Tactile presentation device

Abstract

To provide a tactile presentation device for presenting hardness / softness, which is made by applying a material whose hardness changes by light irradiation.SOLUTION: A tactile presentation device 1 contains a polymer material including a branch part (a) with three or more branches, a polymer chain (b) bonded to the branch part, and a photoresponsive group (c) bonded to the polymer chain in which the bond cleaves by light absorption and rebonds by thermal motion. The polymer material preferably has absorbance of 8 or less per 1 mm thick in light irradiation wavelength.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a tactile presentation element. [Background technology]

[0002] Recently, XR (Extended Reality) technologies such as AR (Augmented Reality) and VR (Virtual Reality) have been integrated with existing media, allowing many people to experience XR technology. As XR technology evolves further, users will feel as if an object is nearby and will try to reach out and touch it, but since it does not actually exist, they will be unable to touch it, creating a sense of discomfort. Therefore, unless tactile sensations such as hardness and softness can be presented along with visual images, XR technology will be difficult to accept emotionally. Visual images and tactile sensations are like the two wheels of a cart, and presenting tactile sensations is a major challenge for the widespread use of XR technology.

[0003] A conventional tactile presentation technology has been disclosed in which piezoelectric expansion and contraction actuators are arranged two-dimensionally as tactile elements, and the vibration pattern is changed to change the sense of touch (Non-Patent Document 1). Another device has been disclosed in which thin films of indium tin oxide (ITO) and silicon dioxide (SiO2) are laminated on the glass plate of a touch panel display, and a voltage is applied between the ITO film and the user's fingertip, and the frictional force changes due to the electrostatic attraction generated by the applied voltage between the ITO film and the fingertip (Non-Patent Document 2).

[0004] On the other hand, materials generally change hardness by undergoing a phase transition from liquid to solid or vice versa due to heat, and some polymeric materials change hardness while remaining in the solid phase. Some polymeric materials harden when irradiated with light such as ultraviolet light. Furthermore, photochromic compounds are known, which are materials that undergo a reversible phase transition between liquid and solid phases (photo-solid-liquid phase transition materials) with or without light irradiation (e.g., Non-Patent Documents 3 to 6). Generally, the hardness felt when touched with a finger depends on the contact area of ​​the skin (Non-Patent Document 7). In other words, in order to sense a change in hardness, the contact area of ​​the skin needs to be changed. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Xin Xie, et al., “Scalable, MEMS-enabled, vibrational tactile actuators for high resolution tactile displays”, Journal of Micromechanics and Microengineering, Volume 24, 125014, 2014. [Non-patent document 2] Xinyi Li, et al., “Electrowetting: A Consideration in Electroadhesion”, IEEE Transactions on Haptics, Volume 13, 522, 2020. [Non-patent document 3] Satoshi Honda, et al., “Photo-triggered solvent-free metamorphosis of polymeric materials”, Nature Communications, Volume 8, 502, 2017. [Non-patent document 4] Minami Oka, et al., “Photocleavable Regenerative Network Materials with Exceptional and Repeatable Viscoelastic Manipulability”, Advanced Science, Volume 8, 2101143, 2021. [Non-Patent Document 5] Haruhisa Akiyama, et al., “Photochemically Reversible Liquefaction and Solidification of Single Compounds Based on a Sugar Alcohol Scaffold with Multi Azo-Arms”, Advanced Materials, Volume 24, 2353, 2012. [Non-patent document 6] Hongwei Zhou, et al., “Photoswitching of glass transition temperatures of azobenzene-containing polymers induces reversible solid-to-liquid transitions”, Nature Chemistry, Volume 9, 145, 2017. [Non-Patent Document 7] Seiedmuhammad Yazdian, et al., “Compliance Display using a Tilting-Plate Tactile Feedback Device”, 2014 IEEE Haptics Symposium, 13, 2014. Summary of the Invention [Problem to be solved by the invention]

[0006] Conventional technologies that use vibration or static electricity to create changes in tactile sensations, such as those described in Non-Patent Documents 1 and 2, are unable to change the contact area with the skin. On the other hand, when touching a material whose hardness changes due to a solid-liquid phase change caused by light irradiation, or whose hardness changes while still solid, it is thought that the change in hardness of the material could cause a change in the contact area with the skin, but there have been no reports of such applications.

[0007] To produce a significant change in the contact area with the skin, a significant change in the amount of compression of the contacting object is required. This is because the greater the compression, the greater the contact area with the skin. For a contacting object to be significantly compressible, it is effective to make it several millimeters thick. Materials whose hardness changes upon light irradiation undergo this change through the absorption of light by photoresponsive groups contained within the material. However, this light absorption attenuates the light intensity. As a result, the light intensity attenuates as the light penetrates the material from the side closer to the light-irradiated surface. Generally, materials whose hardness changes upon light irradiation are being developed for applications such as adhesives that can be attached or detached upon light irradiation. To maximize the change near the light-irradiated surface, they have a high density of photoresponsive groups and a high absorption coefficient. Therefore, most of the incident light is generally absorbed at thicknesses of several tens of micrometers or less. If the change in hardness is limited to a thickness of several tens of micrometers, there is little compression, and the change in the contact area with the skin is not significant, resulting in the problem of not being able to sense the change in hardness or softness.

[0008] Therefore, an object of the present invention is to solve the above-mentioned problems of the conventional technology and to provide a tactile presentation element for presenting a sense of hardness or softness by applying a material whose hardness changes when irradiated with light. [Means for solving the problem]

[0009] The gist of the configuration of the tactile presentation element of the present invention that solves the above problems is as follows.

[0010] [1] A tactile presentation element characterized by comprising a polymer material having a branched portion (a) with three or more branches, a polymer chain (b) bonded to the branched portion, and a photoresponsive group (c) bonded to the polymer chain, the bond of which is cleaved by light absorption and recombined by thermal motion. The tactile presentation element of the present invention described in [1] above has a large amount of compressive change when touched by the skin, and can present a feeling of hardness or softness.

[0011] [2] The tactile presentation element according to [1], wherein the polymer material has an absorbance per mm of thickness at the wavelength of light irradiation of 8 or less, preferably 4 or less. The tactile sensation presentation element described in [2] above has a larger amount of change in compression when touched by the skin, and can present a more pronounced feeling of hardness and softness.

[0012] [3] The tactile presentation element according to [1] or [2], wherein the polymer chain (b) of the polymer material is polydimethylsiloxane. The tactile sensation providing element described in [3] above has a larger amount of change in compression when touched by the skin, and can provide a greater sense of hardness and softness.

[0013] [4] The tactile presentation element according to any one of [1] to [3], wherein the polymer material has a number average molecular weight (Mn) of 2,000 to 100,000 when all bonds of the photoresponsive group (c) are cleaved. The tactile presentation element described in [4] above has a larger amount of change in compression when touched by the skin, and can present a more pronounced feeling of hardness and softness.

[0014] [5] The photoresponsive group (c) of the polymer material is represented by the following general formula (1): [ka] [wherein * represents a bond to a polymer chain, and R 1 , R 2 , R 3 , R 4 , R 5 and R 6are each independently a substituent, n1 and n4 are each independently an integer of 0 to 4, and n2, n3, n5 and n6 are each independently an integer of 0 to 5.], and the bond is cleaved by light absorption to form a compound represented by the following general formula (2): [ka] [wherein * represents a bond to a polymer chain, and R 1 , R 2 , R 3 , R 4 , R 5 and R 6 are each independently a substituent, n1 and n4 are each independently an integer of 0 to 4, and n2, n3, n5, and n6 are each independently an integer of 0 to 5. The tactile presentation element described in [5] above can easily change its hardness by turning on / off light irradiation.

[0015] [6] The tactile presentation element according to any one of [1] to [5], wherein the polymer chain (b) of the polymer material has neither a COC bond nor a CO—Si bond. The tactile presentation element described in [6] above has a highly stable polymer chain (b), and therefore the hardness of the polymer material can be reversibly changed over a long period of time. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a tactile presentation element for presenting a sense of hardness or softness by applying a material whose hardness changes when irradiated with light. [Brief explanation of the drawings]

[0017] [Figure 1] The optical absorption spectrum of a film of an example of a polymer material in which hexaarylbisimidazole (HABI) is bonded to polydimethylsiloxane (PDMS) is shown. [Figure 2] 1 is a schematic cross-sectional view illustrating an example of a tactile presentation element according to an embodiment of the present invention. [Figure 3] 1 is a schematic cross-sectional view illustrating an example of a tactile presentation device incorporating the tactile presentation element of this embodiment. [Figure 4] FIG. 2 is a schematic diagram illustrating a method for measuring the amount of compressive deformation. [Figure 5] 10 is an example of measurement results of a compression test. [Figure 6] FIG. 1 is a schematic diagram illustrating the difference in hardness change between materials with different densities of photoresponsive groups. DETAILED DESCRIPTION OF THE INVENTION

[0018] The tactile presentation element of the present invention will be described in detail below by way of example based on its embodiments.

[0019] <Tactile display element> The tactile presentation element of this embodiment is characterized by comprising a polymer material having a branched portion (a) with three or more branches, a polymer chain (b) bonded to the branched portion, and a photoresponsive group (c) bonded to the polymer chain, the bond of which is cleaved by light absorption and recombined by thermal motion.

[0020] The polymer material contained in the tactile presentation element of this embodiment has a photoresponsive group (c) whose bond is cleaved by light absorption and recombines by thermal motion, and the photoresponsive group (c) acts as a cross-linking group between polymer chains (b). When the bond of the photoresponsive group (c) is cleaved by light absorption, the cross-link between the polymer chains (b) is cleaved, and the hardness of the polymer material decreases. Furthermore, the cleaved bond of the photoresponsive group (c) recombines by thermal motion, and the hardness of the polymer material increases (returns to original). Therefore, the hardness of the polymer material contained in the tactile presentation element of this embodiment can be changed by turning light irradiation on and off. Furthermore, the polymer material contained in the tactile presentation element of this embodiment has a branched portion (a) with three or more branches, and therefore has three or more polymer chains (b), and the polymer chains (b) are crosslinked with photoresponsive groups (c), so that the material has high hardness when light irradiation is off, but when light irradiation is on, the hardness becomes sufficiently low, and the change in hardness is sufficiently large. Furthermore, the polymer material contained in the tactile presentation element of this embodiment has a branched portion (a) and a polymer chain (b) in addition to the photoresponsive group (c). The branched portion (a) and the polymer chain (b) have low light absorption, allowing light to reach deep within. Therefore, the polymer material contained in the tactile presentation element of this embodiment exhibits a large change in hardness due to the on / off state of light irradiation, not only near the surface but also deep within. Furthermore, the polymer material contained in the tactile presentation element of this embodiment exhibits a large change in compression when in contact with the skin with the on and off state of light irradiation, and because this large change in compression occurs, the change in contact area with the skin is also large. As described above, the tactile presentation element of this embodiment contains a polymer material whose contact area with the skin changes greatly depending on whether light irradiation is turned on or off, and therefore can present a sense of hardness or softness.

[0021] (polymer material) The polymer material included in the tactile presentation element of this embodiment has a branched portion (a) with three or more branches. The branched portion (a) may be three or more branches, for example, three-branched, four-branched, five-branched, or six-branched. In one embodiment, a three-branched portion is preferable. The branched portion (a) of the polymer material can be formed, for example, from a ring structure such as a benzene ring, a naphthalene ring, or a cyclohexane ring, or a branched chain structure. When the branched portion (a) is three-branched, the branched portion (a) can be formed, for example, from a benzenetriyl group (also called a "phenenyl group"), an alkanetriyl group, or the like. Specific examples of the benzenetriyl group include a benzene-1,2,3-triyl group, a benzene-1,2,4-triyl group, and a benzene-1,3,5-triyl group. Among these, a benzene-1,3,5-triyl group is preferred. Examples of the alkanetriyl group include a methanetriyl group, an ethane-1,1,1-triyl group, and an ethane-1,1,2-triyl group.

[0022] The polymer material contained in the tactile presentation element of this embodiment has polymer chains (b) bonded to the branched portions. By having the polymer chains (b), the hardness of the polymer material can be sufficiently reduced when light irradiation is turned on (i.e., when the crosslinks caused by the photoresponsive groups (c) are cleaved), and the amount of light absorbed by the entire polymer material is reduced, allowing light to be delivered to deep areas.

[0023] The polymer chains (b) of the polymer material preferably have not too large an interaction between the polymer chains, and can be deformed when pressed with a finger under light irradiation (i.e., when the crosslinking by the photoresponsive group (c) is cleaved). A preferred polymer chain (b) having such properties is polysiloxane. When not crosslinked, polysiloxane is a fluid material like polysiloxane oil, and can be sufficiently deformed when pressed with a finger.

[0024] The polysiloxane exhibits oil properties when it has a linear structure with 2,000 or less siloxane bonds (for example, polydimethylsiloxane (PDMS) has a linear structure with a number-average molecular weight (Mn) of 116,000 or less). In this embodiment, the polysiloxane is in a solid state when crosslinked with the photoresponsive group (c). However, when the crosslinking by the photoresponsive group (c) is cleaved, the polysiloxane approaches or becomes a liquid state, resulting in a large change in hardness. To achieve this large change in hardness, the softer the polysiloxane is, and the more preferable it is a liquid when the crosslinking by the photoresponsive group (c) is cleaved. Furthermore, the fact that the polysiloxane is in a liquid state even with a number-average molecular weight of tens of thousands leads to the ability to sufficiently reduce the concentration of the photoresponsive group (c) introduced for crosslinking. By using polysiloxane as the polymer chain (b), the amount of light absorption can be kept small, making polysiloxane suitable for application to tactile presentation elements that exhibit hardness / softness changes.

[0025] Furthermore, the polysiloxane has a helical structure in the solid state. The interior of the helix is ​​hollow, so there is a space that can be compressed. This characteristic of polysiloxane also makes it suitable for application to a tactile presentation element that exhibits hardness / softness changes. Thus, a soft and compressible polymer material, even with a number-average molecular weight of tens of thousands or more, is suitable for the polymer chain (b) (polymer skeleton) of the polymer material. Note that the polymer chain (b) may be a polymer chain other than polysiloxane, as long as it has these characteristics.

[0026] For example, polyethylene is liquid at room temperature when the number of carbon atoms is between 5 and 17, and solid when the number of carbon atoms is greater. This is because the intermolecular forces between the carbon chains increase as the number of carbon atoms increases. In this embodiment, when the crosslinking due to the photoresponsive group (c) is broken, the polyethylene must be soft enough to be compressed with a finger. Therefore, if polyethylene is used for the polymer chain (b) (polymer backbone), a low molecule with approximately 17 carbon atoms is used. However, if the photoresponsive group (c) is incorporated at the end of such a low molecule, the density of the photoresponsive group (c) must be increased. Therefore, from the viewpoint of keeping the amount of light absorption low, the above-mentioned polysiloxane is preferred for the polymer chain (b).

[0027] The polysiloxane is particularly preferably polydimethylsiloxane (PDMS). When the polymer chain (b) is polydimethylsiloxane (PDMS), it is soft even if its number-average molecular weight is tens of thousands or more, and has a cavity inside the spiral, so that the amount of change in compression when it comes into contact with the skin becomes larger depending on whether light irradiation is on or off, and because the amount of change in compression is large, the change in the contact area with the skin becomes larger, and it is possible to further present a hard / soft feeling.

[0028] It is preferable that the polymer chain (b) of the polymer material does not have either a C-O-C bond or a C-O-Si bond. C-O-C bonds and C-O-Si bonds are susceptible to attack by radicals, for example, there is a risk of being attacked by radicals generated when the crosslinking by the photoresponsive group (c) is broken. In contrast, when the polymer chain (b) does not have either a C-O-C bond or a C-O-Si bond, the polymer chain (b) is highly stable, making it possible to reversibly change the hardness of the polymer material over a long period of time by turning light irradiation on and off.

[0029] From the viewpoint of sufficiently delivering light deep into the material, the polymer chain (b) of the polymer material preferably has low absorption at the wavelength irradiated to induce photoresponsiveness, and particularly preferably has no absorption. As an example, the absorption spectrum of a polymer material in which hexaarylbisimidazole (HABI) is bonded to polydimethylsiloxane (PDMS) is shown in Figure 1. The absorption edge of HABI is approximately 450 nm, and absorption is sufficiently low in the wavelength region at the base of the absorption band from 400 nm to 450 nm. Furthermore, polysiloxane has no absorption in this wavelength region. Thus, when the photoresponsive group (c) is hexaarylbisimidazole (HABI), the polymer chain (b) preferably has no light absorption in the 400 nm to 450 nm region. Furthermore, since polydimethylsiloxane (PDMS) does not absorb light in the 400nm to 450nm region, a polymer material in which hexaarylbisimidazole (HABI) is bonded to polydimethylsiloxane (PDMS) can deliver light sufficiently deep into the material, and has excellent ability to present a sense of hardness and softness.

[0030] The polymer material contained in the tactile presentation element of this embodiment has photoresponsive groups (c) attached to the polymer chains, whose bonds are cleaved by light absorption and recombined by thermal motion. The photoresponsive groups (c) act as cross-linking groups between polymer chains (b), and when the bonds of the photoresponsive groups (c) are cleaved by light absorption, the cross-links between the polymer chains (b) are cleaved, reducing the hardness of the polymer material. On the other hand, the cleaved bonds of the photoresponsive groups (c) are recombined by thermal motion, increasing the hardness of the polymer material. This allows the hardness of the polymer material to be changed by turning light irradiation on and off.

[0031] The photoresponsive group (c) has the function of repeatedly breaking the crosslinking by light irradiation and re-crosslinking by thermal motion. As an example, the following polymer material is shown, in which hexaarylbisimidazole (HABI) is introduced as a crosslinking group at the end of the polymer chain (b). [ka]

[0032] As shown in the reaction scheme above, light irradiation breaks the cross-linking bond connecting two imidazole moieties, generating triphenylimidazole radicals (TPIR). The severing of the cross-links softens the polymeric material. Meanwhile, this TPIR can recombine with other TPIRs at room temperature through thermal motion, forming re-cross-links. Therefore, when light irradiation is stopped, only the re-cross-linking reaction of TPIR occurs, and the polymeric material gradually hardens.

[0033] The polymer material contained in the tactile presentation element of this embodiment can use the above-mentioned HABI as the photoresponsive group (c), but any photoresponsive group having such functionality is not particularly limited. When the photoresponsive group (c) is HABI, a portion of the phenyl group may be substituted, or a substituent may be incorporated into the site connecting the HABI to the polymer chain (b) such as PDMS. When incorporating a substituent, it is preferable to prevent absorption in the 400-450 nm region from increasing. More preferably, the substitution effect increases the absorption band gap, reducing the absorption intensity in the 400-450 nm region compared to the unsubstituted region. Furthermore, it is preferable that the substituent does not react with radicals such as TPIR. Radicals such as TPIR generated by cleavage of HABI have a different absorption band from that of HABI. It is preferable to introduce the substituent so that this absorption band does not overlap with the 400-450 nm region.

[0034] The photoresponsive group (c) preferably exhibits a photoresponsiveness even in the wavelength region at the base of the absorption band where the absorption on the long-wavelength side of the photoresponsive light absorption band is sufficiently small, and this wavelength region can be used as the light irradiation wavelength for photoresponsiveness. Generally, the short-wavelength side is not suitable as a light irradiation wavelength because other absorption bands overlap. The hexaarylbisimidazole (HABI) has such properties and can sufficiently photoresponsive even when irradiated with an LED light source with a wavelength of 430 nm. In the tactile presentation element of this embodiment, the photoresponsive group (c) of the polymer material is not limited to HABI. Any photoresponsive group that has similar properties and repeatedly undergoes crosslinking / cleavage in response to light can be suitably used in the same way as HABI.

[0035] In the polymer material contained in the tactile presentation element of this embodiment, the magnitude of absorption can be changed by changing the density of the photoresponsive group (c). By reducing the density of the photoresponsive group (c), the amount of light absorption can be reduced, allowing light of sufficient intensity to penetrate deep into the polymer material when irradiated. In this embodiment, the absorbance at the wavelength at which a 1 mm thick polymer material is irradiated and responds is preferably 8 or less, more preferably 4 or less, even more preferably 2 or less, and particularly preferably 1 or less. When the absorbance per mm of the polymer material at the light irradiation wavelength is 8 or less, light of sufficient intensity can penetrate further deep into the polymer material, further increasing the amount of compression change when the material comes into contact with the skin between on and off light irradiation. Furthermore, because the amount of compression change is even greater, the change in contact area with the skin is even greater, allowing for a more pronounced sensation of hardness and softness. The lower the absorbance of the polymer material, the thicker the tactile presentation element can be made, but if the absorbance is too low, the change before and after light irradiation will be small. Therefore, it is preferable that the polymer material have an absorbance of 0.1 or more as the lower limit. In this specification, absorbance is measured using an absorptiometer.

[0036] In an embodiment using hexaarylbisimidazole (HABI) as the photoresponsive group (c), the light absorption intensity is proportional to the density of the HABI. Therefore, to reduce the absorption, the density of the HABI can be reduced. For example, when a three-branched polysiloxane is used as the polymer chain (b), HABI is introduced only at the three terminal positions. Therefore, to reduce the HABI density, the molecular weight of the polysiloxane can be increased. Increasing the molecular weight and reducing the HABI density reduces the light absorption intensity, allowing light to penetrate deeper into the polymer material. In addition to increasing the molecular weight, narrowing the molecular weight distribution is also important for controlling the HABI density. For example, the method described in Hiroshi Okamoto, et al., “Synergetic Binary Organocatalyzed Ring Opening Polymerization for the Precision Synthesis of Polysiloxanes,” Communications Chemistry, Volume 7, 61, 2024, can be effectively used to control the molecular weight distribution of the polymer chain (b) of PDMS, etc. By using such a polymer material, even if it is only a few millimeters thick, light can penetrate deep into the polymer material when irradiated, causing most of the polymer material to soften. This makes it possible to compress the polymer material until the change in contact area with the skin is sufficiently noticeable, thereby presenting a more pronounced sense of hardness and softness.

[0037] The polymer material preferably has a number average molecular weight (Mn) of 2,000 to 100,000 when all bonds of the photoresponsive group (c) are cleaved. As mentioned above, in order to reduce the density of the photoresponsive group (c) such as HABI and thereby reduce the amount of light absorption, it is preferable to increase the molecular weight of the polymer material, and it is also preferable that the polymer material is sufficiently soft even if it has a molecular weight of tens of thousands. If the number average molecular weight (Mn) of the polymer material when all bonds of the photoresponsive group (c) are cleaved is 2,000 or more, the amount of light absorption of the polymer material is sufficiently small, and if it is 100,000 or less, the hardness of the polymer material is sufficiently low. Therefore, when the number average molecular weight (Mn) of the polymeric material when all bonds of the photoresponsive group (c) are cleaved is 2,000 to 100,000, the amount of change in compression when the material comes into contact with the skin becomes even larger when light irradiation is turned on and off, and since the amount of change in compression is even larger, the change in the contact area with the skin also becomes even larger, allowing the sensation of hardness and softness to be presented more significantly. In this specification, the number average molecular weight (Mn) of a polymeric material is measured by size exclusion chromatography (SEC) and is expressed as a polystyrene equivalent value.

[0038] The photoresponsive group (c) of the polymer material is represented by the following general formula (1): [ka] [wherein * represents a bond to a polymer chain, and R 1 , R 2 , R 3 , R 4 , R 5 and R 6 are each independently a substituent, n1 and n4 are each independently an integer of 0 to 4, and n2, n3, n5 and n6 are each independently an integer of 0 to 5.], and the bond is cleaved by light absorption to form a compound represented by the following general formula (2): [ka] [wherein * represents a bond to a polymer chain, and R 1 , R 2 , R 3 , R4 , R 5 and R 6 are each independently a substituent, n1 and n4 are each independently an integer of 0 to 4, and n2, n3, n5, and n6 are each independently an integer of 0 to 5. When the photoresponsive group (c) of the polymer material is represented by the above general formula (1) and is converted into a group represented by the above general formula (2) by cleavage of the bond upon light absorption, the photoresponsive group represented by the above general formula (1) and the group represented by the above general formula (2) have different absorption bands, and cleavage and crosslinking can be repeated reversibly upon photoresponse, making it easy to change the hardness by turning light irradiation on and off.

[0039] In the above general formulas (1) and (2), * indicates a bond to the polymer chain (b). In addition, in the above general formulas (1) and (2), R 1 , R 2 , R 3 , R 4 , R 5 and R 6 are each independently a substituent (monovalent substituent), and examples of the monovalent substituent include linear or branched alkyl groups having 1 to 20 carbon atoms, such as a methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, and tert-butyl group; cyclic alkyl groups having 3 to 7 carbon atoms, such as a cyclopropyl group, cyclopentyl group, cyclohexyl group, and cycloheptyl group; linear or branched alkoxy groups having 1 to 20 carbon atoms, such as a methoxy group, ethoxy group, propoxy group, isopropoxy group, butoxy group, isobutoxy group, tert-butoxy group, pentyloxy group, hexyloxy group, heptyloxy group, and octyloxy group; halogen atoms such as a fluorine atom, chlorine atom, bromine atom, and iodine atom; haloalkyl groups such as a fluoromethyl group, difluoromethyl group, and trifluoromethyl group; a nitro group; and a cyano group. In the general formulas (1) and (2), n1, n2, n3, n4, n5, and n6 represent the number of substituents on the benzene ring, and n1 and n4 are each independently an integer of 0 to 4, and n2, n3, n5, and n6 are each independently an integer of 0 to 5. From the viewpoint of ease of synthesis, however, n1, n2, n3, n4, n5, and n6 are preferably 0.

[0040] The synthesis method of the polymer material is not particularly limited. In one example, first, a monomer is polymerized and added to an initiator that will form a branched portion (a) with three or more branches to form a polymer chain (b). Next, a photoresponsive group (c) is introduced to the end of the polymer chain (b) bonded to the branched portion, thereby synthesizing the target polymer material. The initiator is not particularly limited, but for example, benzene-1,3,5-triyl-tris(dimethylsilanol) or the like can be used. The monomer may be hexamethylcyclotrisiloxane, etc. When hexamethylcyclotrisiloxane is used as the monomer, the polymerization reaction proceeds by ring-opening polymerization. Furthermore, vinyllophine and the like can be used as the compound used to introduce the photoresponsive group. When vinyllophine is used, a polymer material can be synthesized by introducing vinyllophine to the end of the polymer chain (b) and then crosslinking the vinyllophine moiety. In this synthesis method, the number average molecular weight (Mn) of the polymer material in a state where all bonds of the photoresponsive group (c) are cleaved corresponds to the number average molecular weight (Mn) in the state before crosslinking the vinyllophine moiety, i.e., in the state where vinyllophine is introduced to the end of the polymer chain (b).

[0041] Next, one embodiment of the tactile presentation element of the present invention will be described in detail with reference to the drawings. Figure 2 is a cross-sectional view illustrating an example of the tactile presentation element of this embodiment.

[0042] The tactile presentation element 1 shown in FIG. 2 includes a substrate 2 and a tactile presentation member 3 disposed on the substrate 2. The tactile presentation element 1 shown in FIG.

[0043] The substrate 2 is made of a material such as glass, quartz, or plastic, and can be used as appropriate. Examples of plastic materials that can be used for the substrate 2 include polyethylene terephthalate, polyethylene naphthalate, cycloolefin polymer, polyamide, polyethersulfone, polymethyl methacrylate, polycarbonate, and polyarylate. The substrate 2 may be made of one material or a combination of two or more materials.

[0044] The tactile sensation providing member 3 includes a polymer material having the above-mentioned branched portion (a) having three or more branches, a polymer chain (b) bonded to the branched portion, and a photoresponsive group (c) bonded to the polymer chain, the bond of which is cleaved by light absorption and recombined by thermal motion, and may be composed of only the polymer material, or may contain other materials, or may be coated with other components.

[0045] In one example, the tactile sense presentation member 3 may include a porous elastic body in addition to the polymer material. Examples of the porous elastic body include urethane foam, silicone foam, polystyrene foam, polyethylene foam, foamed rubber, etc. For example, when the polymer material absorbs light, the cross-linked structure is cleaved and the polymer material becomes liquid, the tactile sense presentation member 3 may be formed by impregnating the porous elastic body with the polymer material in a liquid state.

[0046] The tactile sense presentation member 3 may also be configured by sealing the polymer material in a bag. Even when the polymer material absorbs light, the cross-linked structure is cleaved, and the polymer material becomes liquid, sealing the polymer material in a bag can prevent the polymer material from leaking out. Examples of materials for the bag include fluororesins such as polyvinylidene fluoride and copolymers of polyvinylidene fluoride and hexafluoropropylene, and silicone resins such as polydimethylsiloxane.

[0047] The thicker the tactile sense providing member 3, the greater the amount of compressive deformation and the greater the change in the contact area with the skin when light irradiation is turned on and off. From the viewpoint of increasing the change in the contact area with the skin, the thickness of the tactile sense providing member 3 is preferably 1 mm or more, more preferably 2 mm or more, and even more preferably about 3 mm to 10 mm.

[0048] <Tactile presentation device> Next, one embodiment of a tactile presentation device incorporating the tactile presentation element of the present invention will be described in detail with reference to the drawings. Fig. 3 is a cross-sectional schematic diagram illustrating an example of a tactile presentation device incorporating the tactile presentation element of this embodiment.

[0049] The tactile presentation device 10 shown in Figure 3 comprises a wiring board 4, a light source 5 arranged on the wiring board 4, a substrate 2 arranged on the light source 5, a tactile presentation member 3 arranged on the substrate 2, and a sheet member 6 arranged on the tactile presentation member 3.

[0050] The wiring board 4 is not particularly limited, but may be configured as a known printed circuit board having terminals connected to the light sources 5 and wiring electrically connecting the terminals to a power source, with wiring formed of metal film or metal foil on both surfaces or interfaces of one or more laminated insulating substrates. The wiring board 4 has wiring capable of supplying current to one or more arbitrarily selected light sources, and for example, wiring connected to each light source 5 may be provided for each light source 5.

[0051] The light source 5 is provided independently for each tactile sense provision member 3, and by turning on / off the light irradiation, the cross-links of the polymer material that constitutes the tactile sense provision member 3 are switched between cleavage and recombination, thereby changing the hardness of the tactile sense provision member 3. In Fig. 3, the light sources 5 are arranged two-dimensionally directly below the tactile sense provision member 3. For example, an LED or the like can be used as the light source 5.

[0052] The tactile sense providing members 3 are two-dimensionally arranged on the substrate 2 with gaps between them. The tactile sense providing members 3 present tactile sensations by changing their hardness depending on whether light is irradiated by the light source 5 or not. The greater the thickness (height) of the tactile sense providing members 3, the greater the amount of compressive deformation and the greater the change in the contact area with the skin. To increase the change in the contact area with the skin, the thickness (height) of the tactile sense providing members 3 is preferably 1 mm or more, more preferably 2 mm or more, and even more preferably approximately 3 mm to 10 mm. Furthermore, since the tactile sense providing members 3 are arranged at a narrower pitch, a more detailed in-plane distribution of tactile sensations can be provided. Therefore, the pitch of each tactile sense providing member 3 is preferably 20 mm or less, and even more preferably 10 mm or less. The spatial (surface) resolution of the tactile sense of a human fingertip, etc., is approximately 1 mm to 2 mm. A shorter pitch would result in little perceptible difference in the in-plane distribution of tactile sensations, but would also make manufacturing more difficult. Therefore, the pitch of each tactile sense providing member 3 is preferably 2 mm or more, and may be 3 mm or more. The tactile sense presentation members 3 may be arranged in a rectangular lattice pattern such as a square lattice, or may be arranged in a triangular lattice pattern (like a rice bag) with circular or regular hexagonal shapes in a plan view. The tactile sense presentation members 3 are arranged at intervals so that they can expand and deform laterally when pressed from above by a user. The interval between the tactile sense presentation members 3 is preferably shorter than the length of the tactile sense presentation members 3 in a plan view, and is designed according to the maximum deformation amount of the tactile sense presentation members 3. The length of the tactile sense presentation members 3 in a plan view is designed according to the pitch and interval, and is preferably 1 mm or more. Furthermore, if the thickness (height) of the tactile sense presentation members 3 is large compared to the length in a plan view (aspect ratio is large), it becomes difficult for the tactile sense presentation members 3 to stand on the substrate 2 when softened. Therefore, the aspect ratio is preferably not too large, and is preferably 1 or less.

[0053] The sheet member 6 is a cover for the tactile presentation device 10 and is a member that can be directly touched by the user. It protects the tactile presentation members 3 from damage and preferably flattens the top surface of the tactile presentation device 10 so that the user is less likely to feel unevenness on the top surface due to the tactile presentation members 3 arranged with gaps between them. Even if the tactile presentation members 3 are adhesive, providing the sheet member 6 can prevent them from adhering to the user's fingers. The sheet member 6 is preferably flexible and stretchable. Examples of suitable materials include sheets, woven fabrics, and nonwoven fabrics made of polyurethane, fluororesins such as polyvinylidene fluoride and copolymers of polyvinylidene fluoride and hexafluoropropylene, silicone resins such as polydimethylsiloxane, and resins such as polyvinylidene chloride. The thickness of the sheet member 6 is preferably approximately 0.05 to 0.3 mm from the viewpoints of protecting the tactile presentation members 3 and flattening the top surface of the tactile presentation device 10. The sheet member 6 preferably has light-blocking properties. The sheet member 6 having a light-blocking property can prevent the hardness of the tactile sense provision member 3 from being unintentionally changed by light from outside the tactile sense provision device 10.

[0054] According to the above-described tactile presentation device 10, tactile sensations can be presented by switching the light irradiation on / off for each tactile presentation member 3 and changing the hardness, and a sense of hardness and softness can be presented in XR technologies such as AR / VR. [Example]

[0055] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples in any way.

[0056] <Synthesis of Comparative Example> (Synthesis and Purification of star-PDMS-SiOH) Dried benzene-1,3,5-triyl-tris(dimethylsilanol) (initiator I3) (141.3 mg), hexamethylcyclotrisiloxane (monomer D3) (10.0 g), triazabicyclodecene (catalyst TBD) (98.1 mg), and 3,3',5,5'-tetrakis(trifluoromethyl)-1,3-diphenylurea (catalyst U(4CF3)) (682.9 mg) were weighed and dissolved in anhydrous THF (25 mL). The mixture was mixed and stirred at 20 °C under a nitrogen atmosphere to initiate the reaction. After stirring for 30 min, benzoic acid (1.72 g) dissolved in anhydrous THF (4.2 mL) was added to the reaction solution and stirred for 2 h to quench the reaction. The quenched solution was concentrated and then washed with acetone. Concentration yielded star-PDMS-SiOH. The reaction scheme is shown below. [ka]

[0057] In the above star-PDMS-SiOH, the larger the l, m, and n (repeating numbers), the larger the molecular weight of the PDMS. In the examples described below, the number of vinyllophines introduced is the same as the number of terminals, so the larger the molecular weight, the smaller the vinyllophine density per unit volume, and the smaller the HABI density. The smaller the HABI density, the smaller the absorbance.

[0058] (Synthesis and Purification of star-PDMS-SiH) The star-PDMS-SiOH obtained above was dissolved in dehydrated THF (14.0 mL), and pyridine (6.82 mL) and chlorodimethylsilane (3.13 mL) were added. The mixture was stirred overnight at room temperature under a nitrogen atmosphere, and the reaction was stopped after 13 hours. After concentrating the reaction solution, 20 mL of hexane was added and the mixture was washed with water. Sodium sulfate was added to the solution to remove water, and the mixture was filtered. The filtrate was washed with acetonitrile. After dissolving the star-PDMS-SiOH in chloroform, the mixture was concentrated and dried to obtain liquid star-PDMS-SiH (6.7 g). The number-average molecular weight (Mn) of the resulting star-PDMS-SiH was measured by SEC and found to be 21,000. The number average molecular weight was measured using a Waters e-2695 system (SEC).

[0059] (Synthesis and purification of star-PDMS-Siv) The synthesis and purification of star-PDMS-SiH was carried out in the same manner as above, except that chlorodimethylsilane was replaced with the same molar amount of chlorodimethylvinylsilane. Liquid star-PDMS-SiH (6.5 g) was obtained. The number-average molecular weight (Mn) of the resulting star-PDMS-SiH was measured by SEC and found to be 21,000. The reaction scheme is shown below. [ka]

[0060] (Synthesis of PDMS rubber without photoresponsive groups) Liquid star-PDMS-SiH and liquid star-PDMS-Siv, each with an equimolar number of terminal groups, were mixed, and a trace amount of Karstedt catalyst (1,3-divinyl-1,1,3,3-tetramethyldisiloxane platinum(0)) was added to carry out the hydrosilylation reaction. After one day, it was confirmed that the reaction product had transformed into a rubber-like solid, marking the completion of the synthesis of the comparative PDMS rubber. The reaction scheme is shown below. [ka]

[0061] <Synthesis of Example 1> (Synthesis and Purification of star-PDMS-SiOH) Synthesis and purification were carried out in the same manner as in the comparative example, except that the amounts of raw materials used were changed.

[0062] (Synthesis and Purification of star-PDMS-SiH) Synthesis and purification were carried out in the same manner as in the comparative example, except that the amounts of raw materials used were changed.

[0063] (Synthesis and purification of star-PDMS-lophine) Star-PDMS-SiH (2.0 g), vinylolphen (0.7 g), and a trace amount of Karstedt catalyst were dissolved in dehydrated THF (6 mL), and the mixture was stirred under a nitrogen atmosphere to carry out the hydrosilylation reaction. 1 The progress of the reaction was monitored by H-NMR, and the reaction was stopped when the peak for the SiH proton at the PDMS terminal disappeared. To remove unreacted vinyllophine and the Karstedt catalyst, the reaction solution was washed by reprecipitation into methanol. An appropriate amount of chloroform was added to the solution to dissolve it, and the solution was then concentrated and dried to obtain star-PDMS-lophine (1.3 g). The number-average molecular weight (Mn) of the resulting star-PDMS-lophine was measured by SEC and found to be 9,000. The reaction scheme is shown below. [ka]

[0064] (Synthesis and purification of star-PDMS-HABI) Star-PDMS-lophine (1 g) was dissolved in hexane (250 mL), and potassium ferricyanide (8.40 g) and potassium hydroxide (2.73 g) were dissolved in water (150 mL). The aqueous solution was added to the hexane solution in the dark, and the reaction was carried out at room temperature with vigorous stirring. After stirring for 16 hours, the progress of the reaction was monitored by NMR, confirming the disappearance of the peak derived from lophine. The reaction solution was washed with water, and the aqueous layer was removed. The mixture was then dried over sodium sulfate. The hexane solution was concentrated to obtain solid star-PDMS-HABI (1.3 g). The reaction scheme is shown below. [ka]

[0065] <Synthesis of Example 2> (Synthesis and Purification of star-PDMS-SiOH) It was synthesized and purified in the same manner as in the comparative example.

[0066] (Synthesis and Purification of star-PDMS-SiH) It was synthesized in the same manner as in the comparative example.

[0067] (Synthesis and purification of star-PDMS-lophine) Except for changing the amounts of reagents used, synthesis and purification were carried out in the same manner as in Example 1. The number average molecular weight (Mn) of the obtained star-PDMS-lophine was measured by SEC and was found to be 17,000.

[0068] (Synthesis and purification of star-PDMS-HABI) Synthesis and purification were carried out in the same manner as in Example 1, except that the amounts of the reagents used were changed.

[0069] <Synthesis of Example 3> (Synthesis and Purification of star-PDMS-SiOH) Synthesis and purification were carried out in the same manner as in the comparative example, except that the amounts of the reagents used were changed.

[0070] (Synthesis and Purification of star-PDMS-SiH) Synthesis and purification were carried out in the same manner as in the comparative example, except that the amounts of the reagents used were changed.

[0071] (Synthesis and purification of star-PDMS-lophine) Except for changing the amounts of reagents used, synthesis and purification were carried out in the same manner as in Example 1. The number average molecular weight (Mn) of the obtained star-PDMS-lophine was measured by SEC and was found to be 40,000.

[0072] (Synthesis and purification of star-PDMS-HABI) Synthesis and purification were carried out in the same manner as in Example 1, except that the amounts of the reagents used were changed.

[0073] <Fabrication and evaluation of tactile display elements> The PDMS rubber (comparison example) without photoresponsive groups or the polymeric materials (Examples 1 to 3) synthesized as described above were molded into cylindrical shapes with a diameter of 5 mm and a thickness of 2 mm to prepare samples. This was placed on top of a glass slide, and a 430 nm LED (CL-H1-430-9-1-B, manufactured by Asahi Spectroscopy Inc.) was positioned so that it could be irradiated from below the sample. The indenter of a compression testing device was pressed from above the sample to deform it. The amount of deformation and the force required for deformation were measured. This serves as a measure of the change in hardness felt when pressed with a finger. Polymeric materials with photoresponsive groups may be sticky, and it is preferable to evaluate the hardness / softness without evaluating the sticky property. Therefore, the sample was covered with Saran Wrap (registered trademark) or a fluororesin film that was thin enough not to interfere with the tactile sensation, and the indenter was applied from above to evaluate the sample. A schematic diagram of the measurement method is shown in Figure 4.

[0074] First, a compression test was conducted without irradiating the sample with light. Next, a compression test was conducted while irradiating the sample with light using a 430 nm LED light source. The degree of change in hardness was evaluated using the ratio of the slope of the curve before and after light irradiation at 0.5 mm and 1 mm of deformation in the curve of deformation versus force during compression. An example of the measurement results of the compression test is shown in Figure 5. As the compression test device, for example, a compression test device available from Kato Tech Co., Ltd. or Tech Gihan Co., Ltd. can be used, and the evaluation in this test was carried out using YAWASA from Tech Gihan Co., Ltd.

[0075] (Examples 1 to 3) The molecular structures of the polymer materials used in the examples are shown below. [ka]

[0076] The polymeric materials were prepared by crosslinking the ends of the three-branched PDMS synthesized as described above with HABI. The polymeric materials of Examples 1 to 3 were prepared by controlling the molecular weight and molecular weight distribution to change the density of HABI. Table 1 shows the absorbance per 1 mm of sample thickness at 430 nm and the change in slope before and after light irradiation in a compression test. The absorbance was measured using a Horiba Duetta (absorption photometer).

[0077] [Table 1]

[0078] In the polymeric material of Example 1, which incorporated high-density HABI, the slope change factor was 1.4, while in Example 2, which incorporated medium-density HABI, the factor was 4.3. In Example 3, which incorporated a lower density HABI, the factor was 7.0.

[0079] As described above, by controlling the density of the photoresponsive groups and sufficiently reducing the absorbance at the photoresponsive wavelength, the magnitude of the change in hardness before and after light irradiation increased. This is thought to be because, as shown in Figure 6, light was able to penetrate deep into the sample, causing hardness changes in many parts of the sample, making it more susceptible to compressive deformation. [Industrial Applicability]

[0080] The tactile presentation element of the present invention can be used to present hardness and softness in XR technologies such as AR / VR. [Explanation of symbols]

[0081] 1: Tactile display element 2: Circuit board 3: Tactile presentation material 4: Wiring board 5:Light source 6: Sheet material 10: Tactile presentation device

Claims

1. A tactile presentation element characterized by comprising a polymer material having a branched portion (a) with three or more branches, a polymer chain (b) bonded to the branched portion, and a photoresponsive group (c) bonded to the polymer chain, the bond of which is cleaved by light absorption and recombined by thermal motion.

2. The tactile presentation element according to claim 1 , wherein the polymer material has an absorbance per mm of thickness of 8 or less at the wavelength of light irradiated thereon.

3. The tactile presentation element according to claim 1 , wherein the polymer chain (b) of the polymer material is polydimethylsiloxane.

4. 2. The tactile presentation element according to claim 1, wherein the polymer material has a number average molecular weight (Mn) of 2,000 to 100,000 when all bonds of the photoresponsive group (c) are cleaved.

5. The photoresponsive group (c) of the polymer material is represented by the following general formula (1): 【Chemistry 1】 [wherein * represents a bond to a polymer chain, R １ , R ２ , R ３ , R ４ , R ５ and R ６ are each independently a substituent, n1 and n4 are each independently an integer of 0 to 4, and n2, n3, n5, and n6 are each independently an integer of 0 to 5.], and the bond is cleaved by light absorption to form a compound represented by the following general formula (2): 【Chemistry 2】 [wherein * represents a bond to a polymer chain, R １ , R ２ , R ３ , R ４ , R ５ and R ６ are each independently a substituent, n1 and n4 are each independently an integer of 0 to 4, and n2, n3, n5, and n6 are each independently an integer of 0 to 5.

6. 2. The tactile presentation element according to claim 1, wherein the polymer chain (b) of the polymer material has neither a C—O—C bond nor a C—O—Si bond.

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