JP7672995B2 - Concrete formwork panels - Google Patents

Description

The present invention relates to a panel used as a formwork when pouring concrete. More specifically, it relates to a lightweight, reusable concrete formwork panel.

Many of the concrete formwork panels (hereafter referred to as "companies" where necessary) on the market use plywood imported from Southeast Asia as the base material. For applications that do not require a smooth concrete surface, "unpainted plywood" which uses the plywood as is is often used, while for applications that do require a smooth surface, "painted plywood" which has been painted is often used.

Patent Document 1 is an invention that aims to provide a concrete formwork that has good releasability from hardened concrete and can be used repeatedly, and is characterized in that a resin sheet (corresponding to the "surface layer made of synthetic resin" in Patent Document 1) is laminated on at least the concrete pouring surface of a breathable base material (corresponding to the "dam board" in Patent Document 1), and a large number of micropores are provided in the resin sheet. The micropores prevent the concrete and the resin sheet from firmly adhering to each other as the concrete hardens and shrinks, resulting in good releasability from the concrete and enabling repeated use.

In addition, most of the plywood currently used for plywood is made from lauan, a tropical wood. However, due to the problem of global forest resource depletion, research has begun into alternative plywood base materials to lauan plywood.
Plywood made from coniferous trees or planted trees is known as an alternative to lauan plywood, but these plywoods are less water resistant than lauan plywood and are prone to swelling and warping of the grain due to moisture. In particular, coniferous trees have large density differences in the annual rings and many knot holes and cracks, which causes a problem of lack of smoothness when processed into plywood. Even if a resin sheet is laminated on the surface of these plywoods, it is not possible to obtain a satisfactory smoothness for use as a composite panel, and the wood grain may be transferred to the concrete surface.

Wood fiberboards such as particle boards and MDF, which are made from recycled wood materials, are also known as alternative materials to plywood. Because wood fiberboards have a smooth surface, it is possible to finish the surface of the concrete obtained by using them as concrete formwork panels, but there is a problem that the cost increases in order to obtain wood fiberboards with high water resistance. In addition, because wood fiberboards have a higher density than plywood, they become heavier when processed into composite panels, making them less easy to work with.

JP 2002-106167 A

The objective of the present invention is to provide a concrete formwork panel that has excellent surface smoothness and is equivalent in weight to conventional products. More specifically, the objective is to provide a concrete formwork panel that can produce a finished concrete surface with a smooth finish and that is also easy to work with.

According to the present invention, as a means for solving the above-mentioned problems, there is provided a concrete formwork panel having a coating layer laminated on the surface of a wood composite board, characterized in that the wood composite board is made of plywood and wood fiber board, and a coating layer is laminated on the surface of the wood fiber board of the wood composite board.
The present invention also provides the above-mentioned concrete formwork panel, characterized in that the plywood is any one of Falcata plywood, acacia plywood, and softwood plywood.

The present invention also provides the above-mentioned concrete formwork panel, characterized in that the thickness of the wood fiber board is 1 mm or more and 10 mm or less.
The present invention also provides the above-mentioned concrete formwork panel, wherein the wood fiber board is a particle board or MDF.

The present invention also provides the above-mentioned concrete formwork panel, characterized in that the coating layer is a resin sheet made of a high-density polyethylene film or a polypropylene film that has been corona discharge-treated on only one side, and the corona discharge-treated side is laminated to a wood fiberboard via an adhesive.
The present invention also provides the above-mentioned panel for use in a form for concrete, characterized in that the surface of the resin sheet opposite the wood fiber board side has a wettability index of less than 40 mN/m.
The present invention also provides the above-mentioned panel for use in a form for concrete, characterized in that the coating layer is a paint coating layer formed by coating with paint containing a resin.

The concrete formwork panel of the present invention uses a composite board made of wood fiberboard and plywood, and a coating layer is laminated on the surface of the wood fiberboard, so that concrete with a smooth finished surface can be obtained. In addition, since plywood is used, the plywood is not heavier than conventional products, and when using plywood made from planted trees with a light specific gravity such as Falcata wood or domestic softwood, the weight can be significantly reduced, and workability can be improved.
In addition, because wood fiberboard is laminated on the surface, it is possible to use plywood such as falcata plywood, acacia plywood, and softwood plywood, which have traditionally been difficult to use for plywood due to issues with surface smoothness, thereby contributing to the effective use of wood.
Furthermore, by using a wood fiberboard having a thickness of 1 mm to 10 mm or by using a particle board, the increase in weight of the concrete form panel can be kept to a minimum.

FIG. 1 is a schematic cross-sectional view showing one embodiment of a concrete formwork panel using a resin sheet as a covering layer of the present invention. FIG. 1 is a schematic cross-sectional view showing one embodiment of a concrete formwork panel using a paint coat layer as a covering layer of the present invention.

Hereinafter, the present invention will be described in detail with reference to FIG. 1. However, the present invention is not limited to the following embodiment, and various embodiments can be adopted within the scope of the same effect.
The plywood panel 1 of the present invention mainly comprises a wood composite board 2 and a covering layer 3 .

[Wood composite board]
The present invention is characterized in that the wood composite board 2 is made of a wood fiber board 21 and a plywood 22 .
As the wood fiberboard 21, there can be used, without any particular limitation, particle boards made by chipping wood and molding them with adhesives, MDF made by defibrating wood, hardboards, etc. However, considering the surface smoothness and weight of the resulting plywood panel 1, it is preferable to adopt particle boards in which at least the covering layer side described below is mainly composed of extremely fine chips of less than 100 mesh, and the other parts are mainly composed of chips of about 0.5 to 100 mesh. In addition, both surface layers of the particle board may be mainly composed of the extremely fine chips described above, and the intermediate layer may be mainly composed of chips of about 0.5 to 100 mesh. The particle board has a smooth surface and is relatively lightweight.
The thickness of the wood fiber board 21 is not particularly limited, but if it is too thick, the weight of the plywood 1 increases significantly, and if it is too thin, sufficient surface smoothness cannot be imparted to the plywood 1. Therefore, it is preferable that the thickness be 1 mm or more and 10 mm or less, and particularly 2 mm or more and 6 mm or less.

As the plywood 22, hardwood plywood such as china, birch, ash, beech, oak, lauan, seraya, meranti, capol, and apitong, softwood plywood such as larch, spruce, red pine, Douglas fir, cypress, Japanese cedar, red hemlock, spruce, and radiata pine, and plantation wood plywood such as poplar, falcata, acacia, camellia, eucalyptus, and terminalia, which are fast-growing trees, can be used without any particular limitation. In addition, in the plywood panel 1 of the present invention, since the wood fiber board 21 is laminated on the surface of the plywood 22, the plywood 22 does not require a surface smoothness. Therefore, from the viewpoint of reducing the environmental load, it is preferable to use softwood plywood with poor surface smoothness or plantation wood plywood made of fast-growing plantation trees.
The thickness of the plywood 22 is not particularly limited, but in terms of the balance between strength and cost, it is preferably 2 mm or more and 20 mm or less, more preferably 5 mm or more and 15 mm or less, and particularly preferably 7 mm or more and 12 mm or less, and it is preferable for the plywood to have 3 to 5 plies.

[Coating layer]
The coating layer 3 of the present invention is laminated on the surface of the wood fiberboard of the wood composite board for the purpose of imparting releasability from concrete and surface smoothness. The coating layer is not particularly limited as long as it can achieve the above-mentioned purpose, and can be, for example, any of a resin sheet 31, a paint coat layer 32, resin-impregnated paper, and a layer of melt-pressed resin powder.
Here, the resin sheet 31 and the applied coating layer 32 will be described.

[Resin sheet]
The resin sheet 31 laminated on the surface of the plywood panel 1 of the present invention can be any resin sheet conventionally used in film-finished plywood panels, without any particular limitations, and can be, for example, a sheet made of a polyolefin resin such as polyethylene, polypropylene, or an ethylene-propylene copolymer, a polyester resin such as polyethylene terephthalate or polybutylene terephthalate, a polystyrene resin, a polyamide resin, or a vinyl chloride resin, a sheet made of a thermosetting resin such as a melamine resin or a phenolic resin, or a sheet made by blending or laminating these resins. However, in consideration of the cost, the smoothness of the concrete surface after hardening, the durability of the concrete against alkali, etc., it is preferable to use a film made of a polyethylene resin, and in particular, it is preferable to use a film made of a high-density polyethylene or polypropylene film.
It is more preferable to laminate the resin sheet on the back surface (plywood surface) of the plywood panel 1 of the present invention. This can prevent the plywood panel from swelling due to water. The resin sheet used for the front and back surfaces may be the same or different.
The thickness of the resin sheet 31 is not particularly limited, but in the case where the plywood is to be used repeatedly, it is preferable that the thickness be 10 μm or more and 400 μm or less, and particularly preferable that the thickness be 20 μm or more and 100 μm or less, taking into account the balance between durability and cost.

As will be described later, the resin sheet 31 is laminated to the wood fiber board 21 of the wood composite board 2 via the adhesive 4. Therefore, it is preferable that the wettability of the surface of the resin sheet 31 to which the adhesive 4 is applied is adjusted. More specifically, it is preferable that the wettability of the surface is adjusted to 40 to 60 mN/m by corona discharge treatment, plasma treatment, or the like. If the wettability index is less than 40 mN/m, there is a risk that the resin sheet 31 will peel off from the wood fiber board 21.
It is preferable that the wettability of the resin sheet 31 is adjusted only on the surface to which the adhesive 4 is applied, and that the opposite surface is not adjusted. Specifically, it is preferable that the wettability index of the surface of the resin sheet opposite the wood fiber board side is less than 40 mN/m. The surface of the resin sheet opposite the wood fiber board side comes into direct contact with the concrete, and if the wettability index of this surface is high, it will be difficult to peel off the plywood panel 1 after the concrete has hardened.

To adjust the wettability of only one side of the resin sheet 31, for example, a synthetic resin can be extruded into a cylindrical shape by inflation extrusion molding, and then folded flat with nip rolls or the like and subjected to corona discharge treatment or plasma treatment. By treating the film in a folded flat state, the inner surface of the flat tubular film is not treated, and only the outer surface is treated. Finally, both ends of the flat tubular film are cut to make two films, resulting in a resin sheet 3 with the wettability adjusted on only one side.

[Paint coat layer]
The paint coat layer 32 laminated on the surface of the plywood panel 1 of the present invention can be any that has been conventionally used in plywood panels having a paint coat finish, without any particular limitations. For example, the paint coat layer 32 can be provided by applying a paint containing an acrylic resin, a polyurethane resin, an acrylic urethane resin, a polyester urethane resin, an epoxy resin, or the like.
The amount of the coating material to be applied is not particularly limited, but is preferably 20 to 100 g/ ^m2 , and more preferably 30 to 70 g/ ^m2 .

[Method of manufacturing a panel for concrete formwork (when the covering layer is a resin sheet 31)]
The concrete formwork panel 1 of the present invention can be manufactured, for example, by applying adhesive to one side of a wood fiber board 21, laminating a resin sheet 31 to the applied surface, and then applying adhesive to the other side of the wood fiber board 21 and laminating a plywood 22 to the applied surface.
The adhesive used to bond the wood fiber board 21 to the resin sheet 31 and the adhesive used to bond the wood fiber board 21 to the plywood 22 can be any adhesive that has been conventionally used, without any particular limitations.

[Method of manufacturing a panel for concrete formwork (when the covering layer is a paint coat layer 32)]
The concrete formwork panel 1 of the present invention can be manufactured, for example, by applying paint to one side of a wood fiber board 21 to form a paint coating layer, applying adhesive to the other side of the wood fiber board 21, and laminating plywood 22 to the applied surface.
The method for applying the coating material is not particularly limited, and the coating material can be applied, for example, by using a spray, a roll coater, a flow coater, a knife coater, or the like.

The concrete formwork panels were evaluated by the following methods.
[water resistance]
The concrete formwork panels of the Examples and Comparative Examples were stored for three months under conditions of a temperature of 40°C and a humidity of 90% RH, and the panel thickness was measured before and after storage. If the panel thickness before storage was 1.0, a panel thickness after storage of 1.0 to 1.3 was evaluated as ◯, a panel thickness of 1.3 to 1.5 was △, and a panel thickness of more than 1.5 was evaluated as x.

[Workability]
Concrete is poured using the concrete form panels of the Examples and Comparative Examples. The concrete form panels are rated as ◯ if they are light and have good workability, △ if they are slightly heavy and have slightly poor workability, and × if they are very heavy and have poor workability.

[Surface smoothness]
Concrete is poured using the concrete form panel of the embodiment and comparative example. After the concrete hardens, the concrete form panel is removed and the concrete surface is visually inspected. The concrete surface is rated as ◯ if it is smooth, △ if there are slightly uneven parts, and × if wood grain transfer is observed.

[Reusability]
Concrete is poured using the concrete form panel of the embodiment and comparative example. After the concrete hardens, the concrete form panel is removed and the surface of the concrete form panel is visually inspected. The panel is rated as ◯ when no concrete adhesion is observed, as △ when a small amount of concrete adhesion is observed, and as × when many adhesions are observed.

[Example 1]
A 40 μm-thick high-density polyethylene film (hereinafter referred to as "HDPE", wettability index of corona-treated surface: 42 mN/m, wettability index of non-corona-treated surface: 38 mN/m) was prepared, and an adhesive made of an ethylene-vinyl acetate copolymer was applied to the corona-treated surface of the film. Next, a 3 mm-thick particle board (hereinafter referred to as "PB") was laminated on the adhesive-coated surface. Next, an ethylene-vinyl acetate adhesive was applied to the surface of the PB, and Falcata plywood (5 plies, 9 mm) was laminated to produce a concrete formwork panel.

[Example 2]
A concrete form panel was produced in the same manner as in Example 1, except that softwood plywood (5 plies, 9 mm) made of domestic softwood was used as the plywood.
[Example 3]
A concrete formwork panel was produced in the same manner as in Example 1, except that HDPE having been subjected to a corona discharge treatment on both sides was used as the coating layer.

[Example 4]
A concrete form panel was produced in the same manner as in Example 1, except that a polypropylene film (hereinafter, referred to as "PP") was used as the covering layer.
[Example 5]
A concrete form panel was produced in the same manner as in Example 1, except that a low-density polyethylene film (hereinafter referred to as "LDPE") was used as the covering layer.

[Example 6]
A concrete formwork panel was produced in the same manner as in Example 1, except that a paint coating layer formed by coating with a paint containing a polyurethane resin was used as the coating layer.
[Example 7]
A concrete formwork panel was manufactured in the same manner as in Example 1, except that MDF (3 mm) was used as the wood fiberboard.

[Comparative Example 1]
A 40 μm thick HDPE sheet, which had been corona discharge treated on only one side, was attached to lauan plywood (7 plies, 12 mm) using an adhesive made of an ethylene-vinyl acetate copolymer to produce a panel for use as a concrete formwork.
[Comparative Example 2]
A 40 μm thick HDPE sheet, one side of which had been corona discharge treated, was attached to one surface of a 12 mm thick particle board using an adhesive made of an ethylene-vinyl acetate copolymer to produce a panel for use as a concrete formwork.

The plywood panels of Examples 1 to 7, which used a laminate of particle board, MDF wood fiberboard, and plywood as the wood composite board, were excellent in water resistance and surface smoothness. Among them, the plywood panels of Examples 1 to 5 and 7, which used a resin sheet as the covering layer, were more excellent in water resistance. In particular, the plywood panels of Examples 1 and 3 to 5, which used Falcata plywood as the plywood, were lightweight at about 9.1 kg for a width of 900 mm and a height of 1800 mm, and were excellent in workability. On the other hand, the plywood panel of Example 2, which used softwood plywood as the plywood, was about 12.7 kg for a width of 900 mm and a height of 1800 mm.
In addition, the plywood panels of Examples 1, 2, 4, and 5, which had a resin sheet that had been subjected to a corona discharge treatment on only one side, had no concrete attached to the resin sheet and were excellent in suitability for reuse. Among them, the plywood panels of Examples 1 and 2, which used HDPE, were excellent in peeling workability, being able to be peeled off from the concrete with a light force.
In the plywood panel of Comparative Example 1, the resin sheet was laminated on the plywood, so the wood grain was transferred to the concrete surface. In addition, the plywood panel of Comparative Example 1 was 900 mm wide and 1800 mm high and weighed 14.0 kg, while the plywood panel of Comparative Example 2 was 900 mm wide and 1800 mm high and weighed 14.96 kg, so that transporting and assembling the plywood panels was hard work.

1. Concrete formwork panels (concrete panels)
2 Wood composite board 21 Wood fiber board 22 Plywood 3 Covering layer 31 Resin sheet 32 Paint coat layer 4 Adhesive

Claims (6)

A concrete formwork panel having a coating layer laminated on the surface of a wood composite board,
The wood composite board is made of plywood and wood fiber board,
A coating layer is laminated on the surface of the wood fiber board of the wood composite board via an adhesive ,
The coating layer is a resin sheet,
The thickness of the resin sheet is 20 μm or more and 100 μm or less,
A panel for concrete formwork, characterized in that the thickness of the wood fiber board is 1 mm or more and 10 mm or less . The concrete formwork panel according to claim 1, characterized in that the plywood is falcata plywood, acacia plywood, or softwood plywood. 3. The panel for use in a concrete formwork according to claim 1 or 2 , wherein the wood fiberboard is a particle board or MDF. A panel for concrete formwork as described in any one of claims 1 to 3, characterized in that the coating layer is a resin sheet made of a high-density polyethylene film or a polypropylene film that has been subjected to a corona discharge treatment on only one side, and the corona discharge treated side is laminated to a wood fiber board via an adhesive. 5. The panel for use in a concrete form according to claim 1 , wherein the surface of the resin sheet opposite the wood fiber board has a wettability index of less than 40 mN/m. 6. The concrete form panel according to claim 1 , wherein the adhesive contains an ethylene-vinyl acetate copolymer .

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