JP3345764B2 - Polypropylene fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polypropylene fiber suitable as a raw material for a heat-bondable polypropylene nonwoven fabric. More specifically, the present invention relates to a polypropylene fiber which has good low-temperature adhesiveness and a wide processing temperature range and has excellent suitability for hot roll processing when processed into a nonwoven fabric.

[0002]

2. Description of the Related Art Non-woven fabrics of the heat-bonding type are widely used from the viewpoints of facility, economy, hygiene and the like because no binder is required. Above all, polyolefin-based nonwoven fabrics are used in many fields such as surface materials for disposable diapers and sanitary products, medical and sanitary materials such as surgical gowns, civil engineering materials, agricultural materials, and industrial materials because of their excellent performance and economic efficiency. In this case, a composite fiber of polyethylene / polypropylene and a single fiber of polypropylene are used as the raw material fibers. The method for producing a heat-bonding nonwoven fabric is roughly classified into an air-through method using hot air and a hot roll method. Among them, the air-through method is preferably applied to a polyethylene / polypropylene composite fiber.
Although the nonwoven fabric formed by the air-through method is strong and flexible, the processing speed is lower than that of the hot roll method, and the productivity is poor. Also,
Because polyethylene / polypropylene composite fiber is used,
There is also a disadvantage that there is a waxy feeling peculiar to polyethylene. On the other hand, the heat roll method has the advantages that the processing speed is high and the productivity is high, the nonwoven fabric can be formed even with a single polypropylene fiber for bonding by thermocompression bonding, and there is no waxy feeling caused by polyethylene. ing.

[0003] However, it has been difficult to produce a polypropylene nonwoven fabric having both a strong and soft feel by a hot roll method. The reason is as follows. In order to produce a polypropylene non-woven fabric using a hot roll, it is necessary to improve the fusion bonding between the polypropylene fibers. For that purpose, the non-woven fabric is produced at a high temperature at which the polypropylene fibers are sufficiently softened at the time of fusion bonding. There is a need. However, when the nonwoven fabric is manufactured at a high temperature, the bonding points are deformed into a film shape, and the polypropylene fibers other than the bonding points are also affected by heat, so that the feeling is deteriorated. Further, if processing is performed at a low temperature, the fusion of the bonding points is insufficient, and the strength sufficient for practical use cannot be obtained. For this reason, the temperature range in which a polypropylene nonwoven fabric having a strong and flexible feel is obtained is very narrow, and a slight change in processing temperature weakens the strength or hardens the feel. For this reason, the processing temperature range for obtaining a soft and strong polypropylene nonwoven fabric is wide, and the development of polypropylene fibers suitable for the hot roll method has been awaited.

Japanese Patent Application Laid-Open No. Sho 62-156310 discloses a polypropylene fiber having a softening point of 13 suitable for a hot roll method.
A polypropylene fiber comprising an ethylene-propylene random copolymer at a temperature of 2 ° C. or less and containing a predetermined amount of ethylene has been proposed. However, this fiber has a strong hand and has a strength and hand suitable for practical use. There is a disadvantage that the processing temperature range at which a nonwoven fabric can be manufactured is extremely narrow. In addition, Japanese Unexamined Patent Publication
No. 112456 proposes a nonwoven fabric made of a low stereoregularity polypropylene fiber having a specific isotactic pentad fraction. Although this nonwoven fabric has a good feeling, it is not strong enough. In addition, fibers made of polypropylene having such a low stereoregularity generally have poor carding properties and have disadvantages such as causing a large problem in the production of nonwoven fabrics. Further, Japanese Patent Laid-Open No. 2-2
No. 64012 proposes a polypropylene fiber containing a specific compound, but both the feel and the strength are not sufficient.

[0005]

As described above, many attempts have been made to provide a nonwoven fabric made of polypropylene excellent in both strength and feeling by hot roll processing.
The performance of the nonwoven fabric produced is not sufficient, and the processing temperature range during production is narrow, and satisfactory polypropylene fibers have not yet been developed. An object of the present invention is to provide an excellent polypropylene fiber which can easily produce a high-strength, flexible, high-handed polypropylene nonwoven fabric by hot roll processing, has a wide processing temperature range, and is suitable for hot roll processing. It is in.

[0006]

The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, the birefringence was 0.0
Knowing that a low-orientation polypropylene fiber having an oil agent mainly composed of mineral oil attached to a low-oriented polypropylene fiber of 54 or less gives a nonwoven fabric exhibiting the intended high strength and flexibility even at a low processing temperature range, The present invention has been completed. The present invention has the following configuration. (1) A low-orientation polypropylene fiber having a birefringence of 0.054 or less is mixed with an oil agent mainly containing mineral oil in an amount of 0.1 to
1.0% by weight attached polypropylene fiber. (2) The polypropylene is an olefin-based binary or terpolymer based on propylene (1)
Polypropylene fiber according to 1. (3) The mineral oil is at least one selected from the group consisting of paraffinic hydrocarbons, olefinic hydrocarbons, naphthenic hydrocarbons, aromatic hydrocarbons, and derivatives thereof (1) or (2). Polypropylene fiber according to 1.

Hereinafter, the present invention will be described in detail. In the present invention, the polypropylene fiber refers to a fiber composed of a propylene homopolymer, an olefin-based binary polymer or a terpolymer mainly composed of propylene. Here, as the olefin-based binary copolymer mainly composed of propylene, a random copolymer of 85% or more of propylene and 15% or less of ethylene, or 50% or more of propylene and 50% or less of butene-1 is used. Can be exemplified. Examples of the olefin-based terpolymer mainly composed of propylene include a random copolymer composed of 85% or more of propylene, 10% or less of ethylene, and less than 15% of butene-1.

[0008] The polypropylene fiber of the present invention is manufactured with a low degree of molecular orientation such that the birefringence is 0.054 or less. Such a low degree of orientation can be obtained by controlling the draw ratio at the time of spinning to a value lower than about 4 times or more and usually 3 times or less, preferably 2.5 times or less, more preferably 2.0 times or less. Stretched at a magnification of not more than twice is used. When the stretching ratio exceeds 3.0 times, the degree of molecular orientation increases, the thermal softening point and the melting point increase, and the thermal adhesiveness decreases. Further, when the degree of molecular orientation is high, the effect of osmotic adsorption of the oil agent into the fibers described later cannot be sufficiently obtained.

The mineral oil which is the main component of the oil agent used in the present invention includes paraffinic hydrocarbons represented by liquid paraffin, olefinic hydrocarbons, naphthenic hydrocarbons, and the like.
Aromatic hydrocarbons can be exemplified. Here, the main component means occupying 20% to 90% of the oil agent,
An antistatic agent, an emulsifier and the like are blended as components other than the mineral oil.
These include, for example, sorbitan monolaurate, polyoxyethylene lauryl ether, octyltrimethylammonium dimethyl phosphate, dioctylsulfosuccinate and the like. Further, animal oils and fats, vegetable oils and the like can be added to such an oil agent within a range not to impair the effects of the present invention. In the present invention, the amount of the oil agent attached to the polypropylene fiber is 0.1 to 1.0.
% By weight, preferably in the range of 0.2-0.5% by weight. When the adhesion amount of the oil agent is less than 0.1% by weight, the antistatic property in the carding process is poor, and formation irregularities are easily generated on the web. In order to avoid the occurrence of web formation irregularities, it is necessary to reduce the line speed, which is not economical. On the other hand, if the amount of adhesion is small, the permeation amount of the oil agent into the surface layer of the polypropylene fiber becomes insufficient, so that a skin layer swollen with mineral oil is hardly formed, and the improvement of thermal adhesiveness is hindered. The upper limit of the amount of the oil agent is preferably 1.0% by weight. If the amount of the oil agent exceeds 1.0% by weight, the fiber strength is reduced, the crimp retention rate is reduced, and the card passing property is deteriorated due to the softening of the fiber surface. Known methods such as a method using a touch roll in the fiber spinning step, a method using a touch roll in the drawing step, and a method of spraying after mechanical crimping can be used as a method for attaching the oil agent to the fibers.

Usually, the tensile strength of a nonwoven fabric obtained by the hot roll bonding method largely depends on the strength of the single yarn of the heat-bondable fiber when the bonding points of the fibers are sufficiently strong. On the other hand, when the bonding point is weak, the breaking of the nonwoven fabric is caused by the breaking of the bonding point, so that the tensile strength of the nonwoven fabric is hardly affected by the strength of the single yarn, and its value is very small. In the polypropylene fiber of the present invention, the mineral oil in the attached oil agent diffuses from the surface of the polypropylene fiber to the surface layer to form a skin layer containing the mineral oil, and the molecular weight is adjusted so that the birefringence is 0.054 or less. By suppressing the orientation, the penetration action is promoted. The skin layer swollen with mineral oil has a lower density and a lower softening point than the core layer. As a result, the fiber contacts are softened at a low temperature, and the fiber contacts can be fusion bonded at a low processing temperature without affecting the strength of the core layer,
High nonwoven fabric strength is obtained.

[0011]

The present invention will be described in detail with reference to the following examples, but the present invention is not limited to the examples. The measurement of various physical properties in the examples was performed by the following methods. -Melt flow rate (MFR): ASTM D12
The measurement was performed in accordance with the condition (L) of No. 38. · Nonwoven strong basis weight: weight 20 g / m ² having a width 5cm taken from the nonwoven, the test piece of length 15cm, using a tensile tester, chuck distance 10cm specimens, tensile rate 1
The test was performed under the condition of 0 cm / min, and the breaking strength was measured.

Flexibility: JIS L1018 (6.2
1A). A 5 cm long, 15 cm wide test piece cut from a nonwoven fabric with a basis weight of 20 g / m ² was placed on a horizontal platform (cantilever type testing machine) with a 45-degree slope on one side and a smooth surface and a scale graduated. The nonwoven fabric was gently slid in the direction of the slope manually, and the amount of unreeling when one end of the nonwoven fabric was in contact with the slope was read in mm, and this value was used as an index of flexibility. The smaller this value is, the better the flexibility of the nonwoven fabric is. When the flexibility value is 30 mm or less, the texture of the nonwoven fabric is good. A woven fabric having a flexibility value of more than 30 mm has a hard feeling and cannot be used for sanitary materials used in direct contact with the skin. Processing temperature range: flexibility value 30 mm or less, nonwoven fabric strength 0.
This is the temperature range of the hot roll from which a nonwoven fabric having a performance of 6 kg / 5 cm or more can be obtained. For example, from 130 ° C to 140
If a nonwoven fabric satisfying this condition can be obtained in the range of ° C, the processing temperature range is 10 ° C. -Low-temperature workability: The strength of the nonwoven fabric of a sample prepared at a processing temperature of 134 ° C at which a nonwoven fabric having a flexibility value of 24 mm is easily obtained is shown. 0.6 kg / 5 cm or more is required. -Oil adhesion rate: 10 g of a sample was mixed with a mixed solvent of methanol / petroleum ether = 1/1 using a Soxhlet extractor.
The mixture was extracted by refluxing for an hour, and the weight was measured after removing the solvent. Birefringence: Measurement was performed with a compensator using a polarizing microscope.

(Examples 1, 2 and Comparative Example 1) Fiber was melt-spun at a spinning temperature of 310 ° C. using MFR25 polypropylene. In the take-off process immediately after the spinning, the oil agents described in Tables 3 and 4 were applied by a touch roll. After spinning, it is stretched 1.5 times with a hot roll at 40 ° C., mechanically crimped with a stuffer box, dried and cut to give 2d × 38 m
m short polypropylene fibers were prepared. The short fibers were carded with a roller card machine at a speed of 20 m / min to obtain a web having a basis weight of 20 g / m ² . Subsequently, the web was processed into a nonwoven fabric at the same speed with an embossing roll having a bonding area ratio of 24%. The heating temperature of the embossing roll is 1
A predetermined test piece was prepared from the nonwoven fabric obtained at each heating temperature by changing the temperature in a range of 30 ° C to 145 ° C in 0.5 (deg) increments, and the strength and flexibility of the nonwoven fabric were measured.
The processing temperature width at which a nonwoven fabric strength of g / 5 cm or more was obtained was determined. Table 1 shows these values for each example, together with the card passability.
It is shown in FIG. In Examples 1 and 2, the processing temperature range was wide, the card passing property was good, and even when processed at low temperature, the strength of the nonwoven fabric was high and the texture was good. In Comparative Example 1, the strength of the nonwoven fabric at 134 ° C. was low, and the processing temperature range was narrow. In addition, the generation of static electricity was severe, and the card passing property was poor.

Comparative Example 2 A nonwoven fabric was prepared in the same manner as in Example 1 except that the oil agent was changed as shown in Table 2, and the characteristics were measured. The obtained nonwoven fabric had low strength, and was unsatisfactory in all of the texture, the card passing property, and the processing temperature range. Example 3 A nonwoven fabric was prepared in the same manner as in Example 1 except that the stretching ratio was set to 3 times, and the characteristics were measured. High strength non-woven fabric,
The texture, card passability, and processing temperature range were also satisfactory. Comparative Example 3 A nonwoven fabric was prepared in the same manner as in Example 1 except that the stretching ratio was changed to 4, and the characteristics were measured. The same oil agent as in Example 1 was applied, but the birefringence was 0.062 and the degree of orientation was high, so that no skin layer was formed, the strength of the nonwoven fabric was low, the processing temperature range was narrow, and a satisfactory nonwoven fabric was obtained. Did not.

[0014]

[Table 1]

[0015]

[Table 2]

[0016]

[Table 3]

[0017]

[Table 4]

Generally, the strength of the nonwoven fabric increases as the processing temperature increases. However, the texture of the nonwoven fabric worsens as the processing temperature increases. It is known from past experiments that the upper limit of the flexibility value indicating a high feeling is 30 mm. Therefore,
The upper limit of the processing temperature for obtaining a high texture nonwoven fabric is a temperature corresponding to a flexibility value of 30 mm. As is clear from Tables 1 and 2, the polypropylene fiber of the present invention has a low lower limit of the processing temperature at which the target nonwoven fabric strength (0.6 kg / 5 cm) can be obtained, and an upper limit of the processing temperature corresponding to a flexibility value of 30 mm. The processing temperature range of the nonwoven fabric defined by

[0019]

The polypropylene fiber of the present invention can produce a high-strength, flexible, high-feel polypropylene nonwoven fabric by hot roll processing, and can obtain a nonwoven fabric with high strength even at a lower processing temperature than conventional. Since the processing temperature range is wide, its production is easy.

Claims (3)

(57) [Claims] 1. A polypropylene fiber comprising a low-orientation polypropylene fiber having a birefringence of 0.054 or less and an oil agent mainly composed of mineral oil attached to the fiber in an amount of 0.1 to 1.0% by weight. 2. The polypropylene fiber according to claim 1, wherein the polypropylene is an olefin-based terpolymer or terpolymer based on propylene. 3. The mineral oil according to claim 1, wherein the mineral oil is at least one selected from the group consisting of paraffinic hydrocarbons, olefinic hydrocarbons, naphthenic hydrocarbons, aromatic hydrocarbons, and derivatives thereof. The polypropylene fiber according to claim 2.