The invention relates to a process for producing a lenticular device for an autostereoscopic display apparatus, to a lenticular device obtainable by such process, to a liquid crystal cell comprising such lenticular device, to a production mold for producing a lenticular device, and to a process for producing such production mold.

Electrically switchable two-dimensional and three-dimensional (2D/3D) displays have attracted great attention in the last fifteen years. In one approach, a liquid crystal display (LCD) having rows and columns of pixels is integrated with a lenticular device that comprises an array of semi-cylindrical micro-lenses that can be actuated by switching between two states of a liquid crystalline material in the lenticular device. Each lens is then associated with a group of at least two columns of pixels that extend parallel with the lens, or under an angle thereto. In the 2D mode, the micro-lenses do not have a focusing effect causing the lenticular device to behave as a transparent and flat optical panel. When the lenticular device is switched to the 3D mode, each micro-lens exhibits a focusing effect, which enables a stereoscopic image to be perceived. Therefore, lenticular micro-lens arrays have become a key component in displays that can switch between 2D and 3D modes.

Based on this principle of electrical switching between liquid crystalline states, different set-ups of lenticular devices are possible. The lenses may be convex or concave, they may be of an isotropic or anisotropic material, the switchable liquid crystal may constitute the micro-lenses or be present as a liquid layer on top of the micro-lenses, etc. In many of these set-ups, it is essential that the curved surface of the lenticular micro-lens arrays has liquid crystal alignment properties.

A number of methods is known to equip a flat surface with liquid crystal alignment properties. Usually, an existing surface is modified by a contact- or a non-contact technique. It may be subjected to, for example, rubbing, high-speed buffing, (mechanical) abrasion, chemical milling, ion milling, impacting with high-energy particles, linear photopolymerization or photodecompositon. Many of such methods work satisfactorily only on particular materials, thereby compelling to apply a layer of such material onto an object when the object itself is of a material not capable of exhibiting alignment properties. Such separate layer is known in the art as an alignment layer.

Many of these techniques have severe restrictions for the application on curved surfaces, especially with the high surface curvatures that are common to surfaces that comprise lenses, in particular lenticular lenses. For example, providing such surface with an alignment layer may cause deformation of the surface of the lens, resulting in a disturbed optical performance. This is in particular the case when the layer is applied as a liquid - when applied in the crevices between two neighboring convex lenses, the liquid experiences capillary forces which fill the crevices to an unacceptable extent.

Another disadvantage of applying a layer onto a lenticular surface, is that it makes the manufacturing process of the lenticular device more laborious and more sensitive to defects.

Yet another disadvantage of the presence of an alignment layer on a lenticular surface is the risk of delamination after prolonged use of the device. This may occur due to e.g. an intense exposure to (UV) light and/or many cycles of warming and cooling down when the LCD is turned on and off, respectively.

Further, it is more generally a disadvantage to use contact methods for modifying a surface to provide it with alignment properties, because these produce very fine debris which has to be removed by a separate washing procedure. When not removed from the production site, the debris may be incorporated into the optical elements of the lenticular device and so generate defects therein. In addition, contact methods may damage the surface and so influence the optical performance in a negative way.

A material that is commonly used as a top-layer with alignment properties is polyimide. The high curing temperature of this material is however a drawback, because it limits the choice of the supporting materials. Temperature sensitive materials are prone to degradation when polyimide is applied on it.

It is therefore an object of the present invention, to provide a method for producing a lenticular device that overcomes one or more of these disadvantages. It is a further object to provide a lenticular device that has a higher quality in terms of liquid crystal alignment, and/or a better switchability between the liquid crystalline states, and/or an increased robustness (lifetime).

It has now been found that one or more of these objects can be met by applying a particular method of manufacturing. Accordingly, the present invention relates to a process for producing a lenticular device (1) for an autostereoscopic display apparatus, the lenticular device (1 ) comprising an array of lenticular elements (6) having a surface with liquid crystal alignment properties (5), the process comprising

1 ) providing a production mold (2) having a shaped surface which corresponds in negative relief to the desired surface profile for the array of lenticular elements (6), which shaped surface has a nanomorphology represented by grooves, wherein the nanomorphology of the production mold (2) is obtained by subjecting its shaped surface to abrasion; or

wherein the production mold (2) is produced from a first pre-mold (3) by a molding process, wherein the first pre-mold (3) comprises a shaped surface which corresponds in negative relief to the surface profile for the production mold (2); and wherein the shaped surface of the first pre-mold (3) has a nanomorphology represented by grooves obtained by subjecting the shaped surface to abrasion; or

wherein the production mold (2) is produced from a first pre-mold (3) by a molding process, wherein the first pre-mold (3) comprises a shaped surface which corresponds in negative relief to the surface profile for the production mold (2); which first pre-mold (3) is produced from a second pre-mold (4) by a molding process, wherein the second pre-mold (4) comprises a shaped surface which corresponds in negative relief to the surface profile for the first pre-mold (3); and wherein the shaped surface of the second pre-mold (4) has a nanomorphology represented by grooves obtained by subjecting the shaped surface to abrasion;

2) preparing the lenticular device (1 ) by a molding process with the production mold (2), wherein the shaped surface of the production mold (2), including the nanomorphology, is formed in negative relief as a part of the lenticular device (1 ). Figure 1 schematically displays the steps of a first method according to the invention wherein the production mold is subjected to abrasion.

Figure 2 schematically displays the steps of a second method according to the invention wherein a first pre-mold is subjected to abrasion.

Figure 3 schematically displays the steps of a third method according to the invention wherein a second pre-mold is subjected to abrasion.

Figure 4 displays an AFM image of the surface of a lenticular device obtained by the process of the invention.

Figure 5 displays a liquid crystal cell comprising a lenticular device according to the invention.

Figure 6 displays the switching behavior of a liquid crystal cell comprising a lenticular device according to the invention.

The lenticular device produced by a process of the invention comprises an array of lenticular elements, which are usually convex or concave. Such arrays are generally known in the art, and are also described as lenticular lenses. The lenticular elements in the array are usually lenses. They are of an elongated shape and are configured in rows or columns adjacent and parallel to each other. At a cross-section perpendicular to the longitudinal direction of the lenticular elements, their surface has a particular (lens) shape, e.g. facetted, pyramidal, Fresnel, or curved {e.g. circular). In particular in case of a circular shape, the lenticular elements are usually considered as being part of a cylinder and are therefore often termed cylindrical lenses - an array of such cylindrical lenses then makes up one lenticular lens.

The process of the invention combines the formation of a lenticular structure with the formation of a surface morphology thereon in one step. Such morphology typically comprises nanosized grooves that are present on the surface of that lenticular structure. For the purpose of the invention, such morphology is therefore termed a nanomorphology. This combination is realized by the use of a production mold that comprises the negative of the lenticular structure as well as the negative of the surface’s nanomorphology. In other words, the shaped surface of the production mold corresponds in negative relief to the desired surface profile for the array of lenticular elements, as well as to the nanomorphology provided thereon. Thus, the production mold comprises a shaped suriace with a lenticular structure, on which a nanomorphology represented by grooves is present.

With the production mold, the desired lenticular device can be prepared in accordance with step 2) of the process of the invention. In the process for achieving this, the shaped surface of the production mold, including the

nanomorphology, is formed in negative relief as a part of the lenticular device.

Figure 1 schematically displays the steps of a process according to the invention. The items shown are a production mold (2) and a lenticular device (1 ). Also shown are precursors of both items; these are a production mold (2’) without the nanomorphology (i.e. prior to the abrasion) and a substance (T) from which the lenticular device (1 ) is formed in step 2), wherein the substance (T) is contacted with and allowed to adopt the shape of the production mold (2). In Figure 1 , these items are represented by a cross-sectional view perpendicular to the longitudinal direction of their lenticular elements (6). The cross-sectional shape of their surface is circular; the lenticular elements (6) can thus be regarded as having a cylindrical shape. In this embodiment, the surface of a lenticular element (6) is less than half of the surface of the corresponding cylinder.

In Figure 1 , the cross-sections of the production mold (2) as well as the lenticular device (1) formed therefrom have a knurled edge at the lenticular elements (6). This edge represents the cross-section of the nanomorphology present on the surface of a lenticular elements (6), i.e. the cross-section of the grooves that form the nanomorphology. In reality, the grooves on the surface that represent the nanomorphology are nevertheless aligned but they are not all the same. Their dimensions typically vary from groove to groove, in a random manner (which is explained below in more detail). It is for the sake of clarity, however, that the edges in Figure 1 display a regular pattern of indentations and protrusions.

In the first step of Figure 1 , a concave-shaped mold (2’) is subjected to the abrasion, yielding a first production mold (2) having a surface with liquid crystal alignment properties (5). Thereafter, the production mold (2) is contacted with a substance (1’), which then adopts the shape of the surface of the production mold (2). After this adopted shape of the substance (T) has been made permanent, the convex-shaped lenticular device (1) is formed and released from the production mold (2). The molding process of step 2) of the process of the invention may be performed in different manners. In the molding process, a substance (T) is usually contacted with the shaped surface of the production mold (2). It is then allowed to adopt the shape of the surface, after which the substance (T) is hardened so that it retains its shape after release from the production mold (2). This then yields the lenticular device (1) in step 2). The substance (T) is typically liquid or soft, or at least it is capable of adopting the shape of the mold, including that of the nanomorphology present thereon.

In known molding processes, a mold is usually filled with a liquid that is capable of becoming a solid under certain conditions. After hardening of the liquid, the solidified material is released from the mold to yield the product with the desired shape, thereby also regenerating the free mold which so becomes available for re-use.

In a process of the invention, the production mold may also be filled with a liquid that is capable of becoming a solid under certain conditions (or at least a layer of such liquid is applied over the shaped surface of the production mold), followed by hardening of the liquid. Upon application, such liquid should be able to adopt the exact shape of the production mold, including the

nanomorphology on which the alignment properties in the final product rely, and it should be capable of retaining this shape upon hardening and release from the mold. For example, the viscosity of the liquid should not be too high. A person skilled in the art will be able to find a liquid with appropriate properties by routine experimentation and without exerting inventive effort.

When the solidified material is released from the production mold, a lenticular structure is formed that has the imprint of the nanomorphology of the production mold. In this way, the lenticular device of the invention is provided, wherein its (lenticular) surface with liquid crystal alignment properties is formed from the nanomorphology of the production mold. In addition, after the release, the mold is suitable for re-use, allowing the exact and repeated production not only of the lenticular surface, but also of the nanomorphology thereon.

Accordingly, step 2) in a process of the invention may comprise - applying a layer of a liquid over the shaped surface of the production mold; then - exposing the layer to a stimulus for solidifying the liquid to form a layer of a solid material; then

- releasing the solid material from the production mold to provide the

lenticular device.

Such molding process may in principle also be used to prepare any of the production mold, first pre-mold and the second pre-mold.

Another way of preparing the lenticular device (or any of the production mold, first pre-mold and the second pre-mold) with the production mold in step 2) makes use of a so-called hot-embossing technique. This concerns the stamping of the shaped surface of the production mold as well as the nanomorphology of the surface of the production mold into a polymer softened by raising the temperature of the polymer, in particular to a temperature at just above its glass transition temperature (for example 1-15 or 2-10 °C above). After cooling down and release from the mold, the molded product (the lenticular device) is formed, together with the nanomorphology on its surface. It is in principle also possible that the softened polymer is pre-shaped with the desired lenticular structure, and that the

nanomorphology is stamped into this lenticular surface.

The lenticular device that is formed with the process of the invention comprises an array of lenticular elements, which may have a convex shape or a concave shape. For the purpose of the invention, the mold that is used to directly form the array of lenticular elements (usually convex or concave shaped) of the lenticular device is termed the production mold. This ensures that this mold is distinguished from other molds that may be used in the process of the invention.

Any other molds in the process are termed pre-molds. These molds do not actually form a lenticular device of the invention, but are used for the manufacture of production molds or other pre-molds.

The imprint of the nanomorphology on the surface of the molded product originates from the nanomorphology on the production mold. This mold comprises a surface that corresponds in negative relief to the surface of the molded product. A production mold with such nanomorphology may be obtained in multiple ways.

In a first process according to the invention (see also Figure 1 ), the production mold is obtained by manufacturing an object with the desired surface profile for the array of lenticular elements, followed by subjecting the surface profile to abrasion. This abrasion has to be performed in such a manner that a nanomorphology comprising grooves is formed on the surface. With this method, the nanomorphology further has the property that it is capable of aligning liquid crystals, or at least that the nanomorphology obtained by molding with the production mold (which corresponds in negative relief thereto) is capable of aligning liquid crystals.

In a second process according to the invention, the production mold itself (including its nanomorphology) is obtained by a molding process (see also Figure 2). For such process, a first pre-mold is used which comprises a surface that is shaped in negative relief to the surface profile of the production mold, including the nanomorphology. The first pre-mold is then obtained in a manner analogously to that of the production mold. First, an object with the desired surface profile for the array of lenticular elements is manufactured, which is then followed by subjecting the surface profile to abrasion. This abrasion has to be performed in such a manner that a nanomorphology comprising grooves is formed on the surface. With this method, the nanomorphology further has the property that it is capable of aligning liquid crystals, or at least that the corresponding

nanomorphology obtained after two subsequent molding steps (which corresponds in positive relief thereto) is capable of aligning liquid crystals. When such a first pre-mold is used, the array of lenticular elements as well as the nanomorphology provided thereon correspond in positive relief to those of the final product obtained by the process of the invention (/. e. its shape is not the negative thereof and therefore does not correspond in negative relief).

Accordingly, the present invention further relates to a mold for use in a process for producing a lenticular device comprising an array of lenticular elements (6) having a surface with liquid crystal alignment properties, wherein the mold has a shaped surface

1 ) which corresponds in positive or negative relief to a desired surface profile for the array of lenticular elements in the lenticular device;

2) which comprises a nanomorphology comprising grooves.

The present invention further relates to a process for producing a mold, comprising 1 ) providing an object with a shaped surface which corresponds in positive or negative relief to a desired surface profile for an array of lenticular elements;

2) subjecting the shaped surface to abrasion to generate a nanomorphology comprising grooves, which nanomorphology is capable of providing the molded product with liquid crystal alignment properties.

In a third process according to the invention, the first pre-mold itself (including its nanomorphology) is obtained by a molding process (see also

Figure 3). For such process, yet another pre-mold is used - a second pre-mold. Such mold comprises a surface that is shaped in negative relief to the surface profile of the first pre-mold, including the nanomorphology. The second pre-mold is then obtained in a manner analogously to that of the first pre-mold. First, an object with the desired surface profile for the array of lenticular elements is

manufactured, which is then followed by subjecting the surface profile to abrasion. This abrasion has to be performed in such a manner that a nanomorphology comprising grooves is formed on the surface. With this method, the

nanomorphology further has the property that it is capable of aligning liquid crystals, or at least that the corresponding nanomorphology obtained after three subsequent molding steps (which corresponds in negative relief thereto) is capable of aligning liquid crystals. When such a second pre-mold is used, the array of lenticular elements as well as the nanomorphology provided thereon correspond in negative relief to those of the final product obtained by the process of the invention (i.e. its shape is not the positive thereof and therefore does not correspond in positive relief).

In some processes for manufacturing the lenticular device, the production mold is for single use, for example when it is difficult to obtain the mold after the first molding cycle in a state wherein it is still suitable for re-use. In such case, the disposable production molds are continuously made from the first pre-mold.

The lenticular elements in a lenticular device that is formed with the process of the invention may have a convex shape (protruding surface) or a concave shape (indented surface). This, in combination with the possibility to make use of a first pre-mold next to the production mold, or even to make use of a second pre-mold, allows a number of discrete manners for carrying out the process of the invention. For example, and as exemplified in Figure 1 , in a process of the invention,

1 ) the lenticular device comprises convex lenticular elements;

2) the production mold comprises the corresponding concave shapes; and

3) the nanomorphology of the production mold is obtained by subjecting the shaped surface of the production mold to abrasion.

In order to achieve a sharp crevice between two convex lenticular elements (which is at the intersection of the surfaces of two convex lenticular elements), the production mold should contain sharp ridges between its concave lenticular elements. Depending on the method of abrasion, care has to be taken not to damage these sharp ridges. For example, they may be rounded off which then results in partially filled crevices in the molded product. Therefore, it may be advantageous to manufacture a pre-mold wherein the lenticular elements are convex, i.e. the same as in the molded product. Subjecting the array of convex lenticular elements to abrasion would not damage the sharp ridges (because they are absent in that mold), so that the crevices in the molded product are of the desired shape. Accordingly, another example of a process of the invention, is a process wherein

1 ) the lenticular device comprises convex lenticular elements;

2) the production mold comprises the corresponding concave shapes; and

3) the production mold is produced from a first pre-mold comprising the

corresponding convex shapes, wherein the nanomorphology of the first pre-mold is obtained by subjecting the shaped surface of the first pre-mold to abrasion.

Figure 2 displays such process. In the first step, a convex-shaped mold (3’) is subjected to the abrasion, yielding a first pre-mold (3) having a surface with liquid crystal alignment properties (5). From this first pre-mold (3), a concave shaped production mold (2) is produced via molding. Thereafter, the production mold (2) is contacted with a substance (1’), which then adopts the shape of the surface of the production mold (2). After this adopted shape of the substance (1’) has been made permanent, the lenticular device (1) is formed and released from the production mold (2). It is also possible to have even an extra molding step in the process, in particular to manufacture the first pre-mold not by abrading the first pre-mold, but by molding the first pre-mold from a second pre-mold. The nanomorphology of this second pre-mold can then be obtained by subjecting its shaped surface to abrasion. Accordingly, another example of a process of the invention, is a process wherein

1 ) the lenticular device comprises convex lenticular elements;

2) the production mold comprises the corresponding concave shapes;

3) the production mold is produced from a first pre-mold comprising the

corresponding convex shapes; and

4) the first pre-mold is produced from a second pre-mold comprising the

corresponding concave shapes, wherein the nanomorphology of the second pre-mold is obtained by subjecting the shaped surface of the second pre-mold to abrasion.

Figure 3 displays such process. In the first step, a concave-shaped mold (4’) is subjected to the abrasion, yielding a second pre-mold (4) having a surface with liquid crystal alignment properties (5). From this second pre-mold (4), a convex-shaped first pre-mold (3) is produced via molding. From this first pre-mold (3), a concave-shaped production mold (2) is then produced via molding. Thereafter, the production mold (2) is contacted with a substance (T), which then adopts the shape of the surface of the production mold (2). After this adopted shape of the substance (T) has been made permanent, the lenticular device (1 ) is formed and released from the production mold (2).

Analogously to the above processes, the process may also be applied to produce a lenticular device comprising concave lenticular elements.

Accordingly, another example of a process of the invention, is a process wherein

1 ) the lenticular device comprises concave lenticular elements;

2) the production mold comprises the corresponding convex shapes; and

3) the nanomorphology of the production mold is obtained by subjecting its shaped surface to abrasion.

This method introduces the nanomorphology on the mold by performing the abrasion on convex shapes. As explained hereinabove, such shapes do not have the sharp ridges that need to be handled carefully. However, it is in principle also possible to manufacture the production mold from a first pre-mold comprising the corresponding concave shapes and subject these to abrasion. Accordingly, another example of a process of the invention, is a process wherein

1 ) the lenticular device comprises concave lenticular elements;

2) the production mold comprises the corresponding convex shapes; and

3) the production mold is produced from a first pre-mold comprising the

corresponding concave shapes, wherein the nanomorphology of the first pre-mold is obtained by subjecting the shaped surface of the first pre-mold to abrasion.

Analogously to the above process for the manufacture of a lenticular device comprising concave lenticular elements, this first pre-mold can also be obtained from a second pre-mold. In this method, the abrasion again takes place on convex shapes, which may be advantageous. Accordingly, another example of a process of the invention, is a process wherein

1 ) the lenticular device comprises concave lenticular elements;

2) the production mold comprises the corresponding convex shapes;

3) the production mold is produced from a first pre-mold comprising the

corresponding concave shapes; and

4) the first pre-mold is produced from a second pre-mold comprising the

corresponding convex shapes, wherein the nanomorphology of the second pre-mold is obtained by subjecting the shaped surface of the second pre-mold to abrasion.

An advantage of a process of the invention is that the use of a mold allows an exact and reproducible production of the lenticular device, including the nanomorphology on the lenticular surface.

When an alignment layer of a different material (such as a polyimide) is applied on a lenticular lens, then there is the risk that the alignment layer detaches from the lens (delamination). When this occurs, the optical properties of the lens likely become impaired. In a lens of the invention (and in a lens produced with a process of the invention), the bulk of the lens and the surface with the alignment properties are made of the same material, which cannot give rise to the

delamination as outlined above. The introduction of the grooves by abrasion of the lens surface itself is not desirable because of the debris that is formed during the abrasion. This would require intensive cleaning to prevent the formation of debris-induced optical defects in a subsequent production process (e.g. for the production of a liquid crystal cell comprising the lenticular device). In addition, it is advantageous if the abrasion does not have to be carried out again for each separate lens, because the abrasion requires very accurate production conditions - the multiple replication of an initially created nanomorphology is therefore an advantage.

The surface of the array has liquid crystal alignment properties that originate from the nanomorphology that is present on the surface. Such surface is typically a surface with variations in height in the nanodomain (i.e. from 1 nm to 1 pm, and may therefore also be characterized as a surface with a nanorelief.

Such nanomorphology comprises grooves. The grooves are obtained by the removal of material due to the abrasion process carried out on the surface of the production mold, the first pre-mold or the second pre-mold. In addition to abrasion, deformation of the surface may also take place and so also cause the formation of the nanomorphology. This is in particular the case when the material of the mold is a ductile material, for example a metal such as copper.

When the number of grooves is limited (e.g. up to half of the surface has been abraded so that more than half of the surface has remained intact), then the surface evidently comprises grooves. When a larger part of the original surface has been removed by abrasion (e.g. more than half of it), then many grooves are lying so close to one another (or even overlap) that the surface can also be characterized as comprising ridges. For the purpose of the invention, however, the surface is considered to comprise grooves - eventual ridges that can also be characterized in a surface are ignored since they exist by the grace of grooves.

Figure 4 displays an AFM image of the surface of a lenticular device obtained by the process of the invention. The grooves can clearly be seen. They are aligned but do not have identical shapes. The grooves differ from one another by for example their depth and/or width.

In principle, at least one of the dimensions length and width of a groove is less than 1000 nm. Usually, both the length and width of the grooves are less than 1000 nm. The length of a groove may be shorter or longer than 1000 nm. The grooves typically have a depth of less than 700 nm or less than 400 nm. Usually, the grooves have a depth of 250 nm or less or 150 nm or less. In particular, it is 100 nm or less or 50 nm or less. It may also be 40 nm or less,

30 nm or less, 25 nm or less, 20 nm or less, 15 nm or less or 10 nm or less.

The grooves typically have a width of less than 700 nm or less than 500 nm. Usually, the grooves have a width of 350 nm or less or 250 nm or less. In particular, it is 200 nm or less. It may also be 150 nm or less, 100 nm or less,

75 nm or less or 50 nm or less.

The length of the grooves is typically 1 mm or less. It is usually 500 pm or less. It may also be 400 pm or less, 300 pm or less, 200 pm or less, 100 pm or less, 50 pm or less, 10 pm or less or 1 pm or less.

Typically, the grooves have a depth of 50 nm or less, a width of 200 nm or less and a length of 500 pm or less.

The grooves are all aligned substantially parallel, and preferably extend in substantially the same direction as the direction of elongation of the lenticular elements. In other aspects, however, the grooves have a higher degree of irregularity. Grooves are in principle of any conceivable length; the length of different grooves may demonstrate a natural variation, resulting from the relatively uncontrolled conditions of the abrasion as compared to e.g. grooves obtained by a lithographic process. The start- and endpoints of different grooves are random, like the staggered conformation of boards in a floor, and may only by coincidence be eclipsed. In addition, the depth and the width of the grooves may well vary for different grooves. Also the distance between neighboring grooves may vary.

A disadvantage of highly regular surface protrusions or indentations, as obtained by e.g. an etching process or a lithographic process, is that undesired optical effects may occur when the device is used in an autostereoscopic display apparatus, such as interference with light or the perception of moire patterns.

The generation of a particular nanomorphology (to provide the alignment properties) by abrasion is an essential element of the process, because alignment properties that do not originate from particular morphological features of the physical surface structure, are in principle not transferrable via a molding process. Usually, the nanomorphology of the production mold, the first pre-mold or the second pre-mold is obtained by rubbing or brushing the surface of the production mold, first pre-mold or second pre-mold, respectively, with another object. Depending on the material of the mold, suitable methods may be brushing the surface with a brush, rubbing the surface with a fine sandpaper, and rubbing the surface with a cloth comprising polishing paste ( e.g . tooth paste). Alternatively, the surface may be subjected to a fluid jet spray, e.g. a spray comprising fine solid particles that experiences a pressure drop of up to 10 bar when passing through an opening of e.g. 0.1-1.0 mm. Such methods are known in the art as fluid jet polishing and micro abrasive jet machining. The methods for introducing the nanomorphology of the mold may also be conventional methods wherein alignment layers are created by abrasion.

The direction of brushing, rubbing, spraying, etc. is usually substantially parallel to the direction of the lenticular elements. Accordingly, the direction of the grooves is usually also substantially parallel to the direction of the lenticular elements. Other directions are in principle also possible (for example all grooves are substantially perpendicular to the direction of the lenticular elements), but this may be harder to accomplish due to the curves of the lenticular surface.

When the abrasion is performed in a particular direction, there is the possibility to abrade only in that particular direction (unidirectional abrasion), and there is the possibility to abrade alternately in that particular direction and in the direction opposite thereto (bidirectional abrasion). Both methods yield grooves that extend in one and the same direction. Surprisingly, the lenticular device that was obtained after one or more replications via the molding process of the invention, appeared to have different alignment properties when unidirectional abrasion was applied instead of bidirectional abrasion. A liquid crystalline cell with a lenticular device obtained with the unidirectional abrasion appeared to perform much better in the liquid crystal switching than one that was obtained with the bidirectional abrasion. The switching was found to be significantly slower in the case of bidirectional abrasion. Moreover, more disclinations were observed directly after the switching, while it also took substantially longer before they disappeared.

The presence and absence of disclinations after the switching is illustrated in Figure 6. The left and the right column contain pictures obtained with a cell between polarizers that is the result of unidirectional abrasion and

bidirectional abrasion of the original mold, respectively. The upper row represents a zero voltage situation wherein both cells are uniformly dark, indicating a high quality liquid crystal alignment. The bottom row represents the situation wherein a potential difference of 70 V is applied during five seconds (picture is recorded after five seconds). In the right picture, quite some disclinations are visible, while these are totally absent in the left picture.

The origin of the beneficial effects of unidirectional abrasion is not well understood, but it may be associated with the presence of very subtle structural features in or on the grooves (much smaller than the dimensions of the grooves themselves). These may have an effect on the alignment of the liquid crystal molecules thereon, such as inducing a certain pre-tilt (pre-tilt is known to e.g. reduce the occurrence of disclinations during switching). It needs to be stressed that such subtle structural features then also have to be replicated with the molding process, which is very surprising.

Thus, in a process of the invention, it is preferred that the abrasion is performed in one particular direction. This means that it is not performed in two opposite directions (by e.g. alternating the abrasion in each of the two opposite directions).

The liquid that is applied on the shaped surface of the production mold is capable of solidifying (hardening) under certain controlled conditions. This occurs when it is exposed to a stimulus for which the liquid (or at least a

component thereof) is sensitive. This stimulus is for example a change in temperature or electromagnetic radiation. Thus, the liquid has the property that it solidifies under exposure to a certain stimulus.

In principle, any liquid with this property and which is capable of adopting the exact (nano)structure of the production mold and retain it upon hardening and release, may be used in a process of the invention. For example, lacquers may be used that are conventionally applied in the manufacture of lenticular lenses, such as lacquers comprising a polyepoxide and/or a

polyacrylate. In such cases, the applied liquid comprises a formulation comprising an epoxide and/or an acrylate ester, which are monomers that produce a polyepoxide and/or a polyacrylate, respectively, when polymerized. Hardening of the liquids may rely on e.g. polymerization or congelation. Polymerization may be initiated by exposing the liquid to e.g. UV-light in case it contains a UV-curable monomer. It may also be initiated by activating a catalyst present in the liquid that is capable of catalyzing the polymerization of monomers that are present in the liquid, wherein the activation may be performed by exposure to electromagnetic of an appropriate frequency. Thus, the liquid may comprise a polymer precursor that that is polymerized under the influence of an appropriate stimulus.

Usually, the lacquer formed after hardening is an isotropic lacquer; and the layer applied over the shaped surface of the production mold is usually a layer of an isotropic liquid. It is however possible that the lacquer is an anisotropic lacquer, and that the applied layer comprises a liquid crystal that is aligned prior to the solidification, wherein the anisotropy thus obtained has become fixated during the hardening. It is however also in such cases essential that the nanomorphology is transferred from the production mold to the surface of the anisotropic lacquer and that that surface can function as an alignment layer for a liquid crystal that is in contact with that surface.

The invention further relates to a lenticular device for an

autostereoscopic display apparatus, comprising an array of lenticular elements having a surface comprising a nanomorphology comprising grooves, which nanomorphology provides the surface with liquid crystal alignment properties, characterized in that the lenticular elements (such as the bulk of the lenticular lens) as well as their surfaces with liquid crystal alignment properties consist of the same material (i.e. the surface of the lenticular elements is not of a material that is different from the material of the lenticular elements). In particular, the lenticular elements and their surface they consist of the same isotropic material.

The invention further relates to a lenticular device (1 ) obtainable by the process described hereinabove.

The invention further relates to a liquid crystal cell (10) comprising a lenticular device (1 ) as described hereinabove, wherein a cover layer (8) is facing the array of lenticular elements (6) of the lenticular device (1 ), and wherein the space between the array of lenticular elements (6) and the cover layer (8) is filled with a liquid (9) comprising a liquid crystal that is capable of being aligned by the surface of the array of lenticular elements (6) with liquid crystal alignment properties (5).

Usually, the side of the cover layer (8) that faces the lenticular elements

(6) comprises a surface with liquid crystal alignment properties. The liquid crystal present between the cover layer (8) and the lenticular elements (6) is then capable of being aligned by this surface. A liquid crystal cell (10) of the invention usually also comprises a support layer (7). In a liquid crystal cell (10) of the invention, the lenticular device (1 ) and the liquid (9) are then placed between the support layer

(7) and the cover layer (8). The lenticular device (1 ) is then connected to the support layer, possibly with an adhesive layer and/or an electrode layer (for example a layer of ITO) in between them. Also the side of the cover layer (8) that faces the liquid (9) may comprise an electrode layer (for example a layer of ITO).

Figure 5 displays a liquid crystal cell comprising a lenticular device according to the invention, wherein the lenticular device (1 ) and the liquid (9) are present between the support layer (7) and the cover layer (8). The lenticular device (1) comprises an array of lenticular elements (6) that have a surface with liquid crystal alignment properties (5).

The invention further relates to a process for producing a lenticular device (1) for an autostereoscopic display apparatus, the lenticular device (1 ) comprising an array of lenticular elements (6) having a surface with liquid crystal alignment properties (5), the process comprising the use of a production mold (2) having a shaped surface which corresponds in negative relief to the desired surface profile for the array of lenticular elements (6), which shaped surface has a nanomorphology represented by grooves,

wherein the nanomorphology of the production mold (2) is obtained by subjecting its shaped surface to abrasion; or

wherein the production mold (2) is produced from a first pre-mold (3) by a molding process, wherein the first pre-mold (3) comprises a shaped surface which corresponds in negative relief to the surface profile for the production mold (2); and wherein the shaped surface of the first pre-mold (3) has a nanomorphology represented by grooves obtained by subjecting the shaped surface to abrasion; or wherein the production mold (2) is produced from a first pre-mold (3) by a molding process, wherein the first pre-mold (3) comprises a shaped surface which corresponds in negative relief to the surface profile for the production mold (2); which first pre-mold (3) is produced from a second pre-mold (4) by a molding process, wherein the second pre-mold (4) comprises a shaped surface which corresponds in negative relief to the surface profile for the first pre-mold (3); and wherein the shaped surface of the second pre-mold (4) has a nanomorphology represented by grooves obtained by subjecting the shaped surface to abrasion.

The invention further relates to the use of a mold for the production of a lenticular device for an autostereoscopic display apparatus, the mold having a shaped surface

1 ) which corresponds in negative relief to a desired surface profile for an

array of lenticular elements in the lenticular device;

2) which comprises a nanomorphology comprising grooves.

EXAMPLES

1. Preparation of mold and molded product by using unidirectional abrasion.

A production mold with a lenticular surface (an array of facetted lenticular elements) was prepared by diamond turning a copper plate using a convex-shaped chisel. Subsequently, the concave shaped copper mold was mounted on a block of aluminum.

For the abrasion process, a metal drum was covered with a rub cloth which was provided with a polishing paste. The copper mold was subjected to abrasion by placing it underneath the rotating drum. The lenticular lens direction of the mold was aligned with the drum rotation to create grooves in the lenticular direction. The production mold thus formed was cleaned; debris resulting from the abrasion was removed. The molding was performed on ITO-glass as a substrate using UV-curable acrylate lacquer, followed by post-curing in a nitrogen atmosphere and baking at elevated temperature. This yielded the lenticular device of the invention on the ITO-glass substrate layer, which combination is referred to as the lens glass plate.

The production mold and the molded product obtained by molding with the production mold were measured with confocal microscopy to measure the profile and visualize the grooves. The presence of grooves in the mold due to the abrasion was confirmed in this way, and it was also demonstrated that the facetted lenticular surface profile itself had not been negatively affected. The molded product was also found to contain the grooves. Further, SEM and AFM

measurements revealed grooves with a depth and width in the nanodomain (Figure 4).

A flat spacer ITO-glass cover plate (the cover layer) was provided with polyimide, which was then rubbed to provide it with liquid crystal alignment properties. This combination comprising the cover layer is referred to as the spacer glass plate. A liquid crystal cell was then prepared by gluing the spacer glass plate and the lens glass plate on each other with a UV-curable seal, wherein the lenticular device of the invention is inside the cell. The cell was filled with a nematic liquid crystal by capillary action and closed with the seal material (see also Figure 5).

When placed in between two polarizers, the cell became uniformly dark, indicating a high quality alignment of the liquid crystal. The 3D performance was investigated by measuring the crosstalk. At elevated voltage, the 3D crosstalk was measured to be 1.8 %.

2. Comparing unidirectional abrasion with bidirectional abrasion.

It was investigated whether the abrasion process has an influence on liquid crystal switching behavior in a cell that comprises a molded product according to the invention. To this end, the effects of abrasion in one direction (unidirectional abrasion) were compared with those of abrasion in two directions (bidirectional abrasion). Except for the abrasion method, the experimental procedures as described under section 1 of the examples were applied. The abrasion was not performed by means of a rotating drum, but by manual rubbing. Half of the mold was rubbed in one direction while the other half was alternately rubbed backwards and forwards. The use of one mold that is divided into two areas aims to exclude accidental and unintentional differences in the preparation procedures of both molds as much as possible. Confocal microscope pictures did not reveal any differences between both areas of the mold. A lens was prepared from the mold, from which was then made a liquid crystalline cell comprising the lens. When placed between two polarizers, the cell became uniformly dark, indicating high quality alignment. When an elevated voltage was applied (70 V during 5 seconds), the complete cell became transparent, indicating switching of the liquid crystal. However, the switching was significantly slower for the part which originates from subjection to bidirectional abrasion, than for the part which originates from subjection to unidirectional abrasion. In addition, polarized optical microscopy revealed much more disclinations directly after the switching (five seconds, see also Figure 6), while it also took substantially longer before the disclinations disappeared.