HK1005280B

HK1005280B - Separator paper for alkaline-battery

Info

Publication number: HK1005280B
Application number: HK98103697.3A
Authority: HK
Inventors: 久保好世; 山野上基; 沟渊章夫
Original assignee: 日本高度纸工业株式会社
Priority date: 1996-09-12
Filing date: 1998-04-30
Publication date: 2005-06-03

Description

Alkaline battery separator paper

Technical Field

The present invention relates to a separator paper for separating an anode active material and a cathode active material in several alkaline batteries, such as an alkali manganese battery, a silver oxide battery and an air-zinc battery, each of which uses an alkaline electrolyte; and more particularly, to a separator paper having a high tight density capable of preventing internal short circuits caused by zinc oxide dendrites due to no addition of mercury, and simultaneously having greater power discharge properties due to increased electrolyte liquid permeability.

Background

The characteristics required for the separator paper for separating the anode active material and the cathode active material of the alkaline battery are to prevent internal short circuits due to contact of the anode active material with the cathode active material, and to have desired durability due to the fact that depolarizers such as an electrolyte of potassium hydroxide and manganese dioxide are used without causing shrinkage or deformation, and a sufficient amount of electrolyte required to generate electromotive force is maintained without hindering ion conduction.

The prior art release paper uses a mixed paper composed of synthetic fibers and cellulose fibers, more specifically, it is mixed with vinylon which is alkali-resistant synthetic fibers as a main material, and alkali-resistant cellulose fibers such as viscose rayon, linter pulp containing more than 98% of alpha-cellulose, mercerized wood pulp, polynosic rayon, and polyvinyl alcohol fibers added as a binder.

The present applicant discloses in japanese patent laid-open publication No. 2-119049 a release paper in which the release paper is made by mixing alkali-resistant cellulose fibers suitable for beating, such as mercerized wood pulp, mercerized spanish pulp, mercerized manila hemp pulp, polynosic rayon, and synthetic fibers, the paper containing 10 to 50% by weight of the alkali-resistant cellulose fibers, and the fibers having a beating degree with a CSF (canadian standard freeness) value of 500 to 0 ml. Also disclosed in japanese patent laid-open publication No. 62-154559 is an alkaline battery separator paper in which some or all of the fibers forming the separator paper use synthetic fibers having a fineness of less than 0.8 denier, rather than larger size 1-3 denier fibers used in the prior art.

Further, another release paper is disclosed in Japanese patent laid-open publication No. 5-74439. The release paper is made by beating the polynosic rayon fibers to a CSF of 300-.

These separator papers made from interwoven cellulose fibers and rayon fibers have sufficient resistance to electrolytes and depolarizers, but have an excessively large pore size in terms of preventing internal shorting caused by contact between the two active material electrodes. It is therefore required to take measures such as laminating the paper in layers in order to make the pore diameter relatively small, or laminating the paper with some separator such as a cellophane film having micropores.

Measures have been taken for alkaline batteries using zinc as the cathode active material, in which the surface of zinc amalgam particles is used to convert to the active material in order to prevent cathode self-discharge and promote electromotive force reactions. Recently, as for prevention of ecological destruction caused by mercury pollution, the required mercury consumption is gradually reduced, thereby using mercury-free batteries. That is, the battery does not use mercury, which is a prerequisite since 1992.

If mercury additives are not used, corrosion can occur in the cathode of the active material. This results in the deposition of a conductive crystalline zinc oxide compound called "dendrites" and causes electrical contact between the two electrodes of the active material to create an internal short circuit and greatly reduce the capacity of the battery. To prevent such internal short circuits caused by zinc oxide dendrite deposition, a fine release paper having a smaller pore diameter than the existing release paper is required. More specifically, such release paper having airtightness of more than 2 seconds/100 ml is required for preventing internal short circuit caused by zinc oxide deposition.

Although alkaline batteries, particularly alkaline manganese batteries, have been widely used for portable power sources, and their applications are increasing due to the development toward mercury-free type cathodes; there is also a need to improve battery performance, such as longer discharge times in the form of continuous or intermittent discharges, which would otherwise require high power discharge performance.

As portable electronic devices such as notebook personal computers, liquid crystal display TV devices, and portable telephone devices have been widely used, the demand for alkaline batteries as power sources (requiring high-power discharge) for these electronic devices has rapidly increased, and therefore, improvement in high-power discharge performance has been greatly demanded. These conventional electronic devices require large power, so secondary batteries such as nickel cadmium batteries are generally used for these devices. The use of alkaline manganese cells has attracted attention, and electronic devices requiring high power discharge of alkaline manganese cells have increased because of their ready availability and ease of operation, and because of the increased popularity of energy conservation in electronic devices. The high power discharge may be defined as a high current discharge with a load resistance of less than 3 ohms.

When discharged at high power, a larger current occurs than a light load having a resistance of more than 10 ohms, and for an inside-outside type battery such as an alkali-manganese battery, as the discharge current increases, battery reaction hardly occurs in the inner region of the active material, and the utilization rate of the active material is exponentially decreased in this region, which results in a decrease in battery capacity. For example, it is known that the utilization of active materials drops to less than 20% for a2 ohm resistive load that produces a high power discharge. Thus, extending the discharge time by several minutes is said to be a significant improvement unless achieved with a resistive load of less than 3 ohms, which is of course a desirable and urgent need. To increase the battery capacity in this case, an increase in the active material or a decrease in the resistance value is ineffective. Conversely, it is desirable to increase the amount of liquid permeability of the electrolyte in the separator or active material to increase ion diffusion due to rapid cell reaction. That is, to increase the diffusion of the cathode zinc ions without decreasing the conductivity, more electrolyte should be given to the separator paper. More specifically, a release paper having a liquid permeation characteristic of more than 550% is desirable in view of increasing high power discharge capacity.

However, it is difficult to satisfy both of the above-described airtightness and liquid permeability. That is, although the portion of the electrolyte remaining in the separator in the cell moves toward the anode active material and the cathode side (during discharge), a sufficient amount of the electrolyte required to maintain the electromotive reaction should remain in the fibrous portion of the separator. In fact, the more pores the separator paper is designed into, the more advantageous the liquid permeability for temporary retention of electrolyte. However, in view of preventing short circuit and electrical isolation of both poles, it is desirable that the release paper is manufactured closely. Generally, when the tightness of paper is increased, the resistance is also increased, and the liquid permeability is decreased, which results in a decrease in the discharge performance of the battery. Therefore, no separator paper having increased electrolyte liquid permeability, preventing internal short-circuiting due to zinc oxide dendrites generated without addition of mercury, suitable for high-power discharge, particularly having gas tightness of more than 2 seconds/100 ml, while having liquid permeability of more than 550% has been provided at present.

The applicant has examined the changes in physical properties, such as freeness, liquid permeability, air impermeability, etc., of the release paper provided by mercerized hardwood pulp and polynosic rayon that are pulped to some extent. As an example of considering the use thereof, it is intended to specifically know the relationship between the above-mentioned air-tightness and the liquid permeability of the existing release paper.

Experimental example 1

Furnish was provided by mixing 63% by weight of mercerized hardwood pulp with a freeness ranging from CSF710 ml (unbaked) to 200ml, 25% by weight of vinylon (fineness 0.5 denier x fiber length 2mm), and 12% by weight of polyvinyl alcohol fiber (fineness 1 denier x fiber length 3mm), and then sent to a cylinder machine to provide a single-ply release paper with a basis weight of about 32g/m 2. The relationship among CSF value, air-tightness and liquid permeability of the separator is shown in table 9.

TABLE 9

Examples	Beating degree of cellulose CSF (ml)	Quantitative g/m²	Thickness μm	Tensile strength kg/15mm	Air tightness second/100 ml	Liquid permeability％	Liquid absorbency mm	Expanded thickness μm
Examples	Beating degree of cellulose CSF (ml)	Quantitative g/m²	Thickness μm	Tensile strength kg/15mm	Air tightness second/100 ml	Liquid permeability％	Liquid absorbency mm	Expanded thickness μm	1-1	710 (without beating)	32.2	120	3.3	1.0	480	32	137
1-2	640	32.6	111	3.5	1.7	420	27	121	1-1	710 (without beating)	32.2	120	3.3	1.0	480	32	137
1-2	640	32.6	111	3.5	1.7	420	27	121	1-3	550	32.1	100	3.8	2.8	380	26	114
1-4	430	33.0	96	4.0	5.5	340	23	101	1-3	550	32.1	100	3.8	2.8	380	26	114
1-4	430	33.0	96	4.0	5.5	340	23	101	1-5	320	32.5	89	4.1	10.5	320	19	95
1-6	200	33.0	84	4.2	25.6	310	19	90	1-5	320	32.5	89	4.1	10.5	320	19	95

63% by weight of mercerized hardwood pulp + 25% by weight of vinylon (0.5 denier. times.2 mm) + 12% by weight of polyvinyl alcohol fiber (1 denier. times.3 mm)

Experimental example 2

The furnish was provided by mixing 63% by weight of polynosic rayon (fineness 0.5 denier x fiber length 2mm), having a freeness ranging from CSF740 ml (unbaked) to 210ml, 25% by weight of vinylon (fineness 0.5 denier x fiber length 2mm), and 12% by weight of polyvinyl alcohol fiber (fineness 1 denier x fiber length 3mm), and then fed onto a cylinder machine to provide a basis weight of about 32g/m²The single-layer release paper of (1). The relationship among CSF value, air-tightness and liquid permeability of the separator is shown in table 10.

Watch 10

Examples	Beating degree of cellulose CSF (ml)	Quantitative g/m²	Thickness μm	Tensile strength kg/15mm	Air tightness second/100 ml	Liquid permeability%	Liquid absorbency mm	Expanded thickness μm
Examples	Beating degree of cellulose CSF (ml)	Quantitative g/m²	Thickness μm	Tensile strength kg/15mm	Air tightness second/100 ml	Liquid permeability%	Liquid absorbency mm	Expanded thickness μm	2-1	740 (without beating)	32.2	128	4.0	0.7	770	53	205
2-2	710	31.8	118	4.2	0.8	670	50	180	2-1	740 (without beating)	32.2	128	4.0	0.7	770	53	205
2-2	710	31.8	118	4.2	0.8	670	50	180	2-3	670	33.0	108	4.3	1.1	600	45	162
2-4	600	32.1	102	4.5	1.7	540	40	150	2-3	670	33.0	108	4.3	1.1	600	45	162
2-4	600	32.1	102	4.5	1.7	540	40	150	2-5	530	32.0	98	4.6	2.2	470	38	130
2-6	440	31.7	95	4.8	3.4	420	35	121	2-5	530	32.0	98	4.6	2.2	470	38	130
2-6	440	31.7	95	4.8	3.4	420	35	121	2-7	330	32.2	92	5.0	5.6	380	33	110
2-8	210	32.4	90	5.0	10.5	350	32	105	2-7	330	32.2	92	5.0	5.6	380	33	110

63% by weight of Polynoxicam rayon (0.5 denier. times.2 mm) + 25% by weight of vinylon (0.5 denier. times.2 mm) + 12% by weight of polyvinyl alcohol fiber (1 denier. times.3 mm)

In addition, the relationship among CSF value, air-tightness and liquid permeability relating to the separator paper of experimental examples 1 and 2 shown in tables 9 and 10 is shown in the graph of fig. 4. The air-tightness and liquid permeability of the CSF values of the barrier papers listed in tables 9 and 10 are shown in the graph of fig. 4, in which the symbols black triangles and black dots represent the results of the measurements of examples 1 and 2, respectively.

As is clear from examples 1 and 2, when cellulose, such as mercerized hardwood pulp, polynosic rayon, etc., is beaten, the air tightness of the release paper is increased. That is, the release paper has increased air-tightness and has increased tightness. However, when beating is continued, the liquid permeability of the paper rapidly decreases, and it is difficult to obtain the liquid permeability of more than 550%, even if the airtightness of 2 seconds/100 ml is obtained. Each of the experimental examples 1 to 3 showed airtightness of 2.8 seconds/100 ml, respectively, but had liquid permeability of 380%, and the experimental examples 2 to 5 showed airtightness of 2.2 seconds/100 ml, respectively, but had liquid permeability of 470%, and hardly retained the electrolyte to improve the high-power discharge capacity. On the other hand, if more than 550% liquid permeability is given, the tightness of the paper will be reduced. Therefore, it is difficult to achieve airtightness of more than 2 seconds/100 ml. For example, each of examples 2 to 3 showed a liquid permeability of 600%, but its airtightness was only 1.1 sec/100 ml, which was not sufficient to effectively prevent internal short-circuiting due to zinc oxide. This phenomenon is clearly shown in graph 4, where the liquid permeability is below 500% for each example where the airtightness is as high as 2 seconds/100 ml or more. Thus, the conventional separator paper cannot achieve sufficient liquid permeability suitable for high-power discharge in order to prevent internal short-circuiting caused by zinc oxide dendrites due to no addition of mercury.

To increase air tightness, conventional release paper requires an increase in the number of rolls in order to effectively reduce the diameter of holes in the paper, or to select smaller diameter fibers such as vinylon contained in the paper. Further, release paper disclosed in Japanese patent laid-open No. 2-119049 or 5-74439 is also used.

However, further increasing the number of rolls of separator paper will increase the volume of the separator in the battery, which in turn will decrease the volume of the active material, and thus will inevitably decrease the capacity of the battery. In addition, when synthetic fibers of smaller fineness or synthetic fibers of smaller diameter are used, the compactness of the resulting sheet becomes greater. The fibers contained in the paper are bonded together by thermal fusion or an adhesive, and as a result, the smaller the diameter of the synthetic fibers, the larger the bonding area, which results in the paper sheet being easily degraded in liquid-permeability. Synthetic fibers of small fineness, such as 0.4 denier, which are additionally added to the paper, are expensive, and thus will also increase the cost of the paper sheet.

Further, Japanese patent laid-open Nos. 2-119049 and 5-74439 disclose techniques in which cellulose fibers are fibrillated by beating, and fine branches are separated from the fiber body, thereby producing fine release paper. However, the cellulosic tissue within the cellulosic fibers will undergo cutting at an early stage of beating, i.e., where the vast majority of CSF has not been reduced. That is, even when the cellulose seems not to have been changed, the inside thereof has been inevitably subjected to the destruction by beating. Therefore, even when compared with non-beaten cellulose such as cellulose having a CSF value of 700ml or more, the stiffness thereof has been lowered. Thus, the cellulose fibres have become soft and the paper produced with it will have a high degree of tightness, which will inhibit the expansion of the sheets in the electrolyte and will cause the liquid permeability of the paper to decrease with increasing freeness.

Therefore, in a battery using a separator paper made densely of heavily pulped cellulose fibers, the amount of electrolyte soaked in the paper will inevitably be reduced, which will suppress the ion diffusion required at the time of battery discharge, but the reduction of electrolyte in the paper will not cause a significant problem at the time of battery discharge as long as it is discharged by a light load of, for example, 10 ohms. However, when high-power discharge is performed by a large current such as with a constant value of one ampere or through a resistance of 2 ohms, the utilization rate of the active material of the battery is lowered, which shortens the life of the battery, with the result that, in practical cases, such a battery cannot meet the present-day demand for improvement of high-power discharge capacity of alkaline batteries.

Although the impregnation of the electrolyte can be increased by reducing beating of the cellulose fibers and the separator for high power discharge can be more satisfactory, it will result in a reduced fineness of the separator, which in turn will have an effect on zinc oxide dendrites and on preventing internal short circuits due to migration of active materials (of the anode and cathode) and shorten the life of the battery.

Further, in terms of preventing internal short circuits caused by dendrite deposition such as zinc oxide, these defects can be completely prevented by using a separator material such as a cellophane film having many micropores, which is laminated on each other, and a porous separator paper. However, the tightness of the cellophane film is more than 10,000 seconds/100 ml, which is too large, and therefore, diffusion of ions is hindered, and thus the film is not suitable for high power discharge.

Disclosure of Invention

In view of the above problems, it is an object of the present invention to provide a separator paper for alkaline batteries, which has proper airtightness when preventing internal short circuits due to zinc oxide dendrite deposition in the tendency not to use mercury, and has improved liquid permeability of an electrolyte to provide a starting point for high-power discharge; more specifically, the paper has tightness of airtightness between 2 seconds/100 ml and 100 seconds/100 ml, and has electrolyte permeability higher than 550%.

To accomplish these objects, the present invention provides an electrically insulating separator paper for active materials of an anode and a cathode of an alkaline battery, wherein said separator paper may comprise a tight layer maintaining airtightness, which prevents electrical internal short-circuiting between said two active materials; and a liquid-permeable layer for increasing liquid permeability of an electrolyte in the battery, the compact layer and the liquid-permeable layer being integrally laminated.

Further, the release paper may comprise a compact layer having a certain degree of compactness, and a liquid-permeable layer having a certain liquid permeability, the compact layer preventing internal short-circuiting due to dendritic deposition of zinc oxide; and the liquid-permeable layer is effective to increase the liquid permeability, with the result that the battery is suitable for high-power discharge.

Further, the separator may comprise a compact layer having a certain degree of compaction, and a liquid-permeable layer having a certain liquid permeability, the compact layer being made by mixing alkali-resistant cellulose fibers suitable for beating with synthetic fibers so that the content of the alkali-resistant cellulose fibers is 20 to 80% by weight and the beating degree is 500 to 0ml in terms of CSF value; and the liquid-permeable layer is obtained by mixing alkali-resistant cellulose fibers with synthetic fibers, wherein the alkali-resistant cellulose fibers are contained in an amount of 20 to 80% by weight, and the freeness is 700ml in terms of CSF value.

In addition, the alkali-resistant cellulose fibers suitable for beating for the compact layer may have a beating degree of from 300 to 10ml in CSF.

The alkali-resistant cellulose fibers for the liquid-permeable layer may have a freeness of beating.

Additionally, the alkali resistant cellulosic fibers used in the compact layers and suitable for beating may comprise one or more pulps or fibers selected from the group consisting of mercerized wood pulp, cotton linter pulp, polynosic rayon, rayon formed from organic solvents, and prehydrogenated (prehydroide) pulp.

In addition, the alkali resistant cellulosic fibers may comprise recycled fibers having a fiber length of from 2-10 mm.

In addition, the synthetic fibers used in the dense layer and the liquid-permeable layer may comprise one or more synthetic fibers having high alkali resistance.

In addition, the synthetic fiber having the high alkali resistance may comprise one or more pulps or fibers selected from the group consisting of; the pulp or fiber is: polypropylene fibers, polyethylene fibers, polyamide fibers, vinylon, polyvinyl alcohol fibers, polypropylene-polyethylene composite fibers, polypropylene-ethylene-vinyl alcohol copolymer fibers, polyamide-modified polyamide composite fibers, polypropylene-synthetic pulp, and polyethylene-synthetic pulp.

In addition, the paper may contain polyvinyl alcohol fibers or polyvinyl alcohol powder added as a binder in an amount of 5 to 20% by weight relative to the total weight of the separator paper obtained by laminating the compact layer and the liquid-impregnated layer.

Further, the compact layer may be provided with the liquid-permeable layer integrally laminated on one side or both sides thereof.

Further, the basis weight of said compact layer is less than 50% and said basis weight is greater than 5g/m, relative to the total basis weight of the paper²。

In addition, the paper has an air tightness of from 2 to 100 seconds per 100ml and a liquid permeability of more than 550%.

In addition, the paper has an air tightness of from 2 to 100 seconds per 100ml and a liquid permeability of more than 600%.

According to the present invention, the compact layer and the liquid-impregnated layer can be integrally laminated, whereby the compact layer can provide a desired compactness suitable for preventing dendrite migration of active materials or zinc oxide of both electrodes; and the liquid-permeable layer can also provide liquid permeability required for the electrolyte even when the battery is discharged at high power. That is, the compact layer may provide greater compactness, while the liquid-permeable layer may provide more suitable electrolyte impregnation than a prior art liquid-permeable layer that is a single layer of separator paper.

In addition, the liquid-permeable layer may swell in the electrolyte to impregnate the desired electrolyte mass when the battery is subjected to high power discharge, but when impregnated with the electrolyte, the compact layer comprising beaten cellulose fibers exhibits less thickness swelling than the liquid-permeable layer. That is, even if the liquid permeability is increased by laminating the dense layer and the liquid-permeable layer, the pore radial expansion of the dense layer is insignificant and the tightness of the separator in the electrolyte is hardly affected along with the impregnation of the electrolyte.

Therefore, according to the present invention, it is possible to provide a separator paper having a certain degree of tightness and increased permeability to an electrolyte liquid, that is, the separator paper can satisfy both: compactness that can prevent internal short circuit caused by dendrite deposition of zinc oxide due to no addition of mercury, and liquid permeability that can enhance high-power discharge characteristics of a battery.

Further, the present invention can also provide an improved release paper having increased reliability in preventing internal short circuits; this is because by laminating more than two layers, the pinhole portions and bubbles (which are relatively large) generated in the release paper during the paper making process are greatly reduced and the diameters of various holes are also reduced when compared with the release paper of the prior art having only a single layer. Furthermore, when compared with the prior art having only a single layer (having the same airtightness as the present invention), since the porous liquid-permeable layer is laminated, the absorption rate of the electrolyte is also increased, and the injection time of the electrolyte during the assembly of the battery can be reduced, which is advantageous to the productivity of the battery.

Drawings

Reference is now made to the drawings, in which like reference numerals designate corresponding parts, and in which:

FIG. 1 illustrates a first embodiment of a step of making paper from release paper according to the present invention;

FIG. 2 illustrates a second embodiment of the step of making paper from release paper according to the present invention;

FIG. 3 illustrates a third embodiment of the step of making paper from release paper according to the present invention;

fig. 4 is a graphical representation of the relationship between CSF value and gas tightness and the relationship between CSF value and liquid permeability.

Detailed Description

A preferred embodiment of the separator paper for alkaline batteries of the present invention will now be described. The present invention is characterized in that a separator paper for electrically separating an anode active material and a cathode active material, which prevents internal short-circuiting of a battery due to dendrite deposition of zinc oxide by means of a compact layer maintaining the compactness to prevent internal short-circuiting of the anode active material and the cathode active material, and a liquid-permeable layer for increasing the liquid permeability of an electrolyte are integrally laminated, thereby increasing the liquid permeability of an electrolyte suitable for high-power discharge of the battery.

The inventors of the present invention conducted studies on the relationship between the freeness of cellulose fibers and the physical properties of the separator paper shown in tables 9 and 10, and as a result, it was difficult to satisfy both the compactability and the liquid permeability suitable for high-power discharge with the single-ply separator paper of the prior art.

However, the inventors' objective is to laminate the first and second layers integrally; said first layer has a high CSF value which increases the liquid permeability, that is to say it comprises cellulose fibres of low freeness; the second layer has a low CSF value that maintains tightness. That is, the present invention comprises cellulose fibers of high freeness, and thus, a separator paper for alkaline batteries, which has a certain degree of tightness and increased permeability to electrolyte liquid, that is, which satisfies both: compactness that can prevent internal short circuit caused by zinc oxide dendrite due to no addition of mercury, and electrolyte liquid permeability that can enhance high-power discharge of a battery.

Thus, for the compact layer, the fibers suitable for beating are selected from alkali-resistant cellulose fibers, and then said alkali-resistant cellulose fibers suitable for beating are mixed with synthetic fibers to provide an alkali-resistant cellulose fiber pulp comprising said fibers suitable for beating, wherein the content of said alkali-resistant cellulose fibers suitable for beating is 20-80% by weight, and the freeness of the fibers is from 500 to 0ml in CSF (canadian standard freeness) value.

On the other hand, for the liquid-permeable layer, alkali-resistant cellulose fibers and synthetic fibers are mixed together to provide a pulp comprising said alkali-resistant cellulose fibers, wherein the content of said alkali-resistant cellulose fibers is from 20 to 80% by weight, and the degree of beating of the fibers is unbaked or greater than 700ml in CSF value. In order to avoid damage to the fibers and to maintain liquid permeability, the alkali-resistant cellulose fibers used in the liquid-permeable layer are not subjected to a fibrillation treatment. That is, the fibers can be made using any commercially available fibers that are substantially unbraked and have excellent liquid permeability, and are not limited in any way whether the fibers are suitable for beating or not, except that the fibers already have alkali resistance. Thus, the fibers may be selected from cellulose fibers suitable for beating, such as polynosic rayon, or from cellulose fibers that are difficult to beat, such as conventional viscose rayon.

The compact layer and the liquid-impregnated layer having the above arrangement are integrally laminated together to produce a separator paper. As a method of integrally laminating the respective layers, a method using a paper machine at the papermaking stage is preferable because the method is simpler in terms of manufacturing steps and requires a smaller number of steps, and as a result, the required cost is reduced. It should be noted that the compact layer and the liquid-permeable layer can be separately manufactured and then laminated.

As the alkali-resistant cellulose fiber for the dense layer and the liquid-permeable layer, the most preferable fiber has excellent alkali resistance and does not excessively dissolve or shrink in the electrolyte. The fibers are preferably mercerized wood pulp, which is obtained by treating natural cellulose fibers with cold alkali, and may include hardwood pulp, softwood pulp, Spanish pulp, manila pulp, and Perilla pulp. In particular, mercerized wood pulp including hardwood pulp, and spanish grass pulp are preferable, since these pulps include fibers having a small diameter providing high air-tightness. In addition, fibers containing greater than 97% high alpha-cellulose, such as linter pulp, prehalogenated pulp that is cooked by prehydrolysis cooking and then steamed, have excellent alkali resistance and can be used without mercerization. In addition, regenerated cellulose such as conventional rayon, polynosic rayon, and rayon formed from an organic solvent have excellent alkali resistance, and therefore they are also suitable for alkali-resistant cellulose fibers.

The alkali resistance of the alkali resistant cellulose fibers was evaluated by adding 10% by weight of polyvinyl alcohol fibers as a binder to 90% by weight of cellulose fibers, making the fibers into a sheet by a paper machine, immersing them in a 40% KOH aqueous solution at 60 ℃ for 24 hours, and finally measuring the reduction in area of the paper. The results of the measurements show a reduction in area of less than 15%, indicating that the fibers of the present invention have less shrinkage. Thus, these fibers have excellent alkali resistance when compared to the cellulose fibers of conventional wood pulps (e.g., NUKP) that have shrinkage of about 30%.

Among alkali-resistant cellulose fibers suitable for beating and making compact layers, it is preferred to use fibers which rapidly lower the CSF value by beating, produce fine branches, such as mercerized wood pulp, cotton linter pulp, polynosic rayon, rayon formed from an organic solvent, and prehydrogenated pulp available from Rayonia co. (USA) under the trademark polosana NBKP.

As the alkali-resistant cellulose fibers of the liquid-permeable layer, alkali-resistant cellulose fibers of the above-mentioned dense layer suitable for beating can be used, and more specifically, regenerated cellulose fibers having satisfactory stiffness and a fiber length of 2 to 10mm can be used. These fibers are most preferred due to improved liquid permeability. However, fibers having a fiber length of less than 2mm are not preferable, since these fibers will excessively increase the tightness of the liquid-permeable layer, which in turn will weaken the swelling action of the liquid-permeable layer, resulting in a decrease in liquid permeability. On the other hand, although cellulose fibers having a fiber length of more than 10mm provide a porous liquid-permeable layer having excellent liquid permeability, these long fibers are difficult to dissolve in water, that is, difficult to perform papermaking, and even when used for papermaking, the basis weight is not stable, and as a result, these fibers are not suitable for the production of release paper.

The content of alkali-resistant cellulose fibers used for the compact and liquid-permeable layers should be 20-80% by weight. Although fibers having alkali-resistant cellulose fiber content of more than 80% by weight can provide a high density to the separator paper, the content ratio of synthetic fibers mixed with the cellulose fibers is correspondingly reduced, which would greatly increase the shrinkage of the paper sheet in the electrolyte, which is undesirable for the separator paper. For fibers having alkali resistant cellulose fiber content of less than 20% by weight, the resulting separator paper will have insufficient liquid permeability of the electrolyte, which will not be suitable for high power discharge. The cellulose fibers of the compact layer may have a freeness of CSF of less than 200ml, that is, may have a large freeness so as to provide fine fibers, but, since the compactability of the separator is not sufficient, the content of less than 20% by weight is too low to sufficiently prevent internal short circuits.

It should be noted that if the compact or liquid-permeable layer is made only of cellulose fibres, it is possible to give the paper a higher density or liquid permeability, but its shrinkage increases considerably and it tends to curl due to the ambient humidity of the air, which causes difficulties in working the paper. Therefore, it would be unsuitable to make release paper from these fibers. According to the invention, the content of alkali-resistant cellulose fibres should be 20-80% by weight for the compact layer and the liquid-permeable layer.

The alkali-resistant cellulose fibres used for the compact layer should have a freeness of 500-0ml CSF, more preferably 300-10ml CSF. In the case of a compact layer, alkali-resistant cellulose fibres in excess of 500ml csf will be insufficient for the fibrillation of the fibre and the fibre will only provide a low degree of compaction and air tightness similar to the prior art. If the degree of beating of the cellulose fibers in the compact layer is increased, a compact layer having a smaller thickness can be obtained, which results in a corresponding increase in the thickness of the liquid-permeable layer and enables a highly liquid-permeable separator to be obtained. If the freeness of the cellulose fibres in the compact layer is increased and the cellulose fibres having reached 0ml csf are excessively beaten, these cellulose fibres tend to overflow significantly on the mesh, which undesirably reduces the yield of the paper. In order to increase the liquid-permeability, it is necessary to increase the basis weight of the liquid-permeable layer, which in turn will correspondingly decrease the basis weight of the compact layer. In order to increase the compactness of the compact layer and to increase the basis weight of the liquid-permeable layer, the CSF value of the cellulose fibres used for the compact layer is preferably below 300 ml. On the other hand, in order to prevent excessive beating, it is desirable to limit the CSF to about 10ml or so. Therefore, 300-10ml CSF is preferred for the tight layer of cellulose fibers.

Beating of the alkali-resistant cellulose fibers for the liquid-permeable layer is selected to be non-beating or beating to a certain extent without largely damaging the fibers, but this will be suitable for liquid impregnation of the electrolyte. More specifically, a freeness of greater than 700ml is selected on the CSF value. For CSF values less than 700ml, the liquid permeability will remain at the level of the prior art, with the result that a liquid permeability of more than 550% which can increase the high-power discharge performance of alkaline batteries cannot be obtained. In the beating process, at the beating start stage where the CSF value has not decreased, the cutting of the fiber structure occurs inside the cellulose fibers, the fibers suffer from the breakage caused by beating, and the stiffness thereof is rapidly lost even when no internal change of the fibers is found. Therefore, the tightness of the separator paper thus obtained tends to increase due to softening of the cellulose fibers, and the liquid permeability of the electrolyte of the separator paper thus obtained decreases rapidly as beating progresses, since the expansion of the separator paper in the electrolyte is suppressed. Thus, for a liquid-permeable layer, a beating degree of more than 700ml CSF, or not beaten or comparable, is required for increasing the liquid permeability.

For the synthetic fibers mixed with alkali-resistant cellulose fibers for the compact layer and the liquid-permeable layer, one or more fibers having excellent alkali resistance, such as synthetic fibers, are used, which include: polypropylene fibers, polyethylene fibers, polyamide fibers, vinylon, and polyvinyl alcohol fibers; and composite fibers comprising: polypropylene-polyethylene composite fibers, polypropylene-ethylene vinyl alcohol copolymer fibers (such as UBF fibers, available from Daiwa Spinning Co.), and polyamide-modified polyamide composite fibers (such as Unimelt fiber UL60, available from Unitika Co.); and composite pulps comprising: polypropylene-composite pulp and polyethylene composite pulp.

Among these synthetic fibers, conjugate fibers mean that a low-melting synthetic plastic is bonded to the surface of, for example, polypropylene fibers, and the low-melting component is softened and bonded together when heated by the drying cylinder of a paper machine. These fibers are preferred because they provide sufficient strength of the release paper during the papermaking stage by simply mixing the cellulose fibers.

In addition, in the paper making stage, when the fibers are heated to more than 50 ℃ by the dryer of the paper machine, the polyvinyl alcohol fibers are dissolved by moisture included in the wet paper and are bonded together upon drying. The fibers are preferred, especially preferred for use with other synthetic fibers, because the polyvinyl alcohol added and mixed with the other synthetic fibers provides sufficient strength of the release paper even when the amount of the polyvinyl alcohol added is less than 10% of the amount of the additive.

Synthetic pulps are made by fibrillation of synthetic resins, such as by flash spinning, and include pulps with finely branched fibrils. According to the present invention, the tightness of the resulting separator paper can be increased by mixing the beaten cellulose fibers for the compacted layer.

After soaking the fibers in a 40% KOH solution at 60 ℃ for 24 hours, the weight of the fibers was reduced by 2%, indicating that the fibers had excellent alkali resistance.

According to the present invention, it is preferable to increase the liquid permeability of the release paper by using synthetic fibers having excellent alkali resistance and relatively high hydrophobic property. Therefore, synthetic fibers satisfying these requirements include, for example, polyamide fibers having polar groups, vinylon. They are preferred for providing release papers having excellent alkali resistance properties and good strength. Where these synthetic fibers, such as polyamide fibers, and vinylon, are mixed with cellulose fibers, polyvinyl alcohol fibers or polyvinyl alcohol powder (such as Poval UV-2S from Unitika co.) are added as a binder and mixed with these synthetic fibers before entering another process of papermaking. The amount of these polyvinyl alcohol fiber binders added is preferably 5 to 20% by weight based on the total weight of the release paper produced by bonding the compact layer and the liquid-permeable layer. When the amount of the binder added is less than 5% by weight, the strength of the release paper will be significantly reduced, and when the amount of the binder added is more than 20% by weight, the fibers will not only be sticky but also will be bonded to each other in sheet form between the gaps of the fibers, with the result that the electrical resistance of the paper will undesirably increase, and this will suppress swelling of the paper, resulting in a reduction in the final liquid permeability.

It should be noted that the polyvinyl alcohol powder does not retain the shape of the fibers, but when the powder is mixed with other synthetic fibers and cellulose fibers to prepare a release paper, it remains in the produced release paper after the completion of paper making and functions substantially the same as the polyvinyl alcohol fibers, and thus, the present invention is referred to as polyvinyl alcohol fibers.

Synthetic fibers useful for the compact layer include not only fine fibers having a fineness less than once but also fibers having a relatively large diameter obtainable in a sufficient amount and having a fineness of 1 to 3 denier. To increase the tightness of the compact layer, it is preferable to use finer fibers than once. However, according to the present invention, since the tightness of the tight layer can be determined by mixing the cellulose fibers controlled by beating, paper can also be made using synthetic fibers of relatively large diameter having a fineness of 1 to 3 denier. However, the fiber having a fineness of more than 3 denier has a diameter of about 20 μm, and thus it is difficult to prepare a thin compact layer, and the compactness thereof is undesirably reduced.

In the present invention, the fineness of the synthetic fibers used in the liquid-permeable layer is not particularly limited, but the fineness is preferably less than 5 denier. This is because the diameter of the fiber having the fineness of more than 5 denier is more than about 30 micrometers, that is, more than the suitable diameter of the generally used release paper, which is suitably 100 micrometers in size, and thus, the tensile strength of the release paper will be reduced, and it will also be impossible to manufacture the release paper having the thickness of less than 200 micrometers.

Likewise, cellulose fibers for the liquid-pervious layer having a diameter of more than 30 μm cannot produce a release paper having a suitable thickness, with the result that a suitable fineness is less than 5 denier even if recycled cellulose fibers are used.

According to the present invention, the structural ratio of the compact layer and the liquid-permeable layer to be laminated can be appropriately selected. In order to make the liquid permeability significantly larger than conventional release paper and to provide suitable airtightness capable of preventing internal short circuits due to the deposition of zinc oxide dendrites, it is most preferable that the ratio of the compact layer is less than 50% with respect to the total basis weight, and the basis weight is more than 5g/m²。

Preferably, the barrier paper of the present invention has an air tightness in the range of 2 to 100 seconds per 100 ml. Previously, release paper with a gas tightness of more than 2 seconds/100 ml could be used normally when mercury addition was allowed, but in order to prevent internal short circuits caused by the deposition of zinc oxide dendrites, which are currently not added with mercury, only release paper with a gas tightness of more than 2 seconds/100 ml was used. When the air-tightness of the separator paper is more than 100 seconds/100 ml, the ions are hardly diffused to make it unsuitable for high-power discharge. Further, in order to increase the high power discharge performance of the present invention, it is preferable that the airtightness be in the range of 2 sec/100 ml to 100 sec/100 ml, and the liquid permeability of the electrolyte be more than 550%, particularly more than 600%.

In addition, the separator paper generally needs to have a tensile strength of more than 2kg/15mm, whereby the paper can be processed without any problem at the separator insertion stage of battery preparation or at the time of manufacturing the separator.

Now, a method for producing the separator paper for alkaline batteries of the present invention will be described. The tight layer of separator paper is prepared by dispersing one or two alkali-resistant cellulose fibers suitable for beating in water, beating the fibers to a predetermined CSF using beating equipment for a paper machine, such as a beater or a double disc grinder; mixing the fibers with one or both of said synthetic fibers; and, if it is necessary to increase the strength of the release paper, further mixing it by adding fibers such as polyvinyl alcohol fibers as a binder to provide a raw material slurry; the stock slurry is fed to a paper machine, such as a cylinder machine or fourdrinier machine, and is made into paper using conventional paper making processes.

Further, the liquid-impregnated layer is substantially the same as the compact layer, i.e., one or two alkali-resistant cellulose fibers are dispersed in water, one or two of the fibers are mixed so as to be sufficiently dissolved, and then, if necessary, the strength of the separator is increased, further mixed by adding fibers such as polyvinyl alcohol fibers serving as a binder to provide a raw material slurry; the stock slurry is fed to a paper machine, such as a cylinder machine or fourdrinier machine, and is made into paper using conventional paper making processes.

Furthermore, to ensure dissolution of the fibers when preparing the liquid-permeable layer, dissolution can be accelerated simply by using a papermaking beater such as a beater or a double disc mill. However, dissolution of the cellulose fibres will significantly reduce the liquid permeability of the release paper and therefore care must be taken to ensure a freeness of more than 700 ml.

The integral operation of the compact layer and the liquid-permeable layer is achieved by laminating the liquid-permeable layer to one side or both sides of the compact layer using a paper machine capable of combining the layers in the paper-making stage. Optionally, after the compact layer and the liquid-permeable layer are separately prepared, the latter may be bonded to one or both sides of the former by a subsequent process.

Fig. 1 shows a first embodiment of a double-layer laminated papermaking step of integrally laminating a liquid-impregnated layer on the side of a compact layer using a cylinder multi-layer papermaking machine. Said pulp 2 for the compact layer is contained in the cylinder mould vat 1, while the pulp 6 for the liquid-permeable layer is contained in the cylinder mould vat 5. The pulp 2 contained in the cylinder vat 1 for the compacting layer is filtered through the wire mesh around the cylinder machine rotating in the cylinder vat 1 and forms a compacting layer of paper 8a, which extends from the paper machine 3. The tightly laminated paper layer 8a thus formed is fed from the wire onto the wet carpet 4. Similarly, the pulp 6 for the liquid-permeable layer contained in the cylinder vat 5 is filtered through the mesh around the cylinder paper machine rotating in the cylinder vat 5 and forms a layer 8b of the liquid-permeable layer, which extends from the paper machine 7. The paper layer 8b of the thus formed liquid-permeable layer is fed out of the web and superimposed on the paper layer 8a on the wet blanket 4 to laminate into a single laminated paper layer 8 (paper layer 8a + paper layer 8 b). The paper layer 8 thus laminated is sent to a press roll 9 while the wet felt 4 is moving, and excess water in the paper layer 8 is removed by pressing, and then sent to an upper felt 10. The paper layer 8 on the upper felt 10 is then sent to the periphery of a cylindrical drying cylinder 11 heated by steam or a heat medium. The paper layer 8 laminated with the paper layer 8a and the liquid-impregnated paper layer 8b is brought into contact with a drying cylinder 11 and dried. After the drying is completed, the web is wound into a cylindrical shape by a winding reel and formed into the roll paper 12. Then, the cylindrical roll paper is cut to satisfy the width of the separator, for example, 45mm wide, according to its end use. If desired, a dilute surfactant is then applied to the cylindrical web 12 to increase the liquid permeability of the electrolyte.

Now, a high viscosity aqueous solution, such as high molecular weight polyethylene oxide or polyacrylamide, is added to the raw material slurries 2 and 6 introduced into the cylinder mould tanks 1 and 5. By adding the aqueous solution having a high viscosity, the aqueous dispersion of the raw material slurry is homogenized. In addition, by extending the free time of the stock slurry through the mesh, the ply can be homogenized, with the result that the quantitative change is reduced when compared to other known papermaking processes, such as fourdrinier papermaking. Therefore, the papermaking method is suitable for manufacturing release paper.

In addition, in the first embodiment shown in fig. 1, the paper layer 8a separating the paper tight layer is brought into contact with the surface of the drying cylinder 11 and dried. Alternatively, the liquid-permeable layer of paper layer 8b is brought into contact with the surface of the drying cylinder 11 and dried. It should be noted, however, that in the preparation of such release paper by laminating two layers, different air-tightness and liquid-permeability, respectively, can be obtained by the intimate layer or the liquid-permeable layer being in contact with the surface of the drying cylinder. That is, by contacting the intimate layer with the surface of the drying cylinder, a more air-tight release paper can be obtained, but by contacting the liquid-permeable layer with the surface of the drying cylinder, a lower air-tightness can be obtained than with the intimate layer, but increased liquid permeability will be imparted to the release paper.

A second embodiment of the papermaking method of the present invention for providing an integrated paper for a strike-through layer by laminating liquid-impregnated layers on both sides of a tight layer using a cylinder multi-layer papermaking machine is shown in fig. 2, in which the same components as in the first embodiment shown in fig. 1 are denoted by the same reference numerals and have the same descriptions, and will not be described again. To obtain a three-layer arrangement, the slurry for the liquid-permeable layer is placed in a cylinder mould 13, which is located upstream of the cylinder mould tank 1 in which the slurry 2 for the compact layer is contained. As a result, the cylinder mould tank 1 is located in the middle of the three cylinder mould tanks. The slurry contained in the cylinder tank 13 is filtered on a mesh around a mesh cylinder 15, which mesh cylinder 15 rotates in the cylinder tank 13 and forms a continuous layer 8c of liquid-permeable paper on the cylinder 15. The thus obtained paper layer 8c of the liquid-permeable layer is fed from the cylinder to the wet blanket 4. The paper layer 8c on the wet blanket 4 is then superimposed on the tightly laminated paper layer 8a, and further the paper layer 8b for the liquid-permeable layer is superimposed thereon to form the laminated layer 8 (i.e., paper layer 8c +8a +8b), the same process as described in the first embodiment.

A third embodiment of the papermaking process of the present invention, in which a liquid-pervious layer is laminated on the side of the compact layer by using a cylinder-fourdrinier wire laminator to provide an integrated paper for the liquid-pervious layer, is shown in fig. 3, wherein the same components as in the first embodiment shown in fig. 1 are denoted by the same reference numerals and have the same descriptions, and will not be described again. The third embodiment is a fourdrinier wire with a cylinder-fourdrinier wire combination, which is used to make the compact layer. As shown in fig. 3, a slurry 17 containing a liquid for the compact layer at fourdrinier wire inlet 16 is fed onto the cylindrical surface of fourdrinier wire 18 rotating under inlet 16 to form a continuous layer 8a of liquid-permeable paper on the cylindrical surface of wire 18. The paper layer 8a thus formed is then fed from the fourdrinier wire to the wet carpet 4. Paper layer 8a carried on wet blanket 4 is then superimposed with paper layer 8b for the liquid-permeable layer to form laminated paper layer 8 (i.e., paper layers 8a +8b) in the same manner as described in fig. 1 for the first embodiment, the same process being as described in the first embodiment.

In the papermaking process using a cylinder machine, fibers are first taken out of a raw stock slurry dispersion through a cylinder and attached to the peripheral surfaces of a mesh cylinder located in a cylinder vat, thereby forming a continuous paper layer. In this process, the pulp level in the reticulated cylinder is always controlled at a constant value, which is lower than the pulp level of the cylinder vat. In the papermaking process, the different stock levels thus created are used to even out the paper layer on the wire. Thus, over-pulped raw pulp, which causes deterioration of freeness, tends to be prone to plugging, which in turn reduces freeness. In this case, it is impossible to provide a pulp head larger than the diameter of the cylinder for the over-beaten raw pulp even if the pulp head is made larger to cause a significant reduction in the paper making speed. Paper making by using a cylinder machine is suitable for paper making requiring a tight or liquid-permeable layer comprising a pulp of more than 100ml csf freeness.

On the other hand, in a papermaking method using a fourdrinier machine, fibers are taken out of a raw stock slurry dispersion through an endless rotating wire arranged in the form of a belt, and a continuous paper layer is formed thereon. In this process, the free duration of the aqueous dispersion of the starting material can be extended by using a fourdrinier wire in the form of a conveyor belt, and in addition, in order to increase its fineness, the aqueous dispersion can be passed through a wire in the form of a conveyor belt, and a vacuum pump can be connected below this wire. Therefore, a satisfactory fineness can be secured without any significant problem regardless of whether the raw material pulp is subjected to excessive beating causing deterioration of freeness. Thus, the papermaking by means of an elongated wire is suitable for the papermaking of tight plies comprising over-pulped cellulose fibres with a csf of less than 100 ml.

Certain embodiments of the separator paper for alkaline batteries according to the invention will now be compared with conventionally prepared paper. It should be noted that the measured values of the respective embodiments, examples and conventional release papers were measured according to the following methods.

1) CSF (Canadian Standard freeness)

The measurement was carried out based on the CSF defined in JIS P8121.

2) Thickness of

The thickness of the resulting release paper was determined by measuring at five predetermined positions of the paper using a pointer thickness gauge and averaging the values thus measured.

3) Basis weight and tensile Strength

The quantitative determination of the release paper was measured according to the conditions specified in JIS P8124, and the longitudinal tensile strength of the paper was measured according to the conditions specified in JIS P8113.

4) Air tightness

The airtightness was determined by measuring the time required for 100ml of gas to pass through the cylindrical surface of 6 mm-diameter release paper, which was inserted into a 6 mm-diameter small hole attached to a test piece mounted on the underside of a type B measuring apparatus operating in accordance with JIS P8117 standard, which indicates a permeability test method for paper and cardboard.

5) Liquid permeability

To measure liquid permeability, 50mm x 50mm square pieces of paper were cut from release paper, dried and immersed in 40% KOH solution for 10 minutes. The sample was spread on a tilted glass plate, the state thereof was maintained at 45 degrees for 3 minutes, the weight of the sample was measured during the removal of the excess KOH solution, and the permeability was calculated according to the following equation;

in the formula (W2-W1)/W1 × 100, W1 is the weight before immersion, and W2 is the weight after immersion.

6) Thickness after expansion

To measure the thickness of the release paper, it was immersed in a 40% KOH solution for 30 minutes, and the thickness of the paper was measured with a pointer thickness gauge.

7) Alkali resistance (percent shrinkage)

To measure the alkali resistance of the release paper, a square piece of 100mm x 100mm was cut out precisely from the release paper to provide a sample, which was immersed in a 40% KOH solution for 24 hours and then washed with water. The vertical and longitudinal lengths of the test specimen were measured by the following equations. Here, a1 is the area before immersion, and a2 is the area after immersion.

Percent shrinkage of (A1-A2)/A1X 100

Wherein a1 is the area before immersion and a2 is the area after immersion

8) Liquid absorption property

To measure the liquid absorbency, a rectangular sheet of 15mm × 200mm was cut out from a release paper to provide a sample, the sample was hung vertically, and the lower side thereof was immersed in a 40% KOH solution for 3 minutes for more than 3mm, and then, the penetration height of the solution was measured as the liquid absorbency (mm).

Embodiment 1: the tight layer + liquid-permeable layer of the double structure manufactured by the cylinder machine shown in fig. 1.

For the compact layer, 63% by weight of mercerized hardwood pulp was pulped up to 290ml csf by a double disc mill, mixed with 25% by weight of vinylon (fineness 0.5 denier x fiber length 2mm), and mixed with 12% by weight of polyvinyl alcohol fiber (fineness 1 denier x fiber length 3mm) to provide a furnish. In addition, for the liquid-permeable layer, 63% by weight of polynosic rayon (fineness 0.5 denier x fiber length 2mm), 25% by weight of vinylon (fineness 0.5 denier x fiber length 2mm) and 12% by weight of polyvinyl alcohol fiber (fineness 1 denier x fiber length 3mm) were mixed together to provide a furnish. It should be noted that undashed polynosic rayon was used and the CSF value thereof was 740 ml. These raw materials were fed into two cylinder tanks, respectively, and then laminated. In the manufacture of paperThe basis weight of the compact layer was maintained at 12g/m during the process²As shown in Table 1, only the liquid-permeable layer had a quantitative change, e.g., from 24.6 to 49.5g/m²So as to obtain the separator paper for alkaline batteries of the invention.

TABLE 1

Detailed description of the preferred embodiments	Layer structure (g/m)²) Compact layer liquid permeable layer		Quantitative g/m²	Thickness μm	Tensile strength kg/15mm	Gas tightness second/100 ml	Liquid permeability%	Liquid absorbency mm
Detailed description of the preferred embodiments			Quantitative g/m²	Thickness μm	Tensile strength kg/15mm	Gas tightness second/100 ml	Liquid permeability%	Liquid absorbency mm	1-1	12.0	12.6	24.6	74	3.6	4.1	605	35
1-2	12.0	20.4	32.4	104	5.0	4.3	620	44	1-1	12.0	12.6	24.6	74	3.6	4.1	605	35
1-2	12.0	20.4	32.4	104	5.0	4.3	620	44	1-3	12.0	29.3	41.3	139	6.3	4.5	665	48
1-4	12.0	37.5	49.5	162	7.0	5.2	690	52	1-3	12.0	29.3	41.3	139	6.3	4.5	665	48

In embodiment 1-1, the basis weight of the compact layer and the liquid-permeable layer are substantially the same. By integrally laminating the compact layer and the liquid-permeable layer, airtightness at 4.1 sec/100 ml and liquid-permeability at 605% were obtained. In addition, as shown in embodiments 1-2, 1-3 and 1-4, the liquid permeability was increased to 620, 650 and 690, respectively, by increasing the basis weight, and also increased air-tightness was provided by increasing the basis weight of the entire release paper. In the embodiments 1 to 2 shown in Table 1, the basis weight of the whole release paper was 32.4g/m²The values are essentially the same as the quantitative values in tables 9 and 10, respectively. Table 9 the results of examples 1-4 show that 5.5 s/100 ml air tightness and 605% liquid permeability can be obtained, while the results of examples 2-2 show that 670% liquid permeability can be obtained, but the air tightness is only 0.8 s/100 ml. However, in example 1-2, the airtightness of 4.3 sec/100 ml and the liquid permeability of 620% were obtained, which would simultaneously secure improved tightness, which would enable prevention of internal short-circuiting due to deposition of zinc oxide dendrites accompanied by no addition of mercury; and improved liquid permeability, which will enable increased high power discharge capacity.

It should be noted that the first embodiment has a release paper made by contacting the intimate layer with the dryer surface for self-drying, and when the air tightness of the liquid-permeable layer is compared with the air tightness of the intimate layer where both layers are in contact with the dryer surface, the former exhibits lower air tightness than the latter, but the release paper of the former has higher liquid permeability. For example, in the case where the liquid-permeable layer and the liquid-permeable layer of embodiments 1 to 2 produced by contacting them with a drying cylinder have the same material and the same structure, a separator having an air impermeability of 3.2 seconds/100 ml and a liquid permeability of 650% is obtained.

Embodiment 2 a triple structure of a liquid-permeable layer + a compact layer + a liquid-permeable layer was manufactured by a cylinder multi-layer paper machine shown in the figure.

For the compact layer, 50% by weight of cotton linter pulp was beaten to at most 200ml csf by a double disc mill and mixed with 40% by weight of vinylon (fineness 0.5 denier x fiber length 2mm) and 10% by weight of polyvinyl alcohol fiber (fineness 1 denier x fiber length 3mm) to provide a furnish. In addition, for the liquid-permeable layer, 60% by weight of a usual rayon fiber (fineness 0.7 denier x fiber length 3mm), 28% by weight of vinylon (fineness 0.5 denier x fiber length 2mm) and 12% by weight of a polyvinyl alcohol fiber (fineness 1 denier x fiber length 3mm) were mixed together to provide a furnish. It should be noted that normal, unbaked rayon was used, and the CSF value thereof was 760 ml. These stock solutions are fed separately to the three cylinder mould pots of the paper machine so that the paper layer formed of the tight-layered stock material shown in figure 2 is placed in the middle layer position and the two side liquid-permeable layers formed of the same basis weight and the same stock slurry are placed together equally to provide a laminated paper. The basis weight of the compact layer was maintained at 10g/m during the papermaking process²The constant value of (A) as shown in Table 2, the quantitative amount of the liquid-impregnated layer alone was changed equally from 33.0 to 40.0g/m²So as to obtain the invented separation paper for alkaline cell.

TABLE 2

Detailed description of the preferred embodiments	Layer structure (g/m)²)			Quantitative g/m²	Thickness μm	Tensile strength kg/15mm	Gas tightness second/100 ml	Liquid permeability%	Liquid absorbency mm
	Layer structure (g/m)²)									Liquid-permeable layer	Compact layer	Liquid-permeable layer
	2-1	11.5	10.0							Liquid-permeable layer	Compact layer	Liquid-permeable layer	11.5	33.0	108	4.0	2.5	630	32
2-2	2-1	11.5	10.0	15.0	10.0	15.0	40.0	115	4.9	2.8	640	34	11.5	33.0	108	4.0	2.5	630	32

Embodiment 2 (as shown in Table 2) has a liquid-permeable layer + compact layer + liquid-permeable layer of three-layer structure, which simultaneously attains airtightness at 2.5 sec/100 ml and liquid-permeability at 630% as shown in embodiment 2-1. The invention may be a layer having integrally laminated liquid-permeable layers on both sides of a compact layer. Preferably, for a three-layer structure, the compact layer is in the middle so that the liquid-impregnated layer can hold the electrolyte, and the liquid-impregnated layers are integrally laminated on both sides of the compact layer, respectively. This is because when the close-packed layers are laminated on both sides of the liquid-impregnated layer, the liquid-permeability of the electrolyte is low, and a longer impregnation time is required in the battery impregnation stage, and insufficient impregnation is easily generated due to retention of air bubbles on the fibers on the separator paper. In order to improve high power discharge performance, it is important to maintain the electrolyte in a plane in contact with the active material.

Embodiment 3 a tight layer of a two-layer structure + a liquid-pervious layer was produced by the cylinder-fourdrinier combined paper machine shown in fig. 3.

For the compact layer, the solvent was spun into rayon (fineness 1.5 denier x fiber length 4mm) by a double disc mill: 70% by weight of Tencel (Tencel is a trademark of Coultlose Co. Ltd. of UK) was beaten to at most 10ml of CSF, and mixed with 25% by weight of vinylon (fineness 0.5 denier. times.fiber length 2mm) and with 5% by weight of polyvinyl alcohol fiber (fineness 1. times.fiber length 3mm) to provide a furnish. In addition, for the liquid-permeable layer, 60% by weight of polynosic rayon (fineness 0.5 denier x fiber length 2mm), 25% by weight of vinylon (fineness 0.5 denier x fiber length 2mm) and15% by weight of polyvinyl alcohol fibers (fineness 1 denier x fiber length 3mm) were mixed together to provide a furnish. It should be noted that undashed polynosic rayon was used and the CSF value thereof was 740 ml. These raw materials were fed to the fourdrinier wire inlet of a fourdrinier machine and the raw material slurry of the liquid-impregnated layer was fed to a cylinder vat, to thereby prepare a laminate paper of separator paper for alkaline batteries of the invention, as shown in Table 3, having a basis weight of 20.2 to 39.6g/m²。

TABLE 3

Detailed description of the preferred embodiments	Layer structure (g/m)²)		Quantitative g/m²	Thickness μm	Tensile strength kg/15mm	Gas tightness second/100 ml	Liquid permeability%	Liquid absorbency mm
	Layer structure (g/m)²)								Compact layer	Liquid-permeable layer
	3-1	10.0							Compact layer	Liquid-permeable layer	10.2	20.2	67	3.0	20.4	630	30
3-2	3-1	10.0	10.0	15.2	25.2	80	3.5	25.6	660	38	10.2	20.2	67	3.0	20.4	630	30
3-2	3-3	10.0	10.0	15.2	25.2	80	3.5	25.6	660	38	22.8	32.8	107	4.8	27.5	670	45
3-4	3-3	10.0	17.0	22.6	39.6	121	6.6	57.2	570	45	22.8	32.8	107	4.8	27.5	670	45

A third embodiment is shown in table 3, in which solvent spun rayon was adjusted to 10ml csf, and as a result, the fourdrinier section of a cylinder-fourdrinier combined paper machine was used in preparing the compact layer. As shown in embodiments 3-3, an air tightness of 27.5 seconds/100 ml is obtained, for example, as a tight layer of cellulose fibres, since a large freeness is selected, while a liquid permeability of 670% is also obtained.

Embodiments 4-7 the compact layer + liquid-permeable layer of a two-layer structure was prepared by a multi-layer cylinder machine.

In the same manner as in embodiment 1, in the production of a two-layer laminated paper by means of a multi-cylinder paper making machine equipped with the twin cylinders shown in FIG. 1, the raw materials shown in Table 4 were used, and a laminated paper for separator paper of alkaline batteries of the invention (for example, in Table 5) was produced.

TABLE 4

	Kind of layer	Wood materialMaterial content	Material ratio%
	Kind of layer	Wood materialMaterial content	Material ratio%	Embodiment 4	Compact layer liquid permeable layer	Polynesian rayon (0.5 denier. times.2 mm) CSF470ml beaten vinylon (0.5 denier. times.2 mm) polyvinyl alcohol fiber (1 denier. times.3 mm) Polynesian rayon (0.5 denier. times.2 mm) CSF720ml beaten vinylon (0.5 denier. times.2 mm) polyvinyl alcohol fiber (1 denier. times.3 mm)	602515603010
Embodiment 5	Compact layer liquid permeable layer	Pivot wood prehydrogenated pulp CSF210ml beaten vinylon (0.5 denier. times.2 mm) polyvinyl alcohol fiber (1 denier. times.3 mm) Polynesco rayon (3 denier. times.5 mm) CSF780ml (non-beaten) Nylon-6 fiber (1.5 denier. times.5 mm) polyvinyl alcohol fiber (1 denier. times.3 mm)	306010504010	Embodiment 4	Compact layer liquid permeable layer		602515603010
Embodiment 5	Compact layer liquid permeable layer		306010504010	Embodiment 6	Compact layer liquid permeable layer	Mercerized hardwood pulp CSF220ml beaten vinylon (0.5 denier. times.2 mm) polyvinyl alcohol fiber (1 denier. times.3 mm) rayon (1.5 denier. times.5 mm) CSF770ml (untapped) vinylon (1.0 denier. times.2 mm) polypropylene-polyvinyl alcohol copolymer fiber (2 denier. times.5 mm)	504010254530
Embodiment 7	Compact layer liquid permeable layer	Mercerized hardwood pulp CSF150ml beaten vinylon (0.5 denier x 2mm) polyvinyl alcohol fiberMercerized softwood pulp CSF760ml (unbleached) polynosic rayon (1 denier x 3mm) CSF770ml (unbleached) vinylon (1 denier x 3mm) polyvinyl alcohol fiber (1 denier x 3mm)	30601020502010	Embodiment 6	Compact layer liquid permeable layer		504010254530

TABLE 5

Detailed description of the preferred embodiments	Layer structure (g/m)²)		Quantitative g/m²	Thickness μm	Tensile strength kg/15mm	Gas tightness second/100 ml	Liquid permeability%	Liquid absorbency mm
	Layer structure (g/m)²)								Compact layer	Liquid-permeable layer
	4	20.0							Compact layer	Liquid-permeable layer	12.2	32.2	105	4.3	2.4	590	45
5	4	20.0	10.3	22.2	32.5	115	3.6	2.6	660	44	12.2	32.2	105	4.3	2.4	590	45
5	6	10.6	10.3	22.2	32.5	115	3.6	2.6	660	44	22.0	32.6	107	5.0	4.6	580	40
7	6	10.6	7.0	25.0	32.0	112	4.1	2.8	710	47	22.0	32.6	107	5.0	4.6	580	40

Embodiments 4-7 shown in table 4 show that several specific examples of mixtures of cellulose fibers and synthetic fibers useful in the present invention, and each of these examples, can simultaneously achieve air impermeability and liquid permeability that meet the objectives of the present invention shown in table 5.

Embodiment 8: a compact layer of a double structure + a liquid-permeable layer made by lamination. For the compact layer, 60% by weight of mercerized hardwood pulp was pulped up to 270ml csf by a double disc mill and mixed with 30% by weight of vinylon (fineness 0.5 denier x fiber length 2mm) and 10% by weight of polyvinyl alcohol fiber (fineness 1 denier x fiber length 3mm) to provide a furnish of the raw material. The furnish was then fed to a cylinder mould machine, whereby a basis weight of 9.5g/m was obtained²Single ply base paper for the compact ply.

In addition, for the liquid-permeable layer, 60% by weight of polynosic rayon (fineness 0.5 denier x fiber length 2mm), 30% by weight of vinylon (fineness 0.5 denier x fiber length 2mm) and 10% by weight of polyvinyl alcohol fiber (fineness 1 denier x fiber length 3mm) were mixed together to provide a furnish. Thus, basis weights of 16.2 and 22.4g/m were obtained by means of a cylinder mould machine²Two single-layer base papers for the liquid-permeable layer. An unbaked polynosic rayon fiber was used, and the CSF value thereof was 740 ml. The base paper for the compact layer and the liquid-permeable layer is bonded by using a coater equipped with a drying cylinder. In a first step, a base paper for the compact layer and the liquid-permeable layer is superimposed and dippedSaturated with water and then sent to the surface of a drying cylinder, whereby the superimposed layers are dried and pressed onto the surface by the rollers of the drying cylinder. Thereby, the polyvinyl alcohol fibers contained in the base paper are dissolved again by heating and bond the two layers of the base paper together. In this manner, a separator paper for an alkaline battery of the present invention was obtained (as shown in table 6).

TABLE 6

Detailed description of the preferred embodiments	Laminated base paper			Laminated release paper
	Laminated base paper			Laminated release paper							Quantitative g/m²	Thickness μm	Quantitative g/m²	Thickness μm	Tensile strength kg/15mm	Air tightness second/100 ml	The liquid is soaked in the permeable layer%	Liquid absorbency mm
	8-1	Compact layer-base paper liquid permeable layer-base paper	9.516.2	2580	25.7	90	3.2	2.1	730		Quantitative g/m²	Thickness μm	Quantitative g/m²	Thickness μm	Tensile strength kg/15mm	Air tightness second/100 ml	The liquid is soaked in the permeable layer%	Liquid absorbency mm	38
8-2	8-1	Compact layer-base paper liquid permeable layer-base paper	9.516.2	2580	25.7	90	3.2	2.1	730	Compact layer-base paper liquid permeable layer-base paper	9.522.4	2595	31.9	115	4.1	2.7	740	47	38

The eighth embodiment shown in table 6 shows bonding the compact layer and the liquid-impregnated layer into an integrally laminated layer. The bonding of the laminated layers shows that even if the layer is made of integrally bonded layers as shown in embodiment 8-1, 2.1 sec/100 ml of air-tightness and 730% of liquid permeability can be simultaneously obtained.

Prior art example 1

60% by weight of unpulped mercerized softwood pulp, 25% by weight of vinylon (fineness 1.0 denier x fiber length 3mm) and 15% by weight of polyvinyl alcohol fiber (fineness 1.0 denier x fiber length 3mm) were mixed to provide a furnish. The furnish was fed to a cylinder mould machine to give a basis weight of about 32g/m²Conventional single ply release paper. Such release paper is disclosed in Japanese patent application laid-open No. 54-87824, the applicant of which is the same as the present invention. It should be noted that the addition of mercury to the zinc active material of an alkaline manganese cell has not been prohibited at the time of this patent application.

Prior art example 2

30% by weight of mercerized hardwood pulp adjusted to 280ml CSF freeness, 55% by weight of vinylon (fineness 0.5 denier x fiber length 2mm) and 15% by weight of polyvinyl alcohol fiber (fineness 1.0 denier x fiber length 3mm) were mixed to provide a furnish. The furnish was fed to a cylinder mould machine to give a basis weight of about 32g/m²Conventional single ply release paper. Such release paper is disclosed in japanese patent application laid-open No. 2-119049, the applicant of which is the same as the present invention. Even without the addition of mercury to the zinc active material of the alkaline manganese cell is permissible and the disclosed technology for making separator paper is still useful at present.

Prior art example 3

52% by weight of polynosic rayon having been adjusted to 450ml of CSF freeness, 33% by weight of vinylon (fineness 0.3 denier x fiber length 2mm) and 15% by weight of polyvinyl alcohol fiber (fineness 1.0 denier x fiber length 3mm) were mixed to provide a furnish. The furnish was fed to a cylinder mould machine to give a basis weight of about 32g/m²Conventional single ply release paper. Such separator paper is disclosed in japanese patent application laid-open No. 5-74439, and an object of the technology is to provide an improved alkali manganese battery when mercury is not added to a zinc active material of the battery. Examples 1-3 of these prior art are shown in table 7.

TABLE 7

Examples of the prior art	Beating degree of cellulose fiber CSF (ml)	Quantitative g/m²	Thickness μm	Tensile strength kg/15mm	Gas tightness second/100 ml	Liquid permeability%	Liquid permeability mm
Examples of the prior art	Beating degree of cellulose fiber CSF (ml)	Quantitative g/m²	Thickness μm	Tensile strength kg/15mm	Gas tightness second/100 ml	Liquid permeability%	Liquid permeability mm	123	760280450	32.032.532.1	12510495	3.05.04.7	1.05.73.5	520330400	322729

The prior art example 1 shown in table 7 is not allowed because these techniques are used when mercury can be added, when no internal short circuit needs to be considered and there is no practical problem even when the 1.0 second/100 ml airtightness and liquid permeability per se are selected to be 520%.

Prior art example 2 shown in table 7 is still usable at present, since this technique can achieve gas tightness of e.g. 5.7 seconds/100 ml without addition of mercury, but its liquid permeability is still within 330%, which would not meet the currently required improvement for high power discharge. What is needed is a way to not only prevent internal short circuits due to zinc oxide deposition, but also to increase liquid permeability.

Prior art example 3 shown in table 7 uses vinylon blended with cellulose fibers, which are expensive and have a small fineness such as 3 denier diameter, but still have a liquid permeability of 400%, which is not enough to improve the need for high power discharge.

Thus, LR-6 alkaline manganese batteries were prepared by using the separator paper of the above-described embodiments 1 to 8 and prior art examples 1 to 3, and subjected to a discharge test of 2 ohm load (a time period was measured when the battery voltage was decreased to a final voltage of 0.9V using the 2 ohm load), and to an intermittent discharge test (5 minutes per day of discharge under a 3.9 ohm load, and the battery voltage was measured after 50 days), the results of which are shown in table 8. In manufacturing the battery, the liquid-impregnated layer of the separator was positioned in contact with the anode active material, and the number of rolled sheets thereof was determined so that the separator had an equal basis weight. Optionally, a compact layer may also be provided in contact with the anode active material.

TABLE 8

Release paper						Test results of discharge characteristics
Release paper						Test results of discharge characteristics		Characteristics of release paper					Number of rolls	2 ohm discharge (minutes)	Intermittent discharge (V)
Release paper	Gas tightness second/100 ml	Liquid permeability%	Liquid absorbency mm	Percent shrinkage%				Characteristics of release paper
Release paper	Gas tightness second/100 ml	Liquid permeability%	Liquid absorbency mm	Percent shrinkage%	Embodiments 1 to 1	4.1	605	35	4.1	4	160	1.2
Embodiments 1 to 2	4.3	620	44	4.3	Embodiments 1 to 1	4.1	605	35	4.1	4	160	1.2	3	159	1.1
Embodiments 1 to 2	4.3	620	44	4.3	Embodiments 1 to 4	5.2	690	52	5.0	2	157	1.1	3	159	1.1
Embodiment 2 to 1	2.5	630	32	4.2	Embodiments 1 to 4	5.2	690	52	5.0	2	157	1.1	3	160	1.1
Embodiment 2 to 1	2.5	630	32	4.2	Embodiment 3 to 2	25.6	660	38	4.3	4	158	1.2	3	160	1.1
Embodiments 3 to 3	27.5	670	45	4.7	Embodiment 3 to 2	25.6	660	38	4.3	4	158	1.2	3	153	1.2
Embodiments 3 to 3	27.5	670	45	4.7	Embodiment 4	2.4	590	45	5.0	3	154	1.1	3	153	1.2
Embodiment 5	2.6	660	44	3.7	Embodiment 4	2.4	590	45	5.0	3	154	1.1	3	157	1.1
Embodiment 5	2.6	660	44	3.7	Embodiment 6	4.6	580	40	4.3	3	148	1.1	3	157	1.1
Embodiment 7	2.8	710	47	3.9	Embodiment 6	4.6	580	40	4.3	3	148	1.1	3	159	1.1
Embodiment 7	2.8	710	47	3.9	Embodiment 8 to 1	2.1	730	38	4.4	4	164	1.1	3	159	1.1
Embodiment 8 to 2	2.7	740	47	4.6	Embodiment 8 to 1	2.1	730	38	4.4	4	164	1.1	3	161	1.1
Embodiment 8 to 2	2.7	740	47	4.6	Prior art example 1	1.0	520	32	3.5	3	140	0.2	3	161	1.1
Prior art example 2	5.7	330	27	2.8	Prior art example 1	1.0	520	32	3.5	3	140	0.2	3	135	1.1
Prior art example 2	5.7	330	27	2.8	Prior art example 3	3.5	400	31	5.0	3	138	1.1	3	135	1.1

As shown in table 8, each of the batteries using the separator paper prepared according to the embodiment of the present invention showed that they could maintain a long experimental discharge time of longer than 148 minutes when discharged with a large power of 2 ohm discharge current, and showed improved battery life when compared to prior art examples 1-3. In addition, each of these embodiments showed that each cell could maintain a discharge voltage of more than 1.1V after the intermittent discharge test and could prevent internal short circuits within the cell due to the deposition of zinc oxide dendrites. However, in each of the prior art examples, the discharge time was shorter than that of the embodiment according to the present invention. Each of the embodiments of the present invention showed that an improvement in discharge performance of a minimum of 8 minutes and a maximum of 29 minutes was obtained when compared to prior art examples 1-3. That is to say a significant improvement has been obtained. In addition, as shown in table 8, each of the embodiments of the present invention shows that they have a higher absorption rate of the electrolyte so as to facilitate the reduction of the injection time of the electrolyte. The paper of the present invention showed almost the same shrinkage in relation to its alkali resistance as in prior art examples 1-3, and no significant problems in practical application with respect to alkali resistance occurred.

In prior art example 1, a discharge time of 140 minutes was obtained, but the voltage of the battery had dropped to 0.2V indicating the airtightness of the separator paper due to intermittent discharge, that is, the tightness was so low as not to prevent internal short circuits in the battery due to the deposition of zinc oxide dendrites. Prior art examples 2 and 3 show that the discharge time is less than 140 minutes when the cell voltage is maintained at 1.1V after the intermittent discharge test. This means that the liquid permeability is insufficient and the amount of electrolyte permeation in the separator paper of the battery is already insufficient during high-power discharge, which results in a shortened service life of the battery.

In addition, as shown in table 8, it was demonstrated according to various embodiments of the present invention that it has a higher electrolyte absorption rate so that it helps to reduce the injection time of the electrolyte. The paper of the present invention shows substantially the same shrinkage as the prior art with respect to shrinkage associated with alkali resistance, and it is clear that there are no significant practical problems associated with its alkali resistance.

Although the present invention is intended to improve the alkaline primary battery, it can also be applied to alkaline secondary batteries such as nickel zinc batteries, nickel hydrogen batteries, etc., unless the battery is a low power type battery that allows 10% overcharge.

As described in detail above, the separator paper of the present invention can provide a structure in which the entire ground layer is combined with a compact layer for maintaining its fineness and a liquid-permeable layer for increasing the liquid permeability of an electrolyte, so that the compact layer has a sufficient fineness suitable for preventing migration of zinc oxide dendrites in active materials of both poles and batteries; the liquid-permeable layer may have sufficient liquid permeability to provide an electrolyte required for high-power discharge of the battery; the tightness of the compact layer is higher than that of the prior art, and the liquid-permeable layer can be made to have a more suitable liquid permeability of the electrolyte, that is, the liquid-permeable layer swells in the electrolyte to maintain the amount of electrolyte required at the time of high-power discharge, while the compact layer comprising cellulose fibers adjusted by beating exhibits a much lower thickness expansion effect when compared with the liquid-permeable layer in the electrolyte. Therefore, accompanying the expansion of the compact layers in the electrolyte, the respective pore diameters thereof are only slightly expanded, and although the liquid permeability of the liquid-permeable layer is increased by laminating the compact layers and the liquid-permeable layer, the fineness of the separator paper in the electrolyte is not reduced.

Thus, the release paper of the present invention can provide compactness and high liquid permeability. The isolation paper can meet the requirement of preventing the tightness of internal short circuit caused by zinc oxide dendrite without adding mercury; but also increases the liquid permeability of the high power discharge capacity.

Further, according to the present invention, since there is an integral stacking method of more than two base papers in the papermaking according to the present invention, it is possible to make pinholes and blisters generated during the manufacture of the base papers and holes caused by the change in pore size smaller and narrower, with the result that the reliability of preventing short circuits inside the release paper is increased when compared with the single-ply release paper of the prior art.

Further, according to the present invention, since a plurality of porous liquid-impregnated layers are laminated, the permeation rate of the electrolyte can be increased under conditions of similar airtightness as compared with the single-layer separator paper of the prior art, so that the injection time of the electrolyte can be shortened during the assembly of the battery, which in turn will contribute to the productivity of the battery.

Claims

1. A release paper for electrically separating an anode active material and a cathode active material of an alkaline battery, the release paper comprising:

a compact layer comprising alkali resistant cellulose fibers and synthetic fibers, wherein said alkali resistant cellulose fibers are present in an amount of 20 to 80% by weight and a freeness of 500 to 0ml based on canadian standard freeness, said compact layer providing an air tightness of 2 to 100 seconds per 100 ml;

a liquid-permeable layer integrally laminated with said compact layer and comprising alkali-resistant cellulosic fibers and synthetic fibers, wherein said alkali-resistant cellulosic fibers are present in an amount of 20 to 80% by weight and a freeness greater than 700ml based on canadian standard freeness, said liquid-permeable layer providing a liquid permeability greater than 550%; and

and wherein the fibers of said compact layer have a fineness of less than 3 denier and the fibers of said liquid-permeable layer have a fineness of less than 5 denier.

2. The release paper of claim 1, further comprising another same liquid-permeable layer integrally laminated to said compact layer on the other side of said compact layer.

3. A release paper for electrically separating an anode active material and a cathode active material of an alkaline battery, the release paper comprising:

a liquid-permeable layer integrally laminated with said compact layer and comprising alkali-resistant cellulosic fibers and synthetic fibers, wherein said alkali-resistant cellulosic fibers are present in an amount of 20 to 80% by weight and a freeness greater than 700ml based on canadian standard freeness, said liquid-permeable layer providing a liquid permeability greater than 600%; and

4. The release paper of claim 3, further comprising another same liquid-permeable layer integrally laminated to said compact layer on the other side of said compact layer.

5. A release paper for electrically separating an anode active material and a cathode active material of an alkaline battery, the release paper comprising:

a compact layer;

a liquid-permeable layer integrally laminated with said compact layer;

wherein the compact layer is prepared by mixing alkali-resistant cellulose fibers suitable for beating with synthetic fibers so that the content of the alkali-resistant cellulose fibers is 20 to 80% by weight and the beating degree is 500 to 0ml in terms of canadian standard freeness; and

wherein the liquid-permeable layer is prepared by mixing alkali-resistant cellulose fibers with synthetic fibers, the content of the alkali-resistant cellulose fibers is 20-80 wt%, and the freeness is more than 700ml by Canadian Standard freeness;

6. The release paper according to claim 5, wherein the alkali resistant cellulose fibers suitable for beating used in said compact layer have a beating degree of 300-100ml in Canadian Standard freeness.

7. The release paper of claim 5, wherein the alkali resistant cellulosic fibers suitable for beating used in said densified layer comprise at least one member selected from the group consisting of mercerized wood pulp, cotton linter pulp, polynosic rayon, rayon formed from an organic solvent, and pre-hydrogenated pulp.

8. The release paper of claim 5, wherein said compact ply has a basis weight of greater than 5g/m²And less than 50% of the total basis weight of the release paper.

9. The release paper of claim 5, wherein the alkali resistant cellulosic fibers used in said liquid-permeable layer are unbleached.

10. The release paper according to claim 5, wherein the alkali-resistant cellulosic fibers used in said liquid-permeable layer comprise regenerated fibers having a fiber length of 2 to 10 mm.

11. The release paper of claim 5, wherein said synthetic fibers comprise at least one member selected from the group consisting of polyvinyl alcohol fibers, polypropylene-polyethylene composite fibers, polypropylene-ethylene vinyl alcohol copolymer fibers, polyamide-modified polyamide composite fibers, polypropylene-synthetic pulp, and polyethylene-synthetic pulp.

12. The release paper according to claim 5, further comprising polyvinyl alcohol fibers or polyvinyl alcohol powder added as a binder in an amount of 5 to 20% by weight relative to the total weight of the release paper.

13. The release paper of claim 5, wherein said synthetic fibers for said compact layer and said liquid-permeable layer comprise polyamide fibers.

14. The release paper of claim 5, wherein said synthetic fibers for said dense layer and said liquid-permeable layer comprise vinylon fibers.