Protection element

Abstract

The present invention provides a protection device which includes: a PTC laminar element which is formed of an insulation resin and has at least one throughhole; electrically conductive metal thin layers which are positioned on each of main surfaces of the laminar element, and a fuse layer which is positioned on a side surface defining at least one of said at least one throughhole and electrically connects the electrically conductive metal thin layers which are positioned on each of main surfaces of the laminar element. The protection device of the present invention allows a larger amount of a current to flow therethrough and can provide a protection from an excessive current.

Claims

1. A protection device comprising: an annular PTC laminar element formed of a PTC composition and having a central throughhole and at least one surrounding throughhole; an annular metal foil disposed on each main surface of the PTC laminar element and coaxial with the PTC laminar element; an annular electrically conductive metal thin layer disposed on each of the metal foils and coaxial with the PTC laminar element; and a fuse layer which is positioned on a side surface defining at least one of said at least one surrounding throughhole and electrically connecting the electrically conductive metal thin layers; wherein the fuse layer comprises a first metal layer having a first thickness and a second metal layer having a second thickness greater than the first thickness, and wherein a side surface defining the central throughhole does not include a fuse layer disposed thereon.

2. The protection device according to claim 1, characterized in that the first metal layer consists of a metal having a higher melting point than a melting point of a metal from which the second metal layer is formed.

3. The protection device according to claim 2, characterized in that the metal having the higher melting point is Ni.

4. The protection device according to claim 2, characterized in that the metal having the lower melting point has a melting point lower than a decomposition temperature of a polymer material of the PTC composition.

5. The protection device according to claim 4, characterized in that the metal having the lower melting point is Sn, an SnCu alloy or an SnBi alloy.

6. The protection device according to claim 2, characterized in that the first metal layer is formed by electroless plating with the metal having the higher melting point and the second metal layer is formed by electrolytic plating with the metal having the lower melting point on the first metal layer.

7. The protection device according to claim 2, characterized in that a thickness ratio between the first metal layer and the second metal layer is 1:100-5:1.

8. The protection device according to claim 1, characterized in that the metal foil is a nickel foil.

9. An electrical apparatus comprising the protection device according to claim 1.

10. A washer comprising: an annular PTC laminar element formed of a PTC composition and having a central throughhole and at least one surrounding throughhole, an annular metal foil positioned on each main surface of the PTC laminar element and coaxial with the PTC laminar element; an annular electrically conductive metal thin layer disposed on each of the metal foils and coaxial with the PTC laminar element, and a fuse layer positioned on a side surface defining at least one of said at least one surrounding throughhole and electrically connecting the electrically conductive metal thin layers; wherein the fuse layer comprises a first metal layer having a first thickness and a second metal layer having a second thickness greater than the first thickness, and wherein a side surface defining the central throughhole does not include a fuse layer disposed thereon.

11. The protection device according to claim 10, characterized in that the first metal layer consists of a metal having a higher melting point than a melting point of a metal from which the second metal layer is formed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 schematically shows a protection device of the present invention in a cross-sectional view along its thickness-direction;

(2) FIG. 2 schematically shows in a plane view the protection device which is shown in FIG. 1;

(3) FIG. 3 schematically shows in a cross-sectional view a fuse layer in the protection device which is shown in FIGS. 1 and 2;

(4) FIG. 4 schematically shows a protection device of the present invention of other embodiment in a cross-sectional view along its thickness-direction;

(5) FIG. 5 schematically shows the protection device in a plane view which is shown in FIG. 4; and

(6) FIG. 6 schematically shows in a cross-sectional view a fuse layer in the protection device which is shown in FIGS. 4 and 5.

DETAILED DESCRIPTION OF THE INVENTION

(7) The protection device of the present invention will be described in detail with reference to the accompanied drawings. In FIG. 1, one embodiment of the protection device of the present invention is schematically shown in a cross-sectional view along its thickness-direction (a portion which appears as the cut plane is indicated with an arrow A). Also, in FIG. 2, the protection device shown in FIG. 1 is schematically shown in a plane view. Furthermore, in FIG. 3, a fuse layer in the protection device shown in FIGS. 1 and 2 is schematically shown in a cross-sectional view.

(8) The illustrated protection device 10 comprises an annular PTC laminar element 16 which is formed of the PTC composition and has at least one throughhole (in the illustrated embodiment, two throughholes of a central throughhole 12 having a circular cross-section and a surrounding throughhole 14 having a circular cross-section). The protection device 10 comprises electrically conductive metal thin layers 22 and 24 which are positioned on both main surfaces 18 and 20 respectively of the PTC laminar element 16. It is noted that in the illustrated embodiment, separate metal layers 26 and 28 are present between the PTC laminar element 16 and the electrically conductive metal thin layers.

(9) In the illustrated embodiment, the fuse layer is absent on an inner periphery 30 of the circular ring which defines the central throughhole, i.e. on a side surface inside of the annular ring. In the illustrated embodiment, a fuse layer 40 is present on a peripheral side surface 38 which defines the surrounding throughhole 14 positioned through a main body 36 of the laminar element between the inner periphery 30 and the outer periphery 34.

(10) In a preferable embodiment, as shown in FIG. 3, the fuse layer 40 may comprises a first metal layer 41 located on the peripheral side surface 38 which defines the surrounding throughhole 14 and a second metal layer 42 located on the first metal layer 41.

(11) In the illustrated embodiment, the surrounding throughhole 14 having the fuse layer 40 is only one which is provided at the midpoint of the main body 36 along the diameter (shown with a broken line in FIG. 2) passing through a center O of the PTC laminar element, but such surrounding throughhole may be provided at the opposite side along the diametrical direction. In this case, it results in providing surrounding throughholes at every 180 (totally providing two throughholes) around the center O. In a further other embodiment, three, four, six or eight of the surrounding throughholes having the fuse layer may be provided at an equal angle interval of 120, 90, 60 or 45 around the center O of the circle, respectively.

(12) It is noted that since the diameter of the central throughhole is far larger than the diameter of the surrounding throughhole, the fuse layer is absent on the side surface of the inner periphery 30 of the annular ring. However, the fuse layer may be provided on the side surface of the inner periphery 30 of the annular ring if necessary when the diameter of the central throughhole is the similar to or smaller than the diameter of the surrounding throughhole. It is noted that in a certain embodiment, when a convex part corresponding to the central throughhole is provided to an electrical apparatus to which the protection device is to be disposed, the protection device may be located on the electrical apparatus by fitting the convex part into the large diameter part of the central throughhole. For example, such convex part is provided on a sealing plate of a secondary battery cell, so that the convex part is fitted into the central throughhole, and thereby enabling to position the protection device on the sealing plate.

(13) In other embodiment, the PTC laminar element 16 does not have the central throughhole 12 (therefore, the PTC laminar element is in a disk-shape) and has only at least one surrounding throughhole 14 which may have the fuse layer 40.

(14) A protection device 10 of a further another embodiment of the present invention is shown in FIGS. 4 and 5 similarly to FIGS. 1 and 2. A fuse layer 32 in the preferable embodiment of the protection device shown in FIGS. 4 and 5 is shown in FIG. 6 similarly to FIG. 3. It is noted that the same reference numerals are used for the same elements as in FIGS. 1-3. In the illustrated embodiment, the PTC laminar element 16 does not have the surrounding throughhole 14 and has only the central throughhole 12 which has the fuse layer 32. In a preferably embodiment, the fuse layer 32 may comprises a first metal layer 43 located on the inner periphery 30 which defines the central throughhole 12 and a second metal layer 44 located on the first metal layer 43.

EXAMPLE 1

(15) The protection device of the present invention shown in FIGS. 1 and 2 was produced. Therefore, the protection device 10 was produced which has only the fuse layer 40 but does not have the fuse layer 32. It is noted that eight surrounding throughholes 14 were circumferentially formed at an equal angle interval.

(16) First, a sheet (a thickness of 0.3 mm; corresponding to the laminar element 16) of PTC composition (a high density polyethylene containing a carbon black particulate material) was prepared, nickel foils (having a thickness of 22 m, corresponding to the separate metal layers 26 and 28) were positioned on the both side of the sheet, and they were pressed while heating to be integral to obtain a pressure-bonded product wherein the nickel foils were applied to the both main surfaces.

(17) Throughholes (corresponding to the surrounding throughhole 14) which were of 0.6 mm in a diameter were formed at prescribed positions of the pressure-bonded product, and then plating the pressure-bonded product with Ni by an electrolytic plating process. The thickness of the nickel layer which was formed by plating was about 0.008 mm. Then, the annular element was stamped out from the pressure-bonded product to obtain the protection device 10 of the present invention wherein eight throughholes were positioned in place at every 45 around the center of the annular element as prescribed.

(18) The diameter of the outer peripheral circle 34 of the obtained circular annular element was 15 mm, and the diameter of the obtained inner peripheral circle 30 (i.e. the diameter of the central throughhole) was 6.4 mm. This circular annular element had nickel foils functioning as the separate metal layers 26 and 28 on the both main surfaces of the laminar element 16, and had the surrounding throughholes 14 at the midpoint of the maim body 36 which was a part of the circular annular element. Also, the circular annular element had plated layers as the electrically conductive metal thin layers 22 and 24 on the nickel foils, and had plated layers functioning as the fuse layers 40 on the inner peripheral surfaces which define the surrounding throughholes.

EXAMPLE 2

(19) The protection device of the present invention was obtained similarly to Example 1 except that plating process after the formation of the throughholes (corresponding to the surrounding throughholes) was performed by Ni-plating with an electroless plating process and Sn-plating with an electrolytic plating process to obtain a nickel layer having a thickness of about 1.5 m (corresponding the first metal layer 41) and an Sn layer having a thickness of about 6.5 m (corresponding the second metal layer 42).

(20) Experiment 1

(21) A current (with 60 Vdc) listed in following Table 1 was passed through the protection device of Examples 1 and 2 from one electrically conductive metal thin layer 22 to the other electrically conductive metal thin layer 24. The maximum value of current which continues to flow without blowing for 10 minutes was defined as rated capacity. As a result, the rated capacity of the protection device of Example 1 was 25 A and the rated capacity of the protection device of Example 2 was 22.5 A.

(22) Experiment 2

(23) A current four times the rated capacity defined in Experiment 1 (with 60 Vdc) was applied from one electrically conductive metal thin layer 22 to the other electrically conductive metal thin layer 24 of the protection devices of the Examples 1 and 2 and a current-interrupting time was measured. As a result, the current-interrupting time is within one second in the protection devices of both the Examples.

(24) Experiment 3

(25) After interrupting the excessive current in Experimental Example 2, the applied current was stopped and the protection device was allowed to stand for 10 minutes. Then, a current of 100 A (with 60 Vdc) was passed from one electrically conductive metal thin layer 22 to the other electrically conductive metal thin layer 24 for 6 seconds, and its trip performance checked as to whether the PTC device was activated (tripped). After applying the current for 6 seconds, the current (and voltage) was stopped for 54 seconds. This sequence was defined as one cycle, and each sample was subjected to ten cycles. As a result, it was confirmed that the both samples had the PTC property without firing or fuming.

(26) The results of Experiments 1-3 are shown in following Table 1.

(27) TABLE-US-00001 TABLE 1 Example 1 Example 2 Electroless plated Ni Ni material Electrolytic plated Ni Sn material Thickness of electroless 1.5 1.5 plate (m) Thickness of electrolytic 6.5 6.5 plate (m) Total plate thickness 8.0 8.0 (m) Higher melting point 23.1 23.1 plate/Lower melting point plate ratio (%) Exper- Test current 10 A No blowing for No blowing for iment 1 10 minutes 10 minutes Test current 15 A No blowing for No blowing for 10 minutes 10 minutes Test current 20 A No blowing for No blowing for 10 minutes 10 minutes Test current 22.5 A No blowing for No blowing for 10 minutes 10 minutes Test current 25 A No blowing for 10 minutes Exper- Time to blowing 0.46 second 0.32 second iment 2 (Test current: four times (100 A) (90 A) the rated capacity) Exper- 100 A (60 Vdc) On for having PTC having PTC iment 3 6 seconds, Off for 54 property without property without seconds, 10 cycles firing or fuming firing or fuming

(28) From these results, it has been confirmed that the protection device of the present invention provides protection from an excessive current while allowing a relatively large amount of current such as a the current of 20-25 A to continuously flow. Additionally, it has been confirmed that the current can be continually applied again by eliminating the cause for the excessive current.

(29) The protection device of the present invention can be used as a protection device which interrupts an excessive current when the excessive current flows in an electrical apparatus such as a secondary battery. The protection device of the present invention can also be used as an alternative to a nickel washer, a washer in which a stainless material is nickel-plated or the like which is for example incorporated into a sealing plate in a cylindrical lithium ion secondary battery cell. In this case, since the protection device has the PTC laminar element which is formed of the PTC composition, the function of the protection device as a washer is increased due to elasticity of the resin. Therefore, the present invention can also be used as a washer which has characteristics of the protection device of the present invention as described above.

THE ELEMENT REFERENCE NUMERALS ARE

(30) 10, 10protection device; 12central throughhole 14surrounding throughhole; 16laminar element 18, 20main surface; 22, 24electrically conductive metal thin layer 26, 28other metal layer; 30inner periphery 32fuse layer; 34outer periphery 36main body; 38side surface; 40fuse layer 41first metal layer; 42second metal layer 43first metal layer; 44second metal layer