JPH09225079A - Training board for sport - Google Patents

Abstract

PROBLEM TO BE SOLVED: To securely prevent a board from exfoliation, warp and twist by constituting the board from a three-layer structure consisting of a thermosetting polyurethane foamed body having a glass fiber reinforced plastic and a vent hole and a material comprising in combination one kind or at least two kinds of wood, a metal or a glass fiber reinforced plastic. SOLUTION: A training board 1 for a ball sport is composed of a first layer A consisting of a glass fiber reinforced plastic 2, a second layer B consisting of a thermosetting polyurethane foamed body 4 contacting internally the first layer and having a vent hole 3 and a third layer C consisting of one kind or at least two kinds of materials 5 selected from wood, a metal or a glass fiber reinforced plastic. Thus, the heat energy of the sum beam accumulated in the glass fiber reinforced plastic 2 constituting the first layer A is received through the vent hole 3 and is radiated to generate heat convection, causes to eject heated air K from the hole end 3a of the upper surface, suck cold air K' from the hole end 3a of the lower surface, thus the thermal expansion of the first layer A is restrained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ball game practice board, and more particularly to a ball game practice board which is free from warp, deformation and peeling.

[0002]

2. Description of the Related Art In recent years, ball games using balls, for example, baseball, tennis, soccer, rugby, volleyball, handball and the like have been prominent. In order to fully enjoy these ball games, it is essential to master individual skills, and a practice board for that is required. A practitioner who desires to master individual skills will achieve the intended purpose by striking the ball on the practice board and repeatedly striking the ball that has been bounced back.

For the above-mentioned practice, conventionally, a practice board made of a combination of wood or an iron plate or concrete has been installed outdoors. However, the former absorbs water when it rains and the repulsive effect decreases, and it often takes several days to recover, while the latter has drawbacks in terms of installation cost and construction period.

The above-mentioned drawbacks have been solved by the invention of a practice board for ball games comprising a three-layer structure. In this practice board for ball games, the first layer was composed of glass fiber reinforced plastic, the second layer was composed of thermosetting polyurethane foam, and the third layer was composed of glass fiber reinforced plastic similar to the first layer.

[0005]

However, it has been clarified that the above-mentioned conventional practice board for ball game consisting of the three-layer structure cannot achieve the intended purpose in a specific season. That is, when the temperature rises, especially in summer, the ball repulsed from the practice board for ball games often jumps in an unexpected direction, which seriously reduces the practice effect and efficiency, or in the case of a soccer ball, the ball collides. Depending on the location, the repulsion distance of the ball was halved, and an abnormal sound was generated. Finally, a part of the surface layer of the practice board for ball games was peeled off, resulting in a situation where it could not be used.

Therefore, the present inventor has inspected and analyzed the abnormal part of the conventional practice board for ball game consisting of the above-mentioned three-layer structure, and as a result, it is thought that the following phenomena are accumulated to cause a trouble. It was. That is,

(1) The sunlight rays that directly irradiate the surface of the glass fiber reinforced plastic of the first layer are the first in the form of thermal energy.
Accumulated in layers.

(2) The accumulated heat energy is transferred to
Although the heat is usually radiated by the method of radiation, the polyurethane foam of the second layer acts as a heat insulating material, and the heat conduction is practically negligible and it is limited to the heat radiation by the heat radiation.

(3) Therefore, the first layer can only accumulate a large amount of heat energy by the sun's rays and dissipate heat by minute heat radiation, and as a result, it reaches a considerably high temperature state. In fact, it was confirmed that the surface of the first layer, which was exposed to direct sunlight for several hours in the summer, exceeded 80 ° C as measured by a thermocouple.

(4) The first layer in question, which is kept at high temperature, will undergo thermal expansion, but since its inner surface is adhered to the thermosetting polyurethane foam, the direction of expansion is at its ends. Area and sunlight-irradiated surface. As a result, the following problems were encountered regarding the performance and structure of the above ball training board. In order to disperse the impact force of the ball, reducing the amount of polyurethane resin per unit volume and increasing the expansion ratio will reduce the strength of the foam, and the polyurethane resin layer at the end where the expansion force concentrates will not withstand this and will be destroyed. This results in peeling. If the expansion ratio is reduced to increase the resin content per unit volume in order to avoid this, the expansive force acts on the sunlight irradiation surface, and as a result, the first layer warps in the direction of the irradiation surface and twists, resulting in conflicting problems. There are situations in which it is impossible to solve.

(5) The first problem in such a situation
When a ball is impacted on a layer, in the case of a relatively lightweight ball, such as a tennis ball, the ball repels in a direction that does not correspond to its angle of incidence, and the practitioner cannot improve the practice effect. It will take time to collect the balls.
When the ball is relatively heavy like a soccer ball and is repeatedly subjected to a violent impact force, the strain of the first layer is amplified, the resin layer of the polyurethane foam is broken, and the peeling is accelerated. Naturally, the repulsive force of the ball decreases, it becomes impossible to improve the practice effect, or the resin layer of the polyurethane foam is destroyed when baseball, especially a hard ball, is subjected to extremely local and intense impact force. Not only did this cause peeling, but the first layer, which was unable to disperse the impact force, was finally destroyed, making it impossible to achieve the intended purpose.

The present invention solves the problems and problems of the above-mentioned conventional practice board for ball game consisting of a three-layer structure, and provides a practice board for ball game without peeling, warping or twisting. It is an object. Another object of the present invention is to provide a ball-practice practice board capable of removing the thermal energy accumulated in the first layer and suppressing the expansion rate thereof.

[0013]

To achieve the above object, the present invention provides a first layer of glass fiber reinforced plastic,
A second layer of a thermosetting polyurethane foam having air circulation holes inscribed in the first layer, and a third layer of a material made of a combination of one or more selected from wood, metal or glass fiber reinforced plastic. It is composed of a three-layer structure, and the thermal energy accumulated in the first layer is removed by the air circulation holes arranged in the second layer, so that the thermal expansion can be suppressed, and peeling, warping and twisting can be surely prevented. There is.

Further, according to the invention of claim 2, the hole end of the air circulation hole is provided on the upper and lower surfaces of the second layer or on the left and right surfaces, or is communicated with the through hole provided in the third layer, and the air passage is formed. It is structured so that it can be distributed efficiently.

Further, in the invention according to claim 3, the air circulation holes are evenly dispersed, and the porosity to the thermosetting polyurethane foam is set to 1 to 50%, and the efficiency of heat convection is maintained. It is constructed so that it can sufficiently oppose the impact force of the ball.

Further, in the invention according to claim 4, the weight ratio of the glass fiber / thermoplastic resin of the glass fiber reinforced plastic is set to 20 to 50/80 to 50, and the impact of the ball is repeated. The layer is constructed to withstand the impact sufficiently.

Furthermore, the invention according to claim 5 further comprises the plastic component of the glass fiber reinforced plastic,
The thermosetting unsaturated polyester is used, and the first layer, which is repeatedly subjected to the impact of the ball, is configured to sufficiently withstand the impact.

Further, in the invention according to claim 6, the air circulation hole is reinforced by a tube body selected from iron, copper, aluminum and alloys thereof, and the first layer in which the impact of the ball is repeated. The air circulation hole inscribed in is sufficiently configured to withstand the impact.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. The practice board 1 for ball game of the present application is shown in FIG.
As shown in FIG. 2, a first layer A made of glass fiber reinforced plastic 2 and a second layer B made of thermosetting polyurethane foam 4 having air circulation holes 3 inscribed in the first layer A,
The third layer C is made of one or more materials 5 selected from wood, metal or glass fiber reinforced plastic.

The glass fiber reinforced plastic 2 constituting the first layer A is required to withstand the impact of repeated ball hits, is made of a long sheet having a thickness a of 0.5 to 10 mm, and has a bending strength. It is necessary to have a physical property value of 15 kg / mm ² or more, a bending elastic modulus of 500 kg / mm ² or more, and an Izod impact value (notched) of 40 kg · cm / cm or more (all according to ASTM).

As the glass fiber reinforced plastic 2 satisfying the above-mentioned required values, a hot lamination method or a glass fiber in which a glass fiber mat structure is hot pressed with a thermoplastic resin film in a sandwich form and then cooled The mat-like structure is made of thermoplastic resin powder.
It can be produced by a known method such as a dispersion method of forming a sheet after pellet-suspension mixing and vacuum heat drying. At that time, the weight ratio of the glass fiber mat-shaped structure and the thermoplastic resin was glass fiber / thermoplastic resin = 2.
0-50 / 80-50 is suitable.

The glass fiber mat-shaped structure is usually a glass fiber having a diameter of 3 to 50 μm, preferably 5 to 30 μm. It is a product in which fibrous materials cut to 300 mm are entangled, or a plain, twill, or satin woven fabric is used alone or in combination. As the material of the glass fiber, glass such as E glass, C glass, D glass, S glass and T glass is used.

Examples of the thermoplastic resin include polyethylene, polypropylene, polyamides, polyethylene terephthalate and modified derivatives, polyurethane, polycarbonate, and polymer alloys containing these as the main components. In addition to these antioxidants and ultraviolet absorbers, pigments are added to these thermoplastic resins for coloring.

As another type of the glass fiber reinforced plastic for the first layer used in the present invention, the above-mentioned glass fiber mat structure is impregnated with a composition based on an unsaturated polyester resin and heated. It can also be obtained by a thermosetting method of pressing.

The air circulation hole 3 forming the second layer B of the practice board for ball game 1 of the present application extends vertically in the case of FIG.
Hole ends 3a, 3 formed on the upper and lower surfaces or the left and right surfaces of the second layer B
Air is circulated from b. Also,
The air circulation hole 3 may be formed so as to extend in the thickness direction of the second layer B as shown in FIG. In this case, air is circulated from one hole end 3c communicating with the through hole 6 provided in the third layer C.

That is, the heat energy based on the sun's rays accumulated in the glass fiber reinforced plastic 2 constituting the first layer A is received by the air circulation hole 3 by radiation to generate heat convection, and in FIG. The air K heated up from the end 3a is discharged, the air K'of relatively low temperature is sucked in from the hole end 3b on the lower surface, and the air K heated up from the upper part of the hole end 3c is discharged in FIG. The air K ′ having a relatively low temperature is sucked in from the lower part of 3c. Therefore, as a result of reducing the heat storage energy of the first layer A, thermal expansion of the first layer A is suppressed.

The cooling efficiency depends on the heat radiation and heat convection, that is, the porosity determined by the inner surface area and volume of the first layer A and the air circulation holes 3 inscribed therein. The porosity is measured in a state where the air circulation holes 3 are evenly dispersed.
It is 1 to 50%, preferably 5 to 50%. When the porosity is 1% or less, the efficiency of thermal convection is reduced, so that a substantial effect is not recognized, and conversely, when the porosity is 50% or more, the effect is sufficiently recognized, but the ball impact strength cannot be fully resisted. , The first
This is inconvenient because the glass fiber reinforced plastic 2 of the layer A is destroyed. This porosity is calculated by the following equation. Porosity = volume of air circulation hole 3 / total volume of second layer B × 1
00

The front shape of the air circulation hole 3 extending in the vertical direction is not particularly limited, but a typical example thereof is shown in FIG. FIG.
When (a) is arranged vertically, (b) is inclined and (c) is corrugated,
The same (d) is a case where they are arranged side by side in a grid pattern.

The plane shape of the air circulation hole 3 can be arbitrarily determined, and a representative example thereof is shown in FIG. FIG. 4A is a rectangle, two short sides of which are inscribed in the first layer A and the third layer C, and two long sides of which are thermosetting polyurethane foams 4.
Covered with. The same (b) is a square, and one side is inscribed in the first layer A, and the other three sides are covered with the thermosetting polyurethane foam 4. The same (c) is semicircular,
The plane side is inscribed in the first layer A, and the arc side is covered with the thermosetting polyurethane foam 4. (D) is an isosceles triangle in which the bottom side is inscribed in the first layer A and the apex is inscribed in the third layer C, and the two hypotenuse sides are covered with the thermosetting polyurethane foam 4.

The air circulation hole 3 can be formed as a space of the thermosetting polyurethane foam 4, but the air circulation hole inscribed in the first layer where the impact of the ball is repeated is sufficient for the impact. Iron, to be able to withstand
It may be formed of a tubular body (not shown) selected from copper, aluminum and alloys thereof.

In the thermosetting polyurethane foam 4 constituting the second layer B, when the air circulation hole 3 is formed by the tube, the tube and the first layer A and the third layer C are formed. It has a function of joining and integrating the persons and dispersing the impact force of the ball received by the first layer A.

Further, in the thermosetting polyurethane foam 4,
As described above, in order to have a sufficient function to disperse the impact force of the ball that the first layer A receives, 30 to 300 kg / c
It is preferably a foam having a density of m ³ , and a thickness of 10 to 100 mm is usually used.

Further, the material of the thermosetting polyurethane foam 4 is a semi-hard material which can be obtained by a known method mainly containing polyether polyol, polymeric methylene diisocyanate, crosslinking agent, water, catalyst, foam stabilizer and the like. It is a form.

The material 5 which constitutes the third layer C of the ball game practice board 1 is selected from one kind or a combination of two or more kinds selected from wood, metal and the glass fiber reinforced plastic. This protects the second layer B and
This configuration is necessary as a reinforcing material when the practice board 1 for ball game of the present application is installed at a desired place.

In order to manufacture the practice board for ball game 1 having the three-layer structure, for example, the shape of the air circulation holes 3 arranged at equal intervals on the glass fiber reinforced plastic 2 arranged on the press plate. Or, the polyurethane reaction stock solution is injected to cover the pipe body, and a third layer serving as a reinforcing material is further stacked,
It can be obtained by pressure molding while utilizing the exothermic reaction of polyurethane. In the ball game practice board 1 thus obtained, when the edges of the first layer A and the third layer C have an acute angle, so-called “chamfering” of about 3 to 5R may be performed. .

The chamfering is effective not only for preventing the danger to the human body but also for eliminating the weak points of plastics. That is, since burrs and sharp corners and edges have a defect that they are easily broken, it is effective to remove this defective portion in advance.

The ball-practice practice board 1 of the present application can be constructed by one three-layer structure, but as shown in FIG.
It is also possible to combine the layered structures 10 in the plane direction to form one ball game practice board 1. When a plurality of three-layer structures are combined in the plane direction, it is advisable to provide some gaps L ₁ and L ₂ between the adjacent three-layer structures 10 as shown in FIG.

That is, not only can each "three-layer structure 10" be subjected to "heat convection" in the air circulation hole 3, but even if the three-layer structure vibrates under the impact of a ball, the adjacent layers will It is effective in preventing them from rubbing against each other. In other words, 3
When the layer structures 10 rub against each other, the first layer A and the third layer C
This is to prevent this because the edge part of (1) may be fluffy and a defective part may be created.

In order to provide the gaps L ₁ and L ₂ , as shown in FIG. 6, a spacer 7 made of a flexible material that does not damage the three-layer structure, for example, a rubber-like substance or soft plastic. It is good to intervene. The gaps L ₁ and L ₂
Specifically, it is considered that 1/2 or more of the inner diameter of the air circulation hole 3 is preferable.

In addition, when the practice board 1 for ball game of the present application is actually installed, it is necessary to take the following into consideration. That is, the gap L ₃ between the lowermost end S of the ball game practice board 1 and the installation base G is blocked by mud even if muddy water bounces off in rainy weather. It is necessary to open it with a size that does not allow it, for example, about 30 cm.

Of course, if the installation base G is grounded by artificial grass or the like, the gap L ₃ may be narrow. The gap L between the bottom end S of the practice board for ball game 1 of the present application and the installation base G
When opening ₃ by about 30 cm, it is advisable to install a wire mesh etc. to prevent the driven ball from escaping behind the gap and to ensure safety.

Next, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

[0043]

[Example 1] Mainly made of polypropylene and having a length of 10
4m thickness for melt impregnation of 0-200mm glass fiber
m, size 1000 x 1000 mm stampable sheet (trade name: Azudel, polypropylene: glass fiber = 6
(0: 40% by weight) is set on the lower plate of the press, and five hollow 30 cm square pillars made of aluminum and having open ends at both ends are arranged at the both ends of the sheet and inside thereof at equal intervals. , The urethane stock solution shown in the table of FIG. 7, the solution A and the solution B were injected while being rapidly mixed, and another stampable sheet was placed on this, and 3 kg / m ² while utilizing the exothermic reaction of polyurethane. × pressure molding for 10 minutes,
A three-layer structure having a thickness of 30 mm and a density of 150 kg / m ³ was obtained, allowed to cool for 24 hours, and then subjected to the test.

[0044]

[Embodiment 2] The aluminum square pole of Embodiment 1 is set to 20 m.
A similar operation was performed except that the m-square was changed to obtain a three-layer structure.

[0045]

Example 3 A three-layer structure was obtained by performing the same operation as in Example 1 except that the cross section of an aluminum semi-cylindrical column having a radius of 15 mm was placed on the first layer surface in Example 2.

[0046]

[Example 4] A three-layer structure was obtained by performing the same operation as in Example 3 except that an aluminum semi-column having a radius of 10 mm was used.

[0047]

[Embodiment 5] The height in Embodiment 1 is 30 m with open ends at both ends.
m, 50 mm square aluminum hollow quadrangular prisms, the open ends of which are arranged perpendicularly to the first layer and 25 are arranged at equal intervals, and are cut out in advance with a shearing cutter according to the arrangement and inner dimensions of the quadrangular prisms. The same operation was performed except that the third layer was placed accurately, and a three-layer structure was obtained.

[0048]

Example 6 A three-layer structure was obtained in the same manner as in Example 5, except that a cylinder having a height of 30 mm and a radius of 50 mm was used.

[0049]

[Comparative example] In Example 1, without using the aluminum square column,
Other than that, the same operation was performed to obtain a three-layer structure.

In the three-layer structures obtained in Examples 1 to 6 and Comparative Example, the two adjacent vertices are made of 0.3 mm wire so that the open ends of the aluminum square pillars are vertical. The surface of the first layer was hung in the air, and the surface of the first layer was heated and irradiated with far infrared rays at 90 ° C. for 2 hours. After allowing to cool as it is for 2 hours, the appearance state was observed and the warpage rate was measured. The warpage ratio was measured by applying a 1000 mm straight ruler in parallel to each side, and measuring the maximum distance between the straight ruler and the surface of the first layer with a straight scale.

The results of these tests are shown in the table of FIG. According to FIG. 8, there is no problem at all, except for the fourth embodiment among the first to sixth embodiments. Further, even in the case of Example 4, there is no great difficulty as in the comparative example, and it can be judged that the device can be sufficiently used.

[0052]

As described above, the present invention provides a first layer of glass fiber reinforced plastic, a second layer of thermosetting polyurethane foam having air circulation holes inscribed in the first layer, wood,
Air circulation consisting of a three-layer structure of a third layer of a material made of one or a combination of two or more selected from metal or glass fiber reinforced plastic, in which the thermal energy accumulated in the first layer is arranged in the second layer Since it is removed by holes, there is no accumulation of heat storage energy due to direct sunlight, and the board is peeled off,
This has the effect of reliably preventing warping and twisting.

Further, in the invention according to claim 2, since the hole ends of the air circulation holes are provided on the upper and lower surfaces or the left and right surfaces of the second layer or are communicated with the through holes provided in the third layer, The effect is that the distribution of can be efficiently performed.

Further, in the invention according to claim 3, since the air circulation holes are uniformly dispersed and the porosity to the thermosetting polyurethane foam is set to 1 to 50%, the efficiency of heat convection is maintained. In addition, it is possible to sufficiently oppose the impact force of the ball.

Furthermore, in the invention according to claim 4, since the weight ratio of the glass fiber / thermoplastic resin of the glass fiber reinforced plastic is 20 to 50/80 to 50,
The effect is that the first layer, which is repeatedly subjected to the impact of the ball, can sufficiently withstand the impact.

Further, in the invention according to claim 5, since the plastic component of the glass fiber reinforced plastic is a thermosetting unsaturated polyester, the first layer, which is repeatedly subjected to the impact of the ball, can be sufficiently applied to the impact. It has the effect of enduring.

Furthermore, in the invention according to claim 6, since the air circulation hole is reinforced by a tube body selected from iron, copper, aluminum and alloys thereof, the ball is repeatedly impacted. The effect is that the air circulation holes inscribed in the first layer can sufficiently withstand the impact.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view of a practice board for ball game of the present application.

FIG. 2 is a partially cutaway perspective view of another example of the practice board for ball game of the present application.

FIG. 3 is a schematic front view of the practice board for ball game of the present application, in which (a) to (d) show aspects of the front shape of the air circulation hole.

FIG. 4 is a schematic plan view of the practice board for ball game of the present application, in which (a) to (d) show aspects of the planar shape of the air circulation hole.

FIG. 5 is a front view of the practice board for ball game of the present application when the three-layer structure is combined in the direction of the 35 sheets.

FIG. 6 is a partial front view of the practice board for ball game of the present application showing a state in which a gap is formed between the three-layer structure.

FIG. 7 is a table showing the composition and blending amount of a urethane stock solution.

FIG. 8 is a table showing a warp rate, a peeled state, and judgment in Examples.

[Explanation of symbols]

1 Ball Game Exercise Board 2 Glass Fiber Reinforced Plastic 3 Air Flow Holes 3a, 3b Hole Ends 4 Thermosetting Polyurethane Foam 5 Material 6 Through Hole 7 Spacer 10 3 Layer Structure A 1st Layer B 2nd Layer C 3rd Layer K Heated air K ′ Relatively low temperature air L ₁ , L ₂ , L ₃ Gap S Bottom edge of practice board 1 for the present ball game G Installation base

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] April 22, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0032

[Correction method] Change

[Correction contents]

Further, in the thermosetting polyurethane foam 4,
As described above, in order to have a sufficient function of dispersing the impact force of the ball received by the first layer A, 30 to 300 kg / m
It is preferably a foam having a density of ³ , and a thickness of 10 to 100 mm is usually used.

[Procedure amendment]

[Submission date] June 12, 1996

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] Brief description of drawings

[Correction method] Change

[Correction contents]

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view of a practice board for ball game of the present application.

FIG. 2 is a partially cutaway perspective view of another example of the practice board for ball game of the present application.

FIG. 3 is a schematic front view of the practice board for ball game of the present application, in which (a) to (d) show aspects of the front shape of the air circulation hole.

FIG. 4 is a schematic plan view of the practice board for ball game of the present application, in which (a) to (d) show aspects of the planar shape of the air circulation hole.

FIG. 5 is a front view of the practice board for ball game of the present application when the three-layer structure is combined in the direction of the 35 sheets.

FIG. 6 is a partial front view of the practice board for ball game of the present application showing a state in which a gap is formed between the three-layer structure.

FIG. 7 is a chart showing the composition and blending amount of an undiluted urethane solution.

FIG. 8 is a table showing the warpage rate, the peeled state, and the judgment of the example.

[Explanation of reference numerals] 1 practice board for ball game 2 glass fiber reinforced plastic 3 air circulation holes 3a, 3b hole ends 4 thermosetting polyurethane foam 5 material 6 through hole 7 spacer 10 3 layer structure A 1st layer B 1st 2nd layer C 3rd layer K Heated air K'Relatively low temperature air L ₁ , L ₂ , L ₃ Gap S Bottom edge of practice board 1 for ball game of the present application G Installation base

Claims (6)

[Claims] 1. A ball practice board comprising a three-layer structure of the following (1) to (3). (1) First layer of glass fiber reinforced plastic (2) Second layer of thermosetting polyurethane foam having air circulation holes inscribed in the first layer (3) Selected from wood, metal or glass fiber reinforced plastic Third layer of material made of one kind or a combination of two or more kinds 2. The air circulation hole according to claim 1, wherein the hole ends are provided on the upper and lower surfaces of the second layer, on the left and right surfaces, or communicated with a through hole provided on the third layer. Practice board for ball games. 3. The air flow holes are evenly dispersed and have a porosity of 1 to 5 with respect to the thermosetting polyurethane foam.
It is 0%, The practice board for ball games of Claim 1 or 2 characterized by the above-mentioned. 4. The glass fiber / thermoplastic resin weight ratio of the glass fiber reinforced plastic is from 20 to 50/80.
The practice board for ball games according to claim 1, wherein the practice board is 50. 5. The ball practice board according to claim 1, wherein the glass fiber reinforced plastic uses a thermosetting unsaturated polyester as a plastic component thereof. 6. The ball game according to claim 1, wherein the air circulation hole is reinforced by a tube body selected from iron, copper, aluminum and alloys thereof. Practice board.