JPS5837428B2 - The history of the disease - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a non-woven fibrous web consisting of a thermoplastic high dielectric loss factor component and a low dielectric loss factor component having a smaller dielectric loss factor than that component. By heating, only the high dielectric loss factor component is selectively softened or melted to act as a bonding agent, and the nonwoven fiber web consisting of at least two components is bonded between the low dielectric loss factor components. It relates to a method that enables the production of strong and heat-resistant nonwoven fabrics.

In order to obtain a strong nonwoven fabric that can withstand practical use from a nonwoven fibrous web, it is necessary to fix the fibrous structure of the fibrous web by some method.

One proposed method is to externally heat a non-woven fiber web consisting of a low melting point component and a high melting point component to soften or melt only the low melting point component, thereby joining the high melting point components. has been done.

However, in this method, since the web is heated by external heating, not only the low melting point components but also the high melting point components are heated as well, which often causes undesirable phenomena such as shrinkage, deterioration, and loss of orientation of the high melting point components. As a result, the mechanical properties of the high melting point component, which is the main component of the nonwoven fabric, are reduced, resulting in a reduction in the mechanical properties of the nonwoven fabric.

Furthermore, in conventional external heating methods, the heat resistance of the low melting point component that acts as a binder is generally inferior to that of the high melting point component that is the main component of the nonwoven fabric, so the heat resistance of the nonwoven fabric is the main component. It has a serious drawback that it is inferior to the case where only

As a result of extensive research in order to improve the above-mentioned drawbacks, the inventors of the present invention discovered that when a part of the components constituting the non-woven fiber web is melted and the webs are joined together, selective heating using high-frequency dielectric heating is used. The inventors discovered the surprising fact that a nonwoven fabric with excellent strength and heat resistance can be obtained by utilizing the properties of polyester fibers, leading to the present invention.

That is, in this invention, the dielectric loss rate at 106 cycles per second is o. A non-woven fiber web consisting of a thermoplastic high dielectric loss factor component larger than oi and a low dielectric loss factor component having a dielectric loss factor smaller than the high dielectric loss factor component is subjected to high frequency dielectric heating. selectively softening or melting the high dielectric loss factor components and, if desired, applying pressure to the non-woven fibrous web in an uncured state to join the low dielectric loss factor components. The present invention provides a method for joining a non-woven fibrous web comprising at least two components, characterized by:

The method of the present invention will be explained in detail below.

Generally, when a dielectric material is subjected to high-frequency dielectric heating, the dielectric material generates heat, and the amount of heat generation P follows the following equation.

Here, a is the volume of the dielectric (m3), f is the frequency (cycles/sec), and E is the electric field in the dielectric (volts/m').
ε is a dielectric constant, and tan δ is a dielectric loss tangent.

As is clear from the above equation, the amount of heat generated per unit volume of a dielectric placed under the same high-frequency electric field is calculated by the dielectric loss factor (permittivity x dielectric loss tangent) (hereinafter, dielectric loss factor is called loss factor). omitted)
For example, when a dielectric material made of two or more precepts is subjected to high-frequency dielectric heating, the larger the loss factor, the greater the amount of heat generated, and the easier it is to be heated.

In other words, if the dielectric is subjected to high-frequency dielectric heating, only the dielectric with a substantially large loss factor is selectively heated.

As mentioned above, according to the conventional method of bonding high melting point components using a low melting point component which is softened or melted by external heating of a non-woven fiber web as a bonding agent, the high melting point component is also bonded at the same time. Heating to temperatures close to the softening or melting point of low-melting precepts often accelerates the undesirable phenomena of shrinkage, deterioration, and loss of orientation;
This causes a decrease in the mechanical properties of the high-melting point compound, which is the main component of nonwoven fabrics, especially the tensile strength.

In addition, if one attempts to bring the low melting point closer to the higher melting point in order to prevent the heat resistance of the nonwoven fabric from decreasing, this decrease in mechanical properties becomes an even bigger problem, and it is necessary to improve the heat resistance and mechanical properties. It will be impossible to achieve both this and the improvement of physical characteristics.

In the method of this invention, high-frequency dielectric heating is used as a heating method for the nonwoven fiber web, and substantially only the components with a high loss rate are heated, and the low loss rate components, which are the main components of the nonwoven fabric, are heated. A strong nonwoven fabric can be obtained without deteriorating mechanical properties.

Furthermore, according to the conventional external heating method, it is difficult to uniformly heat the inside of a non-woven fiber web, and especially when heating a thick web, there is a difference in temperature between the near surface and the inside. However, since the high-frequency dielectric heating method of this invention is an internal heating method that generates heat in the dielectric itself, it can heat the inside of even thick webs. It has the important advantage that it can be heated uniformly and therefore can be bonded uniformly to the inside.

From the above description, the advantages of the present invention are clear, and the method of the present invention is most effective when the melting point of the high loss rate component is higher than the melting point of the low loss rate component.

In other words, in the conventional external heating method, the low melting point component is softened or melted and the high melting point component, which is the main component constituting the nonwoven fiber web, is bonded, so the heat resistance of the obtained nonwoven fabric is The heat resistance is determined by the components, and is inferior to the high melting point component which is the main component.

In contrast, according to the high-frequency dielectric heating according to the method of the present invention, based on the selective heating property of high-frequency waves, only the component with a large loss rate is heated, so that the melting point of the high-loss rate component becomes the melting point of the low-loss rate component. Even if the loss rate is higher than that, the high loss rate component is softened or melted, and the low loss rate component, which is the main component that controls the web, is not heated to the actual temperature.

Therefore, the heat resistance of the nonwoven fabric obtained by joining these nonwoven fiber webs is determined by the low loss rate component, which is Form 4. Obtainable.

However, it goes without saying that the method of the present invention is not limited to cases where the melting point of the high loss rate component is higher than the melting point of the low loss rate component.

The method of the invention comprises a non-woven material comprising a thermoplastic high loss rate component having a loss rate of greater than 0.01 at 106 cycles per second and a low loss rate component having a loss rate less than said high loss rate component. Use fiber web.

As is clear from the above equation for the calorific value P, the calorific value is proportional to the loss rate when other conditions are constant.

Therefore, in order to effectively carry out the method of this invention, the high loss rate component must be thermoplastic with a loss rate of greater than 0.01 at 106 cycles per second;
If the loss factor is less than 0.01, the amount of heat generated by high-frequency dielectric heating is small, making it extremely difficult to soften or melt.

Additionally, the high loss component must be thermoplastic because it is softened or melted to act as a bonding agent to join the low loss component.

On the other hand, the low loss rate component does not need to be particularly thermoplastic, as long as its loss rate at 106 cycles per second is smaller than that of the high loss rate component.

Therefore, the method of the present invention can be effectively implemented even if the loss rate at 106 cycles per second of the low loss rate precept is greater than 0.01, as long as it is within a smaller range than that of the high loss rate. .

However, in order to carry out the method of the present invention more preferably, the loss rate of the low loss rate component is preferably one-tenth or less of the loss rate of the high loss rate component.

The non-woven fibrous web for carrying out the method of this invention is
Any web may be used as long as it has at least one high loss rate component and at least one low loss rate component.

In other words, even if a non-woven fiber web is made of composite fibers made by laminating together a high-loss component and a low-loss component, it is a mixture of fibers with a high loss percentage and fibers with a low loss percentage. There is no problem even if two or more layers of a high loss rate component layer and a low loss rate component layer are stacked.

Furthermore, the fibers constituting the web may be long fibers, short fibers, or a mixture of both.

Various methods have been proposed and put into practical use as methods for obtaining non-woven fiber webs, and any of these methods may be used.

Note that when the non-woven fiber web is composed of three or more components, the component with the largest loss rate among them becomes the high loss rate component and is selectively heated.

In the method of the present invention, the above-mentioned non-woven fiber web is subjected to high-frequency dielectric heating to selectively soften or melt the high-loss components and join the low-loss components to join the webs.

The amount of heat generated by the dielectric when subjecting it to high-frequency dielectric heating is:
Other things being equal, it increases proportionally with frequency.

When performing high-frequency dielectric heating according to the method of the present invention, the frequency is not particularly specified, but in order to increase the amount of heat generated, it is preferable to use a frequency in the microwave region of about 2450 megacycles per second.

In addition, in the method of the present invention, the high-loss component, which has been softened or melted by high-frequency dielectric heating, hardens and joins the low-loss components. Pressure may be applied to the non-woven fibrous web in this state to promote bonding.

The method of the present invention will be explained below with reference to Examples.

However, it is clear from the above description that the method of the present invention is not limited to the following examples.

Example 1 A polypropylene filament (melting point 174°C, loss rate at 106 cycles per second of 0.0 0 0 7) and relative viscosity 2.3 (9
A polyprolactam filament (melting point 215°C, 1φ solution of 9% concentrated sulfuric acid) was spun at a spinning temperature of 265°C using a spinneret with 75 nozzles with a nozzle diameter of 0.25xm. A non-woven fibrous web consisting of polypropylene filaments and polycaprolactam filaments with a fiber weight of 100 grams per square meter was formed using an air jet with a loss rate of 0.36).

This fiber web was placed on a polytetrafluoroethylene conveyor and passed through a microwave oven at a speed of 7 m/mm between two silicone rubber pressure rolls at room temperature placed immediately after the microwave oven outlet. suppressed it through.

However, the output of the microwave oscillator was 5 kilowatts and the frequency was 2450 megacycles per second.

In the thus obtained nonwoven fabric, the polyprolactam filament, which is a high-loss component, softens, and the polypropylene filament, which is a low-loss component, does not soften, despite having a lower melting point than the polyprolactam filament. A polypropylene nonwoven fabric using polycaprolactam as a binder was obtained.

The tensile strength and elongation of this nonwoven fabric was measured, and the values are shown in Table 1.
It was shown to.

In addition, the measurement of tensile strength and elongation is based on JIS I followed the instructions.

For comparison with 1068, when the above non-woven fiber web was passed between two heated metal rolls and pressurized, the polypropylene filaments melted first, and polyprolactam was used as the bonding agent. It was not possible to obtain a nonwoven fabric.

Example 2 Intrinsic viscosity 0 in orsoque phenol (35°C)
．． No. 62 polyethylene terephthalate chips were spun at a spinning temperature of 285°C and a nozzle diameter of 0. Polyethylene terephthalate filaments (melting point 262°C, loss rate 0.03 at 106 cycles per second) spun from a spinneret with 250 nozzles of 25 mm and a relative viscosity of 2.3.
A concentric pod core with a composite ratio of 25:75 made by composite spinning polycaprolactam (melting point 215°C, loss rate 036 at 106 cycles per second) and polyethylene terephthalate with an intrinsic viscosity of 0.62 using a spinneret with 160 nozzles. A non-woven fiber web having a fiber weight of 70 grams per square meter was formed by applying an air jet to the filament of the mold (polycaplactam as a sheath component and polyethylene terephthalate as a core component).

This fiber web was placed in the same microwave oven as in Example 1.
When bonding was performed by passing the polyethylene terephthalate at a speed of 6 m/min, the polycaprolactam was selectively heated despite the loss rate of polyethylene terephthalate being greater than 0.01. A terephthalate nonwoven fabric could be obtained.

For comparison, the above non-woven fiber web was prepared at a surface temperature of 175
A polyethylene terephthalate nonwoven fabric with polycapsulactam as a binder was produced by passing it between two metal rolls heated to 0.degree. C. and by conventional external heating.

Table 2 shows the tensile strength and elongation values of each of the nonwoven fabrics thus obtained.

Example 3 A non-woven fiber web with a fiber weight of 300 grams per square meter was formed in the same manner as in Example 2, and
When the web was joined by passing it through the microwave oven of Example 2 at a speed of n, a satisfactory nonwoven fabric was obtained which was uniformly joined to the inside.

On the other hand, when the above-mentioned non-woven fiber web was passed between the metal rolls of Example 2 and heated externally, the resulting non-woven fabric was not bonded to the inside and delamination occurred, making it impossible to obtain a satisfactory non-woven fabric. I couldn't do it.

Example 4 A polyhexamethylene adipamide fiber with a single yarn of 2 denier and a fiber length of 60 mm (melting point 252°C, loss rate at 106 cycles per second of 0.12) and a single yarn of 2 denier with a fiber length of 60 mm
7It7IL polycaprolactam fiber (melting point 215℃
, loss rate 0.36 at 106 cycles per second) and 2
A non-woven fibrous web having a fiber weight of 70 grams per square meter was prepared by mixing in a 1:1 ratio and carding as usual.

The fiber web thus obtained was passed through the joining device of Example 1 to produce a nonwoven fabric.

Further, the above-mentioned fiber web was passed between two metal rolls heated to a surface temperature of 173° C. to apply compression, thereby obtaining a nonwoven fabric by a conventional external heating method.

All of the nonwoven fabrics used polyprolactam as a bonding agent, and the tensile strength and elongation values measured for each are shown in Table 3.

This example is where the loss rate of the low loss rate component is greater than one tenth of the loss rate of the high loss rate component.

Even in this case, the nonwoven fabric produced by the method of this invention is
Although the strength is greater than that of the nonwoven fabric produced by the conventional method, the effect of the method of the present invention is smaller than that of Example 1, where the loss rate of the low loss rate component is less than one-tenth of the loss rate of the high loss rate component.

Reference example Polyethylene fiber with a single yarn of 3 denier and a fiber length of 60 mm (
melting point 130°C, loss rate 0.0012 at 106 cycles per second), single yarn 3 denier, fiber length 60
A non-woven fibrous web having a fiber weight of 70 grams per square meter was prepared by mixing in a 1:1 ratio with our polypropylene fibers (melting point 174°C, loss rate 0.0007 at 1106 cycles per second) and carding as usual. I made it.

This fiber web was placed in the microwave oven of Example 1 for 3 m.
/min, but none of the fibers softened.

As is clear from the above detailed explanation, when high-frequency dielectric heating according to the method of the present invention is used when joining non-woven fiber webs made of at least two components, it is possible to join non-woven fiber webs made of at least two components, compared to conventional joining using external heating. A strong nonwoven fabric can be obtained without any deterioration in the mechanical properties of the main components that make up the nonwoven fabric.

In addition, with conventional external heating methods, it is difficult to uniformly heat the inside of a non-woven fiber web, and especially when joining thick webs, there is a large temperature difference between the near surface and the inside. As a result, uniform bonding cannot be achieved, and in extreme cases, delamination occurs, making it impossible to obtain a nonwoven fabric that can withstand practical use.

On the other hand, high frequency dielectric heating by the method of this invention
Since this is an internal heating method that heats the dielectric itself, even a thick web can be heated evenly to the inside, making it possible to obtain a strong nonwoven fabric.

Furthermore, surprisingly, in conventional bonding of non-woven fibrous webs by external heating, a low melting point compound acts as a bonding agent, so the heat resistance of the obtained nonwoven fabric is determined by the low melting point or the heat resistance of the obtained nonwoven fabric. In contrast, in the method of this invention,
It is also possible for a high melting point substance to act as a bonding agent,
It has the important advantage that a nonwoven fabric with excellent heat resistance can be obtained.

Claims (1)

[Claims] 1 Dielectric loss rate at 106 cycles per second is 0.0
High-frequency dielectric heating of a non-woven fibrous web comprising a thermoplastic high dielectric loss factor component greater than 1 and a low dielectric loss factor component having a dielectric loss factor smaller than the high dielectric loss factor component. 1. A method for joining non-woven fiber webs comprising at least two components, characterized in that a high dielectric loss factor component is selectively softened or melted, and a low dielectric loss factor component is joined for a certain period of time. 2 Dielectric loss rate at 106 cycles per second is 0.0
High-frequency dielectric heating of a non-woven fibrous web consisting of a thermoplastic high dielectric loss factor component greater than 1 and a low dielectric loss factor component having a dielectric loss factor slightly smaller than the high dielectric loss factor. The method is characterized in that the high dielectric loss factor components are selectively softened or melted, and the non-woven fiber web is pressed in an unhardened state to join the low dielectric loss factor components. A method for joining non-woven fibrous webs comprising at least two components.