WO2010133890A1

WO2010133890A1 - A printing ink

Info

Publication number: WO2010133890A1
Application number: PCT/GB2010/050833
Authority: WO
Inventors: Nigel Gould
Original assignee: Sericol Limited
Priority date: 2009-05-22
Filing date: 2010-05-21
Publication date: 2010-11-25
Also published as: GB2482462B; GB201120070D0; GB0908847D0; GB2482462A

Abstract

The present invention relates to an ink-jet ink comprising (25) to 45 % by weight based on the total weight of the ink of an organic carbonate solvent, a glycol ether solvent, a carrier resin and a colouring agent.

Description

A printing ink

This invention relates to a printing ink and in particular to a solvent-based ink for ink- jet printing.

In ink-jet printing, minute droplets of black, white, coloured or colourless ink are ejected through narrow nozzles in a controlled manner from one or more reservoirs or printing heads. The ejected ink forms an image on the substrate, by relative motion between the ejector and substrate which are usually held in close proximity. The shear forces associated with forcing a small volume of ink through the narrow cavities of a print-head require that the ink has a low viscosity. Ink-jet inks are therefore commonly formulated to contain a large proportion of a mobile liquid vehicle or solvent. Solvent-based ink-jet inks dry by evaporation of the solvent and the solvent used therefore needs to be volatile in order to allow the ink to dry in a reasonable time.

Volatile organic compounds (VOCs) are organic compounds that have a high vapour pressure and a low water solubility. A high vapour pressure means that the compounds are able enter the atmosphere where they have the potential to participate in photochemical reactions, causing atmospheric pollution and smog formation. Many countries set limits for the emission of VOCs but the precise definition of "VOC" varies. The United States Environmental Protection Agency (EPA), for example, defines a volatile organic compound (VOC) as "any organic compound that participates in atmospheric photochemical reactions except those designated by EPA as having negligible photochemical reactivity", whereas European Council Directive 1999/13/EC defines a VOC as "any organic compound having at 293.15 K a vapour pressure of 0.01 kPa or more, or having a corresponding volatility under the particular conditions of use".

It is therefore desirable to limit the VOC content of inks. However, this requirement is in conflict with the requirement for a solvent-based ink to include a large proportion of volatile solvent in order to allow fast drying. Indeed, known solvent based ink-jet inks can include up to 90 % by weight VOC content. The present invention aims to provide a solvent-based ink-jet ink that overcomes the above problems.

Accordingly, the present invention provides an ink-jet ink comprising 25 to 45 % by weight based on the total weight of the ink of an organic carbonate solvent, a glycol ether solvent, a carrier resin and a colouring agent.

The inventors of the present invention have found that by carefully selecting the combination of solvents described above, and by closely controlling the amount of organic carbonate solvent provided in the ink, an ink-jet ink having an acceptable VOC content can be provided, without sacrificing the beneficial properties of the ink. In particular, the inks of the present invention meet the viscosity requirements for ink- jet printing, dry quickly when printed on a wide range of substrates, have low odour, low toxicity and good adhesion to substrates. The printed inks also have desirable film properties.

Preferred organic carbonate solvents are alkyl carbonates having the formula R OCOOR , wherein R and R are independently selected from Ci-C₄ linear or branched alkyl, or wherein R¹ and R² together with the carbonate group form a cyclic carbonate in which R¹ and R² together form a linear or branched alkylene group that comprises 2 to 8 carbon atoms. Preferred organic carbonate solvents include cyclic carbonates.

A most preferred organic carbonate solvent is propylene carbonate-

The ink of the invention preferably comprises 25 to 40 % by weight of an organic carbonate solvent based on the total weight of the ink, more preferably 30 to 35 % by weight.

Glycol ether solvents are known for use in ink-jet inks and any glycol ether solvent or mixture of glycol ether solvents that is suitable for use in an ink-jet ink can be used according to the present invention. Suitable solvents include monoalkyl- and dialkyl ethers of mono-, di- or triethylene glycol and monoalkyl- and dialkyl ethers of mono-, di- or tripropylene glycol and mixtures thereof. Examples include ethylene glycol monomethyl ether, diethylene glycol monobuty] ether, diethylene glycol diethyl ether, diethylene glycol methylethyl ether, propylene glycol monomethyl ether, dlpropylene glycol monomethyl ether and tripropylene glycol monomethyl ether. Low odour glycol ether solvents are preferred, such as diethylene glycol diethyl ether and diethylene glycol methylethyl ether.

The inks of the invention preferably comprise 40 to 70 % by weight of glycol ether solvent based on the total weight of the ink, more preferably 40 to 60 % by weight most preferably 45 to 55 % by weight.

In one particularly preferred embodiment, the ink-jet ink of the present invention comprises 25 to 40 % by weight based on the total weight of the ink, preferably 30 to 35 % by weight, of propylene carbonate; 40 to 60 % by weight based on the total weight of the ink, preferably 45 to 55 % by weight, of diethylene glycol diethyl ether or diethylene glycol methylethyl ether; a carrier resin and a colouring agent.

The ink of the present invention preferably comprises 50 to 95 % by weight of solvent based on the total weight of the ink, more preferably 70 to 95 % by weight and most preferably 80 to 90 % by weight.

Other solvents may be included in the ink, but their content is preferably kept to a minimum. A particularly common source of other solvents is derived from the way in which the colouring agent is introduced into the ink-jet ink formulation. The colouring agent is usually prepared in the form of a pigment dispersion in a solvent, e.g. 2-ethylhexyl acetate. The solvent tends to be around 40 to 50 % by weight of the pigment dispersion based on the total weight of the pigment dispersion and the pigment dispersion typically makes up around 5 to 15 % by weight of the ink and sometimes more. In a preferred embodiment, the ink of the invention includes a maximum of 10 % by weight of organic solvent which is other than an organic carbonate solvent or a glycol ether based on the total weight of the ink. In other words, where a solvent or solvents is/are present which is/are not an organic carbonate solvent or a glycol ether, that solvent or solvents is present at 10 % by weight or less. The ink of the present invention is preferably substantially free of water, although some water will typically be absorbed by the ink from the air or be present as impurities in the components of the inks, and such levels are tolerated. For example, the ink may comprise less than 5 % by weight of water, more preferably less than 2 % by weight of water and most preferably less than 1 % by weight of water, based on the total weight of the ink.

The ink of the present invention dries by evaporation of the solvent, as discussed hereinabove, and hence is a solvent-based ink. The ink does not therefore require the presence of curable material, i.e. material comprising functional groups that cross-link or polymerise under the drying conditions to which the ink is exposed, to effect drying of the ink. The ink is preferably substantially free of curable material, although minor amounts can be tolerated. For example, the ink may comprise less than 5 % by weight of curable material, more preferably less than 2 % by weight of curable material and most preferably less than 1 % by weight of curable material, based on the total weight of the ink.

The ink of the present invention also includes a film-forming thermoplastic carrier resin. Carrier resins suitable for use in solvent-based ink-jet inks are known in the art. The resin needs to be chosen such that the carrier resin is soluble in the precise blend of solvents used in each individual ink. Examples of suitable resins include acrylic resins, epoxy resins, ketone resins, nitrocellulose resins, phenoxy resins, polyester resins, or mixtures or copolymers thereof. Preferably the resin is an acrylic resin. The weight average molecular weight of the resin is preferably from 5,000 to 100,000, more preferably from 20,000 to 80,000.

In a preferred embodiment, the resin is a methyl methacrylate/n-butyl methacrylate copolymer, which aids with the low viscosity requirement of the ink, such as Elvacite® 2614 from Lucite International which has a molecular weight of 56,000, a Tg of 79 ⁰C, an acid number of 14 and a Tukon Hardness Knoop No of 13, or, more preferably, Elvacite® 2013 which has a molecular weight of 34,000, a T_g of 76 ⁰C, an acid number of 5 and a Tukon Hardness Knoop No of 13. The ink of the present invention preferably comprises 1 to 20 % by weight of carrier resin, more preferably 2 to 10 % by weight based on the total weight of the ink.

The ink of the present invention also includes a colouring agent, which may be either dissolved or dispersed in the liquid medium of the ink. Preferably the colouring agent is a dispersible pigment which is dispersed in the ink. Colouring agents are known in the art and are commercially available, e.g. Microlith, Cinquasia, and Irgalite (all from Ciba Speciality Chemicals), Paliotol (available from BASF pic), Hostaperm (available from Clariant UK) and Sun Yellow 271-9151 and Yellow 4GO (available from Sun Chemical Performance Pigments). The pigment may be of any desired colour such as, for example, Pigment Yellow 13, Pigment Yellow 83, Pigment Red 9, Pigment Red 184, Pigment Blue 15:3, Pigment Green 7, Pigment Violet 19, Pigment Black 7. Especially useful are black and the colours required for trichromatic process printing (i.e. CMYK), although other colour sets may be used, such as Hexachrome (CMYKOG). Mixtures of pigments may be used in the same ink if required.

The colorant is preferably provided as a pigment concentrate which is present in the ink of the invention in an amount of from 1 to 15 % by weight. The amount of pigment present in the ink of the invention is typically 0.5 to 8 % by weight based on the total weight of the ink.

Other components of types known in the art may be present in the ink to improve the properties or performance. These components may be, for example, dispersants (e.g. Dysperbyk, Tego Dispers, Solsperse etc.), synergist, other surface tension modifiers, defoamers, stabilisers against deterioration by heat or light, reodorants, flow or slip aids (e.g. Tego Glide 100, Tego Aglide A-115, Tego Glide B-1484, Tego Glide 200, Tego Glide ZG-400, Tego Glide 410, Tego Glide 420, Tego Glide 440 and Tego Glide 450 from Tego Chemie Service GmbH; Glanol 110, Glanol 115, Glanol B- 1484, Glanol 200, Glanol 400, Glanol 410, Glanol 420, Glanol 440 and Glanol 450 from Kyoei Chemical Co Ltd; TSF4452 and TSF4460 from Toshiba Silicone Co Ltd; and KF352A, KF615A, KF6008 and KF6012 from Shinetsu Chemical Industry Co Ltd), biocides and identifying tracers. Inks of the present invention may, for example, comprise 0.50 to 3% by weight of a dispersant. Suitable dispersants include Solsperse® 32000, optionally together with the synergist Solsperse® 5000, (available from Lubrizol) and BYK-168 (available from BYK Chemie). Dispersants are usually added as part of the pigment dispersion.

In a preferred embodiment, the ink of the present invention consists essentially of 25 to 45 % by weight based on the total weight of the ink of an organic carbonate solvent, a glycol ether solvent, a carrier resin and a colouring agent, and more preferably consists essentially of 30 to 35 % by weight based on the total weight of the ink of an organic carbonate solvent, a glycol ether solvent, an acrylic carrier resin, a colouring agent and optionally 10 % or less by weight of organic solvents other than of an organic carbonate solvent or a glycol ether solvent based on the total weight of the ink. The ink consists "essentially" of these components because these are the key components for achieving the desired VOC content and drying characteristics. However, the other components conventionally added to the inks described in the previous paragraph may be included in the ink without adversely affecting the VOC content of the ink, or the drying properties of the ink.

The ink-jet inks of the present invention exhibit a desirable low viscosity, i.e. 200 mPas or less, preferably 100 mPas or less, more preferably 50 mPas or less and most preferably 25 mPas or less at 25 ⁰C. Inks jetted at room temperature (say, 25 ⁰C) tend to have a viscosity at or below 50 mPas at 25 ⁰C, but inks jetted using an HSS head may have viscosity at or below 200 mPas when measured at 25 ⁰C (although when ejected through the nozzles, the jetting temperature is often elevated to about 30 ⁰C). Viscosity may be measured using a Brookfield viscometer fitted with a thermostatically controlled cup and spindle arrangement, such as a DVl low- viscosity viscometer running at 20 rpm at 25 ⁰C with spindle 00.

The inks of the present invention may be prepared by known methods such as, stirring with a high-speed water-cooled stirrer, or milling on a horizontal bead-mill.

The present invention also provides a method of ink-jet printing using the above- described ink, and a substrate having the printed ink thereon. The ink of the present invention is particularly suited to piezoelectric drop-on-demand ink-jet printing. The inks of the invention can be used on a wide range of substrates such as styrene, PolyCarb (a polycarbonate), and VIVAK (a polyethylene terephthalate glycol modified) but are particularly suitable for printing on vinyl film substrates, for example polyvinyl chloride film. Suitable vinyl substrates are known in the art and examples include those available under the trade-names Orajet (from Oracal), Control Tac (from 3M), BarmerPVC (a PVC), JetFlex (from Ritrama) and MPI 1005 EZ₅ from Avery.

The present invention further provides an ink-jet ink cartridge containing an ink-jet ink as defined herein. The cartridges comprise an ink container and an ink delivery port which is suitable for connection with an ink-jet printer.

The invention will now be described with reference to the following examples, which are not intended to be limiting.

The advantages of the inks of the present invention are demonstrated in the following examples.

Examples

The inks of example 1 and comparative example 1 were prepared by combining the following components, with a high speed mixer (amounts are shown as weight percentages):

Example 1

Propylene carbonate 34.0

Diethylene glycol diethyl ether 50.97

Elvacite 2013 5.9

Pigment concentrate * 9.1 Tegoglide 410 0.03 * Pigment concentrate formulation (wt %)

Solsperse 22000 2

Solsperse 32000 16

Symlar yellow 4GO 40

2-Ethyl hexyl acetate 42

Comparative Example 1

The ink of this comparative example is a typical solvent based ink-jet composition.

Butyl glycol acetate 67.5

Cyclohexanone 19.01

Vinylite VYHD 4.29

Pigment concentrate* * 9.1 Tegoglide 410 0.1

** Pigment concentrate formulation (wt %)

Solsperse 22000 1.26

Solsperse 32000 7.58

Symlar yellow 4GO 44.24

Butyl glycol acetate 46.92

The calculated VOC content for the above inks is shown below in Table 1. The VOC content is the total weight of VOCs present per 100 g of ink. Propylene carbonate is exempt from the EPA's definition of "VOC" and propylene carbonate is therefore excluded from the calculation for the ink of example 1 of the invention.

Table 1

The ink of example 1 was drawn down onto self adhesive PVC (3 M 180 10IJ available from 3 M) using a No 2 K bar to deposit a 12 micron film. The film had a tack-free surface after 4 minutes at ambient conditions, indicating that the ink has good drying properties. When used in print production the inks would be force-dried at 50 ⁰C and the drying time would therefore be considerably shorter.

Claims

1. An ink-jet ink comprising 25 to 45 % by weight based on the total weight of the ink of an organic carbonate solvent, a glycol ether solvent, a carrier resin and a colouring agent.

2. The ink-jet ink as claimed in claim 1 wherein the organic carbonate solvent is selected from alkyl carbonates having the formula R¹OCOOR², wherein R¹ and R² are independently selected from C₁-C₄ linear or branched alkyl, or wherein R¹ and R² together with the carbonate group form a cyclic carbonate in which R¹ and R² form a linear or branched alkylene group that comprises 2 to 8 carbon atoms.

3. The ink-jet ink as claimed in claim 2 wherein the organic carbonate solvent is a cyclic carbonate, preferably propylene carbonate.

4. The ink-jet ink as claimed in any one of claims 1 to 3 comprising 25 to 40 % by weight of organic carbonate solvent based on the total weight of the ink, preferably 30 to 35 % by weight.

5. The ink-jet ink as claimed in any one of the previous claims wherein the glycol ether solvent is selected from monoalkyl- and dialkyl ethers of mono-, di- or Methylene glycol and monoalkyl- and dialkyl ethers of mono-, di- or tripropylene glycol and mixtures thereof.

6. The ink-jet ink as claimed in claim 5 wherein the glycol ether solvent is selected from ethylene glycol monomethyl ether, diethylene glycol monobutyl ether, diethylene glycol diethyl ether, diethylene glycol methylethyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether and tripropylene glycol monomethyl ether, preferably diethylene glycol diethyl ether and diethylene glycol methylethyl ether.

7. The ink-jet ink as claimed in any one of the previous claims comprising 40 to 70 % by weight of glycol ether solvent based on the total weight of the ink, preferably 40 to 60 % by weight, more preferably 45 to 55 % by weight.

8. The ink-jet ink as claimed in any one of the previous claims wherein the carrier resin is selected from an acrylic resin, an epoxy resin, a ketone resin, a nitrocellulose resin, a phenoxy resin, a polyester resin or a mixture or copolymer thereof.

9. The ink-jet ink as claimed in claim 8, wherein the carrier resin is an acrylic resin.

10. The ink-jet ink as claimed in any preceding claim, wherein the ink has a total solvent content of 50 to 95% by weight based on the total weight of the ink.

11. The ink-jet ink as claimed in any preceding claim, wherein the ink is substantially free of water.

12. The ink-jet ink as claimed in any preceding claim, consisting essentially of 25 to 45 % by weight based on the total weight of the ink of an organic carbonate solvent, a glycol ether solvent, a carrier resin and a colouring agent, and optionally 10% or less by weight of organic solvents other than an organic carbonate solvent or a glycol ether solvent based on the total weight of the ink.

13. A method of ink-jet printing comprising printing the ink-jet ink as claimed in any preceding claim on to a substrate.

14. A substrate having the ink-jet ink as claimed in any of claims 1 to 12 printed thereon.

15. An ink-jet ink cartridge containing the ink-jet ink as claimed in any of claims 1 to 12.