JP2024017554A - Packing sheet manufacturing method and packing sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a packing sheet manufacturing method capable of easily controlling an inner structure and a packing sheet made by the manufacturing method.

SOLUTION: A method for manufacturing a packing sheet S has an accumulation step S12 to produce a web W in which a plurality of first fibers 23A and a plurality of second fibers 23B having a core part 231 and a thermoplastic coating layer 232 for coating the core part 231 are mixed, a heating step S13 to fuse the coating layer 232 by heating the web W, and a pressurizing and cooling step S14 to bond contact points of the second fibers 23B to each other with the coating layer 232 by pressurizing and cooling the web W with the coating layer 232 in a fused state.

SELECTED DRAWING: Figure 5

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a method for manufacturing a packaging sheet and a packaging sheet.

Conventionally, packaging sheets containing natural fibers such as cellulose fibers and resin have been known. For example, Patent Document 1 discloses a plate-shaped fiber base material that includes natural fibers, synthetic resin, and the like, and the content of each material changes in the thickness direction.

JP 2017-48475 Publication

However, the fiber base material described in Patent Document 1 has a problem in that it is difficult to easily control the internal structure. Specifically, in order to form a structure in which the ratio of the content of each material changes, the fiber aggregate is produced by depositing each material so that the ratio of the content gradually changes. This method tends to increase takt time and complicate the manufacturing process, which may affect manufacturing costs. That is, there has been a need for a method of manufacturing a packaging sheet that allows easy control of the internal structure.

A method for producing a packaging sheet includes producing a stacked fiber body in which a plurality of first fibers, which are natural fibers, and a plurality of second fibers having a core and a thermoplastic coating layer covering the core are mixed. a heating step of heating the deposited fibrous body to melt the coating layer; compressing and cooling the deposited fibrous body in a state where the coating layer is molten to form a contact point between the second fibers; The method is characterized by comprising a pressurized cooling step of consolidating the two by the coating layer.

The packaging sheet includes a plurality of first fibers that are natural fibers, a plurality of second fibers having a core and a thermoplastic coating layer covering the core, and the coating layer is melted by heating. The second fibers are compressed and cooled, so that the contact points between the second fibers are bound by the coating layer.

FIG. 2 is a schematic enlarged view of a packaging sheet according to an embodiment. FIG. 2 is a cross-sectional view taken along line AA in FIG. 1. FIG. 2 is a cross-sectional view taken along line BB in FIG. 1. FIG. 3 is a schematic cross-sectional view showing the internal structure of a packing sheet. A flow diagram showing a method for manufacturing a packing sheet. FIG. 1 is a schematic diagram showing the configuration of a packaging sheet manufacturing device. Graph showing the relationship between web density and temperature increase time. FIG. 2 is a block diagram showing the configuration of a first roll, a second roll, and the like. The schematic side view which shows the content of a pressurized cooling process.

In the embodiment described below, a packaging sheet S containing natural fibers and a method for manufacturing the same will be exemplified and explained with reference to the drawings. In each of the following figures, XYZ axes as coordinate axes are attached as necessary, the direction pointed by the arrow is defined as the + direction, and the direction opposite to the + direction is defined as the - direction. The +Z direction is sometimes referred to as upward, and the -Z direction is sometimes referred to as downward. Note that in FIG. 6, the -Z direction coincides with the vertical direction.

Further, for convenience of illustration, the size of each member is made different from the actual size. In the packaging sheet S manufacturing apparatus 10, the end of the web W, which is a stacked fiber body, the packaging sheet S, etc. in the conveyance direction is sometimes referred to as downstream, and the side further back in the conveyance direction is sometimes referred to as upstream. In the web W and the packaging sheet S, the thickness is the distance along the Z-axis, and the thickness direction is the direction along the Z-axis.

1. Packing Sheet The packaging sheet S according to the present embodiment is manufactured by a method for manufacturing a packaging sheet S that will be described later. As shown in FIG. 1, the packing sheet S includes a plurality of first fibers 23A and a plurality of second fibers 23B as raw materials. The plurality of first fibers 23A and the plurality of second fibers 23B are not oriented in a specific direction but are intertwined with each other. The points of contact between the first fibers 23A and the second fibers 23B and the points of contact between the second fibers 23B are bound by a covering layer 232, which will be described later, of the second fibers 23B. The first fiber 23A has one or more contact points with the second fiber 23B. The second fiber 23B also has one or more contact points with the first fiber 23A or other second fibers 23B. The contact points between the first fibers 23A are not bound together, but there are one or more contact points. As described above, in the packing sheet S, the plurality of first fibers 23A and the plurality of second fibers 23B are in contact with each other.

The packaging sheet S has flexibility and strength derived from the above configuration. Examples of items to be packed in the packing sheet S include wristwatches, laptop computers, small game consoles, smartphones, printers, information terminal devices such as projectors, precision parts, models, ceramics, porcelain, glassware, home appliances, fruits and vegetables, etc. can be mentioned.

The first fiber 23A is a natural fiber. In this embodiment, cellulose fibers are used as the first fibers 23A. Cellulose fiber is derived from plants, is a relatively abundant natural material, and is relatively inexpensive and easily available.

Cellulose fibers are obtained by subjecting raw materials such as paper, cardboard, pulp, pulp sheets, sawdust, planer scraps, and wood to a fibrillation process. Cellulose fibers are primarily made of cellulose, but may contain components other than cellulose. Examples of components other than cellulose include hemicellulose and lignin.

The average fiber length of the first fibers 23A is preferably 10 μm or more and 50 mm or less, more preferably 20 μm or more and 5 mm or less. According to this, the plurality of first fibers 23A and the plurality of second fibers 23B become easily entangled, and the mechanical properties such as the strength of the packing sheet S can be improved. The average fiber length of the first fiber 23A and the second fiber 23B is measured by the staple diagram method.

As shown in FIG. 2, the second fiber 23B has a core 231 and a coating layer 232 that covers the core 231. The covering layer 232 has thermoplasticity and is melted by heating during the manufacturing process of the packaging sheet S, which will be described later. FIG. 2 shows a state in which the contact points between the first fibers 23A and the second fibers 23B are bonded by the melted and solidified covering layer 232.

Core portion 231 is an organic fiber. Examples of organic fibers include natural fibers such as the cellulose fibers mentioned above, and synthetic fibers such as polyester and rayon. In this embodiment, polyethylene terephthalate is used as the core portion 231. Polyethylene terephthalate has advantages such as relatively high heat resistance due to its crystallinity and ease of reuse from PET bottles.

Covering layer 232 is a thermoplastic resin. Examples of the thermoplastic resin include polyethylene, polypropylene, polyvinyl chloride, polyurethane, polystyrene, acrylic resin, and polyvinyl acetate. In this embodiment, polyethylene is used as the covering layer 232. The average molecular weight of polyethylene can be easily changed during the manufacturing stage, and the melting point can be set relatively freely.

The melting point of the covering layer 232 is preferably about 20° C. lower than the melting point of the core portion 231. This makes it easy to melt the covering layer 232 without melting the core portion 231 when manufacturing the packaging sheet S. The melting point of the coating layer 232 is preferably 100°C or more and 200°C or less, more preferably 100°C or more and 150°C or less. The melting point of the coating layer 232 is measured according to JIS K 0064:1992 (method for measuring melting point and melting range of chemical products).

The average fiber length of the second fibers 23B, that is, the average fiber length of the core portion 231, is preferably 100 μm or more and 50 mm or less, particularly preferably about 1 mm. According to this, the plurality of second fibers 23B are easily entangled with the plurality of first fibers 23A, and the mechanical properties such as the strength of the packing sheet S can be improved.

The ratio of the diameter D1 of the core portion 231 to the thickness E1 of the coating layer 232 is, for example, preferably 0.2 or more and 2.0 or less, and more preferably 0.5 or more and 1.5 or less. Thereby, in the heating process during manufacturing of the packaging sheet S, the covering layer 232 can be melted and solidified while suppressing deformation of the core portion 231.

As shown in FIG. 3, the covering layer 232 also binds the contact points between the second fibers 23B. The contact points between the second fibers 23B are bonded by the covering layers 232 that are melted and solidified by heating during the manufacturing process. Since the above-described contact points between the first fibers 23A and the second fibers 23B and the contact points between the second fibers 23B are bound by the covering layer 232, the shape of the packaging sheet S is easily maintained. Moreover, the cushioning performance and strength of the packing sheet S are improved.

As shown in FIG. 4, the packaging sheet S has a sheet shape in which the main surface in the +Z direction and the main surface in the -Z direction lie along the XY plane. The interior of the packaging sheet S has a density gradient due to the manufacturing method described below. Specifically, relatively low-density regions L1 are formed near the main surface in the +Z direction and near the main surface in the -Z direction. A relatively high-density region L2 is formed at the center of the principal surface in the direction along the Z-axis. Between the region L1 and the region L2, the density gradually increases from the region L1 to the region L2.

The density gradient inside the packing sheet S is due to the amount of voids between the plurality of first fibers 23A and the plurality of second fibers 23B. That is, the region L1 has a structure in which there are relatively more voids than the region L2. In addition, in FIG. 4, the level of density is expressed by gradation.

2. Packing Sheet Manufacturing Method As shown in FIG. 5, the packaging sheet S manufacturing method according to the present embodiment includes a mixing step S11, a depositing step S12, a heating step S13, a pressurized cooling step S14, and a cutting step S15.

In the method for manufacturing the packaging sheet S, the packaging sheet S is manufactured through each process in the above order from the upstream mixing process S11 to the downstream cutting process S15. Note that the method for manufacturing a packaging sheet of the present invention includes a deposition step S12, a heating step S13, and a pressurized cooling step S14, and the other steps are not limited to the above. Moreover, the packaging sheet of the present invention may be wound into a roll, stored, and sold after the pressurized cooling step S14 has been completed and the cutting step S15 has not been completed.

A specific example of the method for manufacturing the packaging sheet S will be described together with the packaging sheet S manufacturing apparatus 10. The packaging sheet S manufacturing apparatus 10 according to the present embodiment is an example, and is not limited thereto.

As shown in FIG. 6, the manufacturing apparatus 10 includes, from upstream to downstream, a mixing section 11, a depositing section 100, a web conveying section 120, a humidifying section 130, a heating section 140, and a pair of rolls 150 serving as a heating and cooling section. , a cutting section 160, and a tray 170 which is a storage section. Although not shown, the manufacturing apparatus 10 also includes an apparatus control section that integrally controls the operation of each of the above components.

In the mixing section 11, a mixing step S11 is performed. The mixing unit 11 mixes the first fibers 23A, the second fibers 23B, etc. in the air to generate a mixture. The mixing section 11 includes a tubular main body 60, hoppers 13 and 14 connected to the main body 60, supply pipes 61 and 62, and valves 65 and 66.

The hopper 13 communicates with the inside of the main body part 60 via a supply pipe 61. In the supply pipe 61 , a valve 65 is provided between the hopper 13 and the main body 60 . The hopper 13 supplies the first fibers 23A into the main body 60. The valve 65 adjusts the mass of the first fibers 23A supplied from the hopper 13 to the main body portion 60.

The hopper 14 communicates with the interior of the main body portion 60 via a supply pipe 62 . In the supply pipe 62, a valve 66 is provided between the hopper 14 and the main body 60. The hopper 14 supplies the second fibers 23B into the main body portion 60. The valve 66 adjusts the mass of the second fibers 23B supplied from the hopper 14 to the main body portion 60. The valves 65 and 66 adjust the mixing ratio of the first fibers 23A and the second fibers 23B.

Specifically, the mixture containing the first fibers 23A and the second fibers 23B becomes a web W, which is a deposited fiber body, in a depositing section 100, which will be described later. In the web W, the content of the second fibers 23B relative to the content of the first fibers 23A is preferably 12.0% by mass or more and 40.0% by mass or less, and 14.0% by mass or more and 25.0% by mass. It is more preferable that it is below. Thereby, the mechanical properties such as the strength of the packaging sheet S can be improved while suppressing the content of the coating layer 232 of the second fibers 23B.

Here, the second fibers 23B are produced by a separately known device and are supplied to the hopper 14. Alternatively, a heating kneader may be disposed upstream of the hopper 14, and the second fibers 23B produced by the heating kneader may be supplied to the hopper 14. In the heating kneader, a coating layer 232 is formed on the core portion 231 .

Note that as the core portion 231 of the first fiber 23A and the second fiber 23B, fibers made by subjecting waste paper, old cloth, etc. to a fibrillation process may be used. Further, additives may also be supplied from either of the hoppers 13 and 14 and contained in the web W. Examples of additives include colorants, flame retardants, insect repellents, fungicides, antioxidants, ultraviolet absorbers, aggregation inhibitors, and mold release agents.

The first fibers 23A, the second fibers 23B, and the like are mixed while being conveyed within the main body portion 60 to the depositing portion 100 to form a mixture. A blower or the like that generates airflow may be disposed in the main body 60 in order to promote mixture production in the main body 60 and improve transportability of the mixture. The mixture is conveyed to the deposition section 100 via the main body section 60. Then, the process proceeds to the deposition step S12.

In the deposition section 100, a deposition step S12 is performed. The deposition unit 100 deposits the mixture in the air to produce a web W in which the plurality of first fibers 23A and the plurality of second fibers 23B are mixed. The deposition section 100 includes a drum section 101. The deposition section 100 has a substantially box-like shape with an open bottom, and a drum section 101 is disposed above the inside. The deposition section 100 takes the mixture from the main body section 60 into the drum section 101 and deposits it on the mesh belt 122 in a dry manner.

A web conveying section 120 including a mesh belt 122 and a suction mechanism 110 is arranged below the depositing section 100 . The suction mechanism 110 faces the drum section 101 with the mesh belt 122 in between in the direction along the Z-axis.

The drum section 101 is a cylindrical sieve that is rotationally driven by a motor (not shown). A mesh having a sieve function is provided on the side surface of the cylindrical drum portion 101. The drum section 101 allows particles such as fibers and mixtures smaller than the opening size of the sieve mesh to pass from the inside to the outside. The tangled fibers of the mixture are loosened by the drum section 101 and dispersed in the air within the deposition section 100.

The first fibers 23A, the second fibers 23B, and the like are dispersed in the air within the deposition section 100 and randomly deposited on the mesh belt 122. Therefore, in the web W, it becomes difficult for the first fibers 23A and the second fibers 23B to be oriented in a specific direction.

The sieve in the drum section 101 does not need to have the function of sorting out large fibers in the mixture. That is, the drum section 101 may loosen the fibers of the mixture and release all of the mixture into the interior of the deposition section 100. The mixture dispersed in the air in the deposition section 100 is deposited above the mesh belt 122 by gravity and suction by the suction mechanism 110.

The web conveyance section 120 includes a mesh belt 122 and a suction mechanism 110. The web transport section 120 promotes deposition of the mixture onto the mesh belt 122 by means of the suction mechanism 110 . Further, the web transport unit 120 transports the web W formed from the mixture downstream by rotation of the mesh belt 122.

The suction mechanism 110 is arranged below the drum section 101. The suction mechanism 110 sucks air within the deposition section 100 through the plurality of holes that the mesh belt 122 has. As a result, the mixture discharged to the outside of the drum section 101 is sucked downward together with air and deposited on the upper surface of the mesh belt 122. The suction mechanism 110 employs a known suction device such as a blower.

The plurality of holes in the mesh belt 122 allow air to pass through, but it is difficult for the first fibers 23A, second fibers 23B, etc. contained in the mixture to pass therethrough. The mesh belt 122 is an endless belt, and is stretched by three tension rollers 121.

The upper part of the mesh belt 122 moves downstream due to the rotation of the tension roller 121. In other words, the mesh belt 122 rotates clockwise in FIG. 6 . When the mesh belt 122 is rotated by the tension roller 121, the mixture is continuously deposited to form the web W. The web W contains a relatively large amount of air and is soft and swollen. The web W is conveyed downstream as the mesh belt 122 moves.

Among the three tension rollers 121, a scraper 123 is attached below the tension roller 121 that is arranged furthest in the +X direction. The scraper 123 contacts the surface of the mesh belt 122 that has finished conveying the web W. The mixture remaining on the surface of the mesh belt 122 is removed by contacting the scraper 123 while rotating.

A humidifying section 130 is arranged downstream of the deposition section 100. The humidifier 130 sprays water onto the web W on the mesh belt 122 to humidify it. This suppresses scattering of the first fibers 23A, second fibers 23B, etc. contained in the web W. Alternatively, a water-soluble additive or the like may be included in the water used for humidification, and the web W may be impregnated with the additive in parallel with humidification.

The web W is conveyed downstream by the mesh belt 122 and peeled off from the mesh belt 122. Then, it is drawn into the heat radiation section 143 of the heating section 140 by the conveyance roller 147 of the heating section 140 . Then, the process advances to heating step S13.

The heating step S13 is performed using the heating section 140. The heating unit 140 heats the web W drawn into the interior to a temperature higher than the melting point of the coating layer 232 of the second fibers 23B, thereby melting the coating layer 232. The heating section 140 includes a heat source section 141 , a heat radiation section 143 , and an air blowing section 145 .

The heat radiation section 143 has a substantially box shape, and stores the heat source section 141 and the air blowing section 145 above the inside. Below the heat radiation section 143, the web W is conveyed from the -X direction to the +X direction.

The heat source section 141 is arranged above the heat radiation section 143 and faces the web W with the air blowing section 145 in between. The heat source section 141 radiates heat downward within the heat radiating section 143. The heat source section 141 is, for example, a heating device such as an infrared heater.

The blower section 145 blows the heat generated by the heat source section 141 to the web W moving below within the heat radiation section 143 . The web W is heated in a non-contact manner while being conveyed within the heat radiation section 143. Therefore, temperature deviation is less likely to occur in the web W, and deterioration due to insufficient heating or uneven distribution of heat can be suppressed. Note that the conveyance roller 147 may be an endless belt.

The heating temperature of the web W in the heating section 140 is appropriately set based on the melting point of the first fiber 23A, the melting point of the core 231 of the second fiber 23B, and the melting point of the coating layer 232. That is, in the heating section 140, the temperature of the web W is set to be higher than or equal to the melting point of the coating layer 232, lower than the melting point of the first fibers 23A, and lower than the melting point of the core section 231. For example, when the melting point of the core 231 is 260°C and the melting point of the coating layer 232 is 125°C, the web W is heated to 190°C.

Here, we will discuss the advantage of not applying heat and pressure to the web W at the same time using a hot press or the like. The web W is formed by mixing and depositing the first fibers 23A, the second fibers 23B, and the like. Therefore, the web W reaching the heating section 140 is not pressurized, contains a relatively large amount of air, and has a low density.

For samples with different thicknesses and densities of the web W, the time required to raise the temperature from 25° C. to 150° C. was measured by heating with an infrared heater. The results are shown in FIG.

As shown in FIG. 7, regardless of whether the web W has a thickness of 10 mm or 20 mm, the lower the density, the shorter the heating time. That is, by heating the web W in a state where the density is relatively low, the heating efficiency can be improved and the energy required for heating can be reduced. Then, the process proceeds to the pressurized cooling step S14.

Returning to FIG. 6, in the pressurized cooling step S14, the web W is compressed and cooled while the coating layer 232 is in a molten state. As a result, the contact points between the first fibers 23A and the second fibers 23B and the contact points between the second fibers 23B are bound by the covering layer 232.

The web W produced in the deposition step S12 is continuously subjected to a heating step S13 to a pressure cooling step S14. Thereby, since the coating layer 232 is proceeded to the pressurized cooling step S14 while being molten, the molten state of the coating layer 232 is easily maintained. That is, the temperature of the web W becomes difficult to decrease, and the energy consumed for heating in the heating step S13 can be reduced.

In the pressurized cooling step S14, the web W is passed between the pair of rolls 150 using a pair of rolls 150. The pair of rolls 150 is a pair of rotary rollers, and includes a cylindrical first roll 151 and a cylindrical second roll 152. In the pressurized cooling step S14, the first roll 151 is placed above the web W, and the second roll 152 is placed below the web W.

This provides cooling and compression from the upper and lower facing surfaces of the web W. By compressing and cooling the coating layer 232 in a state in which it is melted by heating, the contact points between the first fibers 23A and the second fibers 23B and the contact points between the second fibers 23B are connected by the coating layer 232. It will be worn. Therefore, continuous processing can be performed more easily than, for example, when using a pressure press.

The web W that has undergone the pressurized cooling step S14 becomes a continuous form-shaped packaging sheet S. The thickness of the continuous form-shaped packaging sheet S is reduced by 10% or more compared to the thickness of the web W before passing through the pressure cooling step S14. That is, the thickness is compressed by 10% or more by passing between the pair of rolls 150 in the pressurized cooling step S14. Therefore, the above-mentioned region L1 and region L2 can be more clearly expressed. The detailed configuration and functions of the pair of rolls 150 will be described later. Then, the process proceeds to cutting step S15.

In the cutting section 160, a cutting step S15 is performed. The cutting unit 160 cuts the continuous form-shaped packaging sheet S into a desired shape. Although not shown, the cutting section 160 includes a vertical blade and a horizontal blade.

The vertical blade cuts, for example, the continuous form-shaped packaging sheet S along the X-axis. The horizontal blade cuts, for example, the continuous form-shaped packaging sheet S along the Y-axis. As a result, a substantially rectangular plate-shaped packaging sheet S is manufactured and stored in the tray 170.

3. Pressurized Cooling Step As described above, the pair of rolls 150 of the manufacturing apparatus 10 includes the first roll 151 and the second roll 152. As shown in FIG. 8, the first roll 151 includes a first cooling section 155 and a first control section 153. The second roll 152 has a second cooling section 156 and a second control section 154. Although not shown, the first control unit 153 and the second control unit 154 each include a CPU (Central Processing Unit), a system bus, a ROM (Read Only Memory), a RAM (Random Access Memory), and the like.

The first cooling unit 155 is electrically connected to the first control unit 153. The first cooling unit 155 adjusts the temperature of the first roll 151. That is, the first cooling unit 155 cools the web W from above by making the temperature of the surface of the first roll 151 in contact with the web W lower than room temperature under the control of the first control unit 153. Here, in this specification, normal temperature is 15°C to 30°C.

The first control section 153 includes a first temperature measurement section 157 that measures the above-mentioned surface temperature of the first roll 151. The temperature measured by the first temperature measurement section 157 is calculated by the first control section 153, and the operation of the first cooling section 155 is adjusted according to the calculation result. Thereby, the surface of the first roll 151 reaches a desired temperature.

The second cooling unit 156 is electrically connected to the second control unit 154 . The second cooling unit 156 adjusts the temperature of the second roll 152. That is, the second cooling unit 156 cools the web W from below by making the temperature of the surface of the second roll 152 in contact with the web W lower than room temperature under the control of the second control unit 154.

The second control section 154 includes a second temperature measurement section 158 that measures the above-mentioned surface temperature of the second roll 152. The temperature measured by the second temperature measurement section 158 is calculated by the second control section 154, and the operation of the second cooling section 156 is adjusted according to the calculation result. This brings the surface of the second roll 152 to a desired temperature.

A known cooling device can be applied to the first cooling unit 155 and the second cooling unit 156. In this embodiment, Peltier elements are used as the first cooling unit 155 and the second cooling unit 156.

The first control section 153 and the second control section 154 are controlled by the third control section 210 of the external device 200 for the manufacturing apparatus 10. The third control section 210 is electrically connected to the first control section 153 and the second control section 154. Although not shown, the third control section 210 has a function of adjusting the gap between the first roll 151 and the second roll 152 along the Z axis via the first control section 153 and the second control section 154. . Thereby, the compressive force on the web W is adjusted. External device 200 is, for example, an information terminal device such as a personal computer.

The third control unit 210 includes a third temperature measurement unit 213 that measures the temperature of the web W that proceeds to the pressurized cooling step S14. Note that the third control section 210 may be included in the above-described device control section included in the manufacturing apparatus 10.

Based on the temperature of the web W measured by the third temperature measurement section 213, the third control section 210 instructs the first control section 153 and the second control section 153 to correct the surface temperature of the first roll 151 and the surface temperature of the second roll 152. 2 to the control unit 154.

According to the above, each temperature of the first roll 151, the second roll 152, and the web W is measured individually. Therefore, each temperature can be precisely controlled. A known thermometer is applied to the first temperature measurement section 157, the second temperature measurement section 158, and the third temperature measurement section 213. For example, a thermocouple is applied to the first temperature measurement section 157 and the second temperature measurement section 158, and a non-contact type temperature sensor is applied to the third temperature measurement section 213.

As shown in FIG. 9, the web W heated in the heating step S13 reaches a pair of rolls 150. The temperature of the web W is measured by the third temperature measuring section 213 immediately before the pair of rolls 150 . The web W is then drawn between the first roll 151 and the second roll 152.

When viewed from the side in the −Y direction, the first roll 151 rotates counterclockwise, and the second roll 152 rotates clockwise. In the direction along the Z-axis, the gap between the first roll 151 and the second roll 152 is narrower than the thickness of the web W. Therefore, the web W is compressed from the −Z direction and the +Z direction. By changing the gap, the compressive force applied to the web W changes, and the thickness of the packing sheet S is adjusted.

The web W is cooled by the first cooling unit 155 and the second cooling unit 156 while being compressed by the first roll 151 and the second roll 152. Specifically, the first cooling unit 155 cools the web W from above, and the second cooling unit 156 cools the web W from below.

In the web W reaching the pair of rolls 150, the coating layer 232 of the second fibers 23B is melted by heating in the heating step S13. As the web W moves between the pair of rolls 150 in this state, the temperature of the web W gradually decreases from the upper surface and the lower surface. Therefore, the solidification of the coating layer 232 progresses from the upper and lower surfaces of the web W toward the inside. As solidification progresses, it becomes difficult to be compressed by the pair of rolls 150. That is, the above-mentioned regions L1 having a relatively low density are formed on the upper and lower surfaces of the web W and in the vicinity thereof.

On the other hand, in the central portion of the web W in the thickness direction, cooling is difficult to proceed and solidification of the coating layer 232 is difficult to proceed. Therefore, the central portion is easily compressed by the pair of rolls 150, and the above-mentioned region L2 of relatively high density is formed.

According to this embodiment, the following effects can be obtained.

In the packing sheet S, the internal structure can be easily controlled. Specifically, the coating layer 232 is pressurized and cooled in a molten state. In the web W, the coating layer 232 is cooled and solidified in an area relatively close to the first cooling unit 155 and the second cooling unit 156, and the coating layer 232 is cooled in a relatively distant area. It is difficult to proceed and the molten state is maintained. Therefore, compression due to pressurization is difficult to proceed in the above-mentioned near range, and the internal structure has a relatively low density. On the other hand, in the far range, compression due to pressurization tends to progress, and the internal structure becomes relatively dense. Thereby, the high-density region L2 and the low-density region L1 can be easily formed in the web W, that is, the packaging sheet S, which has undergone the pressurized cooling step S14. That is, it is possible to provide a method for manufacturing the packaging sheet S in which the internal structure can be easily controlled.

Since the heating step S13 is performed before the pressurized cooling step S14, the web W is heated in an uncompressed and relatively low-density state. Therefore, the time required to raise the temperature to a desired temperature is shortened, and the takt time can be reduced.

Since the surface temperature of the first roll 151 and the surface temperature of the second roll 152 are individually controlled, the density can be changed between the range near the first roll 151 and the range near the second roll 152. Further, since the first control section 153 and the second control section 154 are controlled by the third control section 210, the temperatures of the first cooling section 155 and the second cooling section 156 can be controlled in an integrated manner.

It is possible to provide an inexpensive packaging sheet S that has both a relatively low-density region L1 and a relatively high-density region L2. Specifically, the packing sheet S includes a region L1, a region L2, and a region where the density gradually changes between the region L1 and the region L2. The cost can be reduced compared to the case where packaging materials having such a structure are manufactured individually and combined.

10... Manufacturing device, 23A... First fiber, 23B... Second fiber, 140... Heating section, 141... Heat source section, 143... Heat radiation section, 145... Air blowing section, 150... Pair of rolls, 151... First roll, 152... Second roll, 153... First control section, 154... Second control section, 155... First cooling section, 156... Second cooling section, 157... First temperature measuring section, 158... Second temperature measuring section, 210...Third control section, 213...Third temperature measuring section, 231...Core, 232...Coating layer, S...Packaging sheet, S12...Deposition process, S13...Heating process, S14...Pressure cooling process, W...Deposition Web as a fibrous body.

Claims (11)

a deposition step of producing a deposited fiber body in which a plurality of first fibers that are natural fibers and a plurality of second fibers having a core portion and a thermoplastic coating layer covering the core portion are mixed;
a heating step of heating the deposited fiber body to melt the coating layer;
A packaging sheet characterized by comprising a pressurized cooling step of compressing and cooling the deposited fiber body in a state in which the covering layer is molten, and binding the contact points between the second fibers with the covering layer. manufacturing method. The method for manufacturing a packaging sheet according to claim 1, wherein the heating step to the pressurized cooling step are continuously performed on the stacked fiber body produced in the stacking step. 3. The method for manufacturing a packaging sheet according to claim 2, wherein the pressurized cooling step is performed using a pair of rolls, passing the stacked fiber body between the pair of rolls. The pair of rolls includes a first roll disposed above the deposited fiber body and a second roll disposed below the deposited fiber body in the pressurized cooling step,
The first roll has a first cooling part that adjusts the temperature of the first roll, and a first control part that controls the first cooling part,
The second roll has a second cooling part that adjusts the temperature of the second roll, and a second control part that controls the second cooling part,
The method for manufacturing a packaging sheet according to claim 3, wherein the first control section and the second control section are controlled by a third control section. The first control unit includes a first temperature measurement unit that measures the surface temperature of the first roll,
The second control unit includes a second temperature measurement unit that measures the surface temperature of the second roll,
The method for manufacturing a packaging sheet according to claim 4, wherein the third control section includes a third temperature measurement section that measures the temperature of the deposited fiber body. The heating step is performed using a heating section,
The heating section has a heat source section, a heat radiation section, and an air blowing section,
The method for manufacturing a packaging sheet according to claim 1, wherein the blowing section transports the heat generated by the heat source section to the stacked fiber body of the heat radiating section. The packaging sheet according to claim 1, wherein the thickness of the deposited fiber body after the pressure cooling step is reduced by 10% or more with respect to the thickness of the deposited fiber body before the pressure cooling step. Production method. The first fiber is a cellulose fiber,
The method for manufacturing a packaging sheet according to claim 1, wherein the first fibers have an average fiber length of 10 μm or more and 50 mm or less. The core is polyethylene terephthalate,
The covering layer is polyethylene,
The method for manufacturing a packaging sheet according to claim 1, wherein the average fiber length of the second fibers is 100 μm or more and 5 mm or less. The method for manufacturing a packaging sheet according to claim 1, wherein the content of the second fibers relative to the content of the first fibers in the piled fiber body is 12.0% by mass or more and 40.0% by mass or less. comprising a plurality of first fibers that are natural fibers and a plurality of second fibers having a core and a thermoplastic coating layer covering the core,
A packaging sheet characterized in that the covering layer is compressed and cooled in a melted state by heating, so that contact points between the second fibers are bound by the covering layer.

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