KR20120063877A - Manufacturing method of high safety polyolefin micro-porous film and high safety polyolefin micro-porous film therefrom - Google Patents

Abstract

PURPOSE: A manufacturing method of a highly safe polyolefin microporous membrane and a highly stable microporous polyolefin membrane manufactured therefrom are provided to successively manufacture at high speed and to prevent shrinkage in drying. CONSTITUTION: A manufacturing method of a highly safe polyolefin microporous membrane comprises the following steps: a step of obtaining a cold-solidified sheet by melt-mulling and extruding a composition consisting of polyolefin resin and plasticizer; a step of manufacturing a microporous membrane by extending the solidified sheet in at least 1 axis direction; a step of extracting plasticizer from the extended microporous membrane; and a step of drying the microporous membrane on a roll at a dry roll speed of 20-35m/min under a condition which mechanically fixes width of the microporous membrane.

Description

Manufacturing method of high-safety polyolefin microporous membrane and high-safety polyolefin microporous membrane manufactured therefrom TECHNICAL FIELD

The present invention relates to a method for producing a high safety polyolefin microporous membrane and a high safety polyolefin microporous membrane prepared therefrom, and more particularly, to enable high-speed continuous production, and to suppress shrinkage during drying, thereby ensuring high safety and uniformity of quality. It relates to a method for producing a high safety polyolefin microporous membrane that can increase the high safety polyolefin microporous membrane prepared therefrom.

BACKGROUND ART In general, microporous membranes have been widely used as materials for filtration materials such as water purifiers, garment materials requiring air permeability, separators for batteries and separators for electrolytic capacitors. In particular, in recent years, as the demand for the use of lithium ion secondary batteries increases, high performance is also required for separators in addition to high energy density of batteries. In addition, with high energy density, high output, and mass production of batteries, there is an urgent need for improvement in quality uniformity as well as high quality requirements for separators.

In addition, in order to cope with future energy and environmental problems, development of hybrid electric vehicles, electric vehicles, and fuel cell vehicles has been actively conducted. There is an increasing demand for battery size and safety.

And with mass production of batteries, the high speed production of the separator has been strongly demanded. In the technique for producing a microporous membrane, in order to form a microporous membrane precursor from a composition composed of a polymer and a plasticizer, a stretching process is applied, and after stretching, the plasticizer is extracted with a solvent, and the solvent is dried and removed. It is already known to manufacture microporous membranes.

Since this known technique performs the drying of the solvent on a roll, it is impossible to prevent the shrinkage in the width direction of the membrane in the drying process, and it causes a deterioration of permeability and the uniform quality of how much the shrinkage is at the end of the membrane. Microporous membranes cannot be obtained.

Dimensional stability at high temperature is to evaluate the degree of dimensional deformation of the separator due to thermal contraction when the battery internal temperature is raised due to any high temperature treatment or trouble during battery production. In the former case, when the membrane shrinks and deforms in the width direction, the electrode is exposed and internal short-circuited, so that the dimensional stability in the width direction at high temperature is particularly important. In the latter case, if the dimensional stability in the width direction cannot be maintained when the battery is overheated, even the shutdown function becomes meaningless, which is a very serious problem. As described above, a technique for manufacturing a separator that can withstand high temperatures without damaging the shutdown function has not been established in the past.

In the conventional microporous membrane manufacturing technology, it was not possible to continuously produce a microporous membrane of uniform quality at high speed. That is, since drying of the solvent is carried out on a roll, it is impossible to continuously produce at high speed due to wrinkles. In addition, it is impossible to prevent the shrinkage in the width direction of the membrane, but the permeability of the membrane is deteriorated and a microporous membrane of uniform quality cannot be obtained.

Therefore, there is a need in the art to establish a technology for producing a microporous membrane of uniform quality at high speed.

The present invention has been made to solve the above problems, the object of the present invention is a high-safety polyolefin microporous membrane capable of high-speed continuous production, by suppressing shrinkage during drying, to improve the high safety and uniformity of quality It is to provide a method for producing and a high safety polyolefin microporous membrane prepared therefrom.

These and other objects and advantages of the present invention will become more apparent from the following description of a preferred embodiment thereof.

The object is the first step of melt-kneading and extruding a composition composed of a polyolefin resin and a plasticizer to form a cooled solidified sheet, and stretching the solidified sheet at least once before extraction in at least one axial direction. A second step of preparing a microporous membrane, a third step of extracting a plasticizer from the stretched microporous membrane before the extraction, and a drying process in a state in which the width of the microporous membrane from which the plasticizer has been extracted is mechanically constrained. , The drying step is achieved by a method for producing a high safety polyolefin microporous membrane, characterized in that it comprises a fourth step carried out on a roll at a condition of a dry roll speed of 20 ~ 35m / min.

Here, the stretching before extraction in the second step is characterized in that stretching at least once in the biaxial direction or the width direction.

Preferably, after the fourth step, in the state in which the width of the microporous membrane from which the plasticizer has been extracted is mechanically constrained, the stretching process is performed after extraction in the longitudinal direction using a roll type stretching machine, and continuously in the longitudinal direction. It characterized in that it further comprises a fifth step of relaxing to heat treatment.

Preferably, after the fifth step is characterized in that it comprises a sixth step of performing heat treatment in the width direction by performing stretching after extraction in the width direction.

Preferably, the method may further include a seventh step of heat treatment while passing through the heat-setting zone after the sixth step.

In addition, the object is a high-safety polyolefin microporous membrane prepared by the method for producing a high-safety polyolefin microporous membrane, the heat shrinkage in the width direction of the heat shrinkage calculated by the following equation (4) is 10% or less,

(Equation 4)

Heat shrinkage percentage (%) = {1- (value after heating) / (value before heating)} X 100, which is achieved by a high safety polyolefin microporous membrane.

Here, the high safety polyolefin microporous membrane is made of ultra high molecular weight polyethylene (Ultra High Molecular Polyethylene) is characterized in that the weight average molecular weight of 1,000,000 ~ 5,000,000.

Preferably, the high safety polyolefin microporous membrane is made of a polyolefin polymer, characterized in that the weight average molecular weight is 50,000 ~ 1,000,000.

Preferably, the molecular weight distribution (Mw / Mn) of the polyolefin polymer is characterized in that 3 to 8.

According to the present invention, high-speed continuous production is possible, and by suppressing shrinkage during drying, it is possible to increase high safety and uniformity of quality.

Hereinafter, the present invention will be described in detail with reference to embodiments of the present invention. These examples are only presented by way of example only to more specifically describe the present invention, it will be apparent to those skilled in the art that the scope of the present invention is not limited by these examples. .

The present invention relates to a method for producing a high safety polyolefin microporous membrane for use in battery materials such as, for example, a cylindrical battery, a square battery, a thin battery, a button battery, an electrolytic capacitor, and a high safety polyolefin microporous membrane prepared therefrom. As a result of careful study in order to solve the problems of the prior art, in the drying process after extraction, by introducing a method of drying in a state where the width of the film or sheet is mechanically constrained, high-speed continuous production can be realized and shrinkage during drying By suppressing this, the inventors found that the quality and the uniformity of the quality can be improved, thereby completing the present invention.

The method for producing a highly safe polyolefin microporous membrane according to the present invention comprises the first step of melt-kneading and extruding a composition composed of a polyolefin resin and a plasticizer to form a cooled solidified sheet, and the solidified sheet in at least one axial direction. A second step of preparing a microporous membrane by stretching at least once before extraction; a third step of extracting a plasticizer from the stretched microporous membrane before extraction; and a width of the microporous membrane from which the plasticizer is extracted. After the drying process in a confined state, the drying process is characterized in that it comprises a fourth step of performing a dry roll speed of 20 ~ 35m / min on the roll.

First, in the manufacturing method according to the present invention, the first step is a step of melting and kneading and extruding a composition composed of a polyolefin resin and a plasticizer to form a sheet on a cooling solidified sheet. This can be done by known methods.

Next, in the manufacturing method according to the present invention, the second step is a stretching performed before the extraction step of the third step, the stretching before extraction, it is essential that the solidified sheet is drawn at least once in at least one axial direction. . Preferably, the stretching before extraction in the second step is characterized in that stretching at least once in the biaxial direction or the width direction. Here, at least one axial direction includes machine direction uniaxial stretching, width direction uniaxial stretching, simultaneous biaxial stretching and sequential biaxial stretching. In addition, at least 1 time means a 1st stage extending | stretching, a multistage stretching, and many times extending | stretching. In the present invention, the stretching before extraction is performed in a state where the plasticizer is dispersed in a high degree in the micropores, the crystal gaps, and the amorphous parts of the separator, so that the stretchability is improved by the plasticizing effect and the increase in the porosity of the separator is suppressed. In addition, it is possible to achieve high strength capable of high magnification stretching. Furthermore, biaxial stretching is preferred in order to achieve high strength, and more preferably, simultaneous biaxial stretching performs the process, thereby simplifying the process. The stretching temperature is preferably at least 50 ° C lower than the melting point (Tm) lower than the melting point (Tm) of the polyolefin separation membrane, and more preferably 5 ° C lower than the melting point (Tm) above 40 ° C lower than the melting point (Tm) of the polyolefin separation membrane. It is performed below. At this time, when extending | stretching temperature is less than 50 degreeC lower than melting | fusing point (Tm), since extending | stretching property falls and the strain component after extending | stretching remains, dimensional stability at high temperature falls, it is unpreferable. In addition, when the stretching temperature is equal to or higher than the melting point (Tm), the separation membrane is melted and the permeation performance is inhibited, which is not preferable. In addition, although the draw ratio can be set at any magnification, in the case of uniaxial stretching, it is preferable to carry out at 2 to 20 times, more preferably 4 to 10 times. Moreover, it is 2 to 400 times, More preferably, it is 4 to 100 times by biaxial direction area magnification.

Next, the process of extracting the plasticizer of the third step of the manufacturing method according to the present invention is continuously introduced into the tank filled with the extraction solvent, immersed in the tank for a sufficient time to remove the plasticizer and in the tank It is immersed, and at this time, a multi-stage method for dividing the inside of the water tank in multiple stages so that the separators are sequentially introduced into each tank having a difference in concentration, and a countercurrent method for supplying an extraction solvent in a reverse direction with respect to the running direction of the membrane to determine the concentration gradient. Applying the method, it is preferable to increase the extraction efficiency. It is very important to remove the plasticizer substantially from the separator. In addition, if the temperature of the extraction solvent is added within the range below the boiling point of the solvent, the diffusion of the plasticizer and the solvent can be promoted, so that the extraction efficiency can be increased, which is preferable.

Next, in the manufacturing method according to the present invention, the fourth step is a drying process in a state in which the width of the microporous membrane from which the plasticizer has been extracted is mechanically constrained, the drying process is a drying roll speed of 20 ~ 35m on a roll It is characterized by performing under the condition of / min.

Next, the fifth step according to the present invention is the stretching carried out after the drying process of the third and fourth stages, and is called stretching after extraction, stretching in the longitudinal direction. In addition, in the stretching performed after the extraction process, it is more preferable to include a sixth step of stretching in the width direction in a separate process from the stretching in the longitudinal direction described above. Since the stretching after extraction is performed in a state in which the plasticizer is substantially removed from the separation membrane, the stretching process predominantly causes breakage of the polymer interface, thereby increasing the porosity of the separation membrane. Therefore, if only stretching is performed after extraction without performing pre-extraction stretching, which is essential in the present invention, it causes unnecessary increase of porosity unnecessarily, and it is impossible to give the stretching orientation to the separation membrane, resulting in low strength.

In contrast, in the case of the production method of the present invention using the stretching before extraction and the stretching after extraction, the porosity can be increased without impairing the strength of the separator. At this time, the stretching temperature is preferably at least 50 ° C lower than the melting point (Tm) lower than the melting point (Tm) of the polyolefin membrane, more preferably 5 ° C lower than the melting point (Tm) 40 ° C lower than the melting point (Tm) of the polyolefin separator. It is carried out below the low temperature. If the stretching temperature is less than 50 ° C lower than the melting point (Tm) of the polyolefin separation membrane, the stretchability is inferior and the strain component after stretching remains, which is not preferable because the dimensional stability at high temperature is lowered. Although the stretching magnification can be set at any magnification, less than 5 times is preferable at the magnification in the uniaxial direction, and less than 20 times is preferable at the area magnification in the biaxial direction. The stretching in the longitudinal direction can increase the transmission performance without impairing the dimensional stability in the width direction at high temperature. Moreover, when used together with the width direction extending process, the permeation | transmission performance can be improved and the intensity | strength balance between a longitudinal direction and the width direction can be improved. At this time, by stretching in the longitudinal direction and in the width direction in a separate process, each of the stretching ratio can be changed widely. Therefore, by performing the above process, the permeation performance can be controlled in a wide range from a relatively low region to a high region.

In addition, the method of extending | stretching to a longitudinal direction can be performed by employing a roll type drawing machine. Here, it is important to prevent shrinkage in the width direction due to residual stress after stretching before extraction. It is preferable to mechanically restrain the width of the separation membrane by means of strongly pulling both ends of the separation membrane by using a thermal state after stretching the separation membrane on the roll before extraction.

In addition, it is preferable to perform the stretching in the longitudinal direction quickly after the fever. The draw ratio of the roll type stretching machine can be widely changed, and at the same time, the thermal relaxation process described later can be performed.

In addition, when the microporous membrane is thermally heated on the roll, if the width of the separator is not mechanically constrained, the friction between the roll and the separator alone cannot prevent the shrinkage, and the separator contracts in the width direction, thereby deteriorating permeability. . After completion of the residual heat, the residual stress in the width direction is alleviated, so that the shrinkage can be prevented only by the friction between the roll and the separator.

In addition, a method of mechanically restraining the width of the separation membrane is to install a clip at the end of the roll to sandwich the separation membrane with a roll and a clip, to press the microporous membrane with a roll with a belt-like object, and to fix the membrane by sucking the end of the microporous membrane. The method etc. are mentioned.

Moreover, the method of extending | stretching in the width direction is a method of using a tenter type drawing machine. The draw ratio of a tenter type drawing machine can be changed widely, and the heat relaxation mentioned later can also be performed. In the production method of the present invention, the heat treatment step is preferably carried out after the extraction, or after the extraction after extraction. Here, heat treatment includes heat fixation or heat relaxation. The heat setting in the above means that the heat treatment is carried out in a tension state while maintaining or restraining the set draw ratio at the time of stretching after extraction. On the other hand, thermal relaxation is to perform heat treatment in a relaxed state to relax the restrained state. Both the heat setting and the heat relaxation remove the residual stress or deformation component which may be thought to occur during stretching, thereby improving the dimensional stability at high temperature and controlling the permeability represented by the porosity and the permeability. .

In addition, the manufacturing method according to the invention is characterized in that it further comprises a seventh step of heat treatment while passing through the heat-setting zone (Zone) after the sixth step.

In the manufacturing method of the present invention, as long as it does not interfere with the characteristics of the microporous membrane of the present invention, namely, after improving the dimensional stability at high temperature and adjusting the permeability, Processing can be performed. Examples of the post-treatment include hydrophilization treatment with a surfactant and crosslinking treatment with ionizing radiation. The polyolefin resins used in the present invention are resins used in conventional extrusion, injection, inflation, and blow molding, and include ethylene, propylene, 1-butene, 1-butene, 4-methyl-1-pentene, 1-hexene and 1 Homopolymers and copolymers of octenes can be used, and mixed forms of the homopolymers and copolymers are also preferred. Examples of the polymer include low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultra high molecular weight polyethylene, isotactic polypropylene, atactic polypropylene, polybutylene, ethylene propylene rubber, and the like. More preferably, high density polyethylene is used. When the microporous membrane obtained by the manufacturing method of this invention is used as a battery separator, it is preferable to use resin which is a low melting point resin, and at the same time from a high-strength required performance especially a high density polyethylene.

In addition, the high-safety polyolefin microporous membrane according to the present invention is made of ultra high molecular weight polyethylene (Ultra High Molecular Polyethylene), characterized in that the weight average molecular weight of 1,000,000 ~ 5,000,000.

Moreover, the average molecular weight of the polyolefin resin used in this invention is 50,000 or more and less than 1 million, More preferably, it is 100,000 or more and less than 700,000, Most preferably, it is 200,000 or more and less than 500,000. The average molecular weight refers to the weight average molecular weight obtained by GPC (gel filtration chromatography) measurement, etc., but since the average molecular weight of resins having more than 1 million is difficult to accurately measure GPC, as an alternative, the average molecular weight can be adjusted to the viscosity average molecular weight by the viscosity method. Can be. At this time, if the average molecular weight is less than 50,000, it is not preferable at the time of melt molding because the melt tension is lost and the moldability is reduced, or the stretchability is lowered and the strength is lowered. On the other hand, when the average molecular weight exceeds 1 million, since it is difficult to obtain a uniform resin composition, it is preferable not to use it.

The molecular weight distribution of the polyolefin resin used in the present invention is preferably 1 or more and less than 10, more preferably 2 or more and less than 9, and most preferably 3 or more and less than 8. The said molecular weight distribution is represented by the ratio (Mw / Mn) between the weight average molecular weight (Mw) and the number average molecular weight (Mn) obtained by GPC measurement. When the molecular weight distribution exceeds 10, the stretchability tends to be deteriorated, resulting in partial distribution of thickness and reduction in strength.

In addition, the plasticizer used in the present invention can be used as long as it is a non-volatile solvent that is easy to form a homogeneous solution at the melting point of the polyolefin resin when mixed with the polyolefin resin. For example, hydrocarbons such as liquid paraffin and paraffin wax, esters such as dioctyl butyric acid or dibutyl butyric acid, higher alcohols such as oleyl alcohol or stearyl alcohol can be used.

In addition, the mixing ratio between the polyolefin resin and the plasticizer used in the present invention is sufficient to cause fine phase separation and form a separator precursor on a sheet, and at this time, productivity should not be reduced. More specifically, the weight fraction of the polyolefin resin in the composition consisting of the polyolefin resin and the plasticizer is preferably 20 to 70%, more preferably 30 to 60% of the polyolefin resin. At this time, if the weight fraction of the polyolefin resin is less than 20%, the melt stress during the melt molding is insufficient, the moldability is inferior. Although the weight fraction of polyolefin resin can also be performed in less than 20%, in this case, since ultra-high molecular weight polyolefin must be mixed in large quantity in order to raise melt stress, uniform dispersibility falls and it is unpreferable.

In addition, the extraction solvent used in the present invention should be less soluble in polyolefin, at the same time excellent in solubility in plasticizer, and the boiling point should be lower than the melting point of the polyolefin microporous membrane. Such preferred extraction solvents include hydrocarbons such as n-hexane and cyclohexane, halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane, alcohols such as ethanol and isopropanol, diethylethane and tetrahydro Ethers, such as furan, ketones, such as acetone and 2-butanone, can be used. In consideration of environmental adaptability, safety and hygiene, it is preferable to use alcohols and ketones in the solvent.

In addition, the composition used in the present invention can be mixed with additives such as antioxidants, nucleating agents, antistatic agents, flame retardants, lubricants, ultraviolet absorbers and the like within a range that satisfies the purpose without inhibiting the properties of the desired microporous membrane. The separator of the present invention means a porous sheet or film substantially composed of polyolefin, and is used as a battery material of, for example, a separator. Although the form of a battery is not specifically limited, For example, it can apply to uses, such as a rectangular battery, a thin battery, a button type battery, an electrolytic capacitor, including a cylindrical battery.

In another aspect, the present invention provides a high safety polyolefin microporous membrane prepared in the above production method. The membrane thickness of the separator prepared according to the production method of the present invention is preferably 1 to 500 µm, more preferably 5 to 100 µm. At this time, if the film thickness is less than 1 µm, the mechanical strength is insufficient, and if the thickness exceeds 500 µm, the occupancy volume of the separator increases, which is disadvantageous for high battery capacity.

In addition, the air permeability of the separator prepared according to the production method of the present invention is preferably 3000 seconds / 100/25/25 ㎛ or less, more preferably 1000 seconds / 100/25/25 ㎛ or less. The air permeability is defined by the ratio between the air permeation time and the film thickness, but if the air permeability is greater than 3000 sec / 100 μs / 25 μm, the ion permeability is lowered and the pore diameter is extremely small, so that the permeability is eventually reduced.

In addition, the porosity of the separator prepared according to the method of the present invention is preferably 20 to 80%, more preferably 30 to 70%. At this time, if the porosity is less than 20%, the ion permeability associated with air permeability or electrical resistance becomes insufficient, and if it exceeds 80%, the strength related to the piercing strength, the tensile strength, and the like is insufficient.

In addition, the puncture strength of the microporous membrane prepared according to the production method of the present invention is preferably 300 g / 25 μm or more, more preferably 400 g / 25 μm or more. The puncture strength is defined by the ratio of the maximum load and the film thickness in the puncture test. If the puncture strength is less than 300 g / 25 μm, defects such as short circuit defects increase when winding the battery, are not preferable.

The thermal contraction rate of the separator prepared according to the method of the present invention is an index for evaluating the dimensional stability at a high temperature of the microporous membrane, preferably 10% or less, more preferably 5% or less with respect to the width direction of the separator. At this time, if the heat shrinkage exceeds 10%, it is not preferable because it causes a safety problem such as a short circuit inside the battery. Here, the thermal contraction rate may be calculated by the following Equation 4.

(Equation 4)

Thermal contraction rate (%) = {1- (value after heating) / (value before heating)} X 100

Hereinafter, the configuration and effects of the present invention will be described in more detail with reference to Examples and Comparative Examples. However, this embodiment is intended to illustrate the present invention in more detail, and the scope of the present invention is not limited to these examples.

Example 1

Dry mixture of high density polyethylene (weight average molecular weight 300,000, molecular weight distribution 7, density 0.956) and 0.3 parts by weight of 2,6-di-tert-butyl-p-cresol with HENSCHEL MIXER blending) and introduced into a 35mm twin screw extruder. Next, a sheet of 1.1 mm thickness was extruded onto a cooling roll in which fluid paraffin (flow viscosity 75.9 cSt at 37.78 ° C.) was poured into the extruder, melt kneaded at 200 ° C., and passed through a die to maintain a surface temperature of 40 ° C. Got. At this time, the composition ratio was adjusted to 30% by weight of polyethylene and 70% by weight of liquid paraffin. The obtained sheet was stretched 5 × 5 times at 119 ° C. using a tenter-type simultaneous biaxial stretching machine, and then immersed in methylene chloride to extract and remove fluid paraffin, and then, on the heating roll with a clip at the end, It dried with blowing the warm air in the state which constrained the width mechanically. Thereafter, heat setting was carried out at 121 ° C. using a tenter type heat stabilizer. The molding conditions, the width of the membrane before extraction and the width of the membrane after drying, and the dry state are shown in Table 1 below.

[Example 2]

A microporous membrane was obtained in the same manner as in Example 1 except that the molding conditions were performed as described in Table 1. In addition, the results of the measurement of the width of the membrane before extraction and removal, and the width of the membrane after drying are shown in Table 1.

[Example 3]

The high-density polyethylene was weight-average molecular weight 800,000, molecular weight distribution 7, density 0.950, and the sheet of thickness 1.4mm was obtained. Herein, except that the proportion of the composition is adjusted to 20% by weight of polyethylene and 80% by weight of liquid paraffin, it was carried out in the same manner as in Example 1 to obtain a microporous membrane. Table 1 shows the results of measuring the molding conditions, the width of the membrane before extraction and removal, and the width of the membrane after drying.

The measurement results and drying conditions of the molding conditions and the width of the membrane after drying and the width of the membrane before extrusion removal according to Examples 1 to 3 are described in Table 1 below.

Example 1 Example 2 Example 3 Dry roll temperature (℃) 35 35 35 Dry Hot Air Temperature (℃) 80 70 80 Dry Roll Speed (m / min) 20 35 20 Membrane width
(mm) Before extraction
after drying 1530
1510 1530
1514 1530
1520 aridity Good Good Good

Comparative Example 1

After the sheet was obtained as in Example 1, it was drawn before extraction using a tenter type simultaneous biaxial stretching machine, and then immersed in methylene chloride to extract and remove the liquid paraffin, and then mechanically constrain the width of the microporous membrane on a heating roll. It was dried while shooting warm air without. In addition, heat setting was carried out at 121 ° C. using a tenter type heat stabilizer. The molding conditions, the width of the membrane before extraction and the width of the membrane after drying, and the dry state are shown in Table 2 below.

Comparative Example 2

A polyethylene microporous membrane was obtained in the same manner as in Comparative Example 1 except that the molding conditions were carried out as described in Table 2 below. In addition, the results of measuring the width of the membrane before extraction and removal and the membrane width after drying are shown in Table 2 below.

Comparative Example 3

After the sheet was obtained as in Example 3, it was drawn before extraction using a tenter type simultaneous biaxial stretching machine, and then immersed in methylene chloride to extract and remove the liquid paraffin, and then mechanically constrain the width of the microporous membrane on the heating roll. It was dried while shooting warm air without. In addition, heat setting was carried out at 121 ° C. using a tenter type heat stabilizer. The molding conditions, the width of the membrane before extraction and the width of the membrane after drying, and the dry state are shown in Table 2 below.

The measurement results of the molding conditions and the width of the membrane after drying and the width of the membrane after the extrusion and the drying conditions according to Comparative Examples 1 to 3 are described in Table 2 below.

Comparative Example 1 Comparative Example 2 Comparative Example 3 Dry roll temperature (℃) 35 35 35 Dry Hot Air Temperature (℃) 50 60 60 Dry Roll Speed (m / min) 5 10 15 Membrane width
(mm) Before extraction
after drying 1530
1430 1530
1450 1530
1460 Dry state Good Wrinkles and
Partial
Drying defect Wrinkles and
Partial
Drying defect

Physical properties of the microporous membranes according to Examples 1 to 3 and Comparative Examples 1 to 3 were measured through the following experimental examples, and the results are shown in Table 3 below. In addition, samples were taken at three locations from the center of the membrane and at both ends from the left and right ends to measure the physical properties of the microporous membrane.

[Experimental Example]

(1) film thickness

It measured on the dial gauge (PEACOCK NO.25 by Ozaki Corporation).

(2) porosity

A 20 cm square sample was cut out of the microporous membrane, and the volume (cm 3) and weight (g) of the sample were measured, and the porosity (%) was calculated using the following equation (1) from the obtained result.

(1)

% Porosity = {1-weight / (density of resin X volume)} X100

(3) speculation

Based on JIS P-8117, the air permeation time (seconds / seconds) and the film thickness μm obtained by measuring by a Gurley type air permeability meter are calculated by converting the film thicknesses according to the following equation (2). 25 µm) was calculated.

(2)

Speculation = (spec time x 25) / thickness

(4) stone strength

Using a compression tester (KES-G5, manufactured by Kato Tech), the sticking test was conducted under the condition of a radius of curvature of 0.5 mm and a sticking speed of 2 mm / sec at the tip of the needle. The maximum sticking load (g) and film thickness (μm) were as follows. The projection thickness (g / 25 mu m) was calculated by converting the film thickness from the equation (3).

(3)

Penetration strength = (maximum breaking strength X 25) / thickness

(5) breaking strength

It cut | disconnected to width 15mm and measured the test piece based on ASTMD882 about the narrow paper-shaped test piece.

(6) heat shrinkage

A 20 cm square sample was cut out of the microporous membrane and placed in a hot air circulating oven heated to 100 ° C. without restraining all four sides of the sample, and heated for 2 hours. The dimensions in the machine direction and the width direction of the microporous membrane were measured before and after heating to calculate the heat shrinkage rate (%) based on the following equation (4).

(Equation 4)

Thermal contraction percentage (%) = {1- (value after heating / value before heating)} X100

(7) Average molecular weight and molecular weight distribution

According to the following conditions, GPC (gel filtration chromatography) measurement was performed to obtain a weight average molecular weight (Mw) and a number average molecular weight (Mn), and Mw was calculated as the average molecular weight or Mw / Mn was determined as the molecular weight distribution. .

Device: WATERS 150-GPC

Temperature: 140 ℃

Solvent: 1,2,4-trichlorobenzene

Concentration: 0.05% (injection amount: 500µl)

Column: 1 Shodex GPC AT-807 / S, 2 Tosoh TSK-GELGMH6-HT

Melting condition: 160 ℃, 2.5 hours

Calibration curve: 3rd calculation using polyethylene conversion constant 0.48 for polystyrene standard samples

(8) melting point

About 7 mg of sample was left to stand in nitrogen atmosphere using the differential scanning calorimeter DSC-210 by Seiko Electronics Co., Ltd., and it heated up at the rate of 10 degree-C / min at room temperature, and evaluated by the endothermic peak temperature.

(9) relaxation rate

About the microporous membrane dimension after extending | stretching after extraction, the relaxation rate (%) was defined like the following formula (5) from the difference of the setting magnification at the time of extending | stretching after extraction and the setting magnification at the time of heat processing.

(5)

Relaxation rate = (stretching set magnification after extraction-heat treatment set magnification) × 100

Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Thickness
(Μm) Left edge 150mm
Center
Right end 150mm 18.2
18.5
18.2 19.5
19.3
19.3 19.7
19.7
19.5 19.2
19.5
19.1 18.7
18.5
18.5 19.5
19.5
19.3 Porosity
(%) Left edge 150mm
Center
Right end 150mm 38
36
37 36
35
39 38
38
37 37
36
38 39
38
39 36
38
37 Specularity
(second) Left edge 150mm
Center
Right end 150mm 470
465
470 465
460
470 480
480
475 490
485
484 480
476
480 476
475
472 sting
burglar
(g) Left edge 150mm
Center
Right end 150mm 480
475
475 486
484
487 483
482
487 476
477
476 475
477
479 467
469
470

As can be seen in Table 3, according to the manufacturing method of the high-safety polyolefin microporous membrane according to the present invention and the high-safety polyolefin microporous membrane prepared therefrom, high-speed continuous production is possible, by suppressing shrinkage during drying, There is an effect to increase the safety and uniformity of quality.

Therefore, the separator prepared according to the present invention can produce a separator having a variety of permeability, especially to have a high battery safety and to meet the needs of the diversified battery when used as a battery separator.

In the present specification, only a few examples of various embodiments performed by the present inventors are described, but the technical idea of the present invention is not limited thereto, but may be variously modified and implemented by those skilled in the art.

Claims (9)

In the manufacturing method of a high safety polyolefin microporous membrane,
A first step of melt-kneading and extruding a composition composed of a polyolefin resin and a plasticizer to form a cooled solidified sheet;
A second step of preparing the microporous membrane by stretching the solidified sheet at least once before extraction in at least one axial direction;
A third step of extracting a plasticizer from the stretched microporous membrane before the extraction;
The plasticizer is subjected to a drying process in a state in which the width of the microporous membrane from which the plasticizer is extracted is subjected to a drying process, wherein the drying process includes a fourth step of performing a drying roll on a roll at a condition of 20 to 35 m / min. A method for producing a high safety polyolefin microporous membrane. The method of claim 1,
The stretching before extraction in the second step is stretched at least once in the biaxial direction or the width direction, characterized in that the manufacturing method of the high safety polyolefin microporous membrane. The method of claim 1,
After the fourth step, in the state in which the width of the microporous membrane from which the plasticizer has been extracted is mechanically constrained, a stretching process is performed after extraction in the longitudinal direction using a roll type stretching machine, and the heat treatment is performed by relaxing in the longitudinal direction continuously. Method for producing a high safety polyolefin microporous membrane, characterized in that it further comprises a fifth step. The method of claim 3,
And a sixth step of continuously performing heat treatment in the width direction by performing stretching after extraction in the width direction after the fifth step. The method of claim 4, wherein
And a seventh step of performing heat treatment after passing through the heat-setting zone after the sixth step. As a high safety polyolefin microporous membrane prepared by the method for producing a high safety polyolefin microporous membrane according to claim 1,
Among the heat shrink rates calculated by Equation 4 below, the heat shrink rate in the width direction is 10% or less,
(4)
A high safety polyolefin microporous membrane, characterized in that thermal shrinkage (%) = {1- (value after heating) / (value before heating)} X 100. The method of claim 6,
The high safety polyolefin microporous membrane is made of ultra high molecular weight polyethylene (Ultra High Molecular Polyethylene), characterized in that the weight average molecular weight of 1,000,000 ~ 5,000,000, high safety polyolefin microporous membrane. The method of claim 6,
The high safety polyolefin microporous membrane is made of a polyolefin polymer, characterized in that the weight average molecular weight is 50,000 ~ 1,000,000, high safety polyolefin microporous membrane. The method of claim 8,
The molecular weight distribution (Mw / Mn) of the said polyolefin polymer is 3-8, The high safety polyolefin microporous membrane.