CN100545197C - The microporous membrane of making by polyolefine - Google Patents

Abstract

The microporous membrane of making by polyolefine, it comprises polyethylene (PEA) and polypropylene and its molecular weight that has is 10,000 or lower component concentration be 8 to 60wt%, its porosity is 20 to 95% and is 10% or lower 100 ℃ of following degree of heat-shrinkage, containing 8 to 60wt% molecular weight in this polyethylene (PEA) is 10,000 or the ratio Mw/Mn of lower component and its weight-average molecular weight (Mw) and number-average molecular weight (Mn) be that 11-100 and viscosity-average molecular weight (Mv) they are 100,000-1,000,000.

Description

The microporous membrane of making by polyolefine

Technical field

The present invention relates to microporous membrane, it is generally used for for example isolation and selection infiltration of material and the partition member that is used as electrochemical reaction appts such as battery or current condenser.The invention particularly relates to the microporous membrane of making by polyolefine that is suitable as the lithium ion battery dividing plate.

Background technology

The microporous membrane of being made by polyolefine is generally used for the isolation and selection infiltration of various materials for example and as partition member.Specifically, they as the dividing plate of for example micro-filtration membrane, fuel cell or current condenser, be used for filling functional materials and give the matrix of functional membrane of new function and the dividing plate of battery in the hole.When being used for these purposes, specifically, they are suitable as the dividing plate of lithium ion battery of the PC, mobile telephone, digital camera etc. of notebook-sized.Reason is, for example, they not only have such as physical strength and infiltrative characteristic but also have hole plug performance and thermotolerance.

Here employed term " hole plug performance " is meant following ability: when because overcharged grade when causing inside battery overheated, and microporous membrane fusion and, make cell reaction stop, thereby guarantee the safety of battery with its hole plug.It is believed that the influence of safety along with the blocked temperature in hole reduces and increases.Here employed term " thermotolerance " at high temperature also can keep shape to keep the ability of insulativity between electrode even be meant.Microporous membrane requires at high temperature have low thermal shrinkage stress and is not breakable.

In patent document 1 to 3, the present patent application people has been proposed in the hole plug aspect of performance and obtains improved microporous membrane, and this realizes as part or all of component by the polyethylene and the new LDPE (film grade) that use low-melting-point polyethylene such as copolymerization.When adopting this kind method, improved the hole plug performance but the easy thermotolerance that reduces.

In patent document 4 to 6, the microporous membrane of the content of wax has been proposed.When adopting this kind method, improved the hole plug performance, but reduced the homogeneity of the parent material that is used for microporous membrane, so that often caused that film quality reduces, for example do not have the material of fusing to be retained in the film.In addition, estimate that thermotolerance can reduce inevitably when adopting this kind method.

In patent document 7 to 9 and in the applicant's the patent document 10 to 12, proposed to have high-molecular weight one-step polymerization polyethylene and have the microporous membrane that the poly blend of low-molecular-weight one-step polymerization obtains by independent use two-stage polymerization polyethylene or use.In preceding a kind of method, use two step polymerization polyethylene to allow with high polymer concentration discharging.But this microporous membrane is deficiency aspect thermotolerance, in addition, because insufficient its degree of heat-shrinkage of heat setting is estimated higher.On the other hand, in a kind of method in back, having the ultra high molecular weight polyethylene component is being effectively aspect the improvement thermotolerance, and having low-molecular-weight polyethylene component simultaneously is effective improving the hole plug aspect of performance.Therefore, this kind method makes that improving hole plug performance and thermotolerance to a certain extent simultaneously becomes possibility.Yet this kind tendency of improving above-mentioned performance characteristic by this method simultaneously is undesirable to the quality of film, and is separated from one another because lower-molecular-weight component and high molecular weight component tend to, and the parent material homogeneity that causes being used for microporous membrane is low.

In addition, in patent document 13 and 14, the microporous membrane of pbz polymer weight northylen, low molecular weight polyethylene, polypropylene and low-melting-point polyethylene has been proposed.This kind method also is effective improving the hole plug aspect of performance.Yet, because this low-melting component can increase thermal shrinkage stress under the high temperature and the parent material of film is difficult to form homogeneous phase, so be undesirable to the quality of film.In addition, because film does not comprise the lower-molecular-weight component of q.s, so at high temperature often have high thermal shrinkage stress.

Patent document 1: Japanese Patent No. 3113287

Patent document 2:JP-A-2003-217554

Patent document 3:JP-A-2003-231772

Patent document 4:JP-A-8-20659

Patent document 5:JP-A-10-17702

Patent document 6:JP-A-11-106533

Patent document 7: Japanese Patent No. 2657431

Patent document 8: Japanese Patent No. 3009495

Patent document 9:JP-A-11-92587

Patent document 10: Japanese Patent No. 2794179

Patent document 11: Japanese Patent No. 3305006

Patent document 12: Japanese Patent No. 3258737

Patent document 13:JP-A-2001-72788

Patent document 14:JP-A-2001-72792

Summary of the invention

The problem to be solved in the present invention

The present invention relates to provide the microporous membrane of being made by polyolefine, it has improved hole plug performance, heat resistanceheat resistant film rupture, heat shrinkability characteristic and hot strength and can not damage the characteristic of the conventional microporous membrane of being made by polyolefine, keeps film quality simultaneously.

The means of dealing with problems

The problems referred to above are solved first by the present invention.That is of the present invention being constructed as follows.

(1) microporous membrane of making by polyolefine, it comprises polyethylene (PEA) and polypropylene is 10 as main ingredient and its molecular weight that has, 000 or lower component concentration be 8 to 60wt%, its porosity is 20 to 95% and is 10% or lower 100 ℃ of following degree of heat-shrinkage, containing 8 to 60wt% molecular weight in this polyethylene (PEA) is 10,000 or lower component, and the ratio Mw/Mn of its weight-average molecular weight (Mw) and number-average molecular weight (Mn) for more than or equal to 11 and be less than or equal to 100 and viscosity-average molecular weight (Mv) for more than or equal to 100,000 and be less than or equal to 1,000,000.

(2) according to the microporous membrane of making by polyolefine of above-mentioned (1), its ratio that except top (1) described PEA and polypropylene, also comprises Mw/Mn for more than or equal to 1 and be less than or equal to 10 and Mv value be more than or equal to 10,000 and be less than or equal to 500,000 polyethylene (PEB) as main ingredient.

(3) according to the microporous membrane of making by polyolefine of above-mentioned (1), its except top (1) described PEA and polypropylene, also comprise Mw/Mn than for more than or equal to 1 and be less than or equal to 10 and Mv value be more than or equal to 500,000 and be less than or equal to 10,000,000 polyethylene (PEB) is as main ingredient.

(4) according to each the microporous membrane of making by polyolefine in above-mentioned (1) to (3), wherein more than or equal to 100,000 and be less than or equal to 1,000, in 000 molecular weight M (i) scope, as follows between the denary logarithm of the molecular weight M (i) that is measured by GPC/FTIR is worth with terminal methyl concentration C (M (i)) based on the linear approximate relationship of method of least squares:

C(M(i))＝A×log(M(i))+B

(A and B are constants)-0.015≤A≤2.000.

(5) according to above-mentioned (1) to (in 4) each the microporous membrane of being made by polyolefine, it has 25% or lower degree of heat-shrinkage under 120 ℃.

(6) according to each the microporous membrane of being made by polyolefine in above-mentioned (1) to (4), it has 20% or lower degree of heat-shrinkage under 120 ℃.

(7) according to each the microporous membrane of being made by polyolefine in above-mentioned (1) to (6), it has 600kPa or lower TD thermal shrinkage stress under 150 ℃.

(8) according to each the microporous membrane of being made by polyolefine in above-mentioned (1) to (7), wherein above-mentioned PEA is the polyethylene by the acquisition of multistep polymerization method.

(9) according to the microporous membrane of being made by polyolefine of above-mentioned (2) or (3), wherein above-mentioned PEA shows between the peak Y (at the PEA peak of high molecular one side as maximum peak or acromion) of maximum peak at the peak of PEA X (at the PEA peak of lower molecular weight one side as maximum peak or acromion) and PEA of two maximum peaks or acromion and above-mentioned PEB in the molecular weight distribution that obtains by GPC at least.

(10) according to the microporous membrane of being made by polyolefine of above-mentioned (9), it has 25% or lower degree of heat-shrinkage under 120 ℃.

(11) according to the microporous membrane of being made by polyolefine of above-mentioned (9), it has 20% or lower degree of heat-shrinkage under 120 ℃.

(12) according to the microporous membrane of being made by polyolefine of above-mentioned (9), it has 600kPa or lower TD thermal shrinkage stress under 150 ℃.

(13) according to the microporous membrane of being made by polyolefine of above-mentioned (9), wherein above-mentioned PEA is the polyethylene that obtains by the multistep polymerization method.

(14) a kind of preparation is according to the method for each the microporous membrane of being made by polyolefine in above-mentioned (1) to (13), and this method comprises:

With polymer materials and softening agent, perhaps polymer materials, softening agent and inorganic reagent melt-kneaded, and the step that the gained mixture is extruded; With

Stretch and extract this softening agent, perhaps stretch, extract this softening agent and randomly extract this inorganic reagent, carry out the step of heat setting then.

(15) method of the microporous membrane of making by polyolefine according to the preparation of above-mentioned (14), wherein more than or equal to 100 ℃ and less than 135 ℃ temperature under carry out this heat setting with 0.6 to 0.9 relaxation rate.

Advantage of the present invention

The microporous membrane that the present invention is made by polyolefine is compared with the microporous membrane that routine is made by polyolefine has improved hole plug performance, heat resistanceheat resistant film rupture, heat shrinkability characteristic and hot strength.Therefore, the microporous membrane of the application of the invention can improve the security of battery as the dividing plate of battery.In addition, the microporous membrane with these good physical behavior can be provided as the high-quality microporous membrane.

The accompanying drawing summary

[Fig. 1] Fig. 1 is the graphic representation that shows the preference relation example between the molecular weight distribution that can be used for PEA of the present invention and PEB.

[Fig. 2] Fig. 2 is the explanation that is used for measuring the battery of hotting mask break temperature in rapid heating process hole plug temperature and the rapid heating process.

[Fig. 3] Fig. 3 shows the measuring apparatus that is used for measuring hotting mask break temperature in rapid heating process hole plug temperature and the rapid heating process.

Preferred forms of the present invention

The present invention will be described in detail belows.The microporous membrane that the present invention is made by polyolefine comprises and comprises that polyethylene (hereinafter being abbreviated as PE sometimes) and polypropylene (PP sometimes hereinafter abridges) are as main component and preferably formed by these mixture of polymers.More preferably polyethylene is a main matrix.

Molecular weight be 10,000 or the ratio Mw/Mn of the ratio of lower component and weight-average molecular weight (Mw) and number-average molecular weight (Mn) measure by the GPC method.Calculate viscosity-average molecular weight (Mv) by measuring under 135 ℃ the limiting viscosity in the naphthalane solvent [η].The value of the Mw value with Mv basically is identical.In this manual, molecular-weight average is represented with Mv.

PEA and PEB promptly constitute the polyethylene of the microporous membrane that the present invention makes by polyolefine, will make an explanation below.As mentioned above, in this manual, abbreviation " PEA " is meant such polyethylene, its molecular weight that contains 8 to 60wt% is 10,000 or lower component, and the ratio Mw/Mn of its Mw and Mn for more than or equal to 11 and be less than or equal to 100 and Mv for more than or equal to 100,000 and be less than or equal to 1,000,000.On the other hand, abbreviation " PEB " is meant such polyethylene, the ratio of its Mw/Mn for more than or equal to 1 and be less than or equal to 10 and Mv value be more than or equal to 10,000 and less than 500,000, perhaps the ratio of its Mw/Mn for more than or equal to 1 and be less than or equal to 10 and Mv value be more than or equal to 500,000 and be less than or equal to 10,000,000.

For consideration to the hole plug performance, among the PEA molecular weight be 10,000 or lower components contents be 8wt% or higher, preferred 10wt% or higher, especially preferred 15wt% or higher.When this content is 8wt% or when higher, the hole plug performance is improved, in addition, (for example, in test or the baking oven test that overcharges) inside battery has desirably caused the lax fast of the thermal shrinkage stress of microporous membrane own standing to be rapidly heated.On the other hand, for consideration to heat shrinkability characteristic, among the PEA molecular weight be 10,000 or lower components contents be 60wt% or lower, be preferably 50wt% or lower.

For the consideration that hole plug performance and PEA and PEB is formed the ability of homogeneous mixture, the ratio of the Mw/Mn of PEA is more than or equal to 11 and is less than or equal to 100, be preferably more than or equal 15 and be less than or equal to 80, more preferably more than or equal to 20 and be less than or equal to 60.For the consideration that PEA and PEB and polypropylene is formed the ability of homogeneous mixture, the Mv value of PEA is 100,000 or higher, is preferably 150,000 or higher, more preferably greater than 300,000.In addition, be preferably 1,000,000 or lower, be preferably 800,000 or lower.This type of PEA compatibly can obtain by multistep polymerization, and since high productivity and the Yi Ke property obtained, preferred two step polymerisates.Same for the consideration to productivity, this kind can be preferably as follows preparation by the PE that two step polymerization processs obtain: make the lower-molecular-weight component polymerization by first reaction, make the high molecular weight component polymerization by second reaction then.The PE that obtains by this kind multistep polymerization method shows two or more maximum peaks or acromion in gpc measurement, and preferably 10 ³To 10 ⁵Molecular weight show that down maximum peak or acromion are as the peak of lower molecular weight one side with 10 ⁵To 10 ⁷Molecular weight show down maximum peak or acromion peak as high molecular one side.

For the consideration that PEB and PEA and polypropylene is formed the ability of homogeneous mixture, the ratio of the Mw/Mn of PEB is for more than or equal to 1 and be less than or equal to 10, is preferably more than or equals 5 and be less than or equal to 10.Pay attention to therein in the system of hole plug performance, the Mv value of PEB is more than or equal to 10,000 and less than 500,000, is preferably more than or equals 50,000 and be less than or equal to 300,000.On the other hand, pay attention to therein in the system of heat resistanceheat resistant film rupture and hot strength, the Mv value of PEB is more than or equal to 500,000 and be less than or equal to 10,000,000, be preferably more than or equal 700,000 and be less than or equal to 7,000,000, especially be preferably more than or equal 1,000,000 and be less than or equal to 5,000,000.This type of PEB can compatibly obtain by one-step polymerization.

When PEA shows at least two maximum peaks or acromion in the molecular weight distribution that obtains by GPC, the maximum peak of the PEB that is added is preferably between the peak Y (at the PEA peak of high molecular one side as maximum peak or acromion) of the peak of PEA X (at the PEA peak of lower molecular weight one side as maximum peak or acromion) and PEA, as shown in Figure 1.This is because this type of film and the conventional blend that comprises lower molecular weight PE and high molecular PE, or the microporous membranes that only comprise two step polymerization PE compare, owing to lower thermal shrinkage stress has higher intensity.In this case, acromion comprises flex point etc.

As each PEA and PEB, can use one or more polymkeric substance.In addition, as each polyethylene, can use homopolymer or multipolymer.When selecting copolymer polyethylene, for the consideration to heat shrinkability characteristic, its co-monomer content is preferably 2mol% or lower, 1 mole of % or lower more preferably, further 0.6mol% or lower more preferably.Comonomer comprises, for example, and alpha-olefin comonomer such as propylene, 1-butylene, 1-amylene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene, 1-dodecylene, tetradecene, cetene, 1-vaccenic acid, 1-eicosylene etc.; Cyclic olefin comonomer such as cyclopentenes, tetrahydrobenzene, suberene, norbornylene, 5-methyl-2-norbornylene, tetracyclododecane, 2-methyl isophthalic acid .4,5.8-dimethano--1,2,3,4,4a, 5,8,8a-octahydro naphthalene etc.; By general formula CH ₂The compound of=CHR (wherein R is the aryl that contains 6 to 20 carbon atoms) expression is as vinylbenzene, vinyl cyclohexane etc.; And linear, branching or cyclic contain the diene of 4 to 20 carbon atoms, as 1,3-butadiene, 1, and 4-pentadiene, 1,5-hexadiene, 1,4-hexadiene, 1,6-octadiene, 1,7-octadiene, cyclohexadiene etc.Especially preferred alpha-olefin comonomer.

The polymerizing catalyst that is used for each PEA and PEB comprises Ziegler-Natta catalyst, philip catalyst, metalloscene catalyst etc.

For the consideration to hole plug performance and film forming properties, in the gross weight of the film forming all material of structure, the ratio of PEA is preferably 10wt% or higher, and more preferably 20wt% or higher especially is preferably 50wt% or higher.In addition, this ratio is preferably 94wt% or lower, more preferably 90wt% or lower.For the consideration to hole plug performance, heat resistanceheat resistant film rupture and film forming properties, the ratio of PEB is preferably 3wt% or higher, more preferably 5wt% or higher.In addition, this ratio is preferably 90wt% or lower, more preferably 80wt% or lower, especially preferred 50wt% or lower.

Polypropylene as constituting the microporous membrane that the present invention makes by polyolefine can use one or more polypropylene.For the consideration of antagonism hotting mask disruptiveness, polyacrylic Mv value is preferably 150,000 or higher, and for the consideration to film quality, this Mv value is preferably 700,000 or lower.

As employed polypropylene, exemplify and provide homopolymer, random copolymers and segmented copolymer.Employed whole polyacrylic comonomer (normally ethene) content is preferably 1.5mol% or lower, more preferably 1.0mol% or lower.Used polyacrylic polymerizing catalyst is not particularly limited, and comprises Ziegler-Natta catalyst, metalloscene catalyst etc.

For the consideration of antagonism hotting mask disruptiveness, in the gross weight of the film forming all material of structure, polyacrylic ratio is preferably 3wt% or higher, more preferably 5wt% or higher, further more preferably 7wt% or higher.In addition, for the consideration to film forming properties, this ratio is preferably 50wt% or lower, and for to piercing through the physical property balance between intensity and the ventilation property and the consideration of film quality, this ratio is preferably 30wt% or lower, more preferably 15wt% or lower.

The microporous membrane of making by polyolefine with regard to the present invention, more than or equal to 100,000 and be less than or equal to 1,000, in 000 molecular weight M (i) scope, the denary logarithm of the molecular weight M (i) that is measured by GPC/FTIR and the linear approximate relationship based on method of least squares between terminal methyl concentration C (M (the i)) value are preferably as follows:

C(M(i))＝A×log(M(i))+B

(A and B are constants)-0.015≤A≤2.000.

Measuring each molecular weight distribution and the terminal methyl concentration measured by GPC/FTIR all is the value sum that constitutes the polyolefine (for example polyethylene and polypropylene) of microporous membrane of the present invention.Molecular weight M (i) is the molecular weight of representing with polyethylene.Terminal methyl concentration C (M (i)) is defined as the absorption I (CH owing to methyl ₃) (2960cm ^-1The absorption wavenumber at place) with owing to the absorption I (CH of methylene radical ₂-) (2925cm ^-1The absorption wavenumber at place) ratio, I (CH ₃)/I (CH ₂-).At this, C (M (i)) is the value of all polymer side link ends methyl and the value sum of all main polymer chain end methyl.Because the methyl of polypropylene side chain influences C (M (i)) greatly, so polyacrylic molecular weight distribution can be judged by the dependency between M (i) and the C (M (i)) in the film.

In the present invention, in linear approximate relationship based on the method for least squares between C (M (i)) and the logM (i), constant A is preferably more than or equals-0.015 and be less than or equal to 2.0, more preferably greater than or equal-0.012 and be less than or equal to 1.0, further more preferably greater than or equal 0 and be less than or equal to 0.5.Constant A value less than-0.015 means that the amount of polypropylene lower-molecular-weight component in the film is far longer than the amount of polypropylene high molecular weight component.For the consideration of antagonism hotting mask disruptiveness, this is undesirable.For consideration, be difficult to obtain constant A wherein basically greater than 2.0 microporous membrane to film forming properties etc.Though the scope to constant B is not particularly limited, and considers constant A, this constant B is preferably approximately-5 to 5.

As everyone knows, because polypropylene has the fusing point higher than polyethylene, so its moulded product has excellent thermotolerance.Because polypropylene disperses as high molecular weight material, and the polyethylene of stipulating in this specification sheets, contain lower-molecular-weight component and high molecular weight component is effectively aspect stress relaxation, so think and obtained excellent anti hotting mask disruptiveness in the rapid heating process in the present invention.

For consideration to the hole plug performance, in the microporous membrane that the present invention is made by polyolefine molecular weight be 10,000 or lower components contents be 8wt% or higher, be preferably 10wt% or higher.In addition, for the consideration to heat shrinkability characteristic, this content is 60wt% or lower, is preferably 50wt% or lower.

For the consideration to thermotolerance, film toughness and film forming properties, the present invention is preferably 100,000 or higher by the Mv value of the microporous membrane that polyolefine is made, and more preferably 150,000 or higher.In addition, for the consideration to hole plug performance and film forming properties, this Mv value is preferably 2,000, and 000 or lower, more preferably 1,000,000 or lower, further more preferably 800,000 or lower.

For to infiltrative consideration, the present invention is 20% or higher by the porosity of the microporous membrane that polyolefine is made, and is preferably 25% or higher, more preferably 30% or higher, further more preferably 35% or higher.In addition, for the consideration to film toughness, this porosity is 95% or lower, is preferably 80% or lower, more preferably 70% or lower, further more preferably 60% or lower.

For the consideration to film toughness, the present invention is preferably 3 μ m or higher by the thickness of the microporous membrane that polyolefine is made, more preferably 5 μ m or higher.In addition, for to infiltrative consideration, this thickness is preferably 100 μ m or lower, more preferably 50 μ m or lower.

The present invention is preferably 1 second or higher by the ventilation property of the microporous membrane that polyolefine is made, more preferably 50 seconds or higher.In addition, for to infiltrative consideration, this ventilation property is preferably 2000 seconds or lower, more preferably 1000 seconds or lower.

The intensity (at normal temperatures, for example the value under 25 ℃) that pierces through of the microporous membrane that the present invention is made by polyolefine is preferably 0.7 to 20.0N/20 μ m, and more preferably 2.5 to 20.0N/20 μ m.If pierce through intensity less than 0.7N/20 μ m, then when microporous membrane during as the dividing plate of battery, the sharp-pointed part of electrode member etc. can pierce through microporous membrane and facilitate the formation of pin hole or crackle.

The pierce through intensity of microporous membrane under 140 ℃ that the present invention is made by polyolefine is preferably 0.5 to 20.0N/20 μ m, more preferably 0.7 arrives 20.0N/20 μ m.

For battery being added the consideration of pining for safety assurance, under 20 ℃/minute rapid heating condition, the present invention is preferably 140 ℃ or lower by the hole plug temperature of the microporous membrane that polyolefine is made, more preferably 138 ℃ or lower.For battery being added the consideration of pining for safety assurance, under 20 ℃/minute rapid heating condition, the hotting mask break temperature is preferably 175 ℃ or higher, more preferably 190 ℃ or higher.

For battery being added the consideration of pining for safety assurance, the degree of heat-shrinkage of microporous membrane under 100 ℃ that the present invention is made by polyolefine is 10% or lower, is preferably 8% or lower, more preferably 6% or lower.Under 120 ℃, in the time of heating, for example in new cell safety test, degree of heat-shrinkage be even more important and be preferably 25% or lower, more preferably 20% or lower, further more preferably 10% or lower.For battery being added the consideration of pining for safety assurance, do not have under the disruptive situation with film at 150 ℃, the TD thermal shrinkage stress after hole plug is preferably 600kPa or lower, more preferably 400kPa or lower, further 150kPa or lower more preferably especially is preferably 120kPa or lower.In the generation of this kind thermal shrinkage stress, with molecular weight in the whole film be 10,000 or lower components contents be adjusted to 8wt% or higher be effective.In addition, satisfying the condition described in the following heat setting step also is being effective aspect the reduction thermal shrinkage stress.

Therefore, the microporous membrane made by polyolefine of the present invention compare with conventional microporous membrane have improved hot strength, hole plug performance, heat resistanceheat resistant film rupture and heat shrinkability characteristic.

Next, with the preparation method's of the microporous membrane of the present invention of explaining below preferred embodiment.

Microporous membrane of the present invention can followingly obtain: with polymer materials and softening agent, perhaps polymer materials, softening agent and inorganic reagent melt-kneaded are then extruded the mixture of gained; And stretch and extract this softening agent, perhaps stretch, extract this softening agent and randomly extract this inorganic reagent, then carry out heat setting.

Employed inorganic reagent comprises among the present invention, for example, and silicon-dioxide, aluminum oxide, titanium oxide and lime carbonate.

At this, softening agent is meant at the non-volatile solvents that can form homogeneous phase solution under the temperature that is not less than the polyolefine fusing point when with these material mixing.Softening agent comprises, for example, and hydro carbons such as whiteruss, Paraffin Wax Semi Refined etc., di-2-ethylhexyl phthalate (DOP), Di Iso Decyl Phthalate and diheptyl phthalate.

For the consideration to membrane permeability and film forming properties, will carry out the weight of whole mixtures of melt-kneaded, the gross weight ratio of softening agent and inorganic reagent is preferably 20 to 95wt%, more preferably 30 arrives 80wt%.

In order to prevent thermal ageing in the melt-kneaded process and the quality deteriorated that causes thus, preferably introduce oxidation inhibitor.In polyolefinic gross weight, the concentration of oxidation inhibitor is preferably 0.3wt% or higher, more preferably 0.5wt% or higher.In addition, this concentration is preferably 5.0wt% or lower, more preferably 3.0wt% or lower.

As oxidation inhibitor, preferred phenolic antioxidant, primary antioxidant.Oxidation inhibitor comprises, for example, and 2,6 di tert butyl 4 methyl phenol, tetramethylolmethane four [3-(3, the 5-di-tert-butyl-hydroxy phenyl) propionic ester] and octadecyl-3-(3, the 5-di-tert-butyl-hydroxy phenyl) propionic ester.Can use auxiliary antioxidant jointly.Auxiliary antioxidant comprises that for example, phosphorus-containing antioxidant is as three (2, the 4-di-tert-butyl-phenyl) phosphorous acid esters, four (2, the 4-di-tert-butyl-phenyl)-4,4-biphenylene-two phosphinate etc.; And sulfur-bearing oxidation inhibitor such as dilauryl-sulfo--dipropionate etc.

Also may use the polyolefine except that polyethylene of stipulating in this specification sheets and polypropylene jointly, as long as they can not hinder and satisfy desired condition among the present invention.Other polyolefine comprises, for example, and polyethylene, methylpentene multipolymer and cyclic olefin copolymer such as ethene tetracyclododecane multipolymer, vinyl norbornene multipolymer etc.Can use each or two or more combination in them in them jointly.Also can introduce the polymkeric substance except that polyolefine and other organic materials,, not hinder and satisfy among the present invention desired condition and do not reduce advantage of the present invention as long as they are not lowered into film properties.

In addition, words if necessary, metallic soap such as calcium stearate, Zinic stearas etc. and known additives such as UV light absorber, photostabilizer, static inhibitor, antifogging agent, tinting pigment etc. also can mix use with other component, as long as they are not lowered into film properties, do not hinder and satisfy among the present invention desired condition and do not reduce advantage of the present invention.

As for melt-kneaded and the method for extruding, if necessary, at first in Henschel mixing tank, ribbon blender, rotating cylinder blender etc., some or all raw materials are pre-mixed.When they amount hour, can be with its manual stirring.Then, utilize screw extrusion press (for example single screw extrusion machine or twin screw extruder), kneading machine, mixing tank etc. all raw material melts to be mediated and extruded by T-mould, ring mould etc.

With regard to the microporous membrane that the present invention is made by polyolefine, below be preferred: oxidation inhibitor and starting polymer are mixed into predetermined concentration, then replace, and this mixture melt-kneaded is kept nitrogen atmosphere simultaneously with nitrogen atmosphere.Temperature during melt-kneaded is preferably 160 ℃ or higher, more preferably 180 ℃ or higher.In addition, this temperature preferably is lower than 300 ℃, more preferably less than 240 ℃, further more preferably less than 230 ℃.

The melt of being mentioned in this specification sheets can comprise the not fusing inorganic reagent that can extract in the inorganic reagent extraction step.Can allow make by melt-kneaded the homogeneous melt by screen cloth to improve film quality.

Then, if necessary, carry out sheet forming.As for the method for sheet forming, make by melt-kneaded and the melt curing of extruding acquisition by compression and cooling.As method of cooling, illustrational is the method that melt and heat-eliminating medium such as freezing air or water coolant are directly contacted, and the method that melt is contacted with roller or pressing machine with refrigerant cools.The method that melt is contacted with roller or pressing machine with refrigerant cools has gratifying gauge control because this method makes.

Subsequently, stretch and extract softening agent, or stretch, extract softening agent and extraction inorganic reagent.Their order and operation number are not particularly limited.When stretching and extract softening agent, the example of their order is a stretching → extraction softening agent; Extraction softening agent → stretching; And stretching → extraction softening agent → stretching.

When stretching, extract softening agent and extraction during inorganic reagent, the example of their order be stretch-→ extraction softening agent → extraction inorganic reagent; Extraction softening agent → stretching → extraction inorganic reagent; Extraction softening agent → extraction inorganic reagent → stretching; Stretching → extraction inorganic reagent → extraction softening agent; Extraction inorganic reagent → stretching → extraction softening agent; Extraction inorganic reagent → extraction softening agent → stretching; Stretching → extraction softening agent → stretching → extraction inorganic reagent; And stretching → extraction softening agent → extraction inorganic reagent → stretching.For consideration, preferably after the extraction softening agent, carry out the extraction of inorganic reagent to extraction efficiency.If unnecessary, needn't carry out the extraction of inorganic reagent.

As the drawing process that is adopted, illustrational be the MD uniaxial extension (MD is meant machine direction), the TD uniaxial extension (TD is meant the direction perpendicular to machine direction) that adopts tenter machine that adopt the roll-type drawing machine, adopt the roll-type drawing machine and the tenter machine bonded is biaxial stretch-formed one by one and adopt the biaxial stenter of operation simultaneously or biaxial stretch-formed by inflation the time.For to the inhomogeneity consideration of film thickness, the stretch ratio of representing with total area ratio is preferably 8 or higher, and more preferably 15 or higher, most preferably be 40 or higher.

The extraction solvent that is used to extract softening agent is preferably such solvent, and it is the film forming polyolefinic poor solvent of structure, is that the good solvent of softening agent and the boiling point that has are lower than the film forming polyolefinic fusing point of structure.This type of extraction solvent comprises, for example, and hydro carbons such as normal hexane, hexanaphthene etc.; Alcohol is as methyl alcohol, ethanol, Virahol etc.; Ketone such as acetone, methyl ethyl ketone etc.; Ether such as tetrahydrofuran (THF) etc.; And halohydrocarbon such as methylene dichloride, 1, fluorocarbon etc.By from these extraction solvents, suitably selecting, it can be used separately or use with their mixture.In the extraction of softening agent, extract this softening agent by the following method: for example immerse the product of this melt-kneaded in the extraction solvent that exemplifies above or spray the product of this melt-kneaded with the extraction solvent that exemplifies above.Then, with the product finish-drying of this melt-kneaded.

As for the heat setting method, making in predetermined temperature atmosphere, stretched sheet stands the lax relaxation rate of routine processes to obtain to be scheduled to.This program can be undertaken by utilizing tenter machine or roll-type drawing machine.Lax program is the program of instigating film upwards to shorten at MD and/or TD.Term " relaxation rate " is meant following value: by the value that obtains divided by the MD size of film before the lax program with the MD size of film after the lax program or by the value that obtains divided by the TD size of film before the lax program with the TD size of film after the lax program or carry out at the same time under the lax situation of MD and TD by multiply by the value of TD relaxation rate acquisition with the MD relaxation rate.For the consideration to degree of heat-shrinkage, this preset temperature is preferably 100 ℃ or higher; And for to porosity and infiltrative consideration, this temperature preferably is lower than 135 ℃.For the consideration to degree of heat-shrinkage, this predetermined relaxation rate is preferably 0.9 or lower, and more preferably 0.8 or lower.In addition, for, porosity wrinkling to preventing and infiltrative consideration, this predetermined relaxation rate is preferably 0.6 or higher.Though lax program can be carried out on MD and TD both direction simultaneously, even but only by the program that relaxes on the direction in MD and TD, degree of heat-shrinkage also not only can reduce on the direction of lax program and also can with the vertical direction of lax program direction on reduce.

If necessary, surface treatment such as electron beam irradiation, plasma radiation be can carry out, surfactant-coated, chemical modification etc. used, as long as it can not reduce advantage of the present invention.

The various physicalies that are used for this specification sheets are that the basis is measured with following testing method.

(1) calculating of constant A

Molecular weight M (i) in the microporous membrane distributes and terminal methyl concentration C (M (i)) is measured by the GPC/FTIR measurement.Molecular weight M (i) is the molecular weight of representing with polyethylene.C (M (i)) is the absorption I (CH owing to methyl ₃) (2960cm ^-1The absorption wavenumber at place) with owing to the absorption I (CH of methylene radical ₂-) (2925cm ^-1The absorption wavenumber at place) ratio, I (CH ₃)/I (CH ₂-).Constant A is according to more than or equal to 100,000 and be less than or equal to the dependency between the logM (i) and C (M (i)) in 1,000,000 molecular weight M (i) scope by based on the linear approximation method acquisition of method of least squares.

C(M(i))＝A×log(M(i))+B

(A and B are constants)

GPC/FTIR measures and carries out under the following conditions:

[device]

The ALC/GPC 150C type (trade mark) that Waters Corporation makes

[measuring condition]

Post: AT-807S (trade mark) post (Showa Denko K.K. manufacturing) and two GMH-HT6 (trade mark) post (Tosoh Corporation manufacturing) are connected in series.

Moving phase: trichlorobenzene (TCB)

Column temperature: 140 ℃

Flow velocity: 1.0ml/ minute

Specimen preparation: by the 20mg microporous membrane being dissolved in the solution of the 20ml 0.1wt% of 2,6 di tert butyl 4 methyl phenol in TCB 140 ℃ of heating.

Detector: PerkinElmer, the FT-IR 1760X (trade mark) that Inc makes.

(2) molecular weight is 10,000 or the ratio of lower component, and Mw/Mn

To calculate by the basis that is measured as of gel permeation chromatography (GPC).The ALC/GPC 150C type (trade mark) that use is made by WatersCorporation is as device, and use is with two 60cm post TSK-Gel GMH6-HT (trade name of series system connection, Tosoh Corporation makes) and AT-807/S post (trade name, Showa Denko K.K. makes).Contain 1,2 of 10ppm tetramethylolmethane four [3-(3, the 5-di-tert-butyl-hydroxy phenyl) propionic ester] by use, the 4-trichlorobenzene is measured at 140 ℃ as mobile phase solvent.The commercial monodisperse polystyrene that has the known molecular amount by use obtains working curve as reference material.(the Q factor of the poly Q factor/polystyrene=17.7/41.3) obtains the molecular weight distribution data represented with polyethylene to multiply by 0.43 by the molecular weight distribution data of representing with polystyrene that every kind of sample is obtained.

(3) viscosity-average molecular weight Mv

Limiting viscosity in the naphthalane solvent under 135 ℃ [η] is measured according to ASTM-D4020.Poly Mv value is calculated by following formula:

[η]＝6.77×10 ^-4Mv ^0.67

Polyacrylic Mv value is calculated by following formula:

[η]＝1.10×10 ^-4Mv ^0.80

The Mv value of telolemma is calculated with poly formula.

(4) alpha-olefin comonomer content (mol%)

By following calculating: be used in ¹³In the C-NMR spectrum owing to the integrated value of the mole strength of signal of comonomer unit (A) divided by (A) and owing to the integrated value sum of the mole strength of signal of principal monomer unit (B), and the merchant be multiply by 100.

For example, with regard to copolymer polyethylene by using propylene to obtain as comonomer, the following calculating of the content of comonomer:

In following structural models (1):

[general formula 1]

Work as I ₁, I _{1 '}, I ₂, I ₃, I _α, I _β, I _γ, I _mAnd I _MGetting work respectively exists ¹³In the C-NMR spectrum during owing to the strength of signal of corresponding carbon atom, then

Co-monomer content (mol%)=(A)/((A)+(B)) * 100

Wherein

(A)＝(I _1′+I _m+I _α/2)/3

(B)＝(I ₁+I ₂+I ₃+I _M+I _α/2+I _β+I _γ)/2

Therefore, because I _m=I _{1 '}=I _α/ 2=I _β/ 2=I _γ/ 2, so by ignoring I ₁, I ₂, I ₃, above-mentioned formula arrangement is for as follows:

Co-monomer content (mol%)=I _m/ (I _m+ (I _M+ 5I _m)/2) * 100.

(5) film thickness (μ m)

Adopt Toyo Seiki Seisaku-sho under 23 ℃ room temperature, the micro-thickness gauge KBM (trade mark) that Ltd makes measures.

(6) porosity (%)

Downcut 10cm from microporous membrane ²Sample, measure the volume (cm of this sample ³) and quality (g), afterwards by the density (g/cm of volume and quality and film ³) calculate porosity with following formula:

Porosity=(density of volume-quality/film)/volume * 100

Make constant value 0.95 and calculate by the density of film is got.

(7) ventilation property (second)

Adopt Gurley permeability measurement meter (Toyo Seiki Seisaku-sho Ltd makes for G-B2, trade name) to measure according to JIS P-8117.

(8) pierce through intensity (N/20 μ m)

Employing is by Kato tech Co., the KES-G5 hand-held compressed detected device (trade mark) that Ltd makes, in 23 ℃ atmosphere, with needle point radius-of-curvature 0.5mm with pierce through speed 2mm/ and carry out puncture test second, obtain the untreated intensity level (N) that pierces through and pierce through load as maximum.Should untreated value (N) multiply by 20 (μ m)/film thicknesses (μ m), and calculate with what 20 μ m film thicknesses were represented and pierce through intensity.

(9) 140 ℃ pierce through intensity (N/20 μ m)

Be fixed by microporous membrane being clamped between two stainless steel packing rings (internal diameter is 13mm, and external diameter is 25mm), and with its be dipped in 140 ℃ silicone oil (KF-96-10CS (trade mark) Shin-EtsuChemical Co., Ltd) in 60 seconds.When microporous membrane does not break, adopt Kato tech Co., Ltd. the KES-G5 hand-held compressed detected device (trade mark) of Zhi Zaoing pierces through load to obtain 140 ℃ of untreated intensity levels (N) that pierce through as maximum with needle point radius-of-curvature 0.5mm with pierce through speed 2mm/ and second it is carried out puncture test.Should untreated value (N) multiply by 20 (μ m)/film thicknesses (μ m), calculate the intensity that pierces through of 140 ℃ of representing with 20 μ m film thicknesses.

(10) the hole plug temperature in the rapid heating process (℃) and the rapid heating process in the hotting mask break temperature (℃)

The nickel foil (A and B) that to prepare two thickness be 10 μ m.One of nickel foil sheet A is fixed on the slide glass of (trade mark) band that has Teflon, makes square part (10mm is long and 10mm is wide) maintenance not covered (Fig. 2) of sheet A with this belt opaque disk A simultaneously.

On the ceramic plate that another sheet nickel foil B is placed on thermopair is connected, the microporous membrane as the sample that is used to measure that will fully flood (by it being immersed in electrolytic solution 3 hours) with the electrolytic solution of regulation is placed on sheet B.Top slide glass with nickel foil sheet A is placed on this microporous membrane, then silicon rubber is placed on (Fig. 3) on this slide glass.

With the component placement of gained on hot plate and apply the pressure of 1.5MPa simultaneously with hydropress with 20 ℃/minute speed heating.Impedance variations is in this case measured under the alternating-current condition of 1V and 1kHz with the LCR meter.In this measured, the temperature that impedance is reached 1000 Ω was got the hole plug temperature of doing in the rapid heating process, impedance is afterwards become the temperature that is lower than 1000 Ω get the hotting mask break temperature of doing in the rapid heating process.

Electrolytic solution composed as follows of regulation:

The ratio of components of solvent (by volume): Texacar PC/ethylene carbonate/δ-butyrolactone=1/1/2.

Solute ratio: with LiBF ₄Be dissolved in the concentration that rises to 1mol/ in the above-mentioned mixed solvent.

(11) degree of heat-shrinkage

Downcut 12cm from microporous membrane ²Sample, and on its MD and TD direction, make four marks with the distance at a distance of 10cm each other.Sample holder was being left standstill 60 minutes in the baking oven of 100 ℃ (or under 120 ℃ of situations about measuring down, being 120 ℃) between two scraps of paper and with it.This sample taken out from baking oven and cool off, measure the distance (cm) between each mark on MD and the TD direction then and by separately degree of heat-shrinkage on following formula calculating MD and the TD direction:

Degree of heat-shrinkage on the MD direction (%)=(10-is the distance on the MD direction after heating)/10 * 100

Degree of heat-shrinkage on the TD direction (%)=(10-is the distance on the TD direction after heating)/10 * 100

(12) thermal shrinkage stress (kpa)

The TMA50 (trade mark) that makes with Shimadzu Corporation measures.The sample that utilizes chuck will be on the TD direction to downcut with the width of 3mm is fixed, and makes that the distance between the chuck is 10mm, and with sample setup on application specific probe.Initial load is adjusted to 1.0g, and this probe is heated to 200 ℃ from 30 ℃ with 10 ℃/minute speed.Measure the contraction load (g) that applies in this case.Load (g) with following formula during by 150 ℃ calculates thermal shrinkage stress:

Thermal shrinkage stress (kpa)=(contraction load/(3 * t)) * 100 * 9.807 * 10 150 ℃ the time

Wherein, t is sample thickness (μ m).

(13) number of defects

For 0.3mm ²Or bigger not melt polymer gel, observe corresponding to 50m ²Sample whole surface and measure every m ²Average number of defects.

(embodiment)

With reference to following examples explanation the present invention.

[embodiment 1]

In the rotating cylinder blender, with the ratio of 75wt% homopolymer polyethylene (PEA), its Mw/Mn of 15wt% be 8 and the Mv value be 2,000, its Mv value of 000 homopolymer polyethylene (PEB) and 10wt% is 400,000 homopolymer polypropylene is done blend, in this homopolymer polyethylene (PEA) 31wt% be molecular weight be 10,000 or the ratio of lower component and its Mw/Mn be 58 and the Mv value be 250,000.[3-(3 for the tetramethylolmethane four of adding 1wt% in the gained mixture of only being made up of these polymkeric substance of 99wt%, the 5-di-tert-butyl-hydroxy phenyl) propionic ester] as oxidation inhibitor, and it is done blend to obtain the mixture of these polymkeric substance etc. in the rotating cylinder blender.With the gained mixture of these polymkeric substance etc. with nitrogen treatment to replace air, under nitrogen atmosphere, it is added in the twin screw extruder then with feeder.With ram pump with the whiteruss (dynamic viscosity under 37.78 ℃: 7.59 * 10 ^-5m ²/ s) inject the machine barrel of this forcing machine.

Adjust this feeder and pump and make that after melt-kneaded the content of whiteruss is 55wt% in whole mixtures to be extruded.Carry out melt-kneaded under the following conditions: preset temp: 200 ℃, screw rod revolution: 240rpm, discharging speed: 12kg/h.Subsequently, this melt-kneaded product extruded to be cast to through control by the T-mould have on the cooling roller of 25 ℃ of surface temperatures, obtaining thickness is the gel film of 1300 μ m.Then, this gel film is introduced in the simultaneously biaxial stretch-formed tenter machine and biaxial stretch-formed.Default stretching condition is as follows: the MD ratio is 7.0, and the TD ratio is 6.4, and preset temp is 118 ℃.Next, will be the tensile gel film introduce the methyl ethyl ketone container and be immersed in the methyl ethyl ketone it with extraction fully and remove whiteruss, remove methyl ethyl ketone by drying afterwards.Then, will carry out heat setting in the gel film introducing TD tenter machine of so handling.The heat setting temperature is 105 ℃ and the TD relaxation rate is adjusted to 0.66.Table 1 shows the physicals of the microporous membrane of acquisition like this.

[embodiment 2]

In the rotating cylinder blender, with the ratio of 75wt% copolymer polyethylene (PEA), its Mw/Mn of 7wt% be 9 and the Mv value be 4,500, the polypropylene identical with embodiment 1 of 000 homopolymer polyethylene (PEB) and 18wt% done blend, 15wt% is that molecular weight is 10 in this copolymer polyethylene (PEA), 000 or the ratio of lower component and its Mw/Mn be 20 and the Mv value be 320,000 and propylene content be 0.3mol%.[3-(3 to add 1wt% tetramethylolmethane four in the gained mixture of only being made up of these polymkeric substance of 99wt%, the 5-di-tert-butyl-hydroxy phenyl) propionic ester] as oxidation inhibitor, and it is done blend to obtain the mixture of these polymkeric substance etc. in the rotating cylinder blender.With the gained mixture of these polymkeric substance etc. with nitrogen treatment to replace air, under nitrogen atmosphere, it is added in the twin screw extruder then with feeder.With ram pump with the whiteruss (dynamic viscosity under 37.78 ℃: 7.59 * 10 ^-5m ²/ s) inject the machine barrel of this forcing machine.

Adjust this feeder and pump and make that after melt-kneaded the content of whiteruss is 58wt% in whole mixtures to be extruded.The melt-kneaded condition is identical with embodiment 1.Subsequently, this melt-kneaded product extruded to be cast to through control by the T-mould have on the cooling roller of 25 ℃ of surface temperatures, obtaining thickness is the gel film of 2200 μ m.Then, this gel film is introduced in the simultaneously biaxial stretch-formed tenter machine and biaxial stretch-formed.Default stretching condition is as follows: the MD ratio is 7.0, and the TD ratio is 6.4, and preset temp is 126 ℃.Next, will be the tensile gel film introduce the methyl ethyl ketone container and make it be immersed in the methyl ethyl ketone fully and remove whiteruss with extraction, remove methyl ethyl ketone by drying afterwards.Then, will carry out heat setting in the gel film introducing TD tenter machine of so handling.The heat setting temperature is 120 ℃ and the TD relaxation rate is adjusted to 0.80.Table 1 shows the physicals of the microporous membrane of acquisition like this.

[embodiment 3]

In the rotating cylinder blender, with the ratio of 75wt% homopolymer polyethylene (PEA), its Mw/Mn of 18wt% be 9 and the Mv value be 3,000, the polypropylene identical with embodiment 1 of 000 homopolymer polyethylene (PEB) and 7wt% done blend, 45wt% is that molecular weight is 10 in this homopolymer polyethylene (PEA), 000 or the ratio of lower component and its Mw/Mn be 70 and the Mv value be 310,000.[3-(3 to add 1wt% tetramethylolmethane four in the gained mixture of only being made up of these polymkeric substance of 99wt%, the 5-di-tert-butyl-hydroxy phenyl) propionic ester] as oxidation inhibitor, and it is done blend to obtain the mixture of these polymkeric substance etc. in the rotating cylinder blender.With the gained mixture of these polymkeric substance etc. with nitrogen treatment to replace air, under nitrogen atmosphere, it is added in the twin screw extruder then with feeder.With ram pump with the whiteruss (dynamic viscosity under 37.78 ℃: 7.59 * 10 ^-5m ²/ s) inject the machine barrel of this forcing machine.

Adjust this feeder and pump and make that after melt-kneaded the content of whiteruss is 70wt% in whole mixtures to be extruded.The melt-kneaded condition is identical with embodiment 1.Subsequently, this melt-kneaded product extruded to be cast to through control by the T-mould have on the cooling roller of 25 ℃ of surface temperatures, obtaining thickness is the gel film of 1000 μ m.Then, this gel film is introduced in the simultaneously biaxial stretch-formed tenter machine and biaxial stretch-formed.Default stretching condition is as follows: the MD ratio is 7.0, and the TD ratio is 6.4, and preset temp is 123 ℃.Next, will be the tensile gel film introduce the methyl ethyl ketone container and make it be immersed in the methyl ethyl ketone fully and remove whiteruss with extraction, remove methyl ethyl ketone by drying afterwards.Then, will carry out heat setting in the gel film introducing TD tenter machine of so handling.The heat setting temperature is 112 ℃ and the TD relaxation rate is adjusted to 0.73.Table 1 shows the physicals of the microporous membrane of acquisition like this.

[embodiment 4]

In the rotating cylinder blender, with the ratio of PEA, 40wt% its Mw/Mn identical of 50wt% with embodiment 1 be 8 and the Mv value be 950, its Mv value of 000 homopolymer polyethylene (PEB) and 10wt% be 450,000 and ethylene content be that the unregulated polymer polypropylene of 0.9mol% is done blend.In the Henschel mixing tank, with the gained mixture of only forming of 53wt%, 1wt% tetramethylolmethane four [3-(3, the 5-di-tert-butyl-hydroxy phenyl) propionic ester], the 33wt% whiteruss (dynamic viscosity under 37.78 ℃: 7.59 * 10 as oxidation inhibitor by these polymkeric substance ^-5m ²/ s) and 13wt% levigated silicon-dioxide mix to obtain the mixture of these polymkeric substance etc.With the gained mixture of these polymkeric substance etc. with nitrogen treatment to replace air, under nitrogen atmosphere, it is added in the twin screw extruder then with feeder.With ram pump with the whiteruss (dynamic viscosity under 37.78 ℃: 7.59 * 10 ^-5m ²/ s) inject the machine barrel of this forcing machine.

Adjust this feeder and pump and make that after melt-kneaded the content of whiteruss is 60wt% in whole mixtures to be extruded.The melt-kneaded condition is identical with embodiment 1.Subsequently, this melt-kneaded product extruded to be cast to through control by the T-mould have on the cooling roller of 25 ℃ of surface temperatures, obtaining thickness is the gel film of 1500 μ m.Then, this gel film is introduced in the simultaneously biaxial stretch-formed tenter machine and biaxial stretch-formed.Default stretching condition is identical with embodiment 3.Next, will be the tensile gel film introduce the methyl ethyl ketone container and make it be immersed in the methyl ethyl ketone fully and remove whiteruss with extraction, remove methyl ethyl ketone by drying afterwards.In addition, introduce in the sodium hydroxide container gel film of having removed whiteruss with extraction and remove silicon-dioxide, and washing is dry then.Afterwards, will carry out heat setting in the gel film introducing TD tenter machine of so handling.The heat setting temperature is identical with embodiment 3 with the TD relaxation rate.Table 1 shows the physicals of the microporous membrane of acquisition like this.

[embodiment 5]

In the rotating cylinder blender, the identical polypropylene with embodiment 1 of the PEA identical with embodiment 1 of 90wt% and 10wt% is done blend.[3-(3 to add 1wt% tetramethylolmethane four in the gained mixture of only being made up of these polymkeric substance of 99wt%, the 5-di-tert-butyl-hydroxy phenyl) propionic ester] as oxidation inhibitor, and it is done blend to obtain the mixture of these polymkeric substance etc. in the rotating cylinder blender.With the gained mixture of these polymkeric substance etc. with nitrogen treatment to replace air, under nitrogen atmosphere, it is added in the twin screw extruder then with feeder.With ram pump with the whiteruss (dynamic viscosity under 37.78 ℃: 7.59 * 10 ^-5m ²/ s) inject the machine barrel of this forcing machine.

Adjust this feeder and pump and make that after melt-kneaded the content of whiteruss is 55wt% in whole mixtures to be extruded.The melt-kneaded condition is identical with embodiment 1.Subsequently, this melt-kneaded product extruded to be cast to through control by the T-mould have on the cooling roller of 25 ℃ of surface temperatures, obtaining thickness is the gel film of 1300 μ m.Then, this gel film is introduced in the simultaneously biaxial stretch-formed tenter machine and biaxial stretch-formed.Default stretching condition is identical with embodiment 1.Next, will be the tensile gel film introduce the methyl ethyl ketone container and make it be immersed in the methyl ethyl ketone fully and remove whiteruss with extraction, remove methyl ethyl ketone by drying afterwards.Then, will carry out heat setting in the gel film introducing TD tenter machine of so handling.The heat setting temperature is identical with embodiment 1 with the TD relaxation rate.Table 1 shows the physicals of the microporous membrane of acquisition like this.

[embodiment 6]

In the rotating cylinder blender, with the ratio of 75wt% homopolymer polyethylene (PEA), its Mw/Mn of 15wt% be 7 and the Mv value be 120,000 linear copolymers high density polyethylene(HDPE) (comonomer: propylene; Content 0.6mol%) (PEB) and its Mv value of 10wt% be that 400,000 homopolymer polypropylene is done blend, in this homopolymer polyethylene (PEA) 15wt% be molecular weight be 10,000 or the ratio of lower component and its Mw/Mn be 43 and the Mv value be 700,000.[3-(3 to add 1wt% tetramethylolmethane four in the gained mixture of only being made up of these polymkeric substance of 99wt%, the 5-di-tert-butyl-hydroxy phenyl) propionic ester] as oxidation inhibitor, and it is done blend to obtain the mixture of these polymkeric substance etc. in the rotating cylinder blender.With the gained mixture of these polymkeric substance etc. with nitrogen treatment to replace air, under nitrogen atmosphere, it is added in the twin screw extruder then with feeder.With ram pump with the whiteruss (dynamic viscosity under 37.78 ℃: 7.59 * 10 ^-5m ²/ s) inject the machine barrel of this forcing machine.

Adjust this feeder and pump and make that after melt-kneaded the content of whiteruss is 55wt% in whole mixtures to be extruded.Carry out melt-kneaded under the following conditions: preset temp: 200 ℃, screw rod revolution: 240rpm, discharging speed: 12kg/h.Subsequently, this melt-kneaded product extruded to be cast to through control by the T-mould have on the cooling roller of 25 ℃ of surface temperatures, obtaining thickness is the gel film of 2100 μ m.Then, this gel film is introduced in the simultaneously biaxial stretch-formed tenter machine and biaxial stretch-formed.Default stretching condition is as follows: the MD ratio is 7.0, and the TD ratio is 6.4, and preset temp is 118 ℃.Next, will be the tensile gel film introduce the methyl ethyl ketone container and make it be immersed in the methyl ethyl ketone fully and remove whiteruss with extraction, remove methyl ethyl ketone by drying afterwards.Then, will carry out heat setting in the gel film introducing TD tenter machine of so handling.The heat setting temperature is 105 ℃ and the TD relaxation rate is adjusted to 0.80.Table 1 shows the physicals of the microporous membrane of acquisition like this.

[embodiment 7]

In the rotating cylinder blender, with the ratio of 75wt% homopolymer polyethylene (PEA), its Mw/Mn of 15wt% be 8 and the Mv value be 300,000 high-density ceridust (PEB) and its Mv value of 10wt% are 400,000 homopolymer polypropylene is done blend, 15wt% is that molecular weight is 10 in this homopolymer polyethylene (PEA), 000 or the ratio of lower component and its Mw/Mn be 43 and the Mv value be 700,000.[3-(3 to add 1wt% tetramethylolmethane four in the gained mixture of only being made up of these polymkeric substance of 99wt%, the 5-di-tert-butyl-hydroxy phenyl) propionic ester] as oxidation inhibitor, and it is done blend to obtain the mixture of these polymkeric substance etc. in the rotating cylinder blender.With the gained mixture of these polymkeric substance etc. with nitrogen treatment to replace air, under nitrogen atmosphere, it is added in the twin screw extruder then with feeder.With ram pump with the whiteruss (dynamic viscosity under 37.78 ℃: 7.59 * 10 ^-5m ²/ s) inject the machine barrel of this forcing machine.

Adjust this feeder and pump and make that after melt-kneaded the content of whiteruss is 55wt% in whole mixtures to be extruded.Carry out melt-kneaded under the following conditions: preset temp: 200 ℃, screw rod revolution: 240rpm, discharging speed: 12kg/h.Subsequently, this melt-kneaded product extruded to be cast to through control by the T-mould have on the cooling roller of 25 ℃ of surface temperatures, obtaining thickness is the gel film of 2100 μ m.Then, this gel film is introduced in the simultaneously biaxial stretch-formed tenter machine and biaxial stretch-formed.Default stretching condition is as follows: the MD ratio is 7.0, and the TD ratio is 6.4, and preset temp is 118 ℃.Next, will be the tensile gel film introduce the methyl ethyl ketone container and make it be immersed in the methyl ethyl ketone fully and remove whiteruss with extraction, remove methyl ethyl ketone by drying afterwards.Then, will carry out heat setting in the gel film introducing TD tenter machine of so handling.The heat setting temperature is 115 ℃ and the TD relaxation rate is adjusted to 0.80.Table 1 shows the physicals of the microporous membrane of acquisition like this.

[embodiment 8]

Following material is mixed: 30wt% homopolymer polyethylene (PEA), the ratio of its Mw/Mn of 15wt% be 8 and the Mv value be 300,000 high-density ceridust (PEB), its Mv value of 5wt% is 400,000 homopolymer polypropylene, 30.6wt% dioctyl phthalate (DOP) (DOP), [3-(3 as the tetramethylolmethane four of oxidation inhibitor for 18.4wt% levigated silicon-dioxide and 1wt%, the 5-di-tert-butyl-hydroxy phenyl) propionic ester], 15wt% is that molecular weight is 10 in this homopolymer polyethylene (PEA), 000 or the ratio of lower component and its Mw/Mn be 43 and the Mv value be 700,000.With the gained mixture of these polymkeric substance etc. with nitrogen treatment to replace air, under nitrogen atmosphere, it is added in the twin screw extruder then with feeder.

Carry out melt-kneaded under the following conditions: preset temp: 200 ℃, screw rod revolution: 240rpm, discharging speed: 12kg/h.Subsequently, this melt-kneaded product extruded to be cast to through control by the T-mould have on the cooling roller of 80 ℃ of surface temperatures, obtaining thickness is the gel film of 110 μ m.From this gel film, extract and remove DOP and levigated silicon-dioxide to obtain microporous membrane.Two microporous membranes are stacked, and under 110 ℃ with 5 ratio longitudinal stretching, afterwards, be introduced in the TD tenter machine and at 130 times with 2 ratio cross directional stretch.After stretching the TD relaxation rate is adjusted to 0.80.Table 1 shows the physicals of gained microporous membrane.

[embodiment 9]

In the rotating cylinder blender, with the ratio of 75wt% homopolymer polyethylene (PEA), its Mw/Mn of 15wt% be 6 and the Mv value be 120, (hexene content: 2mol%) its Mv value of (PEB) and 10wt% is 400 to ethene-hexene copolymer of 000,000 homopolymer polypropylene is done blend, 20wt% is that molecular weight is 10 in this homopolymer ceridust (PEA), 000 or the ratio of lower component and its Mw/Mn be 43 and the Mv value be 550,000.[3-(3 to add 1wt% tetramethylolmethane four in the gained mixture of only being made up of these polymkeric substance of 99wt%, the 5-di-tert-butyl-hydroxy phenyl) propionic ester] as oxidation inhibitor, and it is done blend to obtain the mixture of these polymkeric substance etc. in the rotating cylinder blender.With the gained mixture of these polymkeric substance etc. with nitrogen treatment to replace air, under nitrogen atmosphere, it is added in the twin screw extruder then with feeder.With ram pump with the whiteruss (dynamic viscosity under 37.78 ℃: 7.59 * 10 ^-5m ²/ s) inject the machine barrel of this forcing machine.

Adjust this feeder and pump and make that after melt-kneaded the content of whiteruss is 55wt% in whole mixtures to be extruded.Carry out melt-kneaded under the following conditions: preset temp: 200 ℃, screw rod revolution: 240rpm, discharging speed: 12kg/h.Subsequently, this melt-kneaded product extruded to be cast to through control by the T-mould have on the cooling roller of 25 ℃ of surface temperatures, obtaining thickness is the gel film of 2000 μ m.Then, this gel film is introduced in the simultaneously biaxial stretch-formed tenter machine and biaxial stretch-formed.Default stretching condition is as follows: the MD ratio is 7.0, and the TD ratio is 6.4, and preset temp is 115 ℃.Next, will be the tensile gel film introduce the methyl ethyl ketone container and make it be immersed in the methyl ethyl ketone fully and remove whiteruss with extraction, remove methyl ethyl ketone by drying afterwards.Then, will carry out heat setting in the gel film introducing TD tenter machine of so handling.The heat setting temperature is 110 ℃ and the TD relaxation rate is adjusted to 0.70.Table 1 shows the physicals of the microporous membrane of acquisition like this.

[comparative example 1]

In the rotating cylinder agitator, with the 85wt% homopolymer polyethylene (wherein 6wt% be molecular weight be 10,000 or the ratio of lower component and its Mw/Mn be 7 and the Mv value be 270,000) and the ratio of its Mw/Mn of 15wt% be 9 and the Mv value be 3,000,000 homopolymer polyethylene is done blend.[3-(3 to add 1wt% tetramethylolmethane four in the gained mixture of only being made up of these polymkeric substance of 99wt%, the 5-di-tert-butyl-hydroxy phenyl) propionic ester] as oxidation inhibitor, and it is done blend to obtain the mixture of these polymkeric substance etc. in the rotating cylinder blender.With the gained mixture of these polymkeric substance etc. with nitrogen treatment to replace air, under nitrogen atmosphere, it is added in the twin screw extruder then with feeder.With ram pump with the whiteruss (dynamic viscosity under 37.78 ℃: 7.59 * 10 ^-5m ²/ s) inject the machine barrel of this forcing machine.

Adjust this feeder and pump and make that after melt-kneaded the content of whiteruss is 65wt% in whole mixtures to be extruded.The melt-kneaded condition is identical with embodiment 1.Subsequently, this melt-kneaded product extruded to be cast to through control by the T-mould have on the cooling roller of 25 ℃ of surface temperatures, obtaining thickness is the gel film of 1200 μ m.Then, this gel film is introduced in the simultaneously biaxial stretch-formed tenter machine and biaxial stretch-formed.Default stretching condition is identical with embodiment 1.Next, will be the tensile gel film introduce the methyl ethyl ketone container and make it be immersed in the methyl ethyl ketone fully and remove whiteruss with extraction, remove methyl ethyl ketone by drying afterwards.Then, will carry out heat setting in the gel film introducing TD tenter machine of so handling.The heat setting temperature is 123 ℃ and the TD relaxation rate is adjusted to 1.00.In the microporous membrane of like this gained, many defectives have been observed and this film does not have the desired quality of battery separator.Table 1 shows the physicals of the microporous membrane that obtains.

[comparative example 2]

In the rotating cylinder blender, the identical PEB with embodiment 1 of the PEA identical with embodiment 1 of 85wt% and 15wt% is done blend.[3-(3 to add 1wt% tetramethylolmethane four in the gained mixture of only being made up of these polymkeric substance of 99wt%, the 5-di-tert-butyl-hydroxy phenyl) propionic ester] as oxidation inhibitor, and it is done blend to obtain the mixture of these polymkeric substance etc. in the rotating cylinder blender.With the gained mixture of these polymkeric substance etc. with nitrogen treatment to replace air, under nitrogen atmosphere, it is added in the twin screw extruder then with feeder.With ram pump with the whiteruss (dynamic viscosity under 37.78 ℃: 7.59 * 10 ^-5m ²/ s) inject the machine barrel of this forcing machine.

Adjust this feeder and pump and make that after melt-kneaded the content of whiteruss is 55wt% in whole mixtures to be extruded.The melt-kneaded condition is identical with embodiment 1.Subsequently, this melt-kneaded product extruded to be cast to through control by the T-mould have on the cooling roller of 25 ℃ of surface temperatures, obtaining thickness is the gel film of 1300 μ m.Then, this gel film is introduced in the simultaneously biaxial stretch-formed tenter machine and biaxial stretch-formed.Default stretching condition is identical with embodiment 2.Next, will be the tensile gel film introduce the methyl ethyl ketone container and make it be immersed in the methyl ethyl ketone fully and remove whiteruss with extraction, remove methyl ethyl ketone by drying afterwards.Then, will carry out heat setting in the gel film introducing TD tenter machine of so handling.The heat setting temperature is identical with embodiment 1 with the TD relaxation rate.Table 1 shows the physicals of gained microporous membrane like this.

[comparative example 3]

In the PEA identical of 99wt%, add 1wt% tetramethylolmethane four [3-(3, the 5-di-tert-butyl-hydroxy phenyl) propionic esters], and it is done blend to obtain the mixture of these polymkeric substance etc. in the rotating cylinder blender as oxidation inhibitor with embodiment 6.With the gained mixture of these polymkeric substance etc. with nitrogen treatment to replace air, under nitrogen atmosphere, it is added in the twin screw extruder then with feeder.With ram pump with the whiteruss (dynamic viscosity under 37.78 ℃: 7.59 * 10 ^-5m ²/ s) inject the machine barrel of this forcing machine.

Adjust this feeder and pump and make that after melt-kneaded the content of whiteruss is 55wt% in whole mixtures to be extruded.The melt-kneaded condition is identical with embodiment 1.Subsequently, this melt-kneaded product extruded to be cast to through control by the T-mould have on the cooling roller of 25 ℃ of surface temperatures, obtaining thickness is the gel film of 2100 μ m.Then, this gel film is introduced in the simultaneously biaxial stretch-formed tenter machine and biaxial stretch-formed.Default stretching condition is identical with embodiment 6.Next, will be the tensile gel film introduce the methyl ethyl ketone container and make it be immersed in the methyl ethyl ketone fully and remove whiteruss with extraction, remove methyl ethyl ketone by drying afterwards.Then, will carry out heat setting in the gel film introducing TD tenter machine of so handling.The heat setting temperature is identical with embodiment 6 with the TD relaxation rate.Table 1 shows the physicals of gained microporous membrane like this.

[comparative example 4]

In the rotating cylinder blender, (wherein 15wt% is that molecular weight is 10 with the 70wt% homopolymer polyethylene, 000 or the ratio of lower component and its Mw/Mn be 7 and the Mv value be 100,000), the ratio of its Mw/Mn of 20wt% be 9 and the Mv value be 3,000, its Mv value of 000 homopolymer polyethylene and 10wt% is 400,000 the dried blend of homopolymer polypropylene.In the PEA identical of 99wt%, add 1wt% tetramethylolmethane four [3-(3, the 5-di-tert-butyl-hydroxy phenyl) propionic esters], and it is done blend to obtain the mixture of these polymkeric substance etc. in the rotating cylinder blender as oxidation inhibitor with embodiment 6.With the gained mixture of these polymkeric substance etc. with nitrogen treatment to replace air, under nitrogen atmosphere, it is added in the twin screw extruder then with feeder.With ram pump with the whiteruss (dynamic viscosity under 37.78 ℃: 7.59 * 10 ^-5m ²/ s) inject the machine barrel of this forcing machine.

Adjust this feeder and pump and make that after melt-kneaded the content of whiteruss is 65wt% in whole mixtures to be extruded.The melt-kneaded condition is identical with embodiment 1.Subsequently, this melt-kneaded product extruded to be cast to through control by the T-mould have on the cooling roller of 25 ℃ of surface temperatures, obtaining thickness is 1200 μ m gel films.。Then, this gel film is introduced in the simultaneously biaxial stretch-formed tenter machine and biaxial stretch-formed.Default stretching condition is identical with embodiment 1.Next, will be the tensile gel film introduce the methyl ethyl ketone container and make it be immersed in the methyl ethyl ketone fully and remove whiteruss with extraction, remove methyl ethyl ketone by drying afterwards.Then, will carry out heat setting in the gel film introducing TD tenter machine of so handling.The heat setting temperature is 115 ℃ and the TD relaxation rate is adjusted to 0.75.In the microporous membrane of like this gained, many defectives have been observed and this film does not have the desired quality of battery separator.Table 1 shows the physicals of gained microporous membrane.

[comparative example 5]

In the rotating cylinder blender, with the ratio of its Mw/Mn of 30wt% be 7 and the Mv value be 2,000, the ratio of 000 homopolymer polyethylene, its Mw/Mn of 40wt% be 6 and the Mv value be 300, the ratio of 000 homopolymer high density polyethylene, its Mw/Mn of 10wt% be 3 and the Mv value be 70,000 ethylene-octene copolymer (octene content is 12.0mol%, and fusing point is 100 ℃) and its Mv value of 20wt% are 400,000 the dried blend of homopolymer polypropylene.Afterwards, carry out the program identical, except being 120 ℃ with the heat setting temperature change with Comparative Examples 4.In the microporous membrane of like this gained, many defectives have been observed and this film does not have the desired quality of battery separator.Table 1 shows the physicals of gained microporous membrane.

[table 1-1]

Industrial applicability

The microporous barrier that the present invention is made by polyolefin relates to the isolation and selection infiltration that for example is used for material And as the microporous barrier of partition member, and especially be suitable as the dividing plate of lithium ion battery etc.

Claims (21)

1. the microporous membrane of making by polyolefine, its molecular weight that comprises that polythene PE A and polypropylene and its have is 10,000 or lower component concentration be 8 to 60wt%, its porosity is 20 to 95% and is 10% or lower 100 ℃ of following degree of heat-shrinkage, and wherein polyacrylic ratio is for more than or equal to 3wt% and be less than or equal to 50wt%; Containing 8 to 60wt% molecular weight among this polythene PE A is 10,000 or lower component, and the ratio Mw/Mn of its weight-average molecular weight Mw and number-average molecular weight Mn for more than or equal to 11 and be less than or equal to 100 and viscosity-average molecular weight Mv for more than or equal to 100,000 and be less than or equal to 1,000,000.

2. according to the microporous membrane of making by polyolefine of claim 1, its ratio that further comprises Mw/Mn for more than or equal to 1 and be less than or equal to 10 and Mv value be more than or equal to 10,000 and be less than or equal to 500,000 polythene PE B.

3. according to the microporous membrane of making by polyolefine of claim 1, its ratio that further comprises Mw/Mn for more than or equal to 1 and be less than or equal to 10 and Mv value be more than or equal to 700,000 and be less than or equal to 7,000,000 polythene PE B.

4. according to the microporous membrane of being made by polyolefine of claim 1, wherein polyacrylic ratio is for more than or equal to 5wt% and be less than or equal to 30wt%.

5. according to the microporous membrane of being made by polyolefine of claim 1, wherein the ratio of polythene PE A is for more than or equal to 10wt% and be less than or equal to 94wt%.

6. according to the microporous membrane of being made by polyolefine of claim 1, wherein the ratio of polythene PE A is for more than or equal to 20wt% and be less than or equal to 90wt%.

7. according to each the microporous membrane of making by polyolefine in the claim 1 to 6, wherein more than or equal to 100,000 and be less than or equal to 1,000, in 000 molecular weight M (i) scope, as follows between the denary logarithm of the molecular weight M (i) that is measured by GPC/FTIR is worth with terminal methyl concentration C (M (i)) based on the linear approximate relationship of method of least squares:

C(M(i))＝A×log(M(i))+B

A and B are constant-0.015≤A≤2.000.

8. according to each the microporous membrane of being made by polyolefine in the claim 1 to 6, it has 25% or lower degree of heat-shrinkage under 120 ℃.

9. according to each the microporous membrane of being made by polyolefine in the claim 1 to 6, it has 20% or lower degree of heat-shrinkage under 120 ℃.

10. according to each the microporous membrane of being made by polyolefine in the claim 1 to 6, it has 600kPa or lower TD thermal shrinkage stress under 150 ℃.

11. according to each the microporous membrane of being made by polyolefine in the claim 1 to 6, wherein above-mentioned PEA is the polyethylene that obtains by the multistep polymerization method.

12. the microporous membrane of making by polyolefine according to claim 2 or 3, wherein above-mentioned PEA shows that in the molecular weight distribution that obtains by GPC the maximum peak of at least two maximum peaks or acromion and above-mentioned PEB is between the peak of the peak of PEA X and PEA Y, wherein the peak X of PEA is at the PEA peak of lower molecular weight one side as maximum peak or acromion, and the peak Y of PEA is at the PEA peak of high molecular one side as maximum peak or acromion.

13. according to the microporous membrane of being made by polyolefine of claim 12, it has 25% or lower degree of heat-shrinkage under 120 ℃.

14. according to the microporous membrane of being made by polyolefine of claim 12, it has 20% or lower degree of heat-shrinkage under 120 ℃.

15. according to the microporous membrane of being made by polyolefine of claim 12, it has 600kPa or lower TD thermal shrinkage stress under 150 ℃.

16. according to the microporous membrane of being made by polyolefine of claim 12, wherein above-mentioned PEA is the polyethylene that obtains by the multistep polymerization method.

17. the microporous membrane of making by polyolefine according to claim 2 or 3, it has 20% or lower degree of heat-shrinkage under 120 ℃, wherein above-mentioned PEA is the polyethylene that obtains by the multistep polymerization method, and wherein above-mentioned PEA shows at least two maximum peaks or acromion in the molecular weight distribution that obtains by GPC, and the maximum peak of above-mentioned PEB is between the peak of the peak of PEA X and PEA Y, wherein the peak X of PEA is at the PEA peak of lower molecular weight one side as maximum peak or acromion, and the peak Y of PEA is at the PEA peak of high molecular one side as maximum peak or acromion.

18. according to each the microporous membrane of being made by polyolefine in the claim 1 to 6, it has 600kPa or lower TD thermal shrinkage stress and have 20% or lower degree of heat-shrinkage under 120 ℃ under 150 ℃.

19. according to the microporous membrane of being made by polyolefine of claim 18, wherein said PEA is the polyethylene that obtains by the multistep polymerization method.

20. a method for preparing according to each the microporous membrane of being made by polyolefine in the claim 1 to 6, this method comprises:

With polymer materials and softening agent, perhaps polymer materials, softening agent and inorganic reagent melt-kneaded, and the step that the gained mixture is extruded; With

Stretch and extract this softening agent, perhaps stretch, extract this softening agent and randomly extract this inorganic reagent, carry out the step of heat setting then.

21. the method for the microporous membrane of making by polyolefine according to the preparation of claim 20, wherein more than or equal to 100 ℃ and less than 135 ℃ temperature under carry out this heat setting with 0.6 to 0.9 relaxation rate.

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