JPH0491267A - Nonwoven fabric made of ultrafine fiber - Google Patents

Abstract

PURPOSE:To provide the subject product made of an ultrafine filament fiber having a small unevenness of fiber diameter, having specified physical properties, having a high tensile strength in both the longitudinal and transverse directions, excellent in dimensional stability and suitable for a filter, etc. CONSTITUTION:An objective nonwoven fabric made of an ultrafine filament fiber having <=5mum average fiber diameter and <=30% unevenness of fiber diameter and having >=40g/cm width.weight (g/m<2>) longitudinal tensile strength, >=20g/cm width.weight (g/m<2>) transverse tensile strength in the direction perpendicular to the longitudinal direction and <=10% dry heat shrinkage factor (160 deg.C for 15min). The above-mentioned nonwoven fabric product can be obtained recommendably using a fiber produced by carrying out spinning in the condition of a polymer temperature in the range of (melting point)-(melting point+45 deg.C), an air temperature in the range of 10-25 deg.C higher than the polymer temperature, 0-8 deg.C angle between an air knife and a polymer-discharging die and 0.3-0.5mm minimum distance from the air knife to the discharging die.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an ultrafine fiber nonwoven fabric that is made of ultrafine fibers with small fiber diameter irregularities, has excellent nonwoven fabric strength, and excellent dimensional stability, and is suitable for use in filters and the like.

(Prior art) Various studies have been conducted on nonwoven fabrics made of ultrafine fibers using the melt blow method, and it has become possible to produce nonwoven fabrics made of ultrafine fibers with an average fiber diameter of 0.5 to 1.5 μm. It's here.

However, such nonwoven fabrics made of ultrafine fibers have the disadvantage that beads are generated due to thread breakage, which significantly deteriorates the texture and properties as a filter. In addition, as a result, the fiber diameter unevenness becomes very large, and the ultrafine fiber nonwoven fabric sheets made by the melt-blowing method currently on the market have a large fiber diameter unevenness of more than 30%.

These nonwoven fabrics also lacked dimensional stability.

Attempts have been made to add special measures such as adding a third component polymer to solve these drawbacks, but
When these different components are added, there is a problem in that the strength of the ultrafine fiber nonwoven fabric decreases.

Furthermore, the average length of the fibers constituting nonwoven fabrics obtained by conventional melt blowing methods is from Low to several hundred, and the dispersion of fiber diameters is extremely low due to the occurrence of beads and fiber breakage. This is large and may cause inconvenience depending on the application. There was also a problem in terms of dimensional stability.

The purpose of the present invention is to eliminate the drawbacks of conventional nonwoven fabrics made of ultrafine fibers, and to provide an ultrafine fiber nonwoven fabric with small fiber diameter irregularities, high tensile strength in the longitudinal and transverse directions, and excellent dimensional stability. shall be.

(Means for Solving the Problems) The present invention takes the following measures to solve the problems described above. That is, the present invention provides an ultrafine fiber nonwoven fabric made of substantially continuous fibers with an average fiber diameter of 5 μm or less and a fiber diameter unevenness of 30% or less, the ultrafine fiber nonwoven fabric having a longitudinal tensile strength of 40% or less. g/cm width/fabric weight (g/F
), the tensile strength in the horizontal direction perpendicular to the longitudinal direction is 20 g
/ am width/fabric weight (g/l/) or more, and the nonwoven fabric has a dry heat shrinkage rate (160° C., 15 minutes) of 10% or less.

The present invention will be explained in detail below.

In order to have the characteristics of a nonwoven fabric with excellent texture, the fiber diameter needs to be 5 μm or less. If this is exceeded, the texture tends to become hard. Also, in terms of filter properties, it is desirable that the fiber diameter be 5 μm or less in order to collect 70% or more of particles with a particle size of 10 μm or less. The heat insulating material also needs to satisfy this condition because the thinner the thread diameter, the better the heat retaining performance. When the thread diameter becomes thicker, it is difficult to differentiate it from conventional woven fabrics or spunbond nonwoven fabrics.

Next, regarding fiber diameter unevenness, the required characteristics differ depending on the application, but there are 3
It is preferably 0% or less, preferably 20% or less. For example, when used as a filter or heat insulating material, channeling occurs in the filtration fluid and heat insulating air layer due to the influence of fibers whose fiber diameters are larger than the average value. Further, the presence of thick fibers makes the texture hard, which is not preferable.

The tensile strength of the sheet varies depending on the orientation and fusion state of the fibers in the sheet, but it is approximately 40g/in the machine direction.
cm width/fabric weight is 20 g/am width in the horizontal direction/
It needs to be eye-catching. Sheets made by the melt-blown method have low strength, which has hindered the development of other applications. Especially in filter applications, they were not strong enough to withstand the pressure loss caused by fluids. In addition, heat insulating materials also have the disadvantage that they cannot maintain their (initial) performance when not worn because the fibers are weakened and the sheets are crushed by the pressure applied when worn. In the present invention, since the nonwoven fabric is composed of oriented crystallized high modinilus fibers, the tensile strength is high. Measuring the modulus of a single yarn is a sheet evaluation because the fiber diameter is small and measuring a single yarn has low accuracy, but the tensile strength in the machine direction is 40 g/cm or more, and the width and area weight is 20 g/cm or more in the transverse direction. If the width and basis weight are above, the modulus of the single yarn is sufficiently large and there is no problem in applying it to commonly thought of uses.

Furthermore, due to the large modulus of the single yarn, sheet sag that is observed in ultrafine fiber nonwoven fabric sheets made by conventional melt blowing methods is not observed. The high modulus of the fibers prevents the occurrence of yarn breakage during the spinning process, thereby significantly reducing the occurrence of beads, so that the fibers become almost continuous filaments.

Furthermore, since the fibers are oriented and crystallized, the dry heat shrinkage rate of the fibers is small even without post-treatment, and therefore the dry heat shrinkage rate of the nonwoven fabric is also low. In the present invention, the dry heat shrinkage rate is 10% or less at 160° C. for 15 minutes. This is for dimensional stability.

Here, the method for producing the ultrafine fiber nonwoven fabric of the present invention will be explained. FIG. 1 is a side view of the melt blow nozzle used in the present invention. In FIG. 1, the diameter D2 of the polymer discharge hole 1 is from 0.15 to 0.35
m11, especially when manufacturing ultrafine fibers, from 0.15 to 0.
It is preferably between 25■■. Discharge hole diameter D2 is 0.35+
If it is larger than n, the draft ratio, which is the ratio of the final yarn area to the orifice area, will increase, making it necessary to pull more yarn, which will require increasing the flow rate of the pulling air or lowering the viscosity of the polymer. However, in the former case, the production cost increases, and the number of Ray nozzles increases, making the flow unstable, resulting in a rapid increase in the occurrence of thread breakage and string-like objects, and the resulting sheet becomes wrinkled. Here, the string-like material refers to a strand-like material made by entwining several fibers. In addition, the latter generally has the disadvantage of increasing yarn breakage and making it difficult to control oriented crystallization during solidification of the polymer, resulting in a high dry heat shrinkage rate of the resulting sheet. In particular, as the fiber diameter becomes smaller, the fibers become more susceptible to disturbances in the flow of the tractive fluid, and the occurrence of yarn breakage and string-like objects rapidly increases. On the other hand, if the diameter is smaller than 0.15 m, dirt may accumulate in the hole, making cleaning difficult and requiring high processing precision. Further, the width D1 of the tip of the nozzle is 90% or less of D2, preferably 30% or more, and more preferably 4
0% or more. By processing in this way, a large area is increased, and it becomes possible to increase the contact area between the traction fluid and the polymer. Additionally, polymer bulge near the orifice exit due to the ballast effect can be suppressed from the side. Hereinafter, this will be referred to as the tip notch effect.

Also, the distance S1 from the air knife surface to the die tip is 0.
It is necessary to go 0.5 inch deep from 1R. This is because the air emitted from the air knife is rapidly decelerated, increasing the contact time between the air and the polymer. On the other hand, if the distance is too large, the molten polymer will adhere to the air knife surface, which will encourage yarn breakage, which is not preferable. At this time, even if the shape of the air knife is not flat, even if it has some kind of curvature, the effect will not change significantly.

When the convergence angle θ* of the nozzle is smaller than 30 degrees, the metal thickness between the orifice through which the polymer passes and the die surface becomes too small, and there is a risk that the nozzle will burst if pressure is applied to it. On the other hand, if the number of zero lines becomes too large, the effect of notching the tip becomes small and, at the same time, flow turbulence due to air collision is promoted, which is not preferable.

The air knife spacing S2 must be between 0.4 mm and 0.8 mm. If the distance is smaller than this, the frequency of contact between the molten polymer and the air knife will increase rapidly, leading to thread breakage. When S2 becomes larger than 0.8 mm, air turbulence increases rapidly. This is because the air knife interval is wider than the point where the air and polymer first come into contact, causing turbulence as the air expands.

The spinning conditions require that the polymer temperature be in the range from the melting point ("C) to the melting point ("C) plus 45°C. If the temperature is higher than the upper limit temperature, beads will be generated due to thermal deterioration of the polymer. Moreover, it becomes impossible to apply stress necessary for oriented crystallization of fibers. Regarding the air temperature, it is necessary to perform spinning at a temperature in the range of 10 to 25 degrees Celsius higher than the polymer temperature for the same reason.

After satisfying these conditions, it is necessary to thin the polymer by selecting the shear rate and polymer intrinsic viscosity so that the melt viscosity becomes 300 poise or more.

Next, the angle θ between the air knife and the polymer discharge die
must be 8 degrees from O.

When θ becomes negative, the air turbulence becomes extremely large, resulting in many thread breakages.On the other hand, when it becomes larger than 8 degrees, the downstream part is affected by the turbulence when the air is compressed in the upstream, so the fibers break where the polymer and air come into contact. This is unsuitable because it increases the disturbance.

The minimum distance S3 between the air knife and the polymer discharge die is 0.
Preferably it is between 3 and 0.5+n. If the minimum distance is less than 0.3 m, it is no longer possible to increase the air flow velocity in the interval due to the development of a boundary layer. 0.5m
When the amount is larger than m, the amount of air becomes too large, which not only increases the utility cost but also makes it difficult to separate the air and polymer when taking up the nonwoven fabric with a net or the like, and increases the generation of string-like substances.

By satisfying these conditions, the yarn diameter unevenness is less than 30% and there is no break in the yarn, compared to the extremely large yarn diameter unevenness of 40% or more in the conventional melt-blown yarn spinning technology. It is possible to obtain a particularly excellent ultrafine fiber nonwoven fabric with a strength of 40 g/am width/fabric weight in the machine direction and a width/fabric weight of 20 g/c++/fabric weight in the transverse direction.

(Example) Examples 1 to 8, Comparative Examples 1 to 8 The measurement method adopted in this example is as follows.

The maximum strength was measured when a sample weighing 10 c* x 2 c was stretched to break with a test length of 50 mm using Tensilon.

This value was converted into a unit width and a unit basis weight into a hit.

1 to 4 The nonwoven fabric was photographed using an electron microscope, 100 fibers were randomly selected from the enlarged photograph, and their diameters were measured.
The average value was adopted.

11L It was calculated using the following formula.

Fiber diameter unevenness (07%) = fiber diameter standard deviation
The arithmetic mean of the rate of change in length in the vertical and horizontal directions when left for 5 minutes was used.

Using the nozzle shown in FIG. 1, a nonwoven fabric was produced using a polyethylene terephthalate polymer by the melt blow method under the conditions shown in Table 1, and its physical properties were measured. The results are shown in Table 1. As is clear from Table 1, the nonwoven fabric of the present invention had small fiber diameter irregularities, was made of ultrafine fibers with small fiber diameters, had excellent dimensional stability, and had high web strength in the machine direction and the transverse direction. .

On the other hand, the comparative examples had problems with web strength, fiber diameter unevenness, etc. because some nozzle conditions were unsatisfactory.

The basis weight of the nonwoven fabric was 40 g/rl, and the occurrence of yarn breakage was determined by sampling for 1 minute.

(Effects of the Invention) The nonwoven fabric of the present invention was made of ultrafine fibers with small fiber diameter irregularities, and had excellent longitudinal tensile strength, transverse tensile strength, and dimensional stability.

[Brief explanation of drawings]

FIG. 1 is a side view of a nozzle used in the present invention. 1...Polymer discharge hole 2...Air knife.

Claims (1)

[Claims] 1. An ultrafine fiber nonwoven fabric consisting of substantially continuous fibers with an average fiber diameter of 5 μm or less and a fiber diameter unevenness of 30% or less, the ultrafine fiber nonwoven fabric having a longitudinal tensile strength of 40 g.
/cm width/fabric weight (g/m^2) or more, tensile strength in the horizontal direction perpendicular to the longitudinal direction is 20g/cm width/fabric weight (g/m^2)
Above, and the dry heat shrinkage rate of the nonwoven fabric (160°C, 15
1. An ultrafine fiber nonwoven fabric characterized in that the fiber content (min) is 10% or less.