Flexible epoxy solvent-free intermediate paint and preparation method thereof

Abstract

The invention discloses a flexible epoxy solvent-free intermediate paint and a preparation method thereof, the flexible epoxy solvent-free intermediate paint comprises a component A and a component B, and the mass ratio of the component A to the component B is (3-4): 1; the component A comprises the following components in percentage by mass: 30-45% of flexible epoxy resin, 15-25% of functional filler, 2-5% of auxiliaries and the balance of solvent which is less than or equal to 5%; the flexible epoxy resin is a compound of bisphenol F type epoxy resin and alicyclic epoxy resin, the ratio of bisphenol F type epoxy resin to alicyclic epoxy resin is (2-3): 1, the molecular weight of the bisphenol F type epoxy resin is 500-1000, the epoxy equivalent of the bisphenol F type epoxy resin is 180-220, the alicyclic epoxy resin is 3, 4-epoxy cyclohexyl methyl-3, 4-epoxy cyclohexyl formate, and the epoxy equivalent of the alicyclic epoxy resin is 150-180. According to the invention, the contradiction that a common solvent-free coating sacrifices the constructability for reducing VOC (Volatile Organic Compounds) is broken through, and the viscosity is adjusted to 80-120s through the reactive diluent, so that the construction requirement of a Tu-4 cup is met.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of epoxy coating compositions, in particular to a flexible epoxy solvent-free intermediate paint and a preparation method thereof. BACKGROUND

[0002] In heavy-duty coating systems, the core function of the intermediate paint is to enhance the overall adhesion of the coating system, shield the penetration of corrosive media, and provide a transitional layer for the primer and topcoat. Traditional intermediate paints are mostly solvent-based epoxy coatings (such as two-component epoxy micaceous iron oxide intermediate paint), using organic solvents such as xylene and n-butanol as dispersion media. Although this type of coating has good corrosion resistance, it has the following outstanding problems:

[0003] Poor environmental performance: high VOC (volatile organic compounds) content (usually > 300 g / L), which releases a large amount of harmful gases during construction, not meeting the requirements of the Atmospheric Pollution Prevention Law and GB30981-2020 Industrial Protective Coatings Harmful Substance Limitation and other regulations.

[0004] Insufficient flexibility: the crosslinking density of epoxy resin itself is high, and the traditional formula has obvious brittleness after film formation. When the substrate is deformed (such as steel structure welding stress release, pipeline thermal expansion and cold contraction), the coating is prone to cracking, which destroys the integrity of the coating system and accelerates the corrosion of the bottom layer.

[0005] Unstable interlayer adhesion: the compatibility with the primer (such as epoxy zinc-rich primer) and topcoat (such as acrylic polyurethane topcoat) depends on the construction process. If the rigidity of the intermediate paint is too high, delamination may occur at the interface between the flexible topcoat or rough primer.

[0006] High-solid epoxy coatings (VOC ≈ 0-150 g / L) are the environmentally friendly development direction to replace solvent-based coatings, but they generally have the contradiction of high crosslinking density leading to low flexibility. To ensure corrosion resistance (such as salt spray resistance), the crosslinking degree of epoxy resin and curing agent needs to be increased, but this will reduce the flexibility and crack resistance of the coating. Therefore, developing an intermediate paint with solvent-free environmental protection, high flexibility, and excellent interlayer adhesion is of great significance to improve the long-term reliability of heavy-duty coating systems.

[0007] Prior art 202411809079.2 A modified epoxy coating composition with high pressure resistance and high toughness, its preparation method and application, uses a flexible aliphatic amine curing agent (polyether amine), introduces flexible segments through ketone amine condensation reaction, and improves the toughness of the paint film, with an elongation at break ≥ 15%.

[0008] Prior art 202310220217.2 A kind of water-based high solid epoxy iron oxide cloud intermediate paint and its preparation method, core filler is mica iron oxide + glass powder, utilize the labyrinth effect of lamellar filler to improve shielding property.

[0009] Prior art 202410701558.6 A kind of coating containing flexible segment epoxy resin and its preparation method, dimer acid modified curing agent introduces flexible segment, improves impact resistance.

[0010] Although high solid epoxy coating can reduce VOC, to ensure salt fog resistance, water resistance and other corrosion protection properties, the crosslinking degree of epoxy resin and curing agent needs to be improved, which will further sacrifice flexibility;While traditional solvent-based epoxy intermediate paint has certain corrosion protection properties (about 1800h of salt fog resistance), but the corrosion width at scratch is >3mm, which cannot meet the long-term protection needs of high corrosion environment such as marine atmosphere and chemical medium. SUMMARY

[0011] The purpose of the present application is to provide a flexible epoxy solvent-free intermediate paint and its preparation method to solve the problems raised in the above background art.

[0012] To achieve the above purpose, the present application provides the following technical scheme: a flexible epoxy solvent-free intermediate paint, comprising component A and component B, the mass ratio of component A to component B is (3-4):1;

[0013] The A component contains 30-45% of flexible epoxy resin, 15-25% of functional filler, 2-5% of auxiliary agent and the rest ≤5% of solvent by mass percentage;The flexible epoxy resin is a compound of bisphenol F type epoxy resin and alicyclic epoxy resin, bisphenol F type: alicyclic is (2-3):1, wherein the molecular weight of bisphenol F type epoxy resin is 500-1000, and the epoxy equivalent weight is 180-220, the alicyclic epoxy resin is 3,4-epoxy cyclohexylmethyl-3,4-epoxy cyclohexylmethyl carboxylate and the epoxy equivalent weight is 150-180;

[0014] The B component contains 100% of flexible curing agent main body by mass percentage;The flexible curing agent main body is a compound of polyamide curing agent and modified aliphatic amine, polyamide: modified aliphatic amine is (1-2):1, wherein the amine value of polyamide curing agent is 150-250 mgKOH / g, and the modified aliphatic amine is polyetheramine D230.

[0015] Further, the functional fillers in the A component include shielding fillers, anti-rust fillers and rheological aids in a mass ratio of (4-5):(3-4):(1-2); the shielding fillers are mica iron oxide with a flake diameter of 5-20 μm and a diameter-thickness ratio ≥8:1; the anti-rust fillers are a compound of zinc phosphate and aluminum tripolyphosphate, the particle size of zinc phosphate ≤5 μm and the particle size of aluminum tripolyphosphate ≤3 μm; and the rheological aids are fumed silica with a specific surface area of 200-300 m 2 / g.

[0016] Further, the additives in the A component are composed of dispersants, defoaming agents, leveling agents and coupling agents; the dispersants are polycarboxylate dispersants with an addition amount of 0.5-1% of the mass of the A component; the defoaming agents are polyether-modified silicone defoaming agents with an addition amount of 0.3-0.8% of the mass of the A component; the leveling agents are acrylate copolymer leveling agents with an addition amount of 0.2-0.5% of the mass of the A component; and the coupling agents are silane coupling agent KH550 with an addition amount of 0.5-1% of the mass of the A component.

[0017] Further, the solvents in the A component include solvent-free active diluents and non-active diluents; the solvent-free active diluents are glycidyl ether with an addition amount ≤3% of the mass of the A component and an epoxy equivalent of 130-160; and the non-active diluents are propylene glycol methyl ether with an addition amount ≤2% of the mass of the A component and a VOC contribution ≤10 g / L.

[0018] Further, the catalyst in the B component is an imidazole catalyst, specifically 2-methylimidazole, with an addition amount ≤0.1% of the mass of the B component.

[0019] Further, 1-2% of a photocuring initiator, specifically 2-hydroxy-2-methyl-1-phenyl-1-propanone (1173), is added to the A component; the solvent-free active diluents in the A component are replaced by castor oil glycidyl ether with an epoxy equivalent of 130-160 and an addition amount ≤3% of the mass of the A component; after the application of the intermediate paint, surface drying is first achieved by irradiation with ultraviolet light of wavelength 365 nm for 30-60 s, and then deep curing is achieved by chemical curing of polyamide and modified fatty amine at 25°C for 24 h, with a VOC content ≤30 g / L and an intercoat adhesion to the primer and topcoat still ≥5 MPa.

[0020] Further, a preparation method of a flexible solvent-free epoxy intermediate paint, comprising an A component preparation step, a B component preparation step and a coating system mixing step.

[0021] The preparation steps of the A component: flexible epoxy resin is added into a dispersion cylinder, a dispersing agent, a defoaming agent and a coupling agent are sequentially added under low-speed stirring at 300-400 rpm, and stirring is performed for 10-15 min until uniformity; the stirring speed is increased to 1000-1200 rpm, a thixotropic agent is added, and dispersion is performed for 20-30 min until no precipitation; the stirring speed is reduced to 600-800 rpm, mica iron oxide, zinc phosphate and aluminum tripolyphosphate are sequentially added, and dispersion is performed for 30-40 min until the fineness is less than or equal to 50 mu m; a non-active diluent is added, the viscosity is adjusted to 80-120 s, the material is filtered out through a 100-mesh filter cloth, and the A component is obtained;

[0022] The preparation steps of the B component: the polyamide curing agent and the modified fatty amine are mixed in proportion, and stirring is performed for 10-15 min under low-speed stirring at 200-300 rpm until uniformity; if low-temperature curing is required, an imidazole catalyst is added, and stirring is continued for 5 min, and the material is filtered out, and the B component is obtained;

[0023] The mixing steps of the coating system: the A component and the B component are mixed in a mass ratio of (3-4):1, stirring is uniformly performed, and then standing and curing are performed for 10-15 min.

[0024] Technical effects and advantages of the present application:

[0025] The present application solves the problem of poor environmental protection: by replacing traditional solvents such as dimethylbenzene and n-butanol with ≤5% solvent-free active diluent (such as AGE) and ≤2% low-VOC non-active diluent, the VOC is controlled at 42 g / L, which not only avoids the high pollution problem of solvent-based coatings, but also breaks the contradiction between VOC reduction and construction performance of ordinary solvent-free coatings, and the viscosity is adjusted to 80-120 s by using active diluent, which meets the 4-cup construction requirement.

[0026] The present application solves the problem of insufficient flexibility: through the synergistic design of bisphenol F type + aliphatic epoxy resin + polyamide + modified fatty amine curing agent, the traditional paradox of high crosslinking density = high corrosion resistance + low flexibility is broken, the balance between high corrosion resistance and high flexibility is achieved, and the coating elongation at break can reach 60%.

[0027] The present application solves the problem of unstable interlayer adhesion: the interface bonding force between fillers and resins is optimized by using silane coupling agent (KH550), and the chemical reactivity between the amino group of the polyamide curing agent and the epoxy group of the primer and the hydroxyl group of the topcoat is utilized to strengthen the chemical bonding between layers, thereby avoiding the compatibility fluctuation caused by the physical adhesion of traditional coatings. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 : The scratch section metallography of the coating of the present application before and after salt spray test for 1000 h;

[0029] Figure 2The curve of the influence of different flexible curing agent ratios on the flexibility of the coating. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the protection scope of the present application.

[0031] Embodiment one:

[0032] The present application provides a flexible epoxy solvent-free intermediate paint as shown in Figures 1-2 The synergistic effect of flexible epoxy resin, ductile curing agent and functional filler solves the problems of poor flexibility and insufficient interlayer adhesion of traditional solvent-free intermediate paint, and achieves the following goals:

[0033] Environmental protection: VOC content ≤ 150 g / L (in line with GB / T38597-2020 "Low Volatile Organic Compound Content Coating Product Technical Requirements");

[0034] Flexibility: can withstand dynamic load or deformation of the substrate (such as 60% elongation at break), and the coating will not crack (flexibility ≤ 1 mm, GB / T1731);

[0035] Interlayer adhesion: adhesion to common primers such as epoxy zinc-rich primer, epoxy zinc phosphate primer, etc. ≥ 5 MPa (circle method ≥ 3 levels, GB / T1720), and no blistering and delamination phenomenon with topcoat such as acrylic polyurethane topcoat, fluorocarbon topcoat, etc.

[0036] Corrosion resistance: salt spray resistance ≥ 2000 h (single edge corrosion width at scratch ≤ 2 mm), water resistance ≥ 30 d without abnormality, and can shield the penetration of corrosive media (air permeability ≤ 0.5 mg / (cm 2 ·h·Pa)).

[0037] The flexible epoxy solvent-free intermediate paint described in the present application belongs to a two-component solvent-free paint (component A: resin / filler mixed system; component B: flexible curing agent). The ratio of component A to component B is (3-4): 1 by mass percentage, and the specific composition is as follows:

[0038] Table one: composition table of component A

[0039]

[0040]

[0041]

[0042] Table II: Composition of B component

[0043]

[0044] Synergistic design of flexible epoxy resin and curing agent:

[0045] The use of bisphenol F epoxy resin (low viscosity, high reactivity) and alicyclic epoxy resin (high flexibility, low shrinkage) is compounded to reduce the molecular crosslinking density; the use of polyamide curing agent (long-chain flexible structure) and modified aliphatic amine (containing ether bond flexible segment) is compounded to dilute the rigid crosslinking point by soft segment, so that the coating still maintains the flexibility (GB / T1731) of ≥1mm after curing, and can withstand the deformation of ±2% of the substrate without cracking.

[0046] Optimized compounding of functional fillers:

[0047] Lamellar mica iron oxide (aspect ratio ≥8:1) blocks water, oxygen and ion penetration through the labyrinth effect, improving corrosion shielding; zinc phosphate and aluminum tripolyphosphate are compounded to inhibit anodic corrosion reaction through chemical chelation (combined with the surface Fe 3+ Gas phase silica is used as a thixotropic agent to maintain high thixotropy of the coating during construction (to prevent sagging) and form a dense coating after drying.

[0048] Balance between solvent-free environmental protection and interlayer adhesion:

[0049] Only ≤5% of solvent-free active diluent (VOC≤50g / L) is used to avoid the high VOC problem of traditional solvent-based intermediate paint; the use of coupling agent (KH550) improves the interfacial bonding force of fillers and resins, and optimizes the functional group matching of curing agent and primer / topcoat (such as the reaction of amino group of polyamide curing agent with epoxy group and hydroxyl group), ensuring the interlayer adhesion of ≥5MPa with epoxy zinc-rich primer (containing zinc powder) and acrylic polyurethane topcoat (containing hydroxyl group).

[0050] Preparation method

[0051] The preparation method of the flexible solvent-free epoxy intermediate paint comprises the following steps:

[0052] Preparation of component A:

[0053] Flexible epoxy resin (30-45%) is added to a dispersion cylinder, and dispersant (0.5-1%), defoaming agent (0.3-0.8%), and coupling agent (0.5-1%) are sequentially added under low-speed stirring (300-400rpm) until uniform after 10-15min of stirring;

[0054] Increase the speed to 1000-1200rpm, add thixotropic agent (fumed silica, 1-2%), disperse for 20-30min until no precipitate;

[0055] Reduce the speed to 600-800rpm, add mica iron oxide (4-5%), zinc phosphate (3-4%), aluminum tripolyphosphate (3-4%) in turn, disperse for 30-40min until fineness≤50μm (detected by spatula fineness meter);

[0056] Finally add non-active diluent (≤2%), adjust the viscosity to 80-120s (coating-4 cup, 25℃), filter (100 mesh filter cloth) to discharge, get A component.

[0057] B component preparation:

[0058] Mix the polyamide curing agent (60-70%) and modified fatty amine (30-40%) in proportion, stir at low speed (200-300rpm) for 10-15min until uniform; if low temperature curing is needed, add imidazole catalyst (≤0.1%), continue to stir for 5min, filter to discharge, get B component.

[0059] Coating system: when used, mix A component and B component in mass ratio (3-4):1, stir uniformly, stand for 10-15min before construction.

[0060] According to the attached Figure 2 The curing agent ratio (polyamide: modified fatty amine) is as follows:

[0061] 1: (100% modified fatty amine)

[0062] 2: (90% modified fatty amine: 10% polyamide)

[0063] 3: (80% modified fatty amine: 20% polyamide)

[0064] 4: (70% modified fatty amine: 30% polyamide)

[0065] 5: (60% modified fatty amine: 40% polyamide)

[0066] 6: (50% modified fatty amine: 50% polyamide)

[0067] 7: (40% modified fatty amine: 60% polyamide)

[0068] 8: (30% modified fatty amine: 70% polyamide)

[0069] 9: (20% modified fatty amine: 80% polyamide)

[0070] 10: (10% modified aliphatic amine: 90% polyamide)

[0071] 11: (100% polyamide)

[0072] Conclusion: Overall downward trend, can be selected according to the actual situation of the most cost-effective ratio of programs.

[0073] Example Two

[0074] A component (by mass percent):

[0075] Bisphenol F type epoxy resin (epoxy equivalent weight 200): 35%

[0076] Cycloaliphatic epoxy resin (3,4-epoxycyclohexylmethyl-3,4- epoxycyclohexylmethyl carboxylate): 10% polyamide curing agent (amine value 200 mg KOH / g): 0 (Note: Curing agent in B component)

[0077] Dispersant (BYK® -P104): 0.8%

[0078] Defoamer (BYK® -066N): 0.5%

[0079] Coupling agent (KH550): 0.8%

[0080] Mica iron oxide (flake diameter 10 μm, diameter-thickness ratio 9:1): 4.5%

[0081] Zinc phosphate (particle size 3 μm): 3.5%

[0082] Aluminum tripolyphosphate (particle size 2 μm): 3.5%

[0083] Fumed silica (thixotropic agent): 1.5%

[0084] Non-reactive diluent (AGE, epoxy equivalent weight 140): 2%

[0085] Deionized water: balance (about 36.6%)

[0086] B component (by mass percent):

[0087] Polyamide curing agent (amine value 200 mg KOH / g): 65%

[0088] Modified aliphatic amine (polyether amine D230): 35%

[0089] Imidazole catalyst (2-methylimidazole): 0.05%

[0090] Preparation method: A, B components are prepared according to the above steps, and when used, A:B = 3:1 is mixed, and after construction, the coating performance is as follows:

[0091] Flexibility: 0.8mm (GB / T 1731);

[0092] Adhesion (scratch circle method): Primer (zinc-rich epoxy) ≥ 5MPa, topcoat (acrylic polyurethane) no delamination;

[0093] Salt spray resistance: 2200h (scratch single side corrosion ≤ 2mm);

[0094] VOC content: 42g / L.

[0095] Example Three (adjusting the proportion of flexible curing agent)

[0096] Reduce the polyamide curing agent to 55%, increase the modified aliphatic amine to 45% (B component), and the rest is the same as Example Two, to prepare paint B (more flexible, suitable for higher deformation substrates).

[0097] Comparative Example 1 (solvent-based comparative sample)

[0098] Contains 25% xylene, 40% epoxy resin, 15% mica iron oxide, and 20% other auxiliaries, VOC > 300g / L, flexibility 2.5mm (easy to crack).

[0099] Comparative Example 2 (ordinary solvent-free comparative sample)

[0100] Contains only bisphenol A type epoxy resin (high crosslinking density), polyamide curing agent, no flexible modification component, flexibility 1.2mm (slight cracking), salt spray resistance 1500h.

[0101] Example Four:

[0102] In this embodiment, 1-2% photoinitiator (1173, 2-hydroxy-2-methyl-1-phenyl-1-propanone) is added to the compounded resin of Example One. After application, the coating is first dried on the surface by UV light (UV, wavelength 365 nm) irradiation for 30-60 s to prevent sagging, and then deep curing is achieved by polyamide + modified aliphatic amine chemical curing (25°C / 24h). A bio-based active diluent, castor oil-based glycidyl ether, is used to replace the original AGE, reducing dependence on fossil-based raw materials. Example One relies only on chemical curing, which requires 4-6h surface drying at 25°C, and large-area construction, such as the outer wall of a storage tank, is prone to sagging. The UV surface drying of this embodiment is fast and firm, and the chemical curing ensures deep performance, with construction efficiency improved by more than 3 times. The photoinitiator (1173) is added in an amount of only 1-2% and does not participate in the chemical curing reaction of epoxy-amine. It only accelerates surface drying by UV irradiation, and deep curing still relies on the original polyamide and modified aliphatic amine. The castor oil-based glycidyl ether has an epoxy equivalent weight (130-160) that matches that of the original AGE diluent, and is added in an amount of ≤3%. The total VOC is reduced to ≤30g / L, and it cooperates with the KH550 coupling agent to maintain an interlayer adhesion of ≥5MPa, without damaging the original environmental protection-adhesion balance.

[0103] Finally, it should be noted that the above only describes the preferred embodiments of the present application and is not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art will still be able to modify the technical solutions described in the foregoing embodiments or make equivalent replacements to some technical features, as long as they are within the spirit and principles of the present application. Any modifications, equivalent replacements, improvements, etc. made in accordance with the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A flexible epoxy solventless intermediate coating, characterized in that, The A component and the B component, the mass ratio of the A component to the B component is (3-4):1; The A component contains 30-45% of flexible epoxy resin, 15-25% of functional filler, 2-5% of auxiliary agent and the rest of ≤5% of solvent by mass percentage; the flexible epoxy resin is a compound of bisphenol F type epoxy resin and alicyclic epoxy resin, the ratio of bisphenol F type to alicyclic is (2-3):1, wherein the molecular weight of bisphenol F type epoxy resin is 500-1000 and the epoxy equivalent weight is 180-220, the alicyclic epoxy resin is 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylmethyl carboxylate and the epoxy equivalent weight is 150-180; The B component contains 100% of flexible curing agent body by mass percentage; the flexible curing agent body is a compound of polyamide curing agent and modified fatty amine, the ratio of polyamide to modified fatty amine is (1-2):1, wherein the amine value of polyamide curing agent is 150-250 mgKOH / g and the modified fatty amine is polyether amine D230.

2. The flexible solvent-free intermediate coating according to claim 1, characterized in that, The functional filler in the A group includes shielding filler, anti-rust filler and rheological agent in a mass ratio of (4-5):(3-4):(1-2); the shielding filler is mica iron oxide with a flake diameter of 5-20 μm and a diameter-thickness ratio of ≥8:1; the anti-rust filler is a compound of zinc phosphate and aluminum tripolyphosphate, the particle size of zinc phosphate ≤5 μm, and the particle size of aluminum tripolyphosphate ≤3 μm; the rheological agent is fumed silica with a specific surface area of 200-300 m 2 / g.

3. The flexible solvent-free intermediate coating according to claim 2, characterized in that, The auxiliary agent in the A component is composed of dispersant, defoaming agent, leveling agent and coupling agent; the dispersant is polycarboxylate dispersant, the addition amount is 0.5-1% of the mass of the A component; the defoaming agent is polyether modified silicone defoaming agent, the addition amount is 0.3-0.8% of the mass of the A component; the leveling agent is acrylate copolymer leveling agent, the addition amount is 0.2-0.5% of the mass of the A component; the coupling agent is silane coupling agent KH550, the addition amount is 0.5-1% of the mass of the A component.

4. The flexible solvent-free intermediate coating according to claim 3, characterized in that, The solvent in the A component includes solvent-free active diluent and non-active diluent; the solvent-free active diluent is glycidyl ether, the addition amount is ≤3% of the mass of the A component, the epoxy equivalent weight is 130-160; the non-active diluent is propylene glycol methyl ether, the addition amount is ≤2% of the mass of the A component, the VOC contribution is ≤10 g / L.

5. The flexible solvent-free intermediate coating according to claim 4, characterized in that, The catalyst in the B component is imidazole catalyst, specifically 2-methylimidazole, the addition amount is ≤0.1% of the mass of the B component.

6. The flexible solvent-free intermediate coating according to claim 5, characterized in that, 1-2% of photocuring initiator is added to the A component, specifically 2-hydroxy-2-methyl-1-phenyl-1-propanone (1173); the solvent-free active diluent in the A component is replaced by castor oil glycidyl ether, the epoxy equivalent weight is 130-160, the addition amount is ≤3% of the mass of the A component; after the intermediate paint is applied, it is first irradiated with ultraviolet light of wavelength 365 nm for 30-60 s to achieve surface dryness, and then it is chemically cured with polyamide and modified fatty amine at 25°C for 24 h to achieve deep curing, the VOC content is ≤30 g / L, and the interlayer adhesion with primer and topcoat is still ≥5 MPa.

7. A process for the preparation of a flexible solvent-free epoxy intermediate coating as claimed in claim 6, characterized in that, The A component preparation step, the B component preparation step and the coating system mixing step are included. The A component preparation step: flexible epoxy resin is added into a dispersion cylinder, dispersant, defoaming agent and coupling agent are added in sequence under low speed stirring of 300-400 rpm, stirring for 10-15 min until uniform; the stirring speed is increased to 1000-1200 rpm, thixotropic agent is added, and dispersion is carried out for 20-30 min until no precipitation; the stirring speed is decreased to 600-800 rpm, mica iron oxide, zinc phosphate and aluminum tripolyphosphate are added in sequence, dispersion is carried out for 30-40 min until fineness is ≤50 μm; non-active diluent is added, viscosity is adjusted to 80-120 s, the material is filtered out through 100 mesh filter cloth, and A component is obtained; The B component preparation step: polyamide curing agent and modified fatty amine are mixed in proportion, and stirring is carried out at low speed of 200-300 rpm for 10-15 min until uniform; If low temperature curing is needed, imidazole catalyst is added, stirring is continued for 5 min, the material is filtered out, and B component is obtained; The coating system mixing step: A component and B component are mixed in mass ratio (3-4):1, stirring is uniformly carried out, and then standing and curing are carried out for 10-15 min.

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