CA1330177C

CA1330177C - Printing ink system for the production of rub-off printings

Info

Publication number: CA1330177C
Application number: CA000610066A
Authority: CA
Inventors: Albert Amon; Dietmar Kiewitz
Original assignee: SICPA Holding SA
Current assignee: SICPA Holding SA
Priority date: 1988-09-05
Filing date: 1989-08-31
Publication date: 1994-06-14
Anticipated expiration: 2011-06-14
Also published as: FI894138A0; HK52396A; FI100663B; ES2051383T3; EP0358610B1; DE58907445D1; KR900004890A; JPH02167372A; NO893544D0; CH674989A5; AU4097389A; AU612884B2; EP0358610A3; EP0358610A2; NO893544L; ATE104324T1; FI894138A; NO306473B1

Abstract

ABSTRACT
The printing ink system of the invention is destined and appropriate for the production of opaque printed areas, which can be removed by rubbing or scratching, on predetermined areas or regions, which should perfectly be covered, of a flexible substrate by typographic or offset processes. The system comprises a release ink and a metal pigment containing covering ink to be printed on the release printings.
The binder phase of both inks which are substantially solvent free, comprises mainly high reactive, oxidation drying products and monomers or prepolymers. Chemical drying is induced either by influence of air oxygen, optionally backed up by additional heat such as infra-red, or under the influence of ultraviolet light.

Description

t PRINTING INR SYSTEM ~OR THE PRODUCTION OF RUB-OFP
pRINTINGS

Thi~ invention belongs to the ~ield of the docu~ent println0 art and i~ related more specifically to an off6et or typographic printing ink system for the production o opaque printing~ which can be removed by 5 rubbing.
It ls well known to produce prin~ed products having mec~anically removable regions or area~ where under-lying, generally pxinted indi~ia are covered by an opague layer which can be removed by rubbing under di~lntegration of the covering layer. Application example~ thereof are lottery ticke~s where th~ customer may find out, immed~ately after the p~rchase of tho ticket, whether it has won or not when he rubs off the indicated areas to loo~ what i~ printed benea~h.
A6 a general rule, damage free removable cove~ing layers on secu~lty documcnts serve to temporarily hiding of alphanumeric indicia or information such as numbers, name~, other group~ of ~etters as well as combinations of numbers and names, but al~o of image in~ormation including colour~. ~he covoring layer must be perfcctly opaque when seen ln incident or traversing light.
; Untll now, the covering~ of the l~dicated kind are produced by offset p~inting of a printing carrier on ` the whole surface, including the region~ to be cover~d ~termed as "cover area~"), and then printing by ~he method of scre~n printing a transparent release layer which may be coloured at will, onto the cover areas. In a fur~her ~creen printing step, the pigment containing . cov~rlng layer forming a d~troyable film, thus the true rub-o~f layor, is appliod. ~he plgment~ are preferably metal particles, espocially o~ aluminum, which could also bo coloured by anodising, in ordor to o~tain a . . ~
~ 1 - ~

r 13~0177 perf-ct opaclt~.
Screen printing ink~ ~re solvent containing ~y8tem8 which must be applied in very thick layers. Scroen printing i~ a time con¢uming coating pro~ess, and after 5ink application, the solvent must be evaporated in the ~o called heat tunnel and tho ink ~ust be dried. ~he solvent which ha~ been evaporated con~titute~ a ~trin-gent problem for mo6t owners of su¢h pr~ntlng plants due to the eevere cloan alr legi~lation in most countries.
10The appllcation of ~uch high layer thicknes~es has of course a great lnfluenco on the costs of the flnal produ~ts.
Screen printing lnstallations do not exlst in mogt offset printing shops so that ~he products having beon printed by off~et or typography must generally be shipped to another printing plant in order to apply the ~`; rub-off coatlngs. Th~refore, there is already a long lasting no~d for a possibility to apply al80 the rub-off layer by typography or offset.
~ 20The reali6atlon of this demand ha~ been hindered by `-~ the technical prejudlce that offset te~hniques would not be capabl~ to proauce cov~ring layers. This opinion i~
b~sed on all exper$ence~ maae until now~ it i~ an accepted ~act that of~set can only produce layer thick-nes~c~ of about 2 - 3 ~m per pr~nting pa~sagc wherea~ by ~creen printing, layers of 20 ~um and more can be ob-~ained.
It h~s now been found th~t ~his prejudice is based on known off~et in~s and their developments and impro~o~
mentR which are ~lthin the knowledge of the m~n ~killed in eh- art.
;The fir~t and main ob~ect of this invention i~ to dov~l~p o~et or typcg~phic ink- which will p~oduce prlnting layer~ bein~ perfectly opaquc when seen ln inciaen~ and trav-r-inq light.

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133~ 77 Another object of the invention is to provide such offset or typographlc inks which for~ a ~ystem capable of producln~ opa~ue printed layers, whlch can be removed by rubbing, on flexible ~ubstrates.
5Still another object o~ the invention is to p~ovide such printlng lnks which can be printed on flexible substrates already printed with indicla or other infor-mation, and which will well adbere even on the already pr~nted area~ the man ~killed in the art knows th~t ~t 0 i8 generally di~ficult to overprint such areais where the adherence of the overprinting is normally low, often unsufficient.
And a further ob~ect oP the invention i8 to provide curable o~fset or typographic ink systems givinq opaque covering layer~ wieh a minlmum of printing passage~ and at low cost.
Theso ob~ects and still other6 are met by the printing ink ~ystem of the invention which will be defined and described below in more detail.
The rub-off prlnt~ng ink ~ystem of the invention now elim~n~tes the drawba~ks of the screen printing pro~
~esses and t~e ~creen printing inks. The printing ink of the inventlon which is applied by the techniques of typography or offset and which gives printing layers capable of being removed by rubbin0 i8 composed of two partial systems whicb will bo described below in detail.
The system comprises a release ink for the production of a relea8e printing, and a covering ink for the production of an opaque, rubbing-off printing on said release pr~nting, wherein ~he release ink and the covering ink are chemical ~urab;le lnks printable by typographic oe o~fset proce~ses. The releaee ink contains at lea~t one unsaturated, polymer~able compound as a binder and an oleophobic polymer or wax as a release agent. ~he covering ink, th~ second part of the ~ys~em, contains at F ' ' . .
. I , . . .

lea~t one unsaturated, polymerizable compound as a b1nd~tr 1~l~ A It~ C~ YIU~IIL a4 all up~:lfl~r-Prlntlng can be accompli~hRd by typography, dry off~et or wet offset~ All ~lexible substrate~ which can 5 be prlnted by the~e processes can be ~sed a~ printing support~. Tbe ink distinguishes by a perfectly approp-riate printing behaviour on all known offs~t printlng machines. The results which are obtain~d can be compared with the 6creen printing quality r~garding opaeity and rubbing~of properties. The mechanical re~i~t~nce~ of the covering metal pigmented printings are better than tho~e of the gcreen prlnting ink~. Furthermore, the printing 6peed i8 substantlally high~r than screen ~rinting ~p~d lS Accoraing to thl6 lnvention, the release lnk is a highly reactive system with chemical drying. Chemical dryl~g ~ ln contra4t to phy~ical d~ylng only compri~i evaporating a volatile solvent, i9 kno~n to be a poly~
merization and/or a curing reactlon tran~Sormin~ liquid component~ lnto soiid one~ (~ee Klages, Lehrbuch der -~ organischen Chemle, ~erl~n 1967, Vol. III, p. 394).
~ow~ver, t~i~ doeJ not necessarily mean that a chemi-cally drying printin0 ink i~ totally free from ~physi-cally drylng) ~olatile ~olvents.
Surprislngly, it ha~ been ound that already very thin rele~se layer~ will be sufficient for the aimed purpo~e, namely the degree of re~ection of the covering layer. Witbout willing to ~e bound by an explanation which co~ld bc l~mit t~e inventlon, there ~e indica~
~n 1 i ~n~ th~t ~h~ o ~gor~o ln ~ho rclo~e~c p~ln~lng ink will mlqrate during the poly~erization of the binde~ ~oward~ ~he surPac-s or will be displaced thereto ~ c~ Lh~y ~L~ IIU lu~ cumpatlb~e wl~n tne po~ymerlzea blnder. ~n ~ny ca~e, the release effect is enhanced after polymerlzation.

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~l 1330177 -As a polymerizable system, modified un~atur~ted vegetable oil~ and fat~ can be used in the relea~e ink a~ well a~ in the covering ink~ Modifylng component~ are I for example colophonium and rosin optionally partially e~terified, aromat$c acids or allphatic alcohol~. In this case, the knOwn metalic cataly~ts, specially ; ~obalt or manganese nophthenate or octoate, can be used.
These ink~ may contain small a~ounts of hlgh boiling solvent~, about up to 10 ~, a~ a vi~cosity controlling ¦ 10 agent.
~he lnvention fur~her comprisee release and covering I ink~ whose dryl~g is initiated by radiation, namely I whose binder~ polymeriz~ or reticulate under the ln-¦ fluence of ultraviolet light (UV light) and which will 1~ 15 be used in ~uch cases where the already existing offset - printing machine is equipped wlth an ultraviolet dryer.
The~e in~ sy~eems of the lnventlon will be used on sheet and rotary printlng machines. An important advan-tage of the printing ~ystems of the invention is the immediate drying of all come~nents ~nd tbus the possi-bility of immediate further proce~sing.
` ~ As a general ~ule, the covering prlntlng ink is a two component ~ys~em. One component contains ~he poly-merizable binder together with the accelerator and any othor additive6, and the other component is a metal '~ pigment paste. Both component~ ar~ normally mixed together lmmediately before printing accordin,g to a ' predete`rminated mlxing ratio.
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A~ a pigment, very finely devided metals normally u~ed in p~inting in~ will the employed. Such metal~ are aluminum whlch ~ay b- coloured by anodisation, bras~
but even copper, sll~er and gold for very high quality I purpo~es.
The compon~nt~ to bo used in ~he peinting inks are 3S gen-rally known per se. Pre~erably, the rele~ae ink 1 ~ _ 5 _ ' .: . - . .

! i $f 1 3 3 ~ 1 7 7 ~

cont~ini as a release agent, a polysiillcon compound together with a mi~rocrystallin~ wax, but these two substance~ can al50 be used separately. Particularly prefered are polysiloxane acrylates a~ release agents in S the relea~e ink.
The following examples are given only for illustra-tion purpo~es. They w~ll no~ llml~ the invention whose s~ope i8 defined by the claims. All amo~nts given in the examples are by weight and refer to the weiqht of the finiished ~nk lf not otherwise indicated.
., ExamPle 1 ,: ~, Air-drying infrared active printing ink ~ -' . ~ ',~.'."
A. Relea~e ink ---- ' - .. .' The following components are mixed together:
- vegetable oil haviny an eleastearinic :~
acid content of about 75 ~ by weight and modified with rosln (Oil CP):25 to 35 - llnseed oil refined and modified with acid, alcohol and ro6in tOil CL~: 30 to 36 - polysillcono and microcrystalline wax: 25 to 35 25 - cobalt naphthenate, mangane~e ; naph~henate 0,10 to 0,20 - aromate free mineral oil, b.p. 240 to 310 Cs 5 to 10~ - -30 ~ Coverinq lnk -~
-: . . , . -- Ol~ CP: S to 15 - Oil C~s 40 to 50 - ~luminum paisite, calculated as Al 35 to 4S~
- cobalt naphthenAte, manganese n~phthenate 0,1 to 0,2 ' ~ _... .. . . . ......... . , ,.. , ... . . ~

133~177 - ~

- aromate free mineral oil, b.p. 240 -to 310 Cs 5 to 10~

For printing, fir~t the releasing ink i~ printed by wet offset or preferably by typography and ary off~et until a glossy printing is produced after drying. In most cases, t~o pas~age~ are sufficient. ~he printing ls then stored for about 48 hour~ in order to complete curing by oxidation.
~hereafter, the covering ink is printed in the same manner where only one passa~e is generally ~ufflcient.
After the chemical drying o~ the covering layer, the rub-off printin~ i6 ready for use.
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. , .
W drying println~ ink A ~elease ink . ... ..
- - prepolymer ba~ed on epoxy-, urethane~
polye~ter- or styrene-butadiene-acrylate, alone o~ in combination tPrepolyme~20 to 50 - - multifunct~onal acrylat~ monomers:20 to 40%
- poly8110xane ~crylate: 10 to 30%
- benzoph~none 4 to 6 ` - amine based co-lnltiators 6 to 15S
- acetophenone deri~ative~ or benzil ketals: 4 to 6S
- 1uorinated organic ~alts: 1 to 3 - paraf~ine and teflon waxe~ 5 to 10 .
_~ .
- prepolymer I~ 80 to 90~ `
. ..
~- 7 - :
. ' ' r 133~177 ..
~ multifunc~lonal acrylate monomers:o to 10 - acetophenone deriv~tives or benzll ketals: 4 to 64 ne ba~ed co-lnltlatori~ 4 to 6%
:
5component 2:metal paste ~ aluminum bron~e (gold or silver bronze) 2 60 to 70%
- solvent and wetting agent: 40 to 30 . ,-.. :.:
The drying of thiiEi ~ystem requires UV drying in~
8tallations which are g~nerally used presently in the field of o~fset and typographic printing. The drying ~8 effected by intermediate and/or final drying and is accompli~ihed ~a~iter than the heat induced chemical drying.
In general, both inks of the system may be applied in dry offset processes and by typography, thicker ~-coverlng layer6 ~elng obtained in typography by means of nyloprint clichQs.
First, the release ink i8 printecl. According to the proper~les of the support, one or two applications may be nece~sary for complete covering. The application can be made ln two printing units by wet-in-wet or wet-on-dry, an intermediate drying being effected by UV. A ~ -su~iciently thick release layer is visible by gloss and the illing degreo o the printing and is a ne~esa~ry condition for the good rubbing effe~t of ~he me~al pigmented covering layer printed afterwards. ~ ;~
When the release printing paiss~8 the UV dryer, spontaneou3 drying, i.e. polymerizatlon~ of the layer i8 obtained. This lay~r will then be oveS~prlnted by the covering printinq ink.
~n order to obtain the covering ink ready for use, ~he Yarni~h (component 1) is thoroughly mixed with the -metal pa~te (component 2) in a weight ratio eomprii3ed , :

1 ... .... .

between about 5:5 and abou~ B22, preferably about 6:4 to about 7:3, according to the desired covering degree. In order to perfeetly coverin~ the undergroUnd colour which i8 already covered by the teansparent release prlnting and which should correspond, as far as pos~ible, to the tone of the metal ink, the appllcation of the covering ink ~hould be made in two prlnting units by wet-in-wet or wet-on-dry with an intermediate drying by UV.
The intermediate drying prod~ce~ a thicker co~ering layer and a ~ub~tantially better overall dryin~ of the printing~
The printing inks of the ~nvention can be modlfled in the scope of the cla~m6 and its aqulvalents. For example, pigments or other dyestuffs can be incorporated in All inks. The nature and the amount of the components can be chan~ed and adapted to speclal uses. It is only important that the inks must be capable o~ chemlcally drying~ The 6ubstrate to be printed may be a paper or any other substrate, for example plastic sheets.

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Claims

1. A printing ink system for the production of opaque printed areas, removable by rubbing, on flexible sub-strates, comprising a release ink for the production of a release printing, and a covering ink for the produc-tion of an opaque, rubbing-off printing on said release printing, wherein the release ink and the covering ink are chemically curable inks printable by typographic or offset processes, said release ink containing at least one unsaturated, polymerizable compound as a binder and an oleophobic polymer or wax as a release agent, and said covering ink containing at least one unsaturated, polymerizable compound as a binder and a metal pigment as an opacifier.

2. The printing ink of claim 1, wherein said covering ink further contains a small amount of an organic silicon compound as an agent facilitating the disinte-gration of the opaque covering printed layer.

3. The printing ink of claim 1, wherein both said release ink and said covering ink contain at least one modified polymerizable vegetable oil as a binder toge-ther with a metal naphthenate or octoate as a accelera-tor, said ink being capable of drying by oxidation.

4. The printing ink of claim 1, wherein both the release ink and the covering ink contain at least one acrylate monomer or prepolymer polymerizable by ultra-violet radiation, as a binder together with an amine as an accelerator and the covering ink is a two component system being mixed just before use, one of the two components containing said polymerizable binder together with accelerator, and any additives, And the other component comprising a metal pigment paste, said ink being capable of drying under ultraviolet radiation.

5. The printing ink of claim 3, wherein said release ink contains a polysilicone compound together with a micro-crystalline wax, as a release agent.

6. The printing ink of claim 4, wherein said release ink contains at least one polysiloxane acrylate as a release agent.