JPH08285189A - Gas cylinder and its manufacture - Google Patents

Abstract

PURPOSE: To reduce weight, and enhance reliability excellent at falling impact by arranging an inner shell having gas barrier performance and an outer shell having withstand voltage performance, and forming its outer shell of CFRP by reinforcing resin by carbon fiber having tensile strength not less than a specific value. CONSTITUTION: A gas cylinder 1 is provided with an inner shell 2 having gas barrier performance and a lightweight outer shell 3 having withstand voltage performance to cover its inner shell 2. An FRP-made reinforcing layer 7 by compounding resin and woven fabric or the like by winding reinforcing fiber thread in a hoop shape, is formed in a barrel part A of the inner shell 2. On the other hand, the outer shell 3 is formed of CFRP by reinforcing resin by carbon fiber having tensile strength not less than 5500MPa. Therefore, weight is reduced, and excellent performance to falling impact is obtained, and it can be inexpensively manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to various gas cylinders, particularly gas cylinders suitable for mounting on automobiles and the like,
And a manufacturing method thereof.

[0002]

2. Description of the Related Art An automobile that uses high-pressure natural gas or liquefied gas such as propane as a fuel is equipped with a pressure-resistant cylinder for the purpose of fuel storage. Generally, pressure cylinders sold and used are made of metal such as steel and aluminum. However, since the metal pressure-resistant cylinder is thick and heavy, it not only has poor workability and is dangerous, but also has a drawback that it requires a large amount of energy for transportation, that is, it lowers fuel consumption of an automobile. In addition, the calorific value per unit weight of gas fuel is about half that of gasoline, so in order to increase the distance that a gas vehicle can run without replenishment to the level equivalent to that of a gasoline fuel vehicle on the market, There is a problem that the gas fuel must be installed.

For this reason, gas cylinders in which an inner shell made of aluminum or plastic is covered with an outer shell made of pressure-resistant FRP (fiber reinforced plastic) have recently been developed for the purpose of weight reduction. Since this gas cylinder is essentially made of plastic, it is considerably lighter than a metal cylinder, and if it is used as a natural gas cylinder for automobiles, it can be expected to improve fuel efficiency. However, since most of the weight of the cylinder is the outer shell, a cylinder with the outer shell made as light as possible is preferable because it is lighter in weight, not only improving fuel efficiency, but also reducing consumption costs such as wear of tires and brake shoes, It can be expected to reduce labor when handling cylinders and reduce accidents.

Another problem with the vehicle-mounted cylinder is damage caused by a drop impact. Since the weight of the cylinder is heavy during the assembly process and the transportation process, the impact energy (impact energy increases in proportion to the weight of the cylinder) acting on the cylinder when the cylinder falls and collides with the ground etc. becomes large, and the heavy cylinder is heavy. The greater the drop impact, the greater the damage.

Further, since the cylinder using the reinforcing fiber having low strength for FRP has a thicker wall, it is difficult to remove voids which cause cracks during molding, and the resin is runaway due to heat generation during curing. In order to avoid the reaction and damage to the inner shell, there is a problem that the curing time becomes long and the productivity is lowered.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of conventional gas cylinders and to provide a highly reliable gas cylinder which is not only lightweight but also excellent in drop impact. To do.

Another object of the present invention is to provide a method for manufacturing such a gas cylinder at low cost.

[0008]

In order to solve the above problems, the present invention has a gas barrier inner shell and a pressure resistant outer shell, and the outer shell has a tensile strength of 5,500 MPa or more. And / or a gas cylinder characterized by comprising CFRP (carbon fiber reinforced plastic) obtained by reinforcing a resin with carbon fibers having a surface specific nitrogen concentration of 0.02 or more and a surface specific oxygen concentration of 0.30 or less. To do.

Further, according to the present invention, as a method for producing such a gas cylinder, a pressure-resistant CFRP outer shell is formed around a gas barrier inner shell by a filament winding method or a tape winding method. When manufacturing a gas cylinder, as carbon fiber,
(A) A carbon fiber having a tensile strength of 5,500 MPa or more and / or (b) a surface specific nitrogen concentration of 0.02 or more and a surface specific oxygen concentration of 0.30 or less is used. .

The present invention will be described in detail with reference to one embodiment thereof. In FIG. 1, a gas cylinder 1 includes an inner shell 2 having a gas barrier property, and a lightweight pressure-resistant material provided so as to cover the inner shell 2. And an outer shell 3. This gas cylinder 1
Has a body portion A as a whole, an end plate portion B following it, a nozzle mounting mouthpiece 4 and a nozzle 5 attached thereto, and a boss 6 provided at the bottom of the cylinder.

In the above, the inner shell has a function of preventing gas leakage. Further, as will be described later, it also acts as a core when forming a lightweight outer shell having pressure resistance.

The inner shell may be made of an extremely thin light metal such as aluminum or magnesium alloy, or a resin such as polyethylene, polypropylene resin, polyamide resin, ABS resin, potybutylene terephthalate resin, polyacetal resin or polycarbonate. ABS resin is preferable in terms of excellent impact resistance. (High density) polyethylene is preferable in terms of excellent gas barrier property.

Such a resin inner shell can be manufactured by a well-known blow molding method. Using the composite blow molding method,
A gas-sealing property may be excellent, for example, a multi-layer structure sandwiched between high-density polyethylene resin layers may be used. Further, the inner shell may be made of FRP. Such an FRP inner shell is formed by injection molding a resin containing inorganic fibers such as glass fibers and carbon fibers, or organic fibers such as aramid fibers and polyethylene fibers, and short fibers having a fiber length of about 2 to 10 mm. It can be manufactured by

The inner shell has the function of preventing gas leakage as described above. In order to improve such action, it is also preferable to form a gas barrier layer on the inner surface and / or the outer surface. For example, when a nitrogen gas containing fluorine is used as a blowing gas at the time of blow molding, a gas barrier layer made of a fluororesin film can be formed on the inner surface of the inner shell. Further, a metal barrier coating of copper, nickel, chromium or the like may be formed on the outer surface to form a gas barrier layer. The metal plating film can be formed by an electrolytic plating method or an electroless plating method. When the inner shell is manufactured by the composite blow molding method, a polyamide resin or the like having excellent gas barrier properties is arranged on the inner side, and an easily-platable, eg ABS resin layer is arranged on the outer side to facilitate the formation of a metal plating film. You can also

The inner shell also has 2.5 to 5c on its inner surface.
Ring-shaped ribs described in the circumferential direction can be provided at intervals of m. Such an inner shell can be obtained, for example, by making a half-divided inner shell made of a plastic with ribs, and joining and integrating them. These ribs improve the rigidity of the inner shell, prevent the inner shell from being deformed when the outer shell described later is formed, reduce the strength of the outer shell due to the meandering and ubiquity of the reinforcing fibers, the variation in strength, and eventually the pressure resistance. Help prevent.

Referring again to FIG. 1, the body portion A of the inner shell is made of FRP which is formed by hoop winding a reinforcing fiber thread described later or by combining a woven fabric of such a reinforcing fiber thread and a resin. Reinforcing layer 7 is formed. The reinforcing layer 7 may extend to a part of the end plate portion B. However, in the present invention, it is not essential to have the reinforcing layer.

On the other hand, the outer shell 3 has a tensile strength of 5,500M.
It is made of CFRP containing carbon fiber and resin having Pa or more. By constructing the outer shell with carbon fibers having a tensile strength of 5,500 MPa or more, the gas cylinder is lightweight and
In addition, it exhibits excellent drop impact performance and is highly reliable.

That is, most of the weight of the cylinder is an outer shell, and in order to reduce the weight of the cylinder and reduce the impact energy value (the impact energy value increases in proportion to the weight of the cylinder) during free fall. , It is necessary to reduce the weight of the outer shell. For this reason, it is also important to reduce the amount of resin and reinforcing fibers that make up the outer shell, but if the resin content is reduced, the reinforcing fibers contact each other and the original strength of the fibers does not develop (so-called strength. There is a problem in that the utilization rate decreases), and there is a limit to reducing the resin content rate. Considering the strength utilization ratio, the resin content is preferably around 35%. Therefore, the strength of the reinforcing fiber used is 5,500M.
It is necessary to be Pa or more. By using a high-strength carbon fiber yarn of 5,500 MPa, the thickness of the outer shell of the cylinder is reduced, the weight of the cylinder is dramatically reduced, the fuel economy of a gas vehicle equipped with this is improved, and the tire is It also reduces the consumption of brake shoes and the like, and can greatly reduce the damage to the cylinder due to the drop impact when handling the cylinder. Furthermore, since the outer shell is thin, there are few voids in the outer shell, and it is possible to manufacture a highly productive cylinder without runaway or damage to the inner shell due to heat generation during curing.

Further, considering fatigue resistance, the elastic modulus of the reinforcing carbon fiber is preferably 220 GPa or more. This is because if it is less than 220 GPa, the deformation amount of the cylinder at the time of gas supply and exhaust gas becomes large and the fatigue resistance performance deteriorates. Such an outer shell can be constructed as follows, for example.

That is, the above-mentioned inner shell may be formed as a so-called mandrel by forming a wound layer of a reinforcing fiber containing a resin around it by a well-known filament winding method or tape winding method and molding it. At this time, if there is a reinforcing layer, the average height of the outer surface of the inner shell including the surface is 10 to 20 μm.
It is preferable to form a rough surface of about m because slippage of the reinforcing fiber yarn at the time of winding can be prevented and disturbance of the distribution of the reinforcing fiber can be reduced.

Among the carbon fibers as the reinforcing fiber yarn,
PAN-based carbon fibers are preferred. Further, these reinforcing fiber yarns are preferably non-twisted fiber yarns having excellent openability in the sense that stress concentration due to bending can be reduced and generation of voids can be reduced. Among such fibers, carbon fibers having a tensile strength of 5,500 MPa or more measured according to JIS-R7601 are preferable. Such a carbon fiber can be manufactured as follows, for example.

That is, a polymer containing at least 90% by weight of acrylonitrile is subjected to wet spinning, dry / wet spinning or dry spinning (preferably dry / wet spinning), and the fineness is 1.1 denier or less. Acrylic fiber with such fineness is obtained. Hereinafter, a manufacturing method based on the dry / wet spinning method will be described.

A polymer solution containing 90% by weight or more of acrylonitrile as a main component is filtered with a filter to remove impurities and internal voids, and once discharged into an inert atmosphere and air, a coagulation bath Introduce inside. The resulting water-swelled yarn is washed with water, drawn, and further subjected to a treatment of uniformly adhering 1 to 2% by weight of a silicone-based oil agent to prevent fusion of the yarns in the flameproofing process and a drying process, and then at 100 ° C or higher. By further drawing at the temperature of, the single yarn diameter is 5 to 1
A precursor of about 5 μm is formed.

Next, the above precursor is heated to 200 to 300 ° C. in the air and while being stretched to make it flame resistant. At this time, it is preferable to reduce the dust concentration in the air as much as possible in order to reduce adhesion of impurities and surface defects.

Next, the above flame-resistant yarn is stretched in an inert atmosphere such as nitrogen gas or argon gas and under stretching.
Heat to 0-800 ° C, then in an inert atmosphere,
And, under tension, it is heated to 1,200 to 1,800 ° C. and subjected to carbonization treatment to obtain carbon fibers. At this time, in order to prevent the adhesion of impurities, it is preferable to reduce the dust concentration in the air between the flameproofing furnace and the carbonization furnace as much as possible.

Further, in order to remove defects on the surface of the fiber and obtain high tensile strength, the carbon fiber is subjected to an electrolytic treatment in an inorganic acid water containing nitric acid as a main component, and then 5 times in an inert gas.
By heating to 00 to 800 ° C. to inactivate the functional groups generated by the electrolytic treatment to the extent that the adhesion with the resin is not impaired,
The carbon fiber can be obtained by removing the surface layer as long as the crystallinity of the surface is not impaired.

The carbon fibers described above have a specific surface oxygen concentration (hereinafter referred to as O / C) and a specific surface nitrogen concentration (hereinafter referred to as N / C) measured by X-ray photoelectron spectroscopy within specific ranges. It is preferable that it is possible to improve the affinity and adhesiveness with the resin described later.

Furthermore, in the carbon fiber used for the outer shell of the gas cylinder according to the present invention, the surface specific oxygen concentration O / C (atomic ratio of oxygen O to carbon C) and the surface measured by X-ray photoelectron spectroscopy Specific nitrogen concentration N / C (carbon C
The ratio of the number of atoms of nitrogen N to () is such that O / C is 0.30 or less and N / C is 0.02 or more. O / C is preferably 0.25 or less, more preferably 0.20 or less. When O / C exceeds 0.30, the chemical bond between the functional group of the resin and the outermost surface of the carbon fiber becomes strong, but the oxide layer, which is much lower in strength than the original carbon fiber substrate itself, has Since it is covered, the resulting outer shell has a low compressive strength.

The lower limit of O / C is 0.04 or more, preferably 0.08 or more, and more preferably 0.10 or more. If O / C is less than 0.04, for example, the reactivity with the resin and the reaction amount are insufficient, and as a result,
The pressure resistance of the outer shell may not be expressed.

The surface specific nitrogen concentration N / C is 0.02 or more, preferably 0.03 or more, and more preferably 0.0.
It is 4 or more. Carbon fiber having N / C less than 0.02 may not be able to improve the reactivity with the resin,
As a result, the pressure resistance of the outer shell cannot be expressed.

The upper limit of N / C is 0.30 or less, preferably 0.25 or less, more preferably 0.20 or less. That is, when N / C exceeds 0.30,
Only the reactivity with the resin and the reaction amount become excessive, and further improvement in strength cannot be expected.

Surface specific oxygen concentration O / C and surface specific nitrogen concentration N / measured by X-ray photoelectron spectroscopy as described above.
The carbon fiber having C in the above-mentioned specific range can be obtained by performing electrolytic oxidation treatment or oxidation treatment in a gas phase or a liquid phase. The manufacturing method based on the electrolytic oxidation treatment method will be described below.

In this case, either an acidic or alkaline aqueous solution can be adopted as the electrolytic solution, and sulfuric acid, nitric acid, hydrochloric acid or the like can be specifically used as the electrolyte of the acidic aqueous solution. An aqueous solution containing ammonium ions is preferable as the alkaline aqueous solution, and specifically, ammonium hydrogen carbonate, ammonium carbonate, tetraalkylammonium hydroxide salt or the like or a mixture thereof can be used. Particularly, ammonium hydrogen carbonate and ammonium carbonate, which can increase the surface specific nitrogen concentration N / C, are preferable.

The amount of electricity for treatment is preferably optimized in accordance with the carbonization degree of the carbon fiber to be treated, but from the viewpoint of preventing the tensile strength of the carbon fiber substrate from decreasing and promoting the deterioration of the crystallinity of the surface layer, electrolytic treatment is performed. The treatment is preferably repeated a plurality of times with a small amount of electricity. Specifically, the amount of electricity supplied per electrolytic cell is preferably 1 coulomb / g · tank (1 g of carbon fiber, the number of coulombs per tank) or more and 40 coulomb / g · tank or less.

As the energization method, either direct energization in which the carbon fiber is brought into direct contact with the electrode roller to energize it or indirect energization in which the carbon fiber and the electrode are energized via an electrolytic solution can be adopted. In order to obtain high tensile strength, indirect energization that suppresses fuzzing during electric treatment, electric sparks, etc. is preferable.

After the electrolytic treatment, it is preferable to wash with water and dry. In this case, in order to improve the affinity and adhesiveness with the resin described later, it is desirable to dry at a temperature as low as possible so that the functional group existing on the outermost surface of the carbon fiber is not thermally decomposed, and specifically, , The drying temperature is 250
It is desirable to dry at or below 0 ° C, and more preferably at or below 210 ° C.

As the matrix resin of CFRP, thermosetting resins such as epoxy resin, unsaturated polyester resin, vinyl ester resin and phenol resin, or polyamide resin, polyethylene terephthalate resin, ABS.
Thermoplastic resins such as resins, polyetherketone resins, polyphenylene sulfide resins, poly-4-methylpentene-1 resins, and polypropylene resins can be used. Particularly, in terms of increasing the strength utilization factor of the fiber, a resin having a large tensile elongation, preferably JIS-K7.
It is preferable to select and use a resin having a breaking elongation measured by 115 of 4% or more, more preferably 6% or more.

By the way, the ratio of the tensile stress in the axial direction of the cylindrical gas cylinder generated by the internal pressure and the tensile stress in the circumferential direction is approximately 1: 2. Therefore, in order to reduce the weight, it is preferable to arrange the reinforcing fibers in the axial direction and the circumferential direction at a ratio of approximately 1: 2. Further, even if it is wound at ± 55 degrees with respect to the axial direction, the strength in the axial direction and the circumferential direction becomes approximately 1: 2, which is preferable.

The outermost layer can also be formed as a resin layer made of a resin having excellent corrosion resistance, acid resistance, alkali resistance and moisture resistance, for example, polyester resin, vinyl ester resin, polyethylene resin, phenol resin or the like. .

[0040]

EXAMPLES The characteristics of the gas cylinder of the present invention will be described in detail with reference to examples. Example 1 Acrylonitrile 99.5% by weight, itaconic acid 0.5
A 20% dimethyl sulfoxide solution of acrylic copolymer (polymer having a solution viscosity of 600 poise at 45 ° C.) consisting of wt% was once discharged into the air through a spinneret and passed through a space of 3 mm. After that, dimethyl sulfoxide 30% was introduced into a coagulation bath at 5 ° C. in a stationary coagulation bath to obtain coagulated fibers. Sequentially, washing with water and drawing in hot water, applying amino-modified silicone oil agent, drying and densifying, drawing in pressurized steam, drawing with a total draw ratio of 10 times and winding, single yarn fineness of 1.0 denier, simple A precursor having 12,000 yarns was obtained (oil agent adhesion amount 1.55% by weight). It is subsequently flameproofed in air with a temperature profile of 230/260 ° C., after which the maximum temperature of 1,30
It is introduced into a carbonization furnace at 0 ° C and 300 to 700 in nitrogen gas.
Temperature rising rate in the temperature range of ℃ is about 300 ℃ / min, 1.0
The temperature rising rate in the temperature range of 00 to 1,200 ° C is about 40
Carbon fiber was obtained by carbonization under the condition of 0 ° C./min. Subsequently, electrolysis was carried out for 1 minute at an energization amount of 5 coulombs / gram (electricity amount per tank: 1.25 coulombs / g. Bath) in an electrolysis bath using an aqueous solution of sulfuric acid having a concentration of 0.05 mol / liter as an electrolytic solution. , Further washed with water, dried at 150 ℃, single yarn diameter:
7 μm, number of single yarn: 12,000, tensile strength: 5,83
0 MPa, tensile modulus: 245 GPa, specific gravity: 1.8
Carbon fiber having 0, surface specific oxygen concentration O / C: 0.18, and surface specific nitrogen concentration N / C: 0.04 was obtained.

Epoxy resin (bisphenol A type epoxy resin, curing agent: dicyandiamide DCMU was added to the above fibers.
(Dichlorophenyldimethylurea type)) is passed through a resin tank and a roller guide to impregnate the filament shell by a filament winding method to form an inner shell made of high density polyethylene resin (outer diameter: 300 m).
m, total length excluding nozzle mounting part: 500 mm, wall thickness: 5 m
m, weight: 2.5 kg) as a so-called mandrel, and the amount of fibers in the axial direction and the circumferential direction (correctly θ = 3 ° and 90 °) of the outer shell is 1: 2 on the inner shell. To form an outer shell.

Then, it was placed vertically in an oven, heated at a temperature rising rate of 1.5 ° C./min and 130 ° C. for 2 hours, and cured at a temperature lowering rate of 2.5 ° C./min to mold the body of the gas cylinder. (Pressure is atmospheric pressure). The outer diameter and the weight of the main body thus obtained were 310 mm and 6.1 kg, respectively.

Next, the main body is lifted up by a lifter and moved to 3 m.
From the height of the concrete to the concrete floor surface (like the body collides with the floor), it is dropped (velocity at the time of collision is about 5 m / s), and the outer shell surface after the collision is visually observed. No damage such as dents or fiber breaks was observed.

Next, water pressure (water temperature of about 15 ° C.) is repeatedly applied from the nozzle mounting portion of the main body (pressurization speed = 5.0 MP).
a / min), the pressure was 53.7 MPa
When it reached the point, a leak (water leak) occurred from the center of the main body.

Further, the main body end plate portion which did not leak was cut into a ring shape, and the cross section was polished (after polishing with # 400 sandpaper, further polishing with # 1,000 and # 2,000 sandpaper). After polishing, the entire cross section was observed with an optical microscope (× 500), and no void was observed.

COMPARATIVE EXAMPLE 1 Amino-modified silicone oil content was 0.12% by weight.
In the same manner as in Example 1 except that drying after washing with water, which was performed following the electric field treatment, was performed at 350 ° C. in a nitrogen atmosphere, single yarn diameter: 7 μm, number of single yarn: 12,000, tensile strength: 3 ，
300 MPa, tensile elastic modulus: 244 GPa, specific gravity: 1.
Carbon fiber having 79, surface oxygen concentration O / C: 0.12, and surface specific nitrogen concentration N / C: 0.01 was obtained. The above fiber was filament wound in the same manner as in Example 1 to obtain a main body. The outer diameter and the weight of the outer shell thus obtained are
It was 320 mm and 9.6 kg.

Next, when the same drop test as in Example 1 was conducted, it was confirmed that part of the outer shell was whitened and the fibers were cut.

Then, when pressure was applied to the main body in the same manner as in Example 1, a leak (water leak) occurred from the body portion near the body end plate portion at 46.0 MPa.

Further, in the same manner as in Example 1, the cross section of the main body end plate portion in which no leak occurred was observed, and 10 or more voids having a length of 50 μm or more were observed.

Comparative Example 2 An electrolytic cell using an aqueous solution of ammonium carbonate having a concentration of 1.0 mol / liter as an electrolytic solution was used, and the drying temperature after washing with water was 150 ° C.
In the same manner as in Comparative Example 1 except that the single yarn diameter was 7 μm,
Number of single yarn: 12,000, Tensile strength: 3,320MP
a, tensile elastic modulus: 244 GPa, specific gravity: 1.79, surface specific oxygen concentration O / C: 0.15, surface specific nitrogen concentration N / C:
A carbon fiber of 0.07 was obtained. The above fiber was filament wound in the same manner as in Example 1 to obtain a main body. The outer diameter and the weight of the outer shell thus obtained are respectively 320 m
m, was 9.6 kg.

Next, when the same drop test as in Example 1 was conducted, it was confirmed that part of the outer shell was whitened and the fibers were cut.

Then, when pressure was applied to the main body in the same manner as in Example 1, a leak (water leak) occurred from the body portion near the main body end plate portion at 49.1 MPa.

Further, when the cross section of the main body end plate portion where no leak occurred was observed in the same manner as in Example 1, 10 or more voids having a length of 50 μm or more were observed.

[0054]

The gas cylinder of the present invention has a tensile strength of 5,500MP so as to cover the inner shell having a gas barrier property.
Since the outer shell made of CFRP containing carbon fiber and resin which is a or more is provided, as is clear from the comparison between the example and the comparative example, it is lightweight and has excellent performance against drop impact. And is highly reliable. Therefore, the gas cylinder of the present invention is a CNG tank (Compressed Natur) for automobiles, which is required to be lightweight and highly reliable.
Al gas tank) is particularly suitable.

Further, in the present invention, the above-mentioned gas cylinder is provided with a carbon fiber having a tensile strength of 5,500 MPa or more and a resin around the inner shell having a gas barrier property by using the filament winding method or the tape winding method. Since it is manufactured by forming the outer shell made of the FRP containing it, it can be manufactured at low cost.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of a gas cylinder according to an embodiment of the present invention.

[Explanation of symbols]

 1 Gas cylinder 2 Inner shell 3 Outer shell 4 Nozzle mounting base 5 Nozzle 6 Boss 7 Reinforcing layer A Body part B End plate part

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Claims (4)

[Claims] 1. A CFRP having a gas barrier inner shell and a pressure resistant outer shell, wherein the outer shell is made of CFRP obtained by reinforcing a resin with carbon fibers having a tensile strength of 5,500 MPa or more. Gas cylinder. 2. A carbon fiber resin having a gas barrier inner shell and a pressure resistant outer shell, the outer shell being a carbon fiber resin having a surface specific nitrogen concentration of 0.02 or more and a surface specific oxygen concentration of 0.30 or less. A gas cylinder characterized by comprising CFRP obtained by strengthening. 3. A gas-barrier inner shell and a pressure-resistant outer shell, wherein the outer shell has a tensile strength of 5,500 MPa or more, a surface specific nitrogen concentration of 0.02 or more, and a surface specific oxygen concentration. CF reinforced with resin with carbon fiber of 0.30 or less
A gas cylinder made of RP. 4. When a gas cylinder is manufactured by forming a pressure-resistant CFRP outer shell around a gas barrier inner shell using a filament winding method or a tape winding method, the carbon fiber is (a) stretched. A method for producing a gas cylinder, which comprises using carbon fibers having a strength of 5,500 MPa or more and / or (b) a surface specific nitrogen concentration of 0.02 or more and a surface specific oxygen concentration of 0.30 or less.