Pulp molded products

Abstract

To provide a pulp molded product having a high strength with a small thickness.SOLUTION: A pulp molded product MP2 of the present invention has a bending elastic modulus of 800 MPa or more with a thickness of 1.5 mm or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to pulp molded products.

Background Art

[0002] In recent years, environmental problems related to the increase in waste have occurred frequently. In view of this, paper containers are being used instead of plastic containers and metal containers for storing toiletries, beverages, and foods. For example, as a liquid paper container such as a milk container, there is a container made of cardboard coated with polyethylene resin on both sides of the paper and having a gable roof shape at the upper part, that is, a so-called gable top paper container. Such paper containers contribute to resource conservation and energy conservation, and also contribute to environmental protection such as being easy to recycle and incinerate when discarded. Therefore, paper containers are widespread in various fields.

[0003] However, since the above-mentioned paper containers are formed by folding and pasting cardboard, the manufacturing process is complicated and the manufacturing cost increases. In addition, since the above-mentioned paper containers have a low degree of freedom in shape, there are problems such as the inability to fully exhibit the appeal of products based on the shape of the container.

[0004] As one means of increasing the degree of freedom in the shape of paper containers, there is a pulp mold that manufactures molded products from a slurry containing pulp and water. In a pulp mold, generally, pulp in the slurry is deposited on a mold to form a pulp layer, this pulp layer is dehydrated, and then it is dried in a furnace. The molded product obtained by this technology, that is, a pulp molded product, is excellent in heat resistance, cold resistance, moisture absorption and desorption properties, etc., which are characteristics in terms of the physical properties of paper-based packaging materials, and has come to be widely used as a paper tray container for foods, a fixed cushioning material for fruits, etc. (Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] The present invention aims to enable the creation of pulp molded articles that are thin and have high strength. [Means for solving the problem]

[0007] According to one aspect of the present invention, a pulp molded article having a thickness of 1.5 mm or less and a flexural modulus of 800 MPa or more is provided. [Effects of the Invention]

[0008] According to the present invention, it is possible to realize pulp molded articles that are thin and have high strength. [Brief explanation of the drawing]

[0009] [Figure 1] A perspective view showing a pulp molded product according to one embodiment of the present invention. [Figure 2] Figure 1 shows a schematic diagram illustrating an example of manufacturing equipment that can be used to produce pulp molded products. [Figure 3] This figure shows the pulp layer formation process in pulp molding using the apparatus shown in Figure 2. [Figure 4] A schematic cross-sectional view showing an example of a pulp layer formed on a mold. [Figure 5] Figure 2 shows the dewatering process in pulp molding using the apparatus shown in Figure 2. [Figure 6] This figure shows the pulp layer transport process in pulp molding using the apparatus shown in Figure 2. [Figure 7] Figure 2 shows the hot press forming process in pulp molding using the apparatus shown in Figure 2. [Figure 8] A schematic cross-sectional view showing an example of a pulp molded product obtained by a hot pressing process. [Figure 9] A diagram showing the conveying process of a pulp molded product in pulp mold molding using the apparatus of FIG. 2. [Figure 10] A diagram showing the state where the conveying process of FIG. 9 is completed.

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Components that exhibit the same or similar functions are given the same reference numerals throughout all the drawings, and duplicate explanations are omitted.

[0011] <1>Pulp Molded Product FIG. 1 is a perspective view showing a pulp molded product according to an embodiment of the present invention. The pulp molded product MP2 shown in FIG. 1 has an opening and tapers in a direction away from the opening. This pulp molded product MP2 is a container. This pulp molded product MP2 includes a bottom portion and a side wall portion and is open at the top.

[0012] The bottom portion has a disk shape. The orthographic projection of the bottom portion onto a plane perpendicular to the depth direction of the container may have a shape other than a circle, for example, a polygonal shape such as a square shape.

[0013] The side wall portion has a cylindrical shape extending upward from the edge of the bottom portion. The side wall portion expands in diameter from the bottom portion toward the opening. The inner surface and the outer surface of the side wall portion may be perpendicular to the upper surface of the bottom portion. However, the pulp molded product MP2 in which the side wall portion expands in diameter from the bottom portion toward the opening is advantageous in achieving high mold release properties and is easy to stack.

[0014] The pulp molded product MP2 can have various shapes such as a cup shape, a bowl shape, a tray shape, and a box shape. The pulp molded product MP2 does not have to be a container as long as it is a three-dimensional molded product, that is, a molded product having a three-dimensional shape rather than a two-dimensional shape like a sheet.

[0015] The pulp molded product MP2 has a thickness of 1.5 mm or less. The thickness of the pulp molded product MP2 is the thickness of the wall portion of the pulp molded product MP2, here, the thickness of the bottom portion and the side wall portion. When the thickness of the wall portion is different between the bottom portion and the side wall portion, the thickness of the pulp molded product MP2 is the thickness of the thinner one of the bottom portion and the side wall portion. The thickness of the pulp molded product MP2 is preferably 1.5 mm or less, more preferably 1.3 mm or less. There is no particular lower limit value for the thickness, but according to one example, it is 0.6 mm or more.

[0016] Here, the thickness of the pulp molded product MP2 is a value obtained by the following method. That is, five test pieces are cut out from an arbitrary position of the pulp molded product MP2. Next, for each test piece, the thickness is measured. For measuring the thickness, for example, a thickness gauge manufactured by Mitutoyo Corporation is used. The thickness of the pulp molded product MP2 is taken as the average value of the measurement results obtained for the five test pieces.

[0017] The pulp molded product MP2 has a flexural modulus of 800 MPa or more. Here, the flexural modulus is a value obtained by the method defined in JIS K7171:2006 "Plastics - Method for Determining Flexural Properties".

[0018] The flexural modulus of the pulp molded product MP2 is preferably 800 MPa or more, more preferably 850 MPa or more. There is no particular upper limit value for the flexural modulus, but according to one example, it is 3000 MPa.

[0019] Despite having a small thickness, the pulp molded product MP2 has a strength to withstand a large bending stress. Also, since the pulp molded product MP2 has a small thickness, it does not take up much space when stacked and is lightweight. Therefore, the pulp molded product MP2 has good convenience during storage and use. Also, making the wall portion of the pulp molded product MP2 thin is advantageous in that it enables the drying during its manufacture to be completed in a short time. <able>

[0020] In pulp molded articles MP2, the average fiber length of the pulp is preferably in the range of 0.5 to 3.0 mm, and more preferably in the range of 0.7 to 2.8 mm. Increasing the average fiber length reduces the strength of the pulp molded article MP2. Decreasing the average fiber length requires a longer drying time during manufacturing.

[0021] Here, the average fiber length of the pulp is obtained by the following method. First, a 5g test piece is taken from the pulp molded product MP2. Next, this test piece is finely shredded and immersed in 500mL of water overnight. Then, it is stirred with a stirrer to separate the pulp from each other. In this way, a dispersion containing pulp is obtained. Next, 10g is taken from this dispersion and diluted with water. This dilution is performed so that the total mass is 200g. Using the sample obtained in this way, the fiber length is measured according to JIS P8226-2:2011 "Pulp - Method for determining fiber length by optical automated analysis - Part 2: Non-polarized method". The average fiber length of the pulp is the length-weighted average fiber length L L It refers to.

[0022] In pulp molded products MP2, the proportion of fibers with a fiber length of 0.9 mm or less in the pulp is preferably in the range of 10 to 40%. More preferably, this proportion is in the range of 20 to 35%. Increasing this proportion makes it easier to increase the density of the pulp molded product MP2 and also increases its strength, which in turn contributes to an improvement in the flexural modulus. Furthermore, increasing this proportion makes it easier to obtain pulp molded products MP2 with excellent aesthetic properties. However, if this proportion is increased excessively, it becomes difficult to complete the drying process in a short time during manufacturing, or it becomes easier for cracks and reduced release properties to occur due to poor drying.

[0023] Here, the proportion of fibers with a fiber length of 0.9 mm or less in the pulp is the ratio of the number of fibers with a fiber length of 0.9 mm or less to the total number of fibers in the pulp. This proportion is obtained by the following method.

[0024] First, a 5g test piece is obtained from the pulp molded product MP2. Next, this test piece is finely shredded and immersed in 500mL of water overnight. Then, it is stirred with a stirrer to separate the pulp from each other. In this way, a dispersion containing pulp is obtained. Next, 10g is taken from this dispersion and diluted with water. This dilution is performed so that the total mass is 200g.

[0025] Using the sample obtained in this way, fiber length measurements are performed according to JIS P8226-2:2011 "Pulp - Method for determining fiber length by automated optical analysis - Part 2: Non-polarized method". From the frequency distribution of fiber lengths obtained by this fiber length measurement, the proportion of fibers with a length of 0.9 mm or less in the pulp is determined.

[0026] The pulp suspension obtained by dispersing the pulp contained in the pulp molded product MP2 in water preferably has a Canadian standard filtration efficiency (CSF) of 700 mL or less, and more preferably 680 mL or less. When this Canadian standard filtration efficiency is high, the pulp molded product MP2 tends to have low strength.

[0027] The above Canadian standard filtration rate is preferably 500 mL or more, and more preferably 550 mL or more. If this Canadian standard filtration rate is low, the pulp molded product MP2 tends to require a long drying time during its manufacture.

[0028] Here, the Canadian standard filtration rate mentioned above is obtained by the following method. First, a test specimen is taken from the pulp molded product MP2, and a dispersion containing pulp is obtained by the same method as described above. Next, this dispersion is diluted with water to obtain an aqueous suspension of pulp with a solid content concentration of 0.3% by mass. Then, 1 L of this suspension is used to perform the measurement specified in JIS P8121-2:2012 "Pulp - Test method for filtration rate - Part 2: Canadian standard filtration rate method". For this measurement, for example, a Canadian Free Tester manufactured by Kumagai Riki Kogyo Co., Ltd. is used. The measured value is corrected by referring to a correction table with the temperature of the suspension, which has been measured in advance. In this way, the Canadian standard filtration rate is obtained.

[0029] The pulp molded article MP2 preferably has a specific tensile strength of 15 N·m / g or more, more preferably 16 N·m / g or more, and even more preferably 17 N·m / g or more. There is no upper limit to the specific tensile strength of the pulp molded article MP2, but one example suggests it is 25 N·m / g or less.

[0030] Here, the specific tensile strength is obtained by the following method. First, a strip-shaped test piece with a width of 10 mm and a length of 100 mm is cut from the non-curved portion of the pulp molded product MP2. Next, the thickness and mass of this test piece are measured. Then, using this test piece, the measurement specified in JIS P8113:2006 "Paper and cardboard - Test methods for tensile properties - Part 2: Constant-speed elongation method" is performed. Here, the strip is gripped with a distance of 50 mm between the grips. The movement speed of the grips, i.e., the elongation speed of the test piece, is set to 20 mm / min. The specific tensile strength is the average value obtained from three measurements.

[0031] The pulp molded product MP2 preferably has a peel strength of 6N or higher, and more preferably 7N or higher. While there is no upper limit to the peel strength of the pulp molded product MP2, one example suggests it is 30N or lower. A higher peel strength increases the bonding within the pulp mold layers, providing resistance to external forces and contributing to an improvement in the flexural modulus.

[0032] Here, the above-mentioned delamination strength is obtained by the following method. First, a test piece with a disc shape and a diameter of 12 mm is cut from the pulp molded product MP2. Next, this test piece is fixed to the test piece with double-sided adhesive tape. For example, Nichiban's Nicetack (registered trademark) NW-P15 is used as the double-sided adhesive tape. An indenter with a circular pressure surface with a diameter of 13 mm is prepared, and a double-sided adhesive tape cut into a circular shape with a diameter of 10 mm is attached to the pressure surface so that their centers coincide. Then, the test piece and the pressure surface are placed facing each other so that their centers coincide, and the indenter is lowered toward the test piece at a speed of 2 mm / min. After the double-sided adhesive tape on the pressure surface makes contact with the test piece, the load is increased. When the load reaches 10 N, the descent of the indenter is stopped and this state is held for 20 seconds. After that, the indenter is raised at a speed of 10 mm / min to cause delamination of the test piece and obtain the maximum load at that time. The delamination strength is defined as the average of the maximum loads obtained from three measurements.

[0033] Pulp molded product MP2 has a density of 0.45 g / cm³. 3 Preferably, it is 0.5 g / cm³ or more. 3 The above is more preferable. Note that there is no upper limit to the density of the pulp molded product MP2, but for example, 1 g / cm³ is preferable. 3 The following is true: High density means improved compactness of the pulp mold, which provides resistance when external forces are applied, and is thought to contribute to an improvement in the flexural modulus.

[0034] Here, the density mentioned above is obtained by the following method: A square or rectangular test piece is cut from the non-curved portion of the pulp molded product MP2, and its dimensions, mass, and thickness are measured. The density is then calculated from the obtained values.

[0035] Pulp molded product MP2 may further contain paper strength enhancers such as polyacrylamide. The use of paper strength enhancers can increase the strength of pulp molded product MP2.

[0036] Pulp molded products MP2 manufactured using paper strength enhancers have a higher nitrogen content compared to pulp molded products MP2 manufactured without paper strength enhancers. The nitrogen content of pulp molded products MP2 manufactured using paper strength enhancers is, in one example, 300 μg / g or more, and in other examples, 500 μg / g or more. While there is no upper limit to the nitrogen content of pulp molded products MP2, in one example, it is 1000 μg / g or less.

[0037] The nitrogen content of the pulp molded product MP2 is obtained by the following method. First, two test pieces are taken from any position on the pulp molded product MP2. The mass of each test piece is 10 mg. Next, each test piece is measured by the chemiluminescence method specified in JIS K2609:1998 "Crude oil and petroleum products - Nitrogen analysis test method". For this measurement, for example, the TN-2100H manufactured by Nitto Seiko Airanatech Co., Ltd. can be used. The nitrogen content is the average value of the measurement results obtained from the two test pieces. Note that the pulp molded product MP2 described above can maintain high strength even without paper strength enhancers.

[0038] <2> Manufacturing equipment for pulp molded products Next, we will describe the manufacturing equipment available for producing pulp molded products MP2. Figure 2 is a schematic diagram showing an example of a manufacturing apparatus that can be used to produce the pulp molded product shown in Figure 1.

[0039] The manufacturing apparatus 1 shown in Figure 2 includes a support 10, a first station 20, a second station 30, and a third station 40.

[0040] The support 10 includes a frame and rails installed on its upper part.

[0041] The first station includes a container 210, a lifting device 220, a cover body 230, a mold 240, a moving device 250, a lifting device 260, and an upper mold 270.

[0042] The container 210 is installed within the frame of the support 10. The container 210 is open at the top. The container 210 contains a slurry S containing pulp and water.

[0043] The lifting device 220 is mounted above the container 210 and attached to the frame of the support 10. The lifting device 220 includes, for example, a hydraulic cylinder. The lifting device 220 supports the cover body 230. The lifting device 220 can raise and lower the cover body 230 to the position of the opening of the container 210.

[0044] The cover body 230 is a hollow body with an opening at the top. A pump (not shown) is connected to the cover body 230.

[0045] The mold 240 is fixed to the opening of the cover body 230. Specifically, the mold 240 is fixed to the opening of the cover body 230 such that one side of the mold 240 and the adjacent space are enclosed by the mold 240 and the cover body 230.

[0046] The mold 240 is a liquid-permeable mold. The mold 240 has a three-dimensional shape. That is, the mold 240 has one or more protrusions and / or one or more recesses on the surface where the pulp is deposited. Specifically, the outer surface of the mold 240, i.e., the back surface of the surface adjacent to the above-mentioned space, has a shape corresponding to the pulp molded product. Here, the mold 240 is a male mold with a protruding top surface.

[0047] The mold 240 includes, for example, a mold body having numerous through holes and an outer surface shaped to correspond to a pulp molded product, and a mesh body provided on the outer surface of the mold body so as to follow the outer surface.

[0048] The mobile device 250 is movable between the first station 20 and the second station 30 along rails on the support 10. The mobile device 250 includes, for example, a motor as a power source. A lifting device 260 is attached to the mobile device 250, which can be transported between the first station 20 and the second station 30.

[0049] The lifting device 260 is attached to the moving device 250 as described above. The lifting device 260 includes, for example, a hydraulic cylinder. The lifting device 260 supports the upper mold 270. The lifting device 260 can raise and lower the upper mold 270.

[0050] The upper mold 270 is a holder that holds the pulp layer, described later, between itself and the paper mold 240 using vacuum suction. The lower surface of the upper mold 270 has a shape corresponding to the outer surface of the paper mold 240. Here, the upper mold 270 is a female mold with a concave lower surface. The upper mold 270 has, for example, numerous through holes, one end of which opens at the lower surface and the other end of which is connected to a pump.

[0051] The second station 30 is located near the first station 20. The second station 30 includes a base 310, a lower die 320, a moving device 330, a pressing device 340, and an upper die 350.

[0052] The base 310 is installed inside the frame of the support 10. The lower mold 320 is installed on the base 310.

[0053] The lower mold 320 is a mold that is permeable to gas and / or liquid. The upper surface of the lower mold 320 has a shape corresponding to the outer surface of the mold 240. Here, the lower mold 320 is a male mold with a protruding upper surface. The lower mold 320 has, for example, numerous through holes and a smooth surface that has a shape corresponding to the outer surface of the mold 240.

[0054] The mobile device 330 is movable along rails on the support 10 between the second station 30 and a fourth station (not shown). The mobile device 330 includes, for example, a motor as a power source. When the mobile device 330 is located at the second station 30, its movement in the vertical, horizontal, and longitudinal directions can be restricted by a locking mechanism. A press device 340 is also attached to the mobile device 330, which can be transported between the second station 30 and the fourth station.

[0055] The press device 340 is attached to the moving device 330 as described above. The press device 340 includes, for example, a hydraulic cylinder. The press device 340 supports the upper die 350. The press device 340 can raise and lower the upper die 350.

[0056] The upper mold 350 is a mold that does not have gas permeability or liquid permeability. The lower surface of the upper mold 350 has a shape corresponding to the outer surface of the mold 240. Here, the upper mold 350 is a female mold with a concave lower surface. The upper mold 350 has a smooth surface that has a shape corresponding to the outer surface of the mold 240.

[0057] The second station 30 further includes a heater and a pump (neither of which are shown). The heater heats at least one of the lower mold 320 and the upper mold 350. The pump is connected to the lower space of the lower mold 320.

[0058] The third station 40 is located near the second station 30. The third station 40 includes a platform 410, a moving device 420, a lifting device 430, and a holder 440.

[0059] The base 410 is installed inside the frame of the support 10. A pulp molded product is placed on the base 410.

[0060] The mobile device 420 is movable between the second station 30 and the third station 40 along rails on the support 10. The mobile device 420 includes, for example, a motor as a power source. A lifting device 430 is attached to the mobile device 420, which can be transported between the second station 30 and the third station 40.

[0061] The lifting device 430 is attached to the moving device 420 as described above. The lifting device 430 includes, for example, a hydraulic cylinder. The lifting device 430 supports the holder 440. The lifting device 430 can raise and lower the holder 440.

[0062] The holder 440 is a holder that holds the pulp molded product, described later, by vacuum suction. The lower surface of the holder 440 has a shape corresponding to the outer surface of the mold 240. Here, the holder 440 has a concave shape on its lower surface. The holder 440 has, for example, a number of through holes, one end of which opens on the lower surface and the other end of which is connected to a pump.

[0063] <3> Method for manufacturing pulp molded products In a manufacturing method according to one embodiment of the present invention, for example, a pulp molded product MP2 is manufactured using the manufacturing apparatus 1 described above. This will be explained with reference to Figures 1 to 10.

[0064] Figure 3 shows the pulp layer formation process in pulp molding using the apparatus shown in Figure 2. Figure 4 is a schematic cross-sectional view showing an example of a pulp layer formed on a mold. Figure 5 shows the dewatering process in pulp molding using the apparatus shown in Figure 2. Figure 6 shows the pulp layer transport process in pulp molding using the apparatus shown in Figure 2. Figure 7 shows the hot press forming process in pulp molding using the apparatus shown in Figure 2. Figure 8 is a schematic cross-sectional view showing an example of a pulp molded product obtained by the hot press process. Figure 9 shows the transport process of the pulp molded product in pulp molding using the apparatus shown in Figure 2. Figure 10 shows the state after the transport process in Figure 9 has been completed.

[0065] In this method, first, prepare slurry S. As described above, slurry S contains pulp and water. Slurry S is a suspension in which pulp is dispersed in water and has high viscosity.

[0066] The pulp contained in slurry S has almost the same characteristics as the pulp contained in pulp molded product MP2 described above.

[0067] There are no particular restrictions on the type of pulp used in slurry S. As pulp, for example, wood pulp such as bleached kraft pulp (NBKP) or unbleached kraft pulp (NUKP) of softwood and bleached kraft pulp (LBKP) or unbleached kraft pulp (LUKP) of hardwood, which are commonly used as raw material pulp in papermaking, or non-wood pulp such as straw, cotton, kenaf, bamboo, and sugarcane can be used individually or in any proportion of two or more types. It is preferable to use non-wood pulp as the pulp.

[0068] Pulp varies in fiber length and other characteristics depending on its raw materials and manufacturing methods. For example, pulp made from sugarcane generally has a shorter average fiber length than pulp made from bamboo. Furthermore, the average fiber length of pulp can be adjusted by any method, such as mechanical processing like beating or crushing. Therefore, pulp with certain characteristics can be obtained, for example, by selecting an appropriate type from among several types of pulp, or by appropriately combining two or more types of pulp.

[0069] The pulp content of slurry S is preferably in the range of 0.1 to 0.4% by mass, and more preferably in the range of 0.15 to 0.35% by mass. If the pulp content is too low, it is difficult to achieve high productivity. If the pulp content is too high, there is a possibility that the thickness of the pulp layer will vary greatly.

[0070] The slurry S may further contain additives. These additives may include organic low-molecular-weight materials, organic high-molecular-weight materials, inorganic materials, or combinations thereof. Examples include agents that impart water resistance or oil resistance; however, the appropriate agent should be selected according to the required performance of the pulp molded container. The proportion of additives to the total of pulp and additives is preferably 10% by mass or less, and more preferably 5% by mass or less. That is, the proportion of pulp to the total solid content of slurry S is preferably 90% by mass or more, and more preferably 95% by mass or more.

[0071] Next, slurry S is supplied into the container 210. Then, as shown in Figure 3, the cover body 230 is lowered by the lifting device 220 so that the upper surface of the mold 240 is positioned well below the liquid level of slurry S. In this state, the pump is driven to reduce the pressure in the space enclosed by the cover body 230 and the mold 240. This creates a flow of slurry S across the mold 240, causing pulp to accumulate on the mold 240. In this way, a pulp layer MP1 is formed on the mold 240 as shown in Figure 4.

[0072] Next, with the pump still running, the cover body 230 is raised by the lifting device 220 as shown in Figure 5, so that the lower part of the mold 240 is positioned well above the liquid surface of the slurry S. This dewaters the pulp layer MP1 under reduced pressure. Next, the lifting device 260 is driven to lower the upper mold 270 until its lower surface contacts the pulp layer MP1. Note that the pulp layer MP1 is not shown in Figure 5. This dewatering process is carried out without heating either the upper mold 270 or the mold 240.

[0073] The depressurization time in the dewatering process is preferably within the range of 1 to 60 seconds, and more preferably within the range of 1 to 10 seconds.

[0074] The moisture content of the pulp layer MP1 immediately after dewatering is preferably in the range of 64 to 75% by mass, and more preferably in the range of 65 to 72% by mass. If the moisture content is too low, the in-plane movement of fibers within the pulp layer may be insufficient during the hot pressing process. If the moisture content is too high, the in-plane movement of fibers within the pulp layer may be excessive during the hot pressing process, or the shape retention of the pulp layer MP1 may be insufficient during the period between the end of the dewatering process and the start of the hot pressing process.

[0075] After stopping the depressurization and pressurization of the above-mentioned space, the pump is driven to adsorb and hold the pulp layer MP1 on the upper mold 270. Note that the suction by the pump and the upper mold 270 does not cause further dewatering of the pulp layer MP1.

[0076] Next, with the pulp layer MP1 adsorbed and held on the upper die 270, the lifting device 260 is driven to raise the upper die 270, as shown in Figure 2. This peels the pulp layer MP1 from the mold 240.

[0077] Next, the moving devices 250 and 330 are driven to move the press device 340 and upper die 350 from the second station 30 to the fourth station, as shown in Figure 6, and the lifting device 260 and upper die 270 from the first station 20 to the second station 30. Subsequently, the lifting device 260 is driven to lower the upper die 270 until the pulp layer MP1 contacts the lower die 320. After that, the suction by the pump and the upper die 270 is stopped to release the pulp layer MP1 from the upper die 270. Then, the lifting device 260 is driven to raise the upper die 270. In this way, the pulp layer MP1 is transferred from the first station 20 to the second station 30 and placed on the lower die 320.

[0078] Next, the moving devices 250 and 330 are driven to move the lifting device 260 and the upper die 270 from the second station 30 to the first station 20, as shown in Figure 2, and the pressing device 340 and the upper die 350 from the fourth station to the second station 30. Subsequently, the pressing device 340 is driven to lower the upper die 350, as shown in Figure 7. Then, the pulp layer MP1 sandwiched between the upper die 350 and the lower die 320 is pressurized. At the same time, the heater is driven to heat the pulp layer MP1. Furthermore, the pump is driven to suck and remove water and / or water vapor from the space sandwiched between the upper die 350 and the lower die 320. This smooths the surface shape of the pulp layer MP1 and densifies and dries the pulp layer MP1. In this way, the pulp molded product MP2 shown in Figure 8 is obtained.

[0079] Furthermore, the moisture content of the pulp layer MP1 immediately before starting this hot pressing process is approximately equal to the moisture content of the pulp layer MP1 immediately after the dewatering process is completed.

[0080] In this hot pressing process, the pressing pressure is preferably 0.2 MPa or higher, and more preferably 0.25 MPa or higher. If the pressing pressure is too low, it may not be possible to obtain a high-density pulp molded product MP2. The pressing pressure is preferably 3 MPa or lower, and more preferably 2.8 MPa or lower. When the pulp layer MP1 contains a large amount of pulp with short fiber length, such pulp is prone to movement within the pulp layer MP1, especially if the pressing pressure is excessively high. Therefore, if the pressing pressure is excessively high in such cases, variations in the thickness of the pulp molded product MP2 are likely to occur.

[0081] In this hot pressing process, the heating temperature of the pulp layer MP1, i.e., the temperature of the upper mold 350 or lower mold 320 heated by the heater, is preferably in the range of 120 to 220°C, and more preferably in the range of 130 to 210°C. When the pulp layer MP1 contains a large amount of pulp with short fiber length, water vapor has difficulty escaping to the outside. Therefore, if the heating temperature is low in such cases, it will take a long time to dry the pulp layer MP1. If the heating temperature is high, the shrinkage of the pulp layer MP1 due to drying will be greater, and as a result, the distortion in the pulp molded product MP2 may become greater.

[0082] The pressing time in the hot pressing process depends on the heating temperature, the shape of the molded product, etc., but is preferably in the range of 70 to 150 seconds, and more preferably in the range of 80 to 140 seconds.

[0083] When the above hot pressing process is completed, the press device 340 is driven to raise the upper die 350, causing the pulp molded product MP2 to detach from the upper die 350.

[0084] Next, the moving devices 330 and 420 are driven to move the press device 340 and upper die 350 from the second station 30 to the fourth station, as shown in Figure 9, and the lifting device 430 and holder 440 are moved from the third station 40 to the second station 30. Subsequently, the lifting device 430 is driven to lower the holder 440 until it contacts the pulp molded product MP2. Air is blown from inside the lower die to release the pulp molded product MP2 from the lower die, and then the pump is driven to hold the pulp molded product MP2 in place by suction on the holder 440.

[0085] Next, with the pulp molded product MP2 held by the holder 440, the lifting device 430 is driven to raise the holder 440. Subsequently, the moving devices 330 and 420 are driven to move the lifting device 430 and the holder 440 from the second station 30 to the third station 40, as shown in Figure 10, and the press device 340 and the upper die 350 from the fourth station to the second station 30. Subsequently, the suction by the pump and the holder 440 is stopped, releasing the pulp molded product MP2 from the holder 440. In this way, the pulp molded product MP2 is transferred from the second station 30 to the third station 40, and the pulp molded product MP2 is placed on the base 410. The pulp molded product MP2 is manufactured in the manner described above.

[0086] Subsequently, if necessary, the pulp molded product MP2 is subjected to post-processing, such as printing with patterns or blanks, coating, or a combination thereof. The coating layer formed by post-processing may be, for example, a layer containing agents that impart water resistance or oil resistance, a layer filled with materials that impart heat insulation, a layer foamed with a foaming agent, or a combination thereof. By performing post-processing, for example, the aesthetic appeal of the pulp molded product MP2 can be further enhanced, or new functions can be added to the pulp molded product MP2.

[0087] According to the method described above, pulp molded articles MP2 can be manufactured that have a large flexural modulus despite their small thickness.

[0088] Pulp molded products MP2 are lightweight due to their thin walls and low stacking height. Therefore, pulp molded products MP2 can achieve high transport efficiency.

[0089] Furthermore, the pulp molded product MP2 obtained by the above method exhibits excellent surface properties. The reason for this is explained below.

[0090] When drying is performed using an oven instead of a hot pressing process, the pulp layer develops significant surface irregularities due to shrinkage. Furthermore, the pulp layer is not sufficiently densified using this method, resulting in pulp molded products with high porosity. Consequently, it is not possible to manufacture pulp molded products with superior surface properties in this case.

[0091] Furthermore, if drying is performed using an oven after the dewatering process, and the dried product is humidified as needed before being subjected to a heat press treatment, the height differences of the surface irregularities created during drying can be reduced by the subsequent humidification and heat press treatment. Also, the porosity can be reduced by the humidification and heat press treatment. However, the height differences of the surface irregularities created during oven drying are very large, so they cannot be sufficiently reduced by the subsequent humidification and heat press treatment. Moreover, even if humidification and heat press treatment are performed after drying, it is difficult to sufficiently reduce the porosity.

[0092] In the method described with reference to Figures 2 to 10, the pulp layer MP1 is dried during the hot pressing process. That is, in the above method, the hot pressing process is carried out after the dewatering process without going through the drying process.

[0093] Since no drying process is performed before the hot pressing process, the surface of the pulp layer MP1 does not develop large irregularities with significant height differences. During the hot pressing process, the upper die 350 and lower die 320 prevent deformation of the pulp layer MP1 due to drying. Furthermore, since the hot pressing process is performed on the pulp layer MP1 with a high moisture content, a moderate amount of fiber movement in the in-plane direction can occur within the pulp layer MP1. The pulp layer MP1 can be densified without causing variations in thickness.

[0094] Therefore, according to the method described with reference to Figures 2 to 10, pulp molded articles MP2 with excellent surface properties can be manufactured. Specifically, pulp molded articles MP2 can be obtained that include portions with an arithmetic mean roughness Ra of 200 μm or less. Such pulp molded articles MP2 have excellent aesthetic properties and facilitate the formation of printed or coated layers.

[0095] The arithmetic mean roughness Ra is preferably 200 μm or less. While there is no lower limit to the arithmetic mean roughness Ra, it is usually 50 μm or more. Here, "arithmetic mean roughness Ra" is a surface texture parameter defined in JIS B0601:2013.

[0096] The pulp molded product MP2 may have the above-described surface properties over its entire surface, or only a portion of its surface may have the above-described surface properties. For example, only the portion including the part to be subjected to post-processing such as printing may have the above-described surface properties, while other portions may not have the above-described surface properties. Alternatively, one side of the pulp molded product MP2 may have the above-described surface properties, while its back surface may not. Such a structure can be realized, for example, by making the surface properties different in a portion of the surface of the upper mold 350 and lower mold 320 that are in contact with the pulp layer MP1, and in other portions of that surface.

[0097] Incidentally, one method for manufacturing pulp molded products involves using a mold and a core. However, as explained below, such a method cannot achieve a high flexural modulus.

[0098] In this method, first, the cavity of a mold consisting of two split molds, each with a net-covered inner surface, is filled with a slurry containing pulp fibers. The split molds are provided with multiple communication holes that connect the cavity to the outside of the mold. Next, while replenishing the slurry, suction is performed through the aforementioned communication holes to discharge the water contained in the slurry inside the cavity to the outside of the mold, and at the same time, pulp fibers are deposited on the inner surface of the mold, forming a pulp layer. In this method, after filling the cavity with slurry, no slurry flow that circulates throughout the entire cavity occurs, and pulp fibers accumulate more in the vicinity of the communication holes compared to areas farther away from the communication holes.

[0099] Next, a core that is expandable and hollow is inserted into the cavity where the pulp layer has formed, and by inflating it, the pulp layer is pressed against the inner surface of the mold. This pressing causes the shape of the pulp layer to conform to the shape of the inner surface of the mold.

[0100] Next, the pressure applied to the inside of the core is further increased in order to expand it. Part of this pressure is used to reduce the thickness of the core. Therefore, it is difficult to apply significant pressure to the pulp layer with this pressure. In other words, it is difficult to sufficiently densify the pulp layer with this pressure.

[0101] Furthermore, as mentioned above, immediately before pressing with the core, more pulp fibers are deposited near the communication holes compared to areas further away from the holes. That is, immediately before pressing with the core, the pulp layer is thicker near the communication holes and thinner in areas further away from the holes. Because the pulp layer has these irregularities, the core expands to conform to the shape of the pulp layer's irregularities. The pressure applied to the pulp layer by the core's expansion is equal in areas with a high concentration of pulp fibers and areas with a low concentration of pulp fibers. Therefore, the expansion of the core does not completely eliminate the variation in the thickness of the pulp layer. Moreover, after pressing with the core, the pulp layer exhibits density variations corresponding to the variations in its thickness. That is, the density is higher in the parts of the pulp layer located near the communication holes and lower in the parts located further away from the holes.

[0102] Thus, if the density of the pulp layer varies from place to place, the Young's modulus of the pulp molded product will also vary from place to place. For this reason, the above method cannot be used to manufacture pulp molded products with a large flexural modulus.

[0103] On the other hand, in the method for manufacturing a pulp molded product according to the embodiment, first, a mold having liquid permeability is immersed in a slurry, and then the pulp is deposited on the mold by driving a pump to create a slurry flow across the mold. With this method, the pulp is deposited uniformly. Next, the pulp layer obtained by this deposition is dewatered to an appropriate moisture content. Next, the pulp layer with a relatively high moisture content is hot-pressed using an upper mold and a lower mold. Since the upper and lower molds are rigid, high pressure can be applied to the entire pulp layer by such hot pressing, and therefore, it is possible to sufficiently densify the pulp layer. In addition, such hot pressing can cause appropriate in-plane fiber movement within the pulp layer. Therefore, the pulp layer can be densified without causing variations in thickness or density.

[0104] Thus, the density of the pulp layer can be made uniform according to the method described above. Therefore, the method described above prevents the formation of low-density areas in the pulp layer. Consequently, according to the method described above, it is possible to manufacture pulp molded products that are thin and have a high flexural modulus. In other words, it is possible to realize pulp molded products that are thin and have high strength.

[0105] Figures 2 to 10 are provided to facilitate understanding of the method for manufacturing pulp molded articles according to one embodiment of the present invention. The method described above can also be carried out using manufacturing equipment with other structures. [Examples]

[0106] The following are specific examples of the present invention. The present invention is not limited to these examples.

[0107] <1> Manufacturing of pulp molded products (Example 1) A slurry consisting of pulp and water was prepared using a pulper. The pulp content of the slurry was 0.18% by mass. Pulp with an average fiber length of 1.6 mm was used.

[0108] Using this slurry, pulp molded articles were manufactured according to the method described with reference to Figures 2 to 10. In this process, the dewatering step was performed so that the moisture content of the pulp layer immediately after dewatering was 69.5% by mass. The hot pressing step was performed with a heating temperature of 180°C, a pressing pressure of 1.5 MPa, and a pressing time of 100 seconds. In both the dewatering and hot pressing steps, the clearance between the upper and lower molds was set to 1.3 mm so that pulp molded articles with a wall thickness of 1.3 mm could be obtained. In this manner, the container was manufactured as a pulp molded product.

[0109] (Example 2) A pulp molded product was manufactured using the same method as in Example 1, except that the amount of pulp deposited was adjusted so that a pulp molded product with a wall thickness of 1 mm could be obtained, and the press pressure in the dewatering and hot pressing processes was set to 2 MPa, the press time to 100 seconds, and the clearance between the upper and lower molds to 1 mm.

[0110] (Example 3) A pulp molded product was manufactured using the same method as in Example 1, except that the amount of pulp deposited was adjusted so that a pulp molded product with a wall thickness of 1 mm could be obtained, and the press pressure in the dewatering and hot pressing processes was set to 0.5 MPa, the press time to 100 seconds, and the clearance between the upper and lower molds to 1 mm.

[0111] (Example 4) To obtain a pulp molded product with a wall thickness of 0.7 mm, a pulp molded product was manufactured using the same method as in Example 1, except that the press pressure was set to 2 MPa, the press time to 70 seconds, and the clearance between the upper and lower dies to 0.7 mm during the dewatering and hot pressing processes.

[0112] (Example 5) Pulp with an average fiber length of 0.9 mm was used as the pulp, and a pulp molded product with a wall thickness of 1 mm was obtained. The pulp molded product was manufactured using the same method as in Example 1, except that the press pressure was set to 1.5 MPa, the press time to 140 seconds, and the clearance between the upper and lower molds to 1 mm during the dewatering and hot pressing processes.

[0113] (Example 6) To obtain a pulp molded product with a wall thickness of 0.7 mm, a pulp molded product was manufactured using the same method as in Example 5, except that the press pressure was set to 1.5 MPa, the press time to 120 seconds, and the clearance between the upper and lower dies to 0.7 mm during the dewatering and hot pressing processes.

[0114] (Comparative Example 1) A pulp molded product was manufactured using the same method as in Example 1, except that pulp with an average fiber length of 2.3 mm was used as the pulp, the press pressure was set to 0 MPa instead of 1.5 MPa, and the clearance between the upper and lower dies was set to 2 mm in the dewatering and hot pressing processes to obtain a pulp molded product with a wall thickness of 2 mm.

[0115] (Comparative Example 2) A pulp molded product was manufactured using the same method as in Comparative Example 1, except that the clearance between the upper and lower molds was set to 1.75 mm during the dewatering and hot pressing processes, so that a pulp molded product with a wall thickness of 1.75 mm could be obtained.

[0116] (Comparative Example 3) Pulp molded products were manufactured using the same method as in Example 1, except that the press pressure was set to 0 MPa instead of 1.5 MPa, and the clearance between the upper and lower dies was set to 1.3 mm during the dewatering and hot pressing processes.

[0117] (Comparative Example 4) Pulp molded products were manufactured using the same method as in Example 1, except that the amount of pulp deposited was adjusted, the press pressure was set to 0 MPa instead of 1.5 MPa, and the clearance between the upper and lower dies was set to 1.3 mm in the dewatering and hot pressing processes.

[0118] <2> evaluation Various measurements were performed on each of the pulp molded articles produced in Examples 1 to 6 and Comparative Examples 1 to 4 using the method described above. In addition, the compressive strength was measured for each of these pulp molded articles. The molded articles were box-shaped with a square base having sides of 150 mm and four walls with a height of 45 mm. Here, "compressive strength" is the maximum compressive load at which the molded article maintains its shape when the load applied in the vertical direction is increased, as specified in JIS Z0212:1998 "Packaged goods and containers - Compression test method".

[0119] The results are shown in Tables 1 and 2 below.

[0120] [Table 1]

[0121] [Table 2]

[0122] As is clear from the comparison between Examples 1 to 6 and Comparative Examples 1 to 4, when a press pressure was applied, pulp molded articles with a flexural modulus of 800 MPa or more were obtained despite having a thickness of 1.5 mm or less. Such pulp molded articles had high density and high compressive strength. On the other hand, when the press pressure was 0 MPa, pulp molded articles with a flexural modulus of less than 800 MPa were obtained. Such pulp molded articles had low density and low compressive strength. [Explanation of symbols]

[0123] 1...Manufacturing equipment, 10...Support, 20...First station, 30...Second station, 40...Third station, 210...Container, 220...Lifting device, 230...Cover body, 240...Mold making, 250...Moving device, 260...Lifting device, 270...Upper mold, 310...Base, 320...Lower mold, 330...Moving device, 340...Pressing device, 350...Upper mold, 410...Base, 420...Moving device, 430...Lifting device, 440...Holder, MP1...Pulp layer, MP2...Pulp molded product, S...Slurry.

Claims

1. A pulp molded product having a thickness in the range of 0.3 to 1.3 mm, a flexural modulus in the range of 1115 to 2697 MPa, and an average fiber length of pulp in the range of 0.9 to 1.6 mm.

2. Density is 0.45 g / cm³ ３ The pulp molded article according to claim 1, as described above.

3. A pulp molded article according to claim 1 or 2, comprising non-wood pulp.

4. A pulp molded article according to any one of claims 1 to 3, having an opening and tapering away from the opening.

5. A pulp molded article according to any one of claims 1 to 4, which is a container.

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