Sheet for extraction bag, and extraction bag

Abstract

Provided is a sheet for an extraction bag made of a polylactic acid resin as a raw material, the sheet for an extraction bag experiencing no shrinkage or little shrinkage even when immersed in high-temperature water (hot water).　This sheet for an extraction bag includes a spun-bonded non-woven fabric layer composed of a polylactic acid resin, wherein the weight-average molecular weight (Mw) of the polylactic acid resin in terms of polystyrene, derived by gel permeation chromatography (GPC), is 5.0 × 104 to 2.0 × 105, and the crystallinity of the polylactic acid resin is 50% or greater. The molecular weight distribution (Mw / Mn) represented by the ratio of the weight-average molecular weight (Mw) of the polylactic acid resin to the number-average molecular weight (Mn) thereof is 3 or less.

Description

Extraction bag sheet and extraction bag

[0001] The present invention relates to a sheet for an extraction bag, which includes a spunbond nonwoven fabric layer made of polylactic acid resin, and to an extraction bag.

[0002] Sheets for extraction bags used to extract coffee, tea, soup stock, etc. have been developed using biodegradable polylactic acid resin as a material to reduce the environmental impact when they are disposed of after use (see, for example, Patent Document 1).

[0003] The tea bag described in Patent Document 1 is made from a linear polylactic acid resin with specific physical properties. According to the document, tea bags made from this polylactic acid resin are said to have properties and processability comparable to those of polyester and nylon fibers, which have traditionally been widely used as materials for tea bags.

[0004] Japanese Patent Application Laid-Open No. 2002-104506

[0005] However, polylactic acid resin has the drawback of low heat resistance. Therefore, when tea bags made from polylactic acid resin, including those in Patent Document 1, are immersed in hot water at approximately 80°C or higher, the entire tea bag shrinks. As a result, the space for extraction in the tea bag becomes narrower, reducing extraction efficiency. Furthermore, the appearance of the shrunken tea bag is poor, reducing its commercial value.

[0006] The present invention has been made in consideration of the above problems, and aims to provide a sheet for an extraction bag and an extraction bag made from polylactic acid resin, which does not shrink or is resistant to shrinkage even when immersed in high-temperature water (hot water).

[0007] The characteristic configuration of the extraction bag sheet according to the present invention for solving the above problems is a sheet for extraction bags including a spunbond nonwoven fabric layer made of polylactic acid resin, wherein the polylactic acid resin has a weight average molecular weight (Mw) of 5.0 × 10 in terms of polystyrene as determined by gel permeation chromatography (GPC). ４ ~2.0 x 10 ５ and the degree of crystallinity is 50% or more.

[0008] In the case of the extraction bag sheet having this configuration, the weight average molecular weight (Mw) of the polylactic acid resin constituting the spunbond nonwoven fabric layer, calculated as polystyrene by gel permeation chromatography (GPC), is 5.0 × 10 ４ ~2.0 x 10 ５ By setting the crystallinity of the polylactic acid resin to 50%, it is possible to maintain a low viscosity of the molten resin obtained by melting the polylactic acid resin. As a result, the fluidity required for drawing the molten yarn spun out from the spinning nozzle or ejector when forming the spunbonded nonwoven fabric layer is sufficiently ensured, and it becomes possible to draw the fiber to a state where the molecular orientation in the amorphous region is reduced. Furthermore, by setting the crystallinity of the polylactic acid resin to 50% or more, it is possible to confirm that the molecular orientation in the amorphous region has plateaued while allowing the fiber to be drawn sufficiently. Furthermore, if the crystallinity of the polylactic acid resin is 50% or more, the amorphous region (amorphous region) in the polylactic acid resin is relatively small, and therefore, even if the molecular chains in the amorphous region are somewhat oriented, the effect of the molecular orientation in the polylactic acid resin as a whole is small. Therefore, even when an extraction bag using the extraction bag sheet of this configuration is immersed in water (hot water) at a temperature (approximately 80°C or higher) higher than the glass transition temperature of polylactic acid resin (approximately 50-60°C), shrinkage caused by relaxation of molecular orientation in the amorphous region (molecular movement) is reduced, ensuring space for extraction in the hot water and allowing for efficient extraction of the extraction target, such as tea leaves. Furthermore, by suppressing shrinkage of the spunbond nonwoven fabric layer, the extraction bag does not undergo significant deformation during use and its appearance is not impaired, thereby increasing the commercial value of the extraction bag. In this way, the extraction bag sheet of this configuration can achieve both excellent extraction efficiency and a beautiful appearance.

[0009] In the sheet for extraction bags according to the present invention, the polylactic acid resin preferably has a molecular weight distribution (Mw / Mn) expressed as the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of 3 or less.

[0010] With the extraction bag sheet of this configuration, by setting the molecular weight distribution (Mw / Mn) to 3 or less, the fluidity of the molten resin obtained by melting the polylactic acid resin can be stabilized, thereby stabilizing the stretching state of the molten yarn spun from the spinning nozzle or ejector and reducing variation in the quality of the produced fibers. Furthermore, since the extraction bag using the extraction bag sheet of this configuration is stable with the shrinkage of the spunbond nonwoven fabric layer suppressed, the extraction bag does not undergo significant deformation during use and its appearance does not deteriorate, thereby increasing the commercial value of the extraction bag.

[0011] The sheet for extraction bags according to the present invention preferably further comprises a meltblown nonwoven fabric layer laminated on the spunbonded nonwoven fabric layer.

[0012] The extraction bag sheet of this configuration can be obtained as a sheet having a multilayer structure in which a meltblown nonwoven fabric layer is laminated on a spunbond nonwoven fabric layer, and can therefore be suitably used as a material for extraction bags such as coffee drip bags and tea bags.

[0013] The characteristic configuration of the extraction bag according to the present invention for solving the above problem is that the above-mentioned extraction bag sheet is used.

[0014] The infusion bag of this configuration, using the infusion bag sheet described above, can significantly suppress shrinkage due to heat (boiling water shrinkage) even when immersed in hot water (approximately 80°C or higher). This ensures sufficient space for extraction in the hot water, allowing for efficient extraction of tea leaves and other infusion targets. Furthermore, suppressing shrinkage of the infusion bag sheet prevents significant deformation of the infusion bag during use and maintains its appearance, thereby enhancing the commercial value of the infusion bag.

[0015] Fig. 1 is an explanatory diagram showing an image of crystalline regions and amorphous regions in a polylactic acid resin, and Fig. 2 is a schematic cross-sectional view showing the layer structure of a sheet for an extraction bag according to one embodiment of the present invention.

[0016] Biodegradable polylactic acid resins (excluding PDLLA) are crystalline polymers having crystalline and amorphous regions, with a glass transition temperature (Tg) of approximately 50-60°C and a melting point (Tm) of approximately 180°C. Figure 1 is an explanatory diagram showing the crystalline and amorphous regions of polylactic acid resin. As shown in Figure 1(a), polylactic acid resin forms a crystalline phase in which molecular chains are highly aligned in the crystalline regions, whereas in the amorphous regions, the molecular chains are essentially random. When producing a spunbonded nonwoven fabric from such polylactic acid resin, a molten thread of polylactic acid resin spun from a spinning nozzle or ejector is stretched, and the molecular chains of the resulting fibers are oriented in the stretching direction (the left-to-right direction in Figure 1(b)), as shown in Figure 1(b). Here, "oriented molecular chains" refers to a state in which molecular chains are aligned in the same direction and movable at a certain distance from each other, as opposed to a "highly aligned molecular chain" state that forms a crystalline phase. Therefore, the molecular chains of the polylactic acid resin that constitutes the spunbond nonwoven fabric are oriented in the drawing direction of the fibers even in the amorphous region.

[0017] When extracting a beverage using an extraction bag made of spunbonded nonwoven fabric of polylactic acid resin, the extraction temperature (approximately 80-100°C) is above the glass transition temperature (Tg) and below the melting point (Tm) of the polylactic acid resin. Therefore, in the crystalline region, the crystals do not melt, and molecular chain movement (relaxation) does not occur. Meanwhile, in the amorphous region, the molecular chains begin to move, and as shown in Figure 1(c), the molecular orientation collapses. Finally, in the amorphous region, the molecular chains ultimately become unoriented. As a result, the polylactic acid resin shrinks in the direction of fiber extension. Therefore, extraction bags such as tea bags made of spunbonded nonwoven fabric of polylactic acid resin generally shrink when immersed in high-temperature water (hot water).

[0018] In order to reduce shrinkage (boiling water shrinkage) caused by immersing an extraction bag in hot water (approximately 80°C or higher), it is essential to minimize the orientation of molecular chains in the amorphous regions of polylactic acid resin. When a thread (fiber) made from molten polylactic acid resin is stretched, the crystalline regions increase, and the molecular orientation of the entire fiber increases. Further stretching of the fiber further increases the molecular orientation in the crystalline regions, but the molecular orientation in the amorphous regions plateaus. As a result, the increase in orientation throughout the entire fiber decreases. The inventors believed that by utilizing this change in molecular orientation in the amorphous regions accompanying fiber stretching (the phenomenon in which molecular orientation plateaus), shrinkage of the entire fiber could be suppressed.

[0019] However, because polylactic acid resin has a high melt viscosity, it is difficult to secure a sufficient amount of air required to stretch the fibers when producing melt-blown nonwoven fabrics, and forcible stretching can result in thread breakage. Furthermore, when attempting to reduce the melt viscosity of polylactic acid resin by heating it to make it easier to stretch, thermal decomposition products of the polylactic acid resin (burnt resin) can become mixed into the fibers as foreign matter, which can cause thread breakage.

[0020] Therefore, in developing a sheet for extraction bags (extraction bags) that is less likely to shrink due to heat, the inventors focused on the molecular weight, crystallinity, and molecular weight distribution of polylactic acid resin, which are related to the melt viscosity of polylactic acid resin.They found that it was possible to confirm that the molecular orientation of the amorphous region, which causes shrinkage, had reached a plateau while avoiding the problem of thread breakage during stretching, and thus completed the present invention.

[0021] Hereinafter, embodiments of the sheet for extraction bag and the extraction bag of the present invention will be described in detail, however, the present invention is not limited to the configurations described below.

[0022] [Basic Structure of the Extraction Bag Sheet] The extraction bag sheet of the present invention is basically composed of a spunbond nonwoven fabric layer made of polylactic acid resin. The polylactic acid resin may be poly-L-lactic acid (PLLA) made of the L-form or poly-D-lactic acid (PDLA) made of the D-form. The spunbond nonwoven fabric layer functions as a filter for extracting the target component. The spunbond nonwoven fabric layer is produced by introducing molten polylactic acid resin extruded from a spinning nozzle into an ejector, stretching the polylactic acid resin discharged from the ejector while cooling and solidifying it to form fibers, and collecting these fibers on a collector to form a web.

[0023] [Polylactic acid resin] The weight average molecular weight (Mw) (polystyrene equivalent) of the polylactic acid resin used as the raw material for the spunbond nonwoven fabric layer is 5.0 × 10 ４ ~2.0 x 10 ５ is 6.0 × 10 ４ ~1.7 × 10 ５ It is preferable that the ４ ~1.2 × 10 ５ It is more preferable that the number average molecular weight (Mn) (polystyrene equivalent) is 1.7 × 10 ４ ~1.2 × 10 ５ Preferably, it is 2.5 × 10 ４ ~1.0 x 10 ５ More preferably, it is 3.5 × 10 ４ ~7.0 x 10 ４It is even more preferable that the weight-average molecular weight (Mw) and number-average molecular weight (Mn) are within the above ranges. This allows the viscosity of the molten resin obtained by melting the polylactic acid resin to be maintained low. As a result, the fluidity required for drawing the molten yarn spun from the spinning nozzle or ejector when forming the spunbonded nonwoven fabric layer is sufficiently ensured, making it possible to draw the fiber to a state where the molecular orientation in the amorphous region is reduced. This allows for both excellent extraction efficiency and a beautiful appearance. If the weight-average molecular weight (Mw) and number-average molecular weight (Mn) are below the lower limits of the broadest ranges, respectively, the fluidity of the molten polylactic acid resin becomes too high, making it impossible to draw the molten yarn at high speed. Furthermore, the strength of the finished fiber is insufficient, making it unsuitable for use as a sheet for an extraction bag. When the weight-average molecular weight (Mw) and the number-average molecular weight (Mn) exceed the upper limit of the broadest range, respectively, the polylactic acid resin must be heated to a temperature close to its decomposition temperature in order to obtain a fluidity suitable for drawing the molten yarn until the molecular orientation in the amorphous region decreases, which may result in contamination with thermal decomposition products of the polylactic acid resin (burnt resin), which may cause yarn breakage.

[0024] The polylactic acid resin constituting the spunbond nonwoven fabric layer is preferably adjusted so that its molecular weight distribution (Mw / Mn), expressed as the ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn), is 3 or less, more preferably 2.5 or less, and even more preferably 2.1 or less. By adjusting the molecular weight distribution (Mw / Mn) to 3 or less, the fluidity of the molten resin obtained by melting the polylactic acid resin can be stabilized, thereby stabilizing the drawing state of the molten yarn spun from the spinning nozzle or ejector and reducing variation in the quality of the produced fiber. Furthermore, a molecular weight distribution (Mw / Mn) of 3 or less does not contain molecules with an excessively high molecular weight range, thereby preventing the formation of insufficiently drawn regions, and does not contain molecules with an excessively low molecular weight range, thereby preventing yarn breakage due to excessive drawing, and enabling stable processing under certain conditions. The lower limit of the molecular weight distribution (Mw / Mn) is not particularly limited, and in principle, a monodisperse (Mw / Mn=1) molecular weight distribution is possible, but in reality, the molecular weight distribution (Mw / Mn) is 1.5 or more. The weight average molecular weight (Mw), number average molecular weight (Mn), and molecular weight distribution (Mw / Mn) of the polylactic acid resin can be measured by gel permeation chromatography (GPC).

[0025] When the polylactic acid resin, the raw material for the spunbonded nonwoven fabric layer, is stretched by blowing airflow through the molten polylactic acid resin, the molecular chains are oriented in the crystalline regions, but the orientation of the molecular chains in the amorphous regions reaches a plateau, thereby minimizing the impact of molecular orientation throughout the polylactic acid resin. Therefore, even when immersed in hot water (hot water) at high temperatures (approximately 80°C or higher), the relaxation of molecular orientation (molecular movement) in the amorphous regions is reduced, resulting in reduced shrinkage in the fiber stretching direction (boiling water shrinkage). As a result, sufficient space for extraction is secured in the hot water, allowing for efficient extraction of tea leaves and other target materials. Furthermore, when the extraction bag sheet of the present invention is processed into tea bags and other products, the reduced shrinkage of the spunbonded nonwoven fabric layer prevents significant deformation during extraction, preventing deterioration in appearance and maintaining the commercial value of the tea bags.

[0026] The polylactic acid resin constituting the spunbond nonwoven fabric layer has a crystallinity of 50% or more. A crystallinity of 50% or more in the polylactic acid resin allows for sufficient fiber drawing while confirming that the molecular orientation in the amorphous region has plateaued. Furthermore, if the crystallinity of the polylactic acid resin is 50% or more, the amorphous region (amorphous region) in the polylactic acid resin is relatively small, and even if the molecular chains in the amorphous region are somewhat oriented, the influence of molecular orientation in the polylactic acid resin as a whole is small. As a result, the relaxation phenomenon of molecular orientation in the amorphous region is reduced, and shrinkage of the polylactic acid resin can be suppressed. While there is no particular upper limit to the crystallinity, stretching a polylactic acid resin with a crystallinity close to 100% will cause thread breakage during spinning, so in practice the crystallinity should be 90% or less.

[0027] The crystallinity of polylactic acid resin is determined as follows. First, a test piece cut from a spunbond nonwoven fabric layer is placed in a differential scanning calorimeter (DSC) and heated at a predetermined rate from a temperature lower than the glass transition temperature Tg (approximately 50-60°C) of the polylactic acid resin to a temperature exceeding the melting point Tm (approximately 150-170°C). For example, the temperature is raised from 30°C to 240°C at a rate of 10°C / min. During this heating process, the amorphous regions (non-crystalline portions) of the polylactic acid resin undergo a phase transition to crystals, and further heating causes the crystals to melt, ultimately resulting in a molten state. Here, if ΔHc is the heat of crystallization when the amorphous portion of the polylactic acid resin undergoes a phase transition to crystal, and ΔHm is the heat of fusion of the crystal when the crystal of polylactic acid melts, the degree of crystallinity χc (%) of polylactic acid is calculated from the following formula (1): χc (%) = (ΔHm - ΔHc) / Q × 100 (1) Here, Q is the heat of fusion of a perfect crystal, and in the case of polylactic acid, Q = 93 J / g.

[0028] [Layer Structure of Extraction Bag Sheet] The extraction bag sheet of the present invention has a spunbond nonwoven fabric layer as its basic component, but may also have a laminated structure (multilayer structure). Figure 2 is a schematic cross-sectional view showing the layer structure of an extraction bag sheet 1 according to one embodiment of the present invention. Note that the layers shown in Figure 2 are simplified for ease of explanation and do not necessarily accurately reflect the relative thicknesses of the layers in the actual extraction bag sheet 1 or the state of the interfaces between the layers. The extraction bag sheet 1 has a multilayer structure in which a meltblown nonwoven fabric layer 3 is laminated on a spunbond nonwoven fabric layer 2. However, the meltblown nonwoven fabric layer 3 has an optional configuration, and the extraction bag sheet of the present invention only needs to have at least the spunbond nonwoven fabric layer 2. The meltblown nonwoven fabric layer 3 functions as an adhesive and prevents powder leakage during bag production. The meltblown nonwoven fabric layer 3 is produced by blowing a high-temperature, high-velocity gas stream onto molten resin extruded from a spinning nozzle, stretching the molten resin and scattering it as it breaks down into fibers, and collecting the resulting fine fibers on a collector to form a web. The resin constituting the meltblown nonwoven fabric layer 3 is preferably a biodegradable resin, polylactic acid resin, similar to that used for the spunbond nonwoven fabric layer 2. By constructing both the spunbond nonwoven fabric layer 2 and the meltblown nonwoven fabric layer 3 from polylactic acid resin, the environmental impact can be reduced, while the laminated structure of the spunbond nonwoven fabric layer 2 and the meltblown nonwoven fabric layer 3 can provide the extraction bag sheet 1 with excellent filter functionality.

[0029] [Method for manufacturing the extraction bag sheet] The extraction bag sheet 1 is manufactured by passing a laminate, in which a meltblown nonwoven fabric layer 3 is laminated on a spunbonded nonwoven fabric layer 2, through a pair of heated nip rolls (not shown). The spinning speed when forming the spunbonded nonwoven fabric is preferably 4000 to 5300 m / min, more preferably 4200 to 4800 m / min. If the spinning speed is within the above range, it is possible to increase the crystallinity of the nonwoven fabric produced by appropriate stretching while suppressing thread breakage during spinning.

[0030] The pair of heated nip rolls used to manufacture the extraction bag sheet 1 can be a combination of two flat rolls, or one may be an embossing roll and the other a flat roll. Here, if the heating temperature of the heated nip roll on the side that comes into contact with the meltblown nonwoven fabric layer 3 is set to a temperature higher than the glass transition temperature Tg of the polylactic acid resin (e.g., Tg + 30°C to 100°C), for example, when the laminate passes through the pair of heated nip rolls, the polylactic acid resin contained in the meltblown nonwoven fabric layer 3 softens, and the meltblown nonwoven fabric layer 3 bites into the spunbond nonwoven fabric layer 2, thereby integrating and bonding the spunbond nonwoven fabric layer 2 and the meltblown nonwoven fabric layer 3.

[0031] [Extraction Bag] The extraction bag sheet of the present invention can be made into a bag by a conventionally known method. For example, the extraction bag of the present invention can be obtained by folding one extraction bag sheet and sealing the edge, or by bonding the edges of two extraction bag sheets together. When making a bag from the extraction bag sheet 1 having the multilayer structure shown in Figure 2, the spunbond nonwoven fabric layer 2 is arranged on the outside and the meltblown nonwoven fabric layer 3 is arranged on the inside.

[0032] Because the extraction bag of the present invention uses the extraction bag sheet of the present invention, shrinkage (boiling water shrinkage rate) when immersed in hot water (about 80°C or higher) can be significantly reduced. As a result, space for extraction is secured in the hot water, allowing for efficient extraction of target substances such as tea leaves. Furthermore, when the extraction bag of the present invention is used for tea bags, etc., the extraction bag remains stable with the spunbond nonwoven fabric layer shrinkage suppressed, so the extraction bag does not undergo significant deformation during use and its appearance does not deteriorate, resulting in high commercial value.

[0033] Next, a manufacturing example of the sheet for extraction bags of the present invention will be described. Table 1 shows the properties (weight average molecular weight (Mw), number average molecular weight (Mn), and molecular weight distribution (Mw / Mn)) of the polylactic acid resin (pellets) used as the raw material.

[0034]

[0035] The properties of the polylactic acid resin (pellets) shown in Table 1 were measured by GPC. The GPC measurement device and measurement conditions are as follows: Device: Gel permeation chromatograph GPC Detector: Differential refractive index detector RI (product name: RI-8020, sensitivity 32, manufactured by Tosoh Corporation) Column: TSKgel GMH ＨＲ -M 2 tubes (manufactured by Tosoh Corporation) Solvent: chloroform Flow rate: 1.0 mL / min Column temperature: 40°C Injection volume: 0.2 mL Standard sample: monodisperse polystyrene (manufactured by Tosoh Corporation)

[0036] Spunbond nonwoven fabrics made of the polylactic acid resins of Examples 1 to 5 were produced by the spunbonding method using the polylactic acid resins (pellets) of Examples 1 to 5 in Table 1. The spunbond nonwoven fabrics of Examples 1 to 5 can be used as extraction bag sheets as they are. Therefore, in the following description, the spunbond nonwoven fabrics will be considered the same as extraction bag sheets and may be referred to as extraction bag sheets (spunbond nonwoven fabrics). The spinning speed during production of the extraction bag sheets (spunbond nonwoven fabrics) in the examples was 4800 m / min. For comparison, the polylactic acid resins (pellets) of Comparative Examples 1 to 4 in Table 1 were used to produce extraction bag sheets (spunbond nonwoven fabrics) made of the polylactic acid resins of Comparative Examples 1 to 4 by the spunbonding method. The spinning speed during production of the extraction bag sheets (spunbond nonwoven fabrics) for the comparative examples was 4,800 m / min for Comparative Examples 1 and 2, 5,500 m / min for Comparative Example 3, and 3,500 m / min for Comparative Example 4.

[0037] Table 2 summarizes the properties and performance of the extraction bag sheets (spunbond nonwoven fabrics) of Examples 1 to 5 and Comparative Examples 1 to 4. The properties of the spunbond nonwoven fabrics in Table 2 (weight average molecular weight (Mw), number average molecular weight (Mn), and molecular weight distribution (Mw / Mn)) were measured by GPC. The GPC measurement device and measurement conditions were the same as those used in the measurement of the polylactic acid resin (pellets) described above.

[0038] The crystallinity of the polylactic acid resin constituting the spunbond nonwoven fabric can be calculated from the above-mentioned formula (1). The heat of crystallization ΔHc and the heat of crystalline fusion ΔHm in formula (1) were measured by DSC. The DSC measurement device and measurement conditions are as follows: Device: Differential scanning calorimeter DSC214Polyma (manufactured by NETZSCH) Atmospheric gas: Nitrogen Measurement temperature: 20 to 200°C Heating rate: 10°C / min

[0039] The boiling water shrinkage of extraction bag sheets (spunbond nonwoven fabric) was measured using the following method. (1) Three 15 cm square test pieces were taken from the nonwoven fabric to be tested. (2) Each test piece was marked with a 10 cm length in three locations in the MD (longitudinal direction) and CD (crosswise direction) as measured at the time of manufacturing the nonwoven fabric. (3) Each test piece was immersed in boiling water for three minutes and allowed to air dry. (4) The length of the marks indicating the length on each test piece was measured to determine the boiling water shrinkage in the MD and CD directions. (5) The average value for the three test pieces was taken to determine the boiling water shrinkage in the MD and CD directions.

[0040] The spinning stability during the production of the extraction bag sheet (spunbond nonwoven fabric) was judged according to the following criteria: A: Less than one thread breakage per hour B: 1 to 3 thread breakages per hour C: 4 or more thread breakages per hour

[0041]

[0042] The extraction bag sheets (spunbond nonwoven fabrics) of Examples 1 to 5 had low boiling water shrinkage in both the MD and CD directions, and were confirmed to be less likely to shrink even when immersed in high-temperature water (hot water). Furthermore, because the spinning speed was appropriately set, the degree of crystallinity was high. The number of yarn breakages per hour during production was less than one or between one and three, demonstrating excellent spinning stability.

[0043] In contrast, the extraction bag sheet (spunbond nonwoven fabric) of Comparative Example 1 used a low-molecular-weight polylactic acid resin, resulting in four or more thread breaks per hour during production and a lack of spinning stability. The extraction bag sheet (spunbond nonwoven fabric) of Comparative Example 2 used a high-molecular-weight polylactic acid resin, resulting in a low degree of crystallinity and a high boiling water shrinkage rate in both the MD and CD directions. The extraction bag sheet (spunbond nonwoven fabric) of Comparative Example 3 used a high-molecular-weight polylactic acid resin, but the spinning speed was increased to increase the crystallinity, resulting in a high number of thread breaks per hour during production, which hindered production. The extraction bag sheet (spunbond nonwoven fabric) of Comparative Example 4 used a polylactic acid resin with an appropriate molecular weight, but the spinning speed was low, resulting in a low degree of crystallinity and a high boiling water shrinkage rate in both the MD and CD directions.

[0044] The extraction bags made from the sheet for extraction bags of the present invention can be suitably used as drip bags for extracting coffee or tea bags for extracting tea, but can also be used as soup stock packs for extracting soup stock from bonito, kelp, etc. Furthermore, the sheet for extraction bags itself, which is not made into a bag, can also be used as a filter, packaging material, etc.

[0045] 1 Extraction bag sheet 2 Spunbond nonwoven fabric layer 3 Meltblown nonwoven fabric layer

Claims

1. A sheet for an extraction bag comprising a spunbond nonwoven fabric layer made of polylactic acid resin, wherein the polylactic acid resin has a weight average molecular weight (Mw) of 5.0 x 10 in terms of polystyrene as determined by gel permeation chromatography (GPC). ４ ~2.0 x 10 ５ A sheet for extraction bags having a crystallinity of 50% or more.

2. A sheet for extraction bags as described in claim 1, wherein the polylactic acid resin has a molecular weight distribution (Mw / Mn) expressed as the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of 3 or less.

3. The sheet for an extraction bag according to claim 1, further comprising a meltblown nonwoven fabric layer laminated to the spunbond nonwoven fabric layer.

4. An extraction bag using the sheet for extraction bags according to any one of claims 1 to 3.

Images