JP3307027B2 - Method for producing porous resin molded article - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the production of porous resin molded articles useful as separation membranes such as battery separators and microfiltration membranes, clothing articles such as air permeable jumpers, sanitary articles such as diapers and sanitary articles. It is about the method.

[0002]

2. Description of the Related Art Porous films or sheets have been widely used for various purposes. Various methods for producing such a porous resin molded article have been proposed. For example, a porous resin molded article for use as a battery separator is generally produced from a resin composition containing ultra-high molecular weight polyethylene and a plasticizer by melt-extrusion of a film or sheet, and then produced. After dissolving and removing the plasticizer contained in the film or sheet with an organic solvent such as isopropanol, ethanol, or hexane, the film is stretched by a stretching machine such as a roll stretching machine or a tenter transverse stretching machine to improve mechanical strength, that is, solid phase deformation It was manufactured by.

[0003]

However, the film or sheet obtained by such solid-phase deformation has a high residual stress due to the entanglement of polyethylene molecular chains of ultra-high-molecular-weight polyethylene, so that the film or sheet may be incorporated into a battery. There is a problem that the membrane is ruptured when a certain temperature or more is applied in a fixed state, and it has been desired to solve the problem.

[0004]

Means for Solving the Problems Accordingly, the present inventors have:
In order to obtain a porous resin molded body with small residual stress, paying attention to the characteristics of ultra-high molecular weight polyethylene that orientation relaxation after melting deformation is unlikely to occur, as a result of intensive study, a film or sheet obtained by melt extrusion molding, It is possible to obtain a porous resin molded body having a small residual stress and excellent heat rupture resistance by applying a deformation stress and melting and deforming (molding) while maintaining it in a molten state. By melt-deformation under the conditions described above, it is possible to obtain a porous resin molded body having improved surface strength.Furthermore, the film or sheet obtained by melt-deformation and cooling is subjected to a further stretching treatment as in the prior art. Without knowing that it is possible to produce a porous resin molded article industrially advantageously,
The present invention has been completed.

That is, the gist of the present invention is to provide a film or sheet obtained by melt-extruding a resin composition containing ultra-high molecular weight polyethylene and a plasticizer into a film or sheet and applying a deformation stress to the film or sheet. And after cooling, removing the plasticizer contained in the film or sheet.

Hereinafter, the present invention will be described in more detail. The resin composition of the present invention contains at least ultrahigh molecular weight polyethylene and a plasticizer. The ultra-high molecular weight polyethylene used in the present invention includes a viscosity average molecular weight (hereinafter simply referred to as “molecular weight”).
That. ) Is 500,000 or more. When used as a battery separator, if the molecular weight is 500,000 or less, the separator built into the battery will cause self-heating within the battery, or
For example, when heated to 180 ° C. by external heat, it becomes difficult to maintain the shape of the separator. Also,
If the molecular weight is too large, for example, 4,000,000 or more, the flowability is too low, the holes in the separator will not be blocked when heated, and short-circuit will cause ignition of the battery. Preferably, 1.5 to 2.5 million are used.

Further, in the present invention, ultra-high molecular weight polyethylene having a melting temperature of 11 is used because of easy melting deformation.
Ethylene homopolymer at 0 to 140 ° C. can be suitably used. As the plasticizer, various kinds of well-known plasticizers having good compatibility with ultra-high-molecular-weight polyethylene and not evaporating during melt-kneading or molding, for example, those having a boiling point higher than the melting temperature of ultra-high-molecular-weight polyethylene are available. Can be used. Specifically, for example, paraffin wax which is solid at normal temperature, or higher aliphatic alcohols such as stearyl alcohol and ceryl alcohol, n-alkane such as n-decane and n-dodecane which are liquid at normal temperature, liquid paraffin, kerosene And the like.

The proportion of the ultrahigh molecular weight polyethylene and the plasticizer is usually 5 to 60% by weight, preferably 10 to 50% by weight of the ultrahigh molecular weight polyethylene, and 40 to 50% by weight of the plasticizer.
It is selected from the range of 95% by weight, preferably 90 to 50% by weight. In the resin composition of the present invention, known various additives, for example, an antioxidant and the like in the resin composition, 0.01
You may use together about 5 weight%.

The respective components of the resin composition are uniformly kneaded with a known single-screw or twin-screw extruder and are melt-extruded.
A twin-screw extruder is preferably used in terms of extrusion amount, extrusion stability, and kneading strength. Melt extrusion is usually carried out at 140-2.
Perform at a temperature of 40 ° C, 5-50μ or 50-300μ
Extruded into a film or sheet with a thickness of In the present invention, the thus extruded film or sheet is melt-deformed. That is, since the molecular weight is extremely large,
The mechanical strength of the porous resin molding finally obtained by melting and deforming utilizing the properties of ultra-high molecular weight polyethylene, which is less likely to relax the orientation of the molecular chains due to deformation and is easy to orient in the direction of deformation To improve.

[0010] Melt deformation is performed by applying a deformation stress while the resin composition constituting the extruded film or sheet is kept in a molten state. Usually, the temperature of the resin composition is about 130-240 ° C., preferably 1
Deformation stress is applied while maintaining the temperature in the range of 60 to 200 ° C. At this time, the deformation can be performed not only in one direction but also in multiple directions. In particular, when used for battery separators, if the deformation is in one direction only, the pores in the film or sheet will be elongated in the deformation direction, the flow path will be slightly narrowed, and the air permeability will decrease. Since the ionic resistivity of the separator tends to increase, it is preferable to apply deformation in a balanced manner in multiple directions so as to widen the pores.

Specifically, for example, when a deformation is applied in one direction, in a T-die or an inflation molding method, preferably in an inflation molding method, the die gap is increased, and the take-up speed is increased. In other words, by increasing the draft rate, MD (machine)
Apply deformation in the direction. When deformation is applied in multiple directions, MD and TD are increased by increasing the draft rate and blow ratio in the inflation molding method.
Melt deformation is applied in the (width) direction. Furthermore, in the case of multi-directional deformation by the T-die molding method, the width direction end of the molten film or sheet is fixed to a caterpillar with a pin tenter, and the width of the two caterpillars is increased in the flow direction to thereby reduce TD. In the MD direction by simultaneously increasing the take-up speed.

The degree of the melt deformation is not particularly limited as long as the effect of the present invention is not impaired, but the melt deformation rate represented by the following formula is 5 to 1000 , preferably 10 to 100.
0, more preferably 30 to 800, particularly preferably
It is preferable to apply a deformation stress so as to be in the range of 50 to 400. For example, if you want to apply vertical and horizontal deformation stress,
The aspect ratio of the deformation ratio is DR / BUR ≦ 50, preferably ≦
20 and particularly preferably ≦ 10.

[0013]

## EQU2 ## Melt deformation rate = (D × ρ ₁ ) / (t × ρ ₂ ) D: Die gap (mm) ρ ₁ : Melt density of resin composition (g / cm ³ ) t: Molded film or sheet Film thickness (mm) ρ ₂ : solid density of molded film or sheet (g / cm
³ )

In the inflation molding method, it is known that a polyethylene film is produced by melting and deforming using an annular die having a die gap of 0.5 mm (Japanese Patent Application Laid-Open No. 62-223245). Conventionally, 10-100μ
When forming a film or sheet having a thickness of m, the die gap is usually 1 mm or less, and at most 1.5 mm or less. However, a film or sheet obtained by molding in the range of a conventional die gap does not always have sufficient strength, particularly pin puncture strength. In order to obtain a battery separator having good strength, the range of the die gap is important together with the cooling rate described below. In the present invention, the die gap is preferably 2
It is good to carry out in the range of 20 mm, particularly preferably 3 mm to 10 mm.

After cooling the melt-deformed film or sheet, the plasticizer contained in the film or sheet is removed to make the film or sheet porous. At this time, the cooling is preferably performed so that the cooling solidification time defined by the following formula is 50 seconds or less, preferably 20 seconds or less. If the cooling and solidifying time is too long, phase separation proceeds, and the pore size increases and the strength decreases. Definition of cooling solidification time

[0016]

(Equation 3) τ: Cooling solidification time (seconds) L: Distance from lip outlet to cooling solidification line (c
m) (Inflation corresponds to the frost line height; T-die corresponds to the air gap) V ₀ … the moving speed of the resin at the lip exit (cm / sec) V ₁ … the resin in the cooling and solidifying line Moving speed (cm / sec)

The plasticizer can be removed, for example, by dissolving the plasticizer in a film or sheet with an organic solvent such as isopropanol, ethanol or hexane and extracting and removing the solvent by solvent replacement, a so-called known organic solvent method. be able to. Depending on the application, the porous film or sheet from which the plasticizer has been removed as described above is then stretched uniaxially or biaxially to improve mechanical strength, or heat-set at about 100 to 180 ° C. You may. In the present invention, it is industrially advantageous because a porous film or sheet having good mechanical strength can be obtained without performing a stretching treatment.
When the film or sheet is used as a battery separator, the stretching treatment tends to reduce the ability to maintain a high-temperature film shape. In this case, it is preferable to use a film or sheet that has not been subjected to a stretching treatment.

According to the present invention, a porous resin molded product having a thickness of usually 10 μm or more can be obtained. Although the physical properties of the porous resin molded article vary depending on the use, for example,
When used as a battery separator, those having an average pore diameter of 1 μ or less, preferably 0.01 to 1 μ, and a porosity of 25 to 80%, preferably 30 to 60% are preferred.

Further, according to the present invention, the obtained porous resin molded article has good mechanical strength, particularly good pin puncture strength and heat-resistant film rupture property. Pin sting strength is Japanese Agriculture and Forestry Standard Notification 10
Measured according to No.19 (pin piercing speed 300mm / min)
100 g / 25μ film thickness or more, preferably 15
A film having a thickness of 0 to 300 g / 25 μm is obtained. Further, the heat-resistant film rupture property is an index of rupture easiness due to shrinkage stress generated by heat of the film or sheet in a high temperature range, and when used as a battery separator, maintains the film shape even at high temperatures, This is an important characteristic because it is necessary to keep the distance.

The test method is as follows. The film is sandwiched between two plates having a hole of 3 cm, fixed in all directions with fasteners such as clips, and placed in a high-temperature atmosphere at 130 ° C. to 5 ° C. every 5 minutes.
As the temperature increases, the temperature at which the film cannot maintain its shape is measured. In the present invention, the heat rupture resistance is usually 1
Those having a temperature of 80 ° C. or higher, preferably 200 ° C. or higher are obtained.

[0021]

The present invention will be described more specifically with reference to the following examples.

Example 1 20 parts by weight of ultrahigh molecular weight polyethylene powder having a melting point of 135 ° C. and a molecular weight (viscosity average) of 2 × 10 ⁶ and 80 parts by weight of ceryl alcohol were fed to a φ40 mm extruder and continuously kneaded at 230 ° C. 400mm wide, 2mm die gap
Extruded from a T-die and taken up at a pulling speed of 2.5 m / min to apply melt deformation in the MD direction.
A sheet of 05 mm was obtained. The die temperature is 170
° C, linear velocity at die gap 7.1 cm / min, draft rate (Dr) 35.1, air gap 10c
m, and the cooling solidification time was 8.8 seconds. Since the melt density of the resin composition used in this example was 0.76 g / cm ³ and the solid density of the extruded sheet was 0.867 g / cm ³ , the melt deformation rate applied in such melt deformation Was 35.1. The obtained sheet is immersed in isopropyl alcohol at 80 ° C. to extract and remove the seryl alcohol from the sheet, and then heat-treated with a heating pinch roll having a surface temperature of 125 ° C. for 30 seconds to obtain a porous film having a thickness of 27 μ. A resin molding was obtained. Table 1 shows the physical properties of the molded product.

Example 2 In Example 1, the width was 500 mm and the die gap was 6.2.
mm T-die, linear velocity at die gap 2.3
cm / min, take-off speed 2.3 m / min (Dr9
8.8), the film thickness of 0.055
mm sheet was prepared. The melt deformation rate applied in such melt deformation is about 98.8, and the air gap 10c
m, and the cooling solidification time was 12.2 seconds. Next, the sheet was subjected to heat treatment after removing seryl alcohol in the same manner as in Example 1 to obtain a 28 μm-thick porous resin molded article. Table 1 shows the physical properties of the molded product.

Example 3 30 parts by weight of ultrahigh molecular weight polyethylene powder having a melting point of 138 ° C. and a molecular weight (viscosity average) of 3 × 10 ⁶ and 70 parts by weight of stearyl alcohol were fed to a φ50 mm extruder, and 200 ° C.
While being kneaded, the material is continuously extruded from an inflation die having a die diameter of 50 mm and a die gap of 4.5 mm, and a take-up speed of 10 m / min (die temperature: 180 ° C., linear velocity at the die gap: 25.4 cm / min, Dr39.3) And melt deformation was applied at a blow ratio (BUR) of 2.4 to obtain a sheet having a thickness of 0.043 mm. Since the melt density of the resin composition used in this example was 0.79 g / cm ³ and the solid density of the extruded sheet was 0.876 g / cm ³ , the melt deformation rate applied in such melt deformation Was about 94.4, the frost line height was 30 cm, and the cooling and solidification time was 6.8 seconds. This sheet was immersed in isopropyl alcohol at 60 ° C. to extract stearyl alcohol, and then heat-treated in the same manner as in Example 1 to obtain a film having a thickness of 2
A 4 μm porous resin molded body was obtained. Table 1 shows the physical properties of the molded product.

Example 4 In Example 3, the die temperature was 170 ° C., the frost line height was 27 cm, the Dr was 1.0, and the BUR was 5.5 from an inflation die having a die diameter of 40 mm and a die gap of 0.28 mm.
Then, plastic deformation was removed and heat treatment was carried out in the same manner as in Example 3 to obtain a porous resin molded product having a thickness of 28 μm. Table 1 shows the physical properties of the molded product.

Example 5 A porous resin molded product having a thickness of 60 μm was obtained in the same manner as in Example 1 except that the air gap was changed to 12 cm.
Table 1 shows the physical properties of the molded product.

Example 6 30 parts by weight of ultrahigh molecular weight polyethylene powder having a melting point of 135 ° C. and a molecular weight (viscosity average) of 2 × 10 ⁶ and 70 parts by weight of ceryl alcohol were fed to a φ90 mm extruder and extruded at 230 ° C. while kneading. Continuous width 500m at 12kg / hr
m, extruded at a die gap linear velocity of 0.2 cm / sec from a T-die having a die gap of 3.5 mm, the temperature of the resin composition was maintained at 170 ° C. by a heating roll and an infrared heater, and the sheet was taken up by a pin tenter with Dr35. 12 width
After being spread to 50 mm and melt-deformed (melt deformation rate: 87.5), the sheet was cooled and solidified for 8 seconds to obtain a sheet having a thickness of 40 µm. Seryl alcohol was removed from this sheet in the same manner as in Example 1, and the sheet was heat-set to obtain a 20 μm-thick porous resin molded article. Table 1 shows the physical properties of the molded product.

Comparative Example 1 30 parts by weight of ultrahigh molecular weight polyethylene powder having a melting point of 135 ° C. and a molecular weight (viscosity average) of 2 × 10 ⁶ and 70 parts by weight of ceryl alcohol were fed to a φ40 mm extruder and extruded at 230 ° C. while kneading. Continuous width 500m at 4kg / hr
m, die temperature 17 from T die with die gap 0.1mm
Extruded at 0 ° C. and a die gap linear velocity of 2.6 cm / sec.
Dr 2.4, take-off speed 6.1 cm / sec, air gap 12 cm, cooling and solidification time 3.9 sec.
A 37 mm sheet was obtained. Seryl alcohol was removed from this sheet in the same manner as in Example 1, and the sheet was heat-fixed to a film thickness of 28.
μ of a porous resin molded product was obtained. Table 1 shows the physical properties of this compact.
It was shown to.

Comparative Example 2 In Comparative Example 1, the die gap was 0.25 mm,
A sheet was obtained in the same manner except that the value was changed to 2.5. Die gap linear velocity is 1.0 cm / sec, take-off velocity is 2.6 cm / sec,
Air gap 12 cm, cooling and solidification time 6.9 seconds. After cooling, the seryl alcohol was removed in the same manner as in Example 1, and then stretched 2.0 times with a roll stretching machine (stretching temperature 125
° C) to obtain a 30 µm-thick porous resin molded body. Table 1 shows the physical properties of the molded product.

[0030]

[Table 1]

[0031]

According to the present invention, the stretching treatment (solid phase deformation)
, And a film or sheet having good mechanical strength can be obtained only by applying a deformation stress in a molten state. In addition, since polyethylene is deformed in the molten state and in the presence of a plasticizer, the degree of freedom of the molecular chain is large, and the residual stress generated during deformation is small, so that it is obtained by performing a stretching treatment as in the past. Even in comparison, the film shape retention in a high temperature range is excellent. Therefore, it can be advantageously used especially as a battery separator.

Continuation of the front page (56) References JP-A-62-132943 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08J 9/26

Claims (4)

(57) [Claims] (1) a viscosity average molecular weight of 500,000 to 4,000,000;
The resin composition containing ultra-high molecular weight polyethylene and a plasticizer is melt-extruded into a film or a sheet into a film or sheet.
Deformation stress is applied so that the deformation rate becomes 5-1000.
After being melted and cooled, included in the film or sheet
Resin molded article characterized by removing a plasticizer
Manufacturing method. ## EQU1 ## Melt deformation rate = (D × ρ1) / (t × ρ2) D: Die gap (mm) ρ1: Melt density of resin composition (g / cm3) t: Film thickness of molded film or sheet (mm) ) Ρ2: solid density of molded film or sheet (g / cm)
3) 2. A resin composition having a die gap of 2 to 20 mm.
2. The production method according to claim 1, wherein the composition is melt-extruded from a die into a film or sheet. 3. The method according to claim 1, wherein the cooling is performed such that the cooling solidification time is 50 seconds or less. 4. The method according to claim 1, wherein the melt deformation rate is 30 to 800.
2. The production method according to 1.