WO2007113594A1

WO2007113594A1 - Printable film

Info

Publication number: WO2007113594A1
Application number: PCT/GB2007/050172
Authority: WO
Inventors: Celine Claudie Christine Denecker; Simon James Read
Original assignee: Innovia Films Limited
Priority date: 2006-03-31
Filing date: 2007-03-30
Publication date: 2007-10-11
Also published as: GB0606458D0

Abstract

Polymeric films having a coating formed from a composition having the following Hansen solubility parameters: • A dispersion component of x ± 15 MPa1/2 • A polar component of y ± 3 MPa1/2 • A hydrogen bonding component of z ± 10 MPa1/2 wherein x, y and z are, respectively, the dispersion, polar and hydrogen bonding Hansen solubility parameters of at least one solvent present in an ink to be applied by inkjet or other digital printing means to the coated surface of the film, and wherein the coat weight on the film is at least about 5.2 g.m-2.

Description

PRINTABLE FILM

The present invention relates to an improved printable film having good ink adhesion properties, and relates more particularly to an improved printable film having good ink adhesion properties when used in inkjet printing.

In recent years, diversification of printed products has required printing on a wide variety of materials in sheets; for example papers, synthetic papers, polymer films such as thermoplastic resin films, metallic foils, metallised sheets, etc. These printed items are printed by methods such as offset printing, gravure, flexography, silkscreen printing and letterpress printing. Commonly, inkjet printing is now used to print directly onto the surface of various types of polymer film, such as polyester film for example.

This invention is particularly concerned with polyolefinic films for use in label and graphic arts applications, but may also find other applications such as in packaging, and may utilise substrates other than polyolefinic films. It is believed however that polyolefinic films may provide an environmentally friendly alternative to PVC films which are commonly used in labels and graphic arts applications at present.

Uncoated PVC film has been used as a film substrate for inkjet printing but has other disadvantages as a substrate for applications such as graphic arts or labels. However, many non-PVC films are not very receptive to common inkjet printable inks such as solvent based inks. It will be desirable to provide a coating which allows other film substrates such as polyolefinic films (e.g. polyethylene or polypropylene films) to be used, and which provides some or all of those properties desired in an inkjet printable surface.

Due to the constraints imposed on the ink due to the nature of the ink jetting process, whether in a thermal or piezo inkjet printer, it is preferable that the ink receiving surface of the substrate is modified rather than the ink itself, to optimise some or all of the desired properties in the final printed image.

Some of the criteria that an ideal inkjet receptive substrate will possess include some or all of the following, depending on the particular application (e.g. for a 'no-label' look transparency is important rather than whiteness or opacity), A suitable inkjet printable substrate will have good optical properties such as brightness, whiteness, gloss, opacity and/or colour range to give high- quality images. The substrate should be compatible with components in the ink to ensure that the final ink image has sufficient fastness and low tendency to fade, for example when exposed to UV light. The absorbency of the film surface is important. InkJet printing places special demands on the substrate which is printed with a large amount of liquid, and yet is expected to dry quickly without changing size or shape. Although paper fibres absorb liquid well, they swell and deform resulting in surface imperfections and such moisture-induced undulations have a detrimental effect on image quality. Paper is unsuitable for many applications as described herein, and a suitable filmic substrate will be durable, and will maintain its structure for the time of the print. Desirable properties of such a film therefore include dimensional stability, tear resistance, thermal stability, and water and light resistance. The inkjet printable coating and film are both relevant considerations when determining the durability of the media. Thus to produce a good image by an inkjet printer the ink receiving surface should be dimensionally and thermally stable, i.e. it should not tear, stretch or deform, and it should be smooth and waterproof, maintain its shape and be resistant to many chemicals, and should not swell or shrink with moisture or humidity to an unacceptable degree.

WO-A-02/072361 discloses coatings for paper products for receiving inkjet printing. The coatings incorporate a primary amine functional polyvinyl alcohol as a polymeric binder.

JP-A-2002002100 discloses an inkjet recording medium comprising an ink receiving layer of a porous polyvinyl butyral resin containing thermoplastic fine particles.

J P-A-2001260520 discloses an inkjet recording medium comprising an ink receptive layer containing polyvinyl butyral.

JP-A-11349889 discloses a coating material having a high pigment incorporating polyvinyl butyral having a specified degree of acetalisation.

VVO- A-03/080356 discloses certain printable inkjet receptive films. US4713280 discloses a transparent sheet capable of receiving oil based inks, the sheet having an ink receptive layer comprising a polymeric material having certain defined Hansen solubility parameters.

it is an object of the present invention to provide a polymer film having an improved inkjet-printable coating. It is a further object of the invention to overcome some of the problems described herein to provide a film substrate which is printable by a digital printing method, preferably inkjet printing, for example by providing a coating suitable for a wide variety of common film types to improve their reception to inkjet inks.

According to the present invention there is a provided a polymeric film having a coating formed from a composition having the following Hansen solubility parameters:

• A dispersion component of x ± 15 MPa^/2

• A polar component of y ± 3 MPa⁷²

• A hydrogen bonding component of z ± 10 MPa

wherein x, y and z are, respectively, the dispersion, polar and hydrogen bonding Hansen parameters of at least one solvent present in an ink to be applied by inkjet or other digital printing means to the coated surface of the film, and wherein the coat weight on the film is at least about 5.2 g.m^"2. Also provided in accordance with the present invention is a polymer film in accordance with the above, printed on its coated surface with an ink comprising at least one solvent having at least one, preferably two, more preferably three, of the said Hansen solubility parameters x, y and z.

The invention also provides a process for inkjet or other form of digital printing comprising providing a film in accordance with the above and supplying to the coated surface of the film by means of an inkjet or other digital printing means, at least one ink comprising a solvent having at least one, preferably two, more preferably three, of the aforesaid Hansen solubility parameters x, y and z.

In some cases it may be possible to more closely match the Hansen parameters of the inkjet solvent with that of the film coating composition. For example, in some cases the Hansen dispersion component of the film coating composition may be x ± 13 MPa^/2, or even x ± 11 MPa^y2. The Hansen polar component of the film coating composition may be y ± 2 MPa^/2, or even y ± 1 MPa^/a. The Hansen hydrogen bonding component of the film coating composition may be z ± 8 MPa^/2, or even z ± 6 MPa^/2.

The Hansen solubility parameters of the coating composition are selected with reference to the intended end use of the film of the invention, in particular with a view to the solubility characteristics of the ink solvent to be applied to the film in use. Because ink solvents vary in their solubility parameters, it may be necessary to vary the solubility parameters of the coating composition to match a particular solvent or solvents. Nevertheless, bearing in mind the general properties of common commercially available ink solvents it is possible to make some general statements as to what the Hansen solubility parameters of the coating composition will be, in absolute terms, in at least the majority of cases.

Thus, the dispersion component from the Hansen solubility parameters of the film coating composition is preferably from about 10 MPa^/2 to about 22 MPa^y2, more preferably from about 12 MPa^/2 to about 20 MPa^/2, most preferably from about 14 MPa^1/2 to about 18 MPa^1/a.

The polar component from the Hansen solubility parameters of the film coating composition is preferably from about 0 MPa^1/2 to about 12 MPa^1/2, more preferably from about 2 MPa"⁴ to about 10 MPa^/2, most preferably from about 4 MPa^1/2to about 8 MPa^1/2.

The hydrogen bonding component from the Hansen solubility parameters of the film coating composition is preferably from about 4 MPa^/2 to about 16 MPa^y2, more preferably from about 6 MPa'⁷² to about 14 MPa^y2' most preferably from about 8 MPa^y2to about 12 MPa⁷².

Preferably the coating composition comprises at least one polymeric component, and the Hansen solubility parameters of that polymeric component are within the stated ranges. The invention therefore provides an inkjet-printable polymeric film having a coating formed from a composition having the Hansen solubility parameters selected from any of the aforesaid ranges.

Before selecting a suitable film coating composition it is desirable to identify the solubility parameters of an inkjet solvent to be used with the film. Common inkjet solvents include methanol, isopropanol, methyl ethyl ketone, ethyl acetate, acetone, ethanol, n-butyl acetate, butyrolactone, dipropylene glycol monomethylether, diethylene glycol diethylether, and combinations of two or more thereof. Preferably the solvent used in the inkjet ink applied to the surface of the coated film of the invention is substantially non-volatile. Such solvents are commonly known as "eco-solvents" in the inkjet printing field. By "non-volatile" is meant that the mechanism of ink reception on the printed surface relies at least partly, preferably primarily, on absorption (and/or solubilisation) of the ink solvent by the substrate, rather than on volatilisation of solvent.

One particular film coating composition which has been identified as having solubility parameters suitable for use with a number of inkjet solvents is a film coating composition comprising an acetal polymer, for example a vinyl acetal polymer. Polyvinyl butyral is particularly preferred.

Accordingly, the present invention also provides a polymeric film having an inkjet-printable coated surface wherein the coated surface comprises an acetal polymer. The present invention further provides a polymeric film having an inkjet- printable coated surface wherein the coated surface comprises a vinyl acetal polymer.

In a preferred embodiment, the present invention provides a polymeric film having an inkjet-printable coated surface wherein the coated surface comprises polyvinyl butyral.

It is believed that the selection of an appropriate film coating composition on the basis of the aforesaid solubility parameters in general, and relative matching of the said solubility parameters with those of the inkjet ink solvent in particular, allow the coated film of the invention to receive the inkjet ink solvent into the coating by absorption and/or by solubilisation. This means that the inkjet ink is received at least substantially within the coating, or at least a surface region thereof, once the film is printed. Therefore the invention provides a printed film comprising a polymeric film substrate, a coating layer comprising polyvinyl butyral, and a solvent ink printed on the coating layer, wherein at least part of the solvent is absorbed and/or solubilised by the matrix of the coating layer.

The coated surface of the film may comprise additional materials such as anti- block additives, opacifiers, fillers, UV absorbers, cross-linkers, colourants and the like. The coated film of the invention is particularly useful in cases where the film substrate beneath the coating is not itself particularly receptive to solvent inks. Therefore the invention provides a coated film in accordance with the above wherein the substrate film has at least one Hansen solubility parameter outside the range stated for the film coating composition. Preferably the film substrate has at least two Hansen solubility parameters outside the said range, more preferably all three Hansen solubility parameters are outside the said range.

In the coated film of the invention, the coat weight is at least about 5.2 g.m^"2, preferably at least about 5.5 g.m^"2, more preferably at least about 6 g.m^"2, and most preferably at least about 8 g.m^"2. Coat weights of from about 5.2 g.m^"2 to about 20 g.m^"2 are contemplated, preferably from about 5.5 g.m^"2 to about 15 g.m^"2, more preferably from about 6 g.m^"2 to about 14 g.m^"2, most preferably from about 6 g.m^"2 to about 13 g.m^"2, and still more preferably from about 6 g.m^"2 to about 12 g.m^"2. We have found that coat weights substantially below 6 g.m^"2, for example below 5.2 g.m^"2 do not perform satisfactorily when printed and do not produce films in accordance with the invention.

The film coating composition may be selected to adhere directly to the polymer film substrate, or such adhesion may be promoted by treating the film prior to coating, by corona discharge treatment for example. In some cases it may be preferable to include a primer layer between the film substrate and the coating. The film substrate may comprise a polyolefin film, for example polyethylene, polypropylene, mixtures thereof, and/or other known polyolefins. The polymeric film can be made by any process known in the art, including, but not limited to, cast sheet, cast film and blown film. The film or sheet may be of monolayer or of multi-layer construction. This invention may be particularly applicable to films comprising cavitated or non-cavitated polypropylene films, with a polypropylene core and skin layers with a thickness substantially below that of the core layer and formed for example from co-polymers of ethylene and propylene or terpolymers of propylene, ethylene and butylene. The film may comprise a biaxially orientated polypropylene (BOPP) film, which may be prepared as balanced films using substantially equal machine direction and transverse direction stretch ratios, or can be unbalanced, where the film is significantly more orientated in one direction (MD or TD). Sequential stretching can be used, in which heated rollers effect stretching of the film in the machine direction and a stenter oven is thereafter used to effect stretching in the transverse direction. Alternatively, simultaneous stretching, for example, using the so-called bubble process, or simultaneous draw stenter stretching may be used.

Alternatively, the film substrate may comprise a polyester film, a polyamide film, or an acetate film, for example. Preferably the film substrate is impervious to the solvent ink, at least to a degree which would give rise to unacceptable inkjet printing directly on the film substrate, in the absence of the coating.

The films used in accordance with the present invention can be of a variety of thicknesses according to the application requirements. For example they can be from about 10 to about 240 μm thick and preferably from about 40 to about 120 μm thick.

The coated film of the invention is suitably manufactured by means of a coating dispersion applied to a film substrate. The dispersion used to coat the substrate should contain about 15-70% solids, preferably 20-60% solids, more preferably 25 to 50% solids, in order to achieve satisfactory film forming properties. The film formed should be uniform and continuous.

The dispersion may be coated onto the surface of the chosen web and dried using any suitable conventional technique. The coating composition of the invention can be applied by any other number of well known techniques, such as dip coating, rod coating, blade coating, air knife coating, gravure coating and reverse roll coating, extrusion coating, slide coating, curtain coating, and the like. After coating, the layer is generally dried by simple evaporation, which may be accelerated by known techniques such as convection heating. The dispersion is preferably applied using a gravure process, and the drying step carried out in an oven. The drying of the coated dispersion removes water from the dispersion leaving a uniform continuous film with any non-film forming particles dispersed in the film.

The invention will now be more particularly described with reference to the following examples.

EXAMPLES

BASE FILM

The compositions of these examples were prepared and tested using various coating compositions on base film of conventional white BOPP film of 58μm thickness and 17.6 m²kg^"1 yield (corona discharge treated on the side to be coated) available commercially under the Trademark Rayoface W58.

COATINGS-FORMULATION

The components of the coating were weighed out individually. The components were then mixed with a paddle stirrer at 1000 rpm to provide a coating dispersion.

COATINGS-APPLICATION

Coated films of the invention were prepared by coating the base film with a dispersion (freshly prepared as described above). A sample of film was placed on the bed of a laboratory draw-down coating machine (K303 multicoater from

RK Print Coat Instruments). A green (number 2) K-bar was locked into position in the coat arms as to provide an even pressure over the total width of the film. The coating formulation was applied at the base of the K-bar using

Liquipipette. The K-bar was dragged down the length of the film to give an

even layer of the coating on the film surface.

PRINT TESTING

All coated samples were printed with the Uniform Cadet SP-750C Printer

(modified Roland VersaCAMM SP-300 printer). The printer uses four inks (C,

M, Y, and K), known as Eco Sol Inks (to be superseded commercially by Eco-

SoI Max inks).

These inks were investigated by GC/MS and found to contain as the largest solvent components, dipropylene glycol monomethylether and diethylene

glycol diethyl ether. Smaller quantities of n-butyl acetate and γ-butyrolactone

were also identified. The Hansen solubility parameters of these solvents [Ref:

Allan F. M. Barton, Handbook of Solubility Parameters and Other Cohesion

Parameters, 2^nd Edition, 1991 , CRC press] are:

The coating formulation, in particular the polyvinyl butyral component, was

chosen to match closely its Hansen solubility parameters to those of the inkjet solvents [Ref: Hansen, CM., Solubility Parameters, in Paint Testing Manual,

Manual 17, Koleske, J. V., Ed., American Society for Testing and Materials,

Philadelphia, 1995, 383-404]:

Polyvinyl butyral was selected on the basis of its solubility parameters

adequately matching at least one of the major solvent components of the inks.

The resin was supplied as a dispersion, commercially available as Butvar FP

from Solutia. The Butvar FP dispersion comprised 46% PVB, 49% water, 3% potassium oleate and 2% butyl ricinoleate. Roland COLORIP version 2.1 is the RIP software operating the printer. The printer head speed was of 500 mm.s^"1. Image resolution with a dpi of 720 was selected. Images were printed with no colour management (i.e. colour correction off, no ICC input and output profiles used with the ink limit set up to 400% (i.e. the maximum)).

Two postscript files provided with the Roland COLORIP called media and RCR_test print were used to assess quality of the media. The first one is a Basic Media Acceptance test. A series of squares are printed, e.g. C, M, Y, K at 100%, R, G, B at 200% and "black squares" gradient from 0% to 400% with 25% ink increment. The second one contains some texts (characters with different standard sizes), squares corresponding to a wide range of colour blend at different ink limits and a picture/photograph (to evaluate parameters such as contrast degree and colour vividity.

The printer was equipped with two heating units one at the front and one at the back of printer. The temperature for each heating unit was set up at 40⁰C.

EXAMPLES 1-4

The following coating formulations were prepared as above:

Component Weight % Weight % Weight % Weight %

(dry) (dry) (dry) (dry)

Formula 1 Formula 2 Formula 3 Formula 4

Butvar FP is a water-based dispersion of polyvinyl butyrate comprising 3-5% plasticizer and is available commercially from Solutia.

Cartabond TSI liquid is a polyhydroxylated cross-linker (glyoxal) supplied by Clariant.

Artpearl GR400 is a spherical acrylic micro particulate anti-block supplied by DKSH.

Each coating formulation was then applied to the base film as described above to give the following coated films:

These coatings were found to be glossy and transparent.

The following print results were obtained:

First Image

Only slightly wet at 175%.

Second Image

The print quality was found to be good, C, M, Y and K all drying instantly at 100%. It was considered that the "tackless" film on drying represented a significant result.

EXAMPLE 5-11

Seven coated films were prepared on the Aqueous RK coater (pilot coater). The following samples were primed with R610 primer and coated with Butvar FP dispersion at various coat weights. The topcoat was applied by using reverse gravure technique.

* Example 11 was made by double pass using the same settings as for Example 9 in order to achieve 20gsm.

The following print results were obtained.

The printing was carried out on the Roland VersaCAMM SP-300 using new inks called ECO SOL MAX available from ROLAND DG CORPORATION 1-6-4 Shin Miyakoda, Hamamatsu-shi, Shizuoka-ken, Japan, 431-2103. Imaging configuration was as follow Resolution: 720^*720dpi

Uni directional printing

Pass count of 16

Head spead of 1000 mm/s

Two PostScript fiies available with the Colorip software were printed for sample evaluations. No colour management was used on these files (i.e. No ICC Input Profile and No ICC output Profile). Precision Stochastic Screens was chosen for halftone properties. Temperatures selected for pre-heater and drying heater were of 50⁰C.

The first file called media allowed the following information in the table below to be drawn i.e.

- on the grey scale, how much ink in percent is dried instantly when print comes out of printer

- Colour quality of Cyan, Magenta, Yellow, Red, Green and Blue. - instant dry of Cyan (100% ink), Magenta (100% ink), Yellow (100% ink)

- instant dry of Red (200% ink), Green (200% ink) and Blue (200% ink)

The second file contains a picture and print quality which was qualitatively assessed with comments added to the same table.

¹⁾ Instant dry: percentage of ink touch dried by on the grey scale (i.e. 0 to

400% ink) when sample comes out of the printer.

²⁾ C (Cyan), M (Magenta), Y (Yellow)

³⁾ R (Red), G (Green), B (Blue) x bad colour quality s good colour quality

(w) wet when samples comes out of printer

(t) print is tacky

(st) print is slightly tacky

These results show that for a coat weight of substantially below 6 gsm, unsatisfactory print performance is evident. Increasing the coat weight further than 6 gsm improves the instant ink drying percentage.

Claims

1. A polymeric film having a coating formed from a composition having the following Hansen solubility parameters:

^■ A dispersion component of x+15 MPa^y2 ^■ A polar component of y+3 MPa^% ^■ A hydrogen bonding component of z±10 MPa^1/4

wherein x, y and z are, respectively, the dispersion, polar and hydrogen bonding components from the Hansen solubility parameters of at least one solvent present in an ink to be applied by inkjet or other digital printing means to the coated surface of the film, and wherein the coat weight on the film is at least about 5.2 g.nf ².

2. A polymer film according to claim 1 printed on its coated surface with an ink comprising at least one solvent having the said Hansen solubility parameters x, y and z.

3. A polymer film according to claim 1 or claim 2 wherein the dispersion component from the Hansen solubility parameters of the film coating composition is x±13 MPa^y2.

4. A polymer film according to any one of claims 1 to 3 wherein the polar component of the Hansen solubility parameters of the film coating composition is y±2 MPa^%.

5. A polymer film according to claim 4 wherein the hydrogen bonding component from the Hansen solubility parameters of the film coating composition is z±8 MPa^/2.

6. A polymer film according to any one of claims 1 to 5 wherein the dispersion component from the Hansen solubility parameters of the film coating composition is from about 10 MPa^y2to about 22 MPa^/2.

7. A polymer film according to any one of claims 1 to 6 wherein the polar component of the Hansen solubility parameters of the film coating composition is from about 0 MPa^y2 to about 12 MPa^y2.

8. A polymer film according to any one of claims 1 to 7 wherein the hydrogen bonding component from the Hansen solubility parameters of the film coating composition is from about 4 MPa^/2to about 16 MPa^/2.

9. A polymer film according to any one of claims 1 to 8 wherein the film coating composition comprises an acetal polymer.

10. A polymer film according to claim 9 wherein the film coating composition comprises a vinyl acetal polymer.

11. A polymer film according to claim 10 wherein the film coating composition comprises polyvinyl butyral.

12. A polymer film according to any one of claims 1 to 11 wherein the substrate film has at least one Hansen solubility parameter outside the range stated for the film coating composition.

13. A polymer film according to any one of claims 1 to 12 wherein the substrate film has at least two Hansen solubility parameters outside the range stated for the film coating composition.

14. A polymer film according to any one of claims 1 to 13 wherein the substrate film has three Hansen solubility parameters outside the range stated for the film coating composition.

15. A polymer film according to any one of claims 1 to 14 wherein the coat weight is at least about 5.5 g.m^"2.

16. A polymer film according to claim 15 wherein the coat weight is at least about 6.0 g.m^"2

17. A polymer film according to any one of claims 1 to 16 wherein a primer layer is provided between the coating and the substrate

18. A polymer film according to any one of claims 1 to 17 comprising a polyolefin or polyester substrate.

19. A polymer film according to claim 18 comprising a biaxially oriented polypropylene substrate.

20. A polymer film according to any one of claims 1 to 19 having a thickness of from about 10 to about 240 μm.

21. A printed film comprising a polymeric film substrate, a coating layer comprising polyvinyl butyral, the coat weight on the film being at least about 5.2 g.rrf², and a solvent ink printed on the coating layer, wherein at least part of the solvent is absorbed and/or solubilised by the matrix of the coating layer.

22. A printed film according to claim 21 wherein the coat weight is at least about 5.5 g.m^"2,

23. A printed film according to claim 22 wherein the coat weight is at least about 6.0 g.m^"2.

24. A printed film according to any one of claims 21 to 23 wherein at least the majority of the solvent is absorbed and/or solubilised by the matrix of the coating layer.

25. A printed film according to any one of claims 21 to 24 wherein the Hansen solubility parameters of the substrate and of the ink solvent are selected such that the ink solvent is receivable in the matrix of the coating layer but not in the matrix of the substrate.

26. A process for inkjet or other form of digital printing comprising providing a film according to any one of claims 1 to 20 and supplying to the coated surface of the film by means of an inkjet or other digital printing means, at least one ink comprising a solvent having the aforesaid Hansen solubility parameters x, y and z.