JP7686485B2 - Hollow plate and manufacturing method thereof - Google Patents

Description

The present invention relates to a hollow plate and a manufacturing method thereof. More specifically, the present invention relates to a hollow plate that is environmentally friendly and has good moldability, and a manufacturing method thereof.

Since polyolefin resins are inexpensive and easy to mold, the so-called plastic cardboard molded from them has excellent impact resistance and compression resistance, as well as water resistance, light transparency, and recyclability, and is used in a wide range of applications, such as packaging cases, returnable boxes and other containers, surface protection packaging materials, partition boards, building materials, and decorative materials. As an example of plastic cardboard, Patent Document 1 discloses a hollow plate made of polypropylene resin molded by coextrusion.

JP 2009-34959 A

However, in recent years, various measures have been taken to achieve the Sustainable Development Goals (SDGs), and in particular, as the issue of waste plastics comes into focus, issues such as reducing the use of petroleum-derived plastics and reducing _CO2 emissions during incineration have been raised as concerns about plastic cardboard. On the other hand, when some of the materials that make up plastic cardboard are changed to environmentally friendly materials in order to address these issues, problems such as molding defects arise.

Therefore, the main objective of the present invention is to develop a hollow plate that is environmentally friendly and has good moldability, and a method for manufacturing the same.

As a result of intensive experimental investigations, the inventors of this application discovered a hollow plate and its manufacturing method that is environmentally friendly and has good moldability, leading to the completion of this invention.

That is, the present invention provides a hollow plate having an intermediate layer having a hollow structure and surface layers on both sides of the intermediate layer, the hollow plate being formed into a hollow plate shape by melt co-extruding an intermediate layer resin consisting of a polyolefin resin and an inorganic substance and having a melt index (ASTM D1238, 230°C) of 0.5 to 2.0 (g/10 min) and a surface layer resin consisting of a polyolefin resin at 190 to 250°C, the content of the inorganic substance being 40 mass% or more relative to the intermediate layer resin, and the weight ratio of the rib to the liner portion in the intermediate layer being 0.1 to 10 .
In the present invention, the thickness of the surface layer may be at least twice the average particle size of the inorganic material.
In the present invention, the inorganic substance may be at least one selected from the group consisting of talc, calcium carbonate, and clay.

The present invention also provides a method for producing a hollow plate having an intermediate layer with a hollow structure and surface layers on both sides of the intermediate layer, the method comprising: a co-extrusion step of melt-extruding an intermediate layer resin consisting of a polyolefin resin and an inorganic substance and having a melt index (ASTM D1238, 230°C) of 0.5 to 2.0 (g/10 min) and a surface layer resin consisting of a polyolefin resin at 190 to 250°C; and a cooling step of cooling the resulting resin using a cooling former after the co-extrusion step, wherein the content of the inorganic substance is 40 mass% or more relative to the intermediate layer resin , and the weight ratio of the rib to the liner portion in the intermediate layer is 0.1 to 10 .

According to the present invention, it is possible to provide a hollow plate which is environmentally friendly and has good moldability, and a method for producing the same.
Note that the effects described here are not necessarily limited to those described herein, and may be any of the effects described in this specification.

FIG. 2 is a schematic diagram showing a cross section of a hollow plate.

1. Hollow plate 1
The hollow plate 1 according to the present invention has an intermediate layer 11 having a hollow structure and surface layers 12 on both sides of the intermediate layer. The intermediate layer resin, which is made of a polyolefin resin and an inorganic substance and has a melt index (ASTM D1238, 230°C) of 0.5 to 2.0 (g/10 min), and the surface layer resin, which is made of a polyolefin resin, are melt-extruded at 190 to 250°C to form a hollow plate, and the content of the inorganic substance is 20% by mass or more relative to the intermediate layer resin.

By using a large amount of inorganic substances and reducing the amount of polyolefin resin used, it is possible to achieve the goals of reducing the use of petroleum-derived plastics and reducing the amount of _CO2 generated during incineration, and to provide an environmentally friendly hollow plate. However, the inventors of the present application conducted extensive experimental studies and found that when 20% by mass or more of inorganic substances are added, the inorganic substances bleed out onto the surface, resulting in surface abnormalities and molding defects due to poor adhesion.

In response to this, the inventors of the present application conducted further intensive experimental studies and found that by melt-extruding an intermediate layer resin containing 20% or more by mass of inorganic matter and a surface layer resin made of a polyolefin resin at 190 to 250°C into a hollow plate, it is possible to prevent the inorganic matter from bleeding out to the surface, thereby providing a hollow plate that is environmentally friendly and has good moldability.

(1) Intermediate layer 11
Examples of the structure of the intermediate layer 11 include a sheet-like structure consisting of a pair of approximately parallel liner portions and a plurality of ribs perpendicular and/or oblique thereto, as described in JP-B-38-4185 and JP-B-38-17182, i.e., a cardboard-like structure as shown in FIG. 1.
The weight ratio of the rib to the liner portion is preferably in the range of 0.1 to 10 from the viewpoint of suppressing warping, more preferably in the range of 0.2 to 5, and further preferably in the range of 0.5 to 2 in consideration of physical properties and molding aspects.

The intermediate layer resin is a resin made of a polyolefin resin and an inorganic substance, and has a melt index (ASTM D1238, 230°C) of 0.5 to 2.0 (g/10 min). Specifically, for example, the resin may be made by blending a polyolefin resin and an inorganic substance in a predetermined blend ratio.

Examples of polyolefin resins include polyethylenes such as low-density polyethylene (LDPE), high-density polyethylene (HDPE), linear low-density polyethylene, and very low-density polyethylene, and polypropylenes such as polypropylene homopolymers, polypropylene random copolymers, and polypropylene block copolymers. Note that a polypropylene block copolymer is a block copolymer of propylene and one or more types of other α-olefins (e.g., ethylene, 1-butene, 4-methyl-1-pentene, 1-pentene, 1-octene, 1-decene, 1-dodecene, etc.).
In the present invention, it is particularly preferable to use polyethylene and/or polypropylene among these. As the polypropylene, an ethylene-propylene block copolymer containing 5.0 to 10.0 mass % of ethylene is particularly preferable from the viewpoint of mechanical properties such as impact resistance.

Examples of inorganic substances include silicates, sulfates, carbonates, phosphates, borates, oxides, or hydrates of these substances, inorganic fibers, etc., of magnesium, aluminum, calcium, titanium, iron, zinc, etc. Specific examples include clays such as talc and kaolin, calcium carbonate, magnesium carbonate, zinc oxide, titanium oxide, silica, alumina, aluminum hydroxide, magnesium hydroxide, aluminum silicate, magnesium silicate, calcium silicate, aluminum sulfate, magnesium sulfate, calcium sulfate, magnesium phosphate, barium sulfate, silica sand, carbon black, zeolite, molybdenum, diatomaceous earth, sericite, shirasu, calcium sulfite, sodium sulfate, potassium titanate, bentonite, wollastonite, dolomite, graphite, glass fibers, microglass, carbon fibers, ceramic fibers, rock wool, etc. These may be prepared by a synthetic method or may be naturally derived. These may be used alone or in combination of two or more types.

In the present invention, it is particularly preferable to use one or more selected from the group consisting of talc, calcium carbonate, and clay, and it is more preferable to use talc and/or calcium carbonate. Talc and/or calcium carbonate have a relatively small particle size and good dispersibility, and therefore are easy to handle. Furthermore, talc and/or calcium carbonate are abundantly found all over the world, and are considered to be sufficient to meet the SDGs. Furthermore, although the price of petroleum has risen recently, they are inexpensive and in large supply, so they have the advantage of being steadily supplied and can be used at low cost.

The shape of the inorganic material is not particularly limited, and may be any of particles, flakes, granules, fibers, etc. Furthermore, the particles may be spherical, as is generally obtained by synthetic methods, or irregularly shaped, as obtained by crushing collected natural minerals.

In the present invention, the content of the inorganic substance is 20% by mass or more relative to the intermediate layer resin, preferably 30% by mass or more, more preferably 40% by mass or more, and particularly preferably 45% by mass or more. This allows the amount of petroleum-derived plastic used and the amount of _CO2 emitted during combustion to be further reduced. In addition, the upper limit of the content of the inorganic substance is preferably 65% by mass or less relative to the hollow layer resin. If the content of the inorganic substance exceeds 65% by mass, the dispersibility becomes poor and the resin connection becomes poor, increasing the probability of molding defects and deterioration of physical properties.

In the present invention, the content of the inorganic substance in the entire hollow plate 1 is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more.
Here, the Recycling Law imposes an obligation on manufacturers of containers and packaging such as plastics to recycle container and packaging waste. One of the means by which manufacturers fulfill their obligation to recycle container and packaging waste is to pay a commission for recycling to the Japan Container and Packaging Recycling Association. It is stipulated that containers and packaging made of multiple materials that are difficult to separate are to be disposed of according to the classification of the material that has the highest ratio by weight among the materials that make up the container and packaging. Therefore, particularly when the content of inorganic matter in the entire hollow plate 1 exceeds 50 mass%, the hollow plate 1 is not classified as plastic, and as a result, it is possible to prevent the manufacturer that produces the hollow plate 1 from being obligated to pay the commission under the Recycling Law.

The melt index (hereinafter also referred to as "MI"), which is an index of the melt viscosity of the intermediate layer resin, is in the range of 0.5 to 2.0 (g/10 min) as measured according to ASTM D1238 [230°C, load 21.18 N (2.16 kg)]. If the MI is less than 0.5 (g/10 min), problems such as peeling of the surface layer and powder fall cracks will occur during co-extrusion. Also, if it exceeds 2.0 (g/10 min), molding defects will occur.

The intermediate layer resin may be a commercially available inorganic polyolefin resin. The intermediate layer resin may also contain dispersants, antioxidants, UV absorbers, antistatic agents, antibacterial agents, flame retardants, light stabilizers, lubricants, etc., as necessary.

From the viewpoints of practicality and continuous moldability, the thickness of the hollow structured intermediate layer 11 is preferably 3,000 to 10,000 μm, and more preferably 4,000 to 7,000 μm.

(2) Surface layer 12
Regarding the structure of the surface layer 12, for example, when the intermediate layer 11 has the above-mentioned cardboard-like structure, it is formed in layers on both sides of a pair of liner portions as shown in FIG.

The surface layer resin is a polyolefin resin, and the specific details are as described above. If a resin other than a polyolefin resin is used as the surface layer resin, the fusion with the intermediate layer resin becomes poor, and molding defects, interfacial peeling, and cracks are likely to occur.
Among these, it is particularly preferable to use polyethylene and/or polypropylene in the present invention. As the polypropylene, an ethylene-propylene block copolymer having an ethylene content of 5.0 to 10.0% by mass is particularly preferable.

The melt index, which is an index of the melt viscosity of the surface layer resin, is in the range of 0.5 to 2.0 (g/10 min) as measured according to ASTM D1238 [230°C, load 21.18 N (2.16 kg)]. If the MI is less than 0.5 (g/10 min), problems such as peeling of the surface layer and powder cracking will occur during co-extrusion. If it exceeds 2.0 (g/10 min), molding defects will occur. Furthermore, in the present invention, from the viewpoint of moldability, it is preferable that the MI of the intermediate layer resin is greater than or equal to the MI of the surface layer resin.

The thickness of the surface layer 12 is preferably at least twice the average particle size of the inorganic material. If the thickness is less than twice the average particle size, the inorganic material will protrude from the surface layer 12, making it difficult to prevent bleeding out.

The average particle size of the inorganic material in the present invention can be the average particle size of the powder calculated from the following formula (1) using the specific surface area value per 1 g of powder measured using, for example, a powder specific surface area measuring device SS-100 manufactured by Shimadzu Corporation.

The average particle size of the inorganic material is preferably 5 to 50 μm, and from the viewpoint of improving dispersibility, more preferably 5 to 20 μm. If the average particle size is less than 5 μm, the dispersibility of the inorganic material will be extremely poor, and extrusion defects and molding defects due to aggregation will easily occur. Furthermore, if the average particle size exceeds 50 μm, problems such as clogging of the filter and die of the extruder will easily occur.

Specifically, the thickness of the surface layer 12 is preferably 20 to 200 μm, more preferably 30 to 150 μm, and even more preferably 40 to 125 μm. If the thickness of the surface layer 12 is less than 20 μm, the processability is poor, such as cracking during processing and poor thermal adhesion, in addition to bleed-out. If the thickness of the surface layer 12 exceeds 200 μm, the content of inorganic matter is reduced, which is not preferable from the viewpoint of reducing the use of petroleum-derived plastics and reducing _CO2 generation during incineration.

Commercially available polyolefin resins may be used for the surface layer resin. In addition, antioxidants, ultraviolet absorbers, antistatic agents, antibacterial agents, flame retardants, light stabilizers, lubricants, etc. may be appropriately blended into the surface layer resin as necessary.

2. Manufacturing method of hollow plate 1 The manufacturing method of hollow plate 1 according to the present invention is a manufacturing method of hollow plate 1 having an intermediate layer 11 having a hollow structure and surface layers 12 on both sides of the intermediate layer 11, and is characterized by having a co-extrusion process of melt-extruding an intermediate layer resin having a melt index (ASTM D1238, 230°C) of 0.5 to 2.0 (g/10 min) made of a polyolefin resin and an inorganic substance and a surface layer resin made of a polyolefin resin at 190 to 250°C, and a cooling process of cooling using a cooling former after the co-extrusion process, and the content of the inorganic substance is 20% by mass or more relative to the intermediate layer resin. In addition, the manufacturing method of hollow plate 1 according to the present invention may include other processes, etc., as necessary.

(1) Co-extrusion process In the co-extrusion process, for example, each resin is guided from a main extruder for extruding an intermediate layer resin and a sub-extruder for extruding a surface layer resin, and the resins are joined in a co-extrusion block equipped with dies for forming a hollow intermediate layer and a surface layer, and melt extrusion is performed by controlling the temperature of the co-extrusion block to 190 to 250° C. As the main extruder and the sub-extruder, for example, a single screw extruder having a predetermined discharge capacity used in normal melt extrusion can be used.

More specifically, for example, the intermediate layer resin containing 20% or more by mass of inorganic matter relative to the intermediate layer resin is melt-kneaded in the main extruder, and the surface layer resin is melt-kneaded in the sub-extruder, and the flows are joined in a co-extrusion block equipped with a die. The layer having a hollow structure is in the form of a sheet consisting of a pair of parallel liner parts and multiple ribs perpendicular and/or oblique thereto, i.e., a cardboard-like die, for example, may have a structure in which a core metal that forms a predetermined thickness and a hollow part for the liner parts is provided in a comb-like shape, and air can be supplied from the center of each core metal. In addition, the surface layer resin is placed on the upper and/or lower surfaces of the intermediate layer, and is guided so as to form the surface layer, and is joined in a layered form by the die.

The temperature of the co-extrusion block including the die is set to a range of 190 to 250°C, and the intermediate layer resin and the surface layer resin are co-extruded. In the present invention, since the intermediate layer resin contains 20% or more by mass of inorganic matter, it is considered that it is difficult to fuse with the surface layer resin. However, it has been found that by setting the temperature within the above range, the fusion between the intermediate layer resin and the surface layer resin can be improved and the bleeding out of inorganic matter can be effectively prevented. In particular, if the temperature of the co-extrusion block including the die is lower than 190°C, the resin viscosity is too high, and the fusion between the surface layer resin and the intermediate layer resin becomes poor, and the inorganic matter adheres to the grooves and surfaces of the cooling former in the cooling process described below, which is likely to cause molding defects. In addition, if the temperature of the co-extrusion block including the die exceeds 250°C, the difference in behavior between the surface layer resin and the intermediate layer resin when cooled and solidified becomes large, resulting in molding defects and a decrease in the physical properties of the manufactured hollow plate.

(2) Cooling process In the cooling process, for example, the intermediate layer and the surface layer, which are joined and integrated in the co-extrusion block and melt-extruded from the die, are guided to a cooling former to produce a hollow plate having a hollow structure. As the cooling former, for example, a structure in which a cooling medium is circulated between two upper and lower metal blocks having a gap corresponding to the thickness of the hollow plate, and the metal blocks are brought into contact with the hollow plate to exchange heat and cool while vacuum suction is performed from the fine holes provided on the contact surface side with the hollow plate, can be used. In addition, air cooling may be used in combination near the entrance of the cooling former, and water mist may be used in combination inside the former to enhance the cooling effect.

In the present invention, although the intermediate layer resin contains 20% by mass or more of inorganic matter, the intermediate layer resin is melt-extruded with the surface layer resin at 190 to 250°C, which prevents the inorganic matter from bleeding out to the surface, and as a result, prevents the inorganic matter from adhering to the metal block that constitutes the cooling former. Therefore, continuous molding can be performed stably for long periods of time.

To form the hollow structure, air at a specified pressure is supplied from the center of the die core metal, and the thickness of the hollow plate is maintained by this internal pressure while it is cooled and solidified, defining the internal hollow structure. In the case of a product form in which the plate is cut to a specified length, a process may be included in which the plate is cut to a specified length in a constant pressure chamber that is installed downstream of the cooling former and controlled to a specified pressure, so that the system becomes open after cutting and the pressure inside the hollow portion does not decrease or fluctuate.

The present invention will now be described in further detail with reference to examples.
The embodiment described below is merely a representative example of the present invention, and the scope of the present invention should not be construed as being narrow.

Example 1
As the intermediate layer resin, a polypropylene block copolymer (compound or dry blend) containing 60% by mass of talc [MI = 1.0 (g/10 min), average particle size 5-20 μm] was used. As the surface layer resin, a polypropylene block copolymer [MI = 0.8 (g/10 min)] was used, and in order to manufacture a hollow plate with a surface layer resin of 99 μm thickness formed on both surfaces of a 5000 μm thick intermediate layer, co-extrusion was performed at a die (including block) temperature of 230-240°C to manufacture a hollow plate with the structure shown in Figure 1. As shown in Figure 1, the obtained hollow plate has an intermediate layer with a hollow structure in which perpendicular ribs of 220 μm thickness are arranged in parallel with a pitch of 5000 μm to a pair of liner parts of 300 μm thickness, and a surface layer of 99 μm thickness is formed on both surfaces, and the overall basis weight was 1000 g/m ² and the basis weight of the intermediate layer was 820 g/m ² . In addition, in this Example 1, the content of talc in the entire hollow plate was 49 mass %.

Example 2
The obtained hollow plate was the same as that in Example 1, except that a surface layer having a thickness of 50 μm was formed on both surfaces of the hollow plate, the total basis weight was 1000 g/m ² , and the basis weight of the intermediate layer was 910 g/m ^2. In this Example 2, the talc content in the entire hollow plate was 54 mass%.

Example 3
A hollow plate was produced in the same manner as in Example 1, except that a polypropylene block copolymer (compound or dry blend) containing 60% by mass of talc [MI=0.5 (g/10 min), average particle size 5 to 20 μm] was used as the intermediate layer resin and co-extruded at a temperature of 250° C. In this Example 3, the content of talc in the entire hollow plate was 49% by mass.

Example 4
A hollow plate was produced in the same manner as in Example 1, except that a high-density polyethylene containing 50% by mass of talc [MI=2.0 (g/10 min), average particle size 5-20 μm] was used as the intermediate layer resin and co-extruded at a temperature of 190-200° C. In this Example 4, the content of talc in the entire hollow plate was 41% by mass.

<Comparative Example 1>
A hollow plate was produced in the same manner as in Example 1, except that a polypropylene block copolymer containing 60% by mass of talc [MI=3.0 (g/10 min), average particle size 5 to 20 μm] was used as the intermediate layer resin and co-extruded at a temperature of 180° C. In addition, in Comparative Example 1, the content of talc in the entire hollow plate was 49% by mass.

<Comparative Example 2>
A hollow plate was produced in the same manner as in Example 1, except that a polypropylene block copolymer containing 60% by mass of talc [MI=0.3 (g/10 min), average particle size 5 to 20 μm] was used as the intermediate layer resin and coextruded at a temperature of 260° C. In addition, in Comparative Example 2, the content of talc in the entire hollow plate was 49% by mass.

<Comparative Example 3>
A hollow plate was produced in the same manner as in Example 1, except that a polypropylene block copolymer containing 60% by mass of talc [MI=0.3 (g/10 min), average particle size 5 to 20 μm] was used as the intermediate layer resin, and a polyarylate resin [MI=3.0 (g/10 min)] was used as the surface layer resin, and they were co-extruded at a temperature of 230° C. In Comparative Example 3, the talc content relative to the entire hollow plate was 49% by mass.

The results are shown in Tables 1 and 2.
The evaluation criteria for each evaluation are described below.

[Environmental]
A: The content of inorganic substances in the entire hollow plate was 40 mass % or more.
B: The content of inorganic substances in the entire hollow plate was 30 mass % or more.
C: The content of inorganic substances in the entire hollow plate was less than 30 mass %.

[Moldability]
A: When visually inspected, no bleeding was observed during production, and there was no extrusion failure or die clogging.
B: Visual inspection revealed some bleeding out during production, and some extrusion defects and die clogging were also observed, but these were not problematic for the finished product.
C: When visually inspected, noticeable bleeding out was observed during production, and extrusion defects and die clogging were also observed.

[Bending stiffness]
A: The bending stiffness in the MD direction was 600 N·cm or more.
B: The bending rigidity in the MD direction was 500 N·cm or more.
C: The bending stiffness in the MD direction was less than 500 N·cm.

[Bending strength]
A: The bending strength in the MD direction was 50 N or more.
B: The bending strength in the MD direction was 40 N or more.
C: The bending strength in the MD direction was less than 40N.

From these results, it was found that the hollow plates of Examples 1 to 4 had a high content of inorganic matter in the entire hollow plate, realizing an environmentally friendly structure, and also had excellent moldability. Furthermore, the hollow plates of Examples 1 to 4 had no problems in terms of physical properties such as bending rigidity and bending strength.

On the other hand, in the hollow plates of Comparative Examples 1 to 3, although the inorganic content in the entire hollow plate was high, the moldability was poor and it was not suitable for continuous and stable industrial production. Furthermore, in Comparative Example 3, the occurrence of interfacial peeling and cracking was also observed. Furthermore, due to the poor moldability, the hollow plates of Comparative Examples 1 to 3 also had poor surface appearance compared to the hollow plates of Examples 1 to 4.

In addition, the hollow plate of Example 2 in particular has an inorganic content of 50% by mass or more relative to the entire hollow plate, and is therefore a hollow plate 1 that is not classified as a plastic, which makes it possible to avoid the obligation to pay the commission fee under the Recycling Law.

The present invention provides an environmentally friendly hollow plate with good moldability and a manufacturing method thereof. In addition, because of its excellent physical properties, it is useful in a wide range of applications, such as packaging cases, returnable boxes and other containers, surface protection packaging materials, partition boards, building materials, and decorative materials.

1: Hollow plate 11: Middle layer 12: Surface layer

Claims (4)

A hollow plate having an intermediate layer having a hollow structure and surface layers on both sides of the intermediate layer,
The hollow plate is formed into a hollow plate shape by melt-extruding an intermediate layer resin having a melt index (ASTM D1238, 230°C) of 0.5 to 2.0 (g/10 min) made of a polyolefin-based resin and an inorganic substance and a surface layer resin made of a polyolefin-based resin at 190 to 250°C;
The content of the inorganic substance is 40 % by mass or more relative to the intermediate layer resin , and
A hollow plate , wherein a weight ratio of the rib to the liner portion in the intermediate layer is 0.1 to 10 . The hollow plate according to claim 1, wherein the thickness of the surface layer is at least twice the average particle size of the inorganic material. The hollow plate according to claim 1 or 2, wherein the inorganic material is at least one selected from the group consisting of talc, calcium carbonate, and clay. A method for manufacturing a hollow plate having an intermediate layer having a hollow structure and surface layers on both sides of the intermediate layer, comprising the steps of:
a co-extrusion step of melt-extruding an intermediate layer resin having a melt index (ASTM D1238, 230°C) of 0.5 to 2.0 (g/10 min) made of a polyolefin-based resin and an inorganic substance and a surface layer resin made of a polyolefin-based resin at 190 to 250°C;
a cooling step of cooling the mixture using a cooling former after the co-extrusion step;
having
A content of the inorganic substance is 40 % by mass or more relative to the intermediate layer resin , and a weight ratio of a rib to a liner portion in the intermediate layer is 0.1 to 10 .