JPH0959860A - Filament nonwoven fabric and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a filament nonwoven fabric excellent in bulkiness and tensile strength by thermally treating a conjugate fiber web having a spiral crimp and compris ing thermoplastic resins having the difference between melting points. SOLUTION: A crystalline polypropylene and a high-density polyethylene having a melting point which is lower than that of the crystalline polypropylene by 15 deg.C or more and having an elastic shrinkage factor which is smaller than that of the polypropylene by 1% or more are subjected to bicomponent spinning into a parallel type or eccentric sheath-core type fiber in a conjugate ratio of (60/40) to (40/60) and the spun yarn is drawn in draw ratio of >=1.2 times at a temperature lower than a melting point of the high density polyethylene and relaxed to form a conjugate fiber in which spiral crimp located on the outside is developed. Then, the conjugate fiber is bundled into two-like shape and then webbed or webbed by a spunbonding method and heat-treated by a hot air oven system or heat pressing system at a temperature not lower than the melting point of the high-density polyethylene and a temperature not higher than a softening point of the crystalline polypropylene and contact point between both fibers is fused and bound to provide the objective integrated long fiber nonwoven fabric.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonwoven fabric produced by a heat fusion method, which is excellent in bulkiness and has a large tensile strength. More specifically, it relates to a long-fiber nonwoven fabric used for sanitary materials, civil engineering materials, agricultural materials, packaging materials and the like.

[0002]

2. Description of the Related Art As a method for manufacturing a non-woven fabric utilizing heat fusion of fibers themselves, there are a heat treatment method for a card web made of staple fibers and a heat treatment method for a long fiber web. The latter method has the advantage that the manufacturing process is simple, but the nonwoven fabric obtained lacks flexibility and has poor bulkiness. Further, conventional long-fiber non-woven fabrics manufactured by the heat fusion method and used for sanitary materials, civil engineering materials, etc. are mainly composed of single-component fibers, and such fibers are not wound. Since the shrinkage did not appear, the bulkiness was inferior. As a method of expressing a spiral three-dimensional crimp (hereinafter referred to as spiral crimp) in a single-component fiber, the spun fiber is taken up while giving a biased quench, and the crimp is caused by the difference in heat shrinkage inside the fiber. A method of developing crimps (Japanese Patent Publication No. 45-1649) or a method of developing crimps due to a difference in crystallinity in which a nucleating agent is blended only in a certain portion of the fiber cross section (JP-A-5-20935)
No. 4) is known. However, in the former case, the crimps are alleviated in the heat treatment step of processing the nonwoven fabric, and the bulkiness of the nonwoven fabric becomes insufficient. Further, since both of them are fibers of a single component, only a thermocompression bonding method can be used as a heat treatment step for processing into a non-woven fabric, which results in crushing the spiral crimps of the fibers, and a preferable bulkiness cannot be obtained. There is also known a method in which a different type of thermoplastic resin is subjected to composite spinning in a parallel type or an eccentric sheath-core type to develop a spiral crimp in the fiber (JP-A-48-1471 and JP-A-63-282).
350). However, in the non-woven fabric using these composite fibers, although the improvement of the bulkiness is recognized, the tensile strength is only the same level as the conventional non-woven fabric composed of the single component fiber (the following), and further improvement is desired. Was there.

[0003]

DISCLOSURE OF THE INVENTION In view of the above-mentioned present situation of long-fiber nonwoven fabrics produced by a heat fusion method, the present invention is intended to provide a long-fiber nonwoven fabric excellent in bulkiness and high in tensile strength. Is.

[0004]

Means for Solving the Problems In order to solve the above problems, the inventors of the present invention have conducted intensive studies as a result of paying attention to the relationship between the spiral crimp expressed in the composite fiber and the arrangement of components in the fiber cross section. In a parallel type or eccentric sheath-core type composite fiber which is formed of a different kind of thermoplastic resin and exhibits spiral crimping by stretching, by using a composite fiber in which a thermoplastic resin having a low melting point is arranged outside the crimp The inventors of the present invention have completed the present invention, knowing that the above object is achieved. That is, the first invention of the present application is a non-woven fabric made of composite filaments having spiral crimps obtained by composite spinning of two kinds of thermoplastic resins having a difference in melting point of 15 ° C. or more, and the outside of the spiral crimps. The long-fiber nonwoven fabric is characterized in that the contact points of the fibers are bonded to each other by fusion bonding of the low melting point thermoplastic resin located at. The second invention of the present application has a first thermoplastic resin, a melting point lower than that of the first thermoplastic resin by 15 ° C. or more, and an elastic shrinkage ratio of 1% or more lower than that of the first thermoplastic resin. The second thermoplastic resin has a composite ratio of 6
In the range of 0/40 to 40/60, the unstretched yarns obtained by compound spinning in a parallel type or in an eccentric sheath-core type so that the second thermoplastic resin serves as a sheath are used as the second thermoplastic resin. After being drawn 1.2 times or more at a temperature lower than the melting point of, the fibers are fused together by heat treatment at a temperature not lower than the melting point of the second thermoplastic resin and not higher than the softening point of the first thermoplastic resin. A method for producing a long-fiber non-woven fabric, comprising:

The present invention will be described in more detail below.
As a thermoplastic resin used as a raw material for composite long fibers, polypropylene, polyethylene, ethylene / propylene copolymer, propylene / butene-1 copolymer, ethylene / propylene / butene-1 copolymer, ethylene / vinyl acetate copolymer Combined, polyolefins such as poly-4-methylpentene-1, polyolefins modified with unsaturated carboxylic acids or unsaturated carboxylic acid anhydrides, polyethylene terephthalate, polyethylene terephthalate.
Various thermoplastic resins such as isophthalate copolymers, polyesters such as polybutylene terephthalate, polyamides such as 6 nylon, 66 nylon, nylon 12 and thermoplastic polyurethane can be exemplified.

In the present invention, a combination of two kinds of thermoplastic resins having different melting points of 15 ° C. or more is selected and used. In this case, it is necessary to use spinning conditions such that the elastic shrinkage of the high melting point thermoplastic resin is 1% or more higher than the elastic shrinkage of the low melting point thermoplastic resin. In the present invention, the composite long fibers are heat treated, and the contact points of the fibers are adhered to each other by fusing only the low melting point thermoplastic resin to form a nonwoven fabric. If the difference between the melting points of the two types of thermoplastic resins used as the raw material of the composite fiber is less than 15 ° C., the temperature range that can be used during heat treatment is narrowed, which is not preferable. Here, the elastic shrinkage means that an undrawn yarn composed of a single component is drawn at the same draw ratio (K) as the drawing conditions of the composite fiber by using a tensile tester,
It is the contraction rate when the load is immediately released and can be expressed by the following formula. Elastic shrinkage S (%) = 100 × (KA-B) / (KA-
A) A: length of undrawn yarn B: length of yarn when the load is released after drawing When the thermoplastic resin (a) cannot be spun with a single component,
Alternatively, when the single component cannot be stretched up to K times, the elastic shrinkage (S1) of the unstretched yarn composed of the single component of the thermoplastic resin (b) having good stretchability and the thermoplastic resin (a) The elastic shrinkage (Sc) of the undrawn yarn of the composite fiber of the thermoplastic resin (b) and the thermoplastic resin (b) is measured, and the elastic shrinkage (S2) of the undrawn yarn of the thermoplastic resin (A) is obtained by the following formula. : S2 = 2Sc-S1

When the difference in elastic shrinkage between the two types of thermoplastic resins is less than 1%, no clear crimp is generated even after stretching the composite fiber, and a sufficiently bulky nonwoven fabric cannot be obtained. When the elastic contraction rate of the high melting point thermoplastic resin of the two types of thermoplastic resin is smaller than the low melting point elastic contraction rate, the low melting point thermoplastic resin is outside the crimp loop generated after stretching the composite fiber. Can not be placed. In the composite long fiber used in the present invention, two kinds of thermoplastic resins selected according to the above criteria are mixed in a composite ratio of 60/40 to 40/6.
Within the range of 0, parallel type or eccentric sheath-core type composite spinning is performed. Since the occurrence of crimp of the composite fiber is based on the difference in elastic shrinkage between the two components, if one component is less than 40%, clear crimp does not occur and a sufficiently bulky nonwoven fabric cannot be obtained.
When the composite type is an eccentric sheath-core type, a low melting point thermoplastic resin is used on the sheath side. As a preferable combination of the two kinds of thermoplastic resins, crystalline polypropylene / polyethylene can be exemplified. Crystalline polypropylene having a wide molecular weight distribution exhibits a relatively large elastic shrinkage, and thus can be preferably used as a thermoplastic resin having a high melting point.

The unstretched yarn obtained by the composite spinning is drawn, and then the tension is immediately released to cause spiral crimping in the composite fiber. The radius of curvature of the spiral depends not only on the physical properties such as the difference in elastic shrinkage of the raw material resins, Young's modulus, fineness, etc., but also on the stretching temperature and the stretching ratio, and depending on the desired degree of bulkiness of the nonwoven fabric, stretching conditions (generally, Is from room temperature to a temperature lower than the melting point of the second thermoplastic resin and is about 1.2 to 4 times). In the composite long fiber thus obtained, the low melting point thermoplastic resin is arranged outside the spiral crimp. In order to obtain a composite long-fiber web having a three-dimensional crimp used in the present invention, two kinds of thermoplastic resins selected according to the above criteria are composite-spun at a predetermined composite ratio and wound on a bobbin or stored in a can. The undrawn yarn tow may be drawn under predetermined drawing conditions and immediately accumulated on the conveyor. In addition, the spun-bond method is used in which the spun composite fiber is taken through a quenching device with a drawing device consisting of a feed roll and a draw roll, and then sucked with an air sucker and accumulated on a conveyor arnet while opening. You can also

In the long-fiber nonwoven fabric of the present invention, the composite long-fiber web having the above-described spiral crimp is heat-treated at a temperature not lower than the melting point of the low-melting thermoplastic resin and not higher than the softening point of the high-melting thermoplastic resin. Obtained. For the heat treatment, a thermocompression bonding device such as an embossing roll, a hot-air circulating suction dryer, or a heating device such as infrared heating can be used. By heat treatment, the fibers are fixed at their contact points by fusion bonding of the low melting point thermoplastic resin, but the composite long fibers used in the present invention have the low melting point thermoplastic resin disposed outside the spiral crimp, The fibers come into contact with each other by the thermoplastic resin having a low melting point, and the fibers are fixed by fusion of the thermoplastic resins of the same kind, so that a nonwoven fabric having a high tensile strength can be obtained. In the case of heat treatment using a thermocompression bonding device, a temperature close to the softening point of the low melting point thermoplastic resin placed outside the spiral crimp can be adopted as the heat treatment temperature, so the high melting point thermoplastic resin is softened by heat. A bulky and flexible non-woven fabric can be obtained without being deformed or deformed. In the case of a composite fiber in which a low melting point thermoplastic resin is arranged inside the spiral crimp, in order to obtain a nonwoven fabric with sufficient strength, it is necessary to perform heat treatment at a higher temperature so that the high melting point thermoplastic resin softens. , The texture of the non-woven fabric becomes hard.

The hot air circulation type suction dryer can supply a sufficient amount of heat without applying pressure to the long fiber web, and is therefore preferable for producing bulky nonwoven fabric at high speed. Also in this case, since the composite long fibers have the low melting point thermoplastic resin arranged outside the spiral crimp, the fibers are in contact with each other by the low melting point thermoplastic resin,
Since the fibers are fixed by fusion bonding of the same kind of thermoplastic resin, a nonwoven fabric having high tensile strength can be obtained. When the low-melting point thermoplastic resin is heated to a melting temperature, the high-melting point thermoplastic resin causes a slight shrinkage due to relaxation of strain during stretching, but the low-melting point thermoplastic resin does not melt. As a result, a large shrinkage occurs, and as a result, a spiral reverse movement occurs so that the high melting point thermoplastic resin is arranged outside the spiral crimp of the composite fiber. Such movement of the fibers increases the number of points of contact / adhesion between the fibers, resulting in a nonwoven fabric having high strength. Further, since the fibers are pulled together at the bonding points, the decrease in bulkiness is small. When a composite fiber in which a low melting point thermoplastic resin is placed inside the spiral crimp is heat treated by a suction dryer, the spiral shrinkage of the composite fiber is small due to the large shrinking force accompanying the melting generated in the low melting point thermoplastic resin. Therefore, the bulkiness of the non-woven fabric is impaired and the number of adhesion points between the low melting point thermoplastic resins is reduced, so that the non-woven fabric strength is also reduced.

[0011]

EFFECTS OF THE INVENTION Since the long-fiber nonwoven fabric of the present invention is obtained by using a composite long fiber in which a thermoplastic resin having a low melting point is arranged outside a spiral crimp as a raw material fiber, It has a tensile strength equal to or higher than that of a fibrous nonwoven fabric, and has a bulkiness not found in conventional long-fiber nonwoven fabrics, and can be preferably used for sanitary materials such as surface materials of paper diapers, geotextiles, packaging materials, backing materials and the like.

[0012]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples. In each example, the evaluation of physical properties was performed by the following methods. Elastic shrinkage ratio: Unstretched yarn composed of a single component and unstretched yarn of a composite fiber were gripped with a tensile tester at an interval of 10c.
Fiber length (c) at a point where the tensile load becomes zero when the sample is drawn at the same magnification (K) as in the examples and comparative examples at m and a pulling speed of 10 cm / min and immediately returned to the original gripping interval at the same speed. Is measured, and the elastic contraction rate (s) is calculated by the following formula. Elastic shrinkage S (%) = 100 × (10K-c) / (10
K-10) S2 = 2Sc-S1 Spiral crimp component arrangement: Cut a length of one cycle of the spiral crimp from the composite fiber, and enclose it with two cover glasses so that it becomes one circle. Using an optical microscope equipped with a hot stage, observe the situation where the low melting point thermoplastic resin melts and make a distinction. Number of crimps: 10 continuous spiral crimps in a tensionless state are cut out, the linear length L (cm) of the fibers is measured, and the number of crimps is calculated by the following formula: Number of crimps (number /Inch)=10×2.54/L Specific volume of non-woven fabric: 4 test pieces of 10 cm each in length and width are stacked, and 4 pieces of test pieces with the same size and a weight of 200 g are placed on the test pieces. The thickness D (cm) of the non-woven fabric is measured and calculated from the separately measured total weight W1 (g) of these four test pieces by the following formula: Specific volume of non-woven fabric (cm ³ / g) = 100 · D / W1 Tensile strength of non-woven fabric: length of the non-woven fabric cut in the machine direction (MD) and the direction perpendicular to this (CD) 20 cm,
Using a tensile tester, a test piece having a width of 5 cm (weight = W2) was held at a gripping interval of 10 cm and a pulling speed of 10 cm / mi.
The maximum load strength P (g) is measured with n and the tensile strength is calculated by correcting the basis weight of the nonwoven fabric according to the following formula: Tensile strength (g / (cm · g / m ² )) = P / 500W 2 Geometric mean Strength = (MD strength / CD strength) ^1/2 Examples 1 to 5, Comparative Examples 1 to 4 Table 1 shows the production conditions and the properties of the raw filaments used in the nonwoven fabrics of Examples and Comparative Examples.

[0013]

[Table 1]

Example 1 in which crystalline polypropylene and high-density polyethylene were combined and spun together and mechanically stretched
In the fibers of Nos. 3 to 3, a preferable spiral crimp in which high-density polyethylene, which is a low-melting component, is arranged outside the spiral crimp, was exhibited. In Example 2, a composite fiber produced under the same spinning / drawing conditions as in Example 1 but having a large number of crimps was obtained, which uses crystalline polypropylene having a wide molecular weight distribution (large Q value). It is thought that this is due to what was done. In the conjugate fiber of Example 3 obtained by using the same raw material as in Example 2 under the same spinning temperature and drawing conditions, a preferable spiral crimp in which high-density polyethylene was arranged was developed, but the conjugate type was changed to an eccentric sheath. The number of crimps was reduced by using the core type. However, by changing the drawing conditions, an eccentric sheath-core type composite fiber with a large number of crimps could be obtained (Example 4). In the fiber composed of a single component of crystalline polypropylene (Comparative Example 1), the spiral crimp did not appear even when the same stretching as in Example 1 was applied. In Comparative Example 2, which was extruded under the same conditions as in Example 1, directly spun with air sucker and not subjected to mechanical stretching, a spiral crimp having a high-density polyethylene, which is a low-melting point component, arranged inside was developed. . In the composite fiber of Comparative Example 3 obtained by spinning and drawing in the same manner as in Example 1 except that the extrusion temperature of the crystalline polypropylene was increased, the difference in elastic shrinkage was small, and the expression of spiral crimp was extremely poor. Met. The webs of various long fibers shown in Table 1 were heat-treated by a hot air circulation type heating furnace or a heating embossing roll to obtain a nonwoven fabric. The processing conditions and the physical properties of the non-woven fabric are shown in Table 2.

[0015]

[Table 2]

The nonwoven fabric of Comparative Example 1 consisting of a single component of crystalline polypropylene is inferior in bulkiness and strength as compared with any other examples. The non-woven fabric of Comparative Example 2-1 made with the same materials and processing conditions as in Example 1 is inferior in bulkiness (thickness / specific volume) and non-woven fabric strength to the non-woven fabric of Example 1. This is because the crystalline polypropylene, which is a component having a large elastic shrinkage ratio, was placed outside the spiral crimp, and the high-density polyethylene, which is an adhesive component, was placed inside the spiral crimp. Conceivable. The nonwoven fabric of Example 2-2 processed with the hot embossing roll is inferior in bulkiness to the nonwoven fabric of Example 2-1, but is excellent in strength. Further, as compared with Comparative Example 2-2 which was also processed by the heating embossing roll, it is excellent in both bulkiness and strength. The non-woven fabrics of Examples 3 and 4 whose material is different from that of Example 1 but the difference in elastic shrinkage and the structure of the spiral crimp satisfy the requirements of the invention of the present application also show good performance equal to or higher than that of Example 1. Show. In comparison, the non-woven fabric of Comparative Example 3 which does not meet the requirements of the present invention is inferior in both bulkiness and strength.

Claims (6)

[Claims] 1. A non-woven fabric composed of composite filaments having spiral crimps obtained by composite spinning of two kinds of thermoplastic resins having a difference in melting point of 15 ° C. or more, which is low outside the spiral crimps. A long-fiber non-woven fabric characterized in that the contact points of the fibers are bonded together by fusion bonding of a thermoplastic resin having a melting point. 2. The continuous fiber non-woven fabric according to claim 1, wherein the composite type of the composite long fibers is a parallel type or an eccentric sheath-core type. 3. A first thermoplastic resin, and a second heat having a melting point lower than that of the first thermoplastic resin by 15 ° C. or more and an elastic shrinkage ratio lower than that of the first thermoplastic resin by 1% or more. An undrawn yarn obtained by composite spinning with a plastic resin in a parallel ratio in the range of 60/40 to 40/60 and in an eccentric sheath-core type so that the second thermoplastic resin serves as a sheath. Is drawn 1.2 times or more at a temperature lower than the melting point of the second thermoplastic resin, and then heat treated at a temperature not lower than the melting point of the second thermoplastic resin and not higher than the softening point of the first thermoplastic resin. A method for producing a long-fiber non-woven fabric, characterized in that the points of contact between the fibers are fused by means of. 4. The method for producing a long-fiber nonwoven fabric according to claim 3, wherein crystalline polypropylene is used as the first thermoplastic resin, and high-density polyethylene is used as the second thermoplastic resin. 5. The method for producing a long fiber non-woven fabric according to claim 3, wherein the heat treatment is performed by a hot air oven method. 6. The method for producing a long-fiber nonwoven fabric according to claim 3, wherein the heat treatment is performed by a thermocompression bonding method.