JPH0364565A - High strength non-woven fabric - Google Patents

Abstract

PURPOSE:To provide the subject non-woven fabric having high strengths in both the longitudinal and transverse directions and excellent punchability and useful for filters by limiting a ratio between the strengths of the non-woven fabric in both the longitudinal and transverse directions in a specific range and specifying the strength of the fabric in the transverse direction at >= a specific value. CONSTITUTION:The objective non-woven fabric is substantially prepared of filaments having an average fiber diameter of <=10mum by a melt blow method and has a DTT/DTM ratio of 1.5-10 between the strength DTT of the fabric in the longitudinal direction and the strength DTM thereof in the transverse direction and the strength of >=5 (g/cm weight) in the transverse direction. For example, polyethylene terephthalate fibers are preferably used as the fibers composing the non-woven fabric.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a high-strength nonwoven fabric that is strong in the machine direction and moderately strong in the transverse direction and has excellent workability.

(Prior art) The ultrafine nonwoven fabric obtained by the melt blowing method was
Although these are disclosed in Japanese Patent Publication No. 883, Japanese Patent Publication No. 43-20248, Japanese Patent Publication No. 44-22232, Japanese Patent Publication No. 33511-1988, etc., the strength of the nonwoven fabric is low in all of them. The improved method is published in Japanese Patent Application Laid-Open No. 53-38767.
It was fabricated in the bulletin. However, although this nonwoven fabric is strong in the vertical direction, it is extremely weak in the horizontal direction, and the reality is that it can only be used in limited tape-like applications.

Further, although JP-A-54-131080 discloses the use of a high molecular weight resin, only a weak resin is obtained due to the use of a plasticizer. Furthermore, JP-A-54-14727
Publication No. 6 discloses a three-dimensionally intertwined product, but the strength ratio of vertical and horizontal strength is smaller than 1, and because it is random, the strength in the horizontal direction is strong, and the strength in the vertical direction is still high. It was impossible.

(Problems to be Solved by the Invention) Conventional techniques have a small strength ratio between longitudinal and (M) and do not have high strength, so problems such as sheet breakage occur frequently during high-speed processing.

The present invention aims to provide a high-strength nonwoven fabric that has excellent high-speed processability and is somewhat strong in the machine direction and strong in the transverse direction.

(Means for Solving the Problems) The present invention improves the strength of single fibers, and by controlling the arrangement of fibers, it is presumed that the number of entanglement points between single fibers increases and the strength of the entanglement points increases. This method was completed after discovering that the strength of a nonwoven fabric in the longitudinal and lateral directions could be controlled by a method, and the following measures were taken to solve the above-mentioned problems. That is, the present invention is made of a nonwoven fabric obtained by a melt blowing method, which has an average fiber diameter of 10 μm or less and is substantially a long fiber, and has a strong DTT in the longitudinal direction.
and the lateral strong DTM ratio DTT/DTM ratio is 1.5
10 or less, and the lateral strong DTM is 5 (g/c
It is a high-strength nonwoven fabric characterized by having a weight per unit area of m) or more.

(Function) The average fiber diameter in the present invention is 10 μm or less, preferably 5 μm or less in order to maintain a soft texture. 10μ
If it exceeds m, the texture becomes hard and undesirable. Furthermore, the entanglement property is also poor, which is not preferable.

The nonwoven fabric of the present invention is obtained by the melt blowing method, which is the most efficient method for producing ultrafine nonwoven fabrics that are bulky and have a degree of flexibility in softness.

The nonwoven fabric of the present invention is substantially long fiber. If there is thread breakage, the number of entanglement points will decrease, leading to a decrease in strength, which is undesirable. In addition, thread breakage at the nozzle, which is unique to the melt blowing method, results in ball-shaped lumps that deteriorate the texture, strength, and functionality such as filtration performance and barrier performance, which is undesirable.

The nonwoven fabric of the present invention has a strong strength DTT in the longitudinal direction and a strong strength D in the lateral direction.
The ratio DTT/DTM with TM is 1.5 or more and 10 or less. If it is less than 1.5, sufficient strength in the longitudinal direction cannot be maintained for practical use. If it exceeds 10, the strength in the lateral direction becomes weak and it is not possible to maintain sufficient practical strength when used with a wide nonwoven fabric. A particularly preferable range of the present invention from the viewpoint of processability is 2 or more and 6 or less.

In order to achieve such a preferable strength balance, the scale length when laminated should be at least 20 am or more 80 c-
The ratio TD/MD of the longitudinally transmitted microwave intensity TD and the horizontally transmitted microwave intensity MD measured with a microwave molecular orientation meter is 1.5 or more and 20 or less when the single fibers are aligned. It is preferable to set it as the state.

The reason for this is not clear, but it is thought to be due to a balance between the moderately random spread of the fibers in the lateral direction and the arrangement in the longitudinal direction. It is also believed that as the scale length increases, the number of entanglement points between single fibers increases, increasing strength.

However, if the scale length is too long, the spread of the single fibers in the lateral direction will be suppressed. For example, if the scale length is longer than 1 m, the lateral strength will be weakened, and if the scale length is over 1.3 m, the DTT/DTM will be 20.
That's all.

Since the strength ratio is expressed only when TD/MD is within an appropriate range, it is not clear that there is some relationship between the degree of entanglement of the single fibers in the thin scales, the degree of alignment, and the degree of orientation of the single fibers. It is thought that such a phenomenon will occur.

The strength in the lateral direction in the present invention is (5 g/cm basis weight) or more, preferably (7 g/cm basis weight) or more, more preferably 1
It is 0 (g/cm basis weight) or more.

The nonwoven fabric of the present invention preferably has a dry heat shrinkage rate of 10 (%) or less. If it exceeds 10 (%), it may become less powerful. Although the reason for this is not clear, it is thought that the strength at the point where single fibers are entangled with each other depends on the strength of the fibers at the point where the single fibers are entangled.

It is believed that the strength depends on the crystallization and orientation degree of the single fibers and the molecular weight.

It is thought that when the dry heat shrinkage rate is high, crystallization is insufficient, making it easier to stretch and the interlacing points to be dislocated, resulting in a decrease in strength.

The fibers constituting the nonwoven fabric of the present invention are not particularly limited in material, but those having as high a molecular weight as possible are preferred. If the molecular weight is high, the strength of the fibers will also be high, so the strength of the nonwoven fabric will also be strong. Further, in order to obtain higher strength, it is preferable that the molecular chain is rigid and the intermolecular bond strength is strong. For example, polyethylene terephthalate is preferred.

It is preferable for the fibers constituting the nonwoven fabric of the present invention that substantially no single fibers are bonded to each other for applications in which the fiber surface is used for functions such as filter applications.

The method for obtaining the nonwoven fabric of the present invention utilizes a melt blowing method.

The melt blowing method is based on a known method, but in order to obtain the nonwoven fabric of the present invention, it is necessary to make the constituent fibers strong, so the molecular chains of the polymer are lengthened, and in order to achieve highly oriented and immobilization, high viscosity and short retention are required. It is preferable to strongly elongate the material at a low temperature for an hour and crystallize it at the same time as the thinning is completed.

For example, polyethylene terephthalate has an intrinsic viscosity of 0.6
Preferably, a polymer having an intrinsic viscosity of 0.65 or more is discharged at a melting point plus 40°C or less, preferably a melting point plus 30°C or less, for example 285°C, with a residence time of 10 minutes or less, preferably 5 minutes or less.

The traction fluid is air below 300″C, preferably 280°C.
Tow at a flow rate of Matsuha 1 or higher below. Heated steam and nitrogen are particularly preferred because they are inert.

The collection method is also important. The known method of random arrangement is not preferable because the strength in the longitudinal direction is significantly weakened. Also, if the spray is applied obliquely onto a sloped or flat surface, the fibers will be arranged too much in the vertical direction, which will weaken the strength in the horizontal direction and cause strings to form frequently, which is not preferable. Furthermore, if the take-off point is too short and fused, the degree of orientation will be lowered and the strength will be lowered because the film will not be stretched later, and the shrinkage rate will also be significantly higher, which is not preferable.

A preferred method for obtaining the nonwoven fabric of the present invention is to stack the fibers on a mountain-shaped net surface with a curvature at the apex at a distance that does not adhere to tM so that the fibers flow down in the direction opposite to the traveling direction, so that the fibers are arranged in the vertical direction and also in the horizontal direction. The entangled thin layers with long scale lengths are laminated and are subjected to a shrinkage treatment with a strong vertical and horizontal coverage, preferably 2% or less, so that the entangled points are firmly entangled and the strength is significantly improved, and the inner layer is bulky. A nonwoven fabric is obtained. If necessary, further entanglement treatment, resin treatment, dyeing treatment, etc. may be performed. Further, embossing, ultrasonic processing, etc. may be performed.

Examples are given below to further clarify the composition and effects of the present invention. Note that the fiber physical properties of the nonwoven fabric structure defined in the present invention refer to values measured by the following method.

Fiber Diameter 100 fibers are randomly selected from an enlarged electron micrograph of the nonwoven fabric, their diameter is measured, and the average fiber diameter is determined by the following formula.

A strong nonwoven fabric with uneven fiber diameter A sample with a width of 2 mm in the longitudinal and transverse directions and a length of 15 mm was prepared, and after humidity was conditioned in a constant temperature room under standard conditions, n = 20 was measured using a Tensilon, with an effective sample length of 10 cm and a chuck gripping width of 2 .5cm, the elongation strain is recorded at 100% elongation speed until breakage, and the maximum strain stress point σj (g/2cm) is obtained and calculated using the following formula. Note that g/male is used as the unit for the basis weight M of the sample.

The strength in the vertical direction is DTT1, and the strength in the lateral direction is DTM.

Strength ratio The ratio of the above DTT and DTM is determined from the following equation.

Strength ratio = DTT/DTM Shrinkage rate The nonwoven fabric was cut into 200 m x 20 cm samples, with a mark marked at the center of 15 cm x 15 cm.The samples were placed in a hot air dryer at 130°C and heat treated for 15 minutes in a free state. The lengths Li of the marks in the vertical and horizontal directions are measured and determined individually using the following formula.

Unless otherwise specified, the value obtained by calculating the vertical and horizontal dimensions separately and calculating the average value is referred to as the shrinkage rate of the nonwoven fabric.

Transmitted microwave intensity ratio The nonwoven fabric was cut into 25 cm x 25 cIll as a sample, and a microwave molecular orientation meter rMDA-2001 (manufactured by Kanzaki Paper Industries Co., Ltd.) was used.
The ratio of the transmitted microwave intensities in the vertical direction and the horizontal direction is calculated using "Type A". Note that one to three samples are measured by stacking them in the circumferential direction, and the thickness effect is determined by the least squares method and the correction is determined based on the value corresponding to the fabric weight of 80 (g/cJ) from the curve.

The scale length sheet is peeled in the longitudinal direction to determine its length L(c+n).

(Example) Examples 1 to 4, Comparative Examples 1 to 2 Polyethylene terephthalate with an intrinsic viscosity of 0.65 was
It is extruded at 0.1 g/min from an orifice with a hole diameter of 0.15 at 0°C, and is thinned by a traction fluid at 295°C, and then lowered to 60 cm.
At I11, the angle between the direction of travel and the horizontal direction is 0 to 75
The material was placed on a suctioned net (FIG. 1) having a gradient of 100°C, and then the surface was continuously heat-treated with a far-infrared heater and wound up. Table 1 shows the properties of each sheet obtained.

A punching test was performed on the obtained sheet using a continuous punching machine at different speeds.

The situation at this time is also listed in Table 1.

The product of the present invention can be punched at a high speed of 10 m/min or more, but the product with DTT/DTM lower than 1.5, which is outside the scope of the invention, can only be punched at a low speed or has low strength in the lateral direction. The punching could not be done cleanly and horizontal cracks occurred.

Examples 5 to 9, Comparative Examples 3 to 4 Table 2 shows the properties of the sheets and the results of the punching test obtained under the same conditions as those for the test. In Comparative Examples 3.4, the punching was poor even though the punching speed was quite low.

14- Example 101 Comparative Examples 5-6 Polypropylene with a melt index of 12 was heated to 240'
Melt Fa L at 265°C. Zaku 5.
6 had a large angle and had low lateral strength, making it impractical.

6- (Effects of the Invention) The high-strength nonwoven fabric of the present invention is strong in the longitudinal direction, strong in both the longitudinal and transverse directions, and has excellent workability such as punching.

[Brief explanation of drawings]

FIG. 1 is a partial side view of an apparatus used for producing the high-strength nonwoven fabric of the present invention.

Claims (1)

[Claims] 1. It is made of a nonwoven fabric obtained by a melt-blowing method with an average fiber diameter of 10 μm or less and substantially long fibers, and has a ratio of strong DTT in the longitudinal direction to strong DTM in the transverse direction DTT/DTM
is 1.5 or more and 10 or less, and the horizontal strong DTM is 5
(g/cm basis weight) or more.