Epoxy resin composition and its uses

Abstract

To provide a cured epoxy resin that can be used as a liner, and an epoxy resin composition that can give the cured epoxy resin.SOLUTION: One embodiment is an epoxy resin composition containing a basis and a curing agent. The basis contains an epoxy compound having a mesogen structure containing a benzene ring. The curing agent includes a curing agent free of a benzene ring. Another embodiment is a cured epoxy resin, which is a cured product of the epoxy resin composition.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an epoxy resin composition and uses thereof. [Background technology]

[0002] Pressure vessels (high-pressure tanks) are containers used to store hydrogen gas, etc. To reduce weight, a known high-pressure tank is equipped with a hollow resin liner and a reinforcing layer (CFRP layer) formed by wrapping carbon fiber reinforced plastic (CFRP) around the outer surface of the liner.

[0003] High-pressure tanks are used as hydrogen tanks for fuel cell (FC) vehicles, and various technologies related to high-pressure tanks are being actively researched and developed. The carbon fiber reinforced resin that makes up high-pressure tanks generally contains a cured epoxy resin, which is a cured epoxy resin composition, as the resin component, and nylon has generally been used as the liner (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-144657 Summary of the Invention [Problem to be solved by the invention]

[0005] The inventors thought that while the resin contained in the carbon fiber reinforced resin currently in use and the resin that makes up the liner are generally different types of resin, using the same type of resin would improve the compatibility between the CFRP layer and the liner.

[0006] Therefore, an object of the present disclosure is to provide an epoxy resin cured product that can be used as a liner, and an epoxy resin composition from which the epoxy resin cured product can be obtained. [Means for solving the problem]

[0007] The present inventors have conducted extensive research to solve the above problems and have found that epoxy resins are generally crosslinkable polymers, and that cured epoxy resins have a network structure, resulting in poor gas barrier properties, and that if the network structure develops too much, elongation tends to be poor. It is therefore difficult for cured epoxy resins to achieve both hydrogen gas barrier properties and low-temperature elongation, which are physical properties generally required of liners.

[0008] As a result of further intensive research, the present inventors have found that a cured epoxy resin product, which is a cured product of a specific epoxy resin composition, can be suitably used as a tank liner, leading to the present disclosure.

[0009] An example aspect of this embodiment is described as follows. (1) An epoxy resin composition containing a base resin and a curing agent, the base resin contains an epoxy compound having a mesogen structure containing a benzene ring, The epoxy resin composition, wherein the curing agent includes a curing agent that does not have a benzene ring. (2) The epoxy resin composition according to (1), wherein the base material contains an epoxy compound having no mesogenic structure in an amount of 25% by mass or less based on 100% by mass of the base material. (3) The epoxy resin composition according to (1) or (2), wherein when the epoxy resin composition is cured to obtain a cured epoxy resin material and the cured epoxy resin material is analyzed under a polarizing microscope, the difference between the maximum and minimum strength values normalized by the strength in parallel Nicols is 0.3 or more, and the minimum strength value normalized by the strength in parallel Nicols is 0.05 or more. (4) A cured epoxy resin product, which is a cured product of the epoxy resin composition according to any one of (1) to (3). (5) The epoxy resin cured product according to (4), in which, when analyzed with a polarizing microscope, the difference between the maximum and minimum values of intensity normalized by the intensity in parallel Nicols is 0.3 or more, and the minimum value of intensity normalized by the intensity in parallel Nicols is 0.05 or more. (6) A tank liner comprising the epoxy resin cured product according to (4) or (5). (7) A tank including a tank liner as described in (6). [Effects of the Invention]

[0010] The present disclosure makes it possible to provide an epoxy resin cured product that can be suitably used as a tank liner, and an epoxy resin composition from which the epoxy resin cured product can be obtained. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic cross-sectional view showing an example of the configuration of a tank 100. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] This embodiment is an epoxy resin composition containing a base agent and a curing agent, wherein the base agent includes an epoxy compound having a mesogenic structure containing a benzene ring, and the curing agent includes a curing agent that does not have a benzene ring. Another embodiment is an epoxy resin cured product that is a cured product of the epoxy resin composition. This embodiment will be described in detail below.

[0013] The epoxy resin composition of this embodiment is a composition containing a base agent and a curing agent. The base agent and curing agent of the epoxy resin composition of this embodiment may be stored separately during distribution and storage. That is, the composition may be distributed and stored as an epoxy resin composition kit containing at least a first part containing a base agent and a second part containing a curing agent. That is, one example of this embodiment is an epoxy resin composition kit containing at least a first part containing a base agent and a second part containing a curing agent.

[0014] The base resin contains an epoxy compound having a mesogenic structure containing a benzene ring. The use of an epoxy compound having a mesogenic structure containing a benzene ring is preferred because the benzene ring allows the cured epoxy resin to exhibit sufficient stacking interaction. The term "epoxy compound" refers to a compound having an epoxy group in the molecule, preferably a plurality of epoxy groups (e.g., 2 to 10, preferably 2 to 4).

[0015] The base resin preferably contains, based on 100% by mass of the base resin, 70% by mass or more, and more preferably 75% by mass or more, of an epoxy compound having a mesogenic structure containing a benzene ring. In one embodiment, the base resin may contain, based on 100% by mass of the base resin, 90% by mass or more, or even 100% by mass, of an epoxy compound having a mesogenic structure containing a benzene ring.

[0016] The epoxy compound having a mesogenic structure containing a benzene ring is not particularly limited as long as it has a mesogenic structure containing a benzene ring as the mesogenic structure. The epoxy compound having a mesogenic structure containing a benzene ring may be used alone or in combination of two or more. The epoxy compound having a mesogenic structure containing a benzene ring may be an epoxy compound having a planar structure with a benzene ring as the minimum unit and having a mesogenic group (mesogenic structure) with conjugation. Examples of epoxy compounds having a mesogenic structure containing a benzene ring include biphenyl-type epoxy resins, triphenylmethane-type epoxy resins, naphthalene-type epoxy resins, and stilbene-type epoxy resins. Here, the term "epoxy resin" refers to a resin before the epoxy group reacts, i.e., before curing, and can be rephrased as "epoxy compound." In the present invention, the mesogenic structure refers to a highly rigid partial structure, and specific examples of mesogenic structures having a benzene ring include a biphenyl structure, a phenylbenzoate structure, an azobenzene structure, a stilbene structure, a terphenyl structure, a naphthalene structure, a triphenylmethane structure, an anthracene structure, derivatives thereof, and structures in which two or more of these mesogenic structures are bonded via a bonding group.

[0017] The base resin may contain an epoxy compound without a mesogenic structure as a component other than the epoxy compound having a mesogenic structure containing a benzene ring. When an epoxy compound without a mesogenic structure is used, the epoxy compound without a mesogenic structure is preferably contained in an amount of 25% by mass or less relative to 100% by mass of the base resin. In one embodiment, the base resin may contain 10% by mass or less of the epoxy compound without a mesogenic structure relative to 100% by mass of the base resin, or may not contain any epoxy compound without a mesogenic structure. In one preferred embodiment, the base resin does not contain an epoxy compound without a mesogenic structure.

[0018] The epoxy compound having no mesogenic structure is not particularly limited as long as it is an epoxy compound having no mesogenic structure. The epoxy compound having no mesogenic structure may be used alone or in combination of two or more. For example, flexible epoxy resins can be used as the epoxy compound having no mesogenic structure, and examples thereof include alkylene glycol diglycidyl ethers such as ethylene glycol diglycidyl ether.

[0019] The curing agent includes a curing agent having no benzene ring. By using an epoxy compound having a mesogen structure containing a benzene ring as the main compound and a curing agent having no benzene ring as the curing agent, the cured epoxy resin exhibits good gas barrier properties and low-temperature elongation, which is preferable.

[0020] The curing agent is not particularly limited as long as it is used as a curing agent for epoxy compounds and does not have a benzene ring in the molecule, and examples of the curing agent include boron trifluoride amine complex salt, polyamine-based curing agents, acid anhydride-based curing agents, imidazole-based curing agents, and carboxylic acid-based curing agents.

[0021] Examples of boron trifluoride amine complex salts include boron trifluoride monoethylamine, boron trifluoride diethylamine, and boron trifluoride isopropylamine.

[0022] Examples of polyamine-based curing agents include aliphatic amine-based curing agents such as diethylenetriamine and triethylenetetramine; alicyclic amine-based curing agents such as isophoronediamine; and dicyandiamide.

[0023] Examples of the acid anhydride curing agent include maleic anhydride, tetrahydrophthalic anhydride, and hexahydrophthalic anhydride.

[0024] Examples of imidazole curing agents include 2-methylimidazole, 2-ethyl-4-methylimidazole, and 1-cyanoethyl-2-ethyl-4-methylimidazole.

[0025] Examples of the carboxylic acid curing agent include succinic acid, adipic acid, glutaric acid, and sebacic acid.

[0026] These curing agents not having a benzene ring may be used alone or in combination of two or more.

[0027] In the epoxy resin composition, the amount of curing agent relative to the total amount of epoxy compounds, i.e., the amount when only epoxy compounds having a mesogenic structure containing a benzene ring are used as epoxy compounds, or the combined amount when epoxy compounds having a mesogenic structure containing a benzene ring and epoxy compounds without a mesogenic structure are used as epoxy compounds, is preferably 0.01 to 15 parts by mass, more preferably 0.3 to 13 parts by mass, even more preferably 0.5 to 10 parts by mass, and particularly preferably 0.6 to 7 parts by mass, per 100 parts by mass of the total amount of epoxy compounds. In one particularly preferred embodiment, the amount of curing agent is 4 to 6 parts by mass per 100 parts by mass of the total amount of epoxy compounds.

[0028] The epoxy resin composition may contain the above-described epoxy compound having a mesogenic structure containing a benzene ring, the curing agent not having a benzene ring, and any other component (other component) other than the epoxy compound not having a mesogenic structure.

[0029] Other components include solvents, curing catalysts, curing accelerators, coupling agents, inorganic fillers, fibers such as glass fibers and ceramic fibers, woven fabrics, nonwoven fabrics, flame retardants, diluents, plasticizers, lubricants, etc.

[0030] The solvent is not particularly limited as long as it can uniformly dissolve or disperse the above-mentioned epoxy compound having a mesogenic structure containing a benzene ring, the curing agent not having a benzene ring, and the optionally used epoxy compound not having a mesogenic structure, and examples thereof include methyl ethyl ketone, ethylene glycol monomethyl ether, methyl isobutyl ketone, dimethylformamide, propylene glycol monomethyl ether, toluene, xylene, acetone, and mixed solvents thereof.

[0031] The epoxy resin composition of the present embodiment can be produced by mixing the above-described epoxy compound having a mesogenic structure containing a benzene ring, the curing agent having no benzene ring, and the optionally used epoxy compound having no mesogenic structure, as well as other components. The specific production method is also not particularly limited, and the composition can be produced based on a conventionally known method for producing an epoxy resin composition.

[0032] The cured epoxy resin material of this embodiment is a cured product of the epoxy resin composition of this embodiment described above.

[0033] The epoxy resin composition of this embodiment is preferably such that, when the epoxy resin composition is cured to obtain a cured epoxy resin product and the cured epoxy resin product is analyzed under a polarizing microscope, the difference between the maximum and minimum strength values when normalized by the strength in parallel Nicols is 0.3 or more and the minimum strength value when normalized by the strength in parallel Nicols is 0.05 or more. In other words, when the epoxy resin cured product of this embodiment is analyzed under a polarizing microscope, the difference between the maximum and minimum strength values when normalized by the strength in parallel Nicols is 0.3 or more and the minimum strength value when normalized by the strength in parallel Nicols is 0.05 or more.

[0034] In order for a cured epoxy resin to exhibit good gas barrier properties, sufficient intermolecular stacking interactions (π-π stacking interactions) are required. A difference of 0.3 or more between the maximum and minimum strength values normalized by the strength in parallel Nicols orientation indicates sufficient molecular orientation, serving as an indicator that the cured epoxy resin exhibits sufficient stacking interactions. Furthermore, in order for an epoxy resin to exhibit sufficient low-temperature elongation, the orientation must be fully developed in three dimensions, not two. If there is an angle at which the strength normalized by the strength in parallel Nicols is zero, this suggests that two-dimensional orientation has developed. Therefore, it is desirable that the minimum strength normalized by the strength in parallel Nicols be 0.05 or greater. In other words, if the difference between the maximum and minimum strength values normalized by the strength in parallel Nicols is 0.3 or greater and the minimum strength normalized by the strength in parallel Nicols is 0.05 or greater, the cured epoxy resin exhibits low angle dependence and high strength when analyzed with a polarizing microscope, suggesting that the cured epoxy resin exhibits isotropic crystal orientation.

[0035] The cured epoxy resin material of this embodiment can be used as a tank liner. The tank liner will hereinafter also be referred to simply as a liner. The cured epoxy resin material has the physical properties required for a tank liner, for example, for a high-pressure tank, and is compatible with the carbon fiber reinforced resin layer that typically contains the cured epoxy resin material, making it suitable for use as a tank liner.

[0036] The tank of this embodiment includes the tank liner described above. The tank of this embodiment is not particularly limited as long as it includes the tank liner described above, but an example of the tank configuration is shown below with reference to FIG.

[0037] FIG. 1 is a cross-sectional view showing an example of the configuration of a tank 100. FIG. 1 shows a cross-sectional view taken along a plane parallel to and passing through the central axis of the tank 100. The central axis of the tank 100 coincides with an axis passing through the center of the circle of the tank body, which has a substantially cylindrical shape. The tank 100 can be used to fill with gas such as compressed hydrogen. For example, the tank 100 is loaded as a high-pressure tank filled with compressed hydrogen into a fuel cell vehicle to supply hydrogen to the fuel cell.

[0038] The tank 100 includes a liner 10, a carbon fiber reinforced resin layer 20 as an outer shell, a valve-side nozzle 30, an end-side nozzle 40, and a valve 50. A protective layer (not shown) may be optionally disposed between the liner 10 and the carbon fiber reinforced resin layer 20. A surface layer, for example, a glass fiber reinforced plastic layer (not shown) that protects the surface may be optionally disposed on the outside of the carbon fiber reinforced resin layer 20. The liner 10 has a hollow shape with a space therein that is filled with hydrogen, and has gas barrier properties that seal the internal space to prevent hydrogen from leaking to the outside.

[0039] The carbon fiber reinforced resin layer 20 is a resin layer formed so as to cover the outside of the liner 10. The liner 10 and the carbon fiber reinforced resin layer 20 are formed so as to cover a part of the valve side nozzle 30 and the end side nozzle 40, respectively. The carbon fiber reinforced resin layer 20 mainly functions to reinforce the liner 10 (reinforcing layer).

[0040] In FIG. 1 , the valve-side nozzle 30 is substantially cylindrical and is fitted and fixed between the liner 10 and the carbon fiber reinforced resin layer 20. The substantially cylindrical opening of the valve-side nozzle 30 functions as the opening of the tank 100. In this embodiment, the valve-side nozzle 30 can be made of, for example, stainless steel, but it may also be made of other metals such as aluminum, or may be made of resin. The valve 50 has a male thread formed on its cylindrical portion, and when the male thread is screwed into the female thread formed on the inner surface of the valve-side nozzle 30, the opening of the valve-side nozzle 30 is closed by the valve 50. The end-side nozzle 40 can be made of, for example, aluminum, and is assembled with a portion exposed to the outside, functioning to guide heat inside the tank to the outside.

[0041] The method for manufacturing the tank is not particularly limited, and the tank may be manufactured using the same method as conventional tanks. For example, the tank may be manufactured by solidifying an epoxy resin composition into a liner, forming a cured epoxy resin liner, wrapping a carbon fiber reinforced resin around the liner, and curing the epoxy resin composition in the carbon fiber reinforced resin to form a reinforcing layer. Alternatively, the tank may be manufactured by molding the carbon fiber reinforced resin into a tank shape using a mandrel or the like, supplying an epoxy resin composition to the inside of the tank-shaped carbon fiber reinforced resin, spreading the epoxy resin composition over the inner surface of the tank-shaped carbon fiber reinforced resin, and then curing the epoxy resin composition to form a liner. In this case, the epoxy resin composition in the tank-shaped carbon fiber reinforced resin may be cured before or simultaneously with the curing of the epoxy resin composition supplied to form the liner. In other words, the liner of this embodiment may be a coated liner (post-formed liner).

[0042] Alternatively, a tank may be manufactured by manufacturing portions of the tank using the above-described method and combining the manufactured portions of the tank.

[0043] Carbon fibers can be prepared by methods conventionally known in the art. Carbon fibers may be any material containing carbon as a main component, such as carbon fibers made from acrylic, pitch, and polyvinyl alcohol. Among these, PAN-based carbon fibers made from polyacrylonitrile fibers are preferred. Continuous fibers are preferred as carbon fibers, as they can further increase the strength of the carbon fiber-reinforced resin layer and the tank. [Example]

[0044] The present embodiment will be described below with reference to examples, but the present disclosure is not limited to these examples.

[0045] In the examples and comparative examples, the following base resins and curing agents were used. Main ingredient 1: Denacol EX-810 (Nagase Chemtec), ethylene glycol diglycidyl ether Main component 2: YL6677 (Mitsubishi Chemical), biphenyl-type epoxy resin (component A: 4,4'-biphenol-type epoxy resin; component B: tris(hydroxyphenyl)methane-type epoxy resin mixture, component A content approximately 25%, component B content approximately 75%) Hardener A: Boron trifluoride monoethylamine (Fujifilm Wako Pure Chemical Industries, Ltd.) Curing agent B: 1,3-phenylenediamine Hardener C: 4,4'-dihydroxybiphenyl

[0046] [Example] Epoxy resin compositions (Nos. 1 to 4) were prepared by mixing the base resin and curing agent according to the formulations shown in Table 1. The prepared epoxy resin compositions were cured on a glass substrate at 150°C for 2 hours to obtain cured epoxy resin products.

[0047] The obtained smooth cured epoxy resin products were analyzed using the following polarizing microscope. The intensity at each angle was normalized by dividing it by the intensity in parallel Nicols. The normalized intensity is also referred to as normalized intensity (au). Note that for cured epoxy resin products that were not analyzed using a polarizing microscope, the polarized intensity column in Table 1 states "not obtained." Polarizing microscope: Nikon ECLIPSE LV100ND Light source: Nikon INTENSILIGHT C-HGFI Spectroscopic detector: Ocean Optics USB2000+XR1-ES1

[0048] [Comparative Example] Epoxy resin compositions (Nos. 5 to 11) were prepared by mixing the base resin and curing agent according to the formulations shown in Table 1 below. The prepared epoxy resin compositions were cured on a glass substrate at 150°C for 2 hours to obtain cured epoxy resin products. Note that some of the epoxy resin compositions did not cure.

[0049] The obtained smooth cured epoxy resin product was analyzed using a polarizing microscope similar to that used in the Examples. The intensity at each angle was normalized by dividing it by the intensity in parallel Nicols. The normalized intensity is also referred to as normalized intensity (au). Epoxy resin compositions that did not cure were not analyzed using a polarizing microscope. Epoxy resin compositions that were not cured and therefore not analyzed using a polarizing microscope are marked with "-" in the polarized intensity column of Table 1. Furthermore, cured epoxy resin products that were not analyzed using a polarizing microscope are marked with "not obtained" in the polarized intensity column of Table 1.

[0050] The formulations and results of the examples and comparative examples are shown in Table 1, and the details of the measurement results using a polarizing microscope are shown in Table 2. Note that when the normalized intensity in Table 2 was negative, it was recorded as 0 in Table 1.

[0051] [Table 1]

[0052] [Table 2]

[0053] The cured epoxy resin products of the Examples had a difference between the maximum and minimum strength values, when normalized by the strength in parallel Nicols, of 0.3 or more, and a minimum strength value, when normalized by the strength in parallel Nicols, of 0.05 or more, whereas the cured epoxy resin products of the Comparative Examples did not satisfy these requirements.

[0054] The upper and / or lower limit values of the numerical ranges described herein can be arbitrarily combined to define a preferred range. For example, the upper and lower limit values of the numerical ranges can be arbitrarily combined to define a preferred range, the upper limit values of the numerical ranges can be arbitrarily combined to define a preferred range, and the lower limit values of the numerical ranges can be arbitrarily combined to define a preferred range.

[0055] Although the present embodiment has been described in detail above, the specific configuration is not limited to this embodiment, and even if there are design changes within the scope that do not deviate from the gist of this disclosure, they are included in this disclosure. [Explanation of symbols]

[0056] 10 Liner 20 Carbon fiber reinforced resin layer 30 Valve side nozzle 40 End side cap 50 valves 100 Tanks

Claims

1. An epoxy resin composition containing a base agent and a curing agent, the base resin contains a triphenylmethane type epoxy resin and further contains one or more selected from a biphenyl type epoxy resin, a naphthalene type epoxy resin, and a stilbene type epoxy resin; the base material further contains alkylene glycol diglycidyl ether, and the content thereof is 25% by mass or less relative to 100% by mass of the base material; The epoxy resin composition, wherein the curing agent comprises a boron trifluoride amine complex salt.

2. 2. The epoxy resin composition according to claim 1, wherein when the epoxy resin composition is cured to obtain a cured epoxy resin material and the cured epoxy resin material is analyzed under a polarizing microscope, the difference between the maximum and minimum strength values normalized by the strength in parallel Nicols is 0.3 or more, and the minimum strength value normalized by the strength in parallel Nicols is 0.05 or more.

3. A cured epoxy resin product, which is a cured product of the epoxy resin composition according to claim 1 or 2.

4. 4. The epoxy resin cured product according to claim 3, wherein, when analyzed with a polarizing microscope, the difference between the maximum and minimum values of intensity normalized by the intensity in parallel Nicols is 0.3 or more, and the minimum value of intensity normalized by the intensity in parallel Nicols is 0.05 or more.

5. A tank liner comprising the epoxy resin cured product according to claim 3 or 4.

6. A tank comprising the tank liner of claim 5.

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