ide an aqueous pigmented flexographic ink which has increased scuff resistance, and has substantially reauced mottle, featherlng and striation.
Thus, in accordance with the present teachings, an ink composition is provided which consists essentially of an aqueous printing ink and polyethylene oxide which has an average molecular weight of from 100,00 to 350,000.
In accordance with a further embodiment of the present teachings, a method is provided for improving the transfer characteristics of an aqueous printing ink which comprises adding to the ink polyethylene oxide which has an average molecular weight of from 100,000 to 350,000.
, O~her objects and advantages will be apparent ~rom the~-description-which follows. The following Examples will serve to i.llustrate specific embodiments of the in~e~tion.

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2 An a~ueous black pi~mented f~exoyraphic ink

3 was prepared by miY.ing together the following lngredients;
36 percent by weight of ink varnish, lS percent by weight carbon black, 5 percent by weigh-t of a combined sur~actant, 6 10 percent by weight of a synthe~ic water-based resin, 1 7 percent by weight of wax, and 28 percent by weight water .
8 The aqueous ink mixture was blended together in a mixer for approximately 20 minutes and then passed through a sand mill to reduce any agglomerated particles and to form 11 a smooth finish ink. A 5 percent by weight portion of a 12 solution consistiny of 12 parts by weight polyethylene 13 oxide in 88 parts by weight water was then added to the ink.
1~ Because the forces applied to the ink during the blending and sand-milling operation have been found to destroy the 1~ improvement in ink transfer proper~ies obtained by the 17 presence of polyethylene oxid* it is important to add ~he 18 polyethylene oxide subsequent to the sand-milling.
19 The ink was put on a flexographic printing press and ~he ink viscosity adjusted by means of an efflux 21 viscometer to 16 ~2 Zahn seconds-and a series of corrugated 2~ cartons printed. The cartons had excellent printing 2~ color coverage. The ink ran well and washed up well on the press.

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, l The ink varnish, along with the water-based :, 2 resin used in the a~ove formulat.ion, functions as a ' vehicle which s,erves as a dispersiny, carrying and binding , .4 medium for the pigment pzrticles. The varnish and .
;`~ resin provide the necessary flow, ~ack and plas~icity ' to allow the ink to distribute o:n the press and tran~er .
from the ~ollers to the plates a:nd in turn, to the surace ' .
~ to be printed. The ink ~arnish used in Example X was a ;- maleic rosin solution, a~ailable ~rom Filtered Rosn Co., 1~: under khe trade designation ~5001. The synthetio water-.lI ~ased resin used was a st~renated soya type, commercially , 12 available from A.E. Staley Co. under the trade des,ig- .
13 . nation P3-103. Numerous ink varnishes and water-based res~ns.
14 are uitable ~or ~lexographic inks, as is known in the a~t, .
The choice of varnish and resin depends,upon the speed o .
l6 drying re~uired, gloss, hardness and adhesion requirements, .' economic factors and.the nature of the surface to be ' l~ .printed. The wax used was Fisher-Tropsch 215F-223F' M.P.
lg commercially a~ailable from Dura Comm~dities Co., under .
~he trade designation Microfine Vl. Solid petroleum l~ .
2} products such as paraffin wax ox micro crystalline wax - ~:
2~ a_e commonly added to printing ink formulations to ¦~
23 reduce or eliminate off-setting, to keep the i~k from pene- ¦
24 trating too rapidly into the stock surfaces and ko impart . 1.
2~ a measure of slip and scuff-resistance. ' '' - .'.
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~1 lOg~g8Z l l l s-13866 1 1 The combined surfactant included minor amounts 2 ¦ of the following; a nonionic surfactant, based on tetra-3 ¦ methyl decynediol, commercially available from Air Produc~s

4 ¦ and ~hemicals, Inc., under the trade designa~ion Su-fyn~i~
¦ 104; lecithin, avcailable from Ross and Rowe,Inc~, a mixed 6 ¦ aminohydroxy compQuna available from Commercial Solvent 7 Corp., and a silicone de~oamer available from Dow Chemical 8 Corp.
The polyethylene oxide used was a nonionic homopolymer, commercially available from Union Carbide 11 under the trade designation ~O~YOX WSR N-80. Rheological 12 measuremen~s indicate tha~ the resin has a relatively 13 narrow distribution of molecular weights and an average 14 molecular weight of 200,000. The viscosity range, at ~5C, using a Brookfield spindle No. l, 50 revolutions per l~ minute, is ~iven as 81-lOS cps for a 5 percent solution.
17 1 Polye~hylene oxide polymers are polar linear l8 ¦ resins characterized by a relatively large number of l9 ~ polar groups in the molecule. Such polyethylena p~lymers ¦ ccin be prepared by polymerizing ethy1ene oxide in 2} ¦ contact wit~ a catalyst such as an alkaline earth 22 ¦ amide or hexammoniates as is well known in the polyme~ ar~.
23 ¦ Polyethylene oxides which can be used in the ~a ¦ present invention are those which have average molecular 26 ¦ weights in the rc~nge of lOO,OOO to 350,000, preferably about 2~ ¦ 200,OGO. The polyethylene can be present in an am~unt 2r ~
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l of ~rom 0.l to 1.5 percent by weight of the ink. Preferably 2 the polyethylene oxide is present in an amount of from - 0.4 to l.0 percent and most desirably, about 0.7 percent.
4 Amounts greater than l.5 percent appeax to create press problems 6 during the printing operation.

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8 For purposes of comparison, but not in accordance 9 with the instant invention, a black pigmented aqueous flexographic ink composition was prepared as described in ll Exa~ple I, except that polyethylene oxide was not added.
12 ~he ink ~iscosity was adjusted to 21 ~2 Zahn seconds, and 13 a series of corrugated cartons printed.
14 A side-by-side comparison of the printed cartons indicated that the composition containing polyethylene 16 oxide showed an increased blackness of print and greater 17 ¦sharpness. The ink containing the polyethylene oxide had 8 ¦increased s~uff resistance and dried faster with less smear.

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iO9698Z
S-13~66 1 EX~PLF, II

2 - A~ueous 1exographic inks haviny the compositions 3 shown below were prepared as described in Example I.

Blue Red Percentage Percentage 6 By Wei~ht B~ Wei~ht Ink varnish 20 Ink varnish 15 8 Synthetic water- Synthetic water-9 b~sed varnish 15 based varnish 14 Suractant 2.5 Surfacta~t 2 -'10 11 *Clay-pigment 15 *Claypigment 5 12 Caxbon black base 2.5 13 Titanium dioxide 16.5 Titanium dioxide 6 1~ Phthalo~yanine blue 3 Molybdate orange 20 r ~ethyl violet base 2.5 Lithol rea 12 15 Wax 1.0 Wax 1 16 ~later 17.5 Water 20 **P~lye~hylene oxide 5 **Polyethylene oxide 5 1~ (watex solution) (water solution) 19 . .
*The clay pigment functions as an extendPr pigment.
21 A suitable extendex is commercially available from Thiele 22 Kaolin Co., under the trade designation Bur~es~ ~80, 23 **Prepared as described in Example I by adding 12 24 parts by weight polyethylene oxide to 88 parts by weight water. ~
26 The inks were placed on a flexographic pxinting 27 pxess and the ink viscosity adjusted to 16 ~2 Zahn seconds.

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l ¦ Comparative tests were conducted using corres-¦ ponding red and blue inks ~hich did not contain poly-3 I ethylene oxide. The color o both the red and blue inks containing polyethylene oxide was more intense on the

5 ¦ cartons than the color of the regular inks. In addition,

6 ¦ the inks oE the instant invention eliminated the striation

7 I which was presant on the cartonsprinted using the regular

8 ¦ ink.
g ¦ Experimental tests were conducted to determine ¦ the effect of substituting carboxymethyl cellulose or ll I polyvinyl alcohol for the polyethylene oxide of the present 12 I invention; no improvement of ink transfer properties was 13 I obtained.
l~ ¦ Further experimental tests indicate that the ¦ a~ueous fl~xographic in~s o~ the instant invention have 16 ¦ numexous advantages over flexographic inks known in 17 ¦ the art. Increased color, sharpness and intensity are 18 ¦ obtained. In addition, the inks pxovide ~irtual elim-l9 1 ination o print striation, minimize print mottle, and ¦ mask roller defects. Other advantages include increased 21 ¦ mileage thrQugh greater tolerance of water dilution, 22 I qreater color uniormity in a high and low viscosity 23 I range, improved printing on rough surfaces and increased 24 ¦ lubricity which reduces die wear.
1 Since xotogravure inks and flexographic inks 26 ¦ both contain signiicant amounts o solvents and have a 27 ¦ low viscosity, a~ueous rotogravure inks, containing polyethylene 28 ¦ oxide to improve ink transer properties and to reduce wear on ¦ the expensive copper or chromium ~aced cylinders can be I prepared.
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Claims (8)

WHAT I CLAIM IS:

1. A method for improving the transfer character-istics of an aqueous printing ink which comprises adding to the ink polyethylene oxide having an average molecular weight of from 100,000 to 350,000.

2. A method as claimed in claim l wherein the amount of polyethylene oxide added is from 0.1 to 1.5 percent by weight.

3. A method as claimed in claim 1 wherein the amount of polyethylene oxide added is 0.7 percent by weight.

4. A method as claimed in claim 1 wherein the ink is an aqueous flexographic ink.

5. An ink-composition consisting essentially of an aqueous printing ink and polyethylene oxide having an average molecular weight of from 100,000 to 350,000.

6. A composition as claimed in claim 5 wherein the amount of polyethylene oxide present is from 0.1 to 1.5 percent by weight.

7. A composition as claimed in claim 5 wherein the amount of polyethylene oxide present is 0.7 percent by weight.

8. A composition as claimed in claim 5 wherein the printing ink is an aqueous flexographic ink.