JP2001283820A - Surface modifying method of synthetic resin and separator for battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve affinity by modifying the surface of synthetic resin. SOLUTION: Synthetic resin, through reduction treatment after oxidization, can be reformed to be furnished with high affinity. Further, the separator for a battery made from this treated synthetic resin can also improve capacity retainability and cycle life characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for modifying the surface of a synthetic resin and a separator for a battery using the modified synthetic resin.

[0002]

2. Description of the Related Art For example, when synthetic resin fibers made of polyolefin such as polyethylene are used as a woven or nonwoven fabric for a separator of a storage battery, the wettability with water is poor.
Therefore, the wettability with the electrolytic solution used for the storage battery is poor, and as a result, there is a problem that the initial capacity of the storage battery is hardly obtained due to an increase in the internal resistance of the storage battery. In order to solve this problem, separators made of these synthetic resin fibers are subjected to a sulfonation treatment by dipping them in concentrated sulfuric acid or coated with a surfactant. This has good wettability with the electrolytic solution and has good hydrophilicity, and is preferable as a separator.

[0003]

However, this separator has a problem that the hydrophilicity of the separator is gradually reduced after a long-term use, so that the life of the storage battery cannot be improved.

[0004]

DISCLOSURE OF THE INVENTION The present invention has been made to obtain a storage battery having a longer service life. After oxidizing a synthetic resin, the synthetic resin is subjected to a reducing treatment with a reducing agent, or is performed in the presence of a reducing agent. By performing a photoreduction reaction by ultraviolet irradiation, this is used as a storage battery separator. Furthermore, the synthetic resin treated as described above is
It has been found that the hydrophilicity is improved and the water retention rate is improved, so that the antistatic effect can be expected to be improved.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiment of the present invention will be described in which a synthetic resin is oxidized, washed with water and dried to remove the oxidizing agent, and then treated with a reducing agent. By this treatment, for example, in the case of polyethylene, for example, hydrogen is included in the molecule by the active oxygen of ozone directly or generated by ultraviolet irradiation, plasma, glow discharge or the like in the presence of an oxidizing agent or oxygen, as shown in Chemical Formula 1. The reaction mechanism in which the carbonyl group is generated by extraction is presumed. At this time,
Carboxyl groups may be introduced into a small amount of alcoholic hydroxyl groups and terminal groups. Although these are hydrophilic groups, the amount is small, so that sufficient hydrophilicity cannot be provided.
When the processing conditions are severe, the hydrophilicity is improved to some extent, but the main chain is cut off at the same time, and the mechanical strength is reduced. The oxidation treatment needs to be appropriately controlled. For the oxidation treatment, use an aqueous solution of potassium dichromate, potassium permanganate, concentrated sulfuric acid, nitric acid, peroxide, or a gas such as ozone, fuming sulfuric acid, fluorine gas, or chlorine gas as the oxidizing agent. Can be. Further, the oxidation treatment can be performed by ultraviolet rays, plasma, glow discharge, or radiation in an oxidizing atmosphere. To make the reaction uniform, a small amount of a surfactant may be added.

[0006]

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Those treated with an aqueous solution of an oxidizing agent are washed with water and dried, and those treated with an expected oxidizing agent are treated with a reducing agent after removing the oxidizing agent as much as possible. Is introduced into the molecule.

[0008]

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At this time, attention must be paid to the strength of the reducing agent. If it is too strong, it returns to hydrocarbons and becomes water repellent. If it is too weak, sufficient hydrophilicity cannot be obtained. Organic reducing agents such as formaldehyde, acetaldehyde, isopropanol and ascorbic acid, and inorganic reducing agents such as stannous enka can be used as the reducing agent. Also, at this time, if ultraviolet rays are irradiated, a photoreduction reaction occurs, so that the reaction proceeds smoothly. It is desirable to use 300 nm or more, which is an n → π ^* absorption band, in order to make the carbonyl compound the lowest excited singlet (S ₁ ) state as the wavelength of the ultraviolet light, because unnecessary decomposition reaction and the like can be suppressed.

As described above, in the treatment, since a large number of alcoholic hydroxyl groups bonded without breaking the main chain are present, a decrease in strength is small and good hydrophilicity is obtained.

The hydrophilicity can be adjusted by the first oxidation treatment condition, and the condition is set according to the purpose. In addition to polyethylene, basically -CH ₂ - or, and> C
It is applicable to all molecules having ＯO.

In addition to the non-woven fabric and the woven fabric, the present invention can be similarly applied to films, plates, and resin coatings of paints. When a woven fabric, a nonwoven fabric, a microporous film, or the like made of a synthetic resin hydrophilized as described above is used as a storage battery separator, a battery having stable performance over a long period of time can be obtained.

[0013]

EXAMPLES A method for modifying the surface of a synthetic resin according to the present invention will be described. (Example 1) A monofilament whose core is covered with polypropylene and the surface of which is sheathed with polyethylene is made into a paper, and a heat-sealed nonwoven fabric (having a basis weight of 85 g / m ² and a thickness of 0.23 mm) is thoroughly washed with water. After drying, this was immersed in a 1M aqueous solution of potassium dichromate at room temperature and left for 1 hour to perform oxidation treatment. After that, it is taken out, washed with water, dried, and immersed in a 5% formaldehyde aqueous solution at room temperature for 24 hours to perform a reduction treatment.
It was taken out, washed with water and dried to obtain a surface-modified synthetic resin. This was designated as nonwoven fabric A.

(Example 2) The heat-sealed nonwoven fabric used in Example 1 was thoroughly washed with water, dried, immersed in a 1 M aqueous solution of potassium dichromate at room temperature, and left for 1 hour for oxidation treatment. It was taken out, washed with water, dried, immersed in a 5% formaldehyde aqueous solution at room temperature, and irradiated with ultraviolet rays mainly having wavelengths of 313 nm and 366 nm for 30 minutes using an ultraviolet lamp equipped with a Pyrex filter in this state. Thereafter, the resultant was washed with water and dried to obtain a non-woven fabric B.

Example 3 The heat-fused nonwoven fabric used in Example 1 was thoroughly washed with water, dried, and then oxidized by irradiating with ultraviolet light having a wavelength of 254 nm for 30 minutes using an ultraviolet lamp equipped with a Pyrex filter. After that, it was immersed in a 5% formaldehyde aqueous solution at room temperature for 24 hours, washed with water and dried to obtain a nonwoven fabric C.

Example 4 The heat-sealed nonwoven fabric used in Example 1 was thoroughly washed with water, dried, and irradiated with ultraviolet rays having a wavelength of 254 nm for 30 minutes using an ultraviolet lamp equipped with a Pyrex filter. The sample was immersed in an aqueous formaldehyde solution at room temperature, and in this state, a wavelength of 313 nm and a wavelength of 36 nm were measured using an ultraviolet lamp equipped with a Pyrex filter.
Irradiation with ultraviolet light mainly of 6 nm for 30 minutes, washing with water, and drying were regarded as non-woven cloth D.

In order to confirm the surface of the synthetic resin fiber nonwoven fabric according to the present invention, FT-
The functional groups were qualitatively determined by IR (Fourier transform infrared absorption spectrum). Both after the oxidation treatment with the oxidizing agent and the ultraviolet light, absorption by the carbonyl group near 1750 cm ⁻¹ that did not appear before the treatment appeared, and the oxidation treatment partially oxidized the polyolefin molecule and introduced the carbonyl group. I understood. 3500cm at the same time
^An absorption peak due to a small hydroxyl group also appeared around ^-1 .

Next, after the reduction treatment, the peak of the carbonyl group became smaller and the peak of the hydroxyl group became larger. Thus, it was confirmed that the alcoholic hydroxyl group, which is a hydrophilic group, was introduced into the polyolefin molecule by this treatment. . In addition, as a result of impregnating with ion-exchanged water in order to easily evaluate hydrophilicity, it was found that water was slightly absorbed after the oxidation treatment, but all water was absorbed immediately after the reduction treatment. Was done.

In each of the embodiments, the method of immersing the nonwoven fabric in the oxidizing agent solution or the reducing agent solution is adopted. However, the present invention is not limited to this method. it can.

(Conventional Example 1) The heat-sealed nonwoven fabric used in Example 1 was thoroughly washed with water, dried, and then concentrated in concentrated sulfuric acid at 110 ° C. for 2 hours.
After immersion for 0 minutes for sulfonation, washing with water and drying were taken as Conventional Example 1. The nonwoven fabric turned brown.

(Conventional Example 2) The heat-sealed nonwoven fabric used in Example 1 was thoroughly washed with water, coated with a surfactant and dried to obtain Conventional Example 2.

(Comparative Example 1) Nylon non-woven fabric (with a basis weight of 95 g /
m ² , thickness 0.22 mm).

(Comparative Example 2) A glass fiber mat used for a lead storage battery or the like was prepared, and Comparative Example 2 was provided.

In order to evaluate the hydrophilicity of each of the obtained nonwoven fabrics, the water absorption rate and the water retention were measured. The water absorption rate was determined by cutting each nonwoven fabric in a water equilibrium state into 2.5 × 20 cm, immersing the lower end in ion-exchanged water by 5 mm at 20 ° C., and measuring the height increased by capillary action in 30 minutes. The water retention rate was determined by cutting each nonwoven fabric to 15 × 15 cm, immersing it in ion-exchanged water for 1 hour, pulling it up, and keeping the weight increase after 10 minutes as water retained as a percentage per sample weight. Table 1 shows the measurement results.

Next, in order to measure the strength, each nonwoven fabric was
× 20 cm, cut according to JIS L1068, with a gripping interval of 10 cm and a tensile speed of 30 cm / min. Table 1 shows the measurement results.

[0026]

[Table 1]

As described above, it was found that the nonwoven fabrics A to D according to the present invention had a higher absorption rate and a higher water retention rate than the conventional examples 1 and 2 and the comparative example 1. In addition, since it is a polyolefin resin having a water retention comparable to that of Comparative Example 2 made of glass fiber having extremely high hydrophilicity and being stable in a sulfuric acid electrolyte, it can be applied to a lead storage battery.

The reason why the tensile strength of the nonwoven fabric of Comparative Example 1 subjected to the sulfonation treatment was low is considered to be that the molecular chain was broken by the treatment.

Next, in order to confirm the performance of these non-woven fabrics as a battery separator, each of the non-woven fabrics was used to obtain a rated capacity of 1%.
A nickel-metal hydride storage battery having an AA size of 500 mA was prepared. For the positive electrode, 5% zinc and 2% cobalt solid solution nickel hydroxide and 7.5% cobalt oxide 0.5% CMC
The resulting mixture was kneaded with an aqueous solution, filled and applied to a foamed nickel substrate, dried, and pressed to obtain a paste-type nickel electrode. The negative electrode was filled applying those kneading hydrogen absorbing alloy powder and carbon powder AB ₅ system with 1% CMC aqueous solution to the perforated sheet iron plated with nickel, dry, using a hydrogen storage alloy electrode was pressed. Each non-woven fabric is wound between the positive electrode and the negative electrode to form a wound electrode plate group, which is housed in a nickel-plated iron bottomed cylindrical can and having a specific gravity of 1.3.
After injecting an electrolyte mainly composed of potassium hydroxide of 0, the can is sealed with a lid to perform initial charge, and batteries using the nonwoven fabrics A to D of the present invention are referred to as batteries A to D, respectively. The batteries using the nonwoven fabrics 1 and 2 were replaced with batteries E and F, Comparative Example 1
The battery using the nonwoven fabric was designated as Battery G.

Using these batteries, self-discharge and cycle life characteristics were evaluated. The self-discharge test was the initial 0.2
C discharge capacity was measured, after charging for 15 hours at 0.1 C, and left for one month in an environment at a temperature of 40 ° C., 0.2 C discharge capacity was measured, and the capacity retention ratio was compared with the initial 0.2 C discharge capacity. I asked. The cycle life test was performed in a 25 ° C constant temperature bath at 1C.
And stop charging by detecting -ΔV.
Discharge was performed with the current of C until the battery voltage reached 1.0 V, and the change in capacity was measured. -ΔV detection is a method of controlling charging by catching a phenomenon in which a negative electrode absorbs oxygen gas generated at the end of charging of a battery to lower the battery voltage, and is a commonly used charging control method. . Table 2 shows the results.

[0031]

[Table 2]

As described above, the batteries A to D using the nonwoven fabric separator according to the present invention exhibited good capacity retention. In the battery E, a low-molecular-weight by-product is generated at the time of sulfonation, and this is eluted into the electrolytic solution, so that the capacity retention is considered to be low. The capacity retention of the battery F was further reduced, presumably because the surfactant was eluted into the electrolyte. Further, the battery G becomes worse, which is presumed to be due to the decomposition of nylon to generate nitrogen compounds (nitrite ions and nitrate ions), causing a so-called shuttle reaction.

FIG. 1 shows the results of the cycle life test.
As is clear from the figure, batteries A to D using the nonwoven fabric separator according to the present invention exhibited good cycle life characteristics. This is because the nonwoven fabric treated according to the present invention exhibited high hydrophilicity over a long period of time. This indicates that the nonwoven fabric is preferable as a battery separator. The capacity of the batteries E and G gradually decreased. It is considered that, during the repetition of the charge / discharge cycle, the hydrophilicity of the nonwoven fabric decreases, so that the interelectrode resistance increases and the discharge capacity decreases. In addition, the battery F showed a rapid decrease in capacity. This is considered to be because the surfactant was eluted into the electrolyte solution early, and the non-woven fabric became water-repellent due to the exposure of the polyolefin poor in hydrophilicity.

[0034]

As described above, the present invention can improve the water absorption rate and water retention of the water-repellent synthetic resin to impart hydrophilicity, and when this is used for a battery separator, the capacity of the battery can be maintained. This has the effect of improving the efficiency and cycle life.

[Brief description of the drawings]

FIG. 1 is a cycle life characteristic diagram.

Claims (3)

[Claims] 1. A method for modifying the surface of a synthetic resin, comprising oxidizing the synthetic resin and then performing a reduction treatment with a reducing agent. 2. The method for modifying the surface of a synthetic resin according to claim 1, wherein after the oxidation treatment, a photoreduction reaction is carried out by irradiating ultraviolet rays in the presence of a reducing agent. 3. A battery using a surface-modified synthetic resin obtained by subjecting a synthetic resin to an oxidation treatment and then performing a reduction treatment with a reducing agent, or performing a photoreduction reaction by ultraviolet irradiation in the presence of the reducing agent. For separator.