JP2000153116A - Filter material, lubricant filter and fuel filter using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a filter material having high filtering efficiency without adding a filter aid, such as a glass microfiber or a metal fiber and an org. fiber having possibility to melt by the heat generated in an engine. SOLUTION: A filter material is constituted by using fibrilated natural fibers with freeness of 500 ml or less obtained by beating natural fibers. As natural fibers to be beaten, it is pref. to use cellulose fibers (lyocel) prepared by directly decomposing wood pulp by an org. solvent and the mixing ratio of the fibrilated natural fibers is pref. 10-60% and the residual part of the filter material is pref. constituted of other natural fibers. Especially, a filter material wherein the mixing ratio of the fibrilated natural fibers is set to 20% or more is suitable as a lubricant filter and a filter material wherein the mixing ratio is set to 40% or less is suitable as a fuel filter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter medium for a filter, and more particularly, to a method for trapping impurities contained in lubricating oil, hydraulic oil, fuel, air and the like used in internal combustion engines, machine tools, hydraulic machines and the like. The present invention relates to a filter material for removing and a filter using the same.

[0002]

2. Description of the Related Art Many lubricating oils are used for lubrication in internal combustion engines and machine tools. Metal wear powder, dust, soot and the like are generated in the lubricating oil due to the use of these engines and the like, and are accumulated in the lubricating oil with time. In particular, in internal combustion engines such as automobile gasoline engines and diesel engines, carbon particles are generated due to incomplete combustion. When these particles are dispersed and accumulated in engine oil, which is a lubricating oil, the viscosity of the lubricating oil increases, Problems such as shortening of service life occur. Since these cause poor lubrication and increase in wear of the internal combustion engine and the like, a filter is used as a method of capturing metal abrasion powder, dust, and carbon particles in oil in a lubrication circuit of the engine and the like and filtering the same. ing.

[0003] As a filter material for this filter, a filter paper made mainly of cellulose fibers or a filter paper made by mixing cellulose and organic fibers (synthetic fibers) has been conventionally used. By mainly increasing the fiber density and reducing the pore size of the filter paper,
Alternatively, a technique of increasing the thickness of the filter paper to improve the filtration efficiency of the fine particles has been used. However, in such a method, there is a problem that the filtration life is significantly shortened while the filtration efficiency of the fine particles is increased by reducing the pore size of the filter paper.

In recent years, in particular, an exhaust gas recirculation (EGR) system for recirculating a part of exhaust gas to an intake system to reduce nitrogen oxides contained in exhaust gas from an engine has been adopted. In other words, the amount of carbon particles in the lubricating oil has increased more than ever. When the increased carbon particles aggregate in the engine and become sludge, or when metal sludge or dust is involved in the sludge, the fluidity of the lubricating oil is disturbed, causing poor lubrication or damaging the lubricated surface. Or will be. For this reason, development of a dispersant (oil additive) for preventing aggregation of carbon particles in a lubricating oil and uniformly dispersing the same is progressing. Refinement of particles has become a major issue in the development of filter media.

[0005] In view of the above, as a measure for removing these fine particles, a filter medium mixed with micro glass fibers which is inexpensive and easily available has been studied, and has been used in some fields. On the other hand, research is being conducted from the viewpoint of enhancing the interaction between the carbon particles and the filter medium to more efficiently adsorb the carbon particles in the oil. For example, JP-A-2-21915 discloses a filter medium in which potassium titanate whiskers are mixed with other fibers, and JP-A-7-60027 discloses a method of charging a polypropylene or the like by utilizing the chargeability of carbon particles. There is disclosed an example in which a filter material is formed by using the organic fibers. This focuses on the fact that carbon particles floating in a lubricating oil have a negative charge, and attempts to adsorb the organic fibers by using Coulomb force by positively charged organic fibers.

Japanese Patent Application Laid-Open No. 10-5515 discloses an example in which an organic fiber material is beaten and a fibril-divided ultrafine splitting fiber is mixed with a cationic resin. It utilizes both the effects of physical capture by cations and electrical adsorption by a cationic resin. Therefore, the non-dissolved components such as metal abrasion powder and carbon particles having a relatively large particle diameter are captured by the fibrillated organic fibers, and fine carbon particles are adsorbed by the cationic resin.

[0007]

However, for example, as described in the above-mentioned Japanese Patent Application Laid-Open No. 2-21915,
Filter media in which metal fibers such as potassium titanate whiskers and aluminum silicate are mixed into other fibers such as cellulose,
For filter media mixed with micro glass fibers, these fibers themselves have low affinity for other fibers and are easy to separate, and both metal fibers and glass fibers are hard fibers compared to the material of the part to be lubricated. For this reason, if these fibers are separated from the filter medium, there is a possibility that the wear of the engine may be accelerated. In addition, there are problems such as difficulty in papermaking for uniformly dispersing metal fibers and increase in papermaking cost.

[0008] For example, as described in Japanese Patent Application Laid-Open No. 7-60027 and the like, a filter material obtained by refining organic fibers, a filter material obtained by mixing these with cellulose fibers, and a filter material obtained by mixing a cationic resin are used. The oil temperature rises due to heat generated by the engine as the oil is fibrillated and miniaturized, increasing the viscosity of the lubricating oil due to melting of the fibrillated fine organic fibers and falling off of the cationic resin, There have been problems such as shortening, and reduction in the efficiency of removing carbon particles due to thermal deformation (condensation deformation, etc.) of the fine organic fibers.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and does not mix metal fibers that cause abrasion to be accelerated on lubricated parts and operating equipment such as engines, machine tools, and hydraulic equipment. The oil temperature rises due to the heat generated by the lubricated parts (cooled parts), and the lubricating oil such as engine oil and the operation can be used without using fine organic fibers that may cause condensation heat deformation of the filter medium constituent fibers. It is an object of the present invention to provide a filter medium for capturing and filtering fine particles dispersed in a fuel such as oil, gasoline or light oil, or a fluid such as air with high efficiency.

[0010]

In order to achieve the above object, in the present invention, natural fibers are beaten and freeness is increased by 500.
A filter medium is obtained by containing the fibrillated natural fibers in a volume of not more than ml and making the paper by a known wet papermaking method.

[0011] The mixing ratio of the filter medium containing the fibrillated natural fibers is such that the fibrillated natural fibers are contained in an amount of 10% by weight or more and 60% by weight or less, and the remaining portion is composed of other natural fibers. Is preferred.

Further, the natural fibers to be beaten include:
Cellulose fibers (lyocell) made by directly decomposing wood pulp with an organic solvent are preferred.

In the filter medium constructed as described above, by using fibrillated natural fibers obtained by beating natural fibers to a freeness of 500 ml or less, ultra-fine fiberized natural fibers are uniformly dispersed in unbeaten skeletal fibers. To form fine meshes and moderate voids. For this reason, the filtration life (that is, the problem of clogging), which is a problem when a filter medium having the same filtration efficiency is constituted only by the non-fibrillated natural fibers and the organic fibers, depends on the three-dimensional shape formed between the fibrillated natural fibers. The fine pores and the mesh structure increased the trapped volume of the fine particles, and as described later in detail in the examples, it was possible to achieve a significant improvement.

In addition, by using natural fibers such as cellulose for both the fibrillated fibers and the skeletal fibers, the organic fibers such as polypropylene and acrylic resin do not melt at the oil temperature increased by the heat generated by the engine. There is no increase in the viscosity of the lubricating oil or shortening of the lubricating oil life due to melting or falling off of other mixed resin (for example, the cationic resin in the above example). Furthermore, the deformation of the filter media due to the thermal deformation of the organic fibers and the condensation of the fibrillated organic fibers,
There is no change in filtration efficiency due to melting.

Further, the filter medium according to the present invention can be constituted without including micro glass fibers, metal fibers and the like as in the above-mentioned known examples. Therefore, there is no concern about wear of the lubricated portion such as the engine due to the detachment of these hard fibers.

As the natural fibers to be fibrillated, cellulose fibers (lyocell) made by directly decomposing wood pulp with an organic solvent are suitable, and examples thereof include COURTAULDS LYOCELL and TENCEL manufactured by Coatles. Can be. These fibers are pure cellulose fibers, have high tensile strength and wet strength, do not melt at high temperatures because of the cellulose fibers, and are capable of producing submicron microfibers by beating.

In addition, when the organic fibers are fibrillated by a beater, a portion that becomes microfibers and a portion that is not fibrillated but has the original fiber diameter are formed,
There was a problem that the filter medium pore diameter became uneven when mixed and formed, but the above-mentioned lyocell could be fibrillated separately so as to tear the whole fiber in the fiber direction by beating, and therefore, like organic fiber. There is no unevenness of the pore diameter in the filter medium.

In the present invention, such a natural fiber is beaten in a wet state using a known beater such as a beater or a refiner. Here, if the conditions for reducing the freeness to 500 ml or less are defined by the beating time, when the raw material fiber is 100% lyocell, the beater is approximately 1.5 hours or more using a beater.
With a pulp: lyocell = 2: 1 raw material, it takes about 2 hours or more. When a refiner is used as a beating machine, fibers having substantially the same freeness can be obtained in a beating time of about 1/2 to 1/3 of the above time.

Here, "freeness" is defined in JIS P
Among the pulp freeness test methods specified in 8121,
It represents the freeness measured by the Canadian standard type, and the outline of this measuring method is as follows.

The fibrillated natural fibers obtained as described above are uniformly dispersed in water to prepare a 0.3% aqueous dispersion (raw material) at 20 ° C. Weigh exactly 1000 ml of raw material into a clean measuring cylinder. A drain tube having an inner diameter of 101.6 ± 0.4 mm and a height of 127 mm having a brass sieve plate formed at the bottom of the cylinder having a thickness of 0.51 mm and a hole of 0.51 mm in diameter and having 969 holes per 1000 mm ² on the surface. Pour the contents of the graduated cylinder and open the cock for weighing. When drainage from the side pipe of the measuring funnel arranged at the lower part of the cylinder stops, the amount of drainage from the side pipe is accurately read. The average value obtained by correcting the discharged water amount to a standard concentration standard temperature of 0.3% and 20 ° C. is defined as a Canadian standard freeness, that is, freeness.

Therefore, as the degree of refining of the fibrillated fiber progresses and the fiber becomes finer, the raw material (water dispersion) which uniformly disperses the fiber becomes closer to a slurry, and the measured freeness becomes a smaller value. For example, according to the study of the inventors, the relationship between the beating time and the freeness when beating the lyocell with a beater is such that the beating time is approximately 1.5 hours, the freeness is approximately 500 ml, and then 2 hours. 370m
1, 190 ml for 3 hours and 100 ml for 4 hours.

It is possible to make the freeness smaller (for example, to make the freeness zero) by further lengthening the beating time, but it is over 5 hours (the freeness is about 50). If the beating is continued further, the fiber is gradually cut, and the probability of the number of detached fibers after the paper making increases, and the number of man-hours required for the beating process, that is, the cost, increases. In general, it is preferable to use a beater with a beater having a freeness of about 50 to 500 to obtain a freeness of about 50 to 500 in consideration of the fact that the cost balance is deteriorated.

The filter medium according to the present invention is prepared by weighing and adding fibrillated natural fibers which have been fibrillated so as to have a predetermined freeness by the beater as described above, and other fibers in accordance with the mixing ratio, and is then placed in water. After kneading, the mixture is formed by a known wet papermaking method using a paper machine such as an inclined wire paper machine or a round-mesh multilayer paper machine.

The fibers mixed with the fibrillated natural fibers are not particularly limited. For example, natural fibers such as wood pulp, hemp, cotton, espart, rayon and regenerated cellulose, rayon, acrylic and polyester One or more kinds of organic fibers such as polypropylene, polyamide and the like can be appropriately selected and blended. However, when a lubricating oil having a relatively high temperature such as an engine oil is targeted, it is fibrillated as described above. It is preferable to use natural fibers in order to prevent troubles caused by melting of the fine organic fibers. Further, the filter medium of the present invention can be used with other filter aids as long as the characteristics of the filter medium are not impaired as necessary, or can be blended with additives required for papermaking. The remainder includes these.

The present invention is a lubricating oil filter using a filter medium containing fibrillated natural fibers in an amount of 20% by weight or more among the filter media thus formed.

Further, the present invention is a fuel filter using a filter medium containing 40% by weight or less of fibrillated natural fibers among the filter media thus formed.

The mixing ratio of the fibrillated fiber is about 1 from the results of a veneer cleanliness test and an element dust injection test described later.
At a mixing ratio of 0% or more, an effect of improving the filtration efficiency can be found. Thus, the higher the mixing ratio, the lower the cleanliness of the veneer, that is, the amount of residual particles after filtration, but the air permeability has the opposite relationship. When the mixing ratio is increased to more than 60%, the fluid is increased. This causes an adverse effect that the passage resistance of the wire becomes excessive.

Therefore, when such a filter medium is used as a filter, there is an appropriate mixing ratio depending on the use. For example, in a lubricating oil bypass filter or the like that contains a relatively large amount of metal powder or carbon particles and does not require too much fluid flow per unit time,
It is preferable that the fibrillated natural fibers are mixed at about 20 to 60% and the other cellulose fibers are mixed at about 80 to 40% to be mixed and formed.

In the case of a full flow type fuel filter or the like having relatively few fine particles such as metal powder and carbon particles, the fibrillated fiber is set to 10 to 40% and the other cellulose fibers are set to 90 to 60%. It is preferable to mix and make a paper.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a filter medium according to the present invention will be described more specifically with reference to examples. The blending ratio of the blending material is indicated by weight%.

Example 1 Cellulose fiber manufactured by Coatles Co., Ltd., trade name: COURTAULDS L
YOCELL (hereinafter simply referred to as lyocell) was beaten for 2 hours in a wet state with a test beater, and mixed with 10% (A1), 33% (A2) and 100% (A3) of natural fiber. Pulp slurry blended into wood pulp,
After papermaking by a known wet papermaking method, the paper was air-dried and the dry weight was 3
After preparing a sheet having a thickness of about 1 mm and a filtration area of 9.6 g / m ^2.
A sample of cm ² was prepared.

Comparative Example 1 5% of micro glass fibers having a fiber diameter of 5 μm or less
(a1) A pulp slurry blended in wood pulp at a blending ratio of 10% (a2) is made into paper by a known wet papermaking method and then air-dried to prepare a sheet having a dry weight of 200 g / m ^{2 and a} thickness of 0.7 mm. Thereafter, a comparative sample having a filtration area of 9.6 cm ² was prepared.

The test pieces A1 to A3 and a1 to a2 are subjected to a veneer cleanliness test shown below, and the vapour cleanliness of the filtrate is measured. As a contaminant to be used for measurement, light oil 5 previously filtered through a 0.8 μm membrane filter was used.
60 mg of JIS type 8 powder was placed in 0 ml, and the powder was uniformly dispersed in light oil using an ultrasonic stirrer or the like.

After the contaminant is subjected to one-pass suction filtration with the test sample, the filtrate that has passed through the test sample is filtered again through a 0.8 μm membrane filter whose weight is measured in advance and whose weight is known. By heating and drying the membrane filter after this filtration and weighing, by calculating the weight increase before and after filtration, i.e., the amount of captured powder,
Evaluate the veneer cleanliness in mg units.

The results obtained by the above tests are summarized in Table 1. The air permeability in the table is based on JIS P8117.
Represents the gas permeation time measured by the air permeability test method specified in, and is expressed in seconds.

[0036]

[Table 1]

From the results, it was found that the mixing ratio of lyocell was 10%.
However, it is possible to obtain almost the same cleanliness as a filter medium obtained by mixing 5 to 10% of microglass fibers, which is generally said to have a high carbon particle removing effect, and to obtain higher cleanliness as the mixing rate is increased. To be found.

Example 2 Lyocell was moistened with a test beater for 2 hours (B1 to B4),
The fibrillated natural fibers beaten for 3 hours (B5 to B8) and for 6 hours (B9 to B12) are respectively 15% (B1, B5, B9) and 30% (B2, B6, B).
A pulp slurry blended in wood pulp at a mixing ratio of 10), 45% (B3, B7, B11) and 60% (B4, B8, B12) was formed into paper by a known wet papermaking method, air-dried, and dried. 295-
After preparing a sheet having a thickness of 305 g / m ^{2 and a} thickness of about 1 mm, the filtration area is 9.
Samples B1 to B12 of 6 cm ² were obtained.

COMPARATIVE EXAMPLE 2 A 100% cellulose fiber was placed in a wet state with a test beater.
The fibers beaten for a given time were made by a known wet papermaking method and then air-dried to prepare a sheet having a dry weight of 295 g / m ^{2 and a} thickness of about 1 mm, and a comparative sample b1 having a filtration area of 9.6 cm ² was obtained.

The specimens B1 to B12, b1 are subjected to the following single plate cleanliness test to measure the filtration efficiency of the filter medium. As a contaminant to be used for measurement, 50 m of light oil previously filtered through a 0.45 μm membrane filter was used.
Into l, 100 mg of JIS 12 type powder was charged, and the powder was uniformly dispersed in light oil using an ultrasonic stirrer or the like.

After the contaminant is subjected to one-pass suction filtration using the test sample, the filtrate that has passed through the test sample is filtered again through a 0.45 μm membrane filter whose weight is measured in advance and whose weight is known. After this filtration, the membrane filter is dried by heating and weighed, the weight increase before and after filtration, that is, the amount of captured powder is calculated, and the filtration efficiency is calculated by the following equation. Filtration efficiency (%) = {(initial amount of powder−amount of captured powder) / initial amount of powder} × 100

The results obtained by the veneer cleanliness test are summarized in Table 2, and from this data, the relationship between the mixing ratio and the filtration efficiency is shown in FIG. 1, and the relationship between the beating time and the filtration efficiency is shown in FIG. Shown in

[0043]

[Table 2]

From these results, even when the beating time is 2 hours, the filtration efficiency is far higher than that of a filter medium obtained by beating general cellulose fibers for 5 hours.
By increasing the above, a high-efficiency filter medium with a filtration efficiency of 90% or more can be obtained, and when the beating time is 3 hours or more, it is high at least in the region of 15% or more of the mixing ratio, regardless of the mixing amount. It can be seen that a filter medium having filtration efficiency can be provided.

Example 3 A fibrillated natural fiber obtained by beating a lyocell with a test beater in a wet state for 3 hours was used.
(C1), 33% (C2), and 45% (C3), and the filter media characteristics such as paper thickness (0.8 mm), air permeability (110 seconds), and pore size (2 μm) are almost the same. Paper was formed and further formed into an element shape to obtain test filter media C1 to C3.

A simple element dust injection test was performed on these test filter media under the following conditions. Table 3 shows the test conditions and Table 4 shows the test results.

[0047]

[Table 3] 1) Oil used 2 liters of actual machine oil (initial solid content 4%) 2) Input dust Approx. 2.4 g of JIS 12 class powder and 30 ml of actual machine concentrated oil 25% total concentration 30% after 1 hour from the start of the test once every minute charged 3) filtered state maintaining constant pressure circulation test (inlet pressure constant at 392 kPa) 4) test temperature 80 ° C. 5) filtering area 2500 cm ² 6) measuring method measuring in-oil carbon concentration at each measurement time 7) Efficiency Efficiency is calculated and evaluated using the following formula. Efficiency (%) = {(cumulative concentration−concentration at each measurement time) / cumulative concentration} × 100

[0048]

[Table 4]

From this example, when a filter medium using fibrillated natural fibers is used as a filter for lubricating oil,
It is understood that the mixing rate is preferably about 20% or more, and particularly, a preferred embodiment is obtained when the mixing rate is 30% or more.

Example 4 In the same manner as in Example 3, a test element D4 having a fibrillated natural fiber blending rate of 33% was obtained.

Comparative Example 4 A filter medium having 100% of natural cellulose fiber, an average pore diameter of 1 μm, and an air permeability of 150 seconds or more, which is generally used as a bypass filter for vehicle engine oil, was used as in Example D4. A comparative test element d4 was obtained by forming the same element shape.

With respect to these test elements D4 and d4, the flow reduction characteristics of the test engine during long-time operation were measured under the following experimental conditions. Table 5 shows the test conditions at this time.

[0053]

[Table 5] 1) Oil used 8 liters of engine oil 2) Test temperature 100-110 ° C 3) Filtration area 2500 cm ² 4) Operating conditions Engine rated continuous operation 5) Operating time 150 hours 6) Measuring method Circulating flow at regular time intervals Is measured with a flow meter

The flow rate reduction characteristics obtained under the above test conditions are as follows:
As shown in FIG. 3, the comparison element d4 using a general filter medium for a bypass filter was changed from the initial several hours to 1 as shown in FIG.
At about 0 hours, the flow rate suddenly drops, and after about 20 hours, it becomes 1/5 or less of the initial flow rate.
On the other hand, the test element D4 containing the fibrillated natural fiber had a flow rate reduction of about 70 hours in the initial stage, but had a gradual decrease characteristic. And
Even after 150 hours, the flow rate is 1/1 of the initial flow rate.
Two or more are secured.

The amount of dust captured by each element at the end of the test, ie, after 150 hours, was measured in Comparative Example d4.
Was 16.5 g, while Example D4 according to the present invention was used.
Weighed 30.2 g, which proved to have a high trapping effect.

[0056]

As described above, according to the filter medium of the present invention, the filter medium comprises fibrillated natural fibers obtained by beating natural fibers to a freeness of 500 ml or less. As a result, it is possible to achieve both a significant improvement in filtration efficiency and a longer filtration life as compared with the case where the fiber is constituted only by other fibers which are not fibrillated.

As the natural fibers to be beaten, it is preferable to use cellulose fibers made by directly decomposing wood pulp with an organic solvent. The mixing ratio in the filter medium is from 10% by weight to 60% by weight of fibrillated natural fibers. Preferably, the remaining portion is made of another natural fiber. With this configuration, high filtration efficiency can be obtained, and the organic fiber does not melt at the oil temperature increased by the heat generated by the engine. There is no increase in the viscosity of the lubricating oil or a reduction in the life of the lubricating oil due to the falling off of the oil. Further, the deformation of the filter medium and the change in the filtration efficiency due to the thermal deformation of the organic fibers do not occur.

Further, in the filter medium according to the present invention, hard metal fibers such as potassium titanate and aluminum silicate, micro glass fibers and the like are not mixed. Therefore, there is no concern that the detachment of these fibers may cause abrasion to be accelerated on parts to be lubricated such as an engine or operating parts of a hydraulic circuit.

Further, the fibrillated natural fibers used in the filter medium according to the present invention are made from wood pulp and can be obtained at a low cost. For this reason, it is possible to improve the problems in the production of the filter medium, such as the cost of the mixed paper material and the increase in the papermaking cost, as in the case of mixing the metal fibers and the finely divided organic fibers. Therefore, it is possible to provide a filter medium having an increased carbon capture ratio at a low cost by a simple method.

The filter medium as described above has a high effect when used as a filter element for a vehicle. For example, the filter medium contains a relatively large amount of metal powder, carbon particles, etc. and has a low fluid flow rate per unit time. In a lubricating oil bypass filter or the like that does not require a large amount, a suitable lubricating oil filter is prepared by mixing the above fibrillated natural fibers to 20 to 60% and other cellulose fibers to about 80 to 40%, and forming the mixture. Can be obtained.

In a full-flow type fuel filter or the like having a relatively small amount of fine particles such as metal powder and carbon particles, the fibrillated fiber is set to 10 to 40% and the other non-fibrillated cellulose fiber is set to 90 to 90%. 60
%, A suitable fuel filter can be obtained.

[Brief description of the drawings]

FIG. 1 is a graph summarizing the results of veneer cleanliness tests performed using Examples B1 to B12 of the filter medium according to the present invention and showing the relationship between the mixing ratio and the filtration efficiency.

FIG. 2 is a graph showing the relationship between beating time and filtration efficiency, summarizing the results of veneer cleanliness tests performed using Examples B1 to B12 of the filter medium according to the present invention.

FIG. 3 is a graph showing flow characteristics during long-term continuous operation performed using Example D4 and Comparative Example d4 of the filter medium according to the present invention.

Claims (5)

[Claims] Claims 1. A natural fiber is beaten, and the freeness is 500.
A filter medium characterized by containing fibrillated natural fibers in a volume of not more than 0.1 ml. 2. 10% by weight of the fibrillated natural fibers
The filter medium according to claim 1, wherein the content is at least 60% by weight and the remaining portion is made of other natural fibers. 3. The filter medium according to claim 1, wherein the natural fiber to be beaten is a cellulose fiber made by directly decomposing wood pulp with an organic solvent. 4. The method according to claim 1, wherein the fibrillated natural fibers are 20% by weight.
A lubricating oil filter using the filter medium according to claim 2 or 3 containing the above. 5. The method according to claim 5, wherein the fibrillated natural fiber is 40% by weight.
A fuel filter using the filter medium according to claim 2 or 3, which contains: