IE45361B1 - Printing ink compositions - Google Patents

Abstract

A method for printing a packaging material comprising (a) printing the packaging material with an ink comprising an epoxy resin, an imine capable of reacting with the epoxy resin, and a substantially inert compatible hard resin, all of these being found ingredients in solution in solvents, and a pigment, (b) evaporate the solvent, (c) overprint the material with a different ink and (d) allow the ink to harden.

Description

When printing on packaging materials, especially plastics films, it is difficult to achieve the desired combination of high gloss and gbod heat and abrasion resistance. Thus if a conventional, unreactive, printing ink is used, if the resin is of sufficient compatibility with the solvent to form a glossy print it necessarily will have a rather low melting point and so will have low heat resistance, and often also low abrasion resistance, while if a resin having a higher melting point is used, so as to obtain better heat resistance, it is very difficult so to formulate the ink that a gloss print is produced.

Accordingly reactive printing inks have been developed. These are based on monomeric or low molecular weight components which are formulated in an ink that gives a glossy print but which cures in situ to give a very high melting point product, so as to obtain good heat resistance. Thus conventionally a background print of a white reactive ink is applied to form a glossy background and this is then overprinted with other inks, which can be conventional non20 reactive inks based on high melting point resins and which, due to the character of the background inks, will give satisfactorily high gloss.

Various reactive inks have been proposed for packaging materials. Polyurethane systems, containing isocyanates, have been proposed extensively but suffer from serious disadvantages. Thus during use the ink tends to give off - 2 45361 toxic fumes, due to evaporation of isocyanate, and polyurethane systems bond well only to a limited number of plastics substrates. Furthermore isocyanate in the reactive form is also reactive to any hydroxyl-containing solvents such as water and alcohol thereby making the isocyanate unavailable for reactive with the other components. Other reactive inks that have been used have been based on epoxy resins cured with amine or amide as the self-curing binder, but such inks again have only bonded well to a limited number of substrates and small rather unpleasant A product according to the invention is substantially non-aqueous and comprises an epoxy resin, a curing agent that is substantially non volatile and is a pyrrolidone or a polymeT of an aziridine and a substantially inert, compatible anti-blocking resin, all dissolved in organic solvent, and a pigment. This product may be formulated with a solids content such that it may be used as a printing ink but often is first made in more concentrated form and often as two separate compositions.

It appears that after application of the ink to the substrate the imine and the epoxy resin react together to form a highly crosslinked ink. Reaction of the imine with the epoxy resin is liable to start as soon as the components are mixed to one another, and so it is convenient to formulate the product in two separate compositions in different containers, the contents of which are mixed prior to printing. Thus there may be s first container containing the epoxy resin dissolvedin solvent and the second container containing the imine dissolved in solvent, one at least of the containers containing the pigment and one at least of the containers containing the hardening resin.

It is usually convenient to include the pigment in the first composition, with the epoxy resin. This of course limits the pigments to pigments that will not react with the epoxy resin, but this is an acceptable limitation, particularly since the preferred pigment Is titanium dioxide or some other white inorganic pigment.

The invention also includes the individual compositions. One such composition is a solution of epoxy resin and anti-blocking resin and also contains pigment. Another composition is a solution of imine and anti-blocking resin.

' The anti-blocking resin also is usually in the first container, with the epoxy resin, but sometimes antiblocking resin is included also in the second container and sometimes there is anti-blocking resin in both the first and the first and the second containers.

The anti-blocking resin must be substantially inert, in the sense that it does not react on storage with the components with which it is stored and must serve as a hardening resin immediately upon printing, without waiting for any reaction to occur between the anti-blocking resin and the other components of the ink. Normally no such reaction does occur. The anti-blocking resin serves to prevent blocking of the ink, that is to say to prevent the ink being stripped from the surface on which it was - 4 4S36* printed to the underside of a layer of substrate subsequently wound over the printed surface before the ink has dried and cured completely. In the ink trade it is common to refer to anti-blocking resins as hardening resins.

The anti-blocking resins must not only be nonreactive, as described above, but must also be compatible, that is to say they must not sweat from the ink and they must reduce blocking instead of increase blocking, which can often happen with many resinous additives. Also, of course, since the resin has to be in solution it must be soluble in a solvent or solvent mixture in which the other components of the ink are soluble. These limitations mean that several conventional anti-blocking resins are inappropriate for use in the invention. For instance nitrocellulose cannot be used, partly because it reacts with imine and partly because of the limitation it places on solvents. The preferred anti-blocking resins used in the invention are acrylic resins, especially hydroxylated acrylic resins and in particular such resins containing a high degree of hydroxylation. Thus they may be copolymers of an alkyl acrylate with an acrylic acid, one of the components being hydroxylated, e.g. copolymers of methyl-, ethyl-, butyl- or iso-butyl-acrylates or methacrylates with hydroxylated methylacrylic acid, ethylacrylic acid, butylacrylic acid, isobutylacrylic acid or acrylic acid.

Preferably they are hydroxylated alkyl, e.g. butyl, acrylates or methacrylates. Preferably the hydroxyl value (calculated 43361 as % by;weight hydroxyl groups based on the total weight of the copolymer) lies between 1 and 10¾, especially 2 and 10%. The molecular weight is preferably from 35000 to 140000, preferably about 40000 to 60000. A preferred resin is a hydroxylated butyl methacrylate having a hydroxyl value of about 2 to 21% and a molecular weight of about 45000.

The epoxy resin is preferably a low molecular weight product, generally having a molecular weight less than 2,000, especially less than 1,000, e.g. having a molecular weight of 300 to 400, and that is preferably a liquid. It is preferably a reaction product of epichlorohydrin and diphenylolpropane. A suitable product is that sold by Shell Chemicals under the name Epikote 836, Epikote being .a trade mark.

The curing agent must be substantially nonvolatile and be capable of being dissolved in the solvent in the ink. It may be a pyrrolidone but preferably it is a polymer of an aziridine. The aziridine may be ethylene imine or a mono or dialkyl substituted aziridines where alkyl is preferably C.^ alkyl (e.g.- 2 methyl, 2 ethyl or 2,2 dimethyl aziridine). Copolymers may be used but homopolymers are preferred. The preferred curing agent is polyethylene imine, e.g. the material sold by B.A.S.F. under the trade mark Polymin P.

The solvent is non-aqueous and is normally selected from alcohols, esters and ketones, and mixtures thereof, the particular solvent (or solvent mixture) depending upon the particular ingredients present in the ink, and in 4S361 particular present in each container. We find ethylacetate, ethyl alcohol, propyl alcohol, acetone, methyl ethyl ketone and mixtures of some or all these to be suitable solvents for our preferred compositions.

Various modifying components can be included in the products of the invention and, when the product is formulated as two separate compositions that are mixed prior to use, these modifying components may be included in either or both of the compositions, depending upon their compatibility and storage stability with the other components of the compositions. Suitable modifying agents include polyvinyl butyral, styrenated allyl alcohol polymers, carboxylated acrylics, polyvinyl alcohol, ketone resins, ethyl cellulose and surfactants, preferably non-ionic surfactants.

The preferred products according to the invention are in two separate compositions and contain in the first container a solution of from 12 to 25 parts of the epoxy resin and from 5 to 20 parts of a hydroxylated acrylic anti-blocking resin, and contains also from 40 to 60 parts titania or other pigment per 100 parts of composition by weight, while the second container preferably contains a solution of from 8 to 16 parts polyethylene imine and 0 to 25 parts hydroxy acrylic anti-blocking resin per 100 parts of composition by weight.

The two compositions are preferably mixed together in proportions such that there are 0.5 to 3, preferably 1 to 2, parts by weight epoxy resin per part by weight imine.

The anti-blocking resin is normally present in the product in an amount of 0.5 to 3, preferably 1 to 2, parts by weight per part by weight imine plus epoxy resin.

Conveniently the compositions are so formulated that the desired proportions of ingredients are obtained when two parts by weight of the first composition are mixed with one part by weight of the second composition.

In the resultant product the solids content is normally 50 to 70¾. preferably 55 to 655, before any reduction with additional solvent. The final solids content in the printing ink will be chosen having regard to press conditions but will generally be in the range of 30 to 60¾„ preferably 40 to 55%, so that additional solvent is generally added to the mixture of the two compositions as soon as the mixture is formed or soon afterwards to reduce IS the solids content to this level.

It is easily possible so to choose the components of the two containers that each container has a satisfactory shelf life of several months and that when the contents of the containers are mixed the mixture has a shelf life of at least two hours, for example about eight hours and, upon further dilution ready for printing, has a shelf life in excess of one day, e.g. 36 hours. Thus the containers generally only contain sufficient solvent for keeping the components of the container in solution, additional solvent being added at the time of mixing the contents of the containers or usually soon afterwards so as to give the resultant liquid composition the desired concentration for printing. 453βί Although a reactive ink can normally he printed on only a limited range of substrates inks according to the invention can very satisfactorily be printed on a very wide range of packaging substrates, including polyolefine films (treated or untreated), coated polyolefine films, cellulose films, coated cellulose films, nylon films, polyester films, coated polyester films, PVDC film, PVC film, foil and coated aluminium foil, rubber hydrochloride film, metallised films of various types and various coated papers. Printing is preferably by flexography but other methods, such as silk screen and gravure, can be used provided the ink is formulated appropriately. Curing of the ink occurs at ambient temperatures over a period of, e.g., several hours and is normally complete within three days.

The white or other ink acts as a base keycoat on the substrate and permits overprinting with more conventional gravure and flexographic colours which themselves would not otherwise adhere to many of the substrates. In a typical process printing is conducted on a multistation press. The novel basecoat of the invention is applied, often as an overall coat, at a first station, the substrate is then heated and/or subjected to forced air to evaporate the solvent and sometimes to initiate curing, and the substrate is then printed with conventional inks at subsequent printing stations. It is then wound up and left to cure, generally at ambient temperature, for a few days.

IS Suitable Inks for the overprinting are those based, on cellulose nitrate, cellulose acetate propionate or modified versions of these. The chemical and physical resistance of the cured ink is high, and high and enhanced chemical and physical resistance is given to the overprinting colour after curing. The resistance of the final products to abrasion, heat, (e.g. in heat sealing) and low· temperatures (e.g. deep freeze uses) is greater than with conventional, non-cured systems. The coloured base coat has good appearance and gloss and the overprint colours have better gloss than when printed over conventional base coats.

The following are Examples of non-aqueous two-pack compositions according to the invention.

Example 1 Part A Rutile Titanium Dioxide 53.00 Polyethylene Imine (e.g. Polymin P) 6.10 Hydroxylated Acrylic Resin 10.92 n-Propanol 9.00 Ethyl Alcohol 6.56 Ethyl Acetate 14,42 Parts by weight - 100.00 48361 Part Β Epoxy resin (e.g. Epikote 828) Hydroxylated Acrylic Resin Methyl Ethyl Ketone Ethyl Alcohol Ethyl Acetate Parts by weight Example 2 Part A Rutile Titanium Dioxide Epoxy Resin (e.g. Epikote 836) Butyl Methacrylate polymer having 214 hydroxylation and a molecular weight of about 4S000 Normal Propanol Ethyl Acetate Acetone or other ketone Parts by weight Bart B Polyethylene Imine (e.g. Polyrain Pl Butyl Methacrylate polymer having . 214 hydroxylation and a molecular weight of about 45000 Ethyl Alcohol Ethyl Acetate 18.20 18.88 34.60 11.32 17.00 - 100.00 45.00 18.00 11.00 7.00 4.00 .00 100.00 12.20 22.00 .00 .80 100.00 Parts by weight 11 I 53 61 The product o£ Example 2 had better properties than the product of Example 1, both in storage and on use.

To use either of these two pack compositions 2 parts by weight of A are mixed with 1 part by weight of B and the resultant mix is diluted by addition of solvent, by the printer, to suit his printing conditions and is then printed in conventional manner by flexography, and overprinted by non-reactive ink and left to cure.

Claims (17)

1. CLAIMS:1. A substantially non-aqueous product comprising an epoxy resin, a curing agent for the epoxy resin which is a substantially non-volatile pyrrolidone or a polymer of an aziridine, and a substantially inert compatible anti-blocking resin, all in solution in organic solvent, and a pigment.

2. A product according to claim 1 in which the curing agent is polyethylene imine.

3. A product according to claim 1 or claim 2 containing 1 to 2 parts by weight epoxy resin per part by weight curing agent.

4. A product according to any preceding claim in which the anti-blocking resin is a hydroxylated acrylic resin.

5. A product according to claim 4 in which the antiblocking resin is a hydroxylated alkyl acrylate or methacrylate and has a hydroxyl value (as herein described) of from 2 to 10Ϊ.

6. A product according to any preceding claim in which the solvent is selected from alcohols, esters and ketones.

7. A product according to claim 6 in which the solvent comprises ethyl alcohol and/or ethyl acetate.

8. A product according to any preceding claim in which the pigment is titanium dioxide.

9. A product according to any preceding claim packed as two separate containers, in which the epoxy resin dissolved in a solvent is in one container and the curing agent dissolved in a solvent is a second container, at least one of the containers containing the pigment and at least one of the containers containing the anti-blocking resin. - 13 43361

10. A product according to claim 9 in which one composition in a· solutation of from 12 to 25 parts epoxy resin 5 to 20 parts of hydroxylated acrylic anti-blocking resin, and contains also 40 to 60 parts pigment, per 100 parts of composition by weight, and the other composition is a solution of from 8 to 16 Parts polyethylene imine and 0 to 25 parts hydroxylated acrylic anti-blocking resin per 100 parts of composition by weight.'

11. A product according to any of claims 1 to 8 in the form of a printing ink having a solids content of 40 to 55Ϊ.

12. A product according to any preceding claim containing 1 to 2 parts by weight anti-blocking resin per unit part by weight of epoxy resin plus curing agent,

13. A product according to claim 1 substantially as herein described with reference to either Example.

14. A method in which a packaging substrate is printed with a printing ink according to any of claims 1 to 8, 11, 12, or 13, the solvent is evaporated, the substrate is overprinted with a different ink, and the ink is then cured..

15. A substantially non-aqueous composition suitable for use in making a product according to claim 1 comprising a solution of a hydroxylated acrylic anti-blocking resin and a curing agent for epoxy resin which is a substantially nonvolatile pyrrolidone or a polymer of an asiridine.

16. A composition according tc claim IS comprising a solution of 8 to 16 parts polyethylene imine and up to 25 parts hydroxylated acrylic anti-blocking resin per 100 parts of composition. »5361

17. A composition according to claim 15 or claim 16 in which the hydroxylated acrylic anti-blocking resin is a hydroxylated alkyl acrylate or methacrylate having a hydroxyl value of between 2 and 105.