EP4676747A1

EP4676747A1 - Methods and uses for controlling dot size

Info

Publication number: EP4676747A1
Application number: EP24707335.6A
Authority: EP
Inventors: Andrew Mcvitie
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 2023-03-09
Filing date: 2024-02-08
Publication date: 2026-01-14
Also published as: WO2024185390A1; GB202303467D0

Abstract

Disclosed is method for controlling dot size in a printed polymer layer, comprising steps of: applying a composition comprising a plastisol and a liquid diluent to a substrate to form a liquid polymer layer, wherein the plastisol comprises a polymer selected from polyvinyl chloride, a copolymer of vinyl chloride and vinyl acetate, and a terpolymer of vinyl chloride, vinyl acetate and ethylene; printing an ink onto the liquid polymer layer to form a liquid printed polymer layer, wherein the ink comprises a colorant and thereby the liquid printed polymer layer comprises the colorant; and curing the liquid printed polymer layer to change the liquid printed polymer layer to a solid printed polymer layer; wherein the liquid diluent is a paraffinic diluent having an aniline point of 70^oC or more. Related uses are also disclosed.

Description

METHODS AND USES FOR CONTROLLING DOT SIZE

The present invention relates to control of dot size in printing processes.

Inkjet printing is used in a variety of printing applications, and can provide high resolution coloured images on a range of substrates. Advantageously, the inkjet printing process provides high quality images. The process should achieve high optical density such that the amount of ink required to achieve the desired image is minimised.

In recent years, inkjet printing has been used in the production of wallpaper. In addition to a printed pattern, wallpaper typically has a resin layer that provides scratch and stain resistance and that also affects the appearance of the wallpaper. WO 2018/110518 describes a printing method that can be used to prepare surface coverings such as wallpaper. In the disclosed method, a liquid polymer layer is applied to a substrate and a pattern is applied to the liquid polymer layer by inkjet printing. The liquid resin layer with the pattern then undergoes curing such that the liquid polymer layer undergoes a phase transition from liquid to solid. In the examples, a liquid plastisol polymer layer composition is applied to fleece-backed paper. The plastisol composition is a dispersion of polyvinyl chloride polymer in an ester-based plasticiser.

WO 2018/110518

The intensity of the printed image that results from the application of the inkjet ink to the liquid polymer layer is affected by the interaction of the liquid polymer layer and the ink. The dot gain, which is a measure of how far the ink drop spreads out when it hits the substrate, can vary depending upon this interaction. Dot gain is significant because too much dot gain will lead to an image that is not sharp, and the print may be darker than intended. Control of dot size, including suppression of dot gain, is an important consideration in any inkjet printing process.

The present inventors have sought to make further improvements to printing processes. In particular, the present inventors have sought to control dot gain and thereby improve optical density in printing processes.

Accordingly, the present invention provides a method for controlling dot size in a printed polymer layer, comprising steps of:
　　applying a composition comprising a plastisol and a liquid diluent to a substrate to form a liquid polymer layer, wherein the plastisol comprises a polymer selected from polyvinyl chloride, a copolymer of vinyl chloride and vinyl acetate, and a terpolymer of vinyl chloride, vinyl acetate and ethylene;
　　printing an ink onto the liquid polymer layer to form a liquid printed polymer layer, wherein the ink comprises a colorant and thereby the liquid printed polymer layer comprises the colorant; and
　　curing the liquid printed polymer layer to change the liquid printed polymer layer to a solid printed polymer layer;
wherein the liquid diluent is a paraffinic diluent having an aniline point of 70^oC or more.

The present invention also provides use of a paraffinic diluent having an aniline point of 70 or more for controlling dot size in a wet-on-wet printing method.

The present invention also provides use of a paraffinic diluent having an aniline point of 70^oC or more for suppressing dot gain in a wet-on-wet printing method.

The inventors have surprisingly found that having a paraffinic diluent having an aniline point of 70^oC or more present in the liquid polymer layer can control dot size, for example by supressing dot gain. Thus, the printed image on the printed substrate of the invention may be sharper.

FIG 1 is schematically depicts an example method of printing onto a substrate of the present invention. FIG 2 is schematically depicts an example apparatus for inkjet printing. FIG 3 is illustrates how the dot size varies with the aniline point of the diluent in the examples and comparative examples of the invention. FIG. 4A is illustrates how the addition of a paraffinic diluent in accordance with the present invention affects dot size. FIG. 4B is illustrates how the addition of a paraffinic diluent in accordance with the present invention affects dot size. FIG. 4C is illustrates how the addition of a paraffinic diluent in accordance with the present invention affects dot size.

The present invention provides a method for controlling dot size in a printed polymer layer, comprising steps of:
　　applying a composition comprising a plastisol and a liquid diluent to a substrate to form a liquid polymer layer, wherein the plastisol comprises a polymer selected from polyvinyl chloride, a copolymer of vinyl chloride and vinyl acetate, and a terpolymer of vinyl chloride, vinyl acetate and ethylene;
　　printing an ink onto the liquid polymer layer to form a liquid printed polymer layer, wherein the ink comprises a colorant and thereby the liquid printed polymer layer comprises the colorant; and
　　curing the liquid printed polymer layer to change the liquid printed polymer layer to a solid printed polymer layer;
wherein the liquid diluent is a paraffinic diluent having an aniline point of 70^oC or more.

As used herein, controlling dot size refers to control of the size of dots formed in the printed polymer layer during the printing step. Dot size is typically expressed as a linear dimension of a dot (e.g. dot diameter). The measurement of dot size is routine in the field of droplet printing (e.g. inkjet printing) and dot size can be measured using any conventional method. In the present invention, controlling dot size may comprise suppressing dot gain. Thus, the method for controlling dot size of the present invention may be a method for suppressing dot gain.

As used herein, suppressing dot gain typically refers to the formation of dots in the solid printed polymer layer which are smaller than would be formed in a reference method which is not of the present invention. The reference method may differ from the method of the present invention in that one or more of the features of the method of the present invention are absent. The reference method may differ from the method of the present invention in that one or more of the features of the method of the present invention are replaced with one or more features which are not of the present invention. Apart from the feature of the present invention which is absent or replaced, the reference method may otherwise be essentially identical to the method of the present invention (e.g. it may be identical to the method of the present invention, or it may differ from the method of the invention only in ways which have no effect on dot size and/or dot gain). For instance, the reference method may differ from the method of the present invention in that, in the reference method, the composition does not contain a liquid diluent. The reference method may differ from the method of the invention in that, in the reference method, the composition comprises a liquid diluent (e.g. a liquid paraffinic diluent) having an aniline point of less than 70^oC (typically 67^oC or less, more typically about 67^oC, still more typically 67^oC) instead of the liquid diluent defined in the method of the invention. The reference method may differ from the method of the invention in that, in the reference method, the composition comprises a liquid diluent (e.g. a liquid paraffinic diluent) having an aniline point of less than 70^oC (typically 67^oC or less, more typically about 67^oC, still more typically 67^oC) instead of the liquid diluent defined in the method of the invention, and, in the reference method, the composition does not comprise a further diluent. Typically, in the method of the present invention, dot gain is suppressed such that the solid printed polymer layer comprises printed dots which are smaller than would be obtained if the composition did not comprise a liquid diluent. Typically, in the method of the present invention, dot gain is suppressed such that the solid printed polymer layer comprises printed dots which are smaller than would be obtained if the composition comprised a liquid diluent having an aniline point of less than 70^oC (typically 67^oC or less, more typically about 67^oC, still more typically 67^oC) in an amount equal to the amount of liquid diluent used in the method of the present invention, and more typically did not contain a further diluent.

As used herein, suppressing dot gain may refer to the formation of dots in the solid printed polymer layer which are 95% or less of the size of dots that would be formed in a reference method as described above (e.g. 90% or less, 85% or less, 80% or less, 75% or less, 70% or less, 65% or less, 60% or less, 55% or less, 50% or less, 45% or less, or 40% or less of the size of dots that would be formed in a reference method as described above). As used herein, suppressing dot gain may refer to the formation of dots in the solid printed polymer layer which are 5% to 95% of the size of dots that would be formed in a reference method as described above (e.g. 5% to 90%, 5% to 85%, 5% to 80%, 5% to 75%, 5% to 70%, 5% to 65%, 5% to 60%, 5% to 55%, 5% to 50%, 5% to 45%, 10% to 95%, 10% to 90%, 10% to 85%, 10% to 80%, 10% to 75%, 10% to 70%, 10% to 65%, 10% to 60%, 10% to 55%, 10% to 50%, 10% to 45%, 20% to 95%, 20% to 90%, 20% to 85%, 20% to 80%, 20% to 75%, 20% to 70%, 20% to 65%, 20% to 60%, 20% to 55%, 20% to 50%, 20% to 45%, 30% to 95%, 30% to 90%, 30% to 85%, 30% to 80%, 30% to 75%, 30% to 70%, 30% to 65%, 30% to 60%, 30% to 55%, 30% to 50%, 30% to 45%, 40% to 95%, 40% to 90%, 40% to 85%, 40% to 80%, 40% to 75%, 40% to 70%, 40% to 65%, 40% to 60%, 40% to 55%, 40% to 50%, or 40% to 45% of the size of dots that would be formed in a reference method as described above).

As used herein, aniline point is a measure of the aromaticity of a substance. It is the temperature, in ^oC, at which the substance becomes miscible in aniline. Thus the lower the aniline point, the higher the aromatic content of the substance. Aniline points referred to herein are typically as measured according to ASTM D611-12(2016).

As used herein, a plastisol is a dispersion of polymer particles in a liquid plasticizer. The plastisol composition may be cured by the application of heat. Upon curing, the polymer particles absorb plasticizer, swell, and ultimately fuse with other polymer particles. Typically, the printed polymer layer will comprise homogeneous coalesced mass of polymer, wherein the plasticizer is intimately mixed with the polymer.

As used herein, wet-on-wet printing is a process which involves depositing a wet (e.g. liquid) ink onto a wet (e.g. liquid) medium. As used herein, wet-on-wet printing typically involves applying a composition comprising a plastisol to a substrate to form a liquid polymer layer. A liquid printed polymer layer is typically formed by printing onto the liquid polymer layer. The liquid printed polymer layer is typically cured to form a solid printed polymer layer. Wet-on-wet printing may be wet-on-wet inkjet printing.

In the method of the invention, a composition comprising a plastisol and a liquid diluent is applied to a substrate. The substrate may be formed of paper, non-woven fabric, plastic, wood, metal or combinations of these materials. Specific examples may be selected from natural paper, plastic film, synthetic paper, non-woven fabric, fleece, cloth, wood, semi-cure wallpaper (in which a solid resin layer is present in the form of a semi-gel), full-cure wallpaper, metal sheet, and metal thin film or any combination of these materials. In a preferred embodiment, the substrate comprises a fleece-backed paper.

The printed polymer layer may be formed across the entirety of a surface of the substrate, but may also be formed on a portion of the surface only. The substrate suitably has a substantially flat surface so that a specific distance between an inkjet head and the surface of the substrate can be maintained during printing.

The plastisol comprises a polymer chosen from one or more of polyvinyl chloride, a copolymer of vinyl chloride and vinyl acetate, and a terpolymer of vinyl chloride, vinyl acetate and ethylene. In a preferred embodiment the polymer is polyvinyl chloride. Suitably, the amount of polymer in the plastisol is from 10wt% to 90wt% based upon the weight of the plastisol, such as from 10wt% to 80wt%, 10wt% to 70wt%, 10wt% to 60wt%, 10wt% to 50wt%, 10wt% to 30wt%, 20wt% to 40wt%, 30wt% to 50wt%, 20wt% to 60wt%, 30wt% to 70wt%, 40wt% to 80wt%, or 50wt% to 90wt%. The plastisol may comprise particles of the polymer, for example particles which typically have an average particle diameter of between 50nm and 5000nm, preferably between 100nm and 2500nm and more preferably between 100nm and 1000nm. A narrower particle size range is preferred as this is likely to improve the stability of the polymer layer (i.e. reducing the likelihood of the layer separating into different phases). The average particle diameter (suitably a volume average) may be measured by techniques such as laser diffraction, dynamic light scatting and single particle optical sizing. The amount of polymer particles per litre of plastisol is suitably from 10⁴ to 10⁹ particles. This may be measured by single particle optical sizing.

The plastisol comprises a plasticizer. A plasticizer is a material that, when added to a polymer, makes it softer or more pliable. The plasticizer reduces interactions between the polymer chains. Plasticizer compounds are typically non-volatile materials that have good compatibility with the polymer. In a preferred embodiment, the plasticizer is an ester-based plasticizer. Preferably the ester-based plasticizer is a phthalate-based plasticizer chosen from one or more of dibutyl phthalate, dinonyl phthalate, dioctyl phthalate, dodecyl phthalate, diisodecyl phthalate, diisononyl phthalate, ditridecyl phthalate, and n-hexyl-n-decyl phthalate. Suitably, the amount of plasticizer in the plastisol is 10wt% to 90wt% based upon the weight of the plastisol, such as from 10wt% to 80wt%, 10wt% to 70wt%, 10wt% to 60wt%, 10wt% to 50wt%, 10wt% to 30wt%, 20wt% to 40wt%, 30wt% to 50wt%, 20wt% to 60wt%, 30wt% to 70wt%, 40wt% to 80wt%, or 50wt% to 90wt%.

The plastisol may comprise further components such as whitening agents (typically titanium dioxide), defoamers, surfactants (e.g. a viscosity depressant such as Viscobyk 5125), stabilisers (e.g. a Ba/Zn compounds such as Adecastab FL-115), blowing agents (e.g. azodicarbonamide) and optical brighteners (e.g. those available as Uvitex^TM or Tinopal^TM). Blowing agents such as azodicarbonamide can have a yellowing effect, so it is often preferred to add a whitening agent such as titanium dioxide when the plastisol comprises a blowing agent.

Suitable plasticisers include commercially available expansible and compact PVC primers such as PS1652 (Expansible) and PS1553 (Compact White) both available from GB Technical Coatings Ltd.

The liquid printed polymer layer and the solid printed polymer layer comprise a polymer. The type and amount of polymer in the liquid printed polymer layer and the solid printed polymer layer is typically as described above with reference to the plastisol.

The composition may comprise a filler. Such fillers might include calcium carbonate, talc (magnesium silicate), barytes (barium sulphate), mica (aluminium sulphate), alumina and other aluminium based minerals. In a preferred embodiment, the printed polymer layer does not comprise any fillers apart from calcium carbonate. If calcium carbonate is present, the weight ratio of calcium carbonate to polymer in the liquid printed polymer layer or the solid printed polymer layer may be in the range of 0.1 to 3.5, preferably is in the range of 0.4 to 3.5 and more preferably is in the range of 0.4 to 1.5. The calcium carbonate may have an average particle size in the range of from 1μm and 10μm. The average particle size is suitably the D50 value, i.e. the mass median diameter.

The method of the invention may comprise a further step, before the composition is applied to a substrate, wherein the substrate is pre-treated. Such a pre-treatment step could include cleaning of the substrate (e.g. wiping with a cloth or by application of a cleaning liquid) or smoothing of the surface of the substrate (e.g. sanding with an abrasive material such as sandpaper). For example, a sheet metal substrate may be degreased, a polymer film substrate may be corona or plasma treated, or a wooden substrate may be cleaned to remove dust before the polymer dispersion is applied.

The composition is applied by any suitable method. For example, the dispersion could be applied by screen printing (flat-bed or rotary), roller coating with a metering roller or a doctor bar, gravure printing or coating line processes such as slot, extrusion, slide and curtain coating.

The thickness of the polymer layer is suitably from 5 to 100 microns, preferably from 12 to 50 microns.

An ink is printed onto the polymer layer to form a printed polymer layer. Suitably the printing is carried out by a droplet printing process, preferably inkjet printing. Any suitable inkjet printing apparatus could be used to print the printed polymer layer. For example, a RICOH Pro 4130 (trademark) wide format latex colour printer could be used. The inkjet print head is suitably heatable to control the viscosity of the inkjet inks. For example, it may be heatable to a temperature in the range 30°C to 60°C, most preferably around 45°C.

Preferably, at least two colours are printed. In accordance with normal inkjet printing techniques, a first colour ink is applied first and at least a second colour ink is applied subsequently. Full colour inkjet printing may be used. Conventional black, cyan, magenta and yellow printing heads may be used.

The ink comprises a colorant. Typical examples of the colorant include carbon black, any type of pigment such as azo pigments, phthalocyanine pigments, quinacridone pigments, quinophthalone pigments, nitroso pigments, nitro pigments, vat-dye pigments, mordant-dye pigments, basic-dye pigments, acid-dye pigments, and natural-dye pigments; and oil-soluble dyes such as diazo dyes and anthraquinone dyes. Each of these dyes and pigments can be used alone or in combination with others. The amount of colorant in the liquid printed polymer layer and the solid printed polymer layer is suitably chosen based upon the requirements of the printed image and can vary widely. However, in many typical applications the amount of colorant in the liquid printed polymer layer and the solid printed polymer layer is from 1wt% to 5wt% based upon the weight of the liquid printed polymer layer or the solid printed polymer layer.

An oil-based ink is suitably used. The oil-based ink comprises the colorant and preferably comprises a carrier such as an oily component. The oil-based ink may optionally include a binder resin.

Preferably, the oily component is an ester oil. Suitable ester oils include phthalic acid esters such as dibutyl phthalate, dicapryl phthalate, diisodecyl phthalate, dioctyl phthalate (DPO), diisononyl phthalate, butyl-2-ethylhexyl phthalate, and di-2-ethylhexyl phthalate; adipic acid esters such as dioctyl adipate (diethylhexyl adipate: DOA) and diisononyl adipate (DINA); sebacic acid esters such as dibutyl sebacate, dioctyl sebacate, and diisononyl sebacate; citric acid esters such as acetyl tributyl citrate (ATBC); azelaic acid esters such as dibutyl azelate, dioctyl azelate, and diisononyl azelate; lauric acid esters such as methyl laurate, ethyl laurate, and isobutyl laurate; myristic acid esters such as isopropyl myristate, isocetyl myristate, and octyldodecyl myristate; palmitic acid esters such as isopropyl palmitate and octyl palmitate; octanoic acid esters such as cetyl octanoate, octyl octanoate (ethylhexyl ethylhexanoate: OOE), and isononyl octanoate; and isononanoic acid esters such as ethylhexyl isononanoate and isononyl isononanoate.

The viscosity of the oily component is preferably in the range from 5mPas to 30 mPas, more preferably from 8mPas to 18 mPas, most preferably from 10mPas to 12 mPas at 45°C. Viscosity is preferably measured using a Brookfield DV-III Ultra Programmable Rheometer.

It is preferred that the oil-based ink comprises less than 1% by weight and more preferably less than 0.1% by weight of volatile organic compound solvent. A volatile organic compound solvent is as defined by the EU Directive 1999/13/EC (Solvent Emissions Directive), an organic compound having at 293.15 K a vapour pressure of 0.01 kPa or more.

Preferably, the oil-based ink is non-aqueous. Preferably, the content of water in the oil-based ink is less than 1% by weight, more preferably less than 0.1 weight percent, based upon the weight of the oil-based ink.

During the printing step, the ink is applied to the liquid polymer layer. The polymer layer is still liquid (because it has not been cured). During printing the colorant becomes an integral part of the polymer layer. The printing step is carried out before the curing step.

The liquid printed polymer layer is cured to change the printed polymer layer from liquid to solid. Curing is achieved by heating the printed polymer layer, suitably at a temperature in the range 150 to 250^oC, preferably at a temperature in the range 180 to 220^oC and most preferably in the range 190 to 210^oC. Upon curing, the polymer particles in the liquid printed polymer layer absorb plasticizer, swell, and ultimately fuse with other polymer particles to form a solid printed polymer layer. Typically, the solid printed polymer layer will consist of a homogeneous coalesced mass of polymer, wherein the plasticizer is intimately mixed with the polymer.

Further finishing steps may optionally be carried out after the curing step. Such finishing steps may include blowing, embossing, overcoating and/or laminating. The finishing steps may add decoration to the cured polymer layer, or may add extra protection.

The paraffinic diluent used in the method has an aniline point of 70^oC or more. Paraffinic diluents with higher aniline points will have a greater effect on dot size control (and particularly dot size suppression). Thus, if a greater degree of dot size control or dot size suppression is desired, a paraffinic diluent with a higher aniline point may be used. For example, paraffinic diluents having an aniline point of 72^oC or more, 74^oC or more, 76^oC or more, 78^oC or more, 80^oC or more, 82^oC or more, 84 ^oC or more, 86^oC or more, 88^oC or more, or 90^oC or more may be used (e.g. 70^oC to 95^oC, 72^oC to 95 ^oC, 74^oC to 95 ^oC, 76^oC to 95 ^oC, 78^oC to 95 ^oC, 80^oC to 95 ^oC, 82^oC to 95 ^oC, 84 ^oC to 95 ^oC, 86^oC to 95 ^oC, 88^oC to 95 ^oC, 90^oC to 95 ^oC, 70^oC to 90^oC, 72^oC to 90 ^oC, 74^oC to 90 ^oC, 76^oC to 90 ^oC, 78^oC to 90 ^oC, 80^oC to 90 ^oC, 82^oC to 90 ^oC, 84 ^oC to 90 ^oC, 86^oC to 90 ^oC, 88^oC to 90 ^oC, 70^oC to 85^oC, 72^oC to 85 ^oC, 74^oC to 85 ^oC, 76^oC to 85 ^oC, 78^oC to 85 ^oC, 80^oC to 85 ^oC, 82^oC to 85 ^oC, 84 ^oC to 85 ^oC, 70^oC to 80^oC, 72^oC to 80 ^oC, 74^oC to 80 ^oC, 76^oC to 80 ^oC, 78^oC to 80 ^oC, 70^oC to 75^oC, 72^oC to 75 ^oC, or 74^oC to 75 ^oC).

The paraffinic diluent typically comprises a C10-C18 alkane, for example a C10-C18 isoalkane. The paraffinic diluent may comprise a C10-C14, C10-C13, C10-C12, C11-C15, C11-C14, C11-C13, C12-C16, C12-C15, C12-C14, C13-C17, C13-C16, C13-C15, C14-C18, C14-C17, C14-C16, C15-C18, C15-C17, or C16-C18 alkane (e.g. isoalkane).

The paraffinic diluent may comprise the C10-C18 alkane or isoalkane (e.g. the C10-C14, C10-C13, C10-C12, C11-C15, C11-C14, C11-C13, C12-C16, C12-C15, C12-C14, C13-C17, C13-C16, C13-C15, C14-C18, C14-C17, C14-C16, C15-C18, C15-C17, or C16-C18 alkane or isoalkane) in an amount of 50 wt% or more, e.g. 50wt% to 100wt%, 50wt% to 90wt%, 50wt% to 80wt%, 50wt% to 70wt%, or 50wt% to 60wt%.

Paraffinic diluents having suitable aniline points are available commercially and include ShellSol D60, ShellSol D60, ShellSol D60, ShellSol D60, ShellSol D60, and Shell GTL GS215, available from Shell.

The paraffinic diluent is typically present in the composition in an amount of up to 10 wt%, based on the weight of the plastisol, e.g. 1 wt% to 10 wt%, 3 wt% to 10 wt%, 1 wt% to 5 wt%, or 3 wt% to 5 wt%.

The dot size in the printed polymer layer will vary depending on the desired characteristics of the printed image. Typically, dot size is desirably small enough to impart sufficient image sharpness, and large enough to impart sufficient image density. Typical dot sizes are in a range from 30 μm to 120 μm, such as from 30 μm to 100 μm or from 30 μm to 85 μm.

The present invention also provides use of a paraffinic diluent having an aniline point of 70^oC or more for controlling dot size in a wet-on-wet printing method. In the use of the present invention, control of dot size typically comprises suppressing dot gain. Thus, the present invention also provides use of a paraffinic diluent having an aniline point of 70^oC or more for suppressing dot gain in a wet-on-wet printing method.

In the uses of the present invention, control of dot size and suppression of dot gain are typically as described above with reference to the method of the present invention.

In the uses of the present invention, the wet-on-wet printing method may comprise:
　　applying a composition comprising a plastisol and a liquid diluent to a substrate to form a liquid polymer layer, wherein the plastisol comprises a polymer selected from polyvinyl chloride, a copolymer of vinyl chloride and vinyl acetate, and a terpolymer of vinyl chloride, vinyl acetate and ethylene;
　　printing an ink onto the liquid polymer layer to form a liquid printed polymer layer, wherein the ink comprises a colorant and thereby the liquid printed polymer layer comprises the colorant; and
　　curing the liquid printed polymer layer to change the liquid printed polymer layer to a solid printed polymer layer.

In the uses of the present invention, features of the wet-on-wet printing method are typically as described above with reference to the method of the present invention.

Figure 1 schematically depicts an example of the method of the present invention. A dispersion of polymer particles is applied to a substrate (1) to form a polymer layer (2). A printed polymer layer (2, 4) is formed by printing (3) onto the polymer layer (2). The printed polymer layer is cured (5).

Figure 2 schematically depicts an example apparatus for inkjet printing that may be used in the method of the invention. An unwinder roller 11 provides the substrate 10. The substrate 10 is fed to a screen coater 12 where a polymer layer is formed on the substrate 10. An inkjet printing station 20 comprising a drum 21 of diameter about 1 metre is used to print onto the polymer layer. Inkjet printing heads 22 are arranged around the drum. The printed polymer layer is cured in the curing oven 30 by heating to a temperature in the range of 120-200°C, preferably 150°C. A surface finish may be applied to the printed polymer layer with a gravure coater/roller 40. The printed polymer layer may undergo further heating in the heating apparatus 50. The finished printed polymer layer may be wound onto a roller rewinder 60 for storage and further transportation.

The following non-limiting examples are illustrative of the invention.

Examples

In the following Examples and Comparative examples, wet-on-wet inkjet printing was carried out onto the compositions shown in Table 1 below.

(1) Commercially available expandable PVC primer (GB Technical Coatings Ltd.)
(2) Commercially available paraffinic diluent with aniline point of 87 ^oC (Shell)
(3) Commercially available paraffinic diluent with aniline point of 70 ^oC (Shell)
(4) Commercially available paraffinic diluent with aniline point of 76 ^oC (Shell)
(5) Commercially available paraffinic diluent with aniline point of 78 ^oC (Shell)
(6) Commercially available paraffinic diluent with aniline point of 67 ^oC (Shell)

The range of dot sizes generated and the subsequent effect on print quality of black, cyan, magenta and yellow inks onto Example 1 and Comparative Example 1 (dot size & line width) are shown in Figure 3. Dilution with 5% GS215 (aniline point 87 ^oC) in Example 1 resulted in a reduction in dot size to 59.7 μm, from 92.3 μm in Comparative Example 1, and a reduction in line width to 185 μm, from 259 μm in Comparative Example 1.

The range of dot sizes generated with black inks onto Comparative Example 2 and Examples 2 to 5 are shown in Figure 4a. Increasing the aniline point to 70^oC, 76^oC, 78^oC and 87^oC in Examples 2 to 5 resulted in a progressive reduction in dot size, as compared to Comparative Example 2 (aniline point 67^oC).

The range of dot sizes generated with cyan inks onto Comparative Example 3 and Examples 6 to 9 are shown in Figure 4b. Increasing the aniline point to 70^oC, 76^oC, 78^oC and 87^oC in Examples 6 to 9 resulted in a progressive reduction in dot size, as compared to Comparative Example 3 (aniline point 67^oC).

The range of dot sizes generated with magenta inks onto Comparative Example 2 and Examples 2 to 5 are shown in Figure 4c. Increasing the aniline point to 70^oC, 76^oC, 78^oC and 87^oC in Examples 2 to 5 resulted in a progressive reduction in dot size, as compared to Comparative Example 2 (aniline point 67^oC).

The present application is based on and claims priority of Great British Patent Application No. 2303467.1 filed on March 9, 2023, the entire contents of which are hereby incorporated herein by reference.

Claims

　　A method for controlling dot size in a printed polymer layer, comprising steps of:
　　　　applying a composition comprising a plastisol and a liquid diluent to a substrate to form a liquid polymer layer, wherein the plastisol comprises a polymer selected from polyvinyl chloride, a copolymer of vinyl chloride and vinyl acetate, and a terpolymer of vinyl chloride, vinyl acetate and ethylene;
　　　　printing an ink onto the liquid polymer layer to form a liquid printed polymer layer, wherein the ink comprises a colorant and thereby the liquid printed polymer layer comprises the colorant; and
　　　　curing the liquid printed polymer layer to change the liquid printed polymer layer to a solid printed polymer layer;
wherein the liquid diluent is a paraffinic diluent having an aniline point of 70^oC or more.
　　A method according to claim 1, wherein controlling dot size comprises suppressing dot gain.
　　A method according to claim 2, wherein dot gain is suppressed such that the solid printed polymer layer comprises printed dots which are smaller than would be obtained if the composition did not comprise a liquid diluent.
　　A method according to claim 3 wherein the printed dots are 80% or less of the size of dots that would be obtained if the composition did not contain a liquid diluent.
　　A method according to any one of claims 2 to 4, wherein dot gain is suppressed such that the solid printed polymer layer comprises printed dots which are smaller than would be obtained if the composition comprised a liquid diluent having an aniline point of 67 ^oC in an amount equal to the amount of liquid diluent used in the method of claim 1. or claim 2.
　　A method according to claim 5 wherein the printed dots are 95% or less of the size of dots that would be obtained if the composition contained a liquid diluent having an aniline point of 67 ^oC in an amount equal to the amount of liquid diluent used in the method.
　　A method according to any one of claims 1 to 6, wherein the liquid diluent used in the method has an aniline point of 76^oC or more.
　　A method according to any one of claims 1 to 7, wherein the liquid diluent used in the method has an aniline point of 78^oC or more.
　　A method according to any one of claims 1 to 8, wherein the liquid diluent used in the method has an aniline point of 87^oC or more.
　　A method according to any one of claims 1 to 9, wherein the paraffinic diluent comprises a C10-C18 alkane.
　　A method according to any one of claims 1 to 10, wherein the paraffinic diluent is present in the composition in an amount of up to 10 wt%, based on the weight of the plastisol.
　　A method according to any one of claims 1 to 11, wherein the printed polymer layer comprises printed dots having a size of from 30 μm to 120 μm.
　　A method according to any one of claims 1 to 12, wherein the plastisol comprises polyvinyl chloride.
　　A method according to any one of claims 1 to 13, wherein the substrate is a fleece-backed paper.
　　A method according to any one of claims 1 to 14, wherein the printed polymer layer is cured by heating to a temperature in the range of 120 to 200^oC.
　　Use of a paraffinic diluent having an aniline point of 70^oC or more for controlling dot size in a wet-on-wet printing method.
　　Use according to claim 16 wherein controlling dot size comprises suppressing dot gain.
　　Use according to claim 17, wherein dot gain is suppressed as defined in any one of claims 3 to 6.
　　Use according to any one of claims 16 to 18, wherein the wet-on-wet printing method comprises:
　　　　applying a composition comprising a plastisol and a liquid diluent to a substrate to form a liquid polymer layer, wherein the plastisol comprises a polymer selected from polyvinyl chloride, a copolymer of vinyl chloride and vinyl acetate, and a terpolymer of vinyl chloride, vinyl acetate and ethylene;
　　　　printing an ink onto the liquid polymer layer to form a liquid printed polymer layer, wherein the ink comprises a colorant and thereby the liquid printed polymer layer comprises the colorant; and
　　　　curing the liquid printed polymer layer to change the liquid printed polymer layer to a solid printed polymer layer.
　　Use according to claim 19, wherein the method is as defined in any one of claims 7 to 15.