JP6681160B2 - Filter material for automobile engine - Google Patents

Description

  The present invention relates to a non-woven filter material for pleated type filters, and more particularly to a non-woven filter material having high rigidity, low ventilation resistance, high collection efficiency and high collection amount, which is suitable for an engine filter for automobiles.

  2. Description of the Related Art Conventionally, automotive engine filters have been required to have high collection efficiency for fine dust and long filter life. As a measure, for example, Patent Documents 1 and 2 disclose a laminated non-woven fabric in which a coarse layer, an intermediate layer, and a dense layer are laminated in the thickness direction of a filter medium so that the average fineness is gradually reduced to provide a density gradient. Has been done. Further, Patent Documents 3 to 4 disclose a method of performing electret processing on fibers to improve collection efficiency. Furthermore, Patent Documents 5 to 6 describe methods using a nonwoven fabric made of ultrafine fibers produced by a melt blow method or the like. In addition, Patent Documents 7 to 8 disclose methods of increasing dust collection efficiency by using ultrafine fibers such as split fibers and nanofibers. Further, conventionally, there is also known a technique of applying a resin to the surface of a non-woven fabric to increase the density in order to improve the collection efficiency. In particular, if the coating liquid is foamed during application, a microporous film can be formed on the nonwoven fabric when the bubbles in the foam coating material are broken, and the presence of this microporous film allows the filtration efficiency to be improved. It is possible to raise.

  On the other hand, conventionally, as a fiber constituting a non-woven fabric, a technique using a fiber obtained by treating raw cotton with an oil agent such as silicone oil is known. Patent Document 9 discloses an air cleaner filter medium for an internal combustion engine, which comprises only fibers treated with an oil agent such as modified dimethyl silicone. Further, Patent Document 10 discloses a needle-punched nonwoven fabric containing silicone-processed fibers as constituent fibers, wherein the entangled states of constituent fibers are different in the thickness direction, and mattresses, bedclothes such as bedding, and the like. A fiber structure suitable for use in the fields of interior furniture such as chairs and sofas and middle materials of vehicle seats is disclosed.

JP, 10-180023, A JP, 2004-243250, A JP, 2010-142703, A Japanese Patent Laid-Open No. 2001-246221 JP, 2008-075227, A JP, 2002-266219, A JP, 2010-281012, A JP, 2010-058328, A JP-A-1-104317 JP-A-2000-220068

  As described above, in the field of filter media, various measures for achieving high rigidity, low ventilation resistance, high collection efficiency and high collection amount have been studied, but a higher level of collection efficiency is demonstrated. In order to do so, for example, a method of further thinning the fibers constituting the filter medium (for example, Patent Documents 5 to 8) and thickening the filter medium can be considered. However, in the former case, if the fibers are thinned to reduce the porosity of the non-woven fabric, the air permeability is also lowered, and the air flow resistance is increased. Then, the filter medium is apt to be clogged, and as a result, there is a problem that the filter life is shortened and the trapping amount is also reduced. In the latter case, if the filter medium is made thicker, it becomes difficult to pleat it, and the surface area of adjacent pleats in the pleated filter medium may reduce the substantial filtration area. If the filtration area is reduced, it becomes difficult to improve the collection efficiency, and the pressure loss increases due to the surface contact, which causes a problem that the filter life becomes short.

  In recent years, filter materials having higher collection efficiency, higher collection amount, and longer life are required. On the other hand, in order to reduce the manufacturing cost of the filter medium, it is necessary to manufacture the filter medium at a lower cost without using the electret-processed fiber or the foamed coating material in the non-woven fabric filter medium.

  Under such circumstances, the present invention has a problem of providing a filter medium having high rigidity, low ventilation resistance, high collection efficiency and high collection amount, and suitable for a long-life automobile engine filter. I raised it.

  As a result of repeated intensive studies to solve the above problems, the present inventors have found that a dense layer, an arbitrary intermediate layer, and a rough layer are a nonwoven fabric filter material integrated by a mechanical entanglement method, and the dense layer is When the intermediate layer is provided, the proportion of the low-melting fiber in the intermediate layer is 40% by weight, when the intermediate layer is provided, the base fiber having silicone oil adhered to a part or all of it and the low-melting point fiber of 57% by weight or more and less than 100% by weight. The present invention has been completed by finding that the above filter media can exhibit high rigidity, low ventilation resistance, high collection efficiency and high collection amount.

  In order to improve the collection efficiency, if the fiber diameter (fineness) of the fibers used in the filter medium is reduced or the number of fibers is increased to reduce the voids for capturing the dust, the fiber surface area increases and It is effective because the collision rate of the fibers increases. In addition, since the filter medium must withstand a large amount of air during use and maintain its pleated shape, it is rare that heat-meltable low melting point fibers are used in the filter medium so that the pleated shape is stable during use. Absent. However, if the nonwoven fabric is processed under strong needle punching conditions by increasing the amount of low melting point fibers contained in the filter medium for the purpose of simply increasing the collection efficiency (increasing the density) and improving the rigidity (maintaining the shape of the pleats), the filter medium itself becomes hard and has a low elongation. There is a possibility that breakage will occur during pleating and molding. However, according to a study made by the present inventors, in order to prevent excessive fiber entanglement between layers, by blending base fibers to which silicone oil adheres in a dense layer, the same elongation as a conventional non-woven filter medium is obtained. It was found that a filter medium having an excellent degree was obtained, and it was a filter medium having high collecting efficiency, high collecting amount, low ventilation resistance, and excellent moldability.

In particular, if the content of low melting point fibers increases, the amount of low melting point fibers melted when molded into an element shape and the flange part becomes harder, resulting in poor resilience and a gap in the seal part of the housing and dust leakage. Although there is a possibility that it will occur, if base fibers with silicone oil adhered to the dense layer are mixed within a predetermined range, the base fibers with silicone oil adhere to the low melting point fibers even if they are compressed by heat when the flange is formed. Since it is hard to be compressed and the compressive stress is easily released, the shape before the compression can be maintained when the compression is released. As a result, the filter material of the present invention is not inferior in resilience and thickness recoverability as compared with the conventional filter material having a low low melting point fiber content.
In addition, since the dense layer contains fibers to which silicone oil is attached, the boundaries between the layers do not become unclear due to mechanical entanglement when integrating the layers, and the original function of each layer is sufficient. It was demonstrated, and as a result, high rigidity, low ventilation resistance, high trapping efficiency and high trapping amount were improved.

That is, the filter medium according to the present invention has the following points.
[1] A two-layer structure having a coarse layer and a dense layer having different fiber densities, or a three-layer structure in which a coarse layer, an intermediate layer, and a dense layer are laminated in this order, and each layer is a mechanical entanglement method. A non-woven filter medium integrated by
The dense layer includes a base fiber having silicone oil attached to a part or all of the dense fiber, and a low melting point fiber having a lower melting point than the base fiber, and the intermediate layer includes at least a low melting point fiber,
A filter medium characterized in that the proportion of low-melting fibers in the dense layer is 57% by weight or more and less than 100% by weight, and the proportion of low-melting fibers in the intermediate layer is 40% by weight or more.
[2] The filter medium according to [1], wherein the base material fibers to which silicone oil adheres are contained in an amount of 1% by weight to 43% by weight in 100% by weight of the dense layer.
[3] The filter medium according to [1] or [2], in which the entanglement density of the dense layer is higher than the entanglement density of the coarse layer.
[4] the fiber density difference dense layer and the intermediate layer is a 0.076~0.120g / cm ^3, the fiber density difference of the intermediate layer and the rough layers are 0.040~0.067g / cm ³ [ The filter material according to 1] to [3].
[5] The filter medium according to [1] to [4], which has a basis weight of 180 to 550 g / m ² and a thickness of 4 to 8.5 mm.
[6] The filter medium according to [1] to [5], wherein the rough layer is a silicone oil-free layer having a content of fibers to which silicone oil adheres is 20% by weight or less.
[7] The filter medium according to [1] to [6], wherein the dense layer has a flat surface without protrusions.

  According to the present invention, a filter medium having high rigidity, low ventilation resistance, high collection efficiency and a high collection amount can be obtained.

FIG. 1 is a schematic cross-sectional view showing an example of an embodiment of the filter medium according to the present invention.

<< filter material >>
FIG. 1 is a schematic cross-sectional view showing an example of an embodiment of the filter medium according to the present invention. The filter medium 10 according to the present invention has a three-layer structure in which a coarse layer 3, an intermediate layer 2, and a dense layer 1 having different fiber densities are laminated in this order, and the layers are integrated by a mechanical entanglement method. It is a filter medium. Since the intermediate layer 2 is an arbitrary layer, the filter medium 10 in the present invention may have a two-layer structure having the rough layer 3 having no intermediate layer 2 and the dense layer 1.

The dense layer 1, the intermediate layer 2 and the rough layer 3 are all made of nonwoven fabric. The dense layer 1 has a function of capturing fine particles having a small particle size. Further, the rough layer 3 has a function of capturing dust having a relatively large particle size. The intermediate layer 2 has a function of capturing dust that could not be captured by the rough layer 3 and adjusting the amount of dust captured by the dense layer 1 in order to prolong the filter life. That is, the filter medium 10 has a density gradient that becomes high density in the order of the coarse layer 3, the intermediate layer 2, and the dense layer 1 (if the intermediate layer 2 is not provided, the coarse layer 3 and the dense layer 1 in this order). There is.
The dense layer 1, the intermediate layer 2, and the rough layer 3 are all non-woven fabrics, but as described later, the filter medium 10 is a method of integrating a web and a laminate including the non-woven fabric by a mechanical entanglement method. It is manufactured by a method of integrating the laminated body of 1., a method of integrating the laminated body of the non-woven fabric, or the like.

In the present invention, the dense layer includes a base fiber having a silicone oil adhered to a part or all of the dense fiber, and a low melting point fiber having a lower melting point than the base fiber, and the proportion of the low melting point fiber in the dense layer is It is 57% by weight or more and less than 100% by weight, and the proportion of low melting point fibers in the intermediate layer is 40% by weight or more. If the dense layer does not contain the base material fibers to which silicone oil adheres, the fibers will be entangled during needle punching, resulting in a thin filter medium, so high collection efficiency and high collection amount cannot be achieved. There is a risk. In addition, if the dense layer is composed of only low melting point fibers, the low melting point fibers after heat treatment become like a film, and the space for collecting dust is reduced, so the collection efficiency and collection amount are reduced. Will fall.
The dense layer may further include base fibers to which silicone oil is not attached.

  When the intermediate layer is provided, the intermediate layer contains at least the low melting point fiber, and the proportion of the low melting point fiber in the intermediate layer needs to be 40% by weight or more. If the proportion of the low-melting-point fibers in the intermediate layer decreases, the rigidity of the filter medium itself will decrease, and it may not be possible to achieve high collection efficiency and high collection amount. The intermediate layer may further include a base fiber having silicone oil attached to a part or the whole thereof and a base fiber having no silicone oil attached thereto.

  The rough layer may include a base fiber having silicone oil adhered to a part or all thereof, a base fiber having no silicone oil adhered thereto, and a low melting point fiber having a lower melting point than the base fiber. .

  In the present invention, the fineness of the fibers contained in each layer (dense layer, intermediate layer and rough layer) is preferably 0.8 to 33 dtex, more preferably 1.3 to 17 dtex, and further preferably, regardless of the type of fiber. Is 1.5 to 10 dtex. When the fineness is within the above range, the filter medium can be provided with appropriate rigidity and the fibers can be sufficiently entangled.

  The fibers used in each layer are preferably short fibers having a fiber length of 100 mm or less (more preferably 20 to 100 mm, further preferably 32 to 76 mm). When the amount exceeds the upper limit, the defibration property on a card machine deteriorates, which is not preferable.

  Hereinafter, the filter material of the present invention will be described in detail, but the term “intermediate layer” in the specification means that it is optionally provided.

<Base fiber (Si fiber) with silicone oil attached>
In the present invention, the fibers forming the skeleton of each layer (hereinafter referred to as “base fiber”) include base fibers to which silicone oil is attached and base fibers to which silicone oil is not attached.

  The base fiber to which silicone oil is attached is a fiber whose surface is coated with silicone oil. By using the base material fibers to which the silicone oil is attached, the friction resistance between the fibers and / or between the fibers and the metal (for example, the needle) is reduced. When the frictional resistance becomes small, the fibers are slippery and the entanglement between the fibers is deteriorated, and the nonwoven fabric becomes sparse. Since the fibers are not over-congested more than necessary, the dust (especially dust with a small particle size) can be efficiently collected, and the effect of increasing the difference between the charged columns with the upper dust is exhibited, resulting in the dust collection. It is possible to improve the collection amount.

  Examples of the fibers include polyester fibers such as polyethylene terephthalate fibers, polybutylene terephthalate fibers, polylactic acid fibers, and polyarylate fibers; polyamide fibers such as nylon 6, nylon 66, and aramid fibers (para-aramid fibers, meta-aramid fibers, etc.). And acrylic fibers such as polyacrylonitrile fiber and polyacrylonitrile-vinyl chloride copolymer fiber; polyolefin fibers such as polyethylene fiber and polypropylene fiber; polyphenylene sulfide fiber; and various synthetic fibers. Among them, polyester fiber is preferably used, and polyethylene terephthalate fiber is particularly preferable because of good balance between performance and price.

  The silicone oil is not particularly limited as long as it can reduce the friction resistance between fibers and / or fibers-metals, but as a treatment agent for fibers (for example, a treatment agent for improving the texture of fibers) Widely used silicone oils are preferred. Examples of the silicone oil include polydimethylsiloxane, polymethylphenylsiloxane, amino-modified silicone oil, polyether-modified silicone oil, alkyl-polyether-modified silicone oil, amino-modified silicone oil, and the like, with polydimethylsiloxane being preferred.

  The silicone oil is preferably contained in an amount of 0.05 to 5% by weight, more preferably 0.1 to 3% by weight, based on 100% by weight of the fiber. When the amount of silicone oil is within the above range, the frictional resistance at the time of entanglement is sufficiently reduced, and the degree of entanglement of fibers is appropriate, so that the shape of the filter medium can be maintained.

Further, the base fiber to which the silicone oil is attached is preferably contained in an amount of 1 to 45% by weight, more preferably 5 to 40% by weight, based on 100% by weight of each layer. When the content is within the above range, the fibers can be sufficiently entangled while the frictional resistance is sufficiently reduced.
In particular, 100% by weight of the dense layer contains 1% by weight or more of the base fiber to which silicone oil is attached, more preferably 5% by weight or more, and further preferably 8% by weight or more. The upper limit is preferably 43% by weight or less, more preferably 30% by weight or less, and further preferably 15% by weight or less. When the content is within the above range, a filter medium having an excellent balance of ventilation resistance and collection performance can be obtained, which is preferable.
Similarly, in 100% by weight of the intermediate layer, the amount of the base fiber to which the silicone oil is attached is preferably 1% by weight or more, more preferably 2% by weight or more, and further preferably 4% by weight or more. The upper limit is preferably 45% by weight or less, more preferably 20% by weight or less, further preferably 15% by weight or less, and particularly preferably 12% by weight or less. When the content is within the above range, a filter medium having an excellent balance of ventilation resistance and collection performance can be obtained, which is preferable. If the base fibers to which silicone oil adheres are contained beyond the specified range, the adhesive strength between the fibers will decrease and the rigidity will not be maintained, or the friction resistance will decrease when the filter media is cut to the required size. Therefore, it may not be possible to cut into a clean cross section, which is not preferable.
In addition, the rough layer is preferably a silicone oil-free layer in which the content of fibers to which silicone oil adheres is 20% by weight or less, more preferably 12% by weight or less, further preferably 8% by weight or less. It is particularly preferably 5% by weight or less. Since the fibers used in the rough layer are thicker than the fibers used in the dense layer and the intermediate layer, it is originally difficult to entangle the fibers. Therefore, since the fibers in the coarse layer are sufficiently entangled with each other, the coarse layer does not substantially contain the base fiber to which the silicone oil is attached (that is, 0 to 2% by weight, and more preferably 0% by weight). ˜1% by weight, particularly preferably 0% by weight).

The fineness of the base fiber (referred to as "Si fiber") to which silicone oil is attached is preferably 0.8 to 33 dtex, more preferably 1.3 to 17 dtex, and further preferably 1.5 to 10 dtex. When the fineness is within the above range, the filter medium can be provided with appropriate rigidity and the fibers can be sufficiently entangled.
The fineness of the Si fibers contained in the dense layer is preferably 0.8 to 3 dtex, more preferably 1.5 to 2.8 dtex, and further preferably 1.7 to 2.5 dtex.
The fineness of the Si fiber contained in the intermediate layer is 3 to 7 dtex, more preferably 3.5 to 5.5 dtex, and further preferably 4 to 4.6 dtex.
Further, the fineness of the Si fiber contained in the rough layer is 3 to 5 dtex, more preferably 3.5 to 4.8 dtex, and further preferably 4 to 4.6 dtex.

From the viewpoint of increasing the collection efficiency of the filter medium, it is desirable that the dense layer contains 20 to 43% by weight of the base material fiber to which the silicone oil is attached, and preferably 35 to 43% by weight. It is desirable that the other fiber constituting the fiber is a low melting point fiber.
From the viewpoint of reducing the ventilation resistance of the filter medium, it is desirable that the dense layer contains 5 to 15% by weight, and preferably 5 to 10% by weight, of the base fiber to which the silicone oil adheres. The other constituent fibers are preferably low melting point fibers.

<Base fiber without silicone oil (R fiber)>
Examples of the base fiber to which the silicone oil is not attached include synthetic fiber, regenerated fiber, natural fiber and the like.
Examples of synthetic fibers include polyester fibers such as polyethylene terephthalate fiber, polybutylene terephthalate fiber, polylactic acid fiber, and polyarylate fiber; polyamide fibers such as nylon 6, nylon 66, and aramid fiber (para-aramid fiber, meta-aramid fiber, etc.). Examples thereof include acrylic fibers such as polyacrylonitrile fibers and polyacrylonitrile-vinyl chloride copolymer fibers; polyolefin fibers such as polyethylene fibers and polypropylene fibers; polyphenylene sulfide fibers; and the like.
Examples of the recycled fiber include rayon, polynosic, cupra and lyocell.
Examples of natural fibers include cotton, pulp, kapok, hemp, wool, silk, and the like.
Among them, the polyester fiber is preferable as the base fiber to which the silicone oil is not attached, and the polyethylene terephthalate fiber is particularly preferable because of good balance between performance and price. The base fibers in each layer may be the same or different.

Content of base fibers to which silicone oil adheres in a dense layer (referred to as "Si fibers") and base fibers to which silicone oil does not adhere (referred to as ordinary fibers, referred to as "R fibers") Is preferably 0: 100 to 100: 0 in terms of weight ratio (Si fiber: R fiber). Since the collection performance is improved by using Si fiber, it is preferably 45:55 to 100: 0, and more preferably Is 90:10 to 100: 0, more preferably 95: 5 to 100: 0, and particularly preferably 100: 0.
The content ratio of Si fibers and R fibers in the intermediate layer is preferably 0: 100 to 100: 0 in terms of weight ratio (Si fibers: R fibers), and more preferably 20:80 in order to adjust the degree of entanglement of fibers. To 80:20, more preferably 30:70 to 70:30, and particularly preferably 40:60 to 60:40.
The content ratio of Si fiber and R fiber in the rough layer is preferably 0: 100 to 100: 0 in weight ratio (Si fiber: R fiber), and more preferably 10:90 to 10 to promote entanglement of fibers. It is 0: 100, more preferably 5:95 to 0: 100, and particularly preferably 0: 100.

  The fineness of the base fiber (referred to as “R fiber”) to which silicone oil is not attached is preferably 0.8 to 33 dtex, more preferably 5 to 25 dtex, and further preferably 10 to 20 dtex. When the fineness is within the above range, the filter medium can be provided with appropriate rigidity and the fibers can be sufficiently entangled.

  As the above-mentioned base fiber, either solid fiber or hollow fiber can be used. Further, the cross-sectional shape of the fiber is not particularly limited, and a round cross section; an irregular cross section such as a triangular cross section, a star cross section, a Y-shaped cross section, or a cross section; The modified cross-section fiber is effective as a means for adjusting the fiber density of the filter medium.

  Further, the above-mentioned base fiber may be a fiber having a three-dimensional crimp such as a coil shape or a spiral shape. In particular, it is preferable that the rough layer contains the three-dimensional crimped fiber because it is possible to suppress the reduction of the thickness due to ventilation and dust load, and it is possible to increase the trapped amount.

<Low melting point fiber>
In addition, the fibers constituting each layer have a melting point lower than that of the base fiber forming the skeleton of each layer so that the formed pleats have a sharp shape, and a heat-meltable fiber (hereinafter referred to as “low melting point fiber”). , Which is a composite fiber having a low melting point portion). The low-melting point fibers have a function of adhering the fibers constituting the filter medium, because a part or all of the fibers are melted by heat treatment. By cooling after heat treatment, the melted low-melting point fiber solidifies, increasing the adhesive strength of the fiber and imparting appropriate strength to the filter medium, so that the size of the filter medium is stable and the filter medium has appropriate rigidity. Can be given. Further, for fixing the fibers, it is common to perform a treatment such as an impregnation process, a spraying process, or a foaming process using an emulsion or latex containing an adhesive resin. It is necessary to dry the water contained therein, which requires a great deal of energy. However, use of a low melting point fiber is preferable because such a problem can be solved. In the present invention, the low melting point fiber is preferably contained in all of the dense layer, the intermediate layer and the rough layer.

  The upper limit of the melting point of the low melting point fiber is preferably 30 ° C. or less from the melting point of the base fiber. When the difference in melting point becomes small (for example, 30 ° C. or less), when heat treatment is performed to melt the low melting point fiber, if an abnormality occurs in the temperature due to some trouble, the fiber is softened or melted to cause thermal deterioration. It is not preferable because it may cause On the other hand, the lower limit of the melting point of the low melting point fiber is preferably 150 ° C. or lower, more preferably 100 ° C. or lower than the melting point of the fiber, so that the low melting point fiber is sufficiently softened or melted. The melting point of the low melting point fiber is preferably 50 to 180 ° C, more preferably 70 to 120 ° C.

  As the low melting point fiber, a composite fiber having a core-sheath structure, an eccentric structure, or a side-by-side structure made of a plurality of resins having different melting points such as polyethylene-polypropylene and polyester-modified polyester; modified polyester fiber; modified polyamide fiber; modified polypropylene Modified polyolefin fibers such as fibers; and the like can be used. In the present invention, the composite fiber is preferably used so that the resin in the low melting point portion functions as an adhesive and the fiber in the high melting point portion functions as a fiber constituting the filter medium, and particularly, one having a core-sheath structure excellent in mechanical properties is preferable. .

The fineness of the low melting point fiber is preferably 0.8 to 40 dtex, and more preferably 1.5 to 25 dtex. When the fineness of the low melting point fiber is within the above range, the low melting point fiber is easily melted, and the heat treatment time can be shortened. The low melting point fiber and the base fiber forming each layer may have the same or different fineness.
The low melting point fiber also preferably has a gradient in the dense layer, the intermediate layer and the rough layer.
The fineness of the low melting point fibers contained in the dense layer is preferably 0.8 to 3 dtex, more preferably 1.5 to 2.8 dtex, and further preferably 1.7 to 2.5 dtex. By mixing the low-melting-point fibers having a fineness in the dense layer, a filter medium having a high rigidity and a low pressure loss and a high collection efficiency can be obtained by the core portion having a fineness that remains after the low-melting fibers are melted.
The fineness of the low melting point fiber contained in the intermediate layer is preferably 3 to 5 dtex, more preferably 3.5 to 4.8 dtex, and further preferably 4 to 4.6 dtex.
Furthermore, the fineness of the low melting point fiber contained in the rough layer is preferably 3 to 40 dtex, more preferably 3.5 to 25 dtex, and further preferably 4 to 20 dtex.

In the present invention, in order to impart rigidity to the filter medium, it is preferable that the content of the low melting point fiber is as high as possible. However, if it is too large, the space between the fibers may be reduced and the amount of dust collected may be decreased. Therefore, the content of the low melting point fiber in the dense layer is 57% by weight or more and less than 100% by weight, preferably 75% by weight or more, more preferably 85% by weight or more, and preferably 98% by weight or less. Yes, and more preferably 95% by weight or less. When the content of the low melting point fibers in the dense layer is high, it is easy to maintain a sharp shape when pleated, and the shape does not change during ventilation to cause fold contact, which is preferable.
In the intermediate layer, 40% by weight or more, preferably 57% by weight or more, more preferably 75% by weight or more, further preferably 85% by weight or more, preferably 100% by weight or less, It is preferably 98% by weight or less, and more preferably 95% by weight or less.
In the rough layer, it is preferably 20% by weight or more, preferably 57% by weight or more, more preferably 75% by weight or more, further preferably 85% by weight or more, preferably 100% by weight or less, It is preferably 98% by weight or less, and more preferably 95% by weight or less.
The content of the low-melting point fiber is as described above, but the rest other than the low-melting point fiber in each layer is a one-component system of the base material fiber to which the silicone oil is attached and / or the base material fiber to which the silicone oil is not attached. Alternatively, it is preferably a two-component system.

  The above-mentioned silicone oil may be attached to the low melting point fiber.

<Unit weight>
The basis weight of the filter medium is 180 to 550 g / m ² , more preferably 230 to 500 g / m ² , and further preferably 280 to 450 g / m ² . When the basis weight is within the above range, the collection efficiency and the collection amount are good, and a filter medium capable of sharply forming the peaks and valleys of the pleats can be obtained, which is preferable.
The basis weight of the dense layer is preferably 100 to 350 g / m ² , more preferably 140 to 260 g / m ² , and further preferably 160 to 250 g / m ² . If the weight per unit area of the dense layer is below the lower limit, the dust collection efficiency may decrease, and if it exceeds the upper limit, the ventilation resistance of the filter medium may increase, which is not preferable.
The weight of the intermediate layer is smaller than that of the dense layer, preferably larger than that of the coarse layer, preferably 40 to 130 g / m ² , more preferably 60 to 120 g / m ² , and further preferably 70 to 100 g. / M ² . If the basis weight is less than the lower limit, it is not preferable because the collection efficiency of coarse dust that could not be collected in the coarse layer may be decreased, and if the upper limit is exceeded, the filter medium may become thick and may not fit in the package, which is preferable. Absent.
Since the coarse layer is intended to capture dust having a relatively large particle size, it requires a certain amount of bulkiness. Therefore, the basis weight of the coarse layer is preferably 30 to 100 g / m ^2, more preferably 40 and 80 g / m ^2, more preferably from 50 to 70 g / m ^2. If the basis weight is less than the lower limit value, the efficiency of collecting dust having a relatively large particle size may decrease, which is not preferable. On the other hand, if it exceeds the upper limit, the filter medium may become thick and may not fit in the package, which is not preferable.

<Thickness>
The thickness of the filter medium is preferably 4 to 8.5 mm, more preferably 4.5 to 7.5 mm, still more preferably 5 to 7.0 mm. When the thickness is within the above range, it is possible to obtain a filter medium that has appropriate rigidity and that does not deform or damage the pleats.
The thickness of the dense layer is preferably 0.7 to 2 mm, more preferably 1.0 to 1.5 mm, and even more preferably 1.0 to 1.3 mm.
The thickness of the intermediate layer is preferably 0.7 to 3 mm, more preferably 1.1 to 2 mm, and even more preferably 1.1 to 1.5 mm.
The thickness of the rough layer is preferably 1.5 to 5 mm, more preferably 2.0 to 4.5 mm, further preferably 2.5 to 4.0 mm.

<Fiber density>
The fiber density of the filter medium is preferably 0.050 to 0.070 g / cm ³ , more preferably 0.052 to 0.065 g / cm ³ , and still more preferably 0.055 to 0.063 g / cm ³ . . When the fiber density of the filter medium is within the above range, high collection efficiency and high collection amount can be achieved.
Particularly, the fiber density of the dense layer is preferably 0.100 to 0.250 g / cm ³ , more preferably 0.140 to 0.200 g / cm ³ , and still more preferably 0.145 to 0.180 g / cm ^3. Is.
The fiber density of the intermediate layer is preferably 0.030 to 0.100 g / cm ³ , more preferably 0.055 to 0.080 g / cm ³ , and still more preferably 0.060 to 0.075 g / cm ³ . is there.
Fiber density of the coarse layer is preferably 0.005~0.030g / cm ^3, more preferably from 0.013~0.025g / cm ^3, more preferably at 0.015~0.022g / cm ³ is there.
The fiber density of each layer is obtained by dividing the basis weight by the thickness.

<Gradient>
In the present invention, the fineness of the fibers blended in each layer is changed so that the fiber density gradually increases from the air inflow side containing dust. Therefore, each layer has a difference in the average fineness of the fibers contained between the layers. In order to efficiently capture a large amount of fine dust, the average fineness difference between the fibers between the layers is preferably 0.1 to 9 dtex, and more preferably 0.1 to 6 dtex. Within the above range, a high level of performance particularly required for automobile engine filter applications can be exhibited, which is preferable.
More specifically, the average fineness difference between the fibers in the dense layer and the intermediate layer is preferably 0.1 to 5 dtex, more preferably 1 to 4 dtex, and even more preferably 1.5 to 3 dtex. As the ratio, the average fineness of the fibers in the intermediate layer is preferably 1.2 to 2.5 times, more preferably 1.5 to 2.3 times, the average fineness of the fibers in the dense layer, and further. It is preferably 1.8 to 2.2 times.
The average fineness difference between the fibers in the intermediate layer and the rough layer is preferably 0.1 to 8 dtex, more preferably 0.5 to 6 dtex, and further preferably 1 to 4 dtex. As the ratio, the average fineness of the fibers in the coarse layer is preferably 1.01 to 3 times, more preferably 1.1 to 1.7 times, and further preferably 1 to the average fineness of the fibers in the intermediate layer. .15 to 1.5 times.

Moreover, in order to obtain a laminated structure having a density gradient, the average fineness of the fibers forming the dense layer is preferably 0.8 to 3 dtex, more preferably 1.5 to 2.8 dtex, and further preferably 1 7 to 2.5 dtex.
The average fineness of the fibers forming the intermediate layer is 2 to 10 dtex, more preferably 3.5 to 7 dtex, and further preferably 4 to 4.6 dtex.
Further, the average fineness of the fibers constituting the rough layer is 5 to 20 dtex, more preferably 5.2 to 12 dtex, and further preferably 5.4 to 10 dtex.

  In the present invention, the average fineness of the fibers contained in each layer is determined by the weight average of all the fibers contained in each layer.

Further, the filter medium according to the present invention preferably has a density gradient in which the density increases in the order of the coarse layer, the intermediate layer, and the dense layer.
When the intermediate layer is provided, the difference in fiber density between the dense layer and the intermediate layer is preferably 0.076 to 0.120 g / cm ³ , more preferably 0.078 to 0.100 g / cm ³ , and further preferably 0. It is 0.080 to 0.095 g / cm ³ .
The fiber density difference of the intermediate layer and the rough layer is preferably 0.040~0.067g / cm ^3, more preferably from 0.045~0.065g / cm ^3, more preferably 0.050~0.060g / Cm ³ .

  Depending on the required quality, it is possible to make the filter media flame-retardant, antibacterial and antifouling. Such various functions may be imparted by a method such as resin processing after manufacturing the filter medium. In particular, when a high level of function is required, a treatment liquid is prepared by adding a highly functionalizing agent such as a flame retardant, an antibacterial agent or an antifouling agent to the base binder resin, and the filter medium is treated with It is preferable to perform resin processing such as impregnation with a liquid, coating (coating) the treatment liquid on the filter medium, and spraying the treatment liquid on the filter medium with a spray or the like. Further, as a constituent fiber, it is also possible to adopt a method in which fibers that have been subjected to various treatments such as flame retardation, antibacterial treatment and antifouling are blended into each layer. It is preferable since the effect can be enjoyed from the stage of manufacturing.

  Further, the filter medium may further have a non-woven fabric layer laminated thereon and may further contain other layers. For example, on the dense layer surface, in order to further improve the rigidity and the fiber density, a net, a net, a non-woven fabric (for example, a spun bond non-woven fabric, a melt blown non-woven fabric, a nanofiber non-woven fabric, etc.) may be laminated or a laminated body.

  Since the filter medium according to the present invention has excellent rigidity, it is possible to achieve a dense layer surface mountain height of 31 mm or more, more preferably 35 mm or more, and further preferably 40 mm or more. The upper limit of the mountain height of the dense layer surface is not particularly limited, but is usually 46 mm or less. The method for measuring the height of the dense layer surface will be described in detail in the section of Examples.

  The ventilation resistance of the filter medium measured according to JIS D1612 (Air cleaner test method for automobiles) can be 365 Pa or less, more preferably 330 Pa or less, and further preferably 310 Pa or less. The lower limit of the ventilation resistance is not particularly limited, but is usually 180 Pa or more. Details of the measuring method will be described in detail in the section of Examples.

  The collection efficiency of the filter medium measured according to the full-life cleaning efficiency test specified in JIS D1612 (air cleaner test method for automobiles) and JIS D1612 9.4 (3) is 97.5% or more, more preferably 97. It is possible to achieve 7% or more, and more preferably 98.0% or more. The upper limit of the collection efficiency is 100%, but there is no problem even if it is 99.5% or less. Details of the measuring method will be described in detail in the section of Examples.

  The collection amount of the filter medium measured according to JIS D1612 (automatic air cleaner test method) and JIS D1612 10 can be 139 g or more, more preferably 141 g or more, and still more preferably 142 g or more. The upper limit of the collected amount is not particularly limited, but is usually 250 g or less. Details of the measuring method will be described in detail in the section of Examples.

<< Method of manufacturing filter medium >>
The method for manufacturing the filter medium according to the present invention will be described. It has a laminated structure of a filter medium and a nonwoven fabric according to the present invention. The method for producing the non-woven fabric is not particularly limited, and various non-woven fabrics such as dry non-woven fabric, wet non-woven fabric and spunbond non-woven fabric can be appropriately used in the present invention. The web bonding method is also not particularly limited, and mechanical entanglement methods such as the needle punch method and the spunlace method (hydroentanglement method); Various bonding methods such as a method of thermally melting a part or the whole to fix fiber intersections (thermal bonding method); Above all, a combined type of a needle punch and a thermal bond method in which fibers are entangled by a needle punch method and then heat treatment is performed is preferable. In the present invention, the entanglement density of the dense layer is preferably higher than the entanglement density of the rough layer. When the entanglement density of the dense layer is higher than that of the coarse layer, the dense layer becomes higher in density, which is preferable.

  The filter medium according to the present invention is a two-layer structure having a rough layer and a dense layer, or a laminate including a three-layer structure in which a coarse layer, an intermediate layer and a dense layer are laminated in this order, and each layer in the filter medium. Are preferably integrated by a mechanical entanglement method. As a method of integrating the layers, (i) a nonwoven fabric (preferably a needle punched nonwoven fabric) is produced from the web for either the dense layer or the rough layer, and the intermediate layer web is formed on the formed nonwoven fabric. , And a method of laminating the rough layer or the dense layer web in order and then performing a mechanical entanglement method such as a needle punching method to integrate the laminate containing the web and the nonwoven fabric, (ii) a dense layer web in advance, A method in which a web for an intermediate layer and a web for a rough layer are respectively manufactured, webs of the respective layers are sequentially laminated, and then mechanical entanglement method such as needle punching method is applied to integrate the laminated body of webs, (iii) dense Non-woven fabrics for layers, intermediate layers, and rough layers (preferably needle-punched non-woven fabrics) may be manufactured in advance, the obtained non-woven fabrics may be laminated, and then a laminate of the non-woven fabrics may be integrated. In the present invention, in particular, as in (i) or (ii), a method of integrating a laminate including a web at least in part by a mechanical entanglement method such as a needle punching method is preferable, in order to increase the density gradient. , A nonwoven fabric for a dense layer is manufactured by a needle punching method, and a web for an intermediate layer and a web for a rough layer are sequentially laminated on the formed needle punching nonwoven fabric, and then a machine such as a needle punching method. The method (i) in which the laminated body including the web and the non-woven fabric is integrated by performing the mechanical entanglement method is preferable. When the filter medium is manufactured in this manner, the dense layer is subjected to needle punching more times than the intermediate layer and the rough layer, and the fibers of the dense layer are entangled. As a result, the entanglement density of the dense layer becomes higher than the entanglement density of the coarse layer, and the dense layer can be further densified, which is preferable. The entanglement density of the intermediate layer may be adjusted to be higher than the entanglement density of the rough layer by changing the density of the needle punch between the intermediate layer and the rough layer.

As in (i), the processing conditions for producing the dense layer or the rough layer of the needle punched non-woven fabric in advance are as follows: Needle punch needle count 36 to 42, needle depth 8 to 17 mm (preferably 10 to 15 mm), driving The number is preferably 80 to 150 lines / cm ² (preferably 90 to 130 lines / cm ² ). In particular, by forming a dense layer of needle-punched non-woven fabric in advance under these conditions, the dense layer has a high density, which improves the collection efficiency and maintains the rigidity of the leeward dense layer. Is less likely to collapse, and as a result, fold contact can be suppressed and increase in ventilation resistance can be suppressed.

In the needle punching process for integrating the layers, it is preferable to insert the needle from the dense layer side. This is because when needle punching is performed from the dense layer side, the fibers in the dense layer are entangled so as to project toward the rough layer side (that is, the windward side), and thus the passage of dust can be suppressed. Further, since the dense layer contains the base fiber to which the silicone oil is attached, the low frictional resistance property of the fiber makes the fiber entanglement between the dense layer and the intermediate layer or the coarse layer moderate. Similarly, in the intermediate layer and the rough layer, fiber entanglement between the layers becomes gentle. In particular, since fibers with a fairly large fineness are used in the coarse layer, it is difficult to entangle the fibers from the beginning, but the entanglement of fibers between layers is fairly gradual, so the needle punch conditions should be strengthened to improve the collection efficiency. Even if the dense layer has a high density, the thickness ratio of the rough layer can be maintained large. Therefore, a dense layer having a function of improving collection efficiency, a coarse layer having a function of capturing large particle size dust to prolong the life, and an intermediate layer having a function of grading the density gradient of these two layers, respectively. It fulfills its intended purpose and can achieve both high collection efficiency and high dust collection amount. Needle punching at this time is performed by needle punching with a needle count of 36 to 42, a needle depth of 7 to 12 mm (preferably 8 to 11 mm), and a driving number of 50 to 110 / cm ² (preferably 60 to 80 / cm ^2). The conditions of () are preferable.

  After the layers are integrated by a mechanical entanglement method such as a needle punch method, the low melting point fibers may be heat-melted by heat treatment to bond the fibers to each other in order to increase the bonding strength between the layers. Needles only from the dense layer surface (under stronger production conditions than the conventional one) because the dense layer contains a low melting point fiber in a large amount of 57% by weight or more and less than 100% by weight, and the base fiber with silicone oil is used. When thermal bonding is performed after punching, high trapping efficiency is achieved, but rigidity is increased and the pleated form can be maintained for a longer period of time than with conventional air filter units, so low pressure loss can be achieved. Since the ratio of the coarse layer can be increased by decreasing the degree of conformity, a filter medium, which is not available in the past and has an increased dust holding capacity, can be obtained. Further, even if needle punching is performed under strong production conditions, needle holes due to needles are less likely to be formed, which contributes to improvement in collection efficiency.

The temperature in the heat treatment is equal to or lower than the melting point of the base fiber and higher than the glass transition temperature of the low melting point fiber, specifically, 175 to 225 ° C is preferable, and 190 to 220 ° C is more preferable. Further, in order to harden the texture of the filter medium, the heating temperature is to the melting point T _L of the low-melting fibers are cotton _{mixing, T L +10 (℃) ~T} L +110 (℃) , more preferably T _L It is +35 (° C) to _TL +90 (° C). When the heating temperature is within the above range, the low melting point fiber can be appropriately melted. The heating time may be appropriately set in consideration of the melting point and content of the low melting point fibers to be mixed, but is preferably 15 to 180 seconds, more preferably 40 to 120 seconds.

  The formed filter medium may be heat-treated by passing through a heat treatment machine (for example, a circulating hot air dryer) adjusted to a desired temperature. At this time, in order to adjust the size of the filter medium, the width (width and width) of the filter medium is pinched by endless belt conveyors capable of fixing the ends (preferably both ends) and the upper and lower surfaces (preferably both front and back) of the filter medium. It is preferable to perform heat treatment while maintaining the thickness.

  Further, the dense layer surface may be smoothed by passing it between heating rolls or heating plates. By performing the smoothing treatment, the collection efficiency can be further improved by improving the rigidity of the nonwoven fabric and increasing the density of the dense layer surface. Examples of the smoothing treatment include calendering. The calendering is preferably performed on the surface of the dense layer side. In addition, when the dense layer is previously formed as a non-woven fabric (preferably a needle-punched non-woven fabric), and a web is overlaid thereon and the layers are integrated by a mechanical entanglement method to produce a filter medium, a calendered non-woven fabric for the dense layer is used. You may laminate the web for other layers on it. The heating temperature of the heating roll and the metal plate is not particularly limited as long as it is higher than the melting start temperature of the low melting point fiber, but is preferably 70 to 200 ° C, more preferably 100 to 190 ° C.

<Pleating>
When the filter material is subjected to pleating, the filter material obtained by the above-mentioned method is adjusted to a predetermined size according to the intended use. The pleating method is not particularly limited, but pleating may be performed with the dense layer surface of the filter medium inside. The pitch and the peak height are preferably 10 to 25 mm, and the peak height is preferably 30 to 100 mm.

  Since the filter medium of the present invention has high rigidity, low ventilation resistance, high collection efficiency and high collection amount, the use area of the filter medium should be reduced by, for example, 10 to 20% as compared with the conventional product. Is possible. As a result, the air filter element can be made smaller and lighter, which contributes to space saving and improved fuel efficiency.

  The filter medium according to the present invention preferably has a relatively smooth surface having only fine irregularities derived from the fibers contained in the nonwoven fabric. Specifically, it is desirable that the surface of the dense layer be a flat surface without protrusions.

  Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited by the following examples as well as the present invention, and may be appropriately modified within a range compatible with the gist of the preceding and the following. Of course, it is possible to carry out, and all of them are included in the technical scope of the present invention.

The measuring method in the examples is as follows.
1. Unit weight: According to JIS L1913 6.2.
2. Thickness: According to JIS L1913 6.1.
3. Fiber density: The unit weight was converted by dividing the basis weight by the thickness.
4. Fiber density difference: The difference between the fiber density of the dense layer and the fiber density of the intermediate layer, and the difference between the fiber density of the intermediate layer and the fiber density of the rough layer were determined as the fiber density difference.

5. Dense layer mountain height;
The filter material was cut into a width of 50 mm, and then pleated at a height of 50 mm and a pitch of 16 mm. As shown in FIG. 1, for any three consecutive peaks in the filter medium after pleating, the height from the bottom b formed by connecting the two tops p and q on the dense layer side of the filter medium to the dense layer surface r of the filter medium is increased. The height h is measured at each of three peaks, and the average value of three points is obtained.

6. Ventilation resistance: According to JIS D1612 (air cleaner test method for automobiles), a ventilation resistance test was carried out under the following conditions.
Effective filtration area: 1760 cm ²
Projected area: 281 cm ²
Air amount: 5.7 m ³ / min Air velocity: 54 cm / sec Pa represents the difficulty of air flow with and without the filter medium.

7. Collection efficiency / collection amount: A filtration performance test was carried out under the following conditions in accordance with JIS D1612 (air cleaner test method for automobiles).
Effective filtration area: 1760 cm ²
Air volume: 5.7 m ³ / min Air velocity: 54 cm / sec Dust: JIS Z8901 8 types Dust concentration: 1 g / m ³
Collection efficiency: According to the full life cleaning efficiency test specified in JIS D1612 9.4 (3). The test termination condition was an increasing resistance of 300 mmAq.
Collection amount: According to JIS D1612 10. Similar to the collection efficiency, the test termination condition was an increasing resistance of 300 mmAq.
The element was prepared by the following method.
Method for producing element: The filter medium obtained by the method described in Examples was cut into a width of 110 mm, and then pleated at a height of 45 mm and a pitch of 16 mm with the dense layer surface of the filter medium inside. The periphery of the thus obtained pleated filter medium was hermetically fixed to a plastic board using a sealing material to prepare an element (width 150 mm × length 290 mm × height 45 mm).

In the performance evaluation, the pass was determined based on the following criteria.
・ Dense layer surface mountain height; pass 31mm or more ・ Ventilation resistance; pass 365 Pa or less ・ Collection efficiency; pass 97.5% or more ・ Collect amount; pass 139 g or more

Example 1
(1) Fabrication of needle punched nonwoven fabric 10% by weight of base fiber (P-800HX manufactured by Kuraray) in which silicone oil is attached to regular polyester fibers having a fineness of 2.2 dtex and a fiber length of 51 mm, a fineness of 2.2 dtex, a fiber length of 51 mm, 90% by weight of core-sheath type polyester composite fiber having a melting point of 160 ° C. is weighed and mixed, carded and cross-lapped, and then the needle depth is 40 with a needle number (Organ FPD1-40). Needle punching was performed at 14 mm and the number of shots was 110 needles / cm ² to produce a dense layer nonwoven fabric.
On the dense layer nonwoven fabric, 5% by weight of polyester fibers having a fineness of 4.4 dtex and a fiber length of 51 mm, and 5% by weight of base fibers in which silicone oil is adhered to regular polyester fibers having a fineness of 4.4 dtex and a fiber length of 51 mm ( Kuraray P-800HX), and fineness of 4.4 dtex, fiber length of 51 mm, melting point of 160 ° C., and core-sheath type polyester composite fiber of 90% by weight are respectively weighed, mixed, carded, cross-lapped, and intermediate. The layer web was laminated.
Then, on the web for the intermediate layer, 10% by weight of a polyester fiber having a fineness of 17 dtex and a fiber length of 51 mm, a fineness of 4.4 dtex, a fiber length of 51 mm, and 90% by weight of a core-sheath type polyester composite fiber with a melting point of 130 ° C. are respectively weighed. After blending, carding and cross wrapping were performed to laminate the web for rough layer.
The obtained laminated body is needle punched from the dense layer side with a needle punch needle number 40 (FPD1-40 made by Organ) at a needle depth of 9 mm and the number of punches 65 / cm ² to make a needle punch nonwoven fabric. did.
(2) Heat treatment Next, a heat treatment was carried out for 47 seconds in a conveyor type continuous heat treatment machine in which the temperature of hot air was kept at 215 ° C. to melt and fix the low melting point fibers, and a filter medium having the characteristics shown in the table was prepared. Using this filter medium, the height of the dense layer surface, the ventilation resistance, the collection efficiency and the collection amount were measured. The results are shown in the table.

Example 2
When producing the dense layer nonwoven fabric, without performing the entanglement of the dense layer web by the needle punching method in advance, the conditions shown in the table for the laminate of the dense layer web, the intermediate layer web, and the rough layer web. A filter medium was prepared in the same manner as in Example 1 except that the elements were integrated by needle punching in 1. As the results show, it can be seen that the dense layer, when integrated with the other layers, can be in the web or in the non-woven state. Further, compared with Comparative Example 2, since the needle punching process was performed under the strong condition using the silicone fiber, it was excellent in all points of the height of the dense layer surface, ventilation resistance, collection efficiency and collection amount. The effect is being demonstrated.

Comparative Example 1
A filter medium was prepared in the same manner as in Example 1 except that the base fiber to which the silicone oil was attached was changed to the polyester fiber. Since the base material fiber to which the silicone oil adhered was not used, when the needle punching process was performed under the same conditions as in Example 1, the thickness was reduced and the ventilation resistance was increased. In addition, the collection efficiency and the collection amount were not satisfactory.

Comparative Example 2
A filter medium was prepared in the same manner as in Example 2 except that the base fiber to which the silicone oil adhered was changed to polyester fiber and the conditions of needle punching during lamination were changed. Although the base material fiber to which the silicone oil is attached is not used, the filter medium has an appropriate thickness and the ventilation resistance does not increase so much because the entanglement condition is weak. However, it was not satisfactory in terms of collection efficiency and collection amount.

Comparative Example 3
A filter medium was prepared in the same manner as in Example 2 except that the base fiber to which silicone oil adhered was changed to polyester fiber. Since the base material fiber to which the silicone oil was attached was not used, when the needle punching process was performed under the same conditions as in Example 2, the thickness was reduced and the ventilation resistance was increased. In addition, the collection efficiency and the collection amount were not satisfactory.

Comparative Example 4
A filter medium was prepared in the same manner as in Comparative Example 2 except that the ratio of fibers in the dense layer, the intermediate layer and the rough layer, the basis weight of the dense layer, and the conditions for needle punching were changed as shown in the table. In Comparative Example 4, since the weight ratio of the low melting point fibers is low in all layers, the rigidity is low (the height of the dense layer surface is low), and the ventilation resistance is higher than that of Comparative Example 2. Further, since the weight of the dense layer is small, the collection efficiency and the collection amount are poor as compared with Comparative Example 2.

  The results are summarized in the table. In each table, the abbreviations of fibers are used in the following meanings.

Examples 3 to 5
A filter medium was prepared using fibers having different fineness. The results are shown in the table together with the results of Example 1. As in the case of Example 3, when the fine layer fibers are mixed in the dense layer, the collection efficiency is greatly improved.

Examples 6-8, Comparative Examples 5-6
A filter medium was prepared by changing the weight ratio of Si fibers in the dense layer. The results are shown in the table together with the results of Example 1 and Example 4. When the weight ratio of the low melting point fibers in the dense layer is increased, the rigidity of the filter medium is increased and the ventilation resistance is lowered. However, when the low-melting point fiber is 100% by weight, the melted fiber becomes like a film and the filter medium becomes thin, so that the nonwoven fabric is not satisfactory in terms of collection efficiency and collection amount. (Comparative example 5). On the other hand, when the weight ratio of the low-melting-point fibers in the dense layer was reduced, the filter medium became thicker, but the rigidity of the filter medium decreased, resulting in an increase in ventilation resistance (Comparative Example 6).
Further, by adjusting the content ratio of the Si fiber and the low melting point fiber in the dense layer, the balance between the collection efficiency and the ventilation resistance can be adjusted. The collection efficiency is good for the filter medium containing 20 to 43% by weight of Si fibers in the dense layer (best is Example 7 in which the dense layer contains 35 to 43% by weight of Si fibers). Is preferable for the filter medium in which the dense layer contains Si fibers in an amount of about 5 to 15% by weight (best is Examples 1 and 4 in which the dense layer contains Si fibers in an amount of about 5 to 10% by weight).
Further, even if the weight ratio of the low melting point fibers in the dense layer is the same, if the weight ratio of the Si fibers is low, the filter medium becomes slightly thin (Example 8). From the viewpoint of ventilation resistance, collection efficiency, collection amount, etc., a filter medium having a high Si fiber content is preferable (Example 7).

Examples 9-10
In order to study the influence of the basis weight in the dense layer, a filter medium having the constitution shown in the table was prepared. The results are shown in the table together with Example 1. It can be seen that when the basis weight of the dense layer is increased, the ventilation resistance is increased, but a filter medium excellent in the collection efficiency and the collection amount can be obtained (Example 10).

Examples 11 to 15 and Comparative Example 7
In order to study the influence of the intermediate layer, the weight ratio of Si fibers in the intermediate layer and the fineness were changed to prepare a filter medium. The results are shown in the table together with Example 1 and Comparative Example 1. The weight ratio of Si fibers in the intermediate layer does not significantly affect the performance of the filter medium (Examples 1, 11 to 15). However, when the weight ratio of the low-melting-point fibers in the intermediate layer is low, the intermediate layer is too soft, so that no good result was obtained in any of the heights of the dense layer surface, ventilation resistance, collection efficiency, and collection amount ( Comparative Example 7).

Examples 16-19
In Example 16, a filter medium was prepared by adding Si fiber to the rough layer. In Examples 17 to 18, a filter material was prepared by changing the basis weight of the intermediate layer. In Example 19, a filter medium having no intermediate layer was prepared. The results are shown in the table together with the results of Example 1. As shown in Example 19, it can be seen that desired performance can be achieved without providing an intermediate layer depending on the configurations of the dense layer and the rough layer.

  The filter medium according to the present invention is preferably used as a filter medium for various pleating filters used as pleats, and particularly preferably as a filter medium for automobile engines such as engine filters.

1: dense layer, 2: intermediate layer, 3: rough layer, 10: filter medium p, q: top, b: bottom, r: dense layer surface of filter medium, h: height

Claims (7)

It has a two-layer structure having a coarse layer and a dense layer having different fiber densities, or a three-layer structure in which a coarse layer, an intermediate layer and a dense layer are laminated in this order, and each layer is integrated by a mechanical entanglement method. A non-woven filter material,
The dense layer includes a base fiber having silicone oil adhered to a part or all of the dense fiber, and a low-melting point fiber having a melting point lower than that of the base fiber by 30 ° C. or more, and the intermediate layer includes at least a low-melting point fiber,
The proportion of low melting point fibers in the dense layer is 57% by weight or more and less than 100% by weight, and the proportion of low melting point fibers in the intermediate layer is 40% by weight or more,
The melting point of the low melting point fibers in the dense layer and the intermediate layer is 50 to 180 ° C., respectively .   The filter medium according to claim 1, wherein the base fiber to which the silicone oil adheres is contained in an amount of 1% by weight or more and 43% by weight or less in 100% by weight of the dense layer.   The filter medium according to claim 1 or 2, wherein the entanglement density of the dense layer is higher than the entanglement density of the coarse layer. Fiber density difference between dense layer and the intermediate layer is a 0.076~0.120g / cm ^3, claim 1 fiber density difference of the intermediate layer and the rough layers are 0.040~0.067g / cm ³ The filter medium according to any one of 3 above. The filter material according to any one of claims 1 to 4, having a basis weight of 180 to 550 g / m ² and a thickness of 4 to 8.5 mm.   The filter medium according to any one of claims 1 to 5, wherein the rough layer is a silicone oil-free layer having a content of fibers to which silicone oil adheres is 20% by weight or less.   The filter medium according to any one of claims 1 to 6, wherein the surface of the dense layer is a flat surface without protrusions.