HK40013426B - Switching fibers for textiles - Google Patents

Description

Conversion fibers for textiles

Cross Reference to Related Applications

This application claims benefit and priority from U.S. provisional application No. 62/520,932 filed on day 16, 6 and 2017 and U.S. provisional application No. 15/997,740 filed on day 5,6 and 2018, the contents of which are incorporated herein by reference in their entirety. The contents of all co-pending and published patent applications and issued patents referred to below are also incorporated herein by reference in their entirety.

Statement of government support in the United states

The invention was made with U.S. government support under the protocol number W15QKN-16-3-0001 awarded by ACC-NJ. The united states government has certain rights in the invention.

Background

Clothing that can be changed as desired has many applications. If modern fabrics are capable of changing color as desired, the consumer can greatly reduce the number of articles of clothing he or she purchases during a lifetime. For example, it is no longer necessary to have three coats of almost the same cut but of different colours. The consumer may simply select the desired color (or pattern) based on the event, season, etc. In this way, the color-changing fabric can greatly reduce the influence of the clothes on the environment. It is estimated that americans currently discard about 1400 million tons of clothing to landfills each year. Furthermore, changing these garments every new fashion season is resource intensive-regardless of the source of the fabric, such as cotton, wool or petrochemicals. Other applications for color changing garments include camouflage and sportswear. For example, a baseball team no longer needs two different sets of uniforms, and the color can change depending on whether the team is in the home or away.

Various techniques have been identified to create fabrics that can reversibly change color. These techniques include: thermochromic dyes that change color when exposed to different temperatures, photochromic dyes that change color when exposed to sunlight, integrated LEDs that illuminate on demand by powering diodes, and liquid crystal inks that allow different colors to be displayed (or not) in the presence of a supplied electric field. These techniques have been emphasized in various prototypes, but only thermochromic dyes are widely introduced into clothes. See "Hypercolor" T-shirt sold by Generra Sportswear. However, since the thermochromic clothing is heat-sensitive, the color pattern is variable. For example, the underarm of a T-shirt with thermochromic ink may always be a different shade, drawing attention to that area. Thus, there remains a need for inexpensive and strong fabrics that can change color as desired.

Summary of The Invention

The present invention overcomes the disadvantages of the prior art by providing a flexible fiber that can be switched between colors as desired. The fibers may be incorporated into the fabric by weaving, knitting, embroidering, thermoforming or matting. The fibers may be incorporated into other materials to achieve the strength, air permeability, or stretchability required by the application. When a suitable electric field is provided, the color of the fiber will switch. Because the pigment is bi-stable, it is not necessary to provide a constant power source to maintain the color state. Rather, once the fabric is converted, it can be stable for a long period of time, e.g., days or weeks.

The invention thus provides a flexible color-changing fiber comprising a hollow fiber comprising at least two electrically insulated wires integrated into the wall of the hollow fiber together with an electro-optical medium disposed in the fiber, wherein the electro-optical medium is switchable by an electric field. The electro-optic medium comprises a non-polar solvent and at least one set of charged pigment particles. In some embodiments, the electro-optic medium comprises first and second sets of charged pigment particles having a different charge and color than the first charged pigment particles. Additional sets of particles may be added to the electro-optic medium. The hollow fibers may be made from various polymers, such as polycarbonate. In some embodiments, the hollow fibers have a substantially rectangular cross-section and comprise four electrically insulated wires. In embodiments having a substantially rectangular cross-section and four electrically insulated wires, the wires may be located at about 1/4 of the width of the larger interior dimension inward of the inner edge of the wall of the hollow fiber. The non-polar solvent is typically a mixture of hydrocarbons and the electro-optic medium may also contain charge control agents.

The preparation of fibers containing bistable electronic ink and subsequent incorporation of the fibers into fabrics and garments and the like will enable the fabric to be converted and then disconnected from the electronics because they appear stable in the absence of a power source. Thus, the drive electronics will not have to be integrated into the fabric unless a variable transition is desired. Thus, in some embodiments, the transfer cartridge, which may be battery powered, is a removable accessory. The lack of drive electronics greatly simplifies the washing of the fibers while also improving durability. If it is desired that the device be actively changed while worn, the conversion electronics can be incorporated into the garment and only briefly turned on during the update process.

These and other aspects of the invention will be apparent in view of the following description.

Brief Description of Drawings

The drawings depict one or more embodiments in accordance with the present inventive concept by way of example only and not by way of limitation. In the drawings, like reference numerals designate identical or similar elements.

FIG. 1A is a side view illustration of a flexible color-changing fiber according to one embodiment of the present invention. The fibres are filled with an electro-optic medium comprising oppositely charged coloured pigments which can be caused to move towards (or away from) the charged wire electrode;

FIG. 1B is a cross-sectional view of a flexible color-changing fiber according to another embodiment of the present invention. The fibres are filled with an electro-optic medium containing oppositely charged coloured pigments which can be moved towards (or away from) the charged wire electrode. The wire is optionally located equidistant between the inner wall and the midline;

FIG. 2 illustrates a method of filling a flexible color-changing fiber with a micro-syringe containing an electro-optic medium;

fig. 3 shows a flexible color changing fiber that is woven into a fabric and then coupled to drive electronics that enable a user to switch the color of the fiber.

Fig. 4 shows a visible photomicrograph of a flexible color-changing fiber according to another embodiment of the invention, which switches between a light state (left) and a dark state (right).

Fig. 5 is a cross-sectional view of a flexible color-changing fiber comprising a conductive polymer according to another embodiment of the present invention.

Fig. 6 shows a visible photomicrograph of a flexible color-changing fiber according to another embodiment of the invention, which switches between a light state (left) and a dark state (right).

FIG. 7 is a cross-sectional view of a flexible color-changing fiber having a geometry that provides a lensing effect, according to another embodiment of the invention.

FIG. 8 is a cross-sectional view of a flexible color-changing fiber having a geometry that provides a lensing effect, according to another embodiment of the invention.

FIG. 9 is a cross-sectional view of a flexible color-changing fiber having a geometry that provides a lensing effect, according to another embodiment of the invention.

FIG. 10 is a cross-sectional view of a flexible color-changing fiber having a geometry that provides a lensing effect, a conductive polymer, and copper electrodes, according to another embodiment of the invention.

FIG. 11 is a cross-sectional view of a flexible color-changing fiber having an insulating layer according to another embodiment of the present invention.

Detailed description of the invention

The present invention provides flexible color-changing fibers that can be incorporated into textiles and other materials. The ability to include electronics in the fibers (i.e., wire electrodes) is useful for obtaining a practical and economical fiber-based display. Many previous attempts at the manufacture of fiber-based displays or conversion fabrics required a large amount of dielectric structural material between the electrodes and the functional electrophoretic material. The described invention makes such a complicated structure unnecessary.

FIG. 1A shows a side cross-sectional view of a conversion fiber 10 of the present invention. An electro-optic medium 16 comprising a non-polar solvent and two types of charged pigment particles 18, 19 is shown arranged between the walls of the hollow fibres 12. In the embodiment shown in fig. 1A, the first set of particles 19 is white and the second set of particles 18 is black, but many other colors may be achieved, as described below. The fibre 10 comprises at least two electrodes 14a, 14b which provide an electric field across the electro-optic medium, thereby causing one pigment or the other to move to one side of the fibre 10. FIG. 1B shows a cross-section taken at B-B of FIG. 1A. In fig. 1B, the shape of the fiber 10 and the positions of the wire electrodes 14a, 14B, 14c, 14d are easily seen. Although the black pigment 18 is shown towards the top of both figures, it will be appreciated that the white pigment 19 may be moved towards the top of the figures by appropriate conversion. In addition, black and white may be used in combination, i.e., to provide gray scale, as described in some of the patents listed below for E Ink Corporation.

Each flexible fiber includes a cavity formed of a material capable of containing an electrophoretic liquid. In some embodiments, the fibers have a substantially rectangular cross-section, and the internal cavity of the interior also has a substantially rectangular cross-section. However, other cross-sectional shapes are possible, such as oval or circular. The rectangular cross-sections may have sharp edges, as shown in fig. 1B, or they may be slightly rounded edges 17. It is desirable to make the fibers thin enough to weave into the device, but thick enough to form an active switching cavity. It is also desirable to make the walls of the fiber as thin as possible to maximize the optical switching volume relative to the thickness of the fiber. However, if the wall is too thin, the fibers may be damaged by breaking, breaking or releasing a wire electrode. For this reason, it is desirable that the thickness of the fiber be about 2mm × 1mm or less and have an inner cavity of 1mm × 0.5mm or less. In a preferred embodiment, the fibers may be about 0.8mm by 0.5mm, with the lumens being about 0.4mm by 0.15 mm. The diameter of the wire electrode in such a fibre may be 50 μm. In these fibers, the proportion of the cavity width that is shielded by the (opaque) wire electrode is about 25% (2 x 50 μm/400 μm). In a more preferred embodiment, the fibers may be about 0.54mm by 0.31mm and the cavities about 0.40mm by 0.10 mm. The diameter of the wire electrode in such a fibre may be 40 μm. In these fibers, the proportion of the cavity width that is shielded by the (opaque) wire electrode is about 20% (2 x 40 μm/400 μm).

After applying an electric field across the fiber cavity in fig. 1, the top of the fiber will show a different color than the bottom of the fiber. Therefore, when integrating the fibers into a fabric, it is important to be able to control the orientation of the fibers in order to obtain a consistent color across the area of the fabric. When the colour-changing fabric is formed by weaving fibres having a rectangular cross-section, it is advantageous that the orientation of the fabric is such that the viewing surface of the fabric comprises a side of the fibres having a wider dimension. When weaving fibers having a rectangular cross-section according to certain embodiments of the present invention, the ratio of the width to the height of the cross-section is typically at least 1.2: 1, more preferably 1.5: 1 or greater.

The aspect ratio is also important for controlling the orientation of the fibers when applying the fibers according to various embodiments of the present invention to a finished fabric, such as an embroidery process. For example, a curved fiber having a rectangular cross-section may twist. This may be undesirable if it is preferred that the viewing surface of the color shifting fibers remain relatively parallel to the underlying fabric. In this case, it is beneficial that the fibers have a cross-section close to a square or rectangular, wherein the depth of the fibers is greater than the width when viewed from the normal viewing side, to reduce the likelihood of any undesired twisting of the fibers in the fabric.

Each flexible fibre comprises at least two electrically conductive wire electrodes extending along its length and as close to the lumen as possible without compromising the ability of the wall to mechanically constrain the wire electrodes. The wire electrode may be formed of tungsten, silver, copper, or other conductive material having good ductility. The electrode cross-sectional shape may be circular, rectangular or other shape that will optimize the uniformity of the electric field across the electro-optic medium. One or a group of wires is located on the viewing side of the cavity and the other or a group of wires is located on the opposite side of the cavity. When the ends of the leads are connected to a power source, an electrical potential can be generated across the cavity, causing a change in the optical state of the electronic ink. The wire should be as small as possible while maintaining sufficient mechanical strength to withstand the fiber manufacturing process. In the embodiment of the present invention, the diameter of the tungsten wire may be 100 μm or less, preferably 50 μm or less, and more preferably 25 μm or less. The optical benefit of the smaller diameter fiber is significant because for a 400 micron wide cavity, two 50 micron wires would obscure 25% of the switching region, while a 25 micron wire would obscure only 12.5% of the switching region. In addition, smaller diameter fibers are more mechanically flexible, which allows for thinner mechanical material in the fiber, including the wire, and greatly increases the flexibility possible in making the fiber. The fibers may be of infinite length, such as 1 meter or more, such as 10 meters or more, such as 100 meters or more.

In one embodiment of the present invention, the color-changing fibers may include four conductive electrode wires arranged in two sets of two wires each. This configuration is illustrated in fig. 1B, where two wires are located on the viewing side of the fiber lumen and two wires are disposed on the opposite side of the lumen. The wires are arranged so that each is placed at 1/4 away from the cavity width of the edge of the cavity towards the middle of the fiber. This is also shown in fig. 1B. This arrangement of the electrode wires results in improved uniformity of the electric field generated by the wires, without the portion of the top of the cavity exceeding 1/4 away from the width of the electrode wires. The fraction of the cavity width covered by the opaque wires is given by the formula f N D/W, where N is the number of wires on one side of the cavity, D is the wire diameter, and W is the cavity width. The fraction f is desirably less than 40%, preferably less than 20%.

As described above, the electrode of the fiber according to various embodiments of the present invention may include copper. For example, copper has a lower modulus than tungsten, and thus copper wire will be more flexible than tungsten wire of equivalent diameter. This flexibility has the secondary effect that less polymeric material is required to mechanically hold the wire, thereby making the wire relatively thin. Copper wires with a lower modulus exert less force on the surrounding polymer fiber material when the fiber is bent, which results in a fiber with better mechanical strength when bent. Higher mechanical strength is preferred because if the wire is threaded through the polymeric material of the fiber during bending, the wire is likely to cross the lumen of the fiber and make electrical contact with another electrode wire in the device. Contact between the electrodes across the cavity can create an electrical short circuit that causes the fiber to lose switching performance and, in many cases, completely lose the ability to switch.

In another embodiment of the invention shown in fig. 5, the electrical properties of the polymer material used to mechanically constrain the wires into the fibers are varied to maximize the electric field across the electrophoretic medium in the cavity. Specifically, a structural polymer, such as polycarbonate, is filled with a conductive material, such as carbon, that exceeds the percolation threshold, such that the resulting polymer/carbon blend material 52a, 52b, 52c, 52d becomes conductive. A variety of polymer materials suitable for fiber formation may be filled with conductive materials, and a variety of conductors may be used as conductive fillers. Electrically Conductive Polycarbonate (CPC) material 52a, 52b, 52c, 52d may be disposed between the wires 54a, 54b, 54c, 54d and the lumen 56 of the hollow fiber 50, as shown in fig. 5. Preferably, the width of the CPC material, at least on the viewing side of the fiber, is approximately equal to the diameter of the wire, as the conductive material is opaque and may obscure the electrophoretic medium. If both the hollow fiber material and the CPC material are thermoplastics, the CPC material may be integrated into the preform using a stacking and hot pressing method. For example, according to one method of processing, a composite of non-conductive polycarbonate and conductive polycarbonate material forming a hollow fiber may be melted together under pressure and/or heat. CPCs enable fibers to switch at lower voltages than polycarbonate lacking any conductive material. Fig. 6 is a photograph of white and dark states of fibers with this arrangement. As is evident from the photographs, the optical performance can be improved by using smaller diameter wires and narrower CPC strips, thereby reducing the shadowing of the electrophoretic material in the cavity. In some embodiments, the fiber may comprise a CPC material and a copper electrode.

The visual impact of a color shifting fiber is directly proportional to the optical fill factor, which is the fraction of the fiber area or width that is actually visible to the color shifting medium when the fiber is viewed from the outside. Ideally, the optical fill factor should be 100% to maximize visual performance. The presence of opaque material (e.g., wire) on top of the color changing media, as well as the inactive wall material required to contain the color changing media, reduces the optical fill factor. To increase the optical fill factor, fibers according to some embodiments of the present invention may include features that provide a lens effect. As used herein throughout the specification and claims, the term "lensing" means a feature that is capable of bending light to mask inactive areas and maximize the appearance of active areas of a color-changing fiber.

The lens effect can be achieved by refraction of light at the interface between two different transparent materials. In order to bend the light, two conditions are required: (1) the two materials need to have different refractive indices, and (2) the angle between the viewing direction and the interface plane needs to be different from 90 °. An example of a simple fiber geometry that provides a lens effect is provided in fig. 7. The fiber 70 has two top chamfer angles 72a, 72b that are at an angle of about 45 to the top surface. The refracted light 74a, 74b, 74c transmitted through the fiber 70 continues undeflected at the interface between the fiber 70 and the outside air. Refracted light transmitted through angled corner regions 72a, 72b to effectively increase the effective width (W) of the light having a width equal to the actual width in the internal cavity_A) Apparent width (W) of active medium 76_L) Is deflected. As a result, more active media and less inactive walls 78a, 78b are visible from the exterior of the fiber 70. Accordingly, fibers according to various embodiments of the present invention may include one or more beveled edges. For example, for a color shifting fabric used in applications where the fabric is visible from either side, a fiber 90 made according to embodiments of the present invention may have four chamfered edges 92a, 92b, 92c, 92d, as shown in FIG. 8.

Fig. 9 shows a fiber structure with a more complex lensing effect according to another embodiment of the present invention. The structure includes chamfered edges 83a, 83b and curved surfaces 81a, 81b, 81c in the top portion of the fibers 80. The chamfered edges 83a, 83b reduce the portion of the inactive walls 85a, 85b visible from the outside of the fiber 80, and the curved surfaces 81a, 81b, 81c reduce the visibility of the two electrodes 84a, 84b present on top of the cavity 87 containing the electrophoretic medium by positioning the end of each curved surface 81a, 81b, 81c within the area of the line electrode 84a, 84 b.

In a preferred embodiment of the present invention, the color-changing fiber 100 may comprise a CPC material 102a that spans the width of the non-viewing side of a cavity comprising an electrophoretic medium 104, as shown in fig. 10. A single copper wire 106a may be placed under and in contact with the CPC material 102 across the width of the non-viewing side of the electrophoretic medium 104, which reduces the total number of conductors 106a, 106b, 106c in the fiber 100 to three and enhances the overall flexibility of the fiber 100. On the viewing side of the fiber 100, there are two copper electrodes 106b, 106c that are positioned at a distance from either edge of the electrophoretic medium 104 that is approximately equal to 1/4 of the width of the electrophoretic medium 104 to enhance electro-optic switching performance, and the CPC material 102b, 102c is positioned between the wires 106b, 106c and the cavity containing the electrophoretic medium 104. The fiber 100 of this embodiment also has shaped corners 108a, 108b for enhancing the lens effect. The combination of wires, copper wires, CPCs, lenses and optimization of the geometric positioning across the non-viewing side electrodes of the CPCs results in a fiber with enhanced flexibility, enhanced electro-optic conversion performance and low voltage operation.

The introduction of a chamfered edge is one feature that can provide a lens effect. Alternatively, lensing may be achieved by coating a light-refracting material on the fibers to cause refraction of light at the interface between the underlying fiber and the coating. The refractive indices of the coating and the fiber should be different and the angle between the interface plane and the viewing direction between the two materials should be less than 90 deg..

In certain applications, such as apparel textiles, the fibers may be subjected to high mechanical stresses, such as excessive bending, kinking or flattening. It is desirable that the entire length of continuous fiber remain functional even if the fiber is locally damaged. To prevent such damage, fibers made according to embodiments of the present invention may include a barrier layer to reduce the likelihood of electrical shorting between the top and bottom electrodes. For example, in fig. 11, the risk of electrical shorts is reduced by the presence of an electrically insulating layer 112 between top conductive materials 110a, 110b (wire + conductive polymer) and bottom conductive material 114 (wire + conductive material). The barrier layer may be made of an insulating polymer material such as polycarbonate. Alternatively, the barrier layer may be made of a partially conductive polymeric material having a conductivity greater than that of polycarbonate but less than that of Conductive Polycarbonate (CPC).

The process of making a color-changing fiber is depicted in fig. 2. In general, an electro-optic medium 20 comprising charged pigment particles in a non-polar solvent is prepared and the electro-optic medium 20 is injected using a micro-injector 24, e.g., introduced into a fiber 22 having an internal cavity and at least two wire electrodes that can provide electrical gradient across the fiber 22. Once the fibers 22 are filled with the electro-optic medium 20, the fibers 20 may be sealed with an adhesive. An alternative method of filling the fibres may be more suitable for producing continuous fibres over 100 metres in length, which method is: a partially drawn fiber is first prepared having an internal cavity larger than the desired final size of the cavity, then ink is inserted into the cavity of the medium size fiber, and then finally the fiber is drawn to final size using a draw tower or fiber draw system. This may avoid long fill times associated with flowing the viscous fluid through a small chamber and over a long length. Typically, the wire electrode is longer than the fiber. These wire "braids" may form the basis for electrical connection to the driver circuit. Alternatively, the fiber walls may be ablated, stripped or cut to establish connection with the wire electrode. Once the fibers are made, they may be introduced, for example, into a woven cloth 30, as shown in fig. 3, and electrically connected to an electronic driver 32 to switch the optical state of the fibers within the woven cloth 30. In particular, because the fibers of the present invention are rectangular in cross-section, they can be arranged to have the same face that is presented outwardly in the fabric. Of course, these color-changing fibers can also be integrated into various other woven materials that can be used for interior design elements, construction, routing, etc.

The terms "bistable" and "bistability" are used herein in their conventional meaning in the art to refer to displays comprising display elements having first and second display states differing in at least one optical property, and such that after any given element is driven by an addressing pulse of finite duration to assume either its first or second display state, that state will continue for at least several times, for example at least four times, the minimum duration of the addressing pulse required to change the state of the display element after the addressing pulse has terminated. Some particle-based, gray scale-capable electrophoretic displays are shown in U.S. patent No. 7,170,670 to be stable not only in their extreme black and white states, but also in their intermediate gray states, and for some other types of electro-optic displays. This type of display is properly referred to as "multi-stable" rather than bistable, but for convenience the term "bistable" may be used herein to cover both bistable and multi-stable displays.

Many patents and applications filed by the Massachusetts Institute of Technology (MIT) and E Ink Corporation or in their name describe various techniques for encapsulating electrophoretic and other electro-optic media. Such encapsulated media comprise a plurality of capsules, each capsule itself comprising an internal phase containing electrophoretically-mobile particles in a fluid medium and a capsule wall surrounding the internal phase. Certain materials and techniques described in the following listed patents and applications are relevant to the manufacture of the variable transfer devices described herein, including:

(a) electrophoretic particles, fluids, and fluid additives; see, e.g., U.S. Pat. Nos. 5,961,804; 6,017,584; 6,120,588; 6,120,839, respectively; 6,262,706, respectively; 6,262,833; 6,300,932, respectively; 6,323,989, respectively; 6,377,387, respectively; 6,515,649, respectively; 6,538,801, respectively; 6,580,545, respectively; 6,652,075, respectively; 6,693,620, respectively; 6,721,083, respectively; 6,727,881, respectively; 6,822,782; 6,870,661, respectively; 7,002,728; 7,038,655, respectively; 7,170,670; 7,180,649, respectively; 7,230,750, respectively; 7,230,751, respectively; 7,236,290, respectively; 7,247,379, respectively; 7,312,916, respectively; 7,375,875, respectively; 7,411,720, respectively; 7,532,388, respectively; 7,679,814, respectively; 7,746,544, respectively; 7,848,006, respectively; 7,903,319, respectively; 8,018,640, respectively; 8,115,729, respectively; 8,199,395, respectively; 8,270,064, respectively; and U.S. patent No. 8,305,341; and 2005/0012980 th; 2008/0266245, respectively; 2009/0009852, respectively; 2009/0206499, respectively; 2009/0225398, respectively; 2010/0148385, respectively; 2010/0207073, respectively; and U.S. patent application No. 2011/0012825;

(b) a bladder, adhesive and encapsulation process; see, e.g., U.S. patent nos. 6,922,276 and 7,411,719;

(c) films and sub-assemblies comprising electro-optic material; see, e.g., U.S. Pat. nos. 6,982,178 and 7,839,564;

(d) backsheets, adhesive layers, and other auxiliary layers and methods for use in displays; see, e.g., U.S. patent nos. 7,116,318 and 7,535,624;

(e) color formation and color adjustment; see, e.g., U.S. patent nos. 7,075,502 and 7,839,564;

(f) a method for driving a display; see, e.g., U.S. Pat. nos. 7,012,600 and 7,453,445;

(g) an application for a display; see, e.g., U.S. patent nos. 7,312,784 and 8,009,348; and

(h) non-electrophoretic displays, such as 6,241,921; 6,950,220, respectively; 7,420,549 and 8,319,759; and U.S. patent application publication No. 2012/0293858.

The electro-optic medium comprises charged pigment particles in a suspending fluid. The fluid used in the variable transmission medium of the present invention will generally have a low dielectric constant (preferably less than 10, and desirably less than 3). Particularly preferred solvents include aliphatic hydrocarbons, for example heptane, octane and petroleum distillates such as(Exxon Mobil) or(Total)。

The charged pigment particles can have a variety of colors and compositions. In addition, the charged pigment particles may be functionalized with surface polymers to improve state stability. Such pigments are described in U.S. patent publication No. 2016/0085132, which is incorporated herein by reference in its entirety. For example, if the charged particles are white, they may be made of materials such as TiO₂、ZrO₂、ZnO、Al₂O₃、Sb₂O₃、BaSO₄、PbSO₄And the like. They may also be of high refractive index: (>1.5) and has a certain size>100nm) to appear white, or composite particles designed to have a desired refractive index. Black charged particles, which mayTo be formed from CI pigment black 26 or 28 or the like (e.g., ferrimanganic black spinel or copper chromium black spinel) or carbon black. Other colors (non-white and non-black) may be formed by organic pigments, such as CI pigments PR254, PR122, PR149, PG36, PG58, PG7, PB28, PB 15: 3. PY83, PY138, PY150, PY155, or PY 20. Other examples include Clariant Hostaperm Red D3G 70-EDS, Hostaperm powder E-EDS, PV fast Red D3G, Hostaperm Red D3G 70, Hostaperm blue B2G-EDS, Hostaperm yellow H4G-EDS, Novoperm yellow HR-70-EDS, Hostaperm Green GNX, BASF Irgazine Red L3630, Cinquasia Red L4100 HD, and Irgazin Red L3660 HD; sun Chemical phthalocyanine blue, phthalocyanine green, diarylaniline yellow, or AAOT diarylaniline yellow. The colored particles can also be formed from inorganic pigments such as CI pigment blue 28, CI pigment green 50, CI pigment yellow 227, and the like. The surface of the charged particles can be modified based on the desired charge polarity and charge level of the particles by known techniques, as described in U.S. patent nos. 6,822,782, 7,002,728, 9,366,935, and 9,372,380, and U.S. patent publication No. 2014-0011913, which are incorporated herein by reference in their entirety.

The particles may exhibit a natural charge, or may be positively charged using a charge control agent, or may acquire a charge when suspended in a solvent or solvent mixture. Suitable charge control agents are well known in the art; they may be polymeric or non-polymeric in nature, or may be ionic or non-ionic. Examples of charge control agents may include, but are not limited to, Solsperse 17000 (active polymeric dispersant), Solsperse 9000 (active polymeric dispersant), OLOA 11000 (succinimide ashless dispersant), unitox 750 (ethoxylate), Span 85 (sorbitan trioleate), Petronate L (sodium sulfonate), Alcolec LV30 (soy lecithin), Petrostep B100 (petroleum sulfonate) or B70 (barium sulfonate), Aerosol OT, polyisobutylene derivatives or poly (ethylene-co-butene) derivatives, and the like. In addition to the suspending fluid and the charged pigment particles, the internal phase may also include stabilizers, surfactants, and charge control agents. When the charged pigment particles are dispersed in the solvent, the stabilizing material may be adsorbed on the charged pigment particles. The stabilizing material keeps the particles separated from each other so that the variable transmission medium is substantially opaque when the particles are in a dispersed state. As is known in the art, dispersion of charged particles (typically carbon black, as described above) in a low dielectric constant solvent can be aided by the use of a surfactant. Such surfactants typically comprise a polar "head group" and a non-polar "tail group" that are compatible or soluble with the solvent. In the present invention, it is preferred that the non-polar tail group is a saturated or unsaturated hydrocarbon moiety, or another group that is soluble in a hydrocarbon solvent, such as a poly (dialkylsiloxane). The polar group can be any polar organic functional group including ionic materials such as ammonium, sulfonate or phosphonate, or acidic or basic groups. Particularly preferred head groups are carboxylic acid or carboxylate groups. Stabilizers suitable for use in the present invention include polyisobutylene and polystyrene. In some embodiments, a dispersant, such as polyisobutylene succinimide and/or sorbitan trioleate, and/or 2-hexyldecanoic acid is added.

Examples

Filling polycarbonate fibers having four internal tungsten wire electrodes and a rectangular cross-section with an optical medium comprisingAnd functionalized titanium dioxide and black spinel particles. The fibers were about 0.8mm by 0.5mm (outer) and the internal cavity was about 0.4mm by 0.2 mm. Two line electrodes on one side are coupled to a power supply and the other two line electrodes are grounded. The fiber can be switched between white and black by providing a +/-voltage signal between 100 and 500V to the wire electrode. (typically, the particles will switch at a voltage of +/-100V, but switching is significantly faster at higher voltages.) FIG. 4 shows a visible light microscope image of the fiber switching between white (left) and black (right). The switching is repeated at least 100 times without any degradation of the fiber or the electro-optical medium. In addition, the fibers will exhibit bistability under appropriate voltage waveforms. Using such a waveform, fibers of the type shown in fig. 4 were color-stabilized for more than three days.

From the foregoing, it can be seen that the present invention can provide color-changing fibers that can be integrated into textiles and other materials. It will be apparent to those skilled in the art that many changes and modifications can be made to the specific embodiments of the invention described above without departing from the scope of the invention. Accordingly, the entire foregoing description is to be construed in an illustrative and not a restrictive sense.

Claims (14)

1. A flexible color-changing fiber comprising:

a hollow fiber having a rectangular cross-section and comprising four electrically insulated wires integrated into the wall of the hollow fiber; wherein the wire is located at 1/4 from the width of the larger interior dimension of the rectangular cross-section inward of the inner edge of the wall of the hollow fiber; wherein two of the electrically insulated conductors are located on the viewing side of the fiber cavity and the remaining two electrically insulated conductors are disposed on opposite sides of the cavity; and

a bistable electro-optic medium disposed within the hollow fibers, the bistable electro-optic medium comprising a non-polar solvent, first charged electrophoretic pigment particles, second charged electrophoretic pigment particles having a different charge and color than the first charged electrophoretic pigment particles, a polymeric stabilizer, and a charge control agent,

wherein the first charged electrophoretic pigment particles move towards the two electrically insulated wires at the viewing side of the fiber lumen when an electric field is applied between the two sets of two electrically insulated wires, wherein the second charged electrophoretic pigment particles move away from the two electrically insulated wires at the viewing side of the fiber lumen when an electric field is applied between the two sets of two electrically insulated wires, and

wherein the first and second charged electrophoretic pigment particles maintain their position relative to the electrically insulated conductive lines when no electric field is applied between the two sets of two electrically insulated conductive lines.

2. The flexible color-changing fiber of claim 1, wherein the hollow fiber comprises a polymer.

3. A flexible color-changing fiber according to claim 2, wherein the polymer comprises polycarbonate.

4. A flexible color-changing fiber according to claim 1, wherein the rectangular cross-section has an aspect ratio of at least 1.2: 1.

5. a flexible color-changing fiber according to claim 1, wherein the lead comprises tungsten.

6. A flexible color-changing fiber according to claim 1, wherein the conductive wire comprises copper.

7. The flexible color-changing fiber of claim 1, further comprising an insulation layer between the at least two electrically insulated wires.

8. The flexible color-changing fiber of claim 1, further comprising one or more features that provide a lens effect.

9. The flexible color-changing fiber of claim 8, wherein the feature comprises a chamfered edge.

10. The flexible color-changing fiber of claim 8, wherein the feature comprises a refractive coating surrounding at least a portion of the outer surface of the fiber.

11. The flexible color-changing fiber of claim 1, further comprising an electrically conductive material between at least one of the electrically insulated conductive wires and the electro-optic medium.

12. A flexible color-changing fiber according to claim 11, wherein the electrically conductive material comprises carbon.

13. The flexible color-changing fiber of claim 1, wherein the non-polar solvent is a mixture of hydrocarbons.

14. A fabric comprising the color-changing fiber of claim 1.