JPH07137070A - Large-sized purifying tank - Google Patents

Abstract

PURPOSE:To obtain the title purifying tank which is easy to mold, light in weight and resistant to an impact and internal and external pressures and can be recycled, by a construction wherein the tank is a molded article of a crosslinked polymer, square-shaped indentation ribs in the longitudinal direction of upper and lower tank parts at least are provided in prescribed numbers in relation to the length of the lateral width of the purifying tank and each of the ribs satisfies specific shape characteristics. CONSTITUTION:A large-sized purifying tank is a molded article of a crosslinked polymer of which upper and lower tanks 1 and 4 at least are obtained by injecting into a mold the mixture of metathesis polymerizable cyclolefin monomer solutions A and B containing a metathesis polymerization catalyst and an activating agent, respectively, and by subjecting it to polymerization and a crosslinking reaction. Square-shaped indentation ribs 2 in the longitudinal direction which the upper and lower tanks 1 and 4 have are provided in the number of 1.5 to 5 for 1m averagely in relation to the length of the lateral width of the purifying tank, and each of the indentation ribs 2 satisfies shape chacteristics expressed by formulas I to IV. In the formulas I to IV, (t) denotes an average thickness of the orthogonal surface to the length direction of the indentation rib 2, H the height of a projection from the surface of the molded article, W the width of the part of indentation, and R and R' the radiuses of the bent parts of the part of indentation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a large-sized septic tank which is lightweight, resistant to collision and excellent in durability. The present invention also relates to a pollution-free, integrally-molded large-sized septic tank that does not require fiber reinforcement, can be recycled, and does not generate harmful gas during waste incineration.

[0002]

2. Description of the Related Art Conventionally, most septic tanks are molded using fiber reinforced plastic (FRP). In particular, it is molded using an unsaturated polyester resin reinforced with glass fiber. When a septic tank is formed by using this unsaturated polyester resin reinforced with glass fibers, there is a problem that a large amount of dust containing glass fibers is generated and the working environment becomes poor. In addition, such a septic tank using FRP has a heavy weight, and has a drawback that cracks easily occur due to the impact when dropped during transportation or hit by pebbles during construction. Further, since the FRP molded product contains glass fiber, it is difficult to crush and crush it at the time of disposal, and even if it is incinerated, a large amount of glass fiber remains and it takes time and labor to process it.

[0003]

SUMMARY OF THE INVENTION Therefore, a first object of the present invention is to provide a septic tank which solves various problems of the conventional septic tank using FRP. Second of the present invention
It is an object of the invention to provide a septic tank which does not cause environmental problems in the manufacturing process and can be molded relatively easily by the reaction injection molding method. A third object of the present invention is that it is lightweight and has sufficient strength against impact,
Another object of the present invention is to provide a septic tank that can sufficiently withstand internal and external pressures after application. Another object of the present invention is to provide a septic tank in which the used resin molded product can be recycled and can be easily disposed of. Still another object of the present invention is to provide a septic tank that can be advantageously used as a large-scale septic tank, especially as a combined septic tank.

[0004]

Means for Solving the Problems As a result of intensive research for solving the above-mentioned object of the present invention, the present inventor has used a metathesis polymerization catalyst system (metathesis catalyst system) to mold a metathesis polymerizable cyclic olefin into a mold. By using the cross-linked polymer obtained by polymerization and cross-linking reaction in the inside, by forming ribs with a specific uneven shape, it is easy to manufacture, weight reduction is possible, strong against impact, durability and pressure resistance. The present invention has been accomplished by discovering that a large-scale septic tank that has recyclability can be obtained.

That is, according to the present invention, it is a large-scale septic tank comprising an upper tank portion and a lower tank portion, or an upper tank portion, a lower tank portion and an intermediate tank portion of a plate-like belt connecting them. The large-scale septic tank comprises (1) at least the upper tank portion and the lower tank portion of a monomer liquid A (solution A) composed of a metathesis polymerizable cyclic olefin containing a catalyst component of the metathesis polymerization catalyst system and a metathesis polymerization catalyst system. Obtained by mixing a monomer liquid B (solution B) containing a metathesis-polymerizable cyclic olefin containing an activator component, injecting the raw material mixed liquid into a mold, and causing polymerization and crosslinking reaction in the mold. (2) At least the upper tank portion and the lower tank portion have rectangular concave-convex ribs in the longitudinal direction, and the concave-convex ribs are flat with respect to the lateral width of the septic tank. Has 1.5 to 5 per 1m and,
(3) Each uneven rib has the following shape characteristics (i) to
(Iv) (i) 10 ≦ H ≦ 50 (ii) 30 ≦ W ≦ 200 (iii) 2 ≦ R <H, 2 ≦ R ′ <H (iv) 3 ≦ t [where t is the length direction of the uneven rib] Shows the average thickness of the molded product in a cross section at right angles, H represents the height of the convex portion from the surface of the molded product, W represents the width of the uneven portion, and R and R'represent the bent portion of the uneven portion. Indicates the radius. The units of t, H, W, R and R'are expressed in millimeters (mm). ] A large-scale septic tank is provided.

[0006] tank capacity According to the present invention is 2m ³ or more preferably 3~15m ^3, particularly preferably provided large septic tank 3~12m ^3. The present invention will be described in more detail below.

As the metathesis-polymerizable cyclic olefin for forming the crosslinked polymer constituting the septic tank of the present invention, a metathesis-polymerizable cycloalkene group is contained in the molecule in an amount of 1 to 1
The one containing two is used. A compound having at least one norbornene skeleton in the molecule is preferable.
Specific examples thereof include dicyclopentadiene, tricyclopentadiene, cyclopentadiene-methylcyclopentadiene co-dimer, 5-ethylidene norbornene, norbornene, norbornadiene, 5-cyclohexenyl norbornene, 1,4,5,8- Dimethano-1,4,
4a, 5,6,7,8,8a-octahydronaphthalene, 1,
4-methano-1,4,4a, 5,6,7,8,8a-octahydronaphthalene, 6-ethylidene-1,4,5,8-dimethano-1,4,4a, 5,6,7, 8,8a-octahydronaphthalene, 6-ethylidene-1,4,5,8-dimethano-
1,4,4a, 5,6,7,8,8a-heptahydronaphthalene, 1,4,5,8-dimethano-1,4,4a, 5,6,7,8,
8a-hexahydronaphthalene, ethylene bis (5-norbornene) and the like can be mentioned, and a mixture thereof can also be used. Particularly, dicyclopentadiene or a mixture thereof containing 50 mol% or more, preferably 70 mol% or more is suitably used. Further, if necessary, a metathesis-polymerizable cyclic olefin having a polar group containing a different element such as oxygen and nitrogen can be used as a copolymerization monomer. Such a copolymerizable monomer also preferably has a norbornene structural unit, and the polar group is preferably an ester group, an ether group, a cyano group, an N-substituted imide group, a halogen group or the like. Specific examples of the copolymerization monomer include 5-methoxycarbonylnorbornene and 5- (2-ethylhexyloxy) carbonyl-5-
Methyl norbornene, 5-phenyloxymethyl norbornene, 5-cyanonorbornene, 6-cyano-1,4,
5,8-Dimethano-1,4,4a, 5,6,7,8,8a-octahydronaphthalene, N-butyl nadecic acid imide, 5
-Chlornorbornene and the like can be mentioned.

The monomer liquid A (solution A) in the present invention contains a catalyst component of a metathesis polymerization catalyst system. As the catalyst component, salts such as halides of metals such as tungsten, rhenium, tantalum and molybdenum are used, and tungsten compounds are particularly preferable. As such a tungsten compound, tungsten hexahalide, tungsten oxyhalide and the like are preferable, and more specifically, tungsten hexachloride, tungsten oxychloride and the like are preferable. Further, organic ammonium tungstate or the like can also be used. It has been found that when such a tungsten compound is directly added to the monomer, it immediately starts cationic polymerization, which is not preferable. Therefore, such a tungsten compound is preferably suspended in an inert solvent such as benzene, toluene, chlorobenzene and the like in advance and solubilized by adding a small amount of an alcohol compound and / or a phenol compound to be used. Further, as described above, it is preferable to add about 1 to 5 mol of Lewis base or chelating agent to 1 mol of the tungsten compound in order to prevent undesired polymerization. Examples of such additives include acetylacetone, acetoacetic acid alkyl esters, tetrahydrofuran, and benzonitrile. When a polar monomer is used, it may be a Lewis base itself as described above, and it may have its action even if the above compound is not added. As described above, the monomer liquid A (solution A) containing the catalyst component has substantially sufficient stability.

On the other hand, the monomer solution B (solution B) in the present invention contains an activator component of the metathesis polymerization catalyst system. This activator component is preferably an organometallic compound centered on an alkylated compound of a metal of Group I to Group III of the Periodic Table, particularly a tetraalkyltin, an alkylaluminum compound, an alkylaluminum halide compound, and specifically a chloride. Diethyl aluminum, diethyl aluminum chloride, trioctyl aluminum, dioctyl aluminum iodide, tetrabutyl tin, and the like. These organometallic compounds as activator components are dissolved in a monomer to prepare a monomer liquid B (solution B ) Is formed.

Basically, the solution A and the solution B are mixed and injected into a mold to obtain a molded article of the desired crosslinked polymer. Is initiated very quickly, so that curing can occur before it has flowed sufficiently into the mold, which is often a problem. Therefore, it is preferable to use an activity regulator. As such a regulator, Lewis bases are generally used, among others, ethers, esters,
Nitriles and the like are used. Specific examples include ethyl benzoate, butyl ether, diglyme and the like. Such a regulator is generally used by adding it to the solution (solution B) side of the component of the activator of the organometallic compound. When a monomer having a Lewis base is used as described above, it can also serve as a regulator.

The amount of the metathesis polymerization catalyst system used is, for example, when a tungsten compound is used as the catalyst component, the conversion rate of the tungsten compound with respect to the above raw material monomer is
It is about 1,000 to 15,000 to 1, preferably about 2,000 to 1 on a molar basis, and when an alkylaluminum is used as the activator component, an aluminum compound for the above raw material monomer The ratio of about 100 to 1 to 10,000 to 1, preferably 20.
The vicinity of 0: 1 to 500: 1 is used. Further, as described above, the masking agent and the adjusting agent can be appropriately adjusted and used depending on the amount of the catalyst system used by experiments.

The molded article of the crosslinked polymer obtained by the present invention may further contain various additives depending on the purpose in order to improve or maintain the characteristics thereof in practical use. Such additives include fillers, pigments, antioxidants, light stabilizers, flame retardants, polymer modifiers and the like. Such additives cannot be added after the crosslinked polymer of the present invention has been molded, and therefore, when added, it is necessary to add them to the above-mentioned raw material solution in advance.

The simplest method is the solution A described above.
And a solution B may be added in advance to either or both of them, but in that case, they do not react to a certain extent with the catalyst component and activator component having strong reactivity in the liquid and do not react to some extent. , And it should not interfere with the polymerization. If the reaction does not substantially hinder the polymerization even when the reaction is unavoidable, it is possible to prepare a third liquid by mixing with the monomer and mix and use it immediately before the polymerization. Further, the polymerization catalyst or activator is used as the third liquid, and solution A or solution B containing no third catalyst
A method of adding the above-mentioned additive to is also conceivable. Further, in the case of a solid filler, when the two components are mixed and the shape is such that the voids can be sufficiently filled immediately before starting the polymerization reaction or during the polymerization, it is filled in the molding die. It is also possible to keep it. Reinforcing agents or fillers as additives are effective in improving the bending modulus. Examples of such a material include glass fiber, mica, carbon black, wollastonite and the like. Those obtained by surface-treating these with a so-called silane coupler can be preferably used.

Further, it is preferable to add an antioxidant to the molded article according to the present invention. Therefore, it is desirable to add a phenol type or amine type antioxidant to the solution in advance. Specific examples of these antioxidants include 2,6-di-t-butyl-p-cresol and N, N '.
-Diphenyl-p-phenylenediamine, tetrakis [methylene (3,5-di-t-butyl-4-hydroxycinnamate)] methane and the like.

Further, the molded product of the present invention can be obtained by adding another polymer in a monomer solution state at the time of molding. As such a polymer additive, the addition of an elastomer is effective in enhancing the impact resistance of the molded product and controlling the viscosity of the solution. Elastomers used for such purpose include styrene-butadiene-styrene triblock rubber, styrene-isoprene-styrene triblock rubber, polybutadiene, polyisoprene,
There may be mentioned a wide range of elastomers such as butyl rubber, ethylene propylene-diene terpolymer, nitrile rubber.

Examples of the material of the mold for molding the septic tank of the present invention include steel, cast or forged aluminum, casting of zinc alloy and the like, thermal spraying, electroforming of nickel and copper, and resin. Also, the structure of the mold is sufficient because the pressure generated in the mold at the time of molding is several kg / cm ² , which is extremely low compared to other molding methods, and is therefore simpler and cheaper than molds of other molding methods. Can be made.

One of the features of the cyclic olefin cross-linked polymer molded article of the present invention is that it has excellent impact resistance and will not be easily broken even if it is dropped or if solid matter such as pebbles collides. . Further, the molded article of the present invention basically does not need to use a reinforcing material such as glass fiber. Therefore, the flexural modulus is generally lower than those using these reinforcing materials. As a means for solving this, it has a shape having a rib having a specific structure. In the case of a large structure such as a septic tank, it is already known that a rib having irregularities is put therein, so that some FRP septic tanks actually have irregular ribs. Once the septic tank is installed, 1
It is used for a long time of 0 to 20 years or more, and since water enters inside, water pressure is applied inside,
Furthermore, when it is buried underground, rigorous durability and heat resistance are required, as pressure is always applied from the outside by earth and sand and groundwater. With respect to such required characteristics, the large-sized septic tank of the present invention does not have a problem in pressure resistance and durability in the short term and the long term by providing a certain number of ribs having a specific unevenness.

Next, the structure of the large-sized septic tank of the present invention will be described with reference to the drawings. The large-scale septic tank of the present invention is basically composed of two or three members. That is, it is composed of two members, an upper tank part and a lower tank part, or three members of an upper tank part, a lower tank part, and an intermediate part of a plate-shaped band connecting them.

FIG. 1 shows an example of a large-scale septic tank according to the present invention. A is a front view thereof and B is a side view thereof. In FIG. 1, 1 is an upper tank part and 4 is a lower tank part.
In FIG. 1, the upper tank part 1 and the lower tank part 4 are fixed by a flange 3. Further, the upper tank part 1 and the lower tank part 4 may be fixed by an intermediate tank part of a plate-like band connecting them.
This intermediate tank part is not shown in FIG. The intermediate tank part
The upper tank portion and the lower tank portion are usually firmly fixed to each other via a flange. By providing this intermediate tank part,
A septic tank having an increased inner volume can be obtained.

In the large-scale septic tank of the present invention, at least the upper tank portion and the lower tank portion are molded products of the crosslinked polymer of the metathesis-polymerizable cyclic olefin described above, preferably the upper tank portion,
All of the lower tank portion and the intermediate tank portion are molded products of this crosslinked polymer. Each of the upper tank portion, the lower tank portion, and the intermediate tank portion is also characterized in that they are integrally molded products.

Since the molded article of the present invention does not contain a reinforcing material such as glass fiber, the material itself has low rigidity, but the rigidity is improved as a structure based on the shape of the ribs of the unevenness. As described above, the uneven rib is provided in the vertical direction of the septic tank as a structure that can withstand the internal pressure and the external pressure.

The shape of the uneven ribs provided in the large-scale septic tank of the present invention satisfies the following (i) to (iv). (I) 10 ≦ H ≦ 50 (ii) 30 ≦ W ≦ 200 (iii) 2 ≦ R <H, 2 ≦ R ′ <H (iv) 3 ≦ t where H, W, R, R ′ and t are Each has the above-mentioned meaning, but these will be basically described with reference to FIG. FIG. 2 shows a sectional view of an example of the uneven rib.

In FIG. 2, the height of the convex portion (or concave portion) of the concave-convex rib is represented by H. This height H is 10-50
It is in the range of mm, and preferably in the range of 15 to 40 mm. When the height H is less than 10 mm, the rigidity of the structure is less improved. On the other hand, when the height H is more than 50 mm, the depth of the uneven ribs is too large, and the handling during transportation and construction becomes troublesome, and the internal structure of the septic tank is further improved. There will be multiple. The width W of the uneven rib is in the range of 30 mm to 200 mm, and preferably 50.
The range is from mm to 180 mm. Narrower than 30 mm or wider than 200 mm is not desirable due to the strong rigidity of the structure. Radius R and R'of the bent portion of the uneven rib
Are independently in the range of 2 mm to Hmm. When the bending radius is 2 mm or less, the concave and convex ribs are bent almost at right angles, and the possibility that the bent portion is bent increases. On the other hand, if the value becomes larger than the height Hmm, the value becomes too gentle, and the rigidity increasing efficiency becomes low. R and R'may be different from each other, but generally they are the same value.

The thickness (t) of the septic tank of the present invention is 3 m in terms of strength.
m or more, preferably 4 mm or more, more preferably 4.5 m
It is m or more. On the other hand, the thicker the structure, the greater the strength and rigidity of the structure, but the heavier and more expensive it becomes. Therefore, the thickness (t) of the septic tank (uneven rib) of the present invention is 15 mm or less, preferably 10 mm.
The following are appropriate:

In the septic tank of the present invention, the shape of the uneven ribs may be the same in one septic tank, or may be different within the range of the shape and size of the present invention. The uneven ribs have an average length of 1.5 to 5 pieces, preferably 2 to 4 pieces per 1 m with respect to the lateral length of the septic tank.
Provide one. If it is less than 1.5 per 1 m, the rigidity of the structure will not be improved, and if it is more than 5, the weight of the septic tank will increase and it is not economical. The positions of the concave and convex ribs are preferably provided at substantially equal intervals in the septic tank, but they need not necessarily be evenly spaced, and are determined in consideration of the position of the partition plate inside the septic tank, the installation location of internal members, and the like.

In the large-sized septic tank of the present invention, ordinary rod-shaped ribs or plate-shaped ribs may be provided in addition to the uneven ribs of the present invention. Furthermore, in terms of the function of the septic tank, a partition plate is required to partition the interior of the septic tank.
As the septic tank structure, the partition plate is important for preventing deformation against internal pressure and external pressure, and by using a material or structure having high rigidity for the partition plate, it is possible to prevent deformation of the entire septic tank. In the present invention, the uneven ribs are installed in the vertical direction of the septic tank. However, when the septic tank is buried underground, the pressure of groundwater to rise is generally large at the bottom of the septic tank. Therefore, it is possible to increase the rigidity of the bottom part by extending a part of the uneven ribs provided in the vertical direction as it is to the bottom part of the septic tank.

The septic tank of the present invention is generally divided into two parts, an upper tank part and a lower tank part, and if necessary an intermediate tank part is formed separately. The molding method is the method disclosed in Japanese Patent Publication No. 3-28451. A flange portion serving as a joint is provided at the openings of the upper tank portion and the lower tank portion, and by combining with the flange, the upper tank portion and the lower tank portion are combined to form a septic tank. In the present invention, the height and volume of the septic tank can be increased by inserting and sandwiching the strip-shaped intermediate tank portion having upper and lower flanges between the flanges of the upper tank portion and the lower tank portion. The flange has a septic tank structure,
The rib structure is provided in the lateral direction, and its thickness is also important. The thickness of the entire flange is 1.5 to the average thickness of the septic tank.
A thickness of 5 times is preferably used.

Although not shown in the figure, the inside of the septic tank of the present invention is the same as the inside of a normal septic tank, and is divided into different materials such as an anaerobic tank, an aerobic tank, and a disinfection tank, and each partition efficiently purifies wastewater. It is filled with various members to do so, and a running water channel is provided. The septic tank of the present invention can be used as a so-called single tank for treating human waste only or as a combined septic tank for purifying both human waste and domestic wastewater. In particular, the septic tank of the present invention is suitable for upsizing, especially for those having an internal volume of 2 m ³ or more, and can be particularly suitably used for the purpose of a combined septic tank, which is in great demand in the future in view of environmental measures.

[0029]

EXAMPLES The present invention will be described below with reference to examples. It should be noted that the embodiments are for explanation, and the present invention is not limited to these.

(Mold) An aluminum mold incorporating the product shape shown in FIG. 1 was used. The dimensions of the septic tank made in the examples were as follows. A = 390 mm B = 520 mm C = 490 mm D
= 340 mm E = 520 mm F = 2260 mm G = 950 mm
H = 800 mm I = 260 mm J = 1140 mm Each of the uneven ribs had the following shape and size in FIG. (I) H = 30 mm (ii) W = 160 mm (iii) R = 25 mm, R ′ = 25 mm (iv) t = 4.3 mm

(Monomer solution) (Preparation of solution A) 20 parts by weight of tungsten hexachloride were added to 70 parts by weight of dry toluene under a nitrogen stream, and then a solution of 2 parts by weight of nonylphenol and 16 parts by weight of toluene was added. To prepare a 0.5 M tungsten-containing catalyst solution, and the solution was purged with nitrogen gas overnight to remove hydrogen chloride gas produced by the reaction of tungsten hexachloride and nonylphenol. 1 part by volume of acetyl ascent was added to the volume part to prepare a polymerization catalyst.

Next, ethylene was added to a monomer mixture consisting of 95 parts by weight of purified dicyclopentadiene (purity 99.7% by weight, hereinafter the same) and 5 parts by weight of purified ethylidene norbornene (purity 99.5% by weight, hereinafter the same). 70
3% by weight of ethylene-propylene-ethylidene norbornene polymer rubber in mol%, and Ethanox 7 as an oxidation stabilizer
The above catalyst solution for polymerization was added to a solution containing 22 parts by weight so that the tungsten content was 0.01 / liter to prepare a monomer solution A (solution A) containing a catalyst component.

(Preparation of Solution B) Trioctylaluminum 85, dioctylaluminum iodide 15 and diglyme 100 were mixed and prepared at a molar ratio of 95 parts by weight of purified dicyclopentadiene and 5 parts by weight of purified ethylidene norbornene. Parts, ethylene content 70
Monomer liquid B (solution B) containing an activator component was prepared by mixing 3 parts by weight of ethylene-propylene-ethylidene-norbornene polymer rubber (mol%) in a monomer mixture at a ratio of aluminum of 0.03 mol / liter. Was prepared. The viscosity of solution B was 300 cps at 30 ° C.

(Molding) An aluminum mold for molding was heated to a cavity mold of 90 ° C. and a core mold of 60 ° C. and the mold was closed. Then, an RIM molding machine was used to mix an equal amount of solution A in the mixing head. Solution B was collisionally mixed and injected. Two minutes after the liquid injection and filling, the mold was opened and after 3.5 minutes, the crosslinked polymer molded product was taken out.

(Evaluation as septic tank) The obtained crosslinked polymer molded article was fixed to the upper and lower tanks with a bolt and an adhesive via a flange portion to obtain a product for evaluation. The product is FRP beforehand
It is fixed with the same bolts and adhesive using three partition plates. The product is a stiffness test based on JISA4101,
All durability tests were satisfied.

[Brief description of drawings]

FIG. 1 shows an example of a large-scale septic tank according to the present invention, where A is a front view and B is a side view.

FIG. 2 shows a cross-sectional view of the uneven ribs in the large-sized septic tank of the present invention.

[Explanation of symbols]

 1 Upper layer of septic tank 2 Uneven rib 3 Flange 4 Lower part of septic tank

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Claims (1)

[Claims] 1. A large-sized septic tank comprising an upper tank part and a lower tank part, or an upper tank part, a lower tank part and an intermediate tank part of a plate-shaped belt connecting them. (1) At least the upper tank part and the lower tank part contain a monomer liquid A (solution A) composed of a metathesis-polymerizable cyclic olefin containing a catalyst component of a metathesis polymerization catalyst system and an activator component of the metathesis polymerization catalyst system. Monomer liquid B containing the metathesis-polymerizable cyclic olefin contained therein (solution B)
A crosslinked polymer molded article obtained by mixing and mixing the raw material mixed solution into a mold, and causing polymerization and crosslinking reaction in the mold, wherein (2) at least an upper tank part and a lower tank The part has rectangular uneven ribs in the vertical direction, and the uneven ribs have an average of 1.5 to 5 per 1 m with respect to the lateral width of the septic tank, and (3) each uneven rib. Satisfies the following shape characteristics (i) to (iv). (I) 10 ≦ H ≦ 50 (ii) 30 ≦ W ≦ 200 (iii) 2 ≦ R <H, 2 ≦ R ′ <H (iv) 3 ≦ t [where t is a cross section perpendicular to the longitudinal direction of the uneven ribs] Shows the average thickness of the molded product, H shows the height of the convex portion from the surface of the molded product, W shows the width of the uneven portion, and R and R ′ respectively show the radius of the bent portion of the uneven portion. . The units of t, H, W, R and R'are expressed in millimeters (mm). ] A large-scale septic tank characterized by being