JPH04323463A - Formwork - Google Patents

Abstract

PURPOSE:To obtain a formwork of which the total weight is light, nailing is possible, cutting is easy, strength as a formwork is held, and mold releasing property is favorable. CONSTITUTION:Foaming synthetic resin core material 1 is used for light weight orientation, reinforcing fiber 2 is contained in the core material 1 for holding strength, foaming synthetic resin, reinforcing fiber 2, and mold releasing sheets 3 are mutually made in one body at foaming the synthetic resin of the core material 1, and cement-series hardened mold releasing sheets are arranged on one side or both sides of the core material 1. Further, skin layers are arranged on the opposite two sides or four sides of the foaming synthetic resin core material 1 containing the reinforcing fiber 2.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is lightweight and can be nailed.
This invention relates to a formwork made of foamed synthetic resin that is easy to cut, maintains strength as a formwork, and has excellent mold releasability.

0002

2. Description of the Related Art Formwork conventionally used for civil engineering and construction purposes includes metal formwork and wooden formwork. The former is made of materials mainly made of iron and aluminum and is used at various civil engineering and construction sites, while the latter is plywood made by polymerizing and bonding thin wooden boards, and is called a compane. Similar to the metal formwork described above, this formwork is also widely used at civil engineering and construction sites. Since metal formwork cannot be cut to suit the conditions of the construction site, many types of formwork are available to accommodate various types of construction work. Companion formwork can be cut as appropriate with a saw, etc., so it is used by cutting it according to the conditions at the construction site and connecting it with nails.

0003

[Problems to be Solved by the Invention] However, among metal formwork and panel formwork, the former uses a material with high strength as mentioned above, but is heavy and difficult to work with, and is easily cut. Because it cannot be used, it cannot be cut and processed according to the construction site, and special fixing metal fittings are required because it cannot be nailed, and in addition, when the concrete and the formwork are fixed. This release from the mold is time-consuming, and there are problems such as damage to the formwork and concrete surface if the mold is removed forcibly.

Although the latter is not as heavy as metal formwork, it is not light enough for individuals to easily carry and work with it, and also has poor mold release properties, so it is always difficult to use the formwork. A mold release agent must be applied to the concrete pouring surface of the concrete, and it cannot be expected to be used very many times, resulting in a problem that it becomes expensive.

The present invention solves the problems with conventional formwork, and provides a formwork that is lightweight, can be nailed, is easy to cut, maintains strength as a formwork, and has good mold releasability. This is what I am trying to do.

[0006]

[Means for Solving the Problems] The object of the present invention is to first provide a core material made of a foamed synthetic resin plate having reinforcing fibers therein, and a core material adhered to one or both surfaces of the core material. It is made of a release sheet for cement-based cured products and a formwork. Glass fiber is used as an example of reinforcing fiber in this formwork,
Also, as foamed synthetic resins, polyurethane, polystyrene,
Single-layer or multi-layer synthetic resins are selected from synthetic resins such as polyethylene and polypropylene, and have good release properties from cement-based cured materials such as polyethylene sheets, high-density polyethylene sheets, and polyethylene terephthalate sheets. A sheet is used. If this is used as a release sheet on one surface of the plate-shaped core material, a hard plate such as plywood, wood board, synthetic resin board, metal plate, etc. is fixed to the other surface. Also used is

[0007] Next, the reinforcing fibers are incorporated into the formwork, and two or four opposing sides of the outer peripheral surface are
A formwork consisting of a plate-shaped core material made of foamed synthetic resin whose sides are skin layers, and a release sheet for cement-based cured material adhered to one or both surfaces of the core material is also used. In this formwork, one or more glass fiber mats are used as reinforcing fibers, and reinforcement can be achieved by incorporating glass fibers into the skin layer, and polyolefin-based synthetic resin is used as the foamed synthetic resin. and various synthetic resins are used, and synthetic resin sheets with good mold releasability from cement-based cured materials such as polyethylene sheets, high-density polyethylene sheets, and polyethylene terephthalate sheets are used as release sheets. . In particular, the release sheet is a rectangular sheet, the outer edges of two or four opposing sides are located inside the outer edge of the surface of the core material, and the outer edge of the sheet is connected to the outer surface of the skin layer at the edge of the core material. It is proposed to use a sheet that is sealed with a layer part and in which the surface of the outer surface layer part and the sheet surface are located substantially on the same plane. Furthermore, a polyethylene sheet, a high-density polyethylene sheet, a polyethylene phthalate sheet, etc. is used as a release sheet, reinforcing fibers are interposed between these two sheets, and a polyurethane resin is filled between the sheets and foamed to form a core material. A sheet formed by bonding a core material and a sheet together is also used, and a paper sheet is also used to improve the adhesion between the core material and the release sheet. Next, in addition to the above-mentioned formwork, a cement-based core material is applied to one side of a foamed synthetic resin plate-shaped core material that contains reinforcing fibers inside and has a skin layer on two or four opposing sides of the outer peripheral surface. A formwork formed by adhering a release sheet for cured products and removably fixing a hard plate or frame to the other surface with nails, screw adhesive tape, clamping fittings, etc.
A release sheet for cement-based cured products is adhered to one side of a plate-shaped core material made of foamed synthetic resin, which has reinforcing fibers inside and has a skin layer on two or four opposing sides of the outer peripheral surface, and Another example of a formwork is a formwork in which a hard plate or a frame is fixed to one side of the formwork.

[0008]

[Function] The formwork according to the present invention as described above has a foamed synthetic resin core material in which reinforcing fibers, such as glass fibers, etc. are embedded in a mat shape at least inside. A release sheet for cement-based hardened materials is adhered to both surfaces, and in some cases, the release sheet is attached to one surface and a hard plate or frame is attached to the other surface. If formwork is used, since the core material is foamed synthetic resin, it is lightweight and easy to handle, and can be easily cut with a saw or the like to adapt to each construction site. When the formwork is used at a civil engineering or construction site to assemble the formwork and pour concrete, the core material contains fiber material such as glass fiber mat as a reinforcing material, so foamed polyurethane resin etc. Even when synthetic resin is used, it maintains the supporting strength as a formwork, and even when trying to connect formworks by nailing, etc., the hardening reinforced by the fiber sheet inside the core material This makes nailing possible in combination with parts and a release sheet, etc., which has a higher strength than the foam core material. In addition,
After the concrete has hardened, when the formwork is to be released from the mold, the release sheet located on the surface of the core material acts as a release agent, making it possible to easily release the formwork from the hardened concrete surface. That is to say. In addition, if a rigid plate or a frame with outwardly facing ribs is fixed to one surface of the formwork, especially the outer side, the formwork cannot be used for concrete pouring. When the formwork is erected, there is no need for vertical crosspieces to be attached directly to the outside of the formwork, and instead of the crosspieces, plate-shaped ribs are used directly, and a piece of butter or the like is placed on top of the ribs to fix the formwork. Can be done. In addition, when attaching a form tie or the like, it is sufficient to drill a hole at a suitable position in the opposed formwork in the same manner as a conventional formwork, and then attach the form tie to the hole in the usual manner.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the invention will be further explained by means of illustrated embodiments. The formwork F1 of the present invention shown in Fig. 1 is a basic example thereof, and 1 in the figure contains powder produced by pulverizing glass fiber, rock wool, metal fiber, carbon fiber, and rice husk. Reinforcing fibers such as wood powder and wood flour are used in sheet or mat form, for example, glass fibers are intertwined in a three-dimensional structure with a thickness of 5 to 10 mm.
It is a plate-shaped core material 1 made of foamed synthetic resin, which has reinforcing fibers 2, such as a matte mat (manufactured by Unifilo Co., Ltd., product name Vetrotex) or simply a state in which short or long fibers are dispersed. Consists of structural materials. As the foamed synthetic resin, one or more selected from synthetic resins such as polyurethane, polystyrene, polyethylene, polypropylene, polyester, polyvinyl chloride, polyphenol, ABS, urea, melamine, etc. are mainly used, and other types can be foamed. Synthetic resins can be used. In particular, a polyurethane resin foamed with one or more glass fiber mats laminated inside and at a foaming degree of several to 20 times is used, especially one that is foamed to a foaming degree of 10 to 15 times. things are used as preferred. The sheet 3 adhered to the surface of the plate-shaped core material 1 made of foamed synthetic resin is a release sheet for a cement-based cured product when used on both surfaces as shown in the figure, or when used on one side. The release sheet 3 is naturally provided on the cement-based hardened material side of the core material 1, and is used to facilitate release from the surface of the formwork F1 when cement, concrete, etc. hardens after curing. ing. The release sheet 3 is generally a polyethylene sheet, a high-density polyethylene sheet, a polyethylene terephthalate sheet, a so-called PET sheet, a polyester sheet, a polyvinyl chloride sheet, a polyphenol sheet, an ABS sheet,
Directly or adhesively attach single-layer or multi-layer sheet-like materials, including film-like, sheet-like, thin-plate-like forms, made of materials that have good mold releasability for cement-based cured products such as urea sheets and melamine sheets. In order to improve its properties, the sheet is subjected to corona discharge machining or surface treated with acid. When the release sheet 3 is used on both sides of the core material 1, both sides can be used as surfaces for molding the cement-based cured product, but the sheet 3 may be positioned only on one side. For example, when the foaming degree of the core material 1 is increased to make it lightweight and inexpensive, the strength of the core material becomes low. Therefore, the release sheet 3 as described above is used on one surface, and the other surface is made of plywood, wood, etc. This is a case where a hard plate such as a synthetic resin plate or a metal plate is fixed to increase the overall strength. In the embodiment shown in FIG. 1, since each peripheral edge of the release sheet 3 is exposed on the outer peripheral surface together with the peripheral edge of the core material 1, water and cement liquid components are likely to enter. In order to waterproof the outer peripheral surface including the peripheral edge of the mold release sheet 3 or to prevent the edge of the release sheet 3 from peeling off from the core material, tape or metal fittings made of synthetic resin or metal are fixed to the outer peripheral edge. Also considered as a desirable example.

[0010] When using such a formwork,
This formwork F1 is designed with a concrete filling space similar to the conventionally used aluminum formwork and Konpane formwork.
A formwork structure is formed by arranging them facing each other and fixing them with form ties or the like. When the release sheet 3 is used on both surfaces of the core material 1, if the release sheet 3 on one surface is damaged and becomes unusable, the other surface of the release sheet 3 can of course be used. If both surfaces are damaged or the core material 1 is bent, it can be discarded.

Next, the mold shown in FIG. 2 and subsequent figures is an example in which a skin layer 4 is disposed on a part or the whole of the outer periphery of the mold. That is, the present formwork F2 represented by FIG. 2 has reinforcing fibers 2 therein, and two or four opposing sides of the outer peripheral surface are made of thin skins with a thickness of, for example, about 0.5 mm to 2 mm. A mold release sheet 3 for cement-based cured products adhered to one or both surfaces of a plate-shaped core material 1 made of foamed synthetic resin, which is a layer 4 or a thick skin layer 4 with a thickness of about several mm.
The formwork consists of Although the basic parts, such as the core material 1 and release sheet 3, are the same as the formwork shown in Fig. 1,
This embodiment differs from the embodiment shown in FIG. 1 in that two or four opposing sides of the plate-shaped core material 1 are used as skin layers 4. skin layer 4
By providing this, the end portion of the formwork can be reinforced, and it is possible to prevent moisture from entering from outside through this portion.Furthermore, when nailing the formwork together, this side end portion can be reinforced. The nail retention strength can be increased. In particular, when a glass fiber mat or the like is used as the reinforcing fiber 2, it is easy to increase the nail retention strength against nail driving from the surface direction, but it is easy to increase the nail retention strength when nailing from the side edge to the inside, that is, from the side edge of the formwork. When nails are driven from the side edges in the width direction, the nails that are driven into the reinforcing fibers naturally do not get entangled with each other, so that the nail holding function deteriorates, and this improvement is required, and the formation of the skin layer 4 was considered. Note that the reinforcing fiber 2 typified by glass fiber etc. is used in the skin layer 4.
By including it inside, the reinforcement of this skin layer 4 portion can be further increased.

In the embodiment shown in FIG.
In contrast to the mold frame F2 of FIG. 2, in which the outer edge 3a of the core material 1 is set at almost the same position as the outer edge 1a of the core material 1, the release sheet 3 is a rectangular sheet, and the outer edges of two or four opposing sides are located at the same position as the outer edge 1a of the core material 1. Located inside the outer edge of the surface of the material 1, the outer edge 3a of the sheet is sealed with the outer surface layer portion 5 of the skin layer 4 at the outer edge portion of the core material 1, and the surface 6 of the outer surface layer portion 5 and the sheet surface are sealed. 7 is a formwork F3 which is located substantially on the same plane as each other. Core material 1
The release sheet 3, reinforcing fiber 2, etc. are shown in Figures 1 and 2.
Although the release sheet 3 is used in the same manner as in the example of
The difference is that the outer edge 1a of the core material 1 is provided in a state in which the outer edge 1a of the core material 1 is protruded outward more than the outer edge 3a of the core material 1.

The details can be further understood by comparison with the partially enlarged sectional view of FIG. In other words, the skin layer 4 portion located at the side edge of the core material 1 is set wider outward than the outer edge 3a portion of the release sheet 3, and the outer surface layer portion 5 of the skin layer, which is the surface side portion, is raised and The surface 6 is set to be substantially flush with the release sheet surface 7,
The outer edge 3a of the sheet is sealed with the outer surface portion 5 of the skin layer.

4 is a formwork F4 in which the outer surface layer portion 5 of the skin layer shown in FIG. 3 is extended to the surface 7 of the release sheet 3, and a part of the sheet 3 is covered with a covering portion 8. be. In this state, the skin layer 4 extends outward from the release sheet 2, and in this state, the outer surface layer part 5 is extended onto the sheet 3 to form a covering part 8 that covers part or all of the sheet periphery. The coated one prevents the periphery of the release sheet 3 from peeling off from the surface of the core material 1, and also prevents the release sheet 3 and core material 1 from being coated with adhesives or paper materials that do not have good water resistance. When using the release sheet 3, the outer surface layer 5 prevents moisture and cement components from entering the core material or the bonded area from the side edges of the release sheet 3 during use of the mold. be. In addition, when the reinforcing fibers 2 are present in this skin layer 4 portion, the skin layer 4 becomes a reinforcing frame material for the formwork F4, imparting extremely high strength to the formwork, and making nailing easier. It tightens it.

[0014] The formwork F3 shown in FIGS. 3 and 4
, F4 are formed by the mold 9 shown in FIG. 8, for example. For example, when creating a core material 1 made of polyurethane resin with a foaming degree of 10 to 15 times, PET sheets 10, 10 are arranged above and below in the molding space of this mold 9, and reinforcing fibers are placed between them. 2, for example, a two-layer glass fiber mat 11 is placed inside, and then foaming polyurethane resin is filled into the molding space 9a, and the sheets 10, 10
Fill the space with resin. At this time, due to the filling pressure, the resin flows between the mold side end inner surface 9b and the sheet side edge in FIG. The outer surface layer portion 5 is formed by entering as shown by the arrow and foam-molded as it is, and the covering portion is formed by extending a part of the outer surface layer portion 5 as shown in FIGS. 4 and 5. At step 8, a release sheet with the surface 7 locked is produced. If the foamed synthetic resin core material 1 is to be continuously molded, it will naturally not be possible to create a mold with skin layers 4 on all four sides like the mold shown in FIG. The skin layer 4 can be formed only at both ends in the direction, and there are simply cut surfaces before and after that. In addition, at this time, the skin layers 4, 4 at both ends
By cutting and removing it, it is possible to create one without skin layers on all sides. Formwork having such a skin layer 4 is lightweight and easy to carry, so it can be easily used at various construction sites, and the skin layer 4 can be easily used during nailing, etc. In addition to being fully usable, if the outer surface layer 5 is formed as shown in FIGS. 4 and 5, or if the covering part 8 is formed, the release sheet 3 is
It is possible to prevent the peripheral edge from peeling off from the core material 1 and to prevent water, cement components, etc. from entering from the peripheral edge.

The formwork F5 shown in FIG. 9 and the formwork F6 shown in FIG. 10 both have the same basic structure as those shown in FIGS. 2 and 4. However, an adhesive intervening layer 12 is provided between the skin layer 4 portion and the foamed synthetic resin plate-shaped core material 1 in order to improve mutual adhesion. As the adhesive intervening layer 12, kraft paper, a paper sheet impregnated with a synthetic resin material, or the like is used. By using the adhesive intervening layer 12 in this situation, and by using the adhesive intervening layer 12 in the cases shown in FIGS. There is no need to adhere the release sheet 2 after making the foamed synthetic resin plate-shaped core material 1, and the whole can be integrally adhered at the time of foaming.

Finally, formworks F7 and F in FIGS. 11 and 12
8 is an example in which crosspieces 13 and plates (not shown) are attached to each of the formworks F1 to F6. The embodiment shown in FIG. 11 basically includes a crosspiece 13 made of wood, metal, synthetic resin, etc. on one side of the formwork F1 shown in FIG. 1 or the formworks F2 to F4 shown in FIGS. 2 to 4. This formwork is formed by removably fixing the frame body 14 with nails, screws, adhesive tape, clamping fittings (not shown), or the like. Furthermore, this crosspiece 13 can be made of wood board, plywood, metal board,
Relatively thick hard plates such as synthetic resin plates are also selectively adopted, and by removably fixing these frames 14 or hard plates, it can be used as a formwork with crosspieces. . As mentioned above, the formwork body uses foamed synthetic resin for the core material 1 and PET sheet etc. for the release sheet 3, so the overall weight is lower than that of the conventional formwork made from a panel. Since it is lighter and easier to handle than the molded material, it can be easily used at various construction sites. By peeling off the adhesive tape and removing nails and screws from the frame body 14 and hard plate body to separate them from each other, changing the front and back sides of the core material 1, and fixing the frame body 14 again, the core material 1 is removed. Both surfaces can be used as formwork surfaces. On the other hand, in the formwork F8 shown in FIG. This shows a structure made by integrally fixing the plates. In the example shown in FIG. 12, when a foamed synthetic resin such as polyurethane resin is foam-molded, a crosspiece frame 15 having a groove is arranged as the crosspiece 13 as shown in the figure, and urethane resin or the like is filled inside and foamed. By letting the release sheet 3
, the plate-shaped core material 1 and the frame body 15 can be formed by integrally foaming and adhering them.
When using the formworks F7 and F8 of No. 2, it is possible to use them without the need to newly attach crosspieces to the outer surface of the formworks.

In each of the above embodiments, reinforcing fibers were filled and dispersed in a foamed synthetic resin, but only the reinforcing fibers were removed and the degree of foaming of the synthetic resin was changed by nailing It should be noted that it is technically possible to use a product with a low foaming level that can maintain the foam and a release sheet or the like arranged on each surface.

[0018]

[Effects of the Invention] As described above, since the formwork according to the present invention uses a core material made of foamed synthetic resin, it uses a plate-shaped core material made of foamed synthetic resin that has reinforcing fibers inside. Therefore, the entire formwork is lightweight, and as a result, the bending strength of the formwork as a whole is high, and it is possible to drive nails, and even if the formwork maintains its strength, it can be easily cut with a saw, etc. The mold release sheet on the surface can exhibit a high mold release effect on cement-based cured products. In particular, when a skin layer is formed on two or four sides facing the foamed synthetic resin plate core material, the skin layer serves as a reinforcing frame for the formwork and at the same time has a nail-retaining function. This creates the appropriate conditions for use as formwork. In addition, if the outer surface layer of this skin layer portion is formed and its surface is substantially flush with the surface of the release sheet, a part of this outer surface layer may be used as a covering portion of the release sheet. When it extends to the surface, it not only increases the strength of the formwork, but also prevents the release sheet from peeling off and prevents water and cement from entering the inside of the release sheet and the adhesive surface with the core material. To efficiently prevent moisture containing ingredients from entering. Furthermore, if a foamed synthetic resin with a foaming ratio of several times to 20 times is used, especially a foamed polyurethane resin with a foaming ratio of around 10 to 15 times, reinforcing fibers such as glass fiber mats can be held inside the core material during foaming. At the same time, if a release sheet is placed on the surface, the core material, reinforcing fibers, and release sheet can be integrated with each other during foaming without the need for adhesives, and the strength of the formwork is increased. and lightweight.

[Brief explanation of drawings]

FIG. 1 is an explanatory perspective view with a part of a formwork according to a first embodiment of the present invention in cross section;

FIG. 2 is a partially sectional perspective view of a formwork according to a second embodiment of the present invention;

FIG. 3 is an explanatory perspective view with a part of the formwork according to the third embodiment of the present invention in section;

FIG. 4 is a partially sectional explanatory perspective view of a formwork according to a fourth embodiment of the present invention.

[Fig. 5] Cross-sectional explanatory diagram that enlarges a part of Fig. 4

[Figure 6] Third
Explanatory perspective view of the embodiment

[Fig. 7] Explanatory perspective view of the third embodiment

[Fig. 8] Explanatory diagram of a mold for manufacturing the formwork of the fourth embodiment

[Figure 9
] An explanatory perspective view with a part of the formwork according to the fifth embodiment of the present invention in section

FIG. 10 is a partially sectional explanatory perspective view of a formwork according to a sixth embodiment of the present invention;

FIG. 11 is a partially sectional explanatory perspective view of a formwork according to a seventh embodiment of the present invention;

FIG. 12 is a partially sectional explanatory perspective view of the formwork according to the eighth embodiment of the present invention;

[Explanation of symbols] 1 Core material 1a Core material outer edge 2 Reinforcement fiber 3 Release sheet 3a　Sheet outer edge 4. Skin layer 5 Outer surface layer 6　　　Outer surface layer surface 7 Sheet surface 8 Covering part 9 Mold 9a Molding space 9b Inner side end 9c Upper and lower inner surfaces 10 PET sheet 11 Glass fiber mat 12 Adhesive intervening layer 13　　　　Sill 14 Frame 15 Grooved frame F1 First embodiment formwork F2 Second embodiment formwork F3 Third embodiment formwork F4 Fourth embodiment formwork F5 Fifth embodiment formwork F6 Sixth embodiment formwork F7 Seventh embodiment formwork F8 Eighth embodiment formwork

Claims (16)

[Claims] 1. A mold release sheet for a cement-based hardwood object, comprising: a plate-shaped core material made of foamed synthetic resin containing reinforcing fibers therein; formwork. 2. The formwork according to claim 1, wherein glass fiber is used as the reinforcing fiber. [Claim 3] As the foamed synthetic resin, polyurethane,
2. The formwork according to claim 1, which is made of one or more synthetic resins selected from polystyrene, polyethylene, polypropylene, polyester, polyvinyl chloride, polyphenol, ABS, urea, melamine, etc. 4. The release sheet is made of a single-layer or multi-layer synthetic resin with good releasability from cement-based cured materials such as polyethylene sheets, high-density polyethylene sheets, polyethylene terephthalate sheets, ABS sheets, MMA sheets, and AS sheets. The formwork according to claim 1, which is formed by using a sheet. 5. The formwork according to claim 1, wherein a release sheet is adhered to one side of the plate-shaped core material, and a hard plate is fixed to the other side. [Claim 6] Incorporating reinforcing fibers inside,
and a plate-shaped core material made of foamed synthetic resin in which two or four opposing sides of the outer circumferential surface are skin layers, and a release sheet for cement-based cured products that is adhered to one or both surfaces of the core material. , consisting of formwork. [Claim 7] Claim 6, wherein a single layer or multiple layers of glass fiber mat is used as the reinforcing fiber.
Formwork as described. 8. The formwork according to claim 5, wherein the skin layer contains glass fibers. [Claim 9] The foamed synthetic resin includes polyurethane,
9. The formwork according to claim 6, 7, or 8, which is made of one or more synthetic resins selected from polystyrene, polyethylene, polypropylene, polyester, polyvinyl chloride, polyphenol, ABS, urea, melamine, etc. 10. The release sheet is made of a single-layer or multi-layer synthetic resin that has good releasability from cement-based cured materials such as polyethylene sheet, high-density polyethylene sheet, polyethylene terephthalate sheet, ABS sheet, MMA sheet, and AS sheet. 7. The formwork according to claim 6, which is formed by using a sheet. 11. The release sheet is a rectangular sheet, and the outer edges of two or four opposing sides are located inside the outer edge of the surface of the core material, and the outer edge of the sheet is attached to the skin of the edge of the core material. 11. The formwork according to claim 6, wherein the formwork is sealed with an outer surface layer portion and the surface of the outer surface layer portion and the sheet surface are set substantially on the same plane. 12. The formwork according to claim 6, wherein the covering portion extends from the outer surface layer portion of the skin layer to the surface of the sheet, and the sheet is locked and fixed to the core material. 13. As a release sheet, a polyethylene sheet, a high-density polyethylene sheet, or a polyethylene terephthalate sheet is used, reinforcing fibers are interposed between two sheets selected from these sheets, and a polyurethane resin is filled between the sheets. 13. The formwork according to claims 6 to 12, which is formed by foaming and bonding the core material and the sheet together. 14. The formwork according to claim 6, wherein a paper sheet is interposed between the core material and the release sheet. 15. Release sheets for cement-based cured products are applied to both sides of a plate-shaped core material made of foamed synthetic resin, which contains reinforcing fibers inside and has skin layers on two or four opposite sides of the outer peripheral surface. A formwork formed by gluing and removably fixing a frame or a hard plate to one side with nails, screws, adhesive tape, clamping fittings, etc. 16. A mold release sheet for cement-based cured products on one side of a plate-shaped core material made of foamed synthetic resin, which has reinforcing fibers inside and has a skin layer on two or four opposite sides of the outer peripheral surface. A formwork made by gluing and fixing a frame or a hard plate to one side of the formwork.