JP2008012699A - Manufacturing method of resin molded article - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a resin molded article capable of more uniformizing the mutual mixed state of resins by the combination of the specific resins and a plasticizer. <P>SOLUTION: After a composition comprising a first resin becoming a main component, the second resin mixed with it and the plasticizer capable of swelling at least the second resin is kneaded under heating, the kneaded composition is extruded into a predetermined cross-sectional shape to obtain an extrusion molded article. In this manufacturing method of the resin molded article, the prescribed swelling time of the second resin calculated on the basis of pulse NMR when the second resin is swollen at 30°C using the plasticizer is set to 25 min or below. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a resin molded product obtained by heat-kneading a composition containing a plurality of types of resins and then extruding to obtain an extruded product, and is particularly useful as a method for producing a porous membrane or film.

  Non-aqueous electrolyte batteries that use light metal ions such as lithium for electrode reactions have high energy density and low self-discharge, and therefore have a wide range of applications due to the high performance and miniaturization of electronic devices. As a configuration of such a nonaqueous electrolyte battery, a spirally wound body or a multilayer stack body in which a wide effective electrode area is secured by laminating or winding a sheet-like positive electrode, a negative electrode, and a separator is used. . The separator basically prevents the electrode from being short-circuited and allows a battery reaction by allowing ions to permeate through the porous structure.

  Currently, lithium ion batteries widely used in the world use lithium cobaltate, lithium manganate, or Co-Mn-Ni lithium as a positive electrode active material, and carbon materials such as graphite and hard carbon as a negative electrode active material Is used. As the separator material, polyolefin materials are usually used because of various necessary properties such as chemical and electrochemical stability, strength, film thickness, and pore diameter.

  With polyolefin materials, the film shape cannot be maintained at temperatures above the melting point. When the battery is in a high temperature state, the polyolefin material porous film cannot maintain the shape of the film, so that it does not have a function of separating the positive electrode and the negative electrode, and there is a risk that the battery will be further heated.

  As separators having high heat resistance, the following Patent Documents 1 and 2 propose battery separators made of a porous film such as a nonwoven fabric made of aramid fibers. However, in these separators, the piercing strength of the membrane is insufficient, and there is a high possibility that when the battery is manufactured, the membrane is broken by the surface pressure between the electrodes and an internal short circuit is caused. In addition, in order to have a strength that does not cause an internal short circuit, the film thickness increases, the internal resistance of the separator portion increases, causing a decrease in battery performance, and the volume occupied by the separator in a certain battery container Therefore, it has a very serious drawback that the energy density of the battery is lowered.

  As a method for solving this problem, Patent Document 3 below discloses a polymer containing a polymer having a C═C double bond and an aliphatic ring having 5 to 10 carbon atoms in the main chain, and another resin. A porous film made of a combined composition has been proposed. This porous film has a sufficient piercing strength for battery production and also has high heat resistance due to cross-linking of C═C double bonds.

  This method for producing a porous film is obtained by extruding a composition containing a resin as a main component, the above-mentioned polymer (norbornene, etc.) to be mixed therewith and a plasticizer with heat mixing using a biaxial kneader or the like. The plasticizer is extracted after the gel-like sheet is formed.

  However, when the resin and the plasticizer are mixed, if the dispersion of norbornene or the like is not uniform, the structure of the finally obtained porous film is not uniform. If the structure of the porous film is not uniform, there are problems such as insufficient battery performance and increased unsafeness in the unsteady state of the battery.

  And the problem by the non-uniform dispersion | distribution at the time of mixing such resin is not restricted to the case of porous films, such as a separator, It is a problem which arises with respect to the resin molding in general.

Japanese Patent No. 3142893 JP-A-5-335005 International Publication WO00 / 68305

  Then, the objective of this invention is providing the manufacturing method of the resin molding which can make the mixing state of resin more uniform by the combination of specific resin and a plasticizer.

  As a result of diligent research on a method for eliminating such non-uniformity as described above, the present inventors have found that a specified swelling time obtained by pulse NMR when swelling at 30 ° C. with a plasticizer is 25 minutes or less. As a result, it was found that the mixed state of the resins can be made more uniform, and the present invention has been completed.

  That is, the method for producing a resin molded product of the present invention heats a composition containing a first resin as a main component, a second resin mixed with the first resin, and a plasticizer capable of swelling at least the second resin. In the method for producing a resin molded product comprising the step of extruding to obtain an extruded product after kneading, the second resin has a specified swelling time of 25 minutes determined by pulse NMR when swollen with the plasticizer at 30 ° C. It is characterized by the following. The specified swelling time in the present invention specifically refers to a value measured by the measuring method described in the examples.

  According to the method for producing a resin molded product of the present invention, since the second resin having a specified swelling time obtained by pulse NMR of 25 minutes or less is used, mixing with the first resin is caused by the swelling effect of the second resin during heating and kneading. And the mixing state between the resins can be made more uniform.

  In the above, it is preferable to include a step of forming the extruded product into a film to obtain a filmed product, and a step of extracting the plasticizer from the filmed product or the molded product before film formation. Through these steps, a film in which the resins are uniformly mixed and the plasticizer is removed can be obtained.

  In that case, it is preferable to obtain a porous membrane. Depending on the conditions during film formation and the composition of the composition, a porous membrane can be obtained by extraction of a plasticizer, and a porous membrane in which resins are uniformly mixed can be obtained.

  The second resin is preferably polynorbornene. Since polynorbornene often has different specified swelling times between products depending on lots, powder shapes, chemical states, and the like, the present invention is particularly effective.

  Embodiments of the present invention will be described below.

  In the method for producing a resin molded product of the present invention, a composition containing a first resin as a main component, a second resin mixed therewith, and a plasticizer capable of swelling at least the second resin is heat-kneaded. Thereafter, the method includes a step of obtaining an extruded product by extrusion with a predetermined cross-sectional shape.

  As the first resin, any resin can be used as long as it is a resin that can be extruded by heating or kneading together with a plasticizer or the like, and various thermoplastic resins and thermoplastic elastomers can be preferably used. . Examples of the first resin include homopolymers or copolymers such as ethylene, propylene, vinyl chloride, styrene, vinylidene chloride, methyl methacrylate, and ethylene fluoride, polyamide, polyester, polycarbonate, polyphenylene oxide, and polyurethane. It is done.

  As 1st resin, it is preferable to contain 50 weight% or more in all the resin components, and it is more preferable to contain 75 weight% or more.

  As the second resin to be mixed with the first resin, any resin that is compatible or dispersible in the first resin can be used. Generally, in order to increase the compatibility or make the dispersed phase finer, it is preferable to select a resin having a repeating unit that is the same as or similar to the first resin as the second resin.

  As 2nd resin, it is preferable to contain 1-50 weight% in all the resin components, and it is more preferable to contain 3-30 weight%. The composition may further contain other resin.

  The plasticizer is used to plasticize the first resin and the second resin to promote the mixing of the resins. However, in the method for producing a porous membrane as described later, the porous material is made porous by an extraction step after phase separation. A structure can be formed.

  Any plasticizer may be used as long as it can swell the second resin. Accordingly, various solvents, liquid compounds and the like in which the second resin has a certain degree of solubility can be used. As a plasticizer, what has a certain amount of solubility also to 1st resin is preferable.

  Heat kneading can be performed with a biaxial kneader or a kneader, and the heating temperature is appropriately determined according to the melting point and solubility of the resin. Extrusion is performed using a die having a predetermined cross-sectional shape as necessary, and an extruded product can be obtained by press molding after the extrusion.

  In this invention, it is preferable to include the process of forming this extrusion molding into a film and obtaining a film formation, and the process of extracting the said plasticizer from the film formation or the molding before film formation. Moreover, it is preferable to obtain a porous membrane by this. Hereinafter, an embodiment in which a porous membrane is obtained by such a process will be described.

  In this embodiment, a composition containing a polyolefin resin as a first resin, a polymer having a double bond as a second resin (such as polynorbornene), and a solvent as a plasticizer is melt-kneaded and cooled after extrusion. Then, after forming a sheet-like molded product, an example including a step of subjecting the sheet-shaped molded product to heat rolling, stretching treatment, and desolvation treatment is shown.

  Examples of the polyolefin-based resin include polyolefin resins such as polyethylene and polypropylene, and modified polyolefin resins such as an ethylene-acrylic monomer copolymer. Further, elastomers containing olefin units such as ethylene propylene rubber (EPR), butyl rubber, styrene butadiene rubber may be used. Among these, ultra high molecular weight polyethylene having a weight average molecular weight of 1,000,000 or more is particularly preferable from the viewpoint of increasing the strength of the porous membrane. These polyolefin resins may be used alone or in admixture of two or more.

  The blending amount of the polyolefin resin is preferably 10 to 40% by weight. When the blending amount of the polyolefin resin is less than 10% by weight, the strength of the porous film to be obtained is weak, and when it exceeds 40% by weight, uniform kneading becomes difficult and thickness unevenness and characteristic unevenness tend to be caused.

  The solvent is not particularly limited as long as it is excellent in solubility of the polyolefin resin. For example, nonane, decane, undecane, dodecane, decalin, liquid paraffin, and other aliphatic or cyclic hydrocarbons, and mineral oil fractions having boiling points corresponding thereto. Or a mixture thereof, but a non-volatile solvent such as paraffin oil is preferred.

  The amount of the solvent is preferably in the range of 60 to 90% by weight of the total weight, and if the range is exceeded, the strength of the porous film obtained becomes extremely weak, and if it is less than the range, uniform kneading becomes difficult and uniform. A porous film having a pore structure cannot be obtained.

In addition, the weight is given for the purpose of providing a shutdown function (function to block the current by melting the microporous film to prevent accidents such as ignition when the temperature in the battery film rises) One or more kinds of polyolefins having an average molecular weight of less than 5 × 10 ⁵ , thermoplastic elastomers, and graft copolymers may be contained.

  Moreover, in order to heat-crosslink a porous membrane, you may add the polymer which has a reactive functional group. Examples of such a polymer include a polymer having a double bond, a polymer grafted with an acid anhydride group, a polymer having an epoxy group, and the like.

  As the polymer having a double bond, for example, at least one polymer among polynorbornene (norbornene ring-opening polymer), ethylene-propylene-terpolymer, and polybutadiene is preferable.

  Note that additives such as an antioxidant, an antistatic agent, an ultraviolet absorber, a dye, a nucleating agent, a pigment, a flame retardant, and a filler are added to the resin composition as necessary. You may add in the range which does not impair.

  In the production method of the present invention, a second resin having a specified swelling time obtained by pulse NMR of 25 minutes or less, preferably 20 minutes or less, when swollen at 30 ° C. using a plasticizer (solvent). Is used. In the present embodiment, for example, polynorbornene is used as the second resin.

  Polynorbornene swells with a non-volatile solvent containing a large amount of alicyclic hydrocarbons such as liquid paraffin, which is suitably used when producing a gel-like sheet. This swelling property changes depending on the shape and chemical state of polynorbornene. If the swelling property is low, the kneading step of the step of producing the gel-like sheet is not sufficiently crushed and the dispersion becomes insufficient. Since the dispersibility of the resin is determined by the gel-like sheet after kneading, if the dispersibility is insufficient in this step, the structure of the finally obtained porous film becomes non-uniform, and the battery performance cannot be sufficiently obtained. Or inconveniences such as an increase in unsafeness during the unsteady state of the battery.

The present inventors evaluated the swelling property of polynorbornene into a plasticizer by pulse NMR of a mixture of polynorbornene and liquid paraffin. Using pulsed NMR, the time course of ¹ H relaxation time is measured by the Solid Echo method, and the relaxation curve is regarded as three components: a short relaxation component, an intermediate component, and a long component, and is analyzed using the least square method. -Separated and determined the ratio of each component. The component having a short relaxation time is a component of polynorbornene not swollen, and the intermediate component is a component of polynorbornene swollen with liquid paraffin.

  The component having a long relaxation time is a liquid paraffin component which is a liquid. As described above, polynorbornene shifts from an initial short relaxation time component to an intermediate relaxation time component by swelling with liquid paraffin. From the change of these two components, the swelling property of polynorbornene can be evaluated.

  Specifically, the relationship between the elapsed time after mixing polynorbornene and liquid paraffin and the component ratio of the components of the short relaxation time and the intermediate relaxation time at each time is illustrated. The time was defined as the specified swelling time. In order to obtain a porous film having high resin dispersibility at the time of kneading and a uniform structure, the specified swelling time needs to be 25 minutes or less. When it exceeds 25 minutes, crushing during the kneading process of polynorbornene becomes insufficient, the dispersibility of the resin becomes low, and the structure of the finally obtained porous film becomes non-uniform.

  In the melt-kneading step, the polyolefin resin and the solvent are mixed in a uniform slurry, and the resulting composition is kneaded at a temperature in the range of 140 to 220 ° C., preferably 150 to 180 ° C. to obtain a uniform kneaded product. Prepare.

  In this embodiment, in order to obtain sufficient entanglement of polymer chains, it is important to knead the polyolefin resin and solvent mixture by applying a high shearing force. When sufficient shearing force cannot be applied at the time of kneading, the entanglement becomes insufficient and the strength cannot be increased. Therefore, a kneader or a biaxial kneader that can give a strong shearing force to the mixture is preferably used for kneading the polyolefin-based composition and the solvent.

  The melt-kneaded product thus obtained is extruded into a sheet shape and cooled to obtain a sheet-shaped molded product. The cooling method at this time is, for example, a method of cooling by passing through a sizing die cooled to a predetermined temperature, a method of cooling by immersing in a refrigerant cooled to a predetermined temperature, or a roll cooled to a predetermined temperature. The method of cooling by making it contact is mention | raise | lifted.

  2-20 mm is preferable and, as for the thickness of the sheet-like molding (gel-like sheet) gelatinized after cooling, 4-10 mm is more preferable. Since the thermal conductivity of the gel-like sheet is not large, it tends to be less cooled as it is closer to the center than the surface layer. In particular, this tendency is remarkable in a thick sheet of 5 mm or more, and the surface layer is cooled to a temperature close to the cooling medium in a few seconds, but the temperature decreases slowly in the center.

  Next, the obtained sheet-like molded product is heat-rolled and stretched. In general, the heat rolling and stretching are performed at a temperature of crystal dispersion temperature to melting point (onset temperature in DSC measurement) + 5 ° C. or less of the polyolefin-based composition. When ultra high molecular weight polyethylene is used as the polyolefin resin, the temperature is preferably 100 to 125 ° C, more preferably 110 to 120 ° C.

  This embodiment is particularly effective when heat rolling is performed at 100 ° C. or higher. Although it does not specifically limit about the method of heat rolling, It can carry out by well-known methods, such as press rolling and roll rolling. The hot rolling is preferably performed until the thickness of the sheet becomes 0.5 to 1.5 mm.

  The method for the stretching treatment is not particularly limited, and may be a normal tenter method, a roll method, or a combination of these methods. In addition, any method such as uniaxial stretching and biaxial stretching can be applied, and in the case of biaxial stretching, either longitudinal and transverse simultaneous stretching or sequential stretching may be used. preferable.

  The draw ratio can be appropriately set depending on the target porosity and strength, but it is preferably 5 to 250 times, more preferably 40 to 150 times the area before drawing. preferable.

  The temperature during the stretching treatment is preferably a temperature of the melting point of the polyolefin resin + 5 ° C. or less. If the temperature is too high, the structure may collapse and the strength may decrease. On the other hand, if the temperature is too low, the film may be broken or shrinkage may be increased after stretching.

  Next, the stretched film thus obtained is washed with an appropriate solvent, and a solvent removal treatment for removing the solvent remaining on the film is performed. Solvents used for the solvent removal treatment include, for example, hydrocarbons such as pentane, hexane, heptane and decane, halogenated hydrocarbons such as methylene chloride and carbon tetrachloride, and ethers such as diethyl ether and dioxane. Is preferably used. These solvents are appropriately selected according to the solvent used at the time of kneading. For removing the solvent remaining on the film, for example, the film may be immersed in a solvent.

  Furthermore, in order to reduce the heat shrinkability of the extracted sample, heat setting is performed as necessary. The heat setting treatment is performed at a crystal dispersion temperature of the polyolefin-based composition of −10 ° C. to a melting point or lower. In order to prevent shrinkage, it is preferable to fix the sample around the entire circumference during heat setting. About a heat setting method, it can carry out by well-known methods, such as the method of making it contact with a heating roll, and the method of leaving in a dryer.

  According to the manufacturing method according to the present embodiment, the thickness is 5 to 50 μm, preferably 10 to 30 μm, the piercing strength is 200 gf or more per 16 μm, the porosity is 30 to 60%, and the air permeability is 16 μm. A porous film having a speed of 300 seconds / 100 cc or less can be obtained.

  Since the porous film obtained in the present embodiment can make the mixed state of the resins more uniform, uniform film performance can be obtained, so that it can be suitably used as a separator for various batteries.

  EXAMPLES Hereinafter, although an Example etc. are given and this invention is demonstrated, this invention is not limited at all by an Example. In addition, the characteristic of the material and porous film which were described in the Example and the comparative example was calculated | required as follows.

(1) Normal swelling time After putting 0.2 g of norbornene ring-opening polymer powder (manufactured by Nippon Zeon Co., Ltd., trade name Nosolex NB) into a test tube, 0.4 g of liquid paraffin was added.

After leaving still at 25 degreeC for 5 minutes, it stirred using the shaker for 1 minute. Thereafter, the sample was placed in pulse NMR, and the ¹ H relaxation time after 10 minutes, 40 minutes, 70 minutes, and 130 minutes was measured by the Solid Echo method. The pulse NMR measurement apparatus uses JNM-MU25 manufactured by JEOL Ltd., 90 °, pulse width 2.2 μs, delay time 10.0 μs, repetition time 3.0 s, number of integrations 16 times, measurement temperature 30 ° C., analysis method is nonlinear minimum The square method was used.

  The relaxation curve measured by the above method was regarded as three components of a short relaxation component, an intermediate component, and a long component, and analyzed and separated using the least square method to determine the ratio of each component. Among these, the component ratio between the component having a short relaxation time and the intermediate component was plotted against time, and the time at the intersection of the approximate curves of each component was defined as the specified swelling time.

(2) Evaluation of resin dispersibility The obtained porous membrane was cut into a size of 45 cm × 45 cm, and the number of relatively yellow dark spots was visually measured. The smaller the number of spots, the better the resin dispersibility.

Example 1
As a norbornene ring-opening polymer powder (manufactured by Nippon Zeon Co., Ltd., trade name Nosolex NB), 1 g of LOT A norbornene ring-opening polymer powder having a specified swelling time of 18 minutes and its weight 15 g of ultra-high molecular weight polyethylene having an average molecular weight of 1 million and 85 g of liquid paraffin (dynamic viscosity 59 cst at a freezing point of −15 ° C. and 40 ° C.) are uniformly mixed in a slurry state, and this is mixed with a batch type twin-screw kneader (Toyo The mixture was kneaded at a temperature of 160 ° C. and a rotation speed of 50 rpm for 60 minutes using a Seiki made by Labo Plast Mill 50MR) to extrude the gel product. This gel-like product was formed into a sheet having a thickness of 1 mm at 115 ° C. with a press molding machine, and then stretched 5 × 5 times at 120 ° C. with a biaxial stretching machine. This gel-like stretched sheet was fixed to a SUS frame and immersed in a heptane bath to extract liquid paraffin. After removing from the heptane bath, the heptane was air-dried, then heat-treated in air at 85 ° C. for 6 hours, and further heat-treated in air at 125 ° C. for 1 hour to obtain a porous film. As a result of evaluating resin dispersibility using this porous membrane, the number of spots was 15.

Example 2
In Example 1, except that the same amount of LOT B norbornene ring-opened polymer powder having a specified swelling time of 15 minutes was used, a porous film was obtained under exactly the same conditions as in Example 1, and then the resin dispersibility was Evaluation was performed. As a result, the number of spots was 13.

Comparative Example 1
In Example 1, a porous membrane was obtained under exactly the same conditions as in Example 1 except that the same amount of LOT C norbornene ring-opening polymer powder having a specified swelling time of 28 minutes was used. Evaluation was performed. As a result, the number of spots was 730.

Comparative Example 2
In Example 1, except that the same amount of LOT D norbornene ring-opening polymer powder having a specified swelling time of 33 minutes was used, a porous membrane was obtained under exactly the same conditions as in Example 1, and then the resin dispersibility was Evaluation was performed. As a result, the number of spots was 800.

Claims (3)

A step of heating and kneading a composition containing a first resin as a main component, a second resin mixed with the first resin, and at least a plasticizer capable of swelling the second resin, and then extruding to obtain an extruded product. In the manufacturing method of the resin molding containing,
The method for producing a resin molded product, wherein the second resin has a specified swelling time of 25 minutes or less determined by pulse NMR when swollen at 30 ° C. using the plasticizer.   The method for producing a resin molded product according to claim 1, comprising a step of obtaining a filmed product by forming the extruded product into a film, and a step of extracting the plasticizer from the filmed product or the molded product before filming.   The method for producing a resin molded product according to claim 2, wherein a porous film is obtained.