JP7130196B2 - Fibers for electret processing, nonwoven fabrics containing them, and air filters containing them - Google Patents

Description

TECHNICAL FIELD The present disclosure relates to fibers for electret processing, nonwoven fabrics comprising such fibers, and air filters comprising such nonwoven fabrics.

Development of an air filter using electrically charged non-woven fabric for the purpose of collecting fine suspended matter in gas, for example, fine suspended matter with a size of 0.5 μm or less, smoke dust, pollen, viruses, etc. is being done. Charged non-woven fabrics (such non-woven fabrics are also called charged non-woven fabrics or electrostatic non-woven fabrics) are different types of non-woven fabrics mainly composed of polypropylene fibers and polyester fibers, and are made of different materials, such as nylon resin brushes. In addition to rubbing the surface of the nonwoven fabric and electrifying it by friction, it can be produced by electret processing in which the nonwoven fabric is charged by applying corona discharge or plasma discharge to the nonwoven fabric surface while heating the nonwoven fabric to a temperature below the melting point. .
For example, an electret nonwoven fabric charged by electret processing can be used as an air filter with excellent ability to collect fine suspended matter by appropriately selecting the diameter of the fibers that make up the nonwoven fabric, the basis weight of the nonwoven fabric, and the thickness. , filters for air purifiers, filters for air conditioners, filters for ventilation fans, filters for toner removal used in copiers and printers, filters for vacuum cleaners, filters for precision equipment, pollen filters, dust masks, pollen prevention masks , and various masks such as medical masks, and improvements are being made (for example, Patent Document 1).
In addition, by attaching a fiber treatment agent containing sorbitan fatty acid esters and polyoxyalkylene alkyl ethers having a specific molecular structure to the fibers constituting the nonwoven fabric for air filters, the chargeability and collection efficiency of the nonwoven fabric are improved. is known (for example, Patent Document 2).

JP 2014-73443 A JP-A-2006-2329

When electret non-woven fabric is used as the various air filters described above, it has excellent charging performance including charging voltage immediately after charging treatment (charging performance immediately after charging treatment is called "initial charging performance"), and Efficiency is required.

Some air filters are used in high temperature environments. For example, air filters for vehicles, especially automobiles (air conditioner filters, pollen filters, etc.) may be exposed to an environment of 80°C or higher due to heat from the engine room or direct sunlight. . It is known that electret nonwoven fabrics are charged at such high temperatures, and there is a demand for improvement thereof.
Therefore, in view of the above problems, the present disclosure has excellent performance such as initial chargeability and collection efficiency, and preferably performance such as initial chargeability and collection efficiency even when exposed to a high temperature environment. To provide an air filter, a nonwoven fabric and a fiber therefor, which can maintain the

The present disclosure provides the following “fibers for electret processing”.
A fiber for electret processing, comprising a fiber containing a thermoplastic resin and a fiber treatment agent attached to the fiber,
The fiber treatment agent is attached to the fibers at a rate of 0.01 parts by mass or more and 3 parts by mass or less per 100 parts by mass of the fibers,
The fiber treatment agent has the following formula (1):
HO—(A ¹ O) _n —H (1)
[In the formula,
A ¹ O is an oxyalkylene group composed of at least one selected from the group consisting of an oxyethylene group, an oxypropylene group and an oxybutylene group,
n represents the average number of added moles of A ¹ O, and is 96 to 1135]
Including a polyalkylene glycol represented by
The number average molecular weight (Mn) of the polyalkylene glycol is 5000 or more and 50000 or less,
The polyalkylene glycol is contained in the fiber treatment agent at a rate of 20 parts by mass or more per 100 parts by mass of the fiber treatment agent.
Fiber for electret processing.
The present disclosure also provides a "nonwoven fabric" comprising the above fibers. Furthermore, the present disclosure provides an "air filter" including the above nonwoven fabric.

According to the present disclosure, it is possible to obtain an air filter that is excellent in performance such as initial chargeability and collection efficiency. Air filters, nonwovens and fibers therefor that are more durable are obtained.

1 is an exemplary schematic cross-sectional view of a modified cross-section composite fiber; FIG. FIG. 10 is an exemplary schematic cross-sectional view of another modified cross-section conjugate fiber; FIG. 4 is an exemplary schematic cross-sectional view of another modified cross-section composite fiber; FIG. 10 is an exemplary schematic cross-sectional view of yet another modified cross-section composite fiber;

(Fiber for electret processing)
FIELD OF THE DISCLOSURE The present disclosure relates to fibers for electret processing, comprising fibers comprising a thermoplastic resin, as described in detail below, and fiber treatment agents attached to the fibers. In the present disclosure, "fiber for electret processing" means a fiber that can be charged by a conventionally known electret processing or a fiber that is charged by a conventionally known electret processing (hereinafter abbreviated as "fiber for electret ” or simply “fiber”).

Conventional air filters generally use long-fiber nonwoven fabrics such as meltblown nonwoven fabrics, and short-fiber nonwoven fabrics using fibers with a fiber length of 10 to 120 mm. Short fiber nonwoven fabrics are manufactured by turning fibers into sheet-like fiber webs by, for example, carding or air laying. is required to be less likely to occur. Therefore, in order to suppress the generation of static electricity, a fiber treatment agent containing a surfactant is attached to the surface of the fibers used in the short fiber nonwoven fabric.

However, when electret treatment such as electret processing is performed while fiber treatment agents containing various surfactants such as conventional anionic surfactants and nonionic surfactants remain on the surface of the fiber, the effect of the electrification treatment is reduced. is hindered, that is, the treated fibers are not sufficiently charged, making it difficult to obtain a nonwoven fabric having good initial chargeability. In order to enhance the effect of the electrification treatment, the nonwoven fabric or fiber web may be washed with water before the electrification treatment, or the fiber treatment agent may be removed by forming a hydroentangled nonwoven fabric before the electrification treatment. To increase.

In addition, nonwoven fabrics such as needle-punched nonwoven fabrics and air-through nonwoven fabrics that require bulkiness and flexibility are reduced in bulk and softness when subjected to the above-described water washing treatment and hydroentanglement treatment. In addition, when electret processing is performed on these nonwoven fabrics, the fiber treatment agent used in the fibers suppresses the generation of static electricity in the process of manufacturing the fiber web. It is required that sufficient initial chargeability be obtained without impairing the chargeability.

Therefore, the electret fiber of the present invention includes, as one of the characteristics, that a polyalkylene glycol having a specific number average molecular weight is attached to the fiber as a fiber treatment agent. Thereby, for example, when producing a fibrous web from the fibers, the generation of static electricity can be suppressed. In addition, by heating the fiber assembly containing the fibers immediately before electret processing or during electret processing, the polyalkylene glycol can permeate into the fibers, so the amount of fiber treatment agent present on the fiber surface is reduced, and sufficient initial chargeability can be imparted to the fiber assembly by subsequent electret processing.

In addition, when such polyalkylene glycol penetrates into the fiber, it is difficult to re-elute due to the influence of heat, etc., so even if the electret-processed fiber aggregate is exposed to a high-temperature environment, the charging performance is maintained. It becomes difficult to decrease.

The fiber treatment agent is used in an amount of, for example, 0.01 to 3 parts by mass, preferably 0.03 to 2 parts by mass, more preferably 0.05 to 1 part by mass, per 100 parts by mass of fibers. (Here, the weight part of the solvent contained in the fiber treatment agent is not taken into account). When the amount of attached fiber is within the above range, the resulting fiber is not only excellent in processability (cardability of fiber) when forming a fiber web using a carding machine, but also does not fall off from the fiber. Textile treatment agents provide advantages such as less contamination of the production line. In addition, the amount of the fiber treatment agent attached to the fibers can be made more appropriate, the efficiency of the electrification treatment can be more maintained, and the initial electrification property can be more maintained.
In the present disclosure, the adhesion amount of the fiber treatment agent to fibers means the value of the adhesion amount that can be measured by the measurement method described in the examples described in detail below.

As will be described in detail below, the electret fiber of the present disclosure can be a fiber aggregate, especially a nonwoven fabric, and an air filter containing such a nonwoven fabric has excellent charging properties immediately after charging by electret processing. , collection efficiency, etc., and even when exposed to a high temperature environment (e.g., 80 ° C. or higher) after charging, properties such as excellent chargeability and collection efficiency immediately after charging are sufficiently maintained. (hereinafter sometimes referred to as "electret nonwoven fabric").

- Fiber treatment agent In the present disclosure, the fiber treatment agent has, as a main component, for example, the following formula (1):
HO—(A ¹ O) _n —H (1)
[In the formula,
A ¹ O is an oxyalkylene group composed of at least one selected from the group consisting of an oxyethylene group (EO), an oxypropylene group (PO) and an oxybutylene group (BO),
n represents the average number of added moles of A ¹ O, for example 96-1135, preferably 190-900, more preferably 280-790, particularly preferably 375-725, most preferably 465-720. ]
Including polyalkylene glycol represented by.

The above polyalkylene glycol may be a commercially available product, or may be synthesized separately according to a polyalkylene glycol synthesis method well known to those skilled in the art.

By using the fiber treatment agent containing the above polyalkylene glycol, the electret fiber of the present invention can be obtained by subjecting the fiber aggregate containing the fiber to electret processing to obtain a fiber aggregate having high initial chargeability. In addition, it is possible to suppress the deterioration of chargeability when the fiber assembly is exposed to a high temperature environment (for example, 80° C. or higher).

Here, general fiber treatment agents using various surfactants such as conventional anionic surfactants and nonionic surfactants tend to inhibit the effect of electrification treatment. That is, even if electrification treatment is performed in a state in which a general fiber treatment agent remains on the fiber surface, the initial electrification property of the fiber assembly after electrification treatment is often not good.
However, the fibers of the present disclosure are attached with a fiber treatment agent containing polyalkylene glycol represented by the above formula (1) as a main component. Since the polyalkylene glycol contains an oxyalkylene group (A ¹ O), the polyalkylene glycol tends to permeate into the thermoplastic resin constituting the fiber when heated in a state attached to the fiber.
When the fibers of the present disclosure are used as a fiber aggregate such as a fiber web or non-woven fabric and subjected to heat treatment, most of the polyalkylene glycol can penetrate into the interior of the thermoplastic resin, so the amount of fiber treatment agent present on the fiber surface can be significantly reduced. That is, the fiber of the present disclosure is subjected to heat treatment before the charging treatment or at the same time as the charging treatment for the fiber assembly containing the fiber, and the polyalkylene glycol permeates the thermoplastic resin to the fiber surface. can significantly reduce the amount of fiber treatment remaining in the When charging treatment such as electret processing is performed in this state, since the amount of the fiber treatment agent (polyalkylene glycol) remaining on the fiber surface is small, the charging treatment is performed efficiently, and a fiber aggregate with high initial chargeability can be obtained. .
^In addition, the polyalkylene glycol attached to the surface of the fiber of the present disclosure has a relatively large molecular weight and a molecular chain is a long polyalkylene glycol. Such polyalkylene glycols are considered to have high viscosity and low fluidity when liquefied. In addition, due to its large molecular weight, it is presumed that it has a high affinity with thermoplastic resins. Re-elution (re-elution to the fiber surface is generally referred to as "bleed-out") is less likely to occur, and the charging performance of the chargeable nonwoven fabric is less likely to decrease even in a fiber aggregate in a high-temperature environment. it is conceivable that. For these reasons, the fibers of the present disclosure are believed to exhibit the excellent effects described above, but the present invention is not limited by these reasons.

The polyalkylene glycol may be, for example, a homopolymer (homopolymer) such as ethylene oxide or propylene oxide, or a copolymer (copolymer). In the case of copolymers, they may be, for example, copolymers of ethylene oxide, propylene oxide and/or butylene oxide. Moreover, when the polyalkylene glycol is a copolymer, the polyalkylene glycol may be either a random polymer or a block polymer. Therefore, in A ¹ O of formula (1), the addition form of the oxyethylene group, oxypropylene group and/or oxybutylene group may be random or block. Also, there is no particular limitation on the repeating pattern of A ¹ O, and all addition forms are included.

The “ethylene group” of the “oxyethylene group” represents —CH ₂ —CH ₂ —.
The oxyethylene group accounts for, for example, 50% or more and 100% or less, preferably 60% or more and 95% or less, more preferably 70% or more and 90% or less, and particularly preferably is contained at a ratio of 75% or more and 85% or less, most preferably 77% or more and 83% or less. In the electret processing fiber of the present invention, the polyalkylene glycol contained in the fiber treatment agent attached to the fiber preferably has an oxyethylene group.

The “propylene group” of the “oxypropylene group” may be linear or branched and may be —CH ₂ —CH ₂ —CH ₂ —, —CH(CH ₃ )—CH ₂ —, —CH ₂ —CH(CH ₃ )- and -CH(CH ₂ CH ₃ )-.
The oxypropylene group may or may not be present, and is, for example, 0% or more and 50% or less, preferably 5% or more and 40%, based on the total number of repeating units (the average addition mole number n). Below, more preferably 10% or more and 30% or less, particularly preferably 15% or more and 25% or less, and most preferably 17% or more and 23% or less. In the electret processing fiber of the present invention, the polyalkylene glycol contained in the fiber treatment agent attached to the fiber preferably contains an oxypropylene group, and is present together with the oxyethylene group. is particularly preferred.

An “oxybutylene group” may be linear or branched and may be —CH ₂ —CH ₂ —CH ₂ —CH ₂ —, —CH(CH ₃ )—CH ₂ —CH ₂ —, —CH ₂ —CH( CH ₃ )-CH ₂ -, -CH ₂ -CH ₂ -CH(CH ₃ )-, -CH(CH ₂ CH ₃ )-CH ₂ -, -CH ₂ -CH(CH ₂ CH ₃ )-, -CH Including (CH ₃ )-CH(CH ₃ )-, -C(CH ₃ ) ₂ -CH ₂ - and -CH ₂ -C(CH ₃ ) ₂ -, -CH(CH(CH ₃ ) ₂ )-.
The oxybutylene group may or may not be present, and is, for example, 0% or more and 10% or less, preferably 0% or more and 8%, based on the total number of repeating units (the average number of added moles n). Below, more preferably 0% or more and 5% or less, particularly preferably 0% or more and 3% or less. In the electret processing fiber of the present invention, it is preferable that the polyalkylene glycol contained in the fiber treatment agent adhered to the fiber does not have an oxybutylene group.

Here, in A ¹ O of the above formula (1), the total number of oxyethylene groups, oxypropylene groups and oxybutylene groups does not exceed 100% with respect to the total number of repeating units (average added mole number n). .

In the above formula (1), A ¹ O is preferably an oxyalkylene group composed of at least one selected from the group consisting of an oxyethylene group and an oxypropylene group, and A ¹ O is an oxyethylene group and More preferably, it contains both oxypropylene groups. A ¹ O particularly preferably consists of an oxyethylene group and an oxypropylene group. In these cases, n is for example 100-1135, preferably 100-1120, more preferably 200-895, even more preferably 300-785, particularly preferably 400-715, most preferably 500-710.

When the A ¹ O contains both an oxyethylene group and an oxypropylene group, the oxyethylene group is, for example, 50% or more and less than 100%, preferably It is contained at a ratio of 60% to 95%, more preferably 70% to 90%, particularly preferably 75% to 85%, and most preferably 77% to 83%.
In addition, the oxypropylene group is more than 0% and 50% or less, preferably 5% or more and 40% or less, more preferably 10% or more and 30% or less, with respect to the total number of repeating units (the average added mole number n), especially It is preferably contained at a ratio of 15% or more and 25% or less, most preferably 17% or more and 23% or less. When the above A ¹ O contains both an oxyethylene group and an oxypropylene group, the ratio of the oxyethylene group to the total number of repeating units and the ratio of the oxypropylene group to the total number of repeating units are within the above ranges. , In the repeating portion of the polyalkylene glycol represented by the above A ¹ O, by maintaining a balance between hydrophilicity and hydrophobicity, not only the card passability of the fiber to which such polyalkylene glycol is attached is improved, but also the above It is possible to obtain effects such as the initial chargeability of the fiber to which the polyalkylene glycol is adhered and the high-temperature durability of the chargeability when the charge treatment is performed, and the like.

When the A ¹ O contains both an oxyethylene group (EO) and an oxypropylene group (PO), the EO/PO ratio (mass/mass) is, for example, 44/56 to 98/2, preferably 54/ 46 to 93/7, more preferably 64/36 to 88/12, particularly preferably 70/30 to 81/19, most preferably 71/29 to 78.5/21.5.
The EO/PO ratio (mol/mol) is, for example, 50/50 to 99/1, preferably 60/40 to 95/5, more preferably 70/30 to 90/10, particularly preferably 75/25. ~85/15, most preferably 77/23 to 83/17. Within the above range, when the above A ¹ O contains both an oxyethylene group and an oxypropylene group, the oxyethylene group and the oxypropylene group are balanced, that is, the hydrophilicity tends to be relatively strong. By maintaining a balance between the oxyethylene group and the oxypropylene group, which tends to be more hydrophobic than the oxyethylene group, not only does the card passability of the fiber to which such polyalkylene glycol is attached improve, but also the fiber surface The adhering polyalkylene glycol is likely to penetrate into the interior of the fiber (penetration of the polyalkylene glycol into the interior of the fiber), and the efficiency of charging treatment, initial charging property, and the like are likely to be improved.
In addition, the polyalkylene glycol has an oxypropylene group, which is considered to have a stronger tendency to be more hydrophobic than an oxyethylene group, so that the thermoplastic resin molecules that make up the fiber (for example, polypropylene molecules) are bound together. The polyalkylene glycol that has been strengthened and permeated into the fibers is less likely to bleed out to the surface of the fibers due to heat, and the high-temperature durability of charging performance is likely to be improved.

The polyalkylene glycol of formula (1) above can also be represented, for example, by the following formula (2), and includes polyalkylene glycols that may be either random polymers or block polymers.
HO—(EO) _x —(PO) _y —(BO) _z —H (2)
[In the formula,
EO represents an oxyethylene group as defined above,
PO represents an oxypropylene group as defined above,
BO represents an oxybutylene group as defined above,
x represents 48 to 1135, preferably 120 to 845, more preferably 215 to 690, particularly preferably 315 to 615, most preferably 410 to 585,
y represents 0 to 490, preferably 12 to 320, more preferably 30 to 215, particularly preferably 60 to 170, most preferably 90 to 155;
z represents 0 to 106, preferably 0 to 65, more preferably 0 to 35, particularly preferably 0 to 20;
The sum of x, y and z is, for example, 96 to 1135, preferably 190 to 900, more preferably 280 to 790, particularly preferably 375 to 725, most preferably 465 to 720]

Also in the polyalkylene glycol of the above formula (2), BO (oxybutylene group) is preferably absent, more preferably both EO and PO are present, and particularly preferably composed of EO and PO. In that case, both the EO/PO ratio (mass/mass) and the EO/PO ratio (mol/mol) are as described above.

In the present disclosure, the above EO/PO ratio is determined by measurement with ¹ H-NMR (also referred to as proton nuclear magnetic resonance), and linear and/or branched alkylene moieties contained in the polyalkylene glycol. can be obtained by calculating from the hydrogen peak integration ratio of . Examples of calculations are provided in the examples below.

The number average molecular weight (Mn) of the polyalkylene glycol of the present disclosure is, for example, 5000 or more and 50000 or less, preferably 10000 or more and 40000 or less, more preferably 15000 or more and 35000 or less, particularly preferably 20000 or more and 32000 or less, most preferably 25000 or more and 32000 or less. It is below. When Mn is within the above range, the viscosity of the polyalkylene glycol is moderate, and the productivity of the fiber of the present disclosure is improved. In addition, since the molecular size of polyalkylene glycol is relatively large, when such polyalkylene glycol is incorporated into the fiber, it is difficult to bleed out from the inside of the resin. It is possible to obtain effects such as improved durability.

The weight average molecular weight (Mw) of the polyalkylene glycol of the present disclosure is, for example, 6000 or more and 60000 or less, preferably 12000 or more and 48000 or less, more preferably 18000 or more and 42000 or less, particularly preferably 24000 or more and 38500 or less, most preferably 30000 or more and 38500 or less. It is below. When Mw is within the above range, the same effects as those obtained with the above preferred range of number average molecular weight can be obtained.

In the present disclosure, Mn and Mw mean values (standard polystyrene equivalent molecular weight) measured by gel permeation chromatography (GPC). Details of the method for measuring Mn and Mw are shown in Examples.

The polyalkylene glycol of the present disclosure is, for example, 20 parts by mass or more, preferably 40 parts by mass or more, more preferably 50 parts by mass or more, particularly preferably 70 parts by mass or more, and most preferably 80 parts by mass per 100 parts by mass of the fiber treatment agent. part or more in the fiber treatment agent (here, parts by mass of the solvent that may be contained in the fiber treatment agent are not taken into account). If it is within the above range, the polyalkylene glycol, which is the main component of the fiber treatment agent that adheres to the fiber surface or partially penetrates into the fiber, has an appropriate fluidity and penetrates into the fiber. , the high-molecular-weight polyalkylene glycol is hard to bleed out even when heated, so that the initial electrification of the fiber to which this fiber treatment agent is attached and the electrification performance when exposed to a high-temperature atmosphere are easily maintained. Become. The upper limit of the polyalkylene glycol contained in the fiber treatment agent is not particularly limited. It may be a fiber treatment agent in which the active ingredients (components other than the solvent such as water) are substantially all composed of the polyalkylene glycol. At this time, the fiber treatment agent is substantially the polyalkylene glycol.

Other components and solvents of the fiber treatment agent are not particularly limited, and components and solvents that can be usually blended in fiber treatment agents for fibers containing general thermoplastic resins can be appropriately used.
Components other than the polyalkylene glycol that can be contained in general fiber treatment agents include surfactants such as sulfate type (e.g. alkyl sulfate), sulfonate type (e.g. paraffin (alkane) sulfonate), Anionic surfactants such as carboxylic acid type (e.g. fatty acid salts) and phosphate type (e.g. POE alkyl (C8 _{- C24} ) phosphate, alkyl phosphate); ammonium type (e.g. alkyltrimethylammonium chloride ₍ C8 ~ _C24 )), benzalkonium type (e.g. alkyldimethylbenzalkonium chloride (C8 _{- C24} )), and alkylamine type (e.g. monomethylamine hydrochloride, dimethylamine hydrochloride, trimethylamine hydrochloride), etc. cationic surfactants of betaine type (e.g. dialkyl (C ₈ -C ₂₄ ) diaminoethyl betaine, alkyl (C ₈ -C ₂₄ ) dimethylbenzyl betaine), alkylamine oxide type (e.g. alkyl (C ₈ -C 8 -C ₂₄ ) dimethylamine N oxide), fatty acid amidopropyl betaine type, amino acid type (e.g. alkyl (C8 _{- C24} ) glutamate), and glycine type (e.g. dialkyl (C8 _{- C24} ) diaminoethylglycine, alkyl (C ₈ -C ₂₄ ) dimethylbenzylglycine); sugar ester type (also called "polyhydric alcohol ester type") (e.g. sorbitan fatty acid ester (C ₁₂ -C ₁₈ )), fatty acid ester type (e.g. POE fatty acid ester (C ₁₂ -C ₁₈ )), alcohol type (e.g. POE alkyl ether), alkylphenol type (e.g. POE alkyl (C ₈ -C ₁₂ ) phenyl ether), alkylamine type (e.g. POE alkylamine (C ₁₂ -C ₁₈ )), bisphenol type (POE fatty acid bisphenyl ether), polyaromatic ring type (POA benzylphenyl (or phenylphenyl) ether), silicone-based, fluorine-based, and vegetable oil-type (e.g., POE Nonionic surfactants (nonionic surfactants) such as castor oil, POE hardened castor oil), and the like. In addition to these various surfactants, various functional agents such as fragrant functional agents, deodorants, antibacterial agents, allergen deactivators, endothermic agents, exothermic agents and flame retardants may be included.

- Fiber In the present disclosure, the fiber to which the fiber treatment agent can be attached is not particularly limited as long as it contains a thermoplastic resin and the fiber targeted by the present disclosure can be obtained. By including a thermoplastic resin, for example, when fabricating a nonwoven fabric, for example, fibers can be fused to each other by heating.

The fineness of the fibers is not particularly limited, but the fineness is preferably 0.1 dtex or more and 100 dtex or less. This is because when the fineness of the fibers satisfies the above range, a nonwoven fabric having a good balance between air permeability and collection efficiency can be obtained. The fineness is more preferably 0.3 dtex or more and 70 dtex or less, particularly preferably 0.5 dtex or more and 30 dtex or less, and most preferably 0.8 dtex or more and 8 dtex or less.

The fiber length of the fiber is not particularly limited, but may be 3 mm or more and 120 mm or less. For example, when manufacturing a nonwoven fabric by a method of manufacturing a fiber web using a carding machine, the fiber length is preferably 20 mm or more and 120 mm or less. When the fiber length is 20 mm or more, the fibers are less likely to come off. When the fiber length is 120 mm or less, it is easy to form a fiber web with a carding machine. When the fiber web is formed by a carding machine, the fiber length of the fibers is more preferably 26 mm or more and 80 mm or less, and particularly preferably 28 mm or more and 65 mm or less. On the other hand, when the fiber web is produced by an air laying method (also referred to as an air laying method) or a wet method, the fiber length of the above fibers is preferably 3 mm or more and 45 mm or less, more preferably 3 mm or more and 35 mm or less. It is preferably 5 mm or more and 30 mm or less, and most preferably 10 mm or more and 25 mm or less.

Examples of the thermoplastic resin include various polyester-based resins such as polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polylactic acid, and polybutylene succinate; various modified polyester-based resins such as acid-modified polyester-based resins; Resin: Various polyethylene resins such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, ultra-high molecular weight polyethylene, etc. Various polypropylene-based resins such as isotactic, atactic, and syndiotactic polymerized using Ziegler-Natta catalysts and metallocene catalysts, various polymethylpentene-based resins, various polybutene-1-based resins, ethylene-vinyl alcohol copolymerization Various polyolefin resins such as resins and ethylene-propylene copolymer resins; Various modified polyolefin resins such as acid-modified polyolefin resins; Polyamide resins such as nylon 6, nylon 66, nylon 11 and nylon 12; polycarbonate, polyacetal, polystyrene , engineering plastics such as cyclic polyolefins;

The fiber preferably contains at least one acid-modified resin selected from the group consisting of acid-modified polyolefin-based resins and acid-modified polyester-based resins as a thermoplastic resin. Acid-modified polyolefin resins are polyolefin resins modified by copolymerizing (for example, graft copolymerizing) unsaturated carboxylic acids or anhydrides of various polyolefin resins (graft modification in the case of graft copolymerization). Acid-modified polyester-based resins are polyester-based resins modified by copolymerizing unsaturated carboxylic acids or their anhydrides to various polyester-based resins. By blending these acid-modified resins into fibers, for example, when the fibers are made into various nonwoven fabrics and then subjected to electrification treatment by electret processing, charges are easily captured by the acid-modified resins and are stable. It is assumed that the charge is retained. In addition, since the acid-modified resin has a polar group and is a resin with a strong compatibilizing effect, it is presumed that the effect of retaining the polyalkylene glycol that has penetrated from the fiber surface into the inside of the fiber is strong. As a result, even if the nonwoven fabric is heated after the electret processing, the polyalkylene glycol incorporated into the fibers is less likely to be re-eluted, and it is presumed that the attenuation resistance in a high-temperature environment is improved.

The above acid-modified polyolefin resins include various polyolefin resins, for example, various polyethylene resins such as low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, ultra high molecular weight polyethylene, isotactic, atactic, Various polypropylene resins such as syndiotactic, polymethylpentene resins, polybutene-1 resins, ethylene-vinyl alcohol copolymer resins, ethylene-propylene copolymer resins, polyolefin resins such as cyclic polyolefins, which are acid-modified polyolefin resins There is no particular limitation. An unsaturated carboxylic acid is preferably used as the acid for modifying the polyolefin resin. Examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, citraconic acid, sorbic acid, maleic anhydride, itaconic anhydride, and citraconic anhydride. , Maleic acid, maleic anhydride, acrylic acid, or methacrylic acid is used to acid-modify a polyolefin resin. A method of dissolving a polyolefin resin in a solvent and adding a graft monomer to copolymerize it, or a method of making various polyolefin resins into an aqueous suspension and then adding a graft monomer to copolymerize it. On the other hand, it is preferable to graft-polymerize an unsaturated carboxylic acid or its anhydride. Commercially available acid-modified polyolefin resins include, for example, Modic (registered trademark) and Rexpearl (registered trademark) sold by Mitsubishi Chemical Corporation, Admer (registered trademark) sold by Mitsui Chemicals, Inc., Umex (registered trademark) sold by Sanyo Kasei Co., Ltd., Nucrel (registered trademark) sold by Mitsui-DuPont Polychemicals Co., Ltd., and the like.

Although the acid value of these acid-modified polyolefin resins is not particularly limited, it is preferably 3 mg(KOH)/L or more and 150 mg(KOH)/L or less. If the acid value of the acid-modified polyolefin resin is within the above range, the fibers containing these acid-modified resins will trap an electric charge inside the fibers when subjected to an electrification treatment, and an air flow using the obtained fiber assembly will occur. The initial chargeability of the filter is improved, and its performance is easily maintained over a long period of time. The acid value of the acid-modified polyolefin resin is more preferably 5 mg (KOH)/L or more and 125 mg (KOH)/L or less, and particularly preferably 5 mg (KOH)/L or more and 100 mg (KOH)/L or less. , 8 mg (KOH)/L or more and 60 mg (KOH)/L or less.
In the present invention, the acid value of the acid-modified polyolefin resin can be measured according to JIS K 0070 3.1 neutralization titration method.

Even if the fiber is a single fiber containing one or more resins selected from the thermoplastic resins, the first component containing one or more resins selected from the thermoplastic resins; It may be a composite fiber containing a second component containing one or more resins selected from thermoplastic resins. Furthermore, the third, fourth, fifth, etc. components containing one or more resins selected from the above thermoplastic resins may be included as necessary.

When the fibers are conjugated fibers, the conjugated state is not particularly limited. For example, the conjugate fiber may be a sheath-core conjugate fiber, an eccentric sheath-core conjugate fiber, a side-by-side conjugate fiber, a split conjugate fiber, or a sea-island conjugate fiber.

When the fiber is a conjugate fiber, it is preferably a core-sheath type conjugate fiber in which the first component forms the sheath portion and the second component forms the core portion.

When the fiber is a core-sheath type composite fiber, the acid-modified resin may be contained in either one or both of the first component (sheath component) and the second component (core component), but at least It is preferably contained in the first component (sheath component). By including the acid-modified resin in the thermoplastic resin that constitutes the first component, the fiber treatment agent adhering to the surface of the fiber can easily penetrate into the interior of the fiber, enhancing the effect of electrification treatment and increasing the initial electrification property. It becomes easier to obtain a fiber aggregate. In addition, for example, when this fiber is made into a non-woven fabric and then charged, the charge is easily captured by the acid-modified resin and the charge is stably retained. is expected to be maintained over the long term. In addition, acid-modified resins tend to have excellent adhesion to thermoplastic resins and materials other than thermoplastic resins (for example, metal materials). When a fibrous web containing fibers is subjected to heat bonding treatment, not only can the fibers be bonded in a short time, but also the fibers can be strongly bonded to each other. is improved, and other effects can be obtained.

The cross-sectional shape of the fibers is not particularly limited, and may be, for example, a circular cross-section, or an irregular cross-section such as oval, Y-shaped, X-shaped, I-shaped, polygonal, star-shaped, and leaf-shaped such as 2 to 8 lobes. may be

Here, FIGS. 1 to 4 more specifically illustrate cross-sectional shapes of conjugate fibers having modified cross sections (or modified cross section conjugate fibers). Each of these figures exemplifies the cross section of a conjugate fiber composed of a first component and a second component.
FIG. 1 has a quatrefoil cross-sectional shape with four protrusions. The conjugate fiber 100 in FIG. 1 is a so-called core-sheath type conjugate fiber in which the first component 1 entirely covers the second component 2, and the outline of the first component 1 and the outline of the second component 2 are substantially similar. ing.
FIG. 2 has an octalobed cross-sectional shape with eight protrusions. The conjugate fiber 100 shown in FIG. 2 is a so-called core-sheath type conjugate fiber in which the first component 1 entirely covers the second component 2, and the outline of the first component and the outline of the second component are substantially similar. .
FIG. 3 has a quatrefoil cross-sectional shape with four protrusions. In the conjugate fiber 100 of FIG. 3, the first component 1 is located only at the tips of the projections. That is, in the conjugate fiber of FIG. 3, the second component 2 has a modified cross section and substantially determines the cross-sectional shape of the fiber, the first component 1 covers a part of the convex part of the second component 2, and the The bicomponent 2 is a conjugate fiber having four protrusions, and the recesses between the protrusions form an acute angle.
The conjugate fiber 100 of FIG. 4 has a tetralobal cross-sectional shape (cross-shaped cross section) with four convex portions. In the conjugate fiber 100 shown in FIG. 4, the cross section of the second component 2 is substantially circular, and the first component 1 covering the outer periphery of the second component 2 forms four projections.
In FIGS. 1 to 4, the concave portions between the convex portions are described as acute angles, but in the present disclosure, the obtuse angles of 90° or more may also be used.
The illustrated cross-sectional shapes are all examples, and the cross-sectional shape of the modified cross-section conjugate fiber may be other shapes. For example, in the modified example of the composite fiber shown in FIG. 4, six or eight protrusions may be formed, or the number of protrusions may be three. Alternatively, the illustrated conjugate fiber may further contain a third component. In that case, a third component with a substantially circular fiber cross-section may be located in the center of the second component, or a third component with a contour that is substantially similar to the contour of the second component. may be placed inside the
Alternatively, the modified cross-section conjugate fiber may have a cross-sectional shape as a whole, for example, in a form in which the second component is divided into two or more pieces.

The fibers of the present disclosure may be so-called solid fibers, which have no cavities inside the fiber, hollow fibers having at least one longitudinally continuous cavity portion, or Hollow fibers having discontinuous cavities in the length direction of the fibers may also be used.

- Attachment of fiber treatment agent The method of attaching the fiber treatment agent to the fiber is not particularly limited as long as the fiber targeted by the present disclosure can be obtained. Examples include spray coating, brush coating, and immersion of the fiber in the fiber treatment agent. Specifically, the fiber treatment agent may be applied to the fibers in at least one stage such as after fiber spinning, before fiber drawing, and after fiber drawing. Alternatively, the web of fibers may be immersed in the fiber treatment agent, or the web of fibers may be impregnated with the fiber treatment agent by spraying or brushing the fiber treatment agent.

The fibers of the present disclosure obtained by adhering the fiber treatment agent to the fibers are subjected to a known electrification treatment, specifically, corona discharge treatment or By subjecting a fiber surface to an electret treatment such as a plasma discharge treatment to polarize and charge the surface of the fiber, the fiber, web or non-woven fabric can be imparted with electrification properties. Here, "chargeability" means a state of being charged with electricity or static electricity, or a state in which electric charge is retained. The conditions for the charging treatment are not particularly limited as long as the fibers aimed at by the present disclosure can be obtained. For example, conditions may be appropriately determined by a method known to those skilled in the art.

(non-woven fabric)
The nonwoven fabric of the present disclosure contains at least the above-described electret fibers, and if necessary, may contain "other fibers" described below.
The nonwoven fabric preferably contains 30% by mass or more of electret fibers. A nonwoven fabric (or air filter) containing electret fibers in this proportion tends to achieve high collection efficiency and long life. The nonwoven fabric preferably contains 50% by mass or more of electret fibers, particularly preferably 70% by mass or more, and most preferably consists of electret fibers alone.

The type of nonwoven fabric is not particularly limited, and the nonwoven fabric obtained by making the above fibers into a fiber web, specifically, the above fibers are processed into parallel webs, semi-random webs, random webs, and cross webs using a wet papermaking method and a carding machine. Alternatively, it may be obtained by fabricating a web by a card method for fabricating a criss-cross web or by an air laying method, and then integrating the web by heat bonding treatment (thermal processing). The thermal adhesion treatment is preferably carried out in order to thermally bond the fibers by melting or softening the thermoplastic resin contained in the fibers with heat.

The heat bonding treatment may be performed using, for example, a hot air processing machine (including an air-through type heat processing machine), an infrared heat processing machine, or a hot roll processing machine. Among them, the heat bonding treatment is preferably performed by passing hot air in the thickness direction of the nonwoven fabric. For example, by blowing hot air onto one side of the nonwoven fabric and sucking the hot air from the other side of the nonwoven fabric, the hot air can be passed through the nonwoven fabric in the thickness direction. By adopting such a process, it is possible to obtain a nonwoven fabric in which fibers are uniformly bonded in the thickness direction of the nonwoven fabric. The thermal adhesion treatment is preferably carried out by blowing hot air using, for example, a hot air penetration heat treatment machine or a hot air blowing heat treatment machine. Therefore, it is preferable to carry out the heat bonding treatment at a temperature higher than the melting point of the thermoplastic resin after spinning by about 0°C to 50°C.

Web consolidation may be performed by one or more methods selected from needle punching and/or high pressure water jet treatment. These treatments may be in addition to the thermal bonding process, for example, the web may be subjected to needle punching and/or high pressure water jet treatment prior to the thermal bonding process.

The basis weight of the non ^- woven fabric is not particularly limited. m ² , preferably 15 g/m ² to 200 g/m ² , more preferably 20 g/m ² to 150 g/m ² . When the basis weight is 10 g/m ² or more, a nonwoven fabric having a more uniform basis weight can be obtained, and collection unevenness is reduced. If it is 300 g/m ² or less, it can be more uniformly charged in the thickness direction by the charging treatment.

In addition, when used as a mask (dust mask, pollen prevention mask, medical mask, etc.), the basis weight is usually 5 g/m ² to 100 g/m ² , preferably 10 g/m ² to 80 g/m ² , or more. It is preferably 15 g/m ² to 70 g/m ² . When the basis weight is 5 g/m ² or more, a nonwoven fabric having a more uniform basis weight can be obtained, and fine suspended matter in the air such as dust and pollen can be easily collected. When it is 100 g/m ² or less, the air permeability is high, and there is a tendency for easier breathing when worn as a mask.

Two or more nonwoven fabrics containing the predetermined electret fibers may be used in a laminated state. Laminated nonwovens may be partially or entirely consolidated, or may be unconsolidated. Integration may be achieved by thermal bonding of the thermoplastic resin, or may be achieved by stitching, entangling of fibers, or adhesive. In addition, the nonwoven fabric may be subjected to a pleating process called pleating. In that case, the laminate may be pleated after laminating two or more nonwoven fabrics, or the pleated ones may be laminated. may

The nonwoven fabric of the present disclosure may be in a state in which one surface is positively charged and the other surface is negatively charged, for example, by being subjected to the charging treatment described above. More specifically, the entire nonwoven fabric can be electrified by modifying the surface of the electret fiber contained in the nonwoven fabric by the charging treatment to polarize the electrical polarity of the fiber surface. By electrifying the nonwoven fabric in this way, the electric charges are concentrated and captured at the intersections of the fibers, the recesses on the surface of the fibers, especially the sharp recesses, and the like, so that the electric charges can be stably retained.

- Other fibers The nonwoven fabric may contain other fibers as long as it contains the predetermined electret fibers (hereinafter, fibers other than the predetermined electret fibers are also referred to as "mixed fibers" for convenience). . The type of mixed fiber is not particularly limited, and ramie (ramie), linen (flax), kenaf (western hemp), abaca (manila hemp), henken (sisal hemp), jute (burlap), hemp (cannabis), palm , palm, paper mulberry, mitsumata, and bagasse, and semi-synthetic fibers (also referred to as regenerated fibers) such as viscose rayon, Tencel (registered trademark), lyocell (registered trademark), and cupra. The mixed fibers are preferably fibers made of synthetic resin.

Examples of synthetic resin fibers that can be used as mixed fibers include single fibers made of known polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polylactic acid, and polybutylene succinate. , low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, ultra-high molecular weight polyethylene, etc. A single fiber, a single fiber made of known polypropylene resins such as isotactic, atactic, and syndiotactic polymerized using a normal Ziegler-Natta catalyst or metallocene catalyst, or a co-polymer of these polyolefin monomers Polymerized resins, or single fibers made of known polyolefin resins such as polyolefins using metallocene catalysts (also called Kaminsky catalysts) when polymerizing these polyolefins, nylon 6, nylon 66, nylon 11, nylon 12, etc. Single fibers made of known polyamide resins, single fibers of (poly)acrylic made of acrylonitrile, single fibers of engineering plastics such as polycarbonate, polyacetal, polystyrene, and cyclic polyolefin, polyesters, polyolefins, polyamides, engineering plastics, etc. Examples include a single fiber of plastic, a composite fiber obtained by combining different types of resins, or resins composed of the same type of different polymer components (for example, polyethylene terephthalate and polytrimethylene terephthalate).

When the mixed fiber is a composite fiber made of a synthetic resin, the composite state is not particularly limited. For example, the conjugate fiber may be a sheath-core conjugate fiber, an eccentric sheath-core conjugate fiber, a side-by-side conjugate fiber, a split conjugate fiber, or a sea-island conjugate fiber. Also, the cross section of the synthetic fiber may or may not be round, and may have the irregular cross section described above.

The mixed fiber is not particularly limited in its cross-sectional shape, material (for example, the type and number of synthetic resins), or in the case of a composite fiber composed of a plurality of resin components, the combination of synthetic resins and the composite form of the constituent resins. is as described above. Further, the fineness, fiber length, cross-sectional shape of the mixed fiber, and the composite ratio when the mixed fiber is a composite fiber are not particularly limited.
The fineness of the mixed fiber is preferably 0.1 dtex or more and 100 dtex or less, and more preferably 0.3 dtex or more and 70 dtex or less. In addition, the fiber length of the mixed fiber is selected according to the method of manufacturing the fiber web in the same manner as the fiber length of the electret fiber, and when the fiber web is formed by a carding machine, the fiber length of the mixed fiber is 26 mm or more and 80 mm. It is preferably 28 mm or more and 65 mm or less. On the other hand, when the fiber web is produced by an air-laid method (also called an air-laid method) or a wet method, the fiber length of the mixed fiber is preferably 3 mm or more and 45 mm or less, and more preferably 3 mm or more and 35 mm or less. It is more preferably 5 mm or more and 30 mm or less, and most preferably 10 mm or more and 25 mm or less.

The nonwoven fabric of the present disclosure may be composed of the electret fibers alone, or may be composed of the electret fibers and the mixed fibers.

(air filter)
The air filter of the present disclosure includes an assembly of the above fibers, especially the above nonwoven fabric, especially an electret nonwoven fabric charged by electret processing, and is Suspended matter, especially particles, with a size of .25 μm to 5 μm can be collected. In addition, when the air filter of the present disclosure is an electret nonwoven fabric, its electrostatic collection ability allows it to collect suspended matter with a size of 0.5 μm or less (e.g., dust, smoke dust, pollen, viruses, etc.). Floating matter larger than 0.5 μm and less than 10 μm can be physically collected at fiber intersections, and suspended matter of 10 μm or more can be physically collected by the gaps between fibers. It is considered possible. Therefore, it can function well as an air filter.

The air filter of the present disclosure may be one that does not substantially hinder the passage of gas, and has an air permeability of, for example, 50 cc/cm ² /sec or more, preferably 80 cc/cm ² /sec or more. In one embodiment of the present invention, the air permeability of an air filter refers to the amount of air passing through a test piece measured according to JIS L 1913:2010 6.8.1 Frazier method.

The field of application of the air filter of the present disclosure is not particularly limited as long as it can be used as an air filter for collecting suspended matter floating in gas. Air filters of the present disclosure include, for example, dust filters, air purifier filters, air conditioner filters, ventilation fan filters, toner removal filters used in copiers and printers, vacuum cleaner filters, and precision equipment filters. , pollen filters, masks (eg, dust masks, pollen masks, medical masks), etc.

EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples of the present invention, but the present invention is not limited to the following examples.
First, materials used in Examples and Comparative Examples are described.

・ Resin polypropylene resin (PP): Novatec (registered trademark) SA03 (product number) manufactured by Japan Polypropylene Corporation (melting point: 160 ° C., MFR: 30 g / 10 minutes)
Acid-modified polypropylene resin (modified PP): Modic (registered trademark) P908 (product number) manufactured by Mitsubishi Chemical Corporation (melting point: 150°C, acid value: 12.8)
Polyethylene terephthalate resin (PET): melting point: 250°C, intrinsic viscosity value (IV value): 0.64)

Fiber treatment agent Fiber treatment agent A: A polyalkylene glycol represented by the above formula (1) having a number average molecular weight (Mn) of about 29000 and a weight average molecular weight (Mw) of about 36000, —A ¹ O— is composed of an oxyethylene group (EO) and an oxypropylene group (PO), the EO/PO molar ratio is 80/20 (mol/mol), and the mass ratio is 75/ 25 (mass/mass) polyalkylene glycol is included as an active ingredient of the fiber treatment agent (aqueous fiber treatment agent solution), that is, in a proportion of 100 parts by weight per 100 parts by weight of components other than water as a solvent. (that is, the active ingredients of the fiber treatment agent are all polyalkylene glycols).
Fiber treatment agent B: ^A polyalkylene glycol represented by the above formula (1) having a number average molecular weight (Mn) of about 30,000 and a weight average molecular weight (Mw) of about 38,000; - is composed of an oxyethylene group (EO) and an oxypropylene group (PO), the molar ratio of EO/PO is 88/12 (mol/mol), and the mass ratio is 85/15 (mass/ polyalkylene glycol is contained in a ratio of 100 parts by mass with respect to 100 parts by mass of components other than water, which is a solvent, as an active ingredient of the fiber treatment agent (aqueous fiber treatment agent solution) (i.e., A fiber treatment agent whose active ingredients are all the above-mentioned polyalkylene glycols.
Fiber treatment agent C: a polyalkylene glycol represented by the above formula (1), having a number average molecular weight (Mn) of about 2100 and a weight average molecular weight (Mw) of ^about 2200; - is composed of an oxyethylene group (EO) and an oxypropylene group (PO), the molar ratio of EO/PO is 80/20 (mol/mol), and the mass ratio is 75/25 (mass/ polyalkylene glycol is contained in a ratio of 100 parts by mass with respect to 100 parts by mass of components other than water, which is a solvent, as an active ingredient of the fiber treatment agent (aqueous fiber treatment agent solution) (i.e., A fiber treatment agent whose active ingredients are all the above-mentioned polyalkylene glycols.
Fiber treatment agent D: A monoester of polyethylene glycol having a molecular weight of 600 and oleic acid (polyethylene glycol oleic acid monoester) is used as an active ingredient of the fiber treatment agent (aqueous fiber treatment agent solution), that is, as a component other than water as a solvent. A fiber treatment agent contained in a ratio of 100 parts by mass to 100 parts by mass (that is, all active ingredients of the fiber treatment agent are the above monoesters).

The molecular weights (Mn and Mw) of the polyalkylene glycol can be measured as follows.
Determination of molecular weight (Mn and Mw) of polyalkylene glycol by GPC (gel permeation chromatography) Using the following GPC apparatus, the elution curve and molecular weight of the polyalkylene glycol (after drying under _N2 gas flow) Molecular weights (Mn and Mw) are determined by constructing distribution curves.

・GPC
Apparatus: HLC-8320GPC manufactured by Tosoh Corporation
Column: Showa Denko KK Shodex (registered trademark) KG + K-805L x 2 + K-800D
Eluent: chloroform Temperature: 40°C
Concentration: 0.1 wt/vol%
Flow rate: 1.0 mL/min
Solubility: complete dissolution Injection volume: 100 μL
Pretreatment: Filtration (0.45 μm filter)
Detector: differential refractometer (RI)

The molecular weights (Mn and Mw) of polyalkylene glycol were calculated as standard polystyrene equivalent molecular weights using a standard polystyrene (standard PS) calibration curve.

ＥＯ（モル比）＝１００×［（ｂ－ａ）／４］／｛［（ｂ－ａ）／４］＋（ａ／３）｝
ＰＯ（モル比）＝１００×（ａ／３）／｛［（ｂ－ａ）／４］＋（ａ／３）｝
ＥＯ（質量比）＝１００×４４×［（ｂ－ａ）／４］／｛４４×［（ｂ－ａ）／４］＋５８×（ａ／３）｝
ＰＯ（質量比）＝１００×５８×（ａ／３）／｛４４×［（ｂ－ａ）／４］＋５８×（ａ／３）｝

必要に応じて、^１３Ｃ－ＮＭＲを用いて、ＥＯ／ＰＯの比（質量比およびモル比）を算出してもよい。 The EO/PO ratio (mass ratio and molar ratio) of the polyalkylene glycol can be measured as follows.
Determination of the EO/PO ratio (mass and molar ratio) of polyalkylene glycol by ¹ H ^- NMR ₍ proton nuclear magnetic resonance). The EO/PO ratio (mass ratio and molar ratio) is determined from the peak areas of the hydrogen atoms contained in EO and PO from the ¹ H-NMR chart of (after drying under low temperature).

・1H ^- NMR
Apparatus: Model AL-400 manufactured by JEOL Ltd. Observation nucleus: ¹ H
Solvent: _CDCl3

·a formula
From the ¹ H-NMR chart, for example, from the peak area ratio of the hydrogen atoms a and b contained in EO and PO shown in the chemical structures below, the EO/PO ratio (mass ratio and molar ratio) is calculated according to the following formula. can be calculated.

EO (molar ratio) = 100 × [(ba) / 4] / {[(ba) / 4] + (a / 3)}
PO (molar ratio) = 100 × (a / 3) / {[(ba) / 4] + (a / 3)}
EO (mass ratio) = 100 x 44 x [(b - a) / 4] / {44 x [(b - a) / 4] + 58 x (a / 3)}
PO (mass ratio) = 100 × 58 × (a / 3) / {44 × [(ba) / 4] + 58 × (a / 3)}

If necessary, ¹³ C-NMR may be used to calculate the EO/PO ratio (mass ratio and molar ratio).

(fineness and fiber length)
The fineness and fiber length were measured according to JIS L 1015:2010.

(Adhesion amount of fiber treatment agent)
The amount of the fiber treatment agent adhered to the fiber was measured by a rapid extraction method using an R-II type rapid residual fat extractor manufactured by Tokai Keiki Co., Ltd.
First, about 4 g of fibers of the following examples and comparative examples for measuring the adhesion amount of the fiber treatment agent were sampled, processed into a fiber web by a carding machine, and the mass (W _F (g)) of the fiber web (sample) obtained was measured. After filling the fiber web whose mass was measured into a metal cylinder (inner diameter 16 mm, length 130 mm, mortar-shaped bottom with a hole of 1 mm diameter at the bottom), 10 mL of methanol was added from the top.
The fiber treatment agent adhering to the surface of the fiber dissolves in the supplied methanol and drips from the hole at the bottom of the metal cylinder. It was received with heating and the methanol was allowed to evaporate.
At this time, the aluminum dish that collects the dripping methanol should be thoroughly washed in advance and then thoroughly dried in a dryer. Mass: W ₁ (g)) is measured.
All the methanol in the metal cylinder is transferred to an aluminum dish, and the methanol is completely evaporated, leaving the fiber treatment agent extracted from the fibers on the aluminum dish.
The mass (W ₂ (g)) of the aluminum dish on which the fiber treatment agent remained was measured, and the amount of the fiber treatment agent adhering to the fibers was calculated from the following formula.

Amount of fiber treatment agent adhered per 100 parts by mass of fiber (parts by mass) = {[W ₂ −W ₁ ]/[W _F −(W ₂ −W ₁ )]}×100
[In the formula,
W ₁ denotes the mass of the aluminum dish,
W ₂ indicates the total mass of the aluminum dish and the textile treatment,
_WF indicates the mass of the sample. ]

Example 1
・Preparation of concentric conjugate fiber The first component (sheath component) is the above polypropylene resin (PP) (resin 1a: 96% by mass) and the above acid-modified polypropylene resin (modified PP) (resin 1b: 4% by mass). The second component (core component) is composed of the above polyethylene terephthalate resin (PET) (resin 2a: 100% by mass), and the first component is concentric on the second component, both with a circular cross section An undrawn concentric conjugate fiber (spun filament fineness: 10 dtex) was prepared by melt spinning. The conjugate ratio (volume ratio) during melt spinning of this concentric conjugate fiber is 50/50 (second component/first component). Next, the undrawn spun filament was subjected to a drawing treatment. The drawing is performed by wet drawing using hot water, and the undrawn spun filament is drawn at a drawing ratio of 2.5 times in a water tank filled with hot water at 80° C. to obtain a drawing of 4.4 dtex. filament.
- Attachment of fiber treatment agent Fiber treatment agent A is diluted with water to prepare an aqueous solution (diluted solution) of fiber treatment agent A having a polyalkylene glycol concentration of 3% by mass. Next, the drawn filaments are impregnated with the prepared diluted solution of the fiber treatment agent A, excess aqueous solution of the fiber treatment agent A is dehydrated with nip rolls, and mechanically crimped with a stuffing box type crimper, 15 crimps/25 mm were applied. Then, the mechanically crimped stretched filaments were simultaneously subjected to annealing treatment and drying treatment in a relaxed state for about 15 minutes using a hot air blower set at 110°C. The well-dried drawn filament was cut into 51 mm fiber lengths to form Example 1 fibers. A fiber treatment agent A (that is, polyalkylene glycol) is attached to the surfaces of the fibers in a proportion of 0.28 parts by mass per 100 parts by mass of the fibers alone.
・Production of nonwoven fabric After opening the above fibers to produce a web, the web is subjected to heat treatment with a hot air penetration type heat treatment machine (170 ° C), and the fibers are thermally bonded with the first component to form a thermally bonded nonwoven fabric ( 1.0 mm thick, 100 g/m ² basis weight) was produced (air-through method).
・Electrification treatment Next, while conveying the nonwoven fabric on a stainless steel mesh conveyor, in an atmosphere of 100 ° C., a DC high electric field of 7 to 20 Kv is generated by an applied electrode in which needles are embedded at regular intervals, and the fiber surface A charged electret nonwoven fabric was obtained by electret processing in which the was polarized and charged.

Example 2
An electret nonwoven fabric was produced in the same manner as in Example 1, except that "fiber treatment agent B" was used as the fiber treatment agent and the amount of the fiber treatment agent applied was set to "0.33 parts by mass".

Example 3
An electret nonwoven fabric was produced in the same manner as in Example 1, except that the amount of the fiber treatment agent applied was set to "0.35 parts by mass".

Example 4
The first component (sheath component) of the fiber is composed of the above polypropylene resin (PP) (resin 1a: 93% by mass) and the above acid-modified polypropylene resin (modified PP) (resin 1b: 7% by mass). , an electret nonwoven fabric was produced in the same manner as in Example 1, except that the amount of the fiber treatment agent applied was set to "0.23 parts by mass".

Example 5
Except that the first component (sheath component) of the fiber is composed of the above polypropylene resin (PP) (resin 1a: 100% by mass), and the amount of the fiber treatment agent attached is set to "0.32 parts by mass", An electret nonwoven fabric was produced in the same manner as in Example 1.

Example 6
In the same manner as in Example 1, except that the fiber fineness was set to "2.2 dtex", the air-through method was changed to the following "needle punch method", and the thickness of the nonwoven fabric before needle punch was set to 1.4 mm. , electret nonwoven fabric was produced.
- Needle Punch Method 100% by mass of fibers (that is, fibers to which 0.28 parts by mass of the fiber treatment agent A is attached) were applied to a parallel card, and a crosslayer was used to prepare a crosslay web. This crosslay web was needle-punched using a conical blade manufactured by Foster Needle Co., Ltd. with a needle depth of 7 mm and a penetration number (front: 6 N/cm ² back: 6 N/cm ² ). The needle-punched web was heat-treated at the above processing temperature for 20 seconds using a hot-air circulating heat treatment machine set at 140° C. to obtain a nonwoven fabric (thickness: 1 mm, basis weight: 100 g/cm ² ).

Example 7
Both the first component and the second component of the fiber are composed of the above polypropylene resin (PP) (96% by mass) and the above acid-modified polypropylene resin (modified PP) (4% by mass). An electret nonwoven fabric was produced in the same manner as in Example 6, except that a single fiber having a four-leaf resin cross section was prepared and the amount of the fiber treatment agent applied was set to "0.3 parts by mass".

Example 8
The first component (sheath component) of the fiber is composed of the above polypropylene resin (PP) (resin 1a: 100% by mass), and the second component (core component) is the above polypropylene resin (PP) (resin 2a: 96% by mass) and the acid-modified polypropylene resin (modified PP) (resin 2b: 4% by mass), and the cross-sectional shape of both the first component and the second component is a tetralobal composite fiber (Fig. 1) An electret nonwoven fabric was produced in the same manner as in Example 6, except that the was prepared.

Example 9
Both the first component and the second component of the fiber are composed of a so-called single resin composed of the above polypropylene resin (PP) (100% by mass), and the cross-sectional shape of the fiber is a single fiber with a four-lobed shape. An electret nonwoven fabric was produced in the same manner as in Example 6, except that the amount of the fiber treatment agent applied was set to "0.29 parts by mass".

Comparative example 1
An electret non-woven fabric was produced in the same manner as in Example 1, except that "fiber treatment agent C" was used as the fiber treatment agent, and the adhered amount was set to "0.33 parts by mass".

Comparative example 2
An electret nonwoven fabric was produced in the same manner as in Example 1, except that "fiber treatment agent D" was used as the fiber treatment agent, and the amount applied was set to "0.25 parts by mass".

Comparative example 3
The first component (sheath component) of the fiber is composed of the above polypropylene resin (PP) (resin 1a: 100% by mass), and as a fiber treatment agent, "fiber treatment agent C" is used, and the adhesion amount is " An electret nonwoven fabric was produced in the same manner as in Example 1, except that the content was 0.33 parts by mass.

Collection efficiency Assuming that the electret nonwoven fabrics produced in Examples and Comparative Examples are used as air filters, (i) immediately after charging, (ii) 120 minutes after heat treatment at 80 ° C., (iii) 120 30 minutes after the heat treatment at °C, the collection efficiency (%) of the air filter was measured according to the following measurement method.
・Heat treatment An electret nonwoven fabric that has been charged under the above conditions is prepared. Next, a constant temperature dryer (manufactured by Yamato Scientific Co., Ltd., air blower constant temperature constant temperature oven, product number DKM600) is prepared and set to 80°C or 120°C. After the temperature of the constant temperature dryer reaches the set temperature, the prepared electret nonwoven fabric subjected to electrification treatment is placed in the constant temperature dryer and held for a predetermined time. When the heat treatment temperature was 80°C, the nonwoven fabric was held in the constant temperature dryer for 120 minutes, and when the heat treatment temperature was 120°C, the nonwoven fabric was held in the constant temperature dryer for 30 minutes.
・Measurement method Each sample (120 mm × 120 mm) of the electret nonwoven fabrics prepared in Examples and Comparative Examples was measured according to JIS B 9908 with a circular surface having a diameter of 100 mm and a measurement speed of 23.8 L / min. was filtered through an electrostatic surface. For particles of 0.3 μm or less before and after filtration, the number of particles was measured, and the collection efficiency (%) was calculated by the following formula. Results are shown in the table below.
Collection efficiency (%) = (1-C2/C1) x 100
where C1 is the number of particles before filtration and C2 is the number of particles after filtration.

・Evaluation It was found that all of the electret nonwoven fabrics of Examples 1 to 9 were excellent in initial electrification property, and all of them had collection efficiencies of 30% or more immediately after the electrification treatment. On the other hand, it was found that the electret nonwoven fabrics of Comparative Examples 1 to 3 did not have sufficient initial electrification properties, and the collection efficiencies immediately after the electrification treatment were all less than 30%, more specifically around 25%. .
In addition, as shown in Examples 3 and 4, for example, it was found that, according to the present invention, a collection efficiency of about 90% can be maintained even after heat treatment at 80°C. Furthermore, surprisingly, Example 7 was able to maintain a collection efficiency of about 80% even after heat treatment at 120°C. On the other hand, in the electret nonwoven fabric of Comparative Example 3, the collection efficiency immediately after the electrification treatment was less than 25%, and after the heat treatment at 80°C, the collection efficiency could be maintained at only 33% immediately after. It was found that the trapping efficiency was remarkably lowered when exposed to a high temperature environment.

The present disclosure includes the following aspects as embodiments.
(Aspect 1)
A fiber for electret processing, comprising a fiber containing a thermoplastic resin and a fiber treatment agent attached to the fiber,
The fiber treatment agent is attached to the fibers at a rate of 0.01 parts by mass or more and 3 parts by mass or less per 100 parts by mass of the fibers,
The fiber treatment agent has the following formula (1):
HO—(A ¹ O) _n —H (1)
[In the formula,
A ¹ O is an oxyalkylene group composed of at least one selected from the group consisting of an oxyethylene group, an oxypropylene group and an oxybutylene group,
n represents the average number of added moles of A ¹ O, and is 96 to 1135]
Including a polyalkylene glycol represented by
The number average molecular weight (Mn) of the polyalkylene glycol is 5000 or more and 50000 or less,
The polyalkylene glycol is contained in the fiber treatment agent at a rate of 20 parts by mass or more per 100 parts by mass of the fiber treatment agent.
Fiber for electret processing.
(Aspect 2)
The fiber for electret processing according to aspect 1, wherein the polyalkylene glycol has a weight average molecular weight (Mw) of 6000 or more and 60000 or less.
(Aspect 3)
The oxyethylene group is contained at a ratio of 50% or more and 100% or less with respect to the total number of repeating units,
The oxypropylene group is contained at a ratio of 0% or more and 50% or less with respect to the total number of repeating units,
The oxybutylene group is contained at a ratio of 0% or more and 10% or less with respect to the total number of repeating units,
A fiber for electret processing according to aspect 1 or 2.
(Aspect 4)
A ¹ O is an oxyalkylene group composed of at least one selected from the group consisting of an oxyethylene group and an oxypropylene group, and n is 100 to 1135. fiber.
(Aspect 5)
The A ¹ O consists of an oxyethylene group and an oxypropylene group,
In the polyalkylene glycol, the oxyethylene group is contained at a ratio of 50% or more and less than 100% with respect to the total number of repeating units,
The oxypropylene group is contained at a ratio of more than 0% to 50% or less with respect to the total number of repeating units,
A fiber for electret processing according to aspect 4.
(Aspect 6)
The fiber for electret processing according to any one of aspects 1 to 5, wherein the polyalkylene glycol is either a random polymer or a block polymer.
(Aspect 7)
Aspects 1 to 6, wherein the thermoplastic resin-containing fiber contains at least one acid-modified resin selected from the group consisting of acid-modified polyolefin-based resins and acid-modified polyester-based resins as the thermoplastic resin. Fiber for electret processing.
(Aspect 8)
The fiber containing the thermoplastic resin is a core-sheath type composite fiber, and includes a first component forming a sheath portion and a second component forming a core portion, and the first component is the acid-modified resin. The fiber for electret processing of aspect 7, comprising:
(Aspect 9)
A nonwoven fabric comprising fibers for electret processing according to any one of aspects 1-8.
(Mode 10)
An air filter comprising the nonwoven fabric of aspect 9.

Since the fibers for electret processing of the present disclosure are excellent in charging performance, nonwoven fabrics containing such fibers can be used, for example, as electret nonwoven fabrics. In addition, the electret nonwoven fabric of the present disclosure can be used as an air filter for collecting fine suspended matter, for example, suspended matter with a size of 0.5 μm or less (dust, smoke dust, pollen, viruses, etc.). . In addition, such an air filter is excellent in performance such as chargeability and collection efficiency immediately after charging, and preferably even after being exposed to a high temperature environment (for example, a temperature of 80 ° C. or higher). Since the performance can be maintained, it can be used as an air filter that can be used in a high temperature environment, such as a vehicle filter, especially an automobile filter (e.g., air conditioner filter, pollen filter).

1 First component 2 Second component 100 Modified cross-section composite fiber

Claims (10)

A fiber for electret processing, comprising a fiber containing a thermoplastic resin and a fiber treatment agent attached to the fiber,
The fiber treatment agent is attached to the fibers at a rate of 0.01 parts by mass or more and 3 parts by mass or less per 100 parts by mass of the fibers,
The fiber treatment agent has the following formula (1):
HO—(A ¹ O) _n —H (1)
[In the formula,
A ¹ O is an oxyalkylene group composed of at least one selected from the group consisting of an oxyethylene group, an oxypropylene group and an oxybutylene group,
n represents the average number of added moles of A ¹ O, and is 96 to 1135]
Including a polyalkylene glycol represented by
The number average molecular weight (Mn) of the polyalkylene glycol is 5000 or more and 50000 or less,
The polyalkylene glycol is contained in the fiber treatment agent at a rate of 20 parts by mass or more per 100 parts by mass of the fiber treatment agent.
Fiber for electret processing. The fiber for electret processing according to claim 1, wherein the polyalkylene glycol has a weight average molecular weight (Mw) of 6000 or more and 60000 or less. The oxyethylene group is contained at a ratio of 50% or more and 100% or less with respect to the total number of repeating units,
The oxypropylene group is contained at a ratio of 0% or more and 50% or less with respect to the total number of repeating units,
The oxybutylene group is contained at a ratio of 0% or more and 10% or less with respect to the total number of repeating units,
The fiber for electret processing according to claim 1 or 2. The electret according to claim 1 or 2, wherein A ¹ O is an oxyalkylene group composed of at least one selected from the group consisting of an oxyethylene group and an oxypropylene group, and n is 100 to 1,135. fiber for processing. The A ¹ O consists of an oxyethylene group and an oxypropylene group,
In the polyalkylene glycol, the oxyethylene group is contained at a ratio of 50% or more and less than 100% with respect to the total number of repeating units,
The oxypropylene group is contained at a ratio of more than 0% to 50% or less with respect to the total number of repeating units,
The fiber for electret processing according to claim 4. The fiber for electret processing according to any one of claims 1 to 5, wherein the polyalkylene glycol is either a random polymer or a block polymer. Any one of claims 1 to 6, wherein the thermoplastic resin-containing fiber contains at least one acid-modified resin selected from the group consisting of acid-modified polyolefin-based resins and acid-modified polyester-based resins as the thermoplastic resin. The fiber for electret processing according to item 1. The fiber containing the thermoplastic resin is a core-sheath type composite fiber, and includes a first component forming a sheath portion and a second component forming a core portion, and the first component is the acid-modified resin. A fiber for electret processing according to claim 7, comprising: A nonwoven fabric comprising the fibers for electret processing according to any one of claims 1 to 8. An air filter comprising the nonwoven fabric of claim 9 .

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