JPH0130942B2 - - Google Patents

Description

[Detailed description of the invention]

In recent years, the demand for nonwoven fabrics has increased significantly, and the growth in the field of thin, ie, low basis weight disposable nonwoven fabrics is particularly remarkable. Nonwoven fabrics that generally belong to the category of low basis weight have a basis weight of 10 to 50 g/m ² , especially 15 to 35 g/m ² ,
Nonwoven fabrics in this field are required to be strong, free of fluff, soft to the touch, and bulky. In nonwoven fabrics bonded with a binder, which have been widely used in the past, if the amount of binder used is increased in response to the demand for increased strength, the texture will be impaired. Furthermore, in applications such as surface materials for disposable diapers, there are significant restrictions on the types of binders that can be used due to legal restrictions on the amount of residual formalin, and hydrophobic synthetic fibers such as polypropylene and polyester are the mainstream raw materials for nonwoven fabrics. There is a tendency to
With the binder method, it is becoming increasingly difficult both technically and economically to maintain both strength and texture. Against this background, and in view of energy savings and equipment costs, a so-called no-binder method for manufacturing nonwoven fabrics, which uses thermoadhesive fibers to fix nonwoven fabric constituent fibers by thermally adhering the fibers, is gaining attention. . However, the conventional method for producing thin nonwoven fabrics using heat-adhesive fibers involves directly heating the web between a heated roll and a cotton roll or a rubber roll, as shown in Figure 3.
It is made into a nonwoven fabric by applying pressure, and it is difficult to balance the strength, bulkiness, and texture of the nonwoven fabric.
In particular, in the dry carding method, it is difficult to avoid the orientation of the fibers that make up the web, resulting in insufficient strength in the lateral direction. The product becomes paper-like and has inferior bulk and texture. The present inventors have arrived at the present invention as a result of extensive research into a method for producing a nonwoven fabric that is strong, bulky, and has a soft texture and is free of fuzz. That is, the present invention provides a fiber aggregate (hereinafter simply referred to as a web) having a basis weight of 10 to 50 g/m ² consisting of heat-adhesive fibers alone or mixed fibers with other fibers containing 20% by weight or more of heat-adhesive fibers. ) is heated to a temperature above the melting point of the heat-adhesive component of the heat-adhesive fiber and below the melting point of other components using a suction drum-type hot air ventilation heating device, and then immediately using a suction drum-type ventilation cooling device. A thermal bond is formed between the fibers by cooling the thermoadhesive component below its softening point, and then an embossing roll is used in which the total area of the convex portions is 20 to 50% of the roll area. This is a method for producing a bulky nonwoven fabric, characterized in that stronger interfiber bonds are partially formed by heat-pressing at a temperature above the softening point of the heat-adhesive component and below the melting point of other components. The present invention will be explained in more detail below. The heat-adhesive fibers used in the present invention include fibers such as polypropylene, polyethylene, polyester, polyamide, and polyvinyl chloride (such fibers may hereinafter be referred to as single-type heat-adhesive fibers). Fibers such as polypropylene, polyethylene, and low melting point polyester, which have relatively low melting points and softening points, can be effectively used because of their ease of thermal bonding. Furthermore, heat-adhesive fibers made by combining components having different melting points (hereinafter sometimes referred to as composite heat-adhesive fibers) can be used. In such fibers, only a part of the composite component is thermoplasticized during heat treatment, so the fiber shape does not disappear, and the resulting fiber molded product has a better texture than a single fiber. and is more preferably used. Such composite fibers include composite fibers in which a polymer with a relatively low melting point is used as a composite component on the low melting point side, such as polyethylene, ethylene-vinyl acetate copolymer or a saponified product thereof, etc., on the low melting point side;
Composite fibers containing polypropylene as a high-melting point component are particularly easy to thermally bond and are therefore preferred. Special Public Service 1977-
17807 and Japanese Patent Publication No. 55-26209 are examples of fibers that are preferably used. Note that although a single type of heat-adhesive fiber may be used, it is also possible to use a mixture of multiple types of heat-adhesive fiber. Thermal adhesive fibers can be used in combination with other fibers. The amount of other fibers mixed in at this time is 80% by weight.
Other fibers that can be used include natural fibers such as cotton, wool, and linen, semi-synthetic fibers such as rayon and acetate, and synthetic fibers such as polyester, polypropylene, and nylon. The only other limitation on the fibers is that the melting point of the thermoadhesive fiber used for the purpose of thermal adhesion must be higher than, preferably 200% higher than the melting point.
It has a melting point higher than ℃. The reason for setting the amount of heat-adhesive fibers to be 20% by weight or more is that if it is less than 20% by weight, it is difficult to obtain sufficient strength of the nonwoven fabric, and furthermore, the surface of the nonwoven fabric becomes fluffy, which is undesirable. The method of obtaining a heat-adhesive fiber alone or a fiber aggregate with a basis weight of 10 to 50 g/ ^m2 containing 20% by weight or more of heat-adhesive fiber is usually to use heat-adhesive fiber or a mixture of heat-adhesive fiber and other fibers. Methods such as card, random Wetsuber dry pulp method, etc. can be used. Next, it will be explained with reference to the drawings. In Figure 1,
The web 15 is supplied by the feed conveyor 1 to a heating section 16 equipped with a suction drum 2, and heat-treated by ventilation heating with hot air to a temperature above the melting point of the heat-adhesive component of the heat-adhesive fiber and below the melting point of other components. be done. When the heat-adhesive fiber is a composite heat-adhesive fiber, the heat treatment temperature can be set to a temperature higher than the melting point of the high melting point component of the composite fiber,
In this case, the composite heat-adhesive fiber loses its fiber shape as in the case of the single-type heat-adhesive fiber, and therefore cannot exhibit the characteristics of the composite fiber. Therefore, when using a composite thermoadhesive fiber, it is preferable to perform heat treatment at a temperature that is higher than the melting point of the low melting point component and lower than the melting point of the high melting point component. FIG. 2 is a detailed explanatory diagram of the heating section. The suction drum 2 has an outer cylinder 3 made of a perforated plate with countless holes, and a wire mesh 4 of fine mesh (15 to 30 mesh) is wrapped around the outer periphery.
It serves to uniformly support the entire surface of thin and weak webs. Furthermore, this wire mesh can also be subjected to surface treatment to improve the mold release effect. A hole 5 is provided in one side plate of the suction drum, and the suction drum is connected to a suction port 7 of a blower 6 through a connecting member 8. Inside the suction drum 2, a buff-full plate 9 is attached to a central fixed shaft 10 for blocking ventilation except for effective ventilation areas. drum 2
The hot air sucked into the suction drum 2 passes through the blower 6 and is discharged downward, is reheated by the heat exchanger 11, and is circulated below the suction drum 2. At this time, the web 15 is adsorbed and held by the negative pressure inside the suction drum 2, and the hot air flows through the web at right angles, so it can be heated very efficiently in a very short time, and the web is not heated by external force. Since it is rarely pressed, it is heat-treated in its bulky state, and thermal adhesion develops between the fibers. The web 15 that has passed through the heating section is conveyed to a cooling section 17 equipped with a cooling suction drum 12 installed subsequently. Cooling suction drum 12
The structure is similar to that of a heating suction drum, but the difference is that the surrounding area is open and the sucked air is released in one pass. Similar to the heating section, the ventilation cooling in the cooling section 17 is very effective because the air flows orthogonally through the web 15, so that the temperature of the thermoadhesive component is rapidly lowered to below the softening point while maintaining the bulkiness of the web. The web is then cooled to fix the thermal bond developed by the heat treatment, and the web becomes a non-woven fabric. Although FIG. 1 shows one suction drum for heating and one for cooling, it is of course possible to use a plurality of suction drums if necessary. The bulky finished primary nonwoven fabric 19 is then sent to the embossing section 18. In the embossing part 18, the total area of the convex parts is 20~20 of the roll area.
Using an embossing roll 13 such as 50%,
Strong interfiber bonds are partially formed by heat-pressing the heat-adhesive fibers at a temperature above the softening point of the heat-adhesive component and below the melting point of the other components.
The reason why the total area of the convex parts of the embossing roll is limited to 20 to 50% of the roll area is that if the total area is less than 20%, the strength improvement effect of embossing is insufficient, and in particular, the mixing ratio of heat-adhesive fibers is If it is low, fluff will be observed in the obtained nonwoven fabric, which is not preferable. On the other hand, if it exceeds 50%, although the effect of improving strength is large, the obtained nonwoven fabric loses its bulkiness and soft feel and becomes hard, which is not preferable. According to this method, it is possible to obtain a nonwoven fabric that has sufficient strength, bulkiness, and soft texture. In FIG. 1, a suction drum-type hot air ventilation heating device, ventilation cooling device, and embossing roll are shown as an in-line device. It is also possible to carry out the steps separately. In the method of the present invention, the most preferable nonwoven fabric can be obtained when the heat shrinkage rate of the web used is 15% or less in both the longitudinal and lateral directions. The heat shrinkage here refers to the shrinkage rate that occurs when the raw material web is heat treated for 5 minutes without the influence of external force using a hot air circulation dryer adjusted to the same temperature as the hot air ventilation treatment. Heat shrinkage rate
If a web exceeding 15% is used, shrinkage of the web will occur on the drum of the hot air ventilation heating device, and if it is in the weft direction, it will cause unevenness in the width direction of the nonwoven fabric and the surface of the nonwoven fabric will also become nonwoven. It becomes uniform. Moreover, if it is in the warp direction, it may cause unevenness in the fabric weight or pinholes in the length direction of the nonwoven fabric, both of which are undesirable. The present invention will be specifically explained below using Examples and Comparative Examples. The definitions and measurement methods of the characteristic values used in each of the implementation and comparative examples are shown below. Non-woven fabric strength: Measured according to JIS L1096 using a 2 cm wide test piece, gripping interval of 10 cm, and elongation rate of 100%. Wet strength: After the test piece was immersed in water for 60 minutes, it was pulled up onto a wire mesh, left for 5 minutes, and the strength was immediately measured. Nonwoven fabric thickness: The thickness of one nonwoven fabric was calculated from the height measured by stacking five 10cm x 10cm nonwoven fabrics and placing a 5cm x 5cm cardboard (3 g) on top of them. Texture: A sensory test was conducted by five panelists.
○ means that everyone agrees that the texture is soft and favorable; △ means that 1 or 2 people agree that the texture is slightly inferior.
A case where three or more people judged that the soft feel was lacking was evaluated as ×. Example 1 Polypropylene (melting point 165°C, softening point 140-160
°C) and high-density polyethylene (melting point 130 °C, softening point
Fabric weight consisting of 50% parallel heat-adhesive composite fiber (1.5d x 51mm) and 50% polyester fiber (2d x 51mm) with composite components (100~115℃)
A card web of 30 g/m ² was passed through a suction drum for heating with hot air at 140°C and then a suction drum for cooling with room temperature air at a speed of 40 m/min. A temperature of 135℃ and a pressure of 3 are applied between an embossing roll with a surface area ratio of 38.5% and a metal flat roll.
A nonwoven fabric was obtained by passing it under the condition of kg/cm. Predetermined physical property evaluations were performed on the obtained nonwoven fabric. The heat shrinkage rate of the web used in this example was 5% in the longitudinal direction and 1% in the lateral direction. Comparative Example 1 Example 1 was repeated. However, no suction drum type heating/cooling treatment was performed. Comparative Example 2 Example 1 was repeated. However, the embossing roll process was not performed. Comparative Example 3 The web used in Example 1 was passed between a metal flat roll and a rubber roll at a temperature of 135° C. and a pressure of 3 kg/cm to obtain a nonwoven fabric, and the specified physical properties were evaluated. Table 1 shows the properties of the nonwoven fabrics obtained in Example 1 and Comparative Examples 1 to 3 and the surface materials of commercially available disposable diapers.

[Table] Example 2 Heat-adhesive composite fiber used in Example 1 (1.5d
x 5 mm) and 75% pulp, with a basis weight of 40 g/m ² obtained by the dry pulping method.
A suction drum for heating with hot air at 145℃, followed by a suction drum for cooling with room temperature air.
After passing at a speed of 50 m/min, the embossing roll having the pattern shown in Figure 4 (2) (convex area ratio 44.4%) and metal flat roll were passed at a temperature of 140°C and a pressure of 6 kg/cm. A nonwoven fabric was obtained by passing it through. Predetermined physical property evaluations were performed on the obtained nonwoven fabric. The heat shrinkage rate of the web used in this example was 1% in both the vertical and horizontal directions. Comparative Example 4 Example 2 was repeated. However, the difference is that the raw material web is composed of 15% heat-adhesive composite fibers and 85% pulp. Table 2 shows the properties of the nonwoven fabrics obtained in the above examples and comparative examples.

[Table] Example 3 Polypropylene fiber (melting point
163°C, softening point 140-160°C, card web with a basis weight of 35 g/m ² consisting of 60% rayon (3d x 64 mm) and 40% rayon (3d x 64 mm) as other fibers,
A suction drum for heating with hot air at ℃, followed by a suction drum for cooling with room temperature air at a distance of 30m/
After passing at a speed of min, continue as shown in Fig. 3
The temperature between the embossing roll and the metal flat roll, which has a pattern of (convex area ratio 50.3%), is 160℃.
A nonwoven fabric was obtained by passing under a pressure of 4 kg/cm.
Predetermined physical property evaluations were performed on the obtained nonwoven fabric. The heat shrinkage rate of the web used in this example was 30% in the longitudinal direction and 7% in the transverse direction. Comparative Example 5, Example 4, Comparative Example 6 Example 3 was repeated using embossing rolls with various patterns described below. Comparative example 5: Fig. 4 4, convex area ratio 60.4% Example 4: Fig. 4 5, convex area ratio 19.6% Comparative example 6: Fig. 4 6, convex area ratio 15.1% Above implementation, comparative example Table 3 shows the properties of the nonwoven fabric obtained.

[Table] Example 5 Composite fiber used in Example 1 as thermal adhesive fiber
25% and ethylene-propylene-butene-1 terpolymer fiber (melting point 134℃, softening point 105-130℃,
3d x 51mm) and 50% polypropylene fiber (2d x 51mm) as other fibers, with a basis weight of 27g/ ^m2 obtained with a random wetting bar.
A suction drum for heating with 140℃ hot air, followed by a suction drum for cooling with room temperature air.
After passing at a speed of m/min, the fourth
A nonwoven fabric was obtained by passing it between an embossing roll and a cotton roll having the pattern shown in Fig. 1 at a temperature of 130°C and a pressure of 5 kg/cm. Table 4 shows the properties of the obtained nonwoven fabric. The heat shrinkage rate of the web used in this example was 13% in the vertical direction and 10% in the horizontal direction.

[Table] *1: Slight pinholes are observed, but Diaper surface material,
Example 6 The card web with a basis weight of 18 g/m ² made of 100% heat-adhesive composite fiber used in Example 1 was used as a surface material for sanitary napkins.
A suction drum heated with 145℃ hot air, then a cooled suction drum with room temperature air at 97 m/min.
A primary nonwoven fabric was obtained by passing at a speed of min. This primary nonwoven fabric is coated with the pattern shown in Fig. 4 (convex area ratio).
43.2%) and a metal flat roll at a speed of 150 m/min and a temperature of 140°C.
A nonwoven fabric was obtained by passing under a pressure of 2 kg/cm.
Table 5 shows the properties of the obtained nonwoven fabric. The heat shrinkage rate of the web used in this example was 9 in the longitudinal direction.
%, and 2% in the lateral direction.

[Table] *2: Although it has a low basis weight, it has sufficient strength, and has good thickness and texture.
It was hot

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram of an apparatus used in the method of the present invention. Figure 2 is an explanatory diagram of the heating suction drum. In Figures 1 and 2, each symbol is 1...feed conveyor, 2...heating suction drum, 3
...Outer cylinder of suction drum, 4...Wire mesh, 5...
...Side plate hole, 6...Blower, 7...Blower suction port,
8... Connecting member, 9... Buffful plate, 10
... Batsuful fixed shaft, 11 ... Heat exchanger, 12 ...
... Cooling suction drum, 13 ... Embossing roll, 15 ... Web, 16 ... Heating section,
17... Cooling section, 18... Embossing section, 19
...Primary nonwoven fabric, 20...Nonwoven fabric. Figure 3 shows an example of the conventional calendar system. Figure 4 shows an example of a convex pattern on an embossing roll.

Claims (1)

[Claims] 1 Fiber aggregates (hereinafter sometimes simply referred to as webs) with a basis weight of 10 to 50 g/m ² consisting of heat-adhesive fibers alone or mixed fibers with other fibers containing 20% by weight or more of heat-adhesive fibers are processed. Immediately after heating the heat-adhesive fiber to a temperature above the melting point of the heat-adhesive component and below the melting point of the other components using a suction drum-type hot air ventilation heating device, the heat-adhesive fiber is heated using a suction drum-type ventilation cooling device to A thermal bond is formed between the fibers by cooling below the softening point of the component, and then the total area of the convex portions is 20 to 50% of the roll area.
% to partially form even stronger interfiber bonds by heating and pressing at a temperature above the softening point of the heat-adhesive component and below the melting point of the other components. A method for producing bulky nonwoven fabric.