JP6753254B2 - Polyethylene spunbonded non-woven fabric - Google Patents

Description

The present invention relates to a polyethylene spunbonded nonwoven fabric having excellent flexibility, high strength, and excellent workability.

Spunbond non-woven fabric made of polyolefin, especially polypropylene spunbond non-woven fabric, is widely used mainly for sanitary materials because of its low cost and excellent flexibility.

Many studies have been conducted on techniques for further enhancing the flexibility, which is a characteristic of polyolefin spunbonded non-woven fabrics, and among them, polyethylene, which has a lower elastic modulus than polypropylene, has been studied.

Although polyethylene spunbond has excellent flexibility, it has a problem that the workability of the sheet is inferior. One of the reasons for this is that polyethylene has poor silk-reeling properties and is prone to thread breakage, so there are many sheet defects, and this defect is the starting point for wrapping around rubber nip rollers, etc., and the fiber strength is high. This is because the sheet strength is low because it is low, and tearing or the like is likely to occur during sheet processing. Due to this problem, polyethylene spunbonds that satisfy practical performance have not yet been obtained industrially.

Further, if an attempt is made to reduce the fineness of a single yarn in order to improve flexibility, the yarn-forming property of polyethylene tends to be further deteriorated, so that there is a problem that the defects are further increased and the workability is further deteriorated.

Regarding the technology for obtaining polyethylene spunbond with low single yarn fineness and few sheet defects, the density is 0.900 to 0.940 g / cm ³ , the melt index value is 5 to 45 g / 10 minutes, and the heat of fusion is 25 cal / g. (That is, 104.7 J / g) or more is disclosed to use linear low-density polyethylene (see Patent Document 1). In this technique, a technique for spinning at high speed using air soccer is disclosed. Although there is a description of 5 denier or less for single yarn fineness, the smallest single yarn fineness reached in the examples is 1.9d. That is, a sufficiently small single yarn fineness of 2.1 dtex and 2.0 dtex or less has not been obtained, and the flexibility has not been improved.

Further, a technique using polyethylene having a density of more than 0.940 g / cm ^{3 and} a melt index of about 4 to about 1000 is also disclosed (see Patent Document 2). No description is found in the technique regarding reducing the single yarn fineness, and the smallest fiber diameter reached in the spunbonded examples is 29.4 μm. Since the resin density at this time is 0.882 g / cm ³ , the single yarn fineness is 6.0 dtex, and a sufficiently small single yarn fineness of 2.0 dtex or less has not been obtained, and the flexibility has not been improved.

Further, a technique using polyethylene having a density of 0.85 to 0.97 g / cm ³ is also disclosed (see Patent Document 3). In the technique, there is usually a description of 5 to 30 μm (0.2 to 7 denier) regarding fiber diameter and fineness, but the smallest single yarn fineness reached in the examples is 2.5 d, that is, 2.8 dtex, which is 2 A sufficiently small single yarn fineness of 0.0 dtex or less has not been obtained, and the flexibility has not been improved.

A technique using polyethylene having a density of 0.955 g / cm ³ is also disclosed (see Patent Document 4). Although there is a description of 0.1 to 50 denier in terms of fineness in the technique, the single yarn fineness obtained in the examples of the technique is 2.5 denier, that is, 2.8 dtex, which is sufficiently small to be 2.0 dtex or less. The thread fineness has not been obtained and the flexibility has not been improved.

A technique using polyethylene having a density of 0.9 to 0.955 g / cm ³ is also disclosed (see Patent Document 5). Although there is a description of the fineness of less than 2.8 dtex in the technique, the single thread fineness of the polyethylene-only spunbond obtained in the examples of the technique is 2.5 dtex, which is sufficiently small as 2.0 dtex or less. Has not been obtained and flexibility has not been improved.

JP-A-64-6161 (pages 1 to 5) Special Table No. 10-510013 (pages 1 to 30) JP-A-2002-105833 (pages 1 to 10) Special Table 2007-535623 (pages 21 to 25) Japanese Unexamined Patent Publication No. 2010-189831 (pages 1 to 20)

An object of the present invention is to provide a polyethylene spunbonded nonwoven fabric having excellent flexibility, high strength, and excellent workability.

The above-mentioned problem of the present invention is achieved by the following means.
It is made of linear low-density polyethylene with a density of 0.945 to 0.965 g / cm ³ , a single yarn fineness of 0.5 dtex or more and 2.0 dtex or less, and a single yarn Δn of 0.035 or more and 0.038. A polyethylene spunbonded non-woven fabric characterized by the following .

The polyethylene spunbonded non-woven fabric of the present invention can further improve the flexibility, and since the single yarn fineness is thin, the tactile sensation is also improved, and the strength of the fiber is also increased, so that there is no tearing during sheet processing, and there are further sheet defects. Since the amount is small, the workability can be further improved.

Hereinafter, the polyethylene spunbonded nonwoven fabric of the present invention will be described in detail.
The polyethylene (hereinafter, also referred to as PE) spunbonded nonwoven fabric of the present invention is made of polyethylene resin fibers. The polyethylene resin means a polymer having an ethylene unit as a repeating unit. By using a polyethylene resin, a non-woven fabric having excellent flexibility can be obtained.

The polyethylene fiber constituting the spunbonded non-woven fabric is preferably a polyethylene single component fiber. In the fiberization of polyethylene, it is possible to combine it with other polymers (core sheath, sea island, side-by-side), but in the present invention, the characteristics of polyethylene are fully expressed and fineness that is difficult to reach by composite spinning is achieved. Therefore, a polyethylene single component is preferable.

A small amount of other component polymer may be blended with the PE resin. Examples of the other component polymer include polyolefin-based polymers having a melting point close to PE, such as polypropylene and poly4-methylpentene, as well as low-melting polyester and low-melting polyamide. However, in order to fully express the characteristics of polyethylene, the weight ratio of the blend is preferably 5 wt% or less, more preferably 2 wt% or less.
Further, a pigment for coloring, an antioxidant, a lubricant such as polyethylene wax, a heat-resistant stabilizer and the like may be added to the PE resin.

The PE resin used in the present invention is linear low density polyethylene (hereinafter, also referred to as LLDPE). PE includes high-density polyethylene (HDPE), low-density polyethylene (LDPE), and LLDPE, which are classified according to differences in manufacturing method and physical properties, and are being studied for fibers. In the present invention, fineness and high strength can be realized by using LLDPE.

The density of the PE resin used in the present invention is 0.945 to 0.965 g / cm ³ . The density of LLDPE varies depending on the type and amount of monomer to be copolymerized, but by setting the density of LLDPE to 0.945 to 0.965 g / cm ³ , which is a high density, appropriate crystallinity is exhibited and the strength is increased. Can be achieved. From this viewpoint, the density is more preferably 0.950 to 0.960 g / cm ³ .

The LLDPE used in the present invention may be copolymerized with other olefin monomers and styrene monomers as long as the object of the present invention is satisfied. As the copolymerization component, heptene and octene are preferable from the viewpoint of reducing sheet defects and fineness, and octene is more preferable. The copolymerization ratio is preferably 3.0 mol% or less, and more preferably 1.0 mol% or less from the viewpoint of increasing the strength.

The basis weight of the polyethylene spunbonded non-woven fabric of the present invention is preferably 5 to 50 g / m ² . When the basis weight is in the above range, the flexibility of the non-woven fabric can be suitably exhibited. From this point of view, the basis weight is more preferably 10 to 30 g / m ² .

The cross-sectional shape of the fibers constituting the polyethylene spunbonded nonwoven fabric of the present invention is preferably round. In a flat or irregular cross section, the geometrical moment of inertia is larger than that of a round cross section having the same cross-sectional area depending on the bending direction, so that the fibers may become hard and the flexibility of polyethylene may be impaired.

The single yarn fineness of the fibers constituting the polyethylene spunbonded nonwoven fabric of the present invention is 2.0 dtex or less. The single yarn fineness referred to in the present invention refers to a value measured by the method described in Examples. By setting the single yarn fineness to 2.0 dtex or less, in addition to the flexibility of polyethylene, the decrease in the moment of inertia of area due to the small single yarn fineness is also exhibited, further improving the flexibility and improving the tactile sensation. To do. From this viewpoint, the single yarn fineness is preferably 1.8 dtex or less, more preferably 1.5 dtex or less. The lower limit of the single yarn fineness is about 0.5 dtex.

For the same reason, the fiber diameter of the fibers constituting the polyethylene spunbonded non-woven fabric is preferably 17.0 μm or less, more preferably 16.0 μm or less, still more preferably 15.0 μm or less. The fiber diameter referred to in the present invention refers to a value measured by the method described in Examples. The lower limit of the fiber diameter is about 8.0 μm.

The Δn of the single yarn constituting the polyethylene spunbonded nonwoven fabric of the present invention is 0.035 or more. Δn in the present invention refers to a value measured by the method described in Examples. When Δn is 0.035 or more, the molecular orientation can be increased and the strength of the fiber can be increased. From this viewpoint, Δn is preferably 0.037 or more.

The single yarn strength constituting the polyethylene spunbonded nonwoven fabric of the present invention is preferably 120 MPa or more. The single yarn strength referred to in the present invention refers to a value measured by the method described in Examples. When the single yarn strength is 120 MPa or more, yarn breakage during processing can be suppressed and the workability is excellent. From this viewpoint, the single yarn strength is more preferably 130 MPa or more.

The melting point of the polyethylene spunbonded non-woven fabric of the present invention is preferably 127 ° C to 131 ° C. The melting point referred to in the present invention refers to a value measured by the method described in Examples. The melting point of the PE resin is generally about 130 to 135 ° C., and the crystallinity is lowered by branching and copolymerization of other kinds of monomers, and the melting point is also lowered. When the melting point is 127 ° C to 131 ° C, the crystallinity is appropriate and the fiber strength is improved.

The heat of crystal melting of the polyethylene spunbonded nonwoven fabric of the present invention is preferably 160 to 175 J / g, more preferably 165 to 175 J / g. The amount of heat of crystal melting referred to in the present invention refers to a value measured by the method described in Examples. Similar to the melting point, the amount of heat of crystal melting also decreases due to branching and copolymerization of other types of monomers, and the amount of heat of crystal melting also decreases. When the amount of heat for melting the crystal is 160 to 175 J / g, the crystallinity is appropriate and the fiber strength is improved.

The polyethylene spunbonded non-woven fabric of the present invention can be widely used for medical hygiene materials, daily life materials, industrial materials, etc., but has excellent flexibility, good tactile sensation, high strength, and few product defects, so that it has good workability. Therefore, it can be particularly preferably used as a sanitary material. Specifically, they are disposable diapers, sanitary napkins, and base cloths for poultices.

Next, a specific example of the method for producing the polyethylene spunbonded nonwoven fabric of the present invention will be described.
The raw material used is LLDPE resin, and its density, copolymerization species and amount, and other additives are as described above.

The melting point of the PE resin is also substantially the same as the melting point of the non-woven fabric, and is preferably 127 ° C. to 131 ° C. Further, the PE resin preferably has a melt index (MI) of 10 to 100 g / 10 minutes, and more preferably 20 to 40 g / 10 minutes. The melt index referred to here refers to a value measured at 190 ° C. and a load of 2.16 kg in accordance with ASTM D1238.

By using LLDPE resin in such a range, even if it is towed at high speed, it has excellent spinnability, so there are few sheet defects and fineness can be achieved, and high-speed towing enhances the molecular orientation and increases the strength of the fiber. Can be enhanced.

The PE resin is subjected to melt spinning without being particularly dried. For melt spinning, a known melt spinning method using an extruder such as a single-screw or twin-screw extruder can be applied. The extruded polymer is weighed by a known weighing device such as a gear pump via a pipe, passed through a foreign matter removing filter, and then guided to a mouthpiece. At this time, the temperature from the polymer pipe to the base (spinning temperature) is set to about 160 to 250 ° C. in order to improve the fluidity.

The mouthpiece used for discharge preferably has a hole diameter D of the mouthpiece hole of 0.10 mm or more and 0.60 mm or less, and has a land length L of the mouthpiece hole (the length of a straight pipe portion same as the hole diameter of the mouthpiece hole). The L / D defined by the quotient divided by the pore size is preferably 1.0 or more and 4.0 or less.

The yarn discharged from the mouthpiece hole is cooled and solidified by air. The temperature of the cooling air may be determined in balance with the cooling air velocity from the viewpoint of cooling efficiency, but is preferably 50 ° C. or less from the viewpoint of fineness uniformity. Further, the cooling gas is allowed to flow in the direction substantially perpendicular to the yarn to cool the yarn. At that time, the speed of the cooling air is preferably 5 m / min or more from the viewpoint of cooling efficiency and fineness uniformity, and preferably 100 m / min or less from the viewpoint of yarn-making stability. Further, it is preferable to start cooling within 20 mm or more and 500 mm or less from the base to cool and solidify. If cooling is started at a distance of less than 20 mm, the surface temperature of the base may drop and the discharge may become unstable. If cooling is not started within 500 mm, the stability of the thinning behavior cannot be maintained and it becomes stable. You may not be able to spin.

The yarn discharged from the mouthpiece hole is towed by an accelerated air flow at a position of 400 mm or more and 7,000 mm or less from the mouthpiece. The accelerating air flow may be made to seal the region where the cooling air is blown, and the air flow velocity may be accelerated by gradually reducing the cross-sectional area of the sealed region toward the downstream of the spinning line, but the air flow velocity may be higher. It is preferable to use an ejector in order to obtain. The yarn is accelerated by this air flow velocity, and the spinning speed, which is the running speed of the fiber, reaches a speed close to the air flow velocity. The spinning speed refers to the value calculated by the following formula.
Spinning speed (km / min) = Q ・ 10 / D
Q: Single hole discharge amount (g / min), D: Single yarn fineness (dtex)
The spinning speed is preferably 3.0 km / min or more for fineness and high strength, and more preferably 4.0 km / min. Similarly, the air flow velocity is preferably 3.0 km / min or more. The upper limit of the spinning speed is about 10.0 km / min.

The air-towed yarn is opened by passing through an opening portion that reduces the flow velocity of the surrounding air, and then lands on a net conveyor that is sucked air from the back surface and is collected. The collected web is conveyed by a conveyor at 10 to 1200 m / min, and then embossed and calendered to obtain a spunbonded non-woven fabric.

Regarding the polyethylene spunbonded non-woven fabric of the present application, important points from the viewpoint of raw materials and processes are described below.
One is to use LLDPE having a density of 0.945 to 0.965 g / cm ³ . Since spunbonding is a process of melt spinning and high speed spinning, a technique using LLDPE having excellent spinnability has been conventionally proposed. What is important here is the density, that is, the degree of crystallinity. In order to obtain a polyethylene spunbonded non-woven fabric with fine fineness and high strength, the inventors investigated the thinning and solidification behavior of the discharged yarn. As a result, HDPE crystallizes quickly, so solidification is fast and yarn breaks at high speed spinning. On the other hand, it was found that even low-density LLDPE yarn breaks in high-speed spinning. Therefore, we succeeded in obtaining a sheet with fine fineness and less thread breakage by using a LLDPE having a high density of 0.945 to 0.965 g / cm ³ . This is due to the extensional viscosity characteristics caused by the branched components (derived from octene and heptene) that are different from HDPE, so that the spinnability is improved and the thinning becomes slower, and the crystallinity is equivalent to HDPE, so solidification due to crystallization also occurs. I presume that it will happen quickly.

Another point is high-speed spinning at a spinning speed of 3 km / min or more. Although spunbonding is a high-speed spinning process, it does not stretch the fibers after solidification, so the strength of the fibers is dominated by the fiber structure formed before solidification. Therefore, in order to increase the strength, it is important to apply high stress to the fibers from the completion of thinning to the solidification and to fix the molecular chains in a highly oriented state. High-speed spinning is effective in spunbonding as a means of applying high stress to the yarn, but depending on the polymer type, thinning tends to proceed upstream of the spinning line (a place near the base), and in some cases yarn breakage occurs. .. In the present invention, the use of LLDPE slows down the thinning, prevents yarn breakage upstream of the spinning line, and applies sufficient stress until solidification due to crystallization to orient the molecular chain and is sufficient. It is speculated that the strength can be increased because the structure can be fixed by crystallization.

In this way, the combination of LLDPE with a density of 0.945 to 0.965 g / cm ³ and air traction at a high speed exceeding 3.0 km / min makes it more flexible due to its fineness, and has high strength and processing. A polyethylene spunbonded non-woven fabric having excellent properties can be obtained.

Hereinafter, the present invention will be described in more detail with reference to Examples. Each characteristic value in the examples was obtained by the following method.

A. Fiber diameter and single yarn fineness The fiber diameter was determined from the microscopic observation of the side surface of the fiber, measured 10 times per level, and the average value was taken as the fiber diameter. Next, the fiber was treated as a round cross section, and the single yarn fineness was determined from the fiber diameter using the following formula.
Single yarn fineness ^{(dtex) = π · ρ ·} d 2/400
ρ: Resin density (g / cm ³ ), d: Fiber diameter (μm).

B. Single yarn Δn
Using a single yarn extracted from the non-woven fabric, measurement was performed three times per sample level by the compensator method using a polarizing microscope (BH-2 manufactured by OLYMPUS), and the average value was obtained.

C. Thermal characteristics Differential scanning calorimetry (DSCQ1000 manufactured by TA Instruments) is used to measure differential scanning calorimetry under nitrogen and at a heating rate of 16 ° C./min. Was ΔHm (J / g).

D. Single yarn strength A web before calendering is collected, a single yarn is pulled out from this by about 50 mm, and according to the method described in JIS L1013: 2010, the sample length is 20 mm and the tensile speed is 20 mm / min. Tensilon UCT-100 manufactured by Orientec Co., Ltd. was used to perform measurements 10 times per level, and the average value was set to strong (cN). In addition, A. The fiber cross section was obtained by assuming that the fiber diameter obtained in 1 was a round cross section, and the strength was divided by the fiber cross section to obtain the single yarn strength (MPa).

E. Sheet defects A 10 cm square area at the center of the spunbonded non-woven fabric in the width (CD) direction is visually observed with a loupe, and the fiber diameter is three times or more larger than the average fiber diameter due to thread breakage. Those with rounded pieces of fibers that appeared to be three times thicker than the average fiber diameter were treated as defects, and the number was counted. This observation was repeated 5 times in the longitudinal direction (MD) of the non-woven fabric, and the total number was taken as the number of sheet defects.

F. Sheet flexibility The sensory evaluation of the sheet tactile sensation was performed, and a score was given by absolute evaluation, with 5 points being excellent in flexibility and 1 point being inferior. This was done by 10 people and the average score was defined as flexibility (points).

G. Sheet workability The sheet was run at 20 m / min for 5 minutes using a rubber nip roller. The state of the roll deposits and the sheet at this time was observed, and points were given according to the following criteria to determine workability (points).
5 points: There are no fiber deposits on the roll, and no fluff or tear of the sheet is seen.
4 points: There are fiber deposits on the roll, but no fluff or tear of the sheet is seen.
3 points: There are fiber deposits on the roll and fluff on the sheet, but no tearing is seen.
2 points: There are fiber deposits on the roll, there is fluff on the sheet, and there is tearing.
1 point: The sheet wraps around the roll due to the tearing of the sheet.

Example 1
Using an LLDPE resin (octene copolymerization ratio 0.3 mol%) having a density and MI values shown in Table 1, melt extrusion was performed with a uniaxial extruder, and the resin was supplied to the spinneret while measuring with a gear pump. .. The spinning temperature (base temperature) is 230 ° C., and the single hole discharge rate is 0.6 g / min from a base having 600 base holes with a hole diameter D of 0.30 mm and a land length L of 0.70 mm in the CD direction. The polymer was discharged under the conditions. The introduction hole located directly above the mouthpiece hole was a straight hole, and the connection portion between the introduction hole and the mouthpiece hole was tapered. The discharged polymer was passed through a heat insulating region of 50 mm, and then cooled and solidified from the outside of the yarn by an air flow at 25 ° C. and 40 m / min. After that, it was towed by an accelerated air flow with an ejector installed at a position 550 mm from the base. The threads that passed through the ejector were collected on a net conveyor and transported at a speed of 20 m / min. Then, calendering was performed to obtain a polyethylene spunbonded non-woven fabric of 18 g / m ² .
Table 1 also shows the spinning speed calculated from the single yarn fineness and the single hole discharge amount. The spinning speed was 4.0 km / min, but during the test for about 10 minutes, no noticeable yarn breakage was observed and the spinnability was good.
The obtained sheet characteristics are also shown in Table 1. As can be seen from Table 1, there are few sheet defects, and since the single yarn fineness is as thin as 2.0 dtex or less, it is excellent in flexibility and workability.

Examples 2, 3 and Comparative Example 1
The test was carried out under the same conditions as in Example 1 except that the traction speed at the ejector was changed to change the spinning speed, and a polyethylene spunbonded non-woven fabric was obtained.
Table 1 shows the spinning speed calculated from the single yarn fineness and the single hole discharge amount. In Example 2 having a spinning speed of 5.0 km / min, no noticeable yarn breakage was observed during the 10-minute test, and the spinnability was good.
The obtained sheet characteristics are shown in Table 1. In Comparative Example 1, since the single yarn fineness is 2.5 dtex, the flexibility is inferior, and since Δn is small, the single yarn strength is low and the workability is also inferior. It can be seen that in Examples 2 and 3, since the single yarn fineness is small, the flexibility is excellent, there are few sheet defects, the single yarn strength is high, and the workability is excellent.

Comparative Examples 2, 3
The test was carried out under the same conditions as in Example 1 except that the PE was changed as shown in Table 1. In each case, thread breakage occurred frequently and a sheet could not be obtained. Therefore, a polyethylene spunbonded non-woven fabric was obtained by using the spinning speeds shown in Table 1.
The obtained sheet characteristics are also shown in Table 1. In Comparative Example 2, since the single yarn fineness is 2.5 dtex, the flexibility is inferior, and since Δn is small, the single yarn strength is low, and there are many sheet defects, so that the workability is inferior. It can be seen that Comparative Example 3 is also inferior in workability because it has many sheet defects.

Claims (1)

It is made of linear low-density polyethylene with a density of 0.945 to 0.965 g / cm ³ , a single yarn fineness of 0.5 dtex or more and 2.0 dtex or less, and a single yarn Δn of 0.035 or more and 0.038. A polyethylene spunbonded non-woven fabric characterized by the following .