CN117716089A

CN117716089A - Pulp molded article and method for producing the same

Info

Publication number: CN117716089A
Application number: CN202280052796.8A
Authority: CN
Inventors: 石井萌; 坂入幸司
Original assignee: Toppan Printing Co Ltd
Current assignee: Toppan Inc
Priority date: 2021-08-02
Filing date: 2022-08-02
Publication date: 2024-03-15

Abstract

A pulp molded article having a small thickness, high strength, and excellent releasability at the time of production can be realized. In the pulp molded article (MP 2), the proportion of the fibers with the fiber length of 1mm or less in the pulp is in the range of 35 to 50%, the average fiber length of the pulp is in the range of 1.2 to 1.5mm, and the density is in the range of 0.65 to 1.3g/cm ³ In the range of 400 to 2000. Mu.g/g.

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 being 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 which is made of a cardboard having polyethylene resin coated on both sides of paper and has a gable-top shape at the top, i.e., a so-called roof-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 pulp 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

The purpose of the present invention is to provide a pulp molded article which has a small thickness, high strength, and excellent mold release properties during production.

According to one aspect of the present invention, there is provided a pulp molded article, wherein a proportion of fibers having a fiber length of 1mm or less in pulp is in the range of 35 to 50%, an average fiber length of the pulp is in the range of 1.2 to 1.5mm, and a density is in the range of 0.65 to 1.3g/cm ³ In the range of 400 to 2000. Mu.g/g.

According to other aspects of the present invention, there is provided the pulp molded article as referred to in the above aspects, wherein the thickness is in the range of 0.5 to 1 mm.

According to another aspect of the present invention, there is provided the pulp molded article according to any one of the above aspects, wherein the density is in the range of 0.65 to 0.80g/cm ³ In the range of 500 to 1000. Mu.g/g.

According to another aspect of the present invention, there is provided the pulp molded article according to any one of the above aspects, wherein the tensile strength is in the range of 30 to 55 kN/m.

According to another aspect of the present invention, there is provided the pulp molded article according to any one of the above aspects, wherein the peel strength is in the range of 0.3 to 0.9N/mm ² Within a range of (2).

According to another aspect of the present invention, there is provided the pulp molded article according to any one of the above aspects, wherein the standard deviation of the weight per unit area is from 2 to 30g/m ² Within a range of (2).

According to another aspect of the present invention, there is provided the pulp molded article according to any one of the above aspects, which is a container.

According to another aspect of the present invention, there is provided a method for producing a pulp molded article, comprising: preparing a slurry containing pulp and water, wherein the proportion of fibers with a fiber length of 1mm or less in the pulp is in the range of 35 to 50%; 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 formed article, which is not dried, between a male die and a female die, and heating at a temperature in the range of 150 to 220 ℃ while pressurizing under a pressure in the range of 0.4 to 4.5 MPa.

According to another aspect of the present invention, there is provided the method for producing a pulp molded article according to the above aspect, wherein depositing the pulp onto the paper making mold comprises: preparing a cover body as a hollow body having an opening; fixing the paper mold to the opening; immersing the paper making mold fixed to the opening in the slurry; and depressurizing a space surrounded by the cover and the paper mold immersed in the slurry.

According to another aspect of the present invention, there is provided the method for producing a pulp molded article according to any one of the above aspects, wherein the paper mold is immersed in the slurry so that the paper mold is positioned above the cover.

According to another aspect of the present invention, there is provided the method for producing a pulp molded article according to any one of the above aspects, wherein the pressurizing and heating of the intermediate molded article, which is not dried, interposed between the male mold and the female mold is performed at a pressure in the range of 0.4 to 2.0MPa and a temperature in the range of 150 to 200 ℃, respectively.

According to the present invention, a pulp molded article having a small thickness, high strength, and excellent releasability at the time of production can be realized.

Drawings

Fig. 1 is a perspective view showing a pulp molded article according to an embodiment of the present invention.

Fig. 2 is a view schematically showing an example of a manufacturing apparatus that can be used to manufacture the pulp molded article of fig. 1.

Fig. 3 is a diagram showing a pulp layer forming process in pulp molding using the apparatus of fig. 2.

Fig. 4 is a cross-sectional view schematically showing an example of a pulp layer formed on a paper die.

Fig. 5 is a diagram showing a dewatering step in pulp molding using the apparatus of fig. 2.

Fig. 6 is a diagram showing a transfer process of a pulp layer in pulp molding using the apparatus of fig. 2.

Fig. 7 is a diagram showing a hot press forming process in pulp molding using the apparatus of fig. 2.

FIG. 8 is a cross-sectional view schematically showing an example of a pulp molded article obtained by the hot pressing step.

Fig. 9 is a diagram showing a conveying process of a pulp molded article in pulp molding using the apparatus of fig. 2.

Fig. 10 is a view showing a state after the completion of the conveying process of fig. 9.

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.

<1> pulp molded article

The pulp molded article MP2 shown in fig. 1 is a container. The pulp molded article MP2 includes a bottom portion and a side wall portion, and is open at an upper portion.

The bottom has a disc shape. The orthographic projection of the bottom portion to 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 quadrangular shape.

The side wall portion has a cylindrical shape extending upward from an edge of the bottom portion. The sidewall portion expands in diameter from the bottom portion toward the opening portion. The inner and outer faces of the side wall portions may be perpendicular to the upper face of the bottom portion. However, the pulp molded article MP2 in which the side wall portion expands in diameter from the bottom portion to the opening portion is advantageous in achieving high releasability and is easy to stack.

The pulp molded article MP2 may have various shapes such as a cup shape, a bowl shape, a tray shape, and a box shape. 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 as in a sheet, and may be a container.

The pulp molded article MP2 has a thickness of 1mm or less. That is, the thickness of the wall portion, here, the bottom portion and the side wall portion of the pulp molded article MP2 is 1mm or less. The pulp molded article MP2 preferably has a thickness of 0.8mm or less. The thick pulp molded article MP2 increases in volume particularly when stacked. In addition, thinning the wall portion of the pulp molded article MP2 is advantageous in that drying at the time of manufacturing thereof can be completed in a short time.

The thickness of the pulp molded article MP2 is preferably 0.5mm or more, more preferably 0.6mm or more, and still more preferably 0.7mm or more. The pulp molded article MP2 having a thin wall portion is liable to be deviated in the thickness of the wall portion.

Here, the thickness of the pulp molded article MP2 is a value obtained by the following method. That is, 5 test pieces were cut out from arbitrary positions of the pulp molded article MP2. Next, the thickness of each test piece was measured. For the measurement of the thickness, for example, a thickness meter manufactured by Mitutoyo Corporation is used. The thickness of the pulp molded article MP2 was set to be the average value of the measurement results obtained for 5 test pieces.

In the pulp molded article MP2, the proportion of the fibers having a fiber length of 1mm or less in the pulp is in the range of 35 to 50%. The proportion is preferably in the range of 40 to 50%, more preferably in the range of 40 to 48%. When this ratio is increased, the density of the pulp molded article MP2 is easily increased, and the strength thereof is also increased. Further, when this ratio is increased, a pulp molded article MP2 excellent in aesthetic appearance is easily obtained. However, when the ratio is too large, it is difficult to complete drying in a short time, or cracks due to drying failure and a decrease in releasability are likely to occur.

The proportion of fibers having a fiber length of 1mm or less in the pulp is the proportion of the number of fibers (roots) having a fiber length of 1mm or less to the total number of fibers (roots) in the pulp. This ratio is obtained by the following method.

First, 5g of a test piece was obtained from the pulp molded article MP 2. Next, the test piece was cut into filaments, and water was added so that the total mass became 500g, and the resultant was immersed overnight. Then, it was stirred with a stirrer to dissociate the pulps from each other. Thus, a pulp-containing dispersion was obtained. Then, an appropriate amount of the dispersion was taken out and diluted with water to prepare an aqueous dispersion having a pulp solid content of 0.05 mass%.

Using the thus obtained sample, pulp was subjected to the method for measuring fiber length by automatic optical analysis according to JIS P8226-2:2011", part 2: the fiber length was measured by the unpolarized light method ". The fiber length measurement is completed when 2 ten thousand or more fibers with a fiber length of 0.2mm or more are detected. From the frequency distribution of the fiber length obtained by the fiber length measurement, the proportion of the fiber having a fiber length of 1mm or less in the pulp was obtained.

In the pulp molded article MP2, the proportion of the fibers having a fiber length of 0.2mm or less in the pulp is preferably in the range of 20 to 35%, more preferably in the range of 25 to 33%. When this ratio is increased, a dense layer is formed with less pulp, and improvement in strength and smoothness of the surface can be expected. However, when the ratio is too large, the drainage property is lowered, the resulting pulp layer becomes uneven, and the production efficiency is lowered due to the time taken for the dewatering step, or the shape is difficult to maintain due to the inability to dewater to a predetermined water content.

The proportion of fibers having a fiber length of 0.2mm or less in the pulp is the proportion of the number of fibers (roots) having a fiber length of 0.2mm or less in the total number of fibers (roots) of the pulp. This ratio is obtained by the following method.

Using the thus obtained sample, pulp was subjected to the method for measuring fiber length by automatic optical analysis according to JIS P8226-2:2011", part 2: the fiber length was measured by the unpolarized light method ". The fiber length measurement is completed when 2 ten thousand or more fibers with a fiber length of 0.2mm or more are detected. From the frequency distribution of the fiber length obtained by the fiber length measurement, the proportion of the fiber having a fiber length of 0.2mm or less in the pulp was obtained.

In the pulp molded article MP2, the average fiber length of the pulp is preferably in the range of 1.2 to 1.5mm, more preferably in the range of 1.3 to 1.5 mm. When the average fiber length is increased, the strength of the pulp molded article MP2 is lowered. When the average fiber length is reduced, it takes longer to dry at the time of manufacture. The average fiber length is a length weighted average fiber length LL obtained by measuring the fiber length according to the above-described method involving the proportion of fibers having a fiber length of 1mm or less in pulp.

The Canadian Standard Freeness (CSF) of the pulp suspension obtained by dispersing the pulp contained in the pulp molded article MP2 in water is preferably 640mL or less, more preferably 620mL or less, and further preferably 610mL or less. In the case where the Canadian standard freeness is large, the strength of the pulp molded article MP2 tends to be low.

The Canadian standard freeness is preferably 500mL or more, more preferably 530mL or more, and further preferably 550mL or more. In the case where the Canadian standard freeness is large, drying of the pulp molded article MP2 at the time of its manufacture tends to take a long time.

Here, the canadian standard freeness described above is a value obtained by the following method. First, a test piece was obtained from the pulp molded article MP2, and a pulp-containing dispersion was obtained by the same method as described above. Then, the dispersion was diluted with water so that the solid content concentration became 0.3 mass%, thereby obtaining an aqueous suspension of pulp. Next, using 1L of this suspension, JIS P8121-2:2012 "pulp-freeness test method-part 2: canadian Standard freeness method. In this measurement, for example, a Canadian freeness tester manufactured by Xiong Guli industrial company is used. The measured value is corrected by referring to the temperature of the suspension measured in advance in the correction table. Thus, canadian standard freeness is obtained.

It is assumed that pulp molded article MP2 or an article put into a container including pulp molded article MP2 as a container main body is placed in overlapping, for example, at the time of transportation or at the time of display. The stacked articles placed in the container may be broken due to, for example, impact accompanying dropping. The pulp molded article MP2 is required to have sufficient strength, particularly sufficient impact resistance under such conditions.

The tensile strength of the pulp molded article MP2 is preferably in the range of 30 to 55kN/m, more preferably in the range of 35 to 55kN/m, still more preferably in the range of 40 to 55 kN/m. When the inter-fiber bonding in the in-plane direction is reinforced, the tensile strength tends to become large. Therefore, when the tensile strength is increased, impact resistance can be improved. However, when the tensile strength is too high, the steel sheet is easily broken in a state where a large impact is applied, for example, in a drop. Namely, the pulp molded article MP2 becomes brittle.

The tensile elongation at break of the pulp molded article MP2 is preferably in the range of 5 to 25%, more preferably in the range of 10 to 25%, still more preferably in the range of 10 to 25%. When the tensile elongation at break of the pulp molded article MP2 is increased, deformation can be tolerated and the impact can be absorbed without occurrence of cracking or the like in the case where a large impact is applied.

Here, the tensile strength and the tensile elongation at break are values obtained by the following methods. First, a test piece having a long strip shape with a width of 15mm and a length of 40mm was cut out from a portion of the pulp molded article MP2 whose surface was not bent. Next, the thickness and mass of the test piece were measured. Next, using the test piece, JIS P8113:2006, test method for paper and cardboard-tensile Property-part 2: constant speed elongation method. Here, the long bars were clamped at a gap of 20 mm. The movement speed of the jigs, that is, the extension speed of the test piece was set to 20 mm/min. The tensile strength and the tensile elongation at break were each an average of values obtained by 3 measurements.

Pulp molded article MP2 excellent in peel strengthSelected from 0.3 to 0.9N/mm ² More preferably in the range of 0.5 to 0.9N/mm ² In the range of 0.6 to 0.9N/mm, further preferred ² Within a range of (2). When the inter-fiber bonding in the thickness direction of the pulp molded article MP2, that is, in the direction perpendicular to the surface, is reinforced, the peel strength tends to become large. When the peel strength is small, the bonding of the fibers in the thickness direction is weak, and when a large impact is applied to the pulp molded product 2, there is a possibility that the breakage occurs from the inside. In addition, when the peel strength is small, when a force in a direction parallel to the surface such as friction is applied, surface peeling or the like is likely to occur. Thus, the peel strength is preferably large from the viewpoint of strength. However, in order to achieve the peel strength exceeding the upper limit value, excessive densification is required, resulting in a decrease in productivity.

Here, the peel strength is measured by "internal bond strength test method-part 1" described in JAPAN TAPPI 18-1: the value obtained by the Z-axis tensile test method ". First, a test piece having a square shape and 25mm on one side was cut out from the pulp molded article MP 2. Next, double-sided adhesive tapes were attached to both sides of the test piece, and the test piece was fixed to the upper and lower jigs via these double-sided adhesive tapes. As the double-sided adhesive Tape, scotch Tape (registered trademark) #400 manufactured by 3M company, for example, is used. These jigs were pressed against each other with a load of 150kgf, and this state was maintained for 20 seconds. Thereby, the sample piece was press-fitted to the jig. Then, while fixing the position of the lower jig, the upper jig was raised at a speed of 20 mm/min to cause interlayer peeling of the test piece, and the maximum load at this time was obtained. The peel strength was an average of values obtained by 2 measurements.

The density of the pulp molded article MP2 is 0.65g to 1.3/cm ³ Within a range of (2). The density of the pulp molded article MP2 is preferably 0.7g to 1.3/cm ³ In the range of from 0.8g to 1.3/cm, more preferably ³ Within a range of (2). The density of the pulp molded article MP2 may be in the range of 0.65 to 0.80g/cm ³ Within a range of (2).

Here, the density is a value obtained by the following method. That is, a square or rectangular test piece was cut out from a portion of the pulp molded article MP2 whose surface was not bent, and the dimensions, mass and thickness were measured. The density was calculated from the obtained values.

The pulp molded article MP2 preferably further contains a paper strength enhancer such as polyacrylamide. When the paper strength enhancer is used, the strength of the pulp molded article MP2 can be improved. Among paper strength enhancers, polyacrylamide is particularly advantageous in the production of pulp molded article MP 2.

The pulp molded article MP2 produced using the paper strength agent has a higher nitrogen content than the pulp molded article MP2 produced without the paper strength agent. The nitrogen content of the pulp molded article MP2 produced using the paper strength agent is in the range of 400 to 2000. Mu.g/g, preferably in the range of 500 to 1500. Mu.g/g, more preferably in the range of 600 to 1500. Mu.g/g. The nitrogen content of the pulp molded article MP2 may be in the range of 500 to 1000. Mu.g/g.

When the nitrogen content of the pulp molded article MP2 is reduced, the strength of the pulp molded article MP2 is reduced, and breakage or the like is likely to occur when a large impact is applied. When the nitrogen content is reduced, there is a possibility that the shape retention of the container is reduced when used as an article placed in the container. When the nitrogen content is too large, the aggregation of fibers becomes large, and the strength-improving effect becomes high with the increase of the nitrogen content.

The nitrogen content of the pulp molded article MP2 was obtained by the following method. First, 2 test pieces were taken from an arbitrary position of the pulp molded article MP 2. The mass of each test piece was set to 10mg. Next, each test piece was measured by a chemiluminescent method specified in JIS K2609:1998, "crude oil and Petroleum products-Nitrogen analysis test method". For example, TN-2100H manufactured by Nittoseiko Analytech Co., ltd. The nitrogen content was set as an average value of measurement results obtained for 2 test pieces.

<2> apparatus for producing pulp molded article

Next, a manufacturing apparatus that can be used to manufacture the pulp molded article MP2 will be described. Fig. 2 is a diagram schematically showing an example of a manufacturing apparatus that can be used to manufacture the pulp molded article of fig. 1.

The manufacturing apparatus 1 shown in fig. 2 includes: a support 10, a 1 st workstation 20, a 2 nd workstation 30, and a 3 rd workstation 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 so that a 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 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 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 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 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 both 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.

<3> method for producing pulp molded article

In the manufacturing method according to an embodiment of the present invention, for example, the pulp molded article MP2 is manufactured using the manufacturing apparatus 1 described above. This will be described with reference to fig. 1 to 10.

Fig. 3 is a diagram showing a pulp layer forming process in pulp molding using the apparatus of fig. 2. Fig. 4 is a cross-sectional view schematically showing an example of a pulp layer formed on a paper making die. Fig. 5 is a diagram showing a dewatering step in pulp molding using the apparatus of fig. 2. Fig. 6 is a diagram showing a transfer process of a pulp layer in pulp molding using the apparatus of fig. 2. Fig. 7 is a diagram showing a hot press molding process in pulp molding using the apparatus of fig. 2. Fig. 8 is a cross-sectional view schematically showing an example of a pulp molded article obtained by the hot pressing step. Fig. 9 is a diagram showing a conveying process of a pulp molded article in pulp molding using the apparatus of fig. 2. Fig. 10 is a diagram showing a state after the conveyance process of fig. 9 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 having a high viscosity in which pulp is dispersed in water.

The pulp contained in the slurry S has substantially the same characteristics as those described above for the pulp contained in the pulp molded article MP 2.

The kind of pulp used in the slurry S is not particularly limited. As pulp, wood pulp, non-wood pulp, waste paper, preferably wood pulp, non-wood pulp, can be exemplified. From the environmental viewpoints of forest conservation, utilization of unused resources, and the like, it is preferable to use non-wood pulp.

Pulp can be classified according to the preparation method thereof. For example, in the case of wood pulp, it can be exemplified that: chemical pulp such as Kraft Pulp (KP), sulfite Pulp (SP), and Alkaline Pulp (AP); semi-chemical pulp (SCP), chemical Groundwood Pulp (CGP) and the like; groundwood Pulp (GP), thermomechanical pulp (TMP), and the like. Among these, chemical pulp is preferably used.

Wood pulp can be classified according to raw materials. Examples of the wood pulp include conifer pulp and hardwood pulp. As conifer pulp, pulp obtained from fir genus, pinus genus, and the like can be exemplified. Further, as the broad-leaved tree pulp, pulp obtained from acacia, eucalyptus, beech, poplar (for example, aspen) and the like can be exemplified.

The non-wood pulp is obtained from fibers extracted from the bark, stem, leaf sheath of the plant. Specifically, pulp obtained from cotton linter, cotton, flax product (linen), hemp, ramie, straw, fine-stalk needle grass (esparto), abaca, sisal (sisal hemp), jute, flax, kenaf, bamboo, sugarcane, goose skin (ganpi), knot (Edgeworthia chrysantha), paper mulberry, mulberry can be cited. Among them, pulp of bamboo and sugar cane is preferable.

These pulps may be used alone or in combination of 2 or more kinds in any ratio.

The fiber length of pulp and the like vary depending on the raw material and the manufacturing method thereof. For example, in general, pulp from sugar cane has a shorter average fiber length than pulp from bamboo. In addition, the average fiber length of the pulp may be adjusted by any method, for example, by mechanical treatment such as beating or pulverizing. Accordingly, pulp having a certain characteristic can be obtained by selecting an appropriate pulp from a plurality of pulps, or appropriately combining 2 or more pulps, for example. As the pulp, non-wood pulp is preferably used, and pulp using sugar cane as a raw material, pulp using bamboo as a raw material, or a combination thereof is preferably used.

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 deviation of the thickness of the pulp layer becomes large.

The slurry S preferably further comprises a paper strength enhancer. The proportion of the paper strength agent in the total of the pulp and the paper strength agent (based on the solid content) is preferably in the range of 0.3 to 3 mass%, more preferably in the range of 0.5 to 2 mass%, still more preferably in the range of 0.7 to 2 mass%.

The slurry S may also contain other additives. As the additive, an organic low molecular material, an organic polymer material, an inorganic material, or a combination thereof may be used, and examples thereof include a reagent imparting water resistance or oil resistance, and the reagent may be selected in accordance with the required performance as a pulp molded container.

The proportion of the additive in 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 in the total solid content contained in the slurry S is preferably 90% by mass or more, more preferably 95% by mass or more.

Next, the slurry S is supplied into the container 210. Next, as shown in fig. 3, 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 crossing 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. 4, the pulp layer MP1 is formed on the paper mold 240.

Next, as shown in fig. 5, 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. 5, the pulp layer MP1 is not shown. 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%, still more preferably in the range of 60 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 MP 1.

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. 2. 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. 6, 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. 2, 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. 7. 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 MP 1. 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. 8 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 process, the pressing pressure is preferably in the range of 0.4 to 4.5MPa, more preferably in the range of 0.8 to 2.5 MPa. When the pressing pressure is low, there is a possibility that the pulp molded article MP2 of high density is not obtained. The pulp layer MP1 contains a large amount of pulp with a relatively short fiber length. Particularly in case of too high a pressing pressure, such pulp tends to move in the pulp layer MP 1. Therefore, when the pressing pressure is too high, the thickness of the pulp molded article MP2 is liable to be deviated. The pressing pressure may be in the range of 0.4 to 2.0 MPa.

In this 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 150 to 220 ℃, more preferably in the range of 150 to 200 ℃, and still more preferably in the range of 165 to 190 ℃. Since the pulp layer MP1 contains a large amount of pulp having a short fiber length, it is difficult for water vapor to escape to the outside. Therefore, when the heating temperature is low, the drying of the pulp layer MP1 takes a long time. When the heating temperature increases, shrinkage of the pulp layer MP1 accompanying drying becomes larger, and as a result, strain in the pulp molded article MP2 is likely to become larger.

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. 9, 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 MP 2. Air is ejected from the inside of the lower die to release the pulp molded article MP2 from the lower die, and then the pump is driven to suction and hold the pulp molded article MP2 on the holder 440.

Next, the lifting device 430 is driven in a state in which the pulp molded article MP2 is sucked and held on the holder 440, and the holder 440 is lifted. Next, the moving means 330 and 420 are driven, and as shown in fig. 10, 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, thereby releasing the pulp molded article MP2 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 or a new function can be imparted to the pulp molded article MP2.

According to the above method, a pulp molded article MP2 having a small thickness and high strength, which can realize excellent releasability at the time of production, can be produced. The excellent releasability means that: the pulp molded article MP2 can be released from the lower die by blowing out air, and no surface peeling or crack generation occurs due to the release.

Since the thickness of the wall portion of the pulp molded article MP2 is small, the height at the time of stacking is small in addition to the light weight. Thus, the pulp molded article MP2 can achieve high conveying efficiency.

Further, according to the above method, drying can be completed in a short time. Therefore, improvement in production efficiency and reduction in energy can be expected.

In addition, 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 step, the pulp layer is shrunk to form irregularities with large level 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.

In addition, in the case where the dried product is dried using an oven after the dehydration step, humidified if necessary, and supplied to the hot press treatment, the level difference of the irregularities generated on the surface accompanying 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. 2 to 10, the pulp layer MP1 is dried in the hot pressing process. That is, in the above-described method, the hot pressing step is performed after the dehydration step, without going through 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 MP 1. 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. 2 to 10, a pulp molded article MP2 excellent in surface properties can be produced. Specifically, a pulp molded article MP2 having a region in which 1 or more of the arithmetic average roughness Ra, the maximum height roughness Rz, and the average length RSm of the roughness curve elements is small on the surface is 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 in the range of 2 to 10 μm, more preferably in the range of 2.5 to 4.5 μm. The maximum height roughness Rz is preferably in the range of 10 to 60 μm, more preferably in the range of 15 to 30 μm. The average length RSm of the roughness curve elements is preferably in the range of 90 to 300 μm, more preferably in the range of 90 to 150 μm, still more preferably in the range of 90 to 130 μm.

Here, "arithmetic average roughness Ra", "maximum height roughness Rz" and "average length RSm of roughness curve elements" are surface property parameters defined in JIS B0601:2001. For measurement of the surface property parameters, for example, a surface roughness measuring machine SJ-210 (tip radius 2 μm, measuring force 0.75 mN) manufactured by Mitutoyo Corporation was used, and the measurement was performed under the following conditions.

And (3) a filter: gasussian

Cut-off λc:0.25mm

Cut-off λs:8 μm

Measuring speed: 0.25mm/s

Number of intervals: 5

The sheet-like sheet was taken out of the pulp molded article MP2, and measured at 5 arbitrary positions, and an average value was calculated.

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, the region including only 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. 2 to 10, a pulp molded article MP2 having a small standard deviation of weight per unit area can be produced. Pulp moldingThe standard deviation of the weight per unit area of the form MP2 is preferably 30g/m ² Hereinafter, more preferably 15g/m ² The following is given. The lower limit of the standard deviation is zero, according to one example 2g/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 long 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 MP 2. 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 MP 2.

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. 2 to 10 (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 to deposit the pulp on the net body. The slurry is supplied into the paper mold in such a manner that the slurry in the paper mold is pressurized.

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 discharge 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 in 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, suction is stopped to release the pulp layer 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, a flow of the circulating slurry can be generated in the paper die during a period from the start of the supply of the slurry into the paper die to the completion of the filling 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, deformation of the elastic body occurs when the pulp layer MP1 is sandwiched between one of the upper die 350 and the lower die 320 and the elastic body and pressurized. 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 any three-dimensional molded article, that is, a molded article having a three-dimensional shape instead of a two-dimensional shape as in a sheet.

Fig. 2 to 10 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.

Examples

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 slurry consisting of pulp, paper strength enhancers and water was prepared using a pulper. The pulp content of the slurry was set to 0.3 mass%. As the pulp, pulp A having an average fiber length of 1.6mm and pulp B having an average fiber length of 0.94mm were used. The amount of pulp a was set to 80 parts by mass with respect to 100 parts by mass of the total amount of pulp. As the paper strength enhancer, polyston (registered trademark) 1280 manufactured by the chemical industry company of waste and Sichuan was used. The proportion of the paper strength agent in the solid content of the slurry was 1 mass%.

Using this slurry, a pulp molded article was produced by the method described with reference to fig. 2 to 10. 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 performed at a heating temperature of 160℃and a pressing pressure of 1.2MPa for a pressing time of 140 seconds. In the dewatering step and the hot pressing step, the gap between the upper die and the lower die was set to 1.0mm to obtain a pulp molded article having a wall portion thickness of 1.0 mm.

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 pulp C having an average fiber length of 0.86mm was used instead of pulp B.

Example 3

A pulp molded article was produced in the same manner as in example 1, except that the amount of pulp a was 70 parts by mass based on 100 parts by mass of the total amount of pulp, and the proportion of the paper strength agent in the solid content of the pulp was 3% by mass.

Example 4

A pulp molded article was produced in the same manner as in example 1, except that the amount of pulp a relative to 100 parts by mass of the total amount of pulp was 70 parts by mass.

Example 5

A pulp molded article was produced in the same manner as in example 1, except that the amount of pulp a was 70 parts by mass based on 100 parts by mass of the total amount of pulp, and the proportion of the paper strength agent in the solid content of the pulp was 0.5% by mass.

Example 6

A pulp molded article was produced in the same manner as in example 1, except that the amount of pulp a relative to 100 parts by mass of the total amount of pulp was 50 parts by mass.

Example 7

A pulp molded article was produced in the same manner as in example 1, except that the amount of pulp a was 50 parts by mass based on 100 parts by mass of the total amount of pulp, and the proportion of the paper strength agent in the solid content of the pulp was 0.5% by mass.

Example 8

A pulp molded article was produced in the same manner as in example 1, except that the amount of pulp a was 70 parts by mass based on 100 parts by mass of the total amount of pulp, and the gap between the upper die and the lower die was 0.7mm in the dewatering step and the hot pressing step, to obtain a pulp molded article having a wall portion with a thickness of 0.7 mm.

Example 9

A pulp molded article was produced in the same manner as in example 1, except that the amount of pulp a was 70 parts by mass based on 100 parts by mass of the total amount of pulp, and the gap between the upper die and the lower die was 0.7mm in the dewatering step and the hot pressing step, to obtain a pulp molded article having a wall portion with a thickness of 0.7 mm. In this example, the pulp molded article was set to have a lower density than example 8.

Example 10

A pulp molded article was produced in the same manner as in example 1, except that the amount of pulp a was 50 parts by mass based on 100 parts by mass of the total amount of pulp, and the proportion of the paper strength agent in the solid content of the pulp was 2% by mass.

Comparative example 1

A pulp molded article was produced in the same manner as in example 1, except that the total amount of pulp was pulp a.

Comparative example 2

A pulp molded article was produced in the same manner as in example 1, except that the amount of pulp a was 30 parts by mass relative to 100 parts by mass of the total amount of pulp.

Comparative example 3

A pulp molded article was produced in the same manner as in example 1, except that the total amount of pulp was pulp B.

Comparative example 4

A pulp molded article was produced in the same manner as in example 1, except that the amount of pulp a was 70 parts by mass based on 100 parts by mass of the total amount of pulp, and the paper strength enhancer was not used.

Comparative example 5

A pulp molded article was produced in the same manner as in example 1, except that the amount of pulp a was 70 parts by mass based on 100 parts by mass of the total amount of pulp, and the proportion of the paper strength agent in the solid content of the pulp was 0.3% by mass.

Comparative example 6

A pulp molded article was produced in the same manner as in example 1, except that the amount of pulp a relative to 100 parts by mass of the total amount of pulp was 70 parts by mass. In this example, the pulp molded article was set to have a low density.

Comparative example 7

A pulp molded article was produced in the same manner as in example 1, except that the amount of pulp a was 70 parts by mass based on 100 parts by mass of the total amount of pulp, and the gap between the upper die and the lower die was 0.7mm in the dewatering step and the hot pressing step, to obtain a pulp molded article having a wall portion with a thickness of 0.7 mm. In this example, the pulp molded article was set to have a low density.

<2> evaluation

By the above-described method, various measurements were made on each of the pulp molded articles produced in examples 1 to 10 and comparative examples 1 to 7. The results are set forth in tables 1 to 3 below.

TABLE 1

TABLE 2

TABLE 3

In tables 1 to 3, the evaluation concerning releasability is as follows. If a drying failure occurs in the pulp molded article MP2, a crack or peeling occurs on the surface of the pulp molded article MP2, or a release failure occurs such that the pulp molded article MP2 cannot be released from the mold, and thus the intended molded article cannot be obtained.

A: can be released from the mold by air ejection and has good surface state

B: can be released from the mold by air ejection, and the surface is peeled off or cracked

C: can not be demolded by the ejection of air

In tables 1 to 3, the "ratio of short fibers" indicates the ratio of fibers having a fiber length of 1mm or less to pulp. In comparative example 3, the pulp molded article was not released from the mold, and thus values of tensile strength, peel strength and density were not described.

As is clear from comparison of examples 1 to 10 with comparative examples 1 to 7, the pulp molded articles having a fiber length of 1mm or less, which have a proportion of the fibers in the pulp, an average fiber length, a density and a nitrogen content within predetermined ranges, have a high strength and are excellent in releasability, although the thickness of the wall portion is small. The pulp molded articles of examples 1 to 10 were each in the range of 2 to 10 μm in arithmetic average roughness Ra, 10 to 60 μm in maximum height roughness Rz, and 90 to 300 μm in average length RSm of the roughness curve elements. In addition, the standard deviation of the weight per unit area of the pulp molded articles of examples 1 to 10 was 2 to 30g/m ² Within a range of (2).

Description of symbols

1 … manufacturing apparatus, 10 … support, 20 … station 1, 30 … station 2, 40 … station 3, 210 … container, 220 … elevator, 230 … cover, 240 … paper die, 250 … moving apparatus, 260 … elevator, 270 … upper die, 310 … table, 320 … lower die, 330 … moving apparatus, 340 … press apparatus, 350 … upper die, 410 … table, 420 … moving apparatus, 430 … elevator, 440 … holder, MP1 … pulp layer, MP2 … pulp molded article, S … pulp.

Claims

1. A pulp molded article, wherein,

the proportion of the fibers with the fiber length of less than 1mm in the pulp is in the range of 35 to 50 percent,

the average fibre length of the pulp is in the range of 1.2 to 1.5mm,

density of 0.65 to 1.3g/cm ³ Within the range of (2),

the nitrogen content is in the range of 400 to 2000. Mu.g/g.

2. The pulp molded article according to claim 1, wherein,

the thickness is in the range of 0.5 to 1 mm.

3. The pulp molded article according to claim 1 or 2, wherein,

density of 0.65 to 0.80g/cm ³ In the range of 500 to 1000. Mu.g/g.

4. A pulp molded article according to claim 1 to 3, wherein,

The tensile strength is in the range of 30 to 55 kN/m.

5. The pulp molded article according to claim 1 to 4, wherein,

peel strength of 0.3 to 0.9N/mm ² Within a range of (2).

6. The pulp molded article according to claim 1 to 5, wherein,

the standard deviation of the weight per unit area is 2 to 30g/m ² Within a range of (2).

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

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

preparing a slurry containing pulp and water, wherein the proportion of fibers with a fiber length of 1mm or less in the pulp is in the range of 35 to 50%;

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 is not dried, is sandwiched between a male mold and a female mold and heated at a temperature in the range of 150 to 220 ℃ while being pressurized at a pressure in the range of 0.4 to 4.5 MPa.

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

depositing the pulp onto the paper making die comprises:

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

Fixing the paper mold to the opening;

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

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

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

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

11. The method for producing a pulp molded article according to any one of claims 8 to 10, wherein,

the pressurization and heating of the intermediate formed article, which is not dried, interposed between the male die and the female die are performed at a pressure in the range of 0.4 to 2.0MPa and a temperature in the range of 150 to 200 ℃, respectively.