JPH0848821A - Filler for polyolefin-based resin sheet - Google Patents

Abstract

PURPOSE:To provide a hydrated silicic acid filler improved in workability when it is blended with a resin and a plasticizer and making it possible to produce a sheet with improved workability while reducing its shrinkage and a method for producing a finely porous sheet by using this filler. CONSTITUTION:This filler for finely porous polyolefin-based resin sheet is composed of hydrated silicic acid having 100 to 200m<2>/g BET specific surface area, 200 to 300cc/100g oil absorption, 4.0 to 9.0mum average particle diameter and >=70% coagulation ratio of particles. Production of a finely porous sheet is carried out by using this filler for finely porous polyolefin-based resin sheet, blending this filler, a polyolefin-based resin and a plasticizer, making a sheet from the resultant mixture and extracting the plasticizer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filler for a microporous polyolefin resin sheet and a method for producing a microporous sheet using this filler. More specifically, the present invention relates to a hydrous silicate filler for a battery separator, which has improved shrinkage during the sheet manufacturing process of a polyethylene battery separator by a plasticizer extraction method.

[0002]

2. Description of the Related Art Conventionally, a microporous sheet having a synthetic resin as a base material has been widely used as a battery separator. These sheets are required to have excellent film resistance, porosity and strength. That is, a film resistance is low, a porosity is generally high, and naturally, a material having excellent strength and life and durability is required. or,
As the filler used for the microporous sheet, hydrous silicic acid or alumina which is inert and durable under strong acidity is generally used.

In this type of microporous sheet, for example, a filler and a plasticizer are mixed in a thermoplastic resin by using a mixer, and after being formed into a sheet by an extruder, the filler or the plasticizer is extracted with a solvent or the like. It is manufactured by In the method of extracting the filler, the pore size of the sheet is almost determined by the particle size of the filler. Therefore, an optional microporous sheet can be obtained by selecting a filler having a specific particle size. However, there is a drawback in that the sheet after the filler is extracted contracts greatly.

On the other hand, in the method of extracting the plasticizer, the shrinkage of the sheet is smaller than that in the method of extracting the filler.
However, when it was attempted to manufacture a sheet having a small membrane resistance and a large porosity, the sheet shrank greatly at the stage of extracting the plasticizer, and the shrinkage rate was not constant.
Therefore, the method of extracting the plasticizer also has a problem in that workability is poor in the production of the sheet as described above.

In addition to the shrinkage of the sheet, there is also a demand to further improve the workability in mixing the resin, the filler and the plasticizer. That is, for example, a hermetic mixer is used for the above-mentioned mixing, but if sufficient mixing is performed in a shorter time at a lower torque, the productivity is improved.

Therefore, an object of the present invention is to improve the workability in mixing a resin, a filler, and a plasticizer in a method for manufacturing a microporous sheet of the type in which a plasticizer is extracted, and at the time of manufacturing the sheet. Another object of the present invention is to provide a hydrous silicic acid filler in which the contraction of the sheet is relaxed and the workability is improved. Still another object of the present invention is to use the above-mentioned hydrous silicic acid filler,
To provide a method for producing a microporous sheet, in which the workability in mixing a resin, a filler, and a plasticizer is further improved, and the shrinkage of the sheet during sheet production is alleviated to improve the processability. is there.

[0007]

[Means for Solving the Problems] In the method for producing a microporous sheet by extracting a plasticizer, the present inventors have investigated the workability and workability during film formation and the shrinkage during extraction of the plasticizer. The BET specific surface area of the agent, the oil absorption amount, the average particle size and the agglomeration specific surface area of the particles have a great influence, and by specifying these physical properties, an excellent filler for a microporous polyolefin resin sheet can be provided. They have found that they can do so and have completed the present invention.

That is, the present invention has a BET specific surface area of 100.
~ ²⁰⁰ m ² / g, oil absorption is 200-300 cc
/ 100 g, an average particle size of 4.0 to 9.0 μm, and a hydrous silicic acid having an agglomeration specific surface area of particles of 70% or more, a filler for a microporous polyolefin resin sheet. Regarding Further, the present invention is a method for producing a microporous sheet by mixing a polyolefin resin, a filler and a plasticizer, forming a sheet, and extracting the plasticizer, wherein the filler of the present invention is used as the filler. Relates to a manufacturing method. According to the present invention,
In the method of producing a microporous sheet by extracting a plasticizer, a processability is improved, and a microporous polyolefin resin sheet having good sheet shrinkage stability is obtained.

The present invention will be further described in detail. The method for producing the microporous sheet of the present invention is carried out by mixing a polyolefin resin, a filler and a plasticizer into a sheet and extracting the plasticizer. The polyolefin resin is not particularly limited and, for example, polypropylene or polyethylene is used. As the filler, the hydrous silicic acid filler of the present invention described later is used.
The plasticizer is not particularly limited and, for example, mineral oil is used. Mixing polyolefin resin, hydrous silicic acid filler and plasticizer with a mixer, forming into a sheet and extracting the plasticizer,
It is carried out by a conventional method. For example, mixing can be performed using a mixer or the like, and sheet formation can be performed by extrusion molding or the like. Furthermore, the extraction of the plasticizer is performed using an organic solvent.
The sheet produced by the method of the present invention is substantially a microporous sheet composed of hydrous silicic acid and a resin.
This microporous sheet is suitable as a battery separator.

As mentioned above, the production of the microporous sheet is
Including a mixing step using a mixer or the like and a sheet forming step, the workability and processability thereof depend on the physical properties and characteristics of the hydrous silicic acid as a filler. In particular, the BET specific surface area and the oil absorption amount have a great influence. The oil absorption performance of general hydrous silicic acid is B
There is a peak near the ET specific surface area of 200 m ² / g, and B
There is a strong correlation between the ET specific surface area and the oil absorption performance. If the BET specific surface area is too low or too high, it is difficult to obtain high oil absorption performance. The BET specific surface area of the hydrous silicic acid which is the filler of the present invention is in the range of 100 to 200 m ² / g. It is preferably 150 to 180 m ² / g. If the BET specific surface area of hydrous silicic acid exceeds the above range and is too high, the cohesive force is increased,
As a result, dispersibility is impaired and workability is adversely affected.
On the other hand, if the amount exceeds the above range and is too low, the oil absorption performance, which is a characteristic of hydrous silicic acid, is insufficient, and it becomes difficult to obtain the target microporous sheet.

Further, the higher the oil absorption performance is, the more advantageous it is, but it is in the range of 200 to 300 cc / 100 g according to the correlation with the BET specific surface area and the aggregation ratio defined below.
It is preferably in the range of 210 to 260 cc / 100 g. If the oil absorption is too low, it becomes difficult to obtain a sheet having a large porosity. Further, if the oil absorption amount is too high, it becomes difficult to maintain the strength after sheet molding.

Average particle size, that is, particle size (secondary agglomerated particles)
Has a great influence on dispersibility and workability, and if the particle size is too small, it deteriorates the biting property in the sheet extruding step, and causes a trouble in handling due to dust and the like. In addition, if the particle size is too large, it causes poor dispersion and further adversely affects the shrinkage stability of the sheet. Therefore, the average particle size is 4.0.
Is in the range of up to 9.0 μm. Preferably 5.0-8.
It is in the range of 0 μm.

It is important that the hydrous silicic acid of the present invention has an aggregation ratio of 70% or more. If the agglomeration ratio is less than 70%, the agglomeration force between particles is weak and the structure is lost, which adversely affects the shrinkage of the microporous sheet. It is preferably 80% or more.
The upper limit of the aggregation ratio is not particularly limited, but generally 95
%. The aggregation ratio tends to increase as the BET specific surface area of hydrous silicic acid increases. However, considering the above-mentioned dispersibility, the BET specific surface area is 200 m ² /
It is suitable that it is g or less and the aggregation ratio is 70% or more.

A major problem in the process of manufacturing the polyolefin battery separator sheet is to suppress the shrinkage of the microporous sheet in the process of extracting the plasticizer, and further to make the shrinkage rate constant. Although not clear, it is presumed that the size of the shrinkage is due to the strength of the entanglement between the resin and the hydrous silicic acid which is the filler forming the skeleton of the microporous sheet. That is, the plasticizer in the sheet is extracted with a solvent to form a microporous sheet, and at that time contraction occurs, but the degree of contraction depends on the strength of the cohesive force between the particles of the filler forming the microporous sheet and It is considered to be determined by the strength of the entanglement with the resin. For example, in carbon black, a particle structure, that is, a structure means a connection form between particles or a connection strength between particles due to aggregation, and is called a chain structure or a chain structure. The more advanced the structure of the particles is, the higher the reinforcing effect is, and it is often used as a rubber reinforcing filler. The hydrous silicic acid which is the filler of the present invention is considered to be similar to this high structural property.

The present inventors replaced this structural property with the strength of cohesiveness between particles and expressed it by a numerical value to be described later, and defined it as an agglomeration ratio. That is, it is represented by the ratio of the respective average particle diameters measured under the conditions of different dispersion forces. In this case, a large value of the agglomeration ratio indicates that the average particle size measured does not become so small even when the particles are dispersed under the condition that the dispersive power is large, and indicates the strength of the agglomeration force of the hydrous silicate particles. It is considered that Further, the cohesive force represents the strength of the binding force between the single particles forming the secondary agglomerated particles of hydrous silicic acid, the cohesive force of hydrous silicic acid is strong, the value of the aggregation ratio is large. In addition, when the oil absorption is high, it is expected that the structure of hydrous silicic acid will be developed and firm, and as a result, the shrinkage of the sheet will be suppressed.

In general, wet-process hydrous silicic acid can be produced by a neutralization reaction of an aqueous solution of an alkali metal silicate and a mineral acid, and is reacted under neutral or alkaline conditions to obtain precipitated silicic acid which is relatively easy to filter. be able to. The precipitation method is disclosed in, for example, Japanese Patent Publication No. 39-12067, and the precipitated silicic acid obtained by growing primary particles so as to have a structure by a neutralization reaction is washed with water, dried and pulverized. Become a product. The precipitated hydrous silicic acid obtained by these methods is mainly used as a general-purpose rubber-reinforcing filler, a pesticide carrier, a paint delustering agent, a viscosity modifier, and the like.

The hydrous silicic acid of the present invention can be produced, for example, by performing a aging step in addition to the neutralization reaction by a precipitation method.
The neutralization reaction in the present invention has at least three neutralization steps and two or more aging steps. The conditions of each step may be appropriately selected so as to obtain a target physical property value, but the division of the neutralization reaction is preferably three times or more, and if less than three times, the target physical property, particularly a hydrous silica having a high aggregation ratio, is preferable. Acid is difficult to obtain. In addition, in the aging step at the stage of carrying out the final neutralization and acidification, it is preferable that the aging is carried out at a high temperature of 90 ° C. or higher and in a weak alkaline range pH 7 to 30 for 30 minutes or more. When the pH is out of the range or the aging time is short, the target hydrous silicic acid of the present invention is similarly difficult to obtain. After acidification, the product obtained can be obtained by filtration, washing with water, drying and, if necessary, grinding. However, the method is not limited to this.

As is clear from the above description, the hydrous silicic acid of the present invention has a BET specific surface area of 100 to 200 m ² / g.
The oil absorption is 200 to 300 cc / 100 g, the average particle size is 4.0 to 9.0 μm, the agglomeration ratio of the particles is 70% or more, and by using this hydrous silicic acid as a filler, The processability of the polyolefin resin sheet can be facilitated and the shrinkage of the microporous sheet can be suppressed.

[0019]

EXAMPLES The present invention will be described more specifically below based on examples and reference examples, but the present invention is not limited to these examples. Each physical property value used in the present invention was measured by the following methods. 1. Powder properties of silica BET specific surface area (m ² / g) Cantasorb (manufactured by QUANTACHROME, USA) 1
It was measured by the point method. Oil absorption (cc / 100 g SiO ₂ ) Measured by the JIS K-5101 pigment test method. Average particle size (μm) Disperse with an ultrasonic cleaner UA50 (manufactured by Kokusai Electric Co., Ltd.) at an output of 20 W × 40 seconds, Coulter Counter T
The average particle size was measured using an A-II (manufactured by COULTER ELECTRONICS) with an aperture tube of 70 μm.

Aggregation ratio (%) The aggregation ratio expresses the strength of the cohesiveness of silica, and represents the strength of the binding force between the silica single particles forming the secondary agglomerated particles. is there. That is, it is represented by the ratio of the average particle diameters due to the difference in dispersive power. Disperse using an ultrasonic cleaner UA50, Coulter Counter TA-
The average particle size was measured by using an ultrasonic homogenizer 250 SONIFIER (manufactured by BRANSON, USA) with an output of 150 W × 60 seconds, and the average particle size was measured in the same manner. The particle size ratio with that of the particles (B μm) was taken as the aggregation ratio. Aggregation ratio (%) = B / A × 100

2. Pretreatment Method for Polyolefin Resin Sheet 15 parts by weight of polyethylene resin and 25 parts by weight of hydrous silicic acid fine powder are placed in a stainless steel container, and 60 parts by weight of a plasticizer (mineral oil) are added in 8 minutes while mixing with a mixer. , Make a mixture of three kinds. Brabender test (Table 1) Torque rise time of the above mixture in an internal mixer Plasticorder (made by Brabender, West Germany),
The peak time and the peak torque value were measured to measure the degree of mixing. That is, as the rise time and peak time of the torque are faster and the torque value is lower, the mixing is smoothly performed. ○ Measurement conditions Mixing temperature: 140 ° C Mixing speed: 50 rpm Measuring time: 30 minutes Sample weight: 45 g

Preparation Method of Polyethylene Resin Sheet and Shrinkage Test (Table 2) A mixture of resin, hydrous silicic acid fine powder and plasticizer treated with a mixer is extruded while being heated and mixed by an extruder, and then is extruded by a 4-inch electric heating roll. A sheet was obtained by molding to a thickness of 0.3 mm to 0.4 mm. Thereafter, the plasticizer in the sheet was extracted with a solvent (trichloroethylene) to obtain a microporous sheet.
Further, in the shrinkage test, the size of the sheet before and after extracting the plasticizer was measured to obtain the shrinkage rate. The plasticizer in the sheet was extracted with a solvent for 60 minutes, and the natural drying shrinkage rate was measured at room temperature of 20 ° C. for one day. ○ Sheet preparation and shrinkage test conditions Extruder temperature: 20 ° C. Roll forming temperature: 130 ° C. Sheet width length: 300 × 300 mm Thickness: 0.3 mm to 0.4 mm Solvent extraction: Extraction with trichlorethylene for 1 hour

Example 1 A stainless steel reaction tank equipped with a stirrer equipped with 200 liters had SiO _{2 of} 120 g / liter, and SiO ₂ and Na ₂
70 aqueous solution of sodium silicate in which the molar ratio of O is 3.3
1 liter and 60 liters of water were added, and steam was blown into the mixture while stirring to raise the temperature to 70 ° C. Next, the required amount of 32% sulfuric acid (18.4 mol /
Liter) was added for 20 minutes. Further, the temperature was maintained as it was, and aging was carried out for 30 minutes. After that, sound raising was started and 40 minutes was required to reach 98 ° C., followed by aging for 15 minutes. After that, the same sulfuric acid is used for pouring for 30 minutes,
After adjusting the pH to 9.0, the sulfuric acid was stopped. Subsequently, the temperature was maintained as it was, followed by heat aging for 60 minutes, and then acidification to stop the reaction at pH 3.0. Further, the obtained reaction product was filtered with a filter press and washed with water to remove impurities as a by-product to obtain a filter cake. This was dried with a spray dryer and then crushed with a hammer crusher to obtain hydrous silicic acid by the wet precipitation method of the present invention. With respect to the obtained hydrous silicic acid, the workability and shrinkability of the polyolefin resin sheet were evaluated.

Example 2 Hydrous silicic acid was obtained in the same manner as in Example 1 except that 40% of a predetermined amount of sulfuric acid required for neutralization of all alkalis was added, and the workability and shrinkability of the sheet were evaluated.

Reference Example 1 Hydrous silicic acid was obtained in the same manner as in Example 1 except that 45% of a predetermined amount of sulfuric acid required for total alkali neutralization was added, and the workability and shrinkability of the sheet were evaluated.

Reference Example 2 A commercially available hydrous silicic acid, Nipsil NS-K (manufactured by Nippon Silica Industry Co., Ltd.) was used for evaluation.

Reference Example 3 Evaluation was performed using a commercially available hydrous silicic acid, Nipsil KM (manufactured by Nippon Silica Industry Co., Ltd.).

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

As is clear from Tables 1 and 2, when the hydrous silicic acid of the present invention is used, in the Brabender test, not only the torque rise time is fast, but also workability and dispersion are smoothly performed. I understand that Further, in the shrinkage test, the shrinkage ratio in the roll width direction is particularly small. Therefore, it can be seen that the use of the filler of the present invention results in excellent shrinkage stability during processing of the resin sheet. As described above, when the filler of the present invention is used for producing a microporous polyolefin-based resin sheet, there are effects that excellent workability can be obtained and that shrinkage of the sheet can be suppressed. Furthermore, the sheet produced using the filler of the present invention is excellent as a battery separator.

Claims (3)

[Claims] 1. A BET specific surface area of 100 to 200 m ² /
g, the oil absorption is 200 to 300 cc / 100 g, the average particle size is 4.0 to 9.0 μm, and the agglomeration ratio of the particles is 70% or more. Filler for porous polyolefin resin sheets. 2. The filler according to claim 1, wherein the microporous polyolefin resin sheet is a battery separator. 3. In the method for producing a microporous sheet by mixing a polyolefin resin, a filler and a plasticizer, forming a sheet, and extracting the plasticizer, the filler according to claim 1 is used as the filler. A manufacturing method characterized by the above.