CN116601082A

CN116601082A - Pulp molded article and method for producing the same

Info

Publication number: CN116601082A
Application number: CN202180085629.9A
Authority: CN
Inventors: 石井萌
Original assignee: Toppan Printing Co Ltd
Current assignee: Toppan Inc
Priority date: 2020-12-25
Filing date: 2021-12-20
Publication date: 2023-08-15
Also published as: EP4269691A1; US20230331425A1; WO2022138563A1; JPWO2022138563A1

Abstract

Provided is a technique capable of producing a pulp molded article having excellent surface properties. A pulp molded article having a region with an arithmetic average roughness Ra of 50 μm or less on the surface. A method of manufacturing a pulp molded article, comprising: preparing a slurry comprising pulp having an average fiber length of less than 3.0mm and water; depositing the pulp on a paper making mold having a three-dimensional shape to form a pulp layer; dewatering the pulp layer to obtain an intermediate formed article; and sandwiching the intermediate molded article, which is not dried, between a male mold and a female mold, and heating while pressurizing.

Description

Pulp molded article and method for producing the same

Technical Field

The present invention relates to a pulp molded article.

Background

In recent years, environmental problems associated with an increase in waste and the like have been more and more common. In view of this, paper containers are used instead of plastic containers or metal containers in the storage of washing products, beverages, foods, and the like. For example, as a paper container for liquid such as a milk container, there are: a container composed of a cardboard sheet having polyethylene resin coated on both sides of the paper and having a mountain-shaped roof shape (wife root cutting shape) at the upper part, that is, a so-called roof box (table-top) paper container. Such paper containers not only contribute to resource saving and energy saving, but also contribute to environmental protection by being easily recycled and incinerated at the time of disposal. Therefore, paper containers are popular in various fields.

However, since the paper container is formed by bending and adhering paper sheets, the manufacturing process is complicated and the manufacturing cost is high. Further, since the degree of freedom in the shape of the paper container is low as described above, there is a problem that the attractive force of the commodity based on the shape of the container cannot be sufficiently exerted.

One of means for improving the degree of freedom in the shape of a paper container is: pulp molding of a molded article is produced from a slurry (slurry) containing pulp and water. In pulp molding, pulp in a slurry is generally deposited on a paper-making mold (paper-making mold) to form a pulp layer, which is dewatered and then dried in an oven. The pulp molded product, which is a molded product obtained by this technique, is excellent in heat resistance, cold resistance, moisture absorption and desorption properties, etc. which are characteristics of physical properties of paper packaging materials, and is widely used as a paper tray container for food, a fixing buffer material for fruits, etc. (patent document 1).

Prior art literature

Patent literature

Patent document 1: japanese patent laid-open No. 2008-285188

Disclosure of Invention

In general, pulp molded articles have irregularities with large level differences on the surface. Such pulp molded articles are not suitable for containers requiring aesthetic appearance, and it is difficult to form printed layers and coatings.

The purpose of the present invention is to provide a technique that enables the production of pulp molded articles having excellent surface properties.

According to the 1 st aspect of the present invention, a pulp molded article having a region with an arithmetic average roughness Ra of 50 μm or less on the surface can be provided.

According to the 2 nd aspect of the present invention, there can be provided a method for producing a pulp molded article, comprising: preparing a slurry comprising pulp having an average fiber length of less than 3.0mm and water; depositing the pulp on a paper making mold having a three-dimensional shape to form a pulp layer; dewatering the pulp layer to obtain an intermediate formed article; and sandwiching the intermediate molded article, which is not dried, between a male mold and a female mold, and heating while pressurizing.

Here, the "arithmetic average roughness Ra" is a surface texture parameter defined in JIS B0601:2013. The "average fiber length" is the length-weighted average fiber length L measured by an optical automatic analysis method defined in JIS P8226-2:2011 _L 。

According to the present invention, a technique capable of producing a pulp molded article excellent in surface properties can be provided.

Drawings

Fig. 1 is a view schematically showing an example of a manufacturing apparatus that can be used to manufacture a pulp molded article according to an embodiment of the present invention.

Fig. 2 is a diagram showing a pulp layer forming process in pulp molding using the apparatus of fig. 1.

Fig. 3 is a cross-sectional view schematically showing an example of a pulp layer formed on a paper making die.

Fig. 4 is a diagram showing a dewatering step in pulp molding using the apparatus of fig. 1.

Fig. 5 is a diagram showing a transfer process of a pulp layer in pulp molding using the apparatus of fig. 1.

Fig. 6 is a diagram showing a hot press process in pulp molding using the apparatus of fig. 1.

Fig. 7 is a cross-sectional view schematically showing an example of a pulp molded article obtained by the hot pressing step.

Fig. 8 is a diagram showing a conveying process of a pulp molded article in pulp molding using the apparatus of fig. 1.

Fig. 9 is a diagram showing a state after the conveyance process of fig. 8 is completed.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that, for components that perform the same or similar functions, the same reference numerals are given to the same components throughout the drawings, and overlapping descriptions are omitted.

Fig. 1 is a diagram schematically showing an example of a manufacturing apparatus that can be used to manufacture a pulp molded article according to an embodiment of the present invention.

The manufacturing apparatus 1 shown in fig. 1 includes: support 10, 1 st workstation (station)

20. Station 230, and station 3 40.

The support 10 includes: a frame body and a rail arranged at the upper part of the frame body.

The 1 st workstation comprises: container 210, lifting device 220, lid 230, paper making die 240, moving device 250, lifting device 260, and upper die 270.

The container 210 is disposed in the frame of the support body 10. The container 210 is open at an upper portion. The vessel 210 contains a slurry S containing pulp and water.

The lifting device 220 is installed on the frame of the support body 10 above the container 210. The lifting device 220 comprises, for example, a hydraulic cylinder. The elevating device 220 supports the cover 230. The lifting device 220 can lift the cover 230 at the position of the opening of the container 210.

The cover 230 is a hollow body having an opening in an upper portion. The cover 230 is connected to a pump not shown.

The paper mold 240 is fixed to the opening of the cover 230. Specifically, the paper mold 240 is fixed to the opening of the cover 230 such that the space adjacent to one surface thereof is surrounded by the paper mold 240 and the cover 230.

The paper mold 240 is a mold having liquid permeability. The paper making die 240 has a three-dimensional shape. That is, the paper mold 240 has 1 or more convex portions and/or 1 or more concave portions on the surface where the pulp is deposited. Specifically, the outer surface of the paper mold 240, that is, the back surface of the surface adjacent to the space has a shape corresponding to the pulp molded product. Here, the paper mold 240 is a male mold protruding above.

The paper mold 240 is provided with a plurality of through holes including: the outer surface has a paper mold body having a shape corresponding to the pulp molded product, and a net body provided on the outer surface of the paper mold body so as to be along the outer surface. The paper mold body is made of a hard material such as metal.

The moving device 250 is capable of moving along the track of the support body 10 between the 1 st work station 20 and the 2 nd work station 30. The mobile device 250 includes, for example, an engine as a power source. The moving device 250 is installed with a lifting device 260 and can be transferred between the 1 st work station 20 and the 2 nd work station 30.

As described above, the elevating device 260 is mounted on the moving device 250. The lifting device 260 includes, for example, a hydraulic cylinder. The elevating device 260 supports the upper die 270. The elevating device 260 may elevate the upper die 270.

The upper die 270 is a holder that holds a pulp layer, which will be described later, by vacuum suction, with the pulp layer interposed between the upper die and the paper making die 240. The upper die 270 is made of a hard material such as metal. The lower surface of the upper mold 270 has a shape corresponding to the outer surface of the paper mold 240. Here, the upper die 270 is a female die recessed below. For example, one end of the upper die 270 is opened at the lower side, and the other end has a plurality of through holes connected to a pump.

The 2 nd working station 30 is disposed in the vicinity of the 1 st working station 20. The 2 nd station 30 includes: a table 310, a lower die 320, a moving device 330, a pressing device 340, and an upper die 350.

The stage 310 is disposed in the frame of the support 10. The stage 310 is provided with a lower die 320.

The lower mold 320 is a mold having gas and/or liquid permeability. The lower die 320 is made of a hard material such as metal. The upper surface of the lower mold 320 has a shape corresponding to the outer surface of the paper mold 240. Here, the lower die 320 is a male die protruding above. The lower die 320 has a plurality of through holes, for example, and a surface having a shape corresponding to the above-described outer surface of the paper die 240 is smooth.

The moving device 330 is movable along the rail of the support 10 between the 2 nd station 30 and a 4 th station, not shown. The mobile device 330 includes, for example, an engine as a power source. When the moving device 330 is located at the 2 nd station 30, the movement in the up-down, left-right, and front-rear directions can be restricted by the lock mechanism. In addition, a pressing device 340 is installed on the moving device 330, and can be transferred between the 2 nd and 4 th work stations 30 and 4 th work station.

As described above, the pressing device 340 is mounted on the moving device 330. The pressing device 340 comprises, for example, a hydraulic cylinder. The pressing device 340 supports the upper die 350. The pressing device 340 may raise and lower the upper mold 350.

The upper mold 350 is a mold having no gas permeability and no liquid permeability. The upper die 350 is made of a hard material such as metal. The lower surface of the upper mold 350 has a shape corresponding to the outer surface of the paper mold 240. Here, the upper mold 350 is a female mold recessed below. The surface of the upper mold 350 having a shape corresponding to the above-mentioned outer surface of the paper mold 240 is smooth.

The 2 nd station 30 further includes a heater and a pump (both not 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.

The 3 rd workstation 40 is disposed in the vicinity of the 2 nd workstation 30. The 3 rd station 40 includes: table 410, moving device 420, lifting device 430, and holder 440.

The stage 410 is disposed in the frame of the support body 10. The pulp molded article is placed on the stage 410.

The moving means 420 can move along the track of the support body 10 between the 2 nd and 3 rd workstations 30 and 40. The mobile device 420 includes, for example, an engine as a power source. The moving means 420 is provided with a lifting means 430 and can be transferred between the 2 nd and 3 rd work stations 30 and 40.

As described above, the elevating device 430 is mounted on the moving device 420. The lifting device 430 includes, for example, a hydraulic cylinder. The lifting device 430 supports a holder 440. The lifting device 430 can lift the holder 440.

The holder 440 is a holder for holding a pulp molded product to be described later by vacuum suction. The lower surface of the holder 440 has a shape corresponding to the outer surface of the paper mold 240. Here, the holder 440 has a shape of a depression below. For example, one end of the holder 440 is opened at the lower surface, and the other end has a plurality of through holes connected to the pump.

In the manufacturing method according to an embodiment of the present invention, for example, a pulp molded article is manufactured using the manufacturing apparatus 1 described above. This will be described with reference to fig. 1 to 9.

Fig. 2 is a diagram showing a pulp layer forming process in pulp molding using the apparatus of fig. 1. Fig. 3 is a cross-sectional view schematically showing an example of a pulp layer formed on a paper making die. Fig. 4 is a diagram showing a dewatering step in pulp molding using the apparatus of fig. 1. Fig. 5 is a diagram showing a transfer process of a pulp layer in pulp molding using the apparatus of fig. 1. Fig. 6 is a diagram showing a hot press process in pulp molding using the apparatus of fig. 1. Fig. 7 is a cross-sectional view schematically showing an example of a pulp molded article obtained by the hot pressing step. Fig. 8 is a diagram showing a conveying process of a pulp molded product in pulp molding using the apparatus of fig. 1. Fig. 9 is a diagram showing a state after the conveyance process of fig. 8 is completed.

In this method, a slurry S is first prepared.

As described above, the slurry S contains pulp and water. The slurry S is a suspension of pulp dispersed in water and having a high viscosity.

The kind of pulp used in the slurry S is not particularly limited. As pulp, chemical pulp is preferably used. As the pulp, for example, the following pulps, which are generally used as raw material pulps in papermaking, may be used alone or 2 or more kinds of pulps may be mixed at an arbitrary ratio: wood pulp such as bleached kraft pulp (NBKP) or unbleached kraft pulp (NUKP) of conifer trees, and bleached kraft pulp (LBKP) or unbleached kraft pulp (LUKP) of broad-leaved trees; non-wood pulp such as straw, kapok, kenaf, bamboo, sugarcane, and the like.

The average fiber length of the pulp is less than 3.0mm. The average fiber length is preferably 1.7mm or less.

When the average fiber length of the pulp is long, aggregation of the pulp is easily generated in the pulp. As a result, in the hot pressing step, the pulp layer is dried while the surface thereof is kept in a state of being uneven due to aggregation. Therefore, a pulp molded article obtained by using a pulp having a long average fiber length cannot have a region having a small arithmetic average roughness Ra on the surface.

When the average fiber length of the pulp is short, it is difficult to generate aggregation of the pulp in the pulp. That is, the pulp is easily dispersed in a short fiber form, or it is difficult to produce large aggregates even if aggregation of the pulp occurs. In addition, when the average fiber length of the pulp is short, the movement of the fibers in the in-plane direction within the pulp layer is not excessively restricted in the hot pressing process. Therefore, a pulp molded article obtained by using pulp having a short average fiber length and sequentially performing the steps described later can have a region having a small arithmetic average roughness Ra on the surface.

The average fiber length of the pulp is preferably 0.5mm or more, more preferably 0.7mm or more.

In this method, a hot pressing process is performed on an undried pulp layer. Namely, a hot pressing process is performed on a pulp layer having a large moisture content. Therefore, when the average fiber length of the pulp is too short, uneven evaporation rate of water tends to occur in the hot pressing step, and uneven shrinkage occurs during drying, which may cause wrinkles, cracks, or decrease in strength.

If the average fiber length of the pulp is long, there is a low possibility that drying unevenness occurs in the pulp layer in the hot pressing process. Thus, it is possible to prevent the production of a pulp molded article having a poor appearance or reduced strength.

The average fiber length of the pulp may be adjusted by any method, for example, by mechanical treatment such as beating or pulverizing.

The pulp content of the slurry S is preferably in the range of 0.01 to 3.0 mass%, more preferably in the range of 0.01 to 0.5 mass%. When the pulp content is small, it is difficult to achieve high productivity. When the pulp content is large, there is a possibility that the thickness deviation of the pulp layer increases.

The slurry S may further comprise additives. As the additive, an organic polymer, an inorganic particle, or a combination thereof may be used. The proportion of the additive to the total of the pulp and the additive is preferably 10 mass% or less, more preferably 5 mass% or less. That is, the proportion of the pulp to the total solid content contained in the slurry S is preferably 90 mass% or more, more preferably 95 mass% or more.

Next, the slurry S is supplied into the container 210. Next, as shown in fig. 2, the cover 230 is lowered by the lifting device 220 so that the upper surface of the paper mold 240 is positioned sufficiently below the liquid surface of the slurry S. In this state, the pump is driven to decompress the space surrounded by the cover 230 and the paper mold 240. Thereby, a flow of the slurry S across the paper forming die 240 is generated, so that the pulp is deposited on the paper forming die 240. In this way, as shown in fig. 3, the pulp layer MP1 is formed on the paper mold 240.

Next, as shown in fig. 4, the cover 230 is lifted by the lifting device 220 in a state where the pump is driven so that the lower portion of the paper mold 240 is positioned sufficiently above the liquid surface of the slurry S. Thereby, the pulp layer MP1 is decompressed and dewatered. Next, the elevating device 260 is driven to lower the upper die 270 until the lower surface thereof contacts the pulp layer MP1. Note that, in fig. 4, the pulp layer MP1 is not depicted. This dehydration step is performed without heating both the upper die 270 and the paper die 240.

The depressurization time in the dehydration step is preferably in the range of 1 to 60 seconds, more preferably in the range of 1 to 10 seconds.

The moisture content of the pulp layer MP1 immediately after dewatering is preferably in the range of 40 to 90 mass%, more preferably in the range of 50 to 70 mass%. When the moisture content is small, movement of the fibers in the in-plane direction within the pulp layer may become insufficient in the hot pressing process. When the moisture content is large, movement of the fibers in the in-plane direction within the pulp layer may become excessive in the hot pressing process; or the shape retention of the pulp layer MP1 may become insufficient from the end of the dewatering process to the start of the hot pressing process.

After stopping the depressurization of the space and the pressurization, the pump is driven to suction and hold the pulp layer MP1 on the upper die 270. It should be noted that the suction of the pump and the upper die 270 does not cause further dewatering of the pulp layer MP1.

Next, the elevating device 260 is driven in a state where the pulp layer MP1 is sucked and held by the upper die 270, and the upper die 270 is elevated as shown in fig. 1. Thereby, the pulp layer MP1 is peeled from the paper mold 240.

Next, the moving means 250 and 330 are driven, as shown in fig. 5, to move the pressing means 340 and the upper die 350 from the 2 nd work station 30 to the 4 th work station, and simultaneously to move the elevating means 260 and the upper die 270 from the 1 st work station 20 to the 2 nd work station 30. Next, the elevating device 260 is driven to lower the upper die 270 until the pulp layer MP1 contacts the lower die 320. Then, suction with the pump and the upper die 270 is stopped, and the pulp layer MP1 is released from the upper die 270. Next, the elevating device 260 is driven to raise the upper die 270. In this way, the pulp layer MP1 is transferred from the 1 st station 20 to the 2 nd station 30, and the pulp layer MP1 is placed on the lower die 320.

Next, the moving means 250 and 330 are driven, as shown in fig. 1, to move the elevating means 260 and the upper die 270 from the 2 nd work station 30 to the 1 st work station 20, and simultaneously to move the pressing means 340 and the upper die 350 from the 4 th work station to the 2 nd work station 30. Next, the pressing device 340 is driven to lower the upper die 350 as shown in fig. 6. Then, the pulp layer MP1 sandwiched therebetween is pressurized by the upper mold 350 and the lower mold 320. In addition, at the same time, the heater is driven to heat the pulp layer MP1. Further, at the same time, the pump is driven to suck water and/or water vapor from the space sandwiched by the upper mold 350 and the lower mold 320. Thereby, the surface shape of the pulp layer MP1 is adjusted, and the pulp layer MP1 is densified and dried. In this way, the pulp molded article MP2 shown in fig. 7 was obtained.

The water content of the pulp layer MP1 immediately before the start of the hot pressing step is substantially equal to the water content of the pulp layer MP1 immediately after the end of the dewatering step.

In the hot pressing step, the pressing pressure is preferably 0.1MPa or more, more preferably 0.3MPa or more. When the pressing pressure is low, there is a possibility that the pulp molded article MP2 having a region with a small arithmetic average roughness Ra on the surface may not be obtained. The pressing pressure is preferably 1.5MPa or less, more preferably 1.0MPa or less. When the pressing pressure is too high, the thickness of the pulp molded article MP2 is liable to be deviated.

In the hot pressing step, the heating temperature of the pulp layer MP1, that is, the temperature of the upper mold 350 or the lower mold 320 heated by the heater is preferably in the range of 120 to 250 ℃, more preferably in the range of 150 to 210 ℃. When the heating temperature is low, drying of the pulp layer MP1 takes a long time. When the heating temperature increases, the shrinkage accompanying the dried pulp layer MP1 becomes larger, and as a result, there is a possibility that the strain in the pulp molded article MP2 becomes larger.

As described above, heating by the heater may be performed only on one of the upper die 350 and the lower die 320, or may be performed on both. In the case where heating is performed by a heater only on one of the upper die 350 and the lower die 320, the temperatures thereof are substantially equal due to heat conduction from one to the other. In either case, therefore, the drying of the pulp layer MP1 takes place almost simultaneously over its entire thickness. Therefore, strain due to the difference in drying speed does not occur in the pulp molded article MP2.

The pressing time in the hot pressing process depends on the heating temperature, the shape of the molded article, and the like, and is preferably in the range of 10 to 300 seconds, more preferably in the range of 20 to 200 seconds.

When the pressing device 340 is driven to raise the upper die 350 at the completion of the hot pressing process, the pulp molded article MP2 is peeled off from the upper die 350.

Next, the moving means 330 and 420 are driven, and as shown in fig. 8, the pressing means 340 and the upper die 350 are moved from the 2 nd working station 30 to the 4 th working station, and the elevating means 430 and the holder 440 are moved from the 3 rd working station 40 to the 2 nd working station 30. Then, the elevating device 430 is driven to lower the holder 440 until the holder 440 contacts the pulp molded article MP2. Then, the pump is driven to hold the pulp molded article MP2 to the holder 440 by suction.

Next, the lifting device 430 is driven in a state where the pulp molded article MP2 is sucked and held by the holder 440, and the holder 440 is lifted. Next, the moving means 330 and 420 are driven, and as shown in fig. 9, the lifting means 430 and the holder 440 are moved from the 2 nd working station 30 to the 3 rd working station 40, and the pressing means 340 and the upper die 350 are moved from the 4 th working station to the 2 nd working station 30. Next, suction by the pump and the holder 440 is stopped, and the pulp molded article MP2 is released from the holder 440. In this way, the pulp molded article MP2 is transported from the 2 nd station 30 to the 3 rd station 40, and the pulp molded article MP2 is placed on the table 410.

In the above manner, pulp molded article MP2 was produced.

Then, the pulp molded article MP2 is subjected to post-treatment, for example, printing such as pattern printing and plain printing, coating, or a combination thereof, as necessary. The coating layer formed by the post-treatment is, for example, a layer containing a water-resistant or oil-resistant agent, a layer filled with a material imparting heat insulation, a layer foamed with a foaming agent, or a combination thereof. By performing the post-treatment, for example, the aesthetic property of the pulp molded article MP2 can be further improved and a new function can be imparted to the pulp molded article MP2.

The pulp molded article MP2 obtained by the above method is excellent in surface properties. The reason for this will be described below.

When drying is performed using an oven instead of the hot pressing process, the pulp layer shrinks to generate uneven surfaces with large height differences on the surface. In addition, in such a method, the pulp layer cannot be sufficiently densified, and thus the pulp molded article has a high porosity. Therefore, in this case, a pulp molded article having excellent surface properties cannot be produced.

After the dehydration step, when the dried product is dried using an oven, humidified if necessary, and supplied to the hot press treatment, the level difference of the irregularities generated on the surface by the drying can be reduced by the subsequent humidification and hot press treatment. In addition, the porosity can be reduced by humidification and hot press treatment. However, since the level difference of the irregularities generated on the surface with the drying using the oven is very large, it cannot be sufficiently reduced by the subsequent humidification and hot press treatment. In addition, even if the humidification and hot press treatment are performed after the drying, it is difficult to sufficiently reduce the porosity.

In the method described with reference to fig. 1 to 9, the pulp layer MP1 is dried in the hot pressing process. That is, in the above method, the hot pressing step is performed after the dehydration step without the drying step. Then, as the pulp, pulp having an average fiber length in the above range is used.

Since the drying step is not performed before the hot pressing step, irregularities having large level differences are not generated on the surface of the pulp layer MP1. In the hot pressing process, the upper mold 350 and the lower mold 320 prevent deformation of the pulp layer MP1 accompanying drying. Further, since the hot pressing step is performed on the pulp layer MP1 having a high moisture content and an average fiber length of pulp within the above range, the movement of the fibers in the in-plane direction within the pulp layer MP1 can be appropriately generated. The pulp layer MP1 can be densified without a thickness deviation.

Accordingly, according to the method described with reference to fig. 1 to 9, a pulp molded article MP2 excellent in surface properties can be produced. Specifically, a pulp molded article MP2 having a region with an arithmetic average roughness Ra of 50 μm or less on the surface thereof was obtained. Such pulp molded article MP2 is excellent in aesthetic properties and is easy to form a printed layer and a coating layer.

The arithmetic average roughness Ra is preferably 40 μm or less. The arithmetic average roughness Ra is not limited to a lower limit, but is usually 20 μm or more.

The pulp molded article MP2 may have the above surface properties over the entire surface, or may have the above surface properties only in a partial region of the surface. For example, only the region including the portion subjected to post-treatment such as printing may have the surface property, and the other region may not have the surface property. Alternatively, one surface of the pulp molded article MP2 may have the surface property, and the back surface may not have the surface property. Such a structure can be achieved by, for example, making the surface properties of a part of the surface of the upper mold 350 and the lower mold 320, which is in contact with the pulp layer MP1, different from those of other regions.

Further, according to the method described with reference to fig. 1 to 9, a pulp molded article MP2 having a small standard deviation of weight per unit area can be produced. The standard deviation of the weight per unit area of the pulp molded article MP2 is preferably less than 30g/m ² More preferably 25g/m ² Hereinafter, it is more preferably 20g/m ² The following is given. The lower limit of the standard deviation is zero, according to one example 5g/m ² According to other examples 8g/m ² Further according to other examples 10g/m ² 。

Here, the standard deviation of the weight per unit area of the pulp molded article MP2 is a value obtained by the following method.

First, 9 test pieces each having a short strip shape with a width of 15mm and a length of 40mm were cut out from a plurality of regions located in a certain plane among the pulp molded article MP2. Subsequently, the mass of these test pieces was measured. Then, for each test piece, the test piece was measured in terms of its mass and area (600 mm ² ) The weight per unit area was calculated. The standard deviation was calculated from the weight per unit area thus obtained.

Next, 9 test pieces were cut out from a plurality of areas located in the other surface among the pulp molded article MP2 in the same manner as described above. For these test pieces, measurement of mass and calculation of weight per unit area and standard deviation thereof were also performed.

In the case where the pulp molded article MP2 further has other surfaces, the cutting out of the test piece, the measurement of the mass, and the calculation of the weight per unit area and the standard deviation thereof were also performed for the remaining surfaces in the same manner as described above.

Then, the maximum value of these standard deviations was regarded as the standard deviation of the weight per unit area of the pulp molded article MP2.

The inventors consider that: the reason why the pulp molded article MP2 having a small standard deviation in weight per unit area can be produced according to the method described with reference to fig. 1 to 9 (hereinafter referred to as the 1 st method) is as follows.

The pulp molded article can be produced by, for example, the method described below (hereinafter referred to as method 2).

In method 2, first, a female mold is prepared as a paper mold. The paper making mold comprises: a paper mold body provided with a plurality of through holes and having an upper surface recessed into a shape corresponding to the pulp molded article; and a net body arranged on the inner surface of the paper mould body in a mode of along the inner surface.

Next, the paper mold is set so that the opening is directed upward. Next, a slurry containing pulp and water is supplied into the cavity of the paper mold, and the paper mold is filled with the slurry. Further, the pulp is continuously supplied into the paper die, and the pulp is deposited on the net body. The slurry is supplied into the paper mold under pressure.

After a sufficient amount of pulp is deposited on the wire, the supply of pulp into the paper mould is stopped. Then, the water remaining in the paper mold is discharged from the paper mold. For example, air is pressed into the paper mold to drain water remaining in the paper mold from the paper mold.

Next, the pulp layer is pressed by the paper making mold and the upper mold as the male mold to dewater the pulp layer. The dewatering step is performed without heating the upper die and the paper die. The moisture content of the pulp layer immediately after dewatering is the same as that of the pulp layer MP1 immediately after dewatering in the method 1.

Next, the pulp layer is sucked and held on the upper die, and the upper die is raised in this state. Thereby, the pulp layer is peeled from the paper mold.

Next, the upper die holding the pulp layer by suction is moved to a position of the lower die serving as a female die. Next, the upper die is lowered until the pulp layer contacts the lower die. Then, the suction is stopped, and the pulp layer is released from the upper die. In this way, the pulp layer is placed on the lower die.

Next, a pulp layer is sandwiched between the upper die and the lower die for hot pressing, and the pulp layer between them is pressurized. In addition, at the same time, the heater is driven to heat the pulp layer. Further, at the same time, the pump is driven to suck water and/or water vapor from the space sandwiched by the upper die and the lower die. In the method 2, a pulp molded article was obtained in the above manner.

In method 2, the circulating slurry can flow in the paper die until the paper die is completely filled with the slurry from the start of the supply of the slurry into the paper die. The recycle stream may prevent sedimentation of the pulp. However, in the method 2, since the paper mold needs to be filled with the slurry, the paper mold cannot be structured to rapidly discharge water. Therefore, even if the pressure of the slurry is increased after the inside of the paper mold is completely filled with the slurry, a circulating flow of the slurry capable of preventing the pulp from settling is not generated, and the pulp settling is generated in the slurry inside the paper mold.

As a result, the amount of pulp deposited on the side wall portion of the paper making die is larger in the lower side than in the upper side. And, when the slurry is supplied until a sufficient amount of pulp is deposited above the side wall portion of the paper mold, an excessive amount of pulp is deposited at the bottom of the paper mold. When the pulp is excessively deposited, the deviation of the deposition amount of the pulp increases. For example, a large difference may occur in the deposition amount of pulp at positions near and far from the through-holes provided in the paper die main body.

Thus, in the method 2, a large deviation is generated in the deposition amount of pulp. When the hot press treatment is performed, the fibers can move in the in-plane direction in the pulp layer, but the movement of each fiber is limited to a narrow range. That is, the deviation of the pulp deposition amount cannot be eliminated by the movement of the fiber at the time of the autoclave treatment. Therefore, according to method 2, a pulp molded article having a small standard deviation of weight per unit area cannot be produced.

In contrast, in method 1, a paper mold 240 is provided on the upper portion of the lid 230, and the composite of these is immersed in the slurry S. The depth of the slurry S is much greater than the height of the paper die 240. Therefore, even if sedimentation of pulp occurs in the slurry S, there is no great difference in pulp concentration between the position of the upper part of the paper making die 240 and the position of the lower part of the paper making die 240. Therefore, according to method 1, the pulp can be deposited substantially uniformly on the paper mold 240, and the pulp molded article MP2 having a small standard deviation of the weight per unit area can be produced.

The pulp molded article MP2 has an opening portion, and does not expand in diameter in a direction away from the opening portion. Here, the pulp molded article MP2 has an opening portion, and tapers in a direction away from the opening portion. According to such a shape, the volume of the laminate in which a plurality of pulp molded articles MP2 are stacked can be reduced.

In the method 1, instead of pressurizing the pulp layer MP1 by the upper die 350 and the lower die 320, when the pulp layer MP1 is sandwiched between one of the upper die 350 and the lower die 320 and the elastic body, the elastic body is deformed. Therefore, a sufficient pressure cannot be applied to the pulp layer MP1, and a pulp molded article excellent in surface properties cannot be obtained.

In method 2, when one of the upper die and the lower die used for the heat press treatment is made of an elastomer, a pulp molded article excellent in surface properties cannot be obtained. In addition, in this case, as described above, the standard deviation of the weight per unit area increases.

The pulp molded article MP2 is, for example, a container. The pulp molded article MP2 may be an article other than a container. The pulp molded article MP2 may be a three-dimensional molded article, that is, a molded article having a three-dimensional shape instead of a two-dimensional shape such as a sheet.

Fig. 1 to 9 are drawings for easy understanding of a method for manufacturing a pulp molded article according to an embodiment of the present invention. The above method may be implemented using a manufacturing apparatus having other structures. For example, in manufacturing apparatus 1, upper mold 270 and upper mold 350 are female molds, and paper making mold 240 and lower mold 320 are male molds. The upper mold 270 and the upper mold 350 may be male molds, and the paper making mold 240 and the lower mold 320 may be female molds. Thus, the manufacturing apparatus 1 and the manufacturing method described above can be variously modified.

Hereinafter, specific examples of the present invention will be described. The present invention is not limited to these specific examples.

<1> manufacture of pulp molded article

Example 1

A pulp consisting of pulp and water was prepared using a pulper (pulper). As pulp, conifer pulp having an average fiber length of 2.3mm was used. The pulp content of the slurry was set to 0.3 mass%.

Using this slurry, a pulp molded article was produced by the 1 st method described with reference to fig. 1 to 9. Here, the dewatering step was performed so that the water content of the pulp layer immediately after dewatering became 65 mass%. The hot pressing step was carried out at a heating temperature of 150℃and a pressing pressure of 0.5MPa for a pressing time of 180 seconds.

In the above manner, a container as a pulp molded article was produced.

Example 2

A pulp molded article was produced in the same manner as in example 1, except that a bamboo pulp having an average fiber length of 1.6mm was used instead of the conifer pulp having an average fiber length of 2.3 mm.

Example 3

A pulp molded article was produced in the same manner as in example 1, except that hardwood pulp having an average fiber length of 0.9mm was used instead of softwood pulp having an average fiber length of 2.3 mm.

Example 4

Conifer pulp having an average fiber length of 2.3mm was pulped to a Canadian standard freeness of 400mLCSF (Canadian Standard Freeness), thereby obtaining pulp having an average fiber length of 1.8 mm. A pulp molded article was produced in the same manner as in example 1, except that the above pulp having an average fiber length of 1.8mm was used instead of the conifer pulp having an average fiber length of 2.3 mm.

Example 5

A slurry consisting of pulp and water was prepared using a pulper. As pulp, bamboo pulp having an average fiber length of 1.6mm was used. The pulp content of the slurry was set to 0.3 mass%.

Using this slurry, a pulp molded article was produced by the above-mentioned method 2. Here, the dewatering step was performed so that the water content of the pulp layer immediately after dewatering became 65 mass%. The hot pressing step was carried out at a heating temperature of 150℃and a pressing pressure of 0.5MPa for a pressing time of 180 seconds.

In the above manner, a container as a pulp molded article was produced.

Comparative example 1

A pulp molded article was produced in the same manner as in example 1, except that conifer pulp having an average fiber length of 3.0mm was used instead of conifer pulp having an average fiber length of 2.3 mm.

Comparative example 2

A pulp molded article was produced in the same manner as in example 1, except that the pressing pressure was set to 0MPa instead of 0.5 MPa.

<2> measurement of surface Properties

From each of the pulp molded articles produced in examples 1 to 5 and comparative examples 1 and 2, a test piece in the form of a short bar having a width of 2cm and a length of 5cm was cut.

Then, for each test piece, the surface corresponding to the outer surface of the pulp molded article was measured by a laser displacement meter, and a profile curve of the surface was obtained. The measurement is performed along a center line dividing the width of the test piece into two parts. Then, an arithmetic average roughness Ra is calculated from each profile curve. The results are shown in the following table.

<3> printing adaptability test

A pattern was printed on the outer surface of each of the pulp molded articles manufactured in examples 1 to 5 and comparative examples 1 and 2 by a screen printing method. The printed pattern was visually observed to confirm the presence or absence of a notch and the presence or absence of abrasion of the pattern. Then, the case where neither chipping nor galling occurred in the pattern was evaluated as "a+", the case where chipping but galling occurred in the pattern was evaluated as "a", and the case where chipping occurred in the pattern was evaluated as "B". The results are shown in the following table.

<4> measurement of standard deviation of weight per unit area

For each of the pulp molded articles produced in examples 1 to 5 and comparative examples 1 and 2, the standard deviation of the weight per unit area was measured by the above-described method. The results are shown in the following table.

TABLE 1

As is evident from the comparison of examples 1 to 5 with comparative example 2: by pressing the pulp layer at the time of drying, the arithmetic average roughness Ra can be reduced. In addition, it is apparent from comparison of examples 1 to 5 with comparative example 1: when the average fiber length is shortened, the arithmetic average roughness Ra becomes smaller. In the method 1, when pulp having an average fiber length of less than 3.0 μm is used, the pattern is free from chipping, and practically sufficient printing adaptability can be achieved. In particular, in the method 1, when pulp having an average fiber length of 1.7 μm or less is used, neither chipping nor abrasion occurs in the pattern, and excellent printing adaptability can be achieved. In addition, it is apparent from the comparison of example 1 with example 5: according to the method 1, the standard deviation of the weight per unit area can be reduced as compared with the method 2.

Description of symbols

1.A manufacturing apparatus, 10.A support, 20.1 station, 30.2 station, 40.3 station, 210.a container, 220.a lifting apparatus, 230.a cover, 240.a paper making mold, 250.a moving apparatus, 260.a lifting apparatus, 270.a top mold, 310.a stage, 320.a bottom mold, 330.a moving apparatus, 340.a pressing apparatus, 350.a top mold, 410.a stage, 420.a moving apparatus, 430.a lifting apparatus, 440.a holding apparatus, MP 1.a pulp layer, MP 2.a pulp molding article, S.a slurry.

Claims

1. A pulp molded article having a region with an arithmetic average roughness Ra of 50 μm or less on the surface.

2. The pulp molded article according to claim 1, wherein the average fiber length of the pulp is less than 3.0mm.

3. The pulp molded article according to claim 2, wherein the average fiber length is 0.5mm or more.

4. The pulp molded article according to any one of claims 1 to 3, wherein the standard deviation of the weight per unit area is less than 30g/m ² 。

5. The pulp molded article according to any one of claims 1 to 4, which has an opening portion and is tapered in a direction away from the opening portion.

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

7. A method of manufacturing a pulp molded article, comprising:

preparing a slurry comprising pulp having an average fiber length of less than 3.0mm and water;

depositing the pulp on a paper making mold having a three-dimensional shape to form a pulp layer;

dewatering the pulp layer to obtain an intermediate formed article; and

the intermediate molded article which has not been dried is sandwiched between a male mold and a female mold, and heated while being pressurized.

8. The method for producing a pulp molded article according to claim 7, wherein,

depositing the pulp onto the paper making die comprises:

preparing a cover body as a hollow body having an opening;

fixing the paper making mold on the opening part;

immersing the paper making die fixed to the opening in the slurry; and

and depressurizing a space surrounded by the cover and the paper mold immersed in the slurry.

9. The method for producing a pulp molded article according to claim 8, wherein,

the paper mold is immersed in the slurry so that the paper mold is positioned above the cover.