JPS63143804A - Electrette laminated fiber sheet and manufacture of the same - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an electret 1 laminated fiber sheet and a method for manufacturing the same.

(Prior Art) There is a method of converting partially heat-embossed synthetic fiber clothing into electret.

This method has two drawbacks.

First, as the fabric weight of the synthetic fiber web increases, the #&
A large amount of the charge injected from the electrode is trapped in the dark blue color, and the charge does not reach the fibers in the inner layer sufficiently, so the performance of the 1q electret is not sufficiently improved.

Second, even if the heat-embossed film surface and the non-embossed surface of the synthetic fiber web are electretized under the same application conditions, the surface potential 1q is different. That is,
The film surface has a high surface potential, while the synthetic web surface has a low surface potential.

(Not sufficiently electretized) For this reason, if an attempt is made to increase the applied voltage so that the surface of the synthetic fiber web is sufficiently electretized, the surface potential of the filmed surface will rise excessively, inducing spark discharge from the electrodes.

As a result, it becomes necessary to use a balanced applied voltage that does not cause spark discharge, which inevitably leads to a disadvantage that the electret properties of the synthetic fiber wear become low.

(Problem to be solved by the invention) Electret fiber sheet, for example, average m group diameter 20 μm
, sheet weight 200/m2. Surface charge density 4.0X10
-Although there are already products in which sheets of 10 clones/12 are laminated, they have drawbacks such as poor morphological stability, easy fluffing, and weak sheet strength. It is clear that improvement is desired. Solving this problem is particularly important for melt-blown nonwoven fabrics.

Although there are various methods for improving sheet strength and hardness of electret sheet laminates having polarization directionality, methods that impair electret properties are undesirable.

The present inventors have developed a method for sea 1 while maintaining electretization.
The present invention was arrived at after conducting extensive research into ways to improve strength, hardness and softness, and maintain air flow.

The present invention aims to provide an electret laminated fiber sheet that has excellent electret properties, excellent filter properties, and excellent shape stability such as handling and sheet strength, and a processing technology for the same. The purpose is to provide a processing technology that increases the sheet strength of electret melt-blown nonwoven fabric, improves its fluffing properties, increases its hardness, gives it ease of passing through the process up to final commercialization, and does not reduce its electret properties. It is something to do.

(Means for solving problems) The present invention has the following configuration.

In other words, (1) A surface NWj density 1X10-1" Clone/C in which the direction of polarization is directional, two or more layers of Nirectu tread fiber sheets are laminated, and there is a partially joined part.
Electret laminated fiber sheet of XK or higher.

(2) Electret &!, which is characterized by laminating two or more layers of electret m11t sheets with directional polarization and partially joining them by heating or wave propagation. [Production method of layered fiber sheet.

(3) The method of partially joining by heating involves guiding the electret fiber sheet between rolls, at least one of which has a protruding portion heated to a temperature range from ■9 to 301f below the melting point of the electret fiber sheet. 1Qkg, C
Claim No. 2, which is joined by strongly pressing and pressing at a pressure of m or more
The manufacturing method of the electret laminated fiber sheet described in Section 1.

(4> The method of partially joining by wave propagation is
The method for manufacturing an electret laminated fiber sheet according to claim 2, which involves joining a metal body that propagates ultrasonic vibrations or high frequencies and a metal roll partially having protrusions.

FIG. 1 shows a surface model diagram of an electret laminated fiber sheet having a partially joined portion according to the present invention. Further, FIG. 2 shows a cross-sectional model diagram of the joint portion shown in FIG. 1 taken along the line CC'.

1 in the figure is an electret laminated fiber sheet. 2 is a joint portion; 3a, 3b, and 3c are electret fiber sheets; 4 is a line that does not actually exist and represents the boundary of the electret fiber sheet; and 5 is an electret fiber.

FIG. 3 is a model diagram showing the charged state of the cross section of the electret fibers 5 of the electret fiber sheet 3, and shows +
- indicates the state of charging.

The electret fiber sheet having a direction of polarization used in the present invention is a sheet having a charging form as shown in FIG.

FIG. 4, FIG. 5, and FIG. 6 are cross-sectional views showing examples of stacking electret fiber sheets, and the arrows in the figures indicate the direction of polarization.

Next, FIGS. 7 and 8 show schematic cross-sectional views of the manufacturing apparatus used in the method of manufacturing the electret laminated fiber sheet of the present invention, viewed from the lateral direction.

FIG. 7 shows a method of producing an electret laminated fiber sheet using a pair of rolls, in which 6 is a metal roll having a protruding portion, and 7 is a metal or rubber roll with a smooth surface or a protruding portion. 8 is a pressure device. The arrow in the figure indicates electret fiber seam 1-3a,
3b, 3G, the respective traveling directions of the metal roll and the electret laminated fiber sheet 1 are shown.

In FIG. 7, several electret fiber sheets 3a, 3b, 3c are guided between metal rolls 6.7, at least one of which is heated and has a protruding portion, and a linear pressure of 10-.
The electret laminated fiber sheet 1 is obtained by strongly crushing with a pressure of cm or more and partially joining. At this time, bonding temperature and linear pressure are required.

In the method of the present invention, an electret fiber sheet is used, so if the bonding temperature is too high, the polarized charges injected into the fibers will disappear or decrease due to the heat, causing a decrease in the electret property.

For this reason, the bonding temperature should be kept as low as possible. The temperature range is preferably 19 degrees or more and 30 degrees or more lower than the melting point of the Electref 1 fiber sheet.

In addition, in order to increase the bonding degree, the bonding pressure (linear pressure) was increased to 10k.
Although it is preferable to carry out the bonding at q, Cm or more, excessive bonding is not preferable because it causes the bonded surface to form a film, resulting in a decrease in air permeability m and a decrease in sheet strength.

FIG. 8 shows a method of performing partial bonding using ultrasonic waves or high frequency waves.

In Fig. 8, 9 is a metal body that transmits ultrasonic waves or high frequency waves to the electret laminated fiber sheet 1, 10 is a metal roll having a protruding portion, 11 is a generator of ultrasonic waves or high frequency waves, and the arrow in the figure is the electret fiber sheet. 3a, 3b, 3c,
Metal roll 10. The traveling direction of each electret laminated fiber sheet 1 is shown.

The electret fiber sheets 3a, 3b, 3c are guided between a metal body 9 that transmits ultrasonic or high frequency waves and a metal roll 10 having a protruding portion, and are connected to an ultrasonic or high frequency generator 1.
The electret laminated fiber sheet 1 is partially joined by the heat generated by the wave propagation generated by the electret fiber sheet 1 .

The metal body 9 may be either a fixed body or a rotating body.

The feature of this method is that it uses the heat generated by the fibers themselves to join, rather than actively heating the parts to be joined.
Since no heat is generated in areas other than the joints, there is no deterioration in the performance of the electret.

Therefore, an excellent electret laminated fiber sheet can be obtained.

That is, in this method, heat is generated and bonded only in the portion sandwiched between the protrusions of the metal roll 10, and heat is not transmitted to other parts.

The deterioration of the electret property of the bonded portion is not a problem because it can be made to such an extent that it does not become a problem at all by optimizing the ultrasonic or high-frequency output or by optimizing the bonding pressure.

Therefore, this method can produce an extremely excellent electret laminated fiber sheet.

In the present invention, sheets with polarization directionality are laminated and bonded because sheets with polarization direction are laminated and bonded together.
This is because it has a higher surface charge density and superior electret properties than electret sheets polarized in random directions.

The polarization direction of the laminated sheets may be any of the orientation patterns shown in FIG. 4, FIG. 5, and FIG. 6.

This is because each layer has a polarization direction and is not randomly polarized, so excellent electret characteristics can be obtained.

It is preferable that the obtained electret laminated fiber sheet has a surface charge density of at least 1.0×10 −10 chlorine/i or more, and for example, when used for wipers, filters, dust adsorbents, etc. If the surface charge density is not higher than the above, sufficient performance cannot be obtained.

The bonding area is 0.5% to 40% of the sheet, preferably 1%
It is about 15%. If it exceeds this range, it is not preferable, especially when used in filter applications, as it will result in poor ventilation resistance.

The average gi fiber diameter of the electret fiber sheet is 0°5μm
~50μm, area weight is 5 (1/v+2~1000/m2
However, in order to produce excellent electret laminated fiber sheets, it is preferable for filter applications, etc. to laminate and join sheets with a thin fIa fiber diameter and a considerable number of days. .

In particular, this is a necessary requirement for ultra-high performance filter applications.

Furthermore, when used as a simple filter, there are many processing ports and the particle size to be captured is large, so it is necessary to have a somewhat large fiber diameter, a large basis weight, and a low pressure loss. All of these are υj reduction conditions imposed by the electret property, and are not constraints from the bonding conditions.

During electretization, sheets with a date exceeding 100 g/1T12 are not sufficiently electretized to the inner layer, as described in the prior art, and thus the resulting electret properties are low. Therefore, with a high cover factor,
An excellent electret laminated fiber sheet can be obtained by first forming a low basis weight sheet into electret, then laminating and bonding multiple sheets of this.

Bonding improves the tensile strength, hardness, and fluffiness of the sheet. This is because the fibers are constrained by the joint. Further, the strength of the sheet is improved by uniformizing the distribution of tensile stress.

Furthermore, for applications that require sheet strength and hardness, sheets with high strength, such as non-spunbond sheets, are used.

This can be done by interposing and joining a sheet with a tensile strength of 3 kg/5 cm or more, such as a woven fabric.

The improvement in bondability was evaluated by sheet strength and feathering, and it was found that polypropylene melt-blown nonwoven fabric (average fiber diameter 4
．． Seat 1, which is made by laminating 3 sheets of 0 μ, 0.16 body thickness, and 20 a/m fabric weight, was 915 cm wide in 3.0, but the sheet joined with a joint area of 15% was 7 kq 15 cm wide or more. showed strength.

In addition, when a load of 1/cnt was placed on a cotton cloth and the surface was rubbed, the sheet before joining broke after a few times, but the joined sheet withstood more than 50 times of friction and showed some pilling. This was the only occurrence.

As described above, the improvement effect of joining can be seen in the improvement of handling properties, post-processing rod passability, and sheet strength.

(Function) Layering polarized electret fiber sheets, 19~@
Since we bond at temperatures as low as possible, such as at a temperature of minus 30 degrees or higher, or by using self-heating of only the bonded area due to ultrasonic vibration or high frequency, the electret properties of the bonded area as well as the non-bonded areas are reduced. almost never happens. Therefore, the partially bonded ELEC 1-let laminated fiber sheet also has an excellent surface charge density, as well as those that have an excellent surface charge density before bonding.

In addition, since the sheets are partially joined and the movement between the fibers is restricted, the fluffiness is improved, the hardness is increased, and the strength of the sheet is increased.

Furthermore, since it can be joined to individual high-strength materials, it has even higher strength and higher-order workability.

(Example) The present invention will be explained in more detail based on examples.

Example 1 Electret melt-blown non-woven fabric with polarizability (surface charge density 3.0×10-10 clones/cJ, average w4m diameter 4.0 μm, basis weight 200/m2, thickness 0.
Three sheets of 16 mm polypropylene were stacked so that the opposing surfaces had different polarities, and the
The fifth roller was introduced between a pair of fully bent rolls (one has a protruding part and the other is a smooth roll) heated at 100°C, with a clearance of 0, a linear pressure of 70 kg・CIII, and a processing speed of 3 m/min.
Lamination was performed using the lamination method shown in the figure to obtain an electret laminated W&fiber sheet with a bonding area of 15%.

The joint area was determined from the ratio of the joint plane area to the unit area of the sheet surface.

The surface charge density of this sheet was measured to be 2.5X.
It was a 10-'' clone/cnf. The evaluation method is shown in FIG.

To determine the surface charge density, the sample 15 is sandwiched between the metal box 16 and the electrode 12 using the method shown in FIG. demand.

((From the obtained potential, determine the surface charge density according to the following formula.

How to find the surface charge density: It is determined using the relational expression Q=CV/S.

[Formula 1] Q: surface charge density (clone/cJ) C: capacitor interval ■2 surface potential S: represents the surface area of the sample (100 cJ).

In addition, when the bending resistance was evaluated using the JIS-L-1079 method, the bending resistance before bonding was 40 mm vertically.

” The length was 25mm, but after joining, it was 120mm vertically,
Yo: It had improved to 178mm and 1].

From the above results, it can be seen that the bonding effect can be increased by 1q without impairing the electret properties.

Example 2 Three layers of the same material as in Example 1 were bonded using the apparatus shown in FIG. 7 between a metal heating roll having protrusions at 110 DEG C. and a rubber roll (room temperature) at a lead wire pressure of 25 kq-Cm. The bond area was 6%. The lamination method was as shown in FIG.

When comparing the ventilation resistance of this sheet, it was found to be 1.0 before joining.
mmAQ was 1.3 mmAQ after bonding, and it was found that there was no large increase in ventilation resistance and that it could be used as a filter. The surface charge density of this sheet is 2.4X1
0-16 clones/cnf.

The ventilation resistance is a value at a passing wind speed of 1.5 m/min.

Example 3 Two layers of the same material as in Example 1 and polyester spunbond (Toshiku Co., Ltd. "Acstar" B505-20P) basis weight 50! ;l/T112, seat strength vertical 22 +115
cnol], yo"116 k'j / 5 cmrjJ
) were partially bonded using high frequency as shown in FIG.

Junction area: 6%, high frequency conditions: 27M1lz, output: 3.
5 layers w current 0.2A, energizing time 1 second, line pressure 10-cm
Processed with.

Surface charge density before bonding: 3.0×10-10 clones/r
For i, the surface charge density after bonding is 2.9X1Q-10
It was clone/i. The lamination method was as shown in FIG.

Next, the sheet strength and bending resistance (JIS-L-1079)
When evaluated, the sheet strength before joining was 4.2 kg vertically.
The width of the sheet was 15cm, but the strength of the sheet after joining was 27k.
It can be seen that sufficient bonding was achieved with a width of 15 cm. Furthermore, the sheet had a bending resistance of 42 mm vertically, but after joining, it was 150 mm vertically.

It can be seen that the sheet has high strength and high bending flexibility without any decrease in electret properties, making it easy to handle.

Example 4 Polarized electret sheet <ta fiber diameter 20 μm, Q, 5 mm, material polypropylene spunbond, basis weight 3
0G/m2. Five layers with a surface charge density of 3.4×10 −10 clones/ri were laminated so that the opposing surfaces had the same polarity as shown in FIG. 6, and bonding was performed using ultrasonic waves as shown in FIG. 8.

Bonding area 6%, ultrasonic processing conditions pressure 20kq・cm,
The processing was carried out at a current of 2 A and a processing speed of 1 m/min.

When the surface charge density after processing was measured, it was found to be 3゜4X10
-1'' clone/- showed no decrease in electret properties at all.

Comparative Example 1 Average fiber diameter 1.5 μm, basis weight 140 g/m2. The raw materials polypropylene melt-blown filament II were partially bonded using the apparatus shown in FIG. 7 with a bonding area of 15%.

An attempt was made to convert these bonded sheets 1 to electret using the method shown in FIG.

FIG. 10 shows that by the electrode 17 to which a DC voltage is applied,
Sample 19 on earth plate 20 was processed using a negative polarity voltage with a distance of 3 cm between the electrode and the earth plate.

However, in some cases, spark discharge occurred at an electric field strength of -7 KV/cm, and holes were formed in the joints of the sheets.

Next, the collection performance of the sheet processed at -6 V/cm is J
As determined by the method of lS-3-9908, it was 99.9
%showed that.

Example 5 Next, a polypropylene melt-blown nonwoven fabric having an average w4 fiber diameter of 1.5 μm and a basis weight of 201 J/m2° was subjected to electret processing at -10 KV/cm using the method shown in FIG. Partial bonding was performed at a bonding temperature of 110°C.

When the collection performance of this product was determined by the method of JIS-8-9908, it was 99.9996% or more. The surface charge density was 3.0x10-+a clone/-.

From this result, it can be seen that electretization is possible with a high electric field strength when a low basis weight sheet is made into electret, and that the sheet bonded after being made into electret exhibits superior electret properties.

(Effects of the Invention) Since the present invention laminates and joins polarized sheets with excellent electret properties, it is possible to obtain an electret laminated fiber sheet that exhibits extremely excellent electret properties even at a high basis weight. In the conventional technology, it is difficult to produce electret with a high basis weight, but the present invention is hardly subject to restrictions on the basis weight.

In addition, by joining, high strength and morphological stability are increased, so high-level processability in handling and final commercialization can be obtained.

In addition, there is no decrease in electret properties and it can be bonded with other high-strength sheets, so it can be used in filter applications that require large areas, dust adsorbents, and sealing and wrapping materials for dust-sensitive equipment. is also available.

In addition, since the hardness and softness are improved, bending workability is improved,
It has great effects such as making it easier to process into filter elements. Furthermore, it can also be used as a separate filter.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the surface appearance of the electret laminated fiber sheet of the present invention. FIG. 2 is a cross section taken along line cc' in FIG. 1. FIG. 3 is a schematic cross-sectional view of a single-layer electret fiber sheet. FIG. 4 to FIG. 6 are examples of lamination of electret fiber sheets. Arrows in the figure indicate the direction of polarization. FIG. 7 shows an example of the method for manufacturing the electret laminated fiber sheet of the present invention. FIG. 8 shows another example of the method for manufacturing an Efi 1-let Efi sheet according to the present invention. FIG. 9 shows an apparatus for measuring the surface charge density of an electret laminated W&fiber sheet. FIG. 10 shows an application device for producing electretized seams 1 to 1. 1: Electret laminated w4 #f1 sheet 2: Joint parts 3.3a, 3b, 3c: Electret laminated fiber sheet 4: Line representing the boundary of the fiber sheet 5: Electret fiber 6: Metal roll with protruding portion 7: Smooth or Metal or rubber roll having a protruding portion 8: Pressure device 9: Metal body 10: Metal roll 11: Ultrasonic or high frequency generator 12: Electrode 13: Condenser 14: Micro ammeter 15: Sample 17: Electrode 18: DC high Voltage generator 19: Sample 20: Metallic ground plate

Claims (4)

[Claims] (1) Two or more layers of electret fiber sheets with polarization directionality are laminated and have a partially bonded surface with a surface charge density of 1 x 10^-^1^0 clones/cm
＾2 or more electret laminated fiber sheets. (2) A method for producing an electret laminated fiber sheet, which comprises laminating two or more layers of electret fiber sheets having directional polarization and partially joining them by heating or wave propagation. (3) The method of partially joining by heating involves guiding at least one roll between the rolls having a protruding portion heated to a temperature range from the Tg of the electret fiber sheet to 30 degrees below the melting point, and applying linear pressure. The method for producing an electret laminated fiber sheet according to claim (2), in which the electret laminated fiber sheet is joined by strongly pressing and pressing with a force of 10 kg, cm or more. (4) The method of partially joining by wave propagation involves joining a metal body that transmits ultrasonic vibration or high frequency waves and a metal roll partially having a protruding portion. ) The method for manufacturing the electret laminated fiber sheet described in item 1.