A housing includes a first case and a second case configured to be joined together to make a housing space; and a double-sided adhesive member having a first surface and a second surface, the double-sided adhesive member including an impermeable, elastic base material, and a plurality of binder layers formed on either surface of the base material, the binder layers on the first and second surfaces being bonded to the first and second cases, respectively, wherein an adhesive force between the first case and the first surface of the double-sided adhesive member is greater on an outer side of the first case than on an inner side of the first case, and wherein an adhesive force between the second case and the second surface of the double-sided adhesive member is greater on an inner side of the second case than on an outer side of the second case.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2011-223437, filed on Oct. 7, 2011, the entire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are related to a housing, a double-sided adhesive tape, and an electronic apparatus.

BACKGROUND

In addition to being compact and thin, a high waterproof performance has also been in demand for housings of portable phones and some other electronic apparatuses. Listed below are two sealing methods of providing housings with a waterproof structure.

The first method involves interposing a rubber seal between two cases which are to be joined while opposing each other to constitute a housing. This rubber can be compressed from the sides to work as a seal. The second method involves using a binder or a double-sided adhesive tape to assemble the cases.

With the first sealing structure, it is difficult to realize desired compact and thin housings for the apparatuses, because the housings have to be robust enough to withstand the rubber compression. When a housing gets deformed, for example, due to the high compression of the rubber, liquid may enter the interior of the housing.

As for the second sealing structure, when the bonding surfaces of these two cases get partially separated, for example, due to the deformation of the housing, liquid may also enter the interior of the housing.[Patent Document] Japanese National Publication of International Patent Application No. 2010-537240[Patent Document] Japanese Laid-open Patent Publication No. 08-151558[Patent Document] Japanese Laid-open Utility Model Publication No. 06-34762[Patent Document] Japanese Laid-open Utility Model Publication No. 06-69246

SUMMARY

According to an aspect of the invention, a housing includes a first case and a second case configured to be joined together to make a housing space; and a double-sided adhesive member having a first surface and a second surface, the double-sided adhesive member including an impermeable, elastic base material, and a plurality of binder layers formed on either surface of the base material, the binder layers on the first and second surfaces being bonded to the first and second cases, respectively, wherein an adhesive force between the first case and the first surface of the double-sided adhesive member is greater on an outer side of the first case than on an inner side of the first case, and wherein an adhesive force between the second case and the second surface of the double-sided adhesive member is greater on an inner side of the second case than on an outer side of the second case.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an exemplified description will be given in detail, of a housing according to embodiments, with reference to the accompanying drawings.

First Embodiment

FIG. 1is a perspective view illustrating the appearance of a waterproof portable phone1(referred to as simply a “portable phone” hereinafter), which is an example of an electronic apparatus according to a first embodiment. This portable phone1includes an operation unit11provided with a numerical keypad and operation keys, and a display unit13attached to the operation unit11through a hinge12in a rotatable manner. The housing of the display unit13contains a liquid crystal display (LCD) that displays an image, and multiple electronic components. The housings of the operation unit11and the display unit13have a waterproof structure. In the following description, the housing of the display unit13will be given as an example. Note that the portable phone1is a folding type phone in this example, but may be a sliding or straight type phone instead.

FIG. 2is a perspective view illustrating the appearance of the display unit13. As illustrated inFIG. 2, the display unit13includes a housing130, and this housing130is formed by coupling or joining a rear case40with a front case30to which an LCD panel20is attached. The first embodiment will be described by giving the front case30and the rear case40as examples of first and second cases, respectively.

FIG. 3is a first exploded perspective view illustrating the display unit13, andFIG. 4is a second exploded perspective view illustrating the display unit13. Specifically,FIGS. 3 and 4are exploded perspective views that illustrate individual components constituting the display unit13as seen from the front and rear sides thereof, respectively. Note that the hinge12is omitted inFIGS. 2 to 4. Herein, the side of the display unit13on which the LCD panel20is installed is defined as a “front side”, whereas the side of the display unit13on which the LCD panel20is not installed is defined as a “rear side”.

Referring toFIGS. 3 and 4, the display unit13mainly includes the LCD panel20, the front case30, the rear case40, and a double-sided adhesive tape50. In addition, the housing130of the display unit13contains a wireless antenna board, an LCD unit (not illustrated), and some other parts. Each of the front case30and the rear case40is a casing having a rectangular, flat shape, and its corners are, for example, rounded or are formed so as to have a round shape. The front case30and the rear case40are bonded to each other through the respective joint surfaces thereof with the double-sided adhesive tape50having a loop or circular-shape. The detailed structure of the double-sided adhesive tape50will be described hereinafter. Note that this double-sided adhesive tape50is given as an example of a double-sided adhesive member.

The front case30mainly includes a frame portion31, and a pair of LCD panel support portions32and32that support the LCD panel20. As illustrated inFIG. 3, the frame portion31has an aperture portion33formed on the inner side thereof, and the LCD panel support portions32are formed on the inner wall surfaces of the respective short sides of the frame portion31. The LCD panel20is bonded to the front side surfaces of the LCD panel support portions32with, for example, a double-sided adhesive tape or a binder. The aperture portion33of the front case30is provided at a location corresponding to or facing the display screen of the LCD unit (not illustrated) which is to be contained in the housing130of the display unit13. The LCD panel20is transparent, and functions as a protective screen that closes and seals the aperture portion33. Through this LCD panel20, the user views the display screen of the LCD unit.

Through holes34are provided close to the outer edges of each LCD panel support portion32in the front case30, and these through holes34allow the screw or shaft portions of fixing screws60to pass therethrough. The fixing screws60are configured to engage with the grooves of screw holes (indicated by reference numeral43inFIG. 3) provided in the rear case40. Reference numeral35inFIG. 3indicates latch portions that are configured to latch onto projection pieces (indicated by reference numeral44inFIG. 3) provided in the rear case40.

FIG. 5is a plan view of the front case30as seen from a rear side thereof. As illustrated inFIG. 5, the through holes34that pass through the LCD panel support portions32are arranged at the four corners of the front case30. In total, eight latch portions35are arranged at corresponding locations on the frame portion31. In more detail, a single latch portion35is disposed at the center of each short side of the frame portion31, and three latch portions35are arranged on each long side thereof at regular intervals. Note that the arrangement pattern, locations, and the number of each of the through holes34and the latch portions35may be changed as appropriate.

With reference toFIGS. 3 and 4again, the rear case40will be described. The rear case40mainly includes a rear bottom portion42that serves as a back surface of the display unit13, and a side wall portion41that stands erect on the circumferential portion of the rear bottom portion42. The inner wall surface of the side wall portion41is provided with screw holes43having a groove therein at individual corners thereof. The through holes34in the front case30and the screw holes43in the rear case40are positioned so as to oppose each other when the front case30is bonded to the rear case40with the double-sided adhesive tape50. In addition to the adhesive force of the double-sided adhesive tape50, with the fixing screws60that engage with the grooves of the screw holes43through the through holes34, the front case30and the rear case40are secured to each other firmly.

As illustrated inFIG. 3, the plurality of projection pieces44are provided on the inner wall surface of the side wall portion41in the rear case40.FIG. 6illustrates the planar locations of the projection pieces44arranged in the rear case40.FIG. 6is a plan view of the rear case40as seen from a front side thereof. As illustrated inFIG. 6, the screw holes43are arranged at the four corners of the rear case40. In total, the eight projection pieces44are arranged. In more detail, a single projection piece44is disposed at the center of each short side of the side wall portion41, and three projection pieces44are arranged on each long side thereof at regular intervals. Note that the arrangement pattern, locations, and number of each of the screw holes43and the projection pieces44and may be changed as appropriate.

When the front case30is bonded to the rear case40with the double-sided adhesive tape50, the latch portions35of the front case30latch onto the corresponding projection pieces44provided in the rear case40. In addition to the adhesive force of the double-sided adhesive tape50, with the latch portions35that latch onto the projection piece44, the front case30and the rear case40are secured to each other firmly.

Next, a description will be given of a detailed structure of the double-sided adhesive tape50. As illustrated inFIGS. 3 and 4, the double-sided adhesive tape50constitutes a flat closed-loop shape on a whole. Furthermore, as illustrated inFIGS. 5 and 6, a joint surface311is formed on the upper surface of the frame portion31in the front case30, and the joint surface411is formed on the upper surface of the side wall portion41in the rear case40. Each of the joint surfaces311and411has a closed-loop shape on the whole. These joint surfaces311and411are bonded to each other through the double-sided adhesive tape50. It is preferable for each of the joint surfaces311and411to be formed to be a smooth surface. Hereinafter, the joint surfaces311and411will be referred to as a “first joint surface” and a “second joint surface”, respectively.

FIG. 7is a view illustrating a schematic configuration of the double-sided adhesive tape50according to the first embodiment. For example,FIG. 7is a cross-sectional view of the double-sided adhesive tape50as seen in the direction of the arrow VII-VII inFIG. 3. The double-sided adhesive tape50is a waterproof double-sided adhesive tape that has impermeable (waterproof) and elastic properties. Specifically, the double-sided adhesive tape50includes an impermeable base material51, and binder layers52and52formed on either surface of the base material51by applying binders521and521thereto. The base material51has an elastic property in the planar direction, or in a direction in which the base material51is spread out. In this case, the planar direction of the base material51may represent any direction that is orthogonal to the thickness direction of the base material51. Specifically, this planar direction may include individual directions along the long and short sides of the closed-loop shape formed by the base material51. Hereinafter, the long and short sides of the closed-loop shape will be referred to as a “loop's long side direction” and a “loop's short side direction”, respectively. In addition, the term “binder” refers to any adhesive including a so-called pressure-sensitive adhesive.

For the base material51that exhibits impermeable and elastic properties, for example, a solid foam base material having a closed cell structure may be employed. By applying the base material51with a closed cell structure (the base material51being referred to as a “solid foam base material” hereinafter) it is possible to effectively stop liquid from passing through the cut surface of the base material51upon molding in a closed-loop shape. With this closed cell structure, each pore in the solid foam base material51is deformed while a tensile force is being applied thereto, and returns to its initial shape once the tensile force is released. In this way, the solid foam base material51sufficiently secures an elastic property in a planar direction, including the loop's long side direction and the loop's short side direction.

As opposed to the planar direction, a limited number of pores are arranged in the thickness direction, because the solid foam base material51is preferably as thin as possible. For this reason, the solid foam base material51has a lower elastic performance in the thickness direction than in the planar direction. Note that the shape or average diameter of each pore which constitutes the closed cell structure of the solid foam base material51is not limited to a specific one.

Examples of the solid foam base material51may include a polyolefin solid foam made of polyethylene, polypropylene, ethylene-propylene polymer, ethylene-vinyl acetate or the like, and an acrylic solid foam. The solid foam base material51made of such a material is obtained by, for example: supplying a polyolefin resin, an acrylic resin or some other resin and a thermal-decomposition-type foaming agent to an extruder to be melted and mixed; pressing the mixture using the extruder to form a resin sheet; and stretching the resin sheet to make it thinner.

Next, a description will be given of the binder layers52and52of the double-sided adhesive tape50. The binder layers52and52are formed on a front surface511and a rear surface512of the solid foam base material51, namely both surfaces of the solid foam base material51. Each of the binder layers52and52in the double-sided adhesive tape50has a binder layer inner circumferential portion513that is placed close to the inner circumferential side of the solid foam base material51in the loop's width direction, and a binder layer outer circumferential portion514that is placed on the outer circumferential side of the binder layer inner circumferential portion513. In addition, the binder layer inner circumferential portion513and the binder layer outer circumferential portion514have different adhesive forces. Specifically, the double-sided adhesive tape50is formed by applying the stronger or weaker relationship between the adhesive forces of the binder layer inner circumferential portion513and the binder layer outer circumferential portion514to the front surface511and the rear surface522of the base material51inversely.

For example, it is assumed that on the front surface511of the solid foam base material51, the adhesive force of the binder layer inner circumferential portion513is greater than that of the binder layer outer circumferential portion514. In this case, on the rear surface512, the adhesive force of the binder layer outer circumferential portion514is set to be greater than that of the binder layer inner circumferential portion513. Meanwhile, when the adhesive force of the binder layer outer circumferential portion514is greater than that of the binder layer inner circumferential portion513on the front surface511of the solid foam base material51, the adhesive force of the binder layer inner circumferential portion513is set to be greater than that of the binder layer outer circumferential portion514on the rear surface512.

The exemplified configuration illustrated inFIG. 7employs the latter case. Herein, the front surface511of the solid foam base material51may be given as an example of a “first surface”, whereas the rear surface512may be given as an example of the “second surface”. In the example illustrated inFIG. 7, in fact, the adhesive force of the binder layer outer circumferential portion514is set to be greater than that of the binder layer inner circumferential portion513on the front surface511of the solid foam base material51. In addition, the adhesive force of the binder layer inner circumferential portion513is set to be greater than that of the binder layer outer circumferential portion514on the rear surface512. In order to set the adhesive forces in this manner, for example, a binder may be applied to only part of the solid foam base material51. In this embodiment, as for the front surface511of the solid foam base material51, a binder521is applied to the binder layer outer circumferential portion514, whereas no binder is applied to the binder layer inner circumferential portion513. Meanwhile, as for the rear surface512, a binder521is applied to the binder layer inner circumferential portion513, whereas no binder is applied to the binder layer outer circumferential portion514. In this way, on the front surface511of the solid foam base material51, the binder layer52is formed at a position shifted toward the outer circumferential side, whereas on the rear surface512, the binder layer52is formed at a position shifted toward the inner circumferential side.

Furthermore, in the double-sided adhesive tape50, respective ones of a binder layer inner circumferential portion513and a binder layer outer circumferential portion514which has a smaller adhesive force on the front surface511and the rear surface512overlap each other. In the example ofFIG. 7, one of a binder layer inner circumferential portion513and a binder layer outer circumferential portion514in which a binder521has been applied to the solid foam base material51is referred to as a “bonding portion PB”, whereas one of a binder layer inner circumferential portion513and a binder layer outer circumferential portion514in which no binder is applied to the solid foam base material51is referred to as a “non-bonding portion” PNB.

In the example ofFIG. 7, as for the front surface511of the solid foam base material51, the binder layer outer circumferential portion514corresponds to the bonding portion PB, whereas the binder layer inner circumferential portion513corresponds to the non-bonding portion PNB. Meanwhile, in the rear surface512thereof, the binder layer inner circumferential portion513corresponds to the bonding portion PB, whereas the binder layer outer circumferential portion514corresponds to the non-bonding portion PNB. The double-sided adhesive tape50is formed such that the respective non-bonding portions PNB formed on the front surface511and the rear surface512overlap each other vertically.

In this embodiment, the cross-sectional structure illustrated inFIG. 7is employed throughout the double-sided adhesive tape50in a lengthwise direction of the closed loop. However, the cross-sectional structure of the double-sided adhesive tape50is not limited to that illustrated inFIG. 7. Alternatively, the cross-sectional structure illustrated inFIG. 7may be employed in at least part of the double-sided adhesive tape50in the lengthwise direction. Meanwhile, acrylic binder (adhesive), silicone binder (adhesive) or some other binder may be given as an example of the binders521and521to be applied to the solid foam base material51of the double-sided adhesive tape50, but the binders521and521are not limited thereto.

FIG. 8is a partial cross-sectional view illustrating the housing130according to the first embodiment. Specifically,FIG. 8illustrates a cross-sectional structure around part of the housing130illustrated inFIG. 2which is enclosed by the dotted line XIII. InFIG. 2, components that have been described up to this point will be given the same reference numbers, and a detailed description thereof will be omitted. InFIG. 8, the reference numeral61denotes an LCD unit, and the reference numeral62denotes a wireless antenna board. Other members have been described already. With reference toFIG. 8, a description will be given of an example in which the front surface511of the double-sided adhesive tape50is bonded to the first joint surface311of the front case30, and the rear surface512is bonded to the second joint surface411of the rear case40. However, the positions of the front surface511and the rear surface512may be reversed.

In the display unit13, the housing130is preferably as thin as possible, for example, in order to realize the compact and thick design of the portable phone1. Accordingly, the housing130(or the front case30and the rear case40) is likely to be deformed by an impacts caused by the housings being dropped or some other external forces, or by the thermal expansion. When the housing130gets deformed, respective forces are exerted on both the front case30and the rear case40constituting the housing130in directions in which the front case30and the rear case40are away from each other. Eventually, the first joint surface311and the second joint surface411get partially separated.

FIG. 20is a view illustrating a waterproof structure in which joint surfaces301and401of a front case300and a rear case400, respectively, are bonded to each other by using a typical double-sided adhesive tape. For example, this typical double-sided adhesive tape is a double-sided adhesive tape in which the binder layer is formed across either surface of the base material in a width direction thereof by applying a binder thereto.

In a double-sided adhesive tape of this type, as illustrated inFIG. 20, when the first joint surface301of the front case300and the second joint surface401of the rear case400get partially separated, the double-sided adhesive tape possibly comes off the first joint surface301or the second joint surface401. In addition, because the base material of the double-sided adhesive tape has a lower elastic property in a thickness direction thereof, the base material itself may also be torn off. In this way, when the double-sided adhesive tape comes off the joint surface301or401and/or when the base material of the double-sided adhesive tape is torn off, the waterproof function of the housing130becomes difficult to maintain.

In contrast, in the double-sided adhesive tape50according to this embodiment, even when the joint surfaces311and411get partially separated, it is possible to stop liquid from entering the interior of the housing130, on the basis of the following principle.FIGS. 9A and 9Bare explanatory views illustrating the waterproof structure of the housing130according to the first embodiment.FIG. 9Aillustrates an initial state where the first joint surface311of the front case30and the second joint surface411of the rear case40are in contact with each other.FIG. 9Billustrates a partial separation state where the first joint surface311of the front case30and the second joint surface411of the rear case40are partially separated.

Here, a bonding interface between the first joint surface311and the front surface511of the double-sided adhesive tape50is defined as a “first bonding interface70”, and a bonding interface between the second joint surface411and the rear surface512of the double-sided adhesive tape50is defined as a “second bonding interface80”. Furthermore, a region where the first bonding interface70corresponds to or opposes the binder layer inner circumferential portion513on the front surface511of the double-sided adhesive tape50is referred to as a “loop inner circumferential portion71”, whereas a region where the first bonding interface70corresponds to or opposes the binder layer outer circumferential portion514is referred to as a “loop outer circumferential portion72”. Moreover, a region of the second bonding interface80which corresponds to or opposes the binder layer inner circumferential portion513on the rear surface512of the double-sided adhesive tape50is referred to as a “loop inner circumferential portion81”, whereas a region of the second bonding interface80which corresponds to or opposes the binder layer outer circumferential portion514is referred to as a “loop outer circumferential portion82”.

As illustrated inFIG. 9A, on the first bonding interface70, the loop inner circumferential portion71is formed close to the inner circumferential side in the loop's width direction, and the loop outer circumferential portion72is formed on the outer circumferential side of the loop inner circumferential portion71. Furthermore, on the second bonding interface80, the loop inner circumferential portion81is formed close to the inner circumferential side in the loop's width direction of the second bonding interface80, and the loop outer circumferential portion82is formed on the outer circumferential side of the loop inner circumferential portion81.

At the first bonding interface70, the bonding portion PB is formed in the binder layer outer circumferential portion514of the double-sided adhesive tape50, and the non-bonding portion PNB is formed in the binder layer inner circumferential portion513. Due to this, at the first bonding interface70, the adhesive force between the double-sided adhesive tape50and the first joint surface311is greater in the loop outer circumferential portion72than in the loop inner circumferential portion71. At the second bonding interface80, the non-bonding portion PNB is formed in the binder layer outer circumferential portion514, and the bonding portion PB is formed in the binder layer inner circumferential portion513. Due to this, at the second bonding interface80, the adhesive force between the double-sided adhesive tape50and the second joint surface411is greater in the loop inner circumferential portion81than in the loop outer circumferential portion82. In the waterproof structure of the housing130, the bonding portions PB are formed at both the first bonding interface70and the second bonding interface80, specifically, in any of the loop inner circumferential portions71and81and any of the loop outer circumferential portions72and82. This is so that the sealing property of the inner space in the housing130is maintained.

When the housing130gets deformed and the first joint surface311and the second joint surface411get partially separated, the housing130enters a state as illustrated inFIG. 9B. Note that in the double-sided adhesive tape50, the non-bonding portion PNB formed on the front surface511overlap the non-bonding portion PNB formed on the rear surface512. In addition, in the double-sided adhesive tape50, parts of the non-bonding portions PNB on the front surface511and the rear surface512which overlap with one another are each referred to as an “overlap portion515”.

In the double-sided adhesive tape50, a non-bonding portion PNB formed on the rear surface512opposes a bonding portion PB on the front surface511, aside from an overlap portion515of this non-bonding portion PNB. In addition, a bonding portion PB formed on the rear surface512opposes a non-bonding portion PNB on the front surface511. This configuration avoids an excess force to be exerted on the bonding portions PB on the front surface511and the rear surface512, even when the joint surfaces311and411of the front case30and the rear case40, respectively, get separated.

Because of the overlap portions515formed at the center of the double-sided adhesive tape50in the loop's width direction, the double-sided adhesive tape50produces the following functional effect. After the joint surfaces311and411of the front and rear cases30and40, respectively, are separated, as they are moving away from each other, the position of the overlap portions515is gradually changed from that being parallel to the joint surfaces311and411to that being parallel to a direction in which the joint surfaces311and411are moving away (referred as to a “partial separation direction” hereinafter). In other words, the planar direction of the overlap portions515is being displaced to be aligned with the partial separation direction of the joint surfaces311and411. This enables the double-sided adhesive tape50to stretch easier in the partial separation direction of the joint surfaces311and411, because the elastic property in the planar direction which the double-sided adhesive tape50has is superior to that in the thickness direction.

Accordingly, even when the first joint surface311and the second joint surface411get separated due to the deformation of the housing130, the double-sided adhesive tape50sufficiently stretches in the partial separation direction of the joint surfaces311and411. This suppresses the bonding portions PB in the double-sided adhesive tape50to come off the first bonding surface311and the second bonding surface411or protect the base material51from damage, so that the waterproof function of the housing130is maintained.

In the housing130according to this embodiment, as described above, the adhesive force between the double-sided adhesive tape50and one of the front case30and the rear case40is greater on the outer circumferential side of the one case than on the inner circumferential side thereof. In addition, the adhesive force between the double-sided adhesive tape50and the other of the front case30and the rear case40is greater on the inner circumferential side of the other case than on the outer circumferential side thereof. This configuration avoids the bonding portions PB of the double-sided adhesive tape50to come off the front case30and the rear case40, protects the base material51from damage, and so on, appropriately. Consequently, it is possible to suppress liquid, dust, and other contaminants to enter the interior of the housing130, thereby maintaining the sealing property of the inner space in the housing130, namely, achieving the high waterproof and dustproof properties thereof.

Because of the overlap portions515formed at the center of the double-sided adhesive tape50, the position of the overlap portions515is being displaced to be aligned with the partial separation direction of the joint surfaces311and411, as the joint surface311and411are moving away from each other. This enables the double-sided adhesive tape50to follow the movement of the joint surfaces311and411, at least by a distance corresponding to the sum of the width of the overlap portions515and an amount at which the overlap portions515are allowed to stretch in the partial separation direction of the joint surfaces311and411. This makes it possible to further enhance the elastic property of the double-sided adhesive tape50in the partial separation direction.

FIG. 10is a view illustrating a schematic configuration of a double-sided adhesive tape50A according to a modification of the first embodiment.FIG. 10illustrates the cross-sectional structure of the double-sided adhesive tape50A. This double-sided adhesive tape50A is different from the double-sided adhesive tape50illustrated inFIG. 7in the locations where bonding portions PB and non-bonding portions PNB are formed. Hereinafter, a description will be mainly given of this difference. On a front surface511of the double-sided adhesive tape50A, a binder521is applied to a binder layer inner circumferential portion513and no binder is applied to a binder layer outer circumferential portion514, so that a binder layer52is formed. Meanwhile, on a rear surface512of the double-sided adhesive tape50A, a binder521is applied to the binder layer outer circumferential portion514and no binder is applied to the binder layer inner circumferential portion513, so that another binder layer52is formed. Thus, in the double-sided adhesive tape50A, a binder layer52is formed on the front surface511at a location shifted toward the inner circumferential side of the solid foam base material51, and another binder layer52is formed on the rear surface512at a location shifted toward the outer circumferential side thereof.

As a result, on the front surface511of the double-sided adhesive tape50A, a bonding portion PB is formed in the binder layer inner circumferential portion513, whereas a non-bonding portion PNB is formed in the binder layer outer circumferential portion514. Meanwhile, on the rear surface512, a bonding portion PB is formed in the binder layer outer circumferential portion514, whereas a non-bonding portion PNB is formed in the binder layer inner circumferential portion513. Moreover, as illustrated inFIG. 10, the respective borders between the bonding portion PB and the non-bonding portion PNB on the front surface511and the rear surface512are aligned with each other in the loop's width direction.

FIG. 11is an explanatory view illustrating a waterproof structure of a housing130according to the modification of the first embodiment. In the double-sided adhesive tape50A, as illustrated inFIG. 11, a bonding portion PB is formed in one of each binder layer inner circumferential portion513and a corresponding binder layer outer circumferential portion514, similar to the first embodiment. Accordingly, at bonding interfaces between the double-sided adhesive tape50A and the first joint surface311and between the double-sided adhesive tape50A and the second joint surface411, namely, at the first bonding interface70and the second bonding interface80, respective bonding portions PB are formed in one of the circumferential portions71and81and one of the loop outer circumferential portions72and82. With this configuration, the sealing property of the inner space of the housing130which electric components are arranged is maintained appropriately.

When the first and second joint surfaces311and411have been partially separated, the non-bonding portions PNB of the double-sided adhesive tape50A come off the respective joint surfaces311and411and, then portions of the double-sided adhesive tape50A which are around borders between the bonding portions PB and the corresponding non-bonding portions PNB stretch in the partial separation direction of the joint surfaces311and411. In this way, the border portions stretch in the partial separation direction while following the movement of the joint surfaces311and411. This avoids the bonding portions PB to come off the joint surfaces311and411, thus making it possible to maintain the waterproof function of the housing130. Note that this modification has been described by giving the rear case40and the front case30as examples of the first and second cases.

In the above embodiment, the bonding portions PB and the non-bonding portions PNB have been formed by applying binders to part of either surface of the solid foam base material51. However, another method may be used. For example, a process may be used, of partially reducing the adhesive force of a binder coated region. In this case, for example, after binders are applied to the whole front surface511and rear surface512of the solid foam base material51, parts of the binder coated regions where the non-bonding portions PNB are to be formed may be subjected to a process of reducing the adhesive force. Printing employing such a process may use, for example, varnish, ink or the like, and be applied to anastatic or flexo printing.

In the double-sided adhesive tape50, an area ratio of a bonding portion PB to a non-bonding portion PNB in the loop's width direction which are formed on each of the front surface511and the rear surface512may be varied as appropriate. A non-bonding portion PNB may be formed so as to be wider than a bonding portion PB or vice versa. Obviously, the widths of a bonding portion PB and a non-bonding portion PNB may be the same as each other. Furthermore, respective area ratios of a bonding portion PB to a non-bonding portion PNB on the front surface511and the rear surface512in the loop's width direction may be the same as or different from each other.

On each of the front surface511and the rear surface512of the double-sided adhesive tape50, the binder layer inner circumferential portion513and the binder layer outer circumferential portion514may be simply set to have different adhesive forces. Specifically, a lower one of the adhesive forces of a binder layer inner circumferential portion513and a binder layer outer circumferential portion514is not set to zero, as opposed to the above embodiment. As long as the adhesive forces of the binder layer inner circumferential portion513and the binder layer outer circumferential portion514are set differently, one having a lower adhesive force comes off a correspond surface promptly when the joint surfaces311and411get separated. This enhances a capacity in which the double-sided adhesive tape50follows the movement of the first and second joint surfaces311and411. Consequently, it is possible to avoid one of the binder layer inner circumferential portion513and the binder layer outer circumferential portion514which is a region with a greater adhesive force to come off a corresponding surface, and to protect the base material51from damage, thus maintaining the waterproof function of the housing130appropriately.

Second Embodiment

Next, a second embodiment will be described. A waterproof structure of a housing130according to this embodiment is different from that of the first embodiment, in a surface structure, or a surface roughness, of the joint surfaces of a front case30and a rear case40, and a configuration of the binder layers in a double-sided adhesive tape. Hereinafter, a description will be mainly given of this difference. In this embodiment, the same components as those in the first embodiment are given the same reference numerals, and a detailed description thereof will be omitted. Note that a basic configuration of a portable phone1in the second embodiment is the same as that of the first embodiment.

FIG. 12is a schematic view illustrating the appearance of a rear case40according to the second embodiment as seen from the front side.FIG. 13is a schematic view illustrating the appearance of a front case30according to the second embodiment as seen from the rear side.FIG. 14is a view illustrating a schematic configuration of a double-sided adhesive tape50B according to the second embodiment. Note thatFIG. 12also schematically illustrates the appearance of the double-sided adhesive tape50B.

First, the double-sided adhesive tape50B will be described. As illustrated inFIG. 12, the double-sided adhesive tape50B constitutes a flat closed-loop shape on a whole, similar to the double-sided adhesive tape50according to the first embodiment.FIG. 14is a cross-sectional view of the double-sided adhesive tape50B as seen in the direction of the arrow XIV-XIV inFIG. 12. The double-sided adhesive tape50B is different from the double-sided adhesive tape50according to the first embodiment in not employing a special cross-sectional structure. Specifically, binders521and521are applied throughout either surface of a solid foam base material51in the loop's wide direction, in order to form binder layers52and52thereon. In other words, in the double-sided adhesive tape50B, the binder layers52and52are formed on the whole front surface511and rear surface512, respectively. This double-sided adhesive tape50B is given as an example of a double-sided adhesive member. In addition, the cross-sectional structure illustrated inFIG. 14is applied to the whole region in the double-sided adhesive tape50B in a lengthwise direction of the closed loop.

Referring toFIGS. 12 and 13, the front case30and the rear case40have a first joint surface311A and a second joint surface411A, respectively, to be bonded to each other through the double-sided adhesive tape50B. As illustrated inFIGS. 12 and 13, the joint surfaces311A and411A each have a closed-loop shape that is the same as the double-sided adhesive tape50B, so as to be bonded to each other through the double-sided adhesive tape50B. The respective structures of the front case30and the rear case40according to this embodiment are the same as those according to the first embodiment, except for the surface structures of the joint surfaces311A and411A.

A description will be given in detail, of the first joint surface311A and the second joint surface411A formed on the front case30and the rear case40, respectively. On the first joint surface311A, a region which is located on the inner circumferential side in the loop's width direction is referred to as a “joint surface inner circumferential portion313”, and a region which is located on the outer circumferential side of the joint surface inner circumferential portion313is referred to as a “joint surface outer circumferential portion314”. Meanwhile, on the second joint surface411A, a region which is located on the inner circumferential side in the loop's width direction is referred to as a “joint surface inner circumferential portion413”, and a region which is located on the outer circumferential side of the joint surface inner circumferential portion413is referred to as a “joint surface outer circumferential portion414”.

In the first embodiment, different adhesive forces are applied to each pair of the binder layer inner circumferential portions513and the binder layer outer circumferential portions514in the double-sided adhesive tape50. As a result, each pair of the loop inner circumferential portions71and81and the loop outer circumferential portions72and82have different adhesive forces. In contrast, in the second embodiment, different surface roughnesses or smoothnesses are applied to the joint surface inner circumferential portion313and the joint surface outer circumferential portion314on the first joint surface311A. Moreover, different surface roughnesses are also applied to the joint surface inner circumferential portion413and the joint surface outer circumferential portion414on the second joint surface411A.

FIGS. 15A and 15Bare an explanatory view illustrating the waterproof structure of the housing130according to the second embodiment.FIG. 15Aillustrates an initial state where the first joint surface311A of the front case30and the second joint surface411A of the rear case40are in contact with each other.FIG. 15Billustrates a partial separation state where the first joint surface311A of the front case30and the second joint surface411A of the rear case40are partially separated.

Referring toFIG. 15A, a description will be given of a basic configuration of a waterproof structure at respective bonding interfaces between the double-sided adhesive tape50B and the joint surface311A and between the double-sided adhesive tape50B and the joint surface411A. In this embodiment, the bonding interface between the first joint surface311A and the front surface511of the double-sided adhesive tape50B is defined as a “first bonding interface70A”. Likewise, the bonding interface between the second joint surface411A and the rear surface512of the double-sided adhesive tape50B is defined as a “second bonding interface80A”. Furthermore, at the first bonding interface70A, a region which corresponds to or opposes the joint surface inner circumferential portion313is defined as a “loop inner circumferential portion71A”, and a region which corresponds to or opposes the joint surface outer circumferential portion314is defined as a “loop outer circumferential portion72A”. Likewise, at the second bonding interface80A, a region which corresponds to or opposes the joint surface inner circumferential portion413on the rear surface512of the double-sided adhesive tape50B is defined as a “loop inner circumferential portion81A”, and a region which corresponds to or opposes the joint surface outer circumferential portion414is defined as a “loop outer circumferential portion82A”. Moreover, in the double-sided adhesive tape50B, a region which is bonded to the joint surface inner circumferential portion313is defined as a “binder layer inner circumferential portion513A”, and a region that is bonded to the joint surface outer circumferential portion314is defined as a “binder layer outer circumferential portion514A”.

For example, on the condition that the same type of binders521, the binder layers52of the same thickness, and solid foam base materials51of the same strength are used, the adhesive force of the double-sided adhesive tape50B is increased in proportion to the areas that are in contact with the joint surfaces311A and411A. In this embodiment, different surface roughnesses are applied to the joint surface inner circumferential portion313and the joint surface outer circumferential portion314on the first joint surface311A. As a result, the loop inner circumferential portion71A and the loop outer circumferential portion72A at the first bonding interface70A have different adhesive forces. Likewise, different surface roughnesses are applied to the joint surface inner circumferential portion413and the joint surface outer circumferential portion414on the second joint surface411A. As a result, the loop inner circumferential portion81A and the loop outer circumferential portion82A at the second bonding interface80A have different adhesive forces.

On the first joint surface311A formed in the front case30, the joint surface inner circumferential portion313has a surface roughness higher than the joint surface outer circumferential portion314, as illustrated inFIG. 15A. In other words, on the first joint surface311A, the joint surface outer circumferential portion314has a surface roughness smaller than the joint surface inner circumferential portion313. Accordingly, at the first bonding interface70A between the first joint surface311A and the double-sided adhesive tape50B, a contact area between the binder layer inner circumferential portion513A and the joint surface inner circumferential portion313is smaller than that between the binder layer outer circumferential portion514A and the joint surface outer circumferential portion314. Thus, at the first bonding interface70A, the adhesive force of the loop inner circumferential portion71A becomes smaller than that of the loop outer circumferential portion72A.

Meanwhile, on the second joint surface411A formed in the fear case40, the joint surface outer circumferential portion414has a surface roughness higher than the inner circumferential side bonding portion413. Accordingly, at the second bonding interface80A between the second joint surface411A and the double-sided adhesive tape50B, a contact area between the binder layer outer circumferential portion514A and the joint surface outer circumferential portion314is smaller than that between the binder layer inner circumferential portion513A and the joint surface inner circumferential portion313. Thus, at the second bonding interface80A, the adhesive force of the loop outer circumferential portion82A becomes smaller than that of the loop inner circumferential portion81A.

In this embodiment, one of the loop inner circumferential portions71A and81A at the first and second joint interfaces70A and80A, respectively, which has a greater adhesive force is referred to as a “strongly bonding portion PSB”, whereas the one having a smaller adhesive force is referred to as a “weakly bonding portion PWB”. Likewise, one of the loop inner circumferential portions72A and82A at the first and second joint interfaces70A and80A, respectively, which has a greater adhesive force is referred to as a “strongly bonding portion PSB”, whereas the one having a smaller adhesive force is referred to as a “weakly bonding portion PWB”. As illustrated inFIG. 15A, the joint surface inner circumferential portion313on the first joint surface311A which has a greater surface roughness overlaps the joint surface outer circumferential portion414on the second joint surface411A which has a greater surface roughness, with the double-sided adhesive tape50B therebetween. Regions where the respective weakly bonding portions PWB at the first bonding interface70A and the second bonding interface80A overlap one another are each referred to as an “overlap portion515A”. In this embodiment, the strongly bonding portion PSB at the first bonding interface70A opposes the weakly bonding portion PWB at the second bonding interface80A, aside from the overlap portion515A at the second bonding interface80A. In addition, the weakly bonding portion PWB at the first bonding interface70A overlaps the strongly bonding portion PSB at the second bonding interface80A, aside from the overlap portion515A at the first bonding interface70A.

As illustrated inFIG. 15B, when the first joint surface311A of the front case30gets separated from the second joint surface411A of the rear case40, the respective weakly bonding portions PWB that have a smaller adhesive force come off the binder layers52and52of the double-sided adhesive tape50B promptly. After that, as the joint surfaces311A and411A are moving away from each other, the position of the overlap portions515A are being changed from that being parallel to the joint surfaces311A and411A to that being parallel to the partial separation direction of the first and second joint surfaces311A and411A.

Finally, the overlap portions515A, which has a highly elastic property in the planar direction, are substantially aligned with the partial separation direction of the first and second joint surfaces311A and411A. Accordingly, even when the first and second joint surfaces311A and411A get partially separated with the deformation of the housing130, the double-sided adhesive tape50B sufficiently stretches in the partial separation direction. This suppresses the strongly bonding portions PSB of the double-sided adhesive tape50B to come off the binder layers52of the double-sided adhesive tape50B, and protects the base material51from damage. Consequently, it is possible to maintain the waterproof function of the housing130appropriately.

As described above, the housing130according to this embodiment constitutes a waterproof structure by adjusting the surface roughness of the first and second joint surfaces311A and411A. Therefore, it is possible to set the adhesive forces of each pair of loop inner circumferential portions71A and81A and the loop outer circumferential portions72A and82A differently from each other, without using a special double-sided adhesive tape such as that illustrated inFIG. 7. Note that it is preferable that the surface roughness of the first and second joint surfaces311A and411A be set by using a method mentioned below.

The surface roughness of the first and second joint surfaces311A and411A may be set, for example, by adjusting the surface roughness or smoothness of a die for use in molding the front case30and the rear case40. For example, the molding surfaces of the above die which correspond to the strongly bonding portions PSB and PSB of the first and second joint surfaces311A and411A may be each formed to be a smooth surface. In addition, the molding surfaces of the above die which correspond to the weakly bonding portions PWB and PWB may be subjected to a pearskin or grain finish, in order to form uneven, fine patterns thereon.

It is preferable that the surface roughness of the first and second joint surfaces311A and411A be adjusted appropriately by changing uneven, fine patterns formed on a molding surface of a die. With this process, it is possible to adjust the difference of an adhesive force between the loop inner circumferential portion71A and the loop outer circumferential portion72A at the first bonding interface70A appropriately. Also, it is possible to adjust the difference of an adhesive force between the loop inner circumferential portion81A and the loop outer circumferential portion82A at the second bonding interface80A appropriately. This produces an advantageous effect of enabling the precise adjustment of timing when a weakly bonding portion PWB comes off a corresponding joint surface after the separation of the first joint surface311A and the second joint surface411A.

In this embodiment, the surface roughness of the first and second joint surfaces311A and411A is adjusted to apply different adhesive forces to each pair of the loop inner circumferential portions71A and81A at the first bonding interface70A and the adhesive forces of the loop outer circumferential portions72A and82A at the second bonding interface80A. However, a process of applying different adhesive forces is not limited thereto, and another process may be employed. As illustrated inFIG. 16, for example, a coating process of applying a coating agent that reduces or removes the adhesive force of the double-sided adhesive tape50B may be applied to respective regions (indicated by the thick, dotted lines inFIG. 16) of the first and second joint surfaces311A and411A in which a weakly bonding portion PWB is to be formed.

Specifically, a coating agent100that reduces or removes the adhesive force of the double-sided adhesive tape50B is applied to one of the joint surface inner circumferential portion313and the joint surface outer circumferential portion314on the first joint surface311A. In addition, the coating agent100is applied to one of the joint surface inner circumferential portion413and the joint surface outer circumferential portion414on the second joint surface411A. In this case, it is preferable that targets on the first joint surface311A and the second joint surface411A to which the coating agent100is applied be not arranged opposite to each other.

In more detail, the coating agent100that reduces or removes the adhesive force of the double-sided adhesive tape50B is applied to an area of the first joint surface311A which opposes one of the loop inner circumferential portion and the loop outer circumferential portion at the first bonding interface70A. Furthermore, the coating agent100is applied to an area of the second joint surface411A which opposes the other of the loop inner circumferential portion and the loop outer circumferential portion at the second bonding interface80A. This process enables the setting of different adhesive forces between each pair of the loop inner circumferential portions71A and81A at the first bonding interface70A and the loop outer circumferential portions72A and82A at the second bonding interface80A. Note that in the example illustrated inFIG. 16, the above coating process is applied to the joint surface inner circumferential portion313on the first joint surface311A and the joint surface outer circumferential portion414on the second joint surface411A. A coating agent for use in the above coating or surface process may be a coating such as a fluorine or UV coating agent, but is not limited thereto. Furthermore, regions of the first and second joint surfaces311A and411A to which a coating agent is applied overlap each other in the loop's width direction, so that the overlap portions515A are formed easily.

[Region of Created Adhesive Force Difference Structure]

In the above-described embodiments, an adhesive force difference structure90has been applied throughout the region where the front case30and the rear case40are joined. This adhesive force difference structure90is created by differently setting adhesive forces between a double-sided adhesive tape and an outer circumferential side on a joint surface and between the double-sided adhesive tape and an inner circumferential side thereon. However, an application of this adhesive force difference structure90is not limited thereto. Referring to the enlarged portion C ofFIG. 13, for example, the reference numeral315denotes a sloped portion that is formed on the first joint surface311A of the front case30.

FIG. 17is an exploded side view illustrating the display unit13. Typically, a so-called fillet is formed on the sloped portion315illustrated inFIGS. 13 and 17, but the radius of this fillet is likely to contain a more considerable production error than a flat portion316. This considerable error may cause the housing130to be deformed with time. When the sloped portion315is deformed, the double-sided adhesive tape50B copes with this deformation to some extent, but the double-sided adhesive tape50B may come off the sloped portion315easier than the flat portion316. Thus, the sloped portion315on the joint surface311A or411A to which the double-sided adhesive tape50B is bonded possibly becomes a weak point that causes the waterproof structure of the housing130to be degraded, in contrast to the flat portion316.

Therefore, as illustrated inFIG. 18, adhesive force difference structures90may be formed on regions of the loop's long sides of the double-sided adhesive tape50B which correspond to sloped portions315that possibly become a weal point of the waterproof structure, and normal bonding structures91may be formed on regions which correspond to flat portions316. This normal bonding structure91refers to a structure in which the adhesive forces are equal to each other in the loop inner circumferential portions71A and81A at the first and second bonding interfaces70A and80A, respectively and the loop outer circumferential portions72A and82A at the first and second bonding interfaces70A and80A, respectively. The normal bonding structure91may be created by applying the same surface roughness to the joint surface inner circumferential portions313and413on the first and second joint surfaces311A and411A, respectively, and the joint surface outer circumferential portions314and414on the first and second joint surfaces311A and411A, respectively.

Referring toFIGS. 3 and 4again, the front case30and the rear case40are secured to each other with fixing screws60at locations corresponding to the corners of the display unit13. Also, the display unit13exhibits higher stiffness in the vicinity of portions where fixing screws60are fixed, and therefore, these portions are less likely to be deformed. Likewise, it is considered that a portion of the housing130where the hinge12is installed is less likely to be deformed due to the high stiffness. In consideration of this fact, the normal bonding structures91may be created near portions where the fixing screws60are fixed, whereas the adhesive force difference structures90may be created in the remaining regions.

As described above, the adhesive force difference structure90may be created in at least part of the loop's long sides of the double-sided adhesive tape50B. In addition, for example, the lengths, locations and the number of the regions where the adhesive force difference structures90are created may be changed as appropriate. In addition, the adhesive force difference structures90may be applied to regions of the first and second bonding surface on the loop's long sides of the double-sided adhesive tape50B which the double-sided adhesive tape50B is likely to come off, whereas the normal bonding structures91may be applied to regions thereof which the double-sided adhesive tape50B is less likely to come off. This makes it possible to secure the waterproof function of the housing130even when the housing130get deformed. Furthermore, by applying the normal bonding structures91to the regions where the double-sided adhesive tape50B is less likely to come off, it is possible to make the manufacture cost of the housing130lower than when the adhesive force difference structure90are created across the housing130.

Next, with regard to the waterproof structure of the housing130according to these embodiments, a description will be given of a method of setting an overlap amount that corresponds to a length of each overlap portion515A. As described above, as the overlap amount of each overlap portion515A increases, the elastic property of the double-sided adhesive tape50B in the partial separation direction of the first and second joint surfaces311A and411A is enhanced.

When the front case30is joined to the rear case40, a projection piece44provided in the rear case40moves beyond a latch piece36of a latch portion35provided in the front case30, and then, the projection piece44is latched onto by the latch portion35, as illustrated inFIG. 19.FIG. 19is a view illustrating a relatively positional relationship between the projection piece44and the latch portion35in an initial state where the front case30and the rear case40are joined together. As illustrated inFIG. 19, there is a clearance of a predetermined width (referred to as an “initial clearance” hereinafter) created between the projection piece44and the latch piece36of the latch portion35in the initial state.

When the first and second joint surfaces311A and411A have been partially separated, for example, due to the deformation of the housing130, as the first and second joint surfaces311A and411A are moving away from each other, the clearance is being narrowed between the projection piece44and the latch piece36of the latch portion35. Then, once the clearance is removed and the projection piece44and the latch piece36of the latch portion35are brought into contact with each other, the first and second joint surfaces311A and411A are no longer allowed to move away from each other. Accordingly, the maximum distance at which joint surfaces311A and411A are allowed to be away from each other since the initial state is substantially equal to the width of the initial clearance. Thus, it is desirable that an amount at which the double-sided adhesive tape50B is allowed to stretch in the partial separation direction of the first and second joint surfaces311A and411A be set to be equal to or more than the width of the initial clearance.

As the initial clearance is widened, a distance at which the first and second joint surfaces311A and411A are away from each other increases. Accordingly, as the initial clearance is wider, it is preferable for the double-sided adhesive tape50B to stretch more greatly in the partial separation direction of the first and second joint surfaces311A and411A. Thus, in these embodiments, the overlap amount of each overlap portion515A is set to be greater, as the initial clearance is wider. By setting the overlap amount of each overlap portion515A in accordance with the width of the initial clearance in this manner, the strongly bonding portions PSB at the first and second bonding interfaces70A and80A do not come off a corresponding joint surface, at least until the latch piece36and the projection piece44are brought into contact with each other. In this way, it is possible to maintain the waterproof function of the housing130appropriately.

Note that the above-described embodiments have been described by giving a portable phone as an example of an electronic apparatus, but an electronic apparatus is not limited thereto. The above-described waterproof structure of a housing is widely applicable to digital cameras, film cameras, transceivers, PDAs, notebook personal computers, calculators, electronic dictionaries, and some other electronic apparatuses. In addition, the individual components and functions of the above-described embodiments may be implemented alone or in a combination as appropriate.