JP2989684B2 - Polymethylpentene ultrafine fiber web and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrafine and highly water-resistant polymethylpentene ultrafine fiber web having an excellent fine uniformity and fiber arrangement by a melt blown method using a specific polymethylpentene resin and its production. It provides a method. The polymethylpentene ultrafine fiber web of the present invention is suitably used for various filters, moisture-permeable waterproof sheets, wipers, sanitary materials, etc. by utilizing its high water repellency, heat resistance, filterability, flexibility, and bulkiness. Is done.

[0002]

2. Description of the Related Art A method of producing a non-woven fabric by melt-spinning a thermoplastic resin, converting the melt into a fiber stream with a high-speed gas, and collecting the resultant in a sheet form is disclosed in JP-A-49-10258 and JP-A-49-10258. Various proposals have been made in, for example, JP-A-49-48921 and JP-A-50-121570, which are referred to as a melt blown method. Further, regarding melt blown webs of polymethylpentene resin (hereinafter referred to as PMP resin), see US Pat.
e.31,087 is provided as an example of a melt blown web of polyolefin polymer. Also, U.
SP 3,481,953 discloses an example in which a PMP resin and polypropylene are blended and melt blown.
Furthermore, Japanese Patent Application Laid-Open No. 1-2224020 discloses that PMP meltblown fibers are electretized to form an electret filter. As described above, it is known that a PMP resin is formed into an ultrafine fiber web by a melt blown method.

[0003]

In the above-mentioned prior art, no detailed proposal has been made on a method for forming a fine fiber web from a PMP resin by melt blown, and other polyolefin polymers, specifically, polypropylene. This was in accordance with the conditions for producing a microfiber web by the melt blown method. However, according to the study of the present inventors, it has been found that such a conventional technique has the following serious problems.

That is, in order to make the fibers constituting the web finer, for example, 5 μm or less, a large amount of high-temperature air must be applied to the melt-discharged polymer stream to promote the thinning. In the case of the PMP resin, unlike the case of the polypropylene, when the amount of air increases, the melt-discharged polymer stream becomes finer fibers and forms a sheet once on a wire mesh belt conveyor or the like having a suction zone and is captured in a web form. Even if collected, the fibers on the web surface are greatly disturbed by a large amount of hot air flowing on the web and a large amount of secondary air sucked from the surroundings. And finally, the web is cut so as to be torn, and there is a problem that it is practically impossible to collect a uniform web. Further, even if the web is not cut, the thinning of the fibers constituting the web does not proceed uniformly and sufficiently, resulting in a large unevenness in the fiber diameter. For this reason, the obtained ultrafine fiber web is not uniform in the basis weight, the fiber diameter, and the arrangement state of the fibers, is likely to have many spots, and has only low water repellency (water resistance).

This is because the crystallization speed of the PMP resin is relatively high and the melting point is about 70 ° C. higher than that of polypropylene or the like. This is considered to be because the formation of fusion is greatly suppressed even when the fibers are in contact with each other during the thinning or after the thinning, so that the bonding due to the fusion between the fibers is reduced and the stability of the web is reduced. . In general, polyolefin-based polymers were regarded as polymers that can be easily made into ultrafine fiber webs by melt blown.
The situation is completely different for crystalline polyolefins, which have a high melting point like P resins.

An object of the present invention is to solve the above-mentioned problems in the conventional method of forming a polyolefin polymer into an ultrafine fiber web by the melt blown method, particularly the PMP resin, to sufficiently promote the thinning of the fiber and to obtain a good basis weight and uniformity. It is an object of the present invention to propose a highly water-repellent PMP ultrafine fiber web having a water-repellent property and a fiber arrangement property, and a method for stably producing the web.

[0007]

Means for Solving the Problems The present inventors have made intensive studies on a method for forming a polyolefin, particularly a PMP resin, into ultrafine fiber webs by a melt blown method, and have reached the present invention.

That is, according to the present invention, when the average diameter of the fibers constituting the nonwoven fabric is D (μm), the density is ρ (g / cm ³ ), and the apparent density of the nonwoven fabric is P (g / cm ³ ), A polymethylpentene ultrafine fiber web, wherein the product of the average inter-fiber distance d (μm) represented by the following formula 2 and the water resistance H (cm water column) is 300 or more,

(Equation 2)

Further, in the melt blown method in which polymethylpentene is melted and discharged from an orifice-shaped nozzle and made into fine fibers by high-temperature and high-speed gas ejected from the vicinity of the nozzle orifice and collected on a sheet to form a web, Penten temperature 250 ℃, 5000g load
Has a melt index of 100 to 800 g / min and a melt viscosity of 30 to 150 when passing through the nozzle.
Poise. Further, the jet pressure of the gas is 0.8 kg / cm.
^{2. A} method for producing a polymethylpentene ultrafine fiber web, wherein the temperature is 260 to 340 ° C. or less.

[0010]

The polymethylpentene (PMP) of the present invention
The resin is a material obtained by dimerizing polypropylene as a starting material into 4-methylpentene-1, and further polymerizing it into a homopolymer and a copolymer thereof. That is, the PMP resin has a melting point of 230 to 240 ° C. and the heat resistance of the ultrafine fiber web obtained as the highest among the polyolefins is excellent. Further, the surface tension is the lowest among the polyolefins, and the water repellency (water resistance) of the obtained ultrafine fiber web is extremely good.

The water resistance of the fiber web is also affected by the basis weight of the fiber web and the contact angle between the polymer constituting the fiber and water and the surface tension, but the most important factor is the opening of the opening due to the arrangement of adjacent fibers. The size (pore diameter). The size of the openings is generally not uniform but has a distribution, and the actual water resistance depends not on the average size of the openings but on the maximum value of the hole diameter. That is, if a large opening exists even if the average pore diameter is small, the water resistance decreases according to the size of the opening. Therefore, when the average pore size of the ultrafine fiber web is the same, the smaller the pore size distribution, that is, the smaller the unevenness of the fiber arrangement state of the web, the higher the water resistance. When the contact angle and the surface tension are the same, the water resistance can be considered as the pressure required to push water into the hole corresponding to the maximum hole diameter, and is considered to be inversely proportional to the hole diameter. The uniformity of the web can be evaluated by the product of the water resistance and the average pore size.

Here, the average pore diameter of the ultrafine fiber web can be replaced by the virtual average fiber-to-fiber distance d expressed by the above equation (2). Although the average pore diameter of the actual nonwoven fabric is considered to be different from the average inter-fiber distance of Equation 2, when considering a virtual arrangement state (virtual average pore diameter), the average pore diameter is equal to the average inter-fiber distance of Equation 2. It is considered to be proportional and can be substituted by Equation 2. Equation 2 can be obtained as the average inter-fiber distance of the following virtual nonwoven fabric model.
When considering a model in which all fiber diameters are equal and are arranged in parallel, and each fiber is evenly separated from the closest packed state, that is, each fiber is arranged in parallel at the position of the vertex of an equilateral triangle, The average inter-fiber distance is determined as follows.

The average diameter of the fibers constituting the nonwoven fabric is D (μ
m), the density is ρ (g / cm ³ ), and the apparent density of the nonwoven fabric is P (g
/ Cm ³ ) and the average fiber-to-fiber distance d (μm), the length of one side of the equilateral triangle is D + d (μm) The area of the equilateral triangle is

(Equation 3) The cross-sectional area of the fiber contained in the equilateral triangle is

(Equation 4) Because the product of the fiber cross-sectional area and the density is equal to the product of the area of the equilateral triangle and the apparent density

(Equation 5) Equation 2 is obtained by rearranging Equation 5.

The ultrafine fiber web of the present invention has an average fiber-to-fiber distance d (μm) determined by equation 2 and JIS L-1092.
The product of the product with the water resistance H (cm) determined by
It is a polymethylpentene microfine fiber web having a high degree of uniformity of the fiber diameter and arrangement state, preferably 350 or more, more preferably 400 or more. If the value of this product is less than 300, the ultrafine fiber web is insufficiently thinned and has a large variation in fiber diameter, a large variation in the basis weight and arrangement of fibers, or both. In areas with a relatively large basis weight, even if there is some unevenness in the fiber diameter or the arrangement of fibers, it is covered to some extent by the thickness, so the water resistance is relatively high. In addition, the unevenness of the fibers and the arrangement of the fibers directly affect the size of the opening, and it is difficult to obtain a material having high water resistance. The ultrafine fiber web of the present invention is particularly effective because a high water resistance can be obtained in a relatively small area having a basis weight of 50 g / m ² or less as compared with the basis weight. When the fiber web is treated with a hydrophilic oil agent or a water repellent agent, the contact angle between the fiber surface and water changes and affects the water resistance. Therefore, the measurement of the water resistance in the present invention is performed by using a treating agent such as an oil agent. Is carried out in a state where the treating agent is removed by treating with a suitable solvent or the like.

Next, the main die portion of one example of the melt blown apparatus used in the present invention is shown in FIG. The polymer stream melt-extruded by the extruder is filtered by a suitable filter (not shown in FIG. 1), and then guided to a melt polymer inlet 2 of a melt blown die 1 and then to a nozzle orifice 3
From the melt. At the same time, the heated air introduced into the heated air inlet 4 is heated by a hot air jet slit 5 formed by the melt blown nozzle die 1 and the lip.
And is ejected from there to act on the melt-discharged polymer stream and to thin it to form fibers. Next, this is collected in a sheet shape to produce an ultrafine fiber web.

The PMP resin used in the present invention is AST
Using the melt indexer described in MD-1238,
It is an essential requirement that the melt index measured under the conditions of a temperature of 250 ° C. and a load of 5000 g is 100 to 800 g / 10 minutes. Melt index is a measure of the degree of polymerization, flowability, and melt viscosity of a molten polymer. When the melt index is 150 g / 10 minutes or less, the PMP polymer stream is sufficiently thinned into fibers (for example, 5 μm in diameter) by a high-temperature air stream without causing thinning failure called a shot.
The following is a low melt viscosity, specifically, 1
In order to reduce the melting temperature of the PMP polymer to 50 poise or less, the melting temperature of the PMP polymer must be set to a very high temperature of 350 ° C. or more. At such a high temperature, the thermal decomposition of the PMP polymer becomes severe and the melt viscosity decreases. It becomes impossible to maintain a stable level. In this state where the melt viscosity fluctuates from time to time, unevenness in the fineness of the microfibers in the web obtained after melt-blown occurs in the sheet width direction, and the quality of the web decreases. The fluffy and scattered fine fibers "fly cotton" occur frequently, causing a decrease in productivity.

On the other hand, the melt index is 800 g / 1
If it exceeds 0 minutes, the degree of polymerization of the PMP resin will be too low, or the strength of the obtained ultrafine fiber web will be small, which is a practical problem. Therefore, the melt index of the PMP resin of the present invention at a temperature of 250 ° C. and a load of 5000 g must be 100 to 800 g / 10 minutes. By using such a PMP resin, it is not necessary to excessively set the temperature of the polymer melting line from the extruder to the melt blown die and the nozzle orifice, and the severe thermal decomposition of the PMP resin is suppressed, and the PMP resin is fine and fine. The fiber web can be manufactured stably.

Next, as an important point in the present invention, since the PMP resin is melted and discharged at the time of melt blown, the melt viscosity when passing through the nozzle may be 30 to 150 poise. When the melt viscosity at the nozzle portion is less than 30 poise, the melt tension of the polymer becomes too small, the fiber forming property is reduced, the cutting of the polymer stream is increased, and the length of the formed fiber becomes very short, and The diameter also becomes uneven. As a result, "fly fly" which is not collected normally in a sheet form and scatters in a cotton-like manner around occurs, and it becomes virtually impossible to continue stable melt blown. Also,
A large amount of streaky fiber bundles are mixed into the obtained web, resulting in poor appearance or low water repellency.

On the other hand, when the melt viscosity of the PMP resin at the nozzle portion exceeds 150 poise, the thinning by the melt blown hardly proceeds first. That is, it is necessary to increase the flow rate of a high-temperature and high-speed gas and to increase the temperature in order to promote the thinning, which is disadvantageous in energy consumption. Further, as a fatal problem, if melt blown is performed and the time is long, colored deposits accumulate around the spinneret. This accumulation increases over time and eventually comes into contact with the discharged polymer stream. In such a case, defective yarn breakage occurs on the spinneret surface. In general, in a melt blown fiber, it is estimated that the formed fiber is not completely continuous, but is a discontinuous fiber having a finite length. It cuts regularly and stably without completely following the deformation.

As described above, the defective yarn breakage is completely different from the above, and is not thickened because it is broken before thinning. This causes a reduction in water repellency. The exact reason for the formation of this deposit is unknown, but in meltblowns with too high melt viscosities, the high temperature and high speed gas causes irregularities in the thinning of the polymer flow to increase, resulting in irregular cutting. It is presumed that a part thereof scatters in directions other than the normal blown direction and adheres around the spinneret. Incidentally, when the attached matter was sampled and analyzed, it was a PMP resin melt-blown and melt-blown. This confirms the above assumption to some extent. For the above reasons, PM
In producing a P ultrafine fiber web, the melt viscosity of the nozzle portion must be 30 to 150 poise. A preferred range is 50-100 poise.

An important point in the present invention is that the injection pressure of the air for making the PMP resin melted and discharged into fine fibers is 0.8 kg / cm ² or more. The ejection pressure was measured at a point near the lip 6 of the heated air introduction unit 4 in FIG. When the ejection pressure exceeds 0.8 kg / cm ² , the flow rate of the heated air is increased, so that the polymer flow becomes thinner and the fiber diameter becomes sufficiently small. However, in this case, even if the thinned fiber stream is collected in the form of a sheet and is to be collected as an ultrafine fiber web, once the web is formed, the air flow ejected at a high speed and the air flow are sucked from the surroundings. The resulting "secondary air" flow easily disturbs the web surface, then deforms the entire web and eventually cuts (breaks) the web, making it impossible to form a uniform microfiber web. . Although the exact reason for such a phenomenon is unknown, it is presumed as follows from the fact that it is not recognized at all in the same polyolefin-based polymer, polypropylene.

That is, as the pressure of the ejected air increases, the adiabatic expansion of the ejected air increases, so that the temperature drop of the ejected air increases. Due to contact, the polymer stream cools rapidly. At this time, the PMP resin is 230 to 2
Since it has relatively high crystallinity at a high melting point of 40 ° C., crystallization proceeds during thinning fiber formation, and fiber streams contact each other and hardly fuse, so that a fusion bond between fibers is formed. It is considered that the collected web was poor in form stability because the reinforcement between the fibers was only entanglement of the fibers.

On the other hand, the jet air is 0.8 kg / cm ²
Since the velocity of the heated air is reduced below, the effect of the air flow itself and the effect on the web from the secondary air caused by the suction of the air flow from the surroundings is reduced. At the same time, the adiabatic expansion of the discharge air also decreases, so the instantaneous temperature drop of the discharge air becomes very gentle, so that the formation of fusion when the thinned fiber streams come into contact with each other also increases moderately, It is considered that the morphological stability of the web is also improved. In order to reduce the effect of the air flow and to improve the stability of the web form, stable collection is possible.

Therefore, the jet pressure of the air for making the PMP resin melted and discharged into fine fibers must be 0.8 kg / cm ² or less. Further, as an important point in the present invention, the jet air temperature may be set to 260 to 340 ° C. When the jet air temperature is lower than 260 ° C., even if the effect of the adiabatic expansion is reduced, the temperature before expansion may be low, and the dimensional stability of the ultrafine fiber web may be moderate because of the low temperature before expansion. Cannot be formed so as to improve the melting point. On the other hand, if the temperature of the blast air exceeds 340 ° C., the fusion between the fibers becomes intense, contrary to the above, and the resulting ultrafine fiber web exhibits a rough and hard feel and feel. It becomes worthless. Therefore, the jet air temperature must be 260-340 ° C.

The average diameter of the fibers constituting the ultrafine fiber web of the present invention is preferably 5 μm or less. Furthermore, the basis weight of the microfiber web produced by the method of the present invention is determined by the intended use, but is generally from 5 to 200 g / g.
m ² . For example, when used for backsheets of sanitary napkins, the weight is low, and when used for masks, air filters, oil filters, surgical gowns, drapes, sterilization wraps, batting for clothing, etc., the weight is low, for agricultural use, civil engineering, and industrial use. When used for various types of moisture-permeable waterproof sheets, the weight is medium or high.

The following are examples of industrial use of the ultrafine fiber web of the present invention.・ Building materials: asphalt roofing base cloth, dew condensation prevention sheet, house wrap base cloth, heat insulation sheet ・ Agricultural materials: shading sheet, seedling raising sheet, water absorption and drainage sheet, root protection sheet, grass protection sheet ・ Lifestyle materials: furoshiki, disposable warmer Bags, curtains, shoji paper, insect repellent sheets, tufted carpet base cloth, work clothes, disposable simple clothing, warming batting, wiping cloth, tea bags, interlining ・ Industrial materials: air filters, oil filters, electric wire holding tapes, Packaging materials, insulating tapes, battery separators, vehicle materials (car mats, car seats, etc.) ・ Medical and hygiene materials: disposable diapers, medical gowns, surgical coverings, cataplasms, napkins

[0027]

The present invention will be described below with reference to specific examples, but the present invention is not limited to these examples. In Examples and Comparative Examples, the thickness of the ultrafine fibers constituting the nonwoven fabric was
Photographs of the nonwoven fabric were magnified 1000 times with an operation type electron microscope, the diameter of 100 arbitrary microfibers in the nonwoven fabric was measured, and the number average was obtained. Although the water pressure of the nonwoven fabric is also called water resistance, the microfiber web is pressed against
% Dot embossing, and measured by the method of JIS L-1092. The melt index was measured using a melt indexer described in the above-mentioned ASTM-D-1238 at a temperature of 250 ° C. and a load of 5000 g. To calculate the average fiber-to-fiber distance d, the densities of the PMP resin and the PP resin were set to 0.83 g / cm ³ and 0.1%, respectively.
Calculated as 91 g / cm ³ .

Examples 1 to 4 and Comparative Examples 1 to 8 Melt blown was performed using a melt blown apparatus having a die width of 2000 mm as shown in FIG. 1 in which orifice-shaped nozzles having a diameter of 0.3 mm were arranged in a line at a pitch of 0.75 mm. Was.
Under the melt blown conditions shown in Table 1, the melt blown was performed in principle continuously for 24 hours, and the melt blown condition, the evaluation of the quality of the nonwoven fabric, the measurement of the water resistance of the nonwoven fabric, and the like were performed. Table 2 shows the results.

[0029]

[Table 1]

[Table 2]

In Examples 1 to 4, which are examples of the present invention, the condition of the melt blown process, the quality of the nonwoven fabric, and the water resistance were all good. On the other hand, in Comparative Examples 1 and 6, which are examples outside the present invention, the melt blown quality evaluation was poor and the water resistance and the product of the water resistance and the average inter-fiber distance were all small. In Comparative Examples 2 to 5 and 7, the web was torn and the process condition was poor. In Comparative Example 8, the raw material polymer was polypropylene, but the process condition was good, but the contact angle was smaller than that of polymethylpentene, so that the water resistance was clearly inferior.

According to the present invention, a highly water-resistant web made of very fine PMP fibers having an average fiber diameter of 5 μm or less using a PMP resin having the highest water repellency among polyolefins as a raw material. It can be manufactured stably. The ultrafine fiber web of the present invention has very high water resistance and flexibility, bulkiness, moisture permeability, air permeability, and filter performance common to ultrafine fiber webs. Furthermore, heat resistance is the highest among polyolefins. Therefore, various filters, moisture-permeable waterproof sheet, wipers,
Can be used for sanitary materials and other wide applications.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a main part of an example of a melt blown die used for manufacturing an ultrafine fiber web of the present invention.

[Explanation of symbols]

 Reference Signs List 1 melt blown die 2 molten polymer introduction part 3 orifice-shaped nozzle 4 heated gas introduction part 5 heated gas ejection slit 6 lip

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-3-113060 (JP, A) JP-A-62-181041 (JP, A) JP-A-1-139864 (JP, A) 199425 (JP, A) JP-A-3-167361 (JP, A) JP-A-2-251563 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) D04H 1/00-5 / 08

Claims (2)

(57) [Claims] The average diameter of the fibers constituting the nonwoven fabric is D
(Μm), the density is ρ (g / cm ³ ), and the apparent density of the nonwoven fabric is P
(G / cm ³ ), the product of the average fiber-to-fiber distance d (μm) represented by the following formula 1 and the water resistance H (cm water column) is 300.
A polymethylpentene ultrafine fiber web characterized by the above. (Equation 1) 2. The melt blown method in which polymethylpentene is melt-discharged from an orifice-shaped nozzle and is made into fine fibers by high-temperature and high-speed gas ejected from the vicinity of the nozzle orifice and collected on a sheet to form a web. The pentene has a melt index of 100 to 800 g / min at a temperature of 250 ° C. and a load of 5000 g, a melt viscosity of 30 to 150 poise when passing through the nozzle, and a jet pressure of the gas of 0.8 kg / cm ² or less. And a temperature of 260 to 340 ° C., the method for producing a polymethylpentene ultrafine fiber web.