Water-soluble sheet and method for manufacturing a water-soluble sheet

Abstract

To provide a water-soluble sheet that has excellent shock absorption, generates little paper dust, is less likely to cause scratches on packaged items when packaging them, and is suitable for recycling as paper, as well as a method for manufacturing a water-soluble sheet. [Solution] A water-soluble sheet 10 having an embossed surface on at least one surface of a water-soluble airlaid nonwoven fabric 11. A method for manufacturing a water-soluble sheet 10, comprising embossing at least one surface of a water-soluble airlaid nonwoven fabric 11.

Description

[Technical Field]

[0001] This invention relates to a hydrolyzable sheet and a method for producing a hydrolyzable sheet. [Background technology]

[0002] Resin packaging materials are known as packaging materials for items such as home appliances. For example, Patent Document 1 discloses a packaging material having a base layer made of a stretched unidirectional nonwoven fabric obtained by stretching a long-fiber nonwoven fabric spun from a thermoplastic resin in one direction, and a synthetic resin layer laminated on the base layer.

[0003] However, plastic packaging materials are difficult to recycle. Therefore, as packaging materials that can be easily recycled as paper, paper-based packaging materials and packaging materials using water-soluble nonwoven fabrics have been proposed. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2004-351859 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, paper packaging materials have poor shock absorption and a low coefficient of friction, making the packaged items prone to slipping. Furthermore, when the packaging material rubs against the packaged items, scratches are likely to occur. Packaging materials using water-soluble nonwoven fabrics have poor shock absorption. In particular, airlaid nonwoven fabrics tend to generate a lot of paper dust. Also, when the packaging material rubs against the packaged item, the packaged item is prone to scratches.

[0006] The present invention aims to provide a hydrolyzable sheet that is excellent in shock absorption, hardly generates paper dust, hardly causes scratches on the packaged object when packaging the packaged object, and is suitable for recycling as paper, and a method for manufacturing the hydrolyzable sheet.

Means for Solving the Problems

[0007] The present invention has the following aspects. [1] A hydrolyzable sheet in which embossing is performed on at least one surface of a hydrolyzable airlaid nonwoven fabric. [2] The hydrolyzable sheet according to [1], in which the embossing is performed on both surfaces of the hydrolyzable airlaid nonwoven fabric. [3] A method for manufacturing a hydrolyzable sheet, in which embossing is performed on at least one surface of a hydrolyzable airlaid nonwoven fabric. [4] The method for manufacturing a hydrolyzable sheet according to [3], in which the embossing is performed on both surfaces of the airlaid nonwoven fabric.

Effects of the Invention

[0008] According to the present invention, it is possible to provide a hydrolyzable sheet that is excellent in shock absorption, hardly generates paper dust, hardly causes scratches on the packaged object when packaging the packaged object, and is suitable for recycling as paper, and a method for manufacturing the hydrolyzable sheet.

Brief Description of the Drawings

[0009] [Figure 1] It is a perspective view schematically showing an example of the hydrolyzable sheet of the present invention. [Figure 2] It is a photograph showing an example of the hydrolyzable sheet shown in FIG. 1, where (a) is a photograph of the first surface side of the hydrolyzable airlaid nonwoven fabric, and (b) is a photograph of the second surface side of the hydrolyzable airlaid nonwoven fabric. [Figure 3] It is a perspective view schematically showing another example of the hydrolyzable sheet of the present invention. [Figure 4] It is a photograph showing an example of the hydrolyzable sheet shown in FIG. 3, where (a) is a photograph of the first surface side of the hydrolyzable airlaid nonwoven fabric, and (b) is a photograph of the second surface side of the hydrolyzable airlaid nonwoven fabric. [Modes for carrying out the invention]

[0010] Hereinafter, an embodiment of the hydrolyzable sheet and the method for manufacturing the hydrolyzable sheet according to the present invention will be described in detail with reference to Figures 1 to 4 as appropriate. In this specification, a numerical range represented by "~" means a range that includes the numbers before and after the "~" as the lower and upper limits, respectively. For example, A~B is equivalent to A or greater and B or less. Furthermore, the drawings used in the following description may, for convenience, show enlarged versions of key features to make them easier to understand, and the dimensional ratios of each component may differ from those in reality. The materials, dimensions, etc., exemplified in the following description are examples only, and the present invention is not limited to them. It can be implemented with appropriate modifications without changing the essence of the invention. Furthermore, in Figure 3, the same reference numerals are used for components that are the same as those in Figure 1, and their explanations are omitted.

[0011] [Water-soluble sheet] Figures 1-4 show an example of the hydrolyzable sheet 10 of the present invention. The illustrated example of the water-soluble sheet 10 is a sheet made by embossing both sides of a water-soluble airlaid nonwoven fabric (hereinafter also referred to as "nonwoven fabric (X)") 11. In this invention, one surface of the nonwoven fabric (X) 11 is referred to as the first surface 111, and the other surface is referred to as the second surface 112.

[0012] <Non-woven fabric (X)> Nonwoven fabric (X)11 is a water-soluble airlaid nonwoven fabric. The water-soluble sheet 10 is composed of nonwoven fabric (X) 11, which provides excellent shock absorption. Moreover, because the nonwoven fabric (X) 11 is water-soluble, the water-soluble sheet 10 can be easily recycled as paper, resulting in excellent recyclability.

[0013] Here, hydrolytic properties refer to the property of dispersing nonwoven fabric (X)11 in water without retaining its original form, as the entangled pulp fibers loosen when the nonwoven fabric (X)11 is immersed in water and stirred. Furthermore, airlaid nonwoven fabric is a nonwoven fabric in which a web is formed by the airlaid method, which uses airflow to randomly layer the fibers that make up the nonwoven fabric in three dimensions.

[0014] The apparent specific gravity of nonwoven fabric (X)11 is 0.01-0.2 g / cm³. 3 Preferably, 0.02 to 0.15 g / cm³ 3 More preferably, 0.03 to 0.1 g / cm³ 3 This is even more preferable. If the apparent specific gravity of the nonwoven fabric (X) 11 is above the lower limit, it is easier to obtain a water-soluble sheet 10 that can easily disperse impact energy in the planar direction, and damage to the packaged goods can be more easily suppressed. If the apparent specific gravity of the nonwoven fabric (X) 11 is below the upper limit, it is easier to obtain a water-soluble sheet 10 that is easily deformable and can easily absorb impact energy. The apparent specific gravity of nonwoven fabric (X)11 is the specific gravity obtained by dividing the basis weight of nonwoven fabric (X)11 by the thickness of nonwoven fabric (X)11, and is also called the apparent density.

[0015] The thickness of the nonwoven fabric (X) 11 is preferably 0.2 to 3.0 mm, more preferably 0.3 to 2.5 mm, and even more preferably 0.4 to 2.0 mm. If the thickness of the nonwoven fabric (X) 11 is within the above range, it is easier to obtain a water-soluble sheet 10 with improved shock absorption. If the thickness of the nonwoven fabric (X) 11 is below the above upper limit, the overall thickness of the water-soluble sheet 10 does not tend to increase, making it easier to package the items to be packaged. The thickness of nonwoven fabric (X)11 is measured according to JIS L 1913:2010.

[0016] The basis weight of nonwoven fabric (X)11 is 30-200 g / m². 2 Preferably, 35-150 g / m² 2 More preferably, 40-100 g / m 2This is even more preferable. If the basis weight of the nonwoven fabric (X) 11 is equal to or greater than the lower limit, a water-soluble sheet 10 with superior shock absorption is more likely to be obtained. If the basis weight of the nonwoven fabric (X) 11 is equal to or less than the upper limit, the adhesion between the fibers constituting the nonwoven fabric (X) 11 is improved, and the tensile strength is increased. The basis weight of nonwoven fabric (X) is a value measured in accordance with JIS L 1913:2010.

[0017] The hardness of the nonwoven fabric (X) 11 is preferably 60 to 92, more preferably 65 to 90, and even more preferably 70 to 88. If the hardness of the nonwoven fabric (X) 11 is above the lower limit, the thickness does not tend to increase, making it easier to pack the items to be packed. If the hardness of the nonwoven fabric (X) 11 is below the upper limit, it is easier to obtain sufficient cushioning for the items to be packed. The hardness of nonwoven fabric (X)11 is the hardness measured perpendicular to the plane of the nonwoven fabric (X)11, and is a value measured using a Type F durometer.

[0018] The fibers constituting the nonwoven fabric (X) 11 (hereinafter also referred to as "raw material fibers X") can be appropriately selected from known fibers used as raw material fibers for nonwoven fabrics, and are not particularly limited, but hydrophilic fibers are preferred from the viewpoint of improving water solubility. As hydrophilic fibers, cellulose fibers are preferred in terms of handling during manufacturing, strength, cost, and environmental friendliness. Cellulosic fibers include, for example, wood pulp made from coniferous or hardwood; mercerized pulp or cross-linked pulp obtained by chemically treating wood pulp; non-wood pulp such as bagasse, kenaf, bamboo, hemp, and cotton (cotton linters, etc.); regenerated cellulose such as rayon and fibril rayon; and semi-synthetic cellulose such as acetate and triacetate. Examples of wood pulp include mechanical pulp such as crushed wood pulp, refiner ground pulp, thermomechanical pulp, and chemothermetic pulp; chemical pulp such as kraft pulp, sulfide pulp, and alkali pulp; and semi-chemical pulp. Among these, bleached coniferous kraft pulp (NBKP) and bleached hardwood kraft pulp (LBKP) are preferred in terms of strength and handling during manufacturing. These cellulosic fibers may be used individually or in combination of two or more types.

[0019] The nonwoven fabric (X) 11 may contain fibers other than hydrophilic fibers as raw material fiber X. Other types of fibers include natural fibers other than hydrophilic fibers, and fibers made from synthetic resins. Examples of natural fibers other than hydrophilic fibers include animal fibers such as wool (e.g., sheep's wool) and silk, and mineral fibers. Examples of synthetic resin fibers include polyesters such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), nylon (registered trademark), polyethylene (PE), polypropylene (PP), and polylactic acid (PLA). In one respect, it is preferable that the synthetic resin fibers do not melt during the heat treatment in the manufacture of the airlaid nonwoven fabric. These other fibers may be used individually or in combination of two or more. However, it is preferable that the amount of animal fibers, mineral fiber paper, and synthetic resin fibers added be limited to a range that allows for recycling as paper.

[0020] The average fiber diameter of the raw material fiber X is preferably 10 to 60 μm, and more preferably 20 to 40 μm. If the average fiber diameter of the raw material fiber X is above the lower limit, neps are less likely to occur when forming the nonwoven fabric (X) 11, that is, the fibers are less likely to clump together, and a homogeneous hydrolytic sheet 10 can be obtained. If the average fiber diameter of the raw material fiber X is below the upper limit, the nonwoven fabric (X) 11 can be kept at an appropriate softness, and scratches are less likely to occur on the packaged item when it comes into contact with it. The average fiber diameter of raw fiber X is calculated by measuring the fiber diameter of 100 fibers under a microscope and taking the average value of those 100 fibers.

[0021] The average fiber length of the raw material fiber X is preferably 1 to 10 mm, and more preferably 3 to 6 mm. If the average fiber length of the raw material fiber X is above the lower limit, the fibers will intertwine appropriately, providing sufficient strength to the nonwoven fabric (X) 11. If the average fiber length of the raw material fiber X is below the upper limit, it is possible to prevent the fibers from intertwining excessively and forming clumps, which would result in an uneven nonwoven fabric (X) 11. The average fiber length of raw material fiber X is calculated by measuring the fiber length of 100 fibers under a microscope and taking the average value of those 100 fibers.

[0022] Nonwoven fabric (X)11 is manufactured, for example, as follows: First, an air-laid web forming device is used to directly deposit raw fiber X onto a mesh-like endless belt while dispersing it in the air to form a web. Alternatively, a permeable carrier sheet is placed on the endless belt, and an air-laid web forming device is used to deposit raw fiber X onto the permeable carrier sheet while dispersing it in the air to form a web. Next, the raw material fibers X contained in the web are bonded together to obtain a nonwoven fabric (X) 11.

[0023] Examples of methods for bonding the raw material fibers X include the latex bonding method, the thermal bonding method, and the multi-bonding method, which combines the latex bonding method and the thermal bonding method. The latex bonding method involves spraying a binder onto the web, drying it with hot air, and then bonding the fibers together. The thermal bonding method involves supplying heat-fusible resin particles or heat-fusible fibers together with raw material fibers X, and then heat-treating them with hot air or the like to achieve thermal bonding. Nonwoven fabrics manufactured by the latex bonding method have superior water solubility and are easily recycled as paper. Therefore, from the viewpoint of further enhancing the recyclability of the water-soluble sheet 10, the latex bonding method is preferred as the bonding method for the raw material fibers X. In other words, the nonwoven fabric (X) 11 may optionally contain one or more of the following in addition to the raw material fibers X: a binder, a heat-fusible resin, and heat-fusible fibers. As an example of a preferred embodiment, the nonwoven fabric (X) 11 contains the raw material fibers X and a binder.

[0024] As a binder, a water-based binder is preferred from the viewpoint of further enhancing the recyclability of the water-soluble sheet 10. Examples of aqueous binders include water-soluble binders such as casein, sodium alginate, hydroxyethylcellulose, sodium carboxymethylcellulose, polyvinyl alcohol (PVA), and sodium polyacrylate; and emulsion-type binders such as polyacrylic acid esters, acrylic acid ester-styrene copolymers, polyvinyl acetate, ethylene-vinyl acetate copolymer (EVA), acrylonitrile-butadiene copolymer, methyl methacrylate-butadiene copolymer, and styrene-butadiene copolymer latex (SBR). Among these, water-soluble binders, especially water-soluble binders that are difficult or impossible to crosslink with heat, are particularly preferred as aqueous binders because they can be easily separated from the raw material fibers X by dissolving in water when the hydrolyzable sheet 10 is recycled as paper. Examples of water-soluble binders that are difficult or impossible to crosslink with heat include sodium carboxymethylcellulose and polyvinyl alcohol (PVA). These binders may be used individually or in combination of two or more types.

[0025] <Embossing> Both sides of the illustrated nonwoven fabric (X) 11 are embossed. That is, the first surface 111 and the second surface 112 of the nonwoven fabric (X) 11 each have an uneven surface structure composed of a plurality of recesses and protrusions between adjacent recesses. Embossing on at least one surface of the nonwoven fabric (X) 11 enhances its shock absorption. In addition, it reduces the generation of paper dust and minimizes scratches on the packaged items when they are wrapped. In particular, if both sides of the nonwoven fabric (X) 11 are embossed, as in the illustrated example, it tends to further reduce the generation of paper dust and minimize scratches on the packaged items.

[0026] If both sides of the nonwoven fabric (X) 11 are embossed, the recesses 111a of the first surface 111 form the protrusions 112b of the second surface 112, and the protrusions 111b of the first surface 111 form the recesses 112a of the second surface 112. In other words, the recesses 112a of the second surface 112 form the protrusions 111b of the first surface 111, and the protrusions 112b of the second surface 112 form the recesses 111a of the first surface 111. Furthermore, as shown in Figure 1, the top of the protrusion 111b and the bottom of the recess 112a may be flat.

[0027] The embossed pattern is not particularly limited as long as it creates a raised or recessed shape, but examples include the pin pattern shown in Figures 1 and 2(a) and (b), and the polka dot pattern shown in Figures 3 and 4(a) and (b). In addition to these, other embossed patterns may include, for example, vertical line patterns, horizontal line patterns, circle patterns, oval patterns, rectangular patterns, grid patterns, diamond patterns, floral patterns, and letters. Figure 2 is a photograph showing an example of the water-soluble sheet shown in Figure 1. Figure 2(a) is a photograph of the first side of the water-soluble airlaid nonwoven fabric, and Figure 2(b) is a photograph of the second side of the water-soluble airlaid nonwoven fabric. Figure 4 is a photograph showing an example of the water-soluble sheet shown in Figure 3. Figure 4(a) is a photograph of the first side of the water-soluble airlaid nonwoven fabric, and Figure 4(b) is a photograph of the second side of the water-soluble airlaid nonwoven fabric.

[0028] The period of the irregularities is not particularly limited, but for example, the spacing P between adjacent recesses 111a is preferably 2 to 20 mm, and more preferably 2.5 to 10 mm. Also, the depth D of the concave portion 111a, that is, the height difference between the concave portion 111a and the convex portion 111b, is preferably 0.2 to 3 mm, more preferably 0.4 to 2 mm. The same applies to the concavo-convex structure of the second surface 112.

[0029] The interval P between adjacent concave portions 111a is the distance from the center of any concave portion 111a to the center of the concave portion 111a adjacent to it, and is obtained by observing with an optical microscope in a front view. The depth D of the concave portion 111a is obtained by cutting the non-woven fabric (X) 11 in the thickness direction, slicing the cross-section, and observing the sliced cross-section with a scanning electron microscope (SEM).

[0030] In particular, when the embossed pattern is a pin pattern as shown in FIGS. 1 and 2(a), (b), the interval P between adjacent concave portions 111a in the flow direction F of the non-woven fabric (X) 11 f is preferably 2 to 10 mm, more preferably 2.5 to 7 mm. The interval P between adjacent concave portions 111a in the width direction W of the non-woven fabric (X) 11 w is preferably 3 to 15 mm, more preferably 5 to 10 mm. Also, the interval P w / interval P f is preferably 1.2 to 3, more preferably 1.5 to 2.5. When the embossed pattern is a polka dot pattern as shown in FIGS. 3 and 4(a), (b), the interval P between adjacent concave portions 111a in the flow direction F of the non-woven fabric (X) 11 f is preferably 2.5 to 10 mm, more preferably 3 to 7 mm. The interval P between adjacent concave portions 111a in the width direction W of the non-woven fabric (X) 11 w is preferably 2.5 to 10 mm, more preferably 3 to 7 mm. Also, the interval P w / interval P f is preferably 0.8 to 1.5, more preferably 0.9 to 1.3. Here, the flow direction F of the non-woven fabric (X) 11 is the conveyance direction of the non-woven fabric (X) 11 when manufacturing the non-woven fabric (X) 11, that is, the traveling direction of the endless belt used for manufacturing the non-woven fabric (X) 11. The width direction W of the non-woven fabric (X) 11 is the direction orthogonal to the flow direction F.

[0031] <Physical properties of hydrolyzable sheets> The apparent specific gravity of the water-soluble sheet 10 is 0.01 to 0.18 g / cm³. 3 Preferably, 0.02 to 0.14 g / cm³ 3 More preferably, 0.03 to 0.12 g / cm³ 3 This is even more preferable. If the apparent specific gravity of the water-soluble sheet 10 is above the lower limit, it is easier to obtain a water-soluble sheet 10 that can easily disperse impact energy in the planar direction, and damage to the packaged goods can be more easily suppressed. If the apparent specific gravity of the water-soluble sheet 10 is below the upper limit, it is easily deformable and can easily absorb impact energy. The apparent specific gravity of the water-soluble sheet 10 is the specific gravity obtained by dividing the basis weight of the water-soluble sheet 10 by the thickness of the water-soluble sheet 10, and is also called the apparent density.

[0032] The thickness of the water-soluble sheet 10 is preferably 0.25 to 4.0 mm, more preferably 0.3 to 3.5 mm, and even more preferably 0.35 to 3.0 mm. If the thickness of the water-soluble sheet 10 is below the above upper limit, the impact will spread more easily inside the water-soluble sheet 10, further improving the impact absorption. If the thickness of the water-soluble sheet 10 is below the above upper limit, it will be easier to package the items to be packaged. The thickness of the water-soluble sheet 10 is the average thickness of the water-soluble sheet 10 measured from images obtained by microscopic observation of the cross-section of the water-soluble sheet 10 at any three locations where convex portions are formed and at any three locations where concave portions are formed.

[0033] The basis weight of water-soluble sheet 10 is 30-200 g / m². 2 Preferably, 35-150 g / m² 2 More preferably, 40-100 g / m 2 This is even more preferable. If the basis weight of the water-soluble sheet 10 is above the lower limit, it offers a better balance of shock absorption and strength. If the basis weight of the water-soluble sheet 10 is below the upper limit, it maintains strength while providing good workability when packaging the items to be packaged. The basis weight of the water-soluble sheet 10 is a value measured in accordance with JIS L 1913:2010. Furthermore, the basis weight of the water-soluble sheet 10 is the same as that of the nonwoven fabric (X) described above, and the basis weight does not change depending on whether or not it is embossed.

[0034] The hardness of the water-soluble sheet 10 is preferably 60 to 92, more preferably 65 to 90, and even more preferably 70 to 88. If the hardness of the water-soluble sheet 10 is above the lower limit, the thickness does not tend to increase, making it easier to pack the items to be packed. If the hardness of the water-soluble sheet 10 is below the upper limit, it is easier to obtain sufficient cushioning for the items to be packed. The hardness of the hydrolyzable sheet 10 is the hardness measured perpendicular to the plane of the hydrolyzable sheet 10, and is a value measured using a Type F durometer.

[0035] <Method for manufacturing a water-soluble sheet> The water-soluble sheet 10 is obtained by embossing both sides of the nonwoven fabric (X) 11. There are no particular limitations on the embossing method, but for example, when applying a pin pattern embossing as shown in Figures 1 and 2(a) and (b) to both sides of the nonwoven fabric (X) 11, an embossing roll engraved with a pin pattern of the desired period and a roll without an embossing pattern (e.g., an anvil roll) are placed opposite each other, and the nonwoven fabric (X) 11 is sandwiched between these rolls and pressed to obtain a water-soluble sheet 10 in which both sides of the nonwoven fabric (X) 11 are embossed with a pin pattern. Furthermore, for example, when applying a polka dot pattern embossing to both sides of the nonwoven fabric (X) 11 as shown in Figures 3 and 4(a) and (b), a pair of male and female embossing rolls, each engraved with a polka dot pattern so as to interlock, are placed opposite each other, and the nonwoven fabric (X) 11 is sandwiched between these male and female embossing rolls and subjected to a pressing process, thereby obtaining a water-soluble sheet 10 in which the polka dot pattern embossing is applied to both sides of the nonwoven fabric (X) 11. Heating may be applied during the pressing process. The heating temperature is preferably 40 to 100°C.

[0036] <Effects and Effects> As described above, the water-soluble sheet of this embodiment is composed of a water-soluble airlaid nonwoven fabric, and therefore has superior shock absorption compared to paper packaging materials. Moreover, since the airlaid nonwoven fabric is water-soluble, the water-soluble sheet of this embodiment can be recycled as paper, thus having a low environmental impact. Furthermore, since both sides of the airlaid nonwoven fabric are embossed, the water-soluble sheet of this embodiment has superior shock absorption, generates less paper dust, and is less likely to cause scratches on the packaged items when they are wrapped.

[0037] <Application> The water-soluble sheet of the present invention is suitable as a packaging material (also called "packaging material") such as a cushioning material. There are no particular restrictions on the items that can be packaged, but examples include home appliances and electronic components; and food products such as fruits, eggs, and vegetables.

[0038] When using water-soluble sheets as packaging materials, they can be used as sheets as is, or processed into bags before use. Hereafter, water-soluble sheets processed into bags will also be referred to as "water-soluble bags." A water-soluble bag can be manufactured, for example, by folding a single water-soluble sheet and sewing or crimping a pair of edges that extend perpendicular to the fold line formed when the sheet is folded (corresponding to the bottom of the bag). Alternatively, a water-soluble bag may be manufactured by overlapping two water-soluble sheets and sewing or crimping three sides together. Instead of sewing or crimping, it is also possible to weld the sheets together using ultrasonic sealing. When suturing, it is preferable to use water-soluble or hydrolyzable sutures. Commercially available water-soluble or hydrolyzable sutures can be used. The method of compression is not particularly limited, but one example is a method of compression by sandwiching the material between a pair of rolls having irregularities formed on their circumferential surfaces, such as an embossing roll or a knurling roll (also called a "knurled roll"). One of the rolls in the pair may be a roll with a smooth circumferential surface, such as an anvil roll. "Ultrasonic sealing" is a technique that uses the amplitude of ultrasonic vibrations to join materials by sandwiching the material to be welded between an ultrasonic horn that emits vibrational energy via ultrasound and a fixing jig (anvil), applying ultrasonic vibrations while pressurizing the material, and melting and welding the material through heat generated by collision, friction, and deformation. Specifically, a water-soluble sheet is sandwiched between a hemispherical ultrasonic horn and a fixing jig at predetermined locations (such as a pair of edges) so that it forms a bag shape, and the ultrasonic horn is vibrated at a specific frequency (for example, a frequency of 28 kHz), applying ultrasonic vibrations while pressing the predetermined location of the water-soluble sheet, and moving the ultrasonic horn, thereby obtaining a water-soluble bag in which the predetermined location of the water-soluble sheet is melted and welded.

[0039] <Other Embodiments> The hydrolytic sheet of the present invention is not limited to the hydrolytic sheet 10 shown in Figures 1 to 4. For example, the water-soluble sheet 10 shown in Figures 1-4 is composed of one nonwoven fabric (X) 11, but it may be composed of two or more nonwoven fabrics (X) 11. Since the nonwoven fabric (X) 11 is an airlaid nonwoven fabric, the nonwoven fabrics (X) 11 are joined together and integrated by embossing without the need for adhesive.

[0040] Furthermore, although the water-soluble sheet 10 shown in Figures 1-4 is made by embossing both sides of the nonwoven fabric (X) 11, the water-soluble sheet may be made by embossing only one side of the nonwoven fabric (X). A water-soluble sheet, in which a nonwoven fabric (X) is embossed on only one side, can be obtained, for example, by bonding an embossed nonwoven fabric (X) to an unembossed nonwoven fabric (X) with a water-soluble adhesive. Examples of water-soluble adhesives include polyvinyl acetate (PVA) adhesives, cellulose adhesives such as cellulose acetate, and starch adhesives mainly composed of starch. [Examples]

[0041] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Embodiments of the present invention can be modified in various ways without changing the essence of the invention.

[0042] [Non-woven fabric] <Nonwoven fabric (X-1): Water-soluble airlaid nonwoven fabric> Nonwoven fabric (X-1) was manufactured using an airlaid nonwoven fabric machine as follows. On a moving mesh conveyor, pulp fibers obtained by defibrating commercially available bleached softwood kraft pulp (NBKP) using a dry defibration device are dropped and deposited along with an airflow, resulting in a basis weight of 76 g / m². 2 It formed a fiber web. On the fiber web, an aqueous binder A (ethylene vinyl acetate copolymer (EVA)) and polyvinyl alcohol (PVA) are mixed, with a solid content of 3 g / m². 2 The material was sprayed in this manner. Next, the fiber web was passed through a hot air dryer (ambient temperature 170°C) to bond the fibers together. Then, the fiber web was inverted, and the same amount of water-based binder A was sprayed onto the opposite side of the surface where the first layer of binder A had been applied, and then passed through the hot air dryer (ambient temperature 170°C) again, resulting in a basis weight of 80 g / m². 2 We obtained an airlaid nonwoven fabric. The apparent specific gravity of the nonwoven fabric (X-1) is 0.08 g / cm³. 3 The thickness is 1.0 mm and the basis weight is 80 g / m². 2 The hardness was 84.

[0043] <Nonwoven fabric (X-2): Water-soluble airlaid nonwoven fabric> Nonwoven fabric (X-2) was manufactured using an airlaid nonwoven fabric machine as follows. On a moving mesh conveyor, pulp fibers obtained by defibrating commercially available bleached softwood kraft pulp (NBKP) using a dry defibration device are dropped and deposited along with an airflow, resulting in a basis weight of 56 g / m². 2 It formed a fiber web. On the fiber web, an aqueous binder B (carboxymethylcellulose sodium (CMC)) is applied, with a solid content of 4 g / m². 2 The material was sprayed in this manner. Next, the fiber web was passed through a hot air dryer (ambient temperature 170°C) to bond the fibers together. Then, the fiber web was inverted, and the same amount of water-based binder B was sprayed on the opposite side of the surface where the first layer of binder B had been applied, and then passed through the hot air dryer (ambient temperature 170°C) again, resulting in a basis weight of 60 g / m². 2 We obtained an airlaid nonwoven fabric. The apparent specific gravity of the nonwoven fabric (X-2) is 0.10 g / cm³. 3 The thickness is 0.6 mm and the basis weight is 60 g / m². 2 The hardness was 86.

[0044] <Nonwoven fabric (X'-3): Water-soluble spunlace nonwoven fabric> As the nonwoven fabric (X'-3), a commercially available spunlace nonwoven fabric (manufactured by Oji F-Tex Co., Ltd., product name "Texcel Flash") was used. The apparent specific gravity of nonwoven fabric (X'-3) is 0.21 g / cm³. 3 The thickness is 0.3 mm and the basis weight is 52 g / m². 2 The hardness was 89.

[0045] <Kraft paper> Commercially available kraft paper (manufactured by Oji Materia Co., Ltd., product name "OK Unbleached Kraft") was used. The apparent specific gravity of kraft paper is 0.73 g / cm³. 3 The thickness is 0.08 mm and the basis weight is 58 g / m². 2 The hardness was 91.

[0046] [Measurement and Evaluation] <Measuring thickness> The thickness of nonwoven fabrics, kraft paper, and water-soluble sheets was measured in accordance with JIS L 1913:2010.

[0047] <Measurement of basis weight> The basis weight of nonwoven fabrics, kraft paper, and water-soluble sheets was measured in accordance with JIS L 1913:2010.

[0048] <Hardness Measurement> The hardness of nonwoven fabrics, kraft paper, and water-soluble sheets was measured using a Type F durometer (manufactured by Polymer Instruments Co., Ltd., product name "Urethane Foam, Sponge, Nonwoven Fabric Hardness Tester ASKER-F").

[0049] <Evaluation of shock absorption> A single chicken egg was wrapped in a sheet and secured with tape, then dropped from a height of 10 cm onto a lauan wood board (18 mm thick). The appearance of the egg after the drop was visually observed, and its impact absorption was evaluated based on the following evaluation criteria. ○: No cracks were observed in the chicken egg after it was dropped, and no leakage of egg white was seen. ×: Cracks were observed in the chicken egg after it was dropped, and egg white leakage was visible.

[0050] <Evaluation of recyclability> The sheets were cut to 100mm and their water-soluble properties were confirmed in accordance with the "ease of disintegration" described in JIS P 4501:1993 for "toilet paper". Furthermore, after disintegrating the water-soluble sheets using a disintegrator, papermaking was performed using the disintegrated raw materials. Papermaking properties were confirmed, and the presence or absence of paper fiber aggregates (flocs) after papermaking was visually inspected. Recyclability was evaluated based on the following evaluation criteria. ○: The paper dissolves in water (ease of breaking down) within 100 seconds, and there are no holes or foreign objects in the handmade paper. ×: The water-soluble (ease of disintegration) is more than 100 seconds, or holes appear in the hand-made paper, or aggregated flocs of 1 mm square or larger are observed.

[0051] <Evaluation of paper dust> Five sheets were stacked and cut into 100mm squares using a commercially available utility knife. The amount of paper dust generated was visually observed while holding the corner of the stacked five sheets in the hand and shaking it back and forth 10 times, and the amount of paper dust generated was evaluated based on the following evaluation criteria. ○: No paper dust was observed. ×: Paper dust generation is observed.

[0052] <Evaluation of resistance to damage> A sheet was pressed against the surface of an acrylic sheet (manufactured by AcrySunday Co., Ltd., product name "AcrySunday Sheet IS432 Reinforced Milky White Semi-Transparent 1mm"), and a JSPS-type colorfastness test was conducted using a JSPS-type colorfastness tester (manufactured by Yasuda Seiki Seisakusho Co., Ltd.) in accordance with JIS L 0849:2013. The surface condition of the acrylic sheet (presence or absence of scratches) after 100 back-and-forth rubs was visually observed, and the resistance to damaging the packaged goods was evaluated based on the following evaluation criteria. ○: No abrasions were observed. △: Slight scratches are present, but this does not affect practical use. ×: Scratches are observed.

[0053] [Example 1] An embossed roll with a pin pattern engraved on it and an anvil roll without an embossed pattern were placed opposite each other, and the nonwoven fabric (X-1) was sandwiched between these rolls. The fabric was then pressed under a pressure of 2 MPa while being heated to 60°C, resulting in a water-soluble sheet with a pin pattern embossed on both sides of the nonwoven fabric (X-1), as shown in Figures 1 and 2(a) and (b). The spacing P between adjacent recesses 111a f The distance is 4.5 mm, and the distance P between adjacent recesses 111a is w It was 8mm. The obtained hydrolytic sheets were measured for thickness, basis weight, and hardness, and their apparent specific gravity was determined. Impact absorption, recyclability, paper dust, and scratch resistance were also evaluated. The results are shown in Table 1.

[0054] [Example 2] A hydrolyzable sheet was manufactured in the same manner as in Example 1, except that nonwoven fabric (X-2) was used instead of nonwoven fabric (X-1). The obtained hydrolytic sheets were measured for thickness, basis weight, and hardness, and their apparent specific gravity was determined. Impact absorption, recyclability, paper dust, and scratch resistance were also evaluated. The results are shown in Table 1.

[0055] [Example 3] A pair of male and female embossing rolls, each engraved with a polka dot pattern so that they interlock, were placed opposite each other. A nonwoven fabric (X-1) was sandwiched between these male and female embossing rolls and pressed under a pressure of 2 MPa while being heated to 60°C, resulting in a water-soluble sheet with a polka dot pattern embossed on both sides of the nonwoven fabric (X-1), as shown in Figures 3 and 4(a) and (b). The spacing P between adjacent recesses 111a f The distance is 5.2 mm, and the distance P between adjacent recesses 111a is w The length was 5.7 mm, and the depth D of the recess 111a was 1.2 mm. The obtained hydrolytic sheets were measured for thickness, basis weight, and hardness, and their apparent specific gravity was determined. Impact absorption, recyclability, paper dust, and scratch resistance were also evaluated. The results are shown in Table 1.

[0056] [Example 4] A hydrolyzable sheet was manufactured in the same manner as in Example 3, except that nonwoven fabric (X-2) was used instead of nonwoven fabric (X-1). The obtained hydrolytic sheets were measured for thickness, basis weight, and hardness, and their apparent specific gravity was determined. Impact absorption, recyclability, paper dust, and scratch resistance were also evaluated. The results are shown in Table 1.

[0057] [Comparative Example 1] The sheet was manufactured in the same manner as in Example 1, except that nonwoven fabric (X'-3) was used instead of nonwoven fabric (X-1). The thickness, basis weight, and hardness of the obtained sheets were measured, and the apparent specific gravity was determined. Impact absorption, recyclability, paper dust, and scratch resistance were also evaluated. The results are shown in Table 2.

[0058] [Comparative Example 2] The sheet was manufactured in the same manner as in Example 3, except that nonwoven fabric (X'-3) was used instead of nonwoven fabric (X-1). The thickness, basis weight, and hardness of the obtained sheets were measured, and the apparent specific gravity was determined. Impact absorption, recyclability, paper dust, and scratch resistance were also evaluated. The results are shown in Table 2.

[0059] [Comparative Example 3] A water-soluble sheet was manufactured in the same manner as in Example 1, except that kraft paper was used instead of nonwoven fabric (X-1). The obtained hydrolytic sheets were measured for thickness, basis weight, and hardness, and their apparent specific gravity was determined. Impact absorption, recyclability, paper dust, and scratch resistance were also evaluated. The results are shown in Table 2.

[0060] [Comparative Example 4] A water-soluble sheet was manufactured in the same manner as in Example 3, except that kraft paper was used instead of nonwoven fabric (X-1). The obtained hydrolytic sheets were measured for thickness, basis weight, and hardness, and their apparent specific gravity was determined. Impact absorption, recyclability, paper dust, and scratch resistance were also evaluated. The results are shown in Table 2.

[0061] [Comparative Example 5] The nonwoven fabric (X-1) was used as a water-soluble sheet, and its impact absorption, recyclability, paper dust reduction, and scratch resistance were evaluated. The results are shown in Table 2.

[0062] [Comparative Example 6] The nonwoven fabric (X-2) was used as a water-soluble sheet, and its impact absorption, recyclability, paper dust reduction, and scratch resistance were evaluated. The results are shown in Table 2.

[0063] [Table 1]

[0064] [Table 2]

[0065] As is clear from the results in Table 1, the hydrolytic sheets obtained in Examples 1-4 exhibited excellent shock absorption and recyclability as paper. Furthermore, they generated minimal paper dust and were less likely to damage the packaged items. On the other hand, as is clear from the results in Table 2, the hydrolyzable sheets obtained in Comparative Examples 1 and 2, which used hydrolyzable spunlace nonwoven fabric, had poor shock absorption. Furthermore, the fiber length of the raw material fibers in spunlace nonwoven fabric is about 10 to 50 mm, which is longer than the typical fiber length of 1 to 5 mm for wood pulp, the raw material for paper. Since the longer fiber length of the raw material fibers causes problems when mixed in during the papermaking process, it also had poor recyclability. The water-soluble sheets obtained in Comparative Examples 3 and 4, which used kraft paper, had poor shock absorption and were prone to damaging the packaged items. In Comparative Examples 5 and 6, the water-soluble sheets obtained from water-soluble airlaid nonwoven fabrics without embossing exhibited poor shock absorption, were prone to generating paper dust, and easily damaged the packaged items. [Explanation of Symbols]

[0066] 10 Water-soluble sheets 11. Water-soluble airlaid nonwoven fabric 111 First side 112 Second side 111a Recess 111b protrusion 112a Recess 112b protrusion

Claims

1. A water-soluble sheet comprising a water-soluble airlaid nonwoven fabric with an embossed surface on at least one surface.

2. The water-soluble sheet according to claim 1, wherein the embossing is applied to both sides of the water-soluble airlaid nonwoven fabric.

3. A method for manufacturing a water-soluble sheet, comprising embossing at least one surface of a water-soluble airlaid nonwoven fabric.

4. A method for manufacturing a water-soluble sheet according to claim 3, wherein the embossing process is applied to both sides of the airlaid nonwoven fabric.

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