JPH0247031A - Manufacture of microporous film - Google Patents

Abstract

PURPOSE:To form fine pores having uniform and excellent permeability and high quality by melting and extruding crystalline thermoplastic resin, and crystallizing it by cooling it under pressure between calender rolls. CONSTITUTION:Crystalline resin is melted and extruded from a base 2, and crystallized by cooling under pressure between one set of calender rolls 1 at 40m/min or less of drawing speed to form a film having 5-1,000mum of thickness. The crystalline resin to be subsequently heat treated, elongated and thermally fixed is of thermoplastic resin having a clear crystallization melting point to be observed by a differential calorimeter, which resin preferably includes polyolefins having excellent medicine resistance, acid resistance, alkaline properties in utility. Among them, polyethylene, polypropylene are satisfactory. Such crystallization under pressure contributes to an orientation in a folding camera structure of polymer chain and so-called hard elastic structure.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a microporous film in which micropores are formed in a crystalline thermoplastic resin and continuously penetrate through the film.

[Conventional technology] The conventional technology for forming continuously penetrating micropores in a thermoplastic resin film is to take it out under a high draft during melt extrusion and cool it, so that the lamellar crystals of polymer chains are aligned and have spring elasticity. There is a method in which a precursor film having a
No., Special Publication No. 59-36575, etc.).

[Problems to be Solved by the Invention] The technical elements listed in this technology include: (1) Forming an elastic film that is taken up at high speed during casting.

(2) Stretch at extremely low speed.

There are two elements.

In order to form high-quality micropores that are uniform and have excellent permeability, it is necessary to increase the drawing speed in (1) and to decrease the stretching speed in (2).
In this technology containing such conflicting technical elements, it is extremely difficult to make the extrusion to stretching process continuous,
The disadvantage was that quality control and cost efficiency were poor.

[Means for Solving the Problems] The present invention provides a crystalline resin having a thickness of 5 to 1000 μm by melt-extruding the crystalline resin from a die and cooling and crystallizing it under pressure between a set of calender rolls at a take-up speed of 40 m/min or less.
The present invention relates to a method for producing a microporous film, which comprises obtaining a film, followed by heat treatment, stretching, and heat setting. The crystalline resin according to the present invention is
Thermoplastic resins with a clear crystalline melting point observed with a differential thermometer (DSC), including polyolefins such as polyethylene, polypropylene, poly4 methylpentene 1, and polybutene 1, polyvinyl fluoride, and polyfluoride. There is no particular limitation as long as it is selected from polyfluorinated olefins such as vinylidene chloride, polyesters exemplified by polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate, polyphenylene sulfide, polyoxymethylene, polyamide, etc. do not have.

However, in order to efficiently form micropores, resins with a high degree of crystallinity are preferable, and among the above-mentioned resins, polyolefins, polyfluorinated olefins, polyamides, polyoxymethylene, etc. are preferable.

In particular, polyolefins with excellent chemical resistance, acid resistance, and alkali resistance are preferable for the purpose of use, and among these, polyethylene,
Polypropylene is preferred.

In the case of polyethylene, the density is 0.93CI/Cm
Medium to high density polyethylene with a melt flow rate of 3 or more, preferably 0.940/cm3 or more is preferred, and a melt flow rate of 0.3 or more, preferably 0.940/cm3 or more.
It is preferable that it is 5-1 QC)/10 minutes.

In the case of polypropylene, the isotactic index is 93% or more, preferably 96% or more, and the intrinsic viscosity is 1.2 to 3.5 dl/g, preferably 1.5 to 2.5 dl/g.
A range of 5 dl/g is preferred.

In the present invention, the above-mentioned resin is melt-extruded from a die and cooled under pressure between a pair of calendar rolls to form a film.

Pressure cooling in the present invention refers to melt extrusion of molten resin into a film through a T-shaped nozzle, and as shown in Fig. 1, cooling while applying pressure between two metal rolls. It is in a molten state until it comes into contact with the rolls, but it needs to be crystallized immediately after it is pressurized between the rolls and leaves the rolls. Such crystallization under pressure orients the folded lamellar structure of the polymer chains, giving it a so-called hard elastic structure.

Commonly known calendar casting methods (for example,
-24457) is used to improve the smoothness and transparency of the resulting film. Its function is to uniformly cool and smooth the molten film from both sides, and not to highly orient the cast film.

In the present invention, the calender casting process is carried out under very special conditions in order to form a hard elastic structure by 1q, in which the resin remains molten until just before it enters a pair of rolls, but crystallizes immediately after the calendering. .

The Japanese Patent Publication No. 59-36575@certificate states that only the blown film extrusion method can form such a hard elastic structure, and it also states that Polymer,
22. P250254 (1981) contains a description of an extended chain structure by calendar casting, but there is no description of a hard elastic structure, and this discovery is completely new.

In the present invention, unlike the blown film extrusion method, there is no need to draw the molten resin film at high speed, and the draft ratio (or blow-up ratio) defined by the ratio of the mouth slit width to the cast film thickness is 1:1 to 50: 1
or 1.5:1 to 30:1.

Furthermore, in order to wind the hard elastic structure in the present invention, if the cast speed is too high, crystallization will not progress sufficiently under pressure, so it is necessary to wind the hard elastic structure at a speed of 40 m/min or less. It is in the range of 1 to 30 m/min, preferably 0.2 to 12 m/min. Here, the lower limit of the take-up speed is set because if it is too slow, the extruded resin film will be air-cooled and the orientation force during calendering will be insufficient, making it difficult to obtain a good hard elastic structure.

In the present invention, from the viewpoint of crystallization while applying pressure,
The molten film must begin contacting both rolls almost simultaneously. g' That is, if the outer diameters of both rolls are the same, the perpendicular bisector of the line connecting the centers of both rolls and the direction in which the molten resin film is taken will almost match. Even when the diameters of both rolls are different, it is preferable that the start of contact with both rolls be the same.
The direction in which the molten resin film is taken off is not limited to this because it depends on the film thickness and roll diameter ratio. In addition, if the size of both rolls is too different, it will be difficult to apply uniform pressure on the front and back sides, causing problems such as curling and poor hole continuity, so use rolls of the same size as much as possible. is preferred.

Here, the pressure during calendering is not constant depending on the calender roll diameter and resin properties, and must be adjusted so as to cause crystallization immediately after calendering, and is not particularly limited, and the higher the pressure, the better. As a result, the elastic recovery rate of the film obtained by calendering is 30% or more,
Preferably, it is adjusted to 40% or more. In particular, when the resin is polypropylene, the birefringence Δn should be 15X10' or more. However, when the calender roll diameter is 200 mm, the normal linear pressure is 100 mm.
It is preferable that it is kCI/Cm or more, preferably 300 kcl/Cm or more.

In addition, the calender roll temperature is below the melt crystallization temperature (TmC) of the resin for the purpose of microporization + 10'C,
Preferably, it is in the range of (Tmc -50°C) to Tmc.

In general, a plurality of crystalline resins may be coextruded and calendered during the calendering.

In this case, if resins with too different thermal behavior are coextruded, it will be difficult to perform uniform calender casting, so the difference in melting point is usually within 60°C, preferably within 40°C, and the difference in melt crystallization temperature is 25°C. within ℃, preferably 15℃
It is preferable to stay within.

Further, in the present invention, at least one
A seed crystalline resin layer and at least one amorphous resin layer may be laminated and melt-extruded between calender rolls.

In this case, a preferred combination for the laminated resin is such that the temperature difference between the melt crystallization temperature of the crystalline resin and the glass transition temperature Tg of the amorphous resin is within 25°C, preferably within 15°C. . In addition, from the viewpoint of extrusion stability, casting stability, etc., it is preferable that the amorphous resin has a glass transition point of 70 to 150°C, more preferably 80 to 120°C.

There are two methods for laminating such resins: one is to use multiple ferrules, and the other is to introduce molten resin from multiple extruders into one ferrule. The lamination inside the base is excellent.

The effect of using such lamination technology is, for example, if the resin to be made microporous is laminated in the center layer and other resins are laminated in both layers, the resins in both layers will act like a protective layer. This is to prevent the calender roll pattern from being transferred and to prevent uneven thickness caused by the die from becoming uneven pressure during calendering.

From this point of view, it is preferable that each of the laminated resin layers is removable. As an advanced application of such technology, it is possible to simultaneously form a plurality of microporous films, which is preferable because cost efficiency can be improved. In this case, for example, [polystyrene (PSt)/] polypropylene/
Two types of microporous films are produced by laminating polyethylene [/PSt] (the numbers in parentheses are provided as necessary) in a die and performing the following operations: calender casting, peeling, heat treatment, stretching, and heat setting. It is possible to form a film at the same time.

Of course, in this case, multiple films of the same type can be formed.

Furthermore, when multiple films of the same type are formed by laminating a plurality of peelable resins and a target resin, each layer is peeled off and then laminated again at least before the stretching process and stretched.
It may be heat-fixed. This is preferable because resin layers of the same type are fused in the stretching process to form an integrated film, which reduces defects such as pinholes.

Subsequent steps require heat treatment, stretching, and heat setting.

First, heat treatment is necessary to form a more highly aligned state of the formed oriented lamellar structure, and usually the melting point (Tml) of the cast film is −30°C to (Tml> −
The range is 5°C. For example, in the case of PP, the melting point of the cast film is in the range of 150 to 170°C, so 120°C
The optimum range for heat treatment is ~165°C.

Further, it is more preferable to perform the heat treatment under stress in order to promote ordering of the lamellar orientation structure, and it is preferable to perform the heat treatment while applying a strain of 10% or less. As a result, the elastic recovery rate of the heat-treated film is preferably 50% or more, preferably 60% or more.

In the subsequent stretching, continuous micropores are formed by stretching the oriented lamellar structure formed as described above.

The stretching direction is the direction oriented by calender casting, the stretching ratio is 1.1 to 4 times, and the stretching temperature is in the range of -70°C to the melting point of the heat-treated film (7m2i5°C).At this time, the stretching speed is slow. It is preferable because the continuous penetration property is improved as much as possible.

Here, the stretching process is a process of opening holes in the spring structure to form continuous holes, and the operations include (1) opening holes in the spring structure (elastic deformation), and (2) opening structure. It is necessary for the second process of expanding the porosity and improving the porosity and continuity of the pores (plastic deformation) to proceed appropriately. For this reason, two-stage stretching in which steps (1) and (2) are performed under optimal conditions is preferable in order to improve the continuity of micropores. In particular, the pore-forming process (1) improves the density of pores and improves the uniformity of pores, and preferably lowers the resin melt crystallization temperature (TmC>), (TmC-5>
It is preferable to carry out the stretching at a temperature below ℃ and a stretching ratio within elastic recovery, usually 100% or less in the case of PP, preferably 50% or less.
The strain is less than %.

Furthermore, from the viewpoint of effectively opening holes, it is preferable to effectively heat only the interlamellar structure (mainly the amorphous region) and stretch while suppressing plastic deformation of the lamellar structure as much as possible. It is preferable to use infrared heating, microwave heating, ultrasonic heating, etc. other than heating in combination because the difference in mobility between the lamellar structure and the interlamellar structure becomes noticeable and the stretching amount and porosity become good. Further, from the same viewpoint, the lower the stretching speed, the better, and it is usually 2,000%/min or less, preferably 1,000%/min or less.

The step (2) of widening the pore structure involves deformation of the lamellar structure, and occurs at nodes of plastic deformation. Therefore, in order to cause effective plastic deformation, the stretching temperature should be at least 1 mc of the resin, below the melting point (Tm2>) of the heat-treated film, preferably above (Tmc+5)°C, (Tm2-5
It is preferable to carry out the reaction at a temperature of >°C or below.

The film stretched as described above must be subsequently heat-set to fix the formed microporous structure. The heat treatment temperature is (Tt -20) with respect to the maximum stretching temperature (T1) and the melting point (Tm3) of the stretched film.
~(Tm3-2) °C, preferably Kuha (Tm3-15)
~(Tm3-5)°C.

Here, in order to impart dimensional stability, it is preferable to perform the heat treatment while allowing relaxation of 20% or less, preferably 2 to 15%, in the stretching direction during the heat treatment.

Furthermore, since the microporous film obtained by the film forming method of the present invention does not contain anything other than the crystalline resin and a stabilizer for the resin that is added as necessary, it usually has low wettability with water, electrolyte, etc. It is necessary to perform hydrophilic treatment as necessary. In this case, the treatment methods include surfactant treatment, corona discharge treatment, low temperature plasma treatment, ultraviolet treatment,
Examples include radiation graft treatment and the like.

Among these, surfactant treatment is preferred because it is relatively inexpensive and effective, and specific examples include polyoxyethylene alkyl ether, polyoxyalkylene nonylphenyl ether, fatty acid alkylolamide, and the like.

Note that less than 40% of the cationic surfactant may be added to the nonionic surfactant. This will improve antistatic properties and reduce troubles during winding of the element.

The microporous film prepared as described above has excellent uniformity and permeability, and can be used as a separator for batteries, various filtration filters, moisture permeable waterproofing, etc.

[Effects of the Invention] The present invention has discovered a method for forming an oriented lamellar structure by melt-extruding a crystalline thermoplastic resin and cooling and crystallizing it under pressure between calendar rolls.
The effects are as follows: (1) Since the oriented lamellar structure can be formed at a relatively low speed, the process from extrusion to stretching can be performed continuously, resulting in excellent cost efficiency.

(2) Because it is possible to perform forced crystallization by pressurized cooling, the pore size can be controlled over a wider range than in normal draft casting.
Although the pore size was 0.2 μm, it is now possible to manufacture pores with a large pore size of 1 to 1.5 μm.

(3) Thickness control is easy, and microporous films with a minimum thickness of about 5 μm to a maximum of about 500 μm can be manufactured.

(4) According to the lamination method, it is possible to simultaneously form a plurality of microporous films, which is advantageous in terms of cost.

[Property Evaluation Method and Effect Evaluation Method 1 Next, the characteristics measurement method and effect evaluation method related to the present invention will be summarized.

(1) Melt flow rate According to ASTM-D-1238.

PE: 190°C, 2,160Ω PP: 230°C, 2,160CI Pst: 200°C, 5,000Q (measurement conditions conform to JIS 7210) (2) Intrinsic viscosity ([η]> ASTM-D- According to 1601, 0.1g of sample is 135
The specific viscosity S
It is calculated according to the following formula.

[η]=S/ (0,1x (1+0.22xS))(
3) 13 isotactic index (II) samples
Vacuum dry at 0°C for 2 hours. From now on, heavy ffiW (mg
> Take a sample, put it in a Soxhlet extractor, and boil it
Extract with hebutane for 12 hours.

Next, take out this sample, wash it thoroughly with acetone, and then
Vacuum drying at 130°C for 6 hours, then weight W' (m(
1) is measured and calculated using the following formula.

II (%) = (W' / W) The endothermic peak associated with the melting of the sample is defined as the melting point (T
m). Here, when multiple peaks are observed, the highest temperature peak is taken as the melting point.

Next, the sample is held in a molten state (280°C) for 5 minutes, and then cooled at a cooling rate of 20°C/min, and the peak of latent heat accompanying crystallization is defined as the melt crystallization temperature (Tmc).

Further, 10 mg of the sample is heated in the stomach at a heating rate of 10° C./min from the liquid nitrogen temperature, and the change in specific heat is read and the center temperature of the inflection point is taken as the glass transition temperature.

(5) Elastic recovery rate (ER50) Sample using tensile tester (effective test specimen 100mm)
Stretched at a stretching speed of 100%/min until it reaches 150 mm (that is, applying a 50% strain), held in the stretched state for 1 minute, and then returned to the stretched state at a recovery speed of 100%/min. At this time, the trial length at which the stretching stress becomes zero is measured, and the elastic recovery rate is determined using the formula below. Note that the measurement atmosphere was 25° C. and normal humidity.

ER50 (%) -100x (150-L)/(15
0-100) (6) Birefringence (Δn) Measure the retardation (R) of the sample using a compensator under a polarizing microscope, and calculate the thickness (
d), it was determined by Δn=R/d.

The thickness can be measured using a dial gauge (JIS B 750
9) was used.

(7) Surface pore diameter (a) The surface average pore diameter of each surface of the sample (front and back) is determined by the method described below, and the average of the front and back surfaces is taken as the surface pore diameter.

Scanning electron microscopy (SEM) observation was performed, and adjustments were made so that 200 ± 50 micropores were included in the observation field, and the micropores that were recognized to exist on the surface of the grain were approximated as ellipses, and the pore diameter was adjusted to a long sleeve (aX ) and the short axis <aV>, the average of each is determined, and the geometric mean expressed by the following formula is taken as the surface pore diameter. Note that if there was a fibril-like substance (single or plural) inside the pores, this fibril-like substance was excluded from the measurement.

a=J (ax - ay > (8) Porosity (P) Sample (10 x 10 cm) After immersing in liquid paraffin for 24 hours and thoroughly wiping off the liquid paraffin on the surface layer, the weight f
Measure f1 (W2) and calculate the weight (Wl) of the wetted surface of the sample.
and the density of liquid paraffin (ρ) using the following formula.

P=(W2-Wl>/(Vxρ)) Here, ■ is the apparent volume of the sample (a value calculated from the thickness and dimensions).

(9) As electrical resistance electrolyte, γ-butyrolactone 80wt% 10O-phthalic acid 12.43wt% 10-triethylamine 7.57wt
% composition is prepared, and the microporous film 33 (±3
)mm rectangle and impregnated with electrolyte,
Sandwiched between electrodes as a stack of 5 sheets, under a load of 250q, 2
The impedance was measured at 5°C and 1 kHz, and the ESR component per separator was determined as electrical resistance.

(unit: Ω) The conditions are as follows.

(1) Electrode: platinum black treated platinum electrode 25 mm opening (2) Impedance characteristic measuring device LCR meter AG-4311 manufactured by Ando Electric Co., Ltd. [Example] Next, examples and comparative examples of this invention will be shown. The effects will be explained in more detail.

Example 1 As PP resin, Mitsui Noblen type FD-100 (
Manufactured by Mitsui Toatsu Co., Ltd., [η] = 2.3 dl/g, II
= 97%) was melt-extruded at 190° C. and cooled and solidified under pressure at a roll temperature of 98° C. using a pair of 200 mm diameter calender rolls.

At this time, the film that came out of the calender roll was almost solidified immediately after that.

Here, the film thickness is 20.50, 100.20
0am level 4 was 1q.

Next, these films were placed in a hot air oven at 150°C and heat treated for 10 minutes, and then stretched at 100°C at a stretching speed of 100%.
Stretched 1.3 times at a speed of 1.3 times per minute, and then stretched 1.3 times at a temperature of 150°C.
Stretched 4 times and allowed 5% relaxation at 160℃
It was heat-treated for 10 seconds and wound.

Table 1 shows the properties of the 1q film as described above, and all of them are microporous films having continuous pores.

Comparative Example 1 In Example 1, the molten film was first brought into contact with one of the calender rolls to cool it, and then calender casting was performed between both rolls to wind up a 20,100 μm film.

These were heat-treated and stretched in the same manner as in Example 1, but although they were whitened, there was no permeability on the front and back sides and no micropore formation occurred.

Example 2 High-density polyethylene resin [HDPE layer (Sumiyuki Senhard 2723A, manufactured by Sumitomo Chemical) as the crystalline resin,
As the amorphous resin, polystyrene resin [Pstl (Styron 679, manufactured by Fukaisei Co., Ltd.) was melt-extruded from each extruder and laminated in the die to produce IDPE/Pst/HDPE.
It was extruded as a three-layer structure, and cooled under pressure using the calendar roll of Example 1 to form a film.

The respective thicknesses were 20tim/40μm/20μm.

The HDPE layer was peeled off from the film and heated at 120°C for 2 hours.
Heat treated for minutes. The film thus jutted had an elastic recovery rate of 87%.

Next, the respective films subjected to peeling heat treatment and 1q were laminated and stretched to 1.2 times at 80°C, and then stretched at 125°C.
The film was stretched to twice its original size and heat set at the same temperature while allowing 5% relaxation in the longitudinal direction.

As a result, the film turned milky white and became microporous. The pore diameter was 0.03 μm, the porosity was 51%, and the electrical resistance when impregnated with electrolyte was 1Ω.

Example 3 Mitsui Noblen FO850 ([η]
= 1.85, II = 97%) As the amorphous resin, polystyrene resin [Pstl (Stylon 679, manufactured by Fuikasei Co., Ltd.) was melt-extruded from each extruder, laminated in the die, and Pst at an extrusion temperature of 190°C. A three-layer grooved film consisting of /PP/PS↑ was extruded and cooled under pressure using the calendar roll of Example 1 to form a film. The roll temperature was 85°C, the pressure was 600 kg/cm, and the casting speed was 4 m/min.

The thickness structure of the film obtained here was such that each film had a thickness of 25 μm and 1 hectal was 75 μm.

Next, the Pst layer of the laminated film was peeled off, and only the PPC was introduced into a subsequent heat treatment oven and heat treated at 150°C for 1 minute. Elastic recovery ER50 = 92%, △n = 20X
10-3 film is 19.

Next, the heat-treated film was stretched 1.4 times in a hot air oven at 70° C. using a roll stretching device at a stretching speed of 100%/min.

Subsequently, it is guided to a clip holding type MD stretching device, and 14
It was stretched 1.8 times at 5°C and wound at 155°C while allowing 5% relaxation in the longitudinal direction.

The microporous film thus obtained has a thickness of 24 μm,
The pore diameter was large at 0.3 μm, and the electrical resistance was small and excellent at 0.4 Ω.

Comparative Example 2 Using the resin groove composition of Example 3, pneumatic pressure casting was carried out on a casting drum at a casting speed of 4 m/min.

Next, as in Example 3, Ps tll was peeled off and PP
The layer was heat treated at 150°C for 10 minutes.

The resulting film had an elastic recovery rate of 30% and an orientation degree Δn of 6×10 −3 and was stretched in the same manner as in Example 3, but due to necking stretching, a uniform film could not be obtained.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram of the casting method of the present invention. 1. Calendar roll, 20 caps 3. Extrusion 4. Melt film; 5. cooling film

Claims (9)

[Claims] (1) A crystalline resin is melt-extruded from a die, cooled and crystallized under pressure between a set of calendar rolls at a withdrawal speed of 40 m/min or less to obtain a film with a thickness of 5 to 1000 μm, followed by heat treatment and stretching. and a method for producing a microporous film, characterized by carrying out heat setting. (2) The method for producing a microporous film according to claim 1, characterized in that during melt extrusion, a plurality of different crystalline resins are laminated and melt extruded between calender rolls. (3) Micropores according to claim 1, characterized in that during melt extrusion, at least one type of crystalline resin layer and at least one type of amorphous resin layer are laminated and melt extruded between calender rolls. Method of manufacturing a sex film. (4) The method for producing a microporous film according to claim 2 or 3, characterized in that the resin is laminated within a die. (5) The resins are non-adhesive to each other, and the laminated film that has been cooled under pressure is peeled off before heat treatment, and the desired crystalline layer is heat treated to perform a post-process. Any method for producing a microporous film. (6) The method for producing a microporous film according to claim 5, wherein the crystalline film obtained after the heat treatment has an elastic recovery rate of 50% or more. (7) The crystalline resin is polyolefins exemplified by polyethylene, polypropylene, poly4 methylpentene 1, polybutene 1, polyfluorinated olefins such as polyvinyl fluoride, polyvinylidene fluoride, polyethylene terephthalate, polyethylene naphthalate, Claims 1 to 6, characterized in that it is at least one selected from polyesters exemplified by polybutylene terephthalate, polyphenylene sulfide, polyoxymethylene, polyamide, etc.
A method for producing a microporous film according to any one of the above. (8) The method for producing a microporous film according to any one of claims 3 to 6, wherein the amorphous resin has a glass transition point of 70 to 150°C. (9) The method for producing a microporous film according to any one of claims 1 to 6 or 8, wherein the crystalline resin is at least one selected from polyethylene and polypropylene.