Heat storage stable polyamide wax as well as preparation method and application thereof

Abstract

The invention relates to the field of coating rheological additives, in particular to heat storage stable type polyamide wax and a preparation method and application thereof.The polyamide wax comprises a polyamide wax matrix which is formed by polycondensation of an organic amine combination containing m-xylylenediamine and linear symmetric diamine and an acid component; polyamide fragments are bonded on the surface of the lamellar silicate nucleating agent through ion exchange; the polyamide fragment is formed by condensation of fatty acid and diamine. According to the preparation method, linear symmetric diamine is introduced into a polyamide wax matrix through a unique'molecular conformation optimization-defect targeted closing 'synergistic mechanism, so that the inherent defect density of the crystal is greatly reduced, and meanwhile, lamellar silicate bonded with polyamide fragments is used for accurately covering residual defect sites, so that a molecular-level physical barrier for blocking solvent invasion is formed; therefore, the coating still keeps the anti-sagging performance close to the initial state after being stored at a high temperature for a long time, and the problem of rheological failure caused by collapse of a crystal structure of a solvent type coating is thoroughly solved.

Description

Technical Field

[0001] This invention relates to the field of coating rheology modifiers, and more particularly to a heat-storage-stabilized polyamide wax, its preparation method, and its application. Background Technology

[0002] Polyamide waxes, as high-performance rheology control agents, hold an irreplaceable position in solvent-based industrial coatings. Their three-dimensional network structure formed by intermolecular hydrogen bonds effectively prevents pigment sedimentation and improves anti-sagging properties. However, semi-aromatic polyamide waxes synthesized based on m-phenylenediamine (MXDA) have significant defects: the rigid steric hindrance of the monomer benzene ring leads to an asymmetric zigzag conformation of the molecular chain, forming local lattice distortion regions during crystallization. These microscale defect sites become preferential channels for solvent molecules (such as xylene and butyl acetate) to invade, inducing the gradual disintegration of the hydrogen bond network under long-term thermal storage conditions, specifically manifested as a continuous decrease in coating viscosity and a collapse in anti-sagging properties.

[0003] Industry authoritative tests show (referencing GB / T 9264-2012) that after 60 days of accelerated aging at 60℃, the critical flow film thickness retention rate of traditional MXDA type polyamide wax is generally less than 45%, forcing downstream manufacturers to accept the industry constraint of a 6-month shelf life, which seriously restricts the long-term protection needs of high-end equipment fields such as ships and construction machinery.

[0004] To overcome the above-mentioned defects, existing technologies mainly focus on three major technical routes: metal complex systems (such as the calcium / magnesium-polyethylene oxide complex of Zhangjiagang Oasis) accelerate crystallization through ion coordination, but the migration of metal ions catalyzes the breakage of polyamide molecular chains, and obvious phase separation occurs after 120 hours of thermal aging; low molecular weight polymer nucleating agents (such as benzoic acid-terminated oligomers of Shandong Guangyin) can increase the initial crystallization temperature by 10-15℃, but the hydrogen bond matching degree between their end carboxyl groups and the polyamide backbone is insufficient, and they cannot penetrate into the interior of crystal defects. In the accelerated aging experiment, the solvent penetration rate is still as high as 68%; nanoparticle functionalization schemes (such as the TMN-22 talc system of Shanxi Chemical Research Institute) rely on heterogeneous nucleation to increase crystal density. However, the coverage of nanoparticles at defect sites is less than 25% (cryo-electron microscopy observation data), and the high surface energy leads to particle aggregation, which exacerbates local stress cracking. It is worth noting that Clariant's Licocare RBW330 and other compound systems attempt to combine lubrication and nucleation functions, but the ester bonds of the renewable wax components hydrolyze during thermal storage, causing molecular weight degradation and the release of polar small molecules, which further accelerates the solvent diffusion process.

[0005] In-depth analysis shows that the prior art has fundamental limitations: first, excessive attention is paid to the improvement of macroscopic crystallization rate (such as shortening the 30% forming cycle), but the closed repair of micro-defect structure is ignored, so that the solvent invasion path is not effectively blocked; second, the interface compatibility of traditional nucleating agents (talc, nano-silicon dioxide, etc.) with the polyamide matrix is insufficient, and interface debonding occurs under the action of shear or heat, exposing new defect channels; third, molecular simulation confirms that the "pocket-like" defects (size about 1.2-2.0nm) formed by the benzene ring side group of MXDA have specific adsorption effect on linear solvent molecules, and the current technology cannot realize the targeted closure of the site. Although some studies attempt to use montmorillonite to improve dispersibility, or introduce fatty acid to modify the interface, these schemes only delay but not block the solvent penetration, and more than 15% of the thixotropic performance is sacrificed.

[0006] Therefore, developing a new modification strategy with defect repair capability and long-term thermal storage stability has become a key path to break through the technical bottleneck of the industry. SUMMARY

[0007] The present application is to overcome the defects that the prior art generally focuses on the optimization of processing performance such as crystallization rate improvement and forming cycle shortening, and ignores the problem of crystal structure collapse caused by solvent invasion during thermal storage. Therefore, a thermal storage stable polyamide wax and its preparation method and application are provided to overcome the above shortcomings.

[0008] To achieve the above application purposes, the present application is realized by the following technical solutions: In a first aspect, the present application first provides a thermal storage stable polyamide wax, comprising, a polyamide wax matrix, which is obtained by polycondensation of an organic amine combination comprising m-xylylenediamine and linear symmetrical diamine and an acid component; a layered silicate nucleating agent, the surface of which is bonded with a polyamide segment through an ion exchange bond; The polyamide segment is formed by condensation of a fatty acid and a diamine.

[0009] As described in the background, the present application finds that the thermal storage stability collapse problem of polyamide wax in solvent-based paint is caused by the crystal defects induced by the rigid benzene ring of m-xylylenediamine. Although the prior art attempts to accelerate crystallization by metal complexation, increase nucleation density by low molecular weight polymer, or enhance physical barrier by nanoparticles, it still cannot overcome two major defects: first, the chemical compatibility of heterogeneous nucleating agents with the polyamide matrix is insufficient, resulting in weak interface bonding, and phase separation is easy to occur after long-term thermal storage; second, traditional nucleating agents can only increase the overall crystallinity, and lack the ability to selectively close the specific "zigzag" conformation defect site of m-xylylenediamine, so solvent molecules can still invade along the defect channel and collapse the hydrogen bond network. This structural contradiction has led the industry to be trapped in the problem of "improving the initial rheological performance at the expense of long-term stability" for a long time.

[0010] The present application overcomes the above technical problems by constructing a dual synergistic mechanism of "molecular conformation optimization-defect targeting repair". Specifically, in the design of the polyamide wax matrix, linear symmetric diamines (such as ethylenediamine, 1,6-hexanediamine) are introduced to form a complex amine system with m-xylylenediamine. The regular molecular chain of the linear symmetric amine can neutralize the steric effect of the benzene ring, making the molecular chain stack more closely, thereby reducing the probability of crystal distortion from the source and improving the crystallinity and stability of the crystal.

[0011] In addition, for the closure of residual defects, the present application discards the traditional physical mixing or surface adsorption modification path, and effectively solves the above problems by adopting the chemical bonding architecture of polyamide segment-silicate lamellar. Specifically, the silicate lamellar (such as montmorillonite) has a unique two-dimensional topological structure, which can maximize the coverage of defect sites and form a physical barrier. However, simple physical coverage cannot block the penetration of solvents along the edge of the silicate, nor can it form a chemical bond with the polyamide matrix. Therefore, the scheme designs a layer of "molecular bridging layer" on the surface of the silicate, that is, a specific molecular weight of polyamide segment is bonded to the surface of the silicate by ion exchange. The segment is condensed from fatty acid and diamine, and its characteristic is the differential design of the functional groups at both ends, so as to realize the stable anchoring of the silicate bonding end through ionic bond, and the free amine group (-NH2) exposed outside forms a high-strength hydrogen bond with the carboxyl group of the polyamide wax matrix. This design makes the silicate lamellar transform from "passive filler" to "active repair unit". In addition, the co-crystallization effect between the polyamide segment and the matrix also drives the silicate lamellar to migrate preferentially to the benzene ring defect area, and the amine group at the end of the segment effectively weaves the silicate and the matrix tightly, thereby completely blocking the penetration channel of the solvent.

[0012] Therefore, the components of the material of the present application also trigger a dynamic synergistic effect. Specifically, the linear symmetric diamine optimized matrix conformation significantly reduces the original defect density, and the silicate bonded with the polyamide segment can accurately repair the residual defects. Moreover, the two are not simply superimposed: the linear amine chain segment in the matrix enhances the compatibility with the polyamide segment, making it easier for the silicate to embed in the crystal lattice; and the physical barrier effect of the silicate lamellar in turn protects the optimized molecular structure from solvent erosion. This closed-loop synergistic mechanism shows good advantages in the heat storage process: the co-crystallization network of the polyamide segment and the matrix adjusts the hydrogen bond density adaptively with temperature changes, and even after long-term thermal cycling, the silicate lamellar is still firmly anchored at the defect site, and the solvent penetration rate is significantly inhibited. In contrast to the traditional nanometer titanium dioxide or talc powder system which can only delay penetration for several months, the present scheme realizes the intrinsic stability of the network structure, and the paint can still maintain the anti-sagging performance close to the initial state after high-temperature storage, effectively solving the "shelf life anxiety".

[0013] More importantly, this structure avoids the prior art solution of regarding nucleating agents as "catalysts" for accelerating crystallization, and endows it with a new function of structural repair in this application, i.e. through the molecular-level combination of polyamide segments with the matrix, making silicates become the organic extension of the polyamide crystal network, thus achieving the intrinsic compatibility of heterogeneous materials from the molecular scale. Experiments have proved that even under strong shear or thermal shock, the silicate lamella is firmly combined with the matrix and does not cause the interface peeling of traditional systems.

[0014] Therefore, in summary, this technical solution in this application significantly improves its thermal storage stability through the dual design of "linear symmetric diamine optimizing matrix conformation" and "polyamide segment bridging targeted repair of lamellar silicate", while overcoming the problem of solvent erosion collapse.

[0015] As a preferred, the lamellar silicate nucleating agent accounts for 0.5-3wt% of the mass of the polyamide wax matrix. Among them, the lamellar silicate is one of montmorillonite, mica or vermiculite, the lamellar thickness is 10-50 nm, and the aspect ratio is ≥100.

[0016] In this application, montmorillonite, mica or vermiculite has a unique layered ion exchange capability, which makes it have the basis of chemical bonding with polyamide segments, while common lamellar minerals such as talc are excluded due to the lack of exchangeable ions. In addition, it is found that too thin lamella (<10 nm) lacks mechanical strength and is prone to failure during thermal storage; too thick lamella (>50 nm) is difficult to embed in the crystal defect area. Therefore, within the range of lamellar thickness of 10-50 nm and aspect ratio ≥100, it can maximize the coverage of defect sites. The content range of 0.5-3wt% precisely matches the defect repair needs. The results show that when it is less than 0.5%, it cannot form a continuous closed network, and when it is higher than 3%, it will cause new stress concentration points due to excessive interface.

[0017] This specific structure of the nucleating agent with a small amount of addition can achieve significant results: the lamellar topological structure is oriented along the (010) crystal plane during gradient cooling, forming a dense "molecular fence" that extends the solvent molecule penetration path by several times; and the chemically bonded polyamide segment firmly fixes the lamella to the defect site, effectively avoiding the interface peeling risk of traditional physical mixed nucleating agents.

[0018] As a preferred, the number average molecular weight of the polyamide segment is 800-2000 g / mol; wherein, The fatty acid is a C12-C18 straight-chain fatty acid, and the diamine is one of ethylenediamine, 1,6-hexanediamine or p-xylylenediamine.

[0019] Preferably, the linear symmetrical diamine accounts for 8-15 wt% of the total mass of the organic amine combination, and is at least one of ethylenediamine, 1,4-butanediamine, and 1,6-hexanediamine.

[0020] The content of 8-15 wt% of the linear symmetrical diamine and the selection of specific types have important effects on solving the problem of crystal defects of m-xylylenediamine. When the proportion of linear amine is too low, it cannot effectively offset the steric hindrance, and when it is too high, it will damage the intrinsic viscosity balance of semi-aromatic polyamide. Experiments have proved that this specific combination enables the silicate sheet layer modified by the polyamide segment to obtain directional driving force during gradient cooling, thereby guiding the silicate sheet layer to accurately cover the residual defect sites. This dynamic self-assembly effect greatly improves the targeted repair efficiency of the nucleating agent, making the solvent barrier effect several times that of ordinary physical mixing systems. More importantly, this content range avoids the rheological performance degradation caused by excessive addition of traditional toughening agents, thereby achieving a leap in thermal storage stability with minimal optimization.

[0021] Preferably, the acid component comprises a hydroxy acid and a fatty acid, and the hydroxy acid accounts for 80-90 wt% of the total mass of the acid component.

[0022] The acid component in the present application comprises a hydroxy acid, and the proportion of hydroxy acid is 80-90%. This proportion can accurately regulate the balance between hydrogen bond density and molecular chain activity: when the proportion of hydroxy acid is less than 80%, the hydrogen bond network will be sparse due to the lack of hydroxyl groups, the co-crystallization driving force of the polyamide segment and the matrix will decrease sharply, and the silicate sheet layer will be difficult to migrate to the defect site in a directional manner; and when the proportion of hydroxy acid is higher than 90%, the conformation adjustment ability of the linear symmetrical diamine will be inhibited due to excessive crosslinking, and the crystal will not be able to form a "molecular guide" to guide the arrangement of the sheet layer.

[0023] In addition, the polar environment provided by the hydroxy acid activates the amine group reactivity of the polyamide segment, enabling it to dynamically repair microcracks during thermal storage, and the appropriate presence of fatty acid prevents the system from being too hydrophilic and reducing the solvent barrier property. Thus, through optimization with linear amine and the formation of a three-level synergistic effect of segment-bonded nucleating agent, a closed-loop mechanism of "conformation optimization-targeted closure-dynamic repair" is achieved.

[0024] In a second aspect, the present application also provides a preparation method of the polyamide wax, comprising the following steps: (a) polycondensing the acid component and the organic amine combination until the acid value of the system is reduced to 15-20; (b) adding a sheet-like silicate nucleating agent and continuing the reaction until the acid value is <5; (c) after cooling, crushing the product to obtain the polyamide wax.

[0025] The traditional process either mixes the nucleating agent at the initial stage of polymerization, resulting in its failure to be wrapped by the polymer chain, or mixes it at the later stage, causing uneven dispersion. These rough operations cannot solve the core contradiction of solvent penetration along the crystal defects. The method creatively locks the addition time of the nucleating agent at the middle stage of polycondensation (acid value 15-20 stage), when the prepolymer molecular weight is about 3000-5000 g / mol to form a unique "semi-open" structure: the remaining carboxyl active site is just like a "molecular lock hole", which can precisely dock with the free amine group on the surface of the nucleating agent; and the moderate viscosity (about 50-200 Pa·s) provides hydrodynamic conditions for the directional arrangement of the layered silicate.

[0026] The operation of continuing to react after adding the nucleating agent to an acid value <5 makes the residual carboxyl group continuously condense with the amine group of the polyamide segment on the surface of the nucleating agent, and the silicate layer is firmly anchored on the polyamide network skeleton through covalent bonds, which can increase the interfacial bonding energy by several times. At the same time, the gradual increase in the viscosity of the system acts as a gentle rheological guiding force, driving the layered silicate to slide along the ordered regions of the molecular chain, and finally forming a tile-shaped covering array at the defect site of the benzene ring.

[0027] As a preferred, after adding the layered silicate nucleating agent in step (b), a gradient cooling process is adopted: first, reduce the temperature to 170-175℃ at a rate of 3-5℃ / min and keep for 20-30 min, and then cool to room temperature at a rate of 8-10℃ / min.

[0028] The present application first relaxes the polyamide molecular chain above the glass transition zone (170-175℃) at a slow cooling rate of 3-5℃ / min, so that the linear symmetric diamine guides the molecular chain to form a regular (010) crystal plane orientation. If direct rapid cooling, the instantaneous freezing of the molecular chain will lead to disordered crystal plane. The subsequent 8-10℃ / min rapid cooling will instantaneously freeze the optimized "silicate-matrix" composite structure, which effectively avoids the traditional slow cooling leading to the segregation of the layered silicate or the interface debonding.

[0029] As a preferred, the layered silicate nucleating agent is pretreated by the following steps: dispersing the silicate in water, adding the condensate of fatty acid and diamine, reacting at 60-80℃ for 2-4 h, and then sequentially passing through centrifugation, drying and grinding to obtain.

[0030] In a third aspect, the present application also provides the application of the polyamide wax in a coating.

[0031] As a preferred, the addition amount of the polyamide wax is 0.5-3 wt% of the total mass of the coating. The coating is any one of solvent-based acrylic resin paint, epoxy resin paint or polyurethane paint.

[0032] Therefore, the present application has the following beneficial effects: The present application introduces linear symmetric diamines into the polyamide wax matrix through a unique "molecular conformation optimization-defect targeting closure" synergistic mechanism, which greatly reduces the inherent defect density of the crystal, and at the same time, the residual defect sites are precisely covered by the sheet-like silicate bonded by the polyamide segment, forming a molecular-level physical barrier that blocks the invasion of solvents; combined with the accurate control of the acid value in the polycondensation stage and the gradient cooling directional assembly process, the polyamide segment and the matrix form a dynamic self-repairing hydrogen bond network, which finally realizes the revolutionary improvement of the thermal storage stability. Thus, the anti-sagging performance remains close to the initial state after long-term high-temperature storage, completely solving the rheological failure problem of solvent-based coatings caused by the collapse of crystal structure, significantly prolonging the shelf life of products and expanding high-end application scenarios. DETAILED DESCRIPTION

[0033] The present application will be further described below in conjunction with specific examples. Those skilled in the art will be able to implement the present application based on these descriptions. In addition, the embodiments of the present application involved in the following description are generally only a part of the embodiments of the present application, not all. Therefore, based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor shall fall within the scope of protection of the present application.

[0034] Preparation of sheet-like silicate nucleating agent Preparation of sheet-like silicate nucleating agent A: 100 g of C36 dimer acid (Pripol 1009), 200 g of stearic acid, and 65.2 g of ethylenediamine were added to a reaction kettle, and reacted at 180℃ for 3h, the acid value was reduced to below 5, obtaining a polyamide oligomer (terminal amine group) with a molecular weight of about 1200 g / mol. 100 g of sodium-based montmorillonite (sheet thickness 10 nm, aspect ratio 100) was dispersed in 1 L of water, 30 g of the above polyamide oligomer was added, then stirred at 80℃ for 4h to anchor the polyamide segment between the layers of montmorillonite through ionic bonds, then 10 g of ammonium stearate was added, treated at 70℃ for 1h, finally centrifuged, dried at 110℃, ground to D90≤5μm to obtain sheet-like silicate nucleating agent A.

[0035] Preparation of laminar silicate nucleating agent B: C36dimer acid (Pripol 1009) 80 g, lauric acid (C12) 180 g, 1,4-butanediamine 72 g were added to a reaction kettle, polycondensation at 170 °C for 3 h to an acid value of 6.5, transparent liquid with a molecular weight of 800 g / mol was obtained. Mica (laminar thickness 50 nm, aspect ratio 150) was treated with 0.5 M HC1 500 mL at 60 °C for 2 h, increasing the surface active sites. Acidified mica was dispersed in 700 mL water, polyamide segment 40 g was added, high shear emulsification (10000 rpm) at 85 °C for 5 h, allowing the segment to be combined by electrostatic adsorption and hydrogen bonding, then ammonium stearate 20 g in ethanol solution was added dropwise, stirring at 65 °C for 2 h, finally centrifugation, vacuum drying at 105 °C, grinding to D90≤5 μm to obtain laminar silicate nucleating agent B.

[0036] Preparation of laminar silicate nucleating agent C: C36dimer acid (Pripol 1009) 120 g, palmitic acid (C16) 160 g, 1,6-hexanediamine 85 g were added to a reaction kettle, raw materials were reacted at 185 °C for 3.5 h to an acid value of 4.0, amber solid with a molecular weight of 2000 g / mol (terminal amine group content 0.50 mmol / g) was obtained. Expanded vermiculite (laminar thickness 30 nm, aspect ratio 120) 100 g was added to a 5 wt% sodium citrate aqueous solution 600 mL, ultrasonic treatment (800 W) for 30 min, then polyamide segment 50 g was added to the expanded vermiculite suspension, stepwise temperature rise: 60 °C / 2 h→75 °C / 2 h→90 °C / 1 h, allowing the interlayer spacing to expand from 1.4 nm to 4.2 nm, then ammonium stearate 25 g was added, 80 °C for 1 h, finally centrifugation, 100 °C fluidized bed drying, grinding through an 800 mesh sieve, to obtain laminar silicate nucleating agent C.

[0037] Example 1 A method for preparing a polyamide wax, comprising the following steps: (a) An acid component composed of 1,2-hydroxystearic acid 360 g and sebacic acid 540 g, and an organic amine combination composed of meta-xylylenediamine (MXDA) 368.0 g and ethylenediamine 32.0 g were added to a reaction kettle, polycondensation at 190 °C for 4 h to an acid value of 20.0 under nitrogen protection; (b) The laminar silicate nucleating agent A 5 g was added to the system in (a), and the reaction was continued at 190 °C for 1 h to an acid value of 4.8; (c) Cooling at 3 °C / min to 175 °C, holding for 20 min, and then cooling at 10 °C / min to room temperature, and then pulverizing to obtain a fine powder.

[0038] Example 2 A method for preparing a polyamide wax, comprising the following steps: (a) the acid component consisting of terephthalic acid 630 g and 1,2-hydroxystearic acid 270 g and the organic amine component consisting of m-xylylenediamine 340 g and 1,6-hexanediamine 60 g were combined in a reaction kettle, and polycondensation was carried out at 185°C for 5 h under nitrogen protection until the acid value was 15.0; (b) the above-mentioned sheet-like silicate nucleating agent B 30 g was added to the system in (b), and the reaction was continued at 185°C for 1.5 h until the acid value was 4.2; (c) cooling was carried out at 5°C / min to 170°C, and the temperature was kept for 30 min, and then cooling was carried out at 8°C / min to room temperature, and the product was pulverized to obtain a fine powder.

[0039] Example 3 A method for preparing a polyamide wax, comprising the following steps: (a) the acid component consisting of sebacic acid 450 g, stearic acid 135 g and 1,2-hydroxystearic acid 315 g and the organic amine component consisting of m-xylylenediamine (MXDA) 354 g and 1,4-butanediamine 46 g were combined in a reaction kettle, and polycondensation was carried out at 182°C for 4.5 h under nitrogen protection until the acid value was 17.5; (b) the above-mentioned sheet-like silicate nucleating agent C 17.5 g was added to the system in (b), and the reaction was continued at 182°C for 1.3 h until the acid value was 4.5; (c) cooling was carried out at 4°C / min to 172.5°C, and the temperature was kept for 25 min, and then cooling was carried out at 9°C / min to room temperature, and the product was pulverized to obtain a fine powder.

[0040] Example 4 A method for preparing a polyamide wax, comprising the following steps: (a) the acid component consisting of terephthalic acid 585 g and 1,2-hydroxystearic acid 315 g and the organic amine component consisting of m-xylylenediamine (MXDA) 360 g and 1,4-butanediamine 46 g were combined in a reaction kettle, and polycondensation was carried out at 190°C for 4.5 h under nitrogen protection until the acid value was reduced to 18.5; (b) the above-mentioned sheet-like silicate nucleating agent B 15 g was added to the system in (b), and the reaction was continued at 190°C for 1.3 h until the acid value was 4.3; (c) cooling was carried out at 5°C / min to 170°C, and the temperature was kept for 30 min, and then cooling was carried out at 8°C / min to room temperature, and the product was pulverized to obtain a fine powder.

[0041] Example 5 A method for preparing a polyamide wax, comprising the following steps: (a) the acid component consisting of sebacic acid 360 g and 1,2-hydroxystearic acid 540 g and the organic amine component consisting of m-xylylenediamine (MXDA) 340 g and 1,6-hexanediamine 60 g were combined in a reaction kettle, and polycondensation was carried out at 185°C for 5.2 h until the acid value was reduced to 16.2; (b) adding the above-mentioned sheet-like silicate nucleating agent C24g into the system in (b), reacting at 185°C for 1.1h to an acid value of 4.0; (c) cooling at 3°C / min to 175°C for 20min, and then cooling at 10°C / min to room temperature, and then pulverizing to obtain a fine powder.

[0042] Example 6 A method for preparing a polyamide wax, comprising the following steps: (a) adding an acid component composed of terephthalic acid 405g, 1,2-hydroxy stearic acid 450g, and stearic acid 45g, and an organic amine combination composed of m-xylylenediamine (MXDA) 352g and ethylenediamine 48g into a reaction kettle, and condensing at 182°C for 4.8h under nitrogen protection until the acid value is reduced to 17; (b) adding the above-mentioned sheet-like silicate nucleating agent A9g into the system in (b), reacting at 182°C for 1.4h to an acid value of 4.6; (c) cooling at 4°C / min to 172°C for 25min, and then cooling at 9°C / min to room temperature, and then pulverizing to obtain a fine powder.

[0043] Comparative Example 1 Comparative Example 1 differs from Example 1 in that the organic amine thereof only contains m-xylylenediamine 400g, without any linear symmetric diamine.

[0044] Comparative Example 2 Comparative Example 2 differs from Example 1 in that the nucleating agent thereof is unmodified sodium-based montmorillonite.

[0045] Comparative Example 3 Comparative Example 3 differs from Example 1 in that the sheet-like silicate nucleating agent is added in the preparation process when the acid value is condensed to 25.0 in step (a).

[0046] Comparative Example 4 Comparative Example 4 is a commercially available competitor (Clariant Licocar RBW330).

[0047] The polyamide waxes in Examples 1-6 and Comparative Examples 1-4 are added to solvent-based acrylic resin paint at a ratio of 0.5wt% and 3wt%, respectively, and the coatings are tested, with the test methods as follows: Thermal storage stability: according to GB / T 9264-2012 standard, 60°C thermal storage for 60 days, measuring the change in film thickness of the sagging film (wet film maker 40μm).

[0048] Solvent penetration depth: dyeing-cryogenic electron microscopy method, adding 0.1wt% rhodamine B dye, slicing after thermal storage and liquid nitrogen freezing, and observing the penetration depth by confocal electron microscopy.

[0049] Crystallinity change (ΔXc): DSC (ISO 11357), second heating method to determine the change of melting enthalpy.

[0050] Thixotropic index (TI): 6 rpm / 60 rpm viscosity ratio determined using ISO 2884-1, Brookfield viscometer.

[0051] Sedimentation rate: The change of solid content was determined by taking the upper 1 / 3 paint after hot storage using ASTM D869.

[0052] The test results are shown in Table 1 and Table 2 below: Table 1 Test results of polyamide wax addition amount 0.5wt% Sample Dripping retention (%) after 60 days Solvent penetration depth (pm) Delta Xc (%) Thixotropic index (TI) before hot storage Thixotropic index (TI) after hot storage Settling rate (%) Example 1 94.8 0.6 +2.9 4.1 3.9 0.7 Example 2 95.2 0.5 +3.1 4.3 4.0 0.5 Example 3 95.0 0.7 +2.8 4.0 3.8 0.8 Example 4 93.5 0.9 +2.5 3.9 3.6 1.2 Example 5 94.1 0.8 +2.7 4.2 3.9 1.0 Example 6 94.3 0.7 +2.6 4.1 3.8 0.9 Comparative Example 1 48.3 8.2 -29.6 4.0 1.8 23.5 Comparative Example 2 60.7 5.8 -20.3 4.1 2.2 17.8 Comparative Example 3 71.5 3.6 -13.2 3.9 2.8 9.4 Comparative Example 4 61.9 6.5 -23.1 4.2 2.4 19.2 Table 2 Test results of polyamide wax addition amount 3wt% Sample Dripping retention (%) after 60 days Solvent penetration depth (pm) Delta Xc (%) Thixotropic index (TI) before hot storage Thixotropic index (TI) after hot storage Settling rate (%) Example 1 97.2 0.3 +3.5 6.5 6.3 0.2 Example 2 97.8 0.2 +3.8 6.8 6.5 0.1 Example 3 96.9 0.4 +3.2 6.3 6.0 0.3 Example 4 95.6 0.6 +2.9 6.0 5.7 0.7 Example 5 96.3 0.5 +3.1 6.4 6.1 0.5 Example 6 96.1 0.4 +3.0 6.2 5.9 0.6 Comparative Example 1 46.8 8.5 -31.2 6.5 2.1 27.3 Comparative Example 2 58.2 6.1 -22.7 6.7 2.8 21.4 Comparative Example 3 69.3 3.9 -14.6 6.1 3.3 11.8 Comparative Example 4 59.7 6.8 -25.3 6.8 2.9 23.6 From the above tests of polyamide wax in solvent-based acrylic resin paint, it is shown that: At an addition amount of 0.5-3.0wt%, the heat storage stable polyamide wax in the present application has a sag retention rate as high as 93-98% and a sedimentation rate of ≤1.2% after 60 days of heat storage, indicating that its stability is more excellent compared with several comparative examples.

[0053] Meanwhile, the crystallinity change (ΔXc) data show that the present application introduces a linear symmetric diamine (such as ethylenediamine, 1,6-hexanediamine) and m-xylylenediamine to form a complex amine system in the structure, the regular molecular chain of the linear symmetric amine can neutralize the steric hindrance effect of the benzene ring, so that the molecular chain is stacked more tightly, so that the crystallinity can be effectively improved. And because this structure can reduce the probability of crystal distortion from the source, therefore, after heat storage, the structure of the more regular crystal of the embodiment can be more perfect and stable, in the embodiment of the present application, the crystallinity change (ΔXc) data not only does not decrease, but on the contrary, the crystallinity realizes a certain positive growth (+2.5~+3.8%), indicating that it has a certain self-enhancing effect. While in the comparative examples, due to the existence of more crystal lattice distortion, it shows more serious deterioration of crystallinity, resulting in a significant decrease in the data of crystallinity change (ΔXc).

[0054] And the solvent penetration depth data show that because the co-crystallization network of the polyamide segment and the matrix in the present application self-adapts the hydrogen bond density with temperature change, even after long-term heat cycle, the silicate sheet layer is still firmly anchored in the defect site, so that the solvent penetration rate is significantly inhibited. Therefore, in the same time, the solvent penetration depth of the embodiment in the present application is shallower compared with several comparative examples.

[0055] Regarding the thixotropic index (TI) data before and after heat storage, the data can clearly show the thixotropic index of the acrylic resin paint containing polyamide wax before and after heat storage. The greater the difference in thixotropic index before and after heat storage, the higher the storage performance, and thus the longer the shelf life. The thixotropic index of several embodiments in the present application fluctuates by less than 0.5 before and after heat storage, thereby solving the "shelf life anxiety" in the prior art.

[0056] In summary, the above effects are due to the fourfold synergy of the optimized molecular conformation of linear symmetric diamines, the targeted closure of crystal defects by sheet-like silicate targets bonded by polyamide fragments, precise control of the acid value in the polycondensation stage, and the gradient cooling orientation process, thereby effectively blocking the solvent infiltration path and activating the structural self-reinforcement mechanism, allowing the coating to maintain near the initial anti-sagging performance after high-temperature storage, and breaking through the 12-month shelf life demand in high-end fields.

[0057] The specific embodiments described herein are merely illustrative of the spirit of the present application. Those skilled in the art of the present application can make various modifications or supplements to the described specific embodiments or replace them with similar ways, without departing from the spirit of the present application or exceeding the scope defined by the appended claims.

Claims

1. A heat-stable polyamide wax, characterized in that, Include, The polyamide wax matrix is ​​formed by the condensation polymerization of an organic amine combination containing m-phenylenediamine and a linear symmetrical diamine with an acid component; A layered silicate nucleating agent, the surface of which is bonded with polyamide segments by ion exchange; The polyamide fragment is formed by the condensation of fatty acids and diamines.

2. The polyamide wax according to claim 1, characterized in that, The layered silicate nucleating agent accounts for 0.5-3 wt% of the polyamide wax matrix; The lamellar silicate is one of montmorillonite, mica or vermiculite, with a lamellar thickness of 10-50 nm and an aspect ratio of ≥100.

3. The polyamide wax according to claim 1, characterized in that, The number-average molecular weight of the polyamide fragment is 800-2000 g / mol; wherein, The fatty acid is a C12-C18 straight-chain fatty acid, and the diamine is one of ethylenediamine, 1,6-hexanediamine, or p-phenylenediamine.

4. The polyamide wax according to claim 1, characterized in that, The linear symmetrical diamine accounts for 8-15 wt% of the total mass of the organic amine combination, and is at least one of ethylenediamine, 1,4-butanediamine, and 1,6-hexanediamine.

5. The polyamide wax according to claim 1, characterized in that, The acid component comprises hydroxy acids and fatty acids, with hydroxy acids accounting for 80-90 wt% of the total mass of the acid component.

6. A method for preparing the polyamide wax according to any one of claims 1-5, characterized in that, Includes the following steps: (a) Polycondense the acid component with an organic amine until the acid value of the system drops to 15-20; (b) Add a layered silicate nucleating agent and continue the reaction until the acid value is <5; (c) After cooling, the material is crushed to obtain polyamide wax.

7. The preparation method according to claim 6, characterized in that, After adding the lamellar silicate nucleating agent in step (b), a gradient cooling process is adopted: first, the temperature is lowered to 170-175℃ at 3-5℃ / min and held for 20-30 min, and then cooled to room temperature at 8-10℃ / min.

8. The preparation method according to claim 6, characterized in that, The layered silicate nucleating agent is obtained by pretreatment through the following steps: silicate is dispersed in water, a condensate of fatty acid and diamine is added, and the mixture is reacted at 60-80℃ for 2-4 h. After the reaction is completed, the mixture is centrifuged, dried and ground in sequence.

9. The use of the polyamide wax as described in any one of claims 1-5 in coatings.

10. The application as described in claim 9, characterized in that, The amount of polyamide wax added is 0.5-3 wt% of the total mass of the coating. The coating is any one of solvent-based acrylic resin paint, epoxy resin paint, or polyurethane paint.