JP7552345B2 - Spunbond nonwoven fabric for filters, filter media for automobile oil filters and automobile oil filters - Google Patents

Description

The present invention relates to a spunbond nonwoven fabric for filters that has excellent liquid permeability and pleating processability, a filter material for automobile oil filters, and an automobile oil filter.

Conventionally, engine oil has been used in automobiles to make the engine run efficiently, and this engine oil is circulated inside the engine and used repeatedly. The engine oil that circulates inside the engine contains contaminants such as carbon particles and metal powder that have been generated due to dirt and wear, and these contaminants must be collected before it can be sent back into the engine.
In order to collect impurities contained in engine oil, oil filters made of nonwoven fabrics are used. The nonwoven fabrics used in such oil filters are paper-made nonwoven fabrics made by mixing cotton linter pulp, wood pulp, and chemical fibers such as polyester, rayon, and acrylic, and processed with thermosetting resins such as phenolic resins to impart physical strength, or fused-type long-fiber nonwoven fabrics. In particular, spunbond nonwoven fabrics that do not use thermosetting resins such as phenolic resins during production have been attracting attention in recent years from the perspective of environmental impact. Nonwoven fabrics for automobile oil filters are known to be used in a pleated shape, and pleating can significantly increase the filtration area, reduce pressure loss, and increase collection efficiency.

Among the nonwoven fabrics used for such automobile oil filters, spunbond nonwoven fabrics are particularly used as filters to be installed in engine oil because they are superior in lint-free properties and strength performance to short fiber nonwoven fabrics, and it is easy to obtain spunbond nonwoven fabrics that have excellent properties. For example, Patent Documents 1 and 2 disclose nonwoven fabrics used for automobile oil filters, in which thermoplastic continuous filaments are first heated and pressed by a pair of flat rolls and then partially fused by a pair of engraved embossing rolls. Patent Document 3 discloses a nonwoven fabric made by mixing thermoplastic continuous filaments of a high melting point component and thermoplastic continuous filaments of a low melting point component, and a nonwoven fabric made of multi-lobed composite fibers made of a high melting point component and a low melting point component.

Patent No. 5422874 Patent No. 5298803 Patent No. 4522671

However, conventional spunbond nonwoven fabrics for oil filters used to remove impurities from automobile engine oil do not have sufficient rigidity for pleating when balancing oil permeability and pleating processability. In other words, if the fusion between fibers is strengthened in an attempt to improve rigidity, the mesh size becomes smaller, leading to a decrease in liquid permeability. On the other hand, if the fusion between fibers is loosened in an attempt to improve liquid permeability, the mesh size becomes larger, and when oil is circulated and filtered at a hydraulic pressure of 300 to 500 kPa, the pleat shape retention decreases, and there is a problem that impurities flow into the oil, which has a negative effect on the engine.
For example, with the techniques disclosed in Patent Documents 1 and 2, it was difficult to achieve both sufficient liquid permeability and rigidity.
On the other hand, in Patent Document 3, the fusion between the fibers is weak, and the fused parts break during pleating, reducing the rigidity of the nonwoven fabric. When used as a filter, there is an issue that the shape retention of the pleats is reduced at high flow rates.

In view of the above problems, the object of the present invention is to provide a spunbond nonwoven fabric for filters, a filter material for automobile oil filters, and an automobile oil filter that have a good balance between the ability to capture contaminants in automobile engine oil and liquid permeability, while also having high rigidity and excellent pleating processability.

As a result of extensive investigations to achieve the above-mentioned object, the inventors have discovered that a spunbonded nonwoven fabric for filters having excellent liquid permeability and sufficient rigidity for pleating and shape retention can be obtained by using a nonwoven fabric made of partially fused thermoplastic continuous filaments, in which the average brightness of the fused parts and non-fused parts obtained from the cross section of the nonwoven fabric is within a specified range.
The present invention has been completed based on these findings, and provides the following inventions.

That is, the spunbond nonwoven fabric for filters of the present invention is a spunbond nonwoven fabric for filters composed of thermoplastic continuous filaments consisting of a high melting point component and a low melting point component, which are partially fused, wherein the average single fiber diameter of the thermoplastic continuous filaments is 8.0 μm or more and 15.0 μm or less, the bending resistance in the MD direction is 20 mN or more and 80 mN or less, and the ratio of the average reflected light luminance (S1) of the fused parts to the average reflected light luminance (S2) of the non-fused parts in the cross section, represented by the following formula (1), is 0.20 or more and 1.00 or less.
R=1-S2/S1...(1)

According to a preferred embodiment of the spunbonded nonwoven fabric for filters of the present invention, the basis weight CV value is 5.0% or less.
In a preferred embodiment of the spunbonded nonwoven fabric for filters of the present invention, the fused portion has an area ratio of 5% or more and 20% or less.
The spunbond nonwoven fabric for filters of the present invention is a spunbond nonwoven fabric for automobile oil filters.
The spunbond nonwoven fabric for automobile oil filters of the present invention is used as a filter material for automobile oil filters.
The filter material for automobile oil filters of the present invention is used in automobile oil filters.

According to the present invention, a spunbond nonwoven fabric for filters, a filter material for automobile oil filters, and an automobile oil filter that are excellent in liquid permeability and pleat processability can be obtained.

FIG. 1 is a schematic perspective view illustrating a filter medium of the present invention. FIG. 2 is a cross-sectional photograph illustrating the structure of the spunbonded nonwoven fabric for filters according to the present invention. FIG. 3 is a diagram for explaining the configuration of a test system for carrying out a collection performance test according to an embodiment of the present invention.

The spunbonded nonwoven fabric for filters of the present invention is composed of thermoplastic continuous filaments consisting of a high melting point component and a low melting point component and is partially fused, wherein the average single fiber diameter of the thermoplastic continuous filaments is 8.0 μm or more and 15.0 μm or less, the bending resistance in the MD direction is 20 mN or more and 80 mN or less, and the ratio of the average reflected light luminance (S1) of the fused parts to the average reflected light luminance (S2) of the non-fused parts in the cross section, represented by the following formula (1), is 0.20 or more and less than 1.00.
R=1-S2/S1...(1)
Hereinafter, each component of the spunbonded nonwoven fabric for filters of the present invention will be described in detail.

(Thermoplastic continuous filament)
As the thermoplastic resin that is the raw material of the thermoplastic continuous filaments that constitute the spunbonded nonwoven fabric for filters of the present invention, polyester is particularly preferably used. Polyester is a polymer having an acid component and an alcohol component as monomers. As the acid component, aromatic carboxylic acids such as phthalic acid (ortho form), isophthalic acid, and terephthalic acid, aliphatic dicarboxylic acids such as adipic acid and sebacic acid, and alicyclic dicarboxylic acids such as cyclohexane carboxylic acid can be used. As the alcohol component, ethylene glycol, diethylene glycol, polyethylene glycol, and the like can be used.

Examples of polyesters include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate, polylactic acid, and polybutylene succinate. Of the polyesters used as high melting point polymers described below, PET is the most preferred, as it has a high melting point, excellent heat resistance, and excellent rigidity.

Additives such as crystal nucleating agents, matting agents, pigments, mildew inhibitors, antibacterial agents, flame retardants, metal oxides, aliphatic bisamides and/or aliphatic monoamides, and hydrophilic agents can be added to these polyester raw materials, provided that the effects of the present invention are not impaired. Among these, metal oxides such as titanium oxide reduce surface friction of the fibers and prevent fusion between the fibers, thereby improving spinnability, and also improve the fusion properties of the nonwoven fabric by increasing thermal conductivity during fusion molding of the nonwoven fabric with a heated roll. Furthermore, aliphatic bisamides such as ethylene bisstearic acid amide and/or alkyl-substituted aliphatic monoamides have the effect of increasing the releasability between the heated roll and the nonwoven fabric web, thereby improving transportability.

The thermoplastic continuous filament used in the present invention is composed of a high melting point component and a low melting point component. The thermoplastic continuous filament is preferably a composite filament in which a polyester-based low melting point polymer, which is a low melting point component having a melting point 10°C to 140°C lower than the melting point of the polyester-based high melting point polymer, is arranged around the polyester-based high melting point polymer, which is a high melting point component. In this way, when a spunbonded nonwoven fabric is formed by fusion, the composite polyester fibers (filaments) that make up the spunbonded nonwoven fabric are firmly fused together, so that the spunbonded nonwoven fabric for filters has excellent mechanical strength and can fully withstand oil treatment under high flow rates.

In the present invention, the melting point of the polyester-based low melting point polymer is at least 10°C lower than the melting point of the polyester-based high melting point polymer, more preferably at least 20°C lower, and even more preferably at least 30°C lower, to ensure the desired fusion properties. On the other hand, the melting point of the polyester-based low melting point polymer is at most 140°C lower than the melting point of the polyester-based high melting point polymer, more preferably at most 120°C lower, and even more preferably at most 100°C lower, to prevent a decrease in heat resistance.

The melting point of the polyester-based high melting point polymer in the present invention is preferably in the range of 200°C or more and 320°C or less. By setting the melting point of the polyester-based high melting point polymer to preferably 200°C or more, more preferably 210°C or more, and even more preferably 220°C or more, a filter with excellent heat resistance can be obtained. On the other hand, by setting the melting point of the polyester-based high melting point polymer to preferably 320°C or less, more preferably 300°C or less, and even more preferably 280°C or less, a large consumption of thermal energy for melting during nonwoven fabric production and a decrease in productivity can be suppressed.

On the other hand, the melting point of the polyester-based low melting point polymer is preferably in the range of 160°C or more and 250°C or less. By setting the melting point of the polyester-based low melting point polymer to preferably 160°C or more, more preferably 170°C or more, and even more preferably 180°C or more, the filter has excellent shape retention even when it goes through a process in which heat is applied during the production of the pleated filter, such as heat setting during pleating. On the other hand, by setting the melting point of the polyester-based low melting point polymer to preferably 250°C or less, more preferably 240°C or less, a filter having excellent fusion properties during the production of the nonwoven fabric and excellent mechanical strength can be obtained.

In the present invention, the melting point of a thermoplastic resin is measured using a differential scanning calorimeter (for example, PerkinElmer's "DSC-2" model) at a heating rate of 20°C/min and a measurement temperature range of 30°C to 300°C, and the temperature at which the obtained melting endothermic curve gives an extreme value is taken as the melting point of the thermoplastic resin. For resins whose melting endothermic curves do not show an extreme value in the differential scanning calorimeter, the resin is heated on a hot plate, and the temperature at which the resin melts under a microscope is taken as the melting point.

When the thermoplastic resin is polyester, examples of the combination of a polyester-based high melting point polymer and a polyester-based low melting point polymer (hereinafter, the order may be polyester-based high melting point polymer/polyester-based low melting point polymer) include combinations such as PET/PBT, PET/PTT, PET/polylactic acid, and PET/copolymerized PET, and among these, the combination of PET/copolymerized PET is preferably used because of its excellent spinnability. In addition, isophthalic acid copolymerized PET is preferably used as the copolymerization component of copolymerized PET, because of its particularly excellent spinnability.

Examples of the composite form of the composite filament include a concentric core-sheath type, an eccentric core-sheath type, and an island-in-the-sea type. Of these, the concentric core-sheath type is preferred because it allows the filaments to be fused uniformly and firmly. Furthermore, the cross-sectional shape of the composite filament may be a circular cross-section, a flat cross-section, a polygonal cross-section, a multi-lobal cross-section, a hollow cross-section, and the like. Of these, a circular cross-sectional shape is a preferred embodiment of the filament.

The composite filament can be produced by, for example, blending fibers made of polyester-based high-melting-point polymers with fibers made of polyester-based low-melting-point polymers. However, in the blending method, uniform fusion is difficult, and for example, fusion is weak where the fibers made of polyester-based high-melting-point polymers are densely packed, resulting in poor mechanical strength and rigidity, making the fabric unsuitable for use as a spunbonded nonwoven fabric for filters. On the other hand, there is also a method in which low-melting-point polymers are applied to fibers made of polyester-based high-melting-point polymers by immersion or spraying, but in either case, it is difficult to apply the low-melting-point polymer uniformly on the surface or in the thickness direction, and the mechanical strength and rigidity are poor, making the fabric unsuitable for use as a spunbonded nonwoven fabric for filters.

The content ratio of the polyester-based high melting point polymer to the polyester-based low melting point polymer in the thermoplastic continuous filaments is preferably in the range of 90:10 to 60:40 by mass, and more preferably in the range of 85:15 to 70:30. By making the polyester-based high melting point polymer 60% by mass or more and 90% by mass or less, the rigidity and heat resistance of the spunbonded nonwoven fabric for filters can be excellent. On the other hand, by making the polyester-based low melting point polymer 10% by mass or more and 40% by mass or less, when a spunbonded nonwoven fabric for automobile oil filters is formed and used by fusion, the composite filaments constituting the spunbonded nonwoven fabric for filters can be firmly fused to each other, and the mechanical strength is excellent and the fabric can fully withstand oil processing under high flow rates.

The average single fiber diameter of the thermoplastic continuous filaments constituting the spunbonded nonwoven fabric for filters of the present invention is in the range of 8.0 μm or more and 15.0 μm or less. By making the average single fiber diameter of the thermoplastic continuous filaments 8.0 μm or more, preferably 8.2 μm or more, more preferably 8.5 μm or more, the liquid permeability of the spunbonded nonwoven fabric for filters can be improved and the pressure loss can be reduced. In addition, the number of thread breaks when forming the thermoplastic continuous filaments can be reduced, and the stability during production can be improved. On the other hand, by making the single fiber diameter of the thermoplastic continuous filaments 15.0 μm or less, more preferably 14.8 μm or less, the uniformity of the spunbonded nonwoven fabric for filters can be improved, the surface of the nonwoven fabric can be made dense, and the collection performance can be improved, such as making it easier to filter engine oil at the surface layer.

In the present invention, the average single fiber diameter (μm) of the spunbonded nonwoven fabric for filters is determined by the following method.
(i) Ten small sample pieces are randomly taken from the spunbond nonwoven fabric for filters.
(ii) The surface of the collected small sample is photographed using a scanning electron microscope or the like at a magnification range of 500 to 2000 times, enabling the thickness of the fibers to be measured.
(iii) From the photographs taken from each small sample, 10 fibers are randomly selected (100 fibers in total) and their thickness is measured. The cross section of the fiber is assumed to be circular, and the thickness is taken as the single fiber diameter.
(iv) The arithmetic average value is rounded off to one decimal place to obtain the average single fiber diameter.

(Method of manufacturing spunbond nonwoven fabric for filters)
Next, a method for producing the spunbonded nonwoven fabric for filters of the present invention will be described. The spunbonded nonwoven fabric for filters of the present invention is produced by sequentially carrying out the following steps (a) to (c).
(a) A process in which a thermoplastic polymer is molten and extruded from a spinneret, and then pulled and drawn by an air sucker to obtain a thermoplastic continuous filament.
(b) A process of depositing the obtained filaments on a moving net conveyor while controlling the fiber arrangement with a fiber-spreading plate to form a fiber web.
(c) subjecting the resulting fibrous web to partial fusion bonding.
Each of the above steps will now be described in more detail.

(a) Thermoplastic continuous filament forming step First, a thermoplastic polymer is melt-extruded from a spinneret. In particular, when a composite filament in which a polyester-based low-melting point polymer having a melting point lower than that of a polyester-based high-melting point polymer is used as a thermoplastic continuous filament, the polyester-based high-melting point polymer and the polyester-based low-melting point polymer are melted at a temperature higher than the melting point and lower than (melting point + 70°C), respectively, and a composite filament in which a polyester-based low-melting point polymer having a melting point lower than that of the polyester-based high-melting point polymer by 10°C to 140°C is arranged around the polyester-based high-melting point polymer is spun out from a fine hole by a spinneret having a temperature higher than the melting point and lower than (melting point + 70°C), and then the filament is pulled and stretched by an air sucker at a spinning speed of 4000m/min to 6000m/min to spin a filament having a circular cross-sectional shape.

(b) Fiber Web Forming Step The spunbonded nonwoven fabric for filters of the present invention has a step of sucking spun thermoplastic continuous filaments with an ejector, ejecting them from a fiber-spreading plate having a slit at the bottom of the ejector, and depositing them on a moving net conveyor to obtain a fiber web.
Even when composite polyester fibers are used, it is important that the spunbonded nonwoven fabric for filters is made of the filaments (long fibers). This makes it possible to increase the rigidity and mechanical strength compared to nonwoven fabrics made of short fibers composed of discontinuous fibers, and makes it preferable as a pleated filter. In the manufacturing method of the spunbonded nonwoven fabric for filters of the present invention, it is also a preferred embodiment to temporarily fuse the fiber web collected on the net conveyer. For the temporary fusion, a method is preferably used in which the collected fiber web is fused with a pair of flat rolls, or a flat roll is placed on the net conveyer and fused between the net conveyer and the flat roll.

The fusion temperature for temporary fusion is preferably a temperature lower than the melting point of the polyester-based low melting point polymer by 70° C. to 120° C. By setting the temperature in this manner, the fibers are not excessively fused to each other, and the conveyability can be improved.
In addition, the linear pressure for temporary fusion is preferably 30 kg/cm or more and 70 kg/cm or less. By setting the linear pressure for temporary fusion to 30 kg/cm or more, more preferably 40 kg/cm or more, it is possible to impart the mechanical strength required for transporting the fiber web to the next process. By setting the linear pressure for temporary fusion to 70 kg/cm or less, more preferably 65 kg/cm or less, it is possible to prevent excessive fusion between the fibers.

(c) Partial fusion process The spunbonded nonwoven fabric for filters of the present invention is partially fused, but the method of partial fusion is not particularly limited. Here, the fused part of the spunbonded nonwoven fabric for filters is called the fused part, and the other unfused part is called the nonfused part. Fusion by a hot embossing roll or a combination of an ultrasonic oscillator and an embossing roll is preferred. In particular, fusion by an embossing roll is most preferred from the viewpoint of improving the strength of the nonwoven fabric. The partial fusion process is preferably processed continuously from the web formation process. By processing continuously from the web formation process, the density of the fused part is increased, and a nonwoven fabric with excellent waist strength and excellent pleat processability can be obtained as a spunbonded nonwoven fabric for filters. The temperature of fusion by a hot embossing roll is preferably 5°C to 60°C lower than the melting point of the polymer with the lowest melting point present on the fiber surface of the nonwoven fabric, and more preferably 10°C to 50°C lower. Excessive fusion can be prevented by setting the temperature difference between the melting points of the polymers with the lowest melting points present on the fiber surfaces of the nonwoven fabric by the hot embossing roll to 5° C. or more, more preferably 10° C. or more. On the other hand, uniform fusion can be achieved within the nonwoven fabric by setting the temperature difference to 60° C. or less, more preferably 50° C. or less.
The line pressure for fusion is preferably 30 kg/cm or more and 90 kg/cm or less. By setting the line pressure for fusion to 30 kg/cm or more, more preferably 40 kg/cm or more, the strength required for pleating can be imparted to the nonwoven fabric when used as a spunbonded nonwoven fabric for filters. By setting the line pressure for fusion to 90 kg/cm or less, more preferably 80 kg/cm or less, excessive fusion can be prevented.

The fusion area ratio of the partial fusion of the spunbonded nonwoven fabric for filters of the present invention (hereinafter, sometimes simply referred to as the fusion area ratio) is the ratio of the fusion part to the total area of the nonwoven fabric, and is preferably in the range of 5% to 20% of the total area of the nonwoven fabric. If the fusion area ratio is 5% or more, more preferably 6% or more, and even more preferably 8% or more, the nonwoven fabric has sufficient mechanical strength and is not prone to fluffing on the surface. On the other hand, if the fusion area ratio is 20% or less, more preferably 19% or less, and even more preferably 18% or less, the gap between the fibers is reduced, the pressure loss increases, and the collection performance does not decrease.
The fusion area ratio of the spunbonded nonwoven fabric is measured using a digital microscope (for example, "VHX-5000" manufactured by Keyence Corporation) and 100 rectangular frames of 1.0 cm x 1.0 cm parallel to the MD and CD directions of the nonwoven fabric are taken from any part of the spunbonded nonwoven fabric at a magnification of 20 times, and the area of the fusion part within the rectangular frame relative to the area of each of the 100 frames is measured and averaged, and the average is rounded off to the nearest whole number to obtain the fusion area ratio (%). When not expressed as a percentage, the fusion area ratio can be calculated by dividing the area ( ^cm2 ) of the fusion part within the rectangular frame by the area of the rectangular frame, 1.0 ^cm2, and then rounding off to the nearest whole number to obtain the fusion area ratio (%).

In the present invention, the MD direction refers to the sheet conveying direction during the production of the spunbond nonwoven fabric for filters, i.e., the winding direction of the nonwoven fabric roll, and the CD direction refers to the direction perpendicular to the sheet conveying direction, i.e., the winding direction of the nonwoven fabric roll. When the spunbond nonwoven fabric for filters is not in a rolled state due to being cut, for example, the MD direction and CD direction are determined by the following procedure.
(a) Within the plane of the spunbond nonwoven fabric for filters, an arbitrary direction is determined, and a test piece having a length of 38.1 mm and a width of 25.4 mm is taken along that direction.
(b) Similarly, test pieces measuring 38.1 mm in length and 25.4 mm in width are taken in directions rotated 30 degrees, 60 degrees, and 90 degrees from the direction in which the test piece was taken.
(c) For the test pieces in each direction, the bending resistance of each test piece is measured based on the method for measuring the bending resistance of a spunbonded nonwoven fabric for filters described below.
(d) The direction in which the measured value is the highest is defined as the MD direction of the spunbond nonwoven fabric for filters, and the direction perpendicular to this is defined as the CD direction.
In addition, when determining the MD and CD directions from a filter material for a filter, in the case of a filter material for an automobile oil filter as exemplified in Figure 1, the direction 25 parallel to the ridge line of the peak portion 22 is the CD direction, and the direction 24 perpendicular to the CD direction is the MD direction.
In the present invention, the MD direction refers to the sheet conveying direction during the production of the spunbonded nonwoven fabric, i.e., the winding direction of the nonwoven fabric roll, and the CD direction refers to the direction perpendicular to the sheet conveying direction, i.e., the winding direction of the nonwoven fabric roll. When the spunbonded nonwoven fabric is not in a rolled state, for example, because it is cut, the MD direction and CD direction are determined by the following procedure.
(a) Within the plane of the spunbond nonwoven fabric, an arbitrary direction is determined, and a test piece 38.1 mm long and 25.4 mm wide is taken along that direction.
(b) Similarly, test pieces measuring 38.1 mm in length and 25.4 mm in width are taken in directions rotated 30 degrees, 60 degrees, and 90 degrees from the direction in which the test piece was taken.
(c) For the test pieces in each direction, the bending resistance of each test piece is measured based on the method for measuring the bending resistance of a spunbond nonwoven fabric described below.
(d) The direction in which the measured value is highest is defined as the MD direction of the spunbond nonwoven fabric, and the direction perpendicular to this is defined as the CD direction.
In addition, when determining the MD and CD directions from filter media for automobile oil filters, in the case of filter media for pleated filters of dust collectors as exemplified in Figure 1, the direction 25 parallel to the ridge line of the peak portion 22 is the CD direction, and the direction 24 perpendicular to the CD direction is the MD direction.

The fused portion forms a depression, and is formed by fusing the thermoplastic continuous filaments that make up the nonwoven fabric together with heat and pressure. In other words, the fused portion is the portion where the thermoplastic continuous filaments are fused and aggregated compared to other portions. When fusing by a thermal embossing roll is adopted as the fusing method, the portion where the thermoplastic continuous filaments are fused and aggregated by the convex portion of the embossing roll becomes the fused portion. For example, when a roll having a predetermined pattern of unevenness only on the upper or lower side is used, and the other roll is a flat roll without unevenness, the fused portion refers to the portion where the thermoplastic continuous filaments of the nonwoven fabric are fused and aggregated by the convex portion of the roll having unevenness and the flat roll. Also, for example, when an embossing roll is used that is composed of a pair of upper and lower rolls on whose surface a plurality of linear grooves arranged in parallel are formed, and the grooves of the upper roll and the grooves of the lower roll are arranged to intersect at a certain angle, the fused portion refers to the portion where the thermoplastic continuous filaments of the nonwoven fabric are fused and aggregated by the convex portion of the upper roll and the convex portion of the lower roll. In this case, the fused portion between the upper convex portion and the lower concave portion, or the fused portion between the upper concave portion and the lower convex portion, is not included in the fused portion.

The area of each fused portion is preferably 0.3 ^mm2 or more and 5.0 ^mm2 or less. By making it 0.3 ^mm2 or more, sufficient mechanical strength as a spunbonded nonwoven fabric for filters can be obtained, and fuzzing on the surface of the nonwoven fabric can be suppressed. By making it 5.0 ^mm2 or less, in addition to the mechanical strength, breathability can be maintained as a spunbonded nonwoven fabric for automobile oil filters, and sufficient collection performance can be obtained.

The shape of the fused portion is not particularly specified, and even when a roll having a predetermined pattern of unevenness only on the upper or lower side is used and the other roll is a flat roll without unevenness, or when an embossing roll is made up of a pair of upper and lower rolls with multiple parallel linear grooves formed on the surface, and the grooves of the upper roll and the grooves of the lower roll are arranged so as to intersect at a certain angle, and the convex parts of the upper roll and the convex parts of the lower roll are fused, the shape of the fused part may be a circle, a triangle, a rectangle, a parallelogram, an ellipse, a rhombus, etc. The arrangement of these fused parts is not particularly specified, and they may be arranged regularly at equal intervals, randomly, or a mixture of different shapes. Among them, fused parts arranged at equal intervals are preferable from the viewpoint of uniformity of the nonwoven fabric. Furthermore, in terms of partially fusing the nonwoven fabric without peeling it off, it is preferable to use an embossing roll consisting of a pair of upper and lower rolls on whose surfaces multiple parallel linear grooves are formed, with the grooves of the upper roll and the grooves of the lower roll intersecting at a certain angle, and to form a parallelogram-shaped fused portion formed by fusing the convex parts of the upper roll and the convex parts of the lower roll.

(Spunbond nonwoven fabric for filters)
The spunbond nonwoven fabric for filters of the present invention has a bending resistance in the MD direction of the nonwoven fabric of 20 mN or more and 80 mN or less. If the bending resistance is 20 mN or more, more preferably 25 mN or more, and even more preferably 30 mN or more, the nonwoven fabric can be pleated while maintaining its strength and shape retention. On the other hand, if the bending resistance is 80 mN or less, more preferably 75 mN or less, and even more preferably 70 mN or less, the folding resistance during pleating is reduced, and the pleats have a sharp peak-valley shape.

The bending resistance in the present invention is a value obtained as follows in accordance with JIS L1913:2010 “Testing methods for general nonwoven fabrics”, 6.7 “Bending resistance (JIS method and ISO method)”, 6.7.4 “Gurley method (JIS method)”.
(i) Test pieces having a length of 38.1 mm (effective sample length L = 25.4 mm) and a width d = 25.4 mm are taken from any five points on the sample. In the present invention, the longitudinal direction of the nonwoven fabric is defined as the MD direction of the sample.
(ii) Each sampled test piece is attached to a chuck and the chuck is fixed so that it is aligned with the 1-1/2" (1.5 inches = 38.1 mm) scale on the movable arm A. In this case, 1/2" (0.5 inches = 12.7 mm) of the sample length is applied to the chuck by 1/4" (0.25 inches = 6.35 mm), and 1/4" (0.25 inches = 6.35 mm) is applied to the tip of the pendulum at the free end of the sample, so the effective sample length L for measurement is the test piece length minus 1/2" (0.5 inches = 12.7 mm).
(iii) Next, attach suitable weights _Wa , _Wb , _Wc (g) to the weight mounting holes a, b, c (mm) below the fulcrum of pendulum B, rotate movable arm A at a constant speed, and read the scale RG (mgf) when the test piece leaves pendulum B. Read the scale to one decimal place. The weights attached to the weight mounting holes can be selected as appropriate, but it is preferable to set the scale RG to be 4 to 6.
(iv) Measurements are performed on five test pieces, five times on each side, for a total of 50 times.
(v) The bending resistance value was calculated from the obtained RG scale value by using the following formula, rounding off to one decimal place. The average value of 50 measurements was rounded off to one decimal place to calculate the bending resistance in the MD direction.

In the spunbonded nonwoven fabric for filters of the present invention, the ratio of the average reflected light brightness (S1) of the fused portion to the average reflected light brightness (S2) of the nonfused portion in the cross section represented by the following formula (1) is 0.20 or more and less than 1.00. FIG. 2 is a cross-sectional photograph for explaining the structure of the spunbonded nonwoven fabric for filters according to the present invention. As shown in FIG. 2, when the cross section of the spunbonded nonwoven fabric for oil filters according to the present invention is observed with a scanning electron microscope (SEM), the fused portion where the thermoplastic continuous filaments are fused has a high brightness due to the dense presence of thermoplastic continuous filaments, and the nonfused portion has a low brightness due to the sparse presence of thermoplastic continuous filaments. The present inventors have found that when the ratio of the average reflected light brightness (S1) of the fused portion to the average reflected light brightness (S2) of the nonfused portion in the cross section represented by the formula (1) is within a predetermined range, a spunbonded nonwoven fabric for filters having a good balance between dust collection performance and air permeability, excellent pleatability, and high rigidity can be obtained. When the value of formula (1) is 0.20 or more, more preferably 0.25 or more, and even more preferably 0.30 or more, the fusion between the fibers is loose and excellent liquid permeability is obtained. On the other hand, when the value of formula (1) is less than 1.00, more preferably 0.90 or less, and even more preferably 0.80 or less, the fusion between the fibers is strong and excellent shape retention is obtained even under high flow rates when used as a filter.
R=1-S2/S1...(1)
In the present invention, the average reflected light luminance (S1) of the fused portion, the average reflected light luminance (S2) of the non-fused portion, and the value of formula (1) are determined as follows.

(1) Average reflected light brightness of the fused portion (S1)
(i) In any fused portion, the intersection of the center line in the MD direction and the center line in the CD direction is defined as the center point of the fused portion.
(ii) Draw a straight line parallel to the CD direction through the center point of the fused portion.
(iii) Starting from two points on the line 0.5 cm away from the center point of the fused portion, a straight line is drawn 1.0 cm long along the MD direction, and a straight line is drawn connecting the end points of the straight line.
(iv) Cut out with a razor blade the area bounded by the 1.0 cm x 1.0 cm squares formed in (i)-(iii).
(v) In the same manner, a total of 100 measurement samples for the fused portion, each measuring 1.0 cm x 1.0 cm, are taken from any location on the spunbonded nonwoven fabric for filters.
(vi) Using a scanning electron microscope (SEM) (for example, "VHX-D500" manufactured by Keyence Corporation), the cross section of the fused portion in the measurement sample for the fused portion is observed at a magnification of 150 times.
(vii) Visually draw a line perpendicular to the cross section of the nonwoven fabric sheet at the thinnest point of the fused portion of each observed image, and take a photograph of the center position at 500x magnification, one for each fused portion measurement sample, for a total of 100 photographs, and save the photographs in JPG format.
(viii) Crop a 1000x1000 pixel image from the saved image.
(ix) Divide into grid units of 40x40 pixels.
(x) In each grid, the average value of reflected light luminance (average reflected light luminance S1) defined in the YUV color space is calculated for each pixel using the following formula:
(Reflected light brightness of each pixel)=0.29891×R+0.58661×G+0.11448×B
Here, R, G, and B represent the reflected light intensities of red, green, and blue, respectively, in the RGB color model.

(2) Average reflected light brightness of non-fused portion (S2)
(i) The midpoint between the center point of any fused portion and the center point of the closest fused portion among the adjacent fused portions is determined as the center point of the non-fused portion.
(ii) A straight line is drawn through the center point of the non-fused portion and parallel to the CD direction.
(iii) Starting from two points on the line 0.5 cm away from the center point of the non-fused portion, a line is drawn 1.0 cm long along the MD direction, and a straight line is drawn connecting the end points of the line.
(iv) Cut out with a razor blade the area bounded by the 1.0 cm x 1.0 cm squares formed in (i)-(iii).
(v) Similarly, a total of 100 measurement samples of 1.0 cm x 1.0 cm for the non-fused portions are taken from any positions within the spunbonded nonwoven fabric for filters.
(vi) Using a scanning electron microscope (SEM) (for example, "VHX-D500" manufactured by Keyence Corporation), the cross section of the non-fused portion in the sample for non-fused portion is observed by adjusting the magnification to 150 times.
(vii) Visually draw a line perpendicular to the cross section of the nonwoven fabric sheet at the thickest point of the non-fused portion of each observed image, and take a photograph of the center position at 500x magnification, one for each measurement sample for the non-fused portion, for a total of 100 photographs, and save the photographs in JPG format.
(viii) Crop a 1000x1000 pixel image from the saved image.
(ix) Divide into grid units of 40x40 pixels.
(x) In each grid, the average value of reflected light luminance (average reflected light luminance S2) defined in the YUV color space is calculated for each pixel using the following formula:
(Reflected light brightness of each pixel)=0.29891×R+0.58661×G+0.11448×B
Here, R, G, and B represent the reflected light intensities of red, green, and blue, respectively, in the RGB color model.

(3) Ratio of Average Brightness The average reflected light brightness (S2) obtained in the above "average reflected light brightness (S2) of non-fused portions" was divided by the average reflected light brightness (S1) obtained in the "average reflected light brightness (S1) of cross section of fused portions" to obtain the value (S2/S1). The calculated value (R) was used as the ratio of average brightness.
R=1-(S2/S1)...(1)

The basis weight of the spunbonded nonwoven fabric for filters in the present invention is preferably in the range of 150 g/m2 or ^more and 300 g/m2 or ^less . If the basis weight is 150 g/m2 or ^more , it is preferable because the necessary rigidity for the pleats can be obtained. On the other hand, if the basis weight is 300 g/m2 or ^less , preferably 270 g/m2 or ^less , more preferably 260 g/m2 ^{or less} , it is possible to suppress an increase in pressure loss, and it is also preferable in terms of cost.
The basis weight referred to here is determined by taking three samples measuring 50 cm in length x 50 cm in width, measuring the mass of each, converting the obtained values (g) into a value per unit area (1 ^m2 ), and rounding off to the first decimal place.

The basis weight CV value of the spunbond nonwoven fabric for filters of the present invention is preferably 5.0% or less. More preferably, it is 4.8% or less, and even more preferably, it is 4.5% or less, because the nonwoven fabric can be made dense with improved uniformity of the nonwoven fabric, which makes it easier to improve collection efficiency and to obtain a satisfactory filter life. On the other hand, it is more preferable that the basis weight CV value is 1.0% or more, because the amount of liquid permeation of the spunbond nonwoven fabric for automobile oil filters is ensured to be constant and the pressure loss is reduced, thereby extending the filter life.

In the present invention, the basis weight CV value (%) of the spunbonded nonwoven fabric for filters is determined as follows.
(i) A total of 100 small pieces of 5 cm x 5 cm are taken from a spunbond nonwoven fabric for automobile oil filters.
(ii) The mass (g) of each small piece is measured and converted to a mass per unit area (1 m ² ).
(iii) The average value (W _ave ) and standard deviation (W _sdv ) of the conversion results in (ii) are calculated.
(iv) Based on the results of (i) to (iii), calculate the basis weight CV value (%) using the following formula, and round off to one decimal place.
Weight CV value (%) = W _{sdv /} W _ave × 100

The thickness of the spunbond nonwoven fabric for filters in the present invention is preferably 0.50 mm or more and 0.80 mm or less, and more preferably 0.51 mm or more and 0.78 mm or less. By making the thickness 0.50 mm or more, it is possible to improve the rigidity and make the spunbond nonwoven fabric for filters suitable for use as a filter. In addition, by making the thickness 0.80 mm or less, it is possible to make the spunbond nonwoven fabric for filters excellent in handleability and processability as a filter.

In the present invention, the thickness (mm) of the spunbonded nonwoven fabric for filters is determined by the following method.
(i) Using a thickness meter (for example, "TECLOCK" (registered trademark) SM-114 manufactured by TECLOCK Corporation), the thickness of the nonwoven fabric is measured at 10 equally spaced points in the CD direction.
(ii) The arithmetic mean value is rounded off to two decimal places to obtain the thickness (mm) of the nonwoven fabric.

The apparent density of the spunbonded nonwoven fabric for filters in the present invention is preferably 0.25 g/cm3 or ^more and 0.40 g/cm3 or less. When the apparent density is 0.25 g/cm3 or ^more and 0.40 g/ ^cm3 or ^less , the spunbonded nonwoven fabric for filters has a dense structure, which makes it difficult for dust to enter the inside, and has excellent dust brushing properties. A more preferable apparent density range is 0.26 g/cm3 ^or more and 0.38 g/cm3 or ^less .
In the present invention, the apparent density (g/cm ³ ) of the spunbonded nonwoven fabric for filters is determined from the basis weight and thickness of the spunbonded nonwoven fabric for filters using the following formula:
Apparent density (g/cm ³ )=weight per unit area (g/m ² )/thickness (mm)/1000

The spunbond nonwoven fabric for filters of the present invention has excellent liquid permeability and pleating processability, and can therefore be suitably used as a filter for filtering impurities in oil circulating at a hydraulic pressure of 300 to 500 kPa. Such a filter medium can be obtained, for example, by pleating the spunbond nonwoven fabric for filters. Furthermore, this filter medium for automobile oil filters can be made into a cylindrical automobile oil filter in which the entire filter medium is formed into a cylindrical shape centered on the axis of the element, and then the upper and lower ends of the cylinder are fixed.

The automobile oil filter of the present invention uses the filter material for automobile oil filters described above, and the automobile oil filter has a structure in which a filter element is housed in a pressure-resistant container made of metal or resin, for example. Engine oil filtration methods include, for example, a full-flow type that mainly filters metal powder generated by friction, a bypass type that removes carbon particles generated by incomplete combustion, and a combination type that combines both types, and the automobile oil filter of the present invention is particularly suitable for combination-type automobile oil filters that are widely used in recent automobiles.

As explained above, the spunbond nonwoven fabric for filters of the present invention balances the performance of collecting contaminants in automobile engine oil with liquid permeability, has high rigidity, is excellent in pleating processability, and can be used as an automobile oil filter by itself without using thermosetting resins such as phenolic resins, making it suitable for use as an automobile oil filter with low environmental impact.

Next, the spunbond nonwoven fabric for filters of the present invention will be specifically described based on examples. However, the present invention is not limited to these examples.

[Measurement method]
The respective characteristic values in the following examples were measured by the following methods. In addition, in the measurement of each physical property, unless otherwise specified, the measurement was carried out based on the above-mentioned method.
(1) Melting point of polyester (℃)
The differential scanning calorimeter used was a "DSC-2 model" manufactured by PerkinElmer Japan Co., Ltd.
(2) Intrinsic Viscosity (IV) of Polyester
The intrinsic viscosity (IV) of the polyester was measured by the following method.
8 g of a sample was dissolved in 100 mL of orthochlorophenol, and the relative viscosity _ηr was calculated at 25° C. using an Ostwald viscometer according to the following formula:
η _r = η/η ₀ = (t×d)/(t ₀ ×d ₀ )
(Here, η represents the viscosity of the polymer solution, η ₀ represents the viscosity of orthochlorophenol, t represents the drop time of the solution (seconds), d represents the density of the solution (g/cm ³ ), t ₀ represents the drop time of orthochlorophenol (seconds), and d ₀ represents the density of orthochlorophenol (g/cm ³ ).)
Next, the intrinsic viscosity (IV) was calculated from the relative viscosity _ηr according to the following formula.
Intrinsic viscosity (IV) = 0.0242η _r +0.2634.

(3) Average Single Fiber Diameter of Thermoplastic Continuous Filaments (μm)
The average single fiber diameter of the thermoplastic continuous filaments was calculated by the above-mentioned method using a scanning electron microscope (SEM) "VHX-D500" manufactured by Keyence Corporation.
(4) Basis weight of spunbond nonwoven fabric for filters (g/ ^m2 )
The basis weight of the spunbond nonwoven fabric for filters was calculated by the above-mentioned method.
(5) Basis weight CV value (%) of spunbond nonwoven fabric for filters
The basis weight CV value of the spunbond nonwoven fabric for filters was calculated by the above-mentioned method.
(6) Thickness of spunbond nonwoven fabric for filters (mm)
The thickness was evaluated by the above-mentioned method using a "TECLOCK" (registered trademark) SM-114 manufactured by TECLOCK Corporation as a thickness gauge.
(7) Bending resistance (mN) of spunbond nonwoven fabric for filters
The bending resistance was measured by the above-mentioned method using a Gurley flexibility tester "GAS-10" manufactured by Daiei Seiki Seisakusho Co., Ltd.

(8) Average reflected light brightness of the fused portion of the spunbond nonwoven fabric for filters (S1)
A scanning electron microscope (SEM) "VHX-D500" manufactured by Keyence Corporation was used, and the average luminance (S1) of reflected light of the fused portion of the spunbond nonwoven fabric for filters was calculated by the above-mentioned method.
(9) Average reflected light brightness of the non-fused portion of the spunbonded nonwoven fabric for filters (S2)
A scanning electron microscope (SEM) "VHX-D500" manufactured by Keyence Corporation was used, and the average luminance (S2) of reflected light of the non-fused portion of the spunbonded nonwoven fabric for filters was calculated by the above-mentioned method.
(10) Average luminance ratio (R)
The average brightness ratio (R) of the spunbonded nonwoven fabric for filters was determined by dividing the average reflected light brightness (S2) obtained in the above "(9) Average reflected light brightness (S2) of non-fused portions of spunbonded nonwoven fabric for filters" by the average reflected light brightness (S1) obtained in "(8) Average reflected light brightness (S1) of fused portions of spunbonded nonwoven fabric for filters" and substituting the result (S2/S1) into the following formula (1), and the calculated value (R) was used as the average brightness ratio.
R=1-(S2/S1)...(1)

(11) Pleating processability of spunbond nonwoven fabric for filters (points)
(i) A spunbond nonwoven fabric for filters was cut to a width of 240 mm, and this spunbond nonwoven fabric for filters was heated to 150°C and compressed while being pleated so that the distance from the ridgeline of one apex of the pleated body to the ridgeline of the next apex was 35 mm, thereby obtaining a pleated body.
(ii) This pleated body was wound 45 times around a porous cylindrical core made of polypropylene, the ends of the pleated body were heat sealed together, and then injection-molded caps were attached to both ends of the cylinder to produce a pleated filter.
(iii) Twenty panelists visually inspected the appearance of the prepared pleated filters and judged the pleatability of the spunbonded nonwoven fabric for automobile oil filters on a five-point scale according to the following criteria. The total score ranged from a minimum of 0 points to a maximum of 100 points, with a score of 80 points or more being considered as passing.
5 points: Very good (the pleats of the pleated body are not in contact with each other, and the pleats are not distorted in shape, and adjacent pleats are parallel and aligned in straight lines.)
4 points: Good (between 3 and 5 points)
3 points: Normal (the pleats are not in contact with each other, but the pleats are distorted in shape).
2 points: Poor (between 1 and 3 points)
1 point: Very bad (the pleats are distorted and the peaks of the pleated body are in contact with each other).

(12) Liquid permeability of spunbond nonwoven fabric for filters (sec/ ^cm3 )
(i) Five samples of 100 mm in MD x 100 mm in CD were cut out from the spunbond nonwoven fabric for filters at equal intervals in the CD direction of the spunbond nonwoven fabric for filters, for a total of five samples.
(ii) A cylinder having a diameter of 2 cm is fixed on the spunbond nonwoven fabric for the filter, and 1 ^cm3 of rapeseed oil having a viscosity of 43 mPa·sec (30°C) is poured from the top of the cylinder.
(iii) The time required for 1 ^cm3 of rapeseed oil to completely soak into the nonwoven fabric was measured, rounded off to the first decimal place, and this value was regarded as the liquid permeability.
(13) Apparent Density of Spunbond Nonwoven Fabric for Filters The apparent density of the spunbond nonwoven fabric for filters was calculated by the method described above.

(12) Collection efficiency (%) of spunbond nonwoven fabric for filters
FIG. 3 is a diagram for explaining the configuration of a test system for carrying out a collection performance test according to an embodiment of the present invention. The test system 51 shown in FIG. 3 includes a sample holder 52 for setting a test sample M, a flowmeter 53, a flow rate control valve 54, a blower 55, a dust supply device 56, a changeover cock 57, and a particle counter 58. The flowmeter 53, the flow rate control valve 54, the blower 55, and the dust supply device 56 are connected to the sample holder 52. The flowmeter 53 is connected to the blower 55 via the flow rate control valve 54. Dust is supplied from the dust supply device 56 to the sample holder 52 by the intake of the blower 55. A particle counter 58 is connected to the sample holder 52, and the number of dust particles on the upstream side and the downstream side of the test sample M can be measured via the changeover cock 57. First, three samples of 15 cm x 15 cm are taken from any part of the nonwoven fabric, and the taken test sample M is set in the sample holder 52. The evaluation area of the test sample ^was 115 cm2. In measuring the collection performance, a 10 wt% solution of polystyrene 0.309U (manufactured by Nacalai Tesque, Inc.) was diluted 200 times with distilled water and filled into the dust supply device 56. The air volume was adjusted with the flow rate control valve 54 so that the filter passing speed was 3.0 m/min, the dust concentration was stabilized in the range of 20,000 to 70,000 particles/(2.83 ^{×10 −4} m ³ (0.01 ft ³ )), and the number of dust particles upstream and downstream of the test sample M was measured with a particle counter 58 (manufactured by Rion Co., Ltd., KC-01D) for dust particle sizes in the range of 0.3 to 0.5 μm. The collected values were substituted into the following calculation formula, and the obtained value was rounded off to the nearest tenth to obtain the collection performance (%).
Collection performance (%) = [1-(D1/D2)] x 100
Here, D1 is the number of dust particles downstream (total of three measurements), and D2 is the number of dust particles upstream (total of three measurements).

(13) Pressure loss (Pa)
The static pressure difference between the upstream and downstream of the test sample M during the above collection performance measurement was read by the pressure gauge 59, and the average value obtained from the three samples was rounded off to the first decimal place to calculate the average value.

[Resin used]
Next, the resins used in the examples and comparative examples will be described in detail.
Polyester resin A: polyethylene terephthalate (PET) dried to a moisture content of 50 ppm by mass or less, having an intrinsic viscosity (IV) of 0.65 and a melting point of 260°C.
Polyester resin B: Copolymerized polyethylene terephthalate (CO-PET) dried to a moisture content of 50 ppm by mass or less, having an intrinsic viscosity (IV) of 0.64, an isophthalic acid copolymerization rate of 11 mol%, and a melting point of 230° C.

[Example 1]
The polyester resin A and the polyester resin B were melted at temperatures of 295°C and 280°C, respectively. Then, the polyester resin A was used as the core component and the polyester resin B was used as the sheath component, and the core:sheath = 80:20 mass ratio was spun from the fine holes at a spinneret temperature of 295°C, and then a filament having a circular cross section was spun at a spinning speed of 4900 m/min by an air sucker, and the fiber arrangement was regulated by a fiber spreader plate and the filament was deposited on a moving net conveyor, and a fiber web consisting of fibers with an average single fiber diameter of 14.8 μm was collected. The collected fiber web was pre-fused by a calendar roll consisting of a pair of flat rolls at a temperature of 140°C and a linear pressure of 50 kg/cm. The nonwoven fabric was then fused at a temperature of 200°C and a linear pressure of 70 kg/ ^cm using an embossing roll consisting of a pair of engraved rolls with a fusion area ratio of 10% and an area per fused portion of 1.6 mm2, to obtain a spunbonded nonwoven fabric for filters with a basis weight of 260 g/ ^m2 . The CV value of the resulting spunbonded nonwoven fabric for filters was 3.3%, the thickness was 0.74 mm, the bending resistance in the MD direction was 53 mN, and the ratio of average reflected light brightness (R) was 0.57. The results are shown in Table 1.

[Example 2]
A spunbonded nonwoven fabric for filters having a basis weight of 260 g/m2 was obtained under the same conditions as in Example ¹ , except that the upper and lower embossing rolls were changed from an embossing roll consisting of a pair of engraved rolls having a fusion area ratio of 10% and an area per fused portion of ^1.6 mm2 to an embossing roll consisting of a pair of engraved rolls having a fusion area ratio of 18% and an area per fused portion of 0.7 ^mm2 . The basis weight CV value of the obtained spunbonded nonwoven fabric for filters was 3.3%, the thickness was 0.73 mm, the bending resistance in the MD direction was 25 mN, and the ratio (R) of the average brightness of reflected light was 0.41. The results are shown in Table 1.

[Example 3]
A spunbond nonwoven fabric for filters having a basis weight of 260 g/m2 was obtained under the same conditions as in Example 1, except that the discharge amount and spinning speed were changed so that the average single fiber diameter was 10.0 μm, and the speed of the net conveyer was changed to make the basis weight the same as in Example ^1. The basis weight CV value of the obtained spunbond nonwoven fabric for filters was 2.7%, the thickness was 0.61 mm, the bending resistance in the MD direction was 62 mN, and the ratio of average reflected light brightness (R) was 0.62. The results are shown in Table 1.

[Example 4]
A spunbonded nonwoven fabric for filters having a basis weight of 260 g/ ^m2 was obtained under the same conditions as in Example 1, except that the temperature of both the upper and lower embossing rolls was changed from 200°C to 180°C and the linear pressure was changed from 70 kg/cm to 80 kg/cm. The basis weight CV value of the obtained spunbonded nonwoven fabric for filters was 3.6%, the thickness was 1.02 mm, the bending resistance in the MD direction was 57 mN, and the ratio of average reflected light brightness (R) was 0.75. The results are shown in Table 1.

[Example 5]
A spunbonded nonwoven fabric for filters having a basis weight of 260 g/m2 was obtained under the same conditions as in Example ¹ , except that the upper and lower embossing rolls were replaced from an embossing roll consisting of a pair of engraved rolls having a fusion area ratio of 10% and an area per fused portion of 1.6 ^mm2 to an embossing roll consisting of a pair of engraved rolls having a fusion area ratio of 8.5% and an area per fused portion of 1.6 ^mm2 . The basis weight CV value of the obtained spunbonded nonwoven fabric for filters was 3.5%, the thickness was 1.21 mm, the bending resistance in the MD direction was 73 mN, and the ratio (R) of the average brightness of reflected light was 0.67. The results are shown in Table 1.

[Example 6]
A spunbonded nonwoven fabric for filters having a basis weight of 260 g/m2 was obtained under the same conditions as in Example ¹ , except that the upper and lower embossing rolls were changed from an embossing roll consisting of a pair of engraved rolls having a fusion area ratio of 10% and an area per fused portion of ^1.6 mm2 to an embossing roll consisting of a pair of engraved rolls having a fusion area ratio of 16% and an area per fused portion of 0.5 ^mm2 . The basis weight CV value of the obtained spunbonded nonwoven fabric for filters was 4.4%, the thickness was 0.61 mm, the bending resistance in the MD direction was 37 mN, and the ratio (R) of the average brightness of reflected light was 0.37. The results are shown in Table 1.

[Comparative Example 1]
In the manufacturing process of Example 1, between the step of pre-fusing the collected fiber web and the step of partially fusing using an embossing roll, a step was added in which the sheet obtained in the pre-fusing step was once wound up, cooled to room temperature, and sent to the embossing roll, i.e., the step of partially fusing using an embossing roll was not performed subsequent to the pre-fusing step, but the same conditions as in Example 1 were used to obtain a spunbonded nonwoven fabric for filters having a basis weight of 260 g/ ^m2 . The basis weight CV value of the obtained spunbonded nonwoven fabric for filters was 3.2%, the thickness was 0.62 mm, the bending resistance in the MD direction was 25 mN, and the ratio (R) of the average brightness of reflected light was 0.16. The results are shown in Table 1.

[Comparative Example 2]
A spunbond nonwoven fabric for filters having a basis weight of 260 g/m2 was obtained under the same conditions as in Example 1, except that the discharge amount and spinning speed were changed so that the average single fiber diameter was 29.2 ^μm , and the speed of the net conveyer was changed to make the basis weight the same as in Example 1. The basis weight CV value of the obtained spunbond nonwoven fabric for filters was 6.1%, the thickness was 1.01 mm, the bending resistance in the MD direction was 81 mN, and the ratio of average reflected light brightness (R) was 0.57. The results are shown in Table 1.

[Comparative Example 3]
A spunbonded nonwoven fabric for filters having a basis weight of 260 g/m2 was obtained under the same conditions as in Example ¹ , except that the upper and lower embossing rolls were changed from an embossing roll consisting of a pair of engraved rolls having a fusion area ratio of 10% and an area per fused portion of ^1.6 mm2 to an embossing roll consisting of a pair of engraved rolls having a fusion area ratio of 24% and an area per fused portion of 0.5 ^mm2 . The basis weight CV value of the obtained spunbonded nonwoven fabric for filters was 3.2%, the thickness was 0.69 mm, the bending resistance in the MD direction was 18 mN, and the ratio of average reflected light brightness (R) was 0.58. The results are shown in Table 1.

[Comparative Example 4]
The polyester resin A and the polyester resin B were melted at temperatures of 295°C and 280°C, respectively. Then, the polyester resin A was used as the core component, and the polyester resin B was used as the sheath component, and the core:sheath = 80:20 mass ratio was spun from the pores at a spinneret temperature of 300°C, and then a filament having a circular cross section was spun at a spinning speed of 4400m/min by an air sucker, and the filament was collided with a metal collision plate installed at the air sucker outlet, and the fibers were charged and opened by frictional charging, and the fiber web consisting of fibers with an average single fiber diameter of 17.2μm was collected on a moving net conveyor. Subsequently, the fibers were fused by an embossing roll consisting of a pair of engraved rolls with a fusion area ratio of 18% and an area per fusion part of ^0.7mm2 at a temperature of 205°C for both the top and bottom, and a linear pressure of 70kg/cm2 to obtain a spunbonded nonwoven fabric for filters with a basis weight of 260g/ ^m2 . The resulting spunbond nonwoven fabric for filters had a basis weight CV value of 10.5%, a thickness of 0.50 mm, a bending resistance in the MD direction of 25 mN, and a ratio (R) of average reflected light luminance of 0.41.

The properties of the obtained spunbond nonwoven fabric for filters are as shown in Table 1, but Comparative Example 1 had a low average reflected light brightness ratio and poor pleating processability. Comparative Example 2, which had a thicker fiber diameter under the same conditions as Example 1, had an improved thickness, high stiffness, and poor pleating processability and liquid permeability. Comparative Example 3, which was embossed with a fusion rate of 24%, had a reduced thickness, low stiffness, and poor pleating processability. Comparative Example 4 had a worsening CV value per unit area, low stiffness, and poor pleating processability.

21: Filter material for automobile oil filters 22: Peaks 23: Valleys 24: Arrow indicating MD direction 25: Arrow indicating CD direction M: Test sample 51: Collection performance measuring device 52: Sample holder 53: Flowmeter 54: Flow rate adjustment valve 55: Blower 56: Dust supply device 57: Switching cock 58: Particle counter 59: Pressure gauge

Claims (5)

A spunbond nonwoven fabric for filters, which is composed of thermoplastic continuous filaments consisting of a high melting point component and a low melting point component and is partially fused,
A spunbond nonwoven fabric for automobile oil filters, wherein the average single fiber diameter of the thermoplastic continuous filaments is 8.0 μm or more and 15.0 μm or less, the bending resistance in the MD (warp) direction is 20 mN or more and 80 mN or less, and the ratio of the average reflected light luminance (S1) of the fused portions to the average reflected light luminance (S2) of the non-fused portions in the cross section, which is represented by the following formula (1), is 0.20 or more and less than 1.0.
R=1-S2/S1...(1) The spunbond nonwoven fabric for automobile oil filters according to claim 1, having a basis weight CV value of 5.0% or less. The spunbond nonwoven fabric for automobile oil filters according to claim 1 or 2, in which the area ratio of the fused portion is 5% or more and 20% or less. An automobile oil filter medium made using the spunbond nonwoven fabric for automobile oil filters according to any one of claims 1 to 3. An automobile oil filter using the filter material for automobile oil filters according to claim 4.

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