WO2005085369A1

WO2005085369A1 - Radiation-curable compositions for inks

Info

Publication number: WO2005085369A1
Application number: PCT/EP2005/002321
Authority: WO
Inventors: Paul Gevaert; Françis BERGIERS; Thierry Randoux
Original assignee: Cytec Surface Specialties, S.A.
Priority date: 2004-03-08
Filing date: 2005-03-04
Publication date: 2005-09-15

Abstract

The present invention relates to radiation-curable compositions comprising at least a ketonic resin based on acetophenone and formaldehyde and at least one (meth)acrylated compound useful as ink vehicles or inks, in particular UV-curable inks, such as UV-litho inks and screen inks for application on glass substrates.

Description

Radiation-curable compositions for inks

The present invention relates to radiation-curable compositions useful as ink vehicles or inks, in particular UV-curable inks, such as UV-litho inks and screen inks.

UV-litho inks based primarily on fatty acid modified polyester acrylate have been used since the 70ies with increasing success. Compared to conventional ink systems UV- inks exhibit faster curing versus oxidative drying and provide an easier printing process because of no drying on the rollers, which leads to short start-up times and less waste. However, fatty acid modified polyester acrylate-based inks still show several performance shortcomings compared to conventional ink systems like the ink- water balance (lack of ink- water emulsion stability on press), pigment wetting (lack of flow in ink duct), higher tack (picking) and higher misting, especially at higher press speeds.

UV-litho inks for plastics are generally based on (chlorinated) polyesters diluted in acrylated diluents such as trimethylolpropane triacrylate, propoxylated trimethylolpropane triacrylate, propoxylated glycerol triacrylate.

While the known UV-litho inks exhibit good performance in some of their parameters, there is still a need for further ink vehicles and inks having improved properties such as improved pigment wetting and improved ink water balance, both combined with high cure speed, and good adhesion, especially onto plastic substrates. Moreover, inks based on chlorinated polyesters possess the disadvantage of producing HC1 during UV/EB curing.

European patent application EP 902065 Al discloses the use of ketonic resins based on urea or urea derivatives and aldehydes as pigment wetting resin for UV- inks. Such inks show low cure speed in comparison to inks based on chlorinated polyesters. Chlorinated polymers have also a bad connotation of being not environmentally friendly.

It has now surprisingly been found that when a ketonic resin based on acetophenone- formaldehyde is used in combination with aciylated compounds in radiation-curable compositions, these problems could be overcome. Therefore, the present invention relates to a radiation-curable composition comprising at least one ketonic resin based on acetophenone-formaldehyde having a structure (I) or/ and (II) wherein n is at least 1 and at least one (meth)acrylated compound.

Acetophenone-formaldehyde based ketonic resins are known in the prior art. Commercially available ketonic resins which can be used in the compositions of the present invention are generally the condensation products of formaldehyde with acetophenone.

Examples of commercially available ketonic resins based on acetophenone and formaldehyde are Kunstharz AP and Kunstharz SK (Degussa).

A process for preparing ketonic resins is for example disclosed in French patent FR

1595632.

Ketonic resins wherein n is at least 3, more preferably at least 5, most preferably at least 7 are preferred. Ketonic resins wherein n does not exceed 100, are preferred; more preferred are resins wherein n does not exceed 20; most preferred are resins wherein n does not exceed 15.

(Meth)acrylated compounds usable in the compositions of the present invention are those currently used in radiation-curable compositions. The (meth)acrylated compound or the mixtures thereof used in the composition of the invention are preferably liquids at room temperature.

The (meth)acrylated compounds used in the present invention can be in the form of monomers, oligomers or mixtures thereof. Acrylated compounds are prefered. Monomers can be mono- or poly-functional and are preferably chosen from acrylates, such as isobornyl acrylate, phenoxyethyl acrylate, tetrahydrofurfuryl aciylate, dipropyleneglycol diacrylate, tripropyleneglycol diacrylate, 1,6-hexanediol diacrylate trimethylolpropane triacrylate, ditrimethylol propane terra acrylate, dipentaerythritol hexa acrylate, pentaerythritol triacrylate, pentaerythritol terra acrylate or alkoxylated acrylates. Alkoxylated acrylates are generally chosen among mono-, di-, tri- and polyhydroxy compounds being alkoxylated and acrylated. The preferred alkoxylates are ethoxylates and propoxylates. Each of the hydroxy groups of the polyhydroxy compounds may bear one or more, generally 1 to 10, preferably 2 to 5, alkoxy moieties, deferred are ethoxylated neopentylglycol diacrylate, propoxylated neopentylglycol diacrylate, ethoxylated trimethylolpropane triacrylate, propoxylated trimethylolpropane triacrylate, ethoxylated glycerol triacrylate, propoxylated glycerol triacrylate, ethoxylated pentaerythritol tri/tetra acrylate, propoxylated pentaerythritol tri/tetra acrylate, acrylated bisphenol A ethoxylate, acrylated bisphenol A propoxylate. Preferred monomers are trimethylolpropane triacrylate, ditrimethylol propane tetra acrylate, 1,6-hexanediol diacrylate, ethoxylated trimethylolpropane triacrylate, propoxylated glycerol triacrylate, ethoxylated pentaerythritol tri/tetra acrylate, more preferred is trimethylolpropane triacrylate. Examples of oligomers include amino (meth)acrylates, polyester (meth)acrylates, urethane (meth) acrylates and epoxy (meth) acrylates. Preferred oligomers are urethane (meth)acrylates.

In case that a very high adhesion of the composition is required, it is especially preferred to use at least one ketonic resin of formula (II).

The compositions according to the invention may comprise other inert resins, which do not take part in the polymerisation reaction, such as hydrocarbons (such as styrene based hydrocarbon resins), acrylics (such as acrylic (co)polymers), styreneallylalcohol, phenolic resins, rosin-modified resins, other ketonic resins, alkyd resins or any combination thereof. The total amount of such inert resin or mixtures thereof does usually not exceed 40 % by weight, preferably it does not exceed 30 % by weight.

Generally, the composition of the present invention comprises the minimum amount of 10% by weight, more preferably a minimum amount of 15% by weight and most preferably a minimum amount of 25% by weight of ketonic resin having a structure (I) or/ and (II), based on the total weight of the composition.

The amount of such ketonic resin in the composition usually does not exceed 90% by weight, preferably does not exceed 85% and more preferably does not exceed 75% by weight.

Generally, the composition of the present invention comprises the minimum amount of 10% by weight, more preferably a minimum amount of 15% by weight and most preferably a minimum amount of 25% by weight of the (meth)acrylated compound, based on the total weight of the composition.

The amount of (meth)acrylated compound in the composition usually does not exceed 90% by weight, preferably does not exceed 85% and more preferably does not exceed 75% by weight.

The composition according to the invention preferably has a viscosity higher than 1 Pa.s measured at a shear rate of 2.5 s^"l at 25 °C (measured using a cone and plate type rheometer with a cone diameter of 25 mm and at an angle of 1° for the cone). The measurement is generally done by measuring a flow curve in controlled shear rate ranging from D = 0, 1 s^{" 1} to D = 100 s^{' 1} at 25 °C.

The composition according to the invention more preferably has a viscosity measured as here above of at least 5 Pa.s. The viscosity of the composition generally does not exceed 500 Pa.s, preferably it does not exceed 250 Pa.s (at 25 °C and 2.5 s"l).

The composition according to the invention permits to obtain improved pigment wetting, improved ink water balance, high cure speed as well as good adhesion on plastic, glass and metal substrates. Furthermore, ketonic resin-based radiation- curable inks are environmentally friendlier than chlorinated polyesters which are typically used in radiation-curable inks for plastics.

The radiation-curable composition of the present invention is therefore useful as ink vehicle for the preparation of inks, such as UV-litho inks and screen inks. Therefore, the composition may further comprise one or more other compounds. These compounds are generally selected from pigments, photoinitiators, fillers and additives.

The pigments usable in the compositions of the invention are every pigments used in paste inks or liquid inks. A list of such pigments can be found in the Color Index. More particularly, those pigments may be cited such as Process Yellow 13 (Diarylide Yellow - Irgalite BAW of Ciba, Permanent GR of Clariant), Process Magenta Pigment 57 (Bona Calcium - Ilobona 4BY of Sun, Irgalite SMA of Ciba), Process Blue 15.3 (Copper Phthalocyanine - Irgalite GLO of Ciba, Hostaperm Blue B2G of Clariant), Process Black 7 (Oxidised Carbon Black - Special Black 250; Special Black 350 of Degussa), Ti0₂, etc. The pigments are preferably used at 0-40 % by weight of the total weight of the composition, more preferably at 1-30 % by weight.

The photoinitiators usable in the compositions of the invention are well known in the art. They can be chosen from α-hydroxyketones, α-aminoketones, benzildimethyl- ketals, acyl phosphines, benzophenone derivatives, thioxanthones and blends of these. They are used at 0 to 15% by weight. Generally, photoactivators are chosen between amine derivatives. The photoinitiators need only be used if the compositions are cured by ultraviolet light. The compositions may also be cured by electron beams rays, and, in this case, no photoinitiator needs to be added to the composition.

The additives are those commonly used in inks, such as stabilizers, substrate wetting agents, anti-foam agents, dispersing agents, etc. The total amount of those additives does usually not exceed 5%. As fillers products such as calciumcarbonate, talc (magnesium silicate), kaolin clay (aluminium silicate), bariumsulphate, aluminium hydroxide, siliciumdioxide can be used . The amount of fillers is generally from 0 to 15%.

The compositions according to the invention can be prepared by any method suitable therefore. They are usually prepared by dissolving the ketonic resin in at least part of the acrylated compound, preferably at a temperature of at least 30 °C, more preferably of at least 60 °C, most preferably of at least 80 °C. The temperature preferably does not exceed 150°C, more preferably it does not exceed 130 °C. Alternatively, the compositions according to the invention can be prepared in the presence of an organic solvent, which is thereafter eliminated from the composition, for example by stripping.

The compositions according to the invention show good adhesion on glass and coated glass, good chemical resistance, improved hot water resistance and good scratch resistance. They are therefore especially suitable to be used for the preparation as screen inks for application on glass substrates. In this case, the compositions preferably contain at least 5 % by weight of inert resin or mixtures thereof. Especially suitable are low molecular weight hydrocarbon resins and acrylic (co)polymers.

The compositions are also particularly suitable for the preparation of litho inks.

The invention also relates to a process for the preparation of inks, in particular litho inks and screen inks, wherein a composition according to the invention is used. Inks are generally made in 2 steps, the pigment dispersion step and the letdown step. The composition according to the invention can be used in one or both of these steps. The composition according to the invention is preferably used as binder at least in the first step. In the first step, the pigments and optionally a photoinitiator, fillers and/or additives are added to at least part of the composition comprising the ketonic resin and (meth)acrylated compound. They are mixed and then dispersed on a triple roll or bead mill. A few passes might be necessary to achieve a good dispersion. Pigments that are difficult to disperse generally require more number of passes. The compositions according to the invention showing good pigment wetting, permit to limit the number of additional passes. Once the pigment has achieved this fineness, the pigment paste is diluted with the letdown. The letdown has to be compatible with the binder used to disperse the pigments.

The finished ink is then printed onto the substrate. The ink film can then be cured under a UV lamp, for example at 120W/cm and 30 m/min. A few passes may be required to cure the ink if the binder is not reactive enough.

The invention also relates to the polymeric compositions obtainable by curing the radiation curable composition as well as to substrates being partially or entirely coated with the polymeric composition.

The invention will now be illustrated by the following non-limiting examples and tests which are by way of illustration only. Unless otherwise indicated, all the test results and properties herein were performed using conventional methods well known to those skilled in the art. The amounts in the tables are given in % by weight based on the total weight of the composition.

Pigment wetting can be evaluated by different methods:

?Rheology: Pigment wetting is a major factor of influence on the rheology. Inks with bad wetting of the pigment are showing a marked shear thinning effect, whereby the viscosity is high at low shear rate and drops as the shear rate is increased. This results in a high shortness index (SI = ratio of low shear viscosity to high shear viscosity. For liquid inks a Newtonian rheology is required. Ideally, this means that the viscosity is independent of the shear rate. (SI = 1). Paste inks are more pseudoplastic, showing a shear depending viscosity. (SI >1). Too high SI (too high low shear viscosity) may result in bad flow in the ink duct.

Optical density: Pigment wetting can also be evaluated by measuring the color density of the printed ink at constant film thickness. In this case the ink is printed using a lab applicator and the color density is measured with a densitometer, which spectrophotometrically compares the reflected light to the incident light. For the present invention the pigment wetting is rated on a scale from 5 = excellent to 0 = bad pigment wetting.

Rheology (yield value, viscosity, shortness index) is measured using a cone and plate type rheometer MCR100 (Paar-Physica). The measurement geometry for measuring the UV offset inks was of a diameter of 25 mm and an angle of 1° for the cone. The measurement was a flow curve in controlled shear rate ranging from D = 0, 1 s^~l to D = 100 s^{" 1} at 25 °C. The measurement geometry for measuring the UV screen inks of Example 2 was of a diameter of 50 mm and an angle of 1° for the cone. The measurement was a flow curve in controlled shear rate ranging from D = 0, 1 s^"l to D = 500 s^{" 1} at 25 °C.

The water balance of the compositions of the present invention was evaluated on lithotronic. Basically, the Lithotronic measures the torque needed for a certain speed (rpm). The torque gives a measure for viscosity. With the Lithotronic, the change in viscosity of an ink is measured when water is emulsified in it.

The measurement consists of two phases: preconditioning and measurement.

During preconditioning, the sample is sheared at constant speed and heated at the same time to a certain preprogrammed temperature. At the end of the preconditioning phase, the sample has reached a stable viscosity. At that moment, controlled metering of fount solution is started. Changes of applied torque (hence viscosity) versus time and emulsion capacity are recorded. When maximum emulsion capacity is reached, a drop in torque is usually experienced because of the free water in the beaker. At first contact with water, change of torque (delta T) should be small. Further, when water is emulsified in the ink, viscosity should only undergo a minor increase. This ensures a good ink transfer on the press. If the emulsion is too fine and too stable (too high increase of viscosity), it will lead to a loss of density and possible ink build up. If the emulsion is too coarse (viscosity decrease), it can lead to unstable press behavior making regular press control necessary.

For the present invention the ink water balance is rated by the type of emulsion (F = good ink water balance characterized by a limited viscosity increase, resulting from a fine emulsion; C = bad ink water balance characterized by a high viscosity decrease, resulting from a coarse emulsion). Example 1 : Compositions were prepared by dissolving the ketonic resins at 100 to 130°C in the acrylated compound. The following compositions (products A1-A3 and B1-B2) were obtained according to the invention:

Table 1

(1) Synthetic resin AP - Degussa (2) Synthetic resin SK - Degussa

The following comparative compositions were prepared as well: Table 2

(3) Laropal A81 - Basf (6) Laropal K80 Basf (4) Synthetic resin TC - Degussa (7) pDAP (5) Synthetic resin CA - Degussa (8) PP430 In the above Table 1 and Table 2 following abbreviations are used: Bis A: bisphenol A TMP: trimethylolpropane EO: ethyleneoxide DA: diacrylate TA: triacrylate Synthetic resin AP : acetophenone-formaldehyde resin having an OH value = 5 and AV < 1. GPC analysis showed a Mw value of 1500 and a Mn value of 920. Synthetic resin SK : acetophenone-formaldehyde resin having an OH value= 325 and AV < 1. GPC analysis showed a Mw value of 1355 and a Mn value of 895.

With the above compositions and comparative compositions the following ink formulations (wherein BisA(EO)₄DA is used as diluent) were prepared: Table 3

ω Stabilizer: polymerization inhibitor (5% solution of NPAL in DPGDA (DiPropyleneGlycolDiAcrylate) ; NPAL = Tris(N-nitroso-N- phenylhydroxylamine) aluminium salt ) ⁽²⁾ PI blend: 15 % Additol^® BP, 30 % Additol^® BDK, Irgacure™ 369 10 %, Additol^® ITX 15 %, Additol^® EPD 30 %

Various properties of the obtained ink formulations were measured. The results are summarized in the following Table 4:

Table 4

Cure speed: m/rnin at 120W/cm Pigment wetting: 0 = bad ; 5 = excellent Emulsion: F = fine ; C = coarse

Table 4 shows that the compositions according to the present invention (A2 and Bl) permit to obtain inks having higher cure speed and better pigment wetting in general in comparison to known compositions. Further ink formulations were prepared with the compositions and comparative compositions from Table 1 and Table 2 (wherein TMP(EO)₃TA is used as diluent). The formulations are summarized in Table 5. Table 5

Various parameters of the obtained inks were measured. The results are summarized in the following Table 6: Table 6

Cure speed: m/min at 120W/cm Pigment wetting: 0 = bad ; 5 = excellent Emulsion: F = fine ; C = coarse

The above results demonstrate that the compositions according to the present invention (A3 and B2) show a higher cure speed in comparison to prior art binders. Moreover, binder B2 exhibits an improved pigment wetting. Furthermore, a comparison between product Al according to the present invention and an ink formulation based on chlorinated polyester in 40%TMPTA (Ebecryl 436) was conducted with various pigments. The ink formulations prepared are summarized in Table 7: Table 7

Various parctmeters of the obtained inks were measured. The results are summarized in the following Table 8: Table 8

Moreover, adhesion of the obtained inks to plastic was measured. The results are summarized in Table 9 below: Table 9

*corona treated before printing

The results in Table 8 and Table 9 show that compared to prior art resins which are diluted chlorinated polyesters, the compositions covered by the invention have similar adhesion, similar or higher cure speed (without the presence of chlorine!), and much better pigment wetting (and better ink water balance.)

Example 2 A reactor was charged with 300 g of acetophenone- formaldehyde resin (Synthetic AP), 430 g 1,6-hexanediol diacrylate, 130 g toluene, 130 g of a low molecular weight acrylic copolymer and 140 g of styrene based hydrocarbon resin. The reactor was heated up to 90 °C under stirring and air-sparge until the solution became clear. The mixture was then cooled down to 80 °C and the toluene was stripped of by air-injection. UV- screen inks were prepared according to the following formulations :

* Photoinitiator blend: Additol™ITX(13.2) / Additol™EDB(13.2) / Additol™BP (13.2) / Additol™BDK(40) / Irgacure™369(20)

The inks were applied on glass substrates, cured by UV light and their performance was evaluated.

This table shows that the UV-cured screen inks present an outstanding adhesion on glass substrates, excellent water resistance, good solvent and fingernail scratch resistance.

Claims

Claims:

Radiation-curable composition, comprismg at least one ketonic resin based on acetophenone and formaldehyde having a structure (I) or/and (II) wherein n is at least 1 and at least one (meth)acrylated compound.

Composition according to claim 1, having a viscosity, measured at 25 °C and a shear rate of 2,

5 s-1, o f higher than 1 Pa.s.

Composition according to claim 1 or 2, comprising 10-90% by weight of ketonic resin and 10-90% by weight (meth)acrylated compound.

Composition according to any of claims 1 to 3, wherein n is at least 3 and does not exceed 100.

Composition according to claim 4 wherein n is at least 7 and does not exceed 15.

6. Composition according to any of the preceding claims, wherein the (meth) acrylated compound is selected from the group consisting of isobornyl acrylate, phenoxyethyl acrylate, tetrahydrofurfuryl acrylate, dipropyleneglycol diacrylate, tripropyleneglycol diacrylate, 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, ditrimethylol propane terra acrylate, dipentaerythritol hexa acrylate, pentaerythritol triacrylate, pentaerythritol tetra acrylate, ethoxylated neopentylglycol diacrylate, propoxylated neopentylglycol diacrylate, ethoxylated trimethylolpropane triacrylate, propoxylated trimethylolpropane triacrylate, ethoxylated glycerol triacrylate, propoxylated glycerol triacrylate, ethoxylated pentaerythritol tri/tetra acrylate, propoxylated pentaerythritol tri/tetra acrylate, acrylated bisphenol A ethoxylate, acrylated bisphenol A propoxylate, amino (meth)acrylates, polyester (meth)acrylates, urethane (meth) acrylates, epoxy (meth) acrylates or mixtures thereof.

7. Composition according to claim 6, wherein the (methjacrylated compound is selected from the group consisting of trimethylolpropane triacrylate, ditrimethylol propane tetraacrylate, 1,6-hexanediol diacrylate, ethoxylated trimethylolpropane triacrylate, propoxylated glycerol triacrylate, ethoxylated pentaerythritol tri/tetra acrylate, urethane (meth)acrylates or mixtures thereof.

8. Composition according to any of the preceding claims, comprising - from 10 to 90 % by weight of ketonic resin, - from 10 to 90 % by weight of (meth) acrylated compound, - from 0 to 40% by weight of inert resin or mixtures thereof, - from 0 to 40% by weight of pigment, - from 0 to 15 % by weight of photoinitiator, - from 0 to 5 % by weight of additive, and - from 0 to 15 % by weight of filler.

9. Use of the radiation-curable composition as claimed in any of claims 1 to 8 as ink vehicle or ink.

10. Polymeric composition obtamable by curing the radiation-curable composition as claimed in any of claims 1 to 8.

11. Substrate partially or entirely coated with the polymeric composition as claimed in claim 10.

12. Process for preparing a composition according to any of claims 1 to 8 wherein the ketonic resin is dissolved in at least part of the (meth) acrylated compound at a temperature of 30°C to 150°C.