WO2010100438A1

WO2010100438A1 - A printing ink

Info

Publication number: WO2010100438A1
Application number: PCT/GB2010/000402
Authority: WO
Inventors: Nigel Gould
Original assignee: Sericol Limited
Priority date: 2009-03-05
Filing date: 2010-03-05
Publication date: 2010-09-10
Also published as: GB2480041A; GB201114984D0; GB2480041B; GB0903780D0

Abstract

This invention relates to an ink-jet ink comprising a solvent blend containing ethyl lactate and a dialkyl ether of an ethylene or propylene glycol, a carrier resin and a colouring agent, wherein the ink has a maximum of 10% by weight of organic solvent which is other than ethyl lactate and a dialkyl ether of an ethylene or propylene glycol based on the total weight of the ink. This ink has been found to have excellent dewetting properties without compromising printing properties.

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

Recently there has been an increasing use of MEMS (MicroElectroMechanical Systems) technology to construct ink-jet printing heads MEMS processes have been developed from the semiconductor Integrated Circuit (IC) industry and hence tend to employ semiconductor materials, such as silicon-based components, including silicon wafers

As a platform technology, MEMS offers several key benefits including precisely defined and accurately located fluid jet nozzles, creation of tightly packed and highly integrated jetting structures, and mechanically robust and chemically inert devices that meet the demands of cutting-edge fluid jetting and deposition requirements Suitable MEMS print-heads are already commercially available, for example the M-class head from Spectra lnc in Lebanon,

US Fig 1 (reproduced herein from Spectra Inc's commercial literature) shows the general configuration of an individual jet This jet 1 has a body 2 and a descender 3 terminating in a nozzle 4 Ink flows through a silicon filter (not shown) and into a pumping chamber 5 via an acoustic terminator 6 The jet 1 is powered by a thin piezoelectric unimorph 7 constructed in the plane of a silicon wafer and incorporating a thin PZT slab bonded to a silicon diaphragm

A print-head has a large number of individually addressable jets disposed in a nozzle plate that allow the ink to be printed on to the substrate

However, the developments in these new technologies present the ink formulator with considerable challenges in maintaining print performance despite changes in print-head materials and construction For instance, the wetting characteristics of silicon nozzle plates are quite different to those of conventional print-head nozzle materials The wetting characteristics are important since uncontrolled wetting of the nozzle plate during the jetting process can lead to excessive build up of ink deposits which in turn can lead to blocked and/or deviated nozzles and hence poor quality prints The technology to control the wetting of inks through formulatory changes is not well understood Accordingly, the present invention provides an ink-jet ink comprising a solvent blend containing ethyl lactate and a dialkyl ether of an ethylene or propylene glycol, a carrier resin and a colouring agent, wherein the ink has a maximum of 10% by weight of organic solvent which is other than ethyl lactate and a dialkyl ether of an ethylene or propylene glycol based on the total weight of the ink

This ink composition has been found to have excellent dewetting properties without compromising other printing properties

The present invention will now be described with reference to the drawings, in which

Fig 1 shows a schematic representation of a MEMS print-head,

Fig 2 shows a representation of a print-head showing a nozzle plate having a plurality of nozzles disposed therein,

Fig 3 shows a photograph of a MEMS print-head following printing using an ink-jet ink of the present invention,

Fig 4 shows a photograph of a MEMS print-head following printing using an ink-jet ink of the present invention having a different formulation to that shown in Fig 3, and

Fig 5 shows a photograph of a MEMS print-head following printing using a comparative ink- jet ink not of the present invention

The ink-jet ink of the present invention thus comprises a solvent blend containing ethyl lactate and a dialkyl ether of an ethylene or propylene glycol

Ethyl lactate (ethyl 2-hydroxypropιonate) is a known solvent and is derived from renewable sources It also has low volatility and is not classed as a HAP (hazardous air pollutant) The dialkyl ether of an ethylene or propylene glycol is also a known class of solvent The size of the ethylene or propylene glycol is not critical, but it is preferably a mono-, dι-, tri- or tetra- ethylene or propylene glycol Mixed glycols may also be used Preferably the glycol is a diethylene or dipropylene glycol and most preferably a diethylene glycol The glycol is in the form of a dialkyl ether The alkyl groups are not limited, but are preferably C₁-_B alkyl, more preferably C_1-4 alkyl, and most preferably ethyl A particularly preferred solvent is diethylene glycol diethyl ether Diethylene glycol diethyl ether has a melting point of -44⁰C and a boiling point of 189°C It has a relative evaporation rate of 0 04 compared to n-butyl acetate (defined as 1) and a surface tension 26 68 dynes/cm

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 The majority of the solvent present is preferably the dialkyl ether of an ethylene or propylene glycol The ink preferably contains 5 to 35% by weight of ethyl lactate based on the total weight of the ink, more preferably 8 to 25% by weight and most preferably 10 to 20% 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 a maximum of 10% by weight of organic solvent which is other than ethyl lactate and a dialkyl ether of an ethylene or propylene glycol based on the total weight of the ink In other words, where a solvent or solvents is/are present which is/are not ethyl lactate or a dialkyl ether of an ethylene or propylene glycol, 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 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 T₉ of 79⁰C, 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 T₉ of 76⁰C₁ 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 5 to 15% by weight and most preferably 6 to 12% 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 lrgalite (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 (ι 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 present in the ink of the invention in an amount of from 1 to 15% by weight, more preferably 2 to 10% by weight and most preferably 3 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 Lubnzol) 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 a solvent blend containing ethyl lactate and a dialkyl ether of an ethylene or propylene glycol, a carrier resin and a colouring agent, and more preferably consists essentially of 50 to 95% by weight based on the total weight of the ink of a solvent blend containing ethyl lactate and a dialkyl ether of an ethylene or propylene glycol, an acrylic carrier resin, a colouring agent and optionally 10% or less by weight of organic solvents other than ethyl lactate and a dialkyl ether of an ethylene or propylene glycol based on the total weight of the ink The ink consists "essentially" of these components because these are the key components for achieving the wetting characteristics of the ink However, the other components conventionally added to the inks described in the previous paragraph may be included in the ink without adversely affecting the wetting characteristics

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 25⁰C Inks jetted at room temperature (say, 25⁰C) tend to have a viscosity at or below 50 mPas at 25⁰C, but inks jetted using an HSS head may have viscosity at or below

200 mPas when measured at 25⁰C (although when ejected through the nozzles, the jetting temperature is often elevated to about 3O⁰C Viscosity may be measured using a Brookfield viscometer fitted with a thermostatically controlled cup and spindle arrangement, such as a

DV1 low-viscosity viscometer running at 20 rpm at 25⁰C 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 In particular, the present invention provides a method of printing the ink-jet ink as described herein through a pπnt- head having a low surface energy nozzle and/or nozzle plate on to a substrate and curing the ink

Fig 2 shows a representation of a print-head 8 The print-head 8 comprises a nozzle plate 9 having one or more nozzles 4 disposed therein The nozzle plate 9 will typically have a plurality of nozzles 4 disposed therein The print-head 8 can also be seen in Fig 3 which is a photograph of a print-head Either the nozzle plate 9 or the one or more nozzles 4 may have a surface having a low surface energy Usually, the nozzle plate 9 and the one or more nozzles 4 will both have a surface having a low surface energy Indeed, in a preferred embodiment, the surface of the nozzle plate 9 and the surface of the one or more nozzles 4 will be the composed of the same material

By "low surface energy" nozzle or nozzle plate is meant a nozzle or nozzle plate having a surface energy lower than conventional ink-jet ink nozzles/plates which are usually made from stainless steel

Typically, the low surface energy nozzle and/or nozzle plate of the present invention will be composed of silicon which is optionally surface treated The silicon may be treated to provide a silicon dioxide or silicon nitride surface Untreated silicon nozzles and/or nozzle plates tend to have a surface energy in the region of 25 dynes/cm, silicon nitride-treated nozzles and/or nozzle plates tend to have a surface energy in the region of 59 dynes/cm, and silicon dioxide- treated nozzles and/or nozzle plates tend to have a surface energy in the region of 76 dynes/cm Low surface energy nozzles and/or nozzle plates are commercially available and techniques for the surface coating of silicon are well known For comparison, stainless steel nozzles and/or nozzle plates have a surface energy of over 800 dynes/cm

The level of surface treatment will therefore vary the surface energy of the nozzle and/or nozzle plate, from an untreated silicon nozzle and/or nozzle plate to a heavily treated nozzle and/or nozzle plate, with milder treatments producing surface energies between these levels Accordingly, the surface energy can be adjusted to suit the head requirements The nozzle and/or nozzle plate of the present invention preferably has a surface energy of 5-200 dynes/cm, more preferably 10-100 dynes/cm, more preferably 15-80 dynes/cm and most preferably 20-40 dynes/cm

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), BannerPVC (a PVC)₁ JetFlex (from Ritrama) and MPI 1005 EZ, 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

Example 1

Inks 1-3 were prepared by combining the following components, with a high speed mixer Ink 1

Diethylene glycol diethyl ether 70 37 wt%

Ethyl lactate 15 0 wt%

Elvacιte 2013 9 74 wt%

Cyan pigment dispersion^* 4 89 wt%

Viscosity 6 58 mPas (cP)

^*Cyan pigment dispersion SOLSPERSE 5000 1 40 wt% SOLSPERSE 32000 14 00 wt%

IRGALITE BLUE GLVO 40 00 wt% 2-Ethyl hexyl acetate 44 60 wt%

Ink 2

Diethylene glycol diethyl ether 77 87 wt%

Ethyl lactate 7 5 wt%

Elvacιte 2013 9 74 wt%

Cyan pigment dispersion* 4 89 wt%

Viscosity 6 4 mPas (cP)

^*Cyan pigment dispersion, as for ink 1

Ink 3 (comparative, not of the present invention) Diethylene glycol diethyl ether 85 37 wt%

Elvacιte 2013 9 74 wt%

Cyan pigment dispersion^* 4 89 wt%

^*Cyan pigment dispersion, as for ink 1

Example 2

The relative head wetting of the inks prepared in Example 2 was assessed using a jet rig fitted with a head composed of a silicon dioxide-treated silicon nozzle

In order to simulate the degree of wetting that occurs over an extended print run it was necessary to develop a test method that could be used on the jet rig It was found that by driving the piezo electric crystal with 16 V pulse, such that the meniscus was merely vibrated rather than causing the ink to jet, the differential wetting of the nozzle plate of the various formulae could be readily determined All tests were run with the ink reservoir temperature set at 35⁰C In each case the inks were loaded into the test rig and allowed to equilibrate The nozzle plate of the head was thoroughly cleaned before the test was commenced. In each case the head was run with the waveform explained hereinabove for 5 minutes before the degree of wetting was assessed.

The nozzle plate wetting results were as follows.

The results for ink 1 (15% ethyl lactate) are shown in Fig. 1 which is a photograph of the print- head. Virtually no wetting of the nozzle plate was evident. The results for ink 2 (7.5% ethyl lactate) are shown in Fig. 3. Some nozzle plate wetting was evident. The results for the comparative ink 3 (no ethyl lactate) are shown in Fig. 4. Severe ink flooding wetting was observed.

Example 3

An indirect test was performed by observing the wetting of the inks drawn down on to a glass plate using a No 2 k bar depositing a 12 micron wet film weight. It was found that this test was a good predictor of head dewetting performance.

Ink 1 showed strong reticulation. Ink 2 still reticulates but is slower. Comparative ink 3 fully wets the glass plate.

Inks based on the formulae of inks 1 and 2 were also tested using n-propyl lactate, n-butyl lactate and ethyl hexyl lactate in place of ethyl lactate. It was surprisingly observed that even these small changes in alkyl chain length significantly reduced the level of dewetting effectiveness. N-Propyl lactate gave rise to some dewetting properties on glass plate but the level of addition of solvent to achieve this was too high for the ink to be of practical use. Neither n-butyl lactate nor ethyl hexyl lactate provided the required dewetting properties.

A number of other solvents, including N-methyl pyrrolidone and propylene carbonate, but these did not provide sufficient dewetting properties.

Claims

1 An ink-jet ink comprising a solvent blend containing ethyl lactate and a dialkyl ether of an ethylene or propylene glycol, a carrier resin and a colouring agent, wherein the ink has a maximum of 10% by weight of organic solvent which is other than ethyl lactate and a dialkyl ether of an ethylene or propylene glycol based on the total weight of the ink

2 An ink-jet ink as claimed in claim 1 , wherein the dialkyl ether of ethylene or propylene glycol is diethylene glycol diethyl ether

3 An ink-jet ink as claimed in claim 1 or 2, 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

4 An ink-jet ink as claimed in claim 3, wherein the carrier resin is an acrylic resin

5 An 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

6 An ink-jet ink as claimed in any preceding claim, wherein the ink contains 5 to 35% by weight of ethyl lactate based on the total weight of the ink

7 An ink-jet ink as claimed in any preceding claim, wherein the ink is substantially free of water

8 An ink-jet ink as claimed in any preceding claim, consisting essentially of 50 to 95% by weight based on the total weight of the ink of a solvent blend containing ethyl lactate and a dialkyl ether of an ethylene or propylene glycol, an acrylic carrier resin, a colouring agent and 10% by weight or less of organic solvents other than ethyl lactate and a dialkyl ether of an ethylene or propylene glycol based on the total weight of the ink

9 A method of ink-jet printing comprising printing the ink-jet ink as claimed in any preceding claim through a print-head having a low surface energy nozzle and/or a low surface energy nozzle plate on to a substrate and curing the ink

10 A method of ink-jet printing as claimed in claim 9, wherein the nozzle and/or nozzle plate is composed of silicon which is optionally surface treated

11 A method of ink-jet printing as claimed in claim 9 or 10, wherein the nozzle and/or nozzle plate has a surface energy of 5-200 dynes/cm

12. A substrate having the ink-jet ink as claimed in any of claims 1 to 8 printed thereon.

13. An ink-jet ink cartridge containing the ink-jet ink as claimed in any of claims 1 to 8.