JPH0547244B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing a charged nonwoven fabric containing polyolefin staple fibers as a main component. [Prior Art] Charged nonwoven fabrics made of synthetic resin staple fibers are used as air filters for collecting dust. The dust collection function of this charged nonwoven fabric includes:
There is a normal mechanical filtration function by the fiber layer and a collection function by the electrostatic force generated by electrification.The mechanical filtration mainly collects relatively large dust, and the electrostatic force mainly collects fine dust. In this way, charged nonwoven fabrics can widen the particle size range of dust that can be collected, improve dust collection efficiency, and significantly reduce pressure loss, making it possible to maintain dust collection for a long time. Because of this, it is attracting attention as an excellent air filter. Synthetic fibers used in the production of such charged nonwoven fabrics include polyolefin-based, polyester-based, vinyl chloride-based, vinylidene chloride-based, and polyclar-based staple fibers. [Problems to be Solved by the Invention] However, nonwoven fabrics made from polyolefin staple fibers are difficult to be charged, and even after being charged, the efficiency of collecting ultrafine particles of less than 1 μm is extremely low. The inventors of the present invention have conducted intensive research to solve these problems with polyolefin staple fiber nonwoven fabrics, and have discovered that the oil adhering to polyolefin staple fibers has a large effect on electrification. We conducted extensive research to ensure that polyolefin staple fibers with such oils attached could be sufficiently charged, and found that by selecting the type of oil and applying a thermal history above a certain temperature, The inventors have discovered that the influence of oil can be eliminated and have completed the present invention. [Means for solving the problem] In other words, the present invention uses 40% (wt%, the same applies hereinafter) of nonionic oil with an HLB value of less than 10 as the oil.
Using an oil agent containing the above, and heating at 110℃ before charging treatment.
The present invention relates to a method for producing a charged polyolefin nonwoven fabric, which is characterized by heat treatment at a temperature above. [Operations and Examples] Oil agents are used in the spinning process of polyolefin staple fibers and in the carding process and fiber entanglement process when producing nonwoven fabrics using the fibers, and oil agents are used in the spinning and processing of polyolefin fibers. It is indispensable. Polyolefin fibers or nonwoven fabrics to which such oils are attached are not sufficiently charged even if they are subjected to charging treatment such as corona discharge. However, 40% of nonionic oils with an HLB value of less than 10 are used as oils.
If a material containing the above is used and a heat history of 110° C. or higher is applied before the charging treatment, sufficient charging can be achieved. If the amount of anionic oil, nonionic oil with an average HLB value of 10 or more, or nonionic oil with an HLB value of less than 10 is small, the nonwoven fabric cannot be sufficiently charged even if the thermal history is applied. Also,
Even if a nonionic oil with an HLB value of less than 10 is used, it cannot be similarly charged unless heat history is added. Examples of the nonionic oil having an HLB value of less than 10 used in the present invention include sorbitan compounds, polyoxyethylene compounds, polyoxysorbitan compounds, and mixtures thereof. The average HLB value is
It may be less than 10, but preferably 1.8 to 8.0. These nonionic oils may be used alone or in combination with other oils. However, when mixing, the amount of nonionic oil with an HLB value of less than 10 should be 40% or more, preferably 60 to 60%.
Must be 100%. Other oils that can be mixed include nonionic compounds such as polyethylene glycol compounds and polyoxy higher alcohol compounds, anionic compounds such as higher fatty acid esters, higher alcohol sodium sulfate, and alkyl phosphoric acid compounds, and cationic compounds such as higher fatty acid esters, higher alcohol sodium sulfate, and alkyl phosphoric acid compounds. Examples include lauryl trimethylammonium chloride and lauryl betaine. The heat treatment in the present invention is carried out at 110°C or higher, preferably at 130-160°C. When processing at a temperature below 110°C, it is not possible to eliminate the influence of oil during the charging process. The heat treatment can be performed before, after, both, or simultaneously with the production of the nonwoven fabric. The heat treatment method is
Various methods can be adopted depending on the nonwoven fabric manufacturing method and the thickness, density, texture, etc. of the intended product. For example, in order to obtain a relatively soft and thick nonwoven fabric with low density, raw cotton may be heat treated. It is possible to obtain a thick nonwoven fabric by heating and bonding the web without applying fiber opening and pressure, or to form a thick matte by spraying an adhesive after opening and then heat treating it. In order to obtain a hard, high-density nonwoven fabric, in addition to the heat treatment of the raw cotton mentioned above, there are also other methods such as pressing the web after opening between multiple heated rolls, or partially adhering it with a heated embossing roll. After that, a method such as further treatment with hot air may be adopted. The heat treatment time may normally be 10 seconds to 10 minutes. It should be noted that the amount of oil adhered hardly changes before and after the heat treatment. Examples of polyolefin staple fibers used in the present invention include polyethylene staple fibers, polypropylene staple fibers, polypropylene-polyethylene composite staple fibers, composite staple fibers whose sheath component is polyethylene or polypropylene and whose core component is polyester or polyamide, and Examples include those subjected to combustion treatment, softening treatment, and high crimp treatment. In addition, at least
It is necessary to contain 40% or more of polyolefin staple fibers in order to obtain a charging effect. If the polyolefin staple fiber content is less than 40%,
It is inappropriate because a sufficient charging effect cannot be obtained. As the method for forming a non-woven fabric, conventionally used fiber bonding methods, point bonding methods, needle punching methods, spray bonding methods using adhesives, etc. can be employed. Heat treatment can be carried out at the same time as non-woven fabric formation in the case of the fiber adhesion method, or at any time before the charging treatment in the point adhesion method and the needle punch method. Incidentally, the nonwoven fabric in the present invention includes not only the nonwoven fabric produced by the method described above but also a net-like fabric. The nonwoven fabric that has been subjected to a thermal history is then subjected to a charging treatment. As the charging treatment, a conventionally conventional method using corona discharge is employed. Corona discharge is usually performed by passing a nonwoven fabric web between a corona electrode and a ground electrode and applying a high voltage between the two electrodes to generate corona discharge.
This is a method of electrically charging nonwoven fabric. The charged nonwoven fabric of the present invention can be used as it is or after being subjected to processing such as reinforcement, pleat formation, hot melt resin coating, etc., and then cut into a predetermined shape for use as air filters, masks, wiping cloths, and the like. Next, the manufacturing method of the present invention will be explained based on Examples, but the present invention is not limited only to these Examples. Example 1 Polypropylene staple fibers (fiber diameter: 2 denier, fiber length: 51 mm) to which the oil shown in Table 1 was attached were subjected to needle punching method (needle density: 150 mm).
The fabric was made into a non-woven fabric (fabric weight: 250 g/cm ² , thickness: 2.0 mm) ^. The resulting punched felt nonwoven fabric is heated to a certain temperature using a hot air circulation dryer.
Heat treatment was performed at 140°C for 2 minutes. The resulting heat-treated nonwoven fabric was charged by corona discharge treatment for 5 seconds at room temperature (25℃) with an applied voltage of 14KV, then cut into 250mm x 250mm pieces, installed in a cylindrical duct, and blown away with dust at a wind speed of 10cm/sec. Through the air,
The collection efficiency of 0.3 μm dust particles was measured. The results are shown in Table 1. Note that the ventilation resistance was 0.2 mmH ₂ O. In Table 1, sorbitan trioleate and polyoxyethylene nonyl phenyl ether
The HLB values were 1.8 and 15.5, respectively.

[Table] Example 2 A nonwoven fabric was produced in the same manner as in Example 1 except that the mixed oil agent shown in Table 2 was used as the oil agent, and after heat treatment, it was subjected to charging treatment.
The collection efficiency was measured in the same manner as above. The results are shown in Table 1.

[Table] Example 3 Polypropylene-polyethylene composite staple fibers (fiber diameter:
3 denier, fiber length: 64 mm) was formed into a sheet by the needle punch method, and then a nonwoven fabric was produced by the fiber adhesion method. The conditions for fiber adhesion were as follows. Heating temperature: Shown in Table 3. Heating time: 3 minutes The resulting heat-treated nonwoven fabric was then subjected to a corona discharge treatment at 26° C. with an applied voltage of 14 to 14.5 KV for 10 seconds, and the collection efficiency was measured in the same manner as in Example 1. The results are shown in Table 3. In addition, the basis weight, thickness, and ventilation resistance of the nonwoven fabrics in experiment numbers 9 to 11 were 255 g/m ² , 2.0 mm, and 2.0 mm, respectively.
2.6 mmH ₂ O, and the basis weight, thickness, and airflow resistance of the nonwoven fabrics of experiment numbers 12 to 14 were 250 g/m ² , respectively.
2.6mm and _2.6mmH2O , and also experiment number 15~
The basis weight, thickness, and air permeability resistance of the nonwoven fabric No. 17 were 220 g/m ² , 2.0 mm, and 1.9 mm H ₂ O, respectively.

[Table] Example 4 Raw polypropylene fiber (fiber diameter: 2 denier, fiber length: 64 mm) was roughly opened using a garnet machine to form a wrap, and then heat treated in a drying oven at 120°C for about 8 minutes. I did it. After heat treatment, the wrap is opened with a card machine to form a web, which has an embossed pattern on one side.170
A relatively high density non-woven fabric (fabric weight: 200g/m ² ,
Thickness: 0.8mm). The obtained nonwoven fabric was subjected to a charging treatment in the same manner as in Example 1, and the collection efficiency was measured. The results are shown in Table 4. The ventilation resistance was 6.9 mmH ₂ O. In addition, the collection efficiency was measured for a nonwoven fabric that was produced in the same manner except that no heat treatment was performed, and that was subjected to a charging treatment. The results are shown in Table 4.

[Table] Example 5 A mixed web in which polypropylene-polyethylene composite fibers (fiber diameter: 3 denier, fiber length: 64 mm) and polyester fibers (fiber diameter: 5 denier, fiber length: 64 mm) were mixed in the proportions shown in Table 5. A relatively thick nonwoven fabric (fabric weight: 250 g/m ² , thickness: 12 mm) was obtained by heat treatment for 2 minutes in a hot air circulating dryer at 145° C. and at the same time adhesion between the fibers. The obtained nonwoven fabric was subjected to a charging treatment in the same manner as in Example 1, and the collection efficiency was measured. The results are shown in Table 5. The ventilation resistance was 0.3 mmH ₂ O.

[Table] [Effects of the Invention] According to the present invention, even for oil-adhered polyolefin nonwoven fabrics that have conventionally been unable to obtain sufficient charging effects, sufficient charging effects can be achieved by using a specific oil and applying a thermal history above a specific temperature. The present invention provides a good charging effect, and the range of usable materials for charged nonwoven fabrics can be expanded to include polyolefin fibers, which are inexpensive and easy to make into nonwoven fabrics.

Claims (1)

[Scope of Claims] 1. When a nonwoven fabric containing at least 40% by weight of polyolefin staple fibers treated with an oil agent in the total constituent fibers is produced and then subjected to charging treatment to produce a charged nonwoven fabric, the oil agent has an HLB value. Using an oil containing 40% by weight or more of a nonionic oil with a concentration of less than 10,
A method for producing a polyolefin-based charged nonwoven fabric, which is characterized in that it is heat-treated at a temperature of 110°C or higher before the charging treatment. 2. The manufacturing method according to claim 1, wherein the heat treatment is performed simultaneously with the production of the nonwoven fabric. 3. The manufacturing method according to claim 1, wherein the heat treatment is performed after producing the nonwoven fabric. 4. The manufacturing method according to claim 1, wherein heat treatment is applied to polyolefin staple fibers. 5. The manufacturing method according to claim 1, wherein the oil is a nonionic oil having an HLB value of less than 10. 6 The oil is a nonionic mixed oil, and the average
The manufacturing method according to claim 1, wherein the HLB value is less than 10. 7. The manufacturing method according to claim 1, wherein the oil is a mixed oil of a nonionic oil and an anionic oil having an HLB value of less than 10. 8. The manufacturing method according to claim 1, wherein the heat treatment temperature is 130°C or higher. 9. The manufacturing method according to claim 1, wherein the heat treatment time is 10 seconds or more.