JP7118623B2 - Nonwoven fabric manufacturing method - Google Patents

Description

The present invention relates to polypropylene-based nonwoven fabrics.

Patent Literature 1 discloses a technique for producing a polypropylene-based nonwoven fabric by a spunbond method. In this technique, a non-woven fabric is obtained by forming a web of continuous fibers that are continuously spun by melting raw material resin and subjecting this web to thermal embossing. In the spunbond method, a nonwoven fabric can be efficiently manufactured from a raw material resin through a series of steps.

JP 2012-12759 A

The strength of the nonwoven fabric described in Patent Document 1 is 0.1 to 1 N/weight per 25 mm width. However, nonwoven fabrics are required to have even higher strength.
Also, in order to reduce the production cost of the nonwoven fabric, it is effective to reduce the basis weight. However, in nonwoven fabrics, the strength decreases as the basis weight decreases. In order to improve the strength of the nonwoven fabric, it is effective to use highly rigid fibers. However, nonwoven fabrics using highly rigid fibers are hard to the touch and tend to lose their texture.

An object of the present invention is to provide a nonwoven fabric having both high strength and good texture.

A nonwoven fabric according to one aspect of the present invention comprises fibers formed from a mixture of a propylene homopolymer and an ethylene-propylene copolymer.
The nonwoven fabric has a thermally fused portion in which the fibers are thermally fused together and a non-thermally fused portion in which the fibers are not thermally fused together.
An endothermic peak with a height of 1300 μW/mg or higher is observed in the DSC curve of the non-thermally-sealed portion in the region of 140° C. or higher and 162° C. or lower.

The nonwoven fabric of the present invention has both high strength and good texture.

It is a figure for demonstrating the spinning process in a spunbond method. FIG. 4 is a cross-sectional view schematically showing thermal embossing in the spunbond method; 4 is a graph showing DSC curves of only non-thermally-sealed portions of nonwoven fabrics according to Examples and Comparative Examples. 4 is a graph showing DSC curves of the entire nonwoven fabrics according to Examples and Comparative Examples. It is a graph which shows the DSC curve after thermal history reset of the nonwoven fabric which concerns on an Example. 4 is a graph showing the results of a tensile test in the MD direction of nonwoven fabrics according to Examples and Comparative Examples.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Schematic structure of nonwoven fabric]
Nonwovens are composed of fibers formed from a mixture of propylene homopolymer and ethylene-propylene copolymer. The fibers constituting the nonwoven fabric are preferably continuous fibers or long fibers.

The nonwoven fabric is composed of a heat-sealed portion and a non-heat-sealed portion. The heat-sealed portions of the nonwoven fabric are formed in substantially circular spot shapes and are regularly arranged at predetermined intervals in the vertical and horizontal directions. The non-heat-sealed portion of the nonwoven fabric occupies a portion of the non-woven fabric other than the heat-sealed portion.

The thickness (fiber diameter) of the fibers constituting the nonwoven fabric is preferably 5 µm or more, more preferably 20 µm or less, and still more preferably 12 µm or less. As a result, the fibers are softened, so that a nonwoven fabric having high smoothness and softness and good texture can be obtained. Further, if the fibers are thin, the number of fibers increases, and the number of fibers per fusion point increases, so that a nonwoven fabric with high strength can be obtained.
In general non-woven fabrics, when the fibers are simply thinned, the fibers tend to become hard and the texture tends to deteriorate, and the elongation of the fibers tends to decrease and the strength tends to decrease. In this respect, the nonwoven fabric according to the present embodiment is configured so as to achieve both good touch and high strength. Details of such a configuration will be described later.

In the heat-sealed portion of the nonwoven fabric, the fibers are heat-sealed to each other. Therefore, the fibers forming the nonwoven fabric are partially integrated at the heat-sealed portion. As a result, in the nonwoven fabric, the sheet shape can be maintained satisfactorily without causing the fibers to separate and come off.

In addition, the fibers are not thermally fused to each other in the non-thermally fused portion of the nonwoven fabric. Therefore, in the non-heat-sealed portion, the original soft feel of the fiber can be obtained. Although the heat-sealed portion has high rigidity due to the heat-sealing, it occupies a small area in the non-woven fabric, so that the non-heat-sealed portion is less likely to lose its good texture.

As the fibers constituting the nonwoven fabric, it is preferable to use fibers in which the ethylene concentration (ethylene monomer content) of the ethylene-propylene copolymer is 10% by weight or more and 25% by weight or less. % by weight or less is more preferable. By setting the ethylene concentration to 10% by weight or more, preferably 13% by weight or more, the rigidity of the fibers becomes low, so that the texture of the nonwoven fabric is further improved and the elongation at break of the fibers is increased, so that a high-strength nonwoven fabric can be obtained. .
In the nonwoven fabric according to the present embodiment, high strength can be obtained due to the structure in which the breaking elongation of the fibers is high. In other words, when the non-woven fabric is pulled, it is observed that the fibers break at the boundary between the heat-sealed portion and the non-heat-sealed portion. Therefore, since the breaking elongation of the fibers is high, the non-woven fabric can be elongated without being broken, thereby obtaining a nonwoven fabric with high strength.
Further, by limiting the ethylene concentration to 25% by weight or less, preferably 20% by weight or less, it becomes easier to secure the rigidity required for the nonwoven fabric. If the ethylene concentration is too high, the resin will stretch, but the strength of the resin itself will decrease, so that the boundary between the heat-sealed portion and the non-heat-sealed portion will likely break. On the other hand, by setting it to the above range, the β crystal of the propylene homopolymer is easily formed under the molding conditions described later, and the fiber has high strength and high elongation, and the boundary between the heat-sealed portion and the non-heat-sealed portion. It is presumed that it becomes difficult to break because the damage at the part is reduced.
The ethylene-propylene copolymer is preferably a random copolymer obtained by randomly copolymerizing ethylene or a block copolymer obtained by copolymerizing ethylene in a block manner.

In addition, in the fibers constituting the nonwoven fabric, the content of the ethylene-propylene copolymer in the above ethylene concentration range is preferably 5% by weight or more, more preferably 10% by weight or more, and 30% by weight. It is preferably 25% by weight or less, more preferably 25% by weight or less. When the content of the copolymer is 5% by weight or more, the rigidity of the fibers is low, so that the texture of the nonwoven fabric is further improved, and the elongation at break of the fibers is increased, so that a high-strength nonwoven fabric can be obtained. Further, by limiting the content of the copolymer to 25% by weight or less, it becomes easier to secure the rigidity required for the nonwoven fabric.
In general, the more the ethylene-propylene copolymer and the less the propylene homopolymer, the higher the elongation but the lower the strength of the nonwoven fabric. For this reason, it is difficult to obtain a nonwoven fabric having higher strength than a nonwoven fabric composed only of a propylene homopolymer by simply blending an ethylene-propylene copolymer.
In this respect, in the nonwoven fabric according to the present embodiment, high strength can be obtained by setting the content of the ethylene-propylene copolymer having the above ethylene concentration within the above range. Although the details will be described later, the nonwoven fabric according to the present embodiment has high strength and high elongation by adopting fiber molding conditions that increase the amount of β crystals of the propylene homopolymer. It is presumed that the boundary between the heat-sealed portion and the non-heat-sealed portion is less likely to be damaged due to less damage.
The melting point of the ethylene-propylene copolymer is preferably 80° C. or higher, more preferably 90° C. or higher, and preferably 130° C. or lower, more preferably 115° C. or lower. Within this numerical range, the ethylene-propylene copolymer becomes a solid phase at a temperature lower than the temperature at which β crystals are formed (estimated 110° C. to 140° C.), so the ethylene-propylene copolymer is in a molten state. Co-crystallization facilitates entry into the crystals of the propylene homopolymer and facilitates the formation of β-crystals under the molding conditions described later, which is preferable.
The ethylene concentration in the ethylene-propylene copolymer and the content of the ethylene-propylene copolymer are measured by NMR and IR measurement methods (Reference: Atsuo Nishioka, Kobunshi, P309, vol.15, No. 169 (1966), Co Confirmation of the polymer, it is obtained by the special table 2016-522335).

The configuration such as the shape and arrangement of the heat-sealed portions in the nonwoven fabric can be changed as appropriate. For example, the heat-sealed parts do not have to be arranged regularly, and may be randomly distributed.
The continuous pattern of the heat-sealed portions in the nonwoven fabric includes, for example, an oblique lattice, an orthogonal lattice, and a pattern in which curved wavy lines intersect. The linear heat-sealed portion preferably has a thickness of 0.3 mm or more and 1.5 mm or less.
Moreover, the pattern of the heat-sealed portions in the nonwoven fabric may be a discontinuous pattern. Examples of non-continuous patterns include regular patterns such as zigzag arrangement, lattice arrangement, and pentagonal, hexagonal, heptagonal, and octagonal patterns. Among them, a combination of tetragons and hexagons is preferable from the viewpoint of forming large and small convex portions. Moreover, the pattern such as the lattice or the polygon may be formed by one or a plurality of dashed lines, and is preferably formed by arranging two or three lines. In this case, it is preferable to shift the discontinuous positions of the dashed lines adjacent to each other in the extending direction, thereby obtaining a nonwoven fabric with high strength. The shape of the heat-sealed portion is preferably circular, elliptical, polygonal such as rectangular, star-shaped, cross-shaped, Y-shaped, or S-shaped. In particular, the configuration in which the cross-shaped and Y-shaped heat-sealed portions are combined is preferable in terms of excellent appearance and feel due to the formation of large and small convex portions. The size of the heat-sealed portion is preferably 0.05 mm ² or more, more preferably 0.15 mm ² or more, and preferably 1.8 mm ² or less, and 0.8 mm ² or less. It is more preferable to have
The pitch between the heat-sealed parts is preferably 0.3 mm or more, and preferably 0.7 mm It is more preferably 10 mm or less, and more preferably 4 mm. Within this numerical range, when the non-fused portion is touched with a hand, the range in which the fibers constituting the non-fused portion can move freely increases, so that the texture is improved and high strength can be obtained. point is preferable.
If the angle formed by the roll axis direction with respect to the imaginary straight line formed by connecting the heat-sealed parts arranged in the CD direction is inclined in the range of 0.5 degrees to 5 degrees, the pressure fluctuation is small and the projections of the embossing roll and the flat roll are formed. Since the impact applied between them is small, it is difficult to perforate and the strength is high, which is preferable.
The area ratio of the heat-sealed portion in the nonwoven fabric is preferably 3% or more, preferably 7% or more, and is preferably 30% or less, more preferably 14% or less. By being within this numerical range, fluffing can be prevented, and both strength and touch can be achieved.

[Crystal structure of propylene homopolymer]
(Overview)
The crystal structure of a propylene homopolymer includes α-crystals with high rigidity and β-crystals with low rigidity. The nonwoven fabric according to the present embodiment is manufactured using fibers containing a large amount of β-crystals of propylene homopolymer. When a molten propylene homopolymer is stretched and quenched, β crystals are observed, but β crystals are hardly observed and α crystals are observed under general fiber spinning conditions. Also, if a β-nucleating agent is added, β-crystals are observed even in propylene homopolymers, but it has been difficult to obtain a nonwoven fabric with high strength. Each crystal of the propylene homopolymer also includes a co-crystallized one in which molecular chains having different microstructures are incorporated in the same crystal. A method for forming a fiber containing a large amount of β crystals of the propylene homopolymer will be described later in the item "Method for producing nonwoven fabric".

The melting point of the α-crystal of the propylene homopolymer is higher than 162°C and 180°C or lower, and the melting point of the β-crystal of the propylene homopolymer is 140°C or higher and 162°C or lower. Therefore, the presence of α crystals and β crystals in the propylene homopolymer can be confirmed by a DSC curve obtained by differential scanning calorimetry (DSC).

In other words, if an endothermic peak P _α is observed in the region above 162° C. and 180° C. or less in the DSC curve obtained by DSC, the existence of α crystals can be confirmed. A large value of the endothermic peak P _α means that there are many α crystals. Also, if an endothermic peak Pβ is observed in the region of 140° C. or higher and 162° C. or lower in the DSC curve obtained by DSC, the presence of _β crystal can be confirmed. A large value of the endothermic peak Pβ means that there are many _β crystals.

In the non-woven fabric, both high strength and good texture can be achieved by making the crystal structure of the propylene homopolymer different between the heat-sealed portion and the non-heat-sealed portion. The crystal structure of the propylene homopolymer in the heat-sealed portion and the non-heat-sealed portion of the nonwoven fabric will be described below.

(Heat-sealed part)
It is preferable that the heat-sealed portion of the nonwoven fabric contains a large amount of α crystals of the propylene homopolymer. As a result, the heat-sealed portion can firmly support the fibers forming the non-heat-sealed portion. This is thought to be because the amount of transition from the β crystal to the α crystal, which will be described later, increases, and the amount of heat generated by the transition increases, increasing the strength of the boundary between the heat-sealed portion and the non-heat-sealed portion, making it more difficult to break. .

A method for forming a heat-sealed portion containing a large amount of α crystals of propylene homopolymer from a fiber containing a large amount of β crystals of propylene homopolymer will be described later in the item "Method for Producing Nonwoven Fabric". In addition, the heat-sealed portion may contain a large amount of β crystals of the propylene homopolymer, if necessary.

(non-heat-sealed part)
The non-thermally fused portion of the nonwoven fabric contains a large amount of β crystals of the propylene homopolymer. In other words, fibers containing a large amount of β crystals of the propylene homopolymer are present as they are in the non-thermally fused portion. For this reason, the non-thermally-sealed portion can obtain the soft feel inherent in the low-rigidity fiber containing a large amount of β-crystals of the propylene homopolymer.

Specifically, in the non-woven fabric, an endothermic peak _Pβ with a height of 1300 μW/mg or more is observed in the region of 140° C. or more and 162° C. or less of the DSC curve obtained by DSC of the non-thermally fused portion, especially 2000 μW/mg. It is preferred that an endothermic peak P _β with a height equal to or greater than 100 is observed. DSC of the non-thermally fused portion is performed using a sample obtained by cutting out only the non-thermally fused portion from the nonwoven fabric.
In the non-heat-sealed portion of the nonwoven fabric, the endothermic peak Pβ in the region of 140°C to 162°C is preferably higher than the _endothermic peak _Pα in the region of more than 162°C to 180°C. Specifically, the ratio P _β /P _α of the endothermic peak P _β to the endothermic peak P _α is preferably 1.2 times or more, more preferably 1.4 times or more. As a result, the non-heat-sealed portion of the nonwoven fabric is less likely to break because the flexibility is improved and the damage at the boundary portion is suppressed. Therefore, the nonwoven fabric has improved elongation and high strength.
Furthermore, the non-thermally bonded portion of the nonwoven fabric preferably has an endothermic peak Pβ in the range of 140°C to 162°C and does not have an _endothermic peak _Pα in the range of more than 162°C to 180°C. As a result, the above effect can be obtained more remarkably.
In addition, the endothermic peak _Pβ only in the non-thermally bonded portion of the nonwoven fabric is preferably higher than the endothermic peak _Pβ in the entire nonwoven fabric. As a result, the non-thermally-sealed portion has relatively more β crystals than the thermally-sealed portion, and the damage applied to the fiber at the boundary between the thermally-sealed portion and the non-thermally-sealed portion is reduced. Therefore, a nonwoven fabric with high strength can be obtained. The ratio of the endothermic peak _Pβ of the entire nonwoven fabric to the endothermic peak _Pβ of the non-thermally fused portion of the nonwoven fabric (former/latter) is preferably 1.1 or more, more preferably 1.2 or more.

For the above measurements, a differential scanning calorimeter DSC7000X manufactured by Hitachi High-Tech Science Co., Ltd. was used, 1 mg ± 0.10 mg of the sample was set in an aluminum saucer with a lid, and the temperature was increased from 25 ° C. at a rate of 10 ° C./ The endothermic peak when the temperature is raised to 300° C. at min is measured as the crystalline melting peak, and the temperature is determined as the melting temperature (Tm). The endothermic peak is obtained by dividing the absolute value (μW) of the endothermic value by the sample weight (mg). Assuming that the number of measurement samples is n=2, the average is obtained. Baseline correction is performed by setting the heat flow at 180° C. to 0. If there is no endothermic peak within the temperature range, the maximum absolute value of endothermic values within that temperature range is obtained as the endothermic peak value.
An electronic balance capable of weighing up to 0.01 mg of the sample is used.
When sampling a nonwoven fabric from a commercially available absorbent article, the sample is taken from a portion where no hot-melt adhesive or the like adheres. If this is not possible, wash away the hot-melt adhesive with a solvent such as toluene, and then dry the solvent at room temperature before measurement.

Due to the action of the β-crystals of the propylene homopolymer, the fibers forming the non-heat-sealed portion are less likely to break even when stretched to a large extent. In other words, the non-heat-sealed portion has a large breaking elongation, which is the elongation at which it is stretched and broken. Specifically, the elongation at break of the nonwoven fabric is preferably 40% or more, more preferably 50% or more. That is, in the nonwoven fabric, the breaking elongation in either the MD direction or the CD direction is preferably within this range, and more preferably the breaking elongation in both the MD direction and the CD direction is within this range. Thereby, a nonwoven fabric with high strength is obtained.

As a result, the non-woven fabric can be greatly stretched with a strong force, although the non-heat-sealed portion has low rigidity. Therefore, the nonwoven fabric has a high breaking strength, which is the strength at which the fibers are partially broken by being stretched. Specifically, the breaking strength of the nonwoven fabric is preferably 4000 cN/50 mm or more, more preferably 4700 cN/50 mm or more, and 1.1 N/25 mm/g/ ^m2 or more per unit basis weight, and further It is preferably 1.3 N/25 mm/g/m ² or more. Furthermore, in the nonwoven fabric, the breaking strength in either the MD direction or the CD direction is preferably within this range, and the breaking strength in both the MD direction and the CD direction is more preferably within this range.

Moreover, it is preferable that the fibers constituting the non-thermally fused portion of the nonwoven fabric contain a large amount of a low isotactic propylene homopolymer as a polymer added to the base polymer. As a result, in the non-woven fabric, the breaking elongation in the non-heat-sealed portion is further increased. Therefore, the non-woven fabric provides even higher breaking strength.
The base polymer of the fibers constituting the nonwoven fabric is a propylene homopolymer, preferably an isotactic propylene homopolymer. It is preferable that the base polymer is contained as a main component in the constituent fibers in an amount of 60% by weight or more, more preferably 75% by weight or more.
From the viewpoint of flexibility, friction reduction, and stickiness prevention, it is preferable to use a softening agent such as a wax emulsion, a reactive softening agent, a silicone compound, or a surfactant in the fibers constituting the nonwoven fabric. In particular, amino group-containing silicones, oxyalkylene group-containing silicones, and surfactants are preferably used. Examples of surfactants include (1) carboxylate-based anionic surfactants, sulfonate-based anionic surfactants, sulfate-based anionic surfactants, and phosphate-based anionic surfactants ( (2) Polyhydric alcohols such as sorbitan fatty acid ester, diethylene glycol monostearate, diethylene glycol monooleate, glyceryl monostearate, glyceryl monostearate, propylene glycol monostearate, etc. Mono fatty acid ester, fatty acid amide, N-(3-oleyloxy-2-hydroxypropyl) diethanolamine, polyoxyethylene hydrogenated castor oil, polyoxyethylene sorbit beeswax, polyoxyethylene sorbitan sesquistearate, polyoxyethylene monooleate, Polyoxyethylene sorbitan sesquistearate, polyoxyethylene glyceryl monooleate, polyoxyethylene monostearate, polyoxyethylene monolaurate, polyoxyethylene monooleate, polyoxyethylene cetyl ether, polyoxyethylene lauryl ether, etc. (3) cationic surfactants such as quaternary ammonium salts, amine salts or amines; (4) aliphatic derivatives of secondary or tertiary amines containing carboxy, sulfonate, sulfate. , or zwitterionic surfactants such as aliphatic derivatives of heterocyclic secondary or tertiary amines. Also, if necessary, known chemicals can be added to the softener of the present invention as secondary additives (minor components). The softening agent is preferably contained in the constituent fibers in an amount of 0.1% by weight or more and 20% by weight or less, more preferably 0.5% by weight or more and 2.0% by weight or less.
Examples of fibers in the nonwoven fabric include conjugate fibers having a single-core structure or side-by-side or core-sheath (concentric or eccentric) fiber cross sections.
At least one type of fiber constitutes the nonwoven fabric, and 50% by weight, preferably 80% by weight or more of the total weight of the nonwoven fabric is preferably composed of the above fibers in order to exhibit sufficient effects. In the case of two or more kinds, a mixed cotton structure and a laminated structure can be mentioned. In the case of lamination, it is preferable to use the above fibers in one or more layers.

[Nonwoven fabric manufacturing method]
(overall structure)
The nonwoven fabric manufacturing apparatus includes a supply section, a stretching section, a net conveyor, a hot embossing section, and a raw fabric roll winding section. The nonwoven fabric manufacturing apparatus is configured to be capable of continuously manufacturing a spunbonded nonwoven fabric from a raw material resin by a spunbonding method.

In addition, the spunbonded nonwoven fabric is not limited to a nonwoven fabric composed only of a spunbond layer manufactured by a spunbond method, but includes a wide range of nonwoven fabrics having a structure using a spunbond layer. For example, the spunbond nonwoven fabric includes a nonwoven fabric (SMS nonwoven fabric) in which a meltblown layer manufactured by a meltblown method is used in addition to the spunbond layer, and the spunbond layer-meltblown layer-spunbond layer are laminated in this order. In this case, each layer may have the same composition or may have a different composition. The fiber diameter may also differ in each layer. Examples include SS, SSS, SSSS structures laminated by spunbonding, SMS, SSMS, SSMMS, SSSMMS, SMMMS, SMMMMS structures combining spunbonding and meltblowing.

The supply part is configured to be able to contain resin. Nozzles are arranged at the bottom of the supply section. The supply unit extrudes the melted resin from the nozzle. Thereby, the supply unit can continuously supply the resin molded to have an outer diameter corresponding to the diameter of the nozzle.

The extension part is arranged below the supply part and formed in a cylindrical shape penetrating vertically. Cold air is blown from above to below inside the extending portion. Thereby, the resin supplied from the supply section is stretched by cold air when passing through the stretching section. As a result, fibers that are continuous fibers are obtained.

Thus, the supply section and the drawing section perform a spinning process for continuously spinning the resin to obtain fibers that are continuous fibers. The details of the spinning process in the feeding section and the drawing section will be described later.

A net conveyor is arranged below the extension. The fibers that have passed through the drawing section are overlapped on the net conveyor to form a web. The net conveyor can continuously transport a web formed of fibers in the MD direction at a predetermined transport speed.

The thermally embossed portion is adjacent to the MD direction of the net conveyor. The heat embossing section performs a heat sealing step of forming a heat sealing section by heat embossing on the web conveyed by the net conveyor. Thereby, a nonwoven fabric is obtained. The details of the heat-sealing process in the heat-embossed portion will be described later.

The raw nonwoven fabric roll is adjacent to the heat embossed portion in the MD direction. The raw nonwoven fabric roll is recovered by winding up the nonwoven fabric that has been thermally embossed at the thermal embossing section. In this manner, the nonwoven fabric manufacturing apparatus can continuously manufacture nonwoven fabrics from the raw material resin.

(Details of the spinning process)
FIG. 1 is a diagram showing the spinning process. FIG. 1 shows a supply section 110, a stretching section 120, and a net conveyor 130 of a nonwoven fabric manufacturing apparatus. FIG. 1 also shows the spinning distance D between the nozzle 111 of the supply section 110 and the net conveyor 130 . Further, FIG. 1 shows the velocity V1 of the resin P extruded from the nozzle 111 of the supply section 110 and the velocity V2 of the fibers passing through the drawing section 120. As shown in FIG. The speed V1 is obtained as follows: speed V1=single-hole nozzle resin extruded weight per unit time/(nozzle hole cross-sectional area/specific gravity of molten resin at nozzle temperature). Also, the speed V2 is obtained as follows: speed V2=single-hole nozzle resin extrusion weight per unit time/(fiber cross-sectional area obtained from the average diameter of nonwoven fabric fibers/nonwoven fabric fiber resin specific gravity).

A spinning magnification S, which is a magnification at which the resin P is stretched in the stretching section 120, can be expressed by the following formula using the velocities V1 and V2.
S=V2/V1
The larger the spinning magnification S, the smaller the fiber thickness (fiber diameter) and the higher the fiber cooling rate. The spinning magnification S can be adjusted by, for example, the speed of cold air in the stretching section 120 .

The average speed of resin P in the spinning process can be expressed as (V1+V2)/2. Assuming that the cooling of the resin P is completed when it reaches the net conveyor 130, the cooling time t of the fiber P can be expressed by the following equation.
t=2D/(V1+V2)

The average cooling rate R of the resin P can be expressed by the following formula using the temperature T1 of the nozzle 111 and the temperature T2 on the net conveyor 130.
R=(T1-T2)/t=(T1-T2)(V1+V2)/2D
As described above, the average cooling rate R of the resin P in the spinning process can be calculated.

In the spinning step, the spinning magnification S of the resin P is preferably 500 times or more, more preferably 900 times or more, and preferably 1500 times or less, and more preferably 1300 times or less. The average cooling rate R of the fiber in the spinning step is preferably 1.6° C./ms or more, more preferably 2.0° C./ms or more, and preferably 3.5° C./ms or less, and 3.0° C./ms. is more preferred. By rapidly cooling the resin P in this manner, a fiber containing a large amount of β-crystals of the propylene homopolymer can be formed without adding a nucleating agent (β-nucleating agent) that serves as nuclei for β-crystals. It is speculated that the ethylene-propylene copolymer enters the crystals of the propylene homopolymer by co-crystallization, thereby facilitating the formation of β-crystals.
When the β-nucleating agent is added, the fiber elongation is lowered, making it difficult to obtain a nonwoven fabric with high strength. Examples of beta-nucleating agents include gamma quinacridone, aluminum salts of quinizarine sulfonic acid, dihydroquinacridine-diones and quinacridine-tetrones, triphenenol ditriazine, calcium silicate, dicarboxylic acids (e.g., suberic acid , pimelic acid, ortho-phthalic acid, isophthalic acid and terephthalic acid), sodium salts of these dicarboxylic acids, salts of these dicarboxylic acids with Group IIA metals of the periodic table (e.g. calcium, magnesium, or barium), δ quinacridone, diamides of adipic acid or suberic acid, various indigosol and sivanthine organic pigments, quinacridone quinone, N',N'-dicyclohexyl-2,6-naphthalene dicarboxamide, anthraquinone red and bisazo yellow pigments, and the like. , preferably not containing these.

In the spinning process, by increasing the spinning magnification S to 500 times or more, it becomes easy to increase the average cooling rate R of the resin P to 1.6° C./ms or more. Further, by keeping the spinning magnification S at 1500 times or less, it is possible to suppress the occurrence of breakage of the resin P in the stretched portion 120 .

The ethylene concentration of the ethylene-propylene copolymer in the resin P is preferably 10% by weight or more and 20% by weight or less. By setting the ethylene concentration to 10% by weight or more, β crystals are easily formed under the molding conditions described above. Further, by limiting the ethylene concentration to 20% by weight or less, it is difficult to break even at a high spinning ratio S in the main spinning step, and good moldability of the resin P can be easily obtained.

Also, the content of the ethylene-propylene copolymer in the resin P is preferably 5% by weight or more and 25% by weight or less. By setting the content of the copolymer to 5% by weight or more, β-crystals are easily formed under the molding conditions described above. Further, by limiting the content of the copolymer to 25% by weight or less, it is difficult to break even at a high spinning ratio S in the main spinning step, and good moldability of the resin P can be easily obtained.

Further, the ethylene-propylene copolymer in resin P is preferably a block copolymer. Block copolymers are copolymers of multiple isotactic blocks and ethylene random blocks, and the isotactic blocks have higher compatibility with propylene homopolymers than random copolymers. Easy to get into crystals. In the propylene homopolymer, the ethylene-propylene copolymer enters the crystals, thereby facilitating the formation of β-crystals.

(Details of heat sealing process)
FIG. 2 is a cross-sectional view schematically showing the heat-sealing process. The thermal embossing section 140 has an embossing roll 141 having protrusions E formed on its surface and a flat roll 142 having a flat surface. The embossing roll 141 and the flat roll 142 are arranged vertically adjacent to each other. The embossing roll 141 and the flat roll 142 are heated so that their surface temperatures are about 140.degree. Also, a difference in surface temperature between the embossing roll 141 and the flat roll 142 is provided, preferably 2° C. or higher, more preferably 5° C. or higher, and preferably 20° C. or lower, more preferably 15° C. or lower. In particular, it is preferable to make the surface temperature of the embossing roll lower than the surface temperature of the flat roll, in order to improve the feel of the surface on which the embossing roll contacts. The linear pressure applied to the embossing roll 141 and the flat roll 142 is preferably 50 kgf/cm or more, more preferably 80 kgf/cm or more, and preferably 200 kgf/cm or less, more preferably 150 kgf/cm or less. In fiber fusion, even if the surface temperature of the embossing roll 141 or the flat roll 142 is lower than the melting point measured by the DSC, the pressure between the embossing roll 141 and the flat roll 142 lowers the melting point of the fibers, causing the fibers to fuse together. It is considered to wear

The web formed by the net conveyor 130 is sandwiched between the embossing roll 141 and the flat roll 142 and further conveyed in the MD direction. When the web passes between the embossing roll 141 and the flat roll 142 , the web is pressed against the flat roll 142 by the projections E of the embossing roll 141 . As a result, the fibers are melted while being in close contact with each other, and the fibers are fused to each other to form a thermally fused portion.

In the state shown in FIG. 2, four fibers F1 to F4 are overlapped in this order from the protrusion E toward the flat roll 142. In FIG. In such a case, heat is less likely to be applied to the fibers F in the central region between the projections E and the flat roll 142 .

That is, the fibers F1 in contact with the projection E and the fiber F4 in contact with the flat roll 142 are likely to be heated, but the fibers F2 and F3 in contact with neither the projection E nor the flat roll 142 are heated. Hard to apply heat. The fibers F2 and F3 are not fused unless the fibers F2 and F3 are melted. On the other hand, if a high temperature is applied to the fibers F in order to melt the fibers F2 and F3 reliably, the fibers F1 and F4 are greatly damaged at the boundary between the heat-sealed portion and the non-heat-sealed portion. Become.

In this regard, in the present embodiment, the fibers F2 and F3 can be fused well without increasing the temperature applied to the fibers F. That is, in the present embodiment, the melting of the fibers F2 and F3 is promoted by the heat generated when the β crystals of the propylene homopolymer forming the fibers F2 and F3 are recrystallized into α crystals. It is believed that the β crystal melts once when it transforms into the α crystal. Therefore, in the non-woven fabric, the fibers F can be more reliably fused together at the heat-sealed portion while suppressing damage to the fibers F at the boundary between the heat-sealed portion and the non-heat-sealed portion. This can also prevent fluffing.

(Manufacturing method of nonwoven fabric other than spunbond method)
Non-woven fabrics may be produced by a heat roll method using short fibers, or by combining an air-through method and an embossing process. A direct spinning method in which spun fibers are collected on a net, a drum, or a belt conveyor is preferred, and representative examples include the spunbond method (S) and the meltblown method (M). Examples of the method for forming the embossed joint portion, which is the fusion bonding point of the fibers, include a heat embossing method and an ultrasonic embossing method, and the heat embossing method is preferable in terms of molding at a high speed. Before or after embossing, hydroentangling, steam entangling, or needle punching may be performed as a fiber entangling treatment. Further, as various treatments after embossing, it is preferable to add a calendering treatment, a treatment of applying a hydrophilic agent or a water-repellent agent, a mechanical treatment with an engaging roll, and a raising treatment.

[Use of nonwoven fabric]
The nonwoven fabric according to the present invention is preferably used as a sheet for forming a surface that comes into contact with human skin in various articles, taking advantage of its good texture. For example, the topsheet of absorbent articles such as sanitary napkins, panty liners, and disposable diapers, and pants-type absorbent articles comprising an absorbent main body including an absorbent body and a pants-shaped outer covering fixing it. It can be used as a constituent member (outer layer material or inner layer material) of an exterior body. Furthermore, it can be suitably used as a cleaning sheet for personal use, a skin care sheet, and the like. The nonwoven fabric according to the present invention may be processed into an uneven shape, and is preferably used with the convex side being the side in contact with the skin.
A laminated sheet obtained by laminating a nonwoven fabric and a resin film can be used, for example, as a backing material for a diaper. When the nonwoven fabric is used, for example, as an outer layer material or an inner layer material sheet of an absorbent article, its basis weight (basis weight) is preferably 7 g/m ² or more, more preferably 10 g/m ² or more. It is preferably 25 g/m ² or less, more preferably 15 g/m ² or less.

[Examples and Comparative Examples]
Examples of the present invention and comparative examples will be described. However, the configuration of the embodiment described below is merely an example of the configuration of the present invention, and the present invention is not limited to the configuration of the embodiment.
Specifically, in Examples and Comparative Examples 1 to 3, nonwoven fabrics were produced using the nonwoven fabric manufacturing apparatus described above, and each nonwoven fabric was evaluated. All nonwoven fabrics were produced under common conditions except for the conditions shown below.

Table 1 shows the production conditions for each nonwoven fabric. Specifically, the content of propylene homopolymer and ethylene-propylene copolymer, and the ethylene concentration in the ethylene-propylene copolymer are shown as the composition of the resin. Also, the spinning conditions (spinning magnification and average cooling rate) and the basis weight of the nonwoven fabric are shown. When the total amount of the propylene homopolymer and the ethylene-propylene copolymer is 100% by weight, 0.5% by weight of fatty acid amide as a softening agent and 0.5% by weight of titanium oxide particles as a whiteness improver are used. has been added to nonwoven fabrics.
The propylene homopolymer resin used in Examples and Comparative Examples 1, 2, and 3 was SA03 manufactured by Japan Polypropylene Corporation, MRF 30 g/10 min, density 0.90 g/cm ³ , tensile strength at break 36 MPa, melting point 164°C. was used. The ethylene-propylene copolymer resin used in the examples was Vistamaxx6202 manufactured by ExxonMobil, having an MFR of 20 g/10 min, a density of 0.863 g/cm ³ , a tensile strength at break of 5.5 MPa or more, and a melting point of 105°C. The ethylene-propylene copolymer resin used in Comparative Examples 2 and 3 was Vistamaxx3980FL manufactured by ExxonMobil, MFR 8 g/10 min, density 0.879 g/cm ³ , tensile strength at break of 19 MPa or more, and melting point of about 120°C. board.

In Comparative Example 1, unlike Examples, no ethylene-propylene copolymer was used, that is, only propylene homopolymer was used. Also, in Comparative Example 1, the spinning magnification and the average cooling rate were increased as in the example. The only difference between Example and Comparative Example 1 is the presence or absence of the ethylene-propylene copolymer.

In Comparative Examples 2 and 3, the spinning magnification and the average cooling rate were lower than those in Example and Comparative Example 1. Also, in Comparative Examples 2 and 3, ethylene-propylene copolymers were used in the same manner as in Examples. However, in Comparative Examples 2 and 3, the content of the ethylene-propylene copolymer and the ethylene concentration in the ethylene-propylene copolymer are different from those of the examples.

In Examples and Comparative Examples 1 to 3, even if the spinning ratio was different, the fiber diameter and basis weight of the nonwoven fabric were adjusted to be the same. The fiber diameter of the nonwoven fabric can be adjusted, for example, by adjusting the nozzle diameter of the supply section. The basis weight of the nonwoven fabric can be adjusted, for example, by the transport speed of the net conveyor.

FIG. 3A is a graph showing DSC curves obtained by DSC of samples obtained by cutting out only non-thermally-sealed portions from nonwoven fabrics according to Examples and Comparative Examples 1 to 3. FIG. In the DSC curve, the horizontal axis indicates temperature and the vertical axis indicates heat flow per mg. In the DSC curve, the positive peak is the exothermic peak and the negative peak is the endothermic peak. Table 2 shows the values of the endothermic peaks P _β and P _α and the value of P _β /P _α for each sample.

In the examples, an endothermic peak Pβ indicating melting of _β crystals of the propylene homopolymer is observed at around 160°C. The endothermic peak P _β is 2050 μW/mg, which is 1300 μW/mg or more, and it can be seen that the non-thermally fused portion of the nonwoven fabric according to the example contains many β crystals of propylene homopolymer.

In Comparative Example 1, an endothermic peak P _α indicating melting of α crystals of the propylene homopolymer is observed at around 165°C. On the other hand, in Comparative Example 1, the endothermic peak Pβ of the _β -crystal of the propylene homopolymer is not observed. Therefore, it can be seen that the non-thermally fused portion of the nonwoven fabric according to Comparative Example 1 hardly contains β crystals of the propylene homopolymer.

In Comparative Example 2, an endothermic peak Pβ of the _β crystal of the propylene homopolymer is observed at around 160°C. However, this endothermic peak P _β is 1280 μW/mg, which is lower than 1300 μW/mg, and in Comparative Example 2, the amount of β crystals of the propylene homopolymer contained in the non-thermally bonded portion of the nonwoven fabric is smaller than that in Examples. Recognize.

In Comparative Example 3, the endothermic peak Pβ of the _β -crystal of the propylene homopolymer is not observed. Therefore, it can be seen that the non-thermally fused portion of the nonwoven fabric according to Comparative Example 3 contains almost no β crystals of the propylene homopolymer. Thus, in Comparative Examples 1 to 3, the amount of β crystals of the propylene homopolymer contained in the non-thermally bonded portion of the nonwoven fabric is smaller than that in Examples.

Next, the crystal structure of the propylene homopolymer contained in the heat-sealed portions of the nonwoven fabrics according to Examples was examined. Since it is difficult to cut out only the heat-sealed portion from the nonwoven fabric, a sample of the entire nonwoven fabric was subjected to DSC. FIG. 3B is a graph showing the DSC curve obtained with the DSC of the whole nonwoven sample. Table 3 shows the values of the endothermic peaks P _β and P _α and the value of P _β /P _α for the samples according to the examples. Table 3 also shows the ratio of P _β (non-thermally fused portion)/P _β (whole), which is the ratio of the endothermic peak P _β of only the non-thermally fused portion shown in Table 2 to the endothermic peak P _β of the entire nonwoven fabric. Values are also shown.

In the examples, in addition to the endothermic peak P _β of the β-crystal of the propylene homopolymer, an endothermic peak P _α of the α-crystal of the propylene homopolymer is observed at around 167°C. Considering that the endothermic peak P _α of α crystals of propylene homopolymer was not observed only in the non-thermally fused portion, it can be seen that α crystals of propylene homopolymer are contained in the thermally fused portion.

FIG. 3B also shows the DSC curves obtained by DSC of the samples of the entire nonwoven fabric for Comparative Examples 1 to 3. Table 3 also shows the values of the endothermic peaks P _β and P _α and the value of P _β /P _α for the samples according to Comparative Examples 1 to 3. Comparing the endothermic peak _Pβ value of only the non-thermally fused portion shown in Table 2 with the endothermic peak _Pβ value of the entire nonwoven fabric shown in Table 3, the endothermic peak Pβ of the non-thermally fused portion of the nonwoven fabric in Examples The endothermic peak P _β of the entire nonwoven fabric was lower than P _β , whereas in Comparative Examples 2 and 3, the endothermic peak P _β of the entire nonwoven fabric was higher than the endothermic peak P _β of the non-thermally bonded portion of the nonwoven fabric. became higher.

Subsequently, samples were prepared for examining the heat history during the manufacturing process of the nonwoven fabrics according to the examples. In this sample, the heat history in the manufacturing process of the nonwoven fabric was reset by heating to 180° C. and then slowly cooling it. FIG. 4 is a graph showing the DSC curve obtained by DSC of this sample.

In this DSC curve, no endothermic peak Pβ of the propylene homopolymer _β -crystal is observed around 160°C, and an endothermic peak Pα of the propylene homopolymer _α -crystal is observed around 165°C. That is, when the thermal history is reset, the β crystals of the propylene homopolymer disappear. Therefore, it can be seen that quenching in the spinning process is necessary for the generation of β crystals in the propylene homopolymer.

The nonwoven fabrics according to Examples and Comparative Examples 1 to 3 were subjected to tensile tests in the MD and CD directions. A nonwoven sample of 200 mm in the MD direction and 50 mm in the CD direction was used for the tensile test in the MD direction. Nonwoven samples of 50 mm in MD and 200 mm in CD were used for tensile tests in the CD direction.

In the tensile test, using Autograph AG-IS manufactured by Shimadzu Corporation, each sample was elongated at a speed of 300 mm/min with a chuck distance of 150 mm, and the tensile load at each elongation was measured. The breaking strength was defined as the maximum point strength under tensile load of each sample. Also, the elongation at the maximum point strength of each sample was defined as the elongation at break. Table 4 shows the breaking strength and breaking elongation in the MD and CD directions for each sample. The number of samples was set to n=5, and the average value was obtained.

In the examples, higher breaking strength than in the comparative examples 1 to 3 was obtained in both the MD direction and the CD direction. It was as high as 1.39 N/25 mm/g/m ² per unit basis weight. FIG. 5 is a graph showing the results of a tensile test in the MD direction. In FIG. 5, the horizontal axis indicates elongation, and the vertical axis indicates tensile load. It should be noted that the tensile test in the CD direction also shows the same tendency as the tensile test in the MD direction.

As shown in FIG. 5 , the rise of the curve in Example is gentler than in Comparative Example 1, and it can be seen that the nonwoven fabric according to Example has lower rigidity than the nonwoven fabric according to Comparative Example 1. However, the nonwoven fabric according to the example has a breaking elongation as high as 58%, so that a significantly higher breaking strength than the nonwoven fabric according to the comparative example having a low breaking elongation of 22% is obtained.

In Comparative Examples 2 and 3, a large elongation at break was obtained as in Examples. However, in the example, the rise of the curve is steeper than in the comparative examples 2 and 3, and it can be seen that the nonwoven fabric according to the example has higher rigidity than the nonwoven fabrics according to the comparative examples 2 and 3. For this reason, the nonwoven fabrics according to Examples have higher breaking strength than the nonwoven fabrics according to Comparative Examples 2 and 3.

DESCRIPTION OF SYMBOLS 110... Supply part 111... Nozzle 120... Stretching part 130... Net conveyor 142... Flat roll E... Projection P... Resin F... Fiber W... Web

Claims (9)

A method for producing a nonwoven fabric by a spunbond method,
A mixture of a propylene homopolymer and an ethylene-propylene copolymer is spun at a spinning magnification of 500 to 1500 times so that the average cooling rate is 1.6° C./ms to 3.5° C./ms. to form fibers,
forming a web of said fibers;
A method for producing a nonwoven fabric, wherein the web is thermally embossed to form a heat-sealed portion in which the fibers are heat-sealed. The method for producing a nonwoven fabric according to claim 1 , wherein the ethylene concentration in the ethylene-propylene copolymer is 10% by weight or more and 25 % by weight or less. The spinning magnification is 900 times or more,
The average cooling rate is 2.0° C./ms or more
A method for producing the nonwoven fabric according to claim 1 or 2. The nonwoven fabric has a non-thermally fused portion where the fibers are not thermally fused,
The DSC curve of the non-thermally-sealed portion has an endothermic peak P with a height of 1300 μW/mg or more in the region of 140° C. or higher and 162° C. or lower. _β can be seen
The method for producing the nonwoven fabric according to any one of claims 1 to 3. The nonwoven fabric has a breaking elongation of 50% or more
The method for producing the nonwoven fabric according to any one of claims 1 to 4. The content of the ethylene-propylene copolymer is 5% by weight or more and 25% by weight or less based on the mixture.
The method for producing the nonwoven fabric according to any one of claims 1 to 5. The ethylene-propylene copolymer is a block copolymer
The method for producing the nonwoven fabric according to any one of claims 1 to 6. The DSC curve of the non-thermally-sealed portion has an endothermic peak P _α is seen,
In the non-thermally fused portion, the endothermic peak P _β is the endothermic peak P _α higher than
The method for producing the nonwoven fabric according to any one of claims 1 to 7. In the DSC curve of the entire nonwoven fabric, an endothermic peak P _β is seen,
Endothermic peak P only in the non-thermally fused portion _β is the endothermic peak P in the entire nonwoven fabric _β higher than
The method for producing the nonwoven fabric according to any one of claims 1 to 8.

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