JP7619145B2 - Manufacturing method of spunbond nonwoven fabric - Google Patents

Description

The present invention relates to a method for producing a spunbond nonwoven fabric with excellent hydrophilicity and flexibility.

Spunbond nonwoven fabrics have excellent productivity and processability, and are therefore used in a wide range of fields, including hygiene materials, medical materials, construction materials, bedding, daily necessities, and industrial materials. Commonly used raw materials for spunbond nonwoven fabrics include polyolefins such as polypropylene and polyethylene, and polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polylactic acid, with the raw materials being selected according to the intended use.

Among these applications, methods of imparting hydrophilicity to nonwoven fabrics are being investigated for applications that require hydrophilicity, such as disposable diapers, sanitary napkins, and wet wipes. A commonly used method of imparting hydrophilicity to nonwoven fabrics is to apply a hydrophilic agent to the nonwoven fabric, but this method has issues such as a decrease in performance due to the runoff of the applied hydrophilic agent and the occurrence of uneven performance due to uneven application.

As a method for solving the above problems, nonwoven fabrics using hydrophilic resins as raw materials have been considered. For example, nonwoven fabrics made of fibers made of hydrophilic resins in which polyalkylene glycol is copolymerized with thermoplastic resins such as polyester resins (see Patent Documents 1 and 2) and laminated nonwoven fabrics in which a spunbonded nonwoven fabric layer made of fibers made of polyester resins copolymerized with polyethylene glycol is laminated on the surface have been proposed (see Patent Document 3).

Separately, as a technology related to a method for producing fibers containing hydrophilic components, a method for producing fibers has been proposed in which a copolymer of hydrophobic and hydrophilic polymers is spun so that the shear rate when passing through a spinneret is within a specific range (see Patent Document 4).

International Publication No. 2019/146660 JP 2006-299424 A JP 2020-16000 A International Publication No. 2015/146790

In the techniques of Patent Documents 1 to 3, by copolymerizing polyalkylene glycol, a nonwoven fabric is obtained that has a certain degree of durable hydrophilicity and flexibility without any deterioration in performance or uneven hydrophilicity. However, when nonwoven fabric is produced by the method described in Patent Documents 1 and 3, etc., the shear rate when passing through the spinneret is low, so discharge from the spinneret is unstable, and the spinning draft is large, so thread breakage is likely to occur, resulting in poor stability of the spinning process and making it difficult to stably produce nonwoven fabric. Furthermore, Patent Document 2 does not make any specific proposals for stably producing nonwoven fabric.

On the other hand, in the technology of Patent Document 4, a fiber having relatively small unevenness in fineness and suppressed occurrence of dyeing unevenness and fluff can be obtained by setting the shear rate during passage through a spinneret to 10,000 to 40,000 sec ^-1 . However, since this technology requires substantially reducing the hole diameter of the spinneret, clogging of the hole is likely to occur and control of the spinneret is difficult, making it difficult to apply this technology to a spunbonding method having a large number of spinneret holes.

The present invention was made in consideration of the above circumstances, and its purpose is to provide a method for drastically improving stability in the spinning and heat bonding processes, and further reducing spinning problems such as clogged holes, thereby enabling the stable production of spunbond nonwoven fabrics with excellent hydrophilicity and flexibility.

As a result of further investigations, the inventors have confirmed that although spunbond nonwoven fabrics made of copolymer polyesters copolymerized with polyethylene glycol having a specific molecular weight have excellent water absorption and flexibility, when the manufacturing conditions for general spunbond nonwoven fabrics are adopted, there arise problems such as frequent thread breakage during spinning and frequent sheet breakage during thermal bonding, making it necessary to improve the stability of the spinning and thermal bonding processes.

The inventors conducted extensive research to achieve the above object, and discovered that by collecting a fiber web that is air-pulled under conditions where the shear speed and spinning draft during passage through the nozzle are within specific ranges when a copolymerized polyester copolymerized with polyethylene glycol having a specific number average molecular weight is extruded from the nozzle holes of the nozzle, and then forming the web into a sheet by thermal bonding, thread breakage during the spinning process and sheet breakage during the thermal bonding process are suppressed, dramatically improving stability in each process, and further, making it easier to manage a spunbond nozzle with many nozzle holes, reducing spinning problems such as clogged holes, which led to the completion of the present invention.

The present invention aims to solve the above problems, and provides the following:

The method for producing a spunbonded nonwoven fabric of the present invention comprises melting a copolymerized polyester, discharging it from an outlet hole of a die, and drawing the resulting fiber web, which is collected on a net conveyor, and thermally bonding the fiber web, wherein the copolymerized polyester is a copolymerized polyester obtained by copolymerizing 3% by mass or more and 40% by mass or less of a polyalkylene glycol having a number average molecular weight of 4,000 or more and 30,000 or less, the shear rate at the time of passing through the die when the copolymerized polyester is discharged from the outlet hole of the die is 3,500 sec ^-1 or more and less than 10,000 sec ^-1 , and the spinning draft of the copolymerized polyester during the drawing is 200 or more and 550 or less.

According to a preferred embodiment of the method for producing a spunbond nonwoven fabric of the present invention, the diameter of the nozzle hole is 0.23 mm or more and 0.80 mm or less.

According to a preferred embodiment of the method for producing a spunbond nonwoven fabric of the present invention, the pulling speed of the copolymer polyester in the air pulling is 3500 m/min or more and 7000 m/min or less.

According to a preferred embodiment of the method for producing a spunbond nonwoven fabric of the present invention, the suction wind speed on the net conveyor in the vertical direction of the center of the die is 8.0 m/sec or more and 18.0 m/sec or less.

In a preferred embodiment of the method for producing a spunbond nonwoven fabric of the present invention, the main repeating unit of the copolymer polyester is ethylene terephthalate.

According to a preferred embodiment of the method for producing a spunbond nonwoven fabric of the present invention, the intrinsic viscosity of the copolymer polyester is 0.50 dL/g or more and 0.80 dL/g or less.

According to a preferred embodiment of the method for producing a spunbonded nonwoven fabric of the present invention, the copolyester is a recycled copolyester obtained by adding the polyalkylene glycol to a low molecular weight product obtained by depolymerizing polyester and repolymerizing the product.

The present invention makes it possible to stably produce spunbond nonwoven fabrics with excellent hydrophilicity and flexibility.

FIG. 1 is a conceptual diagram illustrating and explaining the center part of a die in the method for producing a spunbonded nonwoven fabric of the present invention.

The method for producing a spunbonded nonwoven fabric of the present invention comprises melting a copolymerized polyester, discharging it from an outlet hole of a die, and drawing the resulting fiber web, which is collected on a net conveyor, and thermally bonding the fiber web, wherein the copolymerized polyester is a copolymerized polyester obtained by copolymerizing 3% by mass or more and 40% by mass or less of a polyalkylene glycol having a number average molecular weight of 4,000 or more and 30,000 or less, the shear rate at the time of passing through the die when the copolymerized polyester is discharged from the outlet hole of the die is 3,500 sec ^-1 or more and less than 10,000 sec ^-1 , and the spinning draft of the copolymerized polyester during the drawing is 200 or more and 550 or less.

The present invention is described below, but is not limited to the scope of the following description as long as it does not exceed the gist of the invention.

The copolymer polyester used in the manufacturing method of the spunbond nonwoven fabric of the present invention is a copolymer polyester obtained by copolymerizing 3% by mass or more and 40% by mass or less of a polyalkylene glycol having a number average molecular weight of 4,000 to 30,000.

First, the copolymer polyester according to the present invention is a copolymer polyester copolymerized with polyalkylene glycol. Examples of polyalkylene glycol include polyethylene glycol, polypropylene glycol, and polybutylene glycol. Among them, it is preferable to use polyethylene glycol, which results in a spunbond nonwoven fabric that is low cost and has excellent hydrophilicity.

In the copolymer polyester according to the present invention, the number average molecular weight of the polyalkylene glycol is 4,000 or more and 30,000 or less. By making the number average molecular weight of the polyalkylene glycol 4,000 or more, preferably 5,000 or more, the polyalkylene glycol component forms domains in the polyester, resulting in a spunbond nonwoven fabric with excellent hydrophilicity and flexibility. In addition, by making the number average molecular weight of the polyalkylene glycol 30,000 or less, preferably 25,000 or less, the cost is low and thread breakage during the spinning process can be suppressed.

In addition, the copolymerized polyester according to the present invention has a copolymerization amount of polyalkylene glycol, which is a copolymerization component, of 3% by mass or more and 40% by mass or less. By making the copolymerization amount of polyalkylene glycol 3% by mass or more, preferably 4% by mass or more, and more preferably 5% by mass or more, a spunbond nonwoven fabric with excellent hydrophilicity and flexibility is obtained. Furthermore, by making the copolymerization amount of polyalkylene glycol 40% by mass or less, preferably 30% by mass or less, and more preferably 20% by mass or less, it is possible to reduce costs and suppress thread breakage during the spinning process.

The copolymer polyester according to the present invention preferably has a main repeating unit that is, for example, an aliphatic polyester such as "glycolic acid, lactic acid, hydroxybutyric acid, ethylene succinate, butylene succinate, or butylene adipate," or a semi-aromatic polyester such as "ethylene terephthalate, propylene terephthalate, or butylene terephthalate." Of these, it is preferable that the main repeating unit is a semi-aromatic polyester such as "ethylene terephthalate, propylene terephthalate, or butylene terephthalate," and it is even more preferable that the main repeating unit is ethylene terephthalate. In this way, it is possible to suppress thread breakage during the spinning process, and a spunbond nonwoven fabric having excellent flexibility and mechanical strength is obtained.

The copolymer polyester according to the present invention is produced by a known polymerization method such as transesterification or esterification. For example, in the transesterification method, an ester-forming derivative of a dicarboxylic acid and a diol are charged into a reaction vessel, reacted in the presence of a transesterification catalyst at a temperature in the range of 150°C to 250°C, and then a stabilizer, a polycondensation catalyst, etc. are added, and the mixture is heated at a temperature in the range of 250°C to 300°C under a reduced pressure of 500 Pa or less, and reacted for 3 hours to 5 hours. In the esterification method, a dicarboxylic acid and a diol are charged into a reaction vessel, and an esterification reaction is carried out at a temperature in the range of 150°C to 270°C under nitrogen pressure. After the esterification reaction is completed, a stabilizer, a polycondensation catalyst, etc. are added, and the mixture is heated at a temperature in the range of 250°C to 300°C under a reduced pressure of 500 Pa or less, and reacted for 3 hours to 5 hours.

In addition, in the copolymerized polyester according to the present invention, the timing of adding the polyalkylene glycol in the above polymerization method is not particularly limited, and the polyalkylene glycol may be added together with other raw materials before the esterification reaction or transesterification reaction, or may be added after the esterification reaction or transesterification reaction is completed and before the polycondensation reaction begins.

In the copolymer polyester according to the present invention, an ester exchange catalyst or a polycondensation catalyst is used in the above-mentioned polymerization method. Examples of the ester exchange catalyst include zinc acetate, manganese acetate, magnesium acetate, and titanium tetrabutoxide, and examples of the polycondensation catalyst include antimony trioxide, germanium dioxide, and titanium tetrabutoxide.

The copolymer polyester according to the present invention may also contain various additives, such as inorganic substances such as titanium oxide, silica, barium oxide, and calcium carbonate, colorants such as carbon black, dyes, and pigments, lubricants such as polyethylene wax and fatty acid amide compounds, flame retardants, fluorescent whitening agents, antioxidants, and ultraviolet absorbing agents, to the extent that the effects of the present invention are not impaired.

The copolymer polyester according to the present invention preferably has an intrinsic viscosity of 0.50 dL/g or more and 0.80 dL/g or less. By setting the intrinsic viscosity to 0.50 dL/g or more, more preferably 0.55 dL/g or more, and even more preferably 0.57 dL/g or more, the strength of the fiber is increased, and the handleability of the resulting spunbond nonwoven fabric is improved. In addition, by setting the intrinsic viscosity to 0.80 dL/g or less, more preferably 0.75 dL/g or less, and even more preferably 0.73 dL/g or less, the resin is easily deformed, and thread breakage during the spinning process can be suppressed. The intrinsic viscosity in the present invention can be controlled by the polymerization time, etc. When the above polymerization method is adopted, the longer the polymerization time, the higher the intrinsic viscosity.

In one preferred embodiment, the copolymer polyester according to the present invention is a recycled copolymer polyester obtained by adding polyalkylene glycol to a low molecular weight product obtained by depolymerizing polyester and then repolymerizing it. By using recycled copolymer polyester, the environmental impact when producing spunbonded nonwoven fabric can be reduced. Note that recycled copolymer polyester tends to have lower spinnability compared to virgin copolymer polyester due to the influence of monomer quality and foreign matter, but the method for producing spunbonded nonwoven fabric of the present invention can suppress thread breakage during the spinning process, making it possible to stably produce spunbonded nonwoven fabric made of recycled copolymer polyester.

The copolymer polyester according to the present invention preferably has a melting point of 200°C or higher and 300°C or lower. By setting the melting point to preferably 200°C or higher, more preferably 220°C or higher, and even more preferably 230°C or higher, heat resistance sufficient for practical use can be obtained. In addition, by setting the melting point to preferably 300°C or lower, more preferably 280°C or lower, and even more preferably 260°C or lower, it is possible to lower the processing temperature, thereby reducing the energy costs in the spinning process and heat bonding process.

In the method for producing the spunbonded nonwoven fabric of the present invention, it is preferable to vacuum dry the copolymerized polyester before melting it. This makes it possible to suppress hydrolysis during melting, and to obtain a spunbonded nonwoven fabric with excellent mechanical strength.

In the method for producing the spunbonded nonwoven fabric of the present invention, it is preferable to melt the copolymer polyester at a temperature of 240°C or higher and 320°C or lower. By setting the melting temperature, i.e., the spinning temperature, to preferably 240°C or higher, more preferably 250°C or higher, and even more preferably 260°C or higher, the fluidity of the resin can be increased, so that thread breakage can be suppressed during the spinning process (the process in which the copolymer polyester is melted, discharged from the nozzle of the die, and then pulled), and spunbonded nonwoven fabric can be produced stably. In addition, by setting the spinning temperature to preferably 320°C or lower, more preferably 310°C or lower, and even more preferably 300°C or lower, energy costs can be reduced and thermal decomposition of the resin can be suppressed.

In the manufacturing method of the spunbond nonwoven fabric of the present invention, the molten copolymer polyester is then discharged from the nozzle of the die.

In the manufacturing method of the spunbonded nonwoven fabric of the present invention, various shapes such as round and rectangular shapes can be used for the die and the towing part. Among them, a combination of a rectangular die for the die and a rectangular ejector for the towing part is preferred from the viewpoint that the amount of gas used for towing is relatively small and fusion and abrasion between the yarns are unlikely to occur.

In the method for producing a spunbonded nonwoven fabric of the present invention, the shear rate at the time of passing through the die when the copolymerized polyester is discharged from the discharge hole of the die is 3500 sec ^- 1 or more and less than 10000 sec ^-1 . By setting the shear rate at the time of passing through the die to 3500 sec ^-1 or more, preferably 4000 sec ^-1 or more, and more preferably 4500 sec ^-1 or more, discharge from the die is stabilized, so that yarn breakage in the spinning process can be suppressed, and a spunbonded nonwoven fabric can be stably produced. Furthermore, by setting the shear rate at the time of passing through the die to less than 10000 sec ^-1 , preferably 9000 sec ^-1 or less, and more preferably 8000 sec ^-1 or less, not only is discharge from the die stable, but the hole diameter of the discharge hole of the die can be substantially increased, so that hole clogging and the like are less likely to occur, and the die can also be easily managed.

The shear rate (sec ⁻¹ ) when passing through the die refers to a value calculated by the following formula: Shear rate (sec ⁻¹ )=4×(Q/ρ/60)/(π×((d/10) ³ /8)).
(In the formula, Q represents the single hole discharge rate (g/min), ρ represents the melt density (g/cm ³ ), and d represents the die hole diameter (mm). For the copolymer polyester resin used in the present invention, the melt density ρ value is 1.18.)

In the method for producing a spunbonded nonwoven fabric of the present invention, the linear discharge speed of the resin discharged from the nozzle of the die is preferably 3.0 m/min or more and 20.0 m/min or less. By setting the linear discharge speed to preferably 3.0 m/min or more, more preferably 5.0 m/min or more, and even more preferably 8.0 m/min or more, discharge from the die is stabilized, so that thread breakage during the spinning process can be suppressed, and spunbonded nonwoven fabric can be stably produced. In addition, by setting the linear discharge speed to preferably 20.0 m/min or less, more preferably 18.0 m/min or less, and even more preferably 17.0 m/min or less, not only is discharge from the die stable, but the die hole diameter can be substantially increased, so that hole clogging is less likely to occur, and the die management is also easier.

The term "linear extrusion velocity (m/min)" used here refers to the value calculated by the following formula: Linear extrusion velocity (m/min) = (Q/ρ)/(π×(d/2) ² )
(In the formula, Q represents the single hole discharge rate (g/min), ρ represents the melt density (g/cm ³ ), and d represents the die hole diameter (mm). For the copolymer polyester resin used in the present invention, the melt density ρ value is 1.18.)

In the manufacturing method of the spunbonded nonwoven fabric of the present invention, the hole diameter of the nozzle hole is preferably 0.23 mm or more and 0.80 mm or less. By setting the hole diameter to preferably 0.23 mm or more, more preferably 0.25 mm or more, and even more preferably 0.28 mm or more, clogging of the holes is less likely to occur and the nozzle hole can be easily managed. In addition, by setting the hole diameter of the nozzle hole to preferably 0.80 mm or less, more preferably 0.70 mm or less, and even more preferably 0.60 mm or less, the back pressure of the nozzle hole is not insufficient and the nozzle hole diameter is suppressed, which is preferable.

In the method for producing the spunbonded nonwoven fabric of the present invention, a composite spinneret may be used as well as a single-component spinneret. When a composite spinneret is used, its shape is not particularly limited as long as it does not impair the effects of the present invention, and it can be appropriately selected from core-sheath type, sea-island type, side-by-side type, eccentric core-sheath type, blend type, and the like. When a composite spinneret is used, the resin used together with the copolymerized polyester is preferably a polyester such as polyethylene terephthalate or polybutylene terephthalate, or a polyolefin such as polyethylene or polypropylene, from the viewpoint of process stability and flexibility in the manufacturing process. For example, in the case of a core-sheath type composite fiber, a polyester or polyolefin can be arranged as the core component and the above-mentioned copolymerized polyester can be arranged as the sheath component, or in the case of a side-by-side type composite fiber, the above-mentioned copolymerized polyester and polyester can be arranged adjacent to each other. In particular, by using polyethylene terephthalate as the core component and the above-mentioned copolymerized polyester as the sheath component to produce a core-sheath type composite fiber, a spunbonded nonwoven fabric having excellent hydrophilicity and high mechanical strength can be obtained.

In the manufacturing method of the spunbonded nonwoven fabric of the present invention, not only a round hole die but also a modified cross-section die having a triangular, flat, hexagonal, hollow, or other discharge hole may be used. Of these, it is preferable to use a round hole die, since this results in a spunbonded nonwoven fabric with high productivity and excellent flexibility.

In the method for producing the spunbond nonwoven fabric of the present invention, the molten resin discharged from the spinneret is solidified to form fibers. Methods for forming fibers include, for example, forcibly blowing cold air onto the yarn, naturally cooling at the ambient temperature around the yarn, and adjusting the distance between the spinneret and the ejector used for pulling. Furthermore, a combination of these methods can be used. The fiberization conditions can be appropriately adjusted in consideration of the amount discharged per single hole of the spinneret, the temperature of the molten copolymerized polyester, the ambient temperature, etc.

In the manufacturing method of the spunbond nonwoven fabric of the present invention, the resin discharged from the nozzle of the die is pulled. Gas injected from an ejector or the like can be used for this pulling, and the gas can be air compressed to about 0.05 MPa to 0.25 MPa, nitrogen, water vapor with a humidity of 100% RH or less, etc.

In the method for producing the spunbonded nonwoven fabric of the present invention, the pulling speed of the copolymerized polyester in the above-mentioned pulling is preferably 3500 m/min or more and 7000 m/min or less. By setting the pulling speed to preferably 3500 m/min or more, more preferably 4000 m/min or more, and even more preferably 4500 m/min or more, orientation crystallization advances during fiberization, so that shrinkage in the thermal bonding process can be suppressed and process stability in the thermal bonding process can be improved. In addition, by setting the pulling speed to preferably 7000 m/min or less, more preferably 6500 m/min or less, and even more preferably 6000 m/min or less, thread breakage in the spinning process can be suppressed, and spunbonded nonwoven fabric can be produced stably.

In the method for producing the spunbonded nonwoven fabric of the present invention, the spinning draft of the copolymer polyester is 200 or more and 550 or less. By setting the spinning draft to 200 or more, preferably 250 or more, more preferably 300 or more, a die with a large diameter can be used, which makes it easier to manage the die. In addition, when fibers are formed using this die, orientation crystallization progresses, so that shrinkage of the fiber web can be suppressed during thermal bonding, improving the stability of the thermal bonding process. In addition, by setting the spinning draft to preferably 550 or less, more preferably 530 or less, sudden deformation of the spinning line can be suppressed, so that thread breakage during the spinning process can be suppressed, and spunbonded nonwoven fabric can be produced stably. The spinning draft referred to here refers to the ratio of the traction speed (m/min) to the above-mentioned discharge linear speed (m/min).

In the method for producing a spunbonded nonwoven fabric of the present invention, it is extremely important that the shear rate during passage through the die and the spinning draft are within the above-mentioned ranges. Even if the shear rate is 3500 sec ^-1 or more and less than 10000 ^sec-1 , by setting the spinning draft to 200 or more and 550 or less, the process stability in the spinning process and the thermal bonding process, and the ease of spinneret control can be dramatically improved. Furthermore, since the process stability in the spinning process and the thermal bonding process, and the ease of spinneret control are excellent, it is possible to stably produce a spunbonded nonwoven fabric having excellent hydrophilicity and flexibility.

In the manufacturing method of the spunbond nonwoven fabric of the present invention, the fiber web formed by the above-mentioned pulling is collected on a net conveyor. The conveying speed of the net conveyor can be appropriately adjusted in consideration of the desired basis weight of the spunbond nonwoven fabric.

The copolymerized polyester according to the present invention has a lower coefficient of friction than ordinary polyesters and polyolefins because polyalkylene glycol is copolymerized therein, and has the property of easily slipping on the net conveyor. Therefore, in the manufacturing method of the spunbonded nonwoven fabric of the present invention, it is preferable that the suction wind speed on the net conveyor in the vertical direction of the center of the die is 8.0 m/sec or more and 18.0 m/sec or less. By setting the suction wind speed to preferably 8.0 m/sec or more, more preferably 8.5 m/sec or more, and even more preferably 9.0 m/sec or more, the fiber web collected on the net conveyor is fixed on the conveyor without slipping, resulting in a spunbonded nonwoven fabric with high basis weight uniformity. In addition, by setting the suction wind speed to preferably 18.0 m/sec or less, more preferably 16.0 m/sec or less, and even more preferably 15.0 m/sec or less, the power of the compressor can be suppressed, and energy costs can be reduced.

The "center of the nozzle" here refers to the location within the nozzle outlet, which will be explained below, using Figure 1.

Figure 1 shows an example of the center of the nozzle discharge surface of a rectangular nozzle (Figure 1(a)) and a round nozzle (Figure 1(b)). On the nozzle discharge surface (1), we assume a rectangle (3) (rectangle or square) with the smallest area that contains all the discharge holes (2), and define the intersection of the diagonals of this rectangle (3) as the nozzle center (4).

In the method for producing the spunbonded nonwoven fabric of the present invention, the fiber web collected on the net conveyor is thermally bonded. The fiber web is thermally bonded to form a sheet. As a method for thermal bonding, a method for thermal bonding using various rolls such as a thermal embossing roll having engraved (uneven) portions on the surface of a pair of upper and lower rolls, a thermal embossing roll consisting of a combination of a roll with one flat (smooth) surface and a roll with engraved (uneven) portions on the surface of the other roll, and a thermal calendar roll consisting of a combination of a pair of upper and lower flat (smooth) rolls, or a method for thermal bonding using ultrasonic bonding in which the fibers are thermally welded by ultrasonic vibration of a horn can be adopted. By using such a thermal bonding method, a spunbonded nonwoven fabric having excellent mechanical strength can be obtained. On the other hand, a so-called air-through method, which is a method of blowing hot air onto a fiber web, can also be cited as a method for thermally bonding a fiber web. When this air-through method is adopted, a spunbonded nonwoven fabric having a high volume and excellent texture can be obtained.

In the manufacturing method of the spunbonded nonwoven fabric of the present invention, when an embossing roll is used for thermal bonding, the embossed bonding area ratio is preferably 5% or more and 30% or less. By setting the bonding area ratio to preferably 5% or more, more preferably 8% or more, it is possible to obtain mechanical strength sufficient for practical use as a spunbonded nonwoven fabric. On the other hand, by setting the bonding area ratio to preferably 30% or less, more preferably 20% or less, it is possible to obtain a spunbonded nonwoven fabric with excellent flexibility.

The bonded area ratio (%) here refers to the percentage of the entire nonwoven fabric where the convex parts of the upper roll and the convex parts of the lower roll overlap and come into contact with the nonwoven web, when heat bonding is performed using a pair of rolls with projections and recesses. Also, when heat bonding is performed using a roll with projections and a flat roll, it refers to the percentage of the entire nonwoven fabric where the convex parts of the roll with projections and recesses come into contact with the nonwoven web.

In the manufacturing method of the spunbond nonwoven fabric of the present invention, the engraving shape applied to the above-mentioned hot embossing roll can be a circle, an ellipse, a square, a rectangle, a parallelogram, a rhombus, a regular hexagon, a regular octagon, etc.

In the method for producing the spunbonded nonwoven fabric of the present invention, the linear pressure of the hot embossing roll during thermal bonding is preferably 5 N/cm or more and 70 N/cm or less. By setting the linear pressure of the roll to preferably 5 N/cm or more, more preferably 10 N/cm or more, and even more preferably 20 N/cm or more, sufficient bonding can be achieved and mechanical strength sufficient for practical use as a spunbonded nonwoven fabric can be obtained. On the other hand, by setting the linear pressure of the roll to preferably 70 N/cm or less, more preferably 60 N/cm or less, and even more preferably 50 N/cm or less, a spunbonded nonwoven fabric with excellent flexibility can be obtained.

In the manufacturing method of the spunbond nonwoven fabric of the present invention, a functional agent such as a hydrophilizing agent can be further added to the spunbond nonwoven fabric obtained as described above before winding. Methods for adding a functional agent to the spunbond nonwoven fabric include application by kiss roll or spray, and dip coating.

The spunbond nonwoven fabric obtained by the spunbond manufacturing method of the present invention preferably has an average single fiber diameter of 10 μm or more and 20 μm or less of the fibers made of the copolymerized polyester that constitutes the spunbond nonwoven fabric. By making the average single fiber diameter preferably 10 μm or more, more preferably 11 μm or more, and even more preferably 12 μm or more, it is possible to suppress thread breakage during the spinning process and to stably manufacture the spunbond nonwoven fabric. In addition, by making the average single fiber diameter preferably 20 μm or less, more preferably 18 μm or less, and even more preferably 16 μm or less, the flexibility of the spunbond nonwoven fabric is further improved.

The average single fiber diameter (μm) referred to here refers to a value measured and calculated by the following method.
(1) An image of a cross section of the fiber web after pulling is taken with a scanning electron microscope at a magnification at which a single fiber can be observed.
(2) Using the captured image and image analysis software, the area (μm ² ) formed by the cross-sectional contour of the single fiber is measured, and the diameter of a perfect circle having the same area as this area is calculated.
(3) This is measured for 20 randomly selected fibers constituting the same surface, and the average single fiber diameter is calculated by taking a simple number average value, and then rounded off to one decimal place.

The spunbonded nonwoven fabric obtained by the method for producing a spunbonded nonwoven fabric of the present invention preferably has a basis weight of 5 g/m2 ^or more and 200 g/m2 ^or less. By setting the basis weight to preferably 5 g/m2 ^or more, more preferably 8 g/m2 or ^more , and even more preferably 10 g/m2 ^{or more} , it is possible to suppress thread breakage during sheet conveyance, and in addition, the spunbonded nonwoven fabric has excellent handleability as a product. Furthermore, by setting the basis weight to preferably 200 g/m2 or ^less , more preferably 150 g/m2 or ^less , and even more preferably 100 g/ ^m2 or more, the spunbonded nonwoven fabric has excellent flexibility.

The basis weight (g/ ^m2 ) referred to here refers to a value calculated based on "6.2 Mass per unit area" of JIS L1913:2010 "General nonwoven fabric testing methods", by taking three 20 cm x 25 cm test pieces, measuring the mass (g) of each under standard conditions, calculating the simple number average, and then calculating the mass per 1 ^m2 , rounding off to the first decimal place.

The spunbond nonwoven fabric obtained by the method for producing a spunbond nonwoven fabric of the present invention preferably has a bending resistance of 1.0 mN·cm or less. By setting the bending resistance to preferably 1.0 mN·cm or less, more preferably 0.8 mN·cm or less, and even more preferably 0.6 mN·cm or less, a spunbond nonwoven fabric with excellent flexibility can be obtained. In addition, the lower limit of the bending resistance is preferably 0.1 mN·cm or more, since a bending resistance that is too low may result in poor handling of the nonwoven fabric.

The bending resistance (mm) referred to here refers to a value measured and calculated by the following method in accordance with "6.7 Bending resistance" of "6.7.3 41.5° cantilever method" in JIS L1913:2010 "General nonwoven fabric testing methods".
(1) Take five test pieces measuring 25 mm wide x 150 mm long and place them on a horizontal table with a 45° incline so that the short side of the test pieces is aligned with the scale baseline.
(2) Manually slide the test piece toward the inclined surface, and when the center point of one end of the test piece touches the inclined surface, read the movement length of the position of the other end on the scale.
(3) Measure the front and back of five test pieces to determine the simple number average of the movement length, and then calculate the bending resistance using the bending length C, which is obtained by multiplying the movement length by 1/2, and the basis weight M, using the following formula, and round off to the first decimal place. Bending resistance (mN cm) = M x ^C3 x 0.001
(In the formula, M represents the basis weight (g/m ² ) and C represents the bending length (cm).)

The spunbond nonwoven fabric obtained by the method for producing a spunbond nonwoven fabric of the present invention preferably has a ΔMR of 0.5% or more and 15.0% or less. By setting the ΔMR to preferably 0.5% or more, more preferably 1.0% or more, and even more preferably 2.0% or more, the surface of the spunbond nonwoven fabric is in a moderately hygroscopic state, resulting in a good tactile feel with a moist feeling when touched. In addition, by setting the ΔMR to 15% or less, more preferably 10% or less, and even more preferably 7% or less, the tactile feel is not sticky.

The ΔMR (%) referred to here refers to a value measured and calculated by the following method.
(1) 3 g of a measurement sample is freeze-pulverized and vacuum-dried at a drying temperature of 110° C. for 24 hours, and its bone-dry mass (W) is measured.
(2) The above sample is left for 24 hours in a thermo-hygrostat whose humidity is controlled to a state of 20° C.×65% RH, and the mass (MR1) of the sample that has reached equilibrium is measured.
(3) Next, the settings of the thermo-hygrostat are changed to 30° C.×90% RH, and the mass (MR2) is measured after leaving the sample for another 24 hours.
(4) Take three measurements for each level, find the simple number average, and calculate ΔMR using the following formula, rounding off to one decimal place: ΔMR (%) = (MR2 - MR1)/W.

The spunbond nonwoven fabric obtained by the method for producing a spunbond nonwoven fabric of the present invention preferably has a contact angle with water on the surface of the nonwoven fabric of 30° or less. By making the contact angle with water preferably 30° or less, more preferably 20° or less, and even more preferably 10° or less, the spunbond nonwoven fabric is hydrophilic, so that moisture that comes into contact with the surface is easily absorbed by the spunbond nonwoven fabric, resulting in a spunbond nonwoven fabric with excellent water absorbency. In addition, the lower limit of the contact angle with water is 0°, and a contact angle with water of 0° refers to a state in which all water is absorbed by the spunbond nonwoven fabric in the measurement method described below.

The contact angle (°) of the spunbond nonwoven fabric with water referred to here refers to a value determined as follows.
(1) The spunbond nonwoven fabric is left in a room at a room temperature of 20° C. and a relative humidity of 65% for 24 hours or more.
(2) The spunbond nonwoven fabric that has been subjected to the above treatment is placed on the stage of a contact angle meter installed in the same room.
(3) A 2 μL droplet of ion-exchanged water is prepared on the tip of a needle and applied to a spunbond nonwoven fabric.
(4) The contact angle with the droplet is determined from an image taken 2 seconds after the droplet hits the spunbond nonwoven fabric.
(5) For each level, measurements are taken 5 times at different measurement positions, and the simple number average is calculated to calculate the contact angle with water, which is then rounded off to the nearest whole number. If all the water is absorbed into the spunbond nonwoven fabric within 2 seconds, it is determined that the interface between the droplet and the air is on the same plane as the surface of the spunbond nonwoven fabric, and the contact angle with water is defined as 0°.

The spunbond nonwoven fabric obtained by the method for producing a spunbond nonwoven fabric of the present invention preferably has a water absorption speed measured on the surface of 20 seconds or less. By setting the water absorption speed to preferably 20 seconds or less, more preferably 15 seconds or less, and even more preferably 10 seconds or less, a spunbond nonwoven fabric with excellent water absorbency can be obtained.

The water absorption speed (seconds) referred to here refers to the value calculated based on "7.1.1 Dropping method" of JIS L1907:2010 "Testing method for water absorption of textile products." A single drop of water is dropped onto the surface of the spunbond nonwoven fabric, and the time it takes for the water to be absorbed and for the mirror reflection on the surface to disappear is measured. This is then measured at 10 different points, and the simple number average of the values is calculated to determine the water absorption speed, which is then rounded off to the first decimal place.

The spunbond nonwoven fabric obtained by the method for producing a spunbond nonwoven fabric of the present invention can be widely used for medical and sanitary materials, daily living materials, industrial materials, etc., but since it has excellent hydrophilicity and flexibility, it is particularly suitable for use as sanitary materials. Note that the sanitary materials referred to here are mainly disposable items used for health-related purposes such as medical care and nursing, and examples of such items include disposable diapers, sanitary napkins, gauze, bandages, masks, gloves, bandages, etc., and also include the components thereof, such as the top sheet, back sheet, and side gathers of disposable diapers.

Next, the present invention will be described in detail based on examples. However, the present invention is not limited to these examples. In addition, in the measurement of each physical property, unless otherwise specified, the measurement was performed according to the above-mentioned method.

(1) Spinning Process Stability In the spinning process, a material that did not experience any yarn breakage during 20 minutes of spinning was rated as A, a material that experienced 1 to less than 20 yarn breakages was rated as B, and a material that experienced 20 or more yarn breakages was rated as C.

(2) Thermal bonding process stability During the thermal bonding process, samples that showed almost no shrinkage in the width direction were rated as A, samples that showed shrinkage in the width direction but no sheet breaks were rated as B, and samples that showed significant shrinkage in the width direction or sheet breaks were rated as C.

(3) Ease of spinneret management After removing the spinneret after spinning and removing the polymer, the spinneret holes were inspected to see if there was any dirt or other residue inside the spinneret. The spinneret holes were small and difficult to inspect, so the spinneret was rated as A.

(4) Average Single Fiber Diameter The fiber web after air drawing was collected, and the cross section of the fiber was photographed with a scanning electron microscope "S-5500" manufactured by Hitachi High-Technologies Corporation at a magnification at which a single fiber could be observed. Then, the measurement was performed as described above using "WinROOF2015" manufactured by Mitani Shoji Co., Ltd. as image analysis software.

(5) Weight per unit area The weight per unit area of the spunbonded nonwoven fabric after thermal bonding was measured as described above.

(6) Bending resistance The bending resistance of the spunbonded nonwoven fabric after thermal bonding was measured as described above.

(7) ΔM
The spunbond nonwoven fabric after thermal bonding was measured as described above using a thermohygrometer "LHU-123" manufactured by Espec Corporation.

(8) Contact angle with water The spunbonded nonwoven fabric after thermal bonding was measured using a contact angle meter "DMo-501" manufactured by Kyowa Interface Science Co., Ltd. as described above.

[Example 1]
Polyethylene terephthalate (hereinafter abbreviated as PET) having an intrinsic viscosity of 0.62 dL/g and copolymerized with 8% by mass of polyethylene glycol (hereinafter abbreviated as PEG) having a number average molecular weight of 20,000 was melted in a single screw extruder and spun at a spinning temperature of 290° C. from a rectangular round-hole die having a die hole diameter of 0.30 mm at a single hole throughput of 1.1 g/min. The shear rate at this time was 5861 sec ⁻¹ . The spun yarn was cooled and solidified with cold air, and then air-pulled in a rectangular ejector so that the filamentary pulling speed was 5320 m/min and the spinning draft was 403, to obtain a fiber web, which was collected at a suction air speed of 10.7 m/sec on a net conveyor in the vertical direction of the center of the die. The obtained fiber web was thermally bonded at a line pressure of 50 N/cm and a thermal bonding temperature of 230° C. using a pair of upper and lower thermal embossing rolls consisting of an upper roll made of a metal and engraved with a polka dot pattern and having a bonding area ratio of 16%, and a lower roll made of a metal flat roll, to obtain a spunbonded nonwoven fabric having a basis weight of 30 g/m ^2. The production conditions of the spunbonded nonwoven fabric and the evaluation results of the obtained spunbonded nonwoven fabric are shown in Table 1.

[Example 2]
A spunbonded nonwoven fabric was obtained in the same manner as in Example 1, except that the number average molecular weight of the copolymerized PEG was changed from 20,000 to 8,300. The production conditions of the spunbonded nonwoven fabric and the evaluation results of the obtained spunbonded nonwoven fabric are shown in Table 1.

[Examples 3 and 4]
Spunbonded nonwoven fabrics were obtained in the same manner as in Example 1, except that the copolymerization amount of PEG was changed from 8% by mass to 14% by mass in Example 3 and 4% by mass in Example 4. The production conditions of the spunbonded nonwoven fabrics and the evaluation results of the obtained spunbonded nonwoven fabrics are shown in Table 1.

[Examples 5 and 6]
Spunbonded nonwoven fabrics were obtained in the same manner as in Example 1, except that the polymerization time of the copolymerized PET copolymerized with PEG was adjusted to change the intrinsic viscosity from 0.62 to 0.57 in Example 5 and to 0.72 in Example 6. The production conditions of the spunbonded nonwoven fabrics and the evaluation results of the obtained spunbonded nonwoven fabrics are shown in Table 1.

[Example 7]
A spunbond nonwoven fabric was obtained in the same manner as in Example 1, except that in place of the PET having an intrinsic viscosity of 0.62 dL/g and copolymerized with 8 mass% PEG having a number average molecular weight of 20,000, a low molecular weight material obtained by depolymerizing PET used in PET bottles (abbreviated as recycled PET in Table 1) was used, copolymerized with 8 mass% PEG having a number average molecular weight of 20,000. The production conditions of the spunbond nonwoven fabric and the evaluation results of the obtained spunbond nonwoven fabric are shown in Table 1.

[Examples 8 and 9, Comparative Example 1]
A spunbonded nonwoven fabric was obtained in the same manner as in Example 1, except that the shear rate, extrusion linear speed, and spinning draft were changed by adjusting the single-hole discharge rate and drawing speed, and the suction speed on the conveyor was changed so that the collected fiber web would not slip on the conveyor. The production conditions of the spunbonded nonwoven fabric and the evaluation results of the obtained spunbonded nonwoven fabric are shown in Table 2.

[Comparative Example 2]
Except for changing the die hole diameter from 0.30 mm to 0.20 mm, and changing the shear rate, extrusion linear speed, and spinning draft, a spunbonded nonwoven fabric was obtained in the same manner as in Example 1. The production conditions of the spunbonded nonwoven fabric and the evaluation results of the obtained spunbonded nonwoven fabric are shown in Table 2.

[Examples 10 to 12]
Except for changing the spinning draft by adjusting the drawing speed, a spunbonded nonwoven fabric was obtained in the same manner as in Example 1. The production conditions of the spunbonded nonwoven fabric and the evaluation results of the obtained spunbonded nonwoven fabric are shown in Table 2.

In Examples 1 to 11, a copolymer polyester copolymerized with a specific polyalkylene glycol was used, and the shear rate and spinning draft during melt spinning when passing through the die were in the appropriate range, which not only resulted in excellent process stability and ease of die management in each process, but also demonstrated that the resulting spunbond nonwoven fabric had excellent hydrophilicity and flexibility.

On the other hand, Comparative Example 1 has a large spinning draft, which results in poor spinning process stability. In addition, Comparative Example 2 has a large shear rate, which results in a substantially small nozzle hole diameter, which results in poor nozzle management ease.

1: nozzle outlet surface 2: outlet holes 3: smallest rectangle including all outlet holes 4: nozzle center

Claims (7)

A method for producing a spunbonded nonwoven fabric, comprising melting a copolymerized polyester, discharging it from an outlet hole of a die, and drawing the resulting fiber web, which is collected on a net conveyor, and thermally bonding the fiber web, wherein the copolymerized polyester is a copolymerized polyester obtained by copolymerizing 3% by mass or more and 40% by mass or less of a polyalkylene glycol having a number average molecular weight of 4,000 or more and 30,000 or less, the shear rate at which the copolymerized polyester passes through the die when it is discharged from the outlet hole of the die is 3,500 sec ^-1 or more and less than 10,000 ^sec-1 , and the spinning draft of the copolymerized polyester during the drawing is 200 or more and 550 or less. The method for producing a spunbond nonwoven fabric according to claim 1, wherein the hole diameter of the nozzle is 0.23 mm or more and 0.80 mm or less. The method for producing a spunbonded nonwoven fabric according to claim 1 or 2, wherein the towing speed of the copolymerized polyester is 3500 m/min or more and 7000 m/min or less. The method for producing a spunbond nonwoven fabric according to any one of claims 1 to 3, wherein the suction wind speed on the net conveyor in the vertical direction of the center of the die is 8.0 m/sec or more and 18.0 m/sec or less. The method for producing a spunbond nonwoven fabric according to any one of claims 1 to 4, wherein the main repeating unit of the copolyester is ethylene terephthalate. The method for producing a spunbond nonwoven fabric according to any one of claims 1 to 5, wherein the intrinsic viscosity of the copolymer polyester is 0.50 dL/g or more and 0.80 dL/g or less. The method for producing a spunbonded nonwoven fabric according to any one of claims 1 to 6, wherein the copolyester is a recycled copolyester obtained by adding the polyalkylene glycol to a low molecular weight product obtained by depolymerizing a polyester and repolymerizing the product.

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