PARTICLES FOR ELECTROPHORETIC DISPLAYS

Abstract

This invention relates to polymer particles, a process for their preparation, the use of these particles for the preparation of an electrophoretic device, and electrophoretic displays comprising such particles.

Claims

1.-16. (canceled)

17. A coloured polymer particle for use in electrophoretic devices comprising at least one light stabiliser and monomer units of at least one monomer, at least one polymerisable dye, optionally at least one core particle, optionally of at least one charged co-monomer, and optionally of at least one crosslinking co-monomer.

18. The coloured polymer particle according to claim 17, wherein the light stabiliser is a polymerisable light stabiliser.

19. The coloured polymer particle according to claim 17, wherein the light stabiliser is polymerisable hindered amine.

20. The coloured polymer particle according to claim 17, wherein light stabiliser is a compound of Formula 1 ##STR00020## where R=H, linear or branched, substituted or non-substituted alkyl, cycloalkyl, or aryl, halogen, hydroxy or alkoxy, R=independently H or linear or branched, substituted or non-substituted alkyl, preferably H, R=independently H or linear or branched, substituted or non-substituted alkyl, R=independently H or linear or branched, substituted or non-substituted alkyl, A=a functional group, especially a polymerisable group or a hydroxy group, B=a spacer group, preferably a linear or branched alkylene group, where one or more non-adjacent C atoms may be replaced by O, N and/or S, C is a single bond or O, NH, NR, or CH.sub.2, and a1, and b and c0.

21. The coloured polymer particle according to claim 17, wherein the light stabiliser is a compound of Formula 2 ##STR00021## where R.sup.1=H, linear or branched, substituted or non-substituted alkyl, especially C1-C8 alkyl, cycloalkyl, or aryl, halogen, hydroxy or alkoxy, R.sup.2=independently H or linear or branched, substituted or non-substituted alkyl, preferably H, A=a polymerisable group, especially an acrylate, methacrylate, acrylamide or methacrylamide group, or a hydroxy group, B=a spacer group, preferably a linear or branched alkylene group, where one or more non-adjacent C atoms may be replaced by O, N and/or S, C is a single bond or O, NH, NR, or CH.sub.2, and a1, and b and c0.

22. The coloured polymer particle according to claim 17, wherein the light stabiliser is a compound of Formula 3 ##STR00022## wherein R.sup.1=H, linear or branched, substituted or non-substituted alkyl, especially C1-C8 alkyl, cycloalkyl, or aryl, halogen, hydroxy or alkoxy, especially H, alkyl or halogen, preferably C1-C3 alkyl, R.sup.2=independently H or linear or branched, substituted or non-substituted alkyl, preferably H, and R.sup.3=a polymerisable group, especially an acrylate, methacrylate, acrylamide or methacrylamide group.

23. The coloured polymer particle according to claim 17, wherein the light stabilizer is 1,2,2,6,6-pentamethyl-4-piperidyl methacrylate.

24. Coloured polymer particles according to claim 17, wherein the core particle is an organic or inorganic pigment particle.

25. The coloured polymer particle according to claim 17, wherein a polymerisable dye comprises a chromophore, at least one polymerisable group, optionally at least one linker group, and optionally at least one charged group.

26. A process for the preparation of the coloured polymer particle according to claim 17 for use in electrophoretic devices, comprising a) polymerising at least one monomer, at least one light stabiliser, at least one initiator, at least one polymerisable dye, optionally at least one charged co-monomer, optionally at least one core particle, and optionally at least one crosslinking co-monomer by dispersion or emulsion polymerisation in a non-aqueous, non-polar solvent, and b) optionally washing and drying the polymer particles.

27. A method comprising utilizing the coloured polymer particle according to claim 17 in optical, electrooptical, electronic, electrochemical, electrophotographic, electrowetting and electrophoretic displays and/or devices, and in security, cosmetic, decorative, and diagnostic applications.

28. A method comprising utilizing the coloured polymer particle prepared by a process according to claim 26 in optical, electrooptical, electronic, electrochemical, electrophotographic, electrowetting and electrophoretic displays and/or devices, and in security, cosmetic, decorative, and diagnostic applications.

29. An electrophoretic fluid comprising polymer particles according to claim 17.

30. The electrophoretic fluid comprising polymer particles prepared by a process according to claim 26.

31. An electrophoretic display device comprising an electrophoretic fluid according to claim 29.

32. The electrophoretic display device according to claim 31, wherein the electrophoretic fluid is applied by a technique selected from inkjet printing, slot die spraying, nozzle spraying, and flexographic printing, or any other contact or contactless printing or deposition technique.

Description

EXAMPLES

[0081] All reagents are purchased from Sigma-Aldrich, UK unless otherwise stated. 1,2,2,6,6-Pentamethyl-4-piperidyl methacrylate HALS is obtained from Tokyo Chemical Industry UK. Vazo 67 is obtained from Wako Chemicals. Decorative NAD stabiliser 30% by weight in solvents (obtained from ICI Ltd., product code X190-442) is precipitated in cold methanol, dried and dissolved in a 50:50 mixture of ethyl acetate (Aldrich) and butyl acetate (Aldrich).

[0082] Dye 1 is prepared as reported in example 1 of WO 2013/170935 and has the following structure:

##STR00019##

[0083] NMR Spectroscopy is carried out using a Malvern 300 (GH000103) NMR Spectroscope.

[0084] SEM is carried out on a Neoscope JCM-5000 Scanning Electron Microscope.

[0085] Centrifugation is carried out on a Heraeus Biofuge Stratos Centrifuge.

[0086] Photostability Tests

[0087] Photostability tests are carried out using an Atlas CPS+ Suntest.

[0088] Colour measurements are carried out using the x-rite,

[0089] Comparative Blue Wool samples are acquired from SDC Enterprises Limited, UK, which conform to the requirements of BS EN ISO 105 B08. A Blue Wool Scale must be measured with every photostability test carried out. It is used to measure and calibrate the permanence of coloured dyes. Eight samples of dyed blue wool are used, which incorporate dyes that have sequentially improved photostability over time. Samples are labelled from 1 to 8; a score of zero denotes extremely poor colour fastness, whereas a sample with a score of 8 is deemed not to have altered and can be considered lightfast and permanent. In industry, a score of 5 or better is considered good, but preferably scores of 6 or higher should be achieved. Photostability testing procedure is developed to conform as closely as possible to parameters set out in the International Standard IEC 60068-2-5: Environmental TestingPart 2-5: TestsTest sA: Simulated solar radiation at ground level and guidance for solar radiation testing.

[0090] Samples are prepared by filling a 50 micron ITO-glass cell with the formulated fluid of Examples 3 or 4. The cell is sealed using Araldite glue and checked to ensure no bubbles have formed within the cell. Cells using non-density matched samples are allowed to settle overnight in the dark, in order to prevent anomalous results from a change in colour due to particle settling.

[0091] The Blue Wool scale is assembled behind a sheet of ITO glass, ITO side down.

[0092] Samples are placed flat on a matt black (anodised aluminium) sample holder in the Suntest for 20 hr periods, with a radiation dose of 550 W/m.sup.2 (mimicking 1 hr Miami Peak Sunlight, equivalent to 4 hrs daylight exposure in the UK). Samples are then kept in the dark for a minimum of four hours, before the colour coordinate is measured on the x-rite, and cycled again over a period of 10 days. This is the procedure recommended in IEC 60068-2-5 for experiments where the principal interest is in degradation effects. All samples are kept in the same position, at the same orientation throughout the experiments. X-rite measurements are taken on the same side of the cells and samples, with the blue wool and print scales behind a piece of ITO glass. A metal guide is used to ensure samples are measured in the same position each time.

[0093] A cooling plate is used underneath the samples, which it set at 15 C.

[0094] A testo 175H1 temperature and humidity data-logger is affixed inside the Suntest to monitor ambient conditions.

[0095] The L*a*b* colour coordinate is used to measure the E value of each sample. This value measures the change from the initial baseline colour coordinate measured before any fade is induced on the sample at each time period it is measured.

Example 1 (Comparative Example): Preparation of Dyed Polymer Particles Incorporating Dye 1 at 5 Weight % (Based on Methyl Methacrylate) by Dispersion Polymerisation

[0096] NAD stabiliser 30% by weight is precipitated in cold methanol, dried and dissolved in a 50:50 mixture of ethyl acetate and butyl acetate. Methyl methacrylate (20.58 g), NAD-Stabiliser (3.50 g) and methacrylic acid (0.42 ml) are charged to a 100 ml 3-necked flask equipped with a condenser, nitrogen flow, and an overhead stirrer. Dye 1 (1.03 g) is added and stirred for 1 minute to facilitate dissolution of the dye. Dodecane (25.20 g) is added to the flask, followed by 1-octanethiol (0.13 ml). The mixture is heated with stirring at 300 rpm, once the temperature in the flask is at 75 C., Vazo 67 (0.20 g) is added and the reaction is stirred for 2 hours. The resulting dispersion is filtered through a 50 micron cloth. The dispersion is cleaned using a centrifuge. Centrifugations are carried out at 10 000 rpm for 20 minutes each, replacing the supernatant with dodecane; this is repeated five times. Average particle size is measured by SEM and image analysis: 456 nm.

Example 2: Preparation of Dyed Polymer Particles Incorporating Dye at 5 Weight % and HALS Monomer 1,2,2,6,6-Pentamethyl-4-Piperidyl Methacrylate at 1 Weight % (Based on Methyl Methacrylate) by Dispersion Polymerisation

[0097] Methyl methacrylate (20.58 g), NAD-stabiliser (3.50 g) and methacrylic acid (0.42 ml) are charged to a 100 ml 3-necked flask equipped with a condenser, nitrogen flow, and an overhead stirrer. 1,2,2,6,6-Pentamethyl-4-piperidyl methacrylate HALS (0.21 g) and Dye 1 (1.03 g) are added and stirred for 1 minute to facilitate dissolution of the dye. Dodecane (25.20 g) is added to the flask, followed by 1-octanethiol (0.13 ml). The mixture is heated with stirring at 300 rpm, once the temperature in the flask is at 75 C., Vazo 67 (0.20 g) is added and the reaction is stirred for 2 hours.

[0098] The resulting dispersion is filtered through 50 micron cloth. The dispersion is cleaned using a centrifuge. Centrifugations are carried out at 10 000 rpm for 20 minutes each, replacing the supernatant with dodecane; this is repeated five times. Average particle size is measured by SEM and image analysis: 456 nm.

[0099] Table 3: Similarly prepared are the following cyan coloured polymer particles (5 weight % of dye compared to MMA), additionally containing the following HALS (weight % based on methyl methacrylate).

TABLE-US-00003 TABLE 3 Example % Number HALS Incorporation Example 3 1,2,2,6,6-Pentamethyl-4- 2% piperidyl Methacrylate Example 4 1,2,2,6,6-Pentamethyl-4- 3% piperidyl Methacrylate Example 5 1,2,2,6,6-Pentamethyl-4- 1% piperidine

[0100] FIG. 1 shows that inclusion of HALS in the dispersion polymerisation does not hinder the polymerisation.

[0101] Reactions are monitored by NMR-Spectroscopy, with samples being taken at the start, mid-point and end of the reaction. The results show no significant hindrance of reaction, although the rate of reaction becomes slower on addition of 3% HALS:

Example 6: Preparation of Reflective Particles Incorporating Dye 1 at 3 Weight % and HALS at 1 Weight % (Based on Methyl Methacrylate) by Dispersion Polymerisation

[0102] Polydimethylsiloxane monomethacrylate terminated, mw. 10,000 (Gelest, 2.08 g), dodecane (75 g), titanium dioxide (10.30 g), and Span 85 (0.515 g) are charged to a 250 ml 3-neck round bottom flask. The flask is fitted with an overhead stirrer, condenser and nitrogen bubbler. The flask is placed in an ultrasonic bath and is subjected to 100% power ultrasound (37 Hz) for 30 minutes, followed by degassing for 30 minutes, by bubbling nitrogen through the dispersion with a needle.

[0103] In a separate flask, methyl methacrylate (10.3 g), AIBN (0.214 g), 1,2,2,6,6-Pentamethyl-4-piperidyl Methacrylate HALS (0.103 g), and octane thiol (0.126 ml) are combined and degassed as above for 30 minutes. The dispersion flask is placed in the sonic bath at 80 C., and the contents are stirred with an overhead stirrer at 300 rpm, under a flow of nitrogen. The monomer solution is then added to this dispersion at a rate of 3.8 mL/hour using a syringe pump. The reaction is stirred for four hours from the start of addition.

[0104] On completion, the flask is allowed to cool to room temperature and the contents are filtered through a 50 micron cloth. The dispersion is cleaned by centrifugation. Centrifugations are carried out at 10 000 rpm for 20 minutes each, replacing the supernatant with dodecane; this is repeated five times.

Example 7: Electrophoretic Formulation Containing a Dispersion of Cyan Coloured Particles Incorporating HALS (Mobility and Colour Coordinate Measurements)

[0105] The electrophoretic ink is prepared by vortex mixing 0.1012 g of particles of Example 2 comprising Dye 1 and HALS, 0.0609 g of Dioctyl sulfosuccinate sodium salt (AOT, Sigma Aldrich), and 1.8696 g of dodecane (Sigma Aldrich).

[0106] Colour data for this dispersion is measured using the x-rite and summarised in Table 4.

TABLE-US-00004 TABLE 4 L* a* b* X Y Z x y 47.52 32.19 23.29 10.699 16.421 31.425 0.183 0.280

[0107] The dispersion is allowed to stir overnight on the roller-mixer, before being further diluted in dodecane (ca. 1 drop in 2 ml) and roller-mixed overnight. The sample is measured on the zeta sizer:

[0108] Electrophoretic Mobility (0.02638 mcm/Vs), Zeta Potential (+28.4 mV)

Example 8

Electrophoretic Formulation Containing a Dispersion of Cyan Coloured Particles Incorporating HALS into the Particle (Photostability Measurement)

[0109] The electrophoretic ink is prepared by vortex mixing 0.2107 g of particles of Example 2 comprising Dye 1 and HALS, 0.0636 g of Dioctyl sulfosuccinate sodium salt (AOT, Sigma Aldrich), and 1.8403 g of dodecane (Sigma Aldrich). The dispersion is then roller mixed for 30 minutes.

[0110] The sample is used in photostability tests.

Example 9

Electrophoretic Formulation Containing a Dispersion of Cyan Coloured Particles and 1,2,2,6,6-Pentamethyl-4-Piperidine (Non-Reactive HALS) (Photostability Measurement)

[0111] The electrophoretic ink is prepared by vortex mixing 0.2136 g of particles of Example 1 comprising Dye 1 at 5%, 0.0215 g 1,2,2,6,6-Pentamethyl-4-piperidine (Sigma Aldrich), 0.0643 g of Dioctyl sulfosuccinate sodium salt (AOT, Sigma Aldrich), and 1.8397 g of dodecane (Sigma Aldrich). The dispersion is then roller mixed for 30 minutes.

[0112] The sample is used in photostability tests.

Example 10

Electrophoretic Formulation Containing a Dispersion of Cyan Coloured Particles Incorporating HALS (Photostability Measurement, Density Matched)

[0113] The electrophoretic ink is prepared by vortex mixing particles of Example 2 comprising Dye 1 and HALS, Dioctyl sulfosuccinate sodium salt (AOT, Sigma Aldrich), Halocarbon Oil and dodecane (Sigma Aldrich). The dispersion is then roller mixed for 30 minutes.

[0114] The sample is used in photostability tests.

Example 11

Measurement of a Blue Wool Scale for Use in Photostability Tests

[0115] The blue wool standards are placed in the Suntest with the particle samples that are being tested for their photostability. The degree is fade is measured for all samples, and the fade pattern gained for the samples is compared to the fade patterns gained for the Blue Wool Standards. Samples are then given a score depending on how their fade compares.

[0116] Blue Wool Scale measured for the test described in examples 12-18 is shown in FIG. 2.

Examples 12-18

Photostability Test of Cyan Dye Containing Particles, with HALS Incorporated into the Particle or into the Formulation

[0117] The photostability test is carried out using samples as described in Table 5:

TABLE-US-00005 TABLE 5 Formu- Particle % lation Example Type HALS Used HALS Type Example 12 Example 1 N/A 0% Example 8 Example 13 Example 2 1,2,2,6,6-Pentamethyl-4- 1% Example 8 piperidyl Methacrylate Example 14 Example 3 1,2,2,6,6-Pentamethyl-4- 2% Example 8 piperidyl Methacrylate Example 15 Example 4 1,2,2,6,6-Pentamethyl-4- 3% Example 8 piperidyl Methacrylate Example 16 Example 1 1,2,2,6,6-Pentamethyl-4- 1% Example 9 piperidine Example 17 Example 1 1,2,2,6,6-Pentamethyl-4- 2% Example 9 piperidine Example 18 Example 1 1,2,2,6,6-Pentamethyl-4- 3% Example 9 piperidine

[0118] These samples are measured against a Blue Wool Scale. Photostability scores for these particles are shown in Table 6 (higher BW values show better photostability).

TABLE-US-00006 TABLE 6 Example % HALS HALS Location Score Example 12 0% N/A BW4+ Example 13 1% Particle BW6+ Example 14 2% Particle BW6 Example 15 3% Particle BW6 Example 16 1% Formulation BW5+ Example 17 2% Formulation BW4+ Example 18 3% Formulation BW5+

[0119] The results show that particles with HALS bound into them show improved photostability.

[0120] Surprisingly, only 1% HALS incorporation is required to see this effect. Increasing the %-HALS incorporation does not improve the photostability further.

[0121] Unexpectedly, presence of a non-polymerisable HALS molecule in formulations of cyan containing dyed particles shows no, or very little, improvement in the photostability of the particles. Any small improvement shown is not comparable to that shown by incorporation of HALS into the particle.

[0122] This shows that, to improve photostability, the HALS molecule must be bound into the particle.

[0123] FIGS. 3 and 4 summarise these results.

FIGURES

[0124] FIG. 1: Reaction Progress with Increasing % HALS

[0125] FIG. 2: Blue Wool Scale measured for the test described in Example 12

[0126] FIG. 3: Improvement in photostability for particles incorporating HALS

[0127] FIG. 4: Photostability for particles incorporating HALS into the formulationno marked improvement