JP4497143B2 - PTC element and battery protection system - Google Patents

Description

  The present invention relates to a PTC element used for the purpose of protecting a battery or an electronic circuit from an overcurrent, and a battery protection system having the PTC element.

  A PTC (positive temperature coefficient) element has a characteristic that the resistance value of the element increases when the temperature of the element rises in a predetermined temperature region. In particular, when the temperature of the PTC element reaches the melting temperature of the polymer constituting the element body, the resistance of the PTC element increases rapidly. Such a property is called a PTC characteristic.

  The PTC element is incorporated in an electric circuit such as an electronic device. If an excessive current flows in the circuit for some reason during use of the electronic device, the temperature of the electronic device rises, and the temperature of the PTC element itself rises accordingly. And when the temperature of a PTC element reaches the melting temperature of the polymer which comprises an element main body, the resistance value of a PTC element will increase rapidly. As a result, the PTC element blocks excess current in the electric circuit. Therefore, it is possible to prevent the electrical device from being damaged due to excessive current.

  Thus, the PTC element is used as a safety protection device against overheating and excessive current. Specifically, the PTC element is incorporated in a circuit (protection circuit) for protecting a secondary battery that is a power source of the mobile phone from overcurrent. When an excessive current flows during charging or discharging of the secondary battery, the PTC element cuts off the current and protects the secondary battery.

  An example of such a PTC element is a structure in which an element body (polymer positive temperature coefficient resistor) in which conductive particles are dispersed in a polymer material (crystalline polymer) is sandwiched between electrode plates (or metal foils). There is known a polymer PTC element having a thickness (see Patent Document 1).

  Conventionally, the polymer PTC element is manufactured by the following method. First, a polymer (such as high-density polyethylene) containing a conductive filler such as metal particles and carbon black is extruded to form an element body. Next, the polymer PTC element is completed by thermocompression bonding the electrode plate to the front and back surfaces of the element body.

  When the polymer PTC element is incorporated in a predetermined protection circuit, the electrode plate is joined to a terminal plate electrically connected to the protection circuit. This joining is conventionally performed by soldering, welding, or the like.

  When performing soldering, welding, etc., it is necessary to heat at least a part of the electrode plate and the terminal plate to a high temperature. Since the electrode plate (or metal foil) of the polymer PTC element is very thin, heat applied to the electrode plate during soldering and welding is immediately conducted to the element body. As a result, the element body becomes high temperature and may be thermally deteriorated (softened or melted). When the element body is softened or melted, the dispersibility of the conductive particles in the polymer becomes non-uniform. In a polymer PTC element that has undergone such a thermal history, the resistance value at room temperature (room temperature resistance value) is greatly increased compared to that before this thermal history.

  Further, when the element main body is directly exposed to the atmosphere, there is a problem that the element main body is oxidized by oxygen in the atmosphere. When the element body is oxidized, the room temperature resistance value of the polymer PTC element at room temperature is greatly increased as compared with that before the element body is oxidized. Further, the thermal deterioration of the element body due to the above-described soldering, welding, or the like is promoted by oxidation of the element body.

  Furthermore, if the temperature rise and fall of the polymer PTC element whose element body is thermally deteriorated or oxidized is repeated, the room temperature resistance value of the polymer PTC element becomes higher. In such a polymer PTC element having a high room temperature resistance value, the power consumption increases.

  As described above, the increase in the room temperature resistance value of the polymer PTC element leads to problems such as waste of power or shortening of battery life when mounted on a small device such as a mobile phone.

  As a method for preventing oxidation of the element body, thermal degradation, and increase in the room temperature resistance value of the polymer PTC element due to these, forming a protective film on the exposed surface of the element body that is not covered with the electrode plate can be mentioned. . The protective film is formed by applying a resin having a function of shielding oxygen to the exposed surface of the element body.

In such a conventional protective film forming method, when the resin is applied to the exposed surface of the element body, the resin is applied to the surface of the electrode plate joined to the element body (the portion where the resin should not be applied). However, it becomes a problem that it is covered with a protective film. When a protective film is formed on the surface of the electrode plate, a step is formed there. When joining the terminal plate to the electrode plate, this step (because a protective film is interposed between the electrode plate and the terminal plate) causes a bonding failure. In addition, if the resin that should be applied to the element body is applied to the surface of the electrode plate, the coating thickness of the resin on the exposed surface of the element body may be reduced. As a result, there is a possibility that oxidation of the element body cannot be sufficiently prevented.
International publication WO2004 / 023499

  The present invention has been made in view of such a situation, and an object of the present invention is to provide a PTC element that can prevent the element body from being oxidized and prevent a protective film from being erroneously formed on the surface of the electrode plate. Is to provide. Another object of the present invention is to provide a battery protection system capable of effectively protecting a battery when an excessive current flows.

In order to achieve the above object, the PTC element according to the present invention includes:
An element body whose resistance value increases as the temperature rises in a predetermined temperature range;
A PTC element having a pair of first and second electrode plates bonded to the front and back surfaces of the element body,
A protective film is formed on the exposed surface of the element body that is not covered with the first and second electrode plates,
The element body has a protruding portion protruding outward from an element bonding surface with the first electrode plate. Preferably, the protruding portion protrudes outward from the element bonding surface side in the same plane direction as the element bonding surface.

  Preferably, the element body is a conductive polymer having a positive temperature coefficient.

  In the PTC element according to the present invention, it is possible to prevent the element body from being oxidized by oxygen in the atmosphere by forming a protective film on the exposed surface of the element body. Further, by preventing oxidation of the element body, it is possible to prevent an increase in the room temperature resistance value of the polymer PTC element. Further, the element body can be protected from an external impact by the protective film. That is, the mechanical strength of the element body can be improved by the protective film.

   Moreover, in the PTC element according to the present invention, the element body has a protruding portion that protrudes outward from the element bonding surface with the first electrode plate. Therefore, when resin (protective film forming resin) is applied to the exposed surface of the element body and the protective film is formed, even if the resin wraps around from the exposed surface of the element body toward the first electrode plate, The step between the surface of the first electrode plate and the surface of the protruding portion cannot be overcome. As a result, the resin does not go around on the surface of the first electrode plate and is held only on the surface of the protruding portion. That is, the resin is prevented from being applied to the surface of the first electrode plate (the side to which the terminal plate is joined). Therefore, a protective film is not formed on the surface of the first electrode plate (the side bonded to the terminal plate). Therefore, the first electrode plate and the terminal plate can be adhered and bonded satisfactorily without being interposed in the protective film.

  Further, since the protrusion prevents the protective film from being formed on the surface of the first electrode plate (the side to which the terminal plate is bonded), the bonding position between the first electrode plate and the terminal plate (terminal bonding portion) ) Can be improved in dimensional accuracy. In addition, it is possible to prevent dimensional defects in the width and thickness of the entire PTC element.

  Further, by preventing the resin that should be originally applied to the exposed surface of the element body from being applied to the surface of the first electrode plate (the surface that should not be originally coated with the resin), the exposure of the element body is achieved. The coating thickness of the resin on the surface can be made sufficient. As a result, it is possible to effectively prevent the element body from being oxidized.

  Moreover, in the PTC element according to the present invention, when the element body has the protruding portion, positioning between the element body and the first electrode plate is facilitated. That is, even when a positional deviation of about the dimension of the protruding portion or less occurs at the time of positioning, the element body and the first electrode plate are not exposed to the outside without exposing the surface on the element bonding surface side (element body side). One electrode plate can be satisfactorily bonded.

  As described above, in the PTC element according to the present invention, it is possible to prevent the element body from being oxidized. As a result, the PTC element according to the present invention can reduce the power consumption during normal use and, when necessary, the original function of cutting off the current and protecting the electronic device is effective. Can be demonstrated.

  Preferably, a terminal plate for connecting to a predetermined circuit and the first electrode plate are joined at a terminal joint located at a portion where the terminal plate and the first electrode plate overlap, and the terminal joint The protrusion is located in the vicinity of. More preferably, the protrusion is located on the entire circumference of the element body.

  When the protrusion is located in the vicinity of the terminal joint in the first electrode plate, when the resin for forming the protective film is applied to the exposed surface of the element body, the resin is on the surface of the protrusion located in the vicinity of the terminal joint. And cannot reach the terminal joint. That is, no resin is applied on the surface of the first electrode plate, and no protective film is formed. As a result, in the terminal joint portion, the first electrode plate and the terminal plate can be satisfactorily adhered and joined without being interposed in the protective film.

  In addition, since the protrusions are located on the entire circumference (four sides) of the element body, the resin can be removed from the exposed surface of the element body even when the resin is applied to any side surface (exposed surface) of the element body. Further, it is possible to reliably prevent wrapping around the surface of the first electrode plate (surface on the terminal joint portion side).

  Preferably, the terminal plate is composed of a nickel terminal plate mainly containing nickel.

  By using the terminal plate mainly composed of nickel, the strength of joining (spot welding) with the first electrode plate mainly composed of nickel can be improved.

  Preferably, the second electrode plate is bonded to a clad plate in which two or more kinds of plate materials are laminated.

  When the second electrode plate is made of a material different from that of the battery electrode, a clad plate is interposed between the second electrode plate and the battery electrode. By spot welding, the second electrode plate and the side surface of the clad plate having the same material as the second electrode plate are joined, and the side surface of the clad plate having the same material as the battery electrode is joined to the battery electrode. As a result, the connection between the second electrode plate and the battery electrode is facilitated as compared with the case where no clad plate is used.

  In the present invention, metal foil may be laminated on the front and back surfaces of the element body, and the first and second electrode plates may be bonded to each metal foil. Further, the protective film may cover at least a part of the metal foil located at the protruding portion of the element body.

The battery protection system according to the present invention includes:
A PTC element according to any of the above,
A protection circuit electrically connected to the first electrode plate of the PTC element;
A battery electrically connected to the second electrode plate of the PTC element.

  In the battery protection system according to the present invention, even when an excessive current flows, the battery can be effectively protected. Further, since the battery protection system includes the PTC element having a low room temperature resistance value, the power consumption of the battery protection system and the entire electronic device including the battery protection system can be reduced.

Hereinafter, the present invention will be described based on embodiments shown in the drawings.
FIG. 1 is a cross-sectional view of an essential part showing a use state (battery protection system) of a polymer PTC element according to an embodiment of the present invention;
2 is a cross-sectional view of the polymer PTC element shown in FIG.
FIG. 3 is an enlarged view of a part III shown in FIG.
FIG. 4 is an external view of a polymer PTC element according to an embodiment of the present invention viewed in the IV direction of FIG. 2, and shows the positional relationship among the first electrode plate, the terminal joint, the protective film, and the element body. Schematic showing,
FIG. 5 shows a method for bonding (thermocompression bonding) a first electrode plate to an element bonding surface (first surface) of an element body and a protrusion in a manufacturing process of a polymer PTC element according to an embodiment of the present invention. Schematic showing the formation method of
6A and 6B are schematic views showing a method of applying a resin for forming a protective film on the exposed surface of the element body in the manufacturing process of the polymer PTC element according to an embodiment of the present invention;
FIG. 7 shows a method of bonding (thermocompression bonding) a first electrode plate to an element bonding surface (first surface) of an element body and a protrusion in a manufacturing process of a polymer PTC element according to another embodiment of the present invention. Schematic showing the method of forming the part,
FIG. 8 is a cross-sectional view of a polymer PTC element according to another embodiment of the present invention.

Overall Configuration of Polymer PTC Element First, a polymer PTC element for protecting a secondary battery cell used as a power source of a mobile phone will be described as an embodiment of a PTC element according to the present invention.

  The polymer PTC element 2 shown in FIG. 1 is incorporated between a secondary battery cell 32 that is a power source of a mobile phone and a protection circuit 30 (predetermined circuit) for protecting the secondary battery cell 32 from overcurrent. . The polymer PTC element 2 cuts off the current between the protection circuit 30 and the secondary battery cell 32 when an abnormal increase in cell temperature due to overcharging or an overcurrent due to an external short circuit of the cell flows, and the secondary battery cell 32. Protect.

  Below, first, the whole structure of the polymer PTC element 2 is demonstrated.

  A polymer PTC element 2 shown in FIG. 1 and FIG. 2 includes an element body 4 made of a conductive polymer having a positive resistance temperature characteristic (PTC characteristic). The element body 4 has front and back surfaces (a first surface 6 and a second surface 8 facing each other). A first electrode plate 10 and a second electrode plate 12 are joined to the first surface 6 and the second surface 8, respectively. The first surface 6 of the element body 4 is bonded to the element bonding surface 11 of the first electrode plate 10. Thus, the element body 4 is disposed so as to be sandwiched between the first electrode plate 10 and the second electrode plate 12.

  The shape of the element body 4 is not particularly limited, and examples thereof include a rectangular parallelepiped type and a cylindrical type. When the shape of the element body 4 is a rectangular parallelepiped, the dimensions of the element body 4 are about 3 to 5 mm in length, 2 to 5 mm in width, and about 0.5 to 1.0 mm in thickness.

  The first electrode plate 10 is spot-welded to the terminal plate 16 at a terminal joint portion 9 (see FIG. 4) located at a portion where the terminal plate 16 and the first electrode plate 10 overlap. Terminal plate 16 is electrically connected to protection circuit 30. The first electrode plate 10 is made of nickel or a nickel alloy, and the terminal plate 16 is also made of a nickel terminal plate (a plate mainly containing nickel) that can be easily joined in spot welding with the first electrode plate 10. . Although the thickness of the 1st electrode plate 10 is not specifically limited, Usually, it is about 100-300 micrometers. The thickness of the terminal board 16 is not particularly limited, but is usually about 100 to 300 μm.

  For example, the second electrode plate 12 is spot-welded to a clad plate 18 in which two or more kinds of plate materials are laminated. The second electrode plate 12 is made of nickel metal or nickel alloy. Although the thickness of the 2nd electrode plate 12 is not specifically limited, Usually, it is about 100-300 micrometers. The length of the 2nd electrode plate 12 is not specifically limited, It designs freely according to a use.

  The clad plate 18 is composed of a laminated plate of a nickel layer 20 and an aluminum layer 22. The nickel layer 20 in the clad plate 18 is joined to the second electrode plate 12 made of nickel metal or nickel alloy by spot welding or the like. Further, the aluminum layer 22 in the clad plate 18 comes into contact with the electrode terminal 34 of the secondary battery cell 32 and is joined by spot welding or the like.

  The thickness of the clad plate 18 is not particularly limited, but is usually about 100 to 300 μm. The length of the clad plate 18 is not particularly limited and can be freely designed according to the application.

  The electrode terminal 34 of the secondary battery cell 32 is generally made of an aluminum material and is easily bonded to the aluminum layer 22 in the clad plate 18.

  In the present embodiment, as shown in FIGS. 1 and 2, a protective film 3 is formed on the exposed surface of the element body 4 that is not covered with the first electrode plate 10 and the second electrode plate 12. By forming the protective film 3, it is possible to prevent the element body 4 from being oxidized by oxygen in the atmosphere and to prevent the element body 4 from being deteriorated. Further, by preventing oxidation of the element body, it is possible to prevent the room temperature resistance value of the polymer PTC element 2 from increasing. Moreover, the element main body 4 can be protected from an external impact by the protective film 3.

  The type of the protective film 3 is not particularly limited as long as it has a function of shielding oxygen, and examples thereof include epoxy resin, EVOH (ethylene-vinyl alcohol copolymer), PVA (polyvinyl alcohol), and the like.

The thickness _{t 0} of the protective film 3 shown in FIG. 3 is not particularly limited, preferably, 30 to 500 m, more preferably about 50 to 150 [mu] m. If the thickness t ₀ is too thin, the protective film 3 cannot sufficiently prevent the element body 4 from being oxidized. When the thickness t ₀ is too thick, the resin of the other to form a protective film 3, the surface of the first electrode plate 10 is likely to be applied to the (terminal plate 16 side to be joined). Therefore, these problems can be prevented by setting the thickness t ₀ within the above range.

  In the present embodiment, the element body 4 shown in FIGS. 1 and 2 has a protruding portion 7 that protrudes outward from the element bonding surface with the first electrode plate 10. Note that the element bonding surface with the first electrode plate 10 means a region overlapping the first electrode plate 10 on the first surface 6 of the element body 4. In addition, a region overlapping with the element body 4 in the first electrode plate 10 is hereinafter referred to as a first electrode plate side element bonding surface 11.

   Since the element body 4 has the protrusions 7, when the resin is applied to the exposed surface of the element body 4 and the protective film 3 is formed, the resin wraps around from the exposed surface of the element body 4 to the first electrode plate side. Even so, the resin cannot get over the step between the surface of the first electrode plate 10 and the surface of the protrusion 7. As a result, the resin does not wrap around on the surface of the first electrode plate 10 and is held only on the surface of the protruding portion 7. That is, no resin is applied to the surface of the first electrode plate 10 (the side to which the terminal plate 16 is joined). Therefore, the protective film 3 is not formed on the surface of the first electrode plate 10 (the side to be joined to the terminal plate 16), and the first electrode plate 10 and the terminal plate 16 can be adhered and bonded satisfactorily.

  Furthermore, as shown in FIG. 3, the resin is applied to the vicinity of the step between the surface of the first electrode plate and the surface of the protruding portion (the boundary portion 31 between the element body 4 and the first electrode plate 10). The protective film 3 can be formed thick at the boundary portion 31 between the main body 4 and the first electrode plate 10. As a result, it is possible to effectively prevent the element body 4 from being oxidized.

  Moreover, as a result of preventing the protective film 3 from being formed on the surface of the first electrode plate 10 (the side to which the terminal plate 16 is joined) by the protruding portion 7, the first electrode plate 10 and the terminal plate 16 The dimensional accuracy of the joining position (the position of the terminal joining portion 9 shown in FIG. 4) can be improved. In addition, it is possible to prevent dimensional defects in the width and thickness of the polymer PTC element 2.

  In addition, by preventing the resin that should originally be applied to the exposed surface of the element body 4 from being applied to the surface of the first electrode plate 10 (the surface that should not be coated with the resin), the element body The resin coating thickness on the exposed surface 4 can be made sufficient. As a result, it is possible to effectively prevent the element body 4 from being oxidized.

  Further, in the PTC element 2 according to the present embodiment, the element body 4 has the protruding portion 7, whereby positioning between the element body 4 and the first electrode plate 10 is facilitated. That is, even when a positional deviation of about the dimension of the protrusion 7 or less occurs at the time of positioning, the element body 4 and the first electrode plate 10 are not exposed to the outside without exposing the first electrode plate-side element bonding surface 11 to the outside. Can be bonded satisfactorily.

The protrusion width W ₀ of the protrusion 7 shown in FIG. 3 is not particularly limited, but is preferably about 500 to 1000 μm with respect to the end of the first electrode plate 10.

If the protruding width W ₀ is too small, the resin may wrap around from the exposed surface of the element body 4 to the surface of the first electrode plate 10. If the protrusion width W ₀ is too large, the resin does not sufficiently enter the boundary portion 31 between the element body 4 and the first electrode plate 10 when the protective film 3 is formed on the exposed surface of the element body 4. The resin may not be applied. As a result, the protective film 3 at the boundary portion 31 cannot be made sufficiently thick, and the element body 4 may not be sufficiently prevented from being oxidized. Therefore, these problems can be prevented by setting the protruding width W ₀ within the above range.

  As shown in FIG. 4, the protrusion 7 is preferably located in the vicinity of the terminal joint 9. More preferably, the protruding portion 7 is located on the entire circumference of the element body 4. In other words, the area of the first surface 6 in the element body 4 shown in FIGS. 1 and 2 is preferably larger than the area of the first electrode plate-side element bonding surface 11 in the first electrode plate 10. That is, the first electrode plate side element bonding surface 11 is preferably completely covered by the first surface 6 of the element body 4.

  As shown in FIG. 4, the protrusion 7 of the element body 4 is positioned in the vicinity of the terminal joint 9 in the first electrode plate 10, so that a resin for forming a protective film is applied to the exposed surface of the element body 4. At this time, the resin is held on the surface of the protruding portion 7 located in the vicinity of the terminal joint portion 9. Therefore, the resin cannot wrap around on the surface of the first electrode plate 10. As a result, in the terminal joint portion 9, the first electrode plate 10 and the terminal plate 16 can be satisfactorily adhered and joined (spot welded) without being interposed in the protective film 3 (resin).

  When there is no protrusion 7 in the vicinity of the terminal joint 9, the protective film 3 is formed up to the vicinity of the terminal joint 9, and a step is generated between the protective film 3 and the surface of the first electrode plate 10. If the first electrode plate 10 and the terminal plate 16 are to be joined at the stepped portion, they cannot be brought into close contact with each other due to the step, resulting in poor bonding. Therefore, this problem can be prevented by positioning the protrusion 7 in the vicinity of the terminal joint 9.

  Further, the protruding portion 7 is located on the entire circumference (four sides of the rectangle) of the element body 4 so as to surround the first electrode plate 10. As a result, even when the resin is applied to any side surface of the element body 4, even if the resin wraps around from the exposed surface of the element body 4 to the first electrode plate 10, the resin remains on the surface of the protrusion 7. Retained. Therefore, it is possible to reliably prevent the protective film 3 from being formed on the surface of the first electrode plate 10 without the resin flowing around on the surface of the first electrode plate 10.

  Further, since the area of the first surface 6 of the element body 4 shown in FIG. 2 is larger than the area of the first electrode plate side element bonding surface 11, the element body 4 is bonded to the element body 4 and the first electrode plate 10. 4 makes it easy to position the first electrode plate 10. That is, even if there is some deviation in positioning between the element body 4 and the first electrode plate 10 during bonding, a part of the first electrode plate-side element bonding surface 11 is exposed to the outside. Can be prevented.

  Further, in the present embodiment, the second electrode plate 12 shown in FIG. 1 has an electrode plate protrusion 77 protruding outward from the element joint surface with the element body 4.

  By having the electrode plate protrusion 77, when the resin is applied to the exposed surface of the element body 4 and the protective film 3 is formed, the surface of the second electrode plate 12 (the clad plate 18 is formed from the exposed surface of the element body 4. Resin that tends to go around to the side to be joined is blocked by the electrode plate protrusion 77. That is, it is possible to prevent the resin from being applied to the surface of the second electrode plate 12. Therefore, the protective film 3 is not formed on the surface of the second electrode plate 12, and the second electrode plate 12 and the clad plate 18 (and the spacer 36) can be adhered and bonded satisfactorily.

Manufacturing Method of Polymer PTC Element 2 Next, a manufacturing method of the polymer PTC element 2 shown in FIGS.

(Element body 4)
The element body 4 is generally composed of a resin composition (conductive polymer) including a polymer (polymer compound such as a thermosetting resin or a thermoplastic resin) as main components and conductive particles. The element body 4 may include both a thermosetting resin and a thermoplastic resin as a polymer.

  First, a polymer compound (thermosetting resin, thermoplastic resin, etc.), conductive particles (metal powder, carbon black, etc.), a low molecular organic compound, a reaction initiator for cross-linking the polymer compounds, etc. Weigh and knead to adjust the PTC composition. The kneading method is not particularly limited, and examples thereof include a kneader, an extruder, and a mill. Further, as the conductive particles to be contained in the PTC composition, only conductive particles having a predetermined particle diameter are classified using a sieve or the like. Next, this PTC composition is shape | molded and the element main body 4 (FIG. 1) is obtained.

  Although it does not specifically limit as a thermosetting resin, An epoxy resin, a polyimide resin, unsaturated polyester resin, a silicon resin, a polyurethane resin, a phenol resin, etc. are mentioned. Preferably, an epoxy resin is used as the thermosetting resin. By using an epoxy resin, the polymer PTC element can have a sufficient resistance change amount and heat resistance. As for the molecular weight of the thermosetting resin, the weight average molecular weight Mw is usually about 300 to 10,000. Said thermosetting resin may be used independently and multiple types of resin may be used. Moreover, you may use the compound which has a structure where different kinds of thermosetting resins were bridge | crosslinked.

  Although it does not specifically limit as a thermoplastic resin, Preferably, a crystalline polymer is used. The melting point of the thermoplastic resin is not particularly limited, but is preferably about 70 to 200 ° C. By using a resin having a melting point within this range, it is possible to prevent the thermoplastic resin from melting and flowing and the element body 4 from being deformed during the operation of the polymer PTC element.

  The thermoplastic resin is not particularly limited, but polyolefins such as polyethylene, copolymers such as ethylene-vinyl acetate copolymer, vinyl halides such as polyvinyl chloride, polyvinyl fluoride, and polyvinylidene fluoride, and vinylidene polymers, 12- Examples thereof include polyamide such as nylon, polystyrene, polyacrylonitrile, thermoplastic elastomer, polyethylene oxide, polyacetal, thermoplastic modified cellulose, polysulfones, polymethyl (meth) acrylate and the like.

  Although the weight average molecular weight Mw of a thermoplastic resin is not specifically limited, Preferably, it is 10000-5 million. These thermoplastic resins may be used alone or a plurality of types of resins may be used. Moreover, you may use the compound which has a structure where different types of thermoplastic resins were bridge | crosslinked.

  Although it does not specifically limit as electroconductive particle contained in the element main body 4, Metal powder, carbon black, etc. are illustrated. Preferably, metal powder is used as the conductive particles. As the metal powder, a powder mainly composed of nickel is preferably used. The average particle diameter of the metal powder is preferably 0.1 μm or more, and more preferably about 0.5 to 4.0 μm.

  In the element body 4, the content of the conductive particles in the resin composition is preferably 20 to 80% by mass with respect to the entire resin composition. By setting the content of the conductive particles within this range, the room temperature resistance value during non-operation can be sufficiently lowered, and a large resistance change amount can be obtained. Furthermore, variation in element resistance can be sufficiently reduced.

  The resin composition constituting the element body 4 further includes, for example, a low-molecular organic compound such as wax, oil, fatty acid, and higher alcohol in addition to the above-described thermosetting resin, thermoplastic resin, and conductive particles. But you can. As a result, it is possible to increase the resistance change amount accompanying the temperature rise of the element body 4.

  The element body 4 may include a base material that has a gap inside and can fill the gap with the resin composition. Such a substrate is not particularly limited as long as it can play the above role, and examples thereof include woven fabrics, nonwoven fabrics, and continuous porous bodies.

  The element body 4 is irradiated with an electron beam as necessary. By this electron beam irradiation, the reaction initiator functions and the cross-linking reaction between the polymers is promoted. The energy source for the crosslinking reaction is not limited to electron beams, and gamma rays, ultraviolet rays, heat, and the like are also used. What is necessary is just to adjust suitably the acceleration voltage and electron beam irradiation amount of the electron beam to irradiate according to the kind of high molecular compound contained in the element main body 4, or the dimension of an element main body. The electron beam irradiation may be performed after the electrode plates 10 and 12 are joined.

(Formation of the first electrode plate 10 and the second electrode plate 12)
The first metal plate 10 and the second metal plate 12 are formed by punching a nickel metal plate or nickel alloy plate having a predetermined thickness.

Next, the second electrode plate 12 is thermocompression bonded to the second surface 8 of the front and back surfaces of the element body 4 by a hot press machine or the like. Although the heating temperature at the time of thermocompression bonding depends on the material of the element body 4, it is preferably about 130 to 180 ° C. The pressure during thermocompression bonding is preferably about 1 × 10 ^{6 to} 20 × 10 ⁶ Pa.

(Formation of protrusion 7)
Next, or before and after that, the first electrode plate 10 is thermocompression bonded to the first surface 6 of the front and back surfaces of the element body 4 by a hot press machine or the like. As shown in FIG. 5, when the first electrode plate 10 is thermocompression bonded to the first surface 6 of the element body 4 with a pressure P, the element body 4 is slightly crushed in the thickness direction by the pressurization, so that the first electrode It protrudes slightly to the side of the plate 10. This protruding portion becomes the protruding portion 7. The protrusion 7 is adjusted so that only the protrusion width W ₀ protrudes laterally with respect to the element body 4 before thermocompression bonding.

The heating temperature when the first electrode plate 10 is thermocompression bonded to the first surface 6 of the element body 4 is preferably about 130 to 180 ° C. although it depends on the material of the element body 4. Moreover, the pressure P at the time of thermocompression bonding is preferably about 1 × 10 ^{6 to} 20 × 10 ⁶ Pa. In addition, the protrusion width W ₀ of the protrusion 7 is controlled to be in the range of 500 to 1000 μm by appropriately adjusting the process conditions such as the heating temperature at the time of thermocompression bonding and the pressure P within the above range. .

(Formation of protective film 3)
Next, the protective film 3 is formed on the exposed surface of the element body 4 that is not covered with the first electrode plate 10 and the second electrode plate 12. A method for forming the protective film 3 is not particularly limited, and examples thereof include a method in which the above-described resin is applied and dried as described below.

  First, the plate 50 shown in FIG. 6A is immersed in a liquid reservoir (not shown) filled with resin. Next, by lifting the plate 50 from the liquid reservoir, the protective film forming resin 3 a adheres to the surface of the plate 50.

  Next, the tip of the application rod 52 is pressed against the resin 3 a attached to the surface of the plate 50. As a result, the resin 3 a adheres to the tip of the application rod 52.

  Next, as shown in FIG. 6B, the tip of the application bar 52 to which the resin 3 a is attached is pressed against the exposed surface of the element body 4. By performing this pressing operation on the entire exposed surface of the element body 4, the resin 3 a is applied to the entire exposed surface of the element body 4. Next, the resin 3a applied to the exposed surface of the element body 4 is dried to form the protective film 3 shown in FIGS.

  Note that the dimension of the tip of the application bar 52 pressed against the element body 4 is preferably equal to or smaller than the dimension of the exposed surface (side surface) of the element body 4. If the dimension of the tip of the application bar 52 is too large, the resin 3a may be applied to the surface of the first electrode plate 10. Therefore, such a problem can be prevented by setting the size of the tip of the application bar 52 to be equal to or less than the size of the exposed surface (side surface) of the element body 4.

  In this way, as shown in FIGS. 1 and 2, the polymer PTC element 2 according to the present embodiment is completed.

Assembling Method of Polymer PTC Element 2 The polymer PTC element 2 is assembled between the secondary battery cell 32 and the protection circuit 30 as shown in FIG. In order to connect the polymer PTC element 2 as shown in FIG. 1, for example, first, the second electrode plate 12 in the element 2 is spot-welded to the nickel layer 20 side of the clad plate 18.

  Next or before and after that, the aluminum layer 22 on the clad plate 18 is spot-welded in contact with the electrode terminals 34 of the secondary battery cells 32. When a gap is formed between the element 2 and the secondary battery cell 32, the spacer 36 or the like is disposed between the element 2 and the secondary battery cell 32.

  Next, or before and after, the terminal plate 16 connected to the protection circuit 30 is spot-welded and joined to the first metal plate 10 at the terminal joining portion 9 (see FIG. 4).

  Thus, as shown in FIG. 1, the battery protection system 1 having the polymer PTC element 2, the protection circuit 30, and the secondary battery cell 32 is completed.

  In the polymer PTC element 2 according to this embodiment, as shown in FIGS. 1 and 2, the protective film 3 is formed on the exposed surface of the element body 4 that is not covered with the first electrode plate 10 and the second electrode plate 12. The

  By forming the protective film 3 on the exposed surface of the element body 4, the element body 4 can be prevented from being oxidized by oxygen in the atmosphere. Further, by preventing the element body 4 from being oxidized, an increase in the room temperature resistance value of the polymer PTC element 2 can be prevented. Further, the mechanical strength of the element body can be improved by the protective film.

  Further, the polymer PTC element 2 according to the present embodiment has a protruding portion 7 in which the element body 4 protrudes outward from the element bonding surface with the first electrode plate 10. Therefore, as shown in FIGS. 6A and 6B, when the resin 3 a (protective film forming resin) is applied to the exposed surface of the element body 7 and the protective film 3 is formed, the resin is removed from the exposed surface of the element body 4. Even if the resin 3a goes around to the side of the one electrode plate 10, the resin 3a cannot get over the step between the surface of the first electrode plate and the surface of the protruding portion. As a result, the resin 3a does not wrap around on the surface of the first electrode plate and is held only on the surface of the protruding portion 7. That is, the resin 3a is not applied to the surface of the first electrode plate 10 (the side to which the terminal plate is bonded). Therefore, the protective film 3 is not formed on the surface of the first electrode plate 10 (the side to be bonded to the terminal plate), and the first electrode plate 10 and the terminal plate 16 are well adhered and bonded as shown in FIG. Can be made.

  Further, as shown in FIG. 3, the resin 3 a is applied to the vicinity of the step between the surface of the first electrode plate and the surface of the protruding portion (boundary portion 31 between the element body 4 and the end of the first electrode plate 10). Accordingly, the protective film 3 can be formed thick at the boundary 31 between the element body 4 and the first electrode plate 10. As a result, it is possible to effectively prevent the element body 4 from being oxidized.

  Moreover, since the protective film 3 is prevented from being formed on the surface of the first electrode plate 10 (the side to which the terminal plate 16 is bonded) by the protruding portion 7, the first electrode plate 10 and the terminal plate 16 The accuracy of the joining position (position of the terminal joining portion 9 shown in FIG. 4) can be improved. In addition, it is possible to prevent dimensional defects in the width and thickness of the entire polymer PTC element.

  Further, by preventing the resin 3a originally to be applied to the exposed surface of the element body 4 from being applied to the surface of the first electrode plate 10 (the surface that should not be originally applied with the resin 3a), The coating thickness of the resin 3a (protective film 3) on the exposed surface of the element body 4 can be made sufficient. As a result, it is possible to effectively prevent the element body 4 from being oxidized.

  In addition, since the element body 4 has the protrusions 7, when the element body 4 and the first electrode plate 10 are joined, positioning between the two becomes easy. That is, even when a positional deviation of about the dimension of the protrusion 7 or less occurs at the time of positioning, the element body 4 and the first electrode plate 10 are not exposed to the outside without exposing the first electrode plate-side element bonding surface 11 to the outside. Can be bonded satisfactorily.

  As described above, in the polymer PTC element 2 according to the present embodiment, the element body 4 can be prevented from being oxidized. As a result, in the polymer PTC element 2 according to the present embodiment, the power consumption can be reduced during normal use, and when necessary, the current is interrupted to protect the electronic device. The function can be exhibited effectively.

  Further, in the battery protection system 1 having the polymer PTC element 2, the protection circuit 30, and the secondary battery cell 32 according to the present embodiment, even if an excessive current flows or an impact or pressure acts, The battery can be effectively protected.

  The present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the present invention.

  For example, the polymer PTC element 2 according to the present invention is used not only as an overcurrent protection element for the secondary battery cell 32 but also as a self-control heating element, a temperature sensor, a current limiting element, an overcurrent protection element, and the like. It is possible.

  In the present invention, the method for producing the polymer PTC element 2 is not particularly limited. For example, as in the above-described embodiment, the polymer PTC element 2 is manufactured as follows without joining the element body 4, the first electrode plate 10, and the second electrode plate 12 to each other alone. May be. That is, the sheet-like element body constituting the element body 4 after cutting and the pair of sheet-like electrodes that respectively constitute the first electrode plate 10 and the second electrode plate 12 after cutting are unnecessary after thermocompression bonding. Individual polymer PTC elements 2 may be formed by punching out the parts with a press. In that case, the efficiency of the manufacturing process of the polymer PTC element 2 can be improved by joining the assembly of parts constituting the polymer PTC element 2 at a time.

In the above-described embodiment, as shown in FIG. 5, when the first electrode plate 10 is thermocompression bonded to the element body 4, the protruding portion 7 is formed by protruding the element body 4 to the side of the first electrode plate 10. Form. The formation method of the protrusion part 7 is not restricted to this, For example, as shown in FIG. 7, with respect to the 1st surface 6 of the element main body 4, the 1st electrode side element junction surface 11 whose area is smaller than the 1st surface 6 is shown. The excess protruding portion 72 protruding by thermocompression bonding may be removed. As a result, the protruding portion 7 is formed. When forming the protrusion 7, the excess protrusion 72 is removed so that the protrusion width W ₀ of the protrusion 7 is in the range of 500 to 1000 μm. Even in this case, the same effect as the above-described embodiment can be obtained.

  Moreover, as shown in FIG. 8, the metal foil 60 may be formed in the front and back of the element main body 4 (polymer layer which consists only of conductive polymers). The element body 4 can be formed, for example, by hot pressing the metal foil 60 on both surfaces of a sheet-like polymer layer and then punching it out to a predetermined dimension. The first electrode plate 10 and the metal foil 60 are joined via a solder layer 62. The clad plate 18 and the metal foil 60 are also joined via the solder layer 62. Even in this case, the same effect as the above-described embodiment can be obtained. The thickness of the metal foil 60 is thinner than the thickness of the first electrode plate 10 and is generally about 25 to 30 μm. In FIG. 8, the clad plate 18 also functions as a second electrode plate. The clad plate 18 has a clad plate protrusion 88 protruding outward from the element joint surface with the element body 4. Further, as shown in FIG. 8, the protective film 3 covers at least a part of the metal foil 60 located on the protruding portion 7 of the element body 4.

FIG. 1 is a cross-sectional view of a principal part showing a usage state (battery protection system) of a PTC element according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of the PTC element shown in FIG. FIG. 3 is an enlarged view of a part III shown in FIG. FIG. 4 is an external view of a polymer PTC element according to an embodiment of the present invention viewed in the IV direction of FIG. 2, and shows the positional relationship among the first electrode plate, the terminal joint, the protective film, and the element body. FIG. FIG. 5 shows a method for bonding (thermocompression bonding) a first electrode plate to an element bonding surface (first surface) of an element body, and a protrusion in a manufacturing process of a polymer PTC element according to an embodiment of the present invention. It is the schematic which shows the formation method of these. FIG. 6A is a schematic view showing a method for applying a resin for forming a protective film to the exposed surface of the element body in the manufacturing process of the polymer PTC element according to one embodiment of the present invention. FIG. 6B is a schematic view showing a method of applying a protective film-forming resin to the exposed surface of the element body in the manufacturing process of the polymer PTC element according to an embodiment of the present invention. FIG. 7 shows a method for bonding (thermocompression bonding) the first electrode plate to the element bonding surface (first surface) of the element main body and the protrusion in the manufacturing process of the polymer PTC element according to another embodiment of the present invention. It is the schematic which shows the formation method of these. FIG. 8 is a cross-sectional view of a polymer PTC element according to another embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Battery protection system 2 ... Polymer PTC element 3 ... Protective film 4 ... Element main body 6 ... 1st surface 8 ... 2nd surface 7 ... Protrusion part 10 ... 1st electrode board 12 ... 2nd electrode board 16 ... Terminal board 18 ... Clad plate 30 ... Protection circuit 32 ... Secondary battery cell 34 ... Electrode terminal 60 ... Metal foil 62 ... Solder layer

Claims (8)

An element body that is a conductive polymer having a positive temperature coefficient in which a resistance value increases as the temperature rises in a predetermined temperature range;
A PTC element having a pair of first and second electrode plates bonded to the front and back surfaces of the element body,
By thermocompression-bonding the first electrode plate to the element body and causing the element body to protrude to the side of the first electrode plate, the element body is outward from the element bonding surface with the first electrode plate. have a device projecting portion that protrudes in,
The element protrusion is formed with a width of 500 to 1000 μm so as to have a step between the surface of the first electrode plate and the surface of the element protrusion.
The element body has a rectangular parallelepiped shape of 3 to 5 mm in length and 2 to 5 mm in width,
The first electrode plate has a thickness of 100 to 300 μm,
A protective film is formed on the exposed surface of the element body that is not covered with the first and second electrode plates,
The protective film has a thickness of 50 to 150 μm,
PTC element only the second electrode plate, outward from the element junction surface between the element body, characterized in that it have the electrode plates projecting portion that protrudes more than the thickness of the protective film. A terminal plate for connecting to a predetermined circuit and the first electrode plate are joined at a terminal joining portion located at a portion where the terminal plate and the first electrode plate overlap,
The PTC element according to claim 1, wherein the element projecting portion is positioned in the vicinity of the terminal joint portion. The PTC element according to claim 1 , wherein the element projecting portion is located on the entire circumference of the element body. The PTC element according to claim 2 , wherein the terminal plate is formed of a nickel terminal plate mainly containing nickel. The PTC element according to any one of claims 1 to 4 , wherein the second electrode plate is bonded to a clad plate in which two or more kinds of plate materials are laminated. The PTC element according to any one of claims 1 to 5 , wherein metal foils are laminated on the front and back surfaces of the element body, and the first and second electrode plates are bonded to each metal foil. . The PTC element according to claim 6 , wherein the protective film covers at least a part of the metal foil located at the element protruding portion of the element body. A PTC element according to any one of claims 1 to 7 ,
A protection circuit electrically connected to the first electrode plate of the PTC element;
A battery protection system comprising: a battery electrically connected to the second electrode plate of the PTC element.

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