Reinforced small watch case

Abstract

A wristwatch including a case body (3) and a load reaction surface (2a) which is a surface of a load reaction ring (2) separate from the case body (3), the wristwatch including a protective casing including a crystal glass (1), the case body (3), the load reaction ring (2) housed within the case body (3), the load reaction ring (2) including the load reaction surface (2a) to which the crystal glass (1) applies weight, and a back cover (4) which applies weight to the load reaction ring (2).

Description

[Technical field]

[0001] The present invention relates to a watch case. The present invention also relates to a watch including such a case. [Background technology]

[0002] US Patent No. 5,399,633 discloses a device for fixing the crystal glass of a small watch, said device being integrated into a waterproof small watch capable of withstanding very great depths, typically between 3000 and 5000 meters, and having the particular feature of having side walls designed to withstand the pressure loads encountered at such depths.

[0003] Other solutions for obtaining waterproofing in small watch cases which enable the small watch to reach very great depths are known, for example those disclosed in DE 10 200 03 133 A1.

[0004] Existing solutions provide the ability to withstand the high stress loads encountered at such depths, but they have the drawback of requiring significant thicknesses of miniature watch cases, reaching the maximum possible limit for wristwatch applications, which thus prevents, for example, wristwatches from being developed for greater depths. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] European Patent Application Publication No. 1916576 [Patent Document 2] European Patent Application Publication No. 3896535 Summary of the Invention [Problem to be solved by the invention]

[0006] It is an object of the present invention to provide a watch case having a reduced thickness, suitable for use at great depths and compatible with integration into a watch. [Means for solving the problem]

[0007] For this reason, the invention relies on a watch case comprising sapphire glass, the optical axis of which is perpendicular or substantially perpendicular to the plane of the crystal glass, in particular sapphire glass with a "type C" crystal orientation, in particular sapphire glass obtained by the crystal growth method, by the Kyropoulos technique or by the EFG method. In addition, the inner surface of the crystal weighs against the load-reacting surface of the small watch case. The area of ​​the load-reacting surface, i.e. the area over which the part of the inner surface of the crystal weighs against the load-reacting surface, is called A2a, and the total area of ​​the inner surface of the crystal, including the supported and unsupported parts, is called A1a. According to the invention, the ratio A2a / A1a is greater than or equal to 0.2, or greater than or equal to 0.3, or greater than or equal to 0.35, or greater than or equal to 0.4.

[0008] The invention is particularly defined in the claims.

[0009] The objects, features and advantages of the present invention will be explained in detail in the following non-limiting description of specific embodiments in conjunction with the accompanying drawings. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view of a watch case according to one embodiment of the present invention, taken through a plane perpendicular to the small watch case and including the axis of the small watch case. [Figure 2a] FIG. 2a illustrates a sapphire glass of type A with orientation indicated diagrammatically. [Figure 2b] FIG. 2b illustrates a type C sapphire glass with orientation indicated diagrammatically. [Diagram 3] FIG. 3 is a graph providing a comparison between the average break stress of two batches of sapphire glass of types A and C, respectively. [Figure 4] FIG. 4 is a comparison table comparing the breaking force or the force at which the test was stopped for two other batches of sapphire glass of types A and C, respectively, subjected to the annular bending test. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] An embodiment of a watch 200 including a miniature watch case 100 of axis A100 will be described with reference to Figure 1. The watch further includes a miniature watch movement mounted within the watch case 100, which protects it from the external environment.

[0012] The miniature watch case 100 mainly includes a case body 3, a load reaction ring 2, and a crystal glass 1. The miniature watch case also includes a sealing device.

[0013] The miniature watch case 100 according to the embodiment also includes an annular seal 5 interposed between the case body 3 and the load reaction ring 2. The miniature watch case 100 also includes a clamping ring 6 intended to clamp the annular seal 5. The annular seal 5 allows, among other things, to maintain the contact of the crystal 1 with the load reaction ring 2. Such a design offers the advantage of separating the ability to withstand pressure from the waterproof sealing, since the squeezing of the crystal 1 does not break the seal 5 between the crystal 1 and the load reaction ring 2. The back cover 4 applies a load to the load reaction ring 2 from the side opposite the crystal 1. According to the case embodiment illustrated in FIG. 1, the back cover 4 is one piece and is screwed onto the case body 3. A seal 9 is placed in a groove 4a of the back cover 4 to constitute a waterproof interface between the case body 3 and the back cover 4.

[0014] Thus, the crystal glass 1, the load-reaction ring 2 and the back cover 4 define a protective casing 10. In particular, the casing has a compression-resistant cross section SR in a plane passing through the axis A100, which includes a surface 1a of the crystal glass 1 which bears against a load-reaction surface 2a of the load-reaction ring 2 and a back cover surface 4b which bears against a surface 2b of the load-reaction ring 2, said surfaces being superimposed on one another in a direction parallel to the axis A100, said superposition being effected without discontinuities. Advantageously, the surface 1a is in direct contact with the load-reaction surface 2a. In other words, by preference, there is no seal which is compressed at the interface between the surfaces 1a and 2a.

[0015] According to preference, surfaces 1a and 2a are flat. According to preference, surfaces 1a and 2a extend perpendicular or substantially perpendicular to axis A100. Alternatively, surfaces 1a and 2a may be inclined. As a further alternative, surfaces 1a and 2a may be curved. Similarly, according to preference, surfaces 2b and 4b are flat. According to preference, surfaces 2b and 4b extend perpendicular or substantially perpendicular to axis A100. Alternatively, surfaces 2b and 4b may be inclined. As a further alternative, surfaces 2b and 4b may be curved.

[0016] The bezel 7 is also attached to the clamping ring 6 by means of a connecting ring 8 fixed around said ring 6. The bezel 7 comprises, among other things, a ring 7a cooperating with the connecting ring 8 and a disk 7b fixed to said ring 7a, among other things by hammering or clipping. The bezel 7 may be fixedly mounted on the case body 3. Alternatively, the bezel 7 may be a rotating bezel, i.e. mounted rotatably on the case body 3 around an axis A100.

[0017] According to the invention, the miniature watch case 100 is provided with a crystal glass 1 that is very well suited to withstand very high external pressures. For this purpose, the crystal glass 1 is made of sapphire with an optical axis perpendicular or substantially perpendicular to the plane of the crystal glass 1. In particular, according to this embodiment, the crystal glass 1 has a crystal orientation of "type C", as shown diagrammatically in FIG. 2b, in comparison with a traditional sapphire glass, which is considered to be of "type A", as shown in FIG. 2a. For this reason, FIGS. 2a and 2b respectively show sapphire glasses of types A and C, where the material is shown to be anisotropic. As a result of this anisotropy, the mechanical properties of sapphire, in particular the Young's modulus, the Poisson's ratio and / or the fracture stress, vary according to the direction of the applied stress, as well as the behavior of the two types of sapphire with different orientations.

[0018] In practice, numerous tests have been carried out to illustrate the significant improvement in mean breaking stress achieved by the sapphire glass used in the present invention.

[0019] In particular, as a first bending test, a ball-on-three-ball biaxial bending test (also known as B3B) was carried out with type C crystal glass. The test allows the crystal glass to reproduce a stress field substantially similar to that experienced by the crystal glass during a water resistance test. As an example, FIG. 3 illustrates a graph providing a comparison between the average fracture stresses from the B3B test of two batches of crystal glass of types A and C, respectively. More specifically, batch A includes 292 sapphire glasses with a "type A" crystal orientation, and batch C includes 73 sapphire glasses with a "type C" crystal orientation.

[0020] It can be observed, inter alia, from Figure 3 that the average breaking stress is of the order of 1700 MPa for the batch of crystal glass with traditional orientation (Type A) and of the order of 3500 MPa for the batch of crystal glass with the orientation according to the invention. It is noted that these results are independent of the thickness of the crystal glass, since it is the breaking stress that is considered here.

[0021] As a second bending test, a ring bending test was carried out, which better reproduces the stresses caused by hydrostatic pressure when the small watch case is immersed in water. More specifically, the second test consists in applying a force perpendicular to the top surface of the crystal, directed towards the inside of the small watch case, against the center of the crystal (for example with a ball), while the periphery of the crystal is weighted against the load reaction surface 2a of the load reaction ring 2 of the small watch case. By way of example, the above-mentioned force advantageously passes along the axis A100 illustrated in FIG. 1, while the bottom surface of the crystal is weighted against the load reaction surface 2a of the load reaction ring 2.

[0022] This second test makes it possible to determine the level of the breaking force of crystal glasses of type A and C with a thickness e1 = 5.5 mm, respectively. More specifically, this second test was carried out on a batch A' containing 31 sapphire glasses with a "type A" orientation and on a batch C' containing 33 sapphire glasses with a "type C" orientation. Figure 4 gives the value of the breaking force (suffixed with F) or the value of the force at which the test is stopped (suffixed with S), in case the crystal glasses do not break, and the breaking force is higher than the force at which the test is stopped. The force at which the test is stopped is given by the limitations of the equipment participating in the test, in particular of the fixtures. The force at which the test is stopped is here equal to 55 kN.

[0023] A statistically significant difference in the level of breakage can be observed between the two batches A' and C' tested: Batch A' showed 97% breakage (30 crystal glasses broken at the end of the test out of 31 crystal glasses tested), while batch C' showed 33% breakage (11 crystal glasses broken at the end of the test out of 33 crystal glasses tested).

[0024] A statistical analysis of the distribution of the breaking forces of the two batches A' and C', for example using a normal distribution curve, resulted in significant deviations, both in terms of the mean and the variance. In particular, due mainly to truncation, the mean breaking force of the crystal glass of batch C' was about 50% higher than that of batch A', of the order of 60 kN against 40 kN.

[0025] The results of these tests show that for a given thickness e1 of sapphire glass, the average breaking stress and the average breaking force are higher for crystal glass with a "type C" orientation than for crystal glass with a "type A" orientation. Therefore, by choosing a sapphire glass specifically with a "type C" orientation instead of a thicker crystal glass with a "type A" orientation, it is possible to minimize the thickness of the sapphire glass while maintaining given mechanical properties.

[0026] In particular, the act of selecting a crystal glass of "type C" orientation allows the thickness e1 of the crystal glass 1 of the diving watch 200 capable of remaining waterproof to a depth of 11,000 meters to be minimized, in particular to a value of 11 mm or less. Indeed, as will be explained in detail below, simulations show that a crystal glass of 37 mm total diameter with a thickness e1 equal to 9.5 mm and with a bearing surface characterized by a ratio A2a / A1a=0.45 can withstand a pressure of 137.5 MPa. A sapphire crystal glass of "type C" orientation thus configured can be installed in a diving watch having a protective casing capable of withstanding pressure loads in the range of more than 50 MPa, or more than 130 MPa, and up to 137.5 MPa. In general, the crystal glass according to the present invention may have a thickness of 9.5 mm to 14 mm, or more than 9.5 mm to 11 mm, in order to withstand the above-mentioned high pressures.

[0027] To evaluate these simulations, additional tests were successfully carried out on a sapphire glass according to the invention with a thickness e1 of 9.5 mm and a "type C" orientation, mounted in a virtual case and exposed to a maximum pressure of 145 MPa in a hyperbaric chamber. Impact tests, such as drop tests and impact ram type tests, were also carried out to evaluate the shape of the crystal glass and, in particular, to avoid any risk of delamination during mounting.

[0028] Finally, the choice of sapphire glass according to the invention appears to surprisingly enable it to provide mechanical strength that is twice as high as that of a crystal glass of "Type A" orientation, in which the optical axis is in the plane of the crystal glass.

[0029] The sapphire glass 1 according to this embodiment may be obtained by a crystal growth method known as the "Kyropoulos technique" or as edge-defined film-fed growth (EFG). More generally, the invention relates to the use of a sapphire glass whose optical axis is perpendicular or substantially perpendicular to the plane of the crystal glass 1, i.e. parallel to the axis of the watch case.

[0030] As explained in detail above, the invention relies primarily on the selection of a particularly advantageous sapphire glass. To complement this, an advantageous embodiment consists in the selection of a relatively large load-reaction surface 2a of the small watch case, on which the surface 1a of the crystal glass 1 rests. For this reason, according to this embodiment, the ratio A2a / A1a is greater than or equal to 0.2, or greater than or equal to 0.3, or greater than or equal to 0.35, or greater than or equal to 0.4, where A2a is the area of ​​the load-reaction surface 2a of the load-reaction ring 2, of which at least a part of the surface 1a of the crystal glass 1 is a weight-bearing surface, and A1a is the area of ​​the surface 1a of the crystal glass 1. By way of example, the ratio A2a / A1a is of the order of 0.45 in the watch case embodiment illustrated in FIG. 1. The said area A1a of the crystal glass is preferably measured on its internal surface, i.e. at the surface position facing towards the inside of the small watch case, facing the movement. Preferably, the surface 1a is perpendicular or substantially perpendicular to the axis A100 of the small watch case 100. Preferably, the surface is continuous. Alternatively, the surface may include an inclined portion, which at least partially defines the contour of the crystal towards the inside of the small watch case, to complement the portion perpendicular or substantially perpendicular to the axis A100 of the small watch case 100. The surface 1a may be continuous or discontinuous. The surface 1a may be flat or curved, and may include flat or curved portions. The surface 1a is more generally referred to as the inner surface 1a. The surface includes, in particular, the entire surface of the crystal perpendicular or inclined to the axis A100 of the small watch case 100, which weights the other parts of the small watch, in particular the load reaction ring 2. Advantageously, the entire surface 2a of the load reaction ring 2 weights the crystal 1, in particular at least a portion of the surface 1a of the crystal 1. By preference, the surface 2a is perpendicular or substantially perpendicular to the axis A100 of the watch case 100. Alternatively, the surface may be inclined. The surface 2a may be continuous or discontinuous. The surface 2a may be flat or curved or may include flat or curved portions.

[0031] Moreover, the invention allows the use of crystal glass with a reduced thickness compared to the state of the art, which is of course determined by several parameters such as its diameter, its load-reacting area, but also the performance expected in terms of waterproofness of a small watch case. However, a thickness of 4 mm already seems suitable for underwater diving to very great depths, and a thickness of up to 10 or 11 mm seems sufficient to withstand maximum depths up to a depth of 11,000 meters.

[0032] The case body 3, the back cover 4 and the bezel ring 7a are made, inter alia, of a titanium alloy, in particular a grade 5 or grade 5 ELI (grade 23) titanium alloy, the density of which advantageously makes it possible to minimize the mass of the case 100 to the greatest extent possible for a given case diameter and thickness.

[0033] According to this embodiment, the load reaction ring 2 is made of nitrogen-doped stainless steel, for example the steel known under the reference number P558. More generally, a steel is chosen that has good mechanical properties, in particular a high Young's modulus, in particular of the order of 150,000 MPa and, for example, 200,000 MPa. This property makes it possible not to deform under the effect of the extreme pressures encountered, in particular at a depth of 11,000 meters.

[0034] Moreover, the offset (tensile) yield strength Rp0.2 of such a steel is of the order of 570 MPa. In order to prevent any risk of the load reaction ring 2, for example with a thickness e2 of 6.4 mm and a total diameter of 39.7 mm, entering the plastic zone, especially at its periphery, it has been chosen in the present embodiment to increase the offset (tensile) yield strength Rp0.2 of said steel to a value of more than 620 MPa, in particular to the order of 650 MPa. Such an approach allows the steel to withstand very high pressures, for example of at least 100 MPa. According to the present embodiment, the yield strength of the material from which the load reaction ring 2 is manufactured is increased by work hardening, by forming a blank for the load reaction ring 2 and then deforming it by beating. Tests have revealed that a degree of work hardening of the material of the order of 10% makes it possible to reach a yield strength of the order of 650 MPa. Such a level of work hardening further provides a second advantage, that it allows the load reaction ring 2 to be easily machined whilst still allowing a finishing level in line with the standards of the finest timepieces.To this end, according to an embodiment of the invention, the material from which the load reaction ring 2 is manufactured has a yield strength Rp0.2 of 620 MPa or more, or 640 MPa or more, or 650 MPa or more, so that the protective casing can provide the required specifications.

[0035] Alternatively, the load reaction ring 2 is made of ceramic, in particular zirconia.

[0036] To complement this, according to one embodiment, the back cover 4 is made of a titanium alloy, as mentioned above, in particular an α+β or β titanium alloy, in particular a grade 5 or grade 5 ELI (grade 23) titanium alloy. Such a material advantageously makes it possible to minimize the mass of the miniature watch case 100 while guaranteeing good mechanical properties. Advantageously, the titanium alloy is additionally heat hardened to make it possible to withstand very high pressures, for example 100 MPa, in order to prevent any risk of the back cover 4 entering the plastic zone. Tests have shown that a heat treatment carried out below the beta-transus temperature, ideally in a protective atmosphere, makes it possible to obtain an offset yield strength value Rp0.2 of greater than 1000 MPa, of the order of 1100 MPa, which is an increase of about 25% compared to the offset yield strength Rp0.2 of annealed grade 5 titanium, which is usually between 820 and 860 MPa. More generally, such a heat treatment is particularly advantageous since it makes it possible to harden an α+β titanium alloy or a β titanium alloy, in particular to achieve an offset yield strength value Rp0.2 of 1000 MPa or more, of the order of 1100 MPa. In the particular example of hardening a grade 5 titanium or a grade 5 ELI (grade 23) titanium alloy, an ageing heat treatment carried out by maintaining it at 520°C for 4 hours makes it possible to sufficiently increase the mechanical properties of the alloy, due to the decompression of the metastable phase. The elastic limit value thus obtained makes it possible to prevent any risk of the back cover 4 entering the plastic zone, for the dimensions corresponding to a watch, for example for a back cover with a thickness e4 of 4.8 mm. For this reason, more generally, the material from which the back cover 4 is manufactured has an offset yield strength Rp0.2 of 1000 MPa or more, or more than 1100 MPa, so that the protective casing can provide the required specifications.

[0037] Alternatively, the back cover 4 may be made of ceramic, in particular zirconia.

[0038] To complement this, as mentioned above, the watch case 100 additionally comprises a sealing device formed by at least one seal, in particular annular seal 5, interposed between the case body 3 and the load-reacting ring 2 and between the clamping ring 6 and the crystal 1, allowing the crystal 1 to be assembled to the case body 3, in particular so that the crystal 1 bears against the ring 2. Said annular seal 5 extends against the side of the crystal 1 and does not extend in any way against the internal surface of the crystal, which bears exclusively against the load-reacting surface formed by the load-reacting ring 2. According to the cross section illustrated in FIG. 1, the annular seal extends in a direction parallel to the axis A100 of the miniature watch case 100. According to this embodiment, the sealing device may also comprise a second seal 9 forming a watertight interface between the case body 3 and the back cover 4.

[0039] Of course, the invention is not limited to the shape of the small watch case 100 shown in FIG. 1. In particular, the load reaction surface 2a may be oriented so as to be inclined with respect to the axis A100 of the small watch case 100. In this case, the surface of the crystal glass 1 in contact with the load reaction surface 2a is not the internal surface of the crystal glass 1, i.e. a surface perpendicular to the axis 100, but a surface formed by a side surface having an inclination corresponding to the load reaction surface 2a. In other words, in such a configuration, the side surface of the crystal glass is not parallel to the axis A100 of the small watch case, but is inclined. Thus, for example, the side surface may have a truncated cone shape. Advantageously, in this embodiment, the angle between the inclined load reaction surface 2a and the axis A100 of the case 100 is strictly less than 90 degrees.

[0040] As a further variant, the cross section may include several portions of different shapes and / or inclinations, for example cross sections of different inclinations relative to the axis A100 of the watch case 100.

[0041] Of course, in all cases the peripheral portion of the crystal glass will conform substantially to the same shape as the load-reacting surface.

[0042] According to an alternative embodiment, when the load-reacting surface 2a is tilted, a seal may be placed between said load-reacting surface 2a and the crystal glass 1. To implement such a solution, the load experienced by the seal must be evaluated and verified as being acceptable. In such a case, the crystal glass 1 applies a weight indirectly to the load-reacting surface 2a via the seal, whereas in the embodiment described with reference to FIG. 1, the crystal glass 1 applies a weight directly.

[0043] Furthermore, in the embodiment described, the load reaction ring 2 including the load reaction surface 2 a is separate from the case body 3 .

[0044] As a variant, the load reaction ring 2 and the case body 3 may form a single identical part. In the latter case, the load reaction surface 2a belongs to the case body 3. In this case, the case body 3 (and the load reaction ring 2 which forms a monolithic entity with it) may comprise a flange on which the load reaction surface 2a is arranged.

[0045] To this end, the load reaction ring 2 is separate from the case body 3 and may be housed within the case body, or may be formed integrally with the case body.

[0046] In addition, in all the embodiments described, the back cover 4 and the load reaction ring 2 may be two separate parts or, alternatively, may be one and the same single part.

[0047] In the embodiment described, the small watch case 100 has a cross section perpendicular to the axis A100 of circular contour. Alternatively, other shapes are possible, for example square or rectangular.

[0048] Finally, it has been demonstrated that it is possible to significantly strengthen small watch cases in the first place simply by using a specific sapphire crystal with a specifically selected crystal orientation, the support surface of the crystal being advantageously selected to have a sufficiently large surface area to withstand high loads.

[0049] In addition, it has proven sufficient to advantageously select a load reaction ring 2 made of a specific hardened material with improved mechanical properties, and optionally also a back cover 4 made of a specific hardened material with improved mechanical properties, in order to enable the formation of an extremely strong watch case suitable for the deepest depths and with dimensions compatible with those required for the watch.

[0050] In particular, thanks to the invention it is possible to define a watch with a total thickness of 28 mm or less, or 26 mm or less, or 24 mm or less, capable of withstanding pressure loads in the range of more than 50 MPa, or more than 130 MPa, and potentially up to 137.5 MPa, i.e. at a depth of up to 11,000 meters or so. By preference, the miniature watch case has a total thickness of 18 mm or more, or 22 mm or more.

[0051] The invention also relates to a wristwatch comprising a miniature watch case as defined above. Of course, such a wristwatch is particularly well suited for use in diving to very great depths.

Claims

1. A sapphire glass (1) having an optical axis perpendicular or substantially perpendicular to the plane of the crystal glass (1); a load-reactive surface (2a); Including, A watch case (100), The inner surface (1a) of the crystal glass (1) applies a weight to the load-reacting surface (2a), The ratio A2a / A1a is 0.2 or more, where A2a is the area of ​​the loaded reaction surface (2a), A1a is the area of ​​the inner surface (1a) of the crystal glass (1); Watch case.

2. The sapphire glass (1) is obtained by the crystal growth method, by the Kyropoulos technique or by the EFG method, 2. The watch case according to claim 1.

3. the load-reacting surface (2a) is oriented perpendicular to the main axis (A100) of the small watch case (100), or the load-reacting surface (2a) is at least partially inclined with respect to the main axis (A100) of the small watch case (100); 2. The watch case according to claim 1.

4. The watch case includes a case body (3), and the load reaction surface (2a) is a surface of a load reaction ring (2) separate from the case body (3).

2. The watch case according to claim 1.

5. the watch case comprises a case body (3) forming a flange corresponding to a load reaction ring (2) formed integrally with the case body (3), the load reaction ring (2) comprising the load reaction surface (2 a); 2. The watch case according to claim 1.

6. The watch case includes a protective casing containing the crystal (1), the case body (3) and the load reaction ring (2) are housed within the case body (3), the crystal (1) including the load reaction surface (2a) on which the load reaction ring (2) bears weight, and a back cover (4) bears weight on the load reaction ring (2).

5. The watch case according to claim 4.

7. The load reaction ring (2) is made of a material having an offset yield strength Rp0.2 of 620 MPa or more.

5. The watch case according to claim 4.

8. The load reaction ring (2) is made of a material or materials selected from the group consisting of nitrogen-doped stainless steel, hardened steel, and ceramic.

5. The watch case according to claim 4.

9. The watch case includes an annular seal (5) and a clamping ring (6) that clamps the annular seal (5), the annular seal (5) being interposed between the case body (3) and the load reaction ring (2), and between the clamping ring (6) and the crystal (1).

5. The watch case according to claim 4.

10. The watch case includes a back cover (4), and the back cover (4) is made of a material having an offset yield strength Rp0.2 of 1000 MPa or more.

2. The watch case according to claim 1.

11. The back cover (4) is made of a material or materials selected from the group consisting of titanium alloy and ceramic. The watch case according to claim 10.

12. The back cover (4) is attached to the case body (3), and the watch case includes a seal (9) that forms a waterproof interface between the case body (3) and the back cover (4).

12. The watch case according to claim 11.

13. the watch case has an overall thickness of 28 mm or less, and / or an overall thickness of 18 mm or more; the watch case includes a crystal glass having a thickness in the range of 9.5 mm to 14 mm; The watch case is capable of withstanding a pressure load of more than 50 MPa.

2. The watch case according to claim 1.

14. A wristwatch comprising the small watch case (100) described in claim 1.

15. The sapphire glass (1) has a "type C" crystal orientation.

2. The watch case according to claim 1.

16. The ratio A2a / A1a is 0.4 or more.

2. The watch case according to claim 1.

17. The offset yield strength Rp0.2 of the material from which the load reaction ring (2) is manufactured is 650 MPa or more.

8. The watch case according to claim 7.

18. The material or materials of the load reaction ring (2) are selected from the group consisting of P558 steel, work-hardened steel, and zirconia.

9. The watch case according to claim 8.

19. The offset yield strength Rp0.2 of the material of the back cover (4) is 1100 MPa or more. The watch case according to claim 10.

20. The material or materials of the back cover (4) are selected from the group consisting of α+β or β titanium alloys, titanium alloys hardened by heat treatment, and zirconia.

12. The watch case according to claim 11.

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