Title of Invention

"METHOD OF MOLDING A CASE FOR A STORAGE BATTERY"

Abstract

An object of the present invention is to provide a technique of forming a storage battery case including a plurality of cell chambers partitioned by partition walls, in which the thickness of a partition wall located r.rst close tc the outer wall is equalized substantially to the thickness cf other partition walls, thereby preventing the occurrence of cracking in the partition wall most close tc the outer wall. To achieve this, the first .injection qate is provided to be located in the -old at substantially a central position cf a bottom surface of each of the cell chambers in the battery case, and the second injection gate IG vrovided to be located in the mold at substantially a position corresponding to a bottcrr. portion c: the partition wall that partition the cell chamber ".coated a~ an end portion of the storage case and a next cell chamber adjacent thereto. Then, molten resin is _njected trcm the first injection gate and second .1:. ection o^te at the same time to mold a storage Jc..-.ttery ci.;e.

Full Text

TITLE OF THE INVENTION METHOD OF MOLDING CASE FOR SECONDARY BATTERY BACKGROUND OF THE INVENTION The present invention relates to a method of molding a synthetic resin-made case for a secondary battery, in which a plurality of cell chambers are forced by partitioning the inside by partition walls, by 3. way ;:f injection molding. The conventional secondary battery case is a synthetic resin-made container, in which a plurality of cell chambers are formed by partitioning the inside with partition walls. Usually, the thickness of the outer wall of the case is formed thicker than that of the partition walls of the cell chambers, and thus the case can withstand externally applied shocks. Secondary battery cases of such a type are formed by an infection molding method with use of a metal mold. Jpn. Pat. Appln. KOKAI Publication No. - 48-100237 anc Jpn. Pat. Appln. KOKOKU Publication No. 48-36929 discloses prior art techniques of the molding of secondary battery cases. In both of the above-mentioned prior art techniques, the injection molding is employed, and the battery case is formed by the method in which molten resin is injected into a mold from an injection gate provided in the mold which corresponds to the bottom portion of the case. FIG. 7 is a simplified view of the former one of the prior art techniques, and it shows a oottom surface of a battery case formed by the injection molding. FIG. 7 shows a battery case 30, an outer wall 32 of the case, partition walls 33 provided inside the case and cell chambers 34 partitioned by the parti tier, walls. The battery case 30 is formed by the fcllowir..:: procedure. That is, a mold provided with i n~ ect i -. :;•. gates is used, and resin is injected from the gar. es, tr.ereby forming the case. The injection gates are provided at respective positions corresponding to, those of -he partition walls of the cell chambers 34 and the ;:ottom surface of the outer wall 32 of the case. Therefore, injection gate marks 35 which were made during the molding remain at the positions of the qares a i. *Jie bottom section of the case. The example shown in this figure is a battery case including six cell chambers 34 partitioned by five partition walls. On rhe other hand, the latter prior art document describes that molten resin is injected from injection gates or a mold which corresponds to the bottom portion of the battery case 40 in a similar manner to that describe,: above, as shown in FIG. 8. FIG. 8 is a view of the bottom portion of the battery case 40 formed by the injection molding and it shows an outer wall 42 of the battery case, partition walls 43 provided inside the case and cell chambers 44 partitioned by the partition walls. This example is also a case including six cell chambers, and injection gate marks 45 formed during the molding remain in the bottom portion as shown in the figure. The injection molding marks 45 are each located at approximately the central portion of each respective cell chamber 44 of the battery case 40. The above-described conventional method of melding a case u>i ^ storage battery entails the foliowinc drawback. That is, the molten resin does not sufficiently sneak into the outermost partition wall (the partition wall most close to the outer: wall) of the plurality of number of the partition walls in "he case. For this reason, according to the conventicnal method, the partition wall located at. the outermost side in the case is easily cracked in some cases, or part of the molded product remains on the mold when the product Is unloaded from the mold, thereby creating some trouble in the later step. Thus, the conventional method entails such problems as low workability and low product yield. The inventor of the present invention carried out intensive and various studies on the cause for the above-described drawbacks in the injection molding, and came to focus on the point that the thickness of the outer wall of the case is different from the thickness of the partition walls located close to the outer wall and partitioning the cell chambers. Finally, the inventor found the following technical fact. That is, during injection molding, the flow resistance of molten resin is lower at the section for the thick outer wall as compared to that of the section for the thin partition walls of the cell chambers. Accordingly, a more amount of the molten resin flows into the portion for the thick outer wall. In other words, the flow resistance of the injected molten resin is higher at the sect Jons for the partition walls of the cell chambers, which are thinner than that of the section for the thick outer wall. Accordingly, a less amount of the molten resin flows .into these areas. For the reason provided above, during the injection molding process, the core in the mold is pushed inwards and therefore the thickness of the partition wall 33 (z) (in FIG. 7) or the partition wall 43 (z) (in FIG. 8), which is most close to the outer wall, is reduced, thereby lowering the strength of the partition wall. Thus, the inventor found the cause for the drawback created in the conventional technique, in which the partition wall of the above-mentioned part is cracked in some cases when the molded product is unloaded from the mold. BRIEF SUMMARY OF THE INVENTION As described above, an object of the present invention is to assure sufficient flow of injected resin even in a partition wall located most close to an outer wall in the process of forming a case for a storage battery provided with a plurality of cell chambers partitioned with partition walls inside the case by injection molding. Further, another object of the invention is to provide a technique of forcing a battery case in which the thickness of a partition wall located me=t close to the outer wall is equalized substantially to the thickness of other partition walls, thereby preventing the occurrence of cracking in the partition wall most close to the outer wall. Anotr.er object of the present invention is to avoid a part of a molded storage case provided with a plurality cf cell chambers partitioned by partition walls inside the case, from remaining on the mold when the product, is unloaded from the mold, which may create some trouble in the later step. Further, another object of rhe invention is to manufacture a storage battery case at-a high workability and a high p r o d u c t i o r. y i e 1 d . In order to achieve the above-described object, the preser.T, invention has such a structure that when molding u storage battery case including a plurality of cell chambers partitioned by partition walls inside by an injection molding method which uses a mold, the first injection gate is provided to be located in the mold at substantially a central position of a bottom surface of each of the cell chambers in the battery case. Further, the second injection gate is provided to be located in the mold at substantially a position corresponding to a bottom portion of the partition wall that partition the cell chamber located at an end portion of the storage case and a next cell chamber adjacent thereto. With the above-described structure, molten resin is ir.jected from the first injection gate and second injection gate at the same time to mold a s t o r a ge b a 11 e ry case. According tc the present invention, the molten resin is injected quickly and surely also to the position corresponding to the bottom portion of the partition wail that partition the cell chamber located at an end portion of the storage case and a next cell chamber adjacent thereto. Therefore, the partition wall of I his portion of the case can be formed to have a thickness as designed, and thus it is possible to achieve >.t battery case .including partition walls of a sufficient strength. Additional objects and advantages of the invention will be set forth in the description which follows, and in part will oe covious from the description, or r:.ay be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention. FIG. 1 is a perspective view showing a storage battery ca.~e obtained by a molding method according to an_ embodiment of the present invention; FIG. 1 is a bottom view of the storage battery case obtained by the molding method according to the embodiment of the present invention; FIG. ? is a partially cut-away lateral view of the storage battery case shown in FIG. 2; FIG. 4 is a bottom view of a mold used to form the storage battery case shown in FIG. 2; FIG. 3 is a partially cut-away lateral view of the storage battery case shown in FIG. 4; FIG. c is a bottom view of a battery case in which cell chambers are arranged in two lines; FIG. ~ is a bottom view of a conventional storage battery case; and FIG. 8 is a bottom view of another storage battery case. DETAILED DESCRIPTION OF THE INVENTION FIG. 1 is a perspective view showing a storage battery case obtained by an embodiment of the present invention. FIG. 1 shows a battery case 50, partition walls 52, cell chambers 53 and an outer wall 54. FIG. 2 is a bottom view of the storage battery case. FIG. 3 is a partially cut-away lateral view of the storage battery case shown in FIG. 2. As shown in FIGS. 2 and 3, the battery cell 50 is enclosed with the outer wall 54, and six rectangular-shaped cell chambers 4 are defined with the partition walls 53 formed inside the cell. Further, as,shown in FIGS. 2 and 3, in this battery case, like in general battery cases, the thickness of the outer wall 2 is made thicker than that of the partition walls 3 that partition the cell chambers 4. The battery case 1 is formed by the injection molding method using a mold. FIG. 2 shows marks 5 and 6 of the injection gates through which rein was injected in the injection molding. The injection gate mark 5 is a mark of the first injection gate formed substantially at a center of the bottom surface of each cell chamber 4. On the other hand, the injection gate mark 6 is a mark of the second injection gate located at the bottom portion of the partition wall 3z that partitions the cell chamber 4z located at the end of the battery case 1 and an inner-side cell chamber 4y located adjacent to the cell chamber 4z from each other. The molding of the storage case shown in FIGS. 2 and 3 is carried out using a mold indicated in FIGS. 4 and 5. FIG. 4 is a bottom view of the mold 20 used to form the battery case shown in FIGS. 2 and 3. FIG. 5 is a partially cut-away lateral view of the mold 20. As shown in FIG. 4, the mold 20 includes injection gates 2 ':> ar.d 26 or. its bottom surface, through v.-hich the resin is injected into the mold. The arrangement of the injection gates is as follows. That is, as shown in FIG. A, the first injection gate 25 is set at a position corresponding to the center of the bottom surface of each cell chamber to be molded in the battery case. Further, the second injection gate 26 is set at. a position corresponding to the bottom portion of the partition wail 3z that partitions the cell chamber 4z molded at the end of the battery case 1 and the cell chamber 4y located in an inner side to be adjacent to the cell chamber 4z, from each othe-r. As shown in FIGS. 2 and 4, the second injection gate is provided one for each side of the battery case. A molten resin, for example, a molten propylene resin is injected into the mold 2Q from both of the first and second injection gates 25 and 26 at the same time, thereby molding the case. FIG. 5 is a lateral cross section of the mold provided with the first injection gate and the second injection gate. FIGS. 4 and 5 show an outer wall forming portion 22 of the mold and a partition wall forming portion 23. As described above, the first injection gate 25 is provided at the center of the bottom surface of those of the partition walls which are located in the middle section of the battery case 20 to be molded. With this structure, the injection pressure acts equally or.to each of those of the partition '.vail forming portions 23 situated -iz the middle section of the battery case 20 to be moiued, and therefore the resin is injected equally tc the entire section. Further, according to the present invention, the second injection gate 26 is set at the section corresponding to the bottom portion of the partition wall 23z that partitions the cell chamber -Iz located at the end and the cell chamber 4y located adjacent to the cell chamber 4z, from each other. Kith this arrangement, even if the amount of the resir. supplied to the partition wall forming portion 23z is decreased as-the outer wall forming portion 22 that is designed to form the thick outer wall takes up a great amount of the resin, the resin is injected to the partition wall forming portion 23 from the secor.a injection gate 26. As described above, the resin injected from the first injection gate 25z situated at the center of the bottom of the outermost cell chamber 4z flows into the outer wall forming portion 22 to form the outer wall. At the same time, the partition wall forming portion 23z is replenished with the resin injected via "he second injection gate 26. Thus, a sufficient arr.cunt of the resin is supplied to the partition wall forming portion 23z located at the outermost side. In this manner, all the partition walls can be formed tc have an equal thickness. It should be ncted that the second injection oiaoe 26 should preferably be provided ao a position corresponding to a longitudinal oentral portion of one partition, wall. According to the present invention, one cell chamber.'; of the battery case rr.ay be formed in rectangular and arranged in or.e line such, that ohe short sides of the rectangular chambers are disposed along with one longitudinal direction of one baooery case. Kuror.er, it is alternatively possible as shown in FIG. 6 that the chambers have rectangular opening surface.-.; ar.a are arranged in o ow lines such thao the short sides of the rectangular chambers are disposed along with the longitudinal direction of one baooery case. In this alternative case, the firso injection gate 60 ar.c the second injection date 61 are provided at the respective positions as shown in FIG. 6. It should be noted that FIG. f, shows an outermost cell chamber (51 o . Example I A storage cell case including cell chambers 53 formed by five partition walls to have rectangular opening surfaces as shown in FIG. 1 were molded by injection rr.olding using a mold shown in FIGS. 4 and 5. The triickr.ess of the outer wall of the case was set to 3.0 mm arid the thickness of each partition wall was set to 1.6 mm. The first injection gate 25 and the second injection ..ate 26 of the mold were located as shown in ••'pi/ci f ica 1 Ly, the 't:st injection gate 25 was at a position corresponding to the center of it surface of each cell chamber 4. Meanwhile, d .njection gate ':b was situated at a position d;..tq to the bottom portion of each of the parti i ioii .-.,-.Us 3z partitioning the coll chamber 4z located at -'ach of the right and ;el:t ends of the bat1, ery -•-.!.-•.• 1 ^nd the cell oh.-rnbo-t 4y located i:t an inrei. side to be adjacent to each cell chamber 4~, as F'. '•. 2, A polypro'pylene molten resin was i:'to tto modd through these injection gates 25 ,n..: thu..- the battery case was formed. After the injection oi the resin, when the resin was cooJ bending and cracking especially in the outermost; part-it 10:, walls of the battery case. The results are shown in Table 1 below. Comparative Example 1 Ui.crO of storage cell cases were molded using a •: Y/ded with injection gates 35 fonr.eci ir. the I r:. ion of each partition wall 33 and the bottom : each .side of the outer wa 1 L 32 that Is in ; ,• j.. i: h the partition walls 33 as shown i:\ Yr.jer the same conditions as those of Example .-. ; : ded cases were then inspected i_n terns of aefec! .-• s ;,:h as, bending and cracking especially in the 'n.t'.--nr:. •:•:• partition walls of the battery case. The r es;; 11':•• ;: v- shown in Table 1 below. '"• :: i- rat ive Example 2 ]:';,,. ;n of storage cell cases were molded using a mold {.-'lovided only with an injection gate 45 formed at a pcs.ii i-"•/. corresponding to the center of the bottom portion c: each partition wall 44 as shown in FIG. 8 and withcY.t a second injection gate provided ur.like in Examp]-! 1, under the same conditions as those of Kxampl'i -. The molded cases were then inspected in terms -A. defects such as, bending and cracking especially in the outermost partition walls of the battery case. The results are shown in Table 1 below. Table I (Table Remove) Additional advantages and rr.odifications wi'. . readily occur to those skilled in the art. Ther-tore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown ana described herein. Accordingly, various modifications may be made without departing fron: the spirit or scope of the general inventive concept as defined ry the appended claims and their equivalents. WHAT IS CLAIMED IS: 1. A metre:: of molding a storage battery case including a plurality of cell chambers partitioned by partition walls inside by an injection molding method using a mold, the method wherein a first injection gate is provided to ;:e located in the mold at substar.-ially a central posit_:n ef a bottom surface of each cf the ceil ceauibers i:~. -p.e battery case, a second injection gate i e provide:; ~:.c be located in the mold at suo:.; t ar.r ia 1 ly a position corresponding to a bottom porticr. of the partition wall that partition the cell chamber located i': an end portion of the storage case and a next cell -jr.ar.ber adjacent thereto, and molten resin is injected from the first injection gate and second i :vjectio:: :?a7e, vhereby forming the storage battery cnse. ;:: . The me-':.'id aecerding ~o claim 1, wherein the second : irject Lor. "jare is ..ocated at" a position in the meld, v;h icn cor: espenos 1:o a longitudinal central portior. of a pariition v;all. 3. The me~:.'.od a..:cf-rciing ::o claim 1, wherein the cell c1:,ambers partitioned by tr.e partition walls are each termed to have a rectangular opening surface and arranged in one _Lne such that short sides of the cell chambers are disposed along with a longitudinal direction of the battery case. 4. The method according to claim 1, wherein the cell chambers partitioned by the partition walls are each formed tc have a rectangular opening surface and arranged in two lines such that short sides of t.he cell chambers are disposed along with a longitudinal direction of the battery case. b . The netnod according to claim 1, wherein the outer wall of ::he battery case is formed thicker than each .respective partition wall of the cell charters. 6. '"he method according to claim 'i, wher-.:-ln the partita or; wails of all the cell chambers are frrmed to have substantially the same thickness. '"• . A method of molding case for secondary ba 11: e; y, ,° ubs tant ia 11 y as he i e i nbe f o re describe i w11h reference to FIGS. 1 to 6 of the accompanying drawings.

Documents:

2516-del-2006-Abstract-(22-01-2014).pdf

2516-del-2006-Abstract-(25-03-2014).pdf

2516-del-2006-abstract.pdf

2516-del-2006-assignments.pdf

2516-del-2006-Claims-(22-01-2014).pdf

2516-del-2006-Claims-(25-03-2014).pdf

2516-del-2006-claims.pdf

2516-del-2006-Correspondence Others-(22-01-2014).pdf

2516-del-2006-Correspondence Others-(25-03-2014).pdf

2516-del-2006-Correspondence Others-(27-01-2014).pdf

2516-del-2006-Correspondence-Others-(07-06-2013).pdf

2516-del-2006-correspondence-others.pdf

2516-del-2006-description (complete).pdf

2516-del-2006-Drawings-(25-03-2014).pdf

2516-del-2006-drawings.pdf

2516-del-2006-form-1.pdf

2516-del-2006-form-18.pdf

2516-del-2006-Form-2-(22-01-2014).pdf

2516-del-2006-Form-2-(25-03-2014).pdf

2516-del-2006-form-2.pdf

2516-del-2006-Form-3-(07-06-2013).pdf

2516-del-2006-Form-3-(27-01-2014).pdf

2516-DEL-2006-Form-3.pdf

2516-del-2006-form-5.pdf

2516-del-2006-gpa.pdf