JPS6135663B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to impregnated base paper used in the production of battery separators, and more specifically to high-yield wood pulp with a yield of 60 to 85% based on wood and substantially containing no binding fibers and high-purity cellulose fibers. is an impregnated base paper made from a stock containing 6 to 18% by weight of residual lignin and a water content (CSF) of 500 to 750 ml, which is significantly lower than when using linter base paper. The present invention relates to an impregnated base paper that can produce a battery separator of excellent quality at a low cost. Conventional battery separators are manufactured by impregnating base paper made from cellulose fibers with a water-soluble synthetic resin liquid mainly composed of phenolic resin, pre-drying it, and then subjecting it to a heat curing process. Conventionally, the fiber raw material for base paper has been virtually limited to linters, and with the exception of mercerized kraft pulp, not only high-yield wood pulp but also wood chemical pulp has rarely been used. Not yet. On the other hand, all linters, including unrefined products, are imported, so there are various restrictions on obtaining them.Furthermore, refining unrefined linters domestically may result in wastewater pollution. Not only is it becoming increasingly difficult to secure stability, but it is also becoming more expensive.
There is a strong demand for an impregnated base paper that allows the use of inexpensive pulp made from wood as a paper base material, and further reduces the unit consumption of this paper base material and phenolic resin. The base paper for battery separators must have extremely low density, extremely low air permeability, a certain paper strength, and a uniform texture.
The air permeability of base paper for battery separators is required to be 6 to 12 seconds, which is the number of seconds it takes for 300 ml of air to pass through a 5-sheet sample when measured using a Gurley densometer. There is.
Regarding the air permeability, the air permeability of the base paper when using the linter shown as Comparative Example 1 in Example 1, which will be described later, and the air permeability of the base paper made from dissolving pulp shown as Comparative Example 3 in Example 2. As can be seen from the comparison, the air permeability of base paper made from high-purity wood chemical pulp is extremely high, and it is clear that it cannot be used for battery separators. High-purity wood chemical pulp has flexible fibers, so when making base paper from this wood chemical pulp, the fibers tend to become flat due to compression for dehydration during the papermaking process, resulting in high air permeability. It cannot be used for battery separators, and since general high-yield pulp contains a large amount of fine fibers, base paper made from this high-yield pulp has a high air permeability, so it cannot be used for battery separators. I couldn't do it. As a result of various studies conducted by the present inventors on base paper for battery separators, we found that base papers containing high-yield wood pulp have exactly the same base paper basis weight, and when the conditions for processing them into battery separators are exactly the same. In addition, we have found that the thickness of battery separators can be significantly increased compared to base paper using linters. However, when a general high-yield pulp is blended, the air permeability of the base paper becomes high as mentioned above, and therefore, the battery separator manufactured from this base paper has a high air permeability and cannot be put to practical use. The present inventors found that high-yield wood pulp with a yield of 60-85%, which does not substantially contain large set fibers, and other high-purity cellulosic fiber raw materials were blended, and the residual lignin was 6-18% by weight. The present invention was completed based on the discovery that base paper made from a paper stock containing 500 to 750 ml of water content (csf) has a markedly reduced air permeability and can be used for the production of battery separators. That is, the present invention has a yield of 60 to 85 on wood.
% and contains virtually no binding fibers and other high-purity cellulosic fibers, containing 6-18% by weight of residual lignin, and having a water content of 500-750ml (csf ) to provide an impregnated base paper for battery separators made from a paper stock having the following properties. The impregnated base paper of the present invention is most suitable for use in battery separators, but it can also be used in the same applications as various impregnated base papers, such as filters for which linter pulp has been the main raw material. Hereinafter, the impregnated base paper for battery separators according to the present invention will be explained in detail. The base paper, which is made by blending high-yield wood pulp containing a large amount of residual lignin with other cellulosic fiber raw materials, is immersed in a water-soluble phenolic resin solution and then passed between rotating rolls to squeeze out the excess solution. Even when compressed, the fibers do not flatten and the thickness of the sheet does not increase. This is thought to be due to the residual lignin contained in the base paper providing the sheet with significantly greater compressive elastic recovery. The thickness of the battery separator etc. will be described later in Example 2.
As is clear from Table 2 showing the results of Comparative Examples 2 and 3, when compared at a constant base paper basis weight, the higher the residual lignin content of the paper stock, the higher the residual lignin content, which is preferable in this respect, but on the other hand , paper strength decreases. Therefore, in order to maintain a predetermined paper strength and obtain a predetermined thickness, there is an appropriate range for the residual lignin content, and it is necessary to maintain this range between 6 and 18% by weight. Particularly preferred is a range of 8 to 14% by weight. When the residual lignin content is less than 6% by weight, the compressive elastic recovery of the sheet decreases, so the thickness of the sheet does not increase when it is immersed in a water-soluble phenolic resin liquid and the excess liquid is squeezed out, making it difficult to use as a battery separator. It cannot be used as base paper for commercial purposes. In other words, the residual content of lignin is low;
If the thickness is difficult to reach the specified thickness when used for battery separators, etc., it is necessary to increase the basis weight of the base paper to bring the thickness within the standard value, but increasing the basis weight will increase the air permeability. As a result, it cannot be used for battery separators or the like. On the other hand, if the residual lignin content exceeds 18% by weight, the paper strength of the base paper decreases and it cannot be used for battery separators, etc. Therefore, in the present invention, the residual lignin content is limited to 6 to 18% by weight. Methods for obtaining pulp are broadly classified into chemical pulping methods and mechanical pulping methods, depending on whether or not mechanical defibration treatment is necessary. Whether elaborate mechanical defibration is required to obtain individual fibers depends on the pulp yield, and is necessary when the pulp yield is 60% or more. This value remains constant even if the type of wood and chemicals used for wood treatment change, and is called the point of fiber disintegration. In other words, limiting the yield to wood of the high-yield pulp used in the present invention to 60% or more means that it corresponds to a yield higher than the above-mentioned fiber disintegration point. In other words, this shows that the properties of residual lignin essentially differ across this value. Furthermore, mechanical pulp with a yield of 85% or higher (GP or Asplund process pulp) always contains only bound fibers, and it is almost impossible to selectively separate only bound fibers from the pulp once produced. It is. When the fiber raw material that makes up paper contains a large amount of fine fibers and has a low water content (csf), the void capillaries in the paper tend to close, increasing the air permeability of the paper. On the other hand, if the water content (csf) is too high, it will not be possible to obtain the uniform texture required for base paper for battery separators, so fiber raw materials with high water content are unsuitable. Therefore, in the present invention, the water content (csf) of the paper stock made by blending high-yield wood pulp with a yield of 60-85% with other high-purity cellulosic fiber raw materials is 500-85%.
The volume should be 750 ml, and 550 to 720 ml is particularly preferable. If the water content (csf) is less than 500 ml, the air capillaries in the paper will be closed as described above and the air permeability will increase, making it difficult to obtain the air permeability required for base paper for battery separators, etc. If it exceeds it, it will not be possible to obtain the uniform formation required for base paper for battery separators, etc. In order to maintain such water content, high-purity cellulose fibers may be used as other fiber raw materials to be added to the high-yield pulp. Regenerated cellulose fibers can also be used when air permeability is important, but when paper strength is also important, natural cellulose fibers such as dissolving pulp, bleached kraft pulp, bleached sulfite pulp, and refined linters are suitable. Although crude linters, unbleached sulfite pulp, and unbleached kraft pulp can also be used, the residual lignin contained in these unbleached chemical pulps is not very effective for the purpose of the present invention. Synthetic fibers such as polyethylene are expensive, have low heat resistance, and have poor paper strength, and are therefore not suitable for the present invention. In addition, if large binding fibers are present in the base paper for battery separators, these binding fibers will fall off during battery separator manufacture, creating large holes in the separator base paper, and lead powder from the electrode plates will accumulate in the holes after it is assembled into a storage battery. The negative and positive poles become short-circuited. For this reason, it is necessary to prevent large bundled fibers from being included in the base paper. These large binding fibers are included in general high-yield pulp with a yield of 60% or more, so the high-yield pulp used in the base paper for battery separators is made from special high-yield wood that does not contain large binding fibers. It is necessary to use pulp. Therefore, when the impregnated base paper according to the present invention is used as a battery separator base paper, the high-yield pulp mixed must be a high-yield wood pulp that does not substantially contain large binding fibers. A high-yield wood pulp that does not substantially contain such large binding fibers is one that contains a chemical solution or water that has a pH of 12.7 or less when wood chips are measured at 25°C, as proposed in Japanese Patent Publication No. 42-26121. The first step is mechanical defibration at a high temperature of 120℃ or higher, followed by immersion at 120℃ or lower in an alkaline solution with a pH of 12.7 or higher and 14.0 or lower, measured at 25℃, at the same time as the immersion or for a long period of immersion. After that, the solution is treated while it is contained in the fibers using a beating device or a grinding device to apply mechanical energy to the extent necessary to almost or completely eliminate the bound fibers. The most suitable method is to produce high-yield pulp in combination with the second step, but the method is not limited to this method. yield
Any material containing 60 to 85% binding fibers is sufficient. In addition, depending on the manufacturing process of battery separators, etc., high paper strength may be required for the base paper, in which case dissolving pulp, bleached kraft pulp, bleached sulfite pulp, purified linter, or regenerated cellulose fibers are used as fiber raw materials. When two or more types are mixed, the paper strength is increased, and battery separators and the like can be easily manufactured. Note that a small amount of diatomaceous earth, a wet strength improver, etc. may be added to the impregnated base paper according to the present invention,
The effects of the present invention are not impaired in any way by the presence of such additives. By using the impregnated base paper according to the present invention, the basis weight of base paper for battery separators, etc., required to adjust the thickness of battery separators, etc. to standard values can be significantly reduced compared to the case of conventional linter base paper. Moreover, the electrical resistance, oxidation resistance, and other performances of the manufactured battery separator are comparable to those using linter base paper. For example, even if the impregnated base paper according to the present invention with a basis weight of 170 g/m ² is used, a battery separator or the like can be manufactured with the same thickness as when a linter base paper with a basis weight of 226 g/m ² is used. In other words, when using the impregnated base paper of the present invention, the basis weight of the base paper can be saved by 25% compared to using linter base paper, and in this case, there is no need to change the amount of water-soluble phenolic resin impregnated into the base paper. Phenol resin can also be saved by 25%, which greatly contributes to resource conservation. Furthermore, since wood pulp is used instead of an expensive linter, it is extremely advantageous in that it can be obtained at a low cost. Hereinafter, the impregnated base paper according to the present invention will be further explained in detail with reference to Examples. However, the present invention is not limited to the following Examples, and various conditions may be changed when implementing the invention. All measurement methods are JIS unless otherwise specified.
It was carried out based on the following. 1 Equipment 1 Power source: Constant current DC power supply (with built-in current pressure meter) 2 Recorder: Automatic recorder 3 Electrode plate: 50mm x 50mm x 3mm pure lead (specified in JIS H 2105) 4 Electrode plate: 50mm x 50mm ×1.5mm pure lead (as specified in JIS H 2105) 5 Constant temperature bath: One that can be set at 50±2℃ 6 Electrolytic bath: Glass 102×132×185mm 7 Glass plate: 70×70×2mm 8 Unit: Synthetic resin (Ebonite) 9 Lead block: 5Kg 2 Reagent 1 Sulfuric acid: Specific gravity 1300 (20℃) Compatible with JIS K 1305 3 Sample: 70 x 70 mm 4 Procedure Place the sample on the plate, electrode plate, The glass plates are sandwiched together from above and below, placed on a stand and loaded with lead blocks. Insert the table containing the sample into the electrolytic cell and inject 1000ml of sulfuric acid (d: 1.3). Place the electrolytic cell in a constant temperature bath adjusted to 50±2℃ and leave it until the liquid temperature reaches 50℃. After that, DC 2.5A was applied and the voltage between the electrodes was measured with a recorder, and the voltage difference was 0.2V within 2 hours.
The oxidation resistance test ends when the drop occurs. Example 1 Yield 80 for wood that does not substantially contain large binding fibers and contains 22.0% by weight of residual lignin by the method shown in the example of Japanese Patent Publication No. 42-26121
A paper stock containing 15.4% by weight of residual lignin and a water content (CSF) of 663ml was prepared by blending 70% by weight of high-yield wood pulp and 30% by weight of softwood dissolving pulp. From the raw materials, base paper for hand-made paper was made according to the JIS method. This base paper was immersed in a water-soluble phenol resin liquid to remove excess liquid, pre-dried, and then subjected to a heat curing treatment to produce a battery separator. Note that the water level was measured in accordance with JIS P 8121. Comparative Example 1 A paper stock with the same water content as in Example 1 was prepared using purified linter as a raw material, and a base paper for hand-made paper was made from this stock under the same conditions as in Example 1. Similarly, a battery separator was manufactured by impregnating it with a water-soluble phenolic resin. The properties of the base paper produced in Example 1 and Comparative Example 1 and the properties of the battery separator produced from the base paper were as shown in Table 1.

[Table] As is clear from Table 1, the air permeability of the base paper in Example 1 is lower than that of the base paper in Comparative Example 1 made from a conventional linter, and the air permeability of the base paper in Example 1 is The thickness is greater than that of Comparative Example 1, which was manufactured from linter base paper, and in both cases, Example 1 is superior to Comparative Example 1. The thickness of the battery separator is based on the raw material basis weight of 180g/ ^m2 , and the air permeability is based on JIS P.
It is expressed as the number of seconds required for 300 ml of air to pass through five stacked samples using a Gurley densometer according to 8117, and the results measured using this method are shown below. The basis weight was measured according to JIS P 8110, the thickness was measured according to JIS P 8118, and the tensile strength was measured according to JIS P 8113. Example 2 Three pieces were prepared by blending the same high-yield wood pulp and softwood dissolving pulp as used in Example 1, with residual lignin contents of 17.6% by weight, 8.8% by weight, and 6.6% by weight. Each paper stock was hand-sheeted under the same conditions as in Example 1 to produce base paper, and the base paper was impregnated with a water-soluble phenol resin in the same manner as in Example 1 and processed into battery separators. Comparative Example 2 A base paper was made by hand-papering under the same conditions as in Example 1 using only high-yield wood pulp similar to that used in Example 1, and a water-soluble phenolic resin was applied to this base paper in the same manner as in Example 1. A battery separator was manufactured by impregnation. Comparative Example 3 A base paper and a battery separator were produced in exactly the same manner as in Comparative Example 2 using only the same softwood dissolving pulp as that used in Example 1. The properties of the paper stock prepared in Example 2, Comparative Example 2, and Comparative Example 3, the properties of the base paper made from this paper stock, and the properties of the battery separator produced from the base paper were as shown in Table 2.

[Table] As is clear from Table 2, when the residual lignin content is as high as 22.0% by weight as in Comparative Example 2, the tensile strength of the base paper is weak, making it difficult to stably produce such paper. It is. Further, when there is no residual lignin as in Comparative Example 3, the thickness of the battery separator is thin, and there is not much difference from the case where a linter is used. Example 3 30% by weight of high-yield wood pulp with a yield of 78% for wood containing substantially no large binding fibers and 20.3% by weight of residual lignin, and 30% by weight of softwood dissolving pulp.
A paper stock containing 35% by weight of purified linter, 6.1% by weight of residual lignin, and a water content (CSF) of 700ml was prepared, and this stock was hand-sheeted in the same manner as in Example 1. A base paper was prepared using this method, and a battery separator was manufactured in the same manner as in Example 1 using this base paper. The properties of the base paper and battery separator are as shown in Table 3, and the air permeability of the base paper, the thickness of the battery separator, and other properties were good.

[Table] Example 4 80% by weight of high-yield wood pulp with a yield of 75% containing 19.1% by weight of residual lignin, which is substantially free of large binding fibers, and 20% by weight of bleached softwood kraft pulp were blended, and the residual lignin was Contains 15.3% by weight of lignin, and
A paper stock having a water content (csf) of 570 ml was prepared, and base paper was made from this paper stock using a fourdrinier machine. A battery separator was manufactured in the same manner as in Example 1 using this base paper. The properties of the base paper and battery separator are shown in Table 4, and the air permeability, thickness, and other properties were all good.

[Table] Example 5 50% by weight of high-yield wood pulp with a yield of 78% that does not substantially contain large binding fibers and contains 20.3% by weight of residual lignin, 15% by weight of softwood dissolving pulp,
Contains 15% by weight of softwood bleached kraft pulp and 20% by weight of hardwood bleached kraft pulp to remove residual lignin.
A paper stock containing 10.2% by weight and having a water content (csf) of 630 ml was prepared, and base paper was made from this stock using a fourdrinier machine. A battery separator was produced from this base paper in the same manner as in Example 1. The properties of the base paper and battery separator are shown in Table 5, and the air permeability, thickness, and other properties were all good.

[Table] Example 6 80% by weight of high-yield wood pulp with a yield of 76% containing 20.1% by weight of residual lignin without substantially containing large binding fibers, and 20% by weight of bleached softwood kraft pulp
Blend to prepare a paper stock containing 16.1% by weight of residual lignin and having a water content (csf) of 580ml;
A base paper was made from this stock using a fourdrinier machine.
This base paper was impregnated with phenol resin using a processing machine to produce a battery separator. The properties of the base paper and battery separator are shown in Table 6, and all properties were good.

[Table] When this battery separator was actually incorporated into a battery and a life test was conducted, it withstood 218 to 275 charging and discharging times, which is the same as when using linter base paper, and a large capacity rapid discharge test at low temperatures. Since it was possible to maintain a voltage comparable to that when using linter base paper, it can be seen that an extremely good battery can be obtained using the battery separator base paper of the present invention. As detailed above, the impregnated base paper according to the present invention is
Its air permeability is lower than that of base paper made from linters, which is extremely good, and the basis weight of the base paper required to adjust the thickness of battery separators to standard values is significantly lower than that of conventional linter base paper. I can do it. Therefore, if this impregnated base paper is used to manufacture battery separators, the basis weight of the base paper can be reduced compared to when linter base paper is used. Because it is a common material, water-soluble phenolic resin can be saved, and it can be manufactured at a lower cost than when using conventional linter base paper, and it has excellent quality, as well. Because it uses wood pulp, it has excellent advantages such as being cheaper than using conventional linters, and has great industrial value.

Claims (1)

[Claims] 1. High-yield wood pulp with a yield of 60-85% based on wood and containing substantially no binding fibers and high-purity cellulose fibers are blended, and residual lignin is 6-18% by weight. An impregnated base paper for a battery separator made from paper stock containing the following and having a water content of 500 to 750 ml. 2. The impregnated base paper for battery separators according to claim 1, wherein the high-purity cellulose fibers are dissolving pulp. 3. The impregnated base paper for battery separators according to claim 1, wherein the high purity cellulose fibers are bleached kraft pulp. 4. The impregnated base paper for battery separators according to claim 1, wherein the high-purity cellulose fibers are bleached sulfite pulp. 5. The impregnated base paper for battery separators according to claim 1, wherein the high-purity cellulose fiber is purified linter. 6. The impregnated base paper for battery separators according to claim 1, wherein the high-purity cellulose fibers are regenerated cellulose fibers. 7. The impregnated base paper for battery separators according to claim 1, wherein the high-purity cellulose fiber is a mixture of two or more of dissolving pulp, bleached kraft pulp, bleached sulfite pulp, purified linter, and regenerated cellulose fiber.