JPH1181358A - Manhole cover - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lightweight manhole cover capable of being easily handled and having sufficiently mechanical strength required as the manhole cover as well as low sound. SOLUTION: In a reactive injection molding body resin manhole cover 2 monolithically molded at a thick section 4 in the center part, the ratio (t2/t1) of the thickness (t2) of the thick section 4 molded in the center part to the minimum thickness (t1) of the cover 2 is 0.05-0.8. The ratio (S2/S1) of area (S2) of the thick section formed in the center part to the whole area (S1) of the manhole cover 2 is desirably 0.02-0.8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a manhole cover which is detachably mounted on the ground for maintenance of, for example, sewers, waterworks, electric wiring, gas pipes, and septic tanks buried underground.

[0002]

2. Description of the Related Art As a conventional manhole cover, a metal cover is well known. However, the metal manhole cover has a problem that it is heavy and inconvenient to handle. There is also a problem that noise is generated when a car passes over a manhole.

Therefore, attempts have been made to form the manhole cover with a synthetic resin. However, it is necessary to consider that a vehicle load is applied on the manhole cover. It was believed that the required mechanical strength would not be met.

[0004]

The present invention has been made in view of such circumstances, and provides a manhole cover which is lightweight, easy to handle, has low noise, and has sufficient mechanical strength required for a manhole cover. The purpose is to do.

[0005]

Means for Solving the Problems The present inventors have made intensive studies on a synthetic resin manhole cover, and as a result, by forming a thick portion integrally at the center of the synthetic resin manhole cover, the manhole cover mechanical device is manufactured. It has been found that the mechanical strength is dramatically improved, and the present invention has been completed.

That is, the manhole cover according to the present invention comprises:
A synthetic resin manhole cover in which a thick portion is integrally formed at a center portion, wherein a ratio (t1) between a minimum thickness (t1) of the cover and a thickness (t2) of a thick portion formed at the center portion. / T2)
However, it is characterized by being 0.05 to 0.8, preferably 0.1 to 0.7, more preferably 0.15 to 0.6.

If the ratio (t1 / t2) is too large, the effect of forming the thick portion is small, and if it is too small, molding is difficult, and the weight distribution at the center and the weight distribution at the periphery are reduced. The weight balance is deteriorated and does not contribute to the improvement of the lid strength. The minimum thickness (t1) of the lid is preferably 3
mm or more, more preferably 5 mm or more, particularly preferably 8 mm or more. If the minimum thickness (t1) is too small, the strength at that portion is significantly reduced, which is not preferable.

[0008] With respect to the total area (S1) of the manhole cover,
The ratio (S) of the area (S2) of the thick portion formed at the central portion
2 / S1) is preferably from 0.02 to 0.8, more preferably from 0.05 to 0.7, particularly preferably from 0.07 to 0.7.
0.6. With such an area ratio, a manhole cover excellent in mechanical strength can be realized while being lightweight.

In the present invention, it is preferable that a thick flange is formed on the outer periphery of the manhole cover.
The ratio (t3 / t2) of the thickness (t3) of the flange portion to the thickness (t2) of the thick portion of the lid is preferably 0.5 to
2, more preferably 0.7 to 1.3. The radial width (b) of the flange portion is preferably 5 to 30 m.
m, more preferably 10 to 25 mm. Since this flange portion is in direct contact with the edge of the manhole hole, a predetermined range of thickness and width is required. It is preferable that the outer side surface of the flange portion is an inclined surface whose outer diameter increases in a tapered shape from the bottom surface to the upper surface of the lid. This is for preventing the lid from falling into the hole with the lid attached to the hole.

In the manhole cover according to the present invention, the thick portion formed at the center portion and the flange portion formed at the outer peripheral portion are both formed on the bottom surface side of the cover, and a reinforcing rib is provided therebetween. They may be formed integrally. The reinforcing rib is preferably formed radially from the thick part at the center to the flange at the periphery, but may also be formed in a direction crossing the radial rib. When ribs are formed radially, the number of ribs is 0 to 20, preferably 4 to 12.

The upper surface of the lid preferably has a convex shape that swells at the center. This is to prevent rainwater from accumulating on the lid. Further, in order to improve drainage, a drainage groove may be formed on the upper surface of the lid. Also,
Separately from the drainage grooves, non-slip grooves and irregularities may be formed.

The handle may be integrally formed of synthetic resin on the upper surface of the manhole cover at the time of forming the cover, or a handle made of metal or the like may be attached to the upper surface of the cover later.

In the present invention, the outer shape of the manhole cover is
The shape is not particularly limited, and may be an ellipse, a rectangle, or the like, other than the circle. When the outer shape of the lid is circular, the central portion refers to an area including the center of the circle, and when the lid is rectangular, an area including an intersection of diagonal lines. In the present invention, the term "manhole cover" is used in a broad sense including a checker plate and the like in addition to a normal manhole cover. That is,
The manhole cover according to the present invention means one that is detachably attached to a hole formed in the ground for some purpose.

In the present invention, the synthetic resin constituting the manhole cover is not particularly limited, but is preferably made of a reaction injection molded body. When the manhole cover is formed by reaction injection molding, the reaction solution is not particularly limited, and examples thereof include urethane-based, urea-based, nylon-based, epoxy-based, unsaturated polyester-based, phenol-based, and norbornene-based solutions. However, a norbornene-based resin is particularly preferred because of its excellent impact resistance and durability. As general molding conditions, the reaction stock solution temperature is 20 to 8
At 0 ° C., the viscosity of the reaction stock solution is, for example, 5 cps to 3000 cps, preferably 100 cps at 30 ° C.
It is about 1000 cps.

In such molding, a reinforced polymer (molded article) can be manufactured by placing a reinforcing material in a mold in advance and supplying a reaction liquid into the mold to polymerize.

Examples of the reinforcing material include glass fiber, aramid fiber, carbon fiber, ultra high molecular weight polyethylene fiber, metal fiber, polypropylene fiber, aluminum coated glass fiber, cotton, acrylic fiber, boron fiber, silicon carbide fiber, and alumina fiber. And the like. These reinforcing materials can be used in various shapes, such as those obtained by forming a long fiber or chopped strand into a mat, woven into a cloth, or remaining in a chopped shape. Further, the reinforcing material may be shaped into a predetermined shape in advance before filling in the mold. It is preferable that the surface of these reinforcing materials is treated with a coupling agent such as a silane coupling material in order to improve the adhesion to the resin. The amount of the reinforcing material is not particularly limited, but is usually 10% by weight or more, preferably 20 to 60% by weight, with the total weight of the monomers being 100% by weight. By blending the reinforcing material in such a range, the mechanical strength of the manhole cover can be improved.

Further, in order to further improve the mechanical strength of the manhole cover, a metal rod or a metal plate is inserted in advance into a mold for performing reaction injection molding, and then reaction injection molding is performed (insert molding). ) You can also.
By this insert molding, a manhole cover excellent in mechanical strength, in which a metal rod or a metal plate is integrally formed, can be obtained.

Further, various additives such as an antioxidant, a filler, a pigment, a colorant, a foaming agent, a flame retardant, a slide imparting agent, an elastomer, a dicyclopentadiene-based thermopolymer resin and a hydrogenated product thereof are blended. Thereby, the characteristics of the obtained polymer can be modified.

As the antioxidant, there are various antioxidants for plastics / rubbers such as phenol type, phosphorus type and amine type. Fillers include inorganic fillers such as milled glass, talc, calcium carbonate, aluminum hydroxide, mica, potassium titanate, calcium sulfate, and the like. Examples of the elastomer include natural rubber, polybutadiene, polyisoprene, styrene-butadiene copolymer (SBR), and styrene-butadiene-styrene block copolymer (SB).
S), styrene-isoprene-styrene block copolymer (SIS), ethylene-propylene-diene terpolymer (EPDM), ethylene-vinyl acetate copolymer (EV
A) and hydrides thereof.

The additive is usually mixed in advance with one or both of the reaction solutions.

The mold used for the reaction injection molding is not necessarily made of metal, but is preferably made of a heat-resistant material, and is not particularly limited. For example, Teflon, polyester, epoxy, sand , Wood, ceramics, reaction injection molds of dicyclopentadiene, and the like. Reaction injection molding uses a low-viscosity reaction liquid and can be molded at a relatively low temperature and a low pressure. Therefore, it is not always necessary to use a highly rigid and expensive mold. The inside of the mold may be sealed with an inert gas. The reaction solution used for the polymerization reaction is preferably stored and operated under an atmosphere of an inert gas such as nitrogen gas.

The mold temperature is preferably 10 to 150 °
C, more preferably 20 to 120 ° C, even more preferably 30 to 100 ° C. The temperature control of the mold can be performed by providing a passage for the heat medium in the mold and circulating the heat medium. Mold pressure is usually 0-10
0 kg / cm ² , preferably in the range of 0 to 10 kg / cm ² . The polymerization time may be appropriately selected, but usually,
After the completion of the injection of the reaction solution, it is preferably 30 seconds to 20 minutes.

[0023]

The manhole cover according to the present invention is made of a synthetic resin such as a reaction injection molded resin, so that it is lighter in weight than a metal manhole, and the manhole hole can be easily opened and closed. Also, the noise is less than that of a metal manhole. Moreover, in the present invention, by forming a thick portion integrally at the center of the synthetic resin manhole cover,
The mechanical strength of the manhole cover is dramatically improved, and the mechanical strength required for the manhole cover can be sufficiently satisfied.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments shown in the drawings.

FIG. 1 is a plan view of a manhole cover according to one embodiment of the present invention, FIG. 2 is a schematic sectional view taken along the line II-II shown in FIG. 1, and FIG. 3 is a manhole according to another embodiment of the present invention. FIG. 4 is a plan view showing a half of the lid, and FIG. 4 is a schematic sectional view taken along line IV-IV in FIG.

As shown in FIG. 1 and FIG.
The manhole cover 2 according to the embodiment has a circular outer shape,
At its center, a circular thick portion 4 is projected to the bottom side.
Are integrally molded. On the outer periphery of the manhole cover 2,
A ring-shaped flange portion 6 protruding toward the bottom surface is integrally formed. A relatively thin disk-shaped lid body 8 is integrally formed between the flange portion 6 and the thick portion 4. Lid body 8
Has a uniform thickness from the thick portion 4 to the flange portion 6 or a gradually thinner thickness toward the flange portion 6, and the minimum thickness t1 is 6 to 25 mm.

On the bottom side of the lid body 8 located between the thick part 4 and the flange part 6, a rib 14 extending radially so as to connect the thick part 4 and the flange part 6 is integrally formed. I have. The direction of the rib is not particularly limited (vertical, horizontal, diagonal, cross with respect to the direction connecting the center portion and the flange portion), but since the strength can be more effectively improved with the same weight, the center portion is connected to the flange portion. The direction is preferably radial (from a radial direction for a round shape, a direction including a diagonal line for a square shape), that is, radial from the center. The height t4 of the rib 14 is not particularly limited, and is preferably about 0 to 40 mm. The arrangement pitch angle θ1 of the ribs 14 is not particularly limited, and is preferably 30 to 360 degrees. In the present embodiment, the arrangement pitch angle is 45 degrees, and a total of eight radial ribs 14 are formed. Although the width of each rib 14 is not particularly limited, in the present embodiment, the width is increased toward the outer diameter side.
The rib width angle θ2 defining the width of No. 4 is preferably 0 to 3
It is 5 degrees, more preferably about 6 to 24 degrees. In addition,
In the present invention, it is not always necessary to form the ribs 14,
Moreover, the height t4, the arrangement pitch θ1, and the rib width angle θ2 of the rib 14 are not particularly limited, and can be variously modified.

It is preferable to have one or two handles. In the case where there are two handles, as shown in FIG. 1, it is preferable that the handle is located at a place where there is no rib and that the handle is symmetrical. In the embodiment, the handle is protruded toward the bottom side of the lid body 8. A part forming groove 10 is formed. A fitting hole 12 is formed in the handle portion forming groove 10 as shown in FIG.
A handle, such as a metal bar, fits there.

Further, as shown in FIG.
A pair of lock holes 16 penetrating the front and back surfaces of the lid are formed at the bottom position of the disc-shaped lid main body 8 which is shifted by 90 degrees from 0, and lock pieces are mounted in these lock holes 16. The opening and closing of the manhole cover 2 can be locked.

As shown in FIG. 2, the upper surface of the manhole cover 2 is flat or raised at the center, so that rainwater or the like does not accumulate on the upper surface of the manhole cover 2.
A drain groove may be formed on the upper surface of the lid 2 to improve drainage. Further, in addition to the drain groove, a non-slip groove or unevenness may be formed.

In this embodiment, the area S2 of the thick portion 4
The ratio of S2 / S1 is preferably 0.02 to 0.8, more preferably 0.05 to 0.7, and particularly preferably 0.07 to 0, compared to the total area S1 of the lid 2. .6. With such an area ratio, the manhole cover 2 which is lightweight and has excellent mechanical strength can be realized.

The ratio (t1 / t2) of the minimum thickness t1 of the lid body 8 to the thickness t2 of the thick portion 4 is 0.0
It is determined to be 5 to 0.8, preferably 0.1 to 0.7, and more preferably 0.15 to 0.6. If the ratio t1 / t2 is too large, the effect of forming the thick part 4 is small, and if it is too small, molding is difficult, and the weight balance between the central part and the peripheral part is not balanced. It does not contribute to improving the strength of the manhole cover 2.

In this embodiment, the thickness t3 of the ring-shaped flange portion 6 formed on the outer periphery of the lid 2 is preferably a ratio of t3 / t2 to the thickness t2 of the thick portion of the lid body 8. Is determined to be 0.5 to 2, more preferably 0.7 to 1.3. The radial width b of the flange 6 is preferably 5 to 30 mm, more preferably 10 to 30 mm.
２５25 mm. Since the flange portion 6 is a portion that directly contacts the edge of the manhole hole, a predetermined range of thickness and width is required. The outer surface of the flange portion 6 is an inclined surface 7 whose outer diameter increases in a tapered shape from the bottom surface of the lid 2 to the upper surface. This is for preventing the lid 2 from falling into the hole when the manhole cover 2 is attached to the manhole hole.

The manhole cover 2 according to the present embodiment is formed by the following reaction injection molding of a norbornene-based monomer.

The monomer used in this embodiment may be any monomer having a norbornene ring.
It is preferable to use a tricyclic or higher polycyclic norbornene-based monomer and a mixture thereof because a molded article having excellent heat resistance can be obtained.

Specific examples of the norbornene-based monomer include:
Bicyclics such as norbornene and norbornadiene; tricyclics such as dicyclopentadiene (cyclopentadiene dimer) and dihydrodicyclopentadiene; tetracyclics such as tetracyclododecene; pentacyclics such as cyclopentadiene trimer ;
Heptacyclics such as cyclopentadiene tetramer; alkyls such as methyl, ethyl, propyl, and butyl; alkenyls such as vinyl; alkylidenes such as ethylidene; and aryls such as phenyl, tolyl and naphthyl; Substitutes having a polar group such as an ester group, an ether group, a cyano group, and a halogen atom are exemplified. These monomers may be used in combination of one or more kinds.
Those which do not have a polar group are preferred from the viewpoint of reaction activity, difficulty in attaching marine organisms, and the like. Furthermore, tricyclic, tetracyclic, or pentacyclic monomers and mixtures containing these as a main component are easily available, excellent in reactivity, and excellent in heat resistance of the obtained resin molded product. Is preferred.

The resulting ring-opening polymer is preferably of a thermosetting type. For this purpose, among the norbornene monomers, two reactive double bonds such as cyclopentadiene trimer are used. What contains at least the crosslinkable monomer having the above is used. The proportion of the crosslinkable monomer in all the norbornene-based monomers is usually 2 to 30% by weight.

It should be noted that, within a range not to impair the object of the present invention,
Monocyclic cycloolefins such as cyclobutene, cyclopentene, cyclopentadiene, cyclooctene and cyclododecene, which can be ring-opening copolymerized with norbornene monomers,
It may be used as a comonomer.

In the present invention, a catalyst preferably used for polymerizing norbornene monomers is a metathesis catalyst. The metathesis catalyst is not particularly limited as long as it is capable of ring-opening polymerization of a norbornene-based monomer by a reaction injection molding (RIM) method, and may be a known one. For example, organic molybdates such as tungsten hexachloride, tridodecyl ammonium molybdate, and tri (tridecyl) ammonium molybdate, and organic ammonium molybdates such as ammonium acid are used.

The amount of the metathesis catalyst to be used is generally 0.01 mmol or more, preferably 0.1 mmol or more and 50 mmol or less, preferably 20 mmol or less, per 1 mol of the monomer used in the whole reaction solution. is there. If the amount of the metathesis catalyst used is too small, the polymerization activity is too low and the reaction takes a long time, so the production efficiency is poor.If the amount is too large, the reaction is too vigorous and the resin hardens before being sufficiently filled in the mold. Or the catalyst is likely to precipitate, making it difficult to store homogeneously. The metathesis catalyst is usually used by dissolving it in a monomer. However, as long as the properties of the molded article obtained by the RIM method are not substantially impaired, the metathesis catalyst is suspended and dissolved in a small amount of a solvent, By mixing with the body, precipitation may be suppressed or solubility may be enhanced.

In this embodiment, an activator, also called a metathesis co-catalyst, is used together with a metathesis catalyst to form an RI.
Perform M forming. The activator is not particularly limited as long as it can activate a metathesis catalyst capable of ring-opening polymerization of a norbornene monomer by the RIM method, and may be a known activator. For example,
JP-A-58-127728, JP-A-4-2261
No. 24, JP-A-58-129003 and JP-A-6-145247, organoaluminum alloys such as alkylaluminum, alkylaluminum halide, alkoxyalkylaluminum halide and arylalkylaluminum halide, and organotin compounds And the like. These activators are used alone or in combination of two or more.

The amount of the activator used is not particularly limited,
Usually, 0.1 mol or more, preferably 1 mol or more, and 1 mol per 1 mol of the metathesis catalyst used in the whole reaction solution.
It is at most 00 mol, preferably at most 10 mol. If no activator is used or the amount of activator used is too small,
Since the polymerization activity is too low and the reaction takes time, the production efficiency deteriorates. Conversely, if the amount used is too large, the reaction may be too vigorous and may be cured before the mold is sufficiently filled. The activator is used by dissolving it in the monomer. However, the activator should be suspended in a small amount of solvent and then mixed with the monomer as long as the properties of the molded article by the RIM method are not substantially impaired. May be used to make precipitation difficult or to increase solubility.

In the present embodiment, generally, an activity regulator is used in combination with the above-mentioned activator. The use of an activity regulator can change the reaction rate, the time from the mixing of the reaction solution to the start of the reaction, the reaction activity, and the like.

As the activity regulator, a compound having an action of reducing the metathesis catalyst is used, and as the activity regulator, alcohols, haloalcohols, esters, ethers, nitriles and the like are exemplified. Among them, specific examples of alcohols include n-propanol, n-butanol, n-hexanol, 2-butanol, isobutyl alcohol, isopropyl alcohol, t-butyl alcohol, and the like. Specific examples of halo alcohols Examples include 1,3-dichloro-2-propanol, 2-chloroethanol, 1-chlorobutanol, and the like.

The amount of the activity modifier varies depending on the compound used and is not uniform.

If desired, antioxidants, fillers, pigments,
Various additives such as a coloring agent, a foaming agent, a sliding imparting agent, a flame retardant, a combustible agent, an elastomer, a dicyclopentadiene-based thermopolymerized resin and a hydrogenated product thereof can be blended in the reaction stock solution. The properties of the resulting RIM product can be modified.

In order to obtain a molded article having particularly high mechanical strength, a reinforcing material such as glass fiber, carbon fiber or a matted material thereof is filled in a mold in advance, and then the polymerization reaction solution is poured into the mold. It can also be poured into and cured. The filling amount of the reinforcing material is not particularly limited, but is usually 10% by weight or more of the total weight of the monomer, preferably 20% by weight.
６０60% by weight. If the filling amount is small, the ratio of the mechanical strength is small. If the filling amount is too large, uneven filling may occur without uniform filling, or filling may be hindered.

For the purpose of adjusting the viscosity of the reaction stock solution, an elastomer may be blended with the reaction stock solution. By adding the elastomer to the reaction solution, the impact resistance of the obtained molded article is also improved. The amount of the elastomer added is such that the viscosity of the reaction solution at 30 ° C. is 5 cps or more, preferably 50 cps.
cps or more and 1000 cps or less, preferably 50
It is appropriately selected so as to be 0 cps or less.

These additives may be mixed in advance with one or both of the reaction stock solutions, or may be put in a mold cavity.

The reaction stock solution used in the present embodiment includes a norbornene monomer, a metathesis catalyst, an activator,
An activity regulator and an optional component prepared by dividing into two or more liquids are used. These reaction stock solutions do not undergo bulk polymerization with only one solution, but when all the solutions are mixed, each component has a predetermined ratio, and the norbornene-based monomer undergoes bulk polymerization.

For example, a liquid composed of a norbornene monomer, a metathesis catalyst, and an optional component, and a liquid composed of a norbornene monomer, an activator, an activity regulator, and an optional component do not polymerize as they are. If the total amount of each component contained in the two liquids is the used amount of each component in the present embodiment, each of the two liquids is a reaction stock solution used in the present embodiment, and when both are mixed, they react and undergo bulk polymerization.

For good workability, bulk polymerization is usually carried out using two reaction stock solutions, but three or more reaction stock solutions may be used. In order to allow other components to be sufficiently diffused into the norbornene-based monomer after mixing of the reaction stock solution, all the reaction stock solutions usually contain a norbornene-based monomer, and the other components are composed of a norbornene-based monomer. It is preferable that the monomer is dissolved or dispersed in the monomer, but a reaction stock solution containing no norbornene-based monomer may be present. In addition, since the bulk polymerization starts when the norbornene-based monomer, the metathesis catalyst, and the activator are contained in one reaction stock solution, the metathesis catalyst and the activator are not usually contained in one reaction stock solution. .

As a method of mixing the reaction stock solutions, a method of instantaneously mixing them with a mixing head is generally used. In this case, the containers containing the undiluted solutions serve as separate flow supply sources. As the mixing head, a low-pressure injector such as a collision mixer, a dynamic mixer or a static mixer can be used.

After the reaction solution is mixed, the mixture may be injected or injected several times into the preheated mold, or may be continuously injected, so that the apparatus can be lightened.
It can be operated at low pressure and can produce large and thick molded products. Further, when the filling amount of the filler such as glass fiber is large, it is desirable to use a low-pressure injecting machine capable of uniformly filling the reaction solution in the mold by reducing the injecting speed.

In the above-mentioned RIM process, in order to avoid a problem such as deactivation of the catalyst, the inside of the mold can be made to have an inert atmosphere by purging an inert gas such as N ₂ . Further, when a filler, a fiber reinforcing material, or the like is filled, if it contains adsorbed water, the adsorbed water may be removed by drying in advance.

In the reaction injection molding, the temperature of the mold is preferably from 10 to 150 ° C., more preferably from 15 to 150 ° C.
The temperature is 20 ° C, more preferably 25 to 100 ° C. The mold clamping pressure of the mold is usually in the range of 0 to 100 kg / cm ² . The polymerization time may be appropriately selected, but is usually 30 seconds to 20 minutes after the completion of the injection of the reaction solution. In addition, the mold is generally composed of two molds, a cavity mold and a core mold.
It may be configured to be higher by about 50 ° C. By setting the temperature of one mold high, the reaction proceeds from the mold surface on the higher temperature side, and it becomes easier to form a skin layer on the surface of the molded body.

Since the manhole cover 2 according to this embodiment is made of a reaction injection molded resin, it is lighter in weight than a metal manhole, and the manhole hole can be easily opened and closed. Also, compared to metal manholes,
Low noise. In addition, in the present embodiment, the mechanical strength of the manhole cover 2 is significantly improved by integrally forming the thick portion 4 at the center of the manhole cover 2, and the mechanical strength required for the manhole cover 2 Can be fully satisfied. In particular, in this embodiment, since the manhole cover 2 is formed by reaction injection molding, impact resistance and durability are superior to manhole covers made of other synthetic resins.

The present invention is not limited to the above-described embodiment, but can be variously modified within the scope of the present invention.

For example, as shown in FIGS. 3 and 4, the manhole cover (checker plate) 2A may be formed in a rectangular shape. In that case, the central part of the manhole cover 2A is
It becomes a region including the intersection of diagonal lines connecting the corners of the rectangular manhole cover 2A, and the thick portion 4A formed at the center thereof also has a rectangular shape. Also, the flange portion 6A on which the inclined surface 7A is formed has a rectangular ring shape, and the shape of the lid body 8A located between the flange portion 6A and the thick portion 4A is also rectangular.

However, the relationship between the area S2 of the thick part 4A and the area S1 of the lid 2A, the thickness t2 of the thick part 4A and the minimum thickness t
1, the width b and the thickness t3 of the flange portion 6A are:
This is the same as the above embodiment. The lid 2A is also integrally formed by reaction injection molding of a norbornene-based monomer, similarly to the above embodiment.

[0061]

EXAMPLES Hereinafter, the present invention will be described based on more detailed examples, but the present invention is not limited to these examples. In the following Examples and Comparative Examples, parts and%
Are by weight unless otherwise noted.

Example 1 A circular manhole cover 2 having the shape shown in FIGS. 1 and 2 was formed by the following reaction injection molding.

At the time of reaction injection molding, a norbornene-based monomer composed of 90% of cyclopentadiene dimer (DCP) and 10% of cyclopentadiene trimer is placed in two containers, one of which is diethyl aluminum chloride to the monomer. (DEAC) was added to give a 40 molar concentration and 1,3-dichloro-2-propanol (dcPrOH) 48 molar concentration (Solution A). On the other hand, tri (tridecyl) ammonium molybdate was added to the monomer so as to have a concentration of 10 mmol, and 6% of vinylnorbornene was added (Solution B). These A liquid and B liquid were stored in A tank and B tank, respectively.

From these tanks, the same volumes of solution A and solution B, each having a solution temperature of 25 ° C., are mixed and injected into the mold cavity, and the mold temperature is set to about 50 ° C. and about 10 ° C. After about a minute, a manhole cover 2 made of a reaction injection molded body
Was taken out.

The outer diameter of the manhole cover 2 is 680 mm
And the total area S1 of the lid was about 363000 mm ² . The outer diameter of the circular thick part 4 formed at the center is 200 mm, and the area S2 thereof is about 31400 mm.
^{Was 2} . That is, S2 / S1 was about 0.09.

The minimum thickness t1 of the lid body 8 is about 8 m
m, the thickness t2 of the thick portion 4 is 35 mm, and t
1 / t2 was about 0.2. The thickness t3 of the flange 6 was 30 mm, and t3 / t2 was about 0.9. The width b of the flange 6 was 13 mm.

Further, the ribs 14 are arranged at regular intervals in the circumferential direction.
And the arrangement pitch angle θ1 of the four ribs 14 is 90
And the rib width angle θ2 was 6 degrees. The height t4 of the rib 14 was 20 mm.

Using the manhole cover 2 having such dimensions, a load resistance test and an impact resistance test were performed. In the load-bearing test, a rubber plate having a thickness of 6 mm was placed on the upper surface of the manhole cover 2 placed on the test table, a weight was raised on the rubber plate, and a further load was slowly applied in the vertical direction. The measurement was made, and 1/4 thereof was used as a test value. The test value is 25
It was 0 kg or more. The test was performed at room temperature.

In the impact resistance test, a manhole cover was placed on a test table, and a steel spherical weight having a weight of 1 kg was dropped from a position of 1 m in height at the center of the manhole cover to check for damage. In this example, no breakage was observed.

COMPARATIVE EXAMPLE 1 A thick portion 4 was not formed at the center of a manhole cover.
Reaction injection molding was performed in the same manner as in Example 1 except that the thickness t1 of the lid body 8 was uniformly set to 11.4 mm in the radial direction so as to have the same weight as in Example 1.
A manhole cover was formed.

A load resistance test and an impact resistance test were performed on the manhole cover in the same manner as in Example 1. The test value in the load resistance test was 100 kg or less, and the superiority of Example 1 was confirmed. In the impact resistance test, cracks were observed in the manhole cover according to Comparative Example 1, and the superiority of Example 1 was confirmed.

Example 2 The thickness t2 of the thick portion 4 was 38 mm, and the height t of the rib 14 was
4 was 21.5 mm, θ1 = 45 °, and eight ribs 14 were used to form a manhole cover in the same manner as in Example 1. t1 / t2 was about 0.2. Also,
S2 / S1 was about 0.09.

The manhole cover was subjected to a load resistance test and an impact resistance test in the same manner as in Example 1. The test value in the load resistance test was 500 kg or more. Further, in the impact resistance test, no broken part was observed.

Example 3 The outer diameter of the thick portion 4 was set to 300 mm, and the thickness t2 of the thick portion 4
Is set to 40 mm, the height t4 of the rib 14 is set to 23.0 mm, θ1 = 45 degrees, eight ribs 14 are set, and the rib width angle θ2 is set to 12 degrees.
A manhole cover was formed. t2 / t1 was about 0.2 and S2 / S1 was about 0.2.

A load resistance test and an impact resistance test were performed on the manhole cover in the same manner as in Example 1. The test value in the load resistance test was 1000 kg or more. Further, in the impact resistance test, no broken part was observed.

Example 4 The outer diameter of the thick part 4 was 360 mm, and the thickness t 2 of the thick part 4 was
Is set to 45 mm, the height t4 of the rib 14 is set to 30.0 mm, θ1 = 45 degrees, eight ribs 14 are set, and the rib width angle θ2 is set to 18 degrees.
A manhole cover was formed. t1 / t2 was about 0.2 and S2 / S1 was about 0.3.

A load resistance test and an impact resistance test were performed on this manhole cover in the same manner as in Example 1. The test value in the load resistance test was 1500 kg or more. Further, in the impact resistance test, no broken part was observed.

Example 5 The outer diameter of the thick part 4 was 380 mm, and the thickness t2 of the thick part 4 was
Is 50 mm, the height t4 of the rib 14 is 35.0 mm, θ1 = 45 degrees, eight ribs 14 are used, and the rib width angle θ2 is set to 24 degrees.
A manhole cover was formed. t2 / t1 was about 0.16 and S2 / S1 was about 0.3.

A load resistance test and an impact resistance test were performed on the manhole cover in the same manner as in Example 1. The test value in the load resistance test was 2000 kg or more. Further, in the impact resistance test, no broken part was observed.

Example 6 The outer diameter of the manhole cover was 530 mm, the thickness t2 of the thick portion 4 was 25 mm, and the height t4 of the rib 14 was 15.0 m.
A manhole cover was formed in the same manner as in Example 1 except that m was used. t1 / t2 is about 0.3, and S2 / S1
Was about 0.14.

The manhole cover was subjected to a load resistance test and an impact resistance test in the same manner as in Example 1. The test value in the load resistance test was 250 kg or more. Further, in the impact resistance test, no broken part was observed.

Example 7 The outer diameter of the manhole cover was 530 mm, the thickness t2 of the thick portion 4 was 28 mm, and the height t4 of the rib 14 was 18.0 m.
m, θ1 = 45 degrees, and a manhole cover was formed in the same manner as in Example 1 except that eight ribs 14 were used.
t1 / t2 is about 0.3 and S2 / S1 is about 0.14
Met.

A load resistance test and an impact resistance test were performed on the manhole cover in the same manner as in Example 1. The test value in the load resistance test was 500 kg or more. Further, in the impact resistance test, no broken part was observed.

Example 8 The outer diameter of the manhole cover was 530 mm, the outer diameter of the thick part 4 was 270 mm, the thickness t2 of the thick part 4 was 35 mm, the height t4 of the rib 14 was 23.0 mm, and θ1 = 4
5 degrees, eight ribs 14, and a rib width angle θ2 of 12
A manhole cover was formed in the same manner as in Example 1 except that the temperature was changed. t1 / t2 is about 0.2, and S2 / S1
Was about 0.3.

The manhole cover was subjected to a load resistance test and an impact resistance test in the same manner as in Example 1. The test value in the load resistance test was 1000 kg or more. Further, in the impact resistance test, no broken part was observed.

Example 9 The outer diameter of the manhole cover was 530 mm, the outer diameter of the thick portion 4 was 310 mm, the thickness t2 of the thick portion 4 was 40 mm, the height t4 of the rib 14 was 25.0 mm, and θ1 = 4
5 degrees, eight ribs 14, and a rib width angle θ2 of 18
A manhole cover was formed in the same manner as in Example 1 except that the temperature was changed. t1 / t2 is about 0.2, and S2 / S1
Was about 0.4.

A load resistance test and an impact resistance test were performed on the manhole cover in the same manner as in Example 1. The test value in the load resistance test was 1500 kg or more. Further, in the impact resistance test, no broken part was observed.

Example 10 The outer diameter of the manhole cover was 530 mm, the outer diameter of the thick part 4 was 330 mm, the thickness t2 of the thick part 4 was 45 mm, the height t4 of the rib 14 was 30.0 mm, and θ1 = 4
5 degrees, eight ribs 14, and a rib width angle θ2 of 24
A manhole cover was formed in the same manner as in Example 1 except that the temperature was changed. t2 / t1 is about 0.18, and S2 / S
1 was about 0.4.

The manhole cover was subjected to a load resistance test and an impact resistance test in the same manner as in Example 1. The test value in the load resistance test was 2000 kg or more. Further, in the impact resistance test, no broken part was observed.

[0090]

As described above, the manhole cover according to the present invention is made of a synthetic resin such as a reaction injection molded resin, so that it is lighter in weight than a metal manhole and has a lower manhole hole. Opening and closing work is easy.
Also, the noise is less than that of a metal manhole. In addition, in the present invention, the mechanical strength of the manhole cover is dramatically improved by integrally forming the thick portion at the center of the synthetic resin manhole cover, and the mechanical strength required for the manhole cover is sufficiently increased. Can be satisfied.

[Brief description of the drawings]

FIG. 1 is a plan view of a manhole cover according to one embodiment of the present invention.

FIG. 2 is a schematic sectional view taken along the line II-II shown in FIG.

FIG. 3 is a plan view showing a half of a manhole cover according to another embodiment of the present invention.

FIG. 4 is a schematic sectional view taken along line IV-IV in FIG. 3;

[Explanation of symbols]

 2, 2A ... Manhole cover 4, 4A ... Thick portion 6, 6A ... Flange portion 8, 8A ... Lid body 14 ... Rib

Claims (2)

[Claims] 1. A synthetic resin manhole cover in which a thick portion is integrally formed at a center portion, wherein a minimum thickness of the cover (t1) and a thickness of a thick portion formed at a center portion (t2). Ratio (t1 / t2) is 0.05 to 0.8
A manhole cover, characterized in that: 2. A ratio (S2 / S1) of an area (S2) of a thick portion formed at the center to a total area (S1) of the manhole cover is 0.02 to 0.8. The manhole cover according to claim 1, wherein: