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Microporous polyolefin filmRelated Patent Categories: Synthetic Resins Or Natural Rubbers -- Part Of The Class 520 Series, Natural Rubber Compositions Having Nonreactive Materials (dnrm) Other Than: Carbon, Silicon Dioxide, Glass Titanium Dioxide, Water, Hydrocarbon, Halohydrocarbon, Ethylenically Unsaturated Reactant Admixed With A Preformed Reaction Product Derived From: (a) At Least One Polycarboxylic Acid, Ester, Or Anhydride; (b) At Least One Polyhydroxy Compound; And (c) At Least One Fatty Acid Glycerol Ester, Or A Fatty Acid Or Salt Derived From A Naturally Occurring Glyceride, Tall Oil, Or A Tall Oil Fatty Acid, At Least One Solid Polymer Derived From Ethylenic Reactants Only, Polymer Mixture Of Two Or More Solid Polymers Derived From Ethylenically Unsaturated Reactants Only; Or Mixtures Of Said Polymer Mixture With A Chemical Treating Agent; Or Products Or Processes Of Preparing Any Of The Above Mixtures, Solid Polymer Derived From Ethylene Or PropyleneMicroporous polyolefin film description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070015876, Microporous polyolefin film. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] The present invention relates to a separator used for electrochemical reaction devices such as a battery and a capacitor. BACKGROUND ART [0002] A microporous polyolefin film is used for a microfiltration membrane, a separator for a battery, a separator for a capacitor, fuel cell material, or a basic material for a functional membrane in which a functional material is filled in the pores to give rise to a new function. When the microporous polyolefin film is used, among these applications, as a separator for a battery, particularly a separator for a lithium ion battery, it is required to have a high piercing strength and a high elongation modulus so as to prevent internal short circuit due to foreign bodies and the like within the battery and to prevent the separator from elongating in the flow direction when wound up to form a battery. [0003] Furthermore, "fuse effect" and "heat resistance" securing the safety of a battery are demanded as well as general physical properties in a separator for a high capacity battery of recent years. The fuse effect is a mechanism for securing the safety of a battery by allowing the separator to melt and form a film for covering electrodes and shutoff the battery when inside of the battery is overheated by overcharged states and the like. In the case of a polyethylene microporous film, it is known that the fuse temperature, namely the temperature at which the fuse effect develops, is almost around 140.degree. C. From a viewpoint of stopping runaway reaction inside the battery as soon as possible, the better it is supposed, the lower the fuse temperature is. [0004] Furthermore, the separator after fused should maintain its shape and have a function of keeping the insulation between the electrodes. This is heat resistance and can be grasped by dividing into film breakage properties and thermal shrinkage properties. For example, safety evaluation standard of battery, which prescribe storing at 150.degree. C. in an oven for 10 minutes, are provided in "Standard for Lithium Batteries" of U.S. standard UL1642 from the requirement of securing the safety of battery at 150.degree. C. In order to achieve this safety standard, it is desirable to allow the separator to maintain its shape by, after fusing the pores to be filled up, preventing the film breakage at 150.degree. C. or more and reducing thermal shrinkage as much as possible. When short-circuit parts where the electrodes contact with each other are caused in the batter by film breakage, thermal shrinkage, particularly thermal shrinkage in the width direction of the wound-up battery body, the battery becomes non-safe, and therefore a separator excellent in such a heat resistance is strongly demanded. [0005] Coexistence of the film breakage resistance and low heat shrinkability are important, and heat resistance of a separator can be high when both of them are satisfied. High strength and low heat shrinkability and high film breakage resistance and low heat shrinkability are, however, incompatible characteristics. [0006] For example, as for the viewpoint of high strength, techniques of increasing the molecular weight of polyethylene for creating highly oriented molecular state or increasing the draw ratio for achieving orientation are generally known. However, such a simple high molecular orientation may cause a high shrinkage stress in a fused state, and, as a result, lowers heat resistance. [0007] Furthermore, several attempts to improve heat resistance while maintaining high strength are also known. For example, Patent Document 1 proposed a microporous film having a high film breakage resistance by extrusion molding polyolefin and a polymer cross-linkable therewith followed by cross-linking treatment, but, to the contrary, relaxation at a high temperature was slow and accordingly it was inappropriate due to remaining strong shrinkage stress. In addition, there was a problem in productivity because a thermal cross-linking treatment step, which incurs a long period of time, was included. Meanwhile, Patent Document 2 realized high strength by using a polyolefin having a sharp molecular weight distribution, but it was difficult to have low temperature fuse and high short-circuit ability because the contents of ultra-high-molecular-weight ingredients and low molecular weight ingredients are decreased. [0008] Patent Document 3 discloses a microporous film composed of a polyethylene having a molecular weight of 300,000 or less and a polyethylene having a molecular weight of 1,000,000 or more. However, there is no description in Patent Document 3 about necessity of a step for imparting strength to the microporous film to be heat drawn, that is, a step of drawing the sheet under heating before removing a good solvent, and therefore, it is difficult to obtain a highly strong film. Besides, a step of fusing polyethylenes having a large difference in molecular weight needs a significant period of time and lacks in productivity. [0009] Patent Document 4 discloses a microporous film composed of a polyolefin having a molecular weight of 1,000,000 to 15,000,000 and a polyolefin having a molecular weight of 10,000 to less than 500,000. What is specifically disclosed is, however, a microporous film composed of a polyethylene having a molecular weight of 2,000,000 and a polyethylene having a molecular weight of 350,000 with the molecular weight ratio less than 10. In addition, a microporous film of low thermal shrinkage is obtained in the production method of a microporous film by containing a specific heat-treatment step as an essential step. However, thermal shrinkage was not sufficiently prevented only by the heat-treatment step as described for a microporous film comprising a polyethylene having a molecular weight of 200,000 or less. [0010] Similarly, Patent Document 5 discloses a microporous film containing 1% or more of an ultra-high-molecular-weight polyethylene having a molecular weight of 700,000 or more and composed of a polyolefin composition having a molecular weight distribution of 10 to 300. What is specifically disclosed is, however, a composition composed of a polyethylene having a molecular weight of 2,500,000 and a polyethylene having a molecular weight of 240,000, and does not contain a low molecular weight ingredient having a molecular weight of 10,000 to 200,000 which is essential to the present invention and it is insufficient in fuse property and relaxation rate. TABLE-US-00001 [Patent Document 1] JP-A-2001-181435 [Patent Document 2] Japanese Patent No. 3,351,940 [Patent Document 3] JP-A-02-21559 [Patent Document 4] JP-A-2003-3006 [Patent Document 5] Japanese Patent No. 2,711,633 DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention [0011] An object of the present invention is to solves the above described problems by using a composition comprising an ultra-high-molecular-weight polyethylene having a specific average particle size, melting behavior and a specific surface area and a polyethylene having a molecular weight of 10,000 to less than 200,000, and to provide a separator having both low fuse and high film breakage properties, and besides low heat-shrinkability at a high temperature. Means to Solve the Problems [0012] The present inventors have conducted intensive studies to achieve the purposes mentioned above, and consequently have found that a microporous film can be imparted with low fuse and high short-circuit properties as well as low heat-shrinkability at a high temperature by using a composition comprising an ultra-high-molecular-weight polyethylene having a specific average particle size, melting behavior and a specific surface area and a polyethylene having a molecular weight of 10,000 to 200,000 and thus have completed the present invention. [0013] That is, the present invention is as follows. [0014] (1) A microporous polyolefin film which comprises 5 to 95 wt % of polyethylene (A) having an Mv of 2,000,000 or more, a first melting-peak signal height as determined by DSC (differential scanning calorimetry) of 3.0 mW/mg or more, a specific surface area of 0.7 m.sup.2/g or more, and an average particle size of 1 to 150 .mu.m and 95 to 5 wt % of polyethylene (B) having an Mw of more than 10,000 and less than 200,000, wherein the Mv ratio of the component (A) to the component (B), (A)/(B), is 10 or more, the film as a whole has a molecular weight of 300,000 to 1,500,000, and the film has a fuse temperature of 120 to 140.degree. C., a film breakage temperature of 150.degree. C. or more, and a ratio of the piercing strength at 140.degree. C. to the piercing strength at 25.degree. C. of 0.01 to 0.25. (2) The microporous polyolefin film according to above (1) wherein the fuse temperature is 120 to 135.degree. C. (3) The microporous polyolefin film according to above (1) wherein the fuse temperature is 120 to 133.degree. C. (4) The microporous polyolefin film according to any of above (1) to (3) having a short-circuit temperature of 152.degree. C. or more. (5) The microporous polyolefin film according to any of above (1) to (4) having a thermal shrinkage starting temperature in a TD direction of 90.degree. C. or more. (6)The microporous polyolefin film according to above (5) having a thermal shrinkage starting temperature in the TD direction of 100.degree. C. or more. Continue reading about Microporous polyolefin film... Full patent description for Microporous polyolefin film Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Microporous polyolefin film patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. 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