GB2029433A - Printing Inks - Google Patents

Abstract

A printing ink comprises: (a) a binder system containing (i) one or more polyethylenically unsaturated photopolymerizable monomers, and optionally one or more monoethylenically unsaturated photopolymerizable monomers; and (ii) one or more epoxy resins soluble in the photopolymerizable monomers; (b) a photoinitiator for the photopolymerizable monomers; (c) a cold curing catalyst for the epoxy resin; and (d) a colorant. The ink may be prepared from a two-part pack, one part of which contains the epoxy resin and the other the curing agent therefor, the remainder of the ingredients being present in either or both packs. In use, the ink is printed upon a substrate, especially a polyolefin substrate, exposed to the action of actinic light to convert the printed ink to a tack- free condition, and then allowed to age by the cold curing of the epoxy resin with the curing agent therefor.

Description

SPECIFICATION Printing Inks This invention is concerned with improvements in and relating to printing inks, and especially with printing inks suitable for printing upon polyolefin (e.g. polyethylene) substrates. The invention also relates to a method of printing with such inks.

Basically, the printing inks comprise a binder system containing two classes of polymerizable binder, namely a photopolymerizable binder and a cold curing, epoxy resin based binder. By the use of such a system it has been found that the ink may first be photocured to give a tack-free print and then allowed to further cure in the cold, for example on storage, to develop improved physical properties, particularly resistance to solvents and household chemicals such as detergents and bleaches.

In accordance with one embodiment of the invention, therefore, there is provided a printing ink comprising: (a) a binder system containing to a total of 100% by weight, (i) from 30 to 90% by weight of a liquid photopolymerizable binder comprising one or more polyethylenically unsaturated photopolymerizable monomers and, optionally, one or more monoethylenically unsaturated monomers; and (ii) from 70 to 10% by weight of one or more epoxy resins soluble in said photopolymerizable binder; (b) a photoinitiator for the photopolymerizable binder; (c) a cold curing catalyst or curing agent for the epoxy resin(s); and (d) a colorant.

The first component of the binder system, which preferably forms from 50 to 80% by weight of the binder system, comprises one or more polyethylenically unsaturated photopolymerizable monomers which must be liquid at room temperature and must be solvents for the epoxy resin component. A preferred class of such monomers comprises the polyesters of polyhydric alcohols with monoethylenically unsaturated carboxylic acids, especially acrylic or methacrylic acid. Preferably these polyesters have a molecular weight greater than 1 OG e.g. from 1 50 to 600 and a boiling point above 1 500C. Examples of such esters include triethylene glycol diacrylate and trimethylolpropane triacrylate.

The polyethylenically unsaturated monomers preferably form at least 50% by weight of the total weight of ethylenically unsaturated monomers, more preferably from 60 to 90% by weight of the total mixture.

The balance, if any, of the mixture of ethylenically unsaturated monomer components comprises one or more monoethylenically unsaturated monomers such as the esters of ethylenically unsaturated monocarboxylic acids (especially acrylic or methacrylic acid) and monohydric alcohols, for example tetrahydrofurfuryl methacrylate and 2-ethylhexyl acrylate or other monoethylenically unsaturated monomers such as N-vinyl pyrrolidone.

The second component of the binder system, which preferably forms from 20 to 50% by weight of the binder system, comprises one or more epoxy resins, by which term is meant compounds containing, on average, at least two epoxy groups per molecule. The epoxy resin, which are preferably solids at room temperature, suitably have a molecular weight of from 600 to 5,000, preferably from 900 to 4,000.

The epoxy resins may be saturated or unsaturated, aliphatic, cycloaliphatic aromatic, or heterocylic and may be substituted if desired with non-interfering substituents.

Aromatic epoxy resins are the polymeric reaction products of polynydric mono and polynuclear phenols with polyfunctional halohydrins and/or glycerol dichlorohydrin. A large number of epoxy resins of this type are disclosed in U.S. Patents Nos. 2,585,115 and No. 2,589,245. In addition many of these resins are commercial products. Typical polyhydroxy phenols useful in the preparation of aromatic polyepoxides include resorcinol and various diphenols resulting from the condensation of phenol with aldehydes and ketones such as formaldehyde, acetaldehyde, acetone and methyl ethyl ketone. A typical aromatic polyepoxide is the reaction product of epichlorohydrin and 2,2-bis(p-hydroxy phenyl)propane (Bisphenol A), the resin having the following structural formula:

wherein n is zero or an integer up to 10.

Aliphatic polyepoxides are the reaction products of epihalohydrins with aliphatic polyhydric alcohols such as trimethyl ethane, glycerol, pentaerythritol, sorbitoi, trimethylol propane, erythritol, arabitol, mannitol, trimethylene glycol, tetramethylene glycol, ethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, butylene glycol and polybutylene glycol.

The printing ink in accordance with the invention also contains a photoinitiator for the photopolymerizable monomer(s). A wide variety of photoinitiator are available and suitable for use in the inks of the invention and examples thereof include benzophenone and substituted benzophenones, acetophenone and substituted acetophenones, triphenyiphosphite, substituted anthraquinones (e.g. 2alkyl-anthraquinones), benzoin, benzoin methyl ether and benzoin ethyl ether. The photoiniator is suitably present in the composition (calculated as total binder and photoiniator) in an amount of from 1 to 10% by weight. However, the amount of photoiniator may be raised above this level, e.g. to 15% by weight, in order to overcome any masking or absorbence effect due to the presence of colorant in the ink.

The curing agent employed in the inks of the invention is a cold curing agent, that is one capable of curing the epoxy resin at ambient temperature (e.g. 1 5-250C). A wide variety of such curing agents are known and available. One class of such agent includes amine type agents and examples thereof range from a simple alkylene diamines (such as ethylene diamine) to more complex products such as amino-substituted alkoxy silanes (e.g. N,(amino-ethyl)yfaminopropyl)trimethoxy silane) and adducts of polyalkylene amines, fatty acids and long chain epoxy compounds. Another class of curing agents are polyisocyanate curing agents such as adducts of polyols and polyisocynate for example the product known as Desmodur L which is believed to be an adduct of a polyol and toluene diisocyanate.Curing agents for epoxy resins are discussed in detail in "Handbook of Epoxy Resins", Lee s Neville, McGraw Hill, 1967, especially at chapters 5-10 thereof.

The curing agent should be present in an amount sufficient to cure the epoxy resin and thus is suitably present in an amount sufficient to provide from 0.4 to 1.0 reactive curing groups per epoxy group in the epoxy resin.

Tha coorant will generally be a pigment and will suitably be n an amount of from 1 to 30% by weight of the ink (calculated as binder, photoinitiator, curing agent and colorant). Suitable pigments are well known in the printing ink art and the pigments suitable for use in the inks of the present invention include any of those conventionally employed in the printing ink art.

The printing inks of the invention may contain other ingredients conventional in printing agents such as levelling agents and thixotropic agents in amounts conventional for such additives.

The viscosity of the ink of the invention may be adapted to the required degree by suitable selection of the molecular weight and proportions of the various ingredients. Thus, where desired the inks may be diluted by the use of a greater proportion of monoethylenically unsaturated monomers and vice versa.

As will be appreciated, the inks of the invention are inherently unstable in that they contain both epoxy resin and cold curing agent therefor. It is thus intended that the inks of the invention should be made up shortly before use and to this end the invention also provides a two-part pack, one of which contains the epoxy resin and the other the curing agent therefore, the remainder of the ingredients of the ink being present in either or both packs. Preferably, however, the epoxy resin containing part also contains the remaining ingredients other than the curing agent, the other part consisting solely of the curing agent or, possibly, the curing agent dissolved in a portion of photopolymerizable monomer.

The invention also provides a method of printing upon a substrate which comprises: (1) printing an ink in accordance with the invention upon the substrate, (2) exposing the printed substrated to the action of actinic radiation (ultraviolet light) to convert the printed ink to a tack-free condition; and (e) allowing the cured ink to age to effect curing of the epoxy resin with the curing agent therefor.

The process of the invention is particularly suitable for the printing of polyolefin (e.g.

polyethylene) substrates and in this instance the ink may conveniently be applied to the substrate by a screen printing process. Thus, for example, in the printing of polyethylene bottles the invention provides the advantages that the ink contains no solvents which have to be removed from the print by evaporation, and that the print is readily handleable immediately after curing by U.V. light, the remaining cure of the epoxy resin component taking place during storage to yield a tough adherent print.

In order that the invention may be well understood, the following Examples are given by way of illustration only. In the examples all parts are by weight unless otherwise stated.

Example 1 (a) Preparation of Varnish Bisphenol A. Epoxy resin (Epoxy equivalent 450-51 5) 40 parts Propane-i ,1 ,1 -tris(oxypropyl acrylate) 43.5 parts N-vinyl-2 pyrrolidone 10.0 parts Dimethoxy phenyl acetophenone 5.0 parts Silicon levelling aid (DC 200) 1.5 parts The above components were stirred together with a labatory model high speed mixer until the components were dissolved.

(b) Preparation of Pigment Paste Pigment Red 2 (Napthol Red F2R) 6.3 parts Varnish of Example 1 (a) 85.2 parts N-vinyl pyrrolidone 8.5 parts The above components were hand mixed with a palette knife and then passed over a three roll mill until a NPIRI Fineness of Grind Gauge reading of 5 had been obtained (approximately equal to a particle size of 12.7 microns).

(c) (Catalyst Solution Preparation) 50 parts of ESA Adduct 870 (an adduct of ethylene diamine and epoxy resin supplied by Anchor Chemical Company) were dissolved in 50 parts of N-vinyl-2-pyrrolidone under a high speed mixer.

(d) Preparation of Catalysed Ink fil K fiji) Pigment Paste of Example 1 (b) 88 95 95 Catalyst solution of Example (c) 12 - N,P(aminoethyl)y(aminopropyl)trimethoxy silane - 5 Adduct of methyl epoxy stearate, tall oil fatty acids and tetraethylene pentamine (Genamide 2000) - - 5 In each case the listed components were blended together under a high speed laboratory mixer.

Three polyethylene bottles were pretreated, in the normal manner, by rotating them in a gas air f!ame for approx. 1 second. A sample of the flame treated polyethylene cut from a bottle was screen printed with an ink of Example (d) using a polyurethane squeegee and a 180 mesh nylon screen.

The printed sample (one for each of the three inks of Example 1 (d) was set by passing the sample under two medium-high pressure mercury vapour lamps (each rated at 80 watts per linear centimetre) on a conveyor belt travelling at 80 ft/minute. Each print was tack free and handleable immediately after irradiation.

Each sample was allowed to age at room temperature for 24 hours.

Samples of each print were separately immersed in detergent, household bleach, water and industrial methylated spirits for 24 hours and their adhesion checked by a simple thumb nail test and also by a scotch tape test. In each case the results were assessed as being superior to the performance of similarly treated prints prepared from inks in which the amino catalyst had been omitted.

Example 2 (a) Preparation of Pigment Packs Part A Parts Napthol Red F4R 5.0 - - Phthalocyanine blue BGS - 4.0 Rutile titanium dioxide (RXL) - - 21.0 Varnish of Example 1 25.0 25.0 35.0 2-Chlorothioxanthone - 1.0 1.0 The pigment pastes were each blended in a labatory pug mill and then passed over a three roll mill to a NPIRI Gauge reading of 5 and then blended under a high speed mixer with part B.

PartB Varnish of Example 1(a) 61.5 61.5 34.5 N-vinyl-2-pyrrolidone 8.5 8.5 8.5 (b) Preparation of Catalysed Inks Using the three pigment pastes of Example 2(a) and the proceedures and proportions of Example 1(d), 9 catalysed ink compositions were prepared.

The inks were tested according to the proceedure of Example 1 (d) with comparable results.

Example 3 (a) Preparation of Varnish Bisphenol A epoxy resin (Epoxy equivalent 2500--4000) 40 parts Tripropylene glycol diacrylate 40 parts Dimethoxy phenyl acetophenone 5 parts Silicone levelling aid 0.7 parts N-vinyl-2-pyrrolidone 14.3 parts The above components were stirred together with a laboratory model high speed mixer until the components were dissolved.

(b) Preparation of a Pigment Paste C.l. Orange 13 5.7 parts Varnish of Example 3(a) 76.4 parts N-vinyl-2-pyrrolidone 17.9 parts The above components were hand mixed with a palette knife and then passed over a three roll mill until a NPIRI Fineness of Grind Gauge reading of 5 had been obtained (approx. equal to a particle size of 12.7 microns).

(c) Preparation of Catalysed Ink A catalyst ink was prepared by mixing 9 parts of the pigment paste 3b with 1 part of Desmodur L (Toluene diisocyanate adduct of a polyol).

The ink was screen printed on to a piece of pretreated polyethylene (wetting tension 58 dynes/cm, minimum), using a polyurethane squeegee and a 1 80 mesh nylon screen.

The printed sample was set by passing it under two medium-high pressure mercury vapour lamps (each rated at 80 watts per linear centimetre) on a conveyor belt travelling at approximately 30 ftjmin.

The print was tack-free and handleable immediately after irradiation. Improved product resistance to bleach, detergent, water and industrial methylated spirits, over the uncatalysed system, was achieved after 24 hours storage at room temperature.

Example 4 (a) Preparation of Varnish Epoxy novolak resin (Epoxy equivalent 1 75-182) 49.8 Propane-l,l,l -tris(oxypropyl acrylate) 39.3 N-vinyl-2-pyrrolidone 4,5 Dimethoxy phenyl acetophenone 5.0 Silicone levelling aid 1.0 The above components were stirred together with a laboratory model high speed mixer until the components were dissolved.

(b) Preparation of Pigment Paste Cl. Orange 13 6.3 Varnish of Example 4(a) 90.7 N-vinyl-2-pyrrolidone 3.0 These components were compounded as described in Example 3b.

(c) Preparation of Catalysed Ink 10 Parts of N,(aminoethyl)y(aminopropyl)trimethoxoy silane were mixed with 90 parts of the pigment paste of Example 4(b).

The ink was screen printed as for Example 3(c), but using a conveyor speed of approx. 20 ft/minute.

The print was tack-free and handleable immediately after irradiation. Commercially acceptable product resistance to bleach, detergent and industrial methylated spirits, was achieved after 24 hours storage at room temperature.

Claims (11)

Claims

1. A printing ink comprising: (a) a binder system containing to a total of 100% by weight, (i) from 30 to 90% by weight of a liquid photopolymerizable binder comprising one or more polyethylenically unsaturated photopolymerizable monomers and, optionally, one or more monoethylenically unsaturated monomers; and (ii) from 70 to 10% by weight of one or more epoxy resins soluble in said photopolymerizable binder; (b) a photoinitiator for the photopolymerizable binder; (c) a cold curing catalyst or curing agent for the epoxy resin(s); and (d) a colorant.

2. A printing ink according to claim 1 in which the liquid photopolymerizable binder comonent (i) forms from 50 to 80% by weight of the binder system.

3. A printing ink according to claim 1 or claim 2 in which the polyethylenically unsaturated monomer of component (i) is a polyester of a polyhydric alcohol and a monoethylenically unsaturated carboxylic acid and has a molecular weight greater than 100 and a boiling point above 1 500C.

4. A printing ink according to any one of the preceding claims in which the polyethylenically unsaturated monomer forms from 60 to 90% by weight of component (i).

5. A printing ink according to any one of preceding claims in which the epoxy resin has a molecular weight of from 900 to 4,000.

6. A printing ink according to any one of the preceding claims containing from 1 to 10% by weight of photoinitiator, based on the weight of binder and photoinitiator.

7. A printing ink according to any one of the preceding claims in which the colorant is a pigment and is present in an amount of from 1 to 30% by weight, based on the total weight of the ink.

8. A printing ink according to claim 1 substantially as hereinbefore described with reference to the Examples.

9. A two-part pack for the production of an ink according to claim 1, one pack containing the epoxy resin and the other the curing agent therefore, the remainder of the ingredient of the ink (namely liquid photopolymerizable binder, photoinitiator and colorant) being present in either or both packs.

10. A method of printing upon a substrate which comprises: (1) printing ink according to any one of claims 1-8 upon the substrate.

(2) exposing the printed substrate to the action of actinic radiation (ultraviolet light) to convert the printed ink to a tack-free condition; and (3) allowing the cured ink to age to effect curing of the epoxy resin with the curing agent therefor.

11. A method as claimed in claim 10 in which the substrate is a polyolefin substrate.

1 2. A method as claimed in claim 10 substantially as hereinbefore described with reference to the examples. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~